An Interfacial Protective Layer of Magnetically Ordered Nanorods in a High-Dielectric Matrix for Dendrite-Free Lithium Metal Batteries

The practical implementation of high-energy-density lithium metal batteries is critically hindered by uncontrolled dendrite growth and the unstable solid electrolyte interphase (SEI) on the highly reactive lithium anode. Herein, we report a dual-function composite separator coating (Fe₃O₄@HDF) fabricated by embedding MOF-derived Fe₃O₄ magnetic nanorods within a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix, wherein an external magnetic field is applied during fabrication to induce an aligned nanostructure. This magnetically engineered architecture operates via a synergistic mechanism: the ordered nanorods create low-tortuosity pathways for rapid Li⁺ transport, while the composite simultaneously promotes the formation of the high-dielectric β-phase in the PVDF-HFP matrix, which homogenizes the local electric field to guide uniform lithium deposition. Consequently, the Fe₃O₄@HDF-protected lithium anode achieves exceptional stability, enabling dendrite-free plating/stripping for over 1000 hours in symmetric cells at 1 mA cm⁻² with a low overpotential of 10 mV. Crucially, when paired with a high-loading NCM811 cathode, the Li||NCM811 full cell delivers excellent cycling stability for 350 cycles at 0.5 C with 77% capacity retention, demonstrating its viability in practical high-energy systems. This work presents a new strategy for multifunctional separator design.