The role of boron in B/C/N and B/C materials as an anode of sodium ion batteries

Abstract

Graphite-like layered materials composed of boron/carbon/nitrogen (B/C/N) and boron/carbon (B/C) have been prepared by CVD method using BCl 3 and CH 3 CN or C 2 H 4 as starting materials, respectively. Electrochemical behaviors of B/C/N and B/C materials as anodes of sodium ion batteries have been investigated. Their properties have been compared with those of carbon/nitrogen (C/N) material and carbons prepared by CVD method. B/C/N and B/C materials showed reversible intercalation and de-intercalation on their discharge and charge cycles. The formation of stage structures was observed during the discharge (electrochemical intercalation) in 1 M-NaPF6/ EC+DEC (1:1) electrolyte solution, which was not clearly observed in the cases of C/N material and carbon. Potentials at the beginning of discharge (intercalation of Na+ ion) were higher than those of C/N material and carbons, and depended on the boron content in the material. B/C materials having larger boron content tended to show higher reversible capacity. B/C/N materials showed highest reversible capacity 190mAhg-1 among the materials prepared in this study by using CVD method. These results could be explained by the electronic structure of the material in which electron deficient boron atom lowered the bottom of conduction band, and will provide useful information for designing materials as electrodes.