Synergistic Dual‐Additive Tailored Robust Interphase toward Enhanced Cyclability of Prussian Blue Cathode for K⁺ Storage

Abstract Fe‐based Prussian blue analogs (KFeHCF) are considered as the most promising cathode materials for potassium‐ion batteries (KIBs) owing to their low cost and high energy density. However, the unstable cathode electrolyte interphase (CEI) typically leads to rapid capacity decay upon long‐term cycling, thus limiting its practical application. Herein, for the first time, a dual‐additive strategy has been proposed as an effective and economical approach to regulate the interphase chemistry on KFeHCF surface. The optimized contents of potassium selenocyanate (KSeCN, 0.5 wt.%) and lithium difluoro(oxalato)borate (LiDFOB, 0.5 wt.%) synergistically lead to the formation of a robust, homogeneous, and conductive CEI film, which promote charge transfer and K⁺ diffusion, inhibit side reactions and Fe dissolution, and realize stabilization of KFeHCF structure upon long cycling. As a result, the K∥KFeHCF battery with 0.5 wt.% LiDFOB + 0.5 wt.% KSeCN addition exhibits significantly improved cycling performance with a high capacity retention ratio of 81.5% after 5000 cycles at 500 mA g⁻¹ current density and 4.5 V cutoff voltage. This study provides a new paradigm for designing high performance potassium‐ion battery via dual electrolyte additive incorporation.