Abstract
This study mainly focuses on the synthesis of yttria-stabilized zirconia (YSZ) and vanadium oxide nanomaterials via a microwave- assisted hydrothermal method for electrochemical energy storage. The results were divided into two parts. In the first part, the controllable crystal size of yttria-stabilized zirconia (YSZ) was synthesized by using design of experiments (DOE) in a microwave-assisted hydrothermal synthesis. The different crystal sizes of YSZ can be obtained by controlling the parameters such as reaction temperature, holding time, precursor concentration, dispersant content, organic additives and KOH concentration. Then, we employ the steepest ascent experiment to find out bigger and smaller crystal size of YSZ. According to steepest ascent results, the crystal size of YSZ can be precisely controlled from 1 nm to 6.1 nm, respectively. PS nanospheres were used to prepare the YSZ electrodes with the highly ordered nanoporous structures. In the second part, the lithium-ion doped vanadium oxide was prepared via a microwave-assisted hydrothermal method by using VOSO4 as precursor and by adding different concentration of LiCl as the lithium-ion source in the precursor solution. Cyclic voltammetry was used to optimize the lithium ion doping concentration. Based on the optimized doping concentration, other cations such as KCl and NaCl were also added to the precursor solution to prepare the potassium-ion and sodium-ion doped vanadium oxide, respectively. On comparison with different cations doped vanadium oxides, 50 mM lithium-ion doped vanadium exhibits highest specific capacitance (170.98 F g-1), longer cycle life and excellent electrochemical reversibility. The 50 mM lithium-ion doped vanadium oxide also possesses highest spacing distance between two adjacent oxide layers and large amount of H2V3O8 nanorods are produced before activation. This leads to enhance in the capacity of the lithium-ion intercalation/de-intercalation. After activation, the CV curves shows strong and symmetric redox peaks. It can be proved by the dissolution/re-deposition mechanism. The doped lithium-ion also can help to create the special lithium-ion intercalation/de-intercalation tunnels, which can increase more ion intercalation sites and/or to provide fast diffusion pathways.