The lithium-ion battery separator is one of the key internal components of a lithium-ion battery. The performance of the lithium-ion battery 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.
Performance of lithium-ion battery separators
The separator, located between the positive and negative electrodes, primarily functions to separate the active materials of the electrodes, preventing short circuits caused by contact. Additionally, it maintains the necessary electrolyte and forms channels for ion movement during electrochemical reactions. The separator material is non-conductive, and different types of batteries use different separators. For lithium-ion batteries, since the electrolyte is an organic solvent system, the separator must possess the following properties.
1. Within the battery system, it must have good chemical stability, and the materials used must be resistant to organic solvents.
2. High mechanical strength and long service life.
3. The ionic conductivity of organic electrolytes is lower than that of aqueous solutions. In order to reduce resistance, the electrode area must be as large as possible, therefore the diaphragm must be very thin.
4. When the battery system malfunctions and the temperature rises, to prevent danger, the thermoplastic separator melts and the micropores close at the rapid heat generation temperature (120-140℃), turning into an insulator to prevent electrolyte from passing through, thereby achieving the purpose of cutting off the current.
5. From the perspective of lithium batteries, they must be able to be fully impregnated by organic electrolytes and maintain a high degree of impregnation during repeated charging and discharging.
The separator materials commonly used in batteries are generally microporous membranes made of cellulose or woven 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 membranes, as well as copolymers of propylene and ethylene, and polyethylene homopolymers.
The main performance requirements for lithium-ion battery separators include four major performance indicators: thickness uniformity, mechanical properties (including tensile strength and puncture resistance), air permeability, and physicochemical properties (including wettability, chemical stability, thermal stability, and safety).
