What are the testing methods for lithium battery separator technology?
1. Thickness
There are two main technologies for online thickness control of lithium-ion battery separators: MD (longitudinal) control and CD (lateral) control; and online machine vision testing technology for separators. MD control and CD control refer to closed-loop thickness control in the MD direction by controlling the screw speed or traction speed; and closed-loop data control in the CD direction by measuring data through a scanning frame.
2. Curvature
Some companies also call it arch curvature, which refers to the arc shape that emerges after the lithium-ion battery separator is cut. A distinct arc shape can cause uneven stacking of the sheets, and vortex formation during winding can cause the electrodes to be exposed, leading to short circuits. The detection method involves laying the separator strip flat on a table and comparing its parallelism with the edge of a steel ruler to obtain the curvature of the separator.
3. Breathability
The time it takes for a certain volume of air to pass through the diaphragm under certain conditions is also called the Gurley value. Its value has a certain impact on the performance of lithium-ion batteries and is generally tested using the ASTM method.
4. Porosity
The proportion of the void volume to the total volume can be detected by two methods: liquid absorption calculation and detection. The liquid absorption calculation method involves immersing the lithium battery separator in a known solvent and calculating the void volume occupied by the liquid by measuring the mass difference of the separator before and after immersion. The mercury intrusion detection method uses external force to apply pressure to the separator to force mercury into the pores of the separator, and then calculates the porosity of the separator by measuring the volume of mercury pressed in. After multiple measurements, the average value is taken.
