Stabilizing Interfaces in High‐Temperature NCM811‐Li Batteries via Tuning Terminal Alkyl Chains of Ether Solvents

Abstract Ether electrolytes are promising for lithium metal batteries. Despite the intensive research in recent years, most state‐of‐the‐art ether electrolytes still cannot form reliable electrode‐electrolyte interfaces in NCM811‐Li batteries at diluted concentrations, especially in those operating at elevated temperatures. We report a simple but effective strategy to break this bottleneck and stabilize interfaces in high‐temperature NCM811‐Li batteries in ether electrolytes. We propose that by gradually extending the terminal groups of glycol diethers from methyl groups to n ‐butyl groups, the comprehensive stability of ether electrolytes is improved. An anion‐dominated solvation structure is realized at a concentration of 1 M. Accordingly, the electrode‐electrolyte interactions are suppressed, and a thinner, denser, and more inorganic‐rich solid‐ /cathode‐electrolyte interface is achieved. Additionally, the surface phase transition and structural degradation of NCM811 cathode are alleviated. Consequently, in the ethylene glycol dibutyl ether‐based electrolyte, the Coulombic efficiency for Li−Cu cells working at 60 °C is boosted to 99.41 % with a cycling life of over 200 cycles. The lifespan of high‐temperature NCM811‐Li cells is prolonged by more than 400 % with a stable average Coulombic efficiency of 99.77 % at quasi‐practical conditions of 50 μm Li, lean electrolyte of 10 μL mAh −1 , and medium‐high cathode loading of >2.2 mAh cm −2 .