Atomistic Investigation of Solid Electrolyte Interphase: nanostructure, Chemical Composition and Mechanical Properties

Abstract

Using lithium metal as the anode is a promising way to raise the energy density of batteries, but inevitable lithium dendrite growth hinders the development of this kind of batteries. Albeit great efforts were devoted to uncovering the mystery of the solid electrolyte interphase (SEI), which determines the stability of the plating and stripping of lithium metal, our understanding of SEI at the atomic scale is limited due to its complex structure and composition. This work proposes a computational framework, based on the reactive force field molecular dynamics (ReaxFF), for simulating the SEI formation. Our results suggest the SEI in the standard EC/DEC electrolyte resembles a heterogeneous mosaic structure with inorganic crystalline grains randomly dispersed within the amorphous polymer matrix, as the consequence of the bottom-up growth sequence. When lithium nitrate is present in the electrolyte, the preferential reduction of lithium nitrate effectively regulates the electrolyte decomposition for rendering a bilayer structure with the lithium nitrate reduction products, Li3N and LiNxOy, on top of the amorphous polymer matrix. Although these N-containing compounds are good lithium-ion conducting materials for retaining a uniform, fast lithium-ion transport through the SEI, we observe a significant decrease in the mechanical performance due to the high-porosity structure.