Stabilizing Layered LiCoO 2 Cathode in Aqueous Electrolytes through a Surface‐to‐Bulk Niobium Modification

LiCoO 2 is promising for aqueous lithium‐ion batteries due to its simple production processes and high energy density. However, LiCoO 2 exhibits poor cycle life in aqueous electrolytes, primarily attributed to H + intercalation, interfacial reactions, and irreversible phase transformation, which substantially impedes its practical application. Herein, an integrated surface‐to‐bulk Nb modification strategy combining LiNbO 3 surface coating and gradient Nb doping (N‐LCO@LNO) is proposed to enhance the cycling stability of LiCoO 2 . The LiNbO 3 surface coating serves as a physical barrier to suppress side reactions, while the gradient Nb doping stabilizes the bulk structure and inhibits spinel phase transition. Density functional theory calculations further reveal that this synergistic modification strategy can significantly suppress the structural degradation induced by electrophilic attack of H + . As a result, the N‐LCO@LNO electrode delivers a high‐rate capability of 117.1 mAh g −1 at 4 C and a long‐life stability with 71.4% capacity retention after 100 cycles at 0.5 C, far outperforming the unmodified LiCoO 2 electrode with only 11.1% capacity retention. This study presents a highly promising modification strategy that facilitates the effective utilization of LiCoO 2 in aqueous electrolytes.