In the structure of lithium battery, the performance of the diaphragm determines the interface structure and internal resistance of the battery, which directly affects the capacity, circulation and safety performance of the battery. Excellent performance of the diaphragm plays an important role in improving the comprehensive performance of the battery.
The main function of the diaphragm is to separate the positive and negative electrodes of the battery, prevent the contact between the two poles and short circuit, and also has the function of allowing electrolyte ions to pass through. For lithium battery series, as the electrolyte is an organic solvent system, organic solvent resistant diaphragm materials are needed, and high-strength thin-film polyolefin porous membrane is generally used.
Lithium battery diaphragm requirements
1. with electronic insulation, to ensure the mechanical isolation of positive and negative poles.
2. there is a certain aperture and porosity, to ensure low resistance and high ionic conductivity, lithium ions have good permeability.
3. Since the solvent of the electrolyte is a strongly polar organic compound, the diaphragm must be resistant to electrolyte corrosion and have sufficient chemical and electrochemical stability.
4. the electrolyte of good infiltration and adequate moisture absorption ability.
5. It has sufficient mechanical properties, including puncture strength and tensile strength, but the thickness is as small as possible.
6. Good spatial stability and smoothness.
7. thermal stability and automatic shutdown protection performance is good. Power batteries require more diaphragm and usually use composite membrane.
The market diaphragm material is mainly polyethylene, polypropylene based polyolefin diaphragm. PE products are mainly produced by wet process, PP products are mainly produced by dry process.