Method for recycling lithium iron phosphate offcuts

Abstract

The application discloses a recycling method of lithium iron phosphate offcut, and belongs to the technical field of material recycling. The method effectively separates lithium iron phosphate from a current collector and a binder by adopting vacuum pre-calcination, and does not cause oxidation of the lithium iron phosphate. Then, the lithium iron phosphate is effectively extracted by adopting specific ultrasonic-assisted liquid separation. After subsequent crushing and calcination, high recovery rate recovery of the lithium iron phosphate is realized, and the recovered product has high purity. The recycling method has low energy consumption, is environment-friendly, and does not produce secondary pollutants. The recycled lithium iron phosphate prepared by the recycling method has high purity and good quality, and can be directly applied to preparation of a lithium ion battery positive electrode sheet. The electrochemical performance of the recycled lithium iron phosphate is comparable to that of commercial lithium iron phosphate, and the recycling method is very consistent with the integration concept of recycling and reuse in the lithium iron phosphate industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material recycling, and particularly relates to a recycling method of lithium iron phosphate offcut. BACKGROUND

[0002] Lithium iron phosphate lithium battery is a high electrochemical and high safety power battery. A large amount of lithium iron phosphate offcut is generated in the coating, rolling and slicing stages in the production process. The offcut is mostly semi-finished product, unqualified product or scrap product, and thus cannot be prepared into complete battery and be delithiated. The lithium iron phosphate has not been phase changed, and has high recyclability. On the other hand, the lithium iron phosphate offcut has high output, and if not properly treated, will cause environmental problems.

[0003] At present, the mainstream recycling process of lithium iron phosphate offcut is wet recycling, that is, gradually recycling by acid dissolution, alkali dissolution and organic solvent soaking. However, the product produced by the process is mostly secondary product, such as lithium carbonate and ferrous phosphate, which needs to be further processed to prepare lithium iron phosphate. At the same time, the wet process also produces a large amount of leaching liquid, which also needs to be disposed. In addition, some recycling methods such as pyrometallurgy and direct regeneration have the problems of large yield fluctuation and low product purity. SUMMARY

[0004] The present application aims to overcome the deficiencies of the prior art and provide a recycling method of lithium iron phosphate offcut. The method effectively separates lithium iron phosphate from the current lithium iron phosphate offcut by vacuum pre-calcination, without causing oxidation of lithium iron phosphate. Then, the lithium iron phosphate is effectively extracted by specific ultrasonic-assisted liquid phase separation. After subsequent crushing and calcination, the lithium iron phosphate can be recycled at a high recovery rate, and the recycled product has high purity. The recycling method has low energy consumption, is environmentally friendly and does not produce secondary pollutants.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] A recycling method of lithium iron phosphate offcut, comprising the following steps:

[0007] The recycled lithium iron phosphate offcut electrode sheet is coarsely crushed and pulverized under a nitrogen atmosphere, and the powder is collected by cyclone separation to obtain coarse powder and lithium iron phosphate offcut scrap containing current collector with a size of 5-10 mm;

[0008] The lithium iron phosphate offcut scrap containing current collector is calcined at 80-150 DEG C under a vacuum degree of 0.8-1.2 x 10 -4 Pa for 0.5-2 h to obtain pretreated scrap;

[0009] The pretreated fragments are put into an extraction liquid and treated by ultrasonic stirring at 60-100°C for 10-30 min, and the obtained suspension is subjected to solid-liquid separation, washing, centrifugal separation and drying to obtain fine powder; the extraction liquid comprises an organic solvent and a lye, and the hydroxyl ion concentration of the extraction liquid is 0.005-0.01 mol / L.

[0010] The coarse powder and the fine powder are subjected to crushing and air separation, and then calcined at 400-550°C under a nitrogen atmosphere for 1-3 h to remove fluorine, and the obtained fluorine-removed powder is subjected to air flow crushing and batch magnetic removal to obtain recovered lithium iron phosphate.

[0011] In the method for recycling lithium iron phosphate edge and corner scraps described in this paper, the lithium iron phosphate edge and corner scraps are first crushed and subjected to cyclone separation, and some dust and part of the pure lithium iron phosphate powder are collected in advance to improve the recovery rate of lithium iron phosphate. Since the process is carried out under a nitrogen atmosphere, there is no risk of dust explosion. Subsequently, the edge and corner scrap fragments with carbon-coated aluminum foil, adhesive and other substances are subjected to vacuum calcination at a specific low temperature. Under this condition, neither the aluminum foil nor the lithium iron phosphate will be oxidized to produce impurities, and the adhesion of the carbon coating layer and the adhesive in the pole piece can be greatly reduced. In combination with ultrasonic wet extraction and separation treatment at a specific temperature, the adhesive such as acrylate can be stripped out of the powder. After crushing, air separation, and calcination to remove fluorine, the obtained material is basically high-purity lithium iron phosphate powder. At this time, the fine particles are further air flow crushed into fine particles. In addition to lithium iron phosphate, the fine particles also contain part of the conductive agent, and therefore can be directly used to prepare lithium iron phosphate pole pieces, which has high economic benefits.

[0012] In an embodiment, the crushing frequency during the coarse crushing and pulverizing treatment is 20-100 Hz.

[0013] 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.

[0014] In an embodiment, the solid-liquid ratio of the pretreated fragments to the extraction liquid is 1:(2-5).

[0015] In an embodiment, the organic solvent in the extraction liquid is at least one of N-methylpyrrolidone and N,N-dimethylformamide, and the volume content of the organic solvent in the extraction liquid is 5-20%.

[0016] In an embodiment, the lye in the extraction liquid is at least one of ammonia water and sodium hydroxide aqueous solution.

[0017] In an embodiment, the dispersing agent is at least one of sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and sodium dibutylbenzenesulfonate, and the ratio of the dispersing agent to the mass of the pretreated fragments is (0.000001-0.00005):1.

[0018] In an embodiment, the stirring rate during the ultrasonic stirring treatment is 200-400 r / min.

[0019] In an embodiment, the ultrasonic frequency during the ultrasonic stirring treatment is 20-25 kHz, and the power is 30-35 kW.

[0020] In the common lithium iron phosphate edge scraps, the thickness of the conductive coating reaches 2-6 μm, and it is difficult to separate the impurities such as the binder contained therein by using only the conventional liquid phase stripping. Therefore, a specific liquid phase ultrasonic stirring superposition treatment is required to strip the aqueous impurities, especially the aqueous binder, in the conductive coating into the liquid phase, and separate the lithium iron phosphate from the current collector fragments, which is more conducive to subsequent screening and purification.

[0021] In an embodiment, during the solid-liquid separation, washing, centrifugal separation, and drying treatment of the suspension, the rate during centrifugation is 500-1200 r / min, and the time is 5-20 min; the temperature during drying is 150-200 °C, and the time is 10-30 min.

[0022] The use of the centrifugal procedure can effectively separate the current collector aluminum foil and the powder slurry, and further discharge the liquid phase in the powder after drying.

[0023] In an embodiment, the gas flow rate during the calcination to remove fluorine is 5-10 m 3 / h, the exhaust opening degree is 50-100%, and the pressure is -0.1 to -0.3 Pa.

[0024] Under the conditions, the powder can be effectively defluorinated.

[0025] In an embodiment, the defluorinated powder is subjected to jet milling in a jet mill, the jet pressure is 0.4-0.8 MPa, the feeding frequency is 10-30 Hz, the classification frequency is 100-250 Hz, and the air induction frequency is 5-50 Hz.

[0026] Another object of the present disclosure is to provide a recycled lithium iron phosphate obtained by the recycling method of the lithium iron phosphate edge scraps.

[0027] In an embodiment, the particle size D 10 >0.35 μm, and the particle size D 50= 1.5 ~ 2.0 pm, particle size D 90 < 6.5 pm, particle size D max < 15 pm.

[0028] The recycled lithium iron phosphate particles obtained by the recycling method described herein are small in fineness, high in uniformity, and still contain a certain amount of conductive agent, so they can be directly applied in the preparation of positive electrode sheets according to the requirements of the battery. It has been verified that the recycled lithium iron phosphate described herein is high in purity, and the electrochemical performance after being prepared into a lithium ion battery positive electrode sheet is comparable to that of commercial lithium iron phosphate.

[0029] Compared with the prior art, the beneficial effects of the present application are:

[0030] The present application provides a recycling method for lithium iron phosphate scraps. The method effectively separates lithium iron phosphate from the current lithium iron phosphate scraps by vacuum pre-calcination, without causing oxidation of lithium iron phosphate. Then, specific ultrasonic-assisted liquid separation is used to effectively extract lithium iron phosphate. After subsequent crushing and calcination, high recovery rate of lithium iron phosphate can be achieved, and the recovered product is high in purity. The recycling method is low in energy consumption, environmentally friendly, and does not produce secondary pollutants. The recycled lithium iron phosphate prepared by the recycling method is high in purity and good in quality, and can be directly applied in the preparation of lithium ion battery positive electrode sheets. The electrochemical performance is comparable to that of commercial lithium iron phosphate, which is in line with the concept of recycling and reuse in the lithium iron phosphate industry. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 XRD spectra of recycled lithium iron phosphate obtained by the recycling method described in Example 1 and Example 2 of the present application and commercial lithium iron phosphate.

[0032] Figure 2 Scanning electron microscope image of recycled lithium iron phosphate obtained by the recycling method described in Example 1 of the present application.

[0033] Figure 3 First charge-discharge curve of recycled lithium iron phosphate obtained by the recycling method described in Example 1 of the present application and commercial lithium iron phosphate at 0.1C. DETAILED DESCRIPTION

[0034] To better illustrate the purpose, technical solutions and advantages of the present application, the following will further describe the present application in conjunction with the drawings and specific examples.

[0035] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained by commercial means.

[0036] The lithium iron phosphate edge scraps used in each embodiment and comparative example herein are all commercially recycled semi-finished products or waste products of lithium iron phosphate battery production without liquid injection, and the main components are current collector aluminum foil, lithium iron phosphate, conductive agent and binder.

[0037] Example 1

[0038] One embodiment of the recycling method of lithium iron phosphate edge scraps described herein includes the following steps:

[0039] A recycling method of lithium iron phosphate edge scraps includes the following steps:

[0040] (1) The recycled lithium iron phosphate edge scrap pole piece is subjected to coarse crushing and pulverizing treatment under a nitrogen atmosphere using a counter crusher and a double-shaft crusher at a pulverizing frequency of 100 Hz, and the powder is collected by cyclone separation to obtain coarse powder and edge scrap fragments containing current collectors with a size of about 5 mm;

[0041] (2) The edge scrap fragments containing current collectors are calcined at 100°C for 1 h under a vacuum degree of 1×10 -4 Pa to obtain pretreated fragments;

[0042] (3) The pretreated fragments are placed in an extraction solution at a solid-liquid ratio of 1:2, subjected to ultrasonic treatment at a frequency of 25 kHz and a power frequency of 30 kW and stirring at a speed of 400 r / min for 30 min at 60°C, and polyvinyl alcohol is added at a content of 0.0001% of the mass of the pretreated fragments during the treatment. The obtained suspension is subjected to solid-liquid separation, washing, centrifugal separation at 500 r / min for 20 min, and the obtained powder is dried in a fluidized bed at 150°C for 30 min to obtain fine powder. The extraction solution comprises 5% organic solvent N-methyl pyrrolidone and ammonia water, and the hydroxyl ion concentration of the extraction solution is 0.005 mol / L;

[0043] (4) After the coarse powder and fine powder are screened by a crushing air separator, they are calcined at 400°C for 3 h under a nitrogen atmosphere to remove fluorine. The obtained fluorine-removed powder is subjected to air flow pulverization, batch mixing by a double-helix conical mixer, and magnetic removal by a 12000 Gs electromagnetic iron remover to obtain recycled lithium iron phosphate. The calcination for removing fluorine is performed in a box furnace, and the furnace is loaded with mullite crucibles with a size of 320 mm*320 mm*110 mm, which are placed in double layers and double rows, with a loading height of 2.5 cm. The gas flow rate is 5 m 3 / h, the exhaust opening degree is 50%, and the micro-negative pressure is -0.1 Pa. The air flow pulverization is performed in an air flow pulverizer, with an air flow pressure of 0.6 MPa, a feeding frequency of 20 Hz, a grading frequency of 120 Hz, and an air induction frequency of 35 Hz.

[0044] The particle size D 10 >0.35 μm, the particle size D 50 =1.8 μm, and the particle size D90 <6.5μm, particle size D max <15μm.

[0045] Example 2

[0046] An embodiment of the method for recycling lithium iron phosphate scrap described in this article includes the following steps:

[0047] A method for recycling lithium iron phosphate scrap includes the following steps:

[0048] (1) The recycled lithium iron phosphate scrap electrode sheets were coarsely crushed and pulverized in a nitrogen atmosphere using an impact crusher and a twin-shaft crusher at a crushing frequency of 50Hz, and the powder was collected by cyclone separation to obtain coarse powder and scrap fragments containing current collector with a size of about 10mm.

[0049] (2) The scraps containing the current collector are placed in a 1×10 -4 Calcination at 120°C for 1.5 h under a vacuum of Pa yields pretreated fragments.

[0050] (3) The pretreated fragments were placed in the extraction solution at a solid-liquid ratio of 1:2 and treated with ultrasonication at 25 kHz frequency and 30 kW power at 80 °C and stirring at 400 r / min for 30 min. Sodium dodecyl sulfate with a mass content of 0.005% of the pretreated fragments was also added during the treatment. The resulting suspension was subjected to solid-liquid separation, washing, centrifugation at 1200 r / min for 5 min, and the resulting powder was dried in a fluidized bed at 200 °C for 20 min to obtain a refined powder. The extraction solution included 5% organic solvent N,N-dimethylformamide and sodium hydroxide aqueous solution, and the hydroxide concentration of the extraction solution was 0.007 mol / L.

[0051] (4) After crushing and air-classifying the coarse and fine powders, they are calcined at 550℃ for 1 hour under a nitrogen atmosphere to remove fluorine. The resulting defluorinated powder is then subjected to air-jet milling, batch mixing in a double-spiral conical mixer, and demagnetization treatment by a 12000Gs electromagnetic iron separator to obtain recovered lithium iron phosphate. The calcination and defluorination are carried out in a box furnace, with 320mm*320mm*110m mullite saggers used for loading. The saggers are arranged in double layers and double rows, with a loading height of 3.5cm and an air flow rate of 10m³ / h. 3 / h, exhaust opening 70%, slight negative pressure -0.3Pa; air jet milling is carried out in an air jet mill with an air pressure of 0.8MPa, a feeding frequency of 20Hz, a grading frequency of 120Hz, and an induced draft frequency of 35Hz.

[0052] 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< 15 μm.

[0053] Example 3

[0054] One embodiment of the method for recycling lithium iron phosphate scrap described herein differs from Example 1 only in that the volume content of the organic solvent N-methyl pyrrolidone in the extraction solution is 20%.

[0055] Example 4

[0056] One embodiment of the method for recycling lithium iron phosphate scrap described herein differs from Example 1 only in that step (2) is:

[0057] (2) The set fluid-containing scrap pieces are calcined at 80°C for 0.5 h under a vacuum degree of 1 x 10 -4 Pa to obtain pretreated pieces.

[0058] Comparative Example 1

[0059] A method for recycling lithium iron phosphate scrap includes the following steps:

[0060] (1) The recycled lithium iron phosphate scrap electrode pieces are coarsely crushed and pulverized using a hammer crusher and a double-shaft crusher at a crushing frequency of 100 Hz under a nitrogen atmosphere and the powder is collected by cyclone separation to obtain coarse powder and set fluid-containing scrap pieces with a size of about 5 mm;

[0061] (2) The set fluid-containing scrap pieces are calcined at 100°C for 1 h under a vacuum degree of 1 x 10 -4 Pa to obtain pretreated pieces;

[0062] (3) After the pretreated pieces are separated by a crushing air separator, they are calcined at 400°C for 3 h under a nitrogen atmosphere to remove fluorine. The obtained fluorine-removed powder is treated by jet milling, batch mixing in a double-helix conical mixer, and electromagnetic iron removal at 12,000 G to obtain recycled lithium iron phosphate. The calcination for fluorine removal is performed in a box furnace, which is loaded with mullite crucibles with a size of 320 mm x 320 mm x 110 mm, placed in double layers and double rows, with a loading height of 2.5 cm, a gas flow rate of 5 m 3 / h, an exhaust opening degree of 50%, and a slight negative pressure of -0.1 Pa. The jet milling is performed in a jet mill with a jet pressure of 0.6 MPa, a feeding frequency of 20 Hz, a classification frequency of 120 Hz, and an air induction frequency of 35 Hz.

[0063] Comparative Example 2

[0064] A method for recycling lithium iron phosphate scrap includes the following steps:

[0065] (1) The recycled lithium iron phosphate offcut pole piece is coarsely crushed and pulverized under a nitrogen atmosphere using an impact crusher and a double-shaft crusher at a crushing frequency of 100 Hz, and the powder is collected by cyclone separation to obtain coarse powder and offcut pieces containing the fluid collector with a size of about 5 mm;

[0066] (2) The offcut pieces containing the fluid collector are placed in an extraction solution at a solid-liquid ratio of 1:2, and are treated by ultrasonic waves at a frequency of 25 kHz and a power of 30 kW for 30 min at 60°C and at a stirring rate of 400 r / min. Polyvinyl alcohol is added to the pretreated pieces at a mass content of 0.0001% during the treatment. The obtained suspension is subjected to solid-liquid separation, washing, centrifugal separation at 500 r / min for 20 min, and the obtained powder is dried in a fluidized bed at 150°C for 30 min to obtain fine powder. The extraction solution comprises 5% of an organic solvent N-methyl pyrrolidone and ammonia water, and the hydroxyl ion concentration of the extraction solution is 0.005 mol / L.

[0067] (3) The coarse powder and the fine powder are separated by crushing and air separation, and are calcined at 400°C under a nitrogen atmosphere for 3 h to remove fluorine. The obtained fluorine-removed powder is subjected to air flow pulverization, batch mixing by a double-helix conical mixer, and magnetic removal by a 12000 Gs electromagnetic iron remover to obtain recycled lithium iron phosphate. The calcination for removing fluorine is performed in a box furnace, and the furnace is loaded with mullite crucibles with a size of 320 mm*320 mm*110 mm, which are placed in double layers and double rows, with a loading height of 2.5 cm, an air flow rate of 5 m 3 / h, an exhaust opening degree of 50%, and a slight negative pressure of -0.1 Pa. The air flow pulverization is performed in an air flow pulverizer at an air flow pressure of 0.6 MPa, a feeding frequency of 20 Hz, a classification frequency of 120 Hz, and an air induction frequency of 35 Hz.

[0068] Comparative Example 3

[0069] A method for recycling lithium iron phosphate offcut, which is different from Example 1 only in that the step (2) is:

[0070] (2) The offcut pieces containing the fluid collector are calcined at 300°C for 0.5 h under a vacuum degree of 1*10 -4 Pa to obtain pretreated pieces.

[0071] Comparative Example 4

[0072] A method for recycling lithium iron phosphate offcut, which is different from Example 1 only in that the step (2) is:

[0073] (2) The offcut pieces containing the fluid collector are calcined at 80°C for 0.5 h under normal pressure nitrogen to obtain pretreated pieces.

[0074] Comparative Example 5

[0075] A recycling method of lithium iron phosphate offcut, the difference from example 1 is only that the step (3) is:

[0076] (3) the pretreated fragments are put into the extraction liquid with a solid-liquid ratio of 1:2, and are treated by ultrasonic at 60℃, 25kHz frequency and 30kW power for 30min, and polyvinyl alcohol is added in the pretreated fragments with a mass content of 0.0001% during the treatment, the obtained suspension is subjected to solid-liquid separation, washing, 500r / min centrifugal separation for 20min, and the obtained powder is dried in a fluidized bed at 150℃ for 30min to obtain fine powder; the extraction liquid comprises 5% organic solvent N-methyl pyrrolidone and ammonia water, and the hydroxyl ion concentration of the extraction liquid is 0.005mol / L.

[0077] Comparative example 6

[0078] A recycling method of lithium iron phosphate offcut, the difference from example 1 is only that the step (3) is:

[0079] (3) the pretreated fragments are put into the extraction liquid with a solid-liquid ratio of 1:2, and are treated by ultrasonic at 60℃, 25kHz frequency and 30kW power for 30min, and polyvinyl alcohol is added in the pretreated fragments with a mass content of 0.0001% during the treatment, the obtained suspension is subjected to solid-liquid separation, washing, 500r / min centrifugal separation for 20min, and the obtained powder is dried in a fluidized bed at 150℃ for 30min to obtain fine powder; the extraction liquid comprises 5% organic solvent N-methyl pyrrolidone and ammonia water, and the hydroxyl ion concentration of the extraction liquid is 0.005mol / L.

[0080] Comparative example 7

[0081] A recycling method of lithium iron phosphate offcut, the difference from example 1 is only that the step (3) is:

[0082] (4) the coarse powder and the fine powder are subjected to crushing and air separation screening, and are calcined at 300℃ for 3h under a nitrogen atmosphere to remove fluorine, the obtained fluorine-removed powder is subjected to air flow crushing, batch mixing by a double helix conical mixer, and magnetic removal by a 12000Gs electromagnetic iron remover to obtain recycled lithium iron phosphate; the calcination for removing fluorine is carried out in a box furnace, and 320mm*320mm*110mm mullite crucibles are used for loading, and double-layer double-row placement is adopted, the loading height is 2.5cm, the gas flow is 5m 3 / h, the exhaust opening degree is 50%, and the micro-negative pressure is-0.1Pa; the air flow crushing is carried out in an air flow crusher, the air flow pressure is 0.6MPa, the feeding frequency is 20Hz, the grading frequency is 120Hz, and the air induction frequency is 35Hz.

[0083] Effect example 1

[0084] The recycling methods of each example and comparative example were statistically analyzed in terms of lithium iron phosphate recovery rate, aluminum content of lithium iron phosphate recovery material, fluorine content of lithium iron phosphate recovery material, liquid content of fine powder material, and binder carbonization rate, wherein:

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

[0086] The elemental analysis method was used to test the aluminum content and fluorine content of the lithium iron phosphate recovery material.

[0087] Static powder liquid content (%) = mass difference of fine powder material after drying at 80°C for 60 min / mass of dried fine powder material x 100%;

[0088] Binder carbonization rate (%) = (carbon content after calcination of mixed powder - carbon content before calcination of mixed powder) / carbon content after calcination of mixed powder x 100%, and the carbon content was directly tested by a carbon-sulfur instrument.

[0089] The results are shown in Table 1.

[0090] Table 1

[0091]

[0092] The recovered lithium iron phosphate obtained from Example 1 and Example 2 was subjected to elemental analysis and XRD testing (using commercially available commercial lithium iron phosphate for comparison), and the results are shown in Table 2 and Figure 1 It can be seen that the recovered lithium iron phosphate obtained from the two examples has high purity and less impurities. The product of Example 1 was observed by scanning electron microscope, and as shown in Figure 2 It can be seen that the recovered lithium iron phosphate particles prepared have small size and high uniformity.

[0093] Table 2

[0094] Element Li (%) Fe (%) Li / Fe Al (ppm) Example 1 4.36 35.30 1.02 117 Example 2 4.35 35.35 1.04 105

[0095] Subsequently, the recovered lithium iron phosphate prepared in Example 1 and commercial lithium iron phosphate were prepared into positive electrode sheets using commercially available binders and conductive agents, and then assembled into lithium ion button cells with lithium sheets as negative electrodes, and subjected to first charge-discharge test at 0.1C rate, and the results are shown in Figure 3 It can be seen that the recovered lithium iron phosphate obtained by the recycling method described herein exhibits electrochemical performance comparable to commercial materials.

[0096] Finally, it should be noted that the above examples are only used to illustrate the technical solutions herein and not to limit the scope of protection herein, and although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions herein can be modified or equivalently replaced without departing from the essence and scope of the technical solutions herein.

Claims

1. A method for recycling lithium iron phosphate scrap, characterized by, It comprises the following steps: The recycled lithium iron phosphate offcut pole piece is coarsely broken and crushed under a nitrogen atmosphere, and the powder is collected by cyclone separation to obtain coarse powder and offcut fragments containing the fluid collector with a size of 5-10 mm; The scrap containing the fluid-collecting material is calcined at 80-120°C for 0.5-2h under a vacuum of 0.8-1.2x10 -4 Pa to obtain the pretreated scrap. The pretreated fragments are placed in an extraction liquid and subjected to ultrasonic stirring treatment at 60-100°C for 10-30 min, and the obtained suspension is subjected to solid-liquid separation, washing, centrifugal separation and drying to obtain fine powder; the extraction liquid comprises an organic solvent and a lye, and the hydroxyl ion concentration of the extraction liquid is 0.005-0.01 mol / L; The coarse powder and the fine powder are subjected to crushing and air classification screening, and then calcined at 400-550°C under a nitrogen atmosphere for 1-3 h to remove fluorine, and the obtained fluorine-removed powder is subjected to jet milling and batch mixing to remove magnetism to obtain recycled lithium iron phosphate.

2. The method of recycling lithium iron phosphate scrap according to claim 1, wherein, The solid-liquid ratio of the pretreated fragments to the extraction liquid is 1:(2-5).

3. The method of recycling lithium iron phosphate scrap according to claim 1, wherein, The organic solvent in the extraction liquid is at least one of N-methylpyrrolidone and N,N-dimethylformamide, and the volume content of the organic solvent in the extraction liquid is 5-20%.

4. The method of recycling lithium iron phosphate scrap according to claim 1, wherein The lye in the extraction liquid is at least one of ammonia water and sodium hydroxide aqueous solution.

5. The method of recycling lithium iron phosphate scrap of claim 1, wherein, A dispersant is added during the ultrasonic stirring treatment, and the dispersant is at least one of sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, polyvinyl alcohol and sodium dibutylbenzenesulfonate, and the mass ratio of the dispersant to the pretreated fragments is (0.000001-0.00005):

1.

6. The method of recycling lithium iron phosphate scrap of claim 1, wherein, 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 of recycling lithium iron phosphate scrap according to claim 1, wherein During the solid-liquid separation, washing, centrifugal separation and drying treatment of the suspension, the centrifugal rate 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 of recycling lithium iron phosphate scrap of claim 1, wherein, The gas flow rate during the defluorination calcination is 5 to 10 m 3 / h, the exhaust opening degree is 50 to 100%, and the pressure is -0.1 to -0.3 Pa.

9. The method of recycling lithium iron phosphate scrap of claim 1, wherein, The fluorine-removed powder is subjected to jet milling in a jet mill, the jet pressure is 0.4-0.8 MPa, the feeding frequency is 10-30 Hz, the classification frequency is 100-250 Hz, and the air induction frequency is 5-50 Hz.

10. The recycled lithium iron phosphate offcut recovered by the recycling method according to any one of claims 1-9.

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

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