Molecular conformation engineering of hard carbon precursors for enhanced sodium ion storage

: Unlocking sustainable and high-performance anodes is critical for the large-scale deployment of sodium-ion batteries in grid-scale energy storage. Phenolic resin-derived hard carbons are attractive due to their high carbon yield (∼50%) and scalable synthesis, yet their highly regular microstructure and narrow interlayer spacing restrict sodium storage performance (e.g., specific capacity, initial Coulombic efficiency, and long-term stability). Herein, we introduce a lignin-driven crosslink engineering in which depolymerized lignin fragments with oxygen rich functional groups partially replace phenol in phenol-formaldehyde resins. This molecular-level integration simultaneously enhances crosslinking density and diversifies bonding configurations, disrupting structural regularity during pyrolysis. The resulting hard carbon exhibits a highly disordered microstructure with expanded interlayer spacing, facilitating rapid ion transport and enhanced storage. As a sodium-ion battery anode, it delivers a reversible capacity of 371 mA h g ‒1 , an initial Coulombic efficiency of 91%, and cycling stability exceeding that of state-of-the-art resin-based hard carbons. This work couples a scalable biomass valorization pathway for microstructure-controlled carbons, offering broad potential for high-performance storage systems.