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.