2.2. Gel Polymer Electrolytes Ink Synthesis

Five GPE formulations were used for the experiments: three of them were aqueous and the rest were based on organic solvents. For the aqueous GPEs, PVA was used because of its high solubility in water. Firstly, 5 g PVA was added to 40 mL deionized water in a beaker. The beaker was then inserted in a larger beaker filled with water, and was heated to 80 °C under magnetic stirring. The heated bath method prevents local overheating of PVA at the bottom of the beaker. A conductive substance (H₃PO₄, Na₂SO₄, or LiClO₄) was gradually added to make a solution concentration of 0.5 M. After 30 min of heating, the solution was cooled to room temperature. The resulting aqueous GPE was then transferred to an empty printing tube for the manufacturing of the supercapacitor. For the organic GPEs, PC was used as the solvent. A total of 1.59 g LiClO₄ as the ion-supporting salt was added in 30 mL PC to create 0.5 M solution, and PVDF or PMMA as the polymer matrix was added with a molar ratio of 3:1 (polymer:ion). The solution with conductive substances and polymer matrix was heated at 140 °C for 30 min under magnetic stirring. The resulting organic GPE was then transferred to an empty printing tube for the experiments.