Electrolytes for Low Temperature Operations of Li-Ion Batteries

The factors that limit the low temperature performance of Li- ion batteries were examined using an impedance analysis technique. The charge transfer resistance, Rct, obtained by this technique was increased with decreasing temperature following an Arrhenius relationship and it was the predominant resistance at low temperatures. The limiting step in the charge transfer process was discussed by comparing the activation energy of the charge transfer process and the activation energy obtained at a model interface designed by Abe et al. We also explored some electrolyte systems containing ester/carbonate solvent mixtures and/or LiBF4 salt. Lower Rct and activation energy were obtained for MCMB electrode in these electrolytes. Improved low temperature cell performance was also obtained for cells using these electrolytes.