JPH0413820B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the manufacturing method of a molding mixture with a wire mesh for an organic electrolyte battery that uses heat-treated manganese dioxide as a positive electrode active material, and is aimed at preventing the molding mixture from cracking or chipping when taken out from a mold. purpose. In organic electrolyte batteries that use lithium as the negative electrode active material and organic liquids in which electrolytes such as chlorides, perchlorates, and borofluoride salts are dissolved in various organic solvents as the electrolyte, lithium is stored as the positive electrode active material. Manganese dioxide, which is less soluble in water and has a high monopolar potential, is often used, but manganese dioxide has attached water and a large amount of bound water.
They generate gas during battery storage, causing the battery to swell and reducing battery performance.
In order to remove them and flatten the discharge characteristics due to the phase transition of manganese dioxide, manganese dioxide is subjected to heat treatment in advance in a powder state. In addition, in order to respond to the thinning of batteries accompanying the thinning of battery application equipment, there is a demand for thinner molding mixtures for battery positive electrodes. Since cracks tend to occur at times, the molding mixture is reinforced with a wire mesh, which also serves as a current collector. By the way, the conventional manufacturing method of such a molding mixture with wire mesh is shown in FIGS. 1 to 4 and 7 to 8, for example.
As shown in the figure, first, the space formed by the outer mold 11 and the lower punch 13 is filled with granular or powdered positive electrode mixture 1a (Fig. 1), and the upper punch 12 is lowered to form a positive electrode. The mixture is pressurized and preformed (Fig. 2), and the upper punch 12 is pulled up (Fig. 3).
After placing the wire mesh 2 on the preformed body 1b, the upper punch 12 is lowered again and pressurized to perform the final forming (Figure 4).
Pull the chisel out of the outer mold 11 (Fig. 7), then push up the lower punch 13 to remove the molding mixture 1 with wire mesh.
Since the material is to be taken out from the outer mold 11, as shown in FIG. Spring back occurs, and the molding mixture 1 with wire mesh is warped with the wire mesh 2 side as a recess, and as a result, the peripheral edge of the molding mixture 1 gets caught on the upper end of the outer mold 11, causing chips and cracks. Molding defects such as peeling between the molding mixture 1 and the wire mesh 2 occur. The above-described springback is particularly likely to occur when the manganese dioxide has been previously heat-treated as described above. The present invention was made in light of such circumstances, and includes an outer mold having a cylindrical cavity,
A wire mesh that integrally press-forms a positive electrode mixture made of manganese dioxide, a conductive agent, and a binder that has been heat-treated in advance using a mold equipped with an upper punch and a lower punch that can move up and down within the cavity. In the production of a molded mixture with molding, a granular or powdered positive electrode mixture and a wire mesh are placed in the space formed by the outer and lower punches so that the wire mesh is positioned above or below the positive electrode mixture, After pressure molding, the molding mixture with a wire mesh is removed from the outer mold while being sandwiched between the upper and lower punches, thereby preventing the molding mixture from warping due to spring back when taken out from the outer mold. This prevents defects such as chipping and cracking of the molding mixture. In particular, in the present invention, pressure molding is carried out by filling a granular or powdered positive electrode mixture into the space formed by the outer mold and the lower punch, and then lowering the upper punch to press the precise mixture to prepare the preliminary material. After forming, it is preferable to pull up the upper punch, place a wire gauze over the preform, and then lower the upper punch again to apply pressure and perform main forming. Next, embodiments of the present invention will be described based on FIGS. 1 to 6. First, as shown in FIG. 1, the space formed by the outer wall 11 and the lower punch 13 is filled with granular or powdered positive electrode mixture 1a. Next, the upper punch 12 is lowered and the positive electrode mixture is pressurized at 1 to 5 t/cm ² to preform it (Fig. 2).
(Fig. 3), and then the preformed body 1b
After placing the wire mesh 2 on top, use the upper punch 12 again.
is lowered and pressurized at 5 to 10 t/cm ² for final molding (Fig. 4), and the molded mixture 1 with wire mesh is sandwiched between the upper punch 12 and the lower punch 13 and moved upward. Push up and take out from the outer mold 11 (5th
figure). After taking it out from the outer mold 11, pull up the upper punch 12 and separate it from the molding mixture 1 with wire mesh (Fig. 6).
The molding mixture 1 with wire gauze is pushed out laterally using a pressing member (not shown). Even in this method, when the upper punch 12 is separated from the molding mixture 1 with wire mesh, warping occurs due to springback as shown in FIG. 6, but this occurs after it is taken out from the outer mold. The molding mixture will not be chipped or cracked due to the upper end of the mold 11 being caught. It should be noted that it is preferable that the molding mixture with a wire mesh, which has warped as described above, be heated to correct the warp before being used for battery assembly. Table 1 below shows how molding mixtures with wire mesh (diameter 15.7 mm, thickness 0.51 mm) were prepared using the method of the present invention and the conventional method.
This shows the percentage of good products obtained when 100 units were manufactured. The positive electrode mixture consists of 100 parts of manganese dioxide (by weight, the same applies hereinafter) heat-treated at 400°C for 2 hours, 10 parts of phosphorous graphite, and 1 part of the binder shown in Table 1. Diameter 0.08
mm, 60 mesh stainless steel mesh.
The method of the present invention involves preforming and main forming as shown in Figs. 1 to 4, and then inserting the molding mixture with a wire mesh between an upper punch and a lower punch as shown in Fig. 5 and releasing it from the outer mold. In the conventional method, after preforming and main molding are performed in the same manner, the molding mixture with wire gauze is taken out from the outer mold as shown in FIGS. 7 and 8. And the pressure during preforming for both is
1.5t/cm ² , and the pressure during main molding was 7t/cm ² .

[Table] As shown in Table 1, according to the method of the present invention, the moldability can be greatly improved, and the occurrence of defects can be greatly reduced. In the above examples, a water-soluble polymer binder or an inorganic binder such as sodium silicate was used as the binder, but polytetrafluorethylene, which has been widely used in the past, may be used instead. . Further, although phosphorous graphite is used as a conductive agent, artificial graphite, expanded graphite, acetylene black, etc. may be used instead. In the examples, pressure molding was carried out by preforming the positive electrode mixture, placing a wire mesh, and then performing the main molding. After that, without preforming, a wire mesh may be placed on top of the wire mesh and pressurized to form the positive electrode mixture and the wire mesh together, or after placing the wire mesh, the positive electrode mixture may be placed on top of the wire mesh. Fill it with
The positive electrode mixture and the wire mesh may be integrally molded under pressure.

[Brief explanation of drawings]

Figures 1 to 6 are cross-sectional views schematically showing the main steps in producing a molding mixture with a wire mesh by the method of the present invention, and Figures 7 to 8 are sectional views showing the process of manufacturing a molding mixture with a wire mesh by the conventional method. FIG. 3 is a cross-sectional view schematically showing the process of taking out the molding mixture with wire mesh from the outer mold. 1... Molding mixture, 1a... Granular or powdered positive electrode mixture, 1b... Preformed body, 2... Wire mesh,
11...Outer diameter, 12...Upper punch, 13...Lower punch.

Claims (1)

[Claims] 1. Manganese dioxide, a conductive agent, and a binder that have been heat-treated in advance are prepared using a mold that includes an outer mold having a cylindrical cavity and an upper punch and a lower punch that can move up and down within the cavity. In the production of a molded mixture with a wire mesh for organic electrolyte batteries, in which a positive electrode mixture consisting of a compound and a wire mesh are integrally pressure-molded, a granular or powdered positive electrode mixture is placed in the space formed by the outer mold and the lower punch. After putting the agent and a wire mesh so that the wire mesh is positioned above or below the positive electrode mixture and press-molding, the molded mixture with the wire mesh is sandwiched between the upper punch and the lower punch and is removed from the outer mold. A method for producing a molding mixture with a wire mesh for an organic electrolyte battery, which is characterized in that it can be taken out. 2 Fill the space formed by the outer mold and the lower punch with a granular or powdered positive electrode mixture, lower the upper punch to pressurize the positive electrode mixture to preform, and then press the upper punch. 2. The manufacturing method according to claim 1, wherein the punch is lifted up, a wire mesh is placed over the preform, and the upper punch is lowered again to apply pressure and perform main forming.