We fabricated a single-layer graphene-doped electric double-layer capacitor (EDLC) consisting of glass, indium tin oxide, graphene layers, gel electrolyte, deposited platinum, and a conductive separator. To find the appropriate doping materials and compositions of the EDLC, we conducted experiments using single-layer graphene and ZnO as doping materials. We also varied the doping concentrations of single-layer graphene to find the optimal concentration. The single-layer graphene EDLC was fabricated with different annealing and platinum deposition methods. Different electrolytes were also tested to determine the appropriate compositions and methods to fabricate the EDLC. The performance of the EDLC was assessed by measuring the capacitance, charge–discharge efficiency, charge–discharge cycle, and hysteresis area of cyclic voltammogram (CV). The results revealed that single-layer graphene was better than ZnO for doping the EDLC, and the appropriate concentration was 0.07 wt%. Annealing the single-layer graphene, depositing platinum, and using a gel electrolyte of 10 wt% polyvinyl alcohol (PVA) and 6 M potassium hydroxide (KOH) helped improve the performance of the single-layer graphene EDLC. The capacitance and charge–discharge efficiency were increased by 9.4–72.2 and 3.2–158.6%, respectively, depending on the methods and materials tested in this study. The charge–discharge cycle and hysteresis area were enhanced by 11.5–26.4 and 11.0–24.6%, respectively. Therefore, the annealed single-layer graphene-doped EDLC with deposited platinum and a gel electrolyte is recommended for use in electric vehicles (EVs) and advanced sensors because of its improved performance.