DateMay. 3, 2013
Speaker Martin Z. Bazant (Massachusetts Institute of Technology)
TopicNonequilibrium Thermodynamics of Li-ion Batteries
Abstract: Li-ion batteries involve electrode materials, such as iron phosphate and graphite, which tend to separate into Li-rich and Li-poor phases upon intercalation of lithium. In nanoparticles, this bulk thermodynamic relaxation competes with surface electrochemistry, leading to the fundamental question: What is the reaction rate during a phase transformation? A consistent answer is provided by a theory of chemical thermodynamics that unifies and extends the Cahn-Hilliard and Allen-Cahn equations for chemical kinetics and charge transfer. The reaction rate depends on concentration gradients, elastic stress, and other non-idealities. Simulations based on the theory shed light on the complex nonlinear dynamics of ion intercalation in battery nanoparticles and porous electrodes. A key prediction is the suppression of phase separation at high currents, as reactions stabilize "quasi-solid solution" states far from equilibrium.