新型离子交换法制备具有高倍率和高强度钠离子存储性能的本征赝电容正极材料Na0.44MnO2

Sodium-ion batteries are promising new-generation energy storage devices due to the low cost and rich resource of sodium. Among various cathodes, tunnel-type Na0.44MnO2 with large S-shaped Na+ transport tunnels is considered an appropriate cathode for fast-charging batteries, yet still suffering from sluggish Na+ kinetics. Herein, a novel ion-exchange method is developed for the first time to synthesize Na0.44MnO2 from K0.5MnO2 precursor. By precisely adjusting the synthesis condition, the amount of residual K+ and the size of Na0.44MnO2 are well controlled. The presence of trace K+ in the Na0.44MnO2 structure is demonstrated to broaden the Na+ transport tunnels while the minimized size shortens the Na+ migration distance. Besides, band-like defects with distorted polyhedrons further promote Na+ transport. The as-prepared Na0.44MnO2 with intrinsic pseudo-capacitance characteristic exhibits excellent rate performance of 79.0 mA h g−1 at 20 C between 2 and 4 V. Long-term cycling tests present superior stability of 98.1% retention after 1000 cycles at 20 C and 96.3% retention after 200 cycles at 0.5 C. This work provides a novel way for large-scale production of high-rate and robust Na0.44MnO2 cathode for fast-charging energy storage devices.