WO2013146359A1 - 二次電池用非水電解液およびリチウムイオン二次電池 - Google Patents
二次電池用非水電解液およびリチウムイオン二次電池 Download PDFInfo
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- WO2013146359A1 WO2013146359A1 PCT/JP2013/057445 JP2013057445W WO2013146359A1 WO 2013146359 A1 WO2013146359 A1 WO 2013146359A1 JP 2013057445 W JP2013057445 W JP 2013057445W WO 2013146359 A1 WO2013146359 A1 WO 2013146359A1
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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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0569—Liquid materials characterised by the solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0028—Organic electrolyte characterised by the solvent
- H01M2300/0034—Fluorinated solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a non-aqueous electrolyte for a secondary battery and a lithium ion secondary battery.
- a non-aqueous electrolyte used for a lithium ion secondary battery (hereinafter sometimes simply referred to as “secondary battery”) generally has a high lithium ion conductivity (hereinafter simply referred to as “high lithium ion conductivity”) by dissolving a lithium salt well.
- Carbonate solvents such as ethylene carbonate and dimethyl carbonate have been widely used because they express "conductivity" and have a wide potential window.
- carbonate-based solvents are flammable and may ignite due to battery heat generation.
- the fluorine-based solvent has a low lithium salt solubility and tends to deteriorate the cycle characteristics.
- Non-aqueous electrolysis that is superior in solubility of lithium salt that is complexed with lithium salt and glyme solvent by containing non-flammable (flame retardant) fluorine solvent as the main component and glyme solvent.
- a liquid has been proposed (Patent Document 2).
- nonaqueous electrolytic solutions composed of a fluorine-containing solvent, a cyclic carbonate, a cyclic carboxylic acid ester, and a lithium salt have been proposed (Patent Documents 3 and 4).
- Patent Documents 3 and 4 nonaqueous electrolytic solutions composed of a fluorine-containing solvent, a cyclic carbonate, a cyclic carboxylic acid ester, and a lithium salt.
- the battery temperature of a secondary battery rises due to Joule heat during use or external heating, but if the battery temperature reaches a high temperature exceeding 150 ° C, a thermal runaway may occur and the battery may be damaged. is there.
- heat generation is known due to the reaction between the electrolytic solution, the positive electrode, and the negative electrode, which are decomposed. That is, thermal runaway starts when the temperature of the secondary battery reaches a temperature at which the electrolytic solution reacts with the positive electrode and the negative electrode due to Joule heat or the like and can be thermally decomposed.
- the non-aqueous electrolyte used in the secondary battery has low reactivity with the positive electrode and the negative electrode and hardly generates heat due to reaction with them.
- secondary batteries have been actively studied for application to in-vehicle power sources of electric vehicles that require greater energy, and non-aqueous electrolytes having lower reactivity with positive and negative electrodes are required.
- the reactivity of the positive electrode and the negative electrode and the non-aqueous electrolyte is reduced, and further excellent rate characteristics, initial charge / discharge characteristics, and cycle characteristics are also provided. .
- the present invention has excellent cycle characteristics, low reactivity with the positive electrode and the negative electrode, and the secondary battery is less likely to cause thermal runaway, and further has a practically sufficient conductivity. Further excellent rate characteristics, initial charge / discharge It aims at providing the non-aqueous electrolyte for secondary batteries which has the characteristic, and the lithium ion secondary battery using this non-aqueous electrolyte for secondary batteries.
- a non-aqueous electrolyte comprising a lithium salt and a liquid composition
- the liquid composition comprises at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, a cyclic carboxylic acid ester compound, Including It may contain at least one compound ( ⁇ ) selected from the group consisting of a saturated cyclic carbonate compound having no fluorine atom, a chain carbonate compound having no fluorine atom, a saturated cyclic sulfone compound and a phosphate ester compound,
- the ratio of the mass of the fluorine-containing solvent ( ⁇ ) to the total mass of the non-aqueous electrolyte is 40 to 80% by mass, N A / N Li which is the ratio of the total number of moles of the cyclic carboxylic acid este
- a negative electrode using as an active material a positive electrode having a material capable of inserting and extracting lithium ions as an active material and one or more selected from the group consisting of lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions And a non-aqueous electrolyte for a secondary battery according to any one of [1] to [14].
- the non-aqueous electrolyte for a secondary battery of the present invention has excellent rate characteristics, initial charge / discharge characteristics, and cycle characteristics, low reactivity with the positive electrode and the negative electrode, and the secondary battery is unlikely to cause thermal runaway. Furthermore, a secondary battery having excellent cycle characteristics and practically sufficient conductivity can be obtained. Moreover, since the lithium ion secondary battery of the present invention uses the non-aqueous electrolyte for a secondary battery of the present invention, it is difficult to cause thermal runaway, has excellent rate characteristics, initial charge / discharge characteristics, and cycle characteristics, and is practical. Sufficient conductivity.
- fluorination means that a part or all of hydrogen atoms bonded to a carbon atom is substituted with a fluorine atom.
- the fluorinated alkyl group is a group in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms.
- the partially fluorinated group there are a hydrogen atom and a fluorine atom.
- the perfluoroalkyl group is a group in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms.
- the carbon-carbon unsaturated bond is a carbon-carbon double bond or a carbon-carbon triple bond.
- non-aqueous electrolyte for secondary batteries of the present invention comprises a lithium salt and a liquid composition.
- the liquid composition comprises at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, a cyclic carboxylic acid ester compound, Containing.
- non-aqueous electrolyte for secondary batteries of the present invention includes an unsaturated cyclic carbonate compound having no fluorine atom (hereinafter sometimes referred to as “non-fluorinated unsaturated cyclic carbonate compound”) and a liquid composition. / Or a fluorine-containing cyclic carbonate compound may be included.
- a non-aqueous electrolyte is an electrolyte that does not substantially contain water, and even if it contains water, the amount of water is in a range where performance degradation of a secondary battery using the non-aqueous electrolyte is not observed.
- the amount of water that can be contained in the non-aqueous electrolyte is preferably 500 ppm by mass or less, more preferably 100 ppm by mass or less, and 50 ppm by mass or less with respect to the total mass of the non-aqueous electrolyte. It is particularly preferred.
- the lower limit of the moisture content is 0 mass ppm.
- Lithium salt is an electrolyte that dissociates in a non-aqueous electrolyte and supplies lithium ions.
- LiPF 6 the following compound (A) (where k is an integer of 1 to 5), FSO 2 N (Li) SO 2 F, CF 3 SO 2 N (Li) SO 2 CF 3 , CF 3 CF 2 SO 2 N (Li) SO 2 CF 2 CF 3 , LiClO 4 , the following compound (B), the following compound (C), the following compound (D), the following compound (E), and LiBF 4 A lithium salt selected from the group is preferred.
- lithium salt a lithium salt selected from the group consisting of LiPF 6 , LiBF 4 and the compound (A) is more preferable, and LiPF 6 is more preferable.
- the lithium salt contained in the nonaqueous electrolytic solution of the present invention may be only one type or two or more types.
- the combination in the case of using 2 or more types of lithium salt together includes the combination disclosed in International Publication No. 2009/133899.
- LiPF 6 is used, high conductivity is obtained, but it is difficult to dissolve in a fluorine-containing solvent as compared with other lithium salts such as CF 3 CF 2 SO 2 N (Li) SO 2 CF 2 CF 3 .
- LiPF 6 has the property of being easily pyrolyzed.
- LiPF 6 is used in combination with a cyclic carboxylic acid ester compound even in a fluorine-containing solvent, the solubility of LiPF 6 is improved, and LiPF 6 is uniformly dissolved in the solvent so that it has practically sufficient conductivity. It is easy to obtain a water electrolyte solution, and by including a specific amount of a cyclic carboxylic acid ester compound, thermal runaway is difficult even in an electrolyte solution using LiPF 6 . It is preferable that at least a part of the lithium salt contained in the nonaqueous electrolytic solution of the present invention is LiPF 6 .
- the lower limit of the molar ratio of LiPF 6 with respect to the total number of moles of lithium salt contained in the non-aqueous electrolyte of the present invention is preferably 40 mol%, more preferably 50 mol%, further preferably 65 mol%, particularly preferably 80 mol%. .
- the upper limit of the molar ratio of LiPF 6 with respect to the total number of moles of lithium salt contained in the non-aqueous electrolyte is 100 mol%. If the molar ratio of LiPF 6 with respect to the total number of moles of lithium salt is equal to or higher than the lower limit value, the non-aqueous electrolyte is excellent in conductivity and highly practical.
- Examples of the compound (A) include the following compound (A-1) to compound (A-4).
- the compound (A) is preferably a compound (A-2) in which k is 2 from the viewpoint of easily obtaining a non-aqueous electrolyte with high conductivity, and the compound (A) contained in the non-aqueous electrolyte is More preferably, it consists only of the compound (A-2) in which k is 2.
- the content of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.1 to 3.0 mol / L.
- the lower limit of the lithium salt content is more preferably 0.5 mol / L, and even more preferably 0.8 mol / L.
- the upper limit of the lithium salt content is more preferably 1.8 mol / L, and even more preferably 1.6 mol / L.
- the ratio of the mass of the lithium salt to the total mass of the nonaqueous electrolytic solution is preferably 5 mass% to 25 mass%.
- the lower limit of the mass ratio of the lithium salt is more preferably 7% by mass, and still more preferably 8% by mass.
- the upper limit of the mass ratio of the lithium salt is more preferably 20% by mass, and further preferably 17% by mass.
- the proportion of the lithium salt is equal to or higher than the lower limit, the conductivity of the non-aqueous electrolyte is high.
- the ratio of the said lithium salt is below the said upper limit, lithium salt will be easy to melt
- the liquid composition in the non-aqueous electrolyte of the present invention contains at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound. Including.
- the fluorine-containing solvent ( ⁇ ) is a solvent having a fluorine atom in the molecule, and has excellent flame retardancy.
- the fluorine-containing solvent ( ⁇ ) contained in the liquid composition may be one type or two or more types. When two or more fluorine-containing solvents ( ⁇ ) are contained in the liquid-liquid composition, the ratio between them can be arbitrarily determined.
- the fluorinated solvent ( ⁇ ) contained in the liquid-liquid composition is a fluorinated ether compound.
- the fluorine-containing ether compound is preferably a fluorine-containing ether compound selected from the group consisting of the following compound (1) and the following compound (2).
- the fluorine-containing ether compound contained in the liquid-liquid composition may be one type or two or more types. When two or more kinds of fluorine-containing ether compounds are contained in the liquid-liquid composition, the ratio between them can be arbitrarily determined.
- R 1 and R 2 are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a fluorinated alkyl group having 1 to 10 carbon atoms, or a carbon number of 3
- R 1 and R 2 is a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or a carbon number having one or more etheric oxygen atoms 2 to 10 fluorinated alkyl groups.
- X is an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkylene group having 2 to 5 carbon atoms having one or more etheric oxygen atoms, or A fluorinated alkylene group having 2 to 5 carbon atoms having at least one etheric oxygen atom;
- alkyl group and the alkyl group having an etheric oxygen atom include groups each having a linear structure, a branched structure, or a partially cyclic structure (for example, a cycloalkylalkyl group).
- R 1 and R 2 in the compound (1) has a fluorinated alkyl group having 1 to 10 carbon atoms, a fluorinated cycloalkyl group having 3 to 10 carbon atoms, or one or more etheric oxygen atoms A fluorinated alkyl group having 2 to 10 carbon atoms.
- R 1 and R 2 in the compound (1) may be the same or different.
- compound (1-A) a compound in which R 1 and R 2 are both fluorinated alkyl groups having 1 to 10 carbon atoms (hereinafter referred to as compound (1-A)), and R 1 is one or more compounds.
- a compound which is a fluorinated alkyl group having 2 to 10 carbon atoms and having an etheric oxygen atom, and R 2 is a fluorinated alkyl group having 1 to 10 carbon atoms;
- a compound in which 1 is a fluorinated alkyl group having 1 to 10 carbon atoms and R 2 is an alkyl group having 1 to 10 carbon atoms (hereinafter referred to as compound (1-C)) is preferable.
- compound (1-C) are more preferable, and compound (1-A) is particularly preferable.
- the molecular weight of the compound (1) is preferably 150 to 800, more preferably 150 to 500, and particularly preferably 200 to 500.
- the number of etheric oxygen atoms in the compound (1) affects flammability. Therefore, the number of etheric oxygen atoms in the compound (1) having an etheric oxygen atom is preferably 1 to 4, more preferably 1 or 2, and even more preferably 1.
- the fluorine content in the compound (1) is high, the flame retardancy is excellent. 50 mass% or more is preferable and, as for the fluorine content in a compound (1), 60 mass% or more is more preferable.
- compound (1) is excellent in the solubility with respect to the liquid composition of lithium salt
- the compound whose both R ⁇ 1 > and R ⁇ 2 > are the alkyl groups by which some hydrogen atoms of the alkyl group were fluorinated is preferable.
- the compound (1) is preferably a compound in which one or both ends of R 1 and R 2 are —CF 2 H from the viewpoint of excellent solubility of the lithium salt in the liquid composition.
- the compound (1-A), the compound (1-B), and the fluorine-containing ether compounds other than the compound (1-A) and the compound (1-B) include, for example, International Publication No. 2009/133899. And the compounds described.
- the compound (1-A) is preferable, and CF 3 CH 2 OCF 2 CHF 2 (trade name: AE-3000, manufactured by Asahi Glass Co., Ltd.), CF 3 CH 2 OCF 2 CHFCF 3 , CHF 2 CF 2 More preferred is a compound selected from the group consisting of CH 2 OCF 2 CHF 2 , CH 3 CH 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 OCF 2 CHF 2 , and CHF 2 CF 2 CH 2 OCF 2 CHFCF 3. 3 CH 2 OCF 2 CHF 2 and CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 are particularly preferred.
- X may have a linear structure or a branched structure.
- X is preferably an alkylene group having 1 to 5 carbon atoms, more preferably an alkylene group having 2 to 4 carbon atoms.
- the alkylene group preferably has a linear structure or a branched structure.
- the side chain is preferably an alkyl group having 1 to 3 carbon atoms or an alkyl group having 1 to 3 carbon atoms having an etheric oxygen atom.
- X is -CH 2 -, - CH 2 CH 2 -, - CH (CH 3) CH 2 -, and -CH 2 CH 2 CH 2 - from the group consisting of A compound which is an alkylene group selected is preferable, and a compound where X is —CH 2 CH 2 — and a compound where X is —CH (CH 3 ) CH 2 — are more preferable.
- Specific examples of the compound (2) include a compound represented by the following formula.
- the nonaqueous electrolytic solution dissolves the lithium salt uniformly, is excellent in flame retardancy, and tends to have high conductivity.
- the fluorine-containing ether compound it is preferable to use the compound (1), the compound (2), or a mixture of the compound (1) and the compound (2), and it is more preferable to use the compound (1) alone or the compound (2) alone.
- the compound (1) contained may be only 1 type, and 2 or more types may be sufficient as it.
- the compound (2) contained may be only 1 type, and 2 or more types may be sufficient as it.
- the compound (1) (mass: Va) and the compound (2) (mass: Vb) are used in combination as the fluorine-containing ether compound, the mass ratio (Vb / Va) is preferably 0.01 to 100, 0.1 to 10 is more preferable.
- the fluorine-containing chain carboxylic acid ester compound is a chain compound that does not have a ring structure, has an ester bond, and has a fluorine atom.
- the fluorine-containing chain carbonate compound is a chain compound having no fluorine structure, having a carbonate bond represented by —O—C ( ⁇ O) —O—, and having a fluorine atom.
- the fluorine-containing chain carboxylic acid ester compound As the fluorine-containing chain carboxylic acid ester compound, the following compound (3) is preferable.
- R 3 to R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms, and one or both of R 3 and R 4 are It is a fluorinated alkyl group having 1 to 3 carbon atoms.
- the alkyl group and the fluorinated alkyl group include a linear structure and a branched structure, respectively.
- R 3 and R 4 in the compound (3) may be the same or different.
- R 3 is preferably a methyl group, an ethyl group, a difluoromethyl group, a trifluoromethyl group, a tetrafluoroethyl group or a pentafluoroethyl group, more preferably a difluoromethyl group or a trifluoromethyl group.
- R 4 is preferably a methyl group, an ethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethyl group, or a 2,2,2-trifluoroethyl group.
- the viscosity increases, preferably 3 to 8, more preferably 3 to 6, and further preferably 3 to 5.
- the molecular weight of the compound (3) is preferably 100 to 300, more preferably 100 to 250, and particularly preferably 100 to 200. Moreover, since a flame retardance improves, 25 mass% or more is preferable and, as for fluorine content in a compound (3), 30 mass% or more is more preferable.
- the compound (3) include, for example, acetic acid (2,2,2-trifluoroethyl), methyl difluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate and the like. Of these, methyl difluoroacetate and ethyl trifluoroacetate are preferable from the viewpoint of easy availability and battery performance such as cycle characteristics.
- Two or more fluorine-containing chain carboxylic acid ester compounds may be used. When two or more kinds of fluorine-containing chain carboxylic acid ester compounds are used, the ratio between them can be arbitrarily determined.
- the liquid composition in this invention contains a compound (3), the compound (3) contained may be only 1 type, and 2 or more types may be sufficient as it.
- the fluorine-containing chain carboxylic acid ester compound contained in the liquid composition is preferably at least partially composed of the compound (3), and more preferably composed of only the compound (3).
- the following compound (4) is preferable.
- R 5 to R 6 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms, and one or both of R 5 and R 6 are It is a fluorinated alkyl group having 1 to 3 carbon atoms.
- the alkyl group and the fluorinated alkyl group include a linear structure and a branched structure, respectively.
- the compound (4) is preferably a compound in which both R 5 and R 6 are fluorinated alkyl groups having 1 to 3 carbon atoms.
- R 5 and R 6 are fluorinated alkyl groups having 1 to 3 carbon atoms.
- fluorinated alkyl group having 1 to 3 carbon atoms CF 3 CH 2 — and CHF 2 CF 2 CH 2 — are preferable.
- the total number of carbon atoms in the compound (4) is preferably 4 to 10 and more preferably 4 to 7 because the viscosity becomes too high when it is too large.
- the molecular weight of the compound (4) is preferably 180 to 400, more preferably 200 to 350, and particularly preferably 210 to 300. Moreover, since a flame retardance improves, 25 mass% or more is preferable and, as for fluorine content in a compound (4), 30 mass% or more is more preferable.
- the compound (4) include bis (2,2,2-trifluoroethyl) carbonate, bis (2,2,3,3-tetrafluoropropyl) carbonate, and the like. Of these, bis (2,2,2-trifluoroethyl) carbonate is preferred from the viewpoint of battery performance such as viscosity, availability, and output characteristics.
- Two or more fluorine-containing chain carbonate compounds may be used. When two or more kinds of fluorine-containing chain carbonate compounds are used, the ratio between them can be arbitrarily determined.
- the liquid composition in this invention contains a compound (4), the compound (4) contained may be only 1 type, and 2 or more types may be sufficient as it.
- a fluorine-containing chain carbonate compound contained in a liquid composition it is preferable that at least one part is a compound (4), and it is more preferable that it consists only of a compound (4).
- the liquid composition in the present invention may contain a fluorine-containing alkane compound which is a fluorine-containing solvent other than the fluorine-containing solvent ( ⁇ ).
- a fluorine-containing alkane compound which is a fluorine-containing solvent other than the fluorine-containing solvent ( ⁇ ).
- the fluorine-containing alkane compound refers to a compound in which one or more hydrogen atoms in the alkane are substituted with fluorine atoms and hydrogen atoms remain.
- the fluorine-containing alkane compound is preferably a fluorine-containing alkane compound having 4 to 12 carbon atoms.
- the vapor pressure of the non-aqueous electrolyte is low, and the solubility of the lithium salt is good if the fluorine-containing alkane compound has 12 or less carbon atoms.
- the fluorine content in the fluorinated alkane compound is preferably 50 to 80% by mass. If the fluorine content in the fluorine-containing alkane compound is 50% by mass or more, the flame retardancy is excellent. If the fluorine content in the fluorine-containing alkane compound is 80% by mass or less, the solubility of the lithium salt is easily maintained.
- fluorine-containing alkane compound a compound having a linear structure is preferable.
- the fluorine-containing solvent ( ⁇ ) is used in combination with a fluorine-containing ether compound and at least one selected from the group consisting of a fluorine-containing chain carboxylic acid ester, a fluorine-containing chain carbonate compound and a fluorine-containing alkane compound,
- the ratio between them can be determined arbitrarily.
- the ratio of the mass of the fluorinated solvent ( ⁇ ) to the total mass of the nonaqueous electrolytic solution of the present invention is 40 to 80% by mass.
- the lower limit of the proportion of the fluorinated solvent ( ⁇ ) is preferably 45% by mass, more preferably 50% by mass, and still more preferably 55% by mass.
- 75 mass% is preferable, as for the upper limit of the ratio of the said fluorine-containing solvent ((alpha)), 73 mass% is more preferable, and 70 mass% is further more preferable.
- the non-aqueous electrolyte is excellent in flame retardancy, small in positive electrode reactivity and negative electrode reactivity, hardly causes thermal runaway, and has high voltage resistance.
- the ratio of the said fluorine-containing solvent ((alpha)) is below an upper limit, lithium salt will melt
- the ratio of the mass of the fluorinated solvent ( ⁇ ) to the total mass of the liquid composition is preferably 45 to 90% by mass, more preferably 50 to 85% by mass, further preferably 55 to 80% by mass, and 60 to 75% by mass. Is particularly preferred.
- the liquid composition in the present invention preferably contains a fluorine-containing ether compound as the fluorine-containing solvent ( ⁇ ).
- the ratio of the mass of the fluorinated ether compound to the total mass of the fluorinated solvent ( ⁇ ) is preferably 25 to 100 mass%.
- the lower limit of the proportion of the fluorine-containing ether compound is preferably 30% by mass, more preferably 50% by mass, further preferably 60% by mass, particularly preferably 70% by mass, and most preferably 80% by mass.
- the fluorine-containing solvent ( ⁇ ) is particularly preferably composed of only a fluorine-containing ether compound.
- the ratio of the mass of the fluorinated ether compound to the total mass of the nonaqueous electrolytic solution of the present invention is preferably 10 to 80% by mass.
- the lower limit of the proportion of the fluorine-containing ether compound is more preferably 20% by mass, further preferably 30% by mass, particularly preferably 45% by mass, and most preferably 50% by mass.
- the upper limit value of the ratio of the fluorine-containing ether compound is more preferably 75% by mass, further preferably 73% by mass, and particularly preferably 70% by mass.
- the ratio of the mass of the fluorinated chain carboxylic acid ester compound to the total mass of the fluorinated solvent ( ⁇ ) is: 0.01 to 50% by mass is preferable.
- the upper limit of the proportion of the fluorine-containing chain carboxylic acid ester compound is more preferably 40% by mass, further preferably 30% by mass, and particularly preferably 20% by mass.
- the liquid composition in the present invention contains a fluorine-containing chain carbonate compound as the fluorine-containing solvent ( ⁇ )
- the ratio of the mass of the fluorine-containing chain carbonate compound to the total mass of the fluorine-containing solvent ( ⁇ ) is 0.01 to 50 mass% is preferable.
- the upper limit of the proportion of the fluorine-containing chain carbonate compound is more preferably 40% by mass, further preferably 30% by mass, and particularly preferably 20% by mass.
- the ratio of the mass of the fluorinated alkane compound to the total mass of the non-aqueous electrolyte is 0.01 to 5% by mass. preferable.
- the ratio of the fluorine-containing alkane compound is 0.01% by mass or more, the vapor pressure is low and the flame retardancy is excellent. If the ratio of the fluorine-containing alkane is 5% by mass or less, it is easy to maintain the solubility of the lithium salt.
- the liquid composition in the nonaqueous electrolytic solution of the present invention contains a cyclic carboxylic acid ester compound.
- the nonaqueous electrolytic solution of the present invention contains a cyclic carboxylic acid ester compound as a component of the liquid composition, the lithium salt is uniformly dissolved in the fluorinated solvent ( ⁇ ) by the cyclic carboxylic acid ester compound.
- the use of the cyclic carboxylic acid ester compound makes it difficult for the non-aqueous electrolyte, the positive electrode, and the negative electrode to react with each other, making it difficult for thermal runaway in the secondary battery to occur.
- the cyclic carboxylic acid ester compound is a cyclic compound having an ester bond in the molecule, and a compound having a structure in which a hydroxycarboxylic acid is dehydrated and cyclized in the molecule.
- the ring in the cyclic carboxylic acid ester compound is composed of a carbon atom to which one oxygen atom and an oxo group ( ⁇ O) adjacent to the oxygen atom are bonded, and two or more carbon atoms connecting the oxygen atom and the carbon atom. It is preferably a ring composed of a total of 4 or more atoms.
- the divalent group consisting of two or more carbon atoms connecting the oxygen atom and the carbon atom bonded to the oxo group ( ⁇ O) is preferably an alkylene group.
- the alkylene group is preferably a linear alkylene group, and the alkylene group preferably has 2 to 8 carbon atoms.
- the cyclic carboxylic acid ester compound a saturated cyclic carboxylic acid ester compound having no carbon-carbon unsaturated bond in the molecule is preferable.
- the ring structure in the cyclic carboxylic acid ester compound is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, more preferably a 5- to 6-membered ring, and particularly preferably a 5-membered ring from the viewpoint of availability.
- the ring structure of the cyclic carboxylic acid ester compound is preferably a ring structure having one ester bond.
- the cyclic ester compound may be a compound in which one or more hydrogen atoms of the linear alkylene group are substituted with a substituent. Examples of the substituent include a fluorine atom, a chlorine atom, an alkyl group, and a fluorinated alkyl group.
- the alkyl group preferably has 1 to 2 carbon atoms, and the fluorinated alkyl group preferably has 1 to 2 carbon atoms.
- the cyclic carboxylic acid ester compound is preferably the following compound (5).
- R 7 to R 12 are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or one or more And an alkyl group having 2 to 3 carbon atoms and having an etheric oxygen atom.
- n is an integer of 1 to 3.
- R 7 to R 12 in the compound (5) may be the same or different.
- R 7 to R 12 are each independently preferably a hydrogen atom, a methyl group, or a fluorine atom, and all of R 7 to R 12 are hydrogen atoms, or 1 to 3 of R 7 to R 12. More preferably, one is a methyl group and the other is a hydrogen atom.
- n is preferably 1 to 2, and more preferably 1.
- Examples of the compound (5) include cyclic ester compounds such as ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -hexanolactone, ⁇ -valerolactone, and hydrogen bonded to carbon atoms forming the ring of the cyclic ester compound. 2 or 3 carbon atoms in which one or more of the atoms have a fluorine atom, a chlorine atom, an alkyl group having 1 to 2 carbon atoms, a fluorinated alkyl group having 1 to 2 carbon atoms, or one or more etheric oxygen atoms The compound substituted by the alkyl group is mentioned.
- ⁇ -butyrolactone and ⁇ -valerolactone are preferable, and ⁇ -butyrolactone is more preferable because it is easily available and has a high effect of suppressing thermal runaway.
- 1 type may be sufficient as the cyclic carboxylic acid ester compound contained in the liquid composition of this invention, and 2 or more types may be sufficient as it.
- at least one part is a compound (5) as a cyclic carboxylic acid ester compound contained in the liquid composition in this invention, and it is more preferable that it consists only of a compound (5).
- the ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the nonaqueous electrolytic solution of the present invention is preferably 4 to 50% by mass.
- the lower limit of the ratio of the cyclic carboxylic acid ester compound is more preferably 7% by mass, further preferably 10% by mass, and particularly preferably 15% by mass.
- the upper limit of the ratio of the cyclic carboxylic acid ester compound is more preferably 45% by mass, further preferably 40% by mass, and particularly preferably 35% by mass.
- the ratio of the cyclic carboxylic acid ester compound is not less than the lower limit, the non-aqueous electrolyte uniformly dissolves the lithium salt, and the reactivity between the non-aqueous electrolyte and the positive and negative electrodes is small, causing thermal runaway. hard. Moreover, if content of the said cyclic carboxylic acid ester compound is below an upper limit, nonaqueous electrolyte solution is excellent in a flame retardance.
- N A / N Li which is the ratio of the total number of moles (N A ) of the cyclic carboxylic acid ester compound to the total number of moles (N Li ) of lithium atoms derived from the lithium salt contained in the non-aqueous electrolyte of the present invention is 1.5 to 7.0.
- the lower limit value of the N A / N Li is preferably 2.0, more preferably 2.5, and further preferably 3.0.
- the cyclic carboxylic acid ester compound forms a stable coating on the electrode active material when used, particularly in the positive electrode, and the coating of the electrode, the nonaqueous electrolytic solution, and the like It is estimated that the thermal runaway is suppressed along with this reaction.
- N A / N Li is not less than the lower limit, the non-aqueous electrolyte contains a sufficient amount of the cyclic carboxylic acid ester compound that forms the coating, so that the coating is sufficiently formed. It is considered that a sufficient thermal runaway suppression effect can be obtained by sufficiently exhibiting the reaction suppression effect.
- the lithium salt is the solvent when the N A / N Li is not less than the lower limit. Therefore, it is easy to obtain an electrolytic solution having sufficient conductivity in practical use.
- fluorine-containing compounds such as fluorine-containing ether compounds, fluorine-containing chain carboxylic acid ester compounds, and fluorine-containing chain carbonate compounds are considered to have low affinity with lithium salts and promote the dissolution of lithium salts in solvents. The effect of doing this tends to be very small.
- the upper limit of the N A / N Li is preferably 6.5, more preferably 6.0, more preferably 5.5, particularly preferably 5.0, more preferably 4.5, 4.2 Is most preferred.
- the film formed on the electrode active material is considered to be easily dissolved in a highly polar solvent, and even if a film is formed in a highly polar solvent, the film is likely to be insufficiently formed. It is estimated to be.
- the N A / N Li is not more than the upper limit value, the content of the cyclic carboxylic acid ester compound in the non-aqueous electrolyte does not become excessive, and the polarity of the entire electrolyte is within an appropriate range. It is considered that dissolution of the film formed on the substance is difficult to occur.
- the lithium salt can be uniformly dissolved to obtain sufficient conductivity, and the reactivity between the non-aqueous electrolyte and the positive and negative electrodes can be reduced. Thermal runaway can be suppressed.
- Non-fluorinated unsaturated cyclic carbonate compound The liquid composition in the non-aqueous electrolyte of the present invention preferably further contains a non-fluorinated unsaturated cyclic carbonate compound. Due to the non-fluorinated unsaturated cyclic carbonate compound, the non-aqueous electrolyte is excellent in rate characteristics, initial charge / discharge characteristics and cycle characteristics.
- the non-fluorinated unsaturated cyclic carbonate compound is a compound having a ring structure composed of a carbon atom and an oxygen atom, the ring structure has a carbonate bond, and has a carbon-carbon unsaturated bond in the molecule.
- the ring in the non-fluorinated unsaturated cyclic carbonate compound is composed of a carbon atom to which an oxo group ( ⁇ O) is bonded, two oxygen atoms bonded to the carbon atom, and one or more carbon atoms connecting the two oxygen atoms. It is preferably a ring composed of a total of 4 or more atoms.
- the divalent group connecting the two oxygen atoms is preferably an alkenylene group or an alkylene group.
- a chain alkenylene group and a chain alkylene group are preferred.
- the chain alkenylene group preferably has 2 to 7 carbon atoms, and more preferably 2 to 4 carbon atoms.
- the chain alkylene group preferably has 1 to 7 carbon atoms, more preferably 2 to 4 carbon atoms.
- the ring structure of the non-fluorinated unsaturated cyclic carbonate compound is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, more preferably a 5- to 6-membered ring from the viewpoint of availability, and particularly a 5-membered ring.
- the ring structure of the non-fluorinated unsaturated cyclic carbonate compound is preferably a ring structure having one carbonate bond.
- the carbon-carbon unsaturated bond of the non-fluorinated unsaturated cyclic carbonate compound may be inside the ring structure or outside the ring structure.
- the number of carbon-carbon unsaturated bonds in the non-fluorinated unsaturated cyclic carbonate compound is preferably 1 to 5, more preferably 1 to 3, and the easy availability and durability of the non-aqueous electrolyte solution From the viewpoint, 1 to 2 is more preferable, and 1 is particularly preferable.
- the non-fluorinated unsaturated cyclic carbonate compound the following compound (6) and compound (7) are preferred.
- R 13 and R 14 are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
- R 15 to R 18 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a vinyl group or an allyl group, and at least one of R 15 to R 18 is a vinyl group or An allyl group.
- Examples of the compound (6) include 4,5-dimethyl vinylene carbonate and vinylene carbonate. Of these, vinylene carbonate is preferable.
- Compound (7) includes vinyl ethylene carbonate (also known as 4-vinyl-1,3-dioxolan-2-one), 3-methyl-4-vinylethylene carbonate, 4,5-divinylethylene carbonate, 4,5- Examples thereof include bis (2-methylvinyl) ethylene carbonate. Of these, vinyl ethylene carbonate is preferable.
- non-fluorinated unsaturated cyclic carbonate compound compound (6), compound (7), or a mixture of compound (6) and compound (7) is preferably used.
- Compound (6) alone or compound (7) alone Is more preferable.
- a non-fluorine type unsaturated cyclic carbonate compound contained in the liquid composition in the present invention at least a part thereof is preferably the compound (6), and more preferably only the compound (6).
- the content of the non-fluorinated unsaturated cyclic carbonate compound in the non-aqueous electrolyte of the present invention is preferably 0.01 to 10% by mass.
- the lower limit of the content of the non-fluorinated unsaturated cyclic carbonate compound is more preferably 0.1% by mass, further preferably 0.2% by mass, and particularly preferably 0.5% by mass.
- the upper limit of the content of the non-fluorinated unsaturated cyclic carbonate compound is more preferably 7% by mass, further preferably 5% by mass, and particularly preferably 3% by mass.
- the non-aqueous electrolyte When the content of the non-fluorinated unsaturated cyclic carbonate compound is at least the lower limit value, the non-aqueous electrolyte is excellent in cycle characteristics, initial charge / discharge characteristics, and rate characteristics. In addition, if the content of the non-fluorinated unsaturated cyclic carbonate compound is not more than the upper limit value, the non-aqueous electrolyte is excellent in flame retardancy and voltage resistance, and the reactivity of the non-aqueous electrolyte with the positive electrode and the negative electrode Is small and heat runaway is unlikely to occur.
- the liquid composition in the nonaqueous electrolytic solution of the present invention preferably further contains a fluorine-containing cyclic carbonate compound. Due to the fluorine-containing cyclic carbonate compound, the non-aqueous electrolyte is excellent in rate characteristics, initial charge / discharge characteristics, and cycle characteristics.
- the fluorine-containing cyclic carbonate compound is a compound having a ring structure composed of carbon atoms and oxygen atoms, the ring structure having a carbonate bond, and a fluorine atom in the molecule.
- the ring in the fluorinated cyclic carbonate compound has a total of 4 carbon atoms composed of a carbon atom to which an oxo group ( ⁇ O) is bonded, two oxygen atoms bonded to the carbon atom, and one or more carbon atoms connecting the two oxygen atoms.
- a ring composed of the above atoms is preferable.
- the divalent group connecting the two oxygen atoms is preferably an alkenylene group or an alkylene group.
- a linear alkylene group and a linear alkenylene group are preferred.
- the linear alkylene group preferably has 1 to 7 carbon atoms, more preferably 2 to 4 carbon atoms.
- the linear alkenylene group preferably has 2 to 7 carbon atoms, and more preferably 2 to 4 carbon atoms.
- these linear alkylene group and linear alkenylene group have a fluorine atom or a fluorine-containing substituent such as a fluorine-containing alkyl group.
- the fluorine-containing cyclic carbonate compound is preferably a compound containing no carbon-carbon unsaturated bond in the molecule.
- the ring structure in the fluorinated cyclic carbonate compound is preferably a 4- to 10-membered ring, more preferably a 4- to 7-membered ring, more preferably a 5- to 6-membered ring, and particularly preferably a 5-membered ring from the viewpoint of availability.
- the ring structure of the fluorine-containing cyclic carbonate compound is preferably a ring structure having one carbonate bond, and more preferably a ring structure formed by linking a carbonate bond to a fluorine-containing linear alkylene group.
- the fluorine-containing linear alkylene group is a group in which one or more hydrogen atoms of the linear alkylene group are substituted with fluorine atoms.
- the fluorine-containing linear alkylene group preferably has 1 to 7 carbon atoms, more preferably 1 to 4, more preferably 2 or 3, and particularly preferably 2.
- a fluorine-containing cyclic carbonate compound the compound by which one or more of the hydrogen atoms of the linear alkylene group was substituted by the fluorinated alkyl group is also preferable.
- the fluorine-containing cyclic carbonate compound the following compound (8) is preferable.
- R 19 to R 22 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, an alkyl group having 2 to 4 carbon atoms having an etheric oxygen atom, or 1 carbon atom.
- R 19 to R 22 in the compound (8) may be the same or different.
- R 19 to R 22 are preferably a hydrogen atom, a fluorine atom, a fluorinated alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms having an etheric oxygen atom.
- —CF 3 , —CHF 2 , —CH 2 F, —CF 2 CF 3 , —CH 2 CF 3, or —CH 2 OCH 2 CF 2 CF 3 are more preferred.
- R 19 to R 22 is a fluorine atom or —CF 3 and the other is a hydrogen atom, and part of R 19 to R 22 is a fluorine atom and the other is Particularly preferred is a hydrogen atom.
- the compound (8) the following compounds (8-1) to (8-7) are preferable from the viewpoint of excellent rate characteristics and cycle characteristics. From the viewpoint of availability, the compound (8-1) or the compound (8-4) is preferable. ) Is more preferable, and compound (8-1) is more preferable.
- Specific examples of the compound (8) other than the compounds (8-1) to (8-7) include the following compound (8-8).
- the fluorine-containing cyclic carbonate compound contained in the liquid composition in the present invention may be only one type or two or more types. Moreover, as a fluorine-containing cyclic carbonate compound contained in a liquid composition, it is preferable that at least one part is a compound (8), and it is more preferable that it consists only of a compound (8).
- the content of the fluorine-containing cyclic carbonate compound in the nonaqueous electrolytic solution of the present invention is preferably 0.01 to 10% by mass.
- the lower limit of the content of the fluorine-containing cyclic carbonate compound is more preferably 0.1% by mass, further preferably 0.2% by mass, and particularly preferably 0.5% by mass.
- the upper limit of the content of the fluorine-containing cyclic carbonate compound is more preferably 7% by mass, further preferably 5% by mass, and particularly preferably 3% by mass. If content of the said fluorine-containing cyclic carbonate compound is more than a lower limit, a non-aqueous electrolyte will be excellent in cycling characteristics, initial charge / discharge characteristics, and rate characteristics.
- the non-aqueous electrolyte is excellent in flame retardancy and voltage resistance, and the reactivity between the non-aqueous electrolyte and the positive electrode and the negative electrode is small. Thermal runaway is unlikely to occur.
- the liquid composition of the non-aqueous electrolyte solution of the present invention contains the above-mentioned fluorine-containing solvent ( ⁇ ) and other solvents other than the fluorine-containing cyclic carboxylic acid ester compound, the non-fluorinated unsaturated cyclic carbonate compound and the fluorine-containing cyclic carbonate compound. But you can.
- a saturated cyclic carbonate compound having no fluorine atom hereinafter also referred to as “non-fluorinated saturated cyclic carbonate compound”
- At least one compound ( ⁇ ) selected from the group consisting of a chain carbonate compound having no fluorine atom hereinafter also referred to as “non-fluorine chain carbonate compound”
- a saturated cyclic sulfone compound and a phosphate ester compound is preferable.
- a non-fluorinated saturated cyclic carbonate compound is a compound in which the ring skeleton has a ring structure composed of carbon atoms and oxygen atoms, and the ring structure has a carbonate bond represented by —O—C ( ⁇ O) —O—. It is a compound having a fluorine atom and no carbon-carbon unsaturated bond. Examples thereof include propylene carbonate (PC) and ethylene carbonate (EC).
- the non-fluorine chain carbonate compound is a chain compound that has no ring structure, has a carbonate bond represented by —O—C ( ⁇ O) —O—, and does not have a fluorine atom. .
- DMC dimethyl carbonate
- EMC ethyl methyl carbonate
- DEC diethyl carbonate
- saturated cyclic sulfone compound examples include sulfolane and 3-methylsulfolane.
- phosphoric acid ester compound examples include trimethyl phosphoric acid and triethyl phosphoric acid.
- the nonaqueous electrolytic solution of the present invention may not contain other solvents, but when other solvents are included, the ratio of the mass of the other solvent to the total mass of the nonaqueous electrolytic solution is 0.01 to 30 masses. It is preferably 0.1 to 20% by mass. If the ratio of the said other solvent is below an upper limit, it will be easy to suppress reaction with another solvent and a charging electrode, and the electrolyte solution excellent in stability can be obtained. Moreover, since content of a fluorine-containing solvent ((alpha)) can be increased, the nonaqueous electrolyte solution excellent in the flame retardance is easy to be obtained.
- a fluorine-containing solvent ((alpha)
- the ratio of the mass of the compound ( ⁇ ) to the total mass of the non-aqueous electrolyte is preferably 0.01 to 30% by mass, and 0.1 to 20% by mass Is more preferable.
- the non-aqueous electrolytic solution of the present invention may not contain a non-fluorinated saturated cyclic carbonate compound, but when it contains a non-fluorinated saturated cyclic carbonate compound, the non-fluorinated saturated cyclic carbonate with respect to the total mass of the non-aqueous electrolytic solution.
- the mass ratio of the carbonate compound is preferably 20% by mass or less, more preferably 15% by mass or less, further preferably less than 10% by mass, particularly preferably 5% by mass or less, and most preferably 3% by mass or less.
- the ratio of the mass of the non-fluorinated saturated cyclic carbonate compound to the total mass of the non-aqueous electrolyte is preferably 0.01 to 20% by mass, 0.01 to 15% by mass is more preferable, 0.01% by mass or more and less than 10% by mass is further preferable, 0.01 to 5% by mass is particularly preferable, and 0.01 to 3% by mass is most preferable.
- the ratio of the non-fluorinated saturated cyclic carbonate compound is not more than the upper limit value, the non-fluorinated saturated cyclic carbonate compound and the electrode are unlikely to react, and the non-aqueous electrolyte is excellent in stability and flame retardancy.
- the non-aqueous electrolyte of the present invention may not contain a non-fluorine chain carbonate compound, but if it contains a non-fluorine chain carbonate compound, the viscosity of the electrolyte can be lowered and the conductivity of the electrolyte can be reduced. It is also preferable that a non-fluorine chain carbonate compound is included from the viewpoint of easily increasing the amount.
- the ratio of the mass of the non-fluorine chain carbonate compound to the total mass of the nonaqueous electrolytic solution is preferably 30% by mass or less, more preferably 20% by mass or less, Less than 10% by weight is more preferable, less than 10% by weight is particularly preferable, and 5% by weight or less is most preferable.
- the ratio of the mass of the non-fluorine chain carbonate compound to the total mass of the non-aqueous electrolyte is the same as that of the non-fluorine saturated cyclic carbonate compound.
- 0.01 to 30% by mass is preferable, 0.01 to 20% by mass is more preferable, 0.01 to 15% by mass is further preferable, 0.01% by mass or more and less than 10% by mass is particularly preferable. 0.01 to 5% by mass is most preferable.
- the ratio of the total mass of the non-fluorinated saturated cyclic carbonate compound and the non-fluorinated chain carbonate compound to the total mass of the nonaqueous electrolytic solution of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, It is more preferably less than 10% by weight, and particularly preferably 5% by weight or less.
- the non-aqueous electrolyte of the present invention contains at least one selected from the group consisting of a non-fluorinated saturated cyclic carbonate compound and a non-fluorinated chain carbonate compound
- the non-fluorinated saturated cyclic carbonate with respect to the total mass of the non-aqueous electrolyte
- the ratio of the total mass of the compound and the non-fluorine chain carbonate compound is preferably 0.01 to 20% by mass, more preferably 0.01 to 15% by mass, and further preferably 0.01% by mass or more and less than 10% by mass.
- 0.01 to 5% by mass is particularly preferable.
- the solvent is formed by the cyclic carboxylic acid ester due to the increased polarity.
- the dissolution of the coated film can be suppressed, the reactivity between them and the electrode can be kept low, and it is easy to obtain a non-aqueous electrolyte with excellent stability. Moreover, it is easy to set it as the non-aqueous electrolyte which has the outstanding flame retardance by restraining content of a combustible compound low.
- the non-aqueous electrolyte of the present invention may not contain a saturated cyclic sulfone compound, but when it contains a saturated cyclic sulfone compound, the ratio of the mass of the saturated cyclic sulfone compound to the total mass of the non-aqueous electrolyte is 20 % By mass or less is preferable, less than 15% by mass is more preferable, 10% by mass or less is particularly preferable, and 5% by mass or less is most preferable.
- the ratio of the mass of the saturated cyclic sulfone compound to the total mass of the non-aqueous electrolyte is 0.01 for the same reason as the non-fluorinated saturated cyclic carbonate compound. Is preferably 20 to 20% by mass, more preferably 0.01 to 15% by mass, still more preferably 0.01 to 10% by mass, and particularly preferably 0.01 to 5% by mass.
- the non-aqueous electrolyte of the present invention may not contain a phosphate ester compound, but when it contains a phosphate ester compound, the ratio of the mass of the phosphate ester compound to the total mass of the non-aqueous electrolyte is 5 The mass% or less is preferable.
- the ratio of the mass of the phosphate ester compound to the total mass of the non-aqueous electrolyte of the present invention is the same as that of the non-fluorinated saturated cyclic carbonate compound. 0.01 to 5% by mass is preferable.
- the ratio is the ratio of the total number of moles (N P ) of the phosphate ester compound to the total number of lithium atoms (N Li ) derived from the lithium salt.
- N P / N Li is preferably 0.01 or more and less than 1.0.
- the ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the cyclic carboxylic acid ester compound and the compound ( ⁇ ) is preferably 40 to 100% by mass.
- the lower limit of the proportion of the cyclic carboxylic acid ester compound is preferably 50% by mass, more preferably 60% by mass, further preferably 70% by mass, and particularly preferably 80% by mass.
- the non-aqueous electrolyte solution of the present invention comprises a compound (beta), the total number of moles of lithium atoms from the lithium salt to the (N Li), the total number of moles of the cyclic carboxylic acid ester compound (N A), compound is the ratio of the sum of total moles (N B) of ( ⁇ ) (N a + N B) / N Li is from 3 to 7.0, it is preferable lower limit is 3.0.
- the upper limit is preferably 6.5.
- (N A + N B) / N Li is particularly preferably from 3 to 6.5.
- the lower limit of the (N A + N B) / N Li is 3.2 is preferred, 3.5 is more preferable.
- the compound ( ⁇ ) has a high affinity with the lithium salt similarly to the cyclic carboxylic acid ester compound, and is considered to have an effect of promoting dissolution of the lithium salt in a solvent.
- (N A + N B) / N Li is less than the lower limit, i.e.
- the solubility of the lithium salt in the fluorine-containing solvent ( ⁇ ) is improved, thereby improving the conductivity of the non-aqueous electrolyte, and in particular, when using a lithium salt such as LiPF 6 that is difficult to dissolve in the fluorine-based solvent. Can be dissolved in a fluorine-based solvent, and practically sufficient conductivity is easily obtained.
- the (N A + N B) / N upper limit of Li is preferably 6.5, more preferably 6.0, more preferably 5.5, particularly preferably 5.0, 4.5 is most preferred .
- the flame retardance of a non-aqueous electrolyte is also improved by reducing the content of a highly flammable cyclic carboxylic acid ester compound or compound ( ⁇ ) in the non-aqueous electrolyte.
- a lithium salt containing LiPF 6 and controlling N A / N Li and (N A + N B ) / N Li within the above-mentioned ranges, practically sufficient conductivity and thermal runaway occur. It is easy to obtain a non-aqueous electrolyte solution having both excellent and difficult stability.
- the liquid composition in the present invention includes a nitrile compound such as acetonitrile, and monoglyme. It is preferable not to include an ether compound having no fluorine atom, such as (1,2-dimethoxyethane).
- the ratio of the mass of the nitrile compound to the total mass of the nonaqueous electrolytic solution of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and more preferably 3% by mass or less. Further preferred.
- the ratio of the mass of the ether compound having no fluorine atom to the total mass of the nonaqueous electrolytic solution of the present invention is preferably 10% by mass or less, preferably 5% by mass.
- the following is more preferable, 3% by mass or less is further preferable, and 1% by mass or less is particularly preferable.
- the non-aqueous electrolyte of the present invention may contain components other than those described above as necessary.
- the components other than those described above include, for example, conventionally known overcharge inhibitors, dehydrating agents, deoxidizing agents, capacity maintenance characteristics after high-temperature storage and characteristics improvement aids for improving cycle characteristics, and nonaqueous electrolyte electrodes.
- surfactants that help impregnation of the composite material and the separator.
- overcharge inhibitor examples include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran; 2-fluoro Partially fluorinated products of the above aromatic compounds such as biphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole and 2,6-difluoroaniol Compounds.
- aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl
- An overcharge inhibitor may be used individually by 1 type, and may use 2 or more types together.
- the content of the overcharge inhibitor in the non-aqueous electrolyte is preferably 0.01 to 5% by mass.
- the dehydrating agent examples include molecular sieves, sodium sulfate, magnesium sulfate, calcium hydride, sodium hydride, potassium hydride, lithium aluminum hydride and the like.
- the solvent used in the nonaqueous electrolytic solution of the present invention it is preferable to use a solvent obtained by performing rectification after dehydrating with the dehydrating agent. Moreover, you may use the solvent which performed only the dehydration by the said dehydrating agent, without performing rectification.
- the above components that is, fluorine-containing solvent ( ⁇ ), compound ( ⁇ ), unsaturated cyclic carbonate compound having no fluorine atom, and Carbonate compounds other than fluorine-containing cyclic carbonate compounds
- sulfone compounds other than the compound ( ⁇ ) may be used.
- carbonate compounds such as erythritan carbonate and spiro-bis-dimethylene carbonate; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, Sulfurene, dimethylsulfone, diphenylsulfone, methylphenylsulfone, dibutyldisulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide and other sulfur-containing compounds; heptane, octane And hydrocarbon compounds such as cycloheptane; fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene and hexafluorobenzene.
- any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant may be used. Agents are preferred.
- a fluorine-containing surfactant is preferable from the viewpoint of high oxidation resistance and good cycle characteristics and rate characteristics.
- the anionic fluorine-containing surfactant the following compound (9-1) and compound (9-2) are preferred.
- R 23 and R 24 are each independently a C 4-20 perfluoroalkyl group or a C 4-20 perfluoroalkyl group having one or more etheric oxygen atoms.
- M 1 and M 2 are each independently an alkali metal or NH (R 25 ) 3 (R 25 is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and may be the same group or different groups. Good.)
- R 23 and R 24 are each a C 4-20 perfluoroalkyl group or a C 4 carbon atom having one or more etheric oxygen atoms from the viewpoint of a good degree of reducing the surface tension of the non-aqueous electrolyte.
- a perfluoroalkyl group having 20 to 20 carbon atoms is preferred.
- An alkyl group is more preferred.
- the structure of R 13 and R 14 may be a linear structure or a branched structure, and may contain a ring structure.
- R 23 and R 24 are preferably linear structures because they are easily available and have a good surface activity.
- the alkali metal of M 1 and M 2 Li, Na and K are preferable.
- M 1 and M 2 NH 4 + is particularly preferable.
- Specific examples of the compound (9-1) include C 4 F 9 COO — NH 4 + , C 5 F 11 COO — NH 4 + , C 6 F 13 COO — NH 4 + , C 5 F 11 COO ⁇ .
- C 5 F 11 COO ⁇ NH 4 + , C 5 F 11 COO ⁇ Li + , and C 6 F 13 COO ⁇ Li are preferred because of their good solubility in non-aqueous electrolytes and the effect of reducing surface tension.
- the compound (9-2) include C 4 F 9 SO 3 - NH 4 + , C 5 F 11 SO 3 - NH 4 + , C 6 F 13 SO 3 - NH 4 + , C 4 F 9 SO 3 - NH (CH 3 ) 3 +, C 5 F 11 SO 3 - NH (CH 3) 3 +, C 6 F 13 SO 3 - NH (CH 3) 3 +, C 4 F 9 SO 3 - Li +, C 5 F 11 SO 3 - Li +, C 6 F 13 SO 3 - Li +, C 3 F 7 OCF (CF 3) CF 2 OC (CF 3) FSO 3 - NH 4 +, C 3 F 7 OCF (CF 3) CF 2 OCF ( CF 3) CF 2 OCF (CF 3) SO 3 - NH 4 +, HCF 2 CF 2 OCF 2 CF 2 SO 3 - NH 4 +, CF 3 CFHCF 2 OCF 2 CF 2 SO 3 - NH 4 +, C F 7 OC (CF CF
- solubility in the nonaqueous electrolytic solution from the viewpoint of satisfactory effect of reducing the surface tension, C 4 F 9 SO 3 - NH 4 +, C 6 F 13 SO 3 - NH 4 +, C 4 F 9 SO 3 - Li +, C 6 F 13 SO 3 - Li +, C 8 F 17 SO 3 - Li +, C 3 F 7 OCF (CF 3) CF 2 OCF (CF 3) SO 3 - NH 4 +, C 3 F 7 OCF (CF 3) CF 2 OCF (CF 3) SO 3 - Li +, C 3 F 7 OCF (CF 3) SO 3 - NH 4 + and C 3 F 7 OCF (CF 3 ) SO 3 - Li + Is preferred.
- the contained surfactant may be only one type or two or more types.
- the upper limit of the ratio of the mass of the surfactant to the total mass of the non-aqueous electrolyte is preferably 5% by mass, more preferably 3% by mass. More preferred is mass%.
- the lower limit is preferably 0.05% by mass.
- the lower limit of the conductivity at 25 ° C. of the nonaqueous electrolytic solution of the present invention is preferably 0.30 S / m.
- a secondary battery using an electrolyte having a non-aqueous electrolyte having a conductivity of less than 0.30 S / m at 25 ° C. has poor output characteristics and lacks practicality. If the conductivity of the non-aqueous electrolyte at 25 ° C. is 0.30 S / m or more, the secondary battery is excellent in output characteristics.
- composition 1 LiPF 6 , compound (A), FSO 2 N (Li) SO 2 F, CF 3 SO 2 N (Li) SO 2 CF 3 , CF 3 CF 2 SO 2 N (Li) SO 2 CF 2 CF 3 , LiClO 4
- At least one lithium salt selected from the group consisting of Compound (B), Compound (C), and LiBF 4 At least one lithium salt selected from the group consisting of Compound (B), Compound (C), and LiBF 4 ; and at least one fluorine-containing solvent selected from the group consisting of Compounds (1) to (4) ( a nonaqueous electrolytic solution for a secondary battery, comprising: ⁇ ); and at least one cyclic carboxylic acid ester compound which is the compound (5).
- composition 2 is more preferable.
- Composition 2 At least one lithium salt selected from the group consisting of LiPF 6 , CF 3 SO 2 N (Li) SO 2 CF 3 , CF 3 CF 2 SO 2 N (Li) SO 2 CF 2 CF 3 , LiClO 4 and LiBF 4.
- a compound represented by the formula (2) and X is CH 2 CH 2
- a compound represented by the formula (2) and X is CH (CH 3 ) CH 2
- At least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of compounds; and a group consisting of ⁇ -butyrolactone and ⁇ -valerolactone A non-aqueous electrolyte for a secondary battery comprising at least one cyclic carboxylic acid ester compound selected from the group consisting of:
- composition 3 is particularly preferred.
- Composition 3 A non-aqueous electrolyte for a secondary battery containing LiPF 6 , CHF 2 CF 2 CH 2 OCF 2 CFHCF 3 , and ⁇ -butyrolactone and / or ⁇ -valerolactone.
- composition 4 As the non-aqueous electrolyte in the case of containing a non-fluorinated unsaturated cyclic carbonate-based compound, the following composition 4 is preferable because the intended effect of the present invention is exhibited.
- Composition 4 The group consisting of LiPF 6 , compound (A), FSO 2 N (Li) SO 2 F, CF 3 SO 2 N (Li) SO 2 CF 3 , LiClO 4 , compound (B), compound (C), and LiBF 4 At least one lithium salt selected from the group consisting of compounds (1) to (4); at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of compounds (1) to (4); and at least one cyclic carboxylic acid as compound (5)
- a nonaqueous electrolytic solution for a secondary battery comprising an ester compound and at least one non-fluorinated unsaturated cyclic carbonate compound selected from the group consisting of the compound (6) and the compound (7).
- composition 5 is more preferable.
- Composition 5 At least one lithium salt selected from the group consisting of LiPF 6 , FSO 2 N (Li) SO 2 F, LiClO 4 and LiBF 4 ; and CF 3 CH 2 OCF 2 CHF 2 , CF 3 CH 2 OCF 2 CHFCF 3 , CHF 2 CF 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 CH 2 OCHF 2 , CH 3 CH 2 OCF 2 CHF 2 , CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 , represented by the formula (2) and X
- at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of a compound wherein is CH 2 CH 2 and a compound represented by the formula (2) and X is CH (CH 3 ) CH 2 ;
- At least one cyclic carboxylic acid ester compound selected from the group consisting of -butyrolactone and ⁇ -valerolactone, and a compound ( )
- the compound (7) at least one
- composition 6 is particularly preferred.
- (Composition 6) LiPF 6 , at least one selected from the group consisting of CF 3 CH 2 OCF 2 CHF 2 and CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 , ⁇ -butyrolactone and / or ⁇ -valerolactone, vinylene carbonate, Non-aqueous electrolyte for secondary batteries containing
- composition 7 is preferable as the non-aqueous electrolyte in the case of containing the fluorine-containing cyclic carbonate compound, since the effects aimed at by the present invention are exhibited.
- Composition 7 The group consisting of LiPF 6 , compound (A), FSO 2 N (Li) SO 2 F, CF 3 SO 2 N (Li) SO 2 CF 3 , LiClO 4 , compound (B), compound (C), and LiBF 4 At least one lithium salt selected from the group consisting of compounds (1) to (4); at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of compounds (1) to (4); and at least one cyclic carboxylic acid as compound (5)
- a nonaqueous electrolytic solution for a secondary battery comprising an ester compound and at least one fluorine-containing cyclic carbonate compound which is the compound (8).
- composition 8 is more preferable.
- Composition 8 At least one lithium salt selected from the group consisting of LiPF 6 , FSO 2 N (Li) SO 2 F, LiClO 4 and LiBF 4 ; and CF 3 CH 2 OCF 2 CHF 2 , CF 3 CH 2 OCF 2 CHFCF 3 , CHF 2 CF 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 CH 2 OCHF 2 , CH 3 CH 2 OCF 2 CHF 2 , CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 , represented by the formula (2) and X
- at least one fluorine-containing solvent ( ⁇ ) selected from the group consisting of a compound wherein is CH 2 CH 2 and a compound represented by the formula (2) and X is CH (CH 3 ) CH 2 ;
- At least one cyclic carboxylic acid ester compound selected from the group consisting of -butyrolactone and ⁇ -valerolactone, and a compound ( The non-aqueous electrolyte secondary
- composition 9 is particularly preferred.
- (Composition 9) LiPF 6 , at least one selected from the group consisting of CF 3 CH 2 OCF 2 CHF 2 and CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 , ⁇ -butyrolactone and / or ⁇ -valerolactone, compound (8- 1) and a nonaqueous electrolytic solution for a secondary battery.
- the lithium ion secondary battery of this invention is a secondary battery characterized by having a positive electrode, a negative electrode, and the non-aqueous electrolyte of this invention.
- the positive electrode include an electrode in which a positive electrode layer containing a positive electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector.
- the positive electrode active material may be any material that can occlude and release lithium ions, and known positive electrode active materials for lithium ion secondary batteries can be employed. Examples thereof include lithium-containing transition metal oxides, lithium-containing transition metal composite oxides using one or more transition metals, transition metal oxides, transition metal sulfides, metal oxides, and olivine-type metal lithium salts.
- lithium-containing transition metal oxide examples include lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide.
- the metal contained in the lithium-containing transition metal composite oxide is preferably Al, V, Ti, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Yb, etc.
- transition metal oxides include TiO 2 , MnO 2 , MoO 3 , V 2 O 5 , V 6 O 13 , transition metal sulfides TiS 2 , FeS, MoS 2 , metal oxides SnO 2 , Examples thereof include SiO 2 .
- the olivine-type metallic lithium salt is Li L X x Y y O z F g (where X is Fe (II), Co (II), Mn (II), Ni (II), V (II), or Cu ( II), Y represents P or Si, and represents numbers satisfying 0 ⁇ L ⁇ 3, 1 ⁇ x ⁇ 2, 1 ⁇ y ⁇ 3, 4 ⁇ z ⁇ 12, and 0 ⁇ g ⁇ 1, respectively. Or a complex thereof.
- the active material which forms a positive electrode may be used individually by 1 type, and may use 2 or more types together.
- a material in which a substance having a composition different from that of the substance constituting the main cathode active material is attached to the surface of the cathode active material can be used.
- Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, etc .; lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.
- the lower limit of the mass with respect to the positive electrode active material is preferably 0.1 mass ppm, more preferably 1 mass ppm, and particularly preferably 10 mass ppm.
- the upper limit is preferably 20% by mass, more preferably 10% by mass, and particularly preferably 5% by mass.
- the surface adhering substance can suppress the oxidation reaction of the nonaqueous electrolytic solution on the surface of the positive electrode active material, and can improve the battery life.
- a lithium-containing composite oxide based on an ⁇ -NaCrO 2 structure such as LiCoO 2 , LiNiO 2 , LiMnO 2 or the like, LiMn 2 O, because of its high discharge voltage and high electrochemical stability
- a lithium-containing composite oxide based on a spinel structure such as 4 is preferred.
- Examples of the conductivity-imparting agent include carbon materials, metal substances such as Al, and conductive oxide powders.
- the binder include resin binders such as polyvinylidene fluoride, and rubber binders such as hydrocarbon rubber and fluorine rubber.
- Examples of the current collector include a metal thin film mainly composed of Al or the like.
- Examples of the negative electrode include an electrode in which a negative electrode layer containing a powdery negative electrode active material, a conductivity-imparting agent, and a binder is formed on a current collector.
- Examples of the negative electrode active material include one or more selected from the group consisting of a lithium metal, a lithium alloy, and a carbon material capable of inserting and extracting lithium ions.
- Examples of the carbon material include graphite, coke, and hard carbon.
- Examples of the lithium alloy include a Li—Al alloy, a Li—Pb alloy, and a Li—Sn alloy.
- the negative electrode binder and the conductivity-imparting agent those equivalent to the positive electrode can be used.
- the current collector a metal thin film mainly composed of Cu or the like can be used.
- a negative electrode active material can maintain a shape by itself (for example, lithium metal thin film)
- a negative electrode can be formed only with a negative electrode active material.
- a separator is interposed between the positive electrode and the negative electrode to prevent a short circuit.
- An example of the separator is a porous film.
- a non-aqueous electrolyte is used by impregnating the porous membrane.
- you may use as a gel electrolyte what impregnated the porous film with the nonaqueous electrolyte solution, and was made to gelatinize.
- porous film those which are stable with respect to the non-aqueous electrolyte and excellent in liquid retention can be used, such as polyvinylidene fluoride, polytetrafluoroethylene, a copolymer of ethylene and tetrafluoroethylene, a fluorine resin, polyimide, Or the porous sheet or nonwoven fabric which uses polyolefin, such as polyethylene and a polypropylene, as a raw material is preferable.
- the material of the porous film is preferably a polyolefin such as polyethylene or polypropylene.
- the material of the battery casing used in the lithium ion secondary battery of the present invention include nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, and a film material.
- the shape of the secondary battery may be selected according to the application, and may be any shape such as a coin shape, a cylindrical shape, a square shape, and a laminate shape. Moreover, the shape of a positive electrode and a negative electrode can be suitably selected according to the shape of a secondary battery.
- the charging voltage of the secondary battery of the present invention is preferably 3.4 V or higher, more preferably 4.0 V or higher, and even more preferably 4.2 V or higher.
- the positive electrode active material of the secondary battery is a lithium-containing transition metal oxide, a lithium-containing transition metal composite oxide, a transition metal oxide, a transition metal sulfide, or a metal oxide
- the charging voltage is preferably 4.0 V or more, 4.2V or more is more preferable.
- the positive electrode active material is an olivine type lithium metal salt
- the charging voltage is preferably 3.2 V or higher, and more preferably 3.4 V or higher.
- the secondary battery of the present invention uses the non-aqueous electrolyte of the present invention, the cycle characteristics are excellent, the reactivity between the non-aqueous electrolyte and the positive and negative electrodes is small, and thermal runaway is difficult to occur. It has practically sufficient conductivity. Therefore, the secondary battery of the present invention includes a mobile phone, a portable game machine, a digital camera, a digital video camera, an electric tool, a notebook computer, a portable information terminal, a portable music player, an electric vehicle, a hybrid vehicle, a train, an aircraft, an artificial It can be applied to various uses such as satellites, submarines, ships, uninterruptible power supplies, robots, and power storage systems. In addition, the secondary battery of the present invention is particularly effective as a large-sized secondary battery for electric vehicles, hybrid vehicles, trains, airplanes, artificial satellites, submarines, ships, uninterruptible power supply devices, robots, power storage systems, and the like.
- the conductivity (unit: S / m) was measured at 25 ° C. using the known method described in “Molten salt and high temperature chemistry, 2002, 45, 43” for the obtained nonaqueous electrolytic solution. That is, electrodes having metallic lithium attached thereto were set on both ends of a T-type electrochemical cell having a bottom length of 5 cm and an inner diameter of 4.8 mm. Thereafter, the prepared electrolyte was sufficiently injected and sealed. The solution resistance of the obtained electrochemical cell was allowed to stand in a thermostatic bath at 25 ° C.
- Negative electrode reactivity evaluation test The negative electrode produced by the above method was used as an evaluation electrode, and a lithium metal foil punched out into a circle having a diameter of 19 mm was used as a counter electrode. Between these electrodes, a polyolefin microporous membrane was present as a separator.
- a carbonate-based non-aqueous electrolyte (a non-aqueous electrolyte in which ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of 3: 7 and dissolved so that LiPF 6 is 1.0 M, manufactured by Kishida Chemical Co., Ltd.)
- a non-aqueous electrolyte solution in which vinylene carbonate was added to 2% by mass was added to 5 mL to prepare a single electrode cell composed of graphite electrode-lithium metal foil. The following charging / discharging cycle was implemented about the obtained monopolar cell.
- cycle 1 at 25 ° C., a constant current charge is performed to a current corresponding to 0.04 C up to 0.2 V (negative electrode), a constant current charge is performed to a current corresponding to 0.2 C up to 0.05 V, and the charging lower limit Constant voltage charging was performed until the current value corresponding to 0.02C in voltage was reached. Thereafter, constant current discharge was performed to 1.0 V at a current corresponding to 0.2C.
- cycles 2 to 4 constant current charging was performed up to 0.05 V with a current corresponding to 0.2 C, and further constant voltage charging was performed until the current value reached a current corresponding to 0.02 C at the charging lower limit voltage. Thereafter, constant current discharge was performed to 1.0 V at a current corresponding to 0.2C.
- exothermic peak temperature was the peak top temperature of the exothermic peak that appeared at the lowest temperature among the exothermic peaks with an exothermic amount exceeding 2000 ⁇ W when the exothermic amount at 60 ° C. in the measurement was corrected to zero.
- the exothermic peak temperature is evaluated as “ ⁇ (excellent)” at 200 ° C. or higher, “ ⁇ (good)” at 180 ° C. or higher and lower than 200 ° C., “ ⁇ (bad)” at 150 ° C. or higher and lower than 180 ° C., and below 150 ° C. “ ⁇ (very bad)”.
- the calorific value at 200 ° C.” was the calorific value at 200 ° C. ( ⁇ W) when the calorific value at 60 ° C. in the measurement was corrected to 0.
- Electrode for evaluation positive electrode
- LiCoO 2 manufactured by AGC Seimi Chemical Co., trade name “Selion C”, 32.0 g
- carbon black manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “Denka Black”, 0.80 g
- the step of stirring for 1 minute at a rotational speed of 2000 rpm using the agitator was performed three times.
- the step of adding N-methyl-2-pyrrolidone (7.50 g) and stirring with the stirrer at 2000 rpm for 3 minutes was performed three times.
- N-methyl-2-pyrrolidone 1.0 g
- stirring for 3 minutes at a rotational speed of 2000 rpm using the stirrer was performed three times.
- an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (11% by mass, 7.45 g) was added, and the mixture was stirred for 1 minute at a rotation speed of 2000 rpm using the stirrer to obtain a slurry.
- the slurry was applied to an aluminum foil having a thickness of 20 ⁇ m with a thickness of 150 ⁇ m, dried, and then punched into a circle having a diameter of 18 mm to obtain an evaluation electrode (positive electrode). 2.
- the positive electrode produced by the above method was used as an evaluation electrode, and a lithium metal foil punched out into a circle having a diameter of 19 mm was used as a counter electrode. Between these electrodes, a polyolefin microporous membrane was present as a separator. Further, 0 of a carbonate-based non-aqueous electrolyte (a non-aqueous electrolyte in which ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of 3: 7 and dissolved so that LiPF 6 is 1.0 M, manufactured by Kishida Chemical Co., Ltd.) .5 mL was added, and a single electrode cell made of LiCoO 2 electrode-lithium metal foil was prepared.
- a carbonate-based non-aqueous electrolyte a non-aqueous electrolyte in which ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of 3: 7 and dissolved so that LiPF 6 is 1.0 M, manufactured by Ki
- the obtained positive electrode was washed three times with dimethyl carbonate (2 mL), vacuum-dried and then punched out to a diameter of 5 mm, placed in a sealed container made of SUS, and further sealed with 2 ⁇ L of the nonaqueous electrolyte of each example.
- An evaluation sample was used.
- Each of the obtained evaluation samples was measured with a differential scanning calorimeter (DSC-6000 manufactured by SII Nano Technology) at a temperature range of 50 to 350 ° C. and a heating rate of 5 ° C./min.
- the positive electrode reactivity was evaluated by “exothermic peak temperature” and “exotherm at 200 ° C.” in the same manner as the negative electrode reactivity.
- Examples 1 to 24, 30 to 33 and 39 are Examples, and Examples 25 to 29 and 34 to 38 are Comparative Examples.
- Example 1 LiPF 6 (0.11 g) as a lithium salt was dispersed in CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 (1.23 g) as a fluorine-containing ether compound, and then ⁇ -butyrolactone (1) as a compound (5) 0.24 g) was mixed to obtain a nonaqueous electrolytic solution 1A.
- Nonaqueous electrolytes 2 to 38 were obtained in the same manner as in Example 1, except that the composition of each compound such as lithium salt was changed as shown in Tables 1 to 5.
- the mass% in Tables 1 to 5 is a ratio based on 100% by mass of the entire non-aqueous electrolyte.
- Tables 1-5 The evaluation results for each example are shown in Tables 1-5.
- the abbreviations in Tables 1 to 5 have the following meanings.
- AE3000 CF 3 CH 2 OCF 2 CHF 2 (trade name: AE-3000, manufactured by Asahi Glass Co., Ltd.).
- HFE458 CF 2 HCF 2 CH 2 OCF 2 CF 2 H.
- HFE449 CF 3 CH 2 OCF 2 CFHCF 3.
- HFE5510 CHF 2 CF 2 CH 2 OCF 2 CHFCF 3.
- MFA methyl difluoroacetate.
- ETFA ethyl trifluoroacetate.
- TFEOc bis (2,2,2-trifluoroethyl) carbonate.
- GBL ⁇ -butyrolactone.
- GVL ⁇ -valerolactone.
- EC ethylene carbonate.
- PC Propylene carbonate.
- EMC ethyl methyl carbonate.
- DMC dimethyl carbonate.
- DEC diethyl carbonate.
- TMP trimethyl phosphate.
- SX-1 a compound represented by the following formula:
- the non-aqueous electrolytes of Examples 1 to 24, 30, and 31 containing a fluorine-containing solvent ( ⁇ ) and a cyclic carboxylic acid ester compound consisting of only LiPF 6 are negative electrode reactive Both positive electrode reactivity and small exothermic behavior were exhibited.
- the non-aqueous electrolyte solution of Example 23 in which the cyclic carboxylic acid ester compound is 5 equivalents to the lithium salt and the non-aqueous electrolyte solution of Example 24 in which the cyclic carboxylic acid ester is 6 equivalents to the lithium salt are cyclic carboxylic acid esters.
- the exothermic peak temperature in the reaction with the negative electrode was higher and the exothermic behavior was more excellent as compared with the non-aqueous electrolyte of Example 38 having 8 equivalents to the lithium salt.
- the non-aqueous electrolytes of Examples 20 to 22 in which N A / N Li is 4.0 and (N A + N B ) / N Li is 3 to 7.0 have N A / N Li of 4.0.
- the positive electrode reactivity was small as compared with the nonaqueous electrolytic solution of Example 28 where (N A + N B ) / N Li was as large as 7.4.
- Example 32 in which the lithium salt is composed of LiPF 6 and LiBF 4 and Example 33, in which the lithium salt is composed only of LiBF 4 are both small in negative electrode reactivity and positive electrode reactivity and exhibit good exothermic behavior.
- the nonaqueous electrolytic solution of Example 33 which does not contain LiPF 6 tends to have a low conductivity of the electrolytic solution.
- the nonaqueous electrolytic solution of Example 25 in which the amount of the compound (5) was increased without using the fluorinated solvent ( ⁇ ) had an exothermic peak temperature in the reaction with the negative electrode of 150 ° C. or higher and lower than 180 ° C., and the negative electrode reactivity was low. It was big.
- the nonaqueous electrolytic solution of Example 26 in which the compound (5) is not used has a low exothermic peak temperature for both the positive electrode and the negative electrode, and has a large exothermic amount at 200 ° C. and low stability.
- the nonaqueous electrolytic solution of Example 28 in which the content of the fluorinated solvent ( ⁇ ) is less than 40% by mass has a lower calorific value at 200 ° C. than that of Example 27 in which no cyclic carboxylic acid ester is contained.
- the exothermic peak temperature in the reaction was 150 ° C. or higher and lower than 180 ° C., and the positive electrode reactivity was large.
- Example 29 in which LiPF 6 was used as the lithium salt and N A / N Li was less than 1.5, the lithium salt could not be dissolved uniformly.
- Examples 34 and 35 in which N A / N Li is greater than 7.0 the exothermic peak temperature in the reaction with the positive electrode and the negative electrode is less than 200 ° C., and compared with Examples 1 to 24, The reactivity with the electrode was great.
- Example 36A in which N A / N Li is 1.5 to 7.0 but (N A + N B ) / N Li is greater than 7.0 is low in negative electrode reactivity and thermal runaway due to reaction at the negative electrode However, the positive electrode reactivity was large.
- Example 39 A cell comprising a LiCoO 2 electrode-graphite electrode, with the positive electrode and the negative electrode facing each other, a polyolefin microporous membrane as a separator between them, and the non-aqueous electrolyte (0.5 mL) of Example 12 added. It was created. The resulting cell was subjected to the following charge / discharge cycle. In cycle 1, constant current charging is performed up to 3.4 V at a current corresponding to 0.01 C at 25 ° C., and constant current charging is performed up to 4.2 V at a current corresponding to 0.2 C. Constant voltage charging was performed until the current value reached a current corresponding to 0.02C.
- the cell using the non-aqueous electrolyte of the present invention showed good cycle characteristics.
- Example II> The following are examples relating to an electrolytic solution containing a non-fluorinated cyclic carbonate compound.
- Examples 1A to 5A are examples, and examples 6A and 7A are comparative examples.
- [Example 1A] After diffusing LiPF 6 (0.15 g), which is a lithium salt, into CF 3 CH 2 OCF 2 CF 2 H (trade name: AE-3000, manufactured by Asahi Glass Co., Ltd.) (1.02 g), which is compound (1) Then, ⁇ -butyrolactone (0.34 g) as compound (5) was mixed to obtain a uniform solution. Then, vinylene carbonate which is a compound (6) was added so that it might become 2 mass% with respect to this solution, and it was set as nonaqueous electrolyte 1A.
- Examples 2A-7A Nonaqueous electrolytes 2A to 7A were obtained in the same manner as in Example 1A, except that the composition of each compound such as lithium salt was changed as shown in Table 7.
- the abbreviations in Table 7 have the following meanings.
- VC vinylene carbonate.
- FEC Fluoroethylene carbonate. Others are the same as in ⁇ Example I>.
- Ion conductivity was evaluated in the same manner as in ⁇ Example I>.
- the discharge was 0.1 C in cycle 11, 0.2 C in cycle 12, 0.5 C in cycle 13, 1.0 C in cycle 14, 1.0 C in cycle 15, and a constant current discharge to 3.0 V at a current equivalent to 2.0 C. .
- an average discharge voltage at 2.0 C discharge was measured.
- constant current charging was performed up to 4.2 V with a current corresponding to 0.2 C, and constant voltage charging was performed until the current value reached a current corresponding to 0.02 C at the charging lower limit voltage.
- constant current discharge was performed to 3.0 V at a current corresponding to 0.2 C.
- the cycle characteristics were evaluated based on the discharge capacity retention ratio of cycle 30 and cycle 50 with respect to the discharge capacity per unit weight of positive electrode active material of cycle 10. The results are shown in Table 7.
- Examples 1A to 5A using the nonaqueous electrolytic solution of the present invention containing a cyclic carboxylic acid ester compound and a non-fluorinated unsaturated cyclic carbonate compound As shown in Table 7, in Examples 1A to 5A using the nonaqueous electrolytic solution of the present invention containing a cyclic carboxylic acid ester compound and a non-fluorinated unsaturated cyclic carbonate compound, sufficient initial charge / discharge characteristics were obtained, Excellent cycle characteristics and rate characteristics were obtained. On the other hand, in Examples 6A and 7A in which the non-fluorinated unsaturated cyclic carbonate compound was not used, all of the initial charge / discharge characteristics, rate characteristics, and cycle characteristics were inferior to those in Examples 1A to 5A.
- Example III The following are examples relating to the case of an electrolytic solution containing a fluorine-containing cyclic carbonate compound.
- Examples 1B to 5B are examples, and examples 6B and 7B are comparative examples.
- [Example 1B] After diffusing LiPF 6 (0.15 g), which is a lithium salt, into CF 3 CH 2 OCF 2 CF 2 H (trade name: AE-3000, manufactured by Asahi Glass Co., Ltd.) (1.02 g), which is compound (1) Then, ⁇ -butyrolactone (0.34 g) as compound (5) was mixed to obtain a uniform solution. Thereafter, the compound (8), fluoroethylene carbonate (4-fluoro-1,3-dioxolan-2-one, compound (8-1)), is added to the solution so as to be 2% by mass. Electrolytic solution 1B was obtained.
- Nonaqueous electrolytes 2B to 7B were obtained in the same manner as in Example 1B, except that the composition of each compound such as lithium salt was changed as shown in Table 8.
- the abbreviations in Table 8 have the same meaning as described above.
- the non-aqueous electrolyte for secondary batteries of the present invention can be suitably used as a non-aqueous electrolyte for use in lithium ion secondary batteries for various applications such as mobile phones, laptop computers, and electric vehicles. It can also be used for other charging devices such as capacitors and lithium ion capacitors.
- Japanese Patent Application No. 2012-071067 filed on March 27, 2012, Japanese Patent Application No. 2012-071068 filed on March 27, 2012, Japanese Patent Application filed on October 22, 2012 The entire contents of the specifications, claims and abstracts of Japanese Patent Application No. 2012-233286 and Japanese Patent Application No. 2013-022593 filed on Feb. 7, 2013 are hereby incorporated herein by reference. As it is incorporated.
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Abstract
Description
非水電解液の性能を落とさずに不燃性(難燃性)を高める方法としては、フッ素系溶媒を添加することが提案されている(特許文献1)。しかし、フッ素系溶媒は、リチウム塩の溶解能が低く、サイクル特性が悪くなる傾向にある。
また、含フッ素溶媒と環状カーボネートと環状カルボン酸エステル及びリチウム塩からなる非水電解液が提案されている(特許文献3、特許文献4)。しかし本発明者らが検討を行ったところ、電極との反応性が高く、安定性が不充分であるか、または伝導度が低く、実用性に乏しいといういずれかの問題があった。このように、実用的に充分な伝導度を確保しつつ、非水電解液と電極との反応性を低くすることは困難である。
近年、二次電池は、より大きなエネルギーを必要とする電気自動車の車載電源等への適用が盛んに検討されており、正極および負極との反応性がより小さい非水電解液が求められている。
また、より大きなエネルギーを効率良く得るには、正極および負極と非水電解液の反応性を低減したうえで、さらに優れたレート特性、初回充放電特性およびサイクル特性も兼ね備えていることが求められる。
[1]リチウム塩と液状組成物からなる非水電解液であって、
前記液状組成物が、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物および含フッ素鎖状カーボネート化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と、環状カルボン酸エステル化合物とを含み、
フッ素原子を有しない飽和環状カーボネート化合物、フッ素原子を有しない鎖状カーボネート化合物、飽和環状スルホン化合物およびリン酸エステル化合物からなる群から選ばれる少なくとも1種の化合物(β)を含んでもよく、
前記非水電解液の総質量に対する前記含フッ素溶媒(α)の質量の割合が40~80質量%であり、
前記リチウム塩由来のリチウム原子の総モル数(NLi)に対する前記環状カルボン酸エステル化合物の総モル数(NA)の比率であるNA/NLiが1.5~7.0であり、
前記NLiに対する、前記NAと、前記化合物(β)の総モル数(NB)との和の比率である(NA+NB)/NLiが3~7.0であることを特徴とする二次電池用非水電解液。
[3]前記液状組成物がさらにフッ素原子を有しない不飽和環状カーボネート化合物を含む、[2]の二次電池用非水電解液。
[4]前記非水電解液中の前記フッ素原子を有しない不飽和環状カーボネート化合物の含有量が0.01~10質量%である、[3]の二次電池用非水電解液。
[5]前記液状組成物がさらに含フッ素環状カーボネート化合物を含む、[2]の二次電池用非水電解液。
[6]前記非水電解液中の前記含フッ素環状カーボネート化合物の含有量が0.01~10質量%である、[5]の二次電池用非水電解液。
[7]前記液状組成物が前記フッ素原子を有しない飽和環状カーボネート化合物を含む、[1]~[6]のいずれかの二次電池用非水電解液。
[8]前記液状組成物が前記フッ素原子を有しない鎖状カーボネート化合物を含む、[1]~[7]のいずれかの二次電池用非水電解液。
[10]前記環状カルボン酸エステル化合物が、γ-ブチロラクトンおよびγ-バレロラクトンからなる群から選ばれる少なくとも1種である、[1]~[9]のいずれかの二次電池用非水電解液。
[11]前記非水電解液の総質量に対する前記環状カルボン酸エステル化合物の質量の割合が4~50質量%である、[1]~[10]のいずれかの二次電池用非水電解液。
[12]前記非水電解液の25℃におけるリチウムイオン伝導度が0.3S/m以上である、[1]~[11]のいずれかの二次電池用非水電解液。
[13]前記リチウム塩の少なくとも一部がLiPF6である、[1]~[12]のいずれかの二次電池用非水電解液。
[14]前記非水電解液中の前記リチウム塩の含有量が0.1~3.0mol/Lである、[1]~[13]のいずれかの二次電池用非水電解液。
また、本発明のリチウムイオン二次電池は、本発明の二次電池用非水電解液を用いているため、熱暴走を起こし難く、レート特性、初回充放電特性、およびサイクル特性に優れ、実用的に充分な伝導度も有している。
本明細書において、フッ素化とは、炭素原子に結合した水素原子の一部または全部がフッ素原子に置換されることをいう。フッ素化アルキル基は、アルキル基の水素原子の一部または全部がフッ素原子に置換された基である。一部がフッ素化された基中には、水素原子およびフッ素原子が存在する。また、パーフルオロアルキル基とは、アルキル基の水素原子の全部がフッ素原子に置換された基である。また、炭素-炭素不飽和結合とは、炭素-炭素二重結合または炭素-炭素三重結合である。
本発明の二次電池用非水電解液(以下、単に「非水電解液」ということがある。)は、リチウム塩と液状組成物からなる。前記液状組成物は、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物および含フッ素鎖状カーボネート化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と、環状カルボン酸エステル化合物とを含有する。
また、本発明の二次電池用非水電解液は、液状組成物として、フッ素原子を有しない不飽和環状カーボネート化合物(以下、「非フッ素系不飽和環状カーボネート化合物」ということがある。)および/または含フッ素環状カーボネート化合物を含んでいてもよい。
リチウム塩は、非水電解液中で解離してリチウムイオンを供給する電解質である。リチウム塩としては、LiPF6、下記化合物(A)(ただし、kは1~5の整数である。)、FSO2N(Li)SO2F、CF3SO2N(Li)SO2CF3、CF3CF2SO2N(Li)SO2CF2CF3、LiClO4、下記化合物(B)、下記化合物(C)、下記化合物(D)、下記化合物(E)、およびLiBF4からなる群から選ばれるリチウム塩が好ましい。リチウム塩としては、LiPF6、LiBF4および化合物(A)からなる群から選ばれるリチウム塩がより好ましく、LiPF6がさらに好ましい。
本発明の非水電解液に含有されるリチウム塩は1種のみでもよく、2種以上であってもよい。2種以上のリチウム塩を併用する場合の組み合わせは、国際公開第2009/133899号に開示される組み合わせが挙げられる。
LiPF6を使用すると、高い伝導度が得られるものの、CF3CF2SO2N(Li)SO2CF2CF3等の他のリチウム塩に比べて含フッ素溶媒に溶解しにくい。また、LiPF6は熱分解しやすい性質を持つ。しかし、含フッ素溶媒下でもLiPF6を環状カルボン酸エステル化合物と併用することによりLiPF6の溶解性が向上し、LiPF6が溶媒に均一に溶解することで実用的に充分な伝導度を有する非水電解液を得やすく、また特定の量の環状カルボン酸エステル化合物を含むことで、LiPF6を用いた電解液においても熱暴走しにくくなる。
本発明の非水電解液に含まれるリチウム塩としては少なくともその一部がLiPF6であることが好ましい。本発明の非水電解液に含有されるリチウム塩の総モル数に対する、LiPF6のモル比の下限値は40mol%が好ましく、50mol%がより好ましく、65mol%がさらに好ましく、80mol%が特に好ましい。前記非水電解液に含有されるリチウム塩の総モル数に対する、LiPF6のモル比の上限値は100mol%である。リチウム塩の総モル数に対する、LiPF6のモル比が下限値以上であれば、伝導度に優れ、実用性の高い非水電解液となる。
質量%に換算すると、非水電解液の総質量に対するリチウム塩の質量の割合は、5質量%~25質量%が好ましい。前記リチウム塩の質量の割合の下限値は、7質量%がより好ましく、8質量%がさらに好ましい。また前記リチウム塩の質量の割合の上限値は、20質量%がより好ましく、17質量%がさらに好ましい。
前記リチウム塩の割合が前記下限値以上であれば、非水電解液の伝導度が高い。また、前記リチウム塩の割合が前記上限値以下であれば、リチウム塩が液状組成物に均一に溶解しやすく、また低温条件でもリチウム塩が析出しない。
本発明の非水電解液における液状組成物は、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物および含フッ素鎖状カーボネート化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)を含む。含フッ素溶媒(α)は、分子内にフッ素原子を有する溶媒であり、難燃性が優れている。液状組成物に含まれる含フッ素溶媒(α)は1種でもよく、2種以上であってもよい。液液状組成物に含まれる含フッ素溶媒(α)が2種以上の場合、それら相互の間の比率は任意に決めることができる。
液液状組成物に含まれる含フッ素溶媒(α)は、少なくともその一部が含フッ素エーテル化合物であることが好ましい。含フッ素エーテル化合物としては、下記化合物(1)および下記化合物(2)からなる群から選ばれる含フッ素エーテル化合物が好ましい。液液状組成物に含まれる含フッ素エーテル化合物は1種でもよく、2種以上であってもよい。液液状組成物に含まれる含フッ素エーテル化合物が2種以上の場合、それら相互の間の比率は任意に決めることができる。
また、式(2)中、Xは炭素数1~5のアルキレン基、炭素数1~5のフッ素化アルキレン基、1個以上のエーテル性酸素原子を有する炭素数2~5のアルキレン基、または1個以上のエーテル性酸素原子を有する炭素数2~5のフッ素化アルキレン基である。
化合物(1)におけるR1およびR2の一方または両方は、炭素数1~10のフッ素化アルキル基、炭素数3~10のフッ素化シクロアルキル基、または1個以上のエーテル性酸素原子を有する炭素数2~10のフッ素化アルキル基である。R1およびR2の一方または両方がこれらの基であると、リチウム塩の非水電解液への溶解性および非水電解液の難燃性が優れる。化合物(1)におけるR1とR2は同じであってもよく、異なっていてもよい。
化合物(1)としては、R1およびR2が、いずれも炭素数1~10のフッ素化アルキル基である化合物(以下、化合物(1-A)という。)と、R1が1個以上のエーテル性酸素原子を有する炭素数2~10のフッ素化アルキル基であり、R2が炭素数1~10のフッ素化アルキル基である化合物(以下、化合物(1-B)という。)と、R1が炭素数1~10のフッ素化アルキル基であり、R2が炭素数1~10のアルキル基である化合物(以下、化合物(1-C)という。)とが好ましく、化合物(1-A)および化合物(1-C)がより好ましく、化合物(1-A)が特に好ましい。
特に、化合物(1)は、リチウム塩の液状組成物に対する溶解度に優れる点から、R1およびR2の一方または両方の末端が-CF2Hである化合物が好ましい。
化合物(2)の具体例としては、例えば、下式で表される化合物等が挙げられる。
本発明における液状組成物が化合物(1)を含有する場合、含有される化合物(1)は1種のみでもよく、2種以上であってもよい。また、本発明における液状組成物が化合物(2)を含有する場合、含有される化合物(2)は1種のみでもよく、2種以上であってもよい。
含フッ素エーテル化合物として、化合物(1)(質量:Va)と化合物(2)(質量:Vb)が併用される場合、それらの質量比(Vb/Va)は、0.01~100が好ましく、0.1~10がより好ましい。
前記アルキル基、フッ素化アルキル基としては、それぞれ、直鎖構造、分岐構造が挙げられる。
R3およびR4の一方または両方が該フッ素化アルキル基であることで、化合物(3)の耐酸化性および難燃性が向上する。化合物(3)におけるR3とR4は同じであってもよく、異なっていてもよい。
R3としては、メチル基、エチル基、ジフルオロメチル基、トリフルオロメチル基、テトラフルオロエチル基、およびペンタフルオロエチル基が好ましく、ジフルオロメチル基、およびトリフルオロメチル基がより好ましい。
R4としては、メチル基、エチル基、トリフルオロメチル基、2-フルオロエチル基、2,2-ジフルオロエチル基、および2,2,2-トリフルオロエチル基が好ましく、メチル基、エチル基、または2,2,2-トリフルオロエチル基がより好ましく、メチル基、およびエチル基がさらに好ましい。
含フッ素鎖状カルボン酸エステル化合物は2種以上使用してもよい。含フッ素鎖状カルボン酸エステル化合物が2種以上使用される場合、それら相互間の比率は任意に決めることができる。
本発明における液状組成物が化合物(3)を含有する場合、含有される化合物(3)は1種のみでもよく、2種以上であってもよい。
液状組成物に含まれる含フッ素鎖状カルボン酸エステル化合物としては、少なくともその一部が化合物(3)であることが好ましく、化合物(3)のみからなることがより好ましい。
前記アルキル基、フッ素化アルキル基としては、それぞれ、直鎖構造、分岐構造が挙げられる。
R5およびR6の一方または両方が該フッ素化アルキル基であることで、リチウム塩の非水電解液への溶解性および難燃性が向上する。化合物(4)におけるR5とR6は同じであってもよく、異なっていてもよい。
含フッ素鎖状カーボネート化合物は2種以上使用してもよい。含フッ素鎖状カーボネート化合物が2種以上使用され場合、それら相互間の比率は任意に決めることができる。
本発明における液状組成物が化合物(4)を含有する場合、含有される化合物(4)は1種のみでもよく、2種以上であってもよい。
液状組成物に含まれる含フッ素鎖状カーボネート化合物としては、少なくともその一部が化合物(4)であることが好ましく、化合物(4)のみからなることがより好ましい。
本発明における液状組成物が含フッ素アルカン化合物を含む場合、非水電解液は、蒸気圧が抑制され、難燃性がさらに優れる。含フッ素アルカン化合物とは、アルカンの水素原子の1個以上がフッ素原子に置換され、水素原子が残っている化合物をいう。含フッ素アルカン化合物としては、炭素数4~12の含フッ素アルカン化合物が好ましい。炭素数6以上の含フッ素アルカン化合物を用いた場合は、非水電解液の蒸気圧が低く、炭素数が12以下の含フッ素アルカン化合物であればリチウム塩の溶解度が良好である。また、含フッ素アルカン化合物中のフッ素含有量は、50~80質量%が好ましい。含フッ素アルカン化合物中のフッ素含有量が50質量%以上であれば、難燃性に優れる。含フッ素アルカン化合物中のフッ素含有量が80質量%以下であれば、リチウム塩の溶解性を保持しやすい。
前記含フッ素溶媒(α)の割合が下限値以上であれば、非水電解液は、難燃性に優れ、正極反応性および負極反応性が小さく、熱暴走を起こし難く、耐高電圧特性を有する。前記含フッ素溶媒(α)の割合が上限値以下であれば、リチウム塩が均一に溶解し、また低温下においてリチウム塩が析出し難く、伝導度が低下しない。
液状組成物の総質量に対する含フッ素溶媒(α)の質量の割合は、45~90質量%が好ましく、50~85質量%がより好ましく、55~80質量%がさらに好ましく、60~75質量%が特に好ましい。
含フッ素溶媒(α)の総質量に対する含フッ素エーテル化合物の質量の割合は、25~100質量%が好ましい。前記含フッ素エーテル化合物の割合の下限値は、30質量%が好ましく、50質量%がより好ましく、60質量%がさらに好ましく、70質量%が特に好ましく、80質量%が最も好ましい。含フッ素溶媒(α)は、含フッ素得エーテル化合物のみからなることが特に好ましい。
本発明の非水電解液の総質量に対する含フッ素エーテル化合物の質量の割合は、10~80質量%が好ましい。前記含フッ素エーテル化合物の割合の下限値は、20質量%がより好ましく、30質量%がさらに好ましく、45質量%が特に好ましく、50質量%が最も好ましい。また、前記含フッ素エーテル化合物の割合の上限値は、75質量%がより好ましく、73質量%がさらに好ましく、70質量%が特に好ましい。
本発明における液状組成物が含フッ素溶媒(α)として含フッ素鎖状カーボネート化合物を含む場合、含フッ素溶媒(α)の総質量に対する含フッ素鎖状カーボネート化合物の質量の割合は、0.01~50質量%が好ましい。前記含フッ素鎖状カーボネート化合物の割合の上限値は、40質量%がより好ましく、30質量%がさらに好ましく、20質量%が特に好ましい。
本発明の非水電解液における液状組成物は、環状カルボン酸エステル化合物を含む。
本発明の非水電解液が液状組成物の成分として環状カルボン酸エステル化合物を含有すると、環状カルボン酸エステル化合物により、含フッ素溶媒(α)にリチウム塩が均一に溶解される。また、本発明では、環状カルボン酸エステル化合物を用いることで、非水電解液と正極および負極とが反応し難く、二次電池における熱暴走が起き難くなる。
環状カルボン酸エステル化合物における環は、1個の酸素原子とその酸素原子に隣接したオキソ基(=O)が結合した炭素原子と、それら酸素原子と炭素原子とを連結する2以上の炭素原子からなる合計4以上の原子から構成される環であることが好ましい。上記酸素原子とオキソ基(=O)が結合した炭素原子とを連結する2以上の炭素原子からなる2価の基はアルキレン基であることが好ましい。該アルキレン基としては直鎖アルキレン基が好ましく、アルキレン基の炭素数は2~8が好ましい。
環状カルボン酸エステル化合物としては、分子内に炭素-炭素不飽和結合を含まない飽和環状カルボン酸エステル化合物が好ましい。
環状カルボン酸エステル化合物における環構造は、4~10員環が好ましく、4~7員環がより好ましく、入手容易な点から、5~6員環がさらに好ましく、5員環が特に好ましい。
環状カルボン酸エステル化合物の環構造は、エステル結合を1つ有する環構造が好ましい。また、環状エステル化合物は、前記直鎖アルキレン基の水素原子の1個以上を置換基で置換した化合物でもよい。置換基としては、例えば、フッ素原子、塩素原子、アルキル基、フッ素化アルキル基等が挙げられる。アルキル基の炭素数は1~2が好ましく、フッ素化アルキル基の炭素数は1~2が好ましい。
環状カルボン酸エステル化合物は、下記化合物(5)が好ましい。
化合物(5)におけるR7~R12は、同じであってもよく、異なっていてもよい。
また、R7~R12としては、それぞれ独立に、水素原子、メチル基、またはフッ素原子が好ましく、R7~R12の全てが水素原子であるか、またはR7~R12の1~3つがメチル基で他が水素原子であることがより好ましい。
nは、1~2が好ましく、1がより好ましい。
本発明の液状組成物に含まれる環状カルボン酸エステル化合物は、1種のみでもよく、2種以上であってもよい。
また、本発明における液状組成物に含まれる環状カルボン酸エステル化合物としては、少なくともその一部が化合物(5)であることが好ましく、化合物(5)のみからなることがより好ましい。
前記環状カルボン酸エステル化合物の割合が下限値以上であれば、非水電解液は、リチウム塩を均一に溶解し、かつ非水電解液と正極および負極との反応性が小さく、熱暴走が起こり難い。また、前記環状カルボン酸エステル化合物の含有量が上限値以下であれば、非水電解液は難燃性に優れる。
前記NA/NLiの下限値は、2.0が好ましく、2.5がより好ましく、3.0がさらに好ましい。
本発明の非水電解液を二次電池に用いた場合、特に正極において、使用時に環状カルボン酸エステル化合物が電極活物質上に安定な被膜を形成し、該被膜によって電極と非水電解液との反応が抑制され、これに伴って熱暴走が抑制されるものと推定される。
前記NA/NLiが下限値以上であると、非水電解液中に被膜を形成する環状カルボン酸エステル化合物が充分に含まれるので充分に被膜が形成され、電極と非水電解液との反応の抑制効果が充分に発揮されることにより充分な熱暴走の抑制効果が得られると考えられる。また、環状カルボン酸エステル化合物は、リチウム塩との親和性が高く、リチウム塩の溶媒への溶解を促進すると考えられるため、前記NA/NLiが下限値以上であると、リチウム塩が溶媒に充分に溶解しやすくなり、実用状充分な伝導度を持つ電解液を得やすい。なお、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物や含フッ素鎖状カーボネート化合物等の含フッ素化合物は、リチウム塩との親和性が低いと考えられ、リチウム塩の溶媒への溶解を促進する効果も非常に小さい傾向にある。
また、前記NA/NLiの上限値は、6.5が好ましく、6.0がより好ましく、5.5がさらに好ましく、5.0が特に好ましく、4.5がさらに好ましく、4.2が最も好ましい。
前記の電極活物質上に形成された被膜は極性の高い溶媒に溶解しやすいと考えられ、極性が高い溶媒中では被膜が形成されても溶解してしまうことにより、被膜形成が不充分となりやすいと推定される。前記NA/NLiが上限値以下であると、非水電解液中の環状カルボン酸エステル化合物の含有量が過多にならず、電解液全体の極性が適切な範囲となることにより、電極活物質上に形成された被膜の溶解が起こりにくくなると考えられる。電極活物質上に充分な被膜が維持されることにより、電極と非水電解液とによる発熱反応が起こり難くなり、熱暴走も起こり難くなると考えられる。なお、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物や含フッ素鎖状カーボネート化合物等の含フッ素化合物は極性が低いため、前記の被膜を溶解させる効果は非常に低いと考えられる。また、可燃性の高い環状カルボン酸エステルの含有量が少なくなることにより非水電解液の難燃性も向上する。
前記NA/NLiが前記範囲内であれば、リチウム塩を均一に溶解させて充分な伝導度を得つつ、非水電解液と正極および負極との反応性を小さくでき、二次電池の熱暴走が起きることを抑制できる。
本発明の非水電解液における液状組成物は、さらに非フッ素系不飽和環状カーボネート化合物を含むことが好ましい。
非フッ素系不飽和環状カーボネート化合物により、非水電解液は、レート特性、初回充放電特性およびサイクル特性に優れる。
非フッ素系不飽和環状カーボネート化合物における環は、オキソ基(=O)が結合した炭素原子とその炭素原子に結合した2つの酸素原子と、それら2つの酸素原子を連結する1以上の炭素原子からなる合計4以上の原子から構成される環であることが好ましい。上記2つの酸素原子を連結する2価の基はアルケニレン基またはアルキレン基であることが好ましい。これら2価の基としては鎖状アルケニレン基および鎖状アルキレン基が好ましい。また、鎖状アルケニレン基の炭素数は2~7が好ましく、2~4がより好ましい。鎖状アルキレン基の炭素数は1~7が好ましく、2~4がより好ましい。
非フッ素系不飽和環状カーボネート化合物の環構造は、4~10員環が好ましく、4~7員環がより好ましく、入手容易な点から、5~6員環がさらに好ましく、5員環が特に好ましい。
非フッ素系不飽和環状カーボネート化合物の環構造は、カーボネート結合を1つ有する環構造が好ましい。
非フッ素系不飽和環状カーボネート化合物の炭素-炭素不飽和結合は環構造内にあっても環構造の外にあってもよい。また、非フッ素系不飽和環状カーボネート化合物中の炭素-炭素不飽和結合の数は、1~5個が好ましく、1~3個がより好ましく、入手容易な点と非水電解液の耐久性の点から、1~2個がさらに好ましく、1個が特に好ましい。
非フッ素系不飽和環状カーボネート化合物としては、下記化合物(6)、化合物(7)が好ましい。
また、式(7)中、R15~R18はそれぞれ独立に水素原子、炭素数1~3のアルキル基、ビニル基またはアリル基であり、かつR15~R18の少なくとも1つがビニル基またはアリル基である。
化合物(7)としては、ビニルエチレンカーボネート(別名;4-ビニル-1,3-ジオキソラン-2-オン)、3-メチル-4-ビニルエチレンカーボネート、4,5-ジビニルエチレンカーボネート、4,5-ビス(2-メチルビニル)エチレンカーボネート等が挙げられる。なかでも、ビニルエチレンカーボネートが好ましい。
前記非フッ素系不飽和環状カーボネート化合物の含有量が下限値以上であれば、非水電解液は、サイクル特性、初回充放電特性およびレート特性に優れる。また、前記非フッ素系不飽和環状カーボネート化合物の含有量が上限値以下であれば、非水電解液は難燃性および耐電圧性に優れ、かつ非水電解液と正極および負極との反応性が小さく、熱暴走が起こり難い。
本発明の非水電解液における液状組成物は、さらに含フッ素環状カーボネート化合物を含むことも好ましい。
含フッ素環状カーボネート化合物により、非水電解液は、レート特性、初回充放電特性およびサイクル特性に優れる。
含フッ素環状カーボネート化合物における環は、オキソ基(=O)が結合した炭素原子とその炭素原子に結合した2つの酸素原子と、それら2つの酸素原子を連結する1以上の炭素原子からなる合計4以上の原子から構成される環であることが好ましい。上記2つの酸素原子を連結する2価の基はアルケニレン基またはアルキレン基であることが好ましい。これら2価の基としては直鎖アルキレン基および直鎖アルケニレン基が好ましい。また、直鎖アルキレン基の炭素数は1~7が好ましく、2~4がより好ましい。直鎖アルケニレン基の炭素数は2~7が好ましく、2~4がより好ましい。含フッ素環状カーボネート化合物においてはこれら直鎖アルキレン基や直鎖アルケニレン基はフッ素原子を有するかまたは含フッ素アルキル基などの含フッ素置換基を有する。
含フッ素環状カーボネート化合物は、分子内に炭素-炭素不飽和結合を含まない化合物であることが好ましい。
含フッ素環状カーボネート化合物における環構造は、4~10員環が好ましく、4~7員環がより好ましく、入手容易な点から、5~6員環がさらに好ましく、5員環が特に好ましい。
含フッ素環状カーボネート化合物の環構造は、カーボネート結合を1つ有する環構造が好ましく、カーボネート結合が含フッ素直鎖アルキレン基と連結して形成された環構造がより好ましい。含フッ素直鎖アルキレン基とは、直鎖アルキレン基の水素原子の1個以上がフッ素原子に置換された基である。含フッ素直鎖アルキレン基の炭素数は1~7が好ましく、1~4がより好ましく、2または3がさらに好ましく、2が特に好ましい。
また、含フッ素環状カーボネート化合物としては、直鎖アルキレン基の水素原子の1つ以上がフッ素化アルキル基に置換された化合物も好ましい。
含フッ素環状カーボネート化合物としては、下記化合物(8)が好ましい。
R19~R22としては、水素原子、フッ素原子、炭素数1~4のフッ素化アルキル基、またはエーテル性酸素原子を有する炭素数1~4のフッ素化アルキル基が好ましく、水素原子、フッ素原子、-CF3、-CHF2、-CH2F、-CF2CF3、-CH2CF3または-CH2OCH2CF2CF3がより好ましい。入手容易性などの観点から、R19~R22の少なくとも一部がフッ素原子または-CF3で他が水素原子であることがさらに好ましく、R19~R22の一部がフッ素原子で他が水素原子であることが特に好ましい。
化合物(8)としては、レート特性およびサイクル特性に優れる点から、下記化合物(8-1)~(8-7)が好ましく、入手容易性等から化合物(8-1)または化合物(8-4)がより好ましく、化合物(8-1)がさらに好ましい。
また、液状組成物に含有される含フッ素環状カーボネート化合物としては、少なくともその一部が化合物(8)であることが好ましく、化合物(8)のみからなることがより好ましい。
前記含フッ素環状カーボネート化合物の含有量が下限値以上であれば、非水電解液は、サイクル特性、初回充放電特性およびレート特性に優れる。また、前記含フッ素環状カーボネート化合物の含有量が上限値以下であれば、非水電解液は難燃性および耐電圧性に優れ、かつ非水電解液と正極および負極との反応性が小さく、熱暴走が起こり難い。
本発明の非水電解液の液状組成物は、前記含フッ素溶媒(α)および含フッ素環状カルボン酸エステル化合物、非フッ素系不飽和環状カーボネート化合物、含フッ素環状カーボネート化合物以外の他の溶媒を含んでもよい。他の溶媒としては、非水電解液が、リチウム塩の溶解性、伝導度に優れることから、フッ素原子を有しない飽和環状カーボネート化合物(以下「非フッ素系飽和環状カーボネート化合物」ともいう。)、フッ素原子を有しない鎖状カーボネート化合物(以下「非フッ素系鎖状カーボネート化合物」ともいう。)、飽和環状スルホン化合物およびリン酸エステル化合物からなる群から選ばれる少なくとも1種の化合物(β)が好ましい。
非フッ素系飽和環状カーボネート化合物とは、環骨格が炭素原子と酸素原子からなる環構造を有する化合物であり、該環構造が-O-C(=O)-O-で表されるカーボネート結合を有し、フッ素原子および炭素-炭素不飽和結合を有さない化合物である。例えば、プロピレンカーボネート(PC)、エチレンカーボネート(EC)等が挙げられる。
非フッ素系鎖状カーボネート化合物とは、環構造を有さず、-O-C(=O)-O-で表されるカーボネート結合を有し、フッ素原子を有さない鎖状の化合物である。例えば、ジメチルカーボネート(DMC)、エチルメチルカーボネート(EMC)、ジエチルカーボネート(DEC)等が挙げられる。
飽和環状スルホン化合物としては、例えば、スルホラン、3-メチルスルホラン等が挙げられる。
リン酸エステル化合物としては、例えば、トリメチルリン酸、トリエチルリン酸等が挙げられる。
本発明の非水電解液が化合物(β)を含む場合、非水電解液の総質量に対する化合物(β)の質量の割合は、0.01~30質量が好ましく、0.1~20質量%がより好ましい。
本発明の非水電解液が非フッ素系飽和環状カーボネート化合物を含む場合、非水電解液の総質量に対する非フッ素系飽和環状カーボネート化合物の質量の割合は、0.01~20質量%が好ましく、0.01~15質量%がより好ましく、0.01質量%以上10質量%未満がさらに好ましく、0.01~5質量%が特に好ましく、0.01~3質量%が最も好ましい。前記非フッ素系飽和環状カーボネート化合物の割合が上限値以下であれば、非フッ素系飽和環状カーボネート化合物と電極とが反応し難く、非水電解液は安定性に優れ、難燃性に優れる。
非フッ素系鎖状カーボネート化合物を含む場合には、非水電解液の総質量に対する非フッ素系鎖状カーボネート化合物の質量の割合は、30質量%以下が好ましく、20質量%以下がより好ましく、15質量%以下がさらに好ましく、10質量%未満が特に好ましく、5質量%以下が最も好ましい。
本発明の非水電解液が非フッ素系鎖状カーボネート化合物を含む場合、非水電解液の総質量に対する非フッ素系鎖状カーボネート化合物の質量の割合は、非フッ素系飽和環状カーボネート化合物と同様の理由から、0.01~30質量%が好ましく、0.01~20質量%がより好ましく、0.01~15質量%がさらに好ましく、0.01質量%以上10質量%未満が特に好ましく、0.01~5質量%が最も好ましい。
本発明の非水電解液が非フッ素系飽和環状カーボネート化合物および非フッ素系鎖状カーボネート化合物からなる群から選ばれる少なくとも1種を含む場合、非水電解液の総質量に対する非フッ素系飽和環状カーボネート化合物と非フッ素系鎖状カーボネート化合物との合計質量の割合は、0.01~20質量%が好ましく、0.01~15質量%がより好ましく、0.01質量%以上10質量%未満がさらに好ましく、0.01~5質量%が特に好ましい。
前記合計質量の割合が上限値以下であれば、非フッ素系飽和環状カーボネート化合物および非フッ素系鎖状カーボネート化合物を用いた場合でも、前述の溶媒の極性が高くなることによる環状カルボン酸エステルによって形成された被膜の溶解を抑制することができ、それらと電極との反応性を低く抑えることができ、優れた安定性の非水電解液としやすい。また、可燃性の化合物の含有量を低く抑えることにより優れた難燃性を有する非水電解液としやすい。
本発明の非水電解液が飽和環状スルホン化合物を含む場合、非水電解液の総質量に対する飽和環状スルホン化合物の質量の割合は、非フッ素系飽和環状カーボネート化合物と同様の理由から、0.01~20質量%が好ましく、0.01~15質量%がより好ましく、0.01~10質量%がさらに好ましく、0.01~5質量%が特に好ましい。
本発明の非水電解液がリン酸エステル化合物を含む場合、本発明の非水電解液の総質量に対するリン酸エステル化合物の質量の割合は、非フッ素系飽和環状カーボネート化合物と同様の理由から、0.01~5質量%が好ましい。
また、本発明の非水電解液がリン酸エステル化合物を含む場合、リチウム塩由来のリチウム原子の総モル数(NLi)に対する、リン酸エステル化合物の総モル数(NP)の比率であるNP/NLiは、0.01以上1.0未満が好ましい。
前記(NA+NB)/NLiの下限値は、3.2が好ましく、3.5がより好ましい。
化合物(β)は、環状カルボン酸エステル化合物と同様にリチウム塩との親和性が高く、リチウム塩の溶媒への溶解を促進する効果があると考えられる。前記(NA+NB)/NLiが下限値以上、すなわちリチウム塩の溶解促進効果が高いと考えられる環状カルボン酸エステル化合物と化合物(β)の合計量がリチウム塩の量に対して一定以上であれば、含フッ素溶媒(α)に対するリチウム塩の溶解性が向上することにより非水電解液の伝導度が向上し、特にフッ素系溶媒に溶解しにくいLiPF6等のリチウム塩を使用する場合においてもフッ素系溶媒に溶解させることができ、実用的に充分な伝導度が得られやすい。
また、前記(NA+NB)/NLiの上限値は、6.5が好ましく、6.0がより好ましく、5.5がさらに好ましく、5.0が特に好ましく、4.5が最も好ましい。
前述のとおり溶媒の極性が高いと、電極活物質上に形成された環状カルボン酸エステル化合物による被膜が溶解し、被膜形成が不充分となりやすいが、化合物(β)も極性が高く、前記被膜を溶解する作用を示すと考えられる。前記(NA+NB)/NLiが上限値以下、すなわち前記被膜を溶解する作用を示す環状カルボン酸エステル化合物と化合物(β)の合計量がリチウム塩に対して一定以下であれば、前記被膜の溶解性が低く被膜形成が不充分となり難くなると考えられる。その結果、非水電解液と正極および負極との反応性がより小さくなり、二次電池の熱暴走がより起き難くなると推定される。また、非水電解液中の可燃性の高い環状カルボン酸エステル化合物や化合物(β)の含有量が少なくなることにより、非水電解液の難燃性も向上する。
特に、LiPF6を含むリチウム塩を用いて、NA/NLiと(NA+NB)/NLiを前記した範囲に制御することで、実用的に充分な伝導度と、熱暴走が起き難い優れた安定性とを兼ね備えた非水電解液が得られやすい。
液状組成物がニトリル化合物を含有する場合、本発明の非水電解液の総質量に対するニトリル化合物の質量の割合は、10質量%以下が好ましく、5質量%以下がより好ましく、3質量%以下がさらに好ましい。
液状組成物がフッ素原子を有しないエーテル化合物を含有する場合、本発明の非水電解液の総質量に対するフッ素原子を有しないエーテル化合物の質量の割合は、10質量%以下が好ましく、5質量%以下がより好ましく、3質量%以下がさらに好ましく、1質量%以下が特に好ましい。
本発明の非水電解液には、非水電解液の機能を向上させるために、必要に応じて前記以外の成分を含ませてもよい。前記以外の成分としては、例えば、従来公知の過充電防止剤、脱水剤、脱酸剤、高温保存後の容量維持特性およびサイクル特性を改善するための特性改善助剤、非水電解液の電極合材やセパレータへの含浸を助ける界面活性剤等が挙げられる。
非水電解液が過充電防止剤を含有する場合、非水電解液中の過充電防止剤の含有量は、0.01~5質量%であることが好ましい。非水電解液に過充電防止剤を0.01質量%以上含有させることにより、過充電による二次電池の破裂および発火を抑制することがさらに容易になり、二次電池をより安定に使用できる。
具体的には、例えば、エリスリタンカーボネート、スピロ-ビス-ジメチレンカーボネート等の前記以外のカーボネート化合物;エチレンサルファイト、1,3-プロパンスルトン、1,4-ブタンスルトン、メタンスルホン酸メチル、ブスルファン、スルホレン、ジメチルスルホン、ジフェニルスルホン、メチルフェニルスルホン、ジブチルジスルフィド、ジシクロヘキシルジスルフィド、テトラメチルチウラムモノスルフィド、N,N-ジメチルメタンスルホンアミド、N,N-ジエチルメタンスルホンアミド等の含硫黄化合物;ヘプタン、オクタン、シクロヘプタン等の炭化水素化合物;フルオロベンゼン、ジフルオロベンゼン、ヘキサフルオロベンゼン等の含フッ素芳香族化合物が挙げられる。これら特性改善助剤は、1種を単独で用いてもよく、2種以上を併用してもよい。
非水電解液が特性改善助剤を含有する場合、非水電解液中の特性改善助剤の含有量は、0.01~5質量%であることが好ましい。
アニオン性の含フッ素界面活性剤としては、下記化合物(9-1)および化合物(9-2)が好ましい。
M1およびM2はそれぞれ独立にアルカリ金属またはNH(R25)3(R25は水素原子または炭素数1~8のアルキル基であり、同一の基であっても、異なる基であってもよい。)である。
R13およびR14の構造は、直鎖構造でも分岐構造でもよく環構造を含んでいてもよい。入手容易性、界面活性作用が良好であることからR23およびR24の構造は直鎖構造が好ましい。
M1およびM2のアルカリ金属としては、Li、NaおよびKが好ましい。M1およびM2としては、NH4 +が特に好ましい。
なかでも、非水電解液への溶解性、表面張力を低下させる効果が良好な点から、C5F11COO-NH4 +、C5F11COO-Li+、C6F13COO-Li+、C3F7OCF(CF3)COO-NH4 +、C3F7OCF(CF3)CF2OCF(CF3)COO-NH4 +、C3F7OCF(CF3)COO-Li+、C3F7OCF(CF3)CF2OCF(CF3)COO-Li+、C2F5OC2F4OCF2COO-Li+およびC2F5OC2F4OCF2COO-NH4 +が好ましい。
なかでも、非水電解液への溶解性、表面張力を低下させる効果が良好な点から、C4F9SO3 -NH4 +、C6F13SO3 -NH4 +、C4F9SO3 -Li+、C6F13SO3 -Li+、C8F17SO3 -Li+、C3F7OCF(CF3)CF2OCF(CF3)SO3 -NH4 +、C3F7OCF(CF3)CF2OCF(CF3)SO3 -Li+、C3F7OCF(CF3)SO3 -NH4 +およびC3F7OCF(CF3)SO3 -Li+が好ましい。
液状組成物が界面活性剤を含有する場合には、含有される界面活性剤は1種のみでもよく、2種以上であってもよい。
本発明の非水電解液としては、本発明の目的とする効果を奏することから下記組成1が好ましい。
(組成1)
LiPF6、化合物(A)、FSO2N(Li)SO2F、CF3SO2N(Li)SO2CF3、CF3CF2SO2N(Li)SO2CF2CF3、LiClO4、化合物(B)、化合物(C)、およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;化合物(1)~(4)からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;化合物(5)である少なくとも1種の環状カルボン酸エステル化合物と、を含有する二次電池用非水電解液。
(組成2)
LiPF6、CF3SO2N(Li)SO2CF3、CF3CF2SO2N(Li)SO2CF2CF3、LiClO4およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;CF3CH2OCF2CHF2、CF3CH2OCF2CHFCF3、CHF2CF2CH2OCF2CHF2、CH3CH2CH2OCHF2、CH3CH2OCF2CHF2、CHF2CF2CH2OCF2CHFCF3、前記式(2)で表されかつXがCH2CH2である化合物、および前記式(2)で表されかつXがCH(CH3)CH2である化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;γ-ブチロラクトンおよびγ-バレロラクトンからなる群から選ばれる少なくとも1種の環状カルボン酸エステル化合物と、を含有する二次電池用非水電解液。
(組成3)
LiPF6と、CHF2CF2CH2OCF2CFHCF3と、γ-ブチロラクトンおよび/またはγ-バレロラクトンとを含有する二次電池用非水電解液。
(組成4)
LiPF6、化合物(A)、FSO2N(Li)SO2F、CF3SO2N(Li)SO2CF3、LiClO4、化合物(B)、化合物(C)、およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;化合物(1)~(4)からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;化合物(5)である少なくとも1種の環状カルボン酸エステル化合物と:化合物(6)および化合物(7)からなる群から選ばれる少なくとも1種の非フッ素系不飽和環状カーボネート化合物と、を含有する二次電池用非水電解液。
(組成5)
LiPF6、FSO2N(Li)SO2F、LiClO4およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;CF3CH2OCF2CHF2、CF3CH2OCF2CHFCF3、CHF2CF2CH2OCF2CHF2、CH3CH2CH2OCHF2、CH3CH2OCF2CHF2、CHF2CF2CH2OCF2CHFCF3、前記式(2)で表されかつXがCH2CH2である化合物、および前記式(2)で表されかつXがCH(CH3)CH2である化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;γ-ブチロラクトンおよびγ-バレロラクトンからなる群から選ばれる少なくとも1種の環状カルボン酸エステル化合物と、化合物(6)および化合物(7)からなる群から選ばれる少なくとも1種の非フッ素系不飽和環状カーボネート化合物と、を含有する二次電池用非水電解液。
(組成6)
LiPF6と、CF3CH2OCF2CHF2およびCHF2CF2CH2OCF2CHFCF3からなる群から選ばれる少なくとも1種と、γ-ブチロラクトンおよび/またはγ-バレロラクトンと、ビニレンカーボネートと、を含有する二次電池用非水電解液。
(組成7)
LiPF6、化合物(A)、FSO2N(Li)SO2F、CF3SO2N(Li)SO2CF3、LiClO4、化合物(B)、化合物(C)、およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;化合物(1)~(4)からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;化合物(5)である少なくとも1種の環状カルボン酸エステル化合物と:化合物(8)である少なくとも1種の含フッ素環状カーボネート化合物と、を含有する二次電池用非水電解液。
(組成8)
LiPF6、FSO2N(Li)SO2F、LiClO4およびLiBF4からなる群から選ばれる少なくとも1種のリチウム塩と;CF3CH2OCF2CHF2、CF3CH2OCF2CHFCF3、CHF2CF2CH2OCF2CHF2、CH3CH2CH2OCHF2、CH3CH2OCF2CHF2、CHF2CF2CH2OCF2CHFCF3、前記式(2)で表されかつXがCH2CH2である化合物、および前記式(2)で表されかつXがCH(CH3)CH2である化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と;γ-ブチロラクトンおよびγ-バレロラクトンからなる群から選ばれる少なくとも1種の環状カルボン酸エステル化合物と、化合物(8-1)と、を含有する二次電池用非水電解液。
(組成9)
LiPF6と、CF3CH2OCF2CHF2およびCHF2CF2CH2OCF2CHFCF3からなる群から選ばれる少なくとも1種と、γ-ブチロラクトンおよび/またはγ-バレロラクトンと、化合物(8-1)と、を含有する二次電池用非水電解液。
本発明のリチウムイオン二次電池は、正極と、負極と、本発明の非水電解液を有することを特徴とする二次電池である。
[正極]
正極としては、正極活物質と導電付与剤と結着剤を含む正極層が、集電体上に形成されてなる電極が挙げられる。
正極活物質としては、リチウムイオンを吸蔵および放出できる材料であればよく、公知のリチウムイオン二次電池用の正極活物質を採用できる。例えば、リチウム含有遷移金属酸化物、1種類以上の遷移金属を用いたリチウム含有遷移金属複合酸化物、遷移金属酸化物、遷移金属硫化物、金属酸化物、オリビン型金属リチウム塩等が挙げられる。
リチウム含有遷移金属複合酸化物に含有される金属としてはAl、V、Ti、Cr、Mn、Fe、Co、Li、Ni、Cu、Zn、Mg、Ga、Zr、Si、Yb等が好ましく、例えば、LiCoO2等のリチウムコバルト複合酸化物、LiNiO2等のリチウムニッケル複合酸化物、LiMnO2、LiMn2O4、Li2MnO3等のリチウムマンガン複合酸化物、Li(NiaCobMnc)O2(ただし、a,b,c≧0、a+b+c=1である。)等のリチウム三元系複合酸化物、これらのリチウム遷移金属複合酸化物の主体となる遷移金属原子の一部をAl、Ti、V、Cr、Mn、Fe、Co、Li、Ni、Cu、Zn、Mg、Ga、Zr、Si、Yb等の他の金属で置換したもの等が挙げられる。例えば、LiMn0.5Ni0.5O2、LiMn1.8Al0.2O4、LiNi0.85Co0.10Al0.05O2、LiMn1.5Ni0.5O4、LiNi1/3Co1/3Mn1/3O2、LiMn1.8Al0.2O4等が挙げられる。
遷移金属酸化物としては、例えば、TiO2、MnO2、MoO3、V2O5、V6O13、遷移金属硫化物としてはTiS2、FeS、MoS2、金属酸化物としてはSnO2、SiO2等が挙げられる。
オリビン型金属リチウム塩は、LiLXxYyOzFg(ただし、XはFe(II)、Co(II)、Mn(II)、Ni(II)、V(II)、またはCu(II)を示し、YはPまたはSiを示し、0≦L≦3、1≦x≦2、1≦y≦3、4≦z≦12、0≦g≦1である数をそれぞれ示す。)で示される物質またはこれらの複合体である。例えば、LiFePO4、Li3Fe2(PO4)3、LiFeP2O7、LiMnPO4、LiNiPO4、LiCoPO4、Li2FePO4F、Li2MnPO4F、Li2NiPO4F、Li2CoPO4F、Li2FeSiO4、Li2MnSiO4、Li2NiSiO4、Li2CoSiO4等が挙げられる。
正極を形成する活物質は、1種を単独で用いてもよく、2種以上を併用してもよい。
表面付着物質の量としては、正極活物質に対する質量の下限は0.1質量ppmが好ましく、1質量ppmがより好ましく、10質量ppmが特に好ましい。上限は20質量%が好ましく、10質量%がより好ましく、5質量%が特に好ましい。表面付着物質により、正極活物質表面での非水電解液の酸化反応を抑制でき、電池寿命を向上させることができる。
結着剤としてはポリフッ化ビニリデン等の樹脂バインダー、炭化水素ゴムやフッ素ゴム等のゴム系バインダーが挙げられる。
集電体としてはAl等を主体とする金属薄膜が挙げられる。
負極としては、粉末状の負極活物質と導電付与剤と結着剤を含む負極層が、集電体上に形成されてなる電極が挙げられる。
負極活物質としては、リチウム金属、リチウム合金、ならびにリチウムイオンを吸蔵および放出できる炭素材料からなる群から選ばれる1種以上が挙げられる。
炭素材料としては、黒鉛、コークス、ハードカーボン等が挙げられる。
リチウム合金としては、Li-Al合金、Li-Pb合金、Li-Sn合金等が挙げられる。
集電体としては、Cu等を主体とする金属薄膜が使用できる。
なお、負極活物質が、それ自体で形状を保てる場合(例えばリチウム金属薄膜)は、負極活物質のみで負極を形成できる。
多孔膜としては、非水電解液に対して安定であり、かつ保液性に優れるものが使用でき、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、エチレンとテトラフルオロエチレンのコポリマー等のフッ素樹脂、ポリイミド、またはポリエチレン、ポリプロピレン等のポリオレフィンを原料とする多孔性シートまたは不織布が好ましい。多孔膜の材質はポリエチレン、ポリプロピレン等のポリオレフィンが好ましい。
本発明のリチウムイオン二次電池に使用される電池外装体の材質は、ニッケルメッキを施した鉄、ステンレス、アルミニウムまたはその合金、ニッケル、チタン、樹脂材料、フィルム材料等が挙げられる。
[溶解性]
溶解性は、非水電解液の調製後、1時間経過後の該非水電解液の溶解状態を目視により確認して評価した。評価は、均一に溶解しているものを「○」、二相に分離してしまったものを「×」とした。
伝導度(単位:S/m)の測定は、得られた非水電解液について、「溶融塩及び高温化学、2002、45、43」に記載の既知の方法を用いて25℃で行った。すなわち、底部の長さ5cm、内径4.8mmのT型電気化学セルの両端に、金属リチウムを貼り付けた電極をセットした。その後、作成した電解液を十分に注入し、密封した。得られた電気化学セルの溶液抵抗を、25℃恒温槽中に1時間静置したのち、恒温槽中で、ポテンショスタット/ガルバノスタット(BioLogic社製、製品名「VMP3」)を用い、複素インピーダンス法により測定した。得られた溶液抵抗値より、各電解液の伝導度を算出した。
1.評価用電極(負極)の作製
人造黒鉛(4.25g)と、導電付与剤であるアセチレンブラック(0.15g)を混合し、自転公転式撹拌機(株式会社シンキー社製、あわとり練太郎AR-E310)を用いて回転数2000rpmで1分間撹拌する工程を3回行った。次いで、1質量%のカルボキシメチルセルロース水溶液(4.25g)を添加し、さらに前記撹拌機を用いて回転数2000rpmで5分間撹拌する工程を2回行った。さらに1質量%のカルボキシメチルセルロース水溶液(4.25g)を添加し、前記撹拌機を用いて回転数2000rpmで10分間撹拌した。その後、固形分濃度を40質量%に調整したスチレン-ブタジエンゴムラテックス(0.13g)をバインダとして添加し、前記撹拌機を用いて回転数2000rpmで5分間撹拌して電極塗工用スラリーを得た。
厚み20μmの銅箔上に、前記スラリーを150μmの厚みで塗工し、乾燥した後、直径19mmの円形に打ち抜いて評価用電極(負極)とした。
2.負極反応性の評価試験
前記方法で作製した負極を評価用電極とし、リチウム金属箔を直径19mmの円形に打ち抜いたものを対極とした。それら電極の間には、セパレータとしてポリオレフィン系微多孔膜を存在させた。さらに、カーボネート系非水電解液(エチレンカーボネートとエチルメチルカーボネートが質量比3:7で混合され、LiPF6が1.0Mとなるように溶解された非水電解液。キシダ化学社製)の0.5mLに、ビニレンカーボネートを2質量%となるように加えた非水電解液を添加し、黒鉛極-リチウム金属箔からなる単極セルを作成した。
得られた単極セルについて、以下の充放電サイクルを実施した。サイクル1では、25℃において、0.04Cに相当する電流で0.2V(負極)まで定電流充電を行い、さらに0.2Cに相当する電流で0.05Vまで定電流充電し、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で1.0Vまで定電流放電を行った。サイクル2~4では、0.2Cに相当する電流で0.05Vまで定電流充電を行い、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で1.0Vまで定電流放電を行った。サイクル5では、0.2Cに相当する電流で0.05Vまで定電流充電を行った。その後、得られた充電状態の単極セルをアルゴン雰囲気下で分解し、充電状態の負極を得た。得られた負極を、ジメチルカーボネート(2mL)で3回洗浄し、真空乾燥した後に直径5mmの円形に打ち抜き、ステンレス鋼(SUS)製の密封容器に入れ、さらに各例で得られた非水電解液を2μL入れて封止し、評価サンプルとした。得られた各評価サンプルについて、示差走査熱量計(エスアイアイナノテクノロジー社製DSC-6000)によって、温度範囲50~350℃、昇温速度5℃/分で測定を行った。
3.負極反応性の評価
負極反応性の評価には、「発熱ピーク温度」および「200℃における発熱量」を用いた。
「発熱ピーク温度」は、前記測定における60℃での発熱量を0に補正した際の、発熱量が2000μWを超える発熱ピークのうち最も低温に表れる発熱ピークのピークトップの温度とした。発熱ピーク温度の評価は、200℃以上を「◎(優良)」、180℃以上200℃未満を「○(良好)」、150℃以上180℃未満を「△(不良)」、150℃未満を「×(極めて不良)」とした。
「200℃における発熱量」は、前記測定における60℃での発熱量を0と補正した際の、200℃における発熱量(μW)とした。
1.評価用電極(正極)の作製
LiCoO2(AGCセイミケミカル社製、商品名「セリオンC」、32.0g)と、カーボンブラック(電気化学工業社製、商品名「デンカブラック」、0.80g)とを混合し、前記撹拌機を用いて回転数2000rpmで1分間撹拌する工程を3回行った。次いで、N-メチル-2-ピロリドン(7.50g)を加えて前記撹拌機を用いて回転数2000rpmで3分間撹拌する工程を3回行った。次いで、N-メチル-2-ピロリドン(1.0g)を加えて前記撹拌機を用いて回転数2000rpmで3分間撹拌する工程を3回行った。さらに、ポリフッ化ビニリデンのN-メチル-2-ピロリドン溶液(11質量%、7.45g)を加えて前記撹拌機を用いて回転数2000rpmで1分間撹拌し、スラリーとした。該スラリーを厚さ20μmのアルミニウム箔に150μmの厚みで塗工し、乾燥した後、直径18mmの円形に打ち抜いて評価用電極(正極)とした。
2.正極反応性の評価試験
前記方法で作製した正極を評価用電極とし、リチウム金属箔を直径19mmの円形に打ち抜いたものを対極とした。それら電極の間には、セパレータとしてポリオレフィン系微多孔膜を存在させた。さらに、カーボネート系非水電解液(エチレンカーボネートとエチルメチルカーボネートが質量比3:7で混合され、LiPF6が1.0Mとなるように溶解された非水電解液。キシダ化学社製)の0.5mLを添加し、LiCoO2極-リチウム金属箔からなる単極セルを作成した。
得られた単極セルについて、以下の充放電サイクルを実施した。サイクル1~4は、0.5Cに相当する電流で4.5Vまで定電流充電を行い、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電を行った。サイクル5は、0.5Cに相当する電流で4.5Vまで定電流充電を行い、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、得られた充電状態の単極セルをアルゴン雰囲気下で分解し、充電状態の正極を得た。得られた正極を、ジメチルカーボネート(2mL)で3回洗浄し、真空乾燥した後に直径5mmに打ち抜き、SUS製の密封容器に入れ、さらに各例の非水電解液を2μL入れて封止し、評価サンプルとした。得られた各評価サンプルについて、示差走査熱量計(エスアイアイナノテクノロジー社製DSC-6000)によって、温度範囲50~350℃、昇温速度5℃/分で測定を行った。
正極反応性の評価は、負極反応性の評価と同様に、「発熱ピーク温度」および「200℃における発熱量」で行った。
[例1]
リチウム塩であるLiPF6(0.11g)を、含フッ素エーテル化合物であるCHF2CF2CH2OCF2CHFCF3(1.23g)中に分散した後、化合物(5)であるγ-ブチロラクトン(0.24g)を混合して非水電解液1Aとした。
リチウム塩等の各化合物の組成を表1~5に示すように変更した以外は、例1と同様にして非水電解液2~38を得た。
なお、表1~5における質量%は非水電解液全体を100質量%とした割合である。
AE3000:CF3CH2OCF2CHF2(商品名:AE-3000、旭硝子社製)。
HFE458:CF2HCF2CH2OCF2CF2H。
HFE449:CF3CH2OCF2CFHCF3。
HFE5510:CHF2CF2CH2OCF2CHFCF3。
MFA:ジフルオロ酢酸メチル。
ETFA:トリフルオロ酢酸エチル。
TFEOc:ビス(2,2,2-トリフルオロエチル)カーボネート。
GBL:γ-ブチロラクトン。
GVL:γ-バレロラクトン。
EC:エチレンカーボネート。
PC:プロピレンカーボネート。
EMC:エチルメチルカーボネート。
DMC:ジメチルカーボネート。
DEC:ジエチルカーボネート。
TMP:トリメチルリン酸。
SL:スルホラン。
SX-1:下式で表される化合物。
また、NA/NLiが7.0より大きい、例34および例35は、正極および負極との反応における発熱ピーク温度が200℃未満であり、例1~24に比べて非水電解液と電極との反応性が大きかった。また、NA/NLiが1.5~7.0であるが、(NA+NB)/NLiが7.0より大きい例36Aは、負極反応性が低く負極での反応による熱暴走が起き難くなるものの、正極反応性が大きかった。このことから、NA/NLiを1.5~7.0に制御したうえで、さらに(NA+NB)/NLiを3~7.0に制御することでより電池の安定性を高めることができると言える。また、NA/NLiが1.5未満である例37は、正極負極ともに反応性が高かった。
[例39]
前記正極および負極を対向させ、それら電極の間に、セパレータとしてポリオレフィン系微多孔膜を存在させ、例12の非水電解液(0.5mL)を添加し、LiCoO2極-黒鉛極からなるセルを作成した。
得られたセルについて、以下に示す充放電サイクルを行った。サイクル1は、25℃において、0.01Cに相当する電流で3.4Vまで定電流充電を行い、さらに0.2Cに相当する電流で4.2Vまで定電流充電を行い、さらに充電上限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電を行った。サイクル2~50は、0.2Cに相当する電流で4.2Vまで定電流充電を行い、さらに充電上限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電を行った。サイクル10における、正極活物質単位重量当たりの放電容量に対する、サイクル30およびサイクル50における放電容量を放電容量維持率としてサイクル特性を評価した。
サイクル特性の評価結果を表6に示す。
以下は非フッ素系環状カーボネート化合物を含む電解液に関する実施例である。例1A~5Aは実施例、例6A、7Aは比較例である。
[例1A]
リチウム塩であるLiPF6(0.15g)を、化合物(1)であるCF3CH2OCF2CF2H(商品名:AE-3000、旭硝子社製)(1.02g)中に拡散した後、化合物(5)であるγ-ブチロラクトン(0.34g)を混合し均一な溶液を得た。その後、該溶液に対して2質量%となるように化合物(6)であるビニレンカーボネートを加えて非水電解液1Aとした。
リチウム塩等の各化合物の組成を表7に示すように変更した以外は、例1Aと同様にして非水電解液2A~7Aを得た。
なお、表7中の略号は以下の意味を示す。
VC:ビニレンカーボネート。
FEC:フルオロエチレンカーボネート。
他は<実施例I>と同様である。
<実施例I>と同様にして非水電解液の溶解性の評価を行った。
<実施例I>と同様にしてイオン伝導度の評価を行った。
<実施例I>と同様にして作成した正極と負極を対向させ、それら正極と負極の間に、評価用電極セパレータとしてポリオレフィン系微多孔膜を存在させ、各例で得た非水電解液(0.5mL)を添加し、LiCoO2極-黒鉛極からなるセルを作成した。
得られたセルを用いて、サイクル1として、25℃において、0.01Cに相当する電流で3.4Vまで定電流充電し、さらに0.2Cに相当する電流で4.2Vまで定電流充電し、さらに充電上限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電した。サイクル1における充電容量に対する放電容量の割合を初回充放電特性として評価した。
サイクル2~10では、0.2Cに相当する電流で4.2Vまで定電流充電し、さらに充電上限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電した。
サイクル11~15の充電は、0.2Cに相当する電流で4.2Vまで定電流充電し、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。放電は、サイクル11では0.1C、サイクル12は0.2C、サイクル13は0.5C、サイクル14は1.0C、サイクル15は2.0Cに相当する電流で3.0Vまで定電流放電した。レート特性の評価として、2.0C放電時の平均放電電圧を測定した。
その後、サイクル16~50は、0.2Cに相当する電流で4.2Vまで定電流充電し、さらに充電下限電圧において電流値が0.02Cに相当する電流となるまで定電圧充電を行った。その後、0.2Cに相当する電流で3.0Vまで定電流放電した。サイクル10の正極活物質単位重量当たりの放電容量に対する、サイクル30およびサイクル50の放電容量維持率によりサイクル特性を評価した。
結果を表7に示す
一方、非フッ素系不飽和環状カーボネート化合物を用いていない例6Aおよび例7Aでは、例1A~5Aに比べて初回充放電特性、レート特性およびサイクル特性がいずれも劣っていた。
以下は含フッ素環状カーボネート化合物を含む電解液の場合に関する実施例である。例1B~5Bは実施例、例6B、7Bは比較例である。
[例1B]
リチウム塩であるLiPF6(0.15g)を、化合物(1)であるCF3CH2OCF2CF2H(商品名:AE-3000、旭硝子社製)(1.02g)中に拡散した後、化合物(5)であるγ-ブチロラクトン(0.34g)を混合し均一な溶液を得た。その後、該溶液に対して2質量%となるように化合物(8)であるフルオロエチレンカーボネート(4-フルオロ-1,3-ジオキソラン-2-オン、化合物(8-1))を加えて非水電解液1Bとした。
リチウム塩等の各化合物の組成を表8に示すように変更した以外は、例1Bと同様にして非水電解液2B~7Bを得た。なお、表8中の略号は前記と同様の意味を示す。
<実施例I>と同様にして非水電解液の溶解性の評価を行った。
<実施例I>と同様にしてイオン導電性の評価を行った。
[充放電試験]
<実施例II>と同様にして充放電試験を行った。
結果を表8に示す
一方、含フッ素環状カーボネート化合物を用いていない例6Bおよび例7Bでは、例1B~5Bに比べて初回充放電特性、レート特性およびサイクル特性がいずれも劣っていた。
なお、2012年3月27日に出願された日本特許出願2012-071067号、2012年3月27日に出願された日本特許出願2012-071068号、2012年10月22日に出願された日本特許出願2012-233286号および2013年2月7日に出願された日本特許出願2013-022593号の明細書、特許請求の範囲および要約書の全内容をここに引用し、本発明の明細書の開示として、取り入れるものである。
Claims (15)
- リチウム塩と液状組成物からなる非水電解液であって、
前記液状組成物が、含フッ素エーテル化合物、含フッ素鎖状カルボン酸エステル化合物および含フッ素鎖状カーボネート化合物からなる群から選ばれる少なくとも1種の含フッ素溶媒(α)と、環状カルボン酸エステル化合物とを含み、
フッ素原子を有しない飽和環状カーボネート化合物、フッ素原子を有しない鎖状カーボネート化合物、飽和環状スルホン化合物およびリン酸エステル化合物からなる群から選ばれる少なくとも1種の化合物(β)を含んでもよく、
前記非水電解液の総質量に対する前記含フッ素溶媒(α)の質量の割合が40~80質量%であり、
前記リチウム塩由来のリチウム原子の総モル数(NLi)に対する前記環状カルボン酸エステル化合物の総モル数(NA)の比率であるNA/NLiが1.5~7.0であり、
前記NLiに対する、前記NAと、前記化合物(β)の総モル数(NB)との和の比率である(NA+NB)/NLiが3~7.0であることを特徴とする二次電池用非水電解液。 - 前記NA/NLiが1.5~5.5であり、前記(NA+NB)/NLiが3~6.5である、請求項1に記載の二次電池用非水電解液。
- 前記液状組成物がさらにフッ素原子を有しない不飽和環状カーボネート化合物を含む、請求項2に記載の二次電池用非水電解液。
- 前記非水電解液中の前記フッ素原子を有しない不飽和環状カーボネート化合物の含有量が0.01~10質量%である、請求項3に記載の二次電池用非水電解液。
- 前記液状組成物がさらに含フッ素環状カーボネート化合物を含む、請求項2に記載の二次電池用非水電解液。
- 前記非水電解液中の前記含フッ素環状カーボネート化合物の含有量が0.01~10質量%である、請求項5に記載の二次電池用非水電解液。
- 前記液状組成物が前記フッ素原子を有しない飽和環状カーボネート化合物を含む、請求項1~6のいずれか一項に記載の二次電池用非水電解液。
- 前記液状組成物が前記フッ素原子を有しない鎖状カーボネート化合物を含む、請求項1~7のいずれか一項に記載の二次電池用非水電解液。
- 前記液状組成物が前記含フッ素エーテル化合物を含む、請求項1~8のいずれか一項に記載の二次電池用非水電解液。
- 前記環状カルボン酸エステル化合物が、γ-ブチロラクトンおよびγ-バレロラクトンからなる群から選ばれる少なくとも1種である、請求項1~9のいずれか一項に記載の二次電池用非水電解液。
- 前記非水電解液の総質量に対する前記環状カルボン酸エステル化合物の質量の割合が4~50質量%である請求項1~10のいずれか一項に記載の二次電池用非水電解液。
- 前記非水電解液の25℃におけるリチウムイオン伝導度が0.3S/m以上である、請求項1~11のいずれか一項に記載の二次電池用非水電解液。
- 前記リチウム塩の少なくとも一部がLiPF6である、請求項1~12のいずれか一項に記載の二次電池用非水電解液。
- 前記非水電解液中の前記リチウム塩の含有量が0.1~3.0mol/Lである、請求項1~13のいずれか一項に記載の二次電池用非水電解液。
- リチウムイオンを吸蔵および放出できる材料を活物質とする正極と、リチウム金属、リチウム合金、ならびにリチウムイオンを吸蔵および放出できる炭素材料からなる群から選ばれる1種以上を活物質とする負極と、請求項1~14のいずれか一項に記載の二次電池用非水電解液とを有することを特徴とするリチウムイオン二次電池。
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CN106133988B (zh) * | 2014-03-27 | 2019-11-26 | 大金工业株式会社 | 电解液和电化学器件 |
CN106133988A (zh) * | 2014-03-27 | 2016-11-16 | 大金工业株式会社 | 电解液和电化学器件 |
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JP7278658B2 (ja) | 2019-08-30 | 2023-05-22 | エルジー エナジー ソリューション リミテッド | リチウム二次電池用電解質及びこれを含むリチウム二次電池 |
US11973190B2 (en) | 2019-08-30 | 2024-04-30 | Lg Energy Solution, Ltd. | Electrolyte for lithium secondary battery and lithium secondary battery including the same |
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Also Published As
Publication number | Publication date |
---|---|
CN103875116B (zh) | 2016-08-17 |
JPWO2013146359A1 (ja) | 2015-12-10 |
KR20140145127A (ko) | 2014-12-22 |
EP2833468A4 (en) | 2016-03-16 |
CN103875116A (zh) | 2014-06-18 |
EP2833468B1 (en) | 2017-11-29 |
JP2014170730A (ja) | 2014-09-18 |
US9236636B2 (en) | 2016-01-12 |
EP2833468A1 (en) | 2015-02-04 |
JP5488768B2 (ja) | 2014-05-14 |
US20140322616A1 (en) | 2014-10-30 |
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