Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1990-10-19
1992-05-19
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429218, H01M 1040
Patent
active
051148099
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to all solid-state secondary batteries, and more particularly to all solid-state lithium secondary batteries comprising an oxide of layer structure serving as a positive electrode active substance and a polyphosphazene mixture as an electrolyte.
BACKGROUND ART
Secondary batteries presently in wide use include lead batteries and nickel-cadmium batteries wherein the single-cell voltage is about 2 V, and an aqueous solution is used. In recent years, efforts are made to investigate and develop secondary batteries of high energy density which give a high single-cell voltage of at least 3 V and include a negative electrode of lithium. However, when lithium is used which reacts with water or the like, aprotic electrolytes must be used since aqueous electrolytes are not usable. Although polar organic solvents are presently in wide use, a majority of these solvents have a low boiling point (high vapor pressure) are inflammable and therefore involve the likelihood of staining neighboring members and ignition or firing due to a leak or break and the hazard of explosion due to erroneous use of overcharging. Furthermore, repeated discharge and charge of the secondary battery as contemplated form dendrite on the negative electrode, entailing the problem of reduced discharge-charge efficiency and short-circuiting between the positive and negative electrodes. Accordingly, many reports are made on the development of techniques for improving the discharge-charge efficiency of the negative electrode and the cycle life by inhibiting dendrite. Proposed in these reports are, for example, use of a methylated cyclic ether solvent as the solvent for battery electrolytes (K. H. Abraham et al. in "Lithium Batteries," J. P. Gabano, editor, Academic Press, London (1983)), a method of forming an ionically conductive protective film at the Li interface by adding polyethylene glycol, polypropylene glycol, polyethylene oxide or like additive to an electrolyte system (Journal of Power Sources, Vol 12, No. 2, pp. 83-144 (1984) and Unexamined Japanese Patent Publication SHO 60-41773), a method of inhibiting Li dendrite by alloying an electrode per se with Al (Unexamined Japanese Patenmt Publication SHO 59-108281).
On the other hand, M. Armand and N. Duclot disclose a novel secondary battery of high energy density incorporating a thin-film polymer electrolyte in Laid-Open French Patent Publication No. 2442512 and European Patent No. 13199. Yao et al. (J. Inorg. Nucl. Chem., 1967, 29, 2453) and Farrington et al. (Science, 1979, 204, 1371) generally describe inorganic ionically conductive solids. These solids, which are powdery, must be pelletized by a high-pressure press for fabrication into batteries. This offers a great obstacle against productivity, uniformity, etc. The pelletized solid is hard and brittle, is therefore difficult to make into a thin film of increased area, and requires a great pressure when to be adhered to the active electrode substance, so that the procedure has problems in work efficiency and adhesion. Furthermore, the solid encounters difficulty in following and compensating for variations in the volume of electrode materials during the operation of the battery and has the hazard of breaking the electrolyte. Sequlir et al. (Extended Abstracts, 163rd Meeting Electrochemical Society, 1983, 83, 751, Abstract, No. 493) describe a battery of novel design including a solvent-free thin-film polymer electrolyte, stating that the electrolyte is usable at a medium temperature of about 100.degree. C. as determined by testing. However, the conductivity at room temperature is as low as 10.sup.-6 .about.10.sup.-7 S/cm and is insufficient.
P. M. Blonsky et al. (J. Am. Chem. Soc., 106, 6854, 1984) state that polyphosphazene (MEEP) is useful as an electrolyte for electrochemical batteries. However, they merely disclose data as to a.c. conductivity in the range of from 30.degree. C. to 97.degree. C. and have not effected discharge and charge with d.c.
Further Blonsky states in the thesis
REFERENCES:
patent: 4840856 (1989-06-01), Nakacho et al.
Inubushi Akiyoshi
Nakacho Yoshifumi
Tada Yuji
Kalafut Stephen
Otsuka Kagaku Kabushiki Kaisha
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