Sintering of a sodium-based NASICON electrolyte: A comparative study between cold, field assisted and conventional sintering methods

Scandium-substituted NASICON (Na3.4Sc0.4Zr1.6Si2PO12) is a promising electrolyte material for sodium-ion solid state batteries, with the highest ionic conductivity reported to date for a NASICON material. Low-temperature densification and control of microstructure are important factors to enable the low-cost manufacturing of such new battery type. Non-conventional sintering techniques such as Field Assisted Sintering Technology/Spark Plasma Sintering (FAST/SPS) and Cold Sintering are therefore investigated and compared to conventional free sintering. FAST/SPS enables to get rapidly dense samples (99% TD) at lower temperatures than the ones required by conventional sintering routes and with similar electrical properties. Cold sintering experiments, involving the addition of aqueous solutions as sintering aids and high mechanical pressure, enable a moderate densification, but at temperatures as low as 250 degrees C. Further heat treatments still below the conventional sintering temperature increased the achieved density and ionic conductivity.