A composite proton exchange membrane for vanadium flow batteries and a method of making the same

Abstract

The present application relates to the field of proton exchange membrane preparation, and particularly relates to a composite proton exchange membrane for vanadium flow battery and a preparation method thereof. The composite proton exchange membrane is improved from two aspects of material and structure. The main component materials include perfluorosulfonic acid resin and sulfonated polyether ether ketone resin. The microstructure of the membrane includes high-strength resin network and high-ionic-conductivity resin particles, which are organically combined into a whole. The composite proton exchange membrane is mainly prepared through sulfonation treatment of polyether ether ketone resin, preparation of nanoparticles, casting of casting solution and flow casting of composite membrane. The obtained membrane shows excellent ion transmission selectivity, suitable swelling and good mechanical strength, and the comprehensive performance is superior to that of commercially available proton exchange membranes. Meanwhile, the present application has simple technical process, easily available raw materials, and does not need expensive and complex production equipment, and is easy to realize large-scale production. The present application can significantly promote the performance improvement and cost reduction of vanadium flow battery, and promote its popularization in the field of large-scale energy storage.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane preparation, and in particular to a composite proton exchange membrane for vanadium redox flow batteries and its preparation method. Background Technology

[0002] Vanadium redox flow batteries (VRBs) possess advantages such as long cycle life, environmental friendliness, abundant raw materials, high efficiency, low cost, and ease of operation, and have broad development prospects. VRBs can be used as energy storage devices in conjunction with solar and wind power systems to regulate energy supply and demand imbalances. When wind and solar energy are abundant, the batteries store the electricity generated; when energy is insufficient, they output the stored energy, ensuring stable grid operation.

[0003] Proton exchange membranes (PEMs) are key materials for vanadium redox flow batteries and have long been a research hotspot in the field. In recent years, PEMs have undergone rapid improvements in materials, structure, and performance, thus driving the development of flow batteries. Compared to other energy storage devices, vanadium redox flow batteries have significant advantages.

[0004] As a key material, proton exchange membranes need to possess high proton conductivity, low vanadium ion permeability, good mechanical strength and chemical stability, and low cost. Although the Nafion series of proton exchange membranes are currently among the best-performing membrane materials that can be mass-produced, further improvements are needed in ion transfer selectivity, mechanical properties, and economic efficiency to meet the stringent performance requirements of vanadium redox flow batteries.

[0005] Researchers have conducted extensive studies on membrane fabrication technology, among which the composite of materials, allowing for precise design of membrane structure and performance, has become a research hotspot in recent years. Patent CN103296296 describes a membrane-forming solution prepared by ultrasonically dissolving polymeric materials and nano-oxide particles in an organic solvent. A polymer-inorganic porous membrane with an asymmetric morphology is then prepared using a phase transfer method, resulting in improved membrane performance. Researchers have also prepared composite membranes using Nafion and polyvinylidene fluoride, finding a significant improvement in ion selectivity. Furthermore, researchers have prepared sulfonated polyether ether ketone hybrid membranes doped with sulfonated graphene oxide nanosheets. Tests showed that the addition of graphene nanosheets improves the water absorption, ion exchange capacity, and proton conductivity of the hybrid membrane.

[0006] Although there are numerous research reports on composite proton exchange membranes, most of the technologies are relatively complex and still in the experimental stage, far from industrialization. Therefore, exploring simple, high-performance proton exchange membrane fabrication technologies from a materials and structural perspective is of great significance. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a composite proton exchange membrane for vanadium redox flow batteries and its preparation method. This composite proton exchange membrane is mainly composed of perfluorosulfonic acid resin and sulfonated polyetheretherketone resin, possessing a composite structure of a high-strength resin network and highly ion-conductive resin particles. The composite proton exchange membrane is prepared primarily through steps such as sulfonation treatment of polyetheretherketone resin and preparation of nanoparticles, casting solution, and casting of the composite membrane. The membrane material exhibits excellent ion transport selectivity, suitable swelling properties, and good mechanical strength, with overall performance superior to commercially available proton exchange membranes. This invention is technically simple, uses readily available raw materials, and is easily scalable for mass production. It can promote the performance improvement and cost reduction of vanadium redox flow batteries, facilitating their application in large-scale energy storage.

[0008] The technical solution of this invention is:

[0009] A composite proton exchange membrane for vanadium redox flow batteries is improved in terms of both materials and structure. The constituent materials include perfluorosulfonic acid resin and sulfonated polyether ether ketone resin. The microstructure of the membrane is a composite structure that organically combines a high-strength resin network and highly ion-conductive resin particles. The high-strength resin network and highly ion-conductive resin particles play a mutually restraining role, improving the membrane's ion transport selectivity, swelling properties, and mechanical properties.

[0010] Furthermore, in the aforementioned composite proton exchange membrane for a vanadium redox flow battery, the perfluorosulfonic acid resin comprises commercially available new perfluorosulfonic acid resin and recycled perfluorosulfonic acid resin obtained from chlor-alkali membrane treatment, wherein the EW value of the perfluorosulfonic acid resin is 600-1500.

[0011] Furthermore, in the aforementioned composite proton exchange membrane for a vanadium redox flow battery, the sulfonated polyether ether ketone resin is a commercially available polyether ether ketone resin modified by sulfuric acid sulfonation, with a sulfonation degree of 40-90%.

[0012] Furthermore, in the aforementioned composite proton exchange membrane for vanadium redox flow batteries, the high-strength resin network originates from the microstructure of perfluorosulfonic acid resin, the high ionic conductivity resin particles originate from the microstructure of sulfonated polyether ether ketone resin, the mass ratio of perfluorosulfonic acid resin to sulfonated polyether ether ketone resin is 10:1 to 1:1, and the resulting composite proton exchange membrane has a thickness of 15 to 50 μm.

[0013] Furthermore, in the aforementioned composite proton exchange membrane for a vanadium redox flow battery, the sulfonated polyether ether ketone resin is ball-milled at low temperature to obtain highly ionicly conductive resin particles with a size of 20–500 nm.

[0014] Furthermore, in the aforementioned composite proton exchange membrane for vanadium redox flow batteries, the mutual clamping effect refers to the mutual restraint between the perfluorosulfonic acid resin polymer segments and the sulfonated polyether ether ketone resin particles, which has the function of preventing vanadium ions from diffusing through the membrane.

[0015] Furthermore, in the aforementioned composite proton exchange membrane for a vanadium redox flow battery, the ion transfer selectivity refers to the ratio of the permeation rates of hydrogen ions to vanadium ions, wherein the hydrogen ion conductivity is greater than 0.05 S / cm, and the ratio of hydrogen ion conductivity to vanadium ion conductivity is greater than 50.

[0016] A method for preparing a composite proton exchange membrane for vanadium redox flow batteries mainly includes sulfonation treatment of polyetheretherketone resin, preparation of resin nanoparticles, casting solution and casting of the composite membrane, ultimately obtaining a membrane material with excellent performance. The specific steps are as follows:

[0017] Step (1) Sulfonation treatment of polyetheretherketone resin

[0018] Commercially available polyether ether ketone resin is dissolved in concentrated sulfuric acid to obtain a solution with a mass concentration of 3-15%. The solution is continuously stirred at 50-90°C to carry out a sulfonation reaction. Finally, the solution is precipitated in water and dried to obtain sulfonated polyether ether ketone resin.

[0019] Step (2) Preparation of resin nanoparticles

[0020] Sulfonated polyether ether ketone resin was placed in a low-temperature ball mill with a temperature range of -50 to 10°C and a rotation speed range of 600 to 3000 r / min. After ball milling, sulfonated polyether ether ketone resin nanoparticles with a size of 20 to 500 nm were obtained.

[0021] Step (3) Casting preparation of casting solution and composite film

[0022] Sulfonated polyether ether ketone resin particles were doped into a perfluorosulfonic acid resin solution and stirred thoroughly to obtain a uniform casting solution. A composite membrane was prepared using a doctor blade method. After pre-drying and further drying, a composite proton exchange membrane for vanadium redox flow batteries was finally obtained. The pre-drying temperature was 40–80 °C and the time was 1–4 h. The further drying temperature was 100–180 °C and the time was 2–6 h.

[0023] A high-performance vanadium redox flow battery using a composite proton exchange membrane prepared by the above method.

[0024] The advantages and beneficial effects of this invention are:

[0025] This invention constructs a highly efficient proton transport channel by introducing highly sulfonated polyether ether ketone resin particles into perfluorosulfonic acid resin. Furthermore, the network structure of the perfluorosulfonic acid resin prevents the diffusion of vanadium ions, thereby enhancing the ion selectivity of the proton exchange membrane and improving the charge-discharge performance of vanadium redox flow batteries. Simultaneously, the preparation technology of the composite proton exchange membrane is simple and easy to implement, requiring no special equipment, offering excellent economic benefits, and facilitating technological upgrades based on existing proton exchange membrane production processes. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. While not all embodiments can be repeated here, the implementation of the present invention is not limited to the following embodiments. Unless otherwise specified, the materials and processing methods used in the present invention are conventional materials and processing methods in this technical field.

[0027] In this invention, unless otherwise specified, all percentages are mass percentages.

[0028] Example 1

[0029] 20 grams of polyetheretherketone resin were placed in concentrated sulfuric acid and stirred vigorously to obtain a resin solution with a mass concentration of 10%. Stirring was continued at 65°C for 4 hours to complete the sulfonation treatment. The sulfonated resin solution was then precipitated in water, rinsed, and dried to obtain sulfonated polyetheretherketone resin powder, with a sulfonation degree of 60%. The powder was then ball-milled at -20°C and 850 r / min for 4 hours using a low-temperature ball mill to obtain resin particles with a particle size of 125 nm.

[0030] Ten grams of perfluorosulfonic acid resin with an EW value of 1350 were weighed and dissolved in a mixed solvent of ethanol and water to obtain a perfluorosulfonic acid resin solution. Sulfonated polyetheretherketone (PEEK) particles at a mass fraction relative to the resin were further added, and the mixture was vigorously stirred for 8 hours to obtain a homogeneous casting solution. A 230 μm thick wet film was coated onto a glass plate using a doctor blade method. The film was pre-dried at 50 °C for 1.5 hours, then dried at 140 °C for 4 hours, finally obtaining a composite proton exchange membrane with a thickness of 28 μm. A proton exchange membrane without PEEK particle doping was prepared using a similar process and used as a control membrane.

[0031] Performance of composite membranes and contrast membranes:

[0032] The composite membrane of this invention has a hydrogen ion conductivity of 0.15 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 67, a linear swelling of 3%, and a tensile strength of 35 MPa.

[0033] The comparison membrane has a hydrogen ion conductivity of 0.04 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 12.5, a linear swelling rate of 7.6%, and a tensile strength of 21 MPa.

[0034] Example 2

[0035] 20 grams of polyetheretherketone resin were placed in concentrated sulfuric acid and stirred vigorously to obtain a resin solution with a mass concentration of 5%. Stirring was continued at 80°C for 5 hours to complete the sulfonation treatment. The sulfonated resin solution was then precipitated in water, rinsed, and dried to obtain sulfonated polyetheretherketone resin powder, with a sulfonation degree of 77%. The powder was then ball-milled at -45°C and 2250 r / min for 3 hours using a low-temperature ball mill to obtain resin particles with a particle size of 25 nm.

[0036] Ten grams of perfluorosulfonic acid resin with an EW value of 1050 were weighed and dissolved in a mixed solvent of ethanol and water to obtain a perfluorosulfonic acid resin solution. Sulfonated polyetheretherketone (PEEK) particles, at a mass fraction relative to the resin, were further added, and the mixture was vigorously stirred for 12 hours to obtain a homogeneous casting solution. A 300 μm thick wet film was prepared on a glass plate using a doctor blade method. The film was pre-dried at 70 °C for 2.5 hours, then dried at 120 °C for 8 hours, finally obtaining a 45 μm thick composite proton exchange membrane. A proton exchange membrane without sulfonated PEEK particle doping was prepared using a similar process and used as a control membrane.

[0037] Performance of composite membranes and contrast membranes:

[0038] The composite membrane of this invention has a hydrogen ion conductivity of 0.08 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 132, a linear swelling of 1.4%, and a tensile strength of 39 MPa.

[0039] The comparison membrane has a hydrogen ion conductivity of 0.02 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 18.4, a linear swelling of 8.5%, and a tensile strength of 24 MPa.

[0040] Example 3

[0041] 20 grams of polyetheretherketone resin were placed in concentrated sulfuric acid and stirred vigorously to obtain a resin solution with a mass concentration of 15%. Stirring was continued at 50°C for 3 hours to complete the sulfonation treatment. The sulfonated resin solution was then precipitated in water, rinsed, and dried to obtain sulfonated polyetheretherketone resin powder, with a sulfonation degree of 45%. The powder was then ball-milled at -35°C and 2600 r / min for 2.5 hours using a low-temperature ball mill to obtain resin particles with a particle size of 355 nm.

[0042] Ten grams of perfluorosulfonic acid resin with an EW value of 650 were weighed and dissolved in a mixed solvent of ethanol and water to obtain a perfluorosulfonic acid resin solution. Sulfonated polyetheretherketone (PEEK) particles at a mass fraction relative to the resin were further added, and the mixture was vigorously stirred for 24 hours to obtain a homogeneous casting solution. A 120 μm thick wet film was coated onto a glass plate using a doctor blade method. The film was pre-dried at 50 °C for 1 hour, then dried at 170 °C for 2 hours to obtain a 15 μm thick composite proton exchange membrane. A proton exchange membrane without PEEK particle doping was prepared using a similar process and used as a control membrane.

[0043] Performance of composite membranes and contrast membranes:

[0044] The composite membrane of this invention has a hydrogen ion conductivity of 0.24 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 95, a linear swelling of 3.3%, and a tensile strength of 33 MPa.

[0045] The comparison membrane has a hydrogen ion conductivity of 0.07 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 12.5, a linear swelling of 14.6%, and a tensile strength of 19 MPa.

[0046] Example 4

[0047] 20 grams of polyetheretherketone resin were placed in concentrated sulfuric acid and stirred vigorously to obtain a resin solution with a mass concentration of 8%. Stirring was continued at 90°C for 2 hours to complete the sulfonation treatment. The sulfonated resin solution was then precipitated in water, rinsed, and dried to obtain sulfonated polyetheretherketone resin powder, with a sulfonation degree of 77%. The powder was then ball-milled at -30°C and 1200 r / min for 5.5 hours using a low-temperature ball mill to obtain resin particles with a particle size of 480 nm.

[0048] Ten grams of perfluorosulfonic acid resin with an EW value of 950 were weighed and dissolved in a mixed solvent of ethanol and water to obtain a perfluorosulfonic acid resin solution. Sulfonated polyetheretherketone (PEEK) particles at a mass fraction relative to the resin were further added, and the mixture was vigorously stirred for 24 hours to obtain a homogeneous casting solution. A 360 μm thick wet film was coated onto a glass plate using a doctor blade method. The film was pre-dried at 60 °C for 3 hours, then dried at 150 °C for 3 hours, finally obtaining a 32 μm thick composite proton exchange membrane. A proton exchange membrane without sulfonated PEEK particle doping was prepared using a similar process and used as a control membrane.

[0049] Performance of composite membranes and contrast membranes:

[0050] The composite membrane of this invention has a hydrogen ion conductivity of 0.19 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 73, a linear swelling of 2.7%, and a tensile strength of 30 MPa.

[0051] The comparison membrane has a hydrogen ion conductivity of 0.1 S / cm, a hydrogen ion / hydroxyl ion permeation rate ratio of 21.2, a linear swelling of 8.2%, and a tensile strength of 24 MPa.

[0052] The results of the embodiments show that the composite proton exchange membrane of the present invention innovates in both membrane material and membrane structure. By introducing highly sulfonated polyether ether ketone resin particles into perfluorosulfonic acid resin, a highly efficient proton transport channel is constructed, thereby improving the ion selectivity of the proton exchange membrane and enhancing the charge-discharge performance of vanadium redox flow batteries. Furthermore, the technology of the present invention is simple, economical, and easy to scale up for production, which can promote the performance improvement and cost reduction of vanadium redox flow batteries, and facilitate their application in the field of large-scale energy storage.

Claims

1. A composite proton exchange membrane for vanadium redox flow batteries, characterized in that: This composite proton exchange membrane is improved in terms of both materials and structure. The constituent materials include perfluorosulfonic acid resin and sulfonated polyether ether ketone resin. The microstructure of the membrane is a composite structure that organically combines a high-strength resin network and highly ion-conductive resin particles. The high-strength resin network and highly ion-conductive resin particles play a mutually restraining role, improving the membrane's ion transfer selectivity, swelling and mechanical properties. The high-strength resin network is derived from the microstructure of perfluorosulfonic acid resin, and the high ionic conductivity resin particles are derived from the microstructure of sulfonated polyether ether ketone resin. The mass ratio of perfluorosulfonic acid resin to sulfonated polyether ether ketone resin is 10:1 to 1:1, and the thickness of the resulting composite proton exchange membrane is 15 to 50 μm. The mutual clamping effect refers to the mutual restriction between the perfluorosulfonic acid resin polymer chain segments and the sulfonated polyether ether ketone resin particles, which has the function of preventing vanadium ions from diffusing through the membrane. The sulfonated polyetheretherketone resin is a modified resin of commercially available polyetheretherketone resin after sulfuric acid sulfonation treatment, with a sulfonation degree of 40-90%. The sulfonated polyether ether ketone resin was ball-milled at low temperature to obtain highly ionicly conductive resin particles with a size of 20–500 nm.

2. The composite proton exchange membrane for a vanadium redox flow battery according to claim 1, characterized in that: The perfluorosulfonic acid resin includes commercially available new perfluorosulfonic acid resin and recycled perfluorosulfonic acid resin obtained from chlor-alkali membrane treatment, and the EW value of the perfluorosulfonic acid resin is 600 to 1500.

3. The composite proton exchange membrane for a vanadium redox flow battery according to claim 1, characterized in that: The ion transport selectivity refers to the ratio of the permeation rates of hydrogen ions and vanadium ions, wherein the conductivity of hydrogen ions is greater than 0.05 S / cm and the ratio of the conductivity of hydrogen ions to vanadium ions is greater than 50.

4. A method for preparing a composite proton exchange membrane for a vanadium redox flow battery according to any one of claims 1 to 3, characterized in that: The composite proton exchange membrane is prepared by sequentially sulfonating polyether ether ketone resin, preparing resin nanoparticles, casting solution and casting of composite membrane, and finally obtaining a membrane material with excellent performance.

5. The method for preparing a composite proton exchange membrane for a vanadium redox flow battery according to claim 4, specifically comprising the following steps: Step (1) Sulfonation treatment of polyetheretherketone resin Commercially available polyether ether ketone resin is dissolved in concentrated sulfuric acid to obtain a solution with a mass concentration of 3-15%. The solution is continuously stirred at 50-90°C to carry out a sulfonation reaction. Finally, the solution is precipitated in water and dried to obtain sulfonated polyether ether ketone resin. Step (2) Preparation of resin nanoparticles Sulfonated polyether ether ketone resin was placed in a low-temperature ball mill with a temperature range of -50 to 10°C and a rotation speed range of 600 to 3000 r / min. After ball milling, sulfonated polyether ether ketone resin nanoparticles with a size of 20 to 500 nm were obtained. Step (3) Casting preparation of casting solution and composite film Sulfonated polyether ether ketone resin particles were doped into a perfluorosulfonic acid resin solution and stirred thoroughly to obtain a uniform casting solution. A composite membrane was prepared using a doctor blade method. After pre-drying and further drying, a composite proton exchange membrane for vanadium redox flow batteries was finally obtained. The pre-drying temperature was 40–80 °C and the time was 1–4 h. The further drying temperature was 100–180 °C and the time was 2–6 h.

6. A high-performance vanadium redox flow battery based on a composite proton exchange membrane for vanadium redox flow batteries prepared by any one of the methods of claims 4 to 5.