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

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• All-solid-state batteries (ASSBs) offer enhanced safety and energy density.
• Filament formation, short-circuiting, and electrolyte fracture are critical failure modes in ASSBs.
• Garnet-type solid electrolytes, such as Li7La3Zr2O12 (LLZO), are promising candidates for ASSBs.

Purpose of the Study:

• To investigate the chemo-mechanical behavior of polycrystalline garnet solid electrolytes at the grain level.
• To understand the failure mechanisms, including filament formation and fracture, in LLZO electrolytes.
• To identify microstructural features that influence the degradation of solid electrolytes.

Main Methods:

• Utilized a coupled far-field high-energy diffraction microscopy (FF-HEDM) and tomography approach.
• Performed in situ monitoring of grain-level stress responses within the solid electrolyte.
• Combined experimental data with transport and mechanics modeling.

Main Results:

• Identified stochastic failure mechanisms influenced by local microstructural heterogeneity.
• Revealed phase heterogeneity, potentially involving the cubic polymorph of LLZO, affecting local chemo-mechanics.
• Demonstrated how microstructural variations contribute to the degradation of polycrystalline garnet solid electrolytes.

Conclusions:

• Microstructural and phase heterogeneity are key factors in the failure of garnet solid electrolytes.
• Understanding these heterogeneities is crucial for designing and processing high-performing ASSBs.
• The study provides insights into processing strategies for robust solid-state battery electrolytes.