Recent Advances of High‐Rate Hard Carbon Anodes for Sodium‐Ion Batteries: Correlations Between Performance and Microstructure

Abstract Hard carbon anodes have emerged as essential components for advanced sodium‐ion batteries (SIBs), owing to their high reversible capacity, excellent cycling stability, and abundant precursors. However, the practical implementation of hard carbon anodes in high‐rate applications remains challenging due to sluggish sodium‐ion diffusion kinetics, insufficient electronic conductivity, and unstable electrode/electrolyte interfaces. Although numerous studies have explored strategies to improve the rate capability of hard carbon anodes, there is currently a lack of comprehensive reviews systematically summarizing these advances and theoretical correlation between rate performance and capacity. In this review, recent progress in designing hard carbon anodes with enhanced rate capability is critically analyzed, beginning with a detailed discussion on sodium‐storage mechanisms. Key structural and compositional factors influencing the rate capability are highlighted, including microstructural engineering, heteroatom doping, surface/interface modification, and nanostructure construction. Additionally, the apparent role of machine‐assisted learning and various synthesis strategies is investigated to provide mechanism insights. Finally, existing scientific challenges and future research directions are proposed, offering valuable guidance toward developing advanced hard carbon anodes suitable for fast‐charging and high‐power SIB applications.