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

ABSTRACT

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.

KEYWORDS:

• Molecular dynamics simulation
• deep eutectic solvents
• li-ion battery
• electrolytes

Acknowledgements

We wish to acknowledge the department of chemical engineering at the National Institute of Technology Warangal, Telangana, India (NITW) for providing access to the design and simulation laboratory for carrying out research work related to computer simulation. We thank Dr. Imre Bako at Research Centre for Natural Sciences, Hungary and Dr. Rajasekaran M. at Indian Institute of Sciences Bangalore, India for useful comments on the contents of manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supporting information

Force field parameters, density calculation on varying number of molecules for ethaline system, annealing information, hydrogen bond labels, β parameter, diffusivity fitted parameter and diffusion coefficient in the range 298–328 K.

Additional information

Funding

This work was supported by Science and Engineering Research Board [Grant Number EEQ/2020/000480].