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 electrolytes.
• non-aqueous electrolyte solutions and materials thereof for use in secondary batteries have been studied.
• the applicant has found through his studies that a non-aqueous electrolyte solution containing a sulfonylimide compound such as lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 ) as an electrolyte salt improves the battery performance of lithium ion secondary batteries, such as 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 non-aqueous electrolyte deteriorates during storage and its characteristics change, this can have a significant impact on battery performance.
• a non-aqueous electrolyte with excellent storage stability is desirable.
• the present disclosure has been made in consideration of these points, and its purpose is to achieve both storage stability and a reduction in the resistance of a secondary battery that includes a non-aqueous electrolyte solution that contains a sulfonylimide compound.
• the present inventors have found that by using a nitrogen-containing compound having a branched or linear alkyl group with a carbon number within a specific range as an additive to a non-aqueous electrolyte solution containing a sulfonylimide compound and specifying the content ratio, not only can all three types of resistance described above be reduced in a secondary battery equipped with this non-aqueous electrolyte solution, but the storage stability of the non-aqueous electrolyte solution is also improved.
• the present disclosure is as follows.
• the nonaqueous electrolyte solution 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 at least one nitrogen-containing compound selected from the group consisting of an amide compound having a branched alkyl group having 3 to 6 carbon atoms and a nitrile compound having a branched alkyl group having 3 to 6 carbon atoms, wherein the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6,000 ppm by mass or less.
• the nonaqueous electrolyte solution of the present disclosure is characterized in that it contains a sulfonylimide compound represented by the above general formula (1) and at least one nitrogen-containing compound selected from the group consisting of an amide compound having a linear alkyl group with 3 to 6 carbon atoms and a nitrile compound having a linear alkyl group with 3 to 6 carbon atoms, and the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6000 ppm by mass or less.
• the sulfonylimide compound represented by the general formula (1) may contain LiN(FSO 2 ) 2.
• the nonaqueous electrolyte solution of the present disclosure may further contain another electrolyte, and in this case, the molar ratio of the sulfonylimide compound represented by the general formula (1) to the other electrolyte may be 1:25 or more and 2:1 or less.
• a non-aqueous electrolyte solution containing a sulfonylimide compound can achieve both storage stability and a reduction in the resistance of a secondary battery that includes the electrolyte solution.
• 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 less than 2.1 mol/L, more preferably 2 mol/L or less, 1.9 mol/L or less, 1.8 mol/L or less, 1.7 mol/L or less, and 1.6 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 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. Furthermore, the concentration is preferably less than 30% by mass, more preferably 25% by mass or less, and even more preferably 20% by mass or less, 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 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).
• the non-lithium salt include a compound represented by the formula (hereinafter referred to as "fluoroboric acid compound ( 3 )"), lithium hexafluoroarsenate (LiAsF6), LiSbF6 , LiClO4 , LiSCN, LiAlF4 , CF3SO3Li , LiC[( CF3SO2 ) 3 ], LiN(
• 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 conventionally known 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 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 electrolyte viscosity.
• 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, at least one nitrogen-containing compound selected from the group consisting of amide compounds having a branched alkyl group with 3 to 6 carbon atoms and nitrile compounds having a branched alkyl group with 3 to 6 carbon atoms (hereinafter collectively referred to as "branched alkyl nitrogen-containing compounds”), or at least one nitrogen-containing compound selected from the group consisting of amide compounds having a linear alkyl group with 3 to 6 carbon atoms and nitrile compounds having a linear alkyl group with 3 to 6 carbon atoms (hereinafter collectively referred to as "linear alkyl nitrogen-containing compounds”) as an essential component.
• at least one nitrogen-containing compound selected from the group consisting of amide compounds having a branched alkyl group with 3 to 6 carbon atoms and nitrile compounds having a branched alkyl group with 3 to 6 carbon atoms hereinafter collectively referred to as "
• linear alkyl nitrogen-containing compound is distinguished from the “branched alkyl nitrogen-containing compound” in that the linear alkyl group with 3 to 6 carbon atoms does not have a branched (branched) structure.
• the "branched alkyl nitrogen-containing compound” and the “linear alkyl nitrogen-containing compound” may be used alone or in combination of two or more types.
• the "branched alkyl nitrogen-containing compound” and the “linear alkyl nitrogen-containing compound” are collectively referred to as "linear alkyl nitrogen-containing compounds”.
• amide compounds having a branched alkyl group with 3 to 6 carbon atoms include isobutyramide (2-methylpropionamide) and N,N-dimethylisobutyramide.
• nitrile compounds having a branched alkyl group with 3 to 6 carbon atoms include mononitrile compounds such as isobutyronitrile (isopropyl cyanide) and isovaleronitrile (isobutyl cyanide).
• isobutylamide and isobutyronitrile are preferred from the viewpoint of improving battery performance (especially reducing resistance).
• amide compounds having a linear alkyl group with 3 to 6 carbon atoms include n-butylamide and N,N-dimethylbutylamide.
• nitrile compounds having a linear alkyl group with 3 to 6 carbon atoms include mononitrile compounds such as butyronitrile (propyl cyanide) and valeronitrile (butyl cyanide).
• n-butylamide and butyronitrile are preferred from the viewpoint of improving battery performance (especially reducing resistance).
• the content of the chain alkyl nitrogen-containing compound relative to the sulfonylimide compound (1) is 10 mass ppm or more and 6000 mass ppm or less. That is, in the nonaqueous electrolyte according to this embodiment, the quantitative ratio relationship between the sulfonylimide compound (1) and the chain alkyl nitrogen-containing compound is specified. This improves the storage stability of the nonaqueous electrolyte and reduces the resistance of a secondary battery equipped with this nonaqueous electrolyte.
• the content of the chain alkyl nitrogen-containing compound (the total when two or more types are used in combination) is 10 mass ppm or more, preferably 20 mass ppm or more, more preferably 100 mass ppm or more, even more preferably 500 mass ppm or more, and even more preferably 1000 mass ppm or more, relative to the sulfonylimide compound (1) (the total when two or more types are used in combination).
• the upper limit of the content is 6000 mass ppm or less, preferably 5000 mass ppm or less, and more preferably 3000 mass ppm or less.
• the amount of the chain alkyl nitrogen-containing compound in the nonaqueous electrolyte is preferably 2 ppm by mass or more, more preferably 4 ppm by mass or more, even more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, and even more preferably 200 ppm by mass or more.
• the upper limit of the amount is preferably 1200 ppm by mass or less, more preferably 1000 ppm by mass or less, and even more preferably 500 ppm by mass or less.
• the non-aqueous electrolyte may contain, in addition to the chain alkyl nitrogen-containing 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 salt
• 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; 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 non-aqueous electrolyte thus constructed is essentially composed of the sulfonylimide compound (1) and the branched alkyl nitrogen-containing compound or linear alkyl nitrogen-containing compound (chain alkyl nitrogen-containing compound), and may also contain other components such as other electrolyte salts, electrolyte solvents, and various additives (other than the chain alkyl nitrogen-containing compound) as necessary.
• the non-aqueous electrolyte can be prepared, for example, by mixing these components in a predetermined composition ratio.
• the nonaqueous electrolyte according to this embodiment is used, for example, in batteries (batteries having a charge/discharge mechanism), electricity storage (electrochemical) devices (or the ionic conductor materials that constitute these), etc.
• the electrolyte can be used as an electrolyte that constitutes, for example, primary batteries, secondary batteries (e.g., lithium (ion) secondary batteries), fuel cells, electrolytic capacitors, electric double layer capacitors, solar cells, electrochromic display elements, etc.
• primary batteries e.g., lithium (ion) secondary batteries
• secondary batteries e.g., lithium (ion) secondary batteries
• fuel cells e.g., electrolytic capacitors, electric double layer capacitors, solar cells, electrochromic display elements, etc.
• the secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.
• the non-aqueous electrolyte according to the present embodiment is used to reduce the resistance of the secondary battery, and improve the battery performance.
• the positive electrode and the negative electrode are not particularly limited, and a conventionally known secondary battery (particularly a lithium ion secondary battery) can be used.
• the secondary battery may include a separator separating the positive electrode and the negative electrode.
• the separator is not particularly limited, and a conventionally known separator can be used.
• the shape of the battery is not particularly limited, and any conventionally known shape such as a cylindrical type, a square type, a laminated type, a coin type, a large type, etc. can be used.
• a high-voltage power source severe tens of volts to several hundreds of volts
• it can also be a battery module configured by connecting individual batteries in series.
• the nonaqueous electrolyte according to the present embodiment has the following constituent materials: - containing a sulfonylimide compound (1) and a branched alkyl nitrogen-containing compound or a linear alkyl nitrogen-containing compound (a chain alkyl nitrogen-containing compound),
• the amount of the sulfonylimide compound (1) and the chain alkyl nitrogen-containing compound is specified to be 10 ppm by mass or more and 6000 ppm by mass or less relative to the amount of the sulfonylimide compound (1).
• the nonaqueous electrolyte solution according to the above-mentioned configuration not only has excellent storage stability, but also reduces three types of resistance when used in a secondary battery, i.e., initial resistance, resistance associated with battery use, and resistance after high-temperature storage.
• Example 1 Series ⁇ Preparation of non-aqueous electrolyte>
• LiFSI manufactured by Nippon Shokubai, a sulfonylimide compound
• EMC ethyl methyl carbonate
• the branched alkyl nitrogen-containing compound or linear alkyl nitrogen-containing compound shown in Table 1 was added to the standard electrolyte solution to the content shown in Table 1 (content of chain alkyl nitrogen-containing compound relative to LiFSI) and dissolved to prepare a "nitrogen-containing electrolyte solution" (each of the Examples and Comparative Examples 1-2 to 1-5).
• “IBA” indicates isobutyramide (commercial product)
• "IBN” indicates isobutyronitrile (commercial product)
• BA indicates n-butylamide (commercial product)
• BN butyronitrile
• the content of LiFSI in the solution (nonaqueous electrolyte) dissolved in the above mixed solvent as the electrolyte solvent is about 18.4 mass%.
• LiFePO4 commercial product
• 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 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 condition 1 to complete the evaluation battery.
• ⁇ 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 25 mA (1C), 3.6 V, and 0.5 mA termination. - 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 5mA (0.2C) for 10 seconds. Then, after waiting 30 minutes, the battery was discharged at 25mA (1C) for 10 seconds. Finally, after waiting 30 minutes, the battery was discharged at 75mA (3C) 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: 3.6V, 25mA (1C), 0.5mA (0.05C) termination, 10 minutes rest ⁇ discharge: 25mA (1C), 2.0V termination, 10 minutes rest.
• 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.
• Each non-aqueous electrolyte was diluted 100 times with ultrapure water (over 18.2 ⁇ cm) to prepare a measurement solution.
• the concentration of sulfate ions contained in each non-aqueous electrolyte was measured using an ion chromatography system ICS-3000 (manufactured by Nippon Dionex Co., Ltd.). The measurement conditions were as follows.
• the "nitrogen-containing electrolyte solution” suppressed the decomposition of LiFSI and had good storage stability compared to the "reference electrolyte solution”.
• the electrolyte in which the content of the chain alkyl nitrogen-containing compound relative to LiFSI exceeds 6000 ppm by mass exceeds 6000 ppm by mass (Comparative Examples 1-2 and 1-3)
• the sulfate ion concentration after storage at 45°C for one month is higher than that of the "reference electrolyte,” and therefore it was confirmed that the decomposition of LiFSI progresses and the storage stability is inferior.
• the chain alkyl nitrogen-containing compound shown in Table 3 or 4 was added and dissolved in the reference electrolyte to the content shown in Table 3 or 4 (content of chain alkyl nitrogen-containing compound relative to LiFSI), to prepare a "nitrogen-containing electrolyte" (each Example, Comparative Example 2-2 to 2-7).
• the content of LiFSI in the solution (nonaqueous electrolyte) dissolved in the above mixed solvent as the electrolyte solvent is about 9.2% by mass.
• ⁇ 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 a cutoff of 0.6 mA. - 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.
• 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 (initial DCR).
• the reduction rate of the initial DCR was calculated in the same manner as in Example 1 series.
• 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 in Example 1 series.
• 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 in Example 1 series. The reduction rate of DCR after 28 days at 60°C was calculated in the same manner as in Example 1 series.
• the content of the chain alkyl nitrogen-containing compound relative to LiFSI exceeds 6000 ppm by mass (Comparative Examples 2-4 and 2-7), the sulfate ion concentration after storage at 45°C for one month is higher than that of the "reference electrolyte,” and therefore it was confirmed that the decomposition of LiFSI progresses and the storage stability is inferior.
• a "nitrogen-containing electrolyte solution” containing an electrolyte salt of a mixed salt composition including LiFSI and LiPF 6 (another electrolyte) also has the effect of excellent storage stability, similar to a "nitrogen-containing electrolyte solution” containing an electrolyte salt of a simple salt composition including LiFSI alone.
• a "nitrogen-containing electrolyte solution” containing an electrolyte salt of a simple salt composition including LiFSI alone it is predicted that the effect of excellent storage stability can be obtained even if the branched alkyl nitrogen-containing compound is changed to a linear alkyl nitrogen-containing compound in a "nitrogen-containing electrolyte” (Table 2) containing an electrolyte salt having a simple salt composition containing LiFSI alone.

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