Synchronous separation and direct repair method of waste lithium iron phosphate positive electrode material

Abstract

The invention relates to a synchronous separation and direct repair method of a waste lithium iron phosphate positive electrode material. The method comprises the following steps: placing a positive electrode plate of a waste lithium iron phosphate battery in a mixed solution containing a lithium supplement agent and an acidic reducing agent for reaction; and after reaction, filtering and drying to obtain aluminum foil and repaired lithium iron phosphate. According to the method, separation pretreatment of the lithium iron phosphate and the aluminum foil is not needed, a high-temperature and high-pressure reaction environment is not needed in the repairing and regenerating process, and separation of the waste lithium iron phosphate and the aluminum foil and repairing of the lithium iron phosphate are directly and synchronously completed.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate battery recycling, and in particular to a method for synchronously separating and directly repairing waste lithium iron phosphate positive electrode materials. Background Art

[0002] In recent years, with the continuous increase in electric vehicle production, the consumption of lithium-ion batteries has increased dramatically. The large number of scrapped batteries has brought numerous environmental and resource problems, making the treatment and recycling of used lithium-ion batteries an urgent challenge. Lithium iron phosphate (LiFePO4, LFP) batteries have become one of the mainstream lithium batteries used in electric vehicles due to their significant advantages such as high stability and long cycle life. However, existing LFP recycling methods are complex and highly polluting, and the recovered products are mostly alloys or metal salts that can only be used as battery precursors.

[0003] Before recycling waste lithium iron phosphate batteries, pretreatment is usually required. Pretreatment can effectively improve the recovery rate, reduce energy consumption in subsequent processes, and separate the different components and active materials of the battery in a safe and efficient manner. Among them, the pretreatment separation of the aluminum foil of the positive electrode and the lithium iron phosphate is the key first step. Currently common separation methods include heat treatment and organic solvent methods. The organic solvent method separates lithium iron phosphate from aluminum foil by dissolving the binder, which can avoid the introduction of metal impurities in lithium iron phosphate. However, the organic solvents used in this method are expensive and mostly toxic, posing potential hazards to the environment and human health. In contrast, although the heat treatment method is simple to operate, it consumes a lot of energy, and toxic gases are easily generated during the high-temperature calcination of PVDF, which is not conducive to environmental protection and sustainable development. Therefore, the development of more environmentally friendly and efficient pretreatment technologies is an important research direction in the current field of waste lithium iron phosphate battery recycling.

[0004] The separated lithium iron phosphate is subsequently repaired and regenerated using high temperature or hydrothermal direct regeneration technology. This is a non-destructive repair method that can repair the crystal structure of the material and restore its electrochemical properties without leaching treatment. For example, patents CN114744315B, CN117080605A, and CN113072052B all use hydrothermal repair methods for waste lithium iron phosphate positive electrode materials, with a reaction temperature of 80-240°C and a reaction time of 2-10 hours. The hydrothermal synthesis method can achieve self-saturation in the solution, thereby achieving a stoichiometric composition. It does not require the precise quantitative addition of a lithium source, and also avoids the possibility of introducing miscellaneous impurities due to uneven contact between the lithium source and the waste lithium iron phosphate. However, the large-scale application of the hydrothermal synthesis method is limited by the high-pressure environment it requires. In order to ensure the presence of a liquid phase under high temperature conditions, the method usually needs to be carried out in a high-pressure environment and equipped with a special reactor. Summary of the Invention

[0005] The present invention aims to provide a method for the synchronous separation and direct repair of waste lithium iron phosphate positive electrode materials. Not only does it not require the separation pretreatment of lithium iron phosphate and aluminum foil, but the repair and regeneration process also does not require a high-temperature and high-pressure reaction environment. The separation of waste lithium iron phosphate and aluminum foil and the repair of lithium iron phosphate can be directly and synchronously completed.

[0006] In order to solve the above technical problems, the specific solution adopted by the present invention is: a method for the synchronous separation and direct repair of waste lithium iron phosphate positive electrode materials, wherein the positive electrode sheet of the waste lithium iron phosphate battery is placed in a mixed solution containing a lithium supplement agent and an acidic reducing agent for reaction; after the reaction, the aluminum foil and the repaired lithium iron phosphate are obtained by filtration and drying.

[0007] Preferably, the repaired lithium iron phosphate is uniformly mixed with a lithium salt and a carbon source, and calcined under a protective gas atmosphere to obtain regenerated lithium iron phosphate.

[0008] Preferably, the carbon source is a combination of one or more of citric acid, glucose, and sucrose; and the lithium salt is a combination of one or two of lithium hydroxide and lithium carbonate.

[0009] Preferably, the molar ratio of lithium iron phosphate to lithium salt and carbon source in the positive electrode sheet of the waste lithium iron phosphate battery is 1: (1%-5%): (1%-15%).

[0010] Preferably, the calcination temperature is 400-700° C., the heating rate is 2-10 min, and the calcination time is 3-6 h.

[0011] Preferably, the positive electrode sheet of the waste lithium iron phosphate battery is cut or sliced into 1 cm×1 cm-10 cm×10 cm, and then placed in the mixed solution for reaction.

[0012] Preferably, the lithium supplement in the mixed solution is a combination of one or more of lithium chloride, lithium nitrate, lithium hydroxide, lithium acetate, and lithium sulfate, and the concentration of the lithium supplement is 0.01-1 mol / L.

[0013] Preferably, the acidic reducing agent in the mixed solution is a combination of one or more of hydroxylamine sulfate, thioacetamide, chromium chloride, hydroxylamine hydrochloride, hydroxylamine-O-sulfonic acid, hydroxylamine phosphate, aminosulfonic acid, hydroxylamine nitrate, ammonium thiosulfate, and meta-hydroxylamine bitartrate.

[0014] Preferably, the concentration of the acidic reducing agent is 0.01-1 mol / L.

[0015] Preferably, the reaction temperature in the mixed solution is 20-60° C., the reaction time is 5-60 min, and the solid-liquid ratio of the positive electrode sheet of the waste lithium iron phosphate battery to the mixed solution is 2.5-50 g / L.

[0016] Unlike the prior art method of pre-treating and separating the lithium iron phosphate from the aluminum foil and then repairing and regenerating it under high temperature and high pressure, the present invention directly places the positive electrode of the used lithium iron phosphate battery (including the aluminum foil and the lithium iron phosphate attached to the aluminum foil via a binder) into a mixed solution containing a lithium replenisher and an acidic reducing agent for reaction. During the reaction, on the one hand, the acidic environment created by the acidic reducing agent causes a slight reaction in the aluminum foil, allowing the lithium iron phosphate to be directly peeled off the aluminum foil; on the other hand, as the aluminum foil reaction proceeds, the consumed hydrogen ions cause the pH value of the mixed solution to gradually increase. This change helps to lower the reduction potential of the reducing agent and improve its reducing properties, thereby promoting the rapid insertion of liquid lithium into the lithium-deficient lithium iron phosphate at room temperature and pressure, thereby promoting the lithium replenishment and repair of the lithium-deficient lithium iron phosphate.

[0017] This allows the lithium iron phosphate stripping process and lithium replenishment repair process to proceed simultaneously, eliminating the need for separate pretreatment of the lithium iron phosphate and aluminum foil, and eliminating the need to create a high-temperature, high-pressure reaction environment during the lithium iron phosphate repair process. This significantly reduces the temperature and time required for the reaction. The entire reaction process does not require high temperature or high pressure conditions, resulting in a simple and efficient process flow and significantly improved implementation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 XRD patterns of aluminum foil and lithium iron phosphate after simultaneous separation and lithium supplementation of the lithium iron phosphate positive electrode sheet disassembled in Example 1 of the present invention;

[0020] Figure 3 This is a cycle performance diagram of waste lithium iron phosphate, lithium iron phosphate repaired by lithium supplementation, and lithium iron phosphate regenerated by annealing in Example 1 of this application. DETAILED DESCRIPTION

[0021] like Figure 1 As shown, the process flow of the invented method for synchronous separation and direct repair of waste lithium iron phosphate positive electrode materials includes the following steps:

[0022] 1) After discharging and disassembling, the waste lithium iron phosphate batteries are directly separated into components such as the diaphragm, positive electrode sheet, and negative electrode sheet;

[0023] 2) Cut or slice the positive electrode sheet into 1cm×1cm~10cm×10cm;

[0024] 3) Immerse the cut positive electrode sheet in a mixed solution containing a lithium supplement agent and an acidic reducing agent. The acidic environment created by the acidic reducing agent in the mixed solution can easily separate the aluminum foil from the lithium iron phosphate positive electrode material. In this process, as the reaction proceeds, the consumed hydrogen ions (H + ) will cause the pH value of the solution to gradually increase. This change is conducive to reducing the reduction potential of the reducing agent, thereby promoting the lithium replenishment and repair of lithium-deficient lithium iron phosphate. Specifically:

[0025] The lithium replenisher is one of lithium chloride, lithium nitrate, lithium hydroxide, lithium acetate, and lithium sulfate, with a concentration of 0.01-1 mol / L; the acidic reducing agent is one of hydroxylamine sulfate, thioacetamide, chromium chloride, hydroxylamine hydrochloride, hydroxylamine-O-sulfonic acid, hydroxylamine phosphate, sulfamic acid, hydroxylamine nitrate, ammonium thiosulfate, and meta-hydroxylamine bitartrate, with a concentration of 0.01-1 mol / L; the reaction temperature is 20-60°C, the reaction time is 5-60 minutes, and the solid-liquid ratio of the positive electrode sheet to the mixed solution is 2.5-50 g / L; after the reaction, the aluminum foil and the repaired lithium iron phosphate are obtained by filtering and drying.

[0026] 4) The repaired lithium iron phosphate is mixed uniformly with a lithium salt and a carbon source by ball milling. The resulting mixed powder is then calcined under an inert atmosphere such as nitrogen or argon to obtain a regenerated lithium iron phosphate cathode material. The lithium salt is one of lithium hydroxide and lithium carbonate, and the carbon source is one of citric acid, glucose, and sucrose. The molar ratio of lithium iron phosphate to lithium source and carbon source is 1:(1%-5%):(1%-15%). The calcination temperature is 400-700°C, the heating rate is 2-10 minutes, and the calcination time is 3-6 hours.

[0027] The present invention is further described below by means of three embodiments:

[0028] Example 1

[0029] 1) Used lithium iron phosphate batteries are discharged and disassembled to obtain components such as positive electrode sheets, negative electrode sheets and diaphragms.

[0030] 2) Cut or slice the positive electrode sheet into 1cm×1cm;

[0031] 3) Weigh the desired cut cathode sheet and immerse it in a mixed solution containing lithium sulfate and the acidic reducing agent hydroxylamine sulfate. The concentration of lithium sulfate used is 0.1 mol / L, and the concentration of the reducing agent hydroxylamine sulfate is 0.5 mol / L. The reaction temperature is 40°C, the reaction time is 10 minutes, and the solid-to-liquid ratio is 10 g / L. After the reaction is completed, collect the aluminum foil and the recharged lithium iron phosphate from the solution and dry them.

[0032] 4) The lithium iron phosphate after lithium supplementation and repair was evenly mixed with an excess of 3% LiOH lithium source and 5% citric acid carbon source by ball milling. The ball-milled powder was placed in an argon atmosphere and heated to 700°C at a rate of 5°C / min and calcined for 3 hours to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

[0033] Figure 2 This is the XRD pattern of the waste lithium iron phosphate cathode sheet, which was simultaneously separated and repaired with lithium supplementation in this example. The characteristic peaks of the aluminum foil correspond to those of the standard card, with sharp peaks and no stray peaks. Similarly, the repaired lithium iron phosphate is completely consistent with its standard card (JCPDS: 02-1109), with no stray peaks, indicating that the lithium iron phosphate has been successfully repaired and has good crystallinity and phase purity.

[0034] Figure 3 The figure shows the cycle performance of the waste, lithium-repaired and rapidly annealed lithium iron phosphate in this embodiment. It can be seen from the figure that at a current density of 1C, the first discharge specific capacity of the three materials is 111.2, 133.5 and 138.2 mA h g -1 It can be seen that the discharge capacity of the material is significantly improved due to the recovery of the material composition and structure. After 300 cycles, the discharge capacity of the lithium iron phosphate after lithium replenishment and annealing regeneration is 129.8 and 134.5 mA h g -1 , the capacity retention rate exceeds 97%, and it has good cycle stability.

[0035] Example 2

[0036] 1) Used lithium iron phosphate batteries are discharged and disassembled to obtain components such as positive electrode sheets, negative electrode sheets and diaphragms.

[0037] 2) Cut or slice the positive electrode sheet into 3cm×3cm;

[0038] 3) Weigh the desired cut positive electrode sheets and immerse them in a mixed solution containing lithium hydroxide and the acidic reducing agent hydroxylamine hydrochloride. The concentration of lithium hydroxide used is 0.1 mol / L, and the concentration of the reducing agent hydroxylamine hydrochloride is 1.0 mol / L. The reaction temperature is 30°C, the reaction time is 30 minutes, and the solid-to-liquid ratio is 15 g / L. After the reaction is completed, collect the aluminum foil and the recharged lithium iron phosphate from the solution and dry them.

[0039] 4) The lithium iron phosphate after lithium supplementation and repair was evenly mixed with an excess of 3% LiOH lithium source and 10% citric acid carbon source by ball milling. The ball-milled powder was placed in an argon atmosphere and heated to 650°C at a rate of 5°C / min and calcined for 3h to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

[0040] The characteristic peaks of the separated aluminum foil correspond to those of its standard card. Secondly, the repaired lithium iron phosphate is also completely consistent with its standard card, with no impurity peaks, indicating that the lithium iron phosphate has been successfully repaired.

[0041] The discharge specific capacities of lithium iron phosphate after 300 cycles were 130.2 and 136.1 mA h g -1 Compared with waste lithium iron phosphate, the discharge capacity of the material is significantly improved.

[0042] Example 3

[0043] 1) Used lithium iron phosphate batteries are discharged and disassembled to obtain components such as positive electrode sheets, negative electrode sheets and diaphragms.

[0044] 2) Cut or slice the positive electrode sheet into 1cm×1cm;

[0045] 3) Weigh the desired cut cathode sheet and immerse it in a mixed solution containing lithium chloride and the acidic reducing agent sulfamic acid. The concentration of lithium chloride used is 0.5 mol / L, and the concentration of the reducing agent hydroxylamine hydrochloride is 1.0 mol / L. The reaction temperature is 50°C, the reaction time is 60 minutes, and the solid-to-liquid ratio is 15 g / L. After the reaction is complete, collect the aluminum foil and the recharged lithium iron phosphate from the solution and dry them.

[0046] 4) The lithium iron phosphate after lithium supplementation and repair was evenly mixed with an excess of 3% LiOH lithium source and 10% glucose carbon source by ball milling. The ball-milled powder was placed in an argon atmosphere and heated to 700°C at a rate of 5°C / min and calcined for 3 hours to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

[0047] The characteristic peaks of the separated aluminum foil closely matched those of the standard card. Furthermore, the spectrum of the repaired lithium iron phosphate was completely consistent with the standard card, without any impurity peaks, fully demonstrating that the lithium iron phosphate had been successfully repaired.

[0048] After lithium supplementation and annealing regeneration treatment, the discharge capacity of lithium iron phosphate after 300 cycles of charge and discharge test was 126.8mA hg -1 and 132.5mA hg -1 Compared with untreated waste lithium iron phosphate, the discharge specific capacity of the material has been significantly improved, showing a good electrochemical performance recovery effect.

Claims

1. A method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials, characterized by: The positive electrode of the waste lithium iron phosphate battery is placed in a mixed solution containing a lithium supplement agent and an acidic reducing agent for reaction; after the reaction, the aluminum foil and the repaired lithium iron phosphate are obtained by filtering and drying.

2. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The repaired lithium iron phosphate is evenly mixed with lithium salt and carbon source, and calcined under a protective gas atmosphere to obtain regenerated lithium iron phosphate.

3. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 2, characterized in that: The carbon source is a combination of one or more of citric acid, glucose, and sucrose; and the lithium salt is a combination of one or two of lithium hydroxide and lithium carbonate.

4. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 3, characterized in that: The molar ratio of lithium iron phosphate to lithium salt and carbon source in the positive electrode sheet of the waste lithium iron phosphate battery is 1: (1%-5%): (1%-15%).

5. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 2, characterized in that: The calcination temperature is 400-700°C, the heating rate is 2-10min, and the calcination time is 3-6h.

6. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The positive electrode sheet of the waste lithium iron phosphate battery is cut or sliced into 1cm×1cm-10cm×10cm, and then placed in the mixed solution for reaction.

7. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The lithium supplement in the mixed solution is a combination of one or more of lithium chloride, lithium nitrate, lithium hydroxide, lithium acetate, and lithium sulfate, and the concentration of the lithium supplement is 0.01-1 mol / L.

8. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The acidic reducing agent in the mixed solution is a combination of one or more of hydroxylamine sulfate, thioacetamide, chromium chloride, hydroxylamine hydrochloride, hydroxylamine-O-sulfonic acid, hydroxylamine phosphate, sulfamic acid, hydroxylamine nitrate, ammonium thiosulfate, and meta-hydroxylamine bitartrate.

9. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 8, characterized in that: The concentration of the acidic reducing agent is 0.01-1 mol / L.

10. The method for synchronous separation and direct repair of waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The reaction temperature in the mixed solution is 20-60° C., the reaction time is 5-60 minutes, and the solid-liquid ratio of the positive electrode sheet of the waste lithium iron phosphate battery to the mixed solution is 2.5-50 g / L.

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