LAUSR

Dendrite formation and growth remains a major obstacle toward high‐performance all solid‐state batteries using Li metal anodes. The ceramic Li(1+x)Al(x)Ti(2−x)(PO4)3 (LATP) solid‐state electrolyte shows a higher than expected stability against electrochemical decomposition despite a bulk electronic conductivity that exceeds a recently postulated threshold for dendrite‐free operation. Here, transmission electron microscopy, atom probe tomography, and first‐principles based simulations are combined to establish atomistic structural models of glass‐amorphous LATP grain boundaries. These models reveal a nanometer‐thin complexion layer that encapsulates the crystalline grains. The distinct composition of this complexion constitutes a sizable electronic impedance. Rather than fulfilling macroscopic bulk measures of ionic and electronic conduction, LATP might thus gain the capability to suppress dendrite nucleation by sufficient local separation of charge carriers at the nanoscale.