Porous lithium-poor electrode, preparation method therefor, and use thereof

Abstract

The present disclosure provides a porous lithium-poor electrode, a preparation method therefor, and a use thereof. The preparation method comprises the following steps: (1) mixing an electrode active material, manganese dioxide, a conductive agent, a binder, and a solvent to obtain a slurry, and coating the slurry onto a surface of a current collector to obtain a lithium-rich electrode; (2) using the lithium-rich electrode as a positive electrode and an AgCl electrode as a negative electrode, adding a first electrolyte solution, and carrying out a first step of constant voltage treatment to obtain a lithium-poor electrode; and (3) using the lithium-rich electrode as a positive electrode and the lithium-poor electrode as a negative electrode, adding a second electrolyte solution, and carrying out a second step of constant voltage treatment to obtain the porous lithium-poor electrode. The voltage of the second step of constant voltage treatment is 1.5-2.5 V. The porosity of the interior of the porous lithium-poor electrode of the present disclosure is controllable, the mass transfer effect in the electrode is high, and the lithium extraction performance is good.

Description

A porous lithium-deficient electrode and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of lithium extraction from salt lakes and relates to a porous lithium-deficient electrode and a preparation method and application thereof. Background Art

[0002] Lithium is a key strategic resource widely used in lithium batteries. The rapid development of the new energy sector has driven a rapid increase in market demand for lithium resources, making low-cost, efficient lithium resource development a crucial factor for companies to compete in this market. Discovered lithium resources are primarily found in salt lake brines, seawater, and ores, with salt lake lithium accounting for approximately 70%. Due to the high cost and difficulty of mining lithium ore, and its increasing depletion and depletion with continued mining, extracting lithium from salt lake brines has become a trend in lithium resource development.

[0003] There are many salt lakes in western my country, but their development level is low due to their high magnesium-to-lithium ratio. Currently, the main methods for extracting lithium from brine at home and abroad include precipitation, solvent extraction, evaporation crystallization, electrodialysis, ion exchange adsorption, etc. Precipitation, as a mature lithium extraction technology, has the disadvantages of high energy consumption, complex process flow, high cost, and low lithium recovery rate. The extraction method has a fast lithium extraction rate, but the dissolution of the extractant in the brine can easily cause environmental pollution; the adsorption method has problems such as low adsorption capacity, adsorbent dissolution, and high water consumption. In recent years, many researchers at home and abroad have conducted extensive exploration and research on new lithium extraction processes. Electrochemical lithium extraction technology has good use value and application prospects.

[0004] The principle of electrochemical lithium extraction is to charge the working electrode to release lithium ions to form a lithium ion sieve, discharge it in brine to allow lithium ions to selectively enter the lithium ion sieve, and achieve lithium enrichment through cyclic operation of the charge and discharge process.

[0005] To improve the mass transfer of solutions within electrodes, creating pores to increase the solution's transport pathways is an effective method. Adding a certain proportion of soluble or easily pyrolyzed inorganic salts as pore-forming agents during electrode slurry preparation can create pores within the electrode plates. These porous structures provide excellent mass transfer pathways for solutions within the electrodes. However, pore-forming agents, when used to create pores, result in fixed pore sizes after electrode preparation and cannot be adjusted.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The purpose of the present disclosure is to provide a porous lithium-poor electrode and its preparation method and application. The porosity inside the porous lithium-poor electrode described in the present disclosure is controllable, the mass transfer effect inside the electrode is high, and the lithium extraction effect is good.

[0009] To achieve this disclosure purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, an embodiment of the present disclosure provides a method for preparing a porous lithium-deficient electrode, the method comprising the following steps:

[0011] (1) mixing an electrode active material, manganese dioxide, a conductive agent, a binder, and a solvent to obtain a slurry, and coating the slurry on a current collector surface to obtain a lithium-rich electrode;

[0012] (2) using the lithium-rich electrode as the positive electrode and the AgCl electrode as the negative electrode, adding a first electrolyte, and subjecting the electrolyte to a one-step constant voltage treatment to obtain a lithium-poor electrode;

[0013] (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;

[0014] The voltage of the two-step constant voltage treatment is 1.5-2.5V, for example, 1.5V, 1.8V, 2V, 2.2V or 2.5V.

[0015] In the disclosed embodiment, manganese dioxide is added to the electrode slurry. At a high voltage (1.5V or above), the manganese dioxide decomposes into manganese trioxide or manganese tetraoxide, releasing oxygen. The particle size and morphology of the manganese dioxide change, forming pores in the original position. The disclosed 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 thereby improving the lithium extraction efficiency of the electrode.

[0016] In one embodiment, the electrode active material in step (1) includes any one of lithium iron phosphate, lithium manganese oxide, or lithium nickel cobalt manganese oxide, or a combination of at least two thereof.

[0017] In one embodiment, the median particle size D50 of the electrode active material is 0.5-10 μm, for example, 0.5 μm, 1 μm, 2 μm, 5 μm or 10 μm.

[0018] 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.

[0019] In one embodiment, the mass ratio of the manganese dioxide to the electrode active material is (2-4):10, for example, 2:10, 2.5:10, 3:10, 3.5:10 or 4:10.

[0020] In one embodiment, the conductive agent includes acetylene black and / or conductive carbon black.

[0021] 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.

[0022] In one embodiment, the binder includes polyvinylidene fluoride.

[0023] In one embodiment, the mass ratio of the binder to the electrode active material is (1-1.5):10, for example: 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10 or 1.5:10, etc.

[0024] In one embodiment, the current collector in step (1) comprises carbon fiber cloth and / or titanium mesh.

[0025] In one embodiment, the coating density is 150-200 mg / cm 2 , for example: 15mg / cm 2 、16mg / cm 2 、17mg / cm 2 、18mg / cm 2 or 20 mg / cm 2 wait.

[0026] In one embodiment, the solute of the first electrolyte in step (2) includes KCl and / or NaCl.

[0027] In one embodiment, the concentration of the first electrolyte is 0.05-0.1 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.

[0028] In one embodiment, the voltage of the one-step constant voltage treatment is 0.8-1.2V, for example, 0.8V, 0.9V, 1V, 1.1V or 1.2V.

[0029] In one embodiment, in step (3), the second electrolyte comprises a NaCl solution.

[0030] In one embodiment, the concentration of the second electrolyte is 0.05-0.1 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.

[0031] In one embodiment, the two-step constant voltage treatment lasts for 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0032] In a second aspect, an embodiment of the present disclosure provides a porous lithium-poor electrode, wherein the porous lithium-poor electrode is prepared by the method described in the first aspect.

[0033] In a third aspect, an embodiment of the present disclosure provides a method for extracting lithium from a salt lake, the method comprising the following steps:

[0034] (1) using an anion exchange membrane to separate the electrolysis device into an anode chamber and a cathode chamber, placing a lithium-rich electrode in the anode chamber, placing the porous lithium-poor electrode described in the second aspect in the cathode chamber, adding salt lake brine to the cathode chamber, and adding anolyte to the anode chamber;

[0035] (2) Power on to carry out lithium extraction reaction. When the current drops to 150 mA, stop the reaction. If the lithium extraction time is ≤ 5 h, exchange the anode and cathode to continue lithium extraction. If the lithium extraction time is > 5 h, remove the electrode in the anode chamber as the negative electrode, use the lithium-rich electrode as the positive electrode, add electrolyte, and perform constant voltage reaction to increase the porosity. Use the electrode obtained by constant voltage reaction as the cathode and the lithium-rich electrode as the anode to continue the salt lake lithium extraction reaction.

[0036] (3) The electrode obtained by the constant voltage reaction is used as the cathode and the lithium-rich electrode is used as the anode, and the operation of step (2) is repeated 2 to 5 times to end the lithium extraction reaction.

[0037] During the lithium extraction process from the salt lake described in the embodiment of the present disclosure, the current is as low as 150 mA, and the lithium extraction reaction reaches equilibrium. If it is found that the lithium extraction time is too long, the pores are adjusted by the method described in the first aspect. The controllable adjustment of the pores improves the mass transfer effect of the solution inside the electrode, further increasing the lithium extraction reaction rate.

[0038] In one embodiment, the solute of the anolyte in step (1) includes KCl and / or NaCl.

[0039] In one embodiment, the concentration of the anolyte is 0.05-0.1 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.

[0040] In one embodiment, the voltage of the power supply in step (2) is 0.3-1.2V, for example, 0.3V, 0.5V, 0.8V, 1V or 1.2V.

[0041] In one embodiment, the electrolyte in step (2) includes a NaCl solution.

[0042] In one embodiment, the concentration of the electrolyte is 0.05-0.1 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.

[0043] In one embodiment, the voltage of the constant voltage reaction is 1.5-2.5V, for example, 1.5V, 1.8V, 2V, 2.2V or 2.5V.

[0044] 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.

[0045] The present disclosure has the following beneficial effects:

[0046] (1) The present invention discloses a porous lithium-poor electrode with controllable porosity by adding manganese dioxide to the electrode slurry. In the subsequent process of lithium extraction from salt lakes, the porosity of the electrode can be judged based on the actual lithium extraction efficiency and adjusted to improve the lithium extraction efficiency.

[0047] (2) After lithium extraction by the method disclosed in the present invention, the lithium concentration in the brine can reach below 0.15 g / L, and the lithium concentration in the recovered liquid obtained by lithium extraction can reach above 2.97 g / L. By adjusting various parameters in 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 obtained by lithium extraction can reach 3.22 g / L.

[0048] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0050] FIG1 is a schematic flow chart of the method for extracting lithium from salt lakes according to an embodiment of the present disclosure.

[0051] FIG2 is a graph showing changes in lithium concentration in the anolyte during the first lithium extraction process in Examples 1-3 of the present disclosure.

[0052] FIG3 is a graph showing changes in lithium concentration in the anolyte during the second lithium extraction process in Example 1-2 of the present disclosure. DETAILED DESCRIPTION

[0053] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0054] Example 1

[0055] This embodiment provides a method for extracting lithium from a salt lake. The process diagram of the method is shown in FIG1 . The method comprises the following steps:

[0056] (1) 100g lithium iron phosphate (D 50 =500nm) and 20g manganese dioxide (D 50 =50nm), 20g acetylene black and 15g PVDF were mixed and added to NMP to form an electrode slurry. The slurry was adjusted to 150mg / cm 2 The lithium-rich electrode was coated on a titanium mesh current collector at a density of 1.0 V, and then dried at 80° C. for 4 h to obtain a lithium-rich electrode. The lithium-rich electrode was used as a positive electrode, an AgCl electrode was used as a negative electrode, and a 0.05 mol / L KCl solution was used as an electrolyte. The lithium-rich electrode was delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0057] (2) Using a lithium-rich electrode as the positive electrode, a lithium-poor electrode as the negative electrode, and a 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;

[0058] (3) The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and a lithium-rich electrode and a lithium-poor electrode are placed in the anode chamber and the cathode chamber respectively. Brine is injected into the cathode chamber, and a 0.05 mol / L KCl solution is injected into the anode chamber. Lithium is extracted at a constant voltage of 0.3 V. When the current is as low as 150 mA, the time taken to end the reaction equilibrium is 8 hours (the change of lithium concentration in the anode liquid during lithium extraction is shown in Figure 2). The lithium extraction rate is slow. The electrode in the anode chamber is taken out 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 salt lake lithium extraction reaction (the change of lithium concentration in the anode liquid during lithium extraction is shown in Figure 3). Step (3) is repeated 3 times to end the lithium extraction reaction.

[0059] Example 2

[0060] This embodiment provides a method for extracting lithium from a salt lake, the method comprising the following steps:

[0061] (1) 100g lithium iron phosphate (D 50 =200nm) and 30g manganese dioxide (D50 =80nm), 10g acetylene black and 10g PVDF were mixed and added to NMP to form an electrode slurry. The slurry was adjusted to 150mg / cm 2 The lithium-rich electrode was coated on a titanium mesh current collector at a density of 1.0 V, and then dried at 50° C. for 8 h to obtain a lithium-rich electrode. The lithium-rich electrode was used as a positive electrode, an AgCl electrode was used as a negative electrode, and a 0.05 mol / L KCl solution was used as an electrolyte. The lithium-rich electrode was delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0062] (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;

[0063] (3) The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and a lithium-rich electrode and a lithium-poor electrode are placed in the anode chamber and the cathode chamber respectively. Brine is injected into the cathode chamber, and a 0.08 mol / L KCl solution is injected into the anode chamber. Lithium is extracted at a constant voltage of 0.5 V. When the current is as low as 150 mA, the time taken to end the reaction equilibrium is 7 hours (the change of lithium concentration in the anode liquid during lithium extraction is shown in Figure 2). The lithium extraction rate is slow. The electrode in the anode chamber is taken out 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 salt lake lithium extraction reaction (the change of lithium concentration in the anode liquid during lithium extraction is shown in Figure 3). Step (3) is repeated 3 times to end the lithium extraction reaction.

[0064] Example 3

[0065] This embodiment provides a method for extracting lithium from a salt lake, the method comprising the following steps:

[0066] (1) 100g lithium iron phosphate (D 50 =800nm) and 25g manganese dioxide (D 50 =20nm), 15g acetylene black and 15g PVDF were mixed and added to NMP to form an electrode slurry. The slurry was adjusted to 150mg / cm 2 The lithium-rich electrode was coated on a titanium mesh current collector at a density of 1.0 V, and then dried at 60° C. for 5 h to obtain a lithium-rich electrode. The lithium-rich electrode was used as a positive electrode, an AgCl electrode was used as a negative electrode, and a 0.05 mol / L KCl solution was used as an electrolyte. The lithium-rich electrode was delithiated at a constant voltage of 1.0 V to obtain a lithium-poor electrode.

[0067] (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;

[0068] (3) The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane, and the lithium-rich electrode and the lithium-poor electrode are placed in the anode chamber and the cathode chamber respectively. Brine is injected into the cathode chamber and 0.05 mol / L KCl solution is injected into the anode chamber. Lithium is extracted at a constant voltage of 0.5 V. When the current is as low as 150 mA, the time taken to end the reaction equilibrium is 5 hours (the change of lithium concentration in the anode liquid during the lithium extraction process is shown in Figure 2). The lithium extraction rate is fast, and the anode and cathode are exchanged to continue the salt lake lithium extraction reaction. Step (3) is repeated 3 times to end the lithium extraction reaction.

[0069] Example 4

[0070] The only difference between this embodiment and embodiment 1 is that the mass of manganese dioxide is 15 g, and other conditions and parameters are exactly the same as those in embodiment 1.

[0071] Example 5

[0072] The only difference between this embodiment and embodiment 1 is that the mass of manganese dioxide is 45 g, and other conditions and parameters are exactly the same as those in embodiment 1.

[0073] Example 6

[0074] The only difference between this embodiment and embodiment 1 is that the power-on time in step (2) is 1 hour, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0075] Example 7

[0076] The only difference between this embodiment and embodiment 1 is that the power-on time in step (2) is 7 hours, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0077] Comparative Example 1

[0078] The only difference between this comparative example and Example 1 is that manganese dioxide is not added to the electrode slurry, and other conditions and parameters are exactly the same as those in Example 1.

[0079] Comparative Example 2

[0080] The only difference between this comparative example and Example 1 is that the voltage of power supply in step (2) is 1.2V, and the other conditions and parameters are exactly the same as those in Example 1.

[0081] Comparative Example 3

[0082] The only difference between this comparative example and Example 1 is that the voltage of power supply in step (2) is 3V, and the other conditions and parameters are exactly the same as those in Example 1.

[0083] Performance testing:

[0084] The test results of the lithium ion concentrations in the brine and the recovered liquid (anolyte) before and after lithium extraction in the embodiment and comparative example are shown in Table 1:

[0085] Table 1

[0086] As can be seen from Table 1, according to Examples 1-3, the lithium concentration in the brine after lithium extraction by the method of the present disclosure can reach below 0.15 g / L, and the lithium concentration in the recovered liquid obtained by lithium extraction can reach above 2.97 g / L. By adjusting various parameters in 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 obtained by lithium extraction can reach 3.22 g / L.

[0087] By comparing Example 1 and Examples 4-5, it can be seen that the amount of manganese dioxide added in the electrode slurry described in the present disclosure 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 obtained 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.

[0088] By comparing Example 1 with Examples 6-7, it can be seen that in the preparation process of the porous lithium-poor electrode described in the present disclosure, the time of applying voltage will affect the effect of lithium extraction. When the time is controlled within 2 to 6 hours, the lithium extraction effect of the obtained electrode is better. If the power-on time is too long, the porosity formed is too large or the electrode structure is destroyed, thereby reducing the mechanical strength of the electrode. If the power-on time is too short, it is difficult to achieve the effect of decomposing manganese dioxide to form pores.

[0089] By comparing Example 1 and Comparative Example 1, it can be seen that the present disclosure adds manganese dioxide to the electrode slurry. The manganese dioxide decomposes into manganese trioxide or manganese tetraoxide at a high voltage (1.5V) and releases oxygen. The particle size and morphology of the manganese dioxide change, and pores are formed 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.

[0090] By comparing Example 1 and Comparative Examples 2-3, it can be seen that during the preparation process of the porous lithium-deficient electrode described in the present disclosure, the magnitude of the applied voltage will affect the lithium extraction effect. When the voltage is controlled at 1.5-2.5V, the lithium extraction effect of the obtained electrode is better. If the voltage is too high, it will cause damage to the internal structure of the electrode and reduce the cycle stability. If the applied voltage is too small, lower than the decomposition voltage of manganese dioxide, manganese dioxide will not decompose and will have no pore-forming function.

Claims

1. A method for preparing a porous lithium-deficient electrode, the method comprising the following steps: (1) mixing an electrode active material, manganese dioxide, a conductive agent, a binder and a solvent to obtain a slurry, and coating the slurry on a 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 subjecting the electrolyte to 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 subjecting the electrolyte to a two-step constant voltage treatment to obtain the porous lithium-poor electrode; The voltage of the two-step constant voltage treatment is 1.5-2.5V.

2. The preparation method according to claim 1, wherein The electrode active material in step (1) includes any one of lithium iron phosphate, lithium manganese oxide or lithium nickel cobalt manganese oxide, or a combination of at least two thereof; Optionally, the median particle size D50 of the electrode active material is 0.5 to 10 μm.

3. The preparation method according to claim 1 or 2, wherein: The median particle size D50 of the manganese dioxide is 20 to 100 nm; Optionally, the mass ratio of the manganese dioxide to the electrode active material is (2-4):

10.

4. The preparation method according to any one of claims 1 to 3, wherein The conductive agent includes acetylene black and / or conductive carbon black; Optionally, the mass ratio of the conductive agent to the electrode active material is (1-2):

10.

5. The preparation method according to any one of claims 1 to 4, wherein: The binder includes polyvinylidene fluoride; Optionally, the mass ratio of the binder to the electrode active material is (1-1.5):

10.

6. The preparation method according to any one of claims 1 to 5, wherein: The current collector in step (1) comprises carbon fiber cloth and / or titanium mesh; Optionally, the coating density is 150-200 mg / cm 2 .

7. The preparation method according to any one of claims 1 to 6, wherein: Step (2) The solute of the first electrolyte includes KCl and / or NaCl; Optionally, the concentration of the first electrolyte is 0.05-0.1 mol / L; Optionally, the voltage of the one-step constant voltage treatment is 0.8-1.2V.

8. The preparation method according to any one of claims 1 to 7, wherein: Step (3) the second electrolyte includes a NaCl solution; Optionally, the concentration of the second electrolyte is 0.05-0.1 mol / L; Optionally, the two-step constant voltage treatment lasts for 2 to 6 hours.

9. A porous lithium-deficient electrode, wherein the porous lithium-deficient electrode is prepared by the method according to any one of claims 1 to 5.

10. A method for extracting lithium from a salt lake, the method comprising the following steps: (1) using an anion exchange membrane to separate the electrolysis device into an anode chamber and a cathode chamber, placing a lithium-rich electrode in the anode chamber, placing the porous lithium-poor electrode as claimed in claim 9 in the cathode chamber, adding salt lake brine to the cathode chamber, and adding anolyte to the anode chamber; (2) Power is applied to carry out lithium extraction reaction, and the reaction is stopped when the current is as low as 150 mA. If the lithium extraction time is ≤ 5 h, the cathode and anode are exchanged to continue lithium extraction. If the lithium extraction time is > 5 h, the electrode in the anode chamber is taken out as the negative electrode, and the lithium-rich electrode is used as the positive electrode. An electrolyte is added to carry out constant voltage reaction 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; (3) Repeat step (2) 2 to 5 times to complete the lithium extraction reaction.

11. The method of claim 10, wherein: The solute of the anolyte in step (1) comprises KCl and / or NaCl; Optionally, the concentration of the anolyte is 0.05-0.1 mol / L.

12. The method according to claim 10 or 11, wherein: The voltage of the power supply in step (2) is 0.3 to 1.2V.

13. The method according to any one of claims 10 to 12, wherein: The electrolyte in step (2) comprises a NaCl solution; Optionally, the concentration of the electrolyte is 0.05-0.1 mol / L; Optionally, the voltage of the constant voltage reaction is 1.5 to 2.5 V; Optionally, the constant voltage reaction time is 2 to 6 hours.

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