Linear ether-based highly concentrated electrolytes for Li-sulfur batteries.

Li-S batteries have attracted attention as next-generation rechargeable batteries owing to their high theoretical capacity and cost-effectiveness. Sparingly solvating electrolytes hold promise because they suppress the dissolution and shuttling of polysulfide intermediates to increase the coulombic efficiency and extend the cycle life. This study investigated the solubility of polysulfide (Li2S8) in a range of liquid electrolytes, including organic electrolytes, highly concentrated electrolytes, and ionic liquids. The Li2S8 solubility was well correlated with the donor number (DNNMR), estimated via23Na-NMR, and was lower than 100 mM_(elemental sulfur) in electrolytes with DNNMR < 14, regardless of the type of electrolyte. Highly concentrated electrolytes comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and linear chain dialkyl ethers such as methyl propyl ether (MPE), n-butyl methyl ether (BME), and ethyl propyl ether (EPE) were studied as sparingly solvating electrolytes for Li-S batteries. Monomethyl ethers, such as BME, showed more pronounced Li-ion coordination and higher ionic conductivity, whereas the steric hindrance of the longer alkyl chains in EPE lowered the solvation number, enhanced ion association, and lowered the ionic conductivity despite the solvents having similar dielectric constants. The charge-discharge rate capabilities of Li-S cells with dialkyl ether-based electrolytes were more impressive than those of cells with a localized high-concentration electrolyte using sulfolane (SL) and hydrofluoroether (HFE), [Li(SL)2][TFSA]-2HFE. The higher rate performance was attributed to the superior Li-ion transport properties of the dialkyl ether-based electrolytes. A pouch-type cell using lightweight [Li(BME)3][TFSA] demonstrated an energy density exceeding 300 W h kg-1 under lean electrolyte conditions.

Special Issue: Recent Advances in Ionic Liquids.

This special issue on ionic liquids provides a comprehensive overview of recent advances in the field, including their synthesis, characterization, and applications.

Ion Transport in Glyme- and Sulfolane-Based Highly Concentrated Electrolytes.

Highly concentrated electrolytes (HCEs) have a similarity to ionic liquids (ILs) in high ionic nature, and indeed some of HECs are found to behave like an IL. HCEs have attracted considerable attention as prospective candidates for electrolyte materials in future lithium secondary batteries owing to their favorable properties both in the bulk and at the electrochemical interface. In this study, we highlight the effects of the solvent, counter anion, and diluent of HCEs on the Li+ ion coordination structure and transport properties (e. g., ionic conductivity and apparent Li+ ion transference number measured under anion-blocking conditions, t L i a b c ${{t}_{{\rm L}{\rm i}}^{{\rm a}{\rm b}{\rm c}}}$ ). Our studies on dynamic ion correlations unveiled the difference in the ion conduction mechanisms in HCEs and their intimate relevance to t L i a b c ${{t}_{{\rm L}{\rm i}}^{{\rm a}{\rm b}{\rm c}}}$ values. Our systematic analysis of the transport properties of HCEs also suggests the need for a compromise to simultaneously achieve high ionic conductivity and high t L i a b c ${{t}_{{\rm L}{\rm i}}^{{\rm a}{\rm b}{\rm c}}}$ values.

Does Li-ion transport occur rapidly in localized high-concentration electrolytes?

The ionic conductivity and lithium-ion transference number of electrolytes significantly influence the rate capability of Li-ion batteries. Highly concentrated Li-salt/sulfolane (SL) electrolytes exhibit elevated Li+ transference numbers due to lithium-ion hopping via a ligand exchange mechanism within their -Li+-SL-Li+- network. However, highly concentrated electrolytes (HCEs) are extremely viscous and have an ionic conductivity that is one order of magnitude less than that of conventional electrolytes. Dilution of HCEs with a non-coordinating hydrofluoroether (HFE) lowers the viscosity and produces localized high-concentration electrolytes (LHCE). However, the mechanism of Li+ transport in LHCEs is unclear. This study investigated the transport properties of LHCEs prepared by diluting a SL-based HCE with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. Electrolyte viscosity decreases dramatically upon dilution, whereas ionic conductivity increases only slightly. Ion diffusivity increases with increasing HFE content due to the decrease in electrolyte viscosity. However, the Li+ transference number declines, because the HFE interferes with conduction via the Li+ hopping mechanism. The resulting decrease in the product of ionic conductivity and Li+ transference number indicates superior lithium-ion transport in the parent HCE compared with LHCEs.

On the concentration polarisation in molten Li salts and borate-based Li ionic liquids.

Electrolytes that transport only Li ions play a crucial role in improving rapid charge and discharge properties in Li secondary batteries. Single Li-ion conduction can be achieved via liquid materials such as Li ionic liquids containing Li+ as the only cations because solvent-free fused Li salts do not polarise in electrochemical cells, owing to the absence of neutral solvents that allow polarisation in the salt concentration and the inevitably homogeneous density in the cells under anion-blocking conditions. However, we found that borate-based Li ionic liquids induce concentration polarisation in a Li/Li symmetric cell, which results in their transference (transport) numbers under anion-blocking conditions (tabcLi) being well below unity. The electrochemical polarisation of the borate-based Li ionic liquids was attributed to an equilibrium shift caused by exchangeable B-O coordination bonds in the anions to generate Li salts and borate-ester solvents at the electrode/electrolyte interface. By comparing borate-based Li ionic liquids containing different ligands, the B-O bond strength and extent of ligand exchange were found to be directly linked to the tabcLi values. This study confirms that the presence of dynamic exchangeable bonds causes electrochemical polarisation and provides a reference for the rational molecular design of Li ionic liquids aimed at achieving single-ion conducting liquid electrolytes.

High-concentration LiPF6/sulfone electrolytes: structure, transport properties, and battery application.

Non-flammable and oxidatively stable sulfones are promising electrolyte solvents for thermally stable high-voltage Li batteries. In addition, sulfolane-based high-concentration electrolytes (HCEs) show high Li+ ion transference numbers. However, LiPF6 has not yet been investigated as the main salt in sulfone-based HCEs for Li batteries. In this study, we investigated the phase behaviors, solvate structures, and transport properties of binary and ternary mixtures of LiPF6 and the following sulfone solvents: sulfolane (SL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and 3-methyl sulfolane (MSL). The stable crystalline solvates Li(SL)4PF6 and Li(DMS)2.5PF6 with high melting points were formed in the LiPF6/SL and LiPF6/DMS mixtures, respectively. In contrast, LiPF6/EMS, LiPF6/MSL, and LiPF6/SL/another sulfone mixtures remained liquids over a wide temperature range. Raman spectroscopy revealed that SL and another sulfone are competitively coordinated to Li+ ions to dissociate LiPF6 in the ternary mixtures. Although the ionic conductivity decreased with increasing LiPF6 concentration due to an increase in viscosity, Li+ ions diffused faster than PF6-via exchanging ligands in the HCE [LiPF6]/[SL]/[DMS] = 1/2/2, resulting in a higher Li ion transference number than that in conventional Li battery electrolytes.

Tetra-arm poly(ethylene glycol) gels with highly concentrated sulfolane-based electrolytes exhibiting high Li-ion transference numbers.

We demonstrate that tetra-arm poly(ethylene glycol) gels containing highly concentrated sulfolane-based electrolytes exhibit high Li+ transference numbers. The low polymer concentration and homogeneous polymer network in the gel electrolyte are useful in achieving both mechanical reliability and high Li+ transport ability.

Li+ transference number and dynamic ion correlations in glyme-Li salt solvate ionic liquids diluted with molecular solvents.

Highly concentrated electrolytes (HCEs) have attracted significant interest as promising liquid electrolytes for next-generation Li secondary batteries, owing to various beneficial properties both in the bulk and at the electrode/electrolyte interface. One particular class of HCEs consists of binary mixtures of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and oligoethers that behave like ionic liquids. [Li(G4)][TFSA], which comprises an equimolar mixture of LiTFSA and tetraglyme (G4), is an example. In our previous works, the addition of low-polarity molecular solvents to [Li(G4)][TFSA] was found to effectively enhance the conductivity while retaining the unique Li-ion solvation structure. However, it remains unclear how the diluents affect another key electrolyte parameter-the Li+ transference number-despite its critical importance for achieving the fast charging/discharging of Li secondary batteries. Thus, in this study, the effects of diluents on the extremely low Li+ transference number under anion-blocking conditions in [Li(G4)][TFSA] were elucidated, with a special focus on the polarity of the additional solvents. The concentration dependence of the dynamic ion correlations was further studied in the framework of the concentrated electrolyte theory. The results revealed that a non-coordinating diluent is not involved in the modification of the ion transport mechanism, and therefore the low Li+ transference number is inherited by the diluted electrolytes. In contrast, a coordinating diluent effectively reduces the anti-correlated ion motions of [Li(G4)][TFSA], thereby improving the Li+ transference number. This is the first time that the significant effects of the coordination properties of the diluting solvents on the dynamic ion correlations and Li+ transference numbers have been reported for diluted solvate ionic liquids.

A study combining magic-angle spinning NMR and small-angle X-ray scattering on the interaction in the mixture of poly(benzyl methacrylate) and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide.

A mixture of poly(benzyl methacrylate) (PBnMA) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]) exhibits lower-critical-solution-temperature (LCST)-type phase separation. An investigation combining magic-angle spinning NMR spectroscopy and small-angle scattering was performed to gain new insights into the interaction between PBnMA and the ionic liquid. The molecular mobility and the solute-solvent interaction in the system were investigated using 1H high-resolution magic-angle spinning NMR. Applying a magic-angle spinning frequency of 2 kHz allowed identifying the PBnMA peaks, which were not observed by conventional solution-state NMR. The peaks of [C2mim]+ almost coincided in the presence and absence of PBnMA, indicating the decoupling of the bulk solvent and polymer. The conformational state of PBnMA in [C2mim][NTf2] was investigated using small-angle X-ray scattering (SAXS). The pair distribution functions of PBnMA chains calculated from SAXS profiles suggest that PBnMA adopts a random coil conformation upon dissolution in [C2mim][NTf2]. The combined study clarifies the decoupled low mobility of polymers with a random coil conformation. It is considered that the specific decoupled low mobility is one of the origins of the decoupling conductivity of [C2mim][NTf2] in a matrix polymer. In addition, an increase in temperature induced a downfield shift and broadening of the [C2mim]+ peaks, suggesting that a larger amount of [C2mim]+ was bound to the PBnMA chains even at temperatures approaching the LCST.

Direct Observation of Photo-Induced Reversible Sol-Gel Transition in Block Copolymer Self-Assembly Containing an Azobenzene Ionic Liquid.

Using atomic force microscopy, the photo-induced reversible changes in a block copolymer self-assembly containing an azobenzene ionic liquid, which undergoes sol-gel transition is directly observed. This is the first report on the sol-gel transition of an ABA-type block copolymer consisting of upper critical solution temperature (UCST)-type A blocks in a photoresponsive ionic liquid mixture. The sol-gel transition is accompanied by an order-to-disorder structural change, which subsequently induces a change in the ionic conductivity. Surprisingly, the photo-induced ionic conductivity and rheological changes occurs rapidly (≈30 s) despite the dense (≈80 wt%) polymeric system. The rapid structural change is probably attributable to the fast diffusion of the ionic liquid.

Anion effects on Li ion transference number and dynamic ion correlations in glyme-Li salt equimolar mixtures.

To achieve single-ion conducting liquid electrolytes for the rapid charge and discharge of Li secondary batteries, improvement in the Li+ transference number of the electrolytes is integral. Few studies have established a feasible design for achieving Li+ transference numbers approaching unity in liquid electrolytes consisting of low-molecular-weight salts and solvents. Previously, we studied the effects of Li+-solvent interactions on the Li+ transference number in glyme- and sulfolane-based molten Li salt solvates and clarified the relationship between this transference number and correlated ion motions. In this study, to deepen our insight into the design principles of single-ion conducting liquid electrolytes, we focused on the effects of Li+-anion interactions on Li ion transport in glyme-Li salt equimolar mixtures with different counter anions. Interestingly, the equimolar triglyme (G3)-lithium trifluoroacetate (Li[TFA]) mixture ([Li(G3)][TFA]) demonstrated a high Li+ transference number, estimated via the potentiostatic polarization method (tPPLi = 0.90). Dynamic ion correlation studies suggested that the high tPPLi could be mainly ascribed to the strongly coupled Li+-anion motions in the electrolytes. Furthermore, high-energy X-ray total scattering measurements combined with all-atom molecular dynamics simulations showed that Li+ ions and [TFA] anions aggregated into ionic clusters with a relatively long-range ion-ordered structure. Therefore, the collective motions of the Li ions and anions in the form of highly aggregated ion clusters, which likely diminish rather than enhance ionic conductivity, play a significant role in achieving high tPPLi in liquid electrolytes. Based on the dynamic ion correlations, a potential design approach is discussed to accomplish single-ion conducting liquid electrolytes with high ionic conductivity.

Solvate electrolytes for Li and Na batteries: structures, transport properties, and electrochemistry.

Polar solvents dissolve Li and Na salts at high concentrations and are used as electrolyte solutions for batteries. The solvents interact strongly with the alkali metal cations to form complexes in the solution. The activity (concentration) of the uncoordinated solvent decreases as the salt concentration is increased. At extremely high salt concentrations, all the solvent molecules are involved in the coordination of the ions and form the solvates of the salts. In this article, we review the structures, transport properties, and electrochemistry of Li/Na salt solvates. In molten solvates, the activity of the uncoordinated solvent is negligible; this is the main origin of their peculiar characteristics, such as high thermal stability, wide electrochemical window, and unique ion transport. In addition, the solvent activity greatly influences the electrochemical reactions in Li/Na batteries. We highlight the attractive features of molten solvates as promising electrolytes for next-generation batteries.

Thermodynamic aspect of sulfur, polysulfide anion and lithium polysulfide: plausible reaction path during discharge of lithium-sulfur battery.

The elucidation of elemental redox reactions of sulfur is important for improving the performance of lithium-sulfur batteries. The energies of stable structures of Sn, Sn˙-, Sn2-, [LiSn]- and Li2Sn (n = 1-8) were calculated at the CCSD(T)/cc-pVTZ//MP3/cc-pVDZ level. The heats of reduction reactions of S8 and Li2Sn with Li in the solid phase were estimated from the calculated energies and sublimation energies. The estimated heats of the redox reactions show that there are several redox reactions with nearly identical heats of reaction, suggesting that several reactions can proceed simultaneously at the same discharge voltage, although the discharging process was often explained by stepwise reduction reactions. The reduction reaction for the formation of Li2Sn (n = 2-6 and 8) from S8 normalized as a one electron reaction is more exothermic than that for the formation of Li2S directly from S8, while the reduction reactions for the formation of Li2S from Li2Sn are slightly less exothermic than that for the formation of Li2S directly from S8. If the reduction reactions with large exotherm occur first, these results suggest that the reduction reactions forming Li2Sn (n = 2-6 and 8) from S8 occur first, then Li2S is formed, and therefore, a two-step discharge-curve is observed.

Rheological and Ionic Transport Properties of Nanocomposite Electrolytes Based on Protic Ionic Liquids and Silica Nanoparticles.

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO2CF3)2]), [DBU][TfO] ([TfO] = [CF3SO3]), and [DBU][TFA] ([TFA] = [CF3CO2]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH3SO3]) system. A relatively strong interaction between the silanol groups and the ions of [DBU][MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

Effect of network homogeneity on mechanical, thermal and electrochemical properties of solid polymer electrolytes prepared by homogeneous 4-arm poly(ethylene glycols).

Mechanically tough solid polymer electrolytes (SPEs) are required to meet the demand for flexible and stretchable electrochemical devices for diverse applications, especially for wearable devices. It is well known that the inhomogeneity of a polymer network greatly affects its mechanical properties, but the evaluation of its effect on electrolyte properties including mechanical properties has not been accomplished yet because of the coexistence of various inhomogeneities (e.g., dangling bonds, loops, chain entanglements, and inhomogeneous distribution of cross-linking points). Herein, we discuss the effect of distribution of cross-linking densities in SPEs on its electrolyte properties by employing a model polymer network composed of a homogeneous 4-arm poly(ethylene glycol) (tetra-PEG) network and Li[TFSA] ([TFSA]: bis(trifluoromethanesulfonyl)amide). Tetra-PEGs having different molecular weights (Mn = 5, 10, 20, and 40 kDa) are subjected to the Michael addition reaction to induce network inhomogeneity while the average cross-linking densities are matched. It was found that thermal and ion transport properties of tetra-PEG SPEs do not depend on network inhomogeneity but on the average network size, which indicates that these properties reflect the averaged thermal fluctuation of polymer chains in terms of spatial and temporal dimensions. On the other hand, the mechanical toughness was largely dependent on the network homogeneity, and fracture strain, energy, and Young's modulus decreased by introducing network inhomogeneity. Rheological measurements showed that a transient cross-linking between Li cations and oxygens of tetra-PEG as well as the homogeneous distribution of the chemical cross-linking points contribute to the excellent mechanical properties of SPEs.

Solvent effects on Li ion transference number and dynamic ion correlations in glyme- and sulfolane-based molten Li salt solvates.

The Li+ transference number of electrolytes is one of the key factors contributing to the enhancement in the charge-discharge performance of Li secondary batteries. However, a design principle to achieve a high Li+ transference number has not been established for liquid electrolytes. To understand the factors governing the Li+ transference number tLi, we investigated the influence of the ion-solvent interactions, Li ion coordination, and correlations of ion motions on the Li+ transference number in glyme (Gn, n = 1-4)- and sulfolane (SL)-based molten Li salt solvate electrolytes with lithium bis(trifluoromethansulfonyl)amide (LiTFSA). For the 1 : 1 tetraglyme-LiTFSA molten complex, [Li(G4)][TFSA], the Li+ transference number estimated using the potentiostatic polarisation method (t = 0.028) was considerably lower than that estimated using the self-diffusion coefficient data with pulsed filed gradient (PFG)-NMR (t = 0.52). The dynamic ion correlations (i.e., cation-cation, anion-anion, and cation-anion cross-correlations) were determined from the experimental data on the basis of Roling and Bedrov's concentrated solution theory, and the results suggest that the strongly negative cross-correlations of the ion motions (especially for cation-cation motions) are responsible for the extremely low t of [Li(G4)][TFSA]. In contrast, t is larger than t in the SL-based electrolytes. The high t of the SL-based electrolytes was ascribed to the substantially weaker anti-correlations of cation-cation and cation-anion motions. Whereas the translational motions of the long-lived [Li(glyme)]+ and [TFSA]- dominate the ionic conduction for [Li(G4)][TFSA], Li ion hopping/exchange conduction was reported to be prevalent in the SL-based electrolytes. The unique Li ion conduction mechanism is considered to contribute to the less correlated cation-cation and cation-anion motions in SL-based electrolytes.

Highly concentrated LiN(SO2CF3)2/dinitrile electrolytes: Liquid structures, transport properties, and electrochemistry.

Liquid structures, transport properties, and electrochemical properties of binary mixtures of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and dinitrile solvents [succinonitrile (SN), glutaronitrile (GN), and adiponitrile (ADN)] were investigated. In the LiTFSA/SN and LiTFSA/ADN systems, the stable crystalline solvates of LiTFSA-(SN)1.5 [melting point (Tm): 59 °C] and LiTFSA-(ADN)1.5 (Tm: 50 °C) were formed, respectively. In contrast, the LiTFSA/GN mixtures of a wide range of compositions were found to be glass-forming liquids at room temperature. Raman spectroscopy of LiTFSA/GN liquid mixtures revealed that increasing the LiTFSA concentration results in the formation of the solvent-bridged network structure Li+-GN-Li+. In addition, the considerable formation of contact ion pairs and ionic aggregates was observed in highly concentrated electrolytes. In the liquids, the Li+ ion dynamically exchanged ligands (GN and TFSA) and higher LiTFSA concentrations led to an increase in the ratio of the self-diffusion coefficients of Li+ and TFSA-, DLi/DTFSA, as determined by pulsed field gradient NMR spectroscopy. The Li+ transference number (tLi+ ) of the [LiTFSA]/[GN] = 1/1.5 electrolyte in an electrochemical cell under anion-blocking conditions was estimated to be as high as 0.74. Furthermore, electrochemical measurements revealed that the reductive stability of the LiTFSA/GN electrolyte increases with increasing LiTFSA concentration. A [LiTFSA]/[GN] = 1/1.5 electrolyte is stable against the Li metal electrode, provided that the polarization is relatively small. Owing to high tLi+ , a Li-S battery with the [LiTFSA]/[GN] = 1/1.5 electrolyte showed a high rate discharge capability despite its low ionic conductivity (0.21 mS cm-1) at room temperature.

Recent progress in self-healable ion gels.

Ion gels, soft materials that contain ionic liquids (ILs), are promising gel electrolytes for use in electrochemical devices. Due to the recent surge in demand for flexible and wearable devices, highly durable ion gels have attracted significant amounts of attention. In this review, we address recent advances in the development of ion gels that can heal themselves when mechanically damaged. Light- and thermally induced healing of ion gels are discussed as stimuli-responsive healing strategies, after which self-healable ion gels based on supramolecular and dynamic covalent chemistry are addressed. Tough, highly stretchable, and self-healable ion gels have recently been fabricated through the judicious design of polymer nanostructures in ILs in which polymer chains and IL cations and anions interact. The applications of self-healable ion gels to electrochemical devices are also briefly discussed.

Solvate Ionic Liquids for Li, Na, K, and Mg Batteries.

From the viewpoint of element strategy, non-Li batteries with promising negative and positive electrodes have been widely studied to support a sustainable society. To develop non-Li batteries having high energy density, research on electrolyte materials is pivotal. Solvate ionic liquids (SILs) are an emerging class of electrolytes possessing somewhat superior properties for battery applications compared to conventional ionic liquid electrolytes. In this account, we describe our recent efforts regarding SIL-based electrolytes for Li, Na, K, and Mg batteries with respect to structural, physicochemical, and electrochemical characteristics. Systematic studies based on crystallography and Raman spectroscopy combined with thermal/electrochemical stability analysis showed that the balance of competitive cation-anion and cation-solvent interactions predominates the stability of the solvate cations. We also demonstrated battery applications of SILs as electrolytes for non-Li batteries, particularly for Na batteries.

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices.

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties become unique (i.e., not easily achieved by other materials) must be explored. Thus, through strong demands for research and consideration of ILs unique properties, we will be able to identify indispensable applications for ILs.