JP2017162793A - Nonaqueous electrolyte solution and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte solution and a nonaqueous electrolyte secondary battery which enable the exhibition of high cycle characteristics.SOLUTION: A nonaqueous electrolyte solution comprises a fluorosulfonyl imide compound, a sulfone compound, and an oxalate compound represented by the general formula (3) below. (Mis B or P; Ais a metal ion, a hydrogen ion, or an onium ion; "a" and "b" are independently 1 to 3; "p" is b/a; "q" is 1 to 3; "m" is 0 to 4; "n" is 0 or 1; Ris F, a cyano group, or a fluorinated alkyl group with Cto C; Ris an alkylene group with Cto C, or a halogenated alkylene group with Cto C; and Xand Xeach independently represent O or S.)SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery using the same.

  Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries are used as power sources for smartphones and personal computers, and further as power sources for automobiles. In the batteries used for these applications, various studies have been repeated for the purpose of improving various characteristics such as high output, high energy density, and improvement of cycle characteristics and rate characteristics.

  In a conventional lithium ion battery, a cyclic carbonate such as ethylene carbonate and a chain carbonate such as dimethyl carbonate and ethyl methyl carbonate have been mainly used as a solvent for the electrolytic solution. Among these, ethylene carbonate is known to decompose on a graphite negative electrode to form a protective film called SEI, and to allow deionization and insertion of Li ions into the negative electrode. This is an essential component in the lithium ion battery.

  By the way, since sulfolane has a high dielectric constant and is electrochemically stable and has a high boiling point, it is expected to contribute to improving the performance of the battery by using it as a solvent for a non-aqueous electrolyte. . However, it is known that sulfolane is easily decomposed on the carbon negative electrode, and when used as a main solvent, the capacity during charge and discharge is reduced.

  For example, in Patent Document 1, in a non-aqueous electrolyte secondary battery including a negative electrode using a carbon material as an active material and a positive electrode using a lithium metal composite oxide as an active material, sulfolane and ethyl are used as solvents for the non-aqueous electrolyte. It is disclosed that cycle characteristics are improved by using a mixed solvent of methyl carbonate as compared with the use of dimethyl carbonate. However, there was room for further improvement in cycle characteristics. Further, when used in combination with ethyl methyl carbonate, the characteristics such as electrochemical stability and high boiling point inherent to sulfolane cannot be fully exhibited.

  Moreover, in patent document 2, it consists of 10 to 70 volume% of cyclic | annular sulfone compounds with respect to the whole nonaqueous solvent, the carbonate which has an unsaturated bond, the carbonate which has a halogen atom, a monofluorophosphate, and a difluorophosphate. It is disclosed that a non-aqueous electrolyte characterized by having at least one compound selected from the group can improve characteristics at high capacity and high current density. However, the solvent of cyclic sulfone compound: ethyl methyl carbonate = 3: 7 was used here, too, and the characteristics of the sulfone compound were not fully exhibited, and there was room for improvement.

Japanese Unexamined Patent Publication No. 2000-12078 JP 2008-269980 A

  Under the circumstances described above, an object of the present invention is to provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery that can exhibit high cycle characteristics.

  The non-aqueous electrolyte of the present invention includes a fluorosulfonylimide compound represented by the following general formula (1):

(In the general formula (1), M ⁺ represents an alkali metal ion, and X represents a fluorine atom or a fluoroalkyl group having 1 to 6 carbon atoms.)
A sulfone compound represented by the following general formula (2);

(In General Formula (2), R ¹ and R ² are the same or different and each represents a monovalent or divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group, and R ¹ and R ² are bonded to each other. A ring may be formed.)
An oxalato compound represented by the following general formula (3);

(In General Formula (3), M ¹ is B or P, A ^{a +} is a metal ion, hydrogen ion, or onium ion, a is 1 to 3, b is 1 to 3, p is b / a, q is 1 to 3, m represents 0 to 4, n represents 0 or 1, R ³ represents fluorine, a cyano group or a C _{1 to} C ₁₀ fluorinated alkyl group, R ⁴ represents a C _{1 to} C ₁₀ alkylene group or C ₁ halogenated alkylene group ~C _10, X ^1, X ² represents O or S each independently.)
It is a non-aqueous electrolyte characterized by including.

  The nonaqueous electrolytic solution of the present invention preferably contains 0.01 to 10% by mass of the compound represented by the general formula (3).

  The present invention also includes a non-aqueous electrolyte secondary battery provided with the non-aqueous electrolyte of the present invention.

  Since the non-aqueous electrolyte of the present invention contains an oxalato compound in addition to the sulfone compound, a non-aqueous electrolyte secondary battery with improved cycle characteristics could be provided.

  The non-aqueous electrolyte of the present invention includes a fluorosulfonylimide compound represented by the general formula (1), a sulfone compound represented by the general formula (2), and an oxalato represented by the general formula (3). It is characterized in that it contains a compound. It is considered that the fluorosulfonylimide compound represented by the general formula (1) has a smaller molecular size than the imide compound such as LiTFSI and the size of the formed contact ion pair. Moreover, it is thought that the sulfone compound represented by General formula (2) takes a different coordination state from the carbonate type solvent normally used for a lithium ion battery. Thus, in a non-aqueous electrolyte containing a fluorosulfonylimide compound and a sulfone compound, lithium ions and sodium ions (hereinafter sometimes represented by lithium ions) are different from those when other imide compounds or solvents are used. It is considered to be in a coordinated state.

  On the other hand, when lithium ions are inserted into the carbon-based negative electrode, the solvent or anion coordinated to the lithium salt is eliminated, but when a normal electrolyte salt is used, the solvent is inserted during insertion of lithium ions into the carbon-based negative electrode. Is not desorbed, co-insertion occurs, and destruction of the carbon-based negative electrode is said to occur. Therefore, when a carbon-based negative electrode is used, a solvent that forms SEI such as ethylene carbonate is used in combination, and lithium ions can be deinserted by suppressing co-insertion of the solvent and anions. In the non-aqueous electrolyte of the present invention, lithium ions are in a coordinated state different from ordinary imide compounds and solvents, so that lithium ions can be desorbed well with respect to the carbon-based negative electrode without the need for ethylene carbonate. And is considered to exhibit good capacity and cycle characteristics.

  In addition, the oxalato compound is decomposed on the negative electrode or the positive electrode surface to form a composite film with the fluorosulfonylimide compound, and this composite film is considered to suppress co-insertion of the solvent when lithium ions are desorbed into the carbon-based negative electrode. It is done. Moreover, it is thought that this composite coating also suppresses decomposition of the electrolytic solution. Hereinafter, the non-aqueous electrolyte of the present invention will be described in detail.

1. Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention is a fluorosulfonylimide compound represented by the above general formula (1), a sulfone compound represented by the above general formula (2), and the above general formula (3). It is characterized by including the oxalato compound represented.

1-1. Fluorosulfonylimide compound The non-aqueous electrolyte of the present invention contains a fluorosulfonylimide compound represented by the following general formula (1) (sometimes referred to as a fluorosulfonylimide compound (1)).

(In the general formula (1), M ⁺ represents an alkali metal ion, and X represents a fluorine atom or a fluoroalkyl group having 1 to 6 carbon atoms.)

  The C1-C6 fluoroalkyl group is a group in which some or all of the hydrogen atoms of the C1-C6 alkyl group are substituted with fluorine. The fluoroalkyl group may be linear, branched, cyclic, or a combination of two or more of these, but a linear or branched fluoroalkyl group is preferred, and linear fluoro An alkyl group is more preferred. Specific examples of the fluoroalkyl group include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a tetrafluoroethyl group, a pentafluoroethyl group, and a fluoropropyl group. , Fluorobutyl group, fluoropentyl group, fluorohexyl group and the like. Among these, a fluorine atom and a C1-C3 fluoroalkyl group are preferable as X.

In the general formula (1), the alkali metal ion represented by M ⁺ is preferably a lithium ion, a sodium ion, a potassium ion, a rubidium ion or a cesium ion, more preferably a lithium ion or a sodium ion, still more preferably Lithium ion.

  Specific examples of the fluorosulfonylimide compound (1) include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, lithium (Fluorosulfonyl) lithium salt of fluorosulfonylimide such as (heptafluoropropylsulfonyl) imide; sodium bis (fluorosulfonyl) imide, sodium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, sodium (fluorosulfonyl) (pentafluoroethyl Sulfonyl) imide, sodium salt of fluorosulfonylimide such as sodium (fluorosulfonyl) (heptafluoropropylsulfonyl) imide Fluorosulfonyl such as potassium bis (fluorosulfonyl) imide, potassium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, potassium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, potassium (fluorosulfonyl) (heptafluoropropylsulfonyl) imide Imide potassium salt; and the like. Preferred are lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, sodium bis (fluorosulfonyl) imide, sodium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, more preferably lithium. Bis (fluorosulfonyl) imide and lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide.

  The nonaqueous electrolytic solution of the present invention may contain one type of fluorosulfonylimide compound (1) alone, or may contain two or more types of fluorosulfonylimide compounds (1). As the fluorosulfonylimide compound (1), a commercially available product may be used, or a product synthesized by a conventionally known method may be used.

1-2. Other Electrolyte Salt The non-aqueous electrolyte of the present invention may further contain other electrolyte salt. As other electrolyte salt, what is normally used as electrolyte salt of a nonaqueous electrolyte secondary battery can be used. Preferred electrolyte salts are lithium and sodium salts.

Examples of suitable lithium salts are LiPF ₆ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N (LiTFSI), Li (C ₂ F ₅ SO ₂ ) ₂ N (LiBETI) ), LiSCN, LiCF ₃ SO ₃ , LiAlF ₄ , LiClO ₄ , LiN (NO ₂ ) ₂ , LiB ₁₂ F _{12 -x} H _{x and the} like. Preferable lithium salts include LiPF ₆ , LiBF ₄ , LiTFSI, LiBETI and the like, and more preferably LiPF ₆ and LiBF ₄ .

As a suitable sodium salt, a sodium salt used as an electrolyte salt of a sodium ion secondary battery can be used. Specific examples of the sodium salt include NaPF ₆ , NaPF ₃ (CF ₂ CF ₃ ) ₃ , NaBF ₄ , Na (CF ₃ SO ₂ ) ₂ N (NaTFSI), Na (C ₂ F ₅ SO ₂ ) ₂ N (NaBETI ) And the like. Preferred sodium salts are NaPF ₆ , NaBF ₄ , NaTFSI and the like.
These other electrolyte salts may be used individually by 1 type, and may be used in combination of 2 or more type.

1-3. Amount of fluorosulfonylimide compound (1) In the nonaqueous electrolytic solution of the present invention, the content of the fluorosulfonylimide compound (1) is 20 mol in a total of 100 mol% of the fluorosulfonylimide compound (1) and another electrolyte salt. % Or more is preferable. More preferably, it is 40 mol% or more, More preferably, it is 60 mol% or more, Most preferably, it is 80 mol% or more. It is also a preferred embodiment to use 100 mol% of the fluorosulfonylimide compound (1). Further, the concentration of the electrolyte salt in the non-aqueous electrolyte (total concentration of the fluorosulfonylimide compound (1) and other electrolyte salt) is preferably 0.6 mol / L or more, more preferably 0.00. 8 mol / L or more, more preferably 1.0 mol / L or more, preferably 6.0 mol / L or less, more preferably 5.0 mol / L or less, still more preferably 3.0 mol / L. L or less, and most preferably 2.0 mol / L or less. If the concentration of the electrolyte salt in the non-aqueous electrolyte is too high, the viscosity of the non-aqueous electrolyte may increase and the ionic conductivity may decrease. On the other hand, if the concentration is too low, battery performance may be inferior.

1-4. Sulfone Compound The non-aqueous electrolyte solution of the present invention contains a sulfone compound represented by the following general formula (2) (hereinafter sometimes referred to as a sulfone compound (2)).

(In General Formula (2), R ¹ and R ² are the same or different and each represents a monovalent or divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group, and R ¹ and R ² are bonded to each other. A ring may be formed.)

In the general formula (2), when R ¹ and R ² are a monovalent saturated aliphatic hydrocarbon group or a monovalent aromatic hydrocarbon group, the sulfone compound (2) is a chain sulfone compound (sulfonyl group). Is a sulfone compound that does not form a part of a cyclic structure, which may be hereinafter referred to as a chain-like sulfone compound (2)), and R ¹ and R ² are divalent saturated aliphatic hydrocarbon groups or 2 In the case of a valent aromatic hydrocarbon group, the sulfone compound (2) becomes a cyclic sulfone compound in which the sulfonyl group forms part of the cyclic structure. The number of carbon atoms of the monovalent saturated aliphatic hydrocarbon group is preferably 1-8. R ¹ and R ² are preferably a methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group and the like. When R ¹ and R ² are monovalent aromatic hydrocarbon groups, the number of carbon atoms is preferably 6 to 14. Preferably, a phenyl group, a naphthyl group, an anthranyl group, etc. can be mentioned. R ¹ and R ² may have a substituent, and examples of the substituent include a halogen atom and an alkyl group having 1 to 5 carbon atoms. In addition, when a part of the hydrogen atoms of R ¹ and R ² is substituted with a halogen atom, the halogen atom is preferably a fluorine atom.

  Specific examples of the chain sulfone compound (2) include dimethylsulfone, diethylsulfone, dipropylsulfone, diisopropylsulfone, dibutylsulfone, methylethylsulfone, methylpropylsulfone, methylisopropylsulfone, ethylpropylsulfone, ethylisopropylsulfone, Diphenylsulfone, dibenzylsulfone, benzylphenylsulfone, dixylylsulfone, methylphenylsulfone, ethylphenylsulfone, benzylmethylsulfone, benzylethylsulfone, difluoromethylphenylsulfone, difluorophenylmethylsulfone, ethynyl-p-tolylsulfone, 4- Fluorophenyl methyl sulfone etc. are mentioned.

When the sulfone compound (2) is a cyclic sulfone compound in which R ¹ and R ² are bonded to each other in the general formula (2) and the sulfonyl group forms part of the cyclic structure, the cyclic structure is formed by a hydrocarbon group. Preferably it is. The hydrocarbon group is more preferably an alkylene group having 3 to 8 carbon atoms. The carbon number in this case means the carbon number of a cyclic structure in which R ¹ and R ² are bonded to each other. That is, the above carbon number means the number of carbon atoms contained in the element constituting the cyclic structure, and the carbon atom contained in the substituent described later is not included in the above carbon number. More preferred is an alkylene group having 3 to 6 carbon atoms, and most preferred is an alkylene group having 4 carbon atoms, that is, a tetramethylene group. The divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group may have a substituent, such as a halogen atom, an alkyl group optionally substituted with a halogen atom, or a halogen atom. The aryl group which may be substituted is mentioned. Of the halogen atoms, the most preferred is a fluorine atom. As an alkyl group, a C1-C5 alkyl group is mentioned, Preferably it is C1-C4, More preferably, it is C1-C2. The alkyl group substituted with a halogen atom is preferably an alkyl group having 1 to 4 carbon atoms substituted with a fluorine atom, and more preferably an alkyl group having 1 to 2 carbon atoms substituted with a fluorine atom.

  Specific examples of the cyclic sulfone compound (2) include tetramethylene sulfone (sulfolane), 2-methyl sulfolane, 3-methyl sulfolane, 2-ethyl sulfolane, 3-ethyl sulfolane, 3-propyl sulfolane, 3-butyl sulfolane, 3 -Sulfolane compounds such as pentyl sulfolane, 3-isopropyl sulfolane, 3-isobutyl sulfolane, 3-isopentyl sulfolane, 2,4-dimethyl sulfolane, 2-phenyl sulfolane, 3-phenyl sulfolane, dibenzosulfolane; And cyclic sulfone compounds having a double bond such as methylsulfolene.

  Among the sulfone compounds (2), dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, ethyl isopropyl sulfone, and sulfolane are more preferable, and dimethyl sulfone, methyl ethyl sulfone, and sulfolane are more preferable. The said sulfone compound (2) may be used individually by 1 type, and may be used in combination of 2 or more type.

  The sulfone compound (2) is preferably used in a concentration range of 30% to 95% by mass in the nonaqueous electrolytic solution of the present invention. More preferably, it is used in the range of 35 mass% to 92 mass%, more preferably 40 mass% to 90 mass%. When the amount of the sulfone compound (2) used is too small, the viscosity of the electrolytic solution increases and sufficient ionic conductivity cannot be obtained, and there is a possibility that sufficient performance as a battery cannot be obtained. On the other hand, when the sulfone compound (2) is used in a large amount, the electrolyte salt concentration in the electrolytic solution decreases, and there is a possibility that sufficient battery performance may not be obtained.

1-5. Oxalato Compound The non-aqueous electrolyte of the present invention is characterized in that it also contains an oxalate compound represented by the following general formula (3) (hereinafter sometimes referred to as oxalato compound (3)).

(In General Formula (3), M ¹ is B or P, A ^{a +} is a metal ion, hydrogen ion, or onium ion, a is 1 to 3, b is 1 to 3, p is b / a, q is 1 to 3, m represents 0 to 4, n represents 0 or 1, R ³ represents fluorine, a cyano group or a C _{1 to} C ₁₀ fluorinated alkyl group, R ⁴ represents a C _{1 to} C ₁₀ alkylene group or C ₁ halogenated alkylene group ~C _10, X ^1, X ² represents O or S each independently.)

  It was found that the capacity of the lithium ion secondary battery using the electrolytic solution containing the fluorosulfonylimide compound (1) and the sulfone compound (2) slightly decreased. As a result of studies by the present inventor, in the electrolytic solution using the fluorosulfonylimide compound (1) and the sulfone compound (2), the fluorosulfonylimide compound (1) decomposes on the negative electrode to form SEI. Lithium ions can be removed and inserted into graphite. However, there is still room for improvement in this SEI, and further investigations have continued. By adding the oxalato compound (3) to the electrolyte, the battery capacity and It was found that cycle characteristics were improved. This is because the oxalato compound (3) undergoes reductive decomposition at the negative electrode during the initial charge and forms a film on the negative electrode, so that the sulfone compound (2) is not co-inserted into the graphite but lithium ions are inserted into the graphite. It is presumed that Furthermore, since the composite SEI of the fluorosulfonylimide compound (1) and the oxalato compound (3) suppresses the decomposition of the electrolytic solution during the cycle test, it is considered that the cycle characteristics are also improved.

As the metal ion represented by A ^{a +} in the general formula (3), an alkali metal or an alkaline earth metal is preferable, Li ⁺ , Na ⁺ , Mg ²⁺ , and Ca ²⁺ are more preferable, and Li ⁺ is more preferable. Na ⁺ , and Li ⁺ is particularly preferable. Accordingly, a, b, and p are preferably 1.

As the onium cation represented by A ^{a +} in the general formula (3), the general formula: L ⁺ -R _s (wherein L represents C, Si, N, P, S or O, and R represents The same or different organic groups, which may be bonded to each other, s represents the number of R bonded to L, and is 3 or 4. Note that s is directly bonded to the valence of element L and L The onium cation represented by (the value determined by the number of double bonds) is preferred.

  The “organic group” represented by R means a group having at least one hydrogen atom, fluorine atom, or carbon atom. The “group having at least one carbon atom” only needs to have at least one carbon atom, and may have another atom such as a halogen atom or a hetero atom, a substituent, or the like. Good. Examples of the substituent include amino group, imino group, amide group, ether bond group, thioether bond group, ester group, hydroxyl group, alkoxy group, carboxyl group, carbamoyl group, cyano group, disulfide group, nitro group. Group, nitroso group, sulfonyl group and the like.

The alkylene group of the general formula (3) C ₁ ~C ₁₀ of R ⁴ in a methylene group, an ethylene group, a propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decalene group These may be branched. As the C ₁ -C ₁₀ halogenated alkylene group, a group in which part or all of the hydrogen of the C ₁ -C ₁₀ alkylene group is replaced with F, Cl, Br or I (among others, F is preferable, for example, Fluoromethylene group or fluoroethylene group). R ⁴ is preferably an alkylene group having 1 to 4 carbon atoms or a fluorinated alkylene group having 1 to 4 carbon atoms in which part of hydrogen of the alkylene group is substituted with fluorine. More preferably, it is a C1-C2 alkylene group or a fluorinated alkylene group. n is 0 or 1, and when n is 0, it represents a direct bond of a carbonyl group, and the compound of the general formula (3) becomes oxalatoborate or oxalatophosphonium. n is preferably 0.

R ³ is a fluorine atom, a cyano group or a C _{1 to} C ₁₀ fluorinated alkyl group. Examples of the C _{1 to} C ₁₀ fluorinated alkyl group include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, and a fluoroethyl group. Group, difluoroethyl group, trifluoroethyl group, tetrafluoroethyl group, perfluoroethyl group, fluoropropyl group, perfluoropropyl group, perfluorobutyl group, perfluorooctyl group and the like. R ³ is preferably a fluorinated alkyl group having 1 to 2 carbon atoms, a cyano group, or a fluorine atom, and more preferably a fluorine atom.

X ¹ and X ² each independently represents O or S, but it is preferable that both are O for ease of availability.

In the general formula (3), when M ¹ is B, q is more preferably 1 or 2, and when q is 1, m is 2, and R ^{3 at} this time is F. Is preferred. When q is 2, m is 0. Further, when M ¹ is P, q is 1 to 3, when q is 1, m is 4, when q is 2, m is 2, and when q is 3, m is 0.

  Specific examples of the compound represented by the general formula (3) include difluorooxalatoborate salt, dicyanooxalatoborate salt, cyanofluorooxalatoborate salt, bisoxalatoborate salt, tetrafluorooxalatophosphonium salt, difluorobis ( Oxalato) phosphonium salts and tris (oxalato) phosphonium salts can be mentioned, and one or more of these can be used.

  The compound represented by the general formula (3) is preferably used in the range of 0.01 to 10% by mass in 100% by mass of the nonaqueous electrolytic solution. If the amount is less than 0.01% by mass, the effect of suppressing the decomposition of the electrolytic solution may be insufficient. If the amount exceeds 10% by mass, the increase in resistance due to film formation increases and the battery performance itself decreases. This is not preferable. More preferably 0.02% by mass or more, still more preferably 0.05% by mass or more, further preferably 0.1% by mass or more, more preferably 5% by mass or less, and still more preferably 2% by mass. % Or less, more preferably 1% by mass or less. When the non-aqueous electrolyte is used in a high-temperature environment (for example, about 60 ° C. or higher), the content of the oxalato compound (3) is 0.01% by mass or more in 100% by mass of the non-aqueous electrolyte. It is preferable to set it as the mass% or less. By using within the said range, the effect by an oxalato compound (3) is exhibited more effectively. More preferably, it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more, More preferably, it is 2 mass% or less, More preferably, it is 1 mass% or less.

1-6. Solvent Since the nonaqueous electrolytic solution of the present invention uses the sulfone compound (2) as a solvent, other solvents are not necessary, but nonaqueous solvents other than conventionally known carbonate solvents and carbonate solvents, and polymers In addition, a conventionally known solvent used for batteries, such as a medium such as a polymer gel, may also be used.

  Examples of carbonate solvents include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, and methyl phenyl carbonate; ethylene carbonate (ethylene carbonate), propylene carbonate (propylene Carbonates), saturated cyclic carbonates such as 2,3-dimethylethylene carbonate (2,3-butanediyl carbonate), 1,2-butylene carbonate and erythritan carbonate; fluoroethylene carbonate, 4,5-difluoroethylene carbonate and tri Examples include fluorine-containing cyclic carbonates such as fluoropropylene carbonate.

  As other solvent, a solvent having a large dielectric constant, high solubility of the electrolyte salt, a boiling point of 60 ° C. or more, and a wide electrochemical stability range is preferable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. Examples of such organic solvents include 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 Ethers such as dioxane and 1,3-dioxolane; aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate; lactones such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; trimethyl phosphate , Phosphate esters such as ethyldimethyl phosphate, diethylmethyl phosphate, triethyl phosphate; acetonitrile, propionitrile, methoxypropionitrile, glutarony Nitriles such as ril, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; aromatic nitriles such as benzonitrile, tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, Examples include 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3-methyl-2-oxazolidinone, and the like.

  It is preferable that the usage-amount of the said solvent is 70 vol% or less with respect to the total amount of a sulfone compound (2) and a solvent. More preferably, it is 60 vol% or less, More preferably, it is 50 vol% or less, Most preferably, it is 40 vol% or less. It is preferable that the ratio of the said solvent is 70 mass% or less with respect to the total amount of the said sulfone compound (2) and a solvent. More preferably, it is 60 mass% or less, More preferably, it is 50 mass% or less, Most preferably, it is 40 mass% or less.

  When a polymer or polymer gel is used, the following method may be employed. That is, a polymer formed by a conventionally known method, an electrolyte salt or the like in the above-mentioned non-aqueous solvent (the electrolyte salt or the like includes the fluorosulfonylimide compound (1), the sulfone compound (2), the oxalato compound (3), and the necessary A method in which a solution in which an electrolyte salt or additive is dissolved is added dropwise and impregnated with and supported by an electrolyte salt or a non-aqueous solvent; a polymer at a temperature equal to or higher than the melting point of the polymer. A method in which a nonaqueous solvent is impregnated into a film after melting and mixing the electrolyte salt and electrolyte salt, etc .; a battery is prepared using a solution in which a monomer, an electrolytic solution and a polymerization initiator are mixed, and then monomer polymerization is performed by heat. A method in which a monomer, electrolytic solution, and a photopolymerization initiator mixed solution are coated on an electrode sheet and UV cured (hereinafter referred to as a gel electrolyte); an electrolyte salt or the like is previously dissolved in a non-aqueous solvent. After mixing the non-aqueous electrolyte and the polymer, the film is formed by the casting method or coating method, and the organic solvent is volatilized; the polymer and the electrolyte salt are melted and mixed at a temperature higher than the melting point of the polymer. And the like (intrinsic polymer electrolyte);

  As the polymer used in the above method, a homopolymer or copolymer of an epoxy compound (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.), a polyether polymer such as polyethylene oxide (PEO), polypropylene oxide, Methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluoropolymers such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof Is mentioned.

1-7. Other Components The non-aqueous electrolyte solution according to the present invention may contain an additive for the purpose of improving various characteristics of the non-aqueous electrolyte secondary battery.
As additives, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC), phenyl ethylene carbonate (4-phenyl-1,3-dioxolan-2-one) Cyclic carbonates having an unsaturated bond such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic acid Carboxylic anhydrides such as dianhydrides and phenylsuccinic anhydrides; ethylene sulfite, 1,3-propane sultone, 1,3-prop-1-ene sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, Tetramethi Sulfur-containing compounds such as thiuram monosulfide and trimethylene glycol sulfate; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone And nitrogen-containing compounds such as N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; saturated hydrocarbon compounds such as heptane, octane and cycloheptane; Among these, it is preferable to use cyclic carbonate having an unsaturated bond such as vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and 1,3-propane sultone. More preferred are cyclic carbonates having unsaturated bonds such as vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

The additive is preferably used in a range of 0.1% by mass or more and 10% by mass or less in 100% by mass of the nonaqueous electrolytic solution of the present invention (more preferably 0.2% by mass or more and 8% by mass or less, More preferably 0.3 mass% or more and 5 mass% or less). When the amount of the additive used is too small, it may be difficult to obtain an effect derived from the additive.On the other hand, even if another additive is used in a large amount, it is difficult to obtain an effect commensurate with the added amount. There is a possibility that the viscosity of the non-aqueous electrolyte increases and the conductivity decreases.
The non-aqueous electrolyte 100% by mass means other electrolyte salt, other medium, and additive used as necessary in addition to the fluorosulfonylimide compound (1), the sulfone compound (2) and the oxalato compound (3). It means the total of all components contained in the non-aqueous electrolyte.

2. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte of the present invention is suitably used for various power storage devices. Examples of the electricity storage device include a lithium ion battery, a sodium ion battery, a lithium metal battery, a non-aqueous electrolyte secondary battery such as a sodium metal battery, and a lithium ion capacitor having both the electric storage principle of an electric double layer capacitor and a lithium ion battery. . Therefore, the non-aqueous electrolyte secondary battery of the present invention includes the above-described non-aqueous electrolyte of the present invention. Hereinafter, the nonaqueous electrolyte secondary battery will be described.

2-1. Positive electrode In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material may be any material that can occlude / release lithium ions and sodium ions, and is used in conventionally known lithium ion secondary batteries and sodium ion secondary batteries. The positive electrode active material to be used can be used.

As the active material for lithium ion secondary batteries, lithium cobalt acid, lithium nickel acid, lithium manganese _{acid, LiNi 1-xy Co x Mn} y O 2 or _{LiNi 1-xy Co x Al y} O 2 (0 ≦ x ≦ 1 , 0 ≦ y ≦ 1), transition metal oxides such as ternary oxides, compounds having an olivine structure such as LiAPO ₄ (A = Fe, Mn, Ni, Co), and a plurality of transition metals Solid solution material (solid solution of electrochemically inactive layered Li ₂ MnO ₃ and electrochemically active layered LiMO ₂ (transition metals such as M = Co and Ni)), LiCo _x Mn _{1− x O 2 (0 ≦ x ≦} 1), LiNi x Mn 1-x O 2 (0 ≦ x ≦ 1), Li 2 APO 4 F (a = Fe, Mn, Ni, Co) fluoride olivine structure such as Or the like. These may be used alone or in combination.
As active materials of the sodium ion secondary battery, NaNiO ₂ , NaCoO ₂ , NaMnO ₂ , NaVO ₂ , NaFeO ₂ , Na (Ni _x Mn _1-x ) O ₂ (0 <X <1), Na (Fe _x Mn) _1-X ) O ₂ (0 <X <1), NaVPO ₄ F, Na ₂ FePO ₄ F, Na ₃ V ₂ (PO ₄ ) _{3 and the} like.

  The positive electrode is formed by supporting a positive electrode mixture containing a conductive additive and a binder on a positive electrode current collector, and is usually formed into a sheet shape.

  The method for producing the positive electrode is not particularly limited. For example, (i) a positive electrode active material composition in which a positive electrode mixture is dissolved or dispersed in a dispersion solvent is applied to a positive electrode current collector by a doctor blade method or the like. A method of immersing the current collector in the positive electrode active material composition and then drying; (ii) bonding a sheet obtained by kneading and drying the positive electrode active material composition to the positive electrode current collector through a conductive adhesive (Iii) A positive electrode active material composition added with a liquid lubricant is applied or cast onto a positive electrode current collector to form a desired shape, and then the liquid lubricant is removed. Then, the method of extending | stretching to a uniaxial or multiaxial direction; etc. are mentioned. Moreover, you may pressurize the positive mix layer after drying as needed. Thereby, the adhesive strength with the positive electrode current collector is increased, and the electrode density is also increased.

  The material used for the positive electrode current collector, conductive additive, binder, and positive electrode active material composition (solvent for dispersing or dissolving the positive electrode mixture) is not particularly limited, and each conventionally known material should be used. For example, each material described in JP 2014-13704 A can be used.

  The amount of the positive electrode active material used is preferably 75 parts by mass or more and 99 parts by mass or less with respect to 100 parts by mass of the positive electrode mixture, more preferably 85 parts by mass or more, and further preferably 90 parts by mass or more. Yes, more preferably 98 parts by mass or less, still more preferably 97 parts by mass or less.

  In the case of using a conductive additive, the content of the conductive additive in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more preferably Preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 10% by mass). If the amount of the conductive assistant is too small, the conductivity is extremely deteriorated and the load characteristics and the discharge capacity may be deteriorated. On the other hand, when the amount is too large, the bulk density of the positive electrode mixture layer is increased, and the content of the binder needs to be further increased.

In the case of using the binder, the content of the binder in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more preferably 0.5% by mass). % To 9% by mass, more preferably 1% to 8% by mass). If the amount of the binder is too small, good adhesion cannot be obtained, and the positive electrode active material and the conductive additive may be detached from the current collector. On the other hand, if the amount is too large, the internal resistance may be increased, and the battery characteristics may be adversely affected.
The blending amounts of the conductive auxiliary agent and the binder can be appropriately adjusted in consideration of the intended use of the battery (emphasis on output, importance on energy, etc.), ion conductivity, and the like.

2-2. Negative electrode The negative electrode is formed by supporting a negative electrode active material, a binder, and, if necessary, a negative electrode mixture containing a conductive auxiliary agent on a negative electrode current collector, and is usually formed into a sheet shape.
As a manufacturing method of the negative electrode, a method similar to the manufacturing method of the positive electrode can be employed. In addition, the same conductive auxiliary agent, binder, and material dispersing solvent as used in the positive electrode are used in the production of the negative electrode.

  As the material of the negative electrode current collector and the negative electrode active material, conventionally known negative electrode active materials can be used. The negative electrode is formed by supporting a negative electrode active material, a binder, and, if necessary, a negative electrode mixture containing a conductive auxiliary agent on a negative electrode current collector, and is usually formed into a sheet shape.

As the negative electrode active material, conventionally known negative electrode active materials used in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries can be used, and alkali ions such as lithium ions and sodium ions can be used. Any material that can occlude and release metal may be used. More specifically, carbon materials such as graphite (artificial graphite, natural graphite), coal, mesophase fired body made from petroleum pitch, non-graphitizable carbon, etc .; alkali metals such as Li and Na; Si, Si alloy, SiO, etc. Si-based negative electrode materials; Sn-based negative electrode materials such as Sn alloys; lithium-based materials such as lithium alloys such as lithium metal and lithium-aluminum alloys; and titanium-based negative electrodes such as Li ₄ Ti ₅ O ₁₂ can be used.

  Preferably carbon materials such as graphite materials such as artificial graphite and natural graphite, mesophase fired bodies made from coal and petroleum pitch, carbon materials such as non-graphitizable carbon, more preferably artificial graphite and natural graphite, etc. Graphite materials and non-graphitizable carbon are preferable, and graphite materials such as artificial graphite and natural graphite are more preferable.

2-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. The separator is not particularly limited, and any conventionally known separator can be used in the present invention. Specifically, for example, a porous sheet (for example, a polyolefin microporous separator or a cellulose separator) made of a polymer that can absorb and hold a non-aqueous electrolyte, a nonwoven fabric separator, a porous metal body, and the like can be given. .

  Examples of the material for the porous sheet include polyethylene, polypropylene, a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene, and cellulose. Examples of the material of the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., depending on the mechanical strength required for the non-aqueous electrolyte layer, etc. The materials exemplified above can be used alone or in combination.

  In addition, when a polymer or a polymer gel is used instead of the organic solvent of the non-aqueous electrolyte (so-called polymer electrolyte or gel electrolyte), the separator is not necessarily required, but the porous sheet and nonwoven fabric separator described above are used as the electrolyte support. Can be used in combination with a polymer electrolyte or a gel electrolyte. By using these separators in combination, the performance of the polymer electrolyte or gel electrolyte can be improved, and the performance of the battery can be improved.

2-4. Battery exterior materials Battery elements equipped with a positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. can be used as battery exterior materials to protect battery elements from external impacts and environmental degradation when using non-aqueous electrolyte secondary batteries. Be contained. In the present invention, the material of the battery exterior material is not particularly limited, and any conventionally known exterior material can be used.

  The shape of the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited, and any conventionally known shape as a shape of the nonaqueous electrolyte secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, etc. Can also be used. Further, when used as a high voltage power source (several tens of volts to several hundreds of volts) for mounting on an electric vehicle, a hybrid electric vehicle, etc., a battery module configured by connecting individual batteries in series can be used. .

  The rated charging voltage of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but is preferably 4.2 V or higher. The effect of the present invention is particularly remarkable when used at a voltage exceeding 4.2V. More preferably, it is 4.3 V or more, and further preferably 4.35 V or more. The higher the rated charging voltage, the higher the energy density, but if it is too high, it may be difficult to ensure safety. Therefore, the rated charging voltage is preferably 5 V or less. More preferably, it is 4.9 V or less.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

(Electrolytic solution 1)
To 0.94 g of lithium bis (fluorosulfonyl) imide represented by the following formula: LiFSI (manufactured by Nippon Shokubai Co., Ltd.), 5.00 g of sulfolane (manufactured by Kishida Chemical Co., Ltd.) melted at 35 ° C. was added, and 1 mol / kg of LiFSI. A sulfolane solution (electrolytic solution 1) was prepared.

(Electrolytic solution 2)
A 1 mol / kg LiFSI sulfolane solution (mass: 5.94 g, the same applies to the electrolytes 3 to 4) was prepared in the same manner as the electrolytic solution 1, and 0.100 g of lithium bis (oxalato) borate ( (LiBOB) was added to prepare an electrolytic solution 2.

(Electrolytic solution 3)
A 1 mol / kg LiFSI sulfolane solution was prepared in the same manner as the electrolytic solution 1, and 0.100 g of lithium difluoro (oxalato) borate (described below) (LiDFOB) was added to the solution to prepare an electrolytic solution 3.

(Electrolytic solution 4)
A 1 mol / kg LiFSI sulfolane solution was prepared in the same manner as the electrolytic solution 1, and 0.100 g of vinylene carbonate (VC) was added to the solution to prepare an electrolytic solution 4.

(Positive electrode sheet)
Mixing positive electrode active material (LiCoO ₂ ), conductive additive 1 (acetylene black, AB), conductive additive 2 (graphite) and binder (polyvinylidene fluoride, PVdF) in a mass ratio of 92: 2: 2: 4 And it was made to disperse | distribute to N-methylpyrrolidone, it was set as the positive electrode mixture slurry, and it apply | coated on the aluminum foil (positive electrode collector), and dried, and produced the positive electrode sheet.

(Negative electrode sheet)
A negative electrode active material (natural graphite), a conductive additive (carbon fiber, “VGCF (registered trademark)”, manufactured by Showa Denko KK), and a binder (polyvinylidene fluoride, PVdF) were 95.7: 0.5: 3. The negative electrode mixture slurry mixed at a mass ratio of 0.8 was coated on a copper foil (negative electrode current collector) and dried to prepare a negative electrode sheet.

(Production of coin-type lithium ion secondary battery)
The positive electrode sheet, the negative electrode sheet, and the glass fiber filter paper (manufactured by Whatman, GF / F) were each punched into a circle (positive electrode φ12 mm, negative electrode φ14 mm, glass fiber filter paper φ16 mm). CR2032 coin-type battery parts purchased from Hosen Co., Ltd. (positive electrode case (made of aluminum clad SUS304L), negative electrode cap (made of SUS316L), spacer (1 mm thickness, made of SUS316L), wave washer (made of SUS316L), gasket (made of polypropylene) )) To produce a coin-type lithium battery. Specifically, a negative cap with a gasket, a wave washer, a spacer, a negative electrode sheet (installed so that the copper foil side of the negative electrode faces the spacer), a separator are stacked in this order, and then 100 μL of a non-aqueous electrolyte is added. A polyethylene separator was impregnated. Next, a positive electrode sheet was placed so that the surface coated with the positive electrode mixture was opposed to the negative electrode active material layer side, a positive electrode case was stacked thereon, and caulking was performed to produce a coin cell type lithium ion secondary battery.

(Battery evaluation: Full cell evaluation)
Using a charge / discharge test apparatus (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the discharge capacity of the coin cell type lithium ion secondary battery was measured in an environment at a temperature of 25 ° C. Charge / discharge conditions were: 4.35V constant current / constant voltage charging at a charging rate of 0.2C up to a current amount of 0.02C, and then discharging at a discharging rate of 0.2C until the voltage reached 3.0V. After repeating this charge / discharge at 0.2C five times, charge / discharge was repeated 300 times under the same conditions as at 0.2C except that the charge rate was 1C and the discharge rate was 1C. Table 1 shows the discharge capacity after 300 cycles.

(Electrolyte 5-7)
Lithium bis (fluorosulfonyl) imide; LiFSI (manufactured by Nippon Shokubai Co., Ltd.) and sulfolane (manufactured by Kishida Chemical Co., Ltd.) melted at 35 ° C. are mixed, and a 1.5 mol / L LiFSI sulfolane solution (electrolytic solution 5) Was prepared.
Lithium bis (oxalato) borate (LiBOB) was added to the obtained electrolytic solution 5 so as to have a concentration shown in Table 2 to prepare electrolytic solutions 6 to 8.

(Positive electrode sheet 2)
A positive electrode sheet 2 is produced in the same manner as the positive electrode sheet except that a ternary oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) is used as the positive electrode active material instead of LiCoO _2. did.

(Production of coin-type lithium ion secondary battery)
The coin cell type lithium ion secondary batteries 5 to 7 are produced in the same manner as in the case of the batteries 1 to 4 except that the positive electrode sheet 2 and a cellulose separator are used as the separator, and the electrolytic solution having the composition shown in Table 2 below is used. did.

(Battery evaluation)
Using a charge / discharge test apparatus (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the discharge capacity of the coin cell type lithium ion secondary battery was measured in an environment at a temperature of 25 ° C. The charging / discharging conditions were as follows: 4.2V constant current / constant voltage charging at a charging rate of 0.2C was performed to a current amount of 0.02C, and then discharging was performed at a discharging rate of 0.2C until the voltage reached 3.0V. This charge / discharge at a charge rate of 0.2C was repeated 5 times. Next, charging and discharging were repeated 100 times under the same conditions as when the charging rate was 0.2 C, except that the charging rate was changed to 1 C and the discharging rate 1 C in an environment at a temperature of 60 ° C. Table 2 shows the discharge capacity after 100 cycles.

  The non-aqueous electrolyte of the present invention is useful as a non-aqueous electrolyte of a non-aqueous electrolyte secondary battery, and the lithium ion secondary battery of the present invention is useful as a power source for smartphones, personal computers, a power source for automobiles, etc. It is.

Claims (3)

A fluorosulfonylimide compound represented by the following general formula (1);

(In the general formula (1), M ⁺ represents an alkali metal ion, and X represents a fluorine atom or a fluoroalkyl group having 1 to 6 carbon atoms.)
A sulfone compound represented by the following general formula (2);

(In General Formula (2), R ¹ and R ² are the same or different and each represents a monovalent or divalent saturated aliphatic hydrocarbon group or aromatic hydrocarbon group, and R ¹ and R ² are bonded to each other. A ring may be formed.)
An oxalato compound represented by the following general formula (3);

(In General Formula (3), M ¹ is B or P, A ^{a +} is a metal ion, hydrogen ion, or onium ion, a is 1 to 3, b is 1 to 3, p is b / a, q is 1 to 3, m represents 0 to 4, n represents 0 or 1, R ³ represents fluorine, a cyano group or a C _{1 to} C ₁₀ fluorinated alkyl group, R ⁴ represents a C _{1 to} C ₁₀ alkylene group or C ₁ halogenated alkylene group ~C _10, X ^1, X ² represents O or S each independently.)
A non-aqueous electrolyte characterized by containing.   The nonaqueous electrolytic solution according to claim 1, comprising 0.01 to 10% by mass of the compound represented by the general formula (3).   A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to claim 1.