JPS61267262A - Flat battery - Google Patents

Abstract

PURPOSE:To reduce the possibility of an internal short circuit accident resulting from the change in the volume of a positive electrode depolarizing mix along the progress in discharge, by making the porosity of the peripheral portion of the mix larger than that of its central portion. CONSTITUTION:A positive electrode terminal plate 11 is made of stainless steel at a thickness of 0.03-0.05mm and bears a positive electrode depolarizing mix 12 having a thickness of 0.06mm and composed of baked manganese dioxide, an electroconductive substance and a binder. The porosity of the peripheral portion of the mix 12, which extends inward by 2mm from the peripheral surface of the mix, is 65%, while that of the other inner portion thereof is 30%. The quantity of discharge per volume in the peripheral portion of the mix 12 is thus reduced to suppress the quantity of expansion thereof under the discharge. The expansion of the volume of the peripheral portion is absorbed by its pores.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a flat battery, and particularly to a flat battery in which the structure of a positive electrode mixture, which is one of the power generating elements, is improved.

[Technical background of the invention and its problems]

In recent years, as electronic devices have become smaller and thinner, there has been an increasing demand for thinner batteries that power these devices. However, with conventional button-type and coin-type batteries, the thickness can only be reduced to at least about 1.0 m, which does not fully satisfy the above requirements.

For this reason, a flat battery having the structure shown in FIG. 2 has already been proposed (Japanese Patent Application Laid-Open No. 128232/1982).

That is, numeral 1 in the figure is a positive terminal plate that supports the positive electrode mixture 2. 3 in the figure is a negative terminal plate that supports the negative electrode 4.

Between the positive electrode mixture 2 and the negative electrode 4 of these terminal plates 1.3,
A separator 5 impregnated with a non-aqueous electrolyte is interposed, and a frame-shaped insulating sealing body 6 made of thermoadhesive resin is interposed at the peripheral edge between the terminal boards 1 and 3. The positive electrode mixture 2, the negative electrode 4, and the separator 5 are sealed by heat-sealing the positive electrode mixture 2, the negative electrode 4, and the separator 5 with the insulating sealing body 6. According to a flat battery having such a structure, the thickness can be reduced to 1
．． It can be made thinner than 0# and fully satisfy the above requirements.

By the way, the active substances of the positive and negative electrodes in a typical battery change their volumes as discharge progresses.

In particular, in a non-aqueous electrolyte battery using a negative electrode active material made of lithium, the negative electrode active material is Li−+L i
Discharge progresses through a lithium consumption reaction of 10e-, while the positive electrode action substance takes in lithium ions to progress discharge, so that the volume change of the positive electrode action material becomes significant.

However, in the flat battery shown in FIG. 1 described above, from the viewpoint of thinning the film and sealing properties, the positive electrode mixture 2 and the frame-shaped insulating sealing body 6 are spaced apart so that they do not come in contact with each other, and reinforcement is required. The structure is such that the ring is not placed on the positive electrode mixture 2. For this reason, the volume of the positive electrode mixture 2 expands as the discharge progresses as described above, and the expansion and volume change are particularly significant at the periphery of the positive electrode mixture 2 where the outer periphery is not regulated in any way.
1. It reaches the negative terminal plate 3 and causes an internal short circuit.
There were drawbacks.

[Object of the Invention] The present invention aims to provide a flat battery that reduces the risk of internal short-circuit accidents caused by changes in the volume of the positive electrode mixture as discharge progresses.

[Summary of the invention]

In the present invention, a positive terminal plate carrying a positive electrode mixture and a negative terminal plate carrying a negative electrode are laminated with a separator interposed therebetween, and a frame-shaped frame made of thermoadhesive resin is attached to the peripheral edge of each opposing terminal plate. In a flat battery in which the positive electrode mixture, negative electrode, and separator are sealed by heat-sealing each of the terminal plates and the insulating sealing body with an insulating sealing plate interposed therebetween, the porosity of the positive electrode mixture is determined by adjusting the porosity at the periphery. It is characterized by using a part that is larger than the center part. According to the present invention, since the porosity of the periphery of the positive electrode mixture is larger than that of the center, the amount of discharge per volume at the periphery can be reduced, and the amount of expansion accompanying discharge can be suppressed. The pores at the periphery can absorb volumetric expansion. As a result, the apparent expansion amount of the positive electrode mixture can be suppressed and the positive electrode mixture can be prevented from reaching the negative electrode terminal plate and causing an internal short circuit.

[Embodiments of the invention]

Hereinafter, an example in which the present invention is applied to a flat type lithium/manganese dioxide type organic solvent battery will be described with reference to FIG.

11 in the figure is a stainless steel positive electrode terminal plate with a wall thickness of 0.03 to 0.05 m that supports a positive electrode mixture 12 with a wall thickness of 0.06 m made of calcined manganese dioxide, a conductive material, and a binder. . This positive electrode mixture has a porosity of 65% in a peripheral portion having a width of 2 seconds from the periphery inward, and a porosity of 30% in a central portion located inside of the peripheral edge. 1 in the diagram
3 is a negative electrode 1 made of lithium and having a wall thickness of 0.06 #, for example.
This is a negative terminal plate similar to the terminal plate 11 carrying 4. The positive electrode mixture 12 of these positive and negative terminal plates 11 and 13
A separator 15 made of, for example, polypropylene non-woven fabric impregnated with a non-aqueous electrolyte is interposed between the negative electrode 14 and a separator 15 is interposed between the terminal plates 11 and 14, and a frame with a wall thickness of 0°211111+1 is formed on the opposing peripheral edge of each terminal plate 11.13. A frame-shaped insulation sealing body 16 made of modified polyethylene with two widths is interposed to
enter. The non-aqueous electrolyte is made of propylene carbonate in which lithium perchlorate is dissolved at a ratio of 1 mol/liter. Then, by heating and pressurizing each of the terminal plates 11, 13 and the insulating sealing body to fuse them together,
It has a structure in which the positive electrode mixture 12, the negative electrode 14, and the separator 15 are sealed.

Therefore, 20 batteries of this example and a porosity of 30%
When 20 flat batteries (conventional example) having the same configuration as in the example except that a positive electrode mixture of Ta. Note that A in FIG. 3 indicates the range of discharging variation in the battery of this embodiment, and B indicates the range of discharging variation in the battery of the conventional example. As is clear from Fig. 3, the N battery of the present invention has small discharge variations and is distributed on the high discharge life side, whereas the conventional battery has a wide distribution from low discharge life to high discharge life. I can see that When we removed one of the conventional batteries with a low life expectancy, disassembled it, and examined its internal condition, we found that the positive electrode mixture had expanded and reached the negative terminal plate, causing an internal short circuit. Ta.

In addition, although the above-mentioned example explained a lithium manganese dioxide type organic solvent battery, it is not limited to this. For example, other organic solvent batteries such as lithium fluorocarbon organic solvent batteries, other primary batteries such as alkaline manganese batteries,
Alternatively, the same effects as in the embodiment can be achieved in a secondary battery such as a nickel-cadmium battery.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to provide a highly reliable flat battery that reduces the risk of internal short circuit accidents caused by changes in the volume of the positive electrode mixture as discharge progresses.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a flat battery according to an embodiment of the present invention, FIG. 2 is a sectional view of a conventional flat battery, and FIG. 3 is a diagram showing discharge characteristics of the battery of this embodiment and a conventional battery. It is. 11... Positive electrode terminal plate, 12... Positive electrode mixture, 13...
- Negative electrode terminal plate, 14... negative electrode, 15... separator, 16... frame-shaped insulating sealing body. Applicant's agent Patent attorney Suzue Takehiko Ward Ward - Hemi Aji (8) Go) f body

Claims (1)

[Claims] A positive terminal plate carrying a positive electrode mixture and a negative terminal plate carrying a negative electrode are laminated with a separator interposed therebetween, and a frame-shaped insulating sealing plate made of thermoadhesive resin is attached to the peripheral edge of each opposing terminal plate. In a flat battery in which the positive electrode mixture, the negative electrode, and the separator are sealed by interposing the terminal plates and the insulating sealing body by heating and fusing them, the porosity of the positive electrode mixture is increased from the center to the periphery. A flat battery characterized by using a large battery.