Conductivity, microstructure and mechanical properties of tape-cast LATP with LiF and SiO2 additives

LATP sheets with LiF and SiO2 addition prepared by tape cast as electrolytes for solid-state batteries were characterized regarding conductivity, microstructure and mechanical properties aiming toward an optimized composition. The use of additives permitted a reduction of the sintering temperature. Rietveld analyses of the samples with additives revealed a phase mixture of NaSICON modifications crystallizing with rhombohedral and orthorhombic symmetry as a superstructure with space group Pbca. It seems that LiF acts as a sintering additive but also as a mineralizer for the superstructure of LATP. As general trend, higher LiF to SiO2 ratios led to lower porosities and higher values of elastic modulus and hardness determined by indentation testing, but the presence of the orthorhombic LATP leads to a decrease in the ionic conductivity. Micro-pillar testing was used to assess the crack growth behavior revealing weak grain boundaries.