Interlayer Spacing Engineering of Cellulose-Derived Hard Carbon for Enhanced Na⁺ Diffusivity and Optimized Na⁺ Storage in Anode Materials

Cellulose-derived hard carbon (HC) is a promising candidate for a sodium-ion battery (as the optimally configured renewable energy storage system) due to its low cost and environmental sustainability. However, the sodium storage capacity and rate performance are limited by the restricted interlayer spacing, requiring further optimization for practical applications. This study presents a scalable and cost-effective approach to regulating the interlayer spacing of cellulose-derived HC using a preliminary chemical cross-linking (PCC) strategy. The PCC method increases interlayer spacing and introduces structural disorder, thereby significantly improving sodium-ion diffusion kinetics and storage capacity. The HC samples (denoted as PCHC-X, in which X = 1, 2, and 3 stands for the degree of cross-linking) exhibit reversible capacities of up to 312.3 mAh g–1, outperforming cellulose-derived hard carbon (222.8 mAh g–1). Besides, the PCHC-3 shows notable improvements in sodium-ion transport, with a capacity of 253.6 mAh g–1 at a 5C rate and excellent cycling stability (84.1% retention after 150 cycles at 0.5C). Cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS) analyses further confirm superior Na+ diffusivity and storage properties for PCHC-3. Deep insights into interlayer spacing engineering will greatly advance the rational design of hard carbon anodes with enhanced electrochemical performances.