Proton exchange membrane capable of being subjected to laser welding and preparation method thereof

Abstract

The invention discloses a proton exchange membrane capable of being subjected to laser welding and a preparation method thereof. The proton exchange membrane for laser welding is of a double-layer composite structure composed of a weldable layer and a proton exchange layer. The weldable layer is formed by calendering or melt extrusion of a mixed material, and the mixed material comprises polyolefin resin, a plasticizer, hydrophilic silicon dioxide, a coloring agent and an antioxidant; the proton exchange layer is formed by coating the surface of the weldable layer with resin slurry of non-fluorine polymer resin containing sulfonic acid groups; the proton exchange membrane can realize laser welding with the electrode plate frame, and the welding part is not cracked after being soaked in electrolyte. The membrane material provided by the invention can realize laser welding with an electrode plate frame, can improve the stability of a galvanic pile, reduces the use amount of sealing gaskets, and reduces the stacking volume and cost. Based on the synergistic effect of proton exchange and micropore screening, the membrane material has excellent proton conductivity and vanadium resistance. The membrane materials are all fluoride-free environment-friendly materials, acid and alkali resistance and low cost are achieved, and continuous batch processing can be achieved.

Description

Technical Field

[0001] This invention relates to a laser-weldable proton exchange membrane and its preparation method, belonging to the field of battery separator technology. Background Technology

[0002] Vanadium redox flow batteries (VRBs) are a key technology in the new energy field, characterized by long-term energy storage, high safety, and long lifespan. However, currently industrialized VRB stacks still suffer from high initial installation costs and issues such as leakage and bubbling. In recent years, laser welding technology has been widely used in VRB stack assembly to improve stack stability and reduce leakage. Chinese patent application CN 113823806 B discloses a method for welding the separator to the electrode frame, reducing the use of sealing gaskets and improving the sealing reliability of VRBs, but it does not describe the preparation method of this weldable membrane. Chinese patent application CN 103618057 B discloses a laser-weldable microporous membrane, which is prepared by melt extrusion and further shaped and thinned after calendering or uniaxial stretching. However, microporous membranes produced by this process have low strength and cannot meet the requirements of NBT 42080-2023 (General Technical Conditions and Test Methods for Ion Conductive Membranes for Vanadium Redox Flow Batteries).

[0003] Currently, proton exchange membranes used in commercial flow batteries are mainly perfluorosulfonic acid resin membranes, which achieve high proton conductivity through a continuous hydrophilic phase structure. However, they have two inherent drawbacks: first, high vanadium ion permeability leads to battery self-discharge and capacity decay; second, high cost increases the initial installation cost of the battery stack. Furthermore, due to their high melting point, perfluorosulfonic acid membranes cannot be laser-welded to the electrode plates and frames, requiring sealing with gaskets, which significantly increases the installation volume and material usage of the battery stack. This invention is therefore proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a laser-weldable proton exchange membrane and its preparation method, which has the characteristics of being able to be welded to electrode plates and frames, having low vanadium ion permeation, good ion selectivity, and low cost, and can be mass-produced, thus solving some bottleneck problems of current commercial membranes themselves and during stacking.

[0005] The laser-weldable proton exchange membrane provided by the present invention is a double-layer composite structure composed of a weldable layer and a proton exchange layer; The weldable layer is formed by calendering or melt extrusion of a mixture, the mixture including polyolefin resin, plasticizer, hydrophilic silica, colorant and antioxidant; The proton exchange layer is formed by coating the surface of the weldable layer with a resin slurry containing a non-fluorinated polymer resin with sulfonic acid groups; The proton exchange membrane can be laser-welded to the electrode plate frame, and the welded part does not crack after being immersed in the electrolyte.

[0006] In the proton exchange membrane of the present invention, the thickness of the weldable layer is 100-300 μm and the pore size is 10 nm-1 μm; The thickness of the proton exchange layer is 5-50 μm, preferably 15-20 μm.

[0007] In the proton exchange membrane of the present invention, the mass composition of the mixture is as follows: 20-40 parts polyolefin resin; 40-60 parts plasticizer; 10-25 parts hydrophilic silica; 1-2 parts colorant; 1-2 parts antioxidant; The polyolefin resin is ultra-high molecular weight polyethylene or ultra-high molecular weight polypropylene. The plasticizer is selected from at least one of white oil, isoalkanes, high-density polyethylene, and low-density polyethylene; The antioxidant is selected from one or both of antioxidant-1010 and antioxidant-168.

[0008] In the proton exchange membrane of the present invention, the resin slurry has the following mass composition: 15-25 parts sulfonated polymer resin; 75-85 parts polar solvent; The sulfonated polymer resin is selected from at least one of sulfonated polyether ether ketone, sulfonated polybenzimidazole, and sulfonated polyether sulfone, and can be prepared by post-sulfonation method: the resin is placed in a three-necked flask containing concentrated sulfuric acid and reacted at 50-70°C for 4-8 hours under a nitrogen atmosphere. After the reaction is completed, the solution turns dark red. After cooling the solution to room temperature, it is slowly poured into an ice-water mixture and stirred continuously to obtain a fibrous white precipitate. The precipitate is washed repeatedly with a large amount of deionized water until the pH of the final washing solution is neutral. The precipitate is dried at 30-60°C for 24-36 hours to obtain sulfonated polyether ether ketone, sulfonated polybenzimidazole, and sulfonated polyether sulfone with a sulfonation degree of 50-70%.

[0009] In the proton exchange membrane of the present invention, the polar solvent is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, ethanol, isopropanol, water, and dimethyl sulfoxide.

[0010] The present invention also provides a method for preparing the proton exchange membrane, comprising the following steps: S1. The mixture is formed into a sheet by calendering or extrusion, and the sheet is then extracted and dried to obtain the weldable layer. S2. The resin slurry is loaded onto the weldable layer through slit coating, casting, scraping or micro-recessed coating, and then dried to form the proton exchange membrane.

[0011] In step S1, the polyolefin resin, the plasticizer, the hydrophilic silica, the colorant and the antioxidant are mixed and stirred for 1-2 hours, and then allowed to stand at 60-80°C for 12-24 hours to obtain the mixture, so that the plasticizer impregnates the resin.

[0012] In step S1, the calendering method includes the following steps: the mixture is continuously calendered 2-4 times in a calender with a roller gap of 0.05-0.20 mm and a roller temperature of 120-140℃, and then extracted and dried after winding to form a porous skeleton structure. The extrusion method includes the following steps: the mixture is extruded into a sheet by a twin-screw extruder at 180-220℃, and then extracted and dried after calendering and stretching to form a porous skeleton structure.

[0013] In step S2, the sulfonated polymer resin is mixed and stirred with a polar solvent for 8-24 hours, and then allowed to stand for 12-24 hours to defoam and eliminate coating defects, thereby obtaining the resin slurry. The drying and molding temperature is 80-110℃ to achieve interlayer molecular-level bonding; The coating speed is 0.5-2 m / min.

[0014] Before the coating in step S2, the following modification steps 1) or 2) are also included. 1) Perform vacuum plasma treatment on the weldable layer for 3-5 seconds; 2) Or, a surfactant may be added to the resin slurry to enhance interfacial bonding.

[0015] The present invention has the following beneficial technical effects: (1) The membrane material of the present invention can be laser welded to the electrode plate frame, which can improve the stability of the stack, reduce the amount of sealing gasket, and reduce the stack volume and cost.

[0016] (2) The membrane material of the present invention has excellent proton conductivity and vanadium barrier properties based on the synergistic effect of proton exchange and microporous sieving.

[0017] (3) The membrane materials of the present invention are all made of fluorine-free environmentally friendly materials, which are resistant to acid and alkali, have low cost, and can realize continuous batch processing. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the laser-weldable proton exchange membrane of the present invention.

[0019] Figure 2 Battery efficiency data for laser-weldable proton exchange membranes provided by this invention. Detailed Implementation

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0021] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0022] Example 1: Preparation of a laser-weldable proton exchange membrane (1) Weldable layer raw material mixing: Weigh 30 parts of ultra-high molecular weight polyethylene resin (molecular weight 100W), 50 parts of isoalkanes, 18 parts of hydrophilic silica, 1 part of color masterbatch and 1 part of antioxidant (antioxidant-1010 and antioxidant-168) by weight, and mix them with a high-speed mixer for 1 hour; place the mixture in a constant temperature box at 80°C and let it stand for 12 hours to allow the oil to fully impregnate the resin, which is convenient for subsequent processing and feeding.

[0023] (2) Weldable layer forming: The mixture is fed between two parallel rollers of a horizontal calender with a roller spacing of 0.20 mm and a roller surface temperature of 137-140 °C. o C. The sheet is extruded from below the parallel rollers and immediately passes through the second and third sets of pressure rollers for multiple calendering processes. The roller spacing is 0.06-0.1 mm, and the roller surface temperature is 130-137°C. o C. The sheet after secondary calendering is wound up, and after extraction and drying, a weldable layer material is obtained; the thickness of the weldable layer is 150-200μm, and the pore size is 10nm-80nm.

[0024] (3) Preparation of proton exchange resin slurry: The sulfonation method was used for preparation: 10g of polyether ether ketone resin was put into a three-necked flask containing 100mL of concentrated sulfuric acid and reacted at 60°C for 6h under a nitrogen atmosphere. After the reaction was completed, the solution turned dark red. After cooling the solution to room temperature, it was slowly poured into an ice-water mixture and stirred continuously to obtain a fibrous white precipitate. The precipitate was washed repeatedly with a large amount of deionized water until the pH of the final washing solution was neutral. It was dried at 50°C for 24h to obtain sulfonated polyether ether ketone with a sulfonation degree of 60%. 18 parts by weight of sulfonated polyether ether ketone resin and 82 parts by weight of a mixed solvent of N,N-dimethylformamide and ethanol were weighed, mixed and stirred for 12h, and allowed to stand for 12h to defoam, to obtain the resin slurry.

[0025] (4) Preparation of proton exchange layer: The prepared slurry is coated onto the weldable layer through a slit at a speed of 0.5 m / min and a drying temperature of 95°C. After drying, the membrane is rolled up to obtain a proton exchange membrane with a thickness of 15-18 μm.

[0026] A schematic diagram of the laser-weldable proton exchange membrane prepared in this embodiment is shown below. Figure 1 As shown.

[0027] Example 2: Preparation of a laser-weldable proton exchange membrane (1) Weldable layer raw material mixing: Weigh 25 parts of ultra-high molecular weight polyethylene resin (molecular weight 200W), 50 parts of white oil, 25 parts of hydrophilic silica, 1 part of color masterbatch, and 1 part of antioxidant-1010 and antioxidant-168 in total, and mix them with a high-speed mixer for 1 hour. Place the mixture in a constant temperature box at 80°C and let it stand for 12 hours to allow the oil to fully impregnate the resin, which is convenient for subsequent processing and feeding.

[0028] (2) Weldable layer processing and molding: The mixture is fed into a twin-screw melt extruder, and the extrusion temperature is 180-200℃. o C. The extruded sheet is calendered, stretched, and then wound up. After extraction and drying, a weldable layer material is obtained with a thickness of 220-250μm and a pore size of 50nm-0.5μm.

[0029] (3) Preparation of proton exchange resin slurry: Calculate by weight, weigh a total of 20 parts of sulfonated polyether ether ketone and sulfonated polyether sulfone, and 80 parts of N,N-dimethylacetamide and isopropanol mixed solvent, mix and stir for 12 hours, let stand for 12 hours to defoam, and obtain resin slurry.

[0030] (4) Preparation of proton exchange layer: The prepared slurry is loaded onto the weldable layer by casting method at a casting speed of 2m / min and a drying temperature of 80℃. After drying, it is rolled up to obtain a proton exchange membrane with a thickness of 18-20um.

[0031] A schematic diagram of the laser-weldable proton exchange membrane prepared in this embodiment is shown below. Figure 1 As shown.

[0032] Example 3: Preparation of a laser-weldable proton exchange membrane (1) Weldable layer raw material mixing: Weigh 30 parts of ultra-high molecular weight polyethylene resin (molecular weight 200W), 62 parts of white oil, 5 parts of hydrophilic silica, 2 parts of color masterbatch and 1 part of antioxidant-1010 and antioxidant-168 by weight, and mix them with a high-speed mixer for 1 hour; place the mixture in a constant temperature box at 80℃ and let it stand for 12 hours to allow the oil to fully impregnate the resin, which is convenient for subsequent processing and feeding.

[0033] (2) Weldable layer processing and molding: The mixture is fed into a twin-screw melt extruder, and the extrusion temperature is 180-200℃. o C. The extruded sheet is stretched longitudinally and then wound up. After extraction and drying, a weldable layer material is obtained with a thickness of 100-120μm and a pore size of 50nm-1μm.

[0034] (3) Preparation of proton exchange resin slurry: Calculate by weight, weigh 22 parts of sulfonated polyether ether ketone, 78 parts of N,N-dimethylacetamide, ethanol and water mixed solvent, mix and stir for 12h, let stand for 12h to defoam, and obtain resin slurry. (4) Preparation of proton exchange layer: The weldable layer is pretreated with vacuum plasma for 4 seconds. Then, the prepared slurry is immediately loaded onto the treated weldable layer by scraping method at a scraping speed of 1.5 m / min and a drying temperature of 110℃ to obtain a proton exchange membrane with a thickness of 18-20 μm.

[0035] A schematic diagram of the laser-weldable proton exchange membrane prepared in this embodiment is shown below. Figure 1 As shown.

[0036] Figure 2 Battery efficiency data for laser-weldable proton exchange membranes provided by this invention; The weldable proton exchange membrane prepared according to this invention was assembled into a single vanadium redox flow battery for testing, achieving an 80 mA / cm² reading. 2 Under current density conditions, Example 1 exhibited a coulombic efficiency of 98.6%, an energy efficiency of 88.2%, and a voltage efficiency of 89.5%; Example 2 showed a coulombic efficiency of 99.4%, an energy efficiency of 86.2%, and a voltage efficiency of 86.7%. Overall, the coulombic efficiency of the membranes was greater than 98%, and the energy efficiency was greater than 86%, indicating that the membrane possesses both excellent vanadium barrier properties and high proton conductivity. The membrane was laser-welded to a PE electrode frame, and after immersion in electrolyte for several weeks to several months, no cracking or detachment occurred at the weld joint.

[0037] The vanadium redox flow battery testing system uses a 3W battery and a 5V 12A charge / discharge meter. The membrane sample is placed flat inside the battery, and the charge / discharge meter is used to record the battery voltage, charging capacity (ampere-hours), discharging capacity (ampere-hours), coulombic efficiency, and energy efficiency in real time.

[0038] Comparative Example 1 Testing of perfluorosulfonic acid membrane in a single vanadium redox flow battery, 80 mA / cm 2 Under current density conditions, the Nafion membrane has a coulombic efficiency of 95.1%, an energy efficiency of 87.9%, and a voltage efficiency of 92.3%. Overall, the perfluorosulfonic acid membrane has excellent energy efficiency, but its coulombic efficiency is relatively low.

[0039] Comparative Example 2 Preparation of proton exchange layer monolayer and its testing in a single vanadium redox flow battery.

[0040] The sulfonated polyether ether ketone slurry from Example 1 was applied to a PET film via slit coating at a speed of 0.5 m / min and dried at 95°C. After drying, the film was wound up and peeled off from the PET film, with a thickness of 15-18 μm measured. (At 80 mA / cm...) 2 Tested under current density conditions, the measured coulombic efficiency was 95.9%, energy efficiency was 87.8%, and voltage efficiency was 91.6%. This indicates that the coulombic efficiency of a single-layer proton exchange membrane is relatively low, due to the poor vanadium barrier properties of the proton exchange membrane itself. The presence of a weldable layer effectively solves this problem, allowing the coulombic efficiency of the laser-weldable proton exchange membrane to remain above 98%. Furthermore, because the weldable layer is a porous material, it ensures that protons passing through the proton exchange layer can still efficiently pass through the weldable layer.

Claims

1. A laser-weldable proton exchange membrane, comprising a double-layer composite structure consisting of a weldable layer and a proton exchange layer; The weldable layer is formed by calendering or melt extrusion of a mixture, the mixture including polyolefin resin, plasticizer, hydrophilic silica, colorant and antioxidant; The proton exchange layer is formed by coating the surface of the weldable layer with a resin slurry containing a non-fluorinated polymer resin with sulfonic acid groups; The proton exchange membrane can be laser-welded to the electrode plate frame, and the welded part does not crack after being immersed in the electrolyte.

2. The proton exchange membrane according to claim 1, characterized in that: The thickness of the weldable layer is 100-300μm, and the pore size is 10nm-1μm; The thickness of the proton exchange layer is 5-50 μm.

3. The proton exchange membrane according to claim 1 or 2, characterized in that: The mass composition of the mixture is as follows: 20-40 parts polyolefin resin; 40-60 parts plasticizer; 10-25 parts hydrophilic silica; 1-2 parts colorant; 1-2 parts antioxidant; The polyolefin resin is ultra-high molecular weight polyethylene or ultra-high molecular weight polypropylene. The plasticizer is selected from at least one of white oil, isoalkanes, high-density polyethylene, and low-density polyethylene; The antioxidant is selected from one or both of antioxidant-1010 and antioxidant-168.

4. The proton exchange membrane according to any one of claims 1-3, characterized in that: The resin slurry has the following composition by weight: 15-25 parts sulfonated polymer resin; 75-85 parts polar solvent; The sulfonated polymer resin is selected from at least one of sulfonated polyether ether ketone, sulfonated polybenzimidazole, and sulfonated polyether sulfone.

5. The proton exchange membrane according to claim 4, characterized in that: The polar solvent is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, ethanol, isopropanol, water, and dimethyl sulfoxide.

6. A method for preparing the proton exchange membrane according to any one of claims 1-5, comprising the following steps: S1. The mixture is formed into a sheet by calendering or extrusion, and the sheet is then extracted and dried to obtain the weldable layer. S2. The resin slurry is loaded onto the weldable layer through slit coating, casting, scraping or micro-recessed coating, and then dried to form the proton exchange membrane.

7. The preparation method according to claim 6, characterized in that: In step S1, the polyolefin resin, the plasticizer, the hydrophilic silica, the colorant and the antioxidant are mixed and stirred for 1-2 hours, and then allowed to stand at 60-80°C for 12-24 hours to obtain the mixture.

8. The preparation method according to claim 6 or 7, characterized in that: In step S1, the calendering method includes the following steps: the mixture is continuously calendered 2-4 times in a calender with a roller gap of 0.05-0.20 mm and a roller temperature of 120-140℃, and then extracted and dried after winding. The extrusion method includes the following steps: extruding the mixture into the sheet using a twin-screw extruder at 180-220℃, followed by calendering, stretching, extraction, and drying.

9. The preparation method according to any one of claims 6-8, characterized in that: In step S2, the sulfonated polymer resin is mixed and stirred with a polar solvent for 8-24 hours, and then allowed to stand for 12-24 hours to defoam in order to obtain the resin slurry. The drying and molding temperature is 80-110℃; The coating speed is 0.5-2 m / min.

10. The preparation method according to any one of claims 6-9, characterized in that: Before step S2 coating, the following steps 1) or 2) are also included. 1) Perform vacuum plasma treatment on the weldable layer for 3-5 seconds; 2) Or, a surfactant may be added to the resin slurry to enhance interfacial bonding.

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