Thermophysical properties of choline chloride:4ethylene glycol and LiPF6 mixtures for lithium battery applications

Abstract

Batteries are versatile energy storage technologies that are being developed to enhance efficiency and lower costs. Deep eutectic solvents (DES) are eco-friendly alternatives to traditional electrolytes, and their properties have been studied to improve the performance of lithium-based batteries. We investigated choline chloride/ethylene glycol (ChlCl/Eg) mixtures with LiPF₆ salt in four concentrations through experimental and MD simulation. The thermophysical and transport properties of the mixture, including density, diffusion coefficient, viscosity, and ionic conductivity, were calculated across a temperature range of 298.15–398.5 K. Our findings quantitatively demonstrate that increasing the LiPF6 concentration from 0.0 to 0.1502 M results in a significant “average” increase in viscosity, from 15.45 to 20.46 cP experimentally (32.43% increase) and from 14.83 to 19.36 cP in MD simulations (30.53% increase). Conversely, ionic conductivity showed a substantial “average” decrease experimentally from 7.595 mS cm⁻¹ at 0.0 M to 6.004 mS cm⁻¹ at 0.1502 M (20.95% reduction). These findings suggest that an increase in salt concentration leads to significant alterations in viscosity and nuanced changes in ionic conductivity, providing valuable insights into the behavior of DES mixtures and aiding in the design and optimization of DES-based processes for use in lithium-based batteries.