Ball Milling Solid‐State Synthesis of Highly Crystalline Prussian Blue Analogue Na2−xMnFe(CN)6Cathodes for All‐Climate Sodium‐Ion Batteries

With a series of merits, Prussian blue analogs (PBAs) have been considered as superior cathode materials for sodium-ion batteries (SIBs). Their commercialization, however, still suffers from inferior stability, considerable [Fe(CN)6 ] defects and interstitial water in the framework, which are related to the rapid crystal growth. Herein, a "water-in-salt" nanoreactor is proposed to synthesize highly crystallized PBAs with decreased defects and water, which show both superior specific capacity and rate capability in SIBs. The air-stability, all-climate, and full-cell properties of our PBA have also been evaluated, and it exhibits enhanced electrochemical performance and higher volume yield than its counterpart synthesized via the water-based co-precipitation method. Furthermore, their highly reversible sodium-ion storage behavior has been measured and identified via multiple in situ techniques. This work could pave the way for the PBA-based SIBs in grid-scale energy-storage systems.