  All-solid-state lithium batteries promise significant improvements in energy
density and safety over traditional liquid electrolyte batteries. The Al-doped
AlxLi7-3xLa3Zr2O12 (LLZO) solid-state electrolyte shows excellent potential
given its high ionic conductivity and good thermal, chemical, and
electrochemical stability. Nevertheless, further improvements on LLZOs
electrochemical and mechanical properties call for an incisive understanding of
its local microstructure. Here, we employ Bragg Coherent Diffractive Imaging to
investigate the atomic displacements inside single grains of LLZO with various
Al-doping concentrations, resulting in cubic, tetragonal, and cubic-tetragonal
mixed structures. We observe coexisting domains of different crystallographic
orientations in the tetragonal structure. We further show that Al doping leads
to crystal defects such as dislocations and phase boundary in the mixed- and
cubic-phase grain. This study addresses the effect of Al-doping on the
nanoscale structure within individual grains of LLZO, which is informative for
the future development of solid-state batteries.
