The Synthesis And Electrochemical Properties Of Graphene Loaded With Metal Oxide/Sulfide

With the rapid development of economy, exploiting and utilization of clean green resources has become the prior affairs of any country. As a novel apparatus for energy transformation and transportation, lithium-ion battery has obtained increasing attention for its high-octane density, high-output potential, as well as non-pollution. It has gained adaptability in pony electronics, such as mobile, camera and laptop, and shows respectable prospect in the new energy resources save and electro-mobile industry simultaneously.Lithium-ion battery loaded with metal oxide/sulfide has been on the research focus, for its low-cost and highly academic volume (double of the carbon) as the cathodic material. Repeatedly convergent-divergent may occur when metal oxide/ sulfide serves as the electrode material in the process of charging-discharging, which brings out the pulverization of the electrode material, speedy decline of the volume, hindering its application.Possessing fine two-dimensional structure, tremendous specific surface area, favorable electro-conductivity, super-duper stability etc., so graphene is an ideal carrier of the high performance composite excavation. Researches show that graphene nano-composite not only maintains the virtues of both graphene and loading materials, but also leads to a novel synergistic effect, which makes the composite performance greatly improved, thus of significant value.According to the synergistic principle between Graphene and transitional metal oxide/sulfide, oxidized graphene is provided as the precursor to produce graphene loaded with metal oxide/sulfide(CoS2, WO3, MoS2, Co3O4), which is new-structure- possessing and energy-storing. Materials phase characterization and electrochemical performance tests are mainly conducted on scanning electron microscope(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), cyclic voltammetry (CV), EDS, and electrochemical testing et al. The main results are as follows:1.Oxidized graphene(GO) is synthesized by the optimized hummers method. The layer-by-layer assembled composite of graphene nanosheets(GNSs) wrapped monodie- sperse cobalt sulfides(CoS2) nanocages has been prepared via a solvothermal method. The flexible GNSs in the layered composite act as the effective matrix to encapsulate the monodisperse CoS2 nanocages, buffer the volume changes and prevent the aggregation of the CoS2 nanocages during electrochemical cycling. The loosely stacked GNSs, which are induced with the insertion of CoS2, are convenient for electrolyte wetting and serve as highway for the rapid electron and lithium transport. The monodisperse nanocages can supply additional space to tolerate the volume changes, shorten lithium diffusion path, and do not tend to aggregate. As a result, the specific sample can deliver a high capacity approaching 800 mAh g-1 after 150 cycles at 100 mA g-1 and 697 mAh g-1 after 300 cycles at 500 mA g-1, in addition to good capacity retention and excellent rate capability.2.Multi-level MoS2 nanosheet grows on the flexible graphene by the method of solvothermal synthesis to create a layered nanostructure MoS2/graphene (MoS2/G). The sheet-on-sheet structure can effectively prevent self-aggregation and structural degradation of MoS2/G composite upon cycling, while their 2D building blocks can ensure facile lithium ion transport. Benefiting from the integration of the advantages mentioned above, it displays remarkably high specific capacity (570 mAh g-1), excellent high-rate performance, and stable cyclic capability (550 mAh g-1 retention after 250 cycles) when it is used as LIBs anode.3.WO3 is well-distributed in the rGO nanosheet via the solvothermal method. Electrochemical testing indicates that the capacity and the cycle performance of the WO3/rGO nano-composite is remarkably improved with the addition of rGO with good electrical conductivity and mechanical flexibility, The specific discharge capacity of the composite reaches 1135.7 mAh g-1 during its first discharging, what’s more, it still remains the discharge capacity of 780 mAh g-1 after 200 circles.4.Three-dimensional Co3O4-Graphene (3D-CGFs) framework is synthesized by the simple hydrothermal synthesis method as the anode material of LIBs. Three- dimensional Co3O4-graphene frameworks (3D-CGFs) are prepared with a one-pot hydrothermal method. Co3O4 particles are in situ anchored on graphene sheets, and the resulting composite self-assembles into 3D architecture during the hydrothermal treatment. Scanning electron microscope, transmission electron microscope, powder X-ray powder diffraction, and Raman spectroscopy are employed to characterize the sample. When tested as anode materials for lithium-ion batteries,3D-CGFs demonstrate remarkable electrochemical lithium storage properties, such as large and stable reversible capacity (530 mAh g-1 at 500 mA g-1 over 300 cycles), good capacity retention (88% retention after 300 cycles at 500 mA g-1 compared with the 4th cycle), excellent high-rate performance (515 mAh g-1 at 1 A g-1), making it a promising candidate for high-performance anode materials, especially for high-rate lithium-ion batteries.