Improving High‐Voltage Performance of a LiNi0.5Co0.2Mn0.3O2 Cathode with Triallyl Phosphite as an Electrolyte Additive

Abstract Triallyl phosphite (TAPi) is studied as an electrolyte additive for high‐voltage LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathodes. Theoretical calculations combined with linear sweep voltammetry (LSV) tests demonstrate that TAPi tends to be preferentially oxidized and suppresses the decomposition of traditional carbonate‐based electrolytes. In addition, the hydrolysis of LiPF 6 salt in the electrolyte is investigated by 19 F nuclear magnetic resonance spectra, which prove that TAPi inhibits the decomposition of LiPF 6 . The results of charge/discharge measurements show that TAPi is effective to improve the capacity retention of LiNi 0.5 Co 0.2 Mn 0.3 O 2 /Li half‐cell and LiNi 0.5 Co 0.2 Mn 0.3 O 2 /graphite full‐cell. The mechanism of TAPi is studied by a series of physical characterizations, the results indicate that TAPi forms a protective interphase film on the cathode surface after cycling. The TAPi‐derived film protects the cathode structure from destruction to improve the electrochemical performance of the LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode at high voltage.