High Crystalline Prussian White Nanocubes as a Promising Cathode for Sodium-ion Batteries

Prussian blue and its analogues (PBAs) have been recognized as one of the most promising cathode materials for room-temperature sodium-ion batteries (SIBs). Herein, we report high crystalline and Na-rich Prussian white Na₂ CoFe(CN)₆ nanocubes synthesized by an optimized and facile co-precipitation method. The influence of crystallinity and sodium content on the electrochemical properties was systematically investigated. The optimized Na₂ CoFe(CN)₆ nanocubes exhibited an initial capacity of 151 mA h g^-1 , which is close to its theoretical capacity (170 mA h g^-1 ). Meanwhile, the Na₂ CoFe(CN)₆ cathode demonstrated an outstanding long-term cycle performance, retaining 78 % of its initial capacity after 500 cycles. Furthermore, the Na₂ CoFe(CN)₆ Prussian white nanocubes also achieved a superior rate capability (115 mA h g^-1 at 400 mA g^-1 , 92 mA h g^-1 at 800 mA g^-1 ). The enhanced performances could be attributed to the robust crystal structure and rapid transport of Na ions through large channels in the open-framework. Most noteworthy, the as-prepared Na₂ CoFe(CN)₆ nanocubes are not only low-cost in raw materials but also contain a rich sodium content (1.87 Na ions per lattice unit cell), which will be favorable for full cell fabrication and large-scale electric storage applications.