A method for recycling waste lithium iron phosphate positive electrode sheet, regenerated lithium iron phosphate material and lithium ion battery

Abstract

The application relates to the technical field of waste lithium iron phosphate positive plate recycling, in particular to a waste lithium iron phosphate positive plate recycling method, regenerated lithium iron phosphate material and a lithium ion battery. The recycling method comprises the following steps: (1) crushing the waste lithium iron phosphate positive plate, adding the waste lithium iron phosphate positive plate into an alkaline leaching solution, reacting, filtering to obtain aluminum-removed material and a leaching solution; (2) using a repairing solution to treat the aluminum-removed material in step (1), and then performing roasting; the alkaline leaching solution comprises an alkaline leaching agent, a complex stabilizer and an interface protective agent; the complex stabilizer is used for forming a soluble complex with aluminum ions; the interface protective agent is used for in-situ forming a protective layer on the surface of the lithium iron phosphate; the repairing solution comprises a lithium source, a surfactant and a chelating agent. Full-element high-value recycling and a green process are realized.

Description

Technical Field

[0001] This application relates to the field of waste lithium iron phosphate cathode recycling technology, and particularly to a method for recycling waste lithium iron phosphate cathodes, regenerated lithium iron phosphate materials, and lithium-ion batteries. Background Technology

[0002] In the field of wet recycling technology for spent lithium-ion batteries, especially retired lithium iron phosphate battery cathode materials, the core objective is to achieve efficient and clean separation and regeneration of valuable components. Among these, the selective removal of aluminum current collectors in the cathode sheet, as the main impurity, is a key step in the recycling process. It is necessary to efficiently separate aluminum while ensuring the structural integrity of the lithium iron phosphate active material.

[0003] To achieve the above objectives, chemical leaching is commonly used in related technologies. One common approach is leaching with strong acid solutions. While this method can effectively dissolve various metals, including aluminum, it inevitably leads to severe equipment corrosion and generates large amounts of acidic wastewater requiring complex treatment, resulting in a heavy environmental burden. Another approach is leaching with alkaline solutions (such as sodium hydroxide), which utilizes the amphoteric nature of aluminum to achieve dissolution. However, since lithium iron phosphate materials also exhibit chemical instability in alkaline environments, conventional alkaline leaching processes, while dissolving aluminum, also erode the crystal structure of lithium iron phosphate, causing lithium loss and material damage, thereby impairing its electrochemical performance after regeneration.

[0004] Therefore, related technologies face a persistent contradiction when processing waste lithium iron phosphate cathode sheets: how to simultaneously suppress the structural erosion of the lithium iron phosphate substrate by a mild chemical environment that enables efficient leaching of aluminum impurities. This contradiction restricts the selectivity, economy, and product quality of the recycling process, urgently requiring a new technological approach to solve. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, a method for recycling waste lithium iron phosphate cathode sheets is provided. By using an alkaline leaching solution containing an alkaline leaching agent, a complexing stabilizer, and an interface protectant for leaching, and simultaneously treating with a remedial solution and calcining, the interface protectant forms a protective layer on the lithium iron phosphate surface, and the complexing stabilizer forms a soluble complex with aluminum ions. This achieves efficient and highly selective dissolution of aluminum impurities under mild conditions, effectively inhibits the erosion of the lithium iron phosphate material lattice by the alkaline environment, maintains the structural integrity and electrochemical performance of the material, and avoids equipment corrosion and wastewater treatment problems, thus improving the environmental friendliness and economy of the recycling process.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a method for recycling waste lithium iron phosphate cathode sheets is provided, comprising: (1) After crushing the waste lithium iron phosphate positive electrode sheet, add it to the alkaline leachate, react, filter and obtain the aluminum-free material and leachate. (2) The material after aluminum removal in step (1) is treated with a repair solution and then roasted. The alkaline leachate includes: an alkaline leachate, a complexing stabilizer, and an interface protectant; The complexing stabilizer is used to form a soluble complex with aluminum ions; The interface protectant is used to form a protective layer in situ on the surface of lithium iron phosphate; The repair solution includes a lithium source, a surfactant, and a chelating agent.

[0007] In some of these embodiments, the interface protectant comprises an oxyacid salt.

[0008] In some of these embodiments, the oxyacid salt includes phosphates or silicates.

[0009] In some of these embodiments, the phosphate includes at least one of sodium phosphate, potassium phosphate, and disodium hydrogen phosphate.

[0010] In some of these embodiments, the silicate includes sodium silicate and / or potassium silicate.

[0011] In some embodiments, the alkaline leaching agent comprises an alkali metal hydroxide; preferably, the alkali metal hydroxide comprises sodium hydroxide.

[0012] In some embodiments, the complexing stabilizer is selected from hydroxycarboxylate salts or aminopolycarboxylate salts; preferably, the hydroxycarboxylate salt includes at least one of sodium gluconate, sodium citrate, potassium citrate, and sodium salicylate; the aminopolycarboxylate salt includes disodium ethylenediaminetetraacetate and / or trisodium methylglycine diacetate.

[0013] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0014] In some embodiments, the surfactant is selected from alkylbenzene sulfonates, lignin sulfonates, or alkyl sulfates. Preferably, the surfactant includes at least one of sodium hexadecylbenzene sulfonate, sodium lignin sulfonate, and sodium dodecyl sulfate.

[0015] In some of these embodiments, the chelating agent includes ethylenediaminetetraacetic acid and / or citric acid.

[0016] In some of these embodiments, an ultrasonic field is applied during the reaction; preferably, the frequency of the ultrasonic field is 20-40 kHz.

[0017] In some of these embodiments, the calcination conditions in step (2) include: heating to 300-400°C and holding at that temperature in an inert atmosphere, and then heating to 500-650°C and holding at that temperature.

[0018] In some of these embodiments, the leachate from step (1) is post-treated to prepare an aluminum-containing product.

[0019] In some embodiments, the post-processing sequentially includes vacuum concentration, cooling crystallization, and drying dehydration; preferably, the cooling crystallization temperature is 20-40°C.

[0020] In some of these embodiments, the process of crushing the waste lithium iron phosphate cathode sheet in step (1) includes: first, thermally removing the binder from the waste lithium iron phosphate cathode sheet, and then mechanically crushing it.

[0021] In some embodiments, the pyrolysis conditions include: an inert atmosphere and a temperature of 500-600°C.

[0022] In some of these embodiments, the particle size of the material obtained after mechanical crushing is 20-50 mesh.

[0023] In some of these embodiments, the reaction temperature in step (1) is 50-70°C and the time is 30-60 minutes.

[0024] In some of these embodiments, the solid-liquid mass-volume ratio of the waste lithium iron phosphate cathode sheet to the alkaline leachate is 5:1 to 10:1 g / mL.

[0025] In some embodiments, the concentration of the alkaline leaching agent in the alkaline leachate is 1.0-3.0 mol / L; preferably 1.5-2.5 mol / L.

[0026] In some embodiments, the concentration of the interfacial protectant in the alkaline leachate is 0.1-0.5 wt%.

[0027] In some embodiments, the concentration of the complexing stabilizer in the alkaline leachate is 3-8 wt%.

[0028] In some embodiments, the concentration of the lithium source in the repair solution is 0.05-5 mol / L.

[0029] In some embodiments, the concentration of the surfactant in the repair solution is 0.05-0.2 wt%.

[0030] In some embodiments, the concentration of the chelating agent in the repair solution is 0.01-1 mol / L.

[0031] In some of these embodiments, the mass-to-volume ratio of the aluminum-removed material to the repair solution in step (1) is 1:5 to 1:10 g / mL.

[0032] According to another aspect of the present invention, a recycled lithium iron phosphate material is provided, which is obtained by the above-described recycling method.

[0033] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, wherein the material of the positive electrode comprises the above-described recycled lithium iron phosphate material.

[0034] This application discloses a method for recycling waste lithium iron phosphate cathode sheets, regenerated lithium iron phosphate materials, and lithium-ion batteries. The recycling method includes: crushing waste lithium iron phosphate cathode sheets and reacting them in an alkaline leachate; filtering to obtain aluminum-free material and leachate; treating the aluminum-free material with a remediation solution, followed by calcination. The alkaline leachate contains an alkaline leaching agent, a complexing stabilizer, and an interface protectant. The complexing stabilizer forms a soluble complex with aluminum ions, and the interface protectant forms a protective layer in situ on the lithium iron phosphate surface. The remediation solution contains a lithium source, a surfactant, and a chelating agent. This method achieves highly selective separation of aluminum impurities by using an interface protectant to inhibit erosion of the lithium iron phosphate material during alkaline leaching; simultaneously, the complexing stabilizer prevents aluminum ion hydrolysis and reprecipitation, ensuring complete aluminum removal; and the remediation solution treats and repairs lithium loss and structural defects in the material, thereby improving the electrochemical performance of the recycled material.

[0035] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. An innovative ternary synergistic selective leaching system consisting of an alkaline leaching agent, a complexing stabilizer, and an interface protector was constructed. The alkaline leaching agent (such as sodium hydroxide) is responsible for rapidly dissolving the aluminum foil; the complexing stabilizer (such as sodium gluconate) can instantly form a stable soluble complex with the dissolved aluminum ions, effectively preventing the hydrolysis and reprecipitation of aluminum ions and ensuring an aluminum removal rate of over 99%; the interface protector (such as sodium phosphate or sodium silicate) can form a nanoscale "dynamic sacrificial layer" on the surface of lithium iron phosphate particles in situ, significantly blocking the erosion of the lithium iron phosphate active material lattice by the alkaline environment, thereby maximizing the preservation of the structural integrity of the cathode material and reducing lithium loss while efficiently removing aluminum.

[0036] 2. Introducing an ultrasonic field to assist the leaching process. The cavitation effect and strong mechanical stirring effect generated by ultrasound can accelerate the desorption and dispersion of the positive electrode black powder from the aluminum foil surface, enhance the mass transfer efficiency between the liquid and solid phases, and enable the reactants to maintain continuous and efficient contact with the fresh aluminum interface, thereby promoting the rapid and complete dissolution of aluminum, shortening the reaction time, and helping to further improve the purity of the product.

[0037] 3. A repair solution comprising a lithium source, surfactant, and chelating agent was designed, combined with negative pressure treatment. The addition of the surfactant significantly reduced the surface tension of the repair solution. Under the synergistic effect of the negative pressure environment, the repair solution could fully penetrate into the micro-nano pores inside the lithium iron phosphate aggregates, achieving "full wetting" lithium replenishment from the particle surface to the interior. The chelating agent helps stabilize the ionic state in the solution, promoting the migration and solidification of lithium ions into the material lattice, thereby effectively repairing lithium loss and structural defects caused by cycling and recycling processes.

[0038] 4. This method achieves high-value recovery of all elements and a green process. It not only efficiently recovers lithium iron phosphate cathode materials but also directly converts the aluminum-rich leachate generated during the aluminum removal step into anhydrous sodium aluminate byproduct through a vacuum concentration-cooling crystallization-drying dehydration process. This achieves full resource utilization of valuable elements such as lithium, iron, phosphorus, and aluminum, greatly enhancing the economic value of the process. Simultaneously, the entire process uses water as the main reaction medium, avoiding the problems of large-scale use of strong acids and organic solvents in traditional wet recycling. It generates less waste, aligning with green and sustainable manufacturing principles. Attached Figure Description

[0039] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0040] Figure 1 This is a schematic diagram of the process flow for the recycling method of waste lithium iron phosphate cathode sheets of the present invention.

[0041] Figure 2 This is a scanning electron microscope (SEM) image of the regenerated lithium iron phosphate in Example 1.

[0042] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the regenerated lithium iron phosphate in Example 1.

[0043] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0044] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0045] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] In the field of wet recycling of waste lithium iron phosphate cathode sheets to separate aluminum foil, chemical leaching is commonly used to achieve efficient removal of aluminum impurities. Specifically, this method involves contacting a mixture containing aluminum and lithium iron phosphate with a specific leaching agent to dissolve the aluminum. The basic working principle is to utilize the chemical reaction between the leaching agent and metallic aluminum, converting it into soluble ions that enter the solution, thereby achieving solid-liquid separation. Using alkaline leaching solutions (such as sodium hydroxide solution) is a common practice, primarily because it has good dissolving power for metallic aluminum and avoids the equipment corrosion and wastewater treatment problems caused by strong acid environments.

[0052] However, this alkaline leaching method performs poorly when applied to recycling scenarios where the structural integrity of the lithium iron phosphate cathode material needs to be maintained simultaneously. A fundamental contradiction lies in the fact that, in order to optimize its aluminum dissolution efficiency, the inherently strong alkaline environment of this method inevitably erodes the crystal structure of the lithium iron phosphate material, leading to the loss of active lithium and a decline in the material's electrochemical performance. Specifically, during the aluminum removal process, sodium hydroxide not only reacts with aluminum but also attacks the surface of the lithium iron phosphate particles, destroying their olivine structure, resulting in a capacity decay in the recovered material, making it unusable for direct battery remanufacturing.

[0053] Through in-depth analysis, the inventors discovered that the root causes of the aforementioned contradictions are multifaceted: From a thermodynamic perspective, under strongly alkaline conditions, lithium iron phosphate is in a metastable state and tends to decompose due to OH- attack. From a kinetic perspective, aluminum dissolution and lithium iron phosphate corrosion are simultaneous competing processes, and conventional methods lack effective suppression of the latter. Furthermore, the aluminum ions generated during dissolution are easily hydrolyzed and redeprecipitated in an alkaline environment, potentially re-attaching to the material surface, causing secondary pollution and incomplete separation. These factors collectively limit the application of alkaline leaching methods in the recovery of high-quality cathode materials.

[0054] To overcome the aforementioned contradictions, this invention proposes a different technical approach. Its core concept lies in introducing an interface protectant into the alkaline leachate to form a protective interface layer in situ on the surface of lithium iron phosphate particles. This achieves efficient aluminum dissolution while significantly inhibiting the erosion of the lithium iron phosphate material by the alkaline solution. In other words, it provides a method that combines selective leaching and targeted protection, solving the problem of simultaneously achieving aluminum separation and cathode material preservation under alkaline conditions. This achieves the technical effect of efficiently separating aluminum impurities and maintaining the structural stability of the lithium iron phosphate material under mild conditions. Specifically, this invention adopts the following technical solution: According to one aspect of the present invention, a method for recycling waste lithium iron phosphate cathode sheets is provided, comprising: (1) After crushing the waste lithium iron phosphate positive electrode sheet, add it to the alkaline leachate, react, filter and obtain the aluminum-free material and leachate. (2) The material after aluminum removal in step (1) is treated with a repair solution and then roasted. The alkaline leachate includes: an alkaline leachate, a complexing stabilizer, and an interface protectant; The complexing stabilizer is used to form a soluble complex with aluminum ions; The interface protectant is used to form a protective layer in situ on the surface of lithium iron phosphate; The repair solution includes a lithium source, a surfactant, and a chelating agent.

[0055] In the process of selectively dissolving aluminum using an alkaline leaching system, the aluminum ions generated by dissolution are prone to hydrolysis and reprecipitation in an alkaline environment, leading to incomplete aluminum separation and product contamination. This problem is solved by adding a specific complexing agent that can form a stable and soluble complex with aluminum ions to the alkaline leaching solution.

[0056] After selective aluminum removal, lithium iron phosphate materials may experience lithium loss and structural damage during the recycling process, leading to a decline in their electrochemical performance. This problem is solved by using a repair solution containing a lithium source, surfactant, and chelating agent to perform liquid-phase permeation treatment on the aluminum-removed material, followed by calcination.

[0057] In some of these embodiments, the interface protectant comprises an oxyacid salt.

[0058] In some of these embodiments, the oxyacid salt includes phosphates or silicates; In some of these embodiments, the phosphate includes at least one of sodium phosphate, potassium phosphate, and disodium hydrogen phosphate.

[0059] In some of these embodiments, the silicate includes sodium silicate and / or potassium silicate.

[0060] In some embodiments, the alkaline leaching agent comprises an alkali metal hydroxide; preferably, the alkali metal hydroxide comprises sodium hydroxide.

[0061] In some embodiments, the complexing stabilizer is selected from hydroxycarboxylate salts or aminopolycarboxylate salts; preferably, the hydroxycarboxylate salt includes at least one of sodium gluconate, sodium citrate, potassium citrate, and sodium salicylate; the aminopolycarboxylate salt includes disodium ethylenediaminetetraacetate and / or trisodium methylglycine diacetate.

[0062] In this application, "complexing stabilizer" refers to any chemical substance that can coordinate with aluminum ions (Al³⁺) in an alkaline environment to form a stable complex with good solubility in water, thereby preventing the hydrolysis, precipitation, or re-adsorption of aluminum ions. Its function is to "lock" the dissolved aluminum in the solution phase, ensuring complete aluminum separation and avoiding secondary contamination of the solid product. Examples include, but are not limited to: hydroxycarboxylate salts (such as gluconate, citrate, salicylate), aminopolycarboxylate salts (such as ethylenediaminetetraacetic acid salt, methylglycine diacetic acid salt), or combinations thereof. These substances coordinate with Al³⁺ through multiple electron-donating groups (such as carboxyl groups, hydroxyl groups) in their molecules, forming mixed ligand complexes such as [Al(OH)₄]⁻ combined with organic ligands, significantly improving the stability of aluminum in alkaline solutions.

[0063] In this application, "interface protectant" refers to any chemical additive that, during alkaline leaching, preferentially adsorbs onto the surface of lithium iron phosphate particles and / or interacts with the lithium iron phosphate surface, thereby thermodynamically or kinetically inhibiting or slowing down the erosion of the lithium iron phosphate bulk lattice by alkaline media (such as OH⁻ ions). Its core function is to act as a "sacrificial layer" or "isolation layer," protecting the structural integrity of valuable cathode materials without affecting aluminum dissolution. For example, it may include, but is not limited to: oxyacid salts (such as phosphates, silicates, borates), hydroxide precursors of certain amphoteric metals, or combinations thereof. Specifically, phosphate (PO₄³⁻) or silicate (SiO₃²⁻ / SiO₄) 4 ⁻) Plasma may undergo specific adsorption or even weak surface reactions on the surface of lithium iron phosphate, competitively occupying active sites or forming a thin and dense passivation film, thereby blocking or significantly slowing down the attack of OH⁻ on the iron-oxygen and phosphorus-oxygen bonds inside the material.

[0064] In this application, "repair solution" refers to any liquid-phase treatment medium used to treat lithium iron phosphate materials after selective aluminum removal, in order to replenish the lithium element lost during the recycling process, repair any surface or bulk structural defects, and ultimately restore or improve their electrochemical performance. It acts on the material through mechanisms such as penetration, wetting, ion exchange, or surface modification. For example, it may include, but is not limited to, a mixed aqueous or organic solution containing a lithium source compound (providing Li⁺), a surfactant (reducing the surface tension of the solution to promote penetration), and a chelating agent (potentially complexing impurity ions or regulating the reaction microenvironment). The lithium source can be a soluble lithium salt such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium acetate; the surfactant can be anionic (such as alkylbenzene sulfonates or alkyl sulfates) or polymeric (such as lignin sulfonates); and the chelating agent can be ethylenediaminetetraacetic acid, citric acid, etc.

[0065] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0066] In some embodiments, the surfactant is selected from alkylbenzene sulfonates, lignin sulfonates, or alkyl sulfates. Preferably, the surfactant includes at least one of sodium hexadecylbenzene sulfonate, sodium lignin sulfonate, and sodium dodecyl sulfate.

[0067] In some of these embodiments, the chelating agent includes ethylenediaminetetraacetic acid and / or citric acid.

[0068] In some of these embodiments, an ultrasonic field is applied during the reaction; preferably, the frequency of the ultrasonic field is 20-40 kHz.

[0069] In the process of alkaline leaching to separate aluminum, the oxide film on the aluminum foil surface and the aluminum shavings formed by the breakage of the electrode sheet can hinder the effective contact between the alkaline solution and the metallic aluminum, affecting the dissolution kinetics and stripping efficiency. This problem is solved by applying an ultrasonic field during the leaching reaction to enhance mass transfer and stripping.

[0070] The introduction of an ultrasonic field offers two main advantages. First, the cavitation microjets powerfully impact and peel away the alumina film adhering to the aluminum foil surface, as well as any remaining lithium iron phosphate black powder, exposing fresh aluminum surface. This allows the alkali solution to react directly with the aluminum, significantly accelerating the initial reaction rate. Second, the intense ultrasonic stirring greatly enhances mass transfer between the liquid and solid phases, enabling reactants (OH-, complexing agents) to quickly reach the aluminum surface and products (aluminum complexes) to rapidly diffuse away. This ensures the continuous and efficient progress of the reaction while maintaining a homogeneous system and preventing localized overheating or uneven concentration. Those skilled in the art will understand that alternative methods for enhancing the reaction include high-pressure jet stirring and high-shear stirring, but the ultrasonic field exhibits unique advantages due to its concentrated energy, microscopic effect, and ease of integration with the reaction vessel. For more specific optimization, the frequency of the ultrasonic field can be controlled within the range of 20-40 kHz. This frequency range provides a strong ultrasonic cavitation effect with acceptable equipment wear. For example, ultrasonic probes or trough-type ultrasonic reactors with frequencies of 28 kHz or 35 kHz can be used.

[0071] In this application, "ultrasonic field" refers to a mechanical vibration wave field with a frequency higher than the upper limit of human hearing (typically >20 kHz) applied during the leaching reaction. Its function is to utilize physical mechanisms such as cavitation, microjets, and enhanced mass transfer to break up the oxide film on the aluminum foil surface, promote the peeling of fine aluminum shavings adhering to the cathode material after electrode breakage, and accelerate the diffusion of reactants and products at the solid-liquid interface, thereby improving the overall aluminum dissolution kinetics and separation efficiency. For example, it may include, but is not limited to, ultrasonic fields with frequencies in the range of 20 kHz to 40 kHz generated by an immersion ultrasonic probe or a tank-type ultrasonic reactor. The applied ultrasonic power density can be adapted according to the volume of the reaction system and the characteristics of the container, for example, reaching power levels of tens to hundreds of watts per liter of solution.

[0072] It should be noted that the synergistic effect of the three components in the alkaline leachate provides a key technical means to resolve the core contradiction between selective aluminum separation and material protection. The complexing stabilizer ensures thorough aluminum dissolution and solution stability, while the interface protector directly safeguards the lithium iron phosphate matrix. The synergistic effect of the three components in the remediation solution guarantees the performance recovery of the material after leaching. The surfactant-promoted deep penetration ensures uniform lithium source replenishment, while the chelating agent purifies the remediation environment. The combined application of these two multi-component systems enables the entire recycling process to achieve efficient aluminum removal and high-quality regeneration in a relatively mild alkaline aqueous system, thereby jointly solving the problems mentioned in the background technology regarding incomplete aluminum removal and structural damage to the cathode material, making performance recovery difficult.

[0073] In some of these embodiments, the calcination conditions in step (2) include: heating to 300-400°C and holding at that temperature in an inert atmosphere, and then heating to 500-650°C and holding at that temperature.

[0074] By employing the aforementioned two-stage inert atmosphere calcination conditions, this preferred solution ensures complete removal of the repair solution additives and full optimization of the material structure, thereby obtaining regenerated materials with good crystallinity, low impurity content, and excellent electrochemical performance. This further helps to solve the problems of organic residue or material overburning that may occur with single-stage high-temperature calcination, thus synergistically enhancing the overall technical effect of this invention in effectively repairing and improving material performance. Those skilled in the art can easily combine the two-stage calcination procedure in this embodiment with the specific repair solution formulation in the foregoing embodiments; this combination can simultaneously achieve the effects of uniform lithium replenishment and structural optimization.

[0075] In some of these embodiments, the leachate from step (1) is post-treated to prepare an aluminum-containing product.

[0076] In this application, "aluminum-containing products" broadly refers to solid aluminum compound products with specific chemical compositions, morphologies, and higher economic value obtained through subsequent processing of the aluminum-rich solution produced in the selective leaching step. This aims to achieve high-value utilization of aluminum resources and improve the economics of the entire recycling process. Examples include, but are not limited to, anhydrous sodium aluminate (NaAlO2), aluminum hydroxides, or other aluminum salt products prepared through unit operations such as concentration, crystallization, and dehydration. Specific product forms can be crystalline powders, granules, or lumps, and their purity can reach industrial-grade or higher standards depending on the precision of the subsequent processing. In this application, "alkaline leachate" broadly refers to any solution system capable of providing an alkaline environment to dissolve the aluminum components contained in the material. Examples include, but are not limited to, a combined solution based on an aqueous solution of an alkali metal hydroxide (such as sodium hydroxide) and possibly further containing additives (such as complexing stabilizers and interface protectants) to achieve specific auxiliary functions.

[0077] In some embodiments, the post-processing sequentially includes vacuum concentration, cooling crystallization, and drying dehydration; preferably, the cooling crystallization temperature is 20-40°C.

[0078] First, the concentration of aluminates (and complexes) in the leachate is increased by vacuum concentration to bring it close to or to a supersaturated state. Then, the solubility of aluminates is reduced by lowering the temperature (cooling crystallization), inducing them to precipitate in crystalline form. Finally, residual water of crystallization or surface adsorbed water in the crystals is removed by drying and dehydration to obtain a dry aluminum product. Preferably, the cooling crystallization temperature is controlled between 20-40°C. This temperature range balances the crystallization rate, crystal purity, and energy consumption; too low a temperature may lead to eutectic impurities, while too high a temperature will reduce the yield. More generally, post-processing may also include other steps, such as filtration before concentration to remove trace amounts of suspended solids; or adding a recrystallization step after crystallization to improve product purity; or using different processes such as spray drying or evaporation crystallization to directly obtain the aluminum product.

[0079] In some of these embodiments, the process of crushing the waste lithium iron phosphate cathode sheet in step (1) includes: first, thermally removing the binder from the waste lithium iron phosphate cathode sheet, and then mechanically crushing it.

[0080] In some embodiments, the pyrolysis conditions include: an inert atmosphere and a temperature of 500-600°C.

[0081] In some of these embodiments, the particle size of the material obtained after mechanical crushing is 20-50 mesh.

[0082] By employing the optimized pretreatment and reaction conditions described above, this preferred scheme ensures the full release of valuable components from the electrode and creates a uniform and suitable reaction environment for subsequent highly selective leaching. This further helps to solve the problems of difficult aluminum black powder separation or uneven reaction caused by improper pretreatment, thereby synergistically enhancing the overall technical effect of the present invention in terms of process stability and recovery efficiency.

[0083] In some of these embodiments, the reaction temperature in step (1) is 50-70°C and the time is 30-60 minutes.

[0084] In some of these embodiments, the solid-liquid mass-volume ratio of the waste lithium iron phosphate cathode sheet to the alkaline leachate is 5:1 to 10:1 g / mL.

[0085] In some embodiments, the concentration of the alkaline leaching agent in the alkaline leachate is 1.0-3.0 mol / L.

[0086] In some embodiments, the concentration of the alkaline leaching agent in the alkaline leachate is 1.5-2.5 mol / L.

[0087] The problem of converting the aluminum-containing solution generated in the selective leaching step into a byproduct with higher economic value to achieve high-value recovery of all elements is solved by sequentially subjecting the aluminum-rich leachate to vacuum concentration, cooling crystallization, and drying dehydration to prepare anhydrous sodium aluminate. In this application, "alkaline leachate" refers to any liquid-phase treatment medium containing alkaline substances that can selectively dissolve aluminum impurities without significantly corroding the lithium iron phosphate material lattice. Its core function is to provide a suitable alkaline chemical environment to achieve efficient aluminum dissolution, while controlling negative impacts on the target cathode material (lithium iron phosphate) through the synergistic effect of other components. For example, it may include, but is not limited to: aqueous solutions containing alkali metal hydroxides, or solutions containing other strong bases or alkaline salts. Typically, its pH value is maintained in a strongly alkaline range, such as pH greater than 12, to effectively dissolve metallic aluminum; and the concentration of the alkaline substances can be adjusted according to the properties of the processed material and reaction conditions, for example, the concentration of sodium hydroxide is between 1.0 and 3.0 mol / L.

[0088] In some embodiments, the concentration of the interfacial protectant in the alkaline leachate is 0.1-0.5 wt%.

[0089] In some embodiments, the concentration of the complexing stabilizer in the alkaline leachate is 3-8 wt%.

[0090] In some embodiments, the concentration of the lithium source in the repair solution is 0.05-5 mol / L.

[0091] In some embodiments, the concentration of the surfactant in the repair solution is 0.05-0.2 wt%.

[0092] In some embodiments, the concentration of the chelating agent in the repair solution is 0.01-1 mol / L.

[0093] In some of these embodiments, the mass-to-volume ratio of the aluminum-removed material to the repair solution in step (1) is 1:5 to 1:10 g / mL.

[0094] According to another aspect of the present invention, a recycled lithium iron phosphate material is provided, which is obtained by the above-described recycling method.

[0095] According to another aspect of the present invention, a lithium-ion battery is provided, wherein the positive electrode is prepared using the above-described recycled lithium iron phosphate material.

[0096] In a specific embodiment of the present invention, the battery can be a battery module assembled from individual battery cells. The battery module can contain one or more battery cells, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In the battery module, the multiple battery cells can be arranged sequentially along the length of the battery module; of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells can be fixed using fasteners. The battery module may also include a housing with a receiving space, in which the multiple battery cells are received.

[0097] In the description of this invention, "a plurality of" means two or more.

[0098] In a specific embodiment of the present invention, the battery can also be a battery pack assembled from the aforementioned battery modules. The battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack. Specifically, the battery pack may include a battery box and multiple battery modules disposed within the battery box; the battery box includes an upper box and a lower box, the upper box covering the lower box and forming a closed space for accommodating the battery modules. The multiple battery modules can be arranged in the battery box in any manner.

[0099] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0100] Example 1: A method for preparing recycled lithium iron phosphate includes the following steps: S1: Pretreatment: The disassembled waste lithium iron phosphate cathode sheets are placed in an atmosphere furnace and pyrolyzed at 550℃ for 2 hours under nitrogen protection to remove the binder; the pyrolyzed electrode sheets are mechanically crushed and passed through a 40-mesh standard sieve to obtain a mixed powder of aluminum scrap and cathode black powder.

[0101] S2: Selective leaching separation: Prepare a selective leaching system: Use deionized water as solvent, prepare a 2.0 mol / L sodium hydroxide solution as an alkaline leaching agent, add 5% wt sodium gluconate as a complexing stabilizer, add 0.3% wt sodium phosphate as an interface protectant, and stir evenly.

[0102] The mixed powder obtained in step S1 was added to the above selective leaching system at a solid-liquid ratio of 8:1 (g / mL). The reaction was carried out in an ultrasonic reactor at a reaction temperature of 60°C, with a mechanical stirring speed of 400 rpm, an ultrasonic power of 600 W, a frequency of 30 kHz, and a reaction time of 45 min. After the reaction, the mixture was filtered and separated to obtain an aluminum-rich leachate and an aluminum-removed cathode material.

[0103] S3: High-value utilization of aluminum resources: The aluminum-rich leachate obtained in step S2 is transferred to a rotary evaporator and concentrated under reduced pressure at 80℃ and a vacuum of -0.07MPa until the solution density reaches 1.4g / cm³; the concentrate is transferred to a crystallizer and allowed to stand at 25℃ for 15h to crystallize; the precipitated crystals are collected by filtration and dried in an oven at 170℃ for 2.5h to obtain anhydrous sodium aluminate product.

[0104] S4: Synergistic Lithium Supplementation and Repair: Preparation of Regeneration and Repair Solution: Using deionized water as solvent, prepare a 2.0 mol / L lithium hydroxide solution as the lithium source, add 0.1% wt sodium dodecyl sulfate as the surfactant, add 0.05 mol / L ethylenediaminetetraacetic acid as the chelating agent, and stir evenly.

[0105] S5: The aluminum-removed cathode material obtained in step S2 is washed with pure water until neutral, then transferred to the above-mentioned regeneration and repair solution and soaked under negative pressure for 2.5 hours to ensure the repair solution fully wets the material. After filtration, the filter cake is placed in a vacuum drying oven and dried at 80°C. The dried powder is placed in a tube furnace and calcined in two stages under a nitrogen atmosphere: first, the temperature is increased to 350°C at 5°C / min and held for 1.5 hours, then increased to 600°C at 3°C / min and held for 4 hours. The furnace is then cooled to room temperature to obtain the regenerated lithium iron phosphate material. Its scanning electron microscope (SEM) image is shown below. Figure 2 ,from Figure 2 It can be seen that the particle size distribution of the recycled lithium iron phosphate material is uniform; Figure 3 X-ray diffraction (XRD) pattern of recycled lithium iron phosphate material, from Figure 3 It can be seen that the phase of the recycled lithium iron phosphate material is LiFePO4.

[0106] Example 2: A method for preparing recycled lithium iron phosphate includes the following steps: This embodiment is basically the same as Embodiment 1, except that: in step S2, the interface protectant is 0.2%wt sodium silicate; in step S3, the vacuum degree of the reduced pressure concentration is -0.08MPa; and in step S4, the final calcination temperature is 650℃.

[0107] The remaining steps and parameters are the same as in Example 1.

[0108] Example 3: A method for preparing recycled lithium iron phosphate includes the following steps: This embodiment is basically the same as Embodiment 1, except that: in step S2, the alkaline leaching agent is a 1.5 mol / L sodium hydroxide solution, and the complexing stabilizer is 3% wt sodium citrate; in step S4, the lithium source is a 1.5 mol / L lithium carbonate solution, the surfactant is 0.1% wt sodium hexadecylbenzenesulfonate, the chelating agent is 0.05 mol / L citric acid, and the final calcination temperature is 550℃.

[0109] The remaining steps and parameters are the same as in Example 1.

[0110] Example 4: A method for preparing recycled lithium iron phosphate includes the following steps: This embodiment is basically the same as Embodiment 1, except that: in step S2, the alkaline leaching agent is a 2.5 mol / L sodium hydroxide solution, the complexing stabilizer is 8% wt sodium gluconate, and the interface protectant is 0.5% wt sodium phosphate; in step S3, the vacuum concentration temperature is 70°C, and the crystallization temperature is 20°C; in step S4, the lithium source is a 1.0 mol / L lithium nitrate solution, the surfactant is 0.1% wt sodium lignosulfonate, the chelating agent is 0.05 mol / L ethylenediaminetetraacetic acid, and the final calcination temperature is 500°C.

[0111] The remaining steps and parameters are the same as in Example 1.

[0112] Comparative Example 1: A method for preparing recycled lithium iron phosphate includes the following steps: The difference between this comparative example and Example 1 is that the lithium replenishment repair step is omitted.

[0113] The specific steps are as follows: the aluminum-free cathode material obtained in step S2 is washed with pure water until neutral, filtered, dried, and used directly as a control sample without undergoing the lithium replenishment soaking and roasting treatment in step S4.

[0114] The remaining steps (S1, S2, S3) are the same as in Example 1.

[0115] Comparative Example 2: A method for preparing recycled lithium iron phosphate includes the following steps: The difference between this comparative example and Example 1 is that the interface protectant in the selective leaching system is omitted.

[0116] The specific steps are as follows: The leaching system prepared in step S2 contains only alkaline leaching agent (2.0 mol / L sodium hydroxide) and complexing stabilizer (5% wt sodium gluconate), without adding interface protectant.

[0117] The remaining steps (S1, S3, S4) are the same as in Example 1.

[0118] Comparative Example 3: A method for preparing recycled lithium iron phosphate includes the following steps: The difference between this comparative example and Example 1 is that ultrasound assistance is omitted.

[0119] The specific steps are as follows: In step S2, only mechanical stirring (400 rpm) is used for the reaction, and the ultrasonic equipment is not turned on.

[0120] The remaining steps (S1, S3, S4) are the same as in Example 1.

[0121] Test methods and results: I. Testing Methods 1. Elemental determination: The regenerated lithium iron phosphate samples prepared in each example and comparative example were digested with aqua regia, and the elemental content in the samples was determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0122] 2. Electrochemical performance testing: The prepared lithium iron phosphate sample, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone (NMP) was added, and the mixture was mixed evenly in a high-speed mixer. The mixture was then coated onto aluminum foil, dried, rolled, and cut into sheets to obtain the positive electrode sheet.

[0123] A CR2032 button cell was assembled in an argon glove box using pure lithium foil as the counter electrode. The electrolyte was 1 mol / L LiPF6 / EC+DMC+EMC (volume ratio 1:1:1).

[0124] At room temperature of 25℃, the assembled battery was charged at a constant current of 0.1C to 3.75V, and then charged at a constant voltage until the current dropped to 0.05C. The initial charge capacity was recorded. Then, the battery was discharged at a constant current of 0.1C to 2.0V, and the initial discharge capacity was recorded.

[0125] The initial charge / discharge efficiency is calculated using the following formula: Initial efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100%.

[0126] Table 1. Performance analysis of the regenerated lithium iron phosphate prepared in Examples 1-4 and Comparative Examples 1-3 and the batteries prepared therefrom. Examples 1-4 all achieved excellent regeneration results. The aluminum content in the regenerated lithium iron phosphate was controlled below 200 ppm (minimum 138 ppm), and the 0.1C discharge capacity reached above 158 mAh / g, with an initial efficiency exceeding 99%, indicating that the process of this invention can effectively remove aluminum impurities and repair the electrochemical performance of the cathode material.

[0127] Compared with Example 1, Comparative Example 1 (without lithium replenishment) showed a significant decrease in discharge capacity (153.41 mAh / g) and a reduction in initial efficiency to 96.65%, demonstrating that the lithium replenishment repair step plays a crucial role in restoring the material's capacity.

[0128] Compared with Example 1, Comparative Example 2 (without interface protectant) showed a significant increase in aluminum content (358 ppm) and a decrease in discharge capacity, indicating that the interface protectant can effectively block the erosion of the positive electrode material by the alkaline solution and prevent aluminum residue and material damage.

[0129] Compared with Example 1, Comparative Example 3 (without ultrasonic assistance) showed a slightly higher aluminum content (421 ppm) and a lower discharge capacity, indicating that the ultrasonic field can enhance separation efficiency and improve product purity.

[0130] In summary, this invention achieves efficient recycling and high-value regeneration of waste lithium iron phosphate cathode sheets through an integrated process of "selective leaching system - ultrasonic enhancement - multi-component regeneration and repair solution". The regenerated products have excellent performance and there is a significant synergistic effect among the various technical features.

[0131] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0132] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0133] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling waste lithium iron phosphate cathode sheets, characterized in that, include: (1) After crushing the waste lithium iron phosphate positive electrode sheet, add it to the alkaline leachate, react, filter and obtain the aluminum-removed material and leachate respectively. (2) The material after aluminum removal in step (1) is treated with a repair solution and then roasted. Regenerated lithium iron phosphate was obtained; The alkaline leachate includes: an alkaline leachate, a complexing stabilizer, and an interface protectant; The complexing stabilizer is used to form a soluble complex with aluminum ions; The interface protectant is used to form a protective layer in situ on the surface of lithium iron phosphate; The repair solution includes a lithium source, a surfactant, and a chelating agent.

2. The method for recycling waste lithium iron phosphate cathode sheets according to claim 1, characterized in that, The interface protectant comprises an oxyacid salt; preferably, the oxyacid salt comprises a phosphate and / or a silicate; the phosphate comprises at least one of sodium phosphate, potassium phosphate, and disodium hydrogen phosphate; the silicate comprises sodium silicate and / or potassium silicate. And / or, the alkaline leaching agent comprises an alkali metal hydroxide; preferably, the alkali metal hydroxide comprises sodium hydroxide; And / or, the complexing stabilizer is selected from hydroxycarboxylate or aminopolycarboxylate; preferably, the hydroxycarboxylate includes at least one of sodium gluconate, sodium citrate, potassium citrate, and sodium salicylate; the aminopolycarboxylate includes disodium ethylenediaminetetraacetate and / or trisodium methylglycine diacetate; And / or, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate; And / or, the surfactant comprises at least one of alkylbenzene sulfonate, lignin sulfonate, and alkyl sulfate; preferably, the surfactant comprises at least one of sodium hexadecylbenzene sulfonate, sodium lignin sulfonate, and sodium dodecyl sulfate; And / or, the chelating agent includes ethylenediaminetetraacetic acid and / or citric acid.

3. The method for recycling waste lithium iron phosphate cathode sheets according to claim 1, characterized in that, During the reaction, an ultrasonic field is applied; preferably, the frequency of the ultrasonic field is 20-40 kHz.

4. The method for recycling waste lithium iron phosphate cathode sheets according to claim 1, characterized in that, The calcination conditions described in step (2) include: heating to 300-400℃ and holding at that temperature under an inert atmosphere, and then heating to 500-650℃ and holding at that temperature.

5. The method for recycling waste lithium iron phosphate cathode sheets according to claim 1, characterized in that, It also includes post-treatment of the leachate from step (1) to prepare aluminum-containing products.

6. The method for recycling waste lithium iron phosphate cathode sheets according to claim 5, characterized in that, The post-processing includes, in sequence, vacuum concentration, cooling crystallization, and drying dehydration; preferably, the cooling crystallization temperature is 20-40℃.

7. The method for recycling waste lithium iron phosphate cathode sheets according to claim 1, characterized in that, The process of crushing waste lithium iron phosphate cathode sheets in step (1) includes: firstly, thermally decomposing the waste lithium iron phosphate cathode sheets to remove the binder, and then mechanically crushing them; preferably, the pyrolysis conditions include: under an inert atmosphere, the temperature is 500-600℃; preferably, the particle size of the material obtained after mechanical crushing is 20-50 mesh. And / or, the reaction temperature in step (1) is 50-70℃ and the time is 30-60 minutes.

8. The method for recycling waste lithium iron phosphate cathode sheets according to any one of claims 1-7, characterized in that, The solid-liquid mass-volume ratio of the waste lithium iron phosphate cathode sheet to the alkaline leachate is 5:1~10:1 g / mL; And / or, the concentration of the alkaline leaching agent in the alkaline leachate is 1.0-3.0 mol / L; preferably 1.5-2.5 mol / L; And / or, the concentration of the interfacial protectant in the alkaline leachate is 0.1-0.5 wt%; And / or, the concentration of the complexing stabilizer in the alkaline leachate is 3-8 wt%; And / or, the concentration of lithium source in the repair solution is 0.05-5 mol / L; And / or, the concentration of surfactant in the repair solution is 0.05-0.2 wt%; And / or, the concentration of the chelating agent in the repair solution is 0.01-1 mol / L; And / or, the mass-to-volume ratio of the aluminum-removed material to the repair solution in step (1) is 1:5~1:10 g / mL.

9. A recycled lithium iron phosphate material, characterized in that, Obtained by the recycling method according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, Includes a positive electrode, the material of which includes the recycled lithium iron phosphate material as described in claim 9.

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