JP2001052735A - Nonaqueous electrolytic solution and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent battery cycle characteristic and provide excel lent battery characteristics such as electrical capacity and a storage characteris tic in a charged state by including a specific wt.% of a disulfide derivative containing oxygen in its substituted group in a nonaqueous electrolytic solution. SOLUTION: This nonaqueous electrolytic solution contains 0.01-5 wt.% of a disulfide derivative containing oxygen in its substituted group expressed by formula I. In formula I, X1 and X2 each independently represents a 1-6C alkyl group, 2-6C alkenyl group, 3-6C cycloalkyl group, aryl group, 2-7C acyl group, 1-7C alkanesulfonyl group, 6-10C arylsulfonyl group or 2-7C ester group. It is also preferable that 0.01-5 wt.% of a disulfide derivative containing halogen in a substituted group expressed by formula II instead of formula I is included in the electrolytic solution. In formula II, X3 and X4 each independently represents F, Cl, Br, I, CF3, CCl3 or CBr3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte capable of providing a lithium secondary battery having excellent battery characteristics such as cycle characteristics, electric capacity and storage characteristics of a battery, and lithium using the same. Related to secondary batteries.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power sources for driving small electronic devices and the like. Lithium secondary batteries are mainly composed of a positive electrode, a non-aqueous electrolyte, and a negative electrode. In particular, a lithium secondary battery using a lithium composite oxide such as LiCoO ₂ as a positive electrode and a carbon material or lithium metal as a negative electrode has been developed. It is preferably used. As the non-aqueous electrolyte for the lithium secondary battery, ethylene carbonate (EC), propylene carbonate (P
Carbonates such as C) are preferably used.

[0003]

However, regarding the battery characteristics such as the cycle characteristics and the electric capacity of the battery,
There is a demand for a secondary battery having more excellent characteristics.
As the positive electrode, for example, LiCoO ₂ , LiMn ₂ O ₄ , Li
Lithium secondary batteries using NiO ₂ or the like have a problem in that the solvent in the non-aqueous electrolyte partially oxidizes and decomposes at the time of charging, and the decomposition products hinder a desirable electrochemical reaction of the battery. This results in reduced performance. This is thought to be due to electrochemical oxidation of the solvent at the interface between the positive electrode material and the non-aqueous electrolyte. In addition, in a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as the negative electrode, the solvent in the nonaqueous electrolyte is reductively decomposed on the surface of the negative electrode during charging, and as a nonaqueous electrolyte solvent Even in ECs that are generally widely used, reductive decomposition occurs partially during repetition of charge / discharge, and battery performance deteriorates. Therefore, at present, the battery characteristics such as the cycle characteristics and the electric capacity of the battery are not always satisfactory.

The present invention solves the above-mentioned problems relating to the non-aqueous electrolyte for a lithium secondary battery, and is excellent in battery cycle characteristics, and is also excellent in battery characteristics such as electric capacity and storage characteristics in a charged state. It is an object of the present invention to provide a non-aqueous electrolyte for a lithium secondary battery that can constitute a lithium secondary battery, and a lithium secondary battery using the same.

[0005]

The present invention relates to a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following formula (I):

[0006]

Embedded image (However, X ¹ and X ² are each independently an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms,
6, an alkynyl group, a cycloalkyl group having 3 to 6 carbon atoms,
An aryl group, an acyl group having 2 to 7 carbon atoms, an alkanesulfonyl group having 1 to 7 carbon atoms, an arylsulfonyl group having 6 to 10 carbon atoms, and an ester group having 2 to 7 carbon atoms are shown. A disulfide derivative containing oxygen in the substituent represented by the following formula (II):

[0007]

Embedded image (However, X ³ and X ⁴ are each independently F, Cl, B
r, I, CF ₃ , CCl ₃ , and CBr ₃ are shown. The present invention relates to a non-aqueous electrolyte solution characterized by containing 0.01 to 5% by weight of a disulfide derivative containing halogen in the substituent represented by the formula (1). In a lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, the following formula (I) is contained in the non-aqueous electrolyte.

[0008]

Embedded image (However, X ¹ and X ² are each independently an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms,
6, an alkynyl group, a cycloalkyl group having 3 to 6 carbon atoms,
An aryl group, an acyl group having 2 to 7 carbon atoms, an alkanesulfonyl group having 1 to 7 carbon atoms, an arylsulfonyl group having 6 to 10 carbon atoms, and an ester group having 2 to 7 carbon atoms are shown. A disulfide derivative containing oxygen in the substituent represented by the following formula (II):

[0009]

Embedded image (However, X ³ and X ⁴ are each independently F, Cl, B
r, I, CF ₃ , CCl ₃ , and CBr ₃ are shown. The present invention relates to a lithium secondary battery comprising 0.01 to 5% by weight of a disulfide derivative containing a halogen in a substituent represented by the formula (1).

The non-aqueous electrolyte of the present invention is used as a component of a lithium secondary battery. The constituent members other than the non-aqueous electrolyte constituting the secondary battery are not particularly limited, and various constituent members conventionally used can be used.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In a disulfide derivative represented by the above formula (I) contained in an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, X ¹ and X ² represent a methyl group, an ethyl group,
An alkyl group having 1 to 6 carbon atoms such as a propyl group, a butyl group, a pentyl group and a hexyl group is preferred. The alkyl group may be a branched alkyl group such as an isopropyl group, an isobutyl group or an isopentyl group, or a cycloalkyl group such as a cyclopropyl group or a cyclohexyl group. Also,
It may be an alkenyl group such as a vinyl group, a 1-propenyl group or an allyl group, or an alkynyl group such as an ethynyl group or a 2-propynyl group. Further, an aryl group such as a phenyl group and a p-tolyl group may be used. Further, an acyl group such as an acetyl group, a propionyl group, an acryloyl group, and a benzoyl group may be used, and a sulfonyl group such as a methanesulfonyl group, an ethanesulfonyl group, and a benzenesulfonyl group may be used. Further, an ester group such as a methoxycarbonyl group, an ethoxycarbonyl group, a phenoxycarbonyl group, and a benzyloxycarbonyl group may be used. Further, the formula (I)
In the disulfide derivative represented by I), X ³ and X ⁴
Is preferably a halogen atom such as F, Cl, Br and I, or a substituent containing a halogen atom such as CF ₃ , CCl ₃ and CBr ₃ .

Specific examples of the disulfide derivative represented by the general formula (I) include, for example, bis (4-methoxyphenyl) disulfide [X ¹ , X ² = methyl group], bis (3-methoxyphenyl) disulfide [X ¹ , X ² = methyl group], bis (2-methoxyphenyl) disulfide [X ¹ , X ² = methyl group], bis (4-ethoxyphenyl) disulfide [X ¹ , X ² = ethyl group], bis (4-
Isopropoxyphenyl) disulfide [X ¹ , X ² = isopropyl group], bis (4-cyclohexyloxyphenyl) disulfide [X ¹ , X ² = cyclohexyl group],
Bis (4-allyloxyphenyl) disulfide [X ¹ , X ² = allyl group], bis [4- (2-propynyloxy) phenyl] disulfide [X ¹ , X ² = 2-propynyl group], bis (4- Phenoxyphenyl) disulfide [X ¹ , X ² = phenyl group], bis (4-acetoxyphenyl) disulfide [X ¹ , X ² = acetyl group], bis (4-benzoyloxyphenyl) disulfide [X
^1, X ² = benzoyl group], bis (4-methanesulfonyloxy-phenyl) disulfide [X ^1, X ² = methanesulfonyl group], bis (4-benzenesulfonyloxy-phenyl) disulfide [X ^1, X ² = benzenesulfonyl Group], bis (4-methoxycarbonyloxyphenyl)
Disulfide [X ¹ , X ² = methoxycarbonyl group], bis (4-phenoxycarbonyloxyphenyl) disulfide [X ¹ , X ² = phenoxycarbonyl group] and the like. Specific examples of the disulfide derivative represented by the general formula (II) include, for example, bis (4-fluorophenyl) disulfide [X ³ , X ⁴ = F] and bis (4-chlorophenyl) disulfide [X ³ , X ⁴ = C
l], bis (4-bromophenyl) disulfide [X ³ , X ⁴ = Br], bis (4-iodophenyl) disulfide [X ³ , X ⁴ = I], bis (4-trifluoromethylphenyl) disulfide [ X ³ , X ⁴ = CF ₃ ], bis (4-trichloromethylphenyl) disulfide [X
_^3, X ⁴ = CCl ^3], and a bis (4-bromomethylphenyl) disulfide [X _^3, X ⁴ = CBr ^3].

If the content of the disulfide derivative containing oxygen in the substituent represented by the formula (I) contained in the non-aqueous electrolyte is too large, the battery performance may be deteriorated. Sufficient battery performance, which is expected to be excessively small, cannot be obtained. Therefore, the content thereof is preferably in the range of 0.01 to 5% by weight based on the weight of the non-aqueous electrolyte, because cycle characteristics are improved.

The non-aqueous solvent used in the present invention is preferably a solvent composed of a high dielectric constant solvent and a low viscosity solvent. Preferred examples of the high dielectric constant solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). These high dielectric constant solvents may be used alone or in combination of two or more.

Examples of the low-viscosity solvent include dimethyl carbonate (DMC) and methyl ethyl carbonate (M
EC), chain carbonates such as diethyl carbonate (DEC), tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane And lactones such as γ-butyrolactone, nitriles such as acetonitrile, esters such as methyl propionate, and amides such as dimethylformamide. These low-viscosity solvents may be used alone or in combination of two or more. The high dielectric constant solvent and the low viscosity solvent are arbitrarily selected and used in combination. The high dielectric constant solvent and the low viscosity solvent are used in a volume ratio (high dielectric constant solvent: low viscosity solvent) of usually 1: 9 to 4: 1, preferably 1: 4 to 7: 3. You.

As the electrolyte used in the present invention, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (S
O ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂
CF ₃ ) _{3 and the} like. These electrolytes may be used alone or in combination of two or more. These electrolytes are usually 0.1 to
It is used after being dissolved at a concentration of 3M, preferably 0.5 to 1.5M.

The nonaqueous electrolytic solution of the present invention is prepared by, for example, mixing the above-mentioned high dielectric constant solvent or low-viscosity solvent, dissolving the above-mentioned electrolyte therein, and adding oxygen to the substituent represented by the above formula (I). Is obtained by dissolving a disulfide derivative containing

For example, as the positive electrode active material, a composite metal oxide of lithium and at least one metal selected from the group consisting of cobalt, manganese, nickel, chromium, iron and vanadium is used. Examples of such a composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ ,
LiNiO _{2 and the} like.

The positive electrode is prepared by kneading the positive electrode active material with a conductive agent such as acetylene black and carbon black, a binder such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) and a solvent, and mixing the mixture with a solvent. After that, this positive electrode material is applied to an aluminum foil or a stainless steel lath plate as a current collector, dried and pressed, and then heat-treated under a vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It is produced by doing.

Examples of the negative electrode active material include lithium metals, lithium alloys, and carbon materials having a graphite type crystal structure capable of inserting and extracting lithium (pyrolytic carbons, cokes,
Materials such as graphites (artificial graphite, natural graphite, etc.), organic polymer compound burners, carbon fibers] and composite tin oxide are used. In particular, the spacing (d) of the lattice plane (002)
( ₀₀₂ ) is preferably a carbon material having a graphite-type crystal structure having a diameter of 0.335 to 0.340 nm (nanometers). A powder material such as a carbon material is used as a negative electrode mixture by kneading with a binder such as ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

The structure of the lithium secondary battery is not particularly limited. A coin-type battery having a positive electrode, a negative electrode and a single-layer or multi-layer separator, and a cylindrical battery having a positive electrode, a negative electrode and a roll-shaped separator And a prismatic battery. As the separator, a known microporous polyolefin membrane, woven fabric, nonwoven fabric, or the like is used.

[0022]

Next, the present invention will be specifically described with reference to examples and comparative examples. Example 1 [Preparation of non-aqueous electrolyte] EC: DMC (volume ratio) = 1: 2
Was prepared and a non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ to a concentration of 1 M, and then bis (4-methoxyphenyl) disulfide [X ¹ , X ² =
Methyl group] was added so as to be 0.1% by weight based on the non-aqueous electrolyte.

[Preparation of Lithium Secondary Battery and Measurement of Battery Characteristics] 80% by weight of LiCoO ₂ (positive electrode active material), 10% by weight of acetylene black (conductive agent), and 10% by weight of polyvinylidene fluoride (binder) % Of the mixture, a 1-methyl-2-pyrrolidone solvent was added to the mixture, and the mixture was applied onto an aluminum foil, dried, press-molded, and heat-treated to prepare a positive electrode. 90% by weight of natural graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) were added, and a 1-methyl-2-pyrrolidone solvent was added thereto. Applied, dried,
A negative electrode was prepared by pressure molding and heat treatment. Then, using a separator made of a polypropylene microporous film, the above non-aqueous electrolyte was injected, and a coin battery (20 mm in diameter,
(Thickness: 3.2 mm). This coin battery was charged at room temperature (20 ° C.) at a constant current and a constant voltage of 0.8 mA to a final voltage of 4.2 V for 5 hours, and then charged at a current of 0.8 m
Under the constant current of A, the battery was discharged to a final voltage of 2.7 V, and this charge / discharge was repeated. The initial charge / discharge capacity is EC-DMC (1
/ 2) as the non-aqueous electrolyte (Comparative Example 1), and the battery characteristics after 60 cycles were measured. The discharge capacity retention ratio when the initial discharge capacity was 100% was 93. 0.5%. Also, the low-temperature characteristics were good. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 2 As an additive, bis (4-methoxyphenyl) disulfide [X ¹ , X ² = methyl group] was added to a non-aqueous electrolyte at a concentration of 0.1%.
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the battery was used in an amount of 05% by weight, and a coin battery was manufactured. The battery characteristics after 60 cycles were measured. The discharge capacity retention was 92.1%. . Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 3 As an additive, bis (4-methoxyphenyl) disulfide [X ¹ , X ² = methyl group] was added to a non-aqueous electrolyte at a concentration of 0.1%.
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 2% by weight was used to prepare a coin battery, and the battery characteristics after 60 cycles were measured. The discharge capacity retention was 92.4%. . Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 4 The same as Example ¹ except that bis (4-acetoxyphenyl) disulfide [X ¹ , X ² = acetyl group] was used as an additive in an amount of 0.1% by weight based on the non-aqueous electrolyte. A non-aqueous electrolyte solution was prepared to prepare a coin battery, and the battery characteristics after 60 cycles were measured. The discharge capacity retention ratio was 91.2%.
Met. Table 1 shows the coin battery fabrication conditions and battery characteristics.
Shown in

Example 5 As an additive, bis (4-methanesulfonyloxyphenyl) disulfide [X ¹ , X ² = methanesulfonyl group]
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 0.1% by weight was used in the non-aqueous electrolyte, a coin battery was manufactured, and the battery characteristics after 60 cycles were measured. The retention was 92.9%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 6 Example 2 was repeated except that bis (4-methoxycarbonyloxyphenyl) disulfide [X ¹ , X ² = methoxycarbonyl group] was used as an additive in an amount of 0.1% by weight based on the non-aqueous electrolyte. A coin battery was prepared by preparing a non-aqueous electrolyte solution in the same manner as in Example 1, and the battery characteristics after 60 cycles were measured. As a result, the discharge capacity retention ratio was 92.7%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 7 As in Example 1, except that bis (4-fluorophenyl) disulfide [X ³ , X ⁴ = F] was used as an additive in an amount of 0.1% by weight based on the non-aqueous electrolyte. A coin battery was prepared by preparing a non-aqueous electrolyte, and the battery characteristics after 60 cycles were measured. As a result, the discharge capacity retention ratio was 92.8%.
Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 8 The same procedure as in Example 1 was repeated except that bis (4-chlorophenyl) disulfide [X ³ , X ⁴ = Cl] was used as an additive in an amount of 0.1% by weight based on the nonaqueous electrolyte. A coin battery was prepared by preparing an aqueous electrolyte, and the battery characteristics after 60 cycles were measured. As a result, the discharge capacity retention ratio was 91.6%.
Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 9 Example 1 was repeated except that bis (4-trifluoromethylphenyl) disulfide [X ³ , X ⁴ = CF ₃ ] was used as an additive in an amount of 0.1% by weight based on the non-aqueous electrolyte. A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as described above, and the battery characteristics after 60 cycles were measured.
2.5%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 10 A non-aqueous solvent of EC: PC: DMC (volume ratio) = 1: 1: 2 was prepared, and LiPF ₆ was dissolved therein to a concentration of 1 M to prepare a non-aqueous electrolyte. Then, bis (4-methoxyphenyl) disulfide [X ¹ , X ² = methyl group]
Was added so as to be 0.1% by weight with respect to the non-aqueous electrolyte. Using this non-aqueous electrolyte, a coin battery was prepared in the same manner as in Example 1, and the battery characteristics were measured. The initial discharge capacity was only EC-DMC (capacity ratio 1/2) as the non-aqueous electrolyte. When the battery characteristics after 60 cycles were measured, the discharge capacity retention ratio when the initial discharge capacity was 100% was 93.0%. Also, the low-temperature characteristics were good. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 11 A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1 except that artificial graphite was used instead of natural graphite as the negative electrode active material, and the battery characteristics after 60 cycles were evaluated. As a result of the measurement, the discharge capacity retention ratio was 90.3%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 12 As a positive electrode active material, LiMn ₂ O ₄ was used instead of LiCoO _2.
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 to prepare a coin battery, and the battery characteristics after 60 cycles were measured. As a result, the discharge capacity retention ratio was 94.5%.
Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Example 1 A non-aqueous solvent of EC: DMC (volume ratio) = 1: 2 was prepared.
LiPF ₆ was dissolved therein to a concentration of 1M.
At this time, no disulfide was added. Using this non-aqueous electrolyte, a coin battery was produced in the same manner as in Example 1, and the battery characteristics were measured. The discharge capacity retention rate after 60 cycles was 83.8% of the initial discharge capacity. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Example 2 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that diphenyl disulfide [X ³ , X ⁴ = none] was used as an additive in an amount of 0.1% by weight based on the non-aqueous electrolyte. Then, a coin battery was manufactured, and the battery characteristics after 60 cycles were measured. As a result, the discharge capacity retention ratio was 88.7%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery. As described above, when the electrolytic solution containing the additive of the present invention was used, the cycle characteristics were dramatically improved as compared with the system without the additive. This is considered to be due to the fact that the additive is oxidatively decomposed on the positive electrode during charging to form a film that improves the reversibility of the battery. Also,
With the additive of the present invention, better cycle characteristics were obtained as compared with the diphenyl disulfide addition system having no substituent on the benzene ring. The reason for this is that substitution of atoms having a large number of lone pairs such as oxygen or halogen in the benzene ring causes electrons to flow from those atoms to the positive electrode during charging, resulting in a smoother oxidation reaction. I think that the. In addition to the cycle characteristics, the additive of the present invention had better solubility in the electrolytic solution than diphenyl disulfide. This is probably because the presence of a substituent on the benzene ring increases the polarity. Furthermore, the additive of the present invention has clearly less offensive odor peculiar to the disulfide compound than diphenyl disulfide. This also seems to be due to the effect of the substituent on the benzene ring. As described above, the additive of the present invention has not only cycle characteristics but also solubility in an electrolytic solution and low handling of odors, as compared with diphenyl disulfide having no substituent in the benzene ring. Since it has superiority, it can be said that it is more excellent as an additive for the electrolytic solution.

It should be noted that the present invention is not limited to the embodiments described above, and various combinations that can be easily inferred from the gist of the invention are possible. In particular, the combinations of the solvents in the above examples are not limited. Further, while the above embodiments relate to coin batteries, the present invention is also applicable to cylindrical and prismatic batteries.

[0038]

[Table 1]

[0039]

According to the present invention, the cycle characteristics of the battery,
A lithium secondary battery having excellent battery characteristics such as electric capacity and storage characteristics can be provided.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Matsumori 10-figure, 1978 Kogushi, Obe-shi, Ube-shi, Yamaguchi F-term in the Ube Chemical Plant Ube Chemical Plant (reference) 5H029 AJ00 AJ05 AK03 AL07 AL08 AL12 AM03 AM04 AM05 AM07 DJ08 EJ11 HJ02

Claims (4)

[Claims] 1. A non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following formula (I): (However, X ¹ and X ² are each independently an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms,
6, an alkynyl group, a cycloalkyl group having 3 to 6 carbon atoms,
An aryl group, an acyl group having 2 to 7 carbon atoms, an alkanesulfonyl group having 1 to 7 carbon atoms, an arylsulfonyl group having 6 to 10 carbon atoms, and an ester group having 2 to 7 carbon atoms are shown. The disulfide derivative containing oxygen in the substituent represented by the formula (1) is 0.1.
A non-aqueous electrolyte solution containing 0.1 to 5% by weight. 2. A non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following formula (II): (However, X ³ and X ⁴ are each independently F, Cl, B
r, I, CF ₃ , CCl ₃ , and CBr ₃ are shown. A non-aqueous electrolyte characterized by containing 0.01 to 5% by weight of a disulfide derivative containing a halogen in the substituent represented by the formula (1). 3. A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following formula (I): (However, X ¹ and X ² are each independently an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms,
6, an alkynyl group, a cycloalkyl group having 3 to 6 carbon atoms,
An aryl group, an acyl group having 2 to 7 carbon atoms, an alkanesulfonyl group having 1 to 7 carbon atoms, an arylsulfonyl group having 6 to 10 carbon atoms, and an ester group having 2 to 7 carbon atoms are shown. The disulfide derivative containing oxygen in the substituent represented by the formula (1) is 0.1.
A lithium secondary battery characterized by being contained in an amount of from 0.01 to 5% by weight. 4. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following formula (II): (However, X ³ and X ⁴ are each independently F, Cl, B
r, I, CF ₃ , CCl ₃ , and CBr ₃ are shown. A lithium secondary battery comprising a disulfide derivative containing halogen in the substituent represented by the formula (1) in an amount of 0.01 to 5% by weight.