Coating with macroporous polyarylate via a nonsolvent induced phase separation process for enhancement of polyethylene separator thermal stability

Separator shutdown is a useful safety feature for preventing thermal runaway reactions in lithium ion batteries. Since after shutdown the cell temperature continues to increase before finally beginning to cool, the separator should maintain robust mechanical properties above the shutdown temperature to work as an insulator. To fabricate a separator that maintains its mechanical properties after shutdown, a polyethylene (PE) separator was coated with porous polyarylate (PAR) via a nonsolvent induced phase separation (NIPS) process. The formation of a porous coating layer on the PE separator and changes in morphology with the casting solution compositions were confirmed by electron microscopy. For the PE separator coated with macroporous PAR, the shutdown temperature (around 135 °C) was not changed, while the meltdown temperature increased to 188 °C with an acceptable reduction in air permeability.