Oxygen functionalities incorporation into hard carbon anodes for high rate sodium ion storage

The sodium storage performance of hard carbon (HC) derived from biomass is influenced by the composition and structure of the precursor. The changes in carbon structure resulting from pyrolysis pretreatment, and their modulation of HC properties, require systematic investigation. Herein, different pretreatments were employed to obtain HC containing varying degrees of oxygen functionalities, which are demonstrated to result in a non-negligible effect. We confirmed the presence of the effective oxygen-containing functional groups by Fourier transform infrared spectroscopy (FTIR) and found these further affected the structure of HC. Intriguingly, the controlled effect was found to enhance the proportion of sp 2 -hybridized carbon configuration so that the diffusion of sodium ions and the transport of electrons were tuned. Furthermore, rich defects caused by variation of oxygen functionalities serve as reversible active sites for sodium storage. The HC showcases an excellent specific capacity (378.1 mAh g −1 at 0.1 C), based on the participation of oxygen functionalities in the formation process, accounting for 302.0 Wh kg −1 of full cell. The insights for the mechanism by which the electrochemical performance of HC is affected by oxygen functionalities, which provide a rational method to design biomass-based HC anode with high performance.