| Along with the rapid development of science and technology, people's demands for energy enlarge extremely fast. However the severe state of environment does not allow people to overuse the fossil fuels. In addition, the fossil fuels which are about to run out are insufficient to meet the demand for energy. Human beings need to seek new efficient renewable clean energy, such as solar, wind, etc. Due to the dispersion and intermittent of these renewable energy, we need more efficient and stable energy storage devices. Electrochemical supercapacitors are the most promising devices, which are efficient and environmentally friendly.Electrochemical supercapacitors, known as supercapacitors or ultracapacitors, combine the advantages of secondary batteries(e.g. Li-ion batteries) and traditional electrostatic capacitors. It has many advantages, for example, long cycle life, high specific capacitor, rapid charging/discharging, environmentally friendly. Supercapacitors have a broad application prospect in many fields of human life, spaceflight, national defense, etc.This paper studied the electrochemical performance of the electrodes based on the nanostructured nickel hydroxide supported by nickel foam and the nickel hydroxide and manganese dioxide composite material. Furthermore we studied the electrochemical performance of the flexible all-solid-state supercapacitors that used the composite material electrode. The main contents of this paper as follows:(1) We synthesized nanostructured nickel hydroxide on a piece of pre-treated nickel foam by a simple hydrothermal method. The as-synthesized electrode material was analyzed by X-ray diffraction(XRD), scanning electron microscopy(SEM) to study its structure and morphology. The results showed that the as-prepared materials were nickel hydroxide with nanoflakes morphology and the active materials covered the surface of nickel foam completely. The electrochemical performance, including CV, GCD, EIS, was conducted by a three-electrode-system with 3 M KOH as the electrolyte. Excluding of the contribution of nickel foam, the GCD test results show that the areal specific capacitor(Cs) reached 2.5 F/cm2(at the current density of 2 mA/cm2). After 1000 cycles the Cs remained 92.5% of the initial Cs. The electrode materials present good cycle stability. The method which synthesizes active material on the current collector simplifies the consolidating procedure of the electrode. This leads to reduce the influence of the conductive agent and binder.(2) We synthesized composite electrode materials based on the as-prepared electrode by hydrothermal method. The composition and morphology of the composite materials were confirmed by XRD, SEM, EDS. Then the electrochemical performance was conducted in the same conditions as the former. Compared with the pure nickel hydroxide, the Cs of the composite electrode is approximately 4 times of the pure one, reaching 9.56 F/cm2(at the current density of 5 mA/cm2). Besides, the cycle stability also significantly increased. The Cs of the composite electrode kept 92.3% after 2000 cycles at a high current density of 20 mA/cm2.(3) We fabrication a flexible all-solid-state supercapacitors with composite materials as electrode and PVA-KOH gel electrolyte. The Cs of the flexible device reached 241 mF/cm2 at 1 mA/cm2. After 5000 cycles the Cs kept 98% of the initial one at the current density of 2 mA/cm2. Moreover we studied the mechanical stability of the flexible device to discuss whether the composite material can keep up with the trend of miniature, flexible, wearable intelligent electronic products. The results show that electrochemical performance of the all-solid-state device kept good performance stability at various bending degrees. |
PDF Full Text Request