Electro-chemo-mechanical failure of solid-state electrolyte caused from intergranular or transgranular damage propagation in polycrystalline aggregates

Electro-chemo-mechanical failure of solid-state electrolytes (SEs) caused by the internal growth of lithium dendrites significantly impedes the application of solid-state batteries under high applied current density. The grain boundary is usually the key to the mechanical properties of polycrystalline ceramic SEs. Here, strength and width of grain boundary in SEs that are exampled by garnet-type Li ₇La ₃Zr ₂O ₁₂ are evaluated under the deposition of lithium by visualizing the stress field, damage accumulation and crack propagation. The enhancement of grain boundary strength triggers a dramatic increase stress when the ratio of tensile strength between grain boundary and grain (λ) is lower than 0.9. With the variation of λ, three damage processes are revealed as intergranular-damage, inter/transgranular-damage and transgranular-damage, leading to different propagation of cracks and the transformation of intergranular failure to transgranular failure. Furthermore, the width of the grain boundary is found to induce more transgranular-damage with its widening. A critical value of grain boundary width for the formation of displacement is obtained under various strengths, as δ = 21 nm for λ = 0.2, δ = 25 nm for λ = 0.5 and δ = 31 nm for λ = 0.9. The findings in this work indicate the coupling effect of grain boundary width and strength on the failure of SEs, providing an insightful perspective for the future design of solid-state batteries.