Electric double-layer capacitors (EDLC) store ionic charge electrostatically at the interface of high surface area electrodes such as carbon in a liquid electrolyte.1 Despite significant improvements in electrode and materials design, virtually all state-of-the-art non-aqueous electrochemical capacitors use the same electrolyte: tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (ACN). This electrolyte has an exceptionally high conductivity which minimizes resistive losses and enables capacitors to operate at very high power. However, this electrolyte has a practical voltage window around only 2.7 V, beyond which the capacitor lifetime is significantly shortened.2 Since the energy stored in a capacitor increases quadratically with voltage, extending this electrochemical window could significantly improve the energy density. In this study we report on electrolytes consisting of sodium salts in tetraethylene glycol dimethyl ether (TEGDME) and dimethoxyethane (DME) which clearly show a 4 V electrochemical window. The extended voltage window doubles the energy density that can be achieved with any given capacitor electrode. Electrolyte conductivities range from 1-10 mS/cm, which are comparable to ionic liquids and adequate for moderate power applications. Importantly, all salts and solvents are commercially available, which should enable these electrolytes to be as cost-effective and scalable as the current generation of commercial supercapacitor electrolytes. Acknowledgement This work is supported by Laboratory Directed Research and Development (LDRD) program of Oak Ridge National Laboratory under the seed project S12-056. References (1) Conway, B. E. Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications; Plenum Publishers: New York, 1999. (2) Beguin, F.; Presser, V.; Balducci, A.; Frackowiak, E. Adv. Mater. 2014, 26, 2219.

Stable 4 volt electrolytes for high energy electrochemical capacitors

249th National Meeting (2015)

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