Synergistic Fe-N dual sites of amino-functionalized MIL-101(Fe) modified polypropylene separators enable high-performance lithium metal batteries

A well-designed Fe-N dual sites amino-functionalized (MIL-101(Fe)-NH 2 ) separator is fabricated. • The unsaturated Fe sites in the MOF act as strong anionphilic modifiers to adsorb PF 6 − . • The polar -NH 2 groups act as Lewis's base sites to enhance electrolyte wettability. • The synergistic Fe-N sites induce the formation of a stable solid electrolyte interphase. • This separator can regulate lithium deposition and enable high-performance lithium metal batteries. Lithium-based batteries utilizing metallic lithium anodes have attracted widespread research interest due to their exceptional theoretical energy density. However, the growth of dendritic lithium structures, unstable solid electrolyte interphase (SEI) and associated safety concerns pose substantial obstacles to their commercial application. Traditional polypropylene (PP) separators suffer from poor electrolyte affinity and electrochemical inertness, causing heterogeneous Li + distribution and severe interfacial polarization. Herein, an amino-functionalized MIL-101(Fe)-modified PP separator is successfully developed to regulate Li deposition through the synergistic effects of Fe-N dual active sites. The unsaturated Fe sites in the MOF act as strong anionphilic modifiers to adsorb PF 6 − and suppress anion migration; the polar -NH 2 groups act as Lewis's base sites to enhance electrolyte wettability and accelerate ion transport. These synergistic Fe-N sites induce the in-situ formation of a stable LiF/Li 3 N-rich and flexible inorganic-organic hybrid SEI, preventing the penetration of dendritic lithium. Electrochemical testing reveals that the Li|Li symmetric cells achieve more than 650 h of uniform lithium deposition and also stable cycling at elevated temperatures. Furthermore, the LiFePO 4 |Li cells and the LiFe 0.5 Mn 0.5 PO 4 |Li cells employing this modified separator demonstrate superior cycling stability and enhanced rate capability. Modifying separators with functionalized metal-organic frameworks (MOFs) presents a plausible strategy to improve the performance of electrochemical batteries, contributing to an in-depth discussion of the application of MOFs in lithium battery technology. Amino-functionalized separators (PP@MIL-101-NH 2 ) are successfully designed to regulate ion transport for high-performance lithium metal batteries. The unsaturated Fe sites in the MOF act as strong anionphilic modifiers to adsorb PF 6 − ; the polar -NH 2 groups act as Lewis's base sites to enhance electrolyte wettability. Synergistic Fe-N sites induce the formation of a stable LiF/Li 3 N-rich solid electrolyte interphase, preventing the penetration of dendritic lithium. Download: Download high-res image (365KB) Download: Download full-size image