A method of recovering lithium metal from a spent all-solid-state lithium metal battery by joule heating

Abstract

This invention discloses a method for recovering lithium metal from waste all-solid-state lithium metal batteries using the Joule heating process. The method includes the following steps: 1) disassembling the waste all-solid-state lithium metal battery and collecting the lithium metal sheets from the negative electrode side; 2) pressing ferrous chloride powder into tablets; 3) placing the ferrous chloride tablets in a graphite boat and tightly placing the lithium metal sheets on top of the ferrous chloride tablets; 4) uniformly coating the surface of the lithium sheet / ferrous chloride tablet system with a solution composed of paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer resin, and solvent; 5) transferring the system to a Joule heating apparatus and reacting under an inert atmosphere; 6) dispersing the product obtained in step 5) in water and filtering to obtain an iron- and lithium-containing solution; 7) removing ferrous ions from the iron- and lithium-containing solution; 8) converting the lithium in the lithium chloride solution into lithium carbonate. This invention can safely and efficiently recover lithium metal from waste all-solid-state lithium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery recycling technology, and in particular to a method for recovering lithium metal from waste all-solid-state lithium metal batteries using the Joule thermal method. Background Technology

[0002] Lithium is a key strategic metal supporting the development of the new energy industry. With the commercialization and large-scale application of all-solid-state lithium metal batteries, the disposal of the highly active lithium metal anodes generated after their disposal will become a major challenge restricting the industry's sustainable development. Lithium metal reacts violently with water or air, posing extremely high safety risks such as combustion and explosion, making traditional battery recycling methods unsuitable. Therefore, there is an urgent need to develop a safe, efficient, and dedicated recycling technology system to address the environmental and safety pressures brought about by the future wave of all-solid-state battery disposals. At the same time, there is still a structural shortage risk in lithium resource supply, and effectively recovering lithium resources from waste batteries is an important supplement to primary lithium resources. Existing pyrometallurgical and hydrometallurgical recycling methods generally suffer from problems such as long processes, high energy consumption, poor safety, and low lithium recovery rates when processing these lithium metal-containing batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a method for recovering lithium metal from waste all-solid-state lithium metal batteries using the Joule thermal method. This method can safely and efficiently recover lithium metal from waste all-solid-state lithium metal batteries, thereby solving the technical problems of severe reaction risks, complex recovery processes, and low lithium recovery rates during dismantling, transfer, and conversion.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for recycling lithium metal from waste all-solid-state lithium metal batteries, comprising the following steps:

[0006] 1) After discharging the discarded all-solid-state lithium metal battery, disassemble it in the inert atmosphere of the glove box, separate and collect the metal lithium sheet on the negative electrode side.

[0007] 2) Compress ferrous chloride powder into tablets to obtain ferrous chloride tablets;

[0008] 3) In the inert atmosphere of a glove box, the ferrous chloride tablet is placed in a graphite boat, and the lithium metal sheet is placed tightly on top of the ferrous chloride tablet to obtain a lithium / ferrous chloride tablet system.

[0009] The molar ratio of the lithium metal sheet to the ferrous chloride tablet is 1:(0.5-0.7).

[0010] 4) A solution composed of paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer resin (EVA) and solvent is uniformly coated on the surface of the lithium / ferrous chloride tableting system and left to stand to form a solid composite barrier film.

[0011] 5) Transfer the system obtained in step 4) to a flash Joule heating (FJH) apparatus and heat it to 350-450°C in an inert atmosphere to react and convert active lithium into lithium chloride;

[0012] 6) Disperse the product obtained in step 5) in water and filter to remove the solid iron produced in the reaction, to obtain an iron and lithium-containing solution;

[0013] 7) Remove iron ions from the iron- and lithium-containing solution to obtain a lithium chloride solution;

[0014] 8) Convert the lithium in the lithium chloride solution into lithium carbonate and collect the lithium carbonate.

[0015] Based on the above technical solutions, this invention disassembles waste all-solid-state batteries and recovers lithium metal under an inert atmosphere. It uses an EVA-reinforced wax barrier film to achieve safe encapsulation and stable transfer of lithium metal in the air. With the help of flash Joule heating and ferrous chloride mineralizing agent, active lithium is efficiently converted into a stable product that is easy to handle. Finally, high-purity lithium carbonate is obtained through water leaching to remove impurities and precipitation purification, thus realizing the safe and efficient closed-loop recovery of lithium resources in all-solid-state lithium metal batteries.

[0016] According to an embodiment of the present invention, in the discharge step described in step 1), the discharge is performed until the voltage is <0.5V. This discharge can be achieved by connecting the discarded all-solid-state lithium metal battery to a Blue Electric testing system and discharging it fully to below a safe voltage, or by immersing the discarded all-solid-state lithium metal battery in salt water and discharging it to below a safe voltage. Further, the salt water concentration can be 0.1–0.2 mol / L.

[0017] To prevent the effects of moisture and oxygen on lithium metal, the inert environment in the glove box is further required to have an oxygen / water content of less than 0.1 ppm.

[0018] According to an embodiment of the present invention, in the pressing step described in step 2), the pressure is controlled at 20 MPa, and the pressing time is 30–60 min, such as 60 min. Specifically, a certain amount of anhydrous ferrous chloride (FeCl2) powder is weighed and pressed into dense tablets in a mold using a tablet press. The pressing of ferrous chloride into tablets is based on the following three considerations: First, tableting transforms the point contact between powder particles into stable surface contact with the lithium sheet, thereby significantly increasing the effective reaction area and improving reaction efficiency; second, the dense, sheet-like structure facilitates rapid heat conduction during the Joule heating reaction, ensuring timely and uniform heat transfer to the upper lithium sheet, whereas loose powder, due to its poor thermal conductivity and short reaction time, is prone to uneven heat transfer and incomplete reaction; finally, tableting effectively prevents the powder from splashing during rapid heating due to violent gas release or airflow disturbance, which reduces reaction efficiency and affects the stability of the reaction system.

[0019] According to an embodiment of the present invention, in step 3), the molar ratio of the lithium metal sheet to the ferrous chloride tablet is 1:(0.5-0.7), preferably 1:0.6. The inventors have found that this molar ratio affects the maximum temperature and lithium recovery rate during the water immersion process. The recovery rate is higher within a molar ratio of 1:(0.5-0.7) between the lithium metal sheet and the ferrous chloride tablet, and the water immersion temperature is lowest, the reaction is most complete, and the recovery rate is highest when the molar ratio is 1:0.6. Placing the lithium sheet at the top utilizes its low melting point and gravity, allowing it to melt during the reaction and automatically and uniformly immerse itself into the FeCl2 tablet, thereby achieving maximum reaction contact and conversion.

[0020] According to an embodiment of the present invention, in the solution described in step 4), the mass ratio of paraffin wax, microcrystalline wax, and EVA resin is 1:1:1. The addition of EVA resin increases the toughness and adhesion of the composite separator, avoiding the risk of easy detachment and contributing to safe encapsulation and stable transfer. The inventors, by observing the highest temperature and experimental phenomena during the leaching process of composite separators with and without EVA in water, found that the composite separator with added EVA resin has a better waterproof effect.

[0021] The solvent is ethyl acetate, and the mass ratio of the solvent to the total mass of paraffin, microcrystalline wax, and EVA resin is 7.5:1. The solution preparation steps include dissolving paraffin, microcrystalline wax, and ethylene-vinyl acetate copolymer (EVA) resin in the solvent, placing the mixture in a sealed container, and continuously stirring in a glove box for 4–6 hours until the solids are completely dissolved to obtain a homogeneous solution. The oxygen / water content in the glove box is below 0.1 ppm.

[0022] Furthermore, the method further includes, before coating, transferring the solution to a vacuum transition chamber for degassing to remove dissolved and entrained gases. For example, the degassing time is 10 minutes. During the coating step, it is necessary to ensure that the graphite boat is completely covered. The settling is carried out in a glove box, and the settling time can specifically be 12 hours, to allow the ethyl acetate to fully evaporate, thereby forming a dense, flexible solid composite barrier film for isolating air.

[0023] According to an embodiment of the present invention, in the reaction step described in step 5), the temperature is instantly raised to the target temperature within 1 second, and the holding time is 30 seconds. The Joule heating reaction apparatus rapidly heats the system to the target temperature in a very short time by applying a high instantaneous current. The inventors have found that if the reaction temperature is too low, the conversion reaction is incomplete, and the residual lithium metal reacts with water exothermically, leading to a significant temperature rise; while if the temperature is too high, it will cause partial volatilization of lithium metal, which also reduces the recovery rate. The Joule heating reaction temperature is preferably 350-400℃, more preferably 400℃. The inert atmosphere can specifically be argon. The main components of the product after the Joule heating reaction are LiCl and Fe, as well as excess FeCl2.

[0024] According to an embodiment of the present invention, in the dispersion step described in step 6), the stirring time is 6 hours. To investigate whether the lithium metal has been completely converted, the temperature change during the water immersion process needs to be monitored. The LiCl generated in the reaction is readily soluble in water, while metallic iron is insoluble. A preliminary separation of the iron slag and the lithium-containing solution is achieved through filtration.

[0025] According to an embodiment of the present invention, the step of removing ferrous ions in step 7) includes first adding hydrogen peroxide to the iron- and lithium-containing solution to remove Fe. 2+ Oxidized to Fe 3+ Then add an alkaline reagent to make Fe 3+ The hydrogen peroxide is converted into Fe(OH)3 precipitate, which is then removed. The amount of hydrogen peroxide added is excess, sufficient to convert Fe... 2+ Fully oxidized to Fe 3+ The alkaline reagent can specifically be sodium hydroxide (NaOH) solution. The solution is precisely adjusted to the pH value that produces Fe(OH)3 precipitate, and then the Fe(OH)3 precipitate is removed by filtration. For example, for every 0.705g of FeCl2 powder, 1.0-1.5mL of 30% H2O2 solution and 25-30mL of 1mol / L NaOH solution are added to adjust the pH of the solution to 3.5.

[0026] According to an embodiment of the present invention, the step of converting lithium carbonate in step 8) includes adding an alkaline reagent to the lithium chloride solution to adjust the pH to 10.5, and then adding a lithium precipitating agent to generate lithium carbonate at 90°C. Specifically, the alkaline reagent may be sodium hydroxide (NaOH).

[0027] Further, the lithium precipitant is sodium carbonate, and the molar ratio of sodium carbonate to lithium in the lithium metal sheet is (0.5-0.7):1. Specifically, the sodium carbonate can be added in the form of a saturated sodium carbonate (Na₂CO₃) solution, followed by aging at a controlled temperature after the reaction. The inventors have discovered that the amount of saturated sodium carbonate solution added within this range can fully convert lithium in the lithium chloride solution into lithium carbonate. It is understood that the method also includes vacuum filtration of the generated white precipitate, repeated washing with hot deionized water, and finally drying in a vacuum drying oven.

[0028] The present invention has the following beneficial effects:

[0029] This invention introduces an EVA-reinforced wax composite barrier film to achieve safe encapsulation and stable transfer of lithium metal in air. Utilizing flash Joule heating technology, the lithium metal is melted instantaneously, significantly improving the kinetic efficiency of its solid-state reaction with ferrous chloride while reducing energy consumption. This enables rapid mineral-phase conversion of lithium to readily soluble and chemically stable lithium chloride. By selecting ferrous chloride, which has moderate oxidizing properties rather than a strong oxidant, the reaction process is ensured to be mild and controllable, avoiding violent exothermic reactions. Finally, high-value-added lithium products are obtained through green wet separation and purification. This invention provides a novel technical approach for the large-scale safe recovery of highly active lithium metal, possessing both good engineering adaptability and environmental benefits. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention.

[0031] Figure 2 This is a schematic diagram of the composite barrier film / lithium metal / FeCl2 tablet structure in this invention. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0033] Unless otherwise specified, the methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials and reagents used in the above examples are all commercially available. Ferrous chloride was obtained from Shanghai Titan Technology Co., Ltd., with a purity higher than 99.5%, containing trace amounts of impurities such as calcium and magnesium, conforming to the People's Republic of China Chemical Industry Standard (HG / T 4538-2022). Unless otherwise specified, the materials and reagents used in the following examples are all commercially available.

[0034] Method for determining the highest temperature during water immersion: The highest temperature during water immersion is determined by monitoring the reaction system throughout the process with an infrared thermometer and recording its peak temperature.

[0035] Lithium recovery rate calculation method: Dissolve the product in a certain volume V (unit: L) of 1 mol / L hydrochloric acid solution and then measure its lithium ion concentration C. Li (g / L), and calculate the lithium recovery rate (R). Li ).

[0036] ( m Li: The mass of the lithium sheet in step (2), in g).

[0037] Example 1

[0038] according to Figure 1 The process flow diagram shown illustrates the recycling of lithium metal from waste all-solid-state lithium metal batteries. The specific steps are as follows:

[0039] (1) First, connect the waste all-solid-state lithium metal battery to the Blue Electric test system and discharge it to 0.3V. Then, transfer the discharged battery to a glove box filled with inert gas (oxygen / water content is less than 0.1ppm), manually disassemble the battery casing, and separate and collect the lithium metal on the negative electrode side.

[0040] (2) Weigh 0.064g of lithium metal flakes and 0.705g of FeCl2 powder (the molar ratio of lithium metal to FeCl2 is 1:0.6). Compress the powder into a dense tablet using a tablet press in a mold at a pressure of 20 MPa for 60 min. Place the tablet in a graphite boat and place the lithium metal flakes tightly on top of the ferrous chloride tablet.

[0041] (3) Weigh 2g of paraffin wax, 2g of microcrystalline wax, and 2g of ethylene-vinyl acetate copolymer (EVA) resin, respectively, and dissolve them in 45g of ethyl acetate solvent. Place the mixture in a sealed container and stir continuously for 6 hours in a glove box (oxygen / water content is less than 0.1ppm) until the solids are completely dissolved to obtain a homogeneous solution. Then transfer the solution to a vacuum transition chamber for degassing treatment (degassing in a vacuum environment for 10min) to remove dissolved and entrained gases. After the bubbles are completely eliminated, use a pipette to quantitatively absorb the solution and uniformly coat it on the surface of the assembled "lithium sheet / ferrous chloride tablet" system to ensure that the graphite boat is completely covered (structural schematic diagram as shown in the figure). Figure 2 (As shown). Then, it is left to stand in a glove box for 12 hours to allow the ethyl acetate to fully evaporate, thereby forming a dense, flexible solid composite barrier film for isolating air.

[0042] (4) Transfer the packaged system to FJH, evacuate and fill with argon (repeat three times). Then, instantly raise the temperature to 400℃ within 1 second, hold for 30 seconds and allow to cool.

[0043] (5) The product after the Joule heating reaction was dissolved in deionized water by stirring for 6 h. To investigate whether the lithium metal was completely converted, the temperature change during the water immersion process was monitored, and the highest temperature during the water immersion process was recorded. The LiCl produced by the reaction is easily soluble in water, while metallic iron is insoluble. Through filtration, solid iron and a solution containing iron and lithium were obtained.

[0044] (6) Add 1.5 mL of 30% H2O2 solution to the filtered lithium-containing solution, stir, and remove the small amount of Fe remaining in the solution. 2+ Completely oxidized to Fe 3+ Then, add an appropriate amount of NaOH solution to adjust the pH of the solution to 3.5, and then filter out the Fe(OH)3 precipitate.

[0045] (7) Add an appropriate amount of NaOH to the purified LiCl solution after iron removal to adjust the pH of the solution to 10.5, and then heat to 90℃. While stirring, slowly add 2.66 ml of saturated Na2CO3 solution (concentration: 0.22 g / ml, molar ratio of Na2CO3 to Li: 0.6:1), and keep warm and age after the reaction is complete. Vacuum filter the generated white precipitate, wash it repeatedly with deionized water, and finally dry it in a vacuum drying oven to obtain high-purity lithium carbonate. Dissolve the product in 100 ml of 1 mol / L hydrochloric acid solution and measure its lithium ion concentration C. Li (g / L), and calculate the lithium recovery rate (R). Li ).

[0046] Example 2

[0047] This embodiment follows a similar method to that of Example 1 for recycling. The difference from Example 1 is that in step (2), only 0.58g of FeCl2 is used (the molar ratio of lithium metal to FeCl2 is 1:0.5). The remaining steps are the same as in Example 1.

[0048] Example 3

[0049] This embodiment follows a similar method to Example 1 for recycling. The difference from Example 1 is that in step (2), only 0.81g of FeCl2 is used (the molar ratio of lithium metal to FeCl2 is 1:0.7). The remaining steps are the same as in Example 1.

[0050] Example 4

[0051] This embodiment follows a similar method to that of Embodiment 1 for recycling. The difference from Embodiment 1 is that in step (4), the temperature is controlled at 350°C. The remaining steps are the same as in Embodiment 1.

[0052] Example 5

[0053] This embodiment follows a similar method to that of Embodiment 1 for recycling. The difference from Embodiment 1 is that in step (4), the temperature is controlled at 450°C. The remaining steps are the same as in Embodiment 1.

[0054] Example 6

[0055] This embodiment follows a similar method to Example 1 for recycling. The difference from Example 1 is that in step (7), the amount of lithium precipitation agent Na2CO3 (concentration: 0.22g / ml) added is 2.22ml (the molar ratio of Na2CO3 to Li is 0.5:1). The remaining steps are the same as in Example 1.

[0056] Example 7

[0057] This embodiment follows a similar method to Example 1 for recycling. The difference from Example 1 is that in step (7), the amount of lithium precipitation agent Na2CO3 (concentration: 0.22g / ml) added is 3.11ml (the molar ratio of Na2CO3 to Li is 0.7:1). The remaining steps are the same as in Example 1.

[0058] Comparative Example 1

[0059] Compared with Example 1, this comparative example uses FeCl3 in step (2), while the other steps are the same.

[0060] Comparative Example 2

[0061] Compared with Example 1, this comparative example differs in that FeCl2 mineralizer and EVA gas barrier film are not used in steps (2)-(3), the heating atmosphere in the Joule heating instrument in step (4) is air, and the subsequent water immersion and lithium precipitation steps are the same as in Example 1.

[0062] Comparative Example 3

[0063] The difference between this comparative example and Example 1 is that EVA in step (3) is omitted.

[0064] Performance testing

[0065] (1) Compactness of composite membrane

[0066] To verify the compactness of the composite membrane, the composite membrane / lithium sheet / ferrous chloride systems from Example 1 and Comparative Example 3 were individually immersed in water to observe the highest temperature during the leaching process. By comparing the highest temperature and experimental phenomena, the effectiveness of the composite membrane in isolating air / water vapor was verified.

[0067] The highest water immersion temperatures in Example 1 and Comparative Example 3 in step (3) are shown in Table 1.

[0068]

[0069] As shown in the table above, the addition of EVA to the composite barrier membrane resulted in a very good waterproof effect.

[0070] Comparing the phenomena of Example 1 and Comparative Example 3, in Example 1, the composite film / lithium sheet / argon ferric chloride tablet initially produced a small number of intermittent bubbles upon contact with water, and the temperature remained below 30°C. In contrast, in Comparative Example 3, obvious shrinkage and microcracks were observed on the surface of the pure waxy film layer. Upon immersion in water, the reaction occurred violently. A large number of continuous, rapidly rising bubbles were immediately generated in the water, accompanied by a distinct hissing sound, indicating that the lithium metal reacted upon contact with water, and its effect in blocking water vapor was limited.

[0071] (2) Method safety and lithium recovery rate

[0072] The highest water immersion temperature in step (5) of Examples 1-7 and Comparative Examples 1-2, as well as the lithium recovery rate and lithium carbonate purity of Examples 1-7 and Comparative Examples 1-2 are shown in Table 2.

[0073]

[0074] As can be seen from the comparison of data in Table 2, the water immersion process used in Example 1 has the mildest conditions, the highest lithium recovery rate, and the lithium carbonate purity can reach 98.1%.

[0075] Comparing Examples 1, 2, and 3, it can be seen that insufficient FeCl2 content leads to residual metallic lithium, which reacts violently with water during leaching, causing a sudden rise in system temperature. Conversely, excessive FeCl2 content results in a decrease in lithium recovery rate. This is because excess FeCl2 volatilizes at high temperatures during the Joule heating reaction, carrying away some lithium components and causing lithium loss. Since FeCl2 in the raw material contains trace amounts of impurity elements, it also affects the purity of the final product, lithium carbonate. The purity analysis shows that insufficient FeCl2 content significantly improves the final lithium carbonate purity. This is because a lower FeCl2 content directly reduces the total amount of impurities introduced into the system, thus contributing to improved product purity. Furthermore, the lower FeCl2 content results in residual lithium metal. During leaching, lithium metal undergoes violent exothermic reactions, making the solution alkaline. This process causes some calcium and magnesium to precipitate, which is then removed during the subsequent iron slag filtration, further reducing the impurity content in the final product and improving the purity of lithium carbonate.

[0076] Comparing Examples 1, 4, and 5, it is evident that when the reaction temperature is too low, the conversion reaction is incomplete, and the residual lithium metal reacts exothermically with water, leading to a significant temperature increase. Conversely, excessively high temperatures cause partial volatilization of lithium metal, similarly reducing the recovery rate. Furthermore, it was observed that the final lithium carbonate purity increased at a temperature of 350°C. The reason for this is similar to that in Example 2: the lithium metal undergoes intense exothermic reaction during water immersion, simultaneously making the solution alkaline. This process causes some calcium and magnesium to precipitate, which is subsequently removed during the iron slag filtration process, further reducing the impurity content in the final product and thus improving the purity of lithium carbonate.

[0077] Comparing Examples 1, 6, and 7, it can be seen that if the amount of lithium precipitation agent saturated sodium carbonate solution added is too low, the recovery will be incomplete, and when the amount added exceeds a certain amount, the recovery rate will no longer increase.

[0078] In Comparative Example 1, the reaction was forced to stop. When the system temperature reached 120℃, due to the combined effect of the strong oxidizing property of FeCl3 and the strong reducing property of lithium metal, the reaction became violently out of control, instantly releasing intense white light and dense smoke, and the experiment was stopped.

[0079] Comparative Example 2 involved directly exposing lithium metal to air to convert it into lithium oxide. However, the highest temperature during water immersion still reached 91°C. This was because the lithium oxide film formed on the surface hindered further oxidation of the internal lithium metal, and the dissolution of lithium oxide was exothermic, resulting in a significant temperature rise during water immersion.

[0080] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for recycling lithium metal from waste all-solid-state lithium metal batteries, comprising the following steps: 1) After discharging the discarded all-solid-state lithium metal battery, disassemble it in the inert atmosphere of the glove box, separate and collect the metal lithium sheet on the negative electrode side. 2) Compress ferrous chloride powder into tablets to obtain ferrous chloride tablets; 3) In the inert atmosphere of a glove box, the ferrous chloride tablet is placed in a graphite boat, and the lithium metal sheet is placed tightly on top of the ferrous chloride tablet to obtain a lithium / ferrous chloride tablet system. The molar ratio of the lithium metal sheet to the ferrous chloride tablet is 1:(0.5-0.7). 4) A solution composed of paraffin wax, microcrystalline wax, ethylene-vinyl acetate copolymer resin and solvent is uniformly coated on the surface of the lithium / ferrous chloride tableting system, wherein the solvent is ethyl acetate, and the mixture is allowed to stand to form a solid composite barrier film. 5) Transfer the system obtained in step 4) to a Joule heating apparatus and heat it to 350-450°C in an inert atmosphere to react and convert active lithium into lithium chloride. 6) Disperse the product obtained in step 5) in water and filter to remove the solid iron produced in the reaction, to obtain an iron and lithium-containing solution; 7) Remove ferrous ions from the iron- and lithium-containing solution to obtain a lithium chloride solution; 8) Convert the lithium in the lithium chloride solution into lithium carbonate and collect the lithium carbonate.

2. The method according to claim 1, characterized in that: In the discharge step described in step 1), the voltage is discharged until it is <0.5V.

3. The method according to claim 1, characterized in that: In step 2), the pressure is controlled at 20 MPa and the pressing time is 30 to 60 minutes.

4. The method according to claim 1, characterized in that: In the solution described in step 4), the mass ratio of the paraffin, the microcrystalline wax, and the ethylene-vinyl acetate copolymer resin is 1:1:

1.

5. The method according to claim 4, characterized in that: The mass ratio of the solvent to the total mass of the paraffin, microcrystalline wax, and EVA resin is 7.5:

1.

6. The method according to claim 1, characterized in that: In the reaction step described in step 5), the temperature is instantly raised to the target temperature within 1 second, and the holding time is 30 seconds.

7. The method according to claim 1, characterized in that: In the dispersion step described in step 6), the stirring time is 6 hours.

8. The method according to claim 1, characterized in that: The step of removing ferrous ions in step 7) includes first adding hydrogen peroxide to the iron- and lithium-containing solution to remove Fe. 2+ Oxidized to Fe 3+ Then add an alkaline reagent to make Fe 3+ It is converted into Fe(OH)3 precipitate and then removed.

9. The method according to claim 1, characterized in that: The step of converting lithium carbonate in step 8) includes adding an alkaline reagent to the lithium chloride solution to adjust the pH to 10.5, and then adding a lithium precipitation agent to generate lithium carbonate at 90°C.

10. The method according to claim 9, characterized in that: The lithium precipitation agent is sodium carbonate, and the molar ratio of sodium carbonate to lithium in the lithium metal sheet is (0.5~0.7):1.

Images