Preparation method and application of a colloidal electrode for electrochemically lithiating and regenerating waste cathode materials

Abstract

The present invention discloses a preparation method and application of a colloidal electrode for electrochemically lithiating and regenerating waste cathode materials. The preparation method is to add waste cathode powder at a ratio of 15-65 g / L to absolute ethanol, stir for 10 min at a temperature of 20-100 °C, and then add it to an aqueous solution of polyvinyl alcohol with a concentration of 0.08-0.75 g / mL, and dry at a temperature of 120 °C to obtain a colloidal electrode for electrochemically lithiating and regenerating waste cathode materials. The method of the present invention can prepare different types of waste cathode materials into the form of electrode sheets. The obtained colloidal electrode has excellent stress-strain elasticity, wettability and tensile elasticity, can effectively realize electrochemical lithiation regeneration, and can effectively remove the PVDF impurities carried in the waste cathode materials. The regenerated cathode material powder can be obtained by tempering, without going through cumbersome processes such as coating, peeling, and impurity removal, and can obtain more excellent regenerated cathode materials with a shorter process and lower energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of waste cathode materials, and particularly relates to a preparation method and application of a colloidal electrode for electrochemical lithiation regeneration of waste cathode materials. Background Art

[0002] Lithium-ion batteries (LIBs) are crucial for electric vehicle (EV) technology, thanks to their high energy density, long cycle life, and superior efficiency. Among the various cathode materials used in lithium-ion batteries, ternary materials (LiNixCoyMn1-x-yO2, NCM) and lithium iron phosphate (LiFePO4, LFP) have become the main choices. Each material has been matched to different application scenarios according to its characteristics. However, they all have the same bottleneck - irreversible working principles and limited life cycles. Generally, lithium-ion batteries face retirement after 3 to 10 years of use. These discarded batteries contain a large amount of precious metals, and inadequate recycling practices will lead to a huge loss of these precious resources. In addition, improper disposal of waste LFP batteries may release harmful substances, polluting the soil and water and potentially affecting human health through the food chain. Currently, the recycling methods mainly include hydrometallurgical recycling, pyrometallurgical recycling, and direct regeneration methods. Traditional hydrometallurgical recycling is a technique that uses chemical solutions to extract precious metals. However, this method uses and generates a large amount of chemical liquids, which may cause secondary environmental pollution. Pyrometallurgical recycling uses high-temperature heating to treat used batteries. Although this method is effective for metal recycling, it is associated with high energy consumption and may produce harmful gases, having an adverse impact on the environment. Therefore, researchers and the market have focused on the direct regeneration recycling strategy, which not only promises to reduce energy consumption and environmental impact but also enables the closed-loop recycling of active materials, effectively improving the recovery rate of valuable metals and the added value of recycled products.

[0003] Electrochemical lithiation regeneration is regarded as a direct regeneration method with low energy consumption, less pollution, sustainability, and scalability. In recent years, waste cathode powder has usually been prepared into electrode sheets or directly used for electrochemical lithium supplementation of waste electrode sheets in a lithium-containing solution. However, this method is limited in lithium iron phosphate. Because after the electrochemical lithiation of cathode materials such as ternary cathode materials, lithium manganese oxide cathode materials, and lithium cobalt oxide cathode materials, the cathode material powder can be peeled off from the current collector by sintering in air, and PVDF in the electrode sheet can be removed. However, the regeneration of lithium iron phosphate needs to be carried out in a reducing atmosphere, which makes it difficult to remove PVDF in the electrode sheet during the tempering stage after electrochemical lithiation of lithium iron phosphate electrode sheets, introducing impurities that are difficult to remove into the regenerated material and thus affecting its electrochemical performance.

[0004] The present invention aims to provide a preparation method of a colloidal electrode for electrochemical lithiation regeneration of waste cathode materials. Summary of the Invention

[0005] The first object of the present invention is to provide a preparation method of a colloidal electrode for electrochemical lithiation regeneration of waste cathode materials, and the second object of the present invention is to provide the application of the preparation method.

[0006] The first object of the present invention is achieved as follows. A preparation method of a colloidal electrode for electrochemical lithiation regeneration of waste cathode materials is to add waste cathode powder to absolute ethanol at a ratio of 15 - 65 g / L, stir at a temperature of 20 - 100 °C for 10 - 20 min, and then add it to an aqueous solution of polyvinyl alcohol with a concentration of 0.08 - 0.75 g / mL, and dry at a temperature of 120 °C to obtain a colloidal electrode for electrochemical lithiation regeneration of waste cathode materials;

[0007] The mass ratio of polyvinyl alcohol to waste cathode powder is 1:3 - 5.

[0008] The second object of the present invention is achieved as follows. The application of the preparation method is the application in the electrochemical lithiation regeneration of waste lithium iron phosphate cathode materials.

[0009] The beneficial effects of the present invention are as follows:

[0010] 1. The method of the present invention can prepare different types of waste cathode materials into the form of electrode sheets. The obtained colloidal electrode has excellent stress-strain elasticity, wettability and tensile elasticity, can effectively realize electrochemical lithiation regeneration, and can effectively remove the PVDF impurities carried in the waste cathode materials. By tempering, the regenerated cathode material powder can be obtained without going through cumbersome processes such as coating, peeling, and impurity removal, and can obtain more excellent regenerated cathode materials with a shorter process and lower energy consumption.

[0011] 2. The method for electrochemically lithiating and regenerating waste lithium iron phosphate materials using the colloidal electrode prepared by the present invention is simple and easy to operate, does not require the preparation of electrodes, and does not introduce other impurities. Moreover, in the high-temperature stage after electrochemical lithiation, the carbon coating of lithium iron phosphate can be effectively realized, effectively improving the conductivity and cycle stability of the regenerated lithium iron phosphate, and is worthy of popularization and application. Description of the Drawings

[0012] Figure 1 is a physical diagram of the colloidal electrode;

[0013] Figure 2 is the SEM diagram of the colloidal electrode obtained in Example 1;

[0014] Figure 3 is the stress-strain diagram of the colloidal electrode obtained in Example 1;

[0015] Figure 4Contact angle wetting diagram of the colloidal electrode obtained in Example 1 for lithium ethanolate;

[0016] Figure 5 Contact angle wetting diagram of the traditional current collector electrode for lithium ethanolate;

[0017] Figure 6 Comparison diagram of the flow performance of lithium ethanolate and deionized water;

[0018] Figure 7 XRD diagrams of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0019] Figure 8 XPS-Fe spectra of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0020] Figure 9 XPS-C spectra of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0021] Figure 10 XPS-F spectra of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0022] Figure 11 Raman spectra of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0023] Figure 12 BET diagrams of waste lithium iron phosphate material (SLFP), electrochemically lithiated colloidal electrode (ELLFP), and regenerated lithium iron phosphate material (CRLFP) prepared in Example 1;

[0024] Figure 13 Physical diagram of the traditional current collector electrode;

[0025] Figure 14 Electrochemical performance diagrams of waste lithium iron phosphate material (SLFP), regenerated lithium iron phosphate material (CRLFP) prepared in Example 1, and regenerated lithium iron phosphate material (RLFP) obtained from the traditional current collector electrode in Comparative Example 1;

[0026] Figure 15Charge-discharge efficiency diagrams of waste lithium iron phosphate material (SLFP), regenerated lithium iron phosphate material (CRLFP) prepared in Example 1, and regenerated lithium iron phosphate material (RLFP) obtained from the conventional current collector electrode in Comparative Example 1. Detailed implementation manners

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited in any way. Any transformation or improvement made based on the teachings of the present invention falls within the protection scope of the present invention.

[0028] A preparation method of a colloidal electrode for electrochemically lithiating and regenerating waste cathode materials, characterized in that waste cathode powder is added to absolute ethanol at a ratio of 15 - 65 g / L, stirred at a temperature of 20 - 100 °C for 10 - 20 min, and then added to an aqueous solution of polyvinyl alcohol with a concentration of 0.08 - 0.75 g / mL, and dried at a temperature of 120 °C to obtain a colloidal electrode for electrochemically lithiating and regenerating waste cathode materials;

[0029] The mass ratio of polyvinyl alcohol to waste cathode powder is 1:3 - 5.

[0030] The waste cathode material is waste lithium iron phosphate.

[0031] The present invention also provides an application of the above preparation method in electrochemically lithiating and regenerating waste lithium iron phosphate cathode materials.

[0032] A method for electrochemically lithiating and regenerating waste lithium iron phosphate cathode materials is as follows: The prepared colloidal electrode is placed in a lithium-containing solution to complete re-lithiation, and a regenerated lithium iron phosphate material is obtained.

[0033] The specific method for electrochemically lithiating and regenerating waste lithium iron phosphate cathode materials is as follows: The prepared colloidal electrode is immersed in a lithium-containing solution as the cathode, and the anode is a graphite electrode. After lithiation at a voltage of 0.1 - 2 V for 10 - 20 s, it is directly sintered under a protective atmosphere: First, the temperature is raised to 500 °C at a heating rate of 10 °C / min and held for 2 h, and then the temperature is raised to 700 °C at a heating rate of 5 °C / min and held for 2 h to obtain regenerated lithium iron phosphate powder.

[0034] The lithium-containing solution is a lithium ethoxide solution.

[0035] Example 1

[0036] 1. Add 8 g of polyvinyl alcohol to 40 mL of deionized water, and stir at 120 °C for 10 min to obtain an aqueous solution of polyvinyl alcohol.

[0037] 2. Add 40 g of waste lithium iron phosphate powder (SLFP) to 1 L of absolute ethanol. After stirring for 10 min at 40 °C, add it to the polyvinyl alcohol aqueous solution obtained in step 1, stir again for 3 min, and dry at 120 °C to obtain a colloidal electrode. From Figure 1 and Figure 3 it can be seen that the obtained colloidal electrode is in a solid form and has excellent stress-strain elasticity and tensile elasticity, proving that the colloidal electrode obtained by this method can be applied to more application scenarios and larger scales. From Figure 2 it can be seen that the obtained colloidal electrode can effectively fix the lithium iron phosphate particles uniformly, which is beneficial for more uniform lithiation.

[0038] 3. Use the colloidal electrode as the cathode, select graphite as the anode, connect and immerse them simultaneously in the lithium ethoxide solution. After lithiation at 0.5 V for 10 s, directly place the electrochemically lithiated colloidal electrode in a container and sinter it under a protective atmosphere: first, heat it to 500 °C at a heating rate of 10 °C / min, hold for 2 h, then heat it to 700 °C at a heating rate of 5 °C / min and hold for 2 h to obtain the recycled lithium iron phosphate material (CRLFP). From Figure 4 and Figure 5 it can be seen that when comparing the waste lithium iron phosphate prepared into a colloidal electrode with the traditional current collector electrode (commercial in the market), the lithium ethoxide is immediately infiltrated when dropped on the colloidal electrode, while the traditional current collector electrode still has a contact angle, indicating that it cannot be immediately infiltrated. This proves that preparing the waste lithium iron phosphate into a colloidal electrode can more effectively improve the wettability of the waste lithium iron phosphate in the lithium-containing solution, thus achieving a more efficient lithiation effect.

[0039] Figure 6 It shows that the lithium ethoxide solution and deionized water have similar rheological properties, which also helps the progress of electrochemistry lithiation.

[0040] Figures 7 - 10 It shows that the method of the present invention can well repair the FePO4 impurity phase (15 - 20°) and trivalent iron ions of the original waste lithium iron phosphate (SLFP). Different forms of C in the waste lithium iron phosphate are repaired and normalized, and coated on the surface of the recycled lithium iron phosphate material, which helps to improve the conductivity of the recycled lithium iron phosphate. And through the comparison of the XPS-F spectra, it is found that the PVDF impurities in the waste lithium iron phosphate can be effectively removed after being prepared into a colloidal electrode and electrochemically lithiated.

[0041] Figure 11 It shows that the method of the present invention can effectively restore the characteristic peaks and binding bonds of the waste lithium iron phosphate.

[0042] Figure 12 It shows that the recycled lithium iron phosphate obtained by the method of the present invention has excellent mesopores and specific surface area.

[0043] Example 2

[0044] 1. Add 5 g of polyvinyl alcohol to 60 mL of deionized water, and stir for 10 min in an environment of 120 °C to obtain an aqueous polyvinyl alcohol solution.

[0045] 2. Add 15 g of waste lithium iron phosphate powder to 1 L of absolute ethanol, stir for 10 min at 40 °C, then add it to the aqueous polyvinyl alcohol solution obtained in Step 1, stir again for 3 min, and dry at 120 °C to obtain a colloidal electrode.

[0046] 3. Use the colloidal electrode as the cathode, select graphite as the anode, connect and immerse them simultaneously in a lithium ethanol solution, lithiate for 30 s at a voltage of 0.1 V, then directly place the electrochemically lithiated colloidal electrode in a container and sinter it under a protective atmosphere: first, heat it to 500 °C at a heating rate of 10 °C / min, hold for 2 h, then heat it to 700 °C at a heating rate of 5 °C / min and hold for 2 h to obtain a regenerated lithium iron phosphate material.

[0047] Example 3

[0048] 1. Add 15 g of polyvinyl alcohol to 20 mL of deionized water, and stir for 10 min in an environment of 120 °C to obtain an aqueous polyvinyl alcohol solution.

[0049] 2. Add 65 g of waste lithium iron phosphate powder to 1 L of absolute ethanol, stir for 10 min at 60 °C, then add it to the aqueous polyvinyl alcohol solution obtained in Step 1, stir again for 3 min, and dry at 120 °C to obtain a colloidal electrode.

[0050] 3. Use the colloidal electrode as the cathode, select graphite as the anode, connect and immerse them simultaneously in a lithium ethanol solution, lithiate for 5 s at a voltage of 2 V, then directly place the electrochemically lithiated colloidal electrode in a container and sinter it under a protective atmosphere: first, heat it to 500 °C at a heating rate of 10 °C / min, hold for 2 h, then heat it to 700 °C at a heating rate of 5 °C / min and hold for 2 h to obtain a regenerated lithium iron phosphate material.

[0051] Comparative Example 1

[0052] In this comparative example, the same waste lithium iron phosphate as in Example 1 was regenerated by the method of preparing a traditional current collector electrode. The current collector electrode was used as the cathode, graphite was selected as the anode, and they were connected and immersed in a lithium ethanol solution at the same time. After lithiation at 0.5 V for 10 s, different from that, the lithiated electrode of the current collector electrode could not be directly placed in a container like the colloidal electrode and sintered under a protective atmosphere to obtain the regenerated material. Instead, the current collector electrode needed to be sintered in air at 550 °C for 2 h. After cooling, the current collector electrode was taken out and the lithium iron phosphate black powder was peeled off from the aluminum foil. The black powder was placed in a container and sintered under a protective atmosphere: first, it was heated to 500 °C at a heating rate of 10 °C / min, held for 2 h, then heated to 700 °C at a heating rate of 5 °C / min and held for 2 h to obtain the regenerated lithium iron phosphate material (RLFP).

[0053] Detection Example

[0054] The electrochemical performance of the regenerated lithium iron phosphate materials prepared in Example 1 and Comparative Example 1 was detected. The specific detection method is as follows:

[0055] The regenerated lithium iron phosphate material and acetylene black were ground evenly in a mortar, and NMP in which PVDF was dissolved was added, and stirred until a slurry without particles was obtained. The mass ratio of the regenerated lithium iron phosphate material: acetylene black: PVDF was 8:1:1. The uniform slurry was coated on the aluminum foil, and then vacuum dried overnight at 80 °C. The dried electrode sheet was cut into circular pieces with a diameter of 12 mm for assembling a coin cell (type: CR2032), and the average mass loading was about 5.8 mg / cm 2 . A lithium metal chip was used as the anode of the half-cell structure, and the electrolyte was composed of LiPF6, FEC, DMC, and DEC in proportion. The obtained button cell could be used to test the electrochemical performance.

[0056] Result Analysis:

[0057] From Figures 14 - 15 it can be seen that the regenerated lithium iron phosphate material obtained in Example 1 has more excellent discharge specific capacity and cycle retention rate than that in Comparative Example 1, and the charge-discharge efficiency is excellent. It shows that the colloidal electrode obtained by the method of the present invention can obtain more excellent regenerated materials with a shorter process and lower energy consumption.

Claims

1. A method for preparing a colloidal electrode for electrochemical lithiation regeneration of waste positive electrode materials, characterized in that: The waste positive electrode powder is added to anhydrous ethanol at a ratio of 15-65 g / L, stirred evenly, added to a polyvinyl alcohol aqueous solution with a concentration of 0.08-0.75 g / mL, mixed evenly, and finally dried at a temperature of 120° C. to obtain a colloidal electrode for electrochemical lithium regeneration of waste positive electrode materials; The mass ratio of polyvinyl alcohol to waste positive electrode powder is 1:3-5.

2. The method for preparing a colloidal electrode for electrochemical lithiation regeneration of waste positive electrode materials according to claim 1, characterized in that: The stirring temperature is 20-100°C and the stirring time is 10-20 minutes.

3. The method for preparing a colloidal electrode for electrochemical lithiation regeneration of waste positive electrode materials according to claim 1, characterized in that: The waste positive electrode material is waste lithium iron phosphate.

4. Application of the preparation method according to claim 1 in electrochemical lithiation regeneration of waste lithium iron phosphate positive electrode materials.

5. The application according to claim 4, characterized in that: The method for electrochemically regenerating waste lithium iron phosphate positive electrode materials is as follows: placing the prepared colloidal electrode in a lithium-containing solution to complete regeneration lithiation to obtain regenerated lithium iron phosphate materials.

6. The use according to claim 5, characterized in that: The specific method for electrochemical lithiation regeneration of waste lithium iron phosphate positive electrode materials is as follows: immerse the prepared colloidal electrode in a lithium-containing solution as the cathode, and use a graphite electrode as the anode. After lithiation for 10 to 20 s at a voltage of 0.1-2V, directly sinter under a protective atmosphere: first, heat to 500°C at a heating rate of 10°C / min, keep warm for 2H, then heat to 700°C at a heating rate of 5°C / min, keep warm for 2h, and obtain regenerated lithium iron phosphate powder.

7. The use according to claim 6, characterized in that: The lithium-containing solution is a lithium ethoxide solution.

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