Salt Anion's Donor Number Strategy Achieving Stable NCM622 Cathode at 4.7 V

Abstract The donor number (DN) has emerged as an important descriptor for optimizing lithium metal battery (LMB) performance, especially in regulating solvation structures and constructing high‐quality electrode/electrolyte interphases. However, high DN solvents can compromise the intrinsic high‐voltage stability (>5 V) of conventional electrolytes due to their limited electrochemical stability. In this study, a novel strategy is presented that utilizes the anion's DN for non‐destructive regulation of ionic liquids (IL) to achieve advanced electrolytes at 5.3 V. It is demonstrated that introducing high DN salt anions competes with EMIM + in EMIM‐TFSI, forming strong interactions with EMIM and enhancing the stability of the IL electrolyte. The expelled TFSI − ions tend to coordinate with Li + , facilitating the formation of high‐quality solid/cathode electrolyte interphases. Consequently, the Li//NCM622 cells with high DN salt anions (LiClO 4 ‐IL and LiOTF‐IL) show remarkable capacity retention rates of 93.5% and 94.6%, respectively, after 100 cycles over a voltage range of 2.8–4.7 V. Moreover, the Li//NCM622 cells using LiClO 4 ‐IL maintain a capacity retention of 81.6% and an average Coulombic efficiency of 99.4% after 350 cycles at 2.8–4.6 V. The proposed DN tuning mechanism is believed to offers new insights for designing high‐energy‐density LMBs.