Full-chain integrated combined salt lake lithium extraction and ammonia production method

Abstract

The present disclosure provides a full-chain integrated combined salt lake lithium extraction and ammonia production method, the method comprises the following steps (1) using a lithium-rich electrode as an anode and a first carbon electrode as a cathode, injecting an electrolyte to perform discharge treatment to obtain a lithium-poor electrode; (2) using the lithium-poor electrode as a cathode and a second carbon electrode as an anode, placing them in a salt lake brine to perform one-step constant voltage electrolysis to obtain a lithium-embedded electrode; (3) using the lithium-embedded electrode as an anode and a porous carbon electrode as a cathode, separating the same using a diaphragm, injecting an organic purification liquid, continuously introducing nitrogen into the organic purification liquid of the cathode, and performing two-step constant voltage electrolysis; (4) taking out the porous carbon electrode and placing it in water, reacting to obtain a lithium-rich solution, collecting the gas, and obtaining ammonia. The method described in the present disclosure can obtain ammonia while obtaining a lithium salt solution with low impurities, thereby improving the production value of a salt lake lithium extraction process.

Description

A fully integrated method for extracting lithium from salt lakes and producing ammonia Technical Field

[0001] The present invention belongs to the technical field of lithium extraction from salt lakes, and relates to a method for extracting lithium from salt lakes and producing ammonia in a fully integrated manner. Background Art

[0002] In recent years, lithium and its compounds have been widely used in many fields such as aerospace, electronic machinery, high-energy batteries, nuclear power generation, especially in the field of electric vehicles. It is one of the country's very valuable green resources and strategic mineral resources. The mining of lithium resources is difficult and the technology is complex, which limits the full utilization of lithium resources.

[0003] Lithium resources are primarily found in lithium ore and salt lakes, with salt lakes comprising a much larger proportion than lithium ore. As the reserves of easily mined lithium ore gradually decline, lithium extraction from salt lakes has gradually attracted attention. The cost of extracting lithium from salt lakes is lower than that from ore, making them an important source of lithium resources. Currently, the more mature methods for extracting lithium from salt lakes include precipitation, adsorption, membrane, electro-deintercalation, and extraction. Precipitation is the most mature and has a long history. The general process flow is: brine → evaporation and concentration → boron removal → calcium and magnesium removal → lithium precipitation with sodium carbonate. Although this method offers low production costs, it can only be used to treat brines with low magnesium-to-lithium ratios and high lithium concentrations, resulting in low lithium recovery rates. It also consumes significant amounts of water resources and generates significant wastewater.

[0004] The electro-deintercalation method is to reduce iron phosphate (lithium-rich electrode) in brine to adsorb lithium ions and embed them into its lattice structure to form lithium iron phosphate (lithium-intercalated electrode). The lithium-intercalated electrode is then placed in an electrolyte for oxidation, so that the lithium in the lithium iron phosphate is desorbed into the electrolyte, thereby completing the extraction of lithium. However, in the process of adsorbing lithium ions, due to the Mg 2+ 、Na + , K + The ion size and Li + Close to, and the concentration is much higher than Li + Therefore, these impurity cations will also enter the iron phosphate during the adsorption process, and will be desorbed from the lithium iron phosphate into the electrolyte during the desorption process. Therefore, the electrolyte needs to be treated to obtain a pure lithium salt solution.

[0005] At present, there is no simple and feasible method for directly obtaining pure lithium salt solution by electro-deintercalation and lithium extraction.

[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 fully integrated method for extracting lithium from salt lakes and producing ammonia. The method disclosed in the present disclosure can obtain ammonia gas while obtaining a low-impurity lithium salt solution, thereby improving the production value of the salt lake lithium extraction process.

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

[0010] In a first aspect, the present disclosure provides a fully integrated method for extracting lithium from salt lakes and producing ammonia, the method comprising the following steps:

[0011] (1) using a lithium-rich electrode as an anode and a first carbon electrode as a cathode, injecting an electrolyte for discharge treatment to obtain a lithium-poor electrode;

[0012] (2) The lithium-deficient electrode is used as the cathode and the second carbon electrode is used as the anode, and the electrodes are placed in salt lake brine for one-step constant voltage electrolysis to obtain a lithium-intercalated electrode;

[0013] (3) placing a lithium-intercalated electrode in an anode tank as an anode, placing a porous carbon electrode in a cathode tank as a cathode, separating the cathode tank and the anode tank with a diaphragm, injecting an organic purification liquid into both the anode tank and the cathode tank, continuously introducing nitrogen into the organic purification liquid in the cathode tank, and performing a two-step constant voltage electrolysis;

[0014] (4) The porous carbon electrode is taken out and placed in water to react to obtain a lithium-rich solution. The generated gas is collected to obtain ammonia.

[0015] In the embodiment of the present disclosure, a lithium-poor electrode is prepared in advance, which is then used as a cathode to extract lithium from a salt lake to obtain a lithium-intercalated electrode. In the subsequent electrolysis process, the lithium in the lithium-intercalated electrode lattice enters the organic purification liquid and moves toward the cathode, while the nitrogen near the cathode is reduced and reacts with lithium ions to form lithium nitride attached to the porous carbon electrode. Other impurity cations cannot react with nitrogen under this condition to produce stable nitrides, thereby achieving the separation of lithium elements and other impurity cations without introducing other anions. The porous carbon electrode is placed in water, and the reaction of lithium nitride with water can directly obtain lithium hydroxide and ammonia. The generated ammonia is collected, thereby increasing the production value.

[0016] Taking lithium iron phosphate as the lithium-intercalated electrode as an example, the equations involved in the electrolysis process are as follows:

[0017] Anode: LiFePO4=FePO4+Li + +e -

[0018] Cathode: 6Li + +6e - +N2=2Li3N

[0019] Overall reaction formula: 6LiFePO4+N2=6FePO4+2Li3N;

[0020] The reaction equation of Li3N and water is as follows:

[0021] Li3N+3H2O=3LiOH+NH3↑.

[0022] In one embodiment, the lithium-rich electrode in step (1) includes any one of a lithium iron phosphate electrode, a lithium nickel cobalt manganate electrode or a lithium manganate electrode.

[0023] In one embodiment, the electrolyte comprises a potassium chloride solution.

[0024] In one embodiment, the concentration of the potassium chloride solution is 0.03-0.08 mol / L, for example, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L or 0.08 mol / L.

[0025] In one embodiment, the voltage of the discharge treatment in step (1) is 1 to 1.5V, for example, 1V, 1.1V, 1.2V, 1.4V or 1.5V.

[0026] In one embodiment, the voltage of the one-step constant voltage electrolysis in step (2) is 0.5-1V, for example, 0.5V, 0.6V, 0.7V, 0.8V or 1V.

[0027] In one embodiment, the one-step constant voltage electrolysis lasts for 4 to 8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours.

[0028] In the disclosed embodiments, a lithium-deficient electrode is used as a cathode and a second carbon electrode as an anode to extract lithium from a salt lake, thereby obtaining the lithium-intercalated electrode. The obtained lithium-intercalated electrode contains a high concentration of impurity cations. Using the methods described in the disclosed embodiments, the impurity cations adsorbed by the lithium-intercalated electrode can be effectively separated from the lithium through a subsequent electrolysis process.

[0029] In one embodiment, the morphology of the porous carbon electrode in step (3) includes a mesh shape.

[0030] In one embodiment, the pore diameter of the porous carbon electrode is 2 to 50 nm, for example, 2 nm, 5 nm, 10 nm, 20 nm or 50 nm, and preferably 10 to 30 nm.

[0031] The porous carbon electrode described in the embodiments of the present disclosure is in a mesh-like shape, with pores ranging from 10 to 30 nm. This porous carbon electrode with the aforementioned structure and pores allows for a better reaction with nitrogen, improving purification efficiency. If the pores are too large, it is difficult for the gas to remain within the porous carbon electrode, reducing purification efficiency. If the pores are too small, it is difficult for the gas to enter the porous carbon electrode for reaction, and similarly, high purification efficiency cannot be achieved.

[0032] In one embodiment, the porous carbon electrode comprises carbon fiber felt.

[0033] The carbon fiber felt described in the embodiment of the present disclosure has a porous structure with extremely high specific surface area and electrical conductivity, which can ensure the high speed of the reaction.

[0034] In one embodiment, the diaphragm in step (3) comprises a PTFE diaphragm.

[0035] In one embodiment, the solvent of the organic purification liquid in step (3) includes any one of a carbonate solvent, a lipid solvent or an ether solvent, or a combination of at least two of them.

[0036] In one embodiment, the solute of the organic purification liquid includes any one of lithium hexafluorophosphate, LiFSI or LiClO4, or a combination of at least two thereof.

[0037] In one embodiment, the molar concentration of the solute in the organic purification solution in step (3) is 0.5 to 1.5 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L or 1.5 mol / L.

[0038] In one embodiment, the voltage of the two-step constant voltage electrolysis in step (3) is 1.5 to 2.5 V, for example, 1.5 V, 1.8 V, 2 V, 2.2 V or 2.5 V, etc., preferably 1.8 to 2.2 V.

[0039] In one embodiment, the two-step constant voltage electrolysis is performed for 4 to 10 hours, for example, 4 hours, 5 hours, 6 hours, 8 hours, or 10 hours.

[0040] As an optional solution of the embodiment of the present disclosure, the method includes the following steps:

[0041] (1) using a lithium-rich electrode as an anode and a first carbon electrode as a cathode, injecting 0.03-0.08 mol / L electrolyte, and performing a discharge treatment at 1-1.5 V to obtain a lithium-poor electrode;

[0042] (2) The lithium-deficient electrode is used as the cathode and the second carbon electrode is used as the anode, and placed in salt lake brine, and electrolyzed at a constant voltage of 0.5 to 1 V for 4 to 8 hours to obtain a lithium-intercalated electrode;

[0043] (3) placing a lithium-intercalated electrode in an anode tank as an anode, placing a porous carbon electrode with a pore diameter of 2 to 50 nm in a cathode tank as a cathode, separating the cathode tank and the anode tank with a PTFE diaphragm, injecting an organic purification solution with a molar concentration of 0.5 to 1.5 mol / L into both the anode tank and the cathode tank, continuously introducing nitrogen into the organic purification solution in the cathode tank, and performing two-step constant voltage electrolysis at 1.5 to 2.5 V for 4 to 10 hours;

[0044] (4) The porous carbon electrode is taken out and placed in water to react to obtain a lithium-rich solution. The generated gas is collected to obtain ammonia.

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

[0046] (1) The method disclosed in the present invention can obtain ammonia gas while obtaining a low-impurity lithium salt solution, thereby improving the production value of the salt lake lithium extraction process.

[0047] (2) The salt lake lithium extraction method disclosed in the present invention can still ensure a high lithium recovery rate, and the obtained lithium-rich solution has an extremely low content of impurity cations and can be directly used to prepare battery-grade lithium hydroxide. At the same time, ammonia can be recovered to improve production value.

[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] Figure 1 is a schematic diagram of the device for the full-chain integrated salt lake lithium extraction and combined ammonia production method described in an embodiment of the present disclosure, 1-lithium-poor electrode, 2-second carbon electrode, 3-salt lake brine, 4-lithium-intercalated electrode, 5-carbon fiber felt porous carbon electrode, 6-purification device, 7-anode tank, 8-cathode tank, 9-diaphragm. DETAILED DESCRIPTION

[0051] 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.

[0052] The compositions of the brine used in the examples and comparative examples of the present disclosure are shown in Table 1 below:

[0053] Table 1

[0054] The lithium iron phosphate electrodes used in the embodiments and comparative examples of the present disclosure were prepared by the following method:

[0055] The lithium iron phosphate material, the binder PVDF and the conductive graphite were mixed in a mass ratio of 8:1:1 and added into NMP to form a positive electrode slurry. The positive electrode slurry was then coated on the titanium mesh with a coating density of 100 mg / cm 2 , coating area is 10*10cm 2 , dried at 120℃ for 10h, and then cooled to obtain lithium iron phosphate electrode.

[0056] Example 1

[0057] This embodiment provides a fully integrated method for extracting lithium from salt lakes and producing ammonia. The apparatus used in the method is shown in FIG1 . The method includes the following steps:

[0058] (1) Using a lithium iron phosphate electrode as an anode and a first carbon electrode as a cathode, injecting a 0.05 mol / L potassium chloride solution, and performing a discharge treatment at 1.2 V to obtain a lithium-deficient electrode 1;

[0059] (2) The lithium-deficient electrode 1 is used as a cathode and the second carbon electrode 2 is used as an anode, and placed in salt lake brine 3, and electrolyzed at a constant voltage of 0.8 V for 6 hours to obtain a lithium-intercalated electrode 4;

[0060] (3) The lithium-intercalated electrode 4 is placed in the anode tank 7 of the purification device 6 as the anode, and the carbon fiber felt porous carbon electrode 5 (pore size of 20 nm) is placed in the cathode tank 8 of the purification device 6 as the cathode. The anode tank 7 and the cathode tank 8 are separated by a PTFE diaphragm 9. A 1 mol / L lithium hexafluorophosphate DMC solution (organic purification liquid) is injected into the anode tank 7 and the cathode tank 8. Nitrogen is continuously introduced into the organic purification liquid in the cathode tank 8, and two-step constant voltage electrolysis is performed at 2 V for 6 hours;

[0061] (4) The carbon fiber felt porous carbon electrode 5 is taken out and placed in water to react to obtain a lithium-rich solution, and the generated gas is collected to obtain ammonia.

[0062] Example 2

[0063] This embodiment provides a fully integrated method for extracting lithium from salt lakes and producing ammonia. The apparatus used in the method is shown in FIG1 . The method includes the following steps:

[0064] (1) Using a lithium iron phosphate electrode as an anode and a first carbon electrode as a cathode, injecting a 0.08 mol / L potassium chloride solution, and performing a discharge treatment at 1 V to obtain a lithium-deficient electrode 1;

[0065] (2) The lithium-deficient electrode 1 is used as a cathode and the second carbon electrode 2 is used as an anode, and placed in salt lake brine 3, and electrolyzed at a constant voltage of 0.5 V for 8 hours to obtain a lithium-intercalated electrode 4;

[0066] (3) The lithium-intercalated electrode 4 is placed in the anode tank 7 of the purification device 6 as the anode, and the carbon fiber felt porous carbon electrode 5 (pore size of 25 nm) is placed in the cathode tank 8 of the purification device 6 as the cathode. The anode tank 7 and the cathode tank 8 are separated by a PTFE diaphragm 9. A 1 mol / L DMC solution of lithium hexafluorophosphate (organic purification liquid) is injected into the anode tank 7 and the cathode tank 8. Nitrogen is continuously introduced into the organic purification liquid in the cathode tank 8, and two-step constant voltage electrolysis is performed at 1.5 V for 6 hours.

[0067] (4) The carbon fiber felt porous carbon electrode 5 is taken out and placed in water to react to obtain a lithium-rich solution, and the generated gas is collected to obtain ammonia.

[0068] Example 3

[0069] This embodiment provides a fully integrated method for extracting lithium from salt lakes and producing ammonia. The apparatus used in the method is shown in FIG1 . The method includes the following steps:

[0070] (1) Using a lithium iron phosphate electrode as an anode and a first carbon electrode as a cathode, injecting a 0.05 mol / L potassium chloride solution, and performing a discharge treatment at 1.2 V to obtain a lithium-deficient electrode 1;

[0071] (2) The lithium-deficient electrode 1 is used as a cathode and the second carbon electrode 2 is used as an anode, and placed in salt lake brine 3, and electrolyzed at a constant voltage of 0.8 V for 6 hours to obtain a lithium-intercalated electrode 4;

[0072] (3) The lithium-intercalated electrode 4 is placed in the anode tank 7 of the purification device 6 as the anode, and the carbon fiber felt porous carbon electrode 5 (pore size of 20 nm) is placed in the cathode tank 8 of the purification device 6 as the cathode. The anode tank 7 and the cathode tank 8 are separated by a PTFE diaphragm 9. A 1 mol / L lithium hexafluorophosphate DMC solution (organic purification liquid) is injected into the anode tank 7 and the cathode tank 8. Nitrogen is continuously introduced into the organic purification liquid in the cathode tank 8, and two-step constant voltage electrolysis is performed at 2.5 V for 6 hours;

[0073] (4) The carbon fiber felt porous carbon electrode 5 is taken out and placed in water to react to obtain a lithium-rich solution, and the generated gas is collected to obtain ammonia.

[0074] Example 4

[0075] The only difference between this embodiment and embodiment 1 is that the pore diameter of the porous carbon electrode is 2 nm, and other conditions and parameters are exactly the same as those in embodiment 1.

[0076] Example 5

[0077] The only difference between this embodiment and embodiment 1 is that the pore diameter of the porous carbon electrode is 50 nm, and other conditions and parameters are exactly the same as those in embodiment 1.

[0078] Example 6

[0079] The only difference between this embodiment and embodiment 1 is that the lithium iron phosphate electrode is replaced with a lithium manganate electrode, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0080] The preparation method of the lithium manganate electrode is as follows:

[0081] LiMn2O4 material, binder PVDF and conductive graphite were mixed in a mass ratio of 8:1:1 and added into NMP to form a positive electrode slurry. The positive electrode slurry was then coated on a titanium mesh with a coating density of 100 mg / cm 2 , coating area is 10*10cm 2 , dried at 120℃ for 10h, and then cooled to obtain lithium manganate electrode.

[0082] Example 7

[0083] The only difference between this embodiment and embodiment 1 is that the organic purification liquid is replaced with a 1 mol / L LISFI TEGDME solution, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0084] Comparative Example 1

[0085] The only difference between this comparative example and Example 1 is that the organic purification liquid is replaced with a 1 mol / L NaCl aqueous solution, and the other conditions and parameters are exactly the same as those in Example 1.

[0086] Performance testing:

[0087] The lithium-rich solutions obtained in Examples 1-7 and Comparative Example 1 were subjected to ICP testing. The test results are shown in Table 1:

[0088] Table 1

[0089] As can be seen from Table 1, Examples 1-7 show that the salt lake lithium extraction method disclosed herein can still ensure a high lithium recovery rate, and the resulting lithium-rich solution has an extremely low content of impurity cations, allowing it to be directly used to prepare battery-grade lithium hydroxide. Ammonia can also be recovered, thereby increasing production value. However, the lithium-rich solution obtained in the comparative example has a higher impurity content and requires a series of subsequent purification treatments, which further reduces its recovery rate and increases the cost of lithium extraction.

[0090] By comparing Example 1 with Examples 2-3, it can be seen that in the method described in the present disclosure, the voltage of step (3) will affect the lithium extraction effect. When the voltage is controlled at 1.8 to 2.2 V, the lithium extraction effect is better. If the voltage is too low, the deintercalated lithium ions cannot be fully converted into lithium nitride. If the voltage is too high, the electrolyte may produce by-products covering the surface of the porous carbon electrode, affecting the formation of lithium nitride. After multiple cycles, the lithium recovery rate will be further reduced.

[0091] By comparing Example 1 with Examples 4-5, it can be seen that in the method disclosed in the present invention, the pore size of the porous carbon electrode used in step (3) will affect the lithium extraction effect. When the pore diameter of the porous carbon electrode is controlled within 10 to 30 nm, the lithium extraction effect is better. If the pore is too small, it is difficult for the gas to enter the porous carbon electrode for reaction, and a high purification efficiency cannot be achieved. If the pore is too large, it is difficult for the gas to remain in the porous carbon electrode, and the contact area and time between the gas and the porous carbon electrode are short, the purification efficiency is reduced, and the lithium recovery rate is also reduced.

[0092] From the comparison between Example 1 and Example 6, it can be seen that the use of different types of electrodes also affects the lithium extraction effect. The lithium manganate electrode has a higher selectivity for Li, and the impurity content of the lithium-rich solution obtained using the lithium manganate electrode is lower.

[0093] From the comparison between Example 1 and Example 7, it can be seen that the present disclosure can use a wide variety of organic purification liquids, and different types of organic purification liquids can achieve good results.

[0094] From the comparison between Example 1 and Comparative Example 1, it can be seen that the present disclosure uses an organic purification liquid, and the lithium in the lithium-embedded electrode lattice enters the organic purification liquid and moves toward the cathode, while the nitrogen near the cathode is reduced and reacts with lithium ions to form lithium nitride attached to the porous carbon electrode. Other impurity cations cannot react with nitrogen under this condition to produce stable nitrides, thereby realizing the separation of lithium elements and other impurity cations without introducing other anions. When using conventional electrolytes, lithium elements cannot be separated from other impurity cations, resulting in a large amount of impurities in the lithium-rich solution, which requires further purification.

Claims

1. A method for extracting lithium from salt lakes and producing ammonia in a fully integrated chain, the method comprising the following steps: (1) using the lithium-rich electrode as an anode and the first carbon electrode as a cathode, injecting an electrolyte for discharge treatment to obtain a lithium-poor electrode; (2) placing the lithium-deficient electrode as a cathode and the second carbon electrode as an anode in salt lake brine for a one-step constant voltage electrolysis to obtain a lithium-intercalated electrode; (3) placing the lithium-intercalated electrode in an anode tank as an anode, placing the porous carbon electrode in a cathode tank as a cathode, separating the cathode tank and the anode tank with a diaphragm, injecting an organic purification liquid into both the anode tank and the cathode tank, continuously introducing nitrogen into the organic purification liquid in the cathode tank, and performing a two-step constant voltage electrolysis; (4) taking out the porous carbon electrode and placing it in water to react to obtain a lithium-rich solution, and collecting the generated gas to obtain ammonia.

2. The method of claim 1, wherein: The lithium-rich electrode in step (1) includes any one of a lithium iron phosphate electrode, a nickel cobalt lithium manganese oxide electrode or a lithium manganese oxide electrode.

3. The method according to claim 1 or 2, wherein: The electrolyte includes a potassium chloride solution.

4. The method of claim 3, wherein: The concentration of the potassium chloride solution is 0.03-0.08 mol / L.

5. The method according to any one of claims 1 to 4, wherein: The voltage of the discharge treatment in step (1) is 1 to 1.5V.

6. The method according to any one of claims 1 to 5, wherein: The voltage of the one-step constant voltage electrolysis in step (2) is 0.5 to 1 V; Optionally, the one-step constant voltage electrolysis lasts for 4 to 8 hours.

7. The method according to any one of claims 1 to 6, wherein: The morphology of the porous carbon electrode in step (3) includes a mesh shape.

8. The method according to any one of claims 1 to 7, wherein: The pore diameter of the porous carbon electrode is 2-50 nm.

9. The method of claim 8, wherein: The pore diameter of the porous carbon electrode is 10-30 nm.

10. The method according to any one of claims 1 to 9, wherein: The porous carbon electrode includes carbon fiber felt.

11. The method according to any one of claims 1 to 10, wherein: The diaphragm in step (3) comprises a PTFE diaphragm.

12. The method according to any one of claims 1 to 11, wherein: The solvent of the organic purification liquid in step (3) includes any one of a carbonate solvent, a lipid solvent or an ether solvent, or a combination of at least two thereof; Optionally, the solute of the organic purification solution includes any one of lithium hexafluorophosphate, LiFSI or LiClO4, or a combination of at least two thereof.

13. The method according to any one of claims 1 to 12, wherein: The molar concentration of the solute in the organic purification solution in step (3) is 0.5 to 1.5 mol / L.

14. The method according to any one of claims 1 to 13, wherein: The voltage of the two-step constant voltage electrolysis in step (3) is 1.5 to 2.5 V; Optionally, the two-step constant voltage electrolysis is performed for 4 to 10 hours.

15. The method of claim 14, wherein: The voltage of the two-step constant voltage electrolysis in step (3) is 1.8 to 2.2V.

16. The method according to any one of claims 1 to 15, wherein: The method comprises the following steps: (1) using the lithium-rich electrode as an anode and the first carbon electrode as a cathode, injecting 0.03-0.08 mol / L electrolyte, and performing a discharge treatment at 1-1.5 V to obtain a lithium-poor electrode; (2) placing the lithium-deficient electrode as the cathode and the second carbon electrode as the anode in salt lake brine, and performing constant voltage electrolysis at 0.5 to 1 V for 4 to 8 hours to obtain a lithium-intercalated electrode; (3) placing a lithium-intercalated electrode in an anode tank as an anode, placing a porous carbon electrode with a pore diameter of 2 to 50 nm in a cathode tank as a cathode, separating the cathode tank and the anode tank with a PTFE diaphragm, injecting an organic purification liquid with a molar concentration of 0.5 to 1.5 mol / L into both the anode tank and the cathode tank, continuously introducing nitrogen into the organic purification liquid in the cathode tank, and performing two-step constant voltage electrolysis at 1.5 to 2.5 V for 4 to 10 hours; (4) The porous carbon electrode is taken out and placed in water to react to obtain a lithium-rich solution, and the generated gas is collected to obtain ammonia.

Images