Phase Transformation Dynamics in Porous Battery Electrodes

Porous electrodes composed of multiphase active materials are widely used in Li-ion batteries, but their dynamics are poorly understood. Two-phase models are largely empirical, and no models exist for three or more phases. Using a modified porous electrode theory based on non-equilibrium thermodynam...

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Bibliographic Details
Published inarXiv.org
Main Authors Ferguson, Todd R, Bazant, Martin Z
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 06.02.2014
Subjects
Computer simulation
Electrodes
Free energy
Lithium-ion batteries
Nonequilibrium thermodynamics
Nucleation
Open circuit voltage
Phase transitions
Rechargeable batteries
Stability
Thermodynamic equilibrium
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Summary:Porous electrodes composed of multiphase active materials are widely used in Li-ion batteries, but their dynamics are poorly understood. Two-phase models are largely empirical, and no models exist for three or more phases. Using a modified porous electrode theory based on non-equilibrium thermodynamics, we show that experimental phase behavior can be accurately predicted from free energy models, without artificially placing phase boundaries or fitting the open circuit voltage. First, we simulate lithium intercalation in porous iron phosphate, a popular two-phase cathode, and show that the zero-current voltage gap, sloping voltage plateau and under-estimated exchange currents all result from size-dependent nucleation and mosaic instability. Next, we simulate porous graphite, the standard anode with three stable phases, and reproduce experimentally observed fronts of color-changing phase transformations. These results provide a framework for physics-based design and control for electrochemical systems with complex thermodynamics.
ISSN:2331-8422