Preparation and characterization of cross-linked composite polymer electrolytes

Cross-linkable composite electrolytes were prepared from poly(ethylene glycol) dimethyl ether (PEGDME)-500, LiClO4, fumed silica, and 10 wt % methyl, butyl, or octyl methacrylate. The silicas used were chemically modified by attaching methacrylate groups to the silica surface through Cs and Cs tethers. Before cross-linking, the electrolytes were thixotropic and had ionic conductivities of >2 x 10(-4) S/cm. After ultraviolet (UV)-induced cross-linking, the electrolytes were rubbery and dimensionally stable, and the conductivities were unchanged. Conductivity, extraction, and thermal analysis data all support a model where the added methacrylate monomer and growing polymer chains phase separate from the electrolyte phase during photopolymerization to yield a methacrylate-rich silica/polymer phase and little or no polymer in the PEGDME-500 phase. Thus, the mechanical properties of the composite electrolyte and its ionic conductivity are decoupled and can be optimized independently.