A continuum electro-chemo-mechanical gradient theory coupled with damage: Application to Li-metal filament growth in all-solid-state batteries

Abstract

We formulate a continuum electro-chemo-mechanical gradient theory which couples electrochemical reactions with mechanical deformation and damage in solids. The framework models species transport across the host due to diffusion/migration and concurrent electrochemical reaction at damaged sites within the host, where ionic species are reduced to form a new compound. The theory is fully-coupled with electrodeposition impacting mechanical deformation, stress generation and damage of the host. Conversely, electrodeposition kinetics are affected by mechanical stresses via a thermodynamically-consistent, physically motivated driving force that distinguishes chemical, electrical and mechanical contributions. The theory also captures the interplay between growth-induced fracture of the host and deposition of a new material inside cracks by tracking damage and extent of electrodeposition via separate phase-field variables. While the framework is general in nature, we specialize it to model a Li-metal-Li7La3Zr2O12 (LLZO) system and demonstrate the ability to capture both intergranular and transgranular crack and Li-filament growth mechanisms, which have been experimentally observed. In addition, we elucidate how mechanical confinement in solid-state batteries plays a key role in the resulting crack/electrodeposition morphology. In modeling this system, we demonstrate the manner in which our framework can elucidate the critical coupling between mechanics and electrodeposition kinetics and its role in dictating Li-filament growth. Beyond this, the framework should serve useful in a number of engineering problems of relevance in which electrochemical reactions take place within a damage zone, depositing new material at these sites.

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