NaTFSI-doped guar gum biopolymer electrolytes for sodium-ion EDLCs: ionic transport and electrochemical performance

A sustainable biopolymer-based polymer electrolyte (BBPE) was developed by incorporating sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) into a guar gum (GG) matrix using 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as a functional ionic-liquid medium. FTIR and SEM results indicated changes in the local chemical environment and a relatively uniform surface morphology, although these techniques do not directly establish crystallinity, bulk salt homogeneity, or molecular-level ion distribution. The optimized S3 electrolyte exhibited an ionic conductivity of 2.84 × 10 −3 S cm −1 at ambient temperature, an apparent Arrhenius activation energy of 0.2177 eV, and a reduced T g of 83.2 °C. The apparent Na + transference number was 0.55, indicating significant Na + related cationic transport in the multicomponent electrolyte. LSV identified an anodic oxidation onset at approximately 1.75 V under the specified conditions, rather than a complete electrochemical stability window. An EDLC fabricated with S3 showed stable cycling over 1000 cycles, although the specific capacitance was modest at approximately 2.03 mF g −1 . These results demonstrate the potential of GG–NaTFSI–[Bmim]Cl as a sustainable gel polymer electrolyte for low-voltage EDLC applications.

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