JP2000208166A - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Abstract

(57) [Problem] To provide a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics, electric capacity and charge storage characteristics. SOLUTION: In a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, the following general formula (I) is contained in the non-aqueous electrolytic solution. (Wherein R is an alkyl group having 1 to 6 carbon atoms, 2 to 6 carbon atoms)
Alkynyl group having 2 to 6 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, and aryl group. The present invention relates to a non-aqueous electrolyte solution containing a glycerin carbonate derivative represented by the formula (1), and a lithium secondary battery using the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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. A lithium secondary battery is 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 is used. It is preferably used. And
Examples of the electrolyte for the lithium secondary battery include ethylene carbonate (EC) and propylene carbonate (PC).
Such carbonates 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 nonaqueous solvent used in the electrolyte of the lithium secondary battery, high dielectric constant solvents such as EC and PC are preferably used. However, these high dielectric solvents alone have high viscosity and sufficient ionic conductivity. In general, a low-viscosity solvent such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), or diethyl carbonate (DEC) is mixed at an appropriate mixing ratio so that the highest possible conductivity can be obtained. An electrolyte is being prepared. However, in a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as the negative electrode, the electrolyte solution decomposes at the negative electrode to increase the irreversible capacity, and in some cases, the carbon material peels off. It can happen. The increase in the irreversible capacity and the peeling of the carbon material are caused by the decomposition of the solvent in the electrolytic solution at the time of charging, and are caused by the electrochemical reduction of the solvent at the interface between the carbon material and the electrolytic solution. . Among them, PC having a low melting point (−55 ° C.) and a high dielectric constant
Although they have high electrical conductivity even at low temperatures, when a graphite negative electrode is used, there is a problem that PC is decomposed and cannot be used for a lithium secondary battery. on the other hand,
EC is partially decomposed during repeated charge / discharge, resulting in a decrease in battery performance. In addition, since the melting point is 38 ° C., there is a problem that when used at a low temperature, the electrolytic solution solidifies and no electric capacity can be obtained. Therefore, when these PC-based or EC-based electrolytes are used, the battery characteristics such as cycle characteristics and electric capacity of the battery are not always satisfactory at present.

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

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a glycerol carbonate derivative represented by the general formula (I) has been substituted for EC or PC. It has been found that the above problem can be achieved by using. That is, the glycerin carbonate derivative has a high dielectric constant, a low melting point, and does not decompose even on the graphite negative electrode, so that it exhibits excellent characteristics as compared with the conventional high dielectric constant solvent. 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 general formula (I)

Embedded image (Wherein R is an alkyl group having 1 to 6 carbon atoms, 2 to 6 carbon atoms)
Alkynyl group having 2 to 6 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, and aryl group. The present invention relates to a non-aqueous electrolyte characterized by containing a glycerin carbonate derivative represented by the formula (1).

Further, the present invention provides 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 general formula (I)

Embedded image (Wherein R is an alkyl group having 1 to 6 carbon atoms, 2 to 6 carbon atoms)
Alkynyl group having 2 to 6 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, and aryl group. The present invention relates to a lithium secondary battery containing the glycerin carbonate derivative represented by the formula (1).

The glycerol carbonate derivative represented by the general formula (I) contained in the electrolytic solution is partially reduced on the surface of the carbon material as the negative electrode during charging, and plays a role of forming a passive film. Have. In this way, by covering the active and highly crystallized carbon material such as natural graphite or artificial graphite with the passivation film, decomposition of the electrolytic solution is suppressed, and normal charge and discharge can be performed without impairing the reversibility of the battery. It is thought to be repeated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In a glycerol carbonate derivative represented by the above general formula (I) contained in an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, R represents a methyl group, an ethyl group, a propyl group, or a butyl group. An alkyl group having 1 to 6 carbon atoms such as a 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. Further, it may be an alkenyl group having 2 to 6 carbon atoms such as vinyl group, 1-propenyl group and allyl group, or an alkynyl group having 2 to 6 carbon atoms such as ethynyl group and propargyl group. Further, an aryl group such as a phenyl group and a p-tolyl group may be used.

Specific examples of the glycerin carbonate derivative represented by the general formula (I) include, for example, 4-acetoxymethyl-1,3-dioxolan-2-one [R =
Methyl group], 4-propionyloxymethyl-1,3-
Dioxolan-2-one [R = ethyl group], 4-butyryloxymethyl-1,3-dioxolan-2-one [R
= N-propyl group], 4-isobutyryloxymethyl-
1,3-dioxolan-2-one [R = i-propyl group], 4-pivaloyloxymethyl-1,3-dioxolan-2-one [R = t-butyl group], 4-cyclohexanecarbonyloxymethyl -1,3-dioxolane-
2-one [R = cyclohexyl group], 4-acryloyloxymethyl-1,3-dioxolan-2-one [R =
Vinyl group], 4-methacryloyloxymethyl-1,3
-Dioxolan-2-one [R = methallyl group], 4-crotonoyloxymethyl-1,3-dioxolan-2-
ON [R = trans-1-propenyl group], 4-propioyloxymethyl-1,3-dioxolan-2-
ON [R = ethynyl group], benzoyloxymethyl-
1,3-dioxolan-2-one [R = phenyl group],
4-p-toluoyloxymethyl-1,3-dioxolan-2-one [R = p-tolyl group] and the like.

If the content of the glycerol carbonate derivative represented by the general formula (I) is excessively high, the viscosity of the electrolyte is too high to obtain sufficient battery characteristics. Since a sufficient film is not formed and the decomposition of the electrolytic solution on the surface of the negative electrode cannot be suppressed, the range of 5 to 60% by volume, particularly 10 to 50% by volume based on the volume of the nonaqueous solvent is preferable.

The non-aqueous solvent used together with the glycerin carbonate derivative in the present invention includes a low-viscosity solvent.
For example, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (D
Chain carbonates such as EC), tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-
Ethers such as dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, lactones such as γ-butyrolactone, nitriles such as acetonitrile, and 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. Further, EC or PC which is a high dielectric constant solvent may be mixed in a non-aqueous solvent.

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 added to the non-aqueous solvent at a concentration of 0.1
It is used after being dissolved at a concentration of ３3M, preferably 0.5-1.5M.

The electrolytic solution of the present invention can be obtained, for example, by mixing the glycerin carbonate derivative represented by the general formula (I) and the low-viscosity solvent, and dissolving the electrolyte in the mixture.

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

For example, 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 as the positive electrode material (positive electrode active material). Examples of such a composite metal oxide include LiCoO ₂ , L
iMn ₂ O ₄ , LiNiO _{2 and the} like can be mentioned.

The positive electrode is prepared by kneading the positive electrode material with a conductive agent such as acetylene black and carbon black and a binder such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) to form a positive electrode mixture. After applying this positive electrode material to a foil or lath plate made of aluminum or stainless steel as a current collector, drying and pressing,
It is produced by performing a heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.

Examples of the negative electrode active material include lithium metals, lithium alloys, and carbon materials capable of occluding and releasing lithium (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), and organic polymer compound combustion. Materials such as body, carbon fiber, and composite tin oxide. In particular, the spacing (d ₀₀₂ ) of the lattice plane ( ₀₀₂ ) is 0.335.
It is preferable to use a carbon material having a graphite-type crystal structure of about 0.340 nm (nanometer). In addition,
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.

[0019]

Next, the present invention will be specifically described with reference to examples and comparative examples. Example 1 [Preparation of electrolytic solution] A non-aqueous solvent of 4-acetoxymethyl-1,3-dioxolan-2-one [R = methyl group]: DMC (volume ratio) = 33: 67 was prepared, and LiPF was added thereto.
₆ was dissolved to a concentration of 1 M to prepare an electrolytic solution.

[Preparation of Lithium Secondary Battery and Measurement of Battery Characteristics] LiCoO ₂ (cathode active material) was 80% by weight, acetylene black (conductive agent) was 10% by weight, and polyvinylidene fluoride (binder) was 10% by weight. %, And 1-methyl-2-pyrrolidone was added to the mixture to form a slurry, which was applied on an aluminum foil. Thereafter, it was dried and molded under pressure to prepare a positive electrode. 90% by weight of natural graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) are mixed, and 1-methyl-2-pyrrolidone is added thereto to form a slurry to form a slurry on a copper foil. Applied. Thereafter, this was dried and molded under pressure to prepare a negative electrode. Then, using a separator made of polypropylene microporous film, impregnated with the above-mentioned electrolytic solution, a coin battery (diameter of 20 m) was obtained.
m, 3.2 mm in thickness). Using this coin battery, the battery was charged to a final voltage of 4.2 V for 5 hours at a constant current and a constant voltage of 0.8 mA at room temperature (20 ° C.).
Under the constant current of A, the battery was discharged to a final voltage of 2.7 V, and the charging and discharging were repeated. The capacity reduction due to repeated cycles is smaller than that in the case where 1 M LiPF ₆ + EC / DMC (1/2) is used as the electrolyte (Comparative Example 2), and the discharge capacity retention ratio in 10 to 100 cycles is as follows:
79.5%. Also, the low-temperature characteristics were good.
Table 1 shows the manufacturing conditions and battery characteristics of the coin battery. In Table 1, DGC in the column of electrolyte composition represents a glycerin carbonate derivative.

Example 2 As a glycerin carbonate derivative, 4-propionyloxymethyl-1,3-dioxolan-2-one [R
= Ethyl group], except that an electrolytic solution was prepared in the same manner as in Example 1 to produce a coin battery.
When the discharge capacity retention ratio at 0 cycle was measured,
The discharge capacity retention was 80.2%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 3 As a glycerin carbonate derivative, 4-isobutyryloxymethyl-1,3-dioxolan-2-one [R
= I-propyl group], except that an electrolytic solution was prepared in the same manner as in Example 1 to produce a coin battery. The discharge capacity retention ratio was measured from 10 cycles to 100 cycles. 0.9%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 4 As a glycerin carbonate derivative, 4-cyclohexanecarbonyloxymethyl-1,3-dioxolane-
Except for using 2-one [R = cyclohexyl group], an electrolytic solution was prepared in the same manner as in Example 1 to prepare a coin battery.
When the discharge capacity retention ratio was measured from 10 cycles to 100 cycles, the discharge capacity retention ratio was 78.7%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 5 As a glycerin carbonate derivative, 4-acryloyloxymethyl-1,3-dioxolan-2-one [R
= Vinyl group], except that an electrolytic solution was prepared in the same manner as in Example 1 to produce a coin battery.
When the discharge capacity retention ratio at 0 cycle was measured,
The discharge capacity retention was 77.9%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 6 An electrolyte was prepared in the same manner as in Example 1 except that 4-propioyloxymethyl-1,3-dioxolan-2-one [R = ethynyl group] was used as a glycerin carbonate derivative. The coin battery was manufactured in this manner, and the discharge capacity retention ratio in 10 to 100 cycles was measured. As a result, the discharge capacity retention ratio was 81.3%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 7 As a glycerin carbonate derivative, 4-benzoyloxymethyl-1,3-dioxolan-2-one [R =
A phenyl group] was used, an electrolyte solution was prepared in the same manner as in Example 1 to prepare a coin battery, and 10 to 10 cycles were used.
When the discharge capacity retention ratio at 0 cycle was measured,
The discharge capacity retention ratio was 78.8%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 8 A coin battery was prepared by preparing an electrolytic solution in the same manner as in Example 1 except that 4-acetoxymethyl-1,3-dioxolan-2-one: DMC (volume ratio) = 10: 90. Made, 1
When the discharge capacity retention rate was measured from 0 cycle to 100 cycles, the discharge capacity retention rate was 77.4%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 9 A coin battery was prepared by preparing an electrolyte in the same manner as in Example 1 except that 4-acetoxymethyl-1,3-dioxolan-2-one: DMC (volume ratio) was set to 50:50. Made, 1
When the discharge capacity retention rate was measured from 0 cycle to 100 cycles, the discharge capacity retention rate was 78.0%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 10 An electrolytic solution was prepared in the same manner as in Example 1 except that 4-acetoxymethyl-1,3-dioxolan-2-one: DEC (volume ratio) = 33: 67 was used as the non-aqueous solvent. The coin battery was prepared, and the discharge capacity retention rate was measured from 10 cycles to 100 cycles. As a result, the discharge capacity retention rate was 80.7%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 11 An electrolytic solution was prepared in the same manner as in Example 1 except that 4-acetoxymethyl-1,3-dioxolan-2-one: THF (volume ratio) = 33: 67 was used as a non-aqueous solvent. The coin battery was prepared, and the discharge capacity retention rate was measured in 10 to 100 cycles. As a result, the discharge capacity retention rate was 75.6%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 12 As negative electrode active material, artificial graphite (manufactured by Osaka Gas Co., Ltd., MCM
Except for using B6-28), an electrolytic solution was prepared in the same manner as in Example 1 to fabricate a coin battery.
When the discharge capacity retention ratio in the 00 cycle was measured, the discharge capacity retention ratio was 77.1%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Example 13 A coin battery was prepared by preparing an electrolytic solution in the same manner as in Example 1 except that spinel-type LiMn ₂ O ₄ was used as a positive electrode active material, and a discharge capacity retention ratio in 10 to 100 cycles was prepared. Was measured, the discharge capacity retention ratio was 78.
1%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Example 1 A non-aqueous solvent of PC: DMC (volume ratio) = 33: 67 was prepared, and LiPF ₆ was dissolved therein to a concentration of 1M. Using this electrolyte, a coin battery was prepared in the same manner as in Example 1, and the battery characteristics were measured.
C was decomposed and no discharge was possible. As a result of disassembling and observing the battery after the first charge, peeling was observed in the graphite negative electrode. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

Comparative Example 2 A non-aqueous solvent of EC: DMC (volume ratio) = 50: 50 was prepared, and LiPF ₆ was dissolved therein to a concentration of 1M. Using this electrolytic solution, a coin battery was produced in the same manner as in Example 1, and the discharge capacity retention ratio was measured from 10 cycles to 100 cycles.
0.0%. Table 1 shows the manufacturing conditions and battery characteristics of the coin battery.

[0035]

[Table 1]

It should be noted that the present invention is not limited to the described embodiments, and various combinations that can be easily analogized 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.

[0037]

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

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Matsumori 5F, 1978 Kogushi, Ube City, Ube City, Yamaguchi Prefecture F-term in the Ube Research Laboratory, Ube Industries, Ltd. 5H029 AJ03 AJ04 AJ05 AK03 AL03 AL06 AL07 AL12 AM02 AM03 AM04 AM05 AM07 CJ08 HJ02

Claims (2)

[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 general formula (I): (Wherein R is an alkyl group having 1 to 6 carbon atoms, 2 to 6 carbon atoms)
Alkynyl group having 2 to 6 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, and aryl group. A non-aqueous electrolyte solution comprising a glycerin carbonate derivative represented by the following formula: 2. A non-aqueous electrolyte in which an electrolyte is dissolved in a positive electrode, a negative electrode, and a non-aqueous solvent, wherein the non-aqueous electrolyte contains the following general formula (I): (Wherein R is an alkyl group having 1 to 6 carbon atoms, 2 to 6 carbon atoms)
Alkynyl group having 2 to 6 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, and aryl group. A lithium secondary battery comprising the glycerin carbonate derivative represented by the formula (1).