Polymer electrolytes based on agarose dissolved in DMSO solvent complexed with different weight percentages of Mg(NO₃)₂ ranging from 0 to 35 wt% were prepared using a solution casting method. Electrochemical impedance spectroscopy (EIS) was applied to study the electrical properties of this polymer electrolyte, such as ionic conductivity at room and different temperatures, dielectric and modulus properties. The highest conducting film has been obtained at 1.48 × 10⁻⁵ S·cm⁻¹ by doping 30 wt% of Mg(NO₃)₂ into the polymer matrix at room temperature. This high ionic conductivity value is achieved due to the increase in the amorphous nature of the polymer electrolyte, as proven by X-ray diffractometry (XRD), where broadening of the amorphous peak can be observed. The intermolecular interactions between agarose and Mg(NO₃)₂ are studied by Fourier transform infrared (FTIR) spectroscopy by observing the presence of –OH, –CH, N–H, CH₃, C–O–C, C–OH, C–C and 3,6-anhydrogalactose bridges in the FTIR spectra. The electrochemical properties for the highest conducting agarose–Mg(NO₃)₂ polymer electrolyte are stable up to 3.57 V, which is determined by using linear sweep voltammetry (LSV) and supported by cyclic voltammetry (CV) that proves the presence of Mg²⁺ conduction.

Electrochemical energy storage devices (EES) such as batteries and supercapacitors depend significantly on electrolytes, which have properties that significantly impact their energy capacity, rate performance, cyclability, and safety. Agarose–Mg(ClO4)2–based polymer electrolyte was prepared using the solution casting method by incorporating various amounts of Mg(ClO4)2 from 0 – 35 wt%. The presence of Mg(ClO4)2 as the dopant in agarose-matrix enhanced the ionic conductivity of the system from 1.796 × 10-8 S∙cm-1 to 6.247 × 10-4 S∙cm−1 in the composition of 30 wt% Mg(ClO4)2 due to the production of free ions. This system obeys the Arrhenius rule as it records the conductivity increment when temperature increases. This increment shows the amorphous nature of electrolytes, which XRD analyses by determining the crystallite size and degree of crystallinity of agarose–Mg(ClO4)2 polymer electrolyte. High ionic conductivity at room temperature has increased attention to this polymer electrolyte based on agarose–Mg(ClO4)2.

The exponential concern about environmental concerns has heavily driven the development of green technology. In light of these needs, Deep Eutectic Solvent (DES) emerged as a green solvent and additive due to its minimal toxicity and volatility, biodegradability, biocompatibility, simplicity of synthesis, high yields and purity, and the availability of its precursors. This review is intended to summarise and discuss polymer electrolytes based on DES for better insight into the potential of replacing conventional organic solvents or ionic liquids for energy storage applications in the aspect of their electrical and structural properties. Therefore, an examination of dielectric studies is conducted as they hold significance in establishing a correlation between the rise in ionic conductivity and the augmentation of freely movable ions, thereby highlighting the importance of investigating the dielectric properties of an electrolyte. Besides, XRD and morphological studies in this work can show how ionic conductivities can influence the size of pores in DES-based polymer electrolytes.

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.

The electrochemical stability and charge-transport properties of biopolymer blend films are significantly affected by blend composition, as each polymer component contributes uniquely to segmental mobility, bulk resistance, amorphous structure, and interfacial stability. In this study, salt-free agarose:phytagel (AG:PY) biopolymer blend films were fabricated at various weight ratios using the solution-casting method to identify an optimal host matrix for the development of salt-doped electrolytes. Linear voltammetry measurements showed that the 50:50 mass ratio AG:PY mixture has an electrochemical stability window of 3.25 V, indicating substantial resistance to electrochemical decomposition within the tested potential range. Electrochemical impedance spectro­scopy analysis showed that the 50:50 blend achieved the highest room-temperature conductivity of 1.56 mS cm⁻¹, attributed to reduced bulk resistance and indicating more favourable charge-transport characteristics within the polymer host. X-ray diffraction analysis verified this finding, revealing the lowest crystallinity in the 50:50 mass ratio, suggesting increased amorphous content and greater polymer chain flexibility. Fourier-transform infrared spectroscopy spectral shifts confirmed interactions between the functional groups of agarose and phytagel, indicating improved blend compatibility. Collectively, the 50:50 mass ratio AG:PY blend exhibited the most advantageous combination of electrochemical stability, ionic conductivity, amorphous structure, and polymer interaction, establishing it as a promising sustainable host matrix for future salt-doped biopolymer electrolyte applications.

Solid polymer electrolyte was prepared by blending two different polymers to improve their mechanical properties using solution casting method. The conductivity of films was measured by electrical impendence spectroscopy (EIS) and showed a highest conductivity when 10 wt.% of NaCl incorporated with blending polymer of potato starch and chitosan at 4.82 × 10−6 S.cm−1. This phenomenon is best clarified as the dissociation of ion is higher at this rate and the energy barrier is lowered leads to increase the conductivities. The plot of log σ versus 1000/T for all systems follow the Vogel-Tamman- Fulcher (VTF) rule. ATR-FTIR studies the interaction after addition of salt, shows the shifted band of carboxamide and amine group due to the interaction of salt (Na+ ion and Cl− ion). From the X- Ray diffraction analysis, the blending 50 wt.% starch and 50 wt.% chitosan is the most amorphous blend exhibit to the higher conductivity of addition of 10 wt.% of NaCl into the blending system. The morphology of the systems was observed using scanning electron microscope (SEM). The morphology of highest conductivity film shows the roughness and pores in the systems indicate the space for the ions to moves and increase the conductivities compared the morphology of films beyond 10 wt.% of NaCl. It was showed that the crystalline structure and the movement of ions were inhibited and decreased the conductivity of films.