JP2005340151A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery in which an open circuit voltage between battery terminals after battery charging is finished is high, and in which gas generation amount at the time of continuous charging can be suppressed. <P>SOLUTION: In the lithium secondary battery provided with a positive electrode, a negative electrode, and a nonaqueous electrolytic solution, lactones having carbon-carbon unsaturated bond in the nonaqueous electrolytic solution is made to be contained 0.01 wt% or more and 5 wt% or less, while the open circuit voltage between the battery terminals is made to be 4.25 V or more at 25°C when the battery charging is finished. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery using a non-aqueous electrolyte.

  Lithium secondary batteries have the advantages of high energy density and less self-discharge. Therefore, in recent years, it has been widely used as a power source for consumer mobile devices such as mobile phones, notebook computers, and PDAs.

  A conventional electrolyte for a lithium secondary battery is composed of a lithium salt that is a supporting electrolyte and a nonaqueous solvent. The nonaqueous solvent used here is required to have a high dielectric constant in order to dissociate the lithium salt, to exhibit high ionic conductivity in a wide temperature range, and to be stable in the battery. Since it is difficult to achieve these requirements with a single solvent, usually a combination of a high boiling point solvent typified by propylene carbonate, ethylene carbonate and the like and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate, Used as a non-aqueous solvent.

  In addition, in order to improve various characteristics of lithium secondary batteries, the initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics, trickle charge (continuous charge) characteristics, self-discharge characteristics, overcharge prevention characteristics, etc. have been improved. For this purpose, many methods have been reported so far in which various auxiliary agents are contained in the electrolyte solution in small amounts. However, a universal electrolyte for all properties has not yet been found.

  On the other hand, attempts have been made to increase the end-of-charge voltage of lithium secondary batteries for the purpose of improving energy density. Specifically, when a conventional general lithium secondary battery was charged at 25 ° C., the open circuit voltage between the battery terminals at the end of charging was usually 4.2 V or less. For this reason, there has been an attempt to develop a lithium secondary battery in which, when charged at 25 ° C., the open circuit voltage between the battery terminals at the end of charging exceeds 4.2V. However, the higher the voltage, the more unavoidable side reactions are caused by the decomposition of the electrolyte in the positive electrode, and the cycle deterioration becomes extremely large. Therefore, the conventional lithium secondary voltage is increased until the open circuit voltage between the battery terminals exceeds 4.2V. When the battery was charged, it was not practical.

  In response to such a desire to increase the end-of-charge voltage, Patent Document 1 proposes a technique using an electrolytic solution composed of a non-aqueous solvent containing 50% by volume or more of γ-butyrolactone, which is a saturated lactone, and a lithium salt. ing. In this Patent Document 1, it is described that the capacity of a secondary battery whose open circuit voltage between battery terminals at 25 ° C. at full charge is 4.3 V or more is increased by the above technique, and further, cycle characteristics and the like are improved. Yes.

JP 2003-272704 A

  In recent years, the demand for higher performance of lithium secondary batteries has been increasing, and it has been required to achieve various characteristics such as high capacity, cycle characteristics, high temperature storage characteristics, and continuous charge characteristics at a high level. ing. Among them, improvement of continuous charging characteristics has been particularly demanded recently due to the growing demand for office notebook computers.

However, conventionally proposed lithium secondary batteries generate significant hydrogen gas on the negative electrode and have insufficient continuous charge characteristics. This is the same in the technique that has been proposed in the past in Patent Document 1 and the like that a lithium secondary battery having a high open circuit voltage between battery terminals at the end of charging can be obtained.
The present invention was devised in view of the above problems, and provides a lithium secondary battery that can increase the open circuit voltage between battery terminals at the end of charging and can suppress the amount of gas generated during continuous charging. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the inventor of the present invention has a battery terminal at the end of charging by containing a small amount of a lactone having a carbon-carbon unsaturated bond in a non-aqueous electrolyte solution. The inventors have found that the open circuit voltage can be increased and that the amount of gas generated during continuous charging can be suppressed, and the present invention has been completed.

  That is, the gist of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte solution containing 0.01% by weight to 5% by weight of a lactone having a carbon-carbon unsaturated bond. An open circuit voltage between battery terminals at 4 ° C. is 4.25 V or more. The present invention resides in a lithium secondary battery (claim 1).

At this time, the open circuit voltage between the battery terminals is preferably 4.3 V or more (claim 2).
Furthermore, the lactone ring of the lactone is preferably either a 5-membered ring or a 6-membered ring (Claim 3).
The lactones are preferably either α, β-unsaturated lactones or β, γ-unsaturated lactones (Claim 4).

Further, the lactones are preferably those represented by the following general formula (1). However, in the general formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent. R ³ represents a divalent hydrocarbon group which may have a substituent.

In addition, the lactones are preferably those represented by the following general formula (2) (claim 6). However, in the general formula (2), R ⁴ and R ⁵ each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent. R ⁶ represents a divalent hydrocarbon group which may have a substituent.

Furthermore, the lactones are preferably those represented by the following general formula (3) (claim 7). However, in the general formula (3), R ⁷ and R ⁸ each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent.

また、該非水系電解液中における該ラクトン類の含有量は、０．１重量％以上２重量％以下であることが好ましい（請求項８）。

In addition, the content of the lactone in the nonaqueous electrolytic solution is preferably 0.1% by weight or more and 2% by weight or less (claim 8).

Furthermore, the lactones include 3-methyl-2 (5H) -furanone, α-methylene-γ-butyrolactone, α-angelica lactone, 4,6-dimethyl-α-pyrone, 5,6-dihydro-2H-pyran. It is preferably selected from the group consisting of 2-one and α-pyrone.
Moreover, it is preferable that this non-aqueous electrolyte contains unsaturated carbonates (Claim 10).

  ADVANTAGE OF THE INVENTION According to this invention, while being able to charge to a high open circuit voltage between battery terminals in a lithium secondary battery, the amount of gas generation at the time of continuous charge can be suppressed.

Hereinafter, the present invention will be described. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented.
The lithium secondary battery of the present invention comprises a non-aqueous electrolyte, and a positive electrode and a negative electrode capable of inserting and extracting lithium. In addition, the lithium secondary battery of the present invention may have other configurations.

[I. Non-aqueous electrolyte]
The non-aqueous electrolyte solution used in the lithium secondary battery of the present invention (hereinafter, appropriately referred to as “non-aqueous electrolyte solution in the present invention”) is a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent, A lactone having a carbon-carbon unsaturated bond is contained at a concentration of 0.01 wt% or more and 5 wt% or less.

[1. Lactones]
[1-1. type]
The lactone contained in the non-aqueous electrolyte in the present invention (hereinafter referred to as “the lactone of the present invention” as appropriate) is not limited as long as it is a lactone having a carbon-carbon unsaturated bond, and any lactone is used. be able to. The carbon-carbon unsaturated bond may be inside the lactone ring or outside the lactone ring. However, among carbon-carbon unsaturated bonds, a carbon-carbon double bond is preferable because it is easy to produce and inexpensive.

The lactone ring of the lactone of the present invention may have any number of members, but a 5-membered or 6-membered ring is preferable because it is easy to produce, chemically stable and inexpensive.
Furthermore, in the lactones of the present invention, α, β-unsaturated lactone or β, γ-unsaturated lactone is preferred. The α, β-unsaturated lactone refers to lactones in which the bond between the α-position carbon and the β-position carbon of the lactone is a carbon-carbon unsaturated bond. The β, γ-unsaturated lactone refers to lactones in which the bond between the β-position carbon and the γ-position carbon of the lactone is a carbon-carbon unsaturated bond.

  However, as the lactones of the present invention, those represented by the following general formulas (1) to (3) are usually stable in the non-aqueous electrolyte solution of the present invention and are relatively easy to produce. It is preferable because it can be obtained at low cost. Here, the lactones represented by the general formulas (1) and (2) are a kind of α, β-lactone, and the lactones represented by the general formula (3) are a kind of β, γ-lactone.

In the general formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group.
When R ¹ and R ² are hydrocarbon groups, the carbon number is usually 1 or more and usually 8 or less.
Furthermore, although the kind of hydrocarbon group used as R ¹ and R ² is arbitrary, examples thereof include an alkyl group, an alkenyl group, an aryl group, and an aralkyl group.

When R ¹ and R ² are alkyl groups, the alkyl group usually has 1 or more carbon atoms and usually 6 or less, preferably 4 or less, more preferably 2 or less. If this upper limit is exceeded, the compatibility or solubility of lactones in the non-aqueous electrolyte decreases, and the protective coating formed on the positive electrode becomes brittle. Therefore, a battery of a lithium secondary battery using the non-aqueous electrolyte The capacity may be insufficient.

In addition, when R ¹ and R ² are alkyl groups, specific examples of the alkyl group preferable as R ¹ and R ² include a methyl group, an ethyl group, a propyl group, and a butyl group. Among these, a methyl group, an ethyl group, and a propyl group are more preferable.

When R ¹ and R ² are alkenyl groups, the carbon number of the alkenyl group is usually 2 or more, and usually 6 or less, preferably 4 or less. If this upper limit is exceeded, as in the case of alkyl groups, the compatibility or solubility of lactones with respect to the non-aqueous electrolyte decreases, and the protective coating formed on the positive electrode becomes brittle. The lithium secondary battery used may have insufficient battery capacity.

Further, when R ¹ and R ² are alkenyl groups, specific examples of alkenyl groups preferable as R ¹ and R ² include vinyl group, isoprobenyl group, and allyl group. Among these, a vinyl group and an allyl group are more preferable.

When R ¹ and R ² are aryl groups, the aryl group usually has 6 or more carbon atoms and usually 8 or less, preferably 7 or less. If this upper limit is exceeded, as in the case of alkyl groups and alkenyl groups, the compatibility or solubility of unsaturated lactones in the non-aqueous electrolyte decreases, and the protective coating formed on the positive electrode becomes brittle, so that There is a possibility that the battery capacity of the lithium secondary battery using the aqueous electrolyte is insufficient.

In addition, when R ¹ and R ² are aryl groups, specific examples of aryl groups preferable as R ¹ and R ² include phenyl group, tolyl group, ethylphenyl group, and dimethylphenyl group. Among these, a phenyl group and a tolyl group are more preferable.

When R ¹ and R ² are an aralkyl group, the carbon number of the aralkyl group is usually 7 or 8. When the number of carbon atoms is larger than 8, as in the case of alkyl groups, alkenyl groups, and aryl groups, the compatibility or solubility of lactones in a non-aqueous electrolyte decreases, and the protective film formed on the positive electrode becomes brittle. Therefore, there is a possibility that the battery capacity of the lithium secondary battery using the non-aqueous electrolyte is insufficient.

Further, when R ^1, R ² is an aralkyl group, examples of preferred aralkyl groups as R ^1, R ² is benzyl, alpha-phenethyl, etc. β- phenethyl group. Among these, a benzyl group is more preferable.

Furthermore, among the above-described compounds, R ¹ and R ² are preferably a hydrogen atom and an alkyl group. Among these, it is most preferable that one of R ¹ and R ² is a hydrogen atom and the other is an alkyl group. However, the number of carbon atoms of the alkyl group at this time is usually preferably 1 or more and 3 or less. This is because the reactivity in the non-aqueous electrolyte can be made appropriate, and an effective film can be formed on the positive electrode when used in a lithium secondary battery.

Moreover, the hydrocarbon group used as R ¹ and R ² may further have a substituent. The type of the substituent is arbitrary, but specific examples include an alkoxy group, an ester group, an amide group, and a halogen group. Moreover, these substituents may form a ring.

In the general formula (1), R ³ represents a divalent hydrocarbon group. Further, the carbon number of R ³ is usually 1 or more and 5 or less.
The type of R ³ is arbitrary, and examples thereof include alkylene groups such as methylene group, ethylene group, propylene group and butylene group, alkenylene groups such as vinylene group and the like. Of these, a methylene group, an ethylene group, and a vinylene group are preferable.

The hydrocarbon group used as R ³ may further have a substituent. The type of the substituent is arbitrary, but specific examples thereof include alkyl groups such as methyl group and ethyl group; hydrocarbon groups such as alkenyl group such as vinyl group and allyl group; alkoxy groups such as methoxy group and ethoxy group Groups; halogen groups such as a fluoro group, a chloro group, and a bromo group. Further, when the substituent R ³ has is an organic group, the number of carbon atoms is usually 1 or more 3 or less.

In the general formula (2), R ⁴ and R ⁵ each independently represent a hydrogen atom or a monovalent hydrocarbon group.
When R ⁴ and R ⁵ are hydrocarbon groups, the carbon number is usually 1 or more and usually 8 or less.
Furthermore, the kind of hydrocarbon group to be R ⁴ and R ⁵ is arbitrary, and examples thereof include an alkyl group, an alkenyl group, an aryl group, an aralkyl group, and the like.

When R ⁴ and R ⁵ are any of an alkyl group, an alkenyl group, an aryl group, and an aralkyl group, the number of carbon atoms and specific examples thereof are as follows: R ¹ and R ² are hydrocarbon groups in the description of the general formula (1) Are the same as those described for the alkyl group, alkenyl group, aryl group, and aralkyl group.

Among these, as R ⁴ and R ⁵ , a hydrogen atom and an alkyl group are preferable. Of these, R ⁴ and R ⁵ are most preferably hydrogen atoms. This is because the reactivity in the non-aqueous electrolyte can be made appropriate, and an effective film can be formed on the positive electrode when used in a lithium secondary battery.

Moreover, the hydrocarbon group used as R ⁴ and R ⁵ may further have a substituent, similarly to R ¹ and R ² . The kind of the substituent is arbitrary, but specific examples include an alkoxy group, an ester group, an amide group, and a halogen group. Moreover, these substituents may form a ring.

In the general formula (2), R ⁶ represents a divalent hydrocarbon group. Further, the carbon number of R ⁶ is usually 1 or more and 6 or less.
The type of R ⁶ is arbitrary, and examples thereof include alkylene groups such as methylene group, ethylene group, propylene group and butylene group, and alkenylene groups such as vinylene group. Of these, ethylene group and propylene group are preferable.

R ⁶ may further have a substituent. This type of substituents is optional, and specific examples thereof are the same as those of the substituent which may be possessed by R ^3. However, if the substituents R ⁶ has is a hydrocarbon group, the number of carbon atoms is usually 1 or more and 4 or less.

Further, in the general formula (3), R ⁷ and R ⁸ each independently represent a hydrogen atom or a monovalent hydrocarbon group.
Further, when R ⁷ and R ⁸ are hydrocarbon groups, the carbon number is usually 1 or more and usually 8 or less.
Furthermore, although the kind of hydrocarbon group used as R ⁷ and R ⁸ is arbitrary, examples thereof include an alkyl group, an alkenyl group, an aryl group, and an aralkyl group.

When R ⁷ and R ⁸ are any of an alkyl group, an alkenyl group, an aryl group, and an aralkyl group, the number of carbon atoms and specific examples thereof are as follows: R ¹ and R ² are hydrocarbon groups in the description of the general formula (1) Are the same as those described for the alkyl group, alkenyl group, aryl group, and aralkyl group.

Furthermore, among the above-mentioned, as R ⁷ and R ⁸ , a hydrogen atom and an alkyl group are preferable. Among these, it is particularly preferable that R ⁷ is a hydrogen atom and R ⁸ is an alkyl group. However, the number of carbon atoms of the alkyl group at this time is usually preferably 1 or more and 3 or less. This is because the reactivity in the non-aqueous electrolyte can be made appropriate, and an effective film can be formed on the positive electrode when used in a lithium secondary battery.

Further, the hydrocarbon group used as R ⁷ and R ⁸ may further have a substituent as in R ¹ , R ² , R ⁴ and R ⁵ . The kind of the substituent is arbitrary, but specific examples include an alkoxy group, an ester group, an amide group, and a halogen group. Moreover, these substituents may form a ring.

  Furthermore, the lactones of the present invention have a molecular weight of usually 70 or more, usually 250 or less, preferably 200 or less, more preferably 150 or less. If the upper limit of this range is exceeded, the compatibility or solubility of lactones with respect to the non-aqueous electrolyte decreases, and the protective film formed on the positive electrode becomes brittle, so a lithium secondary battery using the non-aqueous electrolyte The battery capacity of the battery may be insufficient.

Hereinafter, although the specific example of the lactone of this invention is given, the lactone of this invention is not limited to the following illustrations. Incidentally, in parentheses after the compound name "<>" indicates the R ¹ to R ⁸ in the case of applying the respective compound in the general formula (1) to (3). In the following description, Me represents a methyl group, Et represents an ethyl group, Pr represents a propyl group, and Ph represents a phenyl group.

Specific examples of the lactones of the present invention include 2 (5H) -furanone <R ¹ , R ² = H, R ³ = methylene group>, 5-methoxy-2 (5H) -furanone <R ¹ , R ² = H, R ³ = methoxymethylene group>, 5-ethoxy-2 (5H) -furanone <R ¹ , R ² = H, R ³ = ethoxymethylene group>, 5-methoxymethyl-2 (5H) -furanone <R ¹ , R ² = H, R ³ = methoxymethylmethylene group>, 5-acetoxy-2 (5H) -furanone <R ¹ , R ² = H, R ³ = acetoxymethylene group>, 5-chloro-2 (5H ) -Furanone <R ¹ , R ² = H, R ³ = chloromethylene group>, 3-methyl-2 (5H) -furanone <R ¹ = H, R ² = Me, R ³ = methylene group>, 4- methyl -2 (5H) - furanone ^{<R 1 = Me, R 2} = H, R 3 = methylene group>, 5-methylcarbamoyl -2 (5H) - furanone ^{<R 1, R 2 = H} , R 3 = methylmethylene group>, 3-ethyl -2 (5H) - furanone ^{<R 1 = H, R 2} = Et, R 3 = methylene >, 4-ethyl-2 (5H) -furanone <R ¹ = Et, R ² = H, R ³ = methylene group>, 5-ethyl-2 (5H) -furanone <R ¹ , R ² = H, R ³ = ethyl methylene group>, 3-vinyl -2 (5H) - furanone ^{<R 1 = H, R 2} = vinyl group, R ³ = methylene group>, 4-vinyl -2 (5H) - furanone <R ¹ = a vinyl ^{group, R 2 = H, R 3} = methylene group>, 5-vinyl -2 (5H) - furanone ^{<R 1, R 2 = H} , R 3 = vinyl methylene group>, 3-phenyl -2 (5H) - furanone ^{<R 1 = H, R 2} = Ph, R 3 = methylene group>, 4-phenyl -2 (5H) - furanone ^{<R 1 = Ph, R 2} = H R ³ = methylene group>, 3-benzyl -2 (5H) - furanone ^{<R 1 = H, R 2} = benzyl group, R ³ = methylene group>, 4-benzyl -2 (5H) - furanone <R ¹ = Benzyl group, R ² = H, R ³ = methylene group>, 3,4-dimethyl-2 (5H) -furanone <R ¹ = Me, R ² = Me, R ³ = methylene group>, 3,5-methyl -2 (5H) -furanone <R ¹ = H, R ² = Me, R ³ = methylmethylene group>, 4,5-methyl-2 (5H) -furanone <R ¹ = Me, R ² = H, R ³ = methylmethylene group>, 2 (5H) -furanone derivatives such as;

5,6-dihydro -2H- pyran-2-one ^{<= R 1, R 2 H} , R 3 = ethylene group>, 5,6-dihydro-3-methyl--2H- pyran-2-one <R ¹ = H, R ² = Me, R ³ = ethylene group>, 5,6-dihydro-4-methyl-2H-pyran-2-one <R ¹ = Me, R ² = H, R ³ = ethylene group>, 5 , 6-Dihydro-5-methyl-2H-pyran-2-one <R ¹ = H, R ² = H, R ³ = β-methylethylene group>, 5,6-dihydro-6-methyl-2H-pyran 2-one <R ¹ = H, R ² = H, R ³ = α-methylethylene group>, 5,6-dihydro-3-ethyl-2H-pyran-2-one <R ¹ = H, R ² = Et, R ³ = ethylene group>, 5,6-dihydro-4-ethyl-2H-pyran-2-one <R ¹ = Et, R ² = H, R ³ = ethylene group> 5,6-dihydro-5-ethyl-2H-pyran-2-one <R ¹ = H, R ² = H, R ³ = β-ethylethylene group>, 5,6-dihydro-6-ethyl-2H -Pyran-2-one <R ¹ = H, R ² = H, R ³ = α-ethylethylene group>, 5,6-dihydro-3-phenyl-2H-pyran-2-one <R ¹ = H, R ² = Ph, R ³ = ethylene group>, 5,6-dihydro-4-phenyl-2H-pyran-2-one <R ¹ = Ph, R ² = H, R ³ = ethylene group>, etc. , 6-Dihydro-2H-pyran-2-one derivatives;

α-pyrone <R ¹ = H, R ² = H, R ³ = vinylene group>, 3-methyl-α-pyrone <R ¹ = H, R ² = Me, R ³ = vinylene group>, 4-methyl- α-pyrone <R ¹ = Me, R ² = H, R ³ = vinylene group>, 5-methyl-α-pyrone <R ¹ , R ² = H, R ³ = β-methyl vinylene group>, 6-methyl -Α-pyrone <R ¹ , R ² = H, R ³ = α-methylvinylene group>, 3-ethyl-α-pyrone <R ¹ = H, R ² = Et, R ³ = vinylene group>, 4- Ethyl-α-pyrone <R ¹ = Et, R ² = H, R ³ = vinylene group>, 5-ethyl-α-pyrone <R ¹ , R ² = H, R ³ = β-ethyl vinylene group>, 6 -Ethyl-α-pyrone <R ¹ , R ² = H, R ³ = α-ethyl vinylene group>, 6-propyl-α-pyrone <R ¹ , R ² = H, R ³ = α-propyl vinylene group> , 3-fu Cycloalkenyl -α- pyrones ^{<R 1 = H, R 2} = Ph, R 3 = vinylene group>, 4-phenyl -α- pyrone ^{<= R 1 Ph, R 2} = H, R 3 = vinylene group>, 4, 6-dimethyl-α-pyrone <R ¹ = Me, R ² = H, R ³ = α-methylvinylene group>, 4,6-diethyl-α-pyrone <R ¹ = Et, R ² = H, R ³ Α-pyrone derivatives such as = α-ethylvinylene group>, 4,6-diprotyl-α-pyrone <R ¹ = Pr, R ² = H, R ³ = α-propyl vinylene group>;

α-methylene-β-propiolactone <R ⁴ , R ⁵ = H, R ⁶ = methylene group>, α-ethylidene-β-propiolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = methylene group >, Α-benzylidene-β-propiolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = methylene group>, etc .;

α-methylene-β-butyrolactone <R ⁴ , R ⁵ = H, R ⁶ = methylmethylene group>, α-methylene-γ-butyrolactone <R ⁴ , R ⁵ = H, R ⁶ = ethylene group>, α-ethylidene -Β-butyrolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = methylmethylene group>, α-ethylidene-γ-butyrolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = ethylene group>, α- Benzylidene-β-butyrolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = methylmethylene group>, α-benzylidene-γ-butyrolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = ethylene group>, etc. A butyrolactone derivative of

α-methylene-γ-valerolactone <R ⁴ , R ⁵ = H, R ⁶ = α-methylethylene group>, α-methylene-δ-valerolactone <R ⁴ , R ⁵ = H, R ⁶ = propylene group> , Α-ethylidene-γ-valerolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = α-methylethylene group>, α-ethylidene-δ-valerolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = propylene group, α-benzylidene-γ-valerolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = α-methylethylene group>, α-benzylidene-δ-valerolactone <R ⁴ = H, R Valerolactone derivatives such as ⁵ = Ph, R ⁶ = propylene group;

α-methylene-γ-caprolactone <R ⁴ , R ⁵ = H, R ⁶ = α-ethylethylene group>, α-methylene-δ-caprolactone <R ⁴ , R ⁵ = H, R ⁶ = α-methylpropylene group >, Α-methylene-ε-caprolactone <R ⁴ , R ⁵ = H, R ⁶ = butylene group>, α-ethylidene-γ-caprolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = α-ethylethylene Group>, α-ethylidene-δ-caprolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = α-methylpropylene group>, α-ethylidene-ε-caprolactone <R ⁴ = H, R ⁵ = Me, R ⁶ = butylene group>, α-benzylidene-γ-caprolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = α-ethylethylene group>, α-benzylidene-δ-caprolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = α-methylpropylene group>, α-benzylyl Caprolactone derivatives such as den-ε-caprolactone <R ⁴ = H, R ⁵ = Ph, R ⁶ = butylene group>;

Dihydrofuran-2-one <R ⁷ , R ⁸ = Me>, α-angelicalactone <R ⁷ = H, R ⁸ = Me>, 5-ethyl-dihydrofuran-2-one <R ⁷ = H, R ⁸ = Et>, 5-propyl-dihydrofuran-2-one <R ⁷ = H, R ⁸ = Pr>, 5-phenyl-dihydrofuran-2-one <R ⁷ = H, R ⁸ = Ph>, 4, Examples include dihydrofuran-2-one derivatives such as 5-dimethyl-dihydrofuran-2-one <R ⁷ = Me, R ⁸ = Me>.

  Among those exemplified above, 2 (5H) -furanone derivatives include 2 (5H) -furanone, 3-methyl-2 (5H) -furanone, 4-methyl-2 (5H) -furanone, 5-methyl-2 ( 5H) -furanone, 3-ethyl-2 (5H) -furanone, 4-ethyl-2 (5H) -furanone, 5-ethyl-2 (5H) -furanone and the like are preferable, and 5,6-dihydro-2H-pyran In 2-one derivatives, 5,6-dihydro-2H-pyran-2-one, 5,6-dihydro-3-methyl-2H-pyran-2-one, 5,6-dihydro-4-methyl-2H -Pyran-2-one, 5,6-dihydro-5-methyl-2H-pyran-2-one, 5,6-dihydro-6-methyl-2H-pyran-2-one and the like are preferable, and α-pyrone derivatives Then, α-pyrone, 3-methyl-α- Ron, 4-methyl-α-pyrone, 5-methyl-α-pyrone, 6-methyl-α-pyrone, 4,6-dimethyl-α-pyrone, 4,6-diethyl-α-pyrone, 4,6- Diprotyl-α-pyrone and the like are preferable.

  In addition, α-methylene-β-propiolactone, α-benzylidene-β-propiolactone and the like are preferable for propiolactone derivatives, and α-methylene-β-butyrolactone and α-methylene-γ-butyrolactone are preferable for butyrolactone derivatives. , Α-benzylidene-β-butyrolactone, α-benzylidene-γ-butyrolactone and the like are preferable, and valerolactone derivatives include α-methylene-γ-valerolactone, α-methylene-δ-valerolactone, α-benzylidene-γ-valero Lactone, α-benzylidene-δ-valerolactone and the like are preferable, α-methylene-ε-caprolactone, α-benzylidene-ε-caprolactone and the like are preferable for the caprolactone derivative, and α-angelicalactone for the dihydrofuran-2-one derivative. 5-phenyl-dihydrofura 2-one and the like are preferable.

Further, among these, in particular, 2 (5H) -furanone derivatives are preferably 2 (5H) -furanone, 3-methyl-2 (5H) -furanone, and 3-ethyl-2 (5H) -furanone. As the dihydro-2H-pyran-2-one derivative, 5,6-dihydro-2H-pyran-2-one is preferable, and as the α-pyrone derivative, α-pyrone, 6-methyl-α-pyrone, 4,6- Dimethyl-α-pyrone, 4,6-diethyl-α-pyrone and the like are more preferable.
Further, in the butyrolactone derivative, α-methylene-γ-butyrolactone, α-benzylidene-γ-butyrolactone and the like are preferable, and in the valerolactone derivative, α-methylene-γ-valerolactone, α-methylene-δ-valerolactone and the like are preferable. Among the dihydrofuran-2-one derivatives, α-angelica lactone and the like are preferable.

Among them, 3-methyl-2 (5H) -furanone, 2 (5H) -furanone, 5,6-dihydro-2H-pyran-2-one, α-pyrone, 4,6-dimethyl-α-pyrone, α -Methylene-γ-butyrolactone, α-angelicalactone, and the like are more preferable. These lactones have moderate oxidation resistance, and form a stable film on the positive electrode when they are contained in the non-aqueous electrolyte. Therefore, the storage characteristics of lithium secondary batteries using the non-aqueous electrolyte are included. Is to improve.
Moreover, the lactones of the present invention described above may be used alone or in combination of two or more in any combination and ratio.

[1-2. composition]
The nonaqueous electrolytic solution in the present invention contains the lactone of the present invention in an amount of usually 0.01% by weight or more, preferably 0.1% by weight or more, and usually 5% by weight or less, preferably 2% by weight or less. Below the lower limit of this range, the non-aqueous electrolyte in the present invention may not be able to improve the high temperature retention characteristics. If the upper limit is exceeded, a thick film is formed on the positive electrode, and since this film has a high resistance, Li ions do not easily move between the non-aqueous electrolyte and the positive electrode, and the battery characteristics such as rate characteristics decrease. There is a risk. In addition, when using 2 or more types of lactones of this invention together, it is made for the sum total of the density | concentration of the lactones to be used to be in the said range.

[2. Nonaqueous solvent]
There is no restriction | limiting in particular about a non-aqueous solvent, Although a well-known non-aqueous solvent can be used arbitrarily, Usually, an organic solvent is used. Examples of non-aqueous solvents include chain carbonates, cyclic carbonates, chain esters, cyclic esters (lactone compounds), chain ethers, cyclic ethers, sulfur-containing organic solvents, and the like. Among them, as a solvent that exhibits high ionic conductivity, chain carbonates, cyclic carbonates, chain esters, cyclic esters, chain ethers, and cyclic ethers are usually preferable.

Specific examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.
Specific examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate and the like.
Specific examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether and the like.

Specific examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane and the like.
Specific examples of the chain esters include methyl formate, methyl acetate, and methyl propionate.
Specific examples of cyclic esters include γ-butyrolactone and γ-valerolactone.

  However, when the non-aqueous solvent contains cyclic esters (lactones), lactones having a carbon-carbon unsaturated bond among the lactones are regarded as the lactones of the present invention described above. Moreover, when the non-aqueous solvent contains unsaturated carbonates, the unsaturated carbonates are regarded as a film forming agent described later.

  Furthermore, the non-aqueous solvent may be used alone or in combination of two or more in any combination and ratio. However, it is preferable to use a mixture of two or more non-aqueous solvents so as to exhibit desired characteristics, that is, continuous charge characteristics. In particular, it is preferable to mainly consist of cyclic carbonates and chain carbonates or cyclic esters. Here, “being mainly” specifically means that the non-aqueous solvent contains a total of 70% by weight or more of cyclic carbonates and chain carbonates or cyclic esters.

  When two or more kinds of non-aqueous solvents are used in combination, examples of preferable combinations include binary solvents such as ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and γ-butyrolactone; ethylene carbonate and dimethyl carbonate And ternary solvents such as ethylene methyl carbonate, ethylene carbonate, methyl ethyl methyl carbonate, and diethyl carbonate. Nonaqueous solvents mainly containing these are preferably used because they satisfy various properties in a well-balanced manner.

  When an organic solvent is used as the non-aqueous solvent, the carbon number of the organic solvent is usually 3 or more, and usually 13 or less, preferably 7 or less. If the number of carbon atoms is too large, the solubility in the electrolytic solution is deteriorated, and there is a possibility that the effect of the present invention of improving the continuous charging characteristics cannot be sufficiently exhibited. On the other hand, if the number of carbon atoms is too small, the volatility increases, causing an increase in the battery internal pressure, which is not preferable.

  The molecular weight of the organic solvent used as the non-aqueous solvent is usually 50 or more, preferably 80 or more, and usually 250 or less, preferably 150 or less. If the molecular weight is too large, the solubility in the electrolytic solution is deteriorated, and there is a possibility that the effect of the present invention of improving the continuous charge characteristics cannot be sufficiently exhibited. On the other hand, if the molecular weight is too small, the volatility is increased, which causes an increase in the internal pressure of the battery, which is not preferable.

  Further, when a binary or higher nonaqueous solvent using two or more kinds of nonaqueous solvents is used, the ratio of the cyclic carbonate in the binary or higher nonaqueous solvent is usually 10% by volume or higher, preferably 15%. The volume is not less than volume%, more preferably not less than 20 volume%, and is usually not more than 60 volume%, preferably not more than 50 volume%, more preferably not more than 40 volume%. If the lower limit of the above range is not reached, dissociation of the Li salt is less likely to occur, and the conductivity is reduced, so the high load capacity is likely to decrease.If the upper limit is exceeded, the viscosity becomes too high and Li ions are less likely to move. Capacity tends to decrease. However, when γ-butyrolactone is used, its concentration is preferably 20% by weight or less.

[3. Electrolytes]
There is no restriction | limiting in particular about electrolyte, Although a well-known thing can be used arbitrarily if it is used as an electrolyte of a lithium secondary battery, Usually, lithium salt is used.
As the lithium salt used for the electrolyte, either an inorganic lithium salt or an organic lithium salt may be used. Examples of inorganic lithium salts include inorganic fluoride salts such as LiPF ₆ , LiAsF ₆ , LiBF ₄ and LiSbF ₆ ; inorganic chloride salts such as LiAlCl ₄ ; perhalogenates such as LiClO ₄ , LiBrO ₄ and LiIO _4. Etc. Examples of organic lithium salts include perfluoroalkane sulfonates such as CF ₃ SO ₃ Li and C ₄ F ₉ SO ₃ Li; perfluoroalkane carboxylates such as CF ₃ COOLi; (CF ₃ CO) Perfluoroalkanecarbonimide salts such as ₂ NLi; fluorine-containing organic lithium salts such as perfluoroalkanesulfonimide salts such as (CF ₃ SO ₂ ) ₂ NLi and (C ₂ F ₅ SO ₂ ) ₂ NLi.

Among these, LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, and the like are preferable because they are easily soluble in a solvent and exhibit a high degree of dissociation. In addition, electrolyte may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio. In particular, the combined use of LiPF ₆ and LiBF ₄ or the combined use of LiPF ₆ and (CF ₃ SO ₂ ) ₂ NLi is preferable because it has an effect of improving the continuous charge characteristics.

  The concentration of the electrolyte in the non-aqueous electrolyte is usually 0.5 mol / L or more, preferably 0.75 mol / L or more, and usually 2 mol / L or less, preferably 1. 75 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity is lowered due to an increase in viscosity, and precipitation at a low temperature is likely to occur, and the performance of the lithium secondary battery tends to be lowered.

[4. Film-forming agent]
The nonaqueous electrolytic solution in the present invention preferably contains an unsaturated carbonate as a film forming agent for the purpose of forming a film on the negative electrode and improving battery characteristics. The unsaturated carbonate is not particularly limited as long as it is a carbonate having a carbon-carbon unsaturated bond, and any unsaturated carbonate can be used. Examples thereof include carbonates having an aromatic ring and carbonates having carbon-carbon unsaturated bonds such as carbon-carbon double bonds and carbon-carbon triple bonds.

Specific examples of the unsaturated carbonate include vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate; -Ethylene carbonate derivatives substituted with a substituent having a carbon-carbon unsaturated bond such as divinylethylene carbonate, phenylethylene carbonate, 1,2-diphenylethylene carbonate; diphenyl carbonate, methylphenyl carbonate, t-butylphenyl carbonate, etc. Phenyl carbonates; vinyl carbonates such as divinyl carbonate and methyl vinyl carbonate; diallyl carbonate, allyl methyl carbonate Allyl carbonate such as theft and the like. Among these, vinylene carbonate derivatives and ethylene carbonate derivatives substituted with a substituent having a carbon-carbon unsaturated bond are preferable. In particular, vinylene carbonate, 1,2-diphenyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, and vinyl ethylene carbonate are more preferable. By using these unsaturated carbonates, a stable interface protective film is formed on the negative electrode, so that the recovery capacity after high-temperature storage is improved, and the cycle characteristics of the lithium secondary battery are also improved.
In addition, unsaturated carbonates may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The carbon number of the unsaturated carbonate is usually 3 or more, and usually 20 or less, preferably 15 or less. If the upper limit of the above range is exceeded, the solubility in the electrolytic solution tends to deteriorate.

  Furthermore, there is no particular lower limit to the molecular weight of the unsaturated carbonate, but it is usually 80 or more, and usually 250 or less, preferably 150 or less. If the molecular weight is too large, the solubility in the electrolytic solution is deteriorated, and there is a possibility that the effect of the present invention of improving the continuous charge characteristics cannot be sufficiently exhibited.

  The concentration of unsaturated carbonates in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.3% by weight or more, and usually 10% by weight or less. , Preferably 7% by weight or less, more preferably 5% by weight or less. If the concentration of the unsaturated carbonates is too large, the high-temperature storage characteristics tend to deteriorate, and further, the amount of gas generated increases when the battery is used, and the capacity retention rate may be reduced. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited. In addition, when using 2 or more types of unsaturated carbonate together, it is made for the sum total of the density | concentration of the used unsaturated carbonate to be in the said range.

  Here, the reason why the nonaqueous electrolytic solution in the present invention preferably contains an unsaturated carbonate will be described. Unsaturated carbonates partly or entirely decompose on the negative electrode during initial charging to form a film. As a result, the subsequent reductive decomposition reaction of the non-aqueous solvent can be suppressed, so that the recovery capacity of the lithium secondary battery after high-temperature storage is increased and the cycle characteristics are improved. However, when the unsaturated carbonates remain in the non-aqueous electrolyte even after the initial charge, the unsaturated carbonates are liable to undergo an oxidation reaction at the positive electrode and tend to generate gas during high-temperature storage. On the other hand, the lactones of the present invention form a film on the positive electrode and suppress the oxidative decomposition reaction of unsaturated carbonates and the subsequent nonaqueous solvent. That is, it is one of the advantages of the present invention that the problem of gas generation by unsaturated carbonates can be solved by introducing the lactones of the present invention.

[5. Other auxiliaries]
The non-aqueous electrolyte in the present invention may contain other auxiliary agents for the purpose of improving the wettability, overcharge characteristics, etc. of the non-aqueous electrolyte in a range that does not impair the effects of the present invention.
Examples of auxiliaries include acid anhydrides such as maleic anhydride, succinic anhydride, and glutaric anhydride; carboxylic acid esters such as vinyl acetate, divinyl adipate, and allyl acetate; diphenyl disulfide, 1,3-propane sultone, Sulfur-containing compounds such as 1,4-butane sultone, dimethyl sulfone, divinyl sulfone, dimethyl sulfite, ethylene sulfite, 1,4-butanediol dimethanesulfonate, methyl methanesulfonate, 2-propynyl methanesulfonate; t- Aromatic compounds such as butylbenzene, biphenyl, o-terphenyl, 4-fluorobiphenyl, fluorobenzene, 2,4-difluorobenzene, cyclohexylbenzene, diphenyl ether, 2,4-difluoroanisole, trifluoromethylbenzene and the fragrance Such as those compounds substituted with fluorine atom.
Moreover, 1 type may be used independently for an adjuvant, and 2 or more types may be used together by arbitrary combinations and a ratio.

  The concentration in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.05% by weight or more, and usually 10% by weight or less, preferably 5% by weight or less. In addition, when using 2 or more types of adjuvants together, it is made for the sum total of these density | concentrations to be settled in the said range.

[6. Non-aqueous electrolyte state]
The non-aqueous electrolytic solution usually exists in a liquid state, but it may be gelled with a polymer to form a semi-solid electrolyte. The polymer used for the gelation is arbitrary, and examples thereof include polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyethylene oxide, polyacrylate, and polymethacrylate. In addition, the polymer | macromolecule used for gelatinization may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio. When a non-aqueous electrolyte is used as a semi-solid electrolyte, the ratio of the non-aqueous electrolyte in the semi-solid electrolyte is usually 30% by weight or more, preferably 50% by weight with respect to the total amount of the semi-solid electrolyte. Above, more preferably 75% by weight or more, and usually 99.95% by weight or less, preferably 99% by weight or less, more preferably 98% by weight or less. If the ratio of the non-aqueous electrolyte is too large, it is difficult to hold the electrolyte and liquid leakage tends to occur. Conversely, if it is too small, the charge / discharge efficiency and capacity may be insufficient.

[7. Method for producing non-aqueous electrolyte]
The non-aqueous electrolyte solution in the present invention can be prepared by dissolving an electrolyte, the lactones of the present invention, and if necessary, unsaturated carbonates and other auxiliary agents in a non-aqueous solvent.
In preparing the non-aqueous electrolyte, each raw material of the non-aqueous electrolyte, that is, the electrolyte, the lactone of the present invention, the non-aqueous solvent, the unsaturated carbonate, and other auxiliary agents may be dehydrated in advance. preferable. The degree of dehydration is usually 50 ppm or less, preferably 30 ppm or less. In the present specification, ppm means a ratio based on weight.

If water is present in the non-aqueous electrolyte, electrolysis of water, reaction between water and lithium metal, hydrolysis of lithium salt, and the like may occur, which is not preferable.
The dehydration means is not particularly limited. For example, when the object to be dehydrated is a liquid such as a non-aqueous solvent, a molecular sieve or the like may be used. When the object to be dehydrated is a solid such as an electrolyte, it may be dried at a temperature lower than the temperature at which decomposition occurs.

[II. Lithium secondary battery]
The lithium secondary battery of the present invention includes the above-described non-aqueous electrolyte solution according to the present invention, and a positive electrode and a negative electrode capable of inserting and extracting lithium. In addition, the lithium secondary battery of the present invention may have other configurations. For example, a lithium secondary battery usually includes a spacer.

[1. Positive electrode]
The positive electrode is usually configured by providing a positive electrode active material layer on a current collector. Note that the positive electrode may include other layers as appropriate.
[1-1. Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not limited as long as it can occlude and release lithium ions. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides of transition metals and lithium, and sulfides of transition metals.

Specific examples of transition metal oxides include MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ . Specific examples of the composite oxide of transition metal and lithium include a lithium nickel composite oxide whose basic composition is LiNiO ₂ ; a lithium cobalt composite oxide whose basic composition is LiCoO ₂ ; a basic composition of LiMnO ₂ and LiMnO. _And lithium manganese composite oxide such as ₄ . Further, specific examples of the transition metal sulfide include TiS ₂ and FeS. Among these, a composite oxide of lithium and a transition metal is preferable because it can achieve both high capacity and high cycle characteristics of a lithium secondary battery.

  Further, in the above-described composite oxide of transition metal and lithium, some of the main transition metal atoms are Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg. Replacing with other metals such as Ca and Ga is preferable because they can be stabilized. Of these, replacement with Al, Mg, Ca, Ti, Zr, Co, Ni, and Mn is particularly preferable because deterioration of the positive electrode at a high voltage is suppressed.

In addition, the surface of the composite oxide of transition metal and lithium described above is oxidized with metals such as Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, and Ga. It is preferable to coat with an object because the oxidation reaction of the solvent at a high voltage is suppressed. Of these, Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and MgO are particularly preferable because they have high strength and exhibit a stable coating effect.
In addition, any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.

The specific surface area of the positive electrode active material is usually 0.1 m ² / g or more, preferably 0.2 m ² / g or more, and usually 10 m ² / g or less, preferably 5.0 m ² / g or less, more preferably Is 3.0 m ² / g or less. If the specific surface area is too small, the rate characteristics and capacity may be reduced. If the specific surface area is too large, an undesirable reaction with a non-aqueous electrolyte or the like may be caused and cycle characteristics may be deteriorated.

  Furthermore, the average secondary particle size of the positive electrode active material is usually 0.2 μm or more, preferably 0.3 μm or more, and usually 20 μm or less, preferably 10 μm or less. If the average secondary particle size is too small, the cycle deterioration of the lithium secondary battery may be increased and handling may be difficult. If the average secondary particle size is too large, the internal resistance of the battery may be increased and output may be difficult to output.

  The thickness of the positive electrode active material layer is arbitrary, but is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, most preferably 40 μm or more, and usually 200 μm or less, preferably 150 μm or less, Preferably it is 100 micrometers or less. If it is too thin, the coating becomes difficult and it becomes difficult to ensure uniformity, and the capacity of the battery may be small. On the other hand, if it is too thick, there is a risk that the rate characteristics will deteriorate.

  The positive electrode active material layer is formed by slurrying the above-described positive electrode active material, a binder (binder), and various auxiliary agents as necessary with a solvent to form a coating solution, and using the coating solution as a current collector. It can be manufactured by applying and drying. Further, the positive electrode active material described above may be roll-formed to form a sheet electrode, or may be formed into a pellet electrode by compression molding. Hereinafter, a case where the slurry is applied to the positive electrode current collector and dried will be described.

The binder is not particularly limited as long as it is a material that is stable with respect to the non-aqueous solvent used in the non-aqueous electrolyte solution or the solvent used during electrode production, but weather resistance, chemical resistance, heat resistance, difficulty It is preferable to select in consideration of flammability and the like. Specific examples include inorganic compounds such as silicate and water glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene and polymethylstyrene. , Polymers having rings such as polyvinyl pyridine, poly-N-vinyl pyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, Acrylic derivative polymers such as polyacrylamide; Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl chloride, halogen-containing polymers of polyvinylidene chloride; polyvinyl alcohol polymers such as polyvinyl alcohol such as a conductive polymer such as polyaniline can be used. In addition, mixtures such as the above polymers, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used. Among these, preferred binders are a fluororesin and a CN group-containing polymer.
In addition, a binder may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  When a resin is used as the binder, the weight average molecular weight of the resin is usually 10,000 or more, preferably 100,000 or more, and usually 3 million or less, preferably 1 million or less. If the molecular weight is too low, the strength of the electrode tends to decrease. On the other hand, if the molecular weight is too high, the viscosity becomes high and it may be difficult to form an electrode.

  Furthermore, the amount of the binder used is the positive electrode active material (a negative electrode active material when used for the negative electrode. Hereinafter, the positive electrode active material and the negative electrode active material are simply referred to as “active material”) 100. The amount is usually 0.1 parts by weight or more, preferably 1 part by weight or more, and usually 30 parts by weight or less, preferably 20 parts by weight or less with respect to parts by weight. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if the amount of the binder is too large, the ionic conductivity tends to decrease.

  The electrode may contain various auxiliaries as described above. Examples of the auxiliary agent include a conductive material that increases the conductivity of the electrode, and a reinforcing material that improves the mechanical strength of the electrode. Specific examples of the conductive material are not particularly limited as long as an appropriate amount can be mixed with the active material to impart conductivity. However, carbon powders such as acetylene black, carbon black, and graphite, and various metals are usually used. Examples include fibers and foils. As specific examples of the reinforcing material, various inorganic, organic spherical, fibrous fillers and the like can be used. In addition, these adjuvants etc. may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The solvent for forming the slurry is not particularly limited in type as long as it is a solvent capable of dissolving or dispersing the active material, the binder, and auxiliary agents used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N -N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. Is mentioned. In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.

[1-2. Current collector]
As a material for the current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the current collector for the positive electrode include aluminum, nickel, and SUS (stainless steel). Among these, aluminum is preferable as the positive electrode current collector. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.

  Furthermore, in order to improve the binding effect between the current collector and the active material layer formed on the surface, it is preferable that the surface of these current collectors is roughened in advance. The surface roughening method includes blasting or rolling with a rough roll, and the surface of the current collector with a wire brush equipped with abrasive cloth paper, grindstone, emery buff, steel wire, etc. to which abrasive particles are fixed. Examples thereof include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.

  Further, the shape of the current collector is arbitrary. For example, in order to reduce the weight of the battery, that is, to improve the energy density per weight, a perforated type current collector such as an expanded metal or a punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when a coating layer is formed on both surfaces of such a perforated current collector, the coating layer tends to be more difficult to peel due to the rivet effect of the coating layer through the hole, but the aperture ratio is too high. When it becomes high, the contact area between the coating layer and the current collector becomes small, so the adhesive strength is rather low.

  When a thin film is used as the positive electrode current collector, the thickness thereof is arbitrary, but it is usually 1 μm or more, preferably 5 μm or more, and is usually 100 μm or less, preferably 50 μm or less. If it is too thick, the capacity of the entire battery will be reduced. Conversely, if it is too thin, handling will be difficult.

[2. Negative electrode]
The negative electrode is usually configured by providing a negative electrode active material layer on a current collector, as in the case of the positive electrode. Note that, similarly to the positive electrode, the negative electrode may include other layers as appropriate.

[2-1. Negative electrode active material]
The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions, and a known negative electrode active material can be arbitrarily used. For example, it is preferable to use carbonaceous materials such as coke, acetylene black, mesophase micro beads, and graphite; lithium metal; lithium alloys such as lithium-silicon and lithium-tin. From the viewpoint of high capacity per unit weight and good safety, lithium alloys are particularly preferred, and from the viewpoint of good cycle characteristics and safety, it is particularly preferred to use a carbonaceous material. In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The particle size of the negative electrode active material is usually 1 μm or more, preferably 15 μm or more, and usually about 50 μm or less, preferably about 30 μm or less, in terms of excellent battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics.

  In addition, those obtained by coating the above carbonaceous material with an organic substance such as pitch and baked, those obtained by forming a carbon more amorphous than the above carbonaceous material on the surface using a CVD method, etc. Can be suitably used. Here, organic substances used for coating include coal tar pitch from soft pitch to hard pitch; coal heavy oil such as dry distillation liquefied oil; straight heavy oil such as atmospheric residual oil and vacuum residual oil; crude oil And petroleum heavy oils such as cracked heavy oil (for example, ethylene heavy end) produced as a by-product during thermal decomposition of naphtha and the like. Moreover, what pulverized the solid residue obtained by distilling these heavy oils at 200-400 degreeC to 1-100 micrometers can also be used. Furthermore, a vinyl chloride resin, a phenol resin, an imide resin, etc. can also be used.

  As in the case of the positive electrode active material layer, the negative electrode active material layer is usually a coating liquid obtained by slurrying the above-described negative electrode active material, a binder, and various auxiliary agents as necessary with a solvent. Can be manufactured by applying to a current collector and drying. As the solvent, binder, auxiliary agent and the like for forming the slurry, the same materials as those described above for the positive electrode active material can be used.

[2-2. Current collector]
As a material for the current collector of the negative electrode, a known material can be arbitrarily used. For example, a metal material such as copper, nickel, or SUS is used. Among these, copper is particularly preferable from the viewpoint of ease of processing and cost.

The negative electrode current collector is also preferably subjected to a roughening treatment in advance, as with the positive electrode current collector.
Further, like the positive electrode, the shape of the current collector is also arbitrary, and a perforated current collector such as expanded metal or punching metal can also be used. Moreover, the preferable thickness when using a thin film as a current collector is the same as that of the positive electrode.

[3. Spacer]
In order to prevent a short circuit, a spacer is usually interposed between the positive electrode and the negative electrode. The material and shape of the spacer are not particularly limited, but those that are stable with respect to the non-aqueous electrolyte described above, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable.
As a material for the spacer, for example, polyolefin such as polyethylene and polypropylene, polytetrafluoroethylene, polyethersulfone and the like can be used, and polyolefin is preferable.
The spacer is preferably porous. In this case, the non-aqueous electrolyte is used by impregnating a porous spacer.

  The thickness of the spacer is usually 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the spacer is too thin, the insulation and mechanical strength may be deteriorated. If the spacer is too thick, not only the battery performance such as the rate characteristic is deteriorated, but also the energy density of the whole battery is lowered.

When a porous film is used as the spacer, the porosity of the spacer is usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less. More preferably, it is 75% or less. If the porosity is too small, the membrane resistance increases and the rate characteristics tend to deteriorate. On the other hand, if it is too large, the mechanical strength of the film tends to decrease and the insulating property tends to decrease.
Furthermore, the average pore diameter of the spacer is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If it is too large, a short circuit tends to occur, and if it is too small, the film resistance increases and the rate characteristics may deteriorate.

[4. Assembly of secondary battery]
The lithium secondary battery of the present invention is manufactured by assembling the above-described non-aqueous electrolyte solution according to the present invention, a positive electrode, a negative electrode, and a spacer used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary. Furthermore, the shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various shapes generally employed according to the application. For example, a coin-type battery, a cylindrical battery, a square battery, etc. are mentioned. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

  At the time of assembly, the non-aqueous electrolyte containing the lactone of the present invention as described above at a specific concentration is used for a lithium secondary battery, so that the open circuit voltage between battery terminals at 25 ° C. at the end of charging is Even when charged to 4.25V or higher, preferably 4.30V or higher, more preferably 4.40V or higher, the generation of gas can be greatly suppressed, and the recovery capacity deterioration can be reduced. Become.

[5. Others]
[5-1. Regarding the open circuit voltage between battery terminals at the end of charging]
In this specification, the open circuit voltage between battery terminals is a battery voltage in a state where no current flows in the circuit. Although the measuring method is arbitrary, it can measure with a normal charging / discharging apparatus, for example.

[5-2. About charging]
When charging a lithium secondary battery, it is generally charged in a state where a voltage drop of a resistor is added. That is, the charging voltage is obtained by adding the product of the charging current and the resistance to the open circuit voltage between the battery terminals. Therefore, the difference between the charging voltage and the open circuit voltage between the battery terminals increases as the charging current increases and as the internal resistance of the lithium secondary battery or the resistance of the protection open circuit increases.

In the lithium secondary battery of the present invention, the charging method is not particularly limited and can be charged by any charging method. For example, constant current charging (CC charging), constant current-constant voltage charging (CCCV charging), pulse charging, reverse taper charging, or the like is used.
As for the end of charging, the charging may be performed for a predetermined time (for example, longer than the time required for calculation for completion of charging), or it may be detected that the charging current value has become a specified value or less. The voltage value may reach the specified value.

  In current lithium secondary batteries, the open circuit voltage between battery terminals at the end of charging is usually in the range of 4.08V to 4.20V. The higher the open circuit voltage between the battery terminals at the end of charging, the higher the capacity (mAh) of the lithium secondary battery. In addition, the higher the open circuit voltage between the battery terminals at the end of charging, the higher the voltage of the lithium secondary battery itself, so the weight energy density (mWh / kg) also increases, and the lithium secondary battery is light and long in duration. Can be obtained.

[5-3. mechanism]
Hereafter, the mechanism which the inventor of this invention guesses and the effect of this invention is acquired is demonstrated.
As described above, the development of a lithium secondary battery capable of increasing the open circuit voltage between battery terminals at the end of charging has been desired in the past. However, in the conventional technology, it is mainly positive under a high voltage condition of 4.25 V or higher. Since the oxidation reaction of the electrolyte solution at the extreme occurred remarkably, the cycle characteristics were poor, and a practical secondary battery could not be obtained. On the other hand, in the lithium secondary battery of the present invention, the main factor is that the lactones of the present invention can form a protective film on the positive electrode and suppress the oxidation reaction of the non-aqueous electrolyte solution. A lithium secondary battery excellent in storage characteristics and continuous charge characteristics can be obtained.

  Further, since the lactones of the present invention have a carbon-carbon unsaturated bond, they are easily oxidized and cause a polymerization reaction. Furthermore, since lactones are cyclic esters, ring-opening polymerization can occur. Therefore, the lactones of the present invention have two sites in the molecule, ie, a carbon-carbon unsaturated bond and an ester group as sites capable of undergoing a polymerization reaction. For this reason, a coating film having a network structure can be formed on the surface of the positive electrode by a polymerization reaction, and contact between the positive electrode active material and the electrolytic solution can be suppressed. Note that a film is formed on the positive electrode even with a lactone having no carbon-carbon unsaturated bond. However, since the structure is one-dimensional, it is unstable, and sufficient battery characteristics may not be achieved under high voltage conditions.

  Moreover, since lactones having a carbon-carbon unsaturated bond have low reduction resistance as well as oxidation resistance, they also act on the negative electrode side. That is, it is partially reduced in the initial stage of charging to form a protective film on the negative electrode, and the reaction of the non-aqueous electrolyte at the negative electrode is suppressed. When a film-forming agent such as unsaturated carbonate is used in combination, both reduced products become protective films and improve battery characteristics such as cycle characteristics and storage characteristics.

  That is, the lactones of the present invention can form a more stable protective film on the positive electrode than the other lactones, and also form a protective film on the negative electrode. For this reason, the lithium secondary battery of the present invention can increase the open circuit voltage between the battery terminals at the end of charging, and can achieve significant gas generation suppression and recovery capacity improvement during continuous charging.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples unless it exceeds the gist.

[Production of positive electrode]
A mixture obtained by mixing 92 parts by weight of lithium cobaltate (LiCoO ₂ ), 4 parts by weight of polyvinylidene fluoride (hereinafter referred to as “PVdF”) and 4 parts by weight of acetylene black, and adding N-methylpyrrolidone to form a slurry. The positive electrode was obtained by applying and drying both sides of a current collector made of aluminum.

[Manufacture of negative electrode]
90 parts by weight of graphite powder and 10 parts by weight of PVdF were mixed, and a slurry obtained by adding N-methylpyrrolidone was applied to one side of a current collector made of copper and dried to obtain a negative electrode.

[Manufacture of lithium secondary batteries]
FIG. 1 shows a schematic cross-sectional view of a lithium secondary battery.
After applying and impregnating the electrolyte solution described later to the above positive electrode, negative electrode, and polyethylene biaxially stretched porous film (separator: spacer) having a film thickness of 16 μm, a porosity of 45%, and an average pore diameter of 0.05 μm. , Negative electrode (2), separator (3), positive electrode (1), separator (3), and negative electrode (2) were laminated in this order. The battery element thus obtained was first sandwiched between polyethylene terephthalate (PET) films (4). Next, positive and negative terminals were protruded from a laminate film (7) having a resin layer formed on both sides of an aluminum foil and vacuum sealed to produce a sheet-like lithium secondary battery. Moreover, the lead | read | reed (8) with a sealing material was attached to the terminal of a positive electrode and a negative electrode. Furthermore, in order to improve the adhesion between the electrodes, the sheet-like battery was sandwiched between the silicon rubber (5) and the glass plate (6) and pressurized at a pressure of 3.4 × 10 ⁻⁴ Pa.

[Capacity evaluation]
The discharge rate per hour of lithium cobaltate was set to 160 mAh / g, and the rate was set by obtaining the discharge rate 1C from this and the amount of active material of the positive electrode of the lithium secondary battery for evaluation, and then a constant temperature bath at 25 ° C. In the middle, after constant current-constant voltage charge to 0.2 V at 0.2 C (hereinafter referred to as “CCCV charge” as appropriate), it was discharged to 3 V at 0.2 C, and an initial formation was performed. Subsequently, after CCCV charge to 4.4V at 0.7C, it discharged again to 3V at 0.2C, and the initial discharge capacity was obtained. Note that the cut current at the time of charging was 0.05C.

[4.35V continuous charge characteristics evaluation]
The battery for which the capacity evaluation test was completed was placed in a constant temperature bath at 60 ° C., charged at a constant current of 0.7 C, and switched to constant voltage charging when 4.35 V was reached. After charging for 7 days, the battery was cooled to 25 ° C., and the open circuit voltage between the battery terminals was measured. Next, the battery was immersed in an ethanol bath and the buoyancy was measured (Archimedes principle), and the amount of gas generated was determined from the buoyancy. In addition, in order to evaluate the degree of capacity deterioration after continuous charging, first discharge to 3V at 0.2C, then charge to 4.4V at 0.7C, and further discharge to 3V at 0.2C. The discharge capacity {recovery capacity (mAh)} was measured, and the recovery capacity maintenance rate after continuous charging was determined according to the following formula. A larger value indicates less battery deterioration.

[4.45V continuous charge characteristics evaluation]
The battery for which the capacity evaluation test was completed was placed in a constant temperature bath at 60 ° C., charged at a constant current of 0.7 C, and switched to constant voltage charging when it reached 4.45V. After charging for 7 days, the battery was cooled to 25 ° C., and the open circuit voltage between the battery terminals was measured. Next, the battery was immersed in an ethanol bath and the buoyancy was measured (Archimedes principle), and the amount of gas generated was determined from the buoyancy.

<Example 1>
A mixed solvent of ethylene carbonate (EC) is a cyclic carbonate and ethyl methyl carbonate is a chain carbonate (EMC) (volume mixing ratio of 1: 3) to, those of LiPF ₆ as the electrolyte was dissolved in a proportion of 1 mol / L Was added to the base electrolyte (I), and 3-methyl-2 (5H) -furanone as a lactone was added so that the concentration with respect to the non-aqueous electrolyte was 1% by weight. An aqueous electrolyte was used.

  Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1. In Table 1, the numerical values described in parentheses in the columns of lactones, unsaturated carbonates, and electrolytes represent compositions in the non-aqueous electrolyte solution, respectively. Moreover, the numerical value described in parentheses in the column of the non-aqueous solvent represents the mixing ratio of the non-aqueous solvent.

<Example 2>
In accordance with the above-described method, lithium was added to the base electrolyte (I) using a non-aqueous electrolyte obtained by adding α-methylene-γ-butyrolactone as a lactone so that the concentration with respect to the non-aqueous electrolyte was 1% by weight. A secondary battery was prepared, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 9>
In accordance with the above-mentioned method, lithium was added to the base electrolyte (I) using a non-aqueous electrolyte in which α-methylene-γ-butyrolactone as a lactone was added so that the concentration with respect to the non-aqueous electrolyte was 3% by weight. A secondary battery was prepared, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Comparative Example 1>
Using the base electrolyte (I) itself, a lithium secondary battery was prepared according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Comparative example 4>
In accordance with the above-mentioned method, lithium was added to the base electrolyte (I) using a non-aqueous electrolyte obtained by adding α-methylene-γ-butyrolactone as a lactone so that the concentration with respect to the non-aqueous electrolyte was 6% by weight. A secondary battery was prepared, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 3>
In the base electrolyte (I), 3-methyl-2 (5H) -furanone as a lactone and vinylene carbonate as an unsaturated carbonate are 1% by weight and 2% by weight, respectively, with respect to the non-aqueous electrolyte. Using the non-aqueous electrolyte added in this manner, a lithium secondary battery was prepared according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 4>
Addition of α-methylene-γ-butyrolactone as the lactone and vinylene carbonate as the unsaturated carbonate to the base electrolyte (I) so that the concentration with respect to the non-aqueous electrolyte is 1 wt% and 2 wt%, respectively. Using the non-aqueous electrolyte solution, a lithium secondary battery was produced according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 5>
A non-aqueous system in which α-angelica lactone as a lactone and vinylene carbonate as an unsaturated carbonate are added to the base electrolyte (I) so that the concentration with respect to the non-aqueous electrolyte is 1 wt% and 2 wt%, respectively. Using the electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 6>
In the base electrolyte (I), 4,6-dimethyl-α-pyrone as the lactone and vinylene carbonate as the unsaturated carbonate so that the concentration with respect to the non-aqueous electrolyte is 1% by weight and 2% by weight, respectively. Using the non-aqueous electrolyte added to the battery, a lithium secondary battery was produced according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 7>
In the base electrolyte (I), 5,6-dihydro-2H-pyran-2-one as lactones and vinylene carbonate as unsaturated carbonates, the concentration with respect to the non-aqueous electrolyte is 1% by weight and 2%, respectively. Using the non-aqueous electrolyte solution added so as to be%, a lithium secondary battery was produced according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Example 8>
1 mol of LiPF ₆ is used as an electrolyte in a mixed solvent (mixing volume ratio 1: 1: 1) of ethylene carbonate (EC), which is a cyclic carbonate, and ethyl methyl carbonate (EMC), which is a chain carbonate, and diethyl carbonate (DEC). The base electrolyte (II) was dissolved at a ratio of / L, and 3-methyl-2 (5H) -furanone as lactones and vinylene carbonate as unsaturated carbonates were added to the base electrolyte (II). A non-aqueous electrolyte solution was prepared by adding 1% by weight and 2% by weight to the aqueous electrolyte solution, respectively. Using the obtained non-aqueous electrolyte solution, a lithium secondary battery was produced according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Comparative example 2>
A lithium secondary battery according to the above-described method using a non-aqueous electrolyte solution in which vinylene carbonate as an unsaturated carbonate is added to the base electrolyte solution (I) so that the concentration with respect to the non-aqueous electrolyte solution is 2% by weight. The 4.35V continuous charge characteristic evaluation and the 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

<Comparative Example 3>
Non-aqueous electrolysis in which γ-butyrolactone as a lactone and vinylene carbonate as an unsaturated carbonate are added to the base electrolyte (I) so that the concentration with respect to the non-aqueous electrolyte is 1 wt% and 2 wt%, respectively. Using the liquid, a lithium secondary battery was prepared according to the above-described method, and 4.35V continuous charge characteristic evaluation and 4.45V continuous charge characteristic evaluation were performed. The results are shown in Table 1.

  From Table 1, a continuous charge characteristic test in the case of charging until a high open circuit voltage between battery terminals such as 4.35 V and 4.45 V is obtained by adding a specific lactone to the non-aqueous electrolyte in a predetermined concentration. It can be seen that the amount of gas generated at the time can be reduced, and further the recovery capacity maintenance rate at 4.35 V can be improved. In particular, in the case of using a non-aqueous electrolyte mixed with unsaturated carbonates, it can be seen that suppression of generated gas and improvement of recovery capacity can be achieved at a high level.

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, etc.

It is a schematic sectional drawing which shows the structure of the lithium secondary battery which implemented this invention.

Explanation of symbols

1 Positive electrode 2 Negative electrode 3 Separator (spacer)
4 PET film 5 Silicon rubber 6 Glass plate 7 Laminated film 8 Lead with sealing material

Claims (10)

A positive electrode, a negative electrode, and a nonaqueous electrolytic solution containing 0.01% by weight to 5% by weight of a lactone having a carbon-carbon unsaturated bond,
A lithium secondary battery, wherein an open circuit voltage between battery terminals at 25 ° C. at the end of charging is 4.25 V or more.   2. The lithium secondary battery according to claim 1, wherein the open circuit voltage between the battery terminals is 4.3 V or more.   The lithium secondary battery according to claim 1 or 2, wherein the lactone ring of the lactone is a 5-membered ring or a 6-membered ring.   4. The lithium secondary battery according to claim 1, wherein the lactone is any one of α, β-unsaturated lactone and β, γ-unsaturated lactone. 5. The lithium secondary battery according to claim 1, wherein the lactone is represented by the following general formula (1).

{In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent. R ³ represents a divalent hydrocarbon group which may have a substituent. } The lithium secondary battery according to any one of claims 1 to 4, wherein the lactone is represented by the following general formula (2).

{In General Formula (2), R ⁴ and R ⁵ each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent. R ⁶ represents a divalent hydrocarbon group which may have a substituent. } The lithium secondary battery according to claim 1, wherein the lactone is represented by the following general formula (3).

{In General Formula (3), R ⁷ and R ⁸ each independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a substituent. }   The lithium secondary battery according to any one of claims 1 to 7, wherein a content of the lactone in the nonaqueous electrolytic solution is 0.1 wt% or more and 2 wt% or less.   The lactone is 3-methyl-2 (5H) -furanone, α-methylene-γ-butyrolactone, α-angelica lactone, 4,6-dimethyl-α-pyrone, 5,6-dihydro-2H-pyran-2 The lithium secondary battery according to any one of claims 1 to 8, wherein the lithium secondary battery is selected from the group consisting of -on and α-pyrone.   The lithium secondary battery according to any one of claims 1 to 9, wherein the nonaqueous electrolytic solution contains unsaturated carbonates.

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