<p>The separator is a pivotal factor influencing the properties of lithium-ion batteries, including wettability, thermal stability, and electrochemical performance. In view of the expanding market demand for high-capacity, long-cycle batteries, conventional polypropylene (PP) separators exhibit deficiencies in terms of thermal and cycling stability. In the present study, the aforementioned issues are addressed concurrently by the double-layer design of PDA layer and functionalized SiO₂ layers. A modification process was employed on commercial polypropylene (PP) separators, utilizing a polyethylene imine (PEI)-functionalized silica nanoparticle impregnation method. In particular, a silane coupling agent (KH560) was utilized to generate epoxy groups on the surface of nanosilica, which was subsequently subjected to a chemical crosslinking process with PEI through the ring-opening reaction between epoxy groups and amino groups. It was observed that the modified PP separator displayed augmented wettability, electrolyte absorption rate, and ionic conductivity, which in turn enhanced the cycling and rate performance and other electrochemical properties of the lithium-ion battery. In particular, the optimized sample (4 wt%) demonstrated the highest specific capacity (148.9 mAh g⁻¹ @1C, LiFePO₄IILi) at 1 C when compared to the unmodified commercial PP (140.4 mAh g⁻¹ @1C, LiFePO₄ II Li). In addition, the modified PP separator demonstrated enhanced thermal stability in comparison to the pristine PP separator, thereby ensuring the stable operation of lithium-ion batteries even under extreme conditions.</p>