Kinetics, Mechanics, and Structural Disorder: Non-Equilibrium Phase Transformation in Lithium-Ion Battery Materials

The equilibrium phase diagram is a poor guide for lithium-ion battery electrodes under load. Operating electrodes are open, driven systems in which transformation pathways are governed as much by kinetics and mechanics as by thermodynamics -departures from equilibrium are large, mechanistically coherent, and exploitable for engineering. This review surveys the field of non-equilibrium phase transformation in lithium-ion battery materials across three interconnected themes: kinetic and mechanical suppression of first-order phase transitions in olivine LiFePO₄ and layered transition-metal oxides; chemo-mechanical feedback by which electrode mechanics reshapes surface reaction kinetics; and the pathway-altering mechanisms by which the free energy landscape is restructured under non-equilibrium conditions, producing qualitatively opposite transformation behavior in LiFePO₄ and NMC. Finite-deformation continuum models formally derive diffusion-induced creep and kinetic plasticity as inelastic mechanisms, coupling mechanical state to surface reaction kinetics through a modified Butler-Volmer boundary condition. Crystal-scale analysis establishes that defect stress fields shift the electrochemical landscape in LiFePO₄ by amounts consequential for electrode design. Multilayered free-energy theories introduce structural disorder as a dynamically evolving state variable that selects between competing transformation pathways, reproducing solid-solution behavior in LiFePO₄ at high rates and anomalous phase separation in NMC111 within a single unified framework. Operando imaging confirms predicted intra-particle heterogeneities; chemo-mechanical crack feedback and guided phase transitions extend the engineering reach. Four research priorities emerge: a unified finite-deformation phase-field model incorporating damage mechanics; longitudinal operando validation of the predicted amorphization threshold; extension to Ni-rich oxides, conversion cathodes, and solid-state architectures; and electrode-scale modeling that integrates chemo-mechanical coupling with operando-measurable heterogeneity dynamics.