Electrode material for extracting lithium ions from seawater and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium extraction by electrochemistry, and specifically discloses an electrode material for extracting lithium ions from seawater as well as a preparation method and application thereof. The prepared LiFeFe(CN)6 electrode material and FeFe(CN)6 electrode material can be used as an anode and a cathode of a lithium extraction device. By applying a voltage of 0.75V-1.0V between the anode and the cathode, efficient extraction of lithium ions from seawater can be realized, the embedding of other interfering ions can be avoided, and the separation efficiency of lithium ions and the recovery rate of lithium ions can be improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical lithium extraction technology, and in particular to an electrode material for extracting lithium ions from seawater, its preparation method, and its application. Background Technology

[0002] With the advent of the 5G era and the rise of new energy vehicles, the lithium battery field has gradually developed, leading to an unprecedented demand for lithium. However, lithium ore and brine resources, the main sources of lithium, will be insufficient to meet future needs. Therefore, developing a new lithium resource is crucial. Seawater, with its enormous lithium storage capacity, possesses abundant lithium resources and is gradually becoming another major source of lithium. However, seawater has a complex ionic composition, containing not only lithium ions but also interfering ions such as sodium, magnesium, and potassium ions. Due to their similar physicochemical properties to lithium ions, extracting lithium ions from seawater is challenging. Therefore, this invention aims to solve the problem of separating lithium ions from the numerous ions in seawater, thereby meeting the demand for lithium ions.

[0003] Currently, lithium-ion separation technologies include adsorbent methods, solvent extraction methods, membrane methods, and electrochemical methods. Adsorbents are widely used for lithium separation due to their excellent lithium-ion adsorption capacity and selectivity; however, large-scale application still faces many challenges. For example, adsorbent granulation is difficult, and framework collapse during elution requires further investigation and solutions. The high cost of extractants in solvent extraction methods limits their commercial application and also poses environmental pollution problems. Membrane methods, particularly the membrane itself, suffer from uneven pore distribution, grain boundaries, and defects, leading to problems such as poor lithium ion separation. + The separation efficiency is still insufficient, and the membrane is not very operable.

[0004] Therefore, there is an urgent need to develop an electrode material for extracting lithium ions from seawater in order to achieve the purpose of lithium separation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an electrode material for extracting lithium ions from seawater, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention is implemented according to the following technical solution: The first technical solution provided by this invention is a method for preparing an electrode material for extracting lithium ions from seawater, comprising the following steps: Synthesis of S1 and NaFeFe(CN)6 powder: 2 mmol of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was added to 100 mL of deionized water and stirred until clear to obtain solution A. Then, 1 mL of hydrochloric acid solution was added, and the solution was heated and stirred in a water bath at 60 °C for 4 hours to obtain solution B. Solution B was centrifuged for 5 min, and the resulting blue suspension was added to deionized water and ethanol in sequence, and centrifuged 3 times each to obtain a blue precipitate. The precipitate was then transferred to a vacuum drying oven and dried at 55 °C for 12 h to obtain NaFeFe(CN)6 powder. Synthesis of S2 and LiFeFe(CN)6 electrode materials: Polyvinylidene fluoride (PVDF), carbon powder, and N-methylpyrrolidone (NMP) were added to synthesized NaFeFe(CN)6 powder. The mass ratio of NaFeFe(CN)6 powder, PVDF, carbon powder, and NMP was 8:1:1:(5-8). After mixing and stirring for 10 min, a NaFeFe(CN)6 electrode coating was obtained. The NaFeFe(CN)6 electrode coating was then coated onto hydrophobic carbon cloth and subsequently vacuum dried at 55 °C to obtain the NaFeFe(CN)6 electrode material. The obtained NaFeFe(CN)6 electrode material was assembled in a three-electrode electrolytic cell, with the NaFeFe(CN)6 electrode material as the working electrode, a platinum mesh as the counter electrode, and a silver / silver chloride electrode as the reference electrode. A 1M sodium chloride solution was added to the three-electrode electrolytic cell, and constant current charging was performed on the working electrode and the counter electrode to remove Na from the NaFeFe(CN)6 electrode material. + The Li₂O₃ is removed to form a FeFe(CN)₆ electrode material; subsequently, the FeFe(CN)₆ electrode material is placed in a 1 M lithium chloride solution for discharge, thereby removing Li₂O₃. + The material is embedded in the material, eventually forming the LiFeFe(CN)6 electrode material.

[0007] Furthermore, in step S1, the hydrochloric acid solution has a mass fraction of 37%.

[0008] Furthermore, in step S1, the centrifugation speed is 11,000 rpm.

[0009] Furthermore, in step S2, the active area of ​​the NaFeFe(CN)6 electrode coating applied to the hydrophobic carbon cloth is 1-4 cm². 2 .

[0010] The second technical solution provided by this invention is the LiFeFe(CN)6 electrode material and the FeFe(CN)6 electrode material prepared by the above method.

[0011] The third technical solution provided by this invention is the application of the above-mentioned LiFeFe(CN)6 electrode material and FeFe(CN)6 electrode material in the extraction of lithium ions from seawater, including the following steps: 1) Construction of a lithium extraction device: The lithium extraction device includes a feed liquid chamber and a recovery liquid chamber separated by an ion exchange membrane. The recovery liquid chamber is equipped with a positive electrode, and the feed liquid chamber is equipped with a negative electrode. The positive electrode is made of LiFeFe(CN)6 electrode material; the negative electrode is made of FeFe(CN)6 electrode material; the recovery liquid in the recovery liquid chamber is a sodium chloride solution; and the liquid in the feed liquid chamber is seawater. 2) Applying a voltage of 0.75V-1.0V between the anode and cathode of the lithium extraction device causes an oxidation reaction at the anode, thereby removing Li from the LiFe(CN)6 material. + The lithium is extracted and, driven by voltage, moves through the ion exchange membrane towards the cathode. During this process, the anode changes from LiFeFe(CN)6 to FeFe(CN)6; the cathode undergoes a reduction reaction, initiating lithium intercalation. Thus, the cathode removes Li from the seawater in the feed chamber. + Embedding, thereby enabling the capture of Li in seawater + During extraction, the cathode changes from FeFe(CN)6 to LiFeFe(CN)6. The lithium ion recovery process is achieved through two processes: the adsorption of lithium ions from seawater by the cathode FeFe(CN)6 and the release of lithium ions by the anode LiFeFe(CN)6. Therefore, cathode insertion is the lithium ion adsorption process, and the process of the cathode material releasing lithium ions into the recovery liquid is the recovery process. Because the cathode and anode are symmetrical electrodes, the cathode material becomes the anode material after the reaction, and the anode material becomes the cathode material after the reaction. If you want to continue extraction, you can interchange the two electrodes to continue lithium extraction.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. The LiFeFe(CN)6 electrode material and FeFe(CN)6 electrode material prepared by this invention can be used as the anode and cathode of a lithium extraction device. By applying a voltage of 0.75V-1.0V between the anode and cathode, efficient extraction of lithium ions from seawater can be achieved, avoiding the intercalation of other interfering ions and improving the separation efficiency and recovery rate of lithium ions.

[0013] 2. All reagents used in this invention are inorganic salt reagents, posing no risk of environmental pollution.

[0014] 3. The electrode material is made from no expensive materials, enabling large-scale, industrialized lithium extraction and practical application.

[0015] 4. Since the reactions of the cathode and anode in the lithium extraction device are reversible, the electrode materials used for lithium extraction can be recycled, reducing costs. Attached Figure Description

[0016] Figure 1 This is a diagram of the apparatus for extracting lithium ions from seawater according to the present invention.

[0017] Figure 2 The image shows the XRD pattern of the LiFeFe(CN)6 electrode material in Example 1.

[0018] Figure 3 This is a charging diagram of the FeFe(CN)6 electrode material formed in Example 1.

[0019] Figure 4 This is a discharge diagram of the LiFeFe(CN)6 electrode material formed in Example 1.

[0020] Figure 5 The figure shows the cyclic voltammetry curves of the three-electrode system in lithium chloride solution.

[0021] Figure 6 The figures show the cyclic voltammetry curves of the three-electrode system in potassium chloride, sodium chloride, and magnesium chloride solutions.

[0022] Figure 7 The figure shows the cyclic voltammetry curves of the three-electrode system in cobalt sulfate solution. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0024] Example 1: Preparation of electrode materials for extracting lithium ions 1) Synthesis of NaFeFe(CN)6 powder: 2 mmol of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was added to 100 mL of deionized water and stirred at 300 rpm until clear to obtain solution A. Then, 1 mL of hydrochloric acid solution (HCl, 37%) was added, and the solution was heated in a water bath with stirring at 600 rpm for 4 hours at 60 °C to obtain solution B. Solution B was centrifuged at 11000 rpm for 5 min, and the resulting blue suspension was added to deionized water and ethanol in sequence, and centrifuged three times at 11000 rpm each time to obtain a blue precipitate. The precipitate was then transferred to a vacuum drying oven and dried at 55 °C for 12 h to obtain NaFeFe(CN)6 powder. 2) Synthesis of LiFeFe(CN)6 electrode material: Polyvinylidene fluoride (PVDF), carbon powder, and N-methylpyrrolidone (NMP) were added to the synthesized NaFeFe(CN)6 powder. The mass ratio of NaFeFe(CN)6 powder, PVDF, carbon powder, and NMP was 8:1:1:6. After mixing and stirring for 10 min, a NaFeFe(CN)6 electrode coating was obtained. Subsequently, the NaFeFe(CN)6 electrode coating was coated on hydrophobic carbon cloth, with an active area of ​​2 cm × 2 cm = 4 cm. 2 Subsequently, after vacuum drying at 55 °C, NaFeFe(CN)6 electrode material was obtained. The obtained NaFeFe(CN)6 electrode material was assembled in a three-electrode electrolytic cell (three-electrode system), with the NaFeFe(CN)6 electrode material as the working electrode, a platinum mesh as the counter electrode, and a silver / silver chloride electrode as the reference electrode. A 1M sodium chloride solution was added to the three-electrode electrolytic cell, and constant current charging was performed between the working electrode and the counter electrode to remove Na from the NaFeFe(CN)6 electrode material. + The Li₂O₃ is removed to form a FeFe(CN)₆ electrode material; subsequently, the FeFe(CN)₆ electrode material is placed in a 1 M lithium chloride solution for discharge, thereby removing Li₂O₃. + The material is embedded in the electrode, ultimately forming a LiFeFe(CN)6 electrode material. The charge-discharge images are shown below. Figure 3 , Figure 4 As shown.

[0025] X-ray diffraction (XRD) was performed on the synthesized LiFeFe(CN)6, and the obtained XRD images are shown below. Figure 2 As shown, the test range is ,Depend on Figure 2 It can be seen that LiFeFe(CN)6 was successfully synthesized.

[0026] Cyclic voltammetry was performed on the LiFeFe(CN)6 electrode material: A three-electrode electrolytic cell was used, with the working electrode being the LiFeFe(CN)6 electrode material, the counter electrode being a platinum mesh (Pt), and the reference electrode being a silver / silver chloride (Ag / AgCl) electrode. These electrodes were placed in solutions of lithium chloride (LiCl), sodium chloride (NaCl), magnesium chloride (MgCl2), potassium chloride (KCl), and cobalt sulfate (CoSO4), respectively. The cells were connected to an electrochemical workstation for testing at a scan rate of 0.01 V / s. The resulting cyclic voltammetry curves are shown below. Figure 5 , Figure 6 and Figure 7 As shown, by Figure 5 , Figure 6 and Figure 7It can be seen that the upper peak of the curve is the oxidation peak, which corresponds to the voltage and current values ​​of ion extraction, and the lower peak is the reduction peak, which corresponds to the voltage and current values ​​of ion insertion. By observing the reduction potential of the curve, the insertion potentials of lithium ions, sodium ions, magnesium ions, and potassium ions of the LiFeFe(CN)6 electrode material can be obtained. The insertion potential range of lithium ions is 0.75V-1.0V, that of sodium ions is 0.1V-0.3V, that of magnesium ions is 0V-0.2V, and the peak value of potassium ions is approximately -0.1V. Co ions are not inserted. Therefore, by selecting a suitable insertion potential of 0.75V-1.0V for lithium ions and adding it to the device, the specific extraction of lithium ions can be achieved.

[0027] Example 2: Application of LiFeFe(CN)6 electrode materials and FeFe(CN)6 electrode materials in the extraction of lithium ions from seawater This embodiment first constructs a lithium extraction device: such as Figure 1 As shown, the lithium extraction device in this embodiment includes a recovery liquid chamber 1 and a feed liquid chamber 2 separated by an ion exchange membrane 3. The recovery liquid chamber 1 contains a positive electrode 4, and the feed liquid chamber 2 contains a negative electrode 5. The positive electrode 4 is the LiFeFe(CN)6 electrode material prepared in Example 1; the negative electrode 5 is the FeFe(CN)6 electrode material prepared in Example 1. The recovery liquid in the recovery liquid chamber 1 is 1 L of 0.5 M NaCl solution. The liquid in the feed liquid chamber 2 is simulated seawater, which is prepared by adding LiCl to a 35.0 g / L sea salt solution. The simulated seawater solution contains lithium ions (Li... + The content was 6.968 mg / L; 2) Applying a voltage of 0.75V-1.0V between the anode and cathode of the lithium extraction device causes an oxidation reaction at the anode, thereby removing Li from the LiFe(CN)6 material. + The lithium is extracted and, driven by voltage, moves through the ion exchange membrane towards the cathode. During this process, the anode changes from LiFeFe(CN)6 to FeFe(CN)6; the cathode undergoes a reduction reaction, initiating lithium intercalation. Thus, the cathode removes Li from the seawater in the feed chamber. + Embedding, thereby enabling the capture of Li in seawater +Extraction is performed, and the cathode changes from FeFe(CN)6 to LiFeFe(CN)6. The lithium ion recovery process is achieved through two processes: the adsorption of lithium ions from seawater by the cathode FeFe(CN)6 and the release of lithium ions by the anode LiFeFe(CN)6. Therefore, cathode embedding is the lithium ion adsorption process, and the release of lithium ions from the cathode material into the recovery solution is the recovery process. Because the cathode and anode are symmetrical electrodes, the cathode material becomes the anode material after the reaction, and the anode material becomes the cathode material after the reaction. If further extraction is desired, the two electrodes are interchanged to continue lithium extraction. In this embodiment, only one lithium extraction was performed. After the experiment, the lithium ion concentration in the feed solution was measured to be 6.738 mg / L, and the lithium ion content in the recovery solution was 0.156 mg / L. According to the formula... , , Q For adsorption capacity, C 0 This represents the initial ion concentration of the feed solution. V 0 This represents the initial feed volume. C s Vs represents the initial ion concentration of the feed solution after the reaction, and Vs represents the volume of the feed solution after the reaction. T To recover capacity, C t The concentration of ions in the recovered liquid. V t For the volume of the recovered liquid, W e Based on the mass of the electrode material, the calculated lithium-ion adsorption capacity is 5.75 mg·(1 g LiFeFe(CN)6). ⁻¹ The recovery capacity was 3.9 mg·(1 g LiFeFe(CN)6)⁻¹; based on the adsorption capacity and recovery capacity, the lithium recovery rate was calculated to be 67.8%, indicating that this embodiment has an objective lithium ion recovery rate.

[0028] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrode material for extracting lithium ions from seawater, characterized in that, Includes the following steps: Synthesis of S1 and NaFeFe(CN)6 powder: 2 mmol of sodium ferrocyanide (Na4Fe(CN)6·10H2O) was added to 100 mL of deionized water and stirred until clear to obtain solution A. Then, 1 mL of hydrochloric acid solution was added, and the solution was heated and stirred in a water bath at 60 °C for 4 hours to obtain solution B. Solution B was centrifuged for 5 min, and the resulting blue suspension was added to deionized water and ethanol in sequence, and centrifuged 3 times each to obtain a blue precipitate. The precipitate was then transferred to a vacuum drying oven and dried at 55 °C for 12 h to obtain NaFeFe(CN)6 powder. Synthesis of S2 and LiFeFe(CN)6 electrode materials: Polyvinylidene fluoride (PVDF), carbon powder, and N-methylpyrrolidone (NMP) were added to synthesized NaFeFe(CN)6 powder. The mass ratio of NaFeFe(CN)6 powder, PVDF, carbon powder, and NMP was 8:1:1:(5-8). After mixing and stirring for 10 min, a NaFeFe(CN)6 electrode coating was obtained. The NaFeFe(CN)6 electrode coating was then coated onto hydrophobic carbon cloth and subsequently vacuum dried at 55 °C to obtain the NaFeFe(CN)6 electrode material. The obtained NaFeFe(CN)6 electrode material was assembled in a three-electrode electrolytic cell, with the NaFeFe(CN)6 electrode material as the working electrode, a platinum mesh as the counter electrode, and a silver / silver chloride electrode as the reference electrode. A 1M sodium chloride solution was added to the three-electrode electrolytic cell, and constant current charging was performed on the working electrode and the counter electrode to remove Na from the NaFeFe(CN)6 electrode material. + The Li₂O₃ is removed to form a FeFe(CN)₆ electrode material; subsequently, the FeFe(CN)₆ electrode material is placed in a 1 M lithium chloride solution for discharge, thereby removing Li₂O₃. + The material is embedded in the material, eventually forming the LiFeFe(CN)6 electrode material.

2. The method for preparing electrode material for extracting lithium ions from seawater according to claim 1, characterized in that: In step S1, the hydrochloric acid solution has a mass fraction of 37%.

3. The method for preparing electrode material for extracting lithium ions from seawater according to claim 1, characterized in that: In step S1, the centrifugation speed is 11,000 rpm.

4. The method for preparing electrode material for extracting lithium ions from seawater according to claim 1, characterized in that: In step S2, the active area of ​​the NaFeFe(CN)6 electrode coating applied to the hydrophobic carbon cloth is 1-4 cm². 2 .

5. A LiFeFe(CN)6 electrode material prepared by the method according to any one of claims 1-4 and a material prepared by the method according to any one of claims 1-4 without Li intercalation. + The prepared FeFe(CN)6 electrode material.

6. The application of the LiFeFe(CN)6 electrode material and the FeFe(CN)6 electrode material as described in claim 5 in the extraction of lithium ions from seawater.

7. The application according to claim 6, characterized in that, Includes the following steps: 1) Construction of a lithium extraction device: The lithium extraction device includes a feed liquid chamber and a recovery liquid chamber separated by an ion exchange membrane. The recovery liquid chamber is equipped with a positive electrode, and the feed liquid chamber is equipped with a negative electrode. The positive electrode is made of LiFeFe(CN)6 electrode material, and the negative electrode is made of FeFe(CN)6 electrode material. The recovery liquid in the recovery liquid chamber is a sodium chloride solution, and the liquid in the feed liquid chamber is seawater. 2) Applying a voltage of 0.75V-1.0V between the anode and cathode of the lithium extraction device causes an oxidation reaction at the anode, thereby removing Li from the LiFe(CN)6 material. + The lithium is extracted and, driven by voltage, moves through the ion exchange membrane towards the cathode. During this process, the anode changes from LiFeFe(CN)6 to FeFe(CN)6; the cathode undergoes a reduction reaction, initiating lithium intercalation. Thus, the cathode removes Li from the seawater in the feed chamber. + Embedding, thereby enabling the capture of Li in seawater + During extraction, the cathode changes from FeFe(CN)6 to LiFeFe(CN)6. The process of the cathode releasing lithium ions into the recovery solution is the LiFeFe(CN)6 extraction. + The recycling process involves using symmetrical electrodes, where the cathode reacts to become the anode material, and the anode material reacts to become the cathode material. By swapping the two electrodes, lithium extraction can continue.

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