Methods for recovering lithium and iron from lithium iron phosphate cathodes

Abstract

This invention provides a method for recovering lithium and iron from lithium iron phosphate (LFP) cathode sheets. The method includes: soaking and drying the LFP cathode sheets removed from the battery to remove surface electrolyte; cutting the LFP cathode sheets to serve as the cathode end of an electro-Fenton electrolysis system, using a graphite plate as the anode end, and a sodium sulfate solution as the electrolyte; and introducing oxygen to perform an electrolysis reaction until the powder is completely detached from the current collector and enters the electrolyte, thereby obtaining a lithium-containing cathode. + PO4 3‑ and Fe 3+ The leachate; acid is added to the leachate to carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + Filtrate; in Li-containing + Alkali is added to the filtrate until a lithium-containing precipitate is completely formed; the iron phosphate precipitate and the lithium-containing precipitate are then dried. This recovery method not only effectively recovers valuable metals such as lithium and iron, but also eliminates the need to crush the positive electrode current collector throughout the process, producing no debris and achieving lossless recovery of the positive electrode current collector. Furthermore, it is environmentally friendly and has low operating costs.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling and utilization technology, particularly to the recycling and utilization of cathode materials, and even more particularly to methods for recovering lithium and iron from lithium iron phosphate cathode sheets. Background Technology

[0002] Since their commercialization, lithium-ion batteries have enjoyed a broad market prospect due to their numerous advantages. With the development of electric vehicles and hybrid electric vehicles, the demand for lithium-ion products has increased several times over. After a certain number of charge-discharge cycles, the capacity of lithium-ion batteries gradually decreases until they become unusable. Increased usage will generate a large number of waste lithium-ion batteries.

[0003] Lithium-ion batteries, while called "green batteries" because they do not contain highly toxic heavy metals such as mercury, cadmium, and lead, are not necessarily pollution-free. Improper disposal of used lithium-ion batteries can still impact the environment and human health. For example, heavy metals in the cathode material can raise the pH level of the environment, affecting the ecosystem. Furthermore, heavy metals and lithium in the cathode material are elements found in very small amounts in nature, relatively high compared to mined minerals. Therefore, conducting research on the recycling and utilization of materials from used lithium-ion batteries can not only mitigate environmental impact but also bring certain economic benefits.

[0004] Currently, the main materials recycled from spent lithium-ion batteries are the negative electrode current collector (commonly copper foil), the positive electrode current collector (commonly aluminum foil), and the positive and negative electrode active materials. Electrode recycling typically involves three main steps: first, discharging the spent battery and disassembling it to remove the electrodes; second, separating the materials from the current collector; and third, recovering and utilizing valuable metals. In the second step of separation, the industry uses physical methods, such as mechanical crushing and ultrasonic-assisted separation, to aid in the separation of the positive electrode active material. However, this method often results in the simultaneous crushing and destruction of the positive electrode current collector (copper foil), generating debris and making subsequent separation and material purification difficult. Alternatively, the industry uses strong acids and bases, leveraging their high acidity and alkalinity to analyze the active material and current collector in the positive electrode. However, the use of strong acids and bases is difficult to recycle, increasing costs and being detrimental to environmental protection. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to provide a method for recovering lithium and iron from lithium iron phosphate cathode sheets. This recovery method can not only effectively recover valuable metals such as lithium and iron, but also does not require crushing of the cathode current collector throughout the process, does not generate debris, and can achieve non-destructive recovery of the cathode current collector. At the same time, it is green and environmentally friendly and has low operating costs.

[0006] To achieve the above objectives, the present invention provides a method for recovering lithium and iron from lithium iron phosphate cathode sheets, comprising:

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

[0008] (2) The lithium iron phosphate cathode sheet is cut to serve as the cathode of the electro-Fenton electrolysis system, the graphite plate as the anode, and the sodium sulfate solution as the electrolyte. Oxygen is introduced to carry out the electrolysis reaction until the powder is completely stripped from the current collector and enters the electrolyte, thereby obtaining a Li-containing... + PO4 3- and Fe 3+ The leachate;

[0009] (3) Add acid to the leachate to carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + filtrate;

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

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

[0012] The technical solution adopted in this invention has at least the following technical effects.

[0013] (1) The positive electrode sheet after disassembly of the battery is dried and soaked to remove the electrolyte on the surface. The treated positive electrode sheet is cut and used as the cathode for electrolysis to separate the electrodes. It is not crushed, so the debris and impurities formed during crushing can be avoided, which would cause difficulties in the subsequent separation of different metals. After the powder is completely peeled off from the current collector, the current collector can be completely recycled, avoiding the loss of current collector recycling due to the crushing process.

[0014] (2) During the electrolysis process, the following reaction occurs at the cathode: O2 + H2O + e - →H₂O₂. The resulting H₂O₂ will oxidize the positive electrode, releasing some Fe. 2+ It enters the electrolyte. At this point, the main electro-Fenton reaction, Fe2+, occurs. + +H₂O₂→Fe₃ + The generated ·OH+OH- ions have oxidizing properties and will further accelerate the oxidative decomposition of the binder in the electrode, promoting the peeling off of the powder. The powder is in the form of Fe... 2+ and PO4 3- Form leaching. Simultaneously, Fe3+ produced by the Fenton reaction... + It will be reduced to Fe2 at the cathode. + This promotes the continuous progress of the Fenton reaction. Ultimately, lithium iron phosphate is completely leached from the positive electrode, transforming into Li... + PO43- and Fe 3+ The leached form exists in the solution. Furthermore, a complete and corrosion-free metal current collector can be obtained.

[0015] (3) Adding an appropriate amount of acid to the leachate can make PO4 3- and Fe 3+ Solid-liquid separation is achieved by forming FePO4·2H2O precipitate to obtain FePO4·2H2O and Li-containing compounds. + Filtrate. Then add an appropriate amount of alkali to the filtrate to neutralize the acidity until Li... + Precipitation is achieved to obtain lithium-containing precipitate, thereby realizing the recovery of lithium and iron from lithium iron phosphate cathodes.

[0016] As a technical solution of the present invention, the lithium iron phosphate cathode sheet includes lithium iron phosphate active material, binder and 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, and 0.95≤a≤1.08, 0.9≤x≤1.

[0018] As one technical solution of the present invention, the adhesive includes PVDF.

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

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

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

[0022] As one 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 one technical solution of the present invention, the acid is dilute sulfuric acid and the pH value of the leachate is 2 to 6 after the acid is added.

[0024] As one technical solution of the present invention, the alkali is sodium carbonate or sodium bicarbonate. Detailed Implementation

[0025] This invention provides a method for recovering lithium and iron from lithium iron phosphate cathode sheets, which enables the recycling of lithium and iron.

[0026] The lithium iron phosphate (LFP) based cathode sheet of this invention refers to a cathode sheet containing a LFP-based cathode active material. The LFP-based cathode sheet includes a cathode active material, a binder, and a conductive agent. The cathode active material includes a LFP-based cathode active material with the chemical formula 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, with 0.95 ≤ a ≤ 1.08 and 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, binder, and conductive agent can be, but is not limited to, 90–98:1.0–5.0:1.0–5.0. A positive electrode sheet can be obtained by preparing a slurry from the positive electrode active material, binder, and conductive agent using a solvent, coating it onto a positive electrode current collector, and then drying and rolling it.

[0027] The method for recovering lithium and iron from the lithium iron phosphate cathode of the present invention includes the following steps.

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

[0029] (2) A lithium iron phosphate cathode sheet is cut to serve as the cathode of an electro-Fenton electrolysis system, a graphite plate is used as the anode, and sodium sulfate solution is used as the electrolyte. Oxygen is introduced to carry out the electrolysis reaction until the powder is completely stripped from the current collector and enters the electrolyte, thereby obtaining a Li-containing... + PO4 3- and Fe 3+ The leachate;

[0030] (3) Add acid to the leachate to carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + filtrate;

[0031] (4) Containing Li + Add alkali to the filtrate until a lithium-containing precipitate is completely formed;

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

[0033] In step (1), existing conventional techniques are used to discharge and disassemble the waste lithium-ion batteries, and then the positive and negative electrode sheets are collected separately. The drying temperature is 50°C to 60°C, but not limited to 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, and 60°C. The drying time is 8h to 12h, but not limited to 8h, 9h, 10h, 11h, and 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 methyl ethyl carbonate. Soaking and drying can remove the electrolyte from the surface of the positive electrode sheet to avoid affecting the subsequent reaction.

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

[0035] In step (3), the acid can be dilute sulfuric acid, and the pH of the leachate after adding the acid is 2 to 6. For example, the pH can be, but is not limited to, 2, 3, 4, 5, or 6. At this pH, PO4... 3- Can be combined with Fe 3+ FePO4·2H2O precipitate is formed to achieve solid-liquid separation, thereby recovering iron from lithium iron phosphate cathode sheets.

[0036] In step (4), the alkali is sodium carbonate or sodium bicarbonate, preferably sodium carbonate. The sodium carbonate content needs to be sufficient to neutralize the acid in the filtrate and also to remove Li + All of the material is precipitated to obtain lithium carbonate precipitate, thereby recovering lithium from the lithium iron phosphate cathode.

[0037] In step (5), the iron phosphate precipitate and lithium carbonate precipitate are dried to obtain iron salt and lithium salt recovered from the lithium iron phosphate cathode, thereby realizing the separation and recovery of metallic lithium and iron.

[0038] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0039] Example 1

[0040] This embodiment describes a method for recovering lithium and iron metals from lithium iron phosphate cathode sheets, 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 hours and dried at 55°C for 10 hours to remove the electrolyte on the surface.

[0042] (2) A lithium iron phosphate cathode sheet was cut to serve as the cathode of an electro-Fenton electrolysis system, a graphite plate was used as the anode, 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 carry out the electrolysis reaction until the powder was completely stripped from the current collector and entered the electrolyte, in order to obtain a Li-containing cathode. + PO4 3- and Fe 3+ The leachate.

[0043] (3) Add dilute sulfuric acid to the leachate to control the pH of the system to 4, and carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + filtrate.

[0044] (4) Containing Li + Sodium carbonate was added to the filtrate until lithium carbonate precipitate was completely formed.

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

[0046] In this embodiment, the aluminum foil stripped in step (2) is a whole sheet with 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 rates of iron and lithium obtained by the recovery method of the present invention are high.

[0047] Example 2

[0048] This embodiment describes a method for recovering lithium and iron metals from lithium iron phosphate cathode sheets, 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 hours and dried at 60°C for 8 hours to remove the electrolyte on the surface.

[0050] (2) A lithium iron phosphate cathode sheet was cut to serve as the cathode of an electro-Fenton electrolysis system, a graphite plate was used as the anode, and a 4 g / L sodium sulfate solution was used as the electrolyte. Oxygen was introduced at a rate of 1.2 L / min to carry out the electrolysis reaction until the powder was completely stripped from the current collector and entered the electrolyte, in order to obtain a Li-containing cathode. + PO4 3- and Fe 3+ The leachate.

[0051] (3) Add dilute sulfuric acid to the leachate to control the pH of the system to 3, and carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + filtrate.

[0052] (4) Containing Li + Sodium carbonate was added to the filtrate until lithium carbonate precipitate was completely formed.

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

[0054] In this embodiment, the aluminum foil stripped in step (2) is a whole sheet with 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 rates of iron and lithium obtained by the recovery method of the present invention are high.

[0055] Example 3

[0056] This embodiment describes a method for recovering lithium and iron metals from lithium iron phosphate cathode sheets, 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) A lithium iron phosphate cathode sheet was cut to serve as the cathode of an electro-Fenton electrolysis system, a graphite plate was used as the anode, 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 carry out the electrolysis reaction until the powder was completely stripped from the current collector and entered the electrolyte, in order to obtain a Li-containing cathode. + PO4 3- and Fe 3+ The leachate.

[0059] (3) Add dilute sulfuric acid to the leachate to control the pH of the system to 5, and carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + filtrate.

[0060] (4) Containing Li + Sodium carbonate was added to the filtrate until lithium carbonate precipitate was completely formed.

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

[0062] In this embodiment, the aluminum foil stripped in step (2) is a whole sheet with 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 rates of iron and lithium obtained by the recovery method of the present invention are high.

[0063] 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, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for recovering lithium and iron from lithium iron phosphate cathode sheets, characterized in that, include: (1) Soak and dry the lithium iron phosphate positive electrode sheet removed from the battery to remove the electrolyte on the surface; (2) The lithium iron phosphate cathode sheet is cut to serve as the cathode of the electro-Fenton electrolysis system, the graphite plate as the anode, and the sodium sulfate solution as the electrolyte. Oxygen is introduced to carry out the electrolysis reaction until the powder is completely stripped from the current collector and enters the electrolyte, thereby obtaining a Li-containing... + PO4 3- and Fe 3+ The leaching solution, wherein the sodium sulfate solution has a mass concentration of 2-4 g / L, and the oxygen introduction rate is 0.5-1.5 L / min; (3) Add acid to the leachate to carry out a precipitation reaction to obtain ferric phosphate precipitate and Li-containing precipitate. + The filtrate, wherein the acid is dilute sulfuric acid and the pH of the leachate is 2 to 6 after the addition of the acid; (4) In the Li-containing + Add alkali to the filtrate until a lithium-containing precipitate is completely formed; (5) Dry the iron phosphate precipitate and the lithium-containing precipitate.

2. The method for recovering lithium and iron from lithium iron phosphate cathode sheets according to claim 1, characterized in that, The lithium iron phosphate cathode includes lithium iron phosphate active materials, binders, and conductive agents.

3. The method for recovering lithium and iron from lithium iron phosphate cathode sheets according to claim 2, characterized in that, The chemical formula of the lithium iron phosphate-based 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, and 0.95≤a≤1.08, 0.9≤x≤1.

4. The method for recovering lithium and iron from lithium iron phosphate cathode sheets according to claim 2, characterized in that, The adhesive includes PVDF.

5. The method for recovering lithium and iron from lithium iron phosphate cathode sheets according to claim 2, characterized in that, The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene.

6. The method for recovering lithium and iron from a lithium iron phosphate cathode according to claim 1, characterized in that, The solvent used for the soaking is a carbonate-based organic solvent.

7. The method for recovering lithium and iron from a lithium iron phosphate cathode according to claim 6, characterized in that, The carbonate organic solvents include at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

8. The method for recovering lithium and iron from lithium iron phosphate cathode sheets according to claim 1, characterized in that, The alkali is sodium carbonate or sodium bicarbonate.