Nanostructured Ionic Liquid Containing Block Copolymer Electrolytes for Solid-State Supercapacitors

Abstract

We report on the physiochemical behaviour of membranes based on three different polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) block copolymers and an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI)) and their use as solid-state electrolytes in supercapacitors. The nanostructured block copolymers form free standing membranes at high ionic liquid uptake with conductivities above 1 mS/cm at 25 °C, keeping ordered morphologies. We used small angle X-ray scattering (SAXS) to propose the correlation between domain spacing, the copolymer chain length (N) and the interaction parameter (χ_eff) in the block copolymers. We explored the potential of the electrolytes in two high voltage (3.0 V) device configurations, first using carbon nanotube (CNT) electrodes, with excellent electrical conductivity and high-rate capability exhibiting a power density of 5.7 KW/kg at 4 A/g, while devices based on high surface area activated carbon exhibited high energy density of 20.7 Wh/kg at 4 A/g. Overall, both devices deliver superior specific energy and power densities than that of commercial state-of-the-art supercapacitors, based on liquid electrolyte. Additionally, the CNT|Solid-state|CNT device displays higher power density compared to the AC|Solid-state|AC device, highlighting its better suitability for high power applications, while the AC|Solid-state|AC device, is better suited for energy density applications.