The scientific community's growing interest in environmentally friendly solvents has led to a focus on Deep Eutectic Solvents (DESs), composed of natural components, as potential alternatives to traditional organic solvents. Type V DESs, employing neutral compounds with adjustable polarity and hydrophobicity, have recently emerged as promising candidates for various applications.
This study investigates the transport properties of Type V DES electrolytes, formed by thymol (Thy) or menthol (Men) as hydrogen bond donors (HBD) and camphor (Cam) or trioctylphosphine oxide (TOPO) as hydrogen bond acceptors (HBA), doped with varying concentrations of lithium bis(trifluoromethane)sulfonimide (LiTFSI). We explore self-diffusion, viscosity, density, and conductivity, critical parameters for their potential use in lithium-ion batteries (LIBs).
Our investigation reveals the intricate interplay between lithium salt and DES components. Viscosity measurements indicate progressive increases upon lithium doping due to Coulombic interactions associated with LiTFSI. However, all systems exhibit poor ionic conductivity values decoupled from fluidity trends, limiting their suitability as LIB electrolytes. LiTFSI selectively affects HBA and HBD diffusion, disrupting the hydrogen-bond network, particularly in thymol-containing DESs. Notably, similar diffusion coefficients for Li⁺ and TFSI^- ions suggest the formation of long-lived ion pairs, contributing to lower conductivity.
Overall, our findings shed light on the transport properties of Type V DES electrolytes, capable of dissolving significant amounts of LiTFSI. However, the formation of ion pairs hinders their practical application. Future research aims to introduce additives to disrupt ion-ion interactions and enhance transport properties, leveraging the sustainable appeal of DESs for advanced energy storage technologies.

Type V DES electrolytes

Miguel Munoz

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