A Synergistic Cu/Ca Dual‐Doping Strategy for High‐Stability and Fast‐Charging O3‐Type Cathode in Sodium‐Ion Batteries

The O3‐type layered oxide cathodes are highly promising for sodium‐ion batteries due to their high specific capacity. However, the sluggish kinetics and poor interlayer stability caused by narrow layer spacing and volumetric stress accumulation limit their fast‐charging and long‐cycle performance. Herein, targeted interlayer regulation is conducted on O3‐type layered oxide by introducing Cu 2+ and Ca 2+ into the transition metal (TM) and alkali metal (AM) layers, respectively. The introduction of Cu 2+ effectively enlarges sodium‐ion transport channels, mitigates oxygen arrangement around TM octahedra, and suppresses Na + /vacancy ordering, which is evidenced by scanning transmission electron microscopy and density functional theory calculations. Additionally, Ca 2+ in the AM layer effectively mitigates volume variation during electrochemical reactions and preserves structural integrity, as confirmed by in situ X‐ray diffraction, resulting in lower lattice stress and mitigated phase evolution. The result is an exceptionally high‐rate capability of 86.02 mAh g −1 at 10 C (2.4 A g −1 ), accompanied by a prolonged lifetime with 80.64% retention after 300 cycles. This work demonstrates synergistic regulation of ion transport and lattice stability, providing new insights for cathode design.