Intercalation dynamics in rechargeable battery materials: General theory and phase-transformation waves in LiFePO4

Rate-Dependent Morphology of Li2O2 Growth in Li–O2 Batteries

“…Using the same theory for reaction-limited dynamics of a concentration variable,c =h, such a transition was first predicted for lithium intercalation in Li X FePO 4 nanoparticles [27], as the suppression of phase separation into LiFePO 4 and FePO 4 domains. The only difference lies in the thermodynamics of intercalation, given by a Cahn-Hilliard regular solution model [26]. Li X FePO 4 intercalation is predicted to be stable and uniform above a critical current I c (X), somewhat below the typical Tafel exchange current due to coherency strain [28].…”

“…We describe the current density profile I(x, t) using generalized Butler-Volmer kinetics based on nonequilibrium thermodynamics, recently developed by Bazant et al [25] and applied to intercalation dynamics in Li-ion batteries [26][27][28][29][30]48]. Here, we apply the theory for the first time to surface growth, using a different model for the Li 2 O 2 chemical potential,…”

“…When the film thickness approaches 5 nm, the active surfaces become passivated, as electronic resistance increases with thickness [24]. In this Letter we model the rate-dependent morphological transition in Li 2 O 2 growth, using the recently developed variational theory of electrochemical kinetics [25][26][27][28][29][30] applied to classical surface-growth models [31][32][33]. The theory predicts a transition starting in the first monolayer from particle growth to film growth when the current exceeds the exchange current for the oxygen reduction reaction, consistent with experimental observations.…”

“…This equation generalizes the CH and Allen-Cahn equations for electrochemistry. As in the case of anisotropic LiFePO 4 nanoparticles [26], diffusion can be neglected (M = 0) to yield the Butler-Volmer Allen-Cahn reaction (ACR) equation [25,27], which, using Eqs. normalized by mean height h (see Eq.…”

Thermodynamics of electromechanically coupled mixed ionic-electronic conductors: Deformation potential, Vegard strains, and flexoelectric effect

“…strained films and multilayers [63]) and the effects of individual and multiple defects to be explored [64]. Once available for electrochemical systems, similar advances based on phase-field type models could be achieved [65], [66], [67,68].…”