Method for recycling retired lithium iron phosphate battery through cooperation of electrochemical oxidation and chemical oxidation

Abstract

The invention relates to a method for recycling retired lithium iron phosphate batteries through cooperation of electrochemical oxidation and chemical oxidation. An organic ligand coordinated redox couple is introduced into the electrolyte of the anode chamber to serve as an electron transfer medium, the redox couple selectively acts on the lithium iron phosphate battery positive electrode material, preferential leaching of the lithium element is achieved through directional electron transfer, and dissolution of the iron element is effectively inhibited; the reduction state of the redox couple coordinated by the organic ligand can be regenerated through in-situ electrochemical oxidation of the anode electrode, other oxidants do not need to be additionally added, and a closed-loop regeneration system of the oxidants is formed. An electrode interface direct oxidation channel is established, so that the LFP material in contact with the anode in the circulation process is subjected to synchronous lithium removal through a surface electrochemical oxidation reaction, and a synergistic strengthening effect is formed with a solution phase chemical oxidation path. The redox couple coordinated by the organic ligand can complete electron transfer under a relatively low driving voltage, so that hydrogen evolution / oxygen evolution side reaction is remarkably inhibited, overpotential accumulation is reduced, and electric energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of retired lithium ion battery recycling, in particular to a method for electrochemical oxidation-chemical oxidation synergistic recovery of retired lithium iron phosphate battery. BACKGROUND

[0002] Lithium, as a key strategic resource for new energy revolution, is listed as the first place in the "key mineral list" by the International Energy Agency, and the global demand for lithium resources has increased by 23.6% in the past five years. China's lithium ion battery production has ranked first in the world for eight consecutive years, accounting for 62% of the global total production in 2023, of which the consumption of lithium in the field of power batteries has increased to 58.3%. Lithium iron phosphate (LFP) batteries, with the advantage of high energy density, dominate the high-end electric vehicle market, with a capacity of 142.3 GWh in 2024, accounting for 51.8% of the passenger vehicle market. According to statistics, China will have 1.35 million tons of retired lithium ion batteries in 2025, with 3.2 tons of lithium (equivalent to the lithium content of 300 tons of spodumene concentrate) and 30 tons of heavy metals, 6.2 tons of fluorides in every 100 tons of waste lithium ion batteries, which are important secondary resources. Therefore, it is urgent to explore a green and efficient method for recycling retired lithium ion batteries.

[0003] In the traditional hydrometallurgical process, the retired LFP positive material is mainly treated by high-concentration acid and reducing agent for leaching, so that lithium ions and iron ions are dissolved together to form a mixed solution, and then various separation methods are used to separate the metal components. However, this method has defects such as excessive consumption of high-concentration chemicals, complex pretreatment process, and insufficient selectivity in the metal leaching process. Therefore, in order to break through the bottleneck of traditional process, in recent years, new technologies for selective and selective lithium extraction from retired lithium iron phosphate battery materials have been studied, among which chemical oxidation method and electrochemical oxidation method have become research hotspots. The chemical oxidation method mainly promotes the oxidation state of transition metals by introducing oxidizing agents (such as hydrogen peroxide, ozone and sodium hypochlorite, etc.), and uses the lattice instability of high-valence metals to promote the leaching of lithium ions, which has a very high lithium leaching rate. However, this method has the problem of difficult control of the leaching of impurity ions (such as Fe 3+ , Al 3+ , etc.), resulting in high impurity content in the leaching solution, and a large amount of oxidizing agent is needed in the oxidation process, which is economically poor. The electrochemical oxidation method drives the lithium stripping of the retired LFP positive material by electric field, and the process is similar to the charging and discharging of lithium ion batteries, which can realize the selective recovery of lithium. However, the electrochemical oxidation method needs to apply high cell voltage, which is easy to cause hydrogen evolution and oxygen evolution side reactions on the electrode surface, thereby increasing the overpotential, reducing the current efficiency and increasing the energy consumption, etc. SUMMARY

[0004] To solve the problems in the prior art, the application provides a method for recycling retired lithium iron phosphate batteries through electrochemical oxidation-chemical oxidation synergy. A redox couple coordinated by an organic ligand is introduced into an electrolyte in an anode chamber as an electron transfer medium, which can selectively act on a positive electrode material of the lithium iron phosphate battery, preferentially leaching lithium elements through directional electron transfer, and effectively inhibiting the dissolution of iron elements; the reduced state of the redox couple coordinated by the organic ligand can be regenerated through in-situ electrochemical oxidation of an anode electrode, without the need to add other oxidants, thereby forming a closed-loop regeneration system of oxidants. At the same time, a direct oxidation channel at an electrode interface is established, so that the LFP material contacting the anode in the circulation process is simultaneously delithiated through a surface electrochemical oxidation reaction, and a synergistic strengthening effect is formed with a chemical oxidation path in the solution. Compared with a traditional redox couple, the redox couple coordinated by the organic ligand can complete electron transfer at a lower driving voltage, significantly inhibit the occurrence of side reactions, reduce the accumulation of overpotential, and reduce power consumption.

[0005] To achieve the object of the application, the method for recycling retired lithium iron phosphate batteries through electrochemical oxidation-chemical oxidation synergy comprises the following steps: (1) preparing a redox couple coordinated by an organic ligand The organic ligand and the transition metal ion are mixed to obtain a solution containing the redox couple coordinated by the organic ligand through a coordination reaction.

[0006] In the preferred embodiment of the application, the organic ligand comprises at least one of the following: a carboxylate ligand such as acetate, benzoate and oxalate; a β-diketonate ligand such as acetylacetone and butanedione; a phenolic acid ligand such as phenolate and catecholate; a thiolate or thioesterate ligand such as benzene thiolate and aliphatic thiolate; an amine anion ligand such as a deprotonated amine group or an amide ligand and similar structures such as quinoline or pyrrole in a deprotonated form; a polydentate polyanionic ligand such as ethylenediaminetetraacetic acid, citric acid, diethylenetriamine pentaacetic acid, triacetonitrile triacetate; a phthalocyanine ligand such as a phthalocyanine macrocyclic ligand represented as Pc in a metal phthalocyanine complex; a macrocyclic anion ligand such as a deprotonated crown ether type structure; and other typical anion ligands such as phenylborate and phosphate anions. 2-

[0007] ​According to a preferred embodiment of the present application, the concentration of the organic ligand is 0.01-5 M. According to a further preferred embodiment of the present application, the concentration of the organic ligand is 0.01 M, 0.02 M, 0.04 M, 0.06 M, 0.08 M, 0.1 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, 2.0 M, 2.2 M, 2.4 M, 2.6 M, 2.8 M, 3.0 M, 3.2 M, 3.4 M, 3.6 M, 3.8 M, 4.0 M, 4.2 M, 4.4 M, 4.6 M, 4.8 M, or 5.0 M.

[0008] According to a preferred embodiment of the present application, the transition metal ion comprises at least one of vanadium, chromium, manganese, iron, cobalt, nickel, copper, molybdenum, ruthenium ions. According to a further preferred embodiment of the present application, the transition metal ion is iron or copper ion.

[0009] According to a preferred embodiment of the present application, the concentration of the transition metal ion is 0.01-5 M. According to a further preferred embodiment of the present application, the concentration of the transition metal ion is 0.01 M, 0.02 M, 0.04 M, 0.06 M, 0.08 M, 0.1 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, 2.0 M, 2.2 M, 2.4 M, 2.6 M, 2.8 M, 3.0 M, 3.2 M, 3.4 M, 3.6 M, 3.8 M, 4.0 M, 4.2 M, 4.4 M, 4.6 M, 4.8 M, or 5.0 M.

[0010] According to a preferred embodiment of the present application, the molar ratio of the organic ligand to the transition metal ion is 0.1-3:1. According to a further preferred embodiment of the present application, the molar ratio of the organic ligand to the metal ion is 0.1:1, 0.2:1, 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, or 3:1.

[0011] According to a preferred embodiment of the present application, the pH range in which the organic ligand is mixed with the transition metal ion is 2-12. According to a further preferred embodiment of the present application, the pH in which the organic ligand is mixed with the transition metal ion is 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, or 12.

[0012] According to a preferred embodiment of the present application, the organic ligand is mixed with the transition metal ion under stirring at a stirring speed of 500-1000 rpm. According to a further preferred embodiment of the present application, the stirring speed is 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm.

[0013] According to a preferred embodiment of the present application, the organic ligand is mixed with the transition metal ion under stirring at a stirring speed of 500-1000 rpm. According to a further preferred embodiment of the present application, the stirring speed is 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm.

[0014] In the present application, the redox couple coordinated by the organic ligand has high oxidizability and reversibility, for example has a standard electrode potential of 0.85 V, has a standard electrode potential of 0.472 V, has a standard electrode potential of 0.67 V, so that the lithium iron phosphate can be oxidized to iron phosphate.

[0015] In the present application, the transition metal ion is coordinated with the organic ligand to form an anionic redox couple, which cannot pass through the cation exchange membrane due to its inherent anionic characteristics.

[0016] (2) Construction of lithium extraction system The lithium extraction system adopts a two-chamber system in which the anode chamber and the cathode chamber are separated by a cation exchange membrane.

[0017] The electrode of the anode chamber is made of conductive material, and the electrolyte is the solution containing the redox couple coordinated by the organic ligand prepared as described above, and the retired lithium iron phosphate battery positive electrode powder is added to the electrolyte in the anode chamber and uniformly dispersed.

[0018] The electrode of the cathode chamber is made of conductive material, and the electrolyte is a solution of soluble lithium salt, including but not limited to sodium chloride, ammonium chloride, potassium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, lithium chloride, lithium hydroxide. According to a preferred embodiment of the present application, the electrolyte is a lithium hydroxide solution.

[0019] In the present application, the term "cation exchange membrane" is a membrane that is selective to cations, which only allows cations to pass through, effectively separating the anode chamber and the cathode chamber, so that no anion exchange occurs between the electrolyte of the anode chamber and the electrolyte of the cathode chamber. According to a preferred embodiment of the present application, the cation exchange membrane comprises at least one of CMVN, CMTE, CMF, CSVN, NaFion117.

[0020] According to a preferred embodiment of the present application, the conductive material comprises at least one of: a metallic material, including at least one of titanium, silver, copper, aluminum, in the form of at least one of a wire, a mesh or a plate; an alloy material, such as brass, nichrome; an inorganic non-metallic material, such as graphite; a high molecular conductive material, such as carbon fiber, carbon cloth, carbon felt.

[0021] According to a preferred embodiment of the present application, the concentration of the electrolyte of the anode chamber is 0.001-10 mol / L. According to a further preferred embodiment of the present application, the concentration of the electrolyte of the anode chamber is 0.001 mol / L, 0.01 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L.

[0022] In the present application, the term "retired lithium iron phosphate battery positive electrode powder" is a powder material obtained from the positive electrode of a waste lithium iron phosphate battery. Typically, the lithium iron phosphate battery is completely discharged and disassembled to remove the electrode sheet, and the metal shell and the separator are removed by mechanical crushing and sieving; then the PVDF binder and electrolyte residue are removed by NMP solvent soaking or thermal decomposition in an atmosphere of 350-450°C to obtain LFP / carbon mixed powder; then the high-density LFP particles are separated and enriched in the aqueous phase by ultrasonic classification, magnetic separation or sedimentation, and washed with deionized water; finally, the retired lithium iron phosphate positive electrode powder is obtained by vacuum drying at 80-120°C for several hours.

[0023] According to a preferred embodiment of the present application, the pH of the electrolyte of the anode chamber is 4-5. At this pH, both lithium iron phosphate and iron phosphate remain stable and do not dissolve.

[0024] According to a preferred embodiment of the present application, the volume of the electrolyte in the anode chamber is 0.1-100 L. According to a further preferred embodiment of the present application, the volume of the electrolyte in the anode chamber is 0.1 L, 0.2 L, 0.4 L, 0.6 L, 0.8 L, 1.0 L, 1.5 L, 2.0 L, 2.5 L, 3.0 L, 3.5 L, 4.0 L, 4.5 L, 5.0 L, 5.5 L, 6.0 L, 6.5 L, 7.0 L, 7.5 L, 8.0 L, 8.5 L, 9.0 L, 9.5 L, 10 L, 15 L, 20 L, 25 L, 30 L, 35 L, 40 L, 45 L, 50 L, 55 L, 60 L, 65 L, 70 L, 75 L, 80 L, 85 L, 90 L, 95 L, or 100 L.

[0025] In the present application, a surfactant is added to the electrolyte in the anode chamber to make the retired lithium iron phosphate battery positive electrode powder uniformly dispersed. The type of the surfactant is not particularly limited. According to a preferred embodiment of the present application, the surfactant includes at least one of sodium dodecyl sulfate, sodium alkyl benzene sulfonate, phosphonic acid alkyl polyoxyethylene ether, cetyltrimethylammonium bromide, cetylpyridinium chloride, dimethyldistearylammonium chloride, cocobetaine, alkyl hydroxyl sulfobetaine, and sulfobetaine. According to a preferred embodiment of the present application, the amount of the surfactant added is 0.5-5 g. According to a further preferred embodiment of the present application, the amount of the surfactant added is 0.5 g, 1 g, 1.5 g, 2 g, 2.5 g, 3 g, 3.5 g, 4 g, 4.5 g, or 5 g.

[0026] According to a preferred embodiment of the present application, the solid-liquid ratio (i.e., the ratio of the mass of the retired lithium iron phosphate battery electrode powder to the volume of the electrolyte) in the anode chamber is 10-80 g / L. According to a further preferred embodiment of the present application, the solid-liquid ratio in the anode chamber is 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, or 80 g / L.

[0027] According to a preferred embodiment of the present application, the concentration of the electrolyte in the cathode chamber is 0.001-10 mol / L. According to a further preferred embodiment of the present application, the concentration of the electrolyte in the cathode chamber is 0.001 mol / L, 0.01 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, or 10 mol / L.

[0028] According to a preferred embodiment of the present application, the volume of the electrolyte in the cathode chamber is 0.1-100 L. According to a further preferred embodiment of the present application, the volume of the electrolyte in the cathode chamber is 0.1 L, 0.2 L, 0.4 L, 0.6 L, 0.8 L, 1.0 L, 1.5 L, 2.0 L, 2.5 L, 3.0 L, 3.5 L, 4.0 L, 4.5 L, 5.0 L, 5.5 L, 6.0 L, 6.5 L, 7.0 L, 7.5 L, 8.0 L, 8.5 L, 9.0 L, 9.5 L, 10 L, 15 L, 20 L, 25 L, 30 L, 35 L, 40 L, 45 L, 50 L, 55 L, 60 L, 65 L, 70 L, 75 L, 80 L, 85 L, 90 L, 95 L or 100 L.

[0029] (3) Electrochemical oxidation-chemical oxidation lithium extraction reaction In the initial stage, constant current polarization is implemented, and when the cell voltage rises to a preset cut-off cell voltage, the lithium extraction process is driven in constant voltage mode.

[0030] During the electrolyte circulation, the oxidized state of the organic ligand-coordinated redox couple is oxidized to Fe 2+ in the positive electrode powder of the retired lithium iron phosphate battery 3+ and releases , while the reduced state of the organic ligand-coordinated redox couple is re-oxidized to the oxidized state on the electrode through an electrochemical oxidation reaction; at the same time, a part of the positive electrode powder of the retired lithium iron phosphate battery is directly oxidized to FePO4 through the contact electrode and releases The synergistic effect of this chemical oxidation and electrochemical oxidation significantly improves the leaching efficiency of lithium. Under the driving of the electric field, migrates from the anode chamber to the cathode chamber through the cation exchange membrane and enriches in the cathode chamber. The electrode in the cathode chamber directly carries out the water electrolysis reaction to produce hydrogen and hydroxyl ions. The reaction mechanism is: Anode:

[0031] Cathode:

[0032] According to a preferred embodiment of the present application, the constant current density is 10-70 A / m 2 . According to a further preferred embodiment of the present application, the constant current density is 10 A / m 2 , 15 A / m 2 , 20 A / m 2 , 25 A / m 2 , 30 A / m 2 , 35 A / m 2 , 40 A / m 2 , 45 A / m 250 A / m 2 55 A / m 2 60 A / m 2 65 A / m 2 or 70 A / m 2 .

[0033] According to a preferred embodiment of the present application, the constant voltage is 0.5-1.2V. According to a further preferred embodiment of the present application, the constant voltage is 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V or 1.2V.

[0034] According to a preferred embodiment of the present application, the time for extracting lithium is 1-100h. According to a further preferred embodiment of the present application, the time for extracting lithium is 1h, 5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h or 100h, depending on the mass of lithium iron phosphate powder in the anode chamber and other factors.

[0035] (4) Product recovery After the reaction is completed, the electrolyte in the anode chamber is collected, and solid residues are obtained after filtration. By washing, drying and high-temperature calcination, high-purity iron phosphate (FP) products are obtained. The electrolyte in the cathode chamber is collected, and impurity ions are removed by adjusting the pH to alkaline and then filtering. The filtrate is concentrated, and solid carbonate and / or bicarbonate is added or CO2 is introduced to promote the precipitation of Li2CO3. After solid-liquid separation, solid Li2CO3 is obtained; or LiOH products are directly obtained by evaporation and concentration.

[0036] By the method of the present application, the leaching rate of lithium can reach more than 99%, and the dissolution rate of iron is less than 0.1%, wherein the recovery rate of lithium can reach more than 98%, and the recovery rate of iron phosphate can reach more than 99%.

[0037] Compared with the prior art, the present application has the following beneficial effects: (1) The complex formed by the coordination of the organic ligand and the metal ion has large steric hindrance, which prevents the complex from being adsorbed and deposited in the pores of the cation exchange membrane, significantly improves the stable operation ability of the entire electrochemical device, prolongs the service life of the membrane and maintains the smoothness of the ion conduction channel; the reduced state of the redox couple coordinated by the organic ligand is oxidized on the electrode to regenerate the oxidizing agent, avoiding the accumulation of the decomposition products of the oxidizing agent, constructing an oxidizing agent self-cycle, and greatly reducing the consumption of chemical reagents and secondary pollution.

[0038] (2) Combined with electrochemical oxidation and chemical oxidation, the organic ligand coordinated redox couple acts as an electron transfer medium, and its oxidized state acts on the positive powder of lithium iron phosphate battery to realize the preferential leaching of lithium, and at the same time, a direct oxidation channel is established on the electrode surface to promote the synchronous reaction of lithium extraction from the positive powder of lithium iron phosphate battery and speed up the oxidation reaction kinetics; (3) The anode chamber and the cathode chamber are separated by a cation exchange membrane, and Li+ is driven to migrate from the anode to the cathode by an electric field, and OH - is generated at the cathode, and LiOH is formed, and high-purity LiOH products can be obtained by evaporation and concentration, which has the advantages of simple recovery process, low energy consumption and high product purity compared with traditional hydrometallurgy technology. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The principle schematic diagram of the method for cooperatively recovering the retired lithium iron phosphate battery by electrochemical oxidation-chemical oxidation is shown.

[0040] Figure 2 The lithium leaching rate, current efficiency and iron dissolution rate of Example 1, Comparative Example 1 and Comparative Example 2 under different cell voltages are shown.

[0041] Figure 3 is the Zeta potential diagram of the solution obtained by adding different masses of sodium dodecyl sulfonate (SDS). DETAILED DESCRIPTION

[0042] In order to better explain the present application, the following specific examples are combined for further explanation, but the present application is not limited to the specific examples.

[0043] The experimental methods used in the examples are conventional methods unless otherwise specified, and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0044] Example 1 A method for cooperatively recovering the retired lithium iron phosphate battery by electrochemical oxidation-chemical oxidation, comprising the following steps: (1) Preparation of organic ligand coordinated redox couple 0.2M citric acid and total concentration 0.2M FeCl2 and FeCl3 were mixed in equal volume under the conditions of pH 4 and 700rpm, and stirred at 60℃ water bath temperature for 2h to obtain a solution containing citric acid coordinated redox couple [Fe(citrate)] 2- / [Fe(citrate)] - .

[0045] (2) Lithium extraction system construction The lithium extraction system adopts a two-chamber system in which the anode chamber and the cathode chamber are separated by a cation exchange membrane NaFion117.

[0046] Anode chamber: A titanium plate is used as the anode electrode, and the redox couple [Fe(citrate)] prepared in (1) with citric acid coordination is added. 2- / [Fe(citrate)] - A solution of [unspecified substance] was used as the electrolyte, with a volume of 0.2 L and pH adjusted to 4. 4 g of decommissioned lithium iron phosphate battery cathode material powder (Fe mass percentage approximately 31.3%, Li mass percentage approximately 4.76%) and 0.5 g of sodium dodecyl sulfonate (SDS) were added. The solid-liquid ratio in the anode chamber was 20 g / L, the peristaltic pump speed was 800 rpm, and the electrode area was 42 cm². 2 .

[0047] Cathode chamber: A titanium plate is used as the cathode electrode, and 0.05M LiOH is added as the electrolyte in a volume of 0.2L. The peristaltic pump operates at 800 rpm, and the electrode area is 42 cm². 2 .

[0048] (3) Electrochemical oxidation-chemical oxidation lithium extraction reaction In the initial stage, constant current polarization (current density 25A / m²) is implemented. When the cell voltage reaches the 0.5V cutoff value, it is switched to constant voltage mode for driving. Then, selective lithium extraction is carried out at a constant voltage of 0.5V for 7 hours. The reaction process is recorded by real-time monitoring of current, voltage and reaction capacity.

[0049] (4) Product recycling After the reaction is complete, the electrolyte in the anode chamber is collected, filtered, and a solid residue is obtained. This residue is then washed, dried, and calcined at high temperature to obtain a high-purity iron phosphate product. The electrolyte in the cathode chamber is collected and concentrated by evaporation to obtain the LiOH product.

[0050] Ultimately, the lithium leaching rate was 99.43%, the iron dissolution rate was 0.07%, the current efficiency was 99.29%, and the recovery rates of lithium and iron phosphate were 98.44% and 99.54%, respectively.

[0051] Example 2 A method for the synergistic electrochemical oxidation-chemical oxidation recycling of retired lithium iron phosphate batteries includes the following steps: (1) Preparation of redox couples coordinated with organic ligands 0.2 M EDTA and 0.2 M MnCl2·4H2O were mixed in equal volumes at pH 6 and 700 rpm, and stirred in a water bath at 60 °C for 2 h to obtain a solution containing [Mn(EDTA)]. 2- A solution of the complex was prepared. An equal volume of 0.1M H₂O₂ solution was then added, and the reaction was continued at 60°C for 1 hour to partially oxidize it to [Mn(EDTA)]. -, to obtain a solution containing EDTA-coordinated redox couple [Mn(EDTA)] 2- / [Mn(EDTA)] - .

[0052] (2) Lithium extraction system construction The lithium extraction system adopts a two-chamber system separated by a cation exchange membrane NaFion117.

[0053] Anode chamber: titanium plate as anode electrode, add the solution containing EDTA-coordinated redox couple [Mn(EDTA)] 2- / [Mn(EDTA)] - prepared in (1) as electrolyte, volume is 0.2L, pH is adjusted to 4, add 4g of retired lithium iron phosphate battery positive material powder (Fe mass fraction is about 31.3%, Li mass fraction is about 4.76%) and 0.5g of sodium dodecyl sulfate, the solid-liquid ratio of the anode chamber is 20g / L, the peristaltic pump speed is 800rpm, and the electrode area is 42cm 2 .

[0054] Cathode chamber: titanium plate as cathode electrode, add 0.05M LiOH as electrolyte, volume is 0.2L, peristaltic pump speed is 800rpm, and electrode area is 42cm 2 .

[0055] (3) Electrochemical oxidation-chemical oxidation lithium extraction reaction In the initial stage, constant current polarization (current density 25A / m²) is implemented, when the cell voltage reaches 0.6V cutoff value, it is switched to constant voltage mode driving, then 0.6V constant voltage for 6h for selective lithium extraction, the reaction progress is recorded by real-time monitoring of current, voltage and reaction capacity.

[0056] (4) Product recovery After the reaction is completed, the electrolyte in the anode chamber is collected, and the solid residue is obtained after filtration, and high-purity iron phosphate product is obtained by washing, drying and high-temperature calcination. Collect the electrolyte in the cathode chamber, and obtain LiOH product by evaporation and concentration.

[0057] Finally, the leaching rate of lithium is 99.12%, the dissolution rate of iron is 0.04%, the current efficiency is 99.97%, and the recovery rates of lithium and iron phosphate are 98.72% and 99.34% respectively.

[0058] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the cell voltage is 0.3V.

[0059] Finally, the leaching rate of lithium was 67.22%, the dissolution rate of iron was 1.30%, the current efficiency was 64.73%, and the recovery rates of lithium and iron phosphate were 69.22% and 67.53%, respectively. Compared with Example 1, the leaching rate of lithium and the current efficiency were significantly decreased, which was due to the insufficient power for the oxidation reaction of the reduced state of the redox couple coordinated by the organic ligand caused by the low cell voltage, and the main reaction was changed to the electrochemical oxidation of LFP directly contacting the electrode, so more time was needed for the LFP material to contact the electrode multiple times, resulting in a long time of current maintained at a low range, which was easy to cause the dissolution of iron ions.

[0060] Comparative Example 2 The difference between Comparative Example 2 and Example 1 was that the cell voltage was 0.7 V.

[0061] Finally, the leaching rate of lithium was 71.23%, the dissolution rate of iron was 3.64%, the current efficiency was 61.41%, and the recovery rates of lithium and iron phosphate were 65.31% and 68.47%, respectively. Compared with Example 1, the leaching rate of lithium and the current efficiency were significantly decreased, which was due to the occurrence of the oxygen evolution side reaction on the anode electrode caused by the high cell voltage, the rapid decrease of pH, the excessive local acid concentration leading to the iron dissolution loss of LFP material, and the oxygen bubbles generated by the side reaction adhering to the electrode surface, occupying the active sites of the electrode reaction, which was not conducive to the oxidation reaction of the reduced state of the redox couple coordinated by the organic ligand to regenerate.

[0062] From Figure 2 It can be seen that under the conditions of electrolyte pH of 4 in the anode chamber, solid-liquid ratio of 20 g / L, current density of 25 A / m 2 The cell voltage of 0.5 V was more conducive to the selective leaching of lithium in the positive electrode material powder of the retired lithium iron phosphate battery and the recovery of iron phosphate.

[0063] Comparative Example 3 The difference between Comparative Example 3 and Example 1 was that the pH of the electrolyte in the anode chamber was 1.

[0064] Finally, the leaching rate of lithium was 72.66%, the dissolution rate of iron was 8.64%, the current efficiency was 71.40%, and the recovery rates of lithium and iron phosphate were 65.8% and 63.78%, respectively.

[0065] Compared with Example 1, the leaching rate of lithium and the current efficiency were significantly decreased, which was due to the low pH, the thermodynamic instability of LFP and FP, and the dissolution of Fe³⁺ in the crystal lattice into the solution. At the same time, when the pH was 1, [Fe(citrate)] 2- / [Fe(citrate)] -In acidic media, it decomposes, disrupting the closed-loop regeneration system of the oxidant. This weakens the chemical oxidation capacity of the anolyte, transforming the main reaction into electrochemical oxidation at the LFP direct contact electrode, thus reducing lithium-ion leaching efficiency. Furthermore, excessive iron ions permeate the cation exchange membrane, contaminating the cathode chamber solution. During product recovery, iron ions precipitate as Fe(OH)3 / Fe(OH)2, causing Li... + The recovery rate of FePO4 decreased significantly. (Comparative Example 4) The difference between Comparative Example 4 and Example 1 is that no surfactant is added.

[0066] Ultimately, the lithium leaching rate reached 67.34%, the iron dissolution rate was 0.3%, the current efficiency was 62.21%, and the recovery rates of lithium and iron phosphate were 63.48% and 61.23%, respectively.

[0067] Compared to Example 1, both lithium leaching and product recovery rates were low. For example... Figure 3 As shown, without the addition of surfactant, the zeta potential is -21 mV, resulting in the colloidal stability being at a critical state. Material particles form macroscopic aggregates in the liquid phase, exhibiting significant phase separation and drastically reducing the effective contact area at the solid-liquid interface. This non-uniform dispersion severely hinders the mass transfer process of the chemical oxidation reaction, significantly limiting the kinetics of the anodic oxidation reaction and ultimately leading to low lithium extraction efficiency. With the addition of surfactant, the absolute value of the zeta potential significantly increases, and the colloidal system transforms into a highly stable dispersion state. The uniformly distributed LFP material is in full contact with the electrolyte, providing an ideal mass transfer channel for the redox reaction and effectively promoting lithium ion leaching.

[0068] Comparative Example 5 A method for electrochemical oxidation recycling of retired lithium iron phosphate batteries includes the following steps: (1) Construction of lithium extraction system The lithium extraction system uses a two-chamber system with a cation exchange membrane NaFion117 to separate the anode chamber and the cathode chamber.

[0069] Anode chamber: A titanium plate is used as the anode electrode. A 0.1M NH4Cl solution (0.2L volume) is added as the electrolyte, and the pH is adjusted to 4. 4g of decommissioned lithium iron phosphate battery cathode material powder (approximately 31.3% Fe and 4.76% Li by mass) and 0.5g of sodium dodecyl sulfate are added. The solid-liquid ratio in the anode chamber is 20g / L. The peristaltic pump speed is 800rpm, and the electrode area is 42cm². 2 .

[0070] Cathode chamber: A titanium plate is used as the cathode electrode, and 0.05M LiOH is added as the electrolyte in a volume of 0.2L. The peristaltic pump operates at 800 rpm, and the electrode area is 42 cm². 2 .

[0071] (2) Electrochemical oxidation lithium extraction reaction In the initial stage, constant current polarization (current density 25A / m²) is implemented. When the cell voltage reaches the 0.5V cutoff value, it is switched to constant voltage mode for driving, and then selective lithium extraction is performed at 0.5V constant voltage for 7 hours.

[0072] (3) Product recycling After the reaction is complete, the electrolyte in the anode chamber is collected, filtered, and a solid residue is obtained. This residue is then washed, dried, and calcined at high temperature to obtain a high-purity iron phosphate product. The electrolyte in the cathode chamber is collected and concentrated by evaporation to obtain the LiOH product.

[0073] Ultimately, the lithium leaching rate was 70.22%, the iron dissolution rate was 4.22%, the current efficiency was 67.97%, and the recovery rates of lithium and iron phosphate were 68.22% and 69.14%, respectively.

[0074] Compared to Example 1, Comparative Example 5 showed poorer experimental results. This is because it lacks an organic ligand-coordinated redox couple, and the limited contact area between LFP solid particles and the electrode in solution leads to low electron transfer efficiency. In Example 1, the oxidized state of the organic ligand-coordinated redox couple can rapidly diffuse to the surface of the LFP particles, quickly oxidizing LFP through a chemical reaction. + The leaching rate and reaction rate increase. At the same time, relying solely on electrochemical oxidation will cause a sharp increase in the anolyte potential, which will not only increase energy consumption, but more seriously, it will lead to the dissolution of iron ions in the LFP / FP structure, increasing the iron leaching rate and ultimately affecting the product recovery rate.

Claims

1. A method for the synergistic electrochemical oxidation-chemical oxidation recycling of retired lithium iron phosphate batteries, comprising the following steps: (1) Preparation of redox couples coordinated with organic ligands Organic ligands are mixed with transition metal ions to obtain a solution containing redox couples coordinated by organic ligands; (2) Construction of lithium extraction system The lithium extraction system employs a two-chamber system with a cation exchange membrane separating the anode and cathode chambers; The electrode in the anode chamber is made of conductive material, and the electrolyte is a solution of redox couples containing organic ligands prepared as described above. Furthermore, retired lithium iron phosphate battery cathode powder is added to the electrolyte in the anode chamber and dispersed evenly. (3) Electrochemical oxidation-chemical oxidation lithium extraction reaction In the initial stage, constant current polarization is implemented. When the cell voltage rises to the preset cutoff cell voltage, it switches to constant voltage mode to drive the lithium extraction process. (4) Product recycling After the reaction is complete, the electrolyte in the anode chamber is collected and processed to obtain a high-purity iron phosphate product; the electrolyte in the cathode chamber is collected and processed to obtain a lithium-containing product.

2. The method according to claim 1, wherein the organic ligand comprises at least one of the following: carboxylate ligands, β-diketone ligands, phenolic acid ligands, thiolate or thioester ligands, amine anion ligands, multidentate multi-anion ligands, phthalocyanine ligands, macrocyclic anion ligands; wherein the concentration of the organic ligand is 0.01-5M.

3. The method according to claim 2, wherein the organic ligand comprises at least one of the following: acetate, benzoate, oxalate, acetylacetone, dimethylglyoxalate, phenol, catechol, benzyl thiol, aliphatic thiol, deprotonated amino or amide ligands and similar structures, ethylenediaminetetraacetic acid, citric acid, diethylenetriaminepentaacetic acid, triacetonitrile, phenylboronic acid, and phosphate anions.

4. The method according to claim 1, wherein the transition metal ion includes at least one selected from vanadium, chromium, manganese, iron, cobalt, nickel, copper, molybdenum, and ruthenium ions; and the concentration of the transition metal ion is 0.01-5M.

5. The method according to claim 1, wherein the molar ratio of the organic ligand to the transition metal ion is 0.1-3:1; the pH range for mixing the organic ligand and the transition metal ion is 2-12; the organic ligand and the transition metal ion are mixed at a stirring speed of 500-1000 rpm; and the organic ligand and the transition metal ion are reacted in a water bath at a temperature of 25-60°C for 2-10 h.

6. The method according to claim 1, wherein the cation exchange membrane comprises at least one of CMVN, CMTE, CMF, CSVN, and NaFion117; wherein the conductive material comprises at least one of the following: a metallic material, comprising at least one of titanium, silver, copper, and aluminum, in the form of at least one of wire, mesh, or plate; an alloy material, comprising brass and nickel-chromium alloy; an inorganic non-metallic material, comprising graphite; and a polymeric conductive material, comprising carbon fiber, carbon cloth, and carbon felt.

7. The method according to claim 1, wherein the concentration of the electrolyte in the anode chamber is 0.001-10 mol / L; the pH of the electrolyte in the anode chamber is 4-5; the volume of the electrolyte in the anode chamber is 0.1-100 L; and the solid-liquid ratio of the anode chamber is 10-80 g / L.

8. The method according to claim 1, wherein a surfactant is added to the electrolyte in the anode chamber; wherein the surfactant comprises at least one of the following: sodium dodecyl sulfate, sodium alkylbenzene sulfonate, alkyl polyoxyethylene phosphonate, hexadecyltrimethylammonium bromide, hexadecylpyridine chloride, dimethyl distearate ammonium chloride, coco-betaine, alkyl hydroxy sulfobetaine, and thio-betaine; wherein the amount of surfactant added is 0.5-5 g.

9. The method according to claim 1, wherein the concentration of the electrolyte in the cathode chamber is 0.001-10 mol / L; and the volume of the electrolyte in the cathode chamber is 0.1-100 L.

10. The method of claim 1, wherein the constant current density is 10-70 A / m 2 The constant voltage is 0.5-1.2V; the lithium extraction time is 1-100h.

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