A low ion permeation amount composite ion conduction membrane, a preparation method and application thereof

Abstract

The application discloses a kind of low ion permeation amount composite ion conducting membrane and preparation method thereof.The preparation method includes: (1) preparing chitosan intermediate layer on porous membrane support layer, and preparing chitosan / porous membrane composite base film;(2) the aqueous solution containing polyamine monomer and salt, with the organic phase solution containing polyacyl chloride, with the obtained chitosan / porous membrane composite base film as support base film, polymerization reaction occurs at the interface of aqueous phase-organic phase, and then annealing treatment is carried out, to obtain composite nanofiltration ion conducting membrane.The application enhances the wettability of traditional base film, improves the uniformity of the pore size distribution of base film, and further improves the uniformity and compactness of polyamide functional layer, thereby improving the performance of composite nanofiltration ion conducting membrane, and having industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane materials, specifically relating to a low ion permeation composite ion-conducting membrane and its preparation method. Background Technology

[0002] Flow batteries are gaining increasing attention worldwide due to their large energy storage capacity, high safety, long charge-discharge cycle life, and environmental friendliness, and have a very promising market prospect. However, as one of the key components of flow batteries, the ion exchange membrane has long been monopolized by foreign countries, making it difficult to reduce the cost of flow batteries.

[0003] To address the aforementioned issues, reduce the cost of flow batteries, and promote the industrial application of flow battery energy storage technology, nanofiltration ion-conducting membranes have been discovered. Nanofiltration ion-conducting membranes have pore sizes within the nanometer range, and their working mechanism utilizes pore size sieving and Donan effects to achieve highly selective conduction of active ions. Currently, the base membrane for nanofiltration ion-conducting membranes mainly uses porous membranes such as polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polytetrafluoroethylene as the support layer. On their surfaces, polyamines are used as aqueous monomers, and polyacrylamide chlorides are used as organic monomers, respectively, through interfacial polymerization to prepare nanofiltration composite membranes. However, traditional polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polytetrafluoroethylene membranes suffer from poor wettability and uneven pore size distribution, leading to a loose structure, increased defect rate, poor uniformity, and high ion permeation in the polyamide functional layer obtained by interfacial polymerization. Therefore, in order to obtain a polyamide composite nanofiltration ion-conducting membrane with low ion permeability, uniform pore size distribution, dense structure and good integrity, the thickness of the polyamide functional layer will be appropriately increased. However, this also increases the internal resistance of the flow battery, resulting in a decrease in the battery's energy efficiency.

[0004] Therefore, improving the hydrophilicity and pore size distribution uniformity of the supporting substrate before interfacial polymerization is crucial for enhancing the performance of nanofiltration ion-conducting membranes and the energy efficiency of flow batteries. Generally, chromium hydroxide nanofibers and carbon nanotubes are used to improve the hydrophilicity of the substrate, but both are biotoxic and environmentally toxic, and their preparation costs are high. Therefore, finding a resource-rich, environmentally friendly, non-biotoxic, biodegradable, and low-cost interlayer material is of great significance.

[0005] CN112755812A discloses a high-throughput cross-linked composite nanofiltration membrane with an intermediate layer and its preparation method. This patent uses cellulose nanocrystals as the intermediate layer and utilizes a cross-linking agent to cross-link polyetheramine onto the side of the composite membrane opposite to the base membrane, forming a cross-linked polyetheramine active layer, thereby achieving the preparation of the composite nanofiltration membrane.

[0006] The poor chemical stability and uniformity of the functional layer in composite nanofiltration membranes reduce the ion selectivity of the membrane, thereby decreasing the energy efficiency and lifespan of flow batteries. In contrast, the patent uses a cross-linking method to prepare the polyetheramine active layer, which is prone to swelling, has low tensile strength, and poor stability, resulting in an incomplete active layer, high ion permeability, and reduced battery energy efficiency. The patent also uses cellulose nanocrystals as an intermediate layer. Cellulose nanocrystals have few free active groups, poor hydrophilicity and water retention, and poor modification of the base membrane's wettability and pore size uniformity, leading to a loose structure, increased defect rate, poor uniformity, and high ion permeability in the functional layer grown on it. Furthermore, the patent uses a cross-linking reaction to prepare the active layer, which requires high temperatures (typically 60℃-90℃) and long reaction times. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention uses a microfiltration (MF) membrane as the support layer of a composite membrane, introduces chitosan as an intermediate layer on the surface of the support layer, and forms a polyamide (PA) surface active layer on the intermediate layer, thereby obtaining a composite nanofiltration ion conduction membrane with low ion permeability, uniformity, and density.

[0008] According to a first aspect of the present invention, embodiments of the present invention provide a method for preparing a low-ion-permeability composite nanofiltration ion-conducting membrane, comprising the following steps:

[0009] (1) A chitosan intermediate layer was prepared on a porous membrane support layer to obtain a chitosan / porous membrane composite base membrane;

[0010] (2) An aqueous solution containing polyamine monomers and salts and an organic solution containing polyacryl chlorides are used as a supporting base membrane. The chitosan / porous membrane composite base membrane obtained in step (1) is used as a supporting base membrane. A polymerization reaction occurs at the aqueous-organic phase interface, thereby generating a polyamide functional layer on the surface of the chitosan / porous membrane composite base membrane. After annealing, a low ion permeation composite nanofiltration ion conduction membrane is obtained.

[0011] Furthermore, in some embodiments, the preparation of the intermediate layer in step (1) is carried out using conventional methods in the art. The preparation process generally includes: dispersing chitosan in a solvent to form a dispersion, and then depositing the dispersion onto a porous support membrane to obtain a chitosan / porous membrane composite support membrane. Chitosan, as the intermediate layer, has hydrogel properties, and the solvent used in the chitosan dispersion is deionized water; the intermediate layer needs to be naturally dried before interfacial polymerization.

[0012] Further, in the chitosan / porous membrane composite base membrane obtained in step (1), 10-500 μg of chitosan is deposited per square centimeter of base membrane, preferably 20-300 μg of chitosan. The material of the porous membrane support base membrane includes at least one of polyacrylonitrile, polytetrafluoroethylene, polysulfone, polyethersulfone, and polyvinylidene fluoride, but is not limited thereto. Preferably, the porous membrane support layer is at least one of polyacrylonitrile, polysulfone, polytetrafluoroethylene, and polyvinylidene fluoride, which have strong mechanical properties.

[0013] Furthermore, the polymerization reaction described in step (2) is a conventional operation in the art. In some embodiments, the preparation method specifically includes: fully wetting the surface of the chitosan / porous membrane composite base membrane with the aqueous phase solution for 1 to 10 minutes; and fully wetting the surface of the chitosan / porous membrane composite support base membrane with the organic phase solution; and allowing the polyamine and polyacrylamide chloride to undergo an interfacial polymerization reaction at the aqueous-organic phase interface at a temperature of 20 to 30°C for 1 to 5 minutes.

[0014] Furthermore, the aqueous solution is obtained by dissolving the polyamine monomer in deionized water. The mass fraction of the polyamine monomer in the aqueous solution is 0.01–10%. The polyamine monomer includes, but is not limited to, any one or a combination of two or more of piperazine, 2,5-diaminobenzenesulfonic acid, m-phenylenediamine, p-phenylenediamine, melamine, thiourea, polyethyleneimine, and diethyltriamine.

[0015] Furthermore, the organic phase solution is prepared by dissolving a polyacrylamide chloride (1,3,5-pyromellitic acid chloride or other polyacrylamide chlorides) in an organic solvent. The mass fraction of the polyacrylamide chloride in the organic solution is 0.05–20%. The polyacrylamide chloride includes, but is not limited to, any one or a combination of two or more of 1,3,5-pyromellitic acid chloride, terephthaloyl chloride, isophthaloyl chloride, azeloyl chloride, and adipic acid chloride. The organic solvent may include, but is not limited to, any one or a combination of two or more of n-hexane, Isopar G, toluene, ethyl acetate, and benzene.

[0016] Furthermore, the annealing process in step (2) is a standard procedure in the art. The annealing temperature is generally 35–85°C, preferably 55–85°C; the processing time is generally 5–65 min, preferably 5–40 min.

[0017] Further, in step (2), the chitosan / porous membrane composite base membrane is immersed in the aqueous solution obtained in step S2 for a set time, and then the residual aqueous solution on the surface of the porous base membrane is removed; the obtained porous support base membrane is then immersed in the organic phase solution for a set time to remove the surface solution, and after annealing, a polyamide composite nanofiltration ion conduction membrane product with low ion permeability, uniformity, and density is obtained and stored in deionized water.

[0018] Furthermore, before step (1), step (3) is included: chitosan is sequentially immersed in NaOH solution, NaIO4 solution, and NaClO and / or NaClO2 solution, or sequentially immersed in NaOH solution, TEMPO (2,2,6,6-tetramethylpiperidine oxide) solution, NaClO and / or NaClO2 solution, and ultrasonically dispersed to obtain modified chitosan. After chemical oxidation and physical ultrasonication, the surface of chitosan has a large number of amino and hydroxyl groups, which helps to improve the wettability and pore size distribution uniformity of the base film. The mass fraction of NaOH solution can be 1% to 10%, the mass fraction of NaIO4 solution can be 0.1% to 20%, the mass fraction of TEMPO solution can be 0.1% to 25%, the mass fraction of NaClO and / or NaClO2 solution can be 0.1% to 30%, the ultrasonic treatment time can be 30s to 12h, and the ultrasonic temperature can be 20℃ to 80℃.

[0019] Furthermore, the aqueous solution also contains at least one of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, or calcium chloride. The inventors have discovered that adding the above-mentioned salts to the aqueous solution can improve the interfacial stability of interfacial polymerization, promote the smooth progress of the interfacial polymerization reaction, and thus help obtain a functional layer with low ion permeability and uniform pore size. The mass fraction of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, or calcium chloride in the aqueous solution is generally 0.02%–3.8%.

[0020] Furthermore, the chitosan particles have a diameter in the nanometer range, typically 10-500 nm, preferably 10-200 nm. The concentration of the chitosan dispersion is 0.1-25 g / L.

[0021] According to a second aspect of the invention, the invention also provides a composite nanofiltration membrane having a chitosan intermediate layer, which is prepared by the method described above.

[0022] Furthermore, the composite nanofiltration membrane with a chitosan intermediate layer provided by the present invention comprises a bottom porous membrane support layer, a chitosan intermediate layer, and a polyamide functional layer stacked together. Due to the dense structure and uniform film formation of the polyamide functional layer, the composite ion-conducting membrane exhibits low ion permeation.

[0023] According to a third aspect of the present invention, embodiments of the present invention also provide the application of the aforementioned low-ion-permeability composite nanofiltration ion-conducting membrane in the field of flow batteries.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The composite nanofiltration ion-conducting membrane with chitosan as the intermediate layer provided by this invention improves the wettability and pore size uniformity of traditional porous membranes, reduces the defect rate of the functional layer, and makes the film uniform and dense, thereby reducing the ion permeation of the composite nanofiltration ion-conducting membrane. It also overcomes the biotoxicity and high cost problems caused by previous chromium hydroxide nanofibers or carbon nanotubes. In addition, during the interfacial polymerization reaction, the salt in the aqueous solution can enhance the water retention performance of the chitosan intermediate layer, change the interfacial position during the interfacial polymerization reaction, and improve the interfacial stability, thereby improving the uniformity and density of the polyamide functional layer prepared by polymerization, and synergistically reducing the ion permeation of the composite nanofiltration ion-conducting membrane, thereby improving the service life and energy efficiency of the flow battery.

[0026] 2. The preparation method of the low ion permeation composite nanofiltration ion conduction membrane provided by the present invention is simple, low-cost, and environmentally friendly. Moreover, the composite nanofiltration ion conduction membrane has low ion permeation, is dense and uniform, which can improve the energy efficiency and service life of flow batteries and has industrial application value.

[0027] 3. Through research and practice, the inventors of this application have discovered that chitosan contains a large number of amino and hydroxyl groups. Modifying traditional porous membranes with poor wettability using chitosan can improve the hydrophilicity of the membrane. Furthermore, adding salt to the aqueous solution is preferred to enhance the water retention capacity of the chitosan interlayer, modify the interfacial position during interfacial polymerization, and improve interfacial stability. This further facilitates the stable progress of the interfacial polymerization reaction, resulting in a polyamide functional layer with better uniformity and density. This reduces the ion permeation of the composite nanofiltration ion-conducting membrane, thereby improving the lifespan and energy efficiency of the flow battery. Based on the above findings, the inventors of this application have proposed the technical solution of this invention. Additionally, chitosan is abundant, environmentally friendly, biodegradable, and more economical than traditional cellulose. Implementation

[0028] The technical solution, its specific implementation process and principle of the present invention will be further described in detail below.

[0029] The preparation principle of the low-ion-permeability composite nanofiltration ion-conducting membrane of this invention may lie in the fact that chitosan contains a large number of amino and hydroxyl groups. Using chitosan to modify traditional porous membranes with poor wettability can improve the uniformity of pore size distribution and hydrophilicity of the membrane, thereby improving the uniformity and density of the polyamide functional layer obtained by polymerization and reducing the defect rate of the functional layer. Simultaneously, the addition of salt to the aqueous solution can improve the water retention capacity of the chitosan interlayer, modify the interfacial position during interfacial polymerization, and improve interfacial stability, which is more conducive to improving the uniformity and density of the polyamide functional layer prepared by polymerization, reducing the ion permeability of the composite nanofiltration ion-conducting membrane, and thus improving the lifespan and energy efficiency of the flow battery.

[0030] The following description, in conjunction with several preferred embodiments, provides a more comprehensive and detailed explanation of the technical solution of the present invention. The specific embodiments described below are merely for further illustration and explanation of the present invention and are not intended to limit the invention; any simple improvements based on the method of the present invention should be within the scope of protection of the claims.

[0031] In the examples, the average particle size of chitosan was selected to be 180 nm. Example 1

[0032] Untreated chitosan was deposited on a commercially available polytetrafluoroethylene porous substrate membrane, with a deposition density of 200 μg / cm³. 2 The chitosan / polytetrafluoroethylene composite membrane was immersed in an aqueous solution containing 0.05% piperazine for 8 minutes. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 1.5% (w / w) solution of 1,3,5-trimethylammonium chloride and subjected to interfacial polymerization at 25°C for 120 seconds. After removal, the membrane was cleaned with n-hexane and then heated at 60°C for 35 minutes to obtain the composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1M FeCl3 and 0.1M CrCl3, respectively. Example 2

[0033] The pretreatment process of chitosan includes: immersing chitosan in a 2% NaOH solution for 20 min at 30℃; washing with deionized water, then immersing it in a 0.9% NaIO4 solution for 1 h at 60℃; washing with deionized water again, then immersing it in a 1.3% NaClO solution for 45 min at 25℃; and finally, ultrasonic dispersion for 5 min at 25℃. After washing with deionized water, the treated chitosan forms a chitosan dispersion with a concentration of 0.5 g / L.

[0034] The treated chitosan was deposited on a commercially available polyethersulfone porous substrate membrane at a deposition density of 220 μg / cm³. 2 The chitosan / polyethersulfone composite membrane was soaked in an aqueous solution containing 0.05% piperazine for 10 min. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 1.8% solution of 1,3,5-trimethylammonium chloride and subjected to interfacial polymerization at 25°C for 150 s. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 40 min to obtain the composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1M FeCl3 and 0.1M CrCl3, respectively. Example 3

[0035] The pretreatment process of chitosan includes: immersing chitosan in a 2% NaOH solution for 20 min at 30℃; washing with deionized water, then immersing it in a 0.9% NaIO4 solution for 1 h at 60℃; washing again with deionized water, then immersing it in a 1.5% NaClO solution for 45 min at 25℃; and finally, ultrasonic dispersion for 5 min at 25℃. After washing with deionized water, the treated chitosan forms a chitosan dispersion with a concentration of 0.7 g / L.

[0036] The treated chitosan was deposited onto a commercially available polyacrylonitrile porous membrane at a deposition density of 230 μg / cm³. 2 The chitosan / polyacrylonitrile composite membrane was immersed in an aqueous solution containing 0.04% piperazine and 0.9% calcium chloride for 10 min. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 1.5% (w / w) solution of 1,3,5-trimethylammonium chloride and subjected to interfacial polymerization at 25°C for 140 s. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 40 min to obtain the composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1 M FeCl3 and 0.1 M CrCl3, respectively. Example 4

[0037] The pretreatment process of chitosan included: immersing chitosan in a 3.2% NaOH solution for 15 min at 30°C; washing with deionized water, then immersing it in a 23% TEMPO solution for 20 min at 25°C; washing again with deionized water, then immersing it in a 3% NaClO solution for 20 min at 30°C; and finally, ultrasonic dispersion for 8 h at 25°C. After washing with deionized water, the treated chitosan formed a chitosan dispersion with a concentration of 0.4 g / L.

[0038] The treated chitosan was deposited onto a commercially available polyvinylidene fluoride porous membrane at a deposition density of 10 μg / cm³. 2The chitosan / polyvinylidene fluoride composite membrane was immersed in an aqueous solution containing 0.02% piperazine and 0.06% potassium chloride for 7 minutes. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 0.09% 1,3,5-trimethylpyrrolidone chloride solution for 1 minute at 25°C. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 40 minutes to obtain the composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1M FeCl3 and 0.1M CrCl3, respectively. Example 5

[0039] The pretreatment process of chitosan includes: immersing chitosan in a 9% NaOH solution for 5 minutes at 30°C; washing with deionized water, then immersing it in a 0.4% TEMPO solution for 35 minutes at 40°C; washing again with deionized water, then immersing it in a 20% NaClO2 solution for 5 minutes at 25°C; and finally, ultrasonic dispersion for 30 seconds at 45°C. After washing with deionized water, the treated chitosan forms a chitosan dispersion with a concentration of 0.5 g / L.

[0040] The treated chitosan was deposited on a commercially available polyethersulfone porous substrate membrane at a deposition density of 50 μg / cm³. 2 The chitosan / polyethersulfone composite membrane was immersed in an aqueous solution containing 1.2% piperazine and 0.06% sodium chloride for 7 minutes. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 0.4% (w / w) solution of 1,3,5-trimethylammonium chloride and subjected to interfacial polymerization at 25°C for 1 minute. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 25 minutes to obtain the composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1M FeCl3 and 0.1M CrCl3, respectively.

[0041] Table 1: Effects of Fe on composite conductive membranes containing only untreated chitosan intermediate layer (Example 1) / only pretreated chitosan intermediate layer (Example 2) / including treated chitosan intermediate layer and saline solution (Examples 3-5) 3+ and Cr 3+ The permeation rate (test conditions were room temperature 25℃, relative humidity 60%, and test time 5 days).

[0042] Table 1 Ion permeability (ppm)

[0043] Fe 3+ ]] Cr 3+ ]] Example 1 36.503 59.448 Example 2 10.926 17.094 Example 3 7.432 8.995 Example 4 9.184 12.063 Example 5 2.251 2.816

[0044] The results in Table 1 show that the ion permeation of the membrane with only the untreated chitosan intermediate layer (Example 1) is at least 234.1% higher than that of the membrane with only the pretreated chitosan intermediate layer (Example 2); the ion permeation of the membrane with only the pretreated chitosan intermediate layer (Example 2) is at most 507.0% higher than that of the membrane containing the treated chitosan intermediate layer and the saline solution (Examples 3-5); and the ion permeation of the membrane with only the untreated chitosan intermediate layer (Example 1) is an order of magnitude higher than that of the membrane containing the treated chitosan intermediate layer and the saline solution (Examples 3-5).

[0045] Comparative Example 1

[0046] A polyethersulfone porous membrane was immersed in an aqueous solution containing 1.2% piperazine and 0.06% sodium chloride for 7 minutes. After the aqueous solution on the surface of the composite membrane was dried, the membrane surface was immersed in a 0.4% (w / w) solution of 1,3,5-trimethylammonium chloride and subjected to interfacial polymerization at 25°C for 1 minute. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 25 minutes to obtain a composite nanofiltration ion-conducting membrane. Permeation was tested using 0.1M FeCl3 and 0.1M CrCl3, respectively.

[0047] Comparative Example 2

[0048] Carbon nanotubes were deposited on a polyethersulfone porous membrane. The composite membrane was then immersed in an aqueous solution containing 1.2% piperazine and 0.06% sodium chloride for 7 minutes. After the aqueous solution on the surface of the composite membrane was dried, the membrane was immersed in a 0.4% solution of 1,3,5-trimethylpyrrolidone chloride for 1 minute at 25°C. After removal, the membrane was cleaned with n-hexane and then heated at 55°C for 25 minutes to obtain a composite nanofiltration ion-conducting membrane. Permeation was measured using 0.1M FeCl3 and 0.1M CrCl3, respectively.

[0049] Table 2: Effects of composite conductive membranes with deposited chitosan interlayer (Example 5) / undeposited interlayer (Comparative Example 1) / deposited carbon nanotube interlayer (Comparative Example 2) on Fe 3+ and Cr 3+ The permeation rate was measured (test conditions were room temperature 25°C, relative humidity 60%, and test duration 5 days). The types and mass fractions of salts were the same in all the comparative examples and embodiments above.

[0050] Table 2 Ion permeability (ppm)

[0051] Fe 3+ ]]> Cr 3+ ]]> Example 5 2.251 2.816 Comparative Example 1 73.959 91.745 Comparative Example 2 20.634 38.129

[0052] The results in Table 2 show that, with the same salt types and mass fractions in the aqueous solution, the ion permeability of the membrane without the deposited interlayer (Comparative Example 1) is nearly two orders of magnitude higher than that of the membrane with the deposited chitosan interlayer (Example 5); the ion permeability of the membrane with the deposited carbon nanotube interlayer (Comparative Example 2) is one order of magnitude higher than that of the membrane with the deposited chitosan interlayer (Example 5). This demonstrates that the composite ion-conducting membrane of the pretreated chitosan interlayer and the aqueous salt solution introduced in this invention has extremely low ion permeability.

[0053] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0054] The use of headings and sections in this invention is not intended to limit the invention; each section can be applied to any aspect, embodiment or feature of the invention.

[0055] Throughout this invention, wherever a composition is described as having, containing, or including specific components, or wherever a process is described as having, containing, or including specific process steps, it is contemplated that the compositions taught in this invention are also substantially composed of or comprised of the described components, and that the processes taught in this invention are also substantially composed of or comprised of the described process steps.

[0056] Unless otherwise specifically stated, the use of the terms “comprising” or “having” should generally be understood as open-ended and non-restrictive.

[0057] It should be understood that the order of the steps or the order in which specific actions are performed is not particularly important, as long as the teachings of this invention remain operable. Furthermore, two or more steps or actions can be performed simultaneously.

[0058] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0059] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for preparing a low-ion-permeability composite ion-conducting membrane, comprising the following steps: (1) Chitosan is sequentially immersed in NaOH solution, NaIO4 solution and NaClO and / or NaClO2 solution, or chitosan is sequentially immersed in NaOH solution, TEMPO solution, NaClO and / or NaClO2 solution; ultrasonic dispersion is performed to obtain modified chitosan; the modified chitosan is dispersed in a solvent to form a dispersion, and the dispersion is then deposited on a porous support base membrane to obtain a chitosan / porous membrane composite base membrane; 10-500 μg of chitosan is deposited on each square centimeter of porous support base membrane; (2) An aqueous solution containing polyamine monomers and salts, and an organic solution containing polyacryl chlorides, with the chitosan / porous membrane composite base membrane obtained in step (1) as the supporting base membrane, undergo a polymerization reaction at the aqueous-organic phase interface, thereby generating a polyamide functional layer on the surface of the chitosan / porous membrane composite base membrane, and then undergoing annealing treatment to obtain a low ion permeation composite ion conduction membrane. The salt is at least one of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, or calcium chloride.

2. The preparation method according to claim 1, characterized in that, 20–300 μg of chitosan is deposited on the porous support base membrane per square centimeter.

3. The preparation method according to claim 1 or 2, characterized in that, The porous support base membrane is made of at least one of polyacrylonitrile, polytetrafluoroethylene, polysulfone, polyethersulfone, and polyvinylidene fluoride.

4. The preparation method according to claim 1, characterized in that, Step (2) includes: fully wetting the surface of the chitosan / porous membrane composite base film with an aqueous solution for 1 to 10 minutes; and fully wetting the surface of the chitosan / porous membrane composite base film with an organic solution; and allowing the polyamine and polyacrylamide to undergo interfacial polymerization at the aqueous-organic interface at a temperature of 20 to 30°C for 1 to 5 minutes.

5. The preparation method according to claim 1, characterized in that, The mass fraction of the polyamine monomer in the aqueous solution is 0.01-10%, and the polyamine monomer includes any one or a combination of two or more of piperazine, 2,5-diaminobenzenesulfonic acid, m-phenylenediamine, p-phenylenediamine, melamine, thiourea, polyethyleneimine, and diethyltriamine.

6. The preparation method according to claim 1, characterized in that, The mass fraction of polyacryl chloride in the organic phase solution is 0.05-20%; the polyacryl chloride includes any one or a combination of two or more of 1,3,5-trimethylbenzene chloride, terephthaloyl chloride, isophthaloyl chloride, azeloyl chloride, and adipoyl chloride.

7. The preparation method according to claim 1, characterized in that, The annealing process is carried out at a temperature of 35–85°C for 5–65 minutes.

8. The preparation method according to claim 1, characterized in that, The NaOH solution has a mass fraction of 1% to 10%, the NaIO4 solution has a mass fraction of 0.1% to 20%, the TEMPO solution has a mass fraction of 0.1% to 25%, and the NaClO and / or NaClO2 solution has a mass fraction of 0.1% to 30%.

9. The preparation method according to claim 1, characterized in that, The mass fraction of the salt in the aqueous solution is 0.02–3.8%.

10. The preparation method according to claim 1, characterized in that, The chitosan particles have a diameter of 10-500 nm; the dispersion has a concentration of 0.1-25 g / L.

11. The preparation method according to claim 10, characterized in that, The chitosan particles have a diameter of 10-200 nm.

12. The low ion permeation composite ion-conducting membrane prepared by any of the preparation methods described in claims 1-11.

13. The low ion permeation composite ion-conducting membrane according to claim 12, characterized in that, It includes a bottom layer of porous support base membrane, a chitosan intermediate layer, and a polyamide functional layer, all stacked together.

14. The application of the low ion permeation composite ion-conducting membrane according to claim 12 or 13 in the field of flow batteries.