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

Abstract:

A simple and efficient method is developed to synthesize the nanocomposite of anatase TiO₂ 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 TiO₂ particles were well dispersed in reduced graphene oxide nano-sheets. These graphene-TiO₂ 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 TiO₂ particles provide high electrical conductivity.

Introduction:

TiO₂ 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 TiO₂ 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 TiO₂, 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 TiO₂ owing to its superior electronic conductivity and large surface area.  It is found that TiO₂-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 TiO₂ 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 TiO₂ 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 TiO₂ 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 TiO₂-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 TiO₂ 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 TiO₂anatase 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:

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