Atomic layer deposition (ALD) of Al2O3 is applied on a polypropylene separator for lithium-ion batteries. A thin Al2O3 layer (<10 nm) is coated on every surface of the porous polymer microframework without significantly increasing the total separator thickness. The thin Al2O3 ALD coating results in significantly suppressed thermal shrinkage, which may lead to improved safety of the batteries. More importantly, the wettability of Al2O3 ALD-coated separators in an extremely polar electrolyte based on pure propylene carbonate (PC) solvent is demonstrated, without any decrease in electrochemical performances such as capacity, rate capability, and cycle life. Finally, a LiCoO2/natural graphite full cell is demonstrated under extremely severe conditions (pure PC-based electrolyte and high (4.5 V) upper cut-off potential), which is enabled by the Al2O3 ALD coating on all three components (cathode, anode, and separator).