Classifications

• • 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.
• the present applicant has proposed a non-aqueous electrolyte solution containing LiN(FSO 2 ) 2 as an electrolyte and at least one of a silicon atom-containing compound, a boron atom-containing compound, a carbon atom-containing compound, a sulfur atom-containing compound, and a phosphorus atom-containing compound as an additive in Patent Document 1.
• a specific compound is used to suppress the self-discharge of the battery and to reduce the charge transfer resistance (impedance) and the battery direct current resistance (DCR), thereby improving the battery performance.
• a secondary battery having a non-aqueous electrolyte solution containing a sulfonylimide compound and a positive electrode containing a lithium composite oxide containing Ni (nickel), such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111), which is generally used as a positive electrode active material the use of an additive may actually increase the resistance. That is, depending on the type of positive electrode active material, the additive in the non-aqueous electrolyte solution may cause a decrease in battery performance.
• the present disclosure has been made in consideration of these points, and its purpose is to reduce the resistance of 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-containing lithium composite oxide.
• the present inventors have found that all of the above three types of resistance of a secondary battery can be reduced by using a nitrile compound having a branched or linear alkyl group with a carbon number within a specific range as an additive to a non-aqueous electrolyte containing a sulfonylimide compound in combination with a "high Ni-containing ternary positive electrode active material" as a high Ni-containing lithium composite oxide (positive electrode active material) in which the Ni content of the three transition metals Ni, Co (cobalt) and Mn (manganese) is 50% or more on a molar basis.
• the present disclosure is specifically as follows.
• the nonaqueous electrolyte secondary battery of the present disclosure comprises: 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 a nitrile compound having a branched alkyl group having 3 to 6 carbon atoms;
• the nonaqueous electrolyte secondary battery of the present disclosure has a non-aqueous electrolyte solution containing a sulfonylimide compound represented by the above general formula (1) and a nitrile compound having a linear alkyl group having 3 to 6 carbon atoms;
• the battery is characterized by comprising a positive electrode containing a positive electrode active material represented by the above general formula (2).
• the content of the nitrile compound relative to the sulfonylimide compound may be 10 ppm by mass or more.
• the sulfonylimide compound may contain LiN(FSO 2 ) 2 .
• 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-containing lithium composite oxide.
• the nonaqueous electrolyte secondary battery refers to a secondary battery that includes 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 (Electrolyte Salt)
• the nonaqueous electrolyte according to the present embodiment contains an electrolyte salt represented by the general formula (1): [Chemical formula 1] LiN( RSO2 )( FSO2 )...(1) (hereinafter referred to as "sulfonylimide compound (1)", a fluorine-containing sulfonylimide salt) represented by the following formula:
• the non-aqueous electrolyte solution 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 battery performance (particularly reducing resistance).
• 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 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, even more preferably 50 mol% or more, and even more preferably more than 50 mol% out of a total of 100 mol% of the electrolyte salt contained in the nonaqueous electrolyte.
• the upper limit of the content is 100 mol%.
• the electrolyte salt contained in the nonaqueous electrolyte may contain the sulfonylimide compound (1) alone.
• 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 entire nonaqueous electrolyte (based on 100% by mass of the total amount of 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 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 obtained by synthesis using a conventional method.
• non-imide salt examples include salts of non-imide anions and cations (lithium ions and the above-listed cations).
• Examples of the non-lithium salt include a compound represented by the formula (hereinafter referred to as "fluoroboric acid compound ( 4 )"), lithium hexafluoroarsenate (LiAsF6), LiSbF6 , LiClO4 , LiSCN, LiAlF4 , CF3SO3Li , LiC[( CF3SO2 ) 3 ],
• non- lithium salt examples include salts in which the lithium (ion) in these lithium salts is replaced with the above-mentioned cations (e.g., NaBF4 , NaPF6 , NaPF3 ( CF3 ) 3 , and the like).
• the non-imide salts may be used alone or in combination of two or more kinds.
• the non-imide salt may be a commercially available product, or may be obtained by synthesis using a conventional method.
• non-imide salts are preferred from the viewpoints of ion conductivity, cost, etc., and the like, and the fluorophosphate compound (3), fluoroboric acid compound (4) and LiAsF6 are preferred, with the fluorophosphate compound (3) being more preferred.
• fluorophosphate compound (3) examples include LiPF6 , LiPF3 ( CF3 ) 3 , LiPF3(C2F5)3, LiPF3(C3F7)3, and LiPF3(C4F9 ) 3 .
• fluorophosphate compounds ( 3 ) LiPF6 and LiPF3 ( C2F5 ) 3 are preferred, and LiPF6 is more preferred.
• Examples of the fluoroboric acid compound (4) include LiBF 4 , LiBF(CF 3 ) 3 , LiBF(C 2 F 5 ) 3 , and LiBF(C 3 F 7 ) 3.
• the fluoroboric acid compounds (4) 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 (3) 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 viscosity of the electrolyte.
• 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 sulfonylimide compound (1) to other electrolytes 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, and particularly preferably 1:1 or more, with the upper limit being 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 nonaqueous electrolyte according to the present embodiment contains, as an additive, a nitrile compound having a branched alkyl group having 3 to 6 carbon atoms (hereinafter also referred to as a "branched alkyl nitrile compound”), or a nitrile compound having a linear alkyl group having 3 to 6 carbon atoms (hereinafter also referred to as a "linear alkyl nitrile compound”), as an essential component.
• a nitrile compound having a branched alkyl group having 3 to 6 carbon atoms hereinafter also referred to as a "branched alkyl nitrile compound”
• linear alkyl nitrile compound nitrile compound having a linear alkyl group having 3 to 6 carbon atoms
• linear alkyl nitrile compound is distinguished from the “branched alkyl nitrile compound” in that the linear alkyl group having 3 to 6 carbon atoms does not have a branched (branched) structure.
• the "branched alkyl nitrile compound” and the “linear alkyl nitrile compound” may be used alone, or two or more types may be used in combination.
• the "branched alkyl nitrile compound” and the “linear alkyl nitrile compound” are collectively referred to as “linear alkyl nitrile compounds”.
• branched alkyl nitrile compounds include mononitrile compounds such as isobutyronitrile (isopropyl cyanide) and isovaleronitrile (isobutyl cyanide).
• the branched alkyl nitrile compounds may be used alone or in combination of two or more kinds. Among these, isobutyronitrile is preferred from the viewpoint of improving battery performance (especially reducing resistance).
• Straight-chain alkyl nitrile compounds include, for example, mononitrile compounds such as butyronitrile (propyl cyanide) and valeronitrile (butyl cyanide).
• the straight-chain alkyl nitrile compounds may be used alone or in combination of two or more kinds. Among these, butyronitrile is preferred from the viewpoint of improving battery performance (especially reducing resistance).
• the content of the linear alkyl nitrile compound (the total amount when two or more types are used in combination) is preferably 10 mass ppm or more, more preferably 20 mass ppm or more, even more preferably 100 mass ppm or more, even more preferably 500 mass ppm or more, and even more preferably 1000 mass ppm or more, based on the sulfonylimide compound (1) (the total amount when two or more types are used in combination), from the viewpoint of improving the battery performance (particularly reducing the resistance).
• the upper limit of the content is preferably 6000 mass ppm or less, more preferably 5000 mass ppm or less.
• the content of the linear alkyl nitrile compound relative to the sulfonylimide compound (1) is preferably 10 mass ppm or more and 6000 mass ppm or less.
• the non-aqueous electrolyte may contain, in addition to the linear alkylnitrile compound, 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 during 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; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, and trimethylene glycol sulfate.
• carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic
• Sulfur-containing compounds such as esters; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; saturated hydrocarbon compounds such as heptane, octane, and cycloheptane; carbonate compounds such as vinylene carbonate, fluoroethylene carbonate (FEC), trifluoropropylene carbonate, phenylethylene carbonate, and erythritan carbonate; sulfamic acid (amidosulfuric acid, H 3NSO3 ); sulfamates (alkali metal salts such as lithium salts, sodium salts, potassium salts, etc.; alkaline earth metal salts such as calcium salts, strontium salts , barium salts, etc.; other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt
• the additive is preferably used in the range of 0.1% to 10% by mass, more preferably 0.2% to 8% by mass, and even more preferably 0.3% to 5% by mass, relative to 100% by mass of the total amount of components contained in the non-aqueous electrolyte. If too little additive is used, 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 non-aqueous electrolyte may contain an electrolyte solvent.
• the electrolyte solvent is not particularly limited as long as it can dissolve and disperse the electrolyte salt.
• Examples of the electrolyte solvent include non-aqueous solvents, polymers used in place of electrolyte solvents, polymer gels, and other media, and any solvent generally used in batteries can be used.
• non-aqueous solvent a solvent that has a large dielectric constant, high solubility for the electrolyte, a boiling point of 60°C or higher, and a wide electrochemical stability range is preferable.
• An organic solvent with a low water content is more preferable.
• organic solvents examples include ether-based solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane, and 1,3-dioxolane; chain carbonate ester (carbonate)-based solvents such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate, and methyl phenyl carbonate; saturated cyclic carbonate ester-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), 2,3-dimethyl ethylene carbonate, 1,2-butylene carbonate, and erythritan carbonate; cyclic carbonate ester-based solvents having
• fluorine-containing cyclic carbonate solvents such as methyl benzoate and ethyl benzoate; aromatic carboxylate solvents such as methyl benzoate and ethyl benzoate; lactone solvents such as ⁇ -butyrolactone, ⁇ -valerolactone and ⁇ -valerolactone; phosphate solvents such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate and triethyl phosphate; nitrile solvents such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile and 2-methylglutaronitrile.
• tolyl-based solvents sulfur compound-based solvents such as dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane; aromatic nitrile-based solvents such as benzonitrile and tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, and 3-methyl-2-oxazolidinone; and chain ester-based solvents such as ethyl acetate, butyl acetate, and propyl propionate. These solvents may be used alone or in combination of two or more.
• carbonate solvents such as chain carbonate ester solvents and cyclic carbonate ester solvents, lactone solvents, ether solvents and chain ester solvents
• dimethyl carbonate ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, gamma-butyrolactone and gamma-valerolactone
• carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate.
• the following methods may be used. That is, a method of dripping a solution of electrolyte salt dissolved in a solvent onto a polymer formed into a film by a conventionally known method to impregnate and support the electrolyte salt and non-aqueous solvent; a method of melting and mixing a polymer and electrolyte salt at a temperature above the melting point of the polymer, forming a film, and impregnating the film with the solvent (above, gel electrolyte); a method of mixing a non-aqueous electrolyte in which electrolyte salt has been dissolved in an organic solvent with a polymer, forming a film by a casting method or coating method, and volatilizing the organic solvent; a method of melting a polymer and electrolyte salt at a temperature above the melting point of the polymer, mixing them, and molding them (true polymer electrolyte), etc.
• 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 according to this embodiment is composed of the sulfonylimide compound (1) and the branched alkylnitrile compound or the linear alkylnitrile compound (chain alkylnitrile compound) as essential components, and is composed of other components such as other electrolyte salts, electrolyte solvents, and various additives (other than the chain alkylnitrile compound) as necessary.
• the nonaqueous electrolyte can be prepared, for example, by mixing these components in a predetermined composition 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 according to this embodiment includes a transition metal oxide (high Ni-containing ternary positive electrode active material) such as a ternary oxide in which the Ni content is 50% or more relative to 100% of the total amount of three transition metals, Ni, cobalt (Co) and manganese (Mn), contained in the lithium composite oxide on a molar basis.
• the high Ni-containing ternary positive electrode active material has a higher Ni 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 the use of a high Ni-containing ternary positive electrode active material (having a high Ni-based positive electrode).
• the present invention includes a high Ni-containing ternary positive electrode active material represented by the formula (hereinafter referred to as “high Ni-containing ternary positive electrode active material (2)”).
• the Ni content ("x" in general formula (2)) relative to the total amount of transition metals (100% by mole) 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 (2) (“v", “y”, “z”, and "w” (2+w) in general formula (2)) may be appropriately adjusted within the range of each of the above molar ratios.
• the high Ni-containing ternary positive electrode active material (2) may be used alone or in combination of two or more kinds.
• the high Ni-containing ternary positive electrode active material (2) 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 (2) include LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), etc.
• the positive electrode may contain a positive electrode active material other than the high Ni-containing ternary positive electrode active material.
• the other positive electrode active material may be any material capable of absorbing and releasing lithium ions, and may be, for example, a positive electrode active material used in a conventionally known secondary battery (lithium ion secondary battery).
• 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 (carbon fiber), 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 (SBR) 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 (CMC); and the like.
• SBR styrene-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 (CMC); 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
• Solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, water, etc.
• NMP N-methyl-2-pyrrolidone
• dimethylformamide dimethylacetamide
• methyl ethyl ketone tetrahydrofuran
• acetonitrile acetone
• ethanol ethyl acetate
• water ethyl acetate
• solvents may be used alone, or two or more of them 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 manufacturing 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, and fluorinated polymers such as polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as styrene-maleic acid copolymers and polymeric dispersants such as polyvinylpyrrolidone; thickeners such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, 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 (e.g., polyolefin-based microporous separators and cellulose-based separators) made of polymers capable of absorbing and retaining an electrolyte (non-aqueous electrolyte), 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-mentioned 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 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 non-aqueous electrolyte solution containing a sulfonylimide compound (1) and a branched alkylnitrile compound or a linear alkylnitrile compound (a chain alkylnitrile compound), - A high Ni-based positive electrode containing a high Ni-containing ternary positive electrode active material (2) in which the Ni content in the transition metal is 50 mol % or more (0.5 ⁇ x) is used in combination.
• the above-mentioned configuration not only reduces all three types of resistance, i.e., the initial resistance, the resistance associated with battery use, and the resistance after high-temperature storage, but also provides a high energy density that can meet the performance requirements of EV batteries.
• the branched alkylnitrile compounds and the linear alkylnitrile compounds are collectively referred to as "chain alkylnitrile compounds.”
• NCM111 LiNi 1/3 Co 1/3 Mn 1/3 O 2 , manufactured by Umicore
• NCM523 LiNi 0.5 Co 0.2 Mn 0.3 O 2 , manufactured by Beijing Toben Co., Ltd.
• NCM811 LiNi 0.8 Co 0.1 Mn 0.1 O 2 , manufactured by Beijing Toben Co., Ltd.
• Table 1 acetylene black (Denka, Denka Black), graphite (Nippon Graphite, SP270), and polyvinylidene fluoride (PVdF, #1120, commercially available product) were weighed out in a mass ratio of 100:3:3:3 and dispersed in N-methyl-2-pyrrolidone (NMP, commercially available product) to prepare a slurry.
• NMP N-methyl-2-pyrrolidone
• the prepared slurry was coated on one side of an aluminum foil (NCM111: coating weight 19.7 mg/cm 2 , NCM523: coating weight 19.5 mg/cm 2 , NCM811: coating weight 15.7 mg/cm 2 ), dried, and then roll pressed to prepare a positive electrode.
• NCM111 coating weight 19.7 mg/cm 2
• NCM523 coating weight 19.5 mg/cm 2
• NCM811 coating weight 15.7 mg/cm 2
• O-MAC graphite
• VGCF carbon fiber
• SBR styrene butadiene rubber
• CMC carbboxymethyl cellulose
• the obtained positive and negative electrodes were cut, the polarity lead was ultrasonically welded, and the electrodes were faced with a 25 ⁇ 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 was vacuum sealed and charged at a constant current of 3 mA for 3 hours at 25° C. After that, the battery was left at room temperature for 2 days, and one piece of the laminate exterior was cleaved and vacuum sealed again to degas the battery. After degassing, the battery was charged and discharged under the following conditioning conditions to complete the evaluation battery.
• 1st cycle Charge: 3mA, constant current/constant voltage charge at 4.2V, terminated at 0.3mA ⁇ Discharge: Discharge at 6mA, terminated at 2.75V.
• 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.
• ⁇ DCR Decrease Rate> (Initial DCR) The evaluation battery was charged to a full charge state using a charge/discharge tester at a constant current and constant voltage of 30 mA (1C), 4.2 V, and 0.6 mA termination. - The DCR (DCR before cycle testing) was measured at 25°C from a fully charged state. The DCR was measured after waiting 30 minutes after full charging, and discharging at 6 mA (0.2 C) for 10 seconds. Next, after waiting 30 minutes, discharging at 30 mA (1 C) for 10 seconds. Finally, after waiting 30 minutes, discharging at 90 mA (3 C) for 10 seconds.
• DCR after 200 cycle test The battery after the initial DCR measurement was subjected to 200 cycles of 45° C. cycle testing.
• the cycle conditions were: charge: 4.2 V, 30 mA (1 C), terminated at 0.6 mA (0.05 C), rested for 10 minutes, discharge: 30 mA (1 C), terminated at 2.75 V, rested for 10 minutes.
• the "DCR after 200 cycle testing” was measured and calculated at 25° C. in the same manner as above.
• the reduction rate of DCR after 200 cycles was calculated in the same manner as above in formula (1), except that "initial DCR” was changed to "DCR after 200 cycles". The smaller the reduction rate of DCR after 200 cycles, the more the DCR decreases with use of the battery.
• DCR after 28 days at 60°C After the initial DCR measurement, the battery was fully charged in the same manner as above, stored at 60°C for 28 days, and then allowed to stand at 25°C for 4 hours. Then, the "DCR after 28 days at 60°C” was measured and calculated at 25°C in the same manner as above. The rate of decrease in DCR after 28 days at 60°C was calculated in the same manner as above in formula (1), except that "initial DCR” was changed to "DCR after 28 days at 60°C.” A smaller rate of decrease in DCR after 28 days at 60°C means that the DCR of the battery after high-temperature storage is more decreased.
• the real axis resistance when the imaginary axis resistance became 0 was taken as the bulk resistance
• the value obtained by subtracting the bulk resistance from the real axis resistance at which the imaginary axis resistance was maximum in the low frequency region of 1 kHz or less was taken as the "initial impedance”.
• the reduction rate of the initial impedance was calculated in the same manner as in the above formula (1), except that "initial DCR" was changed to "initial impedance.”
• a smaller reduction rate of the initial impedance means that the initial impedance of the battery is more reduced.

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