High Pressure in-Situ X-Ray CT Measurement of Sulfide Solid Electrolyte for All-Solid-State Lithium Ion Battery

Abstract

The sulfide solid electrolyte has a high ionic conductivity and is a candidate for use as the solid electrolyte in lithium ion batteries used for electrical vehicles [1]. A previous study showed that high ionic conductivity is achieved with compression of solid electrolyte powder by suppressing the void between the solid electrolyte particles as the structure of the solid electrolyte has a strong correlation with the ionic conductivity. However, this correlation has not been discussed directly.In this study, the solid electrolyte three dimensional structure is measured with high pressure in-situ X-ray CT measurement and its ionic conductivity measured by EIS to elucidate the correlation between the structure and ionic conductivity. Moreover, three dimensional electromagnetic field numerical simulations based on the Maxwell and Nernst-Prank equations are conducted with the X-ray CT images to build a numerical model of the ionic conduction in a compressed sulfide solid electrolyte. The solid electrolyte used in this experiment is Li6PS5Cl [2].Figure 1 illustrates the X-ray CT images of the sulfide solid electrolyte with various applied pressures. With a low applied pressure of 10.5 MPa (Fig.1 (a)), solid electrolyte particles exist independently, and there are many voids between them. The ionic conductivity with this structure is 0.35 mS/cm. With the increase in applied pressure to 95.0 MPa, the voids between the solid electrolyte particles disappear as shown in Fig.1 (b). This disappearance is owing to the room temperature sintering with creeping of solid electrolyte with high pressure [3]. The ionic conductivity with this structure is 1.15 mS/cm. The three dimensional electromagnetic numerical results for each X-ray CT image is 0.21 mS/cm and 1.16 mS/cm and these numerical results almost agree with the experimental results. In the numerical simulation, contact resistance, inhomogeneity of the ionic conductivity, and anisotropy of the ionic conductivity are not considered and only the distribution of the solid electrolyte and voids are inputted. Therefore, this numerical result suggests that the contact resistance between solid electrolyte particles can be neglected for numerical simulation of sulfide solid electrolytes.AcknowledgementThis study is partially supported by the Japan Keirin Autorace Foundation (JKA).