The performance of the separator determines the battery's interface structure, internal resistance, and other characteristics, directly affecting the battery's capacity, cycle life, and safety performance. A high-performance separator plays an important role in improving the overall performance of the battery.
The main role of the separator in lithium batteries
1. Separate the positive and negative terminals of the lithium battery to prevent them from coming into contact and causing a short circuit;
2. The micropores in the thin film allow lithium ions to pass through, forming a charging and discharging circuit.
Types of lithium-ion battery separators
Based on differences in physical and chemical properties, lithium battery separators can be classified into: woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, and rolled membranes. Although there are many types, the main commercially available lithium battery separator materials to date are polyethylene and polypropylene microporous membranes.
Performance requirements of lithium-ion battery separators
1. It has electronic insulation properties, ensuring mechanical isolation between the positive and negative electrodes;
2. It has a certain pore size and porosity, ensuring low resistance and high ionic conductivity, and good permeability to lithium ions;
3. It is resistant to electrolyte corrosion and has sufficient chemical and electrochemical stability, due to the fact that the electrolyte solvent is a highly polar organic compound;
4. It has good wettability in electrolytes and strong liquid absorption and moisture retention capabilities;
5. High mechanical stability, including puncture strength and tensile strength, but with the thickness as small as possible;
6. Good spatial stability and flatness;
7. Excellent thermal stability and automatic shutdown protection performance;
8. Low thermal shrinkage rate is essential; otherwise, it can cause short circuits and lead to battery thermal runaway. Furthermore, power batteries typically use composite membranes, which place even higher demands on the separator.
In lithium batteries, the separator absorbs the electrolyte and isolates the positive and negative electrodes to prevent short circuits, while simultaneously allowing lithium-ion conduction. Furthermore, in cases of overcharging or elevated temperature, the separator must possess high-temperature self-sealing properties to block current conduction and prevent explosion. In addition, lithium battery separators must also be characterized by high strength, fire resistance, resistance to chemical reagents, resistance to acid and alkali corrosion, good biocompatibility, and non-toxicity.
