Binary Ionic Liquid Electrolyte Research Articles

Binary ionic liquid electrolyte design for ultrahigh-energy density graphene-based supercapacitors

Although room temperature ionic liquids (ILs) have emerged as potential next-generation electrolytes for their wide electrochemical stability window (ESW), the trade-off between this window and viscosity has hindered their widespread use in energy storage devices. Here, we present for the first time that such a trade-off can be balanced by mixing two ILs with the common anion ([NTf2]−) but different cations ([EMIM]+ and [N1114]+) together. The [EMIM] cation-based IL possesses low viscosity while the [N1114] cation-based IL exhibits wide ESW. Since the concentrations of each IL in the mixtures can result in different electrolyte properties, we demonstrate a systematic approach by exploring the properties of various concentration combinations. In addition, the corresponding cell voltage of their resulting graphene supercapacitors (SCs) accompanied based on the interaction between the binary ionic liquid and the electrodes, and the associated electrochemical performance were studied to determine the optimum electrolyte system for the highest SC energy density. The well-balanced viscosity/ESW trade-off is achieved in binary IL consisting 50 vol% [EMIM][NTf2] and 50 vol% [N1114][NTf2] as evident from the extraordinary electrode specific capacitance of 293.1 F g−1 and the ultrahigh SC energy density of 177 Wh kg−1, which approaches that of a lithium-ion battery.

Fitting the porous texture of carbon electrodes to a binary ionic liquid electrolyte for the realization of low temperature EDLCs

We report on electrical double-layer capacitors (EDLCs) operating effectively at low temperature (down to −40 °C) while implementing nanoporous carbon electrodes and an ionic liquid (IL) electrolyte. For this purpose, the binary mixture of [EMIm][FSI] and [EMIm][BF4] in 1:1 mol ratio has been selected, since it has been previously shown that it remains liquid down to its vitrification at −97 °C, unlike the parent ILs with melting points of −13 °C and 14 °C, respectively. To enhance the mass transport of the IL ions, especially at a low temperature, where the IL electrolyte exhibits a high viscosity, carbon electrode materials with a substantial share of mesopores serving as passageways for bulky ions were selected. These were a carbon black (SC2A) with a broad range of interparticle mesopores in addition to a reasonable amount of micropores, as well as a home-made templated carbon (MP98B) with hierarchical porous texture made of interconnected micropores and well-defined mesopores. From 20 to −40 °C, the capacitor with MP98B electrodes displayed greater specific capacitance, energy and power as well as better charge propagation than the cell with SC2A, whereas on volumetric basis its performance was inferior due to lower electrode density. Advanced SCMP composite electrodes of intermediate density were formulated by mixing these two carbons in the 1:1 mass ratio and harnessed to realize EDLCs with enhanced both specific and volumetric energy. Owing to the adjusted electrode properties, the performance of SCMP-based EDLCs surpassed literature data obtained with analogous constructions based on IL electrolytes and lightweight mesoporous materials, which suffered from poor volumetric metrics.

Photovoltaic Performance of Porphyrin‐Based Dye‐Sensitized Solar Cells with Binary Ionic Liquid Electrolytes

Herein, green porphyrin sensitizer Y350‐based dye‐sensitized solar cells (DSCs) with binary ionic liquid–based electrolytes are studied, which are a mixture of 1‐methyl‐3‐propyl‐imidazolium iodide and 1‐methyl‐1‐butylpyrrolidinium bis(trifluromethylsulfonyl) ‐imide, 1‐butylpyridinium bis(trifluromethylsulfonyl)imide, 1‐methyl‐3‐ethylimidazolium bis(trifluromethylsulfonyl)imide, or 1‐methyl‐3‐ethylimidazolium tetracyanoborate. The best semitransparent green DSC device exhibits a short‐circuit photocurrent density of 9.1 mA cm−2, an open‐circuit photovoltage of 727 mV, and a fill factor of 70%, corresponding to an overall power conversion efficiency (PCE) of 4.9% under standard AM 1.5G illuminations at 100 mW cm−2. The PCE increases to 6.1% with opaque films containing larger light‐scattering TiO2 particles.

Binary ionic liquid electrolytes for copper indium sulfide quantum dot sensitized-TiO2 solar cell to achieve long-term durability

This work demonstrates a straightforward strategy to develop the copper-indium-sulfide (CIS) quantum dot-sensitized solar cells (QDSSCs) consisting of ionic liquids (ILs) as electrolyte instead of any volatile solvent. The power conversion efficiency (PCE) of the solar cell yielded with 0.36% in the presence of 1-butyl-3-methylimidazolium sulfide ([BMIm][S2−/Sn2−]) as electrolyte. Furthermore, binary mixture of [BMIm][S2−/Sn2−] and 1-butyl-3-methylimidazolium thiocyanate ([BMIm][SCN]) exhibited an improvement of JSC and FF yielding with 0.75% (JSC: 8.69 mA cm−2, VOC: 0.32 V, FF 26.8%). It exhibited long-term stability within 20% drops after 72 h-continuous photo-irradiation and subsequent storage for more than 1300 h in dark. It is due to suppression of the volatilization of solvent and decomposition of sulfide/polysulfide (S2−/Sn2−) anions. The solar cell performances were found to promote as an increase of interfacial charge transfer efficiency between electrolyte and electrodes by means of electrochemical impedance spectroscopy.

Comprehensive study of efficient dye-sensitized solar cells based on the binary ionic liquid electrolyte by modifying with additives and iodine

The photovoltaic performance of dye-sensitized solar cells (DSSCs) is enhanced by modifying the binary room temperature ionic liquid (RTIL) electrolyte with additives and iodine. The average photoelectric conversion efficiency (PCE) of 6.39% is achieved. Through electrochemical impedance spectroscopy (EIS), cyclic voltammetry scans and incident photon-to-current conversion efficiency (IPCE) data, the working principles are analyzed. The enhancement is mainly attributed to the improvement of short circuit current which is caused by the reduction of overall internal resistance of the devices. Durability tests are measured at room temperature, and the long-term stability performance can be maintained.

Impact of polyethyleneglycol addition on diffusion coefficients in binary ionic liquid electrolytes composed of dicationic ionic liquid and polyethyleneglycol.

We conduct a comparative study of conductivity and diffusion coefficient of two dicationic ionic liquids (3,3'-(octane-1,8-diyl)bis(1-ethyl-3-imidazolium) bis(trifluoromethylsulfonyl)amide ([IMCI][TFSI], S1) and 3,3'-(2,2'-(ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))bis(1-ethyl-3-imidazolium) bis(trifluoromethylsulfonyl)amide ([IMOI][TFSI], S2)) at various temperatures. The diffusion coefficients of cation and anion in ionic liquids are determined by using pulse gradient spin-echo nuclear magnetic resonance method. S2 shows lower viscosity, higher conductivity, and higher diffusion coefficient than those of S1. Moreover, the influence of polyethyleneglycol (PEG200, Mw =200) addition in PEG200/IL binary solutions is investigated. PEG200/S1 binary solutions show lower viscosity, higher conductivity, and higher diffusion coefficient than those of neat S1. The experimental molar conductivity (Λ) of neat IL and PEG200/IL binary solutions is lower than that of the calculated molar conductivity (ΛNMR ) from pulse gradient spin-echo nuclear magnetic resonance method at various temperatures, indicating that not all the diffusion species belong to the ionic conduction. In other words, NMR diffusion measurements comprise charged and paired (without charge) ions. Copyright © 2017 John Wiley & Sons, Ltd.

Influence of Ionic Liquid Electrolytes on the Photovoltaic Performance of Dye‐Sensitized Solar Cells

AbstractNew binary ionic liquid electrolytes based on 1‐methyl‐1‐butylpyrrolidinium bis(trifluromethylsulfonyl)imide, 1‐butylpyridinium bis(trifluromethylsulfonyl)imide, 1‐methyl‐3‐ethylimidazolium bis(trifluromethylsulfonyl)imide, 1‐methyl‐3‐ethylimidazolium tetracyanoborate, or 1‐methyl‐3‐ethylimidazolium tricyanomethanide coupled with 1‐methyl‐3‐propyl‐imidazolium iodide were developed for dye‐sensitized solar cells (DSCs). We examined these ionic liquid compositions in conjunction in conjunction with a diketopyrrolopyrrole‐based donor‐π bridge acceptor dye (DPP‐13) in dye‐sensitized solar cells and also investigated the influence of adding lithium ions to the electrolyte to enhance the device performance. The best device exhibited a short‐circuit current density of 15.2 mA cm−2, an open‐circuit voltage of 678 mV, and a fill factor of 71 %, corresponding to an overall power conversion efficiency (PCE) of 7.1 % under standard AM 1.5G illumination at 100 mW cm−2.

A higher performance dye-sensitized solar cell based on the modified PMII/EMIMBF4 binary room temperature ionic liquid electrolyte

Additives and iodine (I2) are used to modify the binary room temperature ionic liquid (RTIL) electrolyte to enhance the photovoltaic performance of dye-sensitized solar cells (DSSCs). The short-circuit current density (JSC) of 17.89 mA/cm2, open circuit voltage (VOC) of 0.71 V and fill factor (FF) of 0.50 are achieved in the optimal device. An average photoelectric conversion efficiency (PCE) of 6.35% is achieved by optimization, which is over two times larger than that of the parent device before optimization (2.06%), while the maximum PCE can reach up to 6.63%.

Binary Ionic Liquid Electrolyte for Dye-Sensitized Solar Cells

Binary ionic liquid composed of 1-propyl-3-methylimidazolium iodide (PMII) and 1-butyl-3-methylimidazolium thiocyanate (BMISCN) were mixed at four different ratios to study its effect on the dye-sensitized solar cells’ (DSSCs) efficiency. The addition of low viscosity ionic liquid which is BMISCN is to overcome the low mass transportation of iodide/triiodide faced by pure PMII. Therefore, the effect of mixing different ratios of these ionic liquids on the viscosity and triiodide diffusion coefficient were studied and the best ratio was identified. Based on the experimental work, the mixture of BMISCN with PMII of higher viscosity has allowed reducing the mass transport limitation of tri-iodide in the electrolyte as the effect of lowering the overall ionic liquid's viscosity. The binary electrolyte PMII: BMISCN (1:0.75) give the highest power conversion efficiency of 1.89%, with a fill factor of 0.47, open circuit voltage of 0.62, and short circuit current density of 6.52mA/cm2 and triiodide diffusion coefficient of 8.47 x 10−7 cm2 s-1. This work has provided valuable insight for further development of binary ionic liquid electrolyte for DSSCs.

Impact of lithium salt addition on ionic transporting properties in a binary ionic liquid electrolyte composed of 4-(2-methoxyethyl)-4-methylmorpholinium bis(trifluoromethanesulfonyl)imide and LiTFSI

We conducted a study on the transport properties of an ionic liquid 4-(2-methoxyethyl)-4-methylmorpholin-4-ium bis(trifluoromethylsulfonyl)amide ([MorMEOM][TFSI]) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)-doped [MorMEOM][TFSI] at various temperature and atmospheric pressure states through conductivity, viscosity, and self-diffusion coefficient characterizations. Based on the Walden rule, the α values of neat [MorMEOM][TFSI] and LiTFSI-doped [MorMEOM][TFSI] estimated from the slopes of Walden plots were compared to those calculated from Ea,Λ/Ea,η. The diffusion coefficients of 1H, 19F and 7Li were determined using the PGSE-NMR method to carry out a study of the dynamics of the cations, anions, and ion pairs. All of the neat [MorMEOM][TFSI] and LiTFSI-doped [MorMEOM][TFSI] gave approximately straight lines for change in the D with Tη−1, demonstrating that the Stokes–Einstein equation holds for the ionic diffusivity in the ILs.

An efficient binary ionic liquid based quasi solid-state electrolyte for dye-sensitized solar cells

A novel binary ionic liquid electrolyte containing lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and binary ionic liquids, which is composed of 1-butyl-3-methylimidazolium iodide (BMII) and 1-butyl-3-methylimidazolium thiocyanate (BMISCN), is developed for dye-sensitized solar cells (DSSCs). It is found that incorporation of LiTFSI as charge transfer promoter with BMII has positive effect on the interfacial charge transfer of the dye/TiO2 film, further addition of BMISCN into the above composite electrolyte can take advantage of its low viscosity to enhance the ionic conductivity and reduce the interfacial charge transfer resistance, and a photovoltaic conversion efficiency of 5.55% is obtained from the solar cell fabricated with the optimized binary ionic liquid electrolyte without iodine participation under AM 1.5 illumination at 100mWcm−2, with a 108.6% improvement in the efficiency with lower resistance and higher ionic conductivity as compared to the solar cell fabricated with single BMII ionic liquid-based electrolyte. The above results should be attributed to the reduced charge recombination and the effective interfacial charge transfer in the solar cell.

Efficient, stable, and flexible dye-sensitized solar cells based on nanocomposite gel electrolytes

We have fabricated efficient and stable full-plastic dye-sensitized solar cells (DSCs) based on nanocomposite gel electrolytes. Different compositions of binder-free nanocrystalline TiO2 pastes combined with mechanical compression technique were employed to prepare TiO2 photoanodes on indium-doped tin oxide coated polyethylene naphthalate. The performance and durability of plastic-based DSCs using nanocomposite gel electrolytes which contain ceramic nanoparticles in 3-methoxypropionitrile (MPN)-based or binary ionic liquid electrolytes were investigated. The results show that the compressed photoelectrode composed of commercial titanium powders P25 and 100nm TiO2 powders in conjunction with a TiO2 solidified MPN-based nanocomposite gel electrolyte achieved an energy conversion efficiency of 6.49%. Moreover, the DSCs based on TiO2 solidified bi-IL electrolyte were found to provide better durability than MPN-based nanocomposite gel electrolyte, whereas the efficiency maintained >97% of its original efficiency after 500h of aging test under continuous light irradiation (100mWcm−2) at 60°C.

Photovoltaic performance of bifacial dye sensitized solar cell using chemically healed binary ionic liquid electrolyte solidified with SiO2 nanoparticles

In this study, we investigated the effect of electrolyte composition, photoanode thickness, and the additions of GuSCN (guanidinium thiocyanate), NMB (N-methylbenimidazole), and SiO2 on the photovoltaic performance of DSSCs (dye sensitized solar cells). A bifacial DSSC is realized and irradiated from front and rear sides. The devices give maximum photovoltaic efficiencies for 70% PMII (1-propyl-3-methyl-imidazolium iodide)/30% (EMIB(CN)4) (1-ethyl-3-methyl-imidazolium tetracyanoborate) electrolyte composition and 10μm thick photoanode coating which is considered to be the ideal coating thickness for the diffusion length of electrolyte and dye absorption. A significant increase in the photocurrent for DSSCs with optimum molarity of 0.1M GuSCN was observed due to decreased recombination which is believed to be surface passivation effect at photoanode electrolyte interface suppressing recombination rate. Moreover, optimum NMB molarity was found to be 0.4 for maximum efficiency. Addition of SiO2 to the electrolyte both as an overlayer and dispersed particles enhanced rear side illuminated cells where dispersed particles are found to be more efficient for the front side illuminated cells due to additional electron transport properties. Best rear side illuminated cell efficiency was 3.2% compared to front side illuminated cell efficiency of 4.2% which is a promising result for future rear side dye sensitized solar cell applications where front side illumination is not possible like tandem structures and for cells working from both front and rear side illuminations.

Enhanced photovoltaic performance and long-term stability of dye-sensitized solar cells by incorporating SiO2 nanoparticles in binary ionic liquid electrolytes

Hydrophilic SiO2 nanoparticles in a binary ionic liquid (bi-IL) consisting of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium dicyanimide (EMIDCA) facilitated electron transfer and solidified the electrolyte for a dye-sensitized solar cell (DSC). We investigated the dependence of charge transport and photovoltaic performance on the composition of bi-IL electrolytes with varied ratio of SiO2 nanoparticles. The electrochemical impedance spectra revealed a decreased resistance to charge transfer at the Pt counter electrode (Rct1) when SiO2 (up to 2.0wt.%) was added, improving the photovoltaic parameters. The DSC based on a TiO2 nanocrystalline film (thickness 14.2μm) with a composite ionic gel electrolyte of EMIDCA/PMII bi-IL (33vol.% of EMIDCA) incorporating SiO2 (2wt.%) exhibited a power conversion efficiency of 5.28% under simulated solar illumination (AM 1.5G, 100mWcm−2). The durability of DSC with a SiO2 solidified electrolyte was superior to that of a liquid one, exhibiting good stability at 60°C in darkness during an accelerated test for 1000h.

Binary ionic liquid electrolytes containing organo-magnesium complex for rechargeable magnesium batteries

A binary ionic liquid (IL) system based on a common organic cation, N, N-diethyl- N-methyl- N-(2-methoxyethyl)anmmonium (DEME +), with mixed anion of bis(trifluoromethanesulfonyl)imide (TFSI −) and bis(fluorosulfonyl)imide (FSI −) has been examined as a supporting electrolyte of rechargeable magnesium batteries. Basic properties of the mixed IL were measured as a function of the mixing ratio, n, in the composition of [DEME +][TFSI −] n [FSI −] 1− n . Electrochemical deposition/dissolution behavior of magnesium was investigated in the mixed IL containing an organo-magnesium complex, methyl magnesium bromide with tetrahydrofuran (MeMgBr/THF). Viscosity and ionic conductivity of the mixed IL showed monotonous changes with the mixing ratio, while their thermal properties proved discontinuous changes with the compositions. Coulombic (current) efficiency of 90% or higher was obtained for cathodic deposition of magnesium in the mixed IL containing MeMgBr/THF. The current density for cathodic deposition and anodic dissolution depended on the IL composition, and the maximum value was obtained at the composition of n = 0.5.

Transport Properties and Phase Behaviour in Binary and Ternary Ionic Liquid Electrolyte Systems of Interest in Lithium Batteries

A binary ionic liquid (IL) system based on a common cation, N-methyl-N-propylpyrrolidinium (C(3) mpyr(+)), and either bis(trifluoromethanesulfonyl)imide (NTf(2) (-)) or bis(fluorosulfonyl) imide (FSI(-) as the anion is explored over its entire composition range. Phase behavior, determined by DSC, shows the presence of a eutectic temperature at 247 K and composition around an anion ratio of 2:1 (FSI(-) :NTf(2)(-)) with the phase diagram for this system proposed (under the thermal conditions used). Importantly for electrochemical devices, the single phase melting transition at the eutectic is well below ambient temperatures (247 K). To investigate the effect of such anion mixing on the lithium ion speciation, conductivity and PFG-NMR diffusion measurements were performed in both the binary IL system as well as the Li-NTf(2) -containing ternary system. The addition of the lithium salt to the mixed IL system resulted in a decrease in conductivity, as is commonly observed in the single-component IL systems. For a fixed lithium salt composition, both conductivity and ion diffusion have linear behaviour as a function of the anion ratio, however, the rate of change of the diffusion coefficient seems greater in the presence of lithium. From the application point of view, the addition of the FSI(-) to the NTf(2)(-) IL results in a considerable increase in lithium ion diffusivity at room temperature and no evidence of additional complex ion behaviour.

Anionic structure-dependent photoelectrochemical responses of dye-sensitized solar cells based on a binary ionic liquid electrolyte

Room temperature ionic liquids (RTILs) have been used as electrolytes to investigate the anionic structure dependence of the photoelectrochemical responses of dye-sensitized solar cells (DSCs). A series of RTILs with a fixed cation structure coupling with various anion structures are employed, in which 1-methyl-3-propylimidazolium iodide (PMII) and I(2) are dissolved as redox couples. It is found that both the diffusivity of the electrolyte and the photovoltaic performance of the device show a strong dependence on the fluidity of the ionic liquids, which is primarily altered by the anion structure. Further insights into the structure-dependent physical properties of the employed RTILs are discussed in terms of the reported van der Waals radius, the atomic charge distribution over the anion backbones, the interaction energy of the anion and cation, together with the existence of ion-pairs and ion aggregates. Particularly, both the short-circuit photocurrent and open-circuit voltage exhibit obvious fluidity dependence. Electrochemical impedance and intensity-modulated photovoltage/photocurrent spectroscopy analysis further reveal that increasing the fluidity of the ionic liquid electrolytes could significantly decrease the diffusion resistance of I(3)(-) in the electrolyte, and retard the charge recombination between the injected electrons with triiodide in the high-viscous electrolyte, thus improving the electron diffusion length in the device, as well as the photovoltaic response. However, the variation of the electron diffusion coefficients is trivial primarily due to the effective charge screening of the high cation concentration.

Application of Diaminium Iodides in Binary Ionic Liquid Electrolytes for Dye-Sensitized Solar Cells

N-(2-hydroxyethyl)ethylenediaminium iodides (HEEDAIs) and N-(2-hydroxyethyl)piperazinium iodides (HEPIs) were synthesized, and their thermal properties were analysed. The influence of HEEDAI and HEPI onI3-/I-redox behavior in binary ionic liquid was investigated. The result revealed that HEEDAI can suppress the recombination betweenI3-and the injected electrons in TiO2conduction band and be used as the alternative of 4-tert-butylpyridine in the electrolyte of dye-sensitized solar cells. The electrolyte C, 0.15 mol⋅L−1I2, HEEDAI and MPII with mass ratio of 1 : 4, gave the short-circuit photocurrent density of 9.36 mA⋅cm−2, open-circuit photovoltage of 0.67 V, fill factor of 0.52, and the corresponding photoelectric conversion efficiency of 3.24% at the illumination (air mass 1.5, 100 mW⋅cm−2, active area 0.25 cm2).

Balance between the physical diffusion and the exchange reaction on binary ionic liquid electrolyte for dye-sensitized solar cells

A comprehensive characterizations of viscosities, conductivities, triiodide diffusion coefficients, charge-transfer resistances and photovoltaic performance of a potential dye-sensitized solar cell (DSC) electrolyte systems based on binary ionic liquid (IL) mixtures, namely, 1-ethyl-3-methylimidazolium dicyanamide (EMIDCA)/1-methyl-3-propylimidazolium iodide (PMII) with a fixed iodine concentration at varying EMIDCA volume fraction are investigated in the present study. Viscosity and conductivity values are accurately correlated with regard to temperature and EMIDCA volume fraction. The triiodide diffusion coefficients, the predominant electrolyte parameter for limitation of DSC efficiency, are determined by symmetrical cell methods. The physical diffusion and exchange reactions between the iodide and triiodide dominate the apparent triiodide diffusion coefficients at different range of EMIDCA volume fraction. A balance between the viscosity-dependent physical diffusion and the exchange reactions can get at an optimal volume percents of EMIDCA. Impedance spectroscopy and photovoltaic results both support the existence of an optimized binary IL electrolyte composition. Hence, for optimizing an IL-based electrolyte in regards to triiodide transport, a low viscosity is not the exclusive crucial factor since exchange reactions transport effects also play an important role to resolve the diffusion limitation of DSC efficiency.

An Azo-Spiro Mixed Ionic Liquid Electrolyte for Lithium Metal– LiFePO4 Batteries

Using a binary ionic liquid (IL) electrolyte composed of -methyl--propylpyrrolidinium bis(trifluoromethanesulfonyl)imide and 2-oxo-3,9-dioxa-6-azonia-spiro[5.5]undecane bis(trifluoromethanesulfonyl)imide at an optimized ratio, we investigated battery cycling behavior at temperatures of and above. We achieved an extended cycle life using the binary electrolyte system as the problem of cell short-circuiting (stemming from lithium dendrite growth) was significantly reduced. We provide evidence that 2-oxo-3,9-dioxa-6-azonia-spiro[5.5]undecane bis(trifluoromethanesulfonyl)imide assists in short-circuit prevention through the suppression of lithium dendrites. For batteries employing a lithium metal anode and a cathode, we report capacities in excess of , and by utilizing a pulse charging technique we were able to charge a cell at a current density , which we were not able to achieve using a normal charging regime. We also present lithium cycling data for 2-oxo-3,9-dioxa-6-azonia-spiro[5.5]undecane bis(trifluoromethanesulfonyl)imide in the absence of another IL. We show that poor capacity and a necessarily high operating temperature make this system undesirable although we observed no short-circuiting. We conclude that the structure of the components of the IL and the nature of the charging regime employed can cause a significant reduction in dendrite-induced short-circuiting.