Main performance parameters of lithium-ion battery separator
1. Thickness: For consumable lithium-ion batteries, 25-micron separators are gradually becoming the standard. However, due to the increasing use of portable products, thinner diaphragms, such as 20 microns, 18 microns, 16 microns, and even thinner diaphragms are widely used. For power batteries, due to the mechanical requirements of the assembly process, thicker diaphragms are often required. Of course, for large power batteries, safety is also very important, and thicker diaphragms often mean better safety at the same time.
2. Air permeability: Generally speaking, there will be an air permeability parameter in the diaphragm, which is called Gurley index. The Gurley index refers to the time required for a certain volume of gas to pass through a certain area of diaphragm under certain pressure conditions. The volume of gas is generally 50cc. The Gurley index is proportional to the internal resistance of the battery, the larger the value, the greater the internal resistance.
3. Automatic shutdown mechanism: Automatic shutdown is a safety protection performance of lithium batteries, which is related to the raw material and structure of the diaphragm, and the melting point of the material also determines the closed cell temperature of the diaphragm. Normally, the higher the temperature of the safety window, the better the safety of the battery and the lower the probability of short circuit.
4. Porosity: Porosity refers to the percentage of the pore volume in the bulk material to the total volume of the material in its natural state. Generally, the porosity of the diaphragm is between 35% and 60%.
5. Thermal stability: The separator needs to be stable within the temperature range of the battery (-20°C~60°C). At present, the PE (polyethylene) or PP (polypropylene) materials used in the diaphragm can meet the above requirements.
6. Mechanical strength: high puncture resistance is required; unidirectional stretching, stretching ~50N, transverse ~50N; bidirectional stretching, requiring the same requirements in both directions.
7. Chemical stability: In other words, the separator is required to be inert in the electrochemical reaction. After several years of industrial inspection, it is generally believed that the current diaphragm materials PE or PP meet the requirements of chemical inertness.