Method for recovering lithium in retired lithium iron phosphate battery

Abstract

The invention discloses a method for recovering lithium in a decommissioned lithium iron phosphate battery, which comprises the following steps: carrying out acid treatment on lithium iron phosphate-containing powder in the decommissioned lithium iron phosphate battery to obtain a lithium sulfate solution; and the lithium sulfate solution is subjected to electrolytic treatment, lithium hydroxide is obtained, and finally the lithium resource is recycled in the form of lithium hydroxide. The lithium recovery method disclosed by the invention is green and environment-friendly, and is relatively high in recovery rate and recovery purity.

Description

Technical Field

[0001] The present invention belongs to the technical field of retired battery recycling, and in particular relates to a method for recycling lithium in retired lithium iron phosphate batteries. Background Art

[0002] With the vigorous promotion of new energy electric vehicles, the market retention rate has gradually increased. Lithium-ion batteries represented by lithium iron phosphate batteries have been widely used, and the installed capacity of lithium batteries has increased year by year. Limited by the five to eight years of service life of power batteries, when the number of battery cycles increases to a certain limit, the battery health (SOH) gradually decreases to 80%, and it will no longer be suitable as a power source for the car. At this time, it is necessary to choose to use the battery pack in a cascade, such as continuing to use it as an energy storage device or a battery for a small scooter, until the battery cannot work properly and is retired.

[0003] Since retired lithium batteries contain abundant metal resources such as lithium and iron, the content of which even exceeds the amount of corresponding elements in nature, it is of great economic and environmental benefit to explore a green and environmentally friendly technical route to recycle and reuse lithium resources in retired lithium iron phosphate batteries. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention provides a method for recovering lithium from retired lithium iron phosphate batteries. The recovery method of the present invention is green and environmentally friendly, and has a high recovery rate and recovery purity.

[0005] Therefore, in a first aspect of the present invention, the present invention proposes a method for recovering lithium from retired lithium iron phosphate batteries, comprising the following steps:

[0006] Treating lithium iron phosphate powder in retired lithium iron phosphate batteries with acid to obtain a lithium sulfate solution;

[0007] The lithium sulfate solution is electrolyzed to obtain lithium hydroxide.

[0008] The lithium iron phosphate powder is treated with acid to cause a chemical reaction between the lithium iron phosphate and the acid solution to generate a lithium sulfate solution and iron phosphate. After further purification, the iron phosphate can be used again as a raw material for synthesizing lithium iron phosphate materials. At this time, the lithium element is mainly enriched in the lithium sulfate, and then sulfuric acid and lithium hydroxide can be generated by electrolyzing the lithium sulfate solution, thereby realizing efficient recovery of lithium resources. Therefore, the method of recovering lithium from retired lithium iron phosphate batteries of the present invention has the advantages of being fast, simple, green and environmentally friendly, and having a high recovery rate and recovery purity.

[0009] In some embodiments, the step of subjecting the retired lithium iron phosphate battery to acid treatment of lithium iron phosphate-containing powder includes adding sulfuric acid and hydrogen peroxide.

[0010] In some embodiments, the recycling method satisfies at least one of the following:

[0011] (1) The concentration of sulfuric acid is 0.4-0.6 mol / L;

[0012] (2) The amount of sulfuric acid added is 7-9 mL / g;

[0013] (3) The amount of hydrogen peroxide added is 1 to 3 mL / g.

[0014] In some embodiments, in the step of subjecting the lithium sulfate solution to electrolytic treatment, the electrolytic treatment method includes using bipolar membrane electrodialysis.

[0015] In some embodiments, the voltage of the electrolysis treatment is 33-37V.

[0016] In some embodiments, in the step of electrolyzing the lithium sulfate solution, the anode solution of the electrolysis treatment includes at least one of sulfuric acid and water.

[0017] In some embodiments, in the step of electrolyzing the lithium sulfate solution, the cathode solution of the electrolysis treatment includes at least one of lithium hydroxide and water.

[0018] In some embodiments, before the step of subjecting the retired lithium iron phosphate battery to acid treatment of the lithium iron phosphate powder, the step further includes:

[0019] The retired lithium iron phosphate batteries are crushed to obtain positive and negative electrode mixed powders;

[0020] The positive and negative electrode mixed powders are sorted to obtain lithium iron phosphate-containing powder.

[0021] In some embodiments, in the step of sorting the positive and negative electrode mixed powders, the sorting method includes high-temperature roasting and flotation.

[0022] In some embodiments, flotation includes a flotation agent, and the flotation agent includes at least one of kerosene, methyl isobutyl carbinol, sodium stearate, and liquid paraffin.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0025] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0026] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0027] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0028] In a first aspect of an embodiment of the present invention, the present invention provides a method for recovering lithium from a retired lithium iron phosphate battery, comprising the following steps:

[0029] Treating lithium iron phosphate powder in retired lithium iron phosphate batteries with acid to obtain a lithium sulfate solution;

[0030] The lithium sulfate solution is electrolyzed to obtain lithium hydroxide.

[0031] According to an embodiment of the present invention, the lithium iron phosphate powder is treated with acid to cause a chemical reaction between the lithium iron phosphate and the acid solution to generate lithium sulfate and iron phosphate. After further purification, the iron phosphate can be used again as a raw material for synthesizing lithium iron phosphate materials. At this time, the lithium element is mainly enriched in the lithium sulfate, and then sulfuric acid and lithium hydroxide are generated by electrolyzing the lithium sulfate solution to achieve efficient recovery of lithium resources. The electrolysis method has the advantages of low energy consumption, environmental friendliness, and the ability to efficiently convert salt solutions into acid and alkaline solutions of higher purity.

[0032] During the electrolytic treatment, by energizing the electrolytic equipment, water molecules at the cathode and anode are electrolyzed to produce hydrogen ions and hydroxide ions, and lithium sulfate is electrolyzed to produce lithium ions and sulfate ions. Under the action of an external electric field, lithium ions as cations migrate to the cathode, and sulfate ions as anions migrate to the anode. Electrolysis continues, and eventually lithium ions exist at the cathode to form lithium hydroxide, and sulfate ions exist at the anode to form sulfuric acid. The method of recovering lithium from retired lithium iron phosphate batteries of the present invention has the advantages of being fast, simple, green and environmentally friendly, reducing energy consumption, and having a high recovery rate and recovery purity. Therefore, the present invention can effectively recover lithium from retired lithium iron phosphate batteries, is green and environmentally friendly, and has a high lithium recovery rate and recovery purity.

[0033] In some embodiments of the present invention, the step of subjecting the retired lithium iron phosphate battery to acid treatment of lithium iron phosphate-containing powder includes adding sulfuric acid and hydrogen peroxide.

[0034] The lithium iron phosphate powder is chemically treated with an acidic solution. The chemical equation of the reaction is as follows:

[0035] 2LiFePO 4 +H 2 SO 4 +H 2 O 2 =2FePO 4 +Li 2 SO 4 +2H 2 O

[0036] Among them, H 2 O 2 (Hydrogen peroxide) is an oxidant that can convert LiFePO 4 The iron in Fe +2 Oxidized to Fe +3 , thus generating FePO 4 After sufficient reaction, the solid iron phosphate can be purified and used again as a raw material for synthesizing lithium iron phosphate materials. At this time, the lithium sulfate is electrolyzed to generate sulfuric acid and lithium hydroxide, thereby realizing efficient recovery of lithium resources. Therefore, the present invention can effectively improve the purity of lithium recovery.

[0037] In some embodiments of the present invention, the recovery method satisfies at least one of the following:

[0038] (1) The concentration of sulfuric acid is 0.4-0.6 mol / L;

[0039] (2) The amount of sulfuric acid added is 7-9 mL / g;

[0040] (3) The amount of hydrogen peroxide added is 1 to 3 mL / g.

[0041] As a result, the acid solution can fully react with lithium iron phosphate to generate Li 2 SO 4 , further improving the lithium recovery rate.

[0042] As an example, the concentration of sulfuric acid is 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, etc.

[0043] As an example, the amount of sulfuric acid added is 7 mL / g, 7.5 mL / g, 8 mL / g, 8.5 mL / g, 9 mL / g, etc.

[0044] As an example, the amount of hydrogen peroxide added is 1 mL / g, 1.5 mL / g, 2 mL / g, 2.5 mL / g, 3 mL / g, etc.

[0045] In some embodiments of the present invention, in the step of subjecting the lithium sulfate solution to electrolytic treatment, the electrolytic treatment method includes using bipolar membrane electrodialysis.

[0046] Bipolar membrane electrodialysis is a novel membrane separation technology that combines electrodialysis and ion exchange membrane. According to an embodiment of the present invention, the bipolar membrane is composed of a cation exchange membrane and an anion exchange membrane. The bipolar membrane electrodialysis has four compartments, which respectively carry the electrode solution (circulating protection solution), the anode chamber (acid solution), the cathode chamber (alkaline solution) and the raw material chamber (salt solution). The lithium sulfate solution is added to the raw material chamber, and the corresponding solution is also added to the other three compartments. The pump is turned on and circulated for about 20 minutes to remove bubbles, and then the required voltage is provided to both ends of the bipolar membrane. At this time, the sulfate ions and lithium ions in the raw material chamber are subjected to the action of the electric field force, and the sulfate ions migrate to the anode through the anion exchange membrane, and the lithium ions migrate to the cathode through the cation exchange membrane. Due to the blocking of sulfate ions by the cation exchange membrane and the blocking of lithium ions by the anion exchange membrane, sulfuric acid is finally produced in the anode chamber, and lithium hydroxide is generated in the cathode chamber. The method of bipolar membrane electrodialysis is green and environmentally friendly and reduces energy consumption. Thus, the present invention can effectively recover lithium and has a high recovery purity.

[0047] In some embodiments of the present invention, the voltage of the electrolysis treatment is 33-37V.

[0048] When the voltage is 33-37 V, lithium sulfate can be fully electrolyzed, and the electrolysis time depends on the conductivity or concentration of the salt solution in the raw material chamber. In this way, lithium can be recovered to the greatest extent, thereby further improving the recovery rate.

[0049] As an example, the voltage of the electrolysis process is 33V, 34V, 35V, 36V, 37V, etc.

[0050] In some embodiments of the present invention, in the step of electrolyzing the lithium sulfate solution, the anode solution of the electrolysis treatment includes at least one of sulfuric acid and water. The molar concentration of the sulfuric acid is 0.05-0.15M.

[0051] According to an embodiment of the present invention, 0.05-0.15M sulfuric acid is added to the anode chamber to provide an initial concentration to reduce the internal resistance of the system at the beginning of electrodialysis, thereby improving the current efficiency during the electrodialysis process. The bipolar membrane electrodialysis method can also use water to add to the anode chamber, reducing the use and processing costs of chemical reagents. Thus, the recovery purity of lithium is further improved.

[0052] In some embodiments of the present invention, in the step of electrolyzing the lithium sulfate solution, the cathode solution of the electrolysis treatment includes at least one of lithium hydroxide and water. The molar concentration of the lithium hydroxide is 0.05-0.15M.

[0053] According to an embodiment of the present invention, 0.05-0.15M lithium hydroxide is added to the cathode chamber to provide an initial concentration to reduce the internal resistance of the system at the beginning of electrodialysis, thereby improving the current efficiency during the electrodialysis process. The bipolar membrane electrodialysis method can also use water to add to the cathode chamber, reducing the use and processing costs of chemical reagents. Thus, the recovery purity of lithium is further improved.

[0054] In some embodiments of the present invention, before the step of subjecting the retired lithium iron phosphate battery to acid treatment, the step further includes:

[0055] The retired lithium iron phosphate batteries are crushed to obtain positive and negative electrode mixed powders;

[0056] The positive and negative electrode mixed powders are sorted to obtain lithium iron phosphate-containing powder.

[0057] According to an embodiment of the present invention, the residual voltage of the retired lithium iron phosphate battery is first discharged to avoid safety accidents in the subsequent battery disassembly process. Then the battery casing is disassembled, and the battery cell is crushed, including using a shearing gear roller crusher, so as to obtain a positive and negative electrode mixed powder. The positive and negative electrode mixed powder is then sorted to remove excess impurities and negative electrode materials such as graphite, so as to obtain a positive electrode containing lithium iron phosphate powder, in which the lithium iron phosphate content and purity are higher, but a small amount of impurities such as graphite may still exist. In this way, the purity and recovery rate of lithium recovery can be further improved.

[0058] In some embodiments of the present invention, in the step of sorting the positive and negative electrode mixed powders, the sorting method includes high-temperature roasting and flotation.

[0059] During the high-temperature roasting process, the positive and negative electrode mixed powders are placed in a crucible and then roasted in a tubular furnace. Organic matter such as binders will be oxidized into gases or volatile substances at high temperatures, thereby being removed from the mixed powders. Then flotation is performed. During the flotation process, the flotation agent can be adsorbed on the surface of the graphite particles to form a hydrophobic film, making the graphite particles highly hydrophobic. This hydrophobicity makes it easier for graphite particles to adhere to bubbles and float to the liquid surface, thereby separating from the lithium iron phosphate powder. As a result, the recovery purity and recovery rate of lithium can be further improved.

[0060] In some embodiments of the present invention, flotation includes a flotation agent, and the flotation agent includes at least one of kerosene, methyl isobutyl carbinol, sodium stearate, and liquid paraffin.

[0061] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] (1) Battery disassembly and crushing: The retired lithium iron phosphate batteries are unpacked to obtain individual cells, and all the cells are immersed in a sodium chloride solution to release the remaining power in the battery. Then, a shearing gear roller crusher is used to crush the cells to obtain a mixed powder of positive and negative electrodes.

[0064] (2) Separation of positive and negative electrode mixed powders: After the positive and negative electrode mixed powders are calcined, they are added to deionized water, and kerosene and methyl isobutyl carbinol are added to remove negative electrode graphite to obtain lithium iron phosphate powder.

[0065] (3) Acid treatment of lithium iron phosphate powder: 0.5 mol / L sulfuric acid was added to the lithium iron phosphate powder at a rate of 8 mL / g, and then a hydrogen peroxide solution was added at a rate of 2 mL / g. After the reaction was completed, the lithium sulfate solution and iron phosphate slag were obtained by filtration.

[0066] (4) Electrolysis of lithium sulfate solution: Add electrode solution (circulating protection solution) to the bipolar membrane electrodialysis equipment, add the obtained lithium sulfate solution to the raw material chamber, add 0.1M sulfuric acid solution to the anode chamber, and add 0.1M lithium hydroxide solution to the cathode chamber. First, turn on the pump to circulate fully for 20 minutes to drive away the bubbles. Then provide 35V voltage to both ends of the bipolar membrane to start electrolysis. At this time, the sulfate ions and lithium ions in the raw material chamber are affected by the electric field force and migrate to the anode and cathode through the anion exchange membrane and cation exchange membrane respectively. After the electrolysis is completed, sulfuric acid is generated in the anode chamber and lithium hydroxide solution is generated in the cathode chamber.

[0067] Example 2

[0068] The difference between Example 2 and Example 1: In the acid treatment of lithium iron phosphate powder in step (3) of Example 2, the concentration of sulfuric acid is 0.4 mol / L, and the amount added is 9 mL / g.

[0069] Example 3

[0070] The difference between Example 3 and Example 1: In the acid treatment of lithium iron phosphate powder in step (3) of Example 3, the concentration of sulfuric acid is 0.6 mol / L, and the amount added is 7 mL / g.

[0071] Example 4

[0072] The difference between Example 4 and Example 1: In the step (4) of Example 4, in the electrolysis treatment of the lithium sulfate solution, the electrolysis voltage is 33V.

[0073] Example 5

[0074] The difference between Example 5 and Example 1: In the step (4) of Example 5, in the electrolysis treatment of the lithium sulfate solution, the electrolysis voltage is 37V.

[0075] The lithium recovery rate, lithium hydroxide purity and recovery rate of all the above embodiments and comparative examples were tested. The results are shown in Table 1.

[0076] Table 1 Lithium recovery rate, lithium hydroxide purity and recovery rate results of the embodiments and comparative examples

[0077]

[0078]

[0079] As can be seen from Table 1, the present invention can effectively recover lithium from retired lithium iron phosphate batteries through the electrolysis method. The electrolysis method is green and environmentally friendly, and has a high lithium recovery rate and recovery purity.

[0080] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0081] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for recovering lithium from retired lithium iron phosphate batteries, characterized in that: The steps include: Treating lithium iron phosphate powder in retired lithium iron phosphate batteries with acid to obtain a lithium sulfate solution; The lithium sulfate solution is electrolyzed to obtain lithium hydroxide.

2. The recycling method according to claim 1, characterized in that: The step of subjecting the retired lithium iron phosphate battery to acid treatment of the lithium iron phosphate powder includes adding sulfuric acid and hydrogen peroxide.

3. The recycling method according to claim 2, characterized in that: The recovery method satisfies at least one of the following: (1) The concentration of the sulfuric acid is 0.4 to 0.6 mol / L; (2) The amount of sulfuric acid added is 7 to 9 mL / g; (3) The amount of hydrogen peroxide added is 1 to 3 mL / g.

4. The recycling method according to any one of claims 1 to 3, characterized in that: In the step of electrolyzing the lithium sulfate solution, the electrolysis method includes using bipolar membrane electrodialysis.

5. The recycling method according to any one of claims 1 to 4, characterized in that: The voltage of the electrolysis treatment is 33-37V.

6. The recycling method according to any one of claims 1 to 5, characterized in that: In the step of electrolyzing the lithium sulfate solution, the anode solution of the electrolysis treatment includes at least one of dilute sulfuric acid and water.

7. The recycling method according to any one of claims 1 to 6, characterized in that: In the step of electrolyzing the lithium sulfate solution, the cathode solution of the electrolysis treatment includes at least one of lithium hydroxide and water.

8. The recycling method according to any one of claims 1 to 7, characterized in that: Before the step of subjecting the retired lithium iron phosphate battery to acid treatment of the lithium iron phosphate powder, the method further comprises: The retired lithium iron phosphate batteries are crushed to obtain positive and negative electrode mixed powders; The positive and negative electrode mixed powders are sorted to obtain lithium iron phosphate-containing powders.

9. The recycling method according to claim 8, characterized in that: In the step of sorting the positive and negative electrode mixed powders, the sorting method includes high-temperature roasting and flotation.

10. The recycling method according to claim 9, characterized in that: The flotation comprises a flotation agent, and the flotation agent comprises at least one of kerosene, methyl isobutyl carbinol, sodium stearate, and liquid paraffin.

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