JPH01283764A - Lithium cell - Google Patents

Abstract

PURPOSE:To eliminate the trouble such as a crack of pellets or a cutting at the periphery of pellets by forming a positive electrode composite with a positive electrode active substance powder, a conductive minute powder, metallic short fibers, and a binder. CONSTITUTION:To a positive electrode active substance powder and a conductive carbon powder, metallic fibers of diameter 5-50mum and the length 1-5mm are mixed, and after that, a dispersion type binder is added to make a positive electrode composite. Since metallic short fibers with a good binding property are dispersed evenly in the positive electrode composite, the pellet strength in the processing and formation is improved, and a crack, a cutting, and the like can be reduced. Furthermore, the amount of the binder can be reduced up to about 1/2 the conventional amount, and the electrolyte absorption property of the pellets is improved. As a result, the discharge property of the cell using such positive electrode pellets is also improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a positive electrode mixture for a lithium battery, which is an organic electrolyte battery.

Conventional technology The positive electrode of an organic electrolyte battery is conventionally made by adding a dispersion-type binder to a mixed powder of positive electrode active material powder and conductive carbon powder and kneading the mixture.After drying and sizing this mixture, Previously, the positive electrode mixture pellets created in this way had to be mixed with a large amount of binder to obtain pellet strength. It becomes difficult to mold the pellets, and even if molding is possible, the lack of strength causes chips and cracks at the edges of the pellets due to impact during the transportation process during battery assembly.

In addition, in order to improve the pellet strength, adding a large amount of polytetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene (trade name: NEOFLON), etc., which has been commonly used in the past, will strengthen the pellet. However, there was a problem in that the electrolyte absorption properties of the pellets deteriorated and the discharge utilization rate of the positive electrode active material was poor.

Problems to be Solved by the Invention The present invention aims to solve the problem of the pellet strength of the positive electrode of an organic electrolyte battery without increasing the amount of binder.

Means for Solving the Problems In order to solve this problem, the present invention mixes metal fibers with a diameter of 6 to 60 μm and a length of 1 to 6 ff with positive electrode active material powder and conductive carbon powder, and then mixes them into a dice version. A binder was added to form a positive electrode mixture.

Function In the present invention, short metal fibers with good entanglement properties are uniformly dispersed in the positive electrode mixture, so that the pellet strength during pressure molding is improved and cracking, chipping, etc. can be extremely reduced.

In addition, this method allows the amount of binder to be reduced to about the same level as conventional methods, and as a result, the electrolyte absorption ability of the pellets improves.
It has become clear that the discharge characteristics of batteries using this positive electrode pellet are also improved.

Example The present invention will be explained in detail below.

To 1000 g of a mixed mixture of 97 parts by weight of calcined manganese dioxide powder and 3 parts by weight of Ketchen Black as a conductive carbonaceous powder, 50 g of short fibers of stainless steel 5us430, diameter 30 μm, length 3 decoys were added. Add 41 g of Disverge, a copolymer of propylene hexafluoride and ethylene tetrafluoride (Neoflon), and 460111 g of pure water, and stir and knead.

This wet mixture was dried with hot air at 120° C. to remove moisture, and then sized with a 32-mesh wire mesh to obtain a granular mixture.

This granular mixture was molded using a press molding machine with a weight of 0.35
A positive electrode for an organic electrolyte battery was obtained by pressure molding into a pellet with a diameter of 16 mm and a thickness of 0.72 mlK.

In the description of the above examples, short fibers of 8u8430 are shown, but short fibers of aluminum, titanium, 5uS444, etc. also produce the same effect as the examples of the present invention.

FIG. 1 shows a longitudinal cross-sectional view of the lithium manganese battery of the present invention, in which 1 is a positive electrode can made of stainless steel 5uS430, 2 is a sealing plate made of 5u1430, and 3 is a positive electrode 4 obtained in the example is a sealing plate. A lithium negative electrode is press-fixed to the inner surface of 2, a separator 6 is made of synthetic fiber non-woven fabric, and 6 is a polypropylene gasket, and the cathode can 1 and the sealing plate 2 are press-fitted and sealed via this gasket.This is an organic electrolyte battery. The electrolyte used was a mixture of propylene carbonate and dimethoxyethane in which lithium perchlorate was dissolved.

Table 1 shows the results of the pelletized positive electrode according to the present invention and the conventional method in which Neo 70-day version was used in a mixture of calcined manganese dioxide and Axica carbon in the same mixing amount as in the above example, and manufactured in the same process. Conventional pellet-shaped positive JfMB
This is a comparison of the number of defects per 1,000 pieces when press-molding the molded pellets and the number of cracks that started during the conveyance process of the assembly process after drying the molded pellets with hot air at 200'C for 12 hours. .

Table 1 and FIG. 2 compare the continuous discharge performance under a constant resistance load of 1xΩ of the same type of lithium manganese battery using the positive electrode according to the present invention and the conventional positive electrode B. As is clear from FIG. 2, the discharge performance using the positive electrode of the present invention is slightly better. This difference in discharge performance is thought to be due to the improved utilization of manganese dioxide due to the synergistic effect of the electrolyte absorption of the positive electrode and the formation of an electronic conductive network of the short metal fibers.

As described above, the positive electrode material powder, conductive carbon fine powder, short metal fibers, and neoflon dispersion are stirred and mixed, dried, and the sized mixture is pressure-molded to form a pellet-like positive electrode. By doing so, the strength of the mixture is increased, it is resistant to impact during the transportation process of assembly, and problems such as pellet cracking and chipping of the periphery are avoided, which is of great industrial value.

[Brief explanation of the drawing]

FIG. 1 shows a cathode provided with a positive electrode obtained according to the present invention. 1...Positive electrode can, 2...Sealing plate, 3...
... Positive electrode, 4... Negative i, s... Separator, 6... Gasket.

Claims (1)

[Claims] A lithium battery in which the positive electrode mixture is composed of positive active material powder, conductive fine powder, short metal fibers, and a binder.