Composite diaphragm for zinc-bromine flow battery, preparation method and application of composite diaphragm, and zinc-bromine flow battery

Abstract

The invention provides a composite diaphragm for a zinc-bromine flow battery, a preparation method and application of the composite diaphragm, and the zinc-bromine flow battery. The composite diaphragm for the zinc-bromine flow battery comprises a diaphragm and a chemical oxidation resistant coating on the surface of the diaphragm, the chemical oxidation resistant coating is made of tetrabutylammonium tribromide, the diaphragm is protected by the tetrabutylammonium tribromide coating, and the tetrabutylammonium tribromide can effectively react with zinc metal, so that the chemical oxidation resistant coating is not prone to being oxidized, and the service life of the diaphragm is prolonged. Therefore, zinc dendrites are prevented from penetrating through the diaphragm to cause short circuit, and the cycle life of the battery is remarkably prolonged; according to the preparation method of the composite diaphragm for the zinc-bromine flow battery, any high-cost manufacturing equipment does not need to be used, and the simplified preparation process provides a more convenient way for commercialized production.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and in particular to a composite separator for zinc-bromine flow batteries, its preparation method and application, and zinc-bromine flow batteries. Background Technology

[0002] Energy is fundamental to human survival and development. The continued consumption of fossil fuels and climate change caused by carbon emissions are becoming increasingly prominent. Sustainable clean energy sources, such as wind, solar, and tidal power, are affected by climate and cannot directly generate continuous and stable electricity, resulting in the intermittent nature of new energy applications. Energy storage technology can collect fluctuating energy and output high-quality, stable power. It can be connected to the grid on the generation, transmission, distribution, and user sides to achieve grid load balancing, peak shaving and valley filling, improve power quality, and ensure the safe and stable operation of the grid.

[0003] Flow batteries have attracted widespread attention due to their high safety and capacity-power decoupling. Zinc-bromine flow batteries, with their abundant raw material availability, high power density, and environmental friendliness, have become a promising technology choice in the energy storage field. However, zinc-based flow batteries suffer from poor cycle stability due to the influence of zinc dendrites. The continuous growth of zinc dendrites can penetrate the separator and directly contact the positive electrode, leading to battery failure.

[0004] Common methods for suppressing zinc dendrite formation include electrolyte modification, electrode engineering, electric field modulation, and membrane modulation. However, the formation of zinc dendrites is essentially due to the uncontrollable electrodeposition process of metallic zinc caused by electroplating. Zinc electrodeposition is kinetically controlled, rendering these methods ineffective under stringent operating conditions. Therefore, there is an urgent need to design novel membrane materials to achieve long-life zinc-bromine flow batteries. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a separator for a zinc-bromine flow battery, a method for preparing the separator and its application, and a zinc-bromine flow battery, so as to solve or at least partially solve the defects existing in the prior art.

[0006] In a first aspect, the present invention provides a composite separator for a zinc-bromine flow battery, comprising a separator and a chemically resistant coating on the surface of the separator;

[0007] The material of the chemical oxidation resistant coating is tetrabutylammonium tribromide.

[0008] Preferably, the diaphragm is a porous polyethylene diaphragm.

[0009] Secondly, the present invention also provides a method for preparing the composite separator for the zinc-bromine flow battery, comprising the following steps:

[0010] An oxidizing agent and a dispersant are added to water to obtain a first mixture;

[0011] Add a binder to the first mixture to obtain a second mixture;

[0012] The second mixture is dropped onto the surface of the diaphragm and dried to form a chemically resistant coating on the diaphragm surface, thus obtaining the composite diaphragm.

[0013] The oxidant is tetrabutylammonium tribromide.

[0014] Preferably, the dispersant is a multi-walled carbon nanotube;

[0015] And / or, the adhesive is a Nafion solution.

[0016] Preferably, the concentration of the oxidant in the first mixture is 0.5–1 mg / mL;

[0017] The mass-to-volume ratio of the oxidant, dispersant, and binder is (5-20) mg:(0.5-2) mg:(45-55) μL.

[0018] Preferably, the oxidant and dispersant are added to water and ultrasonically dispersed to obtain a first mixture;

[0019] The ultrasonic power is 150–200W, the frequency is 30–50kHz, and the duration is 15–20min.

[0020] Preferably, in the step of adding the second mixture droplets onto the diaphragm surface, each cm 2 The volume of the second mixture added to the diaphragm surface is 1 to 2 mL.

[0021] Preferably, in the step of adding the second mixture droplets onto the diaphragm surface and drying, the drying temperature is 50–80°C and the drying time is 2–4 hours.

[0022] Thirdly, the present invention also provides the application of the composite separator for zinc-bromine flow batteries described above or the composite separator for zinc-bromine flow batteries prepared by the aforementioned preparation method in the preparation of zinc-bromine flow batteries.

[0023] Fourthly, the present invention also provides a zinc-bromine flow battery, comprising the composite separator for zinc-bromine flow batteries described above or the composite separator for zinc-bromine flow batteries prepared by the preparation method described above.

[0024] The composite separator for zinc-bromine flow batteries of the present invention, its preparation method and application, and the zinc-bromine flow battery thereof, have the following advantages over the prior art:

[0025] 1. The composite separator for zinc-bromine flow batteries of the present invention includes a separator and a chemical oxidation resistant coating on the surface of the separator. The chemical oxidation resistant coating is made of tetrabutylammonium tribromide. The tetrabutylammonium tribromide coating protects the separator and can effectively react with zinc metal, thereby preventing zinc dendrites from penetrating the separator and causing a short circuit, thus significantly improving the cycle life of the battery.

[0026] 2. The method for preparing the composite separator for zinc-bromine flow batteries of the present invention involves adding the oxidant tetrabutylammonium tribromide to the surface of the separator to form a chemically resistant oxidation coating. The tetrabutylammonium tribromide coating can react with zinc dendrites on the surface of the separator to inhibit the damage caused by zinc dendrites piercing the separator, which could lead to battery self-discharge or even failure, thereby extending the cycle life of the battery. The method for preparing the composite separator of the present invention does not require any high-cost manufacturing equipment, and this simplified preparation process provides a more convenient way to achieve commercial production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a scanning electron microscope image of the porous polyethylene membrane used in Example 1;

[0029] Figures 2-3 These are scanning electron microscope images of the composite membrane prepared in Example 1 at different magnifications;

[0030] Figure 4 The XRD patterns are of the porous polyethylene membrane used in Example 1 and the composite membrane prepared in Example 1.

[0031] Figure 5 The graph shows the rate performance test results of the zinc-bromine flow battery in Comparative Example 1.

[0032] Figure 6 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 1.

[0033] Figure 7 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 2.

[0034] Figure 8 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 3.

[0035] Figure 9The AC impedance test diagrams are for the zinc-bromine flow cells in Examples 1-3 and Comparative Example 1.

[0036] Figure 10 This is a comparison chart of the conductivity of zinc-bromine flow batteries in Examples 1-3 and Comparative Example 1;

[0037] Figure 11 For the zinc-bromine flow cell in Comparative Example 1 at 20 mA / cm 2 Cyclic efficiency diagram at current density;

[0038] Figure 12 For the zinc-bromine flow battery in Example 2, at 20 mA / cm 2 Cyclic efficiency diagram at current density;

[0039] Figure 13 This is an electron microscope image of the membrane surface of the zinc-bromine flow battery in Comparative Example 1 after cycling.

[0040] Figure 14 This is an electron microscope image of the membrane surface after cycling in the zinc-bromine flow battery of Example 2. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0043] This application provides a composite separator for a zinc-bromine flow battery, including a separator and a chemically resistant coating on the surface of the separator;

[0044] The material for the chemical oxidation resistant coating is tetrabutylammonium tribromide.

[0045] The composite separator for zinc-bromine flow batteries of the present invention includes a separator and a chemically resistant oxidation coating on the surface of the separator, namely tetrabutylammonium tribromide (chemical formula C). 16 H 36 The Br3N coating, wherein the tetrabutylammonium tribromide coating protects the separator, and the tetrabutylammonium tribromide can effectively react with zinc metal, thereby preventing zinc dendrites from penetrating the separator and causing short circuits, significantly improving the cycle life of the battery. The chemically resistant oxidation coating of this invention can oxidize zinc dendrites that come into contact with the separator during cycling, thereby improving the cycle stability of the battery.

[0046] In some embodiments, the diaphragm is a porous polyethylene diaphragm with a thickness of 0.6-1.0 mm, an average pore size of 20 nm, and a porosity of 55-60%.

[0047] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned composite separator for zinc-bromine flow batteries, comprising the following steps:

[0048] S1. Add the oxidant and dispersant to water to obtain the first mixture;

[0049] S2. Add a binder to the first mixture to obtain the second mixture;

[0050] S3. The second mixture is added dropwise to the surface of the diaphragm and dried to form a chemically resistant coating on the surface of the diaphragm, thus obtaining the composite diaphragm.

[0051] The oxidant is tetrabutylammonium tribromide.

[0052] In some embodiments, the dispersant is a multi-walled carbon nanotube.

[0053] In some embodiments, the binder is a Nafion solution, specifically a perfluorosulfonic acid polymer solution.

[0054] In some embodiments, the concentration of the oxidant in the first mixture is 0.5–1 mg / mL;

[0055] In some embodiments, the mass-to-volume ratio of oxidant, dispersant, and binder is (5-20) mg:(0.5-2) mg:(45-55) μL.

[0056] In some embodiments, an oxidant and a dispersant are added to water and ultrasonically dispersed to obtain a first mixture;

[0057] The ultrasonic power is 150–200W, the frequency is 30–50kHz, and the duration is 15–20min.

[0058] This invention uses water as a solvent, adds an oxidant and a dispersant, and performs ultrasonic treatment to disperse the particles in the solution. By adding a trace amount of tetrabutylammonium tribromide as an oxidant and ultrasonic vibration treatment, the preparation time of the functionalized membrane is shortened to 60 minutes, and no high-cost manufacturing equipment is required. This simplified preparation process provides a more convenient way to achieve commercial production.

[0059] In some embodiments, in the step of adding the second mixture dropwise to the diaphragm surface, per cm 2 The volume of the second mixture added to the diaphragm surface is 0.5 to 2 mL.

[0060] In some embodiments, the second mixture is dropped onto the surface of the diaphragm until the solvent is completely evaporated, wherein the drying temperature is 50–80°C and the drying time is 2–4 hours.

[0061] This invention solves the problem of dendrites piercing the separator during the cycling process of zinc-based flow batteries by preparing a chemically resistant coating of tetrabutylammonium tribromide on the separator surface, thereby improving the cycle stability of the battery.

[0062] Based on the same inventive concept, this invention also provides the application of the above-described composite separator for zinc-bromine flow batteries or the composite separator for zinc-bromine flow batteries prepared by the above-described preparation method in the preparation of zinc-bromine flow batteries. Specifically, the tetrabutylammonium tribromide coating of the composite separator of this invention can react with zinc dendrites on the surface of the separator to suppress the harm caused by zinc dendrites piercing the separator, leading to battery self-discharge or even failure, thereby extending the cycle life of the battery.

[0063] Based on the same inventive concept, the present invention also provides a zinc-bromine flow battery, including the composite separator for zinc-bromine flow batteries described above or the composite separator for zinc-bromine flow batteries prepared by the above preparation method.

[0064] Specifically, the aforementioned zinc-bromine flow battery also includes a negative electrode graphite plate, a positive electrode graphite plate, an activated carbon felt, and an electrolyte; specifically, from bottom to top, the zinc-bromine flow battery consists of a negative electrode graphite plate, an activated carbon felt, a composite separator, an activated carbon felt, and a positive electrode graphite plate, with the side of the composite separator having a chemical oxidation-resistant coating close to the negative electrode graphite plate.

[0065] In some embodiments, the electrolyte comprises potassium salt, zinc salt, bromine complexing agent, and water;

[0066] The potassium salts include, but are not limited to, potassium chloride (KCl), potassium sulfate (K2SO4), potassium nitrate (KNO3), and potassium acetate (CH3COOK); preferably, the potassium salt is potassium chloride (KCl).

[0067] Zinc salts include, but are not limited to, zinc bromide (ZnBr2), zinc chloride (ZnCl2), zinc sulfate (ZnSO4), zinc nitrate (Zn(NO3)2), zinc acetate (Zn(CH3COO)2), etc., with zinc bromide (ZnBr2) being the preferred zinc salt.

[0068] Bromine complexing agents include, but are not limited to, 1-methyl-1-ethylpyrrolidine bromide (MEP), N-methyl-N-butylpyrrolidine bromide, etc.; preferably, the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide (MEP).

[0069] In some embodiments, the concentration of potassium salt in the electrolyte is 2–5 mol / L, the concentration of zinc salt is 2–5 mol / L, and the concentration of bromine complexing agent is 0.2–0.6 mol / L.

[0070] The following further illustrates the composite separator for zinc-bromine flow batteries of the present invention, its preparation method, its application, and the zinc-bromine flow battery itself, using specific embodiments. This section further describes the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0071] The porous polyethylene diaphragms used in the following examples were purchased from Wuhan Zhisheng New Energy Co., Ltd., with a thickness of 0.6-1.0 mm, an average pore size of 20 nm, and a porosity of 55-60%.

[0072] The multi-walled carbon nanotubes were purchased from Shenghui Industrial Co., Ltd., CAS No.: 308068-56-6.

[0073] Nafion solution specifically is Nafion TM The perfluorinated resin solution (D2021CS), CAS No.: 31175-20-9, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0074] Example 1

[0075] This embodiment provides a composite separator for a zinc-bromine flow battery, including a separator and a chemically resistant coating on the surface of the separator;

[0076] The material for the chemical oxidation resistant coating is tetrabutylammonium tribromide;

[0077] The diaphragm has an area of ​​3×3cm. 2 Porous polyethylene diaphragm.

[0078] The preparation method of the composite separator for the zinc-bromine flow battery includes the following steps:

[0079] S1. Add 5 mg of oxidant tetrabutylammonium tribromide and 0.5 mg of dispersant multi-walled carbon nanotubes to 5 mL of deionized water and ultrasonically disperse to form a uniform dispersion to obtain the first mixture; wherein, the ultrasonic power is 180 W, the frequency is 40 kHz, and the time is 18 min.

[0080] S2. Add 50 μL of Nafion adhesive solution to the first mixture in S1 to obtain the second mixture;

[0081] S3. Add the second mixture droplet to an area of ​​3×3cm. 2 The porous polyethylene membrane surface was dried at 60℃ for 4 hours to form a chemically resistant oxidation coating, thus obtaining the composite membrane; the tetrabutylammonium tribromide loading was approximately 0.5 mg / cm³. 2 .

[0082] This application also provides a zinc-bromine flow battery, which includes, from bottom to top, a negative electrode graphite plate, an activated carbon felt, a composite separator, an activated carbon felt, and a positive electrode graphite plate, and the side of the composite separator with a chemical oxidation resistant coating is close to the negative electrode graphite plate; the composite separator is the composite separator prepared in Example 1;

[0083] The electrolyte consists of potassium salt, zinc salt, bromine complexing agent, and water;

[0084] The potassium salt is potassium chloride (KCl); the zinc salt is zinc bromide (ZnBr2); the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide (MEP); the concentration of potassium salt in the electrolyte is 3 mol / L, the concentration of zinc salt is 2 mol / L, and the concentration of bromine complexing agent is 0.4 mol / L.

[0085] Example 2

[0086] This embodiment provides a composite separator for a zinc-bromine flow battery, including a separator and a chemically resistant coating on the surface of the separator;

[0087] The material for the chemical oxidation resistant coating is tetrabutylammonium tribromide;

[0088] The diaphragm has an area of ​​3×3cm. 2 Porous polyethylene diaphragm.

[0089] The preparation method of the composite separator for the zinc-bromine flow battery includes the following steps:

[0090] S1. Add 10 mg of oxidant tetrabutylammonium tribromide and 1 mg of dispersant multi-walled carbon nanotubes to 5 mL of deionized water and ultrasonically disperse to form a uniform dispersion to obtain the first mixture; wherein, the ultrasonic power is 180 W, the frequency is 40 kHz, and the time is 18 min.

[0091] S2. Add 50 μL of Nafion adhesive solution to the first mixture in S1 to obtain the second mixture;

[0092] S3. Add the second mixture droplet to an area of ​​3×3cm. 2 The porous polyethylene membrane surface was dried at 60℃ for 4 hours to form a chemically resistant oxidation coating, thus obtaining the composite membrane; the tetrabutylammonium tribromide loading was approximately 1 mg / cm³. 2 .

[0093] This application embodiment also provides a zinc-bromine flow battery, which includes, from bottom to top, a negative electrode graphite plate, an activated carbon felt, a composite separator, an activated carbon felt, and a positive electrode graphite plate, and the side of the composite separator with a chemical oxidation resistant coating is close to the negative electrode graphite plate; the composite separator is the composite separator prepared in Example 2;

[0094] The electrolyte consists of potassium salt, zinc salt, bromine complexing agent, and water;

[0095] The potassium salt is potassium chloride (KCl); the zinc salt is zinc bromide (ZnBr2); the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide (MEP); the concentration of potassium salt in the electrolyte is 3 mol / L, the concentration of zinc salt is 2 mol / L, and the concentration of bromine complexing agent is 0.4 mol / L.

[0096] Example 3

[0097] This embodiment provides a composite separator for a zinc-bromine flow battery, including a separator and a chemically resistant coating on the surface of the separator;

[0098] The material for the chemical oxidation resistant coating is tetrabutylammonium tribromide;

[0099] The diaphragm has an area of ​​3×3cm. 2 Porous polyethylene diaphragm.

[0100] The preparation method of the composite separator for the zinc-bromine flow battery includes the following steps:

[0101] S1. Add 20 mg of oxidant tetrabutylammonium tribromide and 2 mg of dispersant multi-walled carbon nanotubes to 5 mL of deionized water and ultrasonically disperse to form a uniform dispersion to obtain the first mixture; wherein, the ultrasonic power is 180 W, the frequency is 40 kHz, and the time is 18 min.

[0102] S2. Add 50 μL of Nafion adhesive solution to the first mixture in S1 to obtain the second mixture;

[0103] S3. Add the second mixture droplet to an area of ​​3×3cm. 2The porous polyethylene membrane surface was dried at 60℃ for 4 hours to form a chemically resistant oxidation coating, thus obtaining the composite membrane; the tetrabutylammonium tribromide loading was approximately 2 mg / cm³. 2 .

[0104] This application also provides a zinc-bromine flow battery, which includes, from bottom to top, a negative electrode graphite plate, an activated carbon felt, a composite separator, an activated carbon felt, and a positive electrode graphite plate, and the side of the composite separator with a chemical oxidation resistant coating is close to the negative electrode graphite plate; the composite separator is the composite separator prepared in Example 3;

[0105] The electrolyte consists of potassium salt, zinc salt, bromine complexing agent, and water;

[0106] The potassium salt is potassium chloride (KCl); the zinc salt is zinc bromide (ZnBr2); the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide (MEP); the concentration of potassium salt in the electrolyte is 3 mol / L, the concentration of zinc salt is 2 mol / L, and the concentration of bromine complexing agent is 0.4 mol / L.

[0107] Comparative Example 1

[0108] This comparative example provides a zinc-bromine flow battery, which, from bottom to top, includes a negative electrode graphite plate, an activated carbon felt, a separator, an activated carbon felt, and a positive electrode graphite plate; the separator is a porous polyethylene separator.

[0109] The electrolyte consists of potassium salt, zinc salt, bromine complexing agent, and water;

[0110] The potassium salt is potassium chloride (KCl); the zinc salt is zinc bromide (ZnBr2); the bromine complexing agent is 1-methyl-1-ethylpyrrolidine bromide (MEP); the concentration of potassium salt in the electrolyte is 3 mol / L, the concentration of zinc salt is 2 mol / L, and the concentration of bromine complexing agent is 0.4 mol / L.

[0111] Performance testing

[0112] Figure 1 This is a scanning electron microscope image of the porous polyethylene diaphragm used in Example 1.

[0113] Figures 2-3 The images are scanning electron microscope (SEM) images of the composite membrane prepared in Example 1 at different magnifications.

[0114] from Figures 1-3 As can be seen, the surface of ordinary porous polyethylene diaphragm is relatively smooth and flat; while the surface of the composite diaphragm prepared by this invention has many particles, and carbon nanotubes and tetrabutylammonium tribromide can be clearly seen attached to the diaphragm surface when magnified.

[0115] Figure 4 The XRD patterns are of the porous polyethylene membrane used in Example 1 and the composite membrane prepared in Example 1. Figure 4 In this context, GM represents the porous polyethylene membrane used in Example 1, and SDM represents the composite membrane prepared in Example 1.

[0116] from Figure 4 As can be seen, the surface of ordinary porous polyethylene diaphragm only has the peak of polyethylene, while the surface of the composite diaphragm prepared in Example 1 shows the peak of tetrabutylammonium tribromide (TBABr3), indicating that the chemical oxidation coating has been successfully attached to the diaphragm surface.

[0117] Figure 5 The graph shows the rate performance test results of the zinc-bromine flow battery in Comparative Example 1.

[0118] Figure 6 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 1.

[0119] Figure 7 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 2.

[0120] Figure 8 The graph shows the rate performance test results of the zinc-bromine flow battery in Example 3.

[0121] from Figure 5 As can be seen from the data, the zinc-bromine flow battery in Comparative Example 1, in the current density range of 5–50 mA / cm², achieves good performance. 2 At that time, the voltage efficiency (VE) decreased from 94% to 72%, while the coulombic efficiency (CE) increased from 94% to 99%. Compared to Comparative Example 1, the coulombic efficiency (CE) of the zinc-bromine flow batteries in Examples 1 and 2 remained essentially unchanged, and the voltage efficiency (VE) decay was not significant at low dielectric density, while at 50 mA / cm 2 The voltage efficiency (VE) decreased by 4 percentage points at the current density. The voltage efficiency (VE) of the zinc-bromine flow battery in Example 32 decreased significantly, to 50 mA / cm². 2 At current density, it is only 52%.

[0122] Figure 9 The AC impedance test diagrams are for the zinc-bromine flow batteries in Examples 1-3 and Comparative Example 1.

[0123] from Figure 9 As can be seen, the ohmic resistance of the zinc-bromine flow battery in Comparative Example 1 is 1.174 ohms. As the tetrabutylammonium tribromide load increases, the resistance gradually increases. The ohmic resistances of the zinc-bromine flow batteries in Examples 1 to 3 are 1.451 ohms, 1.619 ohms, and 1.937 ohms, respectively.

[0124] Figure 10 The graph shows a comparison of the conductivity of zinc-bromine flow batteries in Examples 1-3 and Comparative Example 1.

[0125] from Figure 10 As can be seen, increasing the loading of tetrabutylammonium tribromide decreases the conductivity of the membrane by 0.5 mg / cm. 2 1mg / cm 2 2mg / cm 2 The conductivity of the loaded materials was 0.81, 0.73, and 0.61 times that of Comparative Example 1, respectively. The increase in ohmic resistance and the decrease in conductivity indicate that, compared to the porous polyethylene membrane, the composite membrane prepared in this invention hinders the mass transfer of battery active materials. This is because the chemically resistant coating covers the pores in the polyolefin membrane, making it more difficult for particles in the solution to pass through the membrane, and the hindering effect increases with the increase of tetrabutylammonium tribromide loading.

[0126] To achieve long battery cycle life without a significant decrease in battery efficiency, it is essential to maintain a high level of active material on the chemically oxidized separator. Therefore, a concentration of 1 mg / cm³ is selected. 2 (i.e., the loading amount corresponding to Example 2) was used as the final tetrabutylammonium tribromide loading amount for subsequent testing.

[0127] Figure 11 For the zinc-bromine flow cell in Comparative Example 1 at 20 mA / cm 2 Cyclic efficiency graph at current density.

[0128] Figure 12 For the zinc-bromine flow battery in Example 2, at 20 mA / cm 2 Cyclic efficiency graph at current density.

[0129] from Figure 11 As can be seen, for the zinc-bromine flow battery in Comparative Example 1, as the number of cycles increases, the coulombic efficiency (CE) of the battery can be kept relatively stable at around 97%, while the voltage efficiency (VE) gradually decreases from 89% to 82%. This is because zinc grows in the form of dendrites on the negative electrode. Until 120 cycles, the dendrites pierce the separator and come into contact with the positive electrode, causing a short circuit. The voltage efficiency drops sharply, and the battery fails.

[0130] from Figure 12 As can be seen from the data, the zinc-bromine flow battery in Example 2 can run continuously for 360 cycles, which is 3 times higher than that in Comparative Example 1. Moreover, the coulombic efficiency remains stable throughout the cycle, and the voltage efficiency (VE) can still reach 87% after 360 cycles without significant decay, indicating that its charge and discharge process is relatively stable.

[0131] Figure 13 The image shows an electron microscope (EM) image of the membrane surface of the zinc-bromine flow battery in Comparative Example 1 after 100 cycles.

[0132] Figure 14The image shows an electron microscope (EM) image of the membrane surface after 100 cycles of the zinc-bromine flow battery in Example 2.

[0133] from Figures 13-14 As can be seen, after cycling, the surface of the ordinary porous polyethylene membrane in Comparative Example 1 was covered with zinc dendrites, while the surface of the composite membrane in Example 2 had almost no dendrite growth, which verifies its dendrite inhibition effect.

[0134] It is understood that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A composite separator for a zinc-bromine flow battery, characterized in that, Includes a diaphragm and a chemically resistant coating on the surface of the diaphragm; The material of the chemical oxidation resistant coating is tetrabutylammonium tribromide.

2. The composite separator for zinc-bromine flow batteries as described in claim 1, characterized in that, The diaphragm is a porous polyethylene diaphragm.

3. A method for preparing a composite separator for a zinc-bromine flow battery as described in any one of claims 1 to 2, characterized in that, Includes the following steps: An oxidizing agent and a dispersant are added to water to obtain a first mixture; Add a binder to the first mixture to obtain a second mixture; The second mixture is dropped onto the surface of the diaphragm and dried to form a chemically resistant coating on the diaphragm surface, thus obtaining the composite diaphragm. The oxidant is tetrabutylammonium tribromide.

4. The method for preparing the composite separator for a zinc-bromine flow battery as described in claim 3, characterized in that, The dispersant is a multi-walled carbon nanotube; And / or, the adhesive is a Nafion solution.

5. The method for preparing the composite separator for a zinc-bromine flow battery as described in claim 3, characterized in that, The concentration of the oxidant in the first mixture is 0.5–1 mg / mL; The mass-volume ratio of the oxidant, dispersant, and binder is (5-20) mg:(0.5-2) mg:(45-55) μL.

6. The method for preparing the composite separator for a zinc-bromine flow battery as described in claim 3, characterized in that, An oxidant and a dispersant were added to water and ultrasonically dispersed to obtain a first mixture. The ultrasonic power is 150–200W, the frequency is 30–50kHz, and the duration is 15–20min.

7. The method for preparing the composite separator for a zinc-bromine flow battery as described in claim 3, characterized in that, In the step of adding the second mixture dropwise to the diaphragm surface, each cm... 2 The volume of the second mixture added to the diaphragm surface is 1 to 2 mL.

8. The method for preparing the composite separator for a zinc-bromine flow battery as described in claim 3, characterized in that, The second mixture is added dropwise to the surface of the diaphragm. In the drying step, the drying temperature is 50-80℃ and the drying time is 2-4 hours.

9. The application of a composite separator for zinc-bromine flow batteries as described in any one of claims 1 to 2, or a composite separator for zinc-bromine flow batteries prepared by any one of claims 3 to 7, in the preparation of zinc-bromine flow batteries.

10. A zinc-bromine flow battery, characterized in that, This includes the zinc-bromine flow battery composite separator as described in any one of claims 1 to 2, or the zinc-bromine flow battery composite separator prepared by the preparation method described in any one of claims 3 to 7.

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