Recycling process of lithium iron phosphate waste

Abstract

This invention provides a recycling process for lithium iron phosphate waste, comprising: pretreating a positive electrode sheet by infrared heating at 150-250°C to obtain a pretreated electrode sheet; subjecting the pretreated electrode sheet to hydrothermal treatment to obtain coarse positive electrode material powder and a positive electrode current collector; using the coarse positive electrode material powder as the anode and forming an electrolytic cell with a metal cathode, performing electrolytic treatment in an acidic electrolyte at 1.8-4.5V to obtain a first positive electrode material powder; calcining the first positive electrode material powder at 300-500°C to obtain a second positive electrode material powder; pulverizing and sieving the second positive electrode material powder to obtain a third positive electrode material powder with a particle size of 1-10 μm; mixing the third positive electrode material powder with a lithium source and then performing a calcination remediation treatment to obtain regenerated lithium iron phosphate material. This recycling process can effectively separate lithium iron phosphate from the positive electrode current collector and other impurities, obtaining regenerated lithium iron phosphate with good electrochemical performance, and is conducted under mild conditions and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of waste lithium battery resource recycling technology, and in particular to the recycling process of lithium iron phosphate waste. Background Technology

[0002] With the booming development of the new energy vehicle industry, the amount of retired lithium iron phosphate (LiFePO4) power batteries has been increasing year by year, and their resource recycling has become an important part of the new energy circular economy system.

[0003] The recycling methods for lithium iron phosphate waste are mainly divided into three categories: pyrometallurgy, hydrometallurgy, and direct remediation and regeneration. Pyrometallurgy typically requires high-temperature smelting, resulting in high energy consumption and significant lithium volatilization losses; hydrometallurgy requires the use of large amounts of strong acids and alkalis, generating large amounts of wastewater and imposing a heavy environmental burden. Direct remediation and regeneration has attracted widespread attention due to its short process and low energy consumption, but existing methods still have many shortcomings in the separation of cathode materials and current collectors: mechanical stripping is inefficient and damages the current collector; organic solvent immersion is costly and solvent recovery is difficult; and high-temperature calcination can easily lead to excessive growth of the lithium iron phosphate lattice and a decline in electrochemical performance.

[0004] Aluminum impurities in waste lithium iron phosphate cathode materials mainly originate from residual aluminum foil in the cathode current collector. During cathode sheet dismantling and material pulverization, aluminum foil easily breaks into fine particles that mix into the cathode material, resulting in a high aluminum content in the recycled products and severely affecting the electrochemical performance of the regenerated cathode material. Existing aluminum removal methods mainly include alkaline leaching, acid leaching, ion exchange resin exchange, and chemical precipitation, but all of these methods suffer from problems such as high reagent consumption, difficult wastewater treatment, or high costs.

[0005] On the other hand, existing microwave calcination repair processes mostly involve calcination within a single temperature range, failing to specifically remove different components such as electrolyte residues, binders, free water, and carbon impurities in different temperature ranges, thus affecting the purity and electrochemical performance of the final recycled material.

[0006] Therefore, it is of great significance to develop a lithium iron phosphate waste recycling process that can gently and efficiently separate the cathode material and current collector, deeply remove aluminum impurities, and selectively remove free water, electrolyte, binder and carbon impurities in stages. Summary of the Invention

[0007] Based on this, the present invention provides a recycling process for lithium iron phosphate waste, which aims to solve the technical problems of difficulty in separating the cathode material and the current collector and incomplete removal of impurity components in the recycling process of lithium iron phosphate waste.

[0008] The technical solution proposed in this invention is as follows: According to a first aspect of the present invention, a recycling process for lithium iron phosphate waste is provided, comprising the following steps: The positive electrode sheet is pretreated by infrared heating at 150℃~250℃ to obtain a pretreated electrode sheet; the positive electrode sheet includes a positive current collector and a positive electrode material layer, the positive electrode material layer including lithium iron phosphate. The pretreated electrode is subjected to hydrothermal treatment to obtain coarse powder of positive electrode material and positive electrode current collector; Using the coarse powder of the positive electrode material as the anode, an electrolytic cell is formed with a metal cathode, and electrolysis is performed in an acidic electrolyte at a voltage of 1.8V~4.5V to obtain the first positive electrode material powder. The first cathode material powder is calcined at 300℃~500℃ to obtain the second cathode material powder. The second cathode material powder is pulverized and sieved to obtain a third cathode material powder with a particle size of 1μm~10μm; The third cathode material powder is mixed with a lithium source and then subjected to calcination repair treatment to obtain regenerated lithium iron phosphate material.

[0009] In some embodiments, the positive electrode material layer further includes a positive electrode binder; optionally, the positive electrode binder is a water-soluble binder; more preferably, the water-soluble binder is sodium carboxymethyl cellulose (CMC).

[0010] In some embodiments, the infrared heating pretreatment is performed in a first inert atmosphere, which includes one or more of nitrogen and argon.

[0011] In some embodiments, the heating rate of the infrared heating pretreatment is 10℃ / min to 30℃ / min, and the holding time of the infrared heating pretreatment is 30min to 90min.

[0012] In some embodiments, the temperature of the hydrothermal treatment is 100℃~180℃, the time of the hydrothermal treatment is 1h~4h, and the stirring rate of the hydrothermal treatment is 100rpm~300rpm.

[0013] In some embodiments, the metal cathode is a stainless steel plate, a titanium plate, or a copper plate.

[0014] In some embodiments, the acidic electrolyte is a dilute sulfuric acid solution, and the concentration of the acidic electrolyte is 0.1 mol / L to 1.0 mol / L.

[0015] In some embodiments, the acidic electrolyte includes an aluminum ion complexing agent, which includes one or more of oxalic acid and citric acid.

[0016] In some embodiments, the current density of the electrolytic treatment is 50 A / m. 2 ~200A / m 2 .

[0017] In some embodiments, the electrolysis treatment time is 0.5h to 3h.

[0018] In some embodiments, the holding time for the calcination treatment is 30 min to 60 min.

[0019] In some embodiments, prior to the calcination treatment, the recycling process further includes the following steps: performing a first pre-calcination treatment by holding the first cathode material powder at 100°C to 200°C for 10 min to 30 min, and performing a second pre-calcination treatment by holding it at 200°C to 300°C for 15 min to 40 min.

[0020] In some embodiments, the calcination treatment, the first pre-calcination treatment, and the second pre-calcination treatment are carried out in a second inert atmosphere, which includes one or more of nitrogen and argon.

[0021] In some embodiments, the roasting process, the first pre-roasting process, and the second pre-roasting process are roasted by microwave roasting, wherein the heating rate of the microwave roasting is 10℃ / min to 50℃ / min and the microwave power is 1kW to 5kW.

[0022] In some embodiments, the pulverization method is air jet pulverization.

[0023] In some embodiments, the sieving step uses a sieve mesh size of 200 to 400 mesh.

[0024] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium phosphate.

[0025] In some embodiments, the mass of the lithium source is 1% to 5% of the mass of the third cathode material powder.

[0026] In some embodiments, the temperature of the calcination repair treatment is 500℃~600℃, and the holding time of the calcination repair treatment is 20min~60min.

[0027] In some embodiments, the calcination repair treatment is carried out under a protective atmosphere, which includes one or more of nitrogen and argon.

[0028] In some embodiments, the roasting repair treatment uses a microwave roasting device, a tube furnace, or a muffle furnace.

[0029] In some embodiments, the positive electrode is obtained by discharging a lithium iron phosphate battery and disassembling the lithium iron phosphate battery to obtain the positive electrode.

[0030] In some embodiments, the discharge treatment includes the following steps: constant current discharge at a rate of 0.1C to 0.5C until the voltage of a single cell is below 2.0V; allowing the lithium iron phosphate battery to stand at 15°C to 30°C for 12h to 48h to allow the voltage to recover and stabilize; repeating the above constant current discharge and standing steps at least twice until the voltage of a single cell stabilizes below 1.5V.

[0031] Compared with traditional technologies, the present invention has at least the following beneficial effects: (1) The present invention adopts a two-step separation strategy of “infrared heating pretreatment + hydrothermal separation”. It utilizes the characteristic that the positive electrode binder (CMC) begins to denature at a low temperature, and controls the infrared heating at 150℃~250℃ to fully denature the positive electrode binder and lose its binding force, thus avoiding the destruction of the lithium iron phosphate crystal structure by high temperature calcination. Hydrothermal stripping does not require the use of organic solvents such as NMP, which is environmentally friendly and results in high purity of current collector recovery.

[0032] (2) This invention employs an electrochemical selective aluminum removal method, utilizing the difference in dissolution potential between aluminum and lithium iron phosphate in an acidic electrolyte to achieve efficient anodic oxidation dissolution and cathodic deposition recovery of aluminum within a specific voltage range. This method requires no chemical aluminum removal agent throughout the process, the electrolyte can be recycled, there is no additional waste liquid discharge, and the aluminum removal efficiency is high.

[0033] (3) The present invention adopts a three-stage gradient calcination, which specifically removes free water, residual electrolyte and residual binder at 100℃~200℃, 200℃~300℃ and 300℃~500℃ respectively, while fully carbonizing the organic components and realizing the pre-crystallization of the material, thereby achieving "targeted removal" of different impurities.

[0034] (4) The present invention places the lithium mixing step after decarbonization and before the final roasting and repair treatment. The amount of lithium replenishment can be precisely controlled according to the actual state of the material after decarbonization, avoiding the problem of lithium source loss with waste liquid in hydrothermal lithium replenishment, which is conducive to improving the lithium source utilization rate.

[0035] (5) The present invention controls the temperature of the final calcination treatment at 500℃~600℃, which significantly reduces energy consumption compared with traditional high temperature repair (above 700℃), while avoiding excessive grain growth, which is conducive to obtaining regenerated lithium iron phosphate materials with uniform particle size and stable electrochemical performance.

[0036] (6) The carbonized products generated by the modification of the positive electrode binder (CMC) in the infrared heating pretreatment of the present invention can form an in-situ carbon skeleton in a hydrothermal environment. This in-situ carbon skeleton can serve as a conductive auxiliary medium in the subsequent lithium replenishment and repair process, which can improve the uniformity of carbon coating of lithium iron phosphate and the integrity of the conductive network, and is beneficial to improving the electrochemical performance of regenerated lithium iron phosphate. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this document; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2~10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, the terms "multiple" and "various" are used, and unless otherwise specified, they refer to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0042] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0043] In this invention, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used herein are commercially available or can be prepared by existing methods.

[0045] One embodiment of the present invention provides a recycling process for lithium iron phosphate waste, the recycling process comprising the following steps S100 to S600: Step S100: The positive electrode sheet is pretreated by infrared heating at 150℃~250℃ to obtain a pretreated electrode sheet; the positive electrode sheet includes a positive current collector and a positive electrode material layer, the positive electrode material layer including lithium iron phosphate.

[0046] Step S200: Perform hydrothermal treatment on the pretreated electrode to obtain coarse powder of positive electrode material and positive electrode current collector.

[0047] Step S300: Using coarse powder of positive electrode material as the anode, an electrolytic cell is formed with a metal cathode. Electrolysis is carried out in an acidic electrolyte at a voltage of 1.8V~4.5V to obtain the first positive electrode material powder.

[0048] Step S400: The first cathode material powder is calcined at 300℃~500℃ to obtain the second cathode material powder.

[0049] Step S500: The second cathode material powder is crushed and sieved to obtain a third cathode material powder with a particle size of 1μm~10μm.

[0050] Step S600: The third cathode material powder is mixed with the lithium source and then subjected to calcination repair treatment to obtain regenerated lithium iron phosphate material.

[0051] The recycling process for lithium iron phosphate waste described in this application involves first pretreating the disassembled lithium iron phosphate cathode sheet with infrared heating at a specific temperature, then subjecting the pretreated electrode sheet to hydrothermal treatment, followed by electrolytic treatment at a specific voltage, calcination treatment at a specific temperature, then crushing and sieving, mixing with a lithium source, and then calcining and repairing to obtain regenerated lithium iron phosphate cathode material.

[0052] Lithium iron phosphate (LiFePO4) cathode electrodes typically include water-soluble binders (such as CMC), which begin to denature at approximately 80°C. During the infrared heating pretreatment step, the selective heating characteristic of infrared radiation allows energy to be preferentially absorbed by the water-soluble binder molecules. This causes the binder to denature and lose its binding effect at a lower temperature, preventing damage to the LiFePO4 crystal structure from overall high temperatures. After the infrared heating pretreatment, the water-soluble binder has largely denatured, and the bonding force between the cathode material layer and the cathode current collector (such as aluminum foil) is significantly reduced.

[0053] After infrared heating pretreatment to denature and remove the water-soluble binder, the bonding force between the cathode material layer and the current collector is greatly weakened. Hydrothermal treatment further dissolves residual organic impurities and allows the cathode material layer to fully expand and peel off. Hydrothermal treatment avoids the cost and environmental problems associated with the large-scale use of organic solvents such as N-methylpyrrolidone (NMP) in conventional methods, and also avoids the damage to the performance of lithium iron phosphate cathode materials caused by high-temperature calcination. Furthermore, the tiny carbon particles generated by the denaturation of the water-soluble binder during infrared heating pretreatment adhere to the surface of the cathode material. In the hydrothermal environment, these tiny carbon particles form an in-situ carbon framework structure. This structure can serve as a conductive auxiliary medium during subsequent lithium replenishment and repair processes, improving the uniformity of the lithium iron phosphate carbon coating and the integrity of the conductive network.

[0054] In the electrolysis process, the difference in dissolution potential between aluminum and lithium iron phosphate in the acidic electrolyte (the oxidation potential of aluminum is significantly lower than that of iron and lithium in lithium iron phosphate) preferentially induces anodic oxidation dissolution (Al → Al) within a precisely controlled voltage range. 3+ +3e -After aluminum ions migrate to the cathode region, they are deposited as Al(OH)3 precipitate or reduced to elemental aluminum on the cathode plate. The olivine structure of lithium iron phosphate remains stable within a selected potential window, without significant electrochemical decomposition. By electrolyzing at a specific voltage, aluminum removal can be achieved without the use of chemical aluminum removers, and the electrolyte can be recycled.

[0055] After crushing, sieving, and carbon removal, cathode material powder of a specific particle size is mixed with lithium source and then subjected to calcination repair treatment. That is, placing the lithium mixing step after carbon removal and before the final calcination repair allows for precise control of the amount of lithium replenishment based on the actual state of the material after carbon removal, avoiding the problem of lithium source loss with waste liquid during hydrothermal lithium replenishment, and thus improving the utilization rate of lithium source.

[0056] The above-mentioned recycling process for lithium iron phosphate waste effectively solves the problems in existing lithium iron phosphate waste recycling processes, such as difficulty in separating cathode materials from cathode current collectors, incomplete removal of impurities, and significant interference of carbon impurities with lithium replenishment and repair effects. It is beneficial to improve the electrochemical performance of regenerated lithium iron phosphate cathode materials, and the process conditions are mild and environmentally friendly, with good prospects for industrial application.

[0057] In some embodiments, the infrared heating pretreatment is performed in a first inert atmosphere, which includes one or more of nitrogen and argon.

[0058] It is understood that the infrared heating pretreatment temperature can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, or any value within the range formed by any two of the above values. Further optionally, the infrared heating pretreatment temperature is 170℃~230℃, and more preferably 190℃~210℃.

[0059] The calcination temperature can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, or any value within the range formed by any two of the above values. Further optionally, the calcination temperature can be 330℃~470℃, and more preferably 400℃~430℃.

[0060] The voltage for electrolytic treatment can be 1.8V, 1.9V, 2V, 2.2V, 2.4V, 2.5V, 2.6V, 2.8V, 3V, 3.2V, 3.4V, 3.5V, 3.6V, 3.8V, 4V, 4.2V, 4.4V, 4.5V, or any value within the range formed by any two of the above values. Further optionally, the voltage for electrolytic treatment can be 2V to 4.2V, and more preferably 2.5V to 3.5V.

[0061] The particle size of the third cathode material powder refers to its average particle size. The particle size of the third cathode material powder can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value within the range formed by any two of the above values.

[0062] In some embodiments, the positive electrode material layer further includes a positive electrode binder; optionally, the positive electrode binder is a water-soluble binder; more preferably, the water-soluble binder is sodium carboxymethyl cellulose.

[0063] In some embodiments, the heating rate of the infrared heating pretreatment is 10°C / min to 30°C / min, and the holding time of the infrared heating pretreatment is 30 min to 90 min. Under these conditions, it is beneficial to remove the sodium carboxymethyl cellulose binder in the positive electrode material layer.

[0064] It is understood that the heating rate can be 10℃ / min, 12℃ / min, 15℃ / min, 18℃ / min, 20℃ / min, 22℃ / min, 25℃ / min, 28℃ / min, 30℃ / min, or any value within the range formed by any two of the above values. The holding time for the infrared heating pretreatment can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, or any value within the range formed by any two of the above values.

[0065] In some embodiments, the hydrothermal treatment temperature is 100℃~180℃, the hydrothermal treatment time is 1h~4h, and the hydrothermal treatment stirring rate is 100rpm~300rpm. Under these conditions, it is beneficial for the positive electrode material layer to naturally peel off from the positive electrode current collector through the penetration and expansion of the hydrothermal environment, thereby obtaining a pure positive electrode current collector and coarse positive electrode material powder.

[0066] It is understood that the hydrothermal treatment temperature can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, or any value within the range formed by any two of the above values. The hydrothermal treatment time can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.5h, 3h, 3.2h, 3.5h, 3.8h, 4h, or any value within the range formed by any two of the above values. The hydrothermal treatment stirring rate can be 100rpm, 120rpm, 150rpm, 180rpm, 200rpm, 220rpm, 250rpm, 280rpm, 300rpm, or any value within the range formed by any two of the above values.

[0067] In some embodiments, the metal cathode is a stainless steel plate, a titanium plate, or a copper plate.

[0068] In some embodiments, the acidic electrolyte is a dilute sulfuric acid solution with a concentration of 0.1 mol / L to 1.0 mol / L. The concentration of the acidic electrolyte can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, or any value within the range formed by any two of the above values.

[0069] In some embodiments, the acidic electrolyte includes an aluminum ion complexing agent, which may include one or more of oxalic acid and citric acid. This further facilitates aluminum removal.

[0070] In some embodiments, the current density of the electrolysis process is 50 A / m. 2 ~200A / m 2 The electrolysis treatment time is 0.5h to 3h. Electrolysis under the above-mentioned current density and time conditions is beneficial for the deep removal of aluminum from the cathode material. The current density can be 50A / m. 2 60A / m 2 70A / m 2 80A / m 2 90A / m 2 100A / m 2 110A / m 2 120A / m 2 130A / m 2 140A / m 2 150A / m 2 160A / m2 170A / m 2 180A / m 2 190A / m 2 200A / m 2 And any value within the range formed by any two of the above values. The electrolysis treatment time can be 0.5h, 0.8h, 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h, or 3h.

[0071] In some embodiments, the calcination treatment is held for 30 to 60 minutes. This is beneficial for removing impurities from the cathode material. It is understood that the calcination treatment time can be 30 minutes, 32 minutes, 35 minutes, 38 minutes, 40 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 50 minutes, 52 minutes, 55 minutes, 58 minutes, 60 minutes, or any value within the range formed by any two of the above values.

[0072] In some embodiments, before the calcination treatment, the recovery process further includes the following steps: first, pre-calcining the first cathode material powder at 100℃~200℃ for 10min~30min, and then pre-calcining it at 200℃~300℃ for 15min~40min. Thus, by performing the first pre-calcination treatment, then the second pre-calcination treatment, and finally the calcination treatment under the above conditions, a three-stage step-by-step calcination and impurity removal process is formed, which is more conducive to removing impurities from the cathode material.

[0073] The first pre-calcination treatment step at 100℃~200℃ mainly removes residual free water from the cathode material; the second pre-calcination treatment step at 200℃~300℃ mainly removes residual electrolyte from the cathode material; and the calcination treatment step at 300℃~500℃ removes residual binder and other organic impurities, while fully carbonizing the organic components in the cathode material powder and achieving material pre-crystallization.

[0074] It is understood that the temperature of the first pre-calcination treatment can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, or any value within the range formed by any two of the above values; the holding time can be 10min, 12min, 15min, 18min, 20min, 22min, 25min, 28min, 30min, or any value within the range formed by any two of the above values. The temperature of the second pre-calcination treatment can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, or any value within the range formed by any two of the above values; the holding time can be 15min, 18min, 20min, 22min, 25min, 28min, 30min, 32min, 35min, 38min, 40min, or any value within the range formed by any two of the above values.

[0075] In some embodiments, the roasting treatment, the first pre-roasting treatment, and the second pre-roasting treatment are all carried out in a second inert atmosphere, which includes one or more of nitrogen and argon. The roasting method for the roasting treatment, the first pre-roasting treatment, and the second pre-roasting treatment is microwave roasting, with a heating rate of 10℃ / min to 50℃ / min and a microwave power of 1kW to 5kW. After the roasting treatment is completed, the material is removed from the microwave roasting device and allowed to cool naturally to room temperature.

[0076] It is understood that the heating rate of microwave roasting can be 10℃ / min, 12℃ / min, 15℃ / min, 18℃ / min, 20℃ / min, 22℃ / min, 25℃ / min, 28℃ / min, 30℃ / min, 32℃ / min, 35℃ / min, 38℃ / min, 40℃ / min, 42℃ / min, 45℃ / min, 48℃ / min, 50℃ / min, or any value within the range formed by any two of the above values. The microwave power can be 1kW, 1.5kW, 1.8kW, 2kW, 2.5kW, 2.8kW, 3kW, 3.5kW, 3.8kW, 4kW, 4.5kW, 4.8kW, 5kW, or any value within the range formed by any two of the above values.

[0077] In some embodiments, the pulverization method is air jet milling; the sieving step uses a sieve mesh size of 200 to 400 mesh. Air jet milling combined with a sieve of the aforementioned mesh size can effectively remove large particles and powdered carbon from the cathode material. It is understood that the sieve mesh size can be 200 mesh, 220 mesh, 250 mesh, 280 mesh, 300 mesh, 320 mesh, 350 mesh, 380 mesh, 400 mesh, or any value within the range formed by any two of the above values.

[0078] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium phosphate; the mass of the lithium source is 1% to 5% of the mass of the third cathode material powder. Using the above-mentioned types and mass contents of lithium source is beneficial for obtaining good lithium replenishment effect. The mass of the lithium source can be 1%, 1.5%, 1.8%, 2%, 2.5%, 2.8%, 3%, 3.5%, 3.8%, 4%, 4.5%, 4.8%, 5% of the mass of the third cathode material powder, or any value within the range formed by any two of the above values.

[0079] In some embodiments, the calcination repair treatment is carried out at a temperature of 500℃~600℃, and the holding time is 20min~60min. The calcination repair treatment is conducted under a protective atmosphere, which includes one or more of nitrogen and argon. The calcination apparatus used for the calcination repair treatment is a microwave calcination apparatus, a tube furnace, or a muffle furnace. Under the above conditions, it is beneficial to ensure that the supplemented lithium is fully embedded in the lithium iron phosphate crystal lattice structure, thereby completing the crystal structure repair and obtaining a regenerated lithium iron phosphate cathode material with good electrochemical performance.

[0080] Among them, the temperature of the calcination repair treatment is controlled at 500℃~600℃, which significantly reduces energy consumption compared with traditional high-temperature repair (above 700℃). At the same time, it avoids excessive grain growth and is conducive to obtaining regenerated lithium iron phosphate materials with uniform particle size and stable electrochemical performance.

[0081] It is understood that the temperature for the calcination repair treatment can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, or any value within the range formed by any two of the above values. The holding time for the calcination repair treatment can be 20min, 22min, 25min, 28min, 30min, 32min, 35min, 38min, 40min, 42min, 45min, 48min, 50min, 52min, 55min, 58min, 60min, or any value within the range formed by any two of the above values.

[0082] In some embodiments, the positive electrode is obtained by discharging the lithium iron phosphate battery to reduce its residual voltage to below a safe threshold, and then physically disassembling it to separate components such as the positive electrode, negative electrode, separator, and casing.

[0083] Specifically, the discharge process includes the following steps: constant current discharge at a rate of 0.1C to 0.5C until the voltage of a single cell is below 2.0V; then, the lithium iron phosphate battery is left to stand at 15℃ to 30℃ for 12h to 48h to allow the voltage to recover and stabilize; repeat the above constant current discharge and standing steps at least twice until the voltage of a single cell stabilizes below 1.5V.

[0084] The present invention will be further described below with reference to specific embodiments and comparative examples, but these should not be construed as limiting the scope of protection of the present invention.

[0085] Example 1: (1) Physical discharge and disassembly Twenty spent lithium iron phosphate power battery cells (nominal capacity 50Ah, approximately 2000 cycles) were taken and discharged at a constant current rate of 0.3C until the cell voltage dropped to 2.0V, with the ambient temperature controlled at 25℃. After discharge, the batteries were left to stand at 25℃ for 24 hours, and the voltage recovered to approximately 2.6V. They were then discharged again at a constant current rate of 0.3C to 2.0V, and after standing for 24 hours, the cell voltage stabilized in the range of 1.2V~1.5V. At this point, physical disassembly was performed, separating the positive electrode, negative electrode, separator, and casing, yielding approximately 2.5kg of positive electrode material containing lithium iron phosphate.

[0086] (2) Infrared heating pretreatment to remove CMC binder The disassembled positive electrode sheets were appropriately cut according to the roll forming thickness and placed in an infrared heating furnace under a nitrogen protective atmosphere. The infrared heating power was set to 1.5kW, and the temperature was increased to 180℃ at a rate of 15℃ / min, and held for 60 minutes for infrared heating pretreatment. After infrared heating pretreatment, the color of the positive electrode sheets changed slightly, the CMC (sodium carboxymethyl cellulose) binder was basically denatured, and the bonding force between the positive electrode material layer and the aluminum foil current collector decreased significantly.

[0087] (3) Hydrothermal separation The infrared-heated pretreated positive electrode sheet was placed in a sealed hydrothermal reactor equipped with a stirrer, and deionized water was added (liquid-to-solid volume ratio of 8:1). The reactor was hydrothermally treated at 150°C and a stirring speed of 200 rpm for 2 hours. After the reaction, the positive electrode material powder naturally detached from the aluminum foil. The aluminum foil and the crude positive electrode material slurry were separated by filtration. The aluminum foil had a smooth surface and could be directly recycled as a high-purity aluminum raw material. The filtered crude positive electrode material powder was vacuum dried at 80°C for 2 hours, yielding approximately 2.0 kg of crude positive electrode material powder. ICP analysis showed an aluminum content of 825 ppm.

[0088] (4) Electrochemical deep aluminum removal Prepare 5 L of 0.3 mol / L dilute sulfuric acid electrolyte, adding a small amount of oxalic acid (0.02 mol / L) as a complexing agent to promote aluminum dissolution. Use coarse powdered positive electrode material as the anode (placed in a titanium basket), and a stainless steel plate as the cathode (electrode spacing 4 cm). Set the voltage to 2.8 V (relative to a saturated calomel electrode) and the current density to 120 A / m. 2 Electrolysis was performed for 1.5 hours with continuous stirring. After electrolysis, the mixture was filtered and separated. The solid product was washed with deionized water until neutral and then dried under vacuum at 100°C to obtain the first cathode material powder. The deposited Al(OH)3 precipitate was collected in the cathode region and further calcined to recover alumina. ICP analysis showed that the aluminum content of the first cathode material powder after aluminum removal was reduced to 88 ppm, with an aluminum removal rate of approximately 89.3%.

[0089] (5) Microwave gradient roasting for stepwise impurity removal The first cathode material powder was placed in a microwave calcination furnace, and nitrogen gas was introduced (flow rate 200 mL / min). The following steps were performed sequentially: First pre-calcination: Heat to 150℃ and hold for 20 minutes (to remove free water); Second pre-calcination: Heat to 250℃ and hold for 30 minutes (to remove electrolyte); Calcination treatment: Heat to 400℃ and hold for 45 minutes (to remove residual binder, carbonize, and precrystallize).

[0090] The heating rate for each zone was 20℃ / min. After calcination, the material was cooled to room temperature in the furnace and then removed to obtain the second cathode material powder.

[0091] (6) Airflow pulverization and screening for carbon removal The cooled second cathode material powder was pulverized using an air jet mill. After pulverization, it was passed through a 325-mesh sieve to remove large particles and carbon powder, resulting in a carbon-removed third cathode material powder with a particle size of 2μm~8μm.

[0092] (7) Lithium mixture Take 1.0 kg of third cathode material powder, use lithium carbonate as the lithium source, calculate the amount to be added as 3.0% (i.e. 30 g) based on the degree of lithium deficiency in the material, mix in a V-type mixer for 30 min to obtain lithium supplementation precursor powder.

[0093] (8) Final calcination repair The lithium iron phosphate precursor powder was placed in a tube furnace, a nitrogen atmosphere was introduced, the temperature was raised to 550°C, held for 40 minutes, and then cooled to room temperature with the furnace before being passed through a 200-mesh sieve to obtain the regenerated lithium iron phosphate cathode material.

[0094] Electrochemical performance testing: The lithium iron phosphate cathode material obtained in step (8) was analyzed by ICP, and its aluminum content was found to be 82 ppm, while the contents of other impurities (Cu, Fe, etc.) were all below 50 ppm. Using this regenerated lithium iron phosphate cathode material to fabricate a cathode sheet, and with lithium metal as the counter electrode, a coin cell was assembled. The initial discharge specific capacity at 0.1C rate was 156.6 mAh / g; after 500 cycles at 1C rate, the capacity retention rate was 95.3%. This lithium iron phosphate cathode material exhibits good electrochemical performance.

[0095] Example 2: Steps (1) to (3) of this embodiment are the same as those in embodiment 1.

[0096] (4) Electrochemical deep aluminum removal The electrolyte was changed to 0.25 mol / L dilute sulfuric acid and 0.01 mol / L citric acid, the voltage was 2.6 V, and the current density was 100 A / m. 2 Electrolysis time: 1.0 h. The aluminum content of the first cathode material powder after aluminum removal was reduced to 153 ppm.

[0097] Steps (5) to (8) are the same as in Example 1.

[0098] Electrochemical performance testing: The positive electrode was fabricated using the recycled lithium iron phosphate cathode material, and a coin cell was assembled using metallic lithium as the counter electrode. The coin cell had an initial discharge specific capacity of 155.9 mAh / g at 0.1C and a capacity retention rate of 94.9% after 500 cycles at 1C.

[0099] Comparative Example 1: This comparative example is basically the same as Example 1, except that step (4) electrochemical aluminum removal is cancelled, that is, the crude powder of the positive electrode material after hydrothermal separation is directly fed into microwave gradient calcination (step (5)).

[0100] Electrochemical performance testing: ICP analysis revealed that the aluminum content in the recycled lithium iron phosphate cathode material reached 920 ppm. Using this recycled lithium iron phosphate cathode material to fabricate the cathode sheet, and with metallic lithium as the counter electrode, a coin cell was assembled. The coin cell exhibited a 0.1C initial discharge specific capacity of only 150.8 mAh / g, and a capacity retention rate of only 93.2% after 500 cycles at 1C.

[0101] Comparative Example 2: This comparative example is basically the same as Example 1, except that step (6) airflow pulverization and screening to remove carbon is cancelled, that is, after roasting treatment, lithium is directly mixed (without removing carbon), and then step (8) final roasting repair is carried out.

[0102] Electrochemical performance testing: The positive electrode was fabricated using the recycled lithium iron phosphate cathode material, and a coin cell was assembled using lithium metal as the counter electrode. The coin cell had an initial discharge specific capacity of 153.5 mAh / g at 0.1C, and a capacity retention rate of 94.1% after 500 cycles at 1C.

[0103] Comparative Example 3: This comparative example is basically the same as Example 1, except that step (5) is cancelled, and the final calcination repair temperature in step (8) is 750℃ (normal high temperature).

[0104] Electrochemical performance testing: The regenerated lithium iron phosphate cathode material was used to fabricate the cathode sheet, and lithium metal was used as the counter electrode to assemble a coin cell. The coin cell had an initial discharge specific capacity of 154.8 mAh / g at 0.1C, and the material particle size was increased (D50 = 8.2 μm). After 500 cycles at 1C, the capacity retention rate was 94.6%.

[0105] The process conditions and performance data of the above embodiments and comparative examples are shown in Table 1.

[0106] Table 1

[0107] As shown in Table 1, the lithium iron phosphate cathode material regenerated by the combined recycling process of this application has good electrochemical performance.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A recycling process for lithium iron phosphate waste, characterized in that, Includes the following steps: The positive electrode sheet is pretreated by infrared heating at 150℃~250℃ to obtain a pretreated electrode sheet; the positive electrode sheet includes a positive current collector and a positive electrode material layer, the positive electrode material layer including lithium iron phosphate. The pretreated electrode is subjected to hydrothermal treatment to obtain coarse powder of positive electrode material and positive electrode current collector; Using the coarse powder of the positive electrode material as the anode, an electrolytic cell is formed with a metal cathode, and electrolysis is performed in an acidic electrolyte at a voltage of 1.8V~4.5V to obtain the first positive electrode material powder. The first cathode material powder is calcined at 300℃~500℃ to obtain the second cathode material powder. The second cathode material powder is pulverized and sieved to obtain a third cathode material powder with a particle size of 1μm~10μm; The third cathode material powder is mixed with a lithium source and then subjected to calcination repair treatment to obtain regenerated lithium iron phosphate material.

2. The recycling process for lithium iron phosphate waste according to claim 1, characterized in that, Meet one or more of the following: (1) The infrared heating pretreatment is carried out in a first inert atmosphere, which includes one or more of nitrogen and argon; (2) The heating rate of the infrared heating pretreatment is 10℃ / min~30℃ / min, and the holding time of the infrared heating pretreatment is 30min~90min.

3. The recycling process for lithium iron phosphate waste according to claim 1, characterized in that, The hydrothermal treatment temperature is 100℃~180℃, the hydrothermal treatment time is 1h~4h, and the hydrothermal treatment stirring rate is 100rpm~300rpm.

4. The recycling process for lithium iron phosphate waste according to claim 1, characterized in that, Meet one or more of the following: (1) The metal cathode is a stainless steel plate, a titanium plate or a copper plate; (2) The acidic electrolyte is a dilute sulfuric acid solution, and the concentration of the acidic electrolyte is 0.1 mol / L to 1.0 mol / L; (3) The acidic electrolyte includes an aluminum ion complexing agent, which includes one or more of oxalic acid and citric acid; (4) The current density of the electrolytic treatment is 50 A / m 2 ~200A / m 2 ; (5) The electrolysis treatment time is 0.5h to 3h.

5. The recycling process for lithium iron phosphate waste according to claim 1, characterized in that, The holding time for the roasting process is 30 min to 60 min.

6. The recycling process for lithium iron phosphate waste according to any one of claims 1 to 5, characterized in that, Prior to the roasting process, the recycling process further includes the following steps: The first positive electrode material powder is subjected to a first pre-calcination treatment by holding it at 100℃~200℃ for 10min~30min, and then subjected to a second pre-calcination treatment by holding it at 200℃~300℃ for 15min~40min.

7. The recycling process for lithium iron phosphate waste according to claim 6, characterized in that, Meet one or more of the following: (1) The roasting treatment, the first pre-roasting treatment and the second pre-roasting treatment are all carried out in a second inert atmosphere, which includes one or more of nitrogen and argon; (2) The roasting treatment, the first pre-roasting treatment and the second pre-roasting treatment are roasted by microwave roasting, and the heating rate of microwave roasting is 10℃ / min~50℃ / min and the microwave power is 1kW~5kW.

8. The recycling process for lithium iron phosphate waste according to any one of claims 1 to 5 and 7, characterized in that, Meet one or more of the following: (1) The pulverization method is airflow pulverization; (2) The sieve mesh size used in the sieving step is 200 mesh to 400 mesh.

9. The recycling process for lithium iron phosphate waste according to any one of claims 1 to 5 and 7, characterized in that, Meet one or more of the following: (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide and lithium phosphate; (2) The mass of the lithium source is 1% to 5% of the mass of the third cathode material powder; (3) The temperature of the calcination repair treatment is 500℃~600℃, and the holding time of the calcination repair treatment is 20min~60min; (4) The calcination repair treatment is carried out under a protective atmosphere, which includes one or more of nitrogen and argon; (5) The roasting device used in the roasting repair treatment is a microwave roasting device, a tube furnace or a muffle furnace.

10. The recycling process for lithium iron phosphate waste according to any one of claims 1 to 5 and 7, characterized in that, The positive electrode sheet is obtained by the following method: The lithium iron phosphate battery is discharged and then disassembled to obtain the positive electrode sheet. Optionally, the discharge process includes the following steps: constant current discharge at a rate of 0.1C to 0.5C until the voltage of a single cell is below 2.0V; then, the lithium iron phosphate battery is left to stand at 15°C to 30°C for 12 to 48 hours to allow the voltage to recover and stabilize; repeat the above constant current discharge and standing steps at least twice until the voltage of a single cell stabilizes below 1.5V.

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