Diurea cross-linked poly(oxyethylene)/siloxane ormolytes for lithium batteries

Poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with a wide concentration range of lithium triflate (LiCF3SO3) were investigated. The host matrix of these materials [d-U(2000)] is a sol-gel-derived siliceous framework to which POE chains with about 40.5 repeat units are bonded through urea linkages, Xerogels with infinity greater than or equal to n greater than or equal to 5 (n is the molar ratio OCH2CH2 /Li+) were obtained as amorphous monoliths thermally stable up to at least 340degreesC. A crystalline POE/LiCF3SO3 complex was detected spectroscopically in samples with n less than or equal to 10. Below 90degreesC the ormolyte with n = 20 exhibits the highest conductivity (5.8 x 10(-6) Omega(-1) cm(-1) at 26degreesC). The redox stability domain of this material spans 4.1 V. Although Fourier transform infrared spectroscopy data suggest that the Li+ ions are complexed by the POE ether oxygen atoms at n less than or equal to 10, this threshold composition is probably located at slightly lower salt content. "Free" triflate ions and weakly coordinated anions, present in all the samples examined, must be the main charge carriers of the d-U(2000)(20)LiCF3SO3 xerogel. Ion pairs (Li+CF3SO3-) or negatively charged triplets ([Li(CF3SO3)(2)](-)) are formed at n less than or equal to 40. At n less than or equal to 5 positively charged triplets [Li-2(CF3SO3)](+) also appear. Divalent positively charged multiplets [Li-3(CF3 SO3)](2+) occur at n = 1. (C) 2005 The Electrochemical Society. All rights reserved.