Ionic liquid doped polymer electrolytes: Structure to conductivity

Gel polymer electrolytes offer advantages over conventional liquid electrolytes, including enhanced safety and stability. This study investigates poly(ethylene oxide) (PEO)-based electrolytes doped with ionic liquids (ILs), focusing on the influence of various salts containing mono- and multivalent cations  on key electrolyte properties, including ionic conductivity and thermal behavior. The high crystallinity of PEO poses a significant barrier to ion transport; therefore, incorporation of ILs serves as an effective strategy to disrupt crystalline domains and reduce crystallinity by about 50%, thereby enhancing segmental motion and increasing conductivity. Furthermore, the cationic charge density plays a critical role in modulating the thermal transitions of the electrolytes. Due to differences in coordination behavior, specifically, the number of oxygen atoms bound to each cation, the ionic conductivity varies depending on the nature of the salt. For Mg²⁺ with higher charge density, viscosity shows the highest value as well as the conductivity.