Method for recycling waste lithium iron phosphate battery
By adding ferrous salts, lithium acetate, niobium pentoxide and other substances during the recycling process of waste lithium iron phosphate batteries, a uniform carbon coating and a three-dimensional conductive network are formed, which solves the problems of low recovery rate and poor cycle performance of lithium iron phosphate batteries in the existing technology, and realizes the preparation of lithium iron phosphate materials with high specific capacity and good cycle stability.
Patent Information
- Application Number
- CN202511047211.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-29
- Publication Date
- 2025-10-17
AI Technical Summary
Existing methods for recycling waste lithium iron phosphate battery cathode materials suffer from problems such as low Fe and P recovery rates, high Li loss rates, or low iron phosphate purity, resulting in poor specific capacity and cycle performance of the prepared lithium iron phosphate batteries.
By adding ferrous salts to ensure that iron exists in the form of Fe2+, and combining it with the doping of lithium acetate, vanadium nitrate and niobium pentoxide, a uniform carbon coating and a three-dimensional conductive network are formed, which improves lithium ion diffusion and conductivity. The structure is optimized by using a gradient calcination process to prepare lithium iron phosphate materials with high specific capacity and cycle stability.
It significantly improves the specific capacity and cycle stability of lithium iron phosphate materials, enhances battery conductivity and ion diffusion kinetics, reduces interfacial impedance, and achieves a high-efficiency improvement in battery performance.
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Figure CN120793880A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of battery material recycling, and in particular relates to a method for recycling and processing waste lithium iron phosphate batteries. Background Art
[0002] Lithium iron phosphate batteries (LIFP) boast excellent safety, cycle performance, low cost, and non-toxicity, making them widely used, particularly in new energy vehicles. However, with the annual increase in the number of discarded LFP batteries, failure to recycle them will inevitably lead to environmental pollution and resource waste.
[0003] At present, the recycling methods of waste lithium iron phosphate battery positive electrode materials include acid leaching-precipitation method, solid phase method and regeneration lithium iron phosphate method. For example, in the prior art, the metal ions in the waste positive electrode of waste lithium iron phosphate battery are leached, and then converted into industrial raw materials such as iron phosphate, iron hydroxide, lithium carbonate, lithium phosphate, etc. through step-by-step precipitation separation. However, these methods still have problems such as low Fe and P recovery rate, high Li loss rate or low purity of iron phosphate. And when these recycled products are subsequently used to prepare lithium iron phosphate, there will also be the problem of increased costs. Some prior arts directly use waste lithium iron phosphate battery positive electrode materials to prepare battery-grade lithium iron phosphate materials, and then use the recycled lithium iron phosphate materials to prepare lithium iron phosphate batteries with poor specific capacity and cycle performance.
[0004] Therefore, there is an urgent need to provide a method for directly preparing lithium iron phosphate that can be directly used as a positive electrode of a battery using waste lithium iron phosphate batteries, and the corresponding lithium iron phosphate has stable specific capacity and cycle performance. Summary of the Invention
[0005] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention provides a method for recycling and treating spent lithium iron phosphate batteries. The lithium iron phosphate obtained by this recycling method can be directly used to prepare lithium iron phosphate batteries, which exhibit high specific capacity and good cycle stability.
[0006] The waste lithium iron phosphate battery recycling method of the present invention ensures that the iron element in the system is Fe by adding ferrous salt (such as ferrous sulfate). 2+ Exists in the form of Fe 2+ It is easier to form a uniform olivine structure during the sintering process, reducing Fe 3+Impurity phase, improve conductivity; lithium acetate has a low melting point, which can form a liquid phase in the early sintering stage to promote ion diffusion and improve material crystallinity. Further, by adding vanadium nitrate or niobium pentoxide, part of the iron sites in the lattice are replaced, the lithium ion diffusion channel is expanded, and the electrical performance is improved. Among them, vanadium nitrate has good water solubility and can be uniformly dispersed in the slurry. Vanadium exists in the +3 valence state and easily enters the iron site of the lithium iron phosphate lattice. Niobium pentoxide is reduced by carbon at high temperature to generate active niobium, which preferentially occupies the lithium site and inhibits the cyclic phase change stress. Then, polyacrylic acid (PAA) or citric acid is used as a carbon source, and its carboxyl functional group is more easily complexed with metal ions to achieve uniform carbon coating. Finally, by supplementing carbon nanotubes to the precursor, a three-dimensional conductive network is constructed to reduce the interface impedance.
[0007] Fe 2+ The dominant homogeneous structure improves lithium ion intercalation activity, vanadium doping expands the lattice channel, and enhances ion diffusion dynamics, which is beneficial to improve the specific capacity of the prepared lithium iron phosphate material. Uniform carbon coating inhibits electrode crushing, and a three-dimensional conductive network reduces cycle polarization. In particular, the triple protection of carbon coating-conductive network-lattice stability significantly improves the cycle stability.
[0008] The application provides a waste lithium iron phosphate battery recycling method.
[0009] A waste lithium iron phosphate battery recycling method comprises the following steps:
[0010] (1) The positive electrode material of the waste lithium iron phosphate battery, phosphoric acid, monohydrogen lithium phosphate and dihydrogen lithium phosphate are stirred and mixed in water to obtain a mixed solution;
[0011] (2) The pH of the mixed solution obtained in step (1) is adjusted to be acidic, hydrogen peroxide is added and stirred, and then ferrous salt is added and stirred to obtain a slurry;
[0012] (3) Lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, carbon nanotubes and polytetrafluoroethylene emulsion are added to the slurry obtained in step (2) and stirred and mixed, then dispersed, and dried to obtain a precursor;
[0013] (4) The precursor obtained in step (3) is crushed, and then gradient calcination is performed in a nitrogen-hydrogen mixed gas atmosphere to obtain a lithium iron phosphate material.
[0014] Preferably, in step (1), the positive electrode material of the waste lithium iron phosphate battery is obtained by discharging, disassembling, crushing and screening the waste lithium iron phosphate battery.
[0015] Preferably, in step (1), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, monohydrate lithium phosphate, dihydric lithium phosphate, water is 100:(1-6):(2-8):(2-8):(70-160); further preferably, the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, monohydrate lithium phosphate, dihydric lithium phosphate, water is 100:(1-4):(3-8):(3-8):(80-140).
[0016] Preferably, in step (2), the pH of the mixed solution obtained in step (1) is adjusted to 1-3.
[0017] Preferably, in step (2), the mass concentration of the hydrogen peroxide is 1%-1.5%.
[0018] Preferably, in step (2), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to hydrogen peroxide is 100:(1-1.5). The amount of hydrogen peroxide should not be too much, so as to avoid oxidizing divalent iron to trivalent iron.
[0019] Preferably, in step (3), the weight of the ferrous salt is 2%-8% of the weight of the positive electrode material of the waste lithium iron phosphate battery, and further preferably 4%-5%.
[0020] Preferably, in step (3), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, and polytetrafluoroethylene emulsion is 100:(10-15):(0.1-1):(0.1-1):(0.1-1):(0.6-1.8); further preferably, the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, and polytetrafluoroethylene emulsion is 100:(12-15):(0.1-1):(0.1-1):(0.1-1):(0.6-0.8).
[0021] Preferably, the polytetrafluoroethylene emulsion is obtained by mixing polytetrafluoroethylene powder and water in a weight ratio of 1:(3-8), and then ball milling for 2-3h.
[0022] Preferably, in step (3), the drying temperature is 80-100°C, and the time is 4-12h.
[0023] Preferably, in step (3), the volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 90-95:5-10.
[0024] Preferably, in step (3), the process of gradient calcination is: first, increase to 550-600℃ at a rate of 3-5℃ / min, keep for 0.5-1h to remove impurities, then increase to 700-750℃ at a rate of 1-2℃ / min, keep for 3-4h. The use of ladder temperature calcination reduces lattice defects and improves structural stability by slow heating. The weak reducing environment of nitrogen-hydrogen mixed gas inhibits Fe 2+ oxidation. Gradient calcination eliminates internal stress, which is beneficial to reduce the damage of cyclic phase change.
[0025] Preferably, in step (3), after adding the polytetrafluoroethylene emulsion, nitrogen-doped carbon quantum dot material is also added. The three-dimensional conductive network is constructed with the polyacrylic acid or citric acid carbon source, which further improves the cycle stability of the finally prepared lithium iron phosphate.
[0026] Preferably, the amount of nitrogen-doped carbon quantum dot material added is 0.1%-0.8% of the slurry.
[0027] Preferably, the preparation process of the nitrogen-doped carbon quantum dot material includes:
[0028] Lemon acid and ethylenediamine are dissolved in ultrapure water at a weight ratio of 1:(0.4-0.8), and fully stirred and mixed. The obtained mixture is transferred to a reaction kettle, sealed, and reacted at 190-200℃ for 4-6h. After natural cooling, centrifugation is performed at a speed of 8000-9000r / min for 15-20min. The supernatant is filtered through a 0.22μm filter membrane, and then purified by dialysis with a molecular weight cut-off of 1000-3500Da for 10-12h, with water changed every 1-2h. After freeze-drying, the nitrogen-doped carbon quantum dot material is obtained.
[0029] Preferably, a waste lithium iron phosphate battery recycling method includes the following steps:
[0030] (1) At a temperature of 60-70℃, the positive electrode material of the waste lithium iron phosphate battery, phosphoric acid, monobasic lithium phosphate and dibasic lithium phosphate are stirred and mixed in water for 1-2h to obtain a mixed solution, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to ferrous salt, phosphoric acid, monobasic lithium phosphate, dibasic lithium phosphate and water is 100:(1-4):(3-8):(3-8):(80-140);
[0031] (2) Adjust the pH of the mixed solution obtained in step (1) to 1-3, and then at a temperature of 60-70℃, add 1%-1.5% hydrogen peroxide by mass concentration for stirring treatment for 1-3h, and then add ferrous salt for stirring to obtain a slurry. The weight ratio of the positive electrode material of the waste lithium iron phosphate battery to hydrogen peroxide is 100:(1-1.5), and the weight of the ferrous salt is 2%-8% of the weight of the positive electrode material of the waste lithium iron phosphate battery;
[0032] (3) adding lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, carbon nanotubes and polytetrafluoroethylene emulsion into the slurry obtained in step (2), stirring and mixing, then dispersing, drying to obtain a precursor, and the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, polytetrafluoroethylene emulsion is 100:(12-15):(0.1-1):(0.1-1):(0.1-1):(0.3-0.8);
[0033] (4) crushing the precursor obtained in step (3), then in a nitrogen-hydrogen mixed gas (volume ratio 90-95:5-10) atmosphere, first increasing to 550-600 DEG C at 3-5 DEG C / min, holding for 0.5-1 h to remove impurities, then increasing to 700-750 DEG C at 1-2 DEG C / min, holding for 3-4 h to obtain a lithium iron phosphate material.
[0034] The application of the above-mentioned waste lithium iron phosphate battery recycling method in the preparation of batteries.
[0035] Compared with the prior art, the application has the following beneficial effects:
[0036] (1) The waste lithium iron phosphate battery recycling method of the application ensures that the iron element in the system exists in the form of Fe 2+ by adding ferrous salt (such as ferrous sulfate). Fe 2+ is more likely to form a uniform olivine structure during sintering, reducing Fe 3+ impurity phases and improving electrical conductivity; lithium acetate is low-temperature molten to form a liquid phase, promoting the ordered arrangement of Fe 2+ and PO4 3- , forming a synergistic effect with vanadium / niobium doping, the vanadium ions in vanadium nitrate replace Fe sites to expand the lithium ion channel, and the niobium in niobium pentoxide occupies lithium vacancies to inhibit lattice collapse. The carboxyl group of polyacrylic acid (PAA) complexes metal ions to achieve nanoscale carbon coating and form a "point-line" three-dimensional conductive network with carbon nanotubes. Therefore, not only the specific capacity of the prepared lithium iron phosphate material is improved, but also the cycle stability during charging and discharging is improved.
[0037] (2) By adding nitrogen-doped carbon quantum dot materials, a three-dimensional conductive network is constructed with polyacrylic acid or citric acid carbon sources to further improve the cycle stability of the finally prepared lithium iron phosphate. BRIEF DESCRIPTION OF DRAWINGS
[0038] The application will be further described below with reference to the accompanying drawings.
[0039] Figure 1 The discharge cycle curve of the button cell assembled by the lithium iron phosphate prepared in Example 1 of the application. DETAILED DESCRIPTION
[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.
[0041] The raw materials, reagents or devices used in the following examples can be obtained from conventional commercial channels or can be obtained by existing known methods if not otherwise specified.
[0042] The following polytetrafluoroethylene emulsion is obtained by mixing polytetrafluoroethylene powder and water at a weight ratio of 1:4, and then ball milling for 3h.
[0043] The positive electrode material of the waste lithium iron phosphate battery used below is obtained by discharging, disassembling, crushing and sieving the waste lithium iron phosphate battery.
[0044] Example 1
[0045] A waste lithium iron phosphate battery recycling method, comprising the following steps:
[0046] (1) At a temperature of 70℃, the positive electrode material of the waste lithium iron phosphate battery, phosphoric acid, monohydrogen lithium phosphate and dihydrogen lithium phosphate are stirred and mixed in water for 2h to obtain a mixed solution, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, monohydrogen lithium phosphate, dihydrogen lithium phosphate and water is 100:2:4:5:110;
[0047] (2) The pH of the mixed solution obtained in step (1) is adjusted to 2 with phosphoric acid, and then at a temperature of 70℃, 1% hydrogen peroxide solution is added for stirring treatment for 3h, and ferrous sulfate is added and stirred to obtain a slurry, the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to hydrogen peroxide is 100:1.2, and the weight of ferrous sulfate is 4% of the weight of the positive electrode material of the waste lithium iron phosphate battery;
[0048] (3) After the slurry obtained in step (2) is stirred and mixed with lithium acetate, vanadic acid, niobium pentoxide, polyacrylic acid, carbon nanotubes and polytetrafluoroethylene emulsion, it is dispersed, dried at 80℃ for 8h to obtain a precursor, and the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadic acid, niobium pentoxide, polyacrylic acid and polytetrafluoroethylene emulsion is 100:13:0.5:0.1:0.4:0.8;
[0049] (4) The precursor obtained in step (3) is crushed, and then in a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 95:5) atmosphere, first increased to 600 DEG C at 5 DEG C / min, kept for 1 h, then increased to 750 DEG C at 2 DEG C / min, kept for 4 h, to obtain a lithium iron phosphate material.
[0050] Example 2
[0051] A waste lithium iron phosphate battery recycling method comprises the following steps:
[0052] (1) At a temperature of 70 DEG C, the positive electrode material of the waste lithium iron phosphate battery, phosphoric acid, monohydrogen lithium phosphate and dihydrogen lithium phosphate are stirred and mixed in water for 2 h to obtain a mixed solution, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, monohydrogen lithium phosphate, dihydrogen lithium phosphate and water is 100:3:7:6:120;
[0053] (2) The pH of the mixed solution obtained in step (1) is adjusted to 2 with phosphoric acid, and then at a temperature of 70 DEG C, 1.5% hydrogen peroxide is added for stirring treatment for 3 h, and ferrous sulfate is then added and stirred to obtain a slurry, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to hydrogen peroxide is 100:1, and the weight of ferrous sulfate is 5% of the weight of the positive electrode material of the waste lithium iron phosphate battery;
[0054] (3) Lithium acetate, vanadic nitrate, niobium pentoxide, polyacrylic acid, carbon nanotubes and polytetrafluoroethylene emulsion are added to the slurry obtained in step (2) and stirred and mixed, and then dispersed, and dried at 80 DEG C for 8 h to obtain a precursor, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadic nitrate, niobium pentoxide, polyacrylic acid, polytetrafluoroethylene emulsion is 100:14:0.8:0.1:0.7:0.6;
[0055] (4) The precursor obtained in step (3) is crushed, and then in a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 95:5) atmosphere, first increased to 600 DEG C at 5 DEG C / min, kept for 1 h, then increased to 750 DEG C at 2 DEG C / min, kept for 4 h, to obtain a lithium iron phosphate material.
[0056] Example 3
[0057] A waste lithium iron phosphate battery recycling method comprises the following steps:
[0058] (1) At a temperature of 70 DEG C, the positive electrode material of the waste lithium iron phosphate battery, phosphoric acid, monohydrogen lithium phosphate and dihydrogen lithium phosphate are stirred and mixed in water for 2 h to obtain a mixed solution, wherein the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, monohydrogen lithium phosphate, dihydrogen lithium phosphate and water is 100:2:4:5:110;
[0059] (2) the pH of the mixed solution obtained in step (1) is adjusted to 2 with phosphoric acid, then hydrogen peroxide with a mass concentration of 1% is added and stirred at a temperature of 70°C for 3h, ferrous sulfate is added and stirred to obtain a slurry, the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to the hydrogen peroxide is 100:1.2, and the weight of the ferrous sulfate is 4% of the weight of the positive electrode material of the waste lithium iron phosphate battery;
[0060] (3) lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid, carbon nanotubes, and polytetrafluoroethylene emulsion, and nitrogen-doped carbon quantum dot material are added to the slurry obtained in step (2) and stirred and mixed, then dispersed, dried at 80°C for 8h to obtain a precursor, the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid, polytetrafluoroethylene emulsion is 100:13:0.5:0.1:0.4:0.8; the addition amount of the nitrogen-doped carbon quantum dot material is 0.4% of the slurry;
[0061] (4) the precursor obtained in step (3) is crushed, then in a nitrogen-hydrogen mixed gas (volume ratio of nitrogen to hydrogen is 95:5) atmosphere, first increased to 600°C at a rate of 5°C / min and kept for 1h, then increased to 750°C at a rate of 2°C / min and kept for 4h to obtain a lithium iron phosphate material.
[0062] The preparation process of the nitrogen-doped carbon quantum dot material includes:
[0063] Citric acid and ethylenediamine are dissolved in ultrapure water at a weight ratio of 1:0.6, fully stirred and mixed, and the obtained mixture is transferred to a reaction kettle, sealed, and reacted at 195°C for 5h, then naturally cooled, centrifuged at a speed of 9000r / min for 20min, and the supernatant is filtered through a 0.22μm filter membrane, then purified by dialysis with a molecular weight cut-off of 2500Da for 12h, with water changed every 2h, and then freeze-dried to obtain a nitrogen-doped carbon quantum dot material.
[0064] Comparative Example 1
[0065] Comparative Example 1 is different from Example 1 in that an equal amount of phosphoric acid is used instead of ferrous sulfate, and the other processes are the same as Example 1.
[0066] Comparative Example 2
[0067] Comparative Example 2 is different from Example 1 in that an equal amount of lithium carbonate is used instead of lithium acetate, and the other processes are the same as Example 1.
[0068] Comparative Example 3
[0069] The difference between Comparative Example 3 and Example 1 is that the vanadium nitrate is replaced by an equal weight of niobium pentoxide, i.e. the vanadium nitrate is replaced by niobium pentoxide while ensuring the total amount is unchanged, and the other processes are the same as in Example 1.
[0070] Product effect test
[0071] The lithium iron phosphate material prepared in the example and comparative example is taken as a positive electrode material, and is mixed uniformly in a mass ratio of 8:1:1 of the positive electrode material, acetylene black and polyvinylidene fluoride, and is grinded to obtain a uniformly mixed slurry using N-methyl pyrrolidone as a solvent. The slurry is coated on an aluminum foil, dried in a vacuum oven at 120°C for 6h, and then cut into a disc with a diameter of 8mm, and then assembled into a CR2025 button cell. The constant current charge and discharge test is carried out at room temperature with a limited voltage of 2.5V to 3.8V, the first circle discharge capacity is tested under a current density of 1C, and the discharge capacity result at 300 times of charge and discharge cycles is recorded under the test condition. The results are shown in Table 1.
[0072] Table 1
[0073] Item Initial discharge specific capacity (mAh / g) Discharge specific capacity at 300 cycles (mAh / g) Capacity retention rate at 300 cycles (%) Example 1 161.3 153.5 95.2 Example 2 161.8 154.2 95.3 Example 3 168.7 163.7 97.0 Comparative Example 1 151.6 128.9 85.0 Comparative Example 2 149.3 124.0 83.1 Comparative Example 3 157.6 137.1 87.0
[0074] As can be seen from Table 1, the specific capacity and cycle stability of the lithium iron phosphate material prepared in the example of the application are obviously better than those of the comparative example. It can also be seen that the ferrous sulfate, lithium acetate, niobium pentoxide and vanadium nitrate used in the waste lithium iron phosphate battery recycling method of the application play an important role in improving the specific capacity and cycle stability of the material.
[0075] Figure 1 The discharge cycle curve of the button cell assembled by the lithium iron phosphate prepared in Example 1 of the application. From Figure 1 It can be seen that the button cell assembled by the lithium iron phosphate prepared in Example 1 has good cycle stability.
[0076] It should be noted that in this text, terms such as “include, contain” or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or is also included in the inherent elements of such a process, method, article or device.
[0077] Although the embodiments of the application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.
Claims
1. A method for recycling and treating waste lithium iron phosphate batteries, characterized in that: The following steps are involved: (1) stirring and mixing the cathode material of the waste lithium iron phosphate battery, phosphoric acid, lithium monohydrogen phosphate and lithium dihydrogen phosphate in water to obtain a mixed solution; (2) adjusting the pH of the mixed solution obtained in step (1) to acidic, adding hydrogen peroxide and stirring, then adding ferrous salt and stirring to obtain a slurry; (3) adding lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, carbon nanotubes and polytetrafluoroethylene emulsion to the slurry obtained in step (2), stirring and mixing, and then dispersing and drying to obtain a precursor; (4) The precursor obtained in step (3) is crushed, and then gradient calcined in a nitrogen-hydrogen mixed gas atmosphere to obtain a lithium iron phosphate material.
2. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (1), the positive electrode material of the waste lithium iron phosphate battery is obtained by discharging, disassembling, crushing and screening the waste lithium iron phosphate battery.
3. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (1), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to phosphoric acid, lithium monohydrogen phosphate, lithium dihydrogen phosphate and water is 100:(1-6):(2-8):(2-8):(70-160).
4. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the pH of the mixed solution obtained in step (1) is adjusted to 1-3.
5. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (2), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to the hydrogen peroxide is 100:(1-1.5); and / or the weight of the ferrous salt is 2%-8% of the weight of the positive electrode material of the waste lithium iron phosphate battery.
6. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (3), the weight ratio of the positive electrode material of the waste lithium iron phosphate battery to lithium acetate, vanadium nitrate, niobium pentoxide, polyacrylic acid or citric acid, and polytetrafluoroethylene emulsion is 100:(10-15):(0.1-1):(0.1-1):(0.1-1):(0.6-1.8).
7. The method for recycling waste lithium iron phosphate batteries according to claim 1, characterized in that: In step (3), the gradient calcination process is: firstly, the temperature is raised to 550-600°C at 3-5°C / min and kept at this temperature for 0.5-1h to remove impurities, and then the temperature is raised to 700-750°C at 1-2°C / min and kept at this temperature for 3-4h.
8. The method for recycling waste lithium iron phosphate batteries according to any one of claims 1 to 7, characterized in that: In step (3), after adding the polytetrafluoroethylene emulsion, nitrogen-doped carbon quantum dot material is also added.
9. The method for recycling waste lithium iron phosphate batteries according to claim 8, characterized in that: The preparation process of the nitrogen-doped carbon quantum dot material comprises: Citric acid and ethylenediamine were dissolved in ultrapure water at a weight ratio of 1: (0.4-0.8), and the mixture was thoroughly stirred and mixed. The resulting mixture was transferred to a reactor, sealed, and reacted at 190-200°C for 4-6 hours. After natural cooling, the mixture was centrifuged at a speed of 8000-9000 r / min for 15-20 minutes. The supernatant was filtered through a 0.22 μm filter membrane, and then purified by dialysis with a molecular weight cutoff of 1000-3500 Da for 10-12 hours. The water was changed every 1-2 hours, and the mixture was freeze-dried to obtain the nitrogen-doped carbon quantum dot material.
10. Use of the method for recycling waste lithium iron phosphate batteries according to any one of claims 1 to 9 in preparing batteries.