Breaking the Size Constraint: Rational Vacancy Design Activates Submicron Prussian Blue Cathodes for Potassium-Ion Storage

The development of durable high-performance cathodes is paramount to promote the potential application of potassium-ion batteries in grid-scale energy storage. Prussian blue analogues, such as iron hexacyanoferrate (FeHCF), offer superior cyclic stability, but their electrochemical activity is limited by poor K⁺ diffusion depth, leading to a sharp decay in reversible capacity with increasing particle size and thus hindering their practical application. Herein, we demonstrate that the rational introduction of vacancies into the FeHCF framework is pivotal for enhancing potassium-storage kinetics. This approach mitigates the detrimental particle size effect, enabling 500 nm FeHCF particles to retain 72% of the capacity of 50 nm particles. Building upon this, we further propose a local lattice reconstruction strategy to reinforce the framework, promoting reversible capacity and capacity retention. The as-prepared FeHCF with a particle size of 500 nm delivers a high reversible capacity of 90 mAh g⁻¹ at 50 mA g⁻¹ and outstanding cycling stability (82.6% retention after 800 cycles), alongside remarkable rate performance. This work demonstrates the beneficial role of vacancies in optimizing K⁺ storage kinetics in PBAs, providing support for the development of high-performance potassium-ion battery cathodes.