Component Modulation Strategy of Waste Camellia Shell via Hydrogen Bond Competition within Neutral Deep Eutectic Solvent to Construct Hard Carbon as High-Performance Sodium-Ion Battery Anode

Abstract

Deep eutectic solvents (DESs) pretreatment is a key strategy for modulating the three major components of waste biomass (cellulose, hemicellulose, and lignin). However, it is still a challenge to regulate the biomass components via DESs to construct a multi-closed-pore structure within hard carbon. This work presents a novel neutral DES pretreatment approach based on hydrogen bond competition for waste camellia shells to construct a hard carbon anode with a multi-closed-pore structure for high‑performance sodium‑ion batteries. DES pretreatment selectively dissolves and removes amorphous components (partial lignin, hemicellulose, and amorphous cellulose), allowing cellulose chains to rearrange into a more ordered structure, thereby increasing cellulose crystallinity. A higher cellulose-to-lignin ratio in the precursor favors an increase in the closed-pore proportion and promotes the formation of closed-pore walls of the hard carbon material. By optimizing the DES treatment time to 0.5 h, the hard carbon material (HC-0.50) pyrolyzed from the pretreated biomass exhibits a high closed-pore volume and abundant defect sites, which is beneficial for enhancing sodium storage capacity. Furthermore, the flake-like structure and the large interlayer spacing (0.378 nm) favor diffusion kinetics. Consequently, HC-0.50 achieves a reversible capacity of 304.2 mAh g-1 at 0.1 C, which is 72 mAh g-1 higher than that of the untreated sample (HC-0). Additionally, HC-0.5 delivers an initial coulombic efficiency of 81.52% and retains a capacity retention of 82.9% after 800 cycles at 2 C. This work reports a preparation method for a high-performance sodium-storage hard carbon anode by precisely controlling the composition of waste camellia shells.