Large-size thin-wall weather-resistant modified polypropylene electrode frame for flow battery and preparation method of large-size thin-wall weather-resistant modified polypropylene electrode frame

Abstract

The invention discloses a large-size thin-wall weather-resistant modified polypropylene electrode frame for a flow battery and a preparation method of the electrode frame. A modified polypropylene material for forming the electrode frame is prepared from the following raw materials in proportion: 20-53 parts of homo-polypropylene functional master batch, 40-80 parts of impact-resistant co-polypropylene and 5-30 parts of polyolefin elastomer. Wherein the homo-polypropylene functional master batch is prepared from the following components: 20 to 50 parts of homo-polypropylene powder, 0.1 to 0.3 part of a metal deactivator, 0.05 to 0.1 part of a rigid nucleating agent, 0.2 to 0.5 part of an antioxidant, 0.2 to 1 part of a lubricant and 0.5 to 2 parts of a light stabilizer. The raw materials are mixed, granulated through a parallel double-screw extruder and then subjected to injection molding to form the electrode frame. The large-size thin-wall weather-resistant modified polypropylene electrode frame for the flow battery has the advantages of being high in strength, not prone to cracking, high in flatness, good in size stability, resistant to electrolyte corrosion, good in weather resistance and the like, is easy to machine and form, can be subjected to fusion welding through lasers with specific wavelengths, and is widely applied to the energy storage industry.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials, and specifically relates to a large-size, thin-walled, weather-resistant modified polypropylene electrode frame for flow batteries. Background Technology

[0002] A flow battery is a device that uses an electrolyte in a solution to undergo a redox reaction on both sides of a membrane to store and release energy. It has the advantages of safety, power-capacity decoupling, recyclable electrolyte, and long charge-discharge cycle life (up to 20 years). In recent years, the technology has gradually matured and entered the commercialization stage.

[0003] Flow galvanic water storage devices mainly consist of a fuel cell stack, electrolyte, and control system. The fuel cell stack is composed of dozens of battery cells tightly stacked together using different processes. Each battery cell includes components such as an electrode frame, electrodes, bipolar plates, and a separator. The electrode frame primarily provides a reaction site for the active materials in the electrolyte and also serves a supporting role. The electrode frame itself is non-conductive, but its internal design incorporates flow channels to control the flow pattern, flow rate, velocity, and uniformity of the electrolyte. Although the electrode frame does not directly participate in the battery's charging and discharging process, its structure and performance directly affect the battery's efficiency, stability, and lifespan.

[0004] Sulfuric acid and hydrochloric acid in flow battery electrolytes are strong oxidizing agents, making metal unsuitable for electrolyte flow channels. Therefore, polyolefins, which can withstand strong acids for extended periods, are the preferred material for electrode frames. Theoretically, the macromolecular structures of polyolefin materials are mostly regular crystals, which will not enter the electrolyte or react with it, thus allowing the electrolyte to maintain its high efficiency.

[0005] During the operation of flow batteries, temperature and pressure pose challenges to the long-term stability of the stack. The operating temperature range of the stack is approximately 10~50℃. The stack, composed of hundreds of electrode frames, needs to withstand the pressure from the screw fastening. Under these conditions, the electrode frames need to maintain dimensional stability and provide a sealing effect, which also places new demands on polyolefin materials.

[0006] The electrode frame is large and thin, and its structure is quite complex to meet the requirements of electrolyte flow. Its main molding process is melt injection molding. Assembly processes for stacking multiple electrode frames include laser welding, screw fastening, hot melting, or cold pressing. Currently, laser welding / ultrasonic welding and screw fastening are the most mature methods. Commercially available general-purpose polyolefin materials, such as polypropylene (PP), polyethylene (PE), and their glass fiber (GF) reinforced polyolefin composites, are difficult to meet the multiple functional requirements of flow battery electrode frames.

[0007] Electrode frames currently manufactured using common polyolefin materials (such as PP, PE, and PP / GF) can meet the short-term needs of fuel cell stacks, but cannot meet the long-term stable operation requirements of high-quality flow batteries with large size and high energy density. This is because common polyolefin resins are difficult to mold in terms of size control and lack sufficient toughness, failing to meet the requirements of 980nm laser melting welding. During long-term use, the electrode frames are prone to cracking, leading to electrolyte leakage and other problems, thus failing to meet the new industrial demands for long-term stable operation and low-cost maintenance of fuel cell stacks. Furthermore, common polyolefin materials do not contain nucleating agents, light stabilizers, and other functional additives, resulting in rapid performance degradation during UV aging and electrolyte resistance tests. They are unsuitable for long-term contact with strong electrolytes and are difficult to use outdoors.

[0008] Patent CN117964969A, "Electrolyte-Resistant Polypropylene Composite Material and its Preparation Method," discloses an electrolyte-resistant polypropylene composite material obtained by mixing and granulating homopolymer polypropylene, copolymer polypropylene, toughening agent, and filler. It is suitable for use as a material for the stack plates and frames of flow batteries that directly contact the electrolyte. However, this material contains 40-50 parts of silicate mineral powder, preferably talc powder with a silicon content ≥55 wt%. According to the national standard GB / T 15342-2023, talc powder for plastics contains not only silicon dioxide but also metal oxides such as magnesium oxide (≥23 wt%), ferric oxide, aluminum oxide, and calcium oxide. These metal oxides can chemically react with strong oxidizing agents such as sulfuric acid and hydrochloric acid in the electrolyte, accelerating the failure of the electrode frame during use and making it difficult to meet the requirements for long-term stable operation of flow batteries.

[0009] Patent CN103589053A discloses a long glass fiber reinforced polypropylene material, its preparation method, and its application. The material comprises polypropylene, maleic anhydride-grafted polypropylene, glass fiber, coupling agent, composite antioxidant, lubricant, and metal passivator, obtained by impregnating glass fiber with the above raw materials after melt plasticization. This material exhibits excellent water resistance, high resistance to thermal oxidation, and a high flexural modulus, making it suitable for use in washing machine drum materials. However, its impact strength is insufficient, and the addition of glass fiber affects the light transmittance of the product, making laser welding difficult during subsequent assembly. The formulation does not contain light stabilizers, inevitably leading to photodegradation and photoaging after long-term use.

[0010] In summary, there is a need to develop a series of large-size, high-performance electrode frame materials and products with high strength, good stability, and the ability to meet the requirements of laser melting welding at specific wavelengths, in order to satisfy the new demands of the booming fluid energy storage industry. Summary of the Invention

[0011] The present invention aims to solve the problems of easy deformation and cracking, unstable dimensions, and easy aging and degradation of ordinary polypropylene electrode frames currently in use, and to provide a large-size thin-walled electrode frame with high strength, good stability, high flatness, and can be melt-welded by laser of a specific wavelength.

[0012] To achieve the above objectives, the present invention provides a large-size, thin-walled, weather-resistant modified polypropylene electrode frame for flow batteries. The modified polypropylene material constituting the electrode frame is characterized by comprising the following components in parts by weight: 20-53 parts of homopolymer polypropylene functional masterbatch, 40-80 parts of impact-resistant copolymer polypropylene, and 5-30 parts of polyolefin elastomer; wherein the homopolymer polypropylene functional masterbatch is made from the following raw materials in parts by weight: 20-50 parts of homopolymer polypropylene powder, 0.1-0.3 parts of metal passivating agent, 0.05-0.1 parts of rigid nucleating agent, 0.2-0.5 parts of antioxidant, 0.2-1 parts of lubricant, and 0.5-2 parts of light stabilizer.

[0013] Furthermore, the homopolymer polypropylene powder is a high-flow polypropylene powder with an isotactic index ≥94% and a melt mass flow rate ≥30g / 10min under test conditions of 230℃ and 2.16kg.

[0014] Furthermore, the impact-resistant copolymer polypropylene is an ethylene-propylene copolymer, wherein the mass fraction of ethylene is 3-10%, and the melt mass flow rate under the test conditions of 230°C and 2.16kg is 0.5 g / 10min-2.0 g / 10min.

[0015] Furthermore, the polyolefin elastomer is an ethylene-octene copolymer, wherein the mass fraction of octene is 55-60%, and the melt mass flow rate under the test conditions of 190°C and 2.16 kg is 0.2 g / 10 min to 1.0 g / 10 min.

[0016] Furthermore, the metal passivating agent is N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

[0017] Furthermore, the rigid nucleating agent is a sorbitol acetal-based nucleating agent.

[0018] Furthermore, the light stabilizer is one or more of the following: benzotriazole UV absorbers resistant to precipitation, benzophenone UV absorbers, and hindered amine light stabilizers.

[0019] Furthermore, the lubricant is selected from one or more of calcium stearate, zinc stearate, pentaerythritol stearate, lignite ester, and ethylene bis-stearamide.

[0020] Furthermore, the antioxidant is selected from one or a mixture of two of phenolic antioxidants and phosphite antioxidants.

[0021] Furthermore, a method for preparing a large-size, thin-walled, weather-resistant modified polypropylene electrode frame for flow batteries includes the following steps: Step (1) Preparation of homopolymer polypropylene functional masterbatch: Weigh homopolymer polypropylene powder, metal passivator, rigid nucleating agent, antioxidant, lubricant and light stabilizer according to the weight ratio specified in claim 1, place them in a high-speed mixer, stir at low speed for 1.5 min, and then stir at high speed of 1000 rpm for 1.5 min; send the mixed material into a parallel twin-screw extruder for plasticizing and mixing, and after water cooling, traction, pelleting and homogenization, obtain homopolymer polypropylene functional masterbatch; the extrusion temperature of the parallel twin-screw extruder is 180~210℃, the main screw speed is 40 rpm, the feeding speed is 15 rpm, and the pelleting speed is 150 rpm; Step (2) Preparation of modified polypropylene granules: Weigh the homopolymer polypropylene functional masterbatch, impact copolymer polypropylene and polyolefin elastomer obtained in step (1) according to the weight ratio specified in claim 1, place them in a high-speed mixer and stir for 2 minutes, then feed them into a parallel twin-screw extruder for granulation to obtain modified polypropylene granules; the extrusion temperature of the parallel twin-screw extruder is 180~210℃, the main screw speed is 40rpm, the feeding speed is 15rpm, and the pelletizing speed is 150rpm; Step (3) Injection molding: The modified polypropylene granules obtained in step (2) are dried at 60~70℃ for 2 hours, and then added to a high-precision single-screw injection molding machine with large clamping force, small injection volume, high pressure and high speed characteristics to obtain the electrode frame product by injection molding; The process parameters of the injection molding are: injection temperature 200~240℃, hot runner temperature 240℃, maximum clamping pressure 130 bar; Step (4) Post-processing: Demold and cool the electrode frame product obtained in step (3). Avoid stacking during the cooling process to ensure uniform heat dissipation for each product. After the product has completely cooled, stack and pack it. Use products from the same batch for assembly.

[0022] Compared with the prior art, the present invention has the following advantages: While high-flow homopolymer polypropylene possesses advantages such as high strength and high modulus, its poor impact toughness makes it difficult to meet the long-term high-pressure requirements of electrode frames after assembly, leading to a tendency to crack. Therefore, it is necessary to blend impact-resistant polypropylene with homopolymer polypropylene to improve impact toughness. This invention selects impact-resistant polypropylene PP-B M00D and PP-B M02G, both of which have good toughness, as well as good strength and modulus, enabling the modified polypropylene material to possess both toughness and strength.

[0023] To further enhance toughness, the present invention also adds polyolefin elastomer POE XLT 8677, which is an ethylene-octene copolymer with a glass transition temperature as low as -65°C, exhibiting excellent toughening effects; at the same time, its melting temperature can reach 118°C, which will not melt at the working temperature of the modified polypropylene electrode frame product, thus reducing the product creep caused by ordinary polyolefin elastomers and improving the dimensional stability of the electrode frame product.

[0024] This invention uses a combination of high-flow, high-strength homopolymer polypropylene, impact-resistant copolymer polypropylene, and polyolefin elastomers, which retains the advantages of high strength and high flow of homopolymer polypropylene while also possessing good toughness. As the content of homopolymer polypropylene increases, the strength and modulus of the sample increase, but the elongation at break and toughness decrease.

[0025] Most functional additives are in powder form, resulting in poor dispersibility when mixed with granular resins. Therefore, this method involves first granulating homopolymer polypropylene powder with functional additives such as nucleating agents and metal passivators to form a masterbatch. Then, the masterbatch is granulated again with impact copolymer polypropylene and polyolefin elastomers to obtain a uniformly mixed modified polypropylene material with consistent performance. This method also improves the crystallization process of polypropylene. Homopolymer polypropylene has high strength and modulus, but during cooling, it easily forms large spherulites with a size of millimeters, affecting transparency and causing product deformation and warping. The addition of nucleating agents increases the crystallinity and crystallization rate of polypropylene, reducing crystal size to form micron-sized spherulites, thereby improving the strength of the polypropylene material and the dimensional stability of the product. The α-crystal nucleating agent used in this invention has the following advantages: ① reducing spherulite size and improving product transparency; ② accelerating crystallization speed and shortening the molding cycle; ③ improving material strength and modulus, and enhancing creep resistance; ④ improving material impact toughness.

[0026] Some modified polypropylene electrode frames require laser welding during assembly. The electrode frames need to be able to transmit infrared light with a wavelength of 900nm (transmittance 88±3%). The transmittance of ordinary polypropylene is too high. Therefore, this invention selects homopolymer polypropylene, impact copolymer polypropylene and polyolefin elastomer to be used together so that the transmittance of the electrode frame product is maintained within the required range.

[0027] During the synthesis of polypropylene, defects and impurities are introduced into the molecular structure. These defects and impurities are easily degraded and oxidized by heat, oxygen, light, and strong oxidants (electrolytes) during granulation, molding, transportation, and use, leading to a decline in the performance and a shortened lifespan of the polypropylene material. This invention uses a combination of functional additives such as metal passivators, light stabilizers, and antioxidants. The ultraviolet light absorber absorbs energy and releases it as heat; the hindered amine light stabilizer eliminates free radicals generated during oxidation, thus delaying the degradation of the modified polypropylene material under ultraviolet light irradiation; the active groups such as amine and hydroxyl groups in the metal passivator chelate with metal ions, inhibiting their catalytic activity, and can also form a passivation film in a strong oxidizing electrolyte, maintaining the long-term stability of the electrode frame during use; the antioxidant can delay the thermo-oxidative aging of the modified polypropylene material, extending the oxidation induction period to over 30 minutes, and synergistically with the metal passivator to prolong the electrolyte's erosion of the polypropylene.

[0028] As a semi-crystalline material, polypropylene has an injection molding shrinkage rate of up to 2.5%, which can easily lead to dimensional deviations and deformation. Uneven wall thickness further contributes to shrinkage differences, reducing assembly sealing and causing electrolyte leakage. The electrode frame is a flat frame structure with a large projected area and thin walls (only 0.6 mm at its thinnest point). The length-to-thickness ratio of the product often exceeds 100, and some products can reach over 300 (see attached diagram for a schematic diagram of the electrode frame). This invention uses a high-precision injection molding machine with high clamping force, small injection volume, high pressure, and high speed to ensure uniform shrinkage and dimensional stability of the electrode frame product, and to minimize melt degradation due to the short residence time of the melt in the screw.

[0029] The electrode frame provides support and sealing within the fuel cell stack, and its internal flow channel structure regulates electrolyte flow, requiring strict dimensional control. The number of mold gates affects melt flow behavior and stress distribution. Too few gates result in a long melt flow path and rapid cooling, leading to incomplete filling or high shear stress, causing product warping. While multi-gate injection molding can shorten the melt flow path, achieve uniform filling, and reduce the melt cooling gradient, it is prone to weld lines and bubbles, weakening product strength and sealing. Therefore, precise program control is needed to avoid defects. This invention employs a hot runner, multi-gate, and needle valve injection method, using Moldflow software to optimize the gate layout. Timing control of gate opening and closing ensures uniform pressure distribution during filling, avoiding weld lines and bubbles, thus resulting in uniform product shrinkage and consistent dimensions. Furthermore, during molding, it is crucial to ensure stable temperatures in the machine tool, mold, and hot runner to prevent excessive local temperature differences that could cause uneven internal stress in the product, leading to final distortion and deformation.

[0030] In summary, this invention addresses the problems of deformation, cracking, leakage, and battery performance degradation in large-size high-energy-storage flow batteries during long-term operation due to poor electrode frame performance through systematic research on the optimization, modification, crystallization behavior and grain size control of functional polypropylene and its composites, multi-gate hot runner mold design, and injection molding process optimization. It improves the mechanical properties and durability of electrode frame materials and products by optimizing the high-performance design and development of polyolefin materials for electrode frames, manufacturing mold design, and molding processes, thereby enhancing the stability of large-size electrode frames during long-term operation and preventing deformation and cracking. By improving the performance of large-size electrode frames, it reduces the risk of electrolyte leakage and contamination, improving the overall efficiency and stability of the battery stack, thus increasing the operating efficiency and lifespan of the flow battery. Finally, by providing technical support for the large-scale application of flow batteries, it aims to improve battery energy storage efficiency, cycle life, safety, and reduce battery costs, promoting the large-scale application of large-size high-energy-storage flow battery technology and enhancing the competitiveness of my country's flow battery industry in the international energy storage battery market. Attached Figure Description

[0031] Appendix Figure 1 This is a schematic diagram of the framework structure. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0033] The metal passivating agent, antioxidant, and light stabilizer used in the examples were all from BASF.

[0034] Metal passivator Irganox MD 1024, N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

[0035] Antioxidant B215 is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl]phosphite in a mass ratio of 1:2.

[0036] Tinuvin 326, an ultraviolet light absorber (2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole).

[0037] Ultraviolet light absorber Tinuvin P, 2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole.

[0038] Hindered amine light stabilizer Chimassorb 2020, (4-butyl-2-N,4-N-bis(2,2,6,6-tetramethylpiperidin-4-yl)-2-N-[6-[(2,2,6,6-tetramethylpiperidin-4-yl)amino]hexyl]-1,3,5-triazine-2,4-diamine).

[0039] Chimassorb 944, a hindered amine light stabilizer, is a poly[[6-[(1,1,3,3-tetramethylbutyl)amine]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidine)imine]-1,6-dihexadiyl[(2,2,6,6-tetramethyl-4-piperidine)imine]]].

[0040] Polyolefin elastomer POE XLT 8677, ethylene-octene copolymer, from Dow Chemical.

[0041] Sorbitol acetal nucleating agent NX8000, 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonanol, from Milliken Corporation.

[0042] Mild 3988, a sorbitol acetal nucleating agent, is 1,3:2,4-di(3,4-dimethylbenzyl)-D-sorbitol, sourced from Milliken.

[0043] Example 1

[0044] Homopolymer polypropylene functional masterbatch formulation: Homopolymer polypropylene PP-H GD-320 20 parts, metal passivator Irganox MD 1024 0.2 parts, sorbitol acetal nucleating agent NX8000 0.05 parts, antioxidant B215 0.3 parts, calcium stearate 0.3 parts, ultraviolet light absorber Tinuvin 326 0.5 parts, hindered amine light stabilizer Chimassorb 2020 0.5 parts.

[0045] The modified polypropylene electrode frame material formulation consists of 21.85 parts homopolymer polypropylene functional masterbatch, 70 parts impact copolymer polypropylene PP-BM00D, and 20 parts polyolefin elastomer POE XLT 8677.

[0046] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0047] Example 2

[0048] Homopolymer polypropylene functional masterbatch formulation: 25 parts homopolymer polypropylene PP-H GD-320, 0.15 parts metal passivator Irganox MD 1024, 0.05 parts sorbitol acetal nucleating agent NX8000, 0.3 parts antioxidant B215, 0.3 parts pentaerythritol stearate, 0.5 parts ultraviolet light absorber Tinuvin 326, and 0.5 parts hindered amine light stabilizer Chimassorb 2020.

[0049] The modified polypropylene electrode frame material formulation consists of 26.8 parts homopolymer polypropylene functional masterbatch, 70 parts impact copolymer polypropylene PP-BM00D, and 15 parts polyolefin elastomer POE XLT 8677.

[0050] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0051] Example 3

[0052] Homopolymer polypropylene functional masterbatch formulation: 30 parts homopolymer polypropylene PP-H GD-320, 0.1 parts metal passivator IrganoxMD 1024, 0.05 parts sorbitol acetal nucleating agent NX8000, 0.3 parts antioxidant B215, 0.3 parts lignite ester, 0.5 parts ultraviolet light absorber Tinuvin 326, and 0.5 parts hindered amine light stabilizer Chimassorb 2020.

[0053] The modified polypropylene electrode frame material formulation consists of 31.75 parts homopolymer polypropylene functional masterbatch, 65 parts impact copolymer polypropylene PP-BM00D, and 15 parts polyolefin elastomer POE XLT 8677.

[0054] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0055] Example 4

[0056] Homopolymer polypropylene functional masterbatch formulation: 20 parts homopolymer polypropylene PP-H GD-320, 0.2 parts metal passivator IrganoxMD 1024, 0.05 parts sorbitol acetal nucleating agent Mild 3988, 0.3 parts antioxidant 1010, 0.3 parts calcium stearate, 0.5 parts ultraviolet light absorber Tinuvin P, and 0.5 parts hindered amine light stabilizer Chimassorb 944.

[0057] The modified polypropylene electrode frame material formulation consists of 21.85 parts homopolymer polypropylene functional masterbatch, 70 parts impact copolymer polypropylene PP-BM02G, and 30 parts polyolefin elastomer POE XLT 8677.

[0058] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0059] Example 5

[0060] Homopolymer polypropylene functional masterbatch formulation: 25 parts homopolymer polypropylene PP-H GD-320, 0.15 parts metal passivator IrganoxMD 1024, 0.05 parts sorbitol acetal nucleating agent Mild 3988, 0.3 parts antioxidant B215, 0.3 parts pentaerythritol stearate, 0.5 parts ultraviolet light absorber Tinuvin P, and 0.5 parts hindered amine light stabilizer Chimassorb 944.

[0061] The modified polypropylene electrode frame material formulation consists of 26.8 parts of homopolymer polypropylene functional masterbatch, 70 parts of impact copolymer polypropylene PP-BM02G, and 15 parts of polyolefin elastomer POE XLT 8677.

[0062] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0063] Example 6

[0064] Homopolymer polypropylene functional masterbatch formulation: 30 parts homopolymer polypropylene PP-H GD-320, 0.1 parts metal passivator IrganoxMD 1024, 0.05 parts sorbitol acetal nucleating agent Mild 3988, 0.3 parts antioxidant B215, 0.3 parts lignite ester, 0.5 parts ultraviolet light absorber Tinuvin P, and 0.5 parts hindered amine light stabilizer Chimassorb 944.

[0065] The modified polypropylene electrode frame material formulation consists of 31.75 parts homopolymer polypropylene functional masterbatch, 65 parts impact copolymer polypropylene PP-BM02G, and 15 parts polyolefin elastomer POE XLT 8677.

[0066] First, weigh the raw materials in the homopolymer polypropylene functional masterbatch formula, mix and granulate them. Then, mix the masterbatch with impact copolymer polypropylene and polyolefin elastomer in proportion and granulate them. Finally, use an injection molding machine to form a large-size thin-walled weather-resistant modified polypropylene electrode frame for flow batteries.

[0067] Comparative Example 1

[0068] Polypropylene electrode frame material formulation: 100 parts homopolymer polypropylene PP-H GD-320, 0.3 parts antioxidant B215, and 0.3 parts calcium stearate.

[0069] Weigh the raw materials in the polypropylene electrode frame material formula, mix them, granulate them, and then mold them into electrode frames using an injection molding machine.

[0070] Comparative Example 2

[0071] Polypropylene electrode frame material formulation: 20 parts homopolymer polypropylene PP-H GD-320, 80 parts impact copolymer polypropylene PP-BM00D, 0.3 parts antioxidant B215, and 0.3 parts calcium stearate.

[0072] Weigh the raw materials in the polypropylene electrode frame material formula, mix them, granulate them, and then mold them into electrode frames using an injection molding machine.

[0073] Table 1 Mass ratio of homopolymer polypropylene functional masterbatch

[0074] Table 2 Mass ratio of modified polypropylene electrode frame material

[0075] Samples were taken from the electrode frame for mechanical property and infrared transmittance testing (Table 3), and ultraviolet aging and electrolyte (vanadium solution + sulfuric acid) resistance tests were conducted. The ultraviolet testing was performed in an accelerated ultraviolet aging tester (QUV / se, Q-Lab, USA) with a light power of 0.68 W / m². 2 Cyclic conditions: 22 hours of UV exposure, blackboard temperature 55℃; 2 hours of darkness, blackboard temperature 40℃, humidity above 90%. Samples were taken every 500 hours, for a total of 1000 hours of aging. The mechanical property test results are shown in Table 4.

[0076] Electrolyte resistance test procedure: ① Place the prepared electrolyte (vanadium solution + sulfuric acid) into a wide-mouthed glass bottle with a lid. Immerse the sample in the electrolyte using a self-made clamp, seal the bottle, and place it in a cabinet at an ambient temperature of 25℃. ② Take samples every 1000 hours for a total of 2000 hours and test the mechanical properties of the samples (Table 5).

[0077] From the mechanical property results of the examples and comparative examples in Table 3, Examples 1-6 used a combination of high-flow, high-strength homopolymer polypropylene, impact-resistant copolymer polypropylene, and polyolefin elastomers, which retained the high strength and high flowability of homopolymer polypropylene while also possessing good toughness. As the content of homopolymer polypropylene increased, the strength and modulus of the samples increased, but the elongation at break and toughness decreased. The addition of the nucleating agent improved the crystallinity and crystallization rate of polypropylene, reduced the crystal size to form small spherulites, thereby improving the strength of the polypropylene material and the dimensional stability of the product. Comparative Example 1, which used only homopolymer polypropylene, had higher strength and modulus, but its impact strength was only 4.36 kJ / m². 2 This design fails to meet the long-term high-pressure requirements of the electrode frame after assembly, making it prone to cracking. Comparative Example 2 used a blend of homopolymer and copolymer polypropylene, which improved the impact strength of the sample.

[0078] The impact-resistant polypropylene grade used in Examples 1-3 is PP-B M00D, and the grade used in Examples 4-6 is PP-B M02G. Both have low flow and high impact resistance, while also possessing a certain degree of strength, enabling the modified polypropylene material to possess both toughness and strength. The examples also include the addition of the polyolefin elastomer POE XLT 8677, which has a glass transition temperature as low as -65°C and exhibits excellent toughening effects; simultaneously, its melting temperature can reach 118°C, providing a certain degree of strength at room temperature, which can reduce the creep caused by ordinary polyolefin elastomers and improve the dimensional stability of the electrode frame product.

[0079] As can be seen from Tables 4 and 5, the light stabilizers and metal passivators added in the examples slowed down the degradation rate of the modified polypropylene materials under ultraviolet light and strong oxidizing electrolyte environments. However, Comparative Examples 1 and 2 did not contain nucleating agents, light stabilizers, or other functional additives, therefore their performance deteriorated rapidly in ultraviolet aging and electrolyte resistance tests, making them unsuitable for long-term contact with strong electrolytes and difficult to use outdoors.

[0080] Table 3 Mechanical properties and infrared transmittance data of the samples

[0081] Table 4. Mechanical property test results of samples after UV aging

[0082] Table 5 Mechanical properties of samples after electrolyte resistance test

[0083] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many variations can be made based on the foregoing description. The embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A large-size thin-walled weather-modified polypropylene electrode frame for a flow battery, characterized by, The modified polypropylene material constituting the electrode frame is composed of the following components by weight: 20-53 parts of homopolymerization polypropylene functional masterbatch, 40-80 parts of impact copolymer polypropylene, and 5-30 parts of polyolefin elastomer; the homopolymerization polypropylene functional masterbatch is made of the following raw materials by weight: 20-50 parts of homopolymerization polypropylene powder, 0.1-0.3 parts of metal passivator, 0.05-0.1 parts of rigid nucleating agent, 0.2-0.5 parts of antioxidant, 0.2-1 parts of lubricant, and 0.5-2 parts of light stabilizer.

2. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries according to claim 1, characterized in that, The homopolymerization polypropylene powder is a high-flow polypropylene powder with an isotacticity index ≥ 94% and a melt mass flow rate ≥ 30 g / 10 min under the test conditions of 230°C and 2.16 kg.

3. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The impact copolymer polypropylene is an ethylene-propylene copolymer with a mass fraction of ethylene of 3-10% and a melt mass flow rate of 0.5-2.0 g / 10 min under the test conditions of 230°C and 2.16 kg.

4. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The polyolefin elastomer is an ethylene-octene copolymer with a mass fraction of octene of 55-60% and a melt mass flow rate of 0.2-1.0 g / 10 min under the test conditions of 190°C and 2.16 kg.

5. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The metal passivator is N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine.

6. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The rigid nucleating agent is a sorbitol acetal nucleating agent.

7. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The light stabilizer is one or more of a benzotriazole ultraviolet light absorber, a benzophenone ultraviolet light absorber, and a hindered amine light stabilizer.

8. The large-size thin-wall weather-modified polypropylene electrode frame for liquid flow batteries of claim 1, wherein, The lubricant is selected from one or more of calcium stearate, zinc stearate, pentaerythritol stearate, montanic acid ester, and ethylene bis-stearamide.

9. The large size thin walled weather modified polypropylene electrode frame for liquid flow battery according to claim 1, characterized in that, The antioxidant is selected from one or a mixture of both of a phenolic antioxidant and a phosphite antioxidant.

10. A method of making a large size thin walled weather modified polypropylene electrode frame for a flow battery as claimed in any one of claims 1-9, characterized in that, The method comprises the following steps: Step (1): preparing the homopolymerization polypropylene functional masterbatch: weighing the homopolymerization polypropylene powder, metal passivator, rigid nucleating agent, antioxidant, lubricant, and light stabilizer in the proportions defined in claim 1, placing them in a high-speed mixer, stirring at low speed for 1.5 min, and then stirring at high speed at a speed of 1000 rpm for 1.5 min; feeding the mixed materials into a parallel twin-screw extruder for plasticizing and mixing, water cooling, traction, granulation, and homogenization to obtain the homopolymerization polypropylene functional masterbatch; the extrusion temperature of the parallel twin-screw extruder is 180-210°C, the main machine screw rotation speed is 40 rpm, the feeding rotation speed is 15 rpm, and the granulation rotation speed is 150 rpm; Step (2): preparing the modified polypropylene granules: weighing the homopolymerization polypropylene functional masterbatch prepared in step (1), impact copolymer polypropylene, and polyolefin elastomer in the proportions defined in claim 1, placing them in a high-speed mixer, and stirring for 2 min, and then feeding them into a parallel twin-screw extruder for granulation to obtain the modified polypropylene granules; the extrusion temperature of the parallel twin-screw extruder is 180-210°C, the main machine screw rotation speed is 40 rpm, the feeding rotation speed is 15 rpm, and the granulation rotation speed is 150 rpm; Step (3) injection molding: the modified polypropylene pellets prepared in step (2) are dried at 60-70 DEG C for 2h, and then added into a high-precision single screw injection machine with large locking force, small injection volume, high pressure and high speed characteristics, to obtain an electrode frame product by injection molding; the process parameters of the injection molding are as follows: injection temperature 200-240 DEG C, hot runner temperature 240 DEG C, maximum locking pressure 130 bar; Step (4) post-processing: the electrode frame product obtained in step (3) is cooled after ejection, and stacking is avoided during the cooling process to ensure uniform heat dissipation of each product; after the product is completely cooled, it is stacked and boxed; the products used in combination are assembled with the same batch of products.

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