Preparation method of high lithium ion selective open-chain crown ether composite membrane

Abstract

The application relates to the field of membrane separation technology and discloses a preparation method of a high-lithium-ion-selectivity open-chain crown ether composite membrane. The method takes a polysulfone (PSF) membrane as a base film, adds an imine monomer in water, adds an acyl chloride monomer and an o-phenylenedioxydiacetyl chloride (OPDC) monomer in oil, introduces the OPDC monomer into a separation layer through an interfacial polymerization method, and prepares the open-chain crown ether composite membrane with high lithium ion selectivity. The open-chain crown ether composite membrane prepared through the method has excellent lithium ion separation performance and stability, and provides a reference idea for the preparation of ion selective membranes, efficient recovery and extraction of liquid phase lithium resources and other related fields.

Description

Technical Field

[0001] This invention belongs to the fields of materials science and membrane separation, and specifically relates to a method for preparing a high lithium-ion selective open-chain crown ether composite membrane for lithium-ion recovery from liquid solutions, such as a membrane and device for selectively separating lithium ions from brine. Background Technology

[0002] With the continued growth of global energy demand and increasing emphasis on environmental sustainability, efficient and clean energy solutions have become crucial. Lithium-ion batteries, as a core element of energy storage and conversion technologies, are experiencing a surge in market demand. Currently, the main sources of lithium salts include mineral deposits and salt lake resources. Traditional lithium extraction methods typically rely on acid decomposition and chemical leaching of minerals, or on concentrating brine through solar pond evaporation to enrich lithium ions. However, these processes often suffer from problems such as complex procedures, long processing times, large requirements for chemical reagents, or high dependence on climate conditions.

[0003] In contrast, membrane separation technology, due to its advantages such as high selectivity, environmental friendliness, ease of operation, and scalability, has gradually become the ideal choice for lithium extraction. To optimize the lithium extraction process, this invention proposes using open-chain crown ether composite membranes to replace traditional lithium extraction methods. This technology can more efficiently separate and enrich lithium ions while reducing the use of chemical reagents, making the entire process more environmentally friendly and significantly shortening the extraction time, thereby improving the utilization efficiency of lithium resources.

[0004] Crown ether monomers are organic compounds with macrocyclic or polycyclic, multidentate ligands that can coordinate with cations. The oxygen atoms in crown ethers possess unshared electron pairs, giving the crown ether ring a negative charge. Furthermore, different crown ethers contain holes of varying sizes; the combined effect of these two factors generates ion-dipole interactions, enabling crown ethers to bind with metal ions in a host-guest manner to form stable complexes. Among these, crown ether structures containing tetraoxygen atoms often exhibit good recognition with lithium ions, demonstrating excellent lithium-ion selectivity. Moreover, composite membranes prepared via interfacial polymerization show good chemical stability and can effectively resist environmental influences such as corrosion and oxidation from seawater. Therefore, combining crown ethers with membrane technology to prepare highly selective lithium-ion composite membranes has promising application prospects.

[0005] Defects are prone to occur during the preparation of open-chain crown ether composite membranes, leading to a decrease in their separation performance. Therefore, this invention obtains a highly selective and dense open-chain crown ether composite membrane by adjusting the monomer ratio and selecting an air-jet method to remove the aqueous phase.

[0006] Currently, there is an urgent need in this field to develop a lithium-ion selective membrane with high lithium-ion selectivity that can be stably prepared and scaled up. Summary of the Invention

[0007] The purpose of this invention is to overcome the difficulties in lithium extraction in the prior art and to provide a method for preparing a high lithium-ion selective open-chain crown ether composite membrane.

[0008] The technical solution of this invention is as follows:

[0009] A method for preparing a highly selective open-chain crown ether composite membrane, the specific operation of which is as follows:

[0010] A. Synthesis of monomers: o-Phenylidene dioxaacetic acid was dissolved in thionyl chloride solution in a round-bottom flask. The round-bottom flask was wrapped with tin foil to create a light-proof condition. The mixed solution was then heated in an oil bath under a nitrogen atmosphere to form a uniform brown solution. The crude product was obtained by rotary evaporation and purified by sodium bicarbonate column chromatography. The solvent was removed by vacuum distillation to obtain o-Phenylidene dioxaacetyl chloride (OPDC).

[0011] B. Preparation of mixed aqueous phase: At room temperature, a certain mass fraction of amine monomer, camphor sulfonic acid (CSA) and triethylamine (TEA) are added to deionized water, and the mixture is stirred continuously to obtain a mixed aqueous phase;

[0012] C. Preparation of mixed oil phase: At room temperature, a certain mass of acyl chloride monomer is added to a certain mass percentage of o-phenylene dioxydiacetyl chloride and n-hexane, and the mixture is stirred continuously to obtain a mixed oil phase;

[0013] D. Membrane Preparation: The mixed aqueous solution prepared in step B is applied to the PSF base membrane. After a period of time, the aqueous phase is removed, and the membrane surface is allowed to dry and become smooth at room temperature. The mixed oil phase solution prepared in step C is then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution is removed from the membrane surface. The membrane is then subjected to thermal crosslinking and curing in an oven. The membrane surface is rinsed with deionized water to obtain the TFC composite membrane, which is then stored for later use.

[0014] Furthermore, in step A, the molar ratio of o-phenylene dioxyacetic acid to thionyl chloride solution is 0.1-0.2.

[0015] Furthermore, in step A, the oil bath temperature for heating and stirring the mixed solution is 50-70 ℃, and the time is 2-3 h; in step A, the rotary evaporation temperature is 40-50 ℃, and the rotation speed is 30-100 r / min.

[0016] Further, the amine monomer mentioned in step B is one of the monomers m-phenylenediamine (MPD), piperazine (PIP), N-methylpiperazine (NMPIP), and polyethyleneimine (PEI);

[0017] Further, in step B, the amine monomer has a mass fraction of 1.0-5.0 wt%, the camphor sulfonic acid has a mass fraction of 0.5-3.0 wt%, and the triethylamine has a mass fraction of 0.5-7.5 wt%.

[0018] Further, the acyl chloride monomer in step C is either triformyl chloride (TMC) or terephthaloyl chloride (TPC); the mass-volume percentage of the acyl chloride monomer to n-hexane in the oil phase solution is 0.05-0.45 w / v, and the mass-volume percentage of o-phenylene dioxydiacetyl chloride to n-hexane is 0.05-0.45 w / v.

[0019] Furthermore, the method for removing the aqueous phase in step D is air jetting; the air jetting uses an air gun with an air pressure of 0.5-1.0 MPa.

[0020] Furthermore, the characteristic feature is that the thermosetting treatment temperature in step D is 60-80 ℃, and the time is 5-15 min.

[0021] Compared with existing technologies, the advantages of this invention are as follows: The novel monomer o-phenylene dioxydiacetyl chloride synthesized in this invention has a unique tetraoxy cavity structure, which can effectively recognize lithium ions. An open-chain crown ether composite membrane with a dense cross-linked structure was successfully prepared using interfacial polymerization. This membrane exhibits excellent lithium-magnesium separation performance, effectively solving the current difficulties in lithium ion extraction. This invention demonstrates the broad application prospects of highly ion-selective membrane separation. Attached Figure Description

[0022] Figure 1 This is the NMR spectrum of the OPDC prepared in Example 3.

[0023] Figure 2 These are SEM images of the TFC membrane and TFC-OP-10 membrane from Examples 5 and 7.

[0024] Figure 3 a) FTIR characterization test results of OPDC monomers and the prepared composite membranes in Examples 3, 5, 6, 7, and 8; b) XPS total spectrum test results of composite membranes in Examples 5, 6, 7, and 8.

[0025] Figure 4 These are the O1s and C1s peak patterns and crosslinking degree of the TFC membrane and TFC-OP-10 membrane in Examples 5 and 7.

[0026] Figure 5 These are the water contact angle and surface energy of the composite membranes in Examples 5, 6, 7, and 8.

[0027] Figure 6 a) is a schematic diagram of the diffusion membrane assembly shown in Example 6; b) is a schematic diagram of the electrodialysis assembly shown in Example 7 and Example 11.

[0028] Figure 7a) is a diagram showing the ion flux of the TFC membrane and the TFC-OP-10 membrane in Examples 5 and 7; b) is a diagram showing the lithium-magnesium separation performance of the TFC-OP-10 membrane under different voltages in electrodialysis in Example 7.

[0029] Figure 8 The graphs show the lithium-magnesium ion flux and lithium-magnesium separation performance of the TFC-OP-10 membrane, PIP-OP-10 membrane, NMPIP-OP-10 membrane, and PEI-OP-10 membrane under electrodialysis in Examples 5 and 10. Detailed Implementation Example 1

[0030] This example illustrates the preparation of acyl chloride monomers with incomplete acyl chloride chlorination.

[0031] A solution of o-phenylene dioxanediacetic acid (0.1 by mass) and thionyl chloride was dissolved in a round-bottom flask. The flask was wrapped with tin foil to create a light-protected environment. The mixture was then heated in an oil bath at 50 °C for 2 hours under a nitrogen atmosphere to form a homogeneous brown solution. The crude product was obtained by rotary evaporation at 40 °C at a rate of 30 r / min. Purification was performed using sodium bicarbonate column chromatography. The solvent was then removed by vacuum distillation to obtain the monomer that had not undergone complete acylation. Example 2

[0032] This example illustrates the preparation of acyl chloride monomers with incomplete acyl chloride chlorination.

[0033] A solution of o-phenylene dioxane and thionyl chloride (mass ratio 0.15) was dissolved in a round-bottom flask. The flask was wrapped with aluminum foil to create a light-protected environment. The mixture was then heated in a nitrogen atmosphere in an oil bath at 60 °C for 2.5 h to form a homogeneous brown solution. The crude product was obtained by rotary evaporation at 45 °C at a rate of 70 r / min. Purification was performed using sodium bicarbonate column chromatography. The solvent was then removed by vacuum distillation to obtain the monomer that had not undergone complete acylation. Example 3

[0034] This example illustrates the preparation of a novel o-phenylene dioxodiacetyl chloride.

[0035] Dissolve o-phenylene dioxoacetic acid (0.2 by mass) in a thionyl chloride solution in a round-bottom flask. Wrap the flask with tin foil to create a light-protected environment. Heat the mixture in a nitrogen atmosphere at 70 °C in an oil bath for 3 hours to form a homogeneous brown solution. The crude product is obtained by rotary evaporation at 50 °C at a speed of 100 r / min. Purification is performed using sodium bicarbonate column chromatography. The solvent is removed by vacuum distillation to obtain o-phenylene dioxoacetyl chloride (OPDC).

[0036] Figure 1 This is the NMR spectrum of the OPDC prepared in this embodiment. The NMR test confirmed that the OPDC was successfully prepared. It can be seen that the novel monomer o-phenylene dioxydiacetyl chloride has a unique tetraoxy cavity structure. Example 4

[0037] This embodiment illustrates the preparation of composite membranes via interfacial polymerization.

[0038] First, a mixed aqueous phase was prepared. At room temperature, 1.0 wt% MPD monomer, 0.5 wt% CSA, and 0.5 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared, with TPC and n-hexane at a mass-volume percentage of 0.05 w / v%. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 0.5 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution was removed from the membrane surface. The membrane was then subjected to thermal crosslinking and curing in a 60°C oven for 5 min. The membrane surface was rinsed with deionized water to obtain a TFC composite membrane, which was used for lithium-magnesium separation in electrodialysis tests. Example 5

[0039] This embodiment illustrates the preparation of composite membranes via interfacial polymerization.

[0040] First, a mixed aqueous phase was prepared. At room temperature, 1.0 wt% MPD monomer, 0.5 wt% CSA, and 0.6 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared, with TMC and n-hexane at a mass-volume percentage of 0.05 w / v%. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 0.5 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution was removed from the membrane surface. The membrane was then subjected to thermal crosslinking and curing at 60°C for 5 min. The membrane surface was rinsed with deionized water to obtain a TFC composite membrane, which was used for lithium-magnesium separation in electrodialysis tests.

[0041] Figure 2 a and 2b are cross-sectional SEM images and surface morphology images of the TFC membrane in this embodiment. It can be seen that the selective layer thickness of the membrane is about 90 nm, and the membrane surface shows a typical ridge-valley structure. Figure 3 b is the total XPS spectrum of the TFC membrane in this embodiment. Example 6

[0042] This embodiment illustrates the preparation of open-chain crown ether composite membranes via interfacial polymerization.

[0043] First, a mixed aqueous phase was prepared. At room temperature, 2.0 wt% MPD monomer, 1.5 wt% CSA, and 0.6 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared, with TMC and n-hexane at a mass-volume percentage of 0.25 w / v, and the o-phenylene dioxydiacetyl chloride prepared in Example 3 at a mass-volume percentage of 0.05 w / v. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 0.5 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization, and excess oil phase solution was removed. The membrane was then subjected to thermal crosslinking and curing in a 60 °C oven for 5 min, and the membrane surface was rinsed with deionized water to obtain the TFC-OP-05 membrane. Simultaneously, TFC without o-phenylene dioxydiacetyl chloride was prepared as a control group under the same proportions and temperature conditions. Two types of membranes were used for electrodialysis testing to separate lithium and magnesium.

[0044] Figure 3 a is the infrared spectrum of the TFC membrane and the TFC-OP-05 membrane in this embodiment. It can be seen that the TFC-OP-05 membrane has generated COC bonds, indicating that the monomer has been successfully polymerized onto the membrane layer. Figure 3 b is the XPS total spectrum of the TFC membrane and the TFC-OP-05 membrane in this embodiment. Figure 4 ab is the XPS peak profile of the O1s and C1s of the TFC membrane in this embodiment. Figure 4 c is the crosslinking degree diagram of the TFC membrane in this embodiment. Figure 5 These are the water contact angle and surface energy diagrams for TFC membrane and TFC-OP-05 membrane, showing that the membrane is more hydrophilic. Figure 6 a is a schematic diagram of the diffusion membrane assembly device used in this embodiment. Figure 7 a is the ion flux diagram of TFC obtained after diffusion testing in this embodiment. Example 7

[0045] First, a mixed aqueous phase was prepared. At room temperature, 5.0 wt% MPD monomer, 3.0 wt% CSA, and 7.5 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared. The mass-volume percentage of TMC to n-hexane was 0.45 w / v, and the mass-volume percentage of o-phenylene dioxydiacetyl chloride prepared in Example 3 to n-hexane was 0.10 w / v. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 0.7 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution was removed from the membrane surface. The membrane was then subjected to crosslinking and curing treatment in a 75 °C oven for 10 min. The membrane surface was rinsed with deionized water to obtain a TFC-OP-10 membrane composite membrane, which was used for lithium-magnesium separation in electrodialysis tests.

[0046] Figure 2 c and 2d are cross-sectional SEM images and surface morphology images of the TFC-OP-10 membrane in this embodiment. It can be seen that the selective layer thickness of the membrane is about 40 nm, and the membrane surface is smoother than that of the TFC membrane. Figure 3 a is the infrared spectrum of the TFC-OP-10 membrane in this embodiment. It can be seen that COC bonds have been produced, indicating that the monomer has been successfully polymerized onto the membrane layer. Figure 3 b is the XPS total spectrum of the TFC-OP-10 membrane in this embodiment. Figure 4 de is the XPS peak diagram of O1s and C1s of the TFC-OP-10 membrane in this embodiment. Figure 4 f is the crosslinking degree diagram of the TFC-OP-10 membrane in this embodiment. Compared with TFC, the crosslinking degree is reduced. Figure 5 This is a diagram of the water contact angle and surface energy of the TFC-OP-10 membrane. The addition of OPDC increases the hydrophilicity of the membrane surface and the surface energy. Figure 7 a is the ion flux diagram of the TFC-OP-10 membrane obtained after diffusion testing in this embodiment. Figure 6 b is a schematic diagram of the electrodialysis component device used in this embodiment. Example 8

[0047] First, a mixed aqueous phase was prepared. At room temperature, 5.0 wt% MPD monomer, 3.0 wt% CSA, and 7.5 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared. The mass-volume percentage of TMC to n-hexane was 0.45 w / v, and the mass-volume percentage of o-phenylene dioxydiacetyl chloride prepared in Example 3 to n-hexane was 0.15 w / v. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 1.0 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution was removed from the membrane surface. The membrane was then subjected to thermal crosslinking and curing in a 75 °C oven for 10 min. The membrane surface was rinsed with deionized water to obtain a TFC-OP-15 composite membrane, which was used for lithium-magnesium separation in electrodialysis tests.

[0048] Figure 3 a is the infrared spectrum of the TFC-OP-15 membrane in this embodiment. It can be seen that COC bonds have been produced, indicating that the monomer has been successfully polymerized onto the membrane layer. Figure 3 b is the XPS total spectrum of the TFC-OP-15 membrane in this embodiment. Figure 5 This is a diagram of the water contact angle and surface energy of the TFC-OP-15 membrane. The addition of OPDC increases the hydrophilicity of the membrane surface and the surface energy. Example 9

[0049] First, a mixed aqueous phase was prepared. At room temperature, 5.0 wt% MPD monomer, 3.0 wt% CSA, and 7.5 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared, with TMC and n-hexane having a mass-volume percentage of 0.45 w / v, and the o-phenylene dioxydiacetyl chloride prepared in Example 3 having a mass-volume percentage of 0.45 w / v. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 1.0 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution was removed from the membrane surface. The membrane was then subjected to thermal crosslinking and curing in a 75 °C oven for 10 min. The membrane surface was rinsed with deionized water to obtain a TFC-OP-45 composite membrane, which was used for lithium-magnesium separation in electrodialysis tests. Example 10

[0050] First, a mixed aqueous phase was prepared. At room temperature, 5.0 wt% PIP monomer, 3.0 wt% CSA, and 7.5 wt% TEA were added to deionized water, and the mixture was stirred continuously to obtain a mixed aqueous phase. Next, a mixed oil phase was prepared, with TMC and n-hexane having a mass-volume percentage of 0.45 w / v and the o-phenylene dioxydiacetyl chloride prepared in Example 3 having a mass-volume percentage of 0.10 w / v. The mixed aqueous phase solution was applied to the PSF base membrane, and after a period of time, the aqueous phase was removed using a 1.0 MPa air gun. The membrane surface was allowed to dry and become smooth at room temperature. The mixed oil phase solution was then applied to the membrane surface to induce interfacial polymerization, and excess oil phase solution was removed. The membrane was then subjected to thermal crosslinking and curing treatment in an 80 °C oven for 10 min, and the membrane surface was rinsed with deionized water to obtain the PIP-OP-10 composite membrane. Simultaneously, under the same proportions and temperature conditions, NMPIP and PEI were used to replace the PIP monomer as control groups. NMPIP-OP-10 composite membrane and PEI-OP-10 composite membrane were obtained. The three membranes were used for electrodialysis to test the separation of lithium and magnesium.

[0051] Figure 8 The Li in this embodiment refers to the PIP-OP-10 composite membrane, NMPIP-OP-10 composite membrane, and PEI-OP-10 composite membrane obtained after electrodialysis testing. + Mg 2+ Comparison of ion flux and separation factor. Example 11

[0052] This embodiment illustrates the optimal lithium-magnesium ion selectivity of the open-chain crown ether composite membrane TFC-OP-10 by electrodialysis.

[0053] The TFC-OP-10 membrane was used for electrodialysis testing.

[0054] Three solutions—feed solution, lithium enrichment solution, and electrode solution—were successively introduced into the electrodialysis apparatus. The feed solution was a mixed solution of 0.1 mol / L LiCl and 0.1 mol / L MgCl₂, the lithium enrichment solution was a pure aqueous solution, and the electrode solution was a 0.1 mol / L KCl solution. The effective membrane area was 12.56 cm² when the applied voltages to the electrodialysis apparatus were 0.5 V, 1.0 V, 1.5 V, 2.0 V, and 2.5 V. 2 All experiments were conducted at room temperature.

[0055] Over time, lithium will gradually accumulate in the lithium-enriched solution. After 24 hours of electrodialysis testing, the lithium-ion flux of the TFC-OP-10 membrane at voltages of 0.5 V, 1.0 V, 1.5 V, 2.0 V, and 2.5 V was found to be 7.9 mmol·m³. -2 ·h -1 16.46 mmol·m -2 ·h -1 20.8 mmol·m -2 ·h -1 25.6 mmol·m -2 ·h -1 28.75 mmol·m -2 ·h -1 The selectivity for lithium and magnesium were 15.3, 26.6, 17.3, 14.2, and 13.9, respectively. It can be concluded that the separation efficiency of lithium and magnesium was highest when an applied voltage of 1 V was used.

[0056] Figure 6 b is a schematic diagram of the electrodialysis component device used in this embodiment. Figure 7 b is the Li content of the TFC-OP-10 membrane obtained after electrodialysis tests at different voltages in this embodiment. + Mg 2+ Ion flux and separation factor diagram.

Claims

1. A method for preparing a high lithium-ion selective open-chain crown ether composite membrane, characterized in that, The specific operating steps are as follows: A. Synthesis of monomers: o-phenylene dioxoacetic acid was dissolved in thionyl chloride solution in a round-bottom flask. The round-bottom flask was wrapped with tin foil to create a light-proof condition. The mixed solution was then heated in an oil bath under a nitrogen atmosphere to form a uniform brown solution. The crude product was obtained by rotary evaporation and purified by sodium bicarbonate column chromatography. The solvent was removed by vacuum distillation to obtain o-phenylene dioxoacetyl chloride. B. Preparation of mixed aqueous phase: At room temperature, a certain mass fraction of amine monomer, camphor sulfonic acid and triethylamine are added to deionized water and stirred continuously to obtain a mixed aqueous phase; C. Preparation of mixed oil phase: At room temperature, a certain mass percentage of o-phenylene dioxydiacetyl chloride and n-hexane are added to a certain mass percentage of pyromellitic trimethylolpropionate chloride or terephthaloyl chloride, and the mixture is stirred continuously to obtain a mixed oil phase; D. Membrane preparation: The mixed aqueous solution prepared in step B is applied to the PSF base membrane. After a period of time, the aqueous phase is removed, and the membrane surface is allowed to dry and become smooth at room temperature. The mixed oil phase solution prepared in step C is applied to the membrane surface to induce interfacial polymerization. Excess oil phase solution is then removed from the membrane surface. The membrane is then subjected to thermal crosslinking and curing in an oven. The membrane surface is rinsed with deionized water to obtain the TFC composite membrane, which is then stored for later use.

2. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, In step A, the oil bath temperature for heating the mixed solution is 50-70 ℃, and the time is 2-3 h; in step A, the rotary evaporation temperature is 40-50 ℃, and the rotation speed is 30-100 r / min.

3. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, The amine monomer mentioned in step B is one of m-phenylenediamine, piperazine, N-methylpiperazine, and polyethyleneimine.

4. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, In step B, the amine monomer has a mass fraction of 1.0-5.0 wt%, camphor sulfonic acid has a mass fraction of 0.5-3.0 wt%, and triethylamine has a mass fraction of 0.5-7.5 wt%.

5. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, In step C, the mass-volume percentage of pyromellitic trimethylolpropionate chloride or terephthaloyl chloride to n-hexane is 0.05-0.45 w / v, and the mass-volume percentage of o-phenylene dioxydiacetyl chloride to n-hexane is 0.05-0.45 w / v.

6. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, In step D, the water phase is removed by air jetting; the air jetting uses an air gun with an air pressure of 0.5-1.0 MPa.

7. The method for preparing a high lithium-ion selective open-chain crown ether composite membrane according to claim 1, characterized in that, The thermal crosslinking curing treatment in step D is performed at a temperature of 60-80 ℃ for 5-15 min.

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