Acid-catalyzed ethanol pretreatment enables electrochemically improved hard carbon anodes for sodium-ion batteries

Feedstock properties play a significant role in preparing high-performance hard carbon (HC) anode materials for advancing sodium-ion batteries (SIBs) as a viable alternative energy storage solution. In this study, an acid-catalyzed ethanol pretreatment approach was used as an effective technology platform to fractionate sugarcane bagasse into cellulose-rich pulp (EC) and high-purity lignin (EL) for subsequent synthesis of HC. Comprehensive electrochemical analyses reveal that acid-catalyzed ethanol pretreatment enables improved performance in both lignin- and cellulose pulp-based HC compared to HC anodes derived from whole sugarcane bagasse, dilute acid pretreated pulp as well as cellulose pulp and lignin fractions from alkaline pretreatment. EC-HC demonstrates a reversible capacity of 297.7 mAh g −1 with an initial coulombic efficiency (ICE) of 69.6%, which is greater than other cellulose-pulp-based HC. This improvement is mainly attributed to the higher C C content, fewer surface structural defects, reduced open porosity and higher crystallinity resulting from the increased cellulose content. Simultaneously, EL-HC exhibits superior electrochemical performance, achieving the highest reversible capacity of 316.3 mAh g −1 and an enhanced ICE of 78.0%. Moreover, EL-HC maintains exceptional long-term stability, retaining 88.1% of its initial capacity even after 250 cycles. This superior performance of EL-HC primarily originates from their reduced oxygen functional group, lower defects and minimized open porosity, which stem from the improved structural homogeneity of lignin. These results demonstrate that acid-catalyzed ethanol pretreatment provides a highly efficient platform for converting agricultural biomass into HC anode materials with enhanced performance for next-generation SIBs.