Acid-base etching of vinasse-derived precursors for high-performance hard carbon anodes in sodium-ion batteries

Vinasse, an abundantly produced biomass waste, is valorized as low-value products such as animal feed. Its conversion into hard carbon (HC) materials represents a promising route for high-value utilization. However, vinasse-derived HC without targeted compositional regulation fails to meet electrochemical performance benchmarks for practical sodium-ion battery (SIB) applications. To address this challenge, we report a two-step acid-base treatment strategy for vinasse precursor modification, enabling the fabrication of high-performance HC anodes. Sulfuric acid treatment selectively removes hemicellulose and transition metal impurities, while sodium hydroxide treatment eliminates silica and modulates the lignin structure, achieving synergistic chemical reconstruction of the precursor. The resultant HC exhibits a hierarchically optimized microstructure with abundant closed pores, high sp² carbon content, and the absence of ash-related crystalline phases. As a result, the optimized sample delivers a reversible capacity of 349.4 mAh g^-1 at 0.1C with an initial coulombic efficiency (ICE) of 88.7%. Moreover, it demonstrates exceptional cycling stability, retaining 83.6% of its initial capacity after 2000 cycles at 5C, in stark contrast to the untreated sample, which retains 68.3%. This work establishes a scalable and facile route for converting low-cost biomass precursors into high-performance HC anodes, offering a viable pathway toward sustainable and economically competitive SIBs.