Requirements for Lithium Battery Separator
1. It has electronic insulation to ensure the mechanical isolation of positive and negative electrodes.
2. It has a certain pore size and porosity to ensure low resistance and high ionic conductivity, and has good permeability to lithium ions.
3. Since the solvent of the electrolyte is a strong polar organic compound, the diaphragm must be resistant to corrosion by the electrolyte and have sufficient chemical and electrochemical stability.
4. It has good wettability to the electrolyte and has sufficient liquid absorption and moisturizing ability.
5. It has sufficient mechanical properties, including puncture strength, tensile strength, etc., but the thickness is as small as possible.
6. Good spatial stability and flatness.
Seven, thermal stability and automatic shutdown protection performance is good. Power batteries have higher requirements for separators, and composite membranes are usually used.
Separator properties for lithium-ion batteries
The separator is located between the positive electrode and the negative electrode, and its main function is to separate the positive and negative active materials to prevent the two electrodes from short-circuiting due to contact; in addition, during the electrochemical reaction, it can maintain the necessary electrolyte and form a channel for ion movement. The diaphragm material is non-conductive, and the diaphragm used is different for different types of batteries. For lithium-ion batteries, since the electrolyte is an organic solvent system, the separator is required to have the following properties.
① In the battery system, its chemical stability is better, and the materials used are resistant to 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 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 rises. In order to prevent danger, when the rapid heat generation temperature (120 ~ 140 ° C) begins, the thermoplastic diaphragm melts, the micropores are closed, and it becomes an insulator to prevent the electrolyte from passing through, so as to achieve The purpose of interrupting the current.
⑤ From the perspective of lithium batteries, it must be fully impregnated with organic electrolyte, and can maintain a high degree of impregnation during repeated charge and discharge.
The separator materials commonly used in batteries are generally microporous membranes made of cellulose or braided fabrics and synthetic resins. Lithium-ion batteries generally use high-strength, thin-film polyolefin-based porous membranes. Commonly used separators include polypropylene (PP) and polyethylene (PE) microporous separators, as well as copolymers of propylene and ethylene, polyethylene homopolymers, etc. .
Wide range of applications for lithium-ion batteries