Several advanced sintering techniques for solid electrolytes include hot pressing, field-assisted sintering, flash sintering, microwave sintering, and spark plasma sintering.
In this process, samples are heated by convection and/or radiation techniques in furnaces. Sintering is a crucial step for crystalline electrolyte materials as it enhances mechanical strength, reduces porosity, and lowers grain boundary resistance, consequently improving ionic conductivity.
This method is a re-visit of traditional fast firing, using carbon foils under resistance heating to rapidly sinter multiple small pellets (∼5 mm diameter), sandwiched between foil layers. Typical process duration is less than 30 s, reaching temperatures of up to 3000 °C.
The cold sintering process involves the first step being the densification stage, where loosely-packed powders are compacted with the assistance of a liquid phase. According to the proposed mechanism, this step includes particle rearrangement, sliding of powders under fluid mechanics, and grain boundary creep.
Liquid-phase sintering is a viable technique to improve the density of sintered electrolytes . Commonly used sintering aids with a low melting point are oxides such as ZnO, MgO, and B 2 O 3 or lithium salts such as Li 2 O, Li 3 PO 4, Li 3 BO 3 , LiBO 2 or LIF [, , ].
Under flash sintering, an electric field is applied across a ceramic sample, using a pair of electrodes, causing rapid Joule heating of the sample. Most ceramics have a negative temperature coefficient of resistivity, as the ceramic heats its resistance decreases resulting in a runaway process of increasing power dissipation unless curtailed .