High-rate performance O3-NaNi0.4Mn0.4Cu0.1Ti0.1O2 as a cathode for sodium ion batteries

A single phase O3-NaNi0.5-xMn0.5-xCuxTixO2 (x = 0 and 0.1) samples have been synthesized by a sol-gel method and the materials have been studies as cathode materials for sodium ion batteries. Compared with Cu/Ti-free sample, O3-NaNi0.4Mn0.4Cu0.1Ti0.1O2 exhibits a better electrochemical performance, including capacity, cycle performance and rate capability. This material delivers an initial discharge capacity of 116 mA h g−1 at 0.2 C within a voltage range of 2–4.0 V, and a capacity retention of 84% after 100 cycles. Even at 20 C, the capacity is also kept at 60 mA h g−1. The superior electrochemical properties of NaNi0.4Mn0.4Cu0.1Ti0.1O2, especially high-rate performance, can be attributed to the enlarged interslab distance and reversible phase evolution of O3-P3 upon Cu/Ti cosubstitution, which is confirmed by ex-situ XRD studies.