One-Step Fabrication of Fluorine-Doped Graphite Derived from a Low-Grade Microcrystalline Graphite Ore for Potassium-Ion Batteries

Abstract

Graphite has been considered as a promising anode material of potassium-ion batteries (KIBs), the practical applications of which are impeded because of the unsatisfactory cycling stability and poor rate capability. In this study, the favorable effect of fluorine-doping on the K-storage performance of graphite is demonstrated. For a more practical application, a low-grade microcrystalline graphite (MG) ore is chosen as the raw material and is purified through a facile hydrofluoric acid solution immersion method. The results indicate that the mild purification process not only results in a high purity of 98.59 wt % for MG but also realizes the effective F-corporation in the graphite host. The fluorine content of 1.02% with a high semi-ionic bond constituent (70.53%) enlarges the graphite interlayer distance from 3.356 to 3.461 Å, which contributes to an alleviated volume change and faster K-ion diffusion kinetics. Benefiting from the F-doping-induced structural improvement, the modified MG electrode exhibits a prominently elevated reversible capacity (320 mA h g–1), a superior cycling ability with a high capacity retention of 74.6% after 100 cycles, and an enhanced rate performance. This study manifests that F-doping is a feasible route to resolve the obstacles of graphite materials and paves the way for commercial KIBs with high performance.