A phosphite derivative with stronger HF elimination ability as an additive for Li-rich based lithium-ion batteries at elevated temperatures†

Phosphite derivatives as film forming additives can effectively improve the electrochemical performance of cathodes in Li-ion batteries (LIBs). In this work, ethyl bis(trimethylsilyl) phosphite (TMSPE), which contains trimethylsilyl and ethyl functional groups, is used as a P-based additive for improving the electrochemical performance of a Li_1.144Ni_0.136Co_0.136Mn_0.544O₂ cathode. Further, the comparative evaluation of tris(trimethylsilyl) phosphite (TMSPi), TMSPE, and triethyl phosphite (TEP) as phosphite-based additives for Li_1.144Ni_0.136Co_0.136Mn_0.544O₂/Li cells at 45 °C under a high voltage is also presented. Theoretical calculations and surface characterization revealed that TMSPE formed a thinner and stable cathode electrolyte interphase (CEI) on the surface of Li_1.144Ni_0.136Co_0.136Mn_0.544O₂, which has lower interfacial impedance, stronger HF elimination, and transition metal dissolution inhibition, resulting in the best cell performance among the three phosphite-based additives.