Ionic Liquid Mixture Expands the Potential Window and Capacitance of a Supercapacitor in Tandem

Abstract

Mixing room temperature ionic liquids (RTIL) may optimize electrolyte properties for the better performance of electrical double layer capacitors (EDLCs). To understand the composition effects, we theoretically investigate the potential window, interfacial structure, capacitance, and energy density of RTIL mixtures consisting of one common cation and two anions of different sizes. A combination of quantum density functional theory (QDFT) and classical density functional theory (CDFT) calculations indicates that the electrolyte composition has significant effects on the EDL structure and potential of zero charge, thereby altering the integral capacitance and electrochemical potential window. The two quantities can be optimized together to achieve the best EDLC performance.

The electronic structure of ionic liquids based on the TFSI anion: A gas phase UPS and DFT study

“…As stated above, it is possible to relate the HOMO-LUMO gaps of the IL ion-pairs to their liquid phase electrochemical windows [11]. From our calculated HOMO-LUMO gaps, it would seem that EMIM is the most electrochemically stable cation, followed by DEME and PYR1,4.…”

“…Ilawe et al also found that the ωB97X-D functional is superior to M06-2X and B3LYP [10]. Lian et al also used the ωB97X-D functional and claimed that it is quantitatively accurate for predicting the electronic properties of individual ions in vacuum [11].…”

“…In that application, the ionic conductivity and the width of the electrochemical stability window are the most important properties of ILs. In the first approximation, the electrochemical stability window (EW) of ILs is determined by the HOMO and LUMO energies of the ion-pairs they consist of [6][7][8] are used [11]. Very recently, they claimed that this energy gap approximation to the EW calculation has already been verified [12].…”

Hunting ionic liquids with large electrochemical potential windows

“…As established in previous works, the cathodic limits of each anion or cation can be reasonably estimated from the LUMO and the anodic limits are related to the HOMO energies of the anion or the cation. For each ionic species, the cathodic and anodic limit potentials, V CL and V AL , are expressed as where ε LUMO and ε HOMO are the LUMO and HOMO energy levels, and e is the unit charge.…”

Chemical Vapor Deposition of Ionic Liquids for the Fabrication of Ionogel Films and Patterns

“…For the first time, we demonstrated the CVD of an IL. The strength of the IL-CVD method to deposit ionogel microstructures and the ability of the vaporized precursors to conformally coat three-dimensional substrates will facilitate leveraging the properties of ILs in a range of devices and applications including microsupercapacitors and microbatteries, [80][81][82][83] solar cells, [11,12] actuators, [19] sensors, [15,16,29,30] membrane separation processes, [84] and display textiles. [85]…”