Tailoring Microstructure of Lignin-Derived Hard Carbon Nanofibers via Molecular Stitching for Enhanced Sodium-Ion Storage

Renewable lignin is an attractive biomass precursor for sustainable hard carbon in sodium-ion batteries (SIBs) owing to its renewability, high carbon yield, and intrinsically molecular disordered structure. However, severe structural collapse during carbonization and low initial coulombic efficiency (ICE) hinder its practical application. Herein, an integrated strategy of PMDA-mediated molecular stitching and electrospinning with PVP as a fiber-forming aid was used to fabricate binder-free, self-supporting lignin-derived carbon nanofibers (LCNFs). With an optical PMDA content of 10 wt %, LCNF-P10 forms a robust three-dimensional cross-linked network through in situ esterification, effectively suppressing structural collapse during carbonization. Meanwhile, the synergistic effect of molecular stitching and PVP-derived pore engineering generates a highly disordered carbon framework with enlarged interlayer spacing (0.381 nm), hierarchical porosity, and abundant closed nanopores, thereby promoting low-voltage sodium storage. Consequently, LCNF-P10 delivers a high reversible capacity of 374.7 mAh g–1, an exceptional ICE of 89.39%, good rate capability, and excellent long-term cycling stability. The full cell assembled with a Na3V2(PO4)3 cathode achieves a high energy density of 240 Wh kg–1. This work demonstrates a sustainable molecular engineering strategy for converting renewable lignin into high-performance, freestanding hard carbon electrodes, providing new insights into the scalable utilization of biomass resources for practical sodium-ion batteries.