Method for recycling waste lithium iron phosphate battery

Abstract

This invention relates to the field of battery recycling technology and discloses a method for recycling and processing waste lithium iron phosphate batteries, comprising the following steps: The waste lithium iron phosphate batteries are discharged, disassembled, crushed, and sorted to obtain lithium iron phosphate powder; the lithium iron phosphate powder is calcined to obtain calcined powder; the calcined powder is slurried, mixed acid is added for leaching, and the leaching is filtered to obtain leaching solution and leaching residue; iron powder is added to the leaching solution for precipitation reaction, and the leaching is filtered to obtain copper removal solution; the pH of the copper removal solution is adjusted for precipitation reaction, and the leaching is filtered to obtain aluminum removal solution; a complexing agent and a reducing agent are added to the aluminum removal solution, and the pH is adjusted again for precipitation reaction to obtain lithium iron phosphate precursor slurry; the lithium iron phosphate precursor slurry is dried, and then a carbon source is added for calcination to obtain lithium iron phosphate cathode material. This invention has the characteristics of short process, environmental friendliness, and economy. The prepared lithium iron phosphate cathode material has good consistency, uniform particle size, and excellent electrical performance, and can be industrialized for mass production.

Description

Technical Field

[0001] This invention relates to the field of battery recycling technology, and in particular to a method for recycling and processing waste lithium iron phosphate batteries. Background Technology

[0002] In recent years, with the development of lithium-ion battery technology and increasing emphasis on safety, the commercial application scale of lithium iron phosphate batteries has surpassed that of ternary lithium batteries. Leading domestic lithium-ion battery companies such as CATL, EVE Energy, and BYD have successively mass-produced lithium iron phosphate power batteries, which are widely used in the new energy vehicle sector. The lifespan of lithium-ion power batteries is 6-8 years, thus leading to a growing issue of recycling and processing lithium iron phosphate batteries. Currently, the most widely used process in China's battery recycling industry is the wet recycling process.

[0003] Chinese Patent 202110978962.4 discloses a method for the complete recovery of lithium iron phosphate (LFP) cathode materials from waste. The method involves mixing waste LFP materials with phosphorus compounds, subjecting them to heat treatment, leaching with water or dilute acid, filtering and washing to obtain a filtrate, adding an iron-containing compound to the filtrate to adjust the iron-phosphorus ratio, adding an oxidant, and adjusting the pH of the solution to 1-4 to precipitate iron phosphate. The resulting filtrate is then adjusted to a pH of 6-12 to prepare lithium carbonate. This process is lengthy and costly, and may cause secondary pollution. Chinese Patent 202111233873.3 discloses a short-process recycling method for waste LFP cathode materials. Waste LFP battery cathode materials are repeatedly soaked in deionized water at 25°C and 90°C three times, alternating between each soak to obtain sheet-like waste LFP materials. After drying, the materials are ground in a ball mill to obtain powdered active material, which is then placed in NMP solvent for magnetic stirring, filtration, centrifugation, washing, and drying to obtain regenerated cathode materials. The extensive use of NMP solvent easily causes environmental pollution, and the resulting cathode material has high impurity levels and significantly lower electrochemical performance. Chinese Patent 202111493938.8 discloses a method for recycling lithium iron phosphate battery cathode materials. This method uses an organic solvent to dissolve the binder in waste lithium iron phosphate cathode materials, retaining the conductive agent and the carbon coating layer on the surface of the lithium iron phosphate, to obtain lithium iron phosphate intermediate materials. Lithium replenishment is then performed on the lithium iron phosphate intermediate materials to obtain lithium iron phosphate repair materials. This technology is still immature and remains in the laboratory research stage, making industrial application difficult. Chinese Patent 202111593472.9 discloses a comprehensive wet recycling method for waste lithium iron phosphate cathode sheets. This method involves acid leaching and copper and aluminum removal from the cathode powder, adding an oxidant, adjusting the solution pH with ammonia to precipitate iron phosphate, and preparing lithium carbonate from the resulting filtrate after impurity removal. This wet treatment process is long and complex, consuming large amounts of chemical reagents such as acids, alkalis, reducing agents, and oxidizing agents. These chemical reagents cause significant pollution and generate large amounts of wastewater. The resource recovery rate is low, and the technology, economy, and environmental performance are poor, which affects its industrial application and promotion. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a short-process, environmentally friendly and economical method for recycling and processing waste lithium iron phosphate batteries. The resulting lithium iron phosphate cathode material has high purity, excellent performance, and good product consistency, and can be applied industrially.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for recycling and processing waste lithium iron phosphate batteries includes the following steps:

[0007] (1) After being discharged, disassembled, crushed and sorted, waste lithium iron phosphate batteries are obtained as shell, separator, current collector and lithium iron phosphate powder containing active materials.

[0008] The discharge operation described in step (1) above is resistive discharge or physical discharge of carbon powder conductor.

[0009] (2) The lithium iron phosphate powder is calcined in a non-oxidizing atmosphere to obtain calcined powder.

[0010] The calcination temperature in step (2) above is 450–650°C, preferably 500–550°C; the time is 2–6 h, preferably 3–4 h. The non-oxidizing atmosphere is at least one of nitrogen, helium, neon, argon, krypton, and xenon, with a purity of 99.9% or higher.

[0011] Thus, in step (2), the binder PVDF, electrolyte LiPF6, and organic solvent are decomposed into carbonaceous substances at high temperature through calcination, and most of the fluorine evaporates in gaseous form, thereby removing the binder PVDF, electrolyte LiPF6, and organic solvent from the lithium iron phosphate powder. Simultaneously, a non-oxidizing atmosphere is introduced to prevent Fe... 2+ Oxidized to Fe 3+ This avoids the need to introduce a large amount of reduced iron powder in the subsequent copper removal process.

[0012] (3) Pure water is added to the roasted powder to make a slurry, mixed acid is added to adjust the pH value to 2-5 for leaching, and the leaching solution and leaching residue are obtained by filtration.

[0013] The liquid-solid ratio obtained by the slurry preparation operation in step (3) above is (3-6):1, preferably 3:1.

[0014] The mixed acid in step (3) above includes an inorganic acid and an organic acid in a mass ratio of (1-5):1. The inorganic acid is phosphoric acid, and the organic acid is at least one of tartaric acid, oxalic acid, malic acid, citric acid, and ascorbic acid. The leaching operation is carried out at a temperature of 70-90°C for 3-6 hours.

[0015] Thus, in step (3), the elements such as lithium, iron, phosphorus, copper, and aluminum in the calcined powder are dissolved through slurry preparation and leaching operations, and the leaching solution and leaching residue are obtained by filtration. The leaching solution is rich in elements such as lithium, iron, phosphorus, copper, and aluminum, and the leaching residue is mainly graphite, which can be used for the regeneration of carbon materials.

[0016] (4) Iron powder is added to the leachate for precipitation reaction, and the copper removal solution is obtained by filtration.

[0017] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+The molar amount is 1.0 to 1.5 times, preferably 1.1 to 1.2 times. The precipitation reaction is carried out at a temperature of 30 to 85°C for a time of 0.5 to 6 hours, preferably 0.5 to 1.5 hours.

[0018] Thus, in step (4), copper ions are removed by adding iron powder to carry out a precipitation reaction, and the copper-removed solution is obtained by filtration.

[0019] (5) Add a pH adjuster to the copper removal solution to adjust the pH of the solution to 5-7 for precipitation reaction, and filter to obtain aluminum removal solution.

[0020] The pH adjuster mentioned in step (5) above is at least one of lithium hydroxide, ammonia, sodium hydroxide, sodium carbonate, and activated calcium oxide, preferably ammonia, with a solute concentration of 1.0–2.5 mol / L. The precipitation reaction temperature is 30–90°C, preferably 45–55°C; the time is 0.5–3.0 h, preferably 1.0–2.0 h.

[0021] Thus, in step (5), the pH value of the solution is adjusted to 5-7 by adding a pH adjuster to carry out the precipitation reaction, remove aluminum ions, and filter to obtain aluminum-removed solution.

[0022] (6) A complexing agent and a reducing agent are added to the aluminum removal solution, and a pH adjuster is added to adjust the pH of the solution to 8-10. A precipitation reaction is carried out under a non-oxidizing atmosphere to obtain lithium iron phosphate precursor slurry.

[0023] In step (6) above, the aluminum removal solution is subjected to elemental analysis according to an element molar ratio of n. Li :n Fe :n P Add an insufficient amount of element source (usually a lithium source, such as lithium hydroxide or lithium carbonate) in a ratio of 1:1:1, calculate the theoretical number of moles of lithium iron phosphate precursor monomers that can be generated, and then calculate the theoretical total mass of lithium iron phosphate precursor.

[0024] The complexing agent mentioned in step (6) above is at least one of sodium nitrilotriacetate (NTA), ethylenediaminetetraacetate (disodium or tetrasodium EDTA), and diethylenetriaminepentacarboxylate (DTPA). The amount of complexing agent added is equal to the amount of Fe in the aluminum removal solution. 2+ The amount of the reducing agent is 5% to 15% of the molar amount of the lithium iron phosphate precursor; the reducing agent is at least one of ascorbic acid, oxalic acid, and hydrazine hydrate, and the amount of the reducing agent added is 0.5% to 5.0% of the theoretical total mass of the lithium iron phosphate precursor.

[0025] The pH adjuster mentioned in step (6) above is at least one of lithium hydroxide, ammonia, sodium hydroxide, sodium carbonate, and active calcium oxide, preferably ammonia, with a solute concentration of 1.0 to 2.5 mol / L.

[0026] The non-oxidizing atmosphere mentioned in step (6) above is at least one of nitrogen, helium, neon, argon, krypton and xenon, with a purity of 99.9% or higher.

[0027] The precipitation reaction in step (6) above is carried out at a temperature of 70–95°C for 2–6 hours.

[0028] The main reaction equations that occur in step (6) above are as follows:

[0029] pH < 8:

[0030]

[0031] pH > 8:

[0032] 3Li + +PO4 3- →Li3PO4↓

[0033] 3Fe 2+ +2PO4 3- +8H2O→Fe3(PO4)2.8H2O↓

[0034] Li3PO4+Fe3(PO4)2.8H2O→3LiFePO4+8H2O↑

[0035] Thus, step (6) is performed under alkaline conditions due to Fe 2+ Easily oxidized to Fe 3+ By utilizing the oxygen-blocking effect of a non-oxidizing atmosphere and the reducing effect of a reducing agent, Fe is effectively prevented through a dual action. 2+ Oxidized into Fe 3+ Because the Ksp values ​​of Li3PO4 and Fe3(PO4)2·8H2O differ significantly, in order to ensure the equilibrium of their coprecipitation reaction, a complexing agent is used to treat Fe at pH < 8. 2+ It acts as a complexing agent, slowly releasing Fe at pH > 8. 2+ The precipitation rates of Li3PO4 and Fe3(PO4)2·8H2O were adjusted to make them similar, thereby ensuring that Li... + Fe 2+ :P 5+ The molar ratio remains close to 1:1:1, maximizing the formation of the target product LiFePO4 and minimizing the formation of byproducts.

[0036] (7) The lithium iron phosphate precursor slurry is dried to obtain lithium iron phosphate precursor powder, and then a carbon source is added and calcined in a non-oxidizing atmosphere to obtain lithium iron phosphate cathode material.

[0037] The drying operation described in step (7) above is preferably spray drying, with a temperature of 200 to 400°C.

[0038] The carbon source mentioned in step (7) above is at least one of citric acid, oxalic acid, sucrose, glucose, and polyethylene glycol. The amount of carbon source added is 0.1% to 0.5% of the mass of the lithium iron phosphate precursor powder. The calcination operation is carried out at a temperature of 350 to 500°C for 2 to 6 hours.

[0039] Thus, step (7) through spray drying can reduce the loss of lithium, iron, and phosphorus elements in the lithium iron phosphate precursor slurry, achieve the enrichment of major elements, make the actual ratio of lithium, iron, and phosphorus elements in the product more closely match the design ratio, improve the enrichment of useful elements, reduce the error in the actual ratio of useful elements, and improve the purity and electrochemical performance of lithium iron phosphate cathode material. Spray drying also has the function of granulation compared to ordinary drying.

[0040] (8) The lithium iron phosphate cathode material is pulverized to a D50 particle size of 1-16 μm, preferably 1.5-5 μm; then sealed and stored.

[0041] In step (8) above, the pulverization operation is preferably airflow pulverization, and the airflow used is dry compressed air with a dew point below -40°C.

[0042] Thus, the particle size distribution of the lithium iron phosphate material after air jet milling in step (8) meets the national standard requirements for battery-grade lithium iron phosphate.

[0043] Compared with the prior art, the present invention has at least the following advantages:

[0044] The method of this invention is a wet recovery process with relatively high recovery rates of lithium, iron, and phosphorus. Compared with traditional wet processes, the process flow is simple, the amount of chemical reagents used is small, and it is economical and environmentally friendly. Phosphoric acid and organic acid leaching are used to reduce the introduction of foreign impurities; lithium hydroxide is used instead of traditional sodium hydroxide (which introduces a large amount of sodium impurities) and ammonia (which causes environmental pollution) as a pH adjuster; organic complexing agents (specifically aminocarboxylate complexing agents) are added, which have strong complexing ability and can effectively combine lithium, iron, and phosphorus compounds. Compared with traditional wet processes, the method of this invention has simple equipment, low cost, and a short process flow. The use of mixed acid as an acid leaching reagent and lithium hydroxide instead of sodium hydroxide can not only reduce the introduction of foreign impurities, but also reduce reagent costs as a lithium source. Through the prescribed steps (1) to (8), lithium iron phosphate precursor slurry is directly obtained, and after drying, lithium iron phosphate precursor powder can be obtained without the need for traditional washing processes, reducing pure water consumption and effectively reducing wastewater volume. The method of this invention has the characteristics of short process, environmental protection and economy, high yield of lithium iron phosphate precursor, good consistency of prepared lithium iron phosphate cathode material product, uniform particle size, excellent electrical performance, and can realize industrial mass production. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating the steps of a method for recycling and processing waste lithium iron phosphate batteries according to an embodiment of the present invention.

[0047] Figure 2 The diagram shows the first charge-discharge performance of the lithium iron phosphate cathode material in Example 3 of the present invention.

[0048] Figure 3 This is a 10,000x scanning electron microscope image of the lithium iron phosphate cathode material of Example 3 of the present invention.

[0049] Figure 4 This is a 20,000x scanning electron microscope image of the lithium iron phosphate cathode material of Example 3 of the present invention. Detailed Implementation

[0050] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0051] Example 1

[0052] A method for recycling and processing waste lithium iron phosphate batteries includes the following steps:

[0053] (1) After being discharged, disassembled, crushed and sorted, waste lithium iron phosphate batteries are obtained as metal shells, plastic separators, aluminum foil, copper foil and lithium iron phosphate powder containing active materials.

[0054] The discharge operation described in step (1) above is resistive discharge or physical discharge of carbon powder conductor.

[0055] (2) The lithium iron phosphate powder is calcined in a non-oxidizing atmosphere to obtain calcined powder.

[0056] The calcination operation in step (2) above is carried out at a temperature of 450°C for 6 hours. The non-oxidizing atmosphere is nitrogen with a purity of 99.9% or higher.

[0057] (3) Pure water is added to the roasted powder to make a slurry, mixed acid is added to adjust the pH value to 2 for leaching, and the leaching solution and leaching residue are obtained by filtration.

[0058] The liquid-to-solid ratio obtained in the slurry preparation operation in step (3) above is 3:1. The mixed acid includes an inorganic acid and an organic acid in a mass ratio of 1:1, wherein the inorganic acid is phosphoric acid and the organic acid is tartaric acid; the leaching operation is carried out at a temperature of 70°C for 6 hours.

[0059] (4) Iron powder is added to the leachate for precipitation reaction, and the copper removal solution is obtained by filtration.

[0060] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+ The amount is 1.0 times the molar quantity. The precipitation reaction is carried out at a temperature of 30°C for 6 hours.

[0061] (5) Add a pH adjuster to the copper removal solution to adjust the pH of the solution to 5 for precipitation reaction, and filter to obtain aluminum removal solution.

[0062] The pH adjuster mentioned in step (5) above is ammonia. The precipitation reaction is carried out at a temperature of 30°C for 3.0 hours.

[0063] (6) A complexing agent and a reducing agent are added to the aluminum removal solution, and a pH adjuster is added to adjust the pH of the solution to 8. A precipitation reaction is carried out under a non-oxidizing atmosphere to obtain lithium iron phosphate precursor slurry.

[0064] In step (6) above, the aluminum removal solution is subjected to elemental analysis according to an element molar ratio of n. Li :n Fe :n P Add an insufficient amount of lithium source (i.e., lithium hydroxide) in a ratio of 1:1:1, calculate the theoretical number of moles of lithium iron phosphate precursor monomers that can be generated, and then calculate the theoretical total mass of lithium iron phosphate precursors.

[0065] The complexing agent mentioned in step (6) above is sodium nitrilotriacetate (NTA), and the amount of complexing agent added is equal to the Fe content in the aluminum removal solution. 2+ The amount of reducing agent is 5% of the molar amount of the lithium iron phosphate precursor; the reducing agent is oxalic acid, and the amount of reducing agent added is 0.5% of the theoretical total mass of the lithium iron phosphate precursor. The pH adjuster is ammonia. The non-oxidizing atmosphere is nitrogen with a purity of ≥99.9%. The precipitation reaction is carried out at a temperature of 70°C for 6 hours.

[0066] (7) The lithium iron phosphate precursor slurry is dried to obtain lithium iron phosphate precursor powder, and then a carbon source is added and calcined in a non-oxidizing atmosphere to obtain lithium iron phosphate cathode material.

[0067] The drying operation in step (7) above is spray drying at a temperature of 200°C. The carbon source is citric acid, and the amount of carbon source added is 0.1% of the mass of the lithium iron phosphate precursor powder. The calcination operation is carried out at a temperature of 350°C for 6 hours.

[0068] (8) The lithium iron phosphate cathode material is pulverized to a D50 particle size of 1-16 μm and then sealed for storage.

[0069] In step (8) above, the pulverization operation is airflow pulverization, and the airflow used is dry compressed air with a dew point below -40°C.

[0070] Example 2

[0071] A method for recycling and processing waste lithium iron phosphate batteries includes the following steps:

[0072] (1) After being discharged, disassembled, crushed and sorted, waste lithium iron phosphate batteries are obtained as metal shells, plastic separators, aluminum foil, copper foil and lithium iron phosphate powder containing active materials.

[0073] The discharge operation described in step (1) above is resistive discharge or physical discharge of carbon powder conductor.

[0074] (2) The lithium iron phosphate powder is calcined in a non-oxidizing atmosphere to obtain calcined powder.

[0075] The calcination operation in step (2) above is performed at a temperature of 650°C for 2 hours. The non-oxidizing atmosphere is argon with a purity of 99.9% or higher.

[0076] (3) Pure water is added to the roasted powder to make a slurry, mixed acid is added to adjust the pH value to 5 for leaching, and the leaching solution and leaching residue are obtained by filtration.

[0077] The liquid-to-solid ratio obtained in the slurry preparation operation in step (3) above is 6:1. The mixed acid includes an inorganic acid and an organic acid in a mass ratio of 5:1, wherein the inorganic acid is phosphoric acid and the organic acid is oxalic acid; the leaching operation is carried out at a temperature of 90°C for 3 hours.

[0078] (4) Iron powder is added to the leachate for precipitation reaction, and the copper removal solution is obtained by filtration.

[0079] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+ The amount of precipitation was 1.5 times the molar amount. The precipitation reaction was carried out at a temperature of 85°C for 0.5 hours.

[0080] (5) Add a pH adjuster to the copper removal solution to adjust the pH of the solution to 7 for precipitation reaction, and filter to obtain aluminum removal solution.

[0081] The pH adjuster mentioned in step (5) above is lithium hydroxide. The precipitation reaction is carried out at a temperature of 90°C for 0.5 hours.

[0082] (6) A complexing agent and a reducing agent are added to the aluminum removal solution, and a pH adjuster is added to adjust the pH of the solution to 10. A precipitation reaction is carried out under a non-oxidizing atmosphere to obtain lithium iron phosphate precursor slurry.

[0083] In step (6) above, the aluminum removal solution is subjected to elemental analysis according to an element molar ratio of n. Li :n Fe :n P Add an insufficient amount of lithium source (i.e., lithium hydroxide) in a ratio of 1:1:1, calculate the theoretical number of moles of lithium iron phosphate precursor monomers that can be generated, and then calculate the theoretical total mass of lithium iron phosphate precursors.

[0084] The complexing agent mentioned in step (6) above is ethylenediaminetetraacetic acid (EDTA disodium or tetrasodium), and the amount of complexing agent added is equal to the Fe content in the aluminum removal solution. 2+The amount of reducing agent is 15% of the molar amount of the lithium iron phosphate precursor; the reducing agent is hydrazine hydrate, and the amount of reducing agent added is 5% of the theoretical total mass of the lithium iron phosphate precursor. The pH adjuster is lithium hydroxide. The non-oxidizing atmosphere is argon with a purity of ≥99.9%. The precipitation reaction is carried out at a temperature of 95°C for 2 hours.

[0085] (7) The lithium iron phosphate precursor slurry is dried to obtain lithium iron phosphate precursor powder, and then a carbon source is added and calcined in a non-oxidizing atmosphere to obtain lithium iron phosphate cathode material.

[0086] The drying operation in step (7) above is preferably spray drying at a temperature of 400°C. The carbon source is sucrose, and the amount of carbon source added is 0.5% of the mass of the lithium iron phosphate precursor powder; the calcination operation is performed at a temperature of 500°C for 2 hours.

[0087] (8) The lithium iron phosphate cathode material is pulverized to a D50 particle size of 1-16 μm, preferably 1.5-5 μm; then sealed and stored.

[0088] In step (8) above, the pulverization operation is airflow pulverization, and the airflow used is dry compressed air with a dew point below -40°C.

[0089] Example 3

[0090] A method for recycling and processing waste lithium iron phosphate batteries includes the following steps:

[0091] (1) After being discharged, disassembled, crushed and sorted, waste lithium iron phosphate batteries are obtained as metal shells, plastic separators, aluminum foil, copper foil and lithium iron phosphate powder containing active materials.

[0092] The discharge operation described in step (1) above is resistive discharge or physical discharge of carbon powder conductor.

[0093] (2) The lithium iron phosphate powder is calcined in a non-oxidizing atmosphere to obtain calcined powder.

[0094] The calcination operation in step (2) above is carried out at a temperature of 550°C for 4 hours. The non-oxidizing atmosphere is nitrogen with a purity of 99.9% or higher.

[0095] (3) Pure water is added to the roasted powder to make a slurry, mixed acid is added to adjust the pH value to 3.5 for leaching, and the leaching solution and leaching residue are obtained by filtration.

[0096] The liquid-to-solid ratio obtained in the slurry preparation operation in step (3) above is 4.5:1. The mixed acid includes an inorganic acid and an organic acid in a mass ratio of 3:1, wherein the inorganic acid is phosphoric acid and the organic acid is citric acid; the leaching operation is carried out at a temperature of 80°C for 4.5 hours.

[0097] (4) Iron powder is added to the leachate for precipitation reaction, and the copper removal solution is obtained by filtration.

[0098] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+ The molar amount was 1.2 times that of the total molar amount. The precipitation reaction was carried out at a temperature of 58°C for 3 hours.

[0099] (5) Add a pH adjuster to the copper removal solution to adjust the pH of the solution to 6 for precipitation reaction, and filter to obtain aluminum removal solution.

[0100] The pH adjuster mentioned in step (5) above is lithium hydroxide. The precipitation reaction is carried out at a temperature of 60°C for 1.7 hours.

[0101] (6) A complexing agent and a reducing agent are added to the aluminum removal solution, and a pH adjuster is added to adjust the pH of the solution to 9. A precipitation reaction is carried out under a non-oxidizing atmosphere to obtain lithium iron phosphate precursor slurry.

[0102] In step (6) above, the aluminum removal solution is subjected to elemental analysis according to an element molar ratio of n. Li :n Fe :n P Add an insufficient amount of lithium source (i.e., lithium hydroxide) in a ratio of 1:1:1, calculate the theoretical number of moles of lithium iron phosphate precursor monomers that can be generated, and then calculate the theoretical total mass of lithium iron phosphate precursors.

[0103] The complexing agent mentioned in step (6) above is diethylenetriaminepentacarboxylate (DTPA), and the amount of complexing agent added is equal to the Fe content in the aluminum removal solution. 2+ The amount of the reducing agent is 10% of the molar amount of the lithium iron phosphate precursor; the reducing agent is ascorbic acid, and the amount of the reducing agent added is 2.5% of the theoretical total mass of the lithium iron phosphate precursor. The pH adjuster is lithium hydroxide. The non-oxidizing atmosphere is nitrogen with a purity of ≥99.9%. The precipitation reaction is carried out at a temperature of 85°C for 4 hours.

[0104] (7) The lithium iron phosphate precursor slurry is dried to obtain lithium iron phosphate precursor powder, and then a carbon source is added and calcined in a non-oxidizing atmosphere to obtain lithium iron phosphate cathode material.

[0105] The drying operation in step (7) above is spray drying at a temperature of 300°C. The carbon source is oxalic acid, and the amount of carbon source added is 0.3% of the mass of the lithium iron phosphate precursor powder. The calcination operation is carried out at a temperature of 425°C for 4 hours.

[0106] (8) The lithium iron phosphate cathode material is pulverized to a D50 particle size of 1.5-5 μm and then sealed for storage.

[0107] In step (8) above, the pulverization operation is airflow pulverization, and the airflow used is dry compressed air with a dew point below -40°C.

[0108] Comparative Example 1

[0109] It is basically the same as Example 3, except that:

[0110] The roasting operation described in step (2) above is performed at a temperature of 400°C for 7 hours.

[0111] The liquid-to-solid ratio obtained in step (3) above is 2:1. The mixed acid is phosphoric acid. The pH endpoint of the leaching operation is 1.5, the temperature is 60℃, and the time is 7h.

[0112] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+ The amount is 0.5 times the molar quantity. The precipitation reaction is carried out at a temperature of 20°C for 7.0 h.

[0113] The pH endpoint of the precipitation reaction in step (5) above is 4.5, the temperature is 20℃, and the time is 4.0h.

[0114] The amount of complexing agent added in step (6) above is equal to the amount of Fe in the aluminum removal solution. 2+ The amount of reducing agent added is 3% of the molar amount of the lithium iron phosphate precursor; the amount of reducing agent added is 0.3% of the theoretical total mass of the lithium iron phosphate precursor. The precipitation reaction is carried out at a pH of 7.5, a temperature of 60°C, and a time of 7 hours.

[0115] The drying temperature in step (7) above is 150°C. The amount of carbon source added is 0.05% of the mass of the lithium iron phosphate precursor powder; the calcination temperature is 300°C and the time is 7 hours.

[0116] In step (8) above, the pulverization operation is airflow pulverization, and the airflow used is dry compressed air with a dew point of -20°C.

[0117] Comparative Example 2

[0118] It is basically the same as Example 3, except that:

[0119] The roasting operation described in step (2) above is performed at a temperature of 700°C for 1 hour.

[0120] The liquid-to-solid ratio obtained in step (3) above is 6:1. The mixed acid is phosphoric acid. The pH endpoint of the leaching operation is 5.5, the temperature is 100℃, and the time is 2 hours.

[0121] In step (4) above, the amount of iron powder added to the leaching solution is equal to the Cu content in the leaching solution. 2+The amount of precipitation was 2.0 times the molar amount. The precipitation reaction was carried out at a temperature of 95°C for 0.2 hours.

[0122] The pH endpoint of the precipitation reaction described in step (5) above is 7.5, the temperature is 100℃, and the time is 0.2h.

[0123] The amount of complexing agent added in step (6) above is equal to the amount of Fe in the aluminum removal solution. 2+ The amount of reducing agent added is 20% of the molar amount of the lithium iron phosphate precursor; the amount of reducing agent added is 5.5% of the theoretical total mass of the lithium iron phosphate precursor. The precipitation reaction is carried out at a pH of 10.5, a temperature of 105°C, and a time of 1 hour.

[0124] The drying temperature in step (7) above is 450°C. The amount of carbon source added is 1.0% of the mass of the lithium iron phosphate precursor powder; the calcination temperature is 550°C and the time is 1 hour.

[0125] In step (8) above, the pulverization operation is airflow pulverization, and the airflow used is dry compressed air with a dew point of -30°C.

[0126] Comparative Example 3

[0127] It is basically the same as Example 3, except that no complexing agent is added in step (6) above.

[0128] Comparative Example 4

[0129] It is basically the same as Example 3, except that no reducing agent is added in step (6) above.

[0130] Experimental tests showed that the yield of lithium iron phosphate precursor in Example 3 was over 85%, and the purity of lithium iron phosphate cathode material was over 98%.

[0131] Key performance characteristics of the lithium iron phosphate cathode material in Example 3:

[0132] a. Key physicochemical properties

[0133] Compacted density 2.41 g / cm³ 3 ,

[0134] Under conditions of 0.1C / 0.1C and 2.5V to 2.75V, the discharge specific capacity of the lithium iron phosphate cathode material is 156.3mAh / g, and the discharge efficiency is 99.61%.

[0135] b. First-cycle electrical performance (see...) Figure 2 The red curve represents the discharge curve, and the green curve represents the charging curve.

[0136] c. The structure of lithium iron phosphate cathode material is shown in [reference needed]. Figures 3-4 .

[0137] Based on experimental data and Figures 2-4 It can be seen that the lithium iron phosphate cathode material in Example 3 has uniform particles, good product consistency, and good electrochemical performance.

[0138] In terms of data comparison: the lithium iron phosphate precursor yield, lithium iron phosphate cathode material purity, and electrochemical performance of the lithium iron phosphate cathode material in Examples 1 and 2 are similar to those in Example 3, and slightly lower. The lithium iron phosphate precursor yield, lithium iron phosphate cathode material purity, and electrochemical performance of the lithium iron phosphate cathode material in Examples 1-3 are significantly better than those in Comparative Examples 1-2. The lithium iron phosphate precursor yield, lithium iron phosphate cathode material purity, and electrochemical performance of the lithium iron phosphate cathode material in Comparative Examples 3-4 are all far lower than those in Example 3.

[0139] Experiments have shown that the steps of the method of the present invention have a synergistic effect. Only by using the reagent types and amounts, as well as the reaction conditions such as pH value, temperature, time, and liquid-solid ratio specified in the method of the present invention, can the effect of the present invention be achieved, resulting in a lithium iron phosphate precursor yield of over 85%, a lithium iron phosphate cathode material purity of over 98%, a discharge efficiency of over 99.61%, and good electrochemical performance.

[0140] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for recycling and processing waste lithium iron phosphate batteries, characterized in that, Includes the following steps: (1) After being discharged, dismantled, crushed and sorted, waste lithium iron phosphate batteries are obtained as shell, separator, current collector and lithium iron phosphate powder containing active material. (2) The lithium iron phosphate powder is calcined in a non-oxidizing atmosphere to obtain calcined powder; (3) Add mixed acid to the calcined powder to adjust the pH and leach it, and filter to obtain leachate and leach residue; (4) Iron powder is added to the leachate to carry out a precipitation reaction, and the copper removal solution is obtained by filtration. (5) Add a pH adjuster to the copper removal solution to adjust the pH and carry out a precipitation reaction, and filter to obtain an aluminum removal solution; (6) A complexing agent and a reducing agent are added to the aluminum removal liquid, and a pH adjuster is added to adjust the pH. A precipitation reaction is carried out under a non-oxidizing atmosphere to obtain lithium iron phosphate precursor slurry. (7) The lithium iron phosphate precursor slurry is dried to obtain lithium iron phosphate precursor powder, and then a carbon source is added and calcined in a non-oxidizing atmosphere to obtain lithium iron phosphate cathode material. In step (3), the pH value is adjusted to 2-5, and the mixed acid includes an inorganic acid and an organic acid in a mass ratio of (1-5):

1. The inorganic acid is phosphoric acid, and the organic acid is at least one of tartaric acid, oxalic acid, malic acid, citric acid, and ascorbic acid. The leaching operation is carried out at a temperature of 70-90°C for 3-6 hours. In step (5), the pH value is adjusted to 5-7; In step (6), the pH value is adjusted to 8-10, and the complexing agent is at least one of sodium triacetate, ethylenediaminetetraacetate, and diethylenetriaminepentacarboxylate. The amount of complexing agent added is equal to the Fe content in the aluminum removal solution. 2+ The amount of the reducing agent is 5% to 15% of the molar amount of the lithium iron phosphate precursor; the reducing agent is at least one of ascorbic acid, oxalic acid, and hydrazine hydrate, and the amount of the reducing agent added is 0.5% to 5.0% of the theoretical total mass of the lithium iron phosphate precursor; the precipitation reaction is carried out at a temperature of 70 to 95°C for 2 to 6 hours.

2. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, The roasting operation in step (2) is performed at a temperature of 450–650°C for 2–6 hours.

3. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, In step (3), before adding the mixed acid, pure water is added to the calcined powder to prepare a slurry, and the liquid-solid ratio obtained by the slurry preparation operation is (3-6):

1.

4. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, In step (4), the amount of iron powder added is equal to the Cu content in the leachate. 2+ The amount of the precipitate is 1.0 to 1.5 times the molar amount, and the precipitation reaction is carried out at a temperature of 30 to 85°C for 0.5 to 6 hours.

5. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, In step (5), the pH adjuster is at least one of lithium hydroxide, ammonia, sodium hydroxide, sodium carbonate, and active calcium oxide; the precipitation reaction temperature is 30-90℃ and the time is 0.5-3h.

6. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, The carbon source in step (7) is at least one of citric acid, oxalic acid, sucrose, glucose, and polyethylene glycol. The amount of carbon source added is 0.1% to 0.5% of the mass of the lithium iron phosphate precursor powder. The calcination operation is carried out at a temperature of 350 to 500°C for 2 to 6 hours.

7. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1 or 6, characterized in that, The drying operation in step (7) is performed at a temperature of 200–400°C.

8. The method for recycling and processing waste lithium iron phosphate batteries according to claim 1, characterized in that, It also includes step (8) of pulverizing the lithium iron phosphate cathode material to a D50 particle size of 1-16 μm.

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