Lithium bromide in acetonitrile and water: a neutron scattering study

Abstract

The stmcture wound lithium ions in solutions of lithium bromide in acetonilde and waler has been studied by neutron diffraction. For this p u p e the isotopic firstorder difference method bas been applied LO the lithium ion. For a 058 M acetonitrile solution it has been found that the bromide anion enters into the Bnt solvation shell around the lithium ion, whereas in the case of a 1.88 M aqueous solution the first hydration shell of the cation is no1 disturbed by the anion. ?he solvation number i s approximately 3 in he case of acetonitrile and approximately 4.5 in the case of water.

Solvation structure in dilute to highly concentrated electrolytes for lithium-ion and sodium-ion batteries

“…1). The PC based electrolytes (Left panel) show a Li-O peak at 0.21 nm for all concentrations, in excellent agreement with neutron diffraction data [42], while for the ACN based electrolytes (Right panel), the corresponding Li-N peak is found at 0.22 nm for the dilute systems, fairly comparable to diffraction experiments [43]. The latter peak clearly broadens, decreases in intensity, and splits for the highly concentrated systems.…”

“…coordination seems to be the most stable at dilute concentrations, moving to Li(N)3.1(F)1.8 for the concentrated systems, and progressing to a much higher anion content, Li(N)1.9(F)2.5, for the highly concentrated electrolytes. The total coordination number, however, remains close to 4.5 for all cases, larger than the 4-fold coordination reported experimentally by different techniques [43,[46][47][48], suggesting the PM7 method to slightly overestimate the coordination number, the cut-off to be set to high, or possibly that the solvent exchange affects the experimental data. As noted above for both the ACN and the PC based electrolytes an increased salt concentration promotes a substitution of solvent molecules by anions in the first solvation shell, as expected [28].…”

X-ray and neutron scattering studies of the hydration structure of alkali ions in concentrated aqueous solutions

“…For example, aqueous solutions of Li-polyacrylate and lithium hydroxide [37] give values for the Li + hydration number of 4.5(5), with similar distances as in lithium chloride. Similarly, an NDIS study of a 4 m LiBr solution also gives a coordination number closer to 4 than those in lithium chloride at similar concentrations [38]. Because of the wide interest in this ion, many theoretical and simulation studies have been carried out [29,30,39,40].…”

Ligand‐Exchange Processes on Solvated Lithium Cations: Acetonitrile and Hydrogen Cyanide

“…[62,63] Even compounds with mixed coordination of a counterion and acetonitrile were reported to be four coordinate, namely [Li(CH 3 CN) 3 Br] formed from 0.58  LiBr in CH 3 CN. [64] Extensive concentration-dependent ion-pairing was also found for weak coordinating counterions, such as in LiBF 4 [30] and LiClO 4 , [62] by studying the CN vibration. [65] These findings for the coordination number are in good agreement with published X-ray structures.…”