Influence of Co²⁺ on the Structure, Conductivity, and Electrochemical Stability of Poly(Ethylene Oxide)-Based Solid Polymer Electrolytes: Energy Storage Devices

In the present work, using a simple solution cast technique, a series of poly(ethylene oxide) (PEO)-doped cobalt chloride (CoCl₂) solid polymer electrolytes (SPEs) were successfully prepared. The effect of dopant on the morphology, structure, thermal, and electrochemical stability of the PEO films was systematically studied, and their ionic conductivity was examined. The Fourier transform infrared spectroscopy data provide evidence of the complex nature and existence of various microscopic interactions. The PEO ionic conductivity of 8.6 × 10⁻⁸ S cm⁻¹ was found to increase to 3.5 × 10⁻³ S cm⁻¹ upon the inclusion of 5 wt.% of CoCl₂ at 303 K. An effort was made to understand the enhanced conductivity. Several studies were utilized to better understand the fundamental interplay of ion content and segmental motion using the Vogel–Tammann–Fulcher equation with typical investigations based on the fit of temperature-dependent conductivity data. The activation energy (E_a) decreased with increasing dopant concentration. The PCL5 transfer number (t_ion) was determined to be 0.93, evidence of the ionic nature of the doped electrolyte. Further, the purity and electrochemical stability of SPEs were studied using cyclic voltammetry and chronocoulometry. The thermal analysis showed reduced crystallinity and changes in glass transition and melting temperature at lower temperature, indicating enhanced amorphous content, thus confirming faster ion conduction. These SPEs with excellent electrical performance are promising candidates for electrolytes in solid-state batteries and other energy storage devices.