Diffusion of Lithium Cation in Low-Melting Lithium Molten Salts

Abstract

The self-diffusion coefficients of the lithium cation (D(Li + )) and counteranion (D(anion)) in the molten lithium amide, such as lithium bis(fluorosulfonyl)amide (Li [FSA]) and lithium fluorosulfonyl(trifluoromethylsulfonyl)amide (Li[FTA]), were measured by a pulsed-gradient spin− echo nuclear magnetic resonance method at 150 °C. In the relationships between viscosity and the resulting self-diffusion coefficient (the D(Li + ) is 1.4 × 10 −11 m 2 •s −1 and the D(anion) is 5.5 × 10 −12 m 2 •s −1 for the Li[FSA] and the D(Li + ) is 1.7 × 10 −12 m 2 •s −1 and the D(anion) is 6.6 × 10 −13 m 2 •s −1 for the Li[FTA]), the Li[FTA] and Li [FSA] have a stronger intercalation between ions than the high-temperature lithium molten salts. However, their ionic conductivities are higher than those estimated by D(Li + ) and D(anion); specifically, that of the Li[FTA] is three times higher. Therefore, the Li[FTA] would have special conductive behavior, which leads to the superionic nature of the Walden plot and the high rate performance against much higher viscosity in lithium secondary battery. Such unique conduction and battery behaviors using the Li[FTA] might be due to the robust and asymmetric structure of the FTA − .

Effect of Temperature on Li Electrodeposition Behavior in Room-Temperature Ionic Liquids Comprising Quaternary Ammonium Cation

“…We believe that the above requirement can be satisfied by employing a tailored artificial SEI, for example, by using vinylene carbonate to generate an additional surface film. 80 Solid electrolytes or Li single molten salts 90 with a Li-ion transport number of unity can also help solve this problem, because dendrite formation can be suppressed by avoiding diffusion-controlled conditions. 91…”

Electrolytes for Lithium (Sodium) Batteries Based on Ionic Liquids: Highlighting the Key Role Played by the Anion

“…This situation contrasts with that of neat lithium molten salts, including Li[FSI] and Li[FTFSI], where Li + diffuses more quickly than the anions, though the order is reversed in rather complex borates substituted with 1,1,1,3,3,3‐hexafluoro‐2‐propoxy or pentafluorophenoxy radicals where the high NE Δ values reported (as Watanabe “ionicities”) suggest ion association. This has been confirmed by calculation of like‐ion Laity resistance coefficients, which are large and negative .…”

“…An interesting case example is that of lithium fluorosulfonyl(trifluoromethanesulfonyl)amide (lithium [ N ‐trifluoromethylsulfonyl]‐sulfamoylfluoride), a component of some newly suggested battery electrolytes . Kubota et al claim (see their Figure ) that this is truly superionic, based on self‐diffusion measurements at 150 °C, that is, that the conductivity is larger than that predicted by the NE equation and hence Δ in [Eq.…”

Poly(ionic liquid) electrolytes at an extreme salt concentration for solid-state batteries

“…This offers an opportunity to investigate a polyIL-in-salt electrolyte in an extreme salt concentration range, as well as the effect from the use of mixed anions in this case. LiFTFSI is shown to be a good ionic conductor (> 10 − 4 S cm − 1 at 100°C 24,25 ) with a crystallization-resistant feature, helping maintain a glassy state in this polyIL-in-salt system. As the salt concentration increases, ion motion shifts from being decoupled (at a 1:2 ratio) to coupled (at a 1:8 ratio) with the structural dynamics and, therefore, affecting the glass transition temperature (T g ).…”