Operando Visualization of Spatially Heterogeneous Lithium Growth on Ta-Doped LLZO

Spatially uneven lithium (Li) growth in garnet solid electrolytes can accompany local mechanical damage. Here, operando scanning electron microscopy was used to follow Li growth on tantalum-doped lithium lanthanum zirconium oxide (LLZTO) under a localized tungsten-probe contact. Independent measurements on fractured and polished surfaces captured both contact-confined growth and visible extension beyond the initial contact region. On a polished surface, remote filamentary features elongated and branched over tens of micrometers. On a fractured surface, Li growth accompanied progressive opening and displacement of neighboring LLZTO regions. Site-specific scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDX) examined a region after extended growth. The maps showed local Ta and Zr signal variations consistent with compositional nonuniformity. Cryogenic three-dimensional EDX revealed similar signal variations in a separate uncycled region. These elemental observations provide local material context for the growth sequences. Overall, the study documents distinct spatial growth modes and their temporal association with mechanical changes. Local composition is identified as a possible contributing factor alongside evolving contact and surface conditions.