Thermodynamics of multi-sublattice battery active materials: from an extended regular solution theory to a phase-field model of LiMnyFe1-yPO4

Abstract Phase separation during the lithiation of redox-active materials is a critical factor affecting battery performance, including energy density, charging rates, and cycle life. Accurate physical descriptions these are necessary for understanding underlying mechanisms, performance limitations, optimizing storage devices. This work presents an extended regular solution model that captures mutual interactions between sublattices multi-sublattice materials, typically synthesized by metal substitution. We apply to phospho-olivine demonstrate its quantitative accuracy in predicting composition-dependent redox shift plateaus LiMn y Fe 1-y PO 4 (LFMP), LiCo (LFCP), x Mn 1-x-y (LFMCP), as well their phase behavior. Furthermore, we develop phase-field LFMP consistently matches experimental data identifies 0.4 0.6 superior composition favors solid transition, making it ideal high-power applications.