Molecular insight into the structure and dynamics of LiTf2N/deep eutectic solvent: an electrolyte for Li-ion batteries

Two choline-based deep eutectic solvent namely ethaline and glyceline have been used in different applications such as metal extraction, solubility and in electrochemistry because of its easy availability, inexpensive and non-toxic nature. In this work, molecular dynamics simulation was employed to study the structural and transport properties of ethaline and glyceline when blended with Li+ based salt (lithium bis (trifluoromethane sulphonyl) imide (LiTf2N)) in varying concentrations for the application as electrolytes in lithium-ion batteries. The effect of temperature and concentration on the structural and transport properties was explored to understand the diffusion of Li+ at the atomic level. For both the deep eutectic solvents (DESs), all the H-bond between Cl- ion and hydrogen bond acceptor i.e. ethylene glycol/glycerol decreases due to the formation of a network between Li+ and Cl- upon increasing salt concentration. Li+ ions was found to be in the diffusive regime at a very high temperature ( > 400 K) and low molar concentration (< 0.2). It is interesting to note that, for the same salt concentration, self-diffusion coefficient of Li+ ion in ethaline was observed to be tenfold higher than in the glyceline. Therefore, this study provides a microscopic understanding to synthesise a choline-based electrolyte by addition of Li-salt.