A method for selectively recovering lithium iron phosphate batteries and its application

Abstract

The present invention discloses a method for selectively recovering lithium iron phosphate batteries and its application. The method utilizes an acid-based deep eutectic solvent under oxidizing conditions to achieve selective recovery of lithium iron phosphate batteries, and specifically comprises the following steps: mixing a hydrogen bond donor, a hydrogen bond acceptor, and a diluent, and heating to obtain an acid-based deep eutectic solvent; wherein the hydrogen bond donor is acetic acid, and the diluent comprises at least one of ethylene glycol, water, or glycerol; under oxidizing conditions, mixing waste lithium iron phosphate positive electrode material with the acid-based deep eutectic solvent, leaching, and performing solid-liquid separation, and collecting a liquid phase and a solid phase, respectively, wherein the liquid phase contains lithium, copper, and aluminum, and the solid phase contains iron phosphate and graphite. Under oxidizing conditions, utilizing the properties of acetic acid as a hydrogen bond donor and its moderate acid strength, selective leaching of lithium from lithium iron phosphate, the positive active material of lithium batteries, and simultaneous efficient leaching and recovery of other valuable metals can be achieved in one step with simple operation.

Description

Technical Field

[0001] The present invention relates to the technical field of waste lithium battery recycling, and in particular to a method for selectively recycling lithium iron phosphate batteries and applications thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, long cycle life, and high operating voltage, have become the mainstream energy storage solution for consumer electronics and electric vehicles. As a key technology for lithium-ion batteries, lithium iron phosphate (LIFP) batteries, with their olivine-type crystal structure endowed with exceptional thermal and chemical stability, offer unique advantages in energy storage systems, electric buses, and light electric vehicles. The recycling and disposal of spent LFP batteries has become a crucial topic in the current lithium battery circular economy. Traditional processes for the recycling and disposal of spent LFP batteries face significant technical bottlenecks. While pyrometallurgical processes can effectively separate the active material from the current collector, they typically require subsequent steps such as solid-phase regeneration or wet leaching, and are associated with high energy consumption and dust pollution. Wet acid leaching, which selectively extracts lithium through inorganic acid dissolution combined with hydrogen peroxide oxidation, offers advantages such as a simple process and high-purity lithium recovery solutions. However, it faces environmental challenges such as high consumption of acid and alkali reagents and the difficulty in treating heavy metal-containing wastewater.

[0003] As a new generation of green solvent technology, deep eutectic solvents (DES) are self-assembled from hydrogen bond acceptors and hydrogen bond donors through intermolecular hydrogen bonding, demonstrating efficient solubility for transition metal oxides. This system can completely replace traditional strong acid and strong base reagents, eliminating the generation of high-salt wastewater at the source, and has been successfully applied to the clean leaching of layered oxide cathode materials such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium manganese oxide. However, for the lithium iron phosphate system, which has a higher market share, existing research still focuses on selective lithium extraction using non-green systems. This not only continues the reliance on highly corrosive reagents, but also generally neglects the comprehensive recovery of associated valuable metals such as copper, aluminum, nickel, cobalt, and manganese in the cathode materials, resulting in low resource utilization.

[0004] Based on this, it is of great significance to construct a full-component green leaching system based on deep eutectic solvents. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for selectively recovering lithium iron phosphate batteries, which can selectively leach lithium while efficiently leaching other valuable metals.

[0006] The present invention also proposes an application of the above method.

[0007] According to one aspect of the present invention, a method for selectively recycling lithium iron phosphate batteries is proposed, comprising the following steps:

[0008] S1. Preparing an acid-based deep eutectic solvent: mixing a hydrogen bond donor, a hydrogen bond acceptor, and a diluent, and heating to obtain an acid-based deep eutectic solvent; wherein the hydrogen bond donor is acetic acid, and the diluent comprises at least one of ethylene glycol, water, or glycerol; the molar number of the hydrogen bond donor is greater than the molar number of the hydrogen bond acceptor; and the amount of the diluent added is 15 wt% to 50 wt% of the sum of the mass of the hydrogen bond donor and the hydrogen bond acceptor;

[0009] S2. Leaching reaction: Under oxidizing conditions, the waste lithium iron phosphate positive electrode material is mixed with the acid-based deep eutectic solvent, selectively leached under heating and / or ultrasonic conditions, and subjected to solid-liquid separation treatment to collect the liquid phase and solid phase respectively, wherein the liquid phase contains lithium, copper and aluminum, and the solid phase contains iron phosphate and graphite.

[0010] According to the method of the embodiment of the present invention, there are at least the following beneficial effects: the present invention scheme cleverly achieves the selective leaching of lithium through a specific acid-based deep eutectic solvent containing acetic acid, and at the same time, it can also efficiently leach other valuable metals; the present invention scheme adopts a deep eutectic solvent composed of acetic acid, a hydrogen bond acceptor, and a diluent, with acetic acid as a hydrogen bond donor and ethylene glycol, water or glycerol as a leaching medium for the diluent. Under oxidizing conditions, the characteristics of acetic acid as a hydrogen bond donor and its moderate acid strength are utilized, combined with the synergistic effect of the hydrogen bond acceptor and the diluent, and only a simple operation is required to achieve the selective leaching of lithium from lithium iron phosphate, the positive active material of the lithium battery, and the efficient simultaneous leaching and recovery of other valuable metals, such as copper, aluminum and other valuable metal ions, in one step. The diluent used in the present invention can introduce an appropriate amount of hydroxyl functional groups or hydroxyl bonds on the basis of effectively reducing the viscosity of the system and enhancing the mass transfer efficiency, and avoids competitive reactions with the original components of the system through molecular structure design, thereby maintaining the stability of the chemical equilibrium of the system. The solution of the present invention achieves efficient and selective leaching of lithium in one step, obtaining a filtrate containing valuable metal ions and a solid phase product mainly composed of iron phosphate and graphite (no lithium iron phosphate residue is found), which has great economic and environmental value.

[0011] According to some embodiments of the present invention, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2-8:1.

[0012] According to some embodiments of the present invention, the diluent is 15% to 48% of the sum of the mass of the hydrogen bond donor and the hydrogen bond acceptor.

[0013] According to some embodiments of the present invention, the diluent is 20% to 45% of the sum of the mass of the hydrogen bond donor and the hydrogen bond acceptor.

[0014] According to some embodiments of the present invention, the diluent is 25% to 35% of the sum of the mass of the hydrogen bond donor and the hydrogen bond acceptor.

[0015] The present invention utilizes the Cl of hydrogen bond acceptor in deep eutectic solvent - The remaining valuable metals (copper, aluminum, nickel, cobalt, manganese, etc.) in the positive electrode materials of waste lithium iron phosphate batteries, except lithium, are leached and coordinated to form metal chlorate complexes. The deep eutectic solvent can be reused many times. After the metal ions are extracted, the solvent raw materials can be efficiently recovered through operations such as reduced pressure distillation, which basically achieves raw material regeneration while reducing the cost of post-leaching liquid treatment.

[0016] According to some embodiments of the present invention, the hydrogen bond acceptor contains Cl - .

[0017] According to some embodiments of the present invention, the hydrogen bond acceptor comprises at least one of a quaternary ammonium salt or a quaternary phosphonium salt.

[0018] According to some embodiments of the invention, the hydrogen bond acceptor comprises at least one of choline chloride, dimethylammonium hydrochloride, bisdimethylammonium chloride and benzalkonium chloride.

[0019] According to some embodiments of the invention, the hydrogen bond acceptor comprises choline chloride.

[0020] According to some embodiments of the present invention, raw materials for preparing the deep eutectic solvent include acetic acid, choline chloride and ethylene glycol.

[0021] According to some embodiments of the present invention, the heating temperature in step S1 is 60° C. to 80° C., and the water bath heating time is 0.5 h to 2 h.

[0022] According to some embodiments of the present invention, the preparation process of the acid-based deep eutectic solvent in step S1 is carried out under stirring, and the stirring speed is 200 rpm to 400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.

[0023] According to some embodiments of the present invention, the oxidizing conditions include placing the reaction system in an oxygen-containing atmosphere or adding hydrogen peroxide to the reaction system. The oxidizing conditions oxidize the ferrous iron (Fe(II) or Fe3(PO4)2·8H2O) in the intermediate product to iron (III), destroying the olivine structure of the lithium iron phosphate, thereby causing Li + is released into the solution and then selectively leached.

[0024] According to some embodiments of the present invention, the oxidizing condition involves placing the reaction system in an air atmosphere. This method utilizes air as an oxidant, providing the oxidizing environment required for selective leaching of lithium iron phosphate, avoiding the use of additional oxidizing agents. Furthermore, because the synthesized deep eutectic solvent compensates for the volatilization of the raw material acetic acid, the loss rate of the solvent components is low even after repeated use in air. The entire experimental process is simple, convenient, environmentally friendly, and low-cost.

[0025] According to some embodiments of the present invention, the air atmosphere can be maintained in an open environment at normal pressure. This can be a naturally ventilated environment or a gas delivery device that introduces air at a preset flow rate. Both methods meet the experimental conditions required, and natural diffusion or forced convection mode can be selected based on the specific application scenario.

[0026] According to some embodiments of the present invention, the air atmosphere is a ventilated natural environment atmosphere.

[0027] According to some embodiments of the present invention, the liquid phase further comprises at least one of nickel, cobalt, or manganese. For lithium iron phosphate batteries containing nickel, cobalt, and manganese, efficient leaching of nickel, cobalt, and manganese can be achieved simultaneously, further improving economic benefits.

[0028] According to some embodiments of the present invention, the leaching includes leaching at room temperature and / or under heating conditions.

[0029] According to some embodiments of the present invention, the leaching may be performed with the assistance of ultrasound.

[0030] According to some embodiments of the present invention, the leaching is performed at room temperature (e.g., 20-30°C) or under heating and without ultrasonic assistance. This allows for comparable leaching rates without ultrasonic assistance, saving energy. Without the need for ultrasonic oscillation or other auxiliary means, simple heating alone can achieve selective leaching of lithium from lithium iron phosphate (LIFP), the active cathode material for lithium batteries, while simultaneously efficiently leaching and recovering other valuable metals, such as copper and aluminum.

[0031] According to some embodiments of the present invention, the leaching temperature in step S2 is 20° C. to 80° C., and the leaching time is 2 h to 8 h.

[0032] According to some embodiments of the present invention, the leaching temperature in step S2 is 30° C. to 80° C., and the leaching time is 2 h to 8 h.

[0033] According to some embodiments of the present invention, the leaching in step S2 is performed under stirring, and the stirring speed is 300 rpm to 500 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.

[0034] According to some embodiments of the present invention, in step S2, the waste lithium iron phosphate positive electrode material is mixed with the acid-based deep eutectic solvent at a solid-liquid ratio of 20 g / L to 200 g / L.

[0035] According to another aspect of the present invention, the above-mentioned method is used to prepare lithium iron phosphate batteries. The recovered material can be directly processed for use in lithium iron phosphate battery production, or reconstituted through a precursor co-precipitation process for high-performance recycling. This, in turn, establishes a closed-loop power battery industry chain, significantly reducing reliance on primary mineral resources and lowering carbon emissions throughout the entire lifecycle.

[0036] Compared with the prior art, the beneficial effects of the solution of the present invention also include:

[0037] (1) The acid-based deep eutectic solvent designed in the present invention has excellent properties such as being green and low-toxic. The entire leaching process does not involve the use of strong acids or strong bases, and the process flow is simple, with low economic costs and high environmental benefits.

[0038] (2) Adding diluents can significantly reduce the high viscosity defect of deep eutectic solvents. At the same time, it can also improve the wetting ability of the solvent and battery materials. In addition, diluents such as ethylene glycol can also participate in the coordination effect through its hydrogen bond donor characteristics, forming a hydroxyl-carboxylic acid double coordination structure with the carboxylic acid group. This synergistic coordination mode can significantly enhance the hydrogen bond network density of the solvent system, while improving the coordination affinity between the solvent molecules and the solute, and optimizing the dynamic reconstruction efficiency of the solvation layer, thereby simultaneously enhancing the solvent's solubility coordination ability and mass transfer performance. The amount of diluent added is 15wt%~50wt% of the total mass of the hydrogen bond donor and hydrogen bond acceptor, which can take into account both low viscosity and improved Li + The complexing ability with other transition metal ions can better achieve leaching.

[0039] (3) The rational addition of diluents in the present invention overcomes the traditional defect of traditional deep eutectic solvents that they cannot exert good leaching ability at a higher solid-liquid ratio due to their own high viscosity, so that the present invention can still achieve excellent leaching effect even in a higher solid-liquid ratio range.

[0040] (4) The deep eutectic solvent of the present invention has excellent leaching ability after the addition of the diluent. No additional auxiliary operation (such as ultrasonic oscillation, etc.) is required during the experiment. A leachate rich in lithium and other valuable metals can be obtained by simple operations such as simple oil bath heating, thereby reducing the cost of the actual production process.

[0041] (5) The recovered solid phase products can be directly used for the processing of lithium battery positive electrode materials, which not only helps to achieve the recycling and sustainable development of resources, but also promotes the environmental protection and economy of the reprocessing of lithium battery positive electrode materials.

[0042] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 1. A physical image (a) and a scanning electron microscope (SEM) image (b) of the positive electrode active materials from waste lithium batteries to be recycled in the examples of the present invention and the comparative examples.

[0044] Figure 2 1 is the XRD spectrum of the positive electrode active material from the waste lithium battery to be recycled in the examples and comparative examples of the present invention.

[0045] Figure 3 Schematic diagram of the process flow of an embodiment of the present invention.

[0046] Figure 4 This is a physical picture of the leaching residue (a) and the leachate (b) in Example 1 of the present invention.

[0047] Figure 5 1. The scanning electron microscope (SEM) image (a) of the residue after extraction in Example 1 of the present invention and the energy spectrum analysis (EDS) image of iron (Fe) and phosphorus (P) in a selected area (b) are shown.

[0048] Figure 6 This is the XRD pattern of the solid phase product (i.e., leached residue) recovered in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the concept of the present invention and the technical effects produced in conjunction with the embodiments, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Unless otherwise specified, the test methods used in the embodiments are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials obtained from commercial channels. Unless otherwise specified, the same parameter in each embodiment has the same value. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be understood as limitations of the present invention.

[0050] In the description of the present invention, reference to the term "some embodiments" or the like indicates that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0051] The components of the leaching solvent, choline chloride (solid phase), acetic acid (liquid phase), ethylene glycol (liquid phase), and glycerol (liquid phase), are all analytically pure reagents from Sinopharm Reagent Group. They are mixed and heated to obtain a deep eutectic solvent.

[0052] Source of raw materials: The lithium iron phosphate powder to be recycled comes from discarded lithium batteries (LFP18650E-150). The physical and SEM images are as follows: Figure 1 As shown, the X-ray diffraction (XRD) pattern is as follows Figure 2 Its component analysis is shown in Table 1 below.

[0053] Table 1

[0054]

[0055] From the above Figure 1 As can be seen from Table 1, the recycled lithium iron phosphate powder is primarily composed of lithium, iron, and phosphorus, with copper and aluminum as the primary impurities. This batch of raw material also contains very small amounts of nickel, cobalt, and manganese impurities. The used lithium iron phosphate battery cathode material is a black powder containing a significant amount of graphite, resulting in its overall black color. The raw material particles are fine, but some agglomeration is still present. Furthermore, the lithium iron phosphate material is mostly surrounded by even finer graphite particles.

[0056] From the above Figure 2 It can be seen that the diffraction peak of the positive electrode active material to be recycled is consistent with the standard card of LiFePO4 (JCPDS: 81-1173 Orthorhomhic LiFe (PO4)), and the crystal is an orthorhombic system.

[0057] The leaching effect evaluation method of the following examples and comparative examples is as follows:

[0058] The metal ion concentrations in the filtrate and wash water were measured by atomic absorption spectrometry, and the leaching rate η of each element ion was calculated using formula (1).

[0059]

[0060] Where: C1 is the concentration of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, or manganese in the leachate, g / L. V1 is the volume of the leachate, L. C2 is the concentration of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, or manganese in the wash water, g / L. V2 is the volume of the wash water, L. m is the mass of the added lithium iron phosphate cathode material powder, g. W0 is the mass fraction of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, or manganese in the original lithium iron phosphate cathode material powder, wt%.

[0061] Calculate the content of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, or manganese in the leaching solution and wash water. Perform SEM scanning, EDS analysis, and XRD testing on the solid phase product (leaching residue) after washing, drying, and grinding.

[0062] The ventilated natural environment in which the following embodiments and comparative examples are located means that the experimental operations are carried out in a fume hood, the laboratory air conditioner is turned on for a long time, the air is circulated, the room temperature is maintained at 20°C, and the air humidity is 27%.

[0063] Example 1

[0064] This example provides a method for selectively recycling lithium iron phosphate batteries, such as Figure 3 The specific operation process is as follows:

[0065] (1) Add acetic acid and choline chloride in a molar ratio of 6:1 into a glass bottle, and add 30 wt% of ethylene glycol based on the total weight of acetic acid and choline chloride. Heat in an oil bath at 60 °C with a stirring speed of 300 rpm for 0.5 h to obtain a deep eutectic solvent.

[0066] (2) The deep eutectic solvent obtained in step (1) is mixed with the waste lithium iron phosphate battery positive electrode material powder at a solid-liquid ratio of 60 g / L, and the mixture is carried out in a ventilated natural environment (i.e., using oxygen in natural air as the oxidizing atmosphere). After reacting for 4 hours under oil bath conditions at a temperature of 60°C (heated to 60°C at 220V / 50Hz) and a stirring speed of 400 rpm, solid-liquid separation is performed to obtain a filtrate containing lithium and other valuable metals (including lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese) and a solid phase product of iron phosphate and graphite.

[0067] The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate were determined by atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid phase product was analyzed using SEM, EDS, and XRD.

[0068] Example 2

[0069] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the molar ratio of acetic acid to choline chloride during the preparation of the deep eutectic solvent is 2:1. The remaining preparation and leaching procedures are identical to those of Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0070] Example 3

[0071] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the molar ratio of acetic acid to choline chloride during the preparation of the deep eutectic solvent is 4:1. The remaining preparation and leaching procedures are identical to those of Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid product is analyzed using SEM, EDS, and XRD.

[0072] Example 4

[0073] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the molar ratio of acetic acid to choline chloride during the preparation of the deep eutectic solvent is 8:1. The remaining preparation and leaching procedures are identical to those of Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid product is analyzed using SEM, EDS, and XRD.

[0074] Example 5

[0075] This example provides a method for selectively recovering lithium iron phosphate batteries. The method differs from Example 1 in that, in step (2), ultrasonic oscillation is performed at a power of 120 W and a frequency of 40 kHz, while stirring and heating (heating is performed to 60° C. using a built-in heating power of 150 W) for 4 hours. The remaining steps are the same as in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using an atomic absorption spectrometer, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0076] Comparative Example 1

[0077] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that acetic acid, a hydrogen bond donor, is used to directly leach the spent lithium iron phosphate battery positive electrodes. The remaining preparation and leaching procedures are the same as those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using an atomic absorption spectrometer, and the leaching rate of each metal element is calculated.

[0078] Comparative Example 2

[0079] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 3 in that an equimolar amount of formic acid is used instead of acetic acid. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using atomic absorption spectrometry, and the leaching rate of each metal element is calculated.

[0080] The leaching efficiencies of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese measured in Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 2 below.

[0081] Table 2

[0082]

[0083] As shown in Table 2, when acetic acid is used directly to leach the SLFP cathode material, the leaching rates of lithium, copper, aluminum, nickel, cobalt, and manganese are much lower than when DES is used as the leaching solvent. The leaching rates of iron and phosphorus are higher. This may be because acetic acid, even with air as the oxidant, still lacks the ability to selectively leach spent lithium iron phosphate batteries (SLFP). Furthermore, acetic acid's lack of coordination and its reducing properties are insufficient to completely reduce the high-valent transition metal ions in the SLFP cathode material, resulting in suboptimal leaching of each element. When ultrasonic oscillation is used to assist with water bath heating and stirring, comparable leaching results are achieved for lithium and the remaining valuable metal elements. However, considering the cost implications of actual production applications, the significant noise generated during the reaction, and the operational complexity, heating and stirring are preferred. According to Examples 1-4, the molar ratio of acetic acid to hydrogen bond acceptor has a certain influence on leaching efficiency. When the molar ratio of acetic acid to choline chloride is less than 6:1, the H ionized in the DES system is + The leaching efficiency of metal ions showed a downward trend under the same experimental conditions. - It can coordinate with transition metal ions, which enhances the ability of DES solvent to dissolve SLFP cathode material powder and other valuable transition metals. Therefore, when the molar ratio of acetic acid and choline chloride is greater than 6:1, the Cl - As the concentration of metal ions decreases, the leaching rate of metal ions shows a downward trend.

[0084] Example 6

[0085] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the diluent added during the preparation of the deep eutectic solvent is 15 wt %. The remaining preparation and leaching procedures are identical to those of Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate were determined using atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid phase product was analyzed using SEM, EDS, and XRD.

[0086] Example 7

[0087] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the diluent added during the preparation of the deep eutectic solvent is 45 wt %. The remaining preparation and leaching procedures are identical to those of Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0088] Comparative Example 3

[0089] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that ethylene glycol is not added as a diluent during the preparation of the deep eutectic solvent, and the experimental solid-liquid ratio is 200 g / L. The remaining preparation and leaching processes are the same as those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using an atomic absorption spectrometer, and the leaching rate of each metal element is calculated.

[0090] Comparative Example 4

[0091] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that during the preparation of the deep eutectic solvent, the amount of diluent added is 60 wt %. The remaining preparation and leaching processes are the same as in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using an atomic absorption spectrometer, and the leaching rate of each metal element is calculated.

[0092] Comparative Example 5

[0093] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that during the preparation of the deep eutectic solvent, the diluent is replaced with an equal amount of ethanol. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using atomic absorption spectrometry, and the leaching rate of each metal element is calculated.

[0094] The leaching efficiencies of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in Example 1, Examples 6-7, and Comparative Examples 3-4 are shown in Table 3 below.

[0095] Table 3

[0096]

[0097] In Comparative Example 5, no valuable metals could be effectively leached, so they are not shown in the table.

[0098] Table 3 shows that when no diluent is added, the high viscosity of the solvent itself weakens the mass transfer capacity of the entire leaching system, making it impossible to achieve optimal leaching results for lithium and other valuable metals using only heating and stirring. When the amount of ethylene glycol added is low, the viscosity of the DES solvent is relatively high, which affects the mass transfer efficiency of dissolved substances during the leaching process. When the amount of ethylene glycol added exceeds 50wt%, the excessive addition of ethylene glycol weakens the solvent acidity and reduces the leaching capacity, which in turn has a certain impact on the leaching effect of metal ions. When the ethylene glycol addition amount is 60wt%, the excessive ethylene glycol increases the pH of the entire leaching solvent, weakening the solvent acidity. Excessive ethylene glycol interferes with the hydrogen bonding structure formed by acetic acid choline chloride, reducing the leaching capacity and significantly reducing the leaching effect of lithium and other valuable metals. Therefore, it is necessary to control the amount of ethylene glycol added within an appropriate range to ensure optimal leaching results for lithium and other valuable metals.

[0099] Example 8

[0100] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath temperature during the leaching process is 20°C. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0101] Example 9

[0102] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath temperature during the leaching process is 40°C. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0103] Example 10

[0104] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath temperature during the leaching process is 80°C. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0105] The leaching efficiencies of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in Example 1 and Examples 8-10 are shown in Table 4.

[0106] Table 4

[0107]

[0108] Table 4 shows that temperature significantly affects the leaching rate of each metal element. Increasing temperature enhances the leaching and reducing capacity of the reaction system, and the viscosity of the reaction system is also lower at higher temperatures. Therefore, increasing temperature promotes the leaching of metal ions. Comparing the leaching rate data for Examples 1 and 8-10, it was found that the leaching rate of each element was optimal at 60°C, while the reaction tended to equilibrium above 60°C. Therefore, considering economic factors, the leaching temperature is preferably 60°C.

[0109] Example 11

[0110] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath heating time during the leaching process is 2 hours. All other reaction conditions and the DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate were determined using atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid phase product was analyzed using SEM, EDS, and XRD.

[0111] Example 12

[0112] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath heating time during the leaching process is 6 hours. All other reaction conditions and the DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0113] Example 13

[0114] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the oil bath heating time during the leaching process is 8 hours. All other reaction conditions and the DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0115] The leaching efficiencies of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in Example 1 and Examples 11 to 13 are shown in Table 5.

[0116] Table 5

[0117]

[0118] Table 5 shows that as the leaching time increases from 2 h to 8 h, the leaching rate of each metal element gradually increases. As the leaching time continues to increase, the leaching rate tends to balance, indicating that the leaching reaction of the SLFP cathode material powder has reached equilibrium. Therefore, considering economic factors, the preferred leaching time is 4 h.

[0119] Example 14

[0120] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the solid-to-liquid ratio of spent lithium iron phosphate battery cathode material powder to deep eutectic solvent is 20 g / L. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0121] Example 15

[0122] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the solid-to-liquid ratio of spent lithium iron phosphate battery cathode material powder to deep eutectic solvent is 40 g / L. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0123] Example 16

[0124] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the solid-to-liquid ratio of spent lithium iron phosphate battery cathode material powder to deep eutectic solvent is 120 g / L. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0125] Example 17

[0126] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 1 in that the solid-to-liquid ratio of spent lithium iron phosphate battery cathode material powder to deep eutectic solvent is 200 g / L. The remaining reaction conditions and DES preparation process are identical to those in Example 1. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0127] Comparative Example 6

[0128] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 14 in that acetic acid is replaced with an equimolar ratio of salicylic acid (SA):choline chloride (2:1). The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are measured using atomic absorption spectrometry, and the leaching rate of each metal element is calculated.

[0129] Comparative Example 7

[0130] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 17 in that an equimolar amount of lactic acid is used instead of acetic acid, 45 wt% of ethylene glycol is added, the oil bath temperature during leaching is 80°C, and the leaching time is 6 hours. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate were determined using an atomic absorption spectrometer, and the leaching rate of each metal element was calculated. To simplify the testing process, the leaching rates of nickel, cobalt, and manganese were not considered during this comparative test.

[0131] The leaching efficiencies of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in Example 1, Examples 14 to 17, and Comparative Example 6, and the leaching efficiencies of lithium, iron, phosphorus, copper, and aluminum in Comparative Example 7 are shown in Table 6 below.

[0132] Table 6

[0133]

[0134] Table 6 shows the effect of the solid-liquid ratio of SLFP positive electrode material powder and DES solvent on the leaching efficiency. It can be seen that when the solid-liquid ratio is 20g / L, 40g / L, and 60g / L, good leaching effects are achieved. When the solid-liquid ratio continues to increase, the leaching rate decreases, but selective leaching can still be achieved. However, when acetic acid is replaced by lactic acid, selective leaching cannot be achieved. When acetic acid is replaced by salicylic acid, the leaching effect of lithium is significantly reduced. Therefore, this also assists in proving that the use of acetic acid as a hydrogen bond donor has an unexpected effect on the selective leaching of lithium in this method. In terms of solid-liquid ratio selection, a solid-liquid ratio of 60g / L was selected as the optimal solid-liquid ratio for this method after comprehensive consideration.

[0135] Example 18

[0136] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 2 in that water is used as a diluent at a rate of 45 wt %, a solid-to-liquid ratio of 60 g / L, and a leaching reaction time of 6 hours. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD. To simplify the testing process, the leaching rates of nickel, cobalt, and manganese are not considered in this example.

[0137] Example 19

[0138] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 2 in that glycerol is used as a diluent at a rate of 45 wt %, a solid-to-liquid ratio of 60 g / L, and a leaching reaction time of 6 hours. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD. To simplify the testing process, the leaching rates of nickel, cobalt, and manganese are not considered in this example.

[0139] Example 20

[0140] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 19 in that the molar ratio of acetic acid to choline chloride is 4:1. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate were determined using atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid product was analyzed using SEM, EDS, and XRD. To simplify the testing process, this example did not focus on the leaching rates of nickel, cobalt, and manganese.

[0141] The leaching efficiencies of lithium, iron, phosphorus, copper, and aluminum in Example 2 and Examples 18 to 20 are shown in Table 7 below.

[0142] Table 7

[0143]

[0144] It can be seen from Table 7 that when water or glycerol is used as the diluent, selective leaching of lithium can also be achieved well.

[0145] Example 21

[0146] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 3 in that the diluent addition amount is 45 wt%, the solid-to-liquid ratio is 60 g / L, and the leaching reaction time is 6 hours. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate were determined using atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid phase product was analyzed using SEM, EDS, and XRD. To simplify the testing process, the leaching rates of nickel, cobalt, and manganese were not considered during this example.

[0147] Example 22

[0148] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 21 in that a 5% volume fraction of hydrogen peroxide is pre-added to the reaction system, replacing the natural ventilation environment. The concentrations of lithium, iron, phosphorus, copper, and aluminum in the filtrate were determined using atomic absorption spectrometry, and the leaching rate of each metal element was calculated. The solid phase product was analyzed using SEM, EDS, and XRD. To simplify the testing process, the leaching rates of nickel, cobalt, and manganese were not considered during the testing process in this example.

[0149] The leaching efficiencies of lithium, iron, phosphorus, copper, and aluminum in Examples 21 and 22 are shown in Table 8 below.

[0150] Table 8

[0151]

[0152] From the results in Table 8, it can be seen that the leaching effect of providing an oxidizing environment using air as the oxidant or using hydrogen peroxide as the oxidant is equivalent. Using air as the oxidant is cheaper, while using hydrogen peroxide requires the use of an additional oxidant, which increases the cost.

[0153] Example 23

[0154] This example provides a method for selectively recovering lithium iron phosphate batteries. This method differs from Example 3 in that the leaching reaction temperature is 80°C, the solid-to-liquid ratio is 200 g / L, and the reaction time is 6 hours. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are determined using atomic absorption spectrometry, and the leaching rate of each metal element is calculated. The solid phase product is analyzed using SEM, EDS, and XRD.

[0155] After the leaching is completed, an equal proportion of solvent is taken again for a second leaching under the same conditions. The concentrations of lithium, iron, phosphorus, copper, aluminum, nickel, cobalt, and manganese in the filtrate are again measured by atomic absorption spectrometry, and the leaching rate of each metal element is calculated.

[0156] The leaching rates of the two leaching processes are shown in Table 9.

[0157] Table 9

[0158]

[0159] It can be seen from Table 9 above that when the solid-liquid ratio is high, the total leaching effect can be improved by increasing the number of leaching times.

[0160] The actual pictures of the leachate and leach residue of Example 1 are as follows: Figure 4 The SEM image of the residue after extraction and the EDS image of the selected area are shown in Figure 5 The SEM and EDS results of the filter residue product show that after leaching at 60°C, the main structure of the SLFP remains unchanged, but the product with aggregated particles is significantly reduced. At 60°C, DES can effectively penetrate the SLFP material, and the impurity metal ions are effectively released into the leachate. The results of other examples are similar and are not shown individually to avoid redundancy.

[0161] The solid phase product was detected by XRD, and the detection results of Example 1 are as follows: Figure 6 As shown, the results of other embodiments are similar, and to avoid redundancy, they are not shown one by one. Figure 6 As can be seen, the diffraction peaks of the resulting solid-phase product are consistent with those of a standard iron phosphate chart (JCPDS: 37-0478 Orthorhombic (Mn, Fe)PO4). The results indicate that the solid-phase product is primarily composed of FePO4 and graphite, with no residual LiFePO4 observed. This demonstrates that the present invention achieves efficient and selective lithium leaching in a single step by mixing a deep eutectic solvent with the cathode active material powder, yielding a filtrate rich in lithium, copper, and aluminum (as well as nickel, cobalt, and manganese) and a solid-phase product primarily composed of iron phosphate and graphite.

[0162] The present invention adopts the following mechanism to leach lithium and other valuable metals (copper, aluminum, nickel, cobalt, manganese) from waste lithium iron phosphate battery cathode materials using acid leaching deep eutectic solvent in air atmosphere or with the addition of an oxidant such as hydrogen peroxide:

[0163] Ethylene glycol, water or glycerol is added as a diluent to the deep eutectic solvent synthesized by hydrogen bond donor acetic acid and hydrogen bond acceptor. The hydroxyl group or hydroxyl bond in the diluent can act as an additional hydrogen bond donor to react with acetic acid and Cl - A more complex hydrogen bond network is formed, which reduces the viscosity of the solvent and improves the fluidity and wetting effect under high solid-liquid ratio. The acetic acid in the deep eutectic solvent ionizes the acidic proton H + , where H + Directly destroy the FeO6 octahedron to form the intermediate product Fe(II) or Fe3(PO4)2·8H2O. The intermediate product is oxidized to Fe(III)PO4 by oxygen in the air or oxidants such as hydrogen peroxide. The olivine structure of lithium iron phosphate is destroyed, causing the LiO6 octahedron to collapse. + Entering the solution, the released Li + With Cl in choline chloride- Forming metal chlorate complexes or existing in free form; copper and aluminum react with ionized hydrogen ions to produce Cu 2+ 、Al 3+ , then Cu 2+ 、Al 3+ With Cl in choline chloride - Forms a stable complex [CuCl4] 2- 、[AlCl4] - The oxygen atoms in nickel, cobalt and manganese metal oxides react with hydrogen ions to generate water molecules, and the redox reaction releases metal ions, which releases high-valent Ni 3+ 、Co 3 + 、Mn 4+ Metal ions are reduced to low-valent Ni 2+ 、Co 2 + 、Mn 2+ The reduced low-valent metal ions react with the Cl in choline chloride - A metal chlorate complex is formed. Next, the water generated in the reaction hydrolyzes with part of the chlorine complex to form a hydrated metal ion complex. Finally, the chlorinated metal ion complex and the hydrated metal ion complex reach coordination equilibrium. After leaching is completed, acetic acid becomes peracetic acid, and choline chloride only serves as a leaching ligand and does not directly participate in the chemical reaction.

[0164] Compared with the prior art, the method of the present invention has at least one of the following beneficial effects:

[0165] (1) The acid-based deep eutectic solvent designed in the embodiment of the present invention (composed of acetic acid and choline chloride, with ethylene glycol, glycerol or water as the diluent) has excellent properties such as low saturated vapor pressure, not easy to volatilize with gas, green and low toxicity, and the entire leaching process does not involve the use of strong acid or strong base, and the process flow is simple, with low economic cost and high environmental benefits.

[0166] (2) When the present invention uses air atmosphere as an oxidant, it can provide the oxidizing environment required for the selective leaching of lithium iron phosphate, avoid the use of additional oxidizing agents, and save economic costs. At the same time, since the synthesized deep eutectic solvent makes up for the defect of easy volatility of the raw material acetic acid, even after multiple uses in the air, the loss of the various components that make up the solvent is relatively small. The entire experimental process is simple, convenient, green, environmentally friendly, and low in cost.

[0167] (3) The present invention has conducted a large number of experimental verifications on the working principle and dosage of the diluent. The diluent can significantly reduce the high viscosity defect of the deep eutectic solvent and improve the wetting ability of the solvent and the battery material. In addition, the diluent can also serve as a hydrogen bond donor to assist coordination, forming a "carboxylic acid-hydroxyl double coordination" structure, enhancing the hydrogen bond network of the solvent, and improving the coordination and mass transfer capacity of the solvent; the amount of the diluent added as a diluent should be 15wt%~50wt% of the total mass of the hydrogen bond donor and the hydrogen bond acceptor, which can take into account both low viscosity and improved Li + Complexing ability with other transition metal ions.

[0168] (4) The rational addition of diluents in the present invention overcomes the traditional defect of the deep eutectic solvent itself having high viscosity and being unable to exert good leaching ability at a higher solid-liquid ratio, and can achieve excellent leaching effect in a wider range of solid-liquid ratios.

[0169] (5) Since the deep eutectic solvent of the present invention has excellent leaching ability after adding ethylene glycol as a diluent, no additional auxiliary operations (such as ultrasonic oscillation, etc.) can be performed during the experiment. A leachate rich in lithium and other valuable metals can be obtained by simply heating and stirring in an oil bath, thereby reducing the cost of the actual production process.

[0170] (6) The present invention utilizes the Cl bond of hydrogen bond in deep eutectic solvent - The remaining valuable metals (copper, aluminum, nickel, cobalt, and manganese) in the positive electrode materials of waste lithium iron phosphate batteries, except lithium, are leached and coordinated to form metal chlorate complexes. The deep eutectic solvent can be reused many times. After the metal ions are extracted, the solvent raw materials can be efficiently recovered through operations such as reduced pressure distillation, which basically achieves raw material regeneration while reducing the cost of post-leaching liquid treatment.

[0171] (7) The present invention achieves the selective extraction of lithium elements through the ingenious design of solvent molecule combination, and simultaneously establishes a multi-metal collaborative and efficient recovery process route, which has great economic and environmental value.

[0172] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A method for selectively recovering lithium iron phosphate batteries, characterized in that: The steps include: S1. Preparing an acid-based deep eutectic solvent: mixing a hydrogen bond donor, a hydrogen bond acceptor, and a diluent, and heating to obtain an acid-based deep eutectic solvent; wherein the hydrogen bond donor is acetic acid, and the diluent comprises at least one of ethylene glycol, water, or glycerol; the molar number of the hydrogen bond donor is greater than the molar number of the hydrogen bond acceptor; and the amount of the diluent added is 15 wt% to 50 wt% of the sum of the mass of the hydrogen bond donor and the hydrogen bond acceptor; S2, leaching reaction: under oxidizing conditions, mixing the waste lithium iron phosphate cathode material with the acid-based deep eutectic solvent, leaching, and solid-liquid separation treatment, collecting the liquid phase and solid phase respectively, wherein the liquid phase contains lithium, copper and aluminum, and the solid phase contains iron phosphate and graphite; The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2 to 8:1, the oxidizing condition is an oxygen-containing atmosphere or adding hydrogen peroxide to the reaction system, and the hydrogen bond acceptor contains Cl - .

2. The method for selectively recovering lithium iron phosphate batteries according to claim 1, wherein: The hydrogen bond acceptor includes at least one of choline chloride, dimethylammonium hydrochloride, dimethylammonium chloride and benzalkonium chloride.

3. The method for selectively recovering lithium iron phosphate batteries according to claim 1, wherein: The raw materials for preparing the deep eutectic solvent include acetic acid, choline chloride and ethylene glycol.

4. The method for selectively recovering lithium iron phosphate batteries according to claim 1, wherein: The leaching includes leaching at room temperature or under heating, and the leaching also includes leaching with or without ultrasonic assistance.

5. The method for selectively recovering lithium iron phosphate batteries according to claim 1, wherein: The leaching includes at least one of the following conditions: 1) the leaching temperature is 20° C. to 80° C.; 2) the leaching time is 2 h to 8 h; 3) the leaching is carried out under stirring at a speed of 300 rpm to 500 rpm.

6. The method for selectively recovering lithium iron phosphate batteries according to claim 1, wherein: In step S2, the waste lithium iron phosphate positive electrode material is mixed with the acid-based deep eutectic solvent at a solid-liquid ratio of 20 g / L to 200 g / L.

7. Use of the method according to any one of claims 1 to 6 in preparing lithium iron phosphate batteries.

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