Suppressing Lignin Self‐Condensation Enables Microstructure Engineering of Bamboo Derived Hard Carbon for High Performance Sodium‐Ion Batteries

The delignification pretreatments of lignocellulosic biomass have been regarded as the most efficient strategy to enhance the electrochemical performances of as-derived hard carbon anode for sodium-ion batteries. However, the lack understanding of delignification mechanism as well as the overlooked self-condensation of lignin during pretreatment has greatly impeded precise microstructural engineering of hard carbon. Herein, a phenol-assisted hydrothermal pretreatment has been proposed as a new and facile strategy to control the content of lignin in bamboo precursor. It has been demonstrated that the addition of phenol in hydrothermal pretreatment can suppress self-condensation of lignin and enable efficient removal of recalcitrant lignin in bamboo powder. As a result, the as-prepared hard carbon possesses abundant closed pores, expanded interlayer spacing, and increased carbonyl functional groups. When evaluated as an anode for sodium ion battery, the hard carbon can deliver a high reversible capacity of 347.3 mAh g^-1 at 0.1 C, excellent rate performance of 235 mAh g^-1 at 6 C and superior cycle stability with a capacity retention of 93.97% after 2000 cycles at 2 C. This work not only unravels the mechanisms of efficient delignification at molecular level but also proposes a novel strategy to produce high-performance hard carbon from lignocellulosic biomass.