Accelerated lithium-ion diffusion via a ligand ‘hopping’ mechanism in lithium enriched solvate ionic liquids

Abstract

Solvate ionic liquids (SILs), equimolar amounts of lithium salts and polyether glymes, are well studied highly customisable “designer solvents”. Herein the physical, thermal and ion mobility properties of SILs with...

Transitioning from Regular Electrolytes to Solvate Ionic Liquids to High-Concentration Electrolytes: Changes in Transport Properties and Ionic Speciation

“…Finally, attempts have been made to improve the SILs properties by adding an excess of the lithium salt to convert them to HCEs (i.e., [O]/[Li] < 4) . These HCE-SIL electrolytes have been shown to have improved oxidative stability and Li + transport but low ionic conductivity due to their high viscosities. , These studies demonstrate that to enhance the ionic transport of SILs and HCE-SILs while maintaining their advantageous electrochemical properties, it is critical to have a molecular understanding of the influence of ion–solvent and ion–ion interactions on their transport properties.…”

“…However, it has been shown that these Raman modes are not well suited for assigning ionic speciation because of an ambiguity in the spectroscopic signatures for the different ionic species . Other studies have used indirect methods, such as the NMR self-diffusion coefficient ratios and thermal stability of HCEs and SILs, to deduce the possible local structure of Li + . , Molecular dynamics simulations have also been applied to explore the Li + solvation structure and dynamics in HCEs, but most studies do not have the accuracy to reproduce experimental observations . Overall, these previous studies reveal an incomplete picture of the Li + solvation environment in HCEs and SILs, highlighting the need for a better description of the Li + solvation structure and dynamics in relation to the transport properties.…”

“…Other studies involving electrolytes having a salt:solvent molar ratio of 1:1.9 or higher termed their electrolytes as HCEs. ,, Regardless of their definition, these studies demonstrated that SCEs or HCEs have a number of solvent molecules that do not fulfill the lithium-ion (Li + ) tetrahedral coordination structure of [Li­(solvent) 4 ] + , for a monodentate solvent. Under such conditions, the counterion participates in the Li + coordination, leading to the formation of ion pairs, aggregates, ,, and ionic networks. − The distinct Li + solvation structures in HCEs are responsible for the atypical electrolyte properties, such as the enhanced oxidative stability, , thermal stability, and improved Li + transport. ,, …”

“…Under such conditions, the counterion participates in the Li + coordination, leading to the formation of ion pairs, aggregates, 20 , 27 , 34 and ionic networks. 35 − 37 The distinct Li + solvation structures in HCEs are responsible for the atypical electrolyte properties, such as the enhanced oxidative stability, 23 , 34 thermal stability, 38 and improved Li + transport. 34 , 39 , 40 …”

“… 38 , 62 Molecular dynamics simulations have also been applied to explore the Li + solvation structure and dynamics in HCEs, but most studies do not have the accuracy to reproduce experimental observations. 38 Overall, these previous studies reveal an incomplete picture of the Li + solvation environment in HCEs and SILs, highlighting the need for a better description of the Li + solvation structure and dynamics in relation to the transport properties.…”