ZIF‐8 Functionalized Separator Regulating Na‐Ion Flux and Enabling High‐Performance Sodium‐Metal Batteries

The practical application of sodium metal batteries faces significant challenges, such as unpredictable Na dendrite growth and the instability of solid-electrolyte interphase. Herein, a novel separator composed of glass fiber (GF) impregnated with a zeolitic imidazolate framework (ZIF-8) layer, referred to as GF@ZIF-8 is introduced. This optimized separator exhibits enhanced anti-puncture strength, a high Na transference number, and fast Na-ion conductivity. The ZIF-8 layer effectually regulates the spatial concentration distribution of Na ions and their flux vectors, leading to the homogeneous deposition of Na. Consequently, the Na||Na symmetric cells utilizing the GF@ZIF-8 separator demonstrate outstanding cyclability, achieving 850 h at 0.5 mA cm^-2 and 420 h at 1 mA cm^-2, outperforming cells with bare GF (<180 h). Furthermore, the assembled Na₃V₂(PO₄)₃||GF@ZIF-8||Na full cells exhibit remarkably improves rate performance (81 mA h g^-1 at 30 C), cyclability (93.5% capacity retention over 900 cycles at 10 C), and low-temperature applicability (78 mA h g^-1 under 0.2 C and -40 °C). The simulations reveal that, except for regulating Na-ion flux, the introduction of the porous ZIF-8 on the GF separator also enhances the local electric field near the anode, thereby boosting the transfer of Na⁺, which contributes to the improved Na storage performance.