Synthesis And Electrochemical Performance Of Porous Nanostructured CuO As Anode Materials For Lithium-ion Batteries

Lithium-ion batteries have been widely used in various protable electronic devices, and gradually extended into the field of electronic vehicles as power source, but also have broad application prospects in new energy storage and conversion owing to their many advantages including high output voltage, large energy density, long circle-life, environment benignity and so on. However, the current commercialized lithium-ion batteries which mainly use graphite as anodes cannot meet the ever growing demand of high-performance application requirements due to their low theoretical capacities. Metal oxides have been regarded as potential graphite alternative electrode materials because of their high theoretical capacities, natural abundance and environmental friendness. However, the large volume variation during the lithium uptake/release process and intrinsic low electrical conductivity of them result in unsatisfactory electrochemical performance.Porous electrode materials for lithium-ion batteries have numerous benefits including shorter diffusion paths, better charge transport properties and higher stability which will significantly enhance the electrochemical performance of metal oxides anodes. In this thesis, we have focussed on the design and synthesis of porous CuO nanostructured anode materials, and proposed several novel synthetic methods including thermal decomposition of hydroxide, carbonate-assisted hydrothermal method and thermal decomposition of hybrid carbonate. Moreover, hybridization with graphene oxide or Co3O4 has also been considered in order to further optimize the electrochemical performance of CuO for lithium-ion batteries anodes. The main contents and results are as follows:1. A simple, facile method to controllable synthesize porous CuO nanoleaves and nanocrystalline-assembled CuO nanorods through controlling the self-assembly of Cu(OH)2 with different drying mediums has been developed as to the metastability of hydroxide. Cu(OH)2 nanorods prepared by a simple coprecipitation method are chosen as precursor, with different drying mediums H2O and ethanol to control the morphology and subsequent heat treatment, nanocrystalline-assembled CuO nanorods and porous CuO nanoleaves have been successfully synthesized. Fortunately, when applied to lithium-ion batteries as anodes, both porous CuO nanoleaves and nanocrystalline-assembled CuO nanorods electodes display excellent cycling stability. The porous CuO nanoleaves exhibit a reversible capacity of 576 mAh g-1 after 150 discharge-charge cycles at 67.4 mA g-1.2. A simple carbonate-assisted hydrothermal method based on the chemical activity of carbonate has been proposed to successfully realize the self-aggregation, thermal decoposition and Ostwald ripening of Cu2(OH)2CO3 nanoparticles in one-step and synthesize porous CuO microsoheres (MSs). Cu2(OH)2CO3 nanoparticles prepared by a simple coprecipitation method using Na2CO3 as precipitating agent are chosen as precursor. By the surfactant-free carbonate-assisted hydrothermal method, porous CuO MSs with a diameter of about 1.5-2.5 μm are fabricated. Then through engineering the ionic strength in solurion, the CuO MSs are encapsulated with graphene oxide and obtain CuO/GO composites electrodes equipped with excellent electrochemical performance. The CuO/GO composites electrodes deliver a high reversible capacity of 500 mAh g-1 after 500 cycles at a current density of 0.5 C, with high capacity retention of 80.0%. Even at high current density of 4 C, the composite electrodes can still exhibit high reversible capacity of 354 mAh g-1.3. Considering the synergistic lithium storage effect between different metal oxides, and based on the cooperative self-assembly of different carbonates, a simple thermal decomposition of hybrid carbonate method has been developed to synthesize porous CuO/Co3O4 hybrid hierarchical structures, and significantly improve the capacity of CuO anodes. Different hierarchical hybrid carbonate (Cu, Co)2(OH)2CO3 precursors have been successfully synthesized through the cooperative self-assembly of Cu2(OH)2CO3 and COCO3 under hydrothermal condition. After high temperature thermal decomposition, the precursors transform into porous CuO/CO3O4 hybrid hierarchical structures with different mole ratios of CuO to CO3O4. Porous CuO/Co3O4 composites electrode (Cu:Co= 1:2) demonstrates the best electrochemical properties among all the fabricated anodes, it exhibits a high reversible capacity of 1056 mAh g-1 after 500 cycles at a current density of 200 mA g-1, with high capacity retention of 111.2%.