Fluororesin In Different Industries--Green Energy
In 1934, Germany first developed polychlorotrifluoroethylene (PCTFE). In 1938, DuPont developed polytetrafluoroethylene. Since the industrialization, the types of fluororesin have been increasing, and the field should be expanded. Aviation, aerospace, petroleum, chemical, machinery, electronics, construction, pesticides, medicine and living materials.
1 fluororesin properties and types
The fluororesin is obtained by homopolymerization or copolymerization of a fluorine atom-containing monomer. The electronegativity of the F atom is 4.0, the van der Waals radius is 1.35, the CF bond energy is 487.2 kJ/mol, and the CF bond has a polarizability of 0.68 cx. In addition, the special structure makes the fluororesin heat resistant and acid resistant. It has excellent performance in terms of alkali resistance, chemical resistance, weather resistance, hydrophobic oleophobicity, stain resistance, non-stickiness, biocompatibility, gas selective permeability, radiation sensitivity and low friction coefficient. The fluororesin varieties in use mainly include: polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and tetrafluoroethylene-hexafluoropropylene copolymer. (FEP), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-six Fluorine-vinylidene fluoride copolymer (THV) and tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer (TFB).
2 Application of fluororesin in the industry
The secondary lithium-ion battery is a green high-energy battery that emerged in the late 1980s. It has the advantages of high voltage, large capacity, small self-discharge, long cycle life, and environmental protection. It is a defense industry, digital camera, mobile phone, laptop, and space. One of the focuses of energy research and development in recent years in the field of technology. Lithium-ion batteries include liquid-type lithium ion batteries (LIB) and polymer type lithium ion batteries (LIP).
In the liquid type lithium ion battery, the PVDF resin is mainly used as a binder of the active material of the anode and the cathode electrode; in the polymer type lithium ion battery, the PVDF modified resin is made into a polymer electrolyte membrane together with the lithium salt and the solvent. . The PVDF resin is replaced by a fluorine atom having an electronegativity of 4.0 in the hydrogen atom of a carbon atom in the carbon chain, and the fluorine atoms are mutually repelled so that the fluorine atom is spirally distributed along the carbon chain, so that the periphery of the carbon chain is stabilized by a series of properties. Surrounded by fluorine atoms, this almost gap-free steric barrier makes it impossible for any atom or group to enter the interior of its structure and destroy the carbon chain, thus exhibiting extremely high chemical and thermal stability, which not only makes PVDF resin have Sufficient bond strength and also make PVDF resin less susceptible to oxidation or reduction. At the same time, due to the extremely low polarizability of the C-F bond, which is only 0.68c-x, the PVDF resin is also highly insulating.
Therefore, when PVDF resin is applied to a liquid type lithium ion battery, it can guarantee:
(1) Adequate bond strength to prevent the active material from falling off on the current collector or cracking during battery assembly and being detached from the current collector by the cover layer or cracking during repeated charge and discharge cycles; (2) Operating voltage range Within, not easily oxidized or reduced;
(3) An organic solvent insoluble in the electrolytic solution, but soluble in the coating used as the surface of the current collector; (4) a sufficient amount of bonding strength can be provided in a small amount.
In addition, PVDF resin is suitable for promotion and application. A polymer lithium ion battery consists of an anode layer, a cathode layer and a plastic electrolyte layer between the two poles. The role of the electrolyte membrane layer is to separate the positive and negative poles, prevent short circuits, and ensure the passage of lithium ions to provide higher conductivity. As a polymer lithium ion battery electrolyte membrane, generally PVDF modified resin, such as P (VDF-HFP) copolymer, PVDF-PEO crosslinked polymer, etc., they not only inherit the thermal stability and corrosion resistance of PVDF resin. It has the advantages of large dielectric constant and high mechanical strength, and overcomes the shortcomings of poor solubility and flexibility of fluororesin. It is an ideal electrolyte membrane material for polymer lithium ion batteries.
FEP film has high light transmittance and good light resistance and can be used in solar collectors. The FEP membrane is used as a convection barrier in the high-efficiency solar collector produced by Tekno Term AB. The test results show that the concentrator can supply hot water with a temperature greater than 100 °C within one year. The outer layer of the concentrator is made of high-transparency refractory glass, and the FEP film is disposed under the glass layer. Since the transmittance of the FEP film is as high as 96%, the solar light can be almost completely transmitted while being greatly suppressed. Reverse heat flow. The heat collected on the concentrator can be used directly or accumulated in an underwater container. According to Tekno Term AB, this concentrator guarantees a heat loss of <1.6 w/m2. Aluminized or silver FEP film can be used in the temperature control system of the outer surface of the spacecraft. The metal coating can ensure high solar radiation rate, while the FEP film layer absorbs the heat radiation of the spacecraft.