Modeling Finite Deformations in Alloying Electrodes -- A Closer Look at Cracks and Pores During Phase Transformation

TL;DR

This paper presents a continuum modeling approach to understand and mitigate crack formation in nanoporous alloying electrodes during phase transformations, aiming to improve electrode durability.

Contribution

It introduces a coupled diffusion-mechanics framework and a micromechanical model to analyze stress localization and crack propagation in nanoporous electrodes.

Findings

Nanoporous geometries reduce fracture risk during large volume changes.

Diffusion and reaction kinetics influence phase boundary shapes and crack paths.

Engineered electrode architectures can effectively relieve internal stresses.

Abstract

Nanostructured electrodes with voids or interconnected pores accommodate large volume changes, shorten ion diffusion pathways, and enhance the structural reversibility of alloying electrodes. While these nanoporous features improve the performance of architected electrodes over bulk electrodes, they also act as geometric irregularities that localize and concentrate internal stresses. In this work, we investigate the hierarchical interplay between phase boundaries and nanoporous features at the microstructural scale and their collective role in mitigating chemo-mechanical failure at the engineering scale. Using Sb$\to$Li$_2$Sb$\to$Li$_3$Sb as a model system, we develop a continuum framework coupling lithium diffusion and reaction kinetics with the finite deformation of alloying electrodes. We analytically show that large volume changes in the Sb$\rightarrow$Li$_2$Sb transformation induce fracture, which nanoporous geometries can mitigate. Building on this, we develop a micromechanical model using a hyper-elastic neo-Hookean material law to predict the deformations accompanying the Li$_2$Sb$\to$Li$_3$Sb transformation. Our results reveal how diffusion and reaction kinetics shape phase boundary morphology, identify crack geometries likely to propagate, and show how carefully architected electrodes relieve stresses. These findings highlight critical design principles to optimize electrode lifespan and demonstrate a potential application of our continuum model as an electrode design tool.