Organic-inorganic composite membrane selectively transmitting lithium ions, and preparation method and application thereof

Abstract

The present application belongs to the technical field of separation membrane material technology, and relates to an organic-inorganic composite membrane for selectively transferring lithium ions, which is formed by hybridizing an organic polymer and an inorganic solid lithium ion superconductor; and a preparation method thereof is as follows: an organic polymer is dissolved in an organic solvent to prepare an organic polymer solution; inorganic solid lithium ion superconductor powder is added into the organic polymer solution and stirred to obtain a uniform casting solution; and the obtained casting solution is prepared into a membrane. The present application utilizes the difference in cation permeation rate between the organic polymer and the lithium ion superconductor, and applies it to selective separation of lithium and magnesium; and the size screening effect of the inorganic solid lithium ion superconductor is utilized to improve the lithium and magnesium selective separation performance of the organic polymer, so that the doped membrane has high lithium ion transmission flux and selectivity.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane material technology, and relates to an organic-inorganic composite membrane for selectively transferring lithium ions, its preparation method, and its application. Background Technology

[0002] Lithium is an important strategic energy metal, already used in industries such as batteries, ceramics, glass, and aerospace. In recent years, due to the rapid development of electric vehicles, global demand for lithium has increased dramatically. Traditional methods of extracting lithium from ores can no longer meet this huge demand, and lithium mining also suffers from high energy consumption and severe environmental pollution. Therefore, there is an urgent need to extract lithium resources from salt lake brines to improve lithium production capacity.

[0003] Lithium-ion selective transport membranes are for Li + One of the effective methods for selective separation is lithium-ion selective transport membrane materials, which commonly include organic and inorganic membrane materials. However, traditional organic membranes have limited potential for further breakthroughs due to the trade-off between permeation flux and ion selectivity.

[0004] In addition, various inorganic materials are gradually being prepared into membranes for use in the field of ion separation. Although these membranes can overcome the trade-off between ion flux and selectivity, inorganic materials are usually expensive, and the feasibility and reproducibility of their large-scale preparation into membranes have not yet been proven.

[0005] Organic-inorganic composite membranes are prepared by dispersing nanoscale inorganic materials in a polymer matrix. They combine the advantages of inorganic materials, such as adjustable pore size and easily customizable functions, with the economical processing of polymers. Organic-inorganic composite membranes are generally considered more competitive than both organic and inorganic membrane materials. Summary of the Invention

[0006] The purpose of this invention is to provide an organic-inorganic composite membrane for selectively transferring lithium ions, its preparation method, and its application, so as to overcome the problems existing in the above-mentioned background art.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] One aspect of the present invention provides an organic-inorganic composite membrane for selectively transporting lithium ions, characterized in that it comprises an organic polymer and an inorganic solid lithium-ion superconductor, wherein the inorganic solid lithium-ion superconductor is formed by hybridization of the organic polymer.

[0009] Moreover, the inorganic solid lithium-ion superconductor accounts for 5%-90% of the mass of the organic polymer.

[0010] Furthermore, the organic polymers include ion-exchange organic polymers and inherently microporous organic polymers, wherein the ion-exchange organic polymers are selected from any one or a combination of at least two of polyphenylene ether, polysulfone, polyether ether ketone, polydiphenylpiperidine, and polyvinylidene fluoride;

[0011] The intrinsically microporous organic polymer is selected from any one or a combination of at least two of the following: intrinsically microporous polymers without external group modification, intrinsically microporous organic polymers with a methylamine oxime group, and intrinsically microporous polymers modified with Tröger's base.

[0012] Moreover, the inorganic solid lithium-ion superconductor is Li 3x La 2 / 3-x TiO3 (0.03≤x≤0.167), Li 1+x+y Al x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤0.5, 0≤y≤0.4), (Li x La y ZrO z (2≤x≤8, 1≤y≤2, 3≤z≤7) and Li 1+x Al x Ti 2-x (PO4)3 (0≤x≤0.5).

[0013] Another aspect of the present invention provides a method for preparing an organic-inorganic composite membrane for selectively transferring lithium ions, comprising the following steps:

[0014] S1. Preparation of casting solution: Dissolve organic polymer in organic solvent and add inorganic solid lithium-ion superconductor to obtain casting solution in which inorganic solid lithium-ion superconductor is uniformly dispersed.

[0015] S2. Membrane preparation: The casting solution is used to prepare a membrane.

[0016] Furthermore, in S1, the mass ratio of the organic polymer to the organic solvent is 1:15~40; the casting solution is prepared by ultrasonic dispersion or stirring dispersion.

[0017] Furthermore, in S2, the method for preparing the casting solution into a film includes other methods such as casting, scraping, and spin coating, and the drying temperature during film preparation is 10~110 ℃, and the drying time is 5~24 h.

[0018] Moreover, the organic polymer is one of the following: quaternized polyphenylene ether, quaternized polyphenylpiperidine, sulfonated polyvinylidene fluoride, or a metallo-oxime-based organic polymer with inherent microporous structure.

[0019] The inorganic solid lithium-ion superconductor is Li 0.5 La 0.5 TiO3, Li 0.33 La 0.56 TiO3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 One of them.

[0020] In another aspect, the present invention provides an application of an organic-inorganic composite membrane for selectively transporting lithium ions in the extraction of lithium ions from salt lake brine.

[0021] The advantages and beneficial effects of this invention are as follows:

[0022] This invention utilizes concentration gradient diffusion across the membrane to drive the exchange of cations and anions, requiring no additional energy and thus being energy-efficient and environmentally friendly. The incorporation of a solid lithium-ion superconductor provides sieving sites for cations, preferentially allowing smaller cations such as lithium ions to pass through, thereby improving the selectivity of the lithium-ion selective transport membrane. Furthermore, the incorporation of an inorganic solid lithium-ion superconductor provides additional lithium-ion diffusion channels, increasing the membrane's lithium-ion permeability. The incorporation of an inorganic solid lithium-ion superconductor can also suppress the movement of organic polymer chains, reducing membrane swelling. Moreover, the raw materials and preparation process are simple, allowing for easy and large-area fabrication for lithium-ion transport. + Extracted membrane material.

[0023] The organic-inorganic composite membrane for selectively transferring lithium ions of the present invention can be used efficiently and energy-savingly for the extraction of lithium ions from salt lake brine or for the pre-enrichment of lithium ions. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the selective lithium-ion transporting organic-inorganic composite film prepared in Example 1; where: a represents 5% Li 0.5 La 0.5 Reduced cross-sectional view of TiO3@AO-PIM-1;

[0025] b is 5% Li 0.5 La 0.5 Enlarged cross-sectional view of TiO3@AO-PIM-1;

[0026] Figure 2 The image shows a scanning electron microscope (SEM) image of the AO-PIM-1 membrane prepared in Comparative Example 1 of this invention; where a is a reduced cross-sectional view of AO-PIM-1 and b is a magnified cross-sectional view of AO-PIM-1.

[0027] Figure 3 For the present invention Li +Schematic diagram of the extraction capability testing device;

[0028] Figure 4 For the present invention Li 0.5 La 0.5 The graph shows the lithium-magnesium separation performance of the TiO3@AO-PIM-1 membrane in a 1 mol / L LiCl and MgCl2 mixed solution; where the horizontal axis represents Li 0.5 La 0.5 The TiO3 content in the membrane, with the bar chart representing Li + / Mg 2+ Selectivity factor; the dotted line plot represents the Li+ permeation flux.

[0029] Explanation of reference numerals in the attached figures

[0030] 1-Feed bottle, 2-Inlet pipe, 3-Holder, 4-Separation membrane, 5-Outlet pipe, 6-Outlet bottle. Detailed Implementation

[0031] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0032] The selective lithium-ion transport organic-inorganic composite membrane of the present invention comprises an organic polymer and an inorganic solid lithium-ion superconductor. It uses an inherently microporous organic polymer as a matrix and obtains a membrane material with enhanced selective lithium-ion transport performance by incorporating an inorganic solid lithium-ion superconductor. Specifically, the inherently microporous organic polymer is dissolved in an organic solvent to prepare an organic polymer solution; inorganic solid lithium-ion superconductor powder is added to the organic polymer solution and stirred to obtain a uniform casting solution; the obtained casting solution is used to prepare a membrane by solvent evaporation.

[0033] This invention utilizes the difference in cation permeation rate in inherently microporous organic polymers and applies it to the selective separation of lithium and magnesium; it also utilizes the size sieving effect of inorganic solid lithium-ion superconductors to improve the selective separation performance of lithium and magnesium in inherently microporous organic polymers, resulting in doped films with high lithium-ion transport flux and selectivity.

[0034] The preparation process of the selective lithium-ion transport organic-inorganic composite membrane of the present invention can be widely applied to the combination of various organic polymers and inorganic materials.

[0035] Example 1

[0036] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the following steps:

[0037] Preparation of S1 casting solution: Dissolve 0.12 g of amylopectin-modified PIM-1 in 3 mL of N,N-dimethylformamide, stir at 25 °C for 24 h, and then add 6 mg of Li. 0.5 La 0.5 TiO3 powder was ultrasonically dispersed for 30 min to obtain a casting solution in which a solid lithium-ion superconductor was uniformly dispersed.

[0038] The preparation of amine oxime-1: 10.21 g of purified 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane and 6.00 g of 2,3,5,6-tetrafluoroterephthalonitrile were added to a three-necked round-bottom flask containing 200 mL of anhydrous N,N-dimethylformamide. The reaction mixture was placed in an oil bath at 70 °C and stirred continuously under a N2 atmosphere until a clear solution was formed. Then, 8.40 g of anhydrous potassium carbonate was added, and the reaction was stirred for 72 h. The reaction product was poured into deionized water, and the precipitate was collected by filtration. The precipitate was washed with deionized water, acetone, and methanol. The resulting yellow product was dissolved in chloroform, and 0.5 mol / L dilute hydrochloric acid solution was added to the solution. After thorough shaking, the mixture was allowed to stand for 10 min. The solution was then added dropwise to methanol, and the solid was reprecipitated. After filtration, the solid was dried under vacuum at 120 °C for 24 hours. h, to obtain PIM-1. Dissolve 4.8 g of dried PIM-1 in 300 mL of tetrahydrofuran, transfer it to a three-necked flask equipped with a reflux condenser and place it in an oil bath. Heat the solution to 65 °C under a N2 atmosphere, and add 50 mL of hydroxylamine solution dropwise while stirring continuously. Then reflux at 69 °C for 20 h. After the reaction is complete, let the solution cool to room temperature, pour it into 1 L of anhydrous ethanol to precipitate a milky white product. After filtering the precipitate, wash it four times with anhydrous ethanol and dry it under vacuum in an oven at 110 °C for 3 h to obtain amylated PIM-1.

[0039] Among them, inorganic solid lithium-ion superconductor Li 0.5 La 0.5Preparation of TiO3: 1.25 mL of di(2-hydroxypropionic acid)diammonium hydroxide titanium alloy was placed in a 50 mL volumetric flask and diluted with water to obtain a 0.05 mol / L aqueous solution of di(2-hydroxypropionic acid)diammonium hydroxide titanium alloy. This solution was then poured into a beaker. 1.125 g of lanthanum nitrate hexahydrate and 0.096 g of lithium nitrate were dissolved in 20 mL of deionized water and added dropwise to the di(2-hydroxypropionic acid)diammonium hydroxide titanium alloy aqueous solution while stirring until homogeneous. Then, 5 mol / L sodium hydroxide solution was added while continuously stirring until the final sodium hydroxide concentration in the mixture reached 0.6 mol / L. Finally, 1.893 g of hexadecyltrimethylammonium bromide was added and mixed thoroughly. The mixed solution was poured into a hydrothermal reactor lined with para-polyphenol and reacted at 260 ℃ for 24 h. After the reaction, the mixture was cooled to room temperature, centrifuged at 4000 rpm for 4 min in a high-speed centrifuge, washed repeatedly with ethanol, and finally rinsed at 100 °C. Li was dried in an oven at ℃ for 24 h to obtain Li 0.5 La 0.5 TiO3.

[0040] Preparation of S2 membrane: The casting solution obtained in step S1 was spread evenly on a 5 cm × 5 cm glass plate and dried in an oven at 80 ℃ for 12 h. After cooling to room temperature in the oven, the membrane was soaked in deionized water to peel it off from the glass plate, obtaining an organic-inorganic composite membrane that selectively transfers lithium ions, and labeled as 5%Li 0.5 La 0.5 TiO3@AO-PIM-1, the reduced-size and magnified scanning electron microscope images of its cross-section are shown below. Figure 1 .

[0041] Example 2

[0042] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the method in Example 1, the only difference being the addition of 12 mg of Li. 0.5 La 0.5 TiO3 powder was used to obtain an organic-inorganic composite film that selectively transfers lithium ions, labeled as 10%Li 0.5 La 0.5 TiO3@AO-PIM-1.

[0043] Example 3

[0044] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the method in Example 1, the only difference being the addition of 24 mg of Li. 0.5 La 0.5 TiO3 powder was used to obtain an organic-inorganic composite film that selectively transfers lithium ions, labeled as 20% Li. 0.5 La 0.5TiO3@AO-PIM-1.

[0045] Example 4

[0046] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the method in Example 1, the only difference being the addition of 36 mg of Li. 0.5 La 0.5 TiO3 powder was used to obtain an organic-inorganic composite film that selectively transfers lithium ions, labeled as 30% Li. 0.5 La 0.5 TiO3@AO-PIM-1.

[0047] Example 5

[0048] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the following steps:

[0049] Preparation of S1 casting solution: Dissolve 0.12 g of brominated polyphenylene ether in 5 mL of N-methylpyrrolidone and add 0.18 mL of triethylamine solution. Stir at 25 °C for 24 h, then add 84 mg of Li. 0.33 La 0.56 TiO3 powder was ultrasonically dispersed for 120 min to obtain a casting solution in which a solid lithium-ion superconductor was uniformly dispersed.

[0050] The preparation of brominated polyphenylene ether: 30 g of chlorobenzene was added to a three-necked flask containing 6.0 g of polyphenylene ether, and the mixture was stirred continuously until the polyphenylene ether was completely dissolved. Then, a reflux condenser was installed, and the solution was heated to 135 °C. 0.25 g of azobisisobutyronitrile (dissolved in 5.0 g of chlorobenzene) and 6 g of N-bromosuccinimide (dissolved in 20 g of chlorobenzene) were added dropwise to the solution. The liquid mixture was then allowed to react in an oil bath at 135 °C for 4 h. After the reaction product cooled naturally to room temperature, it was slowly poured into anhydrous ethanol, precipitating a fibrous solid. The solid was washed four times with anhydrous ethanol and then dried at 60 °C for 24 h to obtain a pale yellow brominated polyphenylene ether.

[0051] Among them, solid lithium-ion superconductor Li 0.33 La 0.56 Preparation of TiO3: Lithium carbonate (10 mol% excess), lanthanum oxide, and titanium dioxide were precisely weighed according to their stoichiometric ratio. These materials were then ground and mixed in a ball mill, followed by oven drying to obtain a precursor. The precursor was then calcined in air at 800 °C and 1150 °C for 4 h and 24 h, respectively, at a heating rate of 3 °C / min, and ground to obtain Li. 0.33 La 0.56 TiO3 powder.

[0052] Preparation of S2 membrane: The casting solution obtained in step S1 was spread evenly on a 5 cm × 5 cm glass plate and dried in an oven at 100 °C for 24 h. After cooling to room temperature in the oven, the membrane was soaked in deionized water to peel it off from the glass plate. The resulting organic-inorganic composite membrane that selectively transfers lithium ions was labeled as 70%Li 0.33 La 0.56 TiO3@QPPO.

[0053] Example 6

[0054] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the method in Example 5, the only difference being the addition of 96 mg of Li. 0.33 La 0.56 TiO3 powder was used to obtain an organic-inorganic composite film that selectively transfers lithium ions, labeled as 80% Li. 0.33 La 0.56 TiO3@QPPO.

[0055] Example 7

[0056] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the method in Example 5, the only difference being the addition of 108 mg of Li. 0.33 La 0.56 TiO3 powder was used to obtain an organic-inorganic composite film that selectively transfers lithium ions, labeled as 90% Li. 0.33 La 0.56 TiO3@QPPO.

[0057] Example 8

[0058] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the following steps:

[0059] Preparation of S1 casting solution: Dissolve 0.2 g of quaternized poly(m-terphenylpiperidine) in 3 mL of dimethyl sulfoxide, stir at 25 °C for 12 h, and then add 120 mg of Li7La3Zr2O. 12 The powder was ultrasonically dispersed for 60 min to obtain a casting solution in which the solid lithium-ion superconductor was uniformly dispersed.

[0060] The preparation of quaternized poly(m-terphenylpiperidine) was as follows: 4.0 g of m-terphenyl, 2.56 g of N-methyl-4-piperidinone, and 10 mL of dichloromethane were added to a three-necked flask. After complete dissolution, the three-necked flask was transferred to an ice-water bath. While stirring continuously, 1.6 mL of trifluoroacetic acid and 16 mL of trifluoromethanesulfonic acid were added dropwise to the mixed solution. After the reaction continued for 5 h, the resulting viscous, dark brown reaction product was slowly poured into a 5 mol / L NaOH solution, precipitating a pale yellow product. The product was washed several times with deionized water until the pH was neutral, and then vacuum dried at 80 ℃ for 12 h to obtain poly(m-terphenylpiperidine). 2.0 g of dried poly(m-terphenylpiperidine) was dissolved in 40 mL of dimethyl sulfoxide. 0.84 g of potassium carbonate and 1.72 g of iodomethane were added to the solution. The reaction was carried out in the dark at room temperature for 24 h. After the reaction was completed, the solution was added dropwise to ethyl acetate, and a yellow product was precipitated. The product was washed three times with ethyl acetate and deionized water, and then dried under vacuum at 80 °C for 12 h to obtain quaternized poly(m-terphenylpiperidine).

[0061] Among them, the solid lithium-ion superconductor Li7La3Zr2O 12 Preparation: Lithium carbonate, lanthanum oxide, and zirconium oxide were placed in a ball mill jar at a molar ratio of 7.1:3:2, with 10% excess lithium carbonate to compensate for lithium volatilization loss during calcination. Isopropanol and zirconium balls were then added to the ball mill jar at a mass ratio of 1:6:2 (raw material, zirconium balls, solvent). The ball mill was operated at 200 r / min for 12 h. The milled material was dried, ground into a fine powder, and placed in a high-temperature furnace. The temperature was increased to 1000℃ at a rate of 1℃ / min and held for 2 h to obtain Li7La3Zr2O. 12 powder.

[0062] Preparation of S2 film: The casting solution obtained in step S1 was dropped onto the center of a substrate in a high-speed rotating spin coater to spread and form a uniform film. The film was then placed in an oven and dried at 110 °C for 5 h, followed by oven cooling to room temperature. The resulting organic-inorganic composite film selectively transferring lithium ions was labeled as 60%Li7La3Zr2O. 12 @m-PTP.

[0063] Example 9

[0064] An organic-inorganic composite membrane for concentration-driven selective lithium-ion transport was prepared according to the following steps:

[0065] Preparation of S1 casting solution: Dissolve 0.15 g of sulfonated polyvinylidene fluoride in 5 mL of dimethyl sulfoxide, stir at 25 °C for 12 h, and then add 75 mg of Li. 1.3 Al 0.3 Ti 1.7(PO4)3 powder was ultrasonically dispersed for 60 min to obtain a casting solution in which a solid lithium-ion superconductor was uniformly dispersed.

[0066] The preparation of sulfonated polyvinylidene fluoride (PVDF) involved adding 10 mL of purified chlorosulfonic acid to a flask containing 0.5 g of PVDF and stirring the mixture at 40 °C for 16 h. The product was washed with 1,2-dichloroethane and then washed several times with deionized water to remove excess acid. Finally, the product was vacuum dried at 90 °C for 48 h to obtain sulfonated PVDF.

[0067] Among them, solid lithium-ion superconductor Li 1.3 Al 0.3 Ti 1.7 Preparation of (PO4)3: First, 16.029 g of titanium dioxide was dissolved in 9.431 mL of acetylacetone. Then, the solution was mixed with 100 mL of tetrahydrofuran, followed by the addition of 13.543 g of phenylphosphoric acid, 4.285 g of aluminum nitrate, and 2.756 g of lithium nitrate, and stirred until completely dissolved. The resulting solution was dried on an 80 °C heating plate for 3 h to form a gel, and then heated in a muffle furnace at 500 °C for 2 h to form a powder. The resulting precursor powder was then calcined at 950 °C for 2 h at a heating rate of 5 °C / min. Li3 was then ground to obtain Li2O3. 1.3 Al 0.3 Ti 1.7 (PO4)3 powder.

[0068] Preparation of S2 film: The casting solution obtained in step S1 was dropped onto the substrate, and the doctor blade was moved to form a film. The film was then placed in an oven and dried at 90 °C for 20 h, followed by furnace cooling to room temperature. The resulting organic-inorganic composite film selectively transferring lithium ions was labeled as 50%Li 1.3 Al 0.3 Ti 1.7 (PO4)3@SPVDF.

[0069] Comparative Example 1

[0070] Prepare the amylopyridine-oxime-based PIM-1 membrane according to the following steps:

[0071] Preparation of S1 casting solution: A certain amount of 0.12 g of amylopyridine-oxime PIM-1 was dissolved in 3 mL of N,N-dimethylformamide and stirred at 25 °C for 24 h to obtain a uniform casting solution.

[0072] Preparation of S2 membrane: The prepared casting solution was spread evenly on a 5 cm × 5 cm glass plate and dried in an oven at 80 ℃ for 12 h. After cooling to room temperature in the oven, the membrane was soaked in deionized water to peel it off from the glass plate, obtaining a amine oxime-based PIM-1 membrane labeled AO-PIM-1. SEM images of its cross-section, both reduced and magnified, are shown below. Figure 2 .

[0073] Comparative Example 2

[0074] The quaternized polyphenylene ether-based membrane was prepared according to the following steps:

[0075] Preparation of S1 casting solution: Take a certain amount of 0.12 g of brominated polyphenylene ether, dissolve it in 5 mL of N-methylpyrrolidone, add 0.18 mL of triethylamine solution, stir at 25 ℃ for 24 h to obtain a uniform casting solution;

[0076] Preparation of S2 membrane: The prepared casting solution was spread on a 5 cm × 5 cm glass plate and dried in an oven at 100 ℃ for 24 h. After cooling to room temperature in the oven, the membrane was soaked in deionized water to peel it off from the glass plate, and the quaternized polyphenylene ether-based membrane was obtained and labeled as QPPO.

[0077] Comparative Example 3

[0078] Quaternized poly(m-terphenylpiperidine) membranes were prepared according to the following steps:

[0079] Preparation of S1 casting solution: A certain amount of 0.2 g of quaternized poly(m-terphenylpiperidine) was dissolved in 3 mL of dimethyl sulfoxide and stirred at 25 °C for 12 h to obtain a uniform casting solution.

[0080] Preparation of S2 membrane: The prepared casting liquid was dropped onto the center of the substrate of a high-speed rotating spin coater to spread and form a uniform film. The film was then placed in an oven and dried at 110 °C for 5 h. After being cooled to room temperature in the oven, a quaternized poly(m-terphenylpiperidine) membrane was obtained and labeled as m-PTP.

[0081] Comparative Example 4

[0082] Sulfonated polyvinylidene fluoride membranes were prepared according to the following steps:

[0083] Preparation of S1 casting solution: Take a certain amount of 0.15 g of sulfonated polyvinylidene fluoride and dissolve it in 5 mL of dimethyl sulfoxide. After stirring at 25 ℃ for 12 h, a uniform casting solution is obtained.

[0084] Preparation of S2 film: The prepared casting solution was dropped onto the substrate, and the doctor blade was moved to form a film. The film was then placed in an oven and dried at 90 °C for 20 h. After that, it was cooled to room temperature in the oven to obtain a sulfonated polyvinylidene fluoride film, labeled as SPVDF.

[0085] The separation capabilities of the base membranes prepared in Comparative Examples 1-4 and the selective lithium-ion transport organic-inorganic composite membranes prepared in Examples 1-9 were tested in a mixed salt solution system. The separation capability testing apparatus is shown in [reference needed]. Figure 3 The device includes a feed bottle 1 for holding the feed liquid, a discharge bottle 6 for holding the discharge liquid, an inlet pipe 2, an outlet pipe 5, and a clamp 3. The feed pipe is connected to the lower part of the feed bottle, and the discharge pipe is connected to the lower part of the discharge bottle. Clamping platforms are provided around the ends of the feed and discharge pipes. A separation membrane 4 is clamped between the two clamping platforms. This separation membrane is an organic-inorganic composite membrane for selectively transferring lithium ions prepared according to this invention. The two clamping platforms are connected by a clamp, which can be a pipe clamp or a clip. The discharge and feed bottles each form a diffusion chamber. The separation membrane is fixed between the two diffusion chambers by a clamp, and the effective area of ​​the membrane is 1.766 cm². 2 The feed solution is 120 mL of a 1 mol / L lithium chloride and 1 mol / L magnesium chloride solution (sodium chloride solution), and the effluent is 120 mL of deionized water. Driven by osmotic pressure, Li... + and Mg 2+ (Na + The ions migrate from the feed side to the discharge side via transmembrane transport. The ion concentration of the discharge solution is measured using ICP-OES, and the cation flux and Li2O3 flux are calculated. + / M n+ The permeation selectivity is shown in Table 1.

[0086] Table 1:

[0087]

[0088] The results show that the AO-PIM-1 base film has a strong effect on Li + / Mg 2+ It exhibits good separation and selectivity performance under the conditions described in the embodiments of this invention. + / Mg 2+ The separation ratio was 18.43, Li + The flux was 0.62 mol·m -2 ·h -1 The addition of solid lithium-ion superconductor 2D-LLTO to the Li-ion separation membrane + Flux and Li + / Mg 2+ The separation selectivity was significantly improved. Within the doping range of 5%-30%, the Li content of the separation film increased with increasing doping concentration. + The flux increased because 2D-LLTO formed a fast lithium-ion transport channel within the membrane, enhancing the lithium-ion transport capacity of the separation membrane; Li+ / Mg 2+ The separation selectivity is significantly improved, which is due to the special structure of 2D-LLTO, which only allows Li to be separated. + Ions can enter the vacancy within a channel composed of four adjacent TiO6 octahedra and undergo a transition, preventing other larger ions from entering, thus affecting Li. + / Mg 2+ It exhibits significant separation performance. Therefore, in lithium extraction from salt lake brines with a high magnesium-to-lithium ratio, using this membrane for diffusion dialysis can significantly reduce the magnesium-to-lithium ratio, enabling pre-enrichment and selective extraction of lithium ions. This is an energy-saving and environmentally friendly lithium extraction method that requires no external energy input.

[0089] Figure 4 It describes Li 0.5 La 0.5 The graph shows the lithium-magnesium separation performance of the TiO3@AO-PIM-1 membrane in a 1 mol / L LiCl and MgCl2 mixed solution. The horizontal axis represents Li... 0.5 La 0.5 The TiO3 content in the membrane, with the bar chart representing Li + / Mg 2+ Selection factor, represented by a dotted line graph of Li + The permeation flux. As can be seen from this figure, with Li... 0.5 La 0.5 As the TiO3 content in the membrane increases, the Li in the membrane... + Flux and selectivity are constantly increasing, as Li 0.5 La 0.5 When the TiO3 content in the membrane reaches 30 wt.%, the Li in the membrane... + The flux and selectivity reached 2.85 mol / (m²). 2 ·h) and 48.61.

[0090] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. The application of an organic-inorganic composite membrane for selectively transferring lithium ions in the extraction of lithium ions from salt lake brine, specifically for the separation of lithium and magnesium ions, characterized by: The method for preparing the selective lithium-ion transport organic-inorganic composite membrane includes the following steps: S1. Preparation of casting solution: Dissolve organic polymer in organic solvent and add inorganic solid lithium-ion superconductor to obtain casting solution in which inorganic solid lithium-ion superconductor is uniformly dispersed. S2. Membrane preparation: The casting solution is used to prepare a membrane; In S1, the mass ratio of the organic polymer to the organic solvent is 1:15~40; the casting solution is prepared by ultrasonic dispersion or stirring dispersion. In S2, the method for preparing the casting solution into a film includes casting, scraping, and spin coating. The drying temperature during film preparation is 10~110 ℃, and the drying time is 5~24 h. The selective lithium-ion transport organic-inorganic composite membrane comprises an organic polymer and an inorganic solid lithium-ion superconductor, wherein the inorganic solid lithium-ion superconductor is formed by hybridization of the organic polymer. The inorganic solid lithium-ion superconductor accounts for 5%-90% of the mass percentage of the organic polymer; The organic polymer is one of brominated polyphenylene ether, quaternized poly(m-terphenylpiperidine), sulfonated polyvinylidene fluoride, or amine oxime-modified PIM-1; The inorganic solid lithium-ion superconductor is Li 0.5 La 0.5 TiO3, Li 0.33 La 0.56 TiO3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 One of them.

Images