Method for preparing lithium iron phosphate using pole piece waste and lithium iron phosphate positive electrode material

Abstract

The application relates to the technical field of battery materials, in particular to a method for preparing lithium iron phosphate by using pole piece waste and a lithium iron phosphate positive electrode material. The method comprises the following steps: crushing and screening the pole piece waste to obtain recovered powder; dissolving the recovered powder by using alkali, and performing solid-liquid separation to obtain aluminum-removed powder; performing acid leaching on the aluminum-removed powder under a reduction condition, and performing solid-liquid separation to obtain leaching liquor; reducing the leaching liquor to obtain reduced leaching liquor; detecting the contents of phosphorus, iron and lithium in the reduced leaching liquor, adding one or more of a lithium source, an iron source or a phosphorus source according to the molar ratio of lithium iron phosphate, and obtaining a mixed solution; stirring and heating the mixed solution with lithium carbonate or lithium hydroxide to perform a reaction and crystallization, and performing post-treatment to obtain lithium iron phosphate. The method realizes the full-component recovery of phosphorus, iron and lithium, avoids the waste of phosphorus and iron resources, improves the recovery efficiency and economic value, and is environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a method for preparing lithium iron phosphate using electrode waste and lithium iron phosphate cathode material. Background Technology

[0002] With the widespread use of portable products such as mobile phones, laptops, and digital devices, rechargeable batteries, such as lithium-ion batteries, have become essential consumer goods in people's daily lives. In particular, the explosive growth of electric vehicles and energy storage systems using lithium iron phosphate (LFP) batteries has led to a geometric increase in the amount of discarded batteries. Therefore, the recycling and resource utilization of waste batteries has become a current research hotspot, aimed at protecting the environment and alleviating resource scarcity.

[0003] Currently, the main methods for recycling lithium-ion batteries are: crushing, sorting, leaching, impurity removal, and lithium extraction to obtain battery-grade lithium carbonate. The primary goal of this process is lithium recovery, which leads to the waste of phosphorus iron resources. Further recovery of phosphorus iron requires significant electricity and heat, resulting in high energy consumption. Furthermore, the impurity removal process mainly involves precipitation of the leaching solution. Incomplete impurity removal can lead to the waste of other elements or the introduction of new impurities.

[0004] In view of the shortcomings of existing recycling methods, it is necessary to develop a method for the complete and efficient recovery of all components. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for the complete recovery of all components and the direct preparation of lithium iron phosphate cathode materials by adjusting the recycling process and controlling the process parameters in each step.

[0006] To achieve the above objectives, the present invention provides a method for preparing lithium iron phosphate using electrode waste, the method comprising the following steps:

[0007] S1: The electrode waste is crushed and screened to obtain recycled powder; the recycled powder is dissolved with alkali and then separated into solid and liquid to obtain aluminum-removed powder;

[0008] S2: The aluminum-removing powder is acid-leached under reducing conditions, and the leachate is obtained by solid-liquid separation;

[0009] S3: Reduce the leachate with ferric iron to obtain a reduced leachate;

[0010] S4: Detect the content of phosphorus, iron and lithium in the reduced leachate, and increase one or more of lithium source, iron source or phosphorus source according to the lithium iron phosphate molar ratio to obtain a mixed solution;

[0011] S5: The mixed solution is stirred, heated and reacted with lithium carbonate or lithium hydroxide and aged, and lithium iron phosphate is obtained by solid-liquid separation and washing.

[0012] In one embodiment, dissolving the recycled powder using an alkali in step S1 specifically includes:

[0013] A reducing agent, complexing agent, and alkali are prepared into a reducing alkaline solution, and the reducing alkaline solution is mixed with the recovered powder at a ratio of 1:5 to 15 to form a slurry. The mixture is then reacted at a temperature of 25 to 60°C for 30 to 90 minutes.

[0014] In one embodiment of the invention, the reducing alkaline solution comprises:

[0015] The reducing agent is any one of ascorbic acid, sodium thiosulfate, sodium metabisulfite, or sodium sulfide.

[0016] The complexing agent is any one of ethylenediaminetetraacetic acid, potassium sodium tartrate, hexamethylenetetramine, or triethanolamine.

[0017] The alkali is sodium hydroxide or potassium hydroxide;

[0018] The reducing agent in the reducing alkaline solution has a content of 0.1-5%; the complexing agent in the reducing alkaline solution has a content of 0.1-10%; and the alkali content in the reducing alkaline solution has a content of 1-10%.

[0019] In one embodiment of the invention, step S2 specifically includes:

[0020] After the aluminum-removing powder is slurried, a reducing agent is added, and sulfuric acid is added for acid leaching. The leachate is obtained by pressure filtration.

[0021] In one embodiment of the invention, step S3 specifically includes:

[0022] The leachate is mixed with iron powder and reacted at a temperature of 30–70°C and a pH of 1.0–1.8 for 3–5 hours. Then, it is reacted at a temperature of 40–70°C and a pH of 1.8–2.6 for 3–5 hours to obtain a reduced leachate.

[0023] In one embodiment of the invention, the molar ratio of phosphorus:iron:lithium in the lithium iron phosphate molar ratio is 1:(0.99~1.0):(1.1~1.5).

[0024] In one embodiment of the invention, the stirring and heating reaction in step S5 includes the following technical features:

[0025] The stirring speed is 80~120 rpm;

[0026] The reaction temperature is 90~110℃;

[0027] The reaction time is 3-5 hours;

[0028] pH range: 5.0 to 7.0.

[0029] In one embodiment, the method further includes:

[0030] The lithium iron phosphate, sugar, and water are mixed to form a slurry;

[0031] The mixed slurry is spray-dried and then calcined and ground under an inert atmosphere to obtain carbon-coated lithium iron phosphate; the calcination temperature is 700~850℃ and the calcination time is 18~24h.

[0032] In one embodiment of the invention, the mass ratio of lithium iron phosphate, sugars and water is 1:(0.05~0.2):(2~4).

[0033] The present invention also provides a lithium iron phosphate cathode material, which is prepared by the above method.

[0034] The beneficial effects of this invention are reflected in:

[0035] This invention utilizes a process of crushing, sorting, aluminum removal, leaching, pressure filtration, reduction of ferric iron, solution preparation, and crystallization to obtain lithium iron phosphate. This process achieves the complete recovery of phosphorus, iron, and lithium, avoiding the waste of phosphorus and iron resources and improving recovery efficiency and economic value. The lithium iron phosphate battery material is directly prepared through the above process, avoiding the energy consumption in the preparation of other intermediate raw materials, which is environmentally friendly. Furthermore, the recovery process is short and has high production efficiency. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for preparing lithium iron phosphate using electrode waste provided by the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] As shown in the figure, in this embodiment of the invention, battery factory scrap is used as raw material to provide a method for preparing lithium iron phosphate from electrode waste, which can be summarized as follows:

[0039] Step S1: The electrode waste is crushed and screened to obtain recycled powder; the recycled powder is dissolved with alkali and then separated into solid and liquid components to obtain aluminum-removed powder.

[0040] In this process, the electrode waste is first pulverized using an electrode crushing and pulverizing device, and then screened to obtain aluminum particles and recycled powder. The aluminum particles can be sold. The recycled powder is then mixed with a reducing alkaline solution containing 0.1-5% of a first reducing agent, 0.1-10% of a complexing agent, and 1-10% of an alkali, and slurried at a solid-liquid ratio of 1:5-15, utilizing the principle that aluminum dissolves in alkaline solution. The temperature is controlled at 25-60℃, and the reaction is carried out for 30-90 minutes until the aluminum content is measured to be 10-100 PPM, which is considered qualified. The mixture is then washed, filtered, and set aside for later use. The first reducing agent is any one of ascorbic acid, sodium thiosulfate, sodium metabisulfite, or sodium sulfide; the complexing agent is any one of ethylenediaminetetraacetic acid, potassium sodium tartrate, hexamethylenetetramine, or triethanolamine; and the alkali is sodium hydroxide or potassium hydroxide.

[0041] Step S2: The aluminum-removing powder is acid-leached under reducing conditions, and the leachate is obtained by solid-liquid separation.

[0042] In this process, the aluminum-removing powder is first slurried, a second reducing agent is added to create a reducing atmosphere, and sulfuric acid is continuously added until the pH is controlled at 1-3 to complete the reaction, producing a product containing Fe. 2+ PO4 3- Li + and contains a small amount of Fe 3+ The mixed solution is subjected to solid-liquid separation using a filter press, and the filter residue is treated as solid waste to obtain leachate. The second reducing agent is any one of iron powder, ascorbic acid, sodium thiosulfate, sodium metabisulfite, or sodium sulfide.

[0043] Step S3: Reduce the leachate with ferric iron to obtain a reduced leachate.

[0044] In this process, the leachate is mixed with reduced iron powder, and the reduction of ferric iron is achieved by controlling the pH and temperature of the solution. The reaction consists of two stages: Stage 1: Temperature 30–70℃, pH 1.0–1.8, reaction time 3–5 h, ferric iron controlled below 500 ppm; Stage 2: Temperature 40–70℃, pH 1.8–2.6, reaction time 4 h. After solid-liquid separation, the ferric iron in the filtrate is controlled below 30–100 ppm to obtain the reduced leachate.

[0045] Step S4: Detect the content of phosphorus, iron and lithium in the reduced leachate, and add one or more of lithium source, iron source or phosphorus source according to the lithium iron phosphate molar ratio to obtain a mixed solution.

[0046] In this process, since the concentrations of each raw material in the reductive leachate after impurity removal from batches of waste are not the same, the concentrations of phosphorus, iron, lithium, and their pH value in the reductive leachate are measured. Based on a phosphorus:iron:lithium molar ratio of 1:(0.99~1.0):(1.1~1.5), the missing corresponding raw materials, such as one or more of lithium, phosphorus, or iron sources, are added. Specific replacement materials can be phosphoric acid, lithium phosphate, ferrous sulfate, lithium carbonate, or lithium hydroxide. It should be understood that to ensure the stability of the divalent iron in the solution system, a reducing agent such as ascorbic acid is added, and the pH value of the solution system is controlled to be between 4.0 and 7.0.

[0047] Step S5: The mixed solution is stirred, heated and reacted with lithium carbonate or lithium hydroxide and aged. After solid-liquid separation and washing, lithium iron phosphate is obtained.

[0048] In this process, the prepared mixed solution is placed in a crystallization vessel and stirred at a stirring rate of 80-120 rpm. The mixture is heated to 90-110°C, and lithium carbonate suspension (or 1-10% lithium hydroxide solution) is added dropwise while controlling the pH of the reaction process to 5.0-7.0. The reaction is carried out for 3-5 hours, followed by aging for 1 hour and then filtration. The filter residue is dehydrated or filtered using a centrifuge or filter press. After multiple washings, the final conductivity of the washing water is controlled to be 50-200 μS / M. The sulfate, sodium, and potassium ions are controlled within the range of battery-grade lithium iron phosphate to obtain lithium iron phosphate.

[0049] Step S6: Mix the lithium iron phosphate, sugar and water obtained above to form a slurry, then spray dry the slurry and calcine and grind it under an inert atmosphere to obtain carbon-coated lithium iron phosphate; the calcination temperature is 700~850℃ and the calcination time is 18~24h.

[0050] In this process, the moisture content of the lithium iron phosphate is first tested. The mixture is then prepared according to a ratio of lithium iron phosphate:sugar:water = 1:(0.05~0.2):(2~4) to obtain a slurry. The slurry is then spray-dried to obtain a dried powder. This powder is then placed in a calcining kiln and calcined at 700-850℃ for 18-24 hours under nitrogen protection. Finally, the powder is ground to obtain carbon-coated lithium iron phosphate battery material. The sugars used are glucose, sucrose, or reduced starch.

[0051] The embodiments of this invention obtain lithium iron phosphate cathode materials through crushing, sorting, aluminum removal, leaching, pressure filtration, reduction of ferric iron, solution preparation, crystallization, washing, pulping, spray drying, carbon coating, and grinding. This achieves full component recovery, avoids resource waste, and directly prepares battery materials through component adjustment and crystallization, achieving efficient utilization, saving a large number of process steps and energy, and is environmentally friendly.

[0052] In addition, the present invention prepares lithium iron phosphate and sugar into a slurry and obtains a uniformly coated carbon-coated lithium iron phosphate battery material through spray drying and calcination. The method is simple and the obtained battery material has good electrical properties.

[0053] The following specific embodiments provide further details:

[0054] Example 1

[0055] S1: Collect waste electrode sheets from battery factories, crush and grind them using electrode sheet crushing and pulverizing equipment, and obtain aluminum particles and recycled powder after screening. Prepare a reducing alkaline solution of ascorbic acid (3.0%), ethylenediaminetetraacetic acid (0.5%), and sodium hydroxide (2.0%). Mix the recycled powder with the reducing alkaline solution at a solid-liquid ratio of 1:5 to form a slurry. Control the temperature at 25℃ and react for 90 minutes. Filter the residue and press filter to obtain aluminum-removed powder.

[0056] S2: The aluminum removal powder is slurried, and iron powder (accounting for 0.1% of the aluminum removal powder) is added to form a reducing atmosphere. Sulfuric acid is continuously added, and the reaction is completed when the pH value is monitored to be 1~3. The solid and liquid are separated by a filter press, and the filter residue is treated as solid waste to obtain leachate.

[0057] S3: Add iron powder to the leachate for a two-stage reduction reaction: First, react for 4 hours at a temperature of 30℃ and a pH of 1.0. When the ferric iron content is less than 500ppm, adjust the temperature to 40℃ and the pH to 1.8 and react for 4 hours. The resulting reduced leachate is then filtered.

[0058] S4: Detect the concentrations of phosphorus, iron, and lithium in the reducing leachate, where the molar ratio of phosphorus, iron, and lithium is 0.8:1:0.7. Add lithium phosphate and lithium carbonate to adjust the molar ratio of phosphorus, iron, and lithium to 1:1:1.1 to obtain a mixed solution.

[0059] S5: Place the prepared mixed solution in a crystallization vessel, stir at a stirring rate of 80 rpm, heat to 90°C, add lithium carbonate suspension dropwise and control the pH value of the reaction process to 5.0, react for 3 hours, then age for 1 hour and filter. Dehydrate or filter the filter residue using a centrifuge or filter press, and obtain lithium iron phosphate after multiple washings.

[0060] S6: The moisture content in lithium iron phosphate is detected. The raw materials are prepared according to the ratio of lithium iron phosphate: sugar: water = 1:0.05:2. The mixture is then spray-dried to obtain a dry mixed powder. The dry mixed powder is then placed in a calcining kiln and calcined at 700°C for 24 hours under nitrogen protection. Finally, the powder is ground to obtain carbon-coated lithium iron phosphate battery material.

[0061] Example 2

[0062] S1: Collect waste electrode sheets from battery factories, crush and grind them using electrode sheet crushing and pulverizing equipment, and obtain aluminum particles and recycled powder after screening. Prepare a reducing alkaline solution of sodium thiosulfate (1.0%), potassium sodium tartrate (1.0%), and sodium hydroxide (5.0%). Mix the recycled powder with the reducing alkaline solution at a solid-liquid ratio of 1:10 to form a slurry. Control the temperature at 40℃ and react for 60 minutes. Filter the residue and press filter to obtain aluminum-removed powder.

[0063] S2: The aluminum-removing powder is pulped, ascorbic acid is added to form a reducing atmosphere, sulfuric acid is continuously added dropwise, and the reaction is completed when the pH value is monitored to be 1~3. The solid and liquid are separated by a filter press, and the filter residue is treated as solid waste to obtain leachate.

[0064] S3: Add iron powder to the leachate for a two-stage reduction reaction: First, react for 4 hours at a temperature of 50℃ and a pH of 1.5. When the ferric iron content is less than 500 ppm, adjust the temperature to 55℃ and the pH to 2.2 and react for 4 hours. The resulting reduced leachate is then filtered.

[0065] S4: Detect the concentrations of phosphorus, iron, and lithium in the reducing leachate, where the molar ratio of phosphorus, iron, and lithium is 0.8:0.9:1. Add lithium phosphate and lithium carbonate to adjust the molar ratio of phosphorus, iron, and lithium to 1:0.9:1.2 to obtain a mixed solution.

[0066] S5: Place the prepared mixed solution in a crystallization vessel, stir at a stirring rate of 100 rpm, heat to 100°C, add lithium carbonate suspension dropwise and control the pH value of the reaction process to 6.0, react for 4 hours, then age for 1 hour and filter. Dehydrate or filter the filter residue using a centrifuge or filter press, and obtain lithium iron phosphate after multiple washings.

[0067] S6: The moisture content in lithium iron phosphate is tested. The mixture is prepared according to the ratio of lithium iron phosphate: glucose: water = 1:0.1:3, and a slurry is obtained. The slurry is then spray-dried to obtain a dry mixed powder. The dry mixed powder is then placed in a calcining kiln and calcined at 750°C for 22 hours under nitrogen protection. Finally, it is ground to obtain carbon-coated lithium iron phosphate battery material.

[0068] Example 3

[0069] S1: Collect waste electrode sheets from battery factories, crush and grind them using electrode sheet crushing and pulverizing equipment, and obtain aluminum particles and recycled powder after screening. Prepare a reducing alkaline solution of sodium metabisulfite (content 5.0%), triethanolamine (content 3.0%), and sodium hydroxide (content 8.0%). Mix the recycled powder with the reducing alkaline solution at a solid-liquid ratio of 1:15 to form a slurry. Control the temperature at 60℃ and react for 30 minutes. Filter the residue and press filter to obtain aluminum-removed powder.

[0070] S2: The aluminum removal powder is slurried, and iron powder (accounting for 0.1% of the aluminum removal powder) is added to form a reducing atmosphere. Sulfuric acid is continuously added, and the reaction is completed when the pH value is monitored to be 1~3. The solid and liquid are separated by a filter press, and the filter residue is treated as solid waste to obtain leachate.

[0071] S3: Add iron powder to the leachate for a two-stage reduction reaction: First, react for 4 hours at a temperature of 70℃ and a pH of 1.8. When the ferric iron content is less than 500ppm, adjust the temperature to 40℃ and the pH to 2.6 and react for 4 hours. The resulting reduced leachate is then filtered.

[0072] S4: Detect the concentrations of phosphorus, iron, and lithium in the reducing leachate, where the molar ratio of phosphorus, iron, and lithium is 0.7:0.85:0.9. Add lithium phosphate, lithium carbonate, and ferrous phosphate to adjust the molar ratio of phosphorus, iron, and lithium to 1:1.0:1.5 to obtain a mixed solution.

[0073] S5: Place the prepared mixed solution in a crystallization vessel, stir at a stirring rate of 120 rpm, heat to 110°C, add lithium carbonate suspension dropwise and control the pH value of the reaction process to 7.0, react for 5 hours, then age for 1 hour and filter. Dehydrate or filter the filter residue using a centrifuge or filter press, and obtain lithium iron phosphate after multiple washings.

[0074] S6: The moisture content in lithium iron phosphate is tested. The raw materials are prepared according to the ratio of lithium iron phosphate: sucrose: water = 1:0.2:4. The mixture is then spray-dried to obtain a dry mixed powder. The dry mixed powder is then placed in a calcining kiln and calcined at 850°C for 18 hours under a nitrogen-protected atmosphere. Finally, the powder is ground to obtain carbon-coated lithium iron phosphate battery material.

[0075] Comparative Example 1

[0076] Step S3 is omitted, and the remaining operations and steps are the same as in Example 1, to obtain the carbon-coated lithium iron phosphate battery material.

[0077] Comparative Example 2

[0078] Step S3 is modified as follows: iron powder is added to the leachate, and the mixture is reacted for 8 hours at a temperature of 70°C and a pH of 1.8. The resulting reduced leachate is then filtered. The remaining operations and steps are the same as in Example 1, thus obtaining the carbon-coated lithium iron phosphate battery material.

[0079] Comparative Example 3

[0080] Step S3 is modified as follows: iron powder is added to the leachate, and the reaction is carried out at 70°C and pH 2.6 for 8 hours. The resulting reduced leachate is then filtered. The remaining operations and steps are the same as in Example 1, thus obtaining the carbon-coated lithium iron phosphate battery material.

[0081] Comparative Example 4

[0082] In step S1, the reducing alkaline solution was replaced with a sodium hydroxide solution (2.0%) to remove aluminum. The remaining operations and steps were the same as in Example 1 to obtain carbon-coated lithium iron phosphate battery material.

[0083] Comparative Example 5

[0084] In step S5, the pH value of the reaction process is controlled at 4.5, and the remaining operations and steps are the same as in Example 1, to obtain the carbon-coated lithium iron phosphate battery material.

[0085] Comparative Example 6

[0086] The drying process of the mixed slurry in step S6 is replaced with vacuum drying, and the remaining operations and steps are the same as in Example 1, to obtain the carbon-coated lithium iron phosphate battery material.

[0087] Comparative Example 7

[0088] Commercially available lithium iron phosphate was used as raw material, and carbon coating was performed according to step 6 in Example 1 to obtain carbon-coated lithium iron phosphate battery material.

[0089] Performance testing:

[0090] The lithium iron phosphate cathode materials obtained in Examples 1-3 and Comparative Examples 1-7 were used to assemble button cells. Battery performance was obtained by charging and discharging at a current density of 0.1C within a charge / discharge voltage range of 2.5-4.2V. The results are shown in Table 1.

[0091] Table 1 Battery performance test results

[0092]

[0093] As shown in Table 1, the lithium iron phosphate cathode materials recovered in Examples 1-3 exhibit good electrical performance indicators, comparable to those of commercially available lithium iron phosphate after carbon coating, and can be directly used as battery materials. In Comparative Examples 1-6, some steps were omitted, or certain parameters were altered, resulting in relatively poor electrical performance of the obtained lithium iron phosphate cathode materials. When the ferric iron reduction process is omitted, the presence of ferric iron in the system affects the precipitation of lithium iron phosphate, impacting the element recovery rate and the electrical performance of the lithium iron phosphate cathode material. This indicates that the various processes in the recovery process of this invention interact with each other, making it impossible to obtain cathode materials with good electrical performance.

[0094] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lithium iron phosphate using electrode waste, characterized in that, The method includes the following steps: S1: The electrode waste is crushed and screened to obtain recycled powder; the recycled powder is dissolved with alkali and then separated into solid and liquid to obtain aluminum-removed powder; S2: The aluminum-removing powder is acid-leached under reducing conditions, and the leachate is obtained by solid-liquid separation; S3: Reduce the leachate with ferric iron to obtain a reduced leachate; S4: Detect the content of phosphorus, iron and lithium in the reduced leachate, and increase one or more of lithium source, iron source or phosphorus source according to the lithium iron phosphate molar ratio to obtain a mixed solution; S5: The mixed solution is stirred, heated and reacted with lithium carbonate or lithium hydroxide and aged, and lithium iron phosphate is obtained by solid-liquid separation and washing; The step S1, which involves dissolving the recycled powder using alkali, specifically includes: A reducing agent, a complexing agent, and an alkali are prepared into a reducing alkaline solution. The reducing alkaline solution is then mixed with the recovered powder at a material-to-liquid ratio of 1:5 to 15 to form a slurry. The mixture is reacted at a temperature of 25 to 60°C for 30 to 90 minutes. The content of the first reducing agent in the reducing alkaline solution is 0.1 to 5%, the content of the complexing agent is 0.1 to 10%, and the content of the alkali is 1 to 10%. Step S3 specifically includes: The leachate is mixed with iron powder and reacted for 3-5 hours at a temperature of 30-70°C and a pH of 1.0-1.

8. Then, it is reacted for 3-5 hours at a temperature of 40-70°C and a pH of 2.2-2.6 to obtain a reduced leachate.

2. The method for preparing lithium iron phosphate from electrode waste according to claim 1, characterized in that, The reducing alkaline solution includes: The first reducing agent is any one of ascorbic acid, sodium thiosulfate, sodium metabisulfite, or sodium sulfide; The complexing agent is any one of ethylenediaminetetraacetic acid, potassium sodium tartrate, hexamethylenetetramine, or triethanolamine. The alkali is sodium hydroxide or potassium hydroxide; The content of the first reducing agent in the reducing alkaline solution is 0.1-5%; the content of the complexing agent in the reducing alkaline solution is 0.1-10%; and the content of the alkali in the reducing alkaline solution is 1-10%.

3. The method for preparing lithium iron phosphate from electrode waste according to claim 1, characterized in that, Step S2 specifically includes: After the aluminum-removing powder is slurried, a second reducing agent is added, and sulfuric acid is added for acid leaching. The leachate is obtained by pressure filtration. The second reducing agent is any one of iron powder, ascorbic acid, sodium thiosulfate, sodium metabisulfite, and sodium sulfide.

4. The method for preparing lithium iron phosphate from electrode waste according to claim 1, characterized in that, The molar ratio of phosphorus to iron to lithium in the lithium iron phosphate molar ratio is 1: (0.99~1.0): (1.1~1.5).

5. The method for preparing lithium iron phosphate from electrode waste according to claim 1, characterized in that, The stirring and heating reaction in step S5 includes the following technical features: The stirring speed is 80~120 rpm; The reaction temperature is 90~110℃; The reaction time is 3-5 hours; pH range: 5.0 to 7.

0.

6. The method for preparing lithium iron phosphate from electrode waste according to claim 1, characterized in that, The method further includes: The lithium iron phosphate, sugar, and water are mixed to form a slurry; The mixed slurry was spray-dried and then calcined and ground under an inert atmosphere to obtain carbon-coated lithium iron phosphate. The calcination temperature is 700~850℃, and the calcination time is 18~24h.

7. The method for preparing lithium iron phosphate from electrode waste according to claim 6, characterized in that, The mass ratio of lithium iron phosphate, sugars and water is 1:(0.05~0.2):(2~4).

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