Facile Assembly of Flexible Symmetric Micro-Supercapacitors with Wide Working Voltage Window

Abstract

With the upcoming flourishing development of intelligent robots and wearable electronics, demands for high-performance flexible energy storage devices are increasing. In this study, flexible symmetric micro-supercapacitors (MSCs) that could work in wide working voltage window were demonstrated by combining laser-direct-writing graphene (LG) electrodes with phosphoric acid-non-ionic surfactant liquid crystal (PA-NI LC) gel electrolyte. To increase the flexibility and enhance the conformal ability with anisotropic surfaces of the MSC devices, after the interdigitated LG formation on polyimide (PI) film surface, they were further transferred onto a flexible, stretchable and transparent polydimethylsiloxane (PDMS) substrate, which displayed favorable flexibility and mechanical characteristics in the bending test. Furthermore, the electrochemical performance of symmetric MSCs with various electrode widths (300, 400, 500 and 600 μm) was appraised. The findings disclosed that the symmetric MSC devices could be conducted in a large voltage range (0-1.5 V), and the one with 300-μm electrode width (MSC-300) exhibited the largest areal capacitance of 2.3 mF×cm-2 at 0.07 mA×cm-2 and areal (volumetric) energy density of 0.72 μWh×cm-2 (35.9 mWh×cm-3) at 55.07 μW×cm-2 (2753.5 mW×cm-3), along with favorable mechanical and cycling stability. After charging for ~20 s, two MSC-300 devices connected in series could supply energy to a calculator to operate for ~130 s, suggesting the practical application potential as energy storage device.