Epitaxial Nucleation of Na x FeFe(CN) 6 @rGO with Improved Lattice Regularity as Ultrahigh‐Rate Cathode for Sodium‐Ion Batteries

Although Prussian blue analogues are the promising candidate cathode materials for the Na‐ion batteries for the grid storage due to 3D open‐framework structure and large interstitial “A” sites, high content of defects in the crystals obtained in the conventional strategy severely impede Na + migration, leading to an unsatisfactory power density. Here a novel epitaxial nucleation‐assisted controlled crystallization approach to eliminate the structural defects of NaFeHCF crystals is reported. Due to their limited lattice misfit of only 4.87% (< 5%) between the graphene and NaFeHCF as well as the electronegativity of the functional groups (─COOH, ─OH, ─CH(O)CH─), GO can act as the nucleation and subsequent epitaxial growth platform of NaFeHCF, which results in a unique one‐corner‐cut cubic nano‐crystals morphologies with much decreased contents of defects (0.08 per formula unit). This enhanced lattice regularity significantly enhanced the speedy diffusion of Na cations (by 5 times) in the nanocrystals, resulting in the unprecedented rate capability of 96.8 mAh g −1 at an ultra‐high rate of 9 A g −1 (39 s, 23228 W kg −1 ), which is far exceeding that of any previously reported PBA‐based cathodes to the knowledge, authenticating its superiority as a candidate for high‐power sodium‐ion batteries for the reliable grid energy storage.