Method for recovering lithium and iron in lithium iron phosphate positive plate

Abstract

The invention provides a method for recovering lithium and iron in a lithium iron phosphate positive plate. The recovery method comprises the following steps: soaking and drying a lithium iron phosphate positive plate disassembled from the battery to remove electrolyte on the surface; the method comprises the following steps: cutting a lithium iron phosphate positive plate as a cathode end of an electro-Fenton electrolysis system, taking a graphite plate as an anode end, taking a sodium sulfate solution as an electrolyte, and introducing oxygen to carry out an electrolytic reaction until powder is completely stripped from a current collector and enters the electrolyte so as to obtain a leachate containing Li < + >, PO4 < 3-> and Fe < 3 + >; acid is added into the leachate for a precipitation reaction, and iron phosphate precipitate and Li < + >-containing filtrate are obtained; adding alkali into the Li < + >-containing filtrate until a lithium-containing precipitate is completely generated; and drying the iron phosphate precipitate and the lithium-containing precipitate. The recovery method not only can effectively realize recovery of valuable metals such as lithium and iron, but also does not need to crush the positive electrode current collector in the whole process, does not generate scraps, can realize lossless recovery of the positive electrode current collector, and is green, environment-friendly and low in use cost.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and utilization of lithium-ion batteries, in particular to the recycling and utilization of positive electrode materials, and more particularly to a method for recycling lithium and iron in lithium iron phosphate positive electrode sheets. Background Art

[0002] Since the commercialization of lithium-ion batteries, they have a broad market prospect due to their many advantages. With the development of electric vehicles and hybrid electric vehicles, lithium-ion products have increased several times. After a certain number of charge and discharge cycles, the capacity of lithium-ion batteries will gradually decrease until they are scrapped. As the usage increases, a large number of waste lithium-ion batteries will be generated.

[0003] Lithium-ion batteries do not contain heavy metal elements with high toxicity such as mercury, cadmium, and lead. Although they are called green batteries, this does not mean that they are pollution-free products. If waste lithium-ion batteries are not handled properly, they can still have an impact on the environment and human health. For example, the heavy metals contained in the positive electrode materials can increase the pH value of the environment and affect the ecological environment. In addition, the heavy metals and lithium in the positive electrode materials are elements with very small reserves in nature, and their content is higher than that in mined minerals. Carrying out research on the recycling and utilization of materials in waste lithium-ion batteries can not only reduce the impact on the environment, but also bring certain economic benefits.

[0004] At present, the main materials recovered from waste lithium-ion batteries are negative electrode current collectors (commonly copper foil), positive electrode current collectors (commonly aluminum foil), positive electrode active materials and negative electrode active materials. There are usually three main steps in the recycling of pole pieces: first, discharging the waste batteries and disassembling the pole pieces; second, separating the materials in the pole pieces from the current collectors; and third, recycling and utilizing the valuable metals. In the second step of separation, the industry has adopted physical methods, i.e., mechanical crushing and ultrasonic-assisted separation to assist in the separation of positive electrode active materials. However, this auxiliary method will cause the positive electrode current collector (copper foil) to be crushed and destroyed, resulting in debris, making subsequent separation and material purification and recovery difficult. In addition, the industry also uses strong acids and strong bases to achieve the analysis of active substances and current collectors in the positive electrode through the high-strength acidity and alkalinity of strong acids, strong bases and other agents, but the input of strong acids, strong bases and other agents is difficult to recycle, which increases the cost of use and is not conducive to green environmental protection. Summary of the invention

[0005] Based on the above problems, the purpose of the present invention is to provide a method for recovering lithium and iron in lithium iron phosphate positive electrode sheets. This recovery method can not only effectively realize the recovery of lithium and iron valuable metals, but also does not require crushing of the positive electrode collector throughout the process, does not generate debris, and can achieve lossless recovery of the positive electrode collector. At the same time, it is green and environmentally friendly and has low use cost.

[0006] To achieve the above object, the present invention provides a method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet, comprising:

[0007] (1) Soaking and drying the lithium iron phosphate positive electrode sheet removed from the battery to remove the electrolyte on the surface;

[0008] (2) Cut the lithium iron phosphate positive electrode sheet to serve as the cathode end of the electro-Fenton electrolysis system, use the graphite plate as the anode end, use the sodium sulfate solution as the electrolyte, introduce oxygen to carry out the electrolysis reaction until the powder is completely peeled off from the current collector and enters the electrolyte to obtain a Li-containing + PO4 3- and Fe 3+ of the leachate;

[0009] (3) adding acid to the leaching solution to carry out precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate;

[0010] (4) In the Li-containing + Adding alkali to the filtrate until lithium-containing precipitate is completely formed;

[0011] (5) Drying the iron phosphate precipitate and the lithium-containing precipitate.

[0012] The technical solution adopted by the present invention has at least the following technical effects.

[0013] (1) Dry and soak the disassembled positive electrode sheets to remove the electrolyte on the surface. Cut the treated positive electrode sheets and use them as the cathode end for electrolysis for separation. They are not crushed, so the debris impurities formed during the crushing can be avoided, which can prevent the subsequent separation of different metals from being difficult. After the powder is completely peeled off from the current collector, the current collector can be completely recovered, avoiding the loss of the current collector recovery caused by the crushing process.

[0014] (2) During the electrolysis process, the cathode reacts: O2+H2O+e - →H2O2. The resulting H2O2 will oxidize the positive electrode and release some Fe 2+ Entering the electrolyte. At this time, the main electro-Fenton reaction occurs, Fe2 + +H2O2→Fe3 + +·OH+OH-. The generated ·OH is oxidizing and will further accelerate the oxidative decomposition of the binder in the pole piece, promote the peeling of the powder, and the powder is Fe 2+ and PO4 3- At the same time, the Fe3 + It will be reduced to Fe2 + , promoting the continuous Fenton reaction. Finally, the lithium iron phosphate in the positive electrode is completely leached out to Li + ,PO43- and Fe 3+ In addition, a complete metal current collector without corrosion traces can be obtained.

[0015] (3) Adding an appropriate amount of acid to the leaching solution can make PO4 3- and Fe 3+ FePO4·2H2O precipitation is formed and solid-liquid separation is performed to obtain FePO4·2H2O and Li-containing + Filtrate. Then add an appropriate amount of alkali to the filtrate to neutralize the acidity until Li + The lithium-containing precipitate is obtained by precipitation, thereby realizing the recovery of lithium and iron in the lithium iron phosphate positive electrode sheet.

[0016] As a technical solution of the present invention, the lithium iron phosphate positive electrode sheet includes a lithium iron phosphate active material, a binder and a conductive agent.

[0017] As a technical solution of the present invention, the chemical formula of the lithium iron phosphate active material is Li a Fe x M (1-x) PO4, wherein M is at least one of Mg, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Zr and Ti, 0.95≤a≤1.08, 0.9≤x≤1.

[0018] As a technical solution of the present invention, the binder includes PVDF.

[0019] As a technical solution of the present invention, the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene.

[0020] As a technical solution of the present invention, the solvent used for the immersion is a carbonate organic solvent.

[0021] As a technical solution of the present invention, the carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0022] As a technical solution of the present invention, the mass concentration of the sodium sulfate solution is 2-4 g / L, and the oxygen introduction rate is 0.5-1.5 L / min.

[0023] As a technical solution of the present invention, the acid is dilute sulfuric acid and the pH value of the leaching solution after adding the acid is 2-6.

[0024] As a technical solution of the present invention, the alkali is sodium carbonate or sodium bicarbonate. DETAILED DESCRIPTION

[0025] The invention provides a method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet, which can realize the recovery and utilization of lithium and iron.

[0026] The lithium iron phosphate positive electrode sheet of the present invention refers to a positive electrode sheet containing a lithium iron phosphate positive electrode active material. The lithium iron phosphate positive electrode sheet includes a positive electrode active material, a binder and a conductive agent. The positive electrode active material includes a lithium iron phosphate positive electrode active material, and its chemical formula is Li a Fe x M (1-x) PO4, wherein M is at least one of Mg, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Zr and Ti, 0.95≤a≤1.08, 0.9≤x≤1. The binder includes PVDF. The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes and graphene. The mass ratio of the positive electrode active material, the binder and the conductive agent can be, but is not limited to, 90 to 98:1.0 to 5.0:1.0 to 5.0. The positive electrode sheet can be obtained by using a solvent to make a slurry of the positive electrode active material, the binder and the conductive agent and coating the slurry on the positive electrode current collector, drying, rolling, etc.

[0027] The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet of the present invention comprises the following steps.

[0028] (1) Soaking and drying the lithium iron phosphate positive electrode sheet removed from the battery to remove the electrolyte on the surface;

[0029] (2) Cut the lithium iron phosphate positive electrode sheet to serve as the cathode end of the electro-Fenton electrolysis system, use the graphite plate as the anode end, and use the sodium sulfate solution as the electrolyte. Pass oxygen into the electrolyte until the powder is completely peeled off from the current collector and enters the electrolyte to obtain Li-containing + PO4 3- and Fe 3+ of the leachate;

[0030] (3) Adding acid to the leaching solution to perform precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate;

[0031] (4) Yu Hanli + Adding alkali to the filtrate until lithium-containing precipitate is completely formed;

[0032] (5) Drying the iron phosphate precipitate and the lithium-containing precipitate.

[0033] Wherein, in step (1), the waste lithium-ion battery is discharged and disassembled by conventional technology, and then the positive electrode and the negative electrode are collected respectively. The drying temperature is 50°C to 60°C, which can be but not limited to 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C. The time is 8h to 12h, which can be but not limited to 8h, 9h, 10h, 11h, 12h. The solvent used for soaking is a carbonate organic solvent. Further, the carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The electrolyte on the surface of the positive electrode can be removed by soaking and drying to avoid affecting the subsequent reaction.

[0034] In step (2), the electro-Fenton electrolysis system can adopt a conventional electro-Fenton electrolysis device, and its graphite plate can also adopt a conventional anode plate. The mass concentration of the sodium sulfate solution is 2-4%. As an example, the mass concentration can be but not limited to 2%, 3%, and 4%. The oxygen introduction rate needs to be controlled and needs to match the electrolysis reaction to avoid insufficient oxygen content and the powder cannot be completely stripped or excessive oxygen content causes energy consumption. The oxygen introduction rate is 0.5-1.5L / min. As an example, the oxygen introduction rate can be but not limited to 0.5%, 0.6%, 0.7%L / min, 0.8L / min, 0.9L / min, 1.0L / min, 1.1L / min, 1.2L / min, 1.3L / min, 1.4L / min, 1.5L / min.

[0035] In step (3), the acid may be dilute sulfuric acid and the pH value of the leaching solution after the addition of the acid is 2 to 6. For example, the pH value may be, but is not limited to, 2, 3, 4, 5, or 6. At this pH value, PO4 3- Can be used with Fe 3+ FePO4·2H2O precipitation is formed to achieve solid-liquid separation, thereby recovering iron in the lithium iron phosphate positive electrode sheet.

[0036] In step (4), the base is sodium carbonate or sodium bicarbonate, preferably sodium carbonate. The content of sodium carbonate needs to be sufficient to both neutralize the acid in the filtrate and convert Li + All of them are precipitated to obtain lithium carbonate precipitate, thereby recovering the lithium in the lithium iron phosphate positive electrode sheet.

[0037] In step (5), the iron phosphate precipitate and the lithium carbonate precipitate are dried to obtain iron salt and lithium salt that can be recycled from the lithium iron phosphate positive electrode sheet, thereby achieving the separation and recovery of metallic lithium and iron.

[0038] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0039] Example 1

[0040] This embodiment is a method for recovering lithium and iron metals in a lithium iron phosphate positive electrode sheet, and the steps are as follows.

[0041] (1) The lithium iron phosphate positive electrode sheet removed from the battery was soaked in dimethyl carbonate for 2 h and dried at 55° C. for 10 h to remove the electrolyte on the surface.

[0042] (2) The lithium iron phosphate positive electrode sheet was cut to serve as the cathode end of the electro-Fenton electrolysis system, the graphite plate was used as the anode end, and a sodium sulfate solution with a mass concentration of 3 g / L was used as the electrolyte. Oxygen was introduced at a rate of 1.0 L / min to perform an electrolysis reaction until the powder was completely peeled off from the current collector and entered the electrolyte to obtain a Li-containing + PO4 3- and Fe 3+ of the leachate.

[0043] (3) Add dilute sulfuric acid to the leaching solution, control the pH value of the system to 4, and perform precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate.

[0044] (4) Yu Hanli + Sodium carbonate is added to the filtrate until lithium carbonate precipitation is completely generated.

[0045] (5) Drying the iron phosphate precipitate and the lithium carbonate precipitate.

[0046] In this embodiment, the aluminum foil after peeling in step (2) is intact and has no surface damage. The recovery rates of iron and lithium in the obtained iron phosphate precipitate and lithium carbonate precipitate are calculated to be 90.5% and 88.3%, respectively, indicating that the recovery rate of iron and lithium obtained by the recovery method of the present invention is relatively high.

[0047] Example 2

[0048] This embodiment is a method for recovering lithium and iron metals in a lithium iron phosphate positive electrode sheet, and the steps are as follows.

[0049] (1) The lithium iron phosphate positive electrode sheet removed from the battery was soaked in diethyl carbonate for 2 h and dried at 60° C. for 8 h to remove the electrolyte on the surface.

[0050] (2) The lithium iron phosphate positive electrode sheet was cut to serve as the cathode end of the electro-Fenton electrolysis system, the graphite plate was used as the anode end, and a sodium sulfate solution with a mass concentration of 4 g / L% was used as the electrolyte. Oxygen was introduced at a rate of 1.2 L / min to perform an electrolysis reaction until the powder was completely peeled off from the current collector and entered the electrolyte to obtain a Li-containing + PO4 3- and Fe 3+ of the leachate.

[0051] (3) Add dilute sulfuric acid to the leaching solution, control the pH value of the system to 3, and perform precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate.

[0052] (4) Yu Hanli + Sodium carbonate is added to the filtrate until lithium carbonate precipitation is completely generated.

[0053] (5) Drying the iron phosphate precipitate and the lithium carbonate precipitate.

[0054] In this embodiment, the aluminum foil after peeling in step (2) is intact and has no surface damage. The recovery rates of iron and lithium in the obtained iron phosphate precipitate and lithium carbonate precipitate are calculated to be 91.0% and 88.7%, respectively, indicating that the recovery rate of iron and lithium obtained by the recovery method of the present invention is relatively high.

[0055] Example 3

[0056] This embodiment is a method for recovering lithium and iron metals in a lithium iron phosphate positive electrode sheet, and the steps are as follows.

[0057] (1) The lithium iron phosphate positive electrode sheet removed from the battery was soaked in dimethyl carbonate for 1 hour and dried at 60°C for 8 hours to remove the electrolyte on the surface.

[0058] (2) The lithium iron phosphate positive electrode sheet was cut to serve as the cathode end of the electro-Fenton electrolysis system, the graphite plate was used as the anode end, and a sodium sulfate solution with a mass concentration of 2 g / L was used as the electrolyte. Oxygen was introduced at a rate of 0.8 L / min to perform an electrolysis reaction until the powder was completely peeled off from the current collector and entered the electrolyte to obtain a Li-containing + PO4 3- and Fe 3+ of the leachate.

[0059] (3) Add dilute sulfuric acid to the leaching solution, control the pH value of the system to 5, and perform precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate.

[0060] (4) Yu Hanli + Sodium carbonate is added to the filtrate until lithium carbonate precipitation is completely generated.

[0061] (5) Drying the iron phosphate precipitate and the lithium carbonate precipitate.

[0062] In this embodiment, the aluminum foil after peeling in step (2) is intact and has no surface damage. The recovery rates of iron and lithium in the obtained iron phosphate precipitate and lithium carbonate precipitate are calculated to be 89.7% and 87.8%, respectively, indicating that the recovery rate of iron and lithium obtained by the recovery method of the present invention is relatively high.

[0063] 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 is described in detail with reference to the preferred embodiments, it is not limited to those listed in the 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 recovering lithium and iron from a lithium iron phosphate positive electrode sheet, characterized in that: include: (1) Soaking and drying the lithium iron phosphate positive electrode sheet removed from the battery to remove the electrolyte on the surface; (2) Cut the lithium iron phosphate positive electrode sheet to serve as the cathode end of the electro-Fenton electrolysis system, use the graphite plate as the anode end, use the sodium sulfate solution as the electrolyte, introduce oxygen to carry out the electrolysis reaction until the powder is completely peeled off from the current collector and enters the electrolyte to obtain a Li-containing + PO4 3- and Fe 3+ of the leachate; (3) adding acid to the leaching solution to carry out precipitation reaction to obtain iron phosphate precipitate and Li-containing + filtrate; (4) In the Li-containing + Adding alkali to the filtrate until lithium-containing precipitate is completely formed; (5) Drying the iron phosphate precipitate and the lithium-containing precipitate.

2. The method for recovering lithium and iron from a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The lithium iron phosphate positive electrode sheet comprises a lithium iron phosphate active material, a binder and a conductive agent.

3. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 2, characterized in that: The chemical formula of the lithium iron phosphate active material is Li a Fe x M (1-x) PO4, wherein M is at least one of Mg, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Zr and Ti, 0.95≤a≤1.08, 0.9≤x≤1.

4. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 2, characterized in that: The binder includes PVDF.

5. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 2, characterized in that: The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene.

6. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The solvent used for the soaking is a carbonate organic solvent.

7. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 6, characterized in that: The carbonate organic solvent includes at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

8. The method for recovering lithium and iron from a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The mass concentration of the sodium sulfate solution is 2-4 g / L, and the oxygen introduction rate is 0.5-1.5 L / min.

9. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The acid is dilute sulfuric acid and the pH value of the leaching solution is 2-6 after adding the acid.

10. The method for recovering lithium and iron in a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The base is sodium carbonate or sodium bicarbonate.