Improving the electrochemical performance of high voltage spinel cathode at elevated temperature by a novel electrolyte additive

•AMSL is proposed as a novel electrolyte additive for high voltage spinel cathode.•The cycling performance of LiNi0.5Mn1.5O4 is dramatically improved by using AMSL.•A less resistive and high thermal stable SEI film is formed on the cathode surface.•The AMSL derived SEI film is essential to suppress the electrolyte decomposition.

In this work, we report a novel electrolyte additive allyloxytrimethylsilane (AMSL) to improve the electrochemical performance of high voltage LiNi0.5Mn1.5O4 cathode. In presence of 0.5% AMSL, the discharge capacity retention of Li/LiNi0.5Mn1.5O4 cell is improved from 73.1% to 80.2% after 500 cycles at room temperature, and from 52.4% to 92.5% after 100 cycles at 55 °C. Moreover, the Li/LiNi0.5Mn1.5O4 cell with AMSL delivers a superior discharge capacity of 95.6 mAh g−1 at high rate of 3 C, whereas the cell without AMSL only remains 76.8 mAh g−1. Theoretical calculation and experimental results reveal that AMSL is oxidized prior to the carbonate solvents during the first charge process and then creates a less resistive and high thermal stable SEI film on the surface of LiNi0.5Mn1.5O4 cathode. The AMSL derived SEI film, composed of organic silicon-based species, ether moieties and reduced LiF, is responsible for the suppression of serious electrolyte decomposition and dissolution of transition metal ions at high voltage, especially at high temperature.