This study investigated the anodic dissolution of Al current collectors in unconventional electrolytes for high voltage electrochemical double-layer capacitors (EDLCs) containing adiponitrile (ADN), 3-cyanopropionic acid methyl ester (CPAME), 2-methyl-glutaronitrile (2-MGN) as solvent, and tetraethylammonium tetrafluoroborate (Et NBF ) and tetraethylammonium bis(trifluoromethanesulfonyl)imide (Et NTFSI) as conductive salts. To have a comparison with the state-of-the-art electrolytes, the same salts were also used in combination with acetonitrile (ACN). The chemical-physical properties of the electrolytes were investigated. Furthermore, their impact on the anodic dissolution of Al was analyzed in detail as well as the influence of this process on the performance of high voltage EDLCs. The results of this study indicated that in the case of Et NBF -based electrolytes, the use of an alternative solvent is very beneficial for the realization of stable devices. When Et NTFSI is used, the reduced solubility of the complex Al(TFSI) appears to be the key for the realization of advanced electrolytes.

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.

In this study, we report for the first time about the use of aluminum bis­(trifluoromethanesulfonyl)­imide [Al­(TFSI)3] as conducting salt for electrochemical double-layer capacitors (EDLCs). We show that using this salt it is possible to realize highly concentrated electrolytes, which are able to suppress the anodic dissolution of the aluminum current collectors. Because of this ability, the use of this electrolyte makes possible the realization of EDLCs that can retain 80% of their initial performance after floating for 1500 h at 3 V (which is comparable to ∼5000000 cycles of charge and discharge at 1 A g–1).

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