Advanced Materials for the Fabrication of Innovative Micro-Supercapacitors: optimization of laser-induced graphene on polymeric substrates

Researchers have recently begun to study lower-cost graphene preparation methods easy to be scaled up. Among them, laser writing allows a fast photothermal conversion of some polymeric substrates (e.g., polyimide) into porous conductive path of few-layer graphene known as Laser Induced Graphene (LIG). Due to high electrical conductivity and the simple and fast fabrication procedure we focus on LIG for the fabrication of micro-supercapacitors. Supercapacitors are kind of electrochemical energy storage devices which are based on carbon nano materials. Here we report on the optimization of the laser parameter in order to produce and pattern porous graphene-like films on polyimide by absorbing the CO2 infrared laser energy and converting polyimide surface into graphene network. Indeed, noticed several important parameters of the laser (raster, power, frequency, velocity) affect the resistance of samples measured by means of Van der Pauw method. As we know, the performance of a supercapacitor can be characterized by a series of key parameters, including the cell capacitance, operating voltage, equivalent series resistance, power density, energy density and time constant. Therefore, the aim of this work is to minimize sheet resistance to improve performance of LIG-based supercapacitors, and optimize electrodes area (charge balance approach) in order to maximize the operating voltage of the devices. In this thesis work, we exploited two different setups: one is two-electrodes configuration for device characterization and the other one is the three-electrodes configuration fabricated to optimize the electrochemical energy storage of the final device. Electrochemical methods were exploited to characterize and optimize the devices: cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Galvanostatic charge and discharge (GCD). We compared performance of three-electrodes system with two different room temperature ionic liquids (ILs), such as ([EMIM][TFSI] and [PYR14][TFSI],) through analyzing and comparing areal capacitance, coulombic efficiency and so on. The conclusion is that [PYR14][TFSI] has larger stability window. Out of three electrodes measurements we derived an information concerning the asymmetry factor between the electrodes. Finally, we tested stability of new devices printed with new masks by charge and discharge for long cycles. In summary, LIG- based supercapacitors with charge balancing show extremely high stability when compared to unbalanced ones.