Introduction of four new materials for lithium battery separators

by:CTECHi     2021-08-11

High porosity, high thermal resistance, high melting point, high strength, and good wettability to electrolyte are the development directions of lithium battery separator materials in the future. So, in the field of technological development, what new separator materials are there besides polyolefin separators? Researchers have developed a variety of four new types of lithium battery separator materials on the basis of traditional polyolefin separators. Material 1: PMIA PMIA is a kind of aromatic polyamide, which has a benzamide type branch on its skeleton, and has a thermal resistance of up to 400 ℃. Due to its high flame retardant performance, the diaphragm using this material can improve the safety performance of the battery . In addition, due to the relatively high polarity of the carbonyl group, the separator has high wettability in the electrolyte, thereby improving the electrochemical properties of the separator. Make it have the prospect of commercialization. Material 2: PET Polyethylene terephthalate (PET) is a material with excellent mechanical properties, thermodynamic properties, and electrical insulation properties. The most representative product of PET separators is the composite film developed by Germany Degussa with PET separator as the base and coated with ceramic particles. It exhibits excellent heat resistance and the closed cell temperature is as high as 220°C. The melting point of the electrospun PET membrane is much higher than that of the PE film, at 255℃, the maximum tensile strength is 12Mpa, the porosity reaches 89%, and the liquid absorption rate reaches 500%, which is much higher than the Celgard membrane on the market, and the ion conductivity reaches 2.27 ×10-3Scm-1, and the cycle performance is better than Celgard separator. The porous fiber structure of PET separator remains stable after 50 cycles of battery cycle. Material 3: PBO The new polymer material PBO (poly-p-phenylene benzodiazole) is an organic fiber with excellent mechanical properties, thermal stability and flame retardancy. Its matrix is u200bu200ba linear chain structure polymer, which does not decompose below 650°C, has ultra-high strength and modulus, and is an ideal heat-resistant and impact-resistant fiber material. Because the surface of the PBO fiber is extremely smooth and the physical and chemical inertness is extremely strong, the fiber morphology is difficult to change. PBO fiber is only soluble in 100% concentrated sulfuric acid, methanesulfonic acid, fluorosulfonic acid, etc. After strong acid etching, the fibrils on the PBO fiber will peel off from the backbone, forming a split filament morphology, and improve the ratio. Surface area and interface bond strength. Material 4: PI polyimide (PI) is also one of the polymers with good comprehensive properties, with excellent thermal stability, higher porosity, and better high temperature resistance, which can be at -200~300℃ Under long-term use. Due to the strong polarity of PI and good wettability to the electrolyte, the manufactured diaphragm exhibits an excellent liquid absorption rate. Compared with the Celgard diaphragm, the PI diaphragm made by electrospinning has lower impedance and higher rate performance, and the capacity retention rate is still 100% after 100 cycles of 0.2C charge and discharge. Summary In order to improve the safety of the lithium battery and ensure the safe and stable operation of the battery, the battery separator must meet the following conditions: 1. Chemical stability: not react with the electrolyte and electrode materials; 2. Wetting: easy to infiltrate with the electrolyte and No elongation, no shrinkage; 3. Thermal stability: high temperature resistance, high fusing isolation; 4. Mechanical strength: good tensile strength, to ensure that the strength and width remain unchanged during automatic winding; 5. Porosity : Higher porosity to meet the needs of ion conductivity; the performance of the lithium battery separator determines the battery's interface structure, internal resistance, etc., which directly affects the battery's capacity, cycle and safety performance. The excellent performance of the separator can improve the battery's performance. Comprehensive performance plays an important role. In addition, the safety of lithium-ion batteries is a complex and comprehensive issue. The biggest hidden danger of battery safety is the random internal short circuit of the battery, which causes on-site failure and causes thermal runaway. Energy storage is the key support point of the energy revolution. With favorable policies and the implementation of demonstration projects, energy storage has shown important value and broad prospects in renewable energy power generation, auxiliary services, grid-side and distributed energy microgrids. At the same time, energy storage also welcomes the joining of many new forces. In order to jointly promote the development of the energy storage industry, Polaris Power Network and Polaris Energy Storage Network have launched special training courses on energy storage industry.

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