A preparation method of a lithium extraction electrode, a film capacitor device comprising the same, and a circulating system for lithium extraction from salt lake

Abstract

The present application is directed to the field of electrochemical lithium extraction from salt lake brine, and relates to a preparation method of lithium extraction electrode, a membrane capacitor device comprising the same, and a lithium extraction circulation system of salt lake. The present application utilizes ultraviolet light curing crosslinking to prepare electrodes with high active surface area. In addition, the positively charged nanofiltration membrane after quaternization is used to enhance the separation effect of lithium / magnesium ions, and a roll type electrode assembly is assembled to build a membrane capacitor lithium extraction device. A continuous lithium extraction process with good enrichment effect, strong separation capacity and high lithium extraction efficiency is developed. The continuous operation of the membrane capacitor lithium extraction device of the present application is conducive to the efficient and environmentally friendly development of lithium resources in salt lake brine in the western region of China.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium extraction from salt lake brine, and particularly relates to a preparation method of a lithium extraction electrode, a membrane capacitive deionization device comprising the lithium extraction electrode, and a lithium extraction cycle system of a salt lake. BACKGROUND

[0002] The market of new energy vehicles has experienced explosive growth, and the main raw material of lithium batteries, i.e., lithium carbonate, has become a bottleneck restricting the development. The cost of lithium extraction from salt lake brine is relatively low, and industrial-grade lithium carbonate can be directly obtained, which can be converted into deep-processed lithium products after purification. Membrane capacitive deionization technology (MCDI) is a new water treatment technology based on the mechanism of supercapacitors, in which the charged ions in the solution are adsorbed onto the electrode plate with opposite polarity by electrostatic force and are removed in the double electric layer formed between the solution and the electrode surface. The technology has the advantages of low energy consumption, no secondary pollution, and long service life of the electrode. The application develops a membrane capacitive electrochemical lithium extraction process by using the membrane capacitive deionization technology (MCDI), uses lithium-rich lithium battery materials as an anode, and uses porous carbon materials as a cathode. After power-on, the anode is de-lithiated into the anode liquid, the anode and the cathode are exchanged, the voltage is adjusted, and the lithium battery material realizes the enrichment of lithium ions in the brine. After repeated enrichment, the concentration of lithium ions is continuously enriched and improved. Then, through the adsorption-desorption of the salt lake brine, a lithium-precipitated solution suitable for the preparation of Na2CO3 is obtained. The method has high lithium extraction efficiency, but still has the following problems:

[0003] Firstly, the preparation of the electrode: CN 110854393 B discloses a preparation process of a membrane electrode, which uses a step-by-step method to prepare a double-sided catalyst layer. The single-sided catalyst layer is immersed into a catalyst solution, the catalyst is lifted out, and then heated and rolled. The operation is repeated to obtain a double-sided catalyst layer. This method is simple in operation, but the average loading capacity and the uniformity of the loading are limited by the uniformity of the catalyst solution, and the cycle stability of the electrode is poor.

[0004] Secondly, the problem of magnesium ion interference in the lithium extraction process: In addition to lithium ions, there are a large number of alkali metal and alkaline earth metal ions in the salt lake brine, which greatly increases the difficulty of lithium salt separation and extraction. In particular, the ionic hydration radius and chemical properties of magnesium and lithium ions are similar, making the extraction and separation of lithium in a high magnesium-lithium ratio salt lake quite complex.

[0005] Finally, the problem of the circulation system of lithium extraction from salt lake: CN 115925199 A discloses a circulation system for lithium extraction from salt lake, which comprises an ultrafiltration subsystem, an inclined plate sedimentation tank, a continuous ion exchange subsystem, a nanofiltration membrane subsystem, a reverse osmosis membrane subsystem and a bipolar membrane subsystem. Through the multi-stage combined process, the tail liquid and concentrated water at each stage in the system can be effectively utilized or reused to the upstream process, realizing closed-loop circulation of the lithium extraction process from salt lake. However, the lithium extraction process is relatively complicated, and the acid used in the lithium elution process has a greater impact on the environment and is easy to cause system dissolution, thereby reducing the lithium extraction efficiency and the lithium extraction effect is not good.

[0006] Therefore, how to improve the cycle stability of the electrode, reduce Mg 2+ Li + The interference of selective adsorption, high lithium-magnesium separation ratio and high-efficiency lithium enrichment are what people hope for.

[0007] In order to solve the above problems, the present application is proposed. SUMMARY

[0008] The purpose of the present application is to overcome the shortcomings of the lithium extraction technology based on manganese-based adsorbent, provide a lithium extraction electrode preparation method and a membrane capacitor device, improve the cycle stability of the electrode, reduce Mg 2+ Li + The interference of selective adsorption, high lithium-magnesium separation ratio and high-efficiency lithium enrichment.

[0009] The present application proposes a membrane capacitor desalination mechanism, which selectively extracts Li+ in brine by applying voltage on the surface of the positive electrode to achieve the purpose of lithium enrichment; then releases Li+ into the recovered brine through the discharge process, while recovering part of the energy. This electrochemical lithium extraction technology has excellent lithium ion selective adsorption, energy recycling and stable operation, and can be combined with the secondary use of retired lithium batteries, which has great cost advantage and commercial prospect. Based on the above lithium extraction process, the present application further proposes an electrode preparation method using ultraviolet light curing crosslinking to prepare an electrode with high active surface area. In addition, the positively charged nanofiltration membrane after quaternization enhances the separation effect of lithium / magnesium ions, and is assembled into a roll-type electrode assembly to build a membrane capacitor lithium extraction device, and develops a continuous lithium extraction process with good enrichment effect, strong separation capacity and high lithium extraction efficiency.

[0010] The point technical scheme adopted by the present application is:

[0011] The present application provides a lithium extraction electrode preparation method, comprising the following steps:

[0012] (1) stirring and mixing a photoinitiator and a prepolymer to obtain a first viscous solution, then adding manganese-based adsorbent powder and Ti3C2Tx The second viscous solution is obtained by stirring the mixture, and then active diluent is added to the second viscous solution to obtain a slurry by continuing stirring;

[0013] (2) The slurry obtained in step (1) is coated on a porous current collector, and cross-linking and curing adhesion are performed under irradiation of ultraviolet light to obtain a lithium extraction electrode.

[0014] Preferably, in step (1), the photoinitiator is selected from TPO, the prepolymer is selected from polyurethane acrylate, and the active diluent is selected from hydroxyethyl methacrylate;

[0015] The mass ratio of the photoinitiator to the prepolymer in the first viscous solution is 1:20-1:50;

[0016] The second viscous solution comprises 70%-85% of manganese-based adsorbent powder, 5-10% of Ti3C2T x , and 5%-20% of the first viscous solution, based on the mass percentage.

[0017] The active diluent with a particle size of 300-900 μm is added to the second viscous solution to obtain a slurry by continuing stirring for 1-4 h.

[0018] Preferably, in step (1), the Ti3C2T x is prepared by adding 1-5 g of LiF to 10-50 ml of 5-15 mol / L HCl to form a transparent solution by stirring, slowly adding 0.5-3.5 g of Ti3AlC2, reacting at 10-50°C for 15-30 h, then adding deionized water, centrifuging to remove the upper liquid, adding deionized water again, centrifuging, repeating several times until the color of the suspension changes from dark green to transparent light green, collecting the precipitate, filtering, air-drying, and grinding to obtain Ti3C2T x .

[0019] Preferably, in step (2), the porous current collector is placed on a flat glass plate, the prepared slurry obtained in step (1) is poured onto the surface of the porous current collector, a doctor blade is used to scrape a film with a thickness of 1-10 μm, the current collector with the film is placed under an ultraviolet lamp for curing for 1-10 min, and then the current collector is taken out to obtain a lithium extraction electrode.

[0020] Preferably, the distance between the ultraviolet lamp and the current collector is 3-15 cm.

[0021] The wavelength of the ultraviolet light of the ultraviolet lamp is 300-350 nm.

[0022] The second aspect of the present application provides a film capacitor device, wherein the positive electrode is the lithium extraction electrode prepared by the method of the first aspect of the present application, and the negative electrode is the biomass-derived porous activated carbon electrode, wherein the positive electrode is provided with a quaternary ammonium cationic nanofiltration membrane in advance, and the negative electrode is provided with an anion exchange membrane in advance.

[0023] Preferably, the method for preparing the biomass-derived porous activated carbon electrode is as follows:

[0024] (A) A first viscous solution is prepared according to the method, and activated carbon, Ti3C2T x The third viscous solution is obtained by stirring and mixing, and then an active diluent is added to the third viscous solution for continuous stirring to obtain a second mixed slurry;

[0025] (B) The second mixed slurry obtained in step (A) is coated on a porous current collector, and cross-linking and curing adhesion are performed under the irradiation of ultraviolet light to obtain a biomass-derived porous activated carbon electrode;

[0026] In the third viscous solution, the mass ratio of the viscous solution, Ti3C2T x , and activated carbon is 1:1:8-2:1:7.

[0027] Preferably, the method for preparing the quaternary ammonium cationic nanofiltration membrane is an interfacial polymerization method, which comprises the following steps:

[0028] (a) Dissolve PEI in deionized water to obtain a transparent aqueous solution, add propylene oxide dropwise to the PEI solution using a constant pressure dropping funnel under a 5℃ water bath, and stir for 3-10h; then increase the tank temperature to 40℃, and evaporate the unreacted propylene oxide to obtain a tertiary aminated PEI solution;

[0029] (b) Add benzyl chloride to the tertiary aminated PEI solution in a 50℃ water bath, mechanically stir for 20-40h, and then extract with ether several times to remove residual benzyl chloride to obtain a QPEI solution;

[0030] (c) Finally, evaporate the water in the solution in a 50℃ vacuum oven, and freeze-dry for 10-20h to obtain a transparent QPEI sheet;

[0031] (d) Dissolve QPEI, Na3PO4 and SDS in deionized water to obtain a transparent aqueous solution with a PEI concentration of 0.5-6.wt.% by stirring; dissolve TMC in n-hexane to obtain a transparent oil phase solution with a TMC concentration of 0.1-0.5w / v.% by stirring;

[0032] (e) Slowly rinse the PES base film with deionized water to clean the film surface, and after the film surface is dried, quickly pour 20-80 ml of the prepared aqueous phase solution onto the film, maintain for 25-100 s, then remove the base film, remove the excess water on the film surface with a flexible silicone roller, and use nitrogen to blow the film surface; then quickly pour 20-80 ml of the prepared oil phase solution, maintain for 10-70 s of interfacial polymerization, and then quickly transfer to a vacuum oven for thermal compounding at 25-100 DEG C for 1-8 min; finally, remove the composite nanofiltration membrane and rinse the membrane surface with deionized water to obtain a quaternized positive electric nanofiltration membrane.

[0033] In step (a), the molar ratio of propylene oxide to PEI is 2:1.

[0034] Preferably, the lithium extraction electrode and the porous activated carbon electrode are both roll-type electrodes, and the preparation method is to first stack multiple layers and then roll into a multi-layer stacked roll-type electrode. Compared with ordinary flat electrode assemblies, the footprint of the electrode assembly is reduced, and the roll-type electrode assembly can improve the flux of the brine, increase the contact area between the brine and the electrode, balance the relationship between the anti-pollution property, the penetration rate and the packing density, and better improve the separation and enrichment efficiency of the lithium extraction device in actual use.

[0035] The third aspect of the present application provides a lithium extraction cycle system for salt lake, which comprises a brine lithium extraction-cleaning water cleaning-solution recovery three water cycle system and a salt water electrolyte external circulation system; the brine lithium extraction comprises the membrane capacitor device of the second aspect of the present application. The lithium extraction cycle system for salt lake can realize continuous operation, build a brine lithium extraction-cleaning water cleaning-solution recovery three water cycle system and a salt water electrolyte external circulation system for lithium extraction battery, match the charging and discharging with the energy recovery and storage system, and reasonably set the three-way interface to realize the switching of different fluids. The positive and negative electrodes of the power supply are reversely connected to realize the discharging process, and at the same time, the energy is stored in the energy recovery system to save energy, and the salt lake brine circulation channel is opened to make the brine fill the electrolysis chamber. After most of the lithium ions are embedded in the LMO-UV electrode, the salt lake brine circulation channel is closed, the flushing clean water circulation channel is opened to flush away other ions remaining on the electrode, the energy recovery and storage system stores energy at this time to realize the charging process, the recovery salt water channel is opened to make the lithium chloride solution fill the electrolysis chamber, the lithium ions on the LMO-UV electrode are removed, the enrichment process of the lithium ions is realized, and finally, the sodium carbonate solution is added to the lithium-rich recovery solution to generate lithium carbonate precipitate, and the lithium extraction is realized after the collection and selection of the precipitate.

[0036] In summary, the lithium extraction electrode preparation method of this invention is as follows: A photoinitiator TPO and polyurethane acrylate are mixed into a viscous solution, which is then mixed with manganese-based adsorbent powder Ti3C2Tx to form a slurry. Hydroxyethyl methacrylate is added for further dilution, and the mixture is then coated onto the surface of a porous current collector. The slurry is then scraped into a thin film and cured and cross-linked under ultraviolet light. After adhesion, the lithium extraction electrode is obtained. Furthermore, the spiral-wound electrode assembly and the membrane capacitor lithium extraction device have advantages such as high brine flux, high active area, acid-free lithium removal, and high lithium extraction capacity. This invention uses ultraviolet light curing cross-linking to prepare a membrane capacitor lithium extraction electrode with high active contact area and high tortuosity, which is superior to lithium extraction electrodes prepared by traditional methods in terms of active loading, electrode preparation time, active contact area, and electrode dissolution suppression. Simultaneously, the use of a multi-layer stacked spiral-wound electrode assembly and its continuously operating membrane capacitor lithium extraction device is beneficial for the efficient and environmentally friendly development of lithium resources in salt lake brine in western my country. Compared with the prior art, this invention has the following beneficial effects:

[0037] 1. This invention utilizes membrane capacitor deionization (MCDI) technology to develop a membrane capacitor electrochemical lithium extraction process. The working principle is similar to that of a supercapacitor, using lithium-rich lithium battery material as the anode and porous carbon material as the cathode. After energizing, lithium is delithiated from the anode and introduced into the anolyte. The anode and cathode are exchanged, and the voltage is adjusted. The lithium battery material enriches lithium ions in the brine. After repeated cycles, the lithium ion concentration will continue to increase. Then, through the adsorption-delithiation of the brine in the salt lake, a lithium precipitation solution suitable for Na2CO3 preparation is obtained in one step.

[0038] 2. This invention employs ultraviolet (UV) curing to prepare lithium extraction electrodes and porous activated carbon electrodes with high active contact area and high tortuosity. The preparation time is significantly shorter than that of the slurry coating method, making the method more convenient and faster. It surpasses traditional methods in terms of active loading, electrode preparation time, and electrode dissolution loss. Therefore, this invention utilizes UV curing crosslinking technology to prepare electrodes, offering advantages such as high efficiency, uniform loading, and a large formable active area.

[0039] 3. This invention uses Ti3C2T x Coating commercial manganese-based adsorbent powder with Ti3C2T is necessary because commercial manganese-based adsorbent powder itself has poor conductivity. x This significantly increases its conductivity, facilitating electron movement between the positive and negative electrodes, enhancing electron transport rates, and helping lithium ions complete the insertion and desorption processes more rapidly. Furthermore, this invention independently prepared Ti3C2T... x Compared to directly commercially purchased Ti3C2T x The Ti3C2T prepared under the conditions of this invention x It has stronger conductivity, a more stable structure, and is more conducive to ion transport.

[0040] 4. The application sets a positive charge nanofiltration membrane in front of the positive electrode, and the positive charge nanofiltration membrane can realize the separation of monovalent and divalent ions. The positive charge nanofiltration membrane has a low rejection rate for monovalent ions, but has a good rejection effect for high valence ions, so that the magnesium ions with higher valence are subjected to stronger electrostatic repulsion, which is obviously higher than that of lithium ions, and the lithium ions are more easily permeated through the membrane while the magnesium ions are intercepted, so that the two kinds of ions of magnesium and lithium can have a good separation effect. In addition, the nanofiltration separation technology has the characteristics of low operating pressure, small energy consumption, environmental friendliness and the like, and the application of the nanofiltration separation technology to the lithium extraction field of salt lake brine has a very good application prospect. Furthermore, the positive charge nanofiltration membrane is subjected to quaternary ammonium modification, which can further improve the charge density of the positive charge and the rejection rate of divalent cations, reduce the Mg 2+ The Li + The selective adsorption interferes, realizes high lithium-magnesium separation ratio and high-efficiency lithium enrichment.

[0041] 5. The positive charge nanofiltration membrane prepared by the interface polymerization method and subjected to quaternary ammonium modification of PEI can realize a loose functional layer structure, which is beneficial to improve the water flux of the composite membrane.

[0042] 6. The membrane capacitor device for lithium extraction is used, and a roll-type electrode assembly is used to replace a traditional flat plate type electrode assembly, so that the floor area of the electrode assembly is reduced, and the roll-type electrode assembly can improve the flux of the brine, increase the contact area between the brine and the electrode, balance the relationship among the anti-pollution, the penetration rate and the packing density, and better improve the separation and enrichment efficiency of the lithium extraction device in the actual application process.

[0043] 7. The membrane capacitor device for lithium extraction is used, and the ion exchange membrane of the membrane capacitor device has the characteristics of selectively permeating anions and cations, which can not only ensure the normal migration and adsorption process of lithium ions, but also effectively prevent the lithium ions from being taken away due to water flow disturbance, and avoid the secondary adsorption of lithium ions on the negative electrode in the regeneration process, so as to improve the ion removal efficiency and the electrode regeneration efficiency, and improve the lithium extraction efficiency. The membrane capacitor device is simple and easy to operate, and uses the effect of the electric field to adsorb the charged ions in the solution to the electrode plate with opposite electric properties by electrostatic force and remove the ions in the double electric layer formed between the solution and the electrode surface, so as to be a new type of water treatment technology with low energy consumption and environmental friendliness.

[0044] 8. The lithium extraction cycle system of the salt lake can realize continuous operation. A brine lithium extraction-cleaning water cleaning-solution recycling three water cycle system and a salt-in-water electrolyte external circulation system are built to match the charging and discharging and energy storage system, and a three-way interface is reasonably set to realize the switching of different fluids. The positive and negative electrodes of the power supply are reversely connected to realize the discharging process, and at the same time, the energy is stored in the energy recovery system to save energy. The salt lake brine circulation channel is opened to make the brine fill the electrolysis chamber. After most of the lithium ions are embedded in the LMO-UV electrode, the salt lake brine circulation channel is closed, the flushing clean water circulation channel is opened to flush the other ions remaining on the electrode, and the charging process is realized when the energy storage system has energy. The recovered salt water channel is opened to make the lithium chloride solution fill the electrolysis chamber, and the lithium ions on the LMO-UV electrode are removed to realize the enrichment process of lithium ions. Finally, sodium carbonate solution is added to the lithium-rich recovered solution to generate lithium carbonate precipitate, and the precipitate is collected and processed to realize lithium extraction. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 It is a schematic diagram of the multi-cycle membrane capacitor lithium extraction system and the recovered solution post-treatment.

[0046] Figure 2 It is a reaction schematic diagram of the membrane capacitor device.

[0047] Figure 3 It is a linear cyclic voltammetry test diagram, wherein (a) is a linear cyclic voltammetry test diagram of LMO-UV, (b) is a linear cyclic voltammetry test diagram of LMO-1, (c) is a linear cyclic voltammetry test diagram of LMO-2, and (d) is a linear cyclic voltammetry test diagram of LMO-3.

[0048] Figure 4 It is a linear cyclic voltammetry test diagram of LMO-UV at a scan rate of 0.1-1 mv / s.

[0049] Figure 5 It is a SEM diagram of the lithium extraction electrode, wherein (a) is a SEM diagram of LMO prepared by using a traditional slurry method, and (b) is a SEM diagram of LMO-UV prepared by using an ultraviolet light curing method.

[0050] Figure 6 It is a comparison diagram of electrode dissolution of LMO and LMO-UV.

[0051] Figure 7 It is a SEM diagram of a PES-based membrane and a positively charged nanofiltration membrane, wherein (a) is a SEM diagram of a PES-based membrane, and (b) is a SEM diagram of a quaternized positively charged nanofiltration membrane.

[0052] Figure 8The surface Zeta potential diagram of the quaternized positively charged nanofiltration membrane and the unquaternized positively charged nanofiltration membrane at different pH values.

[0053] Figure 9 The impedance comparison diagram of LMO-UV and LMO-4.

[0054] Figure 10 The comparison diagram of the rejection rates of various ions in the brine after the lithium extraction electrode and the lithium extraction device. DETAILED DESCRIPTION

[0055] The application is further described below by examples, which are not limited to the examples. The experimental methods not specified in the examples are generally carried out according to the conventional conditions and the conditions described in the manual, or the general equipment, materials, reagents, etc. used according to the conditions suggested by the manufacturers, and if not otherwise specified, can be obtained from commercial channels.

[0056] The application is further described below by specific examples, which are only descriptive and not limiting, and cannot limit the protection scope of the application.

[0057] The brine used in the following examples is the Qaidam Salt Lake brine (sodium-depleted brine), and its chemical composition is shown in the following table:

[0058]

[0059] The lithium extraction device of the application is shown in Figure 1 The membrane capacitor lithium extraction device can realize continuous operation, build a brine lithium extraction-clean water washing-solution recycling three water circulation system and a salt-in-water electrolyte external circulation system, match the charging and discharging and energy recovery storage system, and reasonably set the three-way interface to realize the switching of different fluids. First, the positive and negative electrodes of the power supply are reversely connected to realize the discharging process, and at the same time, the energy can be stored in the energy recovery system to save energy, and the salt lake brine circulation channel is opened to make the brine fill the electrolysis chamber. After most of the lithium ions are embedded in the LMO-UV electrode, the salt lake brine channel is closed, the flushing clean water circulation channel is opened to flush the other ions remaining on the electrode, and at this time, the energy recovery storage system stores energy to realize the charging process, and the recovered salt water channel is opened to make the lithium chloride solution fill the chamber, and the lithium ions on the LMO-UV electrode are removed to realize the enrichment process of lithium ions. Finally, sodium carbonate solution is added to the lithium-rich recovery solution to generate lithium carbonate precipitate, and the precipitate is collected and processed to realize lithium extraction.

[0060] The reaction of the membrane capacitor device is as follows Figure 2As shown, the lithium extraction electrode is used as the positive electrode, a positive electrode is attached to the anion filtration membrane, a porous activated carbon electrode is used as the negative electrode, a negative electrode is attached to the cation exchange membrane, the brine is passed between the positive electrode and the negative electrode and fills the entire chamber, and the lithium ions are embedded and desorbed on the electrode by the action of the electric field force to complete the lithium extraction process.

[0061] The reaction in which lithium is adsorbed and desorbed on the electrode includes the following reaction steps:

[0062] Li + The adsorption process (discharge process): when using brine as the electrolyte, the positive electrode is discharged, the manganese-based adsorbent on the electrode is reduced by electrons, Mn 4+ is reduced to Mn 3+ , and Li + in the solution is embedded in the corresponding position of the manganese-based adsorbent at the same time, and the chloride ions are captured by the negative electrode, and the water oxidation reaction occurs on the electrode to generate O2, thereby completing the adsorption process.

[0063] Li + The desorption process (charging process): when using the recovery liquid as the electrolyte, the positive electrode is applied with a positive potential to undergo an oxidation reaction, Mn 3+ is oxidized to Mn 4+ , and at the same time, Li + in the manganese-based adsorbent lattice is released into the recovery liquid, and the negative electrode releases chloride ions to complete the desorption process.

[0064] Example 1

[0065] A lithium extraction electrode preparation method:

[0066] The photoinitiator TPO and the polyurethane acrylate are mixed in a mass ratio of 1:20-1:50 to form a viscous solution, the commercial manganese-based adsorbent powder, Ti3C2T x and the viscous solution are mixed to form a slurry, wherein the mass fraction of the commercial manganese-based adsorbent powder is 70%, the mass fraction of Ti3C2T x is 10%, and the mass fraction of the viscous solution is 20%, then 300-900 μm hydroxyethyl methacrylate is added to dilute the slurry, and the slurry is stirred for 2 h with a magnetic stirrer. After uniform mixing, pour it on the surface of the porous current collector, scrape it into a film with a spatula, and then cross-link and adhere under the irradiation of ultraviolet light to obtain the lithium extraction electrode LMO-UV.

[0067] Among them, Ti3C2T xis prepared by slowly adding 1-5 g of LiF into 10-50 ml of 5-15 mol / L HCl to form a transparent solution, then slowly adding 0.5-3.5 g of Ti3AlC2, and reacting at 10-50℃ for 15-30 h, followed by adding an appropriate amount of deionized water, centrifuging to remove the upper liquid, and then adding deionized water and centrifuging, repeating several times until the color of the suspension changes from dark green to transparent light green, and then collecting the precipitate, filtering, air-drying, and grinding to obtain the lithium extraction electrode.

[0068] Example 2

[0069] The difference from Example 1 is that commercial manganese-based adsorbent powder, Ti3C2T x and a viscous solution are stirred and mixed into a slurry, wherein the mass fraction of commercial manganese-based adsorbent powder is 75%, the mass fraction of Ti3C2T x is 10%, and the mass fraction of viscous solution is 15%, and the obtained lithium extraction electrode is LMO-1.

[0070] Example 3

[0071] The difference from Example 1 is that commercial manganese-based adsorbent powder, Ti3C2T x and a viscous solution are stirred and mixed into a slurry, wherein the mass fraction of commercial manganese-based adsorbent powder is 80%, the mass fraction of Ti3C2T x is 10%, and the mass fraction of viscous solution is 10%, and the obtained lithium extraction electrode is LMO-2.

[0072] Example 4

[0073] The difference from Example 1 is that commercial manganese-based adsorbent powder, Ti3C2T x and a viscous solution are stirred and mixed into a slurry, wherein the mass fraction of commercial manganese-based adsorbent powder is 85%, the mass fraction of Ti3C2T x is 10%, and the mass fraction of viscous solution is 5%, and the obtained lithium extraction electrode is LMO-3.

[0074] Comparative Example 1

[0075] The difference from Example 1 is that the lithium extraction electrode is not prepared by the ultraviolet light curing method, but is prepared by the traditional slurry coating method to obtain the lithium extraction electrode LMO.

[0076] Figure 3is the linear cyclic voltammetry test of LMO-UV (a), LMO-1 (b), LMO-2 (c), LMO-3 (d), the test conditions are that the electrolyte solution is 1 mol / L LiCI solution, the voltage window is 0-1.1V, the scan rate is 0.5mv / s, the three-electrode system, the porous activated carbon is used as the counter electrode, the saturated calomel electrode is used as the reference electrode, and LMO-UV, LMO-1, LMO-2, LMO-3 are used as the working electrode respectively. As can be seen from the figure, compared with other electrode sheets, LMO-UV has two pairs of obvious redox peaks, which shows that the commercial manganese-based adsorbent powder, Ti3C2T x The effect of delithiation and lithiation is the best when the mass ratio of the thick solution is 7:1:2.

[0077] Figure 4 is the linear cyclic voltammetry test of LMO-UV at 0.1-1mv / s, the test conditions are that the electrolyte solution is 1 mol / L LiCI solution, the voltage window is 0-1.1V, the scan rate is 0.5mv / s, the three-electrode system, the porous activated carbon is used as the counter electrode, the saturated calomel electrode is used as the reference electrode, and LMO-UV is used as the working electrode. LMO-UV still has two pairs of obvious redox peaks at different scan rates, which shows that the lithium extraction electrode prepared under this ratio has good delithiation and lithiation effect.

[0078] The time consumption of LMO prepared by the traditional slurry coating method and LMO-UV prepared by the ultraviolet curing method are compared, wherein the preparation process of LMO is that the commercial manganese-based adsorbent powder, Ti3C2T x and the binder are mixed and stirred by a magnetic stirrer for 12h to obtain a uniform slurry, the slurry is poured on the surface of the porous current collector, and then placed in a 60℃ oven for 8h to obtain the lithium extraction electrode, and the preparation time is about 21h; while the preparation process of LMO-UV is that the photoinitiator, prepolymer, commercial manganese-based adsorbent powder, Ti3C2T x and active diluent are mixed and stirred by a magnetic stirrer for 2h to obtain a uniform slurry, the slurry is poured on the surface of the porous current collector, and then the current collector is placed under the ultraviolet lamp for 5min to obtain the lithium extraction electrode, and the preparation time is about 3h. Compared with the two, the preparation of the electrode by the ultraviolet curing method consumes very little time, which obviously shortens the experimental time.

[0079] Figure 5 (a) is the SEM image of LMO prepared by the traditional slurry coating method; (b) is the SEM image of LMO-UV prepared by the ultraviolet curing method. The active material loading of LMO prepared by the traditional slurry coating method is 2.4mg·cm -2 , but the active material loading of LMO-UV prepared by the ultraviolet curing method can reach 6.8 mg·cm-2 From the SEM images of both, it can be seen that the LMO electrode prepared by traditional slurry coating method has uneven surface loading and low loading capacity, while the LMO-UV electrode prepared by UV curing method has more uniform surface loading and high loading capacity.

[0080] Figure 6 Figure 6 is a comparison chart of the dissolution loss of the LMO electrode prepared by traditional slurry coating method and the LMO-UV electrode prepared by UV curing method. From the chart, it can be seen that the dissolution loss rate of the LMO electrode prepared by traditional slurry coating method is high, while the dissolution loss rate of the LMO-UV electrode prepared by UV curing method is small, and the LMO-UV electrode is more stable during the lithium extraction process.

[0081] Therefore, as described above, the lithium extraction electrode prepared by the above method is superior to the active electrode prepared by the traditional method in terms of active loading capacity, electrode preparation time and electrode dissolution.

[0082] A membrane capacitive device, as shown in the figure, uses the lithium extraction electrode prepared by the above method as the positive electrode, uses a porous activated carbon electrode as the negative electrode, sets a positively charged nanofiltration membrane in front of the positive electrode, and sets an anion exchange membrane in front of the negative electrode.

[0083] The preparation method of the positively charged nanofiltration membrane is as follows:

[0084] Dissolve PEI in deionized water to obtain a transparent aqueous solution, add propylene oxide dropwise to the PEI solution (molar ratio of propylene oxide: PEI = 2:1) under a 5°C water bath using a constant pressure dropping funnel, mechanically stir the reaction for 3-10h, then control the tank temperature to rise to 40°C, evaporate the unreacted propylene oxide to obtain a tertiary aminated PEI solution; then add benzyl chloride to the tertiary aminated PEI solution (molar ratio of benzyl chloride: PEI = 2.5:1) under a 50°C water bath, mechanically stir the reaction for 20-40h, then extract the residual benzyl chloride with ether several times to obtain a QPEI solution; finally, evaporate the water in the solution in a 50°C vacuum oven, and freeze-dry for 10-20h to obtain a transparent QPEI sheet.

[0085] QPEI, Na3PO4, and SDS were dissolved in deionized water to obtain a transparent aqueous solution with a PEI concentration of 0.5-6 wt.% by stirring. TMC was dissolved in n-hexane to obtain a transparent oil solution with a TMC concentration of 0.1-0.5 w / v.% by stirring. The PES base membrane was slowly rinsed with deionized water to clean the membrane surface. After the membrane surface dried, 20-80 ml of the prepared aqueous solution was quickly poured in and maintained for 25-100 seconds. The base membrane was then removed, and excess water on the membrane surface was removed using a flexible silicone roller. The membrane surface was then purged with nitrogen. Then, 20-80 ml of the prepared oil solution was quickly poured in and maintained for 10-70 seconds for interfacial polymerization. The membrane was then quickly transferred to a vacuum oven for hot lamination at 25-100℃ for 1-8 minutes. Finally, the composite nanofiltration membrane was removed and the membrane surface was rinsed with deionized water to obtain a quaternized positively charged nanofiltration membrane.

[0086] Figure 7 These are SEM images of the PES-based membrane and the quaternized positively charged nanofiltration membrane, where (a) is the SEM image of the PES-based membrane and (b) is the SEM image of the quaternized positively charged nanofiltration membrane. From the images, it can be observed that there is a thin composite layer on the surface of the quaternized positively charged nanofiltration membrane.

[0087] Figure 8 This is a graph showing the surface Zeta potentials of the quaternized positively charged nanofiltration membrane and the non-quaternized positively charged nanofiltration membrane at different pH values. The graph shows that due to enhanced deprotonation, the surface Zeta potentials of both composite nanofiltration membranes decrease with increasing pH. The higher Zeta potential is related to the presence of numerous quaternary ammonium groups on the functional layer surface, proving that the quaternized positively charged nanofiltration membrane has a positive surface charge in a neutral filtration scenario. This also confirms the successful preparation of the quaternized positively charged nanofiltration membrane. Furthermore, it is clearly shown that the Zeta potential of the quaternized positively charged nanofiltration membrane is higher than that of the non-quaternized positively charged nanofiltration membrane; the higher charge density enables more efficient magnesium-lithium separation.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that Ti3C2T is not prepared in-house. x Instead, they used commercially purchased Ti3C2T chips. x LMO-4 was prepared.

[0090] Figure 9 This is an impedance comparison graph of LMO-4 and LMO-UV lithium extraction electrodes. The graph shows that the resistance of LMO-UV is less than that of LMO-4, indicating that the Ti3C2T prepared according to the method of this invention... x It has stronger conductivity, which is beneficial for ion transport and improves lithium extraction efficiency.

[0091] The lithium extraction electrode prepared in Example 1 of the present application and the lithium extraction device are connected and then brine is introduced for experiment.

[0092] Figure 10 The retention rate of various ions in the brine after the brine passes through the lithium extraction electrode and the lithium extraction device, and it can be obviously seen from the figure that the present application retains most of the magnesium ions, and has good retention effect on other ions in the brine, greatly improves the separation efficiency of magnesium and lithium, and realizes efficient enrichment of lithium ions.

[0093] The above has exemplarily described the present application, and it should be indicated that any simple transformation, modification or other equivalent replacement which can not cost creative labor of those skilled in the art without departing from the core of the present application falls into the protection scope of the present application.

Claims

1. A method for preparing a lithium extraction electrode, characterized in that, Includes the following steps: (1) The photoinitiator and prepolymer are stirred and mixed to obtain a first viscous solution, and then manganese-based adsorbent powder and Ti3C2T are added to the first viscous solution. x The mixture is stirred to obtain a second viscous solution. Then, an active diluent is added to the second viscous solution and stirring is continued to obtain a mixed slurry. (2) The mixed slurry obtained in step (1) is coated onto a porous current collector, and cross-linked, cured and adhered under ultraviolet light to obtain a lithium extraction electrode; In step (1), the photoinitiator is selected from TPO, the prepolymer is selected from polyurethane acrylate, and the reactive diluent is selected from hydroxyethyl methacrylate; The mass ratio of photoinitiator to prepolymer in the first viscous solution is 1:20 to 1:50; Based on mass percentage, the second viscous solution comprises 70%-85% manganese-based adsorbent powder and 5-10% Ti3C2T. x 5%-20% of the first viscous solution; Add 300-900 μm of reactive diluent to the second viscous solution and continue stirring for 1-4 hours to obtain a mixed slurry; In step (1), Ti3C2T x The preparation method is as follows: 1-5g LiF is added to 10-50ml of 5-15mol / L HCl and stirred to form a transparent solution. Then, 0.5-3.5g Ti3AlC2 is slowly added and reacted at 10-50℃ for 15-30h. Deionized water is then added, the supernatant is removed after centrifugation, and deionized water is added again and centrifuged. This process is repeated several times until the suspension changes from dark green to transparent light green. The precipitate is collected, filtered, dried, and ground to obtain Ti3C2T. x .

2. The preparation method according to claim 1, characterized in that, In step (2), the porous current collector is placed on a flat glass plate, and the prepared slurry obtained in step (1) is poured onto the surface of the porous current collector. The slurry is scraped into a film of 1-10 μm with a scraper. The current collector with the scraped film is placed under a UV lamp for curing for 1-10 min and then the current collector is taken out to obtain the lithium extraction electrode.

3. The preparation method according to claim 1, characterized in that, The distance between the UV lamp and the current collector should be 3-15cm; The wavelength of ultraviolet light from the ultraviolet lamp is 300-350nm.

4. A film capacitor device, characterized in that, The positive electrode is a lithium extraction electrode prepared by the method according to any one of claims 1-3, and the negative electrode is a porous activated carbon electrode from a biomass source, wherein a quaternized positively charged nanofiltration membrane is disposed before the positive electrode, and an anion exchange membrane is disposed before the negative electrode.

5. The membrane capacitor device according to claim 4, characterized in that, The preparation method of porous activated carbon electrode from biomass source is as follows: (A) A first viscous solution is prepared according to the method of any one of claims 1-3, wherein activated carbon and Ti3C2T are added to the first viscous solution. x The mixture is stirred to obtain a third viscous solution, and then an active diluent is added to the third viscous solution and stirring is continued to obtain a second slurry. (B) The second mixture slurry obtained in step (A) is coated onto a porous current collector, and after cross-linking and curing adhesion under ultraviolet light irradiation, a biomass-sourced porous activated carbon electrode is obtained. In the third viscous solution, viscous solution, Ti3C2T x The mass ratio of activated carbon is 1:1:8-2:1:

7.

6. The membrane capacitor device according to claim 5, characterized in that, The preparation method of the quaternized positively charged nanofiltration membrane is an interfacial polymerization method, which includes the following steps: (a) Dissolve PEI in deionized water and stir to obtain a transparent aqueous solution. Add propylene oxide dropwise to the PEI solution in a constant pressure dropping funnel under a 5°C water bath. After stirring for 3-10 hours, raise the temperature of the control tank to 40°C and evaporate the unreacted propylene oxide to obtain a tertiary amination PEI solution. (b) Add benzyl chloride to the tertiary amination PEI solution in a 50°C water bath and stir mechanically for 20-40 h. Then, remove the residual benzyl chloride by multiple extractions with diethyl ether to obtain the QPEI solution. (c) Finally, the water in the solution is evaporated in a vacuum oven at 50°C, and the solution is freeze-dried for 10-20 hours to obtain transparent sheet-like QPEI. (d) Dissolve QPEI, Na3PO4 and SDS in deionized water and stir to obtain a transparent aqueous solution with a PEI concentration of 0.5-6 wt.%; dissolve TMC in n-hexane and stir to obtain a transparent oil solution with a TMC concentration of 0.1-0.5 w / v.%. (e) Slowly rinse the PES base membrane with deionized water to clean the membrane surface. After the membrane surface dries, quickly pour in 20-80 ml of the prepared aqueous solution and maintain for 25-100 s. Remove the base membrane and remove excess water from the membrane surface with a flexible silicone roller. Purge the membrane surface with nitrogen. Then quickly pour in 20-80 ml of the prepared oil solution and maintain the interfacial polymerization reaction for 10-70 s. Then quickly transfer it to a vacuum oven and heat-composite at 25-100℃ for 1-8 min. Finally, remove the composite nanofiltration membrane and rinse the membrane surface with deionized water to obtain a quaternized positively charged nanofiltration membrane. In step (a), the molar ratio of propylene oxide to PEI is 2:1; in step (b), the molar ratio of benzyl chloride to PEI is 2.5:

1.

7. The membrane capacitor device according to claim 5, characterized in that, Both the lithium extraction electrode and the porous activated carbon electrode are spiral wound electrodes, which are prepared by first stacking multiple layers and then rolling them into a multi-layered spiral wound electrode.

8. A circulating system for lithium extraction from salt lakes, characterized in that, It includes a brine lithium extraction-clean water washing-solution recovery three-water circulation system and a salt-coated water electrolyte external circulation system; the brine lithium extraction includes the membrane capacitor device as described in any one of claims 6-7.

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