Chemical crosslinking regulating microstructure of lignin‐derived hard carbon for high‐performance sodium storage

Abstract Lignin, a biomass derived polymer, has gained considerable recognition as a highly promising precursor of hard carbon primarily due to its ample reserve, eco‐friendliness, and cost‐effectiveness. However, lignin‐derived hard carbon via direct carbonization generally yields suboptimal performance for sodium storage due to the unsuitable microstructure. Herein, a simple phytic acid activation combined high‐temperature annealing strategy is proposed to regulate the microstructure of lignin‐derived hard carbon for high‐performance sodium‐ion batteries (SIBs) anode. Phytic acid activation not only reduces the ordering and creates abundant closed pores through improving the crosslinking degree and thermal stability of lignin but also introduces P heteroatoms to effectively expand the interlayer spacing of the derived hard carbon. High‐temperature carbonization further increases the size of closed pores, leading to a more favorable sodium storage in the plateau region. Consequently, the optimal phytic acid activating lignin derived hard carbon (PLHC 1300) delivers a high capacity of 380.3 mAh g−1 with an enhanced plateau capacity ratio of near 68.1% at 30 mA g−1, and achieves a capacity retention of near 100% after 150 cycles at 1 A g−1. This work significant advances the application of lignin in energy storage and contributes to the progression of commercial SIBs.