JP2005285722A - Non-aqueous electrolytic solution and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic solution superior in storage characteristic at high temperatures. <P>SOLUTION: In a non-aqueous electrolytic solution containing an electrolyte and a non-aqueous solvent, further lactones of ≥0.01% in weight and ≤10% in weight having two electron-donating groups in position α are made to be contained thereinto. The lactones are shown in formula 1. In formula 1, R<SP>1</SP>and R<SP>2</SP>are electron-donating groups independently to each other, which include aryl group, alkenyl group, aralkyl group, alkoxy group, halogen group. R<SP>3</SP>is a bivalent alkylene group in carbon number ≥1 and ≤6 and includes methylene group, ethylene group, propylene group, and the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  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 solvent typified by propylene carbonate and ethylene carbonate and a low-boiling solvent such as dimethyl carbonate and diethyl carbonate is used. doing.

  In addition, various auxiliary agents are included in the electrolyte to improve 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. Many methods have been reported. However, a universal electrolyte for all properties has not yet been found.

  On the other hand, some electrolytic solutions using lactones introduced with a substituent at the α-position as the main solvent have been reported so far. For example, Patent Document 1 discloses an electrolytic solution mainly containing γ-butyrolactone in which at least one of α-position, β-position and γ-position is substituted with an electron-withdrawing group, and reaction of lactones occurring on the oxidation side It is described that the life of the aluminum electrolytic capacitor can be extended by suppressing the above.

  Further, in Patent Document 2, by using an electrolytic solution containing a liquid lactone in which both α-position hydrogens are substituted with an alkyl group as a main solvent, the reaction of the lactone at the negative electrode is suppressed, and the secondary battery It has been reported that the deterioration when stored at high temperatures is improved.

  Patent Document 3 discloses an electrolytic solution using γ-butyrolactone as a main solvent in which the α-position is substituted with a methyl group or a chloro group, and is less susceptible to a reduction reaction at the negative electrode by introducing an electron-donating substituent. As a result, the storage characteristics of the battery are improved.

Japanese Patent Laid-Open No. 7-283083 JP 2002-83630 A Japanese Patent Publication No.7-1966

  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 in high-temperature storage characteristics has been particularly demanded recently due to increasing opportunities to use mobile products outdoors and the growing demand for office notebook computers.

However, the electrolyte solutions that have been proposed as effective for improving the high-temperature storage characteristics, including the techniques described in Patent Documents 1 to 3, have insufficient high-temperature storage characteristics. Specifically, a non-aqueous electrolyte solution excellent in both the amount of gas generated during high-temperature storage and the recovery capacity retention rate has not yet been realized.
The present invention has been made in view of the above problems, and an object thereof is to provide a non-aqueous electrolyte and a lithium secondary battery excellent in high-temperature storage characteristics.

  The inventor of the present invention has made extensive studies to solve the above-mentioned problems. As a result, the non-aqueous electrolyte contains a small amount of a lactone having two electron donating groups at the α-position, thereby achieving high temperature storage characteristics. The inventors have found that an excellent non-aqueous electrolyte solution and a lithium secondary battery can be obtained, and have completed the present invention.

  That is, the gist of the present invention is a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent, further containing 0.01% by weight or more and 10% by weight or less of a lactone having two electron donating groups at the α-position. It exists in the non-aqueous electrolyte solution characterized by the above-mentioned.

｛上記一般式（１）中、Ｒ¹及びＲ²はそれぞれ独立して電子供与基を表す。また、Ｒ³は置換基を有していてもよい炭素数１以上６以下のアルキレン基を表す｝ The lactone is preferably represented by the following general formula (1) (claim 2).

{In the above general formula (1), R ¹ and R ² each independently represents an electron donating group. R ³ represents an optionally substituted alkylene group having 1 to 6 carbon atoms}

  In addition, at least one of the two electron donating groups that the lactone has at the α-position is selected from the group consisting of an optionally substituted aryl group, alkenyl group, aralkyl group, and chloro group (Claim 3).

  Furthermore, it is preferable that at least one of the two electron donating groups which the lactone has at the α-position is a phenyl group which may have a substituent (claim 4).

  The lactones include α, α-diphenyl-β-propiolactone, α, α-diphenyl-β-butyrolactone, α, α-diphenyl-γ-butyrolactone, α, α-diphenyl-γ-valerolactone, At least one selected from the group consisting of α, α-diphenyl-δ-valerolactone, α, α-diphenyl-γ-caprolactone, α, α-diphenyl-δ-caprolactone, and α, α-diphenyl-ε-caprolactone. Preferably it is a seed (claim 5).

  The non-aqueous solvent preferably contains 90% by weight or more of cyclic carbonates and chain carbonates or cyclic esters in total (claim 6).

  Furthermore, the non-aqueous solvent preferably contains unsaturated carbonates (claim 7).

  Another gist of the present invention resides in a lithium secondary battery comprising the non-aqueous electrolyte solution described above, and a negative electrode and a positive electrode capable of inserting and extracting lithium ions (Claim 8).

  According to the present invention, it is possible to obtain a non-aqueous electrolyte solution and a lithium secondary battery excellent in high-temperature storage characteristics.

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.
[I. Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention is a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent, and further 0.01% by weight or more and 10% by weight or less of a lactone having two electron donating groups at the α-position. It is characterized by containing.

[1. Lactones]
[1-1. type]
The lactones contained in the non-aqueous electrolyte of the present invention (hereinafter referred to as “the lactones of the present invention” as appropriate) are not limited as long as they have two electron donating groups at the α-position, and any lactones can be used. Can be used. However, what is represented by the following general formula (1) is usually preferable because it is stable in the non-aqueous electrolyte solution of the present invention and is relatively easy to synthesize and can be obtained at low cost.

In the general formula (1), R ¹ and R ² each independently represents an electron donating group. In the following description, “electron-donating groups R ¹ and R ² ” are not represented by the above general formula (1) as well as R ¹ and R ^{2 in the} general formula (1) unless otherwise specified. The lactones of the present invention include the electron donating group at the α-position. The limit is not an electron-donating group R ^1, R ^2, lactones of the present invention need only optionally have a known electron-donating group.

Examples of the electron donating groups R ¹ and R ² include those described in known literatures, and specific examples thereof include an aryl group, an alkenyl group, an aralkyl group, an alkoxy group, and a halogen group. Further, the electron donating groups R ¹ and R ² may have a substituent. Although this substituent is optional, specific examples include a halogen group, an alkyl group, and an alkenyl group.
When the electron donating groups R ¹ and R ² are aryl groups, the aryl group usually has 6 or more carbon atoms, usually 15 or less, preferably 12 or less. If this upper limit is exceeded, the solubility of lactones in non-aqueous electrolytes will deteriorate, and the viscosity of non-aqueous electrolytes containing lactones will increase, increasing solution resistance. The battery capacity of the rechargeable lithium secondary battery may be insufficient.
Specific examples of preferable aryl groups as the electron donating groups R ¹ and R ² include phenyl group, tolyl group, ethylphenyl group, dimethylphenyl group, α-naphthyl group, β-naphthyl group and the like. Among these, a phenyl group, a tolyl group, and a naphthyl group are more preferable, and a phenyl group is particularly preferable. When the aryl group is substituted with a halogen group such as fluorine, chlorine, bromine or iodine, specific examples of the aryl group substituted with the halogen group include a fluorophenyl group, a chlorophenyl group, and a dichlorophenyl group. .

When the electron donating groups R ¹ and R ² are alkenyl groups, the alkenyl group usually has 2 or more carbon atoms, usually 8 or less, preferably 4 or less. If this upper limit is exceeded, the solubility of the lactones in the non-aqueous electrolyte solution is deteriorated as in the case of the aryl group, and the viscosity of the non-aqueous electrolyte solution containing the lactones is increased and the solution resistance is increased. The battery capacity of the lithium secondary battery using the non-aqueous electrolyte may be insufficient.
Specific examples of preferable alkenyl groups as the electron donating groups R ¹ and R ² include a vinyl group, an isoprobenyl group, and an allyl group. Among these, a vinyl group and an allyl group are more preferable.

When the electron donating groups R ¹ and R ² are aralkyl groups, the aralkyl group usually has 7 or more carbon atoms, usually 12 or less, preferably 8 or less. If this upper limit is exceeded, the solubility of the lactones in the non-aqueous electrolyte solution is deteriorated as in the case of the aryl group and alkenyl group, and the viscosity of the non-aqueous electrolyte solution containing the lactones is increased so that the solution resistance is reduced. Therefore, the battery capacity of the lithium secondary battery using the non-aqueous electrolyte solution may be insufficient.
Specific examples of aralkyl groups preferable as the electron donating groups R ¹ and R ² include benzyl group, α-phenethyl group, β-phenethyl group and the like. Among these, a benzyl group is more preferable.

When the electron donating groups R ¹ and R ² are alkoxy groups, the alkoxy group usually has 1 or more carbon atoms and usually 10 or less, preferably 7 or less. If this upper limit is exceeded, the solubility of lactones in non-aqueous electrolytes deteriorates as in the case of aryl groups, alkenyl groups and aralkyl groups, and the viscosity of non-aqueous electrolytes containing lactones increases. Since the solution resistance increases, the battery capacity of the lithium secondary battery using the non-aqueous electrolyte solution may be insufficient.
Specific examples of preferred alkoxy groups as the electron donating groups R ¹ and R ² include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and a phenoxy group. Among these, a methoxy group, an ethoxy group, and a phenoxy group are more preferable.

When the electron donating groups R ¹ and R ² are halogen groups, specific examples include a chloro group, a bromo group, and an iodo group. Among these, since lactones having a chloro group are stable in an electrolytic solution, a chloro group is more preferable.

In particular, the electron donating groups R ¹ and R ² are those in which at least one of the ^two electron donating groups R ¹ and R ² is selected from the group consisting of an aryl group, an alkenyl group, an aralkyl group, and a chloro group. Preferably there is.

Among them, the electron donating groups R ¹ and R ² have a moderate electron donating effect that at least one of the ^two electron donating groups R ¹ and R ² is a phenyl group, and are stable in the electrolytic solution. It is more preferable in that it can exist.

Further, among the combinations of the electron donating groups R ¹ and R ² exemplified above, the most preferable combinations are phenyl group and phenyl group, tolyl group and tolyl group, naphthyl group and naphthyl group, phenyl group and methoxy group, phenyl group. And ethoxy group, phenyl group and phenoxy group. These combinations are excellent in terms of ease of synthesis and stability in the non-aqueous electrolyte solution of the present invention.
An electron donating group may be bonded to a position other than the α position.

In the general formula (1), R ³ represents a divalent alkylene group having 1 to 6 carbon atoms. Specific types of R ³ are arbitrary, and examples thereof include a methylene group, an ethylene group, a propylene group, and a butylene group.
Further, R ³ may have a substituent. The type of this substituent is arbitrary, and examples thereof include alkyl groups such as a methyl group and an ethyl group; vinyl groups; and hydrocarbon groups such as an alkenyl group such as an allyl group. Further, when the substituent R ³ has is a hydrocarbon group, the carbon number is usually 1 to 4.

  Furthermore, the lactones of the present invention have a molecular weight of usually 100 or more, preferably 200 or more, and usually 400 or less, preferably 300 or less. If the upper limit of this range is exceeded, there is a possibility that the solubility in the non-aqueous electrolyte solution is lowered, and there is a possibility that the high temperature holding property cannot be improved.

  Specific examples of the lactones of the present invention include α, α-diphenyl-β-propiolactone, α, α-di-o-tolyl-β-propiolactone, α, α-di-m-tolyl- β-propiolactone, α, α-di-p-tolyl-β-propiolactone, α, α-diethylphenyl-β-propiolactone, α, α-bis (dimethylphenyl) -β-propiolactone , Α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl-β-propiolactone, α, α-divinyl-β-propiolactone, α, α-diisopropenyl -Β-propiolactone, α, α-diallyl-β-propiolactone, α, α-dibenzyl-β-propiolactone, α, α-di-α-phenethyl-β-propiolactone, α, α -Di-β-phenethyl-β-propiolactone, α, α-dic Ro-β-propiolactone, α, α-dibromo-β-propiolactone, α, α-diiodo-β-propiolactone, α-methoxy-α-phenyl-β-propiolactone, α-ethoxy- β-propiolactone derivatives such as α-phenyl-β-propiolactone, α-phenoxy-α-phenyl-β-propiolactone;

α, α-diphenyl-β-butyrolactone, α, α-di-o-tolyl-β-butyrolactone, α, α-di-m-tolyl-β-butyrolactone, α, α-di-p-tolyl-β- Butyrolactone, α, α-diethylphenyl-β-butyrolactone, α, α-bis (dimethylphenyl) -β-butyrolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl -Β-butyrolactone, α, α-divinyl-β-butyrolactone, α, α-diisopropenyl-β-butyrolactone, α, α-diallyl-β-butyrolactone, α, α-dibenzyl-β-butyrolactone, α, α -Di-α-phenethyl-β-butyrolactone, α, α-di-β-phenethyl-β-butyrolactone, α, α-dichloro-β-butyrolactone, α, α-dibromo-β-butyrolactone, α, β-butyrolactone derivatives such as α-diiodo-β-butyrolactone, α-methoxy-α-phenyl-β-butyrolactone, α-ethoxy-α-phenyl-β-butyrolactone, α-phenoxy-α-phenyl-β-butyrolactone;

α, α-diphenyl-γ-butyrolactone, α, α-di-o-tolyl-γ-butyrolactone, α, α-di-m-tolyl-γ-butyrolactone, α, α-di-p-tolyl-γ- Butyrolactone, α, α-diethylphenyl-γ-butyrolactone, α, α-bis (dimethylphenyl) -γ-butyrolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl -Γ-butyrolactone, α, α-divinyl-γ-butyrolactone, α, α-diisopropenyl-γ-butyrolactone, α, α-diallyl-γ-butyrolactone, α, α-dibenzyl-γ-butyrolactone, α, α -Di-α-phenethyl-γ-butyrolactone, α, α-di-β-phenethyl-γ-butyrolactone, α, α-dichloro-γ-butyrolactone, α, α-dibromo-γ-butyrolactone, α, γ-butyrolactone derivatives such as α-diiodo-γ-butyrolactone, α-methoxy-α-phenyl-γ-butyrolactone, α-ethoxy-α-phenyl-γ-butyrolactone, α-phenoxy-α-phenyl-γ-butyrolactone;

α, α-diphenyl-γ-valerolactone, α, α-di-o-tolyl-γ-valerolactone, α, α-di-m-tolyl-γ-valerolactone, α, α-di-p-tolyl -Γ-valerolactone, α, α-diethylphenyl-γ-valerolactone, α, α-bis (dimethylphenyl) -γ-valerolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α -Di-β-naphthyl-γ-valerolactone, α, α-divinyl-γ-valerolactone, α, α-diisopropenyl-γ-valerolactone, α, α-diallyl-γ-valerolactone, α, α -Dibenzyl-γ-valerolactone, α, α-di-α-phenethyl-γ-valerolactone, α, α-di-β-phenethyl-γ-valerolactone, α, α-dichloro-γ-valerolactone, α , Α-dibromo-γ-valerolactone, α, γ such as α-diiodo-γ-valerolactone, α-methoxy-α-phenyl-γ-valerolactone, α-ethoxy-α-phenyl-γ-valerolactone, α-phenoxy-α-phenyl-γ-valerolactone, etc. -Valerolactone derivatives;

α, α-diphenyl-δ-valerolactone, α, α-di-o-tolyl-δ-valerolactone, α, α-di-m-tolyl-δ-valerolactone, α, α-di-p-tolyl -Δ-valerolactone, α, α-diethylphenyl-δ-valerolactone, α, α-bis (dimethylphenyl) -δ-valerolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α -Di-β-naphthyl-δ-valerolactone, α, α-divinyl-δ-valerolactone, α, α-diisopropenyl-δ-valerolactone, α, α-diallyl-δ-valerolactone, α, α -Dibenzyl-δ-valerolactone, α, α-di-α-phenethyl-δ-valerolactone, α, α-di-β-phenethyl-δ-valerolactone, α, α-dichloro-δ-valerolactone, α , Α-dibromo-δ-valerolactone, α, δ such as α-diiodo-δ-valerolactone, α-methoxy-α-phenyl-δ-valerolactone, α-ethoxy-α-phenyl-δ-valerolactone, α-phenoxy-α-phenyl-δ-valerolactone, etc. -Valerolactone derivatives;

α, α-diphenyl-γ-caprolactone, α, α-di-o-tolyl-γ-caprolactone, α, α-di-m-tolyl-γ-caprolactone, α, α-di-p-tolyl-γ- Caprolactone, α, α-diethylphenyl-γ-caprolactone, α, α-bis (dimethylphenyl) -γ-caprolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl -Γ-caprolactone, α, α-divinyl-γ-caprolactone, α, α-diisopropenyl-γ-caprolactone, α, α-diallyl-γ-caprolactone, α, α-dibenzyl-γ-caprolactone, α, α -Di-α-phenethyl-γ-caprolactone, α, α-di-β-phenethyl-γ-caprolactone, α, α-dichloro-γ-caprolactone, α, α-dibromo-γ-caprolactone, α, γ-caprolactone derivatives such as α-diiodo-γ-caprolactone, α-methoxy-α-phenyl-γ-caprolactone, α-ethoxy-α-phenyl-γ-caprolactone, α-phenoxy-α-phenyl-γ-caprolactone;

α, α-diphenyl-δ-caprolactone, α, α-di-o-tolyl-δ-caprolactone, α, α-di-m-tolyl-δ-caprolactone, α, α-di-p-tolyl-δ- Caprolactone, α, α-diethylphenyl-δ-caprolactone, α, α-bis (dimethylphenyl) -δ-caprolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl -Δ-caprolactone, α, α-divinyl-δ-caprolactone, α, α-diisopropenyl-δ-caprolactone, α, α-diallyl-δ-caprolactone, α, α-dibenzyl-δ-caprolactone, α, α -Di-α-phenethyl-δ-caprolactone, α, α-di-β-phenethyl-δ-caprolactone, α, α-dichloro-δ-caprolactone, α, α-dibromo-δ-caprolactone, α, δ-caprolactone derivatives such as α-diiodo-δ-caprolactone, α-methoxy-α-phenyl-δ-caprolactone, α-ethoxy-α-phenyl-δ-caprolactone, α-phenoxy-α-phenyl-δ-caprolactone;

α, α-diphenyl-ε-caprolactone, α, α-di-o-tolyl-ε-caprolactone, α, α-di-m-tolyl-ε-caprolactone, α, α-di-p-tolyl-ε- Caprolactone, α, α-diethylphenyl-ε-caprolactone, α, α-bis (dimethylphenyl) -ε-caprolactone, α, α-di-α-naphthyl-γ-butyrolactone, α, α-di-β-naphthyl -Ε-caprolactone, α, α-divinyl-ε-caprolactone, α, α-diisopropenyl-ε-caprolactone, α, α-diallyl-ε-caprolactone, α, α-dibenzyl-ε-caprolactone, α, α -Di-α-phenethyl-ε-caprolactone, α, α-di-β-phenethyl-ε-caprolactone, α, α-dichloro-ε-caprolactone, α, α-dibromo-ε-caprolactone, α, ε-caprolactone derivatives such as α-diiodo-ε-caprolactone, α-methoxy-α-phenyl-ε-caprolactone, α-ethoxy-α-phenyl-ε-caprolactone, α-phenoxy-α-phenyl-ε-caprolactone, etc. Is mentioned.

Among them, α, α-diphenyl-β-propiolactone, α, α-diphenyl-β-butyrolactone, α, α-diphenyl-γ-butyrolactone, α, α-diphenyl-γ-valerolactone, α, α- Α, α-Diphenyl-substituted lactones such as diphenyl-δ-valerolactone, α, α-diphenyl-γ-caprolactone, α, α-diphenyl-δ-caprolactone, and α, α-diphenyl-ε-caprolactone are preferred. . 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 of 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 10% by weight or less, preferably 5% by weight or less. Below the lower limit of this range, the non-aqueous electrolyte solution of the present invention cannot 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. To do. 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.

[1-3. mechanism]
Hereinafter, the mechanism that the non-aqueous electrolyte solution containing the lactone of the present invention, which is inferred by the inventor of the present invention, realizes excellent holding characteristics in a lithium secondary battery will be described.

  When the electron donating group is in the α-position, the electron density of the carbonyl group increases, so that the oxidation resistance of lactones decreases. As a result, lactones decompose on the positive electrode to form a protective film, and subsequent decomposition of the main solvent is suppressed, so that the generated gas is reduced in the lithium secondary battery and the recovery capacity after high-temperature storage is increased. . For this reason, the preservation | save characteristic of a lithium secondary battery improves.

  In addition, when there are two electron donating groups at the α-position of the lactone, the oxidation resistance of the lactone is further reduced, and a more effective film can be formed on the positive electrode. In addition, since no α hydrogen is present, hydrogen gas generation due to the reduction reaction hardly occurs on the negative electrode. As a result, the lactones of the present invention exhibit excellent effects in terms of reducing the generated gas and improving the recovery capacity after high-temperature storage, and further improve the storage characteristics of the lithium secondary battery.

  By the way, the use of lactones having a substituent introduced at the α-position is disclosed in Patent Documents 1 to 3. However, these all assume that lactones are used as the main solvent of the electrolytic solution, and the effect is attributed to the fact that the reactivity of the lactones itself is reduced by introducing substituents. . That is, Patent Document 1 uses a lactone that improves the oxidation resistance of lactones and does not easily react at the positive electrode, while Patent Documents 2 and 3 improve the reduction resistance of lactones at the negative electrode. The reaction is suppressed. On the other hand, in the present invention, lactones reduced in oxidation resistance by introducing two electron donating groups at the α-position are used as additives in the electrolyte solution at a specific concentration, not as the main solvent of the non-aqueous electrolyte solution. And positively decomposed at the positive electrode. Thereby, an effective protective film is formed on the positive electrode and the subsequent decomposition of the main solvent is suppressed.

[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 cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate.
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), the cyclic esters (lactones) having two electron donating groups at the α-position among the lactones are those of the present invention described above. Considered lactones. 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 kinds of non-aqueous solvents so as to exhibit desired characteristics, that is, high-temperature storage 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 90% 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 carbon number 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 high-temperature storage 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 high-temperature storage 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.

[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.

  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 of 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 high-temperature storage 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 of the present invention preferably contains unsaturated carbonates 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 solution of the present invention may contain other auxiliary agents for the purpose of improving the wettability, overcharge characteristics, etc. of the non-aqueous electrolyte solution as long as the effects of the present invention are not impaired.
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 nonaqueous electrolytic solution of 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 nonaqueous solvent.
In preparing the non-aqueous electrolyte solution, it is preferable that each raw material of the non-aqueous electrolyte solution, that is, the electrolyte, the lactones of the present invention, the unsaturated carbonates, and other auxiliary agents be dehydrated in advance. 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 non-aqueous electrolytic solution of the present invention can be widely used for ordinary electrolytic solutions, and is particularly suitable as an electrolytic solution for a lithium secondary battery.
The lithium secondary battery of the present invention includes the above-described non-aqueous electrolyte of 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. Substitution with other metals such as Ga is preferable because it can be stabilized.
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. 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.

  The average secondary particle size of the positive electrode active material is usually 0.2 μm or more, preferably 0.5 μm or more, and usually 30 μm or less, preferably 20 μm or less. If the average secondary particle size is too small, the cycle deterioration of the lithium secondary battery may become large and handling may become difficult. If it is too large, the internal resistance of the battery may increase and output may be difficult. .

  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 agent 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 diameter of the negative electrode active material is usually 1 μm or more, preferably 15 μm or more, and is usually about 50 μm or less, preferably about 30 μm or less, from the viewpoint 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 of 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 raised. 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.

  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, respectively. , 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, the laminate film (7) in which the resin layers were formed on both surfaces of the aluminum foil was vacuum-sealed while projecting positive and negative terminals, and a sheet-like lithium secondary battery was produced. 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 140 mAh / g, and the rate was determined by determining the discharge rate 1C from this and the amount of active material of the positive electrode of the lithium secondary battery for evaluation. 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), the battery was discharged to 0.2 V at 0.2 C to perform initial formation. Subsequently, after CCCV charge to 4.2V at 0.7C, it discharged again to 3V at 0.2C, and the initial 0.2C discharge capacity was calculated | required. And after charging to 4.2V at 0.7C further, it discharged to 3V at 2C, and calculated | required initial 2C discharge capacity. Note that the cut current at the time of charging was 0.05C.

[High temperature storage characteristics evaluation]
After the capacity evaluation test was completed, the battery was stored in a thermostatic bath at 85 ° C. for 1 day in a CCCV charge (cut current 0.05 C) to 0.7 V at 0.7 C in a thermostatic bath at 25 ° C. After cooling to ° C., the sample was immersed in an ethanol bath to measure the buoyancy (Archimedes principle), and the amount of gas generated (mL) was determined from the buoyancy. In order to evaluate the capacity degradation after storage, CCCV charge (cut current 0.05C) to 4.2V at 0.7C, then discharge to 3V at 2C, and 2C recovery capacity (mAh / g after high temperature storage). ) Was measured. The larger this value is, the less the high load capacity deterioration associated with high temperature storage.

<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 Is used as a base electrolyte (I), and α, α-diphenyl-γ-butyrolactone as a lactone is added to the base electrolyte (I) so that the concentration with respect to the non-aqueous electrolyte is 1% by weight. An electrolyte was used.
Using the obtained non-aqueous electrolyte solution, a lithium secondary battery was produced according to the method described above, and the high-temperature storage characteristics were evaluated. 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.

<Comparative Example 1>
Using the base electrolyte (I) itself, a lithium secondary battery was produced according to the method described above, and the high-temperature storage characteristics were evaluated. The results are shown in Table 1.

<Example 2>
In the base electrolyte (I), α, α-diphenyl-γ-butyrolactone as the lactone and vinylene carbonate as the unsaturated carbonate are 1% by weight and 2% by weight with respect to the non-aqueous electrolyte, respectively. Using the non-aqueous electrolyte added to the battery, a lithium secondary battery was produced according to the method described above, and the high-temperature storage characteristics were evaluated. The results are shown in Table 1.

<Example 3>
In the base electrolyte (I), α, α-diphenyl-γ-butyrolactone as lactones and vinylene carbonate as unsaturated carbonates are 0.5% by weight and 2% by weight, respectively, with respect to the non-aqueous electrolyte. Using the non-aqueous electrolyte solution added as described above, a lithium secondary battery was prepared according to the method described above, and the high-temperature storage characteristics were evaluated. The results are shown in Table 1.

<Example 4>
In the base electrolyte (I), α, α-diphenyl-γ-butyrolactone as the lactone and vinylene carbonate as the unsaturated carbonate are 2% by weight and 2% by weight, respectively, with respect to the non-aqueous electrolyte. Using the non-aqueous electrolyte added to the battery, a lithium secondary battery was produced according to the method described above, and the high-temperature storage characteristics were evaluated. The results are shown in Table 1.

<Example 5>
1 mol of LiPF ₆ is used as an electrolyte in a mixed solvent of ethylene carbonate (EC), which is a cyclic carbonate, and ethyl methyl carbonate (EMC), which is a chain carbonate, and diethyl carbonate (DEC) (mixing volume ratio 1: 1: 1). The base electrolyte solution (II) is dissolved at a ratio of / L, and α, α-diphenyl-γ-butyrolactone as lactones and vinylene carbonate as unsaturated carbonates are added to the base electrolyte solution (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 method described above, and the high-temperature storage characteristics were evaluated. 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. And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

<Comparative Example 3>
In the base electrolyte (I), α, α-diphenyl-γ-butyrolactone as the lactone and vinylene carbonate as the unsaturated carbonate are 16% by weight and 2% by weight with respect to the non-aqueous electrolyte, respectively. Using the non-aqueous electrolyte added to the battery, a lithium secondary battery was produced according to the method described above, and the high-temperature storage characteristics were evaluated. The results are shown in Table 1.

  From Table 1, it can be seen that when α, α-diphenyl-γ-butyrolactone is contained in the electrolytic solution in a predetermined concentration, the amount of gas generated during the high-temperature storage test is reduced and the recovery capacity at high load is improved. In particular, when a non-aqueous electrolyte solution to which unsaturated carbonates are added is used, it is possible to achieve both high-dimensional suppression of generated gas and improvement of recovery capacity in a high-temperature storage test.

  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 (8)

  A non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent, further comprising 0.01% by weight to 10% by weight of a lactone having two electron donating groups at the α-position Electrolytic solution. The non-aqueous electrolyte solution according to claim 1, wherein the lactone is represented by the following general formula (1).

{In the above general formula (1), R ¹ and R ² each independently represents an electron donating group. R ³ represents an optionally substituted alkylene group having 1 to 6 carbon atoms}   At least one of the two electron donating groups at the α-position of the lactone is selected from the group consisting of an optionally substituted aryl group, alkenyl group, aralkyl group and chloro group. The non-aqueous electrolyte solution according to claim 1 or 2, wherein   The lactone according to any one of claims 1 to 3, wherein at least one of the two electron donating groups at the α-position is a phenyl group which may have a substituent. The non-aqueous electrolyte described.   The lactone is α, α-diphenyl-β-propiolactone, α, α-diphenyl-β-butyrolactone, α, α-diphenyl-γ-butyrolactone, α, α-diphenyl-γ-valerolactone, α, At least one selected from the group consisting of α-diphenyl-δ-valerolactone, α, α-diphenyl-γ-caprolactone, α, α-diphenyl-δ-caprolactone, and α, α-diphenyl-ε-caprolactone The nonaqueous electrolytic solution according to any one of claims 1 to 4, wherein the nonaqueous electrolytic solution is provided.   The nonaqueous solvent according to any one of claims 1 to 5, wherein the nonaqueous solvent contains a total of 90% by weight or more of cyclic carbonates and chain carbonates or cyclic esters. Electrolytic solution.   The nonaqueous electrolytic solution according to any one of claims 1 to 6, wherein the nonaqueous solvent contains unsaturated carbonates.   A lithium secondary battery comprising: the non-aqueous electrolyte solution according to claim 1; and a negative electrode and a positive electrode capable of inserting and extracting lithium ions.

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