A method for preparing lithium iron phosphate positive electrode material by using waste lithium iron phosphate battery

Abstract

The application provides a method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries, comprising the following steps: crushing the waste lithium iron phosphate batteries to obtain positive and negative electrode mixed powder, performing low-temperature alkali leaching reaction to obtain alkali leaching filtrate and residue; adding acid to the alkali leaching filtrate and residue to perform reaction, and filtering to obtain lithium-containing filtrate I and acid leaching filtrate; adding urea to the acid leaching filtrate to remove impurities, adjusting the molar ratio of phosphorus and iron, adjusting pH, and filtering to obtain lithium-containing filtrate II and ferrous phosphate filter cake; mixing the lithium-containing filtrate I and II, adding sulfide and carbonate to remove impurities, mixing with the ferrous phosphate filter cake, adding water and phosphoric acid, and performing hydrothermal reaction to obtain mixed slurry; filtering and washing the mixed slurry, mixing with water and carbon source, grinding, drying, sintering, and crushing to obtain lithium iron phosphate positive electrode material. The application directly recycles the waste lithium iron phosphate batteries into lithium iron phosphate positive electrode material, and simultaneously obtains various high-value byproducts, produces less waste, is safe and environmentally friendly, and has low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste lithium iron phosphate battery recycling, and particularly relates to a method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries. BACKGROUND

[0002] In the prior art, there are generally two processes for recycling waste lithium ion batteries. Process one: the waste lithium ion batteries are disassembled to obtain positive and negative electrode sheets, and then the positive and negative electrode sheets are crushed and sorted to obtain positive electrode powder and negative electrode powder. The positive electrode powder is dissolved and leached with acid to obtain a leaching solution, and then the leaching solution is subjected to aluminum and copper removal, and lithium carbonate and iron phosphate are sequentially extracted. Process two: the waste lithium ion batteries are directly crushed and sorted to obtain positive and negative electrode mixed powder, and then the black powder is dissolved and leached with dilute sulfuric acid to obtain a leaching solution, and then the leaching solution is subjected to aluminum and copper removal, and lithium carbonate and iron phosphate are sequentially extracted.

[0003] Among them, process one needs to disassemble the battery into positive and negative electrode sheets. At present, there is no mature automatic disassembly equipment, and manual participation is required, which has low disassembly efficiency, high cost and is difficult to be industrialized. Process two directly crushes the battery to obtain positive and negative electrode mixed powder. Although the process is simple, the copper and aluminum content in the obtained positive and negative electrode mixed powder is very high, and the subsequent impurity removal process is complex. Both processes directly use acid leaching reaction. After the aluminum is dissolved, it enters the acid leaching filtrate and is mixed with iron ions and ferrous ions, which is difficult to remove completely. Both processes sequentially extract lithium carbonate and iron phosphate, which cannot directly convert waste lithium iron phosphate batteries into lithium iron phosphate positive electrode material in the recycling stage. The traditional lithium iron phosphate production enterprises need to use the extracted lithium carbonate and iron phosphate to produce lithium iron phosphate positive electrode material, which makes the process more complex and the production cost higher. Finally, both processes will produce waste liquid and waste residue, but the further use of the waste liquid and waste residue is not involved. SUMMARY

[0004] In view of this, the application provides a method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries.

[0005] To achieve the above-mentioned purpose, the following technical solutions are adopted in the application:

[0006] A method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries, comprising the following steps:

[0007] The waste lithium iron phosphate batteries are crushed, dried, sieved and air separated to obtain positive and negative electrode mixed powder. The battery shell, copper particles and aluminum particles are also obtained, which can be directly sold.

[0008] An alkali solution is added to the positive and negative electrode mixed powder, and an alkali leaching reaction is carried out at a temperature of 0-15℃. Filtration is performed to obtain an alkali leaching filtrate and an alkali leaching residue.

[0009] adding acid liquid to the alkaline leaching filtrate to adjust the pH to 5.0-9.0, and filtering to obtain lithium-containing filtrate I;

[0010] adding water and acid liquid to the alkaline leaching residue to perform acid leaching reaction, and filtering to obtain acid leaching filtrate and acid leaching residue;

[0011] adding urea to the acid leaching filtrate, heating to 80-100℃, and stirring to react, and filtering when the pH of the reaction liquid is 2.5-4.5, and washing with water to obtain refined acid leaching filtrate;

[0012] adjusting the molar ratio of phosphorus and iron in the refined acid leaching filtrate, adding alkali to adjust the pH to 2.5-5.0, stirring, filtering, and washing with water to obtain lithium-containing filtrate II and ferrous phosphate filter cake;

[0013] mixing the lithium-containing filtrate I and lithium-containing filtrate II, adding alkali to adjust the pH to 9.0-11.0, adding sulfide and carbonate, stirring, filtering, and washing with water to obtain refined lithium-containing filtrate;

[0014] mixing the ferrous phosphate filter cake and refined lithium-containing filtrate uniformly, adding water and phosphoric acid to perform hydrothermal reaction to obtain mixed slurry;

[0015] filtering and washing the mixed slurry, mixing uniformly with water and carbon source, and grinding, drying, sintering, and crushing to obtain lithium iron phosphate positive electrode material.

[0016] Further, it further comprises detecting the pH value of the alkaline leaching filtrate before adding acid liquid thereto, and when the pH of the alkaline leaching filtrate is ≥12, recycling the alkaline leaching filtrate to alkaline leaching reaction of positive and negative electrode mixed powder, and when the pH of the alkaline leaching filtrate is <12, adding acid liquid to the alkaline leaching filtrate again.

[0017] Further, the alkali is any one of sodium hydroxide solution and potassium hydroxide solution.

[0018] Preferably, the concentration of the alkali is 0.1-2 mol / L.

[0019] The weight ratio of the positive and negative electrode mixed powder to the alkali in the alkaline leaching reaction is 1:(3-8).

[0020] Further, the acid liquid is sulfuric acid, and the amount of the acid liquid added in the acid leaching reaction is 1-1.5 times the amount of iron in the alkaline leaching residue, and the amount of water added is such that the solid-liquid ratio in the acid leaching reaction system is 1:(4-8).

[0021] Preferably, the concentration of the sulfuric acid is 30%-50%.

[0022] Further, the amount of urea added is 0.1%-3% of the weight of the acid leaching filtrate.

[0023] Further, the molar mass ratio of phosphorus to iron in the refined acid leaching filtrate after adjustment is 1:(1.5-1.55).

[0024] Preferably, the substance for adjusting phosphorus is any one of phosphoric acid, sodium phosphate, potassium phosphate, ammonium phosphate, monobasic ammonium phosphate, dibasic ammonium phosphate, and the substance for adjusting iron is ferrous sulfate.

[0025] Further, the sulfide is any one of sodium sulfide or potassium sulfide, and the amount added is 0.1%-0.5% of the weight of the mixed solution of the lithium-containing filtrate I and the lithium-containing filtrate II.

[0026] The carbonate is any one of sodium carbonate or potassium carbonate, and the amount added is 0.1%-0.5% of the weight of the mixed solution of the lithium-containing filtrate I and the lithium-containing filtrate II.

[0027] Further, the mixing amount of ferrous phosphate filter cake, refined lithium-containing filtrate and phosphoric acid in the hydrothermal reaction is determined according to the molar ratio of Fe, P and Li = (0.95-1):1:(1-1.05).

[0028] The hydrothermal reaction parameters are: pressure 1-4 MPa, temperature 180-250℃, and time 4-12 h.

[0029] Further, the carbon source is any one of glucose or sucrose, and the amount added is to ensure that the carbon content of the finished product is between 1.3% and 1.8%.

[0030] Preferably, the grinding endpoint is that the D50 of the slurry is between 300 nm and 600 nm.

[0031] The sintering parameters are: sintering at 700-800℃ for 5-15 h under nitrogen protection.

[0032] The pulverization requirement is that the D50 of the product is between 0.6 μm and 2.2 μm.

[0033] Further, it also includes washing the alkali leaching residue with an alkali solution before adding water and acid to the alkali leaching residue for acid leaching reaction, and recycling the obtained washing liquid for washing the alkali leaching residue in the next alkali leaching reaction, and the washing liquid is recycled for 5-10 times and then reused in the alkali leaching reaction of the positive and negative electrode mixed powder.

[0034] The acid leaching reaction also obtains acid leaching residue, which is soaked in 20-40% dilute nitric acid for 1-3 h, filtered, washed with water, dried, and graphitized to obtain artificial graphite negative electrode.

[0035] When the lithium-containing filtrate I is obtained, aluminum-containing residue is also obtained, which is washed with water until the conductivity is 0.2-0.8 ms / cm, and then dried, pulverized, high-temperature calcined, and secondarily pulverized to obtain pure alumina powder.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] (1) The impurity content requirement of the battery powder is not high, the waste lithium iron phosphate battery can be directly crushed and sorted to obtain the battery powder, the process is simple, efficient, low in cost and easy to industrialize.

[0038] (2) The aluminum is removed by low-temperature leaching with alkali solution before acid leaching, which avoids the entry of aluminum ions into the acid leaching filtrate in the acid leaching process and avoids the mixing of aluminum ions with iron ions and ferrous ions, which is difficult to remove completely; at the same time, low-temperature leaching is adopted, which can ensure that the aluminum impurities in the product are completely removed while reducing the dissolution of lithium ions in the alkali solution.

[0039] However, the conventional process uses pH adjustment and fluoride to remove aluminum, but due to the presence of a large amount of iron ions and ferrous ions in the solution, the pH cannot be adjusted too high, otherwise the iron loss will be too large, which will result in incomplete removal of aluminum ions.

[0040] (3) The alkali leaching filtrate after alkali leaching is reused to improve the utilization rate of alkali and reduce the cost; at the same time, the aluminum in the alkali leaching filtrate is extracted to prepare pure alumina powder for recycling; the lithium-containing filtrate I after aluminum extraction contains a small amount of lithium ions, which is reused in the subsequent process, so that the entire aluminum removal process does not produce any solid waste or hazardous waste, which is safe, environmentally friendly and low in cost.

[0041] (4) Urea is used as a decontamination agent, and NH3 and CO2 are generated by hydrolysis of urea when heated to adjust the pH, which ensures the slow increase of the pH of the acid leaching filtrate and avoids the local pH from being too high due to the instantaneous addition of liquid alkali, ammonia and other pH adjusting agents; at the same time, the problem of hydrogen generation caused by adjusting the pH with iron powder is also avoided.

[0042] (5) After the impurities in the acid leaching filtrate are removed, alkali is directly added to the refined acid leaching filtrate to precipitate ferrous phosphate, without using hydrogen peroxide, and the iron in the ferrous phosphate is divalent, which is consistent with the iron valence in the finished product lithium iron phosphate, which is beneficial to the hydrothermal synthesis of lithium iron phosphate.

[0043] (6) When the mixed solution of lithium-containing filtrate I and lithium-containing filtrate II is decontaminated, the pH is directly adjusted to 9-11, which can completely remove the heavy metal ions and calcium and magnesium ions in the lithium-containing filtrate at one time, and there is no loss of lithium.

[0044] (7) The ferrous phosphate obtained in the previous process and the refined lithium-containing filtrate are used as raw materials, an appropriate amount of phosphorus source is added, and lithium iron phosphate is directly synthesized by hydrothermal method under high temperature and high pressure, which saves the process of synthesizing iron phosphate and lithium carbonate, and directly realizes the conversion from waste lithium iron phosphate battery to lithium iron phosphate cathode material. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1Process flow chart for the technical solution of the present application;

[0046] Figure 2 XRD pattern of the lithium iron phosphate positive electrode material provided in Embodiment 1 of the present application;

[0047] Figure 3 SEM pattern of the lithium iron phosphate positive electrode material provided in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0048] The present application will be further described in detail below in combination with specific embodiments, so that those skilled in the art can more clearly understand the present application.

[0049] Source of key test materials and physicochemical parameters:

[0050] The waste lithium iron phosphate battery is from a domestic main machine factory, and its main component composition is as follows:

[0051] Table 1: Composition of waste lithium iron phosphate battery

[0052] Component Positive electrode Negative electrode Binder Separator Electrolyte Aluminum foil Copper foil Steel can Content 33-35％ 18-20％ 1.3-1.5％ 1.5-1.9％ 11-13％ 6-7％ 3-4％ 20-24％

[0053] Table 2: Main component composition of positive and negative electrode mixed powder

[0054] Component Li Fe P Al Cu C Content 2.5％-3.0％ 20％-24％ 11％-13.5％ 0.5％-2.5％ 0.3％-2％ 30％-40％

[0055] In the present application, the specific raw materials are not described, which are already existing substances and can be directly purchased from the market.

[0056] Embodiment 1

[0057] The present embodiment provides a method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate battery, comprising the following steps:

[0058] S1, the waste lithium iron phosphate battery is crushed, dried, sieved and air separated to obtain positive and negative electrode mixed powder, battery shell, diaphragm, copper particles and aluminum particles; the battery shell, copper particles and aluminum particles can be directly sold, and the positive and negative electrode mixed powder enters the subsequent process, the positive and negative electrode mixed powder contains 1% of aluminum and 1% of copper.

[0059] S2, sodium hydroxide solution with a mass of 5 times the mass of the positive and negative electrode mixed powder and a concentration of 1 mol / L is added to the positive and negative electrode mixed powder, cooled to 10 DEG C and kept for 2 hours, filtered, and the alkali leaching filtrate and alkali leaching residue are obtained.

[0060] In addition, the alkali leaching residue is washed with 1 mol / L sodium hydroxide solution, the washed sodium hydroxide solution is recycled for washing of the alkali leaching residue of the next batch, and after 7 cycles, is reused for the alkali leaching reaction of the positive and negative mixed powder; for the alkali leaching filtrate, after each filtration, the pH is detected, and when the pH is greater than or equal to 12, the alkali leaching filtrate is reused for the alkali leaching reaction of the positive and negative mixed powder.

[0061] S3, when the pH of the alkali leaching filtrate in step S2 is less than 12, 40% dilute sulfuric acid is added to adjust the pH to 7.0, and filtration is performed to obtain a lithium-containing filtrate I and an aluminum-containing filter residue.

[0062] In addition, the obtained aluminum-containing filter residue is washed with pure water until the conductivity of the rinsing water is 0.5 ms / cm, and then is dried, crushed, calcined at high temperature, and air-flow crushed to obtain pure aluminum oxide powder.

[0063] S4, 1.2 times the amount of iron in the alkali leaching residue obtained in step S2, 40% dilute sulfuric acid is added to the alkali leaching residue, and water is added to make the solid-liquid ratio of the mixed solution 1:5, and stirring is performed for 2 hours, filtration is performed to obtain an acid leaching filtrate and an acid leaching residue.

[0064] In addition, the obtained acid leaching residue is soaked in 30% dilute nitric acid for 2 hours, filtered, washed with water, dried, and graphitized to obtain artificial graphite negative electrodes.

[0065] S5, 0.5% of the urea of the mass of the acid leaching filtrate obtained in step S4 is added to the acid leaching filtrate, heated to 90°C, and stirring is performed, when the pH of the reaction solution is 2.5, filtration is performed, and the refined acid leaching filtrate is obtained.

[0066] S6, the refined acid leaching filtrate obtained in step S5 is added with ferrous sulfate and stirred uniformly, so that the molar ratio of phosphorus and iron is 1:1.52; 1 mol / L sodium hydroxide solution is slowly added dropwise until the pH is 4.0, and stirring is continued for 60 minutes, filtration is performed, and the ferrous phosphate filter cake and the lithium-containing filtrate II are obtained.

[0067] S7, the lithium-containing filtrate I obtained in step S3 and the lithium-containing filtrate II obtained in step S6 are mixed uniformly, 1 mol / L sodium hydroxide solution is added until the pH is 10.0, 0.3% of sodium sulfide and 0.3% of sodium carbonate of the weight of the mixed solution are added, stirring is performed for 60 minutes, filtration is performed, and the refined lithium-containing filtrate is obtained.

[0068] S8, the ferrous phosphate filter cake obtained in step S6 and the refined lithium-containing filtrate obtained in step S7 are mixed uniformly, water and phosphoric acid are added, nitrogen is introduced into a high-pressure reaction kettle for protection, the pressure is set to 2.3 MPa, the temperature is set to 220°C, and hydrothermal reaction is performed for 8 hours to obtain a mixed slurry.

[0069] The mixture amount of the ferrous phosphate filter cake and the refined lithium-containing filtrate and the phosphoric acid addition amount are determined according to the molar ratio of Fe, P and Li being 0.98:1:1.02.

[0070] S9, filtering the mixed slurry obtained in step S8, and washing the filter cake with pure water to obtain a lithium iron phosphate precursor, and then adding pure water and glucose, uniformly stirring, and then sequentially performing grinding, drying, sintering and crushing to obtain a lithium iron phosphate positive electrode material.

[0071] The addition amount of the glucose is determined according to the carbon content of the finished product being 1.5%; the grinding end point is that the slurry D50 is 450 nm; the sintering parameters are sintering at 750 DEG C for 10 h under nitrogen protection; and the crushing requirement is that the product D50 is 1.2 μm.

[0072] Example 2

[0073] The embodiment provides a method for preparing a lithium iron phosphate positive electrode material by using waste lithium iron phosphate batteries, and the method and steps are basically the same as those of example 1, and the difference lies in that the positive and negative electrode mixed powder obtained in step S1 contains 2% of aluminum and 2% of copper.

[0074] Example 3

[0075] The embodiment provides a method for preparing a lithium iron phosphate positive electrode material by using waste lithium iron phosphate batteries, and the method and steps are basically the same as those of example 1, and the difference lies in that the positive and negative electrode mixed powder obtained in step S1 contains 2% of aluminum and 2% of copper.

[0076] S1, crushing, drying, screening and winnowing the waste lithium iron phosphate batteries to obtain positive and negative electrode mixed powder, battery shell, diaphragm, copper particles and aluminum particles; the battery shell, copper particles and aluminum particles can be directly sold, and the positive and negative electrode mixed powder enters the subsequent process, and the positive and negative electrode mixed powder contains 1% of aluminum and 1% of copper.

[0077] S2, adding a sodium hydroxide solution with a mass of 5 times the mass of the positive and negative electrode mixed powder and a concentration of 1 mol / L to the positive and negative electrode mixed powder, cooling to 5 DEG C and keeping the temperature, stirring for 2 h, filtering to obtain an alkali leaching filtrate and an alkali leaching residue.

[0078] In addition, the alkali leaching residue is washed with a 1 mol / L sodium hydroxide solution, the washed sodium hydroxide solution is recycled for washing of the alkali leaching residue of the next batch, and after 7 cycles, the sodium hydroxide solution is reused for the alkali leaching reaction of the positive and negative electrode mixed powder; for the alkali leaching filtrate, the pH is detected after each filtration, and when the pH is greater than or equal to 12, the alkali leaching filtrate is reused for the alkali leaching reaction of the positive and negative electrode mixed powder.

[0079] S3, when the pH of the alkali leaching filtrate in step S2 is less than 12, 40% dilute sulfuric acid is added to adjust the pH to 5.0, and filtering to obtain a lithium-containing filtrate I and an aluminum-containing residue.

[0080] Further, the obtained aluminum-containing filter residue is washed with pure water until the rinsing water conductivity is 0.5 ms / cm, and then is dried, crushed, high-temperature calcined, and airflow crushed to obtain pure alumina powder.

[0081] S4, 1.05 times of the amount of iron in the alkali leaching filter residue obtained in step S2, dilute sulfuric acid with a concentration of 40% is added to the alkali leaching filter residue, and water is added so that the solid-liquid ratio in the mixed slurry is 1:5, stirring and reacting for 2 h, filtering to obtain an acid leaching filtrate and an acid leaching filter residue.

[0082] Further, the obtained acid leaching residue is soaked with 30% dilute nitric acid for 2 h, filtered, washed with water, dried, and graphitized to obtain an artificial graphite negative electrode.

[0083] S5, 1% of the mass of the acid leaching filtrate obtained in step S4 is added to the acid leaching filtrate, heated to 80°C, and stirred and reacted, and when the pH of the reaction solution is 3.0, filtering and washing with water to obtain a refined acid leaching filtrate.

[0084] S6, ferrous sulfate is added to the refined acid leaching filtrate obtained in step S5 and stirred uniformly so that the molar ratio of phosphorus to iron is 1:1.52; 1 mol / L sodium hydroxide solution is slowly added dropwise until the pH is 3.0, and stirring is continued for 60 min, filtering and washing with water to obtain a ferrous phosphate filter cake and a lithium-containing filtrate II.

[0085] S7, the lithium-containing filtrate I obtained in step S3 and the lithium-containing filtrate II obtained in step S6 are mixed uniformly, 1 mol / L sodium hydroxide solution is added until the pH is 9.0, 0.1% of sodium sulfide by weight of the mixed solution and 0.1% of sodium carbonate by weight of the mixed solution are added, stirring for 60 min, filtering and washing with water to obtain a refined lithium-containing filtrate.

[0086] S8, the ferrous phosphate filter cake obtained in step S6 and the refined lithium-containing filtrate obtained in step S7 are mixed uniformly, water and phosphoric acid are added, nitrogen gas is introduced into a high-pressure reaction kettle for protection, the pressure is set to 4 MPa, the temperature is set to 250°C, and hydrothermal reaction is carried out for 6 h to obtain a mixed slurry.

[0087] The mixing amount of the ferrous phosphate filter cake and the refined lithium-containing filtrate and the addition amount of phosphoric acid are determined according to the molar ratio of Fe, P, and Li being 0.98:1:1.02.

[0088] S9, the mixed slurry obtained in step S8 is filtered, and the filter cake is washed with pure water to obtain a lithium iron phosphate precursor, and then pure water and glucose are added, stirred uniformly, and then ground, dried, sintered, and crushed in sequence to obtain a lithium iron phosphate positive electrode material.

[0089] The addition amount of glucose is to ensure that the carbon content of the finished product is 1.35%; the grinding endpoint is that the slurry D50 is 350 nm; the sintering parameters are sintering at 780°C for 14 h under nitrogen protection; and the crushing requirement is that the product D50 is 0.8 μm.

[0090] Embodiment 4

[0091] The embodiment provides a method for preparing lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries, comprising the following steps:

[0092] S1, crushing, drying, screening and winnowing the waste lithium iron phosphate batteries to obtain positive and negative electrode mixed powder, battery shell, diaphragm, copper particles and aluminum particles; wherein the battery shell, copper particles and aluminum particles can be directly sold, and the positive and negative electrode mixed powder enters the subsequent process, and the positive and negative electrode mixed powder contains 1% of aluminum and 1% of copper.

[0093] S2, adding sodium hydroxide solution with a mass of 5 times that of the positive and negative electrode mixed powder and a concentration of 1 mol / L to the positive and negative electrode mixed powder, cooling to 15°C for preservation, stirring for 2 hours of reaction, and filtering to obtain alkali leaching filtrate and alkali leaching residue.

[0094] In addition, the alkali leaching residue is washed with 1 mol / L sodium hydroxide solution, and the washed sodium hydroxide solution is recycled for washing of the alkali leaching residue of the next batch; after 7 cycles, the sodium hydroxide solution is reused for the alkali leaching reaction of the positive and negative electrode mixed powder; for the alkali leaching filtrate, the pH is detected after each filtration, and when the pH is greater than or equal to 12, the alkali leaching filtrate is reused for the alkali leaching reaction of the positive and negative electrode mixed powder.

[0095] S3, when the pH of the alkali leaching filtrate in step S2 is less than 12, 40% dilute sulfuric acid is added to adjust the pH to 9.0, and then filtered to obtain lithium-containing filtrate I and aluminum-containing residue.

[0096] In addition, the obtained aluminum-containing residue is washed with pure water until the conductivity of the rinsing water is 0.5 ms / cm, and then dried, crushed, high-temperature calcined and air-flow crushed to obtain pure aluminum oxide powder.

[0097] S4, 1.05 times the mass of iron in the alkali leaching residue obtained in step S2 and 40% dilute sulfuric acid are added to the alkali leaching residue, and water is added to make the solid-liquid ratio of the mixed solution 1:5, and then stirred for 2 hours of reaction and filtered to obtain acid leaching filtrate and acid leaching residue.

[0098] In addition, the obtained acid leaching residue is soaked in 30% dilute nitric acid for 2 hours, filtered, washed with water, dried and graphitized to obtain artificial graphite negative electrode.

[0099] S5, 1.5% of urea of the mass of the acid leaching filtrate obtained in step S4 is added to the acid leaching filtrate, heated to 95°C for stirring reaction, and when the pH of the reaction solution is 3.5, filtered and washed with water to obtain refined acid leaching filtrate.

[0100] S6, add ferrous sulfate to the refined acid leaching filtrate obtained in step S5 and stir until the molar ratio of phosphorus to iron is 1:1.52; then slowly add 1 mol / L sodium hydroxide solution until the pH is 4.5, continue stirring for 60 min, filter and wash with water to obtain ferrous phosphate filter cake and lithium-containing filtrate II.

[0101] S7, mix the lithium-containing filtrate I obtained in step S3 and the lithium-containing filtrate II obtained in step S6, add 1 mol / L sodium hydroxide solution until the pH is 11.0, then add 0.5% by weight of sodium sulfide and 0.5% by weight of sodium carbonate based on the weight of the mixture, stir for 60 min, filter and wash with water to obtain a refined lithium-containing filtrate.

[0102] S8, mix the ferrous phosphate filter cake obtained in step S6 and the refined lithium-containing filtrate obtained in step S7, add water and phosphoric acid, and then introduce nitrogen into a high-pressure reaction kettle to protect it, set the pressure to 1 MPa and the temperature to 180°C, and carry out hydrothermal reaction for 10 h to obtain a mixed slurry.

[0103] The mixing amount of the ferrous phosphate filter cake and the refined lithium-containing filtrate and the amount of phosphoric acid added are determined according to the molar ratio of Fe, P and Li being 0.98:1:1.02.

[0104] S9, filter the mixed slurry obtained in step S8, wash the filter cake with pure water to obtain a lithium iron phosphate precursor, then add pure water and glucose, stir until uniform, and then grind, dry, sinter and crush in sequence to obtain a lithium iron phosphate positive electrode material.

[0105] The amount of glucose added is to ensure that the carbon content of the finished product is 1.75%; the grinding endpoint is a slurry D50 of 550 nm; the sintering parameters are sintering at 720°C for 6 h under nitrogen protection; and the crushing requirements are a product D50 of 2 μm.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a lithium iron phosphate positive electrode material using waste lithium iron phosphate batteries, which differs from Example 1 in that steps S2, S3 and S4 are omitted, and the obtained positive and negative electrode mixture powder is directly subjected to acid leaching reaction, and then the acid leaching filtrate is subjected to subsequent steps in sequence.

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing a lithium iron phosphate positive electrode material using waste lithium iron phosphate batteries, which differs from Example 1 in that the step of adding urea to remove impurities in step S5 is omitted, and the step of adding sulfide and carbonate to remove impurities in step S7 is omitted.

[0110] Comparative Example 3

[0111] The comparative example provides a method for preparing lithium iron phosphate positive electrode material by using waste lithium iron phosphate battery, and the difference from example 1 is that the pressure in step S8 is 0.2 MPa and the temperature is 120 DEG C.

[0112] The properties of the lithium iron phosphate positive electrode materials obtained in examples 1-4 and comparative examples 1-3 are detected, and the results are shown in the following table:

[0113] Table 2 Properties of lithium iron phosphate positive electrode materials obtained in examples 1-4 and comparative examples 1-3

[0114]

[0115]

[0116] From the results in table 2, it can be seen that the lithium iron phosphate positive electrode material prepared by the scheme of the present application meets the standard "GB / T 30835-2014 Carbon Composite Lithium Iron Phosphate Positive Electrode Material for Lithium Ion Battery", has good comprehensive performance, and meets the needs of industrial production.

[0117] The above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a lithium iron phosphate cathode material using waste lithium iron phosphate batteries, characterized in that, The method comprises the following steps: The waste lithium iron phosphate battery is crushed, dried, screened and air-separated to obtain positive and negative electrode mixed powder; An alkali solution is added to the positive and negative electrode mixed powder, and an alkali leaching reaction is performed at a temperature of 0-15 DEG C, and then filtration is performed to obtain alkali leaching filtrate and alkali leaching residue; An acid solution is added to the alkali leaching filtrate, and the pH is adjusted to 5.0-9.0, and then filtration is performed to obtain lithium-containing filtrate I and aluminum-containing residue; The alkali leaching residue is added with water and an acid solution, and an acid leaching reaction is performed, and then filtration is performed to obtain acid leaching filtrate and acid leaching residue; Urea is added to the acid leaching filtrate, and the reaction is stirred and heated to 80-100 DEG C, and then filtration is performed when the pH of the reaction solution is 2.5-4.5, and then water washing is performed to obtain refined acid leaching filtrate; The molar ratio of phosphorus and iron in the refined acid leaching filtrate is adjusted, an alkali solution is added to adjust the pH to 2.5-5.0, and then stirring and filtration are performed, and then water washing is performed to obtain lithium-containing filtrate II and ferrous phosphate filter cake; The lithium-containing filtrate I and the lithium-containing filtrate II are mixed, an alkali solution is added to adjust the pH to 9.0-11.0, and then sulfide and carbonate are added, and then stirring and filtration are performed, and then water washing is performed to remove heavy metal ions and calcium and magnesium ions to obtain refined lithium-containing filtrate; The ferrous phosphate filter cake and the refined lithium-containing filtrate are uniformly mixed, water and phosphoric acid are added, and then hydrothermal reaction is performed to obtain mixed slurry; The mixed slurry is filtered and washed, and then water and a carbon source are added and uniformly mixed, and then grinding, drying, sintering and crushing are performed to obtain lithium iron phosphate positive electrode material.

2. The method of claim 1, wherein, Before the acid solution is added to the alkali leaching filtrate, the pH value thereof is detected, when the pH of the alkali leaching filtrate is greater than or equal to 12, the alkali leaching filtrate is recycled to the alkali leaching reaction of the positive and negative electrode mixed powder, and when the pH of the alkali leaching filtrate is less than 12, the acid solution is further added to the alkali leaching filtrate.

3. The method according to claim 1 or 2, characterized in that, The alkali solution is any one of sodium hydroxide solution and potassium hydroxide solution.

4. The method according to claim 1 or 2, characterized in that, The acid solution is sulfuric acid, the amount of the acid solution added in the acid leaching reaction is 1-1.5 times the amount of iron in the alkali leaching residue, and the amount of water added is such that the solid-liquid ratio in the acid leaching reaction system is 1: (4-8).

5. The method according to claim 1 or 2, characterized in that, The amount of the urea added is 0.1%-3% of the weight of the acid leaching filtrate.

6. The method of claim 1 or 2, wherein, After the adjustment, the molar mass ratio of phosphorus and iron in the refined acid leaching filtrate is 1: (1.5-1.55).

7. The method according to claim 1 or 2, characterized in that, The sulfide is any one of sodium sulfide and potassium sulfide, and the amount thereof added is 0.1%-0.5% of the weight of the mixed solution of the lithium-containing filtrate I and the lithium-containing filtrate II. The carbonate is any one of sodium carbonate and potassium carbonate, and the amount thereof added is 0.1%-0.5% of the weight of the mixed solution of the lithium-containing filtrate I and the lithium-containing filtrate II.

8. The method of claim 1 or 2, wherein, In the hydrothermal reaction, the amounts of the ferrous phosphate filter cake, the refined lithium-containing filtrate and the phosphoric acid are determined according to the molar ratio of Fe, P and Li = (0.95-1):1:(1-1.05). The hydrothermal reaction parameters are as follows: pressure, 1-4 MPa; temperature, 180-250 DEG C; and time, 4-12 h.

9. The method of claim 1 or 2, wherein, The carbon source is any one of glucose and sucrose, and the amount thereof added is such that the carbon content in the finished product is 1.3%-1.8%.

10. The method of claim 1, wherein, Before the water and the acid solution are added to the alkali leaching residue for acid leaching reaction, the alkali leaching residue is washed with an alkali solution, and the obtained washing solution is recycled for washing of the alkali leaching residue in the next alkali leaching reaction, and the washing solution is recycled for 5-10 times, and then recycled to the alkali leaching reaction of the positive and negative electrode mixed powder. The acid leaching reaction also obtains acid leaching residue, the acid leaching residue is soaked with 20-40% dilute nitric acid for 1-3 hours, then filtered, washed with water, dried and graphitized to obtain artificial graphite negative electrode; When the lithium-containing filtrate I is obtained, the aluminum-containing residue is also obtained, the aluminum-containing residue is washed with water until the conductivity is 0.2-0.8 ms / cm, then dried, crushed, high-temperature calcined, and secondarily crushed to obtain pure aluminum oxide powder.

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