High-energy hybrid electrochemical capacitor operating down to −40 °C with aqueous redox electrolyte based on choline salts

• Published in: Journal of power sources Vol. 427; pp. 283 - 292
• Main Authors: Przygocki, Patryk, Abbas, Qamar, Gorska, Barbara, Béguin, François
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2019
• Subjects: Carbon/carbon capacitor; Choline salt; Hybrid capacitor; Low temperature; Redox electrolyte; Choline salt; Hybrid capacitor; Carbon/carbon capacitor; Redox electrolyte; Low temperature
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2019.04.082

We report on a carbon/carbon hybrid electrochemical capacitor (hybrid EC) based on an aqueous redox-active electrolyte, which operates efficiently down to −40 °C. The electrolyte comprises choline iodide (ChI; 0.5 mol kg−1) as redox active component and choline nitrate (ChNO3; 5 mol kg−1) as supporting salt which enables the liquid state to be extended down to −42 °C, as proved by differential scanning calorimetry. Interestingly, the hybrid EC displays a high discharge capacitance of 81 F g−1 (at 0.1 A g−1; per total mass of electrodes), which is twice higher than its symmetric counterpart utilizing only an aqueous solution of ChNO3 (41 F g−1). The doubling of cell capacitance results from hybridization of the positive battery-type electrode (harnessing redox reactions of polyiodides trapped in carbon porosity) with the negative electrical double-layer (EDL) capacitive electrode. Even at −40 °C, the hybrid EC retains a high capacitance of 50 F g−1 and shows negligible ohmic drop. As its energy and power performance is in the same range as for EDL capacitors using tetraethylammonium tetrafluoroborate in acetonitrile, this new hybrid EC is a highly cost-effective and green alternative to these traditional systems. An eco-friendly and cost-effective carbon/carbon hybrid capacitor in redox aqueous electrolyte based on choline salts shows excellent performance at sub-ambient temperature. [Display omitted] •Hybrid electrochemical capacitor in aqueous medium operates efficiently down to −40 °C.•Electrolyte comprises redox active choline iodide and choline nitrate supporting salt.•The positive and negative carbon electrodes are of battery- and EDL-type, respectively.•Energy and power of the hybrid EC reach the values of ECs in organic electrolyte.