Physiochemical Characterization and Electrochemical Impedance Spectroscopic Analysis of NASICON‐Based M₁₊xAlxTi₂−x(PO₄)₃ Electrolytes for Solid‐State Batteries

The suitability of NASICON‐based M 1+ x Al x Ti 2− x (PO 4 ) 3 , where M = Li, Na, and x = 0.5 solid‐state electrolytes was investigated. Electrolytes were synthesized using high‐temperature annealing of NH 4 H 2 PO 4 , TiO 2 , and Al 2 O 3 compounds followed by ball milling. Synthesized samples displayed a single crystalline phase like NASICON‐type material with space group . X‐ray photoelectron spectroscopy and Raman spectrum confirmed the absence of impurities in samples, establishing elemental consistency. Microstructure analysis was performed using field emission scanning electron microscopy; samples displayed a granular surface with agglomeration of these grains in a radius of a few micrometers. Electrochemical impedance spectroscopy study showed that the conductivity of samples increased with increasing working temperature, and the highest conductivity values for Li 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 and Na 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 at 150°C were found to be 3.5 × 10 −4 and 5.3 × 10 −4 Scm −1 , respectively. Findings reinforce the suitability of these electrolytes, offering a basis for future work in solid batteries in general and for lithium‐ion and sodium‐ion batteries in particular.