Lithium-conducting Solid Electrolytes Synthesized by the Sol-Gel Method in the System Li7La3Zr2O12-Li5La3Nb2O12

Abstract

Solid electrolytes Li7−xLa3Zr2−xNbxO12 (x = 0.0–2.0) were synthesized by the sol-gel method, with Nb2O5 used as one of the starting compounds. The suggested synthesis procedure made it possible to lower the annealing temperature and shorten the annealing duration as compared with the solid-phase synthesis method, from 1200°C during 36 h to 1150°C during 1 h. The influence exerted by the doping of the Li7La3Zr2O12 compound in the Zr sublattice with niobium (Nb5+) on its crystal structure, morphology, and electrical conductivity. It was found that the compounds obtained with x > 0.1 are single-phase and have the Ia−3d cubic structure. The scanning electron microscopy was used to examine the morphology and the grain size of the resulting solid electrolytes. The average grain size of the ceramic samples was found to be 1–4 µm. The resistivity of the solid electrolytes Li7−xLa3Zr2−xNbxO12 (x = 0.0–2.0) was measured by the method of electrochemical impedance. It was found that Li6.75La3Zr1.75Nb0.25O12 has the highest total lithium-ion conductivity at 25°C: 4.0 × 10−5 S cm−1. It was shown that the sol-gel method is promising and can be used to obtain solid electrolytes based on Li7La3Zr2O12 doped with Nb5+ ions.