Stabilizing the Layer-Structured Oxide Cathode by Modulating the Oxygen Redox Activity for Sodium Ion Batteries

The layer-structured oxide cathode for sodium-ion batteries has attracted a widespread attention due to the unique redox properties and the anionic redox activity providing additional capacity. Nevertheless, such excessive oxygen redox reactions will lead to irreversible oxygen release, resulting in a rapid deterioration of the cycling stability. Herein, sulfur ion is successfully introduced to the O3-NaNi_0.3Mn_0.5Cu_0.1Ti_0.05W_0.05O₂ material through high-temperature quenching, thereby developing a novel Na₂S-modified O3/P2-NaNi_0.3Mn_0.5Cu_0.1Ti_0.05W_0.05O₂ composite with extended cycling life. The S^2- is analyzed for the ability to enhance the reversibility of oxidation-reduction reactions under high voltage and suppress the loss of lattice oxygen during cycling. The stable S─O covalent bonds are found to inhibit the oxygen generation and release within the structure. Benefiting from these improvements, the Na₂S-modified O3/P2-NaNi_0.3Mn_0.5Cu_0.1Ti_0.05W_0.05O₂ exhibited a high reversible capacity of 173.1 mA h g^-1 over a wide voltage range of 1.5-4.3 V under test conditions at 0.1 C and 81.5% capacity retention after 120 cycles at 1 C. The Na₂S-modified O3/P2-NaNi_0.3Mn_0.5Cu_0.1Ti_0.05W_0.05O₂ demonstrates the excellent rate capability with the reversible capacities of 173.1,137.0,114.7,96.7, and 80.1 mA h g^-1 at 0.1, 0.2, 0.5, 1, and 2 C.