Electrochemical Preparation of CNTs-Coated Cu Substrate for Si-O-C Composite Deposition and Characteristics of Si-O-C/CNTs/Cu As an Anode of Li Secondary Batteries
Figure 1 shows the schematic figure of Si-O-C composite deposition process on the CNTs/Cu substrate. In Fig. 1a, 2D-surface morphology of the conventional Cu substrate is obviously indicated. However, it is observed that the CNTs were homogeneously deposited on the Cu substrate forming 3D-structured morphology as shown in Fig. 1b. The Si-O-C composite was deposited on the 3D-structured CNT layer with good uniformity in Fig. 1c. The amount of Si deposited on the CNTs/Cu substrate increases in 33% compared to that of conventional Cu substrate. It is supposed that the electrodeposited Si-O-C composite were filled inside of CNT layer because of increased adhesion between Si-O-C with Cu substrate (see schematic figure in Fig. 1d).
Electrochemical properties were examined with cycle ability for 100 cycles at 0.1 C-rate in Fig. 2. The discharge capacity of Si-O-C/CNTs/Cu delivered 2463.2 and 1340.6 mAh g-1 of Si at the 1st and 100th cycle, which was higher than that of Si-O-C/Cu (1340.9 and 840.0 mAh g-1 of Si at the 1st and the 100th cycle, respectively), as shown in Fig. 2. Coulombic efficiencies of the Si-O-C/CNTs/Cu and the Si-O-C/Cu anodes were compared. The coulombic efficiencies of both anodes at 1st cycle were decreased under the 24.1% because of formation of SEI layer on anode. However, after 2nd cycle the coulombic efficiencies were increased dramatically. Both anodes achieved high coulombic efficiencies over 86.9 and 99.7% at the 2nd and 100th of the cycle test. In addition, after 10th cycle, Si-O-C/CNTs/Cu and Si-O-C/Cu anode show the stable coulombic efficiencies over 99.8%. It is obviously indicates that the Si-O-C/CNTs/Cu was performed as anode with good cycle ability and high coulombic efficiencies for Li secondary batteries.