Multifunctional NaTiO Coating-Enabled High-Voltage and Capacitive-like Sodium-Ion Storage of NaMnO.

Sodium-ion batteries, as an attractive option for large-scale energy storage, still face the problems of low energy density and unsatisfactory rate performance. Among various cathodes, the tunnel-type NaMnO with large S-shaped Na transport tunnels is one of the promising cathode materials for fast and robust sodium-ion storage, yet suffering from Mn dissolution and structural collapse. Herein, a Na-rich layered oxide NaTiO is first constructed as a multifunctional coating layer on the surface of the NaMnO nanorod. NaTiO not only acts as an Na reservoir, but also serves as a protective layer to prevent NaMnO from electrolyte etching. Besides, the derived Ti-doped NaMnO transition layer supplies additional Na diffusion pathways along the radial direction of the nanorod with a short migration distance. The optimized 3 wt % NaTiO-coated NaMnO exhibits enhanced an initial capacity of 127 mAh g at 2-4.5 V. In addition, it shows an ultra-high capacitive-like capacity ratio of 96.7%, hence delivering an excellent rate performance of 80.2 mAh g at 20C. Long-term cycling tests indicate splendid stability against high voltage, achieving 97.7% capacity retention at 20C after 900 cycles. This work provides an effective strategy to improve the rate performance and high-voltage stability of NaMnO for high energy and power density batteries.