Ligand exchange conduction or hopping conduction which means ions move faster than their ligands or solvents, is one of the striking phenomena in electrochemistry. Here, we report a glyme-based electrolyte where ligand exchange conduction takes place. The electrolyte is a concentrated pentaglyme (G5) solution of lithium bis(trifluoromethylsulfonyl)amide (LiTf2N; Tf = SO2CF3) with molar ratio of [G5]/[LiTf2N] = 1/2. Since a diglyme (G2) solution [G2]/[LiTf2N] = 1/1 which has the same molar ratio of ether oxygen to Li+ ([O]/[Li+] = 3) does not show ligand exchange conduction, the glyme chain length may need to be long enough to bridge Li+ ions, by which the momentum exchange of Li+ ions via solvent molecules is allowed.

A dilution effect on the proton conduction of a hydronium solvate ionic liquid [H 3 O + •18C6]Tf 2 N, which consists of hydronium ion (H 3 O +), 18-crown-6-ether ligand (18C6), and bis[(trifluoromethyl)sulfonyl]amide anion (Tf 2 N-; Tf = CF 3 SO 2), has been studied. When [H 3 O + •18C6]Tf 2 N was diluted using equimolar 18C6 solvent, the distinctive fast proton conduction in [H 3 O + •18C6]Tf 2 N was suppressed in stark contrast to the case of common protic ionic liquids. Nuclear magnetic resonance spectroscopy showed that the fast exchange between free 18C6 molecules and coordinated ones, suggesting that the added solvent had induced a local proton exchange rather than a cooperative proton relay.

H3O+ move faster than crown, while as fast as tiara. Coronation matters in hydronium solvate ionic liquids.

The first example of ammonium (NH4 +) solvate ionic liquids (ILs) is reported. The compound is ammonium bis(trifluoromethylsulfonyl)amide-18-crown-6 (1/1), i.e. [NH4 +][Tf2N–]−18C6 (1/1), where Tf represents SO2CF3. Raman spectra, NMR spectra, and DFT calculations support the conclusion that the compound can be described as an ammonium solvate IL [NH4 +·18C6][Tf2N–], which consists of 18C6-coordinated NH4 + cations and Tf2N– anions. The conductivity of the ammonium solvate IL reaches as high as 10 mS cm–1 at 150 °C. The negligible volatility below 200 °C is confirmed by thermogravimetry. Compared with a hydronium (H3O+) solvate IL [H3O+·18C6][Tf2N–], the ammonium solvate IL shows better thermal stability, which strongly suggests long residence time of 18C6 with NH4 + cation. The stability may lead to the vehicular-type translational motions of NH4 + cations with 18C6 solvents as proved by their self-diffusion coefficients. The findings regarding this ammonium solvate IL can provide the guidelines to design new NH4 + or proton conductors for ammonium ion batteries and fuel cells, which work at medium-low temperatures of 150 °C–200 °C.

Solvate ionic liquids (ILs) such as binary equimolar mixtures of glymes (ethyleneglycol-dimethylether or CH3(OCH2CH2) n OCH3) and lithium bis(trifluoromethylsulfonyl)amide (LiTf2N; Tf = SO2CF3) are known to show identical self-diffusion coefficients for glymes and Li+ ions. Here, we report that the addition of LiTf2N to the solvate ILs drastically changes their electrolyte properties. When the lithium salts are added to give the super-concentrated electrolytes with [O]/[Li+] = 3 (molar ratio of ether oxygen to Li+), ligand exchange or hopping conduction of Li+ takes place for triglyme (G3; n = 3) and tetraglyme (G4; n = 4). In addition, the Li+ transference number t Li+(EC), electrochemically measured under anion blocking conditions, increases about 3–6 times compared with the solvate ILs. Consequently, segmental motion of glymes apparently affects the transport properties even for the shorter G3 in the super-concentrated region. The relationship between the coordination structure and the transport properties are also discussed as a function of ionicity, the extent of the contribution of self-diffusion to the actual ion conduction. Plots vs ionicity demonstrate that a clear line can be drawn between the solvate ILs and the super-concentrated electrolytes.