A transparent solid-state ion gel for supercapacitor device applications

A feasibility study of the synthesis of gel polymer electrolytes based in methyl methacrylate (MMA) and 1-vinyl-2-pyrrolidone (VP) using [HEMIm][BF₄] as common ionic liquid has been done. A novel PVP/[HEMIm][BF₄] solid-state and self-standing ion gel electrolyte has been successfully prepared. The thermal degradation of PVP/[HEMIm][BF₄] ion gel occurs in two steps with the first one at above 200 °C and the main one over 390 °C. This solid-state ion gel is transparent, showing an optical transmittance with a maximum value of 90% in the visible wavelength region from 370 to 770 nm. The synthesized PVP/[HEMIm][BF₄] solid-state ion gel exhibits an electrochemical stability window of ca. 5.0 V and an acceptable ionic conductivity of σ = 5.7 10⁻³ S cm⁻¹ at room temperature. A symmetrical pseudocapacitive supercapacitor has been assembled and characterized using this PVP/[HEMIm][BF₄] solid-state ion gel—glass/ITO/PEDOT/PVP/[HEMIm][BF₄]/PEDOT/ITO/glass. It is found that the supercapacitor shows a typical areal specific capacitance of 3.1 mF cm⁻², a maximum energy density of 2.5 μWh cm⁻², and an areal specific power density of ca. 1 mW cm⁻². [Figure not available: see fulltext.]