Wide-Temperature-Range Flexible Micro-Supercapacitors Using Liquid Crystal Gel Electrolyte

In this work, to construct a sunlight-powered energy storage system, single wall carbon nanotubes (SWCNTs)-based symmetric micro-supercapacitors (MSCs) were fabricated by a one-step, facile spraying method. The electrodes exhibited satisfactory conductivity with a sheet resistance of 275 ω/sq. Moreover, potassium hydroxide-poly(vinyl alcohol) (KOH-PVA) and phosphoric acid-nonionic surfactant liquid crystal (PA-NI LC) gel electrolytes were prepared and applied to design all-solid-state MSC devices. Compared to the device assembled using the SWCNTs/KOH-PVA gel electrolyte, the SWCNTs/PA-NI LC electrolyte displayed larger areal capacitance with the largest recorded value of 11.0 mF·cm-2 at a current density of 0.08 mA·cm-2 at room temperature. Additionally, the effect of temperature on the MSC device performance was assessed, and the results revealed that the device based on the SWCNTs/PA-NI LC electrolyte achieved enhanced electrochemical performance at an operating temperature of 65 °C, including a large areal capacitance of 14.7 mF·cm-2 at 0.08 mA·cm-2, a better rate performance of 88% with 12.9 mF·cm-2 at 0.4 mA·cm-2, and a higher energy density of 2.04 μWh·cm-2 at a power density of 40.64 μW·cm-2. In addition, the MSC device featured high cyclic stability under bending conditions (45 or 90°) at room temperature. Furthermore, a sunlight-powered energy storage system was fabricated, combining solar cells with the as-assembled MSC devices. Three MSCs connected in series were charged by solar cells and further acted as the energy supply for a red light-emitting diode (LED), which could be continuously operated for 2 min 30 s. All of the findings herein represent a good indication of the promising practical application potential of the as-prepared MSC devices as energy storage devices at high temperatures.