Electrochemical Performance Optimization of Layered P2‐Type Na 0.67 MnO 2 through Simultaneous Mn‐Site Doping and Nanostructure Engineering

Sodium‐ion batteries are considered as the most promising candidates for grid‐level energy storage applications due to its unique features of much lower cost and comparable energy density to lithium ion batteries. However, searching for suitable cathode materials with high capacity and good cycling stability are still the bottleneck issues due to the involved unmanageable phase transitions and difficult morphology control. Herein, unique fullerene‐like hollow polyhedrons of P2‐type Na 0.67 Ni 0.15 Mn 0.85 O 2 cathode were successfully synthesized via a facile and scalable self‐template strategy, where largely enhanced electrochemical properties can be achieved compared to its bulk counterpart. It can deliver a high specific capacity of 101 mAh g −1 after 120 cycles at a rate of 100 mA g −1 , reaching an excellent capacity retention of 96.8 %. The possible origins of the enhanced performance were further analyzed to be the synergistic effect of hollow interior and novel morphology of the polyhedron, leading to well exposed (002) planes, shorter diffusion path and better structural robust. Importantly, the full battery without pre‐sodiation treatment could deliver a high energy density of 133.1 Wh kg −1 based on the total mass of cathode and anode, which sheds a new light for designing high energy density sodium‐ion full batteries.