A phase-transition-free cathode for sodium-ion batteries with ultralong cycle life

The Sodium-ion-battery, using the layered oxide material as cathodes coupled with carbon anodes, has been proposed for utilization in practice long time ago. However, the prevailing layered oxides is still hindered by serious phase transition and volume strain upon sodium release. Herein, we show a novel copper doped layered P_1 manganese-based oxide material (NCM) with unique bulk and nanoscale Na-free surface structures as a sodium host to overcome the above limitation. Our research disclosed this P_1 NCM material has a wide phasetransition- free zone between 2 V and 4.5 V with a tiny lattice volume change upon cycling. Besides, it delivers an excellent chemical stability during humid air exposure. In contrast to most environmentally sensitive layered materials, after aging for 60 days in humid air, P_1 NCM still exhibits the superior cycling performance (95.8% capacity retention after 1000 cycles) and excellent rate capability as well as an outstanding sodium storage performance in full cells.