Boosting the high voltage performance of spinel LiNi _0.5 Mn _1.5 O ₄ cathode through an all-fluorinated electrolyte

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising high-voltage cathode material for the next generation lithium metal batteries because of its high operating voltage plateau (4.7 V vs. Li⁺/Li), high theoretical specific capacity (147 mAh/g), relatively low cost and environmentally benign properties. Despite promising, the commercialization of LNMO cathodes is hindered by its electrochemical instability using conventional carbonate electrolytes, resulting in lower Coulombic efficiency and poor cycling stability. Herein, we adopt an all-fluorinated electrolyte (AFE) with a wide electrochemical stability window for Li//LNMO cells. Compared to conventional carbonate electrolytes, AFE significantly improves the discharge capacity and rate performance of Li//LNMO cells at various cut-off voltages and temperatures, attributed to the formation of a robust cathode-electrolyte interphase (CEI) layer. Specifically, the resultant Li//AFE//LNMO cells deliver a discharge capacity of 131.7 mAh/g with 84.1% capacity retention after 250 cycles at a charge cut-off voltage of 4.9 V, while it sustains only 114.8 mAh/g with 81.9% capacity retention for the cell using a conventional carbonate electrolyte. The influence of charge/discharge rate and temperature on the performance is also evaluated. Overall, this study presents a facile approach to promote the commercialization of high-voltage LNMO cathodes.