Fiber Bragg grating sensors for in-situ temperature measurement on bending a flexible planar supercapacitor

Abstract

The state of charge (SoC) in a flexible planar supercapacitor is dependent both on in-situ temperature rise as well as its bending angle. Thus there is a need for measurement of rising in temperature of the supercapacitor on bending conditions. The present work demonstrates the applicability of fiber Bragg grating (FBG) sensors for in-situ temperature measurement on bending in flexible planar supercapacitors. For this purpose, two FBG sensors with diameter 125 μm and 40 μm were inserted into a flexible planar supercapacitor at a location away from the bending axis. The FBG with 40 μm diameter was coated with conductive silver ink to enhance the temperature sensitivity and the diameter of this FBG after coating was found to be 80 μm. The planar supercapacitor consisted of multi-walled carbon nanotube adsorbed on filter paper as electrodes and NH4CN as an electrolyte. The temperature and bend sensitivities for FBG with 125 μm diameter was found to be 10 pm/°C and 17 pm/° respectively whereas for the FBG with 80 μm diameter the temperature and bend sensitivities were 16 pm/°C and 21 pm/° respectively. The measurement resolution for temperature and bending angles were found to be 0.2 °C and 0.4°, respectively. Maximum measurement errors of 0.9 °C and 0.8° in the measurement range 0−70 °C and 0−50° respectively were found. The high sensitivity and resolution, along with low measurement error in in-situ temperature measurement on bending revealed that the proposed method was suitable for monitoring the SoC in flexible planar supercapacitors. The study, conducted on the variation of in-situ temperature rise on bending with specific capacitance and equivalent series resistance, opens up new possibility towards the development of supercapacitor temperature management systems for flexible planar supercapacitor.