Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0568—Liquid materials characterised by the solutes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0569—Liquid materials characterised by the solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/364—Composites as mixtures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• This disclosure relates to non-aqueous electrolyte secondary batteries.
• non-aqueous electrolytes and materials for use in secondary batteries have been studied.
• non-aqueous electrolytes containing sulfonylimide compounds such as lithium bis(fluorosulfonyl)imide as electrolyte salts improve the battery performance of lithium-ion secondary batteries, such as high-temperature durability and charge/discharge cycles.
• a battery using a nonaqueous electrolyte containing a sulfonylimide compound has a large self-discharge from a fully charged state during storage compared to a battery using a nonaqueous electrolyte containing only a lithium compound other than a sulfonylimide compound (e.g., LiPF 6 , LiBF 4 , etc.) as an electrolyte salt, and that there is room for improvement in the storage characteristics of the battery.
• a nonaqueous electrolyte containing only a lithium compound other than a sulfonylimide compound e.g., LiPF 6 , LiBF 4 , etc.
• Nonaqueous electrolyte secondary battery which is made up of a nonaqueous electrolyte containing a sulfonylimide compound and a sulfone compound, and a negative electrode containing a specific carbon material (Patent Document 2).
• Patent Documents 3 to 6 propose non-aqueous electrolytes containing additives such as trimethylsilyl polyphosphate.
• Patent Document 1 describes that the self-discharge of a battery using a non-aqueous electrolyte solution containing a sulfonylimide compound can be suppressed by adding a fluorophosphate compound such as vinylene carbonate (VC) or lithium difluorophosphate (LiPO 2 F 2 ) or by dissolving a carbonate component such as CO 2 in the non-aqueous electrolyte solution.
• VC vinylene carbonate
• LiPO 2 F 2 lithium difluorophosphate
• CO 2 carbonate component
• the nonaqueous electrolyte secondary battery of Patent Document 2 uses a negative electrode containing a carbon material having an intensity ratio R (peak intensity at 1350 cm ⁇ 1 / peak intensity at 1580 cm ⁇ 1 ) of 0.1 ⁇ R ⁇ 0.5 in a Raman spectrum excited by an argon laser having a wavelength of 532 nm as a constituent material, but such a carbon material (graphite) has high crystallinity and is relatively expensive.
• R peak intensity at 1350 cm ⁇ 1 / peak intensity at 1580 cm ⁇ 1
• Patent documents 3 to 6 do not provide any detailed description of the non-aqueous electrolyte containing a sulfonylimide compound and the negative electrode as components of the secondary battery, and do not discuss the crystallinity of the graphite used as the negative electrode active material.
• the present disclosure has been made in consideration of these points, and its purpose is to suppress self-discharge (improve storage characteristics) in a nonaqueous electrolyte secondary battery that includes a nonaqueous electrolyte containing a sulfonylimide compound by combining an additive used in the nonaqueous electrolyte with a negative electrode that contains graphite, which has low crystallinity and is relatively inexpensive as the negative electrode active material.
• a third battery using a negative electrode containing graphite with low crystallinity in combination with a non-aqueous electrolyte containing a specific additive has a smaller self-discharge than the second battery.
• this disclosed technology aims to suppress self-discharge in a non-aqueous electrolyte secondary battery containing a sulfonylimide compound by using low-crystalline graphite in combination with a specific additive.
• this disclosure is as follows:
• the nonaqueous electrolyte secondary battery of the present disclosure contains an electrolyte salt represented by the general formula (1): LiN(RSO 2 )(FSO 2 ) (R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms) (1) and at least one carbonate solvent selected from the group consisting of chain carbonate solvents and saturated cyclic carbonate solvents as an electrolyte solvent, and at least one carbonate component selected from the group consisting of carbon dioxide (CO 2 ), carbon monoxide (CO), bicarbonate ion (HCO 3 ⁇ ) and carbonate ion (CO 3 2 ⁇ ) is dissolved as an additive, and/or an unsaturated cyclic carbonate compound, a general formula (4): MPOcFd (M: alkali metal element , c: 1 ⁇ c ⁇ 3, d: 1 ⁇ d ⁇ 3) (4) and a compound represented by general formula (5): [-P
• R 1 represents an alkyl group having 1 to 6 carbon atoms (which may have a substituent), a fluoroalkyl group having 1 to 6 carbon atoms (which may have a substituent), an aryl group (which may have a substituent), a silyl group (which may have a substituent), an alkali metal atom, an onium salt, or a hydrogen atom, and n represents 2 or more.
• the nonaqueous electrolyte secondary battery of the present disclosure comprises the nonaqueous electrolyte and a negative electrode including, as a negative electrode active material, a first graphite having a G band half width greater than 28 cm ⁇ 1 as analyzed by Raman spectroscopy, and a second graphite having a G band half width of 28 cm ⁇ 1 or less in an amount of 0 mass % to 10 mass % relative to 100 mass % of the total amount of the first graphite and the second graphite;
• the battery is characterized by comprising a positive electrode.
• the sulfonylimide compound represented by the general formula (1) may contain LiN(FSO 2 ) 2.
• the unsaturated cyclic carbonate compound may contain vinylene carbonate.
• the compound represented by the general formula (4) may contain at least one selected from the group consisting of Li 2 PO 3 F and LiPO 2 F 2.
• the compound represented by the general formula (5) may contain at least one selected from the group consisting of trimethylsilyl polyphosphate, ethyl polyphosphate, (triisopropylsilyl) polyphosphate, and [(tert-butyl)dimethylsilyl] polyphosphate.
• the additive includes a phosphorus atom-containing compound represented by the general formula (5), and the compound represented by the general formula (5) may contain at least one selected from the group consisting of trimethylsilyl polyphosphate, ethyl polyphosphate, (triisopropylsilyl) polyphosphate, and [(tert-butyl)dimethylsilyl] polyphosphate.
• the electrolyte salt is represented by the general formula (2): LiPF a (C m F 2m+1 ) 6-a (a: 0 ⁇ a ⁇ 6, m: 1 ⁇ m ⁇ 4) ... (2)
• a nonaqueous electrolyte secondary battery having a nonaqueous electrolyte containing a sulfonylimide compound self-discharge can be suppressed (storage characteristics can be improved) by combining an additive used in the nonaqueous electrolyte with a negative electrode containing graphite, which has low crystallinity and is relatively inexpensive, as the negative electrode active material.
• FIG. 1 is a D/G chart (Raman spectrum) of the graphite "MAGE” used in the production example.
• FIG. 2 is a D/G chart of the graphite "SFG15" used in the production example.
• FIG. 3 is a D/G chart of the graphite "SLP50” used in the production example.
• FIG. 4 is a D/G chart of the graphite "O-MAC” used in the production example.
• FIG. 5 is a D/G chart of the graphite "SMG” used in the production example.
• FIG. 6 shows the 31 P-NMR spectrum of the reagent, trimethylsilyl polyphosphate (PPSE-1), used in the Example 4 series.
• FIG. PPSE-1 trimethylsilyl polyphosphate
• FIG. 7 shows the 31 P-NMR spectrum of the polytrimethylsilyl phosphate (PPSE-2) synthesized in Example 4 series.
• FIG. 8 shows the 31 P-NMR spectrum of the polytrimethylsilyl phosphate (PPSE-3) synthesized in Example 4 series.
• the nonaqueous electrolyte secondary battery according to this embodiment is a secondary battery including a nonaqueous electrolyte, a positive electrode, and a negative electrode.
• Non-aqueous electrolyte contains an electrolyte salt, an electrolyte solvent, and an additive.
• the electrolyte salt is represented by the general formula (1): [Chemical formula 1] LiN( RSO2 )( FSO2 )...(1) (hereinafter referred to as “sulfonylimide compound (1)”, which is a fluorine-containing sulfonylimide salt) represented by the following formula:
• the nonaqueous electrolyte secondary battery according to this embodiment includes a nonaqueous electrolyte containing the sulfonylimide compound (1) as an essential component as an electrolyte salt as one of its constituent materials.
• R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.
• alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups.
• alkyl groups having 1 to 6 carbon atoms linear or branched alkyl groups having 1 to 6 carbon atoms are preferred, and linear alkyl groups having 1 to 6 carbon atoms are more preferred.
• Fluoroalkyl groups having 1 to 6 carbon atoms include alkyl groups having 1 to 6 carbon atoms in which some or all of the hydrogen atoms have been replaced with fluorine atoms.
• Fluoroalkyl groups having 1 to 6 carbon atoms include fluoromethyl groups, difluoromethyl groups, trifluoromethyl groups, fluoroethyl groups, difluoroethyl groups, trifluoroethyl groups, and pentafluoroethyl groups.
• the fluoroalkyl groups may be perfluoroalkyl groups.
• a fluorine atom and a perfluoroalkyl group for example, a perfluoroalkyl group having 1 to 6 carbon atoms, such as a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, etc.
• a fluorine atom, a trifluoromethyl group, and a pentafluoroethyl group are more preferred
• a fluorine atom and a trifluoromethyl group are even more preferred
• a fluorine atom is even more preferred.
• the sulfonylimide compound (1) include lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 , LiFSI), lithium (fluorosulfonyl)(methylsulfonyl)imide, lithium (fluorosulfonyl)(ethylsulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide, and lithium (fluorosulfonyl)(heptafluoropropylsulfonyl)imide.
• the sulfonylimide compounds may be used alone or in combination of two or more kinds.
• the sulfonylimide compound (1) may be a commercially available product or may be obtained by synthesis using a conventional method.
• LiN(FSO 2 ) 2 lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide and lithium(fluorosulfonyl)(pentafluoroethylsulfonyl)imide are preferred, and LiN(FSO 2 ) 2 is more preferred.
• LiN(FSO 2 ) 2 is more preferred.
• those containing LiN(FSO 2 ) 2 as the sulfonylimide compound (1) are preferred.
• the concentration (content, total content when two or more types are used) of the sulfonylimide compound (1) in the nonaqueous electrolyte is preferably 0.01 mol/L or more, more preferably 0.05 mol/L or more, even more preferably 0.1 mol/L or more, even more preferably 0.2 mol/L or more, and even more preferably 0.5 mol/L or more, from the viewpoint of improving battery performance.
• the concentration is preferably 5 mol/L or less, more preferably 3 mol/L or less, and even more preferably 2 mol/L or less, from the viewpoint of suppressing a decrease in battery performance due to an increase in the electrolyte viscosity and self-discharge of the battery.
• the content of the sulfonylimide compound (1) in the nonaqueous electrolyte is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and even more preferably 50 mol% or more, based on a total of 100 mol% of the electrolyte salt contained in the nonaqueous electrolyte.
• the content of sulfonylimide compound (1) in the nonaqueous electrolyte is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the components contained in the nonaqueous electrolyte (based on 100% by mass of the total amount of the components contained in the nonaqueous electrolyte), from the viewpoint of improving battery performance.
• the concentration is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on 100% by mass of the total amount of the components contained in the nonaqueous electrolyte, from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte.
• the electrolyte salt may contain the sulfonylimide compound (1), but may also contain other electrolyte salts (electrolyte salts other than the sulfonylimide compound (1)).
• electrolytes include imide salts and non-imide salts.
• the imide salt may be another fluorine-containing sulfonylimide salt (hereinafter referred to as "another sulfonylimide compound") different from the sulfonylimide compound (1).
• the other sulfonylimide compound may be a non-lithium salt of the fluorine-containing sulfonylimide listed as the sulfonylimide compound (1) (for example, a salt in which the lithium (ion) in the sulfonylimide compound (1) is replaced with a cation other than the lithium ion).
• the salt in which a cation other than the lithium ion is replaced may be an alkali metal salt such as a sodium salt, a potassium salt, a rubidium salt, or a cesium salt; an alkaline earth metal salt such as a beryllium salt, a magnesium salt, a calcium salt, a strontium salt, or a barium salt; an aluminum salt; an ammonium salt; or a phosphonium salt.
• the other sulfonylimide compounds may be used alone or in combination of two or more kinds.
• the other sulfonylimide compounds may be commercially available products or may be synthesized by a conventional method.
• non-imide salt examples include salts of non-imide anions and cations (lithium ions and the above-listed cations).
• non-imide salt examples include a compound represented by the formula (hereinafter referred to as "fluoroborate compound (3)"), lithium salts such as lithium hexafluoroarsenate ( LiAsF6 ), LiSbF6 , LiClO4 , LiSCN, LiAlF4 , CF3SO3Li , LiC[( CF3SO2 ) 3 ], LiN( NO2 ), and LiN[(CN) 2 ]; and non-lithium salts (for example, salts in which the lithium (ion) in these lithium salts is substituted with the cations listed above (for example, NaBF4 , NaPF6 , NaPF3 ( CF3 ) 3 , etc.).
• the non-imide salts may be used alone or in combination of two or more kinds.
• the non-imide salts may be commercially available products, or may be obtained by synthesis using a conventional method.
• non-imide salts are preferred from the viewpoints of ion conductivity, cost, etc.
• fluorophosphate compound (2), fluoroboric acid compound (3) and LiAsF6 are preferred, with fluorophosphate compound (2) being more preferred.
• fluorophosphate compound (2) examples include LiPF6, LiPF3(CF3)3, LiPF3(C2F5)3, LiPF3(C3F7 ) 3 , and LiPF3 ( C4F9 ) 3 .
• fluorophosphate compounds ( 2) LiPF6 and LiPF3 ( C2F5 ) 3 are preferred, and LiPF6 is more preferred.
• fluoroboric acid compound (3) examples include LiBF 4 , LiBF(CF 3 ) 3 , LiBF(C 2 F 5 ) 3 , and LiBF(C 3 F 7 ) 3.
• fluoroboric acid compounds (3) LiBF 4 and LiBF(CF 3 ) 3 are preferred, and LiBF 4 is more preferred.
• electrolyte salts sulfonylimide compound (1), other electrolyte salts, etc.
• these electrolyte salts may be present (contained) in the form of ions in the nonaqueous electrolyte.
• the electrolyte salt composition may be an electrolyte salt having a simple salt composition of the sulfonylimide compound (1), or an electrolyte salt having a mixed salt composition containing the sulfonylimide compound (1) and another electrolyte.
• an electrolyte salt having a mixed salt composition an electrolyte salt having a mixed salt composition containing the sulfonylimide compound (1) and a fluorophosphate compound (2) is preferred, and an electrolyte salt having a mixed salt composition containing LiN( FSO2 ) 2 and LiPF6 is more preferred.
• the concentration of the other electrolytes in the nonaqueous electrolyte is preferably 0.1 mol/L or more, more preferably 0.2 mol/L or more, even more preferably 0.5 mol/L or more, even more preferably 0.7 mol/L or more, and even more preferably 1 mol/L or more, from the viewpoint of improving battery performance.
• the concentration is preferably 5 mol/L or less, more preferably 3 mol/L or less, even more preferably 2 mol/L or less, and even more preferably 1.5 mol/L or less, from the viewpoint of suppressing a decrease in battery performance due to an increase in the electrolyte viscosity and self-discharge of the battery.
• the total concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.8 mol/L or more, more preferably 1 mol/L or more, and even more preferably 1.2 mol/L or more, from the viewpoint of improving battery performance.
• the concentration is preferably 5 mol/L or less, more preferably 3 mol/L or less, and even more preferably 2 mol/L or less, from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte.
• the molar ratio of the sulfonylimide compound (1) to the other electrolyte is preferably 1:25 or more, more preferably 1:10 or more, even more preferably 1:8 or more, even more preferably 1:5 or more, even more preferably 1:2 or more, particularly preferably 1:1 or more, and is preferably 25:1 or less, more preferably 10:1 or less, even more preferably 5:1 or less, and even more preferably 2:1 or less.
• the electrolyte solvent contains at least one carbonate-based solvent selected from the group consisting of chain carbonate-based solvents and saturated cyclic carbonate-based solvents (hereinafter also referred to as "specific carbonate-based solvent"). That is, the nonaqueous electrolyte secondary battery according to this embodiment uses, as a constituent material, a nonaqueous electrolyte containing a chain carbonate-based solvent and/or a saturated cyclic carbonate-based solvent as an essential component, together with the sulfonylimide compound (1).
• the electrolyte solvent may contain only one or more chain carbonate-based solvents, may contain only one or more saturated cyclic carbonate-based solvents, or may be a mixed carbonate-based solvent containing a chain carbonate-based solvent and a saturated cyclic carbonate-based solvent.
• mixed carbonate-based solvents are preferred, and those containing EMC and EC described below are more preferred.
• chain carbonate (carbonic acid ester) solvents examples include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate, methyl phenyl carbonate, etc.
• the chain carbonate solvents may be used alone or in combination of two or more kinds.
• DMC, EMC and DEC are preferred, with EMC being more preferred.
• saturated cyclic carbonate solvents examples include ethylene carbonate (EC), propylene carbonate (PC), 2,3-dimethylethylene carbonate, 1,2-butylene carbonate, and erythritan carbonate.
• EC ethylene carbonate
• PC propylene carbonate
• 2,3-dimethylethylene carbonate 1,2-butylene carbonate
• erythritan carbonate examples include erythritan carbonate.
• the saturated cyclic carbonate solvents may be used alone or in combination of two or more.
• EC and PC are preferred, with EC being more preferred.
• the electrolyte solvent may contain a specific carbonate-based solvent, but may also contain other electrolyte solvents (electrolyte solvents other than the specific carbonate-based solvent).
• electrolyte solvents other than the specific carbonate-based solvent.
• electrolyte solvents include non-aqueous solvents other than the specific carbonate-based solvents, and any solvent commonly used in batteries can be used.
• non-aqueous solvent a solvent having a large dielectric constant, high solubility of the electrolyte, a boiling point of 60°C or higher, and a wide electrochemical stability range is preferred. More preferably, it is an organic solvent with a low water content.
• Such organic solvents include cyclic carbonate solvents having unsaturated bonds such as methylvinylene carbonate, ethylvinylene carbonate, 2-vinylethylene carbonate, and phenylethylene carbonate, other than specific carbonate solvents; fluorine-containing cyclic carbonate solvents such as fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate, and trifluoropropylene carbonate; ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane, and 1,3-dioxolane; aromatic carboxylate ester solvents such as methyl benzoate and ethyl benzoate; and ⁇ -but
• lactone solvents such as ⁇ -valerolactone, ⁇ -valerolactone; phosphate solvents such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, triethyl phosphate; nitrile solvents such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; sulfur compound solvents such as dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane; aromatic nitrile solvents such as benzonitrile, tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro
• the electrolyte solvent may be used as a medium such as a polymer or polymer gel used in place of the electrolyte solvent.
• a polymer or polymer gel in place of the electrolyte solvent, the following methods may be adopted. That is, a method of dripping a solution of an electrolyte salt dissolved in an electrolyte solvent onto a polymer formed by a conventionally known method to impregnate and support the electrolyte salt and electrolyte solvent; a method of melting and mixing a polymer and an electrolyte salt at a temperature above the melting point of the polymer, forming a film, and impregnating the film with the electrolyte solvent (above, gel electrolyte); a method of mixing a nonaqueous electrolyte in which an electrolyte salt has been dissolved in an electrolyte solvent in advance with a polymer, forming a film by a casting method or a coating method, and volatilizing the electrolyte solvent
• Polymers that can be used in place of the electrolyte solvent include polyethylene oxide (PEO), which is a homopolymer or copolymer of epoxy compounds (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.), polyether-based polymers such as polypropylene oxide, methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile-based polymers such as polyacrylonitrile (PAN), fluorine-based polymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene, and copolymers of these. These polymers may be used alone or in combination of two or more types.
• PEO polyethylene oxide
• PMMA methacrylic polymers
• PAN nitrile-based polymers
• PVdF polyvinylidene fluoride
• PVdF polyvinylidene fluoride-hexafluoropropy
• the nonaqueous electrolyte secondary battery according to the present embodiment includes at least one selected from the group consisting of phosphorus atom-containing compounds (hereinafter referred to as "phosphorus atom-containing compounds (5)") represented by the formula (1) and a specific carbonate-based solvent, and a nonaqueous electrolyte containing any one of a carbonic acid component such as CO2 , an unsaturated cyclic carbonate-based compound, a fluorophosphate compound (4) and a phosphorus atom-containing compound (5) as an additive as an essential component, as one constituent material.
• phosphorus atom-containing compounds (5) represented by the formula (1) and a specific carbonate-based solvent
• a nonaqueous electrolyte containing any one of a carbonic acid component such as CO2 , an unsaturated cyclic carbonate-based compound, a fluorophosphate compound (4) and a phosphorus atom-containing compound (5) as an additive as an essential component, as one constituent material a carbonic acid
• the specific additive may contain only one or more types of carbonic acid components such as CO2 , may contain only one or more types of unsaturated cyclic carbonate compounds, may contain only one or more types of fluorophosphate compounds (4), may contain only one or more types of phosphorus atom-containing compounds (5), or may be a combination (use in combination) of these.
• a carbonate component such as CO2 as an additive means that a predetermined amount or more (for example, 20 mass ppm or more) of the carbonate component is dissolved in the nonaqueous electrolyte containing the sulfonylimide compound (1).
• the nonaqueous electrolyte according to this embodiment has a carbonate component dissolved therein as an additive. Note that, when the nonaqueous electrolyte according to this embodiment contains a specific additive other than the carbonate component, the carbonate component may not be dissolved therein.
• dissolution of a carbonate component in a non-aqueous electrolyte containing a sulfonylimide compound (1) means that a carbonate component is intentionally dissolved in the non-aqueous electrolyte, but does not exclude, for example, a carbonate component contained in a raw material for the non-aqueous electrolyte, such as an electrolyte solvent, or a carbonate component that is inevitably dissolved in the non-aqueous electrolyte during a normal manufacturing process for the non-aqueous electrolyte or secondary battery.
• the total dissolved amount of carbonate components described below may include the carbonate component intentionally dissolved, as well as the carbonate component in the raw material and the carbonate component that is inevitably dissolved.
• the form of the carbonate component dissolved in the non-aqueous electrolyte is not particularly limited, and it is sufficient that the carbonate component is present in at least one of the forms CO 2 , CO, HCO 3 - and CO 3 2- , and the carbonate component may be present in any one of these forms or in multiple forms.
• the total dissolved amount of carbonate components in the nonaqueous electrolyte is, for example, 20 ppm by mass or more relative to the electrolyte, from the viewpoint of suppressing self-discharge of the battery, preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, even more preferably 200 ppm by mass or more, even more preferably 250 ppm by mass or more, and particularly preferably 500 ppm by mass or more.
• the upper limit of the total dissolved amount is not particularly limited, but is, for example, equal to or less than the saturation concentration at 25°C.
• the total dissolved amount can be measured by the method described in the examples below, for example, gas chromatography, etc.
• the total dissolved amount of carbonate components in the nonaqueous electrolyte solution means: In the preparation process of a non-aqueous electrolyte, the total amount of carbonate components dissolved in the electrolyte is the total amount of carbonate components dissolved immediately after the preparation of the electrolyte, or after an aging period (e.g., one week) has elapsed as necessary to stabilize the amount of dissolved carbonate components, or in the production process of a secondary battery, the total amount of carbonate components dissolved in the electrolyte removed from the battery in, for example, a nitrogen atmosphere after the aging process of the battery has been performed.
• the aging process can be the following process or the conditions described in the examples described later.
• Examples of the method for dissolving a carbonate component in a non-aqueous electrolyte solution containing the sulfonylimide compound (1) include (A) a method for dissolving a carbonate component in a non-aqueous electrolyte solution during the preparation process of the non-aqueous electrolyte solution; (B) a method for dissolving a carbonate component in a non-aqueous electrolyte solution during the production process of a secondary battery.
• the method of dissolving a carbonate component in the non-aqueous electrolyte is, in other words, a method of using a non-aqueous electrolyte containing a sulfonylimide compound (1) and having a predetermined amount or more of a carbonate component dissolved therein (hereinafter also referred to as a "carbonate component-dissolved electrolyte”) and injecting the electrolyte into a secondary battery.
• Examples of the method of dissolving a carbonate component in the non-aqueous electrolyte include a method of contacting a gas containing a carbonate component with the non-aqueous electrolyte (contacting step), a method of blowing a gas containing a carbonate component into the non-aqueous electrolyte (bubbling step), a method of stirring the non-aqueous electrolyte under a gas atmosphere containing a carbonate component (stirring step), a method of contacting a high-pressure gas containing a carbonate component with the non-aqueous electrolyte (a method of pressurizing a gas containing a carbonate component into the non-aqueous electrolyte, pressurizing step), and a method of adding a substance that generates a gas containing a carbonate component to the non-aqueous electrolyte (adding step).
• the substance that generates a gas containing a carbonate component examples include bicarbonate, carbonate, dry ice, etc.
• the carbonic acid component can be dissolved in an electrolyte solvent generally used for a non-aqueous electrolyte
• the sulfonylimide compound (1) may be dissolved in an electrolyte solvent in which a carbonic acid component has been dissolved in advance to prepare a non-aqueous electrolyte. The same method as described above can be used to dissolve the carbonic acid component in the electrolyte solvent.
• Another method is to put a non-aqueous electrolyte prepared in advance into a sealed container so that the volume is about 1/10 of the volume of the container, and then fill the container with the carbonic acid component by repeating the above-mentioned operation several times to replace the air in the container with the carbonic acid component, and finally store the container in a sealed state at a low temperature for several days (substitution step).
• the dissolving step may include at least one of the above-mentioned steps, and may be a combination of multiple steps.
• the dissolving step it is preferable to include at least one of a pressurizing step, a liquid contacting step, a bubbling step, and a substitution step, and it is more preferable to include at least one of a pressurizing step, a liquid contacting step, and a bubbling step, and a pressurizing step and a substitution step (which may be a combination of a pressurizing step and a substitution step) are even more preferable.
• the secondary battery may be assembled in a CO2 atmosphere or an atmosphere containing CO2 from the viewpoint of controlling the total amount of dissolved carbonic acid components in the nonaqueous electrolyte to a constant amount.
• the step of injecting the nonaqueous electrolyte having the carbonic acid components dissolved therein into the battery and the steps after the injection may be performed in a CO2 atmosphere or an atmosphere containing CO2 .
• the battery may be exposed to a high-pressure CO2 atmosphere.
• the carbonate component-dissolved electrolyte used in the method (A) is obtained by the method for producing a nonaqueous electrolyte according to this embodiment.
• This method includes a dissolving step including at least one of the steps described above in order to dissolve a predetermined amount or more of a carbonate component in a nonaqueous electrolyte containing a sulfonylimide compound (1).
• examples of the method of dissolving a carbonate component in the non-aqueous electrolyte include a method of assembling a secondary battery under a CO 2 atmosphere and injecting the non-aqueous electrolyte into the battery (specifically, a method of filling the battery exterior sealed on three sides with CO 2 after creating a nearly vacuum state, and then injecting the non-aqueous electrolyte from the unsealed side and sealing it at normal pressure); a method of injecting the non-aqueous electrolyte into the secondary battery and then replacing the air in the battery with CO 2 , and the like.
• the method of replacing the air in the battery with CO 2 can be the same as the method of replacing the air in the container with CO 2. Specifically, the operation of creating a nearly vacuum state inside the exterior in which the non-aqueous electrolyte is injected and then filling it with CO 2 is repeated multiple times, whereby the air in the exterior is replaced with CO 2 .
• the total amount of dissolved carbonic acid components in the non-aqueous electrolyte varies depending on the temperature of the non-aqueous electrolyte, so it is preferable to control the temperature at a constant level during the non-aqueous electrolyte preparation process and/or the secondary battery manufacturing process.
• the use of the unsaturated cyclic carbonate compound as an additive means that the nonaqueous electrolyte solution containing the sulfonylimide compound (1) contains a predetermined amount or more of the unsaturated cyclic carbonate compound.
• the nonaqueous electrolyte solution according to this embodiment contains the unsaturated cyclic carbonate compound as an additive.
• the unsaturated cyclic carbonate compound may be added to the nonaqueous electrolyte solution, or may be added during the preparation process of the nonaqueous electrolyte solution.
• the nonaqueous electrolyte solution contains a specific additive other than the unsaturated cyclic carbonate compound, it is not necessary to contain the compound.
• unsaturated cyclic carbonate compounds examples include vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, 2-vinylethylene carbonate, and phenylethylene carbonate. Each of the unsaturated cyclic carbonate compounds may be used alone, or two or more of them may be used in combination. Of the unsaturated cyclic carbonate compounds, VC is preferred.
• the use of the fluorophosphate compound (4) as an additive means that a predetermined amount or more of the fluorophosphate compound (4) is contained in a nonaqueous electrolyte solution containing the sulfonylimide compound (1).
• the nonaqueous electrolyte solution according to this embodiment contains the fluorophosphate compound (4) as an additive.
• the fluorophosphate compound (4) may be added to the nonaqueous electrolyte solution or may be added during the preparation process of the nonaqueous electrolyte solution.
• the compound (4) may not be contained.
• examples of the alkali metal element represented by M include lithium, sodium, potassium, rubidium, and cesium. Of these, lithium is preferred.
• fluorophosphate compound (4) examples include lithium monofluorophosphate (Li 2 PO 3 F) and lithium difluorophosphate (LiPO 2 F 2 ).
• the fluorophosphate compound (4) may be used alone or in combination of two or more.
• Li 2 PO 3 F and LiPO 2 F 2 containing at least one selected from the group consisting of Li 2 PO 3 F and LiPO 2 F 2 ) are preferred, and LiPO 2 F 2 is preferred.
• the use of the phosphorus atom-containing compound (5) as an additive means that a predetermined amount or more of the phosphorus atom-containing compound (5) is contained in a non-aqueous electrolyte containing the sulfonylimide compound (1).
• the non-aqueous electrolyte according to this embodiment contains the phosphorus atom-containing compound (5) as an additive.
• the phosphorus atom-containing compound (5) may be added to the non-aqueous electrolyte, or may be added in the preparation process of the non-aqueous electrolyte. Note that, when the non-aqueous electrolyte contains a specific additive other than the phosphorus atom-containing compound (5), the compound (5) may not be contained.
• R 1 represents an alkyl group having 1 to 6 carbon atoms (which may have a substituent), a fluoroalkyl group having 1 to 6 carbon atoms (which may have a substituent), an aryl group (which may have a substituent), a silyl group (which may have a substituent), an alkali metal atom, an onium salt, or a hydrogen atom.
• a linear alkyl group having 1 to 6 carbon atoms (which may have a substituent), a trifluoroalkyl group having 1 to 6 carbon atoms (which may have a substituent), a trialkylsilyl group having 1 to 6 carbon atoms (which may have a substituent), and a silyl group in which an alkyl group having 1 to 6 carbon atoms (which may have a substituent) and two alkyl groups having 1 to 6 carbon atoms (which may have a substituent) differing in carbon number, structure (chain, cyclic, etc.) are bonded are preferred; a linear alkyl group having 1 to 3 carbon atoms (which may have a substituent), a trifluoroalkyl group having 1 to 3 carbon atoms (which may have a substituent), More preferred are a trialkylsilyl group having 1 to 4 carbon atoms (which may have a substituent), and a silyl group in which an alkyl group having
• a trialkylsilyl group having 1 to 6 or 1 to 4 carbon atoms refers to a silyl group in which three alkyl groups having 1 to 6 or 1 to 4 carbon atoms are bonded.
• R 1 may be a trialkoxysilyl group (-Si(-OR) 3 ) in which three alkyl groups (R) having 1 to 6 or 1 to 4 carbon atoms are bonded to a silyl group via an oxygen atom.
• trialkoxysilyl groups include trimethoxysilyl, triethoxysilyl, triisopropoxysilyl, (tert-butoxy)dimethoxysilyl, and (tert-butoxy)diphenoxysilyl.
• the three alkyl or alkoxy groups may be the same or different.
• R 1 is the same group.
• the phosphorus atom-containing compound (5) include ethyl polyphosphate (in the general formula (5), R 1 represents an ethyl group), trimethylsilyl polyphosphate (in the general formula (5), R 1 represents a trimethylsilyl group (TMS)), triethylsilyl polyphosphate (in the general formula (5), R 1 represents a triethylsilyl group (TES)), triisopropylsilyl polyphosphate (in the general formula (5), R 1 represents a triisopropylsilyl group (TIPS)), (tert-butyl)dimethylsilyl polyphosphate (in the general formula (5), R 1 represents a (tert-butyl)dimethylsilyl group (TBDMS)), and (tert-butyl)diphenylsilyl polyphosphate (in the general formula (5), R 1 represents a (tert-butyl)diphenylsilyl polyphosphate (in the general formula
• trimethoxysilyl polyphosphate in the general formula (5), R 1 represents a trimethoxysilyl group
• triethoxysilyl polyphosphate in the general formula (5), R 1 represents a triethoxysilyl group
• (triisopropoxysilyl) polyphosphate in the general formula (5), R 1 represents a triisopropoxysilyl group
• [(tert-butoxy)dimethoxysilyl] polyphosphate in the general formula (5), R 1 represents a (tert-butoxy)dimethoxysilyl group
• [(tert-butoxy)diphenoxysilyl] polyphosphate in the general formula (5), R 1 represents a (tert-butoxy)diphenoxysilyl group
• the phosphorus atom-containing compound (5) may be used alone or in combination of two or more kinds. Among the phosphorus atom-containing compounds (5), trimethylsilyl polyphosphate is preferred.
• Polytrimethylsilylphosphate can be analyzed for structures such as a chain structure represented by the following structural formula ( 5-1 ), a cyclic structure represented by the structural formula (5-2), and a branched structure represented by the structural formula (5-3) by, for example, measuring the presence or absence of peaks showing bonds between phosphorus atoms and groups surrounding them and their abundance ratios (integral ratios of each peak) by 31P-NMR or the like.
• the measurement conditions for 31P -NMR can be, for example, those described in the Examples below.
• TMS represents a trimethylsilyl group
• n represents the degree of polymerization
• Pt, Pm, and Pb represent the peaks of phosphorus atoms.
• Pt represents the peak of a phosphorus atom at the end, in the side chain, etc., specifically a phosphorus atom having one group in which the hydrogen atom of a hydroxyl group is replaced by another adjacent phosphorus atom (hereinafter also referred to as an "-O-P group”).
• Pm represents the peak of a phosphorus atom with a linear structure, specifically a phosphorus atom having two "-O-P groups”.
• Pb represents the peak of a phosphorus atom with a branched structure, specifically a phosphorus atom having three "-O-P groups".
• the presence or absence of branched structures, their abundance ratio, the degree of polymerization n, etc. can be estimated from the presence or absence of Pt, Pm, and Pb and their integral ratios.
• the integral value of the Pt region is 1, the degree of polymerization n is expressed as 2 ⁇ (integral value of Pt)+(integral value of Pm) ⁇ 2 ⁇ 1+(integral value of Pm) ⁇ .
• the degree of polymerization n is expressed as (integral value of Pt)+(integral value of Pm) ⁇ 2+(integral value of Pm).
• the degree of polymerization n is smaller than the above.
• trimethylsilyl polyphosphates from the viewpoint of suppressing self-discharge of the battery and further improving battery performance, those having a Pb peak, that is, those containing a branched structure represented by structural formula (5-3), are preferred.
• a carbonic acid component and a phosphorus atom-containing compound (5) are preferred, a phosphorus atom-containing compound (5) is more preferred, trimethylsilyl polyphosphate, ethyl polyphosphate, (triisopropylsilyl) polyphosphate, and [(tert-butyl)dimethylsilyl] polyphosphate are even more preferred, and trimethylsilyl polyphosphate containing a branched structure represented by structural formula (5-3) is particularly preferred.
• Specific additives other than the carbonate component are preferably used in a range of 0.1% by mass to 10% by mass, more preferably 0.2% by mass to 8% by mass, even more preferably 0.3% by mass to 5% by mass, even more preferably 0.3% by mass to 3% by mass, and even more preferably 0.3% by mass to 1% by mass, based on 100% by mass of the total amount of components contained in the non-aqueous electrolyte, from the viewpoint of suppressing self-discharge of the battery.
• the non-aqueous electrolyte may contain the specific additive, but may also contain other additives (additives other than the specific additive).
• the other additives are additives intended to improve various characteristics of the lithium ion secondary battery.
• the other additives may be added to the non-aqueous electrolyte, or may be added in the preparation process of the non-aqueous electrolyte.
• the other additives include carboxylic anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexane dicarboxylic anhydride, cyclopentane tetracarboxylic dianhydride, and phenylsuccinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, trimethylene Sulfur-containing compounds such as glycol sulfate esters; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl
• the nonaqueous electrolyte according to this embodiment is composed of components such as the sulfonylimide compound (1), a specific carbonate-based solvent and a specific additive, and, if necessary, other electrolyte salts, other electrolyte solvents, and other additives.
• the nonaqueous electrolyte can be prepared, for example, by mixing these components in a predetermined composition (mass) ratio.
• the positive electrode includes a positive electrode current collector and a positive electrode mixture layer, and the positive electrode mixture layer is formed on the positive electrode current collector and is usually formed into a sheet shape.
• Metals used for the positive electrode current collector include, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. Among these, aluminum is preferred. There are no particular limitations on the shape or dimensions of the positive electrode current collector.
• the positive electrode mixture layer is formed from a positive electrode mixture (positive electrode composition).
• the positive electrode mixture contains a positive electrode active material, a conductive additive, a binder, a solvent for dispersing these components, etc.
• the positive electrode ( positive electrode composite material) can preferably be a ternary positive electrode active material such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (NCM111 ) , LiNi0.5Co0.2Mn0.3O2 ( NCM523 ) , LiNi0.6Co0.2Mn0.2O2 ( NCM622 ) , LiNi0.8Co0.1Mn0.1O2 ( NCM811 ), or an iron phosphate positive electrode active material having an olivine structure such as LiFePO4 or LiFe0.995Mn0.005PO4 .
• These positive electrode active materials may be used alone or in combination of two or more kinds.
• the high Ni-containing ternary positive electrode active material represented by the following formula (hereinafter referred to as "high Ni-containing ternary positive electrode active material (6)" is used.
• the Ni content ("x" in general formula (6)) relative to the total amount of transition metals, 100% (100 mol%) on a molar basis is 50% or more (0.5 ⁇ x), preferably 55% or more (0.55 ⁇ x), and more preferably 70% or more (0.7 ⁇ x).
• the upper limit of the content is 90% or less (x ⁇ 0.9), preferably less than 85% (x ⁇ 0.85), and more preferably 80% or less (x ⁇ 0.8).
• the content ratios of each component other than Ni in the high Ni-containing ternary positive electrode active material (6) (“v", “y”, “z”, and "w” (2+w) in general formula (6)) may be appropriately adjusted within the range of each of the above molar ratios.
• the high Ni-containing ternary positive electrode active material (6) may be used alone or in combination of two or more kinds.
• the high Ni-containing ternary positive electrode active material (6) may be a commercially available product or may be synthesized by a conventional method.
• Specific examples of the high Ni-containing ternary positive electrode active material (6) include, for example, NCM523, NCM622, and NCM811.
• the positive electrode preferably contains at least one of the above-mentioned ternary positive electrode active material and iron phosphate positive electrode active material, but may contain other positive electrode active materials.
• the other positive electrode active materials may be any materials capable of absorbing and releasing lithium ions, and may be, for example, positive electrode active materials used in conventionally known secondary batteries (lithium ion secondary batteries).
• the content of the positive electrode active material (the total content when multiple positive electrode active materials are included) is preferably 75% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, relative to 100% by mass of the total amount of the components contained in the positive electrode composite, from the viewpoint of improving the output characteristics and electrical characteristics of the secondary battery, and is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less.
• the conductive assistant is used to improve the output of the lithium-ion secondary battery.
• Conductive carbon is mainly used as the conductive assistant.
• Examples of conductive carbon include carbon black, fibrous carbon, and graphite.
• the conductive assistant may be used alone or in combination of two or more types.
• carbon black is preferred. Examples of carbon black include ketjen black and acetylene black.
• the content of the conductive assistant in the non-volatile matter of the positive electrode composite is preferably 1 to 20 mass %, more preferably 1.5 to 10 mass %, from the viewpoint of improving the output characteristics and electrical characteristics of the lithium-ion secondary battery.
• Binders include fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamideimide; polyolefin resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; cellulose resins such as carboxymethyl cellulose; and the like.
• Each binder may be used alone, or two or more types may be used in combination. Furthermore, the binder may be in a state of being dissolved in a solvent or dispersed in a solvent when used.
• Solvents include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, water, etc.
• Each of the solvents may be used alone, or two or more types may be used in combination. There are no particular limitations on the amount of solvent used, and it may be determined appropriately depending on the production method and materials used.
• the positive electrode mixture may contain other components as necessary, such as non-fluorinated polymers such as (meth)acrylic polymers, nitrile polymers, and diene polymers; polymers such as fluorinated polymers such as polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as polymer dispersants such as styrene-maleic acid copolymers and polyvinylpyrrolidone; thickeners such as carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), and alkali-soluble (meth)acrylic acid-(meth)acrylic acid ester copolymers; preservatives, etc.
• the content of other components in the non-volatile content of the positive electrode mixture is preferably 0 to 15% by mass, and more preferably 0 to 10% by mass.
• the positive electrode mixture can be prepared, for example, by mixing the positive electrode active material, conductive additive, binder, solvent, and other components as necessary, and dispersing the mixture using a bead mill, ball mill, stirring mixer, etc.
• the method for forming the positive electrode is not particularly limited, and examples thereof include (1) a method in which the positive electrode mixture is applied to the positive electrode current collector by a conventional coating method (e.g., doctor blade method, etc.) (and then dried); (2) a method in which the positive electrode current collector is immersed in the positive electrode mixture (and then dried); (3) a method in which a sheet formed of the positive electrode mixture is bonded to the positive electrode current collector (e.g., bonded via a conductive adhesive) and pressed (and then dried); (4) a method in which the positive electrode mixture to which a liquid lubricant has been added is applied or cast onto the positive electrode current collector, formed into a desired shape, and then the liquid lubricant is removed (and then stretched in a uniaxial or multiaxial direction); and (5) a method in which the positive electrode mixture (or the solid content forming the positive electrode mixture layer) is slurried with an electrolyte, transferred in a semi-solid state to a current collector (positive electrode
• the positive electrode composite layer may be dried or pressed after formation or coating (applying) as necessary.
• the negative electrode includes a negative electrode current collector and a negative electrode mixture layer, and the negative electrode mixture layer is formed on the negative electrode current collector and is usually formed into a sheet shape.
• Metals used for the negative electrode current collector include, for example, iron, copper, aluminum, nickel, stainless steel (SUS), titanium, tantalum, gold, platinum, etc. Among these, copper is preferred. There are no particular limitations on the shape or dimensions of the negative electrode current collector.
• the negative electrode mixture layer is formed from a negative electrode mixture (negative electrode composition).
• the negative electrode mixture contains a negative electrode active material, a conductive additive, a binder, a solvent for dispersing these components, etc.
• the negative electrode includes a first graphite (graphite) having a peak area ratio (D/G ratio) of D band and G band analyzed by Raman spectroscopy greater than 0.7 and/or a G band half width greater than 28 cm ⁇ 1 analyzed by Raman spectroscopy as a negative electrode active material, and includes a second graphite having a D/G ratio of 0.7 or less and/or a G band half width of 28 cm ⁇ 1 or less in an amount of 0 mass% to 10 mass% relative to a total amount of 100 mass% of the first graphite and the second graphite.
• first graphite graphite
• D/G ratio peak area ratio
• the negative electrode may include only the “first graphite”, or may be a mixed graphite including the “first graphite” and the “second graphite” having a content ratio of 10 mass% or less.
• the nonaqueous electrolyte secondary battery according to this embodiment includes a negative electrode containing the “first graphite” having low crystallinity as an essential component as one of its constituent materials.
• a negative electrode active material (negative electrode) containing the "first graphite” and a predetermined amount or less of the "second graphite” in combination with a nonaqueous electrolyte solution in which a carbonate component is intentionally dissolved and/or a nonaqueous electrolyte solution containing a specific additive other than the carbonate component, self-discharge of the battery caused by the sulfonylimide compound (1) (particularly LiN(FSO 2 ) 2 ) is suppressed, and the storage characteristics are improved.
• the negative electrode negative electrode active material
• the content ratio of "second graphite” relative to the total amount of "first graphite” and “second graphite” is specified to be 10 mass% or less, so that the decrease in cycle capacity retention rate is suppressed and the charge-discharge cycle characteristics are improved.
• the content of "second graphite” relative to the total amount of "first graphite” and “second graphite” (100% by mass) is 10% by mass or less, preferably 8% by mass or less, and more preferably 5% by mass or less, from the viewpoint of improving the battery capacity.
• the lower limit is 0% by mass or more, and from the viewpoint of suppressing self-discharge of the battery, it is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more.
• the “peak area ratio (D/G ratio) of the D band and the G band analyzed by Raman spectroscopy” refers to the ratio (ID/IG, D band/G band area ratio) between the area of the peak intensity IG at about 1580 cm -1 due to the graphite structure (crystallinity) contained in the carbon material and the area of the peak intensity ID at about 1350 cm -1 due to defects in the graphite structure contained in the carbon material in the Raman spectrum measured with Raman light excited by a laser with a wavelength of 532 nm. Note that these peaks may appear at positions shifted by about ⁇ 10 cm -1 .
• the D/G ratio of the "first graphite” is greater than 0.7, and the upper limit is not particularly limited, but is, for example, 2 or less.
• the "first graphite” having a D/G ratio within the above range refers to graphite with low crystallinity and relatively many disturbances and defects in the graphite structure.
• the D/G ratio of the "second graphite” is 0.7 or less, and the lower limit is not particularly limited, but is, for example, 0.05 or more.
• the “second graphite” having a D/G ratio within the above range refers to graphite having high crystallinity and relatively few disorders and defects in the graphite structure. Examples of the method for measuring the Raman spectrum include the method described in the Examples below.
• G band half width analyzed by Raman spectroscopy refers to the half width of the peak intensity I G at about 1580 cm -1 due to the graphite structure contained in the carbon material in a Raman spectrum measured with Raman light excited by a laser having a wavelength of 532 nm.
• the G band half width is related to the crystallinity or the amount of disorder/defects in the graphite structure.
• the G band half width of the "first graphite” is greater than 28 cm -1 , and the upper limit is not particularly limited, but is, for example, 50 or less.
• the "first graphite” having a G band half width within the above range refers to graphite with low crystallinity and relatively many disorder/defects in the graphite structure.
• the G band half width of the "second graphite” is 28 cm -1 or less, the above effect is exhibited, but from the viewpoint of improving the effect, it is preferably 23 cm -1 , and the lower limit is not particularly limited, but is, for example, 10 cm -1 or more.
• the "second graphite” having a G band half width within the above range refers to graphite having high crystallinity and relatively few disorders and defects in the graphite structure.
• first graphite examples include natural graphite such as O-MAC manufactured by Osaka Gas Chemicals Co., Ltd. and SMG manufactured by Hitachi Chemical Co., Ltd.
• the "first graphite” is a relatively cheaper carbon material than the “second graphite.”
• the “first graphite” may be used alone or in combination of two or more types.
• Examples of the “second graphite” include graphite such as MAGE manufactured by Hitachi Chemical Co., Ltd. and SFG15 and SLP50 manufactured by Imerys.
• the “second graphite” may be used alone or in combination of two or more types.
• mixed graphite is one that contains SMG and SFG15 in a composition (mass) ratio of 99-90:1-10.
• the negative electrode active material may contain the "first graphite” and a predetermined amount or less of the "second graphite", but may also contain other negative electrode active materials.
• the other negative electrode active material a conventionally known negative electrode active material used in various batteries (e.g., lithium secondary batteries) may be used, and any material capable of absorbing and releasing lithium ions may be used.
• carbon materials such as mesophase sintered bodies made from coal and petroleum pitch, and non-graphitizable carbon
• Si-based negative electrode materials such as Si, Si alloys, and SiO
• Sn-based negative electrode materials such as Sn alloys
• lithium alloys such as lithium metal and lithium-aluminum alloys; and the like
• the other negative electrode active materials may be used alone, or two or more types may be used in combination.
• the negative electrode mixture may further contain a conductive additive (conductive substance), a binder, a solvent, etc.
• a conductive additive conductive substance
• the conductive additive, binder, solvent, etc. may be the same components as those described above.
• the proportions of use thereof are also the same as those described above.
• the negative electrode may be manufactured in the same manner as the positive electrode.
• the non-aqueous electrolyte secondary battery according to this embodiment may include a separator.
• the separator is disposed so as to separate the positive electrode from the negative electrode.
• any conventionally known separator may be used in the present disclosure.
• Specific examples of the separator include a porous sheet made of a polymer capable of absorbing and retaining an electrolyte (non-aqueous electrolyte) (e.g., a polyolefin-based microporous separator or a cellulose-based separator), a non-woven fabric separator, a porous metal body, and the like.
• Porous sheet materials include polyethylene, polypropylene, and laminates with a three-layer structure of polypropylene/polyethylene/polypropylene.
• Nonwoven separator Materials for the nonwoven separator include, for example, cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., and depending on the required mechanical strength, etc., the above-listed materials may be used alone or in combination of two or more types.
• a battery element including a positive electrode, a negative electrode, and a nonaqueous electrolyte (and further a separator) is usually housed in a battery exterior material to protect the battery element from external impacts, environmental deterioration, etc., during use of the battery.
• a battery exterior material There are no particular limitations on the material of the battery exterior material, and any of the conventionally known exterior materials can be used.
• the battery exterior may contain expanded metal, fuses, overcurrent protection elements such as PTC elements, lead plates, etc. to prevent pressure buildup inside the battery and overcharging and discharging.
• the shape of the battery is not particularly limited, and any shape that is conventionally known as a shape of a battery (lithium ion secondary battery, etc.) can be used, such as cylindrical, square, laminated, coin, large, etc. Furthermore, when used as a high-voltage power source (several tens of volts to several hundreds of volts) for installation in electric vehicles, hybrid electric vehicles, etc., it can also be made into a battery module consisting of individual batteries connected in series.
• the rated charging voltage of a secondary battery is not particularly limited, but when the secondary battery has a positive electrode containing the above-mentioned ternary positive electrode active material as a main component, it may be, for example, 3.6 V or more, preferably 4.0 V or more, more preferably 4.1 V or more, and even more preferably 4.2 V or more.
• the nonaqueous electrolyte secondary battery according to this embodiment can be easily manufactured, for example, by stacking a positive electrode and a negative electrode (with a separator interposed between them as necessary), placing the resulting laminate in a battery exterior material, injecting a nonaqueous electrolyte into the battery exterior material, and sealing it.
• the nonaqueous electrolyte secondary battery containing the sulfonylimide compound (1) uses a specific nonaqueous electrolyte containing a specific carbonate-based solvent and a specific additive in combination with a specific negative electrode containing either "first graphite” alone as the negative electrode active material or a specific negative electrode containing "first graphite” and a mixed graphite in which the content of "second graphite” is 10% by mass or less relative to the total amount of "first graphite” and "second graphite” (100% by mass).
• the combination of the specific negative electrode and the specific additive provides the effect of improving self-discharge (storage characteristics), and further provides a synergistic effect of improving the charge-discharge cycle characteristics by specifying the content ratio of "second graphite" in the mixed graphite.
• MAGE manufactured by Hitachi Chemical Co., Ltd.
• VGCF carbon fiber
• CMC carboxymethyl cellulose
• SBR styrene butadiene rubber
• a ternary positive electrode LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111), manufactured by Umicore), acetylene black (Denka, Denka Black), graphite (Nippon Graphite, SP270), and PVdF (Kureha, L#7208) were weighed in a composition (mass) ratio of 100:3:3:3 and dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The prepared slurry was coated on one side of an aluminum foil (coating weight 19.8 mg/cm 2 ), dried, and then roll pressed to produce a positive electrode.
• NMP N-methyl-2-pyrrolidone
• the obtained positive electrode was cut to an effective area of 12 cm 2 .
• the negative electrodes obtained in each manufacturing example were cut to have an effective area of 13.44 cm2.
• the types of negative electrodes used are shown in Table 2 below.
• Negative electrodes 2-1 to 2-9 were produced in the same manner as in Production Examples 1 to 9, respectively, except that the coating weight was changed to 10.8 mg/ cm2 using the same composition as negative electrodes 1-1 to 1-9.
• Example 2-1 to 2-6 Comparative Examples 2-1 to 2-4
• a positive electrode was produced in the same manner as in Example 1 series, except that the positive electrode active material was changed to LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) manufactured by Beijing Toben Co., Ltd.
• a non-aqueous electrolyte solution was prepared in the same manner as in Example 1 series, except that the additives were changed to the types and contents or dissolved amounts thereof shown in Table 3.
• a 30 mAh laminate battery was manufactured in the same manner as in Example 1 series, and the battery was charged and discharged under the above-mentioned conditioning condition 1 to complete an evaluation battery.
• the types of the negative electrode and electrolyte used are shown in Table 3 below.
• Negative electrodes 2-1 to 2-9 were produced in the same manner as in Production Examples 1 to 9, respectively, except that the coating weight was changed to 8.8 mg/ cm2 using the same composition as negative electrodes 1-1 to 1-9.
• the positive electrode active material was changed to commercially available LiFePO4 , and LiFePO4 , acetylene black (HS-100), and PVdF (Kureha, L#7208) were weighed in a composition (mass) ratio of 100:9:6 and dispersed in NMP to prepare a slurry.
• the prepared slurry was applied to one side of an aluminum foil (coating weight 20.20 mg/ cm2 ), dried, and then roll pressed to produce a positive electrode.
• a non-aqueous electrolyte solution was prepared in the same manner as in Example 1 series, except that the additives were changed to the types and contents or dissolved amounts thereof shown in Table 4.
• a 25 mAh laminate battery was manufactured in the same manner as in Example 1.
• the types of negative electrode and electrolyte used are shown in Table 4 below. After the electrolyte was injected, the battery was charged at a constant current of 5 mA for 3 hours, one piece was opened, and the battery was vacuum-sealed again to remove gases. The battery after the removal of gases was stored at 25° C. for 48 hours, and then charged and discharged under the following conditioning condition 2 to complete an evaluation battery.
• the 31 P-NMR measurement was performed using a JNM-ECA500 manufactured by JEOL (Japan Electronics Corporation) and a double sample tube as the sample tube, and the chemical shift was determined by setting the phosphorus peak of H 3 PO 4 added to one of the tubes as 0 ppm.
• Polyphosphate [(tert-butyl)dimethylsilyl] (hereinafter also referred to as "PPSE (TBDMS)") was synthesized by carrying out the same procedure as in the synthesis of PPSE (TIPS), except that the triisopropylsilane used in the synthesis of PPSE (TIPS) was changed to tert-butyldimethylsilane.
• Example 4-1 to 4-9 Comparative Examples 4-1 to 4-2
• a positive electrode was produced in the same manner as in Example 1 series, except that the positive electrode active material was changed to LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) manufactured by Beijing Toben Co., Ltd., and the coating weight was changed to 15.7 mg/cm 2 .
• Negative electrode 2-1 or 2-5 produced in Example 2 series was used.
• a non-aqueous electrolyte solution was prepared in the same manner as in Example 1 series, except that the additives were changed to the types and contents or dissolved amounts shown in Tables 5 and 6. Using the obtained positive and negative electrodes, a 30 mAh laminate battery was manufactured in the same manner as in Example 1.
• 2nd cycle Charge: 15mA, constant current/constant voltage charge at 4.2V, terminate at 0.6mA ⁇ Discharge: Discharge at 6mA, terminate at 2.75V.
• 3rd cycle Charge: 15mA, constant current/constant voltage charge at 4.2V, terminate at 0.6mA ⁇ Discharge: Discharge at 30mA, terminate at 2.75V.
• 4th cycle Charge: 15mA, constant current/constant voltage charge at 4.2V, terminate at 0.6mA ⁇ Discharge: Discharge at 60mA, terminate at 2.75V.

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