A seawater lithium extraction electrode material and a preparation method thereof

Abstract

The application discloses a seawater lithium extraction electrode material and a preparation method thereof, and relates to the technical field of lithium electrode materials; the method comprises the following steps: S1, synthesizing a two-dimensional layered precursor nanosheet array on the surface of a flexible conductive carbon cloth; S2, oxidizing the two-dimensional layered precursor nanosheet array to prepare an intermediate product; and S3, preparing a spinel lithium manganate LiMn2O4 electrode material from the intermediate product through a one-step hydrothermal method; the S1 step selects a flexible conductive carbon cloth as a substrate and pastes the flexible conductive carbon cloth on a cathode of an electrolytic cell for electrochemical deposition; the target material is directly grown on the flexible conductive carbon cloth substrate, the use of a traditional adhesive is avoided, the traditional electrode has the problems of low conductivity and poor cycle stability because the adhesive is usually insulating and not electrochemically active, the overall conductivity of the electrode is significantly improved, the cycle stability is enhanced, and the occurrence of manganese dissolution is avoided.

Description

Technical Field

[0001] This invention relates to the field of lithium electrode materials technology, and in particular to a seawater lithium extraction electrode material and its preparation method. Background Technology

[0002] With the global proliferation of electric vehicles and energy storage systems, the demand for lithium-ion batteries is growing exponentially. Global lithium demand is projected to surge more than fivefold by 2040. However, the distribution of exploitable terrestrial lithium resources is extremely uneven, with approximately 60% concentrated in the South American "Lithium Triangle," highlighting increasing geopolitical risks and supply chain fragility. In contrast, the ocean holds approximately 230 billion tons of lithium resources, 16,000 times the total terrestrial reserves. If economically viable extraction can be achieved, the ocean will become an inexhaustible "blue lithium mine," completely resolving the geographical limitations and depletion risks of lithium resources. However, seawater lithium extraction faces challenges. Seawater has an extremely low lithium concentration, approximately one ten-thousandth that of brine and one hundred-thousandth that of ore. This means that tens of thousands of tons of seawater need to be processed to extract just one kilogram of lithium, resulting in enormous energy consumption. Furthermore, the concentration of sodium, potassium, and magnesium ions in seawater is thousands to tens of thousands of times higher than that of lithium. In particular, magnesium ions and lithium ions have similar hydration radii and chemical properties, making them difficult to separate using traditional precipitation methods, easily leading to substandard product purity. Additionally, the process is complex and inefficient. Currently, LMO (lithium spinel manganese oxide, LiMn2O4) is a core functional material in marine lithium extraction technology. Utilizing its unique crystal structure, it acts as a "molecular sieve" or "ion pump" to selectively and efficiently capture and enrich lithium ions from seawater. However, existing LMO electrodes are prone to manganese dissolution and have insufficient specific capacity (conductivity only 10). -6 The low specific surface area (S / cm) of traditional LMO particles limits their practical application. Traditional LMO particle-modified electrodes suffer from low specific surface area and poor exposure of active sites. Furthermore, traditional electrode preparation requires the use of binders, which are typically insulating and electrochemically inactive. This leads to a decrease in the electrode's conductivity, cycle stability, and specific capacity. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by proposing a seawater lithium extraction electrode material and its preparation method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A seawater lithium extraction electrode material and its preparation method, comprising the following steps: S1: Synthesis of a two-dimensional layered precursor nanosheet array on the surface of flexible conductive carbon cloth; S2: Oxidize the two-dimensional layered precursor nanosheet array to prepare an intermediate product; S3: The intermediate product is prepared into spinel-type lithium manganese oxide (LiMn2O4) electrode material by a one-step hydrothermal method.

[0005] Preferably: In step S1, flexible conductive carbon cloth is selected as the substrate and attached to the cathode of the electrolytic cell for electrochemical deposition; hydrogen bubbles generated on the cathode surface are used as dynamic soft templates to guide the continuous stacking of the generated manganese hydroxide Mn(OH)2 to form a two-dimensional layered Mn(OH)2 nanosheet array.

[0006] Furthermore, the cathode voltage of the electrolytic cell is -1.4V.

[0007] Further: In step S2, the flexible conductive carbon cloth with the two-dimensional layered Mn(OH)2 nanosheet array attached after step S1 is taken out and placed at room temperature for timed drying. The unstable Mn(OH)2 is oxidized to well-crystallized manganese tetroxide Mn3O4 by room temperature oxygen.

[0008] As a preferred embodiment of the present invention, the timed drying time is 12-18 hours to ensure that Mn(OH)2 is completely converted into Mn3O4 and to maintain the morphological integrity of the nanosheet array.

[0009] As a further aspect of the present invention: in step S3, the flexible conductive carbon cloth with a two-dimensional layered Mn3O4 nanosheet array attached obtained in step S2 is placed in a reaction vessel containing seawater, and a one-step hydrothermal method is adopted; using LiOH, O2 and H2O in seawater as reactants, Mn3O4 is lithiated to form LiMn2O4 electrode material.

[0010] As a further embodiment of the present invention: the one-step hydrothermal method uses seawater as the reaction medium and heats it at a high temperature of 150-200℃ and a pressure of 4-6MPa.

[0011] Based on the aforementioned scheme: the overall reaction equation is as follows: 8Mn3O4+12LiOH+5O2→ 12LiMn2O4+6H2O.

[0012] A seawater lithium extraction electrode material, wherein the seawater lithium extraction electrode material is a flexible conductive carbon cloth with a two-dimensional layered precursor nanosheet array LiMn2O4 electrode material synthesized on its surface.

[0013] The beneficial effects of this invention are as follows: 1. A seawater lithium extraction electrode material, which directly grows the target material on a flexible conductive carbon cloth substrate, avoiding the use of traditional adhesives. Since adhesives are usually insulating and non-electrochemically active, this material solves the problems of low conductivity and poor cycle stability of traditional electrodes, significantly improves the overall conductivity of the electrode, enhances cycle stability, and avoids manganese dissolution.

[0014] 2. A seawater lithium extraction electrode material, which utilizes hydrogen bubbles in the electrochemical cathode deposition process as a dynamic soft template to guide the continuous stacking of generated Mn(OH)2 to form a two-dimensional layered nanosheet array. Compared with the traditional bubble-free dynamic template, which can only generate uniform precipitated particles, this material changes the structure of the continuously stacked nanoparticles and forms a two-dimensional layered mesoporous nanosheet structure, thus optimizing the microstructure of the material.

[0015] 3. A seawater lithium extraction electrode material, which oxidizes Mn(OH)2 attached to carbon cloth into well-crystallized Mn3O4 in a room-temperature oxygen environment through a room-temperature auto-oxidation reaction, providing a high-quality precursor for subsequent lithiation.

[0016] 4. A seawater-derived lithium electrode material, which uses seawater as the reaction medium to lithiumize Mn3O4 into LiMn2O4 via a one-step hydrothermal method. This method eliminates the need for electrode material transfer and allows for direct conversion on a carbon cloth substrate. The process is simple, the production cycle is shorter, and the complete morphology of the two-dimensional layered nanosheets is preserved.

[0017] 5. A seawater lithium extraction electrode material, calculated using the constructed LMONs@cc surface model and adsorption model, shows that Li... + It can be embedded inside the λ-MnO2 lattice, while Mg 2+ Other ions are adsorbed only on the surface. Experimental data show that the Li separation factor is greater than 1, and the CV test curve also confirms its high selectivity in complex cation coexistence environments, effectively solving the problem of magnesium-lithium separation in seawater and improving lithium extraction efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for preparing a seawater lithium extraction electrode material proposed in this invention; Figure 2 This is a schematic diagram of the Li+ and LMoNs@cc adsorption model of a seawater lithium extraction electrode material proposed in this invention; Figure 3 This is a schematic diagram of a one-step hydrothermal method for preparing a seawater lithium extraction electrode material proposed in this invention; Figure 4 This is a schematic diagram of the separation factor in natural brine for a method of preparing lithium extraction electrode material from seawater proposed in this invention. Detailed Implementation

[0019] The technical solution of this patent will be further described in detail below with reference to specific embodiments.

[0020] The embodiments of this patent are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this patent, and should not be construed as limiting this patent.

[0021] Example 1: A method for preparing a seawater lithium extraction electrode material, such as... Figure 1 As shown, it includes the following steps: S1: A two-dimensional layered Mn(OH)2 nanosheet array was synthesized on the surface of a flexible conductive carbon cloth. First, an electrolytic cell filled with seawater was prepared, and a flexible conductive carbon cloth was selected as the substrate. Then, the flexible conductive carbon cloth was attached to the cathode of the electrolytic cell, and the working electrode voltage was set to -1.4V, so that the flexible conductive carbon cloth could be electrochemically deposited in the seawater. Because the reduction potential of divalent manganese (E0 = -0.828V vs NHE) is more negative than that of hydrogen (E0 = -1.180V vs NHE), when the working electrode voltage is set to -1.4V, a large number of hydrogen bubbles will preferentially be generated on the cathode surface due to the more negative reduction potential of hydrogen. As the reaction proceeds, the OH⁻ concentration increases, and with the electrolysis of water, the OH⁻ concentration in the region near the cathode gradually increases. These excess OH⁻ ions continuously interact with Mn²⁺ in the solution to generate Mn(OH)₂. At the same time, the continuously formed hydrogen bubbles act as a dynamic soft template, guiding the nanoparticles to continuously stack and form a layered structure, ultimately forming a two-dimensional layered Mn(OH)₂ nanosheet array. Traditional bubble-free dynamic templates can only generate uniform precipitated particles; S2: Oxidize the Mn(OH)2 nanosheet array to form Mn3O4; Take the flexible conductive carbon cloth with the two-dimensional layered Mn(OH)2 nanosheet array attached to the surface after the above steps out of the electrolytic cell, and place the flexible conductive carbon cloth at room temperature for timed drying. Since Mn(OH)2 is extremely unstable in the presence of oxygen at room temperature, it is easily oxidized to Mn3O4. The drying time is preferably 12-18 hours to allow Mn(OH)2 to be completely converted into well-crystallized Mn3O4, while maintaining the morphological integrity of the nanosheet array and avoiding structural collapse caused by excessive oxidation. S3; Prepare LiMn2O4 from Mn3O4 on flexible conductive carbon cloth; Place the flexible conductive carbon cloth with a two-dimensional layered Mn3O4 nanosheet array on top prepared in the above steps into a reaction vessel containing seawater, and process it using a one-step hydrothermal method, using seawater as the reaction medium and heating it at a high temperature of 150-200℃ and a pressure of 4-6MPa, using LiOH and O2 in seawater as Mn3O4 precursors, as oxidants, and H2O as the medium; Mn3O4 contains Mn2+ / Mn 3+ Oxidized to Mn by O2 3+ / Mn 4+ Simultaneously, Li⁺ is embedded in a manganese oxide lattice in a high-temperature and high-pressure aqueous solution, and finally lithiated to form LiMn2O4; after hydrothermal treatment, the morphology of the two-dimensional layered nanosheets is completely preserved, the LMO electrode is directly converted on the carbon cloth substrate without transfer, and the electrode material is directly grown on the conductive substrate without adhesive. Overall reaction equation: 8Mn3O4+12LiOH+5O2→ 12LiMn2O4+6H2O.

[0022] Subsequently, an electrode surface model was constructed to predict ion-selective behavior. First, a surface model of the LiMn2O4 nanosheet carbon cloth electrode material, LMOns@cc, was constructed. Then, appropriate cations (such as Li) were inserted into the model. + Mg 2+ Adsorption models were constructed to calculate and determine the binding energies of each cation to the electrode material, thereby exploring the selective behavior between different alkali metal ions and the electrode. Model studies demonstrated that λ-MnO2 and Li... + There is a strong interaction between them, Li + It can be embedded inside the λ-MnO2 lattice, while other alkali metal ions (such as Mg) 2+ Lithium ions (such as α-MnO2) are adsorbed only on the surface of λ-MnO2, thus achieving selective extraction. This technology also uses a predictive model to accurately predict whether the ionic composition of the brine at the selected site can achieve efficient seawater lithium extraction. In terms of experimental verification, CV curves show that both pairs of redox peaks exist only in 0.5 mol / L LiCl solution, and the overall integral area of ​​the CV curve for LiCl is higher than that of other electrolytes. Simultaneously, tests were conducted in natural brine with complex cation coexistence, and the results showed that LiCl… + The separation factors were all greater than 1, which fully verified the ion selectivity and lithium extraction efficiency of the technology.

[0023] This method avoids the problems of decreased conductivity and reduced cycling stability caused by traditional adhesives by growing target materials with highly ordered hierarchical nanostructures on flexible conductive carbon cloth substrates. At the same time, it utilizes electrochemical cathode deposition and hydrogen bubble soft templates to dynamically synthesize two-dimensional hierarchical Mn(OH)2 nanosheet arrays on flexible conductive carbon cloth substrates, changing the continuous stacked nanoparticles into two-dimensional hierarchical mesoporous nanosheet structures, and uses room temperature self-oxidation to oxidize Mn(OH)2 to Mn3O4 in the presence of oxygen at room temperature.

[0024] Compared to existing technologies, this method produces LMO electrodes with Li +With a separation factor >1, it maintains high selectivity even in complex cation coexistence environments. Furthermore, the hierarchical two-dimensional mesoporous nanosheets have a large specific surface area and fully exposed active sites, effectively optimizing the structure. The binder-free design significantly improves electrode conductivity and avoids manganese dissolution issues, resulting in enhanced cycle stability. By optimizing the electrolyte and cycling methods, it is expected to significantly reduce lithium extraction costs. Moreover, the one-step hydrothermal process is simple and has a shorter production cycle.

[0025] The above description represents a preferred embodiment of the present invention. The scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, combined with existing technology or common knowledge, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a seawater lithium extraction electrode material, characterized in that, Includes the following steps: S1: Synthesis of a two-dimensional layered precursor nanosheet array on the surface of flexible conductive carbon cloth; S2: Oxidize the two-dimensional layered precursor nanosheet array to prepare an intermediate product; S3: The intermediate product is prepared into spinel-type lithium manganese oxide (LiMn2O4) electrode material by a one-step hydrothermal method.

2. The method for preparing a seawater lithium extraction electrode material according to claim 1, characterized in that, In step S1, flexible conductive carbon cloth is selected as the substrate and attached to the cathode of the electrolytic cell for electrochemical deposition. Hydrogen bubbles generated on the cathode surface are used as dynamic soft templates to guide the continuous stacking of manganese hydroxide Mn(OH)2 to form a two-dimensional layered Mn(OH)2 nanosheet array.

3. The method for preparing a seawater lithium extraction electrode material according to claim 2, characterized in that, The cathode voltage of the electrolytic cell is -1.4V.

4. The method for preparing a seawater lithium extraction electrode material according to claim 1, characterized in that, In step S2, the flexible conductive carbon cloth with a two-dimensional layered Mn(OH)2 nanosheet array attached after step S1 is taken out and placed at room temperature for timed drying. The unstable Mn(OH)2 is oxidized to well-crystallized manganese tetroxide Mn3O4 using room temperature oxygen.

5. The method for preparing a seawater lithium extraction electrode material according to claim 4, characterized in that, The timed drying period is 12-18 hours to ensure that Mn(OH)2 is completely converted into Mn3O4 and to maintain the morphological integrity of the nanosheet array.

6. The method for preparing a seawater lithium extraction electrode material according to claim 1, characterized in that, In step S3, the flexible conductive carbon cloth with a two-dimensional layered Mn3O4 nanosheet array obtained in step S2 is placed in a reaction vessel containing seawater and a one-step hydrothermal method is used. LiOH, O2 and H2O in seawater are used as reactants to lithilate Mn3O4 to produce LiMn2O4 electrode material.

7. The method for preparing a seawater lithium extraction electrode material according to claim 6, characterized in that, The one-step hydrothermal method uses seawater as the reaction medium and heats it at a high temperature of 150-200℃ and a pressure of 4-6MPa.

8. The method for preparing a seawater lithium extraction electrode material according to claim 7, characterized in that, The overall reaction equation is as follows: 8Mn3O4+12LiOH+5O2→ 12LiMn2O4+6H2O.

9. A seawater lithium extraction electrode material according to any one of claims 1-8, characterized in that, The seawater lithium extraction electrode material is a flexible conductive carbon cloth with a two-dimensional layered precursor nanosheet array of LiMn2O4 electrode material synthesized on its surface.

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