| Rechargeable lithium-ion batteries have been widely used as power sources in different areas owing to their high energy density, high operating potential and a long cycle life. In recent years, as the development of the electric vehicles, the power density and energy density of LIBs have needed to be further improved. On the one hand, the low specific capacity(about 372 mAh g-1) of commercialized graphite-based anode materials cannot satisfy the requirements for high energy density of batteries. On the other hand, the traditional lithium electrode sheet have a long period for preparation, a complex process and an uncontrollability of the coating thickness of the battery. The above two terms are always the problems which need to be solved for a long period in the lithium electricity industry. Therefore, it is urgent to develop new anode materials with high capacity and a new simple method to improve the battery production. Graphene has been considered as a potential hot spot material for lithium-ion battery because of its special properties, such as good electrical conductivity, lithium storage properties, high specific capacity, which was related to its special structure of single or few layers of graphite. Electrostatic flocking is a simple and effective method, at the same time it has a high efficiency, a low cost and a simple equipment, etc. Therefore, the idea applying lithium electrode sheet to the manufacturing process would be a perfect method. In this paper, graphene materials were chosen as research subjects, electrode sheet was prepared by electrostatic flocking method, and porous graphene was prepared by freeze-drying drying method. Finally, we improved the specific capacity, cycling stability and rate performance for LIBs. The research contents of this paper are as follows:(1) Graphene owning lager layer spacing was obtained by oxidizing the natural graphite into oxidation graphite with the modified Hummers method, washing to neutral, drying and thermal reduction in 300 ℃. The results analyzed by SEM, XRD, AFM, Raman and FTIR show that the prepared graphene is full of bend and fold, and the interlayer spacing becomes larger. Simultaneously, the prepared graphenes became completely dissociated into graphene sheet which is monolayer or disordered layered multilayer.(2) Putting the prepared graphenes as raw materials, we obtained lithium-ion battery electrode pads through the methods of coating and electrostatic flocking respectively. Then we researched process and electrochemical properties of the two methods. The results have shown that, compared with the coating method, electrostatic flocking method have shortens the electrode film production projects, made up for the defect of the uncontrollability of traditional coating thickness of the electrode sheet, and the process is simple and contro llable. In addition, the first charging and discharging amounts for the battery have improved 158.4 mAh g-1. It still had stable capacity after 30 cycles. Besides, lithium-ion battery obtained by electrostatic flocking method could achieve the effect of the ones obtained by traditional coatings method.(3) Porous graphene nanosheet owning a high quality was synthesized by a novel facile method involving freeze-drying technology and thermal reduction. Then we researched the influences of freeze-drying technology to microstructure and electrochemical of the obtained porous graphene nanosheet. The results had shown that, the obtained graphene nanosheet had a porous structure with microporous and mesoporous, a lager interlayer distance(0.366 nm), a more superior cycle stability(the capacity retention rate of about 80% after 50 cycles) and a high rate capability(A high capacity of 586.6 m Ah g-1 for the graphene nanosheets is obtained at a current density of 2000 mA g-1) through the freeze-drying process. The fascinating electrochemical performance could be ascribed to the stable porous structure, the increased layer distance between the graphene nanosheets. |
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