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

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 NaMn0.4Fe0.3Ni0.2M0.1O2 (HE-NaMFN, M = Cu/Ti/Zn/Sn/Sb) is developed by high-entropy modulation on NaMn0.5Fe0.3Ni0.2O2. 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 2p and metal d orbitals (Δp-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.