Transitioning from Regular Electrolytes to Solvate Ionic Liquids to High-Concentration Electrolytes: Changes in Transport Properties and Ionic Speciation

Glyme-based lithium-ion electrolytes have received considerable attention from the scientific community due to their improved safety, as well as electrochemical and thermal stability over carbonate-based electrolytes. However, these electrolytes suffer from major drawbacks such as high viscosities. To overcome the challenges that hinder their full potential, the molecular description of glyme-based lithium electrolytes in the high-concentration regime, particularly in the solvate ionic liquid (SIL) and high-concentration electrolyte (HCE) regimes, is needed. In this study, model glyme-based electrolytes based on a lithium thiocyanate and either tetraglyme (G4) or a mixture of monoglyme (G1) and diglyme (G2) were investigated as a function of the solvent-to-lithium ratio using linear and nonlinear IR spectroscopies, in combination with ab initio computations as well as electrochemical methods . The transport properties reveal enhanced ionicities in the HCE and SIL regimes ([O]/[Li] ≤ 5) compared to the regular electrolytes (REs, with [O]/[Li] > 5) in both pure (G4) and mixed (G1:G2) glymes. IR and ab initio computations relate these larger ionicities to the higher concentration of charged aggregates in the HCE and SIL electrolytes ([O]/[Li] ≤ 5). Moreover, it was observed that the use of mixed glymes appears to have a minimal effect on the transport properties of REs but exhibits deleterious effects on SILs. Overall, the results provide a molecular framework for describing the local structure of lithium glyme-based electrolytes and demonstrate the key role that the nature of glyme solvation plays in the molecular structure and consequently the macroscopic properties of the Li-glyme SILs, HCEs, and REs.

Evolving better solvate electrolytes for lithium secondary batteries

The overall performance of lithium batteries remains unmatched to this date. Decades of optimisation have resulted in long-lasting batteries with high energy density suitable for mobile applications. However, the electrolytes used at present suffer from low lithium transference numbers, which induces concentration polarisation and reduces efficiency of charging and discharging. Here we show how targeted modifications can be used to systematically evolve anion structural motifs which can yield electrolytes with high transference numbers. Using a multidisciplinary combination of theoretical and experimental approaches, we screened a large number of anions. Thus, we identified anions which reach lithium transference numbers around 0.9, surpassing conventional electrolytes. Specifically, we find that nitrile groups have a coordination tendency similar to SO2 and are capable of inducing the formation of Li+ rich clusters. In the bigger picture, we identified a balanced anion/solvent coordination tendency as one of the key design parameters.

Accelerated lithium-ion diffusion via a ligand 'hopping' mechanism in lithium enriched solvate ionic liquids

Solvate ionic liquids (SILs), equimolar amounts of lithium salts and polyether glymes, are well studied highly customisable "designer solvents". Herein the physical, thermal and ion mobility properties of SILs with increased LiTFSI (LiTFSA) concentration, with ligand 1 : >1 LiTFSI stoichiometric ratios, are presented. It was found that between 60-80 °C, the lithium cation diffuses up to 4 times faster than the corresponding anion or ligand (glyme). These systems varied from viscous liquids to self-supporting gels, though were found to thin exponentially when heated to mild temperatures (50-60 °C). They were also found to be thermally stable, up to 200 °C, well in excess of normal operating temperatures. Ion mobility, assessed under an electric potential via ionic conductivity, showed the benefit of SIL optimisation for attaining greater concentrations of Li+ cations to store charge during supercapacitor charging and discharging. Molecular dynamics simulations interrogate the mechanism of enhanced diffusion at high temperatures, revealing a lithium hopping mechanism that implicates the glyme in bridging two lithiums through changes in the denticity.

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.

Electric-Field-Induced Spatially Dynamic Heterogeneity of Solvent Motion and Cation Transference in Electrolytes

While electric fields primarily result in migration of charged species in electrolytic solutions, the solutions are dynamically heterogeneous. Solvent molecules within the solvation shells of the cation will be dragged by the field while free solvent molecules will not. We combine electrophoretic NMR measurements of ion and solvent velocities under applied electric fields with molecular dynamics simulations to interrogate different solvation motifs in a model liquid electrolyte. Measured values of the cation transference number (t_{+}^{0}) agree quantitatively with simulation-based predictions over a range of electrolyte concentrations. Solvent-cation interactions strongly influence the concentration-dependent behavior of t_{+}^{0}. We identify a critical concentration at which most of the solvent molecules lie within solvation shells of the cations. The dynamic heterogeneity of solvent molecules is minimized at this concentration where t_{+}^{0} is approximately equal to zero.

The Effect of Fluorinated Solvents on Physicochemical Properties, Ionic Association, and Free Volume of a Prototypical Solvate Ionic Liquid

Solvate ionic liquid synthesis and properties depend on a delicate balancing of cation-solvent and cation-anion interactions to produce materials containing only cation-solvent complexes and solvent-separated anions. Most SILs meeting these characteristics fall within the paradigm of oligomeric ethylene oxides and lithium salts. Targeted functionalization of solvent molecules to achieve desired properties is a relatively unexplored avenue of research. We explore solvent fluorination for a prototypical SIL based on lithium bis(trifluoromethylsulfonyl)imide (LiNTf2) and triethylene glycol (TEG). In the first experiment, TEG is partially substituted with 2,2,4,4,5,5,7,7-octafluoro-3,6-dioxaoctane-1,8-diol (FTEG). This leads to a decrease in ionic conductivity and proliferation of Li(NTf2)2- species. Both results suggest FTEG does not readily coordinate Li+ ; a conclusion that is reinforced by computational studies of [(TEG)1Li]+ and [(FTEG)1Li]+ cation stabilities. A second experiment adds FTEG as a diluent to [(TEG)1Li]NTf2. This places FTEG and TEG in competition to coordinate a limited number of Li+ ions. The resulting mixtures exhibit conductivity and viscosity enhancements over the parent SIL and minimal changes in ion speciation due to the poor Li+ binding by FTEG. Positron annihilation lifetime spectroscopic studies point to increased amounts of free volume upon dilution of FTEG. This likely explains the origin of the conductivity enhancement.

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C₃C₁im][NTf₂], butyl [C₄C₁im][NTf₂] and isobutyl [iC₄C₁im][NTf₂]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C₂C₁im][C_nF_2n+1SO₃], [C₂C₁im][C_nH_2n+1SO₃], [C₂C₁im][CF₃CO₂] and [C₂C₁im][CH₃CO₂] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N_{1 2OH 2OH 2OH}]⁺, with high hydrogen-bonding capability, and the hydrophobic anion [NTf₂]^-. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs.

Multicomponent Phase Separation in Ternary Mixture Ionic Liquid Electrolytes

We investigate the phase behavior of ternary mixtures of ionic liquid, organic solvent, and lithium salt by molecular dynamics simulations. We find that at room temperature, the electrolyte separates into distinct phases with specific compositions; an ion-rich domain that contains a fraction of solvent molecules and a second domain of pure solvent. The phase separation is shown to be entropy-driven and is independent of lithium salt concentration. Phase separation is only observed at microsecond time scales and greatly affects the transport properties of the electrolyte.

Tuning the solvation of indigo in aqueous deep eutectics

The solubility of synthetic indigo dye was measured at room temperature in three deep eutectic solvents (DESs)-1:3 choline chloride:1,4-butanediol, 1:3 tetrabutylammonium bromide:1,4-butanediol, and 1:2 choline chloride:p-cresol-to test the hypothesis that the structure of DESs can be systematically altered, to induce specific DES-solute interactions, and, thus, tune solubility. DESs were designed starting from the well-known cholinium chloride salt mixed with the partially amphiphilic 1,4-butanediol hydrogen bond donor (HBD), and then, the effect of increasing salt hydrophobicity (tetrabutylammonium bromide) and HBD hydrophobicity (p-cresol) was explored. Measurements were made between 2.5 and 25 wt. % H₂O, as a reasonable range representing atmospherically absorbed water, and molecular dynamics simulations were used for structural analysis. The choline chloride:1,4-butanediol DES had the lowest indigo solubility, with only the hydrophobic character of the alcohol alkyl spacers. Solubility was highest for indigo in the tetrabutylammonium bromide:1,4-butanediol DES with 2.5 wt. % H₂O due to interactions of indigo with the hydrophobic cation, but further addition of water caused this to reduce in line with the added water mole fraction, as water solvated the cation and reduced the extent of the hydrophobic region. The ChCl:p-cresol DES did not have the highest solubility at 2.5 wt. % H₂O, but did at 25 wt. % H₂O. Radial distribution functions, coordination numbers, and spatial distribution functions demonstrate that this is due to strong indigo-HBD interactions, which allow this system to resist the higher mole fraction of water molecules and retain its solubility. The DES is, therefore, a host to local-composition effects in solvation, where its hydrophobic moieties concentrate around the hydrophobic solute, illustrating the versatility of DES as solvents.

Quantification of cation-cation, anion-anion and cation-anion correlations in Li salt/glyme mixtures by combining very-low-frequency impedance spectroscopy with diffusion and electrophoretic NMR

Directional correlations between the movements of cations and anions exert a strong influence on the charge and mass transport properties of concentrated battery electrolytes. Here, we combine, for the first time, very-low-frequency impedance spectroscopy on symmetrical Li|electrolyte|Li cells with diffusion and electrophoretic NMR in order to quantify cation-cation, anion-anion and cation-anion correlations in Li salt/tetraglyme (G4) mixtures with Li salt to G4 ratios between 1 : 1 and 1 : 2. We find that all correlations are negative, with like-ion anticorrelations (cation-cation and anion-anion) being generally stronger than cation-anion anticorrelations. In addition, we observe that like-ion anticorrelations are stronger for the heavier type of ion and that all anticorrelations become weaker with decreasing Li salt to G4 ratio. These findings are in contrast to theories considering exclusively anion-cation correlations in form of ion pairs, as the latter imply positive cation-anion correlations. We analyze in detail the influence of anticorrelations on Li+ transference numbers and on the Haven ratio. In order to rationalize our results, we derive linear response theory expressions for all ion correlations. These expressions show that the Li+ ion transport under anion-blocking conditions in a battery is governed by equilibrium center-of-mass fluctuations in the electrolytes. This suggests that in future electrolyte theories and computer simulations, more attention should be paid to equilibrium center-of-mass fluctuations.

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.

Chelation-Induced Reversal of Negative Cation Transference Number in Ionic Liquid Electrolytes

Strong anion-cation interaction in lithium-salt/ionic liquid electrolytes leads to ionic association that decreases the Li transference number, even causing it to be negative. We show that these interactions can be greatly reduced by adding cyclic ethylene oxide molecules, and we quantitatively examine the effect using rigorous multispecies concentrated solution theory coupled with molecular dynamics simulations. The added molecules, primarily lithium ionophore V also known as 12-crown-4, have high affinity to lithium, therefore disrupting the lithium cation-anion coupling, resulting in a significantly improved transference number. First, we investigate the lithium-anion spatial correlation by studying their clusters and show that the 12-crown-4 ether allows the formation of previously nonexisting positively charged lithium-containing complexes. We then prove that the chelators actively compete with the anion to coordinate lithium ions by showing that the persistence-over-time of a given anion coordination cage decreases when ionophore molecules are added to the system. Last, we report an increase in the lithium transference number for a variety of chemistries as a function of added 12-crown-4 (and another ionophore, 18-crown-6) molecules, and even positive values can be reached. Our results provide a foundation for new design and optimization strategies to reverse the sign of and increase the transference number in highly correlated concentrated electrolytes.

Solvate Cation Migration and Ion Correlations in Solvate Ionic Liquids

Lithium salt-glyme mixtures are interesting candidates as electrolytes for battery applications. Depending on the type of glyme or anion and the salt concentration, they either show ionic liquid-like behavior with stable lithium-glyme complex cations or concentrated salt solution-like behavior. Here, we apply electrophoretic NMR (eNMR) to elucidate transport mechanisms by observing the migration of the molecular species in an electric field. We investigate two solvate ionic liquids, i.e., lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and lithium tetrafluoroborate (LiBF₄), in tetraglyme (G4) at different glyme-salt molar ratios X. A field-induced migration of neutral glyme molecules is directly observed, which is due to stable solvate-Li complex formation. Transference numbers, effective charges, and ionicities are derived from electrophoretic mobilities and self-diffusion coefficients, respectively, for the nuclei ¹H, ⁷Li, and ¹⁹F. The effective charges are the highest at the equimolar mixture, X = 1, they differ strongly for lithium and anion, and they show large differences between both systems. These findings are qualitatively interpreted in a speciation model, suggesting anionic clusters and solvate cations as the species dominating charge transport. The resulting effective charges can only be explained taking into account ion-ion anticorrelations in the framework of the Onsager formalism, where anticorrelations between the solvate cation and the anionic complexes arise due to momentum conservation. The contributions to the anticorrelation are most dominant at high salt concentrations and in the system with the LiBF₄^- anion due to its lower mass and ability to form larger asymmetric clusters with Li⁺. Thus, in either system, also the lithium transference number is influenced to a different extent by ion-ion anticorrelations.

Solvate ionic liquids based on lithium bis(trifluoromethanesulfonyl)imide–glyme systems: coordination in MD simulations with scaled charges

Charge scaling in molecular dynamics simulations of lithium bis(trifluoromethanesulfonyl)imide–glyme solvate ionic liquids yields better agreement with experiments.

Oxygen Redox Reaction in Ionic Liquid and Ionic Liquid-like Based Electrolytes: A Scanning Electrochemical Microscopy Study

Improving the stability of the cathode interface is one of the critical issues for the development of high-performance Li/O₂ batteries. The most critical feature to address is the development of electrolytes that mitigate side reactions that bring about cathode passivation. It is well-known that the superoxide anion (O₂^•-) plays a critical role. Here, we propose scanning electrochemical microscopy (SECM) as an analytical tool to screen the electrolyte of Li/O₂ batteries. We demonstrate that by using SECM it is possible to evaluate the stability of O₂^•- and of the cathode to the passivation process occurring during the oxygen redox reaction. Specifically, we report a study carried out at a glassy carbon electrode in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and in tetraethylene glycol dimethyl ether with LiTFSI, the latter ranging from the salt-in-solvent to solvent-in-salt regions.

A Review of Solvate Ionic Liquids: Physical Parameters and Synthetic Applications

Solvate Ionic Liquids (SILs) are a relatively new class of ionic liquids consisting of a coordinating solvent and salt, that give rise to a chelate complex with very similar properties to ionic liquids. Herein is the exploration of the reported Kamlet-Taft parameters, Gutmann Acceptor numbers and the investigation of chelating effects through NMR spectroscopy of multiple atomic nuclei. These properties are related to the application of SILs as reaction media for organic reactions. This area is also reviewed here, including the implication in catalysis for the Aldol and Kabachnik-Fields reactions and electrocyclization reactions such as Diels-Alder and [2+2] cycloaddition. Solvate ILs exhibit many interesting properties and hold great potential as a solvent for organic transformations.

Boosting Rechargeable Batteries R&D by Multiscale Modeling: Myth or Reality?

This review addresses concepts, approaches, tools, and outcomes of multiscale modeling used to design and optimize the current and next generation rechargeable battery cells. Different kinds of multiscale models are discussed and demystified with a particular emphasis on methodological aspects. The outcome is compared both to results of other modeling strategies as well as to the vast pool of experimental data available. Finally, the main challenges remaining and future developments are discussed.

Charge Transport in [Li(tetraglyme)][bis(trifluoromethane) sulfonimide] Solvate Ionic Liquids: Insight from Molecular Dynamics Simulations

Molecular dynamics simulations using fully atomistic polarizable force field have been performed on solvate ionic liquids (SILs), comprised of tetraglyme (G4) solvent molecules, Li⁺ cations, and bis(trifluoromethane) sulfonimide (TFSI) anions, [Li(G4)][TFSI]. The SILs with equimolar salt:G4 composition were investigated in the 303-373 K temperature range, whereas several systems with lower salt concentrations were investigated at 373 K. The simulations using polarizable force field demonstrate very good consistency of structural and dynamic properties with experimental data. The ability to accurately sample the ion transport mechanisms is particularly encouraging, taking into account that previous simulations employing nonpolarizable models had challenges in sampling dynamics in these systems. Here, we correlate Li⁺ ion local environment and glyme conformations with dynamic characteristics, such as residence time of species around Li⁺, self-diffusion coefficients, transference number, and conductivity. The analysis of contributions to Li⁺ mobility due to changing its local environment (i.e., moving from one glyme/anion to another) and from translational motion of Li⁺ with its' coordination environment showed significant dominance of the latter. The contributions of cross-ion dynamic correlations to the total conductivity have been quantified, showing strongly positive contribution from the cation-anion anticorrelation. Despite the high degree of Li-TFSI dissociation and positive contribution of the cation-anion anticorrelated motion to conductivity, the Li⁺ transference numbers for equimolar SILs are very low under the anion blocking conditions.

Thermoelectrochemical cells based on Li+/Li redox couples in LiFSI glyme electrolytes

Thermoelectrochemical cells (TECs) provide conspicuous advantages, including a high Seebeck coefficient (Se), design flexibility, and low cost compared with conventional thermoelectric devices. Here, we investigated TECs employing Li metal electrodes (Li-TECs) and a series of glyme (CH3O[CH2CH2O]nCH3, n = 1-4, nG) solvents with 0.5-3.0 M lithium-imide salts (lithium bis [fluorosulfonyl]imide, LiFSI, and lithium bis[trifluoromethane sulfonyl]imide, LiTFSI). The Se value and power performance of Li-TECs markedly depend on the nature of glyme solvents and Li salt concentration. The dependency of Se on the solvation structure of the Li-ions is examined via Raman measurements, and the internal resistance of Li-TECs is analyzed using electrochemical impedance spectroscopy. Notably, a Li-TEC with 1.0 M LiFSI 1G displays about two times higher power density and about eight times higher conversion efficiency than a conventional Cu-TEC utilizing aqueous electrolytes, which is ascribed to the high Se value and low thermal conductivity of the former. In addition, for a Li-TEC with 1.0 M LiFSI 1G, the low-temperature performance is examined to assess its practical feasibility.

Solvate and protic ionic liquids from aza-crown ethers: synthesis, thermal properties, and LCST behavior

In recent years, solvate and protic ionic liquids (ILs) have attracted much attention. We synthesized both types of ILs from alkyl aza-crown ethers (L = N-propyl-1-aza-15-crown-5 (L¹) and N-C₆F₁₃C₂H₄-1-aza-15-crown-5 (L²)). The solvate ILs [ML][Tf₂N] (M = Na⁺, K⁺) were solids (T_m = 58-68 °C), whereas the solvate ILs [ML][Tf₂N] (M = Li⁺, Ag⁺) and protic ILs [HL][Tf₂N] were liquids with low glass transition temperatures. The ILs containing Na ions were more crystalline and exhibited higher melting points than the other ILs. The decomposition temperatures of the protic ILs were higher than those of the solvate ILs. A protic IL with a paramagnetic anion, [HL¹][FeCl₄] (T_m = 70.5 °C), was also synthesized and its crystal structure was determined. The solvate ILs [NaL²][X] (X = Cl^-, CF₃CO₂^-, TsO^-, PhSO₃^-) exhibited a lower critical solution temperature (LCST)-type behavior in water. The effects of salt addition on the LCST of L² were also investigated. The LCST of these ILs generally increased with increasing hydrophilicity or basicity of the counter anion. This tendency, which is nearly opposite to that of ILs with quaternary onium cations, is ascribed to the amphiphilic nature of the cation. The corresponding protic ILs did not exhibit LCST behavior.

Kamlet–Taft solvent parameters, NMR spectroscopic analysis and thermoelectrochemistry of lithium–glyme solvate ionic liquids and their dilute solutions

NMR, thermoelectrochemical and Kamlet–Taft solvochromatic analyses provide insight into the coordination of lithium in both dilute and concentrated lithium–glyme solutions.

Thermosensitive Phase Separation Behavior of Poly(benzyl methacrylate)/Solvate Ionic Liquid Solutions

We report a lower critical solution temperature (LCST) behavior of binary systems consisting of poly(benzyl methacrylate) (PBnMA) and solvate ionic liquids: equimolar mixtures of triglyme (G3) or tetraglyme (G4) and lithium bis(trifluoromethanesulfonyl)amide. We evaluated the critical temperatures (T_cs) using transmittance measurements. The stability of the glyme-Li⁺ complex ([Li(G3 or G4)]⁺) in the presence of PBnMA was confirmed using Raman spectroscopy, pulsed-field gradient spin-echo NMR (PGSE-NMR), and thermogravimetric analysis to demonstrate that the complex was not disrupted. The interaction between glyme-Li⁺ complex and PBnMA was investigated via ⁷Li NMR chemical shifts. Upfield shifts originating from the ring-current effect of the aromatic ring within PBnMA were observed with the addition of PBnMA, indicating localization of the glyme-Li⁺ complex above and below the benzyl group of PBnMA, which may be a reason for negative mixing entropy, a key requirement of the LCST.

Boundary layer friction of solvate ionic liquids as a function of potential

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li⁺ cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI^- anion rich boundary layer at positive potentials is more lubricating than the Li⁺ cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li⁺ cations for both surfaces at negative potentials. However, at Au(111), the TFSI^- rich boundary layer is less lubricating than the Li⁺ rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO₃ at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO₃^- rich boundary layer.

Deep eutectic-solvothermal synthesis of nanostructured ceria

Ceria is a technologically important material with applications in catalysis, emissions control and solid-oxide fuel cells. Nanostructured ceria becomes profoundly more active due to its enhanced surface area to volume ratio, reactive surface oxygen vacancy concentration and superior oxygen storage capacity. Here we report the synthesis of nanostructured ceria using the green Deep Eutectic Solvent reline, which allows morphology and porosity control in one of the less energy-intensive routes reported to date. Using wide Q-range liquid-phase neutron diffraction, we elucidate the mechanism of reaction at a molecular scale at considerably milder conditions than the conventional hydrothermal synthetic routes. The reline solvent plays the role of a latent supramolecular catalyst where the increase in reaction rate from solvent-driven pre-organization of the reactants is most significant. This fundamental understanding of deep eutectic-solvothermal methodology will enable future developments in low-temperature synthesis of nanostructured ceria, facilitating its large-scale manufacturing using green, economic, non-toxic solvents.

The nanostructure of a lithium glyme solvate ionic liquid at electrified interfaces

Lithium glymes adopt a distinct nanostructure at the negative electrode, unlike that observed with conventional ionic liquids.

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.

Structural effect of glyme–Li+ salt solvate ionic liquids on the conformation of poly(ethylene oxide)

Conformation of poly(ethylene oxide) in solvate ionic liquids is affected by the solvent structure.

The thermoelectrochemistry of lithium–glyme solvate ionic liquids: towards waste heat harvesting

We have investigated the thermoelectrochemical properties of lithium bis(trifluoromethylsulfonyl)imide and tetraglyme mixtures, as dilute electrolytes and solvate ionic liquids.

Determination of Kamlet–Taft parameters for selected solvate ionic liquids

The normalised polarity ENT and Kamlet–Taft parameters of recently described solvate ionic liquids, composed of lithium bis(trifluoromethyl)sulfonimide (LiTFSI) in tri- (G3TFSI) or tetraglyme (G4TFSI) have been determined and compared to the parent glyme (G3 and G4).