Reduction-Induced Topological Phase Transition to\nConstruct K<sub>2</sub>Mn[Fe(CN)<sub>6</sub>] Superstructures for\nHigh-Performance Sodium-Ion Batteries

Potassium\nmanganese-based Prussian blue analogs (KMn-HCF) hold\ngreat potential as cathodes for sodium-ion batteries (SIBs). However,\nthe rapid synthesis process often results in excessively small particle\nsizes, increasing surface area and thereby intensifying side reactions\nwith the electrolyte, which can damage the cathode electrolyte interface\n(CEI) and diminish cycling stability. Herein, we designed a topological\nphase transition strategy to assemble small KMn-HCF particles into\na 600 nm cubic superstructure. Structurally, the assembled structure\nin KMn-HCF significantly improves the cycling stability and durability\nof KMn-HCF as a SIB cathode by reducing defects, enhancing the uniformity\nand stability of the CEI layer, minimizing contact with the electrolyte,\nand reinforcing structural integrity. From a compositional perspective,\nKMn-HCF exhibits lower Jahn–Teller distortion, reducing overall\nlattice distortion while allowing larger K<sup>+</sup> to act as pillars,\nsupporting the Mn-HCF framework and preventing capacity degradation\ncaused by structural deterioration. The robust CEI layer formed in\nthe KMn-HCF cubic superstructure delivered stable charge–discharge\nvoltage profiles and reversible plateaus, achieving a capacity retention\nof 88.4%/89.1% after 1000 cycles at current densities of 0.1 and 0.5\nA g<sup>–1</sup>, respectively.