Electrochemical properties of graphene flakes as an air cathode material for Li–O2 batteries in an ether-based electrolyte

Abstract

We employed graphene flakes as an air-cathode material for Li–O₂ batteries and investigated their electrochemical properties in the dimethyl ether electrolyte. Graphene flakes were prepared by microwave-assisted reduction of graphene oxide, and their electrochemical properties were compared with those of Ketjen Black and carbon nanotubes. The catalytic effect of the prepared graphene flake-air cathode was demonstrated using cyclic voltammetry and discharge–charge testing performed under a limited discharge capacity. The catalytic effect of graphene flakes was also supported by morphological and spectroscopic analysis of the discharge–charge products formed on the graphene surface. Scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy revealed that Li₂O₂, Li₂O, and Li₂CO₃ were the main discharge products on all carbon-air cathode surfaces. Raman spectroscopy revealed that LiRCO₃ was additionally formed on Ketjen Black and carbon nanotubes during the first discharge; however, its formation was not observed on the graphene flakes. The catalytic effect of the graphene flakes and the absence of LiRCO₃ in the discharge product could explain the higher Coulombic efficiency in the discharge–charge tests.