Defect-Regulated Cubic Prussian Blue Analog Cathodes With Exceptional Stability for Potassium-Ion Batteries

Prussian blue analogs (PBAs) have attracted particular attention as promising high-energy-density cathodes for potassium-ion batteries (PIBs). Yet their development is hindered by crystal-degradation-driven capacity fading. Here, a structure-defect-dual-regulation strategy is developed for Fe-based PBAs as a generalizable approach to advance scalable, high-energy PIB cathodes, in which deliberately introduced cation vacancies at Fe³⁺ sites in cubic PB (Iron(III) hexacyanoferrate) lattices are charge-balanced by inserted potassium ions at neighboring octahedral interstitial sites. This approach, in turn, yields a low-anion-defect cubic structure, thereby increasing K⁺ storage capacity and stabilizing the Fe─C octahedral framework. In turn, this design effectively suppresses K⁺ insertion/extraction distortion and preserves low-spin Fe redox activity, while enhancing conductivity and ion diffusion. Cation vacancies mitigate lattice strain and facilitate cooperative coupling between low-spin and high-spin Fe centers, thereby enabling a durable dual-site redox process. The optimized cathode delivers a high reversible capacity of 124.5 mAh g^-1 at 50 mA g^-1 with an initial Coulombic efficiency of 92.21%, and exceptional long-term cycling stability with a capacity retention ratio of 84.9% after 800 cycles at 100 mA g^-1.