Bridging Structure and Performance: Decoding Sodium Storage in Hard Carbon Anodes.

Amorphous carbon, particularly hard carbon (HC), is widely considered as the most promising anode material for sodium-ion batteries (SIBs) due to its high reversible capacity and cost-effectiveness. However, the complex and poorly defined structural properties of HC present challenges in understanding the underlying sodium storage mechanisms. To facilitate the rational design of high-performance HC anodes, a comprehensive understanding of the correlation between microstructure and sodium storage behavior is critical. This Review critically examines the interplay between the structural features of HC and its sodium storage capabilities, focusing on two key factors: pore structure and surface functional groups. It begins by outlining the fundamental sodium storage mechanisms in HC, followed by an in-depth discussion of how pore structure and surface chemistry influence sodium-ion storage. Finally, strategic insights are provided on how to manipulate these structural factors to optimize sodium storage performance. This Review aims to drive the development of next-generation high-performance HC anodes and support the commercialization of SIBs.