Lithium-oxygen (Li-O-2) cells are a promising power source, and carbons are an attractive non-metal catalyst for air electrodes. To improve the electrochemical performance, various carbons are heated in an inert atmosphere. It is found that heat treatment at 900 degrees C can differently improve the electrochemical performance of multiwalled carbon nanotubes (CNTs), acetylene carbon black (AB) and activated carbon (AC), but the improvement of CNTs is the most obvious. After heat treatment, the peak current density of the oxygen reduction reaction (ORR) and the 1st discharge capacity of CNTs increase similar to 30% and similar to 125%, respectively, while the charge transfer reaction resistance and the Warburg diffusion resistance decrease similar to 7.0% and similar to 11.1%, respectively. AC has the highest charge capacities and capacity retention ratio in spite of little influence by heat treatment. The possible mechanism and reasons are analyzed using different techniques. Microstructure is superior to conductivity for enhancing the rechargeability and the cyclability, and heat treatment is effective for some carbon materials in improving the electrochemical performance of Li-O-2 cells. (C) 2014 Elsevier Ltd. All rights reserved.