JPS61294757A - Battery - Google Patents

Abstract

PURPOSE:To semipermanently maintain performance by using polytetra fluoroethylene microporous film as a separator. CONSTITUTION:A 0.05-0.1mm thick polytetrafluoroethylene (PTFE) microporous film is placed as a separator 6, and electrolyte such as propylene carbonate or gamma-butylolactone is poured. A negative case 1 and a positive case 4 are combined, and the opening of the positive case 4 is bent toward the negative case 1 to form a button type battery. As discharge reaction progresses, the positive active material 5 swells toward the negative case 1, and lithium 3 inside the negative case 1 gradually decreases. In the final stage of discharge, the separator 6 is strongly stretched by the swelling of the positive active material 5, but the PTFE microporous film generates no cracks because of its good ductility.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to batteries, and in particular to separators thereof. Conventional battery separators can be made from woven fabrics of synthetic resin fibers, non-woven fabrics, microporous films, and even woven fabrics. Materials such as paper are widely used.

Generally, different materials are used depending on the electrochemical system of each type of battery.

For example, kraft paper is used in Leclanchier batteries using a neutral salt electrolyte, and cellophane, vinylon, polyethylene microporous membrane, and polypropylene microporous membrane are used in alkaline electrolyte batteries such as mercury batteries, silver oxide batteries, and alkaline manganese batteries. is used as a separator.

In addition, in non-aqueous batteries such as lithium batteries, non-woven fabrics such as polypropylene are generally used as separators. Recently, batteries using lithium as a negative electrode active material have been developed due to their high energy density, light weight, etc. It has been widely developed to take advantage of its advantages, and among them, batteries that use copper oxide as the positive electrode active material are attracting attention as power sources for small electronic devices such as watches.

Copper oxide-lithium non-aqueous batteries are similar and compatible with silver oxide batteries in terms of voltage, and are therefore expected to have good performance.

Problems to be Solved by the Invention However, in copper oxide-lithium batteries, as the battery discharge progresses, the negative electrode, which is a beret of metallic lithium, wears out and disappears. There is a phenomenon in which the agent expands.

Due to its structure, a copper oxide-lithium battery has a separator consisting of a sealing ring fitted to the periphery of a negative electrode case with negative electrode lithium crimped onto the inner surface, and a positive electrode active material layer filled and pressure-molded within the positive electrode case. Since the battery is fixed to the surrounding area of the battery, it must be used as a separator to move between the positive and negative electrodes, whose volume changes as the battery discharge progresses.

As described above, various studies have been conducted in the past as separators for batteries in which the volume balance of the positive and negative electrodes changes with discharge.

A number of batteries were unable to follow the negative electrode sufficiently, cracks appeared in the separator during discharge, and a short circuit occurred during discharge.

In order to solve this phenomenon, the present inventors have made efforts such as using multiple sheets of the various separator materials mentioned above to strengthen the strength of the separators, and have found that copper oxide, which has been determined to be a completely non-defective product, has been developed. It was not possible to obtain lithium batteries.

In order to solve the above problems, the present invention investigates separator materials and uses a separator that can follow the change in volume of both positive and negative electrodes due to discharge, thereby suppressing the internal short circuit phenomenon during battery discharge. It aims to solve the problem.

Means for Solving the Problems In order to solve the above problems, the present invention uses a microporous film of polytetrafluoroethylene (FTFKk), which has excellent tensile strength and is extremely chemically stable, as a separator. It was used as

The microporous film of working PTFK can be stretched to more than double its area and will not develop cracks in case of an accident.

Therefore, when used as a battery separator, it is possible to sufficiently follow the growth of the positive electrode active material layer as discharge progresses, and even at the end of discharge, P T
The FK microporous film can be produced without impairing its role as a separator.

Example Hereinafter, an embodiment of the present invention will be explained with reference to FIG. 1 and the second factor.

Reference numeral 1 in FIG. 1 is a negative electrode case, and a sealing ring 2 made of polypropylene is fitted to the peripheral edge of the negative electrode case.

A metal lithium 3 serving as a negative electrode active material is crimped onto the inner top of the negative electrode case 1.04 is a positive electrode case, and a positive electrode active material layer 6 is formed at the inner bottom of the negative electrode case 1.
The positive electrode active material layer 6 is press-molded and is made of copper oxide as a main ingredient, in which approximately 20% by weight of acetylene black is mixed as a conductive material.

A separator 6 with a thickness of 0.05 mm is placed between these two parts.
～(Llmm of PTFK microporous 74k mm is interposed, an electrolyte such as glopylene carbonate or γ-butyrolactone is injected, the negative electrode case 1 and the positive electrode case 40 are fitted together, and the opening of the positive electrode case 4 is inserted. By bending it toward the negative electrode case 1 side, one button type battery is completed.

When the battery constructed in this manner is fully discharged, the positive electrode active material layer 6 expands toward the inside of the negative electrode case 1 along with the discharge reaction, and the metallic lithium 4 in the negative electrode case 1 gradually decreases. This is an example of a cross section of this battery at the final stage of discharge. At the end of discharge, the positive electrode active material layer 6 expands, so the separator 6 is stretched very strongly.

Ordinary separators will crack at this time and cause damage.

Although an internal short circuit occurs in the negative electrode, the PTF used in the present invention
The K microporous film does not crack due to its excellent ductility.

PTFI used for battery separators! The microporous film can be freely processed to a thickness of 0.01 to 0.2 mm, and its pore diameter is 0.1 to 0.6 μm.
It can be processed to about m. Also, its porosity is 20
Since it can be manufactured in a wide range of ~eo%, it is possible to select a separator with sufficiently appropriate physical property values for the separator characteristics required by the battery.

In addition, PTFK can generally be classified into unsintered type and sintered type according to its manufacturing process.Sintered type undergoes a heat treatment process at a temperature of 327℃ or higher, which is the melting point of PTFX. It was manufactured by
The mechanical strength of such a sintered type PTFK film is significantly increased compared to an unsintered type PTFK film.

In particular, in the case of batteries where the volume of both positive and negative active materials changes significantly during the process of battery discharge reaction, sintered type PTFI
The present inventors used a microporous membrane of polypropylene, which is a conventional separator, to form a blown mold and a sintered 2P T F X microporous film of the present invention. The battery (B) using a plastic film and the total copper oxide-lithium battery have an outer diameter of 7 g mm.

A prototype battery with a total height of 3.8 mm, R41 size, and a theoretical capacity of 20 mAh was manufactured and its characteristics were compared. The results are shown in the table below.

As can be seen from the results of the invention effect table, the average value of 20 prototype batteries x 18 mmh or more of batteries/discharge/number of batteries, the separator made of PTFK microporous film can increase the battery capacity by the theoretical capacity. In addition, the internal resistance of the battery was lowered by about 40 degrees compared to conventional microporous polypropylene membranes.

7'2: PTF 0 that can provide excellent batteries for

[Brief explanation of drawings]

FIG. 1 is a half-sectional view of a battery according to an embodiment of the present invention, and FIG. 2 is a half-sectional view of the same battery at the end of discharge.
Negative electrode case, 2... Sealing ring, 3...
・Negative electrode active material, 4...Positive electrode case, 6...
...Positive electrode active material/L 8...Separator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (3)

[Claims] (1) A battery in which the volume of at least one of the positive electrode active material and the negative electrode active material changes as discharge progresses, and the battery is characterized in that the separator is made of a microporous film of polytetrafluoroethylene. (2) The battery according to claim 1, wherein the separator is a microporous film treated in a heating step above the melting point of polytetrafluoroethylene. (3) The battery according to claim 1 or 2, wherein the separator has a porosity of 50% or more.