Competitive Coordination and Dual Interphase Regulation of MOF-Modified Solid-State Polymer Electrolytes for High-Performance Sodium Metal Batteries

Solid-state polymer electrolytes (SPEs) have emerged as prominent candidates for solid-state sodium metal batteries (SMBs) due to their enhanced flexibility and reduced interfacial resistance. However, their performance is limited by poor Na⁺ conductivity at room temperature, disordered ion transport properties and unstable interfaces. Herein, a three-dimensional (3D) interconnected copper metal-organic framework (Cu-MOF) on polyacrylonitrile (PAN) fibers is introduced into polyethylene oxide (PEO)-based SPEs to construct a composite electrolyte (PPNM). The open metal sites (OMS) of the Cu-MOF compete with Na⁺, effectively coordinating with TFSI^- anions and oxygen atoms in PEO, thereby reducing concentration polarization, weakening the Na⁺-O binding strength and facilitating Na⁺ migration. By harnessing the multifunctional properties of Cu-MOF and PAN, the PPNM electrolyte exhibits superior ionic conductivity (1.03×10^-4 S cm^-1) and a high Na⁺ transference number (0.58) at room temperature. The strong anchoring of TFSI^- anions by Cu-MOF promotes the formation of inorganic-rich (NaF and Na₃N) cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) layers, enhancing dual interfacial stability. The Na₃V₂(PO₄)₃@C/PPNM/Na full cells realize robust cycling performance for 2000 cycles at 200 mA g^-1. This work provides a facile strategy for regulating the Na⁺ coordination state and interphase engineering in solid-state SMBs.