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

Na0.44MnO2 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 Na0.44MnO2 cathode (Na0.44Mn0.98Nb0.02O2). Furthermore, NaCrO2 is added into the Na0.44Mn0.98Nb0.02O2 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. The introduction of Nb in tunnel Na0.44MnO2 can simultaneously reinforce the tunnel structure and enable fast electron and Na+ transport, thus resulting in greatly improved cycle life and rate capability. Using NaCrO2 for Na compensation, a high initial coulombic efficiency can be obtained for the tunnel type cathode, and the assembled pouch type full cell achieves a high energy density. image