Molecular design of a metal–organic framework material rich in fluorine as an interface layer for high-performance solid-state Li metal batteries

Unstable electrolyte/electrode interface and uncontrolled Li dendrite growth hinder the large-scale commercial application of Li metal batteries. In this work, an artificial interfacial layer is developed to suppress the dendrite formation and the parasitic reactions between Li metal anode and electrolyte by the rational molecular design of a metal–organic framework material rich in fluorine (UiO-66(F)). The intrinsic nanochannels in UiO-66(F) promote the decomposition of lithium salts and limit the movement of anions. Moreover, the in situ formed LiF inhibits the Li dendrite growth. The composite electrolyte with the UiO-66(F) interfacial layer exhibits a wide electrochemical window (5.13 V vs Li/Li + ), high ionic conductivity (4.9 × 10 -4 S cm −1 ), and ionic transference number (0.51) at room temperature. XPS results demonstrate that the in situ formed solid-electrolyte interface (SEI) is attributed to the active F groups in UiO-66(F). The symmetric cell with the optimized interfacial layer achieves excellent cycling performance over 2200 h at 0.2 mA cm −2 . In addition, the assembled full cell LiFePO 4 ||Li also exhibits a capacity retention rate of 90.71 % after 960 cycles at 0.5 C. Even at higher rate of 2 C, it still exhibits a high discharge capacity of 139.6 mAh g −1 . This molecular design strategy for interfacial layer show great promise for practical applications of Li metal batteries.