Tris(trimethylsily)-Based Additives Enables Practical 5 V LiNi_0.5Mn_1.5O₄ Batteries

LiNi0.5Mn1.5O4 cathode materials have been considered promising candidates for high energy density Li-ion batteries due to their high operation potential. However, to develop 5 V LiNi0.5Mn1.5O4-based batteries, practical electrolytes with high electrochemical stability are yet to be realized. In this work, tris(trimethylsilyl)-based additives, including tris(trimethylsily)borate (TMSB) and tris(trimethylsilyl)phosphite (TMSPi), were selected as electrolyte additives for typical ethylene carbonate (EC)-LiPF6 based electrolyte to develop practical LiNi0.5Mn1.5O4-based batteries. Combining theoretical calculations, physicochemical characterization, and electrochemical measurements, we found that both TMSB and TMSPi can improve the Coulombic efficiency and cycling stability of 5 V LiNi0.5Mn0.5O4-based cells. Specifically, TMSB can act as the stabilizer for PF6- due to its electron deficiency nature, thereby suppressing the increase of cell impedance. In addition, thanks to its high highest occupied molecule orbital (HOMO) energy level. TMSPi can be preferentially oxidized on the surface of charged LiNi0.5Mn1.5O4 electrodes, resulting in a decent rate capacity and high discharge platform. In addition, TMSPi is conducive to the formation of robust solid electrolyte interphase (SEI) on graphite anode through the nucleophilic attack, resulting in enhanced cycle performance. As a result, Graphite parallel to LiNi0.5Mn1.5O4 pouch cells with TMSPi-containing electrolyte displayed capacity retention of 88.9% after 100 cycles at 1C, superior to that in the blank (60.5%) and TMSB-containing (77.4%) electrolytes.