Hybrid Li-air battery cathodes with sparse carbon nanotube arrays directly grown on carbon fiber papers
By Li, Yunfeng; Huang, Zhongping; Huang, Kan; Carnahan, David & Xing, Yangchuan
Published in Energy Environ. Sci.
The Royal Society of Chemistry
2013
Abstract
Sparsely populated, vertically aligned nitrogen doped carbon nanotube arrays (CNTAs) with dislocated-graphene stacking were grown directly on carbon fiber papers and investigated as hierarchical air cathodes in hybrid Li-air batteries with aqueous catholytes. The CNTAs were made with electrodeposited Ni nanocatalysts, followed by plasma-enhanced chemical vapor deposition. The thus obtained CNTAs can reach a population number density as low as [similar]107 per cm2 on the carbon fibers, achieving an extremely high porosity of over 99% for the active layer in the cathode. The sparse CNTAs not only provide effective pathways for the reacting species, but also show a significantly high catalytic activity, which is found to be comparable to that of a supported Pt electrocatalyst. The high activity of the CNTAs is attributed to the rich graphene edges exposed on the CNT surface and nitrogen doping. Hybrid Li-air batteries with such cathodes have shown a consistent discharging capacity of 710 mA h g-1 and a specific energy of 2057 W h kg-1 at 0.5 mA cm-2. Stable charge-discharge cycling at 0.5 mA cm-2 showed an average potential difference of 1.35 V, indicative of a relatively small overpotential and high round trip efficiency (71%). Furthermore, the hybrid Li-air battery based on the hierarchical cathode can reach a power density as high as 10.4 mW cm-2.