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.