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 6.19 Al 0.27 La 3 Zr 2 O 12 (garnet) [LLZO], Li 0.33 La 0.57 TiO 3 (perovskite) [LLTO], and Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 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.