Electrochemical characteristics with the addition of carbon nanotubes and the manufacturing process for sulfur cathode in the Li/S cell.

ABSTRACT

Carbon nanotubes (CNTs) were purified using acid solution, and CNT-sulfur composite powder was prepared via precipitation, using the purified CNTs. In addition, the effect of the purified CNTs (PUCNTs) on the electrochemical performance of the Li/S cell was investigated. After the purification, almost all the impurities in the as-synthesized CNTs (ASCNTs) were removed, and the dispersibility of the CNTs was improved. On the other hand, the concentration of the structural defects and of the disordered structures in the PUCNTs was increased due to the surface oxidation of the tubes during acid treatment. In the case of the PUCNT-S composite powder, the outer wall of the tubes was well covered with sulfur, as opposed to the tubes in the ASCNT-S composite powder. The Li/S cell containing ASCNT-S composite cathode showed a large voltage decrease and a 680 mAh/g capacity during the first discharge process. The Li/S cell with PUCNT-S composite cathode, however, showed a higher discharge capacity and better cycle performance than the cell with ASCNT-S composite cathode. The electrochemical performance of the Li/S cell was improved for the PUCNT-S composite cathode using the CNTs purified by acid treatment.