Li⁺ Local Structure in Li–Tetraglyme Solvate Ionic Liquid Revealed by Neutron Total Scattering Experiments with the ^6/7Li Isotopic Substitution Technique

Abstract

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.

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex II: Neutron Scattering Instruments

“…A variety of scientific fields have been covered by NOVA: hydrogen storage materials (for example [104,105]), battery materials containing amorphous and liquid phases (for example [106,107]), and magnetic structure analysis (for example [108]). The capability of longer d-range measurement is useful for magnetic structure analysis.…”

“…In the neutron-capture cross section measurements of stable isotopes, miss-assigned resonances were found for 112 Sn, 118 Sn, 107 Pd, and 142 Nd. These results show that even in the case of a stable isotope, there are many miss-assigned resonances in the evaluated values [114][115][116].…”

X‐Ray Total Scattering of Electrolytes in Liquid‐Based Fluoride Shuttle Battery: Electrolyte Composition Dependence of the Low‐Q Peak

“…[ 22 ] Saito et al also investigated this system using neutron total scattering with 6/7 Li isotopic substitution. [ 23 ] However, the effects of the fluoride salts on the structure of FSB electrolytes have not been investigated using X‐ray or neutron total scattering.…”

Structural Variation in Carbonate Electrolytes by the Addition of Li Salts Studied by X‐Ray Total Scattering

“…As typical electrolytes are composed of light elements (e.g., H, C, and O), neutron total scattering, which is more sensitive to light elements than X‐ray total scattering, has been mainly used for the structural analysis of electrolytes, such as carbonate electrolyte [ 29,30 ] and solvate ionic liquids. [ 31 ] However, neutron total scattering usually requires isotopic substitution, especially the deuteration, for a reliable analysis, which is not necessarily practical for any kinds of electrolytes. In contrast, X‐ray total scattering is applicable to samples without isotopic substitution and thus a wider variety of electrolytes can be readily analyzed.…”