Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Patent
1993-06-08
1995-08-22
Maples, John S.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
2521821, 429218, H01M 462
Patent
active
054439272
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a cathode composite for use in a primary battery and a secondary battery.
BACKGROUND ART
As a lithium battery, for example, there are primary and secondary batteries, in which a chalcogen compound is used for a positive active material and metallic lithium is used for an anode. This type of battery has generally been composed of a cathode including a cathode composite, an anode including metallic lithium (forming the negative active material), and a separator. This type of battery has been formed by laying the cathode on the anode through the separator and by housing this laminate in a battery can or filling its peripheral edge with a sealing agent. Particles of positive active material, particles of carbon (such as carbon black) forming a conductive agent, polytetrafluoroethylene or solid polymer electrolyte (serving as a binder) and an organic solvent (serving as a diluent) are mixed and formed into a paste and either filled in or applied onto a substrate such as a stainless steel net or stainless steel plate, thus forming the cathode composite. The anode is formed by sticking a metallic lithium sheet onto the stainless steel plate or composed of the metallic lithium sheet alone.
However, the cathode composite has the following problems. When mixing the above materials to form a paste, the positive active material and the conductive agent cohere so as to worsen the wetting of them with the binder and organic solvent. For this reason, uniform mixing and uniform application on the substrate has been difficult, and additionally a surface of the prepared cathode composite is not uniform forming a corrugated shape. Therefore, the positive active material, the conductive agent and the binder are not dispersed uniformly in the above-mentioned cathode composite, so that the cathode composite sometimes cracks or peels off from the substrate. In addition, the initial capacity has been small as compared with the theoretical capacity in the primary battery using the above cathode composite, and the capacity is lowered to a value smaller than a half the initial capacity at 100 cycles in the secondary battery. Further, in the battery using the above cathode composite, convex surface portions have sometimes broken through the separator to reach the anode causing a short- circuiting.
This invention is made in order to solve the foregoing problems. An object of this invention is to provide a cathode composite, in which cracking, peeling-off from a substrate and short-circuiting can be prevented. Additionally with the invention a good discharge characteristic can be exercised when used in either a primary or secondary battery.
DISCLOSURE OF THE INVENTION
The cathode composite of this invention includes a compound with heteroatoms in its molecular structure which will become a polar molecule, and function as a dispersant.
Atoms of nitrogen, oxygen, phosphorus, sulfur and boron etc. may be mentioned as the heteroatom. When these heteroatoms are combined in an end portion, for example, of the molecular structure, a bias will be produced in the entire electron cloud in the above compound so that this compound will become the polar molecule.
The function as a dispersant means a function for preventing particles of solid from cohering or precipitating in liquid.
In this invention, the compound is adsorbed to surfaces of the positive active material and the conductive agent and sterically stabilized, so as to prevent the positive active material and the conductive agent from cohering and also improve wetting of the positive active material and the conductive agent to the organic solvent and the binder. For this reason, the positive active material, the conductive agent and the binder are dispersed uniformly so that these can be mixed uniformly and applied on the substrate evenly. In addition, a cathode composite having a uniform and non-corrugated surface can be obtained. Accordingly, the cracking, the peeling-off from the substrate and the short-circuiting can be prevented. Furth
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Fukutome Hiroyuki
Imachi Hiroshi
Izuchi Syuichi
Nakajima Yasumasa
Maples John S.
Yuasa Corporation
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