Oxygen-Substitution Effects on the Properties of Argyrodite-Type Sulfide Solid Electrolytes (Li_5.5PS_4.5−_xBr_1.5O_x, 0 ≦ x ≦ 0.5) (Supporting Information)

<div>Li-deficient argyrodite-type Li conductors are promising solid electrolytes for all-solid-state batteries because of their high ionic conductivity, favorable mechanical properties, and low synthesis cost. However, challenges such as incompatibility at the electrode/electrolyte interface must be addressed. In this study, Li-deficient argyrodite-type Li_5.5PS_4.5−<i>_x</i>Br_1.5O<i>_x</i> (0 ≦ <i>x</i> ≦ 0.5) was synthesized by oxygen substitution and its crystal structure and electrochemical properties were investigated. Oxygen is soluble at specific crystallographic sites (16<i>e</i>), with substitution increasing systematically as the value of <i>x</i> in Li_5.5PS_4.5−<i>_x</i>Br_1.5O<i>_x</i> increases. Furthermore, it was found that Li_5.5PS_4.5−<i>_x</i>Br_1.5O<i>_x</i> (<i>x</i> = 0.1) showed relatively high ionic conductivity and improved compatibility with the positive electrode. The cells incorporating Li_5.5PS_4.5−<i>_x</i>Br_1.5O<i>_x</i> (<i>x</i> = 0.1) in the cathode composite demonstrate excellent cycle stability, retaining 71.5 % of their capacity after 100 cycles at a 0.1C-rate. These findings clarify the effects and mechanisms of oxygen substitution in argyrodite-type Li_5.5PS_4.5Br_1.5 and provide a strategy for advancing the practical application of all-solid-state batteries.</div>