Enhancing lithium-ion conductivity in NASICON glass-ceramics by adding yttriaElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ce01910f

We demonstrate that the ionic conductivity of Li 1+ x Al x Ge 2− x (PO 4 ) 3 glass-ceramic electrolytes can be tailored by adding Y 2 O 3 to Li 2 O-Al 2 O 3 -GeO 2 -P 2 O 5 melts. We found that the addition of 5 vol% Y 2 O 3 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+ x Al x Ge 2− x (PO 4 ) 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 7 Li NMR. The lithium conductivity of NASICON glass-ceramic electrolytes can be increased 5 times just by using additives, which change the glass crystallization patterns.