Investigation On Layered Architecture Supercapacitor Based On New Type Of Hybrid Electrolyte

At present, with the rapid development of economy, there is high demand tomake efficient use of energy. Meanwhile, the rapid depletion of fossil fuels,increasingly worsened environmental pollution, and climate warming lead to anemergent need for a new type of energy conversion and storage systems.Supercapacitors, also known as electrochemical capacitors, are novel energy storagedevices, having greater power density than that of batteries and much higher energydensity than that of conventional capacitors. Due to higher energy density, greaterpower density and long cycling life, supercapacitors have been successfully applied inmany areas, such as national defense, aerospace, automotive industry, consumerelectronics, communication, power and railway. This type of device is now attractingmuch attention of researchers from all over the world; also receives increasingresearch interest in the field of new energy because of its huge commercialization andwide applications.Activated carbon (AC) as one kind of electrode materials, has been used incarbon-based electrochemical double-layer capacitors (EDLCs) and asymmetricsupercapacitors because of its many positive characters, such as low cost, largesurface area, great corrosion resistance, broad range of working-potential window,gap adjustable structure and simple preparation process. Nevertheless, there are stilldrawbacks need to be overcome: scattered distribution of pore structures and pore sizeand electrolyte being unable to diffuse into all the pores that lead to frustration ofspecific surface area, and threfore lower specific capacitance; electrostatic adsorptionfor production of capacitance limits the charge storage ability; in aqueous medium,the energy density of EDLCs is low, normally not exceeding10Wh/kg. In this work, firstly, we synthesized AC electrode by scraping method andinvestigated the electrochemical properties of the AC by cyclic voltammetry,electrochemical impedance spectroscopy and constant current charge/dischargeelectrochemical method. The morphology and microstructure of the samples wereexamined by X-ray diffraction and scanning electron microscopy.In the process of preparation of AC electrode and performance measurement, wefound that the mass of AC and the ratio of electrode components such as AC,conductive graphite and binder have a certain influence on the specific capacitance.The results of charge/discharge tests and cyclic voltammetry curve measures indicatedthat the mass specific capacitance decreased with the increase of active substanceswhile the area specific capacitance increased (current density:1A/g and5A/g); whenthe ratio of AC: graphite: binder was88:8:4, a good combination property wasachieved. The ratio of electrode components can be well adjusted to meet the actualdemand.Secondly, electric active material has been introduced in the aqueous electrolyteto improve the performance of the EDLCs as the result of redox reaction of the activesubstances at the electrode/electrolyte interfaces. We chose the p-phenylenediamine(PPD) as addictive to the traditional KOH electrolyte and found that the specificcapacitance of single electrode was obviously improved: when the current density is4A/g, the maximum value of AC was increased from152F/g to580F/g (3.8times tothe primary); at16A/g, the maximum value increased from64F/g to278F/g (4.45times to the primary), and the potential window was also widened. As for theassembled AC-AC symmetric supercapacitor without the introduction of thep-phenylenediamine into the pure KOH electrolyte, the specific capacitance was31F/g and the energy density was4.3Wh/kg. The specific capacitance increased to91.3F/g and the energy density was up to32.46Wh/kg if we added PPD. It has beenproved that the addiction of PPD can improve the performance of carbon-basedsupercapacitor significantly.