EAGER: Mesoscopic modeling of complex chemical-physical processes at interfaces

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In many engineering systems, the physics and chemistry occurring at interfaces in a component are critical to the system’s performance, such as the electrochemical reactions in batteries, cavitation in fuel injectors, pumps and blood vessels, or reactions in chemical reactors. Understanding the physical phenomena and interactions between phases at the interfacial level is critical to designing more efficient systems and new technologies, such as high energy density batteries and drug delivery methods. With computational methods, we can visualize the physical nature of interfaces, making it well positioned to study interfacial processes and to isolate critical phenomena to better understand the chemical-physical driving forces within a system. Additionally, modeling can complement experimental work on elucidating the fundamental chemical-physical processes at the core of many complex engineering systems. For instance, in battery electrodes, optimal performance requires balancing the surface area available for reactions, the pore space available for transport of reactive species, and the connectivity of the solid electrode for charge transport. Neglecting any of these critical phenomena reduces battery performance. This study focuses on developing the computational methods needed to resolve chemical-physical processes at interfaces in the air electrode of high energy density lithium batteries. The project focuses on models that explicitly resolve the interfaces and surrounding regions within the complex porous geometry of the air electrode in a lithium-air battery. In this project, meso-scale model development will focus on modeling the air electrode of a lithium metal battery using smoothed particle hydrodynamics, a Lagrangian particle-based modeling method. The air electrode is a porous carbon-based material and the interfacial region where the air, electrolyte and electrode meet, is the site of the electrochemical reactions. During discharge, Li+ ions travel through the electrolyte to the air electrode where they react with oxygen. In an aprotic electrolyte design, the electrochemical reactions result in non-soluble lithium peroxide (Li2O2). The buildup of Li2O2 passivates the surface of the cathode and can lead to clogging of the pores. This limits the capacity of the battery over multiple charge/discharge cycles as the incomplete dissolution of Li2O2 decreases the capacity. The meso-scale model will focus on modeling the meso-scale behavior of the electrode to resolve the interfacial chemical-physical processes such as transport of species and charge to the reaction sites and the electrochemical reactions that produce Li2O2. The model will be used to investigate the meso-scale physics by explicitly resolving the interface and will study how the interplay between the electrode microstructure, electrolyte and reaction site concentration and locations affect electrode performance.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.