Electrochemical performance of lithium‐ion‐conducting alginate biopolymer electrolytes for electric double‐layer capacitor applications

Abstract Alginate‐based polymer electrolytes incorporating lithium salts were prepared via solution casting and evaluated for application in electric double‐layer capacitors (EDLCs). Two systems, ALNO (alginate–LiNO 3 ) and ALIB (alginate–LiBr), achieved ionic conductivities of the order of −10 −4 S cm −1 at ambient temperature. Conductivity spectra confirmed thermally activated Li + transport, with ALNO exhibiting consistently higher conductivity than ALIB. Linear sweep voltammetry revealed wide stability windows of 1.90–1.97 V, while cyclic voltammetry demonstrated nearly ideal capacitive behaviour. Nyquist analysis showed lower series resistance for ALNO, although resistance growth was more pronounced after extended cycling compared to ALIB. Galvanostatic charge–discharge studies confirmed excellent reversibility with coulombic efficiency close to 100%, and long‐term cycling up to 5000 cycles demonstrated superior capacitance and energy power characteristics in ALNO relative to ALIB. These findings highlight ALNO as a promising bio‐based polymer electrolyte for sustainable and high‐performance EDLC applications. © 2026 Society of Chemical Industry.