Electrochemical capacitors with lithium chloride/polyvinyl alcohol solid polymer electrolyte for ionotronic-based thermal sensors

This paper describes an ionotronic-based sensor that can detect changes in temperature using a solid polymer electrolyte (SPE)-based transparent electrochemical capacitor (EC). The EC developed using flexible ITO as an active electrode and polyvinyl alcohol (PVA)- lithium chloride (LiCl) gel composite-based SPE. The electrochemical performances of the sensors are investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charging and discharging (GCD) analysis. The EC was fabricated using a freestanding SPE, which exhibits a specific capacitance of 4.19 μF. cm^-² at a scan rate of 5 mV. s^-1. The direct coating of the SPE on the electrode enhances the specific capacitance and is found to be 18.70 μF.cm^-², which is 12 times higher than the EC fabricated using freestanding SPE. When a temperature was applied to the top of the EC with directly coated SPE, we observed a variation in the device’s capacitance due to the change in the mobility of ions of the SPE, which is directly related to the temperature change. The EC exhibits a sensitivity of 0.30 µF/ °C (R²= 0.9694) for the temperature range of -10 to 50 °C. Due to its ionic reaction, the EC demonstrates a high capacitance value in the range of µF in the low frequency range, which shows its potential application in ionotronic-based sensing and as an energy storage for the next generation of wearable devices.