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.