論文ID: 020102
The surface properties of carbons significantly influence their performance when they are used as the cathode of lithium-air batteries. This study employed carbon nanofiber sheets derived from PAN nanofiber sheets prepared by electrospun (ES-CNF) as a model cathode to investigate the influences of surface properties. The structure of the sheets enabled sufficient access of O2 to the carbon surface. For this investigation, 5 types of ES-CNF sheets having different surface properties were prepared by varying the temperature of heat-treatment in the range of 800-2200°C. Part of the heat-treated samples were further treated with acid. The surface properties of the obtained samples were analyzed in detail by temperature programmed desorption analysis conducted under vacuum in the temperature range of 100-1800°C. The results indicated that discharge and charge voltages depend on the amount of edge-H, and type and amount of functional groups of carbon materials. Oxygen-containing functional groups (OCFGs) on carbon promoted not only surface-route deposition of Li2O2, which can be charged (decomposed) at voltages below 3.7 V, but also undesired side reactions, which can increase the charge voltage up to over 4.0 V. Furthermore, it was also found that carboxyl or phenol/ether groups effectively promote surface-route reactions much more efficiently than N-containing functional groups (NCFGs) and carbonyl groups. The knowledge obtained in this work can be utilized as a new guideline to design cathode carbon for lithium-air batteries.
