A method for recycling lithium-ion battery electrode sheets

Abstract

The present invention relates to a method for recycling lithium-ion battery electrode sheets, belonging to the technical field of battery material recycling. The method for recycling lithium-ion battery electrode sheets provided by the present invention utilizes an inexpensive K3[Fe(CN)6] solution as a leaching solution, effectively extracting lithium ions from the positive electrode material without separating the positive electrode material from the current collector. Furthermore, the present invention utilizes an electrode containing Prussian blue to electrolyze the post-leaching solution, efficiently removing K ions from the LiK3[Fe(CN)6] leaching solution, thereby improving the purity of the recovered lithium ions.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material recycling, and in particular relates to a method for recycling lithium-ion battery electrode sheets. Background Art

[0002] Lithium-ion batteries are widely used for energy storage in portable electronics, electric vehicles, and smart grids. However, the continuous advancement of lithium-ion battery technology and the growing number of new energy vehicles are creating a significant environmental burden. Improper disposal inevitably leads to environmental pollution. Therefore, developing efficient and clean recycling processes for waste lithium-ion batteries has become a research priority for scholars both domestically and internationally.

[0003] The most critical step in the recycling process of electrode sheets is how to recycle the valuable metals in the electrode sheets. The traditional method is to first add organic reagents such as N-methylpyrrolidone (NMP) and then use ultrasound to dissolve the binder and residual electrolyte in the electrode sheets to separate the electrode sheets from the current collector. The second method is acid leaching, which uses H2SO4 and H2O2 as leaching solutions to leach Li ions from the electrode sheets. This method still has many problems. For example, reagents such as NMP, sulfuric acid and H2O2 are highly toxic, endangering the safety of employees, and are expensive, difficult to recycle, and easily damage production equipment. This method has high requirements for enterprises in terms of economy and environmental protection.

[0004] To avoid the use of large amounts of reagents such as NMP and H₂SO₄, our previous work used Li₃[Fe(CN)₆] solution as the leaching solution for electrode sheets. This method extracts lithium ions from the cathode material without separating it from the current collector. The leached solution is then used as the anolyte in a flow electrolysis cell, recycling the Li₃[Fe(CN)₆] solution and simultaneously producing a highly concentrated LiOH solution. While this method offers good leaching efficiency, the extremely high cost of preparing the Li₃[Fe(CN)₆] solution makes it difficult to apply on a large scale. Furthermore, the Li₃[Fe(CN)₆] solution is obtained by reacting ferric ferrocyanide with lithium hydroxide in deionized water and electrochemically oxidizing the filtrate. This process produces a large amount of ferric hydroxide as a byproduct and increases the number of steps required.

[0005] Therefore, it is of great significance to develop a lower-cost recycling method for lithium-ion battery electrode sheets. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a method for recycling lithium-ion battery electrode sheets.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for recycling lithium-ion battery electrode sheets, comprising the following steps:

[0009] (1) soaking the waste LiFePO4 electrode sheet in a K3[Fe(CN)6] solution to obtain a LiK3[Fe(CN)6] soaked solution;

[0010] (2) electrolyzing the LiK3[Fe(CN)6] leaching solution obtained in step (1) using an electrolysis system, wherein the electrolysis system comprises a cathode, a cathode electrolyte, an anode, an anolyte, and a diaphragm; the cathode electrolyte comprises the LiK3[Fe(CN)6] leaching solution; the cathode comprises a current collector and a cathode material coated on the current collector, wherein the cathode material comprises Prussian blue (Fe4[Fe(CN)6]3); and the anolyte contains lithium ions;

[0011] (3) A constant current is applied to the electrolysis system, and the cathode electrolyte is converted into a Li4[Fe(CN)6] solution, thereby realizing the recovery of lithium ions.

[0012] In the present recovery method, the expensive Li3[Fe(CN)6] solution is replaced with a less expensive K3[Fe(CN)6] solution with the same leaching efficiency as the leaching solution. This allows the lithium ions in the positive electrode material to be extracted without separating the positive electrode material from the current collector. However, the use of the K3[Fe(CN)6] solution introduces impurities such as potassium ions into the leaching solution, resulting in a low purity of the final electrolytic product. The present invention further utilizes electrolysis to remove K ions from the LiK3[Fe(CN)6] leaching solution, thereby improving the lithium ion recovery effect. The cathode material of the electrolysis system of the present invention contains Prussian blue (PB). Under constant current electrolysis, K ions in the LiK3[Fe(CN)6] leaching solution are embedded in the Prussian blue (PB) material lattice, achieving the purpose of removing K ions. The Prussian blue is reduced to KFe4[Fe(CN)6]3, and the lithium ions in the anolyte migrate to the cathode electrolyte. The cathode electrolyte gradually changes from LiK3[Fe(CN)6] to Li4[Fe(CN)6] solution, thereby achieving lithium ion enrichment and facilitating improved purity of the final product.

[0013] Generally, the main components of waste LiFePO4 electrode sheets are Al foil current collector and LiFePO4. The present invention uses K3[Fe(CN)6] solution to leach lithium ions, and the reaction that occurs is as follows:

[0014] LiFePO4+K3[Fe(CN)6]→FePO4+LiK3[Fe(CN)6]

[0015] K3[Fe(CN)6] undergoes redox reaction with LiFePO4, while Al foil does not participate in the reaction. LiFePO4 is oxidized to FePO4, Li + K3[Fe(CN)6] is removed from LiFePO4 and enters the leaching solution, where it is reduced to LiK3[Fe(CN)6]. After the reaction is completed, solid-liquid separation is performed, and the color of the solution changes from the original orange to green. The present invention does not impose any restrictions on other parameters such as the immersion time in step (1), as long as the lithium ions can be completely leached. Preferably, in step (1), the concentration of the K3[Fe(CN)6] solution is 0.05 mol / L-0.2 mol / L.

[0016] Preferably, in step (2), the cathode material comprises Prussian blue, a conductive agent and a binder, and the mass ratio of the Prussian blue, the conductive agent and the binder is (6-8): (1-2): (1-2).

[0017] More preferably, the mass ratio of the Prussian blue, the conductive agent and the binder is 8:1:1.

[0018] The present invention uses Prussian blue as a cathode material to intercalate potassium ions during electrolysis, thereby achieving efficient potassium ion removal and improving the purity of the final product. Furthermore, the material ratio in the cathode material also affects the potassium ion removal efficiency. Research by the present invention has found that within the aforementioned preferred mass ratio range, potassium ion removal is more effective.

[0019] Preferably, the conductive agent includes carbon black; and the binder includes polyvinylidene fluoride (PVDF).

[0020] Preferably, the cathode is prepared by uniformly mixing Prussian blue, a conductive agent, and a binder in a certain proportion, adding a solvent to prepare an electrode slurry, coating the electrode slurry on a current collector, and drying to obtain the cathode. Specifically, the current collector comprises carbon felt.

[0021] Preferably, in step (2), the electrode material of the anode includes carbon felt.

[0022] Preferably, in step (2), the anolyte comprises a LiCl solution.

[0023] Preferably, in step (2), the diaphragm is a cation exchange membrane.

[0024] Preferably, the method for recycling lithium-ion battery electrode sheets of the present invention further comprises step (4): using the Li4[Fe(CN)6] solution obtained in step (3) as the anolyte for electrolysis, so that lithium ions are recovered at the cathode, and the [Fe(CN)6] 4-Converted to [Fe(CN)6] 3- .

[0025] Step (3) of the present invention can effectively remove potassium ions in the post-immersion solution, so that the purity of the final Li4[Fe(CN)6] solution is high. Subsequently, the conventional electrolysis process can be used to electrolyze the obtained Li4[Fe(CN)6] solution as the anolyte. 4- Loss electrons and converts to [Fe(CN)6] 3- The lithium ions pass through the diaphragm to the negative electrode and are recovered at the negative electrode. The present invention does not limit the electrolysis of step (4), and the product can be prepared by conventional processes.

[0026] In a specific embodiment of the present invention, the step (4) may be: using the Li4[Fe(CN)6] solution as the anolyte, water as the catholyte, carbon felt as the anode and cathode, and a cation exchange membrane as a diaphragm, so that the [Fe(CN)6] 4- Oxidized to [Fe(CN)6] 3- , H2O in the cathode electrolyte is reduced to H2 and OH - , Li in the cathode electrolyte + Under the action of the electric field, it passes through the cation exchange membrane and migrates to the cathode to form a LiOH mixed solution, thereby achieving [Fe(CN)6] 3- recycling and recovery of lithium ions.

[0027] The present invention has the following beneficial effects: In the recovery method, an inexpensive K3[Fe(CN)6] solution is used as the leaching solution, effectively extracting lithium ions from the positive electrode material without separating the positive electrode material from the current collector. Furthermore, the present invention uses an electrode containing Prussian blue to electrolyze the leaching solution, efficiently removing K ions from the LiK3[Fe(CN)6] leaching solution, thereby improving the purity of the recovered lithium ions. The present method for recycling lithium-ion battery electrode sheets is simple to operate, uses inexpensive products, effectively extracts active ingredients from the electrode sheets, and is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the process of step (1) in Example 1 of the present invention;

[0029] Figure 2 Schematic diagram of the electrolysis system in Example 1 of the present invention;

[0030] Figure 3 This is a physical diagram of the electrolysis system in Example 1 of the present invention;

[0031] Figure 4is the discharge curve of the electrolysis system in Example 1 of the present invention;

[0032] Figure 5 The ICP-OES test results in Example 1 of the present invention are as follows;

[0033] Figure 6 1 is the discharge curve of different working electrodes in Example 2 of the present invention;

[0034] Figure 7 1 and 2 are discharge curves of different working electrodes in Example 3 of the present invention. DETAILED DESCRIPTION

[0035] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0037] Example 1

[0038] A method for recycling lithium-ion battery electrode sheets comprises the following steps:

[0039] (1) Soak 100g of waste LiFePO4 electrode directly in 300mL of 0.1mol / L K3[Fe(CN)6] solution for 5 hours. The process diagram is as follows Figure 1 As shown, LiK3[Fe(CN)6] immersion solution is obtained;

[0040] (2) Prussian blue (Fe4[Fe(CN)6]3), conductive carbon black and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a carbon felt current collector and dried to obtain an electrolytic system cathode. 50 mL of the LiK3[Fe(CN)6] leaching solution obtained in step (1) was used as the cathode electrolyte, the carbon felt was used as the anode, 50 mL of a 0.3 mol / L LiCl solution was used as the anolyte, and a cation exchange membrane was used as the diaphragm to construct an electrolytic system;

[0041] The schematic diagram of the electrolysis system is as follows Figure 2 As shown in the actual picture Figure 3 As shown, its specific composition is as follows:

[0042] The electrolytic cell consists of a stack, a peristaltic pump, a liquid storage tank, and a flow channel. The stack contains two electrode plates, four rubber gaskets, two distributors, a cation exchange membrane, a cathode electrode piece, and a carbon felt anode electrode piece. From left to right, they are the cathode electrode plate, cathode electrode piece, sealing rubber gasket, cathode distributor, sealing rubber gasket, cation exchange membrane, sealing rubber gasket, anode distributor, sealing rubber gasket, anode electrode piece, and anode electrode plate. These components are assembled into a stack, and the electrode plates are fixed with screws. The outlet of the electrolyte storage tank is connected to the inlet of the peristaltic pump through a pipe, and the outlet of the peristaltic pump is connected to the inlet of the stack through a pipe, and the outlet of the stack is connected back to the inlet of the liquid storage tank through a pipe, thus forming a closed loop.

[0043] (3) A constant current of 50 mA was applied to the electrolytic system to discharge the electrolytic cell. The following reaction occurred in the electrolytic cell:

[0044] Anode reaction: Cl - e - →Cl2

[0045] Cathode reaction: K + +Fe4[Fe(CN)6]3+e - →KFe4[Fe(CN)6]3

[0046] At this time, Fe(Ⅲ) in Prussian blue is reduced to Fe(Ⅱ), K ions are embedded in the Prussian blue material lattice from the cathode electrolyte, and Li ions migrate from the anode to the cathode to form Li4[Fe(CN)6] solution. The discharge curve is as follows: Figure 4 As shown, the total discharge time is 9.35 hours, from which the total capacity can be calculated to be 467.5 mAh, and the specific capacity of the Prussian blue electrode reaches 62.17 mAh / g.

[0047] The K ion concentration in the cathode electrolyte before and after the reaction was tested by ICP-OES. The results are as follows: Figure 5 The potassium ion concentration before the reaction was 9173.2 mg / L, and after the reaction, the concentration dropped to 109.54 mg / L, indicating that this method can remove 98.8% of the potassium ions in the leachate.

[0048] The positive electrode material scraped from the current collector of the original waste LiFePO4 electrode sheet (recorded as original LiFePO4) and the positive electrode material scraped from the electrode sheet reacted with K3[Fe(CN)6] solution in step (1) (recorded as FePO4) were sampled and tested by ICP-OES. The test results are as follows: Figure 5 As shown, the calculation formula of the leaching rate η is:

[0049]

[0050] Depend on Figure 5 The data shows that:

[0051]

[0052] The method for leaching waste lithium battery electrodes using a K3[Fe(CN)6] solution achieved a lithium leaching rate of 88.4%. The results of Example 1 demonstrate that the present method for leaching waste lithium battery electrodes using a K3[Fe(CN)6] solution effectively extracts lithium ions from the positive electrode material without separating the positive electrode material from the current collector. Furthermore, the method effectively removes potassium ions present during the reaction, resulting in a higher purity final product.

[0053] Example 2

[0054] This example investigates the specific capacity of Prussian blue and different Prussian blue analogs using the following method:

[0055] (1) Preparation of different working electrodes:

[0056] Prussian blue (Fe4[Fe(CN)6]3), conductive carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a titanium sheet and dried to obtain a Fe4[Fe(CN)6]3 electrode.

[0057] A Prussian blue analogue (Mn2[Fe(CN)6]), conductive carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a titanium sheet and dried to obtain a Mn2[Fe(CN)6] electrode.

[0058] Prussian blue analog (FeAl2[Fe(CN)6]2), conductive carbon black and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a titanium sheet and dried to obtain a FeAl2[Fe(CN)6]2 electrode;

[0059] Prussian blue analog (Ce[Fe(CN)6]), conductive carbon black and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a titanium sheet and dried to obtain a Ce[Fe(CN)6] electrode;

[0060] (2) The above four working electrodes, the counter electrode carbon felt electrode, the reference electrode Ag / AgCl, and the electrolyte 0.1 mol / L KCl solution were constructed into a three-electrode system. A current of 10 mA was applied to the three-electrode system to perform a constant current discharge process. The results are as follows: Figure 6As shown, the specific capacities of Fe4[Fe(CN)6]3, Mn2[Fe(CN)6], FeAl2[Fe(CN)6]2, and Ce[Fe(CN)6] are 66.70 mAh / g, 37.28 mAh / g, 37.65 mAh / g, and 3.08 mAh / g, respectively. Among them, Fe4[Fe(CN)6]3 has the highest specific capacity, making it most suitable for potassium extraction. This demonstrates that the use of Prussian blue as the cathode material in the present invention is more effective in removing potassium from the post-leaching solution.

[0061] Example 3

[0062] This example explores the effect of the mass ratio of Prussian blue, conductive carbon black, and binder PVDF in the cathode material on the electrode performance in the recycling method of the present invention, and the method is as follows:

[0063] Prussian blue (Fe4[Fe(CN)6]3), conductive carbon black and PVDF were mixed in a mass ratio of 8:1:1, 7:2:1 and 6:2:2, respectively, and an appropriate amount of solvent N-methylpyrrolidone was added to prepare an electrode slurry, which was then coated on a titanium sheet and dried to obtain different Fe4[Fe(CN)6]3 electrodes; the specific capacity test was carried out according to the method of Example 2, and the test results are shown in FIG. Figure 7 shown. Figure 7 The results show that the specific capacities of electrodes with mass ratios of 8:1:1, 7:2:1, and 6:2:2 are 66.70 mAh / g, 63.63 mAh / g, and 66.27 mAh / g, respectively. This indicates that the mass ratio of Prussian blue, conductive carbon black, and binder affects the performance of the electrode, and when the mass ratio of Prussian blue, conductive carbon black, and binder is 8:1:1, the performance of the electrode is the best.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for recycling lithium-ion battery electrode sheets, characterized in that: The following steps are involved: (1) using K3[Fe(CN)6] solution to leaching lithium ions in waste LiFePO4 electrode sheets to obtain LiK3[Fe(CN)6] leaching solution; (2) electrolyzing the LiK3[Fe(CN)6] leaching solution obtained in step (1) using an electrolysis system, wherein the electrolysis system comprises a cathode, a cathode electrolyte, an anode, an anolyte, and a diaphragm; the cathode electrolyte comprises the LiK3[Fe(CN)6] leaching solution; the cathode comprises a current collector and a cathode material coated on the current collector, wherein the cathode material comprises Prussian blue; and the anolyte contains lithium ions; (3) A constant current is applied to the electrolysis system, and the cathode electrolyte is converted into a Li4[Fe(CN)6] solution, thereby realizing the recovery of lithium ions.

2. The method for recycling lithium-ion battery electrode sheets according to claim 1, characterized in that: In the step (1), the concentration of the K3[Fe(CN)6] solution is 0.05 mol / L-0.2 mol / L.

3. The method for recycling lithium-ion battery electrode sheets according to claim 1, wherein: In the step (2), the cathode material includes Prussian blue, a conductive agent and a binder, and the mass ratio of the Prussian blue, the conductive agent and the binder is (6-8): (1-2): (1-2).

4. The method for recycling lithium-ion battery electrode sheets according to claim 3, wherein: The mass ratio of the Prussian blue, the conductive agent and the binder is 8:1:

1.

5. The method for recycling lithium-ion battery electrode sheets according to claim 3, characterized in that: The conductive agent includes carbon black; and / or the binder includes polyvinylidene fluoride.

6. The method for recycling lithium-ion battery electrode sheets according to claim 3, characterized in that: The cathode is prepared by uniformly mixing Prussian blue, a conductive agent and a binder in proportion, adding a solvent to prepare an electrode slurry, coating the electrode slurry on a current collector, and drying to obtain the cathode.

7. The method for recycling lithium-ion battery electrode sheets according to claim 1, characterized in that: In the step (2), the electrode material of the anode includes carbon felt.

8. The method for recycling lithium-ion battery electrode sheets according to claim 1, characterized in that: In the step (2), the anolyte is a LiCl solution.

9. The method for recycling lithium-ion battery electrode sheets according to claim 1, characterized in that: In the step (2), the diaphragm is a cation exchange membrane.

10. The method for recycling lithium-ion battery electrode sheets according to claim 1, characterized in that: The method further comprises the following steps: using the Li4[Fe(CN)6] solution obtained in step (3) as the anolyte to carry out electrolysis, so that lithium ions are recovered at the cathode, and the [Fe(CN)6] 4- Converted to [Fe(CN)6] 3- .

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