Method and system for low-temperature liquid-phase quaternary synergistic lithium supplementing and coating regeneration of waste lithium iron phosphate

Abstract

The application discloses a kind of waste lithium iron phosphate low-temperature liquid phase four-element synergic lithium supplement coating regeneration method and system, method includes to waste lithium phosphate raw material multistage impurity preparation high-purity powder to be regenerated;Preparation four-element composite repair liquid with lithium supplement, reduction, complex dispersion, carbon-coated precursor function;Low-temperature liquid phase is completed lithium vacancy filling, trivalent iron reduction, carbon precursor surface load simultaneously;After solid-liquid separation, cleaning and drying obtain solid phase intermediate;Protective atmosphere low-temperature calcination realizes lithium lattice diffusion and carbon layer in-situ coating;Finally, shaping grading is prepared finished product positive electrode material.The application replaces traditional high-temperature process with low-temperature liquid phase, energy consumption is lower, repair liquid can be recycled, raw material impurity is removed thoroughly, powder carbon coating is uniform, and particle size consistency is good, effectively improve the electrochemical performance of regenerated material, reduce production comprehensive cost.

Description

Technical Field

[0001] This invention belongs to the field of recycling technology of waste lithium battery cathode materials, specifically relating to a method and system for low-temperature liquid-phase quaternary synergistic lithium replenishment coating regeneration of waste lithium iron phosphate. Background Technology

[0002] With the large-scale retirement of lithium iron phosphate (LFP) batteries, the efficient resource-based regeneration of spent LFP cathode materials has become a core research direction in the lithium battery recycling field. Current LFP recycling processes mostly employ high-temperature recalcination combined with single-component lithium supplementation modification, resulting in high overall energy consumption, harsh operating conditions, and widespread problems such as insufficient lithium vacancy repair and incomplete reduction of ferric iron. Traditional repair systems rely solely on single-component additives to regulate the reaction, lacking a multi-functional component synergistic adaptation mechanism, leading to poor powder dispersion and easily causing defects such as uneven carbon coating and particle agglomeration. Simultaneously, existing processes have limited raw material purification and impurity removal capabilities, failing to completely remove metallic impurities such as aluminum and copper, and the repair mother liquor is often directly discarded, resulting in low resource utilization and high production costs. Furthermore, existing technologies lack precise liquid-phase reaction atmosphere control, constant temperature control, uniform calcination atmosphere, and precise powder classification systems, leading to poor particle size uniformity and insufficient electrochemical performance stability in recycled LFP materials, making it difficult to meet the standards for mass production applications of power batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a low-temperature liquid-phase quaternary synergistic lithium replenishment coating regeneration method and system for waste lithium iron phosphate, in order to solve the technical defects of existing regeneration processes, such as high high-temperature energy consumption, insufficient repair of lithium vacancies and trivalent iron, poor dispersion and coating effect of single-component repair liquid, incomplete removal of metal impurities from raw materials, inability to recycle repair mother liquor, lack of precise liquid-phase temperature control, reaction atmosphere regulation, uniform calcination atmosphere and powder classification matching system, uneven particle size of regenerated materials and insufficient electrochemical performance stability.

[0004] To achieve the above objectives, this application provides the following technical solution: The first aspect of this application provides a method for the low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating regeneration of waste lithium iron phosphate, comprising: The waste lithium iron phosphate raw material is purified and impurities are removed to obtain lithium iron phosphate powder to be regenerated; A quaternary composite repair solution containing four types of components—lithium replenishment, reduction, complexation dispersion, and carbon coating precursor—was prepared as a powder repair medium. The lithium iron phosphate powder to be regenerated and the quaternary composite repair liquid are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, and lithium vacancy filling, trivalent iron reduction and carbon precursor particle surface loading are achieved simultaneously. The mixture was subjected to solid-liquid separation, and after washing, dehydration and drying, a solid-phase repair intermediate was obtained. The solid-phase repair intermediate is fed into a heat treatment device and calcined at low temperature under a protective atmosphere to allow lithium lattice diffusion and in-situ carbonization of carbon precursors to generate a conductive coating layer. The material obtained after calcination and cooling is processed using a powder shaping and grading equipment to obtain the finished recycled lithium iron phosphate cathode material.

[0005] Further, the lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: The coaxial double-layer stirring paddle and the built-in ultrasonic dispersion component are activated synchronously in a sealed stirred reactor. By combining mechanical disturbance with ultrasonic cavitation through a double-layer stirring paddle, the lithium iron phosphate powder to be regenerated is dispersed and the quaternary composite repair liquid is evenly dispersed, so as to achieve full contact reaction of the materials and obtain a reaction mixture with uniform composition.

[0006] Further, the lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: An online ORP potential sensor and a pH control component, which are linked to the agitator, are installed inside a sealed stirred reactor. The online ORP potential sensor is used to collect the liquid phase redox potential in real time, and the pH of the system is dynamically adjusted simultaneously through the pH control component to stabilize the liquid phase reduction reaction environment and ensure that ferric iron is fully reduced during the reaction.

[0007] Further, the mixture is subjected to solid-liquid separation, and after washing, dehydration and drying, a solid-phase repair intermediate is obtained, specifically including: A mother liquor recycling system is set up to support the solid-liquid separation equipment. The input end of the mother liquor recycling system is connected to the liquid phase outlet of the solid-liquid separation equipment, and the output end of the mother liquor recycling system is connected to the feed inlet of the closed stirred reactor. The liquid mother liquor separated by the solid-liquid separation equipment flows into the mother liquor recycling system and is then returned to the reactor to participate in the low-temperature liquid-phase stirring reaction, so as to realize the recycling of the quaternary composite repair solution.

[0008] Further, the solid-phase repair intermediate is fed into a heat treatment apparatus and calcined at low temperature under a protective atmosphere to allow lithium lattice diffusion and in-situ carbonization of carbon precursors to generate a conductive coating layer, specifically including: A tubular atmosphere furnace is used as a heat treatment device. Independent temperature control modules and uniform atmosphere distribution pipes are arranged in sections along the axial direction of the tubular atmosphere furnace body, and the uniform atmosphere distribution pipes are arranged around the outer periphery of the powder boat. Precise temperature control is achieved through segmented independent temperature control modules, and a protective atmosphere is uniformly delivered through gas distribution pipes surrounding the material boat, ensuring that the carbon precursor is uniformly carbonized during calcination and forms a complete conductive coating layer on the powder surface.

[0009] Furthermore, the purification and impurity removal of waste lithium iron phosphate raw materials to obtain lithium iron phosphate powder to be regenerated specifically includes: A screening machine, a magnetic separator, and a washing tank are sequentially connected in series. The discharge port of the screening machine is connected to the inlet of the magnetic separator, and the discharge port of the magnetic separator is connected to the inlet of the washing tank, forming a step-by-step purification and impurity removal pathway. The raw material undergoes initial screening and impurity removal using a screening machine, followed by removal of magnetic metal impurities using a magnetic separator. Then, it undergoes deep cleaning in a water washing tank to gradually remove metal impurities such as aluminum and copper from the raw material, thereby obtaining high-purity lithium iron phosphate powder ready for regeneration.

[0010] Furthermore, the material obtained after calcination and cooling is processed using powder shaping and grading equipment to obtain the finished recycled lithium iron phosphate cathode material, specifically including: A powder shaping and grading equipment is set up with a low-speed grinder and an air classifier. The discharge port of the low-speed grinder is sealed and connected to the feed end of the air classifier to form a continuous shaping and grading path. The cooled calcined product is shaped and deagglomerated by a low-speed grinding mill, and then precisely screened and sorted by an air classifier to control the D50 particle size range of the regenerated powder, so as to obtain a finished regenerated lithium iron phosphate cathode material with uniform particle size.

[0011] Further, the lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: A dopant feeding branch is set on a closed stirred reactor, and the dopant feeding branch is connected to the repair liquid inlet pipeline. Nitrogen / phosphorus heteroatom dopant components are simultaneously delivered into the repair solution feed pipeline through the dopant feeding branch, so that the dopant components and the quaternary composite repair solution are uniformly mixed and participate in the low-temperature liquid phase stirring reaction, thereby realizing the simultaneous repair of powder and heteroatom modification and doping.

[0012] Further, the lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: A jacketed constant temperature heat exchange component is wrapped around the outer wall of a sealed stirred reactor, and the jacketed constant temperature heat exchange component is linked with the temperature sensor inside the reactor to form a closed-loop linkage control. The reaction temperature inside the reactor is collected in real time by a temperature sensor, and the temperature is dynamically controlled by a closed-loop jacketed constant temperature heat exchange component to stably maintain a low temperature liquid phase reaction range of 40~180℃, ensuring that the liquid phase repair reaction proceeds smoothly and controllably.

[0013] In a second aspect, this application provides a waste lithium iron phosphate low-temperature liquid phase quaternary synergistic lithium replenishment coating and regeneration system, comprising: a raw material purification and impurity removal unit, a repair solution preparation unit, a low-temperature liquid phase reaction unit, a solid-liquid separation and drying unit, a low-temperature calcination heat treatment unit, and a powder shaping and grading unit. The raw material purification and impurity removal unit is equipped with a sieve, a magnetic separator and a water washing tank connected in series. Through a continuous impurity removal process of sieve, magnetic separation and water washing, aluminum and copper metal impurities in the raw material are removed to prepare high-purity lithium iron phosphate powder to be regenerated. The repair solution preparation unit is used to prepare a quaternary composite repair solution containing four functional components: lithium replenishment, reduction, complexation dispersion, and carbon coating precursor. The discharge end is connected to the feed end of the low-temperature liquid phase reaction unit to provide a special medium for the low-temperature repair reaction of powder. The cryogenic liquid phase reaction unit adopts a closed stirred reactor. The closed stirred reactor has a built-in coaxial double-layer stirring paddle and a built-in ultrasonic dispersion component. It is equipped with an online ORP potential sensor and a pH control component that are linked with the stirring paddle. The outer wall is covered with a jacketed constant temperature heat exchange component that is linked in a closed loop with the temperature sensor inside the reactor. The reactor body is also equipped with a dopant feeding branch that is connected to the repair liquid feed pipeline. It is used to complete the integrated cryogenic liquid phase repair reaction of uniform material dispersion, precise control of reaction atmosphere, and synchronous doping of heteroatoms. The solid-liquid separation and drying unit is equipped with a mother liquor recycling system. The input end of the mother liquor recycling system is connected to the liquid phase outlet of the solid-liquid separation equipment, and the output end is connected to the feed inlet of the sealed stirred reactor. While completing the solid-liquid separation, cleaning, dehydration and drying of the mixed material and producing solid phase repair intermediate, the system realizes the closed-loop recycling and reuse of the quaternary composite repair liquid. The low-temperature calcination heat treatment unit is a tubular atmosphere furnace. The tubular atmosphere furnace is equipped with independent temperature control modules in sections along the furnace body axis. At the same time, it is equipped with a uniform gas distribution pipeline around the outer periphery of the powder boat. Through precise segmented temperature control and uniform protective atmosphere supply, the lattice diffusion of lithium element in solid phase repair intermediate and the in-situ uniform carbonization and coating of carbon precursor are realized. The powder shaping and grading unit consists of a sealed, connected low-speed grinding mill and an air classifier. Through continuous shaping, deagglomeration, and precise particle size classification processes, the particle size of the calcined and cooled material is controlled to produce a finished recycled lithium iron phosphate cathode material with uniform particle size.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The low-temperature liquid-phase quaternary composite repair system simultaneously achieves lithium replenishment, reduction, dispersion, and carbon loading, replacing the traditional high-temperature regeneration process. This effectively reduces overall energy consumption. The entire process integrates raw material impurity removal, mother liquor circulation, low-temperature calcination, and powder classification. It can simultaneously repair lithium vacancies, fully reduce ferric iron, ensure uniform carbon coating of powder, and thoroughly remove impurities. The repair solution can be recycled and reused, and the regenerated products have high particle size consistency, effectively improving the electrochemical stability of materials and reducing overall production costs.

[0015] 2. The double-layer stirring paddle and ultrasonic component operate coaxially and synchronously. Relying on the mechanical shearing combined with the ultrasonic cavitation effect, the agglomerated powder is quickly dispersed, which promotes the full contact between the powder to be regenerated and the quaternary repair liquid. This improves the efficiency of the synchronous reaction of lithium vacancy filling and trivalent iron reduction, prevents local accumulation of carbon precursors, ensures uniform material composition in the reactor, provides a uniform precursor for subsequent calcination and coating, and improves the problem of uneven carbon coating thickness in the finished product.

[0016] 3. The ORP potential sensor, pH control component and agitator work together to monitor and dynamically adjust the liquid phase reaction environment in real time, stabilize the reduction atmosphere of the system, ensure that the ferric iron reduction reaction is fully carried out, and avoid capacity decay caused by incomplete reduction; no need to stop the machine for sampling and testing throughout the process, simplifying the operation process, ensuring the synchronous stability of lithium repair and iron reduction, and improving the performance consistency of different batches of recycled materials.

[0017] 4. The system is equipped with a mother liquor recycling system, which returns the liquid mother liquor generated during solid-liquid separation to the reactor for repeated reaction, significantly reducing the amount of reagents added and lowering the cost of waste liquid disposal and resource consumption; the closed-loop pipeline reduces reagent discharge, making it green and environmentally friendly, while stabilizing the concentration of the four functional components in the reactor, ensuring that the liquid phase remediation reaction effect of each batch is uniform and controllable.

[0018] 5. The tubular atmosphere furnace, equipped with segmented independent temperature control modules and gas distribution pipes arranged around the material boat, ensures uniform distribution of furnace temperature and protective atmosphere. The solid-phase repair intermediate is heated without local temperature differences, lithium elements diffuse fully in the crystal lattice, carbon precursors are carbonized synchronously and uniformly, and a complete and continuous conductive coating layer is generated on the powder surface, improving the conductivity of recycled materials and the battery cycle life.

[0019] 6. A screening machine, magnetic separator, and washing tank are connected in series to form a continuous impurity removal channel, which removes coarse particles, magnetic metals, and soluble aluminum and copper impurities in stages. Multi-stage purification improves the purity of the powder to be regenerated; avoids interference of trace metal impurities with the liquid phase repair and high-temperature carbonization process, reduces battery self-discharge, and ensures the electrochemical stability of the regenerated cathode material from the raw material end.

[0020] 7. The low-speed grinding mill and the air classifier are sealed and connected to form a continuous processing path. First, the calcined agglomerated powder is deagglomerated and shaped, and then the powder D50 range is precisely sorted and controlled to reduce the particle size distribution range and ensure that the compaction density of the regenerated powder is uniform. When applied to batteries, it can effectively improve the material's rate discharge capability and long-cycle stability.

[0021] 8. An independent dopant feeding branch is added to the reactor body and merges with the repair solution feed pipeline, which can simultaneously add nitrogen / phosphorus heteroatom components to the reaction system. Powder repair and element modification are completed simultaneously, eliminating the need for a separate modification process. Uniform doping can optimize the electronic conduction channels of the material and further improve the discharge capacity and cycle durability of regenerated lithium iron phosphate.

[0022] 9. The heat exchange components of the outer wall jacket of the reactor and the built-in temperature sensor form a closed-loop linkage control, which dynamically adjusts the temperature inside the reactor in real time and stably maintains the low temperature reaction range of 40~180℃, avoiding temperature fluctuations that could disrupt and restore the reaction equilibrium; the low temperature operation throughout the process reduces heating energy consumption, while inhibiting abnormal grain growth and perfectly preserving the excellent microcrystalline structure of the material. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This invention provides a schematic flowchart of a method for the low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating and regeneration of waste lithium iron phosphate. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0028] To address the technical deficiencies mentioned in the background section, this embodiment provides a method and system for the low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating regeneration of waste lithium iron phosphate.

[0029] The present invention will now be described in further detail with reference to the accompanying drawings: like Figure 1 As shown, in a first aspect of the present invention, a method for low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating regeneration of waste lithium iron phosphate is provided, comprising: S101. Purify and remove impurities from waste lithium iron phosphate raw materials to obtain lithium iron phosphate powder to be regenerated. For example, the equipment is arranged in series with a screening machine, a magnetic separator, and a washing tank. The pipeline and material conveying channel connect the discharge port of the screening machine to the inlet of the magnetic separator, and the discharge port of the magnetic separator is connected to the inlet of the washing tank, forming an uninterrupted, step-by-step purification and impurity removal pathway.

[0030] In actual production, waste lithium iron phosphate powder, after being discharged, disassembled, and crushed from lithium batteries, is continuously fed into the screening machine. The screening machine performs preliminary screening and impurity removal through a fixed-mesh screen, trapping large pieces of separator, aluminum foil fragments, and other coarse particles. The fine powder passing through the screen is automatically conveyed to the inlet of the downstream magnetic separator by a screw feeding mechanism. The magnetic separator has a built-in permanent magnet roller. When the powder passes over the surface of the magnetic roller, ferrous magnetic metal impurities in the raw material are adsorbed and trapped, while non-magnetic lithium iron phosphate powder slides down to the inlet of the washing tank by its own weight. The washing tank has a built-in circulating spray pipeline and a bottom stirring mechanism, continuously introducing deionized water to deeply clean the powder, dissolving soluble aluminum and copper metal ion impurities attached to the powder surface. After cleaning, the powder is pre-dehydrated by pressure filtration to obtain high-purity lithium iron phosphate powder to be recycled. The content of aluminum and copper metal impurities inside the powder is greatly reduced, avoiding impurities from interfering with lattice repair and carbon coating formation in subsequent liquid phase repair and calcination modification processes, thus ensuring the electrochemical stability of the final recycled material from the raw material end. The powder produced in this step is directly stored in a sealed silo and then transferred to the subsequent repair liquid reaction process via a sealed screw conveyor. The entire process is airtight to prevent secondary oxidation of the powder surface and the generation of additional ferric impurities.

[0031] S102. Prepare a quaternary composite repair solution containing four types of components: lithium replenishment, reduction, complexation dispersion, and carbon coating precursor, as a powder repair medium. For example, the liquid preparation unit is equipped with an independent reagent dosing chamber, a stirring and mixing tank, an online concentration detection probe, and a discharge pipeline. The tank's discharge pipeline is directly connected to the inlet of the downstream closed stirred reactor. The preparation operation consists of four types of components added and mixed sequentially: the first type is a lithium replenishment component, used to replenish the missing lithium elements in the lattice of waste lithium iron phosphate, realizing lithium vacancy filling; the second type is a reduction component, used to reduce the trivalent iron in the raw material to divalent iron, restoring the intrinsic crystal structure of lithium iron phosphate; the third type is a complexing and dispersing component, which coats the surface of the powder particles to prevent the powder from agglomerating in the liquid phase system and improves the uniformity of solid-liquid contact; the fourth type is a carbon coating precursor component, which is uniformly adsorbed on the surface of the lithium iron phosphate particles, providing raw materials for the subsequent low-temperature calcination and in-situ carbonization to generate a conductive coating layer. After the four components are added to the mixing tank, the stirring mechanism inside the tank is turned on to continuously stir until all the agents are completely dissolved, forming a uniform and stable quaternary composite repair solution. The online concentration probe monitors the concentration of the four components in real time. If the concentration does not meet the standard, the corresponding agent is automatically added. After the solution is prepared, it is continuously transported to a closed stirred reactor through the delivery pipeline for later use as a special medium for liquid phase synchronous repair.

[0032] S103. The lithium iron phosphate powder to be regenerated and the quaternary composite repair liquid are placed into a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, and lithium vacancy filling, trivalent iron reduction and carbon precursor particle surface loading are achieved simultaneously. For example, firstly, an in-vessel dispersion operation is performed: a coaxial double-layer stirring paddle and a built-in ultrasonic dispersion component are installed inside a sealed stirred reactor. After the equipment is started, the double-layer stirring paddle and the ultrasonic dispersion component work synchronously and continuously. The rotation of the double-layer stirring paddle generates multi-layer mechanical shear disturbance, which, together with the work of the ultrasonic dispersion component, generates a high-frequency ultrasonic cavitation effect. The dual action simultaneously disperses the agglomerated lithium iron phosphate powder to be regenerated in the reactor. The powder particles are completely dispersed and suspended inside the quaternary composite repair liquid, and the solid and liquid phases are in full contact, which improves the lithium replenishment and reduction reaction rate, prevents the local accumulation of carbon coating precursor components, and ensures that the material composition in the entire tank is uniform and consistent, avoiding the defect of uneven thickness of the finished carbon coating layer.

[0033] Second, closed-loop constant temperature control is implemented: the outer wall of the sealed stirred reactor is completely covered with a jacketed constant temperature heat exchange component. The heat exchange component pipeline is connected to an external heat exchanger unit. A temperature sensor is fixedly installed inside the reactor cavity. The signal output terminal of the temperature sensor forms a closed-loop linkage control with the electrical control module of the jacketed heat exchanger unit. The temperature sensor continuously collects the liquid phase reaction temperature inside the reactor in real time, and the data is transmitted to the control system in real time. When the temperature deviates from the preset low temperature reaction range of 40~180℃, the control system automatically adjusts the flow rate and temperature of the heat exchange medium inside the jacket, dynamically adjusts the overall temperature inside the reactor, and maintains a stable low temperature reaction condition throughout the process, avoiding drastic temperature fluctuations that could disrupt the liquid phase reduction and lithium lattice filling reaction equilibrium. At the same time, the entire process operates at a low temperature without the need for high-temperature heating, which significantly reduces production energy consumption, inhibits abnormal growth of lithium iron phosphate grains, and preserves the microscopic crystal structure of the powder.

[0034] Third, a closed-loop control operation for oxidation-reduction and pH is implemented: An online ORP potential sensor and a pH control component are installed inside the sealed stirred reactor chamber, synchronously linked with the double-layer stirring paddle. The sensor probe is immersed in the liquid material along with the stirring paddle, collecting the oxidation-reduction potential and pH values ​​of the liquid system in real time. The control system dynamically drives the pH control component to add acid-base regulators based on the real-time monitoring data, continuously stabilizing the liquid phase reduction reaction environment, ensuring that ferric iron in the reactor is fully reduced to ferrous iron, and avoiding the problem of capacity decay of regenerated batteries due to incomplete reduction. The entire control process is completed online in real time, without the need for shutdown for sampling and testing, simplifying the process operation, ensuring uniform lithium vacancy filling and ferric iron reduction reaction degree in different batches of materials, and improving the consistency of product batch performance.

[0035] Fourth, perform simultaneous heteroatom doping: An independent dopant feeding branch is opened on the side wall of the sealed stirred reactor, and the end pipe of the feeding branch is connected to the front-end repair liquid inlet pipe; during the liquid phase reaction, nitrogen / phosphorus heteroatom dopant components are simultaneously delivered into the pipeline through the independent feeding branch. The dopant components enter the liquid phase system in the reactor along with the quaternary composite repair liquid, and are uniformly dispersed and adsorbed on the surface of lithium iron phosphate powder particles. The four processes of powder lattice repair, trivalent iron reduction, carbon precursor loading, and heteroatom doping are completed simultaneously in a single reactor low-temperature liquid phase reaction, eliminating the need for separate modification reaction processes and shortening the overall process flow; uniform doping of nitrogen and phosphorus heteroatoms optimizes the electron conduction channel of lithium iron phosphate, further improving the discharge capacity and long-cycle durability of the final product. After the low-temperature liquid phase synchronous reaction in the reactor reaches the preset reaction time, a solid-liquid mixture reaction mixture is formed in the reactor. The lithium vacancy filling, trivalent iron reduction, and carbon precursor particle surface loading are completed simultaneously inside the material, thus completing all the process objectives of this step. The bottom discharge valve of the reactor is opened to transport the mixture to the downstream solid-liquid separation and drying unit.

[0036] S104. The mixture is subjected to solid-liquid separation, and after washing, dehydration and drying, a solid phase repair intermediate is obtained. For example, the feed end of the solid-liquid separation equipment receives the reaction mixture output from S103, and the solid and liquid phases are separated inside the equipment by pressure filtration. After separation, the solid material is retained on the surface of the filter plate, and the liquid mother liquor continuously flows out from the liquid phase outlet of the equipment. The input pipeline of the mother liquor recycling system is sealed and connected to the liquid phase outlet of the solid-liquid separation equipment, and the output pipeline of the recycling system is connected to the feed inlet of the closed stirred reactor. All the liquid mother liquor generated by the separation automatically flows into the mother liquor recycling system. After the system simply filters out trace suspended fine powders in the mother liquor, it is continuously returned to the front-end closed stirred reactor by a transfer pump to participate in the next batch of low-temperature liquid phase stirring reaction, realizing the closed-loop recycling and reuse of the quaternary composite repair solution. After being removed from the separation equipment, the solid filter cake is sent to a continuous water washing tank. Deionized water is used to wash away any free repair agents adhering to the powder surface. After washing, the powder is dehydrated again and sent to a low-temperature vacuum drying device to remove residual moisture inside the powder, ultimately yielding a solid-phase repair intermediate. The lithium iron phosphate lattice defects inside the intermediate have been repaired, the trivalent iron has been completely reduced, and the particle surface is uniformly loaded with carbon precursors and nitrogen and phosphorus heteroatoms, providing qualified precursor powder for the subsequent low-temperature calcination conductive coating process. The mother liquor circulation system significantly reduces the amount of fresh repair agent added, lowers waste liquid disposal costs, and eliminates the discharge of large amounts of waste liquid, making the production process green and environmentally friendly. At the same time, the refluxed mother liquor stabilizes the basic concentration of the four types of repair components in the reactor, ensuring that the liquid-phase repair reaction effect of each batch is uniform and controllable.

[0037] S105. The solid-phase repair intermediate is fed into a heat treatment device and calcined at low temperature under a protective atmosphere to allow lithium lattice diffusion and in-situ carbonization of carbon precursors to generate a conductive coating layer. For example, a tubular atmosphere furnace is selected, with segmented independent temperature control modules and uniform atmosphere distribution pipes surrounding the powder boat to fully implement the calcination modification operation. The S104-produced solid-phase repair intermediate is evenly spread and placed inside the powder boat, and the boat is smoothly fed into the furnace chamber of the tubular atmosphere furnace. The tubular atmosphere furnace is arranged in segments along the furnace body axis with multiple sets of independent temperature control modules. Each segment of the temperature control module can be set with the calcination temperature independently. Multiple uniform atmosphere distribution pipes are arranged inside the furnace chamber, and all distribution pipes are arranged around the outer perimeter of the powder boat. After the calcination operation is started, the segmented independent temperature control modules accurately control the temperature of each area of ​​the furnace chamber, eliminating local temperature differences at the front and back and top and bottom of the furnace chamber. At the same time, the distribution pipes surrounding the powder boat continuously and evenly deliver inert protective atmosphere, and the atmosphere inside the furnace chamber is evenly distributed without dead corners. Under low-temperature calcination conditions, lithium elements in the solid-phase repair intermediate undergo full lattice diffusion, further improving the lithium iron phosphate crystal structure. The carbon-coated precursor preloaded on the powder surface is simultaneously carbonized in situ in a uniform protective atmosphere, generating a complete, continuous, and uniformly thick conductive carbon coating layer on the surface of each lithium iron phosphate powder particle. The coating layer significantly improves the electronic conductivity of the recycled material and extends the battery cycle life. After calcination, the heating is stopped, and a low-temperature protective atmosphere is introduced to uniformly cool the powder in the boat. After cooling, the calcined material is taken out and transferred to the downstream powder shaping and grading process.

[0038] S106. The material obtained after calcination and cooling is processed using a powder shaping and grading equipment to obtain the finished recycled lithium iron phosphate cathode material.

[0039] For example, the feed end of the low-speed grinder receives the calcined material cooled by S105, and the discharge port of the low-speed grinder is sealed and connected to the feed end of the air classifier. The material is continuously conveyed through a closed pipeline, with no powder dust leakage. The calcined powder has slight agglomeration. The material first enters the low-speed grinder to complete powder shaping and deagglomeration, gently grinding and breaking up the agglomerated particles without damaging the original crystal structure of lithium iron phosphate. The deagglomerated powder is automatically conveyed into the air classifier. The air classifier uses wind power to precisely control the D50 particle size range of the regenerated powder, screening out excessively large and excessively fine discrete particles, reducing the particle size distribution width of the finished powder, and ensuring uniform compaction density of the regenerated powder. After continuous shaping and precise classification, the final product is a finished regenerated lithium iron phosphate cathode material with uniform particle size, complete crystal lattice, uniform carbon coating, low impurity content, and sufficient heteroatom modification. It can be directly used for the preparation of positive electrode sheets for power batteries. The material's rate discharge performance and long-cycle stability are far superior to unclassified traditional regenerated lithium iron phosphate products.

[0040] In a second aspect, this invention provides a low-temperature liquid-phase quaternary synergistic lithium replenishment and regeneration system for waste lithium iron phosphate, comprising: a raw material purification and impurity removal unit, a repair solution preparation unit, a low-temperature liquid-phase reaction unit, a solid-liquid separation and drying unit, a low-temperature calcination heat treatment unit, and a powder shaping and grading unit; the raw material purification and impurity removal unit consists of a screening machine, a magnetic separator, and a water washing tank connected in series, with the equipment connected through a sealed powder conveying channel, the discharge port of the screening machine and the inlet of the magnetic separator being sealed and connected, and the discharge port pipeline of the magnetic separator being connected to the inlet of the water washing tank, thus forming a continuous step-by-step purification and impurity removal pathway for the entire set of equipment.

[0041] The equipment operates as follows: crushed waste lithium iron phosphate raw materials are first fed into a screening machine, which retains coarse particles; the undersized fine powder is automatically conveyed to a magnetic separator to remove magnetic metal impurities; the non-magnetic powder enters a washing tank for deep cleaning of soluble aluminum and copper impurities, and after washing, a pre-dehydration mechanism is provided to directly output high-purity lithium iron phosphate powder to be regenerated; a sealed storage silo is set at the unit discharge end, and the screw feeder at the bottom of the storage silo is connected to the discharge pipeline of the downstream repair liquid preparation unit. The purified powder is quantitatively conveyed to a low-temperature liquid phase reactor, and multi-stage impurity removal reduces the impurity content of the powder from the source.

[0042] The repair solution preparation unit is located at the front end of the entire system. The main body of the unit is a vertical stirred preparation tank. The side wall of the tank has independent dosing ports for four types of components. An agitator and online component concentration sensors are installed inside the tank. The discharge pipe at the bottom of the tank serves as the main supply pipe for the repair solution, and its end connects to the feed pipe of the cryogenic liquid phase reactor. A connection interface is also provided for a dopant feeding branch. The unit's operating logic is as follows: A manual or automatic feeding system adds four types of components—lithium replenishment, reduction, complexation dispersion, and carbon coating precursor—to the tank. The stirring mechanism inside the tank continuously stirs until the reagents are completely dissolved. Online concentration sensors monitor the content of the four components in real time, and the system automatically replenishes the corresponding reagents when the concentration is insufficient. The prepared quaternary composite repair solution is continuously transported to the rear-end sealed stirred reactor by a delivery pump, providing a stable supply of liquid medium for the cryogenic liquid phase synchronous repair process. The pipeline is sealed throughout to prevent reagent evaporation and loss.

[0043] The cryogenic liquid phase reaction unit is a closed stirred reactor, which is composed of three parts: internal components, external heat exchange components, and auxiliary sensing and feeding components. The internal components include a coaxial double-layer stirring paddle and a built-in ultrasonic dispersion component. The stirring paddle rotation mechanism is electrically linked to the ultrasonic generator, allowing for synchronized start and stop. An online ORP potential sensor and a pH control component probe are submerged in the stirring paddle area, and the probes are simultaneously immersed in the liquid phase material to collect real-time oxidation-reduction potential and pH data. The outer wall of the reactor is fully covered by a jacketed constant-temperature heat exchange component, with heat exchange pipelines connected to an external heat exchanger unit. A temperature sensor is fixed inside the reactor cavity, forming a closed-loop temperature control system with the sensor and heat exchanger unit. An independent dopant feeding branch is located on the side wall of the reactor, with the front end of the feeding branch connected to the main discharge pipe of the repair solution preparation unit. Nitrogen, phosphorus, and heteroatom dopants can be simultaneously fed into the reactor through this branch.

[0044] The regenerated lithium iron phosphate powder and quaternary composite repair solution are simultaneously introduced into the reactor. The double-layer stirring paddle and ultrasonic component are simultaneously activated to disperse the powder. The temperature control system stably maintains a low temperature range of 40~180℃. The ORP and pH components regulate the liquid phase reduction environment online. The dopant branch simultaneously delivers heteroatom components. The powder dispersion, constant temperature and low temperature reaction, reduction atmosphere control, and heteroatom doping are completed simultaneously inside the single reactor. After the reaction is completed, the bottom discharge valve of the reactor is opened, and the mixed materials are transported to the downstream solid-liquid separation and drying unit.

[0045] The solid-liquid separation and drying unit mainly includes a pressure filter solid-liquid separation device, a continuous powder washing tank, and a vacuum low-temperature dryer. The unit is equipped with a dedicated mother liquor circulation and recovery system. The input pipeline of the mother liquor circulation and recovery system is sealed and connected to the liquid phase outlet of the solid-liquid separation device. The recovery system is equipped with a precision filter element. The output pipeline is connected to the feed pipeline at the front end of the low-temperature liquid phase reactor. The solid phase discharge end of the solid-liquid separation device is connected to the continuous washing tank. The discharge port of the washing tank is connected to the feed hopper of the vacuum dryer. The discharge end of the dryer is equipped with a closed powder conveying mechanism, which is connected to the downstream low-temperature calcination heat treatment unit.

[0046] The reaction mixture enters the separation equipment to complete the solid-liquid separation. All the liquid mother liquor enters the recycling system for filtration and return to the reactor for reuse. The solid filter cake is washed with water, dehydrated and dried at low temperature to produce a solid phase repair intermediate. The intermediate is transported to the tubular atmosphere furnace by a closed feeding device.

[0047] The low-temperature calcination heat treatment unit uses a tubular atmosphere furnace. The furnace body is equipped with segmented independent temperature control modules and uniformly distributed gas pipelines around the powder boat. Multiple sets of independent temperature control modules are arranged in sections along the furnace body, and each section of the temperature control module has an independent heating and holding program. Multiple atmosphere distribution pipelines are arranged in parallel inside the furnace chamber. All pipelines are arranged around the outer perimeter of the powder boat, and uniformly distributed gas outlet micropores are opened on the side walls of the pipelines. The inert protective atmosphere is released uniformly from the micropores, and there is no local enrichment or dead zone in the atmosphere inside the furnace chamber. The feeding end of the furnace body is connected to the sealed powder conveying silo, and the discharging end is equipped with a cooling chamber, which is connected to the rear powder shaping and grading unit.

[0048] The solid-phase repair intermediate is spread on a material boat and fed into the furnace. The segmented temperature control module precisely controls the temperature, and the surrounding gas distribution pipeline uniformly delivers the protective atmosphere. The low-temperature calcination process completes lithium lattice diffusion and in-situ carbonization and coating of carbon precursors. After calcination, the powder is cooled at a uniform speed in the furnace tail cooling chamber. After cooling, the powder is automatically discharged and transported to the powder shaping and grading unit.

[0049] The powder shaping and grading unit consists of a low-speed grinder and an air classifier connected in series. The pipelines of the two devices are sealed and connected to form a continuous processing path. The feed hopper of the low-speed grinder receives the calcined powder cooled by the pipe-type atmosphere furnace through a closed conveying pipeline. The discharge pipeline of the low-speed grinder is completely sealed and connected to the feed end of the air classifier. The air classifier is equipped with three discharge ports: coarse powder, qualified powder, and fine powder. Only qualified powder enters the finished product storage hopper, while unqualified powder is returned to the low-speed grinder for secondary processing.

[0050] The agglomerated calcined powder first enters a low-speed grinding mill for gentle deagglomeration and shaping to eliminate particle agglomeration; the deagglomerated powder is then sent to an air classifier for wind separation, precisely controlling the D50 particle size range of the powder and removing discrete coarse and fine particles; finally, the qualified powder is stored in the finished product silo, which is the finished recycled lithium iron phosphate cathode material.

[0051] This invention employs a continuous low-temperature liquid phase regeneration process from S101 to S106, coupled with a matching integrated regeneration system. Compared to traditional high-temperature regeneration processes, it offers significant advantages. Multi-stage series impurity removal equipment progressively removes aluminum and copper metal impurities, improving powder purity from the source and reducing battery self-discharge. The quaternary composite repair solution simultaneously performs multiple functions including lithium replenishment, reduction, dispersion, and carbon loading, simplifying reagent preparation. The reactor integrates stirring, ultrasonic dispersion, closed-loop temperature control, online ORP / pH regulation, and a structure for simultaneous heteroatom feeding. Operating at low temperatures of 40~180℃ significantly reduces energy consumption, ensuring uniform powder dispersion, sufficient reduction of ferric iron, and simultaneous heteroatom modification. A matching mother liquor circulation system enables closed-loop reuse of the repair solution, saving reagents and reducing wastewater discharge. A tubular atmosphere furnace with segmented temperature control and surrounding gas distribution ensures complete and uniform carbonization and coating of the carbon precursor, improving material conductivity. Low-speed grinding combined with airflow classification precisely controls powder particle size, resulting in excellent particle size consistency in the finished product. The entire system consists of six interconnected and automated units, resulting in low production costs, stable electrochemical performance of recycled materials, and suitability for large-scale industrial production.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating and regeneration of waste lithium iron phosphate, characterized in that, include: The waste lithium iron phosphate raw material is purified and impurities are removed to obtain lithium iron phosphate powder to be regenerated; A quaternary composite repair solution containing four types of components—lithium replenishment, reduction, complexation dispersion, and carbon coating precursor—was prepared as a powder repair medium. The lithium iron phosphate powder to be regenerated and the quaternary composite repair liquid are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, and lithium vacancy filling, trivalent iron reduction and carbon precursor particle surface loading are achieved simultaneously. The mixture was subjected to solid-liquid separation, and after washing, dehydration and drying, a solid-phase repair intermediate was obtained. The solid-phase repair intermediate is fed into a heat treatment device and calcined at low temperature under a protective atmosphere to allow lithium lattice diffusion and in-situ carbonization of carbon precursors to generate a conductive coating layer. The material obtained after calcination and cooling is processed using a powder shaping and grading equipment to obtain the finished recycled lithium iron phosphate cathode material.

2. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: The coaxial double-layer stirring paddle and the built-in ultrasonic dispersion component are activated synchronously in a sealed stirred reactor. By combining mechanical disturbance with ultrasonic cavitation through a double-layer stirring paddle, the lithium iron phosphate powder to be regenerated is dispersed and the quaternary composite repair liquid is evenly dispersed, so as to achieve full contact reaction of the materials and obtain a reaction mixture with uniform composition.

3. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: An online ORP potential sensor and a pH control component, which are linked to the agitator, are installed inside a sealed stirred reactor. The online ORP potential sensor is used to collect the liquid phase redox potential in real time, and the pH of the system is dynamically adjusted simultaneously through the pH control component to stabilize the liquid phase reduction reaction environment and ensure that ferric iron is fully reduced during the reaction.

4. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The mixture is subjected to solid-liquid separation, and after washing, dehydration and drying, a solid-phase repair intermediate is obtained, specifically comprising: A mother liquor recycling system is set up to support the solid-liquid separation equipment. The input end of the mother liquor recycling system is connected to the liquid phase outlet of the solid-liquid separation equipment, and the output end of the mother liquor recycling system is connected to the feed inlet of the closed stirred reactor. The liquid mother liquor separated by the solid-liquid separation equipment flows into the mother liquor recycling system and is then returned to the reactor to participate in the low-temperature liquid-phase stirring reaction, so as to realize the recycling of the quaternary composite repair solution.

5. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The solid-phase repair intermediate is fed into a heat treatment apparatus and calcined at low temperature under a protective atmosphere to allow lithium lattice diffusion and in-situ carbonization of carbon precursors to form a conductive coating layer, specifically including: A tubular atmosphere furnace is used as a heat treatment device. Independent temperature control modules and uniform atmosphere distribution pipes are arranged in sections along the axial direction of the tubular atmosphere furnace body, and the uniform atmosphere distribution pipes are arranged around the outer periphery of the powder boat. Precise temperature control is achieved through segmented independent temperature control modules, and a protective atmosphere is uniformly delivered through gas distribution pipes surrounding the material boat, ensuring that the carbon precursor is uniformly carbonized during calcination and forms a complete conductive coating layer on the powder surface.

6. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The purification and impurity removal of waste lithium iron phosphate raw materials to obtain lithium iron phosphate powder to be regenerated specifically includes: A screening machine, a magnetic separator, and a washing tank are connected in series. The discharge port of the screening machine is connected to the inlet of the magnetic separator, and the discharge port of the magnetic separator is connected to the inlet of the washing tank, forming a step-by-step purification and impurity removal pathway. The raw material undergoes initial screening and impurity removal using a screening machine, followed by removal of magnetic metal impurities using a magnetic separator. Then, it undergoes deep cleaning in a water washing tank to gradually remove metal impurities such as aluminum and copper from the raw material, thereby obtaining high-purity lithium iron phosphate powder ready for regeneration.

7. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The material obtained after calcination and cooling is processed using powder shaping and grading equipment to obtain the finished recycled lithium iron phosphate cathode material, specifically including: A powder shaping and grading equipment is set up with a low-speed grinder and an air classifier. The discharge port of the low-speed grinder is sealed and connected to the feed end of the air classifier to form a continuous shaping and grading path. The cooled calcined product is shaped and deagglomerated by a low-speed grinding mill, and then precisely screened and sorted by an air classifier to control the D50 particle size range of the regenerated powder, so as to obtain a finished regenerated lithium iron phosphate cathode material with uniform particle size.

8. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: A dopant feeding branch is set on a closed stirred reactor, and the dopant feeding branch is connected to the repair liquid inlet pipeline. Nitrogen / phosphorus heteroatom dopant components are simultaneously delivered into the repair solution feed pipeline through the dopant feeding branch, so that the dopant components and the quaternary composite repair solution are uniformly mixed and participate in the low-temperature liquid phase stirring reaction, thereby realizing the simultaneous repair of powder and heteroatom modification and doping.

9. The method for cryogenic liquid-phase quaternary synergistic lithium coating and regeneration of waste lithium iron phosphate according to claim 1, characterized in that, The lithium iron phosphate powder to be regenerated and the quaternary composite remediation solution are placed in a reaction device for low-temperature liquid-phase stirring reaction to obtain a mixture, specifically including: A jacketed constant temperature heat exchange component is wrapped around the outer wall of a sealed stirred reactor, and the jacketed constant temperature heat exchange component is linked with the temperature sensor inside the reactor to form a closed-loop linkage control. The reaction temperature inside the reactor is collected in real time by a temperature sensor, and the temperature is dynamically controlled by a closed-loop jacketed constant temperature heat exchange component to stably maintain a low temperature liquid phase reaction range of 40~180℃, ensuring that the liquid phase repair reaction proceeds smoothly and controllably.

10. A low-temperature liquid-phase quaternary synergistic lithium iron phosphate coating and regeneration system for waste lithium iron phosphate, characterized in that, include: The unit includes a raw material purification and impurity removal unit, a repair solution preparation unit, a low-temperature liquid phase reaction unit, a solid-liquid separation and drying unit, a low-temperature calcination heat treatment unit, and a powder shaping and classification unit. The raw material purification and impurity removal unit is equipped with a sieve, a magnetic separator and a water washing tank connected in series. Through a continuous impurity removal process of sieve, magnetic separation and water washing, aluminum and copper metal impurities in the raw material are removed to prepare high-purity lithium iron phosphate powder to be regenerated. The repair solution preparation unit is used to prepare a quaternary composite repair solution containing four functional components: lithium replenishment, reduction, complexation dispersion, and carbon coating precursor. The discharge end is connected to the feed end of the low-temperature liquid phase reaction unit to provide a special medium for the low-temperature repair reaction of powder. The cryogenic liquid phase reaction unit adopts a closed stirred reactor. The closed stirred reactor has a built-in coaxial double-layer stirring paddle and a built-in ultrasonic dispersion component. It is equipped with an online ORP potential sensor and a pH control component that are linked with the stirring paddle. The outer wall is covered with a jacketed constant temperature heat exchange component that is linked in a closed loop with the temperature sensor inside the reactor. The reactor body is also equipped with a dopant feeding branch that is connected to the repair liquid feed pipeline. It is used to complete the integrated cryogenic liquid phase repair reaction of uniform material dispersion, precise control of reaction atmosphere, and synchronous doping of heteroatoms. The solid-liquid separation and drying unit is equipped with a mother liquor recycling system. The input end of the mother liquor recycling system is connected to the liquid phase outlet of the solid-liquid separation equipment, and the output end is connected to the feed inlet of the sealed stirred reactor. While completing the solid-liquid separation, cleaning, dehydration and drying of the mixed material and producing solid phase repair intermediate, the system realizes the closed-loop recycling and reuse of the quaternary composite repair liquid. The low-temperature calcination heat treatment unit is a tubular atmosphere furnace. The tubular atmosphere furnace is equipped with independent temperature control modules in sections along the furnace body axis. At the same time, it is equipped with a uniform gas distribution pipeline around the outer periphery of the powder boat. Through precise segmented temperature control and uniform protective atmosphere supply, the lattice diffusion of lithium element in solid phase repair intermediate and the in-situ uniform carbonization and coating of carbon precursor are realized. The powder shaping and grading unit consists of a sealed, connected low-speed grinding mill and an air classifier. Through continuous shaping, deagglomeration, and precise particle size classification processes, the particle size of the calcined and cooled material is controlled to produce a finished recycled lithium iron phosphate cathode material with uniform particle size.

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