Structural characteristics, storage mechanisms, and rational design in carbon-based anodes for sodium-ion batteries

The growing global population and increasing energy demand have intensified the search for sustainable and cost-effective energy storage technologies. Among them, sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion batteries owing to the natural abundance, low cost, and wide availability of sodium resources. Carbonaceous materials are considered the most attractive anode candidates because of their tunable microstructure, excellent electrical conductivity, high structural stability, and environmental compatibility. This review comprehensively summarizes recent advances in carbonaceous anodes for SIBs, encompassing graphitic carbon, amorphous carbon (hard and soft carbon), and nanocarbon materials. Unlike previous reviews that mainly focus on individual carbon classes, this work provides an integrated perspective by systematically classifying carbon architectures and correlating their structural characteristics with sodium-storage behavior. The relationships among microstructure, physicochemical properties, sodium-storage mechanisms, and electrochemical performance are critically analyzed, while recent optimization strategies including structural regulation, heterostructure construction and surface modification are comprehensively discussed. Current challenges associated with low initial Coulombic efficiency, interfacial instability, and practical implementation are also highlighted. Finally, emerging research directions, including closed-pore engineering, AI-assisted carbon design, multiscale modeling, and scalable manufacturing, are proposed to accelerate the commercialization of high-performance carbonaceous anodes for next-generation sodium-ion batteries.