A method for regenerating waste lithium iron phosphate by oxidation-reduction selective delithiation and closed-loop

Abstract

This invention belongs to the field of waste battery recycling technology and relates to a method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation. The method includes the following steps: placing waste lithium iron phosphate powder in a potassium ferricyanide solution for redox selective delithiation reaction; after the reaction, solid-liquid separation is performed to obtain a solid product and a lithium-containing filtrate; the obtained solid product is heat-treated to recover iron phosphate; the obtained lithium-containing filtrate is subjected to a lithium precipitation reaction to recover lithium carbonate; the recovered iron phosphate, lithium carbonate, and carbon source are mixed uniformly and sintered to obtain regenerated carbon-coated lithium iron phosphate. This invention's method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation does not require additional lithium or iron sources and is applicable to retired lithium iron phosphate cathode materials with different levels of failure.

Description

Technical Field

[0001] This invention belongs to the field of waste battery recycling technology, specifically relating to a method for closed-loop regeneration of waste lithium iron phosphate assisted by lithium extraction via oxidation-reduction. Background Technology

[0002] With countries worldwide actively developing new energy electric vehicles, the market demand for lithium-ion batteries (LIBs) has surged. Among them, lithium iron phosphate (LFP) batteries, which do not contain precious metals such as nickel and cobalt, are widely popular due to their stability and safety. However, LFP batteries have a limited lifespan of only 5-8 years. In particular, when the capacity of an LFP battery drops to 80%, it can no longer meet the operating requirements of electric vehicles. A large number of obsolete LFP batteries urgently need to be recycled. Therefore, considering both environmental and economic benefits, developing green, energy-saving, and efficient LFP battery recycling methods is imperative.

[0003] Currently, the most widely used methods for recycling lithium-ion batteries include pyrometallurgical, wet, and direct regeneration methods.

[0004] (a) Pyrometallurgical recycling follows the traditional pyrometallurgical method, which converts metal oxides in materials into alloys through high-temperature roasting. This method is complex and energy-intensive.

[0005] (ii) Wet recycling relies on acid leaching to extract metal elements from electrode materials and then obtains metal oxides or alloys through processes such as extraction, precipitation and separation. This method has become the mainstream technology for LFP battery recycling due to its advantages such as high multi-component recovery efficiency, high product purity and wide applicability. However, the inorganic or organic acids used in this process will cause irreversible corrosion to the recycling equipment and secondary pollution to the environment.

[0006] (III) Direct regeneration methods include two approaches to remediating lithium resources: solid-state regeneration and hydrothermal regeneration. The solid-phase method involves high-temperature sintering of waste lithium iron phosphate materials by adjusting the element ratio of waste materials or by mixing new materials with waste materials. However, due to the existence of the solid-solid interface, there is a problem of insufficient contact between S-LFP particles and the Li source.

[0007] The hydrothermal method improves cathode materials by replenishing the missing lithium ions in the waste cathode materials with lithium salt solutions, but the reaction time is long and requires low impurity content in the raw materials. In fact, the waste cathodes have been structurally damaged into different degradation levels. Simple external lithium compensation is not only difficult to accurately control the Li / Fe atomic ratio, but may also introduce impurities during the battery disassembly process. The electrochemical performance of the repaired LiFePO4 material is often worse than that of the raw material, requiring further modification.

[0008] These shortcomings pose challenges for its large-scale application in waste battery recycling. Therefore, there is a need to provide an improved technical solution that addresses the deficiencies of the existing technology. Summary of the Invention

[0009] This invention provides a method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation, which helps to solve or improve the problems of current mainstream lithium iron phosphate battery recycling methods, such as high energy consumption, complex processes and harsh conditions, easy equipment corrosion, high requirements for raw material consistency, and the need for precise lithium replenishment, which are not conducive to large-scale unified recycling of batteries with different levels of retirement, or the problem that the electrochemical performance of regenerated lithium iron phosphate cathode materials is limited by the fluctuation of the initial lithium content of raw materials.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation includes the following steps: S1, waste lithium iron phosphate powder is placed in potassium ferricyanide solution to carry out redox selective delithiation reaction; S2, after the reaction is complete, solid-liquid separation is performed to obtain a solid product and a lithium-containing filtrate; S3, the obtained solid product is converted and recovered as iron phosphate by heat treatment; S4, the lithium-containing filtrate is subjected to a lithium precipitation reaction to recover lithium carbonate; S5 involves uniformly mixing the recovered iron phosphate, lithium carbonate, and carbon source, followed by sintering to obtain recycled carbon-coated lithium iron phosphate.

[0011] In step S1, the optimized redox selective delithiation reaction parameters are: the concentration of the potassium ferricyanide solution is 0.006~0.18 mol / L, and the molar ratio of ferricyanide ions to lithium ions contained in waste lithium iron phosphate powder is (0.8~1.2):1.

[0012] In step S1, the optimized redox selective delithiation reaction conditions are as follows: waste lithium iron phosphate powder and potassium ferricyanide solution are ultrasonically dispersed in a closed environment for 1-2 min; the redox selective delithiation reaction temperature is 25-30℃ and the time is 5-50 min.

[0013] In step S3, the reaction conditions for obtaining ferric phosphate are optimized: the obtained solid product is first washed with deionized water, dried at 50~70℃ for 6~12h, and then heat-treated at 600~700℃ for 2~3h in a tube furnace under oxygen or air atmosphere.

[0014] In step S4, the reaction conditions for obtaining lithium carbonate are optimized: the lithium precipitation reaction is to add water-soluble carbonate to the lithium-containing filtrate, and the molar ratio of carbonate ions to lithium ions in the water-soluble carbonate is (1.05~1.25):2.

[0015] In step S5, the carbon source includes at least one of glucose, sucrose, starch, citric acid, and ascorbic acid.

[0016] Furthermore, in step S5, the molar ratio of the recovered iron phosphate, lithium carbonate and carbon source is 2:1.03:(0.175~0.35).

[0017] Furthermore, in step S5, the sintering includes a first-stage calcination and a second-stage calcination; the first-stage calcination is carried out at a temperature of 350°C for 5 hours; the second-stage calcination is carried out at a temperature of 650~750°C for 6~10 hours.

[0018] The beneficial effects of this invention are: 1. This invention uses potassium ferricyanide solution for redox reaction, which can selectively extract lithium from waste lithium iron phosphate in a short time, instead of using various strong acids and alkalis for leaching. The delithiation reaction conditions of this invention are mild and do not cause pollution. The lithium-containing filtrate and iron phosphate residue obtained after the reaction can be simply processed to obtain high-purity lithium carbonate and iron phosphate. The resynthesized lithium iron phosphate cathode material has excellent performance. This closed-loop regeneration method avoids dependence on external commercial lithium and iron sources. It only needs to use retired lithium iron phosphate cathode material to prepare regenerated materials with electrochemical performance comparable to commercial lithium iron phosphate batteries. In addition, this invention is applicable to retired lithium iron phosphate cathode materials with different degrees of failure, without the need to adjust the waste element ratio or external lithium compensation, and has good versatility.

[0019] 2. The lithium carbonate and iron phosphate obtained by this invention have high purity and can be directly used to combine with the existing lithium iron phosphate cathode material generation process. The carbon-coated lithium iron phosphate cathode material prepared has a more stable chemical structure and better electrochemical performance compared with some current direct recycled materials. It also avoids the structural inhomogeneity and poor performance caused by insufficient or excessive local lithium replenishment. The generated lithium iron phosphate cathode material has good rate performance.

[0020] 3. By controlling the concentration of potassium ferricyanide solution, as well as temperature and time, during the redox selective delithiation process, this invention can achieve complete delithiation of waste lithium iron phosphate cathode materials while ensuring that the original crystal phase structure of the lithium iron phosphate cathode materials is not destroyed, thereby ensuring that the regenerated lithium iron phosphate cathode materials have excellent electrochemical performance. Attached Figure Description

[0021] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1This is a schematic diagram of the redox reaction principle for selectively separating lithium ions in this invention; Figure 2 This refers to the lithium removal rate of redox selective delithiation as a function of reaction time in this invention. Figure 3 The XRD pattern of lithium carbonate after repeated filtration and washing is provided in Example 9 of the present invention; Figure 4 XRD patterns are shown; where the S-LFP curve is the XRD pattern of the decommissioned lithium iron phosphate cathode material used in step (1) of Example 9, and the R-LFP curve is the XRD pattern of the regenerated carbon-coated lithium iron phosphate obtained by the method of Example 9. Figure 5 The rate performance diagram of the recycled lithium iron phosphate material provided in Example 9 of the present invention is shown; wherein the corresponding rate is 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 0.1C. Figure 6 The initial charge-discharge curve of lithium iron phosphate provided in Example 9 of the present invention; Figure 7 The chart shows the rate performance comparison of the recycled lithium iron phosphate materials corresponding to Examples 3, 8, and 9 of this invention; where the corresponding rates are 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 0.1C. Figure 8 This is a comparative schematic diagram of the initial charge and discharge curves of lithium iron phosphate corresponding to Embodiments 3, 8, and 9 of the present invention.

[0022] Figure 9 The image shows the XRD pattern of recycled carbon-coated lithium iron phosphate obtained in Example 14 of this invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0024] The core of this invention, a method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation, lies in utilizing redox reactions to achieve selective and efficient leaching of lithium ions. This principle involves selecting a potential-matched oxidant that specifically acts on the ferrous iron in the lithium iron phosphate crystal lattice, promoting the extraction of target lithium ions under charge balance while maximizing the integrity of the phosphorus-iron backbone. This effectively avoids lattice collapse and element co-solution problems caused by strong acids or strong oxidants. As an advanced "decomposition-resynthesis" closed-loop regeneration strategy, this method, combined with hydrometallurgy and materials regeneration technologies, can achieve selective extraction and full-component closed-loop recovery of lithium from complex waste materials.

[0025] like Figure 1 As shown, the reaction principle involved in the implementation of this invention is further explained: Decommissioned lithium iron phosphate cathode material with abundant lithium vacancies is mixed with a potassium ferricyanide solution and reacted under controlled temperature and pH conditions. Potassium ferricyanide acts as an oxidant, reacting with the ferrous iron in the lithium iron phosphate via a redox reaction, causing lithium ions to selectively leach from the crystal lattice into the solution. After the reaction, solid-liquid separation is performed to obtain a lithium-ion-rich leachate and a precipitate containing the iron phosphate precursor. This leachate can be used for further purification to prepare lithium salts, such as lithium carbonate. This method is particularly suitable for the large-scale resource recovery of multi-source mixed waste lithium iron phosphate materials with complex compositions and varying degrees of failure, providing an efficient and precise solution for the closed-loop recycling of power batteries.

[0026] A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation includes the following steps: S1, pulverizing retired lithium iron phosphate cathode material (i.e., crushing retired lithium iron phosphate cathode material to form waste lithium iron phosphate powder) and placing it in potassium ferricyanide solution (preferably, the waste lithium iron phosphate powder and potassium ferricyanide solution can be ultrasonically dispersed in a closed environment) to carry out redox selective delithiation reaction; S2, after the reaction is completed, solid-liquid separation is performed (for example, solid-liquid separation can be achieved by filtering the suspension obtained from the reaction) to obtain a solid product and a lithium-containing filtrate; S3, the collected solid product (preferably, the solid product is washed with deionized water, dried and then heat-treated) is heat-treated to obtain iron phosphate; S4, the collected lithium-containing filtrate is subjected to a lithium precipitation reaction to recover lithium carbonate (preferably, the solid obtained after the lithium precipitation reaction is washed and dried) to obtain lithium carbonate; S5, the recovered lithium carbonate, iron phosphate and carbon source are mixed evenly and sintered to obtain regenerated carbon-coated lithium iron phosphate.

[0027] In a preferred embodiment of the present invention, the concentration of the potassium ferricyanide solution is 0.006~0.18 mol / L (0.006 mol / L, 0.008 mol / L, 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.13 mol / L, 0.15 mol / L, or 0.18 mol / L); wherein the molar ratio of ferricyanide ions to lithium ions contained in the waste lithium iron phosphate powder is (0.8~1.2):1 (e.g., 0.8:1, 0.9:1, 1.1:1, or 1.2:1); then the solid-liquid ratio of the waste lithium iron phosphate powder to the potassium ferricyanide solution is 1~30 g / L (e.g., 1 g / L, 10 g / L, 20 g / L, 30 g / L). The number of moles of lithium ions is calculated based on the amount of lithium contained in the decommissioned lithium iron phosphate cathode material (for example, the lithium content in the decommissioned lithium iron phosphate cathode material can be tested by ICP digestion treatment, and then the number of moles of lithium can be calculated).

[0028] In a preferred embodiment of the present invention, in step S1, the waste lithium iron phosphate powder and potassium ferricyanide solution are first ultrasonically dispersed in a closed environment for 1-2 minutes; then reacted at 25-30°C for 5-50 minutes (e.g., 20 minutes, 30 minutes, 40 minutes, 50 minutes).

[0029] In a preferred embodiment of the present invention, in step S3, the drying temperature is 50~70℃ (e.g., 50℃, 60℃, 70℃), and the drying time is 6~12h (e.g., 6h, 7h, 8h, 9h, 12h); then, the product is heat-treated in a tube furnace at 600~700℃ (e.g., 600℃, 620℃, 640℃, 660℃, 680℃ or 700℃) in an oxygen or air atmosphere for 2~3h (e.g., 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h).

[0030] When the heat treatment temperature is below 600℃, the small amount of carbon and organic impurities remaining in the filter residue (such as complexing agents and binders introduced during the delithiation process) cannot be completely decomposed, forming carbon / organic residual impurities in the iron phosphate. During subsequent synthesis of lithium iron phosphate, these residual impurities will hinder the insertion / extraction of Li⁺, leading to a decrease in cycle stability. When the heat treatment temperature is above 700℃, iron phosphate undergoes a crystal transformation, resulting in particle sintering and agglomeration. This step does not necessarily have to be carried out in an oxygen atmosphere, but oxygen or air atmospheres are preferred because inert atmospheres cannot effectively decompose impurities, and reducing atmospheres will reduce iron phosphate to low-valent iron compounds such as Fe₃O₄.

[0031] In a preferred embodiment of the present invention, in step S4, the lithium precipitation reaction involves adding a water-soluble carbonate to the lithium-containing filtrate, wherein the molar ratio of carbonate ions to lithium ions in the water-soluble carbonate is (1.05~1.25):2 (e.g., 1.05:2, 1.1:2, 1.15:2, 1.2:2 or 1.25:2).

[0032] In a preferred embodiment of the present invention, in step S5, the carbon source is at least one of glucose, sucrose, starch, citric acid, and ascorbic acid.

[0033] In a preferred embodiment of the present invention, in step S5, the molar ratio of the recovered iron phosphate, lithium carbonate and carbon source is 2:1.03:(0.175~0.35) (for example, 2:1.03:0.175, 2:1.03:0.2, 2:1.03:0.25, 2:1.03:0.3 or 2:1.03:0.35).

[0034] In a preferred embodiment of the present invention, sintering includes a first-stage calcination and a second-stage calcination; the first-stage calcination is carried out at a temperature of 350°C for 5 hours; the second-stage calcination is carried out at a temperature of 650~750°C (e.g., 650°C, 680°C, 700°C, 720°C, or 750°C) for 6~10 hours (e.g., 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours); this is to first gently form a carbon network, and then perfect the crystal at a high temperature, avoiding the instantaneous decomposition of the carbon source at high temperature, which would lead to uneven coating or the generation of harmful gases.

[0035] The first stage is low-temperature calcination at 350℃: At this temperature, the carbon source undergoes mild and controllable pyrolysis and carbonization, forming a uniform and continuous initial carbon precursor layer on the surface of the iron phosphate particles. The second stage is high-temperature calcination at 650~750℃: Based on the formed uniform carbon precursor, this temperature range is the optimal range for the formation and growth of the lithium iron phosphate olivine crystal structure. Prolonged heat preservation ensures sufficient diffusion and reaction of lithium, iron, and phosphorus elements, generating a highly crystalline lithium iron phosphate core with a complete crystal structure. Simultaneously, the pre-formed carbon layer further graphitizes at this high temperature, forming a highly conductive network and effectively inhibiting the agglomeration and excessive growth of LiFePO4 particles at high temperatures.

[0036] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0037] In the following embodiments, all raw materials, reagents, or devices used, unless otherwise specified, are available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the methods used for testing or evaluation are conventional methods in the art.

[0038] The following detailed embodiments illustrate the method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation of the present invention. Before implementing this method, the retired lithium iron phosphate cathode material needs to be pulverized to form waste lithium iron phosphate powder. Samples are then taken and tested for lithium content in the waste lithium iron phosphate cathode material through ICP digestion. The following standardized procedures must be followed: 1. Sample pretreatment Weigh: Accurately weigh 0.1g of waste lithium iron phosphate cathode material (accurate to 0.0001g).

[0039] Digestion: Place the sample in a microwave digestion vessel, add a small amount of water to moisten it, then add 0.8–1.0 g of NaOH, and microwave at 750–800 W for 5 min. After cooling, remove the sample and extract the dissolved solids with a hot hydrochloric acid solution (50–60 °C), then wash with a cold hydrochloric acid solution and transfer to a 100 mL volumetric flask, and dilute to the mark.

[0040] 2. Preparation of standard solutions Stock solution: Dilute the Li, P, and Fe standard solutions (1000 μg / mL) with reagent blank solution to prepare a standard stock solution of 100 μg / mL.

[0041] Mixed standard solution: Pipette 10 mL of reagent blank solution into five 10.0 mL volumetric flasks, and add standard stock solution at the following concentrations: Li: 2.00, 4.00, 6.00, 8.00, 10.00μg / mL.

[0042] Fe: 20.00, 25.00, 30.00, 35.00, 40.00μg / mL.

[0043] P: 6.00, 12.00, 18.00, 24.00, 30.00μg / mL.

[0044] 3. ICP-OES determination Instrument parameters: High-frequency power 1.1kW, nebulizer flow rate 0.8L / min, analytical spectral lines: Li: 610.365 nm - axial.

[0045] Fe: 259.940 nm - radial / 12 mm.

[0046] P: 178.222 nm - axial, 213.618 nm - radial / 12 mm.

[0047] Determination: The digested test solution was brought to a final volume of 100 mL, diluted at a ratio of 10:100, and the contents of Li, Fe, and P were determined.

[0048] 4. Data Processing Calibration curve: Standard solutions were prepared using the matrix matching method to eliminate solvent matrix effects.

[0049] Calculation: Based on the strength values ​​of the sample and the standard solution, the computer plots the working curve and calculates the mass fraction of lithium.

[0050] The above methods yielded the following results: by mass fraction, the lithium content in Sample 1 was 4.17%, in Sample 2 was 4.18%, and in Sample 3 was 4.15%. All subsequent examples used waste lithium iron phosphate powder from Sample 1 with a lithium content of 4.17%.

[0051] Example 1 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse the waste lithium iron phosphate powder in a 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0052] The amount of 0.03 mol / L potassium ferricyanide solution used was 10 mL, and the mass of waste lithium iron phosphate powder added was 0.05 g. The solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution was calculated to be 5 g / L by setting the molar ratio of ferricyanide ions to lithium ions to be 1:1.

[0053] The lithium leaching rate was 97.01% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0054] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0055] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0056] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0057] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with glucose in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0058] Example 2 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.033 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0059] The amount of 0.033 mol / L potassium ferricyanide solution used was 10 mL, and the mass of waste lithium iron phosphate powder added was 0.05 g. The solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution was calculated to be 5 g / L by setting the molar ratio of ferricyanide ions to lithium ions to be 1.1:1.

[0060] The lithium leaching rate was 97.26% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0061] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0062] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0063] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0064] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Calcinate the mixture at 350℃ for 5 hours under an argon atmosphere, and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0065] Example 3 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.036 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0066] The amount of 0.036 mol / L potassium ferricyanide solution used was 10 mL, and the mass of waste lithium iron phosphate powder added was 0.05 g. The solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution was calculated to be 5 g / L by setting the molar ratio of ferricyanide ions to lithium ions to be 1.2:1.

[0067] The lithium leaching rate was 98.54% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0068] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0069] Step 3: The solid precipitate obtained in step 2 is washed and placed in a vacuum oven to dry at 60°C for 12 hours. Then, it is heat-treated in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4). Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0070] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0071] Example 4 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.024 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0072] The amount of 0.024 mol / L potassium ferricyanide solution used was 10 mL, and the mass of waste lithium iron phosphate powder added was 0.05 g. The solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution was calculated to be 5 g / L by setting the molar ratio of ferricyanide ions to lithium ions to be 0.8:1.

[0073] The lithium leaching rate was 79% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0074] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0075] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0076] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0077] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0078] Example 5 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.027 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0079] The amount of 0.027mol / L potassium ferricyanide solution used was 10mL, and the mass of waste lithium iron phosphate powder added was 0.05g. The solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution was calculated to be 5g / L by setting the molar ratio of ferricyanide ions to lithium ions to be 0.9:1.

[0080] The lithium leaching rate was 88.5% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0081] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0082] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0083] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0084] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Calcinate the mixture at 350℃ for 5 hours under an argon atmosphere, and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0085] Example 6 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse the waste lithium iron phosphate powder in a 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 5 min at 25℃.

[0086] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0087] The lithium leaching rate was 61.26% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0088] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0089] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0090] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0091] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0092] Example 7 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse the waste lithium iron phosphate powder in a 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 15 min at 25℃.

[0093] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0094] The lithium leaching rate was 75.40% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0095] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0096] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0097] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0098] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0099] Example 8 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse the waste lithium iron phosphate powder in a 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 40 min at 25℃.

[0100] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0101] The lithium leaching rate was 99.85% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0102] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0103] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0104] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0105] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0106] Example 9 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0107] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0108] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0109] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0110] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0111] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0112] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0113] Example 10 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse the waste lithium iron phosphate powder in a 0.06 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0114] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 10 g / L.

[0115] The lithium leaching rate was 79.78% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0116] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0117] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0118] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0119] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0120] Example 11 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.12 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0121] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 20 g / L.

[0122] The lithium leaching rate was 86.92% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0123] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0124] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0125] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0126] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, first calcine at 350℃ for 5 hours, and then calcine at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0127] Example 12 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.18 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0128] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 30 g / L.

[0129] The lithium leaching rate was 67.77% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0130] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0131] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0132] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0133] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0134] Example 13 The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation in this embodiment includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.006 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 30 min at 25℃.

[0135] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 1 g / L.

[0136] The lithium leaching rate was 79.27% ​​as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0137] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0138] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0139] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0140] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the recycled LiFePO4 / C material.

[0141] Example 14 The steps are exactly the same as in Example 9, except that in step 5 the carbon source is replaced with sucrose in an equimolar proportion; the rest are the same as in Example 9.

[0142] Example 15 The steps are exactly the same as in Example 9, except in the fourth step: the water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in the second step are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.125:2.

[0143] Example 16 The steps are exactly the same as in Example 9, except in the fourth step: the water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in the second step are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.25:2.

[0144] Example 17 The steps are exactly the same as in Example 9, except for the third step: the solid precipitate obtained in the second step is washed and placed in a vacuum oven to dry at 60°C for 12 hours, and then heat-treated in a tube furnace at 600°C for 2 hours in an oxygen atmosphere to obtain iron phosphate (FePO4). The subsequent steps are also exactly the same.

[0145] Example 18 The steps are exactly the same as in Example 9, except in the fifth step: FePO4 and Li2CO3 obtained in the above steps are mixed and ground with a carbon source (glucose) in a molar ratio of 2:1.03:0.175, and calcined at 350°C for 5 hours under an argon atmosphere, and then calcined at 700°C for 10 hours.

[0146] Example 19 The steps are exactly the same as in Example 9, except in the fifth step: FePO4 and Li2CO3 obtained in the above steps are mixed and ground with a carbon source (glucose) in a molar ratio of 2:1.03:0.35, and calcined at 350°C for 5 hours under an argon atmosphere, and then calcined at 650°C for 10 hours.

[0147] Example 20 The steps are exactly the same as in Example 9, except in the fifth step: FePO4 and Li2CO3 obtained in the above steps are mixed and ground with a carbon source (glucose) in a molar ratio of 2:1.03:0.35, and calcined at 350°C for 5 hours under an argon atmosphere, and then calcined at 750°C for 10 hours.

[0148] Comparative Example 1 The comparative method for closed-loop regeneration of waste lithium iron phosphate phosphate assisted by redox selective delithiation includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0149] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0150] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0151] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0152] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours to obtain iron phosphate (FePO4).

[0153] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0154] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35. Then, calcine the mixture at 350℃ for 5 hours and at 700℃ for 10 hours under an argon atmosphere.

[0155] Following the steps described above, the target product LiFePO4 / C is obtained.

[0156] The only difference between this comparative example and Example 9 is that the solid precipitate obtained in the third step was not heat-treated in a tube furnace after drying; otherwise, it is consistent with Example 9.

[0157] Comparative Example 2 The comparative method for closed-loop regeneration of waste lithium iron phosphate phosphate assisted by redox selective delithiation includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0158] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0159] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0160] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0161] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours under an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0162] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0163] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.17. Under an argon atmosphere, calcine at 350℃ for 5 hours and then at 700℃ for 10 hours to obtain the target product LiFePO4 / C.

[0164] The difference between this comparative example and Example 9 is that in the fifth step, when synthesizing lithium iron phosphate, the total amount of glucose is reduced, which leads to a reduction in the amount of amorphous carbon formed after its pyrolysis, which is insufficient to uniformly and completely coat all particles.

[0165] Comparative Example 3 The comparative method for closed-loop regeneration of waste lithium iron phosphate phosphate assisted by redox selective delithiation includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0166] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0167] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0168] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0169] The difference between this comparative example and Example 9 is that in the third step, the solid precipitate obtained in the second step is washed and placed in a vacuum oven to dry at 60°C for 12 hours, and then heat-treated in a tube furnace at 550°C for 2 hours in an oxygen atmosphere to obtain a solid product.

[0170] When the heat treatment temperature is below 600℃, the resulting solid is yellow or brown in color, which deviates from the color of commercial ferric phosphate, indicating that organic impurities remain or the crystals are incomplete and the purity is insufficient.

[0171] Comparative Example 4 The comparative method for closed-loop regeneration of waste lithium iron phosphate phosphate assisted by redox selective delithiation includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0172] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0173] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0174] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0175] The difference between this comparative example and Example 9 is that in the third step, the solid precipitate obtained in the second step is washed and placed in a vacuum oven to dry at 60°C for 12 hours, and then heat-treated in a tube furnace at 750°C for 2 hours in an oxygen atmosphere to obtain a solid product.

[0176] When the heat treatment temperature is too high (above 700℃), the product turns reddish-brown, indicating that thermal decomposition has occurred, generating impurities such as iron oxide (Fe2O3). This means that the iron source is no longer pure, and the stoichiometry has deviated from FePO4.

[0177] Comparative Example 5 The comparative method for closed-loop regeneration of waste lithium iron phosphate phosphate assisted by redox selective delithiation includes the following steps: Step 1: Disperse waste lithium iron phosphate powder in 0.03 mol / L potassium ferricyanide solution, ultrasonically disperse for 1-2 min, and react for 50 min at 25℃.

[0178] The molar ratio of ferricyanide ions to lithium ions is 1:1, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution is 5 g / L.

[0179] The lithium leaching rate was 100% as determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Avio-200 instrument.

[0180] Step 2: Separate the reactants from Step 1 into solid and liquid phases to obtain a solid precipitate and a lithium-containing filtrate.

[0181] Step 3: After washing the solid precipitate obtained in step 2, place it in a vacuum oven and dry it at 60°C for 12 hours. Then, heat-treat it in a tube furnace at 700°C for 2 hours in an oxygen atmosphere to obtain high-purity iron phosphate (FePO4).

[0182] Step 4: The water-soluble carbonate (Na2CO3) and the lithium-containing filtrate obtained in Step 2 are subjected to a lithium precipitation reaction at a carbonate to lithium ion molar ratio of 1.05:2. Then, solid-liquid separation is performed to obtain a white solid powder, which is then washed and dried in a vacuum oven to obtain lithium carbonate (Li2CO3).

[0183] Step 5: Mix and grind the FePO4 and Li2CO3 obtained in the above steps with the carbon source (glucose) in a molar ratio of 2:1.03:0.35, and calcine at 700℃ for 10h under an argon atmosphere.

[0184] Following the steps described above, the target product LiFePO4 / C is obtained.

[0185] The difference between this comparative example and Example 9 is that in the fifth step, when synthesizing lithium iron phosphate, a single sintering process is used, that is, calcination at 700°C for 10 hours under an argon atmosphere.

[0186] Experimental Example 1. Based on the data from Examples 1-13, the comparative results of redox-selective delithiation reactions are summarized in the table below: Table 1. Conditions and test results for different embodiments

[0187] Analyze the data in the table: Examples 1-5 were conducted to investigate the effects of the molar ratio of ferricyanide ions to lithium ions and the concentration of potassium ferricyanide as the oxidant on the degree of delithiation. It was observed that Example 3 exhibited the highest degree of delithiation, indicating that a slightly excess of oxidant (molar ratio > 1:1) is beneficial for promoting a more complete delithiation reaction. This is because in actual reaction systems, additional oxidant is needed to compensate for potential side reactions, ensure sufficient reaction kinetics, and overcome the mass transfer resistance at the solid-liquid interface. At similar molar ratios, in Examples 1, 2, and 3, the delithiation rate increased with increasing potassium ferricyanide solution concentration. This demonstrates that, at a given solid-liquid ratio, increasing the reactant concentration helps to improve the reaction rate and final conversion rate. By precisely controlling the molar ratio of oxidant to lithium ions within a range slightly above stoichiometry and matching an appropriate solution concentration, highly selective and efficient extraction of lithium from waste lithium iron phosphate can be achieved under mild conditions.

[0188] Examples 6-9 were conducted to study the effect of delithiation time on the degree of delithiation. It can be seen that the longer the delithiation reaction time, the better the delithiation effect. Furthermore, Examples 8 and 9 show that a delithiation reaction time of 40 minutes or more can completely remove lithium from the waste lithium iron phosphate powder. Based on the conditions set in Examples 6-9, corresponding to delithiation reaction times of 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 40 min, and 50 min, the degree of delithiation was measured and plotted as a bar chart, as shown below. Figure 2 As shown, the same conclusion can be drawn: the longer the delithiation reaction time, the better the delithiation effect.

[0189] Examples 10-13 were designed to investigate the effect of the solid-liquid ratio on the degree of delithiation. It can be seen that under fixed oxidant / lithium molar ratios (1:1) and reaction times (30 minutes), as the concentration of potassium ferricyanide solution increased from 0.006 mol / L to 0.18 mol / L, and the solid-liquid ratio of waste lithium iron phosphate powder to potassium ferricyanide solution increased from 1 g / L to 30 g / L, the delithiation rate exhibited a non-monotonic change, initially slightly improving and then significantly decreasing. In Examples 10 and 11, appropriately increasing the solid content and concentration improved the reaction driving force without severely deteriorating mass transfer, thus increasing the delithiation rate. In Example 12, although the oxidant concentration was the highest, the excessively high solid-liquid ratio led to an overly viscous slurry, reducing the solid-liquid interface and drastically increasing ion diffusion and mass transfer resistance, becoming the dominant factor limiting the reaction rate and severely reducing the delithiation efficiency. The delithiation rate in Example 13 was 79.27%. At this point, the system was thin, and the mass transfer conditions were good, but the reactant concentration was too low, resulting in insufficient reaction driving force and limiting the delithiation efficiency. The results show that neither excessively thin nor excessively thick slurry is conducive to the delithiation reaction, and the optimal solid-liquid ratio range (e.g., 5~20 g / L) is a prerequisite for achieving high-efficiency, low-energy delithiation.

[0190] The above examples contain many examples of low lithium extraction rates, i.e., low delithiation values. These low delithiation rate cases are for exploring the optimal reaction conditions. A low delithiation rate means that undelithiated lithium iron phosphate (impure phase) remains in the iron phosphate filter residue, and the lithium recovery in the lithium-containing filtrate is insufficient. Ultimately, the Li / Fe / P atomic ratio of the regenerated lithium iron phosphate is unbalanced, and impure phases are present, resulting in poor electrochemical performance. Therefore, XRD characterization and electrochemical testing of the regenerated lithium iron phosphate were not performed in Examples 1, 2, 4, 5, 6, 7, 10, 11, 12, and 13.

[0191] 2. Electrochemical tests were conducted on examples with complete delithiation, namely Examples 3, 8, 9, 14-20, Comparative Examples 1-2, and Comparative Example 5.

[0192] The electrochemical testing method is as follows: the obtained closed-loop regenerated cathode material is assembled with lithium sheet into a half cell, and after standing for 24 hours, it is placed on the Xinwei BTSDA test channel for electrochemical performance testing. The charge-discharge rate is 0.1C. The obtained data is the data directly displayed on the Xinwei tester and can be directly taken.

[0193] The electrochemical test results are shown in the table below: Table 2 Electrochemical test results

[0194] Based on the data analysis in Tables 1 and 2, we can conclude that: The typical discharge specific capacity range of commercial-grade lithium iron phosphate (LFP) cathode materials is 140–160 mAh / g (0.1C, 2.5–4.0V). The recycled materials of this invention, particularly Examples 8 and 9, have reached and entered the performance range of commercial materials. Compared with mainstream recycling technologies, the capacity of LFP materials recycled and resynthesized by traditional wet recycling methods is generally 130–145 mAh / g, and the process is complex. Direct regeneration methods often result in capacities below 135 mAh / g due to uneven lithium replenishment. This invention achieves its performance through closed-loop resynthesis after mild and selective delithiation. The capacity of recycled retired LFP cathode materials has typically decayed to below 80%, i.e., 100–128 mAh / g. This invention regenerates them to a capacity recovery rate exceeding 110%, achieving the goal of "reuse".

[0195] In this invention, a sufficient and matched amount of oxidant (ferricyanide ion to lithium ion molar ratio of 1.1~1.2:1) and adequate reaction time (≥30 minutes, preferably 40~50 minutes) ensure highly selective and efficient extraction of lithium ions from the LFP lattice, while maximizing the preservation of the integrity of the phosphorus-iron framework. The high-temperature purification of the precursor (S3 step) and the optimized resynthesis process completely avoid the possibility of organic residues introduced during the delithiation process, enabling the purification of FePO4 crystals and ensuring the uniformity of carbon coating and the perfect reconstruction of the LiFePO4 crystal structure.

[0196] In this invention, the completeness of delithiation is crucial in determining the upper limit of the performance of the recycled material: even with a delithiation rate of 98.54% (Example 3), the final capacity still falls short of that of completely delithiated material (Example 9). This indicates that even trace amounts of residual lithium or stoichiometric deviations can be amplified in subsequent synthesis, affecting the integrity of the crystal structure and lithium-ion transport channels. The process of this invention possesses the capability to achieve "complete delithiation," as demonstrated in Example 9 where 100% delithiation was achieved, yielding an exceptional capacity of up to 151.6 mAh / g. This strongly proves the advantage of this redox-selective delithiation method in terms of extraction thoroughness.

[0197] Example 14 illustrates that even with equimolar substitution of different carbon sources, the electrochemical performance of recycled carbon-coated lithium iron phosphate remains good. Examples 9, 15, and 16 demonstrate that the test results of examples with a carbonate ion to lithium ion molar ratio of (1.05~1.25):2 all exhibit good electrochemical performance. Examples 9 and 17 demonstrate that the test results of examples meeting the requirements of step S3, such as drying at 50~70℃ for 6~12h followed by heat treatment at 600~700℃ for 2~3h in an oxygen or air atmosphere in a tube furnace, all yield high-purity FePO4 precursors, thus enabling the synthesis of high-performance recycled materials. Examples 18 and 9 verify that using FePO4 and Li2CO3 with carbon sources at a molar ratio of 2:1.03:(0.175~0.35), the recycled LiFePO4 / C exhibits good electrochemical performance. The results of Examples 9, 19, and 20 show that a complete olivine structure can be formed in the two-stage calcination temperature range of 650~750℃, with 700℃ being the optimal temperature. At 650℃ and 750℃, the capacity decreases slightly, but is still significantly better than the comparative example.

[0198] In Comparative Example 1, the tube furnace heat treatment step was omitted after drying, which sacrificed the purity and crystallinity of the precursor iron phosphate. This resulted in a severe deterioration in the electrochemical performance of the regenerated LiFePO4 / C material. The impurity of iron phosphate led to impurities in the regenerated lithium iron phosphate, resulting in low capacity and reduced coulombic efficiency.

[0199] The reduced total amount of glucose in Comparative Example 2 resulted in a decrease in the amount of amorphous carbon formed after pyrolysis, which was insufficient to uniformly and completely coat all particles, potentially leading to a significant decrease in electronic conductivity. The carbon coating layer is the main channel for electron transport between LiFePO4 particles; a deterioration in the quality of the carbon layer will severely hinder electron conduction. A slight deficiency in the carbon source leads to a lower capacity, incomplete utilization of active materials, and slowed reaction kinetics due to impaired electron conduction.

[0200] Comparative Examples 3 and 4 could not be tested for electrochemical performance. This also shows that even if the product was heat-treated in a tube furnace for 2 hours after drying, the solid color was yellow or brown when the heat treatment temperature was below 600℃ (Comparative Example 3); and reddish-brown when the heat treatment temperature was above 700℃ (Comparative Example 4). This indicates that the heat treatment temperature was not within the range of 600℃~700℃, and the purity of the product could not be guaranteed.

[0201] Comparative Example 5 used a single sintering process, resulting in a 10%–20% reduction in capacity and poor cycle stability. This indicates that a segmented calcination process can generally achieve more uniform particles and higher capacity.

[0202] 3. XRD test: The products of Examples 3, 8, and 9 all showed a high degree of consistency in XRD analysis results, with lithium carbonate being the standard phase in all cases. The regenerated lithium iron phosphate from Examples 3, 8, and 9 all exhibited a perfect olivine-type structure. Therefore, only the results obtained in Example 9 are presented below.

[0203] In Example 9, the lithium carbonate was repeatedly filtered and washed, and then measured using an X-ray diffractometer to obtain the following results: Figure 3 The XRD pattern of lithium carbonate shown is as follows; Figure 3 It can be seen that the high purity of lithium carbonate shows that the positions and relative intensities of all characteristic diffraction peaks are completely consistent with the spectrum of standard lithium carbonate. The spectrum baseline is stable, and the diffraction peaks are sharp and symmetrical, indicating that the obtained lithium carbonate has high crystallinity and is of high phase purity. In addition, Figure 4 In the figure, the S-LFP curve is the XRD pattern of the decommissioned lithium iron phosphate cathode material used in step (1) of Example 9. The material before delithiation is mainly represented by the diffraction peaks of lithium iron phosphate and iron phosphate (S-LFP curve in the figure); the R-LFP curve is the XRD pattern of the regenerated carbon-coated lithium iron phosphate obtained by the method of Example 9. The diffraction peaks of the R-LFP curve are completely matched with the characteristic peaks of the lithium iron phosphate standard card (PDF#83-2092). There are no impurity phase peaks, the peaks are sharp and the intensity is high, indicating that it has a complete olivine crystal structure and high crystallinity.

[0204] Figure 9The XRD pattern of the recycled carbon-coated lithium iron phosphate obtained in Example 14 shows that it has an olivine-type crystal structure. This indicates that using sucrose as an organic carbon source can also achieve effective regeneration of waste lithium iron phosphate.

[0205] 4. Ratio Performance Test: In Example 9, recycled carbon-coated lithium iron phosphate material was used as the active material, and was uniformly mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) binder at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was uniformly coated onto an aluminum foil current collector, and after drying, rolling, and stamping, a positive electrode sheet was formed. In an argon-filled glove box (H2O, O2 < 0.1ppm), a CR2032 type button half-cell was assembled using a lithium metal sheet as the negative electrode, Celgard 2400 as the separator, and a 1 mol / L LiPF6 EC / DMC (volume ratio 1:1) solution as the electrolyte. After the assembled half-cell was left to stand at room temperature for 24 hours, it was placed on the Xinwei BTSDA battery testing system channel for rate performance testing. The test voltage range was set to 2.5V~4.0V (vs. Li + / Li). The specific test procedure is as follows: First, activation is performed by constant current charge-discharge cycles of 5 times at a rate of 0.1C. Then, constant current charge-discharge tests are performed 5 times each at increasing rates of 0.2C, 0.5C, 1C, 2C, and 5C. Finally, the test is performed again at a rate of 0.1C for 5 cycles. Figure 5 The rate performance diagram of the recycled carbon-coated lithium iron phosphate material provided in Example 9 is shown; where the corresponding rates are 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 0.1C; as can be seen from the figure, the recycled carbon-coated lithium iron phosphate material exhibits excellent rate performance and structural stability. At lower rates of 0.1C and 0.2C, the material releases almost all of its reversible capacity, with a flat discharge plateau and low voltage polarization. As the rate increases to 1C and 2C, the discharge capacity retention remains high (typically above 90% of the 0.1C discharge capacity), and the discharge plateau shows a moderate decrease, indicating a fast diffusion rate of lithium ions in the bulk phase and electrode interior, and low polarization resistance. Even at extremely high rates of 5C, the material can still release considerable reversible capacity. Most importantly, when the rate is switched back from 5C to 0.1C, the discharge capacity can quickly recover to near its initial value, proving that the crystal structure and electrode structure remain intact after experiencing high-rate shocks, without irreversible damage or degradation.

[0206] In Example 9, a battery was prepared using recycled carbon-coated lithium iron phosphate material. The preparation method of the battery used for testing was consistent with that described in the aforementioned rate performance test. After the assembled half-cell was left to stand at room temperature for 24 hours, it was placed on the Newway BTSDA battery testing system and tested at a constant current rate of 0.1C from 2.5V to 4.0V (vs. Li). + The first charge-discharge cycle test was conducted within the voltage range of / Li). The results were obtained. Figure 6 The initial charge-discharge curves of lithium iron phosphate provided in Example 9 are shown in the figure. As can be seen from the figure, both the charge and discharge curves have long and flat voltage plateaus, located around 3.45V and 3.40V respectively (vs. Li). + / Li), which corresponds to the reversible phase transition process between the LiFePO4 and FePO4 phases. The high initial coulombic efficiency indicates that the material structure is stable and the electrode interface is good.

[0207] The recycled carbon-coated lithium iron phosphate materials obtained in Examples 3, 8, and 9 were tested according to the above method, and the results were as follows: Figure 7 and Figure 8 The results shown in the figure demonstrate that the recycled materials from Examples 3, 8, and 9 exhibit excellent and highly consistent capacity retention characteristics at different rate increments. In the rate increment test from 0.1C to 5C, the decay trends of the three curves are gradual, especially at medium-to-high rates such as 1C and 2C, where the capacity retention remains at a high level. When the rate recovers from 5C to 0.1C, the discharge capacity of all three rapidly recovers to near its initial value. Furthermore, the initial charge-discharge curves show a highly similar shape, exhibiting the typical long and flat voltage plateau of lithium iron phosphate materials.

[0208] This fully demonstrates that by adjusting the process within the parameter ranges defined in the claims of this invention, a closed-loop conversion from waste materials to high-purity intermediate products, and then to high-performance recycled cathode materials can be stably achieved, with good process tolerance and high reproducibility.

[0209] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation, characterized in that, Includes the following steps: S1, waste lithium iron phosphate powder is placed in potassium ferricyanide solution to carry out redox selective delithiation reaction; S2, after the reaction is complete, solid-liquid separation is performed to obtain a solid product and a lithium-containing filtrate; S3, the obtained solid product is converted and recovered as iron phosphate by heat treatment; S4, the lithium-containing filtrate is subjected to a lithium precipitation reaction to recover lithium carbonate; S5 involves uniformly mixing the recovered iron phosphate, lithium carbonate, and carbon source, followed by sintering to obtain recycled carbon-coated lithium iron phosphate.

2. The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in claim 1, characterized in that, In step S1, the concentration of the potassium ferricyanide solution is 0.006~0.18 mol / L, and the molar ratio of ferricyanide ions to lithium ions contained in the waste lithium iron phosphate powder is (0.8~1.2):

1.

3. The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in claim 1, characterized in that, In step S1, waste lithium iron phosphate powder and potassium ferricyanide solution are ultrasonically dispersed in a closed environment for 1-2 min; the redox selective delithiation reaction temperature is 25-30℃ and the time is 5-50 min.

4. A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in any one of claims 1 to 3, characterized in that, In step S3, the obtained solid product is first washed with deionized water, dried at 50~70℃ for 6~12h, and then heat-treated in a tube furnace at 600~700℃ for 2~3h under oxygen or air atmosphere.

5. A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in any one of claims 1 to 3, characterized in that, In step S4, the lithium precipitation reaction is to add water-soluble carbonate to the lithium-containing filtrate, wherein the molar ratio of carbonate ions to lithium ions in the water-soluble carbonate is (1.05~1.25):

2.

6. A method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in any one of claims 1 to 3, characterized in that, In step S5, the carbon source includes at least one of glucose, sucrose, starch, citric acid, and ascorbic acid.

7. The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in claim 6, characterized in that, In step S5, the molar ratio of the recovered iron phosphate, lithium carbonate and carbon source is 2:1.03:(0.175~0.35).

8. The method for closed-loop regeneration of waste lithium iron phosphate assisted by redox selective delithiation as described in claim 7, characterized in that, The sintering process includes a first-stage calcination and a second-stage calcination; the first-stage calcination is carried out at a temperature of 350°C for 5 hours; the second-stage calcination is carried out at a temperature of 650-750°C for 6-10 hours.

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