Method for cleaning and recycling waste lithium iron phosphate positive electrode material

Abstract

The application provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps: (1) the waste lithium iron phosphate positive electrode material is pretreated to separate aluminum foil, a binder and carbon, and a mixture containing phosphorus, iron and lithium is obtained; (2) the mixture is subjected to oxidative leaching in a sodium hydroxide solution, and the obtained mixed slurry is subjected to solid-liquid separation to obtain iron hydroxide precipitation and a leaching solution; (3) sodium carbonate and the leaching solution are mixed, lithium is precipitated, and solid-liquid separation is performed to obtain lithium carbonate and a separation solution; the separation solution is subjected to crystallization and solid-liquid separation to obtain sodium phosphate crystals; (4) the lithium carbonate in step (2), the iron hydroxide precipitation in step (3), phosphoric acid and carbon powder are mixed, and calcination is performed to obtain lithium iron phosphate. The clean recycling method can realize high-purity and high-efficiency recycling of the waste lithium iron phosphate positive electrode material, and the process flow is clean and environmentally friendly.

Description

TECHNICAL FIELD

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

[0002] With the maturity of a series of new power lithium ion batteries represented by lithium ion batteries, the rapid development of the electric vehicle industry has become a solid foundation. With the passage of time, the number of LiFePO4 waste batteries will continue to increase. A large number of waste power lithium ion batteries contain harmful substances such as waste organic electrolyte, binder and conductive agent, as well as rich lithium resources. If they are not properly and efficiently treated and recycled, not only will they pollute the ecological environment and threaten human health, but also will they seriously waste resources. Researchers have conducted a lot of research on waste lithium iron phosphate recycling and reuse, but the effect is not good.

[0003] CN113582153A discloses a repaired and regenerated waste lithium iron phosphate positive material and a repairing and regenerating method thereof. The method comprises the following steps: (1) uniformly mixing the waste lithium iron phosphate positive material with material A, a carbon source and metal additive ions to obtain a mixture material B; the material A comprises uniformly mixed lithium carbonate and lithium hydroxide; (2) low-temperature calcining the mixture material B in an inert or reducing atmosphere, and cooling to obtain the repaired and regenerated waste lithium iron phosphate material. The repaired and regenerated waste lithium iron phosphate positive material has a core-shell coating structure, and the coating layer is a carbon layer. The metal additive ions doped lithium iron phosphate is coated by the carbon layer. However, impurities still remain in the lithium iron phosphate obtained by the method, and the electrochemical performance is not good.

[0004] CN113991204A discloses a short-process recycling method of waste lithium iron phosphate positive material. The method comprises the following steps: repeatedly and alternately immersing the waste lithium iron phosphate battery positive sheet material in deionized water at 25 DEG C and 90 DEG C for three times to obtain a sheet waste lithium iron phosphate material; drying the sheet waste lithium iron phosphate material, and grinding it in a ball mill for 1-3 hours to obtain a waste lithium iron phosphate material powder; placing the waste lithium iron phosphate material powder in N-methyl-2-pyrrolidone, and magnetically stirring it for 10-14 hours. After stirring, filtering to obtain black precipitate, using an organic solvent to centrifuge, washing, and drying to obtain the waste lithium iron phosphate positive material. The lithium iron phosphate positive material recycled by the method has the problems of low product purity and difficulty in being directly used as a battery-grade lithium iron phosphate.

[0005] At present, it is necessary to develop a clean and efficient recycling method of waste lithium iron phosphate positive material to improve the electrochemical performance of the recycled lithium iron phosphate. SUMMARY

[0006] In view of the problems in the prior art, the present application provides a clean recycling method for waste lithium iron phosphate positive electrode material, which is simple in operation, can obtain raw materials for synthesizing lithium iron phosphate after wet metallurgical treatment, can re-synthesize battery-grade lithium iron phosphate, and simultaneously obtains a sodium phosphate byproduct, the leaching solution can be recycled for leaching lithium iron phosphate battery positive electrode material, the whole process has no pollutant emission, and is a clean waste battery recycling method.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] The present application provides a clean recycling method for waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0009] (1) The waste lithium iron phosphate positive electrode material is pretreated to separate aluminum foil, a binder and carbon, and a mixture containing phosphorus, iron and lithium is obtained;

[0010] (2) The mixture is subjected to oxidative leaching in a sodium hydroxide solution, and the obtained mixed slurry is subjected to solid-liquid separation to obtain an iron hydroxide precipitate and a leaching solution;

[0011] (3) Sodium carbonate and the leaching solution are mixed to carry out lithium precipitation and solid-liquid separation, and lithium carbonate and a separation solution are obtained; the separation solution is crystallized and subjected to solid-liquid separation to obtain sodium phosphate crystals;

[0012] (4) The lithium carbonate of step (2), the iron hydroxide precipitate of step (3), phosphoric acid and carbon powder are mixed and calcined to obtain lithium iron phosphate.

[0013] In the present application, the lithium iron phosphate battery positive electrode material after separation of aluminum foil, a binder and carbon is subjected to oxidative leaching in a NaOH solution, Fe(II) in LiFePO4 is oxidized to Fe(III) to form Fe(OH)3 precipitate, and the equation is as follows:

[0014] LiFePO4+NaOH+O2→Fe(OH)3+Na3PO4+LiOH

[0015] The leaching solution after the reaction continues to add sodium carbonate to obtain lithium carbonate precipitate, and the reaction equation is as follows:

[0016] 2LiOH+Na2CO3=Li2CO3+2NaOH

[0017] In this way, Li and Fe in the leaching solution are separated, Na3PO4 and excess NaOH still exist in the solution, the solubility of Na3PO4 is very sensitive to temperature, and Na3PO4 crystals can be obtained by the method of crystallization by cooling, and sodium phosphate products can be obtained after purification.

[0018] The Li2CO3, Fe(OH)3 obtained by precipitation, phosphoric acid and carbon powder are mixed in a certain proportion and calcined, Fe(III) is reduced to Fe(II) by the carbon powder, and the battery-grade lithium iron phosphate is obtained.

[0019] The application realizes preparation of battery-grade lithium iron phosphate from waste lithium iron phosphate positive electrode material, and has the advantages of easy industrialization, simple operation, high purity of battery-grade lithium iron phosphate and excellent electrochemical performance.

[0020] Preferably, the pretreatment in step (1) comprises, in sequence, separation of aluminum foil by alkali leaching and ball milling treatment of the waste lithium iron phosphate positive electrode material to obtain a granular material, and separation of the binder by organic solvent soaking and separation of carbon by calcination of the granular material.

[0021] Preferably, the alkali solution for the alkali leaching in step (1) comprises a sodium hydroxide solution and / or a potassium hydroxide solution.

[0022] Preferably, the concentration of the alkali solution is 0.05-1 mol / L, for example, 0.05 mol / L, 0.16 mol / L, 0.27 mol / L, 0.37 mol / L, 0.48 mol / L, 0.58 mol / L, 0.69 mol / L, 0.79 mol / L, 0.9 mol / L or 1 mol / L, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0023] Preferably, the alkali leaching and the ball milling treatment in step (1) comprise drying.

[0024] Preferably, the temperature of the drying is 80-120℃, for example, 80℃, 85℃, 89℃, 94℃, 98℃, 103℃, 107℃, 112℃, 116℃ or 120℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0025] Preferably, the time of the drying is 2-5 h, for example, 2 h, 2.4 h, 2.7 h, 3 h, 3.4 h, 3.7 h, 4 h, 4.4 h, 4.7 h or 5 h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0026] Preferably, the ball milling treatment is followed by sieving.

[0027] Preferably, the sieving controls the particle size of the granular material to be below 15 μm.

[0028] Preferably, the organic solvent soaking is performed under ultrasonic conditions.

[0029] Preferably, the organic solvent for the organic solvent soaking includes any one or a combination of at least two of acetone, N-methyl pyrrolidone or dimethylformamide, wherein a typical but non-limiting combination is a combination of acetone and N-methyl pyrrolidone, a combination of dimethylformamide and N-methyl pyrrolidone, and a combination of acetone and dimethylformamide.

[0030] Preferably, the time for the organic solvent soaking is 1-4h, such as 1h, 1.4h, 1.7h, 2h, 2.4h, 2.7h, 3h, 3.4h, 3.7h or 4h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0031] Preferably, the temperature for the calcination in step (1) is 200-400℃, such as 200℃, 223℃, 245℃, 267℃, 289℃, 312℃, 334℃, 356℃, 378℃ or 400℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0032] Preferably, the time for the calcination is 2-5h, such as 2h, 2.4h, 2.7h, 3h, 3.4h, 3.7h, 4h, 4.4h, 4.7h or 5h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0033] Preferably, the concentration of the sodium hydroxide solution in step (2) is 10-20wt%, such as 10wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0034] It is further preferred in the present application to control the concentration of the sodium hydroxide solution in the above range, which is more conducive to improving the leaching rate, thereby improving the purity of the iron hydroxide precipitation and the purity and recovery rate of the subsequent lithium carbonate.

[0035] Preferably, the temperature for the oxidative leaching is 100-150℃, such as 100℃, 106℃, 112℃, 117℃, 123℃, 128℃, 134℃, 139℃, 145℃ or 150℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0036] Preferably, the partial pressure of oxygen in the oxidative leaching is 0.1-0.5 MPa, for example, it can be 0.1 MPa, 0.13 MPa, 0.15 MPa, 0.17 MPa, 0.19 MPa, 0.22 MPa, 0.24 MPa, 0.26 MPa, 0.28 MPa, 0.3 MPa, 0.4 MPa or 0.5 MPa, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0037] The present application further controls the partial pressure of oxygen in the oxidative leaching and the temperature in the above range, which is beneficial to improve the leaching rate and the purity of the final lithium iron phosphate product.

[0038] Preferably, the time of oxidative leaching is 60-120 min, for example, it can be 60 min, 67 min, 74 min, 80 min, 87 min, 94 min, 100 min, 107 min, 114 min or 120 min, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0039] Preferably, the solid-liquid separation is performed after the oxidative leaching and cooling.

[0040] Preferably, the temperature after cooling is 80-90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0041] Preferably, the amount of sodium carbonate added in step (3) is added according to the molar ratio of carbonate to lithium ions in the leaching solution of 1-2:1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0042] Preferably, the temperature of the mixing in step (3) is 80-95℃, for example, it can be 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, 90℃, 91℃, 92℃, 94℃ or 95℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0043] Preferably, the crystallization includes cooling crystallization.

[0044] Preferably, the end point temperature of the cooling crystallization is 30-40℃, such as 30℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0045] Preferably, the crystallization mother liquor obtained by the solid-liquid separation after the crystallization is recycled to the step (2) for the oxidative leaching after the addition of sodium hydroxide.

[0046] Preferably, the molar ratio of the lithium carbonate, the iron hydroxide precipitate, the phosphoric acid and the carbon powder in the step (4) is (0.98-1.02):(0.98-1.02):(0.98-1.02):(0.28-0.32), such as 0.98:0.98:1.00:0.28, 0.99:0.98:1.00:0.28, 1.00:0.98:1.00:0.28, 1.01:0.98:1.00:0.28, 1.02:0.98:1.00:0.28, 0.99:0.99:1.00:0.28, 0.99:1.00:1.00:0.28, 0.99:1.02:1.00:0.28, 0.99:1.02:1.02:0.32, 0.99:1.02:1.02:0.29, 0.99:1.02:1.02:0.30 or 0.99:1.02:1.02:0.31, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0047] Preferably, the carbon powder comprises any one or a combination of at least two of graphite, acetylene black, carbon black or graphene, wherein a typical but non-limiting combination is a combination of graphite and acetylene black, a combination of carbon black and acetylene black, a combination of graphite and graphene.

[0048] Preferably, the calcination comprises a three-stage calcination, i.e. a first calcination, a second calcination and a third calcination.

[0049] Preferably, the temperature of the first calcination is 280-320℃, such as 280℃, 285℃, 289℃, 294℃, 298℃, 303℃, 307℃, 312℃, 316℃ or 320℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0050] Preferably, the time of the first calcination is 1.5-3h, such as 1.5h, 1.7h, 1.9h, 2h, 2.2h, 2.4h, 2.5h, 2.7h, 2.9h or 3h, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0051] Preferably, the first calcination is performed under vacuum condition.

[0052] Preferably, the temperature of the second calcination is 420-480℃, for example, can be 420℃, 427℃, 434℃, 440℃, 447℃, 454℃, 460℃, 467℃, 474℃ or 480℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0053] Preferably, the time of the second calcination is 2-4h, for example, can be 2h, 2.3h, 2.5h, 2.7h, 2.9h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0054] Preferably, the second calcination is performed in a protective atmosphere.

[0055] Preferably, the temperature of the third calcination is 600-800℃, for example, can be 600℃, 623℃, 645℃, 667℃, 689℃, 712℃, 734℃, 756℃, 778℃ or 800℃, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0056] Preferably, the time of the third calcination is 12-36h, for example, can be 12h, 15h, 18h, 20h, 23h, 26h, 28h, 31h, 34h or 36h, etc., but not limited to the listed values, other values not listed in the range are also applicable.

[0057] Preferably, the third calcination is performed in a protective atmosphere.

[0058] Preferably, the protective atmosphere in the second and third calcination is a nitrogen atmosphere.

[0059] The present application further preferably calcines in three stages, which can prepare the lithium iron phosphate positive electrode material with suitable and uniform particle size.

[0060] Preferably, the cleaning and recycling method comprises the following steps:

[0061] (1) The waste lithium iron phosphate positive electrode material is immersed in an alkali with a concentration of 0.05-1mol / L to separate the aluminum foil, solid-liquid separation, dried at 80-120℃ for 2-5h, ball milling treatment and vibration screening to obtain a granular material with a particle size of less than 15μm; the granular material is sequentially immersed in an organic solvent under ultrasonic condition for 1-4h to separate the binder and calcined at 200-400℃ for 2-5h to separate the carbon, to obtain a mixture containing phosphorus, iron and lithium;

[0062] (2) the mixture is subjected to oxidative leaching at 100-150 DEG C for 60-120 min in a 10-20 wt% sodium hydroxide solution and under an oxygen partial pressure of 0.1-0.5 MPa, the obtained mixed slurry is cooled to 80-90 DEG C and then subjected to solid-liquid separation, thereby obtaining a ferric hydroxide precipitate and a leaching solution;

[0063] (3) sodium carbonate and the leaching solution are mixed according to a molar ratio of carbonate to lithium ions in the leaching solution of 1-2:1, lithium is precipitated and solid-liquid separation is performed, thereby obtaining lithium carbonate and a separation solution; the separation solution is subjected to cooling crystallization, the end point temperature of the cooling crystallization is 30-40 DEG C, and then solid-liquid separation is performed, thereby obtaining sodium phosphate crystals;

[0064] (4) the lithium carbonate in step (2), the ferric hydroxide precipitate in step (3), phosphoric acid and carbon powder are mixed according to a molar ratio of (0.98-1.02):(0.98-1.02):(0.98-1.02):(0.28-0.32), and are sequentially subjected to first calcination at 280-320 DEG C under vacuum for 1.5-3 h, second calcination at 420-480 DEG C in a nitrogen atmosphere for 2-4 h, and second calcination at 600-800 DEG C in a nitrogen atmosphere for 12-36 h, thereby obtaining lithium iron phosphate.

[0065] The solid-liquid separation in the above process is not specially limited, and any device and mode known to those skilled in the art that can be used for solid-liquid separation can be used, and the actual process can also be adjusted, for example, filtration, centrifugal or sedimentation separation, etc., or a combination of different modes.

[0066] The drying in the above process is also not specially limited, and any device and mode known to those skilled in the art that can be used for drying can be used, and the actual process can also be adjusted, for example, air drying, vacuum drying, oven drying or freeze drying, etc., or a combination of different modes.

[0067] The ball milling in the above process is also not specially limited, and any device and mode known to those skilled in the art that can be used for ball milling can be used, and the actual process can also be adjusted, for example, planetary ball milling, etc., or a combination of different modes.

[0068] Compared with the prior art, the present application has at least the following beneficial effects:

[0069] (1) The clean recycling method of waste lithium iron phosphate positive electrode material provided by the application can resynthesize battery-grade lithium iron phosphate, the recovery rates of lithium, phosphorus and iron are respectively above 91%, above 85% and above 91%, the purity of the intermediate product iron hydroxide precipitate is above 99.3%, the purity of lithium carbonate is above 99.9%, the purity of the final lithium iron phosphate is above 99.92%, and a sodium phosphate byproduct is obtained, the purity of the sodium phosphate byproduct is above 99.1%, and no pollutants are discharged in the whole process;

[0070] (2) The lithium iron phosphate product obtained by the clean recycling method of waste lithium iron phosphate positive electrode material provided by the application has high purity, and the particle size of the lithium iron phosphate is in the range of 5-8 mu m, the 0.5 discharge specific capacity is above 144 mAh / g, and the discharge specific capacity after 300 cycles is above 138 mAh / g, and the electrochemical performance is good;

[0071] (3) The clean recycling method of waste lithium iron phosphate positive electrode material provided by the application has high purity and high recovery rate of sodium phosphate byproduct. BRIEF DESCRIPTION OF DRAWINGS

[0072] Figure 1 is a flowchart of the clean recycling method of waste lithium iron phosphate positive electrode material provided by the embodiment 1 of the application. DETAILED DESCRIPTION

[0073] The technical solutions of the application will be further described below by specific embodiments in combination with the drawings.

[0074] The application will be further described below. However, the following examples are only simple examples of the application, and do not represent or limit the protection scope of the application, and the protection scope of the application is subject to the claims.

[0075] Embodiment 1

[0076] The embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, as shown in the figure, the clean recycling method comprises the following steps: Figure 1

[0077] (1) The material after the waste lithium iron phosphate positive electrode material is subjected to 200 r / min stirring and alkali leaching separation of aluminum foil in a sodium hydroxide solution with a concentration of 1 mol / L is filtered and washed, and then dried at 100 DEG C for 3 hours, subjected to ball milling treatment and vibration screening to obtain a granular material with a particle size below 15 mu m; the granular material is sequentially subjected to organic solvent immersion in N-methyl pyrrolidone under ultrasonic conditions (power 90 W) for 4 hours to separate the binder, and then filtered and dried, and then subjected to calcination at 300 DEG C for 4 hours to separate carbon, to obtain a mixture containing phosphorus, iron and lithium;

[0078] ​(2) the mixed slurry is obtained by oxidizing leaching the mixed material at 100°C for 60 min in a 10wt% sodium hydroxide solution under an oxygen partial pressure of 0.1 MPa, the obtained mixed slurry is cooled to 80°C and then subjected to filtration, solid-liquid separation and washing to obtain iron hydroxide precipitate and leaching solution;

[0079] (3) lithium is precipitated by mixing sodium carbonate and the leaching solution in a molar ratio of 1:1 of carbonate to lithium ions in the leaching solution, and then filtration and washing are performed to obtain lithium carbonate and separation solution; the separation solution is subjected to cooling crystallization with an end point temperature of 40°C, and then filtration is performed to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with sodium hydroxide solution and then recycled for use in the oxidizing leaching in step (2);

[0080] (4) lithium carbonate in step (2), iron hydroxide precipitate in step (3), phosphoric acid and carbon powder are mixed in a molar ratio of 0.98:1:0.98:0.3 at 80°C, and then sequentially subjected to first calcination at 300°C for 2 h under vacuum, second calcination at 450°C for 2.5 h in a nitrogen atmosphere, and third calcination at 800°C for 36 h in a nitrogen atmosphere to obtain lithium iron phosphate.

[0081] Example 2

[0082] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0083] (1) the material after the waste lithium iron phosphate positive electrode material is subjected to 240 r / min stirring and alkali leaching separation of aluminum foil in a 0.1 mol / L potassium hydroxide solution is subjected to filtration and washing, and then dried at 100°C for 3 h, ball milled and vibrated and sieved to obtain particulate material with a particle size of less than 15 μm; the particulate material is sequentially subjected to organic solvent dimethylformamide under ultrasonic conditions (power 110 W) for 2 h to separate the binder, and then subjected to filtration and drying, and then calcined at 200°C for 4.5 h to separate carbon, to obtain a mixed material containing phosphorus, iron and lithium;

[0084] (2) the mixed material is subjected to oxidizing leaching at 150°C for 120 min in a 20wt% sodium hydroxide solution under an oxygen partial pressure of 0.5 MPa, the obtained mixed slurry is cooled to 90°C and then subjected to filtration and washing to obtain iron hydroxide precipitate and leaching solution;

[0085] (3) lithium is precipitated by mixing sodium carbonate and the leaching solution in a molar ratio of 2:1 of carbonate to lithium ions in the leaching solution, and then filtration and washing are performed to obtain lithium carbonate and separation solution; the separation solution is subjected to cooling crystallization with an end point temperature of 30°C, and then filtration is performed to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with sodium hydroxide solution and then recycled for use in the oxidizing leaching in step (2);

[0086] (4) Mixing lithium carbonate of step (2), iron hydroxide precipitate of step (3), phosphoric acid and carbon powder in a molar ratio of 1.02:1:1.02:0.3 at 95℃, and sequentially performing first calcination at 300℃ for 2h under vacuum, second calcination at 450℃ for 3h in nitrogen atmosphere and third calcination at 700℃ for 24h in nitrogen atmosphere to obtain lithium iron phosphate.

[0087] Example 3

[0088] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0089] (1) Filtering and washing the material after the waste lithium iron phosphate positive electrode material is subjected to 300r / min stirring and alkali leaching separation of aluminum foil in a 0.2mol / L sodium hydroxide solution, then drying at 100℃ for 3h, ball milling and vibrating sieving to obtain a granular material with a particle size of less than 15μm; sequentially immersing the granular material in dimethylformamide under ultrasonic conditions (power 120W) for 3h to separate the binder, then filtering and drying, and then calcining at 400℃ for 2.5h to separate the carbon to obtain a mixture containing phosphorus, iron and lithium;

[0090] (2) Oxidative leaching the mixture at 120℃ for 90min in a 15wt% sodium hydroxide solution under an oxygen partial pressure of 0.3MPa, cooling the obtained mixed slurry to 85℃, and then filtering and washing to obtain an iron hydroxide precipitate and a leaching solution;

[0091] (3) Mixing sodium carbonate and the leaching solution in a molar ratio of 1.5:1 of carbonate to lithium ions in the leaching solution to precipitate lithium, and filtering and washing to obtain lithium carbonate and a separation solution; cooling crystallization of the separation solution, with the end point temperature of cooling crystallization being 35℃, and then filtering to obtain sodium phosphate crystals, and recycling the crystallization mother liquor after adding sodium hydroxide solution to be used in oxidative leaching in step (2);

[0092] (4) Mixing lithium carbonate of step (2), iron hydroxide precipitate of step (3), phosphoric acid and carbon powder in a molar ratio of 1:0.98:1:0.28 at 85℃, and sequentially performing first calcination at 320℃ for 1.5h under vacuum, second calcination at 480℃ for 2h in nitrogen atmosphere and third calcination at 650℃ for 20h in nitrogen atmosphere to obtain lithium iron phosphate.

[0093] Example 4

[0094] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0095] (1) the material after the waste lithium iron phosphate positive electrode material is stirred at 400 r / min and separated from the aluminum foil by alkali leaching in a 0.8 mol / L sodium hydroxide solution is filtered and washed, then dried at 100°C for 3 h, ball milled and vibrated and sieved to obtain a particulate material with a particle size of less than 15 μm; the particulate material is sequentially soaked in an organic solvent of acetone under ultrasonic conditions (power 80 W) for 5 h to separate the binder, then filtered and dried, and then calcined at 280°C for 4 h to separate carbon to obtain a mixture containing phosphorus, iron and lithium;

[0096] (2) the mixture is subjected to oxidative leaching at 130°C for 110 min in a 10 wt% sodium hydroxide solution under an oxygen partial pressure of 0.2 MPa, the obtained mixed slurry is cooled to 84°C, then filtered and washed to obtain a ferric hydroxide precipitate and a leaching solution;

[0097] (3) sodium carbonate and the leaching solution are mixed according to a molar ratio of carbonate to lithium ions in the leaching solution of 1.2:1 to separate lithium carbonate and a separation solution by filtration and washing; the separation solution is cooled and crystallized, the end point temperature of the cooling and crystallization is 37°C, then filtered to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with a sodium hydroxide solution and recycled for the oxidative leaching in step (2);

[0098] (4) the lithium carbonate in step (2), the ferric hydroxide precipitate in step (3), phosphoric acid and carbon powder are mixed according to a molar ratio of 1.02:1:1:0.3 at 88°C, and sequentially subjected to first calcination at 320°C under vacuum for 1.5 h, second calcination at 420°C in a nitrogen atmosphere for 4 h and third calcination at 750°C in a nitrogen atmosphere for 30 h to obtain lithium iron phosphate.

[0099] Example 5

[0100] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0101] (1) the material after the waste lithium iron phosphate positive electrode material is stirred at 350 r / min and separated from the aluminum foil by alkali leaching in a 0.9 mol / L potassium hydroxide solution is filtered and washed, then dried at 100°C for 3 h, ball milled and vibrated and sieved to obtain a particulate material with a particle size of less than 15 μm; the particulate material is sequentially soaked in an organic solvent of acetone under ultrasonic conditions (power 100 W) for 2 h to separate the binder, then filtered and dried, and then calcined at 330°C for 5 h to separate carbon to obtain a mixture containing phosphorus, iron and lithium;

[0102] (2) the mixed slurry is obtained by oxidizing leaching the mixed material at 140°C for 80 min in a 10wt% sodium hydroxide solution under an oxygen partial pressure of 0.4 MPa, and then the mixed slurry is cooled to 88°C and filtered and washed to obtain the iron hydroxide precipitate and the leaching solution;

[0103] (3) lithium is precipitated by mixing sodium carbonate and the leaching solution in a molar ratio of 1:1 of carbonate to lithium ions in the leaching solution, and then filtered and washed to obtain lithium carbonate and a separation solution; the separation solution is cooled and crystallized, the end point temperature of the cooling and crystallization is 40°C, and then filtered to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with a sodium hydroxide solution and then recycled for use in the oxidizing leaching in step (2);

[0104] (4) lithium carbonate in step (2), the iron hydroxide precipitate in step (3), phosphoric acid and carbon powder are mixed in a molar ratio of 1:1.02:1:0.32 at 90°C, and then sequentially subjected to first calcination at 280°C for 3 h under vacuum, second calcination at 420°C for 4 h in a nitrogen atmosphere, and third calcination at 780°C for 35 h in a nitrogen atmosphere to obtain lithium iron phosphate.

[0105] Example 6

[0106] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0107] (1) the material after the waste lithium iron phosphate positive electrode material is subjected to 380 r / min stirring and aluminum foil separation by alkali leaching in a 0.1 mol / L sodium hydroxide solution is filtered and washed, and then dried at 100°C for 3 h, subjected to ball milling treatment and vibration screening to obtain a particulate material with a particle size of less than 15 μm; the particulate material is sequentially subjected to organic solvent immersion in acetone under ultrasonic conditions (power 50 W) for 1.5 h to separate the binder, and then filtered and dried, and then calcined at 290°C for 2 h to separate the carbon to obtain a mixed material containing phosphorus, iron and lithium;

[0108] (2) the mixed material is subjected to oxidizing leaching at 150°C for 110 min in a 17wt% sodium hydroxide solution under an oxygen partial pressure of 0.35 MPa, the mixed slurry obtained is cooled to 83°C, and then filtered and washed to obtain the iron hydroxide precipitate and the leaching solution;

[0109] (3) lithium is precipitated by mixing sodium carbonate and the leaching solution in a molar ratio of 1.3:1 of carbonate to lithium ions in the leaching solution, and then filtered and washed to obtain lithium carbonate and a separation solution; the separation solution is cooled and crystallized, the end point temperature of the cooling and crystallization is 40°C, and then filtered to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with a sodium hydroxide solution and then recycled for use in the oxidizing leaching in step (2);

[0110] (4) mixing the lithium carbonate of step (2), the iron hydroxide precipitate of step (3), phosphoric acid and carbon powder in a molar ratio of 1:1:1:0.31 at 85℃, and sequentially performing first calcination at 300℃ for 2h under vacuum, second calcination at 450℃ for 3h in nitrogen atmosphere, and third calcination at 700℃ for 33h in nitrogen atmosphere to obtain lithium iron phosphate.

[0111] Example 7

[0112] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which comprises the following steps:

[0113] (1) filtering and washing the material after the waste lithium iron phosphate positive electrode material is subjected to 280.r / min stirring and alkali leaching separation of aluminum foil in a potassium hydroxide solution with a concentration of 0.7mol / L, then drying at 100℃ for 3h, ball milling treatment and vibration sieving to obtain a granular material with a particle size of less than 15μm; sequentially immersing the granular material in an organic solvent of acetone under ultrasonic conditions (power 150W) for 1h to separate the binder, then filtering and drying, and then calcining at 380℃ for 4h to separate carbon to obtain a mixture containing phosphorus, iron and lithium;

[0114] (2) subjecting the mixture to oxidation leaching at 120℃ for 100min in a sodium hydroxide solution with a concentration of 17wt% and an oxygen partial pressure of 0.4MPa, cooling the obtained mixed slurry to 80℃, and then filtering and washing to obtain an iron hydroxide precipitate and a leaching solution;

[0115] (3) mixing sodium carbonate and the leaching solution in a molar ratio of 1:1 to perform lithium precipitation, and filtering and washing to obtain lithium carbonate and a separation solution; the separation solution is subjected to cooling crystallization, the end point temperature of the cooling crystallization is 33℃, and then filtering to obtain sodium phosphate crystals, and the crystallization mother liquor is supplemented with a sodium hydroxide solution and then recycled for oxidation leaching in step (2);

[0116] (4) mixing the lithium carbonate of step (2), the iron hydroxide precipitate of step (3), phosphoric acid and carbon powder in a molar ratio of 1.02:0.98:1:0.3 at 95℃, and sequentially performing first calcination at 300℃ for 2h under vacuum, second calcination at 450℃ for 2h in nitrogen atmosphere, and third calcination at 750℃ for 36h in nitrogen atmosphere to obtain lithium iron phosphate.

[0117] Example 8

[0118] The present embodiment provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as that of Example 1 except that the concentration of the sodium hydroxide solution in step (2) is 25wt%.

[0119] Example 9

[0120] The present example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the concentration of sodium hydroxide solution in step (2) is 5wt%.

[0121] Example 10

[0122] The present example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the oxygen partial pressure of oxidative leaching in step (2) is 0.05 MPa.

[0123] Example 11

[0124] The present example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the oxygen partial pressure of oxidative leaching in step (2) is 0.7 MPa.

[0125] Example 12

[0126] The present example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the first calcination is not performed in step (4).

[0127] Example 13

[0128] The present example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the second calcination is not performed in step (4).

[0129] Comparative Example 1

[0130] The present comparative example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the organic solvent soaking is not performed in step (1).

[0131] Comparative Example 2

[0132] The present comparative example provides a clean recycling method of waste lithium iron phosphate positive electrode material, which is the same as example 1 except that the roasting separation of carbon is not performed in step (1).

[0133] Test method: the purity of lithium carbonate and iron oxalate dihydrate was tested by ICP method, the recovery rate of lithium and iron was calculated by the ratio of Li and Fe content in lithium carbonate and iron hydroxide product to the ratio of Li and Fe content in waste lithium iron phosphate positive electrode material; the purity of lithium iron phosphate and sodium phosphate was tested by ICP method; the recovery rate of phosphorus was calculated by the ratio of P in sodium phosphate product to P in waste lithium iron phosphate positive electrode material; the particle size of lithium iron phosphate was tested by laser particle size distribution instrument method; the electrochemical performance of lithium iron phosphate was tested by electrochemical workstation method.

[0134] The test results of the above examples and comparative examples are shown in Table 1.

[0135] Table 1

[0136]

[0137] From Table 1, the following points can be seen:

[0138] (1) From Examples 1-7, it can be seen that the clean recovery method of waste lithium iron phosphate positive electrode material provided by the present application can realize high-purity and high-efficiency recovery of waste lithium iron phosphate positive electrode material, wherein the recovery rates of lithium, phosphorus and iron are above 91%, above 85% and above 91%, respectively; the purity of the obtained iron hydroxide precipitate is above 99.3%, the purity of lithium carbonate is above 99.9%, the purity of the finally obtained lithium iron phosphate is above 99.92%, and the purity of the by-product sodium phosphate is above 99.1%, the particle size of the obtained lithium iron phosphate is in the range of 5-8 μm, and the charge-discharge performance of the product is excellent, wherein the 0.5 discharge specific capacity is above 144 mAh / g, and the discharge specific capacity after 300 cycles is above 138 mAh / g;

[0139] (2) From Examples 1 and 8-9, it can be seen that the concentration of sodium hydroxide in Example 8 is as high as 25 wt%, and the concentration of sodium hydroxide in Example 9 is only 5 wt%, wherein the recovery rates of Li, Fe and P in Example 8 are slightly higher than those in Example 1, but the discharge performance of the product is lower than that in Example 1, and the recovery rates of lithium, iron and phosphorus in Example 9 decrease significantly, which shows that by controlling the concentration of sodium hydroxide within a certain range, the present application can better ensure the recovery rate and product performance at the same time;

[0140] (3) From Examples 1 and 10-11, it can be seen that in Example 10, the acid leaching oxygen partial pressure is low, and the recovery rates of Li, Fe and P decrease, and in Example 11, the acid leaching oxygen partial pressure is too high, which does not affect the recovery rates of Li, Fe and P, but the performance of the product does not improve, and the oxygen content increases, which shows that by controlling the oxygen partial pressure, the present application can ensure the recovery rate and product performance while reducing oxygen consumption;

[0141] (4) From the comprehensive embodiment 1 and embodiments 12-13, it can be seen that the first calcination and the second calcination are not performed in embodiments 12-13 respectively, the average particle size of the lithium iron phosphate in embodiment 1 is only 5.6 μm, while the average particle sizes in embodiments 12-13 are as high as 34.6 μm and 44.5 μm respectively, and the discharge performance and the cycle performance corresponding thereto are significantly reduced, thus indicating that the performance of the lithium iron phosphate product is significantly improved by strictly controlling the calcination step of the lithium iron phosphate according to the present application;

[0142] (5) From the comprehensive embodiment 1 and comparative examples 1-2, it can be seen that the purity of the lithium carbonate, the iron hydroxide and the lithium iron phosphate is low in comparative example 2 without roasting and separating carbon, and the discharge performance and the cycle performance of the lithium iron phosphate product are poor, and the purity of the lithium carbonate, the iron hydroxide and the lithium iron phosphate is low in comparative example 1 without organic solvent soaking, and the discharge performance and the cycle performance of the lithium iron phosphate product are poor, thus indicating that the roasting and separating carbon and the organic solvent soaking steps are adopted according to the present application, which provides conditions for the subsequent sodium hydroxide leaching process, and finally improves the recovery and treatment effect.

[0143] The above embodiments are used to illustrate the detailed structural features of the present application, but the present application is not limited to the above detailed structural features, i.e. it does not mean that the present application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the selected components of the present application, addition of auxiliary components, selection of specific modes, etc. fall within the protection scope and the disclosure scope of the present application.

Claims

1. A cleaning and recycling method of waste lithium iron phosphate cathode material, characterized in that, The cleaning and recycling method comprises the following steps: (1) the waste lithium iron phosphate positive electrode material is pretreated to separate aluminum foil, binder and carbon to obtain a mixture containing phosphorus, iron and lithium; (2) the mixture is subjected to oxidative leaching in a sodium hydroxide solution with a concentration of 10-20wt%, the oxidative leaching is carried out at an oxygen partial pressure of 0.1-0.5MPa, a temperature of 100-150℃ and a time of 60-120min, and the obtained mixed slurry is subjected to solid-liquid separation to obtain iron hydroxide precipitate and leaching solution; (3) sodium carbonate and the leaching solution are mixed to carry out lithium precipitation and solid-liquid separation to obtain lithium carbonate and separation solution; the separation solution is crystallized and subjected to solid-liquid separation to obtain sodium phosphate crystals; the crystallized and solid-liquid separated mother liquor is recycled to be used in the oxidative leaching in step (2) after adding sodium hydroxide; (4) the iron hydroxide precipitate in step (2), the lithium carbonate in step (3), phosphoric acid and carbon powder are mixed and calcined, the calcination comprises three-stage calcination, i.e. first calcination, second calcination and third calcination, the first calcination is carried out at a temperature of 280-320℃, the second calcination is carried out at a temperature of 420-480℃, and the third calcination is carried out at a temperature of 600-800℃, to obtain lithium iron phosphate.

2. The cleaning recovery method according to claim 1, characterized by, The pretreatment in step (1) comprises, in sequence, alkali leaching to separate aluminum foil and ball milling treatment to obtain granular material; the granular material is sequentially subjected to organic solvent soaking to separate binder and calcination to separate carbon.

3. The cleaning recovery method according to claim 2, characterized by, The alkali solution for the alkali leaching in step (1) comprises sodium hydroxide solution and / or potassium hydroxide solution.

4. The cleaning recovery method according to claim 3, characterized by, The concentration of the alkali solution is 0.05-1mol / L.

5. The cleaning recovery method according to claim 2, wherein The alkali leaching in step (1) is followed by drying.

6. The cleaning recovery method according to claim 5, wherein The drying is carried out at a temperature of 80-120℃.

7. The cleaning recovery method according to claim 5, wherein The drying is carried out for a time of 2-5h.

8. The cleaning recovery method according to claim 2, wherein The ball milling treatment is followed by sieving.

9. The cleaning recovery method according to claim 8, wherein, The sieving controls the particle size of the granular material to be below 15μm.

10. The cleaning recovery method according to claim 2, wherein, The organic solvent soaking is carried out under ultrasonic condition.

11. The cleaning recovery method according to claim 2, wherein The organic solvent for the organic solvent soaking comprises any one or a combination of at least two of acetone, N-methyl pyrrolidone and dimethylformamide.

12. The cleaning recovery method according to claim 2, wherein, The organic solvent soaking is carried out for a time of 1-4h.

13. The cleaning recovery method according to claim 2, wherein, The calcination in step (1) is carried out at a temperature of 200-400℃.

14. The cleaning recovery method according to claim 2, wherein, The calcination is carried out for a time of 2-5h.

15. The cleaning recovery method of claim 1, wherein, The solid-liquid separation is carried out after the oxidative leaching and cooling.

16. The cleaning recovery method of claim 15, wherein, The temperature after the cooling is 80-90℃.

17. The cleaning recovery method of claim 1, wherein, The sodium carbonate is added in step (3) in a molar ratio of carbonate to lithium ions in the leaching solution of 1-2:

1.

18. The cleaning recovery method of claim 1, wherein, The mixing in step (3) is carried out at a temperature of 80-95℃.

19. The cleaning recovery method of claim 1, wherein, The crystallization comprises cooling crystallization.

20. The cleaning recovery method of claim 19, wherein, The final temperature of the cooling crystallization is 30-40℃.

21. The cleaning recovery method of claim 1, wherein, The molar ratio of lithium carbonate, iron hydroxide precipitate, phosphoric acid and carbon powder in step (4) is (0.98-1.02):(0.98-1.02):(0.98-1.02):(0.28-0.32).

22. The cleaning recovery method of claim 1, wherein, The carbon powder comprises any one or a combination of at least two of graphite, acetylene black, carbon black and graphene.

23. The cleaning recovery method of claim 1, wherein, The first calcination time is 1.5-3h.

24. The cleaning recovery method of claim 1, wherein, The first calcination is performed under vacuum condition.

25. The cleaning recovery method of claim 1, wherein, The second calcination time is 2-4h.

26. The cleaning recovery method of claim 1, wherein, The second calcination is performed in a protective atmosphere.

27. The cleaning recovery method of claim 1, wherein, The third calcination time is 12-36h.

28. The cleaning recovery method of claim 1, wherein, The third calcination is performed in a protective atmosphere.

29. The cleaning recovery method of claim 1, wherein, The protective atmosphere in the second and third calcinations is nitrogen atmosphere.

30. The cleaning recovery method of claim 1, wherein, The cleaning and recycling method comprises the following steps: (1) the waste lithium iron phosphate positive electrode material is subjected to aluminum foil separation by alkali leaching with an alkali concentration of 0.05-1mol / L, solid-liquid separation, drying at 80-120℃ for 2-5h, ball milling treatment and vibration screening, to obtain a granular material with a particle size of less than 15μm; the granular material is sequentially subjected to binder separation by organic solvent soaking under ultrasonic condition for 1-4h and carbon separation by calcination at 200-400℃ for 2-5h, to obtain a mixture containing phosphorus, iron and lithium; (2) the mixture is subjected to oxidative leaching at 100-150℃ for 60-120min under the condition of a sodium hydroxide solution with a concentration of 10-20wt% and an oxygen partial pressure of 0.1-0.5MPa, the obtained mixed slurry is cooled to 80-90℃ and then subjected to solid-liquid separation, to obtain iron hydroxide precipitate and leaching solution; (3) sodium carbonate and the leaching solution are mixed according to a molar ratio of carbonate to lithium ion in the leaching solution of 1-2:1, to perform lithium precipitation and solid-liquid separation, to obtain lithium carbonate and separation solution; the separation solution is subjected to cooling crystallization, the end point temperature of the cooling crystallization is 30-40℃, and then solid-liquid separation is performed, to obtain sodium phosphate crystal; (4) the lithium carbonate of step (2), the iron hydroxide precipitate of step (3), phosphoric acid and carbon powder are mixed according to a molar ratio of (0.98-1.02):(0.98-1.02):(0.98-1.02):(0.28-0.32), and are sequentially subjected to first calcination under vacuum condition at 280-320℃ for 1.5-3h, second calcination in a nitrogen atmosphere at 420-480℃ for 2-4h and third calcination in a nitrogen atmosphere at 600-800℃ for 12-36h, to obtain lithium iron phosphate.

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