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.
Highlights
In the recent times, there has been an increase in demand for small flexible electronic devices, such as microrobots, implantable medical devices and wearable sensors, that require an efficient and compact device solution for energy supply and storage.[1, 2] Solutions like 3D micro-batteries and thin films have been proposed, but because of their short life cycle and poor rate performance, they have failed to achieve the requirements.[3]
RESULTS & DISCUSSIONS Before the fabrication of micro-supercapacitor devices, graphene as a material was characterized to study the changes from graphene oxide (GO) to laser scribed graphene (LSG) after reduction
We found that fractal design supercapacitors show better performance in comparison to conventional interdigitated electrodes (IDE) design micro-supercapacitors
Summary
There has been an increase in demand for small flexible electronic devices, such as microrobots, implantable medical devices and wearable sensors, that require an efficient and compact device solution for energy supply and storage.[1, 2] Solutions like 3D micro-batteries and thin films have been proposed, but because of their short life cycle and poor rate performance, they have failed to achieve the requirements.[3]. In terms of charge storage mechanisms, there are two main types for supercapacitors: (1) electric double
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