Method for recycling waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching and application thereof

Abstract

The application discloses a method for recycling waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching and application thereof, and relates to the technical field of resource recycling of waste lithium ion batteries. The method comprises the following steps: taking a positive plate of a waste lithium iron phosphate battery as a working electrode, placing the working electrode in an electrolyte, applying a voltage to perform electrochemical treatment, stripping the positive electrode material from the surface of an aluminum foil, and collecting the positive electrode material powder; then placing the positive electrode material powder in a hydrothermal reaction system to perform leaching treatment under hydrothermal conditions, obtaining a lithium-containing leaching solution and a solid residue after solid-liquid separation; finally, precipitating and recycling lithium salt from the leaching solution. The application also applies the above method to the preparation of lithium carbonate. The method has the advantages of low energy consumption, small pollution, high lithium recovery rate, high product purity, simple process operation and the like, and solves the problems of low separation efficiency, serious aluminum impurity interference and difficult selective leaching in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion battery resource recycling technology, specifically relating to a method and application for electrochemical stripping and hydrothermal leaching to recycle waste lithium iron phosphate. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the use of lithium-ion batteries has increased dramatically, making the recycling of spent lithium-ion batteries an increasingly prominent issue. Lithium iron phosphate (LiFePO4) batteries, due to their high safety, long cycle life, and low cost, are widely used in electric vehicles and energy storage. Spent lithium iron phosphate batteries contain a large amount of valuable metal elements such as lithium, iron, and phosphorus; their effective recycling can not only reduce environmental pollution but also alleviate resource shortages.

[0003] Currently, the main methods for recycling spent lithium iron phosphate batteries include mechanical crushing and sorting, thermal stripping, and wet leaching. Chinese invention patent CN114709504B discloses a clean recycling method for spent lithium iron phosphate cathode materials. This method includes pretreatment to separate aluminum foil, binder, and carbon, obtaining a mixture containing phosphorus, iron, and lithium. This mixture is then oxidatively leached in a sodium hydroxide solution, and finally, recycled lithium iron phosphate is prepared through precipitation and calcination. Chinese invention patent CN111270072B proposes a method using sodium hydroxide solution to dissolve aluminum foil and pyrophosphate solution as the leaching agent to leach lithium iron phosphate powder. This method is simple and low-cost.

[0004] In the field of electrochemical recycling technology, Chinese invention patent CN111763956B discloses a method for separating and recycling valuable metals from waste lithium batteries using electrochemical technology. This method recovers cobalt metal through electrolytic leaching and electrodeposition, and recovers lithium ions in the form of precipitation, avoiding the use of large amounts of acid and alkali reagents and various reducing agents. For the efficient leaching of lithium iron phosphate cathode materials, Chinese invention patent CN114196821A proposes a mechanochemical method that ball-mills waste lithium iron phosphate cathode materials with oxalic acid to achieve efficient lithium leaching with a leaching rate of up to 100%. Chinese invention patent CN110112481B introduces a method for recycling waste lithium iron phosphate batteries to prepare lithium iron phosphate cathode materials. This method separates active materials through steps such as salt water immersion discharge, crushing, freezing, boiling water immersion, and vibrating sieving, and then prepares recycled lithium iron phosphate materials through acid leaching and hydrothermal reaction.

[0005] However, existing technologies still have some problems: in mechanical crushing and sorting technology, the cathode material and aluminum foil current collector are tightly bonded, resulting in low separation efficiency and easy material loss; thermal stripping technology has high energy consumption and may produce harmful gases, failing to meet green environmental protection requirements; in traditional wet leaching technology, due to the stable structure of LiFePO4, high acidity or the addition of reducing agents are required for effective leaching, which not only increases costs but may also cause secondary pollution; in addition, traditional mechanical separation is difficult to completely strip the cathode material, causing aluminum impurities to enter the solution during subsequent leaching, affecting product purity. Especially in the selective recovery of lithium, existing technologies often fail to achieve efficient separation of lithium from iron and phosphorus, resulting in a complex and costly recovery process. At the same time, most methods require the use of large amounts of strong acids, strong alkalis, or organic solvents, which not only increases processing costs but also poses environmental pollution risks. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method and application for electrochemical stripping and hydrothermal leaching recycling of waste lithium iron phosphate, in order to solve the technical problems of low separation efficiency of cathode material and aluminum foil, easy entry of aluminum impurities into the leaching solution affecting product purity, and difficulty in selective leaching of lithium element in the existing waste lithium iron phosphate battery recycling technology.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching, comprising the following steps: The positive electrode sheet of the waste lithium iron phosphate battery is used as the working electrode, placed in the electrolyte, and subjected to electrochemical treatment by applying voltage, so that the positive electrode material is peeled off from the aluminum foil surface of the positive electrode sheet and the positive electrode material powder is collected. The cathode material powder was placed in a hydrothermal reaction system and leached under hydrothermal conditions. After solid-liquid separation, a lithium-containing leachate and a solid residue were obtained. Lithium salts are recovered by precipitation from the leachate.

[0008] A further improvement of the present invention is that the electrolyte is a 0.5~2 mol / L ammonium sulfate solution.

[0009] A further improvement of this invention is that, in the electrochemical treatment, the current density is 10~20 mA / cm². 2 The processing time is 90~150s.

[0010] A further improvement of the present invention is that the hydrothermal conditions include: a temperature of 100~300℃, a time of 5~60min, and a solid-liquid ratio of 20~150 g / L.

[0011] A further improvement of the present invention is that a salt and oxidant system, or a weak acid and a complexing agent, are added to the hydrothermal reaction system.

[0012] A further improvement of the present invention is that the salt and oxidant system is ammonium sulfate and hydrogen peroxide, and the weak acid and complexing agent is citric acid.

[0013] A further improvement of the present invention is that the method for precipitating and recovering lithium salt from the leachate is as follows: sodium carbonate is added to the leachate, the pH value is adjusted to 10-13, and the reaction is carried out at 70-100℃ for 50-80 minutes to obtain lithium carbonate precipitate.

[0014] A further improvement of the present invention is that aluminum foil is obtained after the electrochemical treatment, and the aluminum foil is directly recycled.

[0015] A further improvement of the present invention is that the cathode material powder is washed and dried before entering the hydrothermal reaction system, with a drying temperature of 50~100℃ and a drying time of 5~8h.

[0016] Secondly, the present invention also provides an application of the above-mentioned electrochemical stripping and hydrothermal leaching method for recovering waste lithium iron phosphate in the preparation of lithium carbonate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for electrochemical stripping and hydrothermal leaching to recover waste lithium iron phosphate batteries. The method involves directly placing the waste lithium iron phosphate battery positive electrode sheet as the working electrode in an electrolyte and applying voltage for electrochemical treatment. The bubble effect generated at the electrode interface enables rapid stripping of the positive electrode material from the aluminum foil current collector, eliminating the need for mechanical crushing or high-temperature calcination, significantly reducing energy consumption and avoiding harmful gas emissions. The collected positive electrode material powder after stripping is then introduced into a hydrothermal reaction system for leaching under hydrothermal conditions. The hydrothermal environment promotes the release of lithium ions from the LiFePO4 crystal structure, allowing lithium to enter the leaching solution with high efficiency and selectivity, while iron and phosphorus remain in the solid residue. The lithium recovery rate can reach over 90%. Simultaneously, since the aluminum foil has already separated from the positive electrode material during the electrochemical stripping stage, aluminum impurities are effectively prevented from entering the subsequent leaching solution, improving the purity of the leaching solution and reducing the difficulty of subsequent lithium salt purification. Finally, lithium salt is precipitated and recovered from the leaching solution to directly obtain lithium carbonate. Therefore, the method of the present invention has the advantages of low energy consumption, low pollution, high lithium recovery rate, high product purity and simple process operation, and solves the problems of low separation efficiency, serious interference from aluminum impurities and difficulty in selective leaching in the prior art.

[0018] This invention applies the aforementioned method of electrochemical stripping and hydrothermal selective leaching for recycling spent lithium iron phosphate batteries to the preparation of lithium carbonate, marking the first practical application of this low-energy, high-selectivity recycling process in the field of lithium carbonate production. Utilizing the advantages of electrochemical stripping to avoid aluminum impurity contamination and hydrothermal leaching to achieve highly selective lithium extraction, this method solves the problems of high energy consumption in raw material processing and difficulty in guaranteeing product purity in existing lithium carbonate production processes, providing a clean and efficient new technological path for the resource-based preparation of lithium carbonate from spent lithium batteries. Attached Figure Description

[0019] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0020] Figure 1 This is a flowchart of the electrochemical stripping and hydrothermal leaching method for recovering waste lithium iron phosphate according to the present invention; Figure 2 This is a process flow diagram of electrochemical stripping and hydrothermal leaching for the recovery of waste lithium iron phosphate according to the present invention. Detailed Implementation

[0021] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0022] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0023] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0024] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0025] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0026] like Figure 1 and Figure 2 As shown, this invention provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, comprising the following steps: S1, Battery Pretreatment Waste lithium iron phosphate batteries are discharged and then disassembled to obtain positive electrode sheets.

[0027] S2, electrochemical stripping The obtained positive electrode sheet (consisting of an aluminum foil current collector and a positive electrode material coated on it) was used as the working electrode and placed in an electrochemical reaction tank. A graphite electrode or a stainless steel electrode was used as the counter electrode. The electrolyte was a 0.5-2 mol / L ammonium sulfate solution, and the current density was 10-20 mA / cm². 2 The processing time is 90~150s. During electrolysis, gas (H2 or O2) is generated at the electrode interface, forming a microbubble layer, which causes the positive electrode material to gradually peel off from the aluminum foil surface, with a peeling efficiency of over 90%.

[0028] S3, Solid-Liquid Separation and Material Pretreatment After electrolysis, the obtained cathode material powder is collected by filtration or centrifugation, and the aluminum foil is directly recycled. The obtained cathode material powder is washed with deionized water and dried at 50-100℃ for 5-8 hours to obtain dry cathode material powder.

[0029] S4, hydrothermal selective leaching The dried cathode material powder was added to a hydrothermal reaction system for leaching. The hydrothermal conditions were: temperature 100–300 °C, time 5–60 min, and solid-liquid ratio 20–150 g / L. A salt and oxidant system, or a weak acid and complexing agent, was added to the leaching system; the salt and oxidant system consisted of ammonium sulfate and hydrogen peroxide, and the weak acid and complexing agent was citric acid. Under hydrothermal conditions, the salt provided a stable acidic environment and simultaneously promoted the formation of Li in the LiFePO4 crystal structure through ion exchange and complexation. + The release of lithium allows it to selectively enter the leachate, while iron and phosphorus remain primarily in the solid residue. The reaction is: LiFePO4 → FePO4 + Li + .

[0030] S5, Lithium Salt Recovery After the hydrothermal reaction, the leachate was subjected to solid-liquid separation to obtain a lithium-containing leachate. Sodium carbonate was added to the leachate to adjust the pH to 10-13, and the reaction was carried out at 70-100℃ for 50-80 minutes to precipitate lithium ions as lithium carbonate.

[0031] After filtration, washing and drying, lithium carbonate is obtained, which can be used as a raw material for lithium batteries.

[0032] S6, Solid-phase reuse The solid residue after hydrothermal leaching is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thus realizing the recycling of iron and phosphorus resources.

[0033] The present invention also provides an application of the above-mentioned electrochemical stripping and hydrothermal leaching method for recovering waste lithium iron phosphate in the preparation of lithium carbonate.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0036] Example 1 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0037] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 0.5 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 20 mA / cm². 2The processing time is 90 seconds. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0038] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 80°C for 6 h.

[0039] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing 1 mol / L (NH4)2SO4 solution and 4% hydrogen peroxide. Control the solid-liquid ratio at 100 g / L and perform the hydrothermal reaction at 200℃ for 20 min. Under hydrothermal conditions, the hydrogen peroxide solution oxidizes Fe... 2+ For Fe 3+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0040] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0041] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to about 12, and react at 80℃ for 60 min to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, lithium carbonate product is obtained.

[0042] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0043] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 94%.

[0044] Example 2 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0045] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 0.5 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 10 mA / cm². 2 The processing time is 90 seconds. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0046] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 80°C for 6 h.

[0047] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing a 0.8 mol / L citric acid solution. Maintain a solid-liquid ratio of 20 g / L and perform a hydrothermal reaction at 200°C for 20 min. Under hydrothermal conditions, citric acid can selectively leach Fe... 3+ Reduced to readily soluble Fe 2+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0048] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0049] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to about 10, and react at 80℃ for 60 min to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, lithium carbonate product is obtained.

[0050] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0051] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 96%.

[0052] Example 3 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0053] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 0.5 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 20 mA / cm². 2 The processing time is 90 seconds. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0054] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 80°C for 6 h.

[0055] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing 0.5 mol / L (NH4)2SO4 solution and 4% hydrogen peroxide. Control the solid-liquid ratio at 80 g / L and perform a hydrothermal reaction at 200℃ for 20 min. Under hydrothermal conditions, the hydrogen peroxide solution oxidizes Fe... 2+ For Fe 3+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0056] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0057] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to about 12, and react at 95℃ for 75 minutes to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, lithium carbonate product is obtained.

[0058] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0059] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 97%.

[0060] Example 4 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0061] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 2 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 15 mA / cm². 2 The treatment time is 120 s. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0062] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 50°C for 8 h.

[0063] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing 1 mol / L (NH4)2SO4 solution and 4% hydrogen peroxide. Control the solid-liquid ratio at 150 g / L and perform a hydrothermal reaction at 150℃ for 10 min. Under hydrothermal conditions, the hydrogen peroxide oxidizes Fe... 2+ For Fe 3+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0064] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0065] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to 13, and react at 70℃ for 80 min to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, lithium carbonate product is obtained.

[0066] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0067] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 92%.

[0068] Example 5 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0069] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 1.2 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 15 mA / cm². 2 The treatment time is 120 s. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0070] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 75°C for 6.5 h.

[0071] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing 1 mol / L (NH4)2SO4 solution and 4% hydrogen peroxide. Control the solid-liquid ratio at 150 g / L and perform a hydrothermal reaction at 200℃ for 30 min. Under hydrothermal conditions, the hydrogen peroxide oxidizes Fe... 2+ For Fe 3+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0072] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0073] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to 11.5, and react at 85℃ for 65 min to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, lithium carbonate product is obtained.

[0074] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0075] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 96%.

[0076] Example 6 This embodiment provides a method for recovering waste lithium iron phosphate through electrochemical stripping and hydrothermal leaching, including the following steps: Step 1, Battery Pretreatment: Select waste lithium iron phosphate power batteries, completely discharge the batteries and disassemble them to obtain positive electrode sheets, and cut the positive electrode sheets into small pieces with a size of 2.5±0.5 cm for later use.

[0077] Step 2, Electrochemical stripping: The obtained positive electrode is used as the working electrode, and the graphite electrode is used as the counter electrode to construct an electrochemical reaction system. A 1.5 mol / L (NH₄)₂SO₄ aqueous solution is used as the electrolyte. The electrode is completely immersed in the electrolyte, and the current density is 15 mA / cm². 2 The treatment time is 150 s. During electrolysis, a large number of microbubbles are generated at the electrode interface, causing the positive electrode material to gradually peel off from the aluminum foil surface.

[0078] Step 3, solid-liquid separation and material collection: After electrolysis, the stripped positive electrode material is completely detached by shaking or slight stirring. Then, the stripped lithium iron phosphate positive electrode material powder is collected by filtration, washed several times with deionized water, and then dried at 100°C for 5 h.

[0079] Step 4, Hydrothermal Selective Leaching: Weigh 10 g of dried lithium iron phosphate cathode material powder and add it to a hydrothermal reactor containing 1 mol / L (NH4)2SO4 solution and 4% hydrogen peroxide. Control the solid-liquid ratio at 60 g / L and perform a hydrothermal reaction at 280℃ for 55 min. Under hydrothermal conditions, the hydrogen peroxide oxidizes Fe... 2+ For Fe 3+ Promote Li + Lithium ions migrate from the LiFePO4 lattice into the solution, allowing them to selectively enter the leachate.

[0080] Step 5, solid-liquid separation: After the hydrothermal reaction is completed, the reactor is cooled to room temperature, and the leachate and solid residue are separated by filtration to obtain lithium-containing leachate.

[0081] Step 6, Lithium Salt Recovery: Add Na2CO3 solution to the leachate, adjust the pH of the solution to 12, and react at 100℃ for 50 min to precipitate lithium ions in the solution as lithium carbonate. After filtration, washing and drying, the lithium carbonate product is obtained.

[0082] Step 7, Residue Utilization: The solid residue obtained from filtration is mainly FePO4, which can be used to regenerate LiFePO4 cathode material through lithium supplementation sintering, thereby realizing the recycling of iron and phosphorus resources.

[0083] Experimental results show that under the above conditions, the leaching rate of lithium can reach over 96%.

[0084] Comparative Example 1 A traditional mechanical crushing-acid leaching method was used to recover waste lithium iron phosphate (LFP) cathode materials. Waste LFP battery cathode sheets were mechanically crushed and sieved to obtain cathode material powder, which was then leached in a sulfuric acid and hydrogen peroxide system. Results showed that due to the difficulty in completely separating aluminum foil from the cathode material during mechanical crushing, the concentration of aluminum impurities in the leachate was high, with an aluminum leaching rate reaching 42.3%, severely affecting the purity of subsequent lithium carbonate products. Simultaneously, the lithium leaching rate was approximately 96%, and the iron leaching rate was 90.4%, also exhibiting the problem of lithium, iron, and phosphorus co-dissolution. This method suffers from low mechanical separation efficiency and severe interference from aluminum impurities, increasing the difficulty and cost of subsequent impurity removal processes.

[0085] In summary, the electrochemical stripping and hydrothermal leaching method for recovering waste lithium iron phosphate batteries provided by this invention achieves low-temperature, rapid, and clean separation of the cathode material and aluminum foil through electrochemical bubble stripping, avoiding aluminum impurity contamination caused by mechanical crushing and the high energy consumption problems of high-temperature calcination. Furthermore, under hydrothermal conditions, a salt and reducing agent system or a weak acid is used to achieve highly efficient and selective leaching of lithium, with a lithium leaching rate exceeding 90%, while iron and phosphorus remain in the solid residue, greatly simplifying the subsequent lithium salt purification process. This method has significant advantages such as low energy consumption, low pollution, high lithium recovery rate, high product purity, and simple process operation. It solves the problems of low separation efficiency, severe impurity interference, and difficulty in selective leaching in existing technologies, and is applicable to the resource recovery of waste lithium iron phosphate batteries and the preparation of lithium carbonate.

[0086] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching, characterized in that, Includes the following steps: The positive electrode sheet of the waste lithium iron phosphate battery is used as the working electrode, placed in the electrolyte, and subjected to electrochemical treatment by applying voltage, so that the positive electrode material is peeled off from the aluminum foil surface of the positive electrode sheet and the positive electrode material powder is collected. The cathode material powder was placed in a hydrothermal reaction system and leached under hydrothermal conditions. After solid-liquid separation, a lithium-containing leachate and a solid residue were obtained. Lithium salts are recovered by precipitation from the leachate.

2. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, The electrolyte is a 0.5~2 mol / L ammonium sulfate solution.

3. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, In the electrochemical treatment, the current density is 10~20 mA / cm². 2 The processing time is 90~150s.

4. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, The hydrothermal conditions include: a temperature of 100~300℃, a time of 5~60min, and a solid-liquid ratio of 20~150 g / L.

5. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, The hydrothermal reaction system is supplemented with a salt and oxidant system, or with a weak acid and a complexing agent.

6. The method for electrochemical stripping and hydrothermal leaching recovery of waste lithium iron phosphate according to claim 5, characterized in that, The salt and oxidant system is ammonium sulfate and hydrogen peroxide, and the weak acid and complexing agent is citric acid.

7. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, The method for precipitating and recovering lithium salts from leachate is as follows: add sodium carbonate to leachate, adjust the pH value to 10-13, and react at 70-100℃ for 50-80 minutes to obtain lithium carbonate precipitate.

8. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, The electrochemical treatment also yields aluminum foil, which is then directly recycled.

9. The method for recovering waste lithium iron phosphate by electrochemical stripping and hydrothermal leaching according to claim 1, characterized in that, Before entering the hydrothermal reaction system, the cathode material powder is washed and dried at a temperature of 50-100°C for 5-8 hours.

10. The application of the electrochemical stripping and hydrothermal leaching method for recovering waste lithium iron phosphate according to any one of claims 1-9 in the preparation of lithium carbonate.

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