When a lithium-ion battery is overcharged, it starts to self-heat because of exothermic reactions occurring within the components of the cell. Separator shutdown is a useful safety feature for preventing thermal runaway reactions in lithium-ion batteries. The polyethylene (PE) separators used here had shutdown temperatures of around 135 degrees C. Because the cell temperature continues to increase before actually beginning to cool even after shutdown, the separator should have a higher meltdown temperature than the shutdown temperature to work as an insulator even above the shutdown temperature. To enhance the meltdown temperature of the separator, in this study, a PE separator was coated with polymers synthesized from various ethylene glycol dimethacrylate monomers. When the separator was coated with polymer synthesized from diethylene glycol dimethacrylate (DEGDMA), its shutdown temperature and meltdown temperature were increased to 142 and 155 degrees C, respectively. Furthermore, a slight increase in the air permeability of the separator was observed when the separator was coated with polymer synthesized from an ethanol solution containing the proper amount of DEGDMA.