Fluorine Doping Enhances Surface Adsorption for High-Performance Hard Carbon Anodes in Sodium-Ion Batteries

The inherent kinetic limitations associated with sodium storage in hard carbon (HC) anodes hinder further improvements in the energy density of sodium-ion batteries (SIBs). In this work, we present a facile and scalable synthesis strategy for a fluorine-doped HC anode. The incorporation of fluorine effectively suppresses graphitization during high-temperature carbonization, resulting in a highly disordered carbon structure with an expanded interlayer spacing and abundant surface defects. These structural features introduce numerous active sites and significantly enhance the surface adsorption capability of sodium ions. The optimized material delivers a high reversible specific capacity of 350.3 mAh g –1 in ester-based electrolytes and exhibits superior cycling stability compared to pristine phenolic resin-derived HC─achieving a capacity retention rate of 84.3% after 100 cycles at 100 mA g –1 . This study offers a practical and rational design approach for high-performance HC anodes, paving the way toward their viable application in SIBs.