Synergistic Dual-Polar-Functionalized Metal-Organic Framework-Modified Separator for Stable and High-Performance Sodium Metal Batteries.

Sodium metal, regarded as an ideal anode material for high-energy-density rechargeable sodium metal batteries (SMBs), faces critical challenges, such as sluggish Na transport kinetics and uncontrolled dendritic growth, which severely hinder its cycling stability and practical applications. Herein, the well-designed, multifunctional separator, UFS2@GF, constructed using metal-organic frameworks functionalized with fluorinated (-F) and sulfonic acid (-SOH) groups, synergistically provides more nucleation sites for Na deposition, thereby reducing the nucleation overpotential and achieving uniform deposition. The inorganic-rich solid electrolyte interphase induced by UFS2 facilitates a uniform Na flux and enhances charge transfer efficiency. Structural characterization and density functional theory calculations further demonstrate that the introduction of abundant sodiophilic sites provided by -F and -SOH significantly enhances Na transport kinetics by reducing the energy barriers for Na migration within the UFS2 framework, leading to a higher Na transference number, superior ionic conductivity, and accelerated ion transport. Because of these synergistic effects, the symmetric cell with UFS2@GF achieves stable performance, enabling stable cycling for over 2500 h at 0.25 mA cm while delivering an excellent specific capacity of 87.3 mA h g at 10C in Na∥NaV(PO) cells. These results highlight the critical role of synergistic functional group strategies in addressing the limitations of SMBs.