Mesoporous Single-Crystal FeFe(CN)₆ Microspheres for Superior Potassium-Ion Storage

Metal hexacyanoferrates (HCFs), also known as Prussian blue analogues, are ideal cathodes for potassium-ion batteries (PIBs) due to their nontoxicity and cost-effectiveness. Nevertheless, obtaining metal HCF cathode materials with both long-term cycling stability and high rate performance remains a daunting challenge. In this study, we present mesoporous single-crystalline iron hexacyanoferrate (MSC-FeHCF) microspheres, featuring a single-crystalline structure that contains interconnected pores spanning the entire crystal lattice. This unique architecture not only enables the electrolyte to fully penetrate into the single crystal, but also shorten the K⁺ diffusion distance. Additionally, the confinement effect of mesopores on interior water mitigates the excessive side reactions. The stress during battery cycling can be dispersed through multiple paths to alleviate the internal strain. The MSC-FeHCF microspheres exhibit unprecedented long-term cycling performance, achieving a specific discharge capacity of 123.5 mAh g^-1 at 30 mA g^-1 and 87.1 mAh g^-1 after 2000 cycles at 500 mA g^-1, providing 85.8 % of the initial capacity. More importantly, the MSC-FeHCF microspheres exhibit high rate capability, delivering 86.7 mAh g^-1 at 3 A g^-1. This study introduces an innovative strategy for engineering metal HCF cathode materials, thereby opening a novel avenue for the development of high-efficiency electrode materials for PIBs.