Dynamic interplay between phase transformation instabilities and reaction heterogeneities in particulate intercalation electrodes

Lithium-ion batteries rely on particulate porous electrodes to realize high performance, especially fast-charging capabilities. To minimize the particle-wise reaction heterogeneities, a deeper understanding of these electrodes at mesoscale, i.e., hundreds of particles, is necessary. Here, we report that the seemingly random reaction heterogeneities are actually controlled by the interplay between non-equilibrium material thermodynamics and electrochemical kinetics. Our operando experiments reveal that, under constant current, autonomous dynamic loops exist that control the intra- and inter-particle phase-transformation dynamics that determine the true local current density. The combined theoretical and experimental analyses reveal that unlike other phase-transforming electrodes, not all phase-separation processes in graphite electrodes can be suppressed by high currents. Our results highlight the necessity to examine the concentration-dependent exchange current density for intercalation electrodes undergoing phase-transformation processes. Incorporating non-equilibrium thermodynamics into classical electrochemical models and electro-analytical techniques will ensure self-consistent understandings of practical electrodes toward precision design.