Facile assembly of flexible, stretchable and attachable symmetric microsupercapacitors with wide working voltage...

With the increasing development of intelligent robots and wearable electronics, the demand for high-performance flexible energy storage devices is drastically increasing. In this study, flexible symmetric microsupercapacitors (MSCs) that could operate in a wide working voltage window were developed by combining laser-direct-writing graphene (LG) electrodes with a phosphoric acid-nonionic surfactant liquid crystal (PA-NI LC) gel electrolyte. To increase the flexibility and enhance the conformal ability of the MSC devices to anisotropic surfaces, after the interdigitated LG formed on the polyimide (PI) film surface, the devices were further transferred onto a flexible, stretchable and transparent polydimethylsiloxane (PDMS) substrate; this substrate displayed favorable flexibility and mechanical characteristics in the bending test. Furthermore, the electrochemical performances of the symmetric MSCs with various electrode widths (300, 400, 500 and 600 μm) were evaluated. The findings revealed that symmetric MSC devices could operate in a large voltage range (0-1.5 V); additionally, the device with a 300 μm electrode width (MSC-300) exhibited the largest areal capacitance of 2.3 mF cm^-2 at 0.07 mA cm^-2 and an areal (volumetric) energy density of 0.72 μWh cm^{- 2} (0.36 mWh cm^{- 3}) at 55.07 μW cm^-2 (27.54 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, showing its practical application potential as an energy storage device. Moreover, the device displayed favorable reversibility, stability and durability. After 12 months of aging in air at room temperature, its electrochemical performance was not altered, and after charging-discharging measurements for 5000 cycles at 0.07 mA cm^-2, ~93.6% of the areal capacitance was still retained; these results demonstrated its practical long-term application potential as an energy storage device.