Controlling carbon-oxygen double bond and pseudographic structure in shaddock peel derived hard carbon for enhanced sodium storage properties

Oxygen-containing functional groups and pseudographic structure are key factors that affect the electrochemical properties of biomass derived carbon materials. In this work, the shaddock peel derived hard carbon with abundant carbon-oxygen double bond (CO) and highly ordered pseudographic structure is successfully synthesized by a H2SO4-assisted hydrothermal pretreatment and subsequent KOH-assisted low temperature (600 °C) pyrolysis procedure. The resulting unique structure is beneficial for the co-effective enhancement of Na+ storage sites and electrochemical reaction kinetics. The hard carbon exhibits excellent cycling and rate performances in sodium-ion batteries, delivering a high reversible capacity of 380 mAhg−1 at 50 mAg−1 after 500 cycles, and that of 274 and 199 mAhg−1 even at 500 and 1000 mAg−1, respectively. This performance is superior to the previously reported shaddock peel derived hard carbons. Besides, the surface-controlled redox mechanism of CO and Na+ occurring at the hard carbon is clearly revealed.