JP2018088362A - Electrolytic solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel electrolytic solution capable of contributing to excellent battery characteristics.SOLUTION: The present invention relates to an electrolytic solution containing an electrolyte containing lithium salt represented by following general formula (1), an organic solvent containing linear carbonate represented by following general formula (2), non-saturated cyclic carbonate and an organic compound represented by any one of following general formulas (3-1) to (3-5), wherein (RX)(RSO)NLi, is defined as the general formula (1), ROCOORis defined as the general formula (2), Ar-(CRRR)is defined as the general formula (3-1), Ar-(Ar)is defined as the general formula (3-2), Ar-(Y-R)is defined as the general formula (3-3), Cy-(Y-R)is defined as the general formula (3-4), and RRRC-COORis defined as the general formula (3-5). The electrolytic solution is also characterized in that the linear carbonate is contained in a molar ratio of 3 to 6 in relative to the lithium salt.SELECTED DRAWING: None

Description

  The present invention relates to an electrolytic solution used in a power storage device such as a secondary battery.

In general, a power storage device such as a secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution as main components. An appropriate electrolyte is added to the electrolytic solution in an appropriate concentration range. For example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, or (CF ₃ SO ₂ ) ₂ NLi is added as an electrolyte to the electrolyte solution of a lithium ion secondary battery. Here, the concentration of the lithium salt in the electrolytic solution is generally about 1 mol / L.

  In addition, in order to dissolve the electrolyte suitably, an organic solvent having a high relative dielectric constant and dipole moment, such as ethylene carbonate and propylene carbonate, is mixed and used at about 30% by volume or more for the organic solvent used in the electrolytic solution. It is common.

Actually, Patent Document 1 discloses a lithium ion secondary battery using a mixed organic solvent containing 33% by volume of ethylene carbonate and using an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L.

Patent Document 2 discloses a lithium ion secondary battery using a mixed organic solvent containing 66% by volume of ethylene carbonate and propylene carbonate and using an electrolytic solution containing (CF ₃ SO ₂ ) ₂ NLi at a concentration of 1 mol / L. Is disclosed.

  In addition, for the purpose of improving the performance of the secondary battery, researches for adding various additives to an electrolytic solution containing a lithium salt have been actively conducted.

For example, Patent Document 3 describes an electrolytic solution using a mixed organic solvent containing 30% by volume of ethylene carbonate and adding a small amount of a specific additive to an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L. It is disclosed that a lithium ion secondary battery using this electrolytic solution is excellent in high-temperature storage characteristics.

Also in Patent Document 4, electrolysis using a mixed organic solvent containing 30% by volume of ethylene carbonate and adding a small amount of phenyl glycidyl ether as a hydrogen fluoride scavenger to a solution containing LiPF ₆ at a concentration of 1 mol / L. A lithium ion secondary battery using this electrolytic solution is disclosed.

  In addition, the secondary battery has a problem related to so-called overcharge in which further charging proceeds even though the secondary battery is fully charged. When the secondary battery is overcharged, the components of the secondary battery such as the positive electrode, negative electrode, electrolyte and separator are decomposed or altered, resulting in excessive heat generation or short-circuiting of the positive and negative electrodes. there's a possibility that.

  As a method for suppressing the overcharge of the secondary battery, it has been proposed to add an overcharge inhibitor into the electrolytic solution. And in many literatures, it is reported that the use of cyclohexylbenzene or biphenyl as an overcharge inhibitor and the use of these overcharge inhibitors confirmed the generation of a film-like polymer and gas during overcharge. ing.

  The following Patent Documents 5 to 14 describe the use of various compounds similar to the chemical structure of cyclohexylbenzene or biphenyl as an overcharge inhibitor. Also, many literatures have reported lithium ion secondary batteries including a current interrupt device that interrupts a current path when the internal pressure of the lithium ion secondary battery increases.

  Patent Document 5 states that the voltage of the secondary battery is kept constant even during overcharge due to the presence of aromatic compounds such as benzene compounds, biphenyl compounds, benzodioxane, indoline having an electron donating group. Is described.

  Patent Document 6 describes that the presence of 3-chlorothiophene, furan, 1,2-dimethoxybenzene, biphenyl, and the like increases the internal resistance of the battery during overcharge, thereby protecting the battery.

  Patent Document 7 describes that the presence of a biphenyl compound having an electron donating group such as 4-methylbiphenyl increases the internal resistance of the battery during overcharge and suppresses heating of the battery.

  Patent Document 8 describes that due to the presence of tert-butylbenzene or the like, current is interrupted during overcharge, and heating of the battery is suppressed.

  Patent Document 9 describes that a compound in which a 1,1,1,3,3,3-hexafluoro-2-propyl group is bonded to a benzene ring is a suitable overcharge inhibitor.

  In Patent Document 10, 1,4-dialkoxy-2,5-dihalogenbenzene is capable of a reversible oxidation-reduction reaction (so-called redox shuttle reaction), and 1,4-dialkoxy-2,5. -It is described that a battery containing dihalogen benzene suppresses an increase in voltage during overcharge due to the redox shuttle reaction.

  Patent Document 11 discloses that a compound in which an adamantyl group is bonded to a benzene ring can undergo a redox shuttle reaction, and a battery containing the compound suppresses an increase in voltage during overcharge due to the redox shuttle reaction. It is described that.

  Patent Document 12 describes a large number of aromatic compounds, and describes that a battery containing these aromatic compounds generates gas when overcharged. Then, it is described that a long-term overcharge state can be avoided by arranging an overcharge prevention device that detects an increase in the internal pressure of the battery and interrupts charging in the battery having the aromatic compound. ing.

  Patent Document 13 describes a large number of ester compounds, and describes that these ester compounds can generate carbon dioxide and hydrogen gas when the battery is overcharged. And it is described that a long-time overcharge state can be avoided by arranging an overcharge prevention device that detects an increase in internal pressure of the battery and interrupts charging.

  Patent Document 14 describes a large number of ether compounds, and describes that these ether compounds generate hydrogen gas when the battery is overcharged. Then, it is described that a long-term overcharge state can be avoided by arranging an overcharge prevention device that detects an increase in the internal pressure of the battery and interrupts the charge in the battery having the ether compound. Yes.

Recently, Patent Document 15 and Patent Document 16 reported an electrolytic solution containing a metal salt as an electrolyte in a high concentration and a lithium ion secondary battery including the electrolytic solution.

JP 2013-149477 A JP2013-134922A JP 2013-145724 A JP2013-137873A JP-A-7-302614 JP-A-9-106835 Japanese Patent Laid-Open No. 2001-210364 International Publication No. 2002/029922 JP2013-93320A JP 2013-171659 A JP2013-171715A JP 2014-192153 A JP 2015-18667 A JP 2015-26587 A International Publication No. 2015/045389 International Publication No. 2016/063468

  As described in Patent Documents 1 to 4, conventionally, in an electrolytic solution used for a lithium ion secondary battery, an organic solvent having a high relative dielectric constant and dipole moment such as ethylene carbonate and propylene carbonate is about 30% by volume or more. It has become common technical knowledge to use a mixed organic solvent and to contain a lithium salt at a concentration of approximately 1 mol / L. And as described in Patent Documents 3 to 4, the improvement of the electrolytic solution is generally performed by paying attention to an additive separate from the lithium salt.

  However, there is a demand from the industry to further improve the performance of power storage devices such as lithium ion secondary batteries. The present invention has been made in view of such circumstances, and an object thereof is to provide a new electrolytic solution that can contribute to excellent battery characteristics.

  The present inventor has studied to improve the electrolytic solution described in Patent Document 16. For the purpose of improving battery characteristics, when manufacturing and evaluating a lithium ion secondary battery including an electrolytic solution to which vinylene carbonate, which is an unsaturated cyclic carbonate, is added, the inventors have found that the resistance of this battery increases. confirmed. In addition, for the purpose of preventing overcharge, a lithium ion secondary battery comprising an electrolytic solution to which cyclohexylbenzene, which is an overcharge inhibitor, is manufactured and evaluated, the resistance of this battery also increases. Confirmed. However, when manufacturing and evaluating a lithium ion secondary battery including an electrolytic solution to which both vinylene carbonate and cyclohexylbenzene were added, the present inventor found that an increase in resistance was suppressed for this battery. . Based on this discovery, the present inventor has completed the present invention.

The electrolytic solution of the present invention includes an electrolyte containing a lithium salt represented by the following general formula (1), an organic solvent containing a chain carbonate represented by the following general formula (2), an unsaturated cyclic carbonate, An organic compound represented by any one of the general formulas (3-1) to (3-5),
The chain carbonate is contained in a molar ratio of 3 to 6 with respect to the lithium salt.
(R ¹ X ¹ ) (R ² SO ₂ ) NLi General formula (1)
(R ¹ is hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted with, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, or an alkoxy group which may be substituted with a substituent , An unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, or OCN Is done.
R ² represents hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN The
R ¹ and R ² may be bonded to each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, Si = O.
R ^a and R ^b are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^a and R ^b may combine with R ¹ or R ² to form a ring. )
R ²⁰ OCOOR ²¹ general formula (2)
(R ²⁰ and R ²¹ each independently represent C _n H _a F _b Cl _c Br _d I _e which is a chain alkyl, or C _m H _f F _g Cl _h Br _i I containing a cyclic alkyl in the chemical structure. selected from _j , n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, j are each independently an integer of 0 or more 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j is satisfied.)
Ar ^30- (CR ³⁰ R ³¹ R ³² ) _nGeneral formula (3-1)
(Ar ³⁰ is an aromatic group which may have a substituent.
n is an integer of 0 or more.
R ³⁰ , R ³¹ and R ³² are each independently hydrogen, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, or an alkynyl which may have a substituent. It is selected from a group and an aromatic group which may have a substituent. R ³⁰ , R ³¹ and / or R ³² may form a ring structure together with the carbon to which they are bonded. Ar ³⁰ may combine with R ³⁰ and / or R ³¹ to form a ring structure. )
^{Ar 31} - ^(Ar _{32) n} Formula (3-2)
(Ar ³¹ and Ar ³² are each independently selected from an optionally substituted aromatic group. N is an integer of 1 or more.)
_{^{Ar 33 - (Y-R 33}} m) n Formula (3-3)
(Ar ³³ is selected from aromatic groups which may have a substituent.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
n is an integer of 1 or more.
R ³³ each independently has hydrogen, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, an alkynyl group that may have a substituent, or a substituent. Selected from aromatic groups that may be present. R ³³ may form a ring structure with Y and Ar ³³ . When Y is N, two R ³³ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³³ may jointly form a ring structure. )
Cy- (YR ³⁴ _m ) _n General formula (3-4)
(Cy is selected from a saturated carbocyclic group which may have a substituent and a saturated heterocyclic group which may have a substituent.
n is an integer of 0 or more.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
R ³⁴ is independently selected from an alkyl group which may have a substituent, an alkenyl group which may have a substituent, and an alkynyl group which may have a substituent. R ³⁴ may form a ring structure together with Y and Cy. When Y is N, two R ³⁴ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³⁴ may jointly form a ring structure. )
R ³⁵ R ³⁶ R ³⁷ C-COOR ³⁸ General formula (3-5)
(R ³⁵ , R ³⁶ and R ³⁷ are each independently an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, An aromatic group which may have a substituent, an alkyloxy group which may have a substituent, NR ³⁹ R ⁴⁰ (R ³⁹ and R ⁴⁰ are each independently an alkyl group, an aromatic group and a heterocyclic group. Selected from).
R ³⁵ , R ³⁶ and / or R ³⁷ may form a ring structure together with the carbon to which they are bonded.
R ³⁸ represents an alkyl group which may have a substituent, an alkene group which may have a substituent, an alkylene group which may have a substituent, or an aromatic which may have a substituent. Selected from group. )

  The electrolytic solution of the present invention can contribute to excellent battery characteristics.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as new upper and lower numerical values.

  The electrolytic solution of the present invention includes an electrolyte containing a lithium salt represented by the general formula (1), an organic solvent containing a chain carbonate represented by the general formula (2), an unsaturated cyclic carbonate, and the above An organic compound represented by any one of the general formulas (3-1) to (3-5), wherein the chain carbonate is contained in a molar ratio of 3 to 6 with respect to the lithium salt. And Hereinafter, the lithium ion secondary battery including the electrolytic solution of the present invention is referred to as the lithium ion secondary battery of the present invention.

  The term “may be substituted with a substituent” in the chemical structure represented by the general formula (1) of the electrolytic solution of the present invention will be described. For example, in the case of “an alkyl group that may be substituted with a substituent”, an alkyl group in which one or more of the hydrogens of the alkyl group are substituted with a substituent, or an alkyl group that does not have a particular substituent Means.

  Examples of the substituent in the phrase “may be substituted with a substituent” include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, a halogen, and OH. SH, CN, SCN, OCN, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, Acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group, ureido group, phosphoric acid amide group, sulfo group, carboxyl group, Hydroxamic acid group, Rufino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted with a substituent. When there are two or more substituents, the substituents may be the same or different.

  The lithium salt represented by the general formula (1) is preferably represented by the following general formula (1-1).

(R ³ X ² ) (R ⁴ SO ₂ ) NLi General formula (1-1)
(R ³ and R ⁴ are each independently C _n H _a F _b Cl _c Br _d I _e (CN) _f (SCN) _g (OCN) _h .
n, a, b, c, d, e, f, g, and h are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
R ³ and R ⁴ may combine with each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
X ^{2 _{is, SO 2, C = O,}} C = S, R c P = O, R d P = S, S = O, is selected from Si = O.
R ^c and R ^d are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^c and R ^d may combine with R ³ or R ⁴ to form a ring. )

  The meaning of the phrase “may be substituted with a substituent” in the chemical structure represented by the general formula (1-1) is the same as described in the general formula (1).

In the chemical structure represented by the general formula (1-1), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. Incidentally, the chemical structure represented by the general formula (1-1), ^{when R 3} and ^{R 4} are joined to form a ring, n is preferably an integer of 1 to 8, 1 to 7 Is more preferable, and an integer of 1 to 3 is particularly preferable.

  The lithium salt represented by the general formula (1) is more preferably represented by the following general formula (1-2).

(R ⁵ SO ₂ ) (R ⁶ SO ₂ ) NLi Formula (1-2)
(R ⁵ and R ⁶ are each independently C _n H _a F _b Cl _c Br _d I _e .
n, a, b, c, d, and e are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
R ⁵ and R ⁶ may combine with each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. )

In the chemical structure represented by the general formula (1-2), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. Incidentally, the chemical structure represented by the general formula (1-2), ^{when R 5} and ^{R 6} are joined to form a ring, n is preferably an integer of 1 to 8, 1 to 7 Is more preferable, and an integer of 1 to 3 is particularly preferable.

  In the chemical structure represented by the general formula (1-2), those in which a, c, d, and e are 0 are preferable.

The lithium salt represented by the general formula (1) may be referred to as (CF ₃ SO ₂ ) ₂ NLi (hereinafter sometimes referred to as “LiTFSA”) or (FSO ₂ ) ₂ NLi (hereinafter referred to as “LiFSA”). ), (C ₂ F ₅ SO ₂ ) ₂ NLi, FSO ₂ (CF ₃ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi, FSO ₂ (CH ₃ SO ₂ ) NLi, FSO ₂ (C ₂ F ₅ SO ₂ ) NLi, or FSO ₂ (C ₂ H ₅ SO ₂ ) NLi is particularly preferred.

  One type of lithium salt represented by the general formula (1) in the electrolytic solution of the present invention may be used, or a plurality of types may be used in combination.

  The electrolyte in the electrolytic solution of the present invention may contain other electrolytes that can be used in an electrolytic solution such as a lithium ion secondary battery, in addition to the lithium salt represented by the general formula (1).

Examples of other electrolytes include LiXO ₄ , LiAsX ₆ , LiPX ₆ , LiBX ₄ , and LiB (C ₂ O ₄ ) ₂ (wherein X independently represents F, Cl, Br, I, or CN). . As a suitable aspect of LiXO ₄ , LiAsX ₆ , LiPX ₆ , LiBX ₄ , LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiBF _y (CN) _z (where y is an integer of 0 to 3, z is 1) It is an integer of ˜4 and satisfies y + z = 4).

  In the electrolytic solution of the present invention, the lithium salt represented by the general formula (1) is preferably contained in 70% by mass or more or 70% by mol or more based on the total electrolyte contained in the electrolytic solution of the present invention. More preferably, it is contained at 80% by weight or more or 80% by mole or more, more preferably 90% by weight or more or 90% by mole or more, and particularly preferably 95% by weight or more or 95% by mole or more. . All of the electrolyte contained in the electrolytic solution of the present invention may be a lithium salt represented by the general formula (1).

The chemical structure of the lithium salt represented by the general formula (1) includes SO ₂ . And by charging / discharging of the lithium ion secondary battery of this invention, a part of lithium salt represented by General formula (1) decomposes | disassembles, and S and S on the surface of the positive electrode and / or negative electrode of a lithium ion secondary battery An O-containing film is formed. The S and O containing coating is presumed to have an S = O structure. Since the electrode is covered with the coating, deterioration of the electrode and the electrolytic solution is suppressed, and as a result, the durability of the lithium ion secondary battery of the present invention is considered to be improved. The electrolyte solution of the present invention contains an unsaturated cyclic carbonate, and a carbon-containing film derived from the decomposition of the unsaturated cyclic carbonate is also formed on the surface of the negative electrode when the lithium ion secondary battery of the present invention is charged. . Points regarding the unsaturated cyclic carbonate will be described later.

  The electrolytic solution of the present invention contains an organic solvent containing a chain carbonate represented by the general formula (2).

R ²⁰ OCOOR ²¹ general formula (2)
(R ²⁰ and R ²¹ each independently represent C _n H _a F _b Cl _c Br _d I _e which is a chain alkyl, or C _m H _f F _g Cl _h Br _i I containing a cyclic alkyl in the chemical structure. selected from _j , n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, j are each independently an integer of 0 or more 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j is satisfied.)

  In the chain carbonate represented by the general formula (2), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Of the chain carbonates represented by the general formula (2), those represented by the following general formula (2-1) are particularly preferred.

R ²² OCOOR ²³ general formula (2-1)
(R ²² and R ²³ are each independently selected from either C _n H _a F _b which is a chain alkyl or C _m H _f F _g containing a cyclic alkyl in the chemical structure. N is 1 (The above integers, m is an integer of 3 or more, a, b, f, and g are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b and 2m-1 = f + g.)

  In the chain carbonate represented by the general formula (2-1), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Among the chain carbonates represented by the general formula (2-1), dimethyl carbonate (hereinafter sometimes referred to as “DMC”), diethyl carbonate (hereinafter sometimes referred to as “DEC”), ethylmethyl Carbonate (hereinafter sometimes referred to as "EMC"), fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) Carbonate, fluoromethyldifluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, pentafluoroethyl methyl carbonate, ethyl trifluoromethyl carbonate, bis (2,2,2-trifluoroethyl) ) Carbonate is particularly preferred.

  One kind of the chain carbonate described above may be used for the electrolyte solution, or a plurality of the chain carbonates may be used in combination. By using a plurality of chain carbonates in combination, it is possible to suitably ensure the low temperature fluidity of the electrolyte and the lithium ion transportability at low temperatures.

  In addition to the chain carbonate, the organic solvent in the electrolytic solution of the present invention may be another organic solvent that can be used in an electrolytic solution such as a lithium ion secondary battery (hereinafter simply referred to as “other organic solvent”). .) May be included.

  In the electrolytic solution of the present invention, the chain carbonate is preferably contained in an amount of 70% by mass or more or 70% by mol or more, based on the total organic solvent contained in the electrolytic solution of the present invention. More preferably, it is contained in an amount of not less than mol%, more preferably not less than 90% by mass or not less than 90% by mol, and particularly preferably not less than 95% by mass or not less than 95% by mol. All the organic solvents contained in the electrolytic solution of the present invention may be the chain carbonate.

  In addition, the electrolytic solution of the present invention containing other organic solvents in addition to the chain carbonate has a higher viscosity or lower ionic conductivity than the electrolytic solution of the present invention that does not contain other organic solvents. There is a case. Furthermore, the reaction resistance of the lithium ion secondary battery using the electrolytic solution of the present invention containing another organic solvent in addition to the chain carbonate may increase.

  Specific examples of other organic solvents include nitriles such as acetonitrile, propionitrile, acrylonitrile, malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1, Ethers such as 3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolane, 2-methyltetrahydropyran, 2-methyltetrahydrofuran and crown ether, and cyclic carbonates such as ethylene carbonate and propylene carbonate Amides such as formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, isocyanates such as isopropyl isocyanate, n-propyl isocyanate, chloromethyl isocyanate, , Ethyl acetate, propyl acetate, butyl acetate, methyl propionate, methyl formate, ethyl formate, vinyl acetate, methyl acrylate, methyl methacrylate, and other esters, glycidyl methyl ether, epoxy butane, 2-ethyloxirane, and other epoxies, Oxazoles such as oxazole, 2-ethyloxazole, oxazoline, 2-methyl-2-oxazoline, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acid anhydrides such as acetic anhydride and propionic anhydride, dimethyl sulfone, sulfolane, etc. Sulfones, sulfoxides such as dimethyl sulfoxide, nitros such as 1-nitropropane and 2-nitropropane, furans such as furan and furfural, γ-butyrolactone, γ-valerolactone, δ-valerolactone Cyclic esters, aromatic heterocycles such as thiophene and pyridine, heterocycles such as tetrahydro-4-pyrone, 1-methylpyrrolidine and N-methylmorpholine, phosphate esters such as trimethyl phosphate and triethyl phosphate There can be mentioned.

  The chain carbonate represented by the general formula (2) has a lower polarity than cyclic carbonates such as ethylene carbonate that have been used in conventional electrolyte solutions. Therefore, it is considered that the affinity between the chain carbonate and the metal ion is inferior to the affinity between the cyclic carbonate and the metal ion. Then, when the electrolytic solution of the present invention is used as an electrolytic solution of a lithium ion secondary battery, the aluminum and transition metal constituting the electrode of the lithium ion secondary battery are dissolved as ions in the electrolytic solution of the present invention. It can be said that it is difficult.

  Here, in a lithium ion secondary battery using a conventional general electrolytic solution, aluminum and transition metal constituting the positive electrode are in a highly oxidized state, particularly under a high voltage charging environment, as metal ions that are cations. Dissolved in the electrolyte solution (anode elution), and the metal ions eluted in the electrolyte solution are attracted to the electron-rich negative electrode due to electrostatic attraction, and are reduced by combining with electrons on the negative electrode, and deposited as metal. It is known that there may be. It is known that when such a reaction occurs, the capacity of the positive electrode may be reduced or the electrolytic solution may be decomposed on the negative electrode. However, since the electrolytic solution of the present invention has the characteristics described in the previous paragraph, in the lithium ion secondary battery using the electrolytic solution of the present invention, elution of metal ions from the positive electrode and metal deposition on the negative electrode are suppressed. The

  In the electrolytic solution of the present invention, the chain carbonate represented by the general formula (2) is contained in a molar ratio of 3 to 6 with respect to the lithium salt represented by the general formula (1). Examples of a more preferable molar ratio in the electrolytic solution of the present invention include a range of 3.2 to 4.8 and a range of 3.5 to 4.5. In addition, the conventional electrolyte solution has a molar ratio of the organic solvent to the electrolyte of about 10.

  In the electrolytic solution of the present invention, the concentration of the lithium salt is higher than that of the conventional electrolytic solution. Furthermore, the electrolytic solution of the present invention has an advantage that the fluctuation of the ionic conductivity is small with respect to a slight fluctuation of the lithium salt concentration, that is, it is excellent in robustness. Moreover, the chain carbonate represented by the general formula (2) is excellent in stability against oxidation and reduction. In addition, the chain carbonate represented by the general formula (2) has many free-rotatable bonds and has a flexible chemical structure. Therefore, the electrolytic solution of the present invention using the chain carbonate has a high concentration. Even when a lithium salt at a concentration is contained, a significant increase in the viscosity is suppressed, and high ionic conductivity can be obtained.

  In addition, it can be said that the electrolytic solution of the present invention is different from the conventional electrolytic solution in the presence environment of the lithium salt and the organic solvent. Therefore, in the lithium ion secondary battery having the electrolytic solution of the present invention, the lithium ion transport rate in the electrolytic solution is improved, the reaction rate at the interface between the electrode and the electrolytic solution is improved, and the high rate charge / discharge of the lithium ion secondary battery is performed. It can be expected to alleviate the uneven distribution of the lithium salt concentration of the electrolytic solution, to improve the liquid retention of the electrolytic solution at the electrode interface, and to suppress the so-called liquid withdrawn state where the electrolytic solution is insufficient at the electrode interface. Furthermore, in the electrolytic solution of the present invention, the vapor pressure of the organic solvent contained in the electrolytic solution is lowered. As a result, volatilization of the organic solvent from the electrolytic solution of the present invention can be reduced.

  In the electrolytic solution of the present invention, the distance between adjacent lithium ions is extremely close. When lithium ions move between the positive electrode and the negative electrode during charge / discharge of the lithium ion secondary battery, the lithium ions closest to the destination electrode are first supplied to the electrode. Then, another lithium ion adjacent to the lithium ion moves to the place where the supplied lithium ion was present. That is, in the electrolyte solution of the present invention, it is expected that a domino-like phenomenon occurs in which adjacent lithium ions change their positions one by one toward the electrode to be supplied. For this reason, it is thought that the movement distance of the lithium ion at the time of charging / discharging is short, and the movement speed of the lithium ion is high correspondingly. Due to this, the reaction rate of the lithium ion secondary battery having the electrolytic solution of the present invention is considered to be high.

  The unsaturated cyclic carbonate means a cyclic carbonate having a carbon-carbon double bond in the molecule. Specific examples of the unsaturated cyclic carbonate include compounds represented by the following general formula (A).

(R ¹ and R ² are each independently hydrogen, an alkyl group, a halogen-substituted alkyl group, or halogen.)

  Specific examples of the unsaturated cyclic carbonate represented by the general formula (A) include vinylene carbonate, fluorovinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, and butyl vinylene carbonate. Dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, and trifluoromethyl vinylene carbonate. Among these, vinylene carbonate is preferable.

  Other specific examples of the unsaturated cyclic carbonate include compounds in which the carbon-carbon double bond of the general formula (A) is outside the ring, and specific examples of the compound name include vinyl ethylene carbonate. be able to.

  It is inferred that the unsaturated cyclic carbonate decomposes at an earlier stage than the lithium salt represented by the general formula (1) when the lithium ion secondary battery is charged, and forms a carbon-containing film on the negative electrode active material. Due to the presence of such a carbon-containing coating, it is considered that excessive decomposition of the electrolytic solution, which is one of the causes of irreversible capacity of the lithium ion secondary battery, is suppressed. Further, the carbon-containing film includes a C—O bond, a C═O bond, a C (═O) —O bond, and a O—C (═O) —O bond derived from the chemical structure of the unsaturated cyclic carbonate. , At least one is considered to be present. And since these bonds can be coordinated with lithium ions, it can be said that it can suitably assist the lithium ions moving at high speed in the carbon-containing coating. Then, it is estimated that the lithium ion transport speed between the electrolyte solution and the negative electrode active material interface through the carbon-containing coating is improved, and the resistance during charge / discharge can be suitably suppressed.

  The unsaturated cyclic carbonate is preferably contained in an amount of more than 0 to 6.5% by mass, more preferably 0.1 to less than 2.5% by mass, and more preferably 0.3 to 2. More preferably, it is contained at 0% by mass, particularly preferably 0.5-1.5% by mass. If the unsaturated cyclic carbonate is excessively present, it is assumed that a carbon-containing film derived from the unsaturated cyclic carbonate is excessively formed and it becomes difficult for the lithium ion secondary battery to exhibit sufficient capacity. In addition, if unsaturated cyclic carbonate is present excessively, adsorption of unsaturated cyclic carbonate occurs on the positive electrode side, and / or carbon-containing film due to decomposition products of unsaturated cyclic carbonate is excessively formed on the positive electrode side. As a result, it is also assumed that the resistance of the lithium ion secondary battery increases.

  Next, the organic compounds represented by the general formulas (3-1) to (3-5) will be described. Most of the organic compounds represented by the general formulas (3-1) to (3-5) are generally recognized as overcharge inhibitors. An overcharge inhibitor is a compound that decomposes in an overcharged state, for example, under a voltage generally exceeding 4.2V. However, in the electrolytic solution of the present invention, the organic compound is not in an overvoltage state in which these organic compounds are estimated to be decomposed, but in a normal charge / discharge environment, the resistance of the lithium ion secondary battery of the present invention is suppressed. Demonstrate the effect. Of course, among the organic compounds represented by the general formulas (3-1) to (3-5), the electrolyte solution of the present invention containing a compound recognized as an overcharge inhibitor is in an overcharged state. Is preferably suppressed.

  Since the organic compounds represented by the general formulas (3-1) to (3-5) do not contribute to the charge / discharge reaction in a normal charge / discharge environment, it can be said that they are merely resistors. The mechanism by which such organic compounds represented by the general formulas (3-1) to (3-5) contribute to resistance suppression of the lithium ion secondary battery of the present invention will be considered.

  In the lithium ion secondary battery of the present invention, it is considered that the unsaturated cyclic carbonate present in the electrolytic solution of the present invention is decomposed during the first charge to form a low-resistance carbon-containing film on the negative electrode active material. However, as observed in Evaluation Example 1 to be described later, lithium containing an electrolytic solution containing an unsaturated cyclic carbonate and containing no organic compound represented by the general formulas (3-1) to (3-5). In the ion secondary battery, an increase in resistance occurred. This phenomenon is caused by the fact that the unsaturated cyclic carbonate that did not contribute to the carbon-containing coating on the negative electrode active material was adsorbed on the positive electrode surface, and / or the carbon-containing decomposition product of the unsaturated cyclic carbonate on the positive electrode surface had a high resistance. This is thought to be due to the excessive formation of the film. On the other hand, as supported by Evaluation Example 1 described later, the organic compounds represented by the general formulas (3-1) to (3-5) from the point that resistance increase of the lithium ion secondary battery of the present invention is suppressed. The carbon in which the unsaturated cyclic carbonate that did not contribute to the carbon-containing coating on the negative electrode active material was prevented from adsorbing on the positive electrode surface, and / or the decomposition product of the unsaturated cyclic carbonate on the positive electrode surface had high resistance. It can be said that excessive formation of the containing film was inhibited. Since the resistance suppression effect by this inhibition is remarkably large, it can be said that the entire charge / discharge resistance in the lithium ion secondary battery of the present invention is suppressed.

As the organic compounds represented by the general formulas (3-1) to (3-5), a single compound may be employed or a plurality of compounds may be used in combination. In the case where a plurality of compounds are used in combination, it is preferable that the respective moles be the same. For example, when the mole of the first organic compound is M ₁ and the mole of the second organic compound is M ₂ , the relationship between the _two satisfies 0.5 × M ₁ ≦ M ₂ ≦ 1.5 × M ₁ . More preferably, 0.8 × M ₁ ≦ M ₂ ≦ 1.3 × M ₁ is satisfied, and 0.9 × M ₁ ≦ M ₂ ≦ 1.2 × M ₁ is further satisfied. preferable.

  The organic compounds represented by the general formulas (3-1) to (3-5) are preferably contained in an amount of 0.1 to 10% by mass with respect to the total mass of the electrolytic solution of the present invention. More preferably, it is contained in an amount of 2% by mass, and more preferably 2-6% by mass.

  Hereinafter, the organic compounds represented by the general formulas (3-1) to (3-5) will be described in detail.

Ar ^30- (CR ³⁰ R ³¹ R ³² ) _nGeneral formula (3-1)
(Ar ³⁰ is an aromatic group which may have a substituent.
n is an integer of 0 or more.
R ³⁰ , R ³¹ and R ³² are each independently hydrogen, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, or an alkynyl which may have a substituent. It is selected from a group and an aromatic group which may have a substituent. R ³⁰ , R ³¹ and / or R ³² may form a ring structure together with the carbon to which they are bonded. Ar ³⁰ may combine with R ³⁰ and / or R ³¹ to form a ring structure. )

  The aromatic group in the chemical structure represented by the general formula (3-1) includes an aryl group having a carbon skeleton and a heteroaryl group having a hetero element in the skeleton.

  Examples of the aryl group include a phenyl group, an indenyl group, a fluorenyl group, a naphthyl group, an anthryl group, a phenanthryl group, and a biphenyl group.

  Examples of the heteroaryl group include pyridyl group, pyrazinyl group, pyrimidinyl group, pyridazinyl group, triazinyl group, thiophenyl group, furanyl group, oxazolyl group, thiazolyl group, imidazolyl group and pyrazolyl group.

  The shape of the alkyl group in the chemical structure represented by the general formula (3-1) may be linear, branched or cyclic. Although there is no restriction | limiting in particular in carbon number of an alkyl group, C1-C18 alkyl is preferable from the ease of acquisition or manufacture, C1-C12 alkyl is more preferable, C1-C6 alkyl is especially preferable. In the case of cyclic alkyl, those having 3 to 8 carbon atoms are preferred.

  The shape of the alkenyl group or alkynyl group in the chemical structure represented by the general formula (3-1) may be linear, branched, or cyclic. Although there is no restriction | limiting in particular in carbon number of an alkenyl group or an alkynyl group, C2-C18 alkenyl or alkynyl is preferable from the ease of acquisition or manufacture, C2-C12 alkenyl or alkynyl is more preferable, Carbon number 2-6 alkenyl or alkynyl are particularly preferred. In the case of cyclic alkenyl or cyclic alkynyl, those having 5 to 8 carbon atoms are preferred.

  The term “may have a substituent” in the chemical structure represented by the general formula (3-1) will be described. For example, in the case of “optionally substituted alkyl group”, an alkyl group in which one or more of hydrogens of the alkyl group are substituted with a substituent, or an alkyl having no particular substituent Means group.

  Examples of the substituent in the phrase “may have a substituent” include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, halogen, OH SH, CN, SCN, OCN, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, Acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group, ureido group, phosphoric acid amide group, sulfo group, carboxyl group, Hydroxamic acid group, sul Inomoto, hydrazino group, an imino group, a silyl group. These substituents may be further substituted with a substituent. When there are two or more substituents, the substituents may be the same or different.

  Considering that the organic compound represented by the general formula (3-1) acts as an overcharge inhibitor, the substituent is a radical generated by the decomposition of the organic compound represented by the general formula (3-1). Those that stabilize the intermediate are preferred. For example, it is preferable that a carbon capable of generating a radical has a plurality of electron donating groups and electron withdrawing groups as substituents to stabilize the radical. Moreover, as said substituent, what causes decomposition | disassembly by a specific voltage is preferable.

Preferred substituents include fluoro, methoxy, 2-propyl, tert-butyl, tert-butoxy, trifluoromethyl, cyclohexyl, adamantyl, 2-methoxy-2-propyl, 1,1, 1,3,3,3-hexafluoro-2-methoxy-2-propyl group, 1,1,1,3,3,3-hexafluoro-2-tert-butoxy-2-propyl group, —SO ₃ R , —OCOOR, —OSO ₂ R, —SO ₂ NRR, —OCOR (where each R is independently an alkyl group which may have a substituent, an alkenyl group which may have a substituent, The alkynyl group which may have a substituent and the aromatic group which may have a substituent are selected from the chemical structure represented by the general formula (3-1). Said in Is as bright.) Can be mentioned.

  Specific examples of n in the chemical structure represented by the general formula (3-1) include 0, 1, 2, 3, 4, 5, and 6.

In the chemical structure represented by the general formula (3-1), when any of R ³⁰ , R ³¹ , and R ³² is hydrogen, hydrogen gas can be suitably generated due to decomposition during overcharge.

As one embodiment of the general formula (3-1), a compound represented by the general formula (3-1-1) can be exemplified. The compound represented by the general formula (3-1-1) can generate hydrogen gas more suitably due to decomposition during overcharge.
^{Ar 30 - (CHR 30 CHR 31} R 32) n Formula (3-1-1)
(Ar ³⁰ , n, R ³⁰ , R ³¹ , and R ³² are as described in the general formula (3-1).)

  Specific compounds represented by general formula (3-1) in which n is 0 include thiophene, 3-fluorothiophene, 3-chlorothiophene, 3-bromothiophene, furan, hexafluorobenzene, 1,3-bis. (1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl) benzene, 1,3-bis (1,1,1,3,3,3-hexafluoro-2-tert -Butoxy-2-propyl) benzene.

  Specific compounds represented by general formula (3-1) wherein n is 1 or more include toluene, ethylbenzene, tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, 1-chloro-4-tert. -Butylbenzene, 1-bromo-4-tert-butylbenzene, 1-iodo-4-tert-butylbenzene, 1,3-di-tert-butylbenzene, 1,4-di-tert-butylbenzene, 1, 3,5-tri-tert-butylbenzene, tert-pentylbenzene, 1-methyl-4-tert-pentylbenzene, 1,3-di-tert-pentylbenzene, 1,4-di-tert-pentylbenzene, cyclohexyl Benzene, 1,2,3,4-tetrahydronaphthalene, pentamethylbenzene, hexamethylbenzene, -Tert-butyltoluene, 3,5-di-tert-butyltoluene, 1,4-dichloro-2,3,5,6-tetramethylbenzene, 2,3,5,6-tetrafluoro-p-xylene, 1,4-bis (methoxymethyl) -2,3,5,6-tetramethylbenzene, 2,2-diphenylpropane, (3-methyl-pent-3-yl) benzene, (3-ethyl-penta-3 -Yl) benzene, 2- (1-adamantyl) -4-bromoanisole, 1,1,1,3,3,3-hexafluoro-2-bis (3,4-dimethylphenyl) propane, 1,1, 1,3,3,3-hexafluoro-2-bis (4-methoxyphenyl) propane, 1,1,1,3,3,3-hexafluoro-2-bis (4-tert-butoxyphenyl) propane, 1,1 1,3,3,3-hexafluoro-2-bis (4- (methoxymethoxy) phenyl) propane, phenyl 2,5-dicyclohexyl-benzenesulfonate, 2,4,6-tricyclohexyl-phenyl benzyl carbonate Methanesulfonic acid 2,4,6-tri-cyclohexyl-phenyl, N, N-dibutyl-2,4,6-tri-cyclohexylbenzenesulfonic acid amide, 1,2-ethanedisulfonic acid di-5,6,7 , 8-tetrahydro-2-naphthyl, N, N′-bis (5,6,7,8-tetrahydro-2-naphthylsulfonyl) -N, N′-dimethyl-ethylenediamine, 1,9-nonanedioic acid bis ( 2-cyclohexylphenyl), 1,5-butanedioic acid di-5,6,7,8-tetrahydro-2-naphthyl, 2,2-bis (3 Cyclohexyl-4-acetoxyphenyl) propane, 1,1-bis (4-ethoxycarbonyloxy-phenyl) cyclohexane, 1,3-bis (2,4,6-tri (2-propyl) phenylsulfonyloxy) benzene, 1 , 4-Butanedioic acid bis (4- (2-propyl) -phenyl), partially hydrogenated terphenyl.

^{Ar 31} - ^(Ar _{32) n} Formula (3-2)
(Ar ³¹ and Ar ³² are each independently selected from an optionally substituted aromatic group. N is an integer of 1 or more.)

  The definition of each group in the general formula (3-2) is as described in the chemical structure represented by the general formula (3-1).

  Specific examples of n in the chemical structure represented by the general formula (3-2) include 1, 2, and 3.

  Specific compounds represented by general formula (3-2) include biphenyl, 4-methylbiphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl, 4,4'-dimethoxybiphenyl, o- Examples include terphenyl, m-terphenyl, p-terphenyl, and methanesulfonic acid (2,6-diphenyl) phenyl.

_{^{Ar 33 - (Y-R 33}} m) n Formula (3-3)
(Ar ³³ is selected from aromatic groups which may have a substituent.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
n is an integer of 1 or more.
R ³³ each independently has hydrogen, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, an alkynyl group that may have a substituent, or a substituent. Selected from aromatic groups that may be present. R ³³ may form a ring structure with Y and Ar ³³ . When Y is N, two R ³³ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³³ may jointly form a ring structure. )

  The definition of each group in the general formula (3-3) is as described in the chemical structure represented by the general formula (3-1).

  Specific examples of n in the chemical structure represented by the general formula (3-3) include 1, 2, 3, 4, 5, and 6.

  Specific examples of the compound represented by the general formula (3-3) include anisole, 1,2-dimethoxybenzene, 4-methylanisole, 2,4-dimethylanisole, 2,6-dimethylanisole, and 3,4-dimethyl. Anisole, 1,3,5-trimethoxybenzene, 2,6-dimethoxytoluene, 3,4,5-trimethoxytoluene, 2,4,6-trimethoxytoluene, 1,3,5-trimethyl-2,4 , 6-trimethoxybenzene, 2,3,4,5,6-pentamethylanisole, 2,3,4,5,6-pentafluoroanisole, N, N, 2,4,6-pentamethylaniline, 1 , 3,5-trifluoro-2,4,6-trimethoxybenzene, 4-phenylmorpholine, 1,3-benzodioxole, 3,4,5,6-tetramethyl-1,2- Methylenedioxy) benzene, 1,4-dioxolane, indoline, 1,2,3,4-tetrahydroquinoline, julolidine, tetramethyl julolidine, tris (4-bromophenyl) aniline, diphenyl ether, dibenzofuran and can be exemplified.

Cy- (YR ³⁴ _m ) _n General formula (3-4)
(Cy is selected from a saturated carbocyclic group which may have a substituent and a saturated heterocyclic group which may have a substituent.
n is an integer of 0 or more.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
R ³⁴ is independently selected from an alkyl group which may have a substituent, an alkenyl group which may have a substituent, and an alkynyl group which may have a substituent. R ³⁴ may form a ring structure together with Y and Cy. When Y is N, two R ³⁴ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³⁴ may jointly form a ring structure. )

In consideration of the fact that the organic compound represented by the general formula (3-4) acts as an overcharge inhibitor, with respect to Cy and / or R ³⁴ in the general formula (3-4), hydrogen is bonded to the carbon bonded to Y. Those bonded to each other are preferable, and those bonded to the carbon bonded to the carbon are more preferable.

  Examples of saturated carbocycles include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, decahydronaphthalene, tetradecahydroanthracene, and hexadecahydropyrene.

  Examples of the saturated heterocycle include oxetane, tetrahydrofuran, tetrahydropyran, oxepane, thietane, tetrahydrothiophene, tetrahydrothiopyran, thiepan, azetidine, pyrrolidine, piperidine, azepan, and morpholine.

  In the general formula (3-4), other groups and the like are defined as described in the chemical structure represented by the general formula (3-1).

  Specific examples of n in the chemical structure represented by the general formula (3-4) include 0, 1, 2, 3, 4, 5, and 6.

  Specific examples of the compound represented by the general formula (3-4) include methoxycyclohexane, ethoxycyclohexane, 1-propyloxycyclohexane, and propane-2 other than the compounds exemplified as the saturated carbocycle and the compounds exemplified as the saturated heterocycle. -Yloxycyclohexane, 1-butyloxycyclohexane, 1-pentyloxycyclohexane, 1-methoxy-3-methylcyclohexane, 1-methoxy-2,3-dimethylcyclohexane, 1-methoxy-4- (2-methoxyethyl) cyclohexane 1-methoxy-3-methyl-6- (2-propyl) cyclohexane, 1-cyclohexyl-4-methoxy-cyclohexane, 2-methoxy-decahydronaphthalene, 1-methoxycarbonyl-2-methoxycyclohexane, N, N-dimethyl 1-amino-4-methoxy, 1,4-dimethoxy-cyclohexane, dicyclohexyl ether, 4-methoxy - hexa decahydro pyrene can be exemplified.

R ³⁵ R ³⁶ R ³⁷ C-COOR ³⁸ General formula (3-5)
(R ³⁵ , R ³⁶ and R ³⁷ are each independently an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, An aromatic group which may have a substituent, an alkyloxy group which may have a substituent, NR ³⁹ R ⁴⁰ (R ³⁹ and R ⁴⁰ are each independently an alkyl group, an aromatic group and a saturated heterocyclic ring) Selected from the group).
R ³⁵ , R ³⁶ and / or R ³⁷ may form a ring structure together with the carbon to which they are bonded.
R ³⁸ represents an alkyl group which may have a substituent, an alkene group which may have a substituent, an alkylene group which may have a substituent, or an aromatic which may have a substituent. Selected from group. )

In general formula (3-5), any of R ³⁵ , R ³⁶ , and R ³⁷ is preferably an aromatic group, and with respect to R ³⁸ , one hydrogen is bonded to the carbon bonded to O. Is preferred.

  The definitions of each group in the general formula (3-5) are as described in the chemical structures represented by the general formula (3-1) and the general formula (3-4).

  Specific examples of the compound represented by the general formula (3-5) include 2-propyl-2-methyl-2-phenylpropanoate, cyclohexyl 2-methyl-2-phenylpropanoate, and 1- (4-methylphenyl)- 1- (2-propyloxycarbonyl) cyclohexane, cyclohexen-2-yl 2-methyl-2-phenylpropanoate, 2-propyl 2,2-diphenylpropanoate, N, N, 2-trimethyl-2-aminopropanoic acid 2-propyl, 2-methoxy-2-methylpropanoate 2-propyl, 2- (4- (2-methylpropan-1-yl) -phenyl) -propanoate 2-propyl, 2,2-diphenylethanoic acid 2 -Propyl can be exemplified.

  In the electrolytic solution of the present invention, the blending ratio of the unsaturated cyclic carbonate and the organic compounds represented by the general formulas (3-1) to (3-5) is 1: 0.5 to 1:10 by mass ratio. The range of 1: 1 to 1: 7 is more preferable, and the range of 1: 2 to 1: 5 is more preferable. The molar ratio is preferably in the range of 1: 0.2 to 1: 7, more preferably in the range of 1: 0.5 to 1: 5, and still more preferably in the range of 1: 0.9 to 1: 4. .

  In addition, when the electrolyte solution of the present invention is mixed with a polymer or an inorganic filler to form a mixture, the mixture contains the electrolyte solution and becomes a pseudo solid electrolyte. By using the pseudo-solid electrolyte as the battery electrolyte, leakage of the electrolyte in the battery can be suppressed.

  As said polymer, the polymer used for batteries, such as a lithium ion secondary battery, and the general chemically crosslinked polymer are employable. In particular, a polymer that can absorb an electrolyte such as polyvinylidene fluoride and polyhexafluoropropylene and gel can be used, and a polymer such as polyethylene oxide in which an ion conductive group is introduced.

  Specific polymers include polymethyl acrylate, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, polyglycidol, polytetrafluoroethylene, polyhexafluoropropylene, Polycarboxylic acid such as polysiloxane, polyvinyl acetate, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyitaconic acid, polyfumaric acid, polycrotonic acid, polyangelic acid, carboxymethylcellulose, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene , Polycarbonate, unsaturated polyester copolymerized with maleic anhydride and glycols, substituted It can be exemplified polyethylene oxide derivative, a copolymer of vinylidene fluoride and hexafluoropropylene having. Further, as the polymer, a copolymer obtained by copolymerizing two or more monomers constituting the specific polymer may be selected.

  Polysaccharides are also suitable as the polymer. Specific examples of the polysaccharide include glycogen, cellulose, chitin, agarose, carrageenan, heparin, hyaluronic acid, pectin, amylopectin, xyloglucan, and amylose. Moreover, you may employ | adopt the material containing these polysaccharides as said polymer, The agar containing polysaccharides, such as agarose, can be illustrated as the said material.

  As said inorganic filler, inorganic ceramics, such as an oxide and nitride, are preferable.

  Inorganic ceramics have hydrophilic and hydrophobic functional groups on their surfaces. Therefore, when the functional group attracts the electrolytic solution, a conductive path can be formed in the inorganic ceramic. Furthermore, the inorganic ceramics dispersed in the electrolytic solution can form a network between the inorganic ceramics by the functional groups and serve to contain the electrolytic solution. With such a function of the inorganic ceramics, it is possible to more suitably suppress the leakage of the electrolytic solution in the battery. In order to suitably exhibit the above functions of the inorganic ceramics, the inorganic ceramics preferably have a particle shape, and particularly preferably have a particle size of nano level.

Examples of the inorganic ceramics include general alumina, silica, titania, zirconia, and lithium phosphate. It is also possible but the inorganic ceramic itself has lithium conductivity, _{specifically, Li 3 N, LiI, LiI} -Li 3 N-LiOH, LiI-Li 2 S-P 2 O 5, LiI-Li 2 S _{-P 2 S 5, LiI-Li} 2 S-B 2 S 3, Li 2 O-B 2 S 3, Li 2 O-V 2 O 3 -SiO 2, Li 2 O-B 2 O 3 -P 2 O ₅ , Li ₂ O—B ₂ O ₃ —ZnO, Li ₂ O—Al ₂ O ₃ —TiO ₂ —SiO ₂ —P ₂ O ₅ , LiTi ₂ (PO ₄ ) ₃ , Li-βAl ₂ O ₃ , LiTaO ₃ Can be illustrated.

Glass ceramics may be employed as the inorganic filler. Since glass ceramics can contain an ionic liquid, the same effect can be expected for the electrolytic solution of the present invention. Things as glass _{ceramics, xLi 2 S- (1-x} ) P 2 S 5 ( however, 0 <x <1) compound represented by the well, obtained by replacing a part of S of the compound with other elements And what substituted a part of P of the said compound by germanium can be illustrated.

  Moreover, you may add a well-known additive to the electrolyte solution of this invention in the range which does not deviate from the meaning of this invention. Examples of known additives include carbonate compounds represented by fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride Itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, carboxylic anhydrides typified by phenylsuccinic anhydride; γ-butyrolactone, γ-valerolactone, γ- Lactone represented by caprolactone, δ-valerolactone, δ-caprolactone, ε-caprolactone; cyclic ether represented by 1,4-dioxane; ethylene sulfite, 1,3-propane sultone, 1,4-butane Sulfur-containing compounds represented by ruton, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2 -Nitrogen compounds represented by oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; phosphates represented by monofluorophosphate and difluorophosphate; represented by heptane and octane And saturated hydrocarbon compounds.

  Hereinafter, the lithium ion secondary battery of the present invention including the electrolytic solution of the present invention will be described.

  The lithium ion secondary battery of the present invention includes a negative electrode having a negative electrode active material capable of occluding and releasing lithium ions, a positive electrode having a positive electrode active material capable of occluding and releasing lithium ions, and the electrolytic solution of the present invention.

As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. Accordingly, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. When silicon or the like is used for the negative electrode active material, a silicon atom reacts with a plurality of lithiums, so that it becomes a high-capacity active material. However, there is a problem that volume expansion and contraction due to insertion and extraction of lithium becomes significant. In order to reduce the fear, it is also preferable to employ an alloy or compound in which another element such as a transition metal is combined with a simple substance such as silicon as the negative electrode active material. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated to silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. In addition, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

As a more specific negative electrode active material, graphite having a G / D ratio of 3.5 or more can be exemplified. The G / D ratio is a ratio of G-band and D-band peaks in a Raman spectrum. In the Raman spectrum of graphite, G-band 'is in the vicinity of 1590cm ^-1, D-band is observed as each peak around 1350 cm ^-1. G-band is derived from a graphite structure, and D-band is derived from a defect. Therefore, the higher the G / D ratio, which is the ratio of G-band and D-band, means that the graphite has fewer defects and higher crystallinity. Hereinafter, graphite having a G / D ratio of 3.5 or more may be referred to as high crystalline graphite, and graphite having a G / D ratio of less than 3.5 may be referred to as low crystalline graphite.

  As the highly crystalline graphite, either natural graphite or artificial graphite can be employed. In the classification method by shape, scaly graphite, spherical graphite, massive graphite, earthy graphite, etc. can be adopted. Also, coated graphite whose surface is coated with a carbon material or the like can be employed.

  As a specific negative electrode active material, a carbon material having a crystallite size of 20 nm or less, preferably 5 nm or less can be exemplified. A larger crystallite size means a carbon material in which atoms are arranged periodically and accurately according to a certain rule. On the other hand, it can be said that a carbon material having a crystallite size of 20 nm or less is in a state of poor atomic periodicity and alignment accuracy. For example, if the carbon material is graphite, the size of the graphite crystal is 20 nm or less, or due to the influence of strain, defects, impurities, etc., the regularity of the arrangement of the atoms constituting the graphite becomes poor. The size is 20 nm or less.

  Typical examples of the carbon material having a crystallite size of 20 nm or less include non-graphitizable carbon that is so-called hard carbon and graphitizable carbon that is so-called soft carbon.

  In order to measure the crystallite size of the carbon material, an X-ray diffraction method using CuKα rays as an X-ray source may be used. With the X-ray diffraction method, the crystallite size can be calculated using the following Scherrer equation based on the half-value width and diffraction angle of the diffraction peak detected at the diffraction angle 2θ = 20 degrees to 30 degrees.

L = 0.94λ / (βcosθ)
here,
L: Crystallite size λ: Incident X-ray wavelength (1.54 mm)
β: half width of peak (radian)
θ: Diffraction angle

As a specific negative electrode active material, a material containing silicon can be exemplified. More specifically, SiO _x (0.3 ≦ x ≦ 1.6) disproportionated into two phases of Si phase and silicon oxide phase can be exemplified. The Si phase in SiO _x can occlude and release lithium ions, and changes in volume as the lithium ion secondary battery is charged and discharged. The silicon oxide phase has less volume change associated with charge / discharge than the Si phase. That is, SiO _x as the negative electrode active material realizes a high capacity by the Si phase and suppresses the volume change of the entire negative electrode active material by having the silicon oxide phase. If x is less than the lower limit value, the Si ratio becomes excessive, so that the volume change during charging and discharging becomes too large, and the cycle characteristics of the lithium ion secondary battery deteriorate. On the other hand, when x exceeds the upper limit value, the Si ratio becomes too small and the energy density decreases. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and further preferably 0.7 ≦ x ≦ 1.2.
In the SiO _x as described above, it is believed to alloying reaction with the silicon lithium and Si phase during charging and discharging of the lithium ion secondary battery may occur. And it is thought that this alloying reaction contributes to charging / discharging of a lithium ion secondary battery. Similarly, it is considered that a negative electrode active material containing tin described later can be charged and discharged by an alloying reaction between tin and lithium.

As a specific negative electrode active material, a material containing tin can be exemplified. More specifically, examples include Sn alone, tin alloys such as Cu—Sn and Co—Sn, amorphous tin oxide, and tin silicon oxide. SnB _0.4 P _0.6 O _3.1 can be exemplified as the amorphous tin oxide, and SnSiO ₃ can be exemplified as the tin silicon oxide.

  The material containing silicon and the material containing tin are preferably combined with a carbon material to form a negative electrode active material. Due to the composite, the structure of silicon and / or tin is particularly stabilized, and the durability of the negative electrode is improved. The above compounding may be performed by a known method. As the carbon material used for the composite, graphite, hard carbon, soft carbon or the like may be employed. The graphite may be natural graphite or artificial graphite.

As a specific negative electrode active material, lithium titanate having a spinel structure such as Li _{4 + x} Ti _{5 + y} O ₁₂ (−1 ≦ x ≦ 4, −1 ≦ y ≦ 1), or a ramsdellite structure such as Li ₂ Ti ₃ O ₇ is used. An example is lithium titanate.

  Specific examples of the negative electrode active material include graphite having a major axis / minor axis value of 1 to 5, preferably 1 to 3. Here, the long axis means the length of the longest portion of the graphite particles. The short axis means the length of the longest portion in the direction orthogonal to the long axis. The graphite corresponds to spherical graphite or mesocarbon microbeads. Spherical graphite is a carbon material such as artificial graphite, natural graphite, graphitizable carbon, and non-graphitizable carbon, and has a spherical shape or a substantially spherical shape.

  Spherical graphite is obtained by pulverizing graphite with an impact pulverizer having a relatively small crushing force to form flakes, and then compressing and spheroidizing the flakes. Examples of the impact pulverizer include a hammer mill and a pin mill. It is preferable to perform the above operation with the peripheral linear velocity of the hammer or pin of the mill set to about 50 to 200 m / sec. It is preferable that graphite is supplied to and discharged from the mill while being accompanied by an air current such as air.

Graphite, BET specific surface area is preferably in the range of 0.5~15m ² / g, more preferably in the range of 4~12m ² / g. If the BET specific surface area is too large, the side reaction between the graphite and the electrolyte solution may be accelerated, and if the BET specific surface area is too small, the reaction resistance of the graphite may be increased.

  The average particle diameter of graphite is preferably in the range of 2 to 30 μm, and more preferably in the range of 5 to 20 μm. In addition, an average particle diameter means D50 at the time of measuring with a general laser diffraction scattering type particle size distribution measuring apparatus.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector.

  The current collector refers to a chemically inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid.

  The binder plays a role of tying an active material, a conductive aid, and the like to the surface of the current collector.

  Binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, and styrene butadiene. What is necessary is just to employ | adopt well-known things, such as rubber | gum.

  Moreover, you may employ | adopt the polymer which has a hydrophilic group as a binder. The lithium ion secondary battery of the present invention comprising a polymer having a hydrophilic group as a binder can maintain the capacity more suitably. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, and a phosphate group. Among them, a polymer containing a carboxyl group in a molecule such as polyacrylic acid, carboxymethylcellulose, or polymethacrylic acid, or a polymer containing a sulfo group such as poly (p-styrenesulfonic acid) is preferable.

  A polymer containing many carboxyl groups and / or sulfo groups such as polyacrylic acid or a copolymer of acrylic acid and vinyl sulfonic acid becomes water-soluble. The polymer having a hydrophilic group is preferably a water-soluble polymer, and in terms of chemical structure, a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

  The polymer containing a carboxyl group in the molecule can be produced by, for example, a method of polymerizing an acid monomer or a method of imparting a carboxyl group to the polymer. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc., acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid , Maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylenedicarboxylic acid, etc., acid monomers having two or more carboxyl groups in the molecule Is done.

  A copolymer obtained by polymerizing two or more acid monomers selected from the above acid monomers may be used as a binder.

  Further, for example, a polymer containing in its molecule an acid anhydride group formed by condensation of carboxyl groups of a copolymer of acrylic acid and itaconic acid as described in JP2013-065493A It is also preferable to use as a binder. When the binder has a structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule, it becomes easier for the binder to trap lithium ions etc. before the electrolyte decomposition reaction occurs during charging. It is considered. Furthermore, since the polymer has more carboxyl groups per monomer than polyacrylic acid or polymethacrylic acid, the acidity is increased, but since the predetermined amount of carboxyl groups is changed to acid anhydride groups, the acidity is increased. Is not too high. Therefore, a lithium ion secondary battery having a negative electrode using the polymer as a binder has improved initial efficiency and improved input / output characteristics.

  The blending ratio of the binder in the negative electrode active material layer is preferably a mass ratio of negative electrode active material: binder = 1: 0.005 to 1: 0.3. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, and examples thereof include carbon black, graphite, Vapor Grown Carbon Fiber, and various metal particles. The Examples of carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the active material layer alone or in combination of two or more. The blending ratio of the conductive additive in the negative electrode active material layer is preferably a negative electrode active material: conductive additive = 1: 0.01 to 1: 0.5 in mass ratio. This is because if the amount of the conductive aid is too small, an efficient conductive path cannot be formed, and if the amount of the conductive aid is too large, the formability of the negative electrode active material layer is deteriorated and the energy density of the electrode is lowered.

  A positive electrode used for a lithium ion secondary battery has a positive electrode active material capable of inserting and extracting lithium ions. The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and, if necessary, a binder and / or a conductive aid. The positive electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin , Indium, titanium, ruthenium, tantalum, chromium, molybdenum, and metal materials such as stainless steel.

  When the potential of the positive electrode is 4 V or higher with respect to lithium, it is preferable to employ aluminum as the current collector.

  Specifically, it is preferable to use a positive electrode current collector made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as an aluminum alloy. Examples of the aluminum alloy include Al—Cu, Al—Mn, Al—Fe, Al—Si, Al—Mg, Al—Mg—Si, and Al—Zn—Mg.

  Specific examples of aluminum or aluminum alloy include A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, JIS A8079, A8021, etc. A8000-based alloy (Al-Fe-based).

  The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  What was demonstrated with the negative electrode should just be employ | adopted for the binder and the conductive support agent of a positive electrode by the same compounding ratio.

As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, At least one element selected from Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2.1) and Li ₂ MnO ₃ . Further, as a positive electrode active material, a metal oxide having a spinel structure such as LiMn ₂ O ₄ and a solid solution composed of a mixture of a metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO _4, or Li ₂ MSiO ₄ (formula M in the middle is selected from at least one of Co, Ni, Mn, and Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element contained in the basic composition may be substituted with another metal element. Moreover, you may use as a positive electrode active material the thing which does not contain a charge carrier (for example, lithium ion which contributes to charging / discharging). For example, sulfur alone (S), a compound in which sulfur and carbon are compounded, a metal sulfide such as TiS ₂ , an oxide such as V ₂ O ₅ and MnO ₂ , a compound containing polyaniline and anthraquinone, and these aromatics in the chemical structure In addition, conjugated materials such as conjugated diacetate-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain a charge carrier such as lithium, it is necessary to add a charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or in a non-ionic state such as a metal. For example, when the charge carrier is lithium, it may be integrated by attaching a lithium foil to the positive electrode and / or the negative electrode.

As specific positive electrode active materials, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ having a layered rock salt structure, LiNi _50/100 Co _35/100 Mn _15/100 O _2, LiNi _6/10 Co _{2 / 10} Mn _2/10 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ and LiCoO ₂ can be exemplified. As another specific positive electrode active material, Li ₂ MnO ₃ —LiCoO ₂ can be exemplified.

Specific positive electrode active _{material, Li x A y Mn 2-} y O 4 (A spinel structure, Ca, Mg, S, Si , Na, K, Al, P, Ga, at least one selected from Ge Examples include at least one metal element selected from an element and a transition metal element, 0 <x ≦ 2.2, 0 ≦ y ≦ 1). More specifically, LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ can be exemplified.

Specific examples of the positive electrode active material include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F.

  In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material layer-forming composition containing an active material and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste, and then the collection is performed. After applying to the surface of the electric body, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  A separator is used in the lithium ion secondary battery as necessary. The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. A known separator may be employed, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, polyacrylonitrile or other synthetic resin, cellulose, amylose or other polysaccharide, fibroin. And porous materials, nonwoven fabrics, woven fabrics, and the like using one or more electrical insulating materials such as natural polymers such as keratin, lignin, and suberin, and ceramics. The separator may have a multilayer structure.

A specific method for producing the lithium ion secondary battery of the present invention will be described.
If necessary, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, the electrolyte solution of the present invention is added to the electrode body and lithium ions are added. A secondary battery may be used. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  When the electrolytic solution of the present invention contains a component that decomposes during overcharge to generate gas, the lithium ion secondary battery of the present invention shuts off the charging path or current path when the internal pressure increases. A current interrupt device may be provided.

  A known technique may be adopted as the current interrupt device. For example, by breaking the conductive path electrically connected to the terminal and the electrode when the pressure in the battery rises as described in JP2013-131402A or JP2014-10967A Any technology that cuts off the current may be employed.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy generated by a lithium ion secondary battery for all or a part of its power source. For example, the vehicle may be an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of the electrolyte solution of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, this invention is not limited by these Examples.

Example 1
(FSO ₂ ) ₂ NLi which is a lithium salt, vinylene carbonate which is an unsaturated cyclic carbonate, and cyclohexylbenzene which is an organic compound, in a mixed solvent in which dimethyl carbonate and diethyl carbonate which are chain carbonates are mixed at a molar ratio of 9: 1. The electrolyte solution of Example 1 in which the concentration of (FSO ₂ ) ₂ NLi is 2.4 mol / L, vinylene carbonate is contained at 1% by mass, and cyclohexylbenzene is contained at 2.9% by mass. Manufactured. In the electrolytic solution of Example 1, a chain carbonate is included at a molar ratio of 4 with respect to the lithium salt.

  Using the electrolytic solution of Example 1, the lithium ion secondary battery of Example 1 was manufactured as follows.

94 parts by mass of a lithium-containing metal oxide having a layered rock salt structure represented by LiNi _50/100 Co _35/100 Mn _15/100 O _{2 as} a positive electrode active material, 3 parts by mass of acetylene black as a conductive assistant, and a binder 3 parts by mass of polyvinylidene fluoride as an agent was mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil having a thickness of 15 μm was prepared as a positive electrode current collector. It apply | coated so that the said slurry might become a film | membrane form on both surfaces of this aluminum foil. The aluminum foil coated with the slurry was dried in a 120 ° C. oven to remove N-methyl-2-pyrrolidone by volatilization. Thereafter, this aluminum foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain an aluminum foil on which a positive electrode active material layer was formed. This was used as a positive electrode. The mass of the positive electrode active material layer present on an area of 1 cm ² on one side of the positive electrode current collector was 19.5 mg / cm ² . The lithium-containing metal oxide having a specific surface area of 1.2 m ² / g was used.

98 parts by mass of graphite as a negative electrode active material, 1 part by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 10 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on both sides of the copper foil. The copper foil coated with the slurry was dried to remove water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 100 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. This was used as a negative electrode. The mass of the negative electrode active material layer present on the area of one square centimeter on one side of the negative electrode current collector was 11.1 mg / cm ² .

  A polyolefin microporous film having a thickness of 20 μm was prepared as a separator.

  A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the electrolyte solution of Example 1 was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. This battery was used as the lithium ion secondary battery of Example 1.

(Example 2)
A lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that a lithium-containing metal oxide having a specific surface area of 1.36 m ² / g was used.

(Example 3)
The concentration of (FSO ₂ ) ₂ NLi is 2.4 mol / L and vinylene carbonate is 1 in the same manner as in Example 2 except that the amount of cyclohexylbenzene added is reduced and biphenyl which is an organic compound is added. An electrolytic solution of Example 3 was manufactured, which was contained by mass%, cyclohexylbenzene was contained by 2.5 mass%, and biphenyl was contained by 0.5 mass%. In the electrolytic solution of Example 3, a chain carbonate is included at a molar ratio of 4 with respect to the lithium salt.
Thereafter, a lithium ion secondary battery of Example 3 was produced in the same manner as in Example 2 except that the electrolytic solution of Example 3 was used.

Example 4
The concentration of (FSO ₂ ) ₂ NLi is 2.4 mol / L and vinylene carbonate is 1 mass by the same method as in Example 3 except that the addition amount of cyclohexylbenzene is decreased and the addition amount of biphenyl is increased. %, Cyclohexylbenzene was contained at 1.5% by mass, and biphenyl was contained at 1.5% by mass. In the electrolyte solution of Example 4, a chain carbonate is included at a molar ratio of 4 with respect to the lithium salt.
Thereafter, a lithium ion secondary battery of Example 4 was produced in the same manner as in Example 2 except that the electrolytic solution of Example 4 was used.

(Comparative Example 1)
Except for using no vinylene carbonate, in the same manner as in Example _{1, (FSO 2)} the concentration of 2 NLi was 2.4 mol / L, in Comparative Example 1 in which the cyclohexylbenzene is contained in 2.9 mass% An electrolyte was produced. In the electrolytic solution of Comparative Example 1, chain carbonate is included at a molar ratio of 4 with respect to the lithium salt.
Thereafter, a lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the electrolytic solution of Comparative Example 1 was used.

(Comparative Example 2)
The electrolytic solution of Comparative Example 2 was prepared in the same manner as in Example 1 except that cyclohexylbenzene was not used, and the concentration of (FSO ₂ ) ₂ NLi was 2.4 mol / L and vinylene carbonate was contained at 1% by mass. Manufactured. In the electrolytic solution of Comparative Example 2, a chain carbonate is contained at a molar ratio of 4 with respect to the lithium salt.
Thereafter, a lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the electrolytic solution of Comparative Example 2 was used.

(Reference Example 1)
The electrolytic solution of Reference Example 1 having a concentration of (FSO ₂ ) ₂ NLi of 2.4 mol / L was produced in the same manner as in Example 1 except that vinylene carbonate and cyclohexylbenzene were not used. In the electrolytic solution of Reference Example 1, a chain carbonate is included at a molar ratio of 4 with respect to the lithium salt.
Hereinafter, a lithium ion secondary battery of Reference Example 1 was produced in the same manner as in Example 1 except that the electrolyte solution of Reference Example 1 was used.

(Evaluation example 1)
The lithium ion secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 2 and Reference Example 1 are charged to 4 V at 1 C, and then from 4 V at 60 ° C. and 2 C. 30 cycles of charge / discharge between 3.3 V were performed. The above charging / discharging is called aging.

  Each lithium ion secondary battery prepared to 4 V after aging was charged at a constant current of 1 C for 10 seconds. From the voltage change amount and current value before and after charging, the DC resistance during charging was calculated according to Ohm's law.

  In addition, each lithium ion secondary battery prepared at 3.5 V after aging was discharged at a constant current of 1 C for 10 seconds. From the voltage change amount and current value before and after the discharge, the direct current resistance at the time of discharge was calculated according to Ohm's law.

  Furthermore, the discharge capacity when discharging at 0.15 C to 2.9 V was measured for the lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 prepared to 3.929 V after aging.

The above results are shown in Table 1 for lithium ion secondary batteries using lithium-containing metal oxides having a specific surface area of 1.2 m ² / g, and the specific surface area of lithium-containing metal oxides is 1.36 m. ^The lithium ion secondary battery using ² / g is shown in Table 2. In the table, CHB is an abbreviation for cyclohexylbenzene, BP is an abbreviation for biphenyl, and VC is an abbreviation for vinylene carbonate.

  From the results of Comparative Example 1 and Reference Example 1 in Table 1, it can be seen that the DC resistance during charging and discharging increases due to the addition of cyclohexylbenzene. Under the charge / discharge conditions of Evaluation Example 1, cyclohexylbenzene, which is an overcharge inhibitor, is considered to be undecomposed, so that it can be said that in the lithium ion secondary battery of Comparative Example 1, cyclohexylbenzene itself became a resistor.

  Moreover, it turns out that the direct current resistance at the time of charge and discharge increases from the result of the comparative example 2 and the reference example 1 due to addition of vinylene carbonate. In the lithium ion secondary battery of Comparative Example 2, it is considered that vinylene carbonate is reduced and decomposed under the charge / discharge conditions of Evaluation Example 1 to form a low-resistance carbon-containing film on the negative electrode surface. In the lithium ion secondary battery of Comparative Example 2, the adsorption of vinylene carbonate occurred and / or the carbon-containing film due to the decomposition product of vinylene carbonate was excessively formed on the positive electrode surface. The resistance is thought to have increased.

However, in Example 1, although both cyclohexylbenzene and vinylene carbonate were added, the DC resistance during charging and discharging was equal to or less than that of Reference Example 1. Cyclohexylbenzene inhibited the adsorption of vinylene carbonate, which did not contribute to the formation of the carbon-containing coating on the negative electrode surface, to the positive electrode surface, and / or the carbon-containing coating having a high resistance to the decomposition product of vinylene carbonate on the positive electrode surface. It can be said that the formation of excess was inhibited. Since the resistance suppression effect by this inhibition is remarkably large, it can be said that the entire charge / discharge resistance in the lithium ion secondary battery of Example 1 was suppressed.
Furthermore, in the lithium ion secondary battery of Example 1, it was also confirmed that the discharge capacity was excellent.

  In addition, from the results of Table 2, in Example 3 and Example 4 in which cyclohexylbenzene and biphenyl were used in combination as the organic compound and vinylene carbonate was used, the DC resistance during charging and discharging was cyclohexylbenzene and vinylene carbonate. It was equal to or less than that of Example 2 used.

  It can be said that the electrolytic solution of the present invention containing the unsaturated cyclic carbonate and the organic compound can support the resistance of the lithium ion secondary battery.

Claims (7)

An electrolyte containing a lithium salt represented by the following general formula (1), an organic solvent containing a chain carbonate represented by the following general formula (2), an unsaturated cyclic carbonate, and the following general formula (3-1) An organic compound represented by any one of (3-5),
The electrolytic solution, wherein the chain carbonate is contained in a molar ratio of 3 to 6 with respect to the lithium salt.
(R ¹ X ¹ ) (R ² SO ₂ ) NLi General formula (1)
(R ¹ is hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted with, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, or an alkoxy group which may be substituted with a substituent , An unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, or OCN Is done.
R ² represents hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN The
R ¹ and R ² may be bonded to each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, Si = O.
R ^a and R ^b are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^a and R ^b may combine with R ¹ or R ² to form a ring. )
R ²⁰ OCOOR ²¹ general formula (2)
(R ²⁰ and R ²¹ each independently represent C _n H _a F _b Cl _c Br _d I _e which is a chain alkyl, or C _m H _f F _g Cl _h Br _i I containing a cyclic alkyl in the chemical structure. selected from _j , n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, j are each independently an integer of 0 or more 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j is satisfied.)
Ar ^30- (CR ³⁰ R ³¹ R ³² ) _nGeneral formula (3-1)
(Ar ³⁰ is an aromatic group which may have a substituent.
n is an integer of 0 or more.
R ³⁰ , R ³¹ and R ³² are each independently hydrogen, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, or an alkynyl which may have a substituent. It is selected from a group and an aromatic group which may have a substituent. R ³⁰ , R ³¹ and / or R ³² may form a ring structure together with the carbon to which they are bonded. Ar ³⁰ may combine with R ³⁰ and / or R ³¹ to form a ring structure. )
^{Ar 31} - ^(Ar _{32) n} Formula (3-2)
(Ar ³¹ and Ar ³² are each independently selected from an optionally substituted aromatic group. N is an integer of 1 or more.)
_{^{Ar 33 - (Y-R 33}} m) n Formula (3-3)
(Ar ³³ is selected from aromatic groups which may have a substituent.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
n is an integer of 1 or more.
R ³³ each independently has hydrogen, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, an alkynyl group that may have a substituent, or a substituent. Selected from aromatic groups that may be present. R ³³ may form a ring structure with Y and Ar ³³ . When Y is N, two R ³³ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³³ may jointly form a ring structure. )
Cy- (YR ³⁴ _m ) _n General formula (3-4)
(Cy is selected from a saturated carbocyclic group which may have a substituent and a saturated heterocyclic group which may have a substituent.
n is an integer of 0 or more.
Y is selected from O, S, and N. When Y is O or S, m is 1, and when Y is N, m is 2.
R ³⁴ is independently selected from an alkyl group which may have a substituent, an alkenyl group which may have a substituent, and an alkynyl group which may have a substituent. R ³⁴ may form a ring structure together with Y and Cy. When Y is N, two R ³⁴ may form a ring structure together with N to which they are bonded. When n is 2 or more, a plurality of R ³⁴ may jointly form a ring structure. )
R ³⁵ R ³⁶ R ³⁷ C-COOR ³⁸ General formula (3-5)
(R ³⁵ , R ³⁶ and R ³⁷ are each independently an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, An aromatic group which may have a substituent, an alkyloxy group which may have a substituent, NR ³⁹ R ⁴⁰ (R ³⁹ and R ⁴⁰ are each independently an alkyl group, an aromatic group and a heterocyclic group. Selected from).
R ³⁵ , R ³⁶ and / or R ³⁷ may form a ring structure together with the carbon to which they are bonded.
R ³⁸ represents an alkyl group which may have a substituent, an alkene group which may have a substituent, an alkylene group which may have a substituent, or an aromatic which may have a substituent. Selected from group. )   The electrolytic solution according to claim 1, wherein the organic solvent contains the chain carbonate in an amount of 80% by volume or more or 80% by mole or more.   The electrolyte according to claim 1 or 2, wherein the electrolyte contains the lithium salt at 80 mass% or more or 80 mol% or more. The electrolytic solution according to claim 1, wherein the lithium salt is represented by the following general formula (1-1).
(R ³ X ² ) (R ⁴ SO ₂ ) NLi General formula (1-1)
(R ³ and R ⁴ each independently represent C _n H _a F _b Cl _c Br _d I _e (CN) _f (SCN)
_g (OCN) _h .
n, a, b, c, d, e, f, g, and h are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
R ³ and R ⁴ may combine with each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
X ^{2 _{is, SO 2, C = O,}} C = S, R c P = O, R d P = S, S = O, is selected from Si = O.
R ^c and R ^d are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^c and R ^d may combine with R ³ or R ⁴ to form a ring. ) The electrolytic solution according to claim 1, wherein the lithium salt is represented by the following general formula (1-2).
(R ⁵ SO ₂ ) (R ⁶ SO ₂ ) NLi Formula (1-2)
(R ⁵ and R ⁶ are each independently C _n H _a F _b Cl _c Br _d I _e .
n, a, b, c, d, and e are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
R ⁵ and R ⁶ may combine with each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. ) The lithium salt is (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, FSO ₂ (CF ₃ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ SO ₂ The electrolytic solution according to claim 1, which is NLi) or (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi.   A lithium ion secondary battery comprising the electrolytic solution according to claim 1.