An investigation on strength distribution, subcritical crack growth and lifetime of the lithium-ion conductor Li7La3Zr2O12

Due to the good chemical stability regarding lithium and cathode materials under high voltage, Li₇La₃Zr₂O₁₂ (LLZO) is considered as a promising electrolyte in all-solid-state Li-ion batteries. However, to enable stable long-term operation, knowledge of the mechanical boundary conditions is required. Since mechanical properties of the components and cells depend on the microstructure, the micro- and macro-mechanical properties of LLZO were investigated systemically via indentation tests and ring-on-ring bending (ROR) tests. Hence, fracture stress, elastic modulus, hardness and indentation fracture toughness of the material were characterized under different applied loads. Additionally, room-temperature subcritical crack growth effects were studied on the basis of loading rate-dependent ROR test derived data in order to assess potential reliability issues of LLZO components under application-relevant conditions. A strength–probability–lifetime plot is derived on the basis of these fracture stress data. Complementary optical and electron microscopic investigations were carried out. The Weibull modulus of LLZO is 6, and the stress should not exceed 21 MPa for a lifetime of 3 years to warrant a failure probability of 1%.