It comes down to stress – mechanical stress to be more precise – especially during potent recharging.
This artist’s rendition shows one probe bending from applied pressure, causing a fracture in the solid electrolyte, which is filling with lithium. On the right, the probe is not pressing against the electrolyte and the lithium plates on the ceramic surface, as desired. Credit: Cube3D A scanning electron microscopy video that shows lithium plating as it takes place on a solid electrolyte. Credit: Xin Xu, Geoff McConohy and Wenfang Shi
As Chueh and team show, even a subtle bend, slight twist, or speck of dust caught between the electrolyte and the lithium anode will cause imperceptible crevices. The new understanding was demonstrated repeatedly, the researchers said. They recorded video of the process using scanning electron microscopes – the very same microscopes that were unable to see the nascent fissures in the pure untested electrolyte.
With their new understanding in hand, Chueh’s team is looking at ways to use these very same mechanical forces intentionally to toughen the material during manufacturing, much like a blacksmith anneals a blade during production. They are also looking at ways to coat the electrolyte surface to prevent cracks or repair them if they emerge.