Compositional Engineering to Tailor Pseudographitic Microstructure of Hard Carbon for Enhanced Sodium Storage

ABSTRACT Biomass‐based hard carbons are particularly attractive as the anode materials for Na‐ion batteries due to their tunable microstructure, suitable operating potential, and cost effectiveness. Nevertheless, the complex biomass composition makes the precise tailoring of internal carbon microstructure challenging for boosted Na‐ion storage. In this work, we develop a compositional engineering strategy to tailor the pseudographitic structure of hard carbon by deep eutectic solvent. The green solvent selectively dissolves low‐crystalline compositions (hemicellulose, lignin, and amorphous cellulose), and the remaining crystalline cellulose facilitates the construction of desired pseudo‐graphitic domains with expanded carbon interlayer spacing and abundant ultramicro/closed pores. Consequently, the as‐tailored cotton‐derived hard carbon delivers an enhanced capacity of 318 mAh g −1 at 20 mA g −1 and an impressive initial Coulombic efficiency of 85%. Additionally, the anode can sustain good sodium storage performance at low temperatures and in full cells. This study demonstrates an eco‐friendly and effective strategy for fabricating high‐performance biomass‐based hard carbons and accelerating the development of Na‐ion technology.