Diaphragm is one of the key inner components of lithium battery. The performance of the diaphragm of lithium battery determines the interface structure and internal resistance of the battery, which directly affects the capacity, circulation and safety performance of the battery. The diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery.
Performance of lithium ion battery diaphragm
Diaphragm is located between the positive pole and the negative pole, the main role is to separate the positive and negative active substances, to prevent the poles due to contact and short circuit; In addition, the necessary electrolyte can be maintained during electrochemical reaction to form channels for ion movement. The diaphragm material is non-conductive, and the diaphragm used varies according to the type of battery. For lithium-ion batteries, as the electrolyte is an organic solvent system, the diaphragm is required to have the following properties.
1, in the battery system, its chemical stability is better, the material can withstand organic solvents.
2, mechanical strength, long service life.
3. The ionic conductivity of organic electrolyte is lower than that of aqueous solution. In order to reduce resistance, the electrode area must be as large as possible, so the diaphragm must be very thin.
4, when the battery system abnormal, temperature rise, in order to prevent danger, in the rapid heat production temperature (120 ~ 140℃) at the beginning of the thermoplastic diaphragm melting, micropore closed, into an insulator, to prevent electrolyte through, so as to achieve the purpose of blocking the current.
5, from the point of view of lithium battery, to be able to be fully impregnated with organic electrolyte, and can maintain a high degree of immersion in the repeated charging and discharging process.
The diaphragm material commonly used in the battery is usually made of cellulose, woven fabric and synthetic resin. Lithium ion batteries generally use high strength, thin film polyolefin series porous membrane, commonly used diaphragm polypropylene (PP) and polyethylene (PE) microporous diaphragm, propylene and ethylene copolymer, polyethylene homopolymer and so on.
The main performance requirements of lithium ion battery diaphragm are: thickness uniformity, mechanical properties (including tensile strength and puncture resistance strength), permeability, physical and chemical properties (including wettability, chemical stability, thermal stability, safety) and other four performance indicators.
