Whispers of Entropic Distortion Elevating Voltage and Electrochemical Depth in Potassium Hexacyanoferrate Cathodes

Abstract

Prussian Blue Analogues (PBAs) are regarded as one of the most promising cathode materials for potassium-ion batteries (PIBs) due to their broad operating voltage range, low potassium-ion diffusion barriers, and cost-effective, simple synthesis. However, the passivation of low-spin transition metal centers and inherently poor electronic conductivity severely limit PBAs' potential to achieve high energy density and long-term cycling stability. In this study, the first successful activation of low-spin transition metal reactivity in a non-aqueous PIB system through the incorporation of a high-entropy multimetallic coordination strategy is reported. This approach not only precisely regulates the voltage platform but also significantly enhances the material's energy density. The synthesized high-entropy K1.19Fe0.2Co0.2Ni0.2Cu0.2Mn0.2[Fe(CN)6]0.79□0.21·1.16H2O (HEPBA) cathode achieved a remarkable energy density of 407.67 W h kg−1 at an average working voltage of 3.89 V, with a capacity retention of 88.03% after 2000 cycles at 500 mA g−1. Density functional theory (DFT) and field emission analysis (FEA) calculations revealed that the high-entropy design not only improved the electronic conductivity during K+ intercalation but also significantly reduced ion diffusion barriers. Additionally, the material exhibited reduced volumetric expansion during potassium-ion insertion/extraction, greatly enhancing its long-term cycling stability.