Mechanisms of transverse bowl-shaped crack in all solid-state batteries

Abstract

The initiation and growth of Li dendrites pose significant challenges to the commercialization of all-solid-state batteries (ASSBs). Dendrite initiation begins with spallation with subsurface pore filling and subsequent bowl-shaped crack propagation toward the Li anode/solid electrolyte (SE) interface. In this study, we investigate the mechanism of transverse bowl-shaped crack initiation and propagation associated with Li dendrite initiation, as dendrite growth is inevitable once initiated. We propose a mechano-electrochemical coupling theoretical model to analyze the stress field around a subsurface pore during Li filling, treating the continuous Li deposition at the pore/SE interface as eigenstrain. Stress concentration at the pore edge, which drives crack initiation when exceeding the local fracture strength, can be alleviated by applying stack pressure or utilizing an SE with a low pore aspect ratio, a large pore depth, high electronic resistance, and low area-specific resistances at electrode/SE interface. Furthermore, bowl-shaped crack propagation is simulated by extended finite element method (XFEM) following the maximum principal stress criterion. The attraction from Li anode/SE interface drives the crack to deflect into a bowl-shaped morphology, which can be suppressed by applying lateral pressure. These findings elucidate the underlying mechanisms of bowl-shaped crack formation related to Li dendrite initiation and provide critical insights for mitigating dendrite-induced degradation in ASSBs.