Nanocomposites of TiO₂ Nanoparticles-Graphene with High-Rate Performance for Li-Ion Battery

Abstract

Abstract: A simple and efficient method is developed to synthesize the nanocomposite of anatase TiO 2 and reduced graphene oxide as anode material for Li-ion battery applications. The method involves one-step hydrothermal treatment without any surfactant or high-temperature calcinations. Structure analyse demonstrated that nano-sized anatase TiO 2 particles were well dispersed in reduced graphene oxide nano-sheets. These graphene-TiO 2 hybrid nanocomposites were electrochemically investigated in the coin-type cells versus metallic lithium, and the lithium storage performance showed an enhanced rate capabilities and cycling stability at different charge/discharge rates. These improved electrochemical performance can be mainly attributed to the fact that conductive graphene nano-sheets attached on nanosized TiO 2 particles provide high electrical conductivity. Introduction : TiO 2 has been regarded as a promising anode material for lithium-ion batteries due to its environmental benignity, low cost, and good safety [1–3]. However, its practical capacity and high-rate capability are limited due to the blow Li-ion diffusivity and electronic conductivity during reversible Li-ion insertion/extraction process [4]. In order to improve the electrochemical performance of TiO 2 materials, nanotechnology has been explored to provide increased reaction active sites and short diffusion lengths for both electron and Li-ion transport [5–6]. A variety of approaches have been developed to increase the electronic conductivity of the TiO 2 , such as adding conductive agents [7] and using conductive coating [8]. Graphene has been regarded as an ideal carbon nanostructure to improve the rate capability of TiO 2 owing to its superior electronic conductivity and large surface area. It is found that TiO 2 -graphene nanocomposite exhibited a high capacity and excellent rate capability in the enlarged potential window of 0.01–3.0 V due to the graphene not only as a conductive agent but also as a lithium storage material [9]. Herein, the nanocomposites of anatase TiO 2 nanoparticles and reduced graphene oxide were facilely synthesized, the electrochemical performance of the obtained nanocomposite was investigated as an anode material. Experimental : The nanocomposites of anatase TiO 2 nanoparticles-graphene oxides were synthesized by one-step hydrothermal method. Briefly, 25 mg of graphene oxide was firstly added to 75 mL deionized water, then 5 m L of 1.5M sodium hydroxide solution was added to obtain a colloidal solution that was sonicated for 30 min. Such a colloidal solution was subsequently mixed with 50 mg commercial TiO 2 nano-powders (ca.25 nm diameter) by high-speed stirring for1 h. The resulting solution was put into an autoclave and heated at 180°C for 10 h. When the reduction reaction was finished, the as-synthesized TiO 2 -graphene composites were isolated by centrifugation, washed with pure water and ethanol several times, and dried at 80°C for 2h. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performances of galvanostatic charge-discharge and cyclic voltammetry (CV) were investigated using coin cells (CR2032) at a LAND-CT2001A battery-testing system. Results : The morphology of the nanocomposites were investigated by scanning electron microscopy (SEM). SEM images in Fig.1 showed that the TiO 2 nanoparticles are dispersed uniformly in the graphene oxide with relatively low amounts load. Raman spectra in Fig. 2 shows the typical features of reduced graphene oxide with the presence of D band located at 1340 cm −1 and G band at 1581 cm −1 . In addition, the Raman lines for E g , B 1g , A 1g , and B 1g modes of TiO 2 anatase phase were also observed. Acknowledgement : Financial supports from the President’s Award of University of Waterloo and Natural Sciences and Engineering Research Council of Canada (NSERC) and Waterloo Institute for Nanotechnology (WIN) are greatly appreciated. References: [1] Z. Yang, D. Choi, S. Kerisit, K.M. Rosso, D. Wang, J. Zhang, G. Graff, J. Liu, J. Power Sources 192 (2009) 588. [2] P. Kubiak, T. Fröschl, N. Hüsing, U. Hörmann, U. Kaiser, R. Schiller, C.K. Weiss, K. Landfester, M. Wohlfahrt-Mehrens, Small 7 (2011) 1690. [3] J. S. Chen, X.W. Lou, Electrochemistry Communications 11 (2009) 2332. [4] S. Bach, J. P. Pereira-Ramos, P. Willman, Electrochimica Acta 55 (2010) 4952. [5] Y. H. Jin, S. H. Lee, H.W. Shim, K.H. Ko, D.W. Kim, Electrochimica Acta 55 (2010) 7315. [6] F. Wu, Z. Wang, X. Li, H. Guo, J. Materials Chemistry 21 (2011) 12675. [7] Y. Wang, T. Chen, Q. Mu, J. Materials Chemistry 21 (2011) 6006. [8] J. S. Chen, H. Liu, S. Z. Qiao, X.W. Lou, J. Materials Chemistry 21 (2011) 5687. [9] D.D. Cai, P.C. Lian, X.F. Zhu, S.Z. Liang, W.S. Yang, H.H. Wang, Electrochimica Acta, 74 (2012) 65.