IEEE Access (Jan 2021)
Laser Scribed Graphene-Based Flexible Microsupercapacitors With Fractal Design
Abstract
In recent times, there has been a great increase in the demand of flexible micro-supercapacitors for use in many commercial applications. Flexible capacitors have the potential to replace conventional batteries as they can provide competitive energy storage while being much smaller in size and having greater lifetime than average lithium-ion batteries. The most used design for in-plane flexible micro-supercapacitors is the interdigitated design. However, from findings of various recent studies, it is believed that the capacitance of in-plane EDLC micro-supercapacitors can further be improved by changing electrode designs. Different fractal designs have shown great promise to enhance the electrochemical performance of in-plane micro-supercapacitors by maximizing the active surface area and minimizing the energy lost during ion-transport. In this work, we successfully fabricate graphene-based, laser-scribed flexible micro-supercapacitors and study the effects of change in geometry parameters on total capacitance. Four different geometries for electrode were designed i.e., (1) interdigitated design, (2) fractal F1 (Hilbert) design, (3) fractal F2 (Peano) design, and (4) fractal F3 (Moore) design, and were patterned onto the thin layer of graphene oxide using laser scribing technique. Detailed analysis was presented for the change in capacitance using cyclic voltammetry, galvanic charge-discharge, electrochemical impedance spectroscopy and electrostatic simulation using COMSOL Multiphysics. It was found that fractal design micro-supercapacitors give better performance with higher capacitance and energy density values in comparison to conventional design interdigitated micro-supercapacitors. Among all, Fractal F3 design showed the highest capacitance and energy density value in comparison to other devices. It was found that there were two factors affecting the performance of devices, i.e., (1) a higher active surface area for fractal designs as compared to interdigitated designs with the same unit area, and (2) in addition to electric double layer capacitance, there was also electric field being generated on the edges of electrodes, defined as edging effect. Among both factors, the latter was the major enhancer of capacitance in the fractal design devices.
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