JPS6117103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery using a light metal such as lithium or sodium as a negative electrode active material and a non-aqueous organic electrolyte. The present invention relates to a method for producing a positive electrode, which is heated and rapidly cooled after being molded.

BACKGROUND ART Various metal halides, metal oxides, oxyacids, sulfides, and the like are used as positive electrode active materials in batteries that use light metals such as lithium and sodium as negative electrode active materials and nonaqueous organic electrolytes.
Among these positive electrode active materials, almost none have good electrical conductivity by themselves.
Therefore, electrically conductive powder such as carbon powder or metal powder is mixed with these positive electrode active materials, and then polytetrafluoroethylene powder is mixed in order to bind this powder and the positive electrode active material. It is molded into a positive electrode. However, as mentioned above, simply mixing polytetrafluoroethylene resin powder has the disadvantage that the strength of the positive electrode is low, and if it is immersed in an organic electrolyte for a long time, the positive electrode will collapse and become deformed.

The present invention eliminates the drawbacks of the prior art as described above and provides a method for producing a positive electrode having excellent performance.

The key point of the present invention is to mix a positive electrode active material, a conductive agent, and a polytetrafluoroethylene fine powder, press-mold the mixture, heat it to a temperature at which it softens and does not melt, and then heats it with liquid nitrogen or liquid helium. It is rapidly cooled by immersing it in a cryogenic solution.
By heating, the binding force of polytetrafluoroethylene is strengthened, and then by rapid cooling, the performance of the positive electrode is improved.

In other words, unmolten but softened polytetrafluoroethylene is immersed in an extremely low temperature solution and rapidly cooled, resulting in less crystallinity.As a result, the volume of polytetrafluoroethylene decreases, making it difficult to use as a positive electrode. This has the effect of creating pores that hold the electrolyte inside. Furthermore, when rapid cooling is performed, a large difference occurs in the amount of shrinkage of the positive electrode active material, conductive agent, and polytetrafluoroethylene, which have different shrinkage rates.
Since the volume of the pores and pores in the positive electrode can be increased, the movement of the electrolyte to the positive electrode is facilitated, and the reaction of the battery is promoted accordingly, making it possible to improve performance such as increasing the battery voltage.

The heating temperature must be below the decomposition temperature of polytetrafluoroethylene, but it should not exceed 200℃.
230°C is preferred.

Examples of the present invention will be described below.

Example Manganese dioxide was used as a positive electrode active material, carbon powder was used as a conductive agent, and fine powder of polytetrafluoroethylene was added thereto and thoroughly mixed in a ball mill. The mixing ratio of each substance is manganese dioxide
80 parts, 10 parts of carbon powder, and 10 parts of polytetrafluoroethylene fine powder. After mixing, 0.6 g of this powder was dispersed and pressure molded into a positive electrode with a diameter of 20 mm at a pressure of 3000 Kg/cm ² . Next, this positive electrode was heated to 230℃ in air.
After keeping it for 30 minutes, it was immersed in liquid nitrogen and rapidly cooled. The positive electrode obtained through this treatment was filled in a nickel battery case in a dry inert gas.
A battery was prepared by filling a battery case with a polypropylene nonwoven fabric impregnated with an organic electrolyte consisting of propylene carbonate in which 1 mol/mol of lithium perchlorate was dissolved, and lithium. FIG. 1 shows a cross section of a battery obtained according to the present invention. 1 is a positive electrode according to the present invention, 2 is lithium, 3 is a polypropylene nonwoven fabric impregnated with an organic electrolyte, 4 is a nickel battery case, 5 is a battery top cover, and 6 is a packing made of polymer resin.

Figure 2 shows a battery using the positive electrode obtained by the present invention with 3k
Symbol A indicates the change in battery voltage over time when a constant resistance of Ω is connected and the battery is discharged. For comparison, in FIG. 2, the symbol B indicates the characteristics of a battery using a positive electrode that is not subjected to heating and quenching treatment. It can be seen from FIG. 2 that the battery using the positive electrode according to the present invention has significantly better characteristics. Further, the positive electrode according to the present invention did not deform even when immersed in an organic electrolyte for a long time, and had excellent strength.

In addition, in addition to this example, the heating temperature was 150℃, 200℃
When the constant resistance discharge characteristics of the battery were examined using positive electrodes obtained in the same manner at 250°C and 250°C, those at 200°C showed almost the same characteristics as in this example, and those at other temperatures showed It was slightly inferior to this example. However, it exhibited far better characteristics than the one indicated by symbol B in FIG.

As described above, it is clear that according to the present invention, a positive electrode having far superior performance than the conventional one can be obtained, and therefore, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a battery according to the present invention, and FIG. 2 is a discharge characteristic diagram of a battery using a positive electrode according to the present invention. 1...Positive electrode, 2...Lithium, 3...Nonwoven fabric,
4... Battery case, 5... Battery top cover, 6... Packing.

Claims (1)

[Claims] 1. In a method for producing a positive electrode for a battery having a negative active material made of a light metal such as lithium or sodium and a nonaqueous organic electrolyte, a mixture of the positive active material, conductive agent powders, and fine particles of polytetrafluoroethylene is pressure-molded. A method for producing a positive electrode for a non-aqueous electrolyte battery, which comprises heating the molded mixture to a temperature at which it softens and does not melt, and then immersing it in a cryogenic solution of liquid nitrogen or liquid helium to rapidly cool it.