分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Graphene-based electrodes with high gravimetric and high volumetric capacity simultaneously are crucial to the realization of high energy storage density, but still proved to be challenging to prepare. Herein, we report a three-dimensional porous graphene/Co aerogel with hierarchical porous structure and compressible features as a high-performance binder-free lithium-ion battery anode. In this composite aerogel, graphene nanosheets interconnect to form continuous macropores, and cobalt nanoparticles stemming from decomposition of cobalt salt not only react with carbon atoms of graphene to form nanopores on the graphene nanosheets, but also increase the conductivity of the aerogel. With efficient ion and electron transport pathways as well as high packing density, the compressed porous graphene/ Co electrode exhibits significantly improved electrochemical performance including high gravimetric and volumetric capacity, excellent rate capability, and superior cycling stability. After compression, such a porous graphene/Co nanocomposite can deliver a gravimetric capacity of 900 mA h g 1 and a volumetric capacity of 358 mA h cm 3 at a current density of 0.05 A g 1. Furthermore, after 300 discharge/charge cycles at 1 A g 1, the specific capacity still remains at 163 mA h cm 3, corresponding to 90.5% retention of its initial capacity.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Pore size is a critical parameter that affects the basic physicochemical properties and applications of porous graphene foam, but the preparation of graphene foam with controllable pore size is still a big challenge, especially by a self-assembly method. In this work, graphene oxide (GO) sheets with different lateral sizes by controlling the delamination conditions of graphite oxide were used as building blocks to form graphene foams with adjustable pore size, by a convenient one-step hydrothermal self-assembly method. The pore sizes of graphene foams can be effectively controlled by simply altering the sheet sizes of GO, and the smallest average pore size is $500 nm, which is much smaller than the micrometer-scale pores in the reported graphene foam materials. Static contact angles, nitrogen adsorption–desorption isotherms and adsorption of methylene blue are measured to demonstrate the strong dependence of some important physicochemical properties of graphene foams on their pore sizes. This simple method offers a novel way to rationally synthesize graphene foam with appropriate pore size for various practical applications.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A TiO2(B)–CNT–graphene ternary composite material was prepared by in situ growth of TiO2(B) on a conductive network composed of both graphene and CNTs. TiO2(B) has nanorod morphology and is dispersed uniformly in the carbon matrices. Graphene in this composite acts as sheet-like mini-current collectors that loads TiO2(B), whereas CNTs further enhance the electrical conductivity of TiO2(B) by intimate contact between the two components in local regions, and also prevent the restacking between graphene layers. The composite anode material exhibits a capacity of 190 mA h g 1 even after 200 cycles at 1 C, presenting excellent rate performance.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: The preparation of lightweight materials with electromagnetic interference-shielding effect- iveness higher than 30dB is critical for most industrial and consumer applications. Compounding polymer resin with conductive filler can generate excellent electromagnetic interference-shielding effectiveness but usually leads to a high-sample density, while the foaming of polymer composite suffers from the significant-reduced electromagnetic inter- ference-shielding effectiveness. In this study, polyetherimide composite foams with loading of 10–80 phr (parts per hundred of resins) nickel particles were fabricated to meet the gap. The polyetherimide/nickel composite foams possessed uniform cell structure and low- sample density such as 0.86 g/cm3 at 70 phr nickel. The coupling effects of gravity settle- ment and cell-structure solidification led to the formation of gradient distribution of nickel particles across the foams. The formed novel structure facilitated the enhancement of multi-reflection and multi-scattering among nickel particles and cells. As a consequence, polyetherimide/nickel foam with 70 phr nickel (PEIN70) possessed a high-electromagnetic interference shielding effectiveness of 86.7–106.5 dB over a frequency range of 50–3000MHz. When the sample density was considered, the specific electromagnetic interference shielding effectiveness of PEIN70 foam was as high as 121.3 dB/(g/cm3) at 1 GHz, which was higher than the reported electromagnetic interference-shielding materials. The excellent electromagnetic interference-shielding properties, lightweight, well-defined resin proper- ties ensure polyetherimide/nickel composite foams useful in many advanced applications.