Electrolytes for low-temperature lithium batteries based on ternary mixtures of aliphatic carbonates

The low-temperature performance of lithium-ion cells in mainly limited by t he electrolyte solution, which not only determines the ionic mobility betwe en electrodes but also strongly affects the nature of surface films formed on the carbonaceous anode. The surface films provide kinetic stability to t he electrode (toward electrolyte) and permit charge (electron) transfer acr oss them, which in turn determine the cycle life and rate capability of lit hium-ion cells. Aiming at enhancing low-temperature cell performance, we ha ve studied electrolyte solutions based on different ratios of alkyl carbona te solvent mixtures, i.e., ethylene carbonate (EC), dimethyl carbonate (DMC ), and diethyl carbonate (DEC), in terms of electrolyte conductivity, film resistance, film stability, and kinetics of lithium intercalation and deint ercalation, at various temperatures. Electrolytes based on the ternary mixt ures of EC, DEC, and DMC emerged a preferred combination compared to the bi nary analogues both in terms of conductivity and surface film characteristi cs, especially at low temperatures. These studies are further corroborated in sealed AA cells, which showed a synergistic effect of high durability fr om the DMC-based solutions and improved low-temperature performance from th e DEC-based electrolytes. (C) 1999 The Electrochemical Society. S0013-4651( 98)06-021-2. All rights reserved.