Mechanical properties of three‐dimensional trilayered Li–garnet electrolyte for high‐rate cycling in solid‐state batteries

Abstract Utilizing tape casting–laminating–sintering technique, we developed a three‐dimensional (3D) porous–dense–porous trilayered Li–garnet framework that enables symmetric cycling lithium metal under high current densities for long time (∼3–10 mA/cm 2 for over ∼500 h). To address the reasons that such 3D Li–garnet framework can withhold high current density and long‐term cycling, both experiments (nanoindentation and bending) and simulations (finite element analysis [FEA]) regarding mechanical properties on such 3D framework were employed. The results indicate that (1) the dense layer has high and uniform elastic modulus and hardness so can efficiently prevent lithium penetration and dendrites growth; (2) the porous layer, including the grains and the necking regions, has high nanomechanical properties to withhold the lithium penetration stress; (3) the spherical pores in the porous layer can withhold higher lithium penetration forces/stress compared with rectangular/regular pores based on FEA. The flexural strength of the whole structure was also characterized using the three‐point bending method to demonstrate the high strength (∼30.8–42.1 MPa) of the 3D framework. A rule‐of‐mixtures model was developed, which can be used to estimate the flexural strength of the trilayered framework based on the microstructures. Correlations between the mechanical properties and the high‐rate cycling are further discussed.