2-Methoxyethyl (methyl) carbonate-based electrolytes for Li-ion batteries

2-Methoxyethyl (methyl) carbonate (MOEMC) has been identified as a useful s olvent for rechargeable Li-ion batteries. The conductivity-temperature and viscosity-temperature data for Li salt solutions in MOEMC can be fitted to the Vogel-Tammann-Fulcher (VTF) equation. The electrolytes formulated in MO EMC are characterized by the appearance of glass-transition temperatures wi thout encountering freezing points, and this unique low-temperature behavio r has allowed us to experimentally determine their glass-transition tempera tures. This in turn has enabled us to experimentally demonstrate the applic ation of the VTF theory to explain the conductivity-temperature data of the se electrolytes. The results support a solvent-assisted ion conduction mech anism attributable to the strong interactions between the solvent molecules and Li ions. There appears to be no strong interaction between solvent mol ecules and the anions, but because of ion-pairing, the anion conduction is indirectly assisted by solvent fluctuations. Strong interactions between th e solvent and Li+ have been verified by nuclear magnetic resonance (NMR) an d infrared (IR) spectroscopic data. The electrolytes formulated in MOEMC ha ve been tested for their electrochemical stability and Li cycling performan ce of the graphite anode and the LiCoO2 cathode, thereby demonstrating thei r utility for Li-ion battery development. (C) 2000 Elsevier Science Ltd. Al l rights reserved.