(577b) Theory of Layered-Oxide Cathode Degradation in Li-Ion Batteries By Oxidation-Induced Cation Disorder

Disorder-driven degradation phenomena, such as structural phase transformations and surface reconstructions, can significantly reduce the lifetime of Li-ion batteries, especially those with nickel-rich layered-oxide cathodes. Here, we develop a general free energy model for layered-oxide ion-intercalation materials as a function of the degree of disorder, which represents the density of defects in the host crystal. The model accounts for defect core energies, long-range dipolar electrostatic forces, and configurational entropy of the solid solution. In the case of nickel-rich oxides, we hypothesize that disordered nickel is driven into the bulk by electrostatic forces as oxidation reactions at the solid-electrolyte interface remove oxygen ions at high potentials (>4.3V vs. Li/Li+). The model is used in battery cycling simulations to describe the extent of cathode degradation when using different voltage cutoffs when cycling, in agreement with experimental observations that lower-voltage cycling can substantially reduce cathode degradation. The theory provides a framework to guide the development of cathode compositions, coatings and electrolytes to enhance rate capability and enhance battery lifetime.