A method and application of chitosan sol for remediating waste lithium iron phosphate materials, and lithium-ion batteries.

Abstract

This invention provides a method and application for remediating spent lithium iron phosphate materials using chitosan sol, and for lithium-ion batteries. The remediation method includes the following steps: mixing lithium acetate, chitosan, and spent lithium iron phosphate materials, and using a dispersant to improve the dispersibility of chitosan and lithium acetate; forming a chitosan sol-supported system through sol-gelation and protonation; freeze-drying to maintain the porous structure; and then sintering to simultaneously achieve lithium replenishment and conductive network construction. Chitosan functions as both a reducing agent and a carbon source; the amino and hydroxyl groups in its molecular chain can remove Fe from spent lithium iron phosphate. 3+ Reduced to Fe 2+ Simultaneously, a nitrogen-doped carbon layer is formed after pyrolysis. This invention has the advantages of refining grains, greatly improving powder activity and particle distribution uniformity. It also does not require special equipment, has low energy consumption and low carbon emissions, is safe and controllable, and has low cost, greatly simplifying the repair and regeneration process of waste lithium iron phosphate materials.

Description

Technical Field

[0001] This invention relates to the field of electrode material recycling technology, and in particular to a method and application of chitosan sol for repairing waste lithium iron phosphate materials and lithium-ion batteries. Background Technology

[0002] Lithium iron phosphate (LiFePO4, LFP) has become the mainstream cathode material for electric vehicles and large-scale energy storage facilities due to its core advantages such as stable crystal structure, excellent safety performance, long cycle life, low cost, and environmental friendliness, occupying a significant share of the global lithium-ion battery market. With the widespread application of lithium-ion batteries, a massive amount of waste batteries will be generated after their service life ends—lithium-ion batteries for electronic products have a lifespan of approximately 3 years, while those for electric vehicles have a lifespan of approximately 5-10 years. It is predicted that by 2030, the global production of waste lithium iron phosphate batteries will exceed 3 million tons. Improper disposal of these waste batteries will not only waste valuable resources such as lithium, iron, and phosphorus, but may also cause environmental problems such as soil and water pollution. Therefore, developing efficient, large-scale, economical, and environmentally friendly recycling technologies is of great significance for promoting the sustainable development of the new energy industry.

[0003] Currently, the recycling technologies for waste lithium iron phosphate are mainly divided into three categories: wet recycling, pyrometallurgical recycling, and direct regeneration. Wet recycling is the most widely used technology, extracting valuable elements through multiple processes such as discharge pretreatment, dismantling and sorting, crushing and separation, roasting, acid leaching, and alkali removal. However, this method has significant limitations: it consumes large amounts of acid and alkali reagents, requires highly corrosion-resistant equipment, has high environmental treatment costs, and produces mixed waste residue of iron phosphate and graphite, resulting in low resource utilization. Furthermore, the market price of high-value lithium salts in the recycled lithium iron phosphate products is relatively low, leading to insufficient economic viability for wet recycling and hindering its large-scale application. While pyrometallurgical recycling has a relatively simple process, it suffers from high energy consumption, low reaction efficiency, and uneven additive dispersion. Moreover, the stable olivine structure of lithium iron phosphate increases the difficulty of recycling, further limiting its industrial application.

[0004] To address the economic issues of traditional recycling technologies, direct remediation and regeneration technologies have become a research hotspot in recent years due to their ability to significantly shorten the process and reduce recycling costs. According to the degradation mechanism of lithium iron phosphate batteries, the core reason for capacity decline is the loss of active lithium and Fe... 2 ⁺Oxidized to Fe 3+ The key to repair and regeneration lies in two points: first, restoring the lithium / iron molar ratio; and second, reconstructing the complete olivine crystal structure and eliminating defects.

[0005] Currently, the mainstream direct regeneration technologies mainly include solid-state sintering and hydrothermal methods, but both have significant drawbacks. Solid-state sintering typically requires high-temperature sintering of waste lithium iron phosphate with lithium and carbon sources in an inert or reducing atmosphere to achieve lithium replenishment and structural repair. However, it has high energy consumption and poor uniformity in solid-solid reactions, making it difficult to achieve precise lithium replenishment and easily leading to uneven product performance. Hydrothermal methods require reacting waste materials with lithium, iron, and reducing agents in a hydrothermal reactor under high temperature and high pressure conditions. Subsequent heat treatment is also required, which not only results in long reaction times and complex processes, but also poses safety hazards due to the high temperature and high pressure environment, and the equipment cost is high.

[0006] Given the shortcomings of existing methods for recycling waste lithium iron phosphate cathode materials, it is necessary to improve them. Summary of the Invention

[0007] To address the aforementioned technical deficiencies, this invention provides a method and application for repairing waste lithium iron phosphate materials using chitosan sol, and for lithium-ion batteries. The method for repairing waste lithium iron phosphate materials using chitosan sol, through chitosan sol loading, achieves uniform mixing of waste lithium iron phosphate, lithium acetate, and chitosan, as well as in-situ doping of carbon and nitrogen elements. Simultaneously, it completes precise lithium replenishment, Fe valence state repair, and conductive network precursor preparation. The reaction conditions are mild, the process is simple, safe, and energy-efficient, and it significantly improves the uniformity of material composition and electrochemical performance, offering a significant cost advantage.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for remediating waste lithium iron phosphate materials using chitosan sol, comprising the following steps:

[0010] Lithium acetate, chitosan, and waste lithium iron phosphate materials are mixed to obtain a mixture;

[0011] A dispersant was added to the mixture, and the mixture was ultrasonicated and stirred to obtain a chitosan sol-waste lithium iron phosphate composite precursor.

[0012] The composite precursor was freeze-dried and then sintered under an inert atmosphere to obtain the repaired lithium iron phosphate material.

[0013] Preferably, the dispersant includes at least one of water, anhydrous ethanol, and an aqueous solution of acetic acid with a mass fraction of 1-2%.

[0014] Preferably, in the step of freeze-drying the composite precursor, the freeze-drying specifically involves: pre-freezing the composite precursor at a temperature of -50 to -20°C for 1 to 6 hours, and then freeze-drying it at a vacuum of ≤10 Pa and a temperature of -50 to -20°C for 12 to 24 hours.

[0015] Preferably, the composite precursor is freeze-dried and then sintered in an inert atmosphere. The sintering process specifically includes: first, heating to 150-250°C at a rate of 2-10°C / min and holding for 1-4 hours; then heating to 350-500°C at a rate of 2-10°C / min and holding for 3-6 hours; and finally heating to 650-800°C at a rate of 2-10°C / min and holding for 5-10 hours.

[0016] Preferably, a dispersant is added to the mixture, and the mixture is ultrasonically dispersed at a power of 100~300W for 20~60min, and then stirred at a stirring rate of 200~1500 r / min for 30~600min to obtain a chitosan sol-waste lithium iron phosphate composite precursor.

[0017] Preferably, the mass of the lithium acetate is 10-14% of the mass of the waste lithium iron phosphate material;

[0018] The mass of the chitosan is 10-18% of the mass of the waste lithium iron phosphate material;

[0019] The mass-to-volume ratio of the waste lithium iron phosphate material to the dispersant is (1~5)g:(10~50)mL;

[0020] Lithium acetate, chitosan, and waste lithium iron phosphate materials are ground and mixed for 0.5 to 8 hours to obtain a mixture.

[0021] Preferably, the inert atmosphere includes at least one of nitrogen, helium, neon, argon, and a hydrogen-argon mixture.

[0022] Preferably, the volume fraction of hydrogen in the hydrogen-argon mixture is 5-10%.

[0023] Secondly, the present invention also provides the application of the repaired lithium iron phosphate material obtained by the method in the preparation of lithium-ion batteries.

[0024] Thirdly, the present invention also provides a lithium-ion battery comprising the repaired lithium iron phosphate material obtained by the method.

[0025] The method and application of chitosan sol for repairing waste lithium iron phosphate materials and lithium-ion batteries of the present invention have the following advantages compared with the prior art:

[0026] The present invention provides a method for remediating waste lithium iron phosphate materials using chitosan sol. Chitosan functions as both a reducing agent and a carbon source; the amino and hydroxyl groups in its molecular chain can remove Fe from the waste lithium iron phosphate. 3+ Reduced to Fe 2+Simultaneously, pyrolysis (i.e., the pyrolysis of chitosan after sintering) forms a nitrogen-doped carbon layer. By mixing lithium acetate, chitosan, and waste lithium iron phosphate materials, and using a dispersant to improve the dispersibility of chitosan and lithium acetate, a chitosan sol-supported system (i.e., chitosan sol-waste lithium iron phosphate composite precursor) is formed through sol-gelling and protonation. Freeze-drying maintains the porous structure, and sintering then achieves simultaneous lithium replenishment and conductive network construction. This invention has the advantages of refining grains, greatly improving powder activity, and enhancing particle distribution uniformity. It also requires no special equipment, consumes little energy, has low carbon emissions, is safe and controllable, and is inexpensive, greatly simplifying the repair and regeneration process of waste lithium iron phosphate materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The graph shows the cycle stability of coin cells assembled from the lithium iron phosphate cathode materials repaired in Examples 1-6 and S-LFP (i.e., the waste lithium iron phosphate materials used before repair in Example 1) at a rate of 0.5C.

[0029] Figure 2 The XRD patterns of the lithium iron phosphate cathode material before and after repair in Example 1 are shown.

[0030] Figure 3 The graph shows the cycle performance of coin cells assembled from waste lithium iron phosphate cathode materials before and after repair in Example 1 at 0.5C.

[0031] Figure 4 The CV curves are shown for the coin cells assembled from the repaired lithium iron phosphate cathode material (R-LFP) and the unrepaired waste lithium iron phosphate cathode material in Example 1.

[0032] Figure 5 This is a SEM image of the waste lithium iron phosphate material before repair in Example 1;

[0033] Figure 6 The image shows a SEM image of the repaired lithium iron phosphate material in Example 1.

[0034] Figure 7 The image shows the EDS diagram of the repaired lithium iron phosphate material in Example 1. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0037] This application provides a method for remediating waste lithium iron phosphate materials using chitosan sol, comprising the following steps:

[0038] S1. Mix lithium acetate, chitosan, and waste lithium iron phosphate materials to obtain a mixture;

[0039] S2. Add a dispersant to the mixture, sonicate and stir to obtain chitosan sol-waste lithium iron phosphate composite precursor;

[0040] S3. After freeze-drying the composite precursor, sinter it under an inert atmosphere to obtain the repaired lithium iron phosphate material.

[0041] The present invention provides a method for remediating waste lithium iron phosphate materials using chitosan sol. Chitosan functions as both a reducing agent and a carbon source; the amino and hydroxyl groups in its molecular chain can remove Fe from the waste lithium iron phosphate. 3+ Reduced to Fe 2+Simultaneously, pyrolysis (i.e., the pyrolysis of chitosan after sintering) forms a nitrogen-doped carbon layer. By mixing lithium acetate, chitosan, and waste lithium iron phosphate materials, and using a dispersant to improve the dispersibility of chitosan and lithium acetate, a chitosan sol-supported system (i.e., chitosan sol-waste lithium iron phosphate composite precursor) is formed through sol-gelling and protonation. Freeze-drying maintains the porous structure, and sintering then achieves simultaneous lithium replenishment and conductive network construction. This invention has the advantages of refining grains, greatly improving powder activity, and enhancing particle distribution uniformity. It also requires no special equipment, consumes little energy, has low carbon emissions, is safe and controllable, and is inexpensive, greatly simplifying the repair and regeneration process of waste lithium iron phosphate materials.

[0042] This invention addresses the bottleneck of uneven mixing in traditional solid-phase regeneration processes by innovatively proposing a novel liquid-solid mixing strategy using chitosan sol as both a dispersion medium and a functional precursor. Chitosan not only chelates and activates the surface of waste LFP (lithium iron phosphate) and acts as a carbon source and reducing agent, but its gel network also achieves nanoscale uniform dispersion of lithium acetate and active particles. Combined with freeze-drying to preserve the complete gel structure, the final sintering process forms a regenerated material with both uniform carbon coating and a porous structure, significantly improving electrochemical performance.

[0043] In some embodiments, the dispersant includes at least one of water, anhydrous ethanol, and an aqueous solution of acetic acid with a mass fraction of 1-2%.

[0044] In some embodiments, the step of freeze-drying the composite precursor specifically involves: pre-freezing the composite precursor at a temperature of -50 to -20°C for 1 to 6 hours, and then freeze-drying it at a vacuum of ≤10 Pa and a temperature of -50 to -20°C for 12 to 24 hours.

[0045] This invention addresses the problems of high viscosity in chitosan sol, the tendency of the composite precursor to adhere to container walls after conventional vacuum drying, and the resulting sampling difficulties. The invention innovatively introduces a freeze-drying process. This process not only facilitates the complete sampling and transfer of the precursor, but more importantly, it allows water to sublimate directly from solid ice to gas through low-temperature freezing, completely avoiding the damage to the sol structure caused by capillary forces and surface tension at the gas-liquid interface during drying. Therefore, the conductive carbon layer framework of chitosan and the uniformly encapsulated LFP particles and lithium salt dispersion are completely preserved, forming a dry gel precursor with high porosity and a large specific surface area. This fluffy porous structure is partially retained during subsequent sintering, which not only facilitates mass transfer of reactants and gas expulsion but also significantly optimizes the electrochemical performance of the recycled material.

[0046] Addressing the technical challenge of lithium carbonate's poor solubility in anhydrous ethanol, deionized water, and acetic acid solutions, which can lead to uneven lithium replenishment, this invention selects lithium acetate as the lithium source. Its core advantages lie in: lithium acetate's excellent solubility allows for uniform molecular-level dispersion in chitosan-acetic acid sol, ensuring close atomic-scale contact with waste LFP particles and thus guaranteeing uniform repair of bulk lithium defects; simultaneously, its decomposition characteristics at lower temperatures perfectly match the carbonization process of chitosan, enabling in-situ, simultaneous reaction. More importantly, acetate ions not only release gas and optimize the material's pore structure during pyrolysis, but also act as an additional carbon source, synergistically constructing a more conductive carbon layer with chitosan. These combined characteristics result in a recycled material with superior structure and electrochemical performance.

[0047] In some embodiments, the composite precursor is freeze-dried and then sintered in an inert atmosphere. The sintering process specifically includes: first, heating to 150-250°C at a rate of 2-10°C / min and holding for 1-4 hours; then heating to 350-500°C at a rate of 2-10°C / min and holding for 3-6 hours; and finally heating to 650-800°C at a rate of 2-10°C / min and holding for 5-10 hours.

[0048] In some embodiments, a dispersant is added to the mixture, and the mixture is ultrasonically dispersed at a power of 100-300W for 20-60 minutes, and then stirred at a stirring rate of 200-1500 r / min for 30-600 minutes to obtain a chitosan sol-waste lithium iron phosphate composite precursor.

[0049] In some embodiments, the mass of lithium acetate is 10-14% of the mass of waste lithium iron phosphate material;

[0050] The mass of chitosan is 10-18% of the mass of waste lithium iron phosphate material;

[0051] The mass-to-volume ratio of waste lithium iron phosphate material and dispersant is (1~5)g:(10~50)mL;

[0052] In some embodiments, the mass-to-volume ratio of lithium acetate, chitosan, waste lithium iron phosphate material, and dispersant is (0.5~0.7)g:(0.5~0.7)g:(0.5~0.9)g:(1~5)g:(10~50)mL.

[0053] In some embodiments, lithium acetate, chitosan, and waste lithium iron phosphate material are ground and mixed for 0.5 to 8 hours to obtain a mixture.

[0054] In some embodiments, the inert atmosphere includes at least one of nitrogen, helium, neon, argon, and a hydrogen-argon mixture.

[0055] In some embodiments, the hydrogen-argon mixture is a mixture of argon and hydrogen, wherein the volume fraction of hydrogen in the hydrogen-argon mixture is 5-10%.

[0056] Based on the same inventive concept, the present invention also provides an application of the repaired lithium iron phosphate material obtained by the above-mentioned repair method in the preparation of lithium-ion batteries.

[0057] Based on the same inventive concept, the present invention also provides a lithium-ion battery, including the repaired lithium iron phosphate material obtained by the above-described repair method.

[0058] The following further illustrates the method and application of chitosan sol for repairing waste lithium iron phosphate materials and lithium-ion batteries using specific embodiments. This section further explains the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0059] Example 1

[0060] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0061] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0062] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0063] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0064] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0065] Example 2

[0066] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0067] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0068] S2. Add 14 mL of deionized water to the mixture in step S1, and ultrasonically disperse it for 30 min at a power of 300 W. Then stir it for 120 min at a stirring rate of 600 r / min to obtain the chitosan sol-waste lithium iron phosphate composite precursor.

[0069] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0070] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0071] Example 3

[0072] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0073] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0074] S2. Add 14 mL of anhydrous ethanol to the mixture in step S1, and ultrasonically disperse it for 30 min at a power of 300 W. Then stir it for 120 min at a stirring rate of 600 r / min to obtain the chitosan sol-waste lithium iron phosphate composite precursor.

[0075] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0076] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0077] Example 4

[0078] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0079] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0080] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0081] S3. Place the composite precursor from step S2 in a vacuum drying oven and dry it at 50°C and a vacuum of approximately -0.1 MPa (absolute pressure of 100 Pa) for 12 hours to obtain dried powder.

[0082] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0083] Example 5

[0084] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0085] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0086] S2. Add 14 mL of anhydrous ethanol to the mixture in step S1 and continue grinding for 30 min to obtain the precursor.

[0087] S3. Place the precursor from step S2 in a tube furnace and introduce a hydrogen-argon mixture (hydrogen gas fraction of 10%) as a protective atmosphere. First, raise the temperature to 180°C at 5°C / min and hold for 2.5 hours; then raise the temperature to 450°C at 5°C / min and hold for 2.5 hours; finally, raise the temperature to 650°C at 5°C / min and hold for 6 hours. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 is obtained.

[0088] Example 6

[0089] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0090] S1. Place 0.6g of lithium acetate, 0.7g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0091] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, and continue grinding for 30 min to obtain the precursor;

[0092] S3. Place the precursor from step S2 in a tube furnace and introduce a hydrogen-argon mixture (hydrogen gas fraction of 10%) as a protective atmosphere. First, raise the temperature to 180°C at 5°C / min and hold for 2.5 hours; then raise the temperature to 450°C at 5°C / min and hold for 2.5 hours; finally, raise the temperature to 650°C at 5°C / min and hold for 6 hours. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 is obtained.

[0093] Example 7

[0094] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0095] S1. Place 0.5g lithium acetate, 0.7g chitosan, and 5g waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0096] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0097] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0098] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0099] Example 8

[0100] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0101] S1. Place 0.7g lithium acetate, 0.7g chitosan, and 5g waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0102] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0103] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0104] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0105] Example 9

[0106] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0107] S1. Place 0.6g of lithium acetate, 0.5g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0108] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0109] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0110] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0111] Example 10

[0112] This embodiment provides a method for remediating waste lithium iron phosphate materials using chitosan sol, including the following steps:

[0113] S1. Place 0.6g of lithium acetate, 0.9g of chitosan, and 5g of waste lithium iron phosphate material into a mortar and grind for 30 minutes at room temperature (25℃) to obtain a mixture.

[0114] S2. Add 14 mL of 1% acetic acid aqueous solution to the mixture in step S1, ultrasonically disperse at 300 W for 30 min, and then stir at 600 r / min for 120 min to obtain chitosan sol-waste lithium iron phosphate composite precursor.

[0115] S3. Place the composite precursor from step S2 in a freeze dryer, pre-freeze it at -40℃ for 1 hour, and then freeze-dry it at -40℃ for 24 hours under a vacuum of 1 Pa to obtain dried powder.

[0116] The dried powder was placed in a tube furnace, and a hydrogen-argon mixture (hydrogen gas fraction of 10%) was introduced as a protective atmosphere. The temperature was first increased to 180℃ at 5℃ / min and held for 2.5h; then increased to 450℃ at 5℃ / min and held for 2.5h; finally increased to 650℃ at 5℃ / min and held for 6h. After cooling to room temperature, the repaired lithium iron phosphate material LiFePO4 was obtained.

[0117] Performance testing

[0118] Electrochemical performance tests and analyses were performed on the lithium iron phosphate materials repaired in the above examples and comparative examples. The electrochemical performance tests were performed according to the following method: 0.1g of the repaired lithium iron phosphate materials from each example and comparative example were weighed and compounded with PVDF (polyvinylidene fluoride) and Super P (conductive carbon black) in a mass ratio of 80:10:10. NMP (N-methylpyrrolidone) was used as a dispersant to prepare the slurry. The slurry was coated on a flat aluminum foil, dried in a blower dryer for 2 hours, and dried in a vacuum dryer for 10 hours. The slurry was then stamped into a 12mm diameter positive electrode sheet. In an inert glove box, a lithium metal sheet was used as the negative electrode material, a PE membrane was used as the separator, and 1M LiPF6 was used as the negative electrode material. The electrolyte was prepared using a ratio of DMC:EC:EMC = 1:1:1 (i.e., the solute was lithium hexafluorophosphate (LiPF6), and the solvents were DMC (dimethyl carbonate), EC (ethylene carbonate), and EMC (ethyl methyl carbonate). The volume ratio of DMC, EC, and EMC was 1:1:1, and the concentration of LiPF6 was 1 M (mol / L). The resulting coin cell was then used for performance testing.

[0119] Before testing, the batteries were left to stand at room temperature (25°C) for 12 hours. Then, constant current charge-discharge performance was measured using the NEWARE battery testing system. The operating voltage range was set to 2.5–4.3V. The assembled half-cells were activated five times at a current density of 0.2C, followed by long-term cycle performance testing at 1C. The operating temperature was kept constant at 25°C. CV testing was performed at a scan rate of 0.5 mV / s, with a voltage range of 2.5–4.3V. EIS testing was conducted at frequencies from 0.01 Hz to 1 × 10⁻⁶. 5 It is performed within the Hz range.

[0120] Table 1 shows the first-cycle discharge specific capacity of coin cells assembled from lithium iron phosphate materials repaired with lithium acetate (LiOAc) and chitosan (Cs) at different mass fractions in different embodiments at 0.2C and 0.5C.

[0121] Table 1 - First-cycle discharge specific capacity of different coin cells at 0.2C and 0.5C

[0122]

[0123] As can be seen from Table 1, the coin cells assembled from the lithium iron phosphate material repaired in Example 1 have the best first-cycle discharge specific capacity at 0.2C and 0.5C, reaching 151.21 mAh / g and 145.76 mAh / g, respectively.

[0124] Figure 1The graph shows the cycle stability of coin cells assembled from the lithium iron phosphate cathode materials repaired in Examples 1-6 and S-LFP (i.e., the waste lithium iron phosphate materials used before repair in Example 1) at a rate of 0.5C.

[0125] from Figure 1 It can be seen that the lithium iron phosphate restored in Example 1 exhibits the best cycle performance. In Example 1, 1% acetic acid was used as a medium to fully dissolve chitosan, forming a homogeneous system with lithium acetate. After stirring and dispersion, the lithium source and S-LFP particles achieved molecular-level uniform mixing, and the homogeneous structure was completely preserved after freeze-drying. In contrast, Example 2 used deionized water as a medium, and Example 3 used anhydrous ethanol as a medium. The degree of chitosan dissolution decreased sequentially, and the mixing uniformity decreased accordingly, proving that 1% acetic acid is the basis for achieving molecular-level dispersion.

[0126] Although Example 4 also used 1% acetic acid as a medium to dissolve chitosan, it employed vacuum drying. During the drying process, the evaporation of the liquid pulled the originally uniformly dispersed particles together, causing local agglomeration. At the same time, it was difficult to sample the precursor and the structural integrity was damaged. The performance was significantly lower than that of Example 1, proving that freeze drying is the key to maintaining structural uniformity and ensuring complete recovery.

[0127] Further comparison shows that Example 6 also used 1% acetic acid as the medium, but only ground and then sintered directly. Although the chitosan dissolved, the dispersion was uneven, and conventional drying caused component migration and agglomeration, so the performance was not as good as Example 1. Example 5 used anhydrous ethanol as the dispersion medium and coated the surface of S-LFP particles with chitosan by mechanical grinding. Although the freezing process was avoided, the non-dissolved system could not achieve molecular-level mixing, so the performance was not as good as Example 6. Example 3 also used anhydrous ethanol as the medium and was freeze-dried after ultrasonic stirring. However, the undissolved chitosan particles were pushed and migrated by ice crystals during freezing, which made it difficult for the lithium source and carbon source to make close contact with the S-LFP particles, so the performance was not as good as Example 5.

[0128] The above comparison shows that acetic acid as a medium for dissolving chitosan is the basis for achieving molecular-level mixing, while freeze-drying is the key to maintaining the structure and ensuring complete recovery. The two work together to form the core technology for precise lithium replenishment and uniform carbon coating.

[0129] Figure 2 The XRD patterns of the lithium iron phosphate cathode material before and after repair in Example 1 are shown. Before repair, the waste lithium iron phosphate (S-LFP) cathode material exhibited a coexistence of FePO4 and LiFePO4 phases. After repair, the crystal structure of the waste lithium iron phosphate (R-LFP) cathode material transformed into a single LiFePO4 phase, and the strong and narrow diffraction peaks indicated that the regenerated LiFePO4 sample had good crystallinity. Therefore, this patent supplements the LiFePO4 phase by repairing waste LiFePO4. +The structure was restored, resulting in well-formed LiFePO4 crystals. Simultaneously, the crystallinity of the recovered LiFePO4 particles was improved, promoting crystal growth and formation, thus improving the quantity and size of the crystals.

[0130] Figure 3 This is a graph showing the cycle performance of coin cells assembled from waste lithium iron phosphate cathode materials before and after repair in Example 1 at 0.5C. From... Figure 3 As can be seen, the coin cell assembled with the repaired lithium iron phosphate (R-LFP) cathode material exhibits a higher first-cycle discharge specific capacity at 0.5C than the previous (S-LFP) 112.82 mAh g⁻¹. -1 Increased to 145.76mAhg -1 .

[0131] Figure 4 The CV curves are shown for the coin cells assembled from the repaired lithium iron phosphate cathode material (R-LFP) and the unrepaired waste lithium iron phosphate cathode material in Example 1.

[0132] Figure 4 In order to test the cycle reversibility of the lithium iron phosphate cathode materials before and after repair in Example 1, CV tests were performed on coin cells assembled by R-LFP and S-LFP under the conditions of a scan rate of 0.5 mV / s and a voltage range of 2.5-4.3 V. The polarization voltage of the coin cell assembled by S-LFP was as high as 300 mV; the polarization voltage of the coin cell assembled by R-LFP was 256 mV, which was lower than that of S-LFP (300 mV). This indicates that the cycle reversibility of S-LFP is poor. This further explains why the regenerated LiFePO4 cathode material has superior performance compared to the waste LiFePO4 cathode material.

[0133] The morphology and microstructure of the waste lithium iron phosphate material in Example 1 before and after remediation were studied using scanning electron microscopy (SEM). SEM can observe the particle size and distribution of LiFePO4 particles, particle aggregation, grain growth integrity, and crystal surface smoothness. The SEM image of the waste lithium iron phosphate material before remediation is shown below. Figure 5 As shown, the SEM image of the repaired lithium iron phosphate material is as follows. Figure 6 As shown.

[0134] from Figures 5~6As can be seen, due to the residue of the binder and the collapse of the LiFePO4 structure, severe agglomeration occurs in the S-LFP particles, resulting in uneven particle distribution and irregular particle size. The R-LFP particles have a smaller particle size distribution and more uniform morphology. This is attributed to the use of 1% acetic acid aqueous solution as a dispersant, which makes the LiFePO4 particle distribution more uniform. The carbon layer coating of the LiFePO4 particles after high-temperature pyrolysis of chitosan and acetate effectively controls grain growth and agglomeration.

[0135] Figure 7 The image shows the presence and relatively uniform distribution of C, O, Fe, P, and N elements in the nitrogen-doped carbon-coated regenerated composite material R-LFP in Example 1, indicating good coverage by the regenerated carbon layer. The results demonstrate that the regenerated LiFePO4 possesses excellent structure and uniform elemental distribution, proving that solid-phase regeneration of waste LiFePO4 using nitrogen-doped carbon coating can reduce the particle size of LiFePO4, and the improved microstructure is beneficial for shortening the LiFePO4 production cycle. + The diffusion distance from the LiFePO4 cathode phase to the electrolyte indicates that using chitosan sol as a carbon-nitrogen co-coating agent to coat regenerated LiFePO4 is feasible.

[0136] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for remediating waste lithium iron phosphate materials using chitosan sol, characterized in that, Includes the following steps: Lithium acetate, chitosan, and waste lithium iron phosphate materials are mixed to obtain a mixture; A dispersant was added to the mixture, and the mixture was ultrasonicated and stirred to obtain a chitosan sol-waste lithium iron phosphate composite precursor. The composite precursor was freeze-dried and then sintered under an inert atmosphere to obtain the repaired lithium iron phosphate material.

2. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, The dispersant includes at least one of water, anhydrous ethanol, and an aqueous solution of acetic acid with a mass fraction of 1-2%.

3. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, In the step of freeze-drying the composite precursor, the freeze-drying process specifically involves: pre-freezing the composite precursor at a temperature of -50 to -20°C for 1 to 6 hours, and then freeze-drying it at a vacuum of ≤10Pa and a temperature of -50 to -20°C for 12 to 24 hours.

4. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, The composite precursor is freeze-dried and then sintered in an inert atmosphere. The sintering process specifically includes: first, heating the temperature to 150-250°C at a rate of 2-10°C / min and holding it for 1-4 hours; then heating the temperature to 350-500°C at a rate of 2-10°C / min and holding it for 3-6 hours; and finally heating the temperature to 650-800°C at a rate of 2-10°C / min and holding it for 5-10 hours.

5. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, Add a dispersant to the mixture, ultrasonically disperse it at a power of 100~300W for 20~60min, and then stir it at a stirring rate of 200~1500 r / min for 30~600min to obtain the chitosan sol-waste lithium iron phosphate composite precursor.

6. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, The mass of the lithium acetate is 10-14% of the mass of the waste lithium iron phosphate material; The mass of the chitosan is 10-18% of the mass of the waste lithium iron phosphate material; The mass-to-volume ratio of the waste lithium iron phosphate material to the dispersant is (1~5)g:(10~50)mL; Lithium acetate, chitosan, and waste lithium iron phosphate materials are ground and mixed for 0.5 to 8 hours to obtain a mixture.

7. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 1, characterized in that, The inert atmosphere includes at least one of nitrogen, helium, neon, argon, and a hydrogen-argon mixture.

8. The method for remediating waste lithium iron phosphate materials using chitosan sol as described in claim 7, characterized in that, The volume fraction of hydrogen in the hydrogen-argon mixture is 5-10%.

9. The application of a repaired lithium iron phosphate material obtained by the method according to any one of claims 1 to 8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, characterized in that, Including the repaired lithium iron phosphate material obtained by the method as described in any one of claims 1 to 8.

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