Characterization of PVCA–PVDF/ZnO composite polymer electrolytes for energy storage applications: Microstructure, electrical, and nanoscale free-volume properties

Composite polymer electrolytes (CPEs) are increasingly attracting interest for next-generation, solid-state energy-storage technologies. A green, single-step aqueous casting technique was utilized to synthesize a PVCA-PVDF blend loaded with nanosized ZnO and complexed with dual ionic salts, specifically LiClO₄ and Li₂SO₄. XRD analysis revealed a synergistic reduction in PVDF crystallinity and enhanced amorphousness stemming from blending and salt complexation, while ZnO retained its high crystallinity. FTIR spectra confirmed successful salt complexation and ZnO incorporation, and SEM analysis demonstrated smooth, crack-free surfaces, indicating effective polymer blending and maintained homogeneity after doping. Thermogravimetric analysis (TGA) revealed an increase in the thermal stability of prepared films compared to the blend. Dielectric spectroscopy (permittivity, electric modulus, and Cole-Cole analysis) showed that complexation with 10 wt% LiClO₄ increased σ_ac by five orders to 1.1 × 10⁻⁴ S cm⁻¹ at 25 °C, meeting the benchmark for practical lithium batteries and flexible supercapacitors. Positron annihilation lifetime and Doppler broadening spectroscopy linked this enhancement to ZnO-mediated shrinkage of free-volume holes and suppressed positronium formation, confirming complete LiClO₄ complexation. By correlating nanostructure with ion transport, this work introduces a tunable, water-processable electrolyte platform that combines safety, sustainability, and high conductivity, benefiting society's transition to clean-energy storage.