PVDF Application Areas
Different models of PVDF products are suitable for different application scenarios. According to application fields, PVDF can be divided into conventional grade products and lithium binder products, conventional grade PVDF is used in coating, injection molding, water treatment filter membrane, photovoltaic backsheet, diaphragm coating and other fields, lithium binder PVDF belongs to the higher-end product model, is the most commonly used positive oil binder.
(1) Coating field
PVDF coatings, due to its super weather resistance, outdoor use can reach more than 20 years; excellent temperature resistance, the coating can be used for a long time in the range of -60 ℃ ~ 150 ℃; as well as excellent color retention, resistance to corrosion and turbidity, to become the most important alternative materials for ceramic tiles, clay tiles, and glass curtain walls, decorative panels.
(2) Injection molding field
PVDF processing performance is excellent, can be formed through injection molding of various types of pipes, valves and other plastic parts. As PVDF on chlorine, bromine and halogen compounds have extremely good resistance, and excellent processability, chemical resistance, fatigue and creep, so PVDF is the petrochemical and other industrial equipment, fluid handling system as a whole or lining of valves, pumps, pipe fittings, heat exchangers and tanks, one of the best materials.
(3) Water treatment membrane
Water treatment membrane is another major downstream application of PVDF, in the water treatment process, PVDF is mainly used in desalination, industrial wastewater treatment and municipal sewage treatment and other three areas. Compared with other membrane products, PVDF water treatment membrane in the strength, pure water flux, resistance to strong acids and alkalis, oxidation, pollution resistance and other aspects of the performance of certain advantages.
(4) Photovoltaic backsheet
Photovoltaic backsheet is a key component of photovoltaic module, located at the back of the module, which is used to resist the erosion of light, heat and humidity and other environmental impacts on the battery cell and encapsulation film and other materials, and play the role of weather-resistant insulation. Therefore, the PV backsheet film should have good resistance to UV irradiation, high and low temperature, environmental aging and water vapor barrier performance, in order to achieve the service life of PV modules for 25 years and above. PVDF is an excellent PV backsheet fluorine film material, flame retardant better than the traditional PVF material, excellent weathering so that the PVDF can be a long time exposure to sunlight, the air does not deteriorate, the service life of up to 50 years.
(5) Diaphragm coating
With the development of lithium batteries in the direction of greater energy density and higher power, high-performance diaphragm coating is needed to further enhance the performance of the battery, which mainly includes: enhancing the temperature resistance of the diaphragm; bonding the pole piece and the diaphragm to facilitate the assembly; increasing the diaphragm's wettability of the electrolyte to improve the retention of electrolyte; and increasing the safety of the diaphragm for the high-voltage system.
Due to the extremely stringent technical requirements, not many materials are used for diaphragm coating. Mainstream diaphragm coating materials include high-purity alumina and boehmite, but the proportion of PVDF and ceramic coating is increasing.
PVDF's unrivaled performance in battery diaphragm coating: ensures perfect alignment of diaphragm and electrode bonding to each other in cell production; better electrolyte wettability compared to polyolefins; excellent wet adhesion to prevent cell deformation (no interfacial debonding phenomenon); better thermal dimensional stability, especially bonding to ceramics; and ensures that dry adhesion and wet adhesion do not affect resistivity at the same time. Compared with other coating material solutions, PVDF brings excellent electrolyte solubility, effectively prevents clogging of diaphragm holes, and maintains the low resistivity and overall performance of the battery.
Currently, according to different solvents, there are water-based PVDF coated diaphragms and oil-based PVDF coated diaphragms.
(6) Lithium battery bonding agent
Binder is one of the key component materials of lithium battery pole piece, it is a polymer compound that adheres the conductive agent and active substance in the pole piece to the electrode collector, with the effect of enhancing the contact between the conductive agent, active substance and collector as well as stabilizing the structure of the pole piece, and it is an additional material with high technological content in the materials of lithium battery.
Lithium batteries generally use organic solvents as electrolyte and work at high voltage, so the binder used has high performance requirements. As PVDF has excellent corrosion resistance and chemical stability, it can effectively resist the erosion of polar organic solvent electrolyte, and at the same time has good bonding performance, so it is widely used in lithium battery anode binder, and the current proportion can reach 90%.
At present, the production technology of conventional grade PVDF has been relatively mature, and there are almost no technical barriers, while the production technology of lithium binder PVDF is more demanding, and only a few enterprises have mastered it and possessed mass production capacity. Due to high technical barriers, only a few PVDF models are able to mass produce lithium binder PVDF products verified by battery manufacturers, in 2021 China's lithium binder PVDF annual production capacity is expected to be only 19,000 tons / year.
Conventional homopolymerization-based PVDF products are difficult to meet the requirements of lithium battery binder. Specific performance: easy crystallization makes it difficult for electrolyte molecules to circulate, charging and discharging composite increase; shrinkage rate and collector shrinkage rate difference is large, the active substance is easy to peel off from the collector; molecular weight is insufficient to lead to insufficient bonding capacity, and so on. Therefore, lithium binder PVDF is generally selected PVDF homopolymer modification to solve the problem of reducing crystallinity, improving bonding, appropriate molecular mass and solubility of the electrolyte.
