Disconnected Lithium Metal Damages Solid-State Electrolytes

Solid-state batteries with a lithium-metal anode are energy-storage devices that promise increased energy density and improved safety compared with liquid systems. Despite significant developments, the chemomechanical degradation of solid-state batteries represents a significant challenge to their widespread adoption. Specifically, Li-filled cracks (called "dendrites") and electronically isolated Li inclusions ("dead" Li) are key defects resulting from coupled electrochemical and mechanical degradation during cycling. In this study, we use a symmetrical Li|LLZO|Li cell with a single-crystal electrolyte and demonstrate that an electronically isolated Li-metal inclusion exhibits bipolarity under an external electrical field, which leads to further crack expansion. We suggest that this process of "dead" metal activation accelerates chemomechanical degradation in solid-state batteries with alkali anodes.