Ternary deep eutectic solvent-Mediated rapid extraction of highly crystalline cellulose enabling closed-Pore regeneration of hard carbon anode for ultrafast sodium storage

Biomass is a high-quality precursor for synthesizing advanced hard carbon (HC) anode materials for sodium-ion batteries. The challenges of developing biomass-based hard carbon anode with excellent electrochemical performance are the regulation of closed-pore structures during the carbonization. In this work, a mild deep eutectic solvent of ChCl/EtG/H₂SO₄ (CEH) based on ethylene glycol system is used to treat moso bamboo (MB) for the first time, which selectively dissolves most of the lignin and hemicellulose by breaking the hydrogen bonds to retain highly crystalline cellulose, thus improving the concentration of closed-pore structures in the carbonization. The as-prepared hard carbon material of CEH-MB-120/4 h possesses a rich closed-pore structure and ultrathin disordered pore walls with abundant active sites, which enables the fast ion diffusion kinetics and excellent reversibility of sodium storage. Importantly, without conductive additives, the CEH–HC–120/4 h anodes possess excellent electrochemical properties, including an impressive reversible capacity of 348.6 mAh g⁻¹ at 0.1C, outstanding rate performance of 201.4 mAh g⁻¹ at 10C and exceptional cycling stability with a capacity retention of 90 % over 300 cycles at 1C. This refined approach offers a facile manipulated pathway for designing biomass-based hard carbon anode with high capacity and rate performance for sodium-ion batteries.