Enhanced Na-storage properties of O3-type NaNi0.5Mn0.5O2 cathodes by doping and coating dual-modification strategy

Due to their high theoretical specific capacities and good structural compatibility, O3-layered oxides are considered as high-performance cathode candidates for sodium-ion batteries. However, serious side reactions and structural degradation during long-term cycling have greatly hindered their practical applications. Herein, O3-type NaNi0.5Mn0.5O2 (NNMO) was prepared by partially substituting Ni2+ with Cu2+ and inducing CuO surface coating to enhance the structural stability without sacrificing the high capacity. In Particular, Cu2+ incorporated at a molar ratio of 0.10 greatly improved the electrochemical performance of pristine NNMO. The NaMn0.5Ni0.4Cu0.1O2 electrode exhibited a capacity retention of 64.5% after 300 cycles at 0.5 C. Microscopic and spectral studies revealed that the CuO coating layer suppressed detrimental side reactions upon cycling. Moreover, the bulk doping of Cu2+ ultimately enhanced the structural stability by mitigating irreversible phase transitions. Hence, the integration of bulk Cu2+ doping and CuO surface coating contributed to the increased structural stability and electrochemical performance of NNMO. The doping and coating dual-modification strategy established in this work effectively suppressed the side reactions and structural degradation of NNMO, and this work provides new insight into the effective design of electrode microstructures for use in high-performance batteries.