Reactive Force Field (ReaxFF) and Universal Force Field Molecular Dynamic Simulation of Solid Electrolyte Interphase Components in Lithium-Ion Batteries

Understanding solid electrolyte interphase (SEI) is essential for the diagnosis of lithium-ion batteries because many aspects of battery performance such as safety and efficiency depend on these characteristics. LiF, Li2O, and Li2CO3 are important inorganic components of SEI. This electrode-electrolyte surface forms during the battery's first charging/discharging cycle, preventing electrons' movement through the electrolyte and stabilizing the lithium-ion battery. However, the concern is inorganic SEI components cause rate limitation of lithium-ion diffusivity through the SEI layer. Lithium-ion diffusivity through the SEI layer depends on many factors such as temperature, the width of the SEI layer, and the concentration/density of the layer. Lithium-ion diffusivity dependence on temperature, at working temperatures of lithium-ion batteries was observed at temperatures from 250 K to 400 K and diffusion coefficient data at higher temperatures have also been observed. Lithium-ion diffusivity at varying concentration/density was also observed in this paper using the reactive force field (ReaxFF) molecular dynamic simulation. To improve the lithium-ion diffusivity, vacancy defects were created in the inorganic components of the SEI layer LiF, Li2O, and Li2CO3 and the diffusion coefficient was obtained using the ReaxFF molecular dynamic simulations. Another approach to improve the lithium-ion diffusivity is doping alkali metal ions such Na, Ca, K, and Mg in the inorganic components of SEI layers of LiF, Li2O, and Li2CO3 and simulated using the universal force field (UFF), and the diffusion coefficient was observed.