  Lithium-ion batteries rely on particulate porous electrodes to realize high
performance, especially the fast-charging capability. To minimize the
particle-wise reaction heterogeneities that may lead to local hot spots, deeper
understandings of these electrodes at the mesoscale, i.e. hundreds of
particles, have become an urgent need. This study reveals that the seemingly
random reaction heterogeneities are actually controlled by the interplay
between the non-equilibrium material thermodynamics and the external
electrochemical driving force. Our operando experiments confirm the true
working current density around a single particle that is much higher than the
globally averaged current density, can change the behavior of phase
transformation. The combined theoretical and experimental analyses reveal that
unlike other phase-transforming porous electrodes, not all phase separation
processes in graphite can be suppressed at high currents, due to the
characteristics of the concentration-dependent exchange current density. The
insights highlight the necessity to incorporate materials thermodynamics into
electrochemical models to ensure self-consistent understandings of practical
porous electrodes toward precision design and management.
