Local structure of Li+ in concentrated LiPF6–dimethyl carbonate solutions

Abstract

Neutron diffraction measurements have been carried out at 25 °C for 9.6 mol% *LiPF 6 -deutrerated dimethyl carbonate (DMC-d 6 ) solutions in which the isotopic ratio of 6 Li/ 7 Li was changed. Local structure of Li + in the solution was derived from the least squares fitting analysis of observed difference function, Δ Li (Q). It was revealed that Li + is surrounded by ca. 3 DMC molecules and ca. 1 PF 6 with intermolecular distances of r(Li +… O(DMC)) = 2.08 ± 0.02 Å and r(Li +… F(PF 6 -)) = 2.03 ± 0.06 Å, respectively. Raman experimental study and DFT calculations agree well with neutron structure analysis.

How does the solvent composition influence the transport properties of electrolyte solutions? LiPF6 and LiFSA in EC and DMC binary solvent

“…Based on the average nature of n s , if we assume that the number of species coordinating Li + , including both the solvent and anion, totals four, the anion PF -6 or FSAaccounts for the remaining 4 − n s,total ∼ 1.3-0.5. The neutron diffraction study of LiPF 6 dissolved in pure DMC (9.6 mol%) by Kamada et al 33 concluded that one Li + ion is surrounded by about three DMC molecules and one PF -6 anion, which roughly agrees with our result at x EC = 0. The initial increase in the total number of solvent in the shell with the increase in x EC thus implies the decrease in the number of anions in the vicinity of Li + .…”

Opportunities and Limitations of Ionic Liquid‐ and Organic Carbonate Solvent‐Based Electrolytes for Mg‐Ion‐Based Dual‐Ion Batteries

“… [48c] Even though still some “free” DMC, indicated by the bands at 862 (weak) and 917 cm −1 , is present in Mg‐DMC, the intensity of the Raman bands associated with coordinated DMC is much higher. In good agreement with previous reports[ 48a , 48c , 48d ] of Li + in DMC, upon coordination to Mg 2+ , the ct ‐DMC conformation is preferred, which is clearly shown in the share of areal intensity I of the ct ‐DMC for the uncoordinated bands in pure DMC [ I 861 /( I 861 + I 917 )=3 %], compared to the coordinated bands in Mg‐DMC [ I 882 /( I 882 + I 945 )=77 %]. In addition, the blue shift upon coordination, indicating the coordination strength is with 28 cm −1 for the cc ‐DMC and 21 cm −1 for ct ‐DMC higher than literature reports for Li‐ion‐based systems (e. g., cc ‐DMC: 14 cm −1 , ct ‐DMC: 13 cm −1 by Kameda et al.…”

“…In pure DMC, one main band at 917 cm −1 , corresponding to a cis‐cis conformer of DMC ( cc ‐DMC) is visible. In addition, a weak band at 861 cm −1 indicating a cis‐trans conformer of DMC ( ct ‐DMC) appears [48b,c] . Upon the addition of Mg(TFSI) 2 (Mg‐DMC), two additional peaks at 882 and 945 cm −1 , corresponding to ct ‐DMC, respectively cc ‐DMC coordinated to a cation appear [48c] .…”

“…In addition, a weak band at 861 cm −1 indicating a cis‐trans conformer of DMC ( ct ‐DMC) appears. [ 48b , 48c ] Upon the addition of Mg(TFSI) 2 (Mg‐DMC), two additional peaks at 882 and 945 cm −1 , corresponding to ct ‐DMC, respectively cc ‐DMC coordinated to a cation appear. [48c] Even though still some “free” DMC, indicated by the bands at 862 (weak) and 917 cm −1 , is present in Mg‐DMC, the intensity of the Raman bands associated with coordinated DMC is much higher.…”

“…[ 48b , 48c ] Upon the addition of Mg(TFSI) 2 (Mg‐DMC), two additional peaks at 882 and 945 cm −1 , corresponding to ct ‐DMC, respectively cc ‐DMC coordinated to a cation appear. [48c] Even though still some “free” DMC, indicated by the bands at 862 (weak) and 917 cm −1 , is present in Mg‐DMC, the intensity of the Raman bands associated with coordinated DMC is much higher. In good agreement with previous reports[ 48a , 48c , 48d ] of Li + in DMC, upon coordination to Mg 2+ , the ct ‐DMC conformation is preferred, which is clearly shown in the share of areal intensity I of the ct ‐DMC for the uncoordinated bands in pure DMC [ I 861 /( I 861 + I 917 )=3 %], compared to the coordinated bands in Mg‐DMC [ I 882 /( I 882 + I 945 )=77 %].…”