JPS59149654A - Secondary battery - Google Patents

Abstract

PURPOSE:To reduce self discharge and improve performance by using the carbon fiber cleaned by a solution in which alkaline metallic salt is dissolved as at least the electrode on one side. CONSTITUTION:The carbon fiber cleaned by a solution in which alkaline metallic salt is dissolved is used as at least the electrode on one side. For example, the molded piece of the active carbon fiber whose specific surface area is 500 to 4,000m<2>/g is used as the carbon fiber. Acetonitrile, 1.2-dimethoxyethane propylene carbonate, etc. are used in addition to aceton, methanol, and ethanol as the solvent of the solution used for cleaning. Besides, organic acid ions such as acetate ion and formate ion are used in addition to halide ion, boron fluoride ion, and perchlorate ion as the pair ion of alkaline metallic salt.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an organic solvent-based secondary battery using carbon fiber in at least one of the electrodes.

In recent years, as energy issues have become more important, there has been a demand for lightweight, high-energy-density bichard batteries. A secondary battery that is immersed in an electrolyte solution has been proposed. Various materials can be used as electrodes with a large surface area, but carbon fiber is easy to obtain, chemically stable,
It has many advantages such as being able to take various shapes and having high electrical conductivity, among which the specific surface area is 500 to 400.
0yz2/g activated carbon fiber has many advantages such as having a large specific surface area and being able to be shaped into a sheet without requiring a binder unlike powdered activated carbon.

However, secondary batteries using carbon fibers, not just activated carbon fibers, have the disadvantage that self-discharge after charging is large and the voltage decreases over time.

As a result of various studies conducted by the present inventors in order to improve these drawbacks, the present inventors discovered that the performance could be greatly improved by cleaning the carbon fibers that constitute the electrodes with an organic solvent, and have already proposed (Japanese Patent Application No. No. 128,233), however, the present invention was completed by discovering that self-discharge can be further reduced by cleaning with a solution of an alkali metal salt dissolved in an organic solvent instead of a mere organic solvent.

That is, the present invention provides an organic solvent-based secondary battery characterized in that carbon fibers washed with a solution containing an alkali metal salt are used as at least one electrode.

The carbon fibers used in the present invention are required to have a large specific surface area, low electrical resistance, and chemical stability against electrolyte solutions, and the raw materials used may be phenolic, cellulose thread, pitch, acrylic, or others. be able to. Among them, carbon fiber is activated to increase the specific surface area to 500 to 400.
Activated carbon fiber molded products with a large surface area of 0yi"/g are preferable because they have a large surface area and relatively high conductivity. Activated carbon fiber molded products can be made in various shapes such as paper, cloth, and felt. Although there are some types, cloth-like ones are advantageous because they do not contain additives such as binders, are relatively strong despite being thin, and are easy to handle.

The method of cleaning the carbon fiber electrode (hereinafter referred to as single K "electrode") in the present invention includes a method of immersing the electrode in an electrolyte solution;
Methods include spraying a solution onto the electrode, but among these methods, the method of immersing the electrode in the solution is simple and has a large cleaning effect.〇The solvent for the solution used for cleaning must be one that can dissolve the alkali metal salt. In addition, anything can be used as long as it does not adversely affect the battery system. It is desirable that it be relatively volatile.

In addition to organic solvents, water can also be used provided that it is sufficiently removed after washing. As the organic solvent, in addition to acetone, methanol, and ethanol, organic solvents used in batteries such as acetonitrile and 1,2-dimethoxyethanepropylene carbonate can be used. In this case, if the cleaning is done thoroughly, the subsequent drying can be omitted.

As counter ions for the alkali metal salts, organic soluble ions such as acetate ions, formate ions, etc. can be used in addition to halogen ions, borosulfide ions, perchlorate ions, and the like. The concentration of the solution containing the alkali metal salt is 0.1% by weight or more, preferably 0-5% by weight or more. It is desirable for the user company to use a solution containing o, o i g or more of an alkali metal salt per gram of carbon fiber.

Although the mechanism by which the cleaned carbon fiber electrode according to the present invention suppresses discharge is not necessarily clear, it is thought to be because substances that promote discharge in the carbon fiber electrode are replaced with Ll and excluded.

For drying after washing, a method of heating under normal pressure or reduced pressure, a method of blowing hot air, etc. can be used.

It is advantageous to use a highly volatile solvent because extreme reduced pressure and high temperatures are not required.

The secondary battery of the present invention is manufactured by immersing the cleaned, TFI, and dried electrode in an electrolyte solution using the method described above. The electrolyte may be a known electrolyte used in general organic solvent batteries, such as tetraalkylammonium salts, alkali metal salts, alkaline earth metal salts (counter anions of these include perchlorate ion, phosphorus hexafluoride ion, etc.). , thallium hexafluoride ion, arsenic hexafluoride ion, antimony hexafluoride ion,
Examples include halogen ions, nitrate ions, sulfate ions, rhenium tetraoxide ions, etc.). In addition, as an organic solvent, solvents commonly used in this type of battery, such as dimethyl sulfoxide, acetonitrile, propylene carbonate, 4-butyrolactone, formamide, dimethylformamide, methylformamide, tetrahydrofuran, 1,2-dimethoxyethane, etc., are used. be able to.

The carbon fibers washed in this manner may be used as both electrodes, or an alkali metal such as lithium may be used as one electrode.

Next, the present invention will be explained with reference to Examples.

Example 1 Activated carbon fiber manufactured by Toyobo Co., Ltd. (KF7 ELTO F-1)
600) 1.5 + crn X 1.5
am (approximately 40 mg) and a platinum lead wire are sandwiched and fixed together between two Teflon plates with holes to form an electrode.
Thoroughly wash by immersing in methanol solution. After further washing with methanol, 100” under a vacuum of 30 mm Hg
ClIC is kept dry for 2 hours. The two sets of electrodes are immersed in 0.3 moto solution, both electrodes are connected to an external power source, and charged at a constant voltage of 3 volts for 30 minutes. Thereafter, the electromotive force of this battery is measured using a voltage measuring device.

Immediately after the start of voltage measurement, there was a rapid voltage drop, but the voltage drop decreased thereafter and reached 2.2 volts after 20 hours, and the voltage drop rate at this time was 0.006 volts/hour.

On the other hand, as a comparative example, when using an electrode that was subjected to the same operation except that the cleaning operation by immersion in 2wt%0HaOOONa methanol solution was not performed, the voltage after 20 hours was 2.0 volts, and the voltage drop Speed is also 0
．． 015 volts/hour.

FIG. 1 shows the change in voltage of these two batteries over time, and from this it is clear that the cleaning effect with the 0H300ONa methanol solution is effective.

Example 2 Activated carbon fiber manufactured by Toyobo Co., Ltd.
59-149654(3) F-1600) 1.5 am X 1.5 am(
(approximately 40 mg) and platinum sword wire are sandwiched and fixed together between two Teflon plates with holes to form electrodes. The electrode thus prepared is washed by immersing it in a 10 weight percent lithium chloride-methanol solution. After washing thoroughly with MθOH, the temperature was reduced to 100°C under a reduced pressure of 30 mmHgV.
Keep time to dry. This electrode set, which was made up of a lithium metal wire and a platinum sword wire sandwiched and fixed together between two Teflon plates with holes, was immersed in a propylene carbonate solution containing 0.3 molar lithium perchlorate. , connect the lithium electrode to an external power supply so that the negative activated carbon fiber electrode becomes positive, and continue for 10 minutes until the potential between the two electrodes reaches 4.2V.
Perform constant current charging at mA.

Thereafter, the electromotive force of this battery is measured using a voltage measuring device. Immediately after the start of voltage measurement, there was a rapid voltage drop, but the voltage drop decreased thereafter and reached 3.7 V after 200 hours, with almost no voltage drop observed thereafter.

On the other hand, as a comparative example, when a battery was prepared by immersing an activated carbon fiber electrode in methanol instead of a 10 weight percent lithium chloride-methanol solution and performing a cleaning operation, the voltage at 1 after 200 hours was 3.55 volts. Met.

FIG. 2 shows the temporal changes in the voltages of these two batteries, and it is clear from this that the cleaning α effect of the lithium chloride-methanol solution is present.

[Brief explanation of the drawing]

FIG. 1 is a graph of the time-voltage relationship between the inventive product shown in Example 1 and the comparative product. FIG. 2 is a graph of the time-voltage relationship between the inventive product shown in Example 2 and the comparative product. Patent applicant: Kao Soap Co., Ltd. Agent: Keibu Mochizuki Figure 1 Bolt 10 2° (hours)

Claims (1)

[Claims] 1. An organic solvent-based secondary battery characterized in that carbon fibers washed with a solution containing an alkali metal salt are used as at least one electrode. 2. The secondary battery according to claim 1, wherein the carbon fiber is an activated carbon fiber having a specific surface area of 500 to 4000 2/g.