Manipulating Phase Stability and Kinetics in Prussian Blue Cathode via Entropy Engineering and <i>d</i>¹⁰ Cation Incorporation for Potassium-Ion Batteries

Phase transition and [Fe(CN) 6 ] 4– defects seriously limit electrochemical performance of Prussian blue analogue (PBA) cathodes for potassium-ion batteries (PIBs). Herein, entropy engineering and d 10 cation incorporation are utilized to construct a medium-entropy PBA, K 1.23 Fe 0.42 Mn 0.45 Sn 0.13 [Fe(CN) 6 ] 0.94 ·1.35H 2 O (KFMSHCF), as the cathode material for PIBs. Entropy-induced cation disorder markedly suppresses anion vacancies, while the entropy stabilization effect and Sn 2+ with a d 10 configuration stabilize local coordination environments. High configurational entropy boosts KFMSHCF to exhibit reduced band gap and low K-ion diffusion barrier, thereby ensuring excellent electrochemical kinetic. KFMSHCF undergoes a zero-strain solid-solution mechanism using Fe, Mn and Sn ions as redox centers for charge compensation. Therefore, KFMSHCF delivers a high initial energy density of 364.2 Wh·kg –1, remarkable cycling stability with a capacity retention of 82.1% after 100 cycles and long lifespan over 300 cycles, and significantly enhanced rate capability. The fabricated high-energy-density K-ion full batteries achieve ultralong lifespan over 2500 cycles with an ultralow capacity-decay-rate of 0.017% per cycle.