Iron-induced formation of hierarchical open-pore hard carbon rich in oxygen functional groups for high-performance Na + storage

Abstract

Hard carbon negative electrode of Na + battery derived from biomass faces significant constraints on its practical implementation, primarily stemming from inferior initial coulombic efficiency (ICE) and sluggish electrochemical kinetics, which is mainly due to irreversible sodium capture in disordered regions and closed pores. This work proves that Fe-catalyzed carbonization strategy is used to construct hierarchical open-pore hard carbon rich in oxygen-containing functional groups.By introducing FeCl3 in the initial carbonization process, more oxygen atoms are locked due to the catalytic effect of iron, which is transformed into oxygen functional groups beneficial to sodium storage at high temperature. Meanwhile, the ironcatalyzed hierarchical porous structure (micropore-mesopore) facilitates electrolyte infiltration and the reversible adsorption-desorption of sodium ions (Na⁺). Electrochemical tests showed that FeCl3 modified hard carbon showed 89.6% ICE, and its capacity remained 94.6% after 500 cycles, which was better than that derived from original biomass. Through further research, we found that the hard carbon with graded pore structure constructed by iron catalysis has the mechanism of " adsorption-intercalation-pore filling" for Na + storage. This research presents a valuable reference for the function of catalysts in improving the Na + storage behaviors of hard carbon derived from biomass.