Overcoming Kinetic Limitations of Polyanionic Cathode toward High-Performance Na-Ion Batteries.

Polyanionic cathodes have attracted extensive research interest for Na-ion batteries (NIBs) due to their moderate energy density and desirable cycling stability. However, these compounds suffer from visible capacity fading and significant voltage decay upon the rapid sodium storage process, even if modified through nanoengineering or carbon-coating routes, leading to limited applications in NIBs. Herein, the Na ₃ (VOPO ₄ ) ₂ F cathode material with dominantly exposed {001} active facets is demonstrated by a topochemical synthesis route. Owing to the rational geometrical structure design and thereby directly shortening Na diffusion distance, the electrode delivers a reversible capacity of ∼129 mA h g ^-1 even at a high rate of 10 C, which is very close to the theoretical capacity of 132 mA h g ^-1 , achieving a high energy density of ∼452 W h kg ^-1 coupled with a high-power density of 4660 W kg ^-1 . When further served as a cathode for nonaqueous, aqueous-based, and solid-state full NIBs, respectively, our designed Na ₃ (VOPO ₄ ) ₂ F always enables superior electrochemical performance due to favorable kinetics.