Glyme–Lithium Salt Equimolar Molten Mixtures: Concentrated Solutions or Solvate Ionic Liquids?

To demonstrate a new family of ionic liquids (ILs), i.e., “solvate” ionic liquids, the properties (thermal, transport, and electrochemical properties, Lewis basicity, and ionicity) of equimolar molten mixtures of glymes (triglyme (G3) and tetraglyme (G4)) and nine different lithium salts (LiX) were investigated. By exploring the anion-dependent properties and comparing them with the reported data on common aprotic ILs, two different classes of liquid regimes, i.e., ordinary concentrated solutions and “solvate” ILs, were found in the glyme–Li salt equimolar mixtures ([Li­(glyme)]­X) depending on the anionic structures. The class a given [Li­(glyme)]­X belonged to was governed by competitive interactions between the glymes and Li cations and between the counteranions (X) and Li cations. [Li­(glyme)]­X with weakly Lewis basic anions can form long-lived [Li­(glyme)]⁺ complex cations. Thus, they behaved as typical ionic liquids. The lithium “solvate” ILs based on [Li­(glyme)]­X have many desirable properties for lithium-conducting electrolytes, including high ionicity, a high lithium transference number, high Li cation concentration, and high oxidative stability, in addition to the common properties of ionic liquids. The concept of “solvate” ionic liquids can be utilized in an unlimited number of combinations of other metal salts and ligands, and will thus open a new field of research on ionic liquids

Phase Diagrams and Solvate Structures of Binary Mixtures of Glymes and Na Salts

We prepared a series of binary mixtures composed of selected Na salts and glymes (tetraglyme, G4, and pentaglyme, G5) with different salt concentrations and anionic species ([X]⁻: [N­(SO₂CF₃)₂]⁻ = [TFSA]⁻, [N­(SO₂F)₂]⁻ = [FSA]^–, ClO₄^–, PF₆^–) and studied the effects of concentration, anionic structure, and glyme chain length on their phase diagrams and solvate structures. The phase diagrams clearly illustrate that all the mixtures form 1:1 complexes, [Na­(G4 or G5)₁]­[X]. The thermal stability of the equimolar mixtures was drastically improved in comparison with those of diluted systems, indicating that all the glyme molecules coordinate to Na⁺ cations to form equimolar complexes. Single-crystal X-ray crystallography revealed that [Na­(G5)₁]­[X] forms characteristic solvate structures in the crystalline state irrespective of the paired anion species. A comparison of the solvate structures of the glyme–Na complexes with those of the glyme–Li complexes suggests that the ionic radii of the coordinated alkali-metal cations have substantial effects on the resulting solvate structures. The Raman bands of the complex cations were assigned by quantum chemical calculations. Concentration dependencies of cationic and anionic Raman spectra show good agreement with the corresponding phase diagrams. In addition, the Raman spectra of the 1:1 complexes strongly suggest that the glymes coordinate to Na⁺ cation in the same way in both liquid and crystalline states. However, the aggregated structure in the crystalline state is broken by melting, which is accompanied by a change in the anion coordination

Phase Diagrams and Solvate Structures of Binary Mixtures of Glymes and Na Salts

We prepared a series of binary mixtures composed of selected Na salts and glymes (tetraglyme, G4, and pentaglyme, G5) with different salt concentrations and anionic species ([X]⁻: [N­(SO₂CF₃)₂]⁻ = [TFSA]⁻, [N­(SO₂F)₂]⁻ = [FSA]^–, ClO₄^–, PF₆^–) and studied the effects of concentration, anionic structure, and glyme chain length on their phase diagrams and solvate structures. The phase diagrams clearly illustrate that all the mixtures form 1:1 complexes, [Na­(G4 or G5)₁]­[X]. The thermal stability of the equimolar mixtures was drastically improved in comparison with those of diluted systems, indicating that all the glyme molecules coordinate to Na⁺ cations to form equimolar complexes. Single-crystal X-ray crystallography revealed that [Na­(G5)₁]­[X] forms characteristic solvate structures in the crystalline state irrespective of the paired anion species. A comparison of the solvate structures of the glyme–Na complexes with those of the glyme–Li complexes suggests that the ionic radii of the coordinated alkali-metal cations have substantial effects on the resulting solvate structures. The Raman bands of the complex cations were assigned by quantum chemical calculations. Concentration dependencies of cationic and anionic Raman spectra show good agreement with the corresponding phase diagrams. In addition, the Raman spectra of the 1:1 complexes strongly suggest that the glymes coordinate to Na⁺ cation in the same way in both liquid and crystalline states. However, the aggregated structure in the crystalline state is broken by melting, which is accompanied by a change in the anion coordination

Unadjusted and adjusted effects of each 6 additional months of cinacalcet therapy on hemoglobin levels (intention-to-treat effect).

<p>Unadjusted and adjusted effects of each 6 additional months of cinacalcet therapy on hemoglobin levels (intention-to-treat effect).</p

Cinacalcet initiation during the follow-up period, and mean hemoglobin level by time-varying cinacalcet status (user or non-user).

<p>Cinacalcet initiation during the follow-up period, and mean hemoglobin level by time-varying cinacalcet status (user or non-user).</p

Unadjusted and adjusted effects of each 6 additional months of cinacalcet therapy on the odds of achieving the treatment target (intention-to-treat effect).

<p>Unadjusted and adjusted effects of each 6 additional months of cinacalcet therapy on the odds of achieving the treatment target (intention-to-treat effect).</p

Characteristics of the cinacalcet non-users at registry enrollment and of the cinacalcet initiators at the visit immediately prior to cinacalcet initiation.

<p>Characteristics of the cinacalcet non-users at registry enrollment and of the cinacalcet initiators at the visit immediately prior to cinacalcet initiation.</p

Trajectories of laboratory findings and medication use for the cinacalcet users before and after cinacalcet initiation.

<p>Trajectories of laboratory findings and medication use for the cinacalcet users before and after cinacalcet initiation.</p

Chelate Effects in Glyme/Lithium Bis(trifluoromethanesulfonyl)amide Solvate Ionic Liquids. I. Stability of Solvate Cations and Correlation with Electrolyte Properties

To develop a basic understanding of a new class of ionic liquids (ILs), “solvate” ILs, the transport properties of binary mixtures of lithium bis­(trifluoromethanesulfonyl)­amide (Li­[TFSA]) and oligoethers (tetraglyme (G4), triglyme (G3), diglyme (G2), and monoglyme (G1)) or tetrahydrofuran (THF) were studied. The self-diffusion coefficient ratio of the solvents and Li⁺ ions (<i>D</i>_sol/<i>D</i>_Li) was a good metric for evaluating the stability of the complex cations consisting of Li⁺ and the solvent(s). When the molar ratio of Li⁺ ions and solvent oxygen atoms ([O]/[Li⁺]) was adjusted to 4 or 5, <i>D</i>_sol/<i>D</i>_Li always exceeded unity for THF and G1-based mixtures even at the high concentrations, indicating the presence of uncoordinating or highly exchangeable solvents. In contrast, long-lived complex cations were evidenced by a <i>D</i>_sol/<i>D</i>_Li ∼ 1 for the longer G3 and G4. The binary mixtures studied were categorized into two different classes of liquids: concentrated solutions and solvate ILs, based on <i>D</i>_sol/<i>D</i>_Li. Mixtures with G2 exhibited intermediate behavior and are likely the borderline dividing the two categories. The effect of chelation on the formation of solvate ILs also strongly correlated with electrolyte properties; the solvate ILs showed improved thermal and electrochemical stability. The ionicity (Λ_imp/Λ_NMR) of [Li­(glyme or THF)_<i>x</i>]­[TFSA] exhibited a maximum at an [O]/[Li⁺] ratio of 4 or 5

Solvent Activity in Electrolyte Solutions Controls Electrochemical Reactions in Li-Ion and Li-Sulfur Batteries

Solvent–ion and ion–ion interactions have significant effects on the physicochemical properties of electrolyte solutions for lithium batteries. The solvation structure of Li⁺ and formation of ion pairs in electrolyte solutions composed of triglyme (G3) and a hydrofluoroether (HFE) containing 1 mol dm^–3 Li­[TFSA] (TFSA: bis­(trifluoromethanesulfonyl)­amide) were analyzed using pulsed-field gradient spin–echo (PGSE) NMR and Raman spectroscopy. It was found that Li⁺ is preferentially solvated by G3 and forms a [Li­(G3)]⁺ complex cation in the electrolytes. The HFE scarcely participates in the solvation because of low donor ability and relatively low permittivity. The dissociativity of Li­[TFSA] decreased as the molar ratio of G3/Li­[TFSA] in the solution decreased. The activity of G3 in the electrolyte diminishes negligibly as the molar ratio approaches unity because G3 is involved in 1:1 complexation with Li⁺ ions. The negligible activity of G3 in the electrolyte solutions has significant effects on the electrochemical reactions in lithium batteries. As the activity of G3 diminished, the oxidative stability of the electrolyte was enhanced. The corrosion rate of the Al current collector of the positive electrode was suppressed as the activity of G3 diminished. The high oxidative stability and low corrosion rate of Al in the G3/Li­[TFSA] = 1 electrolyte enabled the stable operation of 4-V-class lithium batteries. The activity of G3 also has a significant impact on the Li⁺ ion intercalation reaction of the graphite electrode. The desolvation of Li⁺ occurs at the interface of graphite and the electrolyte when the activity of G3 in the electrolyte is significantly low, while the cointercalation of Li⁺ and G3 takes place in an electrolyte containing excess G3. The activity of G3 influenced the electrochemical reaction process of elemental sulfur in a Li–S battery. The solubility of lithium polysulfides, which are reaction intermediates of the sulfur electrode, decreased as the activity of G3 in the electrolyte decreased. In the G3/Li­[TFSA] = 1 electrolyte, the solubility of Li₂S_<i>m</i> is very low, and highly efficient charge/discharge of the Li–S battery is possible without severe side reactions