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

Abstract

According to the method for recycling, upgrading and regenerating the lithium iron manganese phosphate from the waste lithium iron phosphate positive electrode material, the waste lithium iron phosphate is leached through a hydrogen peroxide and sulfuric acid system catalyzed by manganese ions, and the acid leaching efficiency is improved. Meanwhile, manganese ions subjected to acid leaching are used as a manganese source to generate a lithium manganese iron phosphate precursor, and finally the high-performance lithium manganese iron phosphate positive electrode material is synthesized. The method is simple in process, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of recycling and reuse of waste lithium ion battery positive electrode materials, and in particular to a method for recycling and regenerating waste lithium iron phosphate (LiFePO4) positive electrode materials into lithium iron manganese phosphate (LiMn x Fe 1-x PO4) method. Background Art

[0002] In recent years, lithium iron phosphate, as an upgraded material of lithium iron phosphate, has become a research hotspot in the field of power batteries and energy storage due to its advantages such as high voltage platform, low cost and high safety. Compared with lithium iron phosphate, lithium iron phosphate increases the voltage platform from 3.4V to 4.1V (vs. LiFePO4) by introducing manganese elements. + / Li), increasing the theoretical energy density by approximately 20% while retaining the thermal stability and long cycle life advantages of lithium iron phosphate. In current industrial production, manganese is typically introduced through the solid-phase method by adding an additional manganese source. However, this method can result in uneven manganese distribution and oversized grains, leading to poor electrochemical performance.

[0003] While research on lithium-ion battery cathode materials is in full swing, the widespread use of lithium-ion batteries in electric vehicles, energy storage devices, and portable electronic products has garnered global attention for their post-disposal recycling and resource reuse. As a key cathode material in the power battery field, lithium iron phosphate (LiFePO4) is widely popular due to its excellent safety, long-lasting cycle performance, and economic efficiency. With the widespread use of LiFePO4 batteries, the challenge of recycling them after retirement has gradually emerged. It is estimated that by 2030, the total amount of discarded LiFePO4 batteries worldwide will exceed 1 million tons. Failure to properly handle these batteries will not only lead to a massive waste of resources but also cause significant damage to the environment.

[0004] Currently, recycling technologies for spent lithium iron phosphate batteries are primarily categorized into three categories: pyrometallurgical recycling, hydrometallurgical recycling, and direct regeneration. Pyrometallurgical recycling extracts metals through a high-temperature process, but the high energy consumption and environmental pollution issues are not negligible. Hydrometallurgical recycling, while effective, involves leaching valuable metals through acidic solutions. However, this process is limited by its cumbersome process and high costs. Direct regeneration repairs spent cathode materials to restore their performance, but this method often struggles to fully restore the material to its original electrochemical state and is difficult to commercialize. Of these technologies, hydrometallurgical recycling dominates, but its inefficient acid leaching process, time-consuming reactions, and complex subsequent separation and purification steps result in high recycling costs.

[0005] Sulfuric acid leaching is a common technique in hydrometallurgy. 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 kinetics of acid leaching. To improve leaching efficiency, existing technologies often use strategies such as increasing temperature, increasing acid concentration, or introducing oxidants (such as hydrogen peroxide), but these methods are often accompanied by environmental pollution and high costs. Summary of the Invention

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

[0007] To achieve the above object, the technical solution of the present invention includes the following steps: 1) acid leaching the waste lithium iron phosphate powder after alkali washing using a 0.1-3 mol / L sulfuric acid solution, adding hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 0.5-1.2) and manganese sulfate (the molar ratio of manganese to iron is 0.43-4) to the sulfuric acid solution, with a solid-liquid ratio of 10-500 g / L, the acid leaching temperature being 20-90° C., the stirring speed being 100-400 r / min, the acid leaching time being 0.5-3 h, and filtering after the reaction and collecting the filtrate; 2) adding aqueous ammonia to the filtrate obtained in step 1) until the pH reaches 5.5 to 10, filtering to separate the precipitate and collecting the filtrate; 3) washing and aging the precipitate obtained in step 2), and then calcining; 4) adding sodium carbonate to the filtrate obtained in step 2) until no more precipitate is generated, filtering and separating the precipitate, collecting the filtrate, washing the precipitate with water, and drying; 5) adding the filtrate obtained in step 4) to the filtrate obtained in step 2) for circulation; 6) The product obtained in step 3) is mixed with the product obtained in step 4), and a carbon source is added to perform ball milling and reduction roasting to prepare lithium manganese iron phosphate.

[0008] The washing temperature in step 3) is 10-50° C., the washing time is 10 min-2 h, and the solid-liquid ratio is 50-500 g / L; the aging temperature is 50-90° C., the aging pH is 5-9, and the aging time is 2-8 h.

[0009] The heating rate of calcination in step 3) is 2-10° C. / min, the calcination temperature is 400-700° C., and the calcination time is 2-6 hours.

[0010] The reaction temperature of step 4) is 10-50° C.; the solid-liquid ratio of washing is 50-500 g / L; the washing time is 0.5-3 h; the drying temperature is 50-90° C.; and the drying time is 4-10 h.

[0011] In step 6), the ball milling speed is 200 to 600 r / min, and the time is 6 to 14 hours.

[0012] The molar ratio of the product obtained in step 3) to the product obtained in step 4) in the mixture in step 6) is 1:(1-1.07).

[0013] The carbon source in step 6) is preferably one or more of glucose, sucrose, mono-polyethylene glycol, and carbon nanotubes, and the amount of the carbon source added is 10% to 20% of the total mass.

[0014] The heating rate of the calcination in step 6) is 2-10°C / min, and the calcination is divided into two stages. The calcination temperature of the first stage is 250-500°C and the calcination time is 2-6 hours. The calcination temperature of the second stage is 500-800°C and the calcination time is 8-14 hours.

[0015] Wherein step 6) is carried out under an inert atmosphere.

[0016] Wherein step 6) the recycled material is LiMn x Fe 1-x PO4 (lithium manganese iron phosphate), Li:(Fe+Mn):P=(1~1.05):(0.96~1):1, 0.3≤x≤0.8.

[0017] The present invention realizes the efficient recycling and regeneration of waste lithium iron phosphate cathode materials, avoiding resource waste and environmental pollution. By introducing manganese elements, the recycled material is lithium manganese iron phosphate (LiMn x Fe 1-x PO4), with a higher voltage platform and energy density, improving the electrochemical performance of the material. This method is simple, low-cost, and suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of the present invention;

[0019] Figure 2 The XRD patterns of the co-precipitated manganese iron phosphate and the upgraded regenerated manganese iron lithium phosphate obtained in Example 1 of the present invention are shown in FIG.

[0020] Figure 3The charge-discharge curve and cycle performance diagram of the lithium manganese iron phosphate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided for a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are intended for exemplary purposes only and are not intended to limit the scope of protection of the present application.

[0022] The main elements and contents of the waste lithium iron phosphate battery powder after alkali washing in the following examples and comparative examples are shown in Table 1: Table 1 Main elements and contents of waste lithium iron phosphate battery powder after alkali washing Element Li Fe P C other Content (wt.%) 5.34 38.24 22.21 14.78 19.43

[0023] Example 1: 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, add hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 1) and manganese sulfate (the molar ratio of Fe:Mn is 4:6), and acid leaching at 60°C for 20min with a stirring speed of 300r / min. Filter to obtain the leachate; 2. Add ammonia water 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°C for 30 minutes, filter and separate the precipitate after washing; 3. The separated precipitate was aged at 80°C for 3 h, the pH was adjusted to 8±0.5, the stirring speed was 300 r / min, the precipitate was filtered and separated, and the obtained precipitate was calcined at 400°C for 4 h at a heating rate of 10°C / min to obtain the product ammonium manganese ferrous phosphate; 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is produced, filter and separate the precipitate, and 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. The ammonium manganese ferrous phosphate obtained by coprecipitation in step 3 and the lithium carbonate obtained in step 4 were mixed in a molar ratio of 1:1.05, and 10% glucose was added, and the mixture was ball-milled at a speed of 600 r / min for 10 h; after ball milling, the mixture was sintered at 350°C for 4 h and 650°C for 10 h in an argon atmosphere, with a heating rate of 5°C / min; the sintered product was lithium manganese ferrous phosphate.

[0024] The above lithium manganese iron phosphate was tested and its manganese to iron ratio was 1.48, and its chemical formula was LiMn 0.6 Fe 0.4PO4, the content of its impurity sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium and lead is ≤0.003%, and the content of its impurity aluminum is ≤0.005%.

[0025] Example 2: 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, add hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 0.8) and manganese sulfate (the molar ratio of Fe:Mn is 3:7), and acid leaching at 60°C for 0.5h with a stirring speed of 350r / min. Filter to obtain the leachate; 2. Add ammonia water to the acid extract 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 1.5 L of deionized water at 35°C for 45 minutes, filter and separate the precipitate after washing; 3. The separated precipitate was aged at 90°C for 4 h, the pH was adjusted to 8.5±0.5, the stirring speed was 350 r / min, the precipitate was filtered and separated, and the obtained precipitate was calcined at 450°C for 5 h at a heating rate of 7.5°C / min to obtain the product ammonium manganese ferrous phosphate; 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is produced, filter and separate the precipitate, and 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; 5. The ammonium manganese ferrous phosphate obtained by coprecipitation in step 3 and the lithium carbonate obtained in step 4 were mixed in a molar ratio of 1:1.07, and 12% glucose was added, and ball milled at a speed of 500 r / min for 12 h; after ball milling, sintering was performed in an argon atmosphere at 400°C for 4 h and 650°C for 12 h, with a heating rate of 7.5°C / min; the sintered product was lithium manganese ferrous phosphate.

[0026] The above lithium manganese iron phosphate was tested and its manganese to iron ratio was 2.33, and its chemical formula was LiMn 0.7 Fe 0.3 PO4, the content of its impurity sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium and lead is ≤0.003%, and the content of its impurity aluminum is ≤0.005%.

[0027] Example 3 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, add hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 0.9) and manganese sulfate (the molar ratio of Fe:Mn is 6:4), and acid leaching at 80°C for 40min with a stirring speed of 400r / min. Filter to obtain the leachate; 2. Add ammonia water to the acid extract 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°C for 60 minutes, filter and separate the precipitate after washing; 3. The separated precipitate was aged at 80°C for 5 h, the pH was adjusted to 8±0.5, the stirring speed was 400 r / min, the precipitate was filtered and separated, and the obtained precipitate was calcined at 500°C for 6 h at a heating rate of 10°C / min to obtain the product ammonium manganese ferrous phosphate; 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is produced, filter and separate the precipitate, and mix the filtrate with the filtrate obtained in step 2; wash the precipitate with 1 L of water and dry it at 80° C. for 10 h to obtain lithium carbonate; 5. The ammonium manganese ferrous phosphate obtained by co-precipitation in step 3 is mixed with the lithium carbonate obtained in step 4 in a molar ratio of 1:1.06, and 15% glucose is added, and the mixture is ball-milled at a speed of 800 r / min for 15 h; after ball milling, the mixture is sintered at 400°C for 6 h and 700°C for 8 h in an argon atmosphere, with a heating rate of 10°C / min; the sintered product is lithium manganese ferrous phosphate.

[0028] The above lithium manganese iron phosphate was tested and its manganese iron ratio was 0.65, and its chemical formula was LiMn 0.4 Fe 0.6 PO4, the content of its impurity sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium and lead is ≤0.003%, and the content of its impurity aluminum is ≤0.005%.

[0029] Comparative Example 1 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 (without adding manganese sulfate), add hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 1), and acid leaching at 60°C for 20min with a stirring speed of 300r / min. Filter to obtain the leachate; 2. Add ammonia water 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°C for 30 minutes, filter and separate the precipitate after washing; 3. The separated precipitate was aged at 80°C for 3 h, the pH was adjusted to 8±0.5, the stirring speed was 300 r / min, the precipitate was filtered and separated, and the obtained precipitate was calcined at 400°C for 4 h at a heating rate of 10°C / min to obtain the product ammonium ferric phosphate; 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is produced, filter and separate the precipitate, and mix the filtrate with the filtrate obtained in step 2; wash the precipitate with 0.5L of water and dry it at 60°C for 8h to obtain lithium carbonate; 5. Mix the ammonium ferric phosphate obtained by co-precipitation in step 3 with the lithium carbonate obtained in step 4 in a molar ratio of 1:1.05, and additionally add manganese sulfate (Mn:Fe=6:4), and then add 10% glucose, and ball mill at a speed of 600r / min for 10h; after ball milling, sinter at 350°C for 4h and 650°C for 10h 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).

[0030] In this comparative example, the Fe leaching rate decreased from 99.45% in Example 1 to 90.47% (a decrease of 8.98%), and the Li leaching rate 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 0.1C first cycle discharge capacity decreased from 154.93mAh / g in Example 1 to 141.44mAh / g (a decrease of 8.7%). As a result, the capacity retention rate of the material after 200 cycles at 1C decreased from 97.76% in Example 1 to 92.13% (a decrease of 5.63%).

[0031] Comparative Example 2 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 the leachate; 2. Add ammonia water to the acid extract 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 1.5 L of deionized water at 35°C for 45 minutes, filter and separate the precipitate after washing; 3. The separated precipitate was aged at 90°C for 4 h, the pH was adjusted to 8.5±0.5, the stirring speed was 350 r / min, the precipitate was filtered and separated, and the obtained precipitate was calcined at 450°C for 5 h at a heating rate of 7.5°C / min to obtain the product ammonium ferric phosphate; 4. Add sodium carbonate to the filtrate obtained in step 2 until no precipitate is produced, filter and separate the precipitate, and 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; 5. The ammonium ferric phosphate obtained by coprecipitation in step 3 was mixed with the lithium carbonate obtained in step 4 in a molar ratio of 1:1.07, and manganese sulfate (Mn:Fe=7:3) was additionally added, and 12% glucose was added, and ball milled at a speed of 500r / min for 12h; after ball milling, sintering was carried out under an argon atmosphere at 400℃ for 4h and 650℃ for 12h, with a heating rate of 7.5℃ / min; the sintered product was lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4).

[0032] In this comparative example, the Fe leaching rate decreased from 99.12% in Example 2 to 89.66% (a decrease of 9.46%), and the Li leaching rate 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 0.1C first cycle discharge capacity decreased from 153.88mAh / g in Example 2 to 139.27mAh / g (a decrease of 9.5%). As a result, the capacity retention rate of the material after 200 cycles at 1C decreased from 97.33% in Example 1 to 90.89% (a decrease of 6.44%).

[0033] Results Test: 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. The results are shown in Table 1.

[0034] Table 1 Lithium and iron leaching rates and electrochemical performance test results

[0035] The results in the table show that the catalytic effect of manganese ions significantly improves acid leaching efficiency, with a significant impact on increasing the leaching rates of Fe and Li. The lower leaching rate in the comparative example requires higher acid concentrations or longer leaching times, which increases overall energy consumption. Impurity levels in the comparative example increased by approximately 0.003% to 0.004%, resulting in a 5% to 7% decrease in cycle performance and an 8% to 10% decrease in specific capacity. Manganese ions catalyze the acid leaching stage and provide a manganese source during the coprecipitation stage, eliminating the need for the subsequent addition of manganese salts, simplifying the process, and improving precursor uniformity and purity.

[0036] The preparation method of the present invention uses manganese sulfate to catalyze sulfuric acid leaching of lithium iron phosphate, while also providing a manganese source for co-precipitation of manganese iron phosphate, achieving efficient recycling of lithium iron phosphate batteries. The regenerated manganese iron phosphate has a higher voltage platform and energy density, improving the electrochemical performance of the material.

[0037] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for recycling and upgrading waste lithium iron phosphate positive electrode materials to regenerate lithium manganese iron phosphate, characterized in that The following steps are involved: 1) acid leaching the waste lithium iron phosphate powder after alkali washing using a 0.1-3 mol / L sulfuric acid solution, adding hydrogen peroxide (the molar ratio of hydrogen peroxide to lithium is 0.5-1.2) and manganese sulfate (the molar ratio of manganese to iron is 0.43-4) to the sulfuric acid solution, with a solid-liquid ratio of 10-500 g / L, the acid leaching temperature being 20-90° C., the stirring speed being 100-400 r / min, the acid leaching time being 0.5-3 h, and filtering after the reaction and collecting the filtrate; 2) heating the filtrate obtained in step 1) to 50-80° C., adding aqueous ammonia until the pH reaches 5.5-10, filtering, separating the precipitate, and collecting the filtrate; 3) washing and aging the precipitate obtained in step 2), and then calcining; 4) adding sodium carbonate to the filtrate obtained in step 2) until no more precipitate is generated, filtering, separating the precipitate and drying it, and collecting the filtrate; 5) adding the filtrate obtained in step 4) to the filtrate obtained in step 2) for circulation; 6) The product obtained in step 3) is mixed with the product obtained in step 4), and a carbon source is added to perform ball milling and reduction roasting to prepare lithium manganese iron phosphate.

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

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

4. The method according to claim 1, wherein The reaction temperature of step 4) is 10-50° C., the drying temperature is 50-90° C., and the drying time is 4-10 hours.

5. The method according to claim 1, wherein 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 The molar ratio of the product obtained in step 3) to the product obtained in step 4) in the mixture in step 6) is 1:(1-1.07).

7. The method according to claim 1, characterized in that The carbon source in step 6) is preferably one or more of glucose, sucrose, mono-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 of the calcination in step 6) is 2-10°C / min, and the calcination is divided into two stages. The calcination temperature of the first stage is 250-500°C, and the calcination time is 2-6h. The calcination temperature of the second stage is 500-800°C, 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 (lithium manganese iron phosphate), Li:(Fe+Mn):P=(1~1.05):(0.96~1):1, 0.3≤x≤0.8.

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