Liquid containing polymer networks as solid electrolytes

#The present invention relates to a polymer network containing ion conductive liquids for use as an electrolyte in solid state electrochemical cells.

#Presently, solid state electrochemical cells are the subject of intense investigation and development. These cells are described extensively in the patent literature. See, for example, U.S. Pat. Nos. 4,303,748 to Armand et al (1981); 4,589,197 to North (1986); and 4,547,440 to Hooper et al (1985). These cells are characterized by an electrolyte which is a solid solution of an ionic compound dissolved within a plastic macromolecular material.

#One problem which research efforts have attempted to overcome in the design of solid state cells is the poor conductivity of polymeric electrolytes at room temperature and below. In many cases, the cells which have been designed to date are used at elevated temperatures due to the low conductivity of the electrolyte at ambient temperatures.

#The invention is illustrated in more detail by the following non-limiting examples.

#In a three-necked flask 10 g of poly(ethylene oxide) of M.W. 600,000 in 200 ml benzene containing 0.6 g poly(ethylene glycol) diacrylate (M.W. 302) and 100 mg 2,2'-azobis(2-methylpropionitrile) was purged with nitrogen gas, and the mixture was stirred and heated to 60 C. and kept there for 6 hours under a nitrogen atmosphere. The flask was then stoppered and allowed to drift to room temperature and left overnight. The viscous solution was poured into moulds and the benzene evaporated under ambient conditions to make films ready to absorb Li salt solutions in aprotic dipolar solvents. The above viscous solution (10 g) was mixed with 0.5 g poly(ethylene glycol) 400-dimethyl ether. This mixture was poured into molds at ambient conditions. A whitish polymer film consisting of 50% (weight) matrix and 50% PEG-dimethyl ether (liquid) resulted.

#In another example 20 g matrix solution was mixed with 0.390 g lithium trifluoromethane sulfonate in 1.0 g poly(ethylene glycol) 400-dimethylether. To ensure lithium salt solution 10 ml of methanol was added. This clear solution formed whitish polymer films under ambient conditions. The films were hygroscopic and turned clear and viscous (sticky) after prolonged exposure to ambient air. They returned to white solid in a desiccator under reduced pressure.