Composite electrode material for electrochemical lithium extraction as well as preparation method and application of composite electrode material

Abstract

The invention discloses a composite electrode material for electrochemical lithium extraction and a preparation method and application thereof. The composite electrode material for electrochemical lithium extraction comprises cobalt lithium manganate nanoparticles and an MXene material, and the cobalt lithium manganate nanoparticles are prepared by mixing and sintering layered cobalt manganese double-metal hydroxide nanosheets and a lithium source. The CoMn-LDH nanosheet is used as a precursor to derive the cobalt lithium manganate nanoparticles and cooperates with d, the high selectivity of LCMO to lithium ions is reserved, meanwhile, an efficient three-dimensional conductive network is constructed by means of MXene, and the stability, the conductivity, the adsorption performance and the electrochemical performance of the composite electrode material can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials and electrochemical extraction, and particularly relates to a composite electrode material for high-selectivity extraction of lithium ions from salt lake brine and a preparation method and application thereof, in particular to a high-stability electrochemical lithium extraction material composed of CoMn-LDH-derived LiCoMnO4 and MXene. BACKGROUND

[0002] With the rapid development of the new energy vehicle industry in China, the demand for lithium-ion power batteries is increasing day by day. However, due to the difficulty and long development cycle of lithium resource development, the contradiction between supply and demand of lithium salt is increasingly prominent.

[0003] At present, the global lithium resource supply system mainly includes ore and salt lake, and the lithium resource amount in salt lake brine accounts for about 70% of the total global lithium resource amount. Therefore, how to efficiently develop the lithium resource in salt lake brine has important significance for alleviating the contradiction between supply and demand of lithium salt and promoting the healthy development of the new energy vehicle industry.

[0004] The main technologies for lithium extraction from salt lake in China include precipitation method, extraction method, electrodialysis method, adsorption method and electrochemical method. The existing electrochemical method for lithium extraction mainly utilizes potential to adjust the embedding / extraction of lithium ions in electrode materials, and generally achieves the effect of lithium extraction through redox reaction in electrode materials. The electrochemical method for lithium extraction can process salt lake brine at different stages and with different lithium concentrations, and the lithium extraction process does not use acid or alkali reagents and does not produce acid or alkali, so that the green and pollution-free extraction of lithium resources in brine can be realized. However, due to the high magnesium-lithium ratio, complex associated ions and low lithium concentration of salt lake brine in China, the poor cycle stability of the working electrode of the electrochemical method for lithium extraction and the dissolution loss of the electrode material, the application and promotion of the electrochemical method in large-scale industry are limited.

[0005] Currently, the electrode materials used for electrochemical lithium extraction mainly include polyanion materials (such as lithium iron phosphate LiFePO4) and spinel materials (such as lithium manganate LiMn2O4). The lithium manganate has a three-dimensional tunnel structure, which can significantly improve the lithium extraction capacity and selectivity. However, the structure of the lithium manganate is seriously affected by the Jiang-Taylor deformation during long-term charging and discharging, resulting in the loss of manganese ions and the decline of lithium extraction performance. At the same time, the lithium manganate has low conductivity, resulting in high energy consumption and low current efficiency in the electrochemical process. The prior art proposes some improvement schemes, for example, CN118479435A discloses a manganese phosphate modified lithium manganate composite electrode for electrochemical lithium extraction, which comprises a lithium manganate base material and manganese phosphate loaded on the surface of the lithium manganate base material. In the phosphate modified lithium manganate composite electrode, the manganese phosphate presents an amorphous surface coating, which can uniformly coat the lithium manganate base material. The manganese phosphate can effectively improve the hydrophilicity of the lithium manganate base material, promote lithium ion diffusion, and enhance the cycle stability of the lithium manganate. The lithium ion extraction and release can be effectively carried out in simulated brine and real Zhabuye alkaline brine containing high sodium / lithium ratio. For another example, CN116829768A discloses an electrode material, which comprises lithium manganate and metal organic framework Ti-MOF coated on the surface of the lithium manganate. The Ti-MOF forms a uniform coating layer on the surface of the lithium manganate electrode active material, which can inhibit the dissolution loss of Mn during the use of the lithium manganate electrode and improve the cycle stability of the electrode.

[0006] However, the coating method hinders the deintercalation of lithium ions, and the uniformity of the coating layer is difficult to control.

[0007] Therefore, it is of great importance to develop suitable electrode materials for electrochemical lithium extraction according to the characteristics of the salt lake brine in China, so as to realize the stability and selectivity of the electrode during the lithium extraction process and promote the industrial application of the electrochemical lithium extraction technology. SUMMARY

[0008] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a composite electrode material for electrochemical lithium extraction and a preparation method and application thereof.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a composite electrode material for electrochemical lithium extraction, which comprises cobalt lithium manganate nanoparticles and MXene material, wherein the cobalt lithium manganate nanoparticles are prepared by mixing layered cobalt-manganese double metal hydroxide nanosheets (abbreviated as CoMn-LDH nanosheets) with a lithium source and sintering.

[0011] In the present application, the lithium cobalt-manganese oxide nanoparticles refer to: the average particle size of the lithium cobalt-manganese oxide particles is 100 nm to 210 nm, for example, can be 100 nm, 120 nm, 140 nm, 150 nm, 170 nm, 180 nm, 190 nm, 200 nm or 210 nm, etc.

[0012] The present application uses CoMn-LDH nanosheets as a precursor to derive lithium cobalt-manganese oxide nanoparticles and cooperates with MXene, which not only retains the high selectivity of LCMO to lithium ions, but also constructs an efficient three-dimensional conductive network with the help of MXene, which can improve the stability, conductivity, adsorption performance and electrochemical performance of the composite electrode material. The technical principle is as follows: first, the lithium cobalt-manganese oxide (chemical formula LiCoMnO4, referred to as LCMO) nanoparticles have small size, which helps to shorten the lithium ion diffusion path, increase the specific surface area of the electrode material, and improve the adsorption efficiency and kinetic performance. Second, the LDH structure gives the metal elements a high uniform distribution, which forms a high crystallinity and stable spinel structure after calcination, which is beneficial to form an electrochemically active center. Third, compared with the traditional co-precipitation which needs to repeatedly control pH, temperature or aging conditions, the present application prepares lithium cobalt-manganese oxide nanoparticles by a simple sintering method, and the reaction conditions are relatively mild (for example, it can be sintered at 750℃ in a non-high pressure environment), which is more controllable and has potential for scale-up. Fourth, by taking advantage of the easy dispersion of layered LDH precursors, the lithium cobalt-manganese oxide nanoparticles obtained after calcination can be better embedded into the highly conductive two-dimensional MXene to construct a stable three-dimensional conductive network, form a structurally stable composite electrode material, and inhibit the phase transition and solution loss of LCMO, thereby better improving the conductivity and structural stability and effectively alleviating the Jahn-Teller distortion problem.

[0013] The composite electrode material of the present application has strong lithium ion selectivity and can still maintain good Li + / Mg 2+ separation capacity. It has high adsorption capacity, low operating energy consumption and excellent cycle stability.

[0014] The following is a preferred technical solution of the present application, but not as a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0015] Preferably, the mass ratio of the MXene material to the lithium cobalt manganese oxide nanoparticles is (30-75):100, for example, it can be 30:100, 35:100, 40:100, 45:100, 50:100, 55:100, 60:100, 65:100, 70:100 or 75:100, etc. By adjusting the mass ratio of the two, the diffusion rate and adsorption capacity of lithium ions can be significantly improved while maintaining high selectivity, providing a new idea for solving the challenges faced by current electrochemical lithium extraction technology.

[0016] Preferably, the average particle size of the layered cobalt-manganese double metal hydroxide nanosheet is below 220 nm, for example, it can be 200 nm, 190 nm, 180 nm, 170 nm, 160 nm, 150 nm, 140 nm, 130 nm, 120 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm or 50 nm, etc., preferably below 200 nm. The present application uses CoMn-LDH nanosheets with the above-mentioned average particle size as a precursor, and the LCMO nanoparticles formed by calcination are smaller, which is beneficial to shorten the lithium ion diffusion path, increase the specific surface area of the electrode material, and improve the adsorption efficiency and kinetic performance.

[0017] In a second aspect, the present application provides a preparation method of the composite electrode material for electrochemical lithium extraction according to the first aspect, the preparation method comprising the following steps:

[0018] Preparation of layered cobalt-manganese double metal hydroxide nanosheet, mixing the layered cobalt-manganese double metal hydroxide nanosheet with a lithium source, sintering to obtain lithium cobalt manganese oxide nanoparticles;

[0019] Dispersing the lithium cobalt manganese oxide nanoparticles and the MXene material into solvents respectively to obtain a first solution and a second solution;

[0020] After uniformly mixing the first solution and the second solution, drying to obtain the composite electrode material for electrochemical lithium extraction.

[0021] The method of the present application is simple, easy to operate, and suitable for industrial production.

[0022] As a preferred technical solution of the method of the present application, the preparation method of the layered cobalt-manganese double metal hydroxide nanosheet comprises the following steps:

[0023] Dispersing cobalt salt, manganese salt, ionic strength regulator and fluoride in a solvent, after a period of reaction, adding an oxidizing agent and adjusting the pH to alkaline, continuing to react, and then aging to obtain the layered cobalt-manganese double metal hydroxide nanosheet.

[0024] In the method of the present application, the ion strength regulator provides cations and anions, for example, Na + and NO3 - . By increasing the ion strength of the solution, an inert ion environment is provided, which helps to control the migration rate of metal ions during the reaction process, avoids the formation of amorphous products or uneven deposition due to rapid precipitation, and promotes slow precipitation and the formation of regular crystals. Moreover, increasing the ion strength can inhibit grain agglomeration and promote the formation of thinner and more uniform nanosheets.

[0025] In the method of the present application, fluoride regulates the crystal structure and interlayer distance of LDH. F- can be doped into the interlayer or lattice of LDH and cooperatively participate in crystal growth with OH-, which helps to stabilize the sheet structure, adjust the interlayer distance, improve the crystallinity and controllability, and limit the longitudinal growth of the crystal to form thinner and more regular nanosheet structures. At the same time, F- can weakly complex Co 2+ , Mn 2+ , delaying the rate of direct reaction with OH-, thereby controlling the nucleation rate, slow precipitation, and promoting uniform crystal growth, avoiding the formation of large amorphous impurities due to one-time rapid precipitation. Moreover, the introduction of F- ions may partially replace OH- to generate surface active sites, which has a positive impact on the electronic structure and interface properties of the subsequent calcined product (such as LCMO). In the method of the present application, the oxidizing agent adjusts the oxidation state of the metal, which can oxidize part of the Mn 2+ to Mn 3+ or Mn 4+ , and the introduction of Mn 3+ / Mn 4+ is conducive to the formation of a stable LDH layered structure and the adjustment of the electronic structure, Mn valence distribution, and oxygen vacancy concentration of the subsequently prepared LCMO, thereby indirectly affecting its electrochemical performance (such as higher lithium adsorption capacity and more stable valence cycle).

[0026] Preferably, the molar ratio of the cobalt salt, manganese salt, ion strength regulator, and fluoride is (1.5-3):1:(2-5):(10-30), wherein the selection range of the cobalt salt is "1.5-3", for example, it can be 1.5, 1.7, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or 3, etc.; the selection range of the ion strength regulator is "2-5", for example, it can be 2, 2.2, 2.5, 2.7, 3, 3.3, 3.6, 4, 4.2, 4.5, 4.8, or 5, etc.; and the selection range of the fluoride is "10-30", for example, it can be 10, 12, 15, 18, 20, 22, 24, 26, 28, or 30, etc.

[0027] Preferably, the ion strength regulator includes at least one of sodium nitrate, potassium nitrate, lithium nitrate, sodium chloride, or ammonium nitrate.

[0028] Preferably, the fluoride comprises at least one of ammonium fluoride, sodium fluoride, potassium fluoride or HF.

[0029] Preferably, the oxidant comprises at least one of hydrogen peroxide, potassium permanganate, sodium nitrate, lithium nitrate, potassium persulfate or ammonium persulfate, preferably hydrogen peroxide. Compared with other oxidants, hydrogen peroxide can not only adjust the oxidation state of metal, which is conducive to the formation of stable LDH layered structure, but also adjust the electronic structure, Mn valence distribution and oxygen vacancy concentration of the subsequently prepared LCMO. Further, the oxidation of hydrogen peroxide can control the reaction rate, promote uniform nucleation, make the co-precipitation process more gentle and orderly, and prevent the formation of amorphous or impurity phases. Moreover, hydrogen peroxide is easy to obtain, environmentally friendly, and suitable for industrial application. Preferably, the amount of the oxidant added is 0.01-0.1 times (for example, it can be 0.01 times, 0.02 times, 0.03 times, 0.04 times, 0.05 times, 0.06 times, 0.07 times, 0.08 times or 0.1 times, etc.) of the molar amount of the cobalt salt, or the volume of the oxidant added is 0.01vol%-0.1vol% (for example, it can be 0.01vol%, 0.02vol%, 0.03vol%, 0.05vol%, 0.06vol%, 0.07vol%, 0.08vol%, 0.09vol% or 0.1vol%, etc.) of the total volume of the reaction solution. Generally, when the oxidant is in a solid state, the amount of the oxidant added is calculated as 0.01-0.1 times of the molar amount of the cobalt salt; when the oxidant is in a liquid state, the volume of the oxidant added is calculated as 0.01vol%-0.1vol% of the total volume of the reaction solution.

[0030] Preferably, the pH is adjusted to 9.0-11.0, for example, it can be 9.0, 9.2, 9.3, 9.5, 9.7, 10.0, 10.2, 10.5, 10.7 or 11.0, etc.

[0031] Preferably, the solvent is water, and the solvent is subjected to oxygen removal treatment before use.

[0032] Preferably, the pH is adjusted using a basic solution, and the basic solution is subjected to oxygen removal treatment before use.

[0033] Preferably, the aging time is 12-16 hours, for example, it can be 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, 15.5 hours or 16 hours, etc.

[0034] As a preferred technical solution of the preparation method of the present application, the preparation method of the MXene material comprises the following steps:

[0035] mixing the acidic solution with the fluorine-containing substance to generate HF by reaction, to obtain a third solution;

[0036] adding the MAX phase material into the third solution and stirring to separate the MXene material.

[0037] In this scheme, HF is generated in the liquid phase by the reaction of the acidic solution with the fluorine-containing substance, and the titanium aluminum carbide is etched, which can accurately remove the A layer metal (such as Al) in the MAX phase material without damaging the main structure (such as Ti3C2), and is easy to peel off the interlayer to obtain a layered MXene structure. This method generates HF in situ, which is better than direct HF etching method, because it is more mild and safer, and can introduce -OH, -F and other functional groups on the surface of MXene, which helps to control the hydrophobicity / hydrophilicity between the layers, enhances the dispersibility, and improves the subsequent composite ability and stability of the material.

[0038] Preferably, the acidic solution comprises an acid and / or an acidic ion exchanger.

[0039] Preferably, the acid comprises at least one of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid or acetic acid.

[0040] Preferably, the hydrogen ion concentration of the acidic solution is 9 mol / L to 10 mol / L, for example, it can be 9 mol / L, 9.2 mol / L, 9.4 mol / L, 9.6 mol / L, 9.8 mol / L or 10 mol / L, etc.

[0041] Preferably, the fluorine-containing substance comprises at least one of lithium fluoride, potassium fluoride, sodium fluoride, ammonium fluoride, LiNO3+HF or LiCl+HF. Among them, LiNO3+HF refers to a mixture of LiNO3 and HF; LiCl+HF refers to a mixture of LiCl and HF.

[0042] Preferably, the acidic solution is hydrochloric acid, and the fluorine-containing substance is lithium fluoride. The reason for preferring this scheme is that it can better guarantee the structural stability of MXene and the safety of the experiment.

[0043] Preferably, the ratio of the volume of the acidic solution to the mass of the fluorine-containing substance is (30-60) mL / 3g, for example, it can be 30 mL / 3g, 35 mL / 3g, 40 mL / 3g, 45 mL / 3g, 50 mL / 3g, 55 mL / 3g or 60 mL / 3g, etc.

[0044] Preferably, the MAX phase material comprises at least one of titanium aluminum carbide Ti3AlC2, Ti2AlC, Ti4AlN3, Nb2AlC, Nb4AlC3, V2AlC, Cr2AlC, Mo2TiAlC2 and Mo2Ti2AlC3. But not limited to the above-mentioned kinds, other commonly used MAX phase materials capable of being used for preparing MXene in the art are also applicable to the present application.

[0045] Preferably, the ratio of the mass of the MAX phase material to the volume of the third solution is 1g:(10-25)mL, for example, it can be 1g:10mL, 1g:15mL, 1g:20mL or 1g:25mL, etc.

[0046] Preferably, the stirring time is 12h-26h, for example, it can be 12h, 14h, 15h, 17h, 18h, 20h, 22h, 24h or 26h, etc.

[0047] Preferably, the obtained MXene material is a MXene solution.

[0048] Preferably, the mass ratio of the layered cobalt-manganese double metal hydroxide nanosheet to the lithium source is (9-11):1, for example, it can be 9:1, 9.2:1, 9.5:1, 9.7:1, 10:1, 10.5:1 or 11:1, etc.

[0049] Preferably, the sintering temperature is 700℃-850℃, for example, it can be 700℃, 725℃, 750℃, 770℃, 800℃, 830℃ or 850℃, etc.

[0050] Preferably, the sintering time is 8h-15h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h or 15h, etc.

[0051] In a second aspect, the present application provides an anode comprising the composite electrode material of the first aspect.

[0052] In a third aspect, the present application provides an electrochemical lithium extraction device comprising the anode of the second aspect.

[0053] The numerical ranges disclosed in the present application include not only the point values listed above, but also any point values between the above-mentioned numerical ranges, which are not listed due to the limitation of the size and for the sake of simplicity. The present application does not list the specific point values included in the range.

[0054] Compared with the prior art, the present application has the following beneficial effects:

[0055] (1) The application uses CoMn-LDH nanosheets as a precursor to derive lithium cobalt manganese oxide nanoparticles and cooperates with MXene, which not only retains the high selectivity of LCMO to lithium ions, but also constructs an efficient three-dimensional conductive network with the help of MXene, which can improve the stability, conductivity, adsorption performance and electrochemical performance of the composite electrode material.

[0056] (2) The lithium ion selectivity of the composite electrode material of the application is strong, and it can still maintain good Li + / Mg 2+ separation capacity in a high magnesium-lithium ratio solution. It has high adsorption capacity, low operating energy consumption and excellent cycle stability.

[0057] (3) The lithium ion adsorption capacity of the electrochemical lithium extraction composite electrode material of the application on lithium chloride solution is 120.13mg g -1 above, preferably 160.18mg g -1 above.

[0058] The lithium ion adsorption capacity of the electrochemical lithium extraction composite electrode material of the application on simulated brine is 0.57μmol g -1 above, preferably 0.84μmol g -1 above.

[0059] The results of the desalination test of the electrochemical lithium extraction composite electrode material of the application show that the separation factor of lithium ions and magnesium ions is 0.85 or more, preferably 0.91 or more.

[0060] The results of the cycle stability test of the electrochemical lithium extraction composite electrode material of the application show that the capacity retention rate is 67.5% or more, preferably 80.8% or more after 100 cycles. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is the SEM image of the LCMO / MXene composite material prepared in Example 2.

[0062] Figure 2 is the XRD image of the LCMO / MXene composite material prepared in Example 2.

[0063] Figure 3 is the CV image of the LCMO / MXene composite material prepared in Example 1, Example 2 and Example 3. DETAILED DESCRIPTION

[0064] The technical solutions of the application will be further described below in conjunction with the drawings and through specific embodiments.

[0065] The specific embodiments described herein are for purposes of illustration only and are not intended to limit the application.

[0066] In the present application, the atmospheric temperature and the room temperature both refer to 22-28℃, and the change of temperature within the range will not affect the preparation of the experiment and the performance of the product prepared.

[0067] Example 1

[0068] The present embodiment provides a preparation method of a composite electrode material for electrochemical lithium extraction, comprising the following steps:

[0069] (1) Preparation of Co-Mn LDH precursor

[0070] S1: At the beginning of synthesis, 2mM Co(NO3)2·6H2O, 1mM Mn(NO3)2·4H2O, 4.8mM NaNO3 and 24mM NH4F were dispersed in 600mL oxygen-free water (obtained by blowing water with argon for 30 minutes), and stirred vigorously at atmospheric temperature. During the synthesis process, argon was continuously introduced into the pink solution to maintain an inert atmosphere.

[0071] S2: After 30 minutes, 125μL H2O2 (concentration of 30wt%) was added to the mixture. Subsequently, the pH value of the solution was adjusted to 10.0 by dropwise adding 0.08M NaOH solution (blown with argon for 30 minutes before use), and the color of the solution gradually changed to yellow, and then quickly changed to black brown. The obtained suspension was aged at room temperature for 15 hours. After aging, the precipitate was collected by centrifugation and washed with ethanol and deionized water for several times.

[0072] S3: Finally, it was dried in a vacuum oven at 60℃ for 12 hours. The synthesized black powder product was identified as layered cobalt-manganese bimetallic oxide nanosheets (abbreviated as Co-Mn LDH). The average particle size of the synthesized Co-Mn LDH particles was 200nm, which could be directly used for the preparation of LCMO.

[0073] (2) Preparation of LCMO

[0074] S1: The Co-Mn LDH prepared in step (1) was uniformly mixed with LiOH·H2O at a mass ratio of 10:1 by grinding, to obtain a uniform mixture. Subsequently, the uniform mixture was transferred to a muffle furnace, the temperature was raised to 750℃, and maintained for 10 hours.

[0075] S2: After sintering was completed, the sample was naturally cooled to room temperature to obtain LCMO nanoparticles with an average particle size of 150nm and positive charge.

[0076] (3) Preparation of MXene

[0077] S1: 40 mL of 9 mol / L hydrochloric acid and 3 g of lithium fluoride were mixed and magnetically stirred at room temperature for 15 minutes until completely dissolved.

[0078] S2: 4 g of titanium aluminum carbide (Ti3AlC2) powder was slowly and uniformly added to the above solution within 20 minutes, and the sealed container was magnetically stirred at 35°C for 24 hours. Then, centrifugal filtration and washing were performed several times, and the centrifugal speed was gradually increased until the pH value of the supernatant was greater than 6.

[0079] S3: The precipitate was collected and added to 60 mL of deionized water, and after ultrasonic dispersion until completely dissolved, the supernatant was collected by centrifugation at a speed of 3000 rpm for 20 minutes, to obtain a black MXene solution.

[0080] (4) Preparation of LCMO / MXene composite material

[0081] 10 mg of MXene was added to 10 mL of deionized water and ultrasonically dispersed until completely dissolved to obtain solution A. 10 mg of positively charged LCMO powder was added to 10 mL of deionized water and ultrasonically dispersed until completely dissolved to obtain solution B. Solution A and solution B were mixed in a ratio of 7:3, respectively, and magnetically stirred for 1 hour. After centrifugation and washing with ethanol and deionized water several times, the precipitate was collected and freeze-dried for 48 hours to obtain an LCMO / MXene composite material, referred to as 30% LCMO@MXene.

[0082] The composite material prepared in this example includes lithium cobalt-manganese oxide nanoparticles and MXene material, and the average particle size of the lithium cobalt-manganese oxide nanoparticles is 160 nm, and the mass fraction of the lithium cobalt-manganese oxide nanoparticles is 30%.

[0083] Figure 1 is the SEM image of the LCMO / MXene composite material prepared in this example. As can be seen from the figure, it presents a combination of two-dimensional sheet structure and granular morphology, and the LCMO nanoparticles are embedded between the MXene layers. The LCMO particles are cubic, with an average particle size of about 150 nm. Compared with traditional spinel oxides, the size is smaller, which is beneficial to improve the specific surface area and ion diffusion rate.

[0084] Figure 2 is the XRD image of the LCMO / MXene composite material prepared in this example. As can be seen from the figure, the crystal structure is not damaged during the compounding of MXene and LCMO, and the spinel structure of LCMO is completely preserved, and the material has good crystallinity and structural stability.

[0085] Example 2

[0086] The difference between this embodiment and embodiment 1 is that in step (4), solution A and solution B are mixed at a ratio of 1:1, respectively.

[0087] The composite material prepared in this embodiment comprises lithium cobalt-manganese oxide nanoparticles and MXene material, the average particle size of the lithium cobalt-manganese oxide nanoparticles is 150 nm, and the mass percentage of the lithium cobalt-manganese oxide nanoparticles is 50%.

[0088] The LCMO / MXene composite material prepared in this embodiment is referred to as 50% LCMO@MXene.

[0089] Embodiment 3

[0090] The difference between this embodiment and embodiment 1 is that in step (4), solution A and solution B are mixed at a ratio of 1:3, respectively.

[0091] The composite material prepared in this embodiment comprises lithium cobalt-manganese oxide nanoparticles and MXene material, the average particle size of the lithium cobalt-manganese oxide nanoparticles is 180 nm, and the mass percentage of the lithium cobalt-manganese oxide nanoparticles is 75%.

[0092] The LCMO / MXene composite material prepared in this embodiment is referred to as 75% LCMO@MXene.

[0093] Embodiment 4

[0094] The embodiment provides a preparation method of a composite electrode material for electrochemical lithium extraction, comprising the following steps:

[0095] (1) Preparation of Co-Mn LDH precursor

[0096] S1: At the beginning of synthesis, 3 mM Co(NO3)2·6H2O, 1 mM Mn(NO3)2·4H2O, 5 mM KNO3 and 30 mM NH4F were dispersed in 600 mL oxygen-free water (obtained by purging water with argon for 30 minutes), and stirred vigorously at atmospheric temperature. During the synthesis process, argon was continuously introduced into the pink solution to maintain an inert atmosphere.

[0097] S2: After 30 minutes, 400 μL of H2O2 (concentration of 30 wt%) was added to the mixture. Subsequently, the pH value of the solution was adjusted to 9.0 by dropwise addition of a 0.08 M NaOH solution (blown with argon for 30 minutes before use). The obtained suspension was aged at room temperature for 12 hours. After aging, the precipitate was collected by centrifugation and washed with ethanol and deionized water for 3 times, respectively.

[0098] S3: Finally, drying in a vacuum oven at 70°C for 10 hours. The synthesized black powder product is identified as Co-Mn LDH. The average particle size of the synthesized Co-Mn LDH particles is 210 nm, which can be directly used to prepare LCMO.

[0099] (2) Preparation of LCMO

[0100] S1: The Co-Mn LDH prepared in step (1) is uniformly mixed with LiOH H2O at a mass ratio of 11:1 by grinding to obtain a uniform mixture. Subsequently, the uniform mixture is transferred to a muffle furnace, the temperature is raised to 800°C, and maintained for 8 hours.

[0101] S2: After sintering is completed, the sample is naturally cooled to room temperature to obtain LCMO nanoparticles with an average particle size of 160 nm and positive charge.

[0102] (3) Preparation of MXene

[0103] S1: Mix 30 mL of 10 mol / L hydrochloric acid and 3 g of lithium fluoride, and magnetically stir at room temperature for 15 minutes until completely dissolved.

[0104] S2: Add 1.2 g of Ti4AlN3 powder to the above solution at a uniform speed for 20 minutes, and magnetically stir the sealed container at 35°C for 18 hours. Then, centrifugal filtration and washing are performed multiple times, and the centrifugal speed is gradually increased until the pH value of the supernatant is greater than 6.

[0105] S3: Collect the precipitate and add 60 mL of deionized water. After ultrasonic dissolution for 30 minutes, centrifuge at 3000 rpm for 20 minutes to collect the supernatant, and obtain a black MXene solution.

[0106] (4) Preparation of LCMO / MXene composite material

[0107] Add 10 mg of MXene to 10 mL of deionized water, and ultrasonic dispersion until completely dissolved to obtain solution A. Add 10 mg of positively charged LCMO powder to 10 mL of deionized water, and ultrasonic dispersion until completely dissolved to obtain solution B. Mix solution A and solution B at a ratio of 6:4, respectively, magnetically stir for 1 hour, centrifuge and wash with ethanol and deionized water multiple times to collect the precipitate, and freeze-dry for 40 hours to obtain an LCMO / MXene composite material.

[0108] The composite material prepared in this example includes lithium cobalt manganese oxide nanoparticles and MXene material, and the average particle size of the lithium cobalt manganese oxide nanoparticles is 160 nm, and the mass fraction of the lithium cobalt manganese oxide nanoparticles is 40%.

[0109] Example 5

[0110] The present embodiment provides a preparation method of a composite electrode material for electrochemical lithium extraction, comprising the following steps:

[0111] (1) Preparation of Co-Mn LDH precursor

[0112] S1: At the beginning of synthesis, 1.5 mM Co(NO3)2·6H2O, 1 mM Mn(NO3)2·4H2O, 3 mM NaNO3 and 18 mM NH4F were dispersed in 600 mL oxygen-free water (obtained by purging water with argon for 30 minutes), and stirred vigorously at atmospheric temperature. During the synthesis, argon was continuously introduced into the pink solution to maintain an inert atmosphere.

[0113] S2: After 30 minutes, 265 μL H2O2 (concentration of 30 wt%) was added to the mixture. Subsequently, the pH value of the solution was adjusted to 9.5 by dropwise addition of a 0.05 M NaOH solution (purged with argon for 30 minutes before use). The resulting suspension was aged at room temperature for 16 hours. After aging, the precipitate was collected by centrifugation and washed several times with ethanol and deionized water.

[0114] S3: Finally, drying was performed in a vacuum oven at 65°C for 14 hours. The synthesized black powder product was identified as Co-Mn LDH. The average particle size of the synthesized Co-Mn LDH particles was 210 nm, which can be directly used to prepare LCMO.

[0115] (2) Preparation of LCMO

[0116] S1: The Co-Mn LDH prepared in step (1) was uniformly mixed with LiOH·H2O at a mass ratio of 9:1 by grinding, to obtain a uniform mixture. Subsequently, the uniform mixture was transferred to a muffle furnace, the temperature was raised to 850°C, and maintained for 9 hours.

[0117] S2: After sintering was completed, the sample was naturally cooled to room temperature to obtain LCMO nanoparticles with an average particle size of 160 nm and positive charge.

[0118] (3) Preparation of MXene

[0119] S1: 60 mL of hydrochloric acid with a concentration of 9.5 mol / L and 5 g of lithium fluoride were mixed and magnetically stirred at room temperature for 20 minutes until complete dissolution.

[0120] S2: 3.5 g of titanium aluminum carbide (Ti3AlC2) powder was slowly and uniformly added to the above solution within 20 minutes, and the sealed container was magnetically stirred at 35°C for 24 hours. Subsequently, it was centrifuged and washed several times, and the centrifugal speed was gradually increased until the pH value of the supernatant was greater than 6.

[0121] S3: Collecting the precipitate, adding 60 mL of deionized water, ultrasonic dispersion for 30 minutes until completely dissolved, centrifuging at 3000 rpm for 20 minutes to collect the supernatant, and obtaining a black MXene solution.

[0122] (4) Preparation of LCMO / MXene composite material

[0123] 10 mg of MXene was added to 10 mL of deionized water, ultrasonic dispersion until completely dissolved to obtain solution A. 10 mg of positively charged LCMO powder was added to 10 mL of deionized water, ultrasonic dispersion until completely dissolved to obtain solution B. Solution A and solution B were mixed in a ratio of 4:6 respectively, magnetic stirring for 1 hour, centrifugation and washing with ethanol and deionized water for several times to collect the precipitate, and freeze-drying for 48 hours to obtain the LCMO / MXene composite material.

[0124] The composite material prepared in this example includes lithium cobalt manganese oxide nanoparticles and MXene material, the average particle size of the lithium cobalt manganese oxide nanoparticles is 160 nm, and the mass fraction of the lithium cobalt manganese oxide nanoparticles is 60%.

[0125] Example 6

[0126] The difference between this example and Example 1 is that the amount of NaNO3 is replaced by 10 mM.

[0127] Example 7

[0128] The difference between this example and Example 1 is that the amount of NaNO3 is replaced by 1 mM.

[0129] Example 8

[0130] The difference between this example and Example 1 is that the amount of NH4F is replaced by 40 mM.

[0131] Example 9

[0132] The difference between this example and Example 1 is that the amount of NH4F is replaced by 5 mM.

[0133] Comparative Example 1

[0134] The difference between this comparative example and Example 1 is that steps (3) and (4) are not performed, and the LCMO nanoparticles prepared in step (2) are directly used as the product.

[0135] Comparative Example 2

[0136] The difference between this comparative example and Example 1 is that steps (1) and (2) are not performed, and LCMO is prepared by co-precipitation method. The specific steps of the co-precipitation method are as follows:

[0137] LiNO3, Co(NO3)2and Mn(NO3)2were dissolved in deionized water in a molar ratio of 1 : 1 : 1 to form a mixed metal ion solution. Another portion of a basic precipitant solution (1 M NaOH solution) was prepared. The basic precipitant solution was slowly added to the mixed metal ion solution under stirring to maintain a pH of 10. The reaction was stirred at room temperature for 1 hour to form a mixed hydroxide precursor, and the reaction mixture was aged for 24 hours to improve crystallinity. The product was washed by centrifugation several times to remove ionic impurities, and then dried at 80 °C under vacuum for 12 hours. The dried precipitate was calcined in a muffle furnace at 750 °C for 10 hours to obtain LCMO.

[0138] Performance test:

[0139] (1) Preparation of anode: The product prepared in each example and comparative example was used as an anode material. 15 mg of the anode material was mixed with carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 8: 1: 1 in a solvent N-methyl pyrrolidone (NMP) to form a slurry, which was applied to a 2 cm x 2 cm area in the center of a graphite paper to form an electrode sheet of a CDI electrode, and then baked at 60 °C for 12 hours to obtain an anode.

[0140] (2) Preparation of cathode: Activated carbon was used as a cathode material. The cathode material was mixed with carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 8: 1: 1 in a solvent NMP to form a slurry, which was applied to a 2 cm x 2 cm area in the center of a graphite paper to form an electrode sheet of a CDI electrode, and then baked at 60 °C for 12 hours to obtain a cathode.

[0141] (3) CDI performance test: The above anode and cathode were used, and the conductivity of the lithium chloride solution was set to 1000 μ8cm -1 . The lithium chloride solution was pumped into a device in which the cathode and anode were placed using a peristaltic pump at a speed of 100 rpm. The voltage range was -1.4 V to 1.4 V, and the desalination amount of the electrode material at a current density of 30 mAg -1 was analyzed. The lithium ion adsorption capacity of the lithium chloride solution was calculated by determining the lithium concentration in the initial and effluent solutions of the lithium chloride solution by ICP-MS. The results are shown in Table 1.

[0142] Adsorption capacity calculation formula:

[0143] V is the volume of the lithium chloride solution, in L; Co represents the initial concentration of lithium in the feed solution, in g / L; C represents the concentration of lithium in the effluent solution, in g / L; and m is the mass of the anode material, in g.

[0144] (4) Desalination capacity test: Keeping the above CDI electrode sample preparation process unchanged, the lithium chloride solution was replaced with simulated brine from Chaka Salt Lake in Jieze, Tibet Autonomous Region. The electrode material was tested at a current of 30 mAg. -1 The desalination rate was determined. The lithium and magnesium concentrations in the initial and effluent solutions of the simulated brine were measured by ICP-MS. The lithium-ion adsorption capacity, magnesium-ion adsorption capacity, and separation factors of lithium and magnesium ions in the simulated brine were calculated. The results are shown in Table 1.

[0145] Adsorption capacity calculation formula:

[0146] V represents the volume of simulated brine in the Jieze Chaka Salt Lake in Tibet Autonomous Region, in L; C0 represents the initial concentration of lithium or magnesium in the feed solution, in mol / L; C represents the concentration of lithium or magnesium in the discharge solution, in mol / L; m represents the mass of the anode material, in g.

[0147] When testing the lithium-ion adsorption capacity of simulated brine, C0 is the initial lithium concentration in the feed solution, and C is the lithium concentration in the effluent solution. Similarly, when testing the magnesium-ion adsorption capacity of simulated brine, C0 is the initial magnesium concentration in the feed solution, and C is the magnesium concentration in the effluent solution.

[0148] Formula for calculating the separation factor of lithium ions and magnesium ions:

[0149] in, For the selectivity of lithium ions, This refers to the selectivity of magnesium ions.

[0150] The formula for calculating selectivity is as follows:

[0151]

[0152] When calculating lithium-ion selectivity, C0 is the initial lithium concentration in the feed solution, and C is the lithium concentration in the effluent solution. When testing the magnesium-ion adsorption capacity against simulated brine, C0 is the initial magnesium concentration in the feed solution, and C is the magnesium concentration in the effluent solution.

[0153] (5) Cyclic stability test: The stability was evaluated through 100 charge-discharge cycles in simulated saline solution, which was an aqueous solution of lithium chloride and magnesium chloride. + The concentration is 0.56 g / L, Mg 2+ The concentration was 0.40 g / L, the current density was set to 30 mA / g, and the voltage range was -1.4 V to +1.4 V. The results are shown in Table 1, where the capacity retention after 100 cycles = (capacity at the 100th cycle / capacity at the first cycle) × 100%.

[0154] Table 1

[0155]

[0156] As can be seen from Table 1, the lithium ion adsorption capacity of the electrochemical lithium extraction composite electrode material of the present application to lithium chloride solution is 120.13 mg g -1 Preferably, the lithium ion adsorption capacity is 160.18 mg g -1 Preferably, the lithium ion adsorption capacity of Example 2 is as high as 188.55 mg g -1 , which exhibits excellent lithium ion adsorption performance.

[0157] The lithium ion adsorption capacity of the electrochemical lithium extraction composite electrode material of the present application to simulated brine is 0.57 μmol g -1 Preferably, the lithium ion adsorption capacity is 0.84 μmol g -1 Preferably, the lithium ion adsorption capacity of Example 2 is as high as 1.39 μmol g -1 , which is 4.93 times the magnesium ion adsorption capacity to simulated brine.

[0158] The results of the desalination test of the electrochemical lithium extraction composite electrode material of the present application show that the separation factor of lithium ion and magnesium ion is 0.85 or higher, preferably 0.91 or higher, and the separation factor of Example 2 is as high as 1.58, which is 1.9 times that of LCMO (Comparative Example 1), exhibiting excellent selective adsorption capacity for lithium ion.

[0159] The results of the cycle stability test of the electrochemical lithium extraction composite electrode material of the present application show that the capacity retention rate is 67.5% or higher, preferably 80.8% or higher, and the capacity retention rate of Example 2 is as high as 92.9%.

[0160] As can be seen from the comparison of Example 1 and Examples 6-7, the amount of ionic strength adjuster used in the preparation of Co-Mn LDH precursor has an optimal range, and by optimizing this range, the performance of the composite electrode material can be improved.

[0161] As can be seen from the comparison of Example 1 and Examples 8-9, the amount of fluoride used in the preparation of Co-Mn LDH precursor has an optimal range, and by optimizing this range, the performance of the composite electrode material can be improved.

[0162] The electrode material of Comparative Example 1 does not introduce MXene, resulting in a decrease in lithium ion adsorption capacity to simulated brine, separation factor of lithium ion and magnesium ion, and cycle performance to different degrees.

[0163] Comparative Example 2 uses a conventional co-precipitation method to prepare LCMO, resulting in a decrease in lithium ion adsorption capacity to lithium chloride solution, lithium ion adsorption capacity to simulated brine, lithium ion and magnesium ion separation factor, and cycle performance to varying degrees.

[0164] (6) The LCMO / MXene composite materials of Example 1, Example 2 and Example 3 were respectively used to prepare electrodes, and CV tests were performed, Figure 3 are the CV images of the LCMO / MXene composite materials of Example 1, Example 2 and Example 3, respectively, from which it can be seen that the composite material of Example 2 exhibits the most optimal electrochemical reaction activity, strong reversibility and maximum capacity in the CV test. Figure 3

[0165] (7) Energy consumption test: according to the CDI performance test described in (3) above, the energy consumed by the LCMO / MXene composite material of Example 2 to remove 1 g of lithium chloride is calculated, by recording the voltage, current and power-on time during the CDI process, and combining the lithium ion adsorption capacity to obtain, the calculation formula is:

[0166] wherein I and U represent the instantaneous current (unit: ampere) and voltage (unit: volt), respectively. ΔC represents the change in lithium ion concentration before and after ion adsorption, with a unit of milligrams per liter; V is the volume of the lithium chloride solution, with a unit of liters. The result is only 1.15 Wh mol-1, indicating low operating energy consumption.

[0167] The applicant declares that the detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.​

Claims

1. A composite electrode material for electrochemically extracting lithium, characterized by comprising a lithium metal oxide and a carbon material. The composite electrode material for electrochemical lithium extraction comprises lithium cobalt-manganese oxide nanoparticles and MXene material, wherein the lithium cobalt-manganese oxide nanoparticles are prepared by mixing layered cobalt-manganese double metal hydroxide nanosheets with a lithium source and sintering. 2.The composite electrode material for electrochemical lithium extraction according to claim 1, characterized in that, The mass ratio of the MXene material to the lithium cobalt-manganese oxide nanoparticles is (30-75):

100. Preferably, the average particle size of the layered cobalt-manganese double metal hydroxide nanosheets is below 220 nm, preferably below 200 nm.

3. A method for preparing the composite electrode material for electrochemically extracting lithium according to claim 1 or 2, characterized by, The preparation method comprises the following steps: Preparation of layered cobalt-manganese double metal hydroxide nanosheets, mixing the layered cobalt-manganese double metal hydroxide nanosheets with a lithium source, and sintering to obtain lithium cobalt-manganese oxide nanoparticles; Dispersing the lithium cobalt-manganese oxide nanoparticles and the MXene material into solvents respectively to obtain a first solution and a second solution; After uniformly mixing the first solution and the second solution, drying to obtain the composite electrode material for electrochemical lithium extraction.

4. The production method according to claim 3, characterized by, The preparation method of the layered cobalt-manganese double metal hydroxide nanosheets comprises the following steps: Dispersing a cobalt salt, a manganese salt, an ionic strength regulator, and a fluoride in a solvent, after a period of reaction, adding an oxidizing agent and adjusting the pH to alkaline, continuing the reaction, and then aging to obtain the layered cobalt-manganese double metal hydroxide nanosheets.

5. The production method according to claim 4, characterized by, The molar ratio of the cobalt salt, the manganese salt, the ionic strength regulator, and the fluoride is (1.5-3):1:(2-5):(10-30). Preferably, the ionic strength regulator comprises at least one of sodium nitrate, potassium nitrate, lithium nitrate, sodium chloride, or ammonium nitrate. Preferably, the fluoride comprises at least one of ammonium fluoride, sodium fluoride, potassium fluoride, or HF. Preferably, the oxidizing agent comprises at least one of hydrogen peroxide, potassium permanganate, sodium nitrate, lithium nitrate, potassium persulfate, or ammonium persulfate. Preferably, the amount of the oxidizing agent added is 0.01-0.1 times the molar amount of the cobalt salt, or the volume of the oxidizing agent added is 0.01vol%-0.1vol% of the total volume of the reaction solution. Preferably, the pH is adjusted to 9.0-11.

0. Preferably, the solvent is water, which is deoxygenated before use. Preferably, the pH is adjusted using a basic solution, which is deoxygenated before use. Preferably, the aging time is 12-16 h.

6. The production method according to claim 4 or 5, characterized by, The average particle size of the layered cobalt-manganese double metal hydroxide nanosheets is below 220 nm, preferably below 200 nm.

7. The method of any one of claims 3-6, wherein, The preparation method of the MXene material comprises the following steps: Mixing an acidic solution with a fluorine-containing substance uniformly to generate HF to obtain a third solution; Adding a MAX phase material to the third solution and stirring to separate the MXene material; Preferably, the acidic solution comprises an acid and / or an acidic ion exchanger. Preferably, the acid comprises at least one of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, or acetic acid. Preferably, the hydrogen ion concentration of the acidic solution is 9-10 mol / L. Preferably, the fluorine-containing substance includes at least one of lithium fluoride, potassium fluoride, sodium fluoride, ammonium fluoride, LiNO3+HF or LiCl+HF; Preferably, the acidic solution is hydrochloric acid, and the fluorine-containing substance is lithium fluoride; Preferably, the ratio of the volume of the acidic solution to the mass of the fluorine-containing substance is (30-60)mL / 3g; Preferably, the MAX phase material includes at least one of titanium aluminum carbide Ti3AlC2, Ti2AlC, Ti4AlN3, Nb2AlC, Nb4AlC3, V2AlC, Cr2AlC, Mo2TiAlC2 and Mo2Ti2AlC3; Preferably, the ratio of the mass of the MAX phase material to the volume of the third solution is 1g:(10-25)mL; Preferably, the stirring time is 12h-26h; Preferably, the obtained MXene material is a MXene solution.

8. The method of any one of claims 1-7, wherein, The mass ratio of the layered cobalt-manganese double metal hydroxide nanosheet to the lithium source is (9-11):1; Preferably, the sintering temperature is 700-900℃; Preferably, the sintering time is 8-15h.

9. An anode characterized by, The anode includes the composite electrode material of claim 1 or 2.

10. An electrochemical lithium extraction device, characterized in that, The electrochemical lithium extraction device includes the anode of claim 9.

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