Structural Modulation for Ultrastable O3‐Type Layered Oxide Cathode Material of Sodium‐Ion Batteries

The O3‐type layered oxide has attracted significant attention as cathode materials for sodium‐ion batteries, yet their performance is hindered by complex phase transitions and sluggish Na⁺ diffusion kinetics. Herein, we report an innovative medium‐entropy O3‐Na 0.85 Mn 0.45 Ni 0.25 Li 0.05 Cu 0.1 Ti 0.15 O 2 (O3‐NMNLCTO) cathode derived from P2‐Na 0.85 Mn 0.7 Ni 0.3 O 2 is presented, which incorporates of P‐type characteristics, notably a large Na interlayer distance of 3.29 Å. By incorporating P‐type characteristics into the O3 framework with multi‐element doping strategy, the O3‐NMNLCTO achieves a rapid O3‐P3 phase transition in the low‐voltage region and induces a P3 + P3' solid‐solution transformation. As a result, the tailored O3‐NMNLCTO cathode delivers a discharge capacity of 135.6 mAh g −1 at 10 mA g −1 , and outstanding cycling stability (91.8% retention after 1500 cycles at 1 A g −1 ), and superior rate capability (77.2 mAh g −1 at 2 A g −1 ). Furthermore, a full cell assembled with O3‐NMNLCTO cathode and hard carbon anode exhibits an energy density of 286.5 Wh kg −1 and a power density of 2491.1 W kg −1 (based on the mass of cathode material) at 800 mA g −1 . Experimental investigations and theoretical calculations are systematically performed to elucidate the origin of the superior electrochemical performance of O3‐NMNLCTO cathode. This work advances the design principles for stable O3‐type layered cathodes for sodium‐ion batteries.