Enhancing lithium-ion conductivity in NASICON glass-ceramics by adding yttria

Abstract

We demonstrate that the ionic conductivity of Li_1+xAl_xGe_2−x(PO₄)₃ glass-ceramic electrolytes can be tailored by adding Y₂O₃ to Li₂O–Al₂O₃–GeO₂–P₂O₅ melts. We found that the addition of 5 vol% Y₂O₃ causes noticeable changes in further glass crystallization process as the key parameters (glass crystallization temperature, viscosity and others) are affected. Small-angle neutron scattering data suggest that Y-containing glasses are suddenly crystallized upon heat treatment producing uniform Li_1+xAl_xGe_2−x(PO₄)₃ ceramics. Due to the lower resistance of intergrain interfaces, such samples demonstrate a specific ionic conductivity of 0.5 mS cm⁻¹, which is nearly 5 times higher in comparison to Y-free ceramics, prepared under similar conditions. We speculate that such an effect is caused primarily by better intergrain contact in Y-containing ceramics, along with better ionic transport in the grain bulk as evidenced by ⁷Li NMR.