Gel polymer electrolytes (GPEs) have attracted considerable attention for rechargeable battery applications because of their high ionic conductivity, mechanical flexibility, and enhanced safety. In the present work, copper-ion-conducting PVA/HPMC gel polymer electrolytes were successfully prepared by the solution casting method using a 50:50 PVA/HPMC blend. Different CuSO₄ concentrations (10, 20, and 30 wt%) were incorporated into the polymer matrix, followed by the addition of 3 mL PANI/[BMIM][BF₄] polyionic liquid. The prepared electrolytes were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). SEM analysis revealed a more homogeneous morphology after incorporating the polyionic liquid, indicating improved compatibility among the polymer components. DSC measurements showed that the glass transition temperature increased from 95 °C for the neat PVA/HPMC blend to 115 °C for the optimized electrolyte, while the melting temperature increased from 220 °C to approximately 285 °C. TGA demonstrated improved thermal stability, with the onset decomposition temperature increasing from 170 °C to 230 °C after CuSO₄ incorporation. The optimized electrolyte also exhibited the lowest bulk resistance 2 Ω and maximum ionic conductivity value of 6.21 × 10⁻³ S cm⁻¹ at room temperature for the electrolyte containing 20 wt% CuSO₄ and 3 mL PANI/[BMIM][BF₄]. The obtained results demonstrate that the synergistic combination of CuSO₄ and PANI/[BMIM][BF₄] effectively enhances the structural, thermal, and electrochemical properties of PVA/HPMC gel polymer electrolytes, making them promising candidates for rechargeable battery applications.
