1. Thickness

There are two important online control technologies for the thickness of lithium-ion battery diaphragms, one is MD (longitudinal) control and CD (transverse) control; the other is diaphragm online machine vision inspection technology. The so-called MD control and CD control refer to the closed-loop control of the thickness in the MD direction by controlling the speed of the feeding screw or the traction speed; and the data measurement through the scanning frame, and finally the closed-loop control of the data in the CD direction.

2. Curvature

Some companies also call it arching, which refers to the arc after slitting the lithium-ion battery separator. When the arc is obvious, the laminations will be uneven and the vortex will appear during winding, causing the pole pieces to be exposed and short-circuited. The test method is to spread the diaphragm flat on the table and compare the parallelism with the edge of the steel ruler to get the curvature of the diaphragm.

3. Air permeability

The time required for a certain volume of air to pass through the diaphragm under certain conditions is also known as the Gurley value. Its size has a certain impact on the performance of lithium-ion batteries, and the ASTM test method is generally used.

4. Porosity

The ratio of the volume of the void to the entire volume. The test methods include liquid absorption calculation method and test method. The liquid absorption calculation method is to immerse the lithium battery diaphragm in a known solvent, and calculate the diaphragm occupied by the liquid by measuring the mass difference before and after the diaphragm is infiltrated. The void volume, mercury intrusion test method uses an external force to apply pressure to the diaphragm to press mercury into the pores of the diaphragm, and then calculate the porosity of the diaphragm by measuring the volume of mercury pressed into it, and take the average value after multiple measurements.