On the role of crack electrolyte wetting in the degradation and performance of battery active particles

TL;DR

This study uses a coupled electro-chemo-mechanical model to show that electrolyte wetting in cracked battery particles significantly affects reaction distribution and stress, impacting capacity and degradation predictions.

Contribution

It introduces a detailed coupled model to quantify how electrolyte wetting influences reaction heterogeneity and stress, improving understanding of battery degradation mechanisms.

Findings

Flux amplification at crack tips is about 8x compared to uniform flux assumptions.

Uniform flux models underestimate capacity by 25% at 1C-rate.

Neglecting crack-electrolyte coupling underestimates tensile stresses by 10%.

Abstract

Cathode particle fracture is widely recognised as a major degradation mechanism in lithium-ion batteries, yet cracking also permits electrolyte wetting of newly exposed internal surfaces, modifying interfacial reaction pathways. The mechanistic role of electrolyte wetting in redistributing reactions within cracked particles remains unclear. Here, we isolate this effect through a controlled comparison between (i) a fully coupled electro-chemo-mechanical model resolving lithium concentration, electrostatic potential, and stress fields in both the active material and the electrolyte inside and outside cracks, and (ii) a single-particle chemo-mechanical model employing the conventional uniform flux assumption. The coupled model predicts strong spatial heterogeneity in interfacial reaction rates, with flux amplification approximately 8x relative to the imposed uniform flux at the crack tip. Reaction redistribution, and thus lithium flux, is governed predominantly by local solid-state lithium concentration and stress variations, while electrolyte potential gradients inside cracks remain secondary under the conditions considered. Uniform flux models can underpredict delivered capacity by 25% at 1C-rate; this discrepancy increases at higher rates. They also underestimate tensile stresses throughout the delithiation process by 10%, directly affecting crack driving conditions. These results demonstrate that neglecting crack-electrolyte coupling leads to systematic underestimation of both utilisation limits and fatigue-relevant stress histories.