Solvothermal-assisted hybridization between reduced graphene oxide and lithium metal oxides: A facile route to graphene-based composite materials

Hybridization between lithium metal oxide and reduced graphene oxide, or RGO, can be achieved by the solvothermal treatment of the water/ethanol-based suspension of graphite oxide, or GO, nanosheets containing powdery lithium metal oxide. The solvothermal treatment for the mixture suspension of GO and Li ₄Ti ₅O ₁₂ gives rise not only to the reduction of GO to RGO but also to the attachment of the Li ₄Ti ₅O ₁₂ particles to the flat surface of RGO 2D nanosheets. The crystal structure and crystal morphology of the Li ₄Ti ₅O ₁₂ particles remain intact after the composite formation with the RGO nanosheets. The formation of chemical bonds and internal electron transfer between the RGO and Li ₄Ti ₅O ₁₂ components is evidenced by micro-Raman and X-ray photoelectron spectroscopy, showing the weakening of the carbon-carbon bonds and the formation of carbon-oxygen bonds. In comparison with the pristine Li ₄Ti ₅O ₁₂ material, the Li ₄Ti ₅O ₁₂-RGO nanocomposites display better anode performance with a larger discharge capacity of ∼175 mAhg ^-1, underscoring the merit of RGO hybridization in improving the electrode performance of bulk metal oxide. Diffuse reflectance UV-vis and photoluminescence spectroscopic analyses reveal a strong electrical connection between lithium titanate and RGO, which is mainly responsible for the observed improvement of the electrode performance upon the composite formation. In addition to the electrode performance, the photocatalytic activity of the lithium titanate for the generation of photocurrent can be remarkably enhanced by the coupling with RGO, confirming the usefulness of the present synthetic method in optimizing the photoinduced functionality of metal oxides. The solvothermal strategy presented here is also applicable for the synthesis of LiMn ₂O ₄-RGO nanocomposite showing much superior electrode performance over the pristine LiMn ₂O ₄. The experimental findings underscore that the present synthetic method can provide a universal way to not only immobilize multicomponent metal oxides on the surface of RGO nanosheets with a strong electrical connection but also improve the electrode and photocatalytic activity of these metal oxides.