Li‐Ion Battery Electrolyte Formulated for Low‐Temperature Applications

Low‐temperature (<0°C) applications of Li‐ion batteries have prompted the search for improved, high‐conductivity electrolytes. Because the performance of the carbonaceous anode is highly sensitive to changes in electrolyte composition, we focused our efforts on this electrode. Electrolytes containing [lithium bis(trifluoromethanesulfonyl)imide], or LiIm, and [lithium tris(trifluoromethanesulfonyl)methide], or LiMe, in methyl formate (MF)‐ethylene carbonate (EC) solvent mixtures were tested in lithium‐graphite half‐cells. The graphite electrodes could be cycled at ambient temperature with high reversible capacity. The best supporting electrolyte was found to be , and the presence of a high concentration of ethylene carbonate and up to 300 ppm in the solution considerably increased the reversible capacity upon cycling. The conductivity values of a binary solvent mixture of methyl formate and ethylene carbonate containing or LiMe were measured between −40°C and room temperature. Graphite electrodes cycled at −2°C in these electrolytes obtained reasonable reversible capacity, approaching 50%.