Regulation of surface oxygen functional groups and pore structure of bamboo-derived hard carbon for enhanced sodium storage performance

Hard carbon materials with long low-voltage plateau have been used as the anode materials for sodium ion batteries which are considered to be one of the most potential large-scale energy storage systems. Herein, carbonyl groups and closed micropores are introduced into bamboo-derived hard carbon materials simulta-neously to enhance the sodium ion storage performance. The carbonyl groups are demonstrated to enhance the reversible Na adsorption in the sloping region and closed micropores are beneficial to sodium ion storage in the low-voltage plateau region. Moreover, the introducing carbonyl groups improve the reversible sloping capacity not at the expense of increasing specific surface area and deteriorating the initial Coulombic efficiency. The hard carbon carbonized at 1300 degrees C delivers a high reversible specific capacity of 348.5 mAh g-1 at a current density of 30 mA g-1 with a charge/discharge Coulombic efficiency of 84.1 %, and keeps a specific capacity of 295.9 mAh g-1 with a capacity retention of 91.6 % at a current density of 300 mA g-1 after 500 cycles. This work provides a novel strategy to precisely regulate the microstructure for biomass-derived hard carbon for superior sodium ion storage performance.