JP2015103360A - Nonaqueous electrolyte and electricity storage device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte capable of improving electrochemical characteristics in a wide temperature range, and an electricity storage device including the nonaqueous electrolyte.SOLUTION: There are provided: a nonaqueous electrolyte including an electrolyte salt dissolved in a nonaqueous solvent, which contains at least one cyclic oxalate ester compound represented by the following general formula (I); and an electricity storage device. (In the formula, X represents a group represented by -C(R)(R)-C(R)(R)- or a 6-20C arylene group that may be substituted by a halogen atom, R, R, R, Reach independently represent a 1-4C alkyl group that may be substituted by a halogen atom or a 6-20C aryl group that may be substituted by a halogen atom.)

Description

  The present invention relates to a nonaqueous electrolytic solution capable of improving electrochemical characteristics at high temperatures and an electricity storage device using the same.

  In recent years, power storage devices, particularly lithium secondary batteries, have been widely used as power sources for electronic devices such as mobile phones and laptop computers, or for electric vehicles and power storage. Batteries mounted on these electronic devices and automobiles are likely to be used under the high temperature of midsummer or in an environment warmed by heat generated by the electronic devices. In thin electronic devices such as tablet terminals and ultrabooks, laminated batteries and square batteries that use a laminated film such as an aluminum laminated film are often used as exterior members. However, these batteries are thin. There is a problem that it is likely to be deformed easily due to a slight expansion of the exterior member, and the influence of the deformation on the electronic device is very large.

A lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, and a non-aqueous electrolyte composed of a lithium salt and a non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC) and propylene. Carbonates such as carbonate (PC) are used.
As negative electrodes of lithium secondary batteries, lithium metal, metal compounds capable of occluding and releasing lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials are known. In particular, non-aqueous electrolyte secondary batteries using carbon materials that can occlude and release lithium, such as coke and graphite (artificial graphite, natural graphite), are widely used. Since the above negative electrode material stores and releases lithium and electrons at a very low potential equivalent to that of lithium metal, many solvents may undergo reductive decomposition, particularly at high temperatures. Regardless of the type, some of the solvent in the electrolyte solution undergoes reductive decomposition on the negative electrode, and lithium ion migration is hindered by decomposition product deposition, gas generation, and electrode swelling. There have been problems such as deterioration of the battery characteristics such as deformation of the battery due to swelling of the electrodes. Furthermore, lithium secondary batteries using lithium metal, alloys thereof, simple metals such as tin or silicon, and oxides as negative electrode materials have high initial capacities, but fine powders progress during the cycle. In comparison, reductive decomposition of nonaqueous solvents occurs at an accelerated rate, and there are known problems such as battery performance and battery performance such as battery capacity and cycle characteristics being greatly degraded at high temperatures and battery deformation due to electrode swelling. .

On the other hand, materials capable of occluding and releasing lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiFePO ₄ used as positive electrode materials, store and release lithium and electrons at a precious voltage of 3.5 V or more on the basis of lithium. Therefore, particularly at high temperatures, many solvents have a possibility of undergoing oxidative decomposition, and the solvent in the electrolyte solution is partially oxidatively decomposed on the positive electrode regardless of the type of the positive electrode material. The deposition of decomposition products and the generation of gas hinder the movement of lithium ions, resulting in a problem that battery characteristics such as cycle characteristics are deteriorated.

  In spite of the above situation, electronic devices equipped with lithium secondary batteries are becoming more and more multifunctional and power consumption is increasing. As a result, the capacity of lithium secondary batteries has been increasing, and the volume occupied by non-aqueous electrolyte in the battery has become smaller, such as increasing the electrode density and reducing the useless space volume in the battery. . Therefore, the battery performance at high temperature is likely to be degraded by a slight decomposition of the non-aqueous electrolyte.

Patent Document 1 proposes a non-aqueous electrolyte secondary battery containing a specific cyclic ester. Even when left at a high temperature, the voltage drop is small, the capacity is small, the resistance is small, and the output is small. It has been suggested to provide a battery having characteristics such as low degradation.
Patent Document 2 discloses that dialkyl oxalate having an alkyl group having 1 to 3 carbon atoms is used at least 1% by volume, more preferably 20 to 80% by volume.

JP2013-175454 JP-A-9-199172

  The present invention provides a non-aqueous electrolyte that can improve high-temperature cycle characteristics, further reduce the rate of increase in electrode thickness after high-temperature cycles, and improve electrochemical characteristics at high temperatures, and an electricity storage device using the same. With the goal.

  As a result of detailed studies on the performance of the above-described prior art non-aqueous electrolyte, the present inventors have found that the non-aqueous electrolyte secondary battery of Patent Document 1 has a small voltage drop and a low capacity even when left at high temperatures. Although characteristics such as a small decrease, a small increase in resistance, and a small decrease in output have been suggested, there is no disclosure about the problem of reducing the rate of increase in electrode thickness associated with charge / discharge. Although Patent Document 2 improves cycle characteristics under high voltage and heavy load discharge conditions, it does not disclose anything about the problem of reducing the increase rate of the electrode thickness accompanying charge / discharge.

  Therefore, as a result of intensive studies to solve the above problems, the present inventors have improved the high-temperature cycle characteristics by containing a specific cyclic oxalate compound in the non-aqueous electrolyte, and further increased the temperature. The inventors have found that the rate of increase in electrode thickness after cycling can be reduced and the electrochemical properties at high temperatures can be improved, and the present invention has been completed.

  That is, the present invention provides the following (1) to (2).

(1) A nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, comprising a cyclic oxalate compound represented by the following general formula (I):

（式中、Ｘは、−Ｃ（Ｒ^１）（Ｒ^２）−Ｃ（Ｒ^３）（Ｒ^４）−で示される基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリーレン基を示し、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４はそれぞれ独立して、ハロゲン原子で置換されていてもよい炭素数１〜４のアルキル基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリール基を示す。）

(In the formula, X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, or an arylene having 6 to 20 carbon atoms which may be substituted with a halogen atom. R ¹ , R ² , R ³ , and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms that may be substituted with a halogen atom, or carbon that may be substituted with a halogen atom. Represents an aryl group of formula 6-20.)

(2) An electricity storage device including the positive electrode, the negative electrode, and the nonaqueous electrolytic solution according to (1).

  According to the present invention, non-aqueous electrolyte that can improve high temperature cycle characteristics, further reduce the rate of increase in electrode thickness after high temperature cycle, and improve electrochemical characteristics under high temperature, and a lithium battery using the same, etc. An electricity storage device can be provided.

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

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention contains a cyclic oxalate compound represented by the following general formula (I) in a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent. It is characterized by.

（式中、Ｘは、−Ｃ（Ｒ^１）（Ｒ^２）−Ｃ（Ｒ^３）（Ｒ^４）−で示される基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリーレン基を示し、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４はそれぞれ独立して、ハロゲン原子で置換されていてもよい炭素数１〜４のアルキル基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリール基を示す。）

(In the formula, X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, or an arylene having 6 to 20 carbon atoms which may be substituted with a halogen atom. R ¹ , R ² , R ³ , and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms that may be substituted with a halogen atom, or carbon that may be substituted with a halogen atom. Represents an aryl group of formula 6-20.)

The reason why the nonaqueous electrolytic solution of the present invention can improve the high-temperature cycle characteristics and further reduce the increase rate of the electrode thickness after the high-temperature cycle is not necessarily clear, but is considered as follows.
The compound represented by the general formula (I) contained in the nonaqueous electrolytic solution of the present invention is a group represented by -C (R < ¹ >) (R < ² >)-C (R < ³ >) (R < ⁴ >)-, Alternatively, the arylene group having 6 to 20 carbon atoms which may be substituted with a halogen atom and an oxalic acid skeleton form a 6-membered ring structure, and there is no hydrogen atom on the 6-membered cyclic oxalate ester. It is said.
When the 6-membered ring portion of the compound represented by the general formula (I) is decomposed inside the battery to form a film, the 6-membered ring is formed compared to the cyclic oxalate compound having a hydrogen atom on the 6-membered ring. Quickly form a composite film with a strong skeleton other than the oxalic acid skeleton and oxalic acid skeleton that does not have hydrogen atoms on the ring at the active site on the negative electrode, improving high-temperature cycle characteristics and suppressing film growth Therefore, it is conceivable to further suppress the increase in electrode thickness.

  The cyclic oxalate compound contained in the nonaqueous electrolytic solution of the present invention is represented by the following general formula (I).

（式中、Ｘは、−Ｃ（Ｒ^１）（Ｒ^２）−Ｃ（Ｒ^３）（Ｒ^４）−で示される基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリーレン基を示し、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４はそれぞれ独立して、ハロゲン原子で置換されていてもよい炭素数１〜４のアルキル基、もしくはハロゲン原子で置換されていてもよい炭素数６〜２０のアリール基を示す。）

(In the formula, X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, or an arylene having 6 to 20 carbon atoms which may be substituted with a halogen atom. R ¹ , R ² , R ³ , and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms that may be substituted with a halogen atom, or carbon that may be substituted with a halogen atom. Represents an aryl group of formula 6-20.)

When X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, R ¹ , R ² , R ³ and R ⁴ are each independently a halogen atom. It is a group selected from an alkyl group having 1 to 4 carbon atoms which may be substituted with an atom, or an aryl group having 6 to 20 carbon atoms which may be substituted with a halogen atom, and may be substituted with a halogen atom Preferred is an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 18 carbon atoms which may be substituted with a halogen atom, or an alkyl group having 1 or 2 carbon atoms which may be substituted with a halogen atom, or An aryl group having 6 to 12 carbon atoms which may be substituted with a halogen atom is more preferable.

When X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, specific examples of R ^1, R ^2, R ^{3 and} R ⁴ include the following groups: It is done.

  Linear alkyl groups such as methyl, ethyl, n-propyl, or n-butyl, branched alkyl groups such as iso-propyl, sec-butyl, or tert-butyl, fluoromethyl Group, difluoromethyl group, trifluoromethyl group, 2-fluoroethyl group, 2,2-difluoroethyl group, fluoroalkyl group such as 2,2,2-trifluoroethyl group, phenyl group, 2-methylphenyl group 2,4-dimethylphenyl group, 2,5-dimethylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 4-tert-butylphenyl group, 2-fluorophenyl group, 4-fluorophenyl group, 4 -Trifluoromethylphenyl group, 2,4-difluorophenyl group, 2-phenylphenyl group, 3-phenylphenyl group, 4-phenylphenyl Preferred examples include an aryl group and an aryl group such as 2,6-diphenylphenyl group. Among them, a methyl group, an ethyl group, an iso-propyl group, a trifluoromethyl group, a phenyl group, or a 4-methylphenyl group is preferable. , A methyl group, a trifluoromethyl group, or a phenyl group is more preferable.

  In the case where X is an arylene group having 6 to 20 carbon atoms which may be substituted with a halogen atom, an arylene group having 6 to 18 carbon atoms which may be substituted with a halogen atom is preferable, and is substituted with a halogen atom. An arylene group having 6 to 12 carbon atoms may be more preferable.

When X is an arylene group having 6 to 20 carbon atoms which may be substituted with a halogen atom, specific examples include the following groups.
1,2-phenylene group, 3-methyl-1,2-phenylene group, 3-ethyl-1,2-phenylene group, 3-propyl-1,2-phenylene group, 3-chloro-1,2-phenylene group 3-fluoro-1,2-phenylene group, 4-methyl-1,2-phenylene group, 3,6-dimethyl-1,2-phenylene group, 3,4,5,6-tetramethyl-1,2 -Phenylene group, 4-fluoro-1,2-phenylene group, 4-trifluoromethyl-1,2-phenylene group, 3,6-difluoro-1,2-phenylene group, 3,4,5,6-tetra Fluoro-1,2-phenylene group, 1,2-naphthyl group and 2,3-naphthyl group are preferred. Among them, 1,2-phenylene group, 3-fluoro-1,2-phenylene group, 4- Fluoro-1,2-phenylene group, 4-tri Fluoromethyl-1,2-phenylene group, 3,6-difluoro-1,2-phenylene group, 3,4,5,6-tetrafluoro-1,2-phenylene group, 1,2-naphthyl group, 2,3 A naphthyl group is preferable, and a 1,2-phenylene group or a 2,3-naphthyl group is more preferable.

In the general formula (I), when X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, specifically, the following compounds are preferably exemplified.

  Among these compounds, compounds having the structural formulas A1, A3, A4, A6, and A7 are preferable, and 5,5,6,6-tetramethyl-1,4-dioxane-2,3-dione (Structural Formula A1) 5,5,6,6-tetrakis (trifluoromethyl) -1,4-dioxane-2,3-dione (structural formula A3) and 5,6-dimethyl-5,6-diphenyl-1,4-dioxane -2,3-dione (Structural Formula A4) is more preferable.

  In the general formula (I), when X is an arylene group having 6 to 20 carbon atoms which may be substituted with a halogen atom, specific examples thereof include the following compounds.

  Among the above compounds, compounds having a structural formula of B1, B2, B9, B10, B12, B13, or B15 are preferred, and benzo [1,4] dioxin-2,3-dione (structural formula B1), 6-fluorobenzo [B] [1,4] dioxin-2,3-dione (structural formula B10) or naphtho [2,3-b] -1,4-dioxin-2,3-dione (structural formula B15) is more preferable. .

  In the non-aqueous electrolyte of the present invention, the content of the cyclic oxalate compound represented by the general formula (I) contained in the non-aqueous electrolyte is 0.001 to 5% by mass in the non-aqueous electrolyte. It is preferable that If the content is 5% by mass or less, there is little possibility that the film is excessively formed on the electrode and the thickness of the electrode increases, and if it is 0.001% by mass or more, the film is sufficiently formed, and the high temperature cycle Since the characteristics are enhanced, the above range is preferable. The content is more preferably 0.05% by mass or more, and further preferably 0.2% by mass or more in the non-aqueous electrolyte. Moreover, the upper limit is more preferably 3% by mass or less, and further preferably 2% by mass or less.

  In the nonaqueous electrolytic solution of the present invention, the cyclic oxalate ester compound represented by the general formula (I) is further combined with a nonaqueous solvent, an electrolyte salt, and other additives described below to further improve the high temperature cycle characteristics. It is improved, and the increase rate of the electrode thickness after the high-temperature cycle is further reduced, and a unique effect of synergistically improving the electrochemical characteristics at high temperature is exhibited.

[Nonaqueous solvent]
As the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention, one or more selected from cyclic carbonates, chain esters, lactones, ethers, and amides are preferably exemplified. Since electrochemical properties are synergistically improved at high temperatures, it is preferable that a chain ester is included, more preferably a chain carbonate is included, and most preferably both a cyclic carbonate and a chain carbonate are included. .

  The term “chain ester” is used as a concept including a chain carbonate and a chain carboxylic acid ester.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans or Cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as “DFEC”), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and 4-ethynyl-1 , 3-dioxolan-2-one (EEC) or two or more selected from ethylene carbonate, propylene carbonate, 4-fluoro-1,3-dioxolan-2-one, vinylene carbonate and 4-ethynyl- Selected from 1,3-dioxolan-2-one (EEC) One or two or more is more preferable.

  In addition, it is preferable to use at least one of unsaturated bonds such as carbon-carbon double bonds or carbon-carbon triple bonds or cyclic carbonates having a fluorine atom, since the electrochemical properties at high temperatures are further improved. More preferably, both a cyclic carbonate containing an unsaturated bond such as a carbon double bond or a carbon-carbon triple bond and a cyclic carbonate having a fluorine atom are included. As the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or carbon-carbon triple bond, VC, VEC, or EEC is more preferable, and as the cyclic carbonate having a fluorine atom, FEC or DFEC is more preferable.

  The content of the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond is preferably 0.07% by volume or more, more preferably 0.8%, based on the total volume of the nonaqueous solvent. 2 vol% or more, more preferably 0.7 vol% or more, and the upper limit thereof is preferably 7 vol% or less, more preferably 4 vol% or less, further preferably 2.5 vol% or less. And, it is preferable because the stability of the coating at a high temperature can be further increased without impairing the Li ion permeability.

  The content of the cyclic carbonate having a fluorine atom is preferably 0.07% by volume or more, more preferably 4% by volume or more, still more preferably 7% by volume or more, based on the total volume of the nonaqueous solvent. The upper limit is preferably 35% by volume or less, more preferably 25% by volume or less, and further 15% by volume or less, because the stability of the coating at high temperatures can be further increased without impairing Li ion permeability. preferable.

  When the non-aqueous solvent contains both a cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond and a cyclic carbonate having a fluorine atom, the carbon to the content of the cyclic carbonate having a fluorine atom The content of the cyclic carbonate having an unsaturated bond such as a carbon double bond or a carbon-carbon triple bond is preferably 0.2% by volume or more, more preferably 3% by volume or more, and further preferably 7% by volume or more. The upper limit is preferably 40% by volume or less, more preferably 30% by volume or less, and further 15% by volume or less, which may further increase the stability of the coating at high temperatures without impairing Li ion permeability. This is particularly preferable because it can be performed.

  Further, when the non-aqueous solvent contains both ethylene carbonate and a cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond, the stability of the coating film formed on the electrode at high temperature is improved. Preferably, the content of cyclic carbonate having an unsaturated bond such as ethylene carbonate and a carbon-carbon double bond or a carbon-carbon triple bond is preferably 3% by volume or more based on the total volume of the nonaqueous solvent. Preferably it is 5 volume% or more, More preferably, it is 7 volume% or more, Moreover, as the upper limit, Preferably it is 45 volume% or less, More preferably, it is 35 volume% or less, More preferably, it is 25 volume% or less.

  These solvents may be used alone, and when two or more types are used in combination, the electrochemical properties at high temperatures are further improved, and it is particularly preferable to use a combination of three or more types. preferable. Preferred combinations of these cyclic carbonates include EC and PC, EC and VC, PC and VC, VC and FEC, EC and FEC, PC and FEC, FEC and DFEC, EC and DFEC, PC and DFEC, VC and DFEC , VEC and DFEC, VC and EEC, EC and EEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and VEC, EC and VC and EEC, EC and EEC and FEC, PC And VC and FEC, EC and VC and DFEC, PC and VC and DFEC, EC and PC and VC and FEC, or EC and PC, VC and DFEC are preferable. Of the above combinations, EC and VC, EC and FEC, PC and FEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and EEC, EC and EEC and FEC, PC and A combination of VC and FEC, or EC, PC, VC and FEC is more preferable.

  As the chain ester, one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, One or more symmetrical linear carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate, pivalate esters such as methyl pivalate, ethyl pivalate, and propyl pivalate Preferable examples include one or two or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, methyl acetate, and ethyl acetate.

  Among the chain esters, chain esters having a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate are preferable, particularly methyl. A chain carbonate having a group is preferred.

  Moreover, when using chain carbonate, it is preferable to use 2 or more types. Further, it is more preferable that both a symmetric chain carbonate and an asymmetric chain carbonate are contained, and it is further more preferable that the content of the symmetric chain carbonate is more than that of the asymmetric chain carbonate.

  The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte decreases and the electrochemical properties at high temperature are low. Since there is little possibility of a fall, it is preferable that it is the said range.

  The volume ratio of the symmetric chain carbonate in the chain carbonate is preferably 51% by volume or more, and more preferably 55% by volume or more. The upper limit is more preferably 95% by volume or less, and still more preferably 85% by volume or less. It is particularly preferred that the symmetric chain carbonate contains dimethyl carbonate. The asymmetric chain carbonate preferably has a methyl group, and methyl ethyl carbonate is particularly preferable. The above case is preferable because the electrochemical characteristics at a higher temperature are further improved.

  The ratio between the cyclic carbonate and the chain ester is preferably 10:90 to 45:55, and 15:85 to 40:60, from the viewpoint of improving electrochemical properties at high temperatures. Is more preferable, and 20:80 to 35:65 is particularly preferable.

  Other nonaqueous solvents include cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane, chains such as 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. Preferable examples include one or more selected from amides such as cyclic ethers, amides such as dimethylformamide, sulfones such as sulfolane, and lactones such as γ-butyrolactone, γ-valerolactone, and α-angelicalactone.

  The above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combination includes, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a chain carboxylic acid ester, a combination of a cyclic carbonate, a chain carbonate and a lactone, and a combination of a cyclic carbonate, a chain carbonate and an ether. A combination or a combination of a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester is preferable.

  In addition, the non-aqueous solvent is an S (═O) group-containing compound, a fluorinated benzene compound, a phosphate ester compound, a carbon-carbon triple bond-containing compound, a carboxylic acid anhydride, an isocyanate compound, or lithium as defined in this specification. Containing at least one of ionic compounds, nitrile compounds, benzene compounds, cyclic acetal compounds, and phosphazene compounds to form a composite film with four or more functional groups or characteristic groups, and electrochemical under high temperature The effect that the characteristics are improved synergistically can be further enhanced.

  The type of the S (═O) group-containing compound is not particularly limited as long as it is a compound having an “S (═O) group” in the molecule.

Specific examples of the S (═O) group-containing compound include the following compounds.
1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, or Sultone such as 5,5-dimethyl-1,2-oxathiolane-4-one 2,2-dioxide, ethylene sulfite, butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, One or more SO ₂ group-containing compounds selected from pentane-1,5-diyl dimethanesulfonate, methylenemethane disulfonate, divinylsulfone, and the like.

  Among the S (═O) group-containing compounds, 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 5 , 5-dimethyl-1,2-oxathiolane-4-one 2,2-dioxide, butane-2,3-diyl dimethanesulfonate, and divinylsulfone are more preferable.

  The type of the fluorinated benzene compound is not particularly limited as long as it is a compound having “a phenyl group in which at least a part of the benzene ring is substituted with fluorine” in the molecule.

Specific examples of the fluorinated benzene compound include the following compounds.
Fluorobenzene, difluorobenzene (o, m, p form), 2,4-difluoroanisole, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene, pentafluoro Phenylmethanesulfonate, 2-fluorophenylmethanesulfonate, 3-fluorophenylmethanesulfonate, 4-fluorophenylmethanesulfonate, 2,4-difluorophenylmethanesulfonate, 3,4-difluorophenylmethanesulfonate, 2,3,4-tri Fluorophenylmethanesulfonate, 2,3,5,6-tetrafluorophenylmethanesulfonate, 4-fluoro-3-trifluoromethylphenylmethanesulfonate, and 4-fluoro-3-trif One or more fluorinated benzene compound selected from Oro methylphenyl methyl carbonate.

  Examples of the fluorinated benzene compound include fluorobenzene, 2,4-difluoroaniol, 1-fluoro-4-cyclohexylbenzene, pantafluorophenylmethanesulfonate, 2-fluorophenylmethanesulfonate, 2,4-difluorophenylmethanesulfonate, And one or more selected from 4-fluoro-3-trifluoromethylphenylmethanesulfonate.

  The phosphoric acid ester compound is not particularly limited as long as it is a compound having a “P (═O) group” in the molecule.

Specific examples of the phosphoric acid ester compound include the following compounds.
Trimethyl phosphate, tributyl phosphate, and trioctyl phosphate, tris (2,2,2-trifluoroethyl) phosphate, bis (2,2,2-trifluoroethyl) methyl phosphate, bis (2, 2,2-trifluoroethyl) ethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2,3 , 3-tetrafluoropropyl, bis (2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bis (2,2,3,3-tetrafluoropropyl) phosphate 2,2,2- Trifluoroethyl and phosphoric acid (2,2,2-trifluoroethyl) (2,2,3,3-tetrafluoropropyl) methyl, phosphoric acid tris (1,1,1,3,3,3-hexafluoro The Pan-2-yl), methyl methylene bisphosphonate, ethyl methylene bisphosphonate, methyl ethylene bisphosphonate, ethyl ethylene bisphosphonate, methyl butylene bisphosphonate, ethyl butylene bisphosphonate, methyl 2- (dimethylphosphoryl) acetate, ethyl 2- ( Dimethylphosphoryl) acetate, methyl 2- (diethylphosphoryl) acetate, ethyl 2- (diethylphosphoryl) acetate, 2-propynyl 2- (dimethylphosphoryl) acetate, 2-propynyl 2- (diethylphosphoryl) acetate, methyl 2- (dimethoxy) Phosphoryl) acetate, ethyl 2- (dimethoxyphosphoryl) acetate, methyl 2- (diethoxyphosphoryl) acetate, ethyl 2- (diethoxyphosphoryl) acetate , 2-propynyl 2- (dimethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate, and methyl pyrophosphate, one or more of the phosphoric acid ester compound selected from ethyl pyrophosphate.

  Among the phosphoric acid ester compounds, tris phosphate (2,2,2-trifluoroethyl), tris phosphate (1,1,1,3,3,3-hexafluoropropan-2-yl), methyl 2 -(Dimethoxyphosphoryl) acetate, ethyl 2- (dimethoxyphosphoryl) acetate, methyl 2- (diethoxyphosphoryl) acetate, ethyl 2- (diethoxyphosphoryl) acetate, 2-propynyl 2- (dimethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate is preferred, Tris phosphate (2,2,2-trifluoroethyl), Tris phosphate (1,1,1,3,3,3-hexafluoropropan-2-yl) , Ethyl 2- (diethoxyphosphoryl) acetate, and 2-propynyl 2- (dieto One or more selected from xylphosphoryl) acetate is more preferable.

  The carbon-carbon triple bond-containing compound is not particularly limited as long as it is a compound having a “carbon-carbon triple bond” in the molecule.

Specific examples of the carbon-carbon triple bond-containing compound include the following compounds.
2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2- (methanesulfonyloxy) propionate, di (2-propynyl) oxalate, methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, di (2-propynyl) glutarate, 2-butyne-1,4-diyl dimethanesulfonate, 2-butyne-1 , 4-diyl diformate, 2,4-hexadiyne-1,6-diyl dimethanesulfonate, etc., or one or more carbon-carbon triple bond-containing compounds.

  Among the triple bond compounds, 2-propynyl methyl carbonate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2- (methanesulfonyloxy) propionate, di (2- One or more selected from propynyl) oxalate, methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, and 2-butyne-1,4-diyl dimethanesulfonate, 2-propynyl methyl carbonate, methanesulfonic acid 2-propynyl, vinyl sulfonic acid 2-propynyl, 2- (methanesulfonyloxy) propionic acid 2-propynyl, di (2-propynyl) oxalate, and 2-butyne-1,4-diyl dimethanesulfonate 1 type or 2 types or more selected from are more preferable.

  The carboxylic acid anhydride is not particularly limited as long as it is a compound having a “C (═O) —O—C (═O) group” in the molecule.

Specific examples of the carboxylic acid anhydride include the following compounds.
Chain carboxylic anhydrides such as acetic anhydride and propionic anhydride, cyclic anhydrides such as succinic anhydride, maleic anhydride, allyl succinic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride 1 type, or 2 or more types of carboxylic acid anhydride chosen from products.

  Among the carboxylic acid anhydrides, succinic anhydride, maleic anhydride, or allyl succinic anhydride is preferable, and one or more selected from succinic anhydride and allyl succinic anhydride are more preferable.

  The type of isocyanate compound is not particularly limited as long as it is a compound having “N═C═O group”.

Specific examples of the isocyanate compound include the following compounds.
1 selected from methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate and the like Seed or two or more isocyanate compounds.

  Among the isocyanate compounds, hexamethylene diisocyanate, octamethylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate are preferable, and hexamethylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate. 1 type or 2 types or more chosen from are more preferable.

  The type of lithium-containing ionic compound is not particularly limited as long as it is a compound having “lithium” as a cationic species.

Specific examples of the lithium-containing ionic compound include the following compounds.
Lithium difluorophosphate, lithium fluorophosphate, lithium fluorosulfonate, difluorobis [oxalate-O, O ′] lithium phosphate (LiPFO), tetrafluoro [oxalate-O, O ′] lithium phosphate, bis [oxalate- O, O ′] lithium borate (LiBOB), difluoro [oxalate-O, O ′] lithium borate, lithium methyl sulfate, lithium ethyl sulfate, lithium propyl sulfate, etc. Ionic compounds.

  Among the lithium-containing ionic compounds, lithium difluorophosphate, lithium fluorosulfonate, difluorobis [oxalate-O, O ′] lithium phosphate (LiPFO), lithium tetrafluoro [oxalate-O, O ′] lithium phosphate, One or more selected from bis [oxalate-O, O ′] lithium borate (LiBOB), difluoro [oxalate-O, O ′] lithium borate, lithium methyl sulfate, lithium ethyl sulfate, and lithium propyl sulfate Is more preferable.

  The type of nitrile compound is not particularly limited as long as it is a compound having a “nitrile group”.

Specific examples of the nitrile compound include the following compounds.
One or more nitrile compounds selected from acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, and sebaconitrile.

  Among the nitrile compounds, one or more selected from succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are more preferable.

  The type of benzene compound is not particularly limited as long as it is a compound having a “phenyl group” in the molecule.

Specific examples of the benzene compound include the following compounds.
Aromatic compounds having branched alkyl groups such as cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, and partial hydrogen of biphenyl, terphenyl (o-, m-, p-isomer), diphenyl ether, anisole, terphenyl 1 type selected from a compound (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl) and a phenyl carbonate compound such as methylphenyl carbonate, ethylphenyl carbonate, or diphenyl carbonate Or two or more aromatic compounds.

  Among the benzene compounds, 1 selected from cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, biphenyl, terphenyl (o-, m-, p-isomer), methylphenyl carbonate, ethylphenyl carbonate, and diphenyl carbonate One or more species are more preferred, and one or more species selected from cyclohexylbenzene, tert-amylbenzene, biphenyl, o-terphenyl, methylphenyl carbonate, ethylphenyl carbonate, and diphenyl carbonate are particularly preferred.

  The cyclic acetal compound is not particularly limited as long as it is a compound having an “acetal group” in the molecule.

Specific examples of the cyclic acetal compound include the following compounds.
One or more cyclic acetal compounds selected from 1,3-dioxolane, 1,3-dioxane, 1,3,5-trioxane and the like.

  Among the cyclic acetal compounds, 1,3-dioxolane or 1,3-dioxane is preferable, and 1,3-dioxane is more preferable.

  The type of the phosphazene compound is not particularly limited as long as it is a compound having “N═PN group” in the molecule.

Specific examples of the phosphazene compound include the following compounds.
One or more phosphazene compounds selected from methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, ethoxyheptafluorocyclotetraphosphazene, and the like.

  Among the phosphazene compounds, cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, or phenoxypentafluorocyclotriphosphazene are preferable, and are selected from methoxypentafluorocyclotriphosphazene and ethoxypentafluorocyclotriphosphazene. 1 type or 2 types or more are still more preferable.

  S (= O) group-containing compound, fluorinated benzene compound, phosphate ester compound, carbon-carbon triple bond-containing compound, carboxylic acid anhydride, isocyanate compound, lithium-containing ionic compound, nitrile compound, benzene compound, cyclic acetal The content of the compound or phosphazene compound is preferably 0.001 to 5% by mass in the non-aqueous electrolyte. In this range, the film is sufficiently formed without becoming too thick, and the effect of further improving the high temperature cycle characteristics and further reducing the increasing rate of the electrode thickness after the high temperature cycle is enhanced. The content is more preferably 0.01% by mass or more, more preferably 0.1% by mass or more in the non-aqueous electrolyte, and the upper limit thereof is more preferably 3.5% by mass or less, and 2.5% by mass. The following is more preferable.

  Moreover, it is preferable to use 2 or more types of compounds used in combination with the said general formula (I). Among the combinations, lithium-containing ionic compounds, S (= O) group-containing compounds, fluorinated benzene compounds, phosphate ester compounds, carbon-carbon triple bond-containing compounds, carboxylic acid anhydrides, isocyanate compounds, nitrile compounds, More preferably, at least one selected from a benzene compound, a cyclic acetal compound, and a phosphazene compound is used in combination, a lithium-containing ionic compound, an S (═O) group-containing compound, a fluorinated benzene compound, a phosphate ester compound, More preferably, at least one selected from a carbon-carbon triple bond-containing compound, an isocyanate compound, a nitrile compound, and a benzene compound is used in combination.

[Electrolyte salt]
The nonaqueous electrolytic solution of the present invention contains LiPF ₆ as an electrolyte. The concentration of LiPF ₆ is usually preferably 0.3 M or higher, more preferably 0.7 M or higher, and even more preferably 1.1 M or higher with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5M or less, more preferably 2.0M or less, and still more preferably 1.6M or less.

LiPF ₆ may be used alone, but can also be used in combination with the following lithium salt. Specific examples of the combination include the following lithium salts.
Examples of the lithium salt include inorganic lithium salts such as LiBF ₄ , LiClO ₄ and LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso -C ₃ F ₇ ) and other lithium salts containing a chain-like fluorinated alkyl group, and cyclic fluorides such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi A lithium salt having an alkylene chain can be used alone or in combination.
Among these, one or more selected from LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ are preferable, and LiBF ₄ , LiN _(SO 2 _{CF 3) 2} and LiN _(SO 2 _F) 1, two or more selected from ₂ being more preferred.

When the proportion of the lithium salt other than LiPF _{6 in the} non-aqueous solvent is 0.001M or more, the effect of improving the electrochemical characteristics at high temperature is easily exhibited, and when it is 0.005M or less, the electrical property at high temperature is increased. This is preferable because there is little concern that the effect of improving chemical properties will be reduced. Preferably it is 0.01M or more, Especially preferably, it is 0.03M or more, Most preferably, it is 0.04M or more. The upper limit is preferably 0.4M or less, particularly preferably 0.2M or less.

[Production of non-aqueous electrolyte]
The non-aqueous electrolyte of the present invention is prepared, for example, by mixing the non-aqueous solvent with the cyclic oxalate ester compound represented by the general formula (I) with respect to the electrolyte salt and the non-aqueous electrolyte. It can be obtained by adding.
At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.

  The nonaqueous electrolytic solution of the present invention can be used in the following first to fourth power storage devices, and not only a liquid but also a gelled one can be used as the nonaqueous electrolyte. Furthermore, the non-aqueous electrolyte of the present invention can be used for a solid polymer electrolyte. In particular, it is preferably used for the first electricity storage device (that is, for a lithium battery) or the fourth electricity storage device (that is, for a lithium ion capacitor) that uses a lithium salt as an electrolyte salt, and is used for a lithium battery. More preferably, it is more preferably used for a lithium secondary battery.

[First power storage device (lithium battery)]
In this specification, the lithium battery is a general term for a lithium primary battery and a lithium secondary battery. In this specification, the term lithium secondary battery is used as a concept including a so-called lithium ion secondary battery. The lithium battery of the present invention comprises the nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent. Components other than the non-aqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular limitation.

  For example, as the positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing one or more selected from cobalt, manganese, and nickel is used. These positive electrode active materials can be used individually by 1 type or in combination of 2 or more types.

Examples of such a lithium composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3. One type or two or more types selected from Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , and LiCo _0.98 Mg _0.02 O ₂ may be mentioned. Moreover, LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, may be used in combination as LiMn ₂ O ₄ and LiNiO _2.

  In addition, in order to improve safety and cycle characteristics during overcharge, or to enable use at a charging potential of 4.3 V or higher, a part of the lithium composite metal oxide may be substituted with another element. . For example, a part of cobalt, manganese, nickel is replaced with at least one element such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, or La. Or a part of O may be substituted with S or F, or a compound containing these other elements may be coated.

Among these, lithium composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo _1-x M _x O ₂ (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ≦ x ≦ 0) .05), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , Li ₂ MnO ₃ and LiMO ₂ (M is Co, Ni, Mn, Fe, etc.) More preferable is a lithium composite metal oxide that can be used at 4.4 V or higher, such as a solid solution with a transition metal. When a lithium composite metal oxide that operates at a high charging voltage is used, the electrochemical characteristics when used in a wide temperature range are liable to deteriorate due to a reaction with the electrolyte during charging, but the lithium secondary battery according to the present invention Then, the deterioration of these electrochemical characteristics can be suppressed. In particular, in the case of a positive electrode containing Mn, the resistance of the battery tends to increase with the elution of Mn ions from the positive electrode, so that the electrochemical characteristics when used in a wide temperature range tend to be lowered. The lithium secondary battery according to the invention is preferable because it can suppress a decrease in these electrochemical characteristics.

Furthermore, lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, a lithium-containing olivine-type phosphate containing one or more selected from iron, cobalt, nickel, and manganese is preferable. Specific examples thereof include one or more selected from LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , and LiMnPO ₄ . Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of iron, cobalt, nickel, and manganese are replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W, and Zr can be substituted with one or more elements selected from, or coated with a compound or carbon material containing these other elements . Among these, LiFePO ₄ or LiMnPO ₄ is preferable. Moreover, lithium containing olivine type | mold phosphate can also be mixed with the said positive electrode active material, for example, and can be used.

As positive electrodes for lithium primary batteries, CuO, Cu ₂ O, Ag ₂ O, Ag ₂ CrO ₄ , CuS, CuSO ₄ , TiO ₂ , TiS ₂ , SiO ₂ , SnO, V ₂ O ₅ , V ₆ O ₁₂ , VO _{x, Nb 2 O 5, Bi} 2 O 3, Bi 2 Pb 2 O 5, Sb 2 O 3, CrO 3, Cr 2 O 3, MoO 3, WO 3, SeO 2, MnO 2, Mn 2 O 3, Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , or an oxide of one or more metal elements such as CoO or a chalcogen compound, sulfur such as SO ₂ and SOCl ₂ Examples thereof include a compound and fluorocarbon (fluorinated graphite) represented by the general formula (CF _x ) _n . Among _{these, MnO 2, V 2 O 5} , fluorinated graphite and the like are preferable.

When the pH of the supernatant liquid when 10.0 g of the positive electrode active material is dispersed in 100 ml of distilled water is 10.0 to 12.5, the effect of improving the electrochemical characteristics in a wider temperature range can be easily obtained. The case of 10.5 to 12.0 is more preferable.
Further, when Ni is contained as an element in the positive electrode, since impurities such as LiOH in the positive electrode active material tend to increase, an effect of improving electrochemical characteristics in a wider temperature range is easily obtained, which is preferable. The case where the atomic concentration of Ni in the substance is 5 to 25 atomic% is more preferable, and the case where it is 8 to 21 atomic% is particularly preferable.

  The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, graphite such as natural graphite (flaky graphite, etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and one or more carbon blacks selected from thermal black, etc. Can be mentioned. Further, graphite and carbon black may be appropriately mixed and used. 1-10 mass% is preferable and, as for the addition amount to the positive mix of a electrically conductive agent, 2-5 mass% is especially preferable.

  The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene. This is mixed with a binder such as copolymer (NBR), carboxymethyl cellulose (CMC), or ethylene propylene diene terpolymer, and a high boiling point solvent such as 1-methyl-2-pyrrolidone is added thereto and kneaded. After forming this agent, this positive electrode mixture is applied to an aluminum foil as a current collector or a stainless steel lath plate, etc., dried and pressure-molded, and then vacuumed at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can produce by heat-processing with.

The density of the part except the collector of the positive electrode is usually at 1.5 g / cm ³ or more, for further increasing the capacity of the battery, it is preferably 2 g / cm ³ or more, more preferably, 3 g / cm ³ It is above, More preferably, it is 3.6 g / cm ³ or more. The upper limit is preferably 4 g / cm ³ or less.

Examples of the negative electrode active material for a lithium secondary battery include lithium metal, lithium alloy, and a carbon material capable of occluding and releasing lithium (easily graphitized carbon and a (002) plane spacing of 0.37 nm or more). Non-graphitizable carbon, graphite with (002) plane spacing of 0.34 nm or less, etc.], tin (simple substance), tin compound, silicon (simple substance), silicon compound, or titanic acid such as Li ₄ Ti ₅ O ₁₂ A lithium compound etc. can be used individually by 1 type or in combination of 2 or more types.

Among the negative electrode active materials, it is more preferable to use a highly crystalline carbon material such as artificial graphite or natural graphite in terms of the ability to occlude and release lithium ions, and the spacing (d ₀₀₂ ) between lattice planes ( ₀₀₂ ). It is more preferable to use a carbon material having a graphite-type crystal structure having a thickness of 0.340 nm (nanometer) or less, particularly 0.335 to 0.337 nm. In particular, artificial graphite particles having a massive structure in which a plurality of flat graphite fine particles are assembled or bonded non-parallel to each other, and mechanical actions such as compressive force, frictional force, shearing force, etc. are repeatedly applied, and scaly natural graphite is spherical. It is preferable to use particles that have been treated.

The peak intensity I (110) of the (110) plane of the graphite crystal obtained from the X-ray diffraction measurement of the negative electrode sheet when the density of the portion excluding the current collector of the negative electrode is pressed to a density of 1.5 g / cm ³ or more. ) And the (004) plane peak intensity I (004) ratio I (110) / I (004) is preferably 0.01 or more because the electrochemical characteristics in a wider temperature range are further improved. More preferably, it is more preferably 0.1 or more. In addition, since the crystallinity may be lowered due to excessive treatment and the discharge capacity of the battery may be lowered, the upper limit of the peak intensity ratio I (110) / I (004) is preferably 0.5 or less. 3 or less is more preferable.

In addition, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material having lower crystallinity than the core material because electrochemical characteristics in a wide temperature range are further improved. The crystallinity of the coating carbon material can be confirmed by TEM.
When a highly crystalline carbon material is used, it reacts with the non-aqueous electrolyte during charging and tends to lower the electrochemical characteristics at low or high temperatures due to an increase in interface resistance. However, in the lithium secondary battery according to the present invention, Excellent electrochemical characteristics over a wide temperature range.

  Examples of metal compounds capable of inserting and extracting lithium as the negative electrode active material include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, and Zn. Preferred examples include compounds containing at least one metal element such as Ag, Mg, Sr, or Ba. These metal compounds may be used in any form such as simple substance, alloy, oxide, nitride, sulfide, boride, or alloy with lithium. Any one is preferable because the capacity can be increased. Among these, those containing at least one element selected from Si, Ge and Sn are preferable, and those containing at least one element selected from Si and Sn are more preferable because the capacity of the battery can be increased.

  The negative electrode is kneaded using the same conductive agent, binder, and high-boiling solvent as in the production of the positive electrode, and then the negative electrode mixture is applied to the copper foil of the current collector. After being dried and pressure-molded, it can be produced by heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.

The density of the portion excluding the current collector of the negative electrode is usually 1.1 g / cm ³ or more, and is preferably 1.5 g / cm ³ or more, more preferably 1.7 g in order to further increase the battery capacity. / Cm ³ or more. The upper limit is preferably 2 g / cm ³ or less.

  Examples of the negative electrode active material for the lithium primary battery include lithium metal and lithium alloy.

  There is no particular limitation on the structure of the lithium battery, and a coin-type battery, a cylindrical battery, a square battery, a laminated battery, or the like having a single-layer or multi-layer separator can be applied.

  Although there is no restriction | limiting in particular as a separator for batteries, The single layer or laminated microporous film of polyolefin, such as a polypropylene and polyethylene, a woven fabric, a nonwoven fabric, etc. can be used.

  The lithium secondary battery according to the present invention has excellent electrochemical characteristics in a wide temperature range even when the end-of-charge voltage is 4.2 V or more, particularly 4.3 V or more, and the characteristics are also good at 4.4 V or more. is there. The end-of-discharge voltage is usually 2.8 V or more, and further 2.5 V or more, but the lithium secondary battery in the present invention can be 2.0 V or more. Although it does not specifically limit about an electric current value, Usually, it uses in the range of 0.1-30C. Moreover, the lithium battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

  In the present invention, as a countermeasure against an increase in the internal pressure of the lithium battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.

[Second power storage device (electric double layer capacitor)]
The 2nd electrical storage device of this invention is an electrical storage device which stores the energy using the electric double layer capacity | capacitance of electrolyte solution and an electrode interface including the non-aqueous electrolyte of this invention. An example of the present invention is an electric double layer capacitor. The most typical electrode active material used for this electricity storage device is activated carbon. Double layer capacity increases roughly in proportion to surface area.

[Third power storage device]
The 3rd electrical storage device of this invention is an electrical storage device which stores the energy using the dope / dedope reaction of an electrode including the non-aqueous electrolyte of this invention. Examples of the electrode active material used in this power storage device include metal oxides such as ruthenium oxide, iridium oxide, tungsten oxide, molybdenum oxide, and copper oxide, and π-conjugated polymers such as polyacene and polythiophene derivatives. Capacitors using these electrode active materials can store energy associated with electrode doping / dedoping reactions.

[Fourth storage device (lithium ion capacitor)]
The 4th electrical storage device of this invention is an electrical storage device which stores the energy using the intercalation of the lithium ion to carbon materials, such as a graphite which is a negative electrode, containing the nonaqueous electrolyte solution of this invention. It is called a lithium ion capacitor (LIC). Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, and those using a π-conjugated polymer electrode doping / dedoping reaction. The electrolytic solution contains at least a lithium salt such as LiPF ₆ .

  Examples of the electrolytic solution using the cyclic oxalate compound of the present invention are shown below, but the present invention is not limited to these examples.

Examples 1-17, Comparative Examples 1-3
[Production of lithium ion secondary battery]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (positive electrode active material); 94% by mass, acetylene black (conductive agent); 3% by mass are mixed in advance, and polyvinylidene fluoride (binder); 3 mass in advance. % Was added to the solution dissolved in 1-methyl-2-pyrrolidone and mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a belt-like positive electrode sheet. Further, silicon (single element, negative electrode active material); 10% by mass, artificial graphite (d ₀₀₂ = 0.335 nm, negative electrode active material); 80% by mass, acetylene black (conductive agent); Vinylidene chloride (binder); 5% by mass was added to and mixed with a solution prepared by dissolving in 1-methyl-2-pyrrolidone to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and cut into a predetermined size to produce a negative electrode sheet. And the positive electrode sheet, the separator made from a microporous polyethylene film, and the negative electrode sheet were laminated | stacked in order, the non-aqueous electrolyte of the composition of Tables 1-2 was added, and the laminate type battery was produced.

[Evaluation of high-temperature cycle characteristics]
Using the battery produced by the above method, the battery was charged in a constant temperature bath at 65 ° C. with a constant current and constant voltage of 1 C for 3 hours to a final voltage of 4.3 V, and then discharged at a constant current of 1 C and a discharge voltage of 3.0 V. Discharging until 1 cycle was repeated until 100 cycles were reached. And the capacity | capacitance maintenance factor after a cycle was calculated | required with the following formula | equation.
Capacity retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100
<Initial anode thickness>
The battery cycled by the above method was disassembled and the initial negative electrode thickness was measured.
<Negative thickness after cycle>
The battery that had been subjected to 100 cycles by the above method was disassembled, and the negative electrode thickness after the high temperature cycle was measured.
<Negative electrode thickness increase rate>
The increase in negative electrode thickness was determined by the following formula.
Negative electrode thickness increase = Negative electrode thickness after high-temperature cycle-Initial negative electrode thickness Negative electrode thickness increase rate (%) was determined by setting the negative electrode thickness increase of Comparative Example 1 as 100%.

Examples 18 and 19 and Comparative Example 4
A positive electrode sheet was prepared using LiNi _1/2 Mn _3/2 O ₄ (positive electrode active material) in place of the positive electrode active material used in Examples 1 to 17 and Comparative Examples 1 to 3.
LiNi _1/2 Mn _3/2 O ₄ (positive electrode active material); 94% by mass, acetylene black (conductive agent); 3% by mass are mixed, and polyvinylidene fluoride (binder); A positive electrode mixture paste was prepared by adding to and mixing with the solution dissolved in methyl-2-pyrrolidone. Example 1 except that this positive electrode mixture paste was applied to one surface of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a belt-like positive electrode sheet. A laminate type battery was prepared in the same manner as described above, and the non-aqueous electrolyte shown in Table 3 was added to evaluate the battery. At this time, the negative electrode thickness increase rate (%) was obtained by setting the negative electrode thickness increase of Comparative Example 4 as 100%.

All of the lithium secondary batteries of Examples 1 to 17 including the general formula (I) suppress the increase in the thickness of the negative electrode after the high-temperature cycle as compared with Comparative Examples 1 to 3. From the above, the effect of reducing the increase rate of the electrode thickness of the present invention is a unique effect when the specific compound of the present invention is contained in the nonaqueous electrolytic solution in which the electrolyte salt is dissolved in the nonaqueous solvent. It turned out to be. Further, from the comparison between Examples 18 and 19 and Comparative Example 4, the same effect is observed when LiNi _1/2 Mn _3/2 O ₄ is used for the positive electrode.

  Furthermore, the non-aqueous electrolyte of the present invention also has an effect of improving the high temperature storage characteristics of the lithium primary battery.

  By using the non-aqueous electrolyte of the present invention, it is possible to improve the high-temperature cycle characteristics, further reduce the increase rate of the electrode thickness after the high-temperature cycle, and obtain an electricity storage device having excellent electrochemical characteristics at high temperatures. . Especially when used as a non-aqueous electrolyte for power storage devices such as lithium secondary batteries mounted on hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric vehicles, etc., the rate of increase in electrode thickness after high-temperature cycling is reduced, It is possible to obtain an electricity storage device in which electrochemical characteristics are not easily lowered.

Claims (2)

A nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, containing at least one cyclic oxalate compound represented by the following general formula (I):

(In the formula, X is a group represented by —C (R ¹ ) (R ² ) —C (R ³ ) (R ⁴ ) —, or an arylene having 6 to 20 carbon atoms which may be substituted with a halogen atom. R ¹ , R ² , R ³ , and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms that may be substituted with a halogen atom, or carbon that may be substituted with a halogen atom. Represents an aryl group of formula 6-20.)   It is an electrical storage device provided with the nonaqueous electrolyte solution by which electrolyte salt is melt | dissolved in the positive electrode, the negative electrode, and the nonaqueous solvent, Comprising: The said nonaqueous electrolyte solution is the nonaqueous electrolyte solution of Claim 1 characterized by the above-mentioned. Power storage device.