Nonflammable Sulfone-Based Electrolytes with Mechanically and Thermally Stable Interfaces Enabling LiNi_0.5Mn_1.5O₄ to Operate at High Temperature

The development of high-energy 5 V-class LiNi_0.5Mn_1.5O₄ batteries is severely limited by the instability of the cathode electrolyte interphase (CEI) at high temperature. Herein, we propose a nonflammable sulfone (SL)-based fluorinated hybrid electrolyte to form stable, uniform, and thin CEI layers, enabling Li||LiNi_0.5Mn_1.5O₄ batteries to achieve elevated electrochemical performance at 60 °C. The formed highly stable inorganic-dominated CEI, comprising Li_xSO_y, Li_xBO_y, and LiF inorganic compositions, exhibits good thermal stability and mechanical strength. Moreover, the robust CEI layer effectively shields the LNMO particles from undesirable side-reactions and stabilizes the interface within the LiNi_0.5Mn_1.5O₄ cathode during high-temperature cycling. In contrast to the conventional electrolyte, the Li||LiNi_0.5Mn_1.5O₄ battery employing a nonflammable SL-based electrolyte exhibits a stable capacity retention of 88.5% after 100 cycles at 60 °C free from the risk of thermal runaway. This study reveals valuable insights into advanced electrolyte technology, paving the way for safer applications of Co-free high-energy batteries in the future.