This paper reported surface modification and characterization of polymeric separators by cyclonic atmospheric-pressure plasma for Li-ion battery use. Water contact angles of the plasma-modified polymeric separator decreased with increasing treatment time and plasma power. Variations in surface morphology and chemical structure of the plasma-modified polymeric separators were confirmed by FESEM and XPS. XPS analysis revealed that the surfaces of plasma-modified polymeric separators had significantly higher concentrations of oxygen functional groups. Moreover, the cyclonic atmospheric-pressure plasma-modified polymeric separators showed excellent performance in electrochemical measurements.