Characterization of Different Conductive Salts in ACN‐Based Electrolytes for Electrochemical Double‐Layer Capacitors

Herein we report a systematic investigation of the chemical and physical properties of acetonitrile‐based electrolytes that contained the salts tetraethylammonium tetrafluroroborate (Et4NBF4), tetraethylammonium bis(trifluoromethanesulfonyl)‐ imide (Et4NTFSI), 1‐butyl‐1‐methylpyrrolidinium tetrafluoroborate (Pyr14BF4), or 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI). The ionic conductivity, viscosity, density, and electrochemical stability windows of these electrolytic solutions have been considered in detail. From these results, the electrolyte Et4NTFSI (1 mol dm−3) in ACN appeared to display a promising set of properties that allow the realization of ACN‐based electrochemical double‐layer capacitors able to display stable behavior at 3.1 V. High voltage! The chemical and physical properties of acetonitrile‐based electrolytes that contain the salts Et4NBF4, Et4NTFSI, Pyr14BF4, or Pyr14TFSI are systematically investigated. Furthermore, these electrolytes are tested for their application in electrochemical double‐layer capacitors (EDLCs) with an operating voltage of >3.0 V.