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.