Study on graphene composites for electrode materials of lithium ion batteries

Low carbon economy and clean renewable energy now become significant topics over the world, due to the increasing demands for energy, decreasing amount of non-renewable energy, such as petrol, coal and natural gas, as well as environmental problems. With the economic development and the improvement of living standards, there is a growing emphasis on the development and utilization of water, wind, solar and other renewable energy. Comparing with the traditional energy, these new forms of energy have many advantages. However, they are subject to the climate and weather, and their output energy peaks do not match the demand. In addition, energy supply often shows big fluctuations. As a result, energy storage devices with high performance are urgently required to use energy more efficiently. Among all the energy storage devices, lithium ion batteries exhibit much more advantages, such as high voltage, high energy density, etc., thus they have been quite popularly used in portable devices since their birth, and now they are nominated as new energy source for vehicles. In order to expand the application of lithium-ion batteries in portable electronic devices and hybrid electric vehicles, we need to improve the cycling performance, rate capability and safety performance of lithiumion batteries. Graphene, as a two-dimensional macromolecular sheet of carbon atoms with a honeycomb structure, has excellent electronic conductivity and mechanical properties, and may be the ideal conductive additive for hybrid nanostructured electrodes. Other advantages of graphene include high surface area (theoretical value of 2630 m2/g) for improved interfacial contact and the potential for low manufacturing costs. Its excellent conductivity could enhance the kinetic properties and rate performance of electrode materials. Meanwhile, the unique two-dimensional structure of the graphene can anchor, wrap and weave the nanomaterials, forming a hybrid random 3D structure. This kind of loose structure could buffer the volume expansion and avoid the agglomeration during the cycling. Furthermore, it may absorb the electrolyte, offering the special ion channels between the different nanoparticles to further improve its conductivity. A series of graphene composites have been synthesized. The preparation, characterization and electrochemical performance of various nanostructured electrode materials are investigated.