Composite ion exchange membrane, preparation method therefor and use thereof, and zinc-iodine flow battery

Abstract

A composite ion exchange membrane, a preparation method therefor and a use thereof, and a zinc-iodine flow battery. By introducing halogen adducts onto a porous membrane, a composite membrane based on a series of localized high iodine concentration (LHIC) coatings is constructed to suppress the problem of crossover of active polyiodide compounds in a catholyte. Specifically, metal oxides exhibit a strong physicochemical adsorption effect toward halogens, and halogen oxide adducts are formed, the halogen oxide adducts becoming effective halogen carriers. An LHIC coating is constructed on the porous membrane by utilizing the strong adsorption characteristic of the carriers and halogen (such as iodine), thereby enhancing the selectivity of the porous membrane toward iodine species. On the basis of Donnan exclusion and concentration gradient effects, a constructed localized high-concentration membrane can effectively suppress the diffusion of halogens from a positive electrode in a zinc-iodine battery / zinc-bromine battery, mitigating the problem of capacity loss of a zinc-iodine / zinc-bromine flow battery, and achieving long-term cyclic stability.

Description

A composite ion exchange membrane, its preparation method and application, zinc-iodine liquid flow battery Technical Field

[0001] The present invention relates to the technical field of liquid flow batteries, and in particular to a composite ion exchange membrane, a preparation method and application thereof, and a zinc-iodine liquid flow battery. Background Art

[0002] Large-scale energy storage technology is a key enabling technology for improving the utilization efficiency of renewable energy sources such as wind and solar power, achieving peak shaving and valley shifting, load compensation, and enhancing grid security. Flow batteries, with their flexible design, scalability, and decoupling of capacity and power, are among the most competitive candidates for large-scale energy storage. Among them, zinc-halide flow batteries, such as zinc-bromine and zinc-iodine flow batteries, are considered a promising type of flow energy storage battery due to their low cost, inherent safety, and excellent electrochemical performance.

[0003] A major challenge of flow batteries is the problem of crossover of active materials. The diaphragms used in flow batteries are usually ion exchange membranes, whose functional requirements are to conduct charge-carrying ions and at the same time prevent the interpenetration of active materials. Specifically, the active materials in the anolyte / cathode electrolyte can slowly diffuse to the opposite side through the diaphragm, causing self-discharge and reducing the coulombic efficiency of the battery. In addition, as large-scale energy storage, flow batteries will be integrated with outdoor clean energy conversion systems and will inevitably operate in high-temperature environments. Active materials at high temperatures will penetrate to the counter electrode side more quickly. In addition, in some flow battery systems, active materials can produce side reactions with the opposite electrode or electrolyte, causing the crossover problem of active materials to lead to irreversible capacity loss and eventual battery failure.

[0004] The primary membrane material currently used both domestically and internationally is the Nafion membrane developed by DuPont in the United States. While it offers excellent selectivity and high Coulombic efficiency, its limited ion permeability results in low voltage efficiency, making it difficult for zinc-iodine flow batteries to simultaneously achieve excellent performance in terms of energy efficiency and power density. Furthermore, its high cost limits the economic viability of flow batteries. Low-cost porous membranes have emerged as viable alternatives for achieving improved power output. These membranes offer good permeability but exhibit poor selectivity. To improve the selectivity of porous membranes in various flow battery systems, an effective strategy is to construct composite membranes by introducing selective coatings onto the membranes. These coatings operate based on the size-selective effect and the Donnan charge repulsion effect. Specifically, the sieving materials used are those with tunable structure and size, such as zeolites, metal-organic frameworks, polyamides, and two-dimensional materials. These size-selective materials require complex synthesis steps, and the cost of constructing precise and selective ion transport pathways is high. However, despite the concept of localized high iodine concentration, few researchers have attempted to develop low-cost coating materials to suppress the crossover of charged iodine species in zinc-iodine flow battery systems.

[0005] Based on the current problem of crossover of the positive electrode active material in zinc-halide flow batteries, it is necessary to improve this.

[0006] Summary of the Invention

[0007] The present invention provides a composite ion exchange membrane, a preparation method and application thereof, and a zinc-iodine liquid flow battery, so as to solve or at least partially solve the defects in the prior art.

[0008] In a first aspect, the present invention provides a composite ion exchange membrane comprising a porous membrane and a metal oxide coating located on the surface of the porous membrane.

[0009] Preferably, in the composite ion exchange membrane, the metal oxide used in the metal oxide coating comprises at least one of MgO, CeO2, ZrO2, TiO2, and Al2O3;

[0010] And / or, the porous membrane includes at least one of a polyolefin porous membrane, a Daramic membrane, and a VANADion membrane.

[0011] Preferably, in the composite ion exchange membrane, the thickness of the porous membrane is 100 to 1000 μm, and the thickness of the metal oxide coating is 5 to 100 μm.

[0012] In a second aspect, the present invention further provides a method for preparing the composite ion exchange membrane, comprising the following steps:

[0013] Adding the binder to the organic solvent and stirring to obtain a blend solution;

[0014] adding metal oxide to the blended solution and stirring to obtain a coating solution;

[0015] The coating solution is applied to the surface of the porous membrane, and dried until the organic solvent in the coating solution is volatilized to form a metal oxide coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane.

[0016] Preferably, in the method for preparing the composite ion exchange membrane, the binder comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and perfluorosulfonic acid polymer;

[0017] and / or, the organic solvent comprises at least one of dimethyl sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide;

[0018] and / or, the particle size of the metal oxide is 10 to 100 nm;

[0019] And / or, the mass ratio of the binder, the organic solvent, and the metal oxide is (0.5-2):(5-20):(5-10).

[0020] Preferably, in the method for preparing the composite ion exchange membrane, in the step of adding the binder to the organic solvent and stirring, the stirring temperature is 20 to 100° C. and the stirring time is 0.5 to 12 hours;

[0021] and / or, in the step of adding the metal oxide to the blend solution and stirring, the stirring temperature is 20 to 100° C. and the stirring time is 0.5 to 12 hours;

[0022] and / or, in the step of coating the coating solution onto the surface of the porous membrane, the coating method comprises at least one of a casting method, a doctor blade method, a spray coating method, and a spin coating method;

[0023] And / or, the coating solution is applied to the surface of the porous membrane, and in the drying step, the drying temperature is 20 to 80° C. and the drying time is 0.5 to 24 hours.

[0024] In a third aspect, the present invention further provides an application of the composite ion exchange membrane or the composite ion exchange membrane prepared by the preparation method in the preparation of a zinc-halogen liquid flow battery.

[0025] In a fourth aspect, the present invention further provides a zinc-iodine liquid flow battery, comprising a diaphragm, wherein the diaphragm is the composite ion exchange membrane or the composite ion exchange membrane prepared by the preparation method.

[0026] Preferably, the zinc-iodine flow battery further comprises a positive electrode electrolyte and a negative electrode electrolyte;

[0027] Wherein, the positive electrode electrolyte comprises ZnI2 and water;

[0028] The negative electrode electrolyte includes ZnBr2, electrolyte and water.

[0029] Preferably, in the zinc-iodine flow battery, the electrolyte comprises any one of KCl, K2SO4, and KBr;

[0030] The concentration of ZnI2 in the positive electrode electrolyte is 0.5 to 2M;

[0031] The concentration of ZnBr2 in the negative electrode electrolyte is 0.5 to 2M;

[0032] The concentration of the electrolyte in the negative electrode electrolyte is 0.5 to 2M;

[0033] The metal oxide coating in the composite ion exchange membrane faces the positive electrode.

[0034] The composite ion exchange membrane, preparation method thereof, and zinc-iodine flow battery of the present invention have the following beneficial effects compared with the prior art:

[0035] 1. The composite ion exchange membrane of the present invention includes a porous membrane and a metal oxide coating. By introducing halogen adducts on the porous membrane, a composite membrane based on a series of localized high iodine concentration (LHIC) coatings is constructed to suppress the cross-over problem of active polyiodine compounds in the cathode electrolyte. Specifically, metal oxides exhibit strong physical and chemical adsorption effects on halogens, forming halogen oxide adducts, which become effective halogen carriers; utilizing the strong adsorption properties of the carrier and halogen (such as iodine), a localized high iodine concentration (LHIC) coating is constructed on the porous membrane, which can enhance the selectivity of the porous membrane for iodine species. Based on the Donna exclusion and concentration gradient effect, the constructed localized high-concentration membrane can effectively suppress the diffusion of halogen positive electrodes of zinc-iodine batteries / zinc-bromine batteries, alleviate the capacity loss problem of zinc-iodine / zinc-bromine flow batteries, and achieve long-term cycle stability;

[0036] 2. The composite ion exchange membrane of the present invention, MgO-iodide (I x - ) adduct has the highest iodine adsorption energy and can form the most effective LHIC layer; the composite ion exchange membrane containing MgO coating has the best effect on suppressing Crossover, effectively improving the Coulombic efficiency of zinc-iodine flow battery and alleviating irreversible capacity loss. Therefore, the LHIC composite membrane based on MgO coating has excellent Donnan exclusion and concentration gradient effect to limit the polyiodide (I x -) shuttle, alleviating the capacity loss problem of zinc-iodine flow batteries and achieving long-term cycle stability; at the same time, the LHIC composite membrane based on the MgO coating has good stability and can still effectively inhibit the shuttle of active substances at high temperatures, thereby improving the coulombic efficiency of zinc-iodine flow batteries;

[0037] 3. The zinc-iodine liquid flow battery of the present invention includes a composite ion exchange membrane. A localized high iodine concentration membrane is formed by introducing halogen adducts on a porous membrane, which is applied to a zinc-halide liquid flow battery. The Donna exclusion and concentration gradient effects are used to exclude the shuttling of active substances, thereby improving the coulombic efficiency of the zinc-halide liquid flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a schematic diagram showing the application principle of the composite ion exchange membrane of the present invention in a zinc-iodine flow battery;

[0039] FIG2 is a composite ion exchange membrane prepared in different embodiments x - permeability maps;

[0040] FIG3 shows the zinc-iodine flow battery in Example 6 and Comparative Example 1 at room temperature (25° C.) and 20 mA cm -2 Charge and discharge performance diagram under current density;

[0041] FIG4 shows the zinc-iodine flow battery in Example 6 and Comparative Example 1 at 60°C and 20 mA cm -2 Charge and discharge performance diagram at current density. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0044] The following are detailed descriptions respectively. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood 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 the range. For example, the range description from 1 to 6 should be considered to have 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., as well as single numbers within the numbered ranges, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0045] The invention provides a composite ion exchange membrane, comprising a porous membrane and a metal oxide coating located on the surface of the porous membrane.

[0046] The composite ion exchange membrane of the present invention comprises a porous membrane and a metal oxide coating, wherein the metal oxide coating is located on one side surface of the porous membrane, and the porous membrane serves as a substrate; the present invention constructs a composite membrane based on a series of localized high iodine concentration (LHIC) coatings by introducing halogen adducts on the porous membrane to suppress the crossover problem of active polyiodine compounds in the cathode electrolyte. Specifically, metal oxides exhibit a strong physicochemical adsorption effect on halogens, forming halogen oxide adducts, which become effective halogen carriers; utilizing the strong adsorption properties of the carrier and halogen (such as iodine), a localized high iodine concentration (LHIC) coating is constructed on the porous membrane, which can enhance the selectivity of the porous membrane for iodine species. Based on the Donna exclusion and concentration gradient effect, the constructed localized high-concentration membrane can effectively suppress the diffusion of the halogen positive electrode of the zinc-iodine battery / zinc-bromine battery, alleviate the capacity loss problem of the zinc-iodine / zinc-bromine flow battery, and achieve long-term cycle stability.

[0047] In some embodiments, the metal oxide used in the metal oxide coating includes at least one of MgO, CeO2, ZrO2, TiO2, and Al2O3. Preferably, the metal oxide is MgO.

[0048] Specifically, the applicant's research on the stability of a series of oxide-halide adducts such as MgO, CeO2, ZrO2, TiO2, Al2O3 shows that MgO-iodide (I x -) adduct has the highest iodine adsorption energy and can form the most effective LHIC layer. The composite ion exchange membrane containing MgO coating has the best effect on suppressing Crossover, effectively improving the Coulomb efficiency of zinc-iodine flow battery and alleviating irreversible capacity loss. Therefore, the LHIC composite membrane based on MgO coating has excellent Donnan exclusion and concentration gradient effect to limit the polyiodide (I x - ) shuttle, alleviating the capacity loss problem of zinc-iodine flow batteries and achieving long-term cycle stability.

[0049] Furthermore, the metal oxide is MgO, and the composite ion exchange membrane formed in this way includes a porous membrane and a MgO coating. The composite ion exchange membrane has good stability and can still effectively inhibit the shuttling of active substances at high temperatures, thereby improving the coulombic efficiency of the zinc-iodine liquid flow battery.

[0050] In some embodiments, the porous membrane comprises at least one of a polyolefin porous membrane, a commercial Daramic membrane, and a commercial VANADion membrane.

[0051] In some embodiments, the thickness of the porous membrane is 100 to 1000 μm. Specifically, the thickness of the porous membrane is 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1000 μm.

[0052] In some embodiments, the pore size of the porous membrane is 10 to 200 nm. Specifically, the pore size of the porous membrane is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm.

[0053] In some embodiments, the porosity of the porous membrane is 10% to 60%. Specifically, the porosity of the porous membrane is 10%, 20%, 30%, 40%, 50%, or 60%.

[0054] In some embodiments, the thickness of the metal oxide coating is 5 to 100 μm. Specifically, the thickness of the metal oxide coating is 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

[0055] In some embodiments, the loading of the metal oxide coating in the composite ion exchange membrane is 1 to 5 mg cm -2 .

[0056] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned composite ion exchange membrane, comprising the following steps:

[0057] S1. Adding a binder to an organic solvent and stirring to obtain a blend solution;

[0058] S2. Adding metal oxide to the blend solution and stirring to obtain a coating solution;

[0059] S3. Applying the coating solution to the surface of the porous membrane and drying it to form a metal oxide coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane.

[0060] In some embodiments, the binder includes at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and perfluorosulfonic acid polymer (Nafion).

[0061] In some embodiments, the organic solvent includes at least one of dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0062] In some embodiments, the particle size of the metal oxide is 10 to 100 nm. Specifically, the particle size of the metal oxide is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0063] In some embodiments, the mass ratio of the binder, the organic solvent, and the metal oxide is (0.5-2):(5-20):(5-10).

[0064] In some embodiments, in the step of adding the binder to the organic solvent and stirring, the stirring temperature is 20 to 100° C. and the stirring time is 0.5 to 12 hours.

[0065] In some embodiments, in the step of adding the metal oxide to the blend solution and stirring, the stirring temperature is 20 to 100° C., and the stirring time is 0.5 to 12 hours.

[0066] In some embodiments, in the step of coating the coating solution onto the surface of the porous membrane, the coating method includes at least one of a casting method, a doctor blade method, a spray coating method, and a spin coating method.

[0067] In some embodiments, the coating solution is applied to the surface of the porous membrane and dried until the organic solvent in the coating solution is volatilized. Specifically, the drying temperature is 20 to 80° C. and the drying time is 0.5 to 24 hours.

[0068] In some embodiments, a method for preparing a composite ion exchange membrane comprises the following steps:

[0069] S1. Adding a binder to an organic solvent and stirring to obtain a blend solution;

[0070] S2. Adding metal oxide to the blend solution and stirring to obtain a coating solution;

[0071] S3. Apply the coating solution to the surface of the porous membrane to form a casting liquid coating with a thickness of 5 to 100 μm, and then dry it until the organic solvent in the casting liquid coating is completely evaporated to obtain a dry composite membrane, and form a metal oxide coating on the surface of the porous membrane to obtain a composite ion exchange membrane.

[0072] The size-screening materials used in the prior art require complex synthesis steps, resulting in high costs for constructing precise and selective ion transport pathways. However, the present invention's composite ion exchange membrane preparation method, based on inexpensive metal oxides, allows for efficient, large-scale production of composite membranes that effectively inhibit polyiodide shuttling. The present invention aims to overcome the crossover issue of cathode active material in existing zinc-halide flow batteries based on economic feasibility. This invention provides an LHIC composite ion exchange membrane for zinc-halide flow batteries that effectively improves ion selectivity, inhibits the shuttling problem of cathode active material, enhances battery cycle life and performance, and addresses capacity fade.

[0073] Based on the same inventive concept, the present invention also provides an application of the above-mentioned composite ion exchange membrane or the composite ion exchange membrane prepared by the above-mentioned preparation method in the preparation of a zinc-halogen liquid flow battery.

[0074] Specifically, the composite ion exchange membrane described above is used as a diaphragm in the preparation of zinc-halide flow batteries, including but not limited to zinc-iodine flow batteries and zinc-bromine flow batteries. The composite ion exchange membrane of the present invention comprises a porous membrane and a metal oxide coating. A localized high-iodine concentration membrane is formed by introducing a halogen adduct onto the porous membrane. This membrane is then applied to zinc-halide flow batteries, utilizing Donna exclusion and concentration gradient effects to prevent the shuttling of active materials, thereby improving the coulombic efficiency of the zinc-halide flow battery.

[0075] Based on the same inventive concept, the present invention also provides a zinc-iodine liquid flow battery, comprising a diaphragm, which is the above-mentioned composite ion exchange membrane or the composite ion exchange membrane prepared by the above-mentioned preparation method.

[0076] In some embodiments, the zinc-iodine flow battery further comprises a positive electrolyte and a negative electrolyte;

[0077] In some embodiments, the positive electrode electrolyte includes ZnI2 and water, that is, the positive electrode electrolyte is a ZnI2 solution formed by dissolving ZnI2 in water.

[0078] In some embodiments, the negative electrode electrolyte includes ZnBr2, an electrolyte, and water, that is, the negative electrode electrolyte is a ZnBr2 solution formed by dissolving ZnBr2 and the electrolyte in water.

[0079] In some embodiments, the electrolyte includes any one of KCl, K2SO4, and KBr.

[0080] In some embodiments, the concentration of ZnI2 in the positive electrode electrolyte is 0.5-2M, preferably, the concentration of ZnI2 is 1M.

[0081] In some embodiments, the concentration of ZnBr2 in the negative electrode electrolyte is 0.5-2M, preferably, the concentration of ZnBr2 is 1M.

[0082] In some embodiments, the concentration of the electrolyte in the negative electrode electrolyte is 0.5-2M. Preferably, the electrolyte is KCl, and the concentration of KCl is 1M.

[0083] In some embodiments, the metal oxide coating of the composite ion exchange membrane faces the positive electrode.

[0084] Further, referring to FIG1 , which shows a schematic structural diagram of a zinc-iodine flow battery, specifically, it includes: a negative electrode, a negative electrolyte, a positive electrode, a positive electrolyte, and a diaphragm; wherein the negative electrolyte is transported to the negative electrode side by a pump, and the positive electrolyte is transported to the positive electrode side by a pump; the diaphragm adopts the composite ion exchange membrane of the present invention, and the metal oxide coating faces the positive electrode side. By introducing halogen adducts on the porous membrane, a composite membrane with a localized high iodine concentration coating is constructed. The LHIC composite membrane has excellent Donnan exclusion and concentration gradient effects to limit the concentration of polyiodide (I x - ) shuttle, which improves the high coulombic efficiency of zinc-iodine flow batteries. However, the conventional porous membrane used as the diaphragm has the problem of crossover, and the polyiodide (I x - ) will shuttle across the septum to the opposite side.

[0085] The following further illustrates the composite ion exchange membrane and its preparation method, and the zinc-iodine flow battery of the present application with specific examples. This section further illustrates the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples 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.

[0086] Example 1

[0087] This embodiment provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0088] S1. Adding a binder polyvinylidene fluoride (PVDF) to an organic solvent N,N-dimethylformamide (DMF), and stirring at 50° C. for 6 h to obtain a blend solution; wherein the mass ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylformamide (DMF) is 1:7;

[0089] S2. Add MgO (average particle size of 50 nm) to the blended solution of S1, and stir at 50° C. for 6 h to obtain a coating solution; wherein the mass ratio of MgO to polyvinylidene fluoride (PVDF) is 8:1;

[0090] S3, applying the coating solution in S2 to the surface of the porous membrane, and drying at a temperature of 50° C. for 24 h to form an 8 μm thick MgO coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane (denoted as MgO composite membrane);

[0091] The porous membrane is a commercial porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.), and the porous polyolefin membrane has a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm.

[0092] Example 2

[0093] This embodiment provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0094] S1. Adding a binder polyvinylidene fluoride (PVDF) to an organic solvent N,N-dimethylformamide (DMF), and stirring at 50° C. for 6 h to obtain a blend solution; wherein the mass ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylformamide (DMF) is 1:7;

[0095] S2. Add Al2O3 (average particle size of 50 nm) to the blended solution of S1, and stir at 50°C for 6 hours to obtain a coating solution; wherein the mass ratio of Al2O3 to polyvinylidene fluoride (PVDF) is 8:1;

[0096] S3, applying the coating solution in S2 to the surface of the porous membrane, and drying at a temperature of 50° C. for 24 h to form an Al2O3 coating with a thickness of 8 μm on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane (denoted as Al2O3 composite membrane);

[0097] The porous membrane is a commercial porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.), and the porous polyolefin membrane has a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm.

[0098] Example 3

[0099] This embodiment provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0100] S1. Adding a binder polyvinylidene fluoride (PVDF) to an organic solvent N,N-dimethylformamide (DMF), and stirring at 50° C. for 6 h to obtain a blend solution; wherein the mass ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylformamide (DMF) is 1:7;

[0101] S2. Add TiO2 (average particle size of 50 nm) to the blended solution of S1, and stir at 50°C for 6 hours to obtain a coating solution; wherein the mass ratio of TiO2 to polyvinylidene fluoride (PVDF) is 8:1;

[0102] S3, applying the coating solution in S2 to the surface of the porous membrane, and drying at a temperature of 50° C. for 24 h to form an 8 μm thick TiO2 coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane (referred to as a TiO2 composite membrane);

[0103] The porous membrane is a porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.), and the porous polyolefin membrane has a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm.

[0104] Example 4

[0105] This embodiment provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0106] S1. Adding a binder polyvinylidene fluoride (PVDF) to an organic solvent N,N-dimethylformamide (DMF), and stirring at 50° C. for 6 h to obtain a blend solution; wherein the mass ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylformamide (DMF) is 1:7;

[0107] S2, adding ZrO2 (average particle size of 50 nm) to the blended solution of S1, stirring at 50°C for 6 hours to obtain a coating solution; wherein the mass ratio of ZrO2 to polyvinylidene fluoride (PVDF) is 8:1;

[0108] S3, applying the coating solution in S2 to the surface of the porous membrane, and drying at a temperature of 50° C. for 24 h to form an 8 μm thick ZrO2 coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane (denoted as ZrO2 composite membrane);

[0109] The porous membrane is a commercial porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.), and the porous polyolefin membrane has a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm.

[0110] Example 5

[0111] This embodiment provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0112] S1. Adding a binder polyvinylidene fluoride (PVDF) to an organic solvent N,N-dimethylformamide (DMF), and stirring at 50° C. for 6 h to obtain a blend solution; wherein the mass ratio of polyvinylidene fluoride (PVDF) to N,N-dimethylformamide (DMF) is 1:7;

[0113] S2. Add CeO2 (average particle size of 50 nm) to the blended solution of S1, and stir at 50°C for 6 h to obtain a coating solution; wherein the mass ratio of CeO2 to polyvinylidene fluoride (PVDF) is 8:1;

[0114] S3, applying the coating solution in S2 to the surface of the porous membrane, and drying at a temperature of 50° C. for 24 h to form an 8 μm thick CeO2 coating on the surface of the porous membrane, thereby obtaining a composite ion exchange membrane (referred to as CeO2 composite membrane);

[0115] The porous membrane is a commercial porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.), and the porous polyolefin membrane has a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm.

[0116] Example 6

[0117] This embodiment provides a zinc-iodine flow battery, including a diaphragm, a positive electrode, a negative electrode, a positive electrode electrolyte, and a negative electrode electrolyte;

[0118] The diaphragm is the composite ion exchange membrane prepared in Example 1, and the effective area of ​​the diaphragm is 4 cm 2 , the MgO coating in the composite ion exchange membrane faces the positive electrode side;

[0119] Both the positive and negative electrodes are carbon felt;

[0120] The positive electrode electrolyte is ZnI2 and water, the concentration of ZnI2 in the positive electrode electrolyte is 1M, and the volume of the positive electrode electrolyte is 4.5mL;

[0121] The negative electrode electrolyte includes ZnBr2, KCl and water, the concentration of ZnBr2 in the negative electrode electrolyte is 1M, the concentration of KCl in the negative electrode electrolyte is 1M, and the volume of the negative electrode electrolyte is 4.5mL.

[0122] Comparative Example 1

[0123] This comparative example provides a zinc-iodine flow battery, comprising a separator, a positive electrode, a negative electrode, a positive electrode electrolyte, and a negative electrode electrolyte;

[0124] The diaphragm is a commercial porous polyolefin membrane (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd.). The thickness of the porous polyolefin membrane is 600 μm, the porosity is 55%, and the pore size is 20 nm. The effective area of ​​the diaphragm is 4 cm 2 ;

[0125] Both the positive and negative electrodes are carbon felt;

[0126] The positive electrode electrolyte is ZnI2 and water, the concentration of ZnI2 in the positive electrode electrolyte is 1M, and the volume of the positive electrode electrolyte is 4.5mL;

[0127] The negative electrode electrolyte includes ZnBr2, KCl and water, the concentration of ZnBr2 in the negative electrode electrolyte is 1M, the concentration of KCl in the negative electrode electrolyte is 1M, and the volume of the negative electrode electrolyte is 4.5mL.

[0128] Performance Testing

[0129] The I values ​​obtained from the composite ion exchange membranes prepared in test examples 1 to 5 and the blank control samples in the permeation experiments that change with time are as follows: x - The permeability results are shown in Figure 2.

[0130] The permeability of the composite ion exchange membrane is determined by the evolution of the UV-visible spectrum on the permeate side of an H-type cell. Permeation experiments are conducted using an H-type cell, with the feed tank filled with 1 M KI3 and the permeate side filled with deionized water. The two cells have a circularly symmetrical transport channel separated by a composite ion exchange membrane or a commercial porous polyolefin membrane. It is assumed that when the KI3 concentration on the permeate side is low, the change in the KI3 concentration in the feed reservoir is negligible and the flux of KI3 through the membrane is constant; that is, pseudo-steady-state conditions exist in both reservoirs during the experiment:

[0131] Among them C A and C B (t) are the concentrations of KI3 on ​​the feed side and the permeate side (mol L -1 ). A and L are the area of ​​the membrane (cm 2 ) and thickness (cm); V is the volume of the permeate solution (ml); P is the membrane permeability (cm 2 min -1 ), t is time (min), t0 is time lag (min); the permeability P can be calculated by -ln(1-C B (t) / C A ) versus t.

[0132] In Figure 2, the MgO composite film corresponds to Example 1, the Al2O3 composite film corresponds to Example 2, the TiO2 composite film corresponds to Example 3, the ZrO2 composite film corresponds to Example 4, the CeO2 composite film corresponds to Example 5, and the blank control sample is the commercial porous polyolefin membrane in Example 1 (specifically, a porous polyethylene membrane purchased from Wuhan Zhisheng New Energy Co., Ltd., with a thickness of 600 μm, a porosity of 55%, and a pore size of 20 nm); wherein, the area of ​​the membrane used in the test is 4 cm 2 .

[0133] As can be seen from Figure 2, the MgO composite film has an impact on the x - The permeability is the lowest. Therefore, the composite ion exchange membrane containing MgO coating has the best Donnan rejection and concentration gradient effect, which can limit the iodide (I x - ) shuttle, which has the best effect in suppressing Crossover and effectively improves the Coulombic efficiency of zinc-iodine flow battery.

[0134] The zinc-iodine flow batteries in Example 6 and Comparative Example 1 were tested at room temperature (25°C) and 20 mA cm -2 The charge and discharge performance at a current density of , is shown in Figure 3. In Figure 3, a corresponds to Example 6, and b corresponds to Example 1.

[0135] As can be seen from Figure 3, at room temperature, the zinc-iodine flow battery in Example 6 maintained a battery capacity of about 80 mAh and a coulombic efficiency (CE) of 94.5% after 170 cycles; at room temperature, the zinc-iodine flow battery in Comparative Example 1 had a battery capacity of only 55 mAh and a coulombic efficiency (CE) of 70.8% after 48 cycles. At room temperature, the energy efficiency (EE) of the zinc-iodine flow battery in Example 6 was 67.3%, and the battery life was >170 cycles. At room temperature, the energy efficiency (EE) of the zinc-iodine flow battery in Comparative Example 1 was 59.5%, and the battery life was 48 cycles.

[0136] The zinc-iodine flow batteries in Example 6 and Comparative Example 1 were tested at 60°C and 20 mA cm -2 The charge and discharge performance at a current density of , is shown in Figure 4. In Figure 4, a corresponds to Example 6, and b corresponds to Example 1.

[0137] As can be seen from Figure 4, at a high temperature of 60°C, the zinc-iodine flow battery in Example 6 maintained a battery capacity of about 80 mAh and a coulombic efficiency (CE) of 97.2% after 75 cycles; at 60°C, the zinc-iodine flow battery in Comparative Example 1 had a battery capacity of only 10 mAh and a coulombic efficiency (CE) of 10% after 15 cycles. At a high temperature of 60°C, the energy efficiency (EE) of the zinc-iodine flow battery in Example 6 was 69.6%, and the battery life was >75 cycles. At a high temperature of 60°C, the energy efficiency (EE) of the zinc-iodine flow battery in Comparative Example 1 was 43.8%, and the battery life was 15 cycles.

[0138] It can be seen from Example 6 and Comparative Example 1 that the use of the composite ion exchange membrane as a diaphragm in the present invention greatly improves the service life, coulombic efficiency and energy efficiency of the zinc-iodine liquid flow battery.

[0139] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite ion exchange membrane, characterized in that, It includes a porous membrane and a metal oxide coating located on the surface of the porous membrane.

2. The composite ion exchange membrane according to claim 1, wherein The metal oxide used in the metal oxide coating includes at least one of MgO, CeO2, ZrO2, TiO2, and Al2O3; and / or, the porous membrane includes at least one of a polyolefin porous membrane, a Daramic membrane, and a VANADion membrane.

3. The composite ion exchange membrane according to claim 1, characterized in that, The thickness of the porous membrane is 100 - 1000 μm, and the thickness of the metal oxide coating is 5 - 100 μm.

4. A method for preparing a composite ion exchange membrane according to any one of claims 1 to 3, characterized in that, It includes the following steps: Add a binder to an organic solvent and stir to obtain a blend solution; Add a metal oxide to the blend solution and stir to obtain a coating solution; Coat the coating solution onto the surface of the porous membrane and dry it to form a metal oxide coating on the surface of the porous membrane, thus obtaining a composite ion exchange membrane.

5. The preparation method of the composite ion exchange membrane according to claim 4, characterized in that, The binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, and perfluorosulfonic acid polymer; and / or, the organic solvent includes at least one of dimethyl sulfoxide, N,N - dimethylacetamide, N - methylpyrrolidone, and N,N - dimethylformamide; and / or, the particle size of the metal oxide is 10 - 100 nm; and / or, the mass ratio of the binder, organic solvent, and metal oxide is (0.5 - 2):(5 - 20):(5 - 10).

6. The preparation method of the composite ion exchange membrane according to claim 4, characterized in that, In the step of adding the binder to the organic solvent and stirring, the stirring temperature is 20 - 100 °C, and the stirring time is 0.5 - 12 h; and / or, in the step of adding the metal oxide to the blend solution and stirring, the stirring temperature is 20 - 100 °C, and the stirring time is 0.5 - 12 h; and / or, in the step of coating the coating solution onto the surface of the porous membrane, the coating method includes at least one of the casting method, the doctor - blade method, the spraying method, and the spin - coating method; and / or, in the step of coating the coating solution onto the surface of the porous membrane and drying, the drying temperature is 20 - 80 °C, and the drying time is 0.5 - 24 h.

7. Application of the composite ion exchange membrane according to any one of claims 1 - 3 or the composite ion exchange membrane prepared by the preparation method according to any one of claims 4 - 6 in the preparation of a zinc - halogen flow battery.

8. A zinc-iodine flow battery, characterized in that, It includes a separator, and the separator is the composite ion exchange membrane according to any one of claims 1 - 3 or the composite ion exchange membrane prepared by the preparation method according to any one of claims 4 - 6.

9. The zinc-iodine flow battery according to claim 8, wherein, It further includes a positive electrolyte and a negative electrolyte; wherein, the positive electrolyte includes ZnI2 and water; the negative electrolyte includes ZnBr2, an electrolyte, and water.

10. The zinc-iodine flow battery according to claim 9, wherein, The electrolyte includes any one of KCl, K2SO4, and KBr; the concentration of ZnI2 in the positive electrolyte is 0.5 - 2 M; the concentration of ZnBr2 in the negative electrolyte is 0.5 - 2 M; the concentration of the electrolyte in the negative electrolyte is 0.5 - 2 M; The metal oxide coating in the composite ion exchange membrane faces the positive electrode.

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