Trimethyl borate and triphenyl borate as electrolyte additives for LiFePO4 cathode with enhanced high temperature performance

Abstract

Alkyl- and phenyl-substituted borate anion receptors, triphenyl borate (TPB) and trimethyl borate (TMB), are investigated as electrolyte additives in lithium ion batteries (LiFePO4 cathode, 1 M LiPF6 EC-DMC 1:1 electrolyte) at 25 and 60 °C. TPB shows formation of a thick surface/electrolyte interface (SEI) which hampers ion flow and does not protect the electrode from degradation. Although useful at 25 °C, TPB at 60 °C results in only 7% capacity after 100 cycles, whereas 0.1 M TMB results in 53% capacity. TMB performance improves with increasing concentration. TMB also suppresses thermal decomposition of the electrolyte and formation of the SEI film.