Method for directly regenerating lithium iron manganese phosphate material from waste lithium iron phosphate and application

Abstract

The invention discloses a method for directly regenerating a lithium iron manganese phosphate material from waste lithium iron phosphate and application, and the method comprises the following steps: discharging, disassembling and separating a waste lithium iron phosphate battery to obtain waste lithium iron phosphate positive electrode powder, and measuring the contents of iron, phosphorus and lithium in the waste lithium iron phosphate positive electrode powder; a lithium source, a manganese source, a phosphorus source and cane sugar are supplemented according to the determination result, so that the molar ratio of Li to Mn to Fe to P in the system reaches 1.05: 0.3: 0.7: 1, and the adding amount of cane sugar accounts for 15% of the mass of the target product lithium manganese iron phosphate; the method comprises the following steps: preparing a phosphorus source and cane sugar into a mixed solution A, independently ball-milling and activating waste positive electrode powder, mixing with a lithium source, a manganese source and the solution A, ball-milling, and drying to obtain powder; and finally, sintering at 600-800 DEG C in an inert atmosphere, and cooling to obtain the lithium iron manganese phosphate positive electrode material. According to the method, in-situ doping of manganese is achieved on the premise that a waste particle framework is reserved, the material is directly repaired and upgraded from lithium iron phosphate to lithium manganese iron phosphate, the energy density is improved by about 20%, excellent electrochemical performance is shown, and good industrialization prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of direct regeneration technology of waste lithium batteries, and in particular to a method and application for the direct regeneration of manganese iron phosphate material from waste lithium iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) batteries, with their superior safety performance, low cost, and long cycle life, have been widely used in new energy vehicles, energy storage systems, and portable electronic devices. With the rapid development of the new energy industry, the market share of LFP batteries continues to grow. Since the service life of LFP batteries is typically 5-8 years, a large number of retired and used LFP batteries have entered the recycling and processing stage.

[0003] Used lithium iron phosphate batteries contain not only valuable metals such as iron, lithium, and phosphorus, but also toxic and hazardous components such as electrolytes and binders. Improper recycling and disposal can lead to a waste of metal resources and potentially cause environmental problems such as soil and water pollution. Currently, the mainstream recycling technologies for used lithium iron phosphate batteries fall into three main categories: (1) Pyrometallurgical recovery technology: Organic components in the battery are removed by high-temperature roasting, and valuable metals are separated by the density difference of molten metal. This technology has problems such as high energy consumption, easy generation of harmful gases, and low metal recovery rate.

[0004] (2) Wet recovery technology: This technology uses acid and alkali solutions to dissolve the metal elements in the cathode material, and separates components such as lithium, iron, and phosphorus stepwise by adjusting the pH value and adding precipitants, and finally recovers them in the form of lithium carbonate, iron phosphate, etc. Although this technology has a high metal recovery rate, the process is complex, the reagent consumption is large, the wastewater treatment cost is high, and the recovered products need to be resynthesized into cathode materials, so it cannot directly achieve the integration of "repair-upgrade".

[0005] (3) Direct regeneration technology: This technology removes impurities from the surface of the cathode material and repairs crystal structure defects through physical or chemical means, without completely decomposing the cathode material into a single metal compound. However, existing direct regeneration technologies mainly target the performance repair of lithium iron phosphate materials and can only restore some of the electrochemical performance of retired battery cathode materials. However, this type of method cannot change the intrinsic low voltage characteristics (discharge plateau ~3.4V) of lithium iron phosphate materials, resulting in the energy density of the regenerated material still being limited to this voltage plateau (theoretical value of about 578Wh / kg), which is difficult to meet the demand for high-energy-density battery materials in fields such as new energy vehicles and high-end energy storage.

[0006] Theoretically, manganese has a high redox potential. Doping lithium iron phosphate crystals with manganese can raise the discharge voltage plateau from 3.4V to over 4.1V, increasing the energy density by approximately 20%. However, applying this principle to the direct regeneration of waste lithium iron phosphate faces challenges, including residual carbon layers on the surface of waste particles, lattice defects, and the presence of some Fe. 2+ Oxidized to Fe 3+ Technical obstacles, such as those hindering the uniform doping of Mn and the complete restoration of the crystal lattice, make it difficult to achieve. Therefore, developing a method for directly regenerating lithium manganese iron phosphate from waste lithium iron phosphate, and simultaneously realizing direct regeneration technology with upgraded manganese doping, can simplify the recycling process, reduce energy consumption and costs, and significantly improve the energy density of the material, thus having significant industrialization value. Summary of the Invention

[0007] This application provides a method and application for directly regenerating lithium manganese iron phosphate from waste lithium iron phosphate, which solves the technical problem that existing direct regeneration technologies can only repair lithium iron phosphate but cannot improve energy density. It achieves the technical effect of upgrading the material into high-voltage lithium manganese iron phosphate by accurately supplementing lithium, manganese, phosphorus and carbon sources while retaining the particle skeleton of waste lithium iron phosphate, so as to allow manganese element to be doped into the crystal lattice in situ, thereby significantly improving the energy density.

[0008] This application provides a method for directly regenerating lithium manganese iron phosphate material from waste lithium iron phosphate, characterized by the following steps: Step 1 involves discharging, dismantling, and separating waste lithium iron phosphate batteries to obtain waste lithium iron phosphate cathode powder, and then determining the content of iron, phosphorus, and lithium in the waste lithium iron phosphate cathode powder. Step Two: Based on the results of Step One, determine the amounts of lithium, manganese, phosphorus, and sucrose that need to be added, so that the molar ratio of lithium, manganese, iron, and phosphorus in the system after supplementation reaches Li:Mn:Fe:P = 1.05:0.3:0.7:1. The amount of sucrose added accounts for 15% of the mass of the target product, lithium manganese iron phosphate. Step 3: Disperse the waste lithium iron phosphate cathode powder weighed in Step 2 in deionized water and ball mill it to activate the surface; disperse the phosphorus source and sucrose weighed in Step 2 in deionized water to prepare mixed solution A; mix the ball-milled waste lithium iron phosphate slurry, lithium source, and manganese source with mixed solution A, ball mill, dry, and grind to obtain precursor powder; Step four involves sintering the precursor powder at 600-800°C under an inert atmosphere, followed by cooling to obtain lithium manganese iron phosphate cathode material.

[0009] Preferably, the ball milling in step three is wet ball milling, the ball milling medium is water or ethanol, the ball milling time is 4-12 hours, and the ball milling speed is 200-600 rpm.

[0010] Preferably, the drying temperature in step three is 60-100℃ and the drying time is 8-16h.

[0011] Preferably, the sintering temperature in step four is 700℃, and the holding time is 8~12h.

[0012] The present invention also provides a lithium manganese iron phosphate cathode material obtained by the method described in any of the above-mentioned methods.

[0013] The present invention also provides an application of the aforementioned lithium manganese iron phosphate cathode material in the preparation of lithium-ion batteries.

[0014] One or more technical solutions provided in the embodiments of this application have at least the following technical effects: 1. This application transforms the product from LiFePO4 to LiMn by introducing manganese during the regeneration process. 0.3 Fe 0.7 With PO4, the discharge voltage platform is increased to 4.1V. According to the energy density formula, the energy density is increased by about 20%. As shown in Example 2, the 0.1C discharge specific capacity of the button cell assembled based on the embodiments of this application reaches 152.3mAh / g. Combined with the voltage increase, the energy density is significantly higher than that of waste LFP.

[0015] 2. This application uses a solid-state method to allow Mn atoms to diffuse into the crystal lattice without destroying the skeleton of waste LFP particles, which not only repairs the defects generated during the recycling process, but also upgrades the material properties.

[0016] 3. This application precisely controls the amount of sucrose used to 15% of the target product mass, which provides a sufficient reducing atmosphere to reduce Fe. 3+ The reduction to Fe 2+ It can also synergize with the residual carbon on the surface of waste LFP to form a uniform gradient conductive carbon layer, which prevents Fe from being released. 2+ Oxidation is avoided, thus preventing kinetic degradation caused by excessive carbon layer thickness. The coin cell assembled based on the embodiments of this application retains 97.2% of its capacity after 100 cycles at 0.2C rate, demonstrating excellent cycle stability. Attached Figure Description

[0017] Figure 1 This is the XRD pattern of the lithium manganese iron phosphate material synthesized in Example 1 of this application.

[0018] Figure 2 The graph shows the charge-discharge performance of the lithium manganese iron phosphate button battery assembled in Example 2 of this application at a rate of 0.1 C.

[0019] Figure 3 The graph shows the cycle performance of the lithium manganese iron phosphate coin cell assembled in Example 2 of this application at a rate of 0.2 C. Detailed Implementation

[0020] This application provides a method and application for directly regenerating lithium manganese iron phosphate (LFP) material from waste lithium iron phosphate. The overall approach is as follows: First, elemental analysis is performed on the waste lithium iron phosphate cathode powder to determine its actual lithium, iron, and phosphorus content, identifying the difference between this and the stoichiometric ratio of the target product, lithium manganese iron phosphate. Then, based on the analysis results, the missing lithium, manganese, phosphorus, and carbon sources are precisely supplemented to achieve the target molar ratio. Next, ball milling is used to ensure sufficient contact between the old and new components and to activate the particle surface. Finally, high-temperature solid-state sintering is performed under a reducing atmosphere provided by sucrose decomposition to achieve Fe... 3+ The reduction of Mn 2+ In-situ doping and lattice repair and reconstruction ultimately regenerate waste lithium iron phosphate directly into high-voltage lithium manganese iron phosphate material.

[0021] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods. Example 1

[0022] (1) A batch of retired lithium iron phosphate power batteries with approximately 1500 cycles and about 75% remaining capacity were immersed in a 10% NaCl solution for 8 hours until fully discharged. Mechanical disassembly was performed in a fume hood to remove the outer casing and separate the positive electrode, negative electrode, and separator. The obtained positive electrode was cut into 2cm × 2cm pieces and placed in a tube furnace. It was then heat-treated at 500℃ for 3 hours under a nitrogen atmosphere to pyrolyze the binder, yielding the positive electrode material and aluminum foil. The heat-treated powder was collected, passed through a 200-mesh sieve, and the waste lithium iron phosphate positive electrode powder was obtained, designated as waste LFP powder, for later use.

[0023] (2) Accurately weigh 1.0 g of the waste LFP powder obtained in step (1) and determine the content of Li, Fe, and P elements in it using inductively coupled plasma optical emission spectrometry (ICP-OES). The results show that the molar ratio of Li, Fe, and P in the waste LFP powder is approximately 0.95:1.00:1.01. Compared with the stoichiometric ratio of 1:1:1 for standard lithium iron phosphate, there is a significant loss of lithium, while the ratio of iron and phosphorus remains basically unchanged.

[0024] (3) The target product of this embodiment is lithium manganese iron phosphate, and its chemical formula is LiMn. 0.3 Fe 0.7PO4, that is, the target molar ratio of Li:Mn:Fe:P in the system is 1.05:0.3:0.7:1. Based on the determination results of step (2), waste LFP powder is used. Specifically: First, weigh 100g of the waste LFP powder obtained in step (1), then weigh lithium carbonate as the lithium source, manganese carbonate as the manganese source, and ammonium dihydrogen phosphate as the phosphorus source, so that the molar ratio of Li, Mn, Fe and P in the supplemented system reaches 1.05:0.3:0.7:1. Weigh sucrose as the carbon source, and its addition amount accounts for 15% of the theoretical mass of the target product lithium manganese iron phosphate.

[0025] (4) Disperse 100g of waste LFP powder weighed in step (3) in 150mL of deionized water and ball mill it at 400rpm for 4h in a planetary ball mill to further refine the powder and activate the surface.

[0026] Dissolve the ammonium dihydrogen phosphate and sucrose weighed in step (3) in 30 mL of deionized water to prepare mixed solution A.

[0027] The lithium carbonate and manganese carbonate weighed in step (3) are mixed with the waste LFP slurry after ball milling, and then mixed solution A is added. After shaking evenly, the mixture is transferred to a zirconia ball mill jar. Zirconia grinding balls (500 mL ball mill jar volume) are added at a ball-to-material mass ratio of 10:1, and the mixture is ball milled at 400 rpm for 6 hours.

[0028] After ball milling, the solution was poured into a glass beaker and dried in an oven at 80°C for 12 hours. The dried block was then ground into powder in a mortar and passed through a 200-mesh sieve to obtain the precursor powder.

[0029] (5) Place the above precursor powder in a quartz boat, put it into the quartz tube of the tubular furnace, use a vacuum pump to draw the quartz tube to negative pressure, and then introduce high-purity argon gas to raise the gas pressure to the outside gas pressure. Repeat this operation three times to fully remove the air inside the tube.

[0030] Under an argon atmosphere, the temperature of the tube furnace was increased from room temperature to 700℃ at a heating rate of 5℃ / min and held for 10 hours. During solid-state sintering, the precursor gradually nucleated and grew. After cooling to room temperature, the synthesized lithium manganese iron phosphate cathode powder was obtained, denoted as LiMn. 0.3 Fe 0.7 PO4.

[0031] For LiMn 0.3 Fe 0.7 For XRD testing of PO4, please refer to [link / reference]. Figure 1 The synthesized lithium manganese iron phosphate exhibits distinct characteristic peaks, high diffraction peak intensities, and the absence of impurity phase peaks, indicating the successful synthesis of highly crystalline lithium manganese iron phosphate material. Example 2

[0032] The lithium manganese iron phosphate cathode powder, conductive agent SuperP, and binder PVDF synthesized in Example 1 were weighed according to a mass ratio of 8:1:1. The powder was dispersed in an appropriate amount of N-methylpyrrolidone solution and magnetically stirred for 10 hours to obtain a uniformly dispersed cathode slurry. The mixed slurry was coated onto aluminum foil and dried in a vacuum oven at 80°C for 12 hours.

[0033] Using lithium manganese iron phosphate as the positive electrode, lithium foil as the negative electrode, and polypropylene as the separator, 15 μL of electrolyte was added to both sides of the positive and negative electrodes. The coin cell was assembled in the following order: positive electrode shell, positive electrode, electrolyte, separator, electrolyte, negative electrode, gasket, spring, and negative electrode shell. After the assembled battery was left to stand at 27°C for 6 hours, its electrochemical performance was tested at 0.1C (1C = 170mAh / g) and 2.5V - 4.5V.

[0034] In this embodiment, the electrolyte, gaskets, springs, battery casings, etc. used in the coin cell assembly are all commercially available materials that are conventional in the art, and their specific specifications are known to those skilled in the art.

[0035] For electrochemical testing of the battery in Example 2, please refer to [reference needed]. Figure 2 LiMn 0.3 Fe 0.7 The initial capacity of PO4 at 0.1C was 152.3 mAh / g. The charge-discharge curves showed dual voltage plateaus at 3.4V and 4.1V, confirming successful Mn doping and participation in the electrochemical reaction. Please refer to [reference needed]. Figure 3 LiMn 0.3 Fe 0.7 The graph shows the change in discharge specific capacity of PO4 after several cycles at 0.2C. After 100 cycles at 0.2C, the capacity retention rate is 97.2%.

[0036] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0037] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for directly regenerating lithium manganese iron phosphate material from waste lithium iron phosphate, characterized in that, Includes the following steps: Step 1 involves discharging, dismantling, and separating waste lithium iron phosphate batteries to obtain waste lithium iron phosphate cathode powder, and then determining the content of iron, phosphorus, and lithium in the waste lithium iron phosphate cathode powder. Step Two: Based on the measurement results in Step One, determine the amounts of lithium, manganese, phosphorus, and sucrose that need to be added, so that the molar ratio of lithium, manganese, iron, and phosphorus in the supplemented system reaches Li:Mn:Fe:P = 1.05:0.3:0.7:

1. The amount of sucrose added accounts for 15% of the mass of the target product, lithium manganese iron phosphate. Step 3: Disperse the waste lithium iron phosphate cathode powder weighed in Step 2 in deionized water and ball mill it to activate the surface; disperse the phosphorus source and sucrose weighed in Step 2 in deionized water to prepare mixed solution A; mix the ball-milled waste lithium iron phosphate slurry, lithium source, and manganese source with mixed solution A, ball mill, dry, and grind to obtain precursor powder; Step four involves sintering the precursor powder at 600-800°C under an inert atmosphere, followed by cooling to obtain lithium manganese iron phosphate cathode material.

2. The method for directly regenerating lithium manganese iron phosphate material from waste lithium iron phosphate as described in claim 1, characterized in that, The ball milling described in step three is a wet ball milling process, with water or ethanol as the milling medium, a milling time of 4-12 hours, and a milling speed of 200-600 rpm.

3. The method for directly regenerating lithium manganese iron phosphate material from waste lithium iron phosphate as described in claim 1, characterized in that, The drying temperature in step three is 60-100℃, and the drying time is 8-16 hours.

4. The method for directly regenerating lithium manganese iron phosphate material from waste lithium iron phosphate as described in claim 1, characterized in that, The sintering temperature in step four is 700℃, and the holding time is 8~12h.

5. The lithium manganese iron phosphate cathode material obtained by the method according to any one of claims 1 to 4.

6. The application of the lithium iron phosphate cathode material according to claim 5 in the preparation of lithium-ion batteries.

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