Prepration And Lithium Storage Performance Of Three-Dimensional Porous Graphene Based Composite Materials

In the past decades, Lithium-ion batteries, as electrical energy storages, have been widely used in portable electronic devices. However, the increasing demand for their emerging applications in electric vehicles and large-scale energy storage requires us to enhance its energy and power densities. Currently, graphite has been the main commercial anode material in LIBs. However the low theoretical specific capacity of 372 mAh g-1 tremendously limits the energy and power densities of LIBs.In recent years, graphene with single-atom thickness, flexible two-dimensional structure has attracted intense interest all over the world due to its exceptional physical and chemical properties. The materials, such as silicon,germanium and tin, that would form alloy with lithium metal have been promising candidate anodes for their high specific capacities. Unfortunately, these materials would undergo a huge volume expansion during lithiation, which leads to electrode pulverization. Using graphene based materials as matrices for in situ synthesis and anchoring of the metal nanostructures is anticipated to solve these problems. Finally we can obtain the composite material which possesses high capacity and long cycle life.In this work, three-dimensional(3D) porous graphene/tin composite has been synthesised by using carbothermal reduction method, in which SnCl2 was as the source of Sn and polystyrene spheres were as the carbon source. The best technology conditions to fabricate the best performance of electrode materials has been confirmed by studying the effect of process parameters on the morphology and electrochemical properties of the electrodes, such as annealing temperature,PS spheres size and various substrates. The discharge specific capacity was 838.9mAh g-1 at the current density of 0.1 A g-1 and it increased gradually during 1000 cycles.3D porous graphene/germanium composite was prepared by the method of ionic liquid electrodeposition. The optimum process conditions of preparation were obtained in this paper by studying the effect of process parameters on the morphology and electrochemical properties of the electrodes, such as PS spheres size, deposition time, annealing temperature. The electrode showed good electrochemical performance and the capacity retention was 40% after 100 cycles at the current density 0.5 A g-1. When the current density increased 50 times, the capacity retention was over 40% that is better than the Ge film and 3D porous Ge electrodes.3D porous graphene/iron carbide composite was prepared by simple one-stepannealing. Although the metal iron can not be lithiation, the iron carbide can facilitate the formation of solid electrolyte interphase(SEI) and increase the contact area between active materials and electrolyte, then the electrochemical performance would be improved. The discharge specific capacity was about 721.2mAh g-1 at the current density of 1 A g-1. When the current density increased 50 times, the capacity retention was 50% of initial capacity. The specific capacity increased gradually instead of decay during 1000 cycles.In this work, three composite electrodes based on graphene have been prepared via micro/nano structure design and showed remarkable electrochemical performance. These electrode materials may be potential anodes for LIBs.