Recycling method of lithium iron phosphate black powder, lithium iron phosphate positive electrode material and application

Abstract

The embodiment of the invention discloses a recycling method of lithium iron phosphate black powder, a lithium iron phosphate positive electrode material and application, the recycling method comprises the steps of acid mixing, sintering, acid leaching, solid-liquid separation and respective treatment, comprehensive recycling of three major valuable elements of lithium, iron and phosphorus in the lithium iron phosphate black powder is achieved, lithium chloride is obtained by treating a liquid phase, and the lithium iron phosphate positive electrode material is recycled. The recovery rate is high, and the iron phosphate with high additional value is obtained by treating a solid phase instead of waste residues. Moreover, according to the recycling method disclosed by the embodiment of the invention, acid mixing and sintering under a preset condition are adopted, so that the phase of the lithium iron phosphate is converted, the occurrence state and the leaching behavior of impurity elements are regulated and controlled, and after treatment in the step, impurities such as Al, Ni, Co and Mn are selectively and efficiently reserved in a liquid phase in subsequent acid leaching, so that the quality of the lithium iron phosphate is improved. Iron and phosphorus are mainly enriched in a solid phase, so that a foundation is laid for subsequent preparation of high-purity iron phosphate.

Description

Technical Field

[0001] This application relates to the technical field of battery cathode material recycling, specifically to a method for recycling lithium iron phosphate black powder, lithium iron phosphate cathode material, and its applications. Background Technology

[0002] With the widespread application of lithium-ion batteries, especially lithium iron phosphate batteries, and the approaching retirement of these batteries, the recycling of lithium iron phosphate black powder—the cathode material of spent batteries—is becoming increasingly important. Meanwhile, the production process of lithium iron phosphate cathode materials generates a large amount of lithium iron phosphate black powder due to ternary doping (introducing Ni, Co, and Mn elements) and material crushing and mixing. This black powder contains valuable lithium, iron, and phosphorus elements, but also introduces metallic impurities such as Al, Ni, Co, and Mn.

[0003] Currently, the main method for recycling lithium iron phosphate black powder is direct acid leaching with hydrochloric acid or sulfuric acid, with the goal of recovering lithium salts in the form of lithium chloride or lithium carbonate.

[0004] However, this method pays less attention to the recovery of iron and phosphorus, resulting in low resource utilization. Even when attempts are made to recover iron and phosphorus to prepare iron phosphate, the resulting iron phosphate contains high levels of impurities such as Al, Ni, Co, and Mn. Summary of the Invention

[0005] This application provides a method for recycling lithium iron phosphate black powder, lithium iron phosphate cathode material, and applications, aiming to solve the problems of ineffective recovery of iron and phosphorus from lithium iron phosphate black powder and high impurity content in the recovered products.

[0006] This application provides a method for recycling lithium iron phosphate black powder, including: Lithium iron phosphate black powder is subjected to acid treatment to obtain acid-treated lithium iron phosphate black powder. The acid-mixed lithium iron phosphate black powder is sintered under preset conditions to obtain sintered black powder. The sintered black powder was subjected to acid leaching treatment, and then filtered to obtain a solid phase and a liquid phase. The liquid phase is processed to obtain lithium chloride; The solid phase is processed to obtain iron phosphate.

[0007] Optionally, in some embodiments of this application, the step of treating the lithium iron phosphate black powder with acid includes: Lithium iron phosphate black powder is mixed with phosphoric acid and stirred evenly to obtain lithium iron phosphate black powder after acid mixing.

[0008] Optionally, in some embodiments of this application, the mass ratio of the lithium iron phosphate black powder to the phosphoric acid ranges from (2-10):1.

[0009] Optionally, in some embodiments of this application, the step of acid leaching the sintered black powder includes: The sintered black powder was dispersed in hydrochloric acid solution, and hydrogen peroxide solution was added for a first acid leaching to obtain a first mixture. The first mixture was heated, and hydrogen peroxide solution was added for a second acid leaching to obtain the second mixture; The pH of the second mixture was adjusted, and the mixture was filtered to obtain a solid phase and a liquid phase.

[0010] Optionally, in some embodiments of this application, the concentration of the hydrochloric acid solution ranges from 0.5 mol / L to 3 mol / L; and / or The temperature range for the heating is 40°C. o C to 90 o C; and / or The pH value ranges from 0.5 to 2.

[0011] Optionally, in some embodiments of this application, the step of treating the liquid phase to obtain lithium chloride includes: Lithium hydroxide was added to the liquid phase, the pH was adjusted to 7-10, and lithium chloride was obtained by filtration.

[0012] Optionally, in some embodiments of this application, the step of treating the solid phase to obtain iron phosphate includes: The solid phase is washed and acid-leached, and then filtered to obtain a filtrate; Adjust the iron-to-phosphorus ratio in the filtrate, add titanium salt, and obtain a solution containing iron, phosphorus, and titanium; A precipitant was added to the solution, the pH was adjusted to 1.5-2.5, and the solution was washed and sintered to obtain ferric phosphate.

[0013] Secondly, embodiments of this application provide a lithium iron phosphate cathode material, which is obtained by recycling using the aforementioned recycling method.

[0014] Thirdly, embodiments of this application provide an application of the aforementioned method for recycling lithium iron phosphate black powder in the recycling of electrode materials for lithium-ion batteries.

[0015] The recycling method for lithium iron phosphate black powder in this application includes a process path of acid mixing, sintering, acid leaching, solid-liquid separation, and separate treatment, achieving comprehensive recovery of the three major valuable elements—lithium, iron, and phosphorus—from the lithium iron phosphate black powder. Lithium chloride is obtained by treating the liquid phase with a high recovery rate, and high-value-added iron phosphate is obtained by treating the solid phase, rather than as waste residue. The recycling target is expanded from a single lithium salt to two high-value-added products: lithium chloride and iron phosphate, greatly improving the comprehensive utilization rate of resources and the economic efficiency of the entire recycling process, realizing a transformation from waste treatment to resource regeneration. Furthermore, the recycling method in this application employs acid mixing followed by sintering under preset conditions, causing a phase transformation of lithium iron phosphate and controlling the occurrence state and leaching behavior of impurity elements. After this step, impurities such as Al, Ni, Co, and Mn are selectively and efficiently retained in the liquid phase during subsequent acid leaching, while iron and phosphorus are mainly enriched in the solid phase, laying the foundation for the subsequent preparation of high-purity iron phosphate. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a recycling method provided by an exemplary embodiment of this disclosure. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The primary goal of the traditional direct acid leaching method is to recover lithium to produce lithium chloride or lithium carbonate. However, the iron and phosphorus that dissolve simultaneously are often considered waste due to a lack of effective separation and purification methods, making them difficult to utilize at high value and resulting in extremely low resource utilization. Furthermore, during direct acid leaching, metallic impurities such as Al, Ni, Co, and Mn in the black powder dissolve along with lithium, iron, and phosphorus in the acid solution. Subsequent attempts to precipitate iron phosphate from this complex solution result in the co-precipitation of these impurities, leading to a high impurity content in the product, making it unsuitable for the reprocessing of high-performance lithium iron phosphate.

[0020] According to a first aspect of the embodiments of this application, a method for recycling lithium iron phosphate black powder is provided. Please refer to [link to relevant documentation]. Figure 1 The method includes the following steps: S100. The lithium iron phosphate black powder is subjected to acid treatment to obtain acid-treated lithium iron phosphate black powder. S200. The acid-mixed lithium iron phosphate black powder is sintered under preset conditions to obtain sintered black powder. S300: The sintered black powder is subjected to acid leaching treatment, and then filtered to obtain solid and liquid phases; S400, The liquid phase is processed to obtain lithium chloride; S500, the solid phase is treated to obtain iron phosphate.

[0021] By adopting the above scheme, through a process involving acid treatment, sintering, acid leaching, and solid-liquid separation, comprehensive recovery of the three major valuable elements—lithium, iron, and phosphorus—from lithium iron phosphate black powder is achieved. Lithium chloride is obtained by treating the liquid phase with a high recovery rate, while high-value-added iron phosphate is obtained through solid phase treatment, rather than as waste residue. Expanding the recovery target from a single lithium salt to two high-value-added products—lithium chloride and iron phosphate—significantly improves the comprehensive utilization rate of resources and the economics of the entire recovery process, realizing a transformation from waste treatment to resource regeneration.

[0022] Moreover, the recycling method in this application adopts acid mixing and sintering under preset conditions to transform the lithium iron phosphate phase and regulate the occurrence state and leaching behavior of impurity elements. After this step, in the subsequent acid leaching, impurities such as Al, Ni, Co, and Mn are selectively and efficiently retained in the liquid phase, while iron and phosphorus are mainly enriched in the solid phase, which lays the foundation for the subsequent preparation of high-purity iron phosphate.

[0023] In some embodiments of this application, the step of acid-mixing lithium iron phosphate black powder includes: Lithium iron phosphate black powder is mixed with phosphoric acid and stirred evenly to obtain lithium iron phosphate black powder after acid mixing.

[0024] By employing the above scheme, the addition of phosphoric acid allows for a solid-state ion exchange reaction between phosphoric acid and lithium iron phosphate during the subsequent sintering step. Specifically, phosphoric acid provides a strongly acidic local environment, facilitating the easier displacement of lithium from the lithium iron phosphate lattice by hydrogen ions, forming soluble lithium salt precursors (such as LiH₂PO₄, Li₃PO₄, etc.). After acid mixing, sintering under the pre-defined environment helps prevent the oxidation of ferrous iron; the oxidized material is essentially impossible to leach, effectively improving the purity after leaching.

[0025] After acid mixing and sintering, the physicochemical properties of the black powder in this embodiment have changed, becoming more porous and reactive. When it is re-contaminated with hydrochloric acid for acid leaching, the leaching resistance of lithium is greatly reduced, which helps to improve the leaching rate of lithium. At the same time, it can also shorten the acid leaching time and effectively reduce acid consumption.

[0026] During the acid mixing process, phosphoric acid is both a reactant and a provider and stabilizer of phosphorus. It ensures that phosphorus exists and is converted stably in the form of phosphate ions throughout the entire process, rather than being lost through volatilization in the form of gases such as phosphine, which helps to ensure a high recovery rate of phosphorus.

[0027] In other words, pre-stirring lithium iron phosphate black powder with phosphoric acid helps to initiate phase reconstruction at low temperatures and activate the material; it also allows for the pre-setting of the direction of impurities, achieving efficient directional separation of iron and phosphorus from impurities, improving subsequent lithium leaching efficiency and phosphorus recovery rate, and laying the foundation for the preparation of high-purity iron phosphate.

[0028] In some embodiments of this application, the mass ratio of lithium iron phosphate black powder to phosphoric acid ranges from (2-10):1. Exemplarily, the mass ratio of lithium iron phosphate black powder to phosphoric acid can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any ratio between two adjacent ratios mentioned above.

[0029] By adopting the above scheme, within the range of (2-10):1, the amount of phosphoric acid used is just right to react effectively with the target impurities (Al, Ni, Co, Mn) in the black powder, transforming them into a form that is easy to enter the liquid phase during subsequent acid leaching, while not excessively dissolving the skeletal structure of the target product, iron and phosphorus. If the proportion of phosphoric acid is too low, the impurity conversion will be incomplete, and some impurities will remain in the solid phase, contaminating the final iron phosphate. If the proportion of phosphoric acid is too high, the excessively acidic environment may cause premature or excessive destruction of some iron and phosphorus structures during sintering and subsequent acid leaching, causing more iron and phosphorus to enter the liquid phase. This not only increases the burden on lithium liquid purification but may also lead to a decrease in the recovery rate of iron and phosphorus and incomplete separation.

[0030] In some embodiments of this application, the preset conditions include a low-oxygen environment or a reducing atmosphere.

[0031] In some embodiments, the oxygen content in the low-oxygen environment is less than 5%, preferably less than 1%, and the low-oxygen environment can be a low-oxygen atmosphere with an oxygen content of 1% or a nitrogen atmosphere.

[0032] In some embodiments, the reducing atmosphere may be a hydrogen atmosphere.

[0033] Iron in lithium iron phosphate is originally in the +2 valence state. If sintering is carried out in an aerobic environment, the +2 valence iron will be oxidized to the +3 valence state by oxygen. The +3 valence iron will precipitate in the subsequent leaching step and cannot enter the solution for further separation and purification, resulting in a significant decrease in iron recovery rate. Phosphorus bound to iron is also encapsulated and lost. The formed colloidal or stable precipitate will encapsulate impurities and other valuable elements, leading to separation failure.

[0034] The embodiments of this application are based on a low-oxygen or reducing atmosphere, mainly where impurities form low-valence phosphates or oxides, making them more soluble. This can be understood as similar to the hydrolysis or acidolysis of ternary materials after reduction. Due to the different acidic atmospheres, the results are fundamentally different: one method completely solidifies the impurities in the carbon slag and removes them through filtration, while the other method removes them by dissolving them in a lithium salt solution and precipitating them out.

[0035] In some embodiments of this application, the sintering temperature ranges from 300°C. o C to 600 o C. For example, the sintering temperature can be 300°C. o C, 350 o C, 400 o C, 450 o C, 500 o C, 550 o C, 600 o C and any value between the two adjacent values ​​mentioned above.

[0036] By adopting the above scheme, the above temperature range helps to ensure the necessary activation energy for the full and rapid progress of the core chemical reaction; while achieving chemical activation, the loose and porous structure of the material is maintained, creating ideal physical conditions for subsequent efficient acid leaching; side reactions such as phosphoric acid decomposition and excessive sintering of materials are avoided, ensuring that the reaction path proceeds in the preset direction.

[0037] In some embodiments of this application, the sintering time ranges from 5 min to 120 min. Exemplarily, the sintering time can be 5 min, 10 min, 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 120 min, or any value between two adjacent values.

[0038] By adopting the above scheme, in 300 o C to 600 oAt the sintering temperature of C, the solid-state ion exchange reaction between lithium iron phosphate powder and phosphoric acid requires a certain amount of time to complete. If the time is too short (e.g., only 1-2 minutes), heat and reactants cannot be fully transferred to all particles, resulting in incomplete reaction and a large amount of lithium iron phosphate not being effectively activated. Furthermore, converting impurities such as Al, Ni, Co, and Mn into forms that easily enter the liquid phase during subsequent acid leaching also requires a certain reaction time. If the time is too long, excessive sintering will also cause slow solid-phase diffusion and sintering between material particles, gradually making the originally loose and porous structure denser, and severely hindering the efficiency of subsequent acid leaching, thus leading to a decrease in leaching rate.

[0039] In some embodiments of this application, the step of acid leaching the sintered black powder includes: The sintered black powder was added to a hydrochloric acid solution and a hydrogen peroxide solution for the first acid leaching to obtain a first mixture. The first mixture was heated, and hydrogen peroxide solution was added for a second acid leaching to obtain the second mixture; The pH of the second mixture was adjusted, and the mixture was filtered to obtain a solid phase and a liquid phase.

[0040] By adopting the above scheme, the lithium in the sintered black powder has been converted into easily soluble lithium salts. In the first acid leaching, lithium can quickly and preferentially dissolve into the hydrochloric acid solution, ensuring the lithium recovery rate. Simultaneously, the first acid leaching temperature is relatively low, making the oxidation process relatively mild and controllable, avoiding losses due to hydrogen peroxide decomposition caused by violent reactions. That is, after the first acid leaching, lithium and organic impurities can be leached out and decomposed; iron and phosphorus are not leached out, and the small amount of leached iron and phosphorus is regenerated into iron phosphate by hydrogen peroxide. The second acid leaching increases the reaction temperature, and hydrogen peroxide acts as an oxidant to oxidize Fe... 2+ Oxidized to Fe 3+ Iron phosphate is generated; at the same time, hydrogen peroxide acts as a reducing agent to reduce ternary materials such as Ni, Co, and Mn into the solution.

[0041] In some embodiments of this application, the concentration of the hydrochloric acid solution ranges from 0.5 mol / L to 3 mol / L. Exemplarily, the concentration of the hydrochloric acid solution can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, or any value between two adjacent values.

[0042] If the concentration of the hydrochloric acid solution is too low, the lithium chloride yield will be low; if the concentration of the hydrochloric acid solution is too high, the ferric phosphate in the black powder will be dissolved by the hydrochloric acid, which may affect the content of the effective components in the product.

[0043] In some embodiments of this application, the temperature range for heating is 40°C. oC to 90 o C. For example, the temperature for heating can be 40°C. o C, 50 o C, 60 o C, 70 o C, 80 o C, 90 o C and any value between the two adjacent values ​​mentioned above.

[0044] By adopting the above scheme, the temperature range helps to increase the reaction rate and improve the recovery rate of Li; at the same time, the appropriate temperature range can also ensure that impurity elements such as Al, Ni, Co, and Mn are fully dissolved, thereby leaving them in the liquid phase and achieving effective separation from iron and phosphorus.

[0045] In some embodiments of this application, the pH value ranges from 0.5 to 2. Exemplarily, pH can be 0.5, 1, 1.5, 2, or any value between two adjacent values ​​mentioned above.

[0046] By adopting the above scheme, if the pH is too low, iron may dissolve in the solution, resulting in a decrease in the Fe recovery rate; if the pH is too high, it may affect the Li leaching rate.

[0047] In some embodiments of this application, the step of treating the liquid phase to obtain lithium chloride includes: Lithium hydroxide was added to the liquid phase, the pH was adjusted to 7-10, and lithium chloride was obtained by filtration.

[0048] By adopting the above method, lithium hydroxide is added to the liquid phase, and impurities in the liquid phase can be relatively easily removed by adjusting the pH, which helps to ensure the purity of lithium chloride.

[0049] In some embodiments of this application, the step of treating the solid phase to obtain ferric phosphate includes: The solid phase is washed and acid-leached, and then filtered to obtain the filtrate; Adjust the iron-to-phosphorus ratio in the filtrate and add titanium salt to obtain a solution containing iron, phosphorus, and titanium. A precipitant is added to the solution, the pH is adjusted to 1.5-2.5, and ferric phosphate is obtained by washing and sintering.

[0050] In some embodiments of this application, the solid phase is ferrophosphorus slag, which is washed until its conductivity is below 500 μS / cm.

[0051] In some embodiments of this application, the iron-phosphorus ratio is adjusted by adding titanium salt, at which point the mass ratio of titanium to iron phosphate in the solution is (0.1~0.3):1.

[0052] In some embodiments of this application, the titanium salt may include one or more of titanium oxychloride, titanium oxysulfate, titanium oxyoxalate, and titanium oxyoxalate ammonium.

[0053] In some embodiments of this application, the content of Al in ferric phosphate is ≤100ppm, Ni ≤10ppm, Co ≤10ppm, Mn ≤50ppm, and Ti content is 0.1% to 0.3%.

[0054] In summary, the recycling method of this application embodiment can achieve full-element recovery, with a recovery rate of over 96% for Li, over 98% for Fe, and over 97% for P. Through acid-sintering technology, Al, Ni, Co, and Mn are directly dissolved in the lithium chloride solution in ionic form, resulting in low impurities in the ferrophosphate slag. The ferrophosphate slag undergoes secondary dissolution and precipitation, leading to high purity of the ferrophosphate.

[0055] According to a second aspect of the embodiments of this application, a lithium iron phosphate cathode material is provided, which is obtained by recycling using the aforementioned recycling method.

[0056] By adopting the above-mentioned scheme, the lithium iron phosphate cathode material of this application embodiment has high purity and low impurity content, which helps to achieve excellent cycle stability and long service life.

[0057] According to a third aspect of the embodiments of this application, an application is provided of the aforementioned method for recycling lithium iron phosphate black powder in the recycling of electrode materials for lithium-ion batteries.

[0058] In one example of this application, reference is made to Figure 1 The recycling method for lithium iron phosphate black powder includes the following steps: S100, Acid Mixing: Mix lithium iron phosphate black powder and phosphoric acid at a mass ratio of (2~10):1 until uniform; S200, sintering: In a low-oxygen (oxygen content less than 5%) or N2 or N2+H2 / CO (≤5%) reducing atmosphere, 300~600 o C. Sintering lithium iron phosphate mixed with acid black powder, sintering time 5~120min; S300, Acid Immersion: Add the sintered black powder to a hydrochloric acid solution, heat and stir for acid immersion; immersion time 0.5~5h, immersion temperature 40~90℃. o C. Hydrogen peroxide is added during the acid leaching process, and the molar ratio of hydrogen peroxide (20%) to Fe in the black powder is controlled at (1~4):1, and the pH of the acid leaching slurry is controlled between 0.5 and 2. S400, Lithium Chloride Preparation: Filter the acid leaching slurry, replace copper ions with iron powder (Fe / Cu 1.1~1.4:1 molar ratio), adjust the pH of the filtrate to 7~10 with lithium hydroxide, filter impurities, concentrate and crystallize the filtrate to obtain lithium chloride; S500, Phosphorus-Iron Slag Purification: Wash the phosphorus-iron slag until the conductivity is below 500 μS / cm, then acid leaching, and filter to obtain filtrate; test the iron, phosphorus and titanium content of the filtrate, then adjust the iron-phosphorus ratio, add titanium salt, and obtain a solution containing iron, phosphorus and titanium. S600, preparation of iron phosphate: Add a precipitant to the above solution, control the pH to 1.5~2.5, wash until the conductivity is less than 300 μS / cm, then age and sinter to obtain iron phosphate powder; S700, Testing: Testing for iron phosphate impurities, preparing lithium iron phosphate from iron phosphate powder; In S500, the Fe / P ratio is adjusted to 0.95~1.1, and the final mass ratio of titanium to iron phosphate in the solution is (0.1~0.3):1. The titanium salt contains one or more of titanium oxychloride, titanium oxysulfate, titanium oxyoxalate, and titanium oxyoxalate ammonia. In S600, the Fe / P ratio is controlled at 0.96~0.99:1, and the aging temperature is 85~95℃. o C, time 1~3h, sintering temperature 550~700 o C, time 20~120min; in ferric phosphate powder, Al≤100ppm, Ni≤10ppm, Co≤10ppm, Mn≤50ppm, and Ti controlled at 0.1~0.3%.

[0059] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0060] Example 1 List of ingredients of lithium iron phosphate black powder

[0061] S100, Acid Mixing: Mix lithium iron phosphate black powder and phosphoric acid evenly at a mass ratio of 5:1; S200, sintering: in a nitrogen atmosphere, at 500 o Lithium iron phosphate black powder was sintered under C for 120 min to obtain sintered black powder; S300, Acid leaching: Add sintered black powder to a 2 mol / L hydrochloric acid solution, add 30% of a 20 wt% hydrogen peroxide solution for the first acid leaching, and leach for 0.5 h to obtain the first mixture; The first mixture was heated to 80°C. o C. Add the remaining hydrogen peroxide solution for a second acid leaching, which lasts for 2.5 hours. The addition time of the hydrogen peroxide solution is the same as the acid leaching time. Control the molar ratio of hydrogen peroxide to Fe in the black powder to be 3:1. After acid leaching, control the pH of the slurry to be approximately 0.8. S400 and lithium chloride preparation: Filter the acid leaching slurry, replace copper ions with iron powder (Fe / Cu 1.2:1 molar ratio), adjust the pH of the filtrate to 10 with lithium hydroxide, filter impurities, concentrate and crystallize the filtrate to obtain lithium chloride; S500, purification of phosphorus-iron slag: The phosphorus-iron slag is washed until the conductivity is below 500 μS / cm, then acid-leached and filtered to obtain the filtrate; the iron, phosphorus and titanium content of the filtrate is tested, and then the iron-phosphorus ratio Fe / P is adjusted to 1, and titanium dichloride is added to obtain a solution containing iron, phosphorus and titanium; the mass ratio of Ti to iron phosphate in the solution is 0.2:1; Preparation of S600 and ferric phosphate: Add a precipitant to the above solution, control the pH to 2, wash until the conductivity is below 300 μS / cm, and then age. After aging, the Fe / P ratio is 0.965:1, and the aging temperature is 90°C. o C, time 1 hour, sintering temperature 650°C o C, time 60 min, sintering to obtain iron phosphate; S700, Testing: Testing for iron phosphate impurities and using this iron phosphate to prepare lithium iron phosphate.

[0062] Example 2 The difference from Example 1 is that the preset condition is a low-oxygen atmosphere with an oxygen content of 1%, while the rest of the steps are the same as in Example 1.

[0063] Example 3 The difference from Example 1 is that the preset condition is a hydrogen atmosphere, while the rest of the steps are the same as in Example 1.

[0064] Example 4 The difference from Example 1 is that the mass ratio of lithium iron phosphate black powder to phosphoric acid is 2:1, while the rest of the steps are the same as in Example 1.

[0065] Example 5 The difference from Example 1 is that the mass ratio of lithium iron phosphate black powder to phosphoric acid is 10:1, while the rest of the steps are the same as in Example 1.

[0066] Example 6 The difference from Example 1 is that the acid leaching process does not involve any steps; the remaining steps are consistent with Example 1. The specific acid leaching process is as follows: S300, Acid Immersion: Add the sintered black powder to a 2 mol / L hydrochloric acid solution, then add a 20 wt% hydrogen peroxide solution for acid immersion. Immerse for 3 hours at a temperature of 80°C. o C, control the molar ratio of hydrogen peroxide to Fe in black powder to be 3:1, and control the pH of the slurry to be about 0.8 after acid leaching.

[0067] Comparative Example 1 The difference from Example 1 is that the acid mixing process is omitted, while the rest of the steps remain unchanged from Example 1.

[0068] Comparative Example 2 The difference from Example 1 is that the sintering process is missing, while the rest of the steps remain the same as in Example 1.

[0069] Comparative Example 3 The difference from Example 1 is that air sintering is used in the sintering process, while the other steps remain unchanged from Example 1.

[0070] Performance testing: The recovery rate and impurity content of the examples and comparative examples were tested by ICP.

[0071] The test results are shown in Table 1. Table 1

[0072] Table 2

[0073] Compared with Comparative Examples 1-3, Examples 1-6 use acid mixing and sintering in a low-oxygen environment or reducing atmosphere, while Comparative Example 1 lacks the acid mixing process, Comparative Example 2 lacks sintering in a low-oxygen environment or reducing atmosphere, and Comparative Example 3 uses acid mixing and sintering in air. According to Table 1-2, Examples 1-6 cause a phase transformation of lithium iron phosphate and regulate the occurrence state and leaching behavior of impurity elements. After this step, impurities such as Al, Ni, Co, and Mn are selectively and efficiently retained in the liquid phase during subsequent acid leaching, while iron and phosphorus are mainly enriched in the solid phase, so as to prepare high-purity iron phosphate in the subsequent process.

[0074] The above provides a detailed description of a method for recycling lithium iron phosphate black powder, lithium iron phosphate cathode material, and applications provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for recycling lithium iron phosphate black powder, characterized in that, include: Lithium iron phosphate black powder is subjected to acid treatment to obtain acid-treated lithium iron phosphate black powder. The acid-mixed lithium iron phosphate black powder is sintered under preset conditions to obtain sintered black powder. The sintered black powder was subjected to acid leaching treatment, and then filtered to obtain a solid phase and a liquid phase. The liquid phase is processed to obtain lithium chloride; The solid phase is treated to obtain iron phosphate; Wherein, the oxygen content of the preset conditions is less than the oxygen content in the air.

2. The method for recycling lithium iron phosphate black powder according to claim 1, characterized in that, The steps of acid treatment for lithium iron phosphate black powder include: Lithium iron phosphate black powder is mixed with phosphoric acid and stirred evenly to obtain lithium iron phosphate black powder after acid mixing.

3. The method for recycling lithium iron phosphate black powder according to claim 2, characterized in that, The mass ratio of lithium iron phosphate black powder to phosphoric acid ranges from (2-10):

1.

4. The method for recycling lithium iron phosphate black powder according to claim 1, characterized in that, The preset conditions include a low-oxygen environment or a reducing atmosphere, wherein the oxygen content in the low-oxygen environment is less than 5%; and / or The sintering temperature ranges from 300°C. o C to 600 o C; and / or The sintering time ranges from 5 min to 120 min.

5. The method for recycling lithium iron phosphate black powder according to claim 1, characterized in that, The step of acid leaching the sintered black powder includes: The sintered black powder was dispersed in hydrochloric acid solution, and hydrogen peroxide solution was added for a first acid leaching to obtain a first mixture. The first mixture was heated, and hydrogen peroxide solution was added for a second acid leaching to obtain the second mixture; The pH of the second mixture was adjusted, and the mixture was filtered to obtain a solid phase and a liquid phase.

6. The method for recycling lithium iron phosphate black powder according to claim 5, characterized in that, The concentration of the hydrochloric acid solution ranges from 0.5 mol / L to 3 mol / L; and / or The temperature range for the heating is 40°C. o C to 90 o C; and / or The pH value ranges from 0.5 to 2.

7. The method for recycling lithium iron phosphate black powder according to claim 1, characterized in that, The step of processing the liquid phase to obtain lithium chloride includes: Lithium hydroxide was added to the liquid phase, the pH was adjusted to 7-10, and lithium chloride was obtained by filtration.

8. The method for recycling lithium iron phosphate black powder according to claim 1, characterized in that, In the iron phosphate, Al ≤ 100 ppm, Ni ≤ 10 ppm, Co ≤ 10 ppm and Mn ≤ 50 ppm.

9. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is recovered using the recycling method described in any one of claims 1 to 8.

10. The application of the method for recycling lithium iron phosphate black powder according to any one of claims 1 to 8 in the recycling of electrode materials for lithium-ion batteries.

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