High‐Entropy Configuration Regulating Interlayer Oxygen Charge Toward High‐Voltage and Air‐Stability Layered Cathode in High‐Loading Sodium Ion Full Batteries

Abstract Revealing interlayer oxygen charge is of great significance in understanding the high‐voltage and air stability of sodium layered cathodes, but it currently lacks attention. Particularly, the stability of sodium ion full batteries under high cathode loading (≥8 mg cm −2 ) also faces extremely challenges. Here, the interlayer oxygen charge and its mechanism for high‐voltage and air stability are revealed in a high‐entropy O3‐Na 0.85 Li 0.1 Al 0.02 Sn 0.08 Cu 0.1 Ti 0.1 Ni 0.3 Mn 0.3 O 2 (HEO) cathode, which enables robust high‐cathode‐loading sodium‐ion full batteries. The high‐entropy doping effectively maintains the transition metal (TM)─O bond covalency, stabilizing interlayer oxygen charge. The stable O─O repulsion avoids structural collapse, realizing the P3‐OP2‐P3 reversible phase transition. Moreover, reduced interlayer oxygen charge achieves the Na layer contraction and the Na─O bond enhancement. These features inhibit the attack of water and Na loss, realizing well air stability. Therefore, the HEO cathode exhibits a good stability up to 900 cycles under 2.0‒4.3 V and a high‐capacity retention of 96.12% after 5 day air exposure. The pouch full cell with ≈16 mg cm −2 cathode loading exhibits ≈60 mAh and lasts for 100 cycles. This work contributes the new insights into both high‐voltage and air stability of layered cathodes for practical sodium ion full batteries.