Effect of surface modification on high-surface-area carbon nanosheets anode in sodium ion battery

Abstract

This paper reports a case study of the effect of nitrogen and oxygen functional groups of high-surface-area carbon nanosheets anode on electrochemical performance in sodium ion batteries. Hemp bast fiber is chosen to fabricate high-surface-area carbon nanosheets (2190 m2 g−1). After being treated with urea under hydrothermal condition, the as-prepared carbon nanosheets are functionalized with nitrogen- and oxygen-containing groups on the surface. Both the as-obtained and functionalized carbon nanosheets are used as anodes for sodium ion batteries, and the effect of nitrogen and oxygen functional groups on the electrochemical performance is investigated. The results indicate that the surface area of functionalized carbon nanosheets is significantly reduced to 840 m2 g−1. However, both the carbon nanosheets display similar high capacity, rate capability and good cyclability. The electrodes deliver a capacity of 162/173 mAh g−1 at 1 A g−1 after 2000 cycles and retain a capacity of 49/62 mAh g−1 at 10 A g−1. Besides the ultrahigh surface area and dilated graphitic layer of porous carbon nanosheets, chemisorption through functional groups are also found to be responsible for the high capacity. Moreover, the functionalized carbon nanosheets exhibit elevated Coulombic efficiency. These results confirm that modifying the surface of carbons is a promising strategy to improve the electrochemical performance.