<p>High-performance electrolytes are crucial for advancing energy storage devices such as batteries and supercapacitors. One approach to enhancing the performance of electrolytes is the incorporation of redox additives, which introduce the redox reactions which will be helpful in improving the charge-storage capabilities of the energy storage device. In the present work, non-redox and redox-additive biopolymer electrolytes are demonstrated. The non-redox biopolymer electrolytes (BPEs) comprise a host polymer cellulose acetate (CA) and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) in which redox-additive potassium iodide (KI) is further incorporated to prepare the redox-additive biopolymer electrolytes (RBPEs). The solution cast technique has been used to synthesize electrolyte systems with different ionic liquid concentrations and redox-additive concentrations. The prepared polymer electrolyte films are characterized for their structural, electrical, and dielectric properties using different characterization tools such as X-ray diffraction, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, linear sweep voltammetry, and Wagner polarization technique. The optimized non-redox and redox-additive biopolymer electrolyte film shows a maximum ionic conductivity of ~ 3.25 × 10⁻⁵ S cm⁻¹ and ~ 1.05 × 10⁻⁴ S cm⁻¹, respectively, and both films are stable up to ~ 2.7&#xa0;V. Further, two supercapacitor cells (Cell#1 and Cell#2) are fabricated utilizing activating carbon based electrode materials and BPE-2 and RBPE-240 as electrolytes respectively. The Cell#1 and Cell#2 show a specific capacitance of 49.28 F g⁻¹ and 215.16 F g⁻¹ at a current density of 0.5 A g⁻¹, and a specific energy of 6.84 Wh kg⁻¹ and 29.88 Wh kg⁻¹ at power densities of 899 W kg⁻¹ and 820 W kg⁻¹ respectively.</p>