TiO2-graphene nanostructures for energy storage: materials and devices

Abstract

Electrical energy storage devices are dominating the market of mobile electronics and their relevance is growing in hybrid vehicles systems. Rechargeable batteries and supercapacitors are the most investigated devices. The current interest in improving the electrochemical properties of materials and devices has been currently focused on the development of composite materials, exploiting their structure and properties. Graphene is an intriguing material due to its high electrical conductivity, flexibility and large theoretical specific surface area. Nanostructures have been suggested to be combined to graphene to achieve electroactive sites for a remarkable electrochemical performance. Titanium dioxide (TiO2) is a promising candidate in connecting its electrochemical properties with the synthesis methods to obtain it as a nanocrystalline material. Composite materials based on TiO2 and graphene have been reported as anode materials in lithium-ion batteries, the highest current technology of rechargeable batteries. Furthermore, this combination has been effective as electrodes in supercapacitors. Improvements in terms of energy and power densities, costs and safety can be obtained. In this research, nanostructured TiO2-graphene based materials have been successfully synthesized to be tested as electrodes in rechargeable Li-ion batteries and micro-supercapacitors. A thermally exfoliated graphite oxide (TEGO) has been chosen as graphene material, to take advantage of its defective structure for an in situ synthesis of anatase TiO2 nanoparticles onto graphene surface, through a hydrothermal route. A solid-state approach has been also performed to obtain the composite material by a high-energy ball milling treatment. TiO2-TEGO materials have been tested as electrode in lithium-ion half cells. To produce laser-scribed micro-supercapacitors, innovative technologies have been investigated by using the DVD burner laser. A novel approach has been optimized to promote the simultaneous synthesis of nanocrystalline anatase and graphene-based material. The electrochemical performance of lithium-ion half-cells and laser-scribed micro-supercapacitors has been improved thanks to the combination of these materials, making TiO2-graphene nanostructures a remarkable candidate in electrical energy storage devices.