Intercalation‐Induced Localized Conversion Reaction in h‐CuSe for Ultrafast‐Rechargeable and Long‐Cycling Sodium Metal Battery

Abstract Cathode materials of sodium‐based batteries with high specific capacity and fast charge–discharge mode, as well as ultralong reversible cycles at wide applied temperatures, are essential for future development of advanced energy storage system. Developing transition metal selenides with intercalation features provides a new strategy for realizing the above cathode materials. Herein, this work reports a storage mechanism of sodium ion in hexagonal CuSe (h‐CuSe) based on the density functional theory (DFT) guidance. This work reveals that the two‐dimensional ion intercalation triggers localized redox reaction in the h‐CuSe bulk phase, termed intercalation‐induced localized conversion (ILC) mechanism, to stabilize the sodium storage structure by forming localized Cu₇Se₄ transition phase and adjusting the near‐edge coordination state of the Cu sites to achieve high reversible capacity and ultra‐long cycling life, while allowing rapid charge–discharge cycling over a wide temperature range.