JPH08138741A - Organic electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide an organic electrolyte secondary battery excellent in a charge/discharge cycle characteristic by using an organic electrolyte composed of a solvent and solute containing a specific chainlike dicarbonic ester. CONSTITUTION: In an organic electrolyte secondary battery provided with an organic electrolyte composed of negative and positive electrodes, a solvent, and solute; the solvent is to contain a chainlike dicarbonic ester expressed by a formula (R and R': alkyl group of methyl, ethyl, propyl, and butyl. R": alkyl group of methylene, ethlene, propylene, and buthylene). This solvent is composed of an annular compound and the chainlike dicarbonic ester, and moreover, a solvent containing a low viscosity solvent is preferable as necessary. As the annular compound, ethylene carbonate, γ-butyrolactone, and sulfolane etc., are preferable, and as the low viscosity solvent, e.g. 1- and 2- dimethoxyethane, and dimethylcarbonate etc., are suitable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery having a high energy density and a high reliability as a power source for driving electronic devices or a power source for holding a memory, and particularly to an organic electrolyte composed of a solute and a solvent. The present invention relates to improvement of a solvent of an electrolytic solution.

[0002]

2. Description of the Related Art In recent years, an organic electrolyte battery using lithium as a negative electrode active material has been attracting attention because of its high energy density and excellent storage performance.

Conventionally, as an electrolyte solvent for such an organic electrolyte battery, cyclic compounds such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane and 3-methylsulfolane are used.
A mixed solvent composed of a low-viscosity solvent such as 1,2-dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propionate or ethyl propionate is generally used.

This kind of solvent reacts a cyclic compound with lithium to form a film having excellent ionic conductivity on the surface of the negative electrode, and when it is used as a mixed solvent with a low-viscosity solvent, the viscosity of the electrolytic solution is increased. To lower the low temperature discharge characteristics.

[0005]

However, since these low-viscosity solvents have a low oxidative decomposition potential, they are easily oxidatively decomposed on the surface of the positive electrode, and an organic electrolyte battery having satisfactory charge-discharge cycle characteristics is still obtained. The reality is not.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an organic electrolyte battery having excellent charge-discharge cycle characteristics.

[0007]

To achieve the above object, an organic electrolyte secondary battery according to the present invention is a battery comprising a negative electrode, a positive electrode, and an organic electrolytic solution containing a solvent and a solute. Where the solvent is

[0008]

It is a mixed system of a chain dicarbonate ester solvent represented by the following formula and a cyclic compound, or a mixed system of a chain dicarbonate ester solvent represented by the above formula, a cyclic compound and a low viscosity solvent. Characterize.

Examples of the cyclic compound in the present invention include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, sulfolane and 3-methylsulfolane.
These cyclic compounds may be used alone or in combination of two or more as required.

Examples of the low-viscosity solvent used in the present invention include 1,2-dimethoxyethane, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methyl propionate, and ethyl propionate. These low viscosity solvents may be used alone or in combination of two or more as needed.

The negative electrode, the positive electrode, the separator and the solute in the present invention are not particularly limited, and various materials conventionally used in organic electrolyte batteries can be used.

As an example of the organic electrolyte secondary battery in the present invention, as a negative electrode material for producing a battery, lithium metal, lithium alloy, graphite capable of inserting and extracting lithium, and low crystalline carbon material are exemplified. Examples of the positive electrode material include titanium disulfide, manganese dioxide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide, and molybdenum trioxide. Examples of the separator include polypropylene, polyethylene, polytetrafluoroethylene, and polyvinylidene fluoride microporous films, and solutes include lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and trifluoride. Examples thereof include lithium methanesulfonate.

[0013]

In the organic electrolyte secondary battery according to the present invention,
A mixed solvent of a cyclic compound and a chain dicarbonate, or a mixed solvent of a cyclic compound, a chain dicarbonate and a low-viscosity solvent is used as a solvent of the electrolytic solution, among which the cyclic compound is a negative electrode active material. It reacts with the substance to form an ion conductive film on the surface of the negative electrode, thereby preventing the reaction between the negative electrode and the electrolytic solution. Further, the chain dicarbonic acid ester solvent strongly solvates lithium ions, thereby improving the oxidation resistance of the electrolytic solution. The low-viscosity solvent improves the ionic conductivity of the electrolytic solution by reducing the viscosity of the electrolytic solution.

Here, since chain dicarbonic acid ester has a higher oxidative decomposition potential than chain carbonic acid esters such as dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, etc., it is less likely to be oxidatively decomposed on the surface of the positive electrode, and battery charging / discharging is performed. It does not adversely affect the cycle characteristics.

[0015]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

(Example 1) For a positive electrode, lithium cobalt composite oxide (LiCoO ₂ ), carbon powder as a conductive agent, and fluororesin powder as a binder were sufficiently mixed in a weight ratio of 90: 3: 7. After that, pressure molding was performed.

The negative electrode was prepared by sufficiently mixing carbon powder and fluororesin powder as a binder in a weight ratio of 91: 9, and then pressure molding.

The organic electrolytic solution was prepared by dissolving lithium hexafluorophosphate as a solute at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate and 1,2-di (methoxycarbonyloxy) propane in an equal volume ratio. Prepared.

Using the above positive electrode, negative electrode and electrolytic solution,
A coin-type organic electrolyte secondary battery according to the present invention was produced.
FIG. 1 is a vertical sectional view of this battery. In this figure,
Reference numeral 1 denotes a case that also functions as a positive electrode terminal, which is formed by punching out an electrolytic solution resistant stainless steel plate. Reference numeral 2 denotes a sealing plate that also functions as a negative electrode terminal, which is formed by punching out an electrolytic solution resistant stainless steel plate, and the negative electrode 3 is in contact with the inner wall of the sealing plate. Reference numeral 5 is a separator made of polypropylene impregnated with an organic electrolytic solution, and 6 is a positive electrode. The battery is hermetically sealed by crimping the opening end of the case 1 which also functions as a positive electrode terminal inward and tightening the outer periphery of the sealing plate 2 which also functions as a negative electrode terminal via the gasket 4.

The size of the prepared battery is 20.0 mm in diameter,
The height is 2.0 mm and the battery capacity is 30 mAh.
The battery according to the present invention was designated as A1.

Further, the present invention is carried out in the same manner as in Example 1 except that a mixed solvent of propylene carbonate and 1,2-di (methoxycarbonyloxy) ethane in an equal volume ratio is used as the organic electrolyte solvent. The battery A2 was produced.

For the purpose of comparison, an organic electrolyte solution was prepared by using the same solvent mixture of ethylene carbonate and diethyl carbonate and a solvent mixture of propylene carbonate and diethyl carbonate in equal volume ratios, respectively. Comparative batteries B1 and B2 were produced in the same manner as in Example 1.

Next, these batteries were charged in a constant temperature bath at a temperature of 60 ° C. with a constant current of 2.0 mA until the terminal voltage reached 4.2 V, and then a constant current of 2.0 mA was also applied. so,
A charge / discharge cycle life test was performed for 300 cycles, in which the terminal voltage was discharged to reach 3V. FIG. 2 shows a change in discharge capacity with the progress of charge / discharge cycles of each battery.

As is clear from the results shown in FIG. 2, the batteries A1 and A2 according to the present invention show a smaller decrease in discharge capacity with the progress of charge / discharge cycles than the comparative batteries B1 and B2.

Example 2 As a solvent for the organic electrolyte, a mixed solvent of ethylene carbonate, 1,2-di (methoxycarbonyloxy) ethane and 1,2-dimethoxyethane in an equal volume ratio, and propylene carbonate and 1 were used, respectively. Batteries A3 and A4 according to the present invention were respectively prepared in the same manner as in Example 1 except that a mixed solvent of 1,2-di (methoxycarbonyloxy) propane and 1,2-dimethoxyethane in an equal volume ratio was used. It was made.

For comparison, as an organic electrolyte solvent, a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane in an equal volume ratio and a mixture of propylene carbonate and 1,2-dimethoxyethane in an equal volume ratio, respectively. Comparative batteries B3 and B4 were prepared in the same manner as in Example 1 except that the solvent was used.

Next, these batteries were charged in a constant temperature bath at a temperature of 60 ° C. with a constant current of 2.0 mA until the terminal voltage reached 4.2 V, followed by a constant current of 2.0 mA. so,
A charge / discharge cycle life test was performed for 300 cycles, in which the terminal voltage was discharged to reach 3V. FIG. 3 shows the change in discharge capacity with the progress of charge / discharge cycles of each battery.

As is clear from the results shown in FIG. 3, the batteries A1 to A4 according to the present invention show a smaller decrease in discharge capacity with the progress of charge / discharge cycles than the comparative batteries B1 and B2.

In the above examples, the volume mixing ratio of the cyclic compound and the chain carbonic acid ester was set to 1: 1 as the solvent of the organic electrolyte, and the volume of the cyclic compound, the chain carbonic acid ester and the low viscosity solvent was adjusted. The case where the mixing ratio is 1: 1: 1 has been described, but the mixing ratio is not particularly limited. When the volume content of the chain carbonic acid ester exceeds 50%, the ionic conductivity is remarkably reduced, but from the viewpoint of charge / discharge cycle characteristics, the range of 1 to 80% is preferable.

In the above examples, the case where 1,2-di (methoxycarbonyloxy) ethane and 1,2-di (methoxycarbonyloxy) propane are used as the chain dicarbonic acid ester has been described. 1] where R and R ′ are alkyl groups selected from methyl, ethyl, propyl, and butyl, and R ″ is an alkyl group selected from methylene, ethylene, propylene, and butylene, a chain dicarbonate ester, Similar effects can be obtained, for example, 1-ethoxycarbonyloxy-2-methoxycarbonyloxyethane, 1,2-di (ethoxycarbonyloxy) ethane, 1-ethoxycarbonyloxy-2.
-Methoxycarbonyloxypropane and 1,2-di (ethoxycarbonyloxy) propane.

Furthermore, in the above-mentioned embodiment, the case where ethylene carbonate and propylene carbonate are used as the cyclic compound and 1,2-dimethoxyethane is used as the low-viscosity solvent has been explained, but the invention is not basically limited. If it has been conventionally used for lithium batteries,
The same effect as the present invention can be obtained.

Examples of the cyclic compound include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, sulfolane and 3-methylsulfolane. These cyclic compounds may be used alone or in combination of two or more as required.

Further, examples of the low-viscosity solvent in the present invention include 1,2-dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propionate and ethyl propionate. These low viscosity compounds may also be used alone,
You may use together 2 or more types as needed.

In the above embodiment, a specific example in which the present invention is applied to a coin type battery has been described, but the shape of the battery is not particularly limited, and the present invention can be used in various shapes such as a cylindrical shape, a square shape or a paper shape. It can be applied to the organic electrolyte secondary battery having the above shape.

[0035]

INDUSTRIAL APPLICABILITY In the organic electrolyte secondary battery according to the present invention, an electrolytic solution solvent comprising a cyclic compound and a chain dicarbonate or an electrolyte comprising a cyclic compound, a chain dicarbonate and a low viscosity solvent. Since a liquid solvent is used,
Excellent charge / discharge cycle performance compared to conventional similar batteries.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal structure of a coin-shaped battery which is an example of an organic electrolyte secondary battery.

FIG. 2 is a diagram showing a change in discharge capacity as a charge / discharge cycle of a test battery progresses.

FIG. 3 is a diagram showing a change in discharge capacity as a charge / discharge cycle of a test battery progresses.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Negative Electrode 4 Gasket 5 Separator 6 Positive Electrode

Claims (5)

[Claims] 1. A negative electrode, a positive electrode, and an organic electrolytic solution containing a solvent and a solute, wherein the solvent is: An organic electrolyte secondary battery containing a chain dicarbonic acid ester represented by: However, in the above chemical formula, R and R ′ are alkyl groups selected from methyl, ethyl, propyl, and butyl, and R ″ is an alkyl group selected from methylene, ethylene, propylene, and butylene. 2. The organic electrolyte secondary battery according to claim 1, wherein the solvent comprises a cyclic compound and the chain dicarbonic acid ester. 3. The organic electrolyte secondary battery according to claim 1, wherein the solvent comprises a cyclic compound, the chain dicarbonic acid ester, and a low viscosity solvent. 4. The cyclic compound is ethylene carbonate,
The organic electrolyte secondary battery according to claim 2, which is at least one selected from propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane. 5. The organic electrolyte solution according to claim 3, wherein the low-viscosity solvent is at least one selected from 1,2-dimethoxyethane, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methyl propionate, and ethyl propionate. Secondary battery.