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Peter G. Winchell Distinguished Lecture Series

September 7 @ 3:30 PM - 5:00 PM - Lecutre in ARMS 1010/reception in MSE Effron Lounge-lobby 2nd floor

Phase Separation Dynamics in Li-ion Batteries

Professor Martin Z. Bazant
Massachusetts Institute of Technology
Chemical Engineering & Mathematics

High-rate Li-ion batteries increasingly involve electrode materials, such as iron phosphate and graphite, which undergo phase separation into Li-rich and Li-poor phases upon intercalation of lithium. New dynamical phenomena arise because phase separation occurs in nanoparticles, limited by surface reactions and far from equilibrium. A general phase-field theory of ion intercalation ki-netics is developed, which unifies the Cahn-Hilliard equation with Butler-Volmer and Marcus kinetics for intercalation reactions. For individual nano-particles, the theory predicts surface-nucleated intercalation waves at low cur-rent, which relax to striped morphologies determined by elastic coherency strain. Above a critical current, typical of battery operation, phase separation is suppressed. At moderate currents, unstable “quasi-solid solutions” lack the time to fully phase separate. In porous electrodes, the theory predicts macro-scopic reaction fronts and mosaic instabilities at low current, giving way to smooth, diffusive intercalation at high current. These results help to explain the revolutionary performance of LiFePO4 as a cathode material in nanoparti-cle form. The general theory can also be applied to water sorption in concrete and other adsorption phenomena with hysteresis.

Martin Z. Bazant is broadly interested in materials physics and applied mathe-matics, motivated by problems in chemical engineering. His PhD in condensed matter physics (Harvard, 1997) produced a popular interatomic potential for molecular dynamics simulations of silicon (“EDIP”). He joined the MIT Depart-ment of Mathematics in 1998 and did seminal work on diffuse charge dynam-ics and “induced-charge electro-osmosis” (including the most cited paper in the Journal of Fluid Mechanics since 2004). He joined the Department of Chemical Engineering in 2008 and founded an experimental laboratory focus-ing on novel electrochemical systems for water desalination and energy con-version. His group combines theory with experiment and draws students from chemical engineering, mechanical engineering, mathematics, physics, and ma-terials science. His honors include the Paris Sciences and Joliot Chairs from ESPCI, Brilliant Ten (2007) from Popular Science Magazine, and a Career Award from the Department of Energy.

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