Structural and Electrochemical Characterization of Thioantimoniate Sodium Solid Electrolyte

In the last couple of years, a major breakthrough has been achieved as several antimony-based sodium sulfide solid electrolytes (SSEs) substituted by aliovalent elements such as W have delivered high ionic conductivities up to 41 mS/cm at 25°C. (Hayashi et al., 2019; Fuchs et al., 2020; Feng et al., 2021) These Na-defective ionic superconductors outperform even the best lithium SEs, such as Li10GeP2S12 (10 mS/cm at 25°C). To date, little is known about the synthesis of this family of materials and the transport properties of these cubic phases defined in the I-43m (no. 217) space group. We have been working on obtaining the Na2.88Sb0.88W0.12S4 variant (hereafter, NSWS) by single step mechanochemical synthesis. Two samples were prepared with different milling conditions: (a) one milled during 10 h at 510 rpm, and (b) one milled during 10 h at 700 rpm. The corresponding synchrotron X-ray diffractograms are displayed in Fig. 1(a), showing a crystalline phase that corresponds to a mixture of the cubic I-43m and the tetragonal P-421c phases. Additional characterisations were carried out by using scanning electron microscope (SEM) to determine the morphology of the crystalline samples. As can be seen in Fig. 1(b), a wide distribution of particle sizes can be noticed with a certain degree of agglomeration. We can also notice two types of particle morphology which can indicate the presence of two different phase, in agreement with the XRD data