Full-element recovery method for decommissioned lithium iron phosphate battery

Abstract

This invention relates to an element recovery method, specifically a method for the full element recovery of retired lithium iron phosphate batteries, belonging to the field of lithium-ion battery and resource recycling technology. The method includes the following steps: nitrogen roasting; dilute sulfuric acid leaching; removal of copper and aluminum impurities; precipitation of iron and phosphorus elements; iron-containing precipitation roasting; and lithium solution evaporation and crystallization. Nitrogen roasting removes the binder, yielding lithium iron phosphate electrode material, and simultaneously reduces high-valence iron to low-valence states, thereby accelerating the leaching process and increasing the leaching rate. It also removes impurities such as fluorine-containing electrolytes and separators. Multiple copper removal methods effectively remove most copper, eliminating the influence of the negative electrode current collector while maintaining strong compatibility. The aluminum removal step is simple and effective, reducing the requirements for current collector separation in the preceding steps. This invention aligns with practical engineering applications, enhancing the practicality and universality of the wet recycling process for spent lithium iron phosphate battery cathode materials, improving the recovery efficiency of lithium, iron, and phosphorus from lithium iron phosphate batteries, and achieving closed-loop reuse of lithium iron phosphate battery cathode materials.

Description

Technical Field

[0001] This invention relates to an element recovery method, and more particularly to a method for the full element recovery of retired lithium iron phosphate batteries, belonging to the field of lithium-ion battery and resource recycling technology. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are a representative type of power battery for new energy vehicles. Due to their robust bonding structure, LFP batteries exhibit excellent stability, safety, and long cycle life, making them widely used in large electric vehicles, hybrid electric vehicles, and some low-cost small electric vehicles. However, the lifespan of LFP batteries is generally 5-8 years, and retired LFP batteries need to be recycled.

[0003] Currently, the main recycling methods for spent lithium iron phosphate batteries include mechanical recycling, pyrometallurgical recycling, hydrometallurgical recycling, and direct recycling, as well as combinations of two or more of these methods. Among these, hydrometallurgy is considered an ideal process for large-scale application due to its low operating temperature, high recovery rate, and high product purity. A typical hydrometallurgical process includes pretreatment, leaching, and separation processes.

[0004] Pretreatment typically involves heat treatment, which helps to volatilize residual electrolytes, decompose binders, thereby promoting separation between the Al / Cu foil and the electrode, and reducing impurities in the electrode material powder. For spent lithium iron phosphate batteries, heat treatment includes calcination in an oxidizing or inert atmosphere. The oxidative calcination of lithium iron phosphate batteries produces Li3Fe2(PO4)3, FePO4, and Li3PO4 as the cathode products. Due to the high valence state of iron, lithium can be selectively leached from these calcination products. However, the remaining mixture of FePO4 and graphite is difficult to separate, resulting in resource waste and posing a significant challenge. Summary of the Invention:

[0005] In response to the current problems of lithium iron phosphate battery recycling focusing on lithium extraction while the recovery level of other components such as iron and phosphorus is low, the difficulty in separating phosphorus iron materials and graphite caused by oxidation roasting, and the difficulty in removing copper and aluminum impurities during the wet recycling process of lithium iron phosphate, this invention proposes a full-element recycling method for retired lithium iron phosphate batteries to recover and regenerate cathode materials.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A method for the complete element recovery of lithium iron phosphate batteries, comprising the following steps:

[0008] (1) Nitrogen roasting: The electrode sheets obtained after mechanical crushing are roasted in a nitrogen furnace to inhibit the oxidation of lithium iron phosphate material and obtain roasted electrode material.

[0009] (2) Acid leaching: The electrode material calcined by nitrogen is added to dilute sulfuric acid and heated and stirred in a reaction vessel until fully reacted to obtain a leaching solution A containing lithium, iron, aluminum, phosphorus and copper.

[0010] (3) Copper removal: Most of the copper in the leachate A is removed by means of displacement, extraction, sulfide precipitation, etc., and the copper-containing substance A and the copper-removed solution B are obtained by filtration or separation.

[0011] (4) Hydrolysis precipitation method for aluminum removal: Add sodium hydroxide to the copper-removed solution B, adjust the pH value of the solution to between 3.5 and 4, stir the reaction and filter to obtain aluminum precipitate B and filtrate C;

[0012] (5) Precipitation of iron phosphate and goethite: Add hydrogen peroxide solution to filtrate C, stir at a constant temperature of 80℃~100℃, filter after the reaction is complete, and wash to obtain a mixed precipitate C of FePO4·2H2O and goethite and lithium-containing filtrate D.

[0013] (6) Iron-containing precipitate roasting: Iron-containing mixed precipitate C is roasted at a temperature of 600-800℃ for 4-6 hours to obtain iron oxide and iron phosphate with improved crystal form, which can be used as raw material for the synthesis of lithium iron phosphate; (7) Lithium precipitation: Lithium-containing filtrate D is heated to 90℃-100℃, concentrated and boiled, soda ash is added, sufficient solid is precipitated, filtered, washed and dried to obtain lithium carbonate, which can be used as lithium source for the synthesis of lithium iron phosphate.

[0014] The method of this invention combines roasting and wet processing to effectively recover lithium, iron, and phosphorus, and separate graphite, achieving closed-loop recycling of battery cathode materials. At the same time, it avoids environmental problems such as the discharge of phosphorus- and fluoride-containing wastewater, and is more in line with engineering applications, providing a feasible solution for industrial recycling methods based on mechanical crushing.

[0015] The method of this invention includes the following steps: nitrogen roasting; dilute sulfuric acid leaching; copper removal by multiple methods; aluminum removal by hydrolysis precipitation; precipitation of iron and phosphorus elements; iron-containing precipitation roasting; and lithium solution evaporation and crystallization. Nitrogen roasting can remove binders, prevent oxidation of lithium iron phosphate electrode materials, ensure the crystal stability of lithium iron phosphate electrode materials, improve leaching rate, and also remove impurities such as PVDF, fluorine-containing electrolyte, and separators. The multiple copper removal methods can remove most of the copper, eliminating the influence of the negative electrode current collector while also having strong compatibility. The aluminum removal step is simple and effective, reducing the requirements for current collector separation in the preceding steps. This invention aligns with practical engineering applications, enhancing the practicality and universality of the wet recycling process for waste lithium iron phosphate battery cathode materials, improving the recovery efficiency of lithium, iron, and phosphorus from lithium iron phosphate batteries, and realizing the closed-loop reuse of lithium iron phosphate battery cathode materials.

[0016] Preferably, in step (1), the atmosphere of the nitrogen furnace has an O2 volume concentration of 0–0.5%, a temperature of 550–650°C, and a roasting time of 120–300 minutes. Preferably, in step (1), the gas atmosphere has an O2 volume concentration of 0%, 0.2%, or 0.5%, a temperature of 550°C, 600°C, or 650°C, and a roasting time of 120, 240, or 300 minutes.

[0017] Preferably, in step (2), the concentration of dilute sulfuric acid is 1–2 mol / L, the solid-liquid ratio of electrode material to dilute sulfuric acid is 80–120 g / L, and the reaction is carried out at room temperature for 180–300 minutes. Preferably, in step (2), the concentration of dilute sulfuric acid is 1 mol / L, 1.8 mol / L, or 2 mol / L, the solid-liquid ratio of electrode material to dilute sulfuric acid is 80 g / L, 100 g / L, or 120 g / L, the stirring speed is 300 r / min, and the reaction is carried out at room temperature for 180, 240, or 300 minutes to ensure the highest element leaching rate.

[0018] As a preferred option, in step (3), copper can be selected by displacement method, extraction method or sulfide precipitation method;

[0019] When using the displacement method, the molar ratio of iron powder to copper is 1.5 to 2:1.

[0020] When using the extraction method, copper is extracted with N902 organic extractant. The volume of the organic extractant and its diluent, sulfonated kerosene, each accounts for 30-50% of the volume of the organic solvent. The oil-water volume ratio O:A = 1-2:1, the pH is 1-2, and the extraction time for the two phases is 5-10 minutes.

[0021] When using the sulfide precipitation method, sodium sulfide is added, and the molar ratio of sodium sulfide to copper is 2 to 4:1.

[0022] Preferably, in step (3), when using the displacement method, the molar ratio of iron powder to copper is 2.0; when using the extraction method, copper is extracted with N902 organic extractant, the volume of the organic extractant and its diluent sulfonated kerosene each accounts for 50% of the organic solvent, the oil-water volume ratio O:A = 1:1, the pH is 1.5, and the two-phase mixing extraction time is 10 minutes; when using the sulfide precipitation method, the molar ratio of sodium sulfide to copper is 3:1.

[0023] Preferably, in step (4), a 2-5 mol / L sodium hydroxide solution is used. Preferably, in step (4), a 2 mol / L, 3 mol / L, or 5 mol / L sodium hydroxide solution is used to adjust the pH to 3.5, 3.7, or 4, respectively.

[0024] Preferably, in step (5), the molar ratio of hydrogen peroxide to iron is 1:2 to 3. Preferably, in step (5), the molar ratio of hydrogen peroxide to iron is 1:2, 1:2.5, or 1:3, the reaction temperature is 90°C, and the reaction time is 6 hours.

[0025] Preferably, in step (7), the molar ratio of sodium carbonate to lithium is 1 to 1.5:1. Preferably, in step (7), the molar ratio of sodium carbonate to lithium is 1:1, 1.2:1, or 1.5:1, and the reaction temperature is 95°C.

[0026] Preferably, in step (6), the iron compound is heated to 600°C, 700°C, and 800°C in a tube furnace at a rate of 5°C / min, and then roasted at this temperature for 4, 5, and 6 hours, and then naturally cooled to room temperature.

[0027] Preferably, in step (1), the atmosphere of the nitrogen furnace is 0.2% O2 volume concentration, 99.8% nitrogen volume concentration, 600℃ roasting temperature, and 240 minutes roasting time.

[0028] The beneficial effects of this invention are as follows: First, based on actual industrial processes, waste lithium iron phosphate batteries are crushed and then subjected to suitable nitrogen roasting conditions to remove binders and fluorine-containing electrolytes, separate electrode materials, and inhibit the oxidation of lithium iron phosphate materials. After acid leaching, copper is removed through various methods such as displacement, extraction, and sulfide precipitation, with excellent impurity removal effects. Aluminum is removed by adjusting the pH and utilizing its hydrolytic properties, which is simple to operate. The solution after impurity removal undergoes subsequent precipitation of iron phosphate and lithium, ultimately yielding raw materials for synthesizing lithium iron phosphate. This invention is highly effective, universally applicable, and practical. Attached Figure Description

[0029] Figure 1 The process flow of a method for the complete element recovery of lithium iron phosphate batteries;

[0030] Figure 2 The composition of the electrode materials before (a) and after (b) nitrogen calcination;

[0031] Figure 3 The XRD patterns of the broken lithium iron phosphate electrode sheets before and after calcination in a nitrogen furnace are shown.

[0032] Figure 4 Mössbauer spectroscopy characterization of lithium iron phosphate electrode sheets after calcination;

[0033] Figure 5 The ratio of the content of each element in the solution after copper removal to the content of each element in the solution before copper removal in Example 1;

[0034] Figure 6 The ratio of the content of each element in the aqueous solution after copper removal in Example 2 to the content of each element in the solution before copper removal;

[0035] Figure 7 The content of each element in the solution before and after copper removal by sulfide precipitation in Example 3;

[0036] Figure 8 The figures show the solubility curves of the main elements in the leachate at different temperatures. Figure a is the solubility curve of the hydroxide precipitation of the main element, and figure b is the solubility curve of the phosphate precipitation of the main element.

[0037] Figure 9 This shows the changes in the content of each element with solution pH during the precipitation process in Comparative Example 2.

[0038] Figure 10 Morphology of lithium iron phosphate electrode sheets calcined at 600℃ for different times under nitrogen atmosphere; Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0040] In this invention, the equipment and raw materials used are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0041] The present invention pertains to cylindrical lithium batteries, including models such as 14500, 14650, 17490, 18500, 18650, and 26500. The following examples use 18650 batteries for testing.

[0042] A process flow for a method of full element recovery from lithium iron phosphate batteries, such as... Figure 1 As shown.

[0043] Example 1: Displacement-Hydrolysis Precipitation Process

[0044] A method for the complete element recovery of lithium iron phosphate batteries, comprising the following steps:

[0045] S1: Nitrogen calcination. The electrode material is placed in a nitrogen furnace for calcination (calcination in a gas atmosphere of 0.2% O2 and 99.8% N2 by volume). The temperature is set at 600℃ and the calcination time is 240 minutes. After completion, it is allowed to cool naturally to room temperature.

[0046] The compositional changes of the crushed lithium iron phosphate electrode sheets before and after calcination in a nitrogen furnace are as follows: Figure 2 As shown, the XRD patterns before and after calcination are as follows: Figure 3 As shown, the Mössbauer spectra of the lithium iron phosphate electrode sheets before and after calcination are as follows: Figure 4As shown. According to Figure 2 It can be seen that the fluorine content in the electrode material decreased significantly after calcination, while the copper and aluminum content increased. This indicates that using high-temperature conditions can remove non-critical components such as fluorine-containing electrolyte and residual membrane. Simultaneously, high-temperature conditions can decompose the binder, causing the electrode material to separate from the positive electrode current collector aluminum and the negative electrode current collector copper, thus enhancing the separation effect of the electrode material. According to... Figure 3 , Figure 4 It can be seen that the crystal form of the electrode material did not change before and after nitrogen roasting, and the main crystal components remained carbon and lithium iron phosphate. This indicates that the nitrogen atmosphere effectively prevents the oxidation of the electrode material during roasting, allowing the lithium iron phosphate material to maintain its orthorhombic crystal morphology, which is easily leachable. The valence state of iron changes from 57Fe Spectroscopy (Mössbauer spectroscopy) is used for measurement. Figure 4 The absorption rate represents the different positions and valence states of iron atoms in the crystal and is specifically used to detect iron in solids. By analyzing the phase composition of each signal, as shown in Table 1, it can be seen that lithium iron phosphate powder is mainly composed of divalent iron, with some Fe2P substances. Divalent iron accounts for the majority, at 95.5%, indicating that the iron in the calcined electrode material still maintains its divalent state and has not been oxidized.

[0047] Table 1 Summary of Mössbauer Spectrum Parameters and Iron Type Assignments

[0048]

[0049] S2: Acid leaching. The calcined electrode material is added to 2 mol / L dilute sulfuric acid, with a solid-liquid ratio of 100 g / L between the electrode material and the dilute sulfuric acid. The electrode material-sulfuric acid mixture is stirred and reacted in a visual reaction vessel. After 240 minutes, the solution is removed to obtain a leachate containing lithium, aluminum, phosphorus, iron, and copper.

[0050] S3: Copper removal by displacement precipitation. Reduced iron powder is added to the leachate at a molar ratio of 2:1 to copper in the solution. This converts free copper ions into elemental copper precipitate and reduces residual ferric iron in the solution to ferrous iron, preventing iron oxidation and precipitation, and avoiding the introduction of new impurities. The copper precipitate and the copper-removed solution are separated by filtration. Analysis of the element content ratios in the solution after copper removal versus before copper removal is shown below. Figure 5 As shown, the copper removal rate can reach 99.8%.

[0051] S4: Aluminum removal by hydrolysis precipitation. Add 3 mol / L sodium hydroxide solution to the copper-removed solution obtained in S3, adjust the pH of the solution to 3.7, filter to obtain filtrate, and achieve 99% aluminum precipitation.

[0052] S5: Precipitate iron and phosphorus. Slowly add 30% hydrogen peroxide solution to the filtrate obtained in S4. The molar ratio of hydrogen peroxide to iron is 1:2. Oxidize the ferrous iron in the solution. The iron ions combine with phosphate to form the precipitate FePO4·2H2O. The excess iron ions precipitate as goethite FeO·OH. Filter and wash the precipitate to obtain the filtrate and mixed precipitate.

[0053] S6: Iron-containing precipitate calcination. The mixed precipitate obtained in S5 is placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min. This temperature is maintained for calcination for 5 hours, followed by natural cooling to room temperature. Iron oxide and iron phosphate with improved crystal structure are obtained, which are the raw materials for synthesizing lithium iron phosphate.

[0054] S7: Precipitate lithium. Heat the lithium-containing filtrate obtained from S5, evaporate and concentrate it at 95°C, then add sodium carbonate with a sodium carbonate:lithium molar ratio of 1.2:1. After sufficient precipitate is formed, filter, wash the precipitate with deionized water, and dry it at 60°C to obtain lithium carbonate for the synthesis of lithium iron phosphate.

[0055] Example 2: Extraction-Hydrolysis-Precipitation Process

[0056] A method for the complete element recovery of lithium iron phosphate batteries, comprising the following steps:

[0057] S1: Nitrogen roasting. The electrode material is placed in a nitrogen furnace for roasting (roasting in a gas atmosphere of 0.5% O2 and 99.5% N2 by volume). The temperature is set at 600℃ and the roasting time is 300 minutes. High temperature conditions are used to remove non-critical components such as fluorine-containing electrolyte and residual membrane, decompose binder, and separate electrode material. The nitrogen atmosphere can effectively prevent the oxidation of electrode material during roasting and maintain the crystal form of lithium iron phosphate material. After roasting, it is naturally cooled to room temperature.

[0058] S2: Acid leaching. The calcined electrode material is added to 1.8 mol / L dilute sulfuric acid, with a solid-liquid ratio of 80 g / L between the electrode material and the dilute sulfuric acid. The electrode material-sulfuric acid mixture is stirred and reacted in a visual reaction vessel. After 300 minutes, the solution is removed to obtain a leachate containing lithium, aluminum, phosphorus, iron, and copper.

[0059] S3: Copper removal by extraction. A 50% N902 organic extractant was added to the sulfuric acid leachate to extract copper. The oil-to-water volume ratio was O:A = 1:1, and the equilibrium pH was 1.5. The two phases were mixed magnetically for 10 minutes and then allowed to stand for phase separation. Copper-containing organic solvent and aqueous solutions containing lithium, aluminum, phosphorus, and iron were obtained. The ratios of the content of each element in the aqueous solution after copper removal to the content of each element in the solution before copper removal were determined as follows: Figure 6 As shown, under these experimental conditions, the copper extraction rate can reach 99.2%.

[0060] S4: Aluminum removal by hydrolysis precipitation. High-purity argon gas is introduced into the copper-removed solution to prevent iron oxidation. At the same time, 2 mol / L sodium hydroxide solution is titrated into the copper-removed solution to adjust the pH value of the solution to 4.0. After filtration, 99% aluminum precipitation is achieved.

[0061] S5: Precipitate iron and phosphorus. Slowly add 30% hydrogen peroxide solution to the filtrate. The molar ratio of hydrogen peroxide to iron is 1:2.5. This oxidizes the ferrous iron in the solution. The iron ions combine with phosphate to form the precipitate FePO4·2H2O. The excess iron ions precipitate as goethite FeO·OH. Filter and wash the precipitate to obtain the filtrate and mixed precipitate.

[0062] S6: Iron-containing precipitate calcination: The iron-containing precipitate is placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min, and calcined at this temperature for 4 hours, followed by natural cooling to room temperature. Iron oxide and iron phosphate with improved crystal structure are obtained, which are the raw materials for synthesizing lithium iron phosphate.

[0063] S7: Precipitate lithium. Heat the lithium-containing filtrate, evaporate and concentrate at 95°C, then add sodium carbonate with a sodium carbonate:lithium molar ratio of 1.5:1. After sufficient precipitate is formed, filter, wash the precipitate with deionized water, and dry at 60°C to obtain lithium carbonate for synthesizing lithium iron phosphate.

[0064] Example 3: Sulfide + Hydrolysis Precipitation Process

[0065] A method for the complete element recovery of lithium iron phosphate batteries, comprising the following steps:

[0066] S1: Nitrogen roasting. The electrode material is placed in a nitrogen furnace for roasting (roasting in a gas atmosphere of 0% O2 and 100% N2 by volume). The temperature is set at 600℃ and the roasting time is 240 minutes. High temperature conditions are used to remove non-critical components such as fluorine-containing electrolyte and residual membrane, decompose binder, and separate electrode material. The nitrogen atmosphere can effectively prevent the oxidation of electrode material during roasting and maintain the crystal form of lithium iron phosphate material. After roasting, it is naturally cooled to room temperature.

[0067] S2: Acid leaching. The calcined electrode material is added to 1 mol / L dilute sulfuric acid, with a solid-liquid ratio of 120 g / L between the electrode material and the dilute sulfuric acid. The electrode material-sulfuric acid mixture is stirred and reacted in a visual reaction vessel. After 180 minutes, the solution is removed to obtain a leachate containing lithium, aluminum, phosphorus, iron, and copper.

[0068] S3: Copper removal using sulfides. Sodium sulfide is added to the leachate at a molar ratio of 3:1 to copper. After thorough stirring, the solution is filtered. Since CuS is extremely insoluble in water at room temperature, most of the copper is removed, achieving a removal rate of 99.7%. The elemental composition of the solution before and after copper removal is as follows: Figure 7As shown, the contents of lithium, iron, and phosphorus elements that need to be recovered remained unchanged before copper removal, while the content of copper impurities decreased significantly. This indicates that the copper removal method using sulfides can effectively remove copper impurities without affecting other elements in the solution.

[0069] S4: Aluminum removal by hydrolysis precipitation. High-purity argon gas is introduced into the copper-removed solution to prevent iron oxidation. At the same time, 5 mol / L sodium hydroxide solution is titrated into the copper-removed solution to adjust the pH value of the solution to 4, achieving 99% aluminum precipitation.

[0070] S5: Precipitate iron and phosphorus by slowly adding 30% hydrogen peroxide solution. The molar ratio of hydrogen peroxide to iron is 1:3. This oxidizes the ferrous iron in the solution. The iron ions combine with phosphate to form the precipitate FePO4·2H2O. The excess iron ions precipitate as goethite FeO·OH. Filter and wash the precipitate to obtain the filtrate and mixed precipitate.

[0071] S6: Iron-containing precipitate calcination: The iron-containing precipitate is placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min, and calcined at this temperature for 6 hours, followed by natural cooling to room temperature. Iron oxide and iron phosphate with improved crystal structure are obtained, which are the raw materials for synthesizing lithium iron phosphate.

[0072] S7: Precipitate lithium. Heat the lithium-containing filtrate, evaporate and concentrate it at 95°C, then add sodium carbonate with a sodium carbonate:lithium molar ratio of 1:1. After sufficient precipitate is formed, filter it, wash the precipitate with deionized water, and dry it at 60°C to obtain lithium carbonate for synthesizing lithium iron phosphate.

[0073] Comparative Example 1: Oxidation Roasting and Leaching Process

[0074] A method for the complete element recovery of lithium iron phosphate batteries, with the same specific steps as in Example 1, except that in S1, the electrode materials are processed in the same tunnel furnace. Air The samples were fired at the same temperature and time under the same atmosphere to examine the differences in the effects of air and nitrogen atmospheres.

[0075] The electrode materials were calcined under different atmospheres for the same time and then leached under the same conditions. The content of key elements and their leaching rate of lithium iron phosphate batteries before and after acid leaching after nitrogen calcination are shown in Table 2. The content of key elements and their leaching rate of lithium iron phosphate batteries before and after acid leaching after air calcination are shown in Table 3.

[0076] Table 2. Content and leaching rate of key elements in lithium iron phosphate batteries before and after nitrogen-calcined battery materials and acid leaching treatment.

[0077]

[0078] Table 3. Content and Leaching Rate of Key Elements in Lithium Iron Phosphate Batteries Before and After Acid Immersion Treatment (Air-baked Battery Materials)

[0079]

[0080]

[0081] According to the results in Tables 2 and 3, after calcination in an air atmosphere, the solid carbon material of the negative electrode vaporizes, leading to an increase in the content of key elements in the electrode material. A comparison of the leaching rates of each element in Tables 1 and 2 shows that the leaching rate of the electrode material after nitrogen calcination is significantly increased, with the leaching rates of lithium, iron, phosphorus, and copper all exceeding 93%. This indicates that nitrogen calcination can further prevent the oxidation of lithium iron phosphate material, maintaining its easily leached structure and preventing the solid vaporization of the negative electrode carbon material, thus achieving efficient leaching of all components of the lithium iron phosphate battery and efficient separation of the positive and negative electrode materials.

[0082] Comparative Example 2: Direct Hydrolysis Precipitation Process

[0083] A method for the complete element recovery of lithium iron phosphate batteries, with specific steps similar to Example 1, differs in that: S3 is omitted, i.e., no impurity removal process is used; instead, a 3 mol / L sodium hydroxide solution is directly titrated into the leaching solution containing lithium, aluminum, phosphorus, iron, and copper obtained in S2 to adjust the pH of the solution to 4.5, followed by filtration to obtain the filtrate and remove copper and aluminum impurities. The changes in the content of each element with solution pH during the precipitation process in Comparative Example 2 are shown below. Figure 9 As shown, by Figure 9 It can be seen that adding sodium hydroxide solution directly to the solution can remove impurities, but a better copper and aluminum removal rate can be obtained after adjusting the solution pH to 4.5.

[0084] The elemental content of the filtrate obtained above and the filtrate obtained in Examples 1-3S4 was determined by inductively coupled plasma mass spectrometry (ICP-MS). The results are shown in Table 4.

[0085] Table 4. Change rate of key element content in leachate

[0086]

[0087] Table 4 compares the elemental contents of Examples 1, 2, 3, and Comparative Example 2. It shows that in Comparative Example 2, although the removal rates of aluminum and copper impurities both reached over 99%, the contents of recoverable lithium, iron, and phosphorus elements decreased, especially the significant loss of iron and phosphorus elements. The solubility curves of the main elements in the leachate at different temperatures are shown below. Figure 8As shown in the figure, where a is the solubility curve of the hydroxide precipitation of the main element and b is the solubility curve of the phosphate precipitation of the main element, it can be seen that the solubility of the hydroxide precipitation of ferric iron and aluminum and the solubility of the phosphate precipitation are quite similar. Therefore, ferric iron and aluminum are difficult to separate by precipitation. However, the solubility of the precipitates of ferrous iron is significantly higher than that of the precipitates of aluminum. Therefore, ferrous iron and aluminum are easily separated by precipitation. Since ferric iron and ferrous aluminum have the same precipitation properties, the loss of iron and phosphorus in Comparative Example 2 is due to the oxidation of iron during the removal of copper and aluminum impurities. Most of the iron is precipitated in the form of ferric phosphate and ferric hydroxide, and a small part is carried away by the large amount of precipitate generated during the titration process. In Examples 1, 2, and 3, due to the use of a two-step method and the introduction of argon gas to prevent iron oxidation, aluminum is removed by utilizing the different precipitation ranges of ferrous iron and ferrous aluminum without causing the loss of other elements.

[0088] Comparative Example 3

[0089] The electrode material was placed in a nitrogen furnace for calcination (calcination in a gas atmosphere of 0.2% O2 and 99.8% N2 by volume) at a temperature of 600℃ for 5 min, 15 min, 30 min, 120 min and 240 min, respectively, to examine the differences in effect of different calcination times.

[0090] The morphology of lithium iron phosphate electrode sheets calcined at 600℃ for different times under nitrogen atmosphere is as follows: Figure 9 As shown in Table 5, the elemental contents of lithium iron phosphate cathode materials obtained after calcination for different times under nitrogen atmosphere are shown in Table 5.

[0091] Table 5. Elemental content of lithium iron phosphate cathode materials obtained after calcination for different times under nitrogen atmosphere.

[0092]

[0093] according to Figure 10 It can be seen that after calcination in a nitrogen atmosphere, the lithium iron phosphate electrode material exhibits excellent separation from the aluminum current collector foil, with almost no electrode material residue remaining on the current collector. This indicates that nitrogen atmosphere calcination effectively solves the problem of separating the electrode material from the current collector for lithium iron phosphate materials. Data from Table 5 shows that the lithium iron phosphate cathode material obtained after calcination in nitrogen for 300 minutes has a relatively high lithium content, indicating that prolonged calcination time allows for complete separation of the electrode material from the aluminum current collector, which is beneficial for subsequent lithium leaching.

[0094] Therefore, the optimal calcination conditions are high-temperature and long-time calcination at 600℃ for more than 240 minutes.

[0095] In summary, this invention addresses the current challenges in lithium iron phosphate battery recycling, which focuses on lithium extraction while neglecting the recovery of other components such as iron and phosphorus. It also addresses difficulties in separating phosphorus-iron materials and graphite due to oxidation roasting, and the challenges in removing copper and aluminum impurities during wet lithium iron phosphate recycling. By nitrogen roasting the battery electrodes and optimizing the roasting time and temperature, under optimal roasting conditions, binders and fluorine-containing electrolytes can be removed, separating the electrode materials. Simultaneously, oxidation of lithium iron phosphate is suppressed, maintaining its orthorhombic crystal form for easy leaching. Under optimal leaching conditions, high leaching rates are achieved for both lithium iron phosphate and negative electrode graphite. Leaching separates lithium iron phosphate from the negative electrode graphite within the electrode material. Meanwhile, to address the copper and aluminum impurities present in the leachate, the invention employs different copper removal methods, which are simple to operate and have excellent impurity removal effects. In particular, to address the challenge of separating trace aluminum impurities from the main iron element in the leachate, nitrogen roasting, iron powder reduction, and argon protection are used to inhibit the oxidation of iron. By utilizing the difference in precipitation behavior between ferrous iron and aluminum, aluminum in the leachate is successfully removed while retaining iron. Ultimately, a method for the full-element recovery of retired lithium iron phosphate batteries is realized to recycle cathode materials.

[0096] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

Claims

1. A method for the complete element recovery of retired lithium iron phosphate batteries, characterized in that... The method includes the following steps: (1) Nitrogen roasting: The electrode sheet obtained after mechanical crushing is roasted in a nitrogen furnace to suppress the oxidation of lithium iron phosphate material and obtain roasted electrode material; the atmosphere of the nitrogen furnace is O2 volume concentration 0~0.5%, the temperature is set to 550~650℃, and the roasting time is 120~300 minutes. (2) Acid leaching: The electrode material after being roasted with nitrogen is added to dilute sulfuric acid and heated and stirred in a reaction vessel until fully reacted to obtain a leaching solution A containing lithium, iron, aluminum, phosphorus and copper; (3) Copper removal: Remove most of the copper in the leachate A by displacement method, extraction method or sulfide precipitation method, and filter or separate to obtain copper-containing substance A and copper-removed solution B; (4) Hydrolysis precipitation method for aluminum removal: Add sodium hydroxide to the copper-removed solution B, adjust the pH value of the solution to between 3.5 and 4, stir the reaction and filter to obtain aluminum precipitate B and filtrate C; (5) Precipitation of iron phosphate and goethite: Add hydrogen peroxide solution to filtrate C, stir at a constant temperature of 80℃~100℃, filter after the reaction is complete, wash to obtain mixed precipitate C of FePO4·2H2O and goethite and lithium-containing filtrate D; the molar ratio of hydrogen peroxide to iron is 1:2~3. (6) Iron-containing precipitate roasting: Iron-containing mixed precipitate C is roasted at a temperature of 600~800℃ for 4~6 hours to obtain iron oxide and iron phosphate with improved crystal form, which can be used as raw material for the synthesis of lithium iron phosphate. (7) Precipitation of lithium: Heating lithium-containing filtrate D to 90℃~100℃, concentrating and boiling it, adding soda ash, precipitating a sufficient amount of solid, filtering, washing and drying to obtain lithium carbonate, which can be used as a lithium source for the synthesis of lithium iron phosphate.

2. The method according to claim 1, characterized in that: In step (2), the concentration of dilute sulfuric acid is 1~2 mol / L, the solid-liquid ratio of electrode material to dilute sulfuric acid is 80~120 g / L, and the reaction is carried out at room temperature for 180~300 minutes.

3. The method according to claim 1, characterized in that: In step (3), copper can be removed by displacement, extraction or sulfide precipitation. When using the displacement method, the molar ratio of iron powder to copper is 1.5~2:1; When using the extraction method, copper is extracted with N902 organic extractant. The volume of the organic extractant and its diluent, sulfonated kerosene, each accounts for 30-50% of the volume of the organic solvent. The oil-water volume ratio O:A = 1-2:1, the pH is 1-2, and the extraction time for the two phases is 5-10 minutes. When using the sulfide precipitation method, sodium sulfide is added, and the molar ratio of sodium sulfide to copper is 2~4:

1.

4. The method according to claim 1, characterized in that: In step (4), a 2-5 mol / L sodium hydroxide solution is used.

5. The method according to claim 1, characterized in that: In step (7), the molar ratio of sodium carbonate to lithium is 1~1.5:

1.

6. The method according to claim 1, characterized in that: In step (1), the atmosphere of the nitrogen furnace is O2 volume concentration of 0.2%, nitrogen volume concentration of 99.8%, roasting temperature of 600℃, and roasting time of 240 minutes.

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