WO2017126697A1 - 非水系リチウム型蓄電素子 - Google Patents
非水系リチウム型蓄電素子 Download PDFInfo
- Publication number
- WO2017126697A1 WO2017126697A1 PCT/JP2017/002031 JP2017002031W WO2017126697A1 WO 2017126697 A1 WO2017126697 A1 WO 2017126697A1 JP 2017002031 W JP2017002031 W JP 2017002031W WO 2017126697 A1 WO2017126697 A1 WO 2017126697A1
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- WIPO (PCT)
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- active material
- positive electrode
- negative electrode
- electrode active
- storage element
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- 238000003860 storage Methods 0.000 title claims abstract description 270
- 239000007773 negative electrode material Substances 0.000 claims abstract description 243
- 239000007774 positive electrode material Substances 0.000 claims abstract description 175
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 132
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 132
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 305
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- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/13—Energy storage using capacitors
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a non-aqueous lithium storage element.
- the first requirement for batteries used in these power storage systems is high energy density.
- As a promising candidate for a high energy density battery capable of meeting such demands development of a lithium ion battery has been vigorously advanced.
- the second requirement is high output characteristics.
- high output discharge characteristics in the power storage system are required during acceleration. Yes.
- electric double layer capacitors, nickel metal hydride batteries, and the like have been developed as high-power storage devices.
- the electric double layer capacitors those using activated carbon as electrodes have output characteristics of about 0.5 to 1 kW / L.
- This electric double layer capacitor has high durability (cycle characteristics and high temperature storage characteristics), and has been considered as an optimum device in the field where the high output is required.
- the energy density is only about 1 to 5 Wh / L. Therefore, further improvement in energy density is necessary.
- nickel-metal hydride batteries currently used in hybrid electric vehicles have a high output equivalent to that of electric double layer capacitors and an energy density of about 160 Wh / L.
- research for increasing the energy density and output and further improving durability (particularly stability at high temperatures) has been energetically advanced.
- research for higher output is also being conducted in lithium ion batteries.
- a lithium ion battery has been developed that can obtain a high output exceeding 3 kW / L at a depth of discharge (a value indicating what percentage of the discharge capacity of the storage element is discharged) 50%.
- the energy density is 100 Wh / L or less, and the high energy density, which is the greatest feature of the lithium ion battery, is intentionally suppressed.
- its durability is inferior to that of an electric double layer capacitor. Therefore, in order to provide practical durability, the discharge depth is used in a range narrower than the range of 0 to 100%. Since the capacity that can actually be used is further reduced, research for further improving the durability is being actively pursued.
- a lithium ion capacitor is a kind of energy storage device (non-aqueous lithium energy storage device) that uses a non-aqueous electrolyte containing a lithium salt, and the negative electrode adsorbs the same as an electric double layer capacitor at about 3 V or more at the positive electrode. It is a power storage element that charges and discharges by a non-Faraday reaction by desorption, and a Faraday reaction by insertion and extraction of lithium ions in the negative electrode, similar to a lithium ion battery.
- the above-mentioned electrode materials and their characteristics can be summarized as follows: High output and high durability are achieved when materials such as activated carbon are used for the electrodes and charging / discharging is performed by ion adsorption / desorption (non-Faraday reaction) on the activated carbon surface. However, the energy density is lowered (for example, 1 time). On the other hand, when an oxide or a carbon material is used for the electrode and charging / discharging is performed by a Faraday reaction, the energy density is increased (for example, 10 times that of a non-Faraday reaction using activated carbon), but durability and output are increased. There is a problem with the characteristics.
- the electric double layer capacitor is characterized in that the positive and negative electrodes use activated carbon (energy density 1 time), and the positive and negative electrodes are charged and discharged by a non-Faraday reaction, resulting in high output and high durability.
- lithium ion capacitors examples include railways, construction machinery, and power storage elements for automobiles. In these applications, both high input / output characteristics and high load charge / discharge cycle characteristics are required.
- Patent Document 1 proposes a lithium ion secondary battery that uses a positive electrode containing lithium carbonate in the positive electrode and has a current interruption mechanism that operates in response to an increase in the internal pressure of the battery.
- Patent Document 2 proposes a lithium ion secondary battery in which lithium composite oxide such as lithium manganate is used for the positive electrode and lithium carbonate is contained in the positive electrode to suppress manganese elution.
- Patent Document 3 proposes a method for recovering the capacity of a deteriorated power storage element by oxidizing various lithium compounds as oxides at the positive electrode.
- the present inventors have found that high-load charge / discharge cycle characteristics are improved by containing a lithium compound in the positive electrode as exemplified in Patent Documents 1 to 3.
- the problem to be solved by the present invention is to provide a non-aqueous lithium storage element having high input / output characteristics and high load charge / discharge cycle characteristics.
- the inventors have obtained a solid 7 Li-NMR spectrum of the positive electrode active material layer, which was obtained by measurement with a repetition waiting time of 10 seconds, from ⁇ 40 ppm to 40 ppm.
- the peak area at ⁇ 40 ppm to 40 ppm obtained by measurement with a peak area at a of 3,000 seconds and a repetition waiting time of 3,000 seconds is b, by adjusting b / a to a specific range, high input / output
- the present inventors have found that characteristics and high load charge / discharge cycle characteristics can be expressed, and have completed the present invention.
- a non-aqueous lithium storage element comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing lithium ions
- the negative electrode has a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material provided on one or both surfaces of the negative electrode current collector
- the positive electrode has a positive electrode current collector, and a positive electrode active material layer including a positive electrode active material provided on one or both surfaces of the positive electrode current collector
- the peak area at ⁇ 40 ppm to 40 ppm obtained by measurement with a repetition waiting time of 10 seconds is a, and the repetition waiting time is 3,000 seconds.
- the nonaqueous lithium storage element wherein 1.04 ⁇ b / a ⁇ 5.56, where b is a peak area at ⁇ 40 ppm to 40 ppm.
- the amount of lithium in the positive electrode calculated from the peak area at ⁇ 40 ppm to 40 ppm is 1 mmol / g or more and 30 mmol / g or less per unit mass of the positive electrode active material layer.
- the non-aqueous lithium storage element according to [1].
- the positive electrode has the following formulas (1) to (3): ⁇ In Formula (1), R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms, and X 1 and X 2 are each independently — (COO) n (where And n is 0 or 1.).
- R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms
- R 2 is hydrogen, an alkyl group having 1 to 10 carbon atoms, carbon A mono- or polyhydroxyalkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a mono- or polyhydroxyalkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group
- X 1 and X 2 are each independently — (COO) n (where n is 0 or 1).
- R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms
- R 2 and R 3 are each independently hydrogen, 1 to 10 carbon atoms
- An aryl group, X 1 and X 2 are each independently — (COO) n (where n is 0 or 1);
- ⁇ At least one selected from the group consisting of compounds represented by the formula: 1.60 ⁇ 10 ⁇ 4 mol / g to 300 ⁇ 10 ⁇ 4 mol / g per unit mass of the positive electrode material layer [2]
- the non-aqueous lithium-type electricity storage element according to
- the non-aqueous lithium storage element according to any one of [1] to [3], wherein the positive electrode contains a lithium compound other than the positive electrode active material.
- the average particle diameter X 1 of the lithium compound is 0.1 ⁇ m or more 10 ⁇ m or less, a non-aqueous lithium-type storage element according to [4].
- the average particle diameter of the positive electrode active material is Y 1 , 2 ⁇ m ⁇ Y 1 ⁇ 20 ⁇ m and X 1 ⁇ Y 1
- the content ratio of the lithium compound in the positive electrode is the positive electrode
- the nonaqueous lithium storage element according to [5] which is 1% by mass or more and 50% by mass or less based on the total mass of the active material layer.
- the average distance between the centers of gravity of the gap and r p, the negative active when the average particle diameter r a of the material, r p / r a is 0.10 to 1.10, the non-described [9] Water-based lithium storage element.
- the negative electrode active material includes a graphite-based carbon material, The negative electrode active material layer occludes lithium ions, and the solid peak 7 Li-NMR spectrum of the negative electrode active material layer has a peak maximum value between 4 ppm and 30 ppm in the spectrum range of ⁇ 10 ppm to 35 ppm.
- any of [1] to [10], wherein the amount of lithium calculated from a peak area of 4 ppm to 30 ppm is 0.10 mmol / g or more and 10.0 mmol / g or less per unit mass of the negative electrode active material layer The non-aqueous lithium-type energy storage device according to claim 1.
- the positive electrode active material contained in the positive electrode active material layer has an amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method as V 1 (cc / g) and less than 20 mm in diameter calculated by the MP method.
- V 1 (cc / g) the amount of micropores derived from these pores
- V 2 (cc / g) 0.3 ⁇ V 1 ⁇ 0.8 and 0.5 ⁇ V 2 ⁇ 1.0 are satisfied, and the BET method
- the non-aqueous lithium storage element according to any one of [1] to [19], which is an activated carbon having a specific surface area measured by a value of 1,500 m 2 / g to 3,000 m 2 / g.
- the positive electrode active material contained in the positive electrode active material layer has an amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method as V 1 (cc / g) and less than 20 mm in diameter calculated by the MP method.
- V 1 (cc / g) the amount of micropores derived from the pores
- V 2 (cc / g) 0.8 ⁇ V 1 ⁇ 2.5 and 0.8 ⁇ V 2 ⁇ 3.0 are satisfied, and the BET method
- the non-aqueous lithium storage element according to any one of [1] to [19], which is an activated carbon having a specific surface area measured by a value of 2,300 m 2 / g to 4,000 m 2 / g.
- a power storage module comprising the non-aqueous lithium storage element according to any one of [1] to [24].
- the non-aqueous lithium storage element according to the present invention exhibits high input / output characteristics and high load charge / discharge cycle characteristics.
- a non-aqueous lithium storage element generally includes a positive electrode, a negative electrode, a separator, and an electrolytic solution as main components.
- an organic solvent containing lithium ions hereinafter also referred to as “non-aqueous electrolytic solution”.
- the positive electrode in the present embodiment includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material provided on one side or both sides thereof.
- the positive electrode in the present embodiment preferably contains a lithium compound as a positive electrode precursor before assembling the non-aqueous lithium storage element.
- the negative electrode in the step of assembling the non-aqueous lithium storage element, it is preferable that the negative electrode be pre-doped with lithium ions.
- a positive electrode precursor containing a lithium compound, a negative electrode, a separator, and a non-aqueous electrolyte solution are used to assemble a non-aqueous lithium storage element. It is preferable to apply a voltage between them.
- the lithium compound may be contained in any form in the positive electrode precursor and the positive electrode.
- the lithium compound may exist between the positive electrode current collector and the positive electrode active material layer, or may exist on the surface of the positive electrode active material layer.
- the lithium compound is preferably contained in the positive electrode active material layer formed on the positive electrode current collector of the positive electrode precursor.
- the positive electrode before the lithium doping step is defined as “positive electrode precursor”, and the positive electrode after the lithium doping step is defined as “positive electrode”.
- the solid 7 Li-NMR spectrum of the positive electrode active material layer of the present embodiment was measured with a peak area at ⁇ 40 ppm to 40 ppm obtained by measurement with a repetition waiting time of 10 seconds, and with a repetition waiting time of 3,000 seconds.
- the peak area at ⁇ 40 ppm to 40 ppm obtained by the above is b, 1.04 ⁇ b / a ⁇ 5.56.
- the b / a is preferably 1.05 ⁇ b / a ⁇ 3.79, more preferably 1.09 ⁇ b / a ⁇ 3.32, and even more preferably 1.14 ⁇ b / a ⁇ 2.86. More preferably, 1.18 ⁇ b / a ⁇ 1.93.
- the lower limit and the upper limit can be any combination.
- the peak area a is considered to be a peak mainly derived from the lithium ions occluded in the positive electrode active material or the attached lithium-containing film, and is considered to represent the amount of the positive electrode active material relatively.
- the peak area b is considered to be obtained by integrating the peaks derived from the lithium compound isolated from the positive electrode active material in addition to the peak area a. That is, the b / a is considered to represent the amount of the lithium compound isolated with respect to the positive electrode active material.
- the lithium compound isolated from the positive electrode active material can maintain high input / output characteristics without hindering electron conduction or ion diffusion between the positive electrode active materials. Furthermore, the high load charge / discharge cycle characteristics are improved by adsorbing an active product such as fluorine ions generated by the lithium compound in the high load charge / discharge cycle.
- isolated means, for example, when the positive electrode active material is an aggregate of activated carbon particles, in which lithium compound particles are isolated and dispersed.
- the amount of the lithium compound relative to the positive electrode active material is sufficient, and the lithium compound adsorbs an active product such as fluorine ions generated in a high-load charge / discharge cycle. High load charge / discharge cycle characteristics are improved.
- this b / a is 5.56 or less, the lithium compound can maintain high input / output characteristics without hindering electron conduction or ion diffusion between the positive electrode active materials.
- the peak area a in the spectrum range of ⁇ 40 ppm to 40 ppm when the repetition waiting time is 10 seconds and the repetition waiting time of 3,000 seconds The area ratio b / a with respect to the peak area b in the spectrum range of ⁇ 40 ppm to 40 ppm can be calculated by the following method.
- a commercially available apparatus can be used as an apparatus for measuring solid 7 Li-NMR. Under a room temperature environment, the spectrum is measured by a single pulse method with a magic angle spinning rotation speed of 14.5 kHz and an irradiation pulse width of 45 ° pulse.
- Measurement is performed for each of the case where the repetition waiting time is 10 seconds and the case where the repetition waiting time is 3,000 seconds, and a solid 7 Li-NMR spectrum is obtained.
- the measurement conditions other than the repetition waiting time that is, the number of integrations, the receiver gain, etc., are all made the same.
- a 1 mol / L lithium chloride aqueous solution is used as a shift reference, and the shift position separately measured as an external standard is 0 ppm.
- the sample is not rotated, and the spectrum is measured by a single pulse method with an irradiation pulse width of 45 ° pulse. Peak areas a and b in the spectrum range of ⁇ 40 ppm to 40 ppm are obtained from the solid 7 Li-NMR spectrum of the positive electrode active material layer obtained by the above method, and b / a is calculated.
- the amount of lithium in the positive electrode calculated from the peak area at ⁇ 40 ppm to 40 ppm is 1 mmol / g or more per unit mass of the positive electrode active material layer. It is preferably 30 mmol / g or less, more preferably 1.2 mmol / g or more and 28 mmol / g or less, further preferably 1.5 mmol / g or more and 26 mmol / g or less, particularly preferably 1.7 mmol / g or more and 24 mmol / g. Hereinafter, it is most preferably 2 mmol / g or more and 22 mmol / g or less.
- the non-aqueous lithium storage element of this embodiment has high load charge / discharge cycle durability while maintaining high input / output characteristics by adjusting the amount of lithium in the positive electrode to a specific range.
- the principle is not clear and is not limited to theory, but it is presumed as follows.
- the amount of lithium is considered to be mainly derived from the lithium-containing film in the positive electrode active material layer. Since this lithium-containing coating is internally polarized, the ion conductivity is high, and even when formed in a large amount, the resistance is not significantly impaired. In addition, the lithium-containing coating can suppress oxidative decomposition of the nonaqueous electrolytic solution.
- lithium-containing coatings exist stably in the charge / discharge process, so that the coatings are less likely to be destroyed even after repeated numerous charge / discharge cycles.
- oxidative decomposition of the non-aqueous electrolyte is less likely to occur. For this reason, the electrical storage element can show a high high load charge / discharge cycle characteristic.
- the amount of lithium in the positive electrode is 1 mmol / g or more per unit mass of the positive electrode active material layer, the amount of the lithium-containing coating formed on the positive electrode active material layer is sufficient. Oxidative decomposition of the liquid is suppressed, and high high load charge / discharge cycle characteristics can be exhibited.
- the amount of lithium in the positive electrode is 30 mmol / g or less, resistance increase due to the lithium-containing coating hardly occurs, and high input / output characteristics can be exhibited.
- the amount of lithium obtained from the solid 7 Li-NMR spectrum of the positive electrode active material layer can be calculated by the following method.
- a commercially available apparatus can be used as an apparatus for measuring solid 7 Li-NMR. Under a room temperature environment, the spectrum is measured by a single pulse method with a magic angle spinning rotation speed of 14.5 kHz and an irradiation pulse width of 45 ° pulse. The measurement is set so that a sufficient waiting time is repeated between measurements.
- a 1 mol / L lithium chloride aqueous solution is used as a shift reference, and the shift position separately measured as an external standard is 0 ppm.
- the sample When measuring a 1 mol / L lithium chloride aqueous solution, the sample is not rotated, and the spectrum is measured by a single pulse method with an irradiation pulse width of 45 ° pulse.
- the peak area is determined for components in the range of ⁇ 40 ppm to 40 ppm. Then, these peak areas are divided by the peak area of a 1 mol / L lithium chloride aqueous solution measured by making the sample height in the rotor for measurement the same as when measuring the positive electrode active material layer, and further, the positive electrode active material used for the measurement By dividing by the mass of the layer, the amount of lithium in the positive electrode can be calculated.
- the mass of the positive electrode active material layer is the mass of the positive electrode active material layer including a film or a deposit contained in the positive electrode active material layer.
- the positive electrode comprises at least one selected from the group consisting of compounds represented by the following formulas (1) to (3), and is 1.60 ⁇ 10 ⁇ 4 mol / unit mass of the positive electrode active material layer. It is preferable to contain g to 300 ⁇ 10 ⁇ 4 mol / g.
- R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms
- X 1 and X 2 are each independently — (COO) n (where And n is 0 or 1.).
- R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms
- R 2 is hydrogen, an alkyl group having 1 to 10 carbon atoms, carbon A mono- or polyhydroxyalkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a mono- or polyhydroxyalkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group
- X 1 and X 2 are each independently — (COO) n (where n is 0 or 1).
- R 1 is an alkylene group having 1 to 4 carbon atoms or a halogenated alkylene group having 1 to 4 carbon atoms
- R 2 and R 3 are each independently hydrogen, 1 to 10 carbon atoms
- An aryl group, X 1 and X 2 are each independently — (COO) n (where n is 0 or 1); ⁇
- Particularly preferred compounds as the compound of formula (1) are not limited, but for example, LiOC 2 H 4 OLi, LiOC 3 H 6 OLi, LiOC 2 H 4 OCOOLi, LiOCOOC 3 H 6 OLi, LiOCOOC 2 H 4 OCOOLi, and LiOCOOC 3 A compound represented by H 6 OCOOLi is given.
- Particularly preferable compounds as the compound of the formula (2) are not limited, but for example, LiOC 2 H 4 OH, LiOC 3 H 6 OH, LiOC 2 H 4 OCOOH, LiOC 3 H 6 OCOOH, LiOCOOC 2 H 4 OCOOH, LiOCOOC 3 H 6 OCOOH, LiOC 2 H 4 OCH 3, LiOC 3 H 6 OCH 3, LiOC 2 H 4 OCOOCH 3, LiOC 3 H 6 OCOOCH 3, LiOCOOC 2 H 4 OCOOCH 3, LiOCOOC 3 H 6 OCOOCH 3, LiOC 2 H 4 OC 2 H 5, LiOC 3 H 6 OC 2 H 5, LiOC 2 H 4 OCOOC 2 H 5, LiOC 3 H 6 OCOOC 2 H 5, LiOCOOC 2 H 4 OCOOC 2 H 5, and LiOCOOC 3 H 6 OCOOC 2 H In compounds represented.
- Particularly preferred compounds as the compound of the formula (3) are not limited, but for example, HOC 2 H 4 OH, HOC 3 H 6 OH, HOC 2 H 4 OCOOH, HOC 3 H 6 OCOOH, HOCOOC 2 H 4 OCOOH, HOCOOC 3 H 6 OCOOH, HOC 2 H 4 OCH 3, HOC 3 H 6 OCH 3, HOC 2 H 4 OCOOCH 3, HOC 3 H 6 OCOOCH 3, HOCOOC 2 H 4 OCOOCH 3, HOCOOC 3 H 6 OCOOCH 3, HOC 2 H 4 OC 2 H 5 , HOC 3 H 6 OC 2 H 5 , HOC 2 H 4 OCOOC 2 H 5 , HOC 3 H 6 OCOOC 2 H 5 , HOCOOC 2 H 4 OCOOC 2 H 5 , HOCOOC 3 H 6 OCOOC 2 H 5 , 3 OC 2 H 4 OCOOC 2 H 5 , 3 OC 2 H 4 OCOOC 2 H 5 , 3 OC 2 H 4 OCOOC 2 H
- the compounds of the formulas (1) to (3) are added to the positive electrode active material layer.
- a method of mixing; a method of adsorbing the compounds of formulas (1) to (3) on the positive electrode active material layer; and a method of electrochemically depositing the compounds of formulas (1) to (3) on the positive electrode active material layer. Can be mentioned.
- a precursor that can be decomposed to produce these compounds is contained in a non-aqueous electrolyte, and non-aqueous lithium is used.
- a method is preferred in which the precursor is decomposed in the step of manufacturing the type electricity storage element and the compound is deposited in the positive electrode active material layer.
- the precursor that decomposes to form the compounds of formulas (1) to (3) includes at least one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and fluoroethylene carbonate Of these, ethylene carbonate and propylene carbonate are preferred.
- the total amount of the compounds of the formulas (1) to (3) is preferably 1.60 ⁇ 10 ⁇ 4 mol / g or more, more preferably 5.0 ⁇ 10 ⁇ 4 mol / g per unit mass of the positive electrode active material layer. g or more.
- the total amount of the compounds of the formulas (1) to (3) is 1.60 ⁇ 10 ⁇ 4 mol / g or more per unit mass of the positive electrode active material layer, the non-aqueous electrolyte solution is less likely to come into contact with the positive electrode active material, It can suppress more effectively that a non-aqueous electrolyte solution decomposes oxidatively.
- the total amount of the compounds of formulas (1) to (3) is preferably 300 ⁇ 10 ⁇ 4 mol / g or less, more preferably 150 ⁇ 10 ⁇ 4 mol / g or less per unit mass of the positive electrode active material layer, Preferably, it is 100 ⁇ 10 ⁇ 4 mol / g or less.
- the total amount of the compounds of the formulas (1) to (3) is 300 ⁇ 10 ⁇ 4 mol / g or less per unit mass of the positive electrode active material layer, the lithium ion diffusion is hardly inhibited and higher input / output characteristics are obtained. Can be expressed.
- the positive electrode active material layer contains a positive electrode active material, and may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer in addition to this.
- the positive electrode active material preferably contains a carbon material.
- the carbon material include carbon nanotubes, conductive polymers, and porous carbon materials, and more preferably activated carbon.
- the positive electrode active material may include a mixture of two or more materials, or may include a material other than a carbon material, such as a composite oxide of lithium and a transition metal.
- the content of the carbon material with respect to the total mass of the positive electrode active material is preferably 50% by mass or more, and more preferably 70% by mass or more. Although the content of the carbon material may be 100% by mass, it is preferably 90% by mass or less and may be 80% by mass or less, for example, from the viewpoint of obtaining the effect of the combined use with other materials. Good.
- the kind of activated carbon and its raw material are not particularly limited. However, in order to achieve both high input / output characteristics and high energy density, it is preferable to optimally control the pores of the activated carbon. Specifically, the amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method is V 1 (cc / g), and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method.
- 0.3 ⁇ V 1 ⁇ 0.8 and 0.5 ⁇ V 2 ⁇ 1.0 are satisfied, and the specific surface area measured by the BET method is 1 , 500 m 2 / g or more and 3,000 m 2 / g or less of activated carbon (hereinafter also referred to as “activated carbon 1”) is preferable
- activated carbon 1 500 m 2 / g or more and 3,000 m 2 / g or less of activated carbon
- 0.8 ⁇ V 1 ⁇ 2.5 and 0.8 ⁇ V 2 ⁇ 3.0 are satisfied, and the specific surface area measured by the BET method is 2, Activated carbon (hereinafter also referred to as “activated carbon 2”) of 300 m 2 / g or more and 4,000 m 2 / g or less is preferable.
- the mesopore amount V 1 of the activated carbon 1 is preferably a value larger than 0.3 cc / g in order to increase input / output characteristics when the positive electrode material is incorporated in a non-aqueous lithium storage element.
- V 1 of the activated carbon 1 is 0.8 cc / g or less from the viewpoint of suppressing a decrease in the bulk density of the positive electrode.
- V 1 of the activated carbon 1 is more preferably 0.35 cc / g or more and 0.7 cc / g or less, and further preferably 0.4 cc / g or more and 0.6 cc / g or less.
- the micropore amount V 2 of the activated carbon 1 is preferably 0.5 cc / g or more in order to increase the specific surface area of the activated carbon and increase the capacity.
- the V 2 of the activated carbon 1 is preferably 1.0 cc / g or less from the viewpoint of suppressing the bulk of the activated carbon, increasing the density as an electrode, and increasing the capacity per unit volume.
- V 2 of the activated carbon 1 is more preferably 0.6 cc / g or more and 1.0 cc / g or less, and further preferably 0.8 cc / g or more and 1.0 cc / g or less.
- the ratio of meso Anaryou V 1 relative to the micropore volume V 2 of the activated carbon 1 is preferably in the range of 0.3 ⁇ V 1 / V 2 ⁇ 0.9. That is, V 1 / V 2 of activated carbon 1 is 0.3 or more from the viewpoint of increasing the ratio of the mesopore amount to the micropore amount to such an extent that the decrease in output characteristics can be suppressed while maintaining a high capacity. Preferably there is. On the other hand, the V 1 / V 2 of the activated carbon 1 is 0.9 or less from the viewpoint of increasing the ratio of the micropore amount to the mesopore amount to such an extent that the decrease in capacity can be suppressed while maintaining high output characteristics. Preferably there is.
- the range of V 1 / V 2 of the activated carbon 1 is more preferably 0.4 ⁇ V 1 / V 2 ⁇ 0.7, and still more preferably 0.55 ⁇ V 1 / V 2 ⁇ 0.7.
- the average pore diameter of the activated carbon 1 is preferably 17 mm or more, more preferably 18 mm or more, and still more preferably 20 mm or more, from the viewpoint of increasing the output of the obtained non-aqueous lithium storage element. From the viewpoint of increasing the capacity, the average pore diameter of the activated carbon 1 is preferably 25 mm or less.
- BET specific surface area of the activated carbon 1 is preferably from 1,500 m 2 / g or more 3,000 m 2 / g, more preferably not more than 1,500 m 2 / g or more 2,500 m 2 / g.
- the BET specific surface area of the activated carbon 1 is 1,500 m 2 / g or more, a good energy density is easily obtained.
- the BET specific surface area of the activated carbon 1 is 3,000 m 2 / g or less, an electrode Since it is not necessary to add a large amount of a binder in order to maintain the strength, the performance per electrode volume is increased.
- the activated carbon 1 having the above-described features can be obtained using, for example, the raw materials and processing methods described below.
- the carbon source used as a raw material of the activated carbon 1 is not particularly limited.
- the carbon source of the activated carbon 1 include wood-based materials such as wood, wood flour, coconut husk, pulp by-products, bagasse and molasses; peat, lignite, lignite, bituminous coal, anthracite, petroleum distillation residue components, petroleum Fossil raw materials such as pitch, coke and coal tar; various synthetic resins such as phenol resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, celluloid, epoxy resin, polyurethane resin, polyester resin, polyamide resin Synthetic rubbers such as polybutylene, polybutadiene, and polychloroprene; other synthetic woods, synthetic pulps, and carbides thereof.
- wood-based materials such as wood, wood flour, coconut hus
- the carbonization and activation methods for producing the activated carbon 1 from these raw materials known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method can be employed.
- an exhaust gas such as combustion exhaust gas, or other gases mainly composed of these inert gases.
- the method include using a mixed gas and baking at about 400 to 700 ° C., preferably about 450 to 600 ° C., for about 30 minutes to 10 hours.
- a gas activation method in which firing is performed using an activation gas such as water vapor, carbon dioxide, or oxygen is preferably used.
- an activation gas such as water vapor, carbon dioxide, or oxygen
- a method using water vapor or carbon dioxide as the activation gas is more preferable.
- the carbide is supplied for 3 to 12 hours, preferably 5 to 11 hours, while supplying the activation gas at a rate of 0.5 to 3.0 kg / h, preferably 0.7 to 2.0 kg / h. More preferably, the temperature is increased to 800 to 1,000 ° C. over 6 to 10 hours for activation.
- the carbide may be activated in advance prior to the activation treatment of the carbide.
- the carbide may be activated in advance.
- the activated carbon 1 having the above characteristics, which is preferable in the present embodiment. it can.
- the average particle diameter of the activated carbon 1 is preferably 2 to 20 ⁇ m.
- the average particle diameter of the activated carbon 1 is more preferably 2 to 15 ⁇ m, still more preferably 3 to 10 ⁇ m.
- the mesopore amount V 1 of the activated carbon 2 is preferably a value greater than 0.8 cc / g from the viewpoint of increasing output characteristics when the positive electrode material is incorporated in a non-aqueous lithium storage element. On the other hand, it is preferably 2.5 cc / g or less from the viewpoint of suppressing a decrease in capacity of the non-aqueous lithium storage element.
- V 1 of the activated carbon 2 is more preferably 1.00 cc / g or more and 2.0 cc / g or less, and further preferably 1.2 cc / g or more and 1.8 cc / g or less.
- the micropore amount V 2 of the activated carbon 2 is preferably a value larger than 0.8 cc / g in order to increase the specific surface area of the activated carbon and increase the capacity.
- the V 2 of the activated carbon 2 is preferably 3.0 cc / g or less, more preferably more than 1.0 cc / g and 2.5 cc. / G or less, more preferably 1.5 cc / g or more and 2.5 cc / g or less.
- the activated carbon 2 having the above-described mesopore size and micropore size has a higher BET specific surface area than activated carbon used for conventional electric double layer capacitors or lithium ion capacitors.
- the specific value of the BET specific surface area of the activated carbon 2 is preferably 2,300 m 2 / g or more and 4,000 m 2 / g or less.
- the lower limit of the BET specific surface area is more preferably 3,000 m 2 / g or more, and further preferably 3,200 m 2 / g or more.
- the upper limit of the BET specific surface area is more preferably 3,800 m 2 / g or less.
- the BET specific surface area of the activated carbon 2 is 2,300 m 2 / g or more, a good energy density is easily obtained, and when the BET specific surface area of the activated carbon 2 is 4,000 m 2 / g or less, the strength of the electrode Since it is not necessary to add a large amount of a binder in order to maintain the resistance, the performance per electrode volume increases.
- the activated carbon 2 having the characteristics as described above can be obtained by using, for example, raw materials and processing methods as described below.
- the carbon source used as a raw material for the activated carbon 2 is not particularly limited as long as it is a carbon source that is usually used as an activated carbon raw material.
- various synthetic resins such as phenol resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, and the like.
- phenol resin and furan resin are particularly preferable because they are suitable for producing activated carbon 2 having a high specific surface area.
- Examples of a method for carbonizing these raw materials or a heating method at the activation treatment include known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method.
- the atmosphere at the time of heating is an inert gas such as nitrogen, carbon dioxide, helium, or argon, or a gas mixed with other gases containing these inert gases as a main component.
- the carbonization temperature is preferably 400 to 700 ° C.
- the lower limit of the carbonization temperature is preferably 450 ° C. or higher, more preferably 500 ° C. or higher.
- the upper limit of the carbonization temperature is preferably 650 ° C. or less.
- the raw material is preferably fired for about 0.5 to 10 hours.
- Examples of the method for activating the carbide after the carbonization treatment include a gas activation method in which firing is performed using an activation gas such as water vapor, carbon dioxide, and oxygen, and an alkali metal activation method in which heat treatment is performed after mixing with an alkali metal compound.
- an alkali metal activation method is preferred.
- the mass ratio of the carbide and the alkali metal compound such as KOH or NaOH is 1: 1 or more (the amount of the alkali metal compound is the same as or more than the amount of the carbide).
- heating is performed in an inert gas atmosphere at a temperature of 600 to 900 ° C., preferably 650 ° C. to 850 ° C. for 0.5 to 5 hours, and then the alkali metal compound is washed and removed with an acid and water. It is preferable to perform drying.
- the mass ratio of carbide: alkali metal compound is 1 : It is preferable that there are more alkali metal compounds than 3, and it is preferable that it is 1: 5.5 or less.
- the amount of pores increases as the number of alkali metal compounds increases with respect to the carbide. However, in consideration of the subsequent processing efficiency such as washing, it is preferably in the range of 1: 5.5 or less.
- the average particle diameter of the activated carbon 2 is preferably 1 ⁇ m or more and 30 ⁇ m or less, more preferably 2 ⁇ m or more and 20 ⁇ m or less, and further preferably 3 ⁇ m or more and 10 ⁇ m or less.
- each of the activated carbons 1 and 2 may be a single activated carbon, or a mixture of two or more kinds of activated carbons, and exhibit the above characteristics as a whole mixture. There may be.
- the activated carbons 1 and 2 may be used by selecting either one of them, or may be used by mixing both.
- the positive electrode active material, activated carbon 1 and 2 other than the materials, for example, active carbon not having the specific V 1 and / or V 2, or material other than the activated carbon, for example, a composite oxide or the like of lithium and transition metal May be included.
- the content of the activated carbon 1, or the content of the activated carbon 2, or the total content of the activated carbons 1 and 2 is preferably more than 50% by mass of the total positive electrode active material, and 70% by mass or more. More preferably, 90 mass% or more is still more preferable, and it is still more preferable that it is 100 mass%.
- the content ratio of the positive electrode active material in the positive electrode is preferably 35% by mass or more and 95% by mass or less based on the total mass of the positive electrode active material layer in the positive electrode precursor.
- As a minimum of the content rate of a positive electrode active material it is more preferable that it is 45 mass% or more, and it is further more preferable that it is 55 mass% or more.
- As an upper limit of the content rate of a positive electrode active material it is more preferable that it is 90 mass% or less, and it is still more preferable that it is 85 mass% or less.
- the “lithium compound” means a lithium compound that is not a positive electrode active material and is not a compound of the formulas (1) to (3).
- a lithium compound lithium carbonate, lithium oxide, lithium hydroxide, lithium fluoride, lithium chloride, lithium oxalate, and iodide can be decomposed at the positive electrode in the lithium doping step described later and release lithium ions.
- examples thereof include at least one selected from the group consisting of lithium, lithium nitride, lithium oxalate, and lithium acetate.
- lithium carbonate, lithium oxide, and lithium hydroxide are preferable, and lithium carbonate is more preferable from the viewpoint that handling in air is possible and hygroscopicity is low.
- Such a lithium compound decomposes upon application of a voltage, functions as a lithium-doped dopant source for the negative electrode, and forms a good film in the positive electrode active material layer, so that the positive electrode exhibits high high load charge / discharge cycle characteristics. Can be formed.
- the lithium compound is preferably particulate.
- the average particle diameter of the particulate lithium compound is preferably 0.1 ⁇ m or more and 10 ⁇ m or less. If the average particle size of the lithium compound is 0.1 ⁇ m or more, the volume of the vacancies remaining after the oxidation reaction of the lithium compound in the positive electrode is sufficiently large to hold the non-aqueous electrolyte solution. Will improve. When the average particle diameter of the particulate lithium compound is 10 ⁇ m or less, the surface area of the lithium compound is not excessively reduced, and the speed of the oxidation reaction of the lithium compound can be ensured.
- a pulverizer such as a ball mill, a bead mill, a ring mill, a jet mill, or a rod mill can be used.
- the content ratio of the lithium compound contained in the positive electrode is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 18% by mass or less, based on the total mass of the positive electrode active material layer in the positive electrode. If the content ratio of the lithium compound contained in the positive electrode is 1% by mass or more, there is a sufficient amount of the lithium compound to trap active products such as fluorine ions generated in the high load charge / discharge cycle. Charge / discharge cycle characteristics are improved. If the content rate of the lithium compound contained in a positive electrode is 20 mass% or less, the energy density of a non-aqueous lithium-type electrical storage element can be raised.
- the content ratio of the lithium compound contained in the positive electrode precursor is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass based on the total mass of the positive electrode active material layer in the positive electrode precursor. It is as follows. By adjusting the content ratio of the lithium compound contained in the positive electrode precursor to 10% by mass or more and 60% by mass or less, it exhibits a function suitable as a dopant source for the negative electrode and has an appropriate degree of porosity for the positive electrode. In addition, since a good film can be formed, it is possible to provide a non-aqueous lithium storage element having excellent high-load charge / discharge cycle characteristics.
- the identification method of the lithium compound contained in a positive electrode is not specifically limited, For example, it can identify by the following method. It is preferable to identify a lithium compound by combining a plurality of analysis methods described below.
- the measurement is performed after disassembling the nonaqueous lithium storage element in an argon box, taking out the positive electrode, and washing the electrolyte adhering to the positive electrode surface. It is preferable to carry out.
- the solvent for washing the positive electrode it is only necessary to wash away the electrolyte attached to the surface of the positive electrode.
- carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate can be suitably used.
- the positive electrode is immersed in a diethyl carbonate solvent 50 to 100 times the mass of the positive electrode for 10 minutes or more, and then the solvent is changed and the positive electrode is immersed again. Thereafter, the positive electrode is taken out from diethyl carbonate and vacuum-dried, and then SEM-EDX, Raman spectroscopy, and XPS analysis are performed.
- the conditions for vacuum drying are such that the remaining amount of diethyl carbonate in the positive electrode is 1% by mass or less in the range of temperature: 0 to 200 ° C., pressure: 0 to 20 kPa, and time: 1 to 40 hours.
- cleaning mentioned later and liquid volume adjustment can be measured, and it can quantify based on the analytical curve created beforehand.
- anions can be identified by analyzing the water after washing the positive electrode with distilled water. If a lithium compound cannot be identified by the above analysis method, other analysis methods include solid-state 7 Li-NMR, XRD (X-ray diffraction), TOF-SIMS (time-of-flight secondary ion mass spectrometry), AES (Auger) Lithium compounds can also be identified by using electron spectroscopy, TPD / MS (heat generation gas mass spectrometry), DSC (differential scanning calorimetry), or the like.
- the lithium compound containing oxygen and the positive electrode active material can be distinguished by oxygen mapping of the SEM-EDX image of the positive electrode surface measured at an observation magnification of 1,000 to 4,000 times.
- the SEM-EDX image can be measured with an acceleration voltage of 10 kV, an emission current of 10 ⁇ A, a measurement pixel number of 256 ⁇ 256 pixels, and an integration count of 50 times.
- the sample can be surface-treated by a method such as vacuum deposition or sputtering of gold, platinum, osmium, or the like.
- the luminance and contrast it is preferable to adjust the luminance and contrast so that there is no pixel that reaches the maximum brightness, and the average brightness is in the range of 40% to 60%.
- the obtained oxygen mapping is binarized on the basis of the average value of brightness, particles containing 50% or more of bright areas in area are defined as lithium compounds.
- the lithium compound containing a carbonate ion and the positive electrode active material can be discriminated by Raman imaging of the positive electrode surface measured at an observation magnification of 1,000 to 4,000 times.
- the excitation light is 532 nm
- the excitation light intensity is 1%
- the long operation of the objective lens is 50 times
- the diffraction grating is 1,800 gr / mm
- the mapping method is point scanning (slit 65 mm, binning 5 pix), 1 mm step
- An example of the condition with a noise filter is that the exposure time per point is 3 seconds, the number of times of integration is one time.
- a straight base line is set in the range of 1,071 to 1,104 cm ⁇ 1, an area is calculated with a positive value from the base line as a carbonate ion peak, and the frequency is integrated. At this time, the frequency with respect to the carbonate ion peak area obtained by approximating the noise component with a Gaussian function is subtracted from the frequency distribution of carbonate ions.
- the bonding state of lithium can be determined.
- the X-ray source is monochromatic AlK ⁇
- the X-ray beam diameter is 100 ⁇ m ⁇ (25 W, 15 kV)
- the path energy is narrow scan: 58.70 eV
- there is charge neutralization and the number of sweeps is narrow scan: 10 times (carbon Oxygen) 20 times (fluorine) 30 times (phosphorus) 40 times (lithium) 50 times (silicon)
- energy step can be exemplified by narrow scan: 0.25 eV. It is preferable to clean the surface of the positive electrode by sputtering before the XPS measurement.
- the surface of the positive electrode can be cleaned under the condition of an acceleration voltage of 1.0 kV and a range of 2 mm ⁇ 2 mm for 1 minute (1.25 nm / min in terms of SiO 2 ).
- the Li1s bond energy of 50 to 54 eV is LiO 2 or Li—C bond
- the peak of 55 to 60 eV is LiF, Li 2 CO 3 , Li x PO y F z (wherein x, y and z are each an integer of 1 to 6)
- a C1s bond energy peak of 285 eV is a C—C bond
- a peak of 286 eV is a CO bond
- a peak of 288 eV is a COO
- a peak of 290 to 292 eV is a peak CO 3 2 ⁇ , C—F bond
- the peak of O1s binding energy of 527 to 530 eV is O 2 ⁇ (Li 2 O)
- the peak of 531 to 532 eV is CO, CO 3 , OH, PO x (wherein x is 1 to 4 integer), in SiO x (wherein, x is an integer of 1 to 4), C-O peaks 533 eV, in Si
- the existing lithium compound can be identified from the measurement result of the obtained electronic state and the result of the ratio of existing elements.
- Anion species eluted in water can be identified by washing the positive electrode with distilled water and analyzing the washed water by ion chromatography.
- an ion exchange type, an ion exclusion type, a reverse phase ion pair type, or the like can be used.
- an electric conductivity detector, an ultraviolet-visible absorption detector, an electrochemical detector, or the like can be used.
- a non-suppressor method using a solution with low conductivity as the eluent can be used.
- an appropriate column can be selected based on lithium compounds identified from analysis results such as SEM-EDX, Raman spectroscopy, XPS, etc. And combining the detectors.
- the sample retention time is constant for each ion species component if the conditions such as the column and eluent used are determined, and the magnitude of the peak response differs for each ion species, but is proportional to the concentration of the ion species. . It is possible to qualitatively and quantitatively determine the ionic species component by measuring in advance a standard solution having a known concentration in which traceability is ensured.
- a method for quantifying the lithium compound contained in the positive electrode is described below.
- the positive electrode is washed with an organic solvent, then washed with distilled water, and the lithium compound can be quantified from the change in the mass of the positive electrode before and after washing with distilled water.
- Area of measurement for the positive electrode is not particularly limited but is preferably from the viewpoint of reducing the variation in measurement is 5 cm 2 or more 200 cm 2 or less, more preferably 25 cm 2 or more 150 cm 2 or less. If the area is 5 cm 2 or more, the reproducibility of measurement is ensured. If the area is 200 cm 2 or less, the sample is easy to handle.
- the organic solvent is not particularly limited as long as it can remove the non-aqueous electrolyte decomposition product deposited on the surface of the positive electrode. This is preferable because elution of the compound is suppressed.
- polar solvents such as methanol and acetone are preferably used.
- the positive electrode is sufficiently immersed in a methanol solution 50 to 100 times the mass of the positive electrode for 3 days or more. At this time, it is preferable to take measures such as covering the container so that methanol does not volatilize. Thereafter, the positive electrode is taken out of the methanol and dried in a vacuum (temperature: 100 to 200 ° C., pressure: 0 to 10 kPa, time: 5 to 20 hours under the condition that the remaining amount of methanol in the positive electrode is 1% by mass or less.
- the GC / MS of water after washing with distilled water which will be described later, can be measured and quantified based on a calibration curve prepared in advance.
- the mass of the positive electrode at that time is M 0 (g).
- the positive electrode is sufficiently immersed in distilled water 100 times the mass of the positive electrode (100 M 0 (g)) for 3 days or more. At this time, it is preferable to take measures such as covering the container so that distilled water does not volatilize.
- X 1 is more than 0.1 [mu] m, it is possible to leave the lithium compound in the positive electrode after lithium pre-doping, a high-load charge-discharge cycle characteristics by adsorbing the fluorine ions generated by the high-load charging and discharging cycle improves.
- X 1 is a 10 ⁇ m or less, since the reaction area with the fluorine ions generated by the high-load charging and discharging cycles increases, it is possible to efficiently adsorb the fluorine ions.
- Y 1 is not less than 2 [mu] m, it can be secured electronic conductivity between the positive electrode active material.
- the reaction area with the electrolyte ions increases, so that high input / output characteristics can be expressed.
- X 1 ⁇ Y 1 the lithium compound is filled in the gap generated between the positive electrode active materials, so that the energy density can be increased while ensuring the electron conductivity between the positive electrode active materials.
- the measurement method of X 1 and Y 1 is not particularly limited, but can be calculated from the SEM image of the positive electrode cross section and the SEM-EDX image.
- BIB processing can be used in which an Ar beam is irradiated from the upper part of the positive electrode and a smooth cross section is produced along the end of the shielding plate placed immediately above the sample.
- the distribution of carbonate ions can be obtained by measuring Raman imaging of the cross section of the positive electrode.
- the lithium compound and the positive electrode active material can be distinguished from each other by oxygen mapping using a SEM-EDX image of the cross section of the positive electrode measured at an observation magnification of 1000 to 4000 times.
- the SEM-EDX image measurement method it is preferable to adjust the luminance and contrast so that there is no pixel that reaches the maximum brightness, and the average brightness is in the range of 40% to 60%.
- a particle containing a bright portion binarized on the basis of the average value of brightness with an area of 50% or more is defined as a lithium compound.
- X 1 and Y 1 can be obtained by image analysis of an image obtained from the positive electrode cross section SEM-EDX measured in the same field of view as the positive electrode cross section SEM.
- the lithium compound particle X and other particles determined in the SEM image of the positive electrode cross section are the positive electrode active material particles Y, and the cross-sectional area of all the X and Y particles observed in the cross-sectional SEM image is as follows. S is obtained, and the particle diameter d is obtained by the following formula (circumference is assumed to be ⁇ ).
- volume average particle diameters X 0 and Y 0 are obtained by the following formula.
- X 0 (Y 0 ) ⁇ [4 / 3 ⁇ ⁇ (d / 2) 3 ⁇ d] / ⁇ [4 / 3 ⁇ ⁇ (d / 2) 3 ] 5 or more positions are measured by changing the field of view of the positive electrode cross section, and the average value of each X 0 and Y 0 is defined as the average particle diameter X 1 and Y 1 .
- the positive electrode active material layer in the present embodiment may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer in addition to the positive electrode active material and the lithium compound as necessary.
- the conductive filler is not particularly limited, and for example, acetylene black, ketjen black, vapor grown carbon fiber, graphite, carbon nanotube, a mixture thereof, and the like can be used.
- the amount of the conductive filler used is preferably 0 to 30 parts by mass, more preferably 0 to 20 parts by mass, and further preferably 1 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material. Or less. If the usage-amount of a conductive filler is 30 mass parts or less, the content rate of the positive electrode active material in a positive electrode active material layer will increase, and the energy density per positive electrode active material layer volume can be ensured.
- the binder is not particularly limited.
- PVdF polyvinylidene fluoride
- PTFE polytetrafluoroethylene
- polyimide latex
- fluororubber acrylic copolymer, etc.
- the amount of the binder used is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 3 parts by mass or more and 27 parts by mass or less, and still more preferably 5 parts by mass or more and 25 parts by mass with respect to 100 parts by mass of the positive electrode active material. Or less. If the usage-amount of a binder is 1 mass part or more, sufficient electrode intensity
- a dispersion stabilizer for example, PVP (polyvinyl pyrrolidone), PVA (polyvinyl alcohol), a cellulose derivative etc. can be used.
- the amount of the dispersion stabilizer used is preferably 0 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. When the amount of the dispersion stabilizer used is 10 parts by mass or less, high input / output characteristics are exhibited without impeding ion entry and exit and diffusion into the positive electrode active material.
- the material constituting the positive electrode current collector in the present embodiment is not particularly limited as long as it is a material that has high electron conductivity and does not easily deteriorate due to elution into a non-aqueous electrolyte and reaction with an electrolyte or ions.
- Metal foil is preferred.
- an aluminum foil is particularly preferable as the positive electrode current collector in the non-aqueous lithium storage element of this embodiment.
- the metal foil may be a normal metal foil having no irregularities or through holes, or a metal foil having irregularities subjected to embossing, chemical etching, electrolytic deposition, blasting, etc., expanded metal, punching metal Alternatively, a metal foil having a through hole such as an etching foil may be used.
- the positive electrode current collector in the present embodiment is preferably a metal foil having no through hole. Without the through-hole, the manufacturing cost is low, the thinning is easy, it can contribute to high energy density, and the current collecting resistance can be lowered, so that high input / output characteristics can be obtained.
- the thickness of the positive electrode current collector is not particularly limited as long as the shape and strength of the positive electrode can be sufficiently maintained, but for example, 1 to 100 ⁇ m is preferable.
- the positive electrode precursor serving as the positive electrode of the non-aqueous lithium storage element can be manufactured by an electrode manufacturing technique in a known lithium ion battery, electric double layer capacitor, or the like.
- a positive electrode active material, a lithium compound, and other optional components used as necessary are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is used as a positive electrode.
- a positive electrode precursor can be obtained by coating on one or both sides of the current collector to form a coating film and drying it. You may press the obtained positive electrode precursor, and may adjust the film thickness and bulk density of a positive electrode active material layer.
- the positive electrode active material, the lithium compound, and other optional components to be used as needed are mixed in a dry method, and the resulting mixture is press-molded and then a conductive adhesive is used.
- a method of attaching to the positive electrode current collector is also possible.
- the coating solution for the positive electrode precursor was dry blended with some or all of the various material powders including the positive electrode active material, and then water or an organic solvent and / or a binder or a dispersion stabilizer was dissolved or dispersed therein. You may prepare by adding a liquid or slurry-like substance.
- a coating solution may be prepared by adding various material powders containing a positive electrode active material to a liquid or slurry substance in which a binder or dispersion stabilizer is dissolved or dispersed in water or an organic solvent.
- a positive electrode active material and a lithium compound, and a conductive filler as necessary are premixed using a ball mill or the like, and premixing is performed to coat a conductive material on a lithium compound having low conductivity. May be. Thereby, a lithium compound becomes easy to decompose
- water is used as the solvent of the coating solution, the addition of a lithium compound may make the coating solution alkaline, so a pH adjuster may be added as necessary.
- a disperser such as a homodisper, a multiaxial disperser, a planetary mixer, a thin film swirl type high speed mixer or the like can be preferably used.
- a peripheral speed of 1 m / s to 50 m / s it is preferable to disperse at a peripheral speed of 1 m / s to 50 m / s.
- a peripheral speed of 1 m / s or more is preferable because various materials can be dissolved or dispersed satisfactorily.
- a peripheral speed of 50 m / s or less is preferable because various materials are not easily broken by heat and shearing force due to dispersion, and reaggregation is reduced.
- the dispersion degree of the coating solution is preferably such that the particle size measured with a particle gauge is 0.1 ⁇ m or more and 100 ⁇ m or less.
- the particle size is more preferably 80 ⁇ m or less, and further preferably the particle size is 50 ⁇ m or less.
- a particle size of 0.1 ⁇ m or more means that various material powders including the positive electrode active material are not excessively crushed during the preparation of the coating liquid. Further, when the particle size is 100 ⁇ m or less, clogging during coating liquid discharge and streaking of the coating film are not generated, and coating can be performed stably.
- the viscosity ( ⁇ b) of the coating solution for the positive electrode precursor is preferably 1,000 mPa ⁇ s to 20,000 mPa ⁇ s, more preferably 1,500 mPa ⁇ s to 10,000 mPa ⁇ s, and even more preferably 1, 700 mPa ⁇ s or more and 5,000 mPa ⁇ s or less. If the viscosity ((eta) b) of the coating liquid of a positive electrode precursor is 1,000 mPa * s or more, the dripping at the time of coating-film formation will be suppressed and the coating-film width and thickness can be controlled favorably.
- the viscosity ( ⁇ b) of the coating liquid for the positive electrode precursor is 20,000 mPa ⁇ s or less, the pressure loss in the flow path of the coating liquid when using a coating machine can be reduced and the coating can be performed stably. It can be controlled to be less than the thickness of the coating film.
- the TI value (thixotropic index value) of the positive electrode precursor coating solution is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. If the TI value of the coating solution for the positive electrode precursor is 1.1 or more, the coating film width and thickness can be controlled well.
- the method for forming the coating film of the positive electrode precursor is not particularly limited, but preferably a coating machine such as a die coater, a comma coater, a knife coater, or a gravure coating machine can be used.
- the coating film may be formed by single layer coating or may be formed by multilayer coating. In the case of multilayer coating, the composition of the coating solution may be adjusted so that the lithium compound content in each layer of the coating film is different.
- the coating speed is preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 70 m / min, and further preferably 1 m / min to 50 m / min. If the coating speed is 0.1 m / min or more, it can be applied stably, and if it is 100 m / min or less, sufficient coating accuracy can be secured.
- the method for drying the coating film of the positive electrode precursor is not particularly limited, but a drying method such as hot air drying or infrared (IR) drying can be preferably used.
- the coating film may be dried at a single temperature or may be dried by changing the temperature in multiple stages. Moreover, you may dry combining several drying methods.
- the drying temperature is preferably 25 ° C. or higher and 200 ° C. or lower, more preferably 40 ° C. or higher and 180 ° C. or lower, and further preferably 50 ° C. or higher and 160 ° C. or lower.
- the drying temperature is 25 ° C. or higher, the solvent in the coating film can be sufficiently volatilized.
- the drying temperature is 200 ° C. or less, cracking of the coating film due to rapid volatilization of the solvent, uneven distribution of the binder due to migration, and oxidation of the positive electrode current collector and the positive electrode active material layer can be suppressed.
- the method for pressing the positive electrode precursor is not particularly limited, but a press such as a hydraulic press or a vacuum press can be preferably used.
- the film thickness, bulk density, and electrode strength of the positive electrode active material layer can be adjusted by the press pressure, gap, and surface temperature of the press part described later.
- the pressing pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and further preferably 2 kN / cm or more and 7 kN / cm or less. If the pressing pressure is 0.5 kN / cm or more, the electrode strength can be sufficiently increased.
- the positive electrode precursor When the pressing pressure is 20 kN / cm or less, the positive electrode precursor is unlikely to be bent or wrinkled, and is easily adjusted to a desired film thickness or bulk density of the positive electrode active material layer.
- the gap between the press rolls can be set to an arbitrary value according to the thickness of the positive electrode precursor after drying so as to have a desired thickness and bulk density of the positive electrode active material layer.
- the pressing speed can be set to an arbitrary speed so as to reduce the bending and wrinkling of the positive electrode precursor.
- the surface temperature of the press part may be room temperature or may be heated if necessary.
- the lower limit of the surface temperature of the press part when heating is preferably the melting point of the binder used minus 60 ° C. or more, more preferably the melting point of the binder minus 45 ° C.
- the upper limit of the surface temperature of the press part when heated is preferably the melting point of the binder used plus 50 ° C. or less, more preferably the melting point of the binder plus 30 ° C. or less, more preferably the melting point of the binder plus 20 It is below °C.
- PVdF polyvinylidene fluoride: melting point 150 ° C.
- it is preferably pressed at 90 ° C. or higher and 200 ° C. or lower, more preferably 105 ° C. or higher and 180 ° C. or lower, and further preferably 120 ° C. or higher and 170 ° C.
- styrene-butadiene copolymer (melting point 100 ° C.) is used as the binder, it is preferably pressed at 40 ° C. or higher and 150 ° C. or lower, more preferably 55 ° C. or higher and 130 ° C. or lower, and even more preferably 70 ° C. or higher and 120 ° C. or lower. Warm the surface of the part.
- the melting point of the binder can be determined at the endothermic peak position of DSC (Differential Scanning Calorimetry). For example, using a differential scanning calorimeter “DSC7” manufactured by PerkinElmer Co., Ltd., 10 mg of sample resin is set in a measurement cell, and the temperature is increased from 30 ° C. to 250 ° C. at a temperature increase rate of 10 ° C./min in a nitrogen gas atmosphere. The temperature is raised, and the endothermic peak temperature in the temperature raising process becomes the melting point. You may press several times, changing conditions of press pressure, a crevice, speed, and surface temperature of a press part.
- DSC7 Different Scanning Calorimetry
- the film thickness of the positive electrode active material layer is preferably 20 ⁇ m or more and 200 ⁇ m or less per side of the positive electrode current collector, more preferably 25 ⁇ m or more and 100 ⁇ m or less, more preferably 30 ⁇ m or more and 80 ⁇ m or less.
- the thickness of the positive electrode active material layer is 20 ⁇ m or more, sufficient charge / discharge capacity can be exhibited. If the thickness of the positive electrode active material layer is 200 ⁇ m or less, the ion diffusion resistance in the electrode can be kept low. Therefore, if the thickness of the positive electrode current collector layer is 20 ⁇ m or more and 200 ⁇ m or less, sufficient output characteristics can be obtained, and the volume of the non-aqueous lithium storage element can be reduced, so that the energy density can be increased.
- the film thickness of the positive electrode active material layer in the case where the positive electrode current collector has through-holes and irregularities is the film of the positive electrode active material layer per side in the portion of the positive electrode current collector that does not have through-holes and irregularities This is the average thickness.
- the bulk density of the positive electrode active material layer in the positive electrode after the lithium doping step described later is preferably 0.50 g / cm 3 or more, more preferably 0.55 g / cm 3 or more and 1.3 g / cm 3 or less.
- the bulk density of the positive electrode active material layer is 0.50 g / cm 3 or more, a high energy density can be expressed, and the size reduction of the nonaqueous lithium storage element can be achieved.
- the bulk density of the positive electrode active material layer is 1.3 g / cm 3 or less, diffusion of the non-aqueous electrolyte in the pores in the positive electrode active material layer is sufficient, and high output characteristics are obtained.
- the negative electrode in the present embodiment includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material provided on one or both surfaces thereof.
- the solid 7 Li-NMR spectrum of the negative electrode active material layer containing a graphite-based carbon material as the negative electrode active material has a peak maximum value between 4 ppm and 30 ppm in the spectrum range of ⁇ 10 ppm to 35 ppm.
- the amount of lithium per unit mass of the negative electrode active material layer occluded with lithium ions (hereinafter also referred to as “the amount of lithium in the negative electrode active material layer”) calculated from the peak area of 4 ppm to 30 ppm is 0.
- It is preferably from 10 mmol / g to 10.0 mmol / g, more preferably from 0.30 mmol / g to 9.0 mmol / g, still more preferably from 0.50 mmol / g to 8.0 mmol / g, particularly Preferably 0.80 mmol / g or more and 7.5 mmol / g or less, most preferably 1.0 mmol / g This is 7.0 mmol / g or less.
- the negative electrode of the present embodiment includes a graphite-based carbon material as a negative electrode active material, and the peak maximum value between 4 ppm and 30 ppm in the spectral range of ⁇ 10 ppm to 35 ppm with respect to the solid 7 Li-NMR spectrum of the negative electrode active material layer. And adjusting the amount of lithium per unit mass of the negative electrode active material layer occluded with lithium ions, which is calculated from the peak area of 4 ppm to 30 ppm, to the above range, the non-aqueous lithium type using this negative electrode
- the storage element exhibits high input / output characteristics and high load charge / discharge cycle characteristics. The principle is not clear and is not limited to theory, but it is presumed as follows.
- the spectrum observed at 30 ppm to 60 ppm is derived from lithium ions occluded in the carbon hexagonal network layer of the graphite portion of the graphite-based carbon material. Since lithium ions in such an occlusion state interact strongly with the carbon hexagonal network surface, a large amount of energy is required for the release of lithium ions, and resistance increases.
- the lithium ions in the occlusion state are occluded / released between the negative electrode and the non-aqueous electrolyte solution through the amorphous part having more reaction sites than the graphite part. . Therefore, in the spectral range of ⁇ 10 ppm to 35 ppm of the solid 7 Li-NMR spectrum of the negative electrode active material layer, the maximum value of the peak is adjusted between 4 ppm and 30 ppm, and the lithium calculated from the peak area of 4 ppm to 30 ppm is calculated. By adjusting the amount to the above range, it is considered that the input / output resistance of the non-aqueous lithium storage element using this negative electrode can be reduced and high input / output characteristics can be exhibited. Moreover, the lithium ion in such an occlusion state can sufficiently respond to a high load charge / discharge cycle that repeats a large current charge / discharge for the above-described reason, and can exhibit good high load charge / discharge cycle characteristics.
- the non-aqueous lithium storage element using the negative electrode including the negative electrode active material layer has high input / output characteristics and high load charge. Discharge cycle characteristics can be shown.
- the amount of lithium in the negative electrode active material layer is 10.0 mmol / g or less, lithium ions occluded in the negative electrode active material can be suppressed from being released by self-discharge.
- the negative electrode according to the present embodiment lithium ions released by self-discharge can be prevented from reacting with the non-aqueous electrolyte solution in the negative electrode active material layer, thereby increasing the film or deposit.
- the non-aqueous lithium storage element using can exhibit high high-load charge / discharge cycle characteristics.
- the amount of lithium per unit mass of the negative electrode active material layer occluded with lithium ions obtained from the solid 7 Li-NMR spectrum of the negative electrode active material layer is determined by the following method. It can be calculated.
- a commercially available apparatus can be used as an apparatus for measuring solid 7 Li-NMR. Under a room temperature environment, the spectrum is measured by a single pulse method with a magic angle spinning rotation speed of 14.5 kHz and an irradiation pulse width of 45 ° pulse. The measurement is set so that a sufficient waiting time is repeated between measurements.
- a 1 mol / L lithium chloride aqueous solution is used as a shift reference, and the shift position separately measured as an external standard is 0 ppm.
- the sample is not rotated, and the spectrum is measured by a single pulse method with an irradiation pulse width of 45 ° pulse.
- the peak area is determined for the component in the range of 4 ppm to 30 ppm. Next, these peak areas are divided by the peak area of a 1 mol / L lithium chloride aqueous solution measured by making the sample height in the rotor for measurement the same as when measuring the negative electrode active material layer, and the negative electrode used for the measurement. By dividing by the mass of the active material layer, the amount of lithium in the negative electrode active material layer can be calculated.
- the mass of the negative electrode active material layer is the mass of the negative electrode active material layer including lithium ions occluded in the negative electrode active material layer, a film or a deposit contained in the negative electrode active material layer, and the like.
- the average distance between centers of gravity (hereinafter also referred to as “r p ”) of voids obtained from the SEM of the negative electrode active material layer cross section is preferably 1 ⁇ m or more and 10 ⁇ m or less, more preferably 1.3 ⁇ m or more. It is 8 ⁇ m or less, more preferably 1.5 ⁇ m or more and 6 ⁇ m or less, particularly preferably 1.7 ⁇ m or more and 5 ⁇ m or less, and most preferably 1.9 ⁇ m or more and 4 ⁇ m or less.
- the non-aqueous lithium storage element of this embodiment uses a positive electrode containing a lithium compound other than the positive electrode active material, and a negative electrode in which the average distance between the centers of gravity of voids obtained from the SEM of the negative electrode active material layer cross section is adjusted to a specific range. Therefore, high input / output characteristics and high load charge / discharge cycle characteristics are exhibited.
- the principle is not clear and is not limited to theory, but it is presumed as follows. It is considered that the average distance between the centers of gravity of the voids obtained from the SEM of the negative electrode active material layer cross section represents the distribution of the non-aqueous electrolyte retained in the negative electrode active material layer.
- a moderate non-aqueous electrolyte can be hold
- active products such as fluorine ions generated at the positive electrode during a high load charge / discharge cycle (for example, HF Etc.) easily diffuses into the negative electrode active material layer.
- active products such as fluorine ions react with lithium ions and non-aqueous electrolytes occluded in the negative electrode active material in the negative electrode active material layer, resulting in coatings and deposits resulting from reductive decomposition of the non-aqueous electrolyte solution Increase.
- the high load charge / discharge cycle characteristics deteriorate.
- the positive electrode contains a lithium compound other than the positive electrode active material
- the lithium compound traps such active products such as fluorine ions, so that an increase in coating film and deposits in the negative electrode active material layer can be suppressed. Good high load charge / discharge cycle characteristics can be exhibited.
- the average distance between the centers of gravity of the voids obtained from the SEM of the negative electrode active material layer cross section is 1 ⁇ m or more, the size of the voids is large, and a sufficient amount of non-aqueous electrolyte solution in the voids can be retained. High input / output characteristics and high load charge / discharge cycle characteristics can be exhibited. If the average distance between the centers of gravity of the voids obtained from the SEM of the negative electrode active material layer cross section is 10 ⁇ m or less, the non-aqueous electrolyte is appropriately distributed in the negative electrode active material layer. And high load charge / discharge cycle characteristics.
- the average distance between the centers of gravity of the voids obtained from the SEM of the negative electrode active material layer cross section can be calculated by the following method.
- the sample used for the measurement may be a negative electrode (hereinafter also referred to as “a negative electrode before use”) that is not incorporated in the non-aqueous lithium storage element, or a negative electrode (hereinafter referred to as “non-aqueous lithium storage element”). , Also referred to as “a negative electrode after use”).
- a negative electrode incorporated in a non-aqueous lithium storage element As a measurement sample, it is preferable to use, for example, the following method as a pretreatment of the measurement sample.
- the nonaqueous lithium storage element is disassembled under an inert atmosphere such as argon, and the negative electrode is taken out.
- the taken-out negative electrode is immersed in chain carbonate (for example, methyl ethyl carbonate, dimethyl carbonate, etc.), non-aqueous electrolyte solution, lithium salt, etc. are removed and air-dried.
- chain carbonate for example, methyl ethyl carbonate, dimethyl carbonate, etc.
- non-aqueous electrolyte solution, lithium salt, etc. are removed and air-dried.
- the following method (1), (2), or (3) is preferably used.
- the obtained negative electrode is immersed in a mixed solvent composed of methanol and isopropanol, the lithium ions occluded in the negative electrode active material are deactivated, and air-dried.
- a measurement sample can be obtained by removing the chain carbonate, the organic solvent, and the like contained in the negative electrode obtained by vacuum drying or the like.
- the obtained negative electrode is used as a working electrode, metallic lithium is used as a counter electrode and a reference electrode, and these are immersed in a non-aqueous electrolyte to produce an electrochemical cell.
- the obtained electrochemical cell is adjusted using a charger / discharger or the like so that the negative electrode potential (vs. Li / Li + ) is in the range of 1.5V to 3.5V.
- the negative electrode is taken out from the electrochemical cell under an inert atmosphere such as argon, soaked in a chain carbonate, removed from the non-aqueous electrolyte, lithium salt, etc., and air-dried.
- a measurement sample can be obtained by removing the chain carbonate and the like contained in the negative electrode obtained by vacuum drying or the like.
- the negative electrode obtained above can be used as a measurement sample as it is.
- the formation of the cross section of the negative electrode active material layer and SEM observation described later are preferably performed in an inert atmosphere such as argon.
- the negative electrode active material layer for the measurement sample obtained above when the horizontal plane with respect to the stacking direction of the negative electrode current collector and the negative electrode active material layer is a cross section and the plane perpendicular to the horizontal plane is a plane.
- the cross section is formed.
- the method for forming the cross section of the negative electrode active material layer is not particularly limited as long as it can suppress damage to the cross section of the negative electrode active material layer due to the formation and processing of the cross section, but is preferably a processing method using an ion beam (for example, BIB). (Broad Ion Beam) processing method, FIB (Focused Ion Beam) processing method), precision mechanical polishing, ultramicrotome, and the like can be used.
- BIB BiB
- a BIB processing method using an argon ion beam from the viewpoint of suppressing damage due to formation / processing on the cross section of the negative electrode active material layer.
- An argon ion beam is irradiated from above the plane of the negative electrode, and a cross section of the negative electrode active material layer perpendicular to the plane of the negative electrode is formed along the end of a shielding plate (mask) placed immediately above the plane of the negative electrode.
- the cross section of the formed negative electrode active material layer is observed with a scanning electron microscope (SEM), and an SEM image of the cross section of the negative electrode active material layer is obtained.
- SEM scanning electron microscope
- a Lower detector that can lower the detection sensitivity of the internal structure of the negative electrode active material layer observed between the negative electrode active materials from the viewpoint of facilitating image analysis such as binarization processing, which will be described later, as necessary. Etc. may be used.
- image analysis is performed on the SEM image of the obtained negative electrode active material layer cross section.
- the image analysis tool is not particularly limited as long as it can perform the processing described later, but IP-1000 (software name: A image-kun) manufactured by Asahi Kasei Corporation, ImageJ, or the like can be used.
- the region for image analysis is extracted from the cross section of the negative electrode active material layer in the SEM image at an observation magnification of 1,000 to 10,000 times, preferably 3,000 times. If necessary, fine noise included in the image may be removed from the extracted region using a median filter or the like before performing the binarization processing described later.
- the median filter in this specification is an operation of replacing the luminance of a pixel of interest with the median luminance of nine pixels of 3 pixels ⁇ 3 pixels around it.
- a binarization process is performed on the extracted region to convert a contrast image into two gradations (for example, white and black). Contrast is adjusted so that the portion including the minimum and maximum values of the luminance histogram of the extracted region and the portion corresponding to the void in the extracted region is a dark portion and the portion corresponding to the negative electrode active material is a bright portion. Perform value processing.
- the gradation located at the bottom of the valley of the luminance histogram of the extracted region is used as a threshold value, and gradation 1 (for example, white) if the luminance of each pixel exceeds the threshold value, If it is lower, the tone is 2 (for example, black). In this case, tone 2 (for example, black) corresponds to the gap.
- the gradation 2 portion of the binarized image is treated as a gap, and the average distance between the centers of gravity of the gap is calculated by the following method.
- the voids having an area larger than 0.2 ⁇ m 2 are used to connect the centroids of adjacent voids with straight lines, and the length of each line segment (centroid The average value of (distance between) is calculated and set as the average distance between the centers of gravity of the air gaps. Note that the way of connecting the centers of gravity is not random, but a figure called a Delaunay diagram or a Delaunay triangulation. Connecting the centroids creates a polygon, but the polygon becomes a triangle except in special cases.
- the negative electrode active material layer contains a negative electrode active material, and may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer as necessary.
- the negative electrode active material a material capable of inserting and extracting lithium ions can be used.
- the negative electrode active material include carbon materials, titanium oxide, silicon, silicon oxide, silicon alloys, silicon compounds, tin, and tin compounds.
- the content of the carbon material is preferably 50% by mass or more, more preferably 70% by mass or more, with respect to the total mass of the negative electrode active material.
- the content of the carbon material may be 100% by mass. However, from the viewpoint of obtaining a good effect in combination with other materials, for example, it is preferably 90% by mass or less, and 80% by mass or less. There may be.
- the negative electrode active material is preferably doped with lithium ions.
- the lithium ion doped in the negative electrode active material mainly includes three forms.
- the first form is lithium ions that are previously occluded as a design value in the negative electrode active material before producing a non-aqueous lithium storage element.
- the second form is lithium ions occluded in the negative electrode active material when a non-aqueous lithium storage element is manufactured and shipped.
- the third form is lithium ions occluded in the negative electrode active material after using the non-aqueous lithium storage element as a device.
- the carbon material examples include non-graphitizable carbon material (hard carbon); graphitizable carbon material (soft carbon); carbon black; carbon nanoparticles; activated carbon; graphite-based carbon material; amorphous carbon such as polyacene-based material
- carbonaceous material obtained by heat treatment of carbonaceous material precursors such as petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, synthetic resin (eg, phenol resin); furfuryl alcohol resin or Examples include pyrolysis products of novolac resins; fullerenes; carbon nanophones; and composite carbon materials thereof.
- Examples of the graphite-based carbon material include graphite materials such as artificial graphite, natural graphite, low crystal graphite, graphitized mesophase carbon spherules, graphite whisker, and high specific surface area graphite, and amorphous materials described later in these graphite materials.
- the carbon material etc. which gave the formation method of the mass part can be used.
- the method for forming the amorphous part of the graphite-based carbon material is not particularly limited, but a method of combining a graphite material and a carbonaceous material described later; laser, plasma, corona on the graphite material A method of performing physical surface modification such as treatment; a method of performing chemical surface modification of the graphite material by immersing the graphite material in an acid or alkali solution and heating; a method of performing graphite-based carbon material such as needle coke; Graphite and amorphous by firing pattern when graphitizing the raw material (for example, rapidly increasing the temperature in the range of 2,000 ° C. to 3,000 ° C. and then decreasing rapidly to 100 ° C.
- the amorphous part may be formed on the surface of the graphite-based carbon material or may be formed inside the graphite-based carbon material, but is preferably formed on the surface of the graphite-based carbon material for the reasons described above. .
- heat treatment is performed in a state where at least one carbon material (hereinafter also referred to as “base material”) and a carbonaceous material precursor coexist.
- base material a carbon material
- a composite carbon material obtained by combining a carbonaceous material derived from a material precursor is preferable.
- the carbonaceous material precursor is not particularly limited as long as it becomes a carbonaceous material by heat treatment, but petroleum-based pitch or coal-based pitch is particularly preferable.
- the substrate and the carbonaceous material precursor may be mixed at a temperature higher than the melting point of the carbonaceous material precursor.
- the heat treatment temperature may be a temperature at which a component generated by volatilization or thermal decomposition of the carbonaceous material precursor to be used becomes a carbonaceous material, preferably 400 ° C. or more and 2500 ° C. or less, more preferably 500 ° C.
- the temperature is 2,000 ° C. or lower, more preferably 550 ° C. or higher and 1,500 ° C. or lower.
- the atmosphere for performing the heat treatment is not particularly limited, but a non-oxidizing atmosphere is preferable.
- composite carbon material are composite carbon materials 1 and 2 described later. Either of these may be used, or both of these may be used in combination.
- the composite carbon material 1 is a composite carbon material in which one or more carbon materials having a BET specific surface area of 100 m 2 / g or more and 3,000 m 2 / g or less are used as a base material.
- the base material of the composite carbon material 1 is not particularly limited as long as the BET specific surface area is 100 m 2 / g or more and 3000 m 2 / g or less, but activated carbon, carbon black, template porous carbon, high specific surface area graphite. Carbon nanoparticles and the like can be suitably used.
- the BET specific surface area of the composite carbon material 1 is preferably 100 m 2 / g or more and 1,500 m 2 / g or less, more preferably 150 m 2 / g or more and 1,100 m 2 / g or less, further preferably 180 m 2 / g or more and 550 m. 2 / g or less. If the BET specific surface area of the composite carbon material 1 is 100 m 2 / g or more, the pores can be appropriately maintained, and the diffusion of lithium ions in the non-aqueous electrolyte solution is improved, so that high input / output characteristics are exhibited.
- the number of reaction sites with lithium ions in the non-aqueous electrolyte can be increased sufficiently, high input / output characteristics can be exhibited.
- the BET specific surface area of the composite carbon material 1 is 1,500 m 2 / g or less, the charge / discharge efficiency of lithium ions is improved, and excessive reductive decomposition of the non-aqueous electrolyte solution can be suppressed. Discharge cycle characteristics are less likely to be impaired.
- the mass ratio of the carbonaceous material to the base material in the composite carbon material 1 is preferably 10% by mass to 200% by mass, more preferably 12% by mass to 180% by mass, and still more preferably 15% by mass to 160% by mass. Hereinafter, it is more preferably 18% by mass or more and 150% by mass or less. If the mass ratio of the carbonaceous material is 10% by mass or more, the micropores of the base material can be appropriately filled with the carbonaceous material, and the charge / discharge efficiency of lithium ions is improved. Cycle characteristics can be shown. When the mass ratio of the carbonaceous material to the base material is 200% by mass or less, the pores can be appropriately retained and lithium ion diffusion is improved, so that high input / output characteristics can be exhibited.
- the doping amount of lithium ions per unit mass of the composite carbon material 1 is preferably 530 mAh / g or more and 2500 mAh / g or less, more preferably 620 mAh / g or more and 2,100 mAh / g or less, more preferably 760 mAh / g or more. It is 1,700 mAh / g or less, More preferably, it is 840 mAh / g or more and 1,500 mAh / g or less.
- the negative electrode potential is lowered by doping the negative electrode with lithium ions. Therefore, when the negative electrode containing the composite carbon material 1 doped with lithium ions is combined with the positive electrode, the voltage of the nonaqueous lithium storage element increases and the utilization capacity of the positive electrode increases. Therefore, the capacity and energy density of the obtained non-aqueous lithium storage element are increased.
- the doping amount of lithium ions per unit mass of the composite carbon material 1 is 530 mAh / g or more, the lithium ions in the composite carbon material 1 are also well doped into irreversible sites that cannot be desorbed once inserted. Furthermore, the amount of the composite carbon material 1 with respect to the desired amount of lithium can be reduced. Therefore, the negative electrode film thickness can be reduced, and a high energy density can be obtained. The larger the doping amount, the lower the negative electrode potential, and the input / output characteristics, energy density, and durability are improved.
- the doping amount of lithium ions per unit mass of the composite carbon material 1 is 2,500 mAh / g or less, side effects such as precipitation of lithium metal are unlikely to occur.
- the composite carbon material 1a has a mesopore amount derived from pores having a diameter of 20 to 500 mm calculated by the BJH method as V m1 (cc / g), and a micropore derived from pores having a diameter of less than 20 mm calculated by the MP method.
- V m1 cc / g
- V m2 cc / g
- the mesopore amount V m1 is more preferably 0.010 ⁇ V m1 ⁇ 0.225, and further preferably 0.010 ⁇ V m1 ⁇ 0.200.
- the micropore amount V m2 is more preferably 0.001 ⁇ V m2 ⁇ 0.200, further preferably 0.001 ⁇ V m2 ⁇ 0.150, and particularly preferably 0.001 ⁇ V m2 ⁇ 0.100. .
- the mesopore amount V m1 is 0.300 cc / g or less, the BET specific surface area can be increased, the lithium ion doping amount can be increased, and the bulk density of the negative electrode can be increased. As a result, the negative electrode can be thinned.
- the micropore amount V m2 is 0.650 cc / g or less, high charge / discharge efficiency for lithium ions can be maintained.
- the mesopore volume V m1 and the micropore volume V m2 are 0.010 ⁇ V m1 and 0.001 ⁇ V m2 , high input / output characteristics can be obtained.
- the BET specific surface area of the composite carbon material 1a is preferably 100 m 2 / g or more and 1,500 m 2 / g or less, more preferably 150 m 2 / g or more and 1,100 m 2 / g or less, and further preferably 180 m 2 / g or more and 550 m. 2 / g or less. If the BET specific surface area of the composite carbon material 1a is 100 m 2 / g or more, the pores can be appropriately maintained, and the diffusion of lithium ions in the non-aqueous electrolyte solution is improved, so that high input / output characteristics are exhibited.
- the number of reaction sites with lithium ions in the non-aqueous electrolyte can be increased sufficiently, high input / output characteristics can be exhibited. Since the BET specific surface area of the composite carbon material 1a is 1,500 m 2 / g or less, the charge / discharge efficiency of lithium ions is improved, and excessive reductive decomposition of the non-aqueous electrolyte solution can be suppressed. Discharge cycle characteristics are less likely to be impaired.
- the average pore diameter of the composite carbon material 1a is preferably 20 mm or more, more preferably 25 mm or more, and further preferably 30 mm or more from the viewpoint of high input / output characteristics. From the viewpoint of high energy density, the average pore diameter of the composite carbon material 1a is preferably 65 mm or less, and more preferably 60 mm or less.
- the average particle diameter of the composite carbon material 1a is preferably 1 ⁇ m or more and 10 ⁇ m or less, the lower limit value is more preferably 2 ⁇ m or more, still more preferably 2.5 ⁇ m or more, and the upper limit value is more preferably 6 ⁇ m or less. More preferably, it is 4 ⁇ m or less. If the average particle diameter of the composite carbon material 1a is 1 ⁇ m or more and 10 ⁇ m or less, good durability is maintained.
- the hydrogen atom / carbon atom number ratio (H / C) of the composite carbon material 1a is preferably 0.05 or more and 0.35 or less, and more preferably 0.05 or more and 0.15 or less.
- H / C of the composite carbon material 1a is 0.35 or less, the structure of the carbonaceous material deposited on the activated carbon surface, typically a polycyclic aromatic conjugated structure is well developed. Thus, capacity (energy density) and charge / discharge efficiency are increased.
- H / C of the composite carbon material 1a is 0.05 or more, since carbonization does not proceed excessively, a good energy density can be obtained. H / C is measured by an elemental analyzer.
- the composite carbon material 1a has an amorphous structure derived from the activated carbon of the base material, but at the same time has a crystal structure mainly derived from the deposited carbonaceous material. According to the X-ray wide angle diffraction method, the composite carbon material 1a has a (002) plane spacing d002 of 3.60 to 4.00 and a c-axis direction crystallite obtained from the half width of this peak.
- the size Lc is preferably 8.0 to 20.0 mm; d002 is 3.60 to 3.75 mm and the crystallite size Lc in the c-axis direction obtained from the half width of this peak is 11 More preferably, it is not less than 0.01 and not more than 16.0.
- the activated carbon used as the base material of the composite carbon material 1a is not particularly limited as long as the obtained composite carbon material 1a exhibits desired characteristics.
- the activated carbon of the composite carbon material 1a for example, commercially available products obtained from various raw materials such as petroleum-based, coal-based, plant-based, and polymer-based materials can be used.
- the average particle diameter of the activated carbon powder is more preferably 2 ⁇ m or more and 10 ⁇ m or less.
- the pore distribution of the activated carbon used for the base material is important.
- the activated carbon used as the base material of the composite carbon material 1a has a mesopore amount derived from pores having a diameter of 20 to 500 mm calculated by the BJH method as V 1 (cc / g), and a fine particle having a diameter of less than 20 mm calculated by the MP method.
- V 1 (cc / g) mesopore amount derived from pores having a diameter of 20 to 500 mm calculated by the BJH method
- V 1 (cc / g) the amount of micropores derived from the holes having a diameter of 20 to 500 mm calculated by the BJH method
- V 2 (cc / g) 0.050 ⁇ V 1 ⁇ 0.500, 0.005 ⁇ V 2 ⁇ 1.000, and 0.2 ⁇ V 1 / V It is preferable that 2 ⁇ 20.0.
- the mesopore amount V 1 is preferably 0.050 ⁇ V 1 ⁇ 0.350, more preferably 0.100 ⁇ V 1 ⁇ 0.300.
- the micropore amount V 2 is preferably 0.005 ⁇ V 2 ⁇ 0.850, more preferably 0.100 ⁇ V 2 ⁇ 0.800.
- the ratio of mesopore amount / micropore amount is preferably 0.22 ⁇ V 1 / V 2 ⁇ 15.0, more preferably 0.25 ⁇ V 1 / V 2 ⁇ 10.0. If mesopore Anaryou V 1 of the activated carbon is 0.500 or less, and when the micropore volume V 2 is 1.000 or less, in order to obtain the pore structure of the composite carbon material 1a in the present embodiment, a suitable amount Therefore, the pore structure can be easily controlled.
- mesopore Anaryou V 1 of the activated carbon is 0.050 or more, and when the micropore volume V 2 is less than 0.005, when V 1 / V 2 is less than 0.2, and V 1 / V Even when 2 is 20.0 or less, a desired pore structure can be easily obtained.
- the carbonaceous material precursor used as a raw material of the composite carbon material 1a is an organic material that can be dissolved in a solid, liquid, or solvent, which can deposit the carbonaceous material on activated carbon by heat treatment.
- the carbonaceous material precursor include pitch, mesocarbon microbeads, coke, and a synthetic resin such as a phenol resin.
- Pitch is roughly divided into petroleum pitch and coal pitch. Examples of petroleum pitches include crude oil distillation residue, fluid catalytic cracking residue (decant oil, etc.), bottom oil derived from thermal crackers, ethylene tar obtained during naphtha cracking, and the like.
- the pitch When using pitch, the pitch is heat-treated in the presence of activated carbon, the volatile component or pyrolysis component of the pitch is thermally reacted on the surface of the activated carbon, and the carbonaceous material is deposited on the activated carbon. Is obtained.
- the deposition of pitch volatile components or pyrolysis components into the activated carbon pores proceeds at a temperature of about 200 to 500 ° C., and the reaction in which the deposited components become carbonaceous materials proceeds at about 400 ° C. or more.
- the peak temperature (maximum temperature reached) during the heat treatment is appropriately determined depending on the characteristics of the obtained composite carbon material 1a, the thermal reaction pattern, the thermal reaction atmosphere, etc., and is preferably 400 ° C.
- the time for maintaining the peak temperature during the heat treatment is preferably 30 minutes to 10 hours, more preferably 1 hour to 7 hours, and further preferably 2 hours to 5 hours.
- the carbonaceous material deposited on the activated carbon surface is considered to be a polycyclic aromatic hydrocarbon.
- the softening point of the pitch is preferably 30 ° C. or higher and 250 ° C. or lower, and more preferably 60 ° C. or higher and 130 ° C. or lower.
- a pitch having a softening point of 30 ° C. or higher can be handled with high accuracy without any problem in handling properties.
- a pitch having a softening point of 250 ° C. or lower contains a relatively large amount of a low molecular weight compound. Therefore, when a pitch having a softening point of 250 ° C. or lower is used, fine pores in activated carbon can be deposited. .
- activated carbon is heat-treated in an inert atmosphere containing a hydrocarbon gas volatilized from a carbonaceous material precursor, and the carbonaceous material is deposited in a gas phase.
- a method is mentioned.
- coating the carbonaceous material precursor dissolved in the solvent to activated carbon and drying it is also possible.
- the mass ratio of the carbonaceous material to the activated carbon in the composite carbon material 1a is preferably 10% by mass to 100% by mass, and more preferably 15% by mass to 80% by mass. If the mass ratio of the carbonaceous material is 10% by mass or more, the micropores of the activated carbon can be appropriately filled with the carbonaceous material, and the charge / discharge efficiency of lithium ions is improved. Less likely to be damaged. If the mass ratio of the carbonaceous material is 100% by mass or less, the pores of the composite carbon material 1a are appropriately maintained and maintained with a large specific surface area. Therefore, the doping amount of lithium ions can be increased, and high output density and high durability can be maintained even if the negative electrode is thinned.
- the composite carbon material 2 is a composite carbon material using as a base material one or more carbon materials having a BET specific surface area of 0.5 m 2 / g to 80 m 2 / g.
- the base material of the composite carbon material 2 is not particularly limited as long as the BET specific surface area is 0.5 m 2 / g or more and 80 m 2 / g or less. Can be suitably used.
- BET specific surface area of the composite carbon material 2 is preferably 1 m 2 / g or more 50 m 2 / g or less, more preferably 1.5 m 2 / g or more 40 m 2 / g or less, more preferably 2m 2 / g or more 25 m 2 / g or less. If the BET specific surface area of the composite carbon material 2 is 1 m 2 / g or more, a sufficiently large number of reaction sites with lithium ions in the non-aqueous electrolyte solution can be secured, so that high input / output characteristics can be exhibited.
- the BET specific surface area of the composite carbon material 2 is 50 m 2 / g or less, the charge / discharge efficiency of lithium ions is improved, and the decomposition reaction of the non-aqueous electrolyte during charge / discharge is suppressed. Discharge cycle characteristics can be shown.
- the average particle diameter of the composite carbon material 2 is preferably 1 ⁇ m or more and 10 ⁇ m or less, more preferably 2 ⁇ m or more and 8 ⁇ m or less, and further preferably 3 ⁇ m or more and 6 ⁇ m or less. If the average particle diameter of the composite carbon material 2 is 1 ⁇ m or more, the charge / discharge efficiency of lithium ions can be improved, and thus high high-load charge / discharge cycle characteristics can be exhibited. If the average particle diameter of the composite carbon material 2 is 10 ⁇ m or less, the reaction sites between the composite carbon material 2 and lithium ions in the non-aqueous electrolyte increase, and therefore high input / output characteristics can be exhibited.
- the mass ratio of the carbonaceous material to the base material in the composite carbon material 2 is preferably 1% by mass to 30% by mass, more preferably 1.2% by mass to 25% by mass, and even more preferably 1.5% by mass. It is 20 mass% or less. If the mass ratio of the carbonaceous material is 1% by mass or more, the carbonaceous material can sufficiently increase the reaction sites with the lithium ions in the non-aqueous electrolyte, and the desolvation of the lithium ions is facilitated. High input / output characteristics can be exhibited. If the mass ratio of the carbonaceous material is 20% by mass or less, the diffusion of lithium ions between the carbonaceous material and the base material in the solid can be satisfactorily maintained, and thus high input / output characteristics can be exhibited. Moreover, since the charge / discharge efficiency of lithium ions can be improved, high high-load charge / discharge cycle characteristics can be exhibited.
- the doping amount of lithium ions per unit mass of the composite carbon material 2 is preferably 50 mAh / g or more and 700 mAh / g or less, more preferably 70 mAh / g or more and 650 mAh / g or less, and further preferably 90 mAh / g or more and 600 mAh / g or less. More preferably, it is 100 mAh / g or more and 550 mAh / g or less.
- the negative electrode potential is lowered by doping the negative electrode with lithium ions. Therefore, when the negative electrode including the composite carbon material 2 doped with lithium ions is combined with the positive electrode, the voltage of the nonaqueous lithium storage element increases and the utilization capacity of the positive electrode increases. Therefore, the capacity and energy density of the obtained non-aqueous lithium storage element are increased.
- the doping amount of lithium ions per unit mass of the composite carbon material 2 is 50 mAh / g or more, the lithium ions in the composite carbon material 2 are also well doped into irreversible sites that cannot be desorbed once inserted. Therefore, a high energy density can be obtained.
- the doping amount of lithium ions per unit mass of the composite carbon material 2 is 700 mAh / g or less, side effects such as precipitation of lithium metal are unlikely to occur.
- the BET specific surface area of the composite carbon material 2a is preferably 1 m 2 / g or more and 50 m 2 / g or less, more preferably 1 m 2 / g or more and 20 m 2 / g or less, and further preferably 1 m 2 / g or more and 15 m 2 / g or less. It is. If the BET specific surface area of the composite carbon material 2a is 1 m 2 / g or more, a sufficiently large number of reaction sites with lithium ions in the non-aqueous electrolyte solution can be secured, so that high input / output characteristics can be exhibited.
- the BET specific surface area of the composite carbon material 2a is 50 m 2 / g or less, the charge / discharge efficiency of lithium ions is improved, and the decomposition reaction of the non-aqueous electrolyte during charge / discharge is suppressed. Discharge cycle characteristics can be shown.
- the average pore diameter of the composite carbon material 2a is preferably 1.5 nm to 25 nm, more preferably 2 nm to 22 nm, still more preferably 3 nm to 20 nm, and particularly preferably 3.5 nm to 18 nm. If the average pore diameter of the composite carbon material 2a is 1.5 nm or more, there are many pores larger than the size of the solvated lithium ion (about 0.9 nm to 1.2 nm) in the non-aqueous electrolyte solution. The diffusion of solvated lithium ions in the carbon material 2a becomes good, and the non-aqueous lithium storage element using this can exhibit high input / output characteristics. On the other hand, if the average pore diameter of the composite carbon material is 25 nm or less, the bulk density of the negative electrode active material layer using the composite carbon material can be sufficiently improved, so that a high energy density can be exhibited.
- the average particle diameter of the composite carbon material 2a is preferably 1 ⁇ m or more and 10 ⁇ m or less, more preferably 2 ⁇ m or more and 8 ⁇ m or less, and further preferably 3 ⁇ m or more and 6 ⁇ m or less. If the average particle diameter of the composite carbon material 2a is 1 ⁇ m or more, the charge / discharge efficiency of lithium ions can be improved, and thus high high-load charge / discharge cycle characteristics can be exhibited. If the average particle diameter of the composite carbon material 2a is 10 ⁇ m or less, the reaction sites with lithium ions in the non-aqueous electrolyte increase, so that high input / output characteristics can be exhibited.
- the mass ratio of the carbonaceous material to the graphite material in the composite carbon material 2a is preferably 1% by mass to 20% by mass, more preferably 1.2% by mass to 15% by mass, and still more preferably 1.5% by mass. % To 10% by mass, and more preferably 2% to 5% by mass. If the mass ratio of the carbonaceous material is 1% by mass or more, the carbonaceous material can sufficiently increase the reaction sites with the lithium ions in the non-aqueous electrolyte, and the desolvation of the lithium ions is facilitated. High input / output characteristics can be exhibited.
- the mass ratio of the carbonaceous material is 20% by mass or less, the diffusion of lithium ions in the solid between the carbonaceous material and the graphite material can be favorably maintained, so that high input / output characteristics can be exhibited. Moreover, since the charge / discharge efficiency of lithium ions can be improved, high high-load charge / discharge cycle characteristics can be exhibited.
- the doping amount of lithium ions per unit mass of the composite carbon material 2a is preferably 50 mAh / g or more and 700 mAh / g or less, more preferably 70 mAh / g or more and 650 mAh / g or less, and further preferably 90 mAh / g or more and 600 mAh / g or less. More preferably, it is 100 mAh / g or more and 550 mAh / g or less.
- the capacity and energy density of the obtained non-aqueous lithium storage element are increased. If the doping amount of lithium ions per unit mass of the composite carbon material 2a is 50 mAh / g or more, lithium ions are well doped even at irreversible sites that cannot be desorbed once the lithium ions in the composite carbon material 2a are inserted. Therefore, a high energy density can be obtained. The larger the doping amount, the lower the negative electrode potential, and the input / output characteristics, energy density, and durability are improved. When the doping amount of lithium ions per unit mass of the composite carbon material 2a is 700 mAh / g or less, side effects such as precipitation of lithium metal are unlikely to occur.
- the BET specific surface area of the graphite material used for the composite carbon material 2a is preferably 0.5 m 2 / g to 80 m 2 / g, more preferably 1 m 2 / g to 70 m 2 / g, and even more preferably 1.5 m. It is 2 / g or more and 60 m 2 / g or less. If the BET specific surface area of the graphite material used for the composite carbon material 2a is within the above range, the BET specific surface area of the composite carbon material 2a can be adjusted to the above range.
- the average particle diameter of the graphite material used for the composite carbon material 2a is preferably 1 ⁇ m or more and 10 ⁇ m or less, more preferably 2 ⁇ m or more and 8 ⁇ m or less. If the average particle diameter of the graphite material used for the composite carbon material 2a is in the range of 1 ⁇ m or more and 10 ⁇ m or less, the average particle diameter of the composite carbon material 2a can be adjusted to the above-described range.
- the carbonaceous material precursor used as a raw material for the composite carbon material 2a is an organic material that can be dissolved in a solid, liquid, or solvent, which can be composited with a graphite material by heat treatment.
- the carbonaceous material precursor include pitch, mesocarbon microbeads, coke, and a synthetic resin such as a phenol resin.
- Pitch is roughly divided into petroleum pitch and coal pitch. Examples of petroleum pitches include crude oil distillation residue, fluid catalytic cracking residue (decant oil, etc.), bottom oil derived from thermal crackers, ethylene tar obtained during naphtha cracking, and the like.
- the negative electrode active material layer in the present embodiment may include optional components such as a conductive filler, a binder, and a dispersion stabilizer as necessary.
- the type of the conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, and vapor grown carbon fiber.
- the amount of the conductive filler used is preferably 0 to 30 parts by mass, more preferably 0 to 20 parts by mass, and even more preferably 0 to 15 parts by mass with respect to 100 parts by mass of the negative electrode active material. Or less.
- the binder is not particularly limited.
- PVdF polyvinylidene fluoride
- PTFE polytetrafluoroethylene
- polyimide latex
- fluororubber acrylic copolymer, etc.
- the amount of the binder used is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 2 parts by mass or more and 27 parts by mass or less, and still more preferably 3 parts by mass or more and 25 parts by mass with respect to 100 parts by mass of the negative electrode active material. Or less. If the usage-amount of a binder is 1 mass part or more, sufficient electrode intensity
- a dispersion stabilizer for example, PVP (polyvinyl pyrrolidone), PVA (polyvinyl alcohol), a cellulose derivative etc. can be used.
- the amount of the dispersion stabilizer used is preferably 0 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the amount of the dispersion stabilizer used is 10 parts by mass or less, high input / output characteristics are exhibited without inhibiting lithium ions from entering and exiting the negative electrode active material.
- the material constituting the negative electrode current collector in this embodiment is preferably a metal foil that has high electron conductivity and is unlikely to deteriorate due to elution into a non-aqueous electrolyte and reaction with an electrolyte or ions.
- a metal foil that has high electron conductivity and is unlikely to deteriorate due to elution into a non-aqueous electrolyte and reaction with an electrolyte or ions.
- metal foil For example, aluminum foil, copper foil, nickel foil, stainless steel foil, etc. are mentioned.
- the negative electrode current collector in the non-aqueous lithium storage element of this embodiment is preferably a copper foil.
- the metal foil may be a normal metal foil having no irregularities or through holes, or a metal foil having irregularities subjected to embossing, chemical etching, electrolytic deposition, blasting, etc., expanded metal, punching metal Alternatively, a metal foil having a through hole such as an etching foil may be used.
- the negative electrode current collector in the present embodiment is preferably a metal foil having no through hole. Without the through-hole, the manufacturing cost is low, the thinning is easy, it can contribute to high energy density, and the current collecting resistance can be lowered, so that high input / output characteristics can be obtained.
- the thickness of the negative electrode current collector is not particularly limited as long as the shape and strength of the negative electrode can be sufficiently maintained, but is preferably 1 to 100 ⁇ m, for example.
- the thickness of the negative electrode current collector is measured based on a portion where no through hole or unevenness exists.
- the negative electrode has a negative electrode active material layer on one side or both sides of the negative electrode current collector.
- the negative electrode active material layer is fixed on one side or both sides of the negative electrode current collector.
- the negative electrode can be manufactured by an electrode manufacturing technique in a known lithium ion battery, electric double layer capacitor or the like.
- various materials including a negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is applied to one or both surfaces of the negative electrode current collector.
- a negative electrode can be obtained by forming a coating film and drying it. You may press the obtained negative electrode and adjust the film thickness and bulk density of a negative electrode active material layer. Alternatively, it is possible to mix various materials including the negative electrode active material dry without using a solvent, press the resulting mixture, and then apply it to the negative electrode current collector using a conductive adhesive. is there.
- the coating liquid is a liquid or slurry in which a part or all of various material powders including the negative electrode active material are dry blended, and then water or an organic solvent and / or a binder or a dispersion stabilizer is dissolved or dispersed therein. It may be prepared by adding these substances. In addition, a coating liquid may be prepared by adding various material powders containing a negative electrode active material to a liquid or slurry substance in which a binder or dispersion stabilizer is dissolved or dispersed in water or an organic solvent. .
- a disperser such as a homodisper, a multiaxial disperser, a planetary mixer, a thin film swirl type high speed mixer or the like can be preferably used.
- a peripheral speed of 1 m / s to 50 m / s it is preferable to disperse at a peripheral speed of 1 m / s to 50 m / s.
- a peripheral speed of 1 m / s or more is preferable because various materials can be dissolved or dispersed satisfactorily.
- a peripheral speed of 50 m / s or less is preferable because various materials are not easily broken by heat and shearing force due to dispersion, and reaggregation is reduced.
- the viscosity ( ⁇ b) of the negative electrode coating solution is preferably 1,000 mPa ⁇ s to 20,000 mPa ⁇ s, more preferably 1,500 mPa ⁇ s to 10,000 mPa ⁇ s, and still more preferably 1,700 mPa ⁇ s. s to 5,000 mPa ⁇ s.
- the viscosity ( ⁇ b) of the coating liquid for the negative electrode is 1,000 mPa ⁇ s or more, dripping at the time of coating film formation is suppressed, and the coating film width and thickness can be controlled well.
- the viscosity ( ⁇ b) of the negative electrode coating liquid is 20,000 mPa ⁇ s or less, there is little pressure loss in the flow path of the coating liquid when a coating machine is used, and the coating can be performed stably.
- the film thickness can be controlled below.
- the TI value (thixotropic index value) of the negative electrode coating solution is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. If the TI value of the negative electrode coating liquid is 1.1 or more, the coating film width and thickness can be controlled well.
- the method for forming the coating film of the negative electrode is not particularly limited, but preferably a coating machine such as a die coater, a comma coater, a knife coater, or a gravure coating machine can be used.
- the coating film may be formed by single layer coating or may be formed by multilayer coating.
- the coating speed is preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 70 m / min, and further preferably 1 m / min to 50 m / min. If the coating speed is 0.1 m / min or more, it can be applied stably, and if it is 100 m / min or less, sufficient coating accuracy can be secured.
- the method for drying the negative electrode coating film is not particularly limited, but a drying method such as hot air drying or infrared (IR) drying can be preferably used.
- the coating film may be dried at a single temperature or may be dried by changing the temperature in multiple stages. Moreover, you may dry combining several drying methods.
- the drying temperature is preferably 25 ° C. or higher and 200 ° C. or lower, more preferably 40 ° C. or higher and 180 ° C. or lower, and further preferably 50 ° C. or higher and 160 ° C. or lower.
- the drying temperature is 25 ° C. or higher, the solvent in the coating film can be sufficiently volatilized.
- the drying temperature is 200 ° C. or lower, it is possible to suppress cracking of the coating film due to rapid volatilization of the solvent, uneven distribution of the binder due to migration, and oxidation of the negative electrode current collector and the negative electrode active material layer.
- the method for pressing the negative electrode is not particularly limited, but a press such as a hydraulic press or a vacuum press can be preferably used.
- the film thickness, bulk density, and electrode strength of the negative electrode active material layer can be adjusted by the press pressure, gap, and surface temperature of the press part described later.
- the pressing pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and further preferably 2 kN / cm or more and 7 kN / cm or less. If the pressing pressure is 0.5 kN / cm or more, the electrode strength can be sufficiently increased.
- the negative electrode When the pressing pressure is 20 kN / cm or less, the negative electrode is unlikely to be bent or wrinkled, and is easily adjusted to a desired film thickness or bulk density of the negative electrode active material layer.
- the gap between the press rolls can be set to an arbitrary value according to the negative electrode film thickness after drying so as to have a desired film thickness and bulk density of the negative electrode active material layer.
- the pressing speed can be set to an arbitrary speed so as to reduce the bending and wrinkling of the negative electrode.
- the surface temperature of the press part may be room temperature or may be heated if necessary.
- the lower limit of the surface temperature of the press part when heating is preferably the melting point of the binder used minus 60 ° C. or more, more preferably the melting point of the binder minus 45 ° C.
- the upper limit of the surface temperature of the press part when heated is preferably the melting point of the binder used plus 50 ° C. or less, more preferably the melting point of the binder plus 30 ° C. or less, more preferably the melting point of the binder plus 20 It is below °C.
- PVdF polyvinylidene fluoride: melting point 150 ° C.
- it is preferably pressed at 90 ° C. or higher and 200 ° C. or lower, more preferably 105 ° C. or higher and 180 ° C. or lower, and further preferably 120 ° C. or higher and 170 ° C.
- styrene-butadiene copolymer (melting point 100 ° C.) is used as the binder, it is preferably pressed at 40 ° C. or higher and 150 ° C. or lower, more preferably 55 ° C. or higher and 130 ° C. or lower, and even more preferably 70 ° C. or higher and 120 ° C. or lower. Warm the surface of the part.
- the melting point of the binder can be determined at the endothermic peak position of DSC (Differential Scanning Calorimetry). For example, using a differential scanning calorimeter “DSC7” manufactured by PerkinElmer Co., Ltd., 10 mg of sample resin is set in a measurement cell, and the temperature is increased from 30 ° C. to 250 ° C. at a temperature increase rate of 10 ° C./min in a nitrogen gas atmosphere. The temperature is raised, and the endothermic peak temperature in the temperature raising process becomes the melting point.
- DSC7 Different Scanning Calorimetry
- ⁇ Pressing may be performed a plurality of times while changing the conditions of pressing pressure, gap, speed, and surface temperature of the pressing part.
- the film thickness of the negative electrode active material layer is preferably 5 ⁇ m or more and 100 ⁇ m or less per side of the negative electrode current collector.
- the lower limit of the film thickness of the negative electrode active material layer is more preferably 7 ⁇ m or more, and even more preferably 10 ⁇ m or more.
- the upper limit of the film thickness of the negative electrode active material layer is more preferably 80 ⁇ m or less, and even more preferably 60 ⁇ m or less.
- the film thickness of the negative electrode active material layer is 100 ⁇ m or less, a high energy density can be expressed by reducing the volume of the non-aqueous lithium storage element.
- the film thickness of the negative electrode active material layer in the case where the negative electrode current collector has through-holes and irregularities is the film thickness of the negative electrode active material layer per side in the part of the negative electrode current collector that does not have through-holes and irregularities This is the average thickness.
- the bulk density of the negative electrode active material layer is preferably 0.30 g / cm 3 or more and 1.8 g / cm 3 or less, more preferably 0.40 g / cm 3 or more and 1.5 g / cm 3 or less, and further preferably 0.45 g. / Cm 3 or more and 1.3 g / cm 3 or less.
- the bulk density of the negative electrode active material layer is 0.30 g / cm 3 or more, sufficient strength can be maintained and sufficient conductivity between the negative electrode active materials can be exhibited. If the bulk density of the negative electrode active material layer is 1.8 g / cm 3 or less, vacancies capable of sufficiently diffusing ions in the negative electrode active material layer can be secured.
- the BET specific surface area per unit volume of the negative electrode active material layer is preferably 1 m 2 / cc to 50 m 2 / cc, more preferably 2 m 2 / cc to 40 m 2 / cc, and even more preferably 3 m 2 / cc to 35 m 2. / Cc or less, particularly preferably 4 m 2 / cc or more and 30 m 2 / cc or less, and most preferably 5 m 2 / cc or more and 20 m 2 / cc or less.
- the BET specific surface area per unit volume of the negative electrode active material layer is 1 m 2 / cc or more, the number of reaction sites per unit volume between lithium ions in the non-aqueous electrolyte and the negative electrode active material layer can be increased sufficiently.
- the non-aqueous lithium storage element using can exhibit high input / output characteristics and high load charge / discharge cycle characteristics.
- the BET specific surface area per unit volume of the negative electrode active material layer is 50 m 2 / cc or less, excessive reductive decomposition of the nonaqueous electrolyte solution in the negative electrode active material layer can be suppressed.
- the power storage element can exhibit high high-load charge / discharge cycle characteristics.
- the average pore diameter of the negative electrode active material layer is preferably 2 nm to 20 nm, more preferably 3 nm to 18 nm, still more preferably 3.5 nm to 16 nm, and particularly preferably 4 nm to 15 nm. If the average pore diameter of the negative electrode active material layer is 2 nm or more, pores larger than the size of solvated lithium ions (about 0.9 nm to 1.2 nm) in the non-aqueous electrolyte solution are formed in the negative electrode active material layer. Since it has a large amount, diffusion of solvated lithium ions in the negative electrode active material layer becomes good, and a non-aqueous lithium storage element using the lithium ion can exhibit high input / output characteristics. On the other hand, if the average pore diameter of the negative electrode active material layer is 20 nm or less, the bulk density of the negative electrode active material layer can be sufficiently improved. .
- the method for adjusting the BET specific surface area per unit volume of the negative electrode active material layer and the average pore diameter of the negative electrode active material layer in the present embodiment to the above-described ranges is not particularly limited, but is included in the negative electrode active material layer. It can adjust with the kind of negative electrode active material or an electroconductive filler, a binder, etc., and the mass ratio in these negative electrode active material layers.
- a negative electrode active material or conductive filler having a BET specific surface area of 1 m 2 / g or more and an average pore diameter of 1.5 nm or more, such as PVdF (polyvinylidene fluoride) that can easily fill pores of 2 nm or less It can be adjusted by using a binder having a chain structure. Moreover, even if it adjusts by the adhesion amount of the film and deposit by reductive decomposition of the nonaqueous electrolyte contained in the negative electrode active material layer adjusted by the composition of the nonaqueous electrolyte and the manufacturing conditions of the nonaqueous lithium storage element Good.
- PVdF polyvinylidene fluoride
- the BET specific surface area per unit volume of the negative electrode active material layer and the average pore diameter of the negative electrode active material layer can be calculated by the following methods.
- the sample used for the measurement may be a negative electrode (hereinafter also referred to as “a negative electrode before use”) that is not incorporated in the non-aqueous lithium storage element, or a negative electrode (hereinafter referred to as “non-aqueous lithium storage element”). , Also referred to as “a negative electrode after use”).
- a negative electrode before use a negative electrode that is not incorporated in the non-aqueous lithium storage element
- non-aqueous lithium storage element hereinafter referred to as “non-aqueous lithium storage element”.
- a negative electrode after use When the negative electrode incorporated in the non-aqueous lithium storage element is used as a measurement sample, it is preferable to use, for example, the following method as a pretreatment of the measurement sample. First, the nonaqueous lithium storage element is disassembled under an inert atmosphere such as argon, and the negative electrode is taken out.
- the taken-out negative electrode is immersed in chain carbonate (for example, methyl ethyl carbonate, dimethyl carbonate, etc.), non-aqueous electrolyte solution, lithium salt, etc. are removed and air-dried.
- chain carbonate for example, methyl ethyl carbonate, dimethyl carbonate, etc.
- non-aqueous electrolyte solution, lithium salt, etc. are removed and air-dried.
- the following method (1), (2), or (3) is preferably used.
- the obtained negative electrode is immersed in a mixed solvent of methanol and isopropanol to deactivate lithium ions occluded in the negative electrode active material, and air-dried.
- a measurement sample can be obtained by removing the chain carbonate, the organic solvent, and the like contained in the negative electrode obtained by vacuum drying or the like.
- the obtained negative electrode is used as a working electrode, metallic lithium is used as a counter electrode and a reference electrode, and these are immersed in a non-aqueous electrolyte to produce an electrochemical cell.
- the obtained electrochemical cell is adjusted using a charger / discharger or the like so that the negative electrode potential (vs. Li / Li + ) is in the range of 1.5V to 3.5V.
- the negative electrode is taken out from the electrochemical cell under an inert atmosphere such as argon, soaked in a chain carbonate, removed from the non-aqueous electrolyte, lithium salt, etc., and air-dried.
- a measurement sample can be obtained by removing the chain carbonate and the like contained in the negative electrode obtained by vacuum drying or the like.
- the negative electrode obtained above can be used as a measurement sample as it is.
- the volume Vano (cc) of a negative electrode active material layer is measured about the measurement sample obtained above.
- adsorption and desorption isotherms are measured using nitrogen or argon as an adsorbate.
- BET by multipoint method or BET1 point method to calculate the BET specific surface area Using suction side of the isotherm obtained here, BET by multipoint method or BET1 point method to calculate the BET specific surface area, a BET specific surface area per anode active material layer per unit volume by dividing this in V ano calculate.
- the average pore diameter of the negative electrode active material layer is calculated by dividing the total pore volume calculated by the above measurement by the BET specific surface area.
- Negative active ratio r p / r a of the average distance between the centers of gravity r p of the average particle diameter r voids obtained from SEM of the negative electrode active material layer section for a material is preferably 0.10 to 1.10, more preferably Is 0.20 or more and 1.00 or less, more preferably 0.25 or more and 0.80 or less, and particularly preferably 0.30 or more and 0.60 or less. If r p / r a is 0.10 or more, the size of the gap is sufficiently large with respect to the negative electrode active material, and a sufficient amount of non-aqueous electrolyte solution can be retained in the gap around the negative electrode active material.
- a non-aqueous lithium storage element that exhibits high input / output characteristics and high load charge / discharge cycle characteristics can be obtained. If r p / r a is 1.10 or less, the non-aqueous electrolyte is appropriately distributed around the negative electrode active material, so that the non-aqueous lithium type exhibiting high input / output characteristics and high load charge / discharge cycle characteristics A power storage element can be obtained.
- the BET specific surface area, mesopore amount, and micropore amount in the present embodiment are values obtained by the following methods, respectively.
- the sample is vacuum-dried at 200 ° C. all day and night, and adsorption and desorption isotherms are measured using nitrogen as an adsorbate.
- the BET specific surface area is determined by the BET multipoint method or the BET single point method, and the average pore diameter is obtained by dividing the total pore volume per mass by the BET specific surface area.
- the amount is calculated by the BJH method, and the amount of micropores is calculated by the MP method.
- the BJH method is a calculation method generally used for analysis of mesopores and proposed by Barrett, Joyner, Halenda et al. (EP Barrett, L. G. Joyner and P. Halenda, J Am. Chem. Soc., 73, 373 (1951)).
- the MP method uses a “t-plot method” (BC Lippens, JH de Boer, J. Catalysis, 4319 (1965)), and uses micropore volume, micropore area, and micropores. Is a method for obtaining the distribution of R. S. This is a method devised by Mikhal, Brunauer, Bodor (R. M. Mikhal, S. Brunauer, EE Bodor, J. Colloid Interface Sci., 26, 45 (1968)).
- the average particle diameter in the present embodiment is the particle diameter at which the cumulative curve becomes 50% when the cumulative curve is determined with the total volume being 100% when the particle size distribution is measured using a particle size distribution measuring device. That is, it refers to a 50% diameter (Median diameter)).
- This average particle diameter can be measured using a commercially available laser diffraction particle size distribution analyzer.
- the dope amount (mAh / g) of the lithium ion of the negative electrode active material in the non-aqueous lithium storage element at the time of shipment and after use in the present embodiment can be known, for example, as follows. First, after the negative electrode active material layer in this embodiment is washed with ethyl methyl carbonate or dimethyl carbonate and air-dried, an extract extracted with a mixed solvent composed of methanol and isopropanol and a negative electrode active material layer after extraction are obtained. This extraction is typically performed at an ambient temperature of 23 ° C. in an Ar box.
- the amount of lithium contained in the extract obtained as described above and the negative electrode active material layer after extraction is quantified using, for example, ICP-MS (inductively coupled plasma mass spectrometer), and the total amount
- the lithium ion doping amount in the negative electrode active material can be known.
- the obtained value may be allocated by the amount of the negative electrode active material used for extraction to calculate the lithium ion dope amount (mAh / g).
- the primary particle size means that a powder is photographed with several fields of view with an electron microscope, and the particle size of particles in these fields of view is 2,000 to 3,000 using a fully automatic image processing apparatus or the like. It can be obtained by a method of measuring the degree and making the arithmetic average of these values the primary particle diameter.
- the dispersity in the present embodiment is a value obtained in accordance with a dispersity evaluation test using a grain gauge defined in JIS K5600. That is, a sufficient amount of sample is poured into the deep tip of the groove with a groove having a desired depth according to the size of the grain and slightly overflows from the groove. Next, place the scraper so that the long side of the scraper is parallel to the width direction of the gauge and the cutting edge is in contact with the deep tip of the grain gauge groove, and hold the scraper so that it is on the surface of the gauge. The surface of the gauge is pulled at a uniform speed to the groove depth of 0 to 1 second for 1 to 2 seconds, and light is applied at an angle of 20 ° to 30 ° within 3 seconds after the drawing is completed. Observe and read the depth at which the grain appears in the groove of the grain gauge.
- shear rate When increasing the shear rate from 2 s ⁇ 1 to 20 s ⁇ 1 , it may be increased in one step, or it is increased while increasing the shear rate in a multistage manner within the above range and acquiring the viscosity at that shear rate as appropriate. You may let them.
- the electrolytic solution in the present embodiment is a non-aqueous electrolytic solution containing lithium ions. That is, this non-aqueous electrolyte contains a non-aqueous solvent described later.
- the non-aqueous electrolyte solution preferably contains 0.5 mol / L or more lithium salt based on the total volume of the non-aqueous electrolyte solution. That is, the non-aqueous electrolyte contains lithium ions as an electrolyte.
- lithium salt examples include (LiN (SO 2 F) 2 ), LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiN (SO 2 CF 3 ) (SO 2 C 2 F 5 ), LiN (SO 2 CF 3 ) (SO 2 C 2 F 4 H), LiC (SO 2 F) 3 , LiC (SO 2 CF 3 ) 3 , LiC (SO 2 C 2 F 5 ) 3 , LiCF 3 SO 3, LiC 4 F 9 SO 3, LiPF 6, and LiBF 4 and the like. These can be used alone or may be used in combination of two or more.
- the lithium salt preferably contains LiPF 6 and / or LiN (SO 2 F) 2 because it can exhibit high conductivity.
- the lithium salt concentration in the non-aqueous electrolyte is preferably 0.5 mol / L or more, and more preferably in the range of 0.5 to 2.0 mol / L.
- the lithium salt concentration is 0.5 mol / L or more, anions are sufficiently present, so that the capacity of the nonaqueous lithium storage element can be sufficiently increased.
- the lithium salt concentration is 2.0 mol / L or less, it is possible to prevent undissolved lithium salt from precipitating in the non-aqueous electrolyte and preventing the viscosity of the non-aqueous electrolyte from becoming too high, resulting in a decrease in conductivity. This is preferable because it is difficult to reduce output characteristics.
- the nonaqueous electrolytic solution in the present embodiment preferably contains a cyclic carbonate and a chain carbonate as a nonaqueous solvent.
- the nonaqueous electrolytic solution containing a cyclic carbonate and a chain carbonate is advantageous in that a lithium salt having a desired concentration is dissolved and a high lithium ion conductivity is exhibited.
- the cyclic carbonate include alkylene carbonate compounds represented by ethylene carbonate, propylene carbonate, butylene carbonate, and the like. The alkylene carbonate compound is typically unsubstituted.
- chain carbonate examples include dialkyl carbonate compounds represented by dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, dibutyl carbonate and the like.
- the dialkyl carbonate compound is typically unsubstituted.
- the total content of the cyclic carbonate and the chain carbonate is preferably 50% by mass or more, more preferably 65% by mass or more, preferably 95% by mass or less, more preferably, based on the total mass of the non-aqueous electrolyte solution. 90% by mass or less.
- a lithium salt having a desired concentration can be dissolved, and high lithium ion conductivity can be expressed.
- the nonaqueous electrolytic solution can further contain an additive described later.
- the non-aqueous electrolyte in the present embodiment may further contain an additive.
- the additive is not particularly limited, and examples thereof include sultone compounds, cyclic phosphazenes, acyclic fluorine-containing ethers, fluorine-containing cyclic carbonates, cyclic carbonates, cyclic carboxylic acid esters, and cyclic acid anhydrides. They can be used alone or in admixture of two or more.
- sultone compounds examples include sultone compounds represented by the following general formulas (5) to (7). These sultone compounds may be used alone or in admixture of two or more.
- R 11 to R 16 represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a halogenated alkyl group having 1 to 12 carbon atoms, and they may be the same or different from each other.
- n is an integer from 0 to 3.
- R 11 to R 14 represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a halogenated alkyl group having 1 to 12 carbon atoms, and they may be the same or different from each other.
- n is an integer from 0 to 3.
- R 11 to R 16 represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a halogenated alkyl group having 1 to 12 carbon atoms, and they may be the same or different from each other. May be. ⁇
- the sultone compound represented by the formula (5) is preferably 1, from the viewpoint of suppressing the gas generation by suppressing the decomposition of the non-aqueous electrolyte at a high temperature with little adverse effect on the resistance.
- examples include 3-propane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-butane sultone, and 2,4-pentane sultone;
- the sultone compound represented by formula (6) is preferably 1,3-propene sultone and 1,4-butene sultone are preferable;
- the sultone compound represented by the formula (7) is preferably 1,5,2,4-dioxadithiepan 2,2,
- examples of other sultone compounds are preferably methylene bis (benzenesulfonic acid), methylene bis (phenylmethanesulfuric acid).
- the total content of sultone compounds contained in the non-aqueous electrolyte solution of the non-aqueous lithium storage element in this embodiment is 0.5% by mass to 15% by mass based on the total mass of the non-aqueous electrolyte solution. Is preferred. If the total content of sultone compounds contained in the non-aqueous electrolyte is 0.5 mass% or more, it is possible to suppress gas generation by suppressing decomposition of the non-aqueous electrolyte at high temperatures. When the total content of sultone compounds is 15% by mass or less, a decrease in ionic conductivity of the nonaqueous electrolytic solution can be suppressed, and high input / output characteristics can be maintained.
- the total content of sultone compounds present in the non-aqueous electrolyte solution of the non-aqueous lithium storage element is preferably 1% by mass or more and 10% by mass or less from the viewpoint of achieving both high input / output characteristics and durability. Preferably they are 3 mass% or more and 8 mass% or less.
- cyclic phosphazene examples include ethoxypentafluorocyclotriphosphazene, diethoxytetrafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene, and at least one selected from these groups is preferable.
- the content of cyclic phosphazene in the non-aqueous electrolyte is preferably 0.5% by mass to 20% by mass based on the total mass of the non-aqueous electrolyte.
- the content rate of cyclic phosphazene is 0.5 mass% or more, it will become possible to suppress gas generation
- the content of cyclic phosphazene is preferably 2% by mass or more and 15% by mass or less, more preferably 4% by mass or more and 12% by mass or less. These cyclic phosphazenes may be used alone or in combination of two or more.
- Examples of the acyclic fluorine-containing ether include HCF 2 CF 2 OCH 2 CF 2 CF 2 H, CF 3 CFHCF 2 OCH 2 CF 2 CF 2 H, HCF 2 CF 2 CH 2 OCH 2 CF 2 CF 2 H, and CF 3. CFHCF 2 OCH 2 CF 2 CFHCF 3 and the like, and among these, from the viewpoint of electrochemical stability, HCF 2 CF 2 OCH 2 CF 2 CF 2 H are preferred.
- the content of the non-cyclic fluorine-containing ether is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, based on the total mass of the non-aqueous electrolyte solution.
- the content of the non-cyclic fluorine-containing ether is 0.5% by mass or more, the stability of the non-aqueous electrolyte solution against oxidative decomposition is improved, and a non-aqueous lithium storage element having high durability at high temperatures can be obtained. If the content of the non-cyclic fluorine-containing ether is 15% by mass or less, the solubility of the electrolyte salt can be kept good, and the ionic conductivity of the non-aqueous electrolyte can be kept high. It becomes possible to express characteristics.
- acyclic fluorine-containing ether may be used individually or may be used in mixture of 2 or more types.
- the fluorine-containing cyclic carbonate is preferably at least one selected from the group consisting of fluoroethylene carbonate (FEC) and difluoroethylene carbonate (dFEC) from the viewpoint of compatibility with other nonaqueous solvents.
- the content of the fluorine-containing cyclic carbonate is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the nonaqueous electrolytic solution.
- the content of the fluorine-containing cyclic carbonate is 0.5% by mass or more, a high-quality film can be formed on the negative electrode, and by suppressing reductive decomposition of the non-aqueous electrolyte on the negative electrode, durability at high temperatures A highly non-aqueous lithium storage element can be obtained. If the content of the fluorine-containing cyclic carbonate is 10% by mass or less, the solubility of the electrolyte salt can be kept good, and the ionic conductivity of the non-aqueous electrolyte can be kept high, and therefore high input / output characteristics. Can be expressed. In addition, a fluorine-containing cyclic carbonate may be used individually or may be used in mixture of 2 or more types.
- the content of the cyclic carbonate is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the nonaqueous electrolytic solution. If the content of the cyclic carbonate is 0.5% by mass or more, a good-quality film on the negative electrode can be formed, and by suppressing reductive decomposition of the non-aqueous electrolyte on the negative electrode, durability at high temperatures A highly non-aqueous lithium storage element can be obtained.
- the content of the cyclic carbonate is 10% by mass or less, the solubility of the electrolyte salt can be maintained well, and the ionic conductivity of the non-aqueous electrolyte can be maintained high, and thus high input / output characteristics are exhibited. It becomes possible to do.
- cyclic carboxylic acid ester examples include gamma butyrolactone, gamma valerolactone, gamma caprolactone, and epsilon caprolactone, and it is preferable to use at least one selected from these groups.
- gamma butyrolactone is particularly preferable in terms of improving battery characteristics derived from an improvement in the degree of lithium ion dissociation.
- the content of the cyclic carboxylic acid ester is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the nonaqueous electrolytic solution.
- cyclic carboxylic acid ester If the content of the cyclic carboxylic acid ester is 0.5% by mass or more, a good-quality film on the negative electrode can be formed, and by suppressing the reductive decomposition of the non-aqueous electrolyte solution on the negative electrode, A non-aqueous lithium storage element having high durability can be obtained. If the content of the cyclic carboxylic acid ester is 5% by mass or less, the solubility of the electrolyte salt can be kept good, and the ionic conductivity of the non-aqueous electrolyte can be kept high. It becomes possible to express. In addition, cyclic carboxylic acid ester may be used individually or may be used in mixture of 2 or more types.
- the cyclic acid anhydride is preferably at least one selected from the group consisting of succinic anhydride, maleic anhydride, citraconic anhydride, and itaconic anhydride. Among them, it is preferable to select from succinic anhydride and maleic anhydride from the viewpoint that the production cost of the non-aqueous electrolyte solution can be suppressed due to industrial availability and that the non-aqueous electrolyte solution can be easily dissolved.
- the content of the cyclic acid anhydride is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on the total mass of the nonaqueous electrolytic solution.
- the content of the cyclic acid anhydride is 0.5% by mass or more, a high-quality film can be formed on the negative electrode, and it is durable at high temperatures by suppressing the reductive decomposition of the non-aqueous electrolyte on the negative electrode. A highly non-aqueous lithium storage element can be obtained. If the content of the cyclic acid anhydride is 10% by mass or less, the solubility of the electrolyte salt can be kept good, and the ionic conductivity of the non-aqueous electrolyte can be kept high. It becomes possible to express.
- a cyclic acid anhydride may be used individually or may be used in mixture of 2 or more types.
- the positive electrode precursor and the negative electrode are generally laminated or wound via a separator to form an electrode laminate or an electrode winding body having a positive electrode precursor, a negative electrode, and a separator.
- a polyethylene microporous film or a polypropylene microporous film used for a lithium ion secondary battery, a cellulose non-woven paper used for an electric double layer capacitor, or the like can be used as the separator.
- a film composed of organic or inorganic fine particles may be laminated on one side or both sides of these separators. Further, organic or inorganic fine particles may be contained inside the separator.
- the thickness of the separator is preferably 5 ⁇ m or more and 35 ⁇ m or less. It is preferable that the thickness of the separator is 5 ⁇ m or more because self-discharge due to an internal micro short circuit tends to be small. It is preferable that the thickness of the separator is 35 ⁇ m or less because the input / output characteristics of the nonaqueous lithium storage element tend to be high.
- the thickness of the film composed of organic or inorganic fine particles is preferably 1 ⁇ m or more and 10 ⁇ m or less.
- a film composed of organic or inorganic fine particles having a thickness of 1 ⁇ m or more is preferable because self-discharge due to internal micro-shorts tends to be small. It is preferable that the thickness of the film composed of organic or inorganic fine particles is 10 ⁇ m or less because the output characteristics of the non-aqueous lithium storage element tend to be high.
- the non-aqueous lithium storage element according to the present embodiment is typically configured such that an electrode laminate or an electrode winding body, which will be described later, is housed in an exterior body together with a non-aqueous electrolyte.
- the non-aqueous lithium storage element of the present invention can be produced, for example, by connecting a plurality of non-aqueous lithium storage elements in series or in parallel.
- the non-aqueous lithium storage element and the storage module of the present invention are a power regeneration system for a hybrid drive system of an automobile that requires high load charge / discharge cycle characteristics, a natural power generation such as a solar power generation or a wind power generation, a power load in a microgrid, etc.
- Non-aqueous lithium storage element of the present invention is preferable because the effects of the present invention are exhibited to the maximum when applied as, for example, a lithium ion capacitor or a lithium ion secondary battery.
- a positive electrode terminal and a negative electrode terminal are connected to a laminate formed by laminating a positive electrode precursor and a negative electrode cut into a sheet shape via a separator, thereby producing an electrode laminate.
- an electrode winding body may be manufactured by connecting a positive electrode terminal and a negative electrode terminal to a winding body obtained by laminating and winding a positive electrode precursor and a negative electrode via a separator.
- the shape of the electrode winding body may be a cylindrical shape or a flat shape.
- the method for connecting the positive electrode terminal and the negative electrode terminal is not particularly limited, but can be performed by a method such as resistance welding or ultrasonic welding.
- a metal can, a laminate packaging material, or the like can be used as the exterior body.
- the metal is preferably made of aluminum.
- the laminate packaging material a film obtained by laminating a metal foil and a resin film is preferable, and a laminate packaging material composed of three layers of outer layer resin film / metal foil / interior resin film is exemplified.
- the outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used.
- the metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel and the like can be suitably used.
- the interior resin film protects the metal foil from the non-aqueous electrolyte contained therein and melts and seals the exterior body during heat sealing. Polyolefin, acid-modified polyolefin, and the like can be suitably used.
- the dried electrode laminate or electrode winding body is preferably housed in an exterior body typified by a metal can or laminate packaging material, and is sealed with only one opening left.
- an exterior body typified by a metal can or laminate packaging material
- the sealing method of an exterior body is not specifically limited, When using a laminate packaging material, methods, such as a heat seal and an impulse seal, can be used.
- the residual solvent it is preferable to remove the residual solvent by drying the electrode laminate or the electrode winding body housed in the exterior body. Although a drying method is not limited, it can dry by vacuum drying etc.
- the residual solvent is preferably 1.5% by mass or less based on the mass of the positive electrode active material layer or the negative electrode active material layer. When the residual solvent is more than 1.5% by mass, the solvent remains in the system, and the self-discharge characteristics and the cycle characteristics may be deteriorated.
- a nonaqueous electrolytic solution is injected into the electrode laminate or the electrode winding body housed in the exterior body. It is desirable that further impregnation is performed after the injection, and the positive electrode, the negative electrode, and the separator are sufficiently immersed in the nonaqueous electrolytic solution. In a state where the non-aqueous electrolyte solution is not immersed in at least a part of the positive electrode, the negative electrode, and the separator, the lithium doping progresses non-uniformly in the lithium doping step described later, and thus the resistance of the obtained non-aqueous lithium storage element Increases or durability decreases.
- the impregnation method is not particularly limited.
- the electrode laminate or electrode winding body after injection is placed in a decompression chamber with the exterior body opened, and the inside of the chamber is decompressed using a vacuum pump.
- a method of returning to atmospheric pressure again can be used.
- the electrode laminate or electrode winding body with the exterior body opened can be sealed by reducing the pressure while reducing the pressure.
- Lithium doping process In the lithium doping step, a voltage is applied between the positive electrode precursor and the negative electrode, the lithium compound in the positive electrode precursor is decomposed to release lithium ions, and the lithium ions are reduced at the negative electrode, thereby reducing the negative electrode active material layer It is preferable to pre-dope liotium ions.
- a gas such as CO 2 is generated with the oxidative decomposition of the lithium compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to provide a means for releasing the generated gas to the outside of the exterior body.
- a method in which a voltage is applied in a state where a part of the exterior body is opened; in a state in which an appropriate gas releasing means such as a gas vent valve or a gas permeable film is previously installed in a part of the exterior body A method of applying a voltage;
- the electrode laminate or the electrode winding body It is preferable to age the electrode laminate or the electrode winding body after the lithium doping step.
- the solvent in the nonaqueous electrolytic solution is decomposed at the negative electrode, and a lithium ion permeable solid polymer film is formed on the negative electrode surface.
- the aging method is not particularly limited, and for example, a method of reacting a solvent in a nonaqueous electrolytic solution under a high temperature environment can be used.
- degassing process It is preferable that after the aging step, further degassing is performed to reliably remove the gas remaining in the non-aqueous electrolyte, the positive electrode, and the negative electrode.
- gas remains in at least a part of the non-aqueous electrolyte, the positive electrode, and the negative electrode, ion conduction is inhibited, and thus the resistance of the obtained non-aqueous lithium storage element increases.
- the degassing method is not particularly limited. For example, a method in which an electrode laminate or an electrode winding body is installed in a decompression chamber with an exterior body opened, and the inside of the chamber is decompressed using a vacuum pump. Can be used. After degassing, the outer package can be sealed by sealing the outer package to produce a non-aqueous lithium storage element.
- the electric energy E (Wh) is a value obtained by the following method. Using the capacitance F (F) calculated by the method described above, A value calculated by F ⁇ (3.8 2 ⁇ 2.2 2 ) / 2 / 3,600 is referred to as electric energy E (Wh).
- the volume of the non-aqueous lithium storage element refers to the volume of the electrode stack or electrode winding body in which the region where the positive electrode active material layer and the negative electrode active material layer are stacked is accommodated by the outer package.
- a region where the positive electrode active material layer and the negative electrode active material layer are present in the electrode laminate or the electrode winding body is present. It is stored in a cup-formed laminate film.
- the volume (V 1 ) of this non-aqueous lithium storage element is the non-aqueous lithium storage element including the outer dimension length (l 1 ), outer dimension width (w 1 ) of this cup-molded portion, and the laminate film.
- E / V i Wh / L
- V i 1, 2, 3
- E / V i 15 or more from the viewpoint of developing sufficient charge capacity and discharge capacity. If E / V i is 15 or more, it is possible to obtain a non-aqueous lithium-type storage element having an excellent volume energy density, the energy storage system using the non-aqueous lithium-type storage element, for example a car engine When used in combination, it is possible to install the power storage system in a limited narrow space in the automobile, which is preferable.
- the upper limit value of E / V i is preferably 50 or less.
- the internal resistance Ra ( ⁇ ) is a value obtained by the following method. First, constant-current charging in which a non-aqueous lithium storage element is constant-current charged until reaching 3.8 V at a current value of 20 C in a thermostat set to 25 ° C., and then a constant voltage charging of 3.8 V is applied. For a total of 30 minutes. Subsequently, constant current discharge is performed up to 2.2 V at a current value of 20 C, and a discharge curve (time-voltage) is obtained.
- Ra ⁇ F is preferably 3.0 or less, more preferably 2.5 or less, and still more preferably 2.2 or less, from the viewpoint of developing sufficient charge capacity and discharge capacity for a large current.
- a power storage system using the non-aqueous lithium storage element and a high-efficiency engine for example, can be combined with a high load applied to the non-aqueous lithium storage element.
- the lower limit of Ra ⁇ F is preferably 0.3 or more.
- the rate of increase in resistance after the high load charge / discharge cycle test is measured by the following method. First, constant-current charging is performed until a non-aqueous lithium storage element is set at 25 ° C. until it reaches 3.8 V at a current value of 300 C, and then 2.2 V is reached at a current value of 300 C. Perform constant current discharge. This high-load charge / discharge cycle is repeated 60,000 times, and the internal resistance is measured in the same manner as the internal resistance Ra ( ⁇ ) described above before and after the start of the test. The internal resistance after the test is Rb ( ⁇ ). The rate of increase in resistance after the high load charge / discharge cycle test before the start of the test is calculated by Rb / Ra.
- the resistance increase rate Rb / Ra after the high load charge / discharge cycle test is preferably 2.0 or less, more preferably 1.5 or less, and still more preferably 1.2 or less. If the rate of increase in resistance after the high-load charge / discharge cycle test is 2.0 or less, the characteristics of the nonaqueous lithium storage element are maintained even after repeated charge / discharge. Therefore, excellent input / output characteristics can be obtained stably for a long period of time, leading to a long life of the non-aqueous lithium storage element.
- the lower limit value of Rb / Ra is preferably 0.9 or more.
- Example 1 [Preparation of activated carbon]
- the crushed coconut shell carbide was put into a small carbonization furnace and carbonized at 500 ° C. for 3 hours under a nitrogen atmosphere to obtain a carbide.
- the obtained carbide was placed in an activation furnace, steam heated in a preheating furnace was introduced into the activation furnace at 1 kg / h, and the temperature was increased to 900 ° C. over 8 hours for activation.
- the activated carbide was taken out and cooled in a nitrogen atmosphere to obtain activated activated carbon.
- the activated carbon thus obtained was washed with water for 10 hours, drained, dried in an electric dryer maintained at 115 ° C.
- activated carbon 1 The average particle size of the activated carbon 1 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and the result was 4.2 ⁇ m. Further, the pore distribution of the activated carbon 1 was measured using a pore distribution measuring device (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics, Inc.
- SALD-2000J laser diffraction particle size distribution analyzer
- AUTOSORB-1 AS-1-MP pore distribution measuring device manufactured by Yuasa Ionics, Inc.
- the BET specific surface area was 2,360 m 2 / g
- mesopores The amount (V 1 ) was 0.52 cc / g
- the micropore amount (V 2 ) was 0.88 cc / g
- V 1 / V 2 0.59.
- Activated carbon 2 The phenol resin was placed in a firing furnace, carbonized at 600 ° C. for 2 hours in a nitrogen atmosphere, pulverized with a ball mill, and classified to obtain a carbide having an average particle size of 7.0 ⁇ m.
- the obtained carbide and KOH were mixed at a mass ratio of 1: 5, put into a firing furnace, and activated by heating at 800 ° C. for 1 hour in a nitrogen atmosphere.
- the activated carbide was taken out, washed with stirring in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, boiled and washed with distilled water until it became stable between pH 5 and 6, and then dried to obtain activated carbon 2.
- Activated carbon 3 The phenol resin was put into a firing furnace, carbonized at 600 ° C. for 2 hours in a nitrogen atmosphere, pulverized with a ball mill, and classified to obtain a carbide having an average particle size of 17.0 ⁇ m.
- the obtained carbide and KOH were mixed at a mass ratio of 1: 5, put into a firing furnace, and activated by heating at 800 ° C. for 1 hour in a nitrogen atmosphere.
- the activated carbide was taken out, stirred and washed in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, boiled and washed with distilled water until stable at pH 5 to 6, and then dried to obtain activated carbon 3.
- a positive electrode precursor was manufactured using the activated carbon 1 obtained above as a positive electrode active material. 42.5 parts by mass of activated carbon 1, 45.0 parts by mass of lithium carbonate having an average particle size of 2.0 ⁇ m as a lithium compound, 3.0 parts by mass of ketjen black, 1.5 parts by mass of PVP (polyvinylpyrrolidone), And 8.0 parts by mass of PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) are mixed, and this is mixed with a thin film swirl type high-speed mixer “Filmix (registered trademark)” manufactured by PRIMIX. A coating solution was obtained by dispersing under conditions of a speed of 17 m / s.
- the viscosity ( ⁇ b) and TI value of the obtained coating solution were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd.
- the viscosity ( ⁇ b) was 2,700 mPa ⁇ s, and the TI value was 3.5.
- the dispersion degree of the obtained coating liquid was measured using the grain gauge made from Yoshimitsu Seiki. As a result, the particle size was 35 ⁇ m.
- the above coating solution is applied to one or both sides of an aluminum foil having a thickness of 15 ⁇ m without through-holes using a die coater manufactured by Toray Engineering Co., Ltd. at a coating speed of 1 m / s and dried at a drying temperature of 100 ° C.
- positive electrode precursors (hereinafter also referred to as “single-sided positive electrode precursor” and “double-sided positive electrode precursor”, respectively) were obtained.
- the obtained positive electrode precursor was pressed using a roll press machine under the conditions of a pressure of 4 kN / cm and a surface temperature of the press part of 25 ° C.
- the composite carbon material 1 was taken out from the furnace.
- the average particle diameter and the BET specific surface area were measured by the method similar to the above.
- the average particle size was 3.2 ⁇ m
- the BET specific surface area was 262 m 2 / g.
- the mass ratio of carbonaceous material derived from coal-based pitch to activated carbon was 78%.
- the negative electrode was manufactured using the composite carbon material 1 as a negative electrode active material.
- 85 parts by mass of composite carbon material 1 10 parts by mass of acetylene black, 5 parts by mass of PVdF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) are mixed, and this is mixed with a thin film swirl type high speed manufactured by PRIMIX Using a mixer “Fillmix (registered trademark)”, a coating liquid was obtained by dispersing under a condition of a peripheral speed of 15 m / s.
- the viscosity ( ⁇ b) and TI value of the obtained coating solution were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd.
- the viscosity ( ⁇ b) was 2,789 mPa ⁇ s, and the TI value was 4.3.
- the above coating solution is applied to both sides of an electrolytic copper foil having a thickness of 10 ⁇ m without a through-hole using a die coater manufactured by Toray Engineering Co., Ltd. at a coating speed of 1 m / s and dried at a drying temperature of 85 ° C.
- negative electrode 1 (hereinafter also referred to as “double-sided negative electrode”) was obtained.
- the obtained negative electrode 1 was pressed using a roll press machine under conditions of a pressure of 4 kN / cm and a surface temperature of the press part of 25 ° C.
- the film thickness of the negative electrode active material layer of the negative electrode 1 obtained above was measured at any 10 locations on the negative electrode 1 using a thickness gauge Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd.
- the film thickness of the negative electrode active material layer of the negative electrode 1 was determined by subtracting the thickness of the copper foil from the average value of the measured film thickness.
- the film thickness of the negative electrode active material layer of the negative electrode 1 was 40 ⁇ m per side.
- the negative electrode active material was prepared and evaluated in the same manner as in the preparation example of the negative electrode 1 except that the base material and its mass part, the coal-based pitch and its mass part, and the heat treatment temperature shown in Table 1 were adjusted. Further, a negative electrode was prepared and evaluated in the same manner as in the preparation example of the negative electrode 1, except that the negative electrode active material obtained above was used to adjust the coating liquid as shown in Table 1 below. The results are shown in Table 1 below.
- the raw materials in Table 1 are as follows.
- Coconut shell activated carbon average particle size 3.0 ⁇ m
- Carbon nanoparticles average particle size 5.2 ⁇ m
- BET specific surface area 859 m 2 / g primary particle size 20 nm
- Artificial graphite 1 Average particle size 4.8 ⁇ m
- Pitch 1 Coal pitch with softening point 50 °C
- EC ethylene carbonate
- EMC methyl ethyl carbonate
- a negative electrode terminal and a positive electrode terminal were connected to the negative electrode 1 and the positive electrode precursor by ultrasonic welding to obtain an electrode laminate.
- This electrode laminate is housed in an exterior body made of an aluminum laminate packaging material, and the exterior body 3 of the electrode terminal part and the bottom part is subjected to conditions of a temperature of 180 ° C., a sealing time of 20 sec, and a sealing pressure of 1.0 MPa. And heat sealed.
- the sealed body was vacuum-dried under the conditions of a temperature of 80 ° C., a pressure of 50 Pa, and a drying time of 60 hours.
- the pressure was reduced from atmospheric pressure to -91 kPa, and then returned to atmospheric pressure.
- the process of depressurizing and returning to atmospheric pressure was repeated a total of 7 times (reduced pressure from atmospheric pressure to ⁇ 95, ⁇ 96, ⁇ 97, ⁇ 81, ⁇ 97, ⁇ 97, and ⁇ 97 kPa, respectively).
- the electrode laminate was impregnated with the non-aqueous electrolyte solution.
- the electrode laminate that is housed in the aluminum laminate packaging material and impregnated with the non-aqueous electrolyte is placed in a vacuum sealer and reduced to ⁇ 95 kPa at 180 ° C. for 10 seconds and 0.1 MPa.
- the aluminum laminate packaging material was sealed by sealing at a pressure of 1 to produce a non-aqueous lithium storage element.
- Lithium doping process Using the charge / discharge device (TOSCAT-3100U) manufactured by Toyo System Co., Ltd., the obtained non-aqueous lithium storage element was charged at a constant current until reaching a voltage of 4.5 V at a current value of 50 mA in a 25 ° C. environment. Then, initial charging was performed by a method in which 4.5 V constant voltage charging was continued for 48 hours, and the negative electrode 1 was doped with lithium.
- the non-aqueous lithium storage element after lithium doping is subjected to constant current discharge until reaching a voltage of 1.8 V at 150 mA in a 25 ° C. environment, followed by constant current charging until reaching a voltage of 4.0 V at 150 mA.
- a constant current / constant voltage charging step of performing 4.0V constant current discharging for 5 hours was performed.
- this non-aqueous lithium storage element was stored in a 55 ° C. environment for 48 hours.
- the capacitance F was obtained by the above-described method using a charge / discharge device (5V, 360A) manufactured by Fujitsu Telecom Networks Co., Ltd. in a thermostat set at 25 ° C.
- the internal resistance Ra at 25 ° C. was calculated, and energy density E / V 1 and Ra ⁇ F were obtained.
- Table 2 The results are shown in Table 2 below.
- Solid 7 Li-NMR Measurement of Positive Electrode With respect to the positive electrode of the obtained nonaqueous lithium storage element, solid 7 Li-NMR measurement of the positive electrode active material layer was performed. First, a constant current up to 2.9 V at an environmental current of 25 ° C. and a current of 50 mA is applied to the non-aqueous lithium storage element manufactured above using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After charging, constant current / constant voltage charging in which a constant voltage of 2.9 V was applied was performed for 2 hours. Next, the positive electrode active material layer was collected in an argon atmosphere. The nonaqueous lithium storage element was disassembled under an argon atmosphere, and the positive electrode was taken out.
- ACD-01 charge / discharge device
- the obtained positive electrode was immersed in diethyl carbonate for 2 minutes or more to remove lithium salt and the like. After dipping in diethyl carbonate again under the same conditions, it was air-dried. Thereafter, a positive electrode active material layer was collected from the positive electrode. Using the obtained positive electrode active material layer as a sample, solid 7 Li-NMR measurement was performed. ECA700 manufactured by JEOL RESONANCE ( 7 Li-NMR resonance frequency is 272.1 MHz) is used as a measurement device, and the rotation speed of magic angle spinning is 14.5 kHz and the irradiation pulse width is 45 ° pulse in a room temperature environment. Measured by the single pulse method.
- the observation range was ⁇ 400 ppm to 400 ppm, and the number of points was 4,096.
- Other measurement conditions other than the repetition waiting time for example, the number of integrations, receiver gain, etc. are all made the same, and the measurement is performed for each case where the repetition waiting time is 10 seconds and 3,000 seconds.
- a 1 mol / L lithium chloride aqueous solution was used as a shift reference, and the shift position separately measured as an external standard was set to 0 ppm.
- the sample was not rotated, and the irradiation pulse width was 45 ° pulse, and measurement was performed by a single pulse method.
- B / a was calculated by the above-described method from the solid 7 Li-NMR spectrum of the positive electrode active material layer obtained by the above method. The results are shown in Table 2 below.
- the obtained non-aqueous lithium storage element was disassembled in an argon box with a dew point temperature of ⁇ 72 ° C., and a positive electrode coated with a positive electrode active material layer on both sides was cut into a size of 10 cm ⁇ 5 cm, and 30 g of diethyl carbonate solvent And was occasionally moved with tweezers and washed for 10 minutes. Subsequently, the positive electrode was taken out, air-dried in an argon box for 5 minutes, immersed in 30 g of diethyl carbonate solvent newly prepared, and washed for 10 minutes in the same manner as described above.
- the positive electrode was taken out of the argon box and dried for 20 hours under the conditions of a temperature of 25 ° C. and a pressure of 1 kPa using a vacuum dryer (manufactured by Yamato Kagaku, DP33) to obtain a positive electrode sample. Cut a small piece of 1cm x 1cm from the positive electrode sample, and use a SM-09020CP made by JEOL, use argon gas, cross section perpendicular to the surface direction of the positive electrode sample under the conditions of acceleration voltage 4kV and beam diameter 500 ⁇ m. Produced. Next, gold was coated on the surface by sputtering in a vacuum of 10 Pa.
- SEM and EDX on the positive electrode surface were measured under atmospheric exposure under the following conditions.
- SEM-EDX measurement conditions ⁇ Measuring device: manufactured by Hitachi High-Technology, field emission scanning electron microscope FE-SEM S-4700 ⁇ Acceleration voltage: 10 kV ⁇ Emission current: 10 ⁇ A ⁇ Measurement magnification: 2,000 times ⁇ Electron beam incident angle: 90 ° -X-ray extraction angle: 30 ° ⁇ Dead time: 15% Mapping element: C, O, F Measurement pixel number: 256 ⁇ 256 pixels Measurement time: 60 sec. -Number of integrations: 50 times-The brightness and contrast were adjusted so that there was no pixel that reached the maximum brightness, and the average brightness was in the range of 40% to 60%.
- the positive electrode sample cut out to a size of 5 cm ⁇ 5 cm was immersed in methanol, the container was covered, and left standing at 25 ° C. for 3 days. Thereafter, the positive electrode was taken out and vacuum-dried at 120 ° C. and 5 kPa for 10 hours. About the methanol solution after washing
- the positive electrode sample was taken out and vacuum-dried at 150 ° C. and 3 kPa for 12 hours. About distilled water after washing
- Examples 2 to 17 and Comparative Examples 1 to 4> A positive electrode precursor was prepared in the same manner as in Example 1 except that the positive electrode active material, the lithium compound and the average particle size thereof, and the mass parts of the positive electrode active material and the lithium compound were as shown in Table 2 below.
- a non-aqueous lithium storage element was prepared and evaluated in the same manner as in Example 1 except that these positive electrode precursors were used in combination with the negative electrode shown in Table 2. The results are shown in Table 2 below.
- ⁇ Comparative Example 5> [Production of positive electrode precursor] 87.5 parts by mass of activated carbon 2, 3.0 parts by mass of ketjen black, 1.5 parts by mass of PVP (polyvinylpyrrolidone), 8.0 parts by mass of PVDF (polyvinylidene fluoride), and NMP (N— Methylpyrrolidone) was mixed and dispersed using a thin film swirl type high speed mixer “Filmix (registered trademark)” manufactured by PRIMIX under the condition of a peripheral speed of 17 m / s to obtain a coating solution.
- a positive electrode precursor was obtained in the same manner as in Example 1 except that the coating solution obtained above was used.
- Nonaqueous Lithium-type Energy Storage Device In the same manner as in Example 1, except that the obtained positive electrode precursor and a negative electrode in which a metal lithium foil corresponding to 211 mAh / g per unit mass of the negative electrode active material was attached to the negative electrode active material layer surface of the negative electrode 3 were used. The assembly, injection, impregnation, and sealing process of the water-based lithium storage element were performed. Next, as the lithium doping step, the non-aqueous lithium storage element obtained above was stored for 72 hours in a constant temperature bath at an environmental temperature of 45 ° C., and metallic lithium was ionized to be doped into the negative electrode 3. Thereafter, the obtained non-aqueous lithium storage element was subjected to an aging process and a degassing process in the same manner as in Example 1 to produce a non-aqueous lithium storage element and evaluated. The results are shown in Table 2 below.
- the viscosity ( ⁇ b) and TI value of the obtained coating solution were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. As a result, the viscosity ( ⁇ b) was 2,820 mPa ⁇ s, and the TI value was 3.2. Moreover, the dispersion degree of the obtained coating liquid was measured using the grain gauge made from Yoshimitsu Seiki. As a result, the particle size was 35 ⁇ m.
- the above coating solution is applied to one or both sides of an aluminum foil having a thickness of 15 ⁇ m without a through hole at a coating speed of 1 m / s, and a drying temperature of 100 ° C. Drying was performed to obtain a positive electrode precursor (hereinafter also referred to as “single-sided positive electrode precursor” and “double-sided positive electrode precursor”, respectively).
- the obtained positive electrode precursor was pressed using a roll press machine under conditions of a pressure of 4 kN / cm and a surface temperature of the pressing part of 25 ° C.
- Lithium content in positive electrode Per positive electrode of a nonaqueous lithium-type storage element obtained above was subjected to solid 7 Li-NMR measurement of the positive electrode active material layer. First, a constant current up to 2.9 V at an environmental current of 25 ° C. and a current of 50 mA is applied to the non-aqueous lithium-type energy storage device produced above using an Aska Electronics charge / discharge device (ACD-01). After charging, constant current / constant voltage charging in which a constant voltage of 2.9 V was applied was performed for 2 hours. Next, the positive electrode active material layer was collected in an argon atmosphere. The nonaqueous lithium storage element was disassembled under an argon atmosphere, and the positive electrode was taken out.
- the obtained positive electrode was immersed in diethyl carbonate for 2 minutes or more to remove lithium salt and the like. After dipping in diethyl carbonate again under the same conditions, it was air-dried. Thereafter, a positive electrode active material layer was collected from the positive electrode and weighed. Using the obtained positive electrode active material layer as a sample, solid 7 Li-NMR measurement was performed. ECA700 manufactured by JEOL RESONANCE ( 7 Li-NMR resonance frequency is 272.1 MHz) is used as a measurement device, and the rotation speed of magic angle spinning is 14.5 kHz and the irradiation pulse width is 45 ° pulse in a room temperature environment. Measured by the single pulse method.
- a 1 mol / L lithium chloride aqueous solution was used as a shift reference, and the shift position separately measured as an external standard was set to 0 ppm.
- the sample was not rotated, and the irradiation pulse width was 45 ° pulse, and measurement was performed by a single pulse method. In the measurement, a sufficient repetition waiting time was taken between measurements, and the repetition waiting time was set to 3,000 seconds.
- the amount of lithium was calculated by the method described above for the solid 7 Li-NMR spectrum of the positive electrode active material layer obtained by the above method. The results are shown in Table 3 below.
- the positive electrode after drying was transferred from the side box to the Ar box in a state where exposure to air was not performed, and immersion extraction was performed with heavy water to obtain a positive electrode extract.
- the analysis of the extract was performed by (i) IC and (ii) 1 H-NMR.
- the abundance (mol / g) of each compound deposited on the positive electrode per unit mass of the positive electrode active material layer was determined.
- the mass of the positive electrode active material layer used for extraction was determined by the following method.
- the mixture (positive electrode active material layer) was peeled off from the positive electrode current collector remaining after the heavy water extraction, and the peeled mixture was washed with water and then vacuum dried.
- the mixture obtained by vacuum drying was washed with NMP or DMF. Subsequently, the obtained positive electrode active material layer was vacuum-dried again and weighed to examine the mass of the positive electrode active material layer used for extraction.
- the positive electrode extract was put into a 3 mm ⁇ NMR tube (PN-002 manufactured by Shigemi Co., Ltd.), and a 5 mm ⁇ NMR tube containing deuterated chloroform containing 1,2,4,5-tetrafluorobenzene (N-5 manufactured by Japan Precision Science Co., Ltd.). ) And 1 H NMR measurement was performed by a double tube method. Normalization was performed with a signal of 1,2,4,5-tetrafluorobenzene of 7.1 ppm (m, 2H), and an integral value of each observed compound was obtained.
- deuterated chloroform containing dimethyl sulfoxide of known concentration is put into a 3 mm ⁇ NMR tube (PN-002 manufactured by Shigemi Co., Ltd.), and the same deuterated chloroform containing 1,2,4,5-tetrafluorobenzene as above.
- PN-002 manufactured by Shigemi Co., Ltd.
- the same deuterated chloroform containing 1,2,4,5-tetrafluorobenzene as above. was inserted into a 5 mm ⁇ NMR tube (N-5 manufactured by Japan Precision Science Co., Ltd.), and 1 H NMR measurement was performed by a double tube method.
- the signal was normalized with 7.1 ppm (m, 2H) of 1,2,4,5-tetrafluorobenzene, and the integral value of 2.6 ppm (s, 6H) of dimethyl sulfoxide was obtained. From the relationship between the concentration of dimethyl sulfoxide used and the integral value, the concentration A of each compound in the positive electrode extract
- the signal (3.7 ppm) is XOCH 2 CH 2 OX of CH 2, since the overlaps with CH 3 CH 2 OX of CH 2 O signals (3.7 ppm), the CH 3 CH 2 OX The amount of XOCH 2 CH 2 OX was calculated by excluding the CH 2 CH 2 OX equivalent of CH 3 CH 2 OX calculated from the CH 3 signal (1.2 ppm).
- X represents — (COO) n Li or — (COO) n R 1 (where n is 0 or 1, R 1 is an alkyl group having 1 to 4 carbon atoms, 1 to 4 carbon atoms, respectively) Of the halogenated alkyl group.
- Examples 19 to 35 and Comparative Examples 7 and 9> A positive electrode precursor was produced in the same manner as in Example 18 except that the positive electrode active material and the lithium compound were as shown in Table 3. Using these positive electrode precursors, in combination with the negative electrodes shown in Table 3 and using the aging process as described in Table 3, a non-aqueous lithium storage element was produced and evaluated in the same manner as in Example 18. It was. The results are shown in Table 3 below.
- Example 18 Manufacture and evaluation of non-aqueous lithium storage elements
- the same procedure as in Example 18 was conducted, except that the obtained positive electrode precursor and a negative electrode in which a metal lithium foil corresponding to 1,150 mAh / g per unit mass of the negative electrode active material was attached to the negative electrode active material layer surface of the negative electrode 2 were used.
- the assembly, injection, impregnation, and sealing steps of the non-aqueous lithium storage element were performed.
- the nonaqueous lithium storage element obtained above was stored for 72 hours in a constant temperature bath at an environmental temperature of 45 ° C., and metallic lithium was ionized to be doped into the negative electrode 2. Thereafter, the obtained nonaqueous lithium electricity storage device was manufactured and evaluated in the same manner as in Example 18 except that the aging process was performed under the conditions shown in Table 3. The results are shown in Table 3 below.
- Example 36 [Preparation of positive electrode precursor] 57.5 parts by mass of the activated carbon 1 obtained in Example 1, 30.0 parts by mass of lithium carbonate having an average particle size of 1.8 ⁇ m as a lithium compound, 3.0 parts by mass of ketjen black, and PVP (polyvinylpyrrolidone) 1.5 parts by mass, 8.0 parts by mass of PVDF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) were mixed, and this was mixed with a thin film swirl-type high-speed mixer “FILMIX (registered trademark)” manufactured by PRIMIX. Was used and dispersed under the condition of a peripheral speed of 17 m / s to obtain a coating solution.
- FILMIX registered trademark
- the viscosity ( ⁇ b) was 2,590 mPa ⁇ s, and the TI value was 2. It was 8.
- the dispersion degree of the obtained coating liquid was measured using the grain gauge made from Yoshimitsu Seiki. The particle size was 35 ⁇ m.
- the above coating solution is applied to one or both sides of an aluminum foil having a thickness of 15 ⁇ m without a through hole at a coating speed of 1 m / s, and a drying temperature of 100 ° C. It dried and obtained the positive electrode precursor (Hereafter, it is called a "single-sided positive electrode precursor” and a “double-sided positive electrode precursor", respectively.).
- the obtained positive electrode precursor was pressed using a roll press machine under conditions of a pressure of 4 kN / cm and a surface temperature of the pressing part of 25 ° C.
- the obtained composite carbon material 4 was cooled to 60 ° C. by natural cooling, and then taken out from the electric furnace. About the obtained composite carbon material 4, the average particle diameter and the BET specific surface area were measured by the method similar to the above. The results are shown in Table 4 below.
- the negative electrode 4 was manufactured using the composite carbon material 4 as a negative electrode active material. 80 parts by mass of composite carbon material 4, 8 parts by mass of acetylene black, 12 parts by mass of PVdF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) are mixed, and this is a thin film swirl type high speed made by PRIMIX Using a mixer “Fillmix (registered trademark)”, a coating liquid was obtained by dispersing under a condition of a peripheral speed of 15 m / s.
- the viscosity ( ⁇ b) was 2,674 mPa ⁇ s, and the TI value was 2. 6.
- the above coating solution is applied to both surfaces of an electrolytic copper foil having a thickness of 10 ⁇ m without a through hole at a coating speed of 1 m / s, and dried at a drying temperature of 85 ° C.
- negative electrode 4 was obtained (hereinafter also referred to as “double-sided negative electrode”). The obtained negative electrode 4 was pressed using a roll press.
- the film thickness of the negative electrode 4 obtained above was measured at any 10 locations on the negative electrode 4 using a thickness gauge Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd.
- the thickness of the copper foil was subtracted from the measured average value of the film thickness to determine the film thickness of the negative electrode active material layer of the negative electrode 4.
- the film thickness of the negative electrode active material layer of the negative electrode 4 was 20 ⁇ m per side.
- Examples of preparation of negative electrodes 5 to 13 As shown in Table 4, the negative electrode active material was produced and evaluated in the same manner as the negative electrode 4 preparation example except that the base material and its mass part, the coal-based pitch and its mass part, and the heat treatment temperature were adjusted. . Further, in the same manner as in the preparation example of the negative electrode 4, except that the coating liquid was prepared using the negative electrode active material shown in Table 4 so as to have the coating liquid composition shown in Table 4, the negative electrodes 5 to Thirteen productions and evaluations were performed. The results are shown in Table 4 below.
- the lithium-doped non-aqueous lithium storage element was discharged at a constant current until reaching a voltage of 2.2 V at 50 mA in a 25 ° C. environment, and then charged at a constant current until a voltage of 4.0 V was reached at 50 mA.
- a constant current / constant voltage charging step of performing 4.0V constant current charging for 30 hours was performed.
- Solid 7 Li-NMR Measurement of Negative Electrode With respect to the negative electrode 4 of the non-aqueous lithium storage element obtained above, solid 7 Li-NMR measurement of the negative electrode active material layer was performed. First, the non-aqueous lithium storage element manufactured as described above was set to 2.9 V at a current of 50 mA at an ambient temperature of 25 ° C. using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After current charging, constant current constant voltage charging was performed in which a constant voltage of 2.9 V was applied for 15 hours. Next, the negative electrode active material layer was collected in an argon atmosphere. The nonaqueous lithium storage element was disassembled under an argon atmosphere, and the negative electrode 4 was taken out.
- ACD-01 charge / discharge device
- the obtained negative electrode 4 was immersed in diethyl carbonate for 2 minutes or more to remove lithium salt and the like. After dipping in diethyl carbonate again under the same conditions, it was air-dried. Thereafter, a negative electrode active material layer was collected from the negative electrode 4 and weighed. Using the obtained negative electrode active material layer as a sample, solid 7 Li-NMR measurement was performed. ECA700 manufactured by JEOL RESONANCE ( 7 Li-NMR resonance frequency is 272.1 MHz) is used as a measurement device, and the rotation speed of magic angle spinning is 14.5 kHz and the irradiation pulse width is 45 ° pulse in a room temperature environment. Measured by the single pulse method.
- a 1 mol / L lithium chloride aqueous solution was used as a shift reference, and the shift position separately measured as an external standard was set to 0 ppm.
- the sample was not rotated, and the irradiation pulse width was 45 ° pulse, and measurement was performed by a single pulse method.
- the position of the maximum value of the peak in the spectrum range of ⁇ 10 ppm to 35 ppm was 16 ppm.
- the amount of lithium per unit mass of the negative electrode active material layer occluded with lithium ions was calculated by the method described above. The results are shown in Table 5 below.
- the BET specific surface area per unit volume of the negative electrode active material layer of the negative electrode after use and the average pore diameter of the negative electrode active material layer were measured.
- the non-aqueous lithium storage element manufactured as described above was set to 2.9 V at a current of 50 mA at an ambient temperature of 25 ° C. using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After current charging, constant current constant voltage charging was performed in which a constant voltage of 2.9 V was applied for 15 hours. Next, the negative electrode 4 was collected in an argon atmosphere.
- the nonaqueous lithium storage element was disassembled under an argon atmosphere, and the negative electrode 4 was taken out. Subsequently, the obtained negative electrode 4 was immersed in diethyl carbonate for 2 minutes or more to remove the non-aqueous electrolyte, lithium salt, and the like, and air-dried. Thereafter, the obtained negative electrode 4 was immersed in a mixed solvent composed of methanol and isopropanol for 15 hours to deactivate lithium ions occluded in the negative electrode active material and air-dried. Subsequently, the obtained negative electrode 4 was vacuum-dried for 12 hours on the conditions of the temperature of 170 degreeC using the vacuum dryer, and the measurement sample was obtained.
- the negative electrode active material layer of the negative electrode after use by the above-described method using a pore distribution measuring device (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics, using nitrogen as an adsorbate The BET specific surface area per unit volume and the average pore diameter of the negative electrode active material layer were measured. The results are shown in Table 5 below.
- Solid 7 Li-NMR Measurement of Positive Electrode With respect to the positive electrode of the obtained nonaqueous lithium storage element, solid 7 Li-NMR measurement of the positive electrode active material layer was performed. First, the non-aqueous lithium storage element manufactured as described above was set to 2.9 V at a current of 50 mA at an ambient temperature of 25 ° C. using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After current charging, constant current constant voltage charging was performed in which a constant voltage of 2.9 V was applied for 15 hours. Next, the positive electrode active material layer was collected in an argon atmosphere. The nonaqueous lithium storage element was disassembled under an argon atmosphere, and the positive electrode was taken out.
- ACD-01 charge / discharge device
- the obtained positive electrode was immersed in diethyl carbonate for 2 minutes or more to remove the nonaqueous electrolytic solution, lithium salt, and the like. After dipping in diethyl carbonate again under the same conditions, it was air-dried. Thereafter, a positive electrode active material layer was collected from the positive electrode. Using the obtained positive electrode active material layer as a sample, solid 7 Li-NMR measurement was performed. ECA700 manufactured by JEOL RESONANCE ( 7 Li-NMR resonance frequency is 272.1 MHz) is used as a measurement device, and the rotation speed of magic angle spinning is 14.5 kHz and the irradiation pulse width is 45 ° pulse in a room temperature environment. Measured by the single pulse method.
- the observation range was ⁇ 400 ppm to 400 ppm, and the number of points was 4,096.
- Measurement conditions other than the repetition waiting time for example, the number of integrations, receiver gain, etc., are all made the same, and the measurement is performed for each case where the repetition waiting time is 10 seconds and 3,000 seconds to obtain an NMR spectrum. It was.
- a 1 mol / L lithium chloride aqueous solution was used as a shift reference, and the shift position separately measured as an external standard was set to 0 ppm.
- the irradiation pulse width was 45 ° pulse, and measurement was performed by a single pulse method.
- B / a was calculated by the above-described method from the solid 7 Li-NMR spectrum of the positive electrode active material layer obtained by the above method. The results are shown in Table 5 below.
- Examples 37 to 59 and Comparative Examples 10 to 11> A positive electrode precursor was produced in the same manner as in Example 36 except that the positive electrode active material, the lithium compound and the average particle diameter thereof, and the mass parts of the positive electrode active material and the lithium compound were as shown in Table 5. Using these positive electrode precursors, in combination with the negative electrode shown in Table 5 and using the lithium doping step as shown in Table 5, a non-aqueous lithium storage element was produced and evaluated in the same manner as in Example 36. Went. The results are shown in Table 5 below.
- the negative electrode contains a graphite-based carbon material as the negative electrode active material, and the solid 7 Li-NMR spectrum of the negative electrode active material layer is 4 ppm to 35 ppm in the spectral range of -10 ppm to 35 ppm.
- the non-aqueous lithium storage element using this negative electrode has a low resistance (the maximum value of the peak is between 30 ppm and the amount of lithium calculated from the peak area of 4 ppm to 30 ppm is adjusted to a specific range. That is, it can be seen that high input / output characteristics) and high high load charge / discharge cycle characteristics can be exhibited.
- Example 60 [Preparation of positive electrode precursor] 57.5 parts by mass of the activated carbon 1 obtained in Example 1, 30.0 parts by mass of lithium carbonate having an average particle size of 2.3 ⁇ m as a lithium compound, 3.0 parts by mass of ketjen black, and PVP (polyvinylpyrrolidone) 1.5 parts by mass, 8.0 parts by mass of PVDF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) were mixed, and this was mixed with a thin film swirl-type high-speed mixer “FILMIX (registered trademark)” manufactured by PRIMIX. Was used and dispersed under the condition of a peripheral speed of 17 m / s to obtain a coating solution.
- FILMIX registered trademark
- the viscosity ( ⁇ b) and TI value of the obtained coating solution were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. As a result, the viscosity ( ⁇ b) was 2,321 mPa ⁇ s, and the TI value was 2.0. Moreover, the dispersion degree of the obtained coating liquid was measured using the grain gauge made from Yoshimitsu Seiki. As a result, the particle size was 35 ⁇ m.
- the above coating solution is applied to one or both sides of an aluminum foil having a thickness of 15 ⁇ m without a through hole at a coating speed of 1 m / s, and a drying temperature of 100 ° C. It dried and obtained the positive electrode precursor (Hereafter, it is called a "single-sided positive electrode precursor” and a “double-sided positive electrode precursor", respectively.).
- the obtained positive electrode precursor was pressed using a roll press machine under conditions of a pressure of 4 kN / cm and a surface temperature of the pressing part of 25 ° C.
- a negative electrode 14 was manufactured using the composite carbon material 12 as a negative electrode active material. 80 parts by mass of the composite carbon material 12, 8 parts by mass of acetylene black, 12 parts by mass of PVdF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) are mixed, and this is mixed with a thin film swirl type high speed manufactured by PRIMIX Using a mixer “Fillmix (registered trademark)”, a coating liquid was obtained by dispersing under a condition of a peripheral speed of 15 m / s. The viscosity ( ⁇ b) and TI value of the obtained coating solution were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd.
- the viscosity ( ⁇ b) was 2,274 mPa ⁇ s, and the TI value was 4.2.
- the above coating solution is applied to both surfaces of an electrolytic copper foil having a thickness of 10 ⁇ m without a through hole at a coating speed of 1 m / s, and dried at a drying temperature of 85 ° C.
- the negative electrode 14 was obtained (hereinafter also referred to as “double-sided negative electrode”).
- the obtained negative electrode 14 was pressed using a roll press machine under the conditions of a pressure of 4 kN / cm, a surface temperature of the press part of 25 ° C., and a gap between press rolls of 30 ⁇ m.
- the film thickness of the negative electrode 14 obtained above was measured at any 10 locations on the negative electrode 14 using a thickness gauge Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd.
- the thickness of the copper foil was subtracted from the measured average value of the film thickness to determine the film thickness of the negative electrode active material layer of the negative electrode 14.
- the film thickness of the negative electrode active material layer of the negative electrode 14 was 20 ⁇ m per side.
- Examples of preparation of negative electrodes 15 to 32 The negative electrode active material was manufactured and evaluated in the same manner as in the preparation example of the negative electrode 14 except that the base material and its mass part, the coal-based pitch and its mass part, and the heat treatment temperature shown in Table 6 were prepared. .
- the negative electrode active material obtained above was used to prepare the coating liquid shown in Table 6, and the formed negative electrode was pressed under the pressing conditions shown in Table 6 and was the same as the preparation example of the negative electrode 14 Thus, the negative electrode was manufactured and evaluated. The results are shown in Table 6.
- the raw materials in Table 6 are as follows. Artificial graphite 5: average particle diameter 0.7 ⁇ m, BET specific surface area 15.2 m 2 / g Artificial graphite 6: average particle size 4.8 ⁇ m, BET specific surface area 6.3 m 2 / g Artificial graphite 7: average particle size 9.8 ⁇ m, BET specific surface area 0.8 m 2 / g Natural graphite 4: Average particle size 5.8 ⁇ m, BET specific surface area 7.4 m 2 / g Natural graphite 5: average particle size 9.2 ⁇ m, BET specific surface area 1.1 m 2 / g High specific surface area graphite 3: Average particle size 2.4 ⁇ m, BET specific surface area 62.2 m 2 / g High specific surface area graphite 4: Average particle size 5.4 ⁇ m, BET specific surface area 45.7 m 2 / g High specific surface area graphite 5: average particle size 9.6 ⁇ m, BET specific surface area 29.4 m 2 / g Pitch
- Lithium doping process Using the charge / discharge device (TOSCAT-3100U) manufactured by Toyo System Co., Ltd., the obtained non-aqueous lithium storage element was charged at a constant current until reaching a voltage of 4.5 V at a current value of 100 mA in a 55 ° C. environment. Then, initial charging was performed by a method in which 4.5 V constant voltage charging was continued for 24 hours, and lithium doping was performed on the negative electrode 14.
- the non-aqueous lithium storage element manufactured as described above was set to 2.9 V at a current of 50 mA at an ambient temperature of 25 ° C. using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After current charging, constant current constant voltage charging was performed in which a constant voltage of 2.9 V was applied for 15 hours.
- ACD-01 charge / discharge device manufactured by Asuka Electronics.
- the negative electrode 14 was collected in an argon atmosphere.
- the non-aqueous lithium storage element was disassembled under an argon atmosphere, and the negative electrode 14 was taken out.
- the obtained negative electrode 14 was immersed in diethyl carbonate for 2 minutes or more to remove the non-aqueous electrolyte, lithium salt, and the like, and air-dried.
- the obtained negative electrode 14 was immersed in a mixed solvent composed of methanol and isopropanol for 15 hours to deactivate lithium ions occluded in the negative electrode active material and air-dried.
- the obtained negative electrode 14 was vacuum-dried for 12 hours under the condition of a temperature of 170 ° C. using a vacuum dryer to obtain a measurement sample.
- the cross section polisher by JEOL Ltd. was used, and the BIB process by an argon ion beam was given by the method mentioned above on the conditions of the acceleration voltage of 4 kV, and the cross section of the negative electrode active material layer of the negative electrode 14 was formed. did.
- the SEM image of the cross section of the obtained negative electrode active material layer was obtained on condition of the following using the scanning electron microscope (SU8220) made from Hitachi High-Technologies.
- Example 61 to 86> A positive electrode precursor was produced in the same manner as in Example 60 except that the positive electrode active material, the lithium compound and the average particle size thereof, and the mass parts of the positive electrode active material and the lithium compound were as shown in Table 7.
- a non-aqueous lithium storage element was produced and evaluated in the same manner as in Example 60 except that these positive electrode precursors were used in combination with the negative electrode shown in Table 7. The results are shown in Table 7 and Table 8 below.
- ⁇ Comparative Example 12> [Production of positive electrode precursor] 87.5 parts by mass of the activated carbon 2 obtained in Example 1, 3.0 parts by mass of ketjen black, 1.5 parts by mass of PVP (polyvinylpyrrolidone), and 8.0 parts by mass of PVDF (polyvinylidene fluoride) And NMP (N-methylpyrrolidone) are mixed and dispersed using PRIM Corporation's thin film swirl type high speed mixer “FILMIX (registered trademark)” at a peripheral speed of 17 m / s. Got.
- a positive electrode precursor was obtained in the same manner as in Example 60 except that the coating liquid obtained above was used.
- Example 60 [Preparation and Evaluation of Nonaqueous Lithium-type Energy Storage Device] The same procedure as in Example 60 except that the negative electrode obtained by pasting the obtained positive electrode precursor and a metal lithium foil corresponding to 280 mAh / g per unit mass of the negative electrode active material on the negative electrode active material layer surface shown in Table 7 was used. Then, the assembly, injection, impregnation and sealing of the non-aqueous lithium storage element were carried out.
- the non-aqueous lithium storage element obtained above was stored for 30 hours in a constant temperature bath at an environmental temperature of 45 ° C., and metallic lithium was ionized to dope the negative electrode shown in Table 7. Thereafter, the obtained non-aqueous lithium storage element was subjected to aging and degassing in the same manner as in Example 60 to produce a non-aqueous lithium storage element and evaluated. The results are shown in Table 7 below.
- the positive electrode contains a lithium compound other than the positive electrode active material, and the average distance between the centers of gravity of the voids obtained from the SEM of the negative electrode active material layer cross section is specified It can be seen that the low resistance (that is, high input / output characteristics) and the high load charge / discharge cycle characteristics can be exhibited by adjusting to the above range.
- Example 2 A non-aqueous lithium storage element was produced in the same manner as in Example 64, and [Measurement of the average distance between the centers of gravity of the voids in the negative electrode active material layer cross section of the negative electrode after use] was performed using the non-aqueous lithium storage element.
- the non-aqueous lithium storage element manufactured as described above was set to 2.9 V at a current of 50 mA at an ambient temperature of 25 ° C. using a charge / discharge device (ACD-01) manufactured by Asuka Electronics. After current charging, constant current constant voltage charging was performed in which a constant voltage of 2.9 V was applied for 15 hours.
- ACD-01 charge / discharge device manufactured by Asuka Electronics.
- the negative electrode 17 was collected in an argon atmosphere.
- the non-aqueous lithium storage element was disassembled under an argon atmosphere, and the negative electrode 17 was taken out.
- the obtained negative electrode 17 was immersed in diethyl carbonate for 2 minutes or more to remove the non-aqueous electrolyte solution, lithium salt, and the like, and air-dried.
- the obtained negative electrode 17 was used as a working electrode, metallic lithium was used as a counter electrode and a reference electrode, and these were immersed in the non-aqueous electrolyte prepared in Example 60 to produce an electrochemical cell.
- the voltage 2.5V that is, the negative electrode potential (vs.
- Li / Li +) of the negative electrode 17 is 2.5V) using a charge / discharge device (TOSCAT-3000U) manufactured by Toyo System Co., Ltd. Then, constant current charging was performed at a current of 10 mA, followed by constant current constant voltage charging in which a constant voltage of 2.5 V was applied for 15 hours.
- the charging here is an operation of releasing lithium ions from the negative electrode 17.
- the negative electrode 17 was taken out from the electrochemical cell under an argon atmosphere, and this was immersed in diethyl carbonate for 2 minutes or more to remove the non-aqueous electrolyte, lithium salt, and the like, and air-dried. Next, the obtained negative electrode 17 was vacuum-dried for 12 hours under the condition of a temperature of 170 ° C. using a vacuum dryer to obtain a measurement sample.
- Example 64 and Reference Examples 1 and 2 the pretreatment method of the measurement sample before and after being incorporated into the non-aqueous lithium storage element, and [Measurement of the average distance between the centers of gravity of the negative electrode active material layer cross section of the negative electrode after use] It can be seen that similar results are obtained regardless of the difference.
- the non-aqueous lithium storage element using the negative electrode of the present invention can be used in combination with an internal combustion engine, a fuel cell, or a motor, for example, in the field of a hybrid drive system of an automobile. It can utilize suitably for etc.
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Abstract
Description
これらの蓄電システムに用いられる電池の第一の要求事項は、エネルギー密度が高いことである。このような要求に対応可能な高エネルギー密度電池の有力候補として、リチウムイオン電池の開発が精力的に進められている。
第二の要求事項は、出力特性が高いことである。例えば、高効率エンジンと蓄電システムとの組み合わせ(例えば、ハイブリッド電気自動車)又は燃料電池と蓄電システムとの組み合わせ(例えば、燃料電池電気自動車)において、加速時には蓄電システムにおける高出力放電特性が要求されている。
現在、高出力蓄電デバイスとしては、電気二重層キャパシタ、ニッケル水素電池等が開発されている。
他方、現在ハイブリッド電気自動車で採用されているニッケル水素電池は、電気二重層キャパシタと同等の高出力を有し、かつ160Wh/L程度のエネルギー密度を有している。しかしながら、そのエネルギー密度及び出力をより一層高めるとともに、耐久性(特に、高温における安定性)を高めるための研究が精力的に進められている。
また、リチウムイオン電池においても、高出力化に向けての研究が進められている。例えば、放電深度(蓄電素子の放電容量の何%を放電した状態かを示す値)50%において3kW/Lを超える高出力が得られるリチウムイオン電池が開発されている。しかしながら、そのエネルギー密度は100Wh/L以下であり、リチウムイオン電池の最大の特徴である高エネルギー密度を敢えて抑制した設計となっている。また、その耐久性(サイクル特性及び高温保存特性)については、電気二重層キャパシタに比べ劣る。そのため、実用的な耐久性を持たせるためには、放電深度が0~100%の範囲よりも狭い範囲での使用となる。実際に使用できる容量は更に小さくなるから、耐久性をより一層向上させるための研究が精力的に進められている。
キャパシタのエネルギーは1/2・C・V2(ここで、Cは静電容量、Vは電圧)で表される。
リチウムイオンキャパシタは、リチウム塩を含む非水系電解液を使用する蓄電素子(非水系リチウム型蓄電素子)の一種であって、正極においては約3V以上で電気二重層キャパシタと同様の陰イオンの吸着・脱着による非ファラデー反応、負極においてはリチウムイオン電池と同様のリチウムイオンの吸蔵・放出によるファラデー反応によって、充放電を行う蓄電素子である。
これらの電極材料の組合せとして、電気二重層キャパシタは、正極及び負極に活性炭(エネルギー密度1倍)を用い、正負極共に非ファラデー反応により充放電を行うことを特徴とし、高出力かつ高耐久性を有するがエネルギー密度が低い(正極1倍×負極1倍=1)という特徴がある。
リチウムイオン二次電池は、正極にリチウム遷移金属酸化物(エネルギー密度10倍)、負極に炭素材料(エネルギー密度10倍)を用い、正負極共にファラデー反応により充放電を行うことを特徴とし、高エネルギー密度(正極10倍×負極10倍=100)だが、出力特性及び耐久性に問題がある。更に、ハイブリッド電気自動車等で要求される高耐久性を満足させるためには放電深度を制限しなければならず、リチウムイオン二次電池では、そのエネルギーの10~50%しか使用できない。
リチウムイオンキャパシタは、正極に活性炭(エネルギー密度1倍)、負極に炭素材料(エネルギー密度10倍)を用い、正極では非ファラデー反応、負極ではファラデー反応により充放電を行うことを特徴とし、電気二重層キャパシタ及びリチウムイオン二次電池の特徴を兼ね備えた新規の非対称キャパシタである。それゆえ、高出力かつ高耐久性でありながら、高エネルギー密度(正極1倍×負極10倍=10)を有し、リチウムイオン二次電池の様に放電深度を制限する必要がないことが特徴である。
また、以下の特許文献2には、リチウムマンガン酸等のリチウム複合酸化物を正極に用い、正極に炭酸リチウムを含有させることでマンガンの溶出を抑制したリチウムイオン二次電池が提案されている。
さらに、以下の特許文献3には、正極で被酸化物としての各種リチウム化合物を酸化し、劣化した蓄電素子の容量を回復させる方法が提案されている。
かかる状況下、本発明が解決しようとする課題は、高い入出力特性と高負荷充放電サイクル特性を有する非水系リチウム型蓄電素子を提供することである。
[1]
正極、負極、セパレータ、及びリチウムイオンを含む非水系電解液を備える非水系リチウム型蓄電素子であって、
該負極が、負極集電体と、該負極集電体の片面又は両面上に設けられた、負極活物質を含む負極活物質層とを有し、
該正極は、正極集電体と、該正極集電体の片面又は両面上に設けられた、正極活物質を含む正極活物質層とを有し、
該正極活物質層の固体7Li-NMRスペクトルにおいて、繰り返し待ち時間10秒とした測定により得られた-40ppm~40ppmにおけるピーク面積をaとし、繰り返し待ち時間3,000秒とした測定により得られた-40ppm~40ppmにおけるピーク面積をbとしたとき、1.04≦b/a≦5.56である、前記非水系リチウム型蓄電素子。
[2]
前記正極活物質層の固体7Li-NMRスペクトルについて、-40ppm~40ppmにおけるピーク面積より計算される前記正極中のリチウム量が、前記正極活物質層の単位質量当たり1mmol/g以上30mmol/g以下である、[1]に記載の非水系リチウム型蓄電素子。
[3]
前記正極は、下記式(1)~(3):
で表される化合物からなる群から選択される少なくとも1種を、前記正極物質層の単位質量当たり1.60×10-4mol/g~300×10-4mol/g含有する、[2]に記載の前記非水系リチウム型蓄電素子。
[4]
前記正極は、前記正極活物質以外のリチウム化合物を含有する、[1]~[3]のいずれか1項に記載の非水系リチウム型蓄電素子。
[5]
前記リチウム化合物の平均粒子径X1が、0.1μm以上10μm以下である、[4]に記載の非水系リチウム型蓄電素子。
[6]
前記正極活物質の平均粒子径をY1とするとき、2μm≦Y1≦20μmであり、かつ、X1<Y1であり、さらに、前記正極中の前記リチウム化合物の含有割合が、前記正極活物質層の全質量を基準として、1質量%以上50質量%以下である、[5]に記載の非水系リチウム型蓄電素子。
[7]
前記正極中の前記リチウム化合物の含有割合が、前記正極活物質層の全質量を基準として1質量%以上20質量%以下である、[4]~[6]のいずれか1項に記載の非水系リチウム型蓄電素子。
[8]
前記リチウム化合物は、炭酸リチウム、酸化リチウム、及び水酸化リチウムから成る群から選択される少なくとも1種である、[4]~[7]のいずれか1項に記載の非水系リチウム型蓄電素子。
[9]
前記負極活物質層断面のSEMより得られる空隙の平均重心間距離が、1μm以上10μm以下である、[4]~[8]のいずれか1項に記載の非水系リチウム型蓄電素子。
[10]
前記空隙の平均重心間距離をrpとし、前記負極活物質の平均粒子径raとしたとき、rp/raが0.10以上1.10以下である、[9]に記載の非水系リチウム型蓄電素子。
[11]
前記負極活物質は、黒鉛系炭素材料を含み、
前記負極活物質層は、リチウムイオンを吸蔵しており、そして
前記負極活物質層の固体7Li-NMRスペクトルについて、-10ppm~35ppmのスペクトル範囲において、4ppm~30ppmの間にピークの最大値があり、かつ4ppm~30ppmのピーク面積より計算されるリチウム量が、前記負極活物質層の単位質量当たり0.10mmol/g以上10.0mmol/g以下である、[1]~[10]のいずれか1項に記載の非水系リチウム型蓄電素子。
[12]
前記負極活物質層の単位体積当たりのBET比表面積が1m2/cc以上50m2/cc以下である、[1]~[11]のいずれか1項に記載の非水系リチウム型蓄電素子。
[13]
前記負極活物質層の平均細孔径が2nm以上20nm以下である、[1]~[12]のいずれか1項に記載の非水系リチウム型蓄電素子。
[14]
前記負極活物質の平均粒子径が1μm以上10μm以下である、[1]~[13]のいずれか1項に記載の非水系リチウム型蓄電素子。
[15]
前記負極活物質が黒鉛質材料と炭素質材料との複合炭素材料を含む、[1]~[14]のいずれか1項に記載の非水系リチウム型蓄電素子。
[16]
前記負極活物質のリチウムイオンのドープ量が、前記負極活物質の単位質量当たり50mAh/g以上700mAh/g以下である、[1]~[15]のいずれか1項に記載の非水系リチウム型蓄電素子。
[17]
前記負極活物質のBET比表面積が1m2/g以上50m2/g以下である、[1]~[16]のいずれか1項に記載の非水系リチウム型蓄電素子。
[18]
前記負極活物質のリチウムイオンのドープ量が、前記負極活物質の単位質量当たり530mAh/g以上2,500mAh/g以下である、[1]~[8]のいずれか1項に記載の非水系リチウム型蓄電素子。
[19]
前記負極活物質のBET比表面積が100m2/g以上1,500m2/g以下である、[1]~[8]及び[18]のいずれか1項に記載の非水系リチウム型蓄電素子。
[20]
前記正極活物質層に含まれる前記正極活物質は、BJH法により算出した直径20Å以上500Å以下の細孔に由来するメソ孔量をV1(cc/g)、MP法により算出した直径20Å未満の細孔に由来するマイクロ孔量をV2(cc/g)とするとき、0.3<V1≦0.8、及び0.5≦V2≦1.0を満たし、かつ、BET法により測定される比表面積が1,500m2/g以上3,000m2/g以下を示す活性炭である、[1]~[19]のいずれか1項に記載の非水系リチウム型蓄電素子。
[21]
前記正極活物質層に含まれる前記正極活物質は、BJH法により算出した直径20Å以上500Å以下の細孔に由来するメソ孔量をV1(cc/g)、MP法により算出した直径20Å未満の細孔に由来するマイクロ孔量をV2(cc/g)とするとき、0.8<V1≦2.5、及び0.8<V2≦3.0を満たし、かつ、BET法により測定される比表面積が2,300m2/g以上4,000m2/g以下を示す活性炭である、[1]~[19]のいずれか1項に記載の非水系リチウム型蓄電素子。
[22]
前記正極集電体及び前記負極集電体が、貫通孔を持たない金属箔である、[1]~[21]のいずれか1項に記載の非水系リチウム型蓄電素子。
[23]
前記非水系リチウム型蓄電素子において、初期の内部抵抗をRa(Ω)、静電容量をF(F)、電力量をE(Wh)、蓄電素子の体積をV(L)としたとき、以下の(a)および(b):
(a)RaとFの積Ra・Fが0.3以上3.0以下である、
(b)E/Vが15以上50以下である、
を満たす、[1]~[22]のいずれか1項に記載の非水系リチウム型蓄電素子。
[24]
前記非水系リチウム型蓄電素子に対して、環境温度25℃、セル電圧2.2Vから3.8V、300Cのレートで充放電サイクルを60,000回行い、前記充放電サイクル後の内部抵抗をRb(Ω)、前記充放電サイクル前の内部抵抗をRa(Ω)としたとき、Rb/Raが0.9以上2.0以下である、[1]~[23]のいずれか1項に記載の非水系リチウム型蓄電素子。
[25]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む蓄電モジュール。
[26]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む電力回生システム。
[27]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む電力負荷平準化システム。
[28]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む無停電電源システム。
[29]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む非接触給電システム。
[30]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含むエナジーハーベストシステム。
[31]
[1]~[24]のいずれか1項に記載の非水系リチウム型蓄電素子を含む蓄電システム。
非水系リチウム型蓄電素子は一般に、正極と、負極と、セパレータと、電解液とを主な構成要素として備える。電解液としては、リチウムイオンを含む有機溶媒(以下、「非水系電解液」ともいう。)を用いる。
本実施形態における正極は、正極集電体と、その片面又は両面上に設けられた、正極活物質を含む正極活物質層とを有する。
固体7Li-NMRの測定装置としては、市販の装置を用いることができる。室温環境下において、マジックアングルスピニングの回転数を14.5kHzとし、照射パルス幅を45°パルスとして、シングルパルス法にてスペクトルを測定する。繰り返し待ち時間を10秒とした場合と3,000秒とした場合のそれぞれについて測定を行い、固体7Li-NMRスペクトルを得る。固体7Li-NMRスペクトルの取得にあたっては繰り返し待ち時間以外の測定条件、すなわち積算回数やレシーバーゲインなどをすべて同一とする。シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとする。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法にてスペクトルを測定する。
上記の方法によって得られる正極活物質層の固体7Li-NMRスペクトルから-40ppm~40ppmのスペクトル範囲におけるピーク面積a、bをそれぞれ取得し、b/aを算出する。
固体7Li-NMRの測定装置としては、市販の装置を用いることができる。室温環境下において、マジックアングルスピニングの回転数を14.5kHzとし、照射パルス幅を45°パルスとして、シングルパルス法にてスペクトルを測定する。測定に際しては測定の間の繰り返し待ち時間を十分に取るように設定する。
シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとする。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法にてスペクトルを測定する。
上記の方法によって得られた正極活物質層の固体7Li-NMRスペクトルについて、-40ppm~40ppmの範囲にある成分についてピーク面積を求める。そして、これらのピーク面積を、測定用ローター中における試料高さを正極活物質層測定時と同じにして測定した1mol/Lの塩化リチウム水溶液のピーク面積で除し、さらに測定に用いる正極活物質層の質量で除すことで、正極中のリチウム量を算出できる。正極活物質層の質量とは、正極活物質層に含有される被膜や堆積物等を含む正極活物質層の質量である。
正極活物質層は正極活物質を含み、これ以外に、必要に応じて、導電性フィラー、結着剤、及び分散安定剤等の任意成分を含んでいてもよい。
正極活物質は、炭素材料を含むことが好ましい。炭素材料としては、好ましくはカーボンナノチューブ、導電性高分子、及び多孔性の炭素材料が挙げられ、さらに好ましくは活性炭である。正極活物質は、2種類以上の材料を混合して含んでもよく、炭素材料以外の材料、例えばリチウムと遷移金属との複合酸化物等を含んでもよい。
正極活物質の合計質量に対する炭素材料の含有率は、好ましくは50質量%以上であり、より好ましくは70質量%以上である。炭素材料の含有率は100質量%であってもよいが、他の材料との併用による効果を良好に得る観点から、例えば、好ましくは90質量%以下であり、80質量%以下であってもよい。
(1)高い入出力特性を得るためには、0.3<V1≦0.8、及び0.5≦V2≦1.0を満たし、かつ、BET法により測定される比表面積が1,500m2/g以上3,000m2/g以下である活性炭(以下、「活性炭1」ともいう。)が好ましく、また、
(2)高いエネルギー密度を得るためには、0.8<V1≦2.5、及び0.8<V2≦3.0を満たし、かつ、BET法により測定される比表面積が2,300m2/g以上4,000m2/g以下である活性炭(以下、「活性炭2」ともいう。)が好ましい。
(活性炭1)
活性炭1のメソ孔量V1は、正極材料を非水系リチウム型蓄電素子に組み込んだときの入出力特性を大きくする点で、0.3cc/gより大きい値であることが好ましい。他方、正極の嵩密度の低下を抑える点から、活性炭1のV1は0.8cc/g以下であることが好ましい。活性炭1のV1は、より好ましくは0.35cc/g以上0.7cc/g以下、更に好ましくは0.4cc/g以上0.6cc/g以下である。
本実施形態では、活性炭1の原料として用いられる炭素源は、特に限定されるものではない。活性炭1の炭素源としては、例えば、木材、木粉、ヤシ殻、パルプ製造時の副産物、バガス、廃糖蜜等の植物系原料;泥炭、亜炭、褐炭、瀝青炭、無煙炭、石油蒸留残渣成分、石油ピッチ、コークス、コールタール等の化石系原料;フェノール樹脂、塩化ビニル樹脂、酢酸ビニル樹脂、メラミン樹脂、尿素樹脂、レゾルシノール樹脂、セルロイド、エポキシ樹脂、ポリウレタン樹脂、ポリエステル樹脂、ポリアミド樹脂等の各種合成樹脂;ポリブチレン、ポリブタジエン、ポリクロロプレン等の合成ゴム;その他の合成木材、合成パルプ等、及びこれらの炭化物が挙げられる。これらの原料の中でも、量産対応及びコストの観点から、ヤシ殻、木粉等の植物系原料、及びそれらの炭化物が好ましく、ヤシ殻炭化物が特に好ましい。
活性炭2のメソ孔量V1は、正極材料を非水系リチウム型蓄電素子に組み込んだときの出力特性を大きくする観点から、0.8cc/gより大きい値であることが好ましい。他方、非水系リチウム型蓄電素子の容量の低下を抑える観点から、2.5cc/g以下であることが好ましい。活性炭2のV1は、より好ましくは1.00cc/g以上2.0cc/g以下、さらに好ましくは1.2cc/g以上1.8cc/g以下である。
活性炭2の原料として用いられる炭素源としては、活性炭原料として通常用いられる炭素源であれば特に限定されるものではなく、例えば、木材、木粉、ヤシ殻等の植物系原料;石油ピッチ、コークス等の化石系原料;フェノール樹脂、フラン樹脂、塩化ビニル樹脂、酢酸ビニル樹脂、メラミン樹脂、尿素樹脂、レゾルシノール樹脂等の各種合成樹脂等が挙げられる。これらの原料の中でも、フェノール樹脂、及びフラン樹脂は、高比表面積の活性炭2を作製するのに適しており、特に好ましい。
正極活物質に活性炭を使用する場合、活性炭1及び2は、それぞれ、単一の活性炭であってもよいし、2種以上の活性炭の混合物であって、混合物全体として上記の特徴を示すものであってもよい。
本願明細書において、「リチウム化合物」とは、正極活物質ではなく、かつ式(1)~(3)の化合物でもないリチウム化合物を意味する。
リチウム化合物としては、後述のリチウムドープ工程において正極で分解し、リチウムイオンを放出することが可能である、炭酸リチウム、酸化リチウム、水酸化リチウム、フッ化リチウム、塩化リチウム、シュウ化リチウム、ヨウ化リチウム、窒化リチウム、シュウ酸リチウム、及び酢酸リチウムからなる群から選択される少なくとも1種が挙げられる。これらの中でも、空気中での取り扱いが可能であり、吸湿性が低いという観点から、炭酸リチウム、酸化リチウム及び水酸化リチウムが好ましく、炭酸リチウムがより好ましい。このようなリチウム化合物は、電圧の印加によって分解し、負極へのリチウムドープのドーパント源として機能するとともに、正極活物質層において良好な被膜を形成するので、高い高負荷充放電サイクル特性を示す正極を形成することができる。
リチウム化合物の微粒子化には、様々な方法を用いることができる。例えば、ボールミル、ビーズミル、リングミル、ジェットミル、ロッドミル等の粉砕機を使用することができる。
正極中に含まれるリチウム化合物の同定方法は特に限定されないが、例えば、下記の方法により同定することができる。リチウム化合物の同定には、以下に記載する複数の解析手法を組み合わせて同定することが好ましい。
上記解析手法にてリチウム化合物を同定できなかった場合、その他の解析手法として、固体7Li-NMR、XRD(X線回折)、TOF-SIMS(飛行時間型二次イオン質量分析)、AES(オージェ電子分光)、TPD/MS(加熱発生ガス質量分析)、DSC(示差走査熱量分析)等を用いることにより、リチウム化合物を同定することもできる。
酸素を含有するリチウム化合物及び正極活物質は、観察倍率を1,000倍~4,000倍にして測定した正極表面のSEM-EDX画像の酸素マッピングにより判別できる。SEM-EDX画像は、例えば、加速電圧を10kV、エミッション電流を10μA、測定画素数を256×256ピクセル、積算回数を50回として測定できる。試料の帯電を防止するために、金、白金、オスミウム等を真空蒸着やスパッタリング等の方法により試料を表面処理することもできる。SEM-EDX画像の測定方法については、明るさは最大輝度に達する画素がなく、明るさの平均値が輝度40%~60%の範囲に入るように輝度及びコントラストを調整することが好ましい。得られた酸素マッピングに対し、明るさの平均値を基準に二値化したとき、明部を面積で50%以上含む粒子をリチウム化合物とする。
炭酸イオンを含むリチウム化合物及び正極活物質は、観察倍率を1,000倍~4,000倍にして測定した正極表面のラマンイメージングにより判別できる。測定条件として、励起光を532nm、励起光強度を1%、対物レンズの長作動を50倍、回折格子を1,800gr/mm、マッピング方式を点走査(スリット65mm、ビニング5pix)、1mmステップ、1点当たりの露光時間を3秒、積算回数を1回、ノイズフィルター有りの条件を例示することができる。測定したラマンスペクトルについて、1,071~1,104cm-1の範囲で直線のベースラインを設定し、ベースラインより正の値を炭酸イオンのピークとして面積を算出し、頻度を積算する。このとき、ノイズ成分をガウス型関数で近似した炭酸イオンピーク面積に対する頻度を炭酸イオンの頻度分布から差し引く。
リチウムの電子状態をXPSにより解析することによりリチウムの結合状態を判別することができる。測定条件として、X線源を単色化AlKα、X線ビーム径を100μmφ(25W、15kV)、パスエネルギーをナロースキャン:58.70eV、帯電中和を有り、スイープ数をナロースキャン:10回(炭素、酸素)20回(フッ素)30回(リン)40回(リチウム)50回(ケイ素)、エネルギーステップをナロースキャン:0.25eVの条件を例示することができる。XPSの測定前に正極の表面をスパッタリングにてクリーニングすることが好ましい。スパッタリングの条件として例えば、加速電圧1.0kV、2mm×2mmの範囲を1分間(SiO2換算で1.25nm/min)の条件にて正極の表面をクリーニングすることができる。
得られたXPSスペクトルについて、Li1sの結合エネルギー50~54eVのピークをLiO2またはLi-C結合、55~60eVのピークをLiF、Li2CO3、LixPOyFz(式中、x、y、及びzは、それぞれ1~6の整数である);C1sの結合エネルギー285eVのピークをC-C結合、286eVのピークをC-O結合、288eVのピークをCOO、290~292eVのピークをCO3 2-、C-F結合;O1sの結合エネルギー527~530eVのピークをO2-(Li2O)、531~532eVのピークをCO、CO3、OH、POx(式中、xは1~4の整数である)、SiOx(式中、xは1~4の整数である)、533eVのピークをC-O、SiOx(式中、xは1~4の整数である);F1sの結合エネルギー685eVのピークをLiF、687eVのピークをC-F結合、LixPOyFz(式中、x、y、及びzは、それぞれ1~6の整数である)、PF6 -;P2pの結合エネルギーについて、133eVのピークをPOx(式中、xは1~4の整数である)、134~136eVのピークをPFx(式中、xは1~6の整である数);Si2pの結合エネルギー99eVのピークをSi、シリサイド、101~107eVのピークをSixOy(式中、x、及びyは、それぞれ任意の整数である)として帰属することができる。
得られたスペクトルについて、ピークが重なる場合には、ガウス関数又はローレンツ関数を仮定してピーク分離し、スペクトルを帰属することが好ましい。得られた電子状態の測定結果及び存在元素比の結果から、存在するリチウム化合物を同定することができる。
正極を蒸留水で洗浄し、洗浄した後の水をイオンクロマトグラフィーで解析することにより、水中に溶出したアニオン種を同定することができる。使用するカラムとしては、イオン交換型、イオン排除型、逆相イオン対型等を使用することができる。検出器としては、電気伝導度検出器、紫外可視吸光光度検出器、電気化学検出器等を使用することができ、検出器の前にサプレッサーを設置するサプレッサー方式、又はサプレッサーを配置せずに電気伝導度の低い溶液を溶離液に用いるノンサプレッサー方式を用いることができる。また、質量分析計又は荷電化粒子検出器を検出器と組み合わせて測定することもできるため、SEM-EDX、ラマン分光法、XPS等の解析結果から同定されたリチウム化合物に基づいて、適切なカラム及び検出器を組み合わせることが好ましい。
サンプルの保持時間は、使用するカラムや溶離液等の条件が決まれば、イオン種成分毎に一定であり、またピークのレスポンスの大きさはイオン種毎に異なるが、イオン種の濃度に比例する。トレーサビリティーが確保された既知濃度の標準液を予め測定しておくことでイオン種成分の定性と定量が可能となる。
正極中に含まれるリチウム化合物の定量方法を以下に記載する。
正極を有機溶媒で洗浄し、その後蒸留水で洗浄し、蒸留水での洗浄前後の正極質量変化からリチウム化合物を定量することができる。測定する正極の面積は特に制限されないが、測定のばらつきを軽減するという観点から5cm2以上200cm2以下であることが好ましく、より好ましくは25cm2以上150cm2以下である。面積が5cm2以上あれば測定の再現性が確保される。面積が200cm2以下であればサンプルの取扱い性に優れる。有機溶媒による洗浄については、正極表面に堆積した非水系電解液分解物を除去できれば良いため、有機溶媒は特に限定されないが、前記リチウム化合物の溶解度が2%以下である有機溶媒を用いることでリチウム化合物の溶出が抑制されるため好ましい。例えば、メタノール、アセトン等の極性溶媒が好適に用いられる。
Z=100×[1-(M1-M2)/(M0-M2)]
リチウム化合物の平均粒子径をX1とするとき、0.1μm≦X1≦10μmであり、正極活物質の平均粒子径をY1とするとき、2μm≦Y1≦20μmであり、かつX1<Y1であることが好ましい。より好ましくは、X1は、0.5μm≦X1≦5μmであり、Y1は、3μm≦Y1≦10μmである。X1が0.1μm以上の場合、リチウムプレドープ後の正極中にリチウム化合物を残存させることができるため、高負荷充放電サイクルで生成するフッ素イオンを吸着することにより高負荷充放電サイクル特性が向上する。他方、X1が10μm以下の場合、高負荷充放電サイクルで生成するフッ素イオンとの反応面積が増加するため、フッ素イオンの吸着を効率良く行うことができる。Y1が2μm以上の場合、正極活物質間の電子伝導性を確保できる。他方、Y1が20μm以下の場合、電解質イオンとの反応面積が増加するために高い入出力特性を発現できる。X1<Y1であれば、正極活物質間に生じる隙間にリチウム化合物が充填されるため、正極活物質間の電子伝導性を確保しつつ、エネルギー密度を高めることができる。
X1及びY1の測定方法は特に限定されないが、正極断面のSEM画像、及びSEM-EDX画像から算出することができる。正極断面の形成方法については、正極上部からArビームを照射し、試料直上に設置した遮蔽板の端部に沿って平滑な断面を作製するBIB加工を用いることができる。正極に炭酸リチウムを含有させる場合、正極断面のラマンイメージングを測定することで炭酸イオンの分布を求めることもできる。
リチウム化合物及び正極活物質は、観察倍率を1000倍~4000倍にして測定した正極断面のSEM-EDX画像による酸素マッピングにより判別できる。SEM-EDX画像の測定方法については、明るさは最大輝度に達する画素がなく、明るさの平均値が輝度40%~60%の範囲に入るように輝度及びコントラストを調整することが好ましい。得られた酸素マッピングに対し、明るさの平均値を基準に二値化した明部を面積50%以上含む粒子をリチウム化合物とする。
X1及びY1は、前記正極断面SEMと同視野にて測定した正極断面SEM-EDXから得られた画像を、画像解析することで求めることができる。前記正極断面のSEM画像にて判別されたリチウム化合物の粒子X、及びそれ以外の粒子を正極活物質の粒子Yとし、断面SEM画像中に観察されるX、Yそれぞれの粒子全てについて、断面積Sを求め、次式により粒子径dを求める(円周率をπとする。)。
d=2×(S/π)1/2
得られた粒子径dを用いて、次式により体積平均粒子径X0及びY0を求める。
X0(Y0)=Σ[4/3π×(d/2)3×d]/Σ[4/3π×(d/2)3]
正極断面の視野を変えて5ヶ所以上測定し、それぞれのX0及びY0の平均値をもって平均粒子径X1及びY1とする。
本実施形態における正極活物質層は、必要に応じて、正極活物質及びリチウム化合物の他に、導電性フィラー、結着剤、分散安定剤等の任意成分を含んでいてもよい。
本実施形態における正極集電体を構成する材料としては、電子伝導性が高く、非水系電解液への溶出及び電解質又はイオンとの反応等による劣化が起こり難い材料であれば特に制限はないが、金属箔が好ましい。本実施形態の非水系リチウム型蓄電素子における正極集電体としては、アルミニウム箔が特に好ましい。
それらの中でも、本実施形態における正極集電体は、貫通孔を持たない金属箔が好ましい。貫通孔を持たない方が、製造コストが安価であり、薄膜化が容易であるため高エネルギー密度化にも寄与でき、集電抵抗も低くできるため高入出力特性が得られる。
本実施形態において、非水系リチウム型蓄電素子の正極となる正極前駆体は、既知のリチウムイオン電池、電気二重層キャパシタ等における電極の製造技術によって製造することが可能である。例えば、正極活物質及びリチウム化合物、並びに必要に応じて使用されるその他の任意成分を、水又は有機溶剤中に分散又は溶解してスラリー状の塗工液を調整し、この塗工液を正極集電体の片面又は両面上に塗工して塗膜を形成し、これを乾燥することにより正極前駆体を得ることができる。得られた正極前駆体にプレスを施して、正極活物質層の膜厚や嵩密度を調整してもよい。或いは、溶剤を使用せずに、正極活物質及びリチウム化合物、並びに必要に応じて使用されるその他の任意成分を乾式で混合し、得られた混合物をプレス成型した後、導電性接着剤を用いて正極集電体に貼り付ける方法も可能である。
プレス圧力は、好ましくは0.5kN/cm以上20kN/cm以下、より好ましくは1kN/cm以上10kN/cm以下、さらに好ましくは2kN/cm以上7kN/cm以下である。プレス圧力が0.5kN/cm以上であれば、電極強度を十分に高くできる。プレス圧力が20kN/cm以下であれば、正極前駆体に撓みやシワが生じ難く、正極活物質層の所望の膜厚や嵩密度に調整し易い。
プレスロール同士の隙間は、正極活物質層の所望の膜厚や嵩密度となるように乾燥後の正極前駆体膜厚に応じて任意の値を設定できる。
プレス速度は、正極前駆体の撓みやシワを低減するよう任意の速度に設定できる。プレス部の表面温度は、室温でもよいし、必要により加熱してもよい。
加熱する場合のプレス部の表面温度の下限は、好ましくは使用する結着剤の融点マイナス60℃以上、より好ましくは結着剤の融点マイナス45℃以上、さらに好ましくは結着剤の融点マイナス30℃以上である。加熱する場合のプレス部の表面温度の上限は、好ましくは使用する結着剤の融点プラス50℃以下、より好ましくは結着剤の融点プラス30℃以下、さらに好ましくは結着剤の融点プラス20℃以下である。例えば、結着剤にPVdF(ポリフッ化ビニリデン:融点150℃)を用いた場合、好ましくは90℃以上200℃以下、より好ましく105℃以上180℃以下、さらに好ましくは120℃以上170℃以下にプレス部の表面を加熱する。結着剤にスチレン-ブタジエン共重合体(融点100℃)を用いた場合、好ましくは40℃以上150℃以下、より好ましくは55℃以上130℃以下、さらに好ましくは70℃以上120℃以下にプレス部の表面を加温する。
プレス圧力、隙間、速度、プレス部の表面温度の条件を変えながら複数回プレスを実施してもよい。
後述のリチウムドープ工程後の正極における正極活物質層の嵩密度は、好ましくは0.50g/cm3以上、より好ましくは0.55g/cm3以上1.3g/cm3以下の範囲である。正極活物質層の嵩密度が0.50g/cm3以上であれば、高いエネルギー密度を発現でき、非水系リチウム型蓄電素子の小型化を達成できる。他方、正極活物質層の嵩密度が1.3g/cm3以下であれば、正極活物質層内の空孔における非水系電解液の拡散が十分となり、高い出力特性が得られる。
本実施形態における負極は、負極集電体と、その片面又は両面上に設けられた、負極活物質を含む負極活物質層とを有する。
負極活物質層の固体7Li-NMRにおいて、30ppm~60ppmに観察されるスペクトルは、黒鉛系炭素材料の黒鉛質部の炭素六角網面層間内に吸蔵されたリチウムイオンに由来するものである。このような吸蔵状態にあるリチウムイオンは、炭素六角網面と強く相互作用しているため、リチウムイオンの放出には大きなエネルギーを必要とし、抵抗が高くなる。
他方、負極活物質層の固体7Li-NMRにおいて4ppm~30ppmに観察されるスペクトルは、黒鉛系炭素材料の非晶質部、黒鉛質部と非晶質部との界面、及びこの界面近傍における黒鉛質部の炭素六角網面層間内に吸蔵されたリチウムイオンが相互に交換するか、又は相互に作用しているものに由来すると考えられる。このような吸蔵状態にあるリチウムイオンは炭素原子との相互作用が弱いためリチウムイオンの放出に大きなエネルギーを必要としない。また、この吸蔵状態にあるリチウムイオンは、黒鉛質部よりも反応サイトが多い非晶質部を介して、負極と非水系電解液との間でリチウムイオンの吸蔵・放出が行われると考えられる。それ故に、負極活物質層の固体7Li-NMRスペクトルの-10ppm~35ppmのスペクトル範囲において、ピークの最大値を4ppm~30ppmの間に調整し、かつ4ppm~30ppmのピーク面積より計算されるリチウム量を上記の範囲に調整することで、この負極を用いた非水系リチウム型蓄電素子の入出力抵抗を低減でき、高い入出力特性を示すことができると考えられる。また、このような吸蔵状態にあるリチウムイオンは、上述した理由により大電流充放電を繰り返す高負荷充放電サイクルにも十分に応答することができ、良好な高負荷充放電サイクル特性を発現できる。
シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとする。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法にてスペクトルを測定する。
上記の方法によって得られた負極活物質層の固体7Li-NMRスペクトルについて、4ppm~30ppmの範囲にある成分についてピーク面積を求める。次に、これらのピーク面積を、測定用ローター中における試料高さを負極活物質層の測定時と同じにして測定した1mol/Lの塩化リチウム水溶液のピーク面積で除し、さらに測定に用いる負極活物質層の質量で除すことで、負極活物質層中のリチウム量を算出できる。本明細書では、負極活物質層の質量とは、負極活物質層に吸蔵されるリチウムイオン、負極活物質層に含有される被膜又は堆積物等を含む負極活物質層の質量である。
(1)得られる負極をメタノールとイソプロパノールとから構成される混合溶媒に浸漬して、負極活物質に吸蔵したリチウムイオンを失活させて、風乾する。次いで、真空乾燥等を用いて得られる負極に含まれる鎖状カーボネートや有機溶媒等を取り除くことにより、測定サンプルを得ることができる。
(2)アルゴン等の不活性雰囲気下で、得られる負極を作用極に、金属リチウムを対極及び参照極に用い、これらを非水系電解液に浸して電気化学セルを作製する。得られる電気化学セルについて充放電機等を用いて、負極電位(vs. Li/Li+)が1.5V~3.5Vの範囲になるように調整する。次いで、アルゴン等の不活性雰囲気下で電気化学セルから負極を取り出し、これを鎖状カーボネートに浸漬し、非水系電解液やリチウム塩等を取り除いて風乾する。次いで、真空乾燥等を用いて得られる負極に含まれる鎖状カーボネート等を取り除くことにより、測定サンプルを得ることができる。
(3)上記で得られる負極をそのまま測定サンプルとして用いることができる。この場合、後述する負極活物質層の断面の形成及びSEM観察は、アルゴン等の不活性雰囲気下で行うことが好ましい。
負極活物質層は、負極活物質を含み、必要に応じて、導電性フィラー、結着剤、分散安定剤等の任意成分を含んでいてもよい。
負極活物質は、リチウムイオンを吸蔵及び放出可能な物質を用いることができる。負極活物質としては、具体的には、炭素材料、チタン酸化物、ケイ素、ケイ素酸化物、ケイ素合金、ケイ素化合物、錫、及び錫化合物等が挙げられる。炭素材料の含有率は、負極活物質の合計質量に対して、好ましくは50質量%以上、より好ましくは70質量%以上である。炭素材料の含有率は100質量%であってもよいが、しかしながら、他の材料との併用による効果を良好に得る観点から、例えば、90質量%以下であることが好ましく、80質量%以下であってもよい。
第一の形態としては、非水系リチウム型蓄電素子を作製する前に、負極活物質に設計値として予め吸蔵させるリチウムイオンである。
第二の形態としては、非水系リチウム型蓄電素子を作製し、出荷する際の負極活物質に吸蔵されているリチウムイオンである。
第三の形態としては、非水系リチウム型蓄電素子をデバイスとして使用した後の負極活物質に吸蔵されているリチウムイオンである。
負極活物質にリチウムイオンをドープしておくことにより、得られる非水系リチウム型蓄電素子の容量及び作動電圧を良好に制御することが可能となる。
本願明細書において、複合炭素材料1とは、BET比表面積が100m2/g以上3,000m2/g以下の炭素材料1種以上を基材として用いた、複合炭素材料である。複合炭素材料1の基材はBET比表面積が100m2/g以上3,000m2/g以下であれば特に制限されるものではないが、活性炭、カーボンブラック、鋳型多孔質炭素、高比表面積黒鉛、カーボンナノ粒子等を好適に用いることができる。
本願明細書において、複合炭素材料2とは、BET比表面積が0.5m2/g以上80m2/g以下の炭素材料1種以上を基材として用いた、複合炭素材料である。複合炭素材料2の基材は、BET比表面積が0.5m2/g以上80m2/g以下であれば特に制限されるものではないが、黒鉛質材料、ハードカーボン、ソフトカーボン、カーボンブラック等を好適に用いることができる。
リチウムイオンを負極にドープすることにより、負極電位が低くなる。従って、リチウムイオンがドープされた複合炭素材料2aを含む負極を正極と組み合わせた場合には、非水系リチウム型蓄電素子の電圧が高くなるとともに、正極の利用容量が大きくなる。そのため、得られる非水系リチウム型蓄電素子の容量及びエネルギー密度が高くなる。
複合炭素材料2aの単位質量当たりのリチウムイオンのドープ量が50mAh/g以上であれば、複合炭素材料2aにおけるリチウムイオンを一旦挿入したら脱離し得ない不可逆なサイトにもリチウムイオンが良好にドープされるため、高いエネルギー密度が得られる。ドープ量が多いほど負極電位が下がり、入出力特性、エネルギー密度、及び耐久性は向上する。
複合炭素材料2aの単位質量当たりのリチウムイオンのドープ量が700mAh/g以下であれば、リチウム金属の析出等の副作用が発生し難くなる。
本実施形態における負極活物質層は、負極活物質の他に、必要に応じて、導電性フィラー、結着剤、分散安定剤等の任意成分を含んでいてもよい。
本実施形態における負極集電体を構成する材料としては、電子伝導性が高く、非水系電解液への溶出及び電解質又はイオンとの反応等による劣化が起こり難い金属箔であることが好ましい。このような金属箔としては、特に制限はなく、例えば、アルミニウム箔、銅箔、ニッケル箔、ステンレス鋼箔等が挙げられる。本実施形態の非水系リチウム型蓄電素子における負極集電体としては、銅箔が好ましい。
それらの中でも、本実施形態における負極集電体は、貫通孔を持たない金属箔が好ましい。貫通孔を持たない方が、製造コストが安価であり、薄膜化が容易であるため高エネルギー密度化にも寄与でき、集電抵抗も低くできるため高入出力特性が得られる。
負極集電体の厚みは、負極の形状及び強度を十分に保持できれば特に制限はないが、例えば1~100μmが好ましい。なお、負極集電体が貫通孔又は凹凸を有するときには、貫通孔又は凹凸が存在しない部分に基づいて負極集電体の厚みを測定するものとする。
負極は、負極集電体の片面又は両面上に負極活物質層を有する。典型的には、負極活物質層は負極集電体の片面又は両面上に固着している。
プレス圧力は、好ましくは0.5kN/cm以上20kN/cm以下、より好ましくは1kN/cm以上10kN/cm以下、さらに好ましくは2kN/cm以上7kN/cm以下である。プレス圧力が0.5kN/cm以上であれば、電極強度を十分に高くできる。プレス圧力が20kN/cm以下であれば、負極に撓みやシワが生じ難く、負極活物質層の所望の膜厚や嵩密度に調整し易い。
プレスロール同士の隙間は、負極活物質層の所望の膜厚や嵩密度となるように乾燥後の負極膜厚に応じて任意の値を設定できる。
プレス速度は、負極の撓みやシワを低減するよう任意の速度に設定できる。プレス部の表面温度は室温でもよいし、必要により加熱してもよい。
加熱する場合のプレス部の表面温度の下限は、好ましくは使用する結着剤の融点マイナス60℃以上、より好ましくは結着剤の融点マイナス45℃以上、さらに好ましくは結着剤の融点マイナス30℃以上である。加熱する場合のプレス部の表面温度の上限は、好ましくは使用する結着剤の融点プラス50℃以下、より好ましくは結着剤の融点プラス30℃以下、さらに好ましくは結着剤の融点プラス20℃以下である。例えば、結着剤にPVdF(ポリフッ化ビニリデン:融点150℃)を用いた場合、好ましくは90℃以上200℃以下、より好ましく105℃以上180℃以下、さらに好ましくは120℃以上170℃以下にプレス部の表面を加熱する。結着剤にスチレン-ブタジエン共重合体(融点100℃)を用いた場合、好ましくは40℃以上150℃以下、より好ましくは55℃以上130℃以下、さらに好ましくは70℃以上120℃以下にプレス部の表面を加温する。
負極活物質層単位体積当たりのBET比表面積が1m2/cc以上であれば、非水系電解液中のリチウムイオンと負極活物質層との単位体積当たりの反応サイトを十分に多くできるため、これを用いた非水系リチウム型蓄電素子は高い入出力特性と高負荷充放電サイクル特性を示すことができる。他方、負極活物質層単位体積当たりのBET比表面積が50m2/cc以下であれば、負極活物質層における非水系電解液の過剰な還元分解を抑制できるため、これを用いた非水系リチウム型蓄電素子は高い高負荷充放電サイクル特性を示すことができる。
負極活物質層の平均細孔径が2nm以上であれば、非水系電解液中の溶媒和したリチウムイオンのサイズ(約0.9nm~1.2nm)よりも大きい細孔を負極活物質層内に多く有するため、負極活物質層内における溶媒和したリチウムイオンの拡散が良好となり、これを用いた非水系リチウム型蓄電素子は高い入出力特性を示すことができる。他方、負極活物質層の平均細孔径が20nm以下であれば、負極活物質層の嵩密度を十分に向上できるため、これを用いた非水系リチウム型蓄電素子は高いエネルギー密度を示すことができる。
非水系リチウム型蓄電素子に組み込まれている負極を測定サンプルに用いる場合には、測定サンプルの前処理として、例えば以下の方法を用いることが好ましい。
先ず、アルゴン等の不活性雰囲気下で非水系リチウム型蓄電素子を解体し、負極を取り出す。取り出した負極を鎖状カーボネート(例えばメチルエチルカーボネート、ジメチルカーボネート等)に浸漬し、非水系電解液やリチウム塩等を取り除いて風乾する。次いで、例えば以下の(1)、(2)、又は(3)の方法を用いることが好ましい。
(1)得られる負極をメタノールとイソプロパノールとから成る混合溶媒に浸漬して負極活物質に吸蔵したリチウムイオンを失活させて、風乾する。次いで、真空乾燥等を用いて得られる負極に含まれる鎖状カーボネートや有機溶媒等を取り除くことにより、測定サンプルを得ることができる。
(2)アルゴン等の不活性雰囲気下で、得られる負極を作用極に、金属リチウムを対極及び参照極に用い、これらを非水系電解液に浸して電気化学セルを作製する。得られる電気化学セルについて充放電機等を用いて、負極電位(vs. Li/Li+)が1.5V~3.5Vの範囲になるように調整する。次いで、アルゴン等の不活性雰囲気下で電気化学セルから負極を取り出し、これを鎖状カーボネートに浸漬し、非水系電解液やリチウム塩等を取り除いて風乾する。次いで、真空乾燥等を用いて得られる負極に含まれる鎖状カーボネート等を取り除くことにより、測定サンプルを得ることができる。
(3)上記で得られる負極をそのまま測定サンプルとして用いることができる。
上記で得られる測定サンプルを用いて、窒素又はアルゴンを吸着質として、吸脱着の等温線の測定を行う。ここで得られる吸着側の等温線を用いて、BET多点法又はBET1点法によりBET比表面積を算出し、これをVanoで除すことにより負極活物質層単位体積当たりのBET比表面積を算出する。負極活物質層の平均細孔径は、上記測定にて算出される全細孔容積をBET比表面積で除すことにより算出する。
先ず、本実施形態における負極活物質層をエチルメチルカーボネート又はジメチルカーボネートで洗浄し風乾した後、メタノール及びイソプロパノールから成る混合溶媒により抽出した抽出液と、抽出後の負極活物質層とを得る。この抽出は、典型的にはArボックス内にて、環境温度23℃で行われる。
上記のようにして得られた抽出液と、抽出後の負極活物質層とに含まれるリチウム量を、それぞれ、例えばICP-MS(誘導結合プラズマ質量分析計)等を用いて定量し、その合計を求めることによって、負極活物質におけるリチウムイオンのドープ量を知ることができる。得られた値を抽出に供した負極活物質量で割り付けて、リチウムイオンのドープ量(mAh/g)を算出すればよい。
本実施形態における電解液は、リチウムイオンを含む非水系電解液である。すなわちこの非水系電解液は、後述する非水溶媒を含む。非水系電解液は、非水系電解液の合計体積を基準として、0.5mol/L以上のリチウム塩を含有することが好ましい。すなわち、非水系電解液は、リチウムイオンを電解質として含む。
非水系電解液における環状ホスファゼンの含有率は、非水系電解液の合計質量を基準として、0.5質量%~20質量%であることが好ましい。環状ホスファゼンの含有率が0.5質量%以上であれば、高温における非水系電解液の分解を抑制してガス発生を抑えることが可能となる。環状ホスファゼンの含有率が20質量%以下であれば、非水系電解液のイオン伝導度の低下を抑えることができ、高い入出力特性を保持することができる。以上の理由により、環状ホスファゼンの含有率は、好ましくは2質量%以上15質量%以下であり、更に好ましくは4質量%以上12質量%以下である。
尚、これらの環状ホスファゼンは、単独で用いてもよく、又は2種以上を混合して用いてもよい。
非環状含フッ素エーテルの含有量は、非水系電解液の合計質量を基準として、0.5質量%以上15質量%以下が好ましく、1質量%以上10質量%以下であることがより好ましい。非環状含フッ素エーテルの含有量が0.5質量%以上であれば、非水系電解液の酸化分解に対する安定性が高まり、高温時耐久性が高い非水系リチウム型蓄電素子が得られる。非環状含フッ素エーテルの含有量が15質量%以下であれば、電解質塩の溶解度が良好に保たれ、かつ、非水系電解液のイオン伝導度を高く維持することができるため、高度の入出力特性を発現することが可能となる。
尚、非環状含フッ素エーテルは、単独で使用しても、2種以上を混合して使用してもよい。
含フッ素環状カーボネートの含有量は、非水系電解液の合計質量を基準として、0.5質量%以上10質量%以下が好ましく、1質量%以上5質量%以下であることがより好ましい。含フッ素環状カーボネートの含有量が0.5質量%以上であれば、負極上に良質な被膜を形成することができ、負極上における非水系電解液の還元分解を抑制することによって、高温における耐久性が高い非水系リチウム型蓄電素子が得られる。含フッ素環状カーボネートの含有量が10質量%以下であれば、電解質塩の溶解度が良好に保たれ、かつ、非水系電解液のイオン伝導度を高く維持することができ、従って高度の入出力特性を発現することが可能となる。
尚、含フッ素環状カーボネートは、単独で使用しても、2種以上を混合して使用してもよい。
環状カルボン酸エステルの含有量は、非水系電解液の合計質量を基準として、0.5質量%以上15質量%以下が好ましく、1質量%以上5質量%以下であることがより好ましい。環状カルボン酸エステルの含有量が0.5質量%以上であれば、負極上の良質な被膜を形成することができ、負極上での非水系電解液の還元分解を抑制することにより、高温時耐久性が高い非水系リチウム型蓄電素子が得られる。環状カルボン酸エステルの含有量が5質量%以下であれば、電解質塩の溶解度が良好に保たれ、かつ非水系電解液のイオン伝導度を高く維持することができ、従って高度の入出力特性を発現することが可能となる。
尚、環状カルボン酸エステルは、単独で使用しても、2種以上を混合して使用してもよい。
環状酸無水物の含有量は、非水系電解液の合計質量を基準として、0.5質量%以上15質量%以下が好ましく、1質量%以上10質量%以下であることがより好ましい。環状酸無水物の含有量が0.5質量%以上であれば、負極上に良質な被膜を形成することができ、負極上における非水系電解液の還元分解を抑制することにより、高温時耐久性が高い非水系リチウム型蓄電素子が得られる。環状酸無水物の含有量が10質量%以下であれば、電解質塩の溶解度が良好に保たれ、かつ非水系電解液のイオン伝導度を高く維持することができ、従って高度の入出力特性を発現することが可能となる。
尚、環状酸無水物は、単独で使用しても、2種以上を混合して使用してもよい。
正極前駆体及び負極は、一般に、セパレータを介して積層又は捲回され、正極前駆体と、負極と、セパレータとを有する電極積層体、又は電極捲回体を形成する。
本実施形態による非水系リチウム型蓄電素子は、典型的には、後述する電極積層体又は電極捲回体が、非水系電解液とともに外装体内に収納されて構成される。
本発明の非水系リチウム型蓄電素子は、例えば、複数個の非水系リチウム型蓄電素子を直列、又は並列に接続して蓄電モジュールを作ることができる。本発明の非水系リチウム型蓄電素子及び蓄電モジュールは、高負荷充放電サイクル特性が求められる自動車のハイブリット駆動システムの電力回生システム、太陽光発電や風力発電等の自然発電やマイクログリッド等における電力負荷平準化システム、工場の生産設備等における無停電電源システム、マイクロ波送電や電解共鳴等の電圧変動の平準化及びエネルギーの蓄電を目的とした非接触給電システム、並びに振動発電等で発電した電力の利用を目的としたエナジーハーベストシステムに好適に利用できる。
本発明の非水系リチウム型蓄電素子は、例えば、リチウムイオンキャパシタ又はリチウムイオン二次電池として適用したときに、本発明の効果が最大限に発揮されるため好ましい。
組み立て工程では、例えば、枚葉の形状にカットした正極前駆体及び負極を、セパレータを介して積層して成る積層体に、正極端子及び負極端子を接続して、電極積層体を作製する。あるいは、正極前駆体及び負極を、セパレータを介して積層及び捲回した捲回体に、正極端子及び負極端子を接続して、電極捲回体を作製してもよい。電極捲回体の形状は円筒型であっても、扁平型であってもよい。
正極端子及び負極端子の接続の方法は特に限定されないが、抵抗溶接や超音波溶接などの方法で行うことができる。
外装体としては、金属缶、ラミネート包材等を使用できる。金属缶としては、アルミニウム製のものが好ましい。ラミネート包材としては、金属箔と樹脂フィルムとを積層したフィルムが好ましく、外層樹脂フィルム/金属箔/内装樹脂フィルムの3層から構成されるラミネート包材が例示される。外層樹脂フィルムは、接触等により金属箔が損傷を受けることを防止するためのものであり、ナイロン又はポリエステル等の樹脂が好適に使用できる。金属箔は水分及びガスの透過を防ぐためのものであり、銅、アルミニウム、ステンレス等の箔が好適に使用できる。また、内装樹脂フィルムは、内部に収納する非水系電解液から金属箔を保護するとともに、外装体のヒートシール時に溶融封口させるためのものであり、ポリオレフィン、酸変成ポリオレフィン等が好適に使用できる。
乾燥した電極積層体又は電極捲回体は、金属缶又はラミネート包材に代表される外装体の中に収納し、開口部を1方だけ残して封止することが好ましい。外装体の封止方法は特に限定されないが、ラミネート包材を用いる場合は、ヒートシールやインパルスシールなどの方法を用いることができる。
外装体の中に収納した電極積層体または電極捲回体は、乾燥することで残存溶媒を除去することが好ましい。乾燥方法は限定されないが、真空乾燥などにより乾燥することができる。残存溶媒は、正極活物質層または負極活物質層の質量を基準として、1.5質量%以下が好ましい。残存溶媒が1.5質量%より多いと、系内に溶媒が残存し、自己放電特性やサイクル特性を悪化させることがあるため好ましくない。
組立工程の終了後に、外装体の中に収納された電極積層体または電極捲回体に、非水系電解液を注液する。注液後に、更に含浸を行い、正極、負極、及びセパレータを非水系電解液で十分に浸すことが望ましい。正極、負極、及びセパレータのうちの少なくとも一部に非水系電解液が浸っていない状態では、後述するリチウムドープ工程において、リチウムドープが不均一に進むため、得られる非水系リチウム型蓄電素子の抵抗が上昇したり、耐久性が低下したりする。含浸の方法としては、特に制限されないが、例えば、注液後の電極積層体または電極捲回体を、外装体が開口した状態で、減圧チャンバーに設置し、真空ポンプを用いてチャンバー内を減圧状態にし、再度大気圧に戻す方法等を用いることができる。含浸後に、外装体が開口した状態の電極積層体または電極捲回体を減圧しながら封止することで密閉することができる。
リチウムドープ工程では、正極前駆体と負極との間に電圧を印加して、正極前駆体中のリチウム化合物を分解してリチウムイオンを放出し、負極でリチウムイオンを還元することにより負極活物質層にリオチウムイオンをプレドープすることが好ましい。
リチウムドープ工程後に、電極積層体又は電極捲回体にエージングを行うことが好ましい。エージング工程では、非水系電解液中の溶媒が負極で分解し、負極表面にリチウムイオン透過性の固体高分子被膜が形成される。
エージングの方法としては、特に制限されないが、例えば高温環境下で非水系電解液中の溶媒を反応させる方法等を用いることができる。
エージング工程後に、更にガス抜きを行い、非水系電解液、正極、及び負極中に残存しているガスを確実に除去することが好ましい。非水系電解液、正極、及び負極の少なくとも一部にガスが残存している状態では、イオン伝導が阻害されるため、得られる非水系リチウム型蓄電素子の抵抗が上昇してしまう。
ガス抜きの方法としては、特に制限されないが、例えば、外装体を開口した状態で電極積層体または電極捲回体を減圧チャンバーに設置し、真空ポンプを用いてチャンバー内を減圧状態にする方法等を用いることができる。ガス抜き後、外装体をシールすることにより外装体を密閉し、非水系リチウム型蓄電素子を作製することができる。
[静電容量]
本明細書では、静電容量F(F)とは、以下の方法によって得られる値である。
先ず、非水系リチウム型蓄電素子を25℃に設定した恒温槽内で、2Cの電流値で3.8Vに到達するまで定電流充電を行い、続いて3.8Vの定電圧を印加する定電圧充電を合計で30分行う。その後、2.2Vまで2Cの電流値で定電流放電を施した際の容量をQとする。ここで得られたQを用いて、F=Q/(3.8-2.2)により算出される値を、静電容量F(F)という。
本明細書では、電力量E(Wh)とは、以下の方法によって得られる値である。
先に述べた方法で算出された静電容量F(F)を用いて、
F×(3.82-2.22)/2/3,600により算出される値を、電力量E(Wh)という。
非水系リチウム型蓄電素子の体積は、電極積層体又は電極捲回体のうち、正極活物質層及び負極活物質層が積重された領域が、外装体によって収納された部分の体積を指す。
例えば、ラミネートフィルムによって収納された電極積層体又は電極捲回体の場合は、典型的には、電極積層体又は電極捲回体のうち、正極活物質層および負極活物質層が存在する領域が、カップ成形されたラミネートフィルムの中に収納される。この非水系リチウム型蓄電素子の体積(V1)は、このカップ成形部分の外寸長さ(l1)と、外寸幅(w1)と、ラミネートフィルムを含めた非水系リチウム型蓄電素子の厚み(t1)とにより、V1=l1×w1×t1で計算される。
角型の金属缶に収納された電極積層体又は電極捲回体の場合は、非水系リチウム型蓄電素子の体積としては、単にその金属缶の外寸での体積を用いる。すなわち、この非水系リチウム型蓄電素子の体積(V2)は、角型の金属缶の外寸長さ(l2)と、外寸幅(w2)と、外寸厚み(t2)とにより、V2=l2×w2×t2で計算される。
また、円筒型の金属缶に収納された電極捲回体の場合においても、非水系リチウム型蓄電素子の体積としては、その金属缶の外寸での体積を用いる。すなわち、この非水系リチウム型蓄電素子の体積(V3)は、円筒型の金属缶の底面または上面の外寸半径(r)と、外寸長さ(l3)とにより、V3=3.14×r×r×l3で計算される。
本明細書において、エネルギー密度とは、非水系リチウム型蓄電素子の電気量E及び体積Vi(i=1、2、3)を用いて、E/Vi(Wh/L)の式により得られる値である。
E/Viは十分な充電容量と放電容量とを発現させる観点から、15以上であることが好ましい。E/Viが15以上であれば、優れた体積エネルギー密度を有する非水系リチウム型蓄電素子を得ることができるため、この非水系リチウム型蓄電素子を用いた蓄電システムを、例えば自動車のエンジンと組み合わせて使用する場合に、自動車内の限られた狭いスペースに蓄電システムを設置することが可能となり、好ましい。E/Viの上限値としては、好ましくは50以下である。
本明細書では、内部抵抗Ra(Ω)とは、以下の方法によって得られる値である。
先ず、非水系リチウム型蓄電素子を25℃に設定した恒温槽内で、20Cの電流値で3.8Vに到達するまで定電流充電し、続いて3.8Vの定電圧を印加する定電圧充電を合計で30分間行う。続いて、20Cの電流値で2.2Vまで定電流放電を行って、放電カーブ(時間-電圧)を得る。この放電カーブにおいて、放電時間2秒及び4秒の時点における電圧値から、直線近似にて外挿して得られる放電時間=0秒における電圧をEoとしたときに、降下電圧ΔE=3.8-Eo、及びRa=ΔE/(20C(電流値A))により算出される値を、内部抵抗Ra(Ω)という。
Ra・Fは、大電流に対して十分な充電容量と放電容量とを発現させる観点から、好ましくは3.0以下、より好ましくは2.5以下、更に好ましくは2.2以下である。Ra・Fが3.0以下であれば、優れた入出力特性を有する非水系リチウム型蓄電素子を得ることができる。そのため、この非水系リチウム型蓄電素子を用いた蓄電システムと、例えば高効率エンジンとを組み合わせること等によって、非水系リチウム型蓄電素子に印加される高負荷にも十分に耐え得ることとなり、好ましい。Ra・Fの下限値としては、好ましくは0.3以上である。
本明細書では、高負荷充放電サイクル試験後の抵抗上昇率は、以下の方法によって測定する。
先ず、非水系リチウム型蓄電素子を25℃に設定した恒温槽内で、300Cの電流値で3.8Vに到達するまで定電流充電し、続いて300Cの電流値で2.2Vに到達するまで定電流放電を行う。この高負荷充放電サイクルを60,000回繰り返し、試験開始前と試験終了後に上述した内部抵抗Ra(Ω)と同様な方法で内部抵抗を測定し、試験開始前の内部抵抗をRa(Ω)、試験終了後の内部抵抗をRb(Ω)とする。試験開始前に対する高負荷充放電サイクル試験後の抵抗上昇率は、Rb/Raにより算出される。
高負荷充放電サイクル試験後の抵抗上昇率Rb/Raは、好ましくは2.0以下、より好ましくは1.5以下、更に好ましくは1.2以下である。高負荷充放電サイクル試験後の抵抗上昇率が2.0以下であれば、充放電を繰り返しても非水系リチウム型蓄電素子の特性が維持される。そのため、長期間安定して優れた入出力特性を得ることができ、非水系リチウム型蓄電素子の長寿命化につながる。Rb/Raの下限値は、好ましくは0.9以上である。
[活性炭の調製]
[活性炭1]
破砕されたヤシ殻炭化物を小型炭化炉内へ入れ、窒素雰囲気下、500℃で3時間炭化処理して炭化物を得た。得られた炭化物を賦活炉内へ入れ、予熱炉で加温した水蒸気を1kg/hで上記賦活炉内へ導入し、900℃まで8時間かけて昇温して賦活した。賦活後の炭化物を取り出し、窒素雰囲気下で冷却して、賦活された活性炭を得た。得られた賦活された活性炭を10時間通水洗浄した後に水切りし、115℃に保持された電気乾燥機内で10時間乾燥した後に、ボールミルで1時間粉砕を行うことにより、活性炭1を得た。
島津製作所社製レーザー回折式粒度分布測定装置(SALD-2000J)を用いて、活性炭1の平均粒子径を測定した結果、4.2μmであった。また、ユアサアイオニクス社製細孔分布測定装置(AUTOSORB-1 AS-1-MP)を用いて、活性炭1の細孔分布を測定した結果、BET比表面積が2,360m2/g、メソ孔量(V1)が0.52cc/g、マイクロ孔量(V2)が0.88cc/g、V1/V2=0.59であった。
フェノール樹脂を、焼成炉内へ入れ、窒素雰囲気下、600℃で2時間炭化処理を行った後、ボールミルで粉砕し、分級して平均粒子径7.0μmの炭化物を得た。得られた炭化物とKOHとを、質量比1:5で混合し、焼成炉内へ入れ、窒素雰囲下、800℃で1時間加熱して賦活した。賦活後の炭化物を取り出し、濃度2mol/Lに調製した希塩酸中で1時間撹拌洗浄し、蒸留水でpH5~6の間で安定するまで煮沸洗浄した後に乾燥することにより、活性炭2を得た。
島津製作所社製レーザー回折式粒度分布測定装置(SALD-2000J)を用いて、活性炭2の平均粒子径を測定した結果、7.1μmであった。また、ユアサアイオニクス社製細孔分布測定装置(AUTOSORB-1 AS-1-MP)を用いて、活性炭2の細孔分布を測定した結果、BET比表面積が3,627m2/g、メソ孔量(V1)が1.50cc/g、マイクロ孔量(V2)が2.28cc/g、V1/V2=0.66であった。
フェノール樹脂を、焼成炉内へ入れ、窒素雰囲気下、600℃で2時間炭化処理を行った後、ボールミルで粉砕し、分級して平均粒子径17.0μmの炭化物を得た。得られた炭化物とKOHとを、質量比1:5で混合し、焼成炉内へ入れ、窒素雰囲下、800℃で1時間加熱して賦活した。賦活後の炭化物を取り出し、濃度2mol/Lに調製した希塩酸中で1時間撹拌洗浄し、蒸留水でpH5~6の間で安定するまで煮沸洗浄した後に乾燥することにより、活性炭3を得た。
島津製作所社製レーザー回折式粒度分布測定装置(SALD-2000J)を用いて、活性炭3の平均粒子径を測定した結果、17.0μmであった。また、ユアサアイオニクス社製細孔分布測定装置(AUTOSORB-1 AS-1-MP)を用いて、活性炭2の細孔分布を測定した結果、BET比表面積が3,111m2/g、メソ孔量(V1)が1.24cc/g、マイクロ孔量(V2)が2.02cc/g、V1/V2=0.62であった。
上記で得た活性炭1を正極活物質として用いて正極前駆体を製造した。
活性炭1を42.5質量部、リチウム化合物として平均粒径2.0μmの炭酸リチウムを45.0質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した。粘度(ηb)は2,700mPa・s、TI値は3.5であった。また、得られた塗工液の分散度をヨシミツ精機社製の粒ゲージを用いて測定した。その結果、粒度は35μmであった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて厚さ15μmの貫通孔を持たないアルミニウム箔の片面又は両面に塗工速度1m/sの条件で塗工し、乾燥温度100℃で乾燥して正極前駆体(以下、それぞれ「片面正極前駆体」、及び「両面正極前駆体」ともいう。)を得た。得られた正極前駆体についてロールプレス機を用いて圧力4kN/cm、プレス部の表面温度25℃の条件でプレスを実施した。
[負極1の調製例]
平均粒子径3.0μm、BET比表面積が1,780m2/gの市販のヤシ殻活性炭150gをステンレススチールメッシュ製の籠に入れ、石炭系ピッチ1(軟化点:50℃)270gを入れたステンレス製バットの上に置き、両者を電気炉(炉内有効寸法300mm×300mm×300mm)内に設置して、熱反応を行うことにより、複合炭素材料1を得た。この熱処理は窒素雰囲気下で行い、600℃まで8時間で昇温し、同温度で4時間保持する方法によった。続いて自然冷却により60℃まで冷却した後、複合炭素材料1を炉から取り出した。
得られた複合炭素材料1について、上記と同様の方法で平均粒子径及びBET比表面積を測定した。その結果、平均粒子径は3.2μm、BET比表面積は262m2/gであった。石炭系ピッチ由来の炭素質材料の活性炭に対する質量比率は78%であった。
複合炭素材料1を85質量部、アセチレンブラックを10質量部、及びPVdF(ポリフッ化ビニリデン)を5質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速15m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した。粘度(ηb)は2,789mPa・s、TI値は4.3であった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて厚さ10μmの貫通孔を持たない電解銅箔の両面に塗工速度1m/sの条件で塗工し、乾燥温度85℃で乾燥して負極1(以下、「両面負極」ともいう。)を得た。得られた負極1についてロールプレス機を用いて圧力4kN/cm、プレス部の表面温度25℃の条件でプレスを実施した。上記で得られた負極1の負極活物質層の膜厚を小野計器社製膜厚計Linear Gauge Sensor GS-551を用いて、負極1の任意の10か所で測定した。測定された膜厚の平均値から、銅箔の厚さを引いて、負極1の負極活物質層の膜厚を求めた。負極1の負極活物質層の膜厚は、片面当たり40μmであった。
表1に示す基材及びその質量部、石炭系ピッチ及びその質量部、熱処理温度となるように調整した他は、負極1の調製例と同様にして、負極活物質の調製し評価した。また、上記で得た負極活物質を用いて、以下の表1に記載の塗工液となるように調整をした他は、負極1の調製例と同様にして、負極を調製し評価した。結果を下記表1に示す。
・ヤシ殻活性炭:平均粒子径3.0μm、BET比表面積1,780m2/g
・カーボンナノ粒子:平均粒子径5.2μm、BET比表面積859m2/g、1次粒子径20nm
・人造黒鉛1:平均粒子径4.8μm、BET比表面積3.1m2/g
・ピッチ1:軟化点50℃の石炭系ピッチ
有機溶媒として、エチレンカーボネート(EC):メチルエチルカーボネート(EMC)=33:67(体積比)の混合溶媒を用い、全非水系電解液に対してLiN(SO2F)2及びLiPF6の濃度比が25:75(モル比)であり、かつLiN(SO2F)2及びLiPF6の濃度の和が1.2mol/Lとなるようにそれぞれの電解質塩を溶解して得た溶液を非水系電解液として使用した。
調製した非水系電解液におけるLiN(SO2F)2及びLiPF6の濃度は、それぞれ、0.3mol/L及び0.9mol/Lであった。
上記で得た正極前駆体と負極1を用いて、後述する条件で複数の非水系リチウム型蓄電素子を製造した。
[組立]
得られた両面負極と片面及び両面正極前駆体とを10cm×10cm(100cm2)にカットした。最上面と最下面は片面正極前駆体を用い、更に両面負極21枚と両面正極前駆体20枚とを用い、負極1と正極前駆体との間に、厚み15μmの微多孔膜セパレータを挟んで積層した。その後、負極1と正極前駆体とに、それぞれ負極端子及び正極端子を超音波溶接にて接続して電極積層体を得た。この電極積層体を、アルミラミネート包材から構成される外装体内に収納し、電極端子部およびボトム部の外装体3方を、温度180℃、シール時間20sec、及びシール圧1.0MPaの条件下でヒートシールした。封止体を、温度80℃、圧力50Paで、乾燥時間60hrの条件で真空乾燥した。
アルミラミネート包材の中に収納された電極積層体に、大気圧下、温度25℃、及び露点-40℃以下のドライエアー環境下にて、上記非水系電解液を約80g注入した。続いて、電極積層体を収納しているアルミラミネート包材を減圧チャンバーの中に入れ、大気圧から-87kPaまで減圧した後、大気圧に戻し、5分間静置した。その後、大気圧から-87kPaまで減圧した後、大気圧に戻す工程を4回繰り返した後、15分間静置した。さらに、大気圧から-91kPaまで減圧した後、大気圧に戻した。同様に減圧し、大気圧に戻す工程を合計7回繰り返した(大気圧から、それぞれ-95,-96,-97,-81,-97,-97,-97kPaまで減圧した)。以上の工程により、非水系電解液を電極積層体に含浸させた。
その後、アルミラミネート包材の中に収納されており、かつ非水系電解液を含浸させた電極積層体を減圧シール機に入れ、-95kPaに減圧した状態で、180℃で10秒間、0.1MPaの圧力でシールすることによりアルミラミネート包材を封止して、非水系リチウム型蓄電素子を作製した。
得られた非水系リチウム型蓄電素子に対して、東洋システム社製の充放電装置(TOSCAT-3100U)を用いて、25℃環境下、電流値50mAで電圧4.5Vに到達するまで定電流充電を行った後、続けて4.5V定電圧充電を48時間継続する手法により初期充電を行い、負極1にリチウムドープを行った。
リチウムドープ後の非水系リチウム型蓄電素子を25℃環境下、150mAで電圧1.8Vに到達するまで定電流放電を行った後、150mAで電圧4.0Vに到達するまで定電流充電行い、さらに4.0V定電流放電を5時間行う定電流定電圧充電工程を実施した。次いで、この非水系リチウム型蓄電素子を55℃環境下で48時間保管した。
エージング後の非水系リチウム型蓄電素子を、温度25℃、露点-40℃のドライエアー環境下でアルミラミネート包材の一部を開封した。続いて、減圧チャンバーの中に上記非水系リチウム型蓄電素子を入れ、KNF社製のダイヤフラムポンプ(N816.3KT.45.18)を用いて大気圧から-80kPaまで3分間かけて減圧した後、3分間かけて大気圧に戻す工程を合計3回繰り返した。その後、減圧シール機に非水系リチウム型蓄電素子を入れ、-90kPaに減圧した後、200℃で10秒間、0.1MPaの圧力でシールすることによりアルミラミネート包材を封止した。
上記で得た非水系リチウム型蓄電素子の内、1つについては後述する[静電容量、Ra・Fの測定]及び[高負荷充放電サイクル試験]を実施した。残りの非水系リチウム型蓄電素子を用いて、後述する[正極の固体7Li-NMR測定]、[正極中のリチウム化合物の平均粒子径の測定]及び[リチウム化合物の定量]をそれぞれ実施した。
得られた非水系リチウム型蓄電素子について、25℃に設定した恒温槽内で、富士通テレコムネットワークス株式会社製の充放電装置(5V,360A)を用いて、上述した方法により、静電容量Fと25℃における内部抵抗Raを算出し、エネルギー密度E/V1とRa・Fを得た。結果を下記表2に示す。
得られた非水系リチウム型蓄電素子について、25℃に設定した恒温槽内で、富士通テレコムネットワークス株式会社製の充放電装置(5V,360A)を用いて、上述した方法により高負荷充放電サイクル試験を実施し、高負荷充放電サイクル試験後の内部抵抗Rbを測定して、Rb/Raを得た。結果を下記表2に示す。
得られた非水系リチウム型蓄電素子の正極につき、正極活物質層の固体7Li-NMR測定を行った。
先ず、上記で製造した非水系リチウム型蓄電素子に対して、アスカ電子製の充放電装置(ACD-01)を用いて、環境温度25℃の下で、50mAの電流で2.9Vまで定電流充電した後、2.9Vの定電圧を印加する定電流定電圧充電を2時間行った。
次いで、正極活物質層の採取をアルゴン雰囲気下で行った。非水系リチウム型蓄電素子をアルゴン雰囲気下で解体し、正極を取り出した。続いて、得られた正極をジエチルカーボネートに2分以上浸漬してリチウム塩等を除去した。同様の条件でジエチルカーボネートへの浸漬をもう1度行った後、風乾した。
その後、正極から正極活物質層を採取した。
得られた正極活物質層を試料として、固体7Li-NMR測定を行った。測定装置としてJEOL RESONANCE社製ECA700(7Li-NMRの共鳴周波数は272.1MHzである)を用い、室温環境下において、マジックアングルスピニングの回転数を14.5kHz、照射パルス幅を45°パルスとして、シングルパルス法により測定した。観測範囲は-400ppm~400ppmの範囲とし、ポイント数は4,096点とした。その他の繰り返し待ち時間以外の測定条件、例えば積算回数、レシーバーゲインなどをすべて同一としたうえで、繰り返し待ち時間を10秒とした場合と3,000秒とした場合についてそれぞれ測定を行い、NMRスペクトルを得た。シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとした。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法により測定した。
上記の方法によって得られた正極活物質層の固体7Li-NMRスペクトルから上述した方法によりb/aを算出した。結果を下記表2に示す。
得られた非水系リチウム型蓄電素子を露点温度-72℃のアルゴンボックス中で解体し、両面に正極活物質層が塗工された正極を10cm×5cmの大きさに切り出し、30gのジエチルカーボネート溶媒に浸し、時折ピンセットで正極を動かし、10分間洗浄した。続いて正極を取り出し、アルゴンボックス中で5分間風乾させ、新たに用意した30gのジエチルカーボネート溶媒に正極を浸し、前記と同様の方法にて10分間洗浄した。正極をアルゴンボックスから取り出し、真空乾燥機(ヤマト科学製、DP33)を用いて、温度25℃、及び圧力1kPaの条件下にて20時間乾燥し、正極試料を得た。
正極試料から1cm×1cmの小片を切り出し、日本電子製のSM-09020CPを用い、アルゴンガスを使用し、加速電圧4kV、及びビーム径500μmの条件下にて正極試料の面方向に垂直な断面を作製した。次いで、10Paの真空中にて金をスパッタリングにより表面にコーティングした。続いて以下に示す条件にて、大気暴露下で正極表面のSEM及びEDXを測定した。
(SEM-EDX測定条件)
・測定装置:日立ハイテクノロジー製、電解放出型走査型電子顕微鏡 FE-SEM S-4700
・加速電圧:10kV
・エミッション電流:10μA
・測定倍率:2,000倍
・電子線入射角度:90°
・X線取出角度:30°
・デッドタイム:15%
・マッピング元素:C,O,F
・測定画素数:256×256ピクセル
・測定時間:60sec.
・積算回数:50回
・明るさは最大輝度に達する画素がなく、明るさの平均値が輝度40%~60%の範囲に入るように輝度及びコントラストを調整した。
前記測定した正極断面SEM及びEDXから得られた画像を、画像解析ソフト(ImageJ)を用いて上述した方法で画像解析することでリチウム化合物の平均粒子径X1及び正極活物質の平均粒子径Y1を算出した。結果を下記表2に示す。
5cm×5cmの大きさに切り出した正極試料を、メタノールに浸し、容器に蓋をして25℃環境下、3日間静置した。その後、正極を取り出し、120℃、5kPaの条件にて10時間真空乾燥した。洗浄後のメタノール溶液について、予め検量線を作成した条件にてGC/MSを測定し、ジエチルカーボネートの存在量が1%未満であることを確認した。続いて、正極質量M0を測定した後に、蒸留水に正極試料を含浸させ、容器に蓋をして45℃環境下、3日間静置した。その後、正極試料を取り出し、150℃、3kPaの条件にて12時間真空乾燥した。洗浄後の蒸留水について、予め検量線を作成した条件にてGC/MSを測定し、メタノールの存在量が1%未満であることを確認した。その後、正極質量M1を測定し、次いで、スパチュラ、ブラシ、刷毛を用いて正極集電体上の活物質層を取り除き、正極集電体の質量M2を測定した。得られたM0、M1、M2を用いて、上述した方法により正極中のリチウム化合物の含有量Z(wt%)を求めた。結果を下記表2に示す。
正極活物質、リチウム化合物及びその平均粒子径、正極活物質及びリチウム化合物の質量部を以下の表2に示す通りとした他は、実施例1と同様にして正極前駆体を調製した。これらの正極前駆体を用いて表2に示した負極と組み合わせた他は、実施例1と同様にして非水系リチウム型蓄電素子を調製し、評価を行った。結果を下記表2に示す。
[正極前駆体の製造]
活性炭2を87.5質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。上記で得た塗工液を用いた他は実施例1と同様にして正極前駆体を得た。
得られた正極前駆体と負極活物質単位質量当たり211mAh/gに相当する金属リチウム箔を負極3の負極活物質層表面に貼り付けた負極を用いた他は、実施例1と同様にして非水系リチウム型蓄電素子の組立及び注液、含浸、封止工程を実施した。
次いで、リチウムドープ工程として、上記で得た非水系リチウム型蓄電素子を環境温度45℃の恒温槽の中で72時間保管し、金属リチウムをイオン化させて負極3にドープした。その後、得られた非水系リチウム型蓄電素子について、実施例1と同様にしてエージング工程、ガス抜き工程を実施して非水系リチウム型蓄電素子を製造し、評価を行った。結果を下記表2に示す。
[正極前駆体の調製]
上記で得た正極前駆体と表1に示す負極1を用い、[リチウムドープ工程]及び[エージング工程]を後述する条件とした他は実施例1と同様にして、複数の非水系リチウム型蓄電素子を製造した。
[リチウムドープ工程]
得られた非水系リチウム型蓄電素子に対して、東洋システム社製の充放電装置(TOSCAT-3100U)を用いて、25℃環境下、電流値50mAで電圧4.6Vに到達するまで定電流充電を行った後、続けて4.6V定電圧充電を72時間継続する手法により初期充電を行い、負極1にリチウムドープを行った。
リチウムドープ後の非水系リチウム型蓄電素子を45℃環境下、100mAで電圧2.0Vに到達するまで定電流放電を行った後、100mAで電圧4.2Vに到達するまで定電流充電行い、さらに4.2V定電流放電を72時間行う定電流定電圧充電工程を実施した。
上記で得た非水系リチウム型蓄電素子の内、1つについては上述した[静電容量、Ra・Fの測定]及び[高負荷充放電サイクル試験]を実施した。結果を下記表3に示す。
残りの非水系リチウム型蓄電素子を用いて後述する[正極中のリチウム量]及び[正極活物質層に含まれる式(1)~(3)の化合物の定量]をそれぞれ実施した。
上記で得た非水系リチウム型蓄電素子の正極につき、正極活物質層の固体7Li-NMR測定を行った。
先ず、上記で作製した非水系リチウム型蓄電素子に対して、アスカ電子製の充放電装置(ACD-01)を用いて、環境温度25℃の下で、50mAの電流で2.9Vまで定電流充電した後、2.9Vの定電圧を印加する定電流定電圧充電を2時間行った。
次いで、正極活物質層の採取をアルゴン雰囲気下で行った。非水系リチウム型蓄電素子をアルゴン雰囲気下で解体し、正極を取り出した。続いて、得られた正極をジエチルカーボネートに2分以上浸漬してリチウム塩等を除去した。同様の条件でジエチルカーボネートへの浸漬をもう1度行った後、風乾した。その後、正極から正極活物質層を採取し、秤量した。
得られた正極活物質層を試料として、固体7Li-NMR測定を行った。測定装置としてJEOL RESONANCE社製ECA700(7Li-NMRの共鳴周波数は272.1MHzである)を用い、室温環境下において、マジックアングルスピニングの回転数を14.5kHz、照射パルス幅を45°パルスとして、シングルパルス法により測定した。シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとした。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法により測定した。測定に際しては測定の間の繰り返し待ち時間を十分にとるようにし、繰り返し待ち時間を3,000秒に設定して測定した。
上記の方法によって得られた正極活物質層の固体7Li-NMRスペクトルについて上述した方法により、リチウム量を算出した。結果を下記表3に示す。
非水系リチウム型蓄電素子を2.9Vに調整した後、23℃の部屋に設置された露点-90℃以下、酸素濃度1ppm以下で管理されているアルゴン(Ar)ボックス内で、非水系リチウム型蓄電素子を解体して正極を取り出した。取り出した正極をジメチルカーボネート(DMC)で浸漬洗浄した後、大気非暴露を維持した状態で、サイドボックス中で真空乾燥させた。
単位質量当たりの存在量(mol/g)=A×B÷C ・・・(数式1)
により、正極に堆積する各化合物の、正極活物質層単位質量当たりの存在量(mol/g)を求めた。
[XOCH2CH2OXについて]
XOCH2CH2OXのCH2:3.7ppm(s,4H)
CH3OX:3.3ppm(s,3H)
CH3CH2OXのCH3:1.2ppm(t,3H)
CH3CH2OXのCH2O:3.7ppm(q,2H)
正極活物質とリチウム化合物を表3に示すとおりとした他は実施例18と同様にして正極前駆体を製造した。これらの正極前駆体を用いて表3に示す負極と組み合わせ、エージング工程を表3に記載の条件とした他は、実施例18と同様にして非水系リチウム型蓄電素子を製造し、評価を行った。結果を下記表3に示す。
[正極前駆体の調製]
実施例1で得た活性炭2を87.5質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。上記で得た塗工液を用いた他は実施例18と同様にして正極前駆体を得た。
得られた正極前駆体と負極活物質単位質量当たり1,150mAh/gに相当する金属リチウム箔を負極2の負極活物質層表面に貼り付けた負極を用いた他は実施例18と同様にして非水系リチウム型蓄電素子の組立及び注液、含浸、封止工程を実施した。
負極活物質単位質量当たり211mAh/gに相当する金属リチウム箔を負極3の負極活物質層表面に貼り付けた負極を用いた他は、比較例6と同様にして非水系リチウム型蓄電素子を製造、評価を行った。結果を下記表3に示す。
[正極前駆体の調製]
実施例1で得た活性炭1を57.5質量部、リチウム化合物として平均粒子径1.8μmの炭酸リチウムを30.0質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した結果、粘度(ηb)は2,590mPa・s、TI値は2.8であった。また、得られた塗工液の分散度をヨシミツ精機社製の粒ゲージを用いて測定した。粒度は35μmであった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて、厚さ15μmの貫通孔を持たないアルミニウム箔の片面又は両面に塗工速度1m/sの条件で塗工し、乾燥温度100℃で乾燥して正極前駆体(以下、それぞれ「片面正極前駆体」、及び「両面正極前駆体」という。)を得た。得られた正極前駆体を、ロールプレス機を用いて圧力4kN/cm、プレス部の表面温度25℃の条件でプレスした。
[負極4の調製例]
平均粒子径が9.7μm、かつBET比表面積が1.2m2/gの人造黒鉛2の使用量150gをステンレススチールメッシュ製の籠に入れ、石炭系ピッチ2(軟化点:65℃)15gを入れたステンレス製バットの上に置き、両者を電気炉(炉内有効寸法300mm×300mm×300mm)内に設置した。これを窒素雰囲気下、1,250℃まで8時間で昇温し、同温度で4時間保持することにより熱反応させ、複合炭素材料4を得た。得られた複合炭素材料4を自然冷却により60℃まで冷却した後、電気炉から取り出した。
得られた複合炭素材料4について、上記と同様の方法で平均粒子径及びBET比表面積を測定した。結果を下記表4に示す。
複合炭素材料4を80質量部、アセチレンブラックを8質量部、及びPVdF(ポリフッ化ビニリデン)を12質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速15m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した結果、粘度(ηb)は2,674mPa・s、TI値は2.6であった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて、厚さ10μmの貫通孔を持たない電解銅箔の両面に塗工速度1m/sの条件で塗工し、乾燥温度85℃で乾燥して負極4を得た(以下、「両面負極」ともいう。)。得られた負極4を、ロールプレス機を用いてプレスした。上記で得られた負極4の膜厚を小野計器社製膜厚計Linear Gauge Sensor GS-551を用いて、負極4の任意の10か所で測定した。測定された膜厚の平均値から銅箔の厚さを引いて、負極4の負極活物質層の膜厚を求めた。負極4の負極活物質層の膜厚は、片面当たり20μmであった。
表4に示すように基材及びその質量部、石炭系ピッチ及びその質量部、並びに熱処理温度を調整した他は、負極4の調製例と同様にして、負極活物質の製造及び評価を行った。また、表4に示される負極活物質を用いて、表4に記載の塗工液の配合となるように塗工液を調製した他は、負極4の調製例と同様にして、負極5~13の製造及び評価を行った。結果を下記表4に示す。
・人造黒鉛2:平均粒子径9.7μm、BET比表面積1.2m2/g
・人造黒鉛3:平均粒子径6.1μm、BET比表面積6.6m2/g
・人造黒鉛4:平均粒子径2.1μm、BET比表面積13.7m2/g
・天然黒鉛1:平均粒子径7.9μm、BET比表面積2.0m2/g
・天然黒鉛2:平均粒子径3.1μm、BET比表面積6.9m2/g
・天然黒鉛3:平均粒子径1.3μm、BET比表面積16.7m2/g
・高比表面積黒鉛1:平均粒子径5.5μm、BET比表面積27.7m2/g
・高比表面積黒鉛2:平均粒子径4.9μm、BET比表面積58.9m2/g
・ピッチ2:軟化点65℃の石炭系ピッチ
上記で得た正極前駆体と負極4を用い、[リチウムドープ工程]及び[エージング工程]を後述する条件とした他は実施例1と同様にして、複数の非水系リチウム型蓄電素子を製造した。
[リチウムドープ工程]
得られた非水系リチウム型蓄電素子に対して、東洋システム社製の充放電装置(TOSCAT-3100U)を用いて、50℃環境下、電流値150mAで電圧4.5Vに到達するまで定電流充電を行った後、続けて4.5V定電圧充電を12時間継続する手法により初期充電を行い、負極4にリチウムドープを行った。
リチウムドープ後の非水系リチウム型蓄電素子を25℃環境下、50mAで電圧2.2Vに到達するまで定電流放電を行った後、50mAで電圧4.0Vに到達するまで定電流充電行い、さらに4.0V定電流充電を30時間行う定電流定電圧充電工程を実施した。
上記で得た非水系リチウム型蓄電素子の内、1つについては上述した[静電容量、Ra・Fの測定]及び[高負荷充放電サイクル試験]を実施した。結果を下記表5に示す。
残りの非水系リチウム型蓄電素子を用いて後述する[負極の固体7Li-NMR測定]、[使用後負極の負極活物質層の解析]、[正極の固体7Li-NMR測定]及び上述した[正極中のリチウム化合物の平均粒子径の測定]をそれぞれ実施した。
上記で得た非水系リチウム型蓄電素子の負極4につき、負極活物質層の固体7Li-NMR測定を行った。
先ず、上記で製造した非水系リチウム型蓄電素子に対して、アスカ電子社製の充放電装置(ACD-01)を用いて、環境温度25℃の下で、50mAの電流で2.9Vまで定電流充電した後、2.9Vの定電圧を15時間印加する定電流定電圧充電を行った。
次いで、負極活物質層の採取をアルゴン雰囲気下で行った。非水系リチウム型蓄電素子をアルゴン雰囲気下で解体し、負極4を取り出した。続いて、得られた負極4をジエチルカーボネートに2分以上浸漬してリチウム塩等を除去した。同様の条件でジエチルカーボネートへの浸漬をもう1度行った後、風乾した。その後、負極4から負極活物質層を採取し、秤量した。
得られた負極活物質層を試料として、固体7Li-NMR測定を行った。測定装置としてJEOL RESONANCE社製ECA700(7Li-NMRの共鳴周波数は272.1MHzである)を用い、室温環境下において、マジックアングルスピニングの回転数を14.5kHz、照射パルス幅を45°パルスとして、シングルパルス法により測定した。シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとした。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法により測定した。
上記の方法によって得られた負極活物質層の固体7Li-NMRスペクトルにおいて、-10ppm~35ppmのスペクトル範囲におけるピークの最大値の位置は16ppmであった。また、得られた負極活物質層の固体7Li-NMRスペクトルについて、上述した方法により、リチウムイオンを吸蔵した負極活物質層の単位質量当たりのリチウム量を算出した。結果を下記表5に示す。
上記で得た非水系リチウム型蓄電素子の負極4について、使用後負極の負極活物質層単位体積当たりのBET比表面積、及び負極活物質層の平均細孔径を測定した。
先ず、上記で製造した非水系リチウム型蓄電素子に対して、アスカ電子社製の充放電装置(ACD-01)を用いて、環境温度25℃の下で、50mAの電流で2.9Vまで定電流充電した後、2.9Vの定電圧を15時間印加する定電流定電圧充電を行った。
次いで、負極4の採取をアルゴン雰囲気下で行った。非水系リチウム型蓄電素子をアルゴン雰囲気下で解体し、負極4を取り出した。続いて、得られた負極4をジエチルカーボネートに2分以上浸漬して非水系電解液やリチウム塩等を除去し、風乾した。その後、得られた負極4をメタノールとイソプロパノールとから成る混合溶媒に15時間浸漬して負極活物質に吸蔵したリチウムイオンを失活させ、風乾した。次いで、得られた負極4を、真空乾燥機を用いて温度170℃の条件にて12時間真空乾燥することにより、測定サンプルを得た。得られた測定サンプルについて、ユアサアイオニクス社製細孔分布測定装置(AUTOSORB-1 AS-1-MP)を用いて、窒素を吸着質として、上述した方法により、使用後負極の負極活物質層単位体積当たりのBET比表面積、及び負極活物質層の平均細孔径を測定した。結果を下記表5に示す。
得られた非水系リチウム型蓄電素子の正極につき、正極活物質層の固体7Li-NMR測定を行った。
先ず、上記で製造した非水系リチウム型蓄電素子に対して、アスカ電子社製の充放電装置(ACD-01)を用いて、環境温度25℃の下で、50mAの電流で2.9Vまで定電流充電した後、2.9Vの定電圧を15時間印加する定電流定電圧充電を行った。
次いで、正極活物質層の採取をアルゴン雰囲気下で行った。非水系リチウム型蓄電素子をアルゴン雰囲気下で解体し、正極を取り出した。続いて、得られた正極をジエチルカーボネートに2分以上浸漬して非水系電解液やリチウム塩等を除去した。同様の条件でジエチルカーボネートへの浸漬をもう1度行った後、風乾した。
その後、正極から正極活物質層を採取した。
得られた正極活物質層を試料として、固体7Li-NMR測定を行った。測定装置としてJEOL RESONANCE社製ECA700(7Li-NMRの共鳴周波数は272.1MHzである)を用い、室温環境下において、マジックアングルスピニングの回転数を14.5kHz、照射パルス幅を45°パルスとして、シングルパルス法により測定した。観測範囲は-400ppm~400ppmの範囲とし、ポイント数は4,096点とした。繰り返し待ち時間以外の測定条件、例えば積算回数、レシーバーゲインなどをすべて同一としたうえで、繰り返し待ち時間を10秒とした場合と3,000秒とした場合についてそれぞれ測定を行い、NMRスペクトルを得た。シフト基準として1mol/Lの塩化リチウム水溶液を用い、外部標準として別途測定したそのシフト位置を0ppmとした。1mol/Lの塩化リチウム水溶液測定時には試料を回転させず、照射パルス幅を45°パルスとして、シングルパルス法により測定した。
上記の方法によって得られた正極活物質層の固体7Li-NMRスペクトルから上述した方法によりb/aを算出した。結果を下記表5に示す。
正極活物質、リチウム化合物及びその平均粒子径、正極活物質及びリチウム化合物の質量部を表5に示すとおりとした他は実施例36と同様にして正極前駆体を製造した。これらの正極前駆体を用いて表5に示す負極と組み合わせ、リチウムドープ工程を表5に示す条件のとおりとした他は、実施例36と同様にして非水系リチウム型蓄電素子を製造し、評価を行った。結果を下記表5に示す。
[正極前駆体の調製]
実施例1で得た活性炭1を57.5質量部、リチウム化合物として平均粒子径2.3μmの炭酸リチウムを30.0質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した。その結果、粘度(ηb)は2,321mPa・s、TI値は2.0であった。また、得られた塗工液の分散度をヨシミツ精機社製の粒ゲージを用いて測定した。その結果、粒度は35μmであった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて、厚さ15μmの貫通孔を持たないアルミニウム箔の片面又は両面に塗工速度1m/sの条件で塗工し、乾燥温度100℃で乾燥して正極前駆体(以下、それぞれ「片面正極前駆体」、及び「両面正極前駆体」という。)を得た。得られた正極前駆体を、ロールプレス機を用いて圧力4kN/cm、プレス部の表面温度25℃の条件でプレスした。
[負極14の調製例]
平均粒子径0.7μm、BET比表面積が15.2m2/gの人造黒鉛5の使用量150gをステンレススチールメッシュ製の籠に入れ、石炭系ピッチ3(軟化点:135℃)30gを入れたステンレス製バットの上に置き、両者を電気炉(炉内有効寸法300mm×300mm×300mm)内に設置した。これを窒素雰囲気下、1,200℃まで8時間で昇温し、同温度で4時間保持することにより熱反応させ、複合炭素材料12を得た。得られた複合炭素材料12を自然冷却により60℃まで冷却した後、電気炉から取り出した。
得られた複合炭素材料12について、上記と同様の方法で平均粒子径及びBET比表面積を測定した。その結果を表6に示す。
複合炭素材料12を80質量部、アセチレンブラックを8質量部、及びPVdF(ポリフッ化ビニリデン)を12質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速15m/sの条件で分散して塗工液を得た。得られた塗工液の粘度(ηb)及びTI値を東機産業社のE型粘度計TVE-35Hを用いて測定した。その結果、粘度(ηb)は2,274mPa・s、TI値は4.2であった。上記塗工液を東レエンジニアリング社製のダイコーターを用いて、厚さ10μmの貫通孔を持たない電解銅箔の両面に塗工速度1m/sの条件で塗工し、乾燥温度85℃で乾燥して負極14を得た(以下、「両面負極」ともいう。)。得られた負極14を、ロールプレス機を用いて圧力4kN/cm、プレス部の表面温度25℃、プレスロール同士の隙間30μmの条件でプレスした。上記で得られた負極14の膜厚を小野計器社製膜厚計Linear Gauge Sensor GS-551を用いて、負極14の任意の10か所で測定した。測定された膜厚の平均値から銅箔の厚さを引いて、負極14の負極活物質層の膜厚を求めた。その結果、負極14の負極活物質層の膜厚は、片面当たり20μmであった。
表6に示す基材及びその質量部、石炭系ピッチ及びその質量部、熱処理温度となるように調製した他は、負極14の調製例と同様にして、負極活物質の製造及び評価を行った。上記で得た負極活物質を用いて、表6に記載の塗工液となるように調製し、形成した負極を表6に記載のプレス条件でプレスした他は、負極14の調製例と同様にして、負極の製造及び評価を行った。その結果を表6に示す。
・人造黒鉛5:平均粒子径0.7μm、BET比表面積15.2m2/g
・人造黒鉛6:平均粒子径4.8μm、BET比表面積6.3m2/g
・人造黒鉛7:平均粒子径9.8μm、BET比表面積0.8m2/g
・天然黒鉛4:平均粒子径5.8μm、BET比表面積7.4m2/g
・天然黒鉛5:平均粒子径9.2μm、BET比表面積1.1m2/g
・高比表面積黒鉛3:平均粒子径2.4μm、BET比表面積62.2m2/g
・高比表面積黒鉛4:平均粒子径5.4μm、BET比表面積45.7m2/g
・高比表面積黒鉛5:平均粒子径9.6μm、BET比表面積29.4m2/g
・ピッチ3:軟化点135℃の石炭系ピッチ
上記で得た正極前駆体と負極14を用い、[リチウムドープ工程]及び[エージング工程]を後述する条件とした他は実施例1と同様にして、複数の非水系リチウム型蓄電素子を製造した。
得られた非水系リチウム型蓄電素子に対して、東洋システム社製の充放電装置(TOSCAT-3100U)を用いて、55℃環境下、電流値100mAで電圧4.5Vに到達するまで定電流充電を行った後、続けて4.5V定電圧充電を24時間継続する手法により初期充電を行い、負極14にリチウムドープを行った。
リチウムドープ後の非水系リチウム型蓄電素子を25℃環境下、100mAで電圧2.0Vに到達するまで定電流放電を行った後、300mAで電圧4.4Vに到達するまで定電流充電行い、さらに4.4V定電流充電を20時間行う定電流定電圧充電を実施した。
上記で得た非水系リチウム型蓄電素子の内、1つについては上述した[静電容量、Ra・Fの測定]及び[高負荷充放電サイクル試験]を実施した。結果を下記表7に示す。
残りの非水系リチウム型蓄電素子を用いて、後述する[使用後負極の負極活物質層断面の空隙の平均重心間距離の測定]、実施例36と同様にして[正極中のリチウム化合物の平均粒子径の測定]、[使用後負極の負極活物質層の解析]及び[正極の固体7Li-NMR測定]をそれぞれ実施した。
上記で得た非水系リチウム型蓄電素子の負極14について、使用後負極の負極活物質層断面の空隙の平均重心間距離を測定した。
・加速電圧:1kV
・エミッション電流:10μA
・測定倍率:3,000倍
・検出器:Lower検出器
・作動距離:8.2mm
得られた負極活物質層の断面のSEM像の画像解析に旭化成社製IP-1000(ソフト名:A像くん)を用いた。得られたSEM像(8bit)について、負極1の負極活物質層の断面のみからなる長方形領域(負極活物質層の厚み方向20μm×幅方向50μm)を抽出し、メディアンフィルタを用いて画像に含まれる微細なノイズを除去した。
正極活物質、リチウム化合物及びその平均粒子径、正極活物質及びリチウム化合物の質量部を表7に示すとおりとした他は実施例60と同様にして正極前駆体を製造した。これらの正極前駆体を用いて表7に示す負極と組み合わせた他は、実施例60と同様にして非水系リチウム型蓄電素子を製造し、評価を行った。結果を下記表7及び表8に示す。
[正極前駆体の製造]
実施例1で得た活性炭2を87.5質量部、ケッチェンブラックを3.0質量部、PVP(ポリビニルピロリドン)を1.5質量部、及びPVDF(ポリフッ化ビニリデン)を8.0質量部、並びにNMP(N-メチルピロリドン)を混合し、それをPRIMIX社製の薄膜旋回型高速ミキサー「フィルミックス(登録商標)」を用いて、周速17m/sの条件で分散して塗工液を得た。上記で得た塗工液を用いた他は実施例60と同様にして正極前駆体を得た。
得られた正極前駆体と負極活物質単位質量当たり280mAh/gに相当する金属リチウム箔を表7に示す負極の負極活物質層表面に貼り付けた負極を用いた他は、実施例60と同様にして非水系リチウム型蓄電素子の組立及び注液、含浸、封止を実施した。
非水系リチウム型蓄電素子に組み込む前の負極17を用いて[使用前負極の負極活物質層断面の空隙の平均重心間距離の測定]を行った。
非水系リチウム型蓄電素子に組み込む前の負極17を測定サンプルとして用いて、実施例60と同様に負極活物質層の断面の形成とそのSEM観察を実施した。得られたSEM像を用いて実施例60と同様に画像解析を実施し、負極17の負極活物質層断面の空隙の平均重心間距離を算出した。結果を下記表8に示す。
実施例64と同様にして非水系リチウム型蓄電素子を製造し、これを用いて以下の方法により[使用後負極の負極活物質層断面の空隙の平均重心間距離の測定]を行った。
上記で得た非水系リチウム型蓄電素子の負極17について、使用後負極の負極活物質層断面の空隙の平均重心間距離を測定した。
Claims (31)
- 正極、負極、セパレータ、及びリチウムイオンを含む非水系電解液を備える非水系リチウム型蓄電素子であって、
該負極が、負極集電体と、該負極集電体の片面又は両面上に設けられた、負極活物質を含む負極活物質層とを有し、
該正極は、正極集電体と、該正極集電体の片面又は両面上に設けられた、正極活物質を含む正極活物質層とを有し、
該正極活物質層の固体7Li-NMRスペクトルにおいて、繰り返し待ち時間10秒とした測定により得られた-40ppm~40ppmにおけるピーク面積をaとし、繰り返し待ち時間3,000秒とした測定により得られた-40ppm~40ppmにおけるピーク面積をbとしたとき、1.04≦b/a≦5.56である、前記非水系リチウム型蓄電素子。 - 前記正極活物質層の固体7Li-NMRスペクトルについて、-40ppm~40ppmにおけるピーク面積より計算される前記正極中のリチウム量が、前記正極活物質層の単位質量当たり1mmol/g以上30mmol/g以下である、請求項1に記載の非水系リチウム型蓄電素子。
- 前記正極は、下記式(1)~(3):
で表される化合物からなる群から選択される少なくとも1種を、前記正極物質層の単位質量当たり1.60×10-4mol/g~300×10-4mol/g含有する、請求項2に記載の前記非水系リチウム型蓄電素子。 - 前記正極は、前記正極活物質以外のリチウム化合物を含有する、請求項1~3のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記リチウム化合物の平均粒子径X1が、0.1μm以上10μm以下である、請求項4に記載の非水系リチウム型蓄電素子。
- 前記正極活物質の平均粒子径をY1とするとき、2μm≦Y1≦20μmであり、かつ、X1<Y1であり、さらに、前記正極中の前記リチウム化合物の含有割合が、前記正極活物質層の全質量を基準として、1質量%以上50質量%以下である、請求項5に記載の非水系リチウム型蓄電素子。
- 前記正極中の前記リチウム化合物の含有割合が、前記正極活物質層の全質量を基準として1質量%以上20質量%以下である、請求項4~6のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記リチウム化合物は、炭酸リチウム、酸化リチウム、及び水酸化リチウムから成る群から選択される少なくとも1種である、請求項4~7のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質層断面のSEMより得られる空隙の平均重心間距離が、1μm以上10μm以下である、請求項4~8のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記空隙の平均重心間距離をrpとし、前記負極活物質の平均粒子径raとしたとき、rp/raが0.10以上1.10以下である、請求項9に記載の非水系リチウム型蓄電素子。
- 前記負極活物質は、黒鉛系炭素材料を含み、
前記負極活物質層は、リチウムイオンを吸蔵しており、そして
前記負極活物質層の固体7Li-NMRスペクトルについて、-10ppm~35ppmのスペクトル範囲において、4ppm~30ppmの間にピークの最大値があり、かつ4ppm~30ppmのピーク面積より計算されるリチウム量が、前記負極活物質層の単位質量当たり0.10mmol/g以上10.0mmol/g以下である、請求項1~10のいずれか1項に記載の非水系リチウム型蓄電素子。 - 前記負極活物質層の単位体積当たりのBET比表面積が1m2/cc以上50m2/cc以下である、請求項1~11のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質層の平均細孔径が2nm以上20nm以下である、請求項1~12のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質の平均粒子径が1μm以上10μm以下である、請求項1~13のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質が黒鉛質材料と炭素質材料との複合炭素材料を含む、請求項1~14のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質のリチウムイオンのドープ量が、前記負極活物質の単位質量当たり50mAh/g以上700mAh/g以下である、請求項1~15のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質のBET比表面積が1m2/g以上50m2/g以下である、請求項1~16のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質のリチウムイオンのドープ量が、前記負極活物質の単位質量当たり530mAh/g以上2,500mAh/g以下である、請求項1~8のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記負極活物質のBET比表面積が100m2/g以上1,500m2/g以下である、請求項1~8及び18のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記正極活物質層に含まれる前記正極活物質は、BJH法により算出した直径20Å以上500Å以下の細孔に由来するメソ孔量をV1(cc/g)、MP法により算出した直径20Å未満の細孔に由来するマイクロ孔量をV2(cc/g)とするとき、0.3<V1≦0.8、及び0.5≦V2≦1.0を満たし、かつ、BET法により測定される比表面積が1,500m2/g以上3,000m2/g以下を示す活性炭である、請求項1~19のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記正極活物質層に含まれる前記正極活物質は、BJH法により算出した直径20Å以上500Å以下の細孔に由来するメソ孔量をV1(cc/g)、MP法により算出した直径20Å未満の細孔に由来するマイクロ孔量をV2(cc/g)とするとき、0.8<V1≦2.5、及び0.8<V2≦3.0を満たし、かつ、BET法により測定される比表面積が2,300m2/g以上4,000m2/g以下を示す活性炭である、請求項1~19のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記正極集電体及び前記負極集電体が、貫通孔を持たない金属箔である、請求項1~21のいずれか1項に記載の非水系リチウム型蓄電素子。
- 前記非水系リチウム型蓄電素子において、初期の内部抵抗をRa(Ω)、静電容量をF(F)、電力量をE(Wh)、蓄電素子の体積をV(L)としたとき、以下の(a)および(b):
(a)RaとFの積Ra・Fが0.3以上3.0以下である、
(b)E/Vが15以上50以下である、
を満たす、請求項1~22のいずれか1項に記載の非水系リチウム型蓄電素子。 - 前記非水系リチウム型蓄電素子に対して、環境温度25℃、セル電圧2.2Vから3.8V、300Cのレートで充放電サイクルを60,000回行い、前記充放電サイクル後の内部抵抗をRb(Ω)、前記充放電サイクル前の内部抵抗をRa(Ω)としたとき、Rb/Raが0.9以上2.0以下である、請求項1~23のいずれか1項に記載の非水系リチウム型蓄電素子。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む蓄電モジュール。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む電力回生システム。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む電力負荷平準化システム。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む無停電電源システム。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む非接触給電システム。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含むエナジーハーベストシステム。
- 請求項1~24のいずれか1項に記載の非水系リチウム型蓄電素子を含む蓄電システム。
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US10646813B2 (en) * | 2016-09-23 | 2020-05-12 | Lehigh University | Gas separation apparatus and methods using same |
TWI704713B (zh) * | 2017-11-14 | 2020-09-11 | 日商旭化成股份有限公司 | 正極塗佈液、正極前驅體及非水系鋰蓄電元件 |
CN110323409B (zh) * | 2019-05-05 | 2020-11-27 | 珠海冠宇电池股份有限公司 | 一种改善高电压循环性能的锂离子电池负极及其制备方法 |
WO2021015054A1 (ja) * | 2019-07-19 | 2021-01-28 | 株式会社クラレ | 炭素質材料、その製造方法、電気化学デバイス用電極活物質、電気化学デバイス用電極および電気化学デバイス |
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