Recycling method for lithium iron phosphate leftover material

Abstract

The present application relates to the technical field of material recycling, and discloses a recycling method for a lithium iron phosphate leftover material. According to the method, for the current lithium iron phosphate leftover material, vacuum pre-calcination is first used to effectively separate lithium iron phosphate from a current collector and a binder, and oxidation of the lithium iron phosphate is not caused; then specific ultrasound-assisted liquid-phase separation is used to effectively extract the lithium iron phosphate, high-recycling-rate recycling of the lithium iron phosphate can be achieved after subsequent treatments such as crushing and calcination, and the purity of a recycled product is high. The recycling method involves low energy consumption, is environmentally-friendly and does not generate secondary pollutants. The recycled lithium iron phosphate prepared by means of the recycling method has high purity and good quality, can be directly applied to preparation of a positive electrode sheet of a lithium-ion battery, demonstrates comparable electrochemical performance to a commercial new lithium iron phosphate material, and extremely conforms to the integrated concept of recycling and reutilization in the lithium iron phosphate industry.

Description

A method for recycling lithium iron phosphate scraps Technical Field

[0001] This article relates to the field of material recycling technology, and in particular to a method for recycling lithium iron phosphate scraps. Background Art

[0002] Lithium iron phosphate batteries are a type of power battery with high electrochemical properties and high safety. During the coating, rolling, slicing and other stages of the production process, a large amount of lithium iron phosphate scraps will be generated. These scraps are mostly semi-finished products, unqualified products or scrapped products. Therefore, they are not prepared into complete battery cells and delithiated. The lithium iron phosphate itself does not undergo phase change and is highly recyclable. On the other hand, the output of lithium iron phosphate scraps is high, and if not properly handled, it will cause environmental problems.

[0003] The current mainstream recycling process for lithium iron phosphate scrap is wet recycling, which involves gradual recovery through acid dissolution, alkali dissolution, and organic solvent soaking. However, this process often produces secondary products. For example, lithium iron phosphate has been converted into lithium carbonate and ferrous phosphate, requiring further processing to reconstitute ferric phosphate. The wet process also produces large amounts of leachate, which also requires disposal considerations. Furthermore, some recovery methods, such as pyrometallurgy and direct regeneration, suffer from large yield fluctuations and low product purity.

[0004] Summary of the Invention

[0005] The purpose of this article is to overcome the shortcomings of the above-mentioned existing technologies and provide a method for recycling lithium iron phosphate scraps. This method first uses vacuum pre-calcination to effectively separate lithium iron phosphate from the current collector and binder without causing oxidation of the lithium iron phosphate; then uses specific ultrasonic-assisted liquid phase separation to effectively extract the lithium iron phosphate, and after subsequent crushing and calcination and other treatments, a high recovery rate of lithium iron phosphate can be achieved, and the recovered product has high purity; the recycling method has low energy consumption, is environmentally friendly and does not produce secondary pollutants.

[0006] To achieve the above objectives, the technical solutions adopted in this paper are:

[0007] A method for recycling lithium iron phosphate scraps comprises the following steps:

[0008] The recovered lithium iron phosphate scraps are coarsely crushed and pulverized under a nitrogen atmosphere and the powder is collected by cyclone separation to obtain coarse powder and current collector scrap fragments with a size of 5 to 10 mm.

[0009] The scraps containing the current collector were collected at 0.8~1.2×10 -4Calcinate at 80-150°C for 0.5-2h under a vacuum degree of Pa to obtain pretreated fragments;

[0010] The pretreated fragments are placed in an extracting solution and ultrasonically stirred at 60-100° C. for 10-30 minutes. The resulting suspension is subjected to solid-liquid separation, washing, centrifugal separation, and drying to obtain a refined powder. The extracting solution includes an organic solvent and an alkali solution, and the hydroxide concentration of the extracting solution is 0.005-0.01 mol / L.

[0011] The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 400-550°C in a nitrogen atmosphere to remove fluorine for 1-3 hours. The obtained defluorinated powder is subjected to air flow crushing and batch mixing demagnetization treatment to recover lithium iron phosphate.

[0012] Since most existing lithium iron phosphates use carbon-coated aluminum foil as the current collector to prepare the electrode, the adhesion is strong and the lithium iron phosphate is not easy to peel off. At the same time, the lithium iron phosphate is tightly connected to the conductive agent, adhesive, etc., making separation difficult. At the same time, if a high-temperature separation method is used, it may cause the aluminum foil to oxidize and introduce uncontrollable impurities. In the recycling method of lithium iron phosphate scraps described in this article, the lithium iron phosphate scraps are first crushed and cyclone-separated, and some dust and some pure lithium iron phosphate powder are pre-collected to improve the recovery rate of lithium iron phosphate. At the same time, because it is carried out under a nitrogen atmosphere, there is no risk of dust explosion. Subsequently, the crushed scraps containing carbon-coated aluminum foil, adhesive and other substances are vacuum calcined at a specific low temperature. Under this condition, neither the aluminum foil nor the lithium iron phosphate will oxidize to produce impurities. At the same time, the adhesion between the carbon coating layer and the adhesive in the electrode can be greatly reduced. Combined with ultrasonic wet extraction and separation treatment at a specific temperature, even if the adhesive such as acrylate is peeled out of the powder, after crushing, air separation, screening and calcination to remove fluorine, the obtained material is basically high-purity lithium iron phosphate powder. At this time, it is further air flow-pulverized into fine particles. In addition to lithium iron phosphate, the fine particles also contain a part of conductive agent, so they can be directly used to prepare lithium iron phosphate electrodes, with high economic benefits.

[0013] In one embodiment, the crushing frequency during the coarse crushing process is 20 to 100 Hz.

[0014] At the frequency, dust accumulation will not occur too quickly, and the current collector particles will not be too small to cause the possibility of deflagration.

[0015] In one embodiment, the solid-liquid ratio of the pretreated fragments to the extract is 1:(2-5).

[0016] In one embodiment, the organic solvent in the extract is at least one of N-methylpyrrolidone and N,N-dimethylformamide, and the volume content of the organic solvent in the extract is 5-20%.

[0017] In one embodiment, the alkaline solution in the extract is at least one of aqueous ammonia and aqueous sodium hydroxide solution.

[0018] In one embodiment, a dispersant is also added during the ultrasonic stirring treatment, and the dispersant is at least one of sodium lauryl sulfate, fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and sodium dibutylbenzene sulfonate. The mass ratio of the dispersant to the pretreated fragments is (0.000001-0.00005):1.

[0019] In one embodiment, the stirring rate during the ultrasonic stirring treatment is 200-400 r / min.

[0020] In one embodiment, the ultrasonic stirring treatment is performed at an ultrasonic frequency of 20 to 25 kHz and a power of 30 to 35 kW.

[0021] In common lithium iron phosphate scraps, the thickness of the conductive coating reaches 2 to 6 μm. It is difficult to separate the impurities such as binders contained therein by using only conventional liquid phase stripping. Therefore, a specific liquid phase ultrasonic stirring and superimposed treatment is required to strip the aqueous impurities in the conductive coating, especially the aqueous binder, into the liquid phase, and to separate the lithium iron phosphate from the current collector fragments, which is more conducive to subsequent screening and purification.

[0022] In one embodiment, when the suspension is subjected to solid-liquid separation, washing, centrifugal separation, and drying treatments, the centrifugal speed is 500-1200 r / min for 5-20 min; the drying temperature is 150-200° C. for 10-30 min.

[0023] The centrifugal process can effectively separate the current collector aluminum foil and the powder slurry, and then further discharge the liquid phase in the powder through drying.

[0024] In one embodiment, the gas flow rate during the calcination and defluorination is 5 to 10 m 3 / h, the exhaust opening is 50~100%, and the pressure is -0.1~-0.3Pa.

[0025] Under the above conditions, the powder can effectively remove fluorine.

[0026] In one embodiment, the defluorination powder is pulverized in an air flow mill with an air flow pressure of 0.4-0.8 MPa, a feeding frequency of 10-30 Hz, a classification frequency of 100-250 Hz, and an induced draft frequency of 5-50 Hz.

[0027] Another purpose of this article is to provide the recycled lithium iron phosphate obtained by the recycling method of the lithium iron phosphate scraps.

[0028] In one embodiment, the particle size D of the recovered lithium iron phosphate 10 >0.35μm, particle size D 50 =1.5~2.0μm, particle size D 90 <6.5μm, particle size D max <15μm.

[0029] The recycled lithium iron phosphate obtained by the recycling method described in this article has small fineness and high uniformity, and still contains a certain amount of conductive agent. Therefore, it can be directly used in the preparation of positive electrode sheets according to the requirements of the battery cell. It has been verified that the recycled lithium iron phosphate described in this article has high purity, and the electrochemical performance after being prepared as lithium-ion battery positive electrode sheets is comparable to that of commercial lithium iron phosphate.

[0030] Compared with the existing technology, the beneficial effects of this article are:

[0031] This article provides a method for recycling lithium iron phosphate scraps. The method first uses vacuum pre-calcination to effectively separate lithium iron phosphate from the current collector and binder without causing oxidation of the lithium iron phosphate; then uses specific ultrasonic-assisted liquid phase separation to effectively extract the lithium iron phosphate, and after subsequent crushing and calcination and other treatments, a high recovery rate of lithium iron phosphate can be achieved, and the recycled product has high purity; the recycling method has low energy consumption, is environmentally friendly and does not produce secondary pollutants; the recycled lithium iron phosphate prepared by the recycling method has high purity and good quality, can be directly used in the preparation of lithium-ion battery positive electrode plates, and the electrochemical performance it exhibits is comparable to that of commercial new lithium iron phosphate materials, which is very consistent with the integrated concept of recycling and reuse in the lithium iron phosphate industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is an XRD spectrum of the recovered lithium iron phosphate and commercial lithium iron phosphate obtained by the recycling method described in Example 1 and Example 2 described herein.

[0033] FIG2 is a scanning electron microscope image of the recovered lithium iron phosphate obtained by the recycling method described in Example 1 herein.

[0034] FIG3 is a graph showing the first charge and discharge curves of the recovered lithium iron phosphate and commercial lithium iron phosphate obtained by the recycling method described in Example 1 herein at 0.1C. DETAILED DESCRIPTION

[0035] To better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below with reference to the accompanying drawings and specific embodiments.

[0036] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained through commercial channels.

[0037] The lithium iron phosphate scraps used in the various embodiments and comparative examples herein are all semi-finished products or waste products of lithium iron phosphate battery production recycled on the market, which have not been injected with liquid. The main components are current collector aluminum foil, lithium iron phosphate, conductive agent and adhesive.

[0038] Example 1

[0039] An embodiment of the method for recycling lithium iron phosphate scraps described herein includes the following steps:

[0040] A method for recycling lithium iron phosphate scraps comprises the following steps:

[0041] (1) The recovered lithium iron phosphate scraps were crushed by an impact crusher and a double-shaft crusher at a crushing frequency of 100 Hz under a nitrogen atmosphere, and the powder was collected by cyclone separation to obtain coarse powder and current collector scrap fragments with a size of about 5 mm;

[0042] (2) The scraps containing the current collector were placed in a 1×10 -4 Calcination at 100 °C for 1 h under a vacuum degree of Pa gave pretreated fragments;

[0043] (3) The pretreated fragments were placed in an extracting solution at a solid-liquid ratio of 1:2, and ultrasonically treated at 60°C with a frequency of 25kHz, a power frequency of 30kW, and a stirring rate of 400r / min for 30min. During the treatment, polyvinyl alcohol with a mass content of 0.0001% of the pretreated fragments was added. The resulting suspension was subjected to solid-liquid separation, washing, and centrifugation at 500r / min for 20min. The resulting powder was dried in a fluidized bed at 150°C for 30min to obtain a refined powder. The extracting solution included 5% organic solvent N-methylpyrrolidone and ammonia water, and the hydroxide concentration of the extracting solution was 0.005mol / L.

[0044] (4) The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 400°C for 3 hours in a nitrogen atmosphere to remove fluorine. The obtained defluorinated powder is subjected to air flow pulverization, batch mixing in a double-helix conical mixer, and demagnetization treatment by a 12000Gs electromagnetic iron remover to recover lithium iron phosphate. The calcination and defluorination are carried out in a box-type furnace, and the furnace is loaded with 320mm*320mm*110m mullite saggers, which are arranged in double layers and double rows, with a loading height of 2.5cm and an air flow rate of 5m 3 / h, exhaust opening 50%, slight negative pressure -0.1Pa; air flow grinding is carried out in an air flow grinder, the air flow pressure is 0.6MPa, the feeding frequency is 20Hz, the classification frequency is 120Hz, and the induced draft frequency is 35Hz.

[0045] The particle size D of the recovered lithium iron phosphate 10 >0.35μm, particle size D 50 =1.8μm, particle size D90 <6.5μm, particle size D max <15μm.

[0046] Example 2

[0047] An embodiment of the method for recycling lithium iron phosphate scraps described herein includes the following steps:

[0048] A method for recycling lithium iron phosphate scraps comprises the following steps:

[0049] (1) The recovered lithium iron phosphate scraps were coarsely crushed by an impact crusher and a double-shaft crusher at a crushing frequency of 50 Hz under a nitrogen atmosphere, and the powder was collected by cyclone separation to obtain coarse powder and current collector scrap fragments with a size of about 10 mm;

[0050] (2) The scraps containing the current collector were placed in a 1×10 -4 Calcination at 120 °C for 1.5 h under a vacuum degree of Pa gave pretreated fragments;

[0051] (3) The pretreated fragments were placed in an extracting solution at a solid-liquid ratio of 1:2 and stirred at 80°C for 30 minutes under a 25kHz frequency, 30kW power ultrasound, and a speed of 400 r / min. During the treatment, 0.005% of the mass content of the pretreated fragments of sodium lauryl sulfate was added. The resulting suspension was subjected to solid-liquid separation, washing, and centrifugation at 1200 r / min for 5 minutes. The resulting powder was dried in a fluidized bed at 200°C for 20 minutes to obtain a refined powder. The extracting solution included 5% of an organic solvent, N,N-dimethylformamide, and a sodium hydroxide aqueous solution, and the hydroxide concentration of the extracting solution was 0.007 mol / L.

[0052] (4) The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 550°C for 1 hour in a nitrogen atmosphere to remove fluorine. The obtained defluorinated powder is subjected to air flow pulverization, batch mixing in a double-helix conical mixer, and demagnetization treatment with a 12000Gs electromagnetic iron remover to recover lithium iron phosphate. The calcination and defluorination are carried out in a box-type furnace. The furnace is loaded with 320mm*320mm*110m mullite saggers, which are arranged in double layers and double rows. The height of the saggers is 3.5cm and the air flow rate is 10m 3 / h, exhaust opening 70%, slight negative pressure -0.3Pa; air flow grinding is carried out in an air flow grinder, the air flow pressure is 0.8MPa, the feeding frequency is 20Hz, the classification frequency is 120Hz, and the induced draft frequency is 35Hz.

[0053] The particle size D of the recovered lithium iron phosphate 10 >0.35μm, particle size D 50 =1.7μm, particle size D 90 <6.5μm, particle size D max<15μm.

[0054] Example 3

[0055] An embodiment of the method for recycling lithium iron phosphate scraps described herein differs from Example 1 only in that the volume content of the organic solvent N-methylpyrrolidone in the extract is 20%.

[0056] Example 4

[0057] An embodiment of the method for recycling lithium iron phosphate scraps described herein differs from embodiment 1 only in that step (2) is:

[0058] (2) The scraps containing the current collector were placed in a 1×10 -4 The pretreated fragments were calcined at 80°C for 0.5h under a vacuum degree of Pa.

[0059] Comparative Example 1

[0060] A method for recycling lithium iron phosphate scraps comprises the following steps:

[0061] (1) The recovered lithium iron phosphate scraps were crushed by an impact crusher and a double-shaft crusher at a crushing frequency of 100 Hz under a nitrogen atmosphere, and the powder was collected by cyclone separation to obtain coarse powder and current collector scrap fragments with a size of about 5 mm;

[0062] (2) The scraps containing the current collector were placed in a 1×10 -4 Calcination at 100 °C for 1 h under a vacuum degree of Pa gave pretreated fragments;

[0063] (3) The pre-treated fragments were crushed and air-selected, and then calcined at 400°C for 3 hours in a nitrogen atmosphere to remove fluorine. The obtained defluorinated powder was subjected to air flow pulverization, batch mixing in a double-helix conical mixer, and demagnetization treatment by a 12000Gs electromagnetic iron remover to recover lithium iron phosphate. The calcination and defluorination were carried out in a box-type furnace. The furnace was loaded with 320mm*320mm*110m mullite saggers, which were arranged in double layers and double rows. The height of the saggers was 2.5cm, and the air flow rate was 5m 3 / h, exhaust opening 50%, slight negative pressure -0.1Pa; air flow grinding is carried out in an air flow grinder, the air flow pressure is 0.6MPa, the feeding frequency is 20Hz, the classification frequency is 120Hz, and the induced draft frequency is 35Hz.

[0064] Comparative Example 2

[0065] A method for recycling lithium iron phosphate scraps comprises the following steps:

[0066] (1) The recovered lithium iron phosphate scraps were crushed by an impact crusher and a double-shaft crusher at a crushing frequency of 100 Hz under a nitrogen atmosphere, and the powder was collected by cyclone separation to obtain coarse powder and current collector scrap fragments with a size of about 5 mm;

[0067] (2) placing the scraps containing the current collector into an extracting solution at a solid-liquid ratio of 1:2, and stirring for 30 minutes at 60°C with a frequency of 25kHz, a power of 30kW, and a speed of 400r / min. During the treatment, polyvinyl alcohol with a mass content of 0.0001% of the pretreated fragments was added. The resulting suspension was subjected to solid-liquid separation, washing, and centrifugation at 500r / min for 20 minutes. The resulting powder was dried in a fluidized bed at 150°C for 30 minutes to obtain a refined powder; the extracting solution included 5% organic solvent N-methylpyrrolidone and ammonia water, and the hydroxide concentration of the extracting solution was 0.005mol / L;

[0068] (3) The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 400°C for 3 hours in a nitrogen atmosphere to remove fluorine. The obtained defluorinated powder is subjected to air flow pulverization, batch mixing in a double-helix conical mixer, and demagnetization treatment by a 12000Gs electromagnetic iron remover to recover lithium iron phosphate. The calcination and defluorination are carried out in a box-type furnace, and the furnace is loaded with 320mm*320mm*110m mullite saggers, which are arranged in double layers and double rows, with a loading height of 2.5cm and an air flow rate of 5m 3 / h, exhaust opening 50%, slight negative pressure -0.1Pa; air flow grinding is carried out in an air flow grinder, the air flow pressure is 0.6MPa, the feeding frequency is 20Hz, the classification frequency is 120Hz, and the induced draft frequency is 35Hz.

[0069] Comparative Example 3

[0070] A method for recycling lithium iron phosphate scraps, which differs from Example 1 only in that step (2) is:

[0071] (2) The scraps containing the current collector were placed in a 1×10 -4 The pretreated fragments were calcined at 300 °C for 0.5 h under a vacuum degree of Pa.

[0072] Comparative Example 4

[0073] A method for recycling lithium iron phosphate scraps, which differs from Example 1 only in that step (2) is:

[0074] (2) The scraps containing the current collector were calcined at 80°C for 0.5 h under normal pressure nitrogen to obtain pretreated fragments.

[0075] Comparative Example 5

[0076] A method for recycling lithium iron phosphate scraps, which differs from Example 1 only in that step (3) is:

[0077] (3) The pretreated fragments were placed in an extracting solution at a solid-liquid ratio of 1:2 and ultrasonically treated at 60°C, 25kHz frequency, and 30kW power for 30 minutes. During the treatment, 0.0001% of polyvinyl alcohol by mass of the pretreated fragments was added. The resulting suspension was subjected to solid-liquid separation, washing, and centrifugal separation at 500 r / min for 20 minutes. The resulting powder was dried in a fluidized bed at 150°C for 30 minutes to obtain a refined powder. The extracting solution included 5% of an organic solvent, N-methylpyrrolidone, and aqueous ammonia, and the hydroxide concentration of the extracting solution was 0.005 mol / L.

[0078] Comparative Example 6

[0079] A method for recycling lithium iron phosphate scraps, which differs from Example 1 only in that step (3) is:

[0080] (3) The pretreated fragments were placed in an extracting solution at a solid-liquid ratio of 1:2 and stirred at 400 r / min at 60°C for 30 min. Polyvinyl alcohol with a mass content of 0.0001% of the pretreated fragments was also added during the treatment. The resulting suspension was subjected to solid-liquid separation, washing, and centrifugation at 500 r / min for 20 min. The resulting powder was dried in a fluidized bed at 150°C for 30 min to obtain a refined powder. The extracting solution included 5% organic solvent N-methylpyrrolidone and ammonia water, and the hydroxide concentration of the extracting solution was 0.005 mol / L.

[0081] Comparative Example 7

[0082] A method for recycling lithium iron phosphate scraps, which differs from Example 1 only in that step (4) is:

[0083] (4) The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 300°C for 3 hours in a nitrogen atmosphere to remove fluorine. The obtained defluorinated powder is subjected to air flow pulverization, batch mixing in a double-helix conical mixer, and demagnetization treatment by a 12000Gs electromagnetic iron remover to recover lithium iron phosphate. The calcination and defluorination are carried out in a box-type furnace. The furnace is loaded with 320mm*320mm*110m mullite saggers, which are arranged in double layers and double rows. The height of the saggers is 2.5cm and the air flow rate is 5m 3 / h, exhaust opening 50%, slight negative pressure -0.1Pa; air flow pulverization is carried out in an air flow pulverizer, the air flow pressure is 0.6MPa, the feeding frequency is 20Hz, the classification frequency is 120Hz, and the induced draft frequency is 35Hz.

[0084] The recycling methods of the embodiments and comparative examples were statistically analyzed for lithium iron phosphate recovery rate, aluminum content of lithium iron phosphate recovered material, fluorine content of lithium iron phosphate recovered material, liquid content of fine powder material, and binder carbonization rate, where:

[0085] Lithium iron phosphate recovery rate (%) = actual recovered lithium iron phosphate mass / theoretical calculated lithium iron phosphate mass × 100%;

[0086] Elemental analysis was used to test the aluminum content and fluorine content of the recycled lithium iron phosphate material;

[0087] Liquid content of static powder (%) = mass difference of fine powder after drying at 80℃ for 60min / mass of fine powder after drying × 100%;

[0088] Binder carbonization rate (%) = (carbon content of mixed powder after calcination - carbon content of mixed powder before calcination) / carbon content of mixed powder after calcination × 100%. The carbon content is directly tested using a carbon-sulfur instrument.

[0089] The results are shown in Table 1.

[0090] Table 1

[0091] The recovered lithium iron phosphate obtained in Example 1 and Example 2 was subjected to elemental analysis and XRD test (commercially available commercial lithium iron phosphate was used for comparison). The results are shown in Table 2 and Figure 1. It can be seen that the recovered lithium iron phosphate obtained in the two examples has high purity and few impurities. The product of Example 1 was observed by scanning electron microscopy, as shown in Figure 2. It can be seen that the prepared recovered lithium iron phosphate particles are small in size and highly uniform.

[0092] Table 2

[0093] Subsequently, the recovered lithium iron phosphate prepared in Example 1 and the commercial lithium iron phosphate were prepared into positive electrode sheets using commercially available binders and conductive agents, and then assembled into lithium-ion button batteries using the lithium sheet as the negative electrode. The first charge and discharge test was carried out at a rate of 0.1C. The results are shown in FIG3 . It can be seen that the electrochemical performance of the recovered lithium iron phosphate obtained by the recycling method described in this article is comparable to that of the commercial material.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A method for recycling lithium iron phosphate scraps, characterized in that: The following steps are involved: The recycled lithium iron phosphate scrap pole pieces are roughly crushed and pulverized in a nitrogen atmosphere, and the powder is collected by cyclone separation to obtain coarse powder and scrap fragments containing current collectors with a size of 5 to 10 mm; The scraps containing the current collector were placed in a range of 0.8 to 1.2 × 10 -4 Calcinate at 80-150°C for 0.5-2h under a vacuum degree of Pa to obtain pretreated fragments; The pre-treated fragments are placed in an extracting solution and subjected to ultrasonic stirring treatment at 60-100° C. for 10-30 minutes. The obtained suspension is subjected to solid-liquid separation, washing, centrifugal separation, and drying to obtain a fine powder; the extracting solution includes an organic solvent and an alkali solution, and the hydroxide concentration of the extracting solution is 0.005-0.01 mol / L; The coarse powder and the fine powder are crushed, air-selected and screened, and then calcined at 400-550°C in a nitrogen atmosphere to remove fluorine for 1-3 hours. The obtained defluorinated powder is subjected to air flow pulverization and batch mixing demagnetization treatment to recover lithium iron phosphate.

2. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The solid-liquid ratio of the pre-treated fragments to the extract is 1:(2-5).

3. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The organic solvent in the extract is at least one of N-methylpyrrolidone and N,N-dimethylformamide, and the volume content of the organic solvent in the extract is 5-20%.

4. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The alkaline solution in the extract is at least one of aqueous ammonia and aqueous sodium hydroxide solution.

5. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: A dispersant is also added during the ultrasonic stirring treatment. The dispersant is at least one of sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and sodium dibutylbenzene sulfonate. The mass ratio of the dispersant to the pretreated fragments is (0.000001-0.00005):

1.

6. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The stirring rate during the ultrasonic stirring treatment is 200-400 r / min, the ultrasonic frequency is 20-25 kHz, and the power is 30-35 kW.

7. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: When the suspension is subjected to solid-liquid separation, washing, centrifugal separation and drying treatment, the centrifugal speed is 500-1200 r / min and the time is 5-20 min; the drying temperature is 150-200° C. and the time is 10-30 min.

8. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The gas flow rate during calcination and defluorination is 5 to 10 m 3 / h, the exhaust opening is 50~100%, and the pressure is -0.1~-0.3Pa.

9. The method for recycling lithium iron phosphate scraps as claimed in claim 1, characterized in that: The defluorination powder is pulverized in an air flow pulverizer, the air flow pressure is 0.4-0.8 MPa, the feeding frequency is 10-30 Hz, the classification frequency is 100-250 Hz, and the induced draft frequency is 5-50 Hz.

10. Recycled lithium iron phosphate obtained by the method for recycling lithium iron phosphate scraps according to any one of claims 1 to 9.

11. The method for recovering lithium iron phosphate according to claim 10, wherein: The particle size D of the recovered lithium iron phosphate 10 >0.35μm, particle size D 50 =1.5~2.0μm, particle size D 90 <6.5μm, particle size D max <15μm.

Images