Advances and Prospects of Lignin-Derived Hard Carbons for Next-Generation Sodium-Ion Batteries

Lignin-derived hard carbon (LHC) has emerged as a highly promising anode material for sodium-ion batteries (SIBs), owing to its renewable nature, structural tunability, and notable electrochemical properties. Although considerable advancements have been made in the development of LHCs in recent years, the absence of a comprehensive and critical review continues to impede further innovation in the field. To address this deficiency, the present review begins by examining the intrinsic characteristics of lignin and hard carbon (HC) to elucidate the underlying mechanisms of LHC microstructure formation. It then systematically categorizes the synthesis strategies, structural attributes, and performance influences of various LHCs, focusing particularly on how feedstock characteristics and fabrication parameters dictate final material behavior. Furthermore, optimization methodologies such as feedstock pretreatment, controlled processing, and post-synthesis modifications are explored in detail to provide a practical framework for performance enhancement. Finally, informed recommendations and future research directions are proposed to facilitate the integration of LHCs into next-generation SIB systems. This review aspires to deepen scientific understanding and guide rational design for improved LHC applications in energy storage.