Recycling method for positive and negative electrode powder of waste lithium iron phosphate battery

Abstract

The invention belongs to the technical field of comprehensive recycling of waste lithium batteries, and particularly relates to a waste lithium iron phosphate battery positive and negative electrode powder recycling method which comprises the following steps: performing heat treatment on waste lithium iron phosphate battery positive and negative electrode powder in an inert atmosphere, and then adding water for pulping; adding sulfuric acid for acid leaching, and filtering to obtain graphite slag and a solution containing lithium, iron and phosphorus; adding an oxidizing agent and alkali liquor into the solution containing lithium, iron and phosphorus to carry out oxidation neutralization reaction, and filtering to obtain precipitates containing iron and phosphorus and a solution containing lithium; adding a precipitator into the lithium-containing solution, and filtering to obtain a lithium salt precipitate; adding water into the iron and phosphorus precipitates, pulping, and adding sulfuric acid to obtain an iron and phosphorus-containing solution; then slowly adding ammonia water to adjust the pH value, and filtering to obtain iron phosphate dihydrate; and carrying out high-temperature heat treatment on the iron phosphate dihydrate to obtain the anhydrous iron phosphate. According to the method, the lithium salt and the iron phosphate can be recovered from the positive and negative electrode powder of the lithium iron phosphate battery, and all-element recovery of the lithium iron phosphate waste is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive recycling and utilization of waste lithium batteries, and particularly relates to a method for recycling and reusing the positive and negative powder materials of waste lithium iron phosphate batteries. Background Art

[0002] In recent years, with the continuous improvement of the energy density of lithium iron phosphate batteries, as well as excellent cycle performance and safety performance, the installed capacity of lithium iron phosphate batteries in new energy vehicle power batteries has reached more than 70%. In addition to new energy vehicles, the application rate of lithium iron phosphate batteries in energy storage systems, consumer electronics and other fields is increasing day by day, and the market share of lithium iron phosphate batteries is expected to further increase. According to data analysis, the number of retired power batteries will be about 650,000 tons in 2024. The China Automotive Engineering Society predicts that the retired power batteries in China will reach 3.5 million tons by 2030, and the market scale of power battery recycling will exceed 100 billion yuan. Waste lithium iron phosphate batteries contain a large number of valuable elements such as Li, Fe, P, etc., as well as substances that are harmful to the environment and human body, such as lithium hexafluorophosphate (which is prone to decomposition when exposed to water to produce HF), organic carbonates, etc. If these waste lithium ion batteries are directly landfilled, it will not only cause waste of resources and serious environmental pollution, but also pose a threat to human health. Therefore, the recycling of lithium iron phosphate batteries is necessary, which not only effectively promotes energy conservation and emission reduction, but also is a key link to help the energy industry promote sustainable development.

[0003] At present, the treatment processes of lithium iron phosphate waste mainly include two categories: pyrometallurgical processes and hydrometallurgical processes. The pyrometallurgical process has a simple recycling process, but it is difficult to control the quality of the recycled products. Moreover, due to energy consumption and environmental pollution problems, the market competitiveness of pyrometallurgical recycled products is relatively weak. The hydrometallurgical process usually converts lithium iron phosphate waste into industrial raw materials such as lithium carbonate, lithium phosphate, iron phosphate, and iron hydroxide through value-added conversion. However, there are problems of difficult separation of impurities in the recycling process. If high-purity recycled products are to be achieved, additional impurity removal processes need to be added, increasing the cost. For example, Chinese Patent No. CN119118083A discloses a method for preparing battery-grade iron phosphate and lithium carbonate from waste cathode materials. The purity of the battery-grade iron phosphate and battery-grade lithium carbonate obtained by this technical solution both reach more than 99.6%. However, a variety of impurity removal agents are used in the recycling process for impurity removal, such as extractants for removing Cu, ammonium sulfate for removing Al, lime for removing iron, phosphorus, silicon, etc. The process flow is complex and the recycling cost is high.

[0004] Therefore, there is an urgent need in this field to propose an effective method for recycling and reusing the positive and negative powder materials of waste lithium iron phosphate batteries to achieve large-scale industrial application. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for recycling and reusing the positive and negative powder materials of waste lithium iron phosphate batteries.

[0006] Specifically, the present invention is achieved through the following technical solutions:

[0007] A method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, comprising:

[0008] (1) Heat-treating the positive and negative powder materials of waste lithium iron phosphate batteries under an inert atmosphere;

[0009] (2) Adding water to make a slurry in the heat-treated positive and negative powder materials of waste lithium iron phosphate batteries, then adding sulfuric acid for acid leaching, and filtering to obtain graphite slag and a solution containing lithium, iron, and phosphorus;

[0010] (3) Adding an oxidant and an alkali solution to the solution containing lithium, iron, and phosphorus for an oxidation and neutralization reaction, and filtering to obtain an iron and phosphorus precipitate and a lithium-containing solution;

[0011] (4) Adding a precipitant to the lithium-containing solution, and filtering to obtain a lithium salt precipitate;

[0012] (5) Adding water to make a slurry in the iron and phosphorus precipitate, then adding sulfuric acid to obtain a solution containing iron and phosphorus; then slowly adding ammonia water to adjust the pH, and filtering to obtain iron phosphate dihydrate;

[0013] (6) Performing high-temperature heat treatment on the iron phosphate dihydrate to obtain anhydrous iron phosphate.

[0014] In the above method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, in step (1), the temperature of the heat treatment is 500°C - 700°C, and the duration is 2 - 4 h.

[0015] In the above method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, in step (2), the sulfuric acid is concentrated sulfuric acid with a mass fraction of 92.5% - 98.3%, and the molar ratio of the sulfuric acid to lithium in the positive and negative powder materials of waste lithium iron phosphate batteries is 3:2 - 4:2.

[0016] In the above method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, in step (2), the temperature of the acid leaching is 70°C - 90°C, and the duration is 2 - 4 h.

[0017] In the above method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, in step (3), the oxidant is one of hydrogen peroxide, oxygen, air, and ozone; the alkali solution is one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0018] In the above method for recycling the positive and negative powder materials of waste lithium iron phosphate batteries, in step (3), the temperature of the oxidation and neutralization reaction is room temperature, the precipitation pH is 2.0 - 3.0, and the reaction duration is 0.5 - 1 h.

[0019] In the method for recycling the cathode and anode powder materials of waste lithium iron phosphate batteries described above, in step (4), the precipitating agent includes sodium carbonate or sodium phosphate.

[0020] In the method for recycling the cathode and anode powder materials of waste lithium iron phosphate batteries described above, in step (5), the mass ratio of the iron- and phosphorus-containing precipitate dry material to sulfuric acid is 1:0.50 - 1:0.65, and the mass ratio to ammonia water is 1:0.63 - 1:1.

[0021] In the method for recycling the cathode and anode powder materials of waste lithium iron phosphate batteries described above, in step (5), ammonia water is slowly added to adjust the pH to 1.5 - 2.4, and the reaction is carried out at a temperature of 40°C - 60°C for 0.5 - 2 h.

[0022] In the method for recycling the cathode and anode powder materials of waste lithium iron phosphate batteries described above, in step (6), the temperature for high-temperature heat treatment of the iron phosphate dihydrate is 500°C - 700°C, and the duration is 1 - 3 h.

[0023] The technical solution of the present invention has the following beneficial effects:

[0024] (1) The method of the present invention can recover lithium salts and iron phosphate from the cathode and anode powder materials of lithium iron phosphate batteries, realizing the full-element recovery of lithium iron phosphate waste.

[0025] (2) The method of the present invention has a recovery rate of lithium, iron, and phosphorus all higher than 95%. Without adding additional impurity removal agents and with few auxiliary materials, the recovery preparation of valuable elements is achieved by regulating the pH value, further reducing the production cost, and having the advantages of simple operation, simple process, and high purity of the recovered products. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to limit the present invention.

[0027] Figure 1 It is a process flow chart of the method for recycling the cathode and anode powder materials of waste lithium iron phosphate batteries of the present invention.

[0028] Figure 2 It is an SEM photograph of the anhydrous iron phosphate prepared in Example 1 at a magnification of 4000X.

[0029] Figure 3 It is an XRD pattern of the anhydrous iron phosphate prepared in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments. Except for the following content, the process methods of the present invention all adopt conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0031] When a numerical range is disclosed herein, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0032] Specifically, a method for recycling the positive and negative electrode powders of waste lithium iron phosphate batteries provided by the present invention includes: (1) heat-treating the positive and negative electrode powders of waste lithium iron phosphate batteries in an inert atmosphere; (2) adding water to the heat-treated positive and negative electrode powders of waste lithium iron phosphate batteries to make a slurry, then adding sulfuric acid for acid leaching, and filtering to obtain graphite slag and a solution containing lithium, iron and phosphorus; (3) adding an oxidant and an alkali solution to the solution containing lithium, iron and phosphorus for an oxidation neutralization reaction, and filtering to obtain an iron and phosphorus precipitate and a lithium-containing solution; (4) adding a precipitant to the lithium-containing solution, and filtering to obtain a lithium salt precipitate; (5) adding water to the iron and phosphorus precipitate to make a slurry, then adding sulfuric acid to obtain a solution containing iron and phosphorus; then slowly adding ammonia water to adjust the pH, and filtering to obtain iron phosphate dihydrate; (6) performing high-temperature heat treatment on the iron phosphate dihydrate to obtain anhydrous iron phosphate.

[0033] The method for recycling the positive and negative electrode powders of waste lithium iron phosphate batteries of the present invention realizes the separation of graphite slag, lithium, iron and phosphorus in the positive and negative electrode powders of waste lithium iron phosphate batteries, and respectively prepares the basic materials for the positive electrode of lithium iron phosphate (i.e., lithium carbonate and iron phosphate). In addition, the method of the present invention consumes less auxiliary materials and can effectively reduce the recycling cost of lithium iron phosphate materials.

[0034] Figure 1 is a process flow chart of a method for recycling and regenerating the positive and negative electrode powders of waste lithium iron phosphate batteries of the present invention. The following combines Figure 1 , and the preferred technical solutions of the present invention will be described in detail:

[0035] (1) Heat treatment

[0036] The positive and negative electrode powders of waste lithium iron phosphate batteries are heat-treated in an inert atmosphere to remove organic matter in the waste lithium iron phosphate batteries, such as organic binders and organic electrolytes; and to destroy the structure of lithium iron phosphate to improve the subsequent leaching efficiency.

[0037] Among them, the waste lithium iron phosphate cathode and anode powder is the waste lithium iron phosphate battery cathode and anode powder with an Al content of less than 0.3%.

[0038] Preferably, the inert atmosphere is nitrogen or argon.

[0039] Preferably, the heat treatment temperature is 500°C - 700°C, and the reaction time is 2 - 4 h.

[0040] More preferably, the heat treatment temperature is 600°C, and the reaction time is 2 h.

[0041] (2) Acid leaching

[0042] Add water to the heat-treated waste lithium iron phosphate battery cathode and anode powder to make a slurry, then add sulfuric acid for acid leaching, and filter to obtain graphite slag and a solution containing lithium, iron, and phosphorus.

[0043] In the present invention, lithium iron phosphate is completely dissolved by using sulfuric acid, and lithium, iron, and phosphorus in lithium iron phosphate are converted into a mixed solution of lithium sulfate, ferrous sulfate, and phosphoric acid, realizing efficient separation from graphite.

[0044] Preferably, the sulfuric acid is a sulfuric acid solution with a mass fraction of 92.5% - 98.3%. The molar ratio of sulfuric acid to lithium in the waste lithium iron phosphate battery cathode and anode powder is 3:2 - 4:2. The temperature of acid leaching is 70°C - 90°C, and the time is 2 - 4 h.

[0045] More preferably, the molar ratio of sulfuric acid to lithium in the waste lithium iron phosphate battery cathode and anode powder is 3:2, the reaction temperature is 90°C, and the reaction time is 3 h.

[0046] In this step, the following chemical reactions mainly occur:

[0047] 2LiFePO4 + 3H2SO4 = Li2SO4 + 2FeSO4 + 2H3PO4

[0048] (3) Separation of lithium from iron and phosphorus

[0049] Add an oxidant and an alkali solution to the solution containing lithium, iron, and phosphorus for an oxidation and neutralization reaction, and filter to obtain an iron and phosphorus precipitate and a lithium-containing solution.

[0050] In the present invention, adding an oxidant to the solution containing lithium, iron, and phosphorus can oxidize ferrous ions into ferric ions. Adding an alkali solution is to provide an alkaline environment to precipitate ferric ions in the form of a precipitate.

[0051] Preferably, the oxidant is one of hydrogen peroxide, oxygen, air, and ozone. The molar ratio of hydrogen peroxide to iron in the solution containing lithium, iron, and phosphorus is 2:2 - 3:2. The alkaline solution is one of sodium hydroxide, potassium hydroxide, and ammonia water. The reaction temperature is room temperature, the precipitation pH is 2.0 - 3.0, and the reaction time is 0.5 - 1 h.

[0052] More preferably, the oxidant is a hydrogen peroxide solution with a mass concentration of 30%. The molar ratio of hydrogen peroxide to iron in the solution containing lithium, iron, and phosphorus is 2:2. The alkaline solution is sodium hydroxide with a concentration of 2 mol / L, the precipitation pH is 2.5, and the reaction time is 1 h.

[0053] Taking hydrogen peroxide as the oxidant and sodium hydroxide as the alkaline solution as an example, the following chemical reactions mainly occur in this step:

[0054] 2Fe 2+ +H2O2+2H + =2Fe 3+ +2H2O

[0055] Fe 3+ +3OH - =Fe(OH)3↓

[0056] Fe 3+ +PO4 3- +2H2O=FePO4·2H2O↓

[0057] (4) Recovery of lithium

[0058] A precipitating agent is added to the lithium-containing solution, and a lithium salt precipitate is obtained by filtration.

[0059] Preferably, the precipitating agent is sodium carbonate or sodium phosphate, and the corresponding crude lithium salts formed are lithium carbonate and lithium phosphate, respectively.

[0060] In this step, the following chemical reactions mainly occur:

[0061] Na2CO3+Li2SO4=Na2SO4+Li2CO3↓

[0062] 2Na3PO4+3Li2SO4=3Na2SO4+2Li3PO4↓

[0063] (5) Recovery of iron and phosphorus

[0064] After adding water to make a slurry in the iron and phosphorus precipitate, sulfuric acid is added for dissolution to obtain a solution containing iron and phosphorus. Then, ammonia water is slowly added to adjust the pH, and iron phosphate dihydrate is obtained by filtration.

[0065] Among them, the sulfuric acid is a sulfuric acid solution with a mass fraction of 92.5% - 98.3%. The concentration of the ammonia water is 20% - 28%.

[0066] Preferably, the mass ratio of the dried iron and phosphorus precipitate to sulfuric acid is 1:0.50 - 1:0.65, and the mass ratio to ammonia water is 1:0.63 - 1:1; ammonia water is added to adjust the pH to 1.5 - 2.4, and the reaction is carried out at a temperature of 40°C - 60°C for 0.5 - 2 h.

[0067] Preferably, the mass ratio of the dried iron and phosphorus precipitate to sulfuric acid is 1:0.54, and the mass ratio to ammonia water is 1:0.65; ammonia water is added to adjust the pH to 1.8, and the reaction is carried out at a temperature of 60°C for 1 h.

[0068] In this step, the following chemical reactions mainly occur:

[0069] 2Fe(OH)3 + 3H2SO4 = Fe2(SO4)3 + 6H2O

[0070] 2FePO4·2H2O + 3H2SO4 = Fe2(SO4)3 + 2H3PO4 + 2H2O

[0071] Fe 3+ +PO4 3- +nH + +nNH3·H2O + 2H2O = FePO4·2H2O↓ + nNH4 + +nH2O

[0072] (6) Dehydration of iron phosphate dihydrate

[0073] Iron phosphate dihydrate is subjected to high-temperature heat treatment to remove the crystal water, and impurities such as ammonium sulfate and ammonium phosphate are removed by thermal decomposition to obtain anhydrous iron phosphate.

[0074] Preferably, the heat treatment temperature is 500°C - 700°C, and the heat treatment reaction time is 1 - 3 h.

[0075] More preferably, the heat treatment temperature is 600°C, and the heat treatment reaction time is 2 h.

[0076] In this step, the following chemical reactions mainly occur:

[0077]

[0078] The method for recycling the positive and negative electrode powder of waste lithium iron phosphate batteries of the present invention has a simple process, high leaching rate, high quality of the recovered product, and does not add additional impurity-removing auxiliary materials, realizing the full recovery of lithium, iron, and phosphorus elements in the waste lithium iron phosphate positive and negative electrode powder, which is beneficial to large-scale industrial application.

[0079] Examples

[0080] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions noted in the following examples, conventional methods and conditions are followed. The raw materials used in the following examples are all obtained through regular commercial purchases.

[0081] Example 1

[0082] (1) 300 g of the positive and negative electrode powder of waste lithium iron phosphate batteries was heat-treated under an argon atmosphere at 600 °C for 2 h to obtain 292 g of the heat-treated positive and negative electrode powder of waste lithium iron phosphate batteries.

[0083] (2) 200 g of the heat-treated positive and negative electrode powder of waste lithium iron phosphate batteries in step (1) (containing 0.81 mol of lithium element) was weighed, slurried with 1 L of water, 121 g of sulfuric acid with a mass fraction of 98% was added, and the reaction was carried out at 90 °C for 3 h and then filtered to obtain 978 mL of a solution containing lithium, iron, and phosphorus and 183 g of wet graphite slag.

[0084] (3) 96 mL of H2O2 with a concentration of 30% was added to the solution containing lithium, iron, and phosphorus in step (2), and then NaOH with a concentration of 2 mol / L was added to adjust the pH of the solution to 2.5. The reaction was carried out at room temperature for 1 h, and 420 g of iron and phosphorus precipitates and 976 mL of lithium-containing solution were obtained by filtration.

[0085] (4) The lithium-containing solution in step (3) was added to saturated sodium carbonate solution, and crude lithium carbonate with a content of 95.47% was obtained by filtration. After calculation, the recovery rate of lithium element was 95.62%.

[0086] (5) The iron and phosphorus precipitates in step (3) (the dry mass of the iron and phosphorus precipitates was 149 g) were slurried with 924 mL of water, 81 g of sulfuric acid with a mass fraction of 98% was added, and the reaction was carried out at 60 °C for 1 h. After the solid was completely dissolved, 97 g of ammonia water with a concentration of 25% was added to adjust the pH of the solution to 1.8, and the reaction was carried out at 60 °C for 1 h and then filtered to obtain 400 g of wet dihydrate iron phosphate. The powder of the dried wet dihydrate iron phosphate was 144 g.

[0087] (6) The dihydrate iron phosphate in step (4) was heat-treated at 600 °C for 2 h to obtain 115 g of anhydrous iron phosphate.

[0088] Among them, the SEM photograph of the anhydrous iron phosphate at a magnification of 4000X is shown in Figure 2 , and the XRD pattern is shown in Figure 3 .

[0089] After calculation, the recovery rates of iron and phosphorus elements were 97.67% and 96.61% respectively.

[0090] Example 2

[0091] (1) Heat-treat 300 g of the cathode and anode powder of waste lithium iron phosphate batteries under an argon atmosphere at 700 °C for 1.5 h to obtain 293 g of heat-treated cathode and anode powder of waste lithium iron phosphate batteries.

[0092] (2) Weigh 200 g of the heat-treated cathode and anode powder of waste lithium iron phosphate batteries in step (1) (containing 0.99 mol of lithium element), add 1 L of water to make a slurry, add 149 g of sulfuric acid with a mass fraction of 98%, react at 80 °C for 3 h, and then filter to obtain 1010 mL of a solution containing lithium, iron, and phosphorus and 180 g of wet graphite residue.

[0093] (3) Add 118 mL of 30% H2O2 to the solution containing lithium, iron, and phosphorus in step (2), then add NaOH with a concentration of 2 mol / L to adjust the pH of the solution to 3, react at room temperature for 1 h, and filter to obtain 456 g of iron- and phosphorus-containing precipitate and 1025 mL of lithium-containing solution.

[0094] (4) Add the lithium-containing solution in step (3) to saturated sodium carbonate solution, filter to obtain crude lithium carbonate with a content of 96.34%. After calculation, the recovery rate of lithium element is 95.72%.

[0095] (5) Add 1003 mL of water to the iron- and phosphorus-containing precipitate in step (3) (the dry mass of the iron- and phosphorus-containing precipitate is 162 g) to make a slurry, add 105 g of sulfuric acid with a mass fraction of 98%, react at 60 °C for 30 min. After the solid is completely dissolved, add 125 g of 25% ammonia water to adjust the pH of the solution to 2.1, react at 60 °C for 1 h, and then filter to obtain 490 g of wet iron phosphate dihydrate. The dried powder of the wet iron phosphate dihydrate is 177 g.

[0096] (6) Heat-treat the iron phosphate dihydrate in step (4) at 600 °C for 2 h to obtain 141 g of anhydrous iron phosphate.

[0097] After calculation, the recovery rates of iron and phosphorus elements are 97.35% and 97.83% respectively.

[0098] Example 3

[0099] (1) Heat-treat 300 g of the cathode and anode powder of waste lithium iron phosphate batteries under an argon atmosphere at 600 °C for 2 h to obtain 292 g of heat-treated cathode and anode powder of waste lithium iron phosphate batteries.

[0100] (2) Weigh 200 g of the heat-treated cathode and anode powder of waste lithium iron phosphate batteries in step (1) (containing 0.81 mol of lithium element), add 1 L of water to make a slurry, add 125 g of sulfuric acid with a mass fraction of 95%, react at 70 °C for 3 h, and then filter to obtain 982 mL of a solution containing lithium, iron, and phosphorus and 181 g of wet graphite residue.

[0101] (3) Add the solution containing lithium, iron, and phosphorus in step (2) to 96 mL of H2O2 with a concentration of 30%, then add NaOH with a concentration of 2 mol / L to adjust the pH of the solution to 3. React at room temperature for 0.5 h, and filter to obtain 428 g of iron- and phosphorus-containing precipitate and 1008 mL of lithium-containing solution.

[0102] (4) Add the lithium-containing solution in step (3) to saturated sodium carbonate solution, and filter to obtain crude lithium carbonate with a content of 95.86%. After calculation, the recovery rate of lithium element is 95.34%.

[0103] (5) Pulp the iron- and phosphorus-containing precipitate in step (3) (the dry mass of the iron- and phosphorus-containing precipitate is 152 g) with 941 mL of water, add 84 g of sulfuric acid with a mass fraction of 95%, and react at 60 °C for 1 h. Wait until the solid is completely dissolved, then add 152 g of ammonia water with a concentration of 25% to adjust the pH of the solution to 2.4. After reacting at 60 °C for 1 h, filter to obtain 423 g of wet iron phosphate dihydrate, and the dried powder of the wet iron phosphate dihydrate is 153 g.

[0104] (6) Heat-treat the iron phosphate dihydrate in step (4) at 700 °C for 2 h to obtain 122 g of anhydrous iron phosphate.

[0105] After calculation, the recovery rates of iron and phosphorus elements are 96.12% and 96.56% respectively.

[0106] The present invention has been disclosed in the above with preferred embodiments. However, those skilled in the art should understand that these embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all equivalent changes and substitutions to these embodiments should be regarded as covered within the scope of the claims of the present invention. Therefore, the protection scope of the present invention should be defined by the scope defined in the claims.

Claims

1. A method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries, characterized in that: include: (1) heat treating the positive and negative electrode powders of waste lithium iron phosphate batteries under an inert atmosphere; (2) adding water to the positive and negative electrode powders of the waste lithium iron phosphate battery after heat treatment to make a slurry, then adding sulfuric acid for acid leaching, and filtering to obtain graphite slag and a solution containing lithium, iron and phosphorus; (3) adding an oxidant and an alkaline solution to the lithium, iron and phosphorus containing solution to carry out an oxidation neutralization reaction, and filtering to obtain an iron and phosphorus containing precipitate and a lithium containing solution; (4) adding a precipitant to the lithium-containing solution and obtaining a lithium salt precipitate by filtering; (5) adding water to the iron and phosphorus precipitates to make a pulp, and then adding sulfuric acid to obtain an iron and phosphorus solution; then slowly adding ammonia water to adjust the pH, and filtering to obtain ferric phosphate dihydrate; (6) subjecting the dihydrate ferric phosphate to high temperature heat treatment to obtain anhydrous ferric phosphate.

2. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (1), the heat treatment temperature is 500°C-700°C, and the duration is 2-4 hours.

3. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the sulfuric acid is concentrated sulfuric acid with a mass fraction of 92.5% to 98.3%, and the molar ratio of the sulfuric acid to the lithium in the positive and negative electrode powders of the waste lithium iron phosphate battery is 3:2 to 4:

2.

4. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the acid leaching temperature is 70°C-90°C and the duration is 2-4 hours.

5. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (3), the oxidant is one of hydrogen peroxide, oxygen, air, and ozone; and the alkali solution is one of sodium hydroxide, potassium hydroxide, and ammonia water.

6. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (3), the temperature of the oxidation neutralization reaction is room temperature, the precipitation pH is 2.0-3.0, and the reaction time is 0.5-1h.

7. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (4), the precipitating agent includes sodium carbonate or sodium phosphate.

8. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (5), the mass ratio of the dry iron- and phosphorus-containing precipitate to sulfuric acid is 1:0.50-1:0.65, and the mass ratio of the dry iron- and phosphorus-containing precipitate to ammonia water is 1:0.63-1:

1.

9. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (5), slowly add ammonia water to adjust the pH to 1.5-2.4, and react at 40°C-60°C for 0.5-2h.

10. The method for recycling positive and negative electrode powders of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (6), the high temperature heat treatment of the ferric phosphate dihydrate is performed at a temperature of 500° C. to 700° C. for a time of 1 to 3 hours.

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