Sodium-ion batteries (SIBs) have emerged as a compelling frontier in sustainable energy storage, offering a cost-effective and earth-abundant alternative to lithium-ion systems. Among diverse anode candidates, biomass-derived hard carbons (BHCs) stand out due to their environmental benignity and unique solid-state architectures for sodium storage. Accumulating evidence indicates that the internal pore topology of hard carbon, specifically its pore topology, governs the sodiation kinetics, interfacial evolution, and reversible capacity. Notably, closed pores (nanoscopic internal voids isolated from the liquid electrolyte) serve as confined solid-state reservoirs for quasi-metallic sodium species, enabling effective ion desolvation, structural buffering, and stabilized solid−solid interphases during cycling. This review systematically elucidates the role of closed-pore architectures in BHCs from the perspective of solid-state sodium storage. By correlating the chemical evolution of biomass precursors with carbonization and activation processes, the formation, stability, and spatial distribution of closed pores are analyzed to establish processing−structure relationships. Furthermore, the mechanistic contributions of closed pores to low-potential plateau capacity are critically examined, with emphasis on nanoconfinement-induced desolvation and confined interfacial chemistry. Finally, design principles for tailoring closed-pore architectures are summarized, highlighting their implications for advanced solid-state anode design and the development of high-performance SIBs.
Yang et al. (Mon,) studied this question.