Method for recovering lithium metal in waste all-solid-state lithium metal battery by Joule thermal method

Abstract

The invention discloses a method for recycling lithium metal in a waste all-solid-state lithium metal battery through a Joule thermal method. The method comprises the following steps: 1) disassembling the waste all-solid-state lithium metal battery, and collecting a metal lithium sheet on a negative electrode side; 2) pressing the ferrous chloride powder into tablets; 3) placing the ferrous chloride tablet in a graphite boat, and tightly placing the metal lithium sheet on the ferrous chloride tablet; 4) uniformly coating the surface of the lithium sheet / ferrous chloride tableting system with a solution composed of paraffin, microcrystalline wax, ethylene-vinyl acetate copolymer resin and a solvent; 5) transferring the system into a Joule thermal reaction instrument, and heating in an inert atmosphere for reaction; the method comprises the following steps of (1) preparing a lithium chloride solution, (2) preparing a lithium chloride solution, (3) dispersing a product obtained in the step (5) in water, and filtering to obtain an iron-containing and lithium-containing solution, (7) removing ferrous ions in the iron-containing and lithium-containing solution, and (8) converting lithium in the lithium chloride solution into lithium carbonate.The method can safely and efficiently recycle metal lithium in the waste all-solid-state lithium metal battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery recycling, and particularly relates to a method for recycling lithium metal in waste full-solid-state lithium metal battery by Joule heat method. BACKGROUND

[0002] Lithium is a key strategic metal supporting the development of new energy industry. In the future, with the commercialization and large-scale application of full-solid-state lithium metal batteries, the treatment of high-activity lithium metal negative electrode generated after the retirement of the batteries will become a major challenge to the sustainable development of the industry. Metal lithium reacts violently with water or air, and there is a high risk of burning and explosion, which makes it difficult for traditional battery recycling methods to be directly applicable. Therefore, it is urgent to develop a safe, efficient and special recycling technology system to cope with the environmental and safety pressure brought by the retirement of full-solid-state batteries. At the same time, there is still a structural shortage risk of lithium resources supply, and effectively recycling lithium resources from waste batteries is also an important supplement to primary lithium resources. The existing recycling methods such as pyrometallurgical method and hydrometallurgical method have problems such as long process, high energy consumption, poor safety and low lithium recovery rate when treating such batteries containing metal lithium. SUMMARY

[0003] The purpose of the present application is to provide a method for recycling lithium metal in waste full-solid-state lithium metal battery by Joule heat method, which can safely and efficiently recycle metal lithium in waste full-solid-state lithium metal battery to solve the technical problems of violent reaction risk, complex recycling process and low lithium recovery rate in the process of disassembly, transfer and conversion.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a method for recycling lithium metal in waste full-solid-state lithium metal battery, comprising the following steps: 1) After discharging the waste full-solid-state lithium metal battery, disassemble it in a glove box inert atmosphere, separate and collect the metal lithium sheet on the negative side; 2) Press the ferrous chloride powder into tablets to obtain ferrous chloride tablets; 3) In the glove box inert atmosphere, place the ferrous chloride tablets in a graphite boat, and place the metal lithium sheet closely on the ferrous chloride tablets to obtain a lithium sheet / ferrous chloride tablet system; The molar ratio of the metal lithium sheet to the ferrous chloride tablet is 1:(0.5-0.7); 4) A solution composed of paraffin, microcrystalline wax, ethylene-vinyl acetate copolymer resin (EVA) and solvent is uniformly coated on the surface of the lithium sheet / ferrous chloride tablet system, and is left to form a solid composite barrier film; 5) The system obtained in step 4) is transferred to a Flash Joule Heating (FJH) reaction instrument, and is reacted by increasing the temperature to 350-450 DEG C in an inert atmosphere to convert the active lithium into lithium chloride; 6) The product obtained in step 5) is dispersed in water, and is filtered to remove the solid iron generated in the reaction, to obtain an iron-lithium-containing solution; 7) The iron ions in the iron-lithium-containing solution are removed, to obtain a lithium chloride solution; 8) The lithium in the lithium chloride solution is converted into lithium carbonate, and the lithium carbonate is collected.

[0005] Based on the above technical scheme, the waste full-solid-state battery is disassembled and the metal lithium is recycled under the protection of an inert atmosphere. The EVA reinforced waxy barrier film is used to realize safe packaging of the metal lithium and stable transfer in air. With the help of flash Joule heating and ferrous chloride mineralizer, the active lithium is efficiently converted into a stable product that is easy to handle. Finally, through water immersion and precipitation purification, high-purity lithium carbonate is obtained, realizing safe and efficient closed-loop recycling of lithium resources in the full-solid-state lithium metal battery.

[0006] According to the embodiment of the present application, in the discharging step of step 1), the discharging is to a voltage <0.5V. The discharging can be fully discharged to a safe voltage by connecting the waste full-solid-state lithium metal battery to a blue electricity test system, or the waste full-solid-state lithium metal battery can be soaked in brine to be discharged to a safe voltage below. Further, the concentration of the brine can be 0.1-0.2 mol / L.

[0007] To prevent the influence of water vapor and oxygen on the lithium metal, further, the inert environment atmosphere in the glove box requires that the oxygen / water content is less than 0.1 ppm.

[0008] According to the embodiment of the present application, in the pressing step of 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 a dense tablet in a mold using a tablet press. The ferrous chloride is pressed into a tablet mainly based on the following three considerations: first, tabletting can change the point contact between the powders into stable surface contact with the lithium tablet, thereby significantly increasing the effective reaction area and improving the reaction efficiency; second, the dense tablet structure is conducive to the rapid conduction of heat during the Joule heating reaction process, ensuring that the heat is timely and uniformly transmitted to the upper lithium tablet. Loose powder is prone to cause uneven heat transfer and incomplete reaction due to poor heat conduction performance and short reaction time; finally, tabletting can effectively prevent the powder from splashing due to violent gas emission or air flow disturbance during the flash heating process, reducing the reaction efficiency and affecting the stability of the reaction system.

[0009] According to the embodiment of the present application, in step 3), the molar ratio of the lithium sheet to the ferrous chloride tablet is 1: (0.5-0.7), preferably 1:0.6. The inventors found that the molar ratio affects the highest temperature in the water immersion process and the lithium recovery rate, and the recovery rate is higher in the range of the molar ratio of the lithium sheet to the ferrous chloride tablet 1: (0.5-0.7), and the water immersion temperature is the lowest, the reaction is the most complete, and the recovery rate is the highest when the molar ratio is 1:0.6. Among them, the lithium sheet is placed above, which can utilize its low melting point characteristics and gravity to make it automatically and uniformly infiltrate into the FeCl2 tablet after melting during the reaction process, thereby realizing the maximum degree of reaction contact and conversion.

[0010] According to the embodiment of the present application, in step 4), the mass ratio of paraffin, microcrystalline wax and EVA resin in the solution is 1:1:1, wherein the addition of EVA resin can increase the toughness and adhesion of the composite diaphragm, avoid the risk of easy falling off, and help safe packaging and stable transfer. The inventors found that the composite diaphragm with added EVA resin has better waterproof effect by observing the highest temperature and experimental phenomena during the immersion process of the composite diaphragm with added EVA into water.

[0011] 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 preparation steps of the solution include dissolving paraffin, microcrystalline wax and ethylene-vinyl acetate copolymer (EVA) resin in a solvent, placing the mixture in a sealed container, and continuously stirring in a glove box for 4-6 hours until the solid material is completely dissolved to obtain a uniform solution. Among them, the content of oxygen / water in the glove box is less than 0.1 ppm.

[0012] Further, the method further comprises, before coating, transferring the solution to a vacuum transition cabin for defoaming treatment to remove dissolved and entrained gas. Illustratively, the defoaming treatment time is 10 min. In the coating step, it is necessary to ensure that the graphite boat is completely coated. The standing in the glove box is carried out, and the standing time can be specifically 12 hours to make the ethyl acetate fully volatilize, thereby forming a dense and flexible solid composite barrier film for air isolation.

[0013] According to the embodiment of the present application, in the reaction step of step 5), the temperature is instantaneously raised to the target temperature within 1 s, and the holding time is 30 s. The Joule heat reaction instrument raises the system to the target temperature in a very short time by applying a high instantaneous current. The inventors found that when the reaction temperature is too low, the conversion reaction is incomplete, and the residual lithium metal reacts with water to release heat, resulting in a significant increase in temperature; while too high temperature will cause partial evaporation of lithium metal, also resulting in reduced recovery rate, and the Joule heat reaction temperature is preferably 350-400°C, more preferably 400°C. The inert atmosphere can be specifically argon. The main components of the product after the Joule heat reaction are LiCl and Fe, and excess FeCl2.

[0014] According to the embodiment of the present application, in the dispersion step of step 6), the stirring time is 6 h. To explore whether the lithium metal is completely converted, the temperature change during the water immersion process needs to be detected. LiCl generated by the reaction is easily soluble in water, while metallic iron is not. By filtration operation, the preliminary separation of iron slag and lithium-containing solution is realized.

[0015] According to the embodiment of the present application, the step of removing ferrous ions in step 7) includes first adding hydrogen peroxide to the iron and lithium-containing solution to oxidize Fe 2+ to Fe 3+ , and then adding an alkaline reagent to convert Fe 3+ to Fe(OH)3 precipitate, and removing the precipitate. The amount of hydrogen peroxide added is in excess, so that Fe 2+ is fully oxidized to Fe 3+ . The alkaline reagent can be specifically sodium hydroxide (NaOH) solution, and the solution is accurately adjusted to a pH value that generates Fe(OH)3 precipitate, and then filtered to remove the Fe(OH)3 precipitate. For example, for every 0.705 g of FeCl2 powder, 1.0-1.5 mL of 30% H2O2 solution and 25-30 mL of 1 mol / L NaOH solution are added, and the solution pH is adjusted to 3.5.

[0016] According to the embodiment of the present application, 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. The alkaline reagent can be specifically sodium hydroxide (NaOH).

[0017] Further, the lithium sinking agent is sodium carbonate, and the molar ratio of sodium carbonate to lithium in the lithium sheet is (0.5-0.7):1. The sodium carbonate can be added in the form of a saturated sodium carbonate (Na2CO3) solution, and the reaction is aged after preservation. The inventors have found that the addition of a saturated sodium carbonate solution in this range can fully convert lithium in the lithium chloride solution into lithium carbonate. It can be 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.

[0018] The present application has the following beneficial effects: The method of the present application enhances the waxy composite barrier film by introducing EVA, realizes the safe packaging and stable transfer of metal lithium in air, and promotes the instantaneous melting of metal lithium by means of flash joule heat technology, greatly improves the kinetic efficiency of solid-state reaction of metal lithium and ferrous chloride, and reduces energy consumption, realizes the rapid mineral phase conversion of lithium to easily soluble and chemically stable lithium chloride; by selecting ferrous chloride with moderate oxidizing property instead of strong oxidizing agent, the reaction process is ensured to be mild and controllable, and violent heat release is avoided; finally, high value-added lithium products are obtained through green wet separation and purification. The present application provides a new technical approach for the large-scale safe recovery of high-activity lithium metal, which has good engineering adaptability and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The process flowchart of the present application.

[0020] Figure 2 The schematic diagram of the composite barrier film / lithium metal / FeCl2 tablet structure in the present application. DETAILED DESCRIPTION

[0021] The present application will be further described in detail below in conjunction with specific embodiments. The examples provided below serve only to illustrate the present application and are not intended to limit the scope of the present application. The examples provided below can serve as a guide for further improvement by those of ordinary skill in the art, and do not in any way constitute a limitation on the present application.

[0022] In the following examples, the methods used are conventional methods, and are performed according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. in the above examples can be obtained commercially. The ferrous chloride is from Shanghai Titan Science and Technology Co., Ltd., with a purity of more than 99.5%, and contains trace amounts of calcium, magnesium and other impurities, in accordance with the People's Republic of China Chemical Industry Standard (HG / T 4538-2022). The materials, reagents, etc. used in the following examples can be obtained commercially, unless otherwise specified.

[0023] Method for determining the highest temperature in the water immersion process: The highest temperature in the water immersion process is determined by monitoring the reaction system throughout the process with an infrared thermometer and recording the peak temperature.

[0024] Method for calculating lithium recovery rate: After dissolving the product in a certain volume V (unit: L) of 1 mol / L hydrochloric acid solution, the lithium ion concentration C Li (g / L) is measured, and the lithium element recovery rate (R Li ) is calculated.

[0025] m Li: The mass of lithium sheet in step (2) is g.

[0026] Example 1 According to the process flow chart shown in Figure 1 , the lithium metal in the waste full-solid-state lithium metal battery is recovered, and the specific steps are as follows: (1) First, connect the waste full-solid-state lithium metal battery to the Blue Electric test system, and fully discharge it to 0.3 V. Then, transfer the discharged battery to a glove box filled with inert gas (oxygen / water content is less than 0.1 ppm), manually disassemble the battery shell, and separate and collect the metal lithium on the negative side.

[0027] (2) Weigh 0.064 g of lithium metal sheet, and weigh 0.705 g of FeCl2 powder (molar ratio of lithium metal to FeCl2 is 1:0.6), and use a tablet press to press it into a dense tablet in a mold, with a pressure of 20 Mpa and a time of 60 min. Place the tablet in a graphite boat, and place the metal lithium sheet tightly on top of the ferrous chloride tablet.

[0028] (3) Respectively weigh 2 g of paraffin, 2 g of microcrystalline wax, and 2 g of ethylene-vinyl acetate copolymer (EVA) resin, dissolve in 45 g of ethyl acetate solvent, place the mixture in a sealed container, and continuously stir in the glove box (oxygen / water content is less than 0.1 ppm) for 6 hours, until the solid material is completely dissolved, to obtain a uniform solution. Then transfer the solution to a vacuum transition chamber for degassing treatment (degas for 10 min in a vacuum environment), to remove dissolved and entrained gases. After the bubbles are completely eliminated, use a pipette to quantitatively draw the solution and uniformly coat it on the surface of the "lithium sheet / ferrous chloride tablet" system that has been assembled, to ensure that the graphite boat is completely covered (structure diagram as Figure 2 shown). Then place it in the glove box for 12 hours to allow the ethyl acetate to fully evaporate, thereby forming a dense and flexible solid composite barrier film for air isolation.

[0029] ​(4) The packaged system is transferred to FJH, vacuumed and filled with argon (repeated three times). Then the temperature is instantaneously increased to 400℃ within 1s, and kept for 30s until cooling.

[0030] (5) The product after Joule heat reaction is put into deionized water and stirred for 6h to dissolve. In order to explore whether the lithium metal is completely converted and detect the temperature change during the water immersion process, the highest temperature during the water immersion process is recorded. LiCl generated in the reaction is easily soluble in water, while the metal iron is not. Through filtration operation, solid iron and iron and lithium containing solution are obtained.

[0031] (6) 1.5 mL of 30% H2O2 solution is added to the filtered lithium-containing solution, and stirred to completely oxidize the residual small amount of Fe 2+ 3+ in the solution to Fe Li . Then, an appropriate amount of NaOH solution is added to adjust the pH value of the solution to 3.5, and then the Fe(OH)3 precipitate is filtered out.

[0032] (7) An appropriate amount of NaOH is added to the iron-free pure LiCl solution to adjust the pH of the solution to 10.5, and then heated to 90℃. Under stirring, 2.66ml of saturated Na2CO3 solution (concentration: 0.22g / ml, Na2CO3 to Li molar ratio is 0.6:1) is slowly added, and the reaction is kept for aging after completion. The white precipitate generated is vacuum filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying box to obtain high-purity lithium carbonate. The product is dissolved in 100ml of 1mol / L hydrochloric acid solution to measure the lithium ion concentration C Li (g / L), and the lithium element recovery rate (R Li ) is calculated.

[0033] Example 2 This example is recovered according to the similar method of Example 1, except that in step (2), only 0.58g of FeCl2 is used (lithium metal to FeCl2 molar ratio is 1:0.5), and the remaining steps are the same as Example 1.

[0034] Example 3 This example is recovered according to the similar method of Example 1, except that in step (2), only 0.81g of FeCl2 is used (lithium metal to FeCl2 molar ratio is 1:0.7), and the remaining steps are the same as Example 1.

[0035] Example 4 This example is recovered according to the similar method of Example 1, except that in step (4), the temperature is controlled at 350℃, and the remaining steps are the same as Example 1.

[0036] Example 5 This example was recovered according to a similar method to Example 1, except that in step (4), the temperature was controlled at 450°C, and the other steps were the same as in Example 1.

[0037] Example 6 This example was recovered according to a similar method to Example 1, except that in step (7), the amount of lithium precipitant Na2CO3 (concentration: 0.22 g / ml) added was 2.22 ml (molar ratio of Na2CO3 to Li was 0.5:1), and the other steps were the same as in Example 1.

[0038] Example 7 This example was recovered according to a similar method to Example 1, except that in step (7), the amount of lithium precipitant Na2CO3 (concentration: 0.22 g / ml) added was 3.11 ml (molar ratio of Na2CO3 to Li was 0.7:1), and the other steps were the same as in Example 1.

[0039] Comparative Example 1 This comparative example was compared with Example 1, except that FeCl3 was used in step (2), and the other steps were the same.

[0040] Comparative Example 2 This comparative example was compared with Example 1, except that no mineralizer FeCl2 and EVA gas barrier film were used in steps (2)-(3), and in step (4), the heating atmosphere in the Joule heating instrument was air, and the subsequent water immersion and lithium precipitation steps were the same as in Example 1.

[0041] Comparative Example 3 This comparative example was compared with Example 1, except that the EVA in step (3) was omitted.

[0042] Performance Test (1) Compactness of the composite separator In order to verify the compactness effect of the composite separator, the composite separator / lithium sheet / ferrous chloride system in Example 1 and Comparative Example 3 was immersed in water alone to observe the highest temperature during the immersion process, and the air / water vapor barrier effect of the composite film was verified by comparing the highest temperature and experimental phenomena.

[0043] The highest temperature of water immersion in step (3) of Example 1 and Comparative Example 3 is shown in Table 1.

[0044]

[0045] As can be seen from the above table, the addition of EVA in the composite barrier film has a good water-proof effect.

[0046] Comparing the phenomena of Example 1 and Comparative Example 3, in Example 1, the composite film / lithium sheet / argon chloride iron sheet generates a small amount of intermittent bubbles at the initial stage of contacting water, and the temperature is always lower than 30°C; while in Comparative Example 3, the surface of the pure wax film layer can be observed to shrink and crack obviously, and when the system is immersed in water, the reaction occurs instantly. A large amount of continuous and rapid rising bubbles are generated in water, accompanied by obvious "sizzle" sound, indicating that the lithium metal contacts water and reacts, and the water vapor barrier effect is limited.

[0047] (2) Method safety and lithium recovery rate The highest temperature of water immersion in step (5) of Example 1-7 and Comparative Example 1-2, and the lithium recovery rate and lithium carbonate purity of Example 1-7 and Comparative Example 1-2 are shown in Table 2.

[0048]

[0049] As can be seen from the data in Table 2, the water immersion process conditions adopted in Example 1 are the most moderate, and the lithium recovery rate is the highest, and the lithium carbonate purity can reach 98.1%.

[0050] As can be seen from Comparative Examples 1, 2 and 3, insufficient amount of mineralizer FeCl2 will cause residual lithium metal, which will react violently with water during the water immersion process, causing the temperature of the system to rise sharply; while too high amount of FeCl2 will cause the lithium recovery rate to decrease, because the excess FeCl2 volatilizes at high temperature during the Joule heat reaction, and carries part of the lithium components, causing lithium loss. Since the FeCl2 contains trace amounts of impurity elements, it also affects the purity of the final product lithium carbonate. Through the purity, it can be found that when the amount of FeCl2 is insufficient, the purity of the final lithium carbonate is greatly improved. On the one hand, the lower amount of FeCl2 directly reduces the total amount of impurities introduced into the system, thereby helping to improve the purity of the product. On the other hand, due to the lower amount of FeCl2, there will be residual lithium metal. The lithium metal will react violently with water during the water immersion process, causing the solution to be alkaline. This process causes part of the calcium and magnesium to form a precipitate, which is removed during the subsequent filtration of iron residue, further reducing the impurity content in the final product, thereby improving the purity of the lithium carbonate.

[0051] As can be seen from Comparative Examples 1, 4 and 5, when the reaction temperature is too low, the conversion reaction is incomplete, and the residual lithium metal reacts with water to release heat, causing the temperature to rise significantly; while too high temperature will cause part of the lithium metal to volatilize, also causing the recovery rate to decrease. And it is observed that when the temperature is 350°C, the purity of the final lithium carbonate increases. The reason is similar to that of Example 2. The lithium metal will react violently with water during the water immersion process, causing the solution to be alkaline. This process causes part of the calcium and magnesium to form a precipitate, which is removed during the subsequent filtration of iron residue, further reducing the impurity content in the final product, thereby improving the purity of the lithium carbonate.

[0052] From Comparative Examples 1, 6 and 7, it can be seen that the recovery is incomplete when the amount of saturated sodium carbonate solution of lithium sink is too low, and the recovery no longer increases when the amount exceeds a certain amount.

[0053] In Comparative Example 1, the reaction process was forced to stop. When the temperature of the system reached 120°C, the reaction was out of control due to the strong oxidation of FeCl3 and the strong reduction of lithium metal, and intense white light and thick smoke were released instantaneously, and the experiment was stopped.

[0054] In Comparative Example 2, lithium metal was directly exposed to air to convert it into lithium oxide. However, the highest temperature during the water immersion process still rose to 91°C, because the lithium oxide film generated on the surface hindered the further oxidation of the internal lithium metal, and the heat of dissolution of lithium oxide was significant, resulting in a significant temperature rise during the water immersion process.

[0055] The above describes the present application in detail. For those skilled in the art, the present application can be implemented within a wider range under equivalent parameters, concentrations and conditions without departing from the spirit and scope of the present application. Although the present application gives a specific example, it should be understood that further improvements can be made to the present application. In summary, according to the principle of the present application, the present application is intended to include any changes, uses or improvements of the present application, including changes made by conventional techniques known in the art, which deviate from the scope disclosed in the present application.

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 and left 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 solvent is ethyl acetate, and 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 iron 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.

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