Phase Separation with Anisotropic Coherency Strain

TL;DR

This paper investigates how anisotropic coherency strain influences phase separation in intercalation materials, particularly in Li-ion batteries, using a phase-field model to analyze both linear and nonlinear phase evolution.

Contribution

It introduces a coupled phase-field and elastic stress model that accounts for fully anisotropic coherency strain, including simultaneous expansion and contraction along different axes, a novel aspect for epo.

Findings

Anisotropic strain causes tilted, striped phase boundaries in equilibrium.

Linear stability analysis reveals conditions for spinodal decomposition.

Nonlinear evolution shows complex phase pattern formation.

Abstract

We consider the effects of anisotropic coherency strain (due to lattice mismatch) on phase separation in intercalation materials, motivated by the high-rate Li-ion battery material \fepo. Using a phase-field model coupled to elastic stresses, we analyze spinodal decomposition (linear instability of the homogeneous state) as well as nonlinear evolution of the phase pattern at constant mean filling. We consider fully anisotropic coherency strain and focus on the novel case of simultaneous expansion and contraction along different crystal axis, as in the case of \fepo, which leads to tilted, striped phase boundaries in equilibrium.