Graphene Based Porous Materials: Preparation And Properties

Recently, lithium ion batteries(LIBs) are widely used in portable electronic devices,such as cell phones, laptops, and tablets. Although graphite is the commonly used anode material in LIBs, the demands for higher energy density, power density, and cyclability require the development of new materials. Graphene, a two-dimensional carbon nanomaterial, has attracted a great deal of attention in recent years. Graphene based porous materials with large specific surface areas are considered as excellent energy storage materials, such as supercapacitors and LIBs.In this thesis, the development, synthesis, characterization and applications of graphene based porous materials have been demonstrated. Various graphene-based porous materials with different function and large specific surface area have been fabricated by different methods. Many characterization techniques, such as scanning, transmission electron microscopy and x-Ray diffraction analysis, were used to investigate the prepared materials. In addition, the as prepared materials were applied into the LIBs and lithium-sulfur batteries to investigate the performance of electrode materials.A novel nitrogen-doped porous graphene material(NPGM) was prepared by freeze-drying a graphene/melamine–formaldehyde hydrogel and subsequent thermal treatment. The use of melamine–formaldehyde resin as a cross-linking agent and nitrogen source enhances the nitrogen content. NPGM possesses a hierarchical porous structure, a large Brunauer–Emmett–Teller surface area(up to 1170 m2 g–1), and a considerable nitrogen content(5.8 at%). NPGM displays a discharge capacity of 672 m A h g–1 at a current density of 100 m A g–1 when used as an anode material for lithium ion batteries,much higher than that observed for a nitrogen-free graphene porous material. In addition,the NPGM electrode also possesses superior cycle stability and rate performance.The N-doped graphene aerogels were fabricated via in situ method through hydrothermal reaction of GO in ammonia solution. Sulfur loaded N-doped graphene aerogels(SNGA) with porous structure were prepared. The effect of different content of sulfur loading and the performance of the samples were studied by using electrochemicalimpedance spectrum, cyclic voltammetry and constant current charge/discharge technique.The sulfur loaded porous N-doped graphene aerogels possess superior performance such as high specific capacitor and excellent rate performance when used as cathode materials of lithium-sulfur battery compared with conventional sulfur cathode.