Method for recovering lithium iron phosphate in lithium iron phosphate battery

Abstract

The invention discloses a method for recovering lithium iron phosphate in a lithium iron phosphate battery, which comprises the following steps: S1, battery pretreatment: carrying out subzero treatment on a waste lithium iron phosphate battery to inhibit the electrochemical activity of the waste lithium iron phosphate battery, and enabling a diaphragm and a binder in the battery to generate glass transition, the waste lithium iron phosphate battery is in an interface embrittlement state; s2, performing low-temperature crushing: performing mechanical crushing on the waste lithium iron phosphate battery in the interface embrittlement state in a low-temperature state, and screening out a mixed crushed material meeting the particle size requirement; s3, induction thermal shock stripping: carrying out induction heating on the mixed crushed material by utilizing a high-frequency alternating magnetic field, so that the lithium iron phosphate active material and the aluminum current collector in the mixed crushed material are physically stripped due to internal shear stress to form a stripped mixture; and S4, multi-stage sorting: carrying out multi-stage physical sorting on the stripping mixture. According to the method, high-purity, high-efficiency and green recovery of a whole-process dry method and no chemical reagent is realized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery recycling, in particular to a recovery method of lithium iron phosphate in a lithium iron phosphate battery. BACKGROUND

[0002] With the explosive growth of new energy vehicles and energy storage industries, the market share of lithium iron phosphate (LiFePO4, LFP) batteries continues to rise due to their high safety, long cycle life and low cost. As a result, the amount of waste lithium iron phosphate batteries is increasing. Unlike ternary lithium batteries (NCM), lithium iron phosphate batteries do not contain high-value precious metals such as cobalt and nickel, and their main recovery value is concentrated on lithium elements, iron phosphate and aluminum, copper and other metal materials. Due to the relatively low material value, traditional pyrometallurgy (high energy consumption, only metal recovery) or full wet metallurgy (high acid and alkali consumption, high wastewater treatment cost) often cannot maintain economic benefits and can easily cause secondary pollution.

[0003] Therefore, physical recovery (i.e., enrichment of active materials through mechanical crushing and sorting) is the mainstream trend for lithium iron phosphate battery recycling. However, in the practical application of physical recovery, the positive active material (LFP powder) and the aluminum current collector are difficult to separate, resulting in low recovery efficiency.

[0004] Therefore, it is urgent to develop a recovery method specifically for lithium iron phosphate batteries to improve recovery efficiency and economic benefits. SUMMARY

[0005] The main purpose of the present application is to provide a recovery method of lithium iron phosphate in a lithium iron phosphate battery, which aims to improve the recovery efficiency and economic benefits of lithium iron phosphate batteries.

[0006] To achieve the above purpose, the recovery method of lithium iron phosphate in a lithium iron phosphate battery provided by the present application comprises the following steps:

[0007] S1, battery pretreatment: deep cooling treatment is performed on the waste lithium iron phosphate battery to inhibit the electrochemical activity of the waste lithium iron phosphate battery, and glass transition of the separator and the binder inside the battery occurs to make the waste lithium iron phosphate battery in an interfacial embrittlement state;

[0008] S2, low-temperature crushing: the waste lithium iron phosphate battery in the interfacial embrittlement state is mechanically crushed under low-temperature conditions, and mixed crushed materials meeting the particle size requirements are screened out;

[0009] S3, induction heat shock stripping: high-frequency alternating magnetic field is used to induce heating of the mixed crushed materials, so that the lithium iron phosphate active material in the mixed crushed materials and the aluminum current collector are physically stripped due to internal shear stress to form a stripped mixture;

[0010] S4, multi-stage sorting: performing multi-stage physical sorting on the stripping mixture, wherein the multi-stage physical sorting is configured to:

[0011] separating metal current collector fragments based on electrical conductivity difference;

[0012] separating light separators and binder residues based on density difference; and

[0013] separating carbonaceous negative electrode materials based on electrical difference.

[0014] In some embodiments, before the waste lithium iron phosphate battery is subjected to the deep cooling treatment, step S1 further includes:

[0015] discharge treatment: discharging the waste lithium iron phosphate battery until the voltage of the waste lithium iron phosphate battery is reduced below a safety threshold.

[0016] In some embodiments, in step S1, the deep cooling treatment includes:

[0017] transporting the waste lithium iron phosphate battery into a deep cooling environment, and cooling the waste lithium iron phosphate battery to -150°C to -180°C within a time window of 20 minutes to 40 minutes.

[0018] In some embodiments, in step S2, the mixed crushed material meeting the particle size requirement is screened, including:

[0019] controlling the particle size distribution of the mixed crushed material, screening the material with a particle size in the range of 2mm to 4mm as the mixed crushed material, and returning the material with a particle size greater than 4mm for secondary crushing.

[0020] In some embodiments, in step S3, the frequency of the high-frequency alternating magnetic field is 150kHz to 300kHz, the output power density is 100kW / m 2 to 300kW / m 2 , the induction heating time is 1 second to 3 seconds, and the heating temperature target of the aluminum current collector is 400°C to 550°C.

[0021] In some embodiments, in step S4, the conductive metal current collector fragments are separated from the stripping mixture based on the electrical conductivity difference, including:

[0022] adopting eddy current sorting to separate the conductive metal current collector fragments from the stripping mixture, wherein the magnetic field strength of the eddy current sorting is 0.2T to 0.5T, and the sorting speed is 2m / s to 4m / s.

[0023] In some embodiments, in step S4, the light separators and binder residues are separated based on the density difference, including:

[0024] The light separator and the binder residue are separated from the stripping mixture by using air flow separation, wherein the air flow speed of the air flow separation is 5 m / s to 8 m / s, and the classified particle size is set to 15 μm to 25 μm.

[0025] In some embodiments, in step S4, the carbonaceous negative electrode material is separated based on the electrical difference, including:

[0026] The material is finely separated by using electrostatic separation to separate the carbonaceous negative electrode material, wherein the voltage of the electrostatic field of the electrostatic separation is 15 kV to 25 kV.

[0027] In some embodiments, after step S4, the recycling method further includes:

[0028] S5, purification and repair: the obtained high-purity lithium iron phosphate powder is subjected to purification treatment to remove residual organic binder and restore the electrochemical performance of the material.

[0029] In some embodiments, the purification treatment is performed by using low-temperature heat treatment, wherein the temperature of the low-temperature heat treatment is 200 ℃ to 300 ℃, and the treatment time is 1 hour to 2 hours.

[0030] The recycling method of lithium iron phosphate in the lithium iron phosphate battery provided in the application has the following beneficial effects:

[0031] 1. The positive electrode material and the aluminum current collector are efficiently and non-destructively separated

[0032] The application utilizes the essential difference in response to the magnetic field between the aluminum foil (conductor) and the lithium iron phosphate (insulator), utilizes the high-frequency alternating magnetic field, and induces the aluminum foil to instantaneously expand in the time of milliseconds to seconds, while the coating lags in temperature rise. This "thermal expansion mismatch" generates a huge shear stress at the microscopic interface, and the active material layer is forcibly collapsed like "popcorn". Compared with the traditional high-temperature roasting, this method avoids the brittleness and pulverization of the aluminum foil due to long-time heating and oxidation, ensures that the aluminum foil after stripping still maintains a large piece of metal form, and is extremely easy to remove by eddy current separation, thereby solving the problem of aluminum impurity polluting the lithium iron phosphate powder from the source.

[0033] 2. Ensure the safety of breaking

[0034] This application employs a cryogenic pretreatment process at -150℃ to -180℃. At this extremely low temperature, the organic electrolyte inside the battery undergoes a phase change and solidifies, completely blocking the ion transport channels and physically eliminating the risk of short-circuit explosion due to charged breakage. Simultaneously, utilizing the glass transition properties of polymer materials, the originally tough separator and binder (PVDF) become embrittled. This not only prevents separator entanglement and blockage during the breakage process but also makes it easier for each component to achieve monomer dissociation at the moment of breakage, significantly improving subsequent sorting efficiency.

[0035] 3. Multi-stage fine sorting enables high-purity recovery of all components.

[0036] Unlike traditional, rudimentary "one-pot" crushing methods, this application constructs a three-stage series separation system: eddy current separation (for copper and aluminum removal), airflow separation (for membrane removal), and electrostatic separation (for positive and negative electrodes). Specifically targeting lithium iron phosphate powder and graphite anode powder, which have extremely similar physical properties, high-voltage electrostatic separation is achieved by utilizing the difference in their conductivity and surface charge. This effectively solves the problem of mixed positive and negative electrodes in physical recycling methods, resulting in high-purity lithium iron phosphate powder that can be used for regeneration and remediation without complex chemical impurity removal.

[0037] 4. The entire process is a green dry process, offering the dual advantages of environmental protection and low carbon emissions.

[0038] This application does not use acids, alkalis, or expensive and toxic organic solvents (such as NMP) throughout the entire process, avoiding the high-salt wastewater and organic waste liquid treatment pressure generated by wet recycling. At the same time, compared with energy-intensive pyrometallurgical or long-term high-temperature roasting processes, the induction heating of this application only performs instantaneous work on the metal current collector, resulting in extremely high energy utilization efficiency, significantly reducing carbon emissions and operating costs, and meeting the requirements of a green, low-carbon, and circular economy.

[0039] 5. Gentle repair and regeneration, maximizing the preservation of material value.

[0040] In the purification stage, this application employs low-temperature heat treatment or physical extraction at 200℃-300℃ to remove only residual organic binders while strictly avoiding damage to the lithium iron phosphate crystal structure or oxidation of iron. This gentle regeneration strategy preserves the original crystal framework and electrochemical activity of the waste material, providing a high-quality precursor for the subsequent direct preparation of high-performance recycled cathode materials. Attached Figure Description

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some of the embodiments of the present application, and the ordinary skilled in the art can obtain other drawings from the drawings shown without any creative effort.

[0042] Figure 1 The flowchart of the embodiment of the method for recovering lithium iron phosphate in the lithium iron phosphate battery of the present application.

[0043] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the drawings. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the ordinary skilled in the art without any creative effort fall within the protection scope of the present application.

[0045] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly.

[0046] In addition, if the embodiments of the present application involve the description of "first", "second", etc., the description of "first", "second", etc. is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing throughout the text is to include three parallel solutions. Taking "A and / or B" as an example, it includes A solution, or B solution, or A and B solutions. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that the ordinary skilled in the art can realize it. When the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope of the present application.

[0047] The present application provides a method for recovering lithium iron phosphate in a lithium iron phosphate battery.

[0048] In the embodiment of the present application, as shown in FIG. 1, the recovery method of lithium iron phosphate in the lithium iron phosphate battery comprises the following steps:

[0049] S1, battery pretreatment: the waste lithium iron phosphate battery is subjected to cryogenic treatment to inhibit the electrochemical activity of the waste lithium iron phosphate battery and to cause the glass transition of the separator and the binder inside the battery, so that the waste lithium iron phosphate battery is in an interfacial embrittlement state.

[0050] The purpose of this step is to solve the safety hazard of combustion explosion of the waste lithium iron phosphate battery when directly crushed at room temperature, and the process problem that the positive active material and the current collector are difficult to peel off.

[0051] Specifically, the waste lithium iron phosphate battery usually has some residual power. At room temperature, lithium ions in the electrolyte have a high migration rate, and once the positive and negative electrodes are short-circuited due to crushing, a thermal runaway is easily triggered. This step reduces the battery temperature to a very low level (for example, below -150°C) through cryogenic treatment. At this time, the electrolyte solidifies or its viscosity increases sharply, and the ionic conductivity decreases to near zero, thereby freezing the ion transport channel inside the battery. Even if a mechanical short circuit occurs later, the battery will not have a violent exothermic reaction due to the lack of ion conduction, thereby ensuring the intrinsic safety of the operation.

[0052] In addition, the binder (usually PVDF, polyvinylidene fluoride) and the separator (usually PE / PP, polyethylene / polypropylene) in the lithium iron phosphate battery are high molecular organic materials. At room temperature, these materials are in a high-elastic state and have good flexibility and very strong adhesion, which are difficult to remove by mechanical force. This step utilizes the glass transition characteristics of the high molecular material to reduce the battery temperature below its glass transition temperature (Tg). At this low temperature, the movement of the high molecular chain segment is frozen, and the binder and the separator are transformed from a "tough state" to a "glass state", and their physical properties become hard and brittle, and the adhesion strength to the current collector decreases significantly. At the same time, due to the large difference in the coefficient of thermal expansion (CTE) between the aluminum foil current collector (metal) and the lithium iron phosphate coating (ceramic / polymer composite). During the rapid cooling process, the shrinkage rate of the metal aluminum is significantly greater than that of the coating, and this differential thermal shrinkage generates a large shear stress at the interface between the two, which, together with the embrittled binder, causes the active material layer to be in an "unwilling-to-peel-off" interfacial embrittlement state.

[0053] Specifically, the cryogenic treatment in this embodiment is achieved by transporting the waste lithium iron phosphate battery to a cryogenic environment (such as a liquid nitrogen freezing tunnel or a cryogenic tank). In the control of process parameters, the system uniformly reduces the overall temperature of the waste lithium iron phosphate battery to -150°C to -180°C within a time window of 20 minutes to 40 minutes.

[0054] In a specific implementation, the waste and old lithium iron phosphate battery to be processed (which can be pre-discharged or charged) is sent into a deep cooling cabin or a deep cooling tunnel through a conveying mechanism (such as a low-temperature resistant conveying belt or a screw conveyor).

[0055] Then, the waste and old lithium iron phosphate battery is subjected to deep cooling treatment by using liquid nitrogen or liquid nitrogen vapor as a deep cooling medium. Among them, liquid nitrogen has an extremely low boiling point (-196°C) and is chemically inert, which can not only provide the required low-temperature environment, but also replace air by vaporization to create an inert atmosphere.

[0056] Specifically, the temperature of the deep cooling environment is controlled between -150°C and -180°C by injecting liquid nitrogen into the deep cooling cabin or the deep cooling tunnel. At this temperature range, most commercial electrolytes will completely freeze, and the glass transition temperature of PVDF (about -35°C) is much lower, ensuring complete embrittlement.

[0057] At the same time, the residence time (i.e. the processing time window) of the waste and old lithium iron phosphate battery in the deep cooling environment is controlled between 20 minutes and 40 minutes. Among them, the residence time of the waste and old lithium iron phosphate battery is too short, which may cause the battery interior (especially the center of the roll core) not to be completely cooled; while the residence time is too long, which reduces the production efficiency. The preferred processing time is dynamically adjusted according to the size and stacking density of the battery to ensure that the battery as a whole reaches thermal equilibrium.

[0058] Further, in order to prevent the condensation of water in the air from blocking the equipment and to prevent the risk of oxidation during crushing, it is also necessary to maintain the oxygen concentration in the deep cooling environment not higher than 1% (volume percentage), forming a micro-positive pressure nitrogen protection environment. The maintenance of this oxygen concentration can be achieved by continuously injecting liquid nitrogen medium into the deep cooling environment.

[0059] After step S1, the shell metal of the waste and old lithium iron phosphate battery becomes brittle, the electrolyte inside the battery solidifies into a solid, the separator hardens like thin glass, the adhesive layer loses adhesion and produces micro-cracks. At this time, the waste and old lithium iron phosphate battery has been converted into a low-temperature, inert and brittle solid composite material, which can directly enter the next process for crushing.

[0060] In some embodiments, in order to build a double security barrier, step S1 also includes S11, discharging treatment, i.e. discharging treatment is performed on the waste and old lithium iron phosphate battery until the voltage of the waste and old lithium iron phosphate battery is reduced to below the safety threshold before the waste and old lithium iron phosphate battery is subjected to deep cooling treatment.

[0061] Specifically, while the deep cooling treatment in step S1 has been able to suppress battery activity by "freezing" ion transport, in industrial-scale large-scale crushing, in order to prevent the risk of battery temperature rising due to accidental failure of the deep cooling system (such as interruption of the coolant) or local frictional heat generation, step S11 aims to eliminate the "potential energy" stored inside the battery from the source.

[0062] Specific discharge implementations can be flexibly selected according to field conditions:

[0063] Physical soaking discharge: immerse the waste battery in a conductive solution (such as 5%-10% sodium chloride brine). Use the solution as a conductive medium to cause controlled micro-short circuiting of the positive and negative electrodes of the battery, thereby slowly releasing residual electricity.

[0064] Load discharge: connect the battery to an electronic load or high-power resistance box for discharge, which is more suitable for battery packs that are intact and have no damage, and the discharged electrical energy can be recycled.

[0065] Regardless of the method used, the core control indicator for this step is the "safety threshold". In this embodiment, the safety threshold is usually set to below 1.0V, or even close to 0V. When the battery voltage drops below this threshold, it means that the lithium ions inside the battery have almost all been embedded in the negative / positive structure due to lattice collapse or excessive delithiation, and the chemical potential energy is exhausted. At this time, even if the subsequent deep cooling fails, or there are intense metal collision sparks during the crushing process, since the battery body has no energy release capability, it will not cause thermal runaway or explosion accidents. This combination process of "discharging energy first and then deep cooling embrittlement" provides the highest level of safety assurance for the entire recycling production line.

[0066] S2, low-temperature crushing: mechanically crushing the interface-embrittled waste lithium iron phosphate battery in a low-temperature state, and screening out mixed crushed materials that meet the particle size requirements.

[0067] Although the binder and separator inside the waste lithium iron phosphate battery have undergone glass transition in step S1, the battery as a whole still maintains its complete physical structure. In order to expose the internal electrode material and provide a suitable heat carrier for subsequent processing, it is necessary to crush the complete battery monomer into fragments.

[0068] During the process, the interface embrittlement state of the battery must be strictly maintained, i.e. in a low-temperature environment. This is because mechanical crushing is essentially a work-heat process. If it is carried out in a normal temperature environment, or the friction heat generated by crushing is not timely discharged, the local temperature of the battery fragments will quickly rise above the glass transition temperature (Tg), causing the electrolyte to melt and leak, the adhesive to regain its viscosity, and thus causing the "sticky knife" phenomenon, and even causing a fire. Therefore, this step needs to be carried out in a full- range cryogenic environment and an inert atmosphere. Of course, if conditions permit, it can also be carried out only in a cryogenic environment.

[0069] In a specific implementation, the "frozen" battery after step S1 is directly conveyed through an insulated conveying channel to a low-temperature crusher placed in a sealed and insulated cabin. In order to prevent the fresh metal fracture surface generated by crushing from being oxidized, and to maintain a continuous low temperature, liquid nitrogen or low-temperature nitrogen is continuously injected into the cabin to maintain the temperature in the cabin below -100°C (preferably consistent with the environment temperature of the cryogenic environment in step S1), and the oxygen concentration is strictly controlled below 1%, creating a low-temperature inert crushing environment.

[0070] In view of the high hardness of the frozen battery and its significant cold brittleness (the fracture mechanism changes from ductile tearing to brittle fracture), the preferred embodiment of the present application uses a double-shaft shearing crusher, which uses two sets of high-strength alloy cutters rotating relative to each other to apply high-torque shearing force and extrusion force to the embrittled battery. Compared with hammer crushing, shearing crushing can better control the particle size of the output and reduce the generation of dust.

[0071] In order to obtain the best sorting effect, the system strictly controls the particle size of the crushing products in a closed loop. Specifically, the mixed crushing material that meets the particle size requirements is selected, including: controlling the particle size distribution of the mixed crushing material, selecting the material with a particle size in the range of 2mm to 4mm as the mixed crushing material, and returning the material with a particle size greater than 4mm for secondary crushing.

[0072] Specifically, this step strictly controls the particle size distribution of the output through the mesh size of the screen below the crusher, crushing the waste lithium iron phosphate battery into mixed crushing material with a particle size in the range of 2mm to 4mm. This particle size range is based on the consideration of the efficiency of the subsequent step S3 induction heating: if the particle size is greater than 4mm, it usually means that the winding structure inside the battery has not been completely opened, and the positive and negative electrode sheets may still be stacked together (i.e. "single cell disintegration" has not been achieved). This part of the material cannot be directly sorted and must be returned to the crusher through the return belt for crushing again. If the particle size is less than 2mm, the crushing is too fine (e.g. all into powder), and the metal and powder are mixed together, making physical sorting exponentially more difficult.

[0073] Therefore, the most ideal physical sorting particle size is to crush the waste lithium iron phosphate battery into a particle size of 2 mm to 4 mm. At this scale, the metal current collector (aluminum / copper) is usually kept in the form of a small piece with a certain area, and the brittle lithium iron phosphate powder exists in a finer form.

[0074] After the above low-temperature mechanical crushing, the waste lithium iron phosphate battery is converted into a mixed crushing material. It needs to be particularly pointed out that at this time, the mixed crushing material has become a fragment in macroscopic view, but in the microstructure, the aluminum current collector fragment and the positive active material on its surface are still closely adhered together, and the composition separation has not been achieved. This "bone and flesh" but broken and dispersed state is the ideal precursor state for step S3 (thermal shock stripping).

[0075] In addition to the above preferred shearing type crushing method, step S2 of the present application is not limited to a single shearing mechanism. In another parallel embodiment, an impact crushing method (such as a low-temperature hammer crusher or an impact crusher) can also be used to process the battery after deep cryogenic embrittlement.

[0076] This embodiment takes full advantage of the feature that the battery material after deep cryogenic treatment is maximized in cold brittleness. In a deep cooling environment, the binder, the separator and the metal shell that have undergone glass transition are extremely sensitive to impact load. When the hammer head or the plate hammer rotating at high speed in the low-temperature crusher hits the battery, the embrittled battery monomer will instantaneously crack in brittleness, rather than the plastic deformation or extension commonly seen at room temperature. This crushing method can also efficiently crush the battery into the required mixed crushing material by adjusting the speed of the rotor and the aperture of the screen plate below the crushing chamber.

[0077] It is worth noting that whether a biaxial shredder using shearing force or a hammer crusher using impact kinetic energy, the core process control point is to physically disintegrate the battery while maintaining a deep cooling and inert environment.

[0078] S3, inductive thermal shock stripping: using a high-frequency alternating magnetic field to inductively heat the mixed crushing material, so that the lithium iron phosphate active material in the mixed crushing material and the aluminum current collector are physically stripped due to internal shear stress, forming a stripping mixture.

[0079] Then, the mixed crushing material obtained in step S2, which is still in a deep cooling state, is immediately sent to the inductive thermal shock stripping area to perform step S3, thermal shock separation. This step aims to use the difference in the response of different materials to the electromagnetic field to create extreme physical conflicts at the micro interface.

[0080] Specifically, the mixed and crushed materials are fed into an alternating magnetic field region mainly composed of a high-frequency induction coil. In order to ensure that the magnetic field energy only acts on the target materials, the conveying device (such as a conveyor belt or a vibrating trough) is preferably made of a high-temperature-resistant non-metallic material (such as ceramic or special glass fiber). When the mixed and crushed materials pass through this region, the present embodiment utilizes the "selective heating feature" to process the materials.

[0081] Regarding the realization of this feature, it is rooted in the stark difference in electromagnetic physical properties between the aluminum current collector and the positive active material: for aluminum current collector fragments, it is essentially a good metal conductor with extremely low resistivity. When placed in an alternating magnetic field, according to Faraday's law of electromagnetic induction, a closed induction current (eddy current) will be generated inside the aluminum foil. Especially under high-frequency magnetic field, the significant "skin effect" causes the induction current to be highly concentrated in the extremely thin surface layer of the aluminum foil, resulting in a significant increase in its effective resistance. According to Joule's law (Q = I^2R), this high-density surface eddy current will instantly convert into huge heat energy, making it a "active heat source" in the magnetic field. In sharp contrast, the positive active material (such as lithium iron phosphate or ternary material) and the residual organic binder exhibit semiconductor or insulator properties in terms of electrical properties, with extremely high resistivity and extremely low dielectric loss. High-frequency magnetic fields cannot induce effective closed eddy current loops inside them, nor can they generate heat through dielectric polarization. Therefore, in the electromagnetic field, the positive active material behaves as an "electromagnetically transparent" or "inert substance" that does not actively warm up.

[0082] Further, for the copper foil (negative current collector) also present in the mixed material of the waste lithium iron phosphate battery, although it also belongs to a metal conductor, its warming rate significantly lags behind that of the aluminum current collector under the specific process parameters set in the present embodiment, and it does not reach the same high temperature (400℃-550℃) within a time window of 1-3 seconds. This is mainly based on the following physical mechanisms:

[0083] 1. Different Joule heat efficiency caused by different resistivities: according to Joule's law, the heat power generated by the eddy current is proportional to the resistivity of the material (under high frequency dominated by the skin effect, where ρ is the resistivity). The resistivity of aluminum (about ) is significantly higher than that of copper (about ). This means that under the same induction current intensity, the aluminum foil has a higher "internal resistance" and can more efficiently convert electrical energy into heat energy; while the copper foil has too good conductivity (too small resistance), and the Joule heat generated is relatively small.

[0084] 2. Difference in specific heat capacity and density: the density of copper (about ) is much greater than the density of aluminum (about ). Although the specific heat capacity of copper is higher than that of aluminum, the heat required to heat the same area of copper foil is much higher than that of aluminum foil at the same volume (or similar thickness). In other words, copper foil has greater thermal inertia.

[0085] 3. Frequency-coupled targeted matching: The frequency range of 150 kHz to 300 kHz selected by the embodiment is specifically optimized for the thickness (12-15 pm) and resistivity characteristics of aluminum foil. At this frequency, the electromagnetic coupling efficiency of aluminum foil reaches a peak. To achieve the same heating efficiency for copper foil, a higher frequency or a stronger magnetic field strength is usually required. In summary, during the short time pulsed heating process of 1 second to 3 seconds, when the aluminum foil has been "burnt red" to above 400°C, the temperature of the copper foil rises relatively slowly (for example, only to about 100°C). This differential heating rate not only highlights the "selectivity" for aluminum foil, but also avoids excessive oxidation or melting of copper foil, which is beneficial for subsequent recycling of high-purity copper metal in the sorting link.

[0086] Based on the above mechanism, in order to achieve the best peeling effect, the parameters of the high-frequency alternating magnetic field are precisely window-locked. Specifically, the frequency of the alternating magnetic field is set to 150 kHz to 300 kHz, and the output power density is set to 100 kW / m 2 to 300 kW / m 2 . The selection of this frequency range is based on the matching relationship between the thickness of aluminum foil (usually 10-20 pm) and the skin depth, ensuring that the eddy current energy is mainly concentrated in the aluminum foil body, maximizing the heating efficiency; and the high power density is to achieve "second-level" temperature rise.

[0087] Under this parameter, the aluminum current collector fragments will instantaneously and sharply rise from a deep cold state (about -150°C) to 400°C to 550°C in a short time window of 1 second to 3 seconds.

[0088] The heating time window is set to 1 second to 3 seconds because due to the extremely short heating time, heat cannot be transferred to the surface-attached active material through heat conduction, thereby achieving an extreme binary temperature distribution of "aluminum foil sharply heating" and "positive active material maintaining a low temperature (close to deep cold temperature)" on a macroscopic scale.

[0089] The heating target temperature of the aluminum current collector is set to 400°C to 550°C because the lower limit of 400°C is sufficient to cause thermal decomposition or carbonization of the residual PVDF binder, completely losing adhesion. And the upper limit of 550°C is because it is strictly below the melting point of aluminum (about 660°C). This ensures that the aluminum foil does not melt during the peeling process and still maintains a solid sheet structure.

[0090] This rapid heating process creates a severe "transient thermal stress". On the one hand, the aluminum current collector expands significantly in a very short time; on the other hand, the surface of the positive active material remains in a low temperature state for a short time due to its large thermal inertia and is not heated by the magnetic field. At this time, at the interface between the aluminum foil and the active material, the rapid expansion of the aluminum foil and the low temperature shrinkage (or constant volume) of the active material form a large shear stress. At the same time, the high temperature of 400-550°C is also enough to cause thermal decomposition or instantaneous gasification of the residual trace amount of binder. Under the dual action of mechanical shear force and gas expansion force, the originally "bone and flesh" active material is instantly "popped off" the surface of the current collector, realizing the physical separation of the active material and the current collector.

[0091] In some embodiments, step S3 can use a flat conveyor belt combined with a flat coil to heat the mixed and crushed material. Specifically:

[0092] The mixed and crushed material obtained in step S2 is uniformly and single-layered laid on a non-metallic conveying belt with high temperature resistance and magnetic permeability through a vibrating feeding device. The conveying belt is preferably made of polytetrafluoroethylene (PTFE) coated glass fiber cloth or ceramic fiber belt, which can withstand the high temperature generated by the aluminum foil (the instantaneous contact temperature can reach more than 400°C) and will not shield or induct heat itself.

[0093] A flat spiral high-frequency induction coil is arranged closely below (or on both sides) the bearing surface of the conveying belt. The flat coil is made of a hollow copper pipe, and circulating cooling water is introduced into the copper pipe to remove the copper loss heat of the coil itself. When the conveying belt carrying the mixed and crushed material passes through the flat coil at a constant speed, the high-frequency alternating magnetic field generated by the coil penetrates the material layer in a direction perpendicular to the surface of the conveying belt. Since the aluminum current collector fragments are mostly flat, this vertical magnetic field can penetrate the cross section of the aluminum foil to the greatest extent, thereby maximizing the heating efficiency in the aluminum foil plane.

[0094] At the same time, the running speed of the conveying belt is accurately controlled by a variable frequency speed regulation motor, and the residence time of the material in the effective magnetic field area of the flat coil is strictly locked in the time window of 1-3 seconds. During this period, the aluminum current collector fragments are rapidly heated to the target temperature (400-550°C) due to the eddy current effect, while the positive active material maintains a low temperature due to contact with the conveying belt and does not heat itself. This flat conveying structure is particularly suitable for continuous processing of sheet-shaped materials, which can effectively avoid the problem of uneven heating or magnetic field shielding caused by material stacking.

[0095] In other embodiments, to adapt to the processing requirements of different scales or material morphologies, step S3 can also adopt free-fall or rotating drum type induction heating structures. For example, in one parallel embodiment, the mixed and crushed material can be allowed to pass vertically through a spiral induction coil (similar to a material falling pipe) under the action of gravity. This way can make the material uniformly heated in 360 degrees during falling, avoiding the shielding effect caused by the stacking of sheet materials.

[0096] In another parallel embodiment, a rotating drum lined with ceramic can be used as a heating cavity, and the induction coil is wound outside the drum. The material advances by tumbling in the drum, which can not only receive magnetic field heating, but also use the mechanical impact force generated by tumbling to assist the shedding of the powder. Regardless of the mechanical structure of the induction device, the core is to use high-frequency alternating magnetic field to achieve selective and sharp heating of the metal current collector, thereby establishing a transient temperature difference stripping mechanism.

[0097] It is worth noting that in addition to the preferred high-frequency alternating magnetic field induction heating method described above, those skilled in the art can also use microwave irradiation heating or contact electric pulse heating as parallel alternative embodiments according to actual working conditions. These methods are also based on the huge difference in physical properties (dielectric constant or electrical conductivity) between aluminum current collectors and positive active materials to achieve differential thermal shock effects.

[0098] In some embodiments, microwave irradiation heating can use the difference in microwave response mechanisms between aluminum current collector fragments and positive active materials to achieve selective heating. Although bulk metals usually reflect microwaves, at the specific broken particle size (2-4 mm) of the present application, metal fragments will produce significant antenna effect or skin effect, causing microwave energy to concentrate on the metal surface and be converted into heat energy. At the same time, microwaves have strong penetrating ability and can penetrate the outer layer of positive active materials (usually transparent to microwaves or weaker in microwave absorption than metal interfaces), and directly act on the bonding interface of aluminum foil and adhesive.

[0099] Specifically, an industrial microwave source with a frequency of 915 MHz or 2.45 GHz can be selected. Since microwave heating has the characteristics of "bulk heating" and "selective heating", it can preferentially heat the polar solvent molecules remaining at the interface or induce the surface of the metal to heat up, thereby establishing a transient temperature difference between the aluminum foil and the active material and achieving stripping.

[0100] In other embodiments, contact electric pulse heating can use the order of magnitude difference in electrical conductivity between aluminum current collectors (good conductors) and positive active materials (poor conductors / semiconductors).

[0101] Specifically, the mixed broken material can be delivered between a pair of charged conductive rollers or high-voltage electrode plates. When the material passes through the electrode gap, the high-voltage pulse current will preferentially transmit along the path with the smallest resistance, that is, through the aluminum current collector fragments. According to Joule's law, a large amount of Joule heat is generated instantaneously when the current flows through the aluminum foil, causing the aluminum foil to heat up sharply; while the positive active material wrapped outside has a very large resistance, and the current hardly passes through, so it does not generate Joule heat and remains at a low temperature.

[0102] This selective heating based on electrical conductivity is also perfectly consistent with the technical principle of "heating the aluminum current collector while maintaining the low temperature of the positive active material".

[0103] S4, multi-stage sorting: performing multi-stage physical sorting on the stripping mixture, wherein the multi-stage physical sorting is configured to separate the metal current collector fragments based on the difference in electrical conductivity, separate the lightweight separator and binder residues based on the difference in density, and separate the carbonaceous negative electrode material based on the difference in electrical properties.

[0104] After the induction heat shock treatment of step S3, the aluminum current collector fragments and the positive active material in the mixed broken material have been physically separated at the micro-interface (i.e., no longer adhered), but in the macro space, the two and the coexisting copper foil fragments, separator fragments, negative electrode graphite powder, etc. are still mixed together. In order to obtain high-purity recycled products, this step separates them one by one through a multi-stage physical sorting system based on the significant physical form differences of each component in electrical conductivity, density, and charge characteristics.

[0105] First, the metal current collector fragments are separated based on the difference in electrical conductivity for primary separation. Specifically, for the metal current collector (aluminum foil and copper foil) in the mixed material, which has a large particle size and excellent electrical conductivity, the embodiment uses eddy current sorting for primary separation.

[0106] Specifically, the mixed stripping material is delivered to the eddy current sorting machine. The device is internally provided with a high-speed rotating magnetic pole roller, which generates a high-frequency alternating magnetic field. When the conductive aluminum and copper current collector fragments enter the magnetic field area, a strong eddy current is induced inside, and a mirror image magnetic field opposite to the original magnetic field direction is generated, thereby obtaining a forward repulsive force (Lorentz force) to "eject" from the material flow in a parabolic trajectory; while the positive active material, separator and negative electrode powder with poor electrical conductivity are not affected by the repulsive force and naturally fall vertically under the action of gravity.

[0107] To ensure that the light and thin aluminum foil fragments can obtain sufficient bounce kinetic energy, while avoiding fine powder being entrained by the airflow, the magnetic field strength of the eddy current sorting is set to 0.2T to 0.5T, and the sorting speed of the belt is controlled at 2m / s to 4m / s. Through this step, more than 95% of the metal current collector is separated out, and the remaining material is mainly mixed powder rich in positive and negative materials and separators.

[0108] Secondly, based on the density difference, the light separator and the adhesive residue are separated for secondary separation. Specifically, after removing the metal current collector, the remaining mixed powder still contains light separator fragments (plastic) and adhesive residue carbonized / powdered during the thermal shock process. In order to remove these light impurities, the embodiment then uses air flow sorting (such as Z-shaped air separator or centrifugal classifier).

[0109] Specifically, the suspension speed difference of solid particles in the airflow is utilized. The density of positive active material (such as lithium iron phosphate, density about 3.6 g / cm³) and negative graphite (density about 2.2 g / cm³) is significantly higher than that of polymer separator (density <1 g / cm³).

[0110] By adjusting the negative pressure of the induced draft fan, the airflow speed in the sorting area is accurately controlled at 5m / s to 8m / s, and the classification particle size cutting point is set to 15μm to 25μm. Under this flow field, the light separator fragments and fine adhesive dust are taken away by the rising airflow into the dust collector, while the heavier positive and negative mixed powder overcomes the airflow resistance and settles at the bottom discharge port, thereby realizing effective separation of light and heavy components.

[0111] Finally, based on the electrical difference, the carbonaceous negative material is separated for end separation. Specifically, after the first two stages of separation, the obtained sediment is mainly a mixture of positive active material powder and negative carbon powder (i.e. "black powder"). In order to further extract high-purity positive materials, the embodiment utilizes the microscopic differences in conductivity or triboelectricity between the two, and uses high-voltage electrostatic separation for fine separation.

[0112] Specifically, the carbonaceous negative material (graphite) has good electrical conductivity, while the positive material (such as lithium iron phosphate) usually behaves as a semiconductor or a poor conductor. When the mixed powder passes through a high-voltage corona field or an electrostatic plate, the conductive carbon particles can quickly acquire electric charge and discharge quickly after contacting the grounded roller, thereby being thrown off the roller; while the positive powder, due to poor conductivity, charges slowly, and is "attracted" to the surface of the roller by electrostatic force until it is brushed off by the brush.

[0113] In order to effectively distinguish the two kinds of micron-sized powders, the embodiment establishes a high-voltage electrostatic field with a voltage of 15kV to 25kV. Under this electric field strength, the movement trajectories of the carbonaceous negative electrode material and the positive electrode active material are significantly separated, so as to fall into different collection tanks respectively.

[0114] Through the above-mentioned three-stage physical sorting process, the method successfully converts the waste lithium battery into high-purity metal aluminum / copper, a separator recovery material, a negative electrode carbon powder, and a high-purity positive electrode active material powder, and completes the physical recovery of all components.

[0115] In some embodiments, after step S4, the recycling method of the application further comprises: S5, purification and repair, that is, the obtained high-purity lithium iron phosphate powder is subjected to purification treatment to remove residual organic binder and restore the electrochemical performance of the material.

[0116] Specifically, although the macroscopic purity of the positive electrode active material has reached an extremely high level (for example, more than 98%) after the multi-stage physical sorting of step S4, at the microscopic level, there may still be a trace amount of binder (PVDF) that is not completely stripped or a trace amount of organic volatile substances adsorbed in the deep cooling crushing process on the surface of the particles. In addition, after the deep cooling (-196°C) of step S1 and the transient thermal shock (~500°C) of step S3, a certain amount of thermal stress or lattice distortion may accumulate inside the crystal structure of the positive electrode material, which may affect its subsequent cycle stability.

[0117] Therefore, the positive electrode active material powder sorted out in step S4 is sent to a continuous atmosphere rotary kiln or a tunnel furnace for purification treatment to remove the residual organic binder and restore the electrochemical performance of the material.

[0118] In the embodiment, the purification treatment is carried out by low-temperature heat treatment, and the temperature window of the heat treatment is strictly controlled to be 200°C to 300°C, and the heat treatment is continuously carried out for 1 hour to 2 hours.

[0119] In this specific low-temperature heating range, two physical and chemical processes occur: first, deep impurity removal. This temperature is sufficient to cause further thermal degradation, carbonization or volatilization of the residual PVDF binder, while completely removing the water and organic solvent molecules adsorbed on the surface of the material, so as to restore the clean surface of the positive electrode particles and expose the active lithium ion transport sites. Second, lattice relaxation and repair. This temperature corresponds to a "low-temperature annealing" process, which can effectively release the residual stress accumulated in the particles due to the previous drastic temperature change, repair the small lattice damage, and thus restore the original electrochemical activity and structural stability of the material.

[0120] Compared with the traditional pyrometallurgical high-temperature calcination of up to 600-1000°C, the mild treatment of 200-300°C in this step not only achieves the purpose of removing organic residues, but also avoids the oxidation and decomposition of the positive electrode material (especially lithium iron phosphate), and maximizes the retention of the original crystal structure of the material, laying a perfect material foundation for subsequent direct sintering through lithium supplementation for recycling.

[0121] Further, setting the processing time of 1-2 hours is based on the dual considerations of reaction kinetics and energy efficiency balance: if the processing time is less than 1 hour, the organic binder remaining in the pores of the positive electrode particles may not be completely pyrolyzed or volatilized, and the thermal stress accumulated in the lattice during the previous deep cooling and thermal shock process cannot be fully released, resulting in incomplete repair; if the processing time exceeds 2 hours, not only unnecessary energy consumption and time cost are increased, but also the active lithium elements on the surface of the positive electrode material may be lost in trace amounts under long-term heat action, or unnecessary growth of the crystal grains may be caused.

[0122] Therefore, locking the heat treatment in the specific window of 200-300°C for 1-2 hours can achieve the best balance between "deep impurity removal" and "crystal performance recovery", and ultimately obtain a battery-grade positive electrode material with a clean surface and complete crystal structure.

[0123] It should be particularly noted that in addition to the low-temperature heat treatment mentioned in the above embodiments, in actual industrial applications, for different aging degrees of waste batteries and different types of binder residues, step S5 can also use the following alternative or combined schemes to achieve purification and repair.

[0124] In some embodiments that are sensitive to heat or pursue extremely high surface cleanliness, purification and repair can be achieved by non-thermal chemical dissolution.

[0125] Specifically, the sorted lithium iron phosphate powder is immersed in a polar organic solvent (such as NMP or dimethyl sulfoxide DMSO), and high-frequency ultrasonic waves (frequency 20-40 kHz) are applied to achieve purification. This method utilizes the principle of "like dissolves like", and the organic solvent directly penetrates and dissolves the PVDF binder layer on the surface of the particles. The "cavitation effect" produced by ultrasonic waves generates extremely strong impact jets on the surface of the micro-particles, which can forcibly strip stubbornly attached carbon black conductive agent and residual colloids.

[0126] This scheme avoids the risk of metal oxidation caused by heating, and the surface of the treated powder is extremely smooth, which is particularly suitable for high-end recycling scenarios that require PPB-level impurity content.

[0127] In some embodiments, for the waste batteries with a large number of cycles and serious lithium ion loss (i.e., large capacity attenuation), simple removal of the binder is insufficient to restore the performance. In such embodiments, S5 is configured as a reactive repair process. Specifically, before the heat treatment, a small amount of lithium source (such as lithium carbonate Li2CO3) and carbon source (such as glucose or sucrose) is added to the sorted lithium iron phosphate powder in a stoichiometric ratio. Then, a medium-temperature short-time sintering (for example, 600-700°C, 2-3 hours) is performed under an inert atmosphere. This scheme utilizes the exogenous lithium ions to diffuse into the crystal lattice of lithium iron phosphate at high temperature, occupying the "lithium vacancies" formed due to long-term cycling, and repairing the crystal structure defects. At the same time, the added carbon source is cracked to form a uniform conductive carbon layer on the surface of the repaired LFP particles.

[0128] In some embodiments that pursue continuous production and high energy efficiency, the purification and repair can use microwave plasma technology. Specifically, the lithium iron phosphate powder can be sent into a microwave plasma cavity through a fluidized bed, and treated with oxygen or argon plasma for milliseconds. This scheme utilizes the high chemical activity of high-energy electrons and active free radicals in the plasma, which can rapidly break the carbon chain of the organic binder at low temperature (bulk temperature < 150°C) and "cold burn" it into gaseous products. At the same time, the plasma bombardment can clean the inert layer on the surface of the particles and activate the electrochemically active sites on the surface of the material. This scheme has a very fast processing speed (seconds) and only 1 / 5 of the energy consumption of traditional heat treatment, and has no thermal damage to the powder body, and is suitable for large-scale continuous operation.

[0129] In summary of the above embodiments, the recovery method of lithium iron phosphate in the lithium iron phosphate battery provided by the present application has the following beneficial effects:

[0130] 1. Efficient and lossless separation of the positive electrode material and the aluminum current collector is achieved

[0131] The present application utilizes the essential difference in response to the magnetic field between the aluminum foil (conductor) and the lithium iron phosphate (insulator), and utilizes the high-frequency alternating magnetic field to induce instantaneous thermal expansion of the aluminum foil within milliseconds to seconds, while the coating lags behind in heating. This "thermal expansion mismatch" generates a huge shear stress at the micro interface, like "popcorn", which forcibly collapses the active material layer. Compared with traditional high-temperature roasting, this method avoids the brittleness and pulverization of the aluminum foil due to long-term heating and oxidation, ensuring that the aluminum foil after peeling remains in a large sheet metal form, which is easily removed by eddy current sorting, and solves the problem of aluminum impurities polluting the lithium iron phosphate powder from the source.

[0132] 2. Ensure the safety of the crushing

[0133] The application adopts a deep cooling pretreatment process of -150℃ to -180℃. At this extremely low temperature, the organic electrolyte inside the battery undergoes phase change and solidification, and the ion transmission channel is completely blocked, thus physically eliminating the risk of short circuit combustion caused by charged fragmentation. At the same time, the glass transition characteristics of the polymer material are utilized to make the originally tough separator and binder (PVDF) brittle. This not only prevents the separator from winding and blocking during fragmentation, but also makes the components more easily achieve monomer dissociation at the moment of fragmentation, greatly improving the subsequent sorting efficiency.

[0134] 3. Multi-stage fine sorting, realizing high-purity recovery of all components

[0135] Unlike traditional "one-pot end" rough fragmentation, the application constructs a three-stage series sorting system of "vortex sorting (copper and aluminum removal) + air flow sorting (separator removal) + electrostatic sorting (positive and negative electrode separation)". Especially for lithium iron phosphate powder and graphite negative electrode powder with extremely close physical properties, high-voltage electrostatic separation is used to take advantage of the difference in conductivity and surface charge between the two, effectively solving the problem of positive and negative electrode mixing in physical recovery, and finally obtaining lithium iron phosphate powder with high purity, which can be used for regeneration and repair without complex chemical impurity removal.

[0136] 4. Green dry process throughout the process, both environmentally friendly and low carbon

[0137] The application does not use acid, alkali or expensive and toxic organic solvents (such as NMP) throughout the process, avoiding the high-salinity wastewater and organic waste liquid treatment pressure generated by wet recovery. At the same time, compared with the energy-intensive pyrometallurgical or long-time high-temperature roasting process, the inductive heating of the application only performs instantaneous work on the metal current collector, with very high energy utilization efficiency, significantly reducing carbon emissions and operating costs, and meeting the requirements of green and low-carbon circular economy.

[0138] 5. Mild repair and regeneration, maximizing material value

[0139] In the purification link, the application scheme adopts low-temperature heat treatment or physical extraction at 200℃-300℃, aiming to remove only the residual organic binder, while strictly avoiding damage to the crystal structure of lithium iron phosphate or oxidation of iron elements. This mild regeneration strategy preserves the original crystal framework and electrochemical activity of the waste material, providing a high-quality precursor for subsequent direct preparation of high-performance regenerated positive electrode materials.

[0140] The above only describes the preferred embodiments of the application, and does not limit the patent scope of the application. Any equivalent structural transformation made according to the application concept, or direct / indirect application in other related technical fields, is included in the patent protection scope of the application.

Claims

1. A method for recovering lithium iron phosphate from lithium iron phosphate batteries, characterized in that, Includes the following steps: S1. Battery pretreatment: Deep cryogenic treatment is performed on the waste lithium iron phosphate batteries to inhibit the electrochemical activity of the waste lithium iron phosphate batteries and to cause the separator and binder inside the battery to undergo glass transition, so that the waste lithium iron phosphate batteries are in an interfacial embrittlement state. S2. Low-temperature crushing: Mechanically crush waste lithium iron phosphate batteries in a state of interface embrittlement at low temperature, and screen out mixed crushed material that meets the particle size requirements. S3, Induction thermal shock peeling: The mixed crushed material is induction heated by a high-frequency alternating magnetic field, so that the lithium iron phosphate active material and the aluminum current collector in the mixed crushed material are physically peeled off due to internal shear stress, forming a peeling mixture; S4. Multi-stage sorting: The stripped mixture is subjected to multi-stage physical sorting, wherein the multi-stage physical sorting is configured as follows: Metal current collector fragments were separated based on differences in conductivity; Lightweight membrane and binder residue were separated based on density differences; and Carbonaceous anode materials were separated based on differences in electrical properties.

2. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, Before subjecting the spent lithium iron phosphate batteries to cryogenic treatment, step S1 further includes: Discharge treatment: Discharge the waste lithium iron phosphate batteries until the voltage of the waste lithium iron phosphate batteries drops below the safety threshold.

3. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S1, the cryogenic treatment includes: Used lithium iron phosphate batteries are transported to a cryogenic environment and cooled to -150°C to -180°C within a 20- to 40-minute time window.

4. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S2, the mixed crushed material that meets the particle size requirements is screened out, including: Control the particle size distribution of the mixed crushed material, screen out materials with a particle size in the range of 2mm to 4mm as mixed crushed material, and return materials with a particle size greater than 4mm for secondary crushing.

5. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S3, the frequency of the high-frequency alternating magnetic field is 150kHz to 300kHz, and the output power density is 100kW / m². 2 Up to 300kW / m 2 The induction heating time is 1 to 3 seconds, and the target heating temperature for aluminum current collectors is 400°C to 550°C.

6. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S4, conductive metal current collector fragments are separated from the stripping mixture based on differences in conductivity, including: Conductive metal current collector fragments are separated from the stripped mixture using eddy current separation, wherein the magnetic field strength of the eddy current separation is 0.2T to 0.5T and the separation speed is 2m / s to 4m / s.

7. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S4, the lightweight membrane and binder residue are separated based on density differences, including: The lightweight diaphragm and binder residue are separated from the stripping mixture by airflow separation, wherein the airflow velocity of the airflow separation is 5 m / s to 8 m / s, and the classification particle size is set to 15 μm to 25 μm.

8. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 1, characterized in that, In step S4, carbonaceous anode materials are separated based on electrical differences, including: The material is finely sorted by electrostatic separation to separate the carbonaceous anode material, wherein the voltage of the electrostatic field for electrostatic separation is 15kV to 25kV.

9. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in any one of claims 1 to 8, characterized in that, After step S4, the recycling method further includes: S5. Purification and Repair: The obtained high-purity lithium iron phosphate powder is purified to remove residual organic binders and restore the electrochemical properties of the material.

10. The method for recovering lithium iron phosphate from a lithium iron phosphate battery as described in claim 9, characterized in that, The purification process is carried out using low-temperature heat treatment, wherein the temperature of the low-temperature heat treatment is 200°C to 300°C, and the treatment time is 1 hour to 2 hours.

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