Mechanical Origin of Lithium Dendrite Penetration in Garnet Solid Electrolyte

Short-circuiting caused by lithium dendrite penetration through solid electrolytes remains a key obstacle to realizing all-solid-state lithium metal batteries. The mechanism by which mechanically-soft lithium dendrites fracture hard ceramic electrolytes remains under debate, due to the challenges of characterizing nanoscale lithium distribution and its microstructure at the dendrite tip. Here, we investigate the fracture process driven by lithium dendrites in garnet electrolytes using multiscale cryogenic electron microscopy and micromechanical fracture models. We directly visualize lithium dendrites fully filling nanoscale crack tips and extending into micrometer-scale cracks. Limited crystal lattice rotation and plasticity in lithium dendrites indicate that the plated lithium generates significant hydrostatic stress, which induces tensile stress in the solid electrolyte and drives both intergranular and transgranular fracture. In contrast, the region ahead of the lithium dendrite tip showed no measurable enrichment of lithium or lithium metal nuclei. Building on the identified mechanical origin of lithium penetration, we introduce geometrically engineered voids into the electrolyte to redirect lithium dendrite growth and mitigate short-circuiting. These findings suggest that grain boundary toughening and defect engineering are effective strategies for designing dendrite-resistant solid electrolytes.