Deciphering the Effect of Microstructural Modification in Sodium Alginate-Based Solid Polymer Electrolyte by Unlike Anions

Microstructure modification in sodium alginate (NaAlg)-based solid polymer electrolytes by the perchlorate (ClO₄^-) and acetate (CH₃COO^-) anions of sodium salts has been reported. ClO₄^- participates in the structure-breaking effect via inter/intramolecular hydrogen bond breaking, while CH₃COO^- changes the amorphous phase, as evident from X-ray diffraction studies. The larger size and negative charge delocalization of ClO₄^- have a plasticizing effect, resulting in a lower glass transition temperature (T_g) compared to CH₃COO^-. Decomposition temperature is strongly dependent on the type of anion. Scanning electron microscopy images showed divergent modifications in the surface morphology in both electrolyte systems, with variations in salt content. The mechanical properties of the NaAlg-NaClO₄ electrolyte systems are better than those of the NaAlg-CH₃ COONa system, indicating weak interactions in the latter. Although most of the studies focus on the cation influence on conductivity, the interaction of the anion and its size certainly have an influence on the properties of solid polymer electrolytes, which will be of interest in the near future for sodium ion-based electrolytes in energy storage devices.