Corrosion and Passivation Mechanisms of Li-Ion Battery Cathodes from Ab Initio Interfacial Reaction Dynamics

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

Corrosion and surface passivation of redox-active materials is a crosscutting theme in electrochemical energy storage and catalysis, but the processes and their fundamental molecular underpinnings remain poorly understood. Active metal dissolution is one of the main reasons for degradation of Li-ion battery (LIB) cathodes, regardless of their crystal structure and chemical composition. The results of this research project will provide fundamental insights into the molecular origins of corrosion and passivation mechanisms necessary to explain and predict degradation behavior. The knowledge obtained will enable the development of an improved methodological foundation to attack other slow and rare event phenomena related to electrochemical interfaces. To capture the transient nature of the LIB dissolution process and account for changes in the electronic structure dynamically, atomistic ab initio molecular dynamics (AIMD) simulations will be employed. Such calculations in combination with enhanced free-energy sampling techniques can provide key insights into the dynamics, mechanism and kinetics of statistically rare events at a single event level. The obtained results can be used to explain experimental findings that are often challenging to interpret and to propose ways to inhibit surface degradation and passivation. The primary objective of the proposed research is to build a detailed atomistic understanding of reaction dynamics at LIB cathode/electrolyte interfaces focusing on transition-metal dissolution and electrolyte decomposition. The research plan focuses on three important classes of oxide-based LIB cathode materials, namely, spinel-type LiM2O4, layered-oxide LiMO2 and phospho-olivine LiMPO4 (M = Mn, Co, Ni, Fe) compounds. The emphasis will be on studying interfacial reactions in the chemically rich environments considering multiphase electrolyte solutions, multi-component cathode materials, structural heterogeneities and elevated temperature effects. The research will focus on understanding the role of: 1) surface chemistry of cathode materials including transition-metal disproportionation reactions; 2) complex mixed electrolyte chemistry involving two or more components in the presence of moisture; and 3) local structural heterogeneities such as the presence of oxygen vacancies and varying state of charge (Li content). The scientific goal of the project is to untangle the intimate relationships between cathode chemistry/structure and mixed electrolyte chemistry through a detailed characterization of elementary reaction steps. A set of simple descriptors will be determined that can be used to predict the propensity of the cathodes to corrode in complex LIB environments. The project will provide unique opportunities for undergraduate and graduate students, including members of underrepresented groups in STEM, to work on the application of first-principles techniques in interfacial reaction dynamics. Key results from the project will be incorporated into course materials and presented to high school students at a Nanophysics High School Camp. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.