ABSTRACT
As a new class of nanocarbon, reduced graphene oxide (RGO) is expected to bring about a breakthrough in many applications including electrochemical energy storage devices due to its large specific surface area, high electrical conductivity, and its chemical and mechanical properties. By the benefit of their outstanding electrical and chemical properties, metal oxide/RGO hybrids have been intensively investigated for the lithium-ion battery applications. The excellent properties of metal oxide/RGO hybrids are generated from synergistic combination of RGO with metal oxide on the nanometer scale. In the hybrids, RGO not only serves as a highly conductive support material, but also provides a large 2-D surface for the well-dispersed deposition of metal oxides at the nanometer scale. Furthermore, attached metal oxides on RGO may efficiently prevent the restacking of individual RGO
in hybrids. In this chapter, we report on the synthesis and electro-chemical characterization of RGO and metal oxide/RGO hybrids for high-rate lithium-ion battery applications. 10.1 IntroductionLithium ion (Li-ion) batteries are widespread application as secondary batteries in numerous applications in consumer electronics, and considered to be one of the best candidates for various forms of electric vehicle (EV).1 However, the power density of Li-ion batteries is still low to support the industrial needs such as EV. Researches on the electrode materials have been widely investigated to improve their high-rate capability, for achieving high-power density of Li-ion batteries.2-4Nanosized metal oxides are expected to enhance the rate capability due to the highly effective interfacial area between the oxide surface and the electrolyte, and the shorter travel length of lithium ions and electrons during charge/discharge.5 Unfortunately, many of the nanosized metal oxides reported in the literature for Li-ion batteries suffer from low electrical conductivity and a tendency of particle agglomeration, resulting in a marginal improvement of rate capability.6,7 Therefore, how to prepare well-dispersed nanosized metal oxides with high electrical conductivity is the key in achieving high-rate capability.6,8One approach is to employ a hybrid composed of nanosized metal oxides and nanocarbon with high electrical conductivity. Dispersing the metal oxide nanoparticles on the highly conductive nanocarbon template hinders the agglomeration of the oxide nanoparticles and improves the electrical conductivity.9 Reduced graphene oxide (RGO) or graphene nanosheets have rapidly emerged as potential electrode materials for electrochemical energy storage due to their large surface area high electrical conductivity, and good mechanical properties, which are comparable with, or better than, those of carbon nanotubes.10 Therefore, RGO can be an ideal template to construct a hybrids with good dispersion of metal oxide nanoparticles and improved electrical conductivity. In the past few years, considerable efforts have been devoted to apply various metal oxide/RGO hybrids to Li-ion battery application. (e.g., Co3O4,11 Fe3O4,12 SnO2,13 Li4Ti5O12,14 and LiMn2O415 with RGO).
