Method for recycling retired lithium-ion battery cathode material

Abstract

The present application relates to the technical field of resource recycling of waste lithium ion batteries, in particular to a recycling method of retired lithium ion battery positive electrode material. The recycling method comprises: mixing the positive electrode powder material from which the binder and the conductive agent are removed with the eutectic solvent and the selective complexing agent to carry out the first stage leaching to form the lithium-rich leaching solution and the first leaching residue; mixing the first leaching residue and the oxidizing agent to carry out the second stage leaching to form the nickel-cobalt-manganese-rich leaching solution and the second leaching residue. The recycling method improves the problems in the existing wet recycling process of the retired lithium ion battery positive electrode material, such as large consumption of acid and alkali, difficulty in separation after synchronous dissolution of multiple valuable metals, and low lithium recovery rate. The recycling method does not need to use inorganic acid, and has high recycling efficiency and good selectivity.

Description

Technical Field

[0001] This invention relates to the field of waste lithium-ion battery resource recycling technology, and more specifically, to a method for recycling cathode materials from retired lithium-ion batteries. Background Technology

[0002] Waste lithium-ion batteries contain large amounts of scarce metal resources such as cobalt, nickel, and lithium. If they are disposed of indiscriminately, it will not only cause serious waste of resources, but also lead to environmental impacts such as heavy metal pollution.

[0003] Currently, the hydrometallurgical recycling of spent lithium-ion battery cathode materials mainly uses acid leaching methods, such as inorganic acid leaching. The inorganic acids used include hydrochloric acid, sulfuric acid, and nitric acid. However, inorganic acid leaching suffers from problems such as strong corrosivity, high costs of subsequent waste acid treatment, and the generation of large amounts of acidic wastewater. Existing technologies for this inorganic acid leaching method include acid-free recycling, such as combining iron salt mechanical activation with pure water leaching to achieve selective leaching under acid-free conditions. However, this method involves simultaneous leaching of lithium and nickel-cobalt-manganese in the same stage, constituting a one-step leaching process. The selectivity depends on the inducing effect of iron salts, and its adaptability to changes in cathode material composition needs improvement. Alternatively, DESs can be used to recycle retired ternary lithium battery cathode materials. However, this method separates the metals by adding water to precipitate nickel-cobalt-manganese after leaching, which is a precipitation separation rather than selective leaching. The separation of lithium from nickel-cobalt-manganese requires an additional precipitation step, making the process lengthy.

[0004] In summary, existing recovery methods that do not employ inorganic acids either rely on special techniques such as mechanical activation and gas-phase conversion, or still have room for improvement in selective separation. Therefore, developing a green, environmentally friendly, selectively leaching-efficient, and simple process for the acid-free recovery of lithium-ion battery cathode materials is of great significance.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for recycling cathode materials from retired lithium-ion batteries. The recycling method provided by this invention improves upon existing wet recycling processes for retired lithium-ion battery cathode materials, which suffer from high acid and alkali consumption, difficulty in separating multiple valuable metals after simultaneous dissolution, and low lithium recovery rates. This recycling method does not require inorganic acids and offers high recycling efficiency and good selectivity.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a method for recycling cathode materials of retired lithium-ion batteries, comprising: mixing cathode powder after removing binders and conductive agents with a eutectic solvent and a selective complexing agent to perform a first-stage leaching to form a lithium-rich leachate and a first leaching residue; The first leaching residue and oxidant are mixed for a second-stage leaching process to form a nickel-cobalt-manganese-rich leaching solution and a second leaching residue.

[0008] In an optional implementation, the conditions for the first-stage leaching satisfy at least one of the following requirements: (1) The temperature is 70-90℃; (2) The time is 2-3 hours; (3) The liquid-to-solid ratio is 5-15 ml / g.

[0009] In an optional embodiment, the eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor, wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(2-4).

[0010] In an optional embodiment, the hydrogen bond acceptor is selected from quaternary ammonium salts, preferably halogenated choline, betaine hydrochloride, or tetramethylammonium chloride; most preferably halogenated choline. And / or, the hydrogen bond donor is selected from polyols, preferably C2-C5 polyols; more preferably ethylene glycol and glycerol; most preferably ethylene glycol; And / or, the molar ratio of the halogenated choline to the ethylene glycol is 1:(2-4).

[0011] In an optional embodiment, the selective complexing agent is an organic acid, preferably at least one of oxalic acid, citric acid, and tartaric acid; And / or, the molar ratio of the eutectic solvent to the selective complexing agent is 1:(0.1-0.4). Preferably, the molar ratio of the hydrogen bond acceptor, the hydrogen bond donor, and the selective complexing agent is 1:(2-3):(0.1-0.4).

[0012] In an optional embodiment, the oxidant is selected from peroxides, preferably at least one of ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide; And / or, the amount of the oxidant is 5-20% of the mass of the positive electrode powder.

[0013] In an optional implementation, the conditions for the second-stage leaching satisfy at least one of the following requirements: (1) The temperature is 60-80℃; (2) The time is 2-3 hours; (3) The liquid-to-solid ratio is 5-15 ml / g.

[0014] In an optional embodiment, the step of forming the cathode powder includes: disassembling, crushing and sieving, and calcining the cathode material of retired lithium-ion batteries; And / or, the roasting conditions include: a temperature of 500-800℃ and a time of 2-3 hours.

[0015] In an optional embodiment, the retired lithium-ion battery cathode material is selected from ternary lithium-ion battery cathode materials, lithium cobalt oxide cathode materials, or lithium manganese oxide cathode materials. Preferably, the ternary lithium-ion battery cathode material includes NCM-type ternary lithium-ion battery cathode material and NCA-type ternary lithium-ion battery cathode material.

[0016] In an optional embodiment, the method further includes: recovering lithium from the lithium-rich leachate and recovering nickel, cobalt, and manganese from the nickel-cobalt-manganese-rich leachate.

[0017] The present invention has the following beneficial effects: (1) The recycling method provided in the embodiments of the present invention does not require the use of strong inorganic acids, and the whole process is green and environmentally friendly. Specifically, strong inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid are not added during the entire leaching process. The weak acidity of the leaching system provided in the embodiments of the present invention comes from the inherent properties of the eutectic solvent and the selective complexing agent, thus avoiding the generation of acid mist and the problem of waste acid treatment.

[0018] (2) The recycling method provided in this embodiment of the invention exhibits significant selective leaching effects. The two-step leaching control strategy provided in this embodiment of the invention achieves highly selective stepwise leaching of lithium with nickel, cobalt, and manganese. In the first stage, the leaching rate of lithium can reach over 95%, while the leaching rates of nickel, cobalt, and manganese are controlled below 5%; in the second stage, the leaching rates of nickel, cobalt, and manganese can reach over 90%. This "lithium-first, then heavy metal" stepwise leaching strategy significantly reduces the difficulty of subsequent metal separation and purification, simplifying the process flow.

[0019] (3) The recycling method provided in this embodiment of the invention has mild conditions and low energy consumption. The leaching temperature in this embodiment of the invention is controlled within the range of 80°C, eliminating the need for high-temperature and high-pressure equipment, and the operation is safe and simple. The leaching time is also relatively short, which helps to improve processing efficiency.

[0020] (4) The recycling method provided in this embodiment of the invention has a wide range of applications. Specifically, the method is applicable to various types of retired lithium-ion battery cathode materials (ternary, lithium cobalt oxide, and lithium manganese oxide), and has good versatility.

[0021] (5) The solvent in the recovery method provided in this embodiment of the invention can be recycled. Specifically, the eutectic solvent can be recycled after simple treatment, which helps to reduce production costs and improve economic efficiency. Attached Figure Description

[0022] 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.

[0023] Figure 1 X-ray diffraction pattern of the first leaching residue provided in Embodiment 1 of the present invention; Figure 2 X-ray diffraction pattern of the second leaching residue provided in Embodiment 1 of the present invention; Figure 3 A graph showing the leaching rate results of the second stage leaching provided in an embodiment of the present invention; Figure 4 The result graph of the leaching rate of the first stage leaching provided in the embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] In a first aspect, the present invention provides a method for recycling cathode materials from retired lithium-ion batteries, comprising: S1, Preprocessing; Retired lithium-ion battery cathode materials are disassembled, crushed, and sieved, then calcined to remove binders and conductive agents, yielding pure cathode powder. The calcination conditions include a temperature of 500-800℃ and a time of 2-3 hours.

[0026] Specifically, the calcination temperature is any value between 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, or 500-800℃. The calcination time is any value between 2 hours, 2.5 hours, 3 hours, or 2-3 hours. The retired lithium-ion battery cathode material can be a ternary lithium-ion battery cathode material (NCM or NCA type), lithium cobalt oxide (LiCoO2) cathode material, or lithium manganese oxide (LiMn2O4) cathode material. The recycling method provided in this invention has good applicability to different types of cathode materials.

[0027] S2, First stage leaching; The aforementioned cathode powder is mixed with a eutectic solvent and a selective complexing agent to form a mixture. The eutectic solvent comprises hydrogen bond acceptors and hydrogen bond donors. The hydrogen bond acceptors are selected from quaternary ammonium salts, preferably choline halides, betaine hydrochloride, or tetramethylammonium chloride; most preferably choline halides (e.g., including but not limited to choline chloride). The hydrogen bond donors are selected from polyols, preferably C2-C5 polyols; more preferably ethylene glycol and glycerol; most preferably ethylene glycol. For example, the eutectic solvent may consist of choline halides and the aforementioned ethylene glycol. This combination has the advantages of low viscosity, low cost, and moderate solubility for metal oxides, facilitating selective leaching.

[0028] Further, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(2-4). For example, it can be any value between 1:2, 1:3, 1:4, or 1:(2-4). For example, the molar ratio of halogenated choline to the ethylene glycol is 1:(2-4).

[0029] Furthermore, the selective complexing agent is an organic acid, preferably at least one of oxalic acid, citric acid, and tartaric acid, with citric acid being the most preferred. Citric acid, as a complexing agent, can synergistically interact with the eutectic solvent, promoting the extraction of lithium ions from the cathode material lattice and their stable dissolution in the eutectic solvent. Simultaneously, the weakly acidic environment of citric acid facilitates lithium leaching but has a weak dissolution effect on nickel, cobalt, and manganese. In addition, citric acid can form a ternary DESs system with the original components of the eutectic solvent, further regulating the solvent's solubility selectivity.

[0030] The molar ratio of the eutectic solvent to the selective complexing agent is 1:(0.1-0.4). Specifically, the molar ratio of the hydrogen bond acceptor, the hydrogen bond donor, and the selective complexing agent is 1:(2-3):(0.1-0.4), for example, any value between 1:2:0.1, 1:2:0.2, 1:2:0.3, 1:2:0.4, 1:3:0.3, 1:3:0.4, or 1:(2-3):(0.1-0.4). Using the above ratio ensures the effectiveness of selective leaching.

[0031] Furthermore, the liquid-to-solid ratio of the mixture is 5-15 ml / g, for example, 5 ml / g, 6 ml / g, 7 ml / g, 8 ml / g, 9 ml / g, 10 ml / g, 11 ml / g, 12 ml / g, 13 ml / g, 14 ml / g, 15 ml / g or any value between 5-15 ml / g.

[0032] Furthermore, the first stage of leaching is carried out by heating and stirring at 70-90℃ for 2-3 hours. After the first stage of leaching, the first solid-liquid separation is performed to form a lithium-rich leachate and a first leaching residue. In this stage, the leaching rate of lithium is greater than 95%, while the leaching rates of nickel, cobalt, and manganese are all less than 5%, achieving highly selective separation of lithium from nickel, cobalt, and manganese.

[0033] S3, Second Stage Leaching; The first leaching residue and an oxidant are mixed, wherein the amount of oxidant is 5-20% of the mass of the cathode powder, for example, any value between 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 18%, 20%, or 5-20%. The oxidant is selected from peroxides, preferably at least one of ammonium persulfate ((NH4)2S2O8), sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and hydrogen peroxide (H2O2). Peroxides such as ammonium persulfate decompose in solution to produce SO4. - Free radicals oxidize nickel, cobalt, and manganese from +2 to +3 or +4 valence, destroying the layered structure of the cathode material and forming soluble sulfate complexes, thus promoting the migration of nickel, cobalt, and manganese from the solid phase to the liquid phase.

[0034] Furthermore, the liquid-to-solid ratio of the second-stage leaching is 5-15 ml / g, for example, 5 ml / g, 6 ml / g, 7 ml / g, 8 ml / g, 9 ml / g, 10 ml / g, 11 ml / g, 12 ml / g, 13 ml / g, 14 ml / g, 15 ml / g or any value between 5-15 ml / g.

[0035] After mixing, the mixture is heated and stirred at 60-80℃ for 2-3 hours for the second stage of leaching. After the second stage of leaching is completed, a second solid-liquid separation is performed to obtain a nickel-cobalt-manganese-rich leaching solution and a second leaching residue. The second leaching residue mainly consists of graphite and a small amount of insoluble impurities, which can be further recycled. In this stage, the leaching rates of nickel, cobalt, and manganese are all greater than 90%.

[0036] Then, lithium (lithium carbonate) is recovered from the lithium-rich leaching solution, and nickel, cobalt and manganese valuable metals are recovered from the nickel-cobalt-manganese-rich leaching solution (by precipitation and calcination to prepare nickel-cobalt-manganese precursors or directly to prepare cathode material regenerated raw materials).

[0037] This invention achieves stepwise selective leaching of lithium with nickel, cobalt, and manganese through the combination of a eutectic solvent, a selective complexing agent, and an oxidizing agent. The first step uses a synergistic system of a eutectic solvent and a selective complexing agent (such as citric acid) to utilize the preferential complexation and migration characteristics of lithium ions in DESs, enabling lithium to leach preferentially under mild conditions, while nickel, cobalt, and manganese are hardly leached. The second step involves adding an oxidizing agent such as persulfate, which oxidizes nickel, cobalt, and manganese from their lower valence states to higher valence states, dissolving them into the DESs, thus achieving stepwise leaching and separation of the two.

[0038] It should be noted that the term "acid-free" in this invention means that no traditional inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid are added as leaching agents during the entire leaching and recycling process of the cathode material. The acidity of the leaching system comes only from the weakly acidic environment generated by the inherent physicochemical properties of the eutectic solvent and the selective complexing agent, rather than from added strong acids or organic acids.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] Example 1 This invention provides a method for recycling cathode materials from retired lithium-ion batteries, comprising: S1, Preprocessing; After fully discharging retired ternary lithium-ion batteries (model 18650), the positive electrode sheets were manually disassembled. The positive electrode sheets were cut into small pieces and crushed in a crusher to a particle size of less than 2 mm. The crushed material was placed in a tube furnace and heated to 600°C at a rate of 5°C / min, then calcined at this temperature for 3 hours to remove the polyvinylidene fluoride (PVDF) binder and acetylene black conductive agent from the positive electrode sheets. The resulting black positive electrode powder was ground and sieved (200 mesh) for later use.

[0041] According to inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, the composition of this batch of cathode powder is as follows: Li content is approximately 7.2 wt%, Ni content is approximately 20.3 wt%, Co content is approximately 8.6 wt%, and Mn content is approximately 10.5 wt%. The corresponding cathode material structure is LiNi0.5Co0.2Mn0.3O2, NCM523 type.

[0042] S2, First stage leaching; Preparation of the eutectic solvent: Choline chloride (ChCl) and ethylene glycol (EG) were mixed in a molar ratio of 1:2 and heated and stirred in an 80°C water bath until a homogeneous and transparent liquid phase was formed. After cooling, ChCl-EG DES was obtained. This ChCl-EG DES is a colorless and transparent liquid at room temperature (25°C), with moderate viscosity and good electrical conductivity.

[0043] Preparation of selective complexing agent: Citric acid (C6H8O7·2H2O) was used as the selective complexing agent, and the molar ratio of choline chloride (ChCl), ethylene glycol (EG) and citric acid was 1:2:0.2. The mixture was stirred at 60℃ for 30 min to obtain a DES mixed leaching system containing citric acid.

[0044] Take 10g of the positive electrode powder obtained in step 1 and mix it with the above-mentioned DES mixed leaching system containing citric acid at a liquid-to-solid ratio of 10:1 (mL / g), i.e., add 100mL of DES leaching system. Place the mixture in a three-necked flask and stir at 300rpm for 3 hours in an 80℃ constant temperature water bath. After the reaction is completed, perform solid-liquid separation by vacuum filtration to obtain lithium-rich leaching solution and first leaching residue.

[0045] S3, Second Stage Leaching; An aqueous solution of ammonium persulfate ((NH4)2S2O8) was prepared as the oxidant solution, with the amount of ammonium persulfate added being 10% of the mass of the cathode powder. The first leaching residue obtained in step 2 was added to the above ammonium persulfate solution at a liquid-to-solid ratio of 8:1 (mL / g). The mixture was placed in a three-necked flask and stirred at 300 rpm for 2 hours in a constant temperature water bath at 70°C. After the reaction was completed, solid-liquid separation was performed by vacuum filtration to obtain a nickel-cobalt-manganese-rich leaching solution and a second leaching residue.

[0046] S4, Organometallic Recycling; (1) Recovery of lithium carbonate from lithium-rich leachate: The lithium-rich leachate obtained from the first stage leaching was concentrated to 1 / 5 of its original volume by vacuum distillation in a rotary evaporator (temperature 70℃, vacuum degree -0.09MPa). After cooling, an equal volume of anhydrous ethanol was added, and lithium hydrogen citrate tetrahydrate (Li3C6H5O7·4H2O) precipitated. After separating the precipitate, the precipitate was dissolved in deionized water, and saturated sodium carbonate solution was added. The mixture was stirred at 90℃ for 2 hours, and the precipitate was filtered to obtain a white lithium carbonate precipitate. After washing with deionized water and drying at 105℃, the lithium carbonate product was obtained. ICP-OES analysis showed that the purity of lithium carbonate reached 98.5wt%, and the overall lithium recovery rate was 93.2%.

[0047] (2) Recovery of nickel, cobalt, and manganese from nickel-rich manganese leaching solution: Slowly add ammonia water to the nickel-rich manganese leaching solution formed in the second stage of leaching to adjust the pH of the solution to 10-11, so that Ni²⁺ + Co² + Mn² + The precipitate was converted into hydroxide. After centrifugation and washing, the precipitate was calcined in air at 500°C for 3 hours to obtain a Ni-Co-Mn mixed oxide (NiO-Co3O4-MnO2). This mixed oxide can be directly used as a precursor for the preparation of ternary cathode materials. ICP-OES analysis showed that the overall recoveries of Ni, Co, and Mn were 92.5%, 91.8%, and 90.3%, respectively.

[0048] analyze: ICP-OES analysis of the lithium-rich leaching solution from Example 1 yielded the following results: Li leaching rate reached 94.1%, Ni leaching rate 3.2%, Co leaching rate 2.8%, and Mn leaching rate 2.5%. The calculated lithium leaching selectivity (defined as Li leaching rate / Ni leaching rate) was as high as 80.7, significantly higher than that of the traditional acid leaching method. The first leaching residue was washed three times with deionized water and dried at 105°C before use.

[0049] X-ray diffraction (XRD) analysis was performed on the first leaching residue of Example 1. The results are shown in [reference needed]. Figure 1 ,according to Figure 1 The results show that, compared with the XRD pattern of the original cathode powder, the intensity of the (003) and (104) characteristic diffraction peaks of LiNi0.5Co0.2Mn0.3O2 in the first leaching residue decreased significantly, but the positions of each characteristic peak remained basically unchanged, indicating that lithium was preferentially "extracted" from the lattice, while the crystal framework structure of nickel, cobalt, and manganese remained basically intact. Scanning electron microscopy (SEM) results show that obvious layered peeling and porous structures appeared on the surface of the particles after leaching, which is a typical microscopic feature of lattice shrinkage after preferential extraction of lithium ions.

[0050] The nickel-cobalt-manganese leaching solution of Example 1 was analyzed by ICP-OES. The results are as follows: the leaching rate of Ni reached 94.2%, the leaching rate of Co reached 93.5%, and the leaching rate of Mn reached 91.8%. The Li remaining in the slag phase was further partially leached, resulting in a slight increase in the Li content in the leaching solution.

[0051] XRD analysis of the second leaching residue (mainly graphite and insoluble impurities) from Example 1 Figure 2 See Figure 2 The absence of obvious nickel, cobalt, and manganese characteristic diffraction peaks indicates that the vast majority of valuable metals have been transferred from the slag to the liquid phase.

[0052] Example 2 This invention provides a method for recycling cathode materials from retired lithium-ion batteries. This recycling method is basically the same as the recycling method provided in Example 1, with the only difference being some conditions, as follows: S1. Pretreatment: The cathode material used is lithium cobalt oxide (LiCoO2), derived from retired lithium-ion batteries. The calcination temperature is 550℃, and the calcination time is 2 hours. The resulting lithium cobalt oxide cathode powder contains approximately 7.4 wt% Li and approximately 60.5 wt% Co.

[0053] S2. Second stage leaching: The choline chloride-ethylene glycol-citric acid mixed system of Example 1 was used, with a liquid-to-solid ratio of 12:1, a leaching temperature of 75°C, and a leaching time of 2.5 h. ICP-OES analysis results showed that the Li leaching rate reached 94.4%, while the Co leaching rate was only 3.5%, and the selective leaching effect of lithium was also significant.

[0054] S3. Second stage leaching: Ammonium persulfate was used as the oxidant, with an amount of ammonium persulfate of 15% of the cathode powder mass. The liquid-to-solid ratio was 8:1, the leaching temperature was 65℃, and the leaching time was 1.5h. ICP-OES analysis results showed that the Co leaching rate reached 95.3%.

[0055] Example 3 This invention provides a method for recycling cathode materials from retired lithium-ion batteries. This recycling method is basically the same as the recycling method provided in Example 1, except that the eutectic solvent and selective complexing agent are different. Specifically, the molar ratio of choline chloride (ChCl), ethylene glycol (EG), and oxalic acid is 1:2:0.3. All other conditions are the same as in Example 1.

[0056] Examples 4-7 This invention provides a method for recycling cathode materials from retired lithium-ion batteries. This recycling method is basically the same as the recycling method provided in Example 1, except that the selected oxidant is different and its amount is a percentage of the cathode powder mass. Specifically: Example 4: 5% ammonium persulfate; Example 5: 10% potassium persulfate; Example 6: 10% sodium persulfate; Example 7: 10% hydrogen peroxide.

[0057] See the second-stage leaching results for Examples 1, 2, and 4-7. Figure 3 .

[0058] Comparative Examples 1-3 Comparative Examples 1-3 each provide a method for recycling cathode materials from retired lithium-ion batteries. These methods are essentially the same as those provided in Example 1, differing only in the selection of the eutectic solvent and the selective complexing agent. Specifically, Comparative Example 1: the molar ratio of ChCl-EG is 1:2; Comparative Example 2: the molar ratio of ChCl-EG is 1:4; and Comparative Example 3: the molar ratio of ChCl-oxalic acid is 1:1.

[0059] The leaching rates for the first stage of leaching in Examples 1, 2, and Comparative Examples 1-3 are shown in Table 1 below. Figure 4 .

[0060] Table 1 Comparison of Leaching Effects in the First Stage

[0061] According to Table 1 and Figure 4 It can be seen that (1) when using ChCl-EG binary, the leaching rate of Li is about 91%, the leaching rate of NiCoMn is 3.5-4.2%, the selectivity is moderate, and the separation effect of lithium and nickel cobalt manganese is not ideal.

[0062] (2) When using ChCl-oxalic acid binary (molar ratio 1:1), the leaching rate of Li dropped to 89.7% and the leaching rate of Co was as high as 10.8%, indicating that DES with oxalic acid as the single hydrogen bond donor has too strong a dissolving ability for nickel, cobalt and manganese and poor selectivity. (3) When using the ChCl-EG-oxalic acid ternary system (molar ratio 1:2:0.3), the leaching rate of Li was significantly increased to 93.8%, while the leaching rate of Ni decreased to 4.2%, the leaching rate of Co decreased to 3.5%, and the leaching rate of Mn decreased to 3.2%, showing good selectivity.

[0063] (4) When using the ChCl-EG-citric acid ternary system (molar ratio 1:2:0.2), the Li leaching rate was significantly increased to 94.1%, while the Ni leaching rate decreased to 3.2%, the Co leaching rate decreased to 2.8%, and the Mn leaching rate decreased to 2.5%, showing the best selectivity.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling cathode materials from retired lithium-ion batteries, characterized in that, include: The cathode powder after removing binders and conductive agents is mixed with a eutectic solvent for selectively leaching and dissolving lithium ions and a selective complexing agent for selectively leaching lithium ions to carry out the first stage of leaching to form a lithium-rich leachate and a first leaching residue. The first leaching residue and oxidant are mixed for a second-stage leaching process to form a nickel-cobalt-manganese-rich leaching solution and a second leaching residue.

2. The recycling method according to claim 1, characterized in that, The conditions for the first-stage leaching must meet at least one of the following requirements: (1) The temperature is 70-90℃; (2) The time is 2-3 hours; (3) The liquid-to-solid ratio is 5-15 ml / g.

3. The recycling method according to claim 1 or 2, characterized in that, The eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor, wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(2-4).

4. The recycling method according to claim 3, characterized in that, The hydrogen bond acceptor is selected from quaternary ammonium salts, preferably halogenated choline, betaine hydrochloride, or tetramethylammonium chloride; most preferably halogenated choline. And / or, the hydrogen bond donor is selected from polyols, preferably C2-C5 polyols; more preferably ethylene glycol and glycerol; most preferably ethylene glycol; And / or, the molar ratio of the halogenated choline to the ethylene glycol is 1:(2-4).

5. The recycling method according to claim 3, characterized in that, The selective complexing agent is an organic acid, preferably at least one of oxalic acid, citric acid and tartaric acid; And / or, the molar ratio of the eutectic solvent to the selective complexing agent is 1:(0.1-0.4). Preferably, the molar ratio of the hydrogen bond acceptor, the hydrogen bond donor, and the selective complexing agent is 1:(2-3):(0.1-0.4).

6. The recycling method according to claim 1, characterized in that, The oxidant is selected from peroxides, preferably at least one of ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide; And / or, the amount of the oxidant is 5-20% of the mass of the positive electrode powder.

7. The recycling method according to claim 1, characterized in that, The conditions for the second-stage leaching must meet at least one of the following requirements: (1) The temperature is 60-80℃; (2) The time is 2-3 hours; (3) The liquid-to-solid ratio is 5-15 ml / g.

8. The recycling method according to claim 1, characterized in that, The steps for forming the cathode powder include: dismantling, crushing and sieving, and calcining the cathode material from retired lithium-ion batteries; And / or, the roasting conditions include: a temperature of 500-800℃ and a time of 2-3 hours.

9. The recycling method according to claim 8, characterized in that, The cathode material of the retired lithium-ion battery is selected from ternary lithium-ion battery cathode materials, lithium cobalt oxide cathode materials, or lithium manganese oxide cathode materials. Preferably, the ternary lithium-ion battery cathode material includes NCM-type ternary lithium-ion battery cathode material and NCA-type ternary lithium-ion battery cathode material.

10. The recycling method according to claim 1, characterized in that, Also includes: Lithium is recovered from the lithium-rich leachate, and nickel, cobalt, and manganese are recovered from the nickel-cobalt-manganese-rich leachate.

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