COMPOSITE POLYMER ELECTROLYTES USING FUMED SILICA FILLERS - RHEOLOGY AND IONIC-CONDUCTIVITY

Composite polymer electrolytes prepared from fumed silica fillers, low molecular weight poly(ethylene glycols) and lithium perchlorate exhibit high room-temperature conductivities (> 10(-4) S/cm), processability and mechanical stability. Samples made using polyethylene glycols with and without methyl end-groups had the same level of conductivity (approximately 2 x 10(-4) S/cm). Dynamic rheological techniques, useful for probing material microstructure, showed that all samples behave as elastic networks with similar elastic moduli (G'); however, those with methyl end-groups were more sensitive to shear-induced microstructural breakdown. The decreased mechanical stability of composites prepared from glycols with methyl end-groups was interpreted in terms of polymer/particle/lithium salt interactions. Steady shear measurements showed all samples to be processable. The unique combination of elastic-like behavior and processability stems from the use of branched, three-dimensional fumed silica fillers that are capable of forming strong networks that can undergo shear but reforms after processing.