  Ion concentration polarization (CP, current-induced concentration gradient
adjacent to a charge-selective interface) has been well studied for
single-phase mixed conductors (e.g., liquid electrolyte), but multiphase CP has
been rarely addressed in literature. In our recent publication, we proposed
that CP above certain threshold currents can flip the phase distribution in
multiphase ion-intercalation nanofilms sandwiched by ion-blocking electrodes.
We call this phenomenon as multiphase polarization (MP). We then proposed that
MP can further lead to nonvolatile interfacial resistive switching (RS) for
asymmetric electrodes with ion-modulated electron transfer, which theory can
reproduce the experimental results of LTO memristors. In this work, we derive a
comprehensive 2D phase-field model for coupled ion-electron transport in
ion-intercalation materials, with surface effects including electron transfer
kinetics, non-neutral wetting, energy relaxation, and surface charge. Then we
use the model to study MP. We present time evolution of phase boundaries, and
analyze the switching time, current, energy, and cyclic voltammetry, for
various boundary conditions. We find that the switching performance can be
improved significantly by manipulating surface conditions and mean
concentration. Finally, we discuss the prospects of MP-based memories and
possible extensions of the current model.
