An investigation about the use of mixtures of sulfonium-based ionic liquids and propylene carbonate as electrolytes for supercapacitors

Abstract

This study describes the use of mixtures of the ionic liquid (IL) trimethyl-sulfonium bis [(trifluoromethyl) sulfonyl]imide (Me 3 STFSI) and propylene carbonate (PC) as electrolytes for carbon-based electrochemical double layer capacitors (EDLCs). Two different mixtures have been investigated. The first one contained the maximum amount of Me 3 STFSI (3.8 mol L À1 ) soluble in PC at room temperature (RT). The second one contained 1.9 mol L À1 of Me 3 STFSI, which is the concentration featuring the highest conductivity among all possible mixtures between PC and Me 3 STFSI at RT. The physicochemical properties, including conductivity, viscosity, and electrochemical and thermal stability of both mixtures, have been initially investigated. Afterward, the use of these mixtures as electrolytes for EDLCs has been considered. This study showed that by using these innovative electrolytes, it is possible to develop EDLCs with an operative voltage as high as 3.0 V. It was clearly demonstrated that the EDLC cycle life strongly depends on the concentration of Me 3 STFSI present in the mixture. Moreover, it was also proved that mixtures containing high concentrations of IL are able to suppress anodic oxidation of the Al current collector at high potential. When a solution with a high salt concentration is used, an EDLC with high energy, high cycle life and a broad temperature range of operation can be realized.

A review of electrolyte materials and compositions for electrochemical supercapacitors

“…476 Vali et al 151 reported that the type of conducting salt could greatly affect the electrochemical stability of Al current collectors in an organic solvent. Brandt et al 314 reported that the possible anodic oxidation of Al current collectors could strongly affect the operation cell voltage of EDLCs when IL-organic electrolyte mixtures (i.e., [Me 3 S][TFSI]-PC) were used. This condition could lead, in turn, to a much lower electrochemical stability when compared to both NaPF 6 -and NaClO 4 -based electrolytes.…”

New electrolyte mixture of propylene carbonate and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N1114 TFSI) for high performance silicon nanowire (SiNW)-based supercapacitor applications

“…1b). This optimal ratio (50:50% w.t) has been widely employed as mixture electrolyte for electrochemical energy storage devices in presence of different ionic liquid chemical structures, as for example Me 3 NHTFSI:PC, PYRNO 3 :PC, Me 3 STFSI:PC or PYR 14 TFSI:PC in the field of supercapacitors [29,24,23]. This ratio demonstrated in all the aforementioned cases physical-chemical properties (h and s) close to pure PC containing salt electrolytes (e.g.…”

“…PYR 14 TFSI or Me 3 STFSI) and organic solvents (e.g. PC) showed h and s values close to pure PC containing 1 M Et 4 NBF4, which exhibited the highest conductivity and lowest viscosity values by comparison between both the pure ionic liquids and the corresponding mixtures [23,24]. Based on this criteria, this mixture ratio was chosen as an optimal electrolyte for the electrochemical performances reported in this study.…”

Mixtures of Azepanium Based Ionic Liquids and Propylene Carbonate as High Voltage Electrolytes for Supercapacitors

“…[21] In the last years several research efforts have concentrated on the application of mixtures of pyrrolidinium-based ILs and organic carbonates as EDLC electrolytes. [22][23][24][25][26] Using these mixtures, an operative voltage higher than 3.0 V could be retained while decreased viscosities and increased conductivities with respect to neat ILs could be reported. [22,23].…”