JP2021111586A - Non-aqueous electrolyte and non-aqueous secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte capable of exhibiting high wettability to a separator in addition to excellent load characteristics and high temperature durability performance, and a non-aqueous secondary battery using the same.SOLUTION: A non-aqueous electrolyte includes a non-aqueous solvent containing 20% by volume to 90% by volume of acetonitrile, a lithium salt, and at least one of dicarboxylic acid ester represented by the following general formulas (1) and (2). {In the formulas, R1 to R7 are as defined in the specification}.SELECTED DRAWING: Figure 1

Description

The present invention relates to a non-aqueous electrolyte solution and a non-aqueous secondary battery.

Non-aqueous secondary batteries such as lithium ion batteries (LIBs) are characterized by their light weight, high energy, and long life, and are widely used as power sources for various portable electronic devices. In recent years, non-aqueous secondary batteries have been expanding for industrial use represented by power tools such as electric tools, and for in-vehicle use in electric vehicles and electric bicycles, and further, electric power for residential energy storage systems and the like. It is also attracting attention in the storage field.

From a practical point of view, it is desirable to use a non-aqueous electrolytic solution as the electrolytic solution of the room temperature operating type lithium ion secondary battery. For example, a combination of a highly dielectric solvent such as a cyclic carbonic acid ester and a low-viscosity solvent such as a lower chain carbonic acid ester is exemplified as a general solvent. However, in addition to having a high melting point, ordinary high-dielectric solvents also cause deterioration of the load characteristics (output characteristics) and low-temperature characteristics of the non-aqueous electrolyte solution depending on the type of electrolyte salt used in the non-aqueous electrolyte solution. obtain.

As one of the solvents for overcoming such a problem, a nitrile solvent having an excellent balance between viscosity and relative permittivity has been proposed. Among them, acetonitrile has a high potential as a solvent used for a non-aqueous electrolyte solution of a lithium ion secondary battery. However, acetonitrile has two drawbacks and has not been able to exhibit practical performance. The first is that acetonitrile is electrochemically reduced and decomposed at the negative electrode, and the second is that acetonitrile is used as a separator compared to commonly used chain carbonates such as diethyl carbonate or ethyl methyl carbonate. It has the disadvantage of low wettability. Several remedies have been proposed for the first problem, where acetonitrile is electrochemically reduced and decomposed at the negative electrode.
The two main improvement measures proposed so far are as follows.

(1) A method of protecting the negative electrode by combining with a specific electrolyte salt, an additive, etc. and suppressing the reducing decomposition of ethylene carbonate For example, in the early days of lithium ion secondary batteries, acetonitrile was used as in Patent Document 1. Non-aqueous electrolyte solutions containing a solvent simply diluted with propylene carbonate and ethylene carbonate have been reported. However, in Patent Document 1, since the high temperature durability performance is determined only by the evaluation of the internal resistance after high temperature storage and the battery thickness, information on whether or not the battery actually operates when placed in a high temperature environment. Is not disclosed. It is actually extremely difficult to suppress the reductive decomposition of a non-aqueous electrolyte solution containing an acetonitrile-based solvent by simply diluting it with ethylene carbonate and propylene carbonate.

(2) Method of Dissolving High Concentration Electrolyte Salt in acetonitrile to Maintain a Stable Liquid State For example, Patent Document 2 states that lithium bis (trifluoromethanesulfonyl) imide (trifluoromethanesulfonyl) imide so as to have a concentration of 4.2 mol / L. It is described that reversible insertion and desorption of lithium into a graphite electrode is possible by using a non-aqueous electrolyte solution in which LiN (SO ₂ CF ₃ ) _{2) is dissolved in acetonitrile.} Further, in Patent Document 3, a cell using a non-aqueous electrolyte solution in which _{lithium bis (fluorosulfonyl) imide (LiN (SO 2} F) ₂ ) is dissolved in acetonitrile so as to have a concentration of 4.5 mol / L is used. On the other hand, as a result of charge / discharge measurement, a Li ⁺ insertion / desorption reaction into graphite was observed, and it was reported that discharge was possible at a high rate.

Japanese Unexamined Patent Publication No. 4-351860 International Publication No. 2013/146714 Japanese Unexamined Patent Publication No. 2014-241198

However, in the techniques described in Patent Documents 1 to 3, the lithium ion secondary battery using the non-aqueous electrolyte solution containing acetonitrile is the existing lithium ion secondary battery using the non-aqueous electrolyte solution containing a carbonate solvent. It is inferior in high temperature durability performance compared to the above, and has not reached the level of commercial products.

In addition, in the techniques described in Patent Documents 1 to 3, the wettability of the non-aqueous electrolyte solution to the separator is lower than that of the existing non-aqueous electrolyte solution containing the chain carbonate solvent. In the technique described in Patent Document 1, propylene carbonate having low wettability to a separator is used for diluting acetonitrile. In the techniques described in Patent Documents 2 and 3, an electrolyte salt is dissolved in acetonitrile at a high concentration, and the wettability decreases as the viscosity increases. These non-aqueous electrolytes do not sufficiently impregnate the separator, contribute to an increase in the internal resistance of the battery, adversely affect the battery characteristics such as cycle characteristics, and have a problem in the liquid injection process during lithium battery manufacturing. ..

The present invention has been made in view of the above circumstances, and is a non-aqueous electrolyte solution capable of exhibiting high wettability to a separator in addition to excellent load characteristics and high temperature durability performance, and a non-aqueous electrolyte solution using the same. The purpose is to provide a secondary battery.

｛式中、Ｒ^１及びＲ^２は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、Ｒ^３及びＲ^４は、それぞれ独立して、水素原子または炭素数１〜４の１価の炭化水素基を示す。ただし、Ｒ^３、Ｒ^４は同時に水素原子ではない。｝
又は下記一般式（２）：

｛式中、Ｒ^５、Ｒ^６は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、
Ｒ^７は炭素数１〜４の２価の炭化水素基を示す。｝
で表されるジカルボン酸エステルの少なくとも一方と；
を含有する、非水系電解液。
［２］
前記ジカルボン酸エステルが、メチルマロン酸ジエチル、２−エチル−２−メチルマロン酸ジエチル、コハク酸ジメチルのうち少なくとも一つである、［１］に記載の非水系電解液。
［３］
前記ジカルボン酸エステルの含有量が、非水系電解液１００質量部に対して０．０１〜２質量部である、［１］または［２］に記載の非水系電解液。
［４］
前記非水系溶媒が更にα位に置換基を有するラクトン類を含有することを特徴とする、［１］〜［３］のいずれか１項に記載の非水系電解液。
［５］
前記非水系溶媒が更に鎖状フッ素化カルボン酸エステルを含有することを特徴とする、［１］〜［４］のいずれか１項に記載の非水系電解液。
［６］
集電体の片面又は両面に、Ｎｉ、Ｍｎ、及びＣｏから成る群より選ばれる少なくとも１種の遷移金属元素又はＦｅ原子を含有する正極活物質層を有する正極と、集電体の片面又は両面に黒鉛を含有する負極活物質層を有する負極と、［１］〜［５］のいずれか１項に記載の非水系電解液とを含む積層体を具備する、非水系二次電池。
［７］
前記正極活物質層を構成する正極活物質が、Ｌｉ_ｚＭＯ_２（ＭはＮｉを含み、且つ、Ｍｎ、Ｃｏ、Ａｌ、及びＭｇから成る群より選ばれる１種以上の金属元素を含み、更に、Ｎｉの元素含有モル比は３０％より多く、そして、ｚは０．９超１．２未満の数を示す。）で表されるリチウム含有複合金属酸化物である、［６］に記載の非水系二次電池。 The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that when the non-aqueous electrolyte solution contains a specific dicarboxylic acid ester, they exhibit high wettability to the separator in addition to excellent load characteristics and high temperature durability, and have completed the present invention. ..
That is, the present invention is as follows.
[1]
With a non-aqueous solvent containing 20% to 90% by volume of acetonitrile;
With lithium salt;
The following general formula (1):

{In the formula, R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 4 carbon atoms, and R ³ and R ⁴ independently represent a hydrogen atom or 1 to 4 carbon atoms, respectively. It shows 4 monovalent hydrocarbon groups. However, R ³ and R ⁴ are not hydrogen atoms at the same time. }
Or the following general formula (2):

{In the formula, R ⁵ and R ⁶ each independently represent a monovalent hydrocarbon group having 1 to 4 carbon atoms.
R ⁷ represents a divalent hydrocarbon group having 1 to 4 carbon atoms. }
With at least one of the dicarboxylic acid esters represented by;
A non-aqueous electrolyte solution containing.
[2]
The non-aqueous electrolyte solution according to [1], wherein the dicarboxylic acid ester is at least one of diethyl methylmalonic acid, diethyl 2-ethyl-2-methylmalonic acid, and dimethyl succinate.
[3]
The non-aqueous electrolyte solution according to [1] or [2], wherein the content of the dicarboxylic acid ester is 0.01 to 2 parts by mass with respect to 100 parts by mass of the non-aqueous electrolyte solution.
[4]
The non-aqueous electrolytic solution according to any one of [1] to [3], wherein the non-aqueous solvent further contains lactones having a substituent at the α-position.
[5]
The non-aqueous electrolyte solution according to any one of [1] to [4], wherein the non-aqueous solvent further contains a chain fluorinated carboxylic acid ester.
[6]
A positive electrode having a positive electrode active material layer containing at least one transition metal element or Fe atom selected from the group consisting of Ni, Mn, and Co on one or both sides of the current collector, and one or both sides of the current collector. A non-aqueous secondary battery comprising a laminate containing a negative electrode having a negative electrode active material layer containing graphite and the non-aqueous electrolyte solution according to any one of [1] to [5].
[7]
The positive electrode active material constituting the positive electrode active material layer _{contains Li z} MO ₂ (M contains Ni, and contains one or more metal elements selected from the group consisting of Mn, Co, Al, and Mg, and further. , The element-containing molar ratio of Ni is more than 30%, and z is a lithium-containing composite metal oxide represented by a number greater than 0.9 and less than 1.2), according to [6]. Non-aqueous secondary battery.

According to the present invention, when the non-aqueous electrolyte solution contains a specific dicarboxylic acid ester, the dicarboxylic acid ester decomposes at a lower potential than acetonitrile to form a negative electrode protective film, thereby suppressing the reductive decomposition of acetonitrile. It is possible to provide a non-aqueous electrolyte solution capable of exhibiting excellent load characteristics and high-temperature durability performance and high wettability to a separator, and a non-aqueous secondary battery using the same.

It is a top view which shows typically an example of the non-aqueous secondary battery of this embodiment. FIG. 5 is a cross-sectional view taken along the line AA of the non-aqueous secondary battery of FIG.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The numerical range described by using "~" in the present specification includes the numerical values described before and after the numerical range.

｛式中、Ｒ^１及びＲ^２は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、かつＲ^３及びＲ^４は、それぞれ独立して、水素原子又は炭素数１〜４の１価の炭化水素基を示す。ただし、Ｒ^３とＲ^４の両方は同時に水素原子になることはない。｝
又は下記一般式（２）：

｛式中、Ｒ^５及びＲ^６は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、Ｒ^７は炭素数１〜４の２価の炭化水素基を示す。｝
で表されるジカルボン酸エステルの少なくとも一方と；
を含有する。 The non-aqueous electrolyte solution of the present embodiment (hereinafter, also simply referred to as “electrolyte solution”) is
With a non-aqueous solvent containing 20% to 90% by volume of acetonitrile;
With lithium salt;
The following general formula (1):

{In the formula, R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 4 carbon atoms, and R ³ and R ⁴ independently represent a hydrogen atom or 1 carbon atom, respectively. Shows a monovalent hydrocarbon group of ~ 4. However, ^{both R 3} and R ⁴ do not become hydrogen atoms at the same time. }
Or the following general formula (2):

{In the formula, R ⁵ and R ⁶ each independently represent a monovalent hydrocarbon group ^{having 1 to 4 carbon atoms, and R 7} represents a divalent hydrocarbon group having 1 to 4 carbon atoms. }
With at least one of the dicarboxylic acid esters represented by;
Contains.

<1. Overall configuration of non-aqueous secondary battery>
The non-aqueous electrolyte solution of the present embodiment can be used, for example, in a non-aqueous secondary battery. The non-aqueous secondary battery of the present embodiment includes, for example, a positive electrode containing a positive electrode material capable of storing and releasing lithium ions as a positive electrode active material, and lithium ions as a negative electrode active material. Examples thereof include a lithium ion secondary battery including a negative electrode material capable of the above, and a negative electrode containing one or more negative electrode materials selected from the group consisting of metallic lithium.
Specifically, the non-aqueous secondary battery of the present embodiment may be the non-aqueous secondary battery shown in FIGS. 1 and 2. Here, FIG. 1 is a plan view schematically showing a non-aqueous secondary battery, and FIG. 2 is a cross-sectional view taken along the line AA of FIG.

The non-aqueous secondary battery 100 includes a laminated electrode body formed by laminating a positive electrode 150 and a negative electrode 160 via a separator 170 in a space 120 of a battery exterior 110 composed of two aluminum laminated films, and a non-aqueous secondary battery 100. Contains an electrolytic solution (not shown). The outer peripheral portion of the battery exterior 110 is sealed by heat-sealing the upper and lower aluminum laminate films. The laminate in which the positive electrode 150, the separator 170, and the negative electrode 160 are laminated in this order is impregnated with a non-aqueous electrolyte solution. In addition, in FIG. 2, in order to avoid complicating the drawings, each layer constituting the battery exterior 110 and each layer of the positive electrode 150 and the negative electrode 160 are not shown separately.
The aluminum laminate film constituting the battery exterior 110 is preferably one in which both sides of the aluminum foil are coated with a polyolefin resin.
The positive electrode 150 is connected to the positive electrode lead body 130 in the battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead body 140 in the battery 100. One end of each of the positive electrode lead body 130 and the negative electrode lead body 140 is pulled out to the outside of the battery exterior 110 so that they can be connected to an external device or the like, and their ionomer portions are 1 of the battery exterior 110. It is heat-sealed together with the sides.

In the non-aqueous secondary battery 100 shown in FIGS. 1 and 2, the positive electrode 150 and the negative electrode 160 each have one laminated electrode body, but the number of laminated positive electrodes 150 and 160 is determined by the capacity design. It can be increased as appropriate. In the case of a laminated electrode body having a plurality of positive electrodes 150 and 160 negative electrodes, tabs of the same electrode may be joined by welding or the like, and then joined to one lead body by welding or the like and taken out of the battery. As the tabs having the same pole, a mode in which the exposed portion of the current collector is formed, a mode in which a metal piece is welded to the exposed portion of the current collector, and the like are possible.
The positive electrode 150 is composed of a positive electrode active material layer prepared from a positive electrode mixture and a positive electrode current collector. The negative electrode 160 is composed of a negative electrode active material layer prepared from a negative electrode mixture and a negative electrode current collector. The positive electrode 150 and the negative electrode 160 are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator 170.

Hereinafter, the positive electrode and the negative electrode are collectively referred to as “electrode”, the positive electrode active material layer and the negative electrode active material layer are collectively referred to as “electrode active material layer”, and the positive electrode mixture and the negative electrode mixture are collectively referred to as “electrode mixture”.
As each of these members, as long as each requirement in the present embodiment is satisfied, a material provided in a conventional lithium ion secondary battery can be used, and for example, a material described later may be used. Hereinafter, each member of the non-aqueous secondary battery will be described in detail.

<2. Non-aqueous electrolyte solution>
The non-aqueous electrolyte solution in the present embodiment includes a non-aqueous solvent containing 20% by volume to 90% by volume of acetonitrile (hereinafter, also simply referred to as “solvent”), a lithium salt, and the above general formula (1) or (2). ), And at least one of the dicarboxylic acid esters. Among the lithium salts, the fluorine-containing inorganic lithium salt is known to have excellent ionic conductivity and greatly contribute to the improvement of battery performance. However, the fluorine-containing inorganic lithium salt has a property of being easily hydrolyzed by a trace amount of water in the solvent and generating an excess free acid component. The generated acid component may have a fatal adverse effect on the battery, such as corroding materials such as electrodes and current collectors or decomposing a solvent.
The non-aqueous electrolyte solution in the present embodiment preferably does not contain water in order to prevent hydrolysis of the fluorine-containing inorganic lithium salt by a trace amount of water, but the amount is very small as long as it does not hinder the solution of the problem of the present invention. It may contain water. The content of such water is preferably 0 to 100 ppm with respect to the total amount of the non-aqueous electrolyte solution.

<2-1. Non-aqueous solvent>
Acetonitrile has high ionic conductivity and can enhance the diffusivity of lithium ions in the battery. Therefore, when the non-aqueous electrolyte solution contains acetonitrile, lithium ions are difficult to reach even in a positive electrode in which the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material, especially when discharging under a high load. Lithium ions can be satisfactorily diffused to the region near the electric body. As a result, it is possible to draw out a sufficient capacity even at the time of high load discharge, and it is possible to obtain a non-aqueous secondary battery having excellent load characteristics.
Further, by using acetonitrile as the non-aqueous solvent of the non-aqueous electrolyte solution, as described above, the ionic conductivity of the non-aqueous electrolyte solution is improved, so that the quick charging characteristics of the non-aqueous secondary battery can be improved. In constant current (CC) -constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time in the CC charging period is larger than the charging capacity per unit time in the CV charging period. When acetonitrile is used as the non-aqueous solvent of the non-aqueous electrolyte solution, the CC charging area can be increased (CC charging time can be lengthened), and the charging current can be increased. Therefore, charging of the non-aqueous secondary battery is started. The time from to full charge can be greatly reduced.

The non-aqueous solvent is not particularly limited as long as it contains acetonitrile, and other non-aqueous solvents may or may not be contained.
The term "non-aqueous solvent" as used in the present embodiment means an element obtained by removing a lithium salt, a dicarboxylic acid ester, and other optional additives from the non-aqueous electrolyte solution. That is, when the non-aqueous electrolyte solution contains the solvent, the lithium salt, the dicarboxylic acid ester, and other optional additives as well as the electrode protection additive described later, the solvent and the electrode protection additive are added. Together, it is called a "non-aqueous solvent". Lithium salts, dicarboxylic acid esters, and other optional additives described below are not included in the non-aqueous solvent.

Examples of the other non-aqueous solvent include alcohols such as methanol and ethanol; aprotic solvents and the like. Of these, an aprotic polar solvent is preferable.

Among the above other non-aqueous solvents, specific examples of the aproton solvent include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene. Cyclic carbonates typified by carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, and vinylene carbonate; fluoroethylene carbonate, 1,2-difluoroethylene Cyclic fluorinated carbonates typified by carbonates and trifluoromethylethylene carbonates; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and lactones typified by ε-caprolactone; , Dimethylsulfoxide, and sulfur compounds typified by ethylene glycol sulfide; cyclic ethers typified by tetrahydrofuran, 2-methyltetrahexyl, 1,4-dioxane, and 1,3-dioxane; ethylmethyl carbonate, dimethyl carbonate, diethyl. Chain carbonates typified by carbonates, methylpropyl carbonates, methylisopropyl carbonates, dipropyl carbonates, methylbutyl carbonates, dibutyl carbonates, ethylpropyl carbonates, and methyltrifluoroethyl carbonates; trifluorodimethyl carbonates, trifluorodiethyl carbonates, and Chain fluorinated carbonate typified by trifluoroethyl methyl carbonate;

Mononitriles represented by propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile; alkoxy group-substituted nitriles represented by methoxynitrile and 3-methoxypropionitrile; malononitrile, succinonitrile, glutaronitrile, adipoinitrile , 1,4-Dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, Dinitriles represented by 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile; cyclic nitriles represented by benzonitrile; Chain ester represented by methyl propionate; Chain ester represented by dimethoxyethane, diethyl ether, 1,3-dioxolane, diglime, triglime, and tetraglyme; Rf ^4- OR ⁸ {In the formula, Rf ⁴ is A fluorinated ether typified by an alkyl group containing a fluorine atom and R ⁸ is an organic group that may contain a fluorinated atom}; ketones typified by acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. In addition, halides typified by these fluorinated compounds can be mentioned. These may be used alone or in combination of two or more.

Among other non-aqueous solvents, it is more preferable to use one or more of cyclic carbonate and chain carbonate together with acetonitrile. Here, as the cyclic carbonate and the chain carbonate, only one of the above-exemplified ones may be selected and used, and two or more kinds (for example, two or more kinds of the above-exemplified cyclic carbonates, the above-mentioned embodiment) may be selected and used. Two or more of the chain carbonates, or one or more of the above-exemplified cyclic carbonates and two or more of the above-exemplified chain carbonates) may be used. Among these, ethylene carbonate, propylene carbonate, vinylene carbonate, or fluoroethylene carbonate is more preferable as the cyclic carbonate, ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate is more preferable as the chain carbonate, and cyclic carbonate is used. Is even more preferable.

Further, according to the present invention, it is more preferable to use one or more of the lactones having a substituent at the α-position together with acetonitrile as the non-aqueous solvent. The content of the lactones having a substituent at the α-position is more preferably 5% by volume or more, and further preferably 10% by volume or more, based on the total amount of the non-aqueous solvent. Further, this value is more preferably 80% by volume or less, and further preferably 50% by volume or less. Examples of lactones having a substituent at the α-position include α-methyl-γ-butyrolactone, α, α-dimethyl-γ-butyrolactone, α-heptyl-γ-butyrolactone, α-acetyl-γ-butyrolactone and the like. Be done. Among these, α-methyl-γ-butyrolactone is preferable.
Lactones having a substituent at the α-position have an excellent balance between dielectric constant and melting point as compared with carbonate-based solvents. That is, lactones having a substituent at the α-position have a high dielectric constant, a low melting point, and are difficult to solidify. Therefore, by using lactones having a substituent at the α-position as the non-aqueous solvent, the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and all other battery characteristics are further improved. Tends to be able to. In addition, lactones having a substituent at the α-position are also excellent in wettability, and when used in a non-aqueous solvent, the impregnation property of the non-aqueous electrolyte solution into the separator is improved. As a result, the increase in the internal resistance of the battery is suppressed, and the battery characteristics such as the cycle characteristics tend to be further improved.

Further, according to the present invention, it is more preferable to use one or more of the chain fluorinated carboxylic acid esters together with acetonitrile as the non-aqueous solvent. The content of the chain fluorinated carboxylic acid ester is more preferably 5% by volume or more, further preferably 15% by volume or more, based on the total amount of the non-aqueous solvent. Further, this value is more preferably 80% by volume or less, and further preferably 50% by volume or less. It is presumed that the chain fluorinated carboxylic acid ester is excellent in oxidation resistance and forms a good film having high ionic conductivity rich in fluorine atoms on the surface of the positive electrode. Therefore, when the content of the fluorinated carboxylic acid ester in the non-aqueous solvent is within the above range, all of the cycle performance, high temperature durability performance and other battery characteristics of the non-aqueous secondary battery are further improved. Tend to be able. Examples of the chain fluorinated carboxylic acid ester include methyl 3,3,3-trifluoropropionate, ethyl trifluoroacetate, ethyl difluoroacetate, 2,2-difluoroethyl acetate, and 2,2,2-trifluoroethyl. Examples include acetate. Among these, 2,2-difluoroethyl acetate is preferable.

Acetonitrile is easily electrochemically reduced and decomposed. Therefore, it is preferable to mix this with another solvent and / or add an electrode protection additive for forming a protective film on the electrode. Further, in order to increase the degree of ionization of the lithium salt that contributes to the charging and discharging of the non-aqueous secondary battery, the non-aqueous solvent preferably contains one or more cyclic aprotic polar solvents, and one or more cyclic carbonates. It is more preferable to include it.

The content of acetonitrile is preferably 20 to 90% by volume with respect to the total amount of the non-aqueous solvent. The content of acetonitrile is more preferably 30% by volume or more, further preferably 40% by volume or more, based on the total amount of the non-aqueous solvent. Further, this value is more preferably 85% by volume or less, and further preferably 66% by volume or less. When the content of acetonitrile is 20% by volume or more with respect to the total amount of the non-aqueous solvent, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, and further, the dissolution of the lithium salt can be promoted. can. Since the dicarboxylic acid ester described below suppresses the increase in the internal resistance of the battery, when the content of acetonitrile in the non-aqueous solvent is within the above range, the cycle characteristics and other factors are maintained while maintaining the excellent performance of acetonitrile. There is a tendency that the battery characteristics can be further improved.

<2-2. Lithium salt>
The lithium salt is not particularly limited as long as it is usually used in a non-aqueous electrolyte solution of a non-aqueous secondary battery and can obtain a predetermined ionic conductivity in combination with other components. It may be a thing. The lithium salt is preferably contained in the non-aqueous electrolyte solution according to the present embodiment at a concentration of 0.1 to 3 mol / L with respect to the total amount of the non-aqueous solvent, and is 0.5 to 2 mol / L. It is more preferably contained in a concentration. When the concentration of the lithium salt is within the above range, the conductivity of the non-aqueous electrolyte solution is maintained higher than that of the non-aqueous electrolyte solution, and at the same time, the charge / discharge efficiency of the non-aqueous secondary battery is higher. It tends to be kept high. The preferable concentration of the lithium salt shown above is in a preferable range of the total concentration of the lithium salts contained in the non-aqueous electrolyte solution, and in the present embodiment, it is higher than the preferable total concentration range of the lithium salts shown above. Priority is given to the preferred range of the concentration of each lithium salt shown below.

The lithium salt in the present embodiment is not particularly limited, but is preferably an inorganic lithium salt. Here, the "inorganic lithium salt" means a lithium salt which does not contain a carbon atom in an anion and is soluble in acetonitrile, and the "organic lithium salt" described later means an anion containing a carbon atom and can be used in acetonitrile. A dissolved lithium salt.

The inorganic lithium salt is not particularly limited as long as it is used as a normal non-aqueous electrolyte, and may be any of them. Specific examples of such inorganic lithium salts include, for example, LiPF ₆ , LiN (SO ₂ F) ₂ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiS _b F ₆ , LiAlO ₄ , LiAlCl ₄ , Examples _{thereof include Li 2} B ₁₂ F _b H _12-b [b is an integer of 0 to 3], a lithium salt bonded to a polyvalent anion containing no carbon atom, and the like. These inorganic lithium salts may be used alone or in combination of two or more. Above all, it is preferable to use an inorganic lithium salt having a fluorine atom as the inorganic lithium salt from the viewpoint of suppressing an increase in internal resistance because a passivation film is formed on the surface of the metal foil which is a positive electrode current collector.

Further, it is more preferable to use an inorganic lithium salt having a phosphorus atom as the inorganic lithium salt because it is easy to release free fluorine atoms, and LiPF ₆ is particularly preferable. It is preferable to use an inorganic lithium salt having a boron atom as the inorganic lithium salt because it is easy to capture an excess free acid component which may cause deterioration of the battery, and LiBF ₄ is particularly preferable from such a viewpoint. ..

The content of the inorganic lithium salt in the non-aqueous electrolyte solution of the present embodiment is preferably 0.05 to 2.5 mol / L, preferably 0.5 to 2 mol / L, based on the total amount of the non-aqueous solvent. It is more preferably present, and further preferably 0.8 to 1.5 mol / L.

The lithium salt in the present embodiment may further contain an organic lithium salt in addition to the inorganic lithium salt.

The content of the organic lithium salt in the non-aqueous electrolyte solution of the present embodiment is preferably 4 mol / L or less, more preferably 2 mol / L or less, based on the total amount of the non-aqueous solvent. The lower limit of the content of the organic lithium salt can be, for example, 0.001 mol / L or more with respect to the total amount of the non-aqueous solvent. When the content of the organic lithium salt is within the above range, it tends to be possible to secure a balance between the function and solubility of the non-aqueous electrolyte solution.

Specific examples of the organic lithium salt, for _{example, LiN (SO 2 CF 3)} 2, LiN (SO 2 C 2 F 5) ₂ or the like _{LiN (SO 2 C m F 2m} + 1) 2 wherein, m is 1 organic lithium salt represented by 8 is an integer from]; LiN _(SO 2 _F) organic lithium salt represented by _2; LiPF ₅ (CF _{3) "LiPF n (C p F 2p +} 1) , such as _6-n [ In the formula, n is an integer of 1 to 5, and p is an integer of 1 to 8.] An organic lithium salt represented by; _{LiBF q} (CsF _{2s + 1} ) _4-q [, such as LiBF ₃ (CF _3). In the formula, q is an integer of 1 to 3 and s is an integer of 1 to 8]. Lithium bis (oxalat) borate represented by _{LiB (C 2} O ₄ ) _2. (LiBOB); Lithium salt of volate with a halogenated organic acid as a ligand; Lithium oxalatodifluoroborate (LiODFB) represented by _{LiBF 2} (C ₂ O _{4 ); LiB (C 3} O ₄ H ₂₎ ) lithium bis represented by ₂ (malonate) borate _{(LiBMB); LiPF 4 (C} 2 O 4 lithium tetrafluoro-oxa Lato phosphate or the like represented by) and the like.

In addition, the following general formulas (4a), (4b) and (4c):
LiC (SO ₂ R ⁹ ) (SO ₂ R ¹⁰ ) (SO ₂ R ¹¹ ) (4a)
LiN (SO ₂ OR ¹² ) (SO ₂ OR ¹³ ) (4b)
LiN (SO ₂ R ¹⁴ ) (SO ₂ OR ¹⁵ ) (4c)
An organic lithium salt represented by is also used. In formulas (4a), (4b) and (4c), R ⁹ , R ¹⁰ , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ and R ¹⁵ represent perfluoroalkyl groups having 1 to 8 carbon atoms. They may be the same or different from each other.

In order to improve the load characteristics and charge / discharge cycle characteristics of the non-aqueous secondary battery, it is preferable to supplementally add an organic lithium salt having an oxalic acid group, LiB (C ₂ O ₄ ) ₂ , LiBF ₂ ( It is particularly preferred to add one or more selected from the group consisting of C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O ₄ ) _2. The organolithium salt having an oxalic acid group may be added to the non-aqueous electrolyte solution, or may be contained in the negative electrode (negative electrode active material layer).

The organic lithium salt having a oxalic acid group is contained in the non-aqueous electrolyte solution at a concentration of 0.005 mol / L or more with respect to the total amount of the non-aqueous solvent from the viewpoint of ensuring the effect of its use. It is more preferable, it is more preferably contained at a concentration of 0.02 mol / L or more, and further preferably it is contained at a concentration of 0.05 mol / L or more. However, if the amount of the organolithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, it may precipitate. Therefore, the organolithium salt having a oxalic acid group is preferably contained in the non-aqueous electrolyte solution at a concentration of 1 mol / L or less, preferably 0.5 mol / L or less, based on the total amount of the non-aqueous solvent. It is more preferable that it is contained in, and it is further preferable that it is contained in a concentration of 0.2 mol / L or less.

<2-3. Electrode protection additive ＞
The non-aqueous electrolyte solution in the present embodiment may contain an additive that protects the electrodes in addition to the dicarboxylic acid ester. The electrode protection additive is not particularly limited as long as it does not hinder the solution of the problem according to the present invention. It may substantially overlap with a substance (ie, the non-aqueous solvent described above) that serves as a solvent for dissolving the lithium salt. The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte solution and the non-aqueous secondary battery in the present embodiment, but also includes substances that are not directly involved in the electrochemical reaction. ..

Specific examples of the electrode protection additive include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, and cis-4,5-difluoro. -1,3-Dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4, Fluoroethylene carbonate typified by 4,5,5-tetrafluoro-1,3-dioxolan-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; Unsaturated bond-containing cyclic carbonates typified by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε -Cyclic ester typified by caprolactone; Cyclic ether typified by 1,4-dioxane; ethylene sulphite, propylene sulphite, butylene sulphite, pentensulfite, sulfolane, 3-methylsulfolane, 1,3-propanesulton , 1,4-Butansulton, and cyclic sulfur compounds typified by tetramethylene sulfoxide. These may be used alone or in combination of two or more.

Since acetonitrile, which is one component of the non-aqueous solvent, is easily chemically reduced and decomposed, the non-aqueous solvent containing acetonitrile includes one kind of cyclic aprotic polar solvent as an additive for forming a protective film on the negative electrode. It is preferable to contain the above, and it is more preferable to contain one or more cyclic sulfur compounds.

The content of the electrode protection additive in the non-aqueous electrolyte solution in the present embodiment is preferably 0.1 to 30% by volume as the content of the electrode protection additive with respect to the total amount of the non-aqueous solvent. , 1 to 20% by volume, more preferably 2 to 15% by volume. When the electrode protection additive is solid at room temperature, it is used by raising the temperature to liquefy it, and if the content of the obtained liquid in the non-aqueous electrolyte solution is within the above preferable range. It should be good.

In the present embodiment, the larger the content of the electrode protection additive, the more the deterioration of the non-aqueous electrolyte solution is suppressed, but the smaller the content of the electrode protection additive, the higher the non-aqueous secondary battery in a low temperature environment. The output characteristics will be improved. Therefore, by adjusting the content of the electrode protection additive within the above range, the non-aqueous electrolyte solution is excellent based on the high ionic conductivity without impairing the basic function as a non-aqueous secondary battery. There is a tendency to maximize performance. By preparing a non-aqueous electrolyte solution with such a composition, the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and all other battery characteristics tend to be further improved. be.

｛式中、Ｒ^１及びＲ^２は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、かつＲ^３及びＲ^４は、それぞれ独立して、水素原子又は炭素数１〜４の１価の炭化水素基を示す。ただし、Ｒ^３とＲ^４の両方は同時に水素原子になることはない。｝

｛式中、Ｒ^５及びＲ^６は、それぞれ独立して、炭素数１〜４の１価の炭化水素基を示し、かつＲ^７は炭素数１〜４の２価の炭化水素基を示す。｝
で表されるジカルボン酸エステルの少なくとも一方を含有する。 <2-4. Dicarboxylic acid ester>
The non-aqueous electrolyte solution in the present embodiment has the following general formula (1) or (2):

{In the formula, R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 4 carbon atoms, and R ³ and R ⁴ independently represent a hydrogen atom or 1 carbon atom, respectively. Shows a monovalent hydrocarbon group of ~ 4. However, ^{both R 3} and R ⁴ do not become hydrogen atoms at the same time. }

{In the formula, R ⁵ and R ⁶ each independently represent a monovalent hydrocarbon group ^{having 1 to 4 carbon atoms, and R 7} represents a divalent hydrocarbon group having 1 to 4 carbon atoms. }
Contains at least one of the dicarboxylic acid esters represented by.

By using the dicarboxylic acid ester as an additive, the non-aqueous secondary battery can exhibit excellent load characteristics and high temperature durability performance. Although the detailed mechanism is unknown, it is presumed that the dicarboxylic acid ester suppresses the reductive decomposition of acetonitrile by contributing to the formation of the negative electrode protective film. Further, since the dicarboxylic acid ester is excellent in wettability, the impregnation property of the non-aqueous electrolyte solution into the separator is improved by using it as an additive. This has the effect of suppressing an increase in the internal resistance of the battery and improving battery characteristics such as cycle characteristics. In addition, the dicarboxylic acid ester has an effect of reducing defective cells in which the separator is not sufficiently impregnated with the non-aqueous electrolyte solution in the liquid injection process during the production of the lithium battery.

At least one or both of the dicarboxylic acid ester represented by the general formula (1) and the dicarboxylic acid ester represented by the general formula (2) can be contained in the non-aqueous electrolyte solution.

In the above formulas (1) and (2), R ¹ and R ² are preferably monovalent hydrocarbon groups having 1 to 2 carbon atoms, and R ^{3 and R 4 are preferably monovalent hydrocarbon groups having 1 to 2 carbon atoms.} preferably a hydrocarbon group, preferably a monovalent hydrocarbon group having 1 to 2 carbon atoms as R ⁵ and R ^6, and R ⁷ is is a divalent hydrocarbon group having 1 to 3 carbon atoms It is preferably a divalent hydrocarbon group having 1 to 2 carbon atoms. Further, R ^{7 can be distinguished from the divalent group represented by −C (−R 3} ) ^{(−R 4} ) − in the general formula (1), and is a linear group, for example, carbon. It can be an alkylene group of number 2-4 or the like.

As the dicarboxylic acid ester in the present embodiment, diethyl methylmalonic acid, 2 It is preferable to use at least one of diethyl-2-ethyl-2-methylmalonate and dimethyl succinate.

The content of the dicarboxylic acid ester in the non-aqueous electrolyte solution in the present embodiment is not particularly limited, but is preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the non-aqueous electrolyte solution, and is 0. It is more preferably 2.02 to 1.5 parts by mass, and further preferably 0.05 to 1 part by mass. In the present embodiment, it is presumed that the dicarboxylic acid ester suppresses the reductive decomposition of acetonitrile by contributing to the formation of the negative electrode protective film. As a result, the non-aqueous secondary battery containing the dicarboxylic acid ester exhibits excellent load characteristics and suppresses a decrease in capacity when the charge / discharge cycle is repeated. However, when the content of the dicarboxylic acid ester in the present embodiment is increased, the coating film of the negative electrode becomes excessively thick and the internal resistance increases, which causes a decrease in the rate performance of the battery. Therefore, by adjusting the content of the dicarboxylic acid ester within the above range, it is possible to suppress the reductive decomposition of acetonitrile while preventing the negative electrode coating from being excessively thickened. By preparing a non-aqueous electrolyte solution with such a composition, the cycle performance, high output performance in a low temperature environment, and other battery characteristics of the obtained non-aqueous secondary battery are all further improved. Tend to be able to.

<2-5. Other optional additives>
In the present embodiment, for the purpose of improving the charge / discharge cycle characteristics of the non-aqueous secondary battery, improving the high temperature storage property, improving the safety (for example, preventing overcharging, etc.), the non-aqueous electrolyte solution, for example, sulfonic acid, is used. Sulfonic acid ester, diphenyldisulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate ester {ethyldiethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P = O) -CH ₂ ( C = O) OC ₂ H ₅ , Tris (Trifluoroethyl) Phosphate (TFEP) :( CF ₃ CH ₂ O) ₃ P = O, Triphenyl Phosphate (TPP): (C ₆ H ₅ O) ₃ P An optional additive selected from = O etc.} and derivatives of these compounds can be appropriately contained. In particular, the above-mentioned phosphate ester has an effect of suppressing side reactions during storage and is effective.

<3. Positive electrode>
The positive electrode 150 is composed of a positive electrode active material layer prepared from a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it acts as a positive electrode of a non-aqueous secondary battery, and may be a known one.

The positive electrode active material layer preferably contains a material capable of occluding and releasing lithium ions as the positive electrode active material.

Among them, according to the present invention, a positive electrode having a positive electrode active material layer containing at least one transition metal element or Fe atom selected from the group consisting of Ni, Mn, and Co on one side or both sides of the current collector. Is more preferable. By using a positive electrode active material containing the above elements, it tends to be possible to obtain a high voltage and a high energy density.

Further, the positive electrode active material layer preferably contains a conductive auxiliary agent and a binder together with the positive electrode active material, if necessary. When such a material is used, it tends to be possible to obtain a high voltage and a high energy density, which is preferable.

Examples of the positive electrode active material include the following general formulas (5a) and (5b):
Li _x MO ₂ (5a)
Li _y M ₂ O ₄ (5b)
{In the formula, M represents one or more metal elements including at least one transition metal element, x represents a number from 0 to 1.1, and y represents a number from 0 to 2. }
Examples thereof include a lithium-containing compound represented by each of the above, and other lithium-containing compounds.

Examples of the lithium-containing compound represented by each of the general formulas (5a) and (5b) include, for example.
Lithium cobalt oxide represented by LiCoO _2;
Lithium manganese oxides typified by LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ Mn ₂ O _4;
Lithium nickel oxide represented by Linio _2;
Represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.8 Co _0.2 O ₂ Li _z MO ₂ {In the formula, M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and is composed of Ni, Mn, Co, Al, and Mg. Lithium-containing composite metal oxides and the like represented by} indicating two or more metal elements selected from the above, and z indicates a number of more than 0.9 and less than 1.2;
Can be mentioned. Among these, the element-containing molar ratio of Ni is preferably greater than 30%, more preferably greater than 45%, and even more preferably greater than 75%.

The lithium-containing compound other than the lithium-containing compound represented by each of the general formulas (5a) and (5b) is not particularly limited as long as it contains lithium. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, a metal chalcogenide having lithium, a metal phosphate compound containing lithium and a transition metal element, and lithium and a transition metal element. silicic acid metal compound (e.g., wherein _Li t _M u SiO ₄ {wherein, M has the same meaning as the general formula (5a), t represents a number of 0 to 1, and the number of u is 0 to 2 , A compound represented by.}. From the viewpoint of obtaining a high voltage, the lithium-containing compounds include lithium, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and chromium (Zn). A composite oxide containing at least one transition metal element selected from the group consisting of Cr), vanadium (V), and titanium (Ti), and a metal phosphate compound are preferred.

More specifically, as the lithium-containing compound, a composite oxide containing lithium and a transition metal element, a metal chalcogenide containing lithium and a transition metal element, and a metal phosphate compound having lithium are more preferable, for example, the following. General formulas (6a) and (6b):
^{_{Li v M I D 2 (6a}} )
Li _w M ^II PO ₄ (6b)
{Wherein, D is an oxygen or chalcogen element, M ^I and M ^II is, each represent one or more transition metal elements, the values of v and w is the charge and discharge state of the battery, v is 0. It represents a number from 05 to 1.10, and w represents a number from 0.05 to 1.10. }
Examples thereof include compounds represented by each of the above.

The lithium-containing compound represented by the above-mentioned general formula (6a) has a layered structure, and the compound represented by the above-mentioned general formula (6b) has an olivine structure. These lithium-containing compounds are those in which a part of the transition metal element is replaced with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, and these metal elements are included in the crystal grain boundary. It may be one in which a part of oxygen atoms is replaced with a fluorine atom or the like, one in which at least a part of the surface of the positive electrode active material is coated with another positive positive active material, or the like.

As the positive electrode active material in the present embodiment, only the above-mentioned lithium-containing compound may be used, or other positive electrode active materials may be used in combination with the lithium-containing compound.

Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layered structure; sulfur; conductive polymers, and the like. Examples of metal oxides or metal chalcogenides having a tunnel structure and a layered structure include MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe. Examples thereof include oxides, sulfides, and serenes of metals other than lithium represented by _2. Examples of the conductive polymer include conductive polymers typified by polyaniline, polythiophene, polyacetylene, and polypyrrole.

The above-mentioned other positive electrode active materials may be used alone or in combination of two or more, and are not particularly limited. However, since lithium ions can be occluded and released in a reversible and stable manner and a high energy density can be achieved, the positive electrode active material layer is at least one transition metal element selected from Ni, Mn, and Co. Is preferably contained.

When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the usage ratio of the lithium-containing compound to the total positive electrode active material is preferably 80% by mass or more in relation to the usage ratio of both. 85% by mass or more is more preferable, and the balance can be composed of other positive electrode active materials.

Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the positive electrode active material.

For the positive electrode active material layer, a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a positive electrode current collector and dried (solvent removal). ), And if necessary, it is formed by pressing. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned.

The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The surface of the positive electrode current collector may be coated with carbon or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

<4. Negative electrode ＞
The negative electrode 160 is composed of a negative electrode active material layer prepared from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 is not particularly limited as long as it acts as a negative electrode of a non-aqueous secondary battery, and may be a known one.

The negative electrode active material layer contains a material capable of storing ^{lithium ions at a potential lower than 0.4 V (vs. Li / Li +} ) as the negative electrode active material from the viewpoint of increasing the battery voltage. Is preferable. The negative electrode active material layer preferably contains a conductive auxiliary agent and a binder together with the negative electrode active material, if necessary.

Examples of the negative electrode active material include amorphous carbon (hard carbon), graphite (artificial graphite, natural graphite), thermally decomposed carbon, coke, glassy carbon, calcined organic polymer compound, mesocarbon microbeads, and carbon fiber. In addition to carbon materials such as activated carbon, carbon colloid, and carbon black, metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetal compounds, organic compounds, inorganic compounds, and metal complexes, Examples include organic polymer compounds.

The negative electrode active material may be used alone or in combination of two or more. Among them, according to the present invention, a negative electrode having a negative electrode active material layer containing graphite on one side or both sides of the current collector is preferable. Graphite is currently the most widely used negative electrode active material, and has an excellent balance of energy density, safety, cycle durability, etc. as compared with other negative electrode active materials.

Examples of the conductive auxiliary agent include acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

Examples of the binder include PVDF, PTFE, polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass with respect to 100 parts by mass of the negative electrode active material.

For the negative electrode active material layer, a negative electrode mixture-containing slurry in which a negative electrode mixture obtained by mixing a negative electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a negative electrode current collector and dried (solvent removal). It is formed by pressing as needed. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned.

The negative electrode current collector is composed of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Further, the negative electrode current collector may have a carbon coat on its surface or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

<5. Separator>
The non-aqueous secondary battery 100 in the present embodiment preferably includes a separator 170 between the positive electrode 150 and the negative electrode 160 from the viewpoint of preventing short circuits between the positive electrode 150 and the negative electrode 160 and imparting safety such as shutdown. As the separator 170, the same one as that provided in a known non-aqueous secondary battery may be used, and an insulating thin film having high ion permeability and excellent mechanical strength is preferable. Examples of the separator 170 include woven fabrics, non-woven fabrics, and microporous membranes made of synthetic resin. Among these, microporous synthetic resin membranes are preferable.

As the synthetic resin microporous membrane, for example, a polyolefin-based microporous membrane such as a microporous membrane containing polyethylene or polypropylene as a main component or a microporous membrane containing both of these polyolefins is preferably used. Examples of the non-woven fabric include a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

The separator 170 may have a structure in which one type of microporous membrane is laminated in a single layer or a plurality of types, or may be a structure in which two or more types of microporous membranes are laminated. The separator 170 may have a single layer or a plurality of laminated layers using a mixed resin material obtained by melt-kneading two or more kinds of resin materials.

<6. Battery exterior ＞
The configuration of the battery exterior 110 of the non-aqueous secondary battery 100 in the present embodiment is not particularly limited, and for example, any battery exterior of a battery can and a laminated film exterior can be used. As the battery can, for example, a metal can made of steel or aluminum can be used. As the laminate film exterior body, for example, a laminate film having a three-layer structure of a heat-melted resin / metal film / resin can be used.

The laminated film exterior is in a state in which two sheets are stacked with the heat-melted resin side facing inward, or bent so that the heat-melted resin side faces inward, and the end portion is sealed by a heat seal. Can be used as an exterior body. When the laminated film exterior body is used, the positive electrode lead body 130 (or the lead tab connected to the positive electrode terminal and the positive electrode terminal) is connected to the positive electrode current collector, and the negative electrode lead body 140 (or the negative electrode terminal and the negative electrode terminal) are connected to the negative electrode current collector. The lead tab to be connected may be connected. In this case, the laminated film outer body is sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or lead tabs connected to the positive electrode terminal and the negative electrode terminal respectively) pulled out to the outside of the outer body. May be good.

<7. Battery manufacturing method>
The non-aqueous secondary battery 100 in the present embodiment has the above-mentioned non-aqueous electrolyte solution, a positive electrode 150 having a positive electrode active material layer on one side or both sides of the current collector, and a negative electrode active material layer on one side or both sides of the current collector. It is made by a known method using a negative electrode 160, a battery exterior 110, and optionally a separator 170.

First, a laminate composed of a positive electrode 150, a negative electrode 160, and a separator 170, if necessary, is formed. For example, an embodiment in which a long positive electrode 150 and a negative electrode 160 are wound in a laminated state in which the long separator is interposed between the positive electrode 150 and the negative electrode 160 to form a laminated body having a wound structure; the positive electrode 150. An embodiment of forming a laminated body having a laminated structure in which the positive electrode sheet and the negative electrode sheet obtained by cutting the negative electrode 160 into a plurality of sheets having a certain area and shape are alternately laminated via a separator sheet; It is possible to form a laminated body having a laminated structure in which the positive electrode body sheet and the negative electrode body sheet are alternately inserted between the zigzag-folded separators by folding the separator of the scale into pieces.

Next, the above-mentioned laminate is housed in the battery exterior 110 (battery case), the non-aqueous electrolyte solution according to the present embodiment is injected into the battery case, and the laminate is immersed in the non-aqueous electrolyte solution for sealing. By doing so, the non-aqueous secondary battery according to the present embodiment can be produced.

Alternatively, a gel-like electrolyte membrane is prepared in advance by impregnating a base material made of a polymer material with a non-aqueous electrolyte solution, and a sheet-shaped positive electrode 150, negative electrode 160, and electrolyte membrane, and necessary A non-aqueous secondary battery 100 can also be manufactured by forming a laminated body having a laminated structure using the separator 170 and then accommodating the laminated body in the battery exterior 110.

The shape of the non-aqueous secondary battery 100 in the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a square cylinder shape, a button shape, a coin shape, a flat shape, a laminated shape, and the like are preferably adopted.

In the present embodiment, when a non-aqueous electrolyte solution using acetonitrile is used, the lithium ions released from the positive electrode during the initial charging of the non-aqueous secondary battery diffuse to the entire negative electrode due to its high ionic conductivity. There is a possibility that it will be done. In a non-aqueous secondary battery, the area of the negative electrode active material layer is generally larger than that of the positive electrode active material layer, but lithium is included in the negative electrode active material layer not facing the positive electrode active material layer. When the ions are diffused and stored, the lithium ions are not released at the time of the first discharge and stay at the negative electrode, so that the contribution of the unreleased lithium ions becomes an irreversible capacity. For this reason, the initial charge / discharge efficiency of a non-aqueous secondary battery using a non-aqueous electrolyte solution containing acetonitrile may be low.

On the other hand, when the area of the positive electrode active material layer is larger than that of the negative electrode active material layer, or when both are the same, current is likely to be concentrated at the edge portion of the negative electrode active material layer during charging, and lithium dendrite is generated. It will be easier.

There is no particular limitation on the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but for the above reason, it is larger than 1.0 and less than 1.1. It is more preferably greater than 1.002 and less than 1.09, more preferably greater than 1.005 and less than 1.08, and particularly greater than 1.01 and less than 1.08. preferable. In a non-aqueous secondary battery using a non-aqueous electrolyte solution containing acetonitrile, the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other is reduced. The initial charge / discharge efficiency can be improved.

Reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means that the negative electrode active material layer does not face the positive electrode active material layer. It means limiting the proportion of the area of the part. As a result, of the lithium ions released from the positive electrode during the initial charge, the amount of lithium ions stored in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (that is, the amount of lithium ions released from the negative electrode during the initial discharge). It is possible to reduce the amount of lithium ions, which has an irreversible capacity, as much as possible. Therefore, by designing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, the load characteristics of the battery can be improved by using acetonitrile. It is possible to improve the initial charge / discharge efficiency of the battery and further suppress the generation of lithium dendrite.

The non-aqueous secondary battery 100 in the present embodiment can function as a battery by the initial charging, but is stabilized by decomposing a part of the non-aqueous electrolyte solution at the initial charging. The method of initial charging is not particularly limited, but the initial charging is preferably performed at 0.001 to 0.3C, more preferably 0.002 to 0.25C, and 0.003 to 0.2C. It is more preferable to be carried out in. It is also preferable that the initial charging is performed via constant voltage charging on the way. The constant current that discharges the rated capacity in 1 hour is 1C. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, a solid electrolyte interface (SEI) is formed on the electrode surface, which has the effect of suppressing an increase in internal resistance including the positive electrode 150. In addition, the reaction product is not firmly immobilized only on the negative electrode 160, and somehow gives a good effect to members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. Therefore, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte solution.

The non-aqueous secondary battery 100 in the present embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of controlling the charge / discharge state of the battery pack, the working voltage range per battery pack is preferably 2 to 5 V, more preferably 2.5 to 5 V, and preferably 2.75 V to 5 V. Especially preferable.

Although the embodiment for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment. The present invention can be modified in various ways without departing from the gist thereof.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples.

(1) Preparation of non-aqueous electrolyte solution Under an inert atmosphere, various non-aqueous solvents are mixed so as to have a predetermined concentration, and further, various lithium salts are added so as to have a predetermined concentration. Aqueous electrolytes (S11) to (S12) were prepared. The composition of these non-aqueous electrolyte solutions is shown in Table 1.

Further, the non-aqueous electrolyte solution (S11) is used as the mother electrolyte solution, and various dicarboxylic acid esters are added to 100 parts by mass of the mother electrolyte solution so as to have a predetermined mass portion to form the non-aqueous electrolyte solution (S21) to (S21). S25) was prepared. The composition of these non-aqueous electrolyte solutions is shown in Table 2.

The abbreviations for the non-aqueous solvent, lithium salt, and various additives in Table 1 have the following meanings.
(Non-aqueous solvent)
AN: Acetonitrile DFA: 2,2-Difluoroethyl acetate GBL: γ-butyrolactone MBL: α-methyl-γ-butyrolactone ES: Ethylene sulfite VC: Vinylene carbonate (lithium salt)
LiPF ₆ : Lithium hexafluorophosphate LiFSI: Lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ )

(2) Wetting property test With respect to the various non-aqueous electrolyte solutions obtained as described above, 5 μL of the non-aqueous electrolyte solution was measured, dropped onto a polypropylene-based separator, and a test was conducted in which the separator was visually observed 60 seconds later. The obtained evaluation results are shown in Table 3. In Table 3, ○ is the non-aqueous electrolyte solution in which the color of the separator in the portion where the non-aqueous electrolyte solution was dropped was observed to change from white to gray, and × is the separator in the portion where the non-aqueous electrolyte solution was dropped. Represents each of the non-aqueous electrolyte solutions in which the color of the above was observed to remain white.

The polypropylene-based separators used in the wettability test are as follows.
Separator: Single-layer polypropylene separator for lithium batteries Celgard # 2500

In Comparative Example 1 containing no dicarboxylic acid ester, the color of the separator in the portion where the non-aqueous electrolyte solution was dropped remained white, and the separator was not impregnated with the non-aqueous electrolyte solution. In Examples 1 to 5 of the non-aqueous electrolyte solution containing the dicarboxylic acid ester, the color of the separator in the portion where the non-aqueous electrolyte solution was dropped changed from white to gray, and the non-aqueous electrolyte solution impregnated the separator. From the above results, it was suggested that the dicarboxylic acid ester contained in the non-aqueous electrolyte solution in the present embodiment has an effect of improving the wettability of the non-aqueous electrolyte solution to the separator.

(3) Fabrication of coin-type non-aqueous secondary battery (3-1) Fabrication of positive electrode (P1) (A) Composite oxide (LiNi) of lithium, nickel, manganese and cobalt having a number average particle diameter of 11 μm as the positive electrode active material _1/3 Mn _1/3 Co _1/3 O ₂ , density 4.70 g / cm ³ ) and (B) as a conductive aid, graphite carbon powder with a number average particle diameter of 6.5 μm (density 2.26 g / cm) ³ ) and acetylene black powder having a number average particle diameter of 48 nm (density 1.95 g / cm ³ ) and (C) vinylidene fluoride (PVDF; density 1.75 g / cm ³ ) as a binder were added at 92: 4: The mixture was mixed at a mass ratio of 4 to obtain a positive electrode mixture.

N-Methyl-2-pyrrolidone as a solvent was added to the obtained positive electrode mixture so as to have a solid content of 68% by mass and further mixed to prepare a positive electrode mixture-containing slurry. A coating width of 240 to 250 mm, a coating length of 125 mm, and a non-coating length of 20 mm are adjusted on one side of an aluminum foil having a thickness of 15 μm and a width of 280 mm, which serves as a positive electrode current collector, while adjusting the basis weight of the slurry containing the positive electrode mixture. The coating was applied using a 3-roll transfer coater so as to have the coating pattern of, and the solvent was dried and removed in a hot air drying furnace. Both sides of the obtained electrode roll were trimmed and cut, and dried under reduced pressure at 130 ° C. for 8 hours. Then, it was rolled by a roll press so that the density of the positive electrode active material layer became 2.9 g / cm ³ , and a positive electrode (P1) composed of the positive electrode active material layer and the positive electrode current collector was obtained. The amount of grain was 23.9 mg / cm ² , and the mass of the positive electrode active material excluding the positive electrode current collector was 22.0 mg / cm ² .

(3-2) Preparation of negative electrode (N1) (a) Artificial graphite powder (density 2.23 g / cm ³ ) with a number average particle diameter of 12.7 μm as the negative electrode active material, and (b) Number as the conductive auxiliary agent Acetylene black powder with an average particle size of 48 nm (density 1.95 g / cm ³ ), (c) carboxymethyl cellulose (density 1.60 g / cm ³ ) solution (solid content concentration 1.83% by mass) and diene as a binder. Rubber (glass transition temperature: -5 ° C, number average particle size when dried: 120 nm, density 1.00 g / cm ³ , dispersion medium: water, solid content concentration 40% by mass), 95.7: 0.5 The mixture was mixed at a solid content mass ratio of 3.8 to obtain a negative electrode mixture.

Water was added to the obtained negative electrode mixture as a solvent so as to have a solid content of 45% by mass, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. A coating width of 240 to 250 mm, a coating length of 125 mm, and a non-coating length of 20 mm are adjusted on one side of a copper foil having a thickness of 8 μm and a width of 280 mm, which serves as a negative electrode current collector, while adjusting the basis weight of the slurry containing the negative electrode mixture. The coating was applied using a 3-roll transfer coater so as to have the coating pattern of, and the solvent was dried and removed in a hot air drying furnace. Both sides of the obtained electrode roll were trimmed and cut, and dried under reduced pressure at 130 ° C. for 8 hours. Then, it was rolled by a roll press so that the density of the negative electrode active material layer became 1.5 g / cm ³ , and a negative electrode (N1) composed of a negative electrode active material layer and a negative electrode current collector was obtained. The amount of grain was 11.5 mg / cm ² , and the mass of the negative electrode active material excluding the negative electrode current collector was 11.0 mg / cm ² .

(3-3) Assembly of coin-type non-aqueous secondary battery A polypropylene gasket is set in a CR2032 type battery case (SUS304 / Al clad), and the positive electrode (P1) obtained as described above is placed in the center thereof. A disk-shaped punch having a diameter of 15.958 mm was set with the positive electrode active material layer facing upward. A glass fiber filter paper (GA-100 manufactured by Advantech) punched into a disk shape having a diameter of 16.156 mm was set from above, and 150 μL of a non-aqueous electrolyte solution was injected, and then obtained as described above. The negative electrode (N1) was punched into a disk shape having a diameter of 16.156 mm and set with the negative electrode active material layer facing downward. Furthermore, after setting the spacer and spring in the battery case, the battery cap was fitted and crimped with a caulking machine. The overflowing non-aqueous electrolyte solution was wiped clean with a waste cloth. The assembly containing the laminate of P1, glass fiber filter paper, and N1 and the non-aqueous electrolyte was held at 25 ° C. for 12 hours, and the laminate was sufficiently blended with the non-aqueous electrolyte to obtain a coin-type non-aqueous secondary battery. ..

(4) Evaluation of coin-type non-aqueous secondary battery With respect to the coin-type non-aqueous secondary battery obtained as described above, first, the initial charging process and the initial charge / discharge capacity measurement are performed according to the procedure of (4-1) below. went. Next, each coin-type non-aqueous secondary battery was evaluated according to the following procedures (4-2) and (4-3). Charging / discharging was performed using a charging / discharging device ACD-M01A (trade name) manufactured by Asuka Electronics Co., Ltd. and a program constant temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., Ltd.
Here, 1C means a current value that is expected to end the discharge in 1 hour after discharging the fully charged battery with a constant current. In the evaluations (4-1) to (4-3) below, 1C specifically discharges from a fully charged state of 4.2 V to 3.0 V at a constant current, and discharge ends in 1 hour. Means the expected current value.

(4-1) Initial charge / discharge treatment of coin-type non-aqueous secondary battery Set the ambient temperature of the coin-type non-aqueous secondary battery to 25 ° C and charge it with a constant current of 0.15 mA, which corresponds to 0.025 C. After reaching 3.1 V, the battery was charged at a constant voltage of 3.1 V for 1.5 hours. Subsequently, after resting for 3 hours, the battery was charged with a constant current of 0.3 mA corresponding to 0.05 C to reach 4.2 V, and then charged with a constant voltage of 4.2 V for 1.5 hours. Then, the battery was discharged to 3.0 V with a constant current of 0.9 mA corresponding to 0.15 C. The initial efficiency was calculated by dividing the discharge capacity at this time by the charge capacity. The discharge capacity at this time was used as the initial capacity.

(4-2) 85 ° C full charge storage test of coin-type non-aqueous secondary battery The ambient temperature of the coin-type non-aqueous secondary battery subjected to the initial charge / discharge treatment by the method described in (4-1) above was set to 25. The temperature was set to ° C., and the battery was charged with a constant current of 6 mA corresponding to 1 C to reach 4.2 V, and then charged with a constant voltage of 4.2 V for 1.5 hours. Next, this coin-type non-aqueous secondary battery was stored in a constant temperature bath at 85 ° C. for 4 hours. Then, the ambient temperature was returned to 25 ° C., and the battery was discharged to 3.0 V with a current value of 1.8 mA corresponding to 0.3 C. The remaining discharge capacity at this time was defined as A. The remaining capacity retention rate was calculated based on the following formula as the measured value of the 85 ° C. full charge storage test.
0.3C remaining capacity retention rate = (0.3C remaining discharge capacity after 85 ° C full charge storage A / initial capacity before 85 ° C full charge storage test) x 100 [%]

(4-3) Output test of coin-type non-aqueous secondary battery The ambient temperature of the coin-type non-aqueous secondary battery that was subjected to the 85 ° C full charge storage test by the method described in (4-2) above was set to 25 ° C. After setting, the battery was charged with a constant current of 6 mA corresponding to 1 C to reach 4.2 V, and then charged with a constant voltage of 4.2 V for 1.5 hours. Then, the battery was discharged to 3.0 V with a current value of 1.8 mA corresponding to 0.3 C. The recovery discharge capacity at this time was defined as B. Next, the battery was charged with a constant current of 6 mA corresponding to 1C, charged until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V for 1.5 hours. After that, the battery was discharged to a battery voltage of 3.0 V with a constant current of 9 mA corresponding to 1.5 C. The discharge capacity at this time was defined as C. As the output test measured values, the charge / discharge efficiency and the recovery capacity maintenance rate were calculated based on the following formulas.
0.3C recovery capacity retention rate = (0.3C recovery discharge capacity after 85 ° C full charge storage test B / initial capacity before 85 ° C full charge storage test) x 100 [%]
1.5C recovery capacity retention rate = (1.5C recovery discharge capacity after 85 ° C full charge storage test / initial capacity before 85 ° C full charge storage test) x 100 [%]

Here, the interpretation of each test result will be described.
The initial charge / discharge initial efficiency indicates the ratio of the initial discharge capacity to the initial charge capacity, but generally tends to be lower than the second and subsequent charge / discharge efficiencies. This is because Li ions are used at the time of SEI formation at the time of initial charging, so that the amount of Li ions that can be discharged decreases. As a result, an irreversible capacity is generated, and the discharge capacity with respect to the charge capacity becomes smaller. Therefore, if the initial charge / discharge initial efficiency is 80% or more, there is no particular problem.
The 0.3C remaining capacity retention rate can be used as an index of the magnitude of self-discharge in the 85 ° C. full charge storage test. It is considered that the larger this value is, the smaller the self-discharge at high temperature is, and it can be used for the purpose of increasing the current from the battery. Therefore, the remaining capacity retention rate of 0.3C is preferably 85% or more, and more preferably 90% or more from a practical point of view.
The 0.3C recovery capacity retention rate is an output index in applications where the energizing current is small. In this case, since it is not easily affected by the resistance inside the battery, the 0.3C recovery capacity retention rate is preferably 90% or more, and more preferably 95% or more.
The 1.5C recovery capacity retention rate is an output index in applications where the energizing current is large. In this case, it is easily affected by the resistance inside the battery, and the recovery capacity retention rate is lower than in the case of 0.3C. Therefore, the 1.5C recovery capacity retention rate is preferably 85% or more, and more preferably 90% or more.

The calculated results are shown in Table 4.

From the comparison between Examples 1 to 5 and Comparative Example 1, it was confirmed that the high temperature durability performance was improved when a non-aqueous electrolyte solution containing acetonitrile and a specific dicarboxylic acid ester was used.

From the above results, when the non-aqueous electrolyte solution contains a specific dicarboxylic acid ester, it exhibits excellent load characteristics and high temperature durability performance by forming a film having good properties of suppressing the reductive decomposition of acetonitrile. At the same time, it was shown that it exhibits high wettability to the separator.

The non-aqueous secondary battery produced by using the non-aqueous electrolyte of the present invention is, for example, a rechargeable battery for portable devices such as mobile phones, portable audio devices, personal computers, and IC (Integrated Circuit) tags; hybrid vehicles, Rechargeable batteries for automobiles such as plug-in hybrid vehicles and electric vehicles; expected to be used as residential power storage systems.

100 Non-aqueous secondary battery 110 Battery exterior 120 Battery exterior space 130 Positive electrode lead body 140 Negative electrode lead body 150 Positive electrode 160 Negative electrode 170 Separator

Claims (7)

With a non-aqueous solvent containing 20% to 90% by volume of acetonitrile;
With lithium salt;
The following general formula (1):

{In the formula, R ¹ and R ² each independently represent a monovalent hydrocarbon group having 1 to 4 carbon atoms, and R ³ and R ⁴ independently represent a hydrogen atom or 1 carbon atom, respectively. Shows a monovalent hydrocarbon group of ~ 4. However, ^{both R 3} and R ⁴ do not become hydrogen atoms at the same time. }
Or the following general formula (2):

{In the formula, R ⁵ and R ⁶ each independently represent a monovalent hydrocarbon group ^{having 1 to 4 carbon atoms, and R 7} represents a divalent hydrocarbon group having 1 to 4 carbon atoms. }
With at least one of the dicarboxylic acid esters represented by;
A non-aqueous electrolyte solution containing. The non-aqueous electrolyte solution according to claim 1, wherein the dicarboxylic acid ester is at least one of diethyl methylmalonic acid, diethyl 2-ethyl-2-methylmalonic acid, and dimethyl succinate. The non-aqueous electrolyte solution according to claim 1 or 2, wherein the content of the dicarboxylic acid ester is 0.01 part by mass to 2 parts by mass with respect to 100 parts by mass of the non-aqueous electrolyte solution. The non-aqueous electrolyte solution according to any one of claims 1 to 3, wherein the non-aqueous solvent further contains lactones having a substituent at the α-position. The non-aqueous electrolyte solution according to any one of claims 1 to 4, wherein the non-aqueous solvent further contains a chain fluorinated carboxylic acid ester. A positive electrode having a positive electrode active material layer containing at least one transition metal element or Fe atom selected from the group consisting of Ni, Mn, and Co on one or both sides of the current collector, and one or both sides of the current collector. A non-aqueous secondary battery comprising a laminate containing a negative electrode having a negative electrode active material layer containing graphite and the non-aqueous electrolyte solution according to any one of claims 1 to 5. The positive electrode active material constituting the positive electrode active material layer is _Liz MO ₂ {in the formula, M contains Ni, and one or more metal elements selected from the group consisting of Mn, Co, Al, and Mg. In addition, the element-containing molar ratio of Ni is greater than 30%, and z indicates a number greater than 0.9 and less than 1.2. } The non-aqueous secondary battery according to claim 6, which is a lithium-containing composite metal oxide represented by.

Images