Synthesis And Electrochemical Properties Of Tin-based Metal Oxide/Reduced Graphene Oxide Composites

Lithium-ion batteries?LIBs? are currently the dominant power source for portable electronic devices and viewed as the most promising commercial candidates to the next generation of rechargeable energy storage equipments. The exploration of new electrode materials is an important guarantee to meet the requirements of modern high energy consumption devices for LIBs and electrochemical supercapacitors?ECs? with high energy density and prolonged cycle life. A family of materials with great potential in this area are the tin-based metal oxides for their higher theoretical capacity, rich resource and morphology diversity. However, the practical use of these materials is greatly hampered by the poor cycling stability and inferior rate performance arising from their low electronic conductivity, which would hinder the transmission of electron, as well as severe aggregation and huge volume changes during the repeated lithium insertion/extraction process. To address these problems, fabricating tin-based metal oxides/carbon nanocomposites via well combination between carbonaceous materials and tin-based metal oxides, especially tin-based metal oxides/graphene hybrids, was proved to be an effective strategy. Considering the unique superiority of tin-based metal oxides in energy storage area, herein, the research works in this dissertation have focused on designing and synthesizing a series of tin-based metal oxides/reduced graphene oxide micro/nanocomposites and investigating their electrochemical properties for potential anode materials of LIBs and active materials of ECs. The main innovative results are displayed as follows:?1? SnO₂/reduced graphene oxide nanocomposite?SGNC? was synthesized using a novel colloid electrostatic self-assembly procedure between the graphene oxide?GO? nanosheets and Sn?OH?₄ colloid nanoparticles?NPs?, following a heat-treatment at 550°C for 2 h under N₂. Transmission electron microscopy and high resolution transmission electron microscopy showed the tiny multi-crystalline SnO₂ NPs?? 5 nm? dispersed homogenously and anchored tightly onto wrinkled reduced graphene oxide?rGO? sheet surface. The electrochemical properties of SGNC were investigated for a potential anode material in LIBs. Briefly, in the case of SGNC, it showed a high specific capacity of 1710.8 mAh/g in the initial discharge at current density of 100 mA/g. In comparison with quick capacity fading upon the extended cycling in pure SnO₂ anode material, the capacity of 553.7 mAh/g is still retained at current density of 500 mA/g after 100 cycles.?2? The capacitive properties of as-synthesized SGNC were also studied as active electrode materials for supercapacitor. The electrochemical performance measurements exhibited that SGNC possessed the specific capacitance of 347.3 F/g at a scan rate of 5 mV/s in 1 M Na2SO4 electrolyte solution. Furthermore, this material also showed excellent cycling stability, the specific capacitance still retained 90% after 3000 cycles. These results indicate that the SGNC is a promising high-performance supercapacitors material.?3? The ZnSnO₃ double metal oxides were successfully synthesized via a facile alkali etching and subsequent pyrolysis method by introducing ZnO having a relatively low volume change into SnO₂ with high theoretical capacity. The morphology analysis indicated the as-synthesized ZnSnO₃ showed an amorphous hollow cube structure, the average edge size of the hollow cube was about 1 ?m. As an anode material for LIBs, the ZnSnO₃ hollow cubes exhibited a high initial specific discharge capacity of 1591 mAh/g and retained 305 mAh/g after 50 cycles at 100 mA/g. These good electrochemical performances could be attributed to the higher theoretical capacity, amorphous property and hollow structure that accommodate the huge volume variety during the lithium insertion/extraction process.?4? 3D ZnSnO₃ hollow cubes/reduced graphene oxide aerogels?ZGAs? were fabricated via a colloid electrostatic self-assembly method between the GO nanosheets and poly?diallyldimethylammonium chloride??PDDA? modified ZnSnO₃ hollow cubes colloid, followed by hydrothermal and freeze-drying treatments. The unique porous architecture of ZnSnO₃ hollow cubes encapsulated by flexible rGO sheets not only effectively retarded the huge volume expansion during repeated charge-discharge cycles, but also facilitated fast lithium ion and electron transport through 3D networks. The ZGAs exhibited a higher initial specific discharge capacity?1987.5 mAh/g at a current of 100 mA/g?, significantly enhanced cycling stability?745.4 mAh/g after 100 cycles at a current of 100 mA/g? and superior rate capability?as high as 552.6 mAh/g at 1200 mA/g?. The results indicate that the ZGAs are promising anode materials for high-performance LIBs.?5? Fine ZnSnO₃/reduced graphene oxide nanocomposites?ZSGNC? were successfully synthesized via a simple colloid flocculation method. Morphology analysis showed that the rugby-like ZnSnO₃ NPs?⁴ nm in size? were well distributed on the rGO sheets. The as-prepared ZSGNC manifested high specific capacity and improved cycling stability for a potential anode material in LIBs, which delivered an initial discharge capacity of 1691 mAh/g at 100 mA/g and retained 713 mAh/g after 100 cycles. These results indicate that the ZSGNC is a promising anode material for high-performance LIBs.