Effect of porosity on electrochemical properties of carbon materials as cathode for lithium-oxygen battery

•Carbon aerogel shows much higher discharge capacity than activated carbons.•Mesopores are more effective in the utilization of pore volume than micropores.•Open pores help the oxygen supply even if they are micropores.

Porosity effect of carbon materials on the electrochemical performances as cathode materials in non-aqueous Li-oxygen cells has been investigated. A carbon aerogel material is chosen to represent mesoporosity and a couple of activated carbon materials are selected to represent microporosity. Carbon aerogel shows at least ten times higher discharge capacity (4155 mAh g−1) than activated carbons. It is found that as much as 61% of pore volume of carbon aerogel is filled with discharge products (Li2O2) while less than 18% of pore volume is occupied with Li2O2 at the end of discharge in activated carbons, indicating that mesopore is more effective than micropore. In another experiments, the electrolyte impregnated electrode shows a capacitor-like discharge behavior, meaning it is necessary to have some open pore for the oxygen supply even though they are micropores.