Microwave‐Field‐Driven Rapid Ultrastructure Reconstruction of Lignocellulose: A Green Strategy to Fabricate High‐Performance Hard Carbon Anodes

ABSTRACT Sustainable lignocellulosic biomass, with widespread availability and inherent hierarchical cellular architecture, has been a promising precursor for scalable hard carbon (HC) anodes in sodium‐ion batteries. The electrochemical performance of HC is profoundly dictated by the microstructure of precursors, and the challenge lies in its rational structural optimization alongside the development of green, high‐efficiency pretreatment technologies. Here we report an innovative microwave‐driven ultrastructure reconstruction strategy, leveraging the inherent hierarchical features of cell wall. This approach allows ultrafast (30 s), reagent‐free engineering of precursors with high component retention while enabling precise HC structure adjustment. The instantaneous thermal effects from microwave field trigger recrystallization of amorphous cellulose, redistribution of lignin, and enrichment of inter‐component interfaces with suppressed large mesopores. The resulting HC featured abundant closed pores, suitable specific surface area, and more disordered carbon structure. Importantly, in situ formation of carbon quantum dots was first confirmed in the HC. Optimized bamboo‐derived HC delivered a high reversible capacity of 398 mAh g −1 and an initial coulombic efficiency of 86.7% at 30 mA g −1 , indicating notably improved sodium storage performance. This work establishes a universal ultrastructure modulation strategy for lignocellulose precursors and unravels the structural evolution mechanisms during conversion biomass into high‐performance HC anodes.