Reaction Environment-Tailored Synthesis of High-Quality Prussian Blue Analogues for Ultra-Stable Potassium Ion Batteries

Fe-based Prussian blue analogues (PB: K2Fe[Fe(CN)6]) have been considered as highly competitive cathode materials for potassium-ion batteries due to their open framework and abundant redox active centers. However, the electrochemical performance of the PB cathode is deteriorated by unavoidable introduction of [Fe(CN)6]4– vacancies and crystal water. This work tailors the synthesis reaction environment, enabling precise control over reactant dissolution kinetics to minimize the level of structural VFeCN and crystal water. The as-prepared PB cathode achieves unprecedented cycling stability: 2500 cycles (running over one year) at 50 mA g–1 and 20,000 cycles at 500 mA g–1, respectively. In situ characterizations reveal that reduced vacancies are conducive to activating the electrochemical activity of the low spin Fe redox centers and ensuring structural stability during long-term cycling. Furthermore, the mother liquor allows for multiple recycling without functional degradation via quantitatively calibrating its concentration, endowing this strategy with significant potential for practical application.