Zinc-assisted modification of hard carbon for enhanced sodium-ion storage

Hard carbon is recognized as a highly promising anode material for sodium-ion batteries (SIBs), with its microstructure playing a critical role in determining Na+ storage performance. Despite recent advancements in improving the Na+ storage capabilities of hard carbon, significant challenges remain in optimizing these materials. In this study, zinc-modified hard carbon was synthesized using coconut shells as the carbon source and ZnCl2 as a modifier. The introduction of ZnCl2 effectively expanded the graphite interlayer spacing, reduced microcrystal size, and created closed pores, leading to significantly enhanced Na+ storage performance. Consequently, the ZnCl2-modified hard carbon exhibited a high reversible capacity of 352.0 mAh/g, with a plateau capacity of 242.6 mAh/g, outperforming the unmodified hard carbon (294.4 mAh/g and 199.8 mAh/g, respectively). Additionally, the modified material showed superior rate performance and cycling stability. The Na+ storage mechanism in the ZnCl2-modified carbon aligns with the "adsorption-intercalation-filling" model. This study highlights the effectiveness of ZnCl2 modification in enhancing Na+ storage, providing a promising strategy for the development of high-performance hard carbon anodes in SIBs.