WO2015030190A1 - 蓄電デバイス用非水電解液 - Google Patents
蓄電デバイス用非水電解液 Download PDFInfo
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- WO2015030190A1 WO2015030190A1 PCT/JP2014/072776 JP2014072776W WO2015030190A1 WO 2015030190 A1 WO2015030190 A1 WO 2015030190A1 JP 2014072776 W JP2014072776 W JP 2014072776W WO 2015030190 A1 WO2015030190 A1 WO 2015030190A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0569—Liquid materials characterised by the solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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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
- 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 nonaqueous electrolytic solution capable of improving electrochemical characteristics in a wide temperature range and a secondary battery using the same in an electricity storage device containing lithium titanate as a negative electrode active material.
- power storage devices particularly lithium secondary batteries
- small electronic devices such as mobile phones and notebook computers, electric vehicles, and power storage.
- These electronic devices, automobiles, and power storage applications may be used in a wide temperature range, such as high temperatures in midsummer or low temperatures in extremely cold temperatures. Is required.
- high temperatures in midsummer or low temperatures in extremely cold temperatures Is required.
- environmentally friendly vehicles equipped with power storage devices consisting of power storage devices such as lithium secondary batteries and capacitors
- HEV hybrid electric vehicles
- PHEV plug-in hybrid electric vehicles
- BEV battery electric vehicles Due to the long travel distance of automobiles, automobiles may be used in areas with a wide temperature range from extremely hot areas in the tropics to extremely cold areas.
- lithium secondary battery is used as a concept including so-called lithium ion secondary batteries.
- the lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, a non-aqueous electrolyte composed of a lithium salt and a non-aqueous solvent, and the non-aqueous solvent includes ethylene carbonate (EC), Carbonates such as propylene carbonate (PC) are used.
- EC ethylene carbonate
- PC propylene carbonate
- metal lithium metal compounds that can occlude and release lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials are known, and in particular, lithium can be occluded and released.
- Lithium secondary batteries using carbon materials such as coke, artificial graphite and natural graphite have been widely put into practical use.
- lithium titanate having a redox potential of 1.5 V on the basis of lithium has been proposed as a negative electrode material that does not generate dendrites.
- lithium titanate has a problem that its electron conductivity is extremely low compared to carbon materials. is there.
- a lithium secondary battery using, for example, LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiFePO 4, or the like as the positive electrode includes a positive electrode material, a non-aqueous electrolyte, and a non-aqueous solvent in a non-aqueous electrolyte in a charged state.
- the degradation products and gas generated by partial oxidative decomposition at the interface of the battery hinder the desired electrochemical reaction of the battery, which also causes degradation of electrochemical characteristics when used in a wide temperature range. I know.
- the battery performance was degraded due to the lithium ion movement being inhibited or the battery being swollen by the decomposition product or gas when the non-aqueous electrolyte was decomposed on the negative electrode or the positive electrode.
- electronic devices equipped with lithium secondary batteries are becoming more and more multifunctional and power consumption is increasing.
- the capacity of lithium secondary batteries has been increasing, and the volume occupied by non-aqueous electrolyte in the battery has become smaller, such as increasing the electrode density and reducing the useless space volume in the battery. . Therefore, there is a situation in which the electrochemical characteristics when used in a wide temperature range are likely to deteriorate with a slight decomposition of the non-aqueous electrolyte.
- Patent Document 1 discloses a non-aqueous electrolyte in which a negative electrode having a negative electrode active material having a lithium occlusion / release potential of 1.0 V (vs Li / Li + ) and a non-aqueous solvent containing an organic compound having an isocyanato group is added.
- a non-aqueous electrolyte battery using a battery has been proposed. And it is described that the gas generation reaction in the non-aqueous electrolyte battery using a material having a high Li storage / release potential as a negative electrode active material is suppressed.
- An object of the present invention is to provide an electricity storage device that can improve electrochemical characteristics in a wide temperature range in an electricity storage device containing lithium titanate as a negative electrode active material.
- the present inventors have examined in detail the performance of the above-described prior art non-aqueous electrolyte.
- the non-aqueous electrolyte secondary battery of Patent Document 1 shows little effect on the problem of improving electrochemical characteristics in a wide temperature range such as low-temperature discharge characteristics after high-temperature storage. It was. Therefore, the present inventors have made extensive studies to solve the above-mentioned problems, and used Scherrer's formula from the specific surface area equivalent diameter D BET calculated from the specific surface area measured by the BET method and the X-ray diffraction measurement result.
- a secondary battery comprising, as a negative electrode active material, lithium oxalate having a ratio D BET / D X ( ⁇ m / ⁇ m) of 3 or less to the calculated crystallite diameter D X , oxalic acid specific to the non-aqueous electrolyte
- a ratio D BET / D X ( ⁇ m / ⁇ m) of 3 or less to the calculated crystallite diameter D X oxalic acid specific to the non-aqueous electrolyte
- the present invention provides the following (1) and (2).
- Nonaqueous electrolysis for use in an electricity storage device comprising a negative electrode containing lithium titanate having an X ( ⁇ m / ⁇ m) of 3 or less as a negative electrode active material, and a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent
- the solution contains 0.01 to 3% by mass of an organic or inorganic compound having an oxalic acid skeleton, and further contains 0.01 to 5% by mass of at least one isocyanate compound represented by the following general formula (I)
- a nonaqueous electrolytic solution for an electricity storage device comprising a negative electrode containing lithium titanate having an X ( ⁇ m / ⁇ m) of 3 or
- —X represents —R 1 —N ⁇ C ⁇ O or —R 1 —O—C ( ⁇ O) —R 2
- R 1 represents that at least one hydrogen atom is substituted with a halogen atom.
- a linear or branched alkylene group having 1 to 6 carbon atoms, wherein R 2 represents an alkyl group having 1 to 6 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom Represents an alkenyl group having 2 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms.
- a nonaqueous electrolytic solution capable of improving electrochemical characteristics in a wide temperature range, particularly low-temperature discharge characteristics after high-temperature storage, and a power storage device using the same Can be provided.
- the lithium titanate used in the present invention is a monodisperse particle in which formation of secondary particles and aggregation of primary particles are suppressed. Therefore, the lithium titanate can shorten the diffusion distance of lithium ions in each particle, and can reduce the internal resistance of the battery. Furthermore, since the lithium titanate is a monodisperse particle, the nonaqueous electrolyte can be brought into contact with the entire surface of each particle. Therefore, the lithium titanate can be received without leaving the protective effect of the specific compound contained in the nonaqueous electrolytic solution of the present invention.
- the lithium titanate used in the present invention is preferably represented by Li 4 Ti 5 O 12 .
- anatase titanium dioxide, rutile titanium dioxide, and Li 2 TiO 3 may be present. However, if these phases are present, the content of Li 4 Ti 5 O 12 is relatively lowered, and electrochemical characteristics such as discharge capacity are lowered. Therefore, it is preferable that these phases are few. From this viewpoint, the other phases (anatase type titanium dioxide, rutile type titanium dioxide, and the peak intensity corresponding to the main peak of Li 4 Ti 5 O 12 among the peaks measured by the X-ray diffraction method are defined as 100.
- Li 2 TiO 3 has a main peak intensity of preferably 3 or less, more preferably 1 or less.
- the peak intensity refers to the height from the baseline to the peak top.
- the volume median particle diameter (D50) of lithium titanate used in the present invention is preferably in the range of 0.01 to 20 ⁇ m. If it is 0.01 ⁇ m or more, aggregation of particles at the time of producing an electrode is suppressed, and if it is 20 ⁇ m or less, the internal resistance can be reduced by increasing the surface area.
- the volume median particle diameter (D50) is preferably 0.05 ⁇ m or more, and more preferably 0.1 ⁇ m or more.
- the upper limit is preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less, and particularly preferably 1 ⁇ m or less.
- BET specific surface area by nitrogen adsorption method of the lithium titanate used in the present invention from the viewpoint of reducing the internal resistance, preferably at least 3m 2 / g, more preferably at least 4m 2 / g, more 5 m 2 / g is particularly preferred .
- 100 m ⁇ 2 > / g or less is preferable, 50 m ⁇ 2 > / g or less is more preferable, and 20 m ⁇ 2 > / g or less is especially preferable.
- the lithium titanate used in the present invention is a ratio between the specific surface area equivalent diameter D BET calculated from the specific surface area measured by the BET method and the crystallite diameter D X calculated from the X-ray diffraction measurement result using the Scherrer equation. It is preferable that D BET / D X ( ⁇ m / ⁇ m) is 3 or less. A larger value of the ratio D BET / D X indicates that the ratio of the grain boundary portion is larger, suggesting that the particles are in a state of being aggregated or forming secondary particles. When the ratio D BET / D X exceeds 3, the interfacial resistance of the particles increases.
- D BET / D X is preferably 3 or less, more preferably 2 or less, and particularly preferably 1.5 or less.
- the crystallite diameter D X was obtained from the following Scherrer equation for the main peak of the X-ray diffraction pattern.
- D X of lithium titanate used in the present invention if the 80nm greater than preferable because low-temperature characteristics after high-temperature charged storage of the electric storage device according to the present invention becomes better, and more preferably 90nm or more, and particularly preferably at least 100nm Most preferably, it is 200 nm or more. Further, D X of lithium titanate of the present invention is preferably 500nm or less. When D X is larger than 500 nm, D BET may be increased, and the low temperature characteristics of the electricity storage device according to the present invention may be deteriorated.
- the ratio D BET / D X between the specific surface area equivalent diameter D BET calculated from the specific surface area measured by the BET method and the crystallite diameter D X calculated using the Scherrer equation from the X-ray diffraction measurement result is 3 or less.
- An electricity storage device contains 0.01 to 3% by mass of an organic or inorganic compound having an oxalic acid skeleton in a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, It contains 0.01 to 5% by mass of at least one isocyanato compound represented by (I).
- the reason why the nonaqueous electrolytic solution of the present invention can greatly improve the electrochemical characteristics of the electricity storage device in a wide temperature range is not necessarily clear, but is considered as follows.
- the organic or inorganic compound having an oxalic acid skeleton used in combination in the present invention undergoes reductive decomposition at a potential nobler than the oxidation-reduction potential of lithium titanate, which is the negative electrode active material, and lithium titanate is produced by the product of reductive decomposition.
- a film is formed on the surface of the particles. However, when this film is stored in a charged state at a high temperature, the film grows due to dissolution and re-formation of the film, so that the interface resistance is greatly increased.
- an inorganic compound having an oxalic acid skeleton refers to a composite compound composed of an organic part containing an oxalic acid skeleton and an inorganic part centered on an element other than carbon (for example, boron or phosphorus). means.
- the organic compound having an oxalic acid skeleton means a compound that includes only an organic part including an oxalic acid skeleton and does not include an inorganic part centered on an element other than carbon.
- compounds having the structure of A1, A4, or A7 to A12 are preferable, A1, A4, A9, or A11 are more preferable, and bis (2-propynyl) oxalate (compound A4) or difluorobis [oxalate] -O, O '] lithium phosphate (compound A11) is particularly preferred.
- the content of the organic or inorganic compound having an oxalic acid skeleton is preferably in the range of 0.01 to 3% by mass in the non-aqueous electrolyte.
- the content is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, further preferably 0.3% by mass or more, and the upper limit is 2.5% by mass or less in the non-aqueous electrolyte. Is preferable, 2 mass% or less is more preferable, and 1.5 mass% or less is still more preferable.
- —X represents —R 1 —N ⁇ C ⁇ O or —R 1 —O—C ( ⁇ O) —R 2
- R 1 represents at least one hydrogen atom substituted with a halogen atom.
- R 2 represents an alkyl group having 1 to 6 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom
- carbon represents an alkenyl group having 2 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms.
- an alkylene group is used as a concept including a methylene group.
- R 1 are as follows: Methylene group, ethane-1,2-diyl group, ethane-1,1-diyl group, propane-1,3-diyl group, propane-1,2-diyl group, propane-1,1-diyl group, butane- Alkylene groups such as 1,4-diyl group, butane-1,3-diyl group, 2-methylpropane-1,2-diyl group, pentane-1,5-diyl group, or hexane-1,6-diyl group Or monofluoromethylene group, difluoromethylene group, 1,2-difluoroethane-1,2-diyl group, 1,1-difluoroethane-1,2-diyl group, 1,3-difluoropropane-1,3-diyl group Or, a halogenated alkylene group such as a 2,2-difluoropropane-1,3-diyl
- R 2 in the general formula (I) represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, which may be substituted with halogen.
- An alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms is more preferable, and an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms is still more preferable.
- R 2 examples include a methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, iso-propyl group, sec-butyl group, or tert-butyl group.
- compounds having the structure of B1 to B5, B13, B14, B16 to B18, B22 to B24, or B39 to B42 are preferable, B2, B4, B5, B16, or B17 is more preferable, and 1,6-di- Isocyanatohexane (Compound B4), 2-isocyanatoethyl acrylate (Compound B16), or 2-isocyanatoethyl methacrylate (Compound B17) is particularly preferred.
- the content of the isocyanate compound represented by the general formula (I) contained in the non-aqueous electrolyte is in the range of 0.01 to 5% by mass in the non-aqueous electrolyte. preferable. If the content is 5% by mass or less, there is little possibility that a film is excessively formed on the electrode and the low-temperature characteristics are deteriorated. If the content is 0.01% by mass or more, the film is sufficiently formed and stored at high temperature. The effect of improving the characteristics is increased.
- the content is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more in the nonaqueous electrolytic solution.
- the upper limit is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less.
- nonaqueous electrolytic solution of the present invention a unique effect of synergistically improving the electrochemical characteristics over a wide temperature range is exhibited by combining the nonaqueous solvent, the electrolyte salt, and other additives described below.
- ethylene carbonate and propylene carbonate are preferable because electrochemical characteristics in a wide temperature range are further improved, and it is more preferable that propylene carbonate is contained.
- the non-aqueous solvent contains ethylene carbonate and / or propylene carbonate
- the resistance of the film formed on the electrode is preferably reduced.
- the content of ethylene carbonate and / or propylene carbonate is based on the total volume of the non-aqueous solvent. Preferably it is at least 3% by volume, more preferably at least 5% by volume, even more preferably at least 7% by volume, and its upper limit is preferably at most 45% by volume, more preferably at most 35% by volume, still more preferably 25% by volume or less.
- the electrochemical characteristics in the range are further improved, more preferably 5:95 to 45:65, and particularly preferably 10:90 to 40:60.
- one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl
- MEC methyl ethyl carbonate
- DMC dimethyl carbonate
- Preferred examples include carboxylic acid esters.
- chain esters having an ethyl group selected from diethyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, ethyl propionate and ethyl acetate are preferable, and chain carbonates having an ethyl group are particularly preferable.
- chain carbonate it is preferable to use 2 or more types. Further, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is further more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.
- diethyl carbonate is contained in the symmetric chain carbonate.
- the asymmetric chain carbonate has an ethyl group, and methyl ethyl carbonate is particularly preferable.
- the above case is preferable because electrochemical characteristics in a wider temperature range are improved.
- the ratio between the cyclic carbonate and the chain ester is preferably 10:90 to 45:55, and 15:85 to 40:55 in terms of the cyclic carbonate: chain ester (volume ratio) from the viewpoint of improving electrochemical characteristics in a wide temperature range. 60 is more preferable, and 20:80 to 35:65 is particularly preferable.
- non-aqueous solvents include cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, etc.
- Preferable examples include one or two or more selected from chain ethers of the above, amides such as dimethylformamide, sulfones such as sulfolane, and lactones such as ⁇ -butyrolactone, ⁇ -valerolactone, or ⁇ -angelicalactone.
- the above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties.
- the combination is, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a chain carboxylic acid ester, a combination of a cyclic carbonate and a lactone, a combination of a cyclic carbonate, a chain carbonate and a lactone, or a cyclic
- a combination of carbonate, chain carbonate and chain carboxylic acid ester is preferred.
- lithium salts include inorganic lithium salts such as LiPF 6 , LiPO 2 F 2 , Li 2 PO 3 F, LiBF 4 and LiClO 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , Lithium salts containing chain-like fluorinated alkyl groups such as LiCF 3 SO 3 and LiC (SO 2 CF 3 ) 3 , (CF 2 ) 2 (SO 2 ) 2 NLi, (CF 2 ) 3 (SO 2 ) 2 Lithium salt having an anion of a lithium salt having a cyclic fluorinated alkylene chain such as NLi, sulfonic acid skeleton such as lithium fluorosulfate (FSO 3 Li), lithium trifluoro ((methanesulfonyl) oxy) borate (LiTFMSB)
- LiPF 6 LiPF 6 , LiPO 2 F 2 , Li 2 PO 3 F, LiBF 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 and LiTFMSB.
- LiPF 6 LiPF 6 is most preferable.
- the concentration of the lithium salt is usually preferably 0.3 M or more, more preferably 0.7 M or more, and further preferably 1.1 M or more with respect to the non-aqueous solvent.
- the upper limit is preferably 2.5M or less, more preferably 2.0M or less, and still more preferably 1.6M or less.
- lithium salts include LiPF 6, further LiPO 2 F 2, Li 2 PO 3 F, LiBF 4, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5 ) 2 , FSO 3 Li, and LiTFMSB are preferably included.
- the proportion of lithium salt other than LiPF 6 in the non-aqueous solvent is 0.001M or more, the effect of improving the electrochemical properties at high temperatures is easily exhibited, and when it is 0.005M or less, the chemistry at high temperatures. This is preferable because there is little concern that the effect of improving characteristics will be reduced.
- it is 0.01M or more, Especially preferably, it is 0.03M or more, Most preferably, it is 0.04M or more.
- the upper limit is preferably 0.4M or less, particularly preferably 0.2M or less.
- the non-aqueous electrolyte of the present invention is prepared, for example, by mixing the non-aqueous solvent, the electrolyte salt, an organic or inorganic compound having an oxalic acid skeleton with respect to the non-aqueous electrolyte, and the general formula (I It can be obtained by adding at least one isocyanato compound represented by At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.
- the nonaqueous electrolytic solution of the present invention can be used for an electricity storage device that stores and releases energy by using lithium ion intercalation and deintercalation to the negative electrode containing lithium titanate.
- Examples of such an electricity storage device include a hybrid capacitor and a lithium battery.
- lithium composite metal oxides examples include LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiCo 1-x Ni x O 2 (0.01 ⁇ x ⁇ 1), LiCo 1/3 Ni 1/3.
- LiCoO 2 and LiMn 2 O 4, LiCoO 2 and LiNiO 2 may be used in combination as LiMn 2 O 4 and LiNiO 2.
- a part of the lithium composite metal oxide is replaced with another element.
- a part of cobalt, manganese, nickel is replaced with at least one element such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La,
- a part of O can be substituted with S or F, or a compound containing these other elements can be coated.
- lithium composite metal oxides such as LiCoO 2 , LiMn 2 O 4 , and LiNiO 2 that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo 1-x M x O 2 (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ⁇ x ⁇ 0.
- a lithium composite metal oxide that operates at a high charging voltage is used, the electrochemical characteristics when used in a wide temperature range are liable to deteriorate due to a reaction with the electrolyte during charging, but the lithium secondary battery according to the present invention Then, the deterioration of these electrochemical characteristics can be suppressed.
- the resistance of the battery tends to increase with the elution of Mn ions from the positive electrode, so that the electrochemical characteristics when used in a wide temperature range tend to be lowered.
- the lithium secondary battery according to the invention is preferable because it can suppress a decrease in these electrochemical characteristics.
- lithium-containing olivine-type phosphate can also be used as the positive electrode active material.
- lithium-containing olivine phosphate containing one or more selected from iron, cobalt, nickel, and manganese is preferable. Specific examples thereof include one or more selected from LiFePO 4 , LiCoPO 4 , LiNiPO 4 , and LiMnPO 4 .
- Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of iron, cobalt, nickel, and manganese are replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb.
- LiFePO 4 or LiMnPO 4 is preferable.
- mold phosphate can also be mixed with the said positive electrode active material, for example, and can be used.
- the pH of the supernatant obtained when 10 g of the positive electrode active material is dispersed in 100 ml of distilled water is 10.0 to 12.5, the effect of improving the electrochemical characteristics in a wider temperature range can be easily obtained.
- the case of 10.5 to 12.0 is more preferable.
- impurities such as LiOH in the positive electrode active material tend to increase, an effect of improving electrochemical characteristics in a wider temperature range is easily obtained, which is preferable.
- the case where the atomic concentration of Ni in the substance is 5 to 25 atomic% is more preferable, and the case where it is 8 to 21 atomic% is particularly preferable.
- this positive electrode mixture was applied to a current collector aluminum foil, a stainless steel lath plate, etc., dried and pressure-molded, and then subjected to vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can be manufactured by heat treatment.
- the density of the part except the collector of the positive electrode is usually at 1.5 g / cm 3 or more, for further increasing the capacity of the battery, it is preferably 2 g / cm 3 or more, more preferably, 3 g / cm 3 It is above, More preferably, it is 3.6 g / cm 3 or more.
- the upper limit is preferably 4 g / cm 3 or less.
- the negative electrode active material for a lithium secondary battery of the present invention contains the above lithium titanate.
- the active material one or more active materials other than lithium titanate may be contained.
- Other active materials include carbon materials that can occlude and release lithium (e.g., graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, and (002) plane Graphite having an interplanar spacing of 0.34 nm or less, etc.], tin (single substance), tin compound, silicon (single substance), and silicon compound can be used singly or in combination of two or more.
- the carbon fiber is more preferably a fine carbon fiber having a single-layer or multilayer graphite layer.
- the addition amount of the conductive agent to the negative electrode mixture is preferably 1 to 10% by mass, and particularly preferably 2 to 5% by mass.
- the negative electrode is kneaded with the above conductive agent, the same binder and high boiling point solvent as in the preparation of the positive electrode to obtain a negative electrode mixture, and this negative electrode mixture is then applied to the aluminum foil of the current collector. Then, after drying and pressure molding, it can be produced by heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.
- the density of the portion excluding the current collector of the negative electrode is usually 1.5 g / cm 3 or more, and is preferably 1.8 g / cm 3 or more, more preferably 2 g / cm 3 in order to further increase the capacity of the battery. 3 or more.
- the upper limit is preferably 3 g / cm 3 or less.
- the structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminated battery, or the like having a single-layer or multi-layer separator can be applied.
- a battery separator there is no restriction
- stacked microporous film of polyolefin, such as a polypropylene or polyethylene, a woven fabric, a nonwoven fabric, or paper (cellulose) etc. can be used.
- the lithium secondary battery of the present invention is excellent in electrochemical characteristics in a wide temperature range even when the end-of-charge voltage is 2.7 V or more, particularly 2.8 V or more, and also has good characteristics even at 2.9 V or more. is there.
- the end-of-discharge voltage is usually 1.6 V or higher, and further 1.5 V or higher.
- the current value is not particularly limited, but is usually used in the range of 0.1 to 30C.
- the lithium battery in the present invention can be charged and discharged at ⁇ 40 to 100 ° C., preferably ⁇ 20 to 80 ° C.
- a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed.
- the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.
- BET specific surface area and specific surface area equivalent diameter D BET A BET specific surface area was measured by a one-point method using liquid nitrogen using a fully automatic specific surface area measuring device, trade name “Macsorb HM model-1208”, manufactured by Mountec Co., Ltd.
- Examples 1 to 16 Comparative Examples 1 to 4 [Production of lithium ion secondary battery] Regarding lithium titanate (Li 4 Ti 5 O 12 ) used in Examples (LTO-A, LTO-B, LTO-C) and Comparative Example (LTO-D), D50 ( ⁇ m), BET specific surface area (m 2 / G), XRD and pH were measured. Moreover, specific surface area equivalent diameter D BET and crystallite diameter D X were calculated
- the lithium titanate (Li 4 Ti 5 O 12 ) used in the examples (LTO-A, LTO-B, LTO-C) and the comparative example (LTO-D) was produced by the following method. That is, Li 2 CO 3 and anatase TiO 2 were used as raw materials, and ion-exchanged water was added and stirred to prepare a mixed slurry. The mixed slurry was pulverized and mixed, and the mixed slurry after pulverized and mixed was fired using a rotary kiln type firing furnace.
- Lithium titanate (Li 4 Ti 5 O 12 ) according to examples (LTO-A, LTO-B, LTO-C) and comparative examples (LTO-D) having the characteristics shown in Table 1 was obtained.
- LiNi 1/3 Co 1/3 Mn 1/3 O 2 ; 94% by mass, acetylene black (conductive agent); 3% by mass were mixed, and polyvinylidene fluoride (binder);
- a positive electrode mixture paste was prepared by adding to and mixing with the solution previously dissolved in methyl-2-pyrrolidone. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, punched out to a predetermined size, and a positive electrode sheet was produced. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm 3 .
- Example 1 A coin battery was produced using the negative electrode sheet, and battery evaluation was performed (Examples 2 and 3, Comparative Example 1). The results are also shown in Table 2. Further, a coin battery was produced in the same manner as in Example 1 except that the non-aqueous electrolyte was changed, and battery evaluation was performed (Examples 4 to 18 and Comparative Examples 2 to 4). The results are shown in Table 3.
- the effect of the present invention is that a non-aqueous electrolyte is used in a lithium secondary battery as an example of an electricity storage device containing the specific lithium titanate of the present invention as a negative electrode active material. It was found that this was a unique effect when the above-mentioned specific compound was contained.
- any of the lithium secondary batteries of Examples 4 to 18 does not contain an organic or inorganic compound having an oxalic acid skeleton or an isocyanato compound represented by the general formula (I) in the nonaqueous electrolytic solution of the present invention.
- Comparative Example 3 Compared with Comparative Example 2 in the case of Comparative Example 3, Comparative Example 3 in which only an organic or inorganic compound having an oxalic acid skeleton was added, and Comparative Example 4 in which only an isocyanate compound represented by the general formula (I) was added, in a wide temperature range.
- the electrochemical properties are significantly improved.
- an electricity storage device such as a lithium secondary battery having excellent electrochemical characteristics in a wide temperature range can be obtained.
- a lithium secondary battery mounted in a hybrid electric vehicle, a plug-in hybrid electric vehicle, a battery electric vehicle or the like the electrochemical characteristics are unlikely to deteriorate over a wide temperature range.
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Abstract
Description
特に地球温暖化防止のため、CO2排出量を削減することが急務となっており、リチウム二次電池やキャパシタ等の蓄電デバイスからなる蓄電装置を搭載した環境対応車の中でも、ハイブリッド電気自動車(HEV)、プラグインハイブリッド電気自動車(PHEV)、バッテリー電気自動車(BEV)の早期普及が求められている。自動車は移動距離が長いため、熱帯の非常に暑い地域から極寒の地域まで幅広い温度範囲の地域で使用される可能性がある。従って、特にこれらの車載用の蓄電デバイスは、高温から低温まで幅広い温度範囲で使用しても電気化学特性が低下しないことが要求されている。尚、本明細書において、リチウム二次電池という用語は、いわゆるリチウムイオン二次電池も含む概念として用いる。
また、負極としては、金属リチウム、リチウムを吸蔵及び放出可能な金属化合物(金属単体、酸化物、リチウムとの合金等)や炭素材料が知られており、特にリチウムを吸蔵及び放出することが可能なコークス、人造黒鉛、天然黒鉛等の炭素材料を用いたリチウム二次電池が広く実用化されている。
ただし、炭素材料は極低温の様な過酷な環境下で充放電を行うと負極上にデンドライトが生成し、内部短絡の原因になるなど電池の信頼性に問題があった。
そこで、酸化還元電位がリチウム基準で1.5Vであるチタン酸リチウムが、デンドライトを生成しない負極材料として提案されているが、チタン酸リチウムは炭素材料と比べて電子伝導性が極めて低いという課題がある。
一方、正極として、例えばLiCoO2、LiMn2O4、LiNiO2、LiFePO4等を用いたリチウム二次電池は、非水電解液中の非水溶媒が充電状態で正極材料と非水電解液との界面において、局部的に一部酸化分解することにより発生した分解物やガスが電池の望ましい電気化学的反応を阻害するため、やはり広い温度範囲で使用した場合における電気化学特性の低下を生じることが分かっている。
その結果、前記特許文献1の非水電解質二次電池では、高温保存後の低温放電特性等の広い温度範囲での電気化学特性を向上させるという課題に対してはほとんど効果を発揮しないことが分かった。
そこで、本発明者らは、上記課題を解決するために鋭意研究を重ね、BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DX(μm/μm)が3以下であるチタン酸リチウムを負極活物質として具備する二次電池において、非水電解液に特定のシュウ酸骨格を有する有機又は無機化合物を特定の添加量で含有し、更に特定のイソシアナト基を有する化合物を1種以上、かつ特定の添加量で含有することによって、広い温度範囲で蓄電デバイスの電気化学特性を改善できることを見出し、本発明を完成した。このような効果は、前記特許文献1にはまったく示唆されていない。
(1)正極、BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DX(μm/μm)が3以下であるチタン酸リチウムを負極活物質として含有する負極、及び非水溶媒に電解質塩が溶解されている非水電解液を備えた蓄電デバイスに用いられる非水電解液において、シュウ酸骨格を有する有機又は無機化合物を0.01~3質量%含有し、更に、下記一般式(I)で表される少なくとも1種のイソシアナト化合物を0.01~5質量%含有することを特徴とする蓄電デバイス用非水電解液。
本発明に係る蓄電デバイスは、BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DX(μm/μm)が3以下であるチタン酸リチウムを負極活物質として具備することを特徴とする。
この観点から、X線回折法によって測定されるピークのうちLi4Ti5O12のメインピークに相当するピーク強度を100とした時の他の相(アナターゼ型二酸化チタン、ルチル型二酸化チタン、及びLi2TiO3)のメインピーク強度は、3以下が好ましく、1以下がより好ましい。
ここで、ピーク強度とは、ベースラインからピークトップまでの高さのことをいう。
ここで、比表面積相当径DBETは、BET法により測定した比表面積Sと立方晶の格子定数から計算される理論密度ρから、粉末粒子が全て一定の直径DBETを有する球状粒子であると仮定し、DBET=6/(ρS)により計算して求めた。また、結晶子径DXはX線回折パターンのメインピークについて下記Scherrerの式より求めた。
ここで、チタン酸リチウムのpHとは、チタン酸リチウム10gを90gの水に分散した時の上澄み液のpHを意味する。
BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DXが3以下でありかつ、pHが前記範囲であるチタン酸リチウムを用いると広い温度範囲で電気化学特性が向上するので好ましい。
本発明に係る蓄電デバイスは、非水溶媒に電解質塩が溶解されている非水電解液において、シュウ酸骨格を有する有機又は無機化合物を0.01~3質量%含有し、更に、前記一般式(I)で表される少なくとも1種のイソシアナト化合物を0.01~5質量%含有することを特徴とする。
本発明で組み合わせて使用されるシュウ酸骨格を有する有機又は無機化合物は、負極活物質であるチタン酸リチウムの酸化還元電位よりも貴な電位で還元分解し、還元分解による生成物によってチタン酸リチウム粒子の表面に被膜を形成する。ところが、この被膜は、高温下に充電状態で保存すると被膜の溶解、再形成によって被膜が成長するため、界面抵抗が大きく増大してしまう。これに対し、本発明の非水電解液は、一般式(I)で表される少なくとも1種のイソシアナト化合物と該シュウ酸骨格を有する化合物とを併せて使用することにより、該シュウ酸骨格を有する化合物と一般式(I)で表される特定のイソシアナト化合物とが相俟って、チタン酸リチウムの活性点に素早く複合被膜を形成する。そして、該複合被膜が高温保存中の被膜の成長を防ぎ、界面抵抗の増加を格段に抑制することが分かった。
なお、本願において、アルキレン基とはメチレン基も含む概念として用いる。
メチレン基、エタン-1,2-ジイル基、エタン-1,1-ジイル基、プロパン-1,3-ジイル基、プロパン-1,2-ジイル基、プロパン-1,1-ジイル基、ブタン-1,4-ジイル基、ブタン-1,3-ジイル基、2-メチルプロパン-1,2-ジイル基、ペンタン-1,5-ジイル基、もしくはヘキサン-1,6-ジイル基等のアルキレン基、又はモノフルオロメチレン基、ジフルオロメチレン基、1,2-ジフルオロエタン-1,2-ジイル基、1,1-ジフルオロエタン-1,2-ジイル基、1,3-ジフルオロプロパン-1,3-ジイル基、もしくは2,2-ジフルオロプロパン-1,3-ジイル基等のハロゲン化アルキレン基が好適に挙げられる。
中でもメチレン基、エタン-1,2-ジイル基、エタン-1,1-ジイル基、プロパン-1,3-ジイル基、プロパン-1,2-ジイル基、プロパン-1,1-ジイル基、ブタン-1,4-ジイル基、ブタン-1,3-ジイル基、2-メチルプロパン-1,2-ジイル基、ペンタン-1,5-ジイル基、ヘキサン-1,6-ジイル基、モノフルオロメチレン基、又はジフルオロメチレン基が好ましく、エタン-1,2-ジイル基、プロパン-1,3-ジイル基、プロパン-1,2-ジイル基、ブタン-1,4-ジイル基、ペンタン-1,5-ジイル基、又はヘキサン-1,6-ジイル基が更に好ましい。
本発明の非水電解液に使用される非水溶媒としては、環状カーボネート、鎖状エステル、ラクトン、エーテル、及びアミドから選ばれる一種又は二種以上が挙げられる。広い温度範囲で電気化学特性が相乗的に向上するため、鎖状エステルが含まれることが好ましく、鎖状カーボネートが含まれることが更に好ましく、環状カーボネートと鎖状カーボネートの両方が含まれることがもっとも好ましい。
なお、「鎖状エステル」なる用語は、鎖状カーボネート及び鎖状カルボン酸エステルを含む概念として用いる。
非水溶媒がエチレンカーボネート及び/又はプロピレンカーボネートを含むと電極上に形成される被膜の抵抗が小さくなるので好ましく、エチレンカーボネート及び/又はプロピレンカーボネートの含有量は、非水溶媒の総体積に対し、好ましくは3体積%以上、より好ましくは5体積%以上、更に好ましくは7体積%以上であり、また、その上限としては、好ましくは45体積%以下、より好ましくは35体積%以下、更に好ましくは25体積%以下である。
また、鎖状カーボネートを用いる場合には、二種以上を用いることが好ましい。さらに対称鎖状カーボネートと非対称鎖状カーボネートの両方が含まれるとより好ましく、対称鎖状カーボネートの含有量が非対称鎖状カーボネートより多く含まれると更に好ましい。
鎖状カーボネート中に対称鎖状カーボネートが占める体積の割合は、51体積%以上が好ましく、55体積%以上がより好ましい。その上限としては、95体積%以下がより好ましく、85体積%以下であると更に好ましい。対称鎖状カーボネートにジエチルカーボネートが含まれると特に好ましい。また、非対称鎖状カーボネートはエチル基を有するとより好ましく、メチルエチルカーボネートが特に好ましい。
上記の場合に一段と広い温度範囲での電気化学特性が向上するので好ましい。
環状カーボネートと鎖状エステルの割合は、広い温度範囲での電気化学特性向上の観点から、環状カーボネート:鎖状エステル(体積比)が10:90~45:55が好ましく、15:85~40:60がより好ましく、20:80~35:65が特に好ましい。
リチウム塩としては、LiPF6、LiPO2F2、Li2PO3F、LiBF4及びLiClO4等の無機リチウム塩、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiCF3SO3及びLiC(SO2CF3)3等の鎖状のフッ化アルキル基を含有するリチウム塩や、(CF2)2(SO2)2NLi、(CF2)3(SO2)2NLi等の環状のフッ化アルキレン鎖を有するリチウム塩をアニオンとするリチウム塩、フルオロ硫酸リチウム(FSO3Li)、リチウム トリフルオロ((メタンスルホニル)オキシ)ボレート(LiTFMSB)等のスルホン酸骨格を有するリチウム塩が好適に挙げられ、これらの一種又は二種以上を混合して使用することができる。
本発明の非水電解液は、例えば、前記の非水溶媒を混合し、これに前記の電解質塩、該非水電解液に対してシュウ酸骨格を有する有機もしくは無機化合物、及び前記一般式(I)で表される少なくとも1種のイソシアナト化合物を添加することにより得ることができる。
この際、用いる非水溶媒及び非水電解液に加える化合物は、生産性を著しく低下させない範囲内で、予め精製して、不純物が極力少ないものを用いることが好ましい。
本発明の非水電解液は、前記チタン酸リチウムを含む負極へのリチウムイオンのインターカレーション、脱インターカレーションを利用してエネルギーを貯蔵、放出する蓄電デバイスに使用することができる。このような蓄電デバイスとしては、例えば、ハイブリッドキャパシタやリチウム電池などが挙げられる。
本発明のハイブリッドキャパシタとしては、正極に、活性炭など電気二重層キャパシタの電極材料と同様の物理的な吸着によって容量が形成される活物質や、グラファイトなど物理的な吸着とインターカレーション、脱インターカレーションによって容量が形成される活物質や、導電性高分子などレドックスにより容量が形成される活物質を使用し、負極として、前記チタン酸リチウムを含む負極を使用するとともに、電解液として、上述した本発明の非水電解液を用いてなるデバイスである。
リチウム電池は、リチウム一次電池及びリチウム二次電池の総称であり、また、本明細書において、リチウム二次電池という用語は、いわゆるリチウムイオン二次電池も含む概念として用いる。
本発明のリチウム電池は、正極、前記チタン酸リチウムを含む負極、及び上述した本発明の非水電解液を備えるものである。正極やセパレータ等の構成部材は特に制限なく使用できる。
例えば、リチウム二次電池用正極活物質としては、コバルト、マンガン及びニッケルから選ばれる一種又は二種以上を含有するリチウムとの複合金属酸化物が使用される。これらの正極活物質は、一種単独で又は二種以上を組み合わせて用いることができる。
このようなリチウム複合金属酸化物としては、例えば、LiCoO2、LiMn2O4、LiNiO2、LiCo1-xNixO2(0.01<x<1)、LiCo1/3Ni1/3Mn1/3O2、LiNi1/2Mn3/2O4、及びLiCo0.98Mg0.02O2から選ばれる一種又は二種以上が挙げられる。また、LiCoO2とLiMn2O4、LiCoO2とLiNiO2、LiMn2O4とLiNiO2のように併用してもよい。
これらの中では、LiCoO2、LiMn2O4、LiNiO2のような満充電状態における正極の充電電位がLi基準で4.3V以上で使用可能なリチウム複合金属酸化物が好ましく、LiCo1-xMxO2(但し、MはSn、Mg、Fe、Ti、Al、Zr、Cr、V、Ga、Zn、及びCuから選ばれる一種又は二種以上の元素、0.001≦x≦0.05)、LiCo1/3Ni1/3Mn1/3O2、LiNi1/2Mn3/2O4、Li2MnO3とLiMO2(Mは、Co、Ni、Mn、Fe等の遷移金属)との固溶体のようなLi基準で4.4V以上で使用可能なリチウム複合金属酸化物がより好ましい。高充電電圧で動作するリチウム複合金属酸化物を使用すると、充電時における電解液との反応により特に広い温度範囲で使用した場合における電気化学特性が低下しやすいが、本発明に係るリチウム二次電池ではこれらの電気化学特性の低下を抑制することができる。
特にMnを含む正極の場合に正極からのMnイオンの溶出に伴い電池の抵抗が増加しやすい傾向にあるため、広い温度範囲で使用した場合における電気化学特性が低下しやすい傾向にあるが、本発明に係るリチウム二次電池ではこれらの電気化学特性の低下を抑制することができるので好ましい。
これらのリチウム含有オリビン型リン酸塩の一部は他元素で置換してもよく、鉄、コバルト、ニッケル、マンガンの一部をCo、Mn、Ni、Mg、Al、B、Ti、V、Nb、Cu、Zn、Mo、Ca、Sr、W、及びZr等から選ばれる一種又は二種以上の元素で置換したり、又はこれらの他元素を含有する化合物や炭素材料で被覆することもできる。これらの中では、LiFePO4又はLiMnPO4が好ましい。
また、リチウム含有オリビン型リン酸塩は、例えば前記の正極活物質と混合して用いることもできる。
また、正極中に元素としてNiが含まれる場合、正極活物質中のLiOH等の不純物が増える傾向があるため、一段と広い温度範囲での電気化学特性の改善効果が得られやすいので好ましく、正極活物質中のNiの原子濃度が5~25atomic%である場合が更に好ましく、8~21atomic%である場合が特に好ましい。
正極の集電体を除く部分の密度は、通常は1.5g/cm3以上であり、電池の容量をさらに高めるため、好ましくは2g/cm3以上であり、より好ましくは、3g/cm3以上であり、更に好ましくは、3.6g/cm3以上である。なお、その上限としては、4g/cm3以下が好ましい。
負極の集電体を除く部分の密度は、通常は1.5g/cm3以上であり、電池の容量をさらに高めるため、好ましくは1.8g/cm3以上であり、より好ましくは2g/cm3以上である。なお、その上限としては、3g/cm3以下が好ましい。
電池用セパレータとしては、特に制限はないが、ポリプロピレン又はポリエチレン等のポリオレフィンの単層又は積層の微多孔性フィルム、織布、不織布または、紙(セルロース)等を使用できる。
(1)体積中位粒径(D50)
測定装置としてレーザ回折・散乱型粒度分布測定機(日機装株式会社、マイクロトラックMT3300EXII)を用いた。50mlのイオン交換水に、約50mgの試料を入れ、更に界面活性剤である0.2%ヘキサメタリン酸ナトリウム水溶液をスポイトで3滴入れ、これを超音波分散機で処理した。得られた溶液を測定セルに入れ、蒸留水を加え、装置の透過率が適性範囲になったところで体積中位粒径(D50)を測定した。
株式会社マウンテック製、全自動比表面積測定装置、商品名「Macsorb HM model-1208」を使用し、液体窒素を用いて一点法でBET比表面積を測定した。比表面積相当径DBETは、BET法により測定した比表面積Sと立方晶の格子定数から計算される理論密度ρから、粉末粒子が全て一定の直径DBETを有する球状粒子であると仮定し、DBET=6/(ρS)により計算して求めた。
CuKα線を用いたX線回折法により、チタン酸リチウムのメインピーク(2θ:18.1~18.5°の範囲内で最大の強度を示すピーク)を測定した。結晶子径DXはX線回折パターンのメインピークについて下記Scherrerの式より求めた。
チタン酸リチウム粒子10gを90gの水に分散した時の上澄み液のpHを室温下、pHメータを用いて測定した。
〔リチウムイオン二次電池の作製〕
実施例(LTO-A、LTO-B、LTO-C)および比較例(LTO-D)に用いたチタン酸リチウム(Li4Ti5O12)について、D50(μm)、BET比表面積(m2/g)、XRD及びpHを測定した。また、比表面積相当径DBET及び結晶子径DXを前述の計算によって求め、DBET/DXを算出した。その結果を表1に示す。
また、LiNi1/3Co1/3Mn1/3O2;94質量%、アセチレンブラック(導電剤);3質量%を混合し、予めポリフッ化ビニリデン(結着剤);3質量%を1-メチル-2-ピロリドンに溶解させておいた溶液に加えて混合し、正極合剤ペーストを調製した。この正極合剤ペーストをアルミニウム箔(集電体)上の片面に塗布し、乾燥、加圧処理して所定の大きさに打ち抜き、正極シートを作製した。正極の集電体を除く部分の密度は3.6g/cm3であった。そして、正極シート、ポリエチレン不織布製セパレータ、負極シートの順に積層し、表2に記載の組成の非水電解液を加えて、2032型コイン電池を作製した。次に実施例1で用いたチタン酸リチウム(LTO-A)に代えて、LTO-B、LTO-C、及びLTO-Dを用いて、実施例1と同様に負極シートを作製し、作製した負極シートを用いてコイン電池を作製し、電池評価を行った(実施例2,3、比較例1)。結果を同じく表2に示す。さらに、非水電解液を代えたことの他は、実施例1と同様にコイン電池を作製し、電池評価を行った(実施例4~18、比較例2~4)。結果を表3に示す。
<初期の放電容量>
上記の方法で作製したコイン電池を用いて、25℃の恒温槽中、1Cの定電流及び定電圧で、終止電圧2.8Vまで3時間充電し、-10℃に恒温槽の温度を下げ、1Cの定電流下終止電圧1.5Vまで放電して、初期の-10℃の放電容量を求めた。
<高温充電保存試験>
次に、このコイン電池を85℃の恒温槽中、1Cの定電流及び定電圧で終止電圧2.8Vまで3時間充電し、2.8Vに保持した状態で3日間保存を行った。その後、25℃の恒温槽に入れ、一旦1Cの定電流下終止電圧1.5Vまで放電した。
<高温充電保存後の放電容量>
更にその後、初期の放電容量の測定と同様にして、高温充電保存後の-10℃の放電容量を求めた。
<高温充電保存後の低温特性>
高温充電保存後の低温特性を下記の-10℃放電容量の維持率より求めた。
高温充電保存後の-10℃放電容量維持率(%)=(高温充電保存後の-10℃の放電容量/初期の-10℃の放電容量)×100
Claims (10)
- 正極、BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DX(μm/μm)が3以下であるチタン酸リチウムを負極活物質として含有する負極、及び非水溶媒に電解質塩が溶解されている非水電解液を備えた蓄電デバイスに用いられる非水電解液において、シュウ酸骨格を有する有機又は無機化合物を0.01~3質量%含有し、更に、下記一般式(I)で表される少なくとも1種のイソシアナト化合物を0.01~5質量%含有することを特徴とする蓄電デバイス用非水電解液。
- 前記シュウ酸骨格を有する有機又は無機化合物が、ビス(2-プロピニル) オキサレート、又はジフルオロビス[オキサレート-O,O’]リン酸リチウムである請求項1に記載の蓄電デバイス用非水電解液。
- 前記一般式(I)で表されるイソシアナト化合物が、1,6-ジイソシアナトヘキサン、2-イソシアナトエチル アクリレート、又は2-イソシアナトエチル メタクリレートである請求項1又は2に記載の蓄電デバイス用非水電解液。
- 前記非水溶媒が、環状カーボネートと鎖状エステルとを含有する請求項1~3のいずれかに記載の蓄電デバイス用非水電解液。
- 前記環状カーボネートが、エチレンカーボネート、プロピレンカーボネート、1,2-ブチレンカーボネート、2,3-ブチレンカーボネート、4-フルオロ-1,3-ジオキソラン-2-オン、トランスもしくはシス-4,5-ジフルオロ-1,3-ジオキソラン-2-オン、ビニレンカーボネート、ビニルエチレンカーボネート、及び4-エチニル-1,3-ジオキソラン-2-オンのいずれか1種以上である請求項4に記載の蓄電デバイス用非水電解液。
- 前記鎖状エステルが、メチルエチルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネート、メチルブチルカーボネート、及びエチルプロピルカーボネートから選ばれる非対称鎖状カーボネート、ジメチルカーボネート、ジエチルカーボネート、ジプロピルカーボネート、及びジブチルカーボネートから選ばれる対称鎖状カーボネート、プロピオン酸メチル、プロピオン酸エチル、酢酸メチル、及び酢酸エチルから選ばれる鎖状カルボン酸エステルのいずれか1種以上である請求項4又は5に記載の蓄電デバイス用非水電解液。
- 前記電解質塩が、リチウム塩である請求項1~6のいずれかに記載の蓄電デバイス用非水電解液。
- 前記電解質塩が、LiPF6、LiPO2F2、Li2PO3F、LiBF4、LiN(SO2CF3)2、LiN(SO2C2F5)2、FSO3Li、及びリチウム トリフルオロ((メタンスルホニル)オキシ)ボレートのいずれか1種以上である請求項1~7のいずれかに記載の蓄電デバイス用非水電解液。
- 正極、BET法により測定した比表面積から計算される比表面積相当径DBETとX線回折測定結果からScherrerの式を用いて計算される結晶子径DXとの比DBET/DX(μm/μm)が3以下であるチタン酸リチウムを負極活物質として含有する負極、及び非水溶媒に電解質塩が溶解されている非水電解液を備えた蓄電デバイスにおいて、該非水電解液中にシュウ酸骨格を有する有機又は無機化合物を0.01~3質量%含有し、更に、下記一般式(I)で表される少なくとも1種のイソシアナト化合物を0.01~5質量%含有することを特徴とする蓄電デバイス。
- 前記正極が、正極活物質として、リチウム複合金属酸化物およびリチウム含有オリビン型リン酸塩から選択される少なくとも1種を含む請求項9に記載の蓄電デバイス。
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KR102019312B1 (ko) | 2016-02-25 | 2019-09-06 | 주식회사 엘지화학 | 겔 폴리머 전해질용 조성물 및 이를 포함하는 리튬 이차전지 |
CN106684448B (zh) * | 2016-12-25 | 2019-01-11 | 钜成新能源(响水)有限公司 | 一种耐高温锂电池电解液的制备方法 |
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