Characteristics, Performance And Classification Of Lithium Battery Separator
Lithium battery separator is one of the key inner components of lithium battery. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety of the battery. The separator with excellent performance plays an important role in improving the overall performance of the battery.
1. Characteristics of lithium battery separator
The main performance requirements of lithium-ion battery diaphragm include: thickness uniformity, mechanical properties (including tensile strength and puncture resistance), air permeability, physical and chemical properties (including wettability, chemical stability, thermal stability, and safety).
2. Performance of lithium battery separator
The lithium battery diaphragm is located between the positive pole and the negative pole, which is mainly used to separate the positive and negative active substances and prevent short circuit due to contact between the two poles; In addition, it can maintain the necessary electrolyte and form a channel for ion movement during electrochemical reaction. The diaphragm material is non-conductive. Different types of batteries use different diaphragms. For lithium-ion batteries, since the electrolyte is an organic solvent system, the membrane requires the following properties.
1) In the battery system, its chemical stability is good, and the materials used can withstand organic solvents.
2) High mechanical strength and long service life.
3) The ionic conductivity of the organic electrolyte is lower than that of the aqueous solution system. In order to reduce the resistance, the electrode area must be as large as possible, so the diaphragm must be very thin.
4) When the battery system is abnormal, the temperature will rise. To prevent danger, at the beginning of the rapid heat generation temperature (120~140 ℃), the thermoplastic diaphragm will melt, the micropores will be closed, and it will become an insulator to prevent the electrolyte from passing through, so as to cut off the current.
5) From the perspective of lithium battery, it should be able to be fully impregnated with organic electrolyte, and maintain a high degree of immersion during repeated charging and discharging.
3. Classification of lithium battery separators
According to different physical and chemical characteristics, lithium battery separators can be divided into woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, diaphragm paper, rolled membrane, etc.
Polyolefin materials have excellent mechanical properties, chemical stability and relatively cheap characteristics. Therefore, polyethylene, polypropylene and other polyolefin microporous membranes have been used as lithium battery separators at the initial stage of research and development of lithium batteries. However, in recent years, there have been studies on the preparation of lithium battery separators with other materials, such as the preparation of lithium battery separators with polyvinylidene fluoride (PVDF) as bulk polymer by phase inversion method, and the research on cellulose composite membranes as lithium battery separator materials.