A polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, a preparation method and application thereof

Abstract

This invention belongs to the field of lithium resource extraction technology, specifically relating to a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, its preparation method, and its application. The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of this invention includes the following steps: S1, mixing MXene colloidal solution with lithium iron phosphate powder, stirring and dispersing to obtain mixture A; adding a pyrrole monomer solution to mixture A, stirring to allow the pyrrole monomer to adsorb onto the surfaces of MXene and lithium iron phosphate; S2, adding an initiator solution to the system obtained in step S1 to initiate in-situ polymerization of the pyrrole monomer, forming an MXene / LFP / PPy composite hydrogel; S3, washing and freeze-drying the composite hydrogel. The polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of this invention helps improve lithium extraction efficiency and exhibits good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium resource extraction technology, specifically relating to a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, its preparation method, and its application. Background Technology

[0002] Lithium, a key strategic resource for new energy vehicles and energy storage systems, is experiencing sustained high-speed growth in global demand. Traditional methods for extracting liquid lithium resources (such as solar evaporation-precipitation and hard rock roasting) suffer from problems such as long production cycles, high energy consumption, and severe environmental pollution, making it difficult to meet the demands of the rapidly increasing lithium resource demand. Electrochemical extraction technology, due to its advantages of high selectivity, low energy consumption, and environmental friendliness, has become an important direction for the development of liquid lithium resources. Among these technologies, the combination of capacitive deionization (CDI) technology and high-efficiency electrode materials is the core to achieving efficient lithium extraction.

[0003] Lithium iron phosphate (LFP) has stable Li + The embedding / extraction performance is ideal for Li + It selectively adsorbs active sites, but has poor conductivity (only 10). -9 ~10 -8 The low conductivity (S / cm) and insufficient hydrophilicity limit its applications. MXene, as a two-dimensional layered conductive material, has a conductivity of up to 24,000 S / cm and has hydrophilic functional groups on its surface, which can improve the conductivity and wettability of LFP. However, MXene sheets are easily oxidized in electrochemical environments, leading to material structure damage and performance degradation.

[0004] In existing technologies, the composite of MXene and LFP is mostly achieved through physical mixing, which makes it difficult to solve the oxidation problem of MXene, and the dispersion and cycle stability of the composite material are poor.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, its preparation method, and its application, so as to help solve or improve the problem of poor selective extraction of lithium by adsorbents in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, comprising the following steps: S1, mixing an MXene colloidal solution with lithium iron phosphate powder, stirring and dispersing to obtain a mixture A; adding a pyrrole monomer solution to the mixture A, stirring to allow the pyrrole monomer to adsorb onto the surfaces of MXene and lithium iron phosphate; S2, adding an initiator solution to the system obtained in step S1 to initiate in-situ polymerization of the pyrrole monomer to form an MXene / LFP / PPy composite hydrogel; S3, washing and freeze-drying the composite hydrogel to obtain the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material.

[0008] Preferably, in step S1, the mass ratio of MXene to lithium iron phosphate in the MXene colloidal solution is 0.1:(0.8~1.6); the amount ratio of pyrrole monomer to lithium iron phosphate is (0.15-0.35)mL:(0.8-1.6)g.

[0009] Preferably, in step S2, the initiator is ammonium persulfate, and the mass ratio of ammonium persulfate to pyrrole monomer is (0.9-1.2):1.

[0010] Preferably, in step S3, the freeze-drying temperature is -60~-50℃, the vacuum degree is 1~10Pa, and the freeze-drying time is 48-72h.

[0011] Preferably, the MXene colloidal solution is prepared by a method comprising the following steps: reacting Ti3AlC2 MAX phase powder with an etchant under acidic conditions, followed by centrifugation, washing and ultrasonic dispersion to obtain the MXene colloidal solution.

[0012] Preferably, the etching agent is concentrated hydrochloric acid and LiF, the concentration of concentrated hydrochloric acid is 10-12 mol / L, the ratio of concentrated hydrochloric acid to Ti3AlC2 MAX phase is (15-25) mL:1g, the mass ratio of LiF to Ti3AlC2 MAX phase is (1.5-1.7):1; the ultrasonic dispersion time is 20-40 min, and the ultrasonic power is 100-150 W.

[0013] The present invention also provides a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, which adopts the following technical solution: a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, wherein the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material is prepared by the method described above.

[0014] The present invention also provides an application of polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, which adopts the following technical solution: the application of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described above in lithium extraction.

[0015] Preferably, the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material is used for the selective extraction of Li from a liquid system. + The process includes the following steps: applying an electrode slurry containing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material to the surface of the working electrode, and then performing Li-ionization using a dual-chamber capacitor deionization device. + Extraction.

[0016] Preferably, the liquid system comprises brine from a salt lake or a low-grade lithium solution, wherein the Li in the liquid system + The concentration is 10-200 mg / L, and coexisting ions include Na+. + K + Mg 2+ One or more of the following; The operating conditions of the dual-chamber capacitive deionization device are as follows: adsorption voltage 0.4-1.2V, adsorption time 30-60min, solution flow rate 3-7mL / min; desorption voltage 1.0-1.2V, desorption electrolyte is potassium salt solution or sodium salt solution; the concentration of the potassium salt solution or sodium salt solution is 450-550mg / L.

[0017] Beneficial effects: In the preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, polypyrrole (PPy), as a conductive polymer, can form hydrogen bonds with the -OH groups on the MXene surface through its NH bonds; and after polymerization, it carries a positive charge, which can interact electrostatically with the negative charge on the MXene sheet surface to form a stable coating layer, which can both inhibit MXene oxidation and not significantly affect the conductivity of the material. Furthermore, preparing the composite material as an aerogel structure can increase the specific surface area and porosity, promote ion transport, and further improve its lithium extraction performance.

[0018] The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention is simple and efficient, requiring no complex equipment. It can be prepared by MXene solution dispersion, LFP loading, in-situ polymerization of pyrrole and freeze drying. The reaction conditions are mild, energy consumption is low, environmentally friendly, and no toxic or harmful byproducts are generated, making it easy to scale up for industrial production.

[0019] This invention addresses the challenge of lithium extraction from solutions with a high magnesium-to-lithium ratio. Through the synergistic effect of PPy coating protection and the porous structure of aerogel, it enables precise identification and capture of Li in complex brine systems. + Effectively avoids Mg2+ Na + K + The interference of coexisting ions enabled highly selective lithium extraction.

[0020] The polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention combines high conductivity, excellent hydrophilicity, and a porous structure. The high conductivity of MXene accelerates the Li... + The insertion / extraction kinetics of the material, the porous structure of the aerogel that increases the contact area between the material and the solution, and the coating layer of PPy that optimizes the ion transport channels, work synergistically to maintain the current efficiency of the material above 85% during the lithium extraction process, and the energy utilization rate is significantly better than that of traditional capacitor deionization materials.

[0021] The polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention has strong adaptability and good lithium extraction effect on different liquid lithium resource systems such as low-grade brine and high magnesium-to-lithium ratio salt lake brine. Moreover, the working voltage is only 0.4~1.2V, and the energy consumption is far lower than the roasting process for lithium extraction from hard rock, which meets the requirements of green lithium extraction and has high practical application value.

[0022] The composite aerogel material prepared by this invention exhibits excellent adsorption properties at a voltage of 1.0V and Li. + At a concentration of 100 mg / L, for Li + The adsorption capacity can reach 30.57 mg / g, and adsorption equilibrium can be reached in 60 minutes. Compared with single LFP or MXene materials, the adsorption capacity is increased by more than 30%, and the lithium extraction efficiency is significantly better than existing electrochemical lithium extraction materials.

[0023] This invention effectively inhibits the oxidation and damage of MXene in the electrochemical environment by coating and modifying MXene sheets with PPy, significantly improving the material's cycle stability. After 5 desorption-adsorption cycles, the adsorption capacity still maintains 95.6% of the initial capacity, which is much higher than that of the unmodified MXene / LFP composite material (69.06%), greatly extending the service life and reducing the replacement cost in practical applications. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 This is a synthetic route diagram of a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material provided in one embodiment of the present invention; Figure 2 The effects of different voltages on PM-0.8LFP, PM-1.2LFP, and PM-1.6LFP at 50 mg / L Li +The adsorption capacity in the solution after 30 minutes; Figure 3 The adsorption isotherm of lithium by PM-1.2LFP in Example 1 of this invention; Figure 4 This is a selective adsorption diagram of lithium by PM-1.2LFP in Example 1 of the present invention; Figure 5 The selective adsorption diagram of lithium by M-0.8LFP in Comparative Example 1 is shown. Figure 6 The diagram shows the adsorption-desorption cycle of lithium ions in M-0.8LFP as a comparative example 1.

[0025] Figure 7 This is an adsorption-desorption cycle experiment diagram of PM-1.2LFP adsorbing lithium ions in Example 1 of the present invention.

[0026] Figure 8 The current efficiency of PM-0.8LFP in Embodiment 1, PM-1.2LFP in Embodiment 2, and PM-1.6LFP in Embodiment 3 under different voltages is shown.

[0027] Figure 9 The current efficiency of the M-0.8LFP under different voltages is shown in Comparative Example 1. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0029] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0030] This invention addresses the problem of poor selective extraction of lithium by adsorbents in existing technologies (especially when the solution contains coexisting ions with the same or similar ionic radius or valence state as lithium ions), and provides a method for preparing polypyrrole-coated MXene / lithium iron phosphate composite aerogel material.

[0031] The preparation method of polypyrrole-coated MXene / lithium iron phosphate composite aerogel material according to an embodiment of the present invention includes the following steps: S1. Mixing MXene colloidal solution with lithium iron phosphate powder, stirring and dispersing to obtain mixture A; adding pyrrole monomer solution to mixture A, stirring to allow pyrrole monomer to be adsorbed onto the surfaces of MXene and lithium iron phosphate; S2. Adding initiator solution to the system obtained in step S1 to allow pyrrole monomer to polymerize in situ, forming MXene / LFP / PPy composite hydrogel; S3. Washing and freeze-drying the composite hydrogel to obtain polypyrrole-coated MXene / lithium iron phosphate composite aerogel material.

[0032] In a preferred embodiment of the method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, in step S1, the mass ratio of MXene to lithium iron phosphate in the MXene colloidal solution is 0.1:(0.8~1.6) (e.g., 0.1:0.8, 0.1:1.0, 0.1:1.2, 0.1:1.4 or 0.1:1.6); the amount ratio of pyrrole monomer to lithium iron phosphate is (0.15-0.35)mL:(0.8-1.6)g (e.g., 0.15mL:0.8g, 0.15mL:1.2g, 0.15mL:1.6g, 0.25mL:0.8g, 0.25mL:1.2g, 0.25mL:1.6g, 0.35mL:0.8g, 0.35mL:1.2g, 0.35mL:1.6g). If the amount of MXene is too low, an effective conductive network cannot be formed, leading to Li + Charge transfer during insertion / extraction is hindered, leading to a significant decrease in adsorption capacity. If the MXene dosage is too high, the two-dimensional sheets are prone to stacking, resulting in the masking of LFP active sites, a decrease in specific surface area, and impaired ion transport. This also increases cost and is detrimental to the construction of three-dimensional porous structures. If the pyrrole dosage is too low, a complete polypyrrole coating layer cannot be formed on the MXene sheet surface, making MXene easily oxidized. If the pyrrole dosage is too high, the polypyrrole coating layer is too thick, significantly increasing the Li... + Diffusion resistance leads to slower adsorption kinetics and reduced adsorption capacity.

[0033] In a preferred embodiment of the preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, in step S2, the initiator is ammonium persulfate, and the mass ratio of ammonium persulfate to pyrrole monomer is (0.9-1.2):1 (e.g., 0.9:1, 1:1, 1.1:1 or 1.2:1).

[0034] In a preferred embodiment of the preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, in step S3, the freeze-drying temperature is -60~-50℃ (e.g., -60℃, -58℃, -56℃, -54℃, -52℃ or -50℃), the vacuum degree is 1-10Pa (e.g., 1Pa, 3Pa, 5Pa, 7Pa, 9Pa or 10Pa), and the freeze-drying time is 48-72h (e.g., 48h, 54h, 60h, 66h or 72h). If the freeze-drying temperature is too high, the ice crystals may partially melt before sublimation, leading to pore structure collapse and a dense, lamellar accumulation of the material, resulting in a significant decrease in specific surface area. If the freeze-drying temperature is too low, the formed ice crystals are too fine, and the pore size after sublimation is not conducive to rapid ion transport, and energy consumption increases.

[0035] In a preferred embodiment of the preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, the MXene colloidal solution is prepared by a method including the following steps: reacting Ti3AlC2 MAX phase powder with an etchant under acidic conditions, followed by centrifugation, washing and ultrasonic dispersion treatment to obtain the MXene colloidal solution.

[0036] In a preferred embodiment of the preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, the etchant is concentrated hydrochloric acid and LiF. The concentration of concentrated hydrochloric acid is 10-12 mol / L (e.g., 10 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L, or 12 mol / L), and the ratio of concentrated hydrochloric acid to Ti3AlC2 MAX phase is (15-25) mL:1g (e.g., 15 mL:1g, 18 mL:1g, 20 mL:1g, 23 mL:1g, or 25 mL:1g). The LiF and Ti3AlC2... The mass ratio of the MAX phase is (1.5-1.7):1 (e.g., 1.5:1, 1.55:1, 1.6:1, 1.65:1 or 1.7:1); the ultrasonic dispersion time is 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min or 40 min); and the ultrasonic power is 100-150 W (e.g., 100 W, 110 W, 120 W, 130 W, 140 W or 150 W).

[0037] The present invention also proposes a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, wherein the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention is prepared by the method described above.

[0038] This invention also proposes an application of a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, as described above, in lithium extraction.

[0039] In a preferred embodiment of the application of the present invention, the following steps are included: coating an electrode slurry containing polypyrrole-coated MXene / lithium iron phosphate composite aerogel material onto the surface of the working electrode, and combining it with a dual-chamber capacitor deionization device for selectively extracting Li from a liquid system. + .

[0040] In a preferred embodiment of the application of the present invention, the working electrode is prepared by a method comprising the following steps: mixing polypyrrole-coated MXene / lithium iron phosphate composite aerogel material with PVDF, activated carbon and solvent to form an electrode slurry; and coating the electrode slurry onto the surface of the working electrode.

[0041] Preferably, the mass ratio of polypyrrole-coated MXene / lithium iron phosphate composite aerogel material to PVDF and activated carbon is 8:1:1; the coating amount of polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in the electrode slurry is 15-30 mg / cm³. 2 (That is, the amount of polypyrrole-coated MXene / lithium iron phosphate composite aerogel material used per square centimeter of working electrode is 15-30 mg; for example, 15 mg / cm².) 2 20mg / cm 2 25mg / cm 2 Or 30mg / cm 2 ) Preferably, the counter electrode is made of distillers' grains carbon.

[0042] In a preferred embodiment of the application of the present invention, the liquid system includes salt lake brine and a low-grade lithium solution, wherein Li... + Concentrations range from 10 to 200 mg / L (e.g., 10 mg / L, 40 mg / L, 70 mg / L, 100 mg / L, 130 mg / L, 160 mg / L, 180 mg / L, or 200 mg / L), with coexisting ions including Na+. + K + and Mg 2+One or more of the following; the operating conditions of the CDI device are: adsorption voltage 0.4-1.2V (e.g., 0.4V, 0.6V, 0.8V, 1.0V or 1.2V), adsorption time 30-60min (e.g., 30min, 40min, 50min or 60min), solution flow rate 3-7mL / min (e.g., 3mL / min, 4mL / min, 5mL / min, 6mL / min or 7mL / min); desorption voltage 1.0-1.2V (e.g., 1.0V, 1.1V or 1.2V), and the desorption electrolyte is a potassium salt solution or a sodium salt solution.

[0043] Preferably, the concentration of the potassium salt solution or sodium salt solution is 450-550 mg / L (e.g., 450 mg / L, 480 mg / L, 500 mg / L, 520 mg / L or 550 mg / L).

[0044] More preferably, the desorption electrolyte is a 500 mg / L KCl solution.

[0045] The following detailed description of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention, its preparation method, and its application are illustrated through specific embodiments.

[0046] The sources of the main raw materials used in the following examples: Table 1 Experimental materials and reagents

[0047] The adsorption experiments were conducted using LiCl solutions of different concentrations; first, a 500 mg / L LiCl solution was prepared. + Solution: Weigh 1.53g of LiCl powder, dissolve it in a beaker, transfer it to a 500mL volumetric flask, and add ultrapure water to the mark. This gives a solution of 500mg / L LiCl. + Solution; a portion of the solution was diluted to 100 mg / L for kinetic adsorption experiments; another portion of the solution was diluted to 10, 30, 50, 100, 150 and 200 mg / L for concentration adsorption experiments.

[0048] The mixed ionic solution consists of Na+ solutions, each with a concentration of 100 mg / L. + K + Li + and Mg 2+ To prepare the solution, weigh out 0.477 g KCl, 0.980 g MgCl2, 1.53 g LiCl and 0.640 g NaCl powder respectively, dissolve them in a beaker, pour them into a 500 mL volumetric flask, add ultrapure water to the mark, and obtain a mixed ionic solution with a concentration of 500 mg / L. Dilute the solution to 100 mg / L.

[0049] The distillery lees carbon (counter electrode) used in the following experiments was prepared using the following steps: Distillery lees were washed with ultrapure water until neutral, dried at 105℃ for 12 hours, pulverized, and passed through a 100-mesh sieve; the sieved lees powder was placed in a tube furnace and pre-carbonized at 450℃ under N2 atmosphere at a rate of 5℃ / min for 30 minutes to obtain a pre-carbonized product; the pre-carbonized product was mixed with KOH at a mass ratio of 1:3 and ground, then activated at 800℃ under N2 atmosphere at a rate of 5℃ / min for 2 hours to obtain an activated product; the activated product was washed with 2 mol / L HCl to remove impurities, then washed with ultrapure water until neutral, and dried at 60℃ for 24 hours to obtain a distillery lees-based porous carbon material (distillery lees carbon). The specific surface area of ​​the obtained distillery lees carbon reached 3642.87 m². 2 / g, pore volume 2.08cm 3 / g.

[0050] The working electrodes used in the following experiments were prepared by the following steps: 0.4g of active material (for example, the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of the present invention can be used as the active material), 50mg of conductive carbon black and 50mg of polyvinylidene fluoride (PVDF) were weighed and ground and mixed evenly in an agate mortar; (2) the mixed powder was transferred to a reagent bottle, 2mL of N-methylpyrrolidone (NMP) was added, and the mixture was magnetically stirred for 5h to form a uniform electrode slurry; (3) the electrode slurry was uniformly coated on the surface of carbon paper with a coating area of ​​4cm×4cm=16cm. 2 The coating amount is 25 mg / cm². 2 (Based on the mass of the active material); (4) Place the coated electrode in a vacuum drying oven and dry at 60°C for 12 hours to obtain the working electrode.

[0051] Example 1 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment includes the following steps (refer to...). Figure 1 ): S1. Preparation of MXene solution: 1.6 g LiF was added to 20 mL of 12 mol / L concentrated hydrochloric acid and stirred at room temperature for 20 min to dissolve, thus obtaining the etching agent; 1 g Ti3AlC2 MAX phase powder was added to the etching agent and etched by stirring in a constant temperature water bath at 40 °C for 48 h; after the etching reaction was completed, the reaction product was centrifuged at 5000 r / min for 1 min to collect the precipitate, and the precipitate was washed three times with 1 mol / L hydrochloric acid, and then washed with ultrapure water until the supernatant was neutral; the precipitate was dispersed in 40 mL of ultrapure water, sonicated in an ice bath for 30 min, centrifuged at 3500 r / min for 15 min, and the upper liquid was collected to obtain a 25 mg / mL MXene colloidal solution, which was then purged with nitrogen and stored under cold.

[0052] S2. Construction of the mixed system: Take 5 mL of MXene colloidal solution, add 1.2 g of lithium iron phosphate (LFP) powder, stir at room temperature for 60 min to obtain mixture A; dissolve 0.25 mL of pyrrole monomer in 0.75 mL of anhydrous ethanol to obtain pyrrole monomer solution; add the pyrrole monomer solution dropwise to mixture A, stir at room temperature for 24 h to obtain mixture B; S3. In-situ polymerization and crosslinking: Dissolve 0.25g of ammonium persulfate in 1.25mL of ultrapure water to obtain an ammonium persulfate solution. After cooling, add the ammonium persulfate solution dropwise to mixture B. The system rapidly crosslinks to form a hydrogel. Then, let it stand at room temperature for 24h to allow the polymerization reaction to be fully completed. Then, repeatedly soak the mixture in anhydrous ethanol and ultrapure water to remove unreacted components until the supernatant becomes clear. S4. Freeze-drying: After washing, freeze-dry at -55℃ for 48 hours (vacuum degree is 1Pa) to obtain the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of this embodiment (denoted as PM-1.2LFP).

[0053] PM-1.2LFP was used as the active material to prepare the working electrode, and distillers' grains carbon was used as the counter electrode to assemble a CDI device. PM-1.2LFP in Li + In a 50 mg / L solution, the adsorption capacity reached 25.27 mg / g after 30 min at 1.0 V.

[0054] PM-1.2LFP reached adsorption equilibrium at a voltage of 1.0V, a concentration of 100mg / L, and an adsorption time of 60min, with an adsorption capacity of 30.57mg / g.

[0055] Example 2 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment includes the following steps: S1. Preparation of MXene solution: 1.6 g LiF was added to 20 mL of 12 mol / L concentrated hydrochloric acid and stirred at room temperature for 20 min to dissolve, thus obtaining the etching agent; 1 g Ti3AlC2 MAX phase powder was added to the etching agent and etched by stirring in a constant temperature water bath at 40 °C for 48 h; after the etching reaction was completed, the reaction product was centrifuged at 5000 r / min for 1 min to collect the precipitate, and the precipitate was washed three times with 1 mol / L hydrochloric acid, and then washed with ultrapure water until the supernatant was neutral; the precipitate was dispersed in 40 mL of ultrapure water, sonicated in an ice bath for 30 min, centrifuged at 3500 r / min for 15 min, and the upper liquid was collected to obtain a 25 mg / mL MXene colloidal solution, which was then purged with nitrogen and stored under cold.

[0056] S2. Construction of the mixed system: Take 5 mL of MXene colloidal solution, add 0.8 g of lithium iron phosphate (LFP) powder, stir at room temperature for 60 min to obtain mixture A; dissolve 0.25 mL of pyrrole monomer in 0.75 mL of anhydrous ethanol to obtain pyrrole monomer solution; add the pyrrole monomer solution dropwise to mixture A, stir at room temperature for 24 h to obtain mixture B; S3. In-situ polymerization and crosslinking: Dissolve 0.25g of ammonium persulfate in 1.25mL of ultrapure water to obtain an ammonium persulfate solution. After cooling, add the ammonium persulfate solution dropwise to mixture B. The system rapidly crosslinks to form a hydrogel. Then, let it stand at room temperature for 24h to allow the polymerization reaction to be fully completed. Then, repeatedly soak the mixture in anhydrous ethanol and ultrapure water to remove unreacted components until the supernatant becomes clear. S4. Freeze-drying: After washing, freeze-dry at -55℃ for 48h (vacuum degree is 1Pa) to obtain the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of this embodiment (denoted as PM-0.8LFP).

[0057] PM-0.8LFP was used as the active material to prepare the working electrode, and distillers' grains carbon was used as the counter electrode to assemble a CDI device. PM-0.8LFP in Li + In a 50 mg / L solution, the adsorption capacity reached 23.82 mg / g after 30 min of adsorption at 1.0 V.

[0058] Example 3 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment includes the following steps: S1. Preparation of MXene solution: 1.6 g LiF was added to 20 mL of 12 mol / L concentrated hydrochloric acid and stirred at room temperature for 20 min to dissolve, thus obtaining the etching agent; 1 g Ti3AlC2 MAX phase powder was added to the etching agent and etched by stirring in a constant temperature water bath at 40 °C for 48 h; after the etching reaction was completed, the reaction product was centrifuged at 5000 r / min for 1 min to collect the precipitate, and the precipitate was washed three times with 1 mol / L hydrochloric acid, and then washed with ultrapure water until the supernatant was neutral; the precipitate was dispersed in 40 mL of ultrapure water, sonicated in an ice bath for 30 min, centrifuged at 3500 r / min for 15 min, and the upper liquid was collected to obtain a 25 mg / mL MXene colloidal solution, which was then purged with nitrogen and stored under cold.

[0059] S2. Construction of the mixed system: Take 5 mL of MXene colloidal solution, add 1.6 g of lithium iron phosphate (LFP) powder, stir at room temperature for 60 min to obtain mixture A; dissolve 0.25 mL of pyrrole monomer in 0.75 mL of anhydrous ethanol to obtain pyrrole monomer solution; add the pyrrole monomer solution dropwise to mixture A, stir at room temperature for 24 h to obtain mixture B; S3. In-situ polymerization and crosslinking: Dissolve 0.25g of ammonium persulfate in 1.25mL of ultrapure water to obtain an ammonium persulfate solution. After cooling, the ammonium persulfate solution is added dropwise to mixture B. The system rapidly crosslinks to form a hydrogel. Then, let it stand at room temperature for 24h to allow the polymerization reaction to be fully completed. Then, repeatedly soak it with anhydrous ethanol and ultrapure water to remove unreacted components until the supernatant becomes clear. S4. Freeze-drying: After washing, freeze-dry at -55℃ for 48 hours (vacuum degree is 1Pa) to obtain the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material of this embodiment (denoted as PM-1.6LFP).

[0060] PM-1.6LFP was used as the active material to prepare the working electrode, and distillers' grains carbon was used as the counter electrode to assemble a CDI device; PM-1.6LFP in Li + In a 50 mg / L solution, the adsorption capacity reached 24.56 mg / g after 30 min at 1.0 V.

[0061] Example 4 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that the amount of pyrrole monomer added in step S2 is 0.15 mL (this amount covers the key active sites of MXene and LFP, avoiding insufficient coating that could lead to MXene oxidation and LFP aggregation); all other aspects are consistent with Example 1.

[0062] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li + In a 50 mg / L solution, the adsorption capacity reached 21.12 mg / g after 30 min at 1.0 V.

[0063] Example 5 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that the amount of pyrrole monomer added in step S2 is 0.35 mL (to avoid excessive pyrrole leading to the formation of a thick PPy layer after polymerization, which would reduce the lithium-ion diffusion coefficient and hinder Li-ion diffusion). + (Transmission); the rest are consistent with Example 1.

[0064] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li + In a 50 mg / L solution, the adsorption capacity reached 22.31 mg / g after 30 min of adsorption at 1.0 V.

[0065] Example 6 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that: the amount of ammonium persulfate added in step S3 is 0.216g (this amount of initiator ensures that the pyrrole monomers crosslink rapidly within 10 seconds to form a hydrogel, and the degree of polymerization is moderate, which can form a complete coating layer without reducing the conductivity due to excessive oxidation of polypyrrole caused by excessive oxidant (ammonium persulfate)); the rest is consistent with Example 1.

[0066] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li + In a 50 mg / L solution, the adsorption capacity reached 20.37 mg / g after 30 min at 1.0 V.

[0067] Example 7 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that the amount of ammonium persulfate added in step S3 is 0.288g (in actual polymerization, ammonium persulfate needs to be slightly in excess to ensure complete polymerization of pyrrole); the rest is consistent with Example 1.

[0068] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li + In a 50 mg / L solution, the adsorption capacity reached 21.27 mg / g after 30 min at 1.0 V.

[0069] Example 8 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that the freeze-drying temperature in step S4 is -50°C; the rest are consistent with Example 1.

[0070] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li + In a 50 mg / L solution, the adsorption capacity reached 22.60 mg / g after 30 min at 1.0 V.

[0071] Example 9 The preparation method of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material in this embodiment differs from that in Example 1 only in that the freeze-drying temperature in step S4 is -60°C; the rest are consistent with Example 1.

[0072] It was used as the active material to prepare the working electrode, and distillers' grains carbon as the counter electrode, and a CDI device was assembled; in Li +In a 50 mg / L solution, the adsorption capacity reached 20.959 mg / g after 30 min at 1.0 V.

[0073] Comparative Example 1 The only difference between this comparative example and Example 1 is that the amount of lithium iron phosphate added is 0.8g, and the steps of adding pyrrole monomer and initiator are omitted; all other aspects are the same as in Example 1.

[0074] The product obtained in this comparative example is an MXene / LFP composite powder, which is a non-aerogel structure.

[0075] The experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and the adsorption capacity reached 20.50mg / g.

[0076] After 5 cycles, the adsorption capacity decreased to 69.06% of the initial value, indicating severe oxidation of MXene and poor structural stability.

[0077] Comparative Example 2 The only difference between this comparative example and Example 1 is that step S4 uses room temperature drying at 60°C for 12 hours instead of freeze drying; the rest are the same as in Example 1.

[0078] The product obtained in this comparative example has a dense lamellar structure without aerogel pores and a significantly reduced specific surface area (1.0V voltage as experimental conditions, solution concentration of 50mg / L, adsorption time of 30min, and adsorption capacity of 15.2mg / g).

[0079] Comparative Example 3 The only difference between this comparative example and Example 1 is that in step S2, 2 mL of MXene solution was taken and 1.2 g of LFP was added; otherwise, the results were the same as in Example 1.

[0080] With reduced MXene dosage and increased LFP dosage, the conductive network became discontinuous and LFP aggregation was severe. The experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and 18.8mg / g adsorption capacity.

[0081] Comparative Example 4 The only difference between this comparative example and Example 1 is that in step S2, 10 mL of MXene solution was taken and 1.2 g of LFP was added; otherwise, the results were the same as in Example 1.

[0082] With increased MXene dosage and decreased LFP dosage, MXene sheets showed severe stacking and insufficient LFP active sites. The experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and 14.52mg / g adsorption capacity.

[0083] Comparative Example 5 The only difference between this comparative example and Example 1 is that 0.05 mL of pyrrole monomer was added in step S2, while the rest remained the same as in Example 1.

[0084] Insufficient pyrrole monomer dosage resulted in incomplete coating and severe MXene oxidation. Experimental conditions included a voltage of 1.0V, a solution concentration of 50mg / L, an adsorption time of 30min, and a capacity retention rate of <80% after 5 cycles (initial adsorption capacity was 20.79mg / g, and adsorption capacity after 5 cycles was 16.63mg / g).

[0085] Comparative Example 6 The only difference between this comparative example and Example 1 is that 0.5 mL of pyrrole monomer was added in step S2, while the rest remained the same as in Example 1.

[0086] Excessive use of pyrrole monomer and excessively thick coating layer, Li + Diffusion was hindered; the experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and 18.29mg / g adsorption capacity.

[0087] Comparative Example 7 The only difference between this comparative example and Example 1 is that 0.125g of ammonium persulfate (APS:Py=0.5:1) is added in step S3; all other steps are the same as in Example 1. Insufficient ammonium persulfate resulted in incomplete polymerization, preventing the formation of a complete hydrogel and leading to a loose material structure. The experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and 15.66mg / g adsorption capacity.

[0088] Comparative Example 8 The only difference between this comparative example and Example 1 is that 0.375g of ammonium persulfate (APS:Py = 1.5:1) is added in step S3; all other steps are the same as in Example 1. Excessive use of ammonium persulfate led to excessive oxidation of polypyrrole, resulting in decreased conductivity. The experimental conditions were 1.0V voltage, 50mg / L solution concentration, 30min adsorption time, and 19.46mg / g adsorption capacity.

[0089] Comparative Example 9 The only difference between this comparative example and Example 1 is that step S4 involves freeze-drying at -55°C for 24 hours (vacuum degree 1 Pa), which is consistent with Example 1. If the freeze-drying time is too short, moisture will remain, the pore structure will collapse, and the specific surface area will decrease.

[0090] Experimental Example 1. Adsorption capacity test under different voltages: The effects of different voltages on PM-0.8LFP, PM-1.2LFP, and PM-1.6LFP at 50 mg / L Li + The adsorption capacity in the solution was tested after 30 minutes of adsorption. Test method: Inject 50 mL of 50 mg / L Li into the cathode cavity of the CDI device. + (2) Turn on the peristaltic pump and set the circulation rate to 5 mL / min. Circulate steadily for 5 min (to ensure uniform distribution of the solution and eliminate concentration gradients). (3) Connect the DC regulated power supply and set the adsorption voltage (0.6V, 0.8V, 1.0V, 1.2V, with a voltage accuracy of ±0.01V). Simultaneously start the timer and precisely control the adsorption time to 30 min. (4) Maintain a constant experimental temperature during adsorption to avoid temperature fluctuations affecting ion migration rates. Observe the device in real time for any leakage or obvious bubble generation. After adsorption, immediately turn off the power supply and peristaltic pump. Use a pipette to accurately transfer the adsorbed solution from the cathode chamber for ICP testing.

[0091] Test results are as follows Figure 2 As shown; by Figure 2 It can be seen that as the voltage gradually increases, the adsorption capacity of PM-0.8LFP, PM-1.2LFP, and PM-1.6LFP materials gradually increases, reaching a maximum at 1.0V, with values ​​of 23.82 mg / g, 25.27 mg / g, and 24.56 mg / g, respectively. PM-1.2LFP exhibits a higher adsorption capacity than the other two materials. This is because a suitable amount of LFP can more uniformly load the MXene sheet surface; too little LFP results in underutilization of the MXene sheet, while too much leads to LFP particle accumulation, reducing the material's conductivity. When the adsorption voltage is 1.2V, the adsorption performance of all materials decreases. This is because under higher voltage conditions, hydrogen evolution occurs on the electrode surface, generating bubbles that adhere to the electrode surface. These bubbles reduce the contact area between the solution and the electrode surface, hindering the adsorption of Li. + The adsorption capacity of the material is reduced as the adsorption enters the material.

[0092] 2. Adsorption kinetics test: PM-1.2LFP from Example 1 and M-0.8LFP from Comparative Example 1 were used as adsorbents for testing.

[0093] The test method is: Li + Desorption and adsorption experiments; First, a desorption experiment was conducted using K+ containing a concentration of 500 mg / L. +50 mL of each solution was used as the electrolyte in the cathode and anode chambers, and desorption was performed for 10, 20, 30, 40, 60 and 120 min, respectively. The peristaltic pump flow rate (the flow rate of electrolyte entering the cathode and anode chambers) was set to 5 mL / min. After rinsing the chamber with ultrapure water, adsorption experiments were performed. The cathode chamber solution was replaced with 50 mL of 100 mg / L Li. + The solution was prepared by setting the peristaltic pump flow rate to 5 mL / min (the flow rate of electrolyte entering the cathode and anode chambers), and adsorption times of 10, 20, 30, 40, 60, and 120 min. The adsorbed solutions were then analyzed using ICP-OES. The adsorption isotherm of lithium by PM-1.2LFP in Example 1 is shown below. Figure 3 As shown.

[0094] The kinetic adsorption fitting parameters of M-0.8LFP and PM-1.2LFP are shown in Table 2 below: Table 2 Kinetic adsorption fitting parameters of M-0.8LFP and PM-1.2LFP

[0095] Experimental results show that PM-0.8LFP and PM-1.2LFP have a positive effect on Li + The correlation coefficients between the adsorption data and the fitting curves of the pseudo-second-order kinetic model reached 0.9878 and 0.9858, respectively, which were higher than the correlation coefficients with the fitting curves of the pseudo-first-order kinetic model. This indicates that the material fits the pseudo-second-order kinetic model better, suggesting that the material exhibits better adhesion to Li. + Adsorption occurs through a chemical reaction.

[0096] 3. Adsorption selectivity performance test: PM-1.2LFP from Example 1 and M-0.8LFP from Comparative Example 1 were used as adsorbents for testing.

[0097] Test method: The desorption solution was a 500 mg / L KCl solution, the time was 60 min, and the voltage was 1 V. Prepare a solution containing Na... + K + Li + and Mg 2+ An adsorption experiment was conducted using a mixed solution with a concentration of 100 mg / L. In the adsorption phase, the solution in the cathode chamber was replaced with a mixed ion solution. The voltage was set to 0.6 V, the time was 60 min, and the flow rate of the peristaltic pump was 5 mL / min. After adsorption, the solution was collected and analyzed using ICP-OES to determine the selective adsorption performance of the adsorbent material for lithium ions in the presence of competing ions.

[0098] Experimental results are as follows Figure 4(Selective adsorption diagram of lithium by PM-1.2LFP in Example 1) and Figure 5 (The selective adsorption diagram of lithium by M-0.8LFP in Comparative Example 1 is shown. The adsorption selectivity parameters of lithium by PM-1.2LFP and M-0.8LFP are shown in Table 3 below.)

[0099] Table 3 Adsorption selectivity parameters of PM-1.2LFP and M-0.8LFP for lithium

[0100] Experimental results show that: Li + K d At the highest, and at the same time, Li + Relative to Na + and Mg 2+ The selection separation factors were 7 and 6.5, respectively, while K + The adsorption capacity of Li is basically 0, indicating that the adsorption capacity of Li is basically 0. + It exhibits high adsorption selectivity in mixed ionic solutions. This is because, under a suitable voltage, only Li... + It can be embedded in the lattice of LFP. The polypyrrole coating and three-dimensional aerogel structure in PM-1.2LFP may optimize the surface charge and pore size of the material, enhancing the charge and size-based sieving effect.

[0101] 4. Cyclic regeneration performance test: PM-1.2LFP from Example 1 and M-0.8LFP from Comparative Example 1 were used as adsorbent materials for testing.

[0102] Test method: The above materials were used as working electrodes, and a CDI device was assembled to conduct five cycles of adsorption-desorption experiments. The desorption solution was a 500 mg / L KCl solution, the time was 60 min, and the voltage was 1 V. The adsorption solution was a 100 mg / L LiCl solution, the time was 60 min, and the voltage was 1 V. The peristaltic pump circulation rate was 5 mL / min. The CDI device was rinsed with ultrapure water between desorption and adsorption experiments.

[0103] Experimental results show that the adsorption-desorption cycle of lithium ions adsorbed by M-0.8LFP in Comparative Example 1 is shown in the figure below. Figure 6As shown, the initial adsorption capacity of the M-0.8LFP material was 30.32 mg / g. In subsequent cycles, the adsorption capacity decreased relatively in the second, third, and fourth cycles, remaining at around 27 mg / g. In the fifth cycle, a significant decrease occurred, to 22.32 mg / g, which was only 69.06% of the initial adsorption capacity. The decrease in electrode adsorption capacity is mainly due to the side reactions of hydrogen absorption and oxygen evolution that occur on the surface of the material electrode during multiple adsorption-desorption cycles. The evolved oxygen bubbles directly contact the MXene component in the material electrode, accelerating the oxidation of the MXene sheets, which leads to the destruction of the overall structure of the material, a significant decrease in conductivity, and thus a reduction in the electrode adsorption capacity.

[0104] The adsorption-desorption cycle experiment diagram of PM-1.2LFP for lithium ions in Example 1 is shown below. Figure 7 As shown, the initial adsorption capacity of PM-1.2LFP material was 27.17 mg / g. During subsequent cycles, the adsorption capacity remained essentially unchanged at around 27 mg / g in the 2nd, 3rd, and 4th cycles. In the 5th cycle, a slight decrease occurred to 25.98 mg / g, maintaining 95.6% of the initial adsorption capacity. This indicates that the material exhibits good cycling performance, with only a slight decrease in adsorption capacity over 5 cycles. This is because pyrrole forms a coating on MXene during polymerization, greatly increasing the antioxidant properties of MXene. This allows MXene to maintain structural stability even during oxygen evolution reactions at the electrode, thus maintaining the adsorption capacity at a certain level.

[0105] 5. The current efficiency of PM-1.2LFP (Example 1), PM-0.8LFP (Example 2), and PM-1.6LFP (Example 3) under different voltages was tested: 50 mL of 50 mg / L Li was injected into the CDI cathode cavity. + (1) Adsorb the solution, turn on the peristaltic pump, maintain a flow rate of 5 mL / min, and circulate for 5 min; (2) Start the data acquisition software, set the sampling interval to 1 s, then turn on the DC power supply, set the adsorption voltage (0.6V, 0.8V, 1.0V, 1.2V, voltage accuracy ±0.01V), and start the stopwatch at the same time. The adsorption time is precisely controlled to 30 min; (3) During the adsorption process, monitor the current change in real time to ensure no abnormal fluctuations (current fluctuation ≤ ±0.1mA), and maintain a stable experimental temperature; (4) After the adsorption is completed, immediately turn off the power supply, peristaltic pump and data acquisition software, and save the current-time data file; use a pipette to take the supernatant and detect Li through ICP-OES. + concentration.

[0106] Test results are as follows Figure 8 As shown; by Figure 8It can be seen that when the voltage is less than 0.8V, the current efficiency of the three materials remains above 95%, indicating that almost all the current is used for Li. + When the voltage increases to a certain level, side reactions occur at the electrode, and the current efficiency gradually decreases. The higher the voltage, the more energy is consumed in the side reactions. When the voltage increases to 1.2 V, the current efficiency of PM-0.8LFP and PM-1.2LFP materials basically decreases to about 80%, while that of PM-1.6LFP decreases to 85.5%. The possible reason is that PM-1.6LFP has a lower conductivity, which reduces the reaction efficiency of the side reactions.

[0107] The current efficiency test results of the M-0.8LFP in Comparative Example 1 under different voltages are as follows: Figure 9 As shown; by Figure 9 It can be seen that when the voltage increases to 1.2 V, the current efficiency of M-0.8LFP material basically drops to below 80%.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, characterized in that, Includes the following steps: S1. Mix MXene colloidal solution with lithium iron phosphate powder, stir and disperse to obtain mixture A; add pyrrole monomer solution to mixture A, stir to allow pyrrole monomer to be adsorbed on the surface of MXene and lithium iron phosphate; S2. Add an initiator solution to the system obtained in step S1 to initiate in-situ polymerization of pyrrole monomers to form MXene / LFP / PPy composite hydrogel; S3. The composite hydrogel is washed and freeze-dried to obtain the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material.

2. The method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 1, characterized in that, In step S1, the mass ratio of MXene to lithium iron phosphate in the MXene colloidal solution is 0.1:(0.8~1.6); The ratio of pyrrole monomer to lithium iron phosphate is (0.15-0.35) mL:(0.8-1.6) g.

3. The method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 1, characterized in that, In step S2, the initiator is ammonium persulfate, and the mass ratio of ammonium persulfate to pyrrole monomer is (0.9-1.2):

1.

4. The method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 1, characterized in that, In step S3, the freeze-drying temperature is -60~-50℃, the vacuum degree is 1~10Pa, and the freeze-drying time is 48-72h.

5. The method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 1, characterized in that, The MXene colloidal solution was prepared by a method including the following steps: reacting phase powder with an etchant under acidic conditions, followed by centrifugation, washing, and ultrasonic dispersion to obtain the MXene colloidal solution.

6. The method for preparing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 5, characterized in that, The etching agent is concentrated hydrochloric acid and LiF. The concentration of concentrated hydrochloric acid is 10-12 mol / L. The ratio of concentrated hydrochloric acid to Ti3AlC2 MAX phase is (15-25) mL:1 g. The mass ratio of LiF to Ti3AlC2 MAX phase is (1.5-1.7):

1. The ultrasonic dispersion time is 20-40 min, and the ultrasonic power is 100-150 W.

7. A polypyrrole-coated MXene / lithium iron phosphate composite aerogel material, wherein the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material is prepared by the method described in any one of claims 1-6.

8. The application of the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material as described in claim 7 in lithium extraction.

9. The application as described in claim 8, characterized in that, Used for selective extraction of Li from liquid systems + ; The process includes the following steps: applying an electrode slurry containing the polypyrrole-coated MXene / lithium iron phosphate composite aerogel material to the surface of the working electrode, and then performing Li-ionization using a dual-chamber capacitor deionization device. + Extraction.

10. The application as described in claim 9, characterized in that, The liquid system includes brine from a salt lake or a low-grade lithium solution, wherein the Li in the liquid system + The concentration is 10-200 mg / L, and coexisting ions include Na+. + K + Mg 2+ One or more of the following; The operating conditions of the dual-chamber capacitive deionization device are: adsorption voltage 0.4-1.2V, adsorption time 30-60min, and solution flow rate 3-7mL / min. The desorption voltage is 1.0-1.2V, and the desorption electrolyte is a potassium salt solution or a sodium salt solution. The concentration of the potassium salt solution or sodium salt solution is 450-550 mg / L.

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