Local Structural Analysis of Sulfide Polymer Electrolytes Prepared via I₂-Induced Polymerization of Li₃PS₄

To avoid the volume change associated with the electrode active material during charge/discharge in all-solid-state batteries, an effective binder that improves the contact between the solid electrolyte and the electrode active material must be developed. To this aim, the polymerization of the sulfide solid electrolyte Li3PS4 offers a promising route. However, the local structure of the resulting solid electrolyte, i.e., a mixture of LiI crystals and glassy sulfide polymers, needs to be elucidated for further development of sulfide polymers as binders. Herein, we analyze the local structure of the isolated mixture via a differential pair distribution function analysis using X-ray total scattering. The presence of disulfide bonds between PS4 anions is confirmed in the glassy phase. The coordination number of the disulfide bonds is 0.65, and each PS4 tetrahedron is connected to two tetrahedrons to form a polymer chain structure of (−P–S–S−)n bonds containing Li ions. The coordination number of Li ions surrounding PS4 anions in the glassy phase is much smaller than that in the pure Li3PS4 glasses. This polymer may find application as a Li-ion conductive binder in sheet-type all-solid-state batteries having low resistance and high capacity retention.