Effect of Heat-Treatment Temperature of Carbon Gels on Cathode Performance of Lithium-Air Batteries

Abstract

Due to their high theoretical energy density, lithium-air batteries (LABs) are expected to become the standard secondary battery system of the next generation. However, for practical usage, their cycle performance needs to be improved. Thus far, few studies have investigated how the structure of carbon cathode materials affects their cycle performance. In this study, meso- to macro-porous carbon gels (CGs) heat-treated at different temperatures were prepared, and were used as model materials to discuss the relationship between carbon structure and cycle performance. Nitrogen adsorption experiments, X-ray diffraction analysis, Raman spectroscopy analysis, and thermal gravimetric analysis were conducted to derive the pore structure, crystal structure, carbon bonding state, and oxidation resistance of CGs, respectively. In addition to standard analysis methods, temperature program desorption measurements were conducted under vacuum to aid the analysis of surface oxygen-containing functional groups. Charge–discharge measurements indicated that cycle performance improves when the carbons were heat-treated at higher temperatures. Functional groups on the carbon surface were found to promote side reactions and reduce reversible capacity. Defects in the carbon are thought to promote uneven deposition of deposits which tend to cause the sudden “death” of LAB.