Interfacial Chemistry at the Surface of Li-Metal Anodes

Abstract

Efficient energy storage is essential not only for the success of renewable energies, but also for many of daily society needs including communications, electronics, and medical and biomedical applications, among others. Electrochemical cells are complex systems integrated by several materials and their corresponding interfaces whose physical-chemical behavior is dominated by highly coupled mass and electron transport and chemical and electrochemical reactions. During lithium ion battery operation for example, during charge, lithium ions move in the electrolyte towards the anode surrounded by coordination spheres that may include solvent, salts, and other species such as additives. Once the solvated ion (inserted in a usually multicomponent network) reaches the anode surface, many additional events will take place because of the sequential and sometimes almost simultaneous reduction of the cation and that of the various components of the coordination shell. To characterize such complex environment, we analyze the Li ion coordination shell as a function of the distance to the electrode surface and electrode potential. We use density functional theory (DFT) and ab initio molecular dynamics (AIMD), to identify structural properties, as well as reactions and reaction mechanisms. Among the various “additional” species we consider the presence of long-chain polysulfides, that migrate in the electrolyte towards the Li metal anode in the Li-S chemistry. In this talk we will discuss physical, chemical, and electrochemical phenomena occurring at solid/electrolyte interfaces of Li-ion batteries and how the methods of first-principles computational analysis may be used to understand them and suggest strategies for practical solutions. In particular we will focus on the solid electrolyte interphase (SEI) occurring due to electrolyte reduction on or near Li anode surfaces and the role of the nature of the solvents, salts, and additives on the resultant SEI properties as well as on dendrite formation and battery performance.