Mechanical behavior of Li-ion-conducting crystalline oxide-based solid electrolytes: a brief review

Li-ion-conducting solid electrolytes are receiving considerable attention for use in advanced batteries. These electrolytes would enable use of a Li metal anode, allowing for batteries with higher energy densities and enhanced safety compared to current Li-ion systems. One important aspect of these electrolytes that has been overlooked is their mechanical properties. Mechanical properties will play a large role in the processing, assembly, and operation of battery cells. Hence, this paper reviews the elastic, plastic, and fracture properties of crystalline oxide-based Li-ion solid electrolytes for three different crystal structures: Li_6.19Al_0.27La₃Zr₂O₁₂ (garnet) LLZO], Li_0.33La_0.57TiO₃ (perovskite) LLTO], and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (NaSICON) LATP]. The experimental Young’s modulus value for (1) LLTO is ~?200 GPa, (2) LLZO is ~?150 GPa, and (3) for LATP ~?115 GPa. The experimental values are in good agreement with density functional theory predictions. The fracture toughness value for all three of LLTO, LLZO, and LATP is approximately 1 MPa m^?2. This low value is expected since, they all exhibit at least some degree of covalent bonding, which limits dislocation mobility leading to brittle behavior.