Porous membrane based on titanium metal organic framework as well as preparation method and application of porous membrane

Abstract

The invention belongs to the technical field of flow batteries, and discloses a porous membrane based on a titanium metal organic framework and a preparation method and application thereof, and the preparation method comprises the following steps: dispersing a titanium source and a carboxylic acid ligand into a preset solvent, and carrying out a hydrothermal reaction to obtain the titanium metal organic framework; preparing a spraying solution by utilizing a titanium metal organic framework; uniformly spraying the spraying solution on the surface of a polyethylene porous membrane, and drying to obtain a porous membrane based on the titanium metal organic framework; through simple hydrothermal reaction and a spraying process, uniform loading of the titanium metal organic framework on the porous membrane is realized, and the original pore structure of the porous membrane can be effectively reserved, so that the porous membrane with high conductivity and good chemical stability is obtained, the problem of low conductivity of a traditional porous membrane is effectively solved, and the preparation method is simple and convenient to operate. And the preparation method has the advantages of simplicity, controllable cost and the like, and provides a new thought and possibility for the development of the diaphragm in the flow battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow batteries, and particularly relates to a porous membrane based on titanium metal-organic framework, a preparation method thereof, and an application thereof. Background Art

[0002] In a flow battery, the performance of the separator plays a crucial role in the overall performance of the battery; traditional commercial porous membranes often have certain limitations in terms of conductivity, resulting in an increase in battery internal resistance and a decrease in energy efficiency, seriously affecting the charge-discharge performance and cycle life of the flow battery; with the continuous development of flow battery technology, the demand for separators with high conductivity is becoming increasingly urgent.

[0003] Currently, means of adding conductive materials to porous membranes or modifying porous membranes have been proposed to improve the conductivity of porous membranes, but most of them cannot effectively meet the requirements of flow batteries for high-conductivity separators; specifically: some studies have attempted to improve conductivity by adding carbon nanomaterials such as carbon nanotubes and graphene to porous membranes; however, the existing carbon nanomaterials have poor dispersibility in porous membranes and are prone to agglomeration, resulting in limited improvement in conductivity and being extremely likely to affect the mechanical properties and chemical stability of the membrane; in addition, the addition of carbon nanomaterials may also increase the cost of the membrane and the complexity of the preparation process; there are also some methods of chemically modifying porous membranes, such as surface grafting of conductive polymers, but they often require complex chemical reaction steps and the grafting rate is difficult to precisely control, which may introduce impurities or change the original pore structure of the membrane, thus having an adverse effect on ion transport and also being unable to effectively meet the requirements of flow batteries for high-conductivity separators. Summary of the Invention

[0004] Aiming at the technical problems existing in the prior art, the present invention provides a porous membrane based on titanium metal-organic framework, a preparation method thereof, and an application thereof, so as to solve the technical problem that the existing means of improving the conductivity of porous membranes cannot effectively meet the requirements of flow batteries for high-conductivity separators.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a preparation method of a porous membrane based on titanium metal-organic framework, comprising: Dispersing a titanium source and a carboxylic acid ligand in a preset solvent, and performing a hydrothermal reaction to obtain a titanium metal-organic framework; Formulating a spraying solution by using the titanium metal-organic framework; Spraying the spraying solution uniformly on the surface of a polyethylene porous membrane, and drying to obtain a porous membrane based on titanium metal-organic framework.

[0006] Further, the molar ratio of the titanium source to the carboxylic acid ligand is (2.5 - 3.5):(20 - 25); the titanium source is tetrabutyl titanate or titanium tetraisopropoxide, and the carboxylic acid ligand is terephthalic acid or 2-aminoterephthalic acid.

[0007] Further, the preset solvent is a DMF / methanol mixed solvent; wherein, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 7:3 - 9:1.

[0008] Further, when dispersing the titanium source and the carboxylic acid ligand into the preset solvent and performing a hydrothermal reaction to obtain the titanium metal-organic framework, the hydrothermal reaction is carried out in an inert gas atmosphere; wherein, the hydrothermal reaction temperature is 140 - 160 °C, and the reaction time is 12 - 24 h.

[0009] Further, the process of preparing the spraying solution using the titanium metal-organic framework includes: Disperse the titanium metal-organic framework into the mixed solvent, add a binder, and then perform ultrasonic dispersion and stirring to obtain the spraying solution; wherein, the mixed solvent is a mixed system of absolute ethanol and isopropanol.

[0010] Further, the ratio of the titanium metal-organic framework, the mixed solvent, and the binder in the spraying solution is (0.5 - 1.0) g:(20 - 30) mL:(0.2 - 0.5) g.

[0011] Further, the binder is one of polyvinyl alcohol, polyvinylpyrrolidone, sodium carboxymethylcellulose, and sodium alginate.

[0012] Further, when uniformly spraying the spraying solution on the surface of the polyethylene porous membrane, the spraying pressure is 0.2 - 0.4 MPa, the spraying distance is 10 - 20 cm, and the spraying amount is 0.4 - 0.8 mL / cm 2 。

[0013] The present invention also provides a porous membrane based on a titanium metal-organic framework, which is prepared by using the preparation method of the porous membrane based on the titanium metal-organic framework described above.

[0014] The present invention also provides an application of the porous membrane based on the titanium metal-organic framework, which is used as a separator of a zinc-bromine flow battery.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The preparation method of the porous membrane based on titanium metal-organic framework provided by the present invention uses a titanium source and a carboxylic acid ligand to prepare a titanium metal-organic framework, enabling the titanium oxygen cluster and the carboxylic acid ligand to form a three-dimensional covalently bonded framework structure. Among them, the d orbitals of the titanium oxygen cluster overlap with the π electron cloud of the ligand to form an electron conduction channel throughout the membrane, significantly enhancing the intrinsic conductivity of the membrane material, so as to achieve the effect of reducing the internal resistance of the battery and improving the energy efficiency. Secondly, the mesopore aperture of the titanium metal-organic framework is relatively small, which can effectively prevent bromine molecules from entering the interior of the mesopores, thereby reducing the bromine shuttle effect and improving the Coulomb efficiency of the battery. In addition, by means of a spraying process, a spraying solution containing the titanium metal-organic framework is sprayed on the surface of the polyethylene porous membrane, enabling the nanoparticles of the titanium metal-organic framework to be uniformly anchored on the membrane surface and enhancing the mechanical strength to avoid swelling and pore collapse. The present invention realizes the uniform loading of the titanium metal-organic framework on the porous membrane through a simple hydrothermal reaction and spraying process, and can effectively retain the original pore structure of the porous membrane to obtain a porous membrane with high conductivity and good chemical stability. It not only effectively solves the problem of low conductivity of traditional porous membranes, but also has the advantages of simple preparation method and controllable cost, providing new ideas and possibilities for the development of diaphragms in flow batteries. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0017] Figure 1 It is the scanning electron microscope (SEM) image of the titanium metal-organic framework prepared in Example 1; Figure 2 It is the X-ray diffraction (XRD) image of the titanium metal-organic framework prepared in Example 1; Figure 3 It is the micrograph of the porous membrane based on the titanium metal-organic framework prepared in Example 1; Figure 4 It is the scanning electron microscope (SEM) image of the titanium metal-organic framework prepared in Example 3; Figure 5 It is the scanning electron microscope (SEM) image of the titanium metal-organic framework prepared in Example 4. Detailed Embodiments

[0018] In order to make the technical problems, technical solutions and beneficial effects solved by this application more clearly understood, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application; obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0019] The present invention provides a method for preparing a porous membrane based on titanium metal-organic framework, comprising the following steps: Step 1: Disperse a titanium source and a carboxylic acid ligand in a preset solvent and perform a hydrothermal reaction to obtain a titanium metal-organic framework (MIL-125). Among them, the molar ratio of the titanium source to the carboxylic acid ligand is (2.5-3.5):(20-25); the titanium source is tetrabutyl titanate or titanium tetraisopropoxide, and the carboxylic acid ligand is terephthalic acid or 2-aminoterephthalic acid; the preset solvent is a DMF / methanol mixed solvent; among them, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 7:3-9:1.

[0020] Specifically, in an inert gas atmosphere, add the titanium source and the carboxylic acid ligand to the DMF / methanol mixed solvent, perform a hydrothermal reaction at 140-160°C for 12-24 h to obtain a hydrothermal reaction product; use ethanol or methanol to wash the hydrothermal reaction product to obtain a titanium metal-organic framework.

[0021] Step 2: Prepare a spraying solution using the titanium metal-organic framework. Specifically, disperse the titanium metal-organic framework in a mixed solvent, add a binder, and perform ultrasonic dispersion at a power of 300-500 W for 2-4 h and mechanical stirring at 600-800 rpm for 3-5 h to obtain a spraying solution; among them, the mixed solvent is a mixed system of anhydrous ethanol and isopropanol, and the ratio of the titanium metal-organic framework, the mixed solvent and the binder in the spraying solution is (0.5-1.0) g:(20-30) mL:(0.2-0.5) g, and the binder is one of polyvinyl alcohol, polyvinylpyrrolidone, sodium carboxymethylcellulose and sodium alginate.

[0022] Step 3: Fix a pre-selected commercial porous membrane on the workbench of the spraying equipment, and use a spray gun or a spraying device to uniformly spray the spraying solution on the surface of the pre-selected commercial porous membrane to obtain a porous membrane based on titanium metal-organic framework; among them, control the spraying pressure to be 0.2-0.4 MPa, the spraying distance to be 10-20 cm, and the spraying amount to be 0.4-0.8 mL / cm 2, ensure that MIL-125 can evenly cover the pre-selected commercial porous membrane and penetrate into its pores; the pre-selected commercial porous membrane is a polyethylene porous membrane; after spraying, perform a drying treatment at 60-80 °C for 4-8 h to volatilize the mixed solvent and cure the binder, ensuring that MIL-125 is firmly attached to the porous membrane to obtain a porous membrane based on titanium metal-organic framework.

[0023] Preparation principle: The preparation method of the porous membrane based on titanium metal-organic framework provided by the present invention uses a titanium source and a carboxylic acid ligand to prepare a titanium metal-organic framework through a hydrothermal reaction, and forms a three-dimensional conjugated electron conduction network through the titanium-oxygen clusters (TiO6 octahedra) in the titanium metal-organic framework and the carboxylic acid ligand; among them, an electron channel penetrating the membrane is constructed by coupling the unoccupied d orbitals of the titanium-oxygen clusters with the ligand π electron cloud, significantly improving the intrinsic conductivity of the membrane material and then reducing the internal resistance of the battery; due to the mesopore aperture of the titanium metal-organic framework being 1.5-2 nm, the mesopores of the titanium metal-organic framework and the macropores of the polyethylene porous membrane are used to form a hierarchical pore structure, selectively blocking the penetration of bromine molecules through the mesopores while allowing the free transport of hydrated ions, taking into account high ionic conductivity and bromine barrier properties, and reducing side reactions of the electrolyte; secondly, the octahedral structure of the titanium-oxygen clusters can be stable in a wide pH range, and its conjugated ligand passivates the surface of the titanium-oxygen clusters to resist acid-base corrosion, so that the porous membrane can exhibit good stability in a variety of solvents and acid-base environments, avoiding affecting the mechanical properties and chemical stability of the membrane; the spraying solution containing the titanium metal-organic framework is sprayed on the surface of the polyethylene porous membrane through a spraying process, so that the nanoparticles of the titanium metal-organic framework can be evenly anchored on the membrane surface; and the binder in the spraying solution is combined to enhance the mechanical strength and avoid swelling and pore collapse; through the synergistic design of low-temperature hydrothermal synthesis and spraying process, the uniform loading of MIL-125 is realized at room temperature, and the original pore structure of the membrane is retained; among them, the solvent system and ratio optimization ensure the integrity of the framework, the process is simple and the cost is low, which is suitable for large-scale production, providing new ideas and possibilities for the development of liquid flow battery diaphragms.

[0024] The porous membrane based on titanium metal-organic framework prepared by the present invention can effectively overcome the defect of low conductivity of traditional commercial porous membranes in the application of liquid flow batteries, significantly improve the conductivity of the porous membrane, reduce the internal resistance of the battery, and improve the charge and discharge efficiency of the liquid flow battery; ensure that while improving the conductivity, it does not affect the mechanical properties, chemical stability and original pore structure of the porous membrane, maintain good ion transport selectivity, and thus extend the cycle life of the liquid flow battery.

[0025] Example 1 Example 1 provides a preparation method of a porous membrane based on titanium metal-organic framework, including the following steps: Step 1, Material Preparation: Select a polyethylene porous membrane with a pore size of 0.05 μm, a porosity of 40%, and a thickness of 30 μm.

[0026] Step 2, Synthesis of Titanium Metal-Organic Framework: Under a nitrogen atmosphere, add 3 mmol of tetrabutyl titanate and 20 mmol of terephthalic acid to a hydrothermal reaction kettle containing 50 mL of a DMF / methanol mixed solvent, and carry out a hydrothermal reaction at 150 °C for 15 h; after the reaction, wash the hydrothermal reaction product with ethanol and dry it to obtain the titanium metal-organic framework; among them, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 9:1.

[0027] Step 3, Preparation of Spraying Solution: Weigh 1 g of the titanium metal-organic framework and disperse it into a mixed system of 25 mL of anhydrous ethanol and isopropanol; then, add 0.3 g of polyvinyl alcohol as a binder; after that, ultrasonically disperse it at a power of 400 W for 3 h and mechanically stir it at 700 rpm for 4 h to obtain the spraying solution; among them, in the mixed system of anhydrous ethanol and isopropanol, the volume ratio of anhydrous ethanol to isopropanol is 3:1.

[0028] Step 4, Spraying and Post-treatment; Fix the polyethylene porous membrane on the spraying equipment, and spray the spraying solution evenly on the surface of the polyethylene porous membrane at a spraying pressure of 0.3 MPa and a spraying distance of 15 cm, and the spraying amount is 0.6 mL / cm 2 , and dry it at 70 °C for 6 h after spraying to obtain a porous membrane based on the titanium metal-organic framework.

[0029] Example 2 This Example 2 provides a preparation method of a porous membrane based on a titanium metal-organic framework, including the following steps: Step 1, Material Preparation: Select a polyethylene porous membrane with a pore size of 0.05 μm, a porosity of 40%, and a thickness of 30 μm.

[0030] Step 2, Synthesis of Titanium Metal-Organic Framework: Under a nitrogen atmosphere, add 3 mmol of tetrabutyl titanate and 23 mmol of terephthalic acid to a hydrothermal reaction kettle containing 50 mL of a DMF / methanol mixed solvent, and carry out a hydrothermal reaction at 160 °C for 12 h; after the reaction, wash the hydrothermal reaction product with ethanol and dry it to obtain the titanium metal-organic framework; among them, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 9:1.

[0031] Step 3, Preparation of spraying solution: Weigh 0.5 g of titanium metal-organic framework and disperse it into a mixed system of 25 mL of anhydrous ethanol and isopropanol; then, add 0.5 g of sodium alginate as a binder; afterwards, ultrasonically disperse it for 2 h at a power of 500 W and mechanically stir it for 5 h at 600 rpm to obtain the spraying solution; among them, in the mixed system of anhydrous ethanol and isopropanol, the volume ratio of anhydrous ethanol to isopropanol is 3:1.

[0032] Step 4, Spraying and post-treatment; Fix the polyethylene porous membrane on the spraying equipment, and spray the spraying solution evenly on the surface of the polyethylene porous membrane at a spraying pressure of 0.4 MPa and a spraying distance of 20 cm, and the spraying amount is 0.6 mL / cm 2 , and after spraying, dry it at 70 °C for 6 h to obtain a porous membrane based on titanium metal-organic framework.

[0033] Example 3 This Example 3 provides a preparation method of a porous membrane based on titanium metal-organic framework, including the following steps: Step 1, Material preparation: Select a polyethylene porous membrane with a pore size of 0.05 μm, a porosity of 40%, and a thickness of 30 μm.

[0034] Step 2, Synthesis of titanium metal-organic framework: Under a nitrogen atmosphere, add 2.5 mmol of titanium tetraisopropoxide and 20 mmol of terephthalic acid to a hydrothermal reaction kettle containing 50 mL of DMF / methanol mixed solvent, and carry out a hydrothermal reaction at 150 °C for 15 h; after the reaction, wash the hydrothermal reaction product with ethanol and dry it to obtain the titanium metal-organic framework; among them, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 8:2.

[0035] Step 3, Preparation of spraying solution: Weigh 0.8 g of titanium metal-organic framework and disperse it into a mixed system of 20 mL of anhydrous ethanol and isopropanol; then, add 0.4 g of polyvinylpyrrolidone as a binder; afterwards, ultrasonically disperse it for 4 h at a power of 300 W and mechanically stir it for 4 h at 700 rpm to obtain the spraying solution; among them, in the mixed system of anhydrous ethanol and isopropanol, the volume ratio of anhydrous ethanol to isopropanol is 3:1.

[0036] Step 4, Spraying and post-treatment; Fix the polyethylene porous membrane on the spraying equipment, and spray the spraying solution evenly on the surface of the polyethylene porous membrane at a spraying pressure of 0.2 MPa and a spraying distance of 15 cm, and the spraying amount is 0.4 mL / cm 2 , and after spraying, dry it at 60 °C for 8 h to obtain a porous membrane based on titanium metal-organic framework.

[0037] Example 4 Example 4 of the present invention provides a method for preparing a porous membrane based on titanium metal-organic framework, comprising the following steps: Step 1, material preparation: Select a polyethylene porous membrane with a pore size of 0.05 μm, a porosity of 40%, and a thickness of 30 μm.

[0038] Step 2, synthesis of titanium metal-organic framework: Under a nitrogen atmosphere, 3.5 mmol of tetrabutyl titanate and 25 mmol of 2-aminoterephthalic acid are added to a hydrothermal reaction kettle containing 50 mL of a DMF / methanol mixed solvent, and a hydrothermal reaction is carried out at 140 °C for 24 h; after the reaction is completed, the hydrothermal reaction product is washed with ethanol and dried to obtain a titanium metal-organic framework; wherein, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 7:3.

[0039] Step 3, preparation of spraying solution: Weigh 1 g of titanium metal-organic framework and disperse it into a mixed system of 30 mL of absolute ethanol and isopropanol; then, add 0.2 g of sodium carboxymethylcellulose as a binder; afterwards, ultrasonically disperse it at a power of 400 W for 3 h and mechanically stir it at 800 rpm for 3 h to obtain a spraying solution; wherein, in the mixed system of absolute ethanol and isopropanol, the volume ratio of absolute ethanol to isopropanol is 3:1.

[0040] Step 4, spraying and post-treatment; Fix the polyethylene porous membrane on the spraying equipment, and uniformly spray the spraying solution on the surface of the polyethylene porous membrane at a spraying pressure of 0.3 MPa and a spraying distance of 10 cm, and the spraying amount is 0.8 mL / cm 2 , and after spraying, dry it at 80 °C for 4 h to obtain a porous membrane based on titanium metal-organic framework.

[0041] Performance test: Assemble zinc-bromine flow batteries using the porous membranes based on titanium metal-organic framework prepared in Examples 1-4 above to form four groups of zinc-bromine flow batteries using the porous membranes based on titanium metal-organic framework; assemble zinc-bromine flow batteries using polyethylene porous membranes to form zinc-bromine flow batteries using polyethylene porous membranes; wherein, in the first four groups of zinc-bromine flow batteries using the porous membranes based on titanium metal-organic framework, use the porous membrane based on titanium metal-organic framework as the separator, and assemble the battery using the conventional electrode materials and electrolyte system of the zinc-bromine flow battery; in the zinc-bromine flow battery using the polyethylene porous membrane, use the polyethylene porous membrane as the separator, and assemble the battery using the conventional electrode materials and electrolyte system of the zinc-bromine flow battery.

[0042] In an electrochemical workstation, perform electrochemical impedance tests on the above five groups of zinc-bromine flow batteries, and the test frequency is 0.01-10000 Hz; in a battery test system, perform charge-discharge tests on the above five groups of zinc-bromine flow batteries, and the charge-discharge rate is 20 mA / cm2 The test temperature was 25°C. Among them, the test results of the battery performance are shown in Table 1 below.

[0043] Table 1 Test Results of Battery Performance

[0044] As can be seen from Table 1, the ionic conductivities of the diaphragms in the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were 4.25 mS / cm, 4.53 mS / cm, 4.38 mS / cm, and 3.88 mS / cm respectively, while the ionic conductivity of the polyethylene porous membrane was 3.26 mS / cm. That is, the ionic conductivities of the diaphragms of the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were all higher than that of the polyethylene porous membrane. This indicates that: the porous membranes based on titanium metal-organic frameworks prepared in Examples 1-4 can effectively improve the ionic conductivity of the polyethylene porous membrane.

[0045] The Coulomb efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were 96.2%, 97.8%, 97.5%, and 94.7% respectively, and the Coulomb efficiency of the zinc-bromine flow battery assembled with the polyethylene porous membrane was 94.5%. That is, the Coulomb efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were all higher than that of the zinc-bromine flow battery assembled with the polyethylene porous membrane. This indicates that: the porous membranes based on titanium metal-organic frameworks prepared in Examples 1-4 can effectively reduce the side reactions in the electrolyte.

[0046] The voltage efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were 86.9%, 87.4%, 87.2%, and 86.7% respectively, and the Coulomb efficiency of the zinc-bromine flow battery assembled with the polyethylene porous membrane was 85.7%. That is, the voltage efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 were all higher than that of the zinc-bromine flow battery assembled with the polyethylene porous membrane. This indicates that: the porous membranes based on titanium metal-organic frameworks prepared in Examples 1-4 can effectively reduce the internal resistance of the battery.

[0047] The energy efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 are 83.6%, 85.2%, 84.9% and 82.1% respectively, and the Coulomb efficiency of the zinc-bromine flow battery assembled with a polyethylene porous membrane is 80.9%; that is, the Coulomb efficiencies of the zinc-bromine flow batteries assembled with the porous membranes based on titanium metal-organic frameworks prepared in Application Examples 1-4 are all higher than that of the zinc-bromine flow battery assembled with a polyethylene porous membrane; this shows that: the porous membranes based on titanium metal-organic frameworks prepared in Examples 1-4 of the present invention have significant advantages in improving battery performance.

[0048] It should be noted that the ionic conductivity of the separator refers to the ability of the separator to allow ions in the electrolyte to be transported through its pore structure, which directly affects the ionic transport efficiency, internal resistance and overall energy conversion performance of the battery. A separator with high ionic conductivity promotes the rapid transport of ions, reduces the ionic transport resistance, thereby improving the Coulomb efficiency, increasing the voltage efficiency, and ultimately enhancing the energy efficiency; the Coulomb efficiency of a zinc-bromine flow battery is the ratio of the actual amount of electricity involved in the reaction during charging and discharging, which is used to reflect the charge transfer efficiency of the battery and the control ability of side reactions; the voltage efficiency is the ratio of the actual output voltage during discharging, which is used to reflect the internal resistance of the battery and the control ability of polarization phenomena; the energy efficiency is the ratio of energy during charging and discharging, which is used to reflect the comprehensive performance of the overall energy conversion and utilization of the battery.

[0049] As shown in the Figure 1 appendix Figure 1 , the scanning electron microscope (SEM) image of the titanium metal-organic framework prepared in Example 1 is given; as can be seen from the Figure 1 appendix, the titanium metal-organic framework prepared in Example 1 of the present invention presents a nano-disc morphology, with a diameter of 150-300 nm and a thickness of 50-100 nm.

[0050] As shown in the Figure 2 appendix Figure 2 , the X-ray diffraction (XRD) pattern of the titanium metal-organic framework prepared in Example 1 is given; as can be seen from the Figure 2 appendix, the X-ray diffraction pattern of the titanium metal-organic framework prepared in Example 1 of the present invention is consistent with the standard card, indicating that the MIL-125 crystal has been successfully prepared.

[0051] As shown in the Figure 3 appendix Figure 3 , the micrograph of the porous membrane based on the titanium metal-organic framework prepared in Example 1 is given; as can be seen from the Figure 3As can be seen, in Example 1 of the present invention, the porous membrane based on titanium metal-organic framework is prepared, and the prepared titanium metal-organic framework is tightly attached to the surface of the substrate, and no obvious phase separation or aggregation phenomenon is observed, indicating that this preparation process can effectively achieve the uniform loading of nanomaterials.

[0052] As shown in the Figure 4 appendix, Figure 4 the scanning electron microscope (SEM) image of the titanium metal-organic framework prepared in Example 3 is given; as can be seen from the Figure 4 appendix, the size of the titanium metal-organic framework nanoparticles prepared in Example 3 is reduced, and the size distribution is uneven, but it still maintains the characteristic disc-shaped morphology; the reason can be attributed to: the hydrolysis rate of titanium isopropoxide is significantly faster than that of tetrabutyl titanate, resulting in a sharp increase in the instantaneous nucleation density of titanium-oxygen clusters in the precursor solution, and the size of nanoparticles is reduced.

[0053] As shown in the Figure 5 appendix, Figure 5 the SEM image of the titanium metal-organic framework prepared in Example 4 is given; as can be seen from the Figure 5 appendix, the titanium metal-organic framework prepared in Example 4 has a relatively large size, about 1.5 - 2 μm, and its morphology evolves into a cube; the reason can be attributed to: the introduction of the amino functional group in the 2-aminoterephthalic acid ligand increases the steric hindrance effect of the ligand molecule, and this steric hindrance can effectively inhibit the rapid aggregation process of titanium-oxygen clusters, thereby promoting the increase of crystal particle size.

[0054] In the preparation method of the porous membrane based on titanium metal-organic framework according to the present invention, the titanium-oxygen clusters (TiO6 octahedra) of the titanium metal-organic framework form a three-dimensional covalently bonded framework structure through carboxylic acid ligands, and its nodes (Ti 4+ ) have unoccupied d orbitals, and the π electron system in the ligand can form a delocalized conjugated structure; when the titanium metal-organic framework is loaded on the surface and pores of the porous membrane, the d orbitals of adjacent titanium-oxygen clusters overlap with the ligand π electron cloud, forming an electron conduction channel throughout the membrane, significantly improving the intrinsic conductivity of the membrane material, reducing the internal resistance of the battery, and significantly improving the energy efficiency; in addition, the mesopore aperture of the titanium metal-organic framework is 1.5 - 2 nm, while the size of bromine molecules is relatively large, and the van der Waals force between bromine molecules and the pore wall is weak, so bromine molecules cannot enter the interior of the mesopores, effectively reducing the bromine shuttle effect in the electrolyte and improving the Coulomb efficiency of the battery; the preparation method of the present invention is relatively simple, the cost is controllable, the synthesis and spraying processes are easy to operate, and the required equipment and reagents are common, which is conducive to large-scale industrial production and application.

[0055] In the present invention, the porous membrane modified by titanium metal-organic framework can significantly improve the conductivity while maintaining the original membrane properties, and the porous membrane based on titanium metal-organic framework can effectively improve the charge-discharge efficiency and cycle life of the battery when applied to a flow battery.

[0056] The above embodiments are merely one of the implementation manners capable of implementing the technical solution of the present invention. The scope of protection required by the present invention is not limited only by this embodiment, but also includes any changes, substitutions and other implementation manners that are easily conceivable by those skilled in the art within the technical scope disclosed by the present invention.

Claims

1. A method for preparing a porous membrane based on titanium metal-organic framework, characterized in that, Including: Disperse a titanium source and a carboxylic acid ligand into a preset solvent, and carry out a hydrothermal reaction to obtain a titanium metal-organic framework; Prepare a spraying solution by using the titanium metal-organic framework; Uniformly spray the spraying solution on the surface of a polyethylene porous membrane and dry it to obtain a porous membrane based on the titanium metal-organic framework.

2. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 1, wherein, The molar ratio of the titanium source to the carboxylic acid ligand is (2.5 - 3.5):(20 - 25); the titanium source is tetrabutyl titanate or titanium tetraisopropoxide, and the carboxylic acid ligand is terephthalic acid or 2-aminoterephthalic acid.

3. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 1, characterized in that, The preset solvent is a DMF / methanol mixed solvent; wherein, in the DMF / methanol mixed solvent, the volume ratio of DMF to methanol is 7:3 - 9:

1.

4. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 1, characterized in that, During the process of dispersing the titanium source and the carboxylic acid ligand into the preset solvent and carrying out a hydrothermal reaction to obtain the titanium metal-organic framework, the hydrothermal reaction is carried out in an inert gas atmosphere; wherein, the hydrothermal reaction temperature is 140 - 160 °C and the reaction time is 12 - 24 h.

5. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 1, wherein The process of preparing a spraying solution by using the titanium metal-organic framework includes: Disperse the titanium metal-organic framework into a mixed solvent, add a binder and then carry out ultrasonic dispersion and stirring to obtain a spraying solution; wherein, the mixed solvent is a mixed system of absolute ethanol and isopropanol.

6. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 5, characterized in that, The ratio of the titanium metal-organic framework, the mixed solvent and the binder in the spraying solution is (0.5 - 1.0) g:(20 - 30) mL:(0.2 - 0.5) g.

7. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 5, characterized in that, The binder is one of polyvinyl alcohol, polyvinylpyrrolidone, sodium carboxymethylcellulose and sodium alginate.

8. The preparation method of a porous membrane based on titanium metal-organic framework according to claim 1, characterized in that, The process of evenly spraying the coating solution on the surface of the polyethylene porous membrane, with a spraying pressure of 0.2 - 0.4 MPa, a spraying distance of 10 - 20 cm, and a spraying volume of 0.4 - 0.8 mL / cm 2 .

9. A porous membrane based on titanium metal-organic framework, characterized in that, Prepared by using the preparation method of the porous membrane based on the titanium metal-organic framework according to any one of claims 1 - 8.

10. Application of a porous membrane based on titanium metal-organic framework, characterized in that, Used as a separator for a zinc-bromine flow battery.

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