Synthesis and characterization of novel urethane cross-linked ormolytes for solid-state lithium batteries

A novel family of Li+-based organic/inoganic materials obtained by the sol- gel process is proposed. The compounds, named urethanesils, are obtained as thin, transparent, elastomeric and amorphous monolithic films. They incorp orate solvating pendant methyl end-capped short poly(oxyethylene) chains wh ich are covalently bonded to the silica backbone by means of urethane cross -links. The urethane linkages are formed by reacting 3-isocyanatepropyltrie thoxysilane with hepta(ethylene glycol) methyl ether (HEGME). Li+ has been introduced in the urethanesils as lithium triflate (LiCF3SO3). Two composit ions of salt have been considered: n = 100 and 8, where n represents the mo lar ratio of (OCH2CH2) units per lithium ion. infrared spectroscopy provide s conclusive evidence that, although the oligopolyether chains of HEGME bec ome less disordered upon formation of the inorganic network, the addition o f salt induces disorder. The FTIR spectrum of the most concentrated urethan esil strongly suggests that the triflate ions are essentially coordinated i n the material. The thermal and mechanical properties of the undoped and do ped urethanesils have been investigated by DSC and DMTA. At 90 degrees C, t he highest ionic conductivity (approximately 10(-6) Ohm(-1) cm(-1)) is obse rved for composition n = 8. The electrochemical stability domain of the lea st concentrated urethanesil spans 5 V. (C) 1999 Published by Elsevier Scien ce B.V. All rights reserved.