# Modeling of internal mechanical failure of all-solid-state batteries during electrochemical cycling, and implications for battery design

## TL;DR

This paper presents a quantitative model analyzing the mechanical failure of all-solid-state batteries during cycling, revealing critical material properties and microstructural factors that influence fracture and battery performance.

## Contribution

It introduces the first comprehensive electro-chemo-mechanical model that links microstructural details to fracture behavior in solid electrolytes, challenging previous assumptions about electrolyte compliance.

## Key findings

- Fracture occurs if electrode expansion exceeds 7.5% and fracture energy is below 4 J/m².
- More compliant electrolytes with Young's modulus around 15 GPa are more prone to micro-cracking.
- Mechanical degradation reduces battery power density and accelerates performance decay.

## Abstract

This is the first quantitative analysis of mechanical reliability of all-solid state batteries. Mechanical degradation of the solid electrolyte (SE) is caused by intercalation-induced expansion of the electrode particles, within the constrain of a dense microstructure. A coupled electro-chemo-mechanical model was implemented to quantify the material properties that cause a SE to fracture. The treatment of microstructural details is essential to the understanding of stress-localization phenomena and fracture. A cohesive zone model is employed to simulate the evolution of damage. In the numerical tests, fracture is prevented only if electrode-particle's expansion is lower than 7.5% and the solid-electrolyte's fracture energy higher than $G_c = 4$ J m$^{-2}$. Perhaps counter-intuitively, the analyses show that compliant solid electrolytes (with Young's modulus in the order of E$_{SE} = 15$ GPa) are more prone to micro-cracking. This result, captured by our non-linear kinematics model, contradicts the speculations that sulfide SEs are more suitable for the design of bulk-type batteries than oxide SEs. Mechanical degradation is linked to the battery power-density. Fracture in solid Li-ion conductors represents a barrier for Li transport, and accelerates the decay of rate performance.