Bis Amide Research Articles

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.

Recovery of tungsten compounds from spent tungstophosphate catalyst using leaching, solvent extraction with phosphonium-based ionic liquids and precipitation

A novel hydrometallurgical process involving leaching, precipitation, solvent extraction (SX) using phosphonium-based ionic liquids (ILs), and crystallization stripping was developed in this study. First, the spent catalyst was completely leached in distilled water at 343 K for 24 h. The leaching percentage of W(VI) was >99.9% according to ICP/SEM/EDX analysis. After leaching, the phosphate ions were separated by precipitation using Fe(NO3)3･9H2O as the precipitating agent. The separation percentage of phosphate was 90.8% at pH 8.11 according to ion-chromatography (IC) analysis. After the removal of phosphate, Alamine 336 and triethyl-n-pentyl phosphonium bis(trifluoromethylaulfonyl)amide ([P2225][NTf2]) were used as the extractant and diluent, respectively, for SX. The extraction percentage (E) of W(VI) reached 94.6% at pH 1.03, and the separation factor, W/P, was 101. The extraction mechanism of W(VI) was based on the ion association reaction related to the extracted complex, [(R3NH)nHxWyOz]IL, where x, y, z, and n are pH-dependent stoichiometric coefficients. After SX, the stripping percentage of W(VI) reached 100% at pH 8. Finally, crystallization proceeded at pH ≈ 4.5, and the obtained precipitate was identified to be ammonium paratungstate (NH4)10(H2W12O42)･4H2O by XRD analysis. A series of novel hydrometallurgical processes using ILs led us to conclude that W(VI) was efficiently recovered from the spent tungstophosphate catalyst.

Electrodeposition of Indium from an Ionic Liquid Investigated by In Situ Electrochemical XPS

The electrochemical behavior and electrodeposition of indium in an electrolyte composed of 0.1 mol/L InCl3 in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) on a gold electrode were investigated. The cyclic voltammogram revealed several reduction and oxidation peaks, indicating a complex electrochemical behavior. In the cathodic regime, with the formation of an In-Au alloy, the reduction of In(III) to In(I) and of In(I) to In(0) takes place. In situ electrochemical X-ray photoelectron spectroscopy (XPS) was employed to investigate the reduction process by monitoring the oxidation states of the components during the cathodic polarization of 0.1 mol/L InCl3/[Py1,4]TFSI on a gold working electrode under ultra-high vacuum (UHV) conditions. The core electron binding energies of the IL components (C 1s, O 1s, F 1s, N 1s, and S 2p) shift almost linearly to more negative values as a function of the applied cell voltage. At −2.0 V versus Pt-quasi reference, In(I) was identified as the intermediate species during the reduction process. In the anodic regime, a strong increase in the pressure in the XPS chamber was recorded at a cell voltage of more than −0.5 V versus Pt quasi reference, which indicated, in addition to the oxidation reactions of In species, that the oxidation of Cl− occurs. Ex situ XPS and XRD results revealed the formation of metallic In and of an In-Au alloy.

Anion Effects on the Mixing States of 1-Methyl-3-octylimidazolium Tetrafluoroborate and Bis(trifluoromethylsulfonyl)amide with Methanol, Acetonitrile, and Dimethyl Sulfoxide on the Meso- and Microscopic Scales

The mixing states of two imidazolium-based ionic liquids (ILs) with different anions, 1-methyl-3-octylimidazolium tetrafluoroborate (C8mimBF4) and bis(trifluoromethylsulfonyl)amide (C8mimTFSA), with three molecular liquids (MLs), methanol (MeOH), acetonitrile (AN), and dimethyl sulfoxide (DMSO), have been investigated on both mesoscopic and microscopic scales using small-angle neutron scattering (SANS), infrared (IR), and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Additionally, molecular dynamics (MD) simulations have been conducted on the six combinations of ILs and MLs to observe the states of their mixtures on the atomic level. The SANS profiles of the IL-ML mixtures suggested that MeOH molecules only form clusters in both C8mimBF4 and C8mimTFSA, whereas AN and DMSO were homogeneously mixed with ILs on the SANS scale. MeOH clusters are more enhanced in BF4--IL than TFSA--IL. The microscopic interactions among IL cations, anions, and MLs should contribute to the mesoscopic mixing states of the IL-ML mixtures. In fact, the IL cation-anion, cation-ML, anion-ML, and ML-ML interactions observed by IR, NMR, and MD simulations clarified the reasons for the mixing states of the IL-ML binary solutions observed by the SANS experiments. In neat ILs, the imidazolium ring of the IL cation more strongly interacts with BF4- than TFSA- due to the higher charge density of the former. The interaction of anions with the imidazolium ring is more easily loosened on adding MLs to ILs in the order of DMSO > MeOH > AN. It does not significantly depend on the anions. However, the replacement of the anion on the imidazolium ring by an ML depends on the anions; the replacement is more proceeded in the order of MeOH > DMSO > AN in BF4--IL, while DMSO > MeOH > AN in TFSA--IL. On the other hand, the solvation of both anions by MLs is stronger in the order of MeOH > DMSO ≈ AN. Despite the stronger interactions of MeOH with both cations and anions, MeOH molecules are heterogeneously mixed with both ILs to form clusters in the mixtures. Therefore, the self-hydrogen bonding among MeOH molecules most markedly governs the mixing state of the binary solutions among the abovementioned interactions.

Dinuclear Chlorotetrylenes of Silicon, Germanium, and Tin Based on a Backbone‐Bridged Bis(amidine)

AbstractBis(chlorotetrylene)s of Si, Ge, and Sn have been synthetically realized starting from the backbone‐bridged bis(amidine) 1. Double deprotonation of 1 and subsequent reaction with trichlorosilane affords the bis(dichorosilane) 2, which is converted to the respective bis(chlorosilylene) 3 by dehydrochlorination using lithium bis(trimethylsilyl)amide. The related bis(chlorogermylene) 4 and the bis(chlorostannylene) 5 are obtained by reacting the dilithium salt with GeCl2 ⋅ (dioxane) and SnCl2, respectively. 2 readily reacts with benzil affording the bis(siladioxolene) 6, while no reaction was observed when using the bis(chlorogermylene) 4. The complexes have been fully characterized and their molecular solid‐state structures have been investigated by means of single‐crystal X‐ray diffraction analysis.

Structural and Magnetic Studies on Lanthanide Bis(benzoxazol‐2‐yl)methanides

AbstractWe describe the syntheses, solid‐state structures, and magnetic properties of lanthanide(III)‐tris(bis(heterocyclo)methanides) [(THF)M{(NCOC6H4)2CH}3], with M=Tb (1), Dy (2), Ho (3), and Er (4), respectively. The corresponding lanthanide bis(trimethylsilyl)amides have been prepared as starting materials to deprotonate the neutral bis(benzoxazol‐2‐yl)methane ({NCOC6H4}2CH2) at the central methylene bridge to generate the monoanionic ligand. In the course of this investigations the hitherto unknown holmium tris(bis(trimethylsilyl)amide) is communicated in here. X‐ray diffraction data of 1–4 demonstrate an almost planar ligand with metal coordination in an N,N'‐chelating fashion. Different to their d‐metal analogous the magnetic data of the f‐metal complexes presented here show no single‐molecule magnet (SMM) properties.

Organic ionic plastic crystal enhanced interface compatibility of PEO-based solid polymer electrolytes for lithium-metal batteries

Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) are appealing solid electrolytes for lithium-metal batteries (LMBs) due to their high safety, low cost and flexibility. However, PEO'snarrow electro-chemical potential window and poor interfacial compatibility with the electrode restrict PEO-based SPE development. Herein, we used a solution-casting method to prepare PEO-based SPE membranes reinforced with an organic ionic plastic crystal—N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide (C2epyrFSI). The as-prepared SPE exhibits high ionic conductivity of 3.02 × 10−4 S cm−1 at 50 °C, an extremely wide electro-chemical window (5.1 V) and flexible mechanical properties. Using SPE, the Li symmetric cells can cycle for 2000 h at a current density of 0.1 mA cm−2 without short circuiting at 50 °C. Furthermore, the Li|SPE|LiFePO4 all-solid-state LMBs have a high initial discharge specific capacity of 157.3 mAh g−1 at 0.2C and a capacity retention rate of 96% after 120 cycles. This study shows that the PEO-C2epyrFSI SPE is a promising electrolyte for all-solid-state LMBs.

Effect of Lithium-Ion on the Structural Organization of Monocationic and Dicationic Ionic Liquids.

In recent times, ionic liquid-based (ILs) electrolytic system has emerged as suitable alternative to the conventional organic solvent-based electrolytic system. However, since, anion of ILs is known to form aggregates in the presence of lithium-ions (Li+), and this can influence the transport properties of Li+ ion in a significant manner, it is, therefore, important to understand how lithium-ions influence the structure and dynamics of ILs. With this objective, in the present study, intermolecular interaction, structural organization, and dynamics of monocationic ILs (MILs) and dicationic IL (DIL) have been studied in the absence and presence of lithium salt. Specifically, for this purpose, two MILs, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide ([C3C1im][NTf2]), 1-hexyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide ([C6C1im][NTf2]), and a DIL, 1,6-bis(3-methylimidazolium-1-yl)hexane bis(trifluoromethylsulfonyl)amide ([C6(mim)2][NTf2]2) have been chosen in such a way that either the alkyl chain of MILs becomes equal or half of the spacer chain length of DIL. To understand the effect of the addition of lithium-ion on the structural organization of MILs and DIL, steady-state absorption and fluorescence spectroscopies, time-resolved fluorescence anisotropy and nuclear magnetic resonance (NMR) techniques have been used. Structural organization in the apolar and polar domains of ILs has been probed by following the rotational diffusion of suitably chosen solute in the concerned media through time-resolved fluorescence anisotropy (TRFA) measurements. TRFA studies have revealed that with the addition of Li+ ion, coordination between the Li+ ions and anions of MILs and DILs takes place in the ionic region leading to a change in the structural organization of the apolar regions of the respective medium. In fact, upon adding lithium-ions, a reduction in the packing of alkyl chains has also been observed for the MILs. However, not much change in the structural organization of the apolar region of the DIL has been observed when Li+ ion is added to it. In the presence of Li+ ions, a similar trend in the change of structural organization of polar regions for both MILs and DIL has been observed. Further, measurements of the self-diffusion coefficient through NMR have also supported the observation that Li+ ion also perturbs the nanostructural organization of the MIL in a significant manner than that it does for the DIL. The behavior of DIL in the presence of Li+ ion, as revealed by the present study, has been rationalized by considering the folded arrangement of DIL in the fluid-structure. Essentially, all of these investigations have suggested that the addition of lithium-ion significantly alters the microscopic behavior of MILs in comparison to that of DIL. The outcome of this study is expected to be helpful in realizing the potentials of these media as electrolytes in battery applications.

Overscreening Induced by Ionic Adsorption at the Ionic Liquid/Electrode Interface Detected Using Neutron Reflectometry with a Rational Material Design

Abstract Neutron reflectometry (NR) has been utilized to study the electric double layer (EDL) of ionic liquids (ILs), however, further improvement of the sensitivity toward interfacial structure would be desirable. We recently proposed two ways to improve the NR sensitivity toward the EDL structure at the IL/electrode interface (J. Phys. Chem. C, 123 (2019) 9223). First, as the electrode, a thin film of metal (Nb) was used with the scattering length density (SLD) and thickness controlled to sensitively analyze the potential dependent EDL structure. Second, the IL cation and anion were chosen so that they have large size and large SLD difference, both of which also increase the sensitivity. In the present study, we have further explored this rational material design for the sensitivity enhancement, by changing the film metal from Nb to Bi whose SLD is closer to those for two bulk materials: Si and the IL used, trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide. We successfully observed not only the first ionic layer in the EDL but also the overlayers, revealing that the IL cation is specifically adsorbed on the electrode and that the cation-rich first layer induces overscreening in the overlayers up to the third ionic layer.

Liquid Metal–Ionic Liquid Composite Gels for Soft, Mixed Electronic–Ionic Conductors

AbstractMixed electronic–ionic conductors with high flexibility and stretchability can serve as key materials in rapidly emerging applications such as soft electronics and soft robotics. The combined use of two functional liquid materials, ionic liquids (ILs) and liquid metals (LMs), is of significant interest in the development of highly deformable mixed conductors. In this study, composite gels embedded with both IL and LM are prepared for the first time using a Ga–In eutectic (eGaIn), 1‐ethyl‐3‐methyl imidazolium bis(trifluoromethanesulfonyl)amide, and poly(vinylidene fluoride‐co‐hexafluoropropylene) as the LM, IL, and polymer matrix, respectively. The composite gels exhibit low electronic conductivities of the order of 10−3 S cm−1. The addition of an optimal amount of Ni particles (NiPs) improve the electronic conductivity to ≈25 S cm−1 while retaining mechanical flexibility. The electronic conductivity is further enhanced upon elongation due to the reversible alignment and elongation of the LM in the gel matrix along the stretching direction. Owing to a bicontinuous structure composed of the IL‐based gel and metal component phases, the composite gels exhibit high ionic conductivity of the order of 10−3 S cm−1. This study demonstrates a rational approach for designing stretchable mixed conductors using ILs and Ga‐based LMs.

Ionic Liquid and Polymer Coated Garnet Solid Electrolytes for High‐Energy Solid‐State Lithium Metal Batteries

Garnet solid‐state electrolytes are promising for lithium metal batteries in terms of safety and stability. However, their rigid and brittle nature under humid air increase the interfacial resistance at the electrode/electrolyte interfaces. Herein, the ionic liquid (IL) 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) is employed to dissolve poly(ethylene oxide) (PEO) polymer microstructures that facilitate ion transport through an amorphous rather than a crystalline polymer matrix. The PEO‐IL coatings on Ga doped garnet (LLZO) solid‐state electrolyte can effectively suppress the formation of Li2CO3 passivation layers on the garnet surface. Electrochemical impedance spectroscopy results show that the interfacial resistance of PEO‐IL coated Ga‐LLZO is much lower than that of uncoated Ga‐LLZO. In addition, the surface of PEO‐IL@Ga‐LLZO is flatter and it has a better contact with the Li anode than uncoated Ga‐LLZO. A symmetric cell of Li/PEO‐IL coated solid electrolyte/Li exhibits flat voltage profiles with overpotentials of less than 15 mV and shows a stable lithium plating/stripping process. A solid‐state battery based on PEO‐IL@Ga‐LLZO solid electrolyte combined with lithium metal anode and LiFePO4 (LFP) cathode delivers a specific capacity of ≈120 mAh g−1 with a Coulombic efficiency greater than 96% at 10 mA g(LFP) −1.

Hydrides, Halides, and Polymers: Some Unexpected Intermediates on the Routes to First-Row Transition Metal M{N(SiMe3)2}n (n = 2, 3) Complexes.

The reaction of 2 equiv of LiN(SiMe3)2·Et2O with TiCl3(NMe3)2 or VCl3(NMe3)2 afforded the dimeric, halide bridged complexes [Ti(μ-Cl){N(SiMe3)2}2]2 (1) or [V(μ-Cl){N(SiMe3)2}2]2 (2) in moderate yields. The reduction of titanium complex 1 with 3 equiv of 5% (wt) Na/NaCl gave the mixed metal titanium/sodium hydride cluster Ti2(μ-H)2{N(SiMe3)2}3{N(SiMe3)(SiMe2CH)}(Na) (3), which was formed by activation of two C-H bonds at a single methyl group of one of the bis(trimethylsilyl)amide ligands. Attempts to form the analogous vanadium complex by reduction of 2 gave only intractable products. Treatment of Co{N(SiMe3)2}2 with 1 equiv of BrN(SiMe3)2 (which was previously shown to give the unique three-coordinate cobalt(III) trisamide Co{N(SiMe3)2}3) afforded the polymeric [(μ-Br)Co{μ-N(SiMe3)(SiMe2CH2CH2Me2Si)(Me3Si)μ-N}Co(μ-Br)]∞ (4) as a second product, which was shown by a structural analysis to possess a carbon-carbon bond formed between the two ligands. Attempts to isolate manganese and iron complexes analogous to 4 were unsuccessful. The role of bromine in these reactions was further studied by examining the reaction of 0.5 equiv of elemental bromine with [Mn{N(SiMe3)2}2]2 or [Co{N(SiMe3)2}2]2, which for manganese was shown to give the previously reported manganese trisamide Mn{N(SiMe3)2}3 but for cobalt gives the dimeric amide-bridged [Co(Br){μ-N(SiMe3)2}]2 (5).

Polymer‐Induced Inversion of the Li+ Drift Direction in Ionic Liquid‐Based Ternary Polymer Electrolytes

AbstractWhile salt‐in‐ionic liquid (IL) electrolytes provide a promising alternative to organic electrolytes, they suffer from large ionic clusters impeding lithium ion transport. Here, a lithium‐coordinating polymer is added and the transition from salt‐in‐IL to IL‐based ternary polymer gel electrolytes is followed, investigating the influence of the composition on Li transport mechanisms. The electrolyte is composed of the salt lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), the IL 1‐butyl‐1‐methylpyrrolidinium (Pyr14) TFSA, and a variable amount of poly(ethylene oxide) (PEO). Impedance spectroscopy, multinuclear (1H, 7Li, and 19F) diffusion NMR and electrophoretic NMR (eNMR) yield electrophoretic mobilities, transference numbers, partial conductivities, and effective charges of all ionic species. As the polymer fraction increases, the lithium ion drift direction is inverted. The sign reversal of Li+ mobility and transference number occurs at the optimum coordination of 5–6 ethylene oxide units per Li+ ion. The dominant Li+ transport mechanism shifts from a vehicular transport via anionic clusters to chain‐dominated transport mechanisms. It is concluded that the lithium transport properties of IL‐based electrolytes can be vastly improved by the addition of PEO. Tuning the composition of the ternary electrolyte reveals optimal Li+ transport properties at moderately high polymer contents as well as high salt concentrations.

Electrochemical Properties of Poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene) Gel Electrolytes with High-Concentration Li Salt/Sulfolane for Lithium Batteries

Combining highly concentrated electrolytes with a polymer network is a valid approach to simultaneously achieve fast Li+ ion transport, high thermal stability, and a wide electrochemical window in a quasi-solid-state form. In this work, flexible gel electrolytes comprising commercially available poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and highly concentrated electrolytes of Li salts/sulfolane (SL) were prepared by a simple solution casting method. The anionic effects of the gel electrolytes on the Li-ion conductivity and charge transfer kinetics at the gel/electrode interface were investigated. The SL-based gel electrolyte with lithium bis(fluorosulfonyl)amide (LiFSA) showed an ionic conductivity of 0.7 mS cm−1 and a high Li transference number (>0.5) at 30 °C. The charge transfer resistance in a [Li/gel/LiCoO2] cell with LiFSA was lower than that of the cells with lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) or LiBF4, indicating faster interfacial charge transfer kinetics in the gel electrolyte with FSA. The Li/LiCoO2 cell with the LiFSA/SL gel electrolyte exhibited a higher capacity than that of the cells with the LiTFSA/SL and LiBF4/SL gel electrolytes. Hence, rationally designed gel electrolytes containing highly concentrated SL-based electrolytes enable the high rate performance of Li batteries.

Research and Development of Thermally Durable Electrolyte for Lithium Ion Battery

For ensuring safety of lithium ion batteries (LIBs), we have extensively investigated the quasi-solid electrolyte where lithium ion conducive liquid is quasi-solidified at silica surfaces as thermally durable electrolyte, and applied it to high capacity and high energy density LIB. For the liquid phase, a solvate ionic liquid, which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge capability at a higher rate, Li(G4)TFSA was diluted by low viscos solvent such as propylene carbonate (PC). The developed electrolyte possessed a favorable volatilization temperature higher than 373 K. A 100-Wh-class laminated LIB with energy density of 363 Wh L−1 was fabricated by employing the electrolyte to graphite-LiNixCoyMnzO2 chemistry, and it generated neither fire nor smoke in a nail-penetration test. The result suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte. In addition, to enhance the cycle life of the LIB, the formation and growth mechanism of a solid-electrolyte interphase on a graphite-based negative electrode was investigated. Nuclear magnetic resonance and hard x-ray photoelectron spectroscopy revealed that the decompositions of LiTFSA, PC, and G4 contributed to the SEI formation at the initial charge, and that continuous decompositions of G4 and PC were a major reason for the SEI growth during charge-discharge cycles. Based on these analysis, we have substituted a highly concentrated sulfolane based liquid which exhibits a high Li ion conductivity with less amount of the low viscos solvent, for the G4 based liquid. The modification effectively improved the electrochemical durability of the electrolyte, leading to a higher capacity retention after charge-discharge cycle test.

Competing characters of Li+‐Glyme complex in a solvate ionic liquid: High stability in the bulk and rapid desolvation on an electrode surface

AbstractSolvate ionic liquids (SILs) composed of glymes and Li salts are potential electrolyte materials for Li ion batteries. Safety and durability of SIL‐based batteries can be realized by competing characters of solvate cations. Solvate structure of Li+ should be stable in the bulk to be nonvolatile, and its desolvation should occur rapidly on electrode surfaces which is considered as a rate‐limiting step in charging or discharging. To investigate such characters, potential‐dependent interfacial structure of [Li(G4)][TFSA], equimolar mixture of tetraglyme and lithium bis(trifluoromethanesulfonyl)amide, on an Au electrode has been investigated at the molecular scale by using surface‐enhanced infrared absorption spectroscopy. Despite discrete solvate ion [Li(G4)]+ is stable in the bulk, partial desolvation of Li+ on the electrode was observed at around the potential of zero charge, much more positive than Li+ reduction reactions. The driving force of the partial desolvation can be ascribed to the breaking of isotropic dielectric environment in the vicinity of the electrode, where image charge induced on the electrode surface stabilizes the partially desolvated structure enabling shorter Li+‐electrode distance.

Probing the Hydrogen Bonded Networks and Ion Interactions in Various Classes of Deep Eutectic Solvents (DESs)

Deep eutectic solvents (DESs) are best defined as mixtures of ionic and non-ionic solid compounds with melting points much lower than the pure compounds. They are comprised of a hydrogen bond donor (HBD) - which is generally the organic salt - and a hydrogen bond acceptor (HBA). They are similar to ionic liquids in turns of their physiochemical properties but are cheaper and easier to make. One of their main tuning parameters is the hydrogen-bonded network since it affects their resulting physiochemical properties. In an effort to characterize the hydrogen-bonded network of various classes of DESs we used multi-(1H, 2H, 13C and 17O) Nuclear Magnetic Resonance (NMR) relaxometry and diffusometry techniques as functions of temperature, frequency and pressure. We studied the ion-ion, ion-solvent and solvent-solvent interactions by focusing on the incorporated dilute probe solute molecules which includes isotopically enriched (13C and 17O) and deuterated (2H) benzene, toluene and carbon dioxide. These measurements were compliment by density, viscosity and ionic conductivity, thereby providing more insight into the effect of intermolecular interactions on the resulting dynamics.Results show that in spite of their high viscosities, the ionic conductivity values (see Fig. 1a) for the DESs were comparable to those obtained for selected ionic liquids comprised of the common 1-alkyl-3-methylimidazolium (CnMIM+) cation and bis(trifluoromethylsulfonyl)amide, bis(pentafluoroethylysulfonyl)amide or bis(fluorosulfonyl)amide anion, which are considered as some of the most conductive. Additionally, their Walden Product (see Fig. 1b) shows their classification as ‘subionic’, suggesting there is either significant cation-anion pairing, or their respective motions are correlated. These results and more will be discussed in detail during our presentation. Figure 1. (a) Variable temperature ionic conductivity data and (b)Walden Productsfor selected DESs. Figure 1

In-situ Analysis of the Solid-Electrolyte Interphase Formed in Li[N(CF3SO2)2] and Li[N(FSO2)2] Tetraglyme Solvate Ionic Liquids

Li metal has attracted attention as the negative electrode for secondary batteries due to its low density and negative redox potential. However, its negative operating potential also leads to the decomposition of electrolytes, resulting in the formation of some interfacial phase on the anode, i.e., solid-electrolyte interphase (SEI). The decomposition of the electrolyte causes the low coulombic efficiency of the Li anode. Therefore, the characterization of SEI is necessary in order to utilize the Li anode.Solvate ionic liquids (SILs) composed of 1:1 equimolar mixture of lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) or bis(fluorosulfonyl)amide (LiFSA) and glyme have been investigated as the alternative electrolytes for lithium secondary batteries because of their high Li+ concentration [1, 2]. The deposition and dissolution of Li were reported to be possible in the SILs, although the cathodic decomposition of the electrolyte also proceeded at the potential more positive than that of Li(I)/Li. We have already reported the improvement of the morphology of Li deposits and the cyclability of the Li anode in LiTFSA-triglyme (G3) by the formation of SEI on a Cu electrode at 0 V vs. Li|Li(I) prior to the deposition of Li [3]. The cyclability of the Li anode in LiFSA-tetraglyme (G4) was found to be superior to that in LiTFSA-G4. However, the difference in the stability of Li deposits in these SILs has not been elucidated. In the present study, the formation of SEI on a Cu electrode and the interfacial reaction of the Li deposits were investigated in LiTFSA-G4 and LiFSA-G4 using electrochemical impedance spectroscopy (EIS) combined with electrochemical quartz crystal microbalance (EQCM).The solvate ionic liquids were prepared by mixing the equimolar quantities of G4 and LiTFSA or LiFSA. EIS and EQCM measurement were conducted on the same Cu-coated EQCM electrode (fundamental frequency: 9 MHz) using an impedance-type EQCM system (SEIKO EG&G, QCM922A) and a computerized electrochemical system (Hokuto Denko, HZ-7000). Li foil was used as a reference and counter electrode, respectively. SEI was formed at 0 V vs. Li|Li(I) on the Cu-coated EQCM electrode prior to the galvanostatic deposition of Li. EIS was performed at the open circuit potential (OCP) in the frequency range from 20 kHz to 1.0 Hz with an amplitude of 5 mV rms during SEI formation and after Li deposition.The resonance frequency (f) of a Cu-coated EQCM electrode gradually decreased with keeping the potential of the electrode at 0 V. A semicircle corresponding to the parallel circuit of the resistance and capacitance of SEI was observed in the Nyquist plots of the Cu electrode after keeping the potential at 0 V. The resistance of SEI, R SEI, increased with the lapse of time over 24 hours, indicating the formation and growth of SEI on the Cu electrode at 0 V in LiTFSA-G4 and LiFSA-G4. The changes in f and R SEI in LiFSA-G4 were smaller than those in LiTFSA-G4, suggesting the SEI formed in LiFSA-G4 was lighter and more conductive.The larger change in f of the Cu-EQCM electrode than that calculated from the passed electric charge implied that SEI was also formed on Li deposits during the galvanostatic cathodic reduction at 0.01 mA cm–2, as observed during cyclic voltammetry in LiTFSA-G3 [4]. Δf in LiFSA-G4 was smaller while the changes in the resonance resistance mainly reflecting the surface roughness of the electrode were close in the SILs, suggesting the reactivity against Li was low in LiFSA-G4. The electrode potential of the Cu-EQCM electrode changed over from that of Li(I)/Li after few tens of hours, suggesting the SEI formed in SILs did not suppress completely the reaction between Li and the electrolyte at the OCP. The transition time of the potential in LiFSA-G4 was longer than that in LiTFSA-G4, indicating Li deposits were more stable in LiFSA-G4.References H. Moon, et al., J. Phys. Chem. C, 118, 20246 (2014).S. Terada, et al., Aust. J. Chem., 72, 70 (2019).N. Serizawa, et al., J. Electrochem. Soc., 167, 110560 (2020).N. Serizawa, et al., J. Electrochem. Soc., 160, A1529 (2013). AcknowledgementThis study was supported in part by the JSPS KAKENHI (Grant No. 19K15682) and Advanced Low Carbon Technology Research and Development Program (ALCA, JPMJAL1301).

Hydrate Melt Electrolyte for Aqueous K-Ion Batteries

Recently, alkali metal hydrate melts, which are molten hydrated salts at room temperature, have attracted attention as electrolytes realizing high-voltage aqueous batteries.1 K+ ion has a smaller Stokes radius than that of Li+ ion due to weaker interaction with water molecules. Thus, K hydrate melt electrolytes demonstrate higher ionic conductivity than the Li ones.1 Our group and Ko et al. reported a new K hydrate melt mixing two anions, bis(fluorosulfonyl)amide (FSA−) and trifluoromethanesulfonate (OTf−).2,3 However, electrochemical performance and reaction mechanism of K+ ion insertion materials in the hydrate melt is not fully understood, and the demonstration of high-voltage aqueous KIBs is still challenging. In this study, we investigate electrochemical performance of potential K+ insertion materials, such as Prussian blue analogues and organic compounds, for high-voltage aqueous K-ion battery (KIB).A series of K(FSA)1-x (OTf) x ·nH2O were prepared at room temperature to check formation of hydrate melt. The electrochemical stability windows were examined by linear sweep voltammetry (LSV). Pt and Al foils were used as working electrodes to evaluate anodic and cathodic stability, respectively. Galvanostatic charge/discharge tests of K2Fe0.5Mn0.5[Fe(CN)6] and 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which is a potential positive electrode and negative electrode, respectively, for aqueous KIBs,4 were conducted with three-electrode cells assembled with activated carbon as a counter electrode. An aqueous K-ion full cell was fabricated by combining the positive electrode and negative electrode in the weight ratio of 1:2.1.Among the prepared K(FSA)1-x (OTf) x ·nH2O solution, K salts monohydrate melt of K(FSA)0.6(OTf)0.4·1.0H2O contains the least H2O content. Figure 1a displays the LSV curves in the electrolytes of K(FSA)0.6(OTf)0.4·1.0H2O and the endmembers of KFSA·1.8H2O and KOTf·2.8H2O. KFSA·1.8H2O and KOTf·2.8H2O had a potential window of 2.67 V and 2.01 V, respectively. On the other hand, K(FSA)0.6(OTf)0.4·1.0H2O exhibited that of 2.89 V, which was much wider than KFSA·1.8H2O and KOTf·2.8H2O. In KOTf·2.8H2O, K2Fe0.5Mn0.5[Fe(CN)6] electrode delivered a low initial capacity of 53 mAh g-1 at the initial cycle and capacity degradation over 50 cycles (Fig. 1b, top). In contrast, the electrode delivered a higher initial capacity of 124 mAh g-1 in K(FSA)0.6(OTf)0.4·1.0H2O and better cycle performance (Fig. 1b, bottom) than that in KOTf·2.8H2O. Similar to the positive electrode, the PTCDI electrode exhibited continuous capacity degradation in KOTf·2.8H2O (Fig. 1c, top), whereas the electrode delivered an excellent cycle performance in K(FSA)0.6(OTf)0.4·1.0H2O over 200 cycles (Fig. 1c, bottom). Figure 1d compares charge/discharge curve of PTCDI//K2Fe0.5Mn0.5[Fe(CN)6] full cells filled with KOTf·2.8H2O and K(FSA)0.6(OTf)0.4·1.0H2O. The K(FSA)0.6(OTf)0.4·1.0H2O cell demonstrated a much better cycle performance over 50 cycles than that in KOTf·2.8H2O. The PTCDI//K2Fe0.5Mn0.5[Fe(CN)6] full cell exhibited average voltage of 1.5 V. Moreover, K(FSA)0.6(OTf)0.4·1.0H2O electrolyte realized 2 V-class aqueous KIBs by selecting a proper negative electrode material. In addition, we will discuss charge/discharge mechanism including insertion species of K2Fe0.5Mn0.5[Fe(CN)6] and PTCDI.

Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Hexyl-3-methylimidazolium Tetrafluoroborate and 1-Ethyl- and 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amides

The viscosities of the ionic liquids 1-hexyl-3-methylimidazolium tetrafluoroborate, [HMIM]BF4, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [EMIM][Tf2N], and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [HMIM][Tf2N], have been measured at pressures up to 400 MPa and between 278 and 363 K for [HMIM]BF4, 960 mPa·s maximum viscosity, between 273 and 363 K for [HMIM][Tf2N], 731 mPa·s maximum viscosity, and between 268 and 363 K for [EMIM][Tf2N], 478 mPa·s maximum viscosity, with a falling-body viscometer. The expanded relative uncertainty is estimated at 100·Ur(η) = 2.5. Modified Litovitz and Vogel–Fulcher–Tammann (VFT) equations are used to represent the temperature and pressure dependence. Comparison is made with other 1-alkyl-3-methylimidazolium ionic liquids measured in this laboratory using density scaling. The values of the scaling factor, γ < 3, are consistent with an interplay between the repulsive van der Waals interactions between the ions, which yield high γ, and the Coulombic attractions of oppositely charged ions that act to decrease it. The Angell equation relating the strength factor D, the VFT parameter T0, and the glass temperature Tg is confirmed and extended to estimate the pressure dependence of Tg for 1-alkyl-3-methylimidazolium ionic liquids. Densities between 273 and 363 K at atmospheric pressure are also reported for [HMIM]BF4.