Understanding of Sodium Storage Mechanism in Hard Carbons: Ongoing Development under Debate

摘要

Hard carbons are promising anode candidates for sodium-ion batteries dueto their excellent Na-storage performance, abundant resources, and lowcost. Despite the recent advances in hard carbons, the interpretation of theNa-storage mechanism in hard carbons remains unclear, with discrepanciesover a general model describing the corresponding structure–propertyrelationship. For the rational structural design of high-performance hardcarbon anodes, a thorough understanding of the charge storage mechanismand the relationship between microstructure and Na-storage performance iscritical. This review provides a comprehensive overview of the known modelsto describe the Na-storage mechanism in hard carbons with a discussionfocused on Na-storage active sites such as interlayer space, pores, heteroatoms,and defects. The present models, including the “insertion-filling”,“adsorption-filling”, “adsorption-insertion”, and “multistage mechanism”and the associated analytical characterization, are elaborately discussed witha view to the present challenges and the prospects for unveiling Na-storagemechanism in hard carbons. The review serves to clarify the Na-storagemechanism in hard carbons with guidance toward the design of high-performanceanodes for sodium-ion batteries.