Carbon-coated lithium iron phosphate material, preparation method and application thereof

Abstract

The invention discloses a preparation method of a carbon-coated lithium iron phosphate material, which comprises the following preparation steps: S1, treating waste lithium iron phosphate batteries to obtain recycled lithium iron phosphate; s2, dispersing the recycled lithium iron phosphate, a carbon source and a dispersing agent in a solvent to form mixed slurry, and separating and drying the mixed slurry to obtain a precursor; and S3, calcining the precursor in an inert atmosphere to obtain the carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material can be used for preparing a lithium-poor lithium iron phosphate electrode. The carbon-coated lithium iron phosphate material provided by the invention is prepared by recycling the waste lithium iron phosphate battery electrode plate, and the method reutilizes the waste material, improves the lithium resource recovery rate, relieves the problem of waste battery accumulation, can also significantly reduce the raw material cost and carbon emission, and has the advantages in cost, environmental protection and performance.

Description

Technical Field

[0001] The present application relates to the field of lithium extraction from salt lakes, and specifically to a carbon-coated lithium iron phosphate material, a preparation method, and applications thereof. Background Art

[0002] Lithium is an indispensable component of high-performance batteries and is widely used in portable electronic devices, electric vehicles, and renewable energy systems. However, global lithium resources are unevenly distributed, and lithium extraction from ores faces problems such as limited resource reserves, high cost, and high energy consumption. Therefore, lithium extraction from salt lake brines has become an important way to meet future lithium demand. However, due to the low lithium concentration and high content of interfering ions, these lithium cannot be extracted by traditional soda lime evaporation. Traditional extraction methods also cause large amounts of water loss, exacerbating the already severe water shortage in arid regions, and cause serious environmental pollution due to the use of toxic chemicals. Therefore, many studies have been devoted to establishing direct (i.e., additive-free) lithium extraction technologies, especially electric field-assisted technologies, because they can quickly extract lithium from low-quality brines (lithium concentration <15 mM).

[0003] Electrochemical deintercalation and extraction of lithium has shown great application potential in the field of lithium extraction from salt lakes due to its significant advantages such as high selectivity, low energy consumption, and environmental friendliness. This technology can achieve efficient separation of lithium from other impurity ions through the selective adsorption and desorption of lithium ions by electrode materials. Compared with traditional lithium extraction processes such as precipitation and extraction, it can effectively reduce production costs, reduce environmental pollution, and improve lithium recovery rates. It is a very promising method for extracting lithium from salt lakes. In the electrochemical deintercalation lithium extraction technology system for salt lakes, the preparation process and performance of electrode materials are key factors in determining the efficiency of lithium extraction and the overall operational performance of the system. The preparation process of the cathode FePO4 electrode is particularly crucial for the industrial application of this technology. Compared to the anode LiFePO4 material, which can be directly obtained through synthesis and modification based on the established preparation process for lithium-ion battery LiFePO4 materials, the preparation of the cathode FePO4 electrode faces more complex technical challenges.

[0004] This complexity stems from the fact that the cathode FePO4 material must have the same olivine-type crystal structure as the LiFePO4 material to ensure efficient migration of lithium ions in the electrode material. However, the FePO4 materials prepared by the currently widely used traditional material synthesis processes such as calcination, co-precipitation, and hydrothermal methods are difficult to precisely control during the crystallization process, and often cannot form a specific crystal structure that meets the requirements of lithium ion migration. In view of this, for the preparation of FePO4 electrode materials with special crystal structures, the industry currently generally adopts a technical route that uses LiFePO4 materials as raw materials and uses electrochemical methods for directional preparation to ensure the matching of electrode material structure and performance.

[0005] Although the electrochemical preparation method using LiFePO4 as raw material has solved the structural matching problem of the cathode FePO4 electrode material to a certain extent, this method has disadvantages such as cumbersome process steps, high equipment requirements, and high production costs, which makes it difficult to meet the needs of industrial large-scale production of lithium extraction from salt lakes. Therefore, developing a simple, easy-to-use, cost-effective method for preparing cathode electrode materials is of great practical significance for promoting the industrialization of electrochemical deintercalation salt lake lithium extraction technology, reducing the cost of lithium resource extraction, and enhancing industry competitiveness. Summary of the Invention

[0006] The purpose of this application is to provide a carbon-coated lithium iron phosphate material, which can be prepared from waste batteries using a simple method and has high economic applicability.

[0007] Another object of the present application is to provide an application of a carbon-wrapped lithium iron phosphate material, which is suitable for use in lithium-poor lithium iron phosphate battery pole pieces in electrochemical deintercalation and lithium extraction technology and has good adsorption performance.

[0008] To achieve the above objectives, the technical solution adopted in this application is: to provide a method for preparing a carbon-coated lithium iron phosphate material, comprising the following preparation steps: S1: treating waste lithium iron phosphate batteries to obtain recycled lithium iron phosphate; S2: dispersing the recycled lithium iron phosphate, carbon source, and dispersant in a solvent to form a mixed slurry, separating and drying the mixed slurry to obtain a precursor; S3: calcining the precursor under an inert atmosphere to obtain the carbon-coated lithium iron phosphate material.

[0009] Preferably, the carbon source is organic carbon with a carbon atom number not exceeding 13.

[0010] As another preference, the carbon source is any one or more combinations of glucose, sucrose, maltose, glutamic acid and glycine.

[0011] As another preference, the mass of the carbon source accounts for 0.5% to 2% of the mass of the recovered lithium iron phosphate.

[0012] As another preferred method, the waste lithium iron phosphate battery is charged to 3-4 V and then disassembled, the lithium iron phosphate positive electrode sheet is peeled off, crushed and acid-treated, calcined and sieved to obtain the recovered lithium iron phosphate.

[0013] As another preferred embodiment, the calcination temperature of the lithium iron phosphate positive electrode sheet is 500-700° C., and the calcination time is 4-6 hours; the calcination temperature of the precursor is 650-850° C., and the calcination time is 4-20 hours.

[0014] As another preference, the mixed slurry is spray-dried after separation, and the temperature of the spray drying feed port is 200-260°C, and the temperature of the spray drying discharge port is 70-110°C.

[0015] More preferably, the median particle size of the mixed slurry is 0.3-0.5 μm, the median particle size of the carbon-coated lithium iron phosphate material is 2-12 μm, and the specific surface area is 4-20 m 2 / g, tap density is 0.5~1.5 g / cm 3 .

[0016] The present application provides a carbon-coated lithium iron phosphate material, the preparation raw materials of which include waste lithium iron phosphate batteries, a carbon source, and a dispersant. The mass of the carbon source accounts for 0.5% to 2% of the mass of the recovered lithium iron phosphate, and the carbon source is organic carbon with no more than 13 carbon atoms.

[0017] The present application provides a lithium-deficient lithium iron phosphate electrode, the raw materials for preparing the electrode include a carbon-coated lithium iron phosphate material prepared by any of the above-mentioned preparation methods.

[0018] Compared with the prior art, the present invention has the following advantages: (1) The carbon-coated lithium iron phosphate material of the present application is prepared by recycling waste lithium iron phosphate battery electrode sheets. This method reuses waste materials, improves the lithium resource recovery rate, alleviates the problem of waste battery accumulation, and can significantly reduce raw material costs and carbon emissions. It has advantages in cost, environmental protection and performance. (2) The lithium-poor lithium iron phosphate battery electrode of the present application is used for electrochemical deintercalation and lithium extraction technology, has good Li adsorption performance and good cycle stability, extends the service life of the electrode sheet, and is economical and applicable. DETAILED DESCRIPTION

[0019] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0020] The terms "comprises" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, product or apparatus.

[0021] The present application provides a carbon-coated lithium iron phosphate material, which is prepared by recycling waste lithium iron phosphate battery electrode sheets. This method reuses waste materials, improves the lithium resource recovery rate, alleviates the problem of waste battery accumulation, and can significantly reduce raw material costs and carbon emissions. It has advantages in cost, environmental protection and performance.

[0022] The present application also provides a method for preparing a carbon-coated lithium iron phosphate material, comprising the following preparation steps: S1: Processing the waste lithium iron phosphate battery electrodes to obtain recycled lithium iron phosphate; S2: dispersing the recovered lithium iron phosphate, carbon source, and dispersant in a solvent to form a mixed slurry, separating and drying the mixed slurry to obtain a precursor; S3: calcining the precursor under an inert atmosphere to obtain a carbon-coated lithium iron phosphate material.

[0023] The preparation method of the carbon-coated lithium iron phosphate material of the present application has a simple and easy-to-understand process flow, uses cheap and easily available raw materials, has low preparation cost and is environmentally friendly, and is suitable for large-scale production.

[0024] In some embodiments, for the treatment of waste lithium iron phosphate battery electrodes, the waste lithium iron phosphate batteries need to be charged to 3-4 V and then disassembled, and the lithium iron phosphate positive electrode sheets are peeled off and crushed.

[0025] Charge the used lithium iron phosphate battery. + Li is released from the positive electrode and embedded in the negative electrode. When the voltage rises to 3~4V, Li + Partial lithium removal occurs, and the positive electrode material gradually changes from LiFePO4 to FePO4. The theoretical capacity of the positive electrode material will be released accordingly according to the actual amount of lithium removal, which will affect the Li adsorption capacity of the subsequent carbon-wrapped lithium iron phosphate material.

[0026] In some preferred embodiments, the used lithium iron phosphate battery is charged to 3.1-3.4 V before being disassembled, more preferably to 3.2 V.

[0027] In some embodiments, the remaining amount of lithium in the waste lithium iron phosphate battery accounts for 3.0% to 1.3% of the total mass of the lithium iron phosphate.

[0028] In some embodiments, the contents of Li and Fe in the crushed lithium iron phosphate positive electrode are measured, and the crushed lithium iron phosphate material is calcined and sieved to obtain a recovered lithium iron phosphate material. The recovered lithium iron phosphate material can be expressed as Li 1-X FePO4, of which 0 <x<1。

[0029] The recovered lithium iron phosphate material has a low lithium-to-iron ratio and a low lithium content, which is conducive to the preparation of carbon-coated lithium iron phosphate material and is suitable for use in the electrochemical deintercalation method to extract lithium from salt lakes.

[0030] In a specific embodiment, the stripped lithium iron phosphate positive electrode is crushed and immersed in a concentrated sulfuric acid solution, filtered after a period of time, and the supernatant is taken for ICP detection to determine the content of Li and Fe therein. The residue obtained after filtration is calcined under an inert atmosphere.

[0031] In some preferred embodiments, the crushed lithium iron phosphate material is calcined at a temperature of 500-700°C for 4-6 hours. After calcination, the material is sieved through a 150-250 mesh sieve to obtain recovered lithium iron phosphate material.

[0032] In some embodiments, the carbon source is an organic carbon source, such as glucose, sucrose, maltose, glutamate, glycine, and the like.

[0033] In some embodiments, the number of carbon atoms in the organic carbon source does not exceed 13. Preferred carbon sources are glucose, sucrose, and maltose.

[0034] In some embodiments, the dispersant is polyethylene glycol, sodium carboxymethyl cellulose, or polyvinyl pyrrolidone, preferably polyethylene glycol.

[0035] In some embodiments, the recovered lithium iron phosphate, carbon source, dispersant and solvent are mixed and ground. The grinding medium is zirconia balls with a particle size of 0.5-0.8 mm. The grinding time is 5-8 hours and the linear speed is 10-25 m / s. After grinding, a mixed slurry is obtained. The median particle size of the mixed slurry is 0.3-0.5 μm, and the preferred median particle size is 0.4 μm.

[0036] In some embodiments, the mass of the added carbon source accounts for 0.5% to 2% of the mass of the recovered lithium iron phosphate.

[0037] In some preferred embodiments, the mass of the added carbon source accounts for 1% to 2% of the mass of the recovered lithium iron phosphate, and more preferably 1.8%.

[0038] In some embodiments, the mixed slurry is separated and then spray-dried. The feed inlet temperature of the spray drying is controlled to be 200-260°C, and the discharge port temperature is controlled to be 70-110°C. The median particle size of the precursor obtained after spray drying is 2-10 µm.

[0039] In some preferred embodiments, the feed inlet temperature of the spray drying is preferably 230° C., the discharge outlet temperature is preferably 95° C., and the median particle size of the precursor obtained after spray drying is 6 μm.

[0040] In some embodiments, the precursor is calcined in an inert gas atmosphere at a temperature of 650 to 850° C., for a time of 4 to 20 h, and at a heating rate of 3 to 10° C. / min.

[0041] In some preferred embodiments, the calcination temperature is 700-800° C., more preferably 720° C.; the calcination time is 8-14 h, more preferably 10 h.

[0042] In some preferred embodiments, the heating rate to 650-850° C. is 3-10° C. / min, more preferably 6-9° C. / min, and even more preferably 8° C. / min.

[0043] In some embodiments, the product of the calcined precursor is sieved with a 150-250 mesh sieve to obtain a carbon-coated lithium iron phosphate material, wherein the carbon-coated lithium iron phosphate material has a median particle size of 2-12 μm and a specific surface area of 4-20 m 2 / g, tap density is 0.5~1.5 g / cm 3 .

[0044] In some preferred embodiments, the carbon-coated lithium iron phosphate material has a median particle size of 6 to 10 μm, more preferably 9 μm; and a specific surface area of 5 to 16 m 2 / g, more preferably 11 m 2 / g; the tap density is preferably 0.9 g / cm 3 .

[0045] The present application also provides a method for preparing a lithium-poor lithium iron phosphate electrode: according to the mass ratio, carbon-coated lithium iron phosphate material, acetylene black, PVDF and NMP are weighed and evenly mixed in the ratio of (10~20): (1~2): (1~2): (60~100), the mixture is coated on the electrode and dried, and compressed and dried using a hot press for 2~5 minutes to obtain a lithium-poor lithium iron phosphate electrode.

[0046] In some embodiments, the coating area density is 550-700 g / m 2 The hot pressing pressure is 2-5 MPa and the temperature is 100-200°C. The preferred coating surface density is 600 g / m 2 The preferred hot pressing pressure is 3.5 Mpa and the preferred temperature is 180°C.

[0047] The present application also provides a method for electrochemical deintercalation and lithium extraction, including preparing a lithium-poor lithium iron phosphate electrode, preparing a lithium-rich chain lithium iron phosphate electrode, preparing an Ag electrode, preparing an AgCl electrode, and extracting lithium. The specific steps are as follows: Preparation of a lithium-poor lithium iron phosphate electrode: according to the mass ratio, carbon-coated lithium iron phosphate material, acetylene black, PVDF and NMP are weighed and mixed evenly, the mixture is coated on the electrode and dried, and compressed and dried using a hot press for 2-5 minutes to obtain a lithium-poor lithium iron phosphate electrode; Preparation of lithium-rich lithium iron phosphate electrode: lithium iron phosphate, PVDF, acetylene black and NMP are weighed and mixed evenly in a mass ratio of (10-20): (1-2): (1-2): (60-100), the mixture is coated on the electrode, and after drying, hot pressing is performed to form the electrode to obtain the lithium-rich lithium iron phosphate electrode; Preparation of Ag electrode: Mix silver powder, carbon black, PVDF, and NMP in a mass ratio of (10-20): (1-2): (1-2): (60-100) to form a uniform slurry, apply it on a titanium mesh, dry it in an oven at 80-120°C for 4-8 h, and compress and dry it in a hot press for 2-5 min to obtain an Ag electrode; Preparation of AgCl electrodes: A three-electrode electrolysis apparatus was constructed using a double silver electrode system and a saturated calomel electrode (SCE). One silver electrode served as the working electrode, the other as the counter electrode, and the SCE as the reference electrode. The three electrodes were immersed in a 0.1 mol / L HCl solution and electrolysis was performed at a constant potential of 0.3 V (vs. SCE) for 2–5 hours. During the electrolysis, the loop current was observed to drop to zero, indicating that the silver electrode had been completely converted to silver chloride. Lithium extraction steps: In the decoupled membraneless (DCMF) battery system for lithium extraction, the cathode chamber (loaded with lithium-containing brine feed) and the anode chamber (loaded with lithium extraction solution) are physically separated to form independent chambers, but are electrochemically coupled through a pair of functional electrodes: the working electrode uses a lithium-poor lithium iron phosphate electrode / lithium-rich lithium iron phosphate electrode pair, and the redox electrode uses an Ag / AgX electrode pair.

[0048] When the system is in operation, a constant voltage is applied under forward bias conditions for a certain period of time, driving the lithium ions in the lithium salt solution to be enriched in the lithium-poor lithium iron phosphate electrode through an electrochemical intercalation reaction. The working electrode and redox electrode are then switched to the opposite electrode compartment (i.e., the original cathode material is placed in the anode compartment, and the original anode material is placed in the cathode compartment). A reverse bias (with constant voltage) is applied for the same period of time, causing the lithium ions to be released from the electrode material into the extraction solution through the reverse reaction. This periodic polarity switching operation completes the directional migration and enrichment of lithium from the low-concentration salt water source to the high-purity extraction solution.

[0049] In some embodiments, the voltage in the lithium extraction step is 0.3-1 V, and the duration of applying the constant voltage is 70-200 min.

[0050] More preferably, the applied voltage is 0.5 V, and the duration of applying the constant voltage is 130 min.

[0051] This application uses waste lithium iron phosphate battery electrode sheets to prepare carbon-coated lithium iron phosphate materials. This material can be used in lithium-deficient lithium iron phosphate electrodes used in electrochemical lithium extraction and deintercalation. The carbon-coated material can improve conductivity and increase cycle life. The preparation method is simple, and the raw materials are recycled waste battery materials, reducing preparation costs and achieving resource recycling.

[0052] Example 1 S1: The old battery is charged to 3.1 V and then disassembled. The lithium iron phosphate positive electrode is peeled off and crushed. After dissolution with concentrated sulfuric acid, the filtrate is taken for ICP measurement to obtain the Li and Fe contents. The filtered carbon residue is calcined at 500-700 °C in a nitrogen atmosphere for 4-6 hours. After sintering, it is sieved through a 200-mesh sieve to obtain the recovered lithium iron phosphate; S2: 500 g of recovered lithium iron phosphate was dispersed in 1725 mL of ultrapure water and sheared and dispersed for 5 min. Subsequently, 2.5 g of glucose and 15 g of polyethylene glycol were added and sheared and dispersed for another 2 h to form a uniformly dispersed slurry. The slurry was transferred to a sand mill and ground at a linear speed of 20 m / s for 6 h. The grinding medium was zirconia balls with a particle size of 0.6 mm. After grinding, a mixed slurry was obtained. The median particle size of the mixed slurry was 200 nm. The mixed slurry was centrifuged and spray-dried, and the temperatures of the spray inlet and outlet were controlled at 240°C and 100°C, respectively, to obtain a precursor with a median particle size of 6 µm. S3: The precursor was calcined in a nitrogen atmosphere at a calcination temperature of 720 °C, a heating rate of 5 °C / min, and a calcination time of 10 h. After calcination, the precursor was cooled to room temperature and the product was passed through a 200-mesh sieve to obtain a carbon-coated lithium iron phosphate material.

[0053] Electrode preparation: Carbon-coated lithium iron phosphate material, acetylene black, PVDF, and NMP were weighed and mixed evenly in a mass ratio of 18:1:1:80, and coated on the electrode with a surface density of 625 g / m 2 After drying, a hot press was used for compression drying for 3 min at a pressure of 4 MPa and a temperature of 120 °C to obtain a lithium-poor lithium iron phosphate electrode.

[0054] Example 2 The charging voltage was adjusted to 3.4 V, and the other preparation methods were consistent with those in Example 1.

[0055] Example 3 The charging voltage was adjusted to 3.2 V, and the other preparation methods were consistent with those in Example 1.

[0056] Example 4 The amount of glucose added was adjusted to 10 g, and the other preparation methods were consistent with those in Example 3.

[0057] Example 5 The amount of glucose added was adjusted to 9 g, and the other preparation methods were consistent with those in Example 3.

[0058] Comparative Example 1 Preparation of lithium-rich lithium iron phosphate electrode: lithium iron phosphate, PVDF, acetylene black and NMP are weighed in a mass ratio of 18:1:1:80, mixed evenly, coated on the electrode, dried and hot-pressed into the electrode to obtain the lithium-rich lithium iron phosphate electrode; Electrochemical delithiation to produce lithium-poor lithium iron phosphate electrode process: The lithium-rich lithium iron phosphate electrode generated in the previous step and the empty electrode are connected to the positive and negative electrodes of the power supply respectively, immersed in a NaCl solution of a certain concentration, and a certain voltage is applied. After 8 to 24 hours, the current drops to close to 0 mA, the positive electrode is removed, and the lithium-poor lithium iron phosphate electrode is obtained after drying, and the Li content in the solution is detected.

[0059] Performance Testing Preparation of lithium-rich lithium iron phosphate electrode: lithium iron phosphate, PVDF, acetylene black and NMP are weighed in a mass ratio of 18:1:1:80, mixed evenly, coated on the electrode, dried and hot-pressed into the electrode to obtain the lithium-rich lithium iron phosphate electrode; Preparation of Ag electrode: Silver powder, carbon black, PVDF, and NMP were mixed in a mass ratio of 18:1:1:80 to form a uniform slurry, which was then coated on a titanium mesh and dried in an oven at 100°C for 6 h. The Ag electrode was then compressed and dried using a hot press for 3 min. Preparation of AgCl electrodes: One Ag electrode was used as the working electrode, another as the counter electrode, and SCE as the reference electrode. The three electrodes were immersed in a 0.1 M HCl solution and a constant potential of 0.3 V vs. SCE was applied for 4 h. After 3 h, the current dropped to zero, indicating that the Ag was completely converted to AgCl, thus obtaining an AgCl electrode. Lithium extraction process: In the decoupled membraneless (DCMF) cell used for lithium extraction, the cathode chamber (brine feed) and the anode chamber (extraction solution) are physically isolated from each other and electrochemically connected through a pair of working electrodes (FePO4 / LiFePO4) and redox electrodes (Ag / AgCl). A certain voltage is applied, and after a certain period of time, the electrodes are removed. The electrode materials are then switched and placed in the other cathode or anode chamber. The same voltage and time are applied to complete lithium extraction.

[0060] The test was repeated 20 times to detect the concentration of Li in the extract and brine. The Li adsorption capacity (mg(Li) / g(LiFePO4)) was calculated. The results of the electrochemical lithium extraction test are shown in Table 1.

[0061] Table 1 Lithium extraction test results of each embodiment and each comparative example

[0062] The test results of the embodiments and the comparative examples were analyzed. The comparative example used a conventional method to prepare a lithium-poor lithium iron phosphate electrode. In the initial Li adsorption capacity test results, the initial lithium Li adsorption performance of the comparative example was better than that of Examples 1 to 5. The initial Li adsorption capacity of Example 2 was approximately 70% of the initial Li adsorption capacity of the comparative example, and the initial Li adsorption capacity of Example 5 was approximately 83% of the initial Li adsorption capacity of the comparative example. The electrochemical deintercalation and lithium extraction method of the present application can achieve better lithium Li adsorption performance.

[0063] Comparing the Li adsorption capacity test results after 20 cycles, and analyzing the decrease in Li adsorption capacity of each embodiment and comparative example, the Li adsorption capacity of the electrode sheet of Example 1 after 20 cycles was approximately 70% of the initial adsorption capacity, the Li adsorption capacity of the electrode sheet of Example 5 after 20 cycles was approximately 27% of the initial adsorption capacity, and the Li adsorption capacity of the electrode sheet of Comparative Example 1 after 10 cycles decreased by approximately 51%. In summary, the lithium-poor lithium iron phosphate electrode of the present application can maintain good cycle performance, and its structural stability is superior to that of the lithium-poor lithium iron phosphate electrode prepared by existing conventional methods.

[0064] Analysis of the performance test results of Examples 1 to 3 shows that adjusting the charging voltage of the waste batteries has a certain impact on the adsorption capacity and cycle performance of the lithium-poor lithium iron phosphate electrode sheet. The ultimate Li adsorption and cycle adsorption performance are obtained when the charging voltage of the waste batteries is 3.2 V.

[0065] Analysis of the performance test results from Examples 3 to 5 shows that the adsorption performance of the lithium-poor lithium iron phosphate electrode sheet can be further improved by adjusting the amount of carbon source added. The optimal amount of glucose added is 9 g. Increasing the carbon content in carbon-coated lithium iron phosphate materials helps increase the conductivity of the lithium iron phosphate electrode and improves cycling stability. However, excessive carbon coating can hinder the migration of lithium ions.

[0066] The present application uses a simple preparation method to prepare a carbon-coated lithium iron phosphate material from waste recycled lithium iron phosphate batteries. The carbon-coated lithium iron phosphate material is suitable for preparing lithium-deficient lithium iron phosphate battery electrodes and is used for electrochemical deintercalation and lithium extraction technology. It has good Li adsorption performance and good cycle stability, extends the service life of the electrode sheet, and is economical and applicable.

[0067] The above describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and the specification merely illustrate the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. These changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon-coated lithium iron phosphate material, characterized in that: The method comprises the following preparation steps: S1: Processing of waste lithium iron phosphate batteries to obtain recycled lithium iron phosphate; S2: dispersing the recovered lithium iron phosphate, carbon source, and dispersant in a solvent to form a mixed slurry, separating and drying the mixed slurry to obtain a precursor; S3: calcining the precursor under an inert atmosphere to obtain the carbon-coated lithium iron phosphate material.

2. The method for preparing the carbon-coated lithium iron phosphate material according to claim 1, wherein: The carbon source is organic carbon with a carbon atom number not exceeding 13.

3. The method for preparing the carbon-coated lithium iron phosphate material according to claim 2, wherein: The carbon source is any one or more combinations of glucose, sucrose, maltose, glutamic acid and glycine.

4. The method for preparing the carbon-coated lithium iron phosphate material according to claim 1, wherein: The mass of the carbon source accounts for 0.5% to 2% of the mass of the recovered lithium iron phosphate.

5. The method for preparing the carbon-coated lithium iron phosphate material according to claim 1, wherein: The waste lithium iron phosphate battery is charged to 3-4 V and then disassembled, and the lithium iron phosphate positive electrode sheet is peeled off, crushed and acid-treated, and then calcined and sieved to obtain the recycled lithium iron phosphate.

6. The method for preparing the carbon-coated lithium iron phosphate material according to claim 5, wherein: The calcination temperature of the lithium iron phosphate positive electrode sheet is 500-700°C, and the calcination time is 4-6 hours; the calcination temperature of the precursor is 650-850°C, and the calcination time is 4-20 hours.

7. The method for preparing the carbon-coated lithium iron phosphate material according to claim 1, wherein: The mixed slurry is spray-dried after separation. The temperature of the spray drying feed port is 200-260°C, and the temperature of the spray drying discharge port is 70-110°C.

8. The method for preparing the carbon-coated lithium iron phosphate material according to claim 1, wherein: The median particle size of the mixed slurry is 0.3-0.5 μm, the median particle size of the carbon-wrapped lithium iron phosphate material is 2-12 μm, and the specific surface area is 4-20 m 2 / g, tap density is 0.5~1.5 g / cm 3 .

9. A carbon-coated lithium iron phosphate material, characterized in that: The raw materials for its preparation include waste lithium iron phosphate batteries, a carbon source, and a dispersant. The waste lithium iron phosphate batteries are processed to obtain recycled lithium iron phosphate, the mass of the carbon source accounts for 0.5% to 2% of the mass of the recycled lithium iron phosphate, and the carbon source is organic carbon with no more than 13 carbon atoms.

10. A lithium-poor lithium iron phosphate electrode, characterized in that: The preparation raw material includes the carbon-wrapped lithium iron phosphate material prepared by the preparation method according to any one of claims 1 to 8, or the carbon-wrapped lithium iron phosphate material according to claim 9.

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