Direct Observations of Dendrite-Induced “Subcritical” Cracking in Oxide Solid Electrolytes

Dendrite-induced short circuits threaten the deployment of solid-state batteries with metal anodes. Dendrites grow from the anode due to plating-induced pressure and subsequent fracture of the electrolyte. Whether electrochemical activity within the electrolyte aids that fracture process has remained a topic of debate. For oxide solid-electrolytes, we address this issue by conducting operando photoelastic microscopy to directly observe the stress fields around dendrites under dynamic electrochemical loading. From this data, we measure the thermodynamic driving force for fracture (i.e., the stress intensity factor, a measure of apparent surface energy) as a function of applied potential. These experiments reveal dendrite growth under “subcritical” conditions, meaning that the stress intensity factor during propagation is less than should be expected based on linear elastic fracture theory. We discuss these results in the context of historical subcritical cracking due to corrosive action. Finally, we develop a mechanistic framework to connect the observations here with expected behavior in sandwich-style cell formats.