Polymorphism of Garnet Solid Electrolytes and Its Implications on Grain Level Chemo-Mechanics

Understanding and mitigating filament formation, short-circuit, and solid electrolyte fracture is a key necessity towards achieving practical SSBs. Herein, we employ a coupled far-fi eld high energy diffraction microscopy -tomography approach for assessing chemo-mechanical behavior for dense, polycrystalline garnet (Li7La3Zr2O12, LLZO) solid electrolytes with grain-level resolution. Tracking the stress response for individual grains through in situ testing, failure onset and short-circuit mechanism is confirmed to be a stochastic, isolated process governed by the presence of local phase heterogenity. Coupling high energy X-ray diffraction and far eld high energy diffraction microscopy measurements, these local regions are proposed to be regions with the presence of a cubic polymorph of LLZO arising potentially from local dopant concentration variation. Interplay of mechanics and transport is evaluated and coupled tomography and FF-HEDM dataset is employed to illustrate the degradation of polycrystalline garnet solid electrolyte. The results showcase pathways for processing high performing SSBs.