JP2016134283A - Nonaqueous electrolyte and power storage device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte capable of suppressing decomposition of a sulfonyl imide anion compound even when being stored at high temperatures of exceeding 100°C thereby to suppress deterioration in capacity, cycle characteristics and rate characteristics, as a battery, and a power storage device including the nonaqueous electrolyte.SOLUTION: A nonaqueous electrolyte of the present invention includes an anion represented by the following general formula (1) and a lithium cation. The nonaqueous electrolyte further includes 4 mass% or less of a radical scavenger and/or an oxidation-reduction stabilizer. [N(XSO)(FSO)](1) (In the general formula (1), X represents a fluorine atom, a 1-6C alkyl group or a 1-6C fluoroalkyl group.)SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte and an electricity storage device including the same.

  For example, lithium ion secondary batteries, which are representative of power storage devices, are used as power sources for smartphones and personal computers, and further as power sources for automobiles. In the batteries used for these applications, research aimed at improving various characteristics such as higher output, higher energy density, improved cycle characteristics and rate characteristics has been repeated.

  As a technique for trying to improve the characteristics of a lithium ion secondary battery from the viewpoint of the electrolytic solution, for example, a technique using an acid anhydride as an additive for a nonaqueous electrolytic solution has been proposed. Patent Document 1 discloses a technique for suppressing a decrease in high-temperature storage characteristics by adding benzoic anhydride, phthalic anhydride, or maleic anhydride to an electrolyte of a nonaqueous electrolyte secondary battery.

Japanese Patent No. 2697365

  As described above, various studies have been made on improving battery characteristics. However, with the expansion of applications, batteries are required to have higher energy density. In order to increase the energy density of the battery, it is necessary to drive the battery under a high voltage. However, when the battery is driven at a high voltage, there is a problem that the electrolyte solution is decomposed at the positive electrode or the transition metal in the positive electrode active material is eluted to deteriorate the cycle characteristics and rate characteristics of the battery. This problem is particularly noticeable when the lithium ion secondary battery is stored at a high temperature.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is to suppress the decomposition of the sulfonylimide anion compound even when stored at a high temperature exceeding 100 ° C. It is an object of the present invention to provide a nonaqueous electrolytic solution capable of suppressing deterioration of cycle characteristics and rate characteristics, and an electricity storage device (particularly a battery or a lithium ion secondary battery) using the same.

The non-aqueous electrolyte solution of the present invention that has achieved the above object is a non-aqueous electrolyte solution containing an anion represented by the following general formula (1) and a lithium cation, and the non-aqueous electrolyte solution comprises: Furthermore, it is characterized in that it contains 4.0% by mass or less of a radical scavenger and / or a redox stabilizer.
[N (XSO ₂ ) (FSO ₂ )] ^- (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.)

It is preferable that the non-aqueous electrolyte further includes at least one anion selected from the group consisting of anions represented by the following general formula (7) and general formula (8).
[PF _l (C _m F _{2m + 1} ) _6−l ] ⁻ (0 ≦ l ≦ 6, 1 ≦ m ≦ 4) (7)
[BF _n (C _o F _{2o + 1} ) _4-n ] ⁻ (0 ≦ n ≦ 4, 1 ≦ o ≦ 4) (8)

  In this case, the content of the anion represented by the general formula (1) in the non-aqueous electrolyte acid is the anion represented by the general formula (1), the general formula (7), and the general formula (8). It is preferable that it is 20 mol% or more in the total 100 mol% of anions represented by.

  The present invention also includes a battery and a lithium ion secondary battery provided with the non-aqueous electrolyte. As for the lithium ion secondary battery of this invention, it is desirable that a rated charging voltage is more than 4.2V.

  The nonaqueous electrolytic solution of the present invention can suppress decomposition of a compound having a sulfonylimide anion at a high temperature. For this reason, it is possible to suppress a decrease in capacity and rate characteristics after storage at high temperatures such as an electricity storage device (particularly a battery or a lithium ion secondary battery) having the non-aqueous electrolyte of the present invention, and to suppress a decrease in capacity maintenance rate during a high temperature cycle. Demonstrate the effect. Therefore, according to the nonaqueous electrolytic solution of the present invention, it is possible to provide an electricity storage device such as a lithium ion secondary battery or a lithium ion capacitor in which a decrease in capacity, rate characteristics, and cycle characteristics is suppressed.

  The inventors of the present invention have obtained the following knowledge as a result of intensive investigations to find out the cause of performance deterioration when stored at a high temperature exceeding 100 ° C. even in a battery having a sulfonylimide anion.

  The applicant of the present application has found that an electrolytic solution containing a lithium sulfonylimide compound is effective in improving storage characteristics at high temperatures (45 ° C. or higher) and has already filed an application (Japanese Patent Application No. 2013-209456). However, the effect is not sufficient under a higher temperature environment. Although the cause has not been clarified, the present inventors think that the battery performance may be reduced due to the decomposition of the electrolyte triggered by radicals generated in a small amount inside the electrolyte. It was.

  The inventors of the present invention have arrived at the present invention because they believe that if these radicals can be captured or stabilized, the decomposition of the electrolyte will be suppressed, leading to a decrease in battery performance. Hereinafter, the present invention will be described in detail.

1. Nonaqueous Electrolytic Solution The nonaqueous electrolytic solution of the present invention is represented by the general formula (1): [N (XSO ₂ ) (FSO ₂ )] ⁻ (in the general formula (1), X is a fluorine atom, 1 to 6 an alkyl group or a C1-C6 fluoroalkyl group), a lithium cation, a radical scavenger and / or a redox agent. It is characterized by including a mold stabilizer.

1-1. Sulfonylimido anion (1)
The sulfonylimide anion (1) according to the present invention is represented by the general formula (1): [N (XSO ₂ ) (FSO ₂ )] ⁻ . In General Formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group. The alkyl group having 1 to 6 carbon atoms is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group. Examples of the fluoroalkyl group having 1 to 6 carbon atoms include those in which some or all of the hydrogen atoms of the alkyl group having 1 to 6 carbon atoms are substituted with fluorine atoms. Specific examples include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, and a pentafluoroethyl group. Among these, a fluorine atom, a trifluoromethyl group, and a pentafluoroethyl group are preferable as X.

  Specific examples of the sulfonylimide anion (1) include bis (fluorosulfonyl) imide anion, (fluorosulfonyl) (methylsulfonyl) imide anion, (fluorosulfonyl) (ethylsulfonyl) imide anion, (fluorosulfonyl) (tri Fluoromethylsulfonyl) imide anion, (fluorosulfonyl) (pentafluoroethylsulfonyl) imide anion, and the like. Preferred are bis (fluorosulfonyl) imide anion, (fluorosulfonyl) (trifluoromethylsulfonyl) imide anion, (fluorosulfonyl) (pentafluoroethylsulfonyl) imide anion, more preferably bis (fluorosulfonyl) imide anion, ( Fluorosulfonyl) (trifluoromethylsulfonyl) imide anion.

  The nonaqueous electrolytic solution of the present invention may contain one sulfonylimide anion (1) alone, or may contain two or more sulfonylimide anions (1).

  In the non-aqueous electrolyte of the present invention, the sulfonylimide anion (1) is present dissociated from the cation, but before being dispersed and dissolved in the non-aqueous electrolyte, it is in a state of a salt ion-bonded with the cation. Exists. The electrolyte solution of the present invention may contain other cations as long as lithium cations are essential, and may contain inorganic cations other than lithium.

  The sulfonylimide compound containing the sulfonylimide anion (1) can function as an electrolyte salt in the nonaqueous electrolytic solution of the present invention, or can function as an additive for improving battery performance. Is possible. That is, when the sulfonylimide compound containing the sulfonylimide anion (1) is, for example, a lithium salt, it can function as an electrolyte salt of an electrolytic solution used for a lithium battery or the like.

Examples of inorganic cations include monovalent inorganic cations such as Li ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , and Pb ⁺ ; Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Pd ²⁺ , Sn ²⁺ , Hg ²⁺ Divalent inorganic cations such as Rh ²⁺ , Cu ²⁺ , Be ²⁺ , Sr ²⁺ , and Ba ²⁺ ; and trivalent inorganic cations such as Ga ³⁺ . Among these, an alkali metal cation and an alkaline earth metal cation are preferable, and Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ are more preferable because they have a small ionic radius and can be easily used for batteries and the like, and Li ⁺ is particularly preferable.

  Examples of the sulfonylimide compound (a compound having a sulfonylimide anion (1)) that dissociates in a nonaqueous electrolytic solution to generate a sulfonylimide anion (1) include the sulfonylimide anion (1) and lithium described above, Any combination with a cation may be used. For example, lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (methylsulfonyl) imide, lithium (fluorosulfonyl) (ethylsulfonyl) imide, lithium (fluorosulfonyl) (trifluoro Methylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide and the like.

  A sulfonylimide compound may be used individually by 1 type, and may be used in combination of 2 or more type. As the sulfonylimide compound, a commercially available product may be used, or a product synthesized by a conventionally known method may be used.

1-2. Other Anions The nonaqueous electrolytic solution of the present invention may further contain at least one anion selected from the group consisting of anions represented by the following general formula (7) and general formula (8).
[PF _l (C _m F _{2m + 1} ) _6−l ] ⁻ (0 ≦ l ≦ 6, 1 ≦ m ≦ 4) (7)
[BF _n (C _o F _{2o + 1} ) _4-n ] ⁻ (0 ≦ n ≦ 4, 1 ≦ o ≦ 4) (8)

Examples of the anion represented by the general formula (7) (hereinafter sometimes referred to as anion (7)) include PF ₆ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , PF ₃ (C ₃ F ₇ ) ₃ ⁻ , PF ₃ (C ₄ F ₉ ) ₃ ^{− and the} like are preferable. More preferred are PF ₆ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ^— , and even more preferred is PF ₆ ^— .

Examples of the anion represented by the general formula (8) (hereinafter sometimes referred to as anion (8)) include BF ₄ ⁻ , BF (CF ₃ ) ₃ ⁻ , BF (C ₂ F ₅ ) ₃ ⁻ , BF ( C ₃ F ₇ ) _3- ^{and the} like are preferred, BF ₄ ^- and BF (CF ₃ ) ₃ ^- are more preferred, and BF ₄ ^- is more preferred.

  In the non-aqueous electrolyte, the content of the sulfonylimide anion is 20 mol% or more in a total of 100 mol% of the sulfonylimide anion and the anions represented by the general formula (7) and the general formula (8). preferable. The content of the sulfonylimide anion is more preferably 30 mol% or more, and further preferably 50 mol% or more of the total anion amount.

The nonaqueous electrolytic solution of the present invention may further contain other anions. Other anions include trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ), perchlorate ion (ClO ₄ ⁻ ), tetracyanoborate ion ([B (CN) ₄ ] ⁻ ), tetrachloroaluminum ion ( AlCl ₄ ⁻ ), tricyanomethide ion (C [(CN) ₃ ] ⁻ ), dicyanamide ion (N [(CN) ₂ ] ⁻ ), tris (trifluoromethanesulfonyl) methide ion (C [(CF ₃ SO ₂ ) ₃ ] ⁻ ), hexafluoroantimonate ion (SbF ₆ ⁻ ), dicyanotriazolate ion (DCTA) and the like.

  These anions can be used by being combined with a cation exemplified as a counter cation of a sulfonylimide anion and being included in a non-aqueous electrolyte as an electrolyte salt.

  Although the total amount of the electrolyte salt (a compound having a sulfonylimide anion, a compound having an anion (7), a compound having an anion (8) and another electrolyte salt) in the nonaqueous electrolytic solution of the present invention is not particularly limited. 0.5 mol / L or more, more preferably 0.6 mol / L or more, still more preferably 0.8 mol / L or more, and preferably 5 mol / L or less, more preferably It is 2.5 mol / L or less, more preferably 1.5 mol / L or less. If the concentration of the electrolyte salt in the non-aqueous electrolyte is too high, the electrolyte salt may be deposited at a low temperature. On the other hand, if the concentration is too low, battery performance may be inferior.

1-3. Lithium cation The non-aqueous electrolyte of the present invention contains a lithium cation. The lithium cation may be derived from a sulfonylimide compound or may be derived from the above electrolyte salt. The concentration of the lithium cation contained in the nonaqueous electrolytic solution of the present invention is preferably 0.5 mol / L or more. The lithium cation concentration of the nonaqueous electrolytic solution of the present invention is more preferably 0.6 mol / L or more, and further preferably 0.8 mol / L or more. If the lithium cation concentration is too high, the viscosity of the electrolytic solution increases and the ionic conductivity may decrease. Therefore, the lithium cation concentration is preferably used at a saturation concentration or less. More preferably, it is 5.0 mol / L or less, More preferably, it is 2.5 mol / L or less, Most preferably, it is 1.5 mol / L or less.

  Here, the “concentration of lithium cations in the non-aqueous electrolyte” is a value based on the total amount of lithium cations contained in the non-aqueous electrolyte of the present invention. For example, an electrolyte salt having two or more lithium cations is used. If used, the total amount of lithium cations generated from the electrolyte salt used, and if the sulfonylimide compound contains a lithium cation, it is included in the electrolyte salt used in combination with the lithium cation contained in the sulfonylimide compound. The value obtained based on the total amount with the lithium cation is defined as the concentration of the lithium cation in the non-aqueous electrolyte. When the sulfonylimide compound does not contain lithium cations, the total concentration of electrolyte salts (containing lithium cations) used in combination may be considered as the lithium cation concentration.

1-4. Radical scavenger and / or oxidation-reduction type stabilizer The nonaqueous electrolytic solution of the present invention contains a radical scavenger and / or a oxidation-reduction type stabilizer in the range of 4% by mass or less. By adding these compounds, at the time of high-temperature storage or application of high pressure, the radicals generated by the decomposition of the solvent and the sulfonylimide anion compound are captured and / or stabilized, and further decomposition of the sulfonylimide anion compound is suppressed, Suppresses deterioration of battery characteristics. However, in order to trap and / or stabilize radicals, the radical scavenger and / or oxidation-reduction type stabilizer is sufficient to be 4% by mass or less, and if added more than that, the battery characteristics itself deteriorates. Then, it shall be 4 mass% or less.

  The amount of the radical scavenger and / or the redox stabilizer is preferably 3% by mass or less, more preferably 2% by mass or less, and particularly preferably 1% by mass or less, in 100% by mass of the non-aqueous electrolyte. The nonaqueous electrolytic solution only needs to contain a radical scavenger and / or a redox stabilizer, and the lower limit is not particularly limited, but is preferably 0.01% by mass or more, and 0.1% by mass The above is more preferable, and 0.5% by mass or more is more preferable.

1-4-1. Radical scavenger Any radical scavenger can be used as long as it is known to be capable of scavenging radicals. For example, an antioxidant, a flame retardant, etc. are mentioned.

  The antioxidant is not particularly limited as long as it is normally used as an antioxidant, but a phenol-based antioxidant, a diphenylamine-based antioxidant, a phosphite-based antioxidant, and a thioether-based antioxidant are used. It is preferable.

  Examples of the phenolic antioxidant include 2,6-di-tert-butyl-p-cresol, 2,6-diphenyl-4-octadecyloxyphenol, stearyl (3,5-di-tert-butyl- 4-hydroxyphenyl) propionate, distearyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate, tridecyl-3,5-di-tert-butyl-4-hydroxybenzylthioacetate, thiodiethylenebis [ (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 4,4′-thiobis (6-tert-butyl-m-cresol), 2-octylthio-4,6-di (3,5 -Di-tert-butyl-4-hydroxyphenoxy) -s-triazine, 2,2'-methylenebis 4-methyl-6-tert-butylphenol), bis [3,3-bis (4-hydroxy-3-tert-butylphenyl) butyric acid] glycol ester, 4,4′-butylidenebis (2,6-di-) tert-butylphenol), 4,4-butylidenebis- (6-tert-butyl-3-methylphenol), 2,2′-ethylidenebis (4,6-di-tert-butylphenol), 1,1,3-tris (2-Methyl-4-hydroxy-5-tert-butylphenyl) butane, bis [2-tert-butyl-4-methyl-6- (2-hydroxy-3-tert-butyl-5-methylbenzyl) phenyl] Terephthalate, 1,3,5-tris (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanur 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxy Benzyl) -2,4,6-trimethylbenzene, 1,3,5-tris [(3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxyethyl] isocyanurate, tetrakis [methylene-3- ( 3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl) propionate] methane, 2-tert-butyl-4-methyl-6- (2-acryloyloxy-3-tert-butyl-5-methyl) Benzyl) phenol, 3,9-bis [2- (3-tert-butyl-4-hydroxy-5-methylhydrocinnamoyloxy) -1,1-dimethyl Ethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, triethylene glycol bis [β- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate] and the like. .

  Examples of the diphenylamine antioxidant include diphenylamine, p, p′-dibutyldiphenylamine, p, p′-di-tert-butyldiphenylamine, p, p′-dipentyldiphenylamine, p, p′-dihexyldiphenylamine, and p. , P′-diheptyldiphenylamine, p, p′-dioctyldiphenylamine, p, p′-dinonyldiphenylamine, monooctyldiphenylamine, monononyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, carbon 4-9 mixed alkyldiphenylamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, 4-n-butylaminophenol, -Butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol, 4-octadecanoylaminophenol, di (4-methoxyphenyl) amine, 2,6-di-tert-butyl-4-dimethyl Aminomethylphenol, 2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, N, N, N ′, N′-tetramethyl-4,4′-diaminodiphenylmethane, 1,2-di [(2- Methylphenyl) amino] ethane, 1,2-di (phenylamino) propane, (o-tolyl) niguanide, di [4- (1 ′, 3′-dimethylbutyl) phenyl] amine, tert-octylated N-phenyl -1-naphthylamine, styrenated diphenylamine, phenothiazine, 10-methylphenothia Down, 2-methyl-phenothiazine, 2-trifluoromethyl phenothiazine, Fenozajin and the like.

  Examples of the phosphite antioxidant include triphenyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, tris (2,5-di-tert-butylphenyl) phosphite, and tris. (Nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (mono-dimixed nonylphenyl) phosphite, diphenyl acid phosphite, 2,2'-methylenebis (4,6-di-tert-butylphenyl) ) Octyl phosphite, diphenyl decyl phosphite, diphenyl octyl phosphite, di (nonylphenyl) pentaerythritol diphosphite, phenyl diisodecyl phosphite, tributyl phosphite, tris (2-ethylhexyl) phosphite, tridecyl phosphite Phyto, trilauryl phosphite, dibutyl acid phosphite, dilauryl acid phosphite, trilauryl trithiophosphite, bis (neopentyl glycol) -1,4-cyclohexanedimethyl diphosphite, bis (2,4-di-tert) -Butylphenyl) pentaerythritol diphosphite, bis (2,5-di-tert-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphos Phyto, bis (2,4-dicumylphenyl) pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, tetra (mixed alkyl having 12 to 15 carbon atoms) -4,4'-isopropylidene diphenylphospha Bis [2,2′-methylenebis (4,6-diamilphenyl)] isopropylidenediphenyl phosphite, tetratridecyl-4,4′-butylidenebis (2-tert-butyl-5-methylphenol) diphosphite, Hexa (tridecyl) -1,1,3-tris (2-methyl-5-tert-butyl-4-hydroxyphenyl) butane-triphosphite, tetrakis (2,4-di-tert-butylphenyl) biphenylene diphosphonite Tris (2-[(2,4,7,9-tetrakis-tert-butyldibenzo [d, f] [1,3,2] dioxaphosphin-6-yl) oxy] ethyl) amine, 9 , 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-butyl-2-ethylpro Pandiol-2,4,6-tri-tert-butylphenol monophosphite, tetrakis (2-tert-butyl-4-methylphenyl) biphenylenediphosphonite, tetrakis (2,4-di-tert-amylphenyl) biphenyl Examples thereof include rangephosphonite, tetrakis (2,4-di-tert-butyl-5-methylphenyl) biphenylene diphosphonite, tetrakis (2-tert-butyl-4,6-dimethylphenyl) biphenylene diphosphonite, and the like.

  Examples of the thioether-based antioxidant include dialkylthiodipropionates such as dilauryl ester, dimyristyl ester, myristyl stearyl ester, distearyl ester of thiodipropionic acid; pentaerythritol tetra (β-dodecyl mercaptopropio) Β-alkyl mercaptopropionic acid esters of polyols such as nate).

  Examples of the flame retardant include bromine-based flame retardant and phosphorus-based flame retardant.

  Examples of brominated flame retardants include tetrabromobisphenol A, decabromodiphenyl ether, tribromophenol, hexabromocyclododecane, ethylenebis (tetrabromophthalimide), bis (pentabromophenyl) ethane, hexabromobenzene, and the like.

  Phosphorus flame retardants include trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl phenyl phosphate, 2-ethylhexyl diphenyl phosphate, tris (Dichloropropyl) phosphate, cyclic phosphazene compounds and the like.

1-4-2. Redox stabilizer As the redox stabilizer, for example, any of the compounds described as overcharge control agents in JP2012-256502A can be used. As the redox stabilizer, 1,2-dimethoxy-4-bromobenzene and 2,4-difluoroanisole are particularly preferable. In addition, although the compound shown by this Unexamined-Japanese-Patent No. 2012-256502 is disclosed using 5 mass% in 100 mass% of non-aqueous electrolytes, the effect as an overcharge inhibitor is expressed. There is no description about stabilizing radicals during high-temperature storage. Moreover, when 5 mass% is added, the battery characteristic itself will fall.

1-5. Solvent The nonaqueous electrolytic solution of the present invention may contain a solvent. The solvent that can be used in the non-aqueous electrolyte of the present invention is not particularly limited as long as it can dissolve and disperse electrolyte salts (sulfonylimide compounds and the above-described lithium salts). Conventionally known solvents used for batteries, such as non-aqueous solvents such as solvents other than cyclic carbonates and media such as polymers and polymer gels used in place of solvents, can be used.

  As the non-aqueous solvent, a solvent having a large dielectric constant, high solubility of the electrolyte salt, a boiling point of 60 ° C. or higher, 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, Ethers such as 1,4-dioxane and 1,3-dioxolane; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate and methyl phenyl carbonate; Ethylene (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate (2,3-butanediyl carbonate), carbonic acid 1,2 Saturated cyclic carbonates such as butylene and erythritan carbonate; vinylene carbonate, methyl vinylene carbonate (MVC; 4-methyl-1,3-dioxol-2-one), ethyl vinylene carbonate (EVC; 4-ethyl-1,3) -Dioxol-2-one), 2-vinylethylene carbonate (4-vinyl-1,3-dioxolan-2-one) and phenylethylene carbonate (4-phenyl-1,3-dioxolan-2-one) Cyclic carbonates having a saturated bond; fluorine-containing cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate and trifluoropropylene carbonate; aromatic carboxylic esters such as methyl benzoate and ethyl benzoate; γ-butyrolactone, γ-valerola Lactones such as t and δ-valerolactone; phosphate esters such as trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, triethyl phosphate; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, Nitriles such as adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; sulfur compounds such as dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane Aromatic nitriles such as benzonitrile and tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3-methyl-2-oxazo Lysinone and the like can be mentioned.

  Among these, carbonate esters (carbonate solvents) such as chain carbonate esters and cyclic carbonate esters, lactones, and ethers are preferable. Dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, γ -Butyrolactone, γ-valerolactone, and the like are more preferable, and carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate are more preferable. The said non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  When the polymer or polymer gel is used in place of a solvent, the following method may be employed. That is, a method in which a solution in which an electrolyte salt is dissolved in the above-mentioned non-aqueous solvent is dropped onto a polymer formed by a conventionally known method so that the electrolyte salt and the non-aqueous solvent are impregnated and supported; In this method, the polymer and the electrolyte salt are melted and mixed, and then formed into a film and impregnated with a non-aqueous solvent (hereinafter referred to as a gel electrolyte); a non-aqueous electrolyte solution in which the electrolyte salt is previously dissolved in an organic solvent and the polymer After mixing, 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 at a temperature equal to or higher than the melting point of the polymer, and mixed to form (the intrinsic polymer electrolyte) );

  Polymers used in place of solvents include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide which are homopolymers or copolymers of epoxy compounds (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.) , Methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluorinated polymers such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof Etc.

  In addition, it is recommended to use a cyclic carbonate as a solvent from the viewpoint of preventing degradation of the solvent and suppressing deterioration of cycle characteristics (life) when the non-aqueous electrolyte of the present invention is used in a lithium ion secondary battery. Is done. Examples of the cyclic carbonate include the above-described saturated cyclic carbonate, cyclic carbonate having an unsaturated bond, and fluorine-containing cyclic carbonate. Among these, saturated cyclic carbonate is preferable from the viewpoint of cost, and ethylene carbonate and propylene carbonate are particularly preferable. A cyclic carbonate may be used individually by 1 type, or may be used in combination of 2 or more type.

The cyclic carbonate is preferably used in such a range that the molar ratio (cyclic carbonate / Li ⁺ ) to all lithium cations contained in the non-aqueous electrolyte is 1 or more and 5 or less. When the cyclic carbonate is used within the above range, the deterioration of the cycle characteristics (life) of the lithium ion secondary battery is further suppressed.

  It is known that one cause of deterioration of the cycle characteristics is decomposition of a solvent constituting the non-aqueous electrolyte. However, deterioration of cycle characteristics can be further suppressed by setting the amount of cyclic carbonate used within the above range with respect to lithium ions. By determining the amount of cyclic carbonate used according to the amount of lithium ions, the amount of cyclic carbonate (free cyclic carbonate) that is not solvated with lithium ions present in the non-aqueous electrolyte can be reduced. That is, since the amount of free cyclic carbonate that can participate in the decomposition reaction is reduced, the decomposition reaction of the solvent is less likely to occur, and the deterioration of the cycle characteristics is suppressed.

When the molar ratio (cyclic carbonate / Li ⁺ ) is too large, free cyclic carbonate excessively present in the nonaqueous electrolytic solution is oxidized and / or reductively decomposed, resulting in deterioration of cycle characteristics. On the other hand, when the molar ratio is too small, the amount of cyclic carbonate is too small, and effects derived from the cyclic carbonate (for example, an effect of forming a film on the negative electrode and suppressing decomposition of the non-aqueous electrolyte) are obtained. In addition, there is a possibility that the non-aqueous electrolyte may become dry due to solvent consumption (film formation, decomposition, etc.) due to repeated charge and discharge. Therefore, the cyclic carbonate is more preferably used in a molar ratio to the lithium ion (cyclic carbonate / Li ⁺ ) in the range of 1 or more, 4 or less, more preferably 3 or less, and particularly preferably 2.0 or less. Yes, and most preferably 1.8 or less.

The molar ratio of cyclic carbonate to lithium cation (cyclic carbonate / Li ⁺ ) may be calculated based on the specific gravity and molar mass of cyclic carbonate. For example, in the case of ethylene carbonate, the specific gravity is 1.321 and the molar mass is 88.06.

  Even when a cyclic carbonate is used, the nonaqueous electrolytic solution may contain a solvent (other solvent) other than the cyclic carbonate. Examples of the other solvent include the above-described non-aqueous solvents (other than cyclic carbonate). Among the non-aqueous solvents, chain carbonic acid esters, aliphatic carboxylic acid esters, lactones, and ethers are preferable, and dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone, and the like are more preferable. . The said other solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  In this case, the amount of the other solvent used is preferably 50% by volume or more, more preferably 55% by volume or more, and further preferably 60% by volume based on 100% by volume of the total amount of the cyclic carbonate and the other solvent. % Or more, preferably 99% by volume or less, more preferably 95% by volume or less, and still more preferably 90% by volume or less.

1-6. Other Components The nonaqueous electrolytic solution according to the present invention may contain an additive for the purpose of improving various characteristics of the lithium ion secondary battery.
Additives include acetic anhydride, propionic anhydride, butyric anhydride, crotonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid Carboxylic anhydrides such as acid anhydrides and cyclopentanetetracarboxylic dianhydrides; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, Sulfur-containing compounds such as tetramethylthiuram monosulfide and trimethylene glycol sulfate; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazo Lydinone, N-methyls Nitrogen-containing compounds such as Shin'imido; monofluorophosphate, phosphates such as difluoro phosphate; heptane, octane, saturated hydrocarbon compounds cycloheptane and the like; and the like.

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 the effect derived from the additive. There is a possibility that the viscosity of the non-aqueous electrolyte increases and the conductivity decreases.
In addition, 100 mass% of nonaqueous electrolyte solution means the sum total of all the components contained in a nonaqueous electrolyte solution, such as the sulfonylimide compound mentioned above, electrolyte salt, a solvent, and the additive used suitably.

2. Electric storage device The non-aqueous electrolyte of the present invention is used as an ion conductive material provided in various electric storage devices such as a primary battery, a lithium ion secondary battery, a lithium ion capacitor, a battery having a charging and discharging mechanism, and a fuel cell. Can do. Below, a lithium ion secondary battery is demonstrated on behalf of these.
The lithium ion secondary battery includes a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte. More specifically, a separator is provided between the positive electrode and the negative electrode, and the non-aqueous electrolyte is contained in the outer case together with the positive electrode, the negative electrode, and the like in a state of being impregnated in the separator. The lithium ion secondary battery of the present invention includes the above-described nonaqueous electrolytic solution of the present invention.

2-1. Positive electrode The positive electrode is formed by supporting a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder and the like 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, the positive electrode active material, the conductive auxiliary agent, the binder, and the solvent used in the positive electrode active material composition (solvent for dispersing or dissolving the positive electrode mixture) is not particularly limited. A material can 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. For example, each material described in JP-A-2014-13704 can be used.

2-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. There is no restriction | limiting in particular in a separator, In this invention, all the conventionally well-known separators can be used, For example, each material as described in Unexamined-Japanese-Patent No. 2014-13704 can be used.

2-4. Battery exterior materials Battery elements equipped with a positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. are housed in battery exterior materials to protect the battery elements from external impacts and environmental degradation when using lithium ion secondary batteries. The 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 lithium ion secondary battery according to the present invention is not particularly limited, and any conventionally known shape can be used as the shape of the lithium ion secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. Can do. 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 lithium ion secondary battery of the present invention is not particularly limited, but is preferably over 4.2V. 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 4.6 V or less. More preferably, it is 4.5 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.

1. Preparation of non-aqueous electrolyte Lithium bis (fluorosulfonyl) imide (LiFSI) is 1.0 mol / L as a compound that produces sulfonylimide anion (1) in propylene carbonate (PC) in non-aqueous electrolyte. Dissolved in.

  This non-aqueous electrolyte was designated as No.1. 0. This non-aqueous electrolyte No. 0, 4% by weight of phenolic antioxidant 2,6-di-tert-p-cresol was added to non-aqueous electrolyte No. Set to 1. Non-aqueous electrolyte No. 2 is non-aqueous electrolyte No.2. 0, 4% by mass of phenothiazine (diphenylamine antioxidant) added to non-aqueous electrolyte No. 3 is a non-aqueous electrolyte No. 3. 0, 4% by mass of decabromodiphenyl ether (brominated flame retardant), non-aqueous electrolyte No. 4 is a non-aqueous electrolyte No. 4; 0, triphenyl phosphate (phosphorus flame retardant) added in an amount of 4% by mass; No. 5 is a non-aqueous electrolyte No. 0, 1,2-dimethoxy-4-bromobenzene (redox stabilizer) added in an amount of 4% by mass; 6 is a non-aqueous electrolyte No. 0 to 4,4% by mass of 2,4-difluoroanisole (redox stabilizer).

These electrolytes were heated at 125 ° C. for 4 hours, and then LiFSI was quantitatively analyzed by ¹⁹ F-NMR. ^{For 19} F-NMR, the structure of the sample was analyzed based on the peak intensity of fluorine using “Unity Plus” (400 MHz) manufactured by Varian. The ¹⁹ F-NMR spectrum was measured by dissolving each non-aqueous electrolyte in deuterated dimethyl sulfoxide, placing it in a glass NMR tube, and measuring the temperature at room temperature (25 ° C.) and 64 times. In the measurement of ¹⁹ F-NMR spectrum, trifluoromethylbenzene was used as a standard substance.

^From the results of ¹⁹ F-NMR, non-aqueous electrolyte No. The residual ratio of LiFSI at 0 was 95% by mass. On the other hand, non-aqueous electrolyte No. 1-No. In all cases, the residual rate of LiFSI was 100% by mass (not decomposed at all). The results are summarized in Table 1.

Claims (6)

A non-aqueous electrolytic solution containing an anion represented by the following general formula (1) and a lithium cation, wherein the non-aqueous electrolytic solution further contains 4 masses of a radical scavenger and / or a redox stabilizer. % Non-aqueous electrolyte characterized by including below.
[N (XSO ₂ ) (FSO ₂ )] ^- (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.) The nonaqueous electrolytic solution according to claim 1, wherein the nonaqueous electrolytic solution further contains at least one kind of anion selected from the group consisting of the anions represented by the following general formula (7) and general formula (8). .
[PF _l (C _m F _{2m + 1} ) _6−l ] ⁻ (0 ≦ l ≦ 6, 1 ≦ m ≦ 4) (7)
[BF _n (C _o F _{2o + 1} ) _4-n ] ⁻ (0 ≦ n ≦ 4, 1 ≦ o ≦ 4) (8)   The content of the anion represented by the general formula (1) in the non-aqueous electrolyte acid is represented by the anion represented by the general formula (1), the general formula (7), and the general formula (8). The nonaqueous electrolytic solution according to claim 1, wherein the amount is 20 mol% or more in a total of 100 mol% of anions.   A battery comprising the nonaqueous electrolytic solution according to claim 1.   A lithium ion secondary battery comprising the nonaqueous electrolytic solution according to claim 1.   The lithium ion secondary battery according to claim 5, wherein the rated charging voltage is over 4.2V.