Nanoindentation: mechanical characterization of LLZO was conducted using an in-situ SEM nanoindenter (NanoFlip, KLA) to protect the sample from air contamination during testing. The nanoindentation was performed at a constant strain rate of 0.2/s up to 50 mN using a cube corner tip. Fracture force was measured based on the first "pop-in" event that is greater than 10 nm in the load-displacement curve.