Improving the Performance of Lithium Ion Batteries at Low Temperature

The ability for Li-ion batteries to operate at low temperatures is extremely critical for the development of energy storage for electric and hybrid electric vehicle technologies. Currently, Li-ion cells have limited success in operating at temperature below –10 deg C. Electrolyte conductivity at low temperature is not the main cause of the poor performance of Li-ion cells. Rather the formation of a tight interfacial film between the electrolyte and the electrodes has often been an issue that resulted in a progressive capacity fading and limited discharge rate capability. The objective of our Phase I work is to develop novel electrolytes that can form low interfacial resistance solid electrolyte interface (SEI) films on carbon anodes and metal oxide cathodes. From the results of our Phase I work, we found that the interfacial impedance of Fluoro Ethylene Carbonate (FEC) electrolyte at the low temperature of –20degC is astonishingly low, compared to the baseline 1.2M LiPFEMC:EC:PC:DMC (10:20:10:60) electrolyte. We found that electrolyte formulations with fluorinated carbonate co-solvent have excellent film forming properties and better de-solvation characteristics to decrease the interfacial SEI film resistance and facilitate the Li-ion diffusion across the SEI film. The very overwhelming low interfacial impedance for FEC electrolytes will translate into Li-ion cells with much higher power for cold cranking and high Regen/charge at the low temperature. Further, since the SEI film resistance is low, Li interaction kinetics into the electrode will remain very fast and thus Li plating during Regen/charge period be will less likely to happen.