Size-dependent phase morphologies in LiFePO4 battery particles

TL;DR

This paper investigates how particle size influences phase morphologies in LiFePO4 battery materials, using phase-field modeling to explain experimental observations and predict various non-equilibrium patterns.

Contribution

It introduces a depth-averaged phase-field model that explains size-dependent phase patterns and predicts complex morphologies in LiFePO4 particles.

Findings

Elastic analysis predicts morphological transition based on particle size.

Simulation shows size-dependent spinodal points affect phase stability.

Rich variety of non-equilibrium patterns influenced by electro-autocatalytic effects.

Abstract

Lithium iron phosphate (LiFePO$_4$) is the prototypical two-phase battery material, whose complex patterns of lithium ion intercalation provide a testing ground for theories of electrochemical thermodynamics. Using a depth-averaged (a-b plane) phase-field model of coherent phase separation driven by Faradaic reactions, we reconcile conflicting experimental observations of diamond-like phase patterns in micron-sized platelets and surface-controlled patterns in nanoparticles. Elastic analysis predicts this morphological transition for particles whose a-axis dimension exceeds the bulk elastic stripe period. We also simulate a rich variety of non-equilibrium patterns, influenced by size-dependent spinodal points and electro-autocatalytic control of thermodynamic stability.