Synergistic Effect of Dual-Doping of Graphene Nanosheets on the Electrochemical Performance of Lithium-Air Cells

Abstract

Rechargeable lithium-air battery is considered as one of the promising next-generation energy storage systems for application in electric vehicles due to its high theoretical energy density. In general, the performance of lithium-air cells in non-aqueous electrolyte is significantly affected by the large polarization in air cathode due to the deposition of discharge products as well as the ineffective electrocatalytic activity of electrode materials during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). To address these issues, noble metals are being used as catalysts, which may increase the cost of lithium-air cells. Recently, graphene nanosheets with a two-dimensional sp2-hybridized carbon structure have been actively explored as metal-free air cathode due to their superior electronic conductivity, mechanical strength, chemical stability, high surface-to-volume ratio and structural flexibility. The edge sites and other defect sites present in the basal plane of graphene prepared by chemical method have been demonstrated as catalytic sites for ORR.1 Furthermore, doping of graphene with heteroatoms such as nitrogen, boron, sulfur and phosphorus breaks the charge neutrality of carbon atoms and acts as catalytic centers.2 In this study, we demonstrate the synergistic effect of dual-doping of graphene nanosheets on the performance of lithium-air cells. Chemical and morphological characterization of the dual-doped graphene nanosheets along with their enhanced electrochemical performance over the single-heteroatom doped graphene as metal-free air-cathode will be presented.