Influence of Biaxial Stress on Lithium Dendrite Nucleation and Growth in Solid Electrolytes

Abstract

Short circuits caused by lithium dendrite penetration remain a critical challenge in all solid-state batteries. The influence of mechanical boundary conditions on dendrite nucleation and propagation remains an important area of interest, with significant implications for failure mitigation and battery performance. Here we present an experimental study using direct optical visualization to observe how dendrites nucleate and propagate in a solid electrolyte (LLZTO) under externally applied in-plane equi-biaxial stress. Our setup uses nearly square, plate-shaped electrolyte samples with two lithium electrodes on the same face, which creates mainly in-plane lithium flux parallel to the plate surfaces while equi-biaxial stress is applied during electrochemical cycling. The results demonstrate that in-plane equi-biaxial tension favors a plane-normal dendrite-growth mode, whereas in-plane equi-biaxial compression promotes a planar dendrite-growth mode. Regarding nucleation, over the investigated stress range of −50 to +10 MPa, both compressive and tensile stresses reduce the threshold current density (TCD), somewhat counterintuitively. The observed stress-dependent dendrite mode selection can be interpreted in terms of two competing mechanisms: modification of the crack-tip driving force due to the stress state and the tendency of the dendrite to deflect toward the free surface depending on the sign of applied stress. Together, the stress-controlled dendrite mode selection and the stress vs. TCD map reveal insights into how in-plane stress influences dendrite nucleation and propagation, providing mechanistic guidance for rational design of more stable solid-state electrolytes.