JPS6122424B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for manufacturing an electrolyte layer or a positive electrode active material layer for a thermal battery, and more specifically, by improving a method for preparing a molding material when manufactured by a powder molding method. The purpose is to provide a highly reliable thermal battery with small variations.

A thermal battery is a battery whose electrolyte is a molten salt that is solid at room temperature but becomes liquid when heated to high temperatures.A typical electrolyte is LiCl-KCl eutectic mixed salt (43:57% by weight). , melting point 352℃) and LiBr−
Examples include KBr eutectic mixed salt (52:48% by weight, melting point 330°C). Since these electrolytes are practically used in the form of anhydrous salts in thermal batteries, it is possible to use negative electrode materials such as Mg and Ca. This is a battery with unique characteristics.

The method of manufacturing the electrolyte layer of this battery can be broadly classified into the following two methods. One is the separator that forms the backbone of the electrolyte layer, such as asbestos paper, glass cloth, porous ceramic, etc.
One is a method of melting and impregnating an electrolyte, and the other is a method of molding a mixture of an electrolyte holding material powder such as kaolin or alumina and an electrolyte powder. The present invention proposes an improvement in the manufacturing method of the latter electrolyte layer.

It is well known that high-performance thermal batteries generally have the following battery configuration.

Ni or Fe/CaCrO ₄ LiCl−KCl/Ca Although the above battery system is an excellent battery system, when activated and the electrolyte becomes molten, Li ⁺
The ions and the negative electrode Ca undergo ion replacement, and Li metal is generated and combines with the negative electrode Ca to form a low melting point alloy of CaLi ₂ (melting point 230°C). If a large amount of this is generated, it will flow out of the battery structure. It also has the disadvantage of causing short circuits. In order to avoid such drawbacks,
As a result of various studies such as the type of retaining material, the appropriate mixing ratio of the retaining material and electrolyte, the mixing method and conditions, and the particle size, it became possible to obtain a certain degree of stability and battery characteristics.

However, although most of them show normal discharge characteristics, occasionally a micro short circuit of unknown cause may occur during discharge.
As a result of investigation from various angles, the authors found that there was a problem in the process of heat treating the mixture of the holding material and the electrolyte. In conclusion, this is because during the heat treatment step, the initially homogeneous mixture becomes a non-uniform mixture, and the electrolyte concentration changes locally depending on the location. The explanation will be given below.

The conventional manufacturing process for an electrolyte layer is to uniformly mix 35% by weight of the retaining material and 65% by weight of the electrolyte powder in a ball mill mixer, and then put it into a porcelain container with an internal volume of 1.
Add 600g of the above mixture, heat it for about 60 minutes in an electric furnace controlled at any temperature between 400 and 800°C, for example 700°C, and take it out after cooling and solidifying →
It was manufactured through a process of pulverization and then pressurized remolding. In this case, the electrolyte in the mixture is heated above its melting point, so there is no problem if it melts and is evenly adsorbed to the holding material, but while some of the melt is adsorbed, the other part is not sufficiently There is a phenomenon in which the particles are not completely absorbed and end up near the bottom of the container. Therefore, the electrolyte ratio at the top of the container will be lower than 65% by weight, and conversely, at the bottom, the electrolyte ratio will be higher than 65% by weight.
The ratio is now 35:65, but if you look at it partially, the ratio between the two is different. When such an electrolyte layer is used, there will be variations even between the same lot, and there will also be variations in each part of a single electrolyte layer, so it is quite convincing that micro short circuits of unknown cause as mentioned above occur. can.

On the other hand, in order to confirm the processing amount conditions, 30g (1/20 of the above amount) of mixed powder was placed in a 50c.c. crucible.
When heat treatment was carried out under similar heat treatment conditions, it was found that although a slight improvement was observed, no essential improvement such as a change in the ratio was made.

Other problems include the fact that the holding material and electrolyte stick to the inner surface of the porcelain container, which takes time to collect, and when processing large quantities, there is a large temperature difference between the inner wall surface and the center of the container, resulting in homogeneous processing. In some respects, it was found to be insufficient.

The present invention aims to improve the above-mentioned drawbacks and provide a highly reliable electrolyte or positive electrode active material layer for thermal batteries with small variations.

Hereinafter, a detailed explanation will be given with reference to representative embodiments of the present invention shown in the drawings.

FIG. 1 is a structural diagram of a unit cell used in the present invention.

Reference numeral 1 denotes a negative electrode active material containing Ca as a main component, which is pressure-bonded to the negative electrode current collector plate 2 and is electrically conductive. 3 is the electrolyte layer of the present invention, in which inorganic retention material powder such as kaolin, alumina, attapulgite, etc. and LiCl-KCl electrolyte powder are weighed out in a ratio of 35:65% by weight, and after sufficiently uniformly mixing in a ball mill mixer, the above mixture is mixed. is sent into a mold and pre-pressurized and hardened before heat treatment. Preforming conditions are 0.1 to 3 tons/cm ²
The amount of powder mixture in the mold was 35 g at a pressure of 1.2 tons/cm ² , and a block having a diameter of 30 mm and a height of 30 mm was produced at a pressure of 1.2 tons/cm 2 . The density when processed in a conventional container is approximately 0.6 g/cc, but
In the above case, the density is 1.8g/cc. Incidentally, the size and density of the above-mentioned block molded product can be arbitrarily changed by changing the amount and pressure of the mixture put into the mold. Thereafter, it is heat-treated in an electric furnace at 700°C for 20 minutes, taken out, and pulverized to a particle size (-60 mesh) suitable for the next process, after which the main forming of the electrolyte layer is performed in order. Reference numeral 4 denotes a positive electrode active material layer, which mainly contains CaCrO ₄ powder and electrolyte powder, and is manufactured in substantially the same manner as electrolyte layer 3 described above. i.e. CaCrO ₄ powder
70% by weight and 30% by weight of electrolyte powder are uniformly mixed, the mixture is fed into a preforming mold,
Preform and harden before heat treatment. After this
Heat treated in an electric furnace at 400-650℃ for 15 minutes and then taken out →
Pulverization→main molding of the positive electrode active material layer, and molding of the two layers together with the electrolyte layer 3 is performed. 5 is the positive electrode current collector plate made of Ni
and Fe board.

FIG. 2 is a schematic cross-sectional view of a stacked thermal battery.

6 is the unit cell shown in FIG. 1, and 7 is a heat generating agent laminated alternately with the unit cell 6, for heating the unit cell 6 and generating electricity. 8 is a starting tool, and external terminal 9 for starting
When a signal current is passed through, a flame is emitted and the vent hole 1
0 to ignite the exothermic agent 7 in each layer. 11 is an output terminal, 12 is a heat insulating layer, and 13 is an exterior body consisting of a lid and a case, the fitting portion of which is completely sealed by inert gas welding.

In the above configuration, in the embodiment of the present invention, it is normally in an inactive state, but when in use, it becomes active by passing a signal current from the starting external terminal 9, and power can be extracted from the output terminal 11. The feature of the present invention is that when manufacturing the electrolyte layer 3 and the positive electrode active material layer 4, the holding material powder and the electrolyte powder
A mixture of powder, cathode active material powder, and electrolyte powder is preformed to form a block body,
After that, it is subjected to heat treatment.

The effects of the present invention will be described below.

In the case of the present invention, the density of the mixed powder is high due to the preforming as described above, and the holding material particles and electrolyte particles are close to each other, so that the electrolyte melted during heat treatment is easily adsorbed by the holding material. , and the shape of the block molded product does not deform or collapse. On the other hand, when a powdered mixture is heat-treated in a conventional container, it shrinks from its bulk height before heating, causing the electrolyte at the bottom of the container to become uneven as described above. In the case of the present invention,
A uniform heat-treated product with no uneven electrolyte distribution can be produced.

Moreover, since the block moldings can be heat-treated by arranging them on a heat-resistant plate without using a container, they are not stuck to the wall of the container, and recovery is very easy. Furthermore, in order to make the temperature distribution uniform when processing a large amount in a container, the only way to achieve uniform temperature distribution is to put a small amount into small containers and process a large number of them side by side, which is industrially impossible, but in the case of the present invention, small blocks Because it is hardened, it can be heated much more uniformly than conventional methods.

Using the electrolyte of the present invention, we fabricated the laminated thermal battery shown in Figure 2, conducted a discharge test, and confirmed its reliability.We found that a micro short circuit occurred during discharge (in most cases 1 to 2 cells). (short circuit phenomenon for 0.1 to 0.5 seconds) out of 20 batteries, compared to 20 batteries of conventional batteries.
The phenomenon that used to occur in 2 to 3 cases has disappeared. Other features include shortening of heat treatment time,
There are many advantages such as ease of mechanical processing and no consumption of containers.

On the other hand, as described in the examples, the positive electrode active material layer has the same problems as the electrolyte layer, such as variations in the ratio of the positive electrode active material and electrolyte, stabilization of temperature distribution during heat treatment, and difficulty in recovery due to sticking to the container. However, by using the present invention, these drawbacks have been overcome.

As described in the above embodiments and effects, according to the present invention, it is possible to improve the material before forming the target electrolyte layer and positive electrode active material layer, and therefore to create a highly reliable thermal battery with small variations. It becomes possible to provide

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a unit cell used in the present invention, and FIG. 2 is a sectional view showing the overall configuration of a laminated thermal battery. 1... Negative electrode active material, 3... Electrolyte layer, 4... Positive electrode active material layer, 5... Positive electrode current collector plate. 〓〓〓〓

Claims (1)

[Claims] 1. A step of uniformly mixing an electrolyte holding material powder made of an inorganic adsorbent and an electrolyte powder made of a molten salt, and then solidifying this mixture by pressure molding, and then heating the molded body. 1. A method for producing a thermal battery, comprising forming an electrolyte layer through a treatment step, a step of pulverizing a molded body to obtain a predetermined particle size, and a step of subsequently remolding the powder. 2. After homogeneously mixing the positive electrode active material and electrolyte powder, the mixture is solidified by pressure molding, and then the molded body is heat-treated, and the molded body is pulverized to a predetermined particle size. 1. A method for producing a thermal battery, comprising forming a positive electrode active material layer by a step and a subsequent step of re-molding the powder.