JPH0554223B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a thermal battery using a molten salt as an electrolyte, and makes it possible to manufacture a thin unit cell for a thermal battery without defective insulation. Thermal batteries use molten salt as an electrolyte, and although current cannot flow at room temperature, when heated to high temperatures during use, the electrolyte melts and becomes extremely conductive, making it possible to discharge at large currents. It becomes possible. For this reason, thermal batteries do not self-discharge when unused and can be stored for long periods of time, making them excellent as highly reliable emergency high-output power sources. Generally, thermal batteries are used by stacking a plurality of unit cells in order to obtain high voltage. A unit cell is composed of three layers: a negative electrode layer, an electrolyte layer, and a positive electrode layer, and is manufactured by integrally press-molding powdered raw materials into the three layers. In order to obtain a higher voltage thermal battery, a thinner unit cell is required, but as the thickness of the unit cell becomes thinner, the insulation resistance of the unit cell decreases rapidly, and the defect rate during manufacturing increases. increased. One of the causes of this is a short circuit inside the unit cell. As the thickness of the unit cell becomes thinner, even the slightest disturbance between the three layers, centering on the electrolyte layer, tends to cause mixing of the positive and negative electrode layers, which is thought to cause internal short circuits. However, it has been found that the main cause of the decrease in insulation resistance of the unit cell is the periphery of the molded unit cell. In other words, in a unit cell, negative electrode raw material powder, electrolyte raw material powder, and positive electrode raw material powder are sequentially filled into a press mold, and the three layers are molded together under pressure to form a disc-shaped compact. At the peripheral edge, it was observed that friction with the cylinder wall of the press mold during pressurization caused turbulent force in the layer, leading to a decrease in insulation resistance due to shortening or contact between the positive and negative electrodes. Such disturbance of the layers at the periphery of the molded body was hardly a problem when the cell was 2 mm or more thick, but in the case of a thin cell with a thickness of around 1 mm,
It has come to have a large effect on the reduction of insulation resistance.
In particular, in thermal batteries that use a lithium alloy such as a lithium-aluminum alloy or a lithium-silicon alloy for the negative electrode and a sulfide such as iron sulfide, iron disulfide, or nickel sulfide for the positive electrode, both the positive and negative electrodes are Because it is a good conductor of electricity, even the slightest disturbance between the three layers caused a drop in insulation resistance. Unit cells with low insulation resistance have a large self-discharge rate, which can cause internal short circuits, so they cannot be used as batteries. The present invention aims to improve such drawbacks, and is to form a disc-shaped compact obtained by pressure-molding three layers of negative electrode raw material powder, electrolyte raw material powder, and positive electrode raw material powder into a negative electrode. The present invention relates to a method for manufacturing a unit cell for a thermal battery, which is characterized by exposing it to an atmosphere of active gas or steam. A part of the negative electrode at the periphery of the unit cell, which is the cause of a decrease in insulation resistance, is made to react with an active gas to become an electrical nonconductor.According to the present invention, a thin thermal battery without poor insulation can be achieved. It is possible to manufacture cell batteries. Examples thereof will be described below. Example 1 FIG. 1 is a sectional view of a unit cell in which the present invention is implemented. In the figure, 1 is a negative electrode layer, 2 is an electrolyte layer, and 3 is a positive electrode layer, and these three layers are integrally press-molded. 4 is the periphery of the unit cell. FIG. 2 is a cross-sectional view of a thermal battery in which unit cells are stacked. In the figure, 5 is each stacked unit cell, and 6 is a heat generating agent which is alternately stacked with the unit cells 5. 7 is a negative terminal, and 8 is a positive terminal. Reference numeral 9 denotes an igniter, and when an instantaneous current is applied to the ignition terminal 10, the igniter 9 ignites, ignites the exothermic agent 6, and activates the battery. 11 is a heat insulator for keeping the battery warm, and 12 is a battery container. 0.75g of lithium-aluminum alloy as negative electrode raw material powder, LICl-KCl as electrolyte raw material powder
2 g of a mixture of eutectic salt and magnesium oxide and 1.5 g of a mixed powder whose main component is iron disulfide as a positive electrode raw material powder were sequentially filled into a press mold, and the mixture was pressed to a thickness of 1.05 mm with a pressing pressure of 1.5 t/cm ² . A disc-shaped compact with a diameter of 54 mm was obtained. Conventionally, this disk-shaped molded body was used as it is as a unit cell of a laminated battery, but in the peripheral part 4, the three layers were disturbed due to friction with the cylinder wall of the press mold during molding, and most of the parts were The insulation resistance of the unit cell was less than 1MΩ, and the failure rate was extremely high. In the present invention, 50 disk-shaped compacts obtained by pressure molding are stacked as a set, the top and bottom of the stack is sandwiched between stainless steel plates, and the stack is taken out into air saturated with thionyl chloride _SOCl2 . It was left for 10 minutes.
The laminated disk-shaped compact reacted selectively with SOCl ₂ on the surface of the negative electrode at the peripheral edge, and a portion of the negative electrode at the peripheral edge was corroded and turned into a nonconductor. In the disc-shaped molded body, by changing the surface of the negative electrode at the peripheral edge to an electrically nonconducting material, it has become possible to improve insulation defects. Example 2 A lithium-aluminum alloy was used as the negative electrode raw material powder, a mixture of 65% LiCl-KCl eutectic salt and 35% magnesium oxide was used as the electrolyte raw material powder, and equal amounts of iron disulfide and nickel sulfide were used as the positive electrode raw material powder. A mixture of 70% and 30% LiCl-KCl eutectic salt was used. 0.75 g of negative electrode raw material powder, 2.0 g of electrolyte raw material powder, and 1.5 g of positive electrode raw material powder were sequentially filled into a press mold in a layered manner and molded at a press pressure of 1.5 t/cm ² .
A disk-shaped molded body with a thickness of 1.0 mm and a diameter of 54 mm was obtained. When the upper and lower parts of this molded body were sandwiched between two stainless steel plates and the insulation resistance between the electrodes was measured in argon gas, it was found to be 0.3 MΩ, which was determined to be a defective product. Next, this molded body was placed between stainless steel plates and left in an atmosphere of 10% chlorine gas and 90% argon gas for 30 minutes. When the insulation resistance between the electrodes was measured again in argon gas, it was 70 MΩ. This disc-shaped molded body was sandwiched between hot valves set at a temperature of 500°C at the top and bottom, and discharged with 10A of electricity.
Discharge was possible for 110 seconds, and no poor contact or self-discharge was observed. A part of the negative electrode at the periphery of the disc-shaped molded body, which was the cause of insulation failure, reacted with chlorine gas, causing LiCl and
This is changed to AlCl ₃ to improve insulation defects.
The same effect can be obtained even if chlorine is replaced with other active gas such as bromine or oxygen. The reaction products are LiBr, Li ₂ O, AlBr ₃ ,
Although it changes to Al ₂ O ₃ etc., none of these has a negative effect on the battery characteristics. Example 3 A lithium-silicon alloy was used as the negative electrode raw material powder, and a eutectic salt of LiCl-KCl was used as the electrolyte raw material powder.
A mixture of 65% magnesium oxide and 35% magnesium oxide, and 70% iron disulfide and LiCl-KCl eutectic salt as the positive electrode raw material powder.
A 30% additive was used. Negative electrode raw material powder 0.5
g, 2.0 g of electrolyte raw material powder, and 1.5 g of positive electrode raw material powder were sequentially filled into a press mold in layers and molded at a press pressure of 2.0 t/cm ² to form a disc-shaped compact with a thickness of 1.0 mm and a diameter of 54 mm. Obtained. When the upper and lower parts of this molded body were sandwiched between two stainless steel plates and the insulation resistance between the electrodes was measured in argon gas, it was found to be 0.5 MΩ, which was determined to be a defective product. Next, this molded body was left between stainless steel plates for 10 minutes in argon gas saturated with sulfuryl chloride SO ₂ Cl ₂ . When we measured the insulation resistance between the electrodes again in argon gas, we found that
It showed 60MΩ, indicating that the insulation defect had been improved. Table 1 compares the insulation resistance measurement results of 200 unit cells using the conventional method that does not expose them to an active atmosphere and the method of the present invention. By the manufacturing method of the present invention, the insulation resistance of almost all unit cells was 1 MΩ or more, and the defective rate was drastically reduced.
Note that the effect of the present invention was not observed in the three unit cells used in the method of the present invention because of short circuits inside the unit cells.

[Table] The atmosphere of active gases and vapors for the negative electrode includes gases such as Cl ₂ , Br ₂ , O ₂ , SO ₃ , SO 2 , NO _{2 ,} NO, SOCl ₂ , SO ₂ Cl ₂ , POCl, etc. Vapors of inorganic solutions are used. These gases and vapors further increase their activity in the presence of trace amounts of water vapor. In the present invention, in order to corrode a part of the negative electrode, disk-shaped molded bodies are laminated or the surface of the negative electrode is covered with a metal plate or the like and exposed to an active atmosphere so that only the peripheral portion reacts selectively. It is desirable to do so.
If only the periphery of the molded body is reacted,
The amount of reacted negative electrode was extremely small, and no effect on battery characteristics was observed. As for thermal batteries, unit cells are not used alone;
Use multiple cells stacked together. According to the present invention, a thin unit cell without insulation defects can be easily manufactured, and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a unit cell manufactured according to the present invention, and FIG. 2 is a sectional view of a stacked battery. 1... Negative electrode layer, 2... Electrolyte layer, 3... Positive electrode layer, 4... Peripheral part of unit cell.

Claims (1)

[Claims] 1 A disk-shaped compact obtained by pressure-molding three layers of negative electrode raw material powder, electrolyte raw material powder, and positive electrode raw material powder is reacted with the negative electrode raw material, so that the peripheral edge of the negative electrode becomes a nonconductor. A method for producing a unit cell for a thermal battery, which is characterized by exposing it to an atmosphere of active gas or steam.