Synthesis Of Structure-controlled Hollow Metal-organic Framework Microspheres And Their Applications In Energy Storage

With the development of modern transport vehicles, such as hybrid electric vehicles and electric vehicles, energy storage device (EES) with high energy density and power density are desperately needed to better meet the demands of modern transports. At the forefront of the new EES system, lithium-ion, Li-S batteries and super capacitor are widely used and concerned, however, all of them can hardly meet all the requirements, such as high energy and power density, higher rate performance, long cycle life, high safety and so on. Therefore, developing special materials with new chemical characteristics and high electrochemical properties and applying them in the electrical energy storage devices have great practical significance. Metal-organic framework (MOFs), as a class of porous crystal material, are assembled by metal centers and organic linkers through the strong coordination, where the metal components can offer intrinsic metal sources to derive metals or metaloxides with nanostructure, while the organic components are ideal carbon sources to prepare nanoporous carbons, thus MOFs have great potential to be used as electrode material for energy storage devices. In this thesis, structure-controlled hollow ZIF-8 microspheres with diameter of 150-200nm have been designed and synthesized on a large scale via a facile emulsion interfacial reaction of Zn2+ and 2-methylimidazole based on the previous work, and the electrochemical performances of their applications in energy storage devices have also been studied and discussed. The research contents were divided into the following three parts,1. Three kinds of ZIF-8 hollow nanospheres with different shell thickness were prepared on a large scale based on the previous work of our group and characterized thoroughly by SEM, TEM, HRTEM, XRD, N2 adsorption-desorption, TGA and so on. Besides, palladium nanocubes were encapsulated in the ZIF-8 nanospheres and investigated for size-selective catalysis of 1-hexene, trans-stilbene and tetraphenylethylene. Results showed that Pd@ZIF-8(T) with thin shell displayed very high selectivity and efficiency for the olefins hydrogenation reactions.2. Structure-controlled hollow carbon nanospheres with high nitrogen-doping, large surface area, thin shell thickness and hierarchical pores were prepared through the simple carbonization of hollow ZIF-8 nanospheres and applied as the LIBs anodematerials. The influences of calcination temperatures and the structure of ZIF-8 precursor on the properties of hollow carbon spheres were carefully investigated. Results showed that NTHCS800 obtained at 800℃ under argon atmospheres had the largest surface area, thinnest shell as well as a high doping-nitrogen of 16.61%, showing the superior electrochemical performances. A stable and superhigh capacity of 2047 mAh g-1 for over 100 cycles at a current density of 100 mA g-1 were obtained which could retain about 97% of the second discharge capacity. Even at very high current density of 5 A g-1, a reversible capacity as high as 879 mAh g-1 could be maintained, demonstrating the superior high rate performance. This work further enriched the application of MOFs for LIBs.3. The NTHCS800 was attempted to be applied in supercapacitor and Li-S batteries, however, relatively poor electrochemical performances showed to need further investigations and improvements.