Comparison of Structural Analysis and Electrochemical Studies of C-Li 4 Ti 5 O 12 and CNT-Li 4 Ti 5 O 12 Nanocomposites
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Comparison of Structural Analysis and Electrochemical Studies of C-Li4Ti5O12 and CNTLi4Ti5O12 Nanocomposites particles used as Anode for Lithium Ion Battery Xiangcheng Sun1, Xuedong Bai2, Yongqing Wang3, M. Hegde4, I. D. Hosein4, P. V. Radovanovic4, Yu Guo Guo3 and Bo Cui1 1
Department of Electrical and Computer Engineering, University of Waterloo, Canada Institute of Physics, Chinese Academy of Sciences, Beijing, China 3 Institute of Chemistry, Chinese Academy of Sciences, Beijing, China 4 Department of Chemistry, University of Waterloo, Canada 2
ABSTRACT Carbon-Li4Ti5O12 (C-LTO) and carbon nanotube-Li4Ti5O12 (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 Li4Ti5O12 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 Li4Ti5O12particles showed the superior initial discharge capacity of more than 200 mA·h/g at 0.1C 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 Li4Ti5O12 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. INTRODUCTION Among various anode materials, spinel–type Li4Ti5O12 has been considered to meet the long cycle life and higher safety and better electrochemical properties as a promising anode with the highest technological potential in lithium ion batteries compared to the current commercial graphite anode materials [1-5]. It has been well known that, such a spinel-type Li4Ti5O12 almost does not change during discharge-charge cycling to show excellent structural ability of zerostrain during lithium ion insertion/extraction, make it achieve the high rate capability and reversibility. It also provides a stable voltage of 1.55 V against a lithium electrode [2, 3] accommodates Li ions with a theoretical capacity of 175 mAh/g, and the actual discharge
