Ultrafast and Highly Efficient Sodium Ion Storage in Manganese‐Based Tunnel‐Structured Cathode

Abstract Na 0.44 MnO 2 with tunnel structure is considered a promising low‐cost cathode material for sodium‐ion batteries. However, the sluggish Na + transport kinetics and low initial Coulombic efficiency restrict its practical applications in rechargeable sodium‐ion batteries. Herein, a manganese‐based tunnel‐structured cathode with high rate capability and high initial Coulombic efficiency is prepared by niobium doping and sodium compensation. Via materials characterizations and theoretical calculations, it is demonstrated that a proper amount of niobium doping in tunnel structure can effectively improve its structural stability and charge transport kinetics, resulting in outstanding rate capability (76.6% capacity retained from 0.5 to 30 C) and superior cycling performance (82.3% capacity retention after 800 cycles at 5 C) for the optimized Nb‐doped Na 0.44 MnO 2 cathode (Na 0.44 Mn 0.98 Nb 0.02 O 2 ). Furthermore, NaCrO 2 is added into the Na 0.44 Mn 0.98 Nb 0.02 O 2 cathode as a self‐sacrificing sodium compensation additive, and a high initial Coulombic efficiency close to 100% is achieved for the composite cathode. This work establishes a facile strategy to design advanced manganese‐based cathode materials for large‐scale energy storage applications.