1 research outputs found
Beyond Constant Current: Origin of Pulse-Induced Activation in Phase-Transforming Battery Electrodes
Mechanistic
understanding of phase transformation dynamics during
battery charging and discharging is crucial toward rationally improving
intercalation electrodes. Most studies focus on constant-current conditions.
However, in real battery operation, such as in electric vehicles during
discharge, the current is rarely constant. In this work we study current
pulsing in LiXFePO4 (LFP),
a model and technologically important phase-transforming electrode.
A current-pulse activation effect has been observed in LFP, which
decreases the overpotential by up to ∼70% after a short, high-rate
pulse. This effect persists for hours or even days. Using scanning
transmission X-ray microscopy and operando X-ray
diffraction, we link this long-lived activation effect to a pulse-induced
electrode homogenization on both the intra- and interparticle length
scales, i.e., within and between particles. Many-particle phase-field
simulations explain how such pulse-induced homogeneity contributes
to the decreased electrode overpotential. Specifically, we correlate
the extent and duration of this activation to lithium surface diffusivity
and the magnitude of the current pulse. This work directly links the
transient electrode-level electrochemistry to the underlying phase
transformation and explains the critical effect of current pulses
on phase separation, with significant implication on both battery
round-trip efficiency and cycle life. More broadly, the mechanisms
revealed here likely extend to other phase-separating electrodes,
such as graphite