Preparation method for high-selectivity lithium super-ion conductor membrane

Abstract

The present invention relates to the technical field of membrane separation. Disclosed is a preparation method for a high-selectivity lithium super-ion conductor membrane. In the method, a lithium super-ion conductor material, i.e. Li7-xLa3Zr2-xTaxO12 (LLZTO), is used as an aggregate and polyvinyl alcohol is added as a sintering aid, LLZTO is firstly pressed into a green body by means of a tableting molding technique, and then the green body is calcined at a high temperature to obtain an LLZTO membrane. In order to further improve the compactness and separation performance of the LLZTO membrane, an organic crosslinking aid is studied and introduced to modify pores of the LLZTO membrane to obtain a dense lithium super-ion conductor membrane. The lithium super-ion conductor membrane exhibits excellent ion separation performance, which provides a reference concept for related fields such as efficient recovery and extraction of lithium resources.

Description

A method for preparing a highly selective lithium superion conductor film Technical Field

[0001] This invention relates to a method for preparing a highly selective lithium superion conductor membrane, lithium ion recovery, and a membrane and apparatus for selectively separating lithium ions from liquid solutions, particularly aqueous solutions such as brine. Background Technology

[0002] With the continuous growth of global energy demand and increasing focus on environmental sustainability, the search for efficient and clean energy solutions has become increasingly important. Lithium-ion batteries play a key role in energy storage and conversion technologies, and the global demand for lithium continues to grow.

[0003] Lithium salts are primarily extracted from mineral sediments and salt lakes. Current methods for extracting lithium and its compounds involve acid decomposition and chemical leaching of minerals or concentration using brine from solar ponds. However, these traditional methods are complex, time-consuming, or highly dependent on chemicals or local climate. Membrane separation technology offers several important advantages, including high selectivity, greater environmental sustainability, ease of operation, and strong scalability, making it an excellent choice for lithium ion extraction.

[0004] To effectively address the above problems, this invention utilizes a solid-state electrolyte membrane to replace traditional lithium extraction methods, which is more time-saving and cleaner. Solid-state electrolyte materials, also known as "superionic conductors," possess high ionic conductivity, effectively promoting the transport rate of lithium ions within the solid electrolyte. In contrast, other materials may suffer from concentration polarization and ion migration issues, affecting lithium ion transport efficiency. Furthermore, lithium superionic conductors exhibit good chemical stability, effectively resisting environmental influences such as corrosion and oxidation from seawater. Therefore, combining solid-state electrolytes with membrane separation technology to prepare highly selective lithium superionic conductor membranes is crucial.

[0005] In the preparation of lithium superion conductor membranes, the membrane is often not dense enough, leading to decreased separation performance and reduced lifespan. Therefore, this invention utilizes an organic crosslinking aid to modify the pores of the lithium superion conductor membrane to obtain a highly selective and dense lithium superion conductor membrane.

[0006] Currently, there is an urgent need in this field to develop a membrane with high lithium-ion selectivity for extracting lithium ions. Technical issues

[0007] The purpose of this invention is to overcome the difficulties in lithium extraction using existing technologies and to prepare a lithium superion conductor separation membrane with high selectivity. Technical solutions

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

[0009] A method for preparing a highly selective lithium superion conductor film, the specific operation steps of which are as follows:

[0010] A. Lithium nitrate, lanthanum nitrate hexahydrate, zirconium propoxide, tantalum ethoxide and deionized water are mixed in proportion to obtain a mixed solution. Then, citric acid and ethylene glycol are slowly added to the mixed solution while stirring continuously to obtain a precursor solution.

[0011] B. The precursor solution was first subjected to constant temperature shaking in a water bath to obtain a semi-transparent sol; then the sol was dried in an oven to obtain a gel; the gel was then calcined in a muffle furnace; finally, it was ball-milled to obtain a lithium superion conductor material Li with a particle size of 1-2 μm. 7-x La3Zr 2-x Ta x O 12 (LLZTO), where x = 0 - 2;

[0012] C. After mixing LLZTO with organic molding aids in a certain mass ratio, the mixture is ball-milled and then pressed into tablets to obtain LLZTO film preforms. The preforms are then placed in a muffle furnace and calcined at high temperature to obtain LLZTO films.

[0013] D. Place the fluorine-containing polymer into an organic solvent and stir continuously to obtain an organic crosslinking aid;

[0014] E. Modify the pores of the LLZTO membrane with an organic crosslinking aid. Coat the LLZTO membrane with the organic crosslinking aid and then heat it in an oven to crosslink it, thereby obtaining a highly selective lithium superion conductor membrane.

[0015] Furthermore, in the above-mentioned method for preparing a highly selective lithium superionic conductor film, in step A, the molar ratio between lithium nitrate, lanthanum nitrate hexahydrate, zirconium propoxide, and tantalum ethoxide is 7-x:3:2-x:x, wherein the mass of deionized water is twice the total mass of all materials containing metal ions, and the molar mass of citric acid and ethylene glycol is twice the total molar mass of all materials containing metal ions.

[0016] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, in step B, the temperature of the precursor solution during the water bath isothermal shaking process is 60-80 ℃, and the shaking time is 3-6 h; the temperature of the sol drying process is 80-120 ℃, and the drying time is 10-15 h; the calcination temperature of the gel during the calcination process is 800-950 ℃, the calcination time is 5-10 h, and the heating rate is 1-5 ℃ / min.

[0017] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the organic molding aid mentioned in step C is a polyvinyl alcohol (PVA) solution with a concentration of 8 wt%-12 wt% and an addition amount of 0%-10% of the mass of the lithium superion conductor material.

[0018] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the ball milling time in step C is 3-6 h, and the ball milling speed is 300-400 rpm.

[0019] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the pressure during the pressing process in step C is 30-65 MPa, and the pressing time is 30-180 s.

[0020] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the calcination process in step C involves first heating to 300-350 ℃ and holding for 2-5 h, then heating to 1100-1300 ℃ and holding for 10-20 h, with the heating rate controlled at 1-5 ℃ / min.

[0021] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the fluorinated polymer in step D is one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl fluoride (PVF), chlorotrifluoroethylene-ethylene copolymer (ECTFE), and polytetrafluoroethylene (PTFE), and the organic solvent is one or more of N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and acetone. The fluorinated polymer accounts for 1 wt%-5 wt% of the molar mass of the organic solvent.

[0022] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor film, the heating temperature in step E is 120-180 ℃ and the heating time is 10-20 h. Beneficial effects

[0023] This invention modifies the pores of LLZTO membranes using organic crosslinking agents. By controlling the concentration of the organic crosslinking agent, the solvent, and the solute, a highly selective lithium superion conductor membrane was successfully prepared. Furthermore, testing of the membrane showed that it achieves good separation performance, thus solving the current difficulty in lithium ion extraction. This provides a reference for more efficient lithium ion extraction in the future. Attached Figure Description

[0024] Figure 1 shows a) SEM image and b) XRD pattern of the LLZTO material prepared in Example 1.

[0025] Figure 2 is a SEM image of the lithium superion conductor films prepared in Examples 3, 5, 7 and 9.

[0026] Figure 3 is a schematic diagram of the water contact angle of the lithium superion conductor films prepared in Examples 3, 5, 7 and 9.

[0027] Figure 4 shows the FTIR characterization test results of Examples 3, 5, 7, and 9.

[0028] Figure 5 is an XPS image of the LLZTO / PVDF-3 membrane prepared in Example 7.

[0029] Figure 6 is a schematic diagram of the electrodialysis membrane module device described in Example 10.

[0030] Figure 7 shows the lithium-sodium separation performance of the lithium superion conductor membrane used in electrodialysis in Example 10. The best embodiment of the present invention Example

[0031] This embodiment illustrates the preparation of LLZTO materials via the sol-gel method.

[0032] Weigh the following materials according to the molar ratio of lithium nitrate: lanthanum nitrate hexahydrate: zirconium isopropoxide: tantalum ethoxide: 6.4:3:1.3:0.6. Weigh 1.9 g of lithium nitrate, 5.06 g of lanthanum nitrate hexahydrate, 1.7 mL of zirconium isopropoxide, and 0.94 mL of tantalum ethoxide, and dissolve them in 20 mL of water, stirring until dissolved. Then add 9.6 g of citric acid and 8.4 mL of ethylene glycol, and stir for 30 min to obtain a precursor solution. Incubate the precursor solution at 80 °C in a water bath with shaking for 3 h to obtain a translucent sol. Dry the sol in a 100 °C oven for 10 h to obtain a gel. Place the gel in a muffle furnace and pre-calcine at 350 °C for 3 h, then calcine at 950 °C for 5 h, with a heating rate of 2 °C / min, to obtain the lithium superion conductor material Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 The material is then ball-milled to a particle size of approximately 1.2 μm.

[0033] Figure 1a) is a SEM image of the LLZTO material prepared in this embodiment, with a particle diameter of approximately 1.2 μm. Figure 1b) is an X-ray diffraction (XRD) pattern of the LLZTO prepared in this example. Example

[0034] This embodiment illustrates the preparation of LLZTO materials via the sol-gel method.

[0035] Weigh the following components according to a molar ratio of lithium nitrate: lanthanum nitrate hexahydrate: zirconium isopropoxide: tantalum ethoxide of 6.4:3:1.3:0.6. Weigh 1.9 g of lithium nitrate, 5.06 g of lanthanum nitrate hexahydrate, 1.7 mL of zirconium isopropoxide, and 0.94 mL of tantalum ethoxide, and dissolve them in 20 mL of water, stirring until dissolved. Then add 9.6 g of citric acid and 8.4 mL of ethylene glycol, and stir for 30 min to obtain a precursor solution. Incubate the precursor solution at 60 °C in a water bath with shaking for 6 h to obtain a translucent sol. Dry the sol in an oven at 80 °C for 15 h to obtain a gel. Place the gel in a muffle furnace and pre-calcine at 350 °C for 3 h, then calcine at 800 °C for 10 h, with a heating rate of 1 °C / min, to obtain the lithium superion conductor material Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 The material is then ball-milled to a particle size of approximately 1.2 μm. Example

[0036] This example illustrates the preparation of LLZTO membranes via high-temperature calcination.

[0037] First, the LLZTO material and binder from Example 1 were mixed and ball-milled for 3 hours at a speed of 400 rpm. The binder was PVA with a concentration of 10 wt% and an addition amount of 1% of the mass of the lithium superion conductor material. The uniformly mixed powder was loaded into a tableting mold and pressed to 30 MPa for 60 seconds to obtain a green compact. Then, the green compact was placed in a muffle furnace and heated to 350 °C at a rate of 2 °C / min and held for 2 hours. Then, it was heated to 1300 °C at a rate of 1 °C / min and held for 10 hours to obtain the LLZTO film.

[0038] Figure 2a is a SEM image of the LLZTO membrane prepared in this embodiment, with the upper right corner showing a magnified view, revealing that the material is in a molten state and uniformly distributed. Figure 2e is a cross-sectional view of the LLZTO membrane prepared in this example. Figure 3a is a schematic diagram of the water contact angle of the LLZTO membrane prepared in this embodiment. Example

[0039] This example illustrates the preparation of LLZTO membranes via high-temperature calcination.

[0040] First, the LLZTO material and binder from Example 1 were mixed and ball-milled for 6 hours at 300 rpm. The binder was PVA with a concentration of 8 wt% and an addition amount of 10% of the mass of the lithium superion conductor material. The uniformly mixed powder was loaded into a tableting mold and pressed to 50 MPa for 30 seconds to obtain a green compact. Then, the green compact was placed in a muffle furnace and heated to 300 °C at a rate of 5 °C / min and held for 5 hours. Then, it was heated to 1100 °C at a rate of 1 °C / min and held for 20 hours to obtain the LLZTO film. Example

[0041] This embodiment illustrates the preparation of a defect-free lithium superion conductor membrane by crosslinking modification of LLZTO membrane.

[0042] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent, wherein the solute of the organic crosslinking agent was PVDF, the solvent was DMF, the concentration was 1 wt%, and the addition amount was 10% of the mass of the lithium superion conductor material. The coated LLZTO membrane was placed in an oven and kept at 170 °C for 10 h, finally obtaining a defect-free lithium superion conductor membrane. This membrane is called LLZTO / PVDF-1 membrane.

[0043] Figure 2b is a SEM image of the LLZTO / PVDF-1 membrane prepared in this embodiment. Figure 2f shows the cross-sectional morphology of the LLZTO / PVDF-1 membrane in this embodiment, with a membrane thickness of approximately 500 μm. Figure 3b is a schematic diagram of the water contact angle of the LLZTO / PVDF-1 membrane prepared in this embodiment. It can be observed that, compared to the LLZTO membrane, the LLZTO / PVDF-1 membrane is more hydrophobic and has a denser surface. Example

[0044] This embodiment illustrates the preparation of a defect-free lithium superion conductor membrane by crosslinking modification of LLZTO membrane.

[0045] First, the LLZTO membrane from Example 4 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF-HFP, the solvent was DMAC, the concentration was 1 wt%, and the addition amount was 5% of the mass of the lithium superion conductor material. The coated LLZTO membrane was placed in an oven and kept at 180 °C for 10 h to obtain a defect-free lithium superion conductor membrane. This membrane is called the LLZTO / PVDF-HFP membrane. Example

[0046] This embodiment illustrates the preparation of a defect-free lithium superion conductor membrane by crosslinking modification of LLZTO membrane.

[0047] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF, the solvent was DMF, the concentration was 3 wt%, and the addition amount was 10% of the mass of the lithium superion conductor material. The coated LLZTO membrane was then placed in an oven and kept at 170 °C for 10 h to obtain a defect-free lithium superion conductor membrane. This membrane was named LLZTO / PVDF-3 membrane.

[0048] Figure 2c is a SEM image of the LLZTO / PVDF-3 membrane prepared in this embodiment. Figure 2g shows the cross-sectional morphology of the LLZTO / PVDF-3 membrane in this embodiment, with a membrane thickness of approximately 500 μm. Figure 3c is a schematic diagram of the water contact angle of the LLZTO / PVDF-3 membrane used in this embodiment, indicating that the membrane is more hydrophobic and dense. Figure 5 is an XPS image of the LLZTO / PVDF-3 membrane used in this embodiment. The XPS image shows the presence of Li-F and La-F peaks, indicating that PVDF has successfully crosslinked with LLZTO, and the membrane preparation was successful. Example

[0049] This embodiment illustrates the preparation of a defect-free lithium superion conductor membrane by crosslinking modification of LLZTO membrane.

[0050] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF-TrFE, the solvent was NMP, the concentration was 3 wt%, and the addition amount was 8% of the mass of the lithium superion conductor material. The coated LLZTO membrane was placed in an oven and kept at 120 °C for 20 h to obtain a defect-free lithium superion conductor membrane. This membrane was named LLZTO / PVDF-4 membrane. Example

[0051] This embodiment illustrates the preparation of a defect-free lithium superion conductor membrane by crosslinking modification of LLZTO membrane.

[0052] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF, the solvent was DMF, the concentration was 5 wt%, and the addition amount was 10% of the mass of the lithium superion conductor material. The coated LLZTO membrane was then placed in an oven and kept at 175 ℃ for 10 h, finally obtaining a defect-free lithium superion conductor membrane. This membrane is called LLZTO / PVDF-5 membrane.

[0053] Figure 2d is a SEM image of the LLZTO / PVDF-5 membrane prepared in this embodiment, showing that the membrane is completely dense. Figure 2h is the cross-sectional morphology of the LLZTO / PVDF-5 membrane in this embodiment. Figure 3d is a schematic diagram of the water contact angle of the LLZTO / PVDF-5 membrane prepared in this embodiment.

[0054] Figure 4 shows the FTIR characterization test results of Examples 3, 5, 7, and 9. It can be seen that the films crosslinked with LLZTO and PVDF exhibit FTIR values ​​at 1050 and 1400 cm⁻¹. -1 The presence of a characteristic peak of F indicates that PVDF has successfully crosslinked with LLZTO, and an LLZTO / PVDF membrane has been successfully prepared. Example

[0055] This embodiment illustrates the performance of lithium superion conductor membranes for lithium-ion separation by testing them using electrodialysis.

[0056] Electrodialysis tests were conducted using LLZTO, LLZTO / PVDF-1, and LLZTO-PVDF-3 membranes.

[0057] Three solutions—lithium enrichment solution, feed 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 NaCl, the lithium enrichment solution was a pure aqueous solution, and the electrode solution was a 300 ppm LiCl solution. The voltage applied to the electrodialysis apparatus was 1 V, and the effective membrane area during testing was 5 × 10⁻⁶. -5 m 2 All experiments were conducted at room temperature.

[0058] As lithium gradually concentrates in the lithium-enriched solution over time, after 24 hours of electrodialysis testing, the lithium-ion fluxes of the LLZTO membrane, LLZTO / PVDF-1 membrane, and LLZTO / PVDF-3 membrane were found to be 51.3 mmol·m⁻¹. -2 •h -1 52 mmol•m -2 •h -1 36 mmol•m -2 •h -1 The lithium-sodium selectivities were 8.55, 32.5, and 58.54, respectively.

[0059] Figure 6 is a schematic diagram of the electrodialysis membrane assembly used in this embodiment. Figure 7 is a graph showing the lithium-sodium separation performance of the lithium superion conductor membrane obtained after electrodialysis testing in this embodiment.

Claims

1. A method for preparing a highly selective lithium superion conductor film, characterized in that: The specific steps are as follows: A. Lithium nitrate, lanthanum nitrate hexahydrate, zirconium propoxide, tantalum ethoxide and deionized water are mixed in a certain proportion to obtain a mixed solution. Then, citric acid and ethylene glycol are slowly added to the mixed solution while stirring continuously to obtain a precursor solution. B. The precursor solution is first subjected to constant temperature shaking in a water bath to obtain a semi-transparent sol; then the sol is dried in an oven to obtain a gel; the gel is then calcined in a muffle furnace; finally, it is ball-milled to obtain Li superion conductor material with a particle size of 1-2 μm. 7-x La3Zr 2-x Ta x O 12 (LLZTO), where x = 0 - 2; C. After mixing LLZTO with organic molding aids in a certain mass ratio, the mixture is ball-milled and then pressed into tablets to obtain LLZTO film preforms. The preforms are then placed in a muffle furnace and calcined at high temperature to obtain LLZTO films. D. Place the fluorine-containing polymer into an organic solvent and stir continuously to obtain an organic crosslinking aid; E. Modify the pores of the LLZTO membrane with an organic crosslinking aid. Coat the LLZTO membrane with the organic crosslinking aid and then heat it in an oven to crosslink it, thus obtaining a highly selective lithium superion conductor membrane.

2. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: In step A, the molar ratio between lithium nitrate, lanthanum nitrate hexahydrate, zirconium propoxide, and tantalum ethoxide is 7-x:3:2-x:x, wherein the mass of deionized water is twice the total mass of all materials containing metal ions, and the molar mass of citric acid and ethylene glycol is twice the total molar mass of all materials containing metal ions.

3. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: In step B, the temperature of the precursor solution during the water bath isothermal shaking process is 60-80 ℃, and the shaking time is 3-6 h; the temperature of the sol during the drying process is 80-120 ℃, and the drying time is 10-15 h; the calcination temperature of the gel during the calcination process is 800-950 ℃, the calcination time is 5-10 h, and the heating rate is 1-5 ℃ / min.

4. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: The organic molding aid mentioned in step C is a polyvinyl alcohol (PVA) solution with a concentration of 8 wt%-12 wt% and an addition amount of 0%-10% of the mass of the lithium superion conductor material.

5. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: In step C, the ball milling time is 3-6 hours and the ball milling speed is 300-400 rpm.

6. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: In step C, the pressure during the tableting process is 30-65 MPa, and the compression time is 30-180 s.

7. The method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: The calcination process in step C involves first heating to 300-350 ℃ and holding for 2-5 h, then heating to 1100-1300 ℃ and holding for 10-20 h, with the heating rate controlled at 1-5 ℃ / min.

8. A method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: The fluorinated polymer mentioned in step D is one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl fluoride (PVF), chlorotrifluoroethylene-ethylene copolymer (ECTFE), and polytetrafluoroethylene (PTFE). The organic solvent is one or more of N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and acetone. The fluorinated polymer accounts for 1 wt%-5 wt% of the molar mass of the organic solvent.

9. A method for preparing a highly selective lithium superion conductor film according to claim 1, characterized in that: In step E, the heating temperature is 120-180 ℃ and the heating time is 10-20 h.

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