Atomistic Origin of Li-Ion Conductivity Reduction at (Li3x La2/3–x )TiO3 Grain Boundary

• Published in: Nano letters 2021-07, Vol.21 (14), p.6282-6288
• Main Authors: Sasano, Shun, Ishikawa, Ryo, Sánchez-Santolino, Gabriel, Ohta, Hiromichi, Shibata, Naoya, Ikuhara, Yuichi
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.1c02174

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.