Highly Crystallized Prussian Blue with Enhanced Kinetics for Highly Efficient Sodium Storage

Prussian blue analogs (PBAs) featuring large interstitial voids and rigid structures are broadly recognized as promising cathode materials for sodium-ion batteries. Nevertheless, the conventionally prepared PBAs inevitably suffer from inferior crystallinity and lattice defects, leading to low specific capacity, poor rate capability, and unsatisfied long-term stability. As the Na⁺ migration within PBAs is directly dependent on the periodic lattice arrangement, it is of essential significance to improve the crystallinity of PBAs and hence ensure long-range lattice periodicity. Herein, a chemical inhibition strategy is developed to prepare a highly crystallized Prussian blue (Na₂Fe₄[Fe(CN)₆]₃), which displays an outstanding rate performance (78 mAh g^-1 at 100 C) and long life-span properties (62% capacity retention after 2000 cycles) in sodium storage. Experimental results and kinetic analyses demonstrate the efficient electron transfer and smooth ion diffusion within the bulk phase of highly crystallized Prussian blue. Moreover, in situ X-ray diffraction and in situ Raman spectroscopy results demonstrate the robust crystalline framework and reversible phase transformation between cubic and rhombohedral within the charge-discharge process. This research provides an innovative way to optimize PBAs for advanced rechargeable batteries from the perspective of crystallinity.