A lithium-selective composite film, its preparation method and application

Abstract

This invention provides a lithium-selective composite membrane, its preparation method, and its application. The preparation method comprises: mixing an inorganic solid electrolyte, a polymer, a halogenated methyl polymer, and a crosslinking agent, followed by a reaction to obtain a casting solution; and coating the casting solution onto a supporting mesh to obtain the lithium-selective composite membrane. The lithium-selective composite membrane provided by this invention exhibits excellent flexibility, stability, mechanical properties, and high Li- content. + Selectivity, Li + and Na + With a separation coefficient higher than 13057, it can be applied to the selective extraction of lithium from low-grade brine. It is prepared by the casting method, which is simple, highly operable, and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to a lithium-selective composite membrane, its preparation method, and its application. Background Technology

[0002] Lithium, the lightest metal in nature, is widely used in batteries, ceramics, nuclear industry, aerospace, and other fields due to its high specific heat, electrical conductivity, and chemical activity, earning it the title of "the energy metal of the 21st century." In recent years, the rapid development of new energy vehicles and electronic products has led to a surge in global demand for lithium resources, making their development and utilization increasingly important. Currently, salt lake brines, with their large lithium reserves and low pollution during development, are gradually becoming the main source of lithium resources. However, efficient extraction of lithium from low-grade brine still faces challenges such as significant interference from coexisting ions and low extraction efficiency. Therefore, developing efficient lithium extraction / recovery technologies is crucial for ensuring the rapid and stable development of the future new energy industry.

[0003] The main methods for lithium resource development include ion exchange and adsorption, precipitation, solvent extraction, electrochemical methods, and membrane separation. Ion exchange and adsorption are simple to operate, but the elution process suffers from drawbacks such as significant solvent loss, high cost, and small adsorption capacity. Precipitation is a mature process, but it is not suitable for systems with a high magnesium-to-lithium ratio. Solvent extraction is simple to operate, but it suffers from problems such as large reagent consumption and severe environmental pollution. Electrochemical methods offer high lithium extraction efficiency, but are not yet industrialized. Membrane separation is efficient, energy-saving, and allows for continuous production, making it one of the most promising technologies for lithium extraction.

[0004] Currently, selective electrodialysis (SED) has seen initial applications in separating lithium and magnesium in high-magnesium-to-lithium ratio brines. However, the organic polymer monovalent selective ion exchange membranes used in SED can only achieve separation between monovalent and multivalent ions, and cannot separate Li... + with Na + or K + The sieving process between these parameters makes it unsuitable for applications with high Na content. + K + Lithium can be directly extracted from the original brine. Membranes used for lithium resource extraction can be divided into three types: organic membranes, inorganic electrolyte membranes, and composite membranes. Among organic membranes, monovalent selective cation exchange membranes are special membranes that achieve the separation of monovalent and multivalent ions based on pore size sieving, electrostatic repulsion, and hydrophilicity / hydrophobicity. Due to their good separation performance between monovalent and multivalent ions, they are gradually being applied to the separation of magnesium and lithium in high magnesium-to-lithium ratio brines. Organic polymer membranes have advantages such as low cost, easy processing, and easy scale-up, but they also have the potential for lithium degradation. +Poor selectivity and membrane blockage have limited its application in the lithium extraction industry. Inorganic electrolyte membranes, due to their high ionic conductivity and high chemical stability, are increasingly being used in lithium resource extraction. + While selective, it is difficult to fabricate over large areas, has poor mechanical properties, and is limited in large-scale applications. An ideal membrane material should possess high Li- content. + It offers selectivity, flexibility, and mechanical properties, and boasts advantages such as scalability and ease of processing.

[0005] Saif et al. prepared a highly selective Li-based compound by dispersing acidified LMO (HMO) and its sulfonated compound HMO-s into a sulfonated polyether ether ketone (SPEEK) matrix. + Migrating hybrid membranes (Saif HM, Huertas RM, Pawlowski S, et al. Development of highly selective composite polymeric membranes for Li + / Mg 2+ Separation [J]. Journal of Membrane Science, 2021, 620: 118891.). Sulfonate polyelectrolytes accelerate the migration of cations along the HMO-s surface, and the HMO-s exhibit better interface compatibility with the SPEEK matrix, resulting in good thermal stability and mechanical properties of the membrane. Li + / Mg 2+ The separation performance is 3.1, Li + / K + The separation performance is only 1.3, which is less than that of Li. + and K + The separation effect is poor.

[0006] Yang et al. proposed a solar electrolysis technology based on lithium extraction from seawater, using Li... 1+x Al y Ge 2-y (PO4)3 (LAGP) is a selective membrane. Under electro-driven action, coexisting ions in seawater pass through the LAGP selective membrane and are transferred to the cathode side (Yang S, Zhang F, Ding H, et al. Lithium Metal Extraction from Seawater[J]. Joule, 2018, 2(9): 1648-1651.). Because LAGP is selective for Li... + It has good selectivity, only Li +The lithium yield was 5.7 mg·dm³ after being transferred to the cathode side and running for 1 hour. -2 ·h -1 This type of membrane is suitable for Li + It has conductivity and high selectivity, but it is a brittle material with poor mechanical properties, making it difficult to prepare and apply on a large scale.

[0007] To address the shortcomings of existing lithium extraction membrane materials, a method for preparing a lithium selective composite membrane (LSCM) was developed. This method results in a LSCM with excellent flexibility, stability, mechanical properties, and high Li- content. + Selectivity, which can be used for lithium extraction from low-grade brine, is a key issue. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-selective composite film, its preparation method, and its applications. Through the design of raw materials and processes, the prepared lithium-selective composite film possesses excellent flexibility, stability, mechanical properties, and high Li- content. + The selective method can be applied to the selective extraction of lithium from low-grade brine, and the preparation method is simple, highly operable, and suitable for large-scale production.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a lithium-selective composite membrane, the method comprising: mixing an inorganic solid electrolyte, a first polymer, a second polymer and a crosslinking agent and reacting them to obtain a casting solution, and coating the casting solution onto a support mesh to obtain the lithium-selective composite membrane, wherein the second polymer is a halogenated methyl polymer.

[0011] Inorganic solid electrolytes, due to their unique "confined" pores, provide Li + The transmission channel, thereby enabling the transmission of Li + Selective extraction; the polymer chains containing quaternary ammonium groups generated after the reaction of the second polymer and the crosslinking agent form a semi-interpenetrating network with the highly stable first polymer. The polymer chains containing quaternary ammonium groups can limit the migration of impurity cations, and the first polymer can enhance the flexibility and mechanical properties of the lithium selective composite film.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] As a preferred technical solution, the inorganic solid electrolyte includes any one or a combination of at least two of the following: perovskite solid electrolyte, NASICON solid electrolyte, or garnet solid electrolyte.

[0014] Preferably, the perovskite solid electrolyte comprises Li 3x La 2 / 3-x TiO3; wherein, 0.1≤x≤0.2, for example, can be 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.2, and specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0015] The perovskite-type solid electrolyte of the present invention can be prepared with reference to CN202210379025.1.

[0016] Preferably, the NASICON-type solid electrolyte comprises Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1+y Al y Ge 2-y (PO4)3 or Li 1.3+b Al 0.3 Ti 1.7 Si b P 3-b O 12 Any one or at least two of the following; where y≤0.7; b≤0.4; for example, y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7, and b can be 0, 0.1, 0.2, 0.3 or 0.4, etc.

[0017] The NASICON-type solid electrolyte described in this invention can be prepared with reference to CN201811537870.7.

[0018] Preferably, the garnet-type solid electrolyte comprises Li7La3Zr2O 12 and / or Li 6.4 La3Zr 1.6 Ta 0.6 O 12 .

[0019] The garnet-type solid electrolyte of the present invention can be prepared with reference to CN201780050508.4.

[0020] Preferably, the inorganic solid electrolyte is a lithium-containing inorganic solid electrolyte.

[0021] Preferably, the first polymer comprises any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0022] Preferably, the weight-average molecular weight of the first polymer is 100,000-1,000,000, for example, it can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0023] The first polymers of this invention can all be obtained by existing technologies. For example, the polyvinylidene fluoride can be selected from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight-average molecular weight of 400,000; the polytetrafluoroethylene can be selected from Jiangsu Aikon Biomedical R&D Co., Ltd.; and the polyvinylidene fluoride-hexafluoropropylene copolymer can be selected from Jiangsu Aikon Biomedical R&D Co., Ltd., with a weight-average molecular weight of 400,000.

[0024] Preferably, the crosslinking agent includes a tertiary amine crosslinking agent.

[0025] Preferably, the tertiary amine crosslinking agent includes tetramethylethylenediamine and / or triethylenediamine.

[0026] The halogenated methyl polymer and tertiary amine crosslinking agent undergo a quaternization reaction, resulting in a quaternized polymer chain containing quaternary ammonium groups. These groups provide positively charged groups, inhibiting the permeation of impurity cations and effectively improving the lithium selectivity of the composite film for Li. + The selectivity.

[0027] Preferably, the crosslinking agent is dissolved in a solvent before use.

[0028] Preferably, the solvent includes any one of dimethyl sulfoxide, dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone.

[0029] Preferably, in the solution composed of the crosslinking agent and the solvent, the concentration of the crosslinking agent is 20-100 g / L, for example, it can be 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L or 100 g / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0030] Preferably, the halogenated methyl polymer comprises any one or a combination of at least two of polyvinyl chloride, polyepoxychloropropane, or polyvinyl chloride.

[0031] Preferably, the weight-average molecular weight of the halogenated methyl polymer is 100,000-1,000,000, for example, it can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0032] The halogenated methyl polymer of the present invention can be obtained by existing technology. For example, the polyvinylbenzyl chloride can be selected from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight average molecular weight of 1,000,000; the polyepoxychloropropane can be selected from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight average molecular weight of 700,000; and the polyvinyl chloride can be selected from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight average molecular weight of 220,000.

[0033] Preferably, the supporting mesh fabric includes any one of nylon mesh fabric, polyester mesh fabric, or non-woven fabric.

[0034] Preferably, the aperture of the supporting mesh is 30-200 μm, for example, it can be 30 μm, 50 μm, 60 μm, 80 μm, 90 μm, 100 μm, 120 μm, 130 μm, 150 μm, 160 μm, 180 μm or 200 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0035] Preferably, the thickness of the supporting mesh is 40-150 μm, for example, it can be 40 μm, 50 μm, 60 μm, 80 μm, 90 μm, 100 μm, 120 μm, 130 μm or 150 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0036] Preferably, the thickness of the lithium selective composite film is 80-200 μm, for example, it can be 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or 200 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0037] Preferably, the mixed materials also include an organic solvent.

[0038] Preferably, the organic solvent includes any one of dimethyl sulfoxide, dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone.

[0039] Preferably, based on the mass of the first polymer being 1 g, the volume of the organic solvent is 5-15 mL, for example, it can be 5 mL, 6 mL, 7 mL, 8 mL, 9 mL, 10 mL, 11 mL, 12 mL, 13 mL, 14 mL or 15 mL, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0040] Preferably, based on the total mass of the inorganic solid electrolyte, the first polymer, the second polymer, and the crosslinking agent as 100%, the mass fraction of the inorganic solid electrolyte is 70-95%, for example, it can be 70%, 72%, 74%, 76%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, or 95%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0041] Preferably, based on the total mass of the inorganic solid electrolyte, the first polymer, the second polymer, and the crosslinking agent as 100%, the sum of the mass fractions of the second polymer and the crosslinking agent is 2-10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0042] Preferably, the mass ratio of the halogenated methyl polymer to the crosslinking agent is (0.8-3):1, for example, it can be 0.8:1, 1.0:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3:1, and the specific ratios between the above ratios are not exhaustively listed in this invention due to space limitations and for the sake of brevity.

[0043] Preferably, the reaction temperature is 50-90 ℃, for example, it can be 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃ or 90 ℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0044] Preferably, the reaction time is 3-60 min, for example, it can be 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0045] Preferably, the coating process further includes a drying step.

[0046] Preferably, the drying time is 12-36 h, for example, it can be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 32 h, 32 h, 34 h or 36 h, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0047] Preferably, the drying temperature is 60-90 ℃, for example, it can be 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃ or 90 ℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0048] Preferably, the preparation method specifically includes: mixing a lithium-containing inorganic solid electrolyte, a first polymer, a second polymer, a tertiary amine crosslinking agent, and an organic solvent, and then reacting them to obtain a casting solution; coating the casting solution onto a support mesh; and then drying it to obtain the lithium-selective composite membrane.

[0049] The aperture of the supporting mesh is 30-200 μm.

[0050] The thickness of the supporting mesh is 40-150 μm.

[0051] The thickness of the lithium-selective composite film is 80-200 μm.

[0052] Based on the total mass of the lithium-containing inorganic solid electrolyte, the first polymer, the second polymer, and the tertiary amine crosslinking agent as 100%, the mass fraction of the lithium-containing inorganic solid electrolyte is 70-95%; the sum of the mass fractions of the second polymer and the tertiary amine crosslinking agent is 2-10%.

[0053] The mass ratio of the halogenated methyl polymer to the tertiary amine crosslinking agent is (0.8-3):1.

[0054] The tertiary amine crosslinking agent is used after being dissolved in a solvent.

[0055] In the solution composed of the tertiary amine crosslinking agent and the solvent, the concentration of the tertiary amine crosslinking agent is 20-100 g / L.

[0056] With the mass of the first polymer being 1 g, the volume of the organic solvent is 5-15 mL.

[0057] The reaction temperature is 50-90 ℃.

[0058] The reaction time is 3-60 min.

[0059] The drying time is 12-36 hours.

[0060] The drying temperature is 60-90 ℃.

[0061] In a second aspect, the present invention provides a lithium-selective composite membrane, which is prepared by the preparation method described in the first aspect.

[0062] Thirdly, the present invention provides an application of the lithium-selective composite membrane as described in the second aspect, wherein the lithium-selective composite membrane is used for the selective extraction of lithium from salt lake brine.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] The lithium-selective composite film provided by this invention possesses excellent flexibility, stability, mechanical properties, and high Li content. + Selectivity, Li + and Na + With a separation coefficient higher than 13057, it can be applied to the selective extraction of lithium from low-grade brine. It is prepared by the casting method, which is simple, highly operable, and suitable for large-scale production. Attached Figure Description

[0065] Figure 1 This is a flowchart of the preparation process of lithium selective composite membrane (LSCM) provided by the present invention;

[0066] Figure 2 This is a diagram of an SED device;

[0067] 1 is the anode chamber, 2 is the raw material chamber, 3 is the recovery chamber, 4 is the cathode chamber, 5 is the anode electrode, 6 is the anion exchange membrane, 7 is the lithium selective composite membrane, 8 is the cathode electrode, and 9 is the DC power supply.

[0068] Figure 3 The selective Li extraction of LSCM-2 provided in Example 2 + Mechanism diagram;

[0069] Figure 4It is Li for LSCM-2, LATP / PVDF, PVDF / PD and CIMS + Na + A comparison chart of flux and separation coefficient;

[0070] Figure 5 It is an LSCM-1 image;

[0071] Figure 6 These are the XRD patterns of LATP and LSCM-1;

[0072] Figure 7 This is a SEM image of the LSCM-1 surface;

[0073] Figure 8 This is a SEM image of the LSCM-1 cross section. Detailed Implementation

[0074] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0075] The sources of some components in the following examples and comparative examples are as follows:

[0076] (1) Polyepoxychloropropane (PECH): purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight-average molecular weight of 700,000;

[0077] (2) Polyvinylidene fluoride (PVDF): purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a weight-average molecular weight of 400,000;

[0078] (3) CIMS commercial film: purchased from ASTOM Corporation, Japan;

[0079] (4) Li 1.3 Al 0.3 Ti 1.7 (PO4)3: Prepared according to CN201811537870.7;

[0080] (5) Li 0.33 La 0.56 TiO3: Prepared according to CN202210379025.1.

[0081] Example 1

[0082] A lithium-selective composite film and its preparation method are disclosed. The preparation method is illustrated in the flowchart below. Figure 1As shown, the specific steps include: dissolving 0.225 g PECH and 0.93 g PVDF in 8 mL of dimethyl sulfoxide (DMSO), dissolving at 80 °C, and then adding 11.61 g Li. 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) was ultrasonically stirred for 1 h, and then 0.135 g of triethylenediamine (DABCO) was dissolved in 2 mL of DMSO and added to the above solution to react and obtain a casting solution. The reaction temperature was 80 ℃ and the reaction time was 30 min. A nylon mesh (pore size of 150 μm and thickness of 98 μm) was placed on a glass plate and coated with a coating film. The plate was placed in an oven and then vacuum dried at 60 ℃ for 24 h to obtain the lithium selective composite film with a thickness of 120 μm. The obtained lithium selective composite film was named LSCM-1.

[0083] Example 2

[0084] A lithium-selective composite membrane and its preparation method are disclosed. The preparation method includes: dissolving 0.15 g PECH and 0.93 g PVDF in 8 mL DMSO at 80 °C, adding 10.53 g LATP, and ultrasonically stirring for 1 h; then dissolving 0.09 g DABCO in 2 mL DMSO and adding the above solution to react and obtain a casting solution. The reaction temperature is 80 °C and the reaction time is 30 min. A nylon mesh (pore size 150 μm, thickness 98 μm) is placed on a glass plate and coated with a coating film. The plate is placed in an oven and then vacuum dried at 60 °C for 24 h to obtain the lithium-selective composite membrane (thickness 160 μm). The obtained lithium-selective composite membrane is named LSCM-2.

[0085] Example 3

[0086] A lithium-selective composite membrane and its preparation method are disclosed, differing from Example 1 in that 11.61 g LATP is used instead of 5.16 g Li. 0.33 La 0.56 TiO3 (LLTO) was used, and other raw materials, process steps and parameters were the same as in Example 1 to obtain the lithium selective composite film with a thickness of 120 μm. The obtained lithium selective composite film was named LSCM-3.

[0087] Comparative Example 1

[0088] A lithium-selective composite membrane and its preparation method are disclosed. The difference between this method and Example 1 is that PECH and DABCO are not added. All other raw materials, process steps and parameters are the same as in Example 1. The resulting lithium-selective composite membrane is named LATP / PVDF.

[0089] Comparative Example 2

[0090] A lithium-selective composite membrane and its preparation method are disclosed. The difference between this method and Example 1 is that LATP is not added. All other raw materials, process steps and parameters are the same as in Example 1. The resulting lithium-selective composite membrane is named PVDF / PD.

[0091] Performance testing:

[0092] (1) The SED device is used. The diagram of the SED device is shown below. Figure 2 As shown, 1 is the anode chamber, 2 is the raw material chamber, 3 is the recovery chamber, 4 is the cathode chamber, 5 is the anode electrode, 6 is the anion exchange membrane, 7 is the lithium-selective composite membrane, 8 is the cathode electrode, and 9 is the DC power supply. 2.5 wt% K₂SO₄ is used as the electrode solution, 0.05 mol / L Li / Na mixture is used as the raw material solution, and 0.05 mol / L KCl is used as the recovery solution. Under the drive of an electric field, ions migrate directionally from the raw material solution to the recovery solution via the lithium-selective composite membrane, achieving the effect of lithium purification and concentration. The lithium-selective composite membranes provided in Examples 1-3 and Comparative Examples 1-2, and the commercial CIMS membrane were used as lithium-selective composite membranes in the SED device. A voltage was applied through the DC power supply, and the experiment was conducted under a constant voltage of 2 V. The experiment ended after 2 hours.

[0093] (2) The ion content in the recovery liquid of the SED device was detected by atomic absorption spectrophotometer (TAS-990F), and the Li content was calculated. + flux and Na + Flux, the formula for calculating flux is J = ( ), where C t C0 and C0 represent the ion concentrations in the recovered solution at time t and the initial time, respectively, in mol / L; V is the volume of the recovered solution, in L; A is the area of ​​the lithium-selective composite membrane, in cm². 2 t is the reaction time, in seconds; due to the presence of Na in the recovered solution... + The concentrations of all samples were below the detection limit of 0.0025 mg / L. The Na concentrations of LSCM-1 and LSCM-2 were calculated. + At flux, according to Na + The concentration of Na was calculated to be 0.0025 mg / L. + Maximum flux. Based on the flux, Li... + and Na + The separation coefficient, the formula for calculating the separation coefficient is α = ( ),in and Na, the initial feed solution + With Li + The concentration, mol / L, and the test results are shown in Table 1 and Figure 4Lithium sulfide (LSCM-2), LATP / PVDF, PVDF / PD and CIMS + Na + The comparison chart of flux and separation coefficient is shown below.

[0094] Table 1 shows that the polymers containing quaternary ammonium groups generated by the reaction of halogenated methyl polymers with tertiary amine crosslinking agents exhibit cation repulsion, and LATP or LLTO exhibit resistance to Li... + The high selectivity of LSCM-1, LSCM-2, and LSCM-3 enables the realization of Li in Li / Na mixed solutions. + with Na + Highly efficient separation; a comparison of LSCM-1 and LSCM-2 shows that both exhibit excellent Li... + / Na + Separation performance, Li + The flux of Li increases with decreasing content of the organic compound PECH-DABCO. This is because the reduced content of quaternary ammonium groups weakens the repulsion of cations, leading to a decrease in the flux of Li. + As flux increases, the separation coefficient also shows an upward trend. A performance comparison between LSCM-1 and LSCM-3 shows that the Li... + The flux and separation performance of LATP are superior to LSCM-3 due to its unique oxygen polyhedral structure, arranged in a "lantern" pattern, which provides a three-dimensional migration channel network suitable for small cations. LLTO, on the other hand, exhibits better flux and separation performance than LSCM-3. + and Na + The separation coefficient was 40.27, which is significantly higher than that of commercial CIMS membranes. (The text abruptly ends here.) Figure 4 It can be seen that the Li in the CIMS film + High flux, but for Li + with Na + The separation coefficient is only 0.59; Li₂ of PVDF / PD + and Na + The fluxes were all below 0.8 × 10⁻⁶. -10 mol·cm -2 ·s -1 This indicates that quaternized organic membranes significantly impede cation permeability; LATP / PVDF significantly impedes the permeability of Li + with Na + The separation coefficient was 11.40, compared to LATP / PVDF, which showed a significant improvement in the separation efficiency of Li by introducing the quaternized polymer LSCM-2. + with Na + The separation coefficient is higher than 13057; at the same time, compared with PVDF / PD, the Li in LSCM-2 after the introduction of solid electrolyte LATP is higher. + Flux increased to 32.01 × 10⁻⁶ -10mol·cm -2 ·s -1 Therefore, by effectively utilizing the lithium-ion transport characteristics of solid electrolytes and the effective blocking of cations by quaternized polymers, high-throughput and high-selectivity lithium-selective composite membranes can be prepared.

[0095] Table 1

[0096]

[0097] (3) X-ray diffraction test: The LSCM-1 was tested using an X-ray diffractometer (Bruker D8 FOCUS, Germany). The test results are as follows: Figure 6 The XRD patterns of LATP and LSCM-1 show that the synthesized LATP matches its standard pattern well, and the crystal structure of LSCM-1 remains unchanged after being reacted to form a film.

[0098] (4) LSCM-1 was tested using a scanning electron microscope (Quanta 450 FEG, USA). The test results are as follows: Figure 7 SEM images of the LSCM-1 surface and Figure 8 The SEM image of the LSCM-1 section is shown below. Figure 7 and Figure 8 It can be seen that the inorganic solid electrolyte is uniformly distributed in the membrane phase and is not excessively buried by the organic polymer.

[0099] Figure 3 The selective Li extraction of LSCM-2 provided in Example 2 + Mechanism diagram, by Figure 3 It can be seen that the quaternary ammonium groups in the lithium-selective composite membrane have a repulsive force on cations, preventing impurity cations from passing through the membrane. The "backbone" of LATP is composed of [MO6] octahedra (M represents the 12c position, occupied by Al and Ti) and [PO4] tetrahedra. Al 3+ The doping increases the overall negative charge of the "backbone", which makes the additional Li... + It enters the structure and occupies additional gap positions within the frame, achieving Li-ray diffusion primarily through gap diffusion under the influence of an electric field. + Selective transport of Li, the quaternary ammonium group and LATP work together to achieve selective transport of Li + High selectivity. Figure 5 The image shows an LSCM-1 image. As can be seen from the image, the lithium-selective composite membrane provided by this invention has flexibility.

[0100] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for preparing a lithium-selective composite film, characterized in that, The preparation method includes: mixing an inorganic solid electrolyte, a first polymer, a second polymer and a crosslinking agent and reacting them to obtain a casting solution; coating the casting solution onto a support mesh to obtain the lithium-selective composite film. The second polymer is a halogenated methyl polymer; The inorganic solid electrolyte includes any one or a combination of at least two of the following: perovskite solid electrolyte, NASICON solid electrolyte, or garnet solid electrolyte. Furthermore, the inorganic solid electrolyte is a lithium-containing inorganic solid electrolyte; The crosslinking agent includes tertiary amine crosslinking agents.

2. The preparation method according to claim 1, characterized in that, The perovskite-type solid electrolyte includes Li 3x La 2 / 3-x TiO3; Where 0.1≤x≤0.

2.

3. The preparation method according to claim 1, characterized in that, The NASICON-type solid electrolyte includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1+y Al y Ge 2-y (PO4)3 or Li 1.3+b Al 0.3 Ti 1.7 Si b P 3-b O 12 Any one or at least two of them; Where y≤0.7; b≤0.

4.

4. The preparation method according to claim 1, characterized in that, The garnet-type solid electrolyte includes Li7La3Zr2O 12 and / or Li 6.4 La3Zr 1.6 Ta 0.6 O 12 .

5. The preparation method according to claim 1, characterized in that, The first polymer includes any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, or polyvinylidene fluoride-hexafluoropropylene copolymer.

6. The preparation method according to claim 1, characterized in that, The weight-average molecular weight of the first polymer is 100,000-1,000,000.

7. The preparation method according to claim 1, characterized in that, The tertiary amine crosslinking agents include tetramethylethylenediamine and / or triethylenediamine.

8. The preparation method according to claim 1, characterized in that, The crosslinking agent is used after being dissolved in a solvent.

9. The preparation method according to claim 8, characterized in that, The solvent includes any one of dimethyl sulfoxide, dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone.

10. The preparation method according to claim 8, characterized in that, In the solution composed of the crosslinking agent and the solvent, the concentration of the crosslinking agent is 20-100 g / L.

11. The preparation method according to claim 1, characterized in that, The halogenated methyl polymer includes any one or a combination of at least two of polyvinyl chloride, polyepoxychloropropane, or polyvinyl chloride.

12. The preparation method according to claim 1, characterized in that, The weight-average molecular weight of the halogenated methyl polymer is 100,000-1,000,000.

13. The preparation method according to claim 1, characterized in that, The supporting mesh fabric includes either nylon mesh fabric or polyester mesh fabric.

14. The preparation method according to claim 1, characterized in that, The aperture of the supporting mesh is 30-200 μm.

15. The preparation method according to claim 1, characterized in that, The thickness of the supporting mesh is 40-150 μm.

16. The preparation method according to claim 1, characterized in that, The thickness of the lithium-selective composite film is 80-200 μm.

17. The preparation method according to claim 1, characterized in that, The mixture also includes organic solvents.

18. The preparation method according to claim 17, characterized in that, The organic solvent includes any one of dimethyl sulfoxide, dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone.

19. The preparation method according to claim 17, characterized in that, With the mass of the first polymer being 1 g, the volume of the organic solvent is 5-15 mL.

20. The preparation method according to claim 1, characterized in that, With the total mass of the inorganic solid electrolyte, the first polymer, the second polymer, and the crosslinking agent being 100%, the mass fraction of the inorganic solid electrolyte is 70-95%.

21. The preparation method according to claim 1, characterized in that, With the total mass of the inorganic solid electrolyte, the first polymer, the second polymer, and the crosslinking agent being 100%, the sum of the mass fractions of the second polymer and the crosslinking agent is 2-10%.

22. The preparation method according to claim 1, characterized in that, The mass ratio of the halogenated methyl polymer to the crosslinking agent is (0.8-3):

1.

23. The preparation method according to claim 1, characterized in that, The reaction temperature is 50-90 ℃.

24. The preparation method according to claim 1, characterized in that, The reaction time is 3-60 min.

25. The preparation method according to claim 1, characterized in that, The coating process also includes a drying step.

26. The preparation method according to claim 25, characterized in that, The drying time is 12-36 hours.

27. The preparation method according to claim 25, characterized in that, The drying temperature is 60-90 ℃.

28. The preparation method according to claim 1, characterized in that, The preparation method specifically includes: mixing a lithium-containing inorganic solid electrolyte, a first polymer, a second polymer, a tertiary amine crosslinking agent, and an organic solvent, and then reacting them to obtain a casting solution; coating the casting solution onto a support mesh, and then drying it to obtain the lithium-selective composite membrane. The aperture of the supporting mesh is 30-200 μm; The thickness of the supporting mesh is 40-150 μm; The thickness of the lithium-selective composite film is 80-200 μm; Based on the total mass of the lithium-containing inorganic solid electrolyte, the first polymer, the second polymer, and the tertiary amine crosslinking agent as 100%, the mass fraction of the lithium-containing inorganic solid electrolyte is 70-95%; the sum of the mass fractions of the second polymer and the tertiary amine crosslinking agent is 2-10%. The mass ratio of the second polymer to the tertiary amine crosslinking agent is (0.8-3):1; The tertiary amine crosslinking agent is used after being dissolved in a solvent; In the solution composed of the tertiary amine crosslinking agent and the solvent, the concentration of the tertiary amine crosslinking agent is 20-100 g / L; With the mass of the first polymer being 1 g, the volume of the organic solvent is 5-15 mL; The reaction temperature is 50-90 ℃; The reaction time is 3-60 min; The drying time is 12-36 h; The drying temperature is 60-90 ℃.

29. A lithium-selective composite membrane, characterized in that, The lithium-selective composite film is prepared by the preparation method described in any one of claims 1 to 28.

30. An application of the lithium-selective composite membrane as described in claim 29, characterized in that, The lithium-selective composite membrane is used for the selective extraction of lithium from salt lake brine.

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