A method for preparing aluminum-doped modified lithium manganese iron phosphate positive electrode material from lithium extraction by-product of waste lithium ion batteries

Abstract

The application discloses a method for preparing aluminum-doped modified lithium manganese iron phosphate positive materials from lithium-extraction by-products of waste lithium ion batteries, which converts metal aluminum in waste lithium iron phosphate positive electrode powder and waste lithium manganese oxide positive electrode powder into aluminum ions, and dopes the aluminum ions into the crystal cell of lithium manganese iron phosphate through ion diffusion in the subsequent calcination process, so as to obtain aluminum-doped modified lithium manganese iron phosphate positive materials. The method of the application utilizes trace metal aluminum impurities in waste electrode materials to perform aluminum ion doping modification on lithium manganese iron phosphate positive materials, which can effectively improve the electrochemical performance of the lithium manganese iron phosphate positive materials, thereby solving the problem that the electrochemical performance of the solid-phase directly regenerated materials cannot meet the commercial application requirements.

Description

Technical Field

[0001] This invention relates to a method for preparing aluminum-doped modified lithium manganese iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion battery electrode materials, belonging to the field of lithium-ion battery recycling and cathode material preparation. Background Technology

[0002] Lithium-ion batteries are widely used in power batteries for new energy vehicles due to their high energy density and low cost. However, due to capacity decay, lithium-ion power batteries will face retirement after 5-8 years of use. It is estimated that by 2025, the amount of retired power lithium batteries will reach 134.49 GWh, amounting to 803,600 tons. The recycling and remanufacturing of lithium-ion battery electrode materials are crucial measures for achieving the sustainable development of lithium-ion batteries.

[0003] Currently, the mainstream methods for lithium-ion battery recycling include hydrometallurgy and pyrometallurgy. However, hydrometallurgical recycling is complex and generates large amounts of wastewater; pyrometallurgy is energy-intensive, struggles to remove metallic impurities, and emits toxic fumes. Furthermore, the byproducts of lithium extraction from both methods, iron phosphate and manganese dioxide, are often discarded directly, resulting in resource waste and environmental risks. Current research challenges lie in the high-value utilization of lithium extraction byproducts and in the environmentally friendly treatment of impurities in waste cathode material mixtures.

[0004] Most existing technologies for recycling waste lithium-ion battery cathode materials using solid-state methods to prepare new cathode materials are based on manual or automated fine sorting of waste cathode materials, without addressing the issue of metal impurity treatment. This invention reveals that after discharging and dismantling retired lithium iron phosphate and lithium manganese oxide batteries to obtain battery cells, residual electrolyte and binders are removed by pyrolysis at 500°C under an inert atmosphere. The mixture is then subjected to crushing, sieving, air separation, magnetic separation, ammonia leaching for copper removal, and flotation (due to the different densities of the waste positive and negative electrode powders, the negative electrode graphite powder floats while the positive electrode powder sinks in the flotation tank; a collector and frother are then added to remove the foam, followed by filtration and drying) to obtain waste cathode powder. Subsequently, these are subjected to acid leaching for lithium extraction (acetic acid for waste lithium iron phosphate cathode powder and sulfuric acid for waste lithium manganese oxide cathode powder). After filtration and drying, lithium extraction byproducts iron phosphate and manganese dioxide powder are obtained. When using this recovered lithium extraction byproduct as raw material, and supplementing it with appropriate amounts of lithium and phosphorus sources to prepare electrode materials for use in lithium-ion batteries, trace amounts of metallic impurities may cause the crystal structure of the positive electrode material to tend towards a metastable state during battery charging and discharging, thus leading to battery performance degradation. The impact of aluminum impurities is most pronounced, considering that Al... 3+ / Thermodynamic standard electrode potential of Al (1.38V vs Li) +The aluminum content ( / Li) is far below the normal operating potential of most cathodes. Therefore, aluminum impurities not only reduce the performance of existing 4V lithium-ion batteries, but also trigger a series of side reactions. In severe cases, the aluminum fragments produced can cause internal short circuits, leading to battery failure. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing aluminum-doped modified lithium manganese iron phosphate cathode material from lithium extraction byproducts of spent lithium-ion batteries. This method aims to solve the problem of degraded electrochemical performance of recycled cathode materials due to the presence of metallic aluminum impurities. By converting the metallic aluminum into aluminum ions, and then incorporating them into the lithium manganese iron phosphate cell through ion diffusion during the subsequent calcination and reprocessing process, not only are the drawbacks of the presence of metallic aluminum impurities resolved, but the electrical conductivity of the material grains is also improved. Aluminum doping modification enhances the relevant electrochemical performance of the reprocessed material, making it suitable for application in energy storage batteries.

[0006] To achieve its objectives, the present invention employs the following technical solution:

[0007] A method for preparing aluminum-doped modified lithium iron phosphate cathode material from lithium extraction byproducts of spent lithium-ion batteries includes the following steps:

[0008] Step 1: Process retired lithium iron phosphate batteries and retired lithium manganese oxide batteries separately to obtain waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder respectively;

[0009] Step 2: The waste lithium iron phosphate cathode powder is treated with a mixture of acetic acid and phosphoric acid to leach lithium ions and produce iron phosphate precipitate, while converting elemental aluminum into aluminum ions. Then, the pH of the system is adjusted with lithium hydroxide solution to convert aluminum ions into aluminum phosphate precipitate. The resulting precipitate is washed with ethanol, filtered and dried to obtain lithium extraction byproduct A.

[0010] Waste lithium manganese oxide cathode powder was leached with a mixture of sulfuric acid and phosphoric acid to leach lithium ions and produce manganese dioxide precipitate, while simultaneously converting elemental aluminum into aluminum ions. The pH of the system was then adjusted with lithium hydroxide solution to convert aluminum ions into aluminum phosphate precipitate. The resulting precipitate was washed with ethanol, filtered, and dried to obtain lithium extraction byproduct B.

[0011] Based on the iron-manganese ratio in the target product, the lithium extraction by-product A and the lithium extraction by-product B are mixed evenly to obtain mixed powder C;

[0012] Step 3: Determine the content of each element in the mixed powder C (using an inductively coupled plasma spectrometer). Adjust the stoichiometric ratio of lithium, iron, manganese, phosphorus and aluminum in the mixed powder C to the range of 1-1.05:0.64-0.68:0.3:1:0.02-0.06 by adding lithium source, phosphorus source and aluminum source. Add 10-20% of glucose or sucrose as carbon source and reducing agent. After mixing by solid-phase ball milling, obtain mixed powder D.

[0013] Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an inert atmosphere to obtain aluminum-doped modified lithium manganese iron phosphate cathode material.

[0014] Further, the specific method of step 1 is as follows: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and binder are removed by pyrolysis at 500℃ under an inert atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, leached with ammonia to remove copper, and floated to remove graphite / carbon, thereby obtaining the corresponding waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder, respectively.

[0015] Furthermore, in step 1, based on the total mass of waste lithium iron phosphate cathode powder or waste lithium manganese oxide cathode powder, the lithium iron phosphate or lithium manganese oxide content in the cathode powder is in the range of 95 to 99.9 wt%, the carbon content is in the range of 0.1 to 2 wt%, and the aluminum content is in the range of 0.5 to 1.3 wt%.

[0016] Furthermore, in step 2: the mixed acid used for the mixed acid leaching treatment of waste lithium iron phosphate cathode powder is a mixture of acetic acid with a concentration of 0.2-1.2 mol / L and phosphoric acid with a concentration of 0.5-2 mol / L at a volume ratio of 5-10:1; the mixed acid used for the mixed acid leaching treatment of waste lithium manganese oxide cathode powder is a mixture of sulfuric acid with a concentration of 1-5 mol / L and phosphoric acid with a concentration of 0.5-2 mol / L at a volume ratio of 5-10:1.

[0017] Furthermore, in step 2, when preparing lithium extraction by-product A or lithium extraction by-product B, the concentration of lithium hydroxide used is 2–2.5 mol / L, and the pH of the system is adjusted to be in the range of 3.0–4.0.

[0018] Furthermore, in step 3, the ball milling speed of the solid phase ball mill is 150 to 1500 rpm, and the ball milling time is 3 to 10 hours.

[0019] Further, in step 3: the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium phosphate, lithium acetate, and lithium dihydrogen phosphate; the phosphorus source is one or more of ammonium dihydrogen phosphate, iron phosphate, lithium phosphate, and lithium dihydrogen phosphate; and the aluminum source is one or more of aluminum phosphate, aluminum chloride, and aluminum oxide.

[0020] Further, in step 4, the calcination is carried out in two steps: first, the temperature is raised to 300-450°C at a heating rate of 1-6°C / min and held for 2-5 hours; then, the temperature is raised to 600-750°C at a heating rate of 1-6°C / min and held for 8-15 hours; finally, the temperature is naturally cooled to room temperature.

[0021] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0022] This invention discloses a method for preparing aluminum-doped modified lithium manganese iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion battery electrode materials: First, retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are processed separately to obtain waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder, respectively; then, they are subjected to mixed acid leaching lithium extraction operations to obtain lithium extraction byproducts iron phosphate and manganese dioxide powder, and the trace aluminum contained therein is converted into aluminum phosphate; using this waste cathode powder containing a small amount of carbon and trace aluminum as raw material, the content of each element is determined, and the stoichiometry of the designed target lithium manganese iron phosphate product is calculated. The iron-manganese ratio was determined, and then appropriate amounts of lithium, phosphorus, and aluminum sources were added to adjust the lithium, iron, manganese, and phosphorus elements in the mixed powder to meet the stoichiometric design requirements. Solid-phase ball milling was used to grind and mix the waste cathode powder uniformly. Simultaneously, trace amounts of aluminum in the recovered powder were used as the aluminum dopant source. By converting the metallic aluminum into aluminum ions, these ions were diffused into the cell of lithium manganese iron phosphate during subsequent calcination and reprocessing. This not only solved the drawbacks of the presence of metallic aluminum impurities but also improved the electrical conductivity of the material grains. Aluminum doping modification enhanced the electrochemical performance of the reprocessed material, making it suitable for energy storage batteries. This invention utilizes aluminum impurities generated during the pretreatment of waste batteries as dopant raw materials to regenerate waste cathode materials into aluminum-doped modified cathode materials. This method effectively solves the problem of low discharge specific capacity caused by metallic aluminum impurities in recycled cathode materials, and the difficulty in meeting the commercial application requirements of materials directly regenerated in solid phase. This achieves the recycling of lithium, iron, manganese, phosphorus, and aluminum elements in retired lithium-ion batteries. Attached Figure Description

[0023] Figure 1 The image shows the XRD pattern of the undoped lithium iron phosphate cathode material obtained in Comparative Example 1.

[0024] Figure 2The image shows the XRD pattern of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1.

[0025] Figure 3 Here is a FESEM image of the undoped lithium iron phosphate cathode material obtained in Comparative Example 1;

[0026] Figure 4 FESEM image of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1;

[0027] Figure 5 The image shows the EDS spectrum of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1.

[0028] Figure 6 The XPS spectrum of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1 is shown below.

[0029] Figure 7 The first charge-discharge curves of coin cells prepared from the undoped lithium iron phosphate cathode material obtained in Comparative Example 1 and the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1 are shown at a current density of 0.1C.

[0030] Figure 8 The rate performance diagram shows the comparison between the undoped lithium iron phosphate cathode material obtained in Comparative Example 1 and the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1.

[0031] Figure 9 The first charge-discharge curve of the coin cell prepared from the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 2 at a current density of 0.1C.

[0032] Figure 10 The first charge-discharge curve of the coin cell prepared from the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 3 at a current density of 0.1C. Detailed Implementation

[0033] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1

[0035] This embodiment provides a method for preparing aluminum-doped modified lithium iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion batteries. The specific steps are as follows:

[0036] Step 1: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and decompose the binder by pyrolysis at 500℃ under nitrogen atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, leached with ammonia to remove copper, and floated to remove graphite / carbon, to obtain waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder.

[0037] Step 2: Mix 1.2 mol / L acetic acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1 to obtain mixed acid A. Immerse the waste lithium iron phosphate cathode powder in mixed acid A and soak at room temperature for 1 hour. Then adjust the pH to 4.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (iron phosphate precipitate and aluminum phosphate precipitate) are washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct A.

[0038] Mixed acid B was obtained by mixing 2 mol / L sulfuric acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1. Waste lithium manganese oxide cathode powder was immersed in mixed acid B and soaked at room temperature for 3 hours. Then, the pH was adjusted to 3.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (manganese dioxide precipitate and aluminum phosphate precipitate) were washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct B.

[0039] Based on the iron-manganese ratio in the target product (iron-manganese molar ratio of 0.68:0.3), lithium extraction by-product A and lithium extraction by-product B are ground and mixed evenly to obtain mixed powder C.

[0040] Step 3: The content of each element C in the mixed powder obtained in Step 2 was determined using an inductively coupled plasma optically spectrometer. Based on the stoichiometric ratio of the designed target product of lithium manganese iron phosphate, the stoichiometric ratio of lithium, iron, manganese, phosphorus and aluminum in the mixed powder C was adjusted to 1.05:0.68:0.3:1:0.02 by adding lithium carbonate, lithium dihydrogen phosphate and aluminum phosphate. 10% of glucose by mass of mixed powder C was added as a carbon source and reducing agent. After mixing by solid-phase ball milling (ball milling speed of 1200 rpm, ball milling time of 6 h), mixed powder D was obtained.

[0041] Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an argon atmosphere (first heat it to 400℃ at a heating rate of 4℃ / min, hold it for 2h, then heat it to 600℃ at a heating rate of 2℃ / min, hold it for 8h, and finally cool it naturally to room temperature) to obtain aluminum-doped modified lithium manganese iron phosphate cathode material.

[0042] The aluminum-doped modified lithium iron phosphate cathode material obtained in step 4 of this embodiment was thoroughly mixed with acetylene black and polyvinylidene fluoride (PVDF) at a ratio of 8:1:1 (mass ratio). NMP (1-methyl-2-pyrrolidone) was added to form a paste, which was then uniformly coated onto aluminum foil to a thickness of 75 μm. The mixture was dried at 80°C, rolled, and cut into cathode sheets with a diameter of 12 mm. After vacuum drying, the cathode sheets were prepared for use. Using a lithium metal sheet as the anode and a Cellgard 2400 polypropylene membrane as the separator, an experimental battery was assembled in an argon glove box. The battery was then subjected to constant voltage and constant current charge-discharge tests at 25°C.

[0043] Comparative Example 1

[0044] This comparative example provides a method for preparing undoped and modified lithium iron phosphate cathode material from lithium extraction byproducts of spent lithium-ion batteries. The specific steps are as follows:

[0045] Step 1: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and decompose the binder by pyrolysis at 500℃ under nitrogen atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, leached with ammonia to remove copper, and floated to remove graphite / carbon, to obtain waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder.

[0046] Step 2: Immerse the waste lithium iron phosphate cathode powder in 1.2 mol / L acetic acid. After soaking at room temperature for 1 hour, the resulting precipitate (iron phosphate precipitate) is washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct A.

[0047] Waste lithium manganese oxide cathode powder was immersed in 2 mol / L sulfuric acid and soaked at room temperature for 3 hours. The resulting precipitate (manganese dioxide precipitate) was washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct B.

[0048] Based on the iron-manganese ratio in the target product (iron-manganese molar ratio of 0.7:0.3), lithium extraction by-product A and lithium extraction by-product B are ground and mixed evenly to obtain mixed powder C.

[0049] Step 3: The content of each element C in the mixed powder obtained in Step 2 was determined using an inductively coupled plasma atomic emission spectrometer. According to the stoichiometric ratio of the designed target product of lithium manganese iron phosphate, the stoichiometric ratio of lithium, iron, manganese and phosphorus in the mixed powder C was adjusted to 1:0.7:0.3:1 by adding lithium carbonate and lithium dihydrogen phosphate. 10% of glucose by mass of mixed powder C was added as a carbon source and reducing agent. After mixing by solid-phase ball milling (ball milling speed of 1200 rpm, ball milling time of 6 h), mixed powder D was obtained.

[0050] Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an argon atmosphere (first heat it to 400℃ at a heating rate of 4℃ / min, hold it for 2h, then heat it to 600℃ at a heating rate of 2℃ / min, hold it for 8h, and finally cool it naturally to room temperature) to obtain the undoped and modified lithium manganese iron phosphate cathode material.

[0051] The undoped modified lithium iron phosphate cathode material obtained in step 4 of this comparative example was thoroughly mixed with acetylene black and polyvinylidene fluoride (PVDF) at a ratio of 8:1:1 (mass ratio). NMP (1-methyl-2-pyrrolidone) was added to form a paste, which was then uniformly coated onto aluminum foil to a thickness of 75 μm. The coating was dried at 80°C, rolled, and cut into cathode sheets with a diameter of 12 mm. After vacuum drying, the sheets were used for later use. Using lithium metal sheets as the anode and Cellgard 2400 polypropylene membrane as the separator, an experimental battery was assembled in an argon glove box. The battery was then subjected to constant voltage and constant current charge-discharge tests at 25°C.

[0052] Figure 1 The image shows the XRD pattern of the undoped lithium iron phosphate cathode material obtained in Comparative Example 1. Figure 2 The image shows the XRD pattern of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1. The image shows that both materials can be indexed as orthorhombic olivine-type structures with space group Pnma. Fe... 2+ Li occupies the 4a position of the octahedron + It occupies the 4c ​​site of the octahedron. The LiO4 octahedrons shared at the edges and the FeO6 octahedrons shared at the corners are both parallel to the c-axis and arranged along the b-axis.

[0053] Table 1 shows the cell parameters of aluminum-doped modified lithium manganese iron phosphate and undoped lithium manganese iron phosphate.

[0054]

[0055] Table 1 shows that the cell parameters a, b, c and cell volume of the co-doped samples all decrease, which is due to the reduction in Al. 3+ Doping may mainly occur in Li + Position substitution, Al 3+ The radius (0.050 nm) is smaller than Fe. 2+ The smaller radius (0.064 nm) leads to a decrease in the unit cell parameter, and the greater Al-O bond energy compared to the Fe-O bond energy results in a smaller unit cell volume. A smaller lattice parameter b can shorten the Li... + This increases the diffusion distance, thereby improving the electronic conductivity and lithium-ion diffusion rate of lithium iron phosphate electrode materials.

[0056] Figure 3 and Figure 4The images show FESEM images of the undoped lithium iron phosphate cathode material obtained in Comparative Example 1 and the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1, respectively. The images show that the particle size of the undoped lithium iron phosphate particles ranges from 0.5 μm to 2 μm, while the aluminum-doped modified lithium iron phosphate cathode material has smaller and more uniform particle sizes (particle size between 0.1 μm and 1 μm). The reduced particle size helps to decrease the lithium-ion diffusion path and increase the high-rate discharge performance of lithium iron phosphate.

[0057] Figure 5 The image shows the EDS spectrum of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1. The stoichiometric ratio Fe:Mn:P:Al ≈ 0.68:0.3:1:1:0.02, which is within the error range and basically conforms to the design value.

[0058] Figure 6 The image shows the XPS spectrum of the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1. The figure shows that Al has a 2p... 3 / 2 Spin splitting orbitals and the observation of satellite peak characteristics unique to trivalent aluminum prove that aluminum is doped into the cell of lithium iron phosphate material in the form of trivalent ions.

[0059] Figure 7 The figures show the first charge-discharge curves of coin cells prepared from the undoped lithium manganese iron phosphate cathode material obtained in Comparative Example 1 and the aluminum-doped modified lithium manganese iron phosphate cathode material obtained in Example 1, at a current density of 0.1C. The figures show that the aluminum-doped modified lithium manganese iron phosphate has a discharge specific capacity of 162.85 mAh / g, while the undoped modified lithium manganese iron phosphate has a discharge specific capacity of 155.71 mAh / g.

[0060] Figure 8 The graph shows the rate performance of coin cells prepared from the undoped lithium iron phosphate cathode material obtained in Comparative Example 1 and the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 1. The graph shows that the aluminum-doped modified lithium iron phosphate cathode material exhibits significantly lower electrode polarization during high-rate charge and discharge compared to the waste cathode powder, and its discharge specific capacity is significantly higher than that of the undoped modified lithium iron phosphate cathode material.

[0061] Example 2

[0062] This embodiment provides a method for preparing aluminum-doped modified lithium iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion batteries. The specific steps are as follows:

[0063] Step 1: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and binder are removed by pyrolysis at 500℃ under nitrogen atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, leached with ammonia to remove copper, and floated to remove graphite / carbon. The waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder are also processed.

[0064] Step 2: Mix 0.8 mol / L acetic acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1 to obtain mixed acid A. Immerse the waste lithium iron phosphate cathode powder in mixed acid A and soak at room temperature for 1 hour. Then adjust the pH to 4.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (iron phosphate precipitate and aluminum phosphate precipitate) are washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct A.

[0065] Mixed acid B was obtained by mixing 3 mol / L sulfuric acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1. Waste lithium manganese oxide cathode powder was immersed in mixed acid B and soaked at room temperature for 3 hours. Then, the pH was adjusted to 3.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (manganese dioxide precipitate and aluminum phosphate precipitate) were washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct B.

[0066] Based on the iron-manganese ratio in the target product (iron-manganese molar ratio of 0.66:0.3), lithium extraction by-product A and lithium extraction by-product B are ground and mixed evenly to obtain mixed powder C.

[0067] Step 3: The content of each element in the mixed powder C obtained in Step 2 was determined using an inductively coupled plasma spectrometer. According to the stoichiometric ratio of the designed target product of lithium manganese iron phosphate, the stoichiometric ratio of lithium, iron, manganese, phosphorus and aluminum in the mixed powder C was adjusted to 1:0.66:0.3:1:0.04 by adding lithium carbonate, lithium dihydrogen phosphate and aluminum phosphate. 10% of glucose by mass of mixed powder C was added as a carbon source and reducing agent. After mixing by solid-phase ball milling (ball milling speed of 1200 rpm, ball milling time of 6 h), mixed powder D was obtained.

[0068] Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an argon atmosphere (first heat it to 400℃ at a heating rate of 4℃ / min, hold it for 2h, then heat it to 600℃ at a heating rate of 2℃ / min, hold it for 8h, and finally cool it naturally to room temperature) to obtain aluminum-doped modified lithium manganese iron phosphate cathode material.

[0069] Figure 9The first charge-discharge curve of the coin cell prepared from the aluminum-doped modified lithium iron phosphate cathode material obtained in Example 2 is shown at a current density of 0.1C. The figure shows that the material's discharge specific capacity is 157.25 mAh / g.

[0070] Example 3

[0071] This embodiment provides a method for preparing aluminum-doped modified lithium iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion batteries. The specific steps are as follows:

[0072] Step 1: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and binder are removed by pyrolysis at 500℃ under nitrogen atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, leached with ammonia to remove copper, and floated to remove graphite / carbon. The waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder are also processed.

[0073] Step 2: Mix 1 mol / L acetic acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1 to obtain mixed acid A. Immerse the waste lithium iron phosphate cathode powder in mixed acid A and soak at room temperature for 1 hour. Then adjust the pH to 4.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (iron phosphate precipitate and aluminum phosphate precipitate) are washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct A.

[0074] Mixed acid B was obtained by mixing 1 mol / L sulfuric acid and 1.2 mol / L phosphoric acid at a volume ratio of 5:1. Waste lithium manganese oxide cathode powder was immersed in mixed acid B and soaked at room temperature for 3 hours. Then, the pH was adjusted to 3.0 with 2 mol / L lithium hydroxide solution. The resulting precipitates (manganese dioxide precipitate and aluminum phosphate precipitate) were washed with ethanol, filtered and dried at 100℃ to obtain lithium extraction byproduct B.

[0075] Based on the iron-manganese ratio in the target product (iron-manganese molar ratio of 0.64:0.3), lithium extraction by-product A and lithium extraction by-product B are ground and mixed evenly to obtain mixed powder C.

[0076] Step 3: The content of each element in the mixed powder C obtained in Step 2 was determined using an inductively coupled plasma spectrometer. According to the stoichiometric ratio of the designed target product of lithium manganese iron phosphate, the stoichiometric ratio of lithium, iron, manganese, phosphorus and aluminum in the mixed powder C was adjusted to 1:0.64:0.3:1:0.06 by adding lithium carbonate, lithium dihydrogen phosphate and aluminum phosphate. 10% of glucose by mass of mixed powder C was added as a carbon source and reducing agent. After mixing by solid-phase ball milling (ball milling speed of 1200 rpm, ball milling time of 6 h), mixed powder D was obtained.

[0077] Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an inert atmosphere such as nitrogen or argon (first heat it to 350℃ at a heating rate of 4℃ / min, hold it for 2h, then heat it to 700℃ at a heating rate of 2℃ / min, hold it for 8h, and finally cool it naturally to room temperature) to obtain aluminum-doped modified lithium manganese iron phosphate cathode material.

[0078] Figure 10 The first charge-discharge curve of the coin cell prepared by the doped modified lithium iron phosphate cathode material obtained in Example 3 is shown in the figure at a current density of 0.1C. It can be seen from the figure that the discharge specific capacity of the material is 150.73 mAh / g.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. All modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing aluminum-doped modified lithium iron phosphate cathode material from lithium extraction byproducts of waste lithium-ion batteries, characterized in that, Includes the following steps: Step 1: Process retired lithium iron phosphate batteries and retired lithium manganese oxide batteries separately to obtain waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder respectively; Step 2: The waste lithium iron phosphate cathode powder is treated with a mixture of acetic acid and phosphoric acid to leach lithium ions and produce iron phosphate precipitate, while converting elemental aluminum into aluminum ions. Then, the pH of the system is adjusted with lithium hydroxide solution to convert aluminum ions into aluminum phosphate precipitate. The resulting precipitate is washed with ethanol, filtered and dried to obtain lithium extraction byproduct A. Waste lithium manganese oxide cathode powder is leached with a mixture of sulfuric acid and phosphoric acid to leach lithium ions and produce manganese dioxide precipitate, while simultaneously converting elemental aluminum into aluminum ions. Then, the pH of the system is adjusted with lithium hydroxide solution to convert aluminum ions into aluminum phosphate precipitate. The resulting precipitate was washed with ethanol, filtered, and dried to obtain lithium extraction byproduct B. Based on the iron-manganese ratio in the target product, the lithium extraction by-product A and the lithium extraction by-product B are mixed evenly to obtain mixed powder C; Specifically: the mixed acid used for the mixed acid leaching treatment of waste lithium iron phosphate cathode powder is a mixture of acetic acid with a concentration of 0.2~1.2 mol / L and phosphoric acid with a concentration of 0.5~2 mol / L at a volume ratio of 5~10:1; the mixed acid used for the mixed acid leaching treatment of waste lithium manganese oxide cathode powder is a mixture of sulfuric acid with a concentration of 1~5 mol / L and phosphoric acid with a concentration of 0.5~2 mol / L at a volume ratio of 5~10:

1. Step 3: Determine the content of each element in the mixed powder C. Adjust the stoichiometric ratio of lithium, iron, manganese, phosphorus and aluminum in the mixed powder C to the range of 1~1.05:0.64~0.68:0.3:1:0.02~0.06 by adding lithium source, phosphorus source and aluminum source. Add 10~20% of glucose or sucrose as carbon source and reducing agent. After mixing by solid phase ball milling, obtain mixed powder D. Step 4: Place the mixed powder D in a corundum calcining boat and calcine it under an inert atmosphere to obtain aluminum-doped modified lithium manganese iron phosphate cathode material. The calcination is carried out in two steps: first, the temperature is raised to 300-450 ℃ at a heating rate of 1-6 ℃ / min and held for 2-5 h; then, the temperature is raised to 600-700 ℃ at a heating rate of 1-6 ℃ / min and held for 8-15 h; finally, it is naturally cooled to room temperature.

2. The method according to claim 1, characterized in that, The specific method of step 1 is as follows: First, the retired lithium iron phosphate batteries and retired lithium manganese oxide batteries are discharged and disassembled to obtain battery cells. The residual electrolyte and binder are removed by negative pressure pyrolysis under an inert atmosphere. Then, the two types of battery cells are crushed, screened, air-separated, magnetically separated, copper-removing by ammonia leaching, and graphite / carbon-removing by flotation, respectively, to obtain the corresponding waste lithium iron phosphate cathode powder and waste lithium manganese oxide cathode powder.

3. The method according to claim 1, characterized in that: In step 1, based on the total mass of waste lithium iron phosphate cathode powder or waste lithium manganese oxide cathode powder, the lithium iron phosphate or lithium manganese oxide content in the cathode powder is in the range of 95~99.9 wt%, the carbon content is in the range of 0.1~2 wt%, and the aluminum content is in the range of 0.5~1.3 wt%.

4. The method according to claim 1, characterized in that, In step 2, when preparing lithium extraction by-product A or lithium extraction by-product B, the concentration of lithium hydroxide used is 2~2.5 mol / L, and the pH of the system is adjusted to be in the range of 3.0~4.

0.

5. The method according to claim 1, characterized in that, In step 3, the ball milling speed of the solid phase ball mill is 150~1500 rpm, and the ball milling time is 6~10 h.

6. The method according to claim 1, characterized in that: In step 3, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium phosphate, lithium acetate, and lithium dihydrogen phosphate, and the phosphorus source is one or more of ammonium dihydrogen phosphate, iron phosphate, lithium phosphate, and lithium dihydrogen phosphate.

7. The method according to claim 1, characterized in that: In step 3, the aluminum source is one or more of aluminum phosphate, aluminum chloride, and aluminum oxide.

8. An aluminum-doped modified lithium manganese iron phosphate cathode material prepared by the method according to any one of claims 1 to 7.

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