Toward New Ion Conductive Liquids via Ionic Liquids.

In the current era that it is strongly expected the SDGs would be achieved, electrolyte solutions in electrochemical devices and processes are being studied from dilute and concentrated solutions, through inorganic molten salts, deep eutectic solvents, and ionic liquids, to super-concentrated solutions. Although concepts based on empirical laws such as the Walden rule and hydrodynamics such as the Stokes rule are still useful for ionic conduction in solution, it is expected that superionic conduction-like mechanisms that are scarcely found in conventional electrolytes. Here, the authors' recent results are described based on the local structure and speciation of ionic species in solution, focusing on protons and lithium ions.

Analytical chemistry toward on-site diagnostics.

Analytical Chemistry, through quantitative and/or qualitative analysis (identification), is a discipline that involves the development of methodologies and the exploration of new principles to obtain answers to given problems. In situ analysis techniques have attracted attention for its ability to elucidate phenomena occurring and to evaluate amount of a certain component in substances at real time and biological samples as applications of such analysis technology. Lots of techniques have been performed to understand the fundamental phenomena in varied fields such as X-ray, vibrational, and electrochemical impedance spectroscopies and also analytical reagents that enable to semi-quantitative analysis just observation. In fact, applying various in situ techniques in analytical chemistry expands to the medical diagnosis, which leads to be able to detect early diseases. Here, we describe some of previous researches in many fields such as electrochemical device for energy storage, biology, environment, and pathology and briefly introduce our recent challenges to analytical chemistry toward the on-site diagnosis.

Tools for studying ion solvation and ion pair formation in ionic liquids: isotopic substitution Raman spectroscopy.

Isotopic H/D or 6/7Li substitution Raman spectroscopy was applied to new kinds of ionic liquids; N-methylimidazole (C1Im) and acetic acid (CH3COOH) as the pseudo-protic ionic liquid (pPIL), and both of the neat and the 2,2,3,3-tetrafluoropropyl ether (HFE) diluted Li-glyme solvate ionic liquids (SIL) [Li(Gn)][TFSA] (Gn, glyme n = 3 or 4); TFSA, bis(trifluoromethanesulfonyl)amide) to clarify the proton transfer or the Li+ solvation/ion pair formation. The isotopic substitution Raman (ISR) spectra were obtained as the difference between the samples containing the same composition except the substituted isotope. The calculated and theoretical ISR spectra were also evaluated for comparison. With the C1Im-CH3COOH(D) pPIL, the Raman bands attributable to the C1Im/C1HIm+ gave signals of differential shape, and they were well reproduced with the curve fitting by taking the small amount of C1HIm+ and CH3COO- generation into consideration. The ISR spectra for the SIL were well explained by the formation of the Li-TFSA contact ion pair (CIP) and the solvent shared ion pair (SSIP) in the [Li(G3)][TFSA] SIL. In addition, the ISR spectra for the HFE-diluted [Li(G4)][TFSA] SIL clearly proved that the HFE hardly coordinates to the Li+ in the HFE-diluted SIL. Here, the ISR spectroscopy is proposed as a new tool for studying the ion solvation and the ion pair formation in ionic liquids.

Local Structure of Li+ in Superconcentrated Aqueous LiTFSA Solutions.

It has been reported that aqueous lithium ion batteries (ALIBs) can operate beyond the electrochemical window of water by using a superconcentrated electrolyte aqueous solution. The liquid structure, particularly the local structure of the Li+, which is rather different from conventional dilute solution, plays a crucial role in realizing the ALIB. To reveal the local structure around Li+, the superconcentrated LiTFSA (TFSA: bis(trifluoromethylsulfonil)amide) aqueous solutions were investigated by means of Raman spectroscopic experiments, high-energy X-ray total scattering measurements, and the neutron diffraction technique with different isotopic composition ratios of 6Li/7Li and H/D. The Li+ local structure changes with the increase of the LiTFSA concentration; the oligomer ([Lip(TFSA)q](p-q)+ (q > 2) forms at the molar fraction of LiTFSA (xLiTFSA) > 0.25. The average structure can be determined in which two water molecules and two oxygen atoms of TFSA anion(s) coordinate to the Li+ in the superconcentrated LiTFSA aqueous solution (LiTFSA)0.25(H2O)0.75. In addition, the intermolecular interaction between the neighboring water molecules was not found, and the hydrogen-bonded interaction in the solution should be significantly weak. According to the coordination number of the oxygen atom (TFSA or H2O), a variety of TFSA- and H2O coordination manners would exist in this solution; in particular, the oligomer is formed in which the monodentate TFSA cross-links Li+.

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.

Effect of Brønsted Acidity on Ion Conduction in Fluorinated Acetic Acid and N-Methylimidazole Equimolar Mixtures as Pseudo-protic Ionic Liquids.

To clarify proton conduction mechanism in protic ionic liquids (PILs) and pseudo-PILs (pPILs), equimolar mixtures of N-methylimidazole (C1Im) with fluorinated acetic acids were investigated by Raman spectroscopy, X-ray scattering, and dielectric relaxation spectroscopy (DRS). Only the ionic species exist in the equimolar mixture of C1Im and HTFA (HTFA: trifluoroacetic acid). On the other hand, the equimolar mixture of C1Im and HDFA (HDFA: difluoroacetic acid) consists of both ionic and electrically neutral species. In particular, not only the electrostatic but also van der Waals interactions with the F atoms were observed in the liquid structures of both [C1hIm+][TFA-] and [C1hIm+][DFA-]. The concept for proton conduction mechanism that we have proposed in previous study was revisited; the proton conduction mechanism could be classified with two linear free energy relationship lines for proton exchange reaction and translation/rotation of proton carriers. Our results exhibit that the proton conduction mechanism changes from proton hopping to vehicle mechanism with increasing acidity of an acid HA in PILs.

Solvation Structure of Li+ in Concentrated Acetonitrile and N,N-Dimethylformamide Solutions Studied by Neutron Diffraction with 6Li/7Li Isotopic Substitution Methods.

Neutron diffraction measurements on 6Li/7Li isotopically substituted 10 and 33 mol % *LiTFSA (lithium bis(trifluoromethylsulfonyl)amide)-AN-d3 (acetonitrile-d3) and 10 and 33 mol % *LiTFSA-DMF-d7(N,N-dimethylformamide-d7) solutions have been carried out in order to obtain structural insights on the first solvation shell of Li+ in highly concentrated organic solutions. Structural parameters concerning the local structure around Li+ have been determined from the least squares fitting analysis of the first-order difference function derived from the difference between carefully normalized scattering cross sections observed for 6Li-enriched and natural abundance solutions. In 10 mol % LiTFSA-AN-d3 solution, 3.25 ± 0.04 AN molecules are coordinated to Li+ with a intermolecular Li+···N(AN) distance of 2.051 ± 0.007 Å. It has been revealed that 1.67 ± 0.07 AN molecules and 2.00 ± 0.01 TFSA- are involved in the first solvation shell of Li+ in the 33 mol % LiTFSA-AN solution. The nearest neighbor Li+···NAN and Li+···OTFSA- distances are obtained to be r(Li+···N) = 2.09 ± 0.01 Å and r(Li+···O) = 1.88 ± 0.01 Å, respectively. The first solvation shell of Li+ in the 10 mol % LiTFSA-DMF-d7 solutions contains 3.4 ± 0.1 DMF molecules with an intermolecular Li+···ODMF distance of 1.95 ± 0.02 Å. In highly concentrated 33 mol % LiTFSA-DMF-d7 solutions, there are 1.3 ± 0.2 DMF molecules and 3.2 ± 0.2 TFSA- in the first solvation shell of Li+ with intermolecular distances of r(Li+···ODMF) = 1.90 ± 0.02 Å and r(Li+···OTFSA-) = 2.01 ± 0.01 Å, respectively. The Li+···TFSA- contact ion pair stably exists in highly concentrated 33 mol % LiTFSA-AN and -DMF solutions.

Transport Properties of Ionic Liquid and Sodium Salt Mixtures for Sodium-Ion Battery Electrolytes from Molecular Dynamics Simulation with a Self-Consistent Atomic Charge Determination.

Ionic liquid (IL) has been considered as a potential electrolyte for developing next-generation sodium-ion batteries. A highly concentrated ionic system such as IL is characterized by the significant influence of intramolecular polarization and intermolecular charge transfer that vary with the combination of cations and anions in the system. In this work, a self-consistent atomic charge determination using the combination of classical molecular dynamics (MD) simulation and density functional theory (DFT) calculation is employed to investigate the transport properties of three mixtures of ILs with sodium salt relevant to the electrolyte for a sodium-ion battery: [1-ethyl-3-methylimidazolium, Na][bis(fluorosulfonyl)amide] ([C2C1im, Na][FSA]), [N-methyl-N-propylpyrrolidinium, Na][FSA] ([C3C1pyrr, Na][FSA]), and [K, Na][FSA]. The self-consistent method is versatile to address the intramolecular polarization and intermolecular charge transfer in response to the cation-anion combination, as well as the variation in their compositions. The structure and dynamic properties of IL mixtures obtained from the method are in line with those from the experimental works. The comparison to the Nernst-Einstein estimates shows that the electrical conductivity is reduced due to correlated motions among the ions, and the contribution to the conductivity from each ion species is not necessarily ranked in the same order as the diffusion coefficient. It is further seen that the increase of the sodium-ion composition reduces the fluidity of the system. The results highlight the potential of the method and the microscopic description that it can provide to assist the investigation toward a sensible design of IL mixtures as an electrolyte for a high-performance sodium-ion battery.

Speciation Analysis and Thermodynamic Criteria of Solvated Ionic Liquids: Ionic Liquids or Superconcentrated Solutions?

Lithium-glyme solvated ionic liquids (Li-G SILs) and superconcentrated electrolyte solutions (SCESs) are expected to be promising electrolytes for next-generation lithium secondary batteries. The former consists of only the oligoether glyme solvated lithium ion and its counteranion, and the latter contains no full solvated Li+ ion by the solvents due to the extremely high Li salt concentration. Although both of them are similar to each other, it is still unclear that both should be room-temperature ionic liquids. To distinctly define them, speciation analyses were performed with the Li-G SIL and the aqueous SCES to evaluate the free solvent concentration in these solutions with a new Raman/infrared spectral analysis technique called complementary least-squares analysis. Furthermore, from a thermodynamic point of view, we investigated the solvent activity and activity coefficient in the gas phase equilibrated with sample solutions and found they can be good criteria for SILs.

Possible Proton Conduction Mechanism in Pseudo-Protic Ionic Liquids: A Concept of Specific Proton Conduction.

In a previous work, we have found that the pseudo-protic ionic liquid N-methylimidazolium acetate, [C1HIm][OAc] or [Hmim][OAc], mainly consists of the electrically neutral molecular species N-methylimidazole, C1Im, and acetic acid, AcOH, even though the mixture has significant ionic conductivity. This system was revisited by employing isotopic substitution Raman spectroscopy (ISRS) and pulsed field gradient (PFG) NMR self-diffusion measurements. The ISRS and PFG-NMR results obtained fully confirm our earlier findings. In particular, the self-diffusion coefficient of the hydroxyl hydrogen atom in AcOH is identical to that of the methyl hydrogen atoms within the experimental uncertainty, consistent with very little ionization. Therefore, a proton conduction mechanism similar to the Grotthuss mechanism for aqueous acid solutions is postulated to be responsible for the observed electrical conductivity. Laity resistance coefficients (rij) are calculated from the transport properties, and the negative values obtained for the like-ion interactions are consistent with the pseudo-ionic liquid description, that is, the mixture is indeed a very weak electrolyte. The structure and rotational dynamics of the mixture were also investigated using high-energy X-ray total scattering experiments, molecular dynamics simulations, and dielectric relaxation spectroscopy. Based on a comparison of activation energies and the well-known linear free energy relationship between the kinetics and thermodynamics of autoprotolysis, we propose for [C1HIm][OAc] a Grotthus-type proton conduction mechanism involving fast AcOH/AcO- rotation as a decisive step.

Solvation Structure of Li+ in Methanol and 2-Propanol Solutions Studied by ATR-IR and Neutron Diffraction with 6Li/7Li Isotopic Substitution Methods.

Neutron diffraction measurements have been carried out on 10 mol % LiTFSA (TFSA: bis(trifluoromethylsulfonil)amide) solutions in methanol- d4 and 2-propanol- d8 to obtain information on the solvation structure of Li+. The detailed coordination structure of solvent molecules within the first solvation shell of Li+ was determined through the least-squares fitting analysis of the difference function between normalized scattering cross sections observed for 6Li/7Li isotopically substituted sample solutions. The nearest-neighbor Li+···O distance and coordination number determined for the 10 mol % LiTFSA-methanol- d4 solution are rLiO = 1.98 ± 0.02 Å and nLiO = 3.8 ± 0.6, respectively. In the 2-propanol- d8 solution, it has been revealed that 2-propanol- d8 molecules within the first solvation shell of Li+ take at least two different coordination geometries with the intermolecular nearest-neighbor Li+···O distance of rLiO = 1.93 ± 0.04 Å. The Li+···O coordination number, nLiO = 3.3 ± 0.3, is determined. Ion-pair formation in the LiTFSA-methanol and LiTFSA-2-propanol solutions has been investigated by the attenuated total reflection infrared spectroscopic method. Mole fractions of free, Li+-bound, and aggregated TFSA- are derived from the peak deconvolution analysis of vibrational bands observed for TFSA-.

Physicochemical compatibility of highly-concentrated solvate ionic liquids and a low-viscosity solvent.

High ionic carrier mobilities are important for the electrolyte solutions used in high-performance batteries. Based on the functional sharing concept, we fabricated mixed electrolytes consisting of solvate ionic liquids (SIL), which are highly concentrated solution electrolyte, and the non-coordinating low-viscosity dilution solvent 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE). We investigated the thermal, transport, and static properties of electrolytes with different ratios of SIL to HFE. In particular, the interactions between the SILs and HFE and static correlations of the coordinating (ether-based molecules), non-coordinating (HFE), and carrier ionic species (lithium salt) were clarified by applying the excess density concept. Ether molecules always formed strong complexes with lithium cations regardless of the absence or presence of HFE. The repulsion force between the SILs and HFE was strongly affected by lithium salt concentration. From our results, we proposed dissociation/association models for these electrolyte systems.

Anion Coordination Characteristics of Ion-pair Complexes in Highly Concentrated Aqueous Lithium Bis(trifluoromethanesulfonyl)amide Electrolytes.

We report on the structures of Li-ion complexes in salt-concentrated aqueous electrolytes based on lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), particularly focusing on the anion coordination behavior of the ion-pair complexes in the high concentration region cLi > 3.0 mol dm-3. Quantitative data analysis of the Raman spectra revealed the following. (1) Li ions do not coordinate with TFSA anions at lower cLi (<3.0 mol dm-3) to exist as ion pair-free ions. (2) In the concentrated region (cLi = 3.0 - 4.0 mol dm-3), the TFSA anions coordinate as monodentate ligands (mono-TFSA) with Li ions to form ion-pair complexes and coexist with free TFSA in the bulk. (3) Further increasing the cLi (4.0 - 5.2 mol dm-3) results in both monodentate and bidentate coordination (bi-TFSA) modes of TFSA anions to Li ions, yielding complicated ion-pair complexes in the first coordination sphere. The Walden plots, based on ionic conductivity and viscosity data, implied that the ion-conducting mechanism in the highly salt-concentrated region was considerably different from that in the dilute region (i.e., vehicle mechanism).

Direct Evidence for Li Ion Hopping Conduction in Highly Concentrated Sulfolane-Based Liquid Electrolytes.

We demonstrate that Li+ hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF4 and sulfolane (SL). Self-diffusion coefficients of Li+ ( DLi), BF4- ( DBF4), and SL ( DSL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF4 ≤ 3, the ratios DSL/ DLi and DBF4/ DLi become lower than 1, suggesting faster diffusion of Li+ than SL and BF4-, and thus the evolution of Li+ hopping conduction. X-ray crystallographic analysis of the LiBF4/SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li+ ions. In addition, the BF4- anion also participates in the bridging coordination of Li+. The Raman spectra of the highly concentrated LiBF4-SL solution suggested that Li+ ions are bridged by SL and BF4- even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li+ exchanges ligands (SL and BF4-) dynamically in the highly concentrated electrolytes, and Li+ hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li+ hopping conduction. Finally, we demonstrate that Li+ hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li+ ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

Enhanced Electrochemical Stability of Molten Li Salt Hydrate Electrolytes by the Addition of Divalent Cations.

Water can be an attractive solvent for Li-ion battery electrolytes owing to numerous advantages such as high polarity, nonflammability, environmental benignity, and abundance, provided that its narrow electrochemical potential window can be enhanced to a similar level to that of typical nonaqueous electrolytes. In recent years, significant improvements in the electrochemical stability of aqueous electrolytes have been achieved with molten salt hydrate electrolytes containing extremely high concentrations of Li salt. In this study, we investigated the effect of divalent salt additives (magnesium and calcium bis(trifluoromethanesulfonyl)amides) in a molten salt hydrate electrolyte (21 mol kg-1 lithium bis(trifluoromethanesulfonyl)amide) on the electrochemical stability and aqueous lithium secondary battery performance. We found that the electrochemical stability was further enhanced by the addition of the divalent salt. In particular, the reductive stability was increased by more than 1 V on the Al electrode in the presence of either of the divalent cations. Surface characterization with X-ray photoelectron spectroscopy suggests that a passivation layer formed on the Al electrode consists of inorganic salts (most notably fluorides) of the divalent cations and the less-soluble solid electrolyte interphase mitigated the reductive decomposition of water effectively. The enhanced electrochemical stability in the presence of the divalent salts resulted in a more-stable charge-discharge cycling of LiCoO2 and Li4Ti5O12 electrodes.

Local Structure of Li+ in Concentrated Ethylene Carbonate Solutions Studied by Low-Frequency Raman Scattering and Neutron Diffraction with 6Li/7Li Isotopic Substitution Methods.

Isotropic Raman scattering and time-of-flight neutron diffraction measurements were carried out for concentrated LiTFSA-EC solutions to obtain structural insight on solvated Li+ as well as the structure of contact ion pair, Li+···TFSA-, formed in highly concentrated EC solutions. Symmetrical stretching vibrational mode of solvated Li+ and solvated Li+···TFSA- ion pair were observed at ν = 168-177 and 202-224 cm-1, respectively. Detailed structural properties of solvated Li+ and Li+···TFSA- contact ion pair were derived from the least-squares fitting analysis of first-order difference function, ΔLi(Q), between neutron scattering cross sections observed for 6Li/7Li isotopically substituted 10 and 25 mol % *LiTFSA-ECd4 solutions. It has been revealed that Li+ in the 10 mol % LiTFSA solution is fully solvated by ca. 4 EC molecules. The nearest neighbor Li+···O(EC) distance and Li+···O(EC)═C(EC) bond angle are determined to be 1.90 ± 0.01 Å and 141 ± 1°, respectively. In highly concentrated 25 mol % LiTFSA-EC solution, the average solvation number of Li+ decreases to ca. 3 and ca. 1.5. TFSA- are directly contacted to Li+. These results agree well with the results of band decomposition analyses of isotropic Raman spectra for intramolecular vibrational modes of both EC and TFSA-.

Effect of the cation on the stability of cation-glyme complexes and their interactions with the [TFSA]- anion.

The interactions of glymes with alkali or alkaline earth metal cations depend strongly on the metal cations. For example, the stabilization energies (Eform) calculated for the formation of cation-triglyme (G3) complexes with Li+, Na+, K+, Mg2+, and Ca2+ at the MP2/6-311G** level were -95.6, -66.4, -52.5, -255.0, and -185.0 kcal mol-1, respectively, and those for the cation-tetraglyme (G4) complexes were -107.7, -76.3, -60.9, -288.3 and -215.0 kcal mol-1, respectively. The electrostatic and induction interactions are the major source of the attraction in the complexes; the contribution of the induction interactions to the attraction is especially significant in the divalent cation-glyme complexes. The binding energies of the cation-G3 complexes with Li+, Na+, K+, Mg2+, and Ca2+ and the bis(trifluoromethylsulfonyl)amide anion ([TFSA]-) were -83.9, -86.6, -80.0, -196.1, and -189.5 kcal mol-1, respectively, and they are larger than the binding energies of the corresponding cation-G4 complexes (-73.6, -75.0, -77.4, -172.1, and -177.2 kcal mol-1, respectively). The binding energies and conformational flexibility of the cation-glyme complexes also affect the melting points of equimolar mixtures of glyme and TFSA salts. Furthermore, the interactions of the metal cations with the oxygen atoms of glymes significantly decrease the HOMO energy levels of glymes. The HOMO energy levels of glymes in the cation-glyme-TFSA complexes are lower than those of isolated glymes, although they are higher than those of the cation-glyme complexes.

Li(+) Local Structure in Li-Tetraglyme Solvate Ionic Liquid Revealed by Neutron Total Scattering Experiments with the (6/7)Li Isotopic Substitution Technique.

Equimolar mixtures of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraglyme (G4: CH3O-(CH2CH2O)4-CH3) yield the solvate (or chelate) ionic liquid [Li(G4)][TFSA], which is a homogeneous transparent solution at room temperature. Solvate ionic liquids (SILs) are currently attracting increasing research interest, especially as new electrolytes for Li-sulfur batteries. Here, we performed neutron total scattering experiments with (6/7)Li isotopic substitution to reveal the Li(+) solvation/local structure in [Li(G4)][TFSA] SILs. The experimental interference function and radial distribution function around Li(+) agree well with predictions from ab initio calculations and MD simulations. The model solvation/local structure was optimized with nonlinear least-squares analysis to yield structural parameters. The refined Li(+) solvation/local structure in the [Li(G4)][TFSA] SIL shows that lithium cations are not coordinated to all five oxygen atoms of the G4 molecule (deficient five-coordination) but only to four of them (actual four-coordination). The solvate cation is thus considerably distorted, which can be ascribed to the limited phase space of the ethylene oxide chain and competition for coordination sites from the TFSA anion.

A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate.

To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa  values of 12 compounds in EAN and in water. In other words, the pKa  value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3 O(+) in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from -1 to 9 on the pH scale based on the pH value in water.

Li(+) Local Structure in Hydrofluoroether Diluted Li-Glyme Solvate Ionic Liquid.

Hydrofluoroethers have recently been used as the diluent to a lithium battery electrolyte solution to increase and decrease the ionic conductivity and the solution viscosity, respectively. In order to clarify the Li(+) local structure in the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) diluted [Li(G4)][TFSA] (G4, tetraglyme; TFSA, bis(trifluoromethanesulfonyl)amide) solvate ionic liquid, Raman spectroscopic study has been done with the DFT calculations. It has turned out that the HFE never coordinates to the Li(+) directly, and that the solvent (G4) shared ion pair of Li(+) with TFSA anion (SSIP) and the contact ion pair between Li(+) and TFSA anion (CIP) are found in the neat and HFE diluted [Li(G4)][TFSA] solvate ionic liquid. It is also revealed that the two kinds of the CIP in which TFSA anion coordinates to the Li(+) in monodentate and bidentate manners (hereafter, we call them the monodentate CIP and the bidentate CIP, respectively) exist with the SSIP of predominant [Li(G4)](+) ion-pair species in the neat [Li(G4)][TFSA] solvate ionic liquid, and that the monodentate CIP decreases as diluting with the HFE. To obtain further insight, X-ray total scattering experiments (HEXTS) were carried out with the aid of MD simulations, where the intermolecular force field parameters, mainly partial atomic charges, have been newly proposed for the HFE and glymes. A new peak appeared at around 0.6-0.7 Å(-1) in X-ray structure factors, which was ascribed to the correlation between the [Li(G4)][TFSA] ion pairs. Furthermore, MD simulations were in good agreement with the experiments, from which it is suggested that the terminal oxygen atoms of the G4 in [Li(G4)](+) solvated cation frequently repeat coordinating/uncoordinating to the Li(+), although almost all of the G4 coordinates to the Li(+) to form [Li(G4)](+) solvated cation in the neat and HFE diluted [Li(G4)][TFSA] solvate ionic liquid.