Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics

Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. Here, we employ a coupled far-field high-energy diffraction microscopy and tomography approach for assessing the chemo-mechanical behaviour for dense, polycrystalline garnet (Li7La3Zr2O12) solid electrolytes with grain-level resolution. In situ monitoring of grain-level stress responses reveals that the failure mechanism is stochastic and affected by local microstructural heterogeneity. Coupling high-energy X-ray diffraction and far-field high-energy diffraction microscopy measurements reveals the presence of phase heterogeneity that can alter local chemo-mechanics within the bulk solid electrolyte. These local regions are proposed to be regions with the presence of a cubic polymorph of LLZO, potentially arising from local dopant concentration variation. The coupled tomography and FF-HEDM experiments are combined with transport and mechanics modelling to illustrate the degradation of polycrystalline garnet solid electrolytes. The results showcase the pathways for processing high-performing solid-state batteries. Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. The effect of polymorphism on the grain-level chemo-mechanical behaviour of dense and polycrystalline garnet solid electrolytes is now investigated.

Automated summary

Understanding and mitigating issues such as filament formation, short-circuiting, and solid electrolyte fracture is crucial for the development of advanced all-solid-state batteries. In this study, a combined far-field high-energy diffraction microscopy and tomography approach was used to analyze the chemo-mechanical behavior of dense, polycrystalline garnet solid electrolytes at the grain-level resolution. The results revealed that the failure mechanism is stochastic and influenced by local microstructural heterogeneity. The presence of phase heterogeneity, potentially caused by local dopant concentration variation, was observed to affect the local chemo-mechanics within the bulk solid electrolyte. These findings provide insights into the degradation process of polycrystalline garnet solid electrolytes and offer pathways for processing high-performing solid-state batteries.