WO2012049723A1 - Nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery Download PDF

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Publication number
WO2012049723A1
WO2012049723A1 PCT/JP2010/067841 JP2010067841W WO2012049723A1 WO 2012049723 A1 WO2012049723 A1 WO 2012049723A1 JP 2010067841 W JP2010067841 W JP 2010067841W WO 2012049723 A1 WO2012049723 A1 WO 2012049723A1
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positive electrode
active material
electrode active
secondary battery
carbon
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PCT/JP2010/067841
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French (fr)
Japanese (ja)
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上田　篤司
山田　直毅
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日立ビークルエナジー株式会社
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Priority to PCT/JP2010/067841 priority Critical patent/WO2012049723A1/en
Priority to JP2012538484A priority patent/JP5528564B2/en
Publication of WO2012049723A1 publication Critical patent/WO2012049723A1/en

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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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • 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
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • 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

Definitions

  • the present invention relates to a non-aqueous electrolyte secondary battery that uses a lithium iron phosphate positive electrode and achieves both high capacity and storage characteristics.
  • lithium cobalt oxide has been the mainstream as a positive electrode active material for non-aqueous electrolyte batteries.
  • cobalt which is the raw material
  • the use of lithium cobaltate increases the production cost of the battery.
  • a battery using lithium cobaltate has a problem in safety when the battery temperature rises at the end of charging.
  • lithium manganate, lithium nickelate, etc. as a positive electrode active material instead of lithium cobaltate is currently being studied.
  • lithium manganate cannot realize a sufficient discharge capacity, and the battery temperature is low. When it becomes higher, there are problems such as elution of manganese.
  • lithium nickelate has problems such as a lower discharge voltage and lower thermal stability at the end of charging.
  • olivine-type lithium iron phosphate such as metal elution hardly LiFePO 4 has attracted attention as a positive electrode active material can be used in place of lithium cobaltate ing.
  • the olivine-type lithium phosphate is represented by a general formula of LiMPO 4 (M is at least one element selected from Co, Ni, Mn, and Fe), and the battery voltage is arbitrarily determined depending on the type of the constituent metal element M. Can be selected. Further, since the use capacity is relatively high at about 140 to 170 mAh / g, there is an advantage that the battery capacity per unit weight can be increased. And when iron and manganese are selected as M, it has the advantage that the production cost can be greatly reduced because the production amount is large and it is inexpensive.
  • lithium iron phosphate becomes iron phosphate in the charged state, and its structural stability and end-of-charge voltage can be charged almost 100% at the lithium metal standard 3.6V, so it is used as the main component of organic electrolyte. 100% can be charged at 4.2 V or less of the decomposition potential of the cyclic carbonate and the chain carbonate. Therefore, it is expected as a positive electrode active material that can suppress decomposition of the electrolytic solution and has high durability.
  • lithium iron phosphate has a NASICON structure, which is an ionic conductor, and therefore has a poor electronic conductivity and a strong crystal structure. Therefore, lithium ion diffusion is limited, and a one-dimensional diffusion path. Therefore, it is known that the diffusion of lithium ions is poor. Therefore, the material has a high resistance value and is not suitable for battery materials.
  • the surface of lithium iron phosphate particles is coated with a highly conductive carbon material, thereby improving the electronic conductivity, reducing the particle size to 1 ⁇ m or less, shortening the reactive path, and reacting.
  • the technique of making it function as a battery material by devising which raises speed has been reported (patent document 1).
  • JP 2002-110162 A Japanese Patent No. 4183403
  • lithium iron phosphate whose surface is coated with a carbon material there arises a problem that battery characteristics, particularly storage characteristics, deteriorate.
  • the specific surface area of lithium iron phosphate whose surface was coated with nano-level carbon particles was as high as 10 to 30 m 2 / g, so that it easily adsorbs moisture in the atmosphere.
  • the moisture is taken into the pores of the nano-sized carbon material, it is difficult to remove it. Therefore, it is considered that the expected battery characteristics cannot be obtained when water mixed in the lithium ion secondary battery reacts with LiPF 6 as an electrolyte to generate hydrofluoric acid.
  • hydrofluoric acid is produced together with lithium fluoride and trifluorophosphoric acid. Since hydrofluoric acid is a strong acid, iron may be eluted from the olivine Fe positive electrode and a solid electrolyte interface (SEI) that is a protective layer of the negative electrode may be eluted. Therefore, gas is generated during charging, charging / discharging efficiency is reduced, and durability is reduced.
  • SEI solid electrolyte interface
  • Lithium iron phosphate is useful because it has high thermal stability and it is difficult to elute metals at high temperatures. However, since it has low reactivity, it is necessary to increase the specific surface area for application to batteries for electric vehicles. However, as described above, when the specific surface area is large, moisture is easily adsorbed, so that moisture is mixed into the battery and battery characteristics are deteriorated. Therefore, an object of the present invention is to achieve both load characteristics and high-temperature storage characteristics of a lithium ion secondary battery using a lithium iron phosphate positive electrode having a large specific surface area by suppressing the influence of moisture.
  • TTFP tristrifluoroethyl phosphate
  • DMA N-dimethylacetamide
  • NMP n-methylpyrrolidone
  • Non-Patent Document 2 reports that when DMA is used as a part of the mixed solvent, the reaction resistance is increased.
  • EC ethylene carbonate
  • DMA is expected to improve load characteristics as a high dielectric constant solvent.
  • the present invention includes the following.
  • a positive electrode comprising a positive electrode active material represented by: A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; and a non-aqueous electrolyte;
  • a non-aqueous electrolyte secondary battery comprising: The surface of the positive electrode active material is coated with carbon, The non-aqueous electrolyte includes N, N-dimethylacetamide, vinylene carbonate, a supporting salt, and an organic solvent; The non-aqueous electrolyte secondary battery, wherein a content of the N, N-dimethylacetamide is 0.01 to 0.7% by weight of the non-aqueous electrolyte.
  • the amount of carbon covering the surface of the positive electrode active material is 1 to 5% by weight of the carbon-coated positive electrode active material, the specific surface area of the carbon-coated positive electrode active material is 10 to 20 m 2 / g, and the carbon
  • the organic solvent is a mixed solvent of ethylene carbonate and chain carbonate, and the content of the chain carbonate is 70 to 80% by volume of the mixed solvent.
  • a structural diagram of a cylindrical battery is shown. The relationship between DMA content rate and initial resistance value is shown. The relationship between DMA content rate and the capacity maintenance rate after high temperature storage is shown.
  • Nonaqueous electrolyte secondary battery Compositional formula LiFe 1-x M x PO 4 having an olivine type structure: [Where M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo; x is 0 ⁇ x ⁇ 1]
  • a positive electrode comprising a positive electrode active material represented by: A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; and a non-aqueous electrolyte; And the surface of the positive electrode active material is coated with carbon, and the non-aqueous electrolyte contains N, N-dimethylacetamide, vinylene carbonate, a supporting salt, and an organic solvent, The content of N-dimethylacetamide is 0.01 to 0.7% by weight of the nonaqueous electrolyte.
  • the positive electrode active material having an olivine structure has high thermal stability, and the metal does not easily elute at a high temperature. Moreover, it is possible to increase the battery capacity per unit weight, and furthermore, by covering the surface with carbon, the electronic conductivity can be improved. However, when the specific surface area is increased by coating with carbon, moisture in the air is easily adsorbed, and the battery characteristics are deteriorated.
  • the above disadvantage can be overcome by using a non-aqueous electrolyte containing N, N-dimethylacetamide and vinylene carbonate. That is, by combining the positive electrode active material having an olivine type structure and the non-aqueous electrolyte, it is possible to sufficiently exert the function of the positive electrode active material having many advantages over the conventional positive electrode active material. Become.
  • a nonaqueous electrolyte battery having the configuration shown in FIG. 1 can be cited.
  • the nonaqueous electrolyte battery includes a positive electrode in which a positive electrode active material, a carbon material of a conductive additive and a binder are formed in a film shape on an aluminum foil, and a negative electrode active material and a binder in a film shape on a copper foil.
  • the structure is filled with a non-aqueous electrolyte solution in a state where the negative electrodes formed on the surface are opposed and electrically isolated by a separator.
  • the positive and negative electrodes are wound as shown in FIG. 1 and stored in a predetermined metal container.
  • There are two types of battery structures one that is housed in cylindrical and square metal containers as shown in the figure, and the other that is a sheet-like positive and negative electrode layered without being wound.
  • M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo; x is 0 ⁇ x ⁇ 1]
  • the positive electrode containing the positive electrode active material represented by these is used.
  • lithium iron manganese phosphate (composition formula: LiFe 1-x Mn x PO 4 where 0 ⁇ x ⁇ 1) in which a part of iron of lithium iron phosphate is substituted with manganese has the same characteristics as lithium iron phosphate. Since it has, it can be used as a positive electrode active material. In addition, since lithium iron phosphate or a part of iron or manganese of lithium manganese phosphate is replaced with Ti, Zr and / or Mo, and the material having improved reactivity basically has the same characteristics, It can be used as a positive electrode active material.
  • lithium iron phosphate, or lithium manganese phosphate in which iron or a part of manganese is substituted with Ni and / or Co can also be used as a positive electrode active material (hereinafter, a part of iron is another metal).
  • the lithium iron phosphate substituted with the element M may also be simply expressed as “lithium iron phosphate”).
  • lithium manganese phosphate (composition formula: LiMnPO 4 ) in which all of iron of lithium iron phosphate is substituted with manganese also has the same characteristics as lithium iron phosphate, and can be used as a positive electrode active material. .
  • x is preferably 0 ⁇ x ⁇ 0.5, more preferably 0 ⁇ x ⁇ 0.3, and particularly preferably x is 0.
  • M is Mn.
  • the average particle diameter is preferably 0.5 ⁇ m or less.
  • the surface of lithium iron phosphate is coated with carbon.
  • coating means that the entire surface is coated or only a part of the surface is coated.
  • the amount of carbon to be coated (hereinafter also simply referred to as “coated carbon”) is not particularly limited, but 1 to 5 of lithium iron phosphate coated with carbon (hereinafter also simply referred to as “carbon-coated positive electrode active material”). % By weight is preferable, and 1 to 3% by weight is particularly preferable. If the amount of the coated carbon is less than 1% by weight, sufficient electron conductivity cannot be imparted and load characteristics may not be obtained.
  • the amount of coated carbon and electronic conductivity are in a proportional relationship, but if the amount of coated carbon exceeds 5% by weight, the specific surface area also increases, so the amount of moisture adsorbed increases and the storage characteristics can be reduced. There is sex. Note that, with respect to the positive electrode mixture after drying, the amount of coated carbon is preferably 1 to 6% by weight, and particularly preferably 1 to 4% by weight.
  • the specific surface area of the carbon-coated positive electrode active material is preferably 10 to 20 m 2 / g, particularly preferably 10 to 15 m 2 / g, although it depends on the amount of coated carbon.
  • a conductive auxiliary agent having a large specific surface area may be added to the positive electrode mixture separately from the coated carbon.
  • the conductive assistant it is preferable to use a carbon material, and it is particularly preferable to use a carbon material having a specific surface area of 10 m 2 / g or more.
  • the amount of the conductive auxiliary is not particularly limited, but is preferably 3 to 8% by weight of the positive electrode mixture after drying.
  • the content of the positive electrode active material in the positive electrode mixture is preferably 83 to 92% by weight, particularly preferably 85 to 92% by weight. If it is less than 83% by weight, the content of lithium iron phosphate decreases, the content of carbon having a low true density increases, the electrode density decreases, and the energy density may decrease. On the other hand, if it exceeds 92% by weight, the lithium iron phosphate particles are fine and have a high specific surface area, so the adhesiveness between the particles and between the particles and the current collector foil is weakened, and a structure having sufficient strength is formed. Can be difficult.
  • the binder is preferably used in an amount of 4 to 8% by weight with respect to the positive electrode mixture after drying.
  • the binder is not particularly limited, but it is preferable to use polyvinylidene fluoride (PVdF).
  • the water content in the carbon-coated positive electrode active material depends on the specific surface area and the amount of coated carbon.
  • the specific surface area of the carbon-coated positive electrode active material is 10 to 20 m 2 / g and the amount of coated carbon is 3 to 5% by weight of the carbon-coated positive electrode active material, the water content is 500 to 2000 ppm.
  • the water content is almost saturated at 2000 ppm.
  • the moisture content depends on the storage condition of the material, it is preferable that the moisture content is 300 to 1000 ppm in a state where drying under reduced pressure at 80 ° C. is performed for 6 hours.
  • the positive electrode paint was first mixed with lithium iron phosphate and acetylene black, impregnated with NMP, then added with a PVdF binder solution, kneaded, added with NMP, and adjusted to a predetermined viscosity.
  • the prepared positive electrode paint was applied on an aluminum foil in the range of 100 to 160 g / m 2 and dried at 120 ° C. for 15 minutes to obtain a positive electrode coating film. Thereafter, pressing was performed and the electrode density adjusted between 1.6 and 2.2 g / cm 3 was used as the positive electrode.
  • the negative electrode active material contained in the negative electrode is not particularly limited as long as it is a substance capable of occluding and releasing lithium ions, and various substances can be used. For example, it is preferable to use graphite as the negative electrode active material.
  • a predetermined amount of a paint in which graphite material, binder carboxymethyl cellulose and styrene butadiene rubber are dispersed in an aqueous solution is applied on a copper foil, and dried at 100 ° C. for 15 minutes.
  • the coating amount of the negative electrode is preferably 1/2 to 2/3 of the coating amount of the positive electrode. When less than 1/2 of the coating amount of the positive electrode, the charging depth of the negative electrode is too deep, and the cycle and the storage life are reduced. On the other hand, when it is more than 2/3, the energy density becomes small.
  • the electrode density of the negative electrode is preferably in the range of 1.3 to 1.7 g / cm 3 .
  • the ratio of the active material in the positive electrode to the negative electrode varies depending on the type of the negative electrode active material, but in general, (weight of the positive electrode active material) / (weight of the negative electrode active material) is 1.5 to 3.5. Preferably there is. Within this range, the characteristics of the lithium iron phosphate can be used well. However, as an anode active material, an alloy containing an element that can be alloyed with lithium, or an alloy mainly containing such an element, a lithium-containing composite nitride, and other components such as those materials and a carbonaceous material When the composite is used, the capacity of the negative electrode becomes too large at the above ratio, so it is desirable that (weight of the positive electrode active material) / (weight of the negative electrode active material) be 4 to 7.
  • Nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery according to the present invention includes N, N-dimethylacetamide (DMA), vinylene carbonate (VC), a supporting salt, and an organic solvent (other than DMA and VC). including.
  • N, N-dimethylacetamide and vinylene carbonate in combination, the high temperature storage characteristics can be improved while maintaining the load characteristics of the secondary battery.
  • an organic solvent-based liquid electrolyte in which a supporting salt is dissolved in an organic solvent that is, an electrolytic solution, a polymer electrolyte in which the electrolytic solution is held in a polymer, or the like can be used.
  • N, N-dimethylacetamide functions as a hydrofluoric acid inhibitor and can reduce the influence of moisture mixed in the secondary battery.
  • the content of N, N-dimethylacetamide is 0.01 to 0.7% by weight of the nonaqueous electrolyte from the viewpoint of improving high-temperature storage characteristics while maintaining the load characteristics of the secondary battery, and 0.05 It is preferably from 0.7 to 0.7% by weight, particularly preferably from 0.1 to 0.7% by weight. When the content is less than 0.01% by weight, the high-temperature storage characteristics tend to decrease, and when the content exceeds 0.7% by weight, both the load characteristics and the high-temperature storage characteristics tend to decrease.
  • the content of vinylene carbonate is not particularly limited, but from the viewpoint of improving high-temperature storage characteristics while maintaining the load characteristics of the secondary battery, and from the viewpoint of forming good SEI when using a graphite negative electrode, It is preferably 0.5 to 3% by weight, more preferably 0.5 to 2% by weight, and particularly preferably 0.5 to 1.5% by weight. If it exceeds 3% by weight, the service life is improved, but the SEI film is formed too much, and the load characteristics may not be obtained.
  • the organic solvent contained in the non-aqueous electrolyte is not particularly limited, but preferably contains a chain ester from the viewpoint of load characteristics.
  • chain esters include chain carbonates typified by dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), ethyl acetate, and methyl propionate. These chain esters may be used alone or in admixture of two or more.
  • the chain ester may occupy 50% by volume or more of the total organic solvent.
  • an ester having a high induction rate (induction rate: 30 or more) is mixed with the chain ester.
  • induction rate induction rate: 30 or more
  • Specific examples of such esters include, for example, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone, ethylene glycol sulfite, and the like, particularly ethylene carbonate, propylene carbonate, and the like. Cyclic esters are preferred.
  • Such an ester having a high dielectric constant is preferably contained in an amount of 10% by volume or more, particularly 20% by volume or more of the total organic solvent from the viewpoint of discharge capacity. Moreover, from the point of load characteristics, 40 volume% or less is preferable and 30 volume% or less is more preferable.
  • examples of the solvent that can be used in addition to the ester having a high dielectric constant include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, and diethyl ether.
  • a fluorine-containing organic solvent can also be used.
  • the supporting salt dissolved in an organic solvent for example, LiClO 4, LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3 ) 2 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , LiC n F 2n + 1 SO 3 (n ⁇ 2) are used alone or in combination of two or more.
  • LiPF 6 and LiC 4 F 9 SO 3 that can obtain good charge / discharge characteristics are preferably used.
  • the concentration of the supporting salt in the nonaqueous electrolyte is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm 3 , particularly about 0.4 to 1.5 mol / dm 3 .
  • LiPF 6 salt is desirable as a supporting salt because it exhibits good load characteristics.
  • Other supporting salts include selective branches such as LiBF 4 , but it is desirable that LiPF 6 be the main component.
  • the mixed organic solvent preferably contains ethylene carbonate and 70 to 80% by volume of a chain carbonate such as dimethyl carbonate or ethyl methyl carbonate.
  • an aromatic compound may be contained in the nonaqueous electrolytic solution.
  • aromatic compound benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.
  • the separator a separator having sufficient strength and capable of retaining a large amount of non-aqueous electrolyte is preferable. From such a viewpoint, the thickness is 5 to 50 ⁇ m, and polypropylene, polyethylene, a copolymer of propylene and ethylene, etc. A polyolefin microporous film or non-woven fabric is preferably used. In particular, when a thin separator of 5 to 20 ⁇ m is used, the characteristics of the battery are likely to deteriorate during charge / discharge cycles and high-temperature storage, but the lithium iron phosphate of the present invention is excellent in stability. Even if such a thin separator is used, the battery can function stably.
  • the lithium iron phosphate positive electrode has high thermal stability, it is possible to provide a lithium ion battery with high thermal stability even when the above polyolefin separator is used.
  • a functional separator that suppresses thermal shrinkage at 150 ° C. or higher by applying 3 to 5 ⁇ m of an oxide such as magnesium oxide or silicon dioxide, the thermal stability of the lithium ion battery can be further improved. Can do.
  • Lithium iron phosphate represented by the composition formula LiFePO 4 consists of 107 g of LiH 2 PO 4 (manufactured by Aldrich), 175 g of FeC 2 O 4 .2H 2 O (manufactured by Kojundo Kagaku) and 16.4 g of dextrin (sum)
  • the zirconia grinding balls were put into a zirconia pot and mixed with a planetary ball mill (manufactured by Frichche) at a rotation speed of 3 levels for 30 minutes.
  • the mixed powder was put into an alumina crucible and calcined at 400 ° C. for 10 hours under an argon flow of 0.3 L / min.
  • the zirconia grinding balls were put into the zirconia pot, rotated at 1 level for 1 minute, crushed, and again put into the alumina crucible, under an argon flow of 0.3 L / min, 700 After firing for 10 hours at °C, the obtained powder was put into a zirconia pot with zirconia grinding balls, rotated at 1 level for 1 minute, crushed, and screened with a 45 ⁇ m mesh. The desired particle size was obtained by adjusting the particle size. As a result of conducting a composition analysis by ICP measurement (manufactured by Shimadzu Corporation), it was Li 1.0 Fe 0.98 P 1.02 O 4 (carbon content: 3.0 wt%).
  • the coating with amorphous carbon was confirmed using a scanning electron microscope (manufactured by Hitachi, Ltd.) and a powder X-ray diffractometer (manufactured by Rigaku Corporation).
  • a fully automatic BET specific surface area measuring device manufactured by Mountec Co., Ltd.
  • vacuum deaeration was performed as a pretreatment at 300 ° C. for 6 hours, and the nitrogen adsorption amount was determined at a liquid nitrogen (77 ° K) temperature.
  • the moisture content was measured using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Industry Co., Ltd.). As a result, the moisture content after vacuum drying at 80 ° C. was 600 ppm.
  • lithium carbonate may be used instead of lithium hydroxide.
  • carbon coated lithium iron phosphate is 87 wt%, and acetylene is used as a conductive aid other than the coated carbon. 6% by weight of black and 7% by weight of PVdF binder were used.
  • the negative electrode As the negative electrode, a natural graphite material having a particle diameter of 20 ⁇ m was used, and 80 g / m 2 of a negative electrode slurry in which carboxymethyl cellulose and styrene butadiene rubber were dispersed in an aqueous solution as a binder was applied and dried at 100 ° C. Then, it pressed so that it might become 1.5 g / cm ⁇ 3 >, and it cut
  • a 18650 size cylindrical battery (diameter: 18 mm, height: 65 mm) was used.
  • Current collector leads made of aluminum and nickel were welded to the positive electrode and negative electrode cut to a predetermined size, respectively, and the separator was wound and assembled using a polyolefin-based porous film having a thickness of 25 ⁇ m.
  • the DC resistance value was measured by the following method in order to evaluate the load characteristics, the capacity retention rate during high temperature storage was determined, and the storage characteristics were evaluated. .
  • the battery was charged at room temperature with a current value of 0.5 CA, an upper limit voltage of 3.6 V, and a final current value of 0.1 CA. Discharge was conducted up to 2.0 V with a current value of 1.0 CA. The capacity at that time was defined as a discharge depth of 0%, and the capacity when charged again under the same conditions was defined as a charge depth of 100%. After discharging at a discharge depth of 50% and leaving it for 1 hour to obtain an open circuit voltage, 1CA, 2CA and 3CA pulses were discharged at room temperature, and a DC resistance was obtained by linear approximation using a closed circuit voltage at the 5th second.
  • the high-temperature storage characteristics are charged to the fully charged state (charging depth 100%) under the above-mentioned charging conditions, stored in a constant temperature bath at 50 ° C. for 10 days, then measured at 1 CA, and the initial capacity as 100%. The maintenance rate was determined.
  • Example 1 Although an Example and a comparative example are shown, the same positive electrode and negative electrode as Example 1 were used, and the production method and evaluation method of both electrodes were also the same as Example 1.
  • Example 2 In the same procedure as in Example 1, 0.1% by weight of N, N-dimethylacetamide as an HF inhibitor was added to a 1% by weight VC solution of 1M LiPF 6 EC / DMC (1/3) as an electrolytic solution. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
  • Comparative Example 1 In the same procedure as in Example 1, a 1M LiPF 6 EC / DMC (1/3) 1 wt% VC solution was examined as an electrolytic solution. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
  • Comparative Example 2 In the same procedure as in Example 1, as electrolyte, 1 M LiPF 6 EC / DMC (1/3) 1 wt% VC solution containing 1.0 wt% of N, N-dimethylacetamide as HF inhibitor was added. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
  • Comparative Example 3 In the same procedure as in Example 1, an electrolyte was prepared by adding 2.0% by weight of N, N-dimethylacetamide as an HF inhibitor in a 1M LiPF 6 EC / DMC (1/3) 1% by weight VC solution. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
  • Comparative Example 4 In the same procedure as in Example 1, an electrolytic solution in which 0.5% by weight of N, N-dimethylacetamide was added to a 1M LiPF 6 EC / DMC (1/3) solution was examined. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
  • Example 1 The results of Examples and Comparative Examples are summarized in Table 1. Moreover, the direct-current resistance value was obtained by comparing the resistance values with Comparative Example 1 as a reference (1.00). The capacity retention rate was summarized as the high temperature storage characteristics.
  • FIG. 2 shows the relationship between the DMA content and the DC resistance value for Example 1 to Comparative Example 3 in order to see the effect of the DMA content with 1% VC as an additive in the electrolyte.
  • FIG. 3 shows the relationship with the capacity maintenance rate.
  • Example 1 when the VC contains or does not contain VC, the VC itself affects the DC resistance value and the high temperature storage characteristics. The effect is different.
  • the DMA content is 0.5%
  • the dependence of the VC on the increase of the DC resistance value is large. Therefore, when the VC is not contained, the DC resistance value is low.
  • the dependence of VC on the high temperature storage characteristics is high, the capacity maintenance rate decreases when VC is not included. From the above, it has been found that by including both VC and DMA, the DC resistance can be effectively lowered and the capacity retention rate can be improved.
  • N, N-dimethylacetamide (DMA) as a hydrofluoric acid inhibitor in an electrolyte containing VC was reduced to 0.
  • DMA N, N-dimethylacetamide

Abstract

The purpose of the present invention is to establish both load characteristics and high temperature storage characteristics for a lithium ion battery that uses a lithium iron phosphate positive electrode. The battery comprises an olivine lithium iron phosphate positive electrode and negative electrode. A battery that maintains a direct current resistance value and for which both output characteristics and high temperature storage characteristics are established is provided by using a nonaqueous electrolyte containing vinylene carbonate and, as a hydrochloric acid controlling agent, 0.01 - 0.7 wt% of a N,N-dimethylacetamide.

Description

非水電解質二次電池Nonaqueous electrolyte secondary battery
　本発明は、リン酸鉄リチウム正極を用い、高容量化と保存特性を両立した非水電解質二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery that uses a lithium iron phosphate positive electrode and achieves both high capacity and storage characteristics.
　非水電解質電池の正極活物質としては、従来、コバルト酸リチウムが主流となっている。しかし、その原料であるコバルトは産出量が少なく高価であるので、コバルト酸リチウムを用いると電池の生産コストが高くなる。またコバルト酸リチウムを用いた電池は、充電末期に電池温度が上昇した場合における安全性に課題を有している。 Conventionally, lithium cobalt oxide has been the mainstream as a positive electrode active material for non-aqueous electrolyte batteries. However, since cobalt, which is the raw material, is low in production and expensive, the use of lithium cobaltate increases the production cost of the battery. A battery using lithium cobaltate has a problem in safety when the battery temperature rises at the end of charging.
　このため、コバルト酸リチウムに代わる正極活物質として、現在、マンガン酸リチウムやニッケル酸リチウムなどの利用が検討されているが、マンガン酸リチウムは、十分な放電容量が実現できず、また電池温度が高くなるとマンガンが溶出するなどの問題点を有している。他方、ニッケル酸リチウムは放電電圧が低くなるとともに、充電末期での熱的安定性がより低くなるなどの問題点を有している。 For this reason, the use of lithium manganate, lithium nickelate, etc. as a positive electrode active material instead of lithium cobaltate is currently being studied. However, lithium manganate cannot realize a sufficient discharge capacity, and the battery temperature is low. When it becomes higher, there are problems such as elution of manganese. On the other hand, lithium nickelate has problems such as a lower discharge voltage and lower thermal stability at the end of charging.
　このようなこともあって、最近、発熱量が低く高温時の安定性が高く、金属溶出し難いＬｉＦｅＰＯ４などのオリビン型リン酸鉄リチウムがコバルト酸リチウムに代替し得る正極活物質として注目されている。 Such that even recently, high stability at high temperature calorific value is low, olivine-type lithium iron phosphate such as metal elution hardly LiFePO 4 has attracted attention as a positive electrode active material can be used in place of lithium cobaltate ing.
　上記オリビン型リン酸リチウムは、一般式がＬｉＭＰＯ４（ＭはＣｏ、Ｎｉ、Ｍｎ、Ｆｅから選ばれる少なくとも１種以上の元素）で表され、その構成金属元素Ｍの種類によって電池電圧を任意に選定することができる。また、利用容量は１４０から１７０ｍＡｈ／ｇ程度と比較的高いので、単位重量当たりの電池容量を大きくすることができるという利点がある。そして、Ｍとして鉄及びマンガンを選定した場合、産出量が多く安価であるということから、生産コストを大幅に低減させることができるという利点を有している。 The olivine-type lithium phosphate is represented by a general formula of LiMPO 4 (M is at least one element selected from Co, Ni, Mn, and Fe), and the battery voltage is arbitrarily determined depending on the type of the constituent metal element M. Can be selected. Further, since the use capacity is relatively high at about 140 to 170 mAh / g, there is an advantage that the battery capacity per unit weight can be increased. And when iron and manganese are selected as M, it has the advantage that the production cost can be greatly reduced because the production amount is large and it is inexpensive.
　特に、リン酸鉄リチウムは充電状態でリン酸鉄となり、その構造安定性と充電終止電圧がリチウム金属基準の３．６Ｖでほぼ１００％充電することができることから、有機電解液の主成分として使用される環状及び鎖状カーボネートの分解電位の４．２Ｖ以下で１００％充電できる。そのため、電解液の分解が抑制でき、耐久性が高い正極活物質として期待されている。 In particular, lithium iron phosphate becomes iron phosphate in the charged state, and its structural stability and end-of-charge voltage can be charged almost 100% at the lithium metal standard 3.6V, so it is used as the main component of organic electrolyte. 100% can be charged at 4.2 V or less of the decomposition potential of the cyclic carbonate and the chain carbonate. Therefore, it is expected as a positive electrode active material that can suppress decomposition of the electrolytic solution and has high durability.
　しかしながら、リン酸鉄リチウムは本来イオン伝導体であるＮＡＳＩＣＯＮ構造を持つために電子伝導性は乏しく、かつ強固な結晶構造を持つが故に、リチウムイオンの拡散は限定されており、一次元の拡散経路しかないためにリチウムイオンの拡散性も乏しいことが知られている。そのため、抵抗値が高く電池材料には適さない材料であった。 However, lithium iron phosphate has a NASICON structure, which is an ionic conductor, and therefore has a poor electronic conductivity and a strong crystal structure. Therefore, lithium ion diffusion is limited, and a one-dimensional diffusion path. Therefore, it is known that the diffusion of lithium ions is poor. Therefore, the material has a high resistance value and is not suitable for battery materials.
　これらを解決するために、導電性の高い炭素材料でリン酸鉄リチウム粒子表面を被覆させることで、電子導電性を向上させるととともに、粒子サイズを１μｍ以下にし、反応性経路を短縮させ、反応速度を高める工夫をすることで、電池材料として機能させるという技術が報告されている（特許文献１）。 In order to solve these problems, the surface of lithium iron phosphate particles is coated with a highly conductive carbon material, thereby improving the electronic conductivity, reducing the particle size to 1 μm or less, shortening the reactive path, and reacting. The technique of making it function as a battery material by devising which raises speed has been reported (patent document 1).
特開２００２－１１０１６２号JP 2002-110162 A 特許第４１８３４０３号明細書Japanese Patent No. 4183403
　しかしながら、表面を炭素材料で被覆したリン酸鉄リチウムを使用した場合、電池特性、特に保存特性が低下するという問題が生じる。本発明者らがこの問題について検討したところ、ナノレベルの炭素粒子で表面を被覆したリン酸鉄リチウムの比表面積は１０～３０ｍ２／ｇと高くなるため、大気中の水分を容易に吸着してしまい、更にその水分はナノサイズの炭素材料の細孔に取り込まれるため、取り除くことは困難となる。従って、リチウムイオン二次電池に混入した水分が電解質のＬｉＰＦ６と反応し、フッ酸が生成することによって、期待する電池特性が得られないと考えられる。 However, when lithium iron phosphate whose surface is coated with a carbon material is used, there arises a problem that battery characteristics, particularly storage characteristics, deteriorate. When the present inventors examined this problem, the specific surface area of lithium iron phosphate whose surface was coated with nano-level carbon particles was as high as 10 to 30 m 2 / g, so that it easily adsorbs moisture in the atmosphere. Furthermore, since the moisture is taken into the pores of the nano-sized carbon material, it is difficult to remove it. Therefore, it is considered that the expected battery characteristics cannot be obtained when water mixed in the lithium ion secondary battery reacts with LiPF 6 as an electrolyte to generate hydrofluoric acid.
　リチウムイオン二次電池に水分が混入すると、水分とＬｉＰＦ６が式（１）： 
　　ＬｉＰＦ６　＋　Ｈ２Ｏ　→　ＬｉＦ　＋　ＰＦ３Ｏ　＋　ＨＦ　　（１）
のように反応し、フッ化リチウムと三フッ化リン酸とともに、フッ酸が生成する。フッ酸は強酸であるため、オリビンＦｅ正極から鉄を溶出させるとともに、負極の保護層である固体電解質界面（Ｓｏｌｉｄ Ｅｌｅｃｔｒｏｌｙｔｅ Ｉｎｔｅｒｆａｃｅ：ＳＥＩ）を溶出させる可能性がある。そのため、充電時にガスが発生し、充放電効率が低下し、耐久性が低下する。 When water is mixed in the lithium ion secondary battery, the water and LiPF 6 are expressed by the formula (1):
LiPF 6 + H 2 O → LiF + PF 3 O + HF (1)
Thus, hydrofluoric acid is produced together with lithium fluoride and trifluorophosphoric acid. Since hydrofluoric acid is a strong acid, iron may be eluted from the olivine Fe positive electrode and a solid electrolyte interface (SEI) that is a protective layer of the negative electrode may be eluted. Therefore, gas is generated during charging, charging / discharging efficiency is reduced, and durability is reduced.
　リン酸鉄リチウムは熱的安定性が高く、高温時に金属が溶出し難いために有用であるが、反応性が低いために電気自動車用電池へ適用するには比表面積を大きくする必要がある。しかしながら、上記の通り、比表面積が大きいと水分が容易に吸着するため、電池内へ水分が混入し、電池特性が低下してしまう。そこで、本発明は、水分の影響を抑制することによって、比表面積の大きいリン酸鉄リチウム正極を用いたリチウムイオン二次電池の負荷特性と高温保存特性を両立させることを目的としている。 鉄 Lithium iron phosphate is useful because it has high thermal stability and it is difficult to elute metals at high temperatures. However, since it has low reactivity, it is necessary to increase the specific surface area for application to batteries for electric vehicles. However, as described above, when the specific surface area is large, moisture is easily adsorbed, so that moisture is mixed into the battery and battery characteristics are deteriorated. Therefore, an object of the present invention is to achieve both load characteristics and high-temperature storage characteristics of a lithium ion secondary battery using a lithium iron phosphate positive electrode having a large specific surface area by suppressing the influence of moisture.
　従来から、高温保存特性を改善するために電解液添加剤としてビニレンカーボネート（ＶＣ）を使用し、負極上に被膜を形成させることが知られており、ＶＣの含有率を増やすことで、高温保存特性が向上することが報告されている。しかしながら、この方法では負極に被膜が形成されることから、電解液から負極活物質中へのリチウムイオンの移動が阻害され、直流抵抗値が上昇するという問題が生じる。 Conventionally, it has been known that vinylene carbonate (VC) is used as an electrolytic solution additive to improve high-temperature storage characteristics, and a film is formed on the negative electrode. By increasing the content of VC, high-temperature storage is achieved. It has been reported that the properties are improved. However, in this method, since a film is formed on the negative electrode, there is a problem in that the movement of lithium ions from the electrolytic solution into the negative electrode active material is hindered and the direct current resistance value increases.
　一方、電解液中の水分の影響を除去するためのフッ酸抑制剤としては、トリストリフルオロエチルフォスフェイト（ＴＴＦＰ）、Ｎ，Ｎ－ジメチルアセトアミド（ＤＭＡ）、及びｎ－メチルピロリドン（ＮＭＰ）が知られている（非特許文献１及び２）。これらのフッ酸抑制剤は、コバルト置換ニッケル酸リチウムＬｉＮｉ０．８Ｃｏ０．２Ｏ２正極と黒鉛負極とを組み合わせた電池系において、支持塩としてＬｉＰＦ６を用いた電解液中でのＰＦ５イオンと水分との反応を抑制してフッ酸（ＨＦ）の生成を抑制し、ビニレンカーボネート（ＶＣ）と同様に、高温保存特性を改善させると報告されている。一方、非特許文献２ではＤＭＡを混合溶媒の一部として使用した場合、反応抵抗を増大させると報告されている。特許文献２では、エチレンカーボネート(ＥＣ)と同じく、ＤＭＡが高誘電率溶媒として負荷特性を改善させることが期待されている。このように、フッ酸抑制剤の電池特性への効能は、適用する電池系、フッ酸抑制剤の種類、電解液中の含有率によって異なる。そのため、フッ酸抑制剤の効能を予測することは非常に困難である。 On the other hand, as a hydrofluoric acid inhibitor for removing the influence of moisture in the electrolyte, tristrifluoroethyl phosphate (TTFP), N, N-dimethylacetamide (DMA), and n-methylpyrrolidone (NMP) are available. It is known (Non-Patent Documents 1 and 2). These hydrofluoric acid inhibitors are PF 5 in an electrolyte solution using LiPF 6 as a supporting salt in a battery system in which a cobalt-substituted lithium nickelate LiNi 0.8 Co 0.2 O 2 positive electrode and a graphite negative electrode are combined. It has been reported that the reaction between ions and moisture is suppressed to suppress the formation of hydrofluoric acid (HF), and the high-temperature storage characteristics are improved as in the case of vinylene carbonate (VC). On the other hand, Non-Patent Document 2 reports that when DMA is used as a part of the mixed solvent, the reaction resistance is increased. In Patent Document 2, as with ethylene carbonate (EC), DMA is expected to improve load characteristics as a high dielectric constant solvent. Thus, the effect of the hydrofluoric acid inhibitor on the battery characteristics varies depending on the battery system to be applied, the type of hydrofluoric acid inhibitor, and the content in the electrolytic solution. Therefore, it is very difficult to predict the efficacy of the hydrofluoric acid inhibitor.
　しかしながら、本発明者らが、リン酸鉄リチウム正極を用いたリチウムイオン二次電池の負荷特性と高温保存特性を両立させることを目的に鋭意検討した結果、非電解質中にビニレンカーボネート、及び所定量のフッ酸抑制剤のＮ，Ｎ－ジメチルアセトアミドを添加することにより、上述の目的を達成できることを見出した。 However, as a result of intensive studies aimed at achieving both load characteristics and high-temperature storage characteristics of lithium ion secondary batteries using lithium iron phosphate positive electrodes, the present inventors have found that vinylene carbonate and a predetermined amount are contained in the non-electrolyte. It was found that the above-mentioned object can be achieved by adding N, N-dimethylacetamide, a hydrofluoric acid inhibitor.
　すなわち、本発明は以下を包含する。 That is, the present invention includes the following.
（１）オリビン型構造を有する組成式ＬｉＦｅ１－ＸＭｘＰＯ４：
[式中、
　ＭはＮｉ、Ｃｏ、Ｍｎ、Ｔｉ、Ｚｒ、及びＭｏからなる群から選択される少なくとも１種であり、
　ｘは０≦ｘ＜１である]
で表される正極活物質を含む正極；
　リチウムイオンを吸蔵放出可能な負極活物質を含む負極；並びに
　非水電解質；
を有する非水電解質二次電池であって、
　前記正極活物質の表面が炭素で被覆されており、
　前記非水電解質がＮ，Ｎ－ジメチルアセトアミド、ビニレンカーボネート、支持塩、及び有機溶媒を含み、
　前記Ｎ，Ｎ－ジメチルアセトアミドの含有量が前記非水電解質の０．０１～０．７重量％である、前記非水電解質二次電池。 (1) Composition formula LiFe 1-X M x PO 4 having an olivine type structure:
[Where
M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo;
x is 0 ≦ x <1]
A positive electrode comprising a positive electrode active material represented by:
A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; and a non-aqueous electrolyte;
A non-aqueous electrolyte secondary battery comprising:
The surface of the positive electrode active material is coated with carbon,
The non-aqueous electrolyte includes N, N-dimethylacetamide, vinylene carbonate, a supporting salt, and an organic solvent;
The non-aqueous electrolyte secondary battery, wherein a content of the N, N-dimethylacetamide is 0.01 to 0.7% by weight of the non-aqueous electrolyte.
（２）正極活物質の表面を被覆する炭素の量が炭素被覆正極活物質の１～５重量％であり、前記炭素被覆正極活物質の比表面積が１０～２０ｍ２／ｇであり、前記炭素被覆正極活物質が３００～１０００ｐｐｍの水分を含む、（１）に記載の非水電解質二次電池。 (2) The amount of carbon covering the surface of the positive electrode active material is 1 to 5% by weight of the carbon-coated positive electrode active material, the specific surface area of the carbon-coated positive electrode active material is 10 to 20 m 2 / g, and the carbon The nonaqueous electrolyte secondary battery according to (1), wherein the coated positive electrode active material contains 300 to 1000 ppm of water.
（３）ビニレンカーボネートの含有量が非水電解質の０．５～３重量％である、（１）または（２）に記載の非水電解質二次電池。 (3) The nonaqueous electrolyte secondary battery according to (1) or (2), wherein the content of vinylene carbonate is 0.5 to 3% by weight of the nonaqueous electrolyte.
（４）ｘが０である、（１）～（３）のいずれかに記載の非水電解質二次電池。 (4) The nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein x is 0.
（５）リチウムイオンを吸蔵放出可能な負極活物質が黒鉛である、（１）～（４）のいずれかに記載の非水電解質二次電池。 (5) The nonaqueous electrolyte secondary battery according to any one of (1) to (4), wherein the negative electrode active material capable of occluding and releasing lithium ions is graphite.
（６）支持塩がＬｉＰＦ６である、（１）～（５）のいずれかに記載の非水電解質二次電池。 (6) The nonaqueous electrolyte secondary battery according to any one of (1) to (5), wherein the supporting salt is LiPF 6 .
（７）有機溶媒がエチレンカーボネートと鎖状カーボネートとの混合溶媒であり、前記鎖状カーボネートの含有量が前記混合溶媒の７０～８０体積％である、（１）～（６）のいずれかに記載の非水電解質二次電池。 (7) The organic solvent is a mixed solvent of ethylene carbonate and chain carbonate, and the content of the chain carbonate is 70 to 80% by volume of the mixed solvent. The nonaqueous electrolyte secondary battery as described.
　本発明を適用することより、リン酸鉄リチウム正極の反応抵抗の上昇を抑えつつ、含まれる水分の影響を低減できることから、リン酸鉄リチウム正極を用いた電池の負荷特性を維持しつつ、高温保存特性を向上させることができる。 By applying the present invention, it is possible to reduce the influence of moisture contained while suppressing an increase in the reaction resistance of the lithium iron phosphate positive electrode, while maintaining the load characteristics of the battery using the lithium iron phosphate positive electrode while maintaining a high temperature. Storage characteristics can be improved.
円筒型電池の構造図を示す。A structural diagram of a cylindrical battery is shown. ＤＭＡ含有率と初期抵抗値との関係を示す。The relationship between DMA content rate and initial resistance value is shown. ＤＭＡ含有率と高温保存後の容量維持率との関係を示す。The relationship between DMA content rate and the capacity maintenance rate after high temperature storage is shown.
　以下、本発明について詳細に説明する。 Hereinafter, the present invention will be described in detail.
　本発明に係る非水電解質二次電池は、
　オリビン型構造を有する組成式ＬｉＦｅ１－ｘＭｘＰＯ４：
[式中、
　ＭはＮｉ、Ｃｏ、Ｍｎ、Ｔｉ、Ｚｒ、及びＭｏからなる群から選択される少なくとも１種であり、
　ｘは０≦ｘ＜１である]
で表される正極活物質を含む正極；
　リチウムイオンを吸蔵放出可能な負極活物質を含む負極；並びに
　非水電解質；
を有するものであり、更に、前記正極活物質の表面が炭素で被覆されており、前記非水電解質が、Ｎ，Ｎ－ジメチルアセトアミド、ビニレンカーボネート、支持塩、及び有機溶媒を含み、前記Ｎ，Ｎ－ジメチルアセトアミドの含有量が前記非水電解質の０．０１～０．７重量％である。 Nonaqueous electrolyte secondary battery according to the present invention,
Compositional formula LiFe 1-x M x PO 4 having an olivine type structure:
[Where
M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo;
x is 0 ≦ x <1]
A positive electrode comprising a positive electrode active material represented by:
A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; and a non-aqueous electrolyte;
And the surface of the positive electrode active material is coated with carbon, and the non-aqueous electrolyte contains N, N-dimethylacetamide, vinylene carbonate, a supporting salt, and an organic solvent, The content of N-dimethylacetamide is 0.01 to 0.7% by weight of the nonaqueous electrolyte.
　従来の正極活物質と比べて、オリビン型構造を有する前記正極活物質は熱的安定性が高く、高温時に金属が溶出し難い。また、単位重量当たりの電池容量を大きくすることが可能であり、更に、その表面を炭素で被覆することにより、電子導電性を向上させることもできる。しかし、炭素による被覆で比表面積が増大すると空気中の水分を容易に吸着し、電池特性が低下するという欠点が存在した。しかし、Ｎ，Ｎ－ジメチルアセトアミドとビニレンカーボネートを含む非水電解質を使用することで前記欠点を克服することができる。つまり、オリビン型構造を有する前記正極活物質と前記非水電解質とを組み合わせることにより、従来の正極活物質に比べて多くの利点を有する前記正極活物質の機能を十分に発揮させることが可能となる。 Compared with a conventional positive electrode active material, the positive electrode active material having an olivine structure has high thermal stability, and the metal does not easily elute at a high temperature. Moreover, it is possible to increase the battery capacity per unit weight, and furthermore, by covering the surface with carbon, the electronic conductivity can be improved. However, when the specific surface area is increased by coating with carbon, moisture in the air is easily adsorbed, and the battery characteristics are deteriorated. However, the above disadvantage can be overcome by using a non-aqueous electrolyte containing N, N-dimethylacetamide and vinylene carbonate. That is, by combining the positive electrode active material having an olivine type structure and the non-aqueous electrolyte, it is possible to sufficiently exert the function of the positive electrode active material having many advantages over the conventional positive electrode active material. Become.
　本発明の一実施形態としては、図１に示す構成の非水電解質電池を挙げることができる。非水電解質電池は、アルミ箔上に正極活物質と導電助剤の炭素材料とバインダの構成物が膜状に形成された正極と、銅箔上に負極活物質とバインダの構成物が膜状に形成された負極が対向し、セパレータで電気的に隔離された状態で、非水電解質溶液で満たされた構造をしている。正負極は図１に示すように捲回され、所定の金属製容器に収納されている。電池構造は、図に示すような円筒型と角型の金属製容器に収容されているものと、捲回せずに、シート状の正負極電極を積層させた構造があるが、本発明は図１に示す電池構造に限定されるものではない。 As an embodiment of the present invention, a nonaqueous electrolyte battery having the configuration shown in FIG. 1 can be cited. The nonaqueous electrolyte battery includes a positive electrode in which a positive electrode active material, a carbon material of a conductive additive and a binder are formed in a film shape on an aluminum foil, and a negative electrode active material and a binder in a film shape on a copper foil. The structure is filled with a non-aqueous electrolyte solution in a state where the negative electrodes formed on the surface are opposed and electrically isolated by a separator. The positive and negative electrodes are wound as shown in FIG. 1 and stored in a predetermined metal container. There are two types of battery structures, one that is housed in cylindrical and square metal containers as shown in the figure, and the other that is a sheet-like positive and negative electrode layered without being wound. The battery structure shown in FIG.
１．正極
　本発明に係る非水電解質二次電池では、オリビン型構造を有する組成式ＬｉＦｅ１－ＸＭｘＰＯ４：
[式中、
　ＭはＮｉ、Ｃｏ、Ｍｎ、Ｔｉ、Ｚｒ、及びＭｏからなる群から選択される少なくとも１種であり、
　ｘは０≦ｘ＜１である]
で表される正極活物質を含む正極を使用する。 1. In the nonaqueous electrolyte secondary battery according to the present invention, the composition formula LiFe 1-X M x PO 4 having an olivine structure:
[Where
M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo;
x is 0 ≦ x <1]
The positive electrode containing the positive electrode active material represented by these is used.
　例えば、リン酸鉄リチウムの鉄の一部をマンガンに置換したリン酸鉄マンガンリチウム（組成式：ＬｉＦｅ１－ｘＭｎｘＰＯ４　式中０＜ｘ＜１）はリン酸鉄リチウムと同じ特徴を持っていることから、正極活物質として使用することができる。また、リン酸鉄リチウム、またはリン酸マンガンリチウムの鉄またはマンガンの一部をＴｉ、Ｚｒ及び／またはＭｏで置換し、反応性を向上させた材料も基本的には同じ特徴を持つことから、正極活物質として使用することができる。更に、リン酸鉄リチウム、またはリン酸マンガンリチウムの鉄またはマンガンの一部をＮｉ及び／またはＣｏで置換したものも正極活物質として使用することができる（以下、鉄の一部を他の金属元素Ｍで置換したリン酸鉄リチウムも、単に「リン酸鉄リチウム」と表現する場合がある）。なお、リン酸鉄リチウムの鉄の全てをマンガンに置換したリン酸マンガンリチウム（組成式：ＬｉＭｎＰＯ４）もリン酸鉄リチウムと同じ特徴を持っていることから、正極活物質として使用することができる。 For example, lithium iron manganese phosphate (composition formula: LiFe 1-x Mn x PO 4 where 0 <x <1) in which a part of iron of lithium iron phosphate is substituted with manganese has the same characteristics as lithium iron phosphate. Since it has, it can be used as a positive electrode active material. In addition, since lithium iron phosphate or a part of iron or manganese of lithium manganese phosphate is replaced with Ti, Zr and / or Mo, and the material having improved reactivity basically has the same characteristics, It can be used as a positive electrode active material. Further, lithium iron phosphate, or lithium manganese phosphate in which iron or a part of manganese is substituted with Ni and / or Co can also be used as a positive electrode active material (hereinafter, a part of iron is another metal). The lithium iron phosphate substituted with the element M may also be simply expressed as “lithium iron phosphate”). Note that lithium manganese phosphate (composition formula: LiMnPO 4 ) in which all of iron of lithium iron phosphate is substituted with manganese also has the same characteristics as lithium iron phosphate, and can be used as a positive electrode active material. .
　生産コストの観点からは、ｘは０≦ｘ≦０．５であることが好ましく、０≦ｘ≦０．３であることがより好ましく、ｘが０であることが特に好ましい。また、鉄の一部を置換する場合には、ＭがＭｎであることが好ましい。 From the viewpoint of production cost, x is preferably 0 ≦ x ≦ 0.5, more preferably 0 ≦ x ≦ 0.3, and particularly preferably x is 0. Moreover, when substituting a part of iron, it is preferable that M is Mn.
　リン酸鉄リチウムは反応活性化するために、平均粒子径が０．５μｍ以下であることが好ましい。 In order to activate the reaction of lithium iron phosphate, the average particle diameter is preferably 0.5 μm or less.
　電子導電性を付与するために、リン酸鉄リチウムの表面は炭素で被覆されている。ここで、「被覆」とは表面全体が被覆されていること、及び表面の一部のみが被覆されていることのいずれをも意味する。被覆する炭素（以下、単に「被覆炭素」ともいう）の量に特に制限はないが、炭素で被覆されたリン酸鉄リチウム（以下、単に「炭素被覆正極活物質」ともいう）の１～５重量％であることが好ましく、１～３重量％であることが特に好ましい。被覆炭素の量が１重量％未満であると、十分な電子伝導性を付与することができず、負荷特性が得られない可能性がある。一方、被覆炭素の量と電子導電性は比例関係にあるが、被覆炭素の量が５重量％を超えると比表面積も大きくなるため、吸着される水分量が多くなり、保存特性は低下する可能性がある。なお、乾燥後の正極合剤に対しては、被覆炭素の量が１～６重量％であることが好ましく、１～４重量％であることが特に好ましい。 In order to impart electronic conductivity, the surface of lithium iron phosphate is coated with carbon. Here, “coating” means that the entire surface is coated or only a part of the surface is coated. The amount of carbon to be coated (hereinafter also simply referred to as “coated carbon”) is not particularly limited, but 1 to 5 of lithium iron phosphate coated with carbon (hereinafter also simply referred to as “carbon-coated positive electrode active material”). % By weight is preferable, and 1 to 3% by weight is particularly preferable. If the amount of the coated carbon is less than 1% by weight, sufficient electron conductivity cannot be imparted and load characteristics may not be obtained. On the other hand, the amount of coated carbon and electronic conductivity are in a proportional relationship, but if the amount of coated carbon exceeds 5% by weight, the specific surface area also increases, so the amount of moisture adsorbed increases and the storage characteristics can be reduced. There is sex. Note that, with respect to the positive electrode mixture after drying, the amount of coated carbon is preferably 1 to 6% by weight, and particularly preferably 1 to 4% by weight.
　炭素被覆正極活物質の比表面積は、被覆炭素の量などに依存するが、１０～２０ｍ２／ｇであることが好ましく、１０～１５ｍ２／ｇであることが特に好ましい。 The specific surface area of the carbon-coated positive electrode active material is preferably 10 to 20 m 2 / g, particularly preferably 10 to 15 m 2 / g, although it depends on the amount of coated carbon.
　十分な電子導電性を付与するために、被覆炭素とは別に、比表面積の大きな導電助剤を正極合剤中に加えてもよい。導電助剤としては炭素材料を使用することが好ましく、比表面積が１０ｍ２／ｇ以上の炭素材料を使用することが特に好ましい。導電助剤の量は特に制限されないが、乾燥後の正極合剤の３～８重量％であることが好ましい。 In order to give sufficient electronic conductivity, a conductive auxiliary agent having a large specific surface area may be added to the positive electrode mixture separately from the coated carbon. As the conductive assistant, it is preferable to use a carbon material, and it is particularly preferable to use a carbon material having a specific surface area of 10 m 2 / g or more. The amount of the conductive auxiliary is not particularly limited, but is preferably 3 to 8% by weight of the positive electrode mixture after drying.
　正極合剤中の正極活物質の含有率は８３～９２重量％であることが好ましく、８５～９２重量％であることが特に好ましい。８３重量％未満ではリン酸鉄リチウムの含有率が少なくなるとともに、真密度の低い炭素の含有率が増え、電極密度が下がり、エネルギー密度が下がる可能性がある。一方、９２重量％を超えると、リン酸鉄リチウムの粒子が細かく高比表面積であるために、粒子間及び粒子と集電箔界面の接着性が弱まり、十分な強度を持つ構造体を形成することが困難となる可能性がある。 The content of the positive electrode active material in the positive electrode mixture is preferably 83 to 92% by weight, particularly preferably 85 to 92% by weight. If it is less than 83% by weight, the content of lithium iron phosphate decreases, the content of carbon having a low true density increases, the electrode density decreases, and the energy density may decrease. On the other hand, if it exceeds 92% by weight, the lithium iron phosphate particles are fine and have a high specific surface area, so the adhesiveness between the particles and between the particles and the current collector foil is weakened, and a structure having sufficient strength is formed. Can be difficult.
　粒子間及び集電箔界面の密着強度を保持するためには、バインダを、乾燥後の正極合剤に対して、４～８重量％の量で使用することが好ましい。バインダとしては、特に制限されないが、ポリフッ化ビニリデン（ＰＶｄＦ）を使用することが好ましい。 In order to maintain the adhesion strength between the particles and at the current collector foil interface, the binder is preferably used in an amount of 4 to 8% by weight with respect to the positive electrode mixture after drying. The binder is not particularly limited, but it is preferable to use polyvinylidene fluoride (PVdF).
　炭素被覆正極活物質中の水分含有量は比表面積及び被覆炭素の量に依存する。炭素被覆正極活物質の比表面積が１０～２０ｍ２／ｇであり、被覆炭素の量が炭素被覆正極活物質の３～５重量％である場合、水分含有量は５００～２０００ｐｐｍとなる。水分含有量は少ないほど良いが、表面を炭素で被覆したリン酸鉄リチウム粒子は、大気中の水分を吸着しやすく、５００ｐｐｍ以上の水分を含む。一方で、被覆炭素の量にもよるが、水分量は２０００ｐｐｍでほぼ飽和する。それ以上の水分を含む場合には、リン酸鉄リチウムは水分と反応し、リン化鉄などが生成するため、その正極活物質としての特性は低下してしまう。また、水分含有量は材料の保管状況によって左右されることから、８０℃で減圧乾燥を６時間実施した状態で、水分含有量が３００～１０００ｐｐｍであるものが好ましい。 The water content in the carbon-coated positive electrode active material depends on the specific surface area and the amount of coated carbon. When the specific surface area of the carbon-coated positive electrode active material is 10 to 20 m 2 / g and the amount of coated carbon is 3 to 5% by weight of the carbon-coated positive electrode active material, the water content is 500 to 2000 ppm. The lower the moisture content, the better, but the lithium iron phosphate particles whose surface is coated with carbon are easy to adsorb moisture in the atmosphere and contain 500 ppm or more of moisture. On the other hand, depending on the amount of coated carbon, the water content is almost saturated at 2000 ppm. When it contains more moisture, lithium iron phosphate reacts with moisture to produce iron phosphide and the like, and its properties as a positive electrode active material are degraded. In addition, since the moisture content depends on the storage condition of the material, it is preferable that the moisture content is 300 to 1000 ppm in a state where drying under reduced pressure at 80 ° C. is performed for 6 hours.
　正極塗料は、はじめにリン酸鉄リチウムとアセチレンブラックを混合し、ＮＭＰを加えて含浸させた後、ＰＶｄＦバインダ溶液を加えて、混練し、ＮＭＰを追加し、所定の粘度に調整した。作製した正極塗料をアルミニウム箔上に１００～１６０ｇ／ｍ２の範囲で塗布して、１２０℃で１５分間乾燥させて正極塗膜とした。その後、プレスし、電極密度を１．６～２．２ｇ／ｃｍ３の間で調整したものを正極とした。 The positive electrode paint was first mixed with lithium iron phosphate and acetylene black, impregnated with NMP, then added with a PVdF binder solution, kneaded, added with NMP, and adjusted to a predetermined viscosity. The prepared positive electrode paint was applied on an aluminum foil in the range of 100 to 160 g / m 2 and dried at 120 ° C. for 15 minutes to obtain a positive electrode coating film. Thereafter, pressing was performed and the electrode density adjusted between 1.6 and 2.2 g / cm 3 was used as the positive electrode.
２．負極
　負極に含まれる負極活物質としては、リチウムイオンを吸蔵放出可能な物質であれば特に制限されず、様々な物質を使用することができる。例えば、負極活物質として黒鉛を使用することが好ましい。 2. The negative electrode active material contained in the negative electrode is not particularly limited as long as it is a substance capable of occluding and releasing lithium ions, and various substances can be used. For example, it is preferable to use graphite as the negative electrode active material.
　本発明の一実施形態としては、黒鉛材料と、結着剤であるカルボキシメチルセルロースとスチレンブタジエンゴムを水溶液中に分散した塗料を、銅箔上に所定量を塗布し、１００℃で１５分間乾燥させたものを負極として使用する。負極の塗布量は正極の塗布量の１／２～２／３であることが好ましい。正極の塗布量の１／２より少ないと、負極の充電深度が深すぎて、サイクル及び保存寿命が低下する。一方、２／３より多いとエネルギー密度が小さくなる。負極の電極密度は１．３～１．７ｇ／ｃｍ３の範囲が好ましい。１．３ｇ／ｃｍ３より小さいとエネルギー密度が小さくなる。一方、１．７ｇ／ｃｍ３より大きいと電極内空孔が少なくなり、電解液の含有量が減り、リチウム反応量が減り、電流が流れ難くなる。 As one embodiment of the present invention, a predetermined amount of a paint in which graphite material, binder carboxymethyl cellulose and styrene butadiene rubber are dispersed in an aqueous solution is applied on a copper foil, and dried at 100 ° C. for 15 minutes. Is used as the negative electrode. The coating amount of the negative electrode is preferably 1/2 to 2/3 of the coating amount of the positive electrode. When less than 1/2 of the coating amount of the positive electrode, the charging depth of the negative electrode is too deep, and the cycle and the storage life are reduced. On the other hand, when it is more than 2/3, the energy density becomes small. The electrode density of the negative electrode is preferably in the range of 1.3 to 1.7 g / cm 3 . If it is less than 1.3 g / cm 3 , the energy density becomes small. On the other hand, when it is larger than 1.7 g / cm 3 , the number of vacancies in the electrode decreases, the content of the electrolytic solution decreases, the amount of lithium reaction decreases, and the current hardly flows.
　正極と負極における活物質の比率としては、負極活物質の種類によっても異なるが、一般的には、（正極活物質の重量）／（負極活物質の重量）が１．５～３．５であることが好ましい。この範囲内であると、上記リン酸鉄リチウムの特性をうまく利用することができる。ただし、負極活物質として、リチウムとの合金化が可能な元素を含む合金、あるいはそれらの元素を主体として含む合金、リチウム含有複合窒化物、及びそれらの材料と炭素質材料などの他の構成要素との複合体を用いる場合には、上記比率では負極の容量が大きくなりすぎるため、（正極活物質の重量）／（負極活物質の重量）を４～７とするのが望ましい。 The ratio of the active material in the positive electrode to the negative electrode varies depending on the type of the negative electrode active material, but in general, (weight of the positive electrode active material) / (weight of the negative electrode active material) is 1.5 to 3.5. Preferably there is. Within this range, the characteristics of the lithium iron phosphate can be used well. However, as an anode active material, an alloy containing an element that can be alloyed with lithium, or an alloy mainly containing such an element, a lithium-containing composite nitride, and other components such as those materials and a carbonaceous material When the composite is used, the capacity of the negative electrode becomes too large at the above ratio, so it is desirable that (weight of the positive electrode active material) / (weight of the negative electrode active material) be 4 to 7.
３．非水電解質
　本発明に係る非水電解質二次電池に使用する非水電解質は、Ｎ，Ｎ－ジメチルアセトアミド（ＤＭＡ）、ビニレンカーボネート（ＶＣ）、支持塩、及び（ＤＭＡ及びＶＣ以外の）有機溶媒を含む。Ｎ，Ｎ－ジメチルアセトアミドとビニレンカーボネートを併用することで二次電池の負荷特性を維持しつつ、高温保存特性を向上させることができる。非水電解質としては、有機溶媒に支持塩を溶解させた有機溶媒系の液状電解質すなわち電解液や、前記電解液をポリマー中に保持させたポリマー電解質などを用いることができる。 3. Nonaqueous electrolyte The nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery according to the present invention includes N, N-dimethylacetamide (DMA), vinylene carbonate (VC), a supporting salt, and an organic solvent (other than DMA and VC). including. By using N, N-dimethylacetamide and vinylene carbonate in combination, the high temperature storage characteristics can be improved while maintaining the load characteristics of the secondary battery. As the non-aqueous electrolyte, an organic solvent-based liquid electrolyte in which a supporting salt is dissolved in an organic solvent, that is, an electrolytic solution, a polymer electrolyte in which the electrolytic solution is held in a polymer, or the like can be used.
　Ｎ，Ｎ－ジメチルアセトアミドはフッ酸抑制剤として機能し、二次電池内に混入した水分の影響を小さくすることができる。Ｎ，Ｎ－ジメチルアセトアミドの含有量は、二次電池の負荷特性を維持しつつ、高温保存特性を向上させる観点から、非水電解質の０．０１～０．７重量％であり、０．０５～０．７重量％であることが好ましく、０．１～０．７重量％であることが特に好ましい。含有量が０．０１重量％未満であると、高温保存特性が低下する傾向にあり、０．７重量％を超えると、負荷特性及び高温保存特性が共に低下する傾向にある。 N, N-dimethylacetamide functions as a hydrofluoric acid inhibitor and can reduce the influence of moisture mixed in the secondary battery. The content of N, N-dimethylacetamide is 0.01 to 0.7% by weight of the nonaqueous electrolyte from the viewpoint of improving high-temperature storage characteristics while maintaining the load characteristics of the secondary battery, and 0.05 It is preferably from 0.7 to 0.7% by weight, particularly preferably from 0.1 to 0.7% by weight. When the content is less than 0.01% by weight, the high-temperature storage characteristics tend to decrease, and when the content exceeds 0.7% by weight, both the load characteristics and the high-temperature storage characteristics tend to decrease.
　ビニレンカーボネートの含有量は特に制限されないが、二次電池の負荷特性を維持しつつ、高温保存特性を向上させる観点、及び黒鉛負極を用いる場合に良好なＳＥＩを形成させる観点から、非水電解質の０．５～３重量％であることが好ましく、０．５～２重量％であることがより好ましく、０．５～１．５重量％であることが特に好ましい。３重量％を超えると、寿命は向上するが、ＳＥＩ被膜が形成されすぎて、負荷特性が得られなくなる可能性がある。 The content of vinylene carbonate is not particularly limited, but from the viewpoint of improving high-temperature storage characteristics while maintaining the load characteristics of the secondary battery, and from the viewpoint of forming good SEI when using a graphite negative electrode, It is preferably 0.5 to 3% by weight, more preferably 0.5 to 2% by weight, and particularly preferably 0.5 to 1.5% by weight. If it exceeds 3% by weight, the service life is improved, but the SEI film is formed too much, and the load characteristics may not be obtained.
　非水電解質に含まれる有機溶媒は特に限定されるものではないが、負荷特性の点からは鎖状エステルを含んでいることが好ましい。そのような鎖状エステルとしては、たとえば、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）に代表される鎖状のカーボネートや、酢酸エチル、プロピオン酸メチルなどが挙げられる。これらの鎖状エステルは、単独でもあるいは２種以上を混合して用いてもよく、特に、低温特性の改善のためには、上記鎖状エステルが全有機溶媒の５０体積％以上を占めることが好ましく、特に鎖状エステルが全有機溶媒の６５体積％以上を占めることが好ましい。 The organic solvent contained in the non-aqueous electrolyte is not particularly limited, but preferably contains a chain ester from the viewpoint of load characteristics. Examples of such chain esters include chain carbonates typified by dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), ethyl acetate, and methyl propionate. These chain esters may be used alone or in admixture of two or more. In particular, in order to improve the low temperature characteristics, the chain ester may occupy 50% by volume or more of the total organic solvent. In particular, it is preferable that the chain ester occupies 65% by volume or more of the total organic solvent.
　ただし、有機溶媒としては、上記鎖状エステルのみで構成するよりも、放電容量の向上を図るために、上記鎖状エステルに誘導率の高い（誘導率：３０以上）エステルを混合して用いることが好ましい。このようなエステルの具体例としては、たとえば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネートに代表される環状のカーボネートや、γ－ブチロラクトン、エチレングリコールサルファイトなどが挙げられ、特にエチレンカーボネート、プロピレンカーボネートなどの環状構造のエステルが好ましい。 However, as an organic solvent, in order to improve the discharge capacity, compared with the chain ester alone, an ester having a high induction rate (induction rate: 30 or more) is mixed with the chain ester. Is preferred. Specific examples of such esters include, for example, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, and the like, particularly ethylene carbonate, propylene carbonate, and the like. Cyclic esters are preferred.
　そのような誘電率の高いエステルは、放電容量の点から、全有機溶媒の１０体積％以上、特に２０体積％以上含有されることが好ましい。また、負荷特性の点からは、４０体積％以下が好ましく、３０体積％以下がより好ましい。 Such an ester having a high dielectric constant is preferably contained in an amount of 10% by volume or more, particularly 20% by volume or more of the total organic solvent from the viewpoint of discharge capacity. Moreover, from the point of load characteristics, 40 volume% or less is preferable and 30 volume% or less is more preferable.
　また、上記誘電率の高いエステル以外に併用可能な溶媒としては、たとえば、１，２－ジメトキシエタン、１，３－ジオキソラン、テトラヒドロフラン、２－メチル－テトラヒドロフラン、ジエチルエーテルなどが挙げられる。そのほか、含フッ素系有機溶媒なども用いることができる。 Further, examples of the solvent that can be used in addition to the ester having a high dielectric constant include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, and diethyl ether. In addition, a fluorine-containing organic solvent can also be used.
　有機溶媒に溶解させる支持塩としては、たとえば、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣＦ３ＣＯ２、Ｌｉ２Ｃ２Ｆ４（ＳＯ３）２、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣｎＦ２ｎ＋１ＳＯ３（ｎ≧２）などが単独でまたは２種以上混合して用いられる。なかでも、良好な充放電特性が得られるＬｉＰＦ６やＬｉＣ４Ｆ９ＳＯ３などが好ましく用いられる。非水電解質中における支持塩の濃度は、特に限定されるものではないが、０．３～１．７ｍｏｌ／ｄｍ３、特に０．４～１．５ｍｏｌ／ｄｍ３程度が好ましい。 The supporting salt dissolved in an organic solvent, for example, LiClO 4, LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3 ) 2 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , LiC n F 2n + 1 SO 3 (n ≧ 2) are used alone or in combination of two or more. Among these, LiPF 6 and LiC 4 F 9 SO 3 that can obtain good charge / discharge characteristics are preferably used. The concentration of the supporting salt in the nonaqueous electrolyte is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm 3 , particularly about 0.4 to 1.5 mol / dm 3 .
　これらの中でも、ＬｉＰＦ６塩は良好な負荷特性を示すため、支持塩として望ましい。他の支持塩としてＬｉＢＦ４などの選択枝があるが、ＬｉＰＦ６を主成分とすることが望ましい。また、実用的な負荷特性を持たせるため、混合有機溶媒にエチレンカーボネート、及び７０～８０体積％のジメチルカーボネートまたはエチルメチルカーボネートなどの鎖状カーボネートが含まれていることが好ましい。 Among these, LiPF 6 salt is desirable as a supporting salt because it exhibits good load characteristics. Other supporting salts include selective branches such as LiBF 4 , but it is desirable that LiPF 6 be the main component. In order to give practical load characteristics, the mixed organic solvent preferably contains ethylene carbonate and 70 to 80% by volume of a chain carbonate such as dimethyl carbonate or ethyl methyl carbonate.
　また、電池の安全性や貯蔵特性を向上させるために、非水電解液に芳香族化合物を含有させてもよい。芳香族化合物としては、シクロヘキシルベンゼンやｔ－ブチルベンゼンなどのアルキル基を有するベンゼン類、ビフェニル、あるいはフルオロベンゼン類が好ましく用いられる。 Moreover, in order to improve the safety and storage characteristics of the battery, an aromatic compound may be contained in the nonaqueous electrolytic solution. As the aromatic compound, benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.
４．セパレータ
　セパレータとしては、強度が充分でしかも非水電解質を多く保持できるものがよく、そのような観点から、５～５０μｍの厚さで、ポリプロピレン製、ポリエチレン製、プロピレンとエチレンとの共重合体などポリオレフィン製の微孔性フィルムや不織布などが好ましく用いられる。特に、５～２０μｍと薄いセパレータを用いた場合には、充放電サイクルや高温貯蔵などにおいて電池の特性が劣化しやすくなるが、本発明のリン酸鉄リチウムは安定性に優れているため、このような薄いセパレータを用いても安定して電池を機能させることができる。 4). As the separator, a separator having sufficient strength and capable of retaining a large amount of non-aqueous electrolyte is preferable. From such a viewpoint, the thickness is 5 to 50 μm, and polypropylene, polyethylene, a copolymer of propylene and ethylene, etc. A polyolefin microporous film or non-woven fabric is preferably used. In particular, when a thin separator of 5 to 20 μm is used, the characteristics of the battery are likely to deteriorate during charge / discharge cycles and high-temperature storage, but the lithium iron phosphate of the present invention is excellent in stability. Even if such a thin separator is used, the battery can function stably.
　リン酸鉄リチウム正極は熱的安定性が高いことから、上記のポリオレフィン系セパレータを用いても熱的安定性の高いリチウムイオン電池を提供することができるが、そのポリオレフィン系セパレータの表面に酸化アルミニウム、酸化マグネシウム、二酸化珪素などの酸化物を３～５μｍ塗布して１５０℃以上での熱収縮を抑えた機能性セパレータを適用することで、そのリチウムイオン電池の熱的安定性をさらに向上させることができる。 Since the lithium iron phosphate positive electrode has high thermal stability, it is possible to provide a lithium ion battery with high thermal stability even when the above polyolefin separator is used. By further applying a functional separator that suppresses thermal shrinkage at 150 ° C. or higher by applying 3 to 5 μm of an oxide such as magnesium oxide or silicon dioxide, the thermal stability of the lithium ion battery can be further improved. Can do.
　以下に本発明の実施例に関して説明する。ただし、本発明はそれらの実施例のみに限定されるものではない。 Hereinafter, examples of the present invention will be described. However, this invention is not limited only to those Examples.
実施例１
　組成式ＬｉＦｅＰＯ４で表されるリン酸鉄リチウムは、１０７ｇのＬｉＨ２ＰＯ４（アルドリッチ製）と１７５ｇのＦｅＣ２Ｏ４・２Ｈ２Ｏ（高純度化学社製）と１６．４ｇのデキストリン（和光純薬社製）を、ジルコニア製ポットにジルコニア製粉砕用ボールを投入し、遊星型ボールミル（フリッチェ社製）を用いて、回転数は３レベルで３０分間混合した。その混合粉体をアルミナ製ルツボに投入して、０．３Ｌ／ｍｉｎのアルゴン流下で、４００℃で１０時間仮焼成を行った。再度、ジルコニア製ポットにジルコニア製粉砕用ボールを投入し、回転数は１レベルで１分間回転させ、解砕し、再度アルミナ製ルツボへ投入して、０．３Ｌ／ｍｉｎのアルゴン流下で、７００℃で１０時間本焼成を行った後、得られた粉体をジルコニア製ポットにジルコニア製粉砕用ボールを投入し、回転数は１レベルで１分間回転させ、解砕し、４５μｍのメッシュの篩で粒度調整を行い、目的の材料を得た。ＩＣＰ測定（島津製作所社製）により、組成分析を実施した結果、Ｌｉ１．０Ｆｅ０．９８Ｐ１．０２Ｏ４（炭素含有率：３．０重量％）であった。非晶質炭素で被覆されたことは、走査型電子顕微鏡（日立製作所社製）と、粉末Ｘ線回折装置（リガク社製）を用いて確認した。Ｂ．Ｅ．Ｔ法によって低温低湿条件下での窒素吸着量から、その比表面積を測定した結果、１５ｍ２／ｇであった。測定には、全自動ＢＥＴ比表面積測定装置（マウンテック社製）を用い、前処理として真空脱気を３００℃で６時間行い、液体窒素（７７°Ｋ）温度下で窒素吸着量から求めた。また、水分量は、カールフィッシャー水分量計（京都電子工業社製）を用いて測定した結果、８０℃真空乾燥後の水分量は６００ｐｐｍであった。ここで、水酸化リチウムの代わりに炭酸リチウムを用いてもよい。 Example 1
Lithium iron phosphate represented by the composition formula LiFePO 4 consists of 107 g of LiH 2 PO 4 (manufactured by Aldrich), 175 g of FeC 2 O 4 .2H 2 O (manufactured by Kojundo Kagaku) and 16.4 g of dextrin (sum) The zirconia grinding balls were put into a zirconia pot and mixed with a planetary ball mill (manufactured by Frichche) at a rotation speed of 3 levels for 30 minutes. The mixed powder was put into an alumina crucible and calcined at 400 ° C. for 10 hours under an argon flow of 0.3 L / min. Again, the zirconia grinding balls were put into the zirconia pot, rotated at 1 level for 1 minute, crushed, and again put into the alumina crucible, under an argon flow of 0.3 L / min, 700 After firing for 10 hours at ℃, the obtained powder was put into a zirconia pot with zirconia grinding balls, rotated at 1 level for 1 minute, crushed, and screened with a 45 μm mesh. The desired particle size was obtained by adjusting the particle size. As a result of conducting a composition analysis by ICP measurement (manufactured by Shimadzu Corporation), it was Li 1.0 Fe 0.98 P 1.02 O 4 (carbon content: 3.0 wt%). The coating with amorphous carbon was confirmed using a scanning electron microscope (manufactured by Hitachi, Ltd.) and a powder X-ray diffractometer (manufactured by Rigaku Corporation). B. E. The specific surface area was measured from the amount of nitrogen adsorbed under low temperature and low humidity conditions by the T method, and as a result, it was 15 m 2 / g. For the measurement, a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd.) was used, and vacuum deaeration was performed as a pretreatment at 300 ° C. for 6 hours, and the nitrogen adsorption amount was determined at a liquid nitrogen (77 ° K) temperature. Further, the moisture content was measured using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Industry Co., Ltd.). As a result, the moisture content after vacuum drying at 80 ° C. was 600 ppm. Here, lithium carbonate may be used instead of lithium hydroxide.
　リン酸鉄リチウム、炭素、バインダがそれぞれ８５重量％、８重量％、７重量％となるように配合するために、炭素被覆リン酸鉄リチウムを８７重量％、被覆炭素以外の導電助剤としてアセチレンブラックを６重量％、ＰＶｄＦバインダを７重量％使用した。 In order to blend lithium iron phosphate, carbon, and binder at 85 wt%, 8 wt%, and 7 wt%, respectively, carbon coated lithium iron phosphate is 87 wt%, and acetylene is used as a conductive aid other than the coated carbon. 6% by weight of black and 7% by weight of PVdF binder were used.
　小型混練機を用いて、炭素被覆リン酸鉄リチウムとアセチレンブラックを混合し、ＰＶｄＦ含有のＮＭＰ溶液を加えて、塗料化させたものを、アルミ箔上に１５０ｇ／ｍ２塗布し、1２０℃で乾燥させた。その後、電極密度を１．７ｇ／ｃｍ３になるようにプレスし、所定のサイズに裁断し正極を作製した。 Using a small kneader, carbon coated lithium iron phosphate and acetylene black were mixed, PVdF-containing NMP solution was added, and the resulting coating was applied to aluminum foil at 150 g / m 2 at 120 ° C. Dried. Then, it pressed so that an electrode density might be set to 1.7 g / cm < 3 >, and it cut | judged to the predetermined size, and produced the positive electrode.
　負極は、粒径２０μｍの天然黒鉛材を用い、バインダとしてカルボキシメチルセルロースとスチレンブタジエンゴムを水溶液中に分散した負極スラリを８０ｇ／ｍ２塗布し、１００℃で乾燥させた。その後、１．５ｇ／ｃｍ３になるようにプレスし、所定のサイズに裁断し負極を作製した。 As the negative electrode, a natural graphite material having a particle diameter of 20 μm was used, and 80 g / m 2 of a negative electrode slurry in which carboxymethyl cellulose and styrene butadiene rubber were dispersed in an aqueous solution as a binder was applied and dried at 100 ° C. Then, it pressed so that it might become 1.5 g / cm < 3 >, and it cut | judged to the predetermined size, and produced the negative electrode.
　電池評価は、１８６５０サイズの円筒型電池（径：１８ｍｍ、高さ：６５ｍｍ）を用いた。所定のサイズに裁断した正極、負極に各々アルミニウムとニッケル製の集電リードを溶接し、セパレータは２５μｍ厚みのポリオレフィン系多孔質膜を用いて、捲回し、組立てた。 For the battery evaluation, a 18650 size cylindrical battery (diameter: 18 mm, height: 65 mm) was used. Current collector leads made of aluminum and nickel were welded to the positive electrode and negative electrode cut to a predetermined size, respectively, and the separator was wound and assembled using a polyolefin-based porous film having a thickness of 25 μm.
　電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）　１重量％ＶＣ溶液中にＨＦ抑制剤としてＮ，Ｎ－ジメチルアセトアミドを０．５重量％加えたものを検討した。その電解液量は５～６ｍｌになるように調整した。 As an electrolytic solution, a 1M LiPF 6 EC / DMC (1/3) 1 wt% VC solution in which 0.5 wt% of N, N-dimethylacetamide was added as an HF inhibitor was examined. The amount of the electrolyte was adjusted to 5 to 6 ml.
　上記の構成で得られた１８６５０円筒型評価電池を用いて、負荷特性を評価するために直流抵抗値を下記手法で測定し、高温保存時の容量維持率を求め、保存特性の評価を行った。 Using the 18650 cylindrical evaluation battery obtained in the above configuration, the DC resistance value was measured by the following method in order to evaluate the load characteristics, the capacity retention rate during high temperature storage was determined, and the storage characteristics were evaluated. .
　室温で充電は電流値０．５ＣＡとして、上限電圧を３．６Ｖとし、０．１ＣＡの終止電流値になるまで充電した。放電は１．０ＣＡの電流値で２．０Ｖまで通電させた。その時の容量を放電深度０％として、再度同じ条件で充電した際の容量を充電深度１００％とした。放電深度５０％に放電し、１時間放置し、開回路電圧としてから、室温で１ＣＡ、２ＣＡ、３ＣＡパルス放電し、５秒目閉回路電圧を用いて直線近似で直流抵抗を求めた。 The battery was charged at room temperature with a current value of 0.5 CA, an upper limit voltage of 3.6 V, and a final current value of 0.1 CA. Discharge was conducted up to 2.0 V with a current value of 1.0 CA. The capacity at that time was defined as a discharge depth of 0%, and the capacity when charged again under the same conditions was defined as a charge depth of 100%. After discharging at a discharge depth of 50% and leaving it for 1 hour to obtain an open circuit voltage, 1CA, 2CA and 3CA pulses were discharged at room temperature, and a DC resistance was obtained by linear approximation using a closed circuit voltage at the 5th second.
　高温保存特性は、上記充電条件で満充電状態（充電深度１００％）まで充電し、５０℃の恒温槽に１０日間保管し、その後の１ＣＡでの容量を測定し、初期容量を１００％として容量維持率を求めた。 The high-temperature storage characteristics are charged to the fully charged state (charging depth 100%) under the above-mentioned charging conditions, stored in a constant temperature bath at 50 ° C. for 10 days, then measured at 1 CA, and the initial capacity as 100%. The maintenance rate was determined.
　以下、実施例及び比較例を示すが、実施例１と同じ正極及び負極を用い、両電極の作製方法及び評価方法も実施例１と同じくした。 Hereinafter, although an Example and a comparative example are shown, the same positive electrode and negative electrode as Example 1 were used, and the production method and evaluation method of both electrodes were also the same as Example 1.
実施例２
　実施例１と同じ手順で、電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）　１重量％ＶＣ溶液中にＨＦ抑制剤としてＮ，Ｎ－ジメチルアセトアミドを０．１重量％加えたものを検討した。作製した１８６５０型試作電池は、実施例１に記述した方法で、直流抵抗値と高温保存特性を評価した。 Example 2
In the same procedure as in Example 1, 0.1% by weight of N, N-dimethylacetamide as an HF inhibitor was added to a 1% by weight VC solution of 1M LiPF 6 EC / DMC (1/3) as an electrolytic solution. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
比較例１
　実施例１と同じ手順で、電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）　１重量％ＶＣ溶液を検討した。作製した１８６５０型試作電池は、実施例１に記述した方法で、直流抵抗値と高温保存特性を評価した。 Comparative Example 1
In the same procedure as in Example 1, a 1M LiPF 6 EC / DMC (1/3) 1 wt% VC solution was examined as an electrolytic solution. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
比較例２
　実施例１と同じ手順で、電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）　１重量％ＶＣ溶液中にＨＦ抑制剤としてＮ，Ｎ－ジメチルアセトアミドを１．０重量％加えたものを検討した。作製した１８６５０型試作電池は、実施例１に記述した方法で、直流抵抗値と高温保存特性を評価した。 Comparative Example 2
In the same procedure as in Example 1, as electrolyte, 1 M LiPF 6 EC / DMC (1/3) 1 wt% VC solution containing 1.0 wt% of N, N-dimethylacetamide as HF inhibitor was added. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
比較例３
　実施例１と同じ手順で、電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）　１重量％ＶＣ溶液中にＨＦ抑制剤としてＮ，Ｎ－ジメチルアセトアミドを２．０重量％加えたものを検討した。作製した１８６５０型試作電池は、実施例１に記述した方法で、直流抵抗値と高温保存特性を評価した。 Comparative Example 3
In the same procedure as in Example 1, an electrolyte was prepared by adding 2.0% by weight of N, N-dimethylacetamide as an HF inhibitor in a 1M LiPF 6 EC / DMC (1/3) 1% by weight VC solution. investigated. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
比較例４
　実施例１と同じ手順で、電解液として、１Ｍ　ＬｉＰＦ６　ＥＣ／ＤＭＣ（１／３）溶液中にＮ，Ｎ－ジメチルアセトアミドを０．５重量％加えたものを検討した。作製した１８６５０型試作電池は、実施例１に記述した方法で、直流抵抗値と高温保存特性を評価した。 Comparative Example 4
In the same procedure as in Example 1, an electrolytic solution in which 0.5% by weight of N, N-dimethylacetamide was added to a 1M LiPF 6 EC / DMC (1/3) solution was examined. The produced 18650 type prototype battery was evaluated for DC resistance and high-temperature storage characteristics by the method described in Example 1.
　実施例と比較例の結果を表１にまとめる。また、その直流抵抗値は、比較例１を基準（１．００）として、その抵抗値を比較した値をまとめた。高温保存特性として、容量維持率をまとめた。電解液中に添加剤としてＶＣを１％含有した状態で、ＤＭＡの含有率の効果を見るために、実施例１から比較例３について、ＤＭＡ含有率と直流抵抗値との関係を図２に、容量維持率との関係を図３に示す。 The results of Examples and Comparative Examples are summarized in Table 1. Moreover, the direct-current resistance value was obtained by comparing the resistance values with Comparative Example 1 as a reference (1.00). The capacity retention rate was summarized as the high temperature storage characteristics. FIG. 2 shows the relationship between the DMA content and the DC resistance value for Example 1 to Comparative Example 3 in order to see the effect of the DMA content with 1% VC as an additive in the electrolyte. FIG. 3 shows the relationship with the capacity maintenance rate.
　図２から見て取れるように、ＤＭＡの含有率が０％（比較例１）である場合、直流抵抗値は最も低い。そして、０．５％までは直流抵抗値は大幅に大きくならず、１．０３で保持している。そして、ＤＭＡ含有率が１％（比較例２）では、その値は１．１０となり、さらに、ＤＭＡ含有率が２％（比較例３）の場合、直流抵抗値は１．２５と急激に大きくなることがわかった。つまり、ＤＭＡ含有率が０．５％以下であれば、ＤＭＡによる直流抵抗値は若干大きくなるものの、大幅な上昇は認められず、負荷特性が低下することはない。一方で、ＤＭＡの含有率が０．５％より大きい場合、直流抵抗値は極端に上昇し、負荷特性は大幅に低下する傾向がある。これは、所定量のＤＭＡがフッ酸抑制に機能し、残ったＤＭＡが電極上で分解し、被膜を形成するためであると考えている。 As can be seen from FIG. 2, when the DMA content is 0% (Comparative Example 1), the DC resistance value is the lowest. The DC resistance value is not significantly increased up to 0.5% and is maintained at 1.03. When the DMA content is 1% (Comparative Example 2), the value is 1.10. When the DMA content is 2% (Comparative Example 3), the DC resistance value is rapidly increased to 1.25. I found out that That is, if the DMA content is 0.5% or less, the direct current resistance value due to DMA is slightly increased, but no significant increase is observed, and the load characteristics are not deteriorated. On the other hand, when the DMA content is higher than 0.5%, the direct current resistance value is extremely increased, and the load characteristics tend to be significantly decreased. This is because a predetermined amount of DMA functions to suppress hydrofluoric acid, and the remaining DMA decomposes on the electrode to form a film.
　一方で、高温保存特性は、図３に示すように、ＤＭＡ含有率が０％（比較例１）から０．５％（実施例１）まで増加させた場合、容量維持率は８５から９２％まで向上し、さらにＤＭＡ含有率を増加させた場合、逆に容量維持率は降下し、ＤＭＡ含有率が１％（比較例２）では８０％、ＤＭＡ含有率が２％（比較例３）の場合には７０％にまで低下することがわかった。以上のことから、ＤＭＡ含有率が０．５％以下までは、高温保存特性が改善するが、それ以上では低下する傾向がある。ＤＭＡ含有率が約１．０％では、ＤＭＡの効果は無くなり、その容量維持率は含有率が０％との時とほぼ同じ値を示した。つまり、ＤＭＡがフッ酸抑制に機能し、残ったＤＭＡは、図２に示すように直流抵抗が増加させるため、１ＣＡ電流で取り出せる容量が減り、結果として容量維持率が低下したと考えている。 On the other hand, as shown in FIG. 3, when the DMA content is increased from 0% (Comparative Example 1) to 0.5% (Example 1), the capacity retention rate is 85 to 92%. When the DMA content is further increased, the capacity retention rate is decreased, and the DMA content is 80% when the DMA content is 1% (Comparative Example 2) and 2% (Comparative Example 3). In some cases, it has been found to decrease to 70%. From the above, when the DMA content is 0.5% or less, the high-temperature storage characteristics are improved, but when the DMA content is more than that, it tends to decrease. When the DMA content was about 1.0%, the effect of DMA disappeared, and the capacity retention rate was almost the same as when the content was 0%. In other words, the DMA functions to suppress hydrofluoric acid, and the remaining DMA increases the direct current resistance as shown in FIG. 2, so that the capacity that can be taken out with 1 CA current decreases, and as a result, the capacity maintenance rate decreases.
　さらに、表１にまとめた実施例１と比較例４の結果から、電解液中にＶＣを含有する場合としない場合では、ＶＣ自体が直流抵抗値及び高温保存特性に影響を与えるため、ＤＭＡの効果は異なる。ＤＭＡが０．５％含有率では、直流抵抗値上昇に関わるＶＣの依存度が大きいため、ＶＣを含有しない場合、直流抵抗値は低くなる。一方で、高温保存特性に関するＶＣの依存度が高いために、ＶＣを含有しない場合、容量維持率は低下する。以上のことから、ＶＣとＤＭＡを共に含有させることで、効果的に直流抵抗を低く、かつ容量維持率を向上させることができることを見出した。 Furthermore, from the results of Example 1 and Comparative Example 4 summarized in Table 1, when the VC contains or does not contain VC, the VC itself affects the DC resistance value and the high temperature storage characteristics. The effect is different. When the DMA content is 0.5%, the dependence of the VC on the increase of the DC resistance value is large. Therefore, when the VC is not contained, the DC resistance value is low. On the other hand, since the dependence of VC on the high temperature storage characteristics is high, the capacity maintenance rate decreases when VC is not included. From the above, it has been found that by including both VC and DMA, the DC resistance can be effectively lowered and the capacity retention rate can be improved.
　以上の結果を検討すると、オリビン型リン酸鉄リチウム正極と黒鉛負極で構成される電池系に、ＶＣを含んだ電解液中にフッ酸抑制剤としてＮ，Ｎ－ジメチルアセトアミド（ＤＭＡ）を０．０１～０．７重量％、好ましくは０．０５～０．７重量％、特に好ましくは０．１～０．７重量％含有させることで、直流抵抗値を維持し、出力特性と高温保存特性を両立させた電池を提供することができる。
Figure JPOXMLDOC01-appb-T000001
 Examining the above results, in a battery system composed of an olivine-type lithium iron phosphate positive electrode and a graphite negative electrode, N, N-dimethylacetamide (DMA) as a hydrofluoric acid inhibitor in an electrolyte containing VC was reduced to 0. By containing 01 to 0.7% by weight, preferably 0.05 to 0.7% by weight, particularly preferably 0.1 to 0.7% by weight, the DC resistance value is maintained, and the output characteristics and high temperature storage characteristics are maintained. Can be provided.
Figure JPOXMLDOC01-appb-T000001
　本明細書で引用した全ての刊行物、特許および特許出願をそのまま参考として本明細書に取り入れるものとする。 All publications, patents and patent applications cited in this specification shall be incorporated into this specification for reference.
1・・・電池缶
2・・・ガスケット
3・・・上蓋
4・・・上蓋ケース
5・・・正極集電部品
6・・・負極集電部品
7・・・軸芯
8・・・電極群
12・・・正極タブ
13・・・負極タブ
14・・・正極電極
15・・・負極電極
16・・・正極合剤
17・・・負極合剤
18a, 18b・・・セパレータ
19・・・テープ 1 ... Battery can
2 ... Gasket
3 ... Top cover
4 ... Upper lid case
5 ... Positive current collector
6 ... Negative current collector
7 ... shaft core
8 ... Electrode group
12 ... Positive electrode tab
13 ... Negative electrode tab
14 ... Positive electrode
15 ... Negative electrode
16 ... Positive electrode mixture
17 ... Negative electrode mixture
18a, 18b ・ ・ ・ Separator
19 ・ ・ ・ Tape

Claims (7)

  1. 　オリビン型構造を有する組成式ＬｉＦｅ１－ＸＭｘＰＯ４：
    [式中、
    　ＭはＮｉ、Ｃｏ、Ｍｎ、Ｔｉ、Ｚｒ、及びＭｏからなる群から選択される少なくとも１種であり、
    　ｘは０≦ｘ＜１である]
    で表される正極活物質を含む正極；
    　リチウムイオンを吸蔵放出可能な負極活物質を含む負極；並びに
    　非水電解質；
    を有する非水電解質二次電池であって、
    　前記正極活物質の表面が炭素で被覆されており、
    　前記非水電解質がＮ，Ｎ－ジメチルアセトアミド、ビニレンカーボネート、支持塩、及び有機溶媒を含み、
    　前記Ｎ，Ｎ－ジメチルアセトアミドの含有量が前記非水電解質の０．０１～０．７重量％である、前記非水電解質二次電池。     Compositional formula LiFe 1-X M x PO 4 having an olivine type structure:
    [Where
    M is at least one selected from the group consisting of Ni, Co, Mn, Ti, Zr, and Mo;
    x is 0 ≦ x <1]
    A positive electrode comprising a positive electrode active material represented by:
    A negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions; and a non-aqueous electrolyte;
    A non-aqueous electrolyte secondary battery comprising:
    The surface of the positive electrode active material is coated with carbon,
    The non-aqueous electrolyte includes N, N-dimethylacetamide, vinylene carbonate, a supporting salt, and an organic solvent;
    The non-aqueous electrolyte secondary battery, wherein a content of the N, N-dimethylacetamide is 0.01 to 0.7% by weight of the non-aqueous electrolyte.
  2. 　正極活物質の表面を被覆する炭素の量が炭素被覆正極活物質の１～５重量％であり、前記炭素被覆正極活物質の比表面積が１０～２０ｍ２／ｇであり、前記炭素被覆正極活物質が３００～１０００ｐｐｍの水分を含む、請求項１に記載の非水電解質二次電池。 The amount of carbon covering the surface of the positive electrode active material is 1 to 5% by weight of the carbon-coated positive electrode active material, the specific surface area of the carbon-coated positive electrode active material is 10 to 20 m 2 / g, The nonaqueous electrolyte secondary battery according to claim 1, wherein the substance contains 300 to 1000 ppm of water.
  3. 　ビニレンカーボネートの含有量が非水電解質の０．５～３重量％である、請求項１または２に記載の非水電解質二次電池。 The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the content of vinylene carbonate is 0.5 to 3% by weight of the non-aqueous electrolyte.
  4. 　ｘが０である、請求項１～３のいずれかに記載の非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein x is 0.
  5. 　リチウムイオンを吸蔵放出可能な負極活物質が黒鉛である、請求項１～４のいずれかに記載の非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the negative electrode active material capable of inserting and extracting lithium ions is graphite.
  6. 　支持塩がＬｉＰＦ６である、請求項１～５のいずれかに記載の非水電解質二次電池。 Supporting salt is LiPF 6, a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5.
  7. 　有機溶媒がエチレンカーボネートと鎖状カーボネートとの混合溶媒であり、前記鎖状カーボネートの含有量が前記混合溶媒の７０～８０体積％である、請求項１～６のいずれかに記載の非水電解質二次電池。 The nonaqueous electrolyte according to any one of claims 1 to 6, wherein the organic solvent is a mixed solvent of ethylene carbonate and chain carbonate, and the content of the chain carbonate is 70 to 80% by volume of the mixed solvent. Secondary battery.
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