Rationally Generating Biomass-Derived Hard Carbons with Closed Pores by Cellulose (C-sp³) Cross-Linking Lignin (C-sp²) for Advanced Sodium-Ion Battery

Hard carbons (HCs) have promising broad applications as prospective anode materials in sodium-ion batteries (SIBs). However, the low initial Coulombic efficiency (ICE) and inferior reversible specific capacity inevitably restrict the commercial application of HCs. Herein, an easy chemical cross-linking reaction between cellulose and lignin is utilized to produce cellulose/lignin hard carbons (MC-LGHCs) with abundant closed pore structures, significantly enhancing both the ICE and reversible specific capacity. The cross-linking strategy effectively disrupts the high crystallinity of cellulose, modulates the C-sp2 and C-sp3 content, and inhibits the formation and growth of the graphitic hard carbon layer in MC-LGHCs during the carbonization process. Electrochemical tests manifest that MC-LG-10-10 significantly delivers the reversible specific capacities of 351 mAh g–1 with ICE of 78% at 30 mA g–1. Besides, the Coulombic efficiency (CE) of MC-LG-10-10 stays around 99.8% after 600 cycles at 0.5 C, and the NVP//MC-LG-10-10 full-cell exhibits a reversible capacity of 145 mAh g–1 after 200 cycles and capacity retention of 88.2% at 1 C. These findings indicate that MC-LGHCs materials hold significant promise as ecofriendly and low-cost anode materials for sodium-ion batteries, offering satisfactory electrochemical performance.