Estudo e desenvolvimento de supercapacitores eletroquímicos usando eletrodos baseados em multicamadas de grafeno

Abstract

Electrochemicals supercapacitors are devices that have been arousing great interest and researches, mainly as alternatives for energy storage. Such interest is due to characteristics like: reduced dimensions, flexibility, high energy and power density, which are crucial to the current demand. Thus, the following thesis has as its objective the research and development of flexible all-solid-state supercapacitors (ASSSC) with electrodes based on multilayer graphene (MLG), by applying a simple methodology with few steps and using a smaller amount of chemical reagents. With that purpose, twenty-one different electrode settings have been tested in ASSSC, settings in which the MLG mass and the pressure it needs to undergo during the production process were changed, trying to investigate the influence and impact these parameters have on the produced devices. For the structural characterization of the MLG electrode, Raman Spectroscopy, X-ray Diffraction, X-ray Photo-Electron Spectroscopy, Atomic Force Microscopy and resistivity measurements were performed using the four-probe method (Van der Pauw). After the characterization of the electrodes, the supercapacitors were made (for all configurations) and electrochemically characterized through cyclic voltammetry and galvanostatic charges and discharges. By analyzing the performance of the supercapacitors, it was observed that for the lower compaction pressures and for the larger masses for MLG used, the best results were obtained (specific capacitance of 31800 µF/cm² for a pressure of 15 kgf/cm² and 35400 µF/cm² for 140 mg of MLG). When the best electrode production parameters were identified, an optimized graphene supercapacitor (OGS) was constructed, using 120 mg of MLG compacted at 20 kgf /cm². The OGS was electrochemically characterized, reaching approximately 58000 µF/cm² of specific capacitance, 2.68 µWh/cm² and 0.11 mW/cm² of energy density and power density, respectively, as well as excellent results in bending tests, proving the supercapacitor flexibility and great retention of capacitance over thousand cycles of charges and discharges.