Method for recycling lithium iron phosphate material from waste batteries

Abstract

The invention provides a method for recovering a lithium iron phosphate material from a waste battery, and relates to the technical field of battery material recovery. The method comprises the following steps: pre-treating the waste battery; treating a positive plate; and material recovery. Wherein the positive plate treatment specifically comprises the step of soaking the positive plate by adopting a first soaking agent. And crushing the positive plate soaked in the first soaking agent. Soaking the crushed positive plate in a second soaking agent, and filtering to obtain a first filter residue taking the positive active material as a main component; and drying, grinding and screening the first filter residue to remove impurities so as to obtain the lithium iron phosphate impurity-removed material. According to the method for recovering the lithium iron phosphate material from the waste battery, provided by the invention, impurities in the recovered lithium iron phosphate material can be reduced, and the purity of the recovered lithium iron phosphate material is increased; the performance of the lithium iron phosphate material synthesized again after the lithium iron phosphate in the waste battery is recycled can meet the brand-new battery-grade raw material requirement.

Description

Technical Field

[0001] This application relates to the technical field of battery material recycling, and particularly to a method for recycling lithium iron phosphate materials from waste batteries. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used due to their high voltage and high energy density. Among them, lithium iron phosphate (LiFePO 4 or LFP) is widely used in electric vehicles due to its high theoretical capacity (about 170 mAh / g), low cost, environmental harmlessness, safety, and good thermal stability. However, the service life of lithium-ion batteries is limited. The service life of these electric vehicle power batteries is generally 5 - 10 years. With the rapid development of electric vehicles, a large number of lithium batteries will be scrapped in the next few years, and the recycling and harmless treatment of failed batteries have become a topic of concern.

[0003] The waste battery recycling process mainly includes two steps: pretreatment and recovery of valuable metals. The pretreatment process mainly includes discharging, disassembling, pulverizing, and separating the active material from the current collector. In current research, the recycling methods of LFP cathode materials can be divided into two categories. One is direct regeneration by cremation recycling (high-temperature solid-phase method), where the regenerated LFP cathode material usually contains a high impurity content, consumes a large amount of energy, and generates waste gas that pollutes the environment. The other recycling method is wet recycling, which extracts valuable elements from failed LFP cathode materials by leaching and precipitation. The recycling process often uses organic or inorganic acids to leach valuable metals.

[0004] However, no matter which method is used for recycling, the existing recycling processes generally have poor impurity removal effects for valuable metals, especially low separation rates of aluminum and iron, which ultimately result in low purity of the recovered iron and lithium. When the lithium iron phosphate synthesized from the recovered iron and lithium is used in batteries, the batteries show a large self-discharge rate, low storage performance, and generally poor calendar life during long-term testing. Summary of the Invention

[0005] This application provides a method for recycling lithium iron phosphate materials from waste batteries, which can reduce the impurities in the recycled lithium iron phosphate materials, increase the purity of the recycled lithium iron phosphate materials, and meet the requirements of new battery-grade raw materials in all aspects for the lithium iron phosphate material synthesized after recycling the lithium iron phosphate in waste batteries.

[0006] This application provides a method for recycling lithium iron phosphate materials from waste batteries, the method comprising:

[0007] Pretreatment of waste batteries: Discharging and disassembling the waste batteries.

[0008] Positive electrode sheet treatment: Separating the positive electrode current collector and the positive electrode active material.

[0009] Material recovery: Separating lithium and iron elements from the positive electrode active material, and recovering lithium in the form of lithium carbonate and iron in the form of iron phosphate.

[0010] Among them, the positive electrode sheet treatment specifically includes:

[0011] Soaking the positive electrode sheet with a first soaking agent to initially separate the positive electrode current collector and the positive electrode active material.

[0012] Performing crushing treatment on the positive electrode sheet soaked with the first soaking agent.

[0013] Soaking the crushed positive electrode sheet with a second soaking agent to separate the positive electrode current collector and the positive electrode active material again, and filtering to obtain a first filter residue mainly composed of the positive electrode active material.

[0014] Performing drying, grinding and sieving on the first filter residue to remove impurities and obtain a lithium iron phosphate impurity-removing material.

[0015] In the above method, pre-treating waste batteries can effectively utilize the residual electrical energy in waste batteries and reduce energy waste; disassembling waste batteries is conducive to separately recycling various materials of the batteries in the subsequent process. The positive electrode sheet treatment is mainly used to separate the positive electrode current collector and the positive electrode active material. In this process, soaking the positive electrode sheet with the first soaking agent can achieve the preliminary loosening and separation of the positive electrode current collector and the positive electrode active material; performing crushing treatment on the positive electrode sheet soaked with the first soaking agent is conducive to changing the long strip-shaped positive electrode sheet into shorter particles, which is conducive to the full contact of the positive electrode sheet with the subsequent second soaking agent, and further conducive to the detachment of the positive electrode active material from the positive electrode current collector, so as to achieve the purpose of separating the positive electrode current collector and the positive electrode active material; the main component of the first filter residue is the positive electrode active material, and the positive electrode active material includes lithium iron phosphate and a binder, but it also contains broken aluminum foil of the positive electrode current collector. By drying and grinding the first filter residue, lithium iron phosphate can be ground into powder with a smaller particle size, while aluminum foil and the binder are difficult to be ground into powder with a smaller particle size due to their large ductility. Based on this, sieving after grinding the first filter residue can remove impurities such as aluminum and the binder in the first filter residue, obtain a relatively pure lithium iron phosphate impurity-removing material, achieve the purpose of impurity removal, and this impurity removal process utilizes the physical properties of impurities and lithium iron phosphate, without using chemical means for impurity removal, will not cause the introduction of new impurities, and the cost is relatively low.

[0016] In a possible design, the first soaking agent includes cold water and hot water, and soaking the positive electrode sheet with the first soaking agent specifically includes: soaking the positive electrode sheet with cold water and hot water alternately for multiple times, and the soaking time for each time is 30 - 60 min.

[0017] Through the above solution, the first soaking agent is configured as cold water and hot water. Water is an easily available substance with low cost. By alternately soaking with cold water and hot water and utilizing the principle of thermal expansion and contraction, it is possible to accelerate the shedding of the positive active material from the positive current collector.

[0018] In a possible design, the second soaking agent includes ammonia water. Soaking the crushed positive electrode sheet with the second soaking agent specifically includes: mixing ammonia water with the crushed positive electrode sheet and soaking at 60 - 100 °C for a time greater than 2 h.

[0019] Through the above solution, ammonia water is used as the second soaking agent. Ammonia water can provide an alkaline environment for the crushed positive electrode sheet, dissolve a part of the binder and aluminum foil, so that the positive current collector and the positive active material are completely separated. Ammonia water can react efficiently with the positive electrode sheet at 60 - 100 °C. A reaction time greater than 2 h can ensure that ammonia water reacts fully with the positive electrode sheet, improving the separation rate of the positive current collector and the positive active material. In addition, after ammonia water decomposes into ammonia gas and water, no new impurities are introduced, achieving green environmental protection.

[0020] In a possible design, drying, grinding, and screening the first filter residue include:

[0021] Using multiple layers of sieve meshes to screen the first filter residue after drying and grinding. The pore sizes of the sieve meshes decrease successively from top to bottom to screen out impurities of different sizes layer by layer.

[0022] Through the above solution, by screening out impurities of different sizes layer by layer, it is possible to prevent the situation where too many impurities are screened out by a single sieve mesh and the mesh holes are blocked, making it difficult for the lithium iron phosphate impurity removal material to fall quickly. In addition, theoretically, among the first filter residue after grinding, the particle size of lithium iron phosphate is smaller than that of the impurities, but there are still a small number of cases where the particle size of lithium iron phosphate is equivalent to that of the impurities or the particle size of lithium iron phosphate is larger than that of the impurities. At this time, the material on the sieve mesh can be further ground according to the content of lithium iron phosphate screened out on each layer of sieve mesh. After the particle size of this part of the larger - sized lithium iron phosphate becomes smaller again, it is screened again to achieve the purpose of impurity removal and no waste of lithium iron phosphate materials.

[0023] In a possible design, material recovery specifically includes: soaking the lithium iron phosphate impurity removal material with organic acid and hydrogen peroxide, and filtering to obtain a second filter residue and a second filtrate. The second filter residue includes iron phosphate, and the second filtrate includes lithium ions.

[0024] Through the above solution, the lithium iron phosphate impurity removal material is soaked with organic acid and hydrogen peroxide, which will not introduce new impurity elements into the recycled material. Therefore, while separating iron phosphate and lithium ions in the lithium iron phosphate impurity removal material, it will not cause secondary pollution to the lithium iron phosphate impurity removal material, and there is no need to further process the recycled waste products, which is beneficial to improving the environmental protection of battery recycling and reducing the subsequent processing cost.

[0025] In a possible design, the material recycling further includes: electrolyzing the second filtrate using an electrolytic cell, where the electrolytic cell includes a cathode cell and an anode cell, and the cathode cell and the anode cell are separated by a proton exchange membrane; during the electrolysis process, the second filtrate is placed in the anode cell, and the LiOH solution is placed in the cathode cell. After the electrolysis ends, a first lithium-rich solution is obtained in the cathode cell.

[0026] Through the above solution, the second filtrate contains a large amount of lithium ions. By electrolyzing the second filtrate using an electrolytic cell, during the electrolysis process, the water in the cathode cell is electrolyzed to generate hydrogen and hydroxide ions. The lithium ions in the anode cell pass through the proton exchange membrane and reach the cathode cell, where they combine with the hydroxide ions to form LiOH, and finally a first lithium-rich solution is obtained in the cathode cell. Among them, placing the LiOH solution in the cathode cell in the initial state can ensure that the concentration of hydroxide ions in the cathode cell reaches a certain amount for combining with lithium ions and does not introduce extra impurity elements.

[0027] In a possible design, the material recycling further includes:

[0028] Sodium carbonate is added to the first lithium-rich solution. After the reaction between the first lithium-rich solution and sodium carbonate is completed, lithium carbonate is obtained by suction filtration.

[0029] The purity of lithium in the lithium carbonate is tested, and purification is carried out when the purity of lithium is lower than the first preset requirement.

[0030] Through the above solution, lithium carbonate precipitate is generated by the reaction of sodium carbonate with lithium hydroxide in the first lithium-rich solution, and then the lithium carbonate precipitate is separated by filtration. The lithium obtained by this chemical + physical purification method theoretically has a higher purity. By further testing the purity of lithium in the lithium carbonate, a more accurate measurement of the purity of lithium in the lithium carbonate can be obtained. When the purity of lithium is lower than the first preset requirement, its purity is improved by purification until it meets the first preset requirement.

[0031] In a possible design, when electrolyzing the second filtrate using an electrolytic cell, the first lithium-rich solution in the cathode cell is recrystallized and then formulated into a LiOH solution and placed in the cathode cell.

[0032] Through the above solution, there is no need to purchase lithium hydroxide during the recycling process of waste batteries. Instead, the lithium hydroxide electrolytically recovered from the second filtrate is formulated into a lithium hydroxide solution for electrolysis, realizing the reuse of the recovered lithium hydroxide and achieving the purpose of cost savings.

[0033] In a possible design, the material recycling further includes:

[0034] Washing the second filter residue with water.

[0035] Sintering the washed second filter residue to obtain iron phosphate.

[0036] Testing the purity of iron in the iron phosphate and performing purification when the purity of iron is lower than the second preset requirement.

[0037] Through the above solution, by washing the second filter residue with water, the substances adhering to the surface of the second filter residue can be removed, improving the purity of the iron phosphate. By sintering the washed second filter residue, the crystallinity of the iron phosphate in the second filter residue is better, improving all aspects of the performance of the iron phosphate. By testing the purity of iron in the iron phosphate, a more accurate measurement of the purity of iron in the iron phosphate can be obtained. When the purity of iron is lower than the second preset requirement, its purity is improved through purification until the second preset requirement is met.

[0038] In a possible design, the method for recycling lithium iron phosphate material from waste batteries further includes: recovering lithium on the negative electrode plate.

[0039] The recovery of lithium on the negative electrode plate specifically includes:

[0040] Crushing the negative electrode plate.

[0041] Soaking the crushed negative electrode plate with a third soaking agent and performing suction filtration to obtain a third filtrate.

[0042] Electrolyzing the third filtrate using an electrolytic cell to obtain a second lithium-rich solution.

[0043] After the battery is used, there are usually unreacted lithium ions and crystalline lithium in the negative electrode plate. In the related art, the lithium in the negative electrode plate is usually easily ignored. Through the above solution, the recovery of lithium on the negative electrode plate can reduce the waste of this part of lithium. Specifically, crushing the negative electrode plate can reduce the volume of the negative electrode plate, enabling the negative electrode plate to come into full contact with the third soaking agent during the soaking process, which is beneficial to the dissolution of lithium on the negative electrode plate. By electrolyzing the third filtrate using an electrolytic cell, a second lithium-rich solution can be obtained. The concentration and purity of lithium in this solution are relatively high, which is beneficial to the further recovery of lithium.

[0044] In a possible design, the material recycling further includes:

[0045] Sodium carbonate is added to the second lithium-rich solution. After the reaction between the lithium-rich solution and sodium carbonate is completed, lithium carbonate is obtained by suction filtration.

[0046] The purity of lithium in the lithium carbonate is tested, and purification is carried out when the purity of lithium is lower than the first preset requirement.

[0047] The lithium carbonate obtained from the positive electrode sheet is mixed with the lithium carbonate obtained from the negative electrode sheet.

[0048] Through the above scheme, lithium carbonate precipitation is generated by the combination of sodium carbonate and lithium ions in the second lithium-rich solution, and then the lithium carbonate precipitation is separated by filtration. The lithium obtained by this chemical + physical purification method is theoretically of high purity. Then, by testing the purity of lithium in the lithium carbonate, a more accurate measurement of the purity of lithium in the lithium carbonate can be obtained. When the purity of lithium is lower than the first preset requirement, its purity is increased by purification until the first preset requirement is met. Since the existing form and concentration of lithium on the positive electrode sheet are different from those of lithium on the negative electrode sheet, before obtaining lithium carbonate with a qualified purity, the positive electrode sheet and the negative electrode sheet can be processed separately, and the finally obtained lithium carbonate that meets the first preset requirement is mixed. At this time, whether the lithium carbonate obtained from the positive electrode sheet or the lithium carbonate obtained from the negative electrode sheet is lithium carbonate that meets the same standard, and mixing them is beneficial to the unified storage and utilization of all recovered lithium carbonate. In a possible design, the method for recovering lithium iron phosphate material from waste batteries further includes material synthesis, and the material synthesis includes:

[0049] The iron phosphate is ball-milled and sieved to obtain iron phosphates with different particle size distributions.

[0050] The lithium carbonate and iron phosphates with different particle sizes are synthesized into iron lithium phosphates with different particle sizes.

[0051] The iron lithium phosphates with different particle sizes are mixed according to a preset ratio to obtain a lithium iron phosphate recovery material.

[0052] Through the above scheme, the above lithium carbonate can be the lithium carbonate recovered from the positive electrode sheet, or the lithium carbonate recovered from the negative electrode sheet, or a mixture of the lithium carbonate recovered from the positive electrode sheet and the lithium carbonate recovered from the negative electrode sheet. Synthesizing iron phosphate and lithium carbonate into lithium iron phosphate is convenient for direct use in subsequent battery manufacturing. Moreover, by grinding iron phosphate into different particle sizes, the finally synthesized lithium iron phosphate also has different particle sizes. By mixing iron lithium phosphates with different particle sizes, the overall density of the lithium iron phosphate recovery material becomes larger, enabling the recovery material to reach the performance level of brand-new battery-grade raw materials. Description of the Drawings

[0053] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0054] Figure 1 FIG. 4 is a process flow chart of the first method for recycling lithium iron phosphate materials from waste batteries provided by an embodiment of the present application.

[0055] Figure 2 FIG. 8 is a process flow chart of the treatment of the positive electrode sheet provided by an embodiment of the present application.

[0056] Figure 3 FIG. 12 is a process flow chart of the first material recycling provided by an embodiment of the present application.

[0057] Figure 4 FIG. 16 is a process flow chart of the second method for recycling lithium iron phosphate materials from waste batteries provided by an embodiment of the present application.

[0058] Figure 5 FIG. 20 is a process flow chart of recycling lithium on the negative electrode sheet provided by an embodiment of the present application.

[0059] Figure 6 FIG. 24 is a process flow chart of the second material recycling provided by the embodiments of the present application.

[0060] Figure 7 FIG. 28 is a method flow chart of the third method for recycling lithium iron phosphate materials from waste batteries provided by an embodiment of the present application.

[0061] Figure 8 FIG. 32 is a process flow chart of a material synthesis provided by an embodiment of the present application.

[0062] Figure 9 FIG. 36 is the first charge-discharge curve of the button batteries prepared from two lithium iron phosphate materials.

[0063] Figure 10 FIG. 40 is a diagram of the half-cell rate discharge capacity retention rate of the button batteries prepared from two lithium iron phosphate materials at different discharge rates.

[0064] Figure 11 FIG. 44 is a curve diagram of the cycle capacity retention rate of the soft-pack batteries prepared from two lithium iron phosphate materials. Detailed Embodiments

[0065] In order to make the object, technical solutions and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments and comparative examples. It should be understood that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention. The formulations, proportions, etc. of the embodiments can be selected according to local conditions without having a substantial impact on the results.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.

[0067] In the description of this application, unless otherwise specified, the meaning of "a plurality" means two or more (including two). Similarly, "a plurality of groups" means two or more groups (including two groups).

[0068] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase "embodiments" appearing at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0069] For the sake of simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recited.

[0070] The above-mentioned invention content of the present invention does not intend to describe every disclosed embodiment or every implementation mode of the present invention. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each instance, the listings are only representative groups and should not be construed as exhaustive.

[0071] The order of the operation steps connected by arrows in the attached drawings of this application is only an example of an execution order, and does not constitute a limitation on the execution order of the steps in the drawings. In actual use, those skilled in the art can adjust the order of execution of each step according to the specific content of the steps.

[0072] This application provides a method for recovering lithium iron phosphate materials from waste batteries. Figure 1 As shown in the process flow diagram of recovering lithium iron phosphate materials from waste batteries provided by the embodiments of this application, Figure 1 as shown, the method includes:

[0073] S100: Pretreatment of waste batteries: Discharge and disassemble the waste batteries.

[0074] In S100, by pretreating the waste batteries, the residual electric energy in the waste batteries can be effectively utilized, reducing energy waste.

[0075] Exemplarily, the waste batteries can be connected to an energy storage device, and the residual electric energy in the waste batteries is discharged into the energy storage device for storage. The electric energy in the energy storage device can be used for subsequent recovery processes or other industrial production, achieving the effect of reducing energy waste.

[0076] After the battery is discharged, the battery is disassembled, that is, the battery case is opened, the electrode assembly therein is taken out, and the positive electrode sheet, negative electrode sheet, and separator of the electrode assembly are collected separately, so as to separately recover and process each material of the electrode assembly subsequently.

[0077] S200: Treatment of positive electrode sheets: Separate the positive electrode current collector and the positive electrode active material.

[0078] Figure 2 As shown in the process flow diagram of treating positive electrode sheets provided by the embodiments of this application, please refer to Figure 2 , and the steps of treating positive electrode sheets specifically include:

[0079] S210: Immerse the positive electrode sheet with a first soaking agent to initially separate the positive electrode current collector and the positive electrode active material.

[0080] S220: Crush the positive electrode sheet soaked with the first soaking agent.

[0081] S230: Immerse the crushed positive electrode sheet with a second soaking agent to separate the positive electrode current collector and the positive electrode active material again, and filter to obtain a first filter residue mainly composed of the positive electrode active material.

[0082] S240: Dry, grind, and screen the first filter residue to remove impurities and obtain a lithium iron phosphate impurity-removing material.

[0083] In S210, soaking the positive electrode sheet with the first soaking agent can preliminarily loosen and separate the positive electrode current collector and the positive electrode active material. Among them, the first soaking agent can be water or an alkaline solution.

[0084] Specifically, in a possible design, the first soaking agent used in S210 includes cold water and hot water. Soaking the positive electrode sheet with the first soaking agent specifically includes: soaking the positive electrode sheet alternately with cold water and hot water for multiple times, and the soaking time for each time is 30 - 60 min. Among them, the number of soakings can be 3 - 5 times, and filtration is required after each soaking.

[0085] Among them, in the above solution, cold water refers to water with a temperature of -10 to 0 °C, and hot water refers to water with a temperature of 40 - 60 °C. Each soaking includes soaking with cold water once and soaking with hot water once. For example, in a specific embodiment, the positive electrode sheet is soaked three times, and each soaking includes soaking the positive electrode sheet with cold water for 20 minutes first, and then soaking the positive electrode sheet with hot water for 30 minutes.

[0086] Configuring the first soaking agent as cold water and hot water, water is an easily obtainable substance with low cost, and by alternately soaking with cold water and hot water, using the principle of thermal expansion and contraction, it can accelerate the shedding of the positive electrode active material from the positive electrode current collector and will not introduce new impurities.

[0087] In S220, the positive electrode sheet soaked with the first soaking agent can be broken into fragments of 20 - 1000 mm 2 by means of air flow crushing. Among them, the air flow crushing method is relatively gentle and is not easy to break the positive electrode current collector into fine aluminum slag. Therefore, it can reduce the aluminum impurities in the positive electrode active material. In addition, when air flow crushing, the impact force of the air flow can also form a certain impact on the positive electrode active material, which is beneficial to accelerating the shedding of the positive electrode active material from the positive electrode current collector.

[0088] By performing crushing treatment on the positive electrode sheet soaked with the first soaking agent in S220, it is beneficial to change the long strip-shaped positive electrode sheet into shorter particles, which is beneficial to making the positive electrode sheet fully contact with the subsequent second soaking agent, and further beneficial to the shedding of the positive electrode active material from the positive electrode current collector, so as to achieve the purpose of separating the positive electrode current collector and the positive electrode active material.

[0089] In a possible design, the second soaking agent includes ammonia water. Soaking the crushed positive electrode sheet with the second soaking agent specifically includes: mixing ammonia water with the crushed positive electrode sheet and soaking at 60 - 100 °C for a time greater than 2 h.

[0090] Among them, the above ammonia water is self-made ammonia water. After ammonia water decomposes, it becomes ammonia gas and water, and will not introduce new impurities while soaking the positive electrode sheet, realizing environmental protection.

[0091] The second soaking agent is ammonia water, which can provide an alkaline environment for the crushed positive electrode sheet, dissolve part of the binder and aluminum foil, and completely separate the positive electrode current collector from the positive electrode active material. Ammonia water can react efficiently with the positive electrode sheet at 60-100 °C, and a reaction time of more than 2 hours can ensure sufficient reaction between ammonia water and the positive electrode sheet, improving the separation rate of the positive electrode current collector and the positive electrode active material. Therefore, the above reaction conditions are conducive to the complete separation of the positive electrode current collector and the positive electrode active material.

[0092] Considering that ammonia water will continuously decompose to produce ammonia gas during the process of soaking the positive electrode sheet, resulting in a gradual decrease in the alkalinity of ammonia water and a gradual weakening of the soaking effect, ammonia water can be replaced multiple times during the soaking process. For example, ammonia water can be replaced 3-5 times during the soaking process to achieve a better soaking effect in a short time.

[0093] In addition, considering the high efficiency of S230, the soaking time can be 2-5 hours, and during the soaking of the positive electrode sheet with ammonia water, additional forces such as stirring, vibration, shaking, etc. can be applied to accelerate the separation of the positive electrode current collector and the positive electrode active material.

[0094] In a specific example, 1 mol / L of self-made ammonia water is mixed with the crushed recycled material at a solid-liquid ratio of 1:3, soaked at 60-100 °C for 3 hours, and ammonia water is replaced 3 times during the soaking process.

[0095] After soaking, filtration is carried out by suction. The main component of the first filter residue obtained by suction filtration is the positive electrode active material, which includes lithium iron phosphate and a binder, but it also contains undissolved aluminum foil.

[0096] In S240, by drying and grinding the first filter residue, lithium iron phosphate can be ground into powder with a smaller particle size, while aluminum foil and the binder are difficult to be ground into powder with a smaller particle size due to their large ductility. Based on this, after grinding the first filter residue, screening is carried out to remove impurities such as aluminum and binder in the first filter residue, obtaining relatively pure lithium iron phosphate impurity removal material, achieving the purpose of impurity removal. Moreover, this impurity removal process utilizes the physical properties of impurities and lithium iron phosphate, does not use chemical means for impurity removal, will not introduce new impurities, and the cost is relatively low.

[0097] In a possible design, the drying, grinding and screening of the first filter residue in S240 include:

[0098] The first filter residue after drying and grinding is screened using multiple layers of sieve meshes, and the pore sizes of the sieve meshes decrease from top to bottom to screen out impurities of different sizes layer by layer.

[0099] Specifically, the grinding can be carried out by a ball mill, and the ball milling time is 3 - 5 hours. The specific grinding time depends on the amount of the first filter residue loaded into the ball mill.

[0100] In a specific example, a vibrating screen is used to screen the first filter residue. The vibrating screen includes three layers of sieve meshes. From top to bottom, the first layer is a sieve mesh with a size of 100 - 150 meshes to remove substances with larger particles; the second layer is a sieve mesh with a size of 250 - 300 meshes to screen out substances with medium-sized particles; the third layer is a sieve mesh with a size of over 500 meshes to screen out substances with slightly larger particles. Finally, the substances passing through the three layers of sieve meshes are those with a particle size greater than 500 meshes. Among them, the substances with a particle size greater than 500 meshes are mainly the impurity-removing materials of lithium iron phosphate with smaller particles.

[0101] In the above example, if it is found that the substances sieved on the third layer of sieve mesh contain a relatively large amount of lithium iron phosphate, the substances on the third layer of sieve mesh can be further ground and then screened again to avoid wasting too much impurity-removing material of lithium iron phosphate.

[0102] By sieving out impurities of different sizes layer by layer, it is possible to prevent the situation where too many impurities are sieved out by a single layer of sieve mesh, resulting in clogging of the mesh holes and making it difficult for the impurity-removing material of lithium iron phosphate to fall quickly. In addition, although theoretically, the particle size of lithium iron phosphate in the ground first filter residue is smaller than that of the impurities, there are still a small number of cases where the particle size of lithium iron phosphate is equivalent to that of the impurities, or the particle size of lithium iron phosphate is larger than that of the impurities. At this time, the materials on the sieve mesh can be further ground according to the content of lithium iron phosphate sieved out on each layer of sieve mesh. After the particle size of this part of lithium iron phosphate with a larger particle size is further reduced, it is sieved again to achieve the purpose of impurity removal and no waste of lithium iron phosphate materials.

[0103] After going through the various steps of S200 above, it is possible to separate the positive electrode current collector and the positive electrode active material, and conduct a preliminary impurity removal on the positive electrode active material. The content of lithium iron phosphate in the obtained impurity-removing material of lithium iron phosphate is relatively high, and the impurities are relatively few.

[0104] As Figure 1 shown, in the method for recycling lithium iron phosphate materials from waste batteries provided by the present application, after the positive electrode sheet treatment in S200, it further includes:

[0105] S300: Material recovery: Separate the lithium element and the iron element in the positive electrode active material, and recover the lithium element in the form of lithium carbonate and the iron element in the form of iron phosphate.

[0106] Figure 3 This is a process flow chart of a material recovery provided by an embodiment of the present application. As Figure 3 shown, in some embodiments, S300 includes:

[0107] S310: Subject the lithium iron phosphate impurity-removed material to high-temperature sintering.

[0108] Specifically, the lithium iron phosphate impurity-removed material obtained in S200 can be sintered in a calcination furnace at a temperature of 400-600 °C for 1-2 hours to further remove the residual graphite particles and binder in the previous steps.

[0109] In a possible design, S300 further includes:

[0110] S320: Immerse the lithium iron phosphate impurity-removed material in an organic acid and hydrogen peroxide, and filter to obtain a second filter residue and a second filtrate. The second filter residue includes iron phosphate, and the second filtrate includes lithium ions.

[0111] Among them, the organic acid can preferably be a green, non-toxic and pollution-free organic acid.

[0112] By immersing the lithium iron phosphate impurity-removed material in an organic acid and hydrogen peroxide, no new impurity elements will be introduced into the recycled material. Thus, while separating iron phosphate and lithium ions in the lithium iron phosphate impurity-removed material, it will not cause secondary pollution to the lithium iron phosphate impurity-removed material, and there is no need to further process the recycled waste products, which is beneficial to improving the environmental protection of battery recycling and reducing the subsequent treatment cost.

[0113] In some embodiments, the organic acid can be L-malic acid. L-malic acid can be self-made. For example, a feasible way to self-make L-malic acid is: use fruits such as grapes, apples, and peaches that are near the expiration date or purchased at low cost in the orchard, crush and boil them, add a certain amount of lime water to react and then filter, and obtain a liquid rich in L-malic acid after treatment.

[0114] In some embodiments, the specific method of immersing the lithium iron phosphate impurity-removed material in an organic acid and hydrogen peroxide in S320 is: mix the lithium iron phosphate impurity-removed material, L-malic acid, and hydrogen peroxide according to the mass of the lithium iron phosphate impurity-removed material: the mass of 1 mol / L L-malic acid: the mass of 30% hydrogen peroxide = 1:(1 - 1.5):(0.3 - 0.6), immerse at 30-60 °C for 30-150 min, and obtain a second filtrate and a second filter residue after suction filtration.

[0115] In a possible design, the material recycling in S300 further includes:

[0116] S330: Electrolyze the second filtrate using an electrolytic cell. The electrolytic cell includes a cathode cell and an anode cell, and the cathode cell and the anode cell are separated by a proton exchange membrane; during the electrolysis process, place the second filtrate in the anode cell and place the LiOH solution in the cathode cell. After the electrolysis is completed, a first lithium-rich solution is obtained in the cathode cell.

[0117] The proton exchange membrane can be a Nafion proton exchange membrane, which only allows lithium ions to pass through. Specifically, the Nafion proton exchange membrane can be of the Nafion 115 type or the Nafion 117 type.

[0118] In some embodiments, the specific operation of electrolyzing the second filtrate using an electrolytic cell is as follows: Place the second filtrate in the anode cell, the cathode cell is a 0.1 mol / L LiOH solution, the volume ratio of the cathode cell to the anode cell solution is 1:1, the electrolysis process is carried out at 30 - 60 °C, and the solutions in the cathode cell and the anode cell are stirred during the electrolysis process, and the stirring speed is 600 - 1500 r / min.

[0119] In this embodiment, the electrolysis process is carried out at 30 - 60 °C, the electrolysis reaction is faster, and the ionization efficiency is high. By stirring the cathode cell and the anode cell, the solutions in the cathode cell and the anode cell can be kept relatively uniform throughout the reaction process, ensuring that the electrolysis process can continue, and at the same time, it can also avoid a large amount of free Li + concentrating near the proton exchange membrane, while the free OH - concentrates at a position far from the proton exchange membrane, and Li + and OH - from not being able to combine in time.

[0120] In order to monitor the progress of electrolysis in real time, an electrochemical workstation is used to detect the degree of electrolysis in real time with an I - T (current - time) curve throughout the electrolysis process. When the current density undergoes a sudden change, the reaction ends.

[0121] Through the above - mentioned scheme, the second filtrate contains a large amount of lithium ions. By electrolyzing the second filtrate using an electrolytic cell, during the electrolysis process, the water in the cathode cell is electrolyzed to generate hydrogen and hydroxide ions. The lithium ions in the anode cell pass through the proton exchange membrane to reach the cathode cell and combine with the hydroxide ions in the cathode cell to form LiOH. Finally, a first lithium - rich solution is obtained in the cathode cell. Among them, placing a LiOH solution in the cathode cell in the initial state can ensure that the concentration of hydroxide ions in the cathode cell reaches a certain amount in the initial state for combining with lithium ions and does not introduce extra impurity elements.

[0122] In a possible design, when using an electrolytic cell to electrolyze the second filtrate, the lithium - rich solution in the cathode cell is recrystallized and then formulated into a LiOH solution and placed in the cathode cell.

[0123] Through the above - mentioned scheme, during the recycling process of waste batteries, there is no need to purchase lithium hydroxide. Instead, the lithium hydroxide electrolytically recovered from the second filtrate is formulated into a lithium hydroxide solution for electrolysis, realizing the reuse of the recovered lithium hydroxide and achieving the purpose of cost savings.

[0124] Please continue to refer to Figure 3 , in a possible design, the S300 material recovery further includes:

[0125] S340: Add sodium carbonate to the first lithium-rich solution. After the reaction between the first lithium-rich solution and sodium carbonate is completed, filter by suction to obtain lithium carbonate.

[0126] S350: Test the purity of lithium in the lithium carbonate and perform purification when the purity of lithium is lower than the first preset requirement.

[0127] In S340, the total amount of Li + in the first lithium-rich solution and the total amount of CO 3 2- in the sodium carbonate solution should be added to the reaction in a ratio of 2:1 to ensure the completeness of the reaction to generate Li 2 CO 3 . Therefore, before performing S340, it is also necessary to obtain the concentration of Li + in the first lithium-rich solution obtained in S330 and the concentration of CO 3 2- in the sodium carbonate solution, so as to rationally mix and use the two solutions. Specifically, the concentration of Li + in the first lithium-rich solution can be detected by ICP detection.

[0128] In S350, the first preset requirement can be a purity higher than or equal to the industry standard. For example, it can be 98%.

[0129] The purity of lithium in the lithium carbonate can be measured by ICP detection. If the measured concentration of lithium is higher than or equal to 98%, the lithium carbonate can be directly encapsulated for subsequent use. If the measured concentration of lithium is lower than 98%, the lithium carbonate is purified, and the measurement is performed after each purification until the purity of lithium is higher than or equal to 98%.

[0130] Among them, the specific purification method of lithium carbonate is not specifically limited in this application, and any relevant purification method can be used.

[0131] Exemplarily, a feasible way to purify lithium carbonate is: put lithium carbonate into pure water, introduce high-purity carbon dioxide, filter by suction, dry, and crystallize to obtain lithium bicarbonate to remove excess impurities. Then, high-purity lithium carbonate is obtained by high-temperature sintering of lithium bicarbonate. The carbon dioxide generated during the high-temperature sintering process can be recycled as appropriate.

[0132] In the above process of recovering lithium carbonate, lithium carbonate precipitate is generated by the reaction of sodium carbonate with lithium hydroxide in the first lithium-rich solution, and then the lithium carbonate precipitate is separated by filtration. The lithium obtained by this chemical + physical purification method is theoretically of high purity. Then, by testing the purity of lithium in lithium carbonate, a more accurate measurement of the purity of lithium in lithium carbonate can be obtained. When the purity of lithium is lower than the first preset requirement, it is purified until the first preset requirement is met.

[0133] Please continue to refer to Figure 3 , in a possible design, the S300 material recovery further includes:

[0134] S360: Wash the second filter residue with water.

[0135] By washing the second filter residue with water, the substances adhered to the surface of the second filter residue can be removed, and the purity of iron phosphate can be improved.

[0136] S370: Sinter the second filter residue washed with water to obtain iron phosphate.

[0137] By sintering the second filter residue washed with water, the crystallinity of iron phosphate in the second filter residue is better, the various properties of iron phosphate are improved, and a certain impurity removal effect can be achieved.

[0138] S380: Test the purity of iron in iron phosphate, and perform purification when the purity of iron is lower than the second preset requirement.

[0139] The second preset requirement is a purity higher than or equal to the industry standard. For example, it can be 98%.

[0140] The purity of iron in iron phosphate can be measured by ICP detection. If the measured iron concentration is higher than or equal to 98%, the iron phosphate can be directly encapsulated for subsequent use. If the measured iron concentration is lower than 98%, the iron phosphate is purified, and the measurement is performed after each purification until the purity of iron is higher than or equal to 98%.

[0141] Among them, the specific purification method of iron phosphate is not specifically limited in this application, and any relevant purification method can be used.

[0142] By testing the purity of iron in iron phosphate, a more accurate measurement of the purity of iron in iron phosphate can be obtained. When the purity of iron is lower than the second preset requirement, it is purified until the second preset requirement is met, so as to obtain iron phosphate with higher purity.

[0143] In the conventional battery recycling process, the lithium remaining in the negative electrode is easily overlooked. However, although the negative electrode sheet material does not include lithium when manufacturing the negative electrode sheet, after the battery is used, there are usually un-discharged lithium ions and crystalline lithium in the negative electrode. When the volume of waste batteries is relatively large, the waste of this part of lithium is also quite considerable.

[0144] For this reason, please refer to Figure 4 , Figure 4 which is the flowchart of the second method for recycling lithium iron phosphate material from waste batteries provided by the embodiments of the present application. In some embodiments, the method for recycling lithium iron phosphate material from waste batteries further includes:

[0145] S400: Recover the lithium on the negative electrode sheet.

[0146] Figure 5 which is the process flowchart for recovering the lithium on the negative electrode sheet provided by an embodiment of the present application. Please refer to Figure 5 , and S400 specifically includes:

[0147] S410: Crush the negative electrode sheet.

[0148] The crushing treatment of the negative electrode sheet can refer to the way of crushing the positive electrode sheet, that is, the negative electrode sheet is crushed into fragments of 20 - 1000 mm 2 by using the air flow crushing method. Among them, the air flow crushing method is relatively gentle and is not easy to crush the negative electrode current collector into fine copper slag. Therefore, it can reduce the copper impurities in the negative electrode active material. In addition, when using the air flow crushing method, the impact force of the air flow can also form a certain impact on the negative electrode active material, which is beneficial to accelerating the detachment of the negative electrode active material from the negative electrode current collector.

[0149] S420: Immerse the crushed negative electrode sheet with a third soaking agent, and perform suction filtration to obtain a third filtrate.

[0150] In one example, the third soaking agent can be pure water, and the water temperature can be normal temperature or warm. During the soaking process, the negative electrode sheet can be stirred to accelerate the dissolution of lithium.

[0151] The negative electrode sheet can be soaked 3 - 5 times, and suction filtration is performed after each soaking. The third filtrate is the sum of the filtrates after multiple soakings. It can be understood that after soaking, the lithium on the negative electrode sheet exists in the third filtrate in the form of lithium hydroxide.

[0152] S430: Electrolyze the third filtrate with an electrolytic cell to obtain a second lithium-rich solution.

[0153] The electrolysis equipment and specific operation steps for electrolyzing the third filtrate can be the same as those in S330, and are not elaborated in this embodiment of the present application.

[0154] The third filtrate is electrolyzed by an electrolytic cell. During the electrolysis process, water in the cathode cell is electrolyzed to generate hydrogen and hydroxide ions. Lithium ions in the anode cell pass through the proton exchange membrane to reach the cathode cell and combine with hydroxide ions in the cathode cell to form LiOH. Eventually, a second lithium-rich solution is obtained in the cathode cell.

[0155] In some embodiments, when the third filtrate is electrolyzed using an electrolytic cell, the second lithium-rich solution in the cathode cell is recrystallized and then formulated into a LiOH solution and placed in the cathode cell. In this way, during the recycling process of waste batteries, there is no need to purchase lithium hydroxide. Instead, lithium hydroxide recovered by electrolysis from the third filtrate is used to prepare the lithium hydroxide solution for electrolysis, realizing the reuse of the recovered lithium hydroxide and achieving the purpose of cost savings.

[0156] It can be understood that the electrolysis equipment and specific operation steps for the third filtrate can be the same as those for the second filtrate, thereby increasing process proficiency, reducing operation difficulty, and achieving the effect of equipment universality on the production line, saving the cost of battery material recycling. Moreover, when electrolyzing the second filtrate and the third filtrate, the lithium hydroxide solution initially input into the cathode cell during the initial stage of electrolysis can also be universal.

[0157] After obtaining the second lithium-rich solution in the above S430, the subsequent treatment process of the second lithium-rich solution can refer to the methods of S340 - S350 described above.

[0158] Specifically, it can be referred to Figure 6 , Figure 6 which is the flowchart of the second material recycling provided by the embodiment of the present application. As Figure 6 shown, in a possible design, when the method for recycling lithium iron phosphate material from waste batteries further includes S400 for recovering lithium on the negative electrode sheet, S300 for material recycling further includes:

[0159] S341: Add sodium carbonate to the second lithium-rich solution. After the reaction between the second lithium-rich solution and sodium carbonate is completed, filter to obtain lithium carbonate.

[0160] Lithium carbonate precipitate is formed by the combination of sodium carbonate and lithium ions in the second lithium-rich solution, and then the lithium carbonate precipitate is separated by filtration. The lithium obtained by this chemical + physical purification method is theoretically of high purity.

[0161] S342: Test the purity of lithium in the lithium carbonate, and perform purification when the purity of lithium is lower than the first preset requirement.

[0162] By testing the purity of lithium in lithium carbonate to obtain a more accurate measurement of the purity of lithium in lithium carbonate, when the purity of lithium is lower than the first preset requirement, the purity is increased through purification until the first preset requirement is met. The first preset requirement here is the same as the first preset requirement described above.

[0163] S343: Mix the lithium carbonate obtained from the positive electrode sheet with the lithium carbonate obtained from the negative electrode sheet.

[0164] It should be noted that since the concentrations of lithium ions and the types of impurities in the first lithium-rich solution obtained from the positive electrode sheet and the second lithium-rich solution obtained from the negative electrode sheet are different, based on this, when reacting to obtain lithium carbonate, the molar amount of carbonate ions to be added is different, and the purification methods used may also be different. Therefore, although the same treatment method is used to treat the first lithium-rich solution and the second lithium-rich solution, the first lithium-rich solution and the second lithium-rich solution need to be treated separately, rather than mixing the first lithium-rich solution and the second lithium-rich solution for treatment.

[0165] In S343, mix the lithium carbonate obtained from the positive electrode sheet in the aforementioned S340 and S350 with the lithium carbonate obtained from the negative electrode sheet in the aforementioned S341 and S342. At this time, whether the lithium carbonate obtained from the positive electrode sheet or the lithium carbonate obtained from the negative electrode sheet, both are lithium carbonate after being purified by the same standard. Therefore, the purity of the lithium carbonate meets the requirements. At this time, the lithium carbonate obtained from the positive electrode sheet can be mixed with the lithium carbonate obtained from the negative electrode sheet, which is beneficial to the unified storage and utilization of all the recovered lithium carbonate.

[0166] Recycling lithium on the negative electrode sheet through the above method can reduce the current industry's neglect of lithium on the negative electrode sheet, fill the gap in the recycling treatment method of lithium on the negative electrode sheet, achieve the complete recycling of lithium elements in waste batteries, and reduce resource waste.

[0167] Figure 7 This is the flow chart of the third method for recycling lithium iron phosphate materials from waste batteries provided by this application. As Figure 7 shown, in a possible design, the method for recycling lithium iron phosphate materials from waste batteries further includes:

[0168] S500: Material synthesis.

[0169] Figure 8 This is the process flow chart of a material synthesis provided by an embodiment of this application. Please refer to Figure 8 , and the material synthesis includes:

[0170] S510: Ball mill and sieve the iron phosphate to obtain iron phosphate with different particle size distributions.

[0171] For example, three kinds of iron phosphate with different particle size distributions can be obtained, namely, 10 - 50 microns; 50 - 80 microns; 80 - 100 microns.

[0172] S520: Synthesize lithium iron phosphate with different particle sizes by using lithium carbonate and iron phosphate with different particle sizes.

[0173] It can be understood that the lithium carbonate in this step can be the lithium carbonate obtained in S350, or the lithium carbonate obtained in S342, or the mixed lithium carbonate in S343.

[0174] The iron phosphate used is the iron phosphate obtained in S510.

[0175] Specifically, any technology for synthesizing lithium iron phosphate from lithium carbonate and iron phosphate in related technologies can be adopted, and the embodiments of the present application do not limit this.

[0176] In some embodiments, glucose can be used to participate in the synthesis of lithium iron phosphate.

[0177] In a specific example, lithium carbonate, iron phosphate and glucose are mixed in a ratio of 1:1:1, ground by a ball mill for 2 h and then continuously sanded for 1 h. Finally, the mixture of the foregoing lithium carbonate, iron phosphate and glucose is sintered at a high temperature of 450 °C for 4 h in an inert atmosphere, and then sintered at 720 °C for 6 h to obtain lithium iron phosphate. After the sintering is completed, the particle size, density, pH value, etc. of the lithium iron phosphate are tested, and demagnetization is carried out.

[0178] S530: Mix lithium iron phosphates with different particle sizes according to a preset ratio to obtain a lithium iron phosphate recycling material.

[0179] Through the above material synthesis scheme, iron phosphate and lithium carbonate are synthesized into lithium iron phosphate, which is convenient for direct use in subsequent battery manufacturing. Moreover, by grinding iron phosphate into different particle sizes, the finally synthesized lithium iron phosphate also has different particle sizes. By mixing lithium iron phosphates with different particle sizes, the overall density of lithium iron phosphate becomes larger, and when it is finally used as the cathode material of the battery, the energy density of the battery can be improved.

[0180] The following conducts various physical and chemical property tests on the lithium iron phosphate recycling material recovered from a certain batch of waste batteries according to the above method, and compares the test results with the physical and chemical properties of the main lithium iron phosphate material in the raw materials of this batch of waste batteries. The comparison results are listed in Table 1 below.

[0181] Table 1

[0182]

[0183]

[0184] As can be seen from the data in Table 1, the physical and chemical properties of the lithium iron phosphate material recovered by the above method are less different from those of the brand-new raw materials of lithium iron phosphate. Based on this, it can be expected that the various service performances of the battery made of the lithium iron phosphate impurity-removing material can basically reach those of the battery made of the lithium iron phosphate raw material, meeting the usage requirements of the battery.

[0185] To further verify the differences in the main performances between the battery made of the lithium iron phosphate recycled material and the battery made of the lithium iron phosphate raw material, in the following examples, the above-mentioned lithium iron phosphate raw material and lithium iron phosphate recycled material were each prepared into button cells, and the performances of the button cells were analyzed.

[0186] Preparation of Button Battery

[0187] The formula of the solid substances in the positive electrode slurry is 96% lithium iron phosphate (LFP), 2% conductive carbon black (SP), and 2% binder (PVDF). After mixing the above three substances well and adding the solvent N-methylpyrrolidone (NMP), it was degassed for 60 min to prepare the positive electrode slurry. The positive electrode slurry was coated on the carbon-coated aluminum foil, and the coating surface density was 16 mg / cm 2 , and then vacuum dried at 80 °C for 12 h. Electrochemical measurements were carried out at 25 °C, using CR2025 coin-type batteries with lithium as the negative electrode. The electrolyte used was a mixed solvent of DMC-EC (dimethyl carbonate-ethylene carbonate) containing 1 mol / L of LiPF 6 and 5% FEC (fluoroethylene carbonate). The battery assembly was carried out in a glove box with the water and oxygen content of <0.1 ppm.

[0188] Button Battery Test

[0189] The Lanhe instrument was used to study the constant current charge-discharge capacity and rate performance of the button cells prepared from the two lithium iron phosphate materials at different current densities in the voltage range of 2.5 - 4.0 V.

[0190] Figure 9 Fig. 23 shows the first charge-discharge curves of the button cells prepared from the two lithium iron phosphate materials. In this figure, the two curves with upward voltage mutations are the charge curves, and the curve with downward voltage mutation is the discharge curve. This figure reflects the situation where the voltage changes with the continuous change of the charge-discharge capacity during the charging or discharging process. In Figure 9 it, curve a represents the charge curve of the button cell prepared from the lithium iron phosphate raw material, curve b represents the charge curve of the button cell prepared from the lithium iron phosphate recycled material, curve c represents the discharge curve of the button cell prepared from the lithium iron phosphate raw material, and curve d represents the discharge curve of the button cell prepared from the lithium iron phosphate recycled material.

[0191] From Figure 9 It can be seen that during the first charging process of the battery, the trends of curve a and curve b are the same, and the two curves basically completely overlap. During the first discharging process of the battery, the trends of curve c and curve d are the same, and the two curves basically completely overlap. Thus, it can be seen that the charge-discharge performance and capacity of the battery prepared with the lithium iron phosphate recycled material can basically meet the same performance requirements as the battery prepared with the lithium iron phosphate raw material.

[0192] Figure 10 It is the half-cell rate discharge capacity retention rate of button batteries prepared with two lithium iron phosphate materials at different discharge rates. Figure 10 In [figure], the left column is the half-cell rate discharge capacity retention rate of the battery prepared with the lithium iron phosphate raw material, and the right column is the half-cell rate discharge capacity retention rate of the battery prepared with the lithium iron phosphate recycled material.

[0193] From Figure 10 It is known that at the same discharge rate, the half-cell rate discharge capacity retention rate of the button battery prepared with the lithium iron phosphate recycled material is basically the same as that of the button battery prepared with the lithium iron phosphate raw material. Thus, it can be seen that the rate performance of the battery prepared with the lithium iron phosphate recycled material can basically reach that of the battery prepared with the lithium iron phosphate raw material and meet the rate requirements of the battery.

[0194] In order to further verify that the lithium iron phosphate material recovered by the method of recovering lithium iron phosphate material from waste batteries in this application can be used in batteries and enable the batteries to maintain electrochemical performance comparable to that of the lithium iron phosphate raw material, soft-pack batteries were also prepared with the lithium iron phosphate recycled material and the lithium iron phosphate raw material respectively, and their relevant performances were tested as follows:

[0195] Preparation of Soft Pack Battery

[0196] The soft-pack batteries were prepared using the soft-pack production line developed by our company. Among them, the lithium iron phosphate added to the positive electrode material of some batteries is the lithium iron phosphate raw material, and the lithium iron phosphate added to the positive electrode material of some batteries is the lithium iron phosphate recycled material obtained by the above recovery method of this application. The remaining materials are general materials on the production line, and finally two 5Ah soft-pack batteries were prepared.

[0197] Soft Pack Battery Test

[0198] The above two soft-pack batteries were tested for the cycle capacity retention rate at 45°C. During the test, the charging and discharging of the batteries were both at a 1C rate.

[0199] Figure 11It is the cycle capacity retention rate curve of the above-mentioned soft-pack battery. In the figure, curve e is the cycle capacity retention rate curve of the soft-pack battery with lithium iron phosphate raw material used as the cathode material, and curve f is the cycle capacity retention rate curve of the soft-pack battery with recycled lithium iron phosphate used as the cathode material. It can be seen that at the beginning of the cycle, the capacity retention rates of curve e and curve f are basically the same. As the number of cycles increases, curve e and curve f gradually show differences. Specifically, curve f is lower than curve e. However, as the number of cycles further increases, roughly after 500 cycles, the gap between curve e and curve f begins to decrease again. Overall, the changing trends of curve e and curve f are consistent, and the difference between the two curves is small. This further verifies that the rate performance of the battery prepared with recycled lithium iron phosphate can basically reach that of the battery prepared with lithium iron phosphate raw material, meeting the rate requirements of the battery.

[0200] In summary, the method for recycling lithium iron phosphate material from waste batteries provided by this application can reduce the impurities in the recycled lithium iron phosphate material, increase the purity of the recycled lithium iron phosphate material. The physical and chemical properties of the recycled lithium iron phosphate material are excellent and can basically reach the same physical and chemical properties as the brand-new lithium iron phosphate material. The battery manufactured with this recycled lithium iron phosphate has a long service life and excellent cycle performance.

Claims

1. A method for recovering lithium iron phosphate material from waste batteries, characterized in that: include: Pretreatment of used batteries: discharging and disassembling used batteries; Positive electrode sheet processing: separation of positive electrode current collector and positive electrode active material; Material recovery: Separate the lithium and iron elements from the positive electrode active material, and recover the lithium element in the form of lithium carbonate and the iron element in the form of iron phosphate; Among them, the positive electrode processing specifically includes: soaking the positive electrode sheet with a first soaking agent to initially separate the positive electrode current collector and the positive electrode active material; Crushing the positive electrode sheet soaked in the first soaking agent; soaking the crushed positive electrode sheet in a second soaking agent to separate the positive electrode current collector and the positive electrode active material again, and filtering to obtain a first filter residue containing the positive electrode active material as a main component; The first filter residue is dried, ground and sieved to remove impurities, thereby obtaining lithium iron phosphate impurity-free material.

2. The method for recovering lithium iron phosphate material from waste batteries according to claim 1, characterized in that: The first soaking agent includes cold water and hot water, and soaking the positive electrode sheet with the first soaking agent specifically includes: The positive electrode sheet is soaked in cold water and hot water alternately for multiple times, and each soaking time is 30-60 minutes.

3. The method for recovering lithium iron phosphate material from waste batteries according to claim 1, characterized in that: The second soaking agent includes ammonia water, and soaking the crushed positive electrode sheet with the second soaking agent specifically includes: Mix ammonia water with the crushed positive electrode sheet and soak it at 60-100°C for more than 2 hours.

4. The method for recovering lithium iron phosphate material from waste batteries according to claim 1, characterized in that: The drying, grinding and screening of the first filter residue comprises: The first filter residue after drying and grinding is screened by using a multi-layer screen, and the aperture of the screen decreases from top to bottom, so as to screen out impurities of different sizes layer by layer.

5. The method for recovering lithium iron phosphate material from waste batteries according to claim 1, characterized in that: The material recycling specifically includes: The lithium iron phosphate impurity-removing material is soaked in organic acid and hydrogen peroxide, and filtered to obtain a second filter residue and a second filtrate, wherein the second filter residue includes iron phosphate and the second filtrate includes lithium ions.

6. The method for recovering lithium iron phosphate material from waste batteries according to claim 5, characterized in that: The material recovery also includes: electrolyzing the second filtrate using an electrolytic cell, wherein the electrolytic cell includes a cathode cell and an anode cell, and the cathode cell and the anode cell are separated by a proton exchange membrane; during the electrolysis process, placing the second filtrate in the anode cell and placing the LiOH solution in the cathode cell, and after the electrolysis is completed, obtaining a first lithium-rich solution in the cathode cell.

7. The method for recovering lithium iron phosphate material from waste batteries according to claim 6, characterized in that: The material recycling also includes: adding sodium carbonate to the first lithium-rich solution, and filtering to obtain lithium carbonate after the lithium-rich solution and sodium carbonate react; The purity of lithium in the lithium carbonate is tested, and purification is performed when the purity of the lithium is lower than a first preset requirement.

8. The method for recovering lithium iron phosphate material from waste batteries according to claim 6, characterized in that: When the second filtrate is electrolyzed by using an electrolytic cell, the first lithium-rich solution in the cathode cell is recrystallized to form a LiOH solution and placed in the cathode cell.

9. The method for recovering lithium iron phosphate material from waste batteries according to claim 5, characterized in that: The material recycling also includes: washing the second filter residue with water; sintering the washed second filter residue to obtain iron phosphate; The purity of iron in the ferric phosphate is tested, and purification is performed when the purity of the iron is lower than a second preset requirement.

10. The method for recovering lithium iron phosphate material from waste batteries according to any one of claims 1 to 9, characterized in that: The method further comprises: collecting lithium on the negative electrode sheet; The collecting of lithium on the negative electrode sheet specifically includes: Crushing the negative electrode sheet; soaking the crushed negative electrode sheet in a third soaking agent, and filtering to obtain a third filtrate; The third filtrate is electrolyzed by using an electrolytic cell to obtain a second lithium-rich solution.

11. The method for recovering lithium iron phosphate material from waste batteries according to claim 10, characterized in that: The material recycling also includes: adding sodium carbonate to the second lithium-rich solution, and filtering to obtain lithium carbonate after the lithium-rich solution and sodium carbonate react; Testing the purity of lithium in the lithium carbonate, and purifying the lithium when the purity of the lithium is lower than a first preset requirement; The lithium carbonate obtained from the positive electrode sheet is mixed with the lithium carbonate obtained from the negative electrode sheet.

12. The method for recovering lithium iron phosphate material from waste batteries according to claim 1, characterized in that: The method further comprises material synthesis, wherein the material synthesis comprises: The iron phosphate is ball-milled and sieved to obtain iron phosphate with different particle size distributions; synthesizing lithium carbonate and iron phosphate of different particle sizes into lithium iron phosphate of different particle sizes; Lithium iron phosphate of different particle sizes is mixed according to a preset ratio to obtain lithium iron phosphate recovery material.

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