Electrical, Structural, and Electronic Insights of Polysaccharide-Based Biopolymer Electrolytes Incorporated with Sodium Perchlorate Salt

The urgent demand for sustainable energy materials aligned with the United Nations Sustainable Development Goal 7 has intensified interest in biopolymer electrolytes (BPEs). Many non-polysaccharide biopolymers exhibit low ionic conductivity and weak salt dissociation at room temperature, limiting their performance in sodium-ion energy storage devices. Polysaccharides such as guar gum provide abundant coordination sites that can enhance Na+ transport. This study investigates the electrical, structural, and electronic behaviour of guar gum–sodium perchlorate (guar gum–NaClO4) BPEs to establish structure–transport relationships. Biopolymer electrolyte films were prepared via solution casting using guar gum (0.5 g) with NaClO4 at six salt loadings: 0, 10, 20, 30, 40, and 50 wt.%. Electrochemical impedance spectroscopy (EIS) was conducted at room temperature for all compositions and at elevated temperatures (303–343 K) for selected samples (0, 30, and 40 wt.%). Structural properties were examined by X-ray diffraction (XRD), and crystallite size was quantified using the Scherrer equation. Electronic properties, including density of states (DOS) and frontier molecular orbitals, were evaluated using density functional theory (DFT) with the DMol3 module. Ionic conductivity increased from 9.13 × 10−9 S·cm−1 in the unadded salt guar gum sample (0 wt.%) to a maximum of 8.40 × 10−4 S·cm−1 at 40 wt.% NaClO4, attributed to enhanced NaClO4 dissociation and reduced bulk resistance. At 50 wt.%, conductivity decreased to 3.37 × 10−4 S·cm−1, indicating ion pairing. Temperature-dependent EIS confirmed Arrhenius behaviour, with the 40 wt.% sample exhibiting the lowest activation energy (7.61 × 10−20 eV). XRD analysis showed progressive amorphization with crystallite size reducing from 5.05 nm (0 wt.%) to 0.82 nm (40 wt.%), correlating with enhanced ionic mobility. DFT findings revealed strong guar gum–NaClO4 interactions and a significant HOMO–LUMO band-gap reduction from 6.6129 eV (unadded salt guar gum) to 0.3813 eV, suggesting improved electronic flexibility and salt dissociation. The combined EIS, XRD, and DFT analyses demonstrate that guar gum–NaClO4 BPEs exhibit strong structure–transport coupling, with 40 wt.% NaClO4 producing optimal ionic conductivity and molecular stability. These findings identify guar gum as a promising, sustainable host polymer for sodium-based solid electrolytes in next-generation energy storage systems.