Hard carbon for sodium-ion batteries: progress, strategies and future perspective

Because of its abundant resources, low cost and high reversible specific capacity, hard carbon (HC) is considered as the most likely commercial anode material for sodium-ion batteries (SIBs). Therefore, reasonable design and effective strategies to regulate the structure of HCs play a crucial role in promoting the development of SIBs. Herein, the progress in the preparation approaches for HC anode materials is systematically overviewed, with a special focus on the comparison between traditional fabrication methods and advanced strategies emerged in recent years in terms of their influence on performance, including preparation efficiency, initial coulombic efficiency (ICE), specific capacity and rate capability. Furthermore, the advanced strategies are categorized into two groups: those exhibiting potential for large-scale production to replace traditional methods and those presenting guidelines for achieving high-performance HC anodes from top-level design. Finally, challenges and future development prospects to achieve high-performance HC anodes are also proposed. We believe that this review will provide beneficial guidance to actualize the truly rational design of advanced HC anodes, facilitating the industrialization of SIBs and assisting in formulating design rules for developing high-end advanced electrode materials for energy storage devices.