Outstanding performance of activated graphene based supercapacitors in ionic liquid electrolyte from −50 to 80 °C

High specific surface area (SSA ∼2000 m2/g) porous KOH-activated microwave exfoliated graphite oxide (‘a-MEGO’) electrodes have been tested in a eutectic mixture of ionic liquids (1:1 by weight or molar ratio N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide (PIP13-FSI) and N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14-FSI)) as electrolyte for supercapacitor applications. By optimizing the carbon/electrolyte system, outstanding capacitive performance has been achieved with high capacitance (up to 180 F/g) and wide electrochemical window (up to 3.5 V) over a wide temperature range from −50 °C to 80 °C. This is the first demonstration of a carbon–ionic liquid system capable of delivering capacitance in excess of 100 F/g below room temperature. The excellent electrochemical response of the proposed couple shows that optimization of the carbon/electrolyte interface is of great importance for improving capacitive energy storage.

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► We show a carbon/electrolyte system to store more than 100 F/g in a temperature window between −50 °C and 80 °C.
► We annealed activated graphene to obtain a graphitic surface with little functionalization.
► We use a eutectic mixture of ionic liquids to operate in a wide temperature window.
► Removal of surface functionality leads to a better electrochemical performance.