First Principles Investigation of Grain Boundary Effects in Perovskite-Type Lithium Lanthanum Titanate Solid Electrolyte

Lithium lanthanum titanate (LLTO) is considered a particularly promising candidate for use as an electrolyte in all-solid-state lithium ion batteries due its good electrochemical stability and high ionic conductivity. However, measured values for the ionic conductivity of LLTO fall far below theoretical predictions, an incongruity which has been attributed to the presence of grain boundaries. Furthermore, recent experimental work has shown that lithium dendrite growth occurs along the grain boundaries in LLTO. While experimental studies have been able to reveal the detailed microstructure of polycrystalline LLTO, but little effort has been made to identify the fundamental mechanisms at work within the grain boundaries which lead to to suppressed ionic conductivity and Li dendrite growth. Using ab-initio calculations, we examine the electronic character of LLTO grain boundaries and investigate the impact of the defect states on ion transport and dendrite formation. Based on a fundamental understanding of the atomic and electronic character of LLTO grain boundaries, material design approaches are proposed to mitigate the impact of grain boundary behavior and improve the viability of LLTO as a practical solid electrolyte. This work was supported by the International Energy Joint R&D Program (No. 20168510011350) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Knowledge Economy, Korean government. This work is also supported by the L&F Co.’s World Class 300 Project of the Korea Institute of Advancement of Technology (KIAT) funded by the Ministry of Trade, industry and Energy (No.S2483103).