Achieving High-Capacity Sodium Insertion of Coal-based Hard Carbon Anodes via Closed-Pore Modification

Abstract

The utilization of low-cost, high-carbon content coal in the production of coal-based hard carbon, a potential carbon anode for sodium-ion batteries, represents a highly promising avenue of research. Nevertheless, the intricate nature of coal and the difficulty of structural regulation contribute to subpar rate performance and low initial coulombic efficiency (ICE). Moreover, the impact of coal structure on microcrystalline structure, sodium storage mechanism and electrochemical properties of hard carbon necessitates further elucidation. This investigation focuses on crafting hard carbons derived from coal with tailored pore structures achieved through a combination of salt template etching and chitosan-derived carbon coating, enabling precise transformation from coal to hard carbon. The microcrystalline structure is controlled by the template, while the surface coating optimizes the surface and defect structure, and the sodium storage behavior and mechanism are further analyzed. The optimized sample exhibited a commendable reversible capacity, delivering a large reversible capacity of 316 mAh g-1. Amazedly, a prominent rate capability of 103 mAh g-1 was demonstrated even at high current density of 10 A g-1. This study provides an effective strategy for engineering high-performance closed-pore carbon anodes utilizing cost-effective, complex coal and its derivatives.