Vacancies‐regulated Prussian Blue Analogues through Precipitation Conversion for Cathodes in Sodium‐ion Batteries with Energy Densities over 500 Wh/kg

Abstract Prussian blue analogues (PBAs) have been widely applied in many fields, especially as cathode materials of sodium‐ion batteries on account of their low cost and open framework for fast ions transport. However, the capacity of reported PBAs has a great distance from its theoretical value. Herein, we proposed that [Fe(CN) 6 ] vacancies are crucial point for the high specific capacity for the first time. The [Fe(CN) 6 ] vacancies may create net electrons and reduce obstacles to ionic transport, which is conducive to rate performance of PBAs by increasing electronic and ionic conductivity to some extent. As a proof of concept, a series of PBAs have been prepared by co‐precipitation method. And then, a novel precipitation conversion method has been designed, by which unique PBAs with a specific quantity of [Fe(CN) 6 ] vacancies was successfully synthesized. Remarkably, the as‐prepared PBAs possessing hierarchical hollow morphology have reached a unprecedent level of high capacity (168 mAh g −1 at 25 mA g −1 , close to PBAs’ theoretical capacity 170 mAh g −1 ), high rate performance (90 mAh g −1 at 5 A g −1 ), and high energy density (over 500 Wh kg −1 ).