Regulation of closed pores in hard carbon for enhanced electrochemical sodium storage

The development of hard carbon materials with high plateau capacity as anode materials for sodium-ion batteries (SIBs) is crucial to improving the energy density of SIBs, while the closed pores are closely related to the low-voltage (<0.1 V) plateau capacity of hard carbon anodes. Herein, through a simple ZnO template method and acid treatment, a wealth of closed pores were created in the hard carbon material derived from camellia shells. Experimental results reveal the mechanism of sodium ions adsorption at the defect sites and the formation of sodium clusters in the closed pores, which corresponds to the slope region and the plateau region, respectively. Notably, being beneficial to the considerable closed pore content and suitable microstructure, the optimized sample exhibits a high reversible capacity of 340 mA h g^-1, which is mainly contributed by the low-voltage plateau process (51%). This work provides a new strategy for precisely regulating the microstructure of biomass-derived hard carbon for sodium-ion storage.