Categorizing Molten Salt Complexes as Ionic Liquids and Their Applications to Battery Electrolytes

Abstract

Certain stoichiometric mixtures of salts and solvents (ligands) yield a salt complex. Salt complexes that are low melting and consist of discrete complex ions and their counter ions in the molten state can together form the essence of an ionic liquid (IL). This stable complex melt can now be categorized into a new subclass of ionic liquids, "solvate (or chelate) ILs." In this paper, we describe the current criteria for this new family of ILs. Concentrated mixtures of lithium salts and oligoether solvents are useful models for these solvate ionic liquids; the effects of the ion-ion and ion-solvent interactions on their structure and properties were investigated to contrast with classical concentrated electrolyte solutions. The performance of solvate ILs as electrolytes for lithium-sulfur (Li-S) batteries is also reported. The dissolution of lithium polysulfides (i.e., reaction intermediates of the sulfur cathode) into the electrolyte, which is a serious issue for the practical application of Li-S cells, was greatly suppressed in the solvate ILs. Therefore, a stable charge-discharge with high Coulombic efficiency was achieved with the solvate IL electrolytes.

Glyme-based electrolytes: suitable solutions for next-generation lithium batteries

“…90 Another study comparing several equimolar mixtures of either G 3 or G 4 with various salts (LiBETI, LiBF 4 , LiTf and LiNO 3 ) revealed that the dissolution of lithium polysulfides may be suppressed whether SILs are employed. 91 On the other hand, the G 4 -LiTf solution with the lithium salt in a 1 mol kg −1 concentration was considered the preferred electrolyte for performing a comparative evaluation of the electrochemical performance of several cathode composites prepared by mixing sulfur with carbon materials of various natures (namely, graphite, mesocarbon microbeads, and multi-walled carbon nanotubes). Besides, the electrolyte characteristics in terms of 1 H, 7 Li, and 19 F nuclei self-diffusion coefficients, ionic conductivity, and ionic association degree were investigated by combining NMR and impedance spectroscopy measurements.…”

Redox Active Glyme-Li Salt Solvate Ionic Liquids Based on Tetrabromoferrate(III)

“…The thermal properties (T g , T m , and 4 ] also raises the possibility that a FeBr 3 -G3 adduct was formed in the decomposition process at high temperature. The Lewis acid-base complex may be responsible for the highly elevated evaporation temperature of G3.…”

“…To avoid shuttling of the redox active anions between the electrodes, a lithium-ion conducting glass-ceramic (OHARA, LICGC, 19 mm in diameter) was also used. 4 ]-based catholyte cell was assembled in the Ar-filled grove box. The galvanostatic charge/ discharge measurements were performed with an automatic charge/ discharge instrument (HJ1001SM8A, Hokuto Denko) at 30°C.…”

“…Unlike aprotic ILs and metal salt binary mixtures employed as typical IL-based battery electrolytes, solvate ILs can provide a high concentration of metal ions required for fast electrode reactions in batteries. 4,5 Furthermore, strong ligand binding to metal cations at extreme salt concentrations improves the electrochemical stability of the solvate IL electrolytes, similar to highly concentrated electrolytes. 6,7 Therefore, solvate ILs play a part in the blooming research field of highly concentrated electrolytes for future energy storage applications.…”

The nanostructure of a lithium glyme solvate ionic liquid at electrified interfaces

“…sub-class of ionic liquids, solvate ionic liquids, have begun to be viewed as another set of potential electrolyte candidates. [7][8][9][10] In these ionic liquids the traditional bulky organic cation is replaced with a long-lived complex consisting of an atomic metal cation bound to solvent. In most cases this complex consists of the metal cation and a single polydentate solvent molecule.…”