Electrical Double‐Layer Capacitors Based on a Ternary Ionic Liquid Electrolyte Operating at Low Temperature with Realistic Gravimetric and Volumetric Energy Outputs

Abstract

We report on electrical double‐layer capacitors (EDLCs) performing effectively at low temperature (down to −40 °C), owing to the tuned characteristics of both the ionic liquid (IL) electrolyte and carbonaceous electrodes. The transport properties of the electrolyte have been enhanced by adding a low‐viscosity IL with the tetracyanoborate anion, [EMIm][TCB], to a mixture of [EMIm][FSI] with [EMIm][BF4], which was already successfully applied for this application. The formulated ternary electrolyte, [EMIm][FSI]0.6[BF4]0.1[TCB]0.3, remained in the liquid state until it reached the glass transition at −99 °C and displayed a relatively low viscosity and high conductivity (η=23.6 mP s and σ=14.2 mS cm−1 at 20 °C, respectively). The electrodes were made of a hierarchical SiO2‐templated carbon with well‐defined and uniform mesopores of ∼9 nm facilitating ion transport to the interconnected micropores accounted for the charge storage, whereas the high density of the electrodes promoted high volumetric energy outputs of the cells.

Ionic Liquid Mixture Electrolyte Matching Porous Carbon Electrodes for Supercapacitors

“…Figure 3 shows that when a small quantity of [Bmim][TFSI] was mixed with [Emim][BF 4 ] ( w < 0.2), the C s value increased up to the maximum (178 F g −1 ) at w = 0.2. This trend should be mainly ascribed to the TFSI − anion: (1) Compared with TFSI − , smaller BF 4 − would selectively enter the micropores of the carbon material ( D / d ion < 2, where D and d ion are the pore diameter of the porous carbon and the ion diameter, respectively), since BF 4 − has a weaker interaction with [Emim] + /[Bmim] + cations when compared with TFSI − [ 22 , 23 , 30 ]. (2) As mentioned above, the TFSI − ion has a variable chain structure, and thus the N atom of TFSI − can access the surface of the electrode in between the absorbed BF 4 − anions in relatively large micropores and mesopores ( D / d ion > 2), which will increase the total quantity of the absorbed anions on the surface area of the positive electrode [ 19 ].…”

“…found selective charging behavior of the IL mixtures with the same anion (BF 4 − ) and different cations. Yambou et al [ 23 ] noted that the ternary mixture of ILs with the same cation (Emim + ) and different anions can work effectively at low temperatures in carbon-based EDLCs. Gogotsi and coworkers discovered that binary IL mixtures used as the electrolyte (binary IL electrolyte) could expand the operating potential window and increase the capacitive performance of the supercapacitors based on two identical onion-like carbon (OLC) electrodes (OLC has an open surface structure, which is free from micropores), because more counterions are accumulated on the electrode surface due to the mixing effect [ 24 , 25 , 26 ].…”

A strong–weak binary solvation structure for unimpeded low-temperature ion transport in nanoporous energy storage materials

“…TEMA-BF 4 in the AN/ACT supercapacitor realizes an outstanding power density of 7924.98 W kg −1 at an energy density of 14.13 W h kg −1 at −60 °C as well as a power density of 6849.35 W kg −1 at an energy density of 11.79 W h kg −1 at −70 °C, which is obviously superior to those of the previously reported low-temperature supercapacitors, including the 1 M TEA-BF 4 /AN commercial supercapacitor (3235.57 W kg −1 @ 12.13 W h kg −1 at −50 °C), PMImNTf 2 -AN-MB supercapacitor (2821.18 W kg −1 @ 5.68 W h kg −1 at −60 °C), 25 supercapacitor (706.83 W kg −1 @ 5.34 W h kg −1 at −50 °C). 48 These results conrm that the novel electrolyte-based supercapacitor is a promising candidate for low-temperature applications.…”

A novel ionic liquid-based electrolyte assisting the high performance of low-temperature supercapacitors

“…4f, where this work shows superiority in terms of energy density. [46][47][48][49] As shown in Fig. 4g, extraordinary cycling durability is achieved for the SC with P-AN-MB at a current density of 1 A g À1 at room temperature, which continuously runs over 10 000 cycles with an 82% capacitance retention relative to the initial specic capacitance.…”