Molecular-level biomass composition and crosslinking regulation towards hard carbon with high initial Coulombic efficiency for sodium-ion battery
Hard carbon (HC) is a leading anode for sodium-ion batteries (SIBs), but its low initial Coulombic efficiency (ICE) causes excessive sodium consumption at the cathode, limiting full-cell energy density and cycle life. This study modulates the lignin, cellulose, and hemicellulose ratios in raw bamboo and employs maleic anhydride (MA)-assisted thermal crosslinking to precisely control carbon layer orientation, graphite-like domain size, and closed pore structure in the resulting HC. Precursor composition regulation promotes sp2 hybridization within the carbon skeleton, generating larger graphite-like microcrystalline domains, while MA-induced crosslinking fosters closed pore development during high-temperature carbonization. The optimized HC (HC-BO-MA) delivers an ICE of 93.9% and a reversible specific capacity of 324 mAh g−1 at 20 mA g−1. This molecular-level strategy provides a rational design pathway for high-performance biomass-derived HC anodes, addressing the trade-off between capacity and ICE that has hindered SIB commercialization. The work demonstrates that simultaneous enhancement of reversible capacity and ICE is achievable through precise control of biomass composition and crosslinking chemistry.