X-ray pair distribution function analysis and electrical and electrochemical properties of cerium doped Li5La3Nb2O12 garnet solid-state electrolyte

Abstract

Garnet solid state electrolytes have been considered as potential candidates to enable next generation all solid state batteries (ASSBs). To facilitate the practical application of ASSBs, a high room temperature ionic conductivity and a low interfacial resistance between solid state electrolyte and electrodes are essential. In this work, we report a study of cerium doped Li₅La₃Nb₂O₁₂ through X-ray pair distribution function analysis, impedance spectroscopy and electrochemical testing. The successful cerium incorporation was confirmed by both X-ray diffraction refinement and X-ray pair distribution function analysis, showing the formation of an extensive solid solution. The local bond distances for Ce and Nb on the octahedral site were determined using X-ray pair distribution function analysis, illustrating the longer bond distances around Ce. This Ce doping strategy was shown to give a significant enhancement in conductivity (1.4 × 10⁻⁴ S cm⁻¹ for Li_5.75La₃Nb_1.25Ce_0.75O₁₂, which represents one of the highest conductivities for a garnet with less than 6 Li) as well as a dramatically decreased interfacial resistance (488 Ω cm² for Li_5.75La₃Nb_1.25Ce_0.75O₁₂). In order to demonstrate the potential of this doped system for use in ASSBs, the long term cycling of a Li//garnet//Li symmetric cell over 380 h has been demonstrated.