A porous lithium-poor electrode, its preparation method and application

Abstract

This disclosure provides a porous lithium-poor electrode, its preparation method, and its application. The preparation method includes the following steps: (1) mixing electrode active material, manganese dioxide, conductive agent, binder, and solvent to obtain a slurry, and coating the slurry onto the surface of a current collector to obtain a lithium-rich electrode; (2) using the lithium-rich electrode as the positive electrode and the AgCl electrode as the negative electrode, adding a first electrolyte, and performing a one-step constant voltage treatment to obtain a lithium-poor electrode; (3) using the lithium-rich electrode as the positive electrode and the lithium-poor electrode as the negative electrode, adding a second electrolyte, and performing a two-step constant voltage treatment to obtain the porous lithium-poor electrode; the voltage of the two-step constant voltage treatment is 1.5 to 2.5V. The porosity inside the porous lithium-poor electrode of this disclosure is controllable, the mass transfer effect inside the electrode is high, and the lithium extraction effect is good.

Description

Technical Field

[0001] This disclosure belongs to the field of lithium extraction technology from salt lakes, and relates to a porous lithium-poor electrode, its preparation method and application. Background Technology

[0002] Lithium is an important strategic resource, widely used in the lithium battery industry. The rapid development of the new energy sector has driven a rapid increase in market demand for lithium resources, making low-cost and efficient lithium resource development a crucial guarantee for companies to compete in the market. Proven lithium resources in nature are mainly found in salt lake brines, seawater, and ores, with salt lake lithium resources accounting for approximately 70%. Due to the high cost and difficulty of lithium ore mining, and its increasing depletion with continuous exploitation, extracting lithium from salt lake brines has become a trend in lithium resource development.

[0003] Western my country has numerous salt lakes, but their development is limited due to their high magnesium-to-lithium ratio. Currently, the main methods for lithium extraction from brine, both domestically and internationally, include precipitation, solvent extraction, evaporation crystallization, electrodialysis, and ion exchange adsorption. Precipitation, as a mature lithium extraction technology, suffers from drawbacks such as high energy consumption, complex processes, high costs, and low lithium recovery rates. Extraction offers fast lithium extraction rates, but the extractant dissolves in the brine, potentially causing environmental pollution. Adsorption methods suffer from low adsorption capacity, adsorbent loss, and high water consumption. In recent years, many researchers both domestically and internationally have extensively explored and studied new lithium extraction processes, with electrochemical lithium extraction technology showing promising application value and prospects.

[0004] The principle of electrochemical lithium extraction is to charge the working electrode to extract lithium ions and form a lithium ion sieve. Discharging in salt water allows lithium ions to selectively enter the lithium ion sieve. The lithium enrichment is achieved through a cyclical charging and discharging process.

[0005] To improve mass transfer within the electrode, creating pores to increase the transport pathways is an effective method. Adding a certain proportion of soluble or easily pyrolytic inorganic salts as pore-forming agents during electrode slurry preparation can achieve the goal of creating pores within the electrode plate. These porous structures provide good mass transfer channels for the solution within the electrode. However, pores created by adding pore-forming agents have fixed pore sizes after electrode fabrication and cannot be adjusted. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] The purpose of this disclosure is to provide a porous lithium-poor state electrode, its preparation method and application. The porous lithium-poor state electrode described in this disclosure has controllable porosity, high mass transfer effect inside the electrode, and good lithium extraction effect.

[0008] To achieve this purpose of disclosure, the following technical solution is adopted:

[0009] In a first aspect, embodiments of this disclosure provide a method for preparing a porous lithium-poor electrode, the method comprising the following steps:

[0010] (1) A slurry is obtained by mixing an electrode active material, manganese dioxide, a conductive agent, a binder and a solvent, and the slurry is coated on the surface of a current collector to obtain a lithium-rich electrode;

[0011] (2) Using the lithium-rich electrode as the positive electrode and the AgCl electrode as the negative electrode, the first electrolyte is added and subjected to a one-step constant voltage treatment to obtain the lithium-poor electrode;

[0012] (3) Using the lithium-rich electrode as the positive electrode and the lithium-poor electrode as the negative electrode, a second electrolyte is added, and the porous lithium-poor electrode is obtained by two-step constant voltage treatment.

[0013] The voltage for the two-step constant voltage processing is 1.5 to 2.5V, for example: 1.5V, 1.8V, 2V, 2.2V or 2.5V, etc.

[0014] In this embodiment, manganese dioxide is added to the electrode slurry. Under high voltage (above 1.5V), the manganese dioxide decomposes into manganese trioxide or manganese tetroxide, releasing oxygen. The particle size and morphology of the manganese dioxide change, forming pores in their original positions. This embodiment controls the decomposition of manganese dioxide by controlling the voltage of the two-step constant voltage treatment, thereby controlling the formation of pores inside the electrode, improving the mass transfer effect of the solution inside the electrode, and thus improving the lithium extraction efficiency of the electrode.

[0015] In one embodiment, the electrode active material in step (1) includes any one or a combination of at least two of lithium iron phosphate, lithium manganese oxide, or lithium nickel cobalt manganese oxide.

[0016] In one embodiment, the median particle size D50 of the electrode active material is 0.5 to 10 μm, for example: 0.5 μm, 1 μm, 2 μm, 5 μm or 10 μm, etc.

[0017] In one embodiment, the median particle size D50 of the manganese dioxide is 20–100 nm, for example: 20 nm, 40 nm, 60 nm, 80 nm, or 100 nm.

[0018] In one embodiment, the mass ratio of manganese dioxide to electrode active material is (2-4):10, for example: 2:10, 2.5:10, 3:10, 3.5:10 or 4:10, etc.

[0019] In one embodiment, the conductive agent comprises acetylene black and / or conductive carbon black.

[0020] In one embodiment, the mass ratio of the conductive agent to the electrode active material is (1-2):10, for example: 1:10, 1.2:10, 1.5:10, 1.8:10 or 2:10, etc.

[0021] In one embodiment, the adhesive comprises polyvinylidene fluoride.

[0022] In one embodiment, the mass ratio of the binder to the electrode active material is (1 to 1.5):10, for example: 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10 or 1.5:10, etc.

[0023] In one embodiment, the current collector in step (1) comprises carbon fiber cloth and / or titanium mesh.

[0024] In one embodiment, the coating density is 150–200 mg / cm³. 2 For example: 15mg / cm 2 16mg / cm 2 17mg / cm 2 18mg / cm 2 Or 20mg / cm 2 wait.

[0025] In one embodiment, the solute in the first electrolyte in step (2) includes KCl and / or NaCl.

[0026] In one embodiment, the concentration of the first electrolyte is 0.05 to 0.1 mol / L, for example: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L or 0.1 mol / L, etc.

[0027] In one embodiment, the voltage of the one-step constant voltage processing is 0.8 to 1.2V, for example: 0.8V, 0.9V, 1V, 1.1V or 1.2V, etc.

[0028] In one embodiment, the second electrolyte in step (3) comprises a NaCl solution.

[0029] In one embodiment, the concentration of the second electrolyte is 0.05 to 0.1 mol / L, for example: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L or 0.1 mol / L, etc.

[0030] In one embodiment, the two-step constant voltage processing time is 2 to 6 hours, for example: 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0031] Secondly, embodiments of this disclosure provide a porous lithium-poor state electrode, which is prepared by the method described in the first aspect.

[0032] Thirdly, this disclosure provides a method for lithium extraction from salt lakes, the method comprising the following steps:

[0033] (1) The electrolysis device is divided into an anode chamber and a cathode chamber by an anion exchange membrane. The lithium-rich electrode is placed in the anode chamber and the porous lithium-poor electrode described in the second aspect is placed in the cathode chamber. Salt lake brine is added to the cathode chamber and anolyte is added to the anode chamber.

[0034] (2) When the current is as low as 150mA, the lithium extraction reaction is stopped. If the lithium extraction time is ≤5h, the anode and cathode are exchanged to continue lithium extraction. If the lithium extraction time is >5h, the electrode in the anode chamber is taken out as the negative electrode and the lithium-rich electrode is taken as the positive electrode. Electrolyte is added and the constant voltage reaction is used to increase the porosity. The electrode obtained by the constant voltage reaction is used as the cathode and the lithium-rich electrode is used as the anode to continue the salt lake lithium extraction reaction.

[0035] (3) Use the electrode obtained from the constant voltage reaction as the cathode and the lithium-rich electrode as the anode, repeat step (2) 2 to 5 times to end the lithium extraction reaction.

[0036] In the lithium extraction process from salt lakes described in this embodiment, the current is as low as 150mA, and the lithium extraction reaction reaches equilibrium. If the lithium extraction time is found to be too long, the pores are adjusted by the method described in the first aspect. Through the controllable adjustment of the pores, the mass transfer effect of the solution inside the electrode is improved, and the lithium extraction reaction rate is further increased.

[0037] In one embodiment, the solute in the anolyte of step (1) includes KCl and / or NaCl.

[0038] In one embodiment, the concentration of the anolyte is 0.05 to 0.1 mol / L, for example: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, or 0.1 mol / L, etc.

[0039] In one embodiment, the voltage applied in step (2) is 0.3 to 1.2V, for example: 0.3V, 0.5V, 0.8V, 1V or 1.2V, etc.

[0040] In one embodiment, the electrolyte in step (2) comprises a NaCl solution.

[0041] In one embodiment, the concentration of the electrolyte is 0.05 to 0.1 mol / L, for example: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, or 0.1 mol / L, etc.

[0042] In one embodiment, the voltage of the constant voltage reaction is 1.5 to 2.5V, for example: 1.5V, 1.8V, 2V, 2.2V or 2.5V, etc.

[0043] In one embodiment, the constant voltage reaction time is 2 to 6 hours, for example: 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0044] This disclosure has the following beneficial effects:

[0045] (1) By adding manganese dioxide to the electrode slurry, this disclosure can prepare a porous lithium-poor electrode with controllable porosity. In the subsequent lithium extraction process in salt lake, the porosity of the electrode can be judged based on the actual lithium extraction efficiency and adjusted accordingly to improve the lithium extraction efficiency.

[0046] (2) The lithium concentration in the brine after lithium extraction by the method described in this disclosure can reach below 0.15 g / L, and the lithium concentration in the recovered liquid after lithium extraction can reach above 2.97 g / L. By adjusting various parameters in the electrode preparation, the lithium concentration in the brine after lithium extraction can reach 0.11 g / L, and the lithium concentration in the recovered liquid after lithium extraction can reach 3.22 g / L.

[0047] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0048] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0049] Figure 1 This is a schematic flowchart of the lithium extraction method from salt lakes as described in the embodiments of this disclosure.

[0050] Figure 2 This is a graph showing the change in lithium concentration in the anolyte during the first lithium extraction process in Examples 1-3 of this disclosure.

[0051] Figure 3 This is a graph showing the change in lithium concentration in the anolyte during the second lithium extraction process in Examples 1-2 of this disclosure. Detailed Implementation

[0052] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0053] Example 1

[0054] This embodiment provides a method for lithium extraction from salt lakes, and the flowchart of the method is shown below. Figure 1As shown, the method includes the following steps:

[0055] (1) 100g of lithium iron phosphate (D 50 =500nm) and 20g manganese dioxide (D 50 =50nm), 20g acetylene black and 15g PVDF are mixed and added to NMP to form an electrode slurry. The slurry is then mixed at 150mg / cm³. 2 The density of the coating is applied to a titanium mesh current collector, and then dried at 80°C for 4 hours to obtain a lithium-rich electrode. Using the lithium-rich electrode as the positive electrode, the AgCl electrode as the negative electrode, and 0.05 mol / L KCl solution as the electrolyte, the lithium-rich electrode is delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0056] (2) Using a lithium-rich electrode as the positive electrode and a lithium-poor electrode as the negative electrode, and 0.05 mol / L NaCl solution as the electrolyte, the electrodes were energized at a constant voltage of 2.0 V for 2 h to obtain a porous lithium-poor electrode.

[0057] (3) The electrolysis device is divided into an anode chamber and a cathode chamber using an anion exchange membrane. Lithium-rich and lithium-poor electrodes are placed in the anode and cathode chambers, respectively. Brine is injected into the cathode chamber, and a 0.05 mol / L KCl solution is injected into the anode chamber. Lithium extraction is carried out under a constant voltage of 0.3 V. When the current drops to 150 mA, the reaction reaches equilibrium in 8 hours. (The change in lithium concentration in the anolyte during lithium extraction is shown in the figure.) Figure 2 (As shown) The lithium extraction rate is slow. The electrode in the anode chamber is removed as the negative electrode, and the lithium-rich electrode is used as the positive electrode. Step (2) is repeated to obtain a porous lithium-poor electrode. The porous lithium-poor electrode is used as the cathode, and the lithium-rich electrode is used as the anode to continue the lithium extraction reaction in the salt lake (the change in lithium concentration in the anolyte during the lithium extraction process is shown in Figure 1). Figure 3 (As shown), repeat step (3) 3 times to end the lithium extraction reaction.

[0058] Example 2

[0059] This embodiment provides a method for lithium extraction from salt lakes, the method comprising the following steps:

[0060] (1) 100g of lithium iron phosphate (D 50 =200nm) and 30g manganese dioxide (D 50 =80nm), 10g acetylene black and 10g PVDF are mixed and added to NMP to form an electrode slurry. The slurry is then mixed at 150mg / cm. 2The density of the coating is applied to a titanium mesh current collector, and then dried at 50°C for 8 hours to obtain a lithium-rich electrode. Using the lithium-rich electrode as the positive electrode, the AgCl electrode as the negative electrode, and 0.05 mol / L KCl solution as the electrolyte, the lithium-rich electrode is delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0061] (2) Using a lithium-rich electrode as the positive electrode, a lithium-poor electrode as the negative electrode, and a 0.08 mol / L NaCl solution as the electrolyte, the electrodes were energized at a constant voltage of 1.8 V for 6 h to obtain a porous lithium-poor electrode.

[0062] (3) The electrolysis device is divided into an anode chamber and a cathode chamber using an anion exchange membrane. Lithium-rich and lithium-poor electrodes are placed in the anode and cathode chambers, respectively. Brine is injected into the cathode chamber, and a 0.08 mol / L KCl solution is injected into the anode chamber. Lithium extraction is carried out under a constant voltage of 0.5 V. When the current drops to 150 mA, the reaction reaches equilibrium in 7 hours. (The change in lithium concentration in the anolyte during lithium extraction is shown in the figure.) Figure 2 (As shown) The lithium extraction rate is slow. The electrode in the anode chamber is removed as the negative electrode, and the lithium-rich electrode is used as the positive electrode. Step (2) is repeated to obtain a porous lithium-poor electrode. The porous lithium-poor electrode is used as the cathode, and the lithium-rich electrode is used as the anode to continue the lithium extraction reaction in the salt lake (the change in lithium concentration in the anolyte during the lithium extraction process is shown in Figure 1). Figure 3 (As shown), repeat step (3) 3 times to end the lithium extraction reaction.

[0063] Example 3

[0064] This embodiment provides a method for lithium extraction from salt lakes, the method comprising the following steps:

[0065] (1) 100g of lithium iron phosphate (D 50 =800nm) and 25g manganese dioxide (D 50 =20nm), 15g acetylene black and 15g PVDF are mixed and added to NMP to form an electrode slurry. The slurry is then mixed at 150mg / cm³. 2 The density of the coating is applied to a titanium mesh current collector, and then dried at 60°C for 5 hours to obtain a lithium-rich electrode. Using the lithium-rich electrode as the positive electrode, the AgCl electrode as the negative electrode, and 0.05 mol / L KCl solution as the electrolyte, the lithium-rich electrode is delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0066] (2) Using a lithium-rich electrode as the positive electrode, a lithium-poor electrode as the negative electrode, and a 0.08 mol / L NaCl solution as the electrolyte, the electrodes were energized at a constant voltage of 2.2 V for 4 h to obtain a porous lithium-poor electrode.

[0067] (3) The electrolysis device is divided into an anode chamber and a cathode chamber using an anion exchange membrane. Lithium-rich and lithium-poor electrodes are placed in the anode and cathode chambers, respectively. Brine is injected into the cathode chamber, and a 0.05 mol / L KCl solution is injected into the anode chamber. Lithium extraction is carried out under a constant voltage of 0.5 V. When the current drops to 150 mA, the reaction reaches equilibrium in 5 hours. (The change in lithium concentration in the anolyte during lithium extraction is shown in the figure.) Figure 2 (As shown) The lithium extraction rate is relatively fast. Exchange the anode and cathode and continue the lithium extraction reaction in the salt lake. Repeat step (3) 3 times to end the lithium extraction reaction.

[0068] Example 4

[0069] The only difference between this embodiment and Embodiment 1 is that the mass of manganese dioxide is 15g, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0070] Example 5

[0071] The only difference between this embodiment and Embodiment 1 is that the mass of manganese dioxide is 45g; all other conditions and parameters are exactly the same as in Embodiment 1.

[0072] Example 6

[0073] The only difference between this embodiment and embodiment 1 is that the power-on time in step (2) is 1 hour, while the other conditions and parameters are exactly the same as in embodiment 1.

[0074] Example 7

[0075] The only difference between this embodiment and embodiment 1 is that the power-on time in step (2) is 7 hours, while the other conditions and parameters are exactly the same as in embodiment 1.

[0076] Comparative Example 1

[0077] The only difference between this comparative example and Example 1 is that manganese dioxide is not added to the electrode slurry; all other conditions and parameters are exactly the same as in Example 1.

[0078] Comparative Example 2

[0079] The only difference between this comparative example and Example 1 is that the voltage applied in step (2) is 1.2V, while the other conditions and parameters are exactly the same as in Example 1.

[0080] Comparative Example 3

[0081] The only difference between this comparative example and Example 1 is that the voltage for energizing in step (2) is 3V, while the other conditions and parameters are exactly the same as in Example 1.

[0082] Performance testing:

[0083] The test results of lithium ion concentration in brine and recovered solution (anolyte) before and after lithium extraction in the examples and comparative examples are shown in Table 1:

[0084] Table 1

[0085]

[0086]

[0087] As can be seen from Table 1, as obtained from Examples 1-3, the lithium concentration in the brine after lithium extraction by the method described in this disclosure can reach below 0.15 g / L, and the lithium concentration in the recovered solution can reach above 2.97 g / L. By adjusting various parameters in the electrode preparation, the lithium concentration in the brine after lithium extraction can reach 0.11 g / L, and the lithium concentration in the recovered solution can reach 3.22 g / L.

[0088] A comparison of Examples 1 and 4-5 shows that the amount of manganese dioxide added to the electrode slurry disclosed in this invention affects the lithium extraction effect. When the mass ratio of manganese dioxide to electrode active material is controlled at (2-4):10, the lithium extraction effect of the electrode is better. If the amount of manganese dioxide added is too large, it is difficult to completely decompose and remains inside the electrode, reducing the lithium extraction capacity and efficiency. If the amount of manganese dioxide added is too small, even if it is completely decomposed, the porosity formed is low, which hinders the mass transfer of the solution.

[0089] A comparison of Examples 1 and 6-7 shows that the duration of voltage application during the preparation of the porous lithium-poor electrode disclosed in this invention affects the lithium extraction effect. Controlling the time to 2-6 hours results in a better lithium extraction effect. If the voltage application time is too long, the porosity will be too large or the electrode structure will be damaged, reducing the mechanical strength of the electrode. If the voltage application time is too short, it will be difficult to achieve the effect of manganese dioxide decomposition to form pores.

[0090] As can be seen from the comparison between Example 1 and Comparative Example 1, the present disclosure adds manganese dioxide to the electrode slurry. When the voltage is above 1.5V, the manganese dioxide will decompose into manganese trioxide or manganese tetroxide and release oxygen. The particle size and morphology of manganese dioxide change, forming pores in the original position, which improves the mass transfer effect of the solution inside the electrode, thereby improving the lithium extraction efficiency of the electrode.

[0091] As can be seen from the comparison between Example 1 and Comparative Examples 2-3, the magnitude of the applied voltage affects the lithium extraction effect during the preparation of the porous lithium-poor state electrode described in this disclosure. Controlling the voltage between 1.5 and 2.5V results in a better lithium extraction effect. If the voltage is too high, it will damage the internal structure of the electrode and reduce the cycle stability. If the applied voltage is too low, it will be lower than the decomposition voltage of manganese dioxide, and manganese dioxide will not decompose, thus failing to create pores.

Claims

1. A method for preparing a porous lithium-poor electrode, the method comprising the following steps: (1) A slurry is obtained by mixing electrode active material, manganese dioxide, conductive agent, binder and solvent, and the slurry is coated on the surface of current collector to obtain lithium-rich electrode; (2) Using the lithium-rich electrode as the positive electrode and the AgCl electrode as the negative electrode, the first electrolyte is added and subjected to a one-step constant voltage treatment to obtain the lithium-poor electrode; (3) Using the lithium-rich electrode as the positive electrode and the lithium-poor electrode as the negative electrode, a second electrolyte is added, and the electrode is subjected to a two-step constant voltage treatment to obtain the porous lithium-poor electrode; The mass ratio of manganese dioxide to electrode active material is (2~4):10, the voltage of the first-step constant voltage treatment is 0.8~1.2V, the voltage of the second-step constant voltage treatment is 1.5~2.5V, and the time of the second-step constant voltage treatment is 2~6h.

2. The preparation method according to claim 1, wherein, The electrode active material in step (1) includes any one or a combination of at least two of lithium iron phosphate, lithium manganese oxide, or lithium nickel cobalt manganese oxide.

3. The preparation method according to claim 1, wherein, The median particle size D50 of the electrode active material is 0.5~10μm.

4. The preparation method according to claim 1, wherein, The median particle size D50 of the manganese dioxide is 20~100nm.

5. The preparation method according to claim 1, wherein, The conductive agent includes acetylene black and / or conductive carbon black.

6. The preparation method according to claim 1, wherein, The mass ratio of the conductive agent to the electrode active material is (1~2):

10.

7. The preparation method according to claim 1, wherein, The adhesive includes polyvinylidene fluoride.

8. The preparation method according to claim 1, wherein, The mass ratio of the binder to the electrode active material is (1~1.5):

10.

9. The preparation method according to claim 1, wherein, The current collector in step (1) includes carbon fiber cloth and / or titanium mesh.

10. The preparation method according to claim 1, wherein, The density of the coating is 150~200 mg / cm³. 2 .

11. The preparation method according to claim 1, wherein, Step (2) The solute in the first electrolyte includes KCl and / or NaCl.

12. The preparation method according to claim 1, wherein, The concentration of the first electrolyte is 0.05~0.1 mol / L.

13. The preparation method according to claim 1, wherein, Step (3) The second electrolyte includes a NaCl solution.

14. The preparation method according to claim 1, wherein, The concentration of the second electrolyte is 0.05~0.1 mol / L.

15. A porous lithium-poor state electrode, said porous lithium-poor state electrode being prepared by the method according to any one of claims 1-14.

16. A method for lithium extraction from salt lakes, the method comprising the following steps: (1) The electrolysis device is divided into an anode chamber and a cathode chamber by an anion exchange membrane, the lithium-rich electrode is placed in the anode chamber, the porous lithium-poor electrode as described in claim 15 is placed in the cathode chamber, salt lake brine is added to the cathode chamber, and anolyte is added to the anode chamber; (2) When the current drops to 150mA, the lithium extraction reaction is stopped. If the lithium extraction time is ≤5h, the anode and cathode are exchanged to continue lithium extraction. If the lithium extraction time is >5h, the electrode in the anode chamber is taken out as the negative electrode and the lithium-rich electrode is taken as the positive electrode. Electrolyte is added and the constant voltage reaction is used to increase the porosity. The electrode obtained by the constant voltage reaction is taken as the cathode and the lithium-rich electrode is taken as the anode to continue the salt lake lithium extraction reaction. (3) Repeat step (2) 2 to 5 times to end the lithium extraction reaction.

17. The method of claim 16, wherein, The solute in the anolyte of step (1) includes KCl and / or NaCl.

18. The method of claim 16, wherein, The concentration of the anolyte is 0.05~0.1 mol / L.

19. The method of claim 16, wherein, The voltage applied in step (2) is 0.3~1.2V.

20. The method of claim 16, wherein, The electrolyte in step (2) includes a NaCl solution.

21. The method of claim 16, wherein, The concentration of the electrolyte is 0.05~0.1mol / L.

22. The method of claim 16, wherein, The voltage of the constant voltage reaction is 1.5~2.5V.

23. The method of claim 16, wherein, The constant voltage reaction takes 2 to 6 hours.

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