Low‐Cost Zinc Substitution of Iron‐Based Prussian Blue Analogs as Long Lifespan Cathode Materials for Fast Charging Sodium‐Ion Batteries

Abstract Iron‐based Prussian blue analogs (Fe‐PBAs) are extensively studied as promising cathode materials for rechargeable sodium‐ion batteries owing to their high theoretical capacity, low‐cost and facile synthesis method. However, Fe‐PBAs suffer poor cycle stability and low specific capacity due to the low crystallinity and irreversible phase transition during excess sodium‐ion storage. Herein, a modified co‐precipitation method to prepare highly crystallized PBAs is reported. By introducing an electrochemical inert element (Zn) to substitute the high‐spin Fe in the Fe‐PBAs (ZnFeHCF‐2), the depth of charge/discharge is rationally controlled to form a highly reversible phase transition process for sustainable sodium‐ion storage. Minor lattice distortion and highly reversible phase transition process of ZnFeHCF‐2 during the sodium‐ions insertion and extraction are proved by in‐situ tests, which have significantly impacted the cycling stability. The ZnFeHCF‐2 shows a remarkably enhanced cycling performance with capacity retention of 58.5% over 2000 cycles at 150 mA g −1 as well as superior rate performance up to 6000 mA g −1 (fast kinetics). Furthermore, the successful fabrication of the full cell on the as‐prepared cathode and commercial hard carbon anode demonstrates their potential as high‐performance electrode materials for large‐scale energy storage systems.