Economic PP (Polypropylene) Disc & Roll (T=25 um, L=800m) as Battery Separator, CBSEPP

5PE (Polyethylene) separator is favored for its superior thermal shutdown characteristics and its ability to be made into thinner, more porous membranes. The key features of PE separator are shown below: (1) Low Melting Point (~135°C): This is the "Goldilocks" temperature for safety. It is high enough for normal operation but low enough to melt and "shut down" the battery (by clogging the pores) before the cell reaches the point of thermal runaway. (2) High Porosity: PE membranes are typically manufactured using a "wet process," which allows for much higher porosity (up to 50%) and more uniform pore distribution compared to the dry-stretched PP process. (3) Flexibility: PE is more flexible and less brittle than PP, making it easier to wind into the tight cylindrical shapes required for 18650 or 21700 cells.

Unlike the dry process used for PP (which relies on mechanical stretching), PE separators are usually made through Phase Inversion (The Wet Process).

References: 

1. B. Li, et al. Surface modification of polypropylene battery separator by direct fluorination with different gas components, Electrochimica Acta, 2014, 290, 137-141.
2. X. Li, et al. Development of plasma-treated polypropylene nonwoven-based composites for high-performance lithium-ion battery separators, Electrohimica Acta, 2015, 167, 396-403.