Nucleation and Growth of Solid Electrolyte Interphase on Lithium Metal Batteries

Abstract

Lithium metal anode is considered a great candidate because of its high theoretical capacity and negative electrochemical potential. However, key factors like poor cyclability as well as the safety issues related to the uneven lithium electrodeposition, dendrite growth, and unstable solid electrolyte interphase (SEI) are keeping lithium metal batteries away from commercialization. Different attempts both experimentally and theoretically have been done to decode the exact structure and distribution of SEI, but due to the inherent dynamic behavior as well as the lithium reactivity, the exact structure of the SEI and its growth mechanisms are still unclear. In this study with the use of molecular simulation and computational chemistry tools, we investigate the initial nucleation and growth dynamics of different SEI components that provide us with thermodynamics and structural information about the nucleating SEI. Different nucleation and growth mechanisms were studied for the SEI components including LiF, Li2O, and LiOH. An initial mechanism of nucleation is based on the assumption that a Li metal cluster represents a portion of the surface where inhomogeneous Li seeds are nucleating, we use ab initio methods to determine the preferential addition sites for OH or O radicals or fluorine anions. This mechanism allows the study of different structures of SEI in lithium-rich environments simulating initial stages of electrolyte decomposition and SEI formation. Multiple models are studied to understand the formation energies and structures for SEI nanocluster formation in which already formed fragments of SEI are joined together to study the formation of larger SEI clusters. Each of the different components of SEI reveals its preferential growth mechanisms showcasing different degrees of crystallinity and electron density distribution leading to a better understanding of the nucleation and growth of SEI.