(A) study on the electrochemical properties of carbon nanotubes and carbon nanotubes/silicon composites

Abstract

The electrochemical properties of carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs), and carbon nanotubes/silicon composites have been studied for application as anode materials in Li-ion rechargeable battery. CNTs with high quality were successfully synthesized on the $Al_2O_3$ aerogel supported Fe/Mo catalysts by thermal CVD, and then effectively purified by an acidic treatment followed by the gas-phase oxidation process. The purified CNTs were chemically etched in acid solution and mechanically ball-milled by the high energy ball-milling process with an impact mode. Also, CNTs/Si composites were produced using purified CNTs and Si powder by the high energy ball-milling process. And then, the Li insertion and extraction mechanism into CNTs and CNTs/Si composites were investigated by various electrochemical test and structural and/or chemical characterization analysis. The purified CNTs were chemically etched in an acid solution and mechanically ball-milled by the high energy ball-milling process for modifying the structural characteristics and the surface functional groups of the purified CNTs. The reversible capacity ($C_{rev}$) of the etched MWNTs and SWNTs increased with increasing etching time, from 351 mAh/g ($Li_{0.9}C_6$) for the purified MWNTs to 681 mAh/g ($Li_{1.8}C_6$) for the etched MWNTs, and from 616 mAh/g ($Li_{1.7}C_6$) for the purified SWNTs to 878 mAh/g ($Li_{2.4}C_6$) for the etched SWNTs. However, the undesirable irreversible capacity (Cirr) of the etched MWNTs and SWNTs also increased, from 1012 mAh/g ($Li_{2.7}C_6$) for the purified MWNTs to 1229 mAh/g ($Li_{3.3}C_6$) for the etched MWNTs, and from 1573 mAh/g ($Li_{4.2}C_6$) for the purified SWNTs to 1726 mAh/g ($Li_{4.6}C_6$) for the etched SWNTs. The purified samples presented more stable cycle capacity than the etched samples during the charge/discharge cycling. In the etched CNTs, lateral defects, opened ends, edges of ...