Transition from Deceleration to Acceleration of Lithiation Front Movement in Hollow Phase Transformation Electrodes

Abstract

In phase transformation electrodes under lithiation, growth of the Li-rich phase from the Li-poor phase usually proceeds with a moving phase boundary. Their high- rate capability is determined by how fast the phase interface can move. Unfortunately recent studies show that the stress-mediated migration velocity of the phase interface is significantly slowed down. We employ a non-linear stress-kinetics coupled model to address the effect of inner surface in hollow structures on the phase interface movement. We demonstrate that the inner surface can trigger a transition from deceleration to acceleration of the phase interface movement. The plastic deformation at the phase interface dissipates extra energy required to drive the inward migration of the phase interface and leads to deceleration. Another plastic zone arises near the inner surface and expands outward as two-phase lithiation proceeds. The coalescence of these two plastic zones significantly decreases the resistance of the phase interface movement and leads to acceleration. Furthermore, we show that tuning the size of hollow spheres regulates the phase interface migration toward high packing density and superior rate capability.