Preparation method of modified carbon nanotubes and electrodes and their application in lithium extraction from salt lakes

Abstract

The present invention discloses a method for preparing modified carbon nanotubes and electrodes and their application in lithium extraction from salt lakes, belonging to the technical field of lithium extraction from salt lakes. The method for preparing modified carbon nanotubes comprises the following steps: uniformly mixing hydroxylated carbon nanotubes, a silane coupling agent, and a first solvent, extracting by reflux, washing, and drying to obtain a precursor; adding the precursor, a chain transfer agent, a magnesium source, a hydrophilic acrylate monomer, an acrylamide monomer, a crosslinking agent, and an initiator to a second solvent for reaction, first washing with ethanol and deionized water, respectively, and drying, and then washing away the magnesium ions with a hydrochloric acid solution to obtain the modified carbon nanotubes. The modified carbon nanotubes can effectively adsorb magnesium ions on the electrode surface, prevent the magnesium ions from embedding into the electrode material, and inhibit cathode polarization, thereby effectively improving the lithium extraction efficiency and cycle stability of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction from salt lakes, and in particular to a method for preparing modified carbon nanotubes and electrodes and their application in lithium extraction from salt lakes. Background Art

[0002] Electrochemical lithium extraction is the process of using lithium-ion battery cathode materials to produce Li + The electrochemical lithium extraction method is achieved by the principle of transfer between the solid electrode and the liquid electrolyte. It has good selectivity and enrichment capacity. However, in the actual production process, the brine contains a large number of impurity ions, especially cations, which are easily adsorbed on the electrode surface, causing cathode polarization and reducing the efficiency of lithium extraction. In the high magnesium-to-lithium ratio brine, the magnesium ion content is relatively high, and the radius of magnesium ions and lithium ions is relatively close, which makes it easy to embed into the electrode material, reducing the selectivity and cycle performance of the electrode material. Therefore, how to reduce the interference of impurity cations coexisting in the solution and the efficiency of lithium extraction is directly related to the production cost of electrochemical lithium extraction, and also has a significant impact on the subsequent treatment of the resulting lithium-rich solution.

[0003] Related technology discloses a method for preparing a highly conductive porous electrode for lithium extraction from salt lakes, which includes the steps of modifying the binder used in the electrode preparation process by blending inorganic nanoparticles and polar hydrophilic polymer organic matter to improve the hydrophilicity of the binder. During the preparation of the electrode slurry, inorganic salt pore-forming agents are added to form pores of varying sizes on the electrode during the drying process, thereby improving the mass transfer effect of the solution inside the electrode plate. Finally, the surface of the prepared electrode material is chemically modified in a conductive polymer monomer solution, which not only improves the overall conductivity of the electrode, but also improves the overall hydrophilicity of the electrode through secondary modification. The prepared electrode has good permeability, selectivity, conductivity and low-temperature lithium extraction properties, and the current density of the lithium extraction system formed with the electrode has been significantly improved; however, its lithium recovery rate and the magnesium-lithium ratio before and after treatment still need to be improved. Summary of the Invention

[0004] The object of the present invention is to overcome the shortcomings of the prior art and provide a modified carbon nanotube, an electrode preparation method and its application in lithium extraction from salt lakes. The electrode prepared from the modified carbon nanotube is applied to lithium extraction from salt lakes, which can effectively reduce the interference of magnesium ions, reduce cathode polarization, and improve lithium extraction efficiency.

[0005] To achieve the above object, in a first aspect of the present invention, the present invention provides a method for preparing modified carbon nanotubes, comprising the following steps:

[0006] The hydroxylated carbon nanotubes, the silane coupling agent and the first solvent are mixed uniformly, subjected to reflux extraction, washing and drying to obtain a precursor;

[0007] The precursor, chain transfer agent, magnesium source, hydrophilic acrylate monomer, acrylamide monomer, crosslinking agent and initiator are added to the second solvent for reaction. After the reaction is completed, the mixture is washed with ethanol and deionized water, dried, and then washed with hydrochloric acid solution to remove magnesium ions to obtain modified carbon nanotubes.

[0008] As a preferred embodiment of the present invention, the usage ratio of the hydroxylated carbon nanotubes, the silane coupling agent, and the first solvent is 1 g: (1-5) g: (0.1-1) L.

[0009] As a preferred embodiment of the present invention, the silane coupling agent includes at least one of γ-(methacryloyloxy)propyltrimethoxysilane, γ-methacryloyloxypropyltri(trimethylsiloxy)silane, γ-methacryloyloxypropyltriisopropoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, and 3-(methacryloyloxy)propylmethyldiethoxysilane.

[0010] As a preferred embodiment of the present invention, the first solvent includes at least one of ethanol, acetone, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, methyl formate, methyl acetate, dimethylacetamide, ethyl acetate, methyl butyrate, ethyl butyrate, ethyl propionate, propyl formate, methyl propionate, pyridine, diphenyl ether, dimethyl sulfoxide, and sulfolane.

[0011] As a preferred embodiment of the present invention, the method for preparing hydroxylated carbon nanotubes comprises the following steps:

[0012] (1) uniformly mixing a nitric acid solution, a sulfuric acid solution, and water to obtain a mixed acid solution, and adding carbon nanotubes to the mixed acid solution to perform a hydrothermal reaction;

[0013] (2) dilute with water, let stand, and remove the supernatant;

[0014] (3) Repeat step (2) until the pH of the solution is 1.5-2.5, filter, wash to neutrality, and dry to obtain hydroxylated carbon nanotubes.

[0015] As a preferred embodiment of the present invention, the volume ratio of the nitric acid solution, the sulfuric acid solution, and water is 1:(1-4):(2-6).

[0016] As a preferred embodiment of the present invention, the solid-liquid ratio of the carbon nanotubes to the mixed acid solution is 1 mg: (0.1-10) mL.

[0017] As a preferred embodiment of the present invention, the mass fraction of the sulfuric acid solution is 70-98%.

[0018] As a preferred embodiment of the present invention, the mass fraction of the nitric acid solution is 60-75%.

[0019] As a preferred embodiment of the present invention, the mass ratio of the precursor, the chain transfer agent, and the second solvent is (0.003-0.009):(0.002-0.006):1.

[0020] As a preferred embodiment of the present invention, the following substances are added to every 1L of the second solvent: 10-20 mmol / L of a magnesium source, 25-75 mmol / L of a hydrophilic acrylate monomer, 25-75 mmol / L of an acrylamide monomer, 50-150 mmol / L of a cross-linking agent, and 2-6 mmol / L of an initiator.

[0021] As a preferred embodiment of the present invention, the magnesium source includes at least one of magnesium chloride, magnesium oxide, magnesium carbonate, magnesium hydroxide, and magnesium sulfate.

[0022] As a preferred embodiment of the present invention, the hydrophilic acrylic ester monomer includes at least one of methyl methacrylate, hydroxyethyl methacrylate, and hydroxyethyl acrylate.

[0023] As a preferred embodiment of the present invention, the acrylamide monomer includes N-n-propyl acrylamide.

[0024] As a preferred embodiment of the present invention, the cross-linking agent includes ethylene glycol dimethacrylate.

[0025] As a preferred embodiment of the present invention, the initiator includes azobisisobutyronitrile.

[0026] As a preferred embodiment of the present invention, the second solvent includes at least one of methanol, ethanol, propanol, butanediol, and water.

[0027] As a preferred embodiment of the present invention, the method for preparing the chain transfer agent comprises the following steps:

[0028] Mixing carbon disulfide, tetrabutylammonium hydrogen sulfate, and the third solvent to obtain a mixed solution;

[0029] Sodium hydroxide solution is added to the mixed solution to carry out a first reaction, and then hydrochloric acid solution and water are added to carry out a second reaction, followed by washing and drying to obtain a chain transfer agent.

[0030] As a preferred embodiment of the present invention, the molar ratio of carbon disulfide to tetrabutylammonium hydrogen sulfate is (4-8):1;

[0031] The volume ratio of carbon disulfide to the third solvent is 1:(10-30); and / or

[0032] The ratio of the sodium hydroxide solution to the mixed solution is 1:(1-4); and / or

[0033] The volume ratio of the sodium hydroxide solution, the hydrochloric acid solution and the water is 1:(1-2):(3-8).

[0034] In a second aspect of the present invention, the present invention provides a method for preparing an electrode, comprising the following steps:

[0035] The modified carbon nanotubes are prepared into a modified carbon nanotube slurry with a mass concentration of 5 to 20%;

[0036] The electrode active material and the modified carbon nanotube slurry are mixed evenly, and then a conductive agent, chopped carbon fibers, a pore-forming agent, a binder and a fourth solvent are added to prepare a positive electrode material slurry. The positive electrode material slurry is evenly coated on the current collector and dried to obtain an electrode;

[0037] The modified carbon nanotubes are prepared by the above-mentioned method for preparing modified carbon nanotubes;

[0038] The mass ratio of the electrode active material, modified carbon nanotubes, conductive agent, chopped carbon fibers, pore-forming agent, binder and fourth solvent is 100: (1.5-10): (1.5-10): (1-4): (10-30): (5-20): (100-200).

[0039] The modified carbon nanotubes are prepared by the above-mentioned method for preparing modified carbon nanotubes;

[0040] The mass ratio of the electrode active material, modified carbon nanotubes, conductive agent, chopped carbon fibers, pore-forming agent, binder and fourth solvent is 100: (1.5-10): (1.5-10): (1-4): (10-30): (5-20): (100-200).

[0041] As a preferred embodiment of the present invention, the electrode active material includes LiMn2O4, LiFePO4, LiNi x Co y Mn z At least one of O2, wherein x+y+z=1.

[0042] As a preferred embodiment of the present invention, the conductive agent includes at least one of acetylene black and carbon black.

[0043] As a preferred embodiment of the present invention, the pore-forming agent includes ammonium bicarbonate or ammonium carbonate.

[0044] As a preferred embodiment of the present invention, the binder includes polyvinylidene fluoride.

[0045] As a preferred embodiment of the present invention, the fourth solvent includes N-methylpyrrolidone.

[0046] In a third aspect of the present invention, the present invention provides the use of an electrode prepared by the above-mentioned electrode preparation method in lithium extraction from salt lakes.

[0047] In a fourth aspect of the present invention, the present invention provides a method for extracting lithium from a salt lake, comprising the following steps:

[0048] The above-mentioned electrode is used as the anode and the nickel foam is used as the cathode. The electrodes are placed in a NaCl solution and a voltage is applied across the electrodes until the current density is less than 0.5 A / m 2 , obtaining a delithiation electrode;

[0049] The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and the delithiated electrode and the corresponding anode are placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine is injected into the cathode chamber, and NaCl solution is injected into the anode chamber. Voltage is applied to the anode and cathode, and electrolysis is carried out at a temperature of >10°C for 3 to 8 hours. Then, the lithium-containing brine in the cathode chamber is replaced with water, and the mixture is shaken in a water bath of <10°C for 2 to 5 hours. Then, the water in the cathode chamber is replaced with KCl solution, and the positive and negative poles of the electrodes connected to the power supply are interchanged. Voltage is applied for electrolysis to obtain a lithium-rich solution.

[0050] The beneficial effects of the present invention are as follows: the present invention premixes hydroxylated carbon nanotubes with a silane coupling agent to obtain a precursor, then reacts the precursor, a chain transfer agent, a magnesium source, a hydrophilic acrylate monomer, an acrylamide monomer, a crosslinking agent, and an initiator, first washes away impurities, and then washes away magnesium ions, thereby obtaining carbon nanotubes loaded with magnesium ion-imprinted polymers (i.e., modified carbon nanotubes), which can effectively adsorb magnesium ions on the electrode surface, prevent magnesium ions from being embedded in the electrode material, and inhibit cathode polarization, thereby effectively improving the lithium extraction efficiency and cycle stability of the electrode, while also increasing the conductivity of the electrode, and its porous multi-layer structure can serve as a lithium ion transmission channel. DETAILED DESCRIPTION

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0052] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0053] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0054] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0055] In the present invention, unless otherwise stated, all parts are parts by mass.

[0056] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0057] An embodiment of the present invention provides a method for preparing modified carbon nanotubes, comprising the following steps:

[0058] The hydroxylated carbon nanotubes, the silane coupling agent and the first solvent are mixed uniformly, subjected to reflux extraction, washing and drying to obtain a precursor;

[0059] The precursor, chain transfer agent, magnesium source, hydrophilic acrylate monomer, acrylamide monomer, crosslinking agent and initiator are added to the second solvent for reaction. After the reaction is completed, the mixture is washed with ethanol and deionized water, dried, and then washed with hydrochloric acid solution to remove magnesium ions to obtain modified carbon nanotubes.

[0060] The present invention premixes hydroxylated carbon nanotubes with a silane coupling agent to obtain a precursor, then reacts the precursor, a chain transfer agent, a magnesium source, a hydrophilic acrylate monomer, an acrylamide monomer, a crosslinking agent, and an initiator, first washes away impurities, and then washes away magnesium ions, thereby obtaining carbon nanotubes loaded with magnesium ion-imprinted polymers (i.e., modified carbon nanotubes). The carbon nanotubes can effectively adsorb magnesium ions on the electrode surface, prevent magnesium ions from embedding into the electrode material, and inhibit cathode polarization, thereby effectively improving the lithium extraction efficiency and cycle stability of the electrode, while also increasing the conductivity of the electrode. Moreover, the porous multi-layer structure can serve as a lithium ion transmission channel.

[0061] Temperature-responsive magnesium ion imprinted polymers were prepared by grafting thermosensitive acrylamide functional monomers, which can be used to adsorb and desorb magnesium ions using temperature. Under the condition of T < 10 ° C, N-propyl acrylamide is in an expanded state, which makes the grafted acrylamide away from Mg 2+ , to achieve desorption of Mg 2+On the contrary, under the condition of T>10℃, N-propyl acrylamide is in a shrinking state, which makes the grafted acrylamide close to Mg 2+ , to achieve Mg 2+ The adsorption effect is achieved, so it is possible to extract lithium while adsorbing magnesium ions on the electrode surface. When lithium ions are released from the electrode material, the magnesium ions are first desorbed at a certain temperature and then a reverse electric field is applied to release the lithium ions and separate magnesium and lithium.

[0062] Methyl methacrylate with hydrophilicity as a functional monomer can improve the hydrophilicity of the ion-imprinted polymer, thereby improving the hydrophilicity of the carbon nanotubes coated on the electrode surface.

[0063] In one embodiment, the usage ratio of the hydroxylated carbon nanotubes, the silane coupling agent, and the first solvent is 1 g: (1-5) g: (0.1-1) L.

[0064] In one embodiment, the mixing method of the hydroxylated carbon nanotubes, the silane coupling agent, and the first solvent includes but is not limited to stirring and ball milling. It should be noted that as long as the three are mixed evenly, the present invention does not specifically limit the specific mixing method. Those skilled in the art can select a specific mixing method according to actual needs.

[0065] For example, the reflux extraction can be performed in a water bath or an oil bath, the temperature of the reflux extraction is 50 to 70° C., and the time of the reflux extraction is 12 to 36 hours.

[0066] In one embodiment, the silane coupling agent includes at least one of γ-(methacryloyloxy)propyltrimethoxysilane, γ-methacryloyloxypropyltri(trimethylsiloxy)silane, γ-methacryloyloxypropyltriisopropoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, and 3-(methacryloyloxy)propylmethyldiethoxysilane.

[0067] In one embodiment, the first solvent includes at least one of ethanol, acetone, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, methyl formate, methyl acetate, dimethylacetamide, ethyl acetate, methyl butyrate, ethyl butyrate, ethyl propionate, propyl formate, methyl propionate, pyridine, diphenyl ether, dimethyl sulfoxide, and cyclopentane.

[0068] In one embodiment, the method for preparing hydroxylated carbon nanotubes comprises the following steps:

[0069] (1) uniformly mixing a nitric acid solution, a sulfuric acid solution, and water to obtain a mixed acid solution, and adding carbon nanotubes to the mixed acid solution to perform a hydrothermal reaction;

[0070] (2) dilute with water, let stand, and remove the supernatant;

[0071] (3) Repeat step (2) until the pH of the solution is 1.5-2.5, filter, wash to neutrality, and dry to obtain hydroxylated carbon nanotubes.

[0072] The hydroxylated carbon nanotubes prepared by the present invention have abundant hydroxyl groups on their surfaces and have certain hydrophilicity. At the same time, the surface area is large, which increases the reactive groups on the surface, thereby chemically grafting silane coupling agents, reducing agglomeration, and facilitating the subsequent loading of hydrophilic acrylate monomers and acrylamide monomers.

[0073] In one embodiment, the volume ratio of nitric acid solution, sulfuric acid solution and water is 1:(1-4):(2-6).

[0074] In one embodiment, the solid-liquid ratio of carbon nanotubes to mixed acid solution is 1 mg: (0.1-10) mL.

[0075] In one embodiment, the mass fraction of the sulfuric acid solution is 70-98%.

[0076] In one embodiment, the mass fraction of the nitric acid solution is 60-75%.

[0077] In one embodiment, the temperature of the hydrothermal reaction is 100-150° C., and the time of the hydrothermal reaction is 1-5 hours.

[0078] In one embodiment, the mass ratio of the precursor, the chain transfer agent, and the second solvent is (0.003-0.009):(0.002-0.006):1.

[0079] In one embodiment, the following substances are added to every 1 L of the second solvent: 10-20 mmol / L of a magnesium source, 25-75 mmol / L of a hydrophilic acrylate monomer, 25-75 mmol / L of an acrylamide monomer, 50-150 mmol / L of a cross-linking agent, and 2-6 mmol / L of an initiator.

[0080] In one embodiment, the magnesium source includes at least one of magnesium chloride, magnesium oxide, magnesium carbonate, magnesium hydroxide, and magnesium sulfate.

[0081] In one embodiment, the hydrophilic acrylic ester monomer includes at least one of methyl methacrylate, hydroxyethyl methacrylate, and hydroxyethyl acrylate.

[0082] In one embodiment, the acrylamide monomer includes N-propyl acrylamide.

[0083] In one embodiment, the crosslinking agent comprises ethylene glycol dimethacrylate.

[0084] In one embodiment, the initiator comprises azobisisobutyronitrile.

[0085] In one embodiment, the second solvent includes at least one of methanol, ethanol, propanol, butanediol, and water.

[0086] In one embodiment, the method for preparing a chain transfer agent comprises the following steps:

[0087] Mixing carbon disulfide, tetrabutylammonium hydrogen sulfate, and the third solvent to obtain a mixed solution;

[0088] Sodium hydroxide solution is added to the mixed solution to carry out a first reaction, and then hydrochloric acid solution and water are added to carry out a second reaction, followed by washing and drying to obtain a chain transfer agent.

[0089] The chain transfer agent prepared by the present invention enables the subsequent polymerization reaction to be effectively controlled, thereby forming a magnesium ion imprinted polymer layer with controllable and uniform thickness on the surface of the carbon nanotube, and the polymer is evenly distributed.

[0090] In one embodiment, the molar ratio of carbon disulfide to tetrabutylammonium hydrogen sulfate is (4-8):1;

[0091] The volume ratio of carbon disulfide to the third solvent is 1:(10-30); and / or

[0092] The ratio of sodium hydroxide solution to the mixed solution is 1:(1-4); and / or

[0093] The volume ratio of sodium hydroxide solution, hydrochloric acid solution and water is 1:(1-2):(3-8).

[0094] In one embodiment, the third solvent includes at least one of acetone, chloroform, petroleum ether, tetrahydrofuran, 2-methyltetrahydrofuran, methyl formate, methyl acetate, dimethylacetamide, ethyl acetate, methyl butyrate, and ethyl butyrate.

[0095] The first reaction is carried out under stirring; and the second reaction is carried out under anaerobic conditions.

[0096] In a second aspect of the present invention, the present invention provides a method for preparing an electrode, comprising the following steps:

[0097] The modified carbon nanotubes are prepared into a modified carbon nanotube slurry with a mass concentration of 5 to 20%;

[0098] The electrode active material and the modified carbon nanotube slurry are mixed evenly, and then a conductive agent, chopped carbon fibers, a pore-forming agent, a binder and a fourth solvent are added to prepare a positive electrode material slurry. The positive electrode material slurry is evenly coated on the current collector and dried to obtain an electrode;

[0099] Wherein, the modified carbon nanotubes are prepared by the above-mentioned preparation method of modified carbon nanotubes;

[0100] The mass ratio of the electrode active material, modified carbon nanotubes, conductive agent, chopped carbon fibers, pore-forming agent, binder and fourth solvent is 100: (1.5-10): (1.5-10): (1-4): (10-30): (5-20): (100-200).

[0101] In one embodiment, the electrode active material includes LiMn2O4, LiFePO4, LiNi x Co y Mn z At least one of O2, wherein x+y+z=1.

[0102] In one embodiment, the conductive agent includes at least one of acetylene black and carbon black.

[0103] In one embodiment, the pore-forming agent includes at least one of ammonium bicarbonate and ammonium carbonate.

[0104] In one embodiment, the binder comprises polyvinylidene fluoride.

[0105] In one embodiment, the fourth solvent comprises N-methylpyrrolidone.

[0106] In a third aspect of the present invention, the present invention provides the use of an electrode prepared by the above-mentioned electrode preparation method in lithium extraction from salt lakes.

[0107] In a fourth aspect of the present invention, the present invention provides a method for extracting lithium from a salt lake, comprising the following steps:

[0108] The above electrode was used as anode and nickel foam was used as cathode in NaCl solution. Voltage was applied across the electrodes until the current density was lower than 0.5A / m 2 , obtaining a delithiation electrode;

[0109] The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and the delithiated electrode and the corresponding anode are placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine is injected into the cathode chamber, and NaCl solution is injected into the anode chamber. Voltage is applied to the anode and cathode, and electrolysis is carried out at a temperature of >10°C for 3 to 8 hours. Then, the lithium-containing brine in the cathode chamber is replaced with water, and the mixture is shaken in a water bath of <10°C for 2 to 5 hours. Then, the water in the cathode chamber is replaced with KCl solution, and the positive and negative poles of the electrodes connected to the power supply are interchanged. Voltage is applied for electrolysis to obtain a lithium-rich solution.

[0110] Illustratively, the concentration of the NaCl solution used in the process of extracting lithium from salt lakes is 18-25 g / L.

[0111] Illustratively, the concentration of the KCl solution used in the process of extracting lithium from salt lakes is 20 to 80 mmol / L.

[0112] The following examples are provided to facilitate understanding of the present invention. These examples are not provided to limit the scope of the claims.

[0113] Example 1

[0114] A method for preparing hydroxylated carbon nanotubes comprises the following steps:

[0115] (1) Water, 98% sulfuric acid solution, and 75% nitric acid solution were added to a reactor in a volume ratio of 3:2:1, and allowed to stand at room temperature to obtain a mixed acid solution. Carbon nanotubes were added to the reactor and subjected to a hydrothermal reaction at 120°C for 3 hours.

[0116] The solid-liquid ratio of carbon nanotubes to mixed acid solution is 10 mg:10 mL;

[0117] (2) adding water to dilute, letting it stand, and removing the supernatant, wherein the amount of water added is 50% of the total volume of the material in the reactor;

[0118] (3) Repeat step (2) until the pH of the solution is 2, filter, wash with anhydrous ethanol until neutral, and dry to obtain hydroxylated carbon nanotubes.

[0119] Example 2

[0120] A method for preparing a chain transfer agent comprises the following steps:

[0121] (1) Prepare a solvent by mixing acetone, chloroform, and petroleum ether in a volume ratio of 5.5:7:30 and set aside;

[0122] (2) 2 mL of carbon disulfide, 24 g of tetrabutylammonium hydrogen sulfate, and 42.5 mL of a solvent were mixed uniformly according to the amount ratio to obtain a mixed solution. 20 mL of a 50% by mass sodium hydroxide solution was added dropwise to the mixed solution, and the mixture was stirred for 9 hours. After the reaction was completed, 100 mL of water and 30 mL of concentrated hydrochloric acid were added, and the mixture was reacted under anaerobic conditions for 30 minutes. The mixture was filtered, washed with anhydrous ethanol and water, and then dried to obtain a chain transfer agent.

[0123] Example 3

[0124] A method for extracting lithium from a salt lake comprises the following steps:

[0125] (1) 1 g of hydroxylated carbon nanotubes, 3 g of γ-(methacryloyloxy)propyltrimethoxysilane, and 0.6 L of anhydrous ethanol were mixed uniformly, refluxed in an oil bath at 60°C for 24 h, washed with anhydrous ethanol, and dried to obtain a precursor;

[0126] (2) The precursor, chain transfer agent, magnesium chloride, methyl methacrylate, N-propyl acrylamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile were added to a 50% methanol solution and reacted in an oil bath at 60°C under anaerobic conditions for 12 h. The product was washed with anhydrous ethanol and deionized water, and dried. The magnesium ions were then washed with a 2 mol / L hydrochloric acid solution, and the product was washed with deionized water until neutral. After drying, the modified carbon nanotubes were obtained.

[0127] The mass ratio of the precursor, the chain transfer agent, and the 50% methanol solution is 0.006:0.004:1.

[0128] Each 1L of 50% methanol solution contains: 15mmol / L of magnesium chloride, 50mmol / L of methyl methacrylate, 50mmol / L of N-n-propyl acrylamide, 100mmol / L of ethylene glycol dimethacrylate, and 4mmol / L of azobisisobutyronitrile.

[0129] The hydroxylated carbon nanotubes in this embodiment are the hydroxylated carbon nanotubes prepared in Example 1.

[0130] The chain transfer agent in this embodiment is the chain transfer agent prepared in Example 2.

[0131] (3) 3.25 g of modified carbon nanotubes were prepared into a slurry with a solid content of 10% using N-methylpyrrolidone. The slurry was evenly mixed with 50 g of LiFePO4 electrode active material. 5 g of acetylene black, 1 g of short carbon fiber, 10 g of ammonium bicarbonate, 5 g of PVDF and 75 g of N-methylpyrrolidone were added to prepare an electrode slurry. The slurry was then heated to 100 mg / cm 2The coating density is uniformly coated on the current collector, first dried at 70°C for 3 hours and then dried at 100°C for 5 hours to form a carbon nanotube-coated electrode loaded with magnesium ion imprinted polymer.

[0132] (4) The electrode in step (3) was used as the anode and the nickel foam was used as the cathode. The solution was placed in a 20 g / L NaCl solution and a voltage of 1 V was applied across the electrodes until the current density was lower than 0.5 A / m 2 , obtaining a delithiation electrode;

[0133] The electrolysis device was separated into an anode chamber and a cathode chamber by an anion exchange membrane. The delithiated electrode and the corresponding anode were placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine was injected into the cathode chamber, and 20 g / L NaCl solution was injected into the anode chamber. A voltage of 0.6 V was applied to the anode and cathode, and electrolysis was carried out at a temperature of 25°C for 5 hours. Then, the lithium-containing brine in the cathode chamber was replaced with water, and the mixture was shaken in a 6°C water bath for 3 hours. The magnesium ions were released into the deionized water. Subsequently, the water in the cathode chamber was replaced with a 50 mmol / L KCl solution (50 mmol / L KCl solution was the recovery liquid). The positive and negative poles of the two electrodes connected to the power supply were interchanged, and a voltage of 0.6 V was applied for electrolysis for 5 hours. The lithium ions in the lithium-embedded electrode were released into the recovery liquid to obtain a lithium-rich solution.

[0134] Example 4

[0135] A method for extracting lithium from a salt lake comprises the following steps:

[0136] (1) 1 g of hydroxylated carbon nanotubes, 3 g of γ-(methacryloyloxy)propyltrimethoxysilane, and 0.6 L of anhydrous ethanol were mixed uniformly, refluxed in an oil bath at 60°C for 24 h, washed with anhydrous ethanol, and dried to obtain a precursor;

[0137] (2) The precursor, chain transfer agent, magnesium chloride, methyl methacrylate, N-propyl acrylamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile were added to a 50% methanol solution and reacted in an oil bath at 60°C under anaerobic conditions for 12 h. The product was washed with anhydrous ethanol and deionized water, dried, and then the magnesium ions were washed with a 2 mol / L hydrochloric acid solution. The product was washed with deionized water until neutral and dried to obtain modified carbon nanotubes.

[0138] The mass ratio of the precursor, the chain transfer agent, and the 50% methanol solution is 0.006:0.002:1.

[0139] Each 1L of 50% methanol solution contains: 10mmol / L of magnesium chloride, 25mmol / L of methyl methacrylate, 25mmol / L of N-n-propyl acrylamide, 50mmol / L of ethylene glycol dimethacrylate, and 2mmol / L of azobisisobutyronitrile.

[0140] The hydroxylated carbon nanotubes in this embodiment are the hydroxylated carbon nanotubes prepared in Example 1.

[0141] The chain transfer agent in this embodiment is the chain transfer agent prepared in Example 2.

[0142] (3) 5 g of modified carbon nanotubes were prepared into a slurry with a solid content of 10% using N-methylpyrrolidone. The slurry was evenly mixed with 50 g of LiFePO4 electrode active material. 5 g of acetylene black, 1 g of short carbon fiber, 10 g of ammonium bicarbonate, 5 g of PVDF and 75 g of N-methylpyrrolidone were added to prepare an electrode slurry. The slurry was then heated to 100 mg / cm 2 The coating density is uniformly coated on the current collector, first dried at 70°C for 3 hours and then dried at 100°C for 5 hours to form a carbon nanotube-coated electrode loaded with magnesium ion imprinted polymer.

[0143] (4) The electrode in step (3) was used as the anode and the nickel foam was used as the cathode. The solution was placed in a 20 g / L NaCl solution and a voltage of 1 V was applied across the electrodes until the current density was lower than 0.5 A / m 2 , obtaining a delithiation electrode;

[0144] The electrolysis device was separated into an anode chamber and a cathode chamber by an anion exchange membrane. The delithiated electrode and the corresponding anode were placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine was injected into the cathode chamber, and 20 g / L NaCl solution was injected into the anode chamber. A voltage of 0.9 V was applied to the anode and cathode, and electrolysis was carried out at a temperature of 20°C for 6 hours. Then, the lithium-containing brine in the cathode chamber was replaced with water, and the mixture was shaken in a 4°C water bath for 4 hours. The magnesium ions were released into the deionized water. Subsequently, the water in the cathode chamber was replaced with a 50 mmol / L KCl solution (50 mmol / L KCl solution was the recovery liquid). The positive and negative poles of the two electrodes were connected to the power supply interchangeably, and a voltage of 0.9 V was applied for electrolysis for 6 hours. The lithium ions in the lithium-embedded electrode were released into the recovery liquid to obtain a lithium-rich solution.

[0145] Example 5

[0146] A method for extracting lithium from a salt lake comprises the following steps:

[0147] (1) 1 g of hydroxylated carbon nanotubes, 3 g of γ-(methacryloyloxy)propyltrimethoxysilane, and 0.6 L of anhydrous ethanol were mixed uniformly, refluxed in an oil bath at 60°C for 24 h, washed with anhydrous ethanol, and dried to obtain a precursor;

[0148] (2) The precursor, chain transfer agent, magnesium chloride, methyl methacrylate, N-propyl acrylamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile were added to a 50% methanol solution and reacted in an oil bath at 60°C under anaerobic conditions for 12 h. The product was washed with anhydrous ethanol and deionized water, dried, and then the magnesium ions were washed with a 2 mol / L hydrochloric acid solution. The product was washed with deionized water until neutral and dried to obtain modified carbon nanotubes.

[0149] The mass ratio of the precursor, the chain transfer agent, and the 50% methanol solution is 0.009:0.006:1.

[0150] Each 1L of 50% methanol solution contains: 20mmol / L of magnesium chloride, 75mmol / L of methyl methacrylate, 75mmol / L of N-n-propyl acrylamide, 150mmol / L of ethylene glycol dimethacrylate, and 6mmol / L of azobisisobutyronitrile.

[0151] The hydroxylated carbon nanotubes in this embodiment are the hydroxylated carbon nanotubes prepared in Example 1.

[0152] The chain transfer agent in this embodiment is the chain transfer agent prepared in Example 2.

[0153] (3) 1.5 g of modified carbon nanotubes were prepared into a slurry with a solid content of 10% using N-methylpyrrolidone. The slurry was evenly mixed with 50 g of LiFePO4 electrode active material. 5 g of acetylene black, 1 g of short carbon fiber, 10 g of ammonium bicarbonate, 5 g of PVDF and 75 g of N-methylpyrrolidone were added to prepare an electrode slurry. The slurry was then heated to 100 mg / cm 2 The coating density is uniformly coated on the current collector, first dried at 70°C for 3 hours and then dried at 100°C for 5 hours to form a carbon nanotube-coated electrode loaded with magnesium ion imprinted polymer.

[0154] (4) The electrode in step (3) was used as the anode and the nickel foam was used as the cathode. The solution was placed in a 20 g / L NaCl solution and a voltage of 1 V was applied across the electrodes until the current density was lower than 0.5 A / m 2 , obtaining a delithiation electrode;

[0155] The electrolysis device was separated into an anode chamber and a cathode chamber by an anion exchange membrane. The delithiated electrode and the corresponding anode were placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine was injected into the cathode chamber, and 20 g / L NaCl solution was injected into the anode chamber. A voltage of 0.4 V was applied to the anode and cathode, and electrolysis was carried out at a temperature of 35°C for 8 hours. Then, the lithium-containing brine in the cathode chamber was replaced with water, and the mixture was shaken in a 7°C water bath for 2 hours. The magnesium ions were released into the deionized water. Subsequently, the water in the cathode chamber was replaced with a 50 mmol / L KCl solution (50 mmol / L KCl solution was the recovery liquid). The positive and negative poles of the two electrodes were connected to the power supply interchangeably, and a voltage of 0.4 V was applied for electrolysis for 8 hours. The lithium ions in the lithium-embedded electrode were released into the recovery liquid to obtain a lithium-rich solution.

[0156] Example 6

[0157] A method for extracting lithium from a salt lake comprises the following steps:

[0158] (1) 1 g of hydroxylated carbon nanotubes, 3 g of γ-(methacryloyloxy)propyltrimethoxysilane, and 0.6 L of anhydrous ethanol were mixed uniformly, refluxed in an oil bath at 60°C for 24 h, washed with anhydrous ethanol, and dried to obtain a precursor;

[0159] (2) The precursor, chain transfer agent, magnesium chloride, methyl methacrylate, N-propyl acrylamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile were added to a 50% methanol solution and reacted in an oil bath at 60°C under anaerobic conditions for 12 h. The product was washed with anhydrous ethanol and deionized water, dried, and then the magnesium ions were washed with a 2 mol / L hydrochloric acid solution. The product was washed with deionized water until neutral and dried to obtain modified carbon nanotubes.

[0160] The mass ratio of the precursor, the chain transfer agent, and the 50% methanol solution is 0.006:0.004:1.

[0161] Each 1L of 50% methanol solution contains: 15mmol / L of magnesium chloride, 50mmol / L of methyl methacrylate, 50mmol / L of N-n-propyl acrylamide, 100mmol / L of ethylene glycol dimethacrylate, and 4mmol / L of azobisisobutyronitrile.

[0162] The hydroxylated carbon nanotubes in this embodiment are the hydroxylated carbon nanotubes prepared in Example 1.

[0163] The chain transfer agent in this embodiment is the chain transfer agent prepared in Example 2.

[0164] (3) 5 g of modified carbon nanotubes were prepared into a slurry with a solid content of 10% using N-methylpyrrolidone. The slurry was evenly mixed with 50 g of LiFePO4 electrode active material. 5 g of acetylene black, 1 g of short carbon fiber, 10 g of ammonium bicarbonate, 5 g of PVDF and 75 g of N-methylpyrrolidone were added to prepare an electrode slurry. The slurry was then heated to 100 mg / cm 2 The coating density is uniformly coated on the current collector, first dried at 70°C for 3 hours and then dried at 100°C for 5 hours to form a carbon nanotube-coated electrode loaded with magnesium ion imprinted polymer.

[0165] (4) The electrode in step (3) was used as the anode and the nickel foam was used as the cathode. The solution was placed in a 20 g / L NaCl solution and a voltage of 1 V was applied across the electrodes until the current density was lower than 0.5 A / m 2 , obtaining a delithiation electrode;

[0166] The electrolysis device was separated into an anode chamber and a cathode chamber by an anion exchange membrane. The delithiated electrode and the corresponding anode were placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine was injected into the cathode chamber, and 20 g / L NaCl solution was injected into the anode chamber. A voltage of 0.7 V was applied to the anode and cathode, and electrolysis was carried out at a temperature of 30°C for 3 hours. Then, the lithium-containing brine in the cathode chamber was replaced with water, and the mixture was shaken in a 9°C water bath for 5 hours. The magnesium ions were released into the deionized water. Subsequently, the water in the cathode chamber was replaced with a 50 mmol / L KCl solution (50 mmol / L KCl solution was the recovery liquid). The positive and negative poles of the two electrodes connected to the power supply were interchanged, and a voltage of 0.7 V was applied for electrolysis for 3 hours. The lithium ions in the lithium-embedded electrode were released into the recovery liquid to obtain a lithium-rich solution.

[0167] Comparative Example 1

[0168] The difference between Comparative Example 1 and Example 3 is that carbon nanotubes are used in place of modified carbon nanotubes in Comparative Example 1, and all other aspects are the same.

[0169] Test Case

[0170] The same lithium-containing brine was used to extract lithium using the methods of Examples 3 to 6 and Comparative Example 1, respectively. The lithium ion concentration and magnesium ion concentration before and after electrolysis were measured using an inductively coupled plasma spectrometer (ICP), as shown in Table 1.

[0171] Table 1

[0172]

[0173] It can be seen from the examples and comparative examples that the lithium recovery rates in the examples are all greater than 90%, the concentration of magnesium ions in the recovered liquid of Example 3 is reduced by 0.23 g / L compared with that of the comparative example, the impurity content in the recovered liquid is reduced, the purity of the lithium ions is improved, and the recovered liquid contains a higher content of magnesium ions, indicating that during the lithium extraction process, the magnesium ion imprinted polymer adsorbs magnesium ions on the electrode surface, prevents magnesium ions from entering the electrode material, reduces cathode polarization, and improves lithium extraction efficiency.

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing modified carbon nanotubes, characterized in that: The following steps are involved: The hydroxylated carbon nanotubes, the silane coupling agent and the first solvent are mixed uniformly, subjected to reflux extraction, washing and drying to obtain a precursor; The precursor, chain transfer agent, magnesium source, hydrophilic acrylate monomer, acrylamide monomer, crosslinking agent, and initiator are added to a second solvent to react. After the reaction is completed, the mixture is washed with ethanol and deionized water, dried, and then washed with hydrochloric acid solution to remove magnesium ions to obtain modified carbon nanotubes. The amount ratio of the hydroxylated carbon nanotubes, the silane coupling agent, and the first solvent is 1g: (1-5)g: (0.1-1)L; The mass ratio of the precursor, the chain transfer agent, and the second solvent is (0.003-0.009): (0.002-0.006): 1; The following substances are added to every 1L of the second solvent: 10-20mmol / L of a magnesium source, 25-75mmol / L of a hydrophilic acrylate monomer, 25-75mmol / L of an acrylamide monomer, 50-150mmol / L of a crosslinking agent, and 2-6mmol / L of an initiator.

2. The method for preparing modified carbon nanotubes according to claim 1, wherein: The silane coupling agent includes at least one of γ-(methacryloyloxy)propyltrimethoxysilane, γ-methacryloyloxypropyltri(trimethylsiloxy)silane, γ-methacryloyloxypropyltriisopropoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, and 3-(methacryloyloxy)propylmethyldiethoxysilane; and / or The first solvent includes at least one of ethanol, acetone, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, methyl formate, methyl acetate, dimethylacetamide, ethyl acetate, methyl butyrate, ethyl butyrate, ethyl propionate, propyl formate, methyl propionate, pyridine, diphenyl ether, dimethyl sulfoxide, and sulfolane.

3. The method for preparing modified carbon nanotubes according to claim 1, wherein: The preparation method of the hydroxylated carbon nanotubes comprises the following steps: (1) uniformly mixing a nitric acid solution, a sulfuric acid solution, and water to obtain a mixed acid solution, and adding carbon nanotubes to the mixed acid solution to perform a hydrothermal reaction; (2) dilute with water, let stand, and remove the supernatant; (3) Repeat step (2) until the pH of the solution is 1.5-2.5, filter, wash to neutrality, and dry to obtain hydroxylated carbon nanotubes.

4. The method for preparing modified carbon nanotubes according to claim 3, wherein: The volume ratio of the nitric acid solution, the sulfuric acid solution and the water is 1:(1-4):(2-6); and / or The solid-liquid ratio of the carbon nanotubes to the mixed acid solution is 1 mg: (0.1-10) mL; and / or The mass fraction of the sulfuric acid solution is 70 to 98%; and / or The mass fraction of the nitric acid solution is 60-75%.

5. The method for preparing modified carbon nanotubes according to claim 1, wherein: The magnesium source comprises at least one of magnesium chloride, magnesium oxide, magnesium carbonate, magnesium hydroxide, and magnesium sulfate; and / or The hydrophilic acrylic acid ester monomer includes at least one of methyl methacrylate, hydroxyethyl methacrylate, and hydroxyethyl acrylate; and / or The acrylamide monomer includes N-n-propyl acrylamide; and / or The cross-linking agent comprises ethylene glycol dimethacrylate; and / or The initiator comprises azobisisobutyronitrile; and / or The second solvent includes at least one of methanol, ethanol, propanol, butanediol, and water.

6. The method for preparing modified carbon nanotubes according to claim 1, wherein: The preparation method of the chain transfer agent comprises the following steps: Mixing carbon disulfide, tetrabutylammonium hydrogen sulfate, and the third solvent to obtain a mixed solution; Sodium hydroxide solution is added to the mixed solution to carry out a first reaction, and then hydrochloric acid solution and water are added to carry out a second reaction, followed by washing and drying to obtain a chain transfer agent.

7. The method for preparing modified carbon nanotubes according to claim 6, characterized in that: The molar ratio of carbon disulfide to tetrabutylammonium hydrogen sulfate is (4-8):1; The volume ratio of carbon disulfide to the third solvent is 1:(10-30); and / or The volume ratio of the sodium hydroxide solution to the mixed solution is 1:(1-4); and / or The volume ratio of the sodium hydroxide solution, the hydrochloric acid solution and the water is 1:(1-2):(3-8).

8. A method for preparing an electrode, characterized in that: The following steps are involved: The modified carbon nanotubes are prepared into a modified carbon nanotube slurry with a mass concentration of 5 to 20%; The electrode active material and the modified carbon nanotube slurry are mixed evenly, and then a conductive agent, chopped carbon fibers, a pore-forming agent, a binder and a fourth solvent are added to prepare a positive electrode material slurry. The positive electrode material slurry is evenly coated on the current collector and dried to obtain an electrode; The modified carbon nanotubes are prepared by the method for preparing modified carbon nanotubes according to any one of claims 1 to 7; The mass ratio of the electrode active material, modified carbon nanotubes, conductive agent, chopped carbon fibers, pore-forming agent, binder and fourth solvent is 100: (1.5-10): (1.5-10): (1-4): (10-30): (5-20): (100-200).

9. The method for preparing an electrode according to claim 8, wherein: The electrode active material includes LiMn2O4, LiFePO4, LiNi x Co y Mn z At least one of O2, wherein x+y+z=1; and / or The conductive agent includes carbon black; and / or The pore-forming agent comprises at least one of ammonium bicarbonate and ammonium carbonate; and / or The binder comprises polyvinylidene fluoride; and / or The fourth solvent includes N-methylpyrrolidone.

10. The method for preparing an electrode according to claim 9, wherein: The carbon black is acetylene black.

11. Use of the electrode prepared by the method for preparing an electrode according to any one of claims 8 to 10 in extracting lithium from salt lakes.

12. A method for extracting lithium from a salt lake, characterized in that: The following steps are involved: The electrode prepared by the method for preparing an electrode according to any one of claims 8 to 10 is used as the anode, and the nickel foam is used as the cathode. The electrode is placed in a NaCl solution, and a voltage is applied across the electrode until the current density is lower than 0.5 A / m 2 , obtaining a delithiation electrode; The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and the delithiated electrode and the corresponding anode are placed in the cathode chamber and the anode chamber respectively. Lithium-containing brine is injected into the cathode chamber, and NaCl solution is injected into the anode chamber. Voltage is applied to the anode and cathode, and electrolysis is carried out at a temperature of >10°C for 3 to 8 hours. Then, the lithium-containing brine in the cathode chamber is replaced with water, and the mixture is shaken in a water bath of <10°C for 2 to 5 hours. Then, the water in the cathode chamber is replaced with KCl solution, and the positive and negative poles of the electrodes connected to the power supply are interchanged. Voltage is applied for electrolysis to obtain a lithium-rich solution.

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