High Energy-Density Capacitor Based on Ammonium Salt Type Ionic Liquids and Their Mixing Effect by Propylene Carbonate

Abstract

Novel ionic liquids comprised of a quaternary ammonium salt type cation have been applied to an electrolyte for high performance electric double-layer capacitors (EDLCs). The novel ionic liquids (IL-B; N, N-diethyl-N-methyl(2-methoxyethyl) ammonium tetrafluoroborate (DEME-BF 4 ) and IL-T; N, N-diethyl-N-methyl(2-methoxyethyl) ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI)) are promising candidates for EDLC electrolytes in terms of a high decomposition voltage (wide voltage window) non-flammability, easy handling, non-volatility and low production costs. Notably, the wide voltage windowindicates that IL-B and IL-T are more advantageous in energy density than a typical propylene carbonate-based electrolytes (i.e., TEA-BF 4 /PC) and a conventional imidazolium type ionic liquid (i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate, EMI-BF 4 ). The effectiveness of IL-B and IL-T on the application to EDLC electrolytes has been confirmed by using KOH-activated mesophase pitch-based carbon fibers (MPCFs) as an electrode material. The combination of IL-T (IL-B) and KOH-activated MPCFs has provided 56 F/g (51 F/g) of high specific capacitance at a maximum (1 mA/cm 2 discharge current density, 3.5V charging voltage), which is equivalent to 224 F/g (204 F/g) in a conventional three-compartment measuring system.In addition, the specific capacitance of both ionic liquids has increased proportional to the increase in the applied voltage from 2.5 to 3.5 V, in contrast to the decline observed for TEA-BF 4 /PC at 3.5 V. Furthermore, the mixture of the IL-B exhibiting high viscosity with propylene carbonate (1 M of IL-B in PC) has been found to provide an excellent capacitance behavior comparable to that observed for the pure IL-B. This indicates that the mixture has a great potential for application to EDLC electrolytes, similar to pure IL-B and IL-T.2

Flexible energy storage devices based on nanocomposite paper

“…This issue is solved here by using a room temperature ionic liquid (RTIL) (17) 1-butyl,3-methylimidazolium chloride ([bmIm][Cl]) (17), which dissolves up to 25% (wt/wt) of unmodified cellulose by using microwave irradiation (18). Interestingly, the ionic nature of RTIL (19) permits it be used as an electrolyte in supercapacitors (20), allowing the assembly of all three components (Fig. 1) (Fig.…”

Ionic Liquids for the Electric Double Layer Capacitor Applications

“…However, we have previously observed that the EDLC using 1M DEME-BF 4 , which a molecular weight of 233.05, has an approximately 10% higher capacitance than a cell using a 1M solution of a conventional ammonium salt, tetraethylammonium tetrafluoroborate (TEA-BF 4 ), which has a molecular weight of 217.6 (Kim et al 2005). However, in the results shown in Fig.…”

Manufacturing of Industrial Supercapacitors

“…Such electrolytes could find applications in niche markets working at high temperatures or working at low power density but at high voltage (if purity is high). Ionic liquids have been tested as salts in organic electrolyte [266], as presented in Figure 10.25 [267]. Two very interesting studies have been dedicated to these mixtures and have demonstrated encouraging results in order to increase the conductivity of ACN-based electrolytes [268] and ACN-free electrolytes [269].…”