Recycling method of lithium ion battery electrode plate

Abstract

The invention relates to a recycling method of a lithium ion battery electrode plate, and belongs to the technical field of battery material recycling. According to the recycling method of the lithium ion battery electrode plate, the K3 [Fe (CN) 6] solution with low price is adopted as the leaching solution, and lithium ions in the positive electrode material can be effectively extracted without separating the positive electrode material from the current collector; moreover, an electrode containing Prussian blue is further adopted to electrolyze the leaching solution, and K ions in the LiK3 [Fe (CN) 6] leaching solution are efficiently removed, so that the recovery purity of lithium ions is improved.

Description

Technical Field

[0001] The 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 in energy storage for portable electronic products, electric vehicles, and smart grids. With the continuous upgrading of lithium-ion battery technology and the continuous increase in the number of new energy vehicles, a large number of waste lithium-ion batteries have put tremendous pressure on the environment, and improper treatment will inevitably cause environmental pollution. Therefore, the use of efficient and clean recycling processes to treat waste lithium-ion batteries has become a research focus for scholars at home and abroad.

[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 the acid leaching method, 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] In order to avoid using a large amount of reagents such as NMP and H2SO4, our previous work used Li3[Fe(CN)6] solution as the leaching solution to leach the electrode sheet. This method does not need to separate the positive electrode material from the current collector, but can extract the lithium ions in the positive electrode material, and use the leaching solution as the anode electrolyte for electrolysis through a flowing electrolytic cell to achieve the purpose of recycling the Li3[Fe(CN)6] solution and obtain a high-concentration LiOH solution at the same time. Although this method has a good leaching efficiency, the preparation cost of the Li3[Fe(CN)6] solution is extremely high, which makes the process difficult to apply on a large scale. In addition, the Li3[Fe(CN)6] solution is obtained by reacting ferric ferrocyanide and lithium hydroxide dissolved in deionized water, and the filtrate is electrochemically oxidized. The entire leaching solution preparation process will produce a large amount of iron hydroxide by-products, and increase the number of operating steps.

[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] soaking 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 recovery method of the present invention, the expensive Li3[Fe(CN)6] solution is replaced with a low-priced K3[Fe(CN)6] solution with the same leaching efficiency as the leaching solution, so that the lithium ions in the positive electrode material can be extracted without separating the positive electrode material from the current collector; however, the use of the K3[Fe(CN)6] solution will introduce impurity potassium ions into the leaching solution, resulting in a low purity of the final electrolytic product. The present invention further uses an electrolytic method to remove K ions in the LiK3[Fe(CN)6] leaching solution, thereby improving the recovery effect of lithium ions. 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 to achieve 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 is gradually transformed from LiK3[Fe(CN)6] to Li4[Fe(CN)6] solution, thereby achieving lithium ion enrichment, which is beneficial to improving the 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 leaching 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 a 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, and 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 orange to green. The present invention does not limit 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 for embedding potassium ions in electrolysis, thereby achieving efficient removal of potassium ions and improving the purity of the final product. In addition, the material ratio in the cathode material will also affect the removal effect of potassium ions. The present invention has found that within the above preferred mass ratio range, the removal of potassium ions has a better effect.

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

[0020] Preferably, the cathode is prepared by mixing Prussian blue, a conductive agent and a binder in a uniform proportion, adding a solvent to prepare an electrode slurry, and then coating the electrode slurry on a current collector and drying to obtain the cathode. Specifically, the current collector includes 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 membrane 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] in the anolyte is 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 final Li4[Fe(CN)6] solution has high purity. 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 reach 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- , the 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 recycling method of the present invention, a low-priced K3[Fe(CN)6] solution is used as the leaching solution, and the lithium ions in the positive electrode material can be effectively extracted without separating the positive electrode material from the current collector; and the present invention further uses an electrode containing Prussian blue to electrolyze the leaching solution to efficiently remove the K ions in the LiK3[Fe(CN)6] leaching solution, thereby improving the recovery purity of lithium ions. The recycling method of the lithium ion battery electrode sheet of the present invention is simple to operate, the product used is low-priced, and the active components in the electrode sheet can be effectively extracted, and it can be promoted on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic flow chart 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 It is the ICP-OES test result in Example 1 of the present invention;

[0033] Figure 6 are discharge curves of different working electrodes in Example 2 of the present invention;

[0034] Figure 7 1 and 1 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. It should be understood by those skilled in the art 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 all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0037] Example 1

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

[0039] (1) 100 g of waste LiFePO4 electrode sheets were directly immersed in 300 mL of 0.1 mol / L K3[Fe(CN)6] solution for 5 hours. The flow chart is shown in the following figure. 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 are mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent N-methylpyrrolidone is added to prepare an electrode slurry, which is then coated on a carbon felt current collector and dried to obtain an electrolytic system cathode, 50 mL of the LiK3[Fe(CN)6] immersion solution obtained in step (1) is used as the cathode electrolyte, the carbon felt is used as the anode, 50 ml of 0.3 mol / L LiCl solution is used as the anode electrolyte, and a cation exchange membrane is used as a 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, wherein the stack contains two electrode plates, four rubber gaskets, two distributors, a cation exchange membrane and 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 is applied to the electrolytic system to discharge the electrolytic cell, and the following reaction occurs 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 leaching solution.

[0048] The positive electrode material scraped from the current collector in 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] That is, the method of leaching waste lithium battery electrode sheets with K3[Fe(CN)6] solution has a lithium leaching rate of 88.4%. The results of Example 1 show that the method of leaching waste lithium battery electrode sheets with K3[Fe(CN)6] solution of the present invention can effectively extract lithium ions in the positive electrode material without separating the positive electrode material from the current collector; and can effectively remove potassium ions present in the reaction process, so that the purity of the final product is higher.

[0053] Example 2

[0054] This example explores the specific capacity of Prussian blue and different Prussian blue analogs, and the method is as follows:

[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] Prussian blue analog (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 for constant current discharge. 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 66.70mAh / g, 37.28mAh / g, 37.65mAh / g and 3.08mAh / g respectively. Among them, Fe4[Fe(CN)6]3 has the largest specific capacity and is most suitable for potassium extraction. This shows that the present invention can more effectively remove potassium from the post-immersion solution by using Prussian blue as the cathode material.

[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 at mass ratios 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 as follows: 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 solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution 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) by 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, characterized in that: 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, characterized in that: 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 preparation method of the cathode is: Prussian blue, a conductive agent and a binder are uniformly mixed in proportion, a solvent is added to prepare an electrode slurry, and then the electrode slurry is coated on a current collector and dried 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 anode electrolyte 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 membrane is a cation exchange membrane.

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

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