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 Cu²⁺ and Ca²⁺ into the transition metal (TM) and alkali metal (AM) layers, respectively. The introduction of Cu²⁺ 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, Ca²⁺ 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.