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: Li6.19Al0.27La3Zr2O12 (garnet) [LLZO], Li0.33La0.57TiO3 (perovskite) [LLTO], and Li1.3Al0.3Ti1.7(PO4)(3) (NaSICON) [LATP]. The experimental Young's modulus value for (1) LLTO is similar to 200 GPa, (2) LLZO is similar to 150 GPa, and (3) for LATP similar to 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.