An electrolyte additive for the improved high voltage performance of LiNi0.5Mn1.5O4 (LNMO) cathodes in Li-ion batteries

High-voltage cathode materials are important for the implementation of high-energy-density Li-ion batteries. However, with increasing cut-off voltages, interfacial instabilities between electrodes and the electrolyte limit their commercial development. This study addresses this issue by proposing a new electrolyte additive, (3-aminopropyl)triethoxysilane (APTS). APTS stabilises the interface between the LiNi0.5Mn1.5O4 (LNMO) cathode and the electrolyte in LNMO||Li half-cells due to its multifunctional character. The amino groups in APTS facilitate the formation of a robust protective cathode layer. Its silane groups improve layer stability by neutralising the electrolyte's detrimental hydrogen fluoride and water. Electrochemical measurements reveal that the addition of 0.5 wt% APTS significantly improves the long-term cycling stability of LNMO||Li half-cells at room temperature and 55 degrees C. APTS-addition to the electrolyte delivers excellent capacity retention of 92% after 350 cycles at room temperature and 71% after 300 cycles at 55 degrees C (1C) contrasting with the much lower performances of the additive-free electrolyte. The addition of a 0.5 wt% (3-glycidyloxypropyl)trimethoxysilane (GLYMO) additive, which contains only the siloxane group, but lacks the amine group, displayed a capacity retention of 73% after 350 cycles at room temperature but degraded significantly upon cycling at 55 degrees C.