Inorganic-organic composite solid polymer electrolytes (CSPEs) have been prepared from the poly(ethylene oxide) (PEO)-like electrolytes of dir general formula polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP)-PEOn-LiX and Li+-conducting ceramic powders. In the PEG-like electrolytes, PVdF-HFP is the copolymer of PVdF and HFP, PEG, is a nonvolatile oligomeric polyethylene oxide of similar to 400 g/mol molecular weight, and LiX is lithium bis(trifluoroethylsulfonyl) imide. Two types of inorganic oxide ceramic powders were used: a highly Li+-conducting material of the composition 14 mol % Li2O-9Al(2)O(3-)38TiO(2)-39P(2)O(5), and the poorly Li+-conducting Li silicates Li4-xMxSiO4 where M is Ca or Mg and x is 0 or 0.05. The composite electrolytes can be prepared as thin membranes in which the Li+ conductivity and good mechanical strength of the Li+-conducting inorganic ceramics are complemented by the structural flexibility and high conductivity of organic polymer electrolytes. Excellent electrochemical and thermal stabilities have been demonstrated for the electrolyte films. Li//composite electrolyte//LiCoO2 rechargeable cells have been fabricated and cycled at room temperature and 50 degrees C.