Biomass-Derived Hard Carbon Anodes Processed with Deep Eutectic Solvents for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are increasingly acknowledged as a promising alternative for large-scale energy storage applications, attributable to the abundant natural availability, widespread geographical distribution, and economic viability of sodium resources. Hard carbon is recognized as one of the leading options for anode materials in sodium-ion batteries (SIBs). It presents several advantages, including a high reversible specific capacity and the availability of abundant precursor sources. The synthesis of hard carbon anodes frequently necessitates the utilization of acids or alkalis, which presents considerable environmental challenges and results in substantial costs associated with waste liquid treatment. Consequently, there is an imperative to establish a cost-effective and environmentally sustainable modification method for hard carbon materials. Herein, we develop a universal reciprocal biomass processing method to prepare a series of high-performance hard carbon anodes derived from biomass. The utilization of biomass-based deep eutectic solvents (DES) leads to the disruption of intramolecular and intermolecular hydrogen bonds within cellulose in biomass feedstock, resulting in increased disorder and expanded interlayer spacings of hard carbon during the pyrolysis process. The optimal hard carbon anode derived from macadamia nut shells (MNSs) exhibits enhanced sodium-ion transport and storage capabilities treated by DES, featuring a high reversible capacity of 297.07 mAh g^-1 at 20 mA g^-1 and good rate performance. Other biomass resources, such as bamboo, coconut, and pine, highlight the versatility of the proposed reciprocal biomass processing method for synthesizing high-performance hard carbon anodes. This study presents a universal and green method to process biomass resources for synthesizing high-performance hard carbon anode materials.