Vitalization of P2–Na2/3Ni1/3Mn2/3O2 at high-voltage cyclability via combined structural modulation for sodium-ion batteries

© 2020 Elsevier B.V. P2-type Na2/3Ni1/3Mn2/3O2 (P2-NaNM) is a promising cathode material for practical applications in Na-ion batteries due to its high capacity. However, the rearrangement of Na+/vacancy order and cathodic charge order across the Na extraction/intercalation and structural rearrangements of P2-NaNM at high voltages result in rapid capacity fading and insufficient rate capability. Here, a combined structural modulation strategy was presented to solve these challenges via reducing the Na layers spacing through substituting Na sites by Mg ions while simultaneously stabilizing the transition metal (TM) layers through Mg/Ti co-doping. Benefited from the symbiotic effect, P2-NaNM exhibits a significantly enhanced cycling stability and rate capability in the voltage range of 3.0–4.4 V. We further revealed that Mn remains Mn4+ while Ni2+ becomes Ni3+ at the surface of Mg/Ti co-substituted P2-NaNM upon charge/discharge process