Series of PAN/UIO-66-X (X = F, NO2, and NH2) Porous Fibrous Membranes as Functional Separators for Lithium-Metal Batteries

Effective functionalization of traditional polymer separators is still highly required for the development of high-performance lithium-metal batteries. Herein, a series of PAN/UIO-66-X (PU-X, X = F, NO₂, and NH₂) porous fibrous membranes are successfully fabricated as functional separators for lithium-metal batteries. The UIO-66-X metal–organic frameworks (MOF) with high crystallinity and interconnected fibrous networks are densely coated around the polyacrylonitrile (PAN) electrospun fibers. Due to the functional UIO-66-X MOF coating, such PU-X integrated separators exhibit superior electrolyte wettability, higher mechanical strength, and wider electrochemical window compared to the pure PAN separator. In addition, the high porosity and abundant active sites in the UIO-66-X coating enable the anchoring of unstable anions or active species in lithium-metal batteries, thereby promoting the fast and uniform transportation and deposition of lithium ions with an ultrahigh transference number of more than 0.7. As a result, the batteries with the PU-X integrated separators deliver excellent performance and the best variant is the PU-F separator, which can achieve a high capacity of 147.4 mA h g^–1 and also a high capacity retention of 86.2% after 300 cycles at 1 C. Even after 1000 cycles at 3 C, the Coulombic efficiency and capacity retention can reach up to 99.07 and 67.16%, respectively.