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

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 constrains of a dense microstructure. A coupled electro-chemo-mechanical model was implemented to quantify the material properties that cause an 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 when electrode-particle's expansion is lower than 7.5% (typical for most Li-intercalating compounds) and the solid-electrolyte's fracture energy higher than G[subscript c]= 4 J m⁻². Perhaps counter-intuitively, the analyses show that compliant solid electrolytes (with Young's modulus in the order of ESE= 15 GPa) are more prone to micro-cracking. This result, captured by our non-linear kinematics model, contradicts the speculation 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.