Comparison of Structural Analysis and Electrochemical Studies of C-Li_4Ti_5O_(12) and CNT- Li_4Ti_5O_(12) Nanocomposites particles used as Anode for Lithium Ion Battery

摘要

Carbon-Li_4Ti_5O_(12) (C-LTO) and carbon nanotube-Li_4Ti_5O_(12) (CNT-LTO) nanocomposite particles have been synthesized by hydrothermal method and a following high-temperature calcinations using a mixture of micro-size Li-Ti-O precursors and conducting black and carbon nanotubes, respectively. Two different types of coating layers have been characterized and analyzed on two kinds of Li_4Ti_5O_(12) particles surface by high resolution transmission electron microscopy images (HR-TEM) and selected area electron diffraction (SAED). Typical HR-TEM images and SAED patterns at nano-scale confirmed and showed that both particles exhibited a well-developed spinel nanocrystal with average sizes around 20-50 nm. The C-LTO particles exhibited the roughly spherical shape with more than 5 nm graphitic coating uniformly on the spherical surfaces; however, the CNT-LTO particles showed uniform square nanocrystal with edge length around 30 nm and a few layers of graphene covering the surface. Electrochemical studies of galvanostatic discharge/charge cycling capacity testing indicated that both Li_4Ti_5O_(12) particles showed the superior initial discharge capacity of more than 200 mA·h/g at 0.1 C rate, and also the CNT-LTO particles show much improved specific capacity than that of the C-LTO particles during different cycling processing. It has been proposed that, grephene covering layers and the CNT interconnection networks are prove to increase electronic conductivity and improve the kinetics of Li_4Ti_5O_(12) toward fast lithium insertion/extraction. The comparative experimental results demonstrated that both nanoscale grephene layer and CNT inter-networks among particles is highly effective in improving the electrochemical properties of the CNT-LTO particles.