Metal oxide and sulfide nanomaterials and nanocomposites for high-performance energy storage
Ayman Amin Abdelhamid Amin
Date of Issue2017-05-29
School of Materials Science and Engineering
Institute of Bioengineering and Nanotechnology
There is an alarming energy problem that needs urgent intervention. It is mainly caused by oil supply instability, rising urban pollution and accelerated global warming. This has resulted in a worldwide policy shift towards sustainable energy and green transport, which need reliable energy storage systems. Li-ion batteries and supercapacitors are among the most promising energy storage solutions; however, they are still not able to meet our needs. This is mainly due to the limited energy storage capabilities of the currently used materials. Novel high-performance energy storage materials are required. Several approaches have been investigated for producing materials with high energy storage capabilities. It was found that size reduction, morphology and structure control, and incorporation of carbonaceous materials are critical factors for a high-performance electrode. However, the current synthesis methods and energy storage performance are still far from optimal. The main objective of this thesis is to develop facile approaches for synthesizing nanomaterials and nanocomposites with excellent energy storage performance. Two different synthesis strategies were developed. The first involved the synthesis of nickel sulfide and graphene-wrapped nickel sulfide nanopyramids, while the second involved metal oxide and graphene-incorporated metal oxide nanosheets. The synthesized materials were applied as Li-ion battery anodes and supercapacitor electrodes, demonstrating very promising energy storage performance. Current nickel sulfide synthesis methods are limited by the relatively large and non-uniform nanomaterials obtained. A one-pot colloidal thermal decomposition approach was developed in this thesis to synthesize uniformly sized nickel sulfide nanopyramids, and to evenly anchor them to the surface of graphene sheets. The nickel sulfide nanopyramids showed very promising supercapacitor performance, but suffered from capacity decay as Li-ion battery anode. Graphene wrapping increased the rate capability of the nanopyramids as supercapacitor, and significantly improved their energy storage performance as Li-ion battery anode. A novel, facile, versatile and generalized strategy was established for the synthesis of metal oxide nanosheets. Graphene oxide was used as sacrificial template to synthesize metal oxide nanosheets, without the need for hydro/solvothermal reactions or laborious template-removal processes, which limit the currently available methods. The graphene oxide planar-confined growth strategy demonstrated interesting versatility, where the nanosheets’ attributes such as crystallinity, crystal structure, crystallite size, surface area, porosity and reduced graphene oxide content could be tuned, simply by adjusting the calcination conditions. The synthesis approach also displayed broad applicability, allowing various binary and doped binary oxide nanosheets, as well as ternary oxide nanosheets to be obtained. The synthesized nanosheets were applied as Li-ion battery anodes and supercapacitor electrodes with very promising energy storage performance. The facile synthesis methods developed throughout this work produced nanomaterials and nanocomposites with controlled structure and composition, achieving high-performance energy storage. The colloidal approach managed to control the size and uniformity of nickel sulfide nanocrystals, and allowed high dispersion on the surface of graphene sheets, while the graphene oxide planar-confined growth strategy produced a wide variety of metal oxides nanosheets with controlled characteristics. These nanomaterials and nanocomposites showed very promising energy storage performance, which was amongst the best reported in the literature. The excellent energy storage performance could be attributed to the critical roles played by size reduction, morphology control and incorporation of graphene, which were attained by the novel synthesis strategies developed in this thesis.