Evaluation of Elastic Properties in Solid Ionics Materials for All-Solid-State Electrochemical Devices Based on Ultrasonic Method

Abstract

To clarify the fundamental issues in the elastic moduli of all-solid-state electrochemical devices such as all-solid-state lithium ion batteries and solid oxide fuel cells, the elastic moduli of the component solid-state-ionics materials: 8 mol% yttria stabilized zirconia (8YSZ) and the composites of lithium cobaltite (LCO) and lithium borate (LBO) were evaluated using the ultrasonic method. For 8YSZ porous materials, variations of up to 10% between the reported Young's modulus were investigated, and it was suggested that the variation was not due to the influence of the measurement method or porosity, but originated from the elastic properties of the sample. In addition, the porosity dependence of Young's modulus in 8YSZ porous materials was evaluated and compared with reported models, and a model applicable to porous materials fabricated by solid-phase sintering was obtained. For LCO-LBO composites, the model obtained based on the 8YSZ porous materials was examined for applicability. The Young's modulus of the composites showed similar porosity dependence to the model based on that of 8YSZ, which was more consistent with the model calculated based on the microstructure consisting of solid spheres. Because the melting point of LBO was close to the sintering temperature, and it was considered to be half melted during sintering, the microstructure of the LCO-LBO composites was likely to be different from that prepared by the solid-phase sintering method. Therefore, the difference in microstructure was suggested to have affected the difference in porosity dependence. From these results, it was confirmed that it was necessary to consider not only the porosity but also the microstructure characteristics to correctly evaluate the elastic modulus of porous materials in the field of solid-state electrochemical devices.