Method for repairing retired lithium iron phosphate cathode material

Abstract

The application discloses a kind of green repair upgrading regeneration technology of decommissioned lithium iron phosphate positive material, comprising the following steps: lithium salt and tea polyphenol are completely dissolved in solvent, to obtain reducing repairant solution;Decommissioned lithium iron phosphate positive material and direct reduction repairant solution are mixed, to obtain mixed suspension;The suspension is loaded into reaction kettle and placed in oven and heated and kept for a period of time, after cooling, precipitate is collected after washing;Precipitate is mixed with aluminum nitrate and diammonium hydrogen phosphate solution, after evaporating dry, add trace lithium salt under nitrogen atmosphere annealing, to obtain upgraded regeneration aluminum phosphate / lithium phosphate coated lithium iron phosphate positive material.The upgrading repair regeneration technology uses abundant natural green reducing repairant-tea polyphenol, and is environmentally friendly and can be recycled and reused;At the same time, the price of aluminum phosphate / lithium phosphate coating layer is low, and the electrochemical performance of lithium iron phosphate waste powder is obviously repaired and improved, which is suitable for industrialization and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a repairing method for retired lithium iron phosphate positive electrode material. BACKGROUND

[0002] Lithium iron phosphate has been widely used as a positive electrode material of a lithium ion battery in the past few years due to its advantages of high safety, low cost and long cycle life, and accounts for more than half of the market share of positive electrode materials of power batteries for new energy vehicles. In the next few years, a large amount of waste lithium iron phosphate positive electrode material that cannot be directly reused due to capacity attenuation needs to be efficiently recycled and regenerated, which plays a crucial role in the benign development of the lithium ion battery industry. At present, the recycling process methods for the retired lithium iron phosphate positive electrode material mainly include metallurgical method and direct regeneration method.

[0003] The metallurgical method mainly includes fire method and wet method. The fire metallurgical recycling mainly crushes and calcines the disassembled waste positive electrode material to collect metal elements. The valuable metal element Fe in lithium iron phosphate has a low price, and the fire metallurgical recycling has high energy consumption, which cannot realize profit driving. The wet metallurgical recycling process uses a large amount of acid and alkali to leach and extract lithium and iron elements in lithium iron phosphate, which can cause secondary pollution and lead to new environmental problems.

[0004] The direct regeneration method is different from the traditional metallurgical recycling method, does not need to break the original structure of the waste lithium iron phosphate positive electrode material, retains its inherent value, and only restores the chemical composition and microstructure of the material through supplement of element sources and reduction repair means. The invention patent CN201710446047.4 discloses a method for recycling retired lithium iron phosphate material through direct repair and regeneration. First, the content of each element in the waste material is tested, the corresponding lithium source, iron source or / and phosphorus source is supplemented to a molar ratio of lithium: iron: phosphorus of (1-1.05): 1: 1, and regenerated lithium iron phosphate is obtained by high-temperature calcination under inert atmosphere. The process flow is simple and the added value of the recycled product is high, but there are still disadvantages such as complex testing of missing element amount, low lithium supplement efficiency and high energy consumption, which are difficult to meet the demand of large-scale recycling. SUMMARY

[0005] Therefore, the present application provides a repairing method for retired lithium iron phosphate positive electrode material, which overcomes the problems of complex process, high energy consumption, secondary pollution and low added value of recycled products in the existing recycling process of retired lithium iron phosphate positive electrode material.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] In a first aspect, the present application discloses a repairing method for retired lithium iron phosphate positive electrode material, comprising the following steps:

[0008] S1, a first lithium salt and tea polyphenol are added into a solvent to be fully dissolved to obtain a repair solution;

[0009] S2, the retired lithium iron phosphate positive electrode powder is added into the repair solution to be uniformly mixed to obtain a suspension;

[0010] S3, the suspension is heated to react, and after cooling, solid-liquid separation is performed, the solid product is washed and dried, and the separated liquid is collected for standby;

[0011] S4, the dried solid product is mixed with an aluminum salt, a phosphate ion, and a second lithium salt in a solvent, heated and stirred until the moisture is evaporated, and then annealed in an inert atmosphere to obtain the repaired lithium iron phosphate positive electrode material; in this step, aluminum ions (Al 3+ ) react with phosphate ions (PO4 3- ) to form aluminum phosphate (AlPO4); at the same time, lithium ions (Li + ) react with phosphate ions (PO4 3- ) to form lithium phosphate (Li3PO4); and finally, after annealing, an aluminum phosphate / lithium phosphate filling and coating layer is formed on the surface of the repaired lithium iron phosphate;

[0012] S5, the liquid collected in step S3 is used as a repair solution, and steps S2-S4 are repeated to repair the next batch of retired lithium iron phosphate positive electrode materials.

[0013] The tea polyphenol is extracted from tea leaves or artificially synthesized, the retired lithium iron phosphate positive electrode powder is a powder obtained by discharging, disassembling, peeling, crushing, and separating a waste power or energy storage lithium iron phosphate battery material; the inert atmosphere is nitrogen, argon, or a mixture of nitrogen and argon; preferably, the inert atmosphere is nitrogen.

[0014] Further scheme: in step S1, the first lithium salt is at least one of lithium hydroxide, lithium nitrate, and lithium acetate; and / or:

[0015] In step S4, the second lithium salt is at least one of lithium carbonate, lithium sulfate, and an organic lithium compound. The trace amount of the second lithium salt added in step S4 is mainly to offset the lithium volatilized during high-temperature annealing, and to supplement the lithium source for the system, which is beneficial to further generate fast ion conductor Li3PO4 to meet the demand of good Li + ion transmission of the system.

[0016] In step S4, the second lithium salt is at least one of lithium carbonate, lithium sulfate, and an organic lithium compound; and / or:

[0017] In step S4, the aluminum ions are derived from aluminum nitrate, aluminum chloride, aluminum sulfate, or aluminum silicate, and the phosphate ions are derived from ammonium dihydrogen phosphate or diammonium hydrogen phosphate.

[0018] Further scheme: in step S1, the first lithium salt concentration in the repair solution is 0.15-0.25 mol / L, and the tea polyphenol concentration is 0.08-0.12 mol / L.

[0019] Further scheme: in steps S1 and S4, the solvent is a mixture of deionized water and ethanol.

[0020] Further scheme: in step S2, the solid-liquid ratio of the retired lithium iron phosphate positive electrode powder and the natural green reduction repair agent is 0.01-0.02 g / mL.

[0021] Further scheme: in step S3, the heating reaction temperature is 100-120℃, and the time is 8-12 hours; and / or:

[0022] In step S3, the precipitate is washed and dried, specifically: using deionized water and anhydrous ethanol to wash and filter alternately and repeatedly for multiple times, and drying at 80-100℃ for 8-10 hours.

[0023] Further scheme: in step S4, the annealing temperature is 600℃-700℃, and the annealing time is 4h-6h; and / or, the annealing heating rate is 3℃ / min-5℃ / min.

[0024] Further scheme: in step S4, the mass ratio of the precipitate, aluminum nitrate, ammonium dihydrogen phosphate, and the second lithium salt is 200:(6.2-31):(1.9-9.5):4.

[0025] In a second aspect, the application discloses a lithium iron phosphate positive electrode material, which is obtained by the repair method.

[0026] In a third aspect, the application discloses a lithium battery, wherein the positive electrode material of the lithium battery comprises the lithium iron phosphate positive electrode material obtained by the repair method.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The direct repair, upgrading and regeneration method of the retired lithium iron phosphate positive electrode material provided in the application uses tea polyphenol naturally extracted from tea leaves as an electron donor, and the multiple hydroxyl groups of the tea polyphenol can repair the structural defects of the waste lithium iron phosphate, create a good reduction environment for the waste lithium iron phosphate, and jointly act with the supplemented lithium salt, which not only helps to convert the decaying FePO4 phase in the waste lithium iron phosphate into a single LiFePO4 phase, but also helps to eliminate harmful Li-Fe anti-site defects; thereby reconstructing Li +A rapid diffusion channel enables the repair of composition and structure. Simultaneously, addressing the damage and loss of the carbon layer on the surface of spent lithium iron phosphate (LFP) batteries, low-cost aluminum and phosphorus sources are introduced to fill the damaged areas of the repaired LFP surface with a composite coating of stable AlPO4 and ion-transport-friendly Li3PO4. This upgraded recycled aluminum phosphate / lithium phosphate-coated LFP can meet the requirements of low cost and high performance in various applications. Compared to introducing a carbon source to form a new carbon layer on the surface of spent LFP, the aluminum phosphate / lithium phosphate composite, due to its preferential binding to LFP, precisely forms an amorphous AlPO4 and Li3PO4 grain composite filling coating at the sites of carbon layer damage and exposed active material. This targeted filling of the damaged carbon layer on the surface of spent LFP helps improve the overall energy density of LFP cathode materials. The AlPO4 used for filling the coating is amorphous and contains Li3PO4 grains that are fast ion conductors. This will stabilize the structure and provide a fast lithium-ion transport channel on the surface of the active material, which will help improve the rate performance of regenerated lithium iron phosphate.

[0029] This invention provides a green remediation and regeneration method for retired lithium iron phosphate cathode materials. This process eliminates the need for secondary treatment that damages the structure of waste lithium iron phosphate materials, and avoids testing to determine their elemental content. It directly uses a natural, green reducing agent to restore the chemical composition and crystal structure, while simultaneously applying a low-cost coating layer, thus upgrading the electrochemical performance and value of the regenerated product. The natural, green reducing agent used in this method is recyclable, the process is simple and environmentally friendly, and its low cost makes it easy to scale up. Attached Figure Description

[0030] Figure 1 A schematic diagram illustrating the process of upgrading, repairing, and regenerating waste lithium iron phosphate.

[0031] Figure 2 The XRD patterns are of unrepaired waste lithium iron phosphate, repaired lithium iron phosphate in Comparative Example 1, and upgraded and regenerated lithium iron phosphate in Examples 1-3.

[0032] Figure 3 Comparison of HAADF-STEM images of waste lithium iron phosphate particles and repaired lithium iron phosphate in Example 1;

[0033] Figure 4 TEM image of waste lithium iron phosphate particles;

[0034] Figure 5 The images show the TEM image and surface elemental distribution energy spectrum of lithium iron phosphate after repair in Example 1.

[0035] Figure 6The graph shows a comparison of the performance of unrepaired waste lithium iron phosphate, lithium iron phosphate in Examples 1-3 and Comparative Examples 1-2 after remediation, after 300 cycles at 2C. Detailed Implementation

[0036] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0038] The raw materials used in the examples and comparative examples are all commercially available, commonly used products.

[0039] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0040] Example 1

[0041] S1: Dissolve 0.3g lithium hydroxide monohydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0042] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0043] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0044] S4: Take 0.2g of the precipitate dried in step S3, mix it with 18.5mg of aluminum nitrate nonahydrate and 5.7mg of ammonium dihydrogen phosphate, add 4mg of lithium carbonate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0045] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0046] Example 2

[0047] S1: Dissolve 0.3g lithium hydroxide monohydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0048] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0049] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0050] S4: Take 0.2g of the precipitate dried in step S3, mix it with 6.2mg of aluminum nitrate nonahydrate and 1.9mg of ammonium dihydrogen phosphate, add 4mg of lithium carbonate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0051] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0052] Example 3

[0053] S1: Dissolve 0.3g lithium hydroxide monohydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0054] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0055] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0056] S4: Take 0.2g of the precipitate dried in step S3, mix it with 31mg of aluminum nitrate nonahydrate and 9.5mg of ammonium dihydrogen phosphate, add 4mg of lithium carbonate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0057] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0058] Example 4

[0059] S1: Dissolve 0.72g lithium acetate dihydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0060] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0061] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0062] S4: Take 0.2g of the precipitate dried in step S3, mix it with 18.5mg of aluminum nitrate nonahydrate and 5.7mg of ammonium dihydrogen phosphate, add 4mg of lithium carbonate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0063] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0064] Example 5

[0065] S1: Dissolve 0.3g lithium hydroxide monohydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0066] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0067] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0068] S4: Take 0.2g of the precipitate dried in step S3, mix it with 18.5mg of aluminum nitrate nonahydrate and 5.7mg of ammonium dihydrogen phosphate, add 4mg of lithium sulfate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0069] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0070] Comparative Example 1

[0071] S1: Dissolve 0.3g lithium hydroxide monohydrate and 1.6g tea polyphenols completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a natural and green direct reduction and repair agent solution.

[0072] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0073] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0074] S4: Take 0.2g of the dried precipitate from step S3 and mix it with 4mg of lithium carbonate. Add it to a mixed solvent of 20ml deionized water and a small amount of anhydrous ethanol. Heat to 90℃ and stir at 400rpm until completely evaporated. After evaporation, anneal at 600℃ for 5h under nitrogen to obtain the repaired and regenerated lithium iron phosphate cathode material.

[0075] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0076] Comparative Example 2

[0077] S1: Dissolve 0.3g of lithium hydroxide monohydrate completely in a mixed solvent of 30mL deionized water and 5mL anhydrous ethanol to obtain a repair agent solution;

[0078] S2: Mix 0.55g of decommissioned lithium iron phosphate cathode material powder with the natural reducing agent solution in step S1 to obtain a mixed suspension;

[0079] S3: The suspension from step S2 is loaded into a reaction vessel and placed in an oven to be heated to 120°C and kept at that temperature for 10 hours. After cooling, the precipitate is collected and washed and filtered repeatedly with deionized water and anhydrous ethanol, and then dried in a 90°C drying oven for 8 hours.

[0080] S4: Take 0.2g of the precipitate dried in step S3, mix it with 18.5mg of aluminum nitrate nonahydrate and 5.7mg of ammonium dihydrogen phosphate, add 4mg of lithium carbonate, add 20ml of deionized water and a small amount of anhydrous ethanol mixed solvent, heat to 90℃ and stir at 400rpm until completely evaporated, after evaporation, anneal at 600℃ for 5h under nitrogen to obtain upgraded regenerated aluminum phosphate / lithium phosphate coated lithium iron phosphate cathode material;

[0081] S5: The repair agent solvent separated in step S3 is recovered and can be recycled for the repair and regeneration of the next batch of retired lithium iron phosphate cathode materials.

[0082] Performance Testing and Results Analysis

[0083] 1. Material Characterization

[0084] Figure 1 This invention illustrates the process of upgrading, repairing, and regenerating waste lithium iron phosphate (LFP) particles. Firstly, addressing the defects in the crystal structure of waste LFP particles, such as numerous lithium vacancies and Li-Fe anti-sites, as well as the irreversible deactivation of the FePO4 phase, this invention utilizes hydrothermal heating as the driving force and natural, environmentally friendly tea polyphenols as electron donors to provide a suitable reduction environment. This reduces ferric iron to ferrous iron, and combined with supplemented lithium salts, repairs the defects in the crystal structure, converting the irreversible FePO4 phase into the electrochemically active LiFePO4 phase. Secondly, addressing the issue of damaged or missing carbon layers on the surface of waste LFP particles, this invention introduces inexpensive aluminum and phosphorus sources during the post-annealing stage. Leveraging the characteristic that aluminum phosphate / lithium phosphate preferentially binds to exposed LFP compared to carbon, this invention targets and fills the damaged or missing carbon layers with a composite coating of amorphous aluminum phosphate and fast-ion conductor lithium phosphate, improving structural stability without reducing the energy density of the active material.

[0085] Figure 2The XRD patterns of unrepaired waste lithium iron phosphate, the repaired lithium iron phosphate in Comparative Example 1, and the upgraded regenerated lithium iron phosphate in Examples 1-3 are shown. It can be seen that the unrepaired waste lithium iron phosphate contains a significant, irreversibly deactivated FePO4 phase in addition to the LiFePO4 phase, which is the reason for its electrical performance degradation. In Comparative Example 1 and Examples 1-3, tea polyphenols were used as electron donors to bind lithium salts, and the irreversible FePO4 phase was completely converted into the electrochemically active LiFePO4 phase through hydrothermal treatment. However, the problem of missing carbon layers on the surface of lithium iron phosphate in Comparative Example 1 was not effectively solved. In Examples 1-3, with the increase of aluminum and phosphorus sources, the fast ion conductor Li3PO4 phase was observed to be generated. Since the AlPO4 phase is amorphous, no corresponding peaks were observed in the XRD pattern; these phases precisely filled the missing carbon layers, repairing the coating.

[0086] Figure 3 The high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images of waste lithium iron phosphate particles and repaired lithium iron phosphate particles from Example 1 are shown for comparison. The waste lithium iron phosphate powder particles have a large number of damages and cracks on their surface, and the carbon layer is obviously destroyed. In contrast, the microcracks on the surface of the repaired lithium iron phosphate particles are repaired, and the particles are more rounded because the damaged areas are filled with a coating.

[0087] Figure 4 TEM images of waste lithium iron phosphate particles are shown. It can be seen that the crystal structure of waste lithium iron phosphate exhibits a clear phenomenon of transition from the LiFePO4 phase through amorphous disordered regions to the irreversibly deactivated FePO4 phase. These irreversibly deactivated FePO4 phases are an important factor in the degradation of its electrochemical performance.

[0088] Figure 5 TEM images and surface elemental distribution energy dispersive spectroscopy (EDS) spectra of the repaired lithium iron phosphate (LiFePO4) in Example 1 are presented. It can be seen that amorphous AlPO4 is distributed on the surface of the LiFePO4 bulk, with fast ion conductor Li3PO4 phase embedded within the amorphous AlPO4. The interior of the bulk contains a homogeneous LiFePO4 phase, indicating that the irreversibly deactivated FePO4 phase has been completely eliminated. The EDS spectra show Al and P signals on the particle surface, further verifying the filling effect of the amorphous AlPO4 coating. The alternating intensity distribution of Al and C elemental signals indicates that the amorphous AlPO4 coating can target and fill the carbon layer deficiencies.

[0089] 2. Electrochemical performance

[0090] Figure 6The electrochemical performance of unrepaired spent lithium iron phosphate and the rehabilitated lithium iron phosphate of Example 1 and Comparative Examples 1-2 after 400 cycles at 2C is presented. It can be seen that compared to spent lithium iron phosphate (whose specific capacity is essentially zero after 400 cycles at 2C), the rehabilitated lithium iron phosphate in Example 1 exhibits a significant improvement in specific capacity at a high current density of 2C (specific capacity is 124.3 mAh g / g after 400 cycles at 2C). -1 The specific capacity of the lithium iron phosphate electrode material was restored to the level of fresh lithium iron phosphate, and the cycle stability was also greatly improved (capacity retention of 92.1% after 400 cycles at 2C). In contrast, the lithium iron phosphate in Comparative Example 1 only repaired the defects in composition and crystal structure by using tea polyphenols as electron donors to bind lithium salts, but the carbon deficiency and damage on the surface were not improved. The exposed lithium iron phosphate was prone to side reactions in the electrolyte, so although the specific capacity was improved significantly, its capacity retention was very low. In Comparative Example 2, although the composition was supplemented and the carbon deficiency and damage on the surface were filled with AlPO4 / Li3PO4, the lithium iron phosphate antisite defects and the irreversible deactivation of the FePO4 phase in the crystal structure were not well repaired and improved, so the electrical performance was also poor. Figure 6 b shows the electrochemical performance of lithium iron phosphate after repair in Examples 1-3 after 400 cycles at 2C. It can be seen that in Example 2, when the amount of Al and P source is small, the specific capacity is high, but the improvement in cycle stability is limited; while in Example 3, when the amount of Al and P source is large, the specific capacity is sacrificed more. Therefore, the amount of Al and P source in Example 1 is optimal.

[0091] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0092] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for repairing decommissioned lithium iron phosphate cathode materials, characterized in that, Includes the following steps: S1. Dissolve the first lithium salt and tea polyphenols in a solvent to obtain a repair solution; S2. Add the decommissioned lithium iron phosphate cathode powder to the repair solution and mix evenly to obtain a suspension; S3. The suspension is heated to react, cooled and then separated into solid and liquid. The solid product is washed and dried, and the separated liquid is collected for later use. S4. The dried solid product is mixed with aluminum ions, phosphate ions and the second lithium salt in a solvent, heated and stirred until the water evaporates, and annealed under an inert atmosphere to obtain the repaired lithium iron phosphate cathode material. S5. Use the liquid collected in step S3 as a repair solution, repeat steps S2-S4, and continue to repair the next batch of retired lithium iron phosphate cathode materials. In step S1, the first lithium salt is at least one of lithium hydroxide, lithium nitrate, and lithium acetate; and / or: In step S4, the second lithium salt is at least one selected from lithium carbonate, lithium sulfate, and organolithium compounds; and / or: In step S4, aluminum ions are derived from aluminum nitrate, aluminum trichloride, aluminum sulfate, or aluminum silicate, and phosphate ions are derived from ammonium dihydrogen phosphate or diammonium hydrogen phosphate. In steps S1 and S4, the solvent is a mixture of deionized water and ethanol; the mass ratio of precipitate, aluminum nitrate, ammonium dihydrogen phosphate, and second lithium salt is 200:(6.2-31):(1.9-9.5):

4.

2. The method for repairing decommissioned lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S1, the concentration of the first lithium salt in the repair solution is 0.15-0.25 mol / L, and the concentration of tea polyphenols is 0.08-0.12 mol / L.

3. The method for repairing decommissioned lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S2, the solid-liquid ratio of the decommissioned lithium iron phosphate cathode powder to the repair solution is 0.01-0.02 g / mL.

4. The method for repairing decommissioned lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S3, the heating temperature is 100-120℃, and the time is 8-12 hours; and / or: In step S3, the precipitate is washed and dried by repeatedly washing and filtering with deionized water and anhydrous ethanol, and then drying at 80-100℃ for 8-10 hours.

5. The method for repairing decommissioned lithium iron phosphate cathode materials according to claim 1, characterized in that, In step S4, the annealing temperature is 600℃-700℃, and the annealing time is 4 hours. The annealing process lasted for 6 hours, with a heating rate of 3℃ / min to 5℃ / min.

6. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is obtained by the repair method described in any one of claims 1 to 5.

7. A lithium battery, characterized in that, The positive electrode material of the lithium battery includes the lithium iron phosphate positive electrode material obtained by the repair method according to any one of claims 1 to 5.

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