Fast lithium-ion insertion of TiO₂ nanotube and graphene composites

Though there have been remarkable growth and widespread application of Li-ion batteries in portable electronics, it is highly desirable to develop the electrode materials with superior performance to meet the challenges of emerging large scale applications in electric vehicles. Here we report the electrochemical lithium insertion performance of TiO₂ nanotube/graphene composites, which have been designed and effectively prepared by a one-step hydrothermal method. The structure and morphology of the products were analyzed by X-ray diffraction, FT-IR spectra, Raman spectra, X-ray photoelectron spectroscopy, transmission electron microscopy and field-emission scanning electron microscopy. The electrochemical properties were investigated by cyclic voltammetry, constant current discharge-charge tests, and electrochemical impedance techniques. Employed as an anode in a lithium-ion battery, the novel composites presented excellent electrochemical performance with high Li storage capacity (357 mAh g^-1 at the rate of 10 mAg ^-1, exceeding the theoretical capacity value 336 mAh g^-1 of TiO₂) and excellent rate performance. The TiO₂ nanotube/graphene composite exhibited excellent rate capacities of 150 mAh g^-1 (at the rate of 4000 mA g^-1) after 50 cycles and 80 mAh g^-1 (at the rate of 8000 mA g^-1) after 2000 cycles; the coulombic efficiency was approximately 99.5%, indicating excellent cycling stability and reversibility. The remarkable Li storage and high-rate capabilities of these nanotube/graphene composites were mainly attributed to the synergetic and interactive effects, namely, the "morphology" and "electronic" interactions of both components, and such kinds of graphene and nanotube composites held great promise as good example for designing future graphene based electrode materials with high electrochemical performances, as well as applications in advanced power batteries of EV and HEV.