How do PE Battery Separators Work?

The physical properties of PE batteries separators mainly include their material characteristics, thickness, pore size, mechanical strength and heat resistance.

It is mainly tensile strength and puncture resistance of PE battery separators that determine the durability and safety of the batteries. PE battery separators should have the right tensile strength to handle the mechanical stress that's applied during battery assemblage, winding, and charging/discharging. Tensile strength is how well the separator holds up to tearing, and is a key measure of mechanical strength of the separator. PE battery separators' tensile strength is typically within some range to be used, in order to keep the separator hard to break during use. Other than tensile strength, puncture resistance is also a useful metric to measure PE battery separators' strength. When the battery is assembled, the separator has to withstand the voltage between the positive and negative electrodes, hence it has to be puncture resistant to avoid short circuit due to separator failure. : Puncture resistance directly influences battery safety performance. Note that the PE separator, although it is strong on dry air, is weak when submerged in a liquid electrolyte. Therefore, when choosing and installing PE battery separators, you should fully check the strength performance on real working conditions.

PE battery separators have pores between the tens of nanometers and the few microns. Not only is this size range of pore sizes sufficient for ions to flow easily through the separator, it also eliminates short circuiting hazards caused by the contact between positive and negative electrodes of the battery. Pore size depends on a lot of parameters including the production process, material composition, and post-treatment process, and the pore size determines the ion conduction efficiency and the battery performance directly. On the basis of safety, proper pore size increase will make the battery better, but too large pore size increases the probability of short circuiting inside the battery. Thus, in the battery manufacture, the size of the pore of the PE battery separator should be well-managed. The PE battery separator usually thickness is between 10 to 40m, ideal separator thickness 25m. The thickness of the separator also affects how the lithium battery works and safety. According to the assumption of mechanical toughness, the less thick the separator, the better. In particular, the majority of current high-energy batteries have a single-layer diaphragm of either 20m or 16m; while in EV and hybrid electric vehicle (HEV) batteries, the diaphragms measure about 40m, which is required for high-current discharge and high capacity of the battery. The diaphragm should not be too thick or it will affect the battery's permeability and energy density; the diaphragm should not be thin or it could lead to safety issues such as short circuit in the battery. It's thus very important to make sure the thickness of the PE battery diaphragm is exactly controlled during battery production.

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