Synthesis of KFeSO ₄ F/C Composite and Its Use as a Cathode for High-Performance Potassium-Ion Batteries

Polyanionic compounds have emerged as one of the most promising cathode materials for potassium-ion batteries (PIBs) owing to their high operating voltage and excellent stability. Among them, the iron-based fluorosulfate KFeSO₄F stands out with its unique 3D framework structure and low cost. However, its intrinsic low electrical conductivity and proneness to agglomeration result in inferior electrochemical performance. Additionally, the solvothermal synthesis method commonly used for its preparation is not amenable to large-scale production. Herein, we report the large-scale synthesis of a low impurity phase, high crystallinity KFeSO₄F/C composite with carbon-induced antiagglomeration properties via a facile room-temperature ball milling method (denoted as KFeSO₄F/C-c). As a high-performance PIB cathode material, KFeSO₄F/C-c exhibits exceptional electrochemical properties: it delivers a high average discharge voltage of 3.63 V and a reversible discharge specific capacity of up to 115.69 mAh g⁻¹ at a current density of 0.1C. Even at an elevated current density of 10C, it maintains a reversible discharge specific capacity of 94.93 mAh g⁻¹. Furthermore, it retains 77% of its initial capacity after 1000 charge-discharge cycles at 5C. This work paves a promising way for the large-scale practical application of PIBs.