Controlling dendrite propagation in solid-state batteries with engineered stress

Metal dendrite penetration is a mode of electrolyte failure that threatens the viability of metal anode based high energy solid-state batteries. Whether dendrites are driven by mechanical failure or electrochemical degradation of solid electrolytes remains an open question. If internal mechanical forces drive failure, superimposing an external compressive load that counters internal stress may mitigate dendrite penetration. Here, we investigate this hypothesis by dynamically applying mechanical loads to growing lithium metal dendrites in Li6.75La3Zr1.75Ta0.25O12 solid electrolytes. Operando microscopy reveals marked deflection in the dendrite growth trajectory at the onset of compressive loading. At loads near 200 MPa, this deflection is sufficient to avert cell failure. Using fracture mechanics, we quantify the impact of stack pressure and in-plane stresses on dendrite trajectory, chart the residual stresses required to prevent short-circuit failure, and propose cell design approaches to achieve such stresses. The model and experiments show that in the materials studied here, dendrite propagation is dictated by fracture of the electrolyte and that electronic conductivity plays a negligible role.