A method for preparing a highly selective lithium superion conductor membrane

Abstract

The present invention relates to the field of membrane separation technology, and discloses a method for preparing a highly selective lithium superion conductor membrane. 7‑x La3Zr 2‑x Ta x O 12 Using lithium nitride (LLZTO) as an aggregate and polyvinyl alcohol as a sintering aid, the LLZTO was first pressed into a green compact via a sheeting technique, and then calcined at high temperature to produce an LLZTO membrane. To further enhance the density and separation performance of the LLZTO membrane, an organic crosslinking agent was introduced to modify the pores of the LLZTO membrane, resulting in a dense lithium superion conductor membrane. This lithium superion conductor membrane exhibits excellent ion separation performance, providing a reference for related fields such as the efficient recovery and extraction of lithium resources.

Description

Technical Field

[0001] The present invention relates to a method for preparing a highly selective lithium superion conductor membrane, lithium ion recovery, and a membrane and device for selectively separating lithium ions from a liquid solution, particularly an aqueous solution such as brine. Background Art

[0002] With the continuous growth of global energy demand and concerns about environmental sustainability, finding efficient and clean energy solutions has become increasingly important. Lithium-ion plays 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 deposits and salt lakes. Current methods for extracting lithium and its compounds involve acid decomposition of the minerals and chemical leaching, or concentration of brine using solar ponds. However, these traditional methods are complex, time-consuming, or require high chemical or local climate requirements. Membrane separation technology offers several key advantages, including high selectivity, greater environmental sustainability, ease of operation, and strong scalability. Therefore, membrane separation technology is a good choice for lithium ion extraction.

[0004] In order to effectively solve the above problems, the present invention uses a solid electrolyte membrane to replace the traditional lithium extraction method, which is more time-saving and clean. Solid electrolyte materials, also known as "superionic conductors", have high ionic conductivity and can effectively promote the transmission speed of lithium ions in solid electrolytes. In contrast, other materials may have problems such as concentration polarization and ion migration, which affect the transmission efficiency of lithium ions. Moreover, lithium superionic conductors have good chemical stability and can effectively resist environmental influences such as corrosion and oxidation from seawater. Therefore, it is very important to combine solid electrolytes with membrane separation technology to prepare highly selective lithium superionic conductor membranes.

[0005] In the preparation of lithium superion conductor membranes, the membranes are prone to being loose, resulting in reduced separation performance and reduced lifespan. Therefore, the present invention utilizes an organic crosslinking agent 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 to extract lithium ions. Summary of the Invention

[0007] The purpose of the present invention is to overcome the difficulties in lithium extraction in the prior art and prepare a lithium superion conductor separation membrane with high selectivity.

[0008] The technical solution of the present invention is:

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

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

[0011] B. The precursor solution is first subjected to constant temperature oscillation in a water bath to obtain a translucent sol; the sol is then placed in an oven to dry to obtain a gel; the gel is then placed in a muffle furnace for calcination; and finally ball milling is performed 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. LLZTO and an organic forming aid are mixed in a mass ratio and then ball-milled, and then a LLZTO film green body is obtained by tableting, and the green body is placed in a muffle furnace and calcined at a high temperature to obtain an LLZTO film;

[0013] D. placing a fluorine-containing polymer into an organic solvent and continuously stirring to obtain an organic cross-linking aid;

[0014] E. Modify the pores of the LLZTO membrane with an organic cross-linking agent, coat the LLZTO membrane with the organic cross-linking agent, and then heat it in an oven to cross-link it, thereby obtaining a highly selective lithium superion conductor membrane.

[0015] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor membrane, in step A, the molar ratio of lithium nitrate, lanthanum nitrate hexahydrate, zirconium n-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 membrane, the temperature of the precursor solution in step B during the constant temperature oscillation in a water bath is 60-80°C, and the oscillation time is 3-6 hours; the temperature during the drying process of the sol is 80-120°C, and the drying time is 10-15 hours; the calcination temperature during the calcination of the gel is 800-950°C, the calcination time is 5-10 hours, and the heating rate is 1-5°C / min.

[0017] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor membrane, the organic forming aid described 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 method for preparing a highly selective lithium superion conductor membrane, 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 membrane, the pressure during the tableting 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 membrane, the calcination process in step C is first heating to 300-350°C and keeping it for 2-5 hours, then heating to 1100-1300°C and keeping it for 10-20 hours, and the heating rate is controlled at 1-5°C / min.

[0021] Furthermore, in the above-mentioned method for preparing a highly selective lithium superion conductor membrane, the fluorinated polymer described 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% to 5 wt% of the molar mass of the organic solvent.

[0022] Furthermore, in the above method for preparing a highly selective lithium superion conductor membrane, the heating temperature in the heating process in step E is 120-180° C. and the heating time is 10-20 h.

[0023] Beneficial Effects: This invention modifies the pores of the LLZTO membrane using an organic crosslinking agent. By regulating the concentration of the organic crosslinking agent, the solvent, and the solute, a highly selective lithium superion conductor membrane is successfully prepared. Furthermore, membrane testing demonstrates that the membrane achieves excellent separation performance, resolving the current difficulties in lithium ion extraction. This provides a reference for more efficient lithium ion extraction in the future. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 These are SEM images of the lithium superion conductor films prepared in Examples 3, 5, 7, and 9.

[0026] Figure 3 Schematic diagram of the water contact angle of the lithium superion conductor membrane prepared in Examples 3, 5, 7, and 9.

[0027] Figure 4 These are the FTIR characterization test charts of Examples 3, 5, 7, and 9.

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

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

[0030] Figure 7 It is the lithium-sodium separation performance of the lithium superion conductor membrane used for electrodialysis in Example 10. DETAILED DESCRIPTION Example 1

[0031] This example is used to illustrate the preparation of LLZTO material by the sol-gel method.

[0032] The molar ratio of lithium nitrate: lanthanum nitrate hexahydrate: zirconium isopropoxide: tantalum ethoxide was weighed at 6.4:3:1.3:0.6. 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 were dissolved in 20 mL of water and stirred until dissolved. 9.6 g of citric acid and 8.4 mL of ethylene glycol were then added and stirred for 30 min to obtain a precursor solution. The precursor solution was kept in an 80 °C water bath for 3 h to obtain a translucent sol. The sol was placed in a 100 °C oven and dried for 10 h to obtain a gel. The gel was placed in a muffle furnace and pre-calcined at 350 °C for 3 h and then calcined at 950 °C for 5 h at 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 was then ball-milled to a particle size of approximately 1.2 μm.

[0033] Figure 1 a) is a SEM image of the LLZTO material prepared in this example, and the particle diameter is about 1.2 μm. Figure 1 b) is the X-ray diffraction (XRD) pattern of the LLZTO prepared in this example. Example 2

[0034] This example is used to illustrate the preparation of LLZTO material by the sol-gel method.

[0035] The materials were weighed in a molar ratio of 6.4:3:1.3:0.6 for lithium nitrate: lanthanum nitrate hexahydrate: zirconium isopropoxide: tantalum ethoxide. 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 were dissolved in 20 mL of water and stirred until dissolved. 9.6 g of citric acid and 8.4 mL of ethylene glycol were then added and stirred for 30 min to obtain a precursor solution. The precursor solution was kept in a water bath at 60 °C for 6 h to obtain a translucent sol. The sol was placed in an oven at 80 °C for 15 h to obtain a gel. The gel was placed in a muffle furnace, pre-calcined at 350 °C for 3 h, and then calcined at 800 °C for 10 h at 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 was then ball-milled to a particle size of approximately 1.2 μm. Example 3

[0036] This example is used to illustrate the preparation of LLZTO film by high-temperature calcination method.

[0037] First, the LLZTO material and binder in Example 1 were mixed and ball milled for 3 h at a speed of 400 rpm. The binder was PVA with a concentration of 10 wt%, and the addition amount was 1% of the mass of the lithium superion conductor material. The evenly mixed powder was loaded into a tablet pressing mold and pressurized to 30 MPa for 60 s to obtain a green body. The green body was then placed in a muffle furnace, heated to 350 °C at a rate of 2 °C / min and kept warm for 2 h, and then heated to 1300 °C at a rate of 1 °C / min and kept warm for 10 h to finally obtain the LLZTO film.

[0038] Figure 2 a is a SEM image of the LLZTO film prepared in this example, wherein the upper right corner is an enlarged image, from which it can be seen that the material is in a molten state and is evenly distributed. Figure 2 e is a cross-sectional view of the LLZTO film prepared in this example. Figure 3 a is a schematic diagram of the water contact angle of the LLZTO film prepared in this example. Example 4

[0039] This example is used to illustrate the preparation of LLZTO film by high-temperature calcination method.

[0040] First, the LLZTO material and binder in Example 1 were mixed and ball-milled for 6 h at a speed of 300 rpm. The binder was PVA with a concentration of 8 wt%, and the addition amount was 10% of the mass of the lithium superion conductor material. The evenly mixed powder was loaded into a tablet pressing mold and pressurized to 50 MPa for 30 s to obtain a green body. The green body was then placed in a muffle furnace, heated to 300 °C at a rate of 5 °C / min and kept warm for 5 h, and then heated to 1100 °C at a rate of 1 °C / min and kept warm for 20 h to finally obtain the LLZTO film. Example 5

[0041] This example is used to illustrate the preparation of a defect-free lithium superion conductor membrane by modifying the LLZTO membrane through cross-linking.

[0042] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF, and the solvent was DMF. The concentration of the organic crosslinking agent was 1 wt%, and the amount added 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 hours. Finally, a defect-free lithium superion conductor membrane was obtained. This membrane is referred to as LLZTO / PVDF-1 membrane.

[0043] Figure 2 b is a SEM image of the LLZTO / PVDF-1 membrane prepared in this example. Figure 2 f is the cross-sectional morphology of the LLZTO / PVDF-1 membrane of this embodiment, and the membrane thickness is about 500 μm. Figure 3 b is a schematic diagram of the water contact angle of the LLZTO / PVDF-1 membrane prepared in this example. It can be observed that compared with the LLZTO membrane, the LLZTO / PVDF-1 membrane is more hydrophobic and the membrane surface is denser. Example 6

[0044] This example is used to illustrate the preparation of a defect-free lithium superion conductor membrane by modifying the LLZTO membrane through cross-linking.

[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, and the solvent was DMAC. The concentration of the organic crosslinking agent 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 hours. Finally, a defect-free lithium superion conductor membrane was obtained. This membrane is referred to as LLZTO / PVDF-HFP membrane. Example 7

[0046] This example is used to illustrate the preparation of a defect-free lithium superion conductor membrane by modifying the LLZTO membrane through cross-linking.

[0047] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF, and the solvent was DMF. The concentration of the organic crosslinking agent was 3 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 hours. Finally, a defect-free lithium superion conductor membrane was obtained. This membrane is referred to as LLZTO / PVDF-3 membrane.

[0048] Figure 2 c is a SEM image of the LLZTO / PVDF-3 membrane prepared in this example. Figure 2 g is the cross-sectional morphology of the LLZTO / PVDF-3 membrane of this embodiment, and the membrane thickness is about 500 μm. Figure 3 c is a schematic diagram of the water contact angle of the LLZTO / PVDF-3 membrane used in this example, and the membrane is more hydrophobic and dense. Figure 5 This is the XPS graph of the LLZTO / PVDF-3 membrane used in this example. From the XPS graph, it can be seen that Li-F and La-F peaks exist, indicating that PVDF is successfully cross-linked with LLZTO and the membrane is successfully prepared. Example 8

[0049] This example is used to illustrate the preparation of a defect-free lithium superion conductor membrane by modifying the LLZTO membrane through cross-linking.

[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, and the solvent was NMP. The concentration of the organic crosslinking agent 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 hours. Finally, a defect-free lithium superion conductor membrane was obtained. This membrane is referred to as LLZTO / PVDF-4 membrane. Example 9

[0051] This example is used to illustrate the preparation of a defect-free lithium superion conductor membrane by modifying the LLZTO membrane through cross-linking.

[0052] First, the LLZTO membrane from Example 3 was coated with an organic crosslinking agent. The solute of the organic crosslinking agent was PVDF, and the solvent was DMF. The concentration of the organic crosslinking agent was 5 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 175°C for 10 hours. Finally, a defect-free lithium superion conductor membrane was obtained. This membrane is referred to as LLZTO / PVDF-5 membrane.

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

[0054] Figure 4 The FTIR characterization test diagrams of Example 3, Example 5, Example 7, and Example 9 show that the cross-linked membranes of LLZTO and PVDF have the following wavelengths at 1050 and 1400 cm -1 The characteristic peak of F was generated at , indicating that PVDF had been successfully cross-linked with LLZTO and the LLZTO / PVDF membrane was successfully prepared. Example 10

[0055] This example is used to illustrate the performance of a lithium superion conductor membrane for lithium ion separation by electrodialysis testing.

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

[0057] Three solutions, namely the lithium-enriched solution, the feed solution, and the electrode solution, were sequentially introduced into the electrodialysis device. The feed solution was a mixed solution of 0.1 mol / L LiCl and 0.1 mol / L NaCl, the lithium-enriched solution was a pure aqueous solution, and the electrode solution was a 300 ppm LiCl solution. The voltage applied to the electrodialysis device was 1 V, and the effective area of ​​the membrane during the test was 5×10 -5 m 2 , all experiments were carried out at room temperature.

[0058] Over time, lithium will gradually concentrate in the lithium-rich solution. After 24 h of electrodialysis test, the lithium ion flux of LLZTO membrane, LLZTO / PVDF-1, and LLZTO / PVDF-3 membranes were 51.3 mmol·m -2 •h -1 、 52mmol•m -2 •h -1 、 36 mmol•m -2 •h -1 , the lithium and sodium selectivities are 8.55, 32.5, and 58.54, respectively.

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

Claims

1. A method for preparing a highly selective lithium superion conductor membrane, characterized in that: The specific steps are as follows: A. lithium nitrate, lanthanum nitrate hexahydrate, zirconium n-propoxide, tantalum ethoxide and deionized water are mixed in a certain proportion to obtain a mixed solution, and then citric acid and ethylene glycol are slowly added to the mixed solution while continuously stirring to obtain a precursor solution; B. The precursor solution is first subjected to constant temperature oscillation in a water bath to obtain a translucent sol; the sol is then placed in an oven to dry to obtain a gel; the gel is then placed in a muffle furnace for calcination; and finally ball milling is performed 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; C. LLZTO and an organic forming aid are mixed in a mass ratio and then ball-milled, and then a LLZTO film green body is obtained by tableting, and the green body is placed in a muffle furnace and calcined at a high temperature to obtain an LLZTO film; D. placing a fluorine-containing polymer into an organic solvent and continuously stirring to obtain an organic cross-linking aid; E. Modify the pores of the LLZTO membrane with an organic cross-linking agent, coat the LLZTO membrane with the organic cross-linking agent, and then heat it in an oven to cross-link it, thereby obtaining a highly selective lithium superion conductor membrane.

2. The method for preparing a highly selective lithium superion conductor membrane according to claim 1, wherein: In step A, the molar ratio of lithium nitrate, lanthanum nitrate hexahydrate, zirconium n-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 membrane according to claim 1, wherein: In step B, the temperature of the precursor solution during the constant temperature oscillation in a water bath is 60-80°C, and the oscillation time is 3-6 hours; the temperature during the drying process of the sol is 80-120°C, and the drying time is 10-15 hours; the calcination process of the gel is calcined at a temperature of 800-950°C, for 5-10 hours, and the heating rate is 1-5°C / min.

4. The method for preparing a highly selective lithium superion conductor membrane according to claim 1, wherein: The organic forming aid described 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 membrane according to claim 1, wherein: In step C, the ball milling time is 3-6 h, and the ball milling speed is 300-400 rpm.

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

7. The method for preparing a highly selective lithium superion conductor membrane according to claim 1, wherein: The calcination process in step C is to first heat the temperature to 300-350°C and keep it for 2-5 hours, then heat the temperature to 1100-1300°C and keep it for 10-20 hours, and the heating rate is controlled at 1-5°C / min.

8. The method for preparing a highly selective lithium superion conductor membrane according to claim 1, wherein: The fluorinated polymer described 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. The method for preparing a highly selective lithium superion conductor membrane according to claim 1, wherein: During the heating process in step E, the heating temperature is 120-180° C. and the heating time is 10-20 h.

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