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.