High Na ⁺ Transference Enabled by BNNs‐Assisted Quasi‐Solid Polymer Electrolyte for Safe and Dendrite‐Resistant Sodium Metal Batteries

Quasi‐solid polymer electrolyte (QSPE) has been shown to balance ionic conductivity and mechanical safety for sodium metal batteries, which are regarded as promising candidates. However, conventional QSPE systems are often constrained by limited ion‐transport efficiency, suboptimal interfacial compatibility, and insufficient mechanical strength, falling short of the concurrent requirements for high safety and long cycle life. Here, a novel organic–inorganic composite QSPE is proposed, in which 3‐aminopropyltriethoxysilane–functionalized boron nitride nanosheets (BNNs‐APTES) are uniformly embedded in a polyacrylonitrile (PAN) matrix. This approach allows for the construction of an anion‐immobilized and high‐efficiency ion‐conduction network, thereby facilitating the coordinated optimization of transport, mechanical robustness, and interfacial stability. Consequently, the PAN‐3 QSPE achieves a high t Na⁺ of 0.76 and maintains thermal stability >200 °C. Furthermore, Na//Na 3 V 2 (PO 4 ) 3 full cells operated at 1C for 550 cycles demonstrate a capacity retention of 95.3%. This integration of inorganic and organic components has been demonstrated to facilitate efficient Na + transport and enhance thermal robustness, thereby paving the way for the development of safe, high‐energy‐density sodium metal batteries.