| Popis: |
The demand for high-performance electrochemical energy storage devices is ever-growing as they are critical components for portable electronics, electric vehicles, and efficient storage media for energy from renewable sources. Electrochemical capacitors (also called supercapacitors) are emerging as one of the most promising candidates due to their rapid charge rate, high power density, good rate capability and excellent lifespan. However, their usage is significantly limited by the disadvantages of low energy density. The main aim of this work is to develop advanced electrode materials for supercapacitors with improved energy density while maintaining high power density and long cycle life. In this thesis, we have developed four novel electrode materials based on the transition metals of Ni and Cu for supercapacitor applications, including the metal oxides (Li2Ni2(MoO4)3 and Cu2O/CuMoO4) and metal sulfides (NiMoS4-A and Ni-Cu-S). These materials were prepared via different techniques, such as combustion, chemical co-precipitation and hydrothermal. Their physical properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) etc. Their electrochemical behaviours were evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and cycling stability etc. To further measure the performance in practical energy storage devices, the materials were tested with a two-electrode configuration. All the four materials were used as positive electrodes, which were paired with proper activated carbon (AC) or nitrogen-doped graphene (NG) negative electrodes to assemble asymmetric supercapacitors (ASCs). At a current density of 1 A g-1, the Cu2O/CuMoO4 electrode exhibits a high specific capacitance of 4264 F g-1, superior to the1137 F g-1 of the Li2Ni2(MoO4)3, 706.5 F g-1 of the NiMoS4-A, and 938.6 F g-1 of the Ni-Cu-S. In terms of the ASCs, the Cu2O/CuMoO4//AC ASC could expand the operation voltage to 1.7 V, at which the energy density can reach 75.1 Wh kg-1 with a power density of 420 W kg-1. The NiMoS4-A//AC ASC displays a high energy density of 35 Wh kg-1 at an average power density of 400 W kg-1. Meanwhile, it exhibits excellent cycle stability, maintaining 82% of the initial capacitance after 10000 charge-discharge cycles at 5 A g-1. These good results suggest that the developed materials are promising for high-performance supercapacitor applications. |
