1. Thickness: For consumable lithium-ion batteries, a 25-micron separator is gradually becoming the standard. However, due to the increasing use of portable products, thinner separators, such as 20 microns, 18 microns, 16 microns, and even thinner separators, are beginning to be widely used. For power batteries, due to the mechanical requirements of the assembly process, thicker separators are often needed. Of course, for large power batteries, safety is also very important, and thicker separators often mean better safety.
2. Air permeability: Generally, the separator has an air permeability parameter, called the Gurley index. The Gurley index refers to the time required for a certain volume of gas to pass through a separator of a certain area under certain pressure conditions. The gas volume is typically 50cc. The Gurley index is directly proportional to the battery's internal resistance; the higher the value, the greater the internal resistance.
3. Automatic Shutdown Mechanism: Automatic shutdown is a safety protection feature of lithium batteries, related to the raw materials and structure of the separator. The melting point of the material also determines the pore-closing temperature of the separator. Normally, the higher the safety window temperature, the better the battery's safety and the lower the probability of short circuit.
4. Porosity: Porosity refers to the percentage of pore volume to the total volume of a bulk material in its natural state. Generally, the porosity of a membrane is between 35% and 60%.
5. Thermal stability: The separator needs to remain stable within the temperature range of battery operation (-20°C to 60°C). Currently, PE (polyethylene) or PP (polypropylene) materials used for separators can meet the above requirements.
6. Mechanical strength: High puncture resistance is required; uniaxial tensile strength ~50N, transverse tensile strength ~50N; biaxial tensile strength, both directions must be consistent.
7. Chemical stability: In other words, the diaphragm must be inert in electrochemical reactions. After several years of industrial testing, it is generally believed that the PE or PP materials currently used for diaphragms meet the requirements for chemical inertness.
