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

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.