Deciphering the Role of <scp>L</scp>i<scp>C</scp>l<scp>O</scp>₄ Salt on Electrochemical Properties of Plasticized Biopolymer Electrolytes for Superior <scp>EDLC</scp> Efficiency at Elevated Temperatures

The advancement of electric double‐layer capacitors capable of operating beyond standard conditions is vital for meeting the demands of modern electronic applications. To realize this, huge efforts have been devoted to the development of biopolymer‐based electrolytes. This study explores the potential application of a plasticized biopolymer‐based electrolyte in electric double‐layer capacitor systems at ambient and elevated temperatures. A plasticized Na CMC/PEO/LiClO 4 electrolyte is successfully synthesized via a solution‐casting approach. Fourier‐transform infrared spectroscopy and X‐ray diffraction verify the material's chemical and amorphous structure, respectively. The sample was designated as R20, with a salt concentration of 20 wt. % exhibits good electrochemical properties, including a high ionic conductivity of 3.73 × 10 −4 S cm −1 and a wide electrochemical stability window of 3.2 V. The sample is placed into an electric double‐layer capacitor cell and subjected to cyclic voltammetry and galvanostatic charge–discharge analyses at both room and high temperatures. The cyclic voltammetry test demonstrates that the electric double‐layer capacitor achieves a specific capacitance ( C p ) of 38 F g −1 at ambient temperature, which increases to 60 F g −1 at 60 °C. Additionally, the electric double‐layer capacitor cell maintains consistent performance, demonstrating stable power and energy densities of 25 W kg −1 and 6 Wh kg −1 , respectively, under both ambient and elevated temperatures.