In this study, we demonstrated the effects of aluminum oxide (Al2O3)-based ceramic coatings deposited by radio-frequency (RF) magnetron sputtering on commercial polyethylene (PE) microporous separators. Due to the superb thermal stability of the ceramic materials themselves, the Al2O3 coatings solved the chronic thermal shrinkage problem of PE separators. Separators with sputtered Al2O3 coatings maintained their initial dimensions even after high temperature exposure at 140 °C for 30 min. The sputtered Al2O3 layer effectively changed the surface of a PE separator from being hydrophobic to hydrophilic too, improving its wettability with liquid electrolyte. Additionally, a sputtered Al2O3 coating can improve the rate capability (~130%) compared with a bare PE separator under a high current density (7.75 mA cm-2, 5 C rate) because the layer does not require additional use of polymeric binder materials, which usually inhibit the formation of pore structures in microporous membranes.