Synthesis Of Graphene-based Metal Sulfides And Application In Energy Storage

Graphene which is a basic building block for graphitic materials of all other dimensionalities, is a high performance material in materials science and condensed-matter physics. This strictly two-dimensional material exhibits excellent electronic behavior and mechanical properties, as well as a large specific surface area, so that it has attracted considerable research interest for many applications.Because the practical applications of LIBs strongly depend on the cycling performance and reversible capacity of electrodes, how to improve these performances of electrodes becomes a hot topic to both chemists and material scientists. Transition metal dichalcogenides (TMDs) are layered inorganic compounds which can be fabricated with a graphene-like structure. Compared with the commercial anode of LIBs like graphite, TMDs are more attractive in terms of its high theoretical specific capacity. Some layered structured metal sulfides, such as FeS, MoS2 and WS2 have been actively studied as electrode materials in LIBs due to their structural advantages in reversible Li storage processes.2D nanosheets of those layered structured metal sulfides can be obtained by exfoliation due to the weak Van Der Waals interaction between S-S layers. However, those layered structured metal sulfides always suffer from large volume expansion during the insertion and extraction of Li ions.Here, the author makes an new attempt to introduce inert silica as dopant into MoS2/graphene system. Amorphous silica can not only prevent the inner-plane aggregation of MoS2 sheets, but also effectively accommodate volume expansion and pulverization of MoS2 electrodes. Simultaneously, we use soft template to induce the synthesis of graphene based MoS2 or FeS hybrids with different morphologies and structures which greatly influence Lithium performance. In addition, graphene, being a soft material, could cushion the volume changes of the Li+ storage host during charge and discharge operations, and the high electronic conductivity and charge mobility of graphene should improve electron conduction in the electrode and electron transfer in the electrode reaction.Graphene oxide was firstly prepared by the oxidization of natural graphite using a modified Hummers method. A soft template-assisted hydrothermal route is developed for the facile synthesis of graphene-like MoS2/graphene composites. The effects of different surfactants on the microstructures and electrochemical performances of the composites for reversible Li+ storage are investigated. As a result, MG(CTAB-90℃)å'ŒMG(PVP) exhibit outstanding reversible capacity and excellent rate performance(100 mA/g,800mAh/g after 50 cycles, 1000mA/g,～600mAh/g).A facile and effective two-step approach has been reported for the synthesis of the unprecedented MoS2/SiO2/graphene hybrids (MSG). The graphene based SiO2 particles were firstly synthesized via in-situ hydrolysis of tetraethylorthosilicate (TEOS) in the presence of graphene oxide (GO) and then subjected as template for the controlled synthesis of MoS2 under hydrothermal treatment, followed by annealing in N2. The resulting hybrids contain crystalline MoS2 as active component and amorphous SiO2 as dopant. The inert silica in the composites can effectively mediate the massive volume expansion of MoS2 during lithiation and delithiation cyclings. As the result, MoS2/SiO2/graphene hybrids manifests superior cycling performance stabilized at 1060 mAh g-1 for more than 100 cycles at the current density of 0.1 A g-1 and excellent rate performance of 580 mAh g-1 at an ultrahigh current density of 8 A g-1 as anode material in LIBs, which outperform those of the MoS2 and MoS2/graphene hybrids.A new composite formulation of the FeS-based anode for lithium-ion batteries is showed, where FeS nanorods loaded in reduced graphene oxide (RGO) are produced via a facile direct-precipitation approach. The resulting nanocomposites FeS/graphene structure has better lithium ion storage properties, exceeding those of pure FeS. The enhanced electrochemical performance is attributed to the nanorods structure with smaller FeS sizes and synergetic effects between FeS and RGO sheets.