A new synthesis route of high-performance P′2-Na0.67Fe0.1Mn0.9O2-δ and its sodium storage properties for sodium-ion batteries

The P2-Na0.67Fe0.1Mn0.9O2 materials with P63/mmc space group structure is a promising cathode material for sodium-ion batteries due to its low cost and high capacity. However, the occurrence of various phase transitions reduces the cycle reversibility of the compound. In this study, P′2-Na0.67Fe0.1Mn0.9O2-δ with Cmcm space group structure is synthesized by regulating oxygen vacancies content for the first time. The effect of oxygen vacancies on the structural evolution of the material during charge-discharge processes is further investigated by in-situ X-ray diffraction (XRD) techniques. Compared to P2-Na0.67Fe0.1Mn0.9O1.98, P′2-Na0.67Fe0.1Mn0.9O2-δ experiences smaller Jahn-Teller distortion when intercalating and deintercalting Na+. Meanwhile, it exhibits better electrochemical performance. The initial discharge capacity reaches 200 mAh g−1 at a current density of 20 mA g−1 with the capacity retention of 70.8% after 200 cycles at the current density of 400 mA g−1.