Firstly, the ionic conductivity of a pristine PAM/LiCl hydrogel electrolyte was measured by electrochemical impedance spectroscopy (EIS). Fig. shows the Nyquist plot of a pristine PAM/LiCl hydrogel electrolyte, measured with two stainless-steel blocking electrodes. The result exhibits a typical non-ideal capacitor behavior, characterized by a constant phase element (CPE) connected to a resistor (R s ) in series because of the electrolyte's high ionic conductivity and the absence of charge transfer reactions. The ionic conductivity of the PAM/LiCl hydrogel calculated from the x-axis intercept is 42.5 mS/cm, which is higher than that of most reported gel polymer electrolytes . The inductively coupled plasma mass spectrometry (ICP-MS) results also show that the high concentration of 10.72 M LiCl in the polyacrylamide hydrogel facilitates ion transportation (Supplementary Note 2).