A fluorine/oxygen co-doping scheme for biomass carbon provides excellent rapid reaction kinetics for sodium/potassium-ion batteries

Hard carbons have broad prospects of application in potassium-ion batteries (PIBs) and sodium-ion batteries (SIBs). However, due to the hindrance of the structural defects of hard carbons, the rate performance and cycle life of PIBs and SIBs need to be further optimized. In this work, F/O co-doped porous flake hard carbons (FO-HCs) were prepared by waste distillers grains. F-doping can optimize the adsorption effect of K+ at oxygen-containing functional groups, thus promoting the adsorption and embedding of K+ at the defects. Using in situ Raman, in situ XRD, and XPS etching, combined with density functional theory (DFT) modeling calculations, it is explained that the storage mechanism of K+ in FO-HCs is mainly the adsorption behavior at defects and surfaces, and there is a certain weak intercalation behavior. Due to the synergistic effect of F/O co-doping and the porous structure of FO-HCs, FO-HC1200 prepared as a negative electrode material for PIBs/SIBs exhibits excellent cycle life (347.2/386.5 mA h g-1 after 1000 cycles at 100 mA g-1) and rate performance (246.3/274.2 mA h g-1 at 5 A g-1). This work provides a new idea for the synthesis and mechanism research of high-performance hard carbons for PIB and SIB anodes. Hard carbons have broad prospects of application in potassium-ion batteries (PIBs) and sodium-ion batteries (SIBs).