Suppressing argyrodite oxidation by tuning the host structure for high areal capacity all-solid-state lithium-sulfur batteries

Sulfide-based solid catholytes such as argyrodite (Li₆PS₅Cl) are promising materials for high-performance solid-state sulfur cells that operate on the reversible conversion of S ↔ Li₂S. However, the electrochemical decomposition of argyrodite above 2.5 V vs Li⁺/Li causes its progressive degradation in the operating window of the cell, because the free S^2- ions in Li₆PS₅Cl are oxidized to sulfur at a similar potential as Li₂S. Here we demonstrate that – in addition to regulating the local electronic contact - creating a strong interaction between the Li-ions in argyrodite and the sulfur host synergistically suppresses oxidation of the argyrodite by inhibiting the first step in the pathway. A carbon nitride/N-doped graphene host serves as proof-of-concept to demonstrate this effect. Additionally, its moderate electron transport easily supports operation of all-solid-state lithium-sulfur batteries but constrains electron mobility at the interface with argyrodite. As a consequence, all-solid-state lithium-sulfur batteries utilizing this host material deliver superior rate capability and stable long-term cycling compared to non-polar conductive carbon materials. An areal capacity of 2 mAh cm^-2 was achieved over 230 cycles at room temperature, while a high capacity of 11.3 mAh cm^-2 was obtained with 90% retention at elevated temperature (60 °C). The newly presented descriptors in this work enrich the understanding of solid electrolyte redox activities and guide the interface and material design in all-solid-state lithium-sulfur batteries.