Molecular Modeling of Energy Barrier of Li Ion Transport from Negative to Positive Electrodes

Abstract

Lithium ion battery is used as a main power supply of a small portable device and large power supplies for electric cars. For further applications, however, an improvement in battery performance from materials level based on rational design of Li ion transport in the battery is needed. In this study, we carried out systematic analysis of energy barrier of Li ion transport from anode to cathode materials using first-principles molecular dynamics and classical molecular dynamics. First, we calculated the energy barrier of diffusion of Li ion through several kinds of electrolyte. To validate the accuracy of calculated transport properties, diffusion coefficients and activation energies for diffusion of ions in LiPF6-DEC-EC at different temperature (-20 ℃ – 20 ℃) and ratio of DEC/EC are compared with experimental data and confirmed the reasonable agreement. Furthermore, the solvation energy of Li ion in electrolytes as well as the salvation structure were investigated by density functional theory and classical molecular dynamics. First principles molecular dynamics and density functional theory were used to calculate the adsorption energy and activation energy fir diffusion of Li ion in cathode materials such as LiCoO2. From these analysis, we conclude that the solvation energy, which is more than 50 kcal/mol for EC/DEC system, is the highest energy barrier for transport of Li ion of which would be the limited step for Li ion transport although it depends on the condition. We also investigated the influence of these transport properties to the battery performance (I-V curve). We will present more concrete data regarding Li ion transport at the conference.