The suggested surface treatment using ammonium persulfate (APS) successfully introduces hydrophilic functional groups onto the microporous structure of the polyethylene (PE) separators, leading to a high affinity toward polar liquid electrolytes without degrading the intrinsic physical properties of the separator. This improves the lithium-ion migration and ionic conductivity of the APS-treated separator, affording a stable cycle performance (92.5% at 90th cycle) and significantly improved rate capability (87.5% at 3 C).