Coal-derived hard carbon for sodium-ion batteries: structural evolution, sodium-storage mechanisms, and regulation strategies.

Driven by the imperative for scalable energy storage and the global carbon neutrality initiatives, coal-derived hard carbon has garnered significant attention as a cost-effective and highly tunable anode material for sodium-ion batteries. This review systematically explores the inherent structure-property relationships of coal-based hard carbon, tracking its microstructural evolution across different coal ranks and molecular architectures. We critically examine the prevailing debates on sodium-storage mechanisms, particularly evaluating the respective contributions of adsorption, interlayer intercalation, and nanopore filling models. To address the persistent challenges of low initial coulombic efficiency (ICE) and limited plateau capacity, a comprehensive summary of advanced microstructural modulation strategies is provided. These cutting-edge approaches include precursor pretreatment, pore-structure engineering, template-confined carbonization, and soft-hard carbon composite construction. Current research underscores that precisely enlarging the graphitic interlayer spacing, constructing well-defined closed-pore networks, and suppressing excessive graphitization are paramount for synergistically boosting both specific capacity and ICE. Finally, this review outlines critical future perspectives, emphasizing the integration of in situ characterization, multiscale simulations, and low-cost scalable manufacturing pathways to accelerate the commercialization of coal-based sodium-ion batteries.