Synchronously modulating the universal diffusion of cations and anions by separator integration: A versatile approach toward safe and high-performance lithium-metal batteries

Despite the great potential of lithium metal batteries (LMBs) for next-generation energy storage systems, the practical application still suffers from safety issues and capacity fading due to irregular ion diffusion from both anode and cathode. Herein, a sandwich separator consisting of PP substrate and two-side coated NH₂-MIL-101 (NM) layers (NM-PP-NM) is designed to integrally modulate the interfacial diffusion of both anions and cations. Ordered micropores of NM endow separator with physical confinement toward cations (Li⁺, Fe²⁺, and Mn²⁺) and anions (polysulfide anions and electrolyte anions), contributing to regulated multi-ion diffusion. Moreover, chemisorptions between NM and ions (polysulfide, Fe²⁺, and Mn²⁺) validated by density functional theory simulations effectively alleviate the undesirable cathode crossover. Meanwhile, amino groups can participate in the formation of solid electrolyte interface and improve interfacial stability. Due to the modulated Li⁺ flux and uniform Li plating/stripping, a desirable lifespan of ∼2600 h with ultralow overpotential for a Li-Li symmetrical cell is achieved by equipping the NM-PP-NM separator. Benefit from the regulated diffusion of both anions and cations, NM-PP-NM exhibits excellent versatility in various LMBs, including lithium-sulfur, Li-LiFePO₄, and Li-LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) battery systems. Both the safety and electrochemical performances of the above LMBs are greatly enhanced, emphasizing the versatility and potential of the developed multifunctional integration strategy for separator modification.