Effect of crosslinker on the electrochemical properties of starch-based water-in-polymer-salt electrolytes

Water-In-Polymer-Salt-Electrolytes (WiPSEs) are identified as the highly conductive electrolytes (~0.01 S/cm) with wide electrochemical stability window (ESW) for the advanced energy storage devices. In our previous reports, we reported that cross-linked starches are good hosts for Polymer-In-Salt-Electrolytes (PISEs) synthesis and by exposure to high humidity atmosphere, it behaves like WiPSE. In the present study, our effort is to understand the effect of change in bonding structure on the mechanical and electrochemical properties of these materials. Hence, in the present case we have varied both, the salt concentration and the crosslinker amount, because crosslinker amount is supposed to enrich the covalent bonding and hence water absorption through hydrogen bonding will be negatively affected. Effect of crosslinking variations of GA (1- to 5-ml Glutaraldehyde for 1-g starch) is studied at three varied salt concentrations (50, 66, 75 wt % salt). Highest conductivity is found to be ~0.03 S/cm with ESW of ~2 V with flexible morphology. Further, a supercapacitor is fabricated by using 75 wt % salt WiSPE with coated carbon cloth-based electrodes. Specific capacitance is of order of 10 F/g at 10 mV/s scan rate with coulombic efficiency greater than ~85%. This work confirms the theoretical understanding that loosely bound structures are better for PISEs/WiPSEs. Being economical and environment-friendly, these electrolytes have the potential to reach commercial level if explored in detail.