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CO2 oxidation of carbon nanotubes for lithium-sulfur batteries with improved electrochemical performance

Wang, Datao, Wang, Ke, Wu, Hengcai, Luo, Yufeng, Sun, Li, Zhao, Yuxing, Wang, Jing, Jia, Lujie, Jiang, Kaili, Li, Qunqing, Fan, Shoushan, Wang, Jiaping
Carbon 2018 v.132 pp. 370-379
air, batteries, carbon, carbon dioxide, carbon nanotubes, cathodes, dispersions, electrochemistry, electrolytes, electrostatic interactions, oxidation, sulfur
The fabrication of high-performance cathodes with high sulfur content is essential for the practical realization of lithium–sulfur (Li–S) systems. The preparation of high-sulfur-content electrodes is currently hindered by poor dispersion of the conductive agents; nonuniformly distributed conductive agents cannot provide sufficient sulfur-loading sites, thereby resulting in aggregation of sulfur/Li2S and severe polarization. To deal with this issue, we prepare CO2 modified carbon nanotube (CNT)-based cathodes for Li–S batteries. CNTs are exposed to CO2 at 900 °C, resulting in uniformly distributed negative charges on the external surface of the tubes; the electrostatic repulsion facilitated the dispersion of CNTs. Compared with the previous work on CNTs prepared by air oxidation (denoted as air-CNTs), the dispersions of the CO2-treated CNTs (denoted as CO2-CNTs) are more stable, which allows higher sulfur loading and improves sulfur utilization. A free-standing CO2-CNT&S electrode with a sulfur content of 80 wt% is fabricated through a sonication-assisted method. The excellent dispersion of the CO2-CNT&S network results in little kinetic barriers, low polarization, and fast charge transport at the interface of the electrode and electrolyte. The CO2-CNT&S electrode delivers a lower capacity fading rate and superior rate performance compared with the air-CNT&S electrode.