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 the electrolyte solution, which not only determines the ionic mobility between electrodes but also strongly affects the nature of surface films formed on the carbonaceous anode. The surface films provide kinetic stability to the electrode (toward electrolyte) and permit charge (electron) transfer across them, which in turn determine the cycle life and rate capability of lithium-ion cells. Aiming at enhancing low-temperature cell performance, we have studied electrolyte solutions based on different ratios of alkyl carbonate 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 deintercalation, at various temperatures. Electrolytes based on the ternary mixtures of EC, DEC, and DMC emerged a preferred combination compared to the binary analogues both in terms of conductivity and surface film characteristics, especially at low temperatures. These studies are further corroborated in sealed AA cells, which showed a synergistic effect of high durability from the DMC-based solutions and improved low-temperature performance from the DEC-based electrolytes. (C) 1999 The Electrochemical Society. S0013-4651(98)06-021-2. All rights reserved.