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
  • H01M10/052—Li-accumulators
• • 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
  • H01M10/056—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
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • 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, including their high-temperature durability and charge/discharge cycles.
• Patent Document 1 the present applicant has proposed an electrolyte solution for a secondary battery having an electrolyte salt concentration of more than 1.1 mol/L, containing a sulfonylimide compound as the electrolyte salt, and containing a cyclic carbonate as the solvent, with the cyclic carbonate/Li + being 1 or more and 3 or less.
• a secondary battery comprising this electrolyte solution and a positive electrode containing a lithium composite oxide (positive electrode active material) containing Ni (nickel), such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111), is expected to have a long life due to suppression of deterioration of cycle characteristics.
• Patent Document 2 proposes a non-aqueous electrolyte secondary battery that includes a positive electrode using a positive electrode active material made of a lithium-containing metal composite oxide having a layered structure, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent, in which the positive electrode active material uses 50 mol % or more of nickel among the metals other than lithium in the lithium-containing metal composite oxide, and 0.1 to 5 wt % of a sulfur-containing cyclic compound having an unsaturated bond in the ring is added to the non-aqueous electrolyte solution.
• Patent Document 2 does not mention anything about nonaqueous electrolyte secondary batteries equipped with a nonaqueous electrolyte solution containing a sulfonylimide compound as the electrolyte.
• the present disclosure has been made in consideration of these points, and its purpose is to suppress the increase in resistance that accompanies use of the battery and to improve the low-temperature discharge capacity (improvement of low-temperature discharge characteristics) in a nonaqueous electrolyte secondary battery that includes a nonaqueous electrolyte containing a sulfonylimide compound and a high-Ni-based positive electrode that contains a high-Ni lithium composite oxide in which the nickel content in the transition metal is 50% or more on a molar basis.
• the present inventors have discovered that in a nonaqueous electrolyte secondary battery comprising a nonaqueous electrolyte containing a sulfonylimide compound and a high Ni-based positive electrode, by specifying the content ratio of saturated cyclic carbonate-based solvent in the electrolyte solvent (specifically, making it lower than in the prior art), the increase in resistance that accompanies use of the battery is suppressed and low-temperature discharge characteristics are also improved.
• the present disclosure is as follows.
• the nonaqueous electrolyte secondary battery of the present disclosure has a 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 an electrolyte solvent containing a saturated cyclic carbonate-based solvent; a positive electrode containing a lithium composite oxide containing nickel; and a negative electrode, wherein the content of nickel relative to 100% of the total amount of transition metals (metals in Groups 3 to 11 of the Periodic Table) contained in the lithium composite oxide is 50% or more, and the content of the saturated cyclic carbonate-based solvent relative to 100% by mass of the total amount of the electrolyte solvent is 30% by mass or less.
• R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms
• the concentration of the sulfonylimide compound represented by the general formula (1) in the nonaqueous electrolyte may be 0.2 mol/L or more.
• the sulfonylimide compound represented by the general formula (1) may contain LiN(FSO 2 ) 2.
• the electrolyte solvent may contain a chain carbonate solvent.
• 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 non-aqueous electrolyte may contain at least one additive selected from the group consisting of hydroxysulfonic acid compounds represented by the general formula (4):
• the non-aqueous electrolyte may contain at least one additive selected from the group consisting of trimethylsilyl polyphosphate, ethyl polyphosphate, (triisopropylsilyl) polyphosphate, and [(tert-butyl)dimethylsilyl] polyphosphate.
• the positive electrode active material may be 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 compound represented by general formula (3): LiBF b (C n F 2n+1 ) 4-b (b: 0 ⁇ b ⁇ 4, n: 1 ⁇ n ⁇ 4) ... (3) and LiAsF6 .
• a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a sulfonylimide compound and a high Ni-based positive electrode containing a high Ni-containing lithium composite oxide in which the nickel content in the transition metal is 50% or more on a molar basis, it is possible to suppress the increase in resistance that occurs with the use of the battery and to improve the low-temperature discharge capacity (improvement of low-temperature discharge characteristics).
• FIG. 1 shows the 31 P-NMR spectrum of the reagent trimethylsilyl polyphosphate (PPSE-1) used in Example 1 series (Example 5).
• FIG. 2 shows the 31 P-NMR spectrum of the polytrimethylsilyl phosphate (PPSE-2) synthesized in Example 1 series (Example 6).
• FIG. 3 shows the 31 P-NMR spectrum of trimethylsilyl polyphosphate (PPSE-3) synthesized in Example 1 series (Example 7).
• the nonaqueous electrolyte secondary battery refers to a secondary battery including a nonaqueous electrolyte.
• the nonaqueous electrolyte secondary battery according to this embodiment includes a nonaqueous electrolyte, a positive electrode, and a negative electrode.
• Non-aqueous electrolyte contains an electrolyte salt and an electrolyte solvent.
• the electrolyte salt according to this embodiment 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 non-aqueous electrolyte according to the present embodiment contains the sulfonylimide compound (1) as an essential component.
• 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 0.2 mol/L or more, more preferably 0.3 mol/L or more, and even more preferably 0.5 mol/L or more, from the viewpoint of improving the battery performance (particularly low-temperature discharge characteristics).
• 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 the deterioration of the battery performance due to the increase in the electrolyte viscosity and the 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 according to the present embodiment contains a saturated cyclic carbonate solvent at a content ratio of 30% by mass or less relative to the total amount of the electrolyte solvent (100% by mass).
• the nonaqueous electrolyte according to the present embodiment contains a saturated cyclic carbonate solvent as an essential component, and the content ratio is specified to be 30% by mass or less.
• a mixed solvent conventional electrolyte solvent
• EC ethylene carbonate
• EMC ethyl methyl carbonate
• the content ratio of the saturated cyclic carbonate solvent in the electrolyte solvent is lower than that of the conventional electrolyte solvent.
• saturated cyclic carbonate solvents examples include ethylene carbonate (EC), propylene carbonate (PC), 2,3-dimethylethylene carbonate, and 1,2-butylene carbonate.
• EC ethylene carbonate
• PC propylene carbonate
• 2,3-dimethylethylene carbonate 2,3-dimethylethylene carbonate
• 1,2-butylene carbonate examples include ethylene carbonate (EC), propylene carbonate (PC), 2,3-dimethylethylene carbonate, and 1,2-butylene carbonate.
• EC and PC are preferred, and EC is more preferred.
• the content of the saturated cyclic carbonate solvent relative to the total amount of the electrolyte solvent (100% by mass) is 30% by mass or less, preferably 20% by mass or less, and more preferably 15% by mass or less. There is no particular lower limit to the content, and it is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more.
• the electrolyte solvent contains other electrolyte solvents other than saturated cyclic carbonate-based solvents.
• the other electrolyte solvents are not particularly limited as long as they can dissolve and disperse the above-mentioned electrolyte salt, and examples include non-aqueous solvents. Any non-aqueous solvent commonly used in batteries can be used, but among them, solvents with a high dielectric constant, high solubility for the above-mentioned electrolyte salt, a boiling point of 60°C or higher, and a wide electrochemical stability range are preferred. Organic solvents with a low water content are more preferred.
• organic solvents examples include chain carbonate (carbonic acid ester) solvents such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate, and methyl phenyl 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; lactone solvents such as ⁇ -butyrolactone, ⁇ -valerolactone, and ⁇ -valerolactone; and trimer phosphate.
• chain carbonate carbonate
• Suitable solvents include phosphate ester solvents such as ethyl, ethyl dimethyl phosphate, diethyl methyl phosphate, and triethyl phosphate; nitrile solvents such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methyl glutaronitrile, valeronitrile, butyronitrile, and isobutyronitrile; sulfur compound solvents such as dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane; aromatic nitrile solvents such as benzonitrile and tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimi
• the electrolyte solvent according to this embodiment is preferably a mixed solvent containing a saturated cyclic carbonate solvent and a chain carbonate solvent, more preferably a mixed solvent composed only of a carbonate solvent containing a saturated cyclic carbonate solvent and a chain carbonate solvent, and even more preferably a mixed solvent containing only a saturated cyclic carbonate solvent and a chain carbonate solvent.
• the saturated cyclic carbonate solvent and the chain carbonate solvent may each be used alone, or two or more types may be used in combination.
• 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 non-aqueous electrolyte may contain an additive for improving various properties of the lithium ion secondary battery.
• the additive may be added to the non-aqueous electrolyte, or may be added in the preparation process of the non-aqueous electrolyte.
• the additive examples include carboxylic acid 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; sultone compounds (sulfur-containing compounds) such as ethylene sulfite, dimethyl sulfate, 1,3-propane sultone (PS), 1-propene 1,3-sultone, and 1,4-butane sultone; sulfur-containing compounds other than sultone compounds such as methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, and trimethylene glycol sulfate;
• a phosphorus atom-containing compound represented by the general formula (5): [Chemical formula 5] ⁇ (OH) c - R2 [-S( O) d (O - )] e ⁇ f ( Mg+ ) h ... (5)
• the additives include hydroxysulfonic acid compounds represented by the formula (hereinafter referred to as "hydroxysulfonic acid compound (5)"). These additives may be used alone or in combination of two or more. These additives may be commercially available products or may be synthesized by a conventional method.
• sulfur-containing compounds, carbonate compounds, fluorophosphate compounds, phosphorus atom-containing compounds (4) and hydroxysulfonic acid compounds (5) are preferred, sultone compounds, unsaturated cyclic carbonate compounds, difluorophosphate compounds, phosphorus atom-containing compounds (4) and hydroxysulfonic acid compounds (5) are more preferred, 1,3-propane sultone, vinylene carbonate, LiPO 2 F 2 , phosphorus atom-containing compounds (4) and hydroxysulfonic acid compounds (5) are even more preferred, and further from the viewpoint of improving the low-temperature discharge capacity (improving the low-temperature discharge characteristics), the phosphorus atom-containing compounds (4) are particularly preferred.
• 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. In general formula (4), it is preferable that R 1 is the same group.
• the phosphorus atom-containing compound (4) include ethyl polyphosphate (in the general formula (4), R 1 represents an ethyl group), trimethylsilyl polyphosphate (in the general formula (4), R 1 represents a trimethylsilyl group (TMS)), triethylsilyl polyphosphate (in the general formula (4), R 1 represents a triethylsilyl group (TES)), triisopropylsilyl polyphosphate (in the general formula (4), R 1 represents a triisopropylsilyl group (TIPS)), (tert-butyl)dimethylsilyl polyphosphate (in the general formula (4), R 1 represents a (tert-butyl)dimethylsilyl group (TBDMS)), and (tert-butyl)diphenylsilyl polyphosphate (in the general formula (4), R 1 represents a (tert-butyl)diphenylsilyl polyphosphate (in the general formula
• trimethoxysilyl polyphosphate in the general formula (4), R 1 represents a trimethoxysilyl group
• triethoxysilyl polyphosphate in the general formula (4), R 1 represents a triethoxysilyl group
• (triisopropoxysilyl) polyphosphate in the general formula (4), R 1 represents a triisopropoxysilyl group
• [(tert-butoxy)dimethoxysilyl] polyphosphate in the general formula (4), R 1 represents a (tert-butoxy)dimethoxysilyl group
• [(tert-butoxy)diphenoxysilyl] polyphosphate in the general formula (4), R 1 represents a (tert-butoxy)diphenoxysilyl group
• the phosphorus atom-containing compound (4) may be used alone or in combination of two or more kinds. Among the phosphorus atom-containing compounds (4), trimethylsilyl polyphosphate is preferred.
• Polytrimethylsilylphosphate can be analyzed for structures such as a chain structure represented by the following structural formula ( 4-1 ), a cyclic structure represented by the structural formula (4-2), and a branched structure represented by the structural formula (4-3) 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 trimethylsilyl group
• n 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 the battery performance, those having a Pb peak, that is, those containing a branched structure represented by structural formula (4-3), are preferred.
• trimethylsilyl polyphosphate, ethyl polyphosphate, (triisopropylsilyl) polyphosphate, and (tert-butyl)dimethylsilyl polyphosphate are more preferred, and trimethylsilyl polyphosphate containing a branched structure represented by structural formula (4-3) is even more preferred.
• R 2 represents a divalent hydrocarbon group which may have a substituent.
• the hydrocarbon group may have a linear or branched chain structure, may have a cyclic structure, or may have both a chain structure and a cyclic structure.
• the hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.
• the number of carbon atoms in the hydrocarbon group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2.
• the hydrocarbon group has a cyclic structure or has both a chain structure and a cyclic structure, the number of carbon atoms in the hydrocarbon group is preferably 3 to 12, more preferably 3 to 10, and even more preferably 5 to 8.
• R2 may have is not particularly limited, and examples thereof include a carboxy group, a sulfonic acid group, a phosphonic acid group, phosphoric acid, and esters and salts thereof; an amino group, a hydroxy group, a ketone group, a sulfone group, a thiol group, and a halogen group.
• M represents a metal atom
• Mg+ represents a metal cation.
• the type of metal element of M is not particularly limited, and examples thereof include alkali metals such as lithium, sodium, potassium, and rubidium; and alkaline earth metals such as beryllium, magnesium, calcium, and strontium. Among these, alkali metals are preferred, and lithium and sodium are more preferred.
• c may be an integer of 1 or more, preferably an integer of 1 to 12, more preferably an integer of 1 to 6, and even more preferably an integer of 1 to 4.
• d is an integer of 1 or 2.
• e is preferably an integer of 1 to 4, more preferably 1 or 2.
• f is preferably an integer of 1 to 3, more preferably 1 or 2.
• hydroxysulfonic acid compounds (5) include alkali metal salts of hydroxymethanesulfonic acid, alkali metal salts of hydroxyethanesulfonic acid, alkali metal salts of hydroxypropanesulfonic acid; alkali metal salts of hydroxymethanesulfinic acid, alkali metal salts of hydroxyethanesulfinic acid, alkali metal salts of hydroxypropanesulfinic acid, alkali metal salts of 2-(2-hydroxyethoxy)ethanesulfonic acid, etc. Hydroxysulfonic acid compounds (5) may be used alone or in combination of two or more kinds. Among hydroxysulfonic acid compounds (5), alkali metal salts of hydroxyethanesulfonic acid are preferred, and sodium 2-hydroxyethanesulfonate (sodium isethionate) is more preferred.
• the additive is used in a range of preferably 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, relative to 100% by mass of the total amount of components contained in the non-aqueous electrolyte. If the amount of additive used is too small, it may be difficult to obtain the effects derived from the additive, and on the other hand, even if a large amount of additive is used, it is difficult to obtain an effect commensurate with the amount added, and there is also a risk that the viscosity of the non-aqueous electrolyte will increase and the conductivity will decrease.
• the nonaqueous electrolyte according to this embodiment is composed of the sulfonylimide compound (1) and the saturated cyclic carbonate solvent as essential components, and, if necessary, other electrolyte salts, other electrolyte solvents, various additives, and other components.
• the nonaqueous electrolyte can be prepared, for example, by mixing these components in a predetermined composition (mass) ratio. At this time, the content of the saturated cyclic carbonate solvent is adjusted to 30 mass% or less with respect to the total amount of the electrolyte solvent, 100 mass%.
• 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 according to this embodiment includes a lithium composite oxide containing nickel as a positive electrode active material, which is a high Ni-containing lithium composite oxide in which the nickel content is 50% or more relative to 100% of the total amount of transition metals (metals in Groups 3 to 11 of the periodic table) contained in the lithium composite oxide on a molar basis.
• the high Ni-containing lithium composite oxide has a higher nickel content in the transition metals than conventional positive electrode active materials (approximately 33% in NCM111), so that a nonaqueous electrolyte secondary battery using it has a high energy density that can meet the performance requirements of EV batteries.
• the nonaqueous electrolyte secondary battery according to this embodiment is premised on using a high Ni-containing lithium composite oxide (having a high Ni-based positive electrode) in order to improve the energy density.
• transition metal oxide examples include a ternary oxide represented by the formula (hereinafter referred to as "high Ni-containing ternary positive electrode active material (6)"); a compound having an olivine structure such as LiNiPO 4 (high Ni-containing iron phosphate positive electrode active material); LiNi p Mn 1-p O 2 (0.5 ⁇ p ⁇ 1); and a compound having a fluorinated olivine structure such as Li 2 NiPO 4 F.
• the high Ni-containing lithium composite oxide may be used alone or in combination of two or more kinds.
• the high Ni-containing lithium composite oxide may be a commercially available product, or may be obtained by synthesis using a conventional method.
• the high Ni - containing ternary positive electrode active material (6) include LiNi0.5Co0.2Mn0.3O2 (NCM523) , LiNi0.6Co0.2Mn0.2O2 (NCM622 ) , LiNi0.8Co0.1Mn0.1O2 (NCM811), etc.
• the high Ni-containing lithium composite oxides the high Ni-containing ternary positive electrode active material (6) is preferred, and NCM523 , NCM622 and NCM811 are more preferred.
• the nickel content ("x" in general formula (6)) relative to 100% (100 mol%) of the total amount of transition metals 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 may be 100%, and is preferably 90% or less (x ⁇ 0.9), more preferably less than 85% (x ⁇ 0.85), and even more preferably 80% or less (x ⁇ 0.8).
• 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 active material may be any of the conventionally known negative electrode active materials used in various batteries (e.g., lithium secondary batteries) and the like, as long as it is capable of absorbing and releasing various ions (e.g., lithium ions).
• Specific negative electrode active materials include graphite materials such as artificial graphite and natural graphite, mesophase sintered bodies made from coal and petroleum pitch, carbon materials such as 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 metal, and lithium alloys such as lithium-aluminum alloys.
• the negative electrode active materials may be used alone or in combination of two or more types.
• 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 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 porous sheets made of polymers capable of absorbing and retaining an electrolyte (non-aqueous electrolyte) (e.g., polyolefin-based microporous separators and cellulose-based separators), non-woven fabric separators, and porous metal bodies.
• 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 non-aqueous electrolyte 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.
• Non-aqueous electrolyte secondary batteries can be easily manufactured, for example, by stacking a positive electrode and a negative electrode (with a separator between them if necessary), placing the resulting laminate in a battery exterior material, injecting a non-aqueous electrolyte into the battery exterior material, and sealing it.
• the nonaqueous electrolyte secondary battery has the following constituent materials: A high Ni-based positive electrode containing a high Ni-containing lithium composite oxide in which the content of nickel in the transition metal is 50 mol% or more; A nonaqueous electrolyte solution containing the sulfonylimide compound (1) and an electrolyte solvent having a saturated cyclic carbonate-based solvent content of 30 mass% or less is used in combination.
• a nonaqueous electrolyte solution containing the sulfonylimide compound (1) and an electrolyte solvent having a saturated cyclic carbonate-based solvent content of 30 mass% or less is used in combination. This allows the nonaqueous electrolyte secondary battery to have a high energy density that meets the performance requirements of EV batteries, as well as a synergistic effect of suppressing the increase in resistance associated with battery use and improving low-
• Example 1 Series Example 1 (1) Preparation of evaluation battery (electrolyte)
• EC/DMC/EMC 10/20/70 (vol%)
• EC ethylene carbonate
• DMC dimethyl carbonate
• EMC ethyl methyl carbonate
• a ternary positive electrode LiNi0.8Co0.1Mn0.1O2 (NCM811), manufactured by Beijing Toben Co.
• acetylene black manufactured by Denka, Denka Black
• graphite manufactured by Nippon Graphite, SP270
• PVdF polyvinylidene fluoride
• NMP N-methyl-2-pyrrolidone
• the obtained positive and negative electrodes were cut, the polarity lead was ultrasonically welded, and the electrodes were faced with a 20 ⁇ m polyethylene (PE) separator, and the three sides were sealed with a laminate exterior.
• the above electrolyte was poured from one of the unsealed sides, and the battery after the electrolyte was poured was precharged at 0.2 C (6 mA) for 2 hours in an unsealed state. It was then vacuum sealed and left at room temperature for 3 days. After 3 days, it was charged and discharged at 4.2 V for 5 hours at 0.5 C (15 mA) ⁇ 0.2 C (6 mA) with a termination of 2.75 V, and one piece of the laminate was opened and vacuum sealed again to degas it.
• PE polyethylene
• ⁇ DCR increase rate The evaluation battery was charged at a constant current of 30 mA, constant voltage of 4.2 V, and a termination current of 0.6 mA until it was fully charged. - The DCR (DCR before cycle testing) was measured at 25°C from a fully charged state. For the DCR measurement, the battery was waited 30 minutes after full charging and discharged at 6 mA (0.2 C) for 10 seconds. Next, after waiting 30 minutes, the battery was discharged at 30 mA (1 C) for 10 seconds. Finally, after waiting 30 minutes, the battery was discharged at 90 mA (3 C) for 10 seconds.
• An IV line was created from the relationship between the difference in voltage immediately before and 10 seconds after the start of discharge at each discharge current and the current, and the slope was calculated as the DCR.
• the battery after DCR measurement was subjected to 500 cycles of 45°C cycle testing. The cycle conditions were: charge: 4.2V, 30mA (1C), terminated at 0.6mA (0.05C), 10 minutes rest ⁇ discharge: 30mA (1C), terminated at 2.75V, 10 minutes rest.
• the DCR (DCR after cycle testing) was measured at 25°C in the same manner as above.
• the DCR increase rate was calculated as 100 ⁇ (DCR after cycle test) / (DCR before cycle test) (%). A smaller DCR increase rate means that the increase in resistance due to use of the battery is more suppressed.
• Example 2 A battery for evaluation was produced in the same manner as in Example 1, except that 1,3-propane sultone (PS, a commercially available product) was added so as to be 0.5% by mass relative to 100% by mass of the total amount of the electrolyte, and the characteristics were evaluated.
• PS 1,3-propane sultone
• Example 3 A battery for evaluation was produced in the same manner as in Example 1, except that sodium isethionate (Na isethionate, commercially available product) was added so as to be 0.5% by mass relative to 100% by mass of the total amount of the electrolyte, and the characteristics were evaluated.
• sodium isethionate Na isethionate, commercially available product
• Example 4 A battery for evaluation was produced in the same manner as in Example 1, except that vinylene carbonate (VC, a commercially available product) was added so that the amount was 0.5% by mass relative to 100% by mass of the total amount of the electrolyte, and the characteristics were evaluated.
• VC vinylene carbonate
• Example 5 A battery for evaluation was prepared in the same manner as in Example 1, except that Sigma-Aldrich reagent polytrimethylsilyl phosphate (hereinafter also referred to as "PPSE-1”) was added so as to be 0.5% by mass relative to the total amount of 100% by mass of the electrolyte. The battery was then evaluated for its characteristics.
• PPSE-1 Sigma-Aldrich reagent polytrimethylsilyl phosphate
• 31P -NMR Analysis When PPSE-1 was analyzed by 31 P-NMR, two peaks were confirmed, a peak (Pt) appearing at a chemical shift of -28 ppm to -33 ppm and a peak (Pm) appearing at a chemical shift of -35 ppm to -41 ppm, as shown in Figure 1.
• a peak (Pb) appearing at -41 ppm to -45 ppm was not confirmed.
• 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.
• Example 6 A battery for evaluation was prepared in the same manner as in Example 1, except that polytrimethylsilyl phosphate (hereinafter also referred to as "PPSE-2") synthesized by the following method was added so that the amount was 0.5% by mass relative to the total amount of 100% by mass of the electrolyte. The battery was then evaluated for its characteristics. (Synthesis of trimethylsilyl polyphosphate (PPSE-2)) 1.553 g of diphosphorus pentoxide was dispersed in 10 mL of methylene chloride as a solvent, and 1.710 g of hexamethylenedisiloxane was gradually added dropwise while stirring, and the mixture was stirred at room temperature for about one day.
• PPSE-2 polytrimethylsilyl phosphate
• PPSE-2 was analyzed by 31 P-NMR in the same manner as above, and three peaks were confirmed, namely, a peak (Pt) appearing at a chemical shift of -28 ppm to -33 ppm, a peak (Pm) appearing at a chemical shift of -35 ppm to -41 ppm, and a peak (Pb) appearing at a chemical shift of -41 ppm to -45 ppm, as shown in Figure 2.
• Example 7 A battery for evaluation was prepared in the same manner as in Example 1, except that polytrimethylsilyl phosphate (hereinafter also referred to as "PPSE-3") synthesized by the following method was added so that the amount was 0.5 mass% relative to the total amount of 100 mass% of the electrolyte solution. The battery was then evaluated for its characteristics.
• PPSE-3 polytrimethylsilyl phosphate
• 1.553 g of diphosphorus pentoxide was dispersed in 10 mL of toluene as a solvent, and 1.710 g of hexamethylenedisiloxane was gradually added dropwise while stirring, and the mixture was stirred at room temperature for about one day.
• PPSE-3 polytrimethylsilyl phosphate
• PPSE-3 was analyzed by 31 P-NMR in the same manner as above, and three peaks were confirmed, namely, a peak (Pt) appearing at a chemical shift of -28 ppm to -33 ppm, a peak (Pm) appearing at a chemical shift of -35 ppm to -41 ppm, and a peak (Pb) appearing at a chemical shift of -41 ppm to -45 ppm, as shown in Figure 3.
• Example 8 An evaluation battery was prepared in the same manner as in Example 1, except that polyethyl phosphate (hereinafter also referred to as "PPE") synthesized by the following method was added so that the amount was 0.5 mass% relative to 100 mass% of the total amount of the electrolyte solution, and the characteristics were evaluated.
• PPE polyethyl phosphate
• the PPE is polyethyl phosphate containing a large amount of branched structures (structures in which TMS is an ethyl group in the branched structure represented by the above structural formula (4-3)).
• Example 9 A battery for evaluation was prepared in the same manner as in Example 1, except that poly(triisopropylsilyl)phosphate (hereinafter also referred to as "PPSE (TIPS)”) synthesized by the following method was added in an amount of 0.5 mass% relative to the total mass of 100 mass% of the electrolyte solution, and the characteristics were evaluated.
• PPSE poly(triisopropylsilyl)phosphate
• 0.53 g of indium bromide (III) was dissolved in 30 mL of tetrahydrofuran, and then 4.75 g of triisopropylsilane was added and stirred at room temperature for one day to carry out the reaction.
• Example 10 A battery for evaluation was prepared in the same manner as in Example 1, except that polyphosphate [(tert-butyl)dimethylsilyl] (hereinafter also referred to as “PPSE (TBDMS)”) synthesized by the following method was added so that the amount was 0.5 mass% relative to 100 mass% of the total amount of the electrolyte solution. The battery was then subjected to characteristic evaluation.
• PPSE polyphosphate [(tert-butyl)dimethylsilyl]
• Example 11 A battery for evaluation was produced in the same manner as in Example 5, except that the positive electrode active material was changed to LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) manufactured by Beijing Toben Co., Ltd., and the characteristics were evaluated.
• NCM622 LiNi 0.6 Co 0.2 Mn 0.2 O 2
• Comparative Example 2 A battery for evaluation was produced in the same manner as in Comparative Example 1 except that PS was added in an amount of 0.5% by mass relative to the total amount of the electrolyte (100% by mass), and the characteristics were evaluated.
• Comparative Example 3 A battery for evaluation was produced in the same manner as in Comparative Example 1 except that LiPO 2 F 2 was added so that the amount was 0.5% by mass relative to 100% by mass of the total amount of the electrolyte, and the characteristics were evaluated.
• Example 1 On the other hand, by comparing Example 1 with Examples 2 to 4 and Comparative Example 1 with Comparative Examples 2 and 3, it was confirmed that, among the various additives, when any one of 1,3-propane sultone (PS), sodium isethionate (Na isethionate), vinylene carbonate (VC), and LiPO 2 F 2 was added, the effect of suppressing the increase in resistance due to the addition was not sufficient, and that the low-temperature discharge characteristics were deteriorated due to these additives.
• PS 1,3-propane sultone
• Na isethionate sodium isethionate
• VC vinylene carbonate
• LiPO 2 F 2 LiPO 2 F 2
• Example 1 In contrast, by comparing Example 1 with Examples 5 to 11, it was confirmed that the addition of any one of trimethylsilyl polyphosphate (PPSE-1, PPSE-2, PPSE-3), ethyl polyphosphate (PPE), (triisopropylsilyl) polyphosphate [PPSE (TIPS)], and [(tert-butyl)dimethylsilyl] polyphosphate (PPSE (TBDMS)) suppressed the increase in resistance and improved the low-temperature discharge characteristics.
• the improvement effect of the additive was high for trimethylsilyl polyphosphate, and was particularly remarkable for trimethylsilyl polyphosphate containing a large amount of branched structures (branched structures represented by the above structural formula (4-3)).
• Example 2 Series (1) Preparation of Evaluation Battery (Example 2-1) In the Example 1 series, the evaluation battery prepared in Example 5 was used.
• Example 2-2 In the Example 1 series, the evaluation battery prepared in Example 11 was used.
• Example 1 series the evaluation battery prepared in Example 1 was used.
• OCV shelf-discharge capacity
• the evaluation battery was charged at a constant current of 30 mA, 4.2 V, and 0.6 mA to a fully charged state.
• the open circuit voltage (OCV) of the battery after full charge was measured (initial (before storage) OCV).
• OCV open circuit voltage
• the battery was stored at 80° C. for 14 days (after high temperature endurance, the same applies below), and the OCV was measured after further storing at 25° C. for 4 hours (80° C. after 14 days (after storage) OCV).
• the difference ( ⁇ V) in OCV before and after storage was calculated as self-discharge. Note that the higher the OCV after storage, i.e., the smaller the self-discharge ( ⁇ V), the more suppressed the self-discharge of the battery is (excellent storage characteristics).
• the evaluation battery was charged at a constant current of 30 mA, 4.2 V, and 0.6 mA to a fully charged state.
• the DCR of the battery after full charge (initial (pre-storage) DCR) was measured in the same manner as in the Example 1 series.
• the battery was then stored at 80°C for 14 days, and the DCR of the battery (post-storage DCR) was measured in the same manner as described above.
• the difference in DCR before and after storage was calculated as the DCR increase rate after storage at 80°C for 14 days (after high-temperature endurance). Note that the smaller the DCR increase rate, the more suppressed the increase in resistance after high-temperature endurance is.
• the measurement sample was analyzed with an ICP emission spectrometer (manufactured by Shimadzu Corporation) to detect the amount of aluminum (Al), cobalt (Co), manganese (Mn), and nickel (Ni) (per battery (cell)) in the measurement sample.
• Example 2 Series In a non-aqueous electrolyte secondary battery using a high Ni-containing lithium composite oxide (NCM811, NCM622) in which the content of nickel in the transition metal is 80 mol% or 60 mol% (50 mol% or more), each example in which the content of saturated cyclic carbonate solvent (EC) in the electrolyte solvent is 30 mass% or less has a relatively high OCV after storage at 80 ° C. for 14 days compared to each comparative example in which the content exceeds 30 mass%, and it was confirmed that self-discharge ( ⁇ V) during storage can be suppressed. It was also confirmed that the volume increase rate and DCR increase rate during storage can be effectively suppressed.
• NCM811, NCM622 high Ni-containing lithium composite oxide
• EC saturated cyclic carbonate solvent
• the above configuration significantly suppresses the elution of transition metals (especially Ni) from the positive electrode as a side reaction even when the storage environment of the battery is a high-load high-temperature environment.
• the amount of Ni eluted from the positive electrode was significantly reduced by adding trimethylsilyl polyphosphate (PPSE-1) in comparison with each of the examples and the reference example. This reduction in side reactions is believed to suppress self-discharge, volume increase, and DCR increase after high-temperature durability.

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