Main Performance Parameters of Lithium ion Battery Separator

The lithium battery separator is one of the key inner layer components of lithium ion batteries. Its performance determines the interface structure and internal resistance of the battery, which directly affects the energy, cycle and safety of the battery. The overall performance of the battery plays an important role. So, what are the main performance parameters of lithium-ion battery separators?

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 have begun to be 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 the Gurley index. 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, and the volume of gas is generally 50cc. The Gurley exponent is proportional to the internal resistance of the battery, and 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. The melting point of the material also determines the closed-cell temperature of the diaphragm. Normally, the higher the safety window temperature, the better the safety of the battery and the smaller 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 separator is between 35% and 60%.

5. Thermal stability: The separator needs to be stable within the temperature range (-20°C~60°C) used by the battery. 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 two directions.

7. Chemical stability: In other words, the separator is required to be inert in electrochemical reactions. After several years of industrial inspection, it is generally believed that the current PE or PP materials for diaphragms meet the requirements of chemical inertness.

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