Towards realistic electrical double layer capacitor device with elevated energy and power densities designed from plasticized nanocomposite PVA-based electrolyte

The current work establishes a breakthrough for the electrical double-layer capacitor (EDLC) device, utilizing biodegradable polymer and non-toxic salt. In this project, polymer electrolytes (PEs) comprising polyvinyl alcohol (PVA), sodium thiocyanate (NaSCN), glycerol (Gly), and various amounts of TiO₂ nanofillers were prepared by solution casting. The electrolyte inserted with 3 wt% TiO₂ showed the maximum DC conductivity, reaching 1.86 × 10^-3 S/cm. Dielectric analysis revealed a high dielectric constant (8.5 × 10⁶), indicating efficient charge storage. The AC conductivity pattern demonstrated a low-frequency spike and a flat region, emphasizing the direct current (DC) component. Additional tests on the highset conducting electrolyte verified that ion transport was the primary mechanism (tion = 0.976) and that the electrolyte maintained good electrochemical stability around 2.5 V. This electrolyte was subsequently employed in the construction of an EDLC device. The cyclic voltammetry (CV) results revealed a non-Faradaic charge storage process characterized by an almost leaf-like profile. Galvanostatic charge-discharge curves close enough to the ideal shape with minimal voltage drop, reinforcing the device's excellent performance. The constructed EDLC exhibited strong performance, delivering 138 F/g in capacitance, with an output power of 4000 W/kg and an energy storage capacity of 17.3 Wh/kg. The Ragone plot showed high power and energy densities comparable to lead-acid and Ni-Cd batteries, highlighting its potential for rapid charge-discharge performance. Finally, the limitations of EDLC devices have been discussed.