Exploring multi-material design strategies to enhance mechanical performance and maintain ionic conductivity in zirconia-based electrolytes

The growing demand for high-efficiency electrochemical energy conversion and storage systems has increased research in zirconia-based solid oxide electrolytes due to their favorable combination of material properties. In order to increase the structural integrity of the cell, a multi-material design has been recently applied to the ceramic electrolyte aiming to increase its strength through the introduction of in-plane surface compressive residual stresses. However, the corresponding in-plane tensile stresses in the core may decrease the ionic conductivity of the electrolyte. In this work, a multilayer approach will be explored to increase the mechanical strength of the electrolyte while maintaining its functional properties. Two different multi-material electrolyte designs shall be attempted, containing surface layers under in-plane compressive or tensile stresses, seeking either higher strength or enhanced damage tolerance, respectively. The materials of study are 8 mol% yttria-stabilized zirconia (8YSZ) alternated with alumina-toughened zirconia (ATZ) layers of different composition (ranging from 30 vol.% to 50 vol.% alumina). An adapted ball-on-three balls (B3B) test is employed to evaluate the strength distribution of the multi-material designs and compared to their monolithic counterparts. Furthermore, thermal shock experiments with a temperature difference of up to 600°C of multi-material designs with internal ATZ layers qualitatively evaluate the crack resistance behavior. Electrochemical impedance spectroscopy (EIS) is conducted between 600°C to 1000°C to measure the ionic conductivity of all samples. Overall, results highlight a trade-off between mechanical performance and ionic conductivity, offering valuable insight into multi-material design strategies for extending the lifespan of future solid oxide cells through strength enhancement and flaw tolerance.