Defect‐Healing Induced Monoclinic Iron‐Based Prussian Blue Analogs as High‐Performance Cathode Materials for Sodium‐Ion Batteries

Abstract Prussian blue analogs (PBAs) have attracted wide interest as a class of ideal cathodes for rechargeable sodium‐ion batteries due to their low cost, high theoretical capacity, and facile synthesis. Herein, a series of highly crystalline Fe‐based PBAs (FeHCF) cubes, where HCF stands for the hexacyanoferrate, is synthesized via a one‐step pyrophosphate‐assisted co‐precipitation method. By applying this proposed facile crystallization‐controlled method to slow down the crystallization process and suppress the defect content of the crystal framework of the PBAs, the as‐prepared materials demonstrate high crystallization and a sodium‐rich induced rhombohedral phase. As a result, the as prepared FeHCF can deliver a high specific capacity of up to 152.0 mA h g −1 (achieving ≈90% of its theoretical value) and an excellent rate capability with a high‐capacity retention ratio of 88% at 10 C, which makes it one of the most competitive candidates among the cathodes reported regarding both capacity and rate performance. A highly reversible three‐phase‐transition sodium‐ion storage mechanism has been revealed via multiple in situ techniques. Furthermore, the full cells fabricated with as‐prepared cathode and commercial hard carbon anode exhibit excellent compatibility which shows great prospects for application in the large‐scale energy storage systems.