High performance of supercapacitors containing an ionic liquid electrolyte by means of electrochemical and computational studies

This study characterizes the electrochemical behavior of symmetric coin cells with AC-based electrodes filled with the ammonium-based ionic liquid, a promising supercapacitor electrolyte due to its large voltage window and ambient temperature operation. We employed cyclic voltammetry, single-step chronoamperometry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge techniques to evaluate the electrochemical performance of the supercapacitors thoroughly. Our findings highlight the quasi-rectangular current-voltage profile up to 3.6 V, beyond which a faradaic current due to electrolyte degradation becomes significant. These results revealed a minor faradaic component, with impedance analysis showing typical behavior of well-formed electrical double layers (EDLs), influenced by the unique properties of ionic liquids. We observed that the ion dynamics and capacitance behavior align well with theoretical models, particularly the Goodwin-Kornishev mean-field theory. The study underscores the potential of ionic liquid-based supercapacitors to achieve high performance, with specific capacitance values reaching ∼2000 F g^-1 and great energy and power output, comparable to lithium-ion batteries. Molecular dynamics simulations further elucidated the charging mechanisms, ion migration, and structural interactions within the EDLs. These comprehensive insights validate the suitability of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide [N₁₁₁₄][NTf₂] for advanced supercapacitor applications, highlighting its ability to deliver exceptional electrochemical performance under optimized conditions.