Ion Diffusivity through the Solid Electrolyte Interphase in Lithium-Ion Batteries

Abstract

Understanding the transport properties of the solid electrolyte interface (SEI) is a critical piece in the development of lithium ion batteries (LIB) with better performance. We studied the lithium ion diffusivity in the main components of the SEI found in LIB with silicon anodes and performed classical molecular dynamics (MD) simulations on lithium fluoride (LiF), lithium oxide (Li<sub>2</sub>O) and lithium carbonate (Li<sub>2</sub>CO<sub>3</sub>) in order to provide insights and to calculate the diffusion coefficients of Li-ions at temperatures in the range of 250 K to 400 K, which is within the LIB operating temperature range. We find a slight increase in the diffusivity as the temperature increases and since diffusion is noticeable at high temperatures, Li-ion diffusion in the range of 130 to 1800 K was also studied and the diffusion mechanisms involved in each SEI compound were analyzed. We observed that the predominant mechanisms of Li-ion diffusion included vacancy assisted and knock-off diffusion in LiF, direct exchange in Li<sub>2</sub>O, and vacancy and knock-off in Li<sub>2</sub>CO<sub>3</sub>. Moreover, we also evaluated the effect of applied electric fields in the diffusion of Li-ions at room temperature.