Ionic liquid–solvent mixtures as supercapacitor electrolytes for extreme temperature operation

Abstract

Ionic liquid (IL)-based electrolytes containing molecular solvents were shown to be attractive for extreme temperature applications in electric double layer capacitors (EDLCs). In particular, the IL-butyronitrile (BuCN) mixture provides high capacitance (around 125 F g 21 at 500 mA g 21 ) independent of testing temperature, and superior performance at high current rates (reduced current dependence at high rates). Importantly, the IL-BuCN electrolyte can safely operate between 220 and + 80 uC, which overcomes the high temperature limitations of current commercial EDLCs. An additional advantage of IL-solvent mixtures is that the higher concentration of IL ions in the mixtures allows a greater specific capacitance (F g 21 ) to be achieved. The conductivity of the ionic liquid N-butyl-n-methylpyrrolidinium bis(trifluoromethane sulfonyl) imide (PYR 14 TFSI) could be increased from 2.48 mS cm 21 up to 45 mS cm 21 by mixing with an appropriate solvent. Importantly, these solvent mixtures also retain a wide electrochemical voltage window, in the range 4-6 V.

Anomalous Capacitance Maximum of the Glassy Carbon–Ionic Liquid Interface through Dilution with Organic Solvents

“…6,7 Additionally, RTILs offer processing advantages over traditional solid salt-based electrolytes, namely, they can be evaporatively consolidated with the active electrode material from a volatile phase (e.g., organic solvent) to form dense electrodes.…”

“…3−5 Such RTIL/solvent mixtures are electrochemically stable up to 4 V and have also shown promise in devices operating at high temperatures. 6,7 Additionally, RTILs offer processing advantages over traditional solid salt-based electrolytes, namely, they can be evaporatively consolidated with the active electrode material from a volatile phase (e.g., organic solvent) to form dense electrodes. 3,8 Though improvements in rate performance have been achieved using these mixtures, the effect of diluting RTILs with organic solvents on the doublelayer capacitance of the electrode−electrolyte interface remains unclear.…”

Physical and Electrochemical Investigations into Blended Electrolytes Containing a Glyme Solvent and Two Bis{(trifluoromethyl)sulfonyl}imide-Based Ionic Liquids

“…Such observations have permitted the speculation of non-homogeneity within the mixture by the formation of microphases wherein the ionic liquid structure is retained upon dilution. 46 To qualitatively probe the interactions between the two components, the excess molar volume, V m E , of the mixtures was calculated using the following series of equations [10] where V m r and V m i represent the experimental molar volume and ideal molar volume, respectively, as a calculated by…”

“…Na-ion, Mg-ion and metal-air batteries) for the development of potentially safer devices. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Furthermore, the high (electro)chemical stabilities and non-volatilities exhibited by many IL structures provides interesting electrolyte media for electrochemical gas sensors (e.g. for O 2 , [16][17][18][19] CO 2 ,20,21 NO 2 22 ) where traditional solvents are prone to evaporation leading to device failure, and also for electromechanical actuator, [23][24][25] and electrodeposition applications.…”

“…The mutual solubility between many ILs and common nonaqueous electrochemical solvents enable the consideration of a wide range of formulations in a given mixture with the prospect of balancing the desired properties. As such, investigating the application of IL/molecular solvent blends as electrolytes for Li-ion batteries, [1][2][3][4] Naion batteries, 13 Li-O 2 chemistry, [32][33][34] and EDLCs, [7][8][9][10] has continually revealed material benefits relating to electrolyte stability and device safety.…”