Graphene-Polymer Nanocomposites and Roll-to-Roll (R2R) Compatible Flexible Solid-State Supercapacitor Based on Graphene Nanoplatelets and Ionic Liquid-Polymer Gel

Abstract

We present the electrical and supercapacitive performance of graphene nanoplatelets in polymer nanocomposites and flexible solid state electrical double layer capacitors (EDLC) respectively. Graphene-doped poly (3,4-ethylenedioxythiophene) (PEDOT) coated polyethylene terephthalate (PET) and glass exhibited transmittance above 95% and electrical conductivity of 2.70 × 10ˉ1 S·cmˉ1 and 9.01 × 10ˉ1 S·cmˉ1 respectively. Graphene loaded polymethyl methacrylate (PMMA) and polystyrene (PS) nanocomposites showed electrical conductivity as high as 2.11 × 10ˉ1 S·cmˉ1 at low loadings of 2 wt%. The use of graphene was necessitated by the need to increase the EDLC capacitance and energy density since it provides high effective surface area. The polymer gel membrane made from polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) and the Ionic Liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate exhibited high porosity which made it suitable for use as separator in the EDLC. The highest recorded specific capacitance was 133.82 F/g which can be attributed to the porosity of the IL containing PVDF-co-HFP membrane and the large surface area of the graphene electrodes. At an operating voltage of 3.5 V the energy density was found to be 56.92 Wh·Kgˉ1. All chemicals were research grade and were obtained from Sigma Aldrich.