Atomistic Origin of Li-Ion Conductivity Reduction at (Li<sub>3<i>x</i></sub>La<sub>2/3–<i>x</i></sub>)TiO<sub>3</sub> Grain Boundary
Shun Sasano, Ryo Ishikawa, Gabriel Sánchez‐Santolino, Hiromichi Ohta, Naoya Shibata, Yuichi Ikuhara
Abstract
Lithium lanthanum titanate (LLTO) is one of the excellent candidates for an electrolyte in the all-solid-state Li-ion battery, owing to the high Li-ion conductivity in the bulk. However, the Li-ion conductivity at the grain boundary (GB) is largely reduced, and it is therefore important to reveal the origin of Li-ion conductivity reduction at the GB. Here, by using atomic-resolution scanning transmission electron microscopy combined with atomic force microscopy, we investigate the charge states, Li-ion conductivities, atomic and electronic structures at the LLTO Σ5 and Σ13 GBs. Although the Σ5 GB has no significant influence on Li-ion conductivity, the Σ13 GB shows the evident reduction of Li-ion conductivity. We further elucidate that the Σ13 GB is positively charged by the formation of oxygen vacancies at the GB. Such a positive charge would form the Li-ion depletion layers adjacent to the GB, which causes the significant reduction of Li-ion conductivity.