Method for recycling manganese iron phosphate from waste lithium iron phosphate positive electrode material

Abstract

This invention provides a method for recycling and upgrading spent lithium iron phosphate (LFP) cathode materials to regenerate lithium manganese iron phosphate (LFP). The method utilizes a manganese ion-catalyzed hydrogen peroxide and sulfuric acid system to leach the spent LFP, improving acid leaching efficiency. Simultaneously, the manganese ions remaining after acid leaching are used as a manganese source to generate LFP precursors, ultimately synthesizing high-performance LFP cathode materials. This invention features a simple process, low cost, and is suitable for large-scale industrial production.

Description

Technical fields:

[0001] This invention relates to the field of recycling and reuse technology for cathode materials of spent lithium-ion batteries, specifically to a method for recycling and upgrading spent lithium iron phosphate (LiFePO4) cathode materials into lithium manganese iron phosphate (LiMn) cathode materials. x Fe 1-x The method of PO4). Background technology:

[0002] In recent years, lithium manganese iron phosphate (LFP), as an upgraded material of lithium iron phosphate (LFP), has become a research hotspot in the fields of power batteries and energy storage due to its advantages such as high voltage platform, low cost, and high safety. Compared to LFP, LFP, by introducing manganese, increases the voltage platform from 3.4V to 4.1V (vs. LiFePO4). + The theoretical energy density is increased by approximately 20% while retaining the thermal stability and long cycle life advantages of lithium iron phosphate (LiFePO4). In current industrial production, manganese is typically introduced by adding a manganese source via a solid-state method. However, this method may lead to uneven manganese distribution and larger grain size, resulting in poor electrochemical performance of the material.

[0003] While research on lithium-ion battery cathode materials is booming, the widespread use of lithium-ion batteries in electric vehicles, energy storage devices, and portable electronic products has brought global attention to the issue of recycling and resource reuse after their disposal. As a crucial cathode material in the power battery field, lithium iron phosphate (LFP) is widely popular due to its excellent safety, long-lasting cycle performance, and economic efficiency. However, with the widespread application of LFP batteries, the challenge of recycling them after retirement is becoming increasingly apparent. It is predicted that by 2030, the total amount of discarded LFP batteries globally will exceed one million tons. If these batteries are not properly disposed of, it will not only lead to a huge waste of resources but also cause significant damage to the environment.

[0004] Currently, recycling technologies for spent lithium iron phosphate batteries are mainly divided into three categories: pyrometallurgical recycling, hydrometallurgical recycling, and direct regeneration. Pyrometallurgical recycling extracts metals through high-temperature processes, but its high energy consumption and environmental pollution are significant issues. Hydrometallurgical recycling leaches valuable metals using acidic solutions; while effective, it is limited by its complex processes and high costs. Direct regeneration restores the performance of spent cathode materials by repairing them; however, this method often fails to fully restore the materials to their initial electrochemical state and is difficult to industrialize. Among these technologies, hydrometallurgical recycling is dominant, but its inefficient acid leaching process, time-consuming reaction, and complex subsequent separation and purification steps result in high recycling costs.

[0005] In the field of hydrometallurgy, sulfuric acid leaching is a common technique; however, its leaching effect on lithium iron phosphate is not ideal, mainly due to the stable crystal structure of lithium iron phosphate and the slow acid leaching reaction kinetics. To improve leaching efficiency, existing technologies often employ strategies such as increasing temperature, increasing acid concentration, or introducing oxidants (e.g., hydrogen peroxide), but these methods are often accompanied by environmental pollution or high costs. Summary of the Invention:

[0006] To address the shortcomings of existing technologies, this invention proposes a method for regenerating lithium iron phosphate (LFP) cathode materials by catalyzing sulfuric acid leaching with manganese sulfate. During the leaching process, manganese sulfate not only acts as a catalyst to improve leaching efficiency but also provides a manganese source for the subsequent co-precipitation of the precursor, iron manganese phosphate, achieving efficient utilization of manganese. Simultaneously, the recovered lithium source and the generated precursor undergo a solid-state reaction to synthesize LFP, realizing the resource utilization and high-value regeneration of waste materials.

[0007] To achieve the above objectives, the technical solution of the present invention includes the following steps:

[0008] 1) The waste lithium iron phosphate powder after alkaline washing is acid-leached with a 0.1-3 mol / L sulfuric acid solution. Hydrogen peroxide (molar ratio of hydrogen peroxide to lithium is 0.5-1.2) and manganese sulfate (molar ratio of manganese to iron is 0.43-4) are added to the sulfuric acid solution. The solid-liquid ratio is 10-500 g / L, the acid leaching temperature is 20-90℃, the stirring speed is 100-400 r / min, and the acid leaching time is 0.5-3 h. After the reaction is completed, the mixture is filtered and the filtrate is collected.

[0009] 2) Add ammonia to the filtrate obtained in step 1) until the pH reaches 5.5-10, filter, separate the precipitate and collect the filtrate;

[0010] 3) The precipitate obtained in step 2) is washed with water and aged, and then calcined;

[0011] 4) Add sodium carbonate to the filtrate obtained in step 2) until no more precipitate is formed, filter and separate the precipitate, collect the filtrate, wash the precipitate with water and dry it;

[0012] 5) Add the filtrate obtained in step 4) to the filtrate obtained in step 2) for circulation;

[0013] 6) Mix the product obtained in step 3) with the product obtained in step 4) and add a carbon source to prepare lithium manganese iron phosphate by ball milling and reduction roasting.

[0014] In step 3), the washing temperature is 10–50℃, the time is 10 min–2 h, and the solid-liquid ratio is 50–500 g / L; the aging temperature is 50–90℃, the aging pH is 5–9, and the aging time is 2–8 h.

[0015] In step 3), the heating rate of calcination is 2-10℃ / min, the calcination temperature is 400-700℃, and the calcination time is 2-6h.

[0016] The reaction temperature in step 4) is 10–50℃; the solid-liquid ratio for water washing is 50–500 g / L; the water washing time is 0.5–3 h; the drying temperature is 50–90℃; and the drying time is 4–10 h.

[0017] In step 6), the ball milling speed is 200-600 r / min, and the time is 6-14 h.

[0018] In step 6), the molar ratio of the product obtained in step 3) to the product obtained in step 4) is 1:(1~1.07).

[0019] In step 6), the preferred carbon source is one or more of glucose, sucrose, polyethylene glycol, and carbon nanotubes, and the amount of carbon source added is 10% to 20% of the total mass.

[0020] In step 6), the heating rate of the calcination is 2-10℃ / min. The calcination is divided into two stages: the first stage calcination temperature is 250-500℃ and the calcination time is 2-6h; the second stage calcination temperature is 500-800℃ and the calcination time is 8-14h.

[0021] Step 6) is carried out under an inert atmosphere.

[0022] In step 6), the recycled material is LiMn. x Fe 1-x PO4 (lithium iron manganese phosphate), Li:(Fe+Mn):P=(1~1.05):(0.96~1):1, 0.3≤x≤0.8.

[0023] This invention achieves efficient recycling and regeneration of waste lithium iron phosphate cathode materials, avoiding resource waste and environmental pollution. By introducing manganese, the recycled material is lithium manganese iron phosphate (LiMn). x Fe 1-x PO4, with its higher voltage plateau and energy density, enhances the electrochemical performance of the material. This method is simple, low-cost, and suitable for large-scale industrial production. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention;

[0025] Figure 2 The XRD patterns are of the coprecipitated product ferromanganese phosphate and the upgraded regenerated lithium manganese phosphate obtained in Example 1 of the present invention.

[0026] Figure 3 The charge-discharge curves and cycle performance diagrams of lithium manganese iron phosphate prepared in Example 1 of this invention are shown. Detailed Implementation

[0027] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0028] The main elements and their contents in the alkaline-washed waste lithium iron phosphate battery powder in the following examples and comparative examples are shown in Table 1:

[0029] Table 1. Main elements and content in waste lithium iron phosphate battery powder after alkaline washing.

[0030] Element Li Fe P C other Content (wt.%) 5.34 38.24 22.21 14.78 19.43

[0031] Example 1:

[0032] 1. Take 30g of waste lithium iron phosphate cathode material powder after alkali washing, mix the powder with 1L of 0.1mol / L dilute sulfuric acid solution, and add hydrogen peroxide (molar ratio of hydrogen peroxide to lithium is 1) and manganese sulfate (molar ratio of Fe:Mn is 4:6). Acid leaching treatment is carried out at 60℃ for 20min with stirring speed of 300r / min. Filter to obtain leachate.

[0033] 2. Add ammonia to the acid leaching solution to adjust the pH to 8±0.5 for co-precipitation, filter and separate the precipitate, and use the filtrate in step 4; wash the precipitate with 1L of deionized water at 30℃ for 30min, filter and separate the precipitate after washing;

[0034] 3. The separated precipitate was aged at 80℃ for 3h, the pH was adjusted to 8±0.5, the stirring speed was 300r / min, the precipitate was filtered and separated, and the precipitate was calcined at 400℃ for 4h at a heating rate of 10℃ / min to obtain the product ammonium manganese phosphate.

[0035] 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is formed. Filter and separate the precipitate. Mix the filtrate with the filtrate obtained in step 2. Wash the precipitate with 0.5 L of water and dry it at 60 °C for 8 h to obtain lithium carbonate.

[0036] 5. The co-precipitated manganese iron ammonium phosphate obtained in step 3 and the lithium carbonate obtained in step 4 were mixed at a molar ratio of 1:1.05, and 10% glucose was added. The mixture was ball-milled at 600 r / min for 10 h. After ball milling, the mixture was sintered at 350℃ for 4 h and 650℃ for 10 h under an argon atmosphere, with a heating rate of 5℃ / min. The sintered product was lithium manganese iron ammonium phosphate.

[0037] The aforementioned lithium manganese iron phosphate, after testing, has a manganese-to-iron ratio of 1.48 and a chemical formula of LiMn. 0.6 Fe 0.4 PO4, with impurities of sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, and lead ≤0.003% and impurity of aluminum ≤0.005%.

[0038] Example 2:

[0039] 1. Take 60g of waste lithium iron phosphate cathode material powder after alkali washing, mix the powder with 1L of 0.2mol / L dilute sulfuric acid solution, and add hydrogen peroxide (molar ratio of hydrogen peroxide to lithium is 0.8) and manganese sulfate (molar ratio of Fe:Mn is 3:7). Acid leaching treatment is carried out at 60℃ for 0.5h with stirring speed of 350r / min. Filter to obtain leachate.

[0040] 2. Add ammonia to the acid leaching solution to adjust the pH to 7.5±0.5 for co-precipitation, filter and separate the precipitate, and use the filtrate in step 4; wash the precipitate with 1.5L of deionized water at 35℃ for 45min, filter and separate the precipitate after washing;

[0041] 3. The separated precipitate was aged at 90℃ for 4 hours, the pH was adjusted to 8.5±0.5, the stirring speed was 350 r / min, the precipitate was filtered and separated, and the precipitate was calcined at 450℃ for 5 hours at a heating rate of 7.5℃ / min to obtain the product ammonium manganese phosphate.

[0042] 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is formed. Filter and separate the precipitate. Mix the filtrate with the filtrate obtained in step 2. Wash the precipitate with 0.75 L of water and dry it at 70 °C for 9 h to obtain lithium carbonate.

[0043] 5. The co-precipitated manganese iron ammonium phosphate obtained in step 3 was mixed with the lithium carbonate obtained in step 4 at a molar ratio of 1:1.07, and 12% glucose was added. The mixture was ball-milled at 500 r / min for 12 h. After ball milling, the mixture was sintered at 400℃ for 4 h and 650℃ for 12 h under an argon atmosphere, with a heating rate of 7.5℃ / min. The sintered product was lithium manganese iron ammonium phosphate.

[0044] The aforementioned lithium manganese iron phosphate, after testing, has a manganese-to-iron ratio of 2.33 and a chemical formula of LiMn. 0.7 Fe 0.3 PO4, with impurities of sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, and lead ≤0.003% and impurity of aluminum ≤0.005%.

[0045] Example 3

[0046] 1. Take 90g of waste lithium iron phosphate cathode material powder after alkali washing, mix the powder with 1L of 1mol / L dilute sulfuric acid solution, and add hydrogen peroxide (molar ratio of hydrogen peroxide to lithium is 0.9) and manganese sulfate (molar ratio of Fe:Mn is 6:4). Acid leaching treatment is carried out at 80℃ for 40min with stirring speed of 400r / min. Filter to obtain leachate.

[0047] 2. Add ammonia to the acid leaching solution to adjust the pH to 9±0.5 for co-precipitation, filter and separate the precipitate, and use the filtrate in step 4; wash the precipitate with 2L of deionized water at 40℃ for 60min, filter and separate the precipitate after washing;

[0048] 3. The separated precipitate was aged at 80℃ for 5h, the pH was adjusted to 8±0.5, the stirring speed was 400r / min, the precipitate was filtered and separated, and the precipitate was calcined at 500℃ for 6h at a heating rate of 10℃ / min to obtain the product ammonium manganese phosphate.

[0049] 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is formed. Filter and separate the precipitate. Mix the filtrate with the filtrate obtained in step 2. Wash the precipitate with 1L of water and dry it at 80°C for 10h to obtain lithium carbonate.

[0050] 5. The co-precipitated manganese iron ammonium phosphate obtained in step 3 was mixed with the lithium carbonate obtained in step 4 at a molar ratio of 1:1.06, and 15% glucose was added. The mixture was ball-milled at 800 r / min for 15 h. After ball milling, the mixture was sintered at 400℃ for 6 h and 700℃ for 8 h under an argon atmosphere, with a heating rate of 10℃ / min. The sintered product was lithium manganese iron ammonium phosphate.

[0051] The aforementioned lithium manganese iron phosphate, after testing, has a manganese-to-iron ratio of 0.65 and a chemical formula of LiMn. 0.4 Fe 0.6 PO4, with impurities of sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, and lead ≤0.003% and impurity of aluminum ≤0.005%.

[0052] Comparative Example 1

[0053] 1. Take 30g of waste lithium iron phosphate cathode material powder after alkaline washing, mix the powder with 1L of 0.1mol / L dilute sulfuric acid solution (without adding manganese sulfate), add hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 1), acid leaching treatment at 60℃ for 20min, stirring speed is 300r / min, and filter to obtain leachate.

[0054] 2. Add ammonia to the acid leaching solution to adjust the pH to 8±0.5 for co-precipitation, filter and separate the precipitate, and use the filtrate in step 4; wash the precipitate with 1L of deionized water at 30℃ for 30min, filter and separate the precipitate after washing;

[0055] 3. The separated precipitate was aged at 80℃ for 3h, the pH was adjusted to 8±0.5, the stirring speed was 300r / min, the precipitate was filtered and separated, and the precipitate was calcined at 400℃ for 4h at a heating rate of 10℃ / min to obtain the product ammonium iron phosphate.

[0056] 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is formed. Filter and separate the precipitate. Mix the filtrate with the filtrate obtained in step 2. Wash the precipitate with 0.5 L of water and dry it at 60 °C for 8 h to obtain lithium carbonate. 5. Mix the iron ammonium phosphate obtained from the co-precipitation in step 3 with the lithium carbonate obtained in step 4 at a molar ratio of 1:1.05, and add manganese sulfate (Mn:Fe = 6:4) and 10% glucose. Ball mill at 600 r / min for 10 h. After ball milling, sinter at 350 °C for 4 h and 650 °C for 10 h under an argon atmosphere, with a heating rate of 5 °C / min. The sintered product is lithium manganese iron phosphate (LiMn). 0.6 Fe 0.4 PO4).

[0057] In this comparative example, the leaching rate of Fe decreased from 99.45% in Example 1 to 90.47% (a decrease of 8.98%), and the leaching rate of Li decreased from 99.54% to 89.33% (a decrease of 10.21%). Impurity content: the content of impurities such as Na and Al increased from ≤0.005% to ≤0.008%. The first-cycle discharge capacity at 0.1C decreased from 154.93 mAh / g in Example 1 to 141.44 mAh / g (a decrease of 8.7%). This resulted in the capacity retention of the material after 200 cycles at 1C decreasing from 97.76% in Example 1 to 92.13% (a decrease of 5.63%).

[0058] Comparative Example 2

[0059] 1. Take 60g of waste lithium iron phosphate cathode material powder after alkali washing, mix the powder with 1L of 0.2mol / L dilute sulfuric acid solution (without adding manganese sulfate), acid leaching at 60℃ for 30min, stirring at 350r / min, and filter to obtain leachate;

[0060] 2. Add ammonia to the acid leaching solution to adjust the pH to 7.5±0.5 for co-precipitation, filter and separate the precipitate, and use the filtrate in step 4; wash the precipitate with 1.5L of deionized water at 35℃ for 45min, filter and separate the precipitate after washing;

[0061] 3. The separated precipitate was aged at 90℃ for 4 hours, the pH was adjusted to 8.5±0.5, the stirring speed was 350 r / min, the precipitate was filtered and separated, and the precipitate was calcined at 450℃ for 5 hours at a heating rate of 7.5℃ / min to obtain the product ammonium iron phosphate.

[0062] 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is formed. Filter and separate the precipitate. Mix the filtrate with the filtrate obtained in step 2. Wash the precipitate with 0.75 L of water and dry it at 70 °C for 9 h to obtain lithium carbonate.

[0063] 5. The iron ammonium phosphate obtained from co-precipitation in step 3 and the lithium carbonate obtained in step 4 were mixed at a molar ratio of 1:1.07, and manganese sulfate (Mn:Fe = 7:3) was added. Then, 12% glucose was added, and the mixture was ball-milled at 500 r / min for 12 h. After ball milling, sintering was performed at 400℃ for 4 h and then at 650℃ for 12 h under an argon atmosphere, with a heating rate of 7.5℃ / min. The sintered product was lithium manganese iron phosphate (LiMn). 0.7 Fe 0.3 PO4).

[0064] In this comparative example, the leaching rate of Fe decreased from 99.12% in Example 2 to 89.66% (a decrease of 9.46%), and the leaching rate of Li decreased from 99.15% to 88.15% (a decrease of 11%). Impurity content: the content of impurities such as Na and Al increased from ≤0.005% to ≤0.008%. The first-cycle discharge capacity at 0.1C decreased from 153.88 mAh / g in Example 2 to 139.27 mAh / g (a decrease of 9.5%). This resulted in the capacity retention of the material after 200 cycles at 1C decreasing from 97.33% in Example 1 to 90.89% (a decrease of 6.44%).

[0065] Results Testing. The lithium and iron leaching rates in the examples and comparative examples were tested, as well as the electrochemical performance of the prepared lithium manganese iron phosphate was tested. The results are shown in Table 1.

[0066] Table 1. Results of lithium and iron leaching rates and electrochemical performance tests.

[0067]

[0068] The results in the table show that the catalytic effect of manganese ions significantly improves acid leaching efficiency, with a marked effect on increasing the leaching rates of Fe and Li. The comparative example, due to its lower leaching rate, requires higher acid concentrations or longer leaching times, leading to increased total energy consumption. The impurity content in the comparative example increased by approximately 0.003%–0.004%, resulting in a 5%–7% decrease in cycle performance and an 8%–10% decrease in specific capacity. Manganese ions play a catalytic role in the acid leaching stage and provide a manganese source in the co-precipitation stage, avoiding the need for subsequent addition of manganese salts, simplifying the process, and improving the uniformity and purity of the precursor.

[0069] The preparation method of this invention involves simultaneously leaching lithium iron phosphate with sulfuric acid using manganese sulfate as a catalyst, and providing a manganese source for the co-precipitation of iron manganese phosphate, thus achieving the dual benefit of efficient recycling of lithium iron phosphate batteries. The regenerated iron manganese phosphate exhibits a higher voltage plateau and energy density, enhancing the electrochemical performance of the material.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for recycling and upgrading waste lithium iron phosphate cathode materials to regenerate lithium manganese iron phosphate, characterized in that... Includes the following steps: 1) The waste lithium iron phosphate powder after alkaline washing is acid-leached with a 0.1-3 mol / L sulfuric acid solution. Hydrogen peroxide and manganese sulfate are added to the sulfuric acid solution. The solid-liquid ratio is 10-500 g / L. The acid leaching temperature is 20-90℃, the stirring speed is 100-400 r / min, and the acid leaching time is 0.5-3 h. After the reaction is completed, the mixture is filtered and the filtrate is collected. The molar ratio of hydrogen peroxide to lithium in the waste lithium manganese iron phosphate is 0.5-1.

2. The molar ratio of manganese in manganese sulfate to iron in the waste lithium manganese iron phosphate is 0.43-4. 2) Heat the filtrate obtained in step 1) to 50-80°C and add ammonia until the pH reaches 5.5-10. Filter, separate the precipitate and collect the filtrate. 3) The precipitate obtained in step 2) is washed with water and aged, and then calcined; 4) Add sodium carbonate to the filtrate obtained in step 2) until no more precipitate is formed, filter, separate the precipitate and dry it, and collect the filtrate; 5) Add the filtrate obtained in step 4) to the filtrate obtained in step 2) for circulation; 6) Mix the product obtained in step 3) with the product obtained in step 4) and add a carbon source to prepare lithium manganese iron phosphate by ball milling and reduction roasting.

2. The method according to claim 1, characterized in that, In step 3), the washing temperature is 10–50℃, the time is 10 min–2 h, and the solid-liquid ratio is 50–500 g / L; the aging temperature is 50–90℃, the aging pH is 5–9, and the aging time is 2–8 h.

3. The method according to claim 1, characterized in that, In step 3), the heating rate of calcination is 2-10℃ / min, the calcination temperature is 400-700℃, and the calcination time is 2-6h.

4. The method according to claim 1, characterized in that, The reaction temperature for step 4) is 10–50°C, the drying temperature is 50–90°C, and the drying time is 4–10 h.

5. The method according to claim 1, characterized in that, Step 6) The ball milling speed is 200-600 r / min, and the time is 1-5 h.

6. The method according to claim 1, characterized in that, In step 6), the molar ratio of the product obtained in step 3) to the product obtained in step 4) in the mixture is 1:(1~1.07).

7. The method according to claim 1, characterized in that, In step 6), the preferred carbon source is one or more of glucose, sucrose, polyethylene glycol, and carbon nanotubes, and the amount of carbon source added is 10% to 20% of the total mass.

8. The method according to claim 1, characterized in that, The heating rate in step 6) is 2-10℃ / min. The calcination is divided into two stages. The first stage calcination temperature is 250-500℃ and the calcination time is 2-6h. The second stage calcination temperature is 500-800℃ and the calcination time is 8-14h.

9. The method according to claim 1, characterized in that, Step 6) is carried out under an inert atmosphere.

10. The method according to claim 1, characterized in that, Step 6) The recycled material is LiMn x Fe 1-x PO4, Li: (Fe+Mn):P=(1~1.05):(0.96~1):1, 0.3≤x≤0.8.

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