Synergetic anion-cation co-doping in Na0.44MnO2 boosting a high-stability and improved-kinetics cathode for sodium ion battery

Tunnel-type manganese-based oxide cathodes of sodium-ion batteries have attracted enormous attentions due to their advantages of low cost, good endurance to the ambient air and superior cycling stability. However, they still suffer from successive phase transitions and sluggish kinetics, which hampers their further practical applications. Herein, we introduce Cu2+ and F− into the typical tunnel material Na0.44MnO2 to improve the abovementioned shortages for the first time. As a result, the ultra-stable cycling performance (capacity retentions of 98.9% after 150 cycles at 120 mA/g and 98.0% after 200 cycles at 360 mA/g) and enhanced Na+ diffusion rate can be achieved thanks to the synergistic effect of anion-cation co-doping. More importantly, with the aid of experiments and theoretical calculations, we unequivocally shed light on the role of Cu2+ and F−, respectively. Besides, the underlying practical value of the optimal case is assessed in the full cell. This work provides a universal perspective for designing oxide cathodes with respectable performance, and paves a new way to promote the practical applications of SIBs.