Realizing improved sodium-ion storage for anthracite-derived hard carbon anode by activation-surface modification strategy.

Abstract

Anthracite offers several advantages, including a high carbon content, a well-developed aromatic structure, and low cost, making it a cost-effective precursor for hard carbon anodes in sodium-ion batteries. However, its higher impurity levels and fewer surface defects limit its broader applications. In this study, we proposed an activation and surface modification strategy to address its shortcomings, specifically low sodium storage-ion capacity and low initial coulombic efficiency (ICE). ZnCl2 was used as an activator to introduce numerous pores into the structure of hard carbon, thereby increasing the sodium-ion storage sites. Furthermore, soft carbon pitch was applied to refine the oversized pore structure in hard carbon, improving its initial coulombic efficiency. As a result, the modified hard carbon achieved a reversible capacity of 240 mAh g⁻¹ and an initial coulombic efficiency of 82.52% at a discharge rate of 0.1C. The PCAC-1200 also demonstrated good cycle stability with 76.2% retention after 100 cycles. Besides, it still has a capacity of 101.2 mAh g⁻¹ at a high magnification of 5C. We believe that this anthracite hard carbon anode prepared by activation-surface modification strategy shows good application prospects in the field of sodium-ion energy storage.