High‐Entropy Modulation on Na‐O Configuration Toward Ultrastable Sodium Layered Oxide

Abstract Although O3‐type layered oxides are promising candidates as cathode materials in sodium‐ion batteries (SIBs), it is still plagued by poor stabilities owing to the inevitable degradation of Na‐O bond and subsequent side reactions as exposed to moist atmosphere. Here, a new O3‐type high‐entropy layered oxide NaMn _0.4 Fe _0.3 Ni _0.2 M _0.1 O ₂ (HE‐NaMFN, M = Cu/Ti/Zn/Sn/Sb) is developed by high‐entropy modulation on NaMn _0.5 Fe _0.3 Ni _0.2 O ₂ . This process involves the implantation of five metal atoms with different d ‐orbital electron numbers into the layered oxide, increasing the energy gap between O 2 p and metal d orbitals (Δ p ‐ d ) from 0.8 to 1.0 eV, associated with the reduced hybridization between O and the metal atoms for the resultant high‐entropy layered oxide. Benefited from the weakened metal‐O interaction, the high‐entropy layered oxide has suppressed Na‐O configuration with an enhanced binding energy, showing ultrastable feature after air exposure for up to 30 days. Consequently, the resultant layered oxide discloses improved structure reversibility, achieving a reversible capacity of 156 mAh g ⁻¹ with a capacity retention of 90%, good rate capability and long‐term cycling stability for sodium storage.