A thermomechanically stable nanofiber separatorwith multiscale MOF networks towards high-efficiency ion transport+

Associate Professor Zhao Huijuan from Qingdao University & Professor Li Lin from Beijing Normal University: A Thermodynamically Stable Nanofiber Separator with Multiscale MOF Networks for High-Efficiency Ion Transport

The pursuit of lithium metal batteries (LMBs) with high energy density and safety is crucial for developing next-generation advanced energy storage systems. However, uneven lithium deposition and uncontrolled dendrite growth make this task quite challenging. Traditional polyolefin separators suffer from low porosity, wide pore size distribution, and poor thermal stability, leading to anisotropic/nonuniform Li+ distribution and thermal runaway risks under extreme conditions. Therefore, constructing high-quality novel separators with optimized microstructure is essential for meeting LMBs' growing safety demands.

Recently, Associate Professor Zhao Huijuan from Qingdao University and Professor Li Lin from Beijing Normal University published their latest research titled "A thermomechanically stable nanofiber separator with multiscale MOF networks towards high-efficiency ion transport" in Journal of Materials Chemistry A. The team proposed an innovative electrospinning-assisted in-situ self-assembly strategy to construct 3D multiscale metal-organic framework (MOF) networks for efficient ion transport.

Figure 1: Schematic diagram of the in-situ self-assembly process and mechanism of the PI@ZIF-8 nanofiber separator constructed based on a 3D multi-scale MOF network.

In this work, electrospun polyimide (PI) nanofiber membranes served as growth substrates, combined with surface etching to induce in-situ self-assembly of ZIF-8 nanocrystals on each PI nanofiber (Figure 1a), creating high-performance PI@ZIF-8 nanofiber separators with 3D multiscale MOF networks. This design uniquely enables ordered MOF nanocrystal assembly along 1D nanofibers, providing continuous Li+ pathways at microscale, while sub-nanopores and Lewis acid sites within MOF units selectively restrict anion movement to accelerate Li+ migration (Figure 1b).

Figure 2: Structural characterization of the constructed PI@ZIF-8 nanofiber separator.

Both PAA and PI nanofiber membranes prepared by electrospinning exhibited interconnected 3D networks composed of smooth 1D nanofibers (Figure 2a,b). MOF nanocrystal self-assembly formed continuous symbiotic MOF shells, with aligned ZIF-8 completely covering PI backbones to create 1D MOF nanofibers (Figure 2c,d). EDS-mapping, FTIR, XPS and XRD analyses (Figure 2e-i) systematically confirmed successful ZIF-8 assembly on PI nanofibers, forming typical core-shell structures.

Figure 3: Physical characterization and ionic conductivity of the constructed PI@ZIF-8 nanofiber separator.

The PI@ZIF-8 separator demonstrated exceptional mechanical stability (Figure 3a,b), high surface area (Figure 3c), and superior electrolyte affinity (Figure 3d-f), achieving high ionic conductivity (2.40 mS cm-1, Figure 3g) and Li+ transference number (0.88, Figure 3h), indicating outstanding ion transport capability.

Figure 4: Analysis of electrochemical lithium deposition/stripping behavior in Li‖Cu cells based on different separators.

To evaluate the separator's role in regulating Li deposition, Li‖Cu cell tests revealed PI@ZIF-8 effectively guided uniform Li nucleation, showing flat dendrite-free morphologies (Figure 4a-h). The Li‖PI@ZIF-8‖Cu cell maintained stable cycling for 300 cycles (Figure 4i) with consistent impedance (Figure 4j), demonstrating superior electrode-electrolyte interface stability.

Figure 5: Electrochemical performance of LMBs based on different separators.

Various LMB configurations verified practical applicability. LFP‖PI@ZIF-8‖Li cells exhibited enhanced kinetics, rate capability, cycling stability (Figure 5a-d). With high electrochemical stability window (Figure 5e), NCM811‖PI@ZIF-8‖Li cells showed excellent cycling performance (Figure 5f). Flexible pouch cells maintained LED illumination under folding/bending (Figure 5g-k), proving the 3D MOF-network separator's reliability and safety for advanced LMBs.