Lithium Thiophosphate Functionalized Zirconium MOFs for Li-S Batteries with Enhanced Rate Capabilities

Zirconium metal-organic frameworks (Zr-MOFs) are renowned for their extraordinary stability and versatile chemical tunability. Several Zr-MOFs demonstrate a tolerance for missing linker defects, which create "open sites" that can be used to bind guest molecules on the node cluster. Herein, we strategically utilize these sites to stabilize reactive lithium thiophosphate (Li₃PS₄) within the porous framework for targeted application in lithium-sulfur (Li-S) batteries. Successful functionalization of the Zr-MOF with PS₄^3- is confirmed by an array of techniques including NMR, XPS, and Raman spectroscopy, X-ray pair distribution function analysis, and various elemental analyses. During electrochemical cycling, we find that even a low incorporation extent of lithium thiophosphate in Zr-MOFs improves sulfur utilization and polysulfide encapsulation to deliver a sustainably high capacity over prolonged cycling. The functionalized MOF additives also prevent cell damage under abusive cycling conditions and recover high capacities when the cell is returned to lower charge/discharge rates, imperative for future energy storage devices. Our unique approach marries the promising chemical attributes of the purely inorganic Li₃PS₄ with the stability and high surface area of MOFs, creating a Li-S cathode architecture with a performance beyond the sum of its component parts. More broadly, this novel functionalization strategy opens new avenues for facile syntheses of "designer materials" where chemical components from discrete disciplines can be united and tailored for specific applications.