LiBOB as salt for lithium-ion batteries. A possible solution for high temperature operation

A new lithium salt based on a chelated borate anion, BOB [bis(oxalato)borate] is evaluated as the electrolyte solute for lithium-ion cells by both electrochemical means and cell testing. Controlled potential coulometry study reveals that the anion can stabilize aluminum substrate to more positive potentials than the popular hexafluorophosphate (PF₆^-) anion does, while slow scan cyclic voltammograms show good compatibility of the salt with graphitizable carbonaceous anode as well as satisfactory stability against charged cathode surface. The lithium-ion cells containing this salt as electrolyte solute exhibit excellent capacity utilization, capacity retention as well as rate capability at room temperature. Probably due to the fact that the new anion contains no labile fluorine and is thermally stable, electrolyte solutions based on it demonstrate stable performance in cells even at 60°C, where LiPF₆-based electrolytes would usually fail. The preliminary results reported herein provide a possible solution to the instability of the Li-ion cell performance at the elevated temperatures anticipated for heavy duty applications such as electric or hybrid electric vehicle missions.