The ionic conductivities of EC-based multi-component electrolytes in various solvent compositions were measured over a wide temperature range of +40 to -40 degreesC, and the factors affecting the low temperature conductivities of the electrolytes were discussed. It is revealed from the experimental results that the co-solvents with high dielectric constant and low viscosity can improve the ionic conductivity at room temperature, whereas, only the co-solvents which possess low melting points can effectively expand the operating temperature range of the electrolyte. The Li-ion batteries using the optimized electrolyte of 1 M LiPF6/EC-DMC-EMC (8.3:25:66.7) show the capacity retentions about 90.3% of their nominal capacities when discharged to 2.0 V at -40 degreesC at 0.1 C, demonstrating excellent low temperature performances. (C) 2004 Elsevier Ltd. All rights reserved.