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 incorporate solvating pendant methyl end-capped short poly(oxyethylene) chains which are covalently bonded to the silica backbone by means of urethane cross-links. The urethane linkages are formed by reacting 3-isocyanatepropyltriethoxysilane with hepta(ethylene glycol) methyl ether (HEGME). Li+ has been introduced in the urethanesils as lithium triflate (LiCF3SO3). Two compositions of salt have been considered: n = 100 and 8, where n represents the molar ratio of (OCH2CH2) units per lithium ion. infrared spectroscopy provides conclusive evidence that, although the oligopolyether chains of HEGME become less disordered upon formation of the inorganic network, the addition of salt induces disorder. The FTIR spectrum of the most concentrated urethanesil strongly suggests that the triflate ions are essentially coordinated in the material. The thermal and mechanical properties of the undoped and doped urethanesils have been investigated by DSC and DMTA. At 90 degrees C, the highest ionic conductivity (approximately 10(-6) Ohm(-1) cm(-1)) is observed for composition n = 8. The electrochemical stability domain of the least concentrated urethanesil spans 5 V. (C) 1999 Published by Elsevier Science B.V. All rights reserved.