Density functional theory calculations and ab initio molecular dynamics simulations for diffusion of Li+ within liquid ethylene carbonate

Abstract

We have performed the density functional theory (DFT) method to study the electronic structure of ethylene carbonate (EC) in the gas phase and ab initio molecular dynamics (AIMD) simulations for its liquid phase at T = 450 K to avoid freezing. The calculated characteristics of EC in both gas and liquid phases are found to be consistent with the experimental results. The coordination of one Li+ with 1–5 EC molecules is studied using the DFT method in the gas phase. At the same time, the formation of the first solvation shell of one Li+ within the EC solution at T = 450 K is investigated using the AIMD simulation technique. The calculated results reveal the stability of the [Li+(EC)4] solvation shell, which contains four strongly bound EC molecules in a tetrahedral arrangement both in gas and liquid phases. The diffusion coefficient of the EC crystal at T = 450 K is found to be 2.42 × 10−9 m2 s−1 and that of Li+ in liquid EC at T = 450 K is found to be 1.27 × 10−9 m2 s−1. The conductivity of Li+ is found to be 5.46 mS cm−1. Such diffusion and conduction of Li+ in liquid EC may be helpful in understanding the formation of the primary solvation shell of Li+ and the solid electrolyte interphase formation mechanism, and hence may be useful in applications of lithium ion batteries.