Surface Spallation Cracking and Mechanical Property Changes of Al-Substituted LLZO Induced by Cell Cycling

Abstract

Al-substituted lithium lanthanum zirconium oxide (LLZO) is a promising ceramic solid electrolyte for use in all-solid-state lithium metal batteries. In this work, Al-substituted LLZO is cycled within a coin cell environment and near-surface crack phenomena are investigated. A series of through-depth focused ion beam-scanning electron microscopy images reveals a propensity for in-plane, near surface cracks that relieve as spallation cracks or through-plane cracks. A significant reduction in Young’s modulus accompanies near-surface cracking in Al-substituted LLZO cycled up to 5 mA/cm2, most notably in regions adjacent to lithium concentration sites. Three-point bending tests confirm the increased presence of critical surface flaws in cycled vs. uncycled LLZO. The results indicate the importance of quantifying ceramic solid electrolyte mechanical degradation occurring with cycling.

Keywords: Ceramics, lithium-ion batteries, nanoindentation, focused ion beam