Understanding the Relationship of Closed Pore Structure in Biomass‐ derived Hard Carbon with Cellulose Regulating Strategy

Abstract Recycling waste biomass to pyrolytic carbon has become a development direction of sodium‐ion batteries (SIBs) anodes. However, it remains a challenge to precisely control the composition and structure of biomass to modify the properties of derived carbon. Herein, a strategy of hydrolyzing cellulose in phellem with sulfuric acid is proposed, which can promote cellulose fracture, reduce the graphitization and increase the content of closed pores in hard carbon. Accordingly, after the regulation of closed pore structure, the reversible capacity increased from 207 to 330 mAh g −1 at 20 mA g −1 , realizing an increase of ≈130 mAh g −1 in the plateau region and the initial Coulombic efficiency (ICE) is enhanced from 78% to 90%. When applied in full cell with O3‐Na[Ni 1/3 Fe 1/3 Mn 1/3 ]O 2 , it showed an energy density of 247 Wh kg −1 . This strategy has certain universality, and it provides the feasibility to use low‐value cellulose‐containing biomass to fabricate high‐performance hard carbon materials.