A method for selectively recovering lithium from waste ternary lithium batteries based on a low-consolute solvent system of reversible redox ligands

Abstract

The application belongs to the technical field of resource recycling of waste lithium ion batteries, and particularly relates to a low eutectic solvent based on reversible oxidation-reduction ligands and a method for selectively recovering lithium in waste ternary lithium batteries. The functionalized low eutectic solvent is made of a hydrogen bond acceptor, a hydrogen bond donor and water, wherein the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is an organic compound containing a "quinone-hydroquinone" reversible oxidation-reduction couple. The application uses the significant difference in the lithium coordination ability of the "quinone-hydroquinone" ligand oxidation-reduction state to design a "switching type" intelligent solvent in principle. The lithium is selectively "captured" in the reduced state, and the lithium is quickly "released" in the oxidized state, which provides a new way to achieve extremely high lithium / transition metal separation selectivity.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology for waste lithium-ion batteries, specifically relating to a eutectic solvent system based on reversible redox ligands and its method for selectively recovering lithium from waste ternary lithium batteries. Background Technology

[0002] With the rapid development of the electric vehicle industry, a large number of lithium-ion batteries are about to reach the end of their service life.

[0003] Direct recycling of spent lithium-ion batteries (SLIBs) is of great significance for developing a circular economy and promoting green ecology. Lithium nickel cobalt manganese oxide (NCM) ternary cathode materials contain a variety of valuable metals such as nickel, cobalt, manganese and lithium, and their efficient recycling has important resource and environmental significance.

[0004] The recycling of waste lithium-ion battery materials is mainly divided into two categories: pyrometallurgical and hydrometallurgical methods. Among them: Pyrometallurgy is a method that directly extracts metals or metal oxides from electrodes using high-temperature treatment. The process is simple, but the purity of the recycled materials is low, and the high-temperature treatment time is long and energy consumption is high. The electrolyte, binder and other organic matter in waste batteries will produce harmful gases due to high-temperature reactions, requiring the installation of supporting facilities for secondary waste gas treatment.

[0005] Hydrometallurgy involves first disassembling the battery casing, crushing and sieving it to obtain electrode materials. Valuable metals in these materials are leached in acid or biological solutions, followed by precipitation or extraction to obtain the corresponding salts or oxides of each metal. Hydrometallurgy is currently the mainstream recycling technology, typically using inorganic acids (such as sulfuric acid) and reducing agents (such as hydrogen peroxide) to synergistically leach all metals, followed by complex solvent extraction and chemical precipitation steps for separation. This process is lengthy, consumes large amounts of reagents, generates significant amounts of saline wastewater, and imposes a heavy environmental burden. Deep eutectic solvents (DES), also known as deep eutectic solvents or deep eutectic solvents, are a class of low-melting-point solvent systems composed of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) in a specific molar ratio.

[0006] Eutectic solvents typically consist of two main components: hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). Hydrogen bond donors are generally selected from one or more of choline chloride, methyltriphenylphosphine bromide, benzyltriphenylhydrobromide, choline bromide, and betaine; hydrogen bond acceptors are generally selected from urea, ethylene glycol, glycerol, amino acids, acetamide, and lactic acid. The two form a stable network structure through strong intermolecular hydrogen bonds. This strong interaction disrupts the original crystal structure of the pure substance, thus significantly lowering the melting point of the system and keeping it liquid at room temperature.

[0007] Literature reports that using the ChCl:EG system, composed of choline chloride and ethylene glycol, as a leaching medium can not only dissolve cathode materials such as LiCoO2 and NMC, but may also promote the leaching of Co³⁺ through the oxidation of ethylene glycol. + High-valence metals are reduced to more soluble low-valence ions. Therefore, DES acts as both a leaching agent and a reducing agent in this process. Through this method, key metals such as Li, Co, Ni, and Mn in the positive electrode active material can enter the liquid phase and be further recovered by precipitation or electrodeposition. At the same time, components such as aluminum foil, PVDF binder, and conductive carbon can also be separated.

[0008] CN112194201 A (application number 202011003908.X) discloses a method for recycling valuable metals from waste lithium-ion batteries and regenerating ternary cathode materials. Example 4 uses a choline chloride-urea eutectic solvent to leach the lithium-ion battery cathode material, but this system has poor selectivity for metals; nickel, cobalt, and manganese are leached simultaneously with lithium. The fundamental reason is that, from a crystal structure perspective, Li... + These ions are tightly coupled with transition metal ions in the layered oxide lattice, and conventional leaching processes simultaneously disrupt their coordination environment. From a solution chemistry perspective, these ions have similar radii and charge densities, making them readily compatible with oxygen-containing donors commonly found in DES (such as...). The coordination of OH and C=O ions in static DES systems makes it difficult to achieve ion recognition and sieving at the source. Even if all metal ions enter the liquid phase, subsequent separation still requires multiple steps such as stepwise precipitation and solvent extraction, which is inefficient and generates secondary pollution. Therefore, it is necessary to develop a method that allows for active control of metal binding capacity and enables "intelligent recognition". The integrated solvent system of "trigger release" is key to simplifying the process and improving selective recovery efficiency. Subsequent studies have introduced functional hydrogen bond donors such as oxalic acid and citric acid to improve the leaching efficiency or selectivity of lithium. Related literature (Journal of Hazardous Materials, 2022, 424: 127555) reports that the choline chloride-oxalic acid-water system has a certain selectivity for lithium, with a lithium leaching rate exceeding 90%. However, the leaching rates for cobalt, nickel, and manganese also reach 15-30%, indicating limited separation efficiency. Furthermore, after leaching, lithium needs to be precipitated from the lithium-rich solution through evaporation concentration and the addition of sodium carbonate, making the process still not simple enough.

[0009] CN116179900A discloses a method using choline chloride. Organic acid / polyol-based natural eutectic solvents (NADES / DES) are used to heat-leach spent lithium-ion battery cathode materials to obtain Li-containing compounds. +Ni² + Co² + Mn² + The leachate is then subjected to multiple subsequent steps such as precipitation, organic solvent extraction, or ion exchange to achieve the separation and recovery of valuable metals (see steps (1)–(3) and the effects section of its instruction manual). Although this type of DES route belongs to the category of green solvents, its selectivity for Li and transition metals still depends on "co-leaching first, followed by multi-step splitting", which requires the introduction of additional precipitants / extractants and generates associated waste liquid load, and lacks the ability to target Li. + Source-selective capture-controlled release mechanism.

[0010] KR102953144B1 (application number KR1020240182994) discloses a method for extracting valuable metals from waste batteries, comprising: mixing a preparation material containing one or more valuable metals selected from cobalt (Co), nickel (Ni), manganese (Mn) and lithium (Li) with a mixture containing organic acid and water in a slurry state at a temperature of 5°C-50°C; after the mixing step, removing organic matter by heat-treating the prepared mixture at a temperature above 350°C and below 450°C; and after the organic matter removal step, leaching the valuable metals by mixing with a solvent containing water; wherein, in the mixing step, the mixture further comprises a eutectic solvent containing hydrogen acceptors and hydrogen donors, the weight of the mixture is 10 to 40 times the weight of the preparation material, and the viscosity of the preparation material and the mixture is 1 poise to 5 poise. Hydrogen acceptors are selected from the following group: choline chloride, betaine or its salts, glycine betaine, carnitine or its salts, proline, trimethylglycine, trimethylammonium chloride, dimethylglycine, and piperazine. Hydrogen donors are selected from ethylene glycol, propylene glycol, butylene glycol, glycerol, sorbitol, mannitol, methylamine, ethylamine, lauroyl glycine, urea, thiourea, squalene, pyrrolidone, sodium gluconate, hydroquinone, and resorcinol. Hydroquinone is also known as hydroquinone, 1,4-benzene, or resorcinol.

[0011] The common problem with existing technologies is that the metal binding capacity of the solvent is static and fixed, the leaching selectivity is limited, and the recovery (precipitation) of metals heavily depends on the subsequent addition of chemical reagents or changes in physical conditions (such as cooling), failing to achieve intelligent and efficient linkage between the "selective leaching" and "directional release" steps.

[0012] Therefore, it is crucial to develop a solvent system with actively adjustable metal bonding capabilities that can achieve integrated "intelligent identification-trigger release" to simplify processes, improve efficiency, and enhance economy. Summary of the Invention

[0013] The primary objective of this invention is to provide a eutectic solvent whose metal coordination ability can be reversibly switched through simple and mild redox stimulation, thereby enabling "intelligent" identification and release of lithium ions. The secondary objective is to provide a method for short-process, highly selective recovery of lithium from spent ternary lithium battery cathode materials using this solvent, while also achieving solvent recycling. This method aims to overcome the shortcomings of existing DES technology, such as insufficient selectivity, lengthy processes, and non-recyclable solvents.

[0014] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a eutectic solvent based on a reversible redox ligand, the raw materials of which contain a hydrogen bond acceptor, a hydrogen bond donor and water, wherein the hydrogen bond acceptor is choline chloride and the hydrogen bond donor is an organic compound containing a reversible redox couple of quinone-hydroquinone.

[0015] Among the above-mentioned functionalized eutectic solvents: The hydrogen bond donor is selected from at least one of anthraquinone derivatives and naphthoquinone derivatives, preferably 2,6-dihydroxyanthraquinone or 1,4-dihydroxyanthraquinone; The molar ratio of choline chloride to hydrogen bond donor is 1:1 to 1:3; The water mass fraction is 5% to 30%, based on the total mass of choline chloride, hydrogen bond donor, and water.

[0016] In the functionalized eutectic solvent described in this invention, the hydrogen bond donor is 2,6 Dihydroxyanthraquinone or 1,4 Dihydroxyanthraquinone, whose molecule simultaneously provides (a) a strong hydrogen bond donor group (phenol) OH) and choline chloride Cl - A DES network is formed, along with (b) a reversible anthraquinone / hydroanthraquinone (AQ / H2AQ) redox couple. In the reduced state (H2AQ), the ortho-diphenol oxygen configuration forms suitable for Li + The chelating / multidentate oxygen donor sites for Li released from the cathode lattice + Significantly Soluble Stabilizing effect, and for Ni² + / Co² + / Mn (mainly Mn) 4+ The dissolution and transfer of Li is inhibited, thereby achieving selective leaching of Li; in the oxidized state (AQ), the chelation site is converted into a carbonyl group, and Li... + Coordination effect is sharply reduced, Li +It is released into the solution and can be precipitated in situ by CO2 / carbonate to Li2CO3. The molar ratio of choline chloride to hydrogen bond donor is 1:1 to 1:3; based on the total mass of choline chloride and hydrogen bond donor, the mass fraction of water is 5% to 30% to adjust the viscosity, promote interfacial mass transfer and provide the necessary proton medium, but without destroying the basic DES network structure of the system.

[0017] The second objective of this invention is to provide a method for preparing a eutectic solvent, comprising the following steps: in an inert atmosphere, choline chloride, a hydrogen bond donor, and water are weighed in proportion and stirred at 60-90°C until a homogeneous, transparent, deep red liquid is formed, thereby obtaining a reduced active solvent.

[0018] The inert gas is nitrogen, argon, or a nitrogen-hydrogen mixture.

[0019] The third objective of this invention is to provide a method for extracting lithium from the cathode material of spent lithium batteries, comprising the following steps: S1. Selective leaching of lithium: Waste NCM cathode material powder is mixed with the eutectic solvent and stirred for 1-6 hours at 70-120°C under an inert atmosphere. S2. Solid-liquid separation: After the reaction is completed, filter or centrifuge while hot to achieve liquid-solid separation and obtain a leaching solution A rich in lithium ions and a leaching residue B rich in valuable metals such as nickel, cobalt, and manganese. S3. Oxidation triggering and lithium carbonate crystallization: The leachate A is transferred to the crystallization reactor, and under stirring, a mixture of oxidizing gas and carbon dioxide gas is introduced into it for oxidation treatment; S4. Product separation: The solid and liquid in step S3 are separated to obtain lithium carbonate solid. After washing and drying, it becomes the product. The mother liquor after separation is mainly a eutectic solvent containing oxidized ligands. The mother liquor is subjected to electrochemical reduction treatment to reduce and regenerate the oxidized organic ligands in the mother liquor into the reduced state. The regenerated solvent is returned to step S1 or S2 for recycling.

[0020] In the above methods: Step S1: The ratio of waste NCM cathode material powder to eutectic solvent is 10-30 mL / g; The waste NCM positive electrode is either a waste NCM811 positive electrode or a waste NCM523 positive electrode.

[0021] In step S4: The oxidizing gas is air, oxygen, or ozone; In a mixture of oxidizing gas and carbon dioxide gas, the volume ratio of air (or oxygen) to carbon dioxide is (1:1) to (10:1).

[0022] The principles behind the above steps: The principle of step S1 is that, under the action of the reduced ligand, the solvent preferentially and selectively binds to lithium in the cathode material, leaching it into the liquid phase, while the leaching of transition metals such as nickel, cobalt, and manganese is effectively suppressed.

[0023] In step S2: Leachate residue B can be used as a high-quality raw material to recover nickel, cobalt and manganese through conventional acid leaching-extraction process.

[0024] In step S3, the introduced air / oxygen oxidizes the reduced ligand (hydroquinone) in the solvent to its oxidized state (quinone), causing a sharp decrease in its coordination ability with lithium ions, thereby releasing lithium ions into the solution. Simultaneously, the introduced carbon dioxide reacts with water to generate carbonate ions, which combine with the released lithium ions to precipitate lithium carbonate (Li₂CO₃) crystals. This step innovatively couples the "oxidation and release" of ligands with the "carbonation and precipitation" of lithium within a single operating unit, efficiently driving lithium recovery.

[0025] Furthermore, the mother liquor after separation in step S4 mainly consists of DES containing oxidized ligands. This mother liquor can be used as an electrolyte in an electrochemical cell. Using an inert electrode (such as a platinum sheet or glassy carbon electrode) as the working electrode, constant potential electrolysis is performed at an appropriate cathode potential (e.g., -0.5V to -1.2V, preferably -0.8V vs. Ag / AgCl). The oxidized ligands (quinones) are reduced and regenerated at the cathode into an active reduced state (hydroquinone). Cyclic voltammetry can monitor the degree of regeneration. The regenerated solvent regains its selective lithium complexing ability and can be recycled back to step S1 or S2, forming a closed-loop process.

[0026] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High selectivity and innovative principle: Utilizing the significant difference in lithium coordination ability between the redox and reduced states of the quinone-hydroquinone ligand, a "switch-type" smart solvent was designed in principle. It selectively "captures" lithium in the reduced state and rapidly "releases" lithium in the oxidized state, providing a new approach to achieving extremely high lithium / transition metal separation selectivity.

[0027] 2. Extremely simplified process and highly efficient coupling: The process creatively combines the "oxidation-triggered release" and "carbonation precipitation" steps into one. By introducing a mixed gas, ligand oxidation and lithium precipitation are completed simultaneously in a single operating unit, eliminating the complex steps of evaporation and concentration, addition of precipitants, and pH adjustment required in traditional processes, thus significantly shortening the process.

[0028] 3. Solvent closed-loop recycling, green economy: The solvent can be efficiently regenerated through a mild electrochemical reduction method. The regenerated solvent has stable performance and can be recycled multiple times, which significantly reduces solvent consumption and process cost, meeting the requirements of green chemistry and process economy.

[0029] 4. Mild conditions and high product purity: The entire process is carried out at normal pressure and medium to low temperatures, without the need for strong acids, strong alkalis, or organic extractants, making it environmentally friendly. Based on highly selective leaching at the source, the resulting lithium carbonate product has high purity and easily meets battery-grade standards.

[0030] 5. Good compatibility with other processes: This method focuses on the highly selective recovery of lithium, and the resulting transition metal-rich slag has a high grade and few impurities, which can be easily treated by existing mature hydrometallurgical processes to achieve full element recovery. Attached Figure Description

[0031] Figure 1 Methods for recovering lithium from lithium battery cathode materials; Figure 2 Schematic diagram of the reversible redox transition of 2,6-dihydroxyanthraquinone (quinone-hydroquinone) and its coordination with lithium ions. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] The waste NCM523 cathode material used in this embodiment was obtained from commercial 18650 batteries through discharge, disassembly, stripping, and heat treatment, and its main component is LiNi. 0.5 Co 0.2 Mn 0.3 O2.

[0034] Example 1: Functionalized Eutectic Solvent 1. Raw materials: 14.04 g (0.1 mol) of choline chloride, 4.80 g (0.02 mol) of 2,6-dihydroxyanthraquinone, and 3.78 g (20% by mass) of deionized water.

[0035] 2. Preparation method: In an argon glove box, accurately weigh 14.04 g (0.1 mol) of choline chloride and 4.80 g (0.02 mol) of 2,6-dihydroxyanthraquinone, and add 3.78 g (20% by mass) of deionized water. Place the mixture in a sealed bottle and stir in an oil bath at 80°C for 3 hours to obtain a deep red, homogeneous, and transparent eutectic solvent.

[0036] Example 2: Functionalized Eutectic Solvent 1. Raw materials: 14.04 g (0.1 mol) of choline chloride, 4.80 g (0.02 mol) of 1,4-dihydroxyanthraquinone, and 3.78 g (20% by mass) of deionized water.

[0037] 2. Preparation method: Accurately weigh choline chloride and 1,4-dihydroxyanthraquinone in an argon glove box, and add deionized water. Place the mixture in a sealed bottle and stir in an oil bath at 80°C for 3 hours to obtain a deep red, homogeneous, and transparent eutectic solvent. Example 3: Treatment of waste NCM523 cathode powder S1. Preparation of reduced solvent: Functionalized eutectic solvent prepared according to the method of Example 1.

[0038] S2. Selective leaching: Weigh 50.0 g of the above-mentioned functionalized eutectic solvent and 5.00 g of waste NCM523 cathode powder, and add them to a 100 mL pressure-resistant reaction flask equipped with a stirrer and argon protection. Stir and react at 90°C for 3 hours.

[0039] S3. Solid-liquid separation: After the reaction is complete, filter while hot under argon protection. Wash the filter residue with a small amount of anhydrous ethanol, dry it, and weigh it. The filtrate is a dark red extract.

[0040] Comparative Example 1: Traditional choline chloride-urea DES The method is the same as in Example 3, except that the solvent is replaced with DES composed of choline chloride and urea in a 1:2 molar ratio (with 20wt% water).

[0041] Comparative Example 2: Choline chloride-oxalate DES, without redox ligands The method is the same as in Example 3, except that DES composed of choline chloride and oxalic acid in a 1:1 molar ratio (with 20 wt% water) is used for leaching.

[0042] Comparative Example 3: Only air is allowed, but CO2 is not. In step S3 of Example 3, only pure air (100 mL / min) was introduced into the leachate, without introducing carbon dioxide. After 2 hours of aeration, the solution color changed as in Example 1, but only a trace amount of precipitate was formed.

[0043] After filtration, the amount of precipitate was less than 0.1 g, and X-ray diffraction results showed that it was mainly lithium hydroxide. This indicates that without a sufficient source of carbonate, lithium is difficult to effectively precipitate and recover as lithium carbonate, verifying the necessity of introducing CO2 to achieve "oxidation-precipitation" coupling.

[0044] Comparative Example 4: DES with hydroquinone (hydroquinone) as hydrogen bond donor Solvent preparation: In an argon glove box, accurately weigh 14.04 g (0.1 mol) of choline chloride and 2.20 g (0.02 mol) of hydroquinone (hydroquinone, the same molar amount as anthraquinone in Example 1), and add 3.24 g of deionized water (20% by mass, based on the total mass of choline chloride and hydroquinone). Place the mixture in a sealed bottle and stir in an oil bath at 80°C for 3 hours to obtain a homogeneous solution.

[0045] Selective leaching and separation: Weigh 50.0 g of the above-mentioned DES solvent and 5.00 g of waste NCM523 cathode powder, and carry out the leaching reaction under the same conditions as in Example 3 (90°C, argon protection, 3 hours). After the reaction, filter while hot to obtain leachate and filter residue.

[0046] Subsequent treatment: The leachate was subjected to oxidation precipitation treatment by introducing a mixture of air and CO2 gas as described in step S4 of Example 3.

[0047] Experimental Example 1: Leaching rates and selective separation factors of various metals 1. Sample: The solvents provided in Examples 1 and 2 were used respectively, and the treatment was carried out according to the method in Example 3; Comparative Examples 1-4, the filtrate and filter residue obtained after the above treatment.

[0048] 2. Detection Method: Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used to analyze the metal content in the filtrate and filter residue. The leaching rate and selective separation factor of each metal were calculated. The leaching rate (η) of a certain metal was calculated according to the principle of mass conservation, as follows: ηM = [m(liquid, M) / (m{liquid, M) + m(residue, M))] × 100%; the selective separation factor was calculated as follows: β(Li / Ni) = [D(Li) / (1 - D(Li))] / [D(Ni) / (1 - D(Ni))] ≈ [η(Li) / (1 - η(Li))] / [η(Ni) / (1 - η(Ni))].

[0049] 3. The test results are shown in Table 1 below: Table 1: Comparison of metal leaching rate and selectivity between Example 1 and Comparative Examples 1 and 2

[0050] Table 1 shows the results: The leaching results of Comparative Example 1 were as follows: the lithium leaching rate was 88.5%, while the leaching rates of nickel, cobalt, and manganese were 45.2%, 38.7%, and 50.1%, respectively, and the lithium / nickel separation factor βLi / Ni was only 7.2.

[0051] The leaching results of Comparative Example 2 showed a lithium leaching rate of 91.3%, and leaching rates of nickel, cobalt, and manganese of 18.3%, 12.6%, and 22.4%, respectively, with a βLi / Ni ratio of approximately 22. These results are superior to those of Comparative Example 1.

[0052] The leaching results of the solvent provided in Example 1 are as follows: lithium leaching rate is 94.2%, nickel, cobalt and manganese leaching rates are 5.8%, 4.1% and 7.2% respectively, and the lithium / nickel separation factor βLi / Ni is 98.

[0053] Example 2 provides solvent leaching results: lithium leaching rate of 92.8%, nickel, cobalt and manganese leaching rates of 6.5%, 4.8% and 8.0% respectively, and βLi / Ni of approximately 78.

[0054] The results show that the functionalized eutectic solvent based on specific dihydroxyanthraquinone (2,6- or 1,4-position) provided by this invention achieves ultra-high selectivity separation at the source when recovering lithium from waste NCM materials.

[0055] The results in Table 1 clearly illustrate the following key issues: This invention successfully solves the fundamental problem of poor selectivity in lithium recovery in existing DES technology. By introducing a specific dihydroxyanthraquinone ligand with "redox-switchable" properties, a "smart" solvent was designed that can efficiently and selectively "capture" lithium in its reduced state, while leaching almost no nickel, cobalt, or manganese, thus achieving efficient separation at the source.

[0056] The superiority of this invention does not stem from the simple use of the "quinone-hydroquinone" concept, but rather from the precise design of the ligand molecular structure (selecting 2,6- or 1,4-dihydroxyanthraquinone). The dramatic improvement in performance compared to the structurally simple hydroquinone (separation factor increased from 12 to 98) strongly demonstrates the unexpected technical effects brought about by this specific molecular structure, which is the core embodiment of the invention's inventiveness.

[0057] This invention provides a practical solution for the industrial application of short-process, highly selective lithium recovery. The extremely high β(Li / Ni) value means that the leaching solution has extremely high purity, which can greatly simplify the subsequent lithium purification and precipitation steps, reduce costs and environmental burden, which is in stark contrast to the pain points of the existing technology pointed out in the background art, namely "lengthy process and complex separation".

[0058] Experiment Example 2: Solvent Cycling Experiment 1. Sample: Filtrate provided in Example 3 (eutectic solvent of Example 1).

[0059] 2. Detection method: S1. Oxidation Triggering and Lithium Carbonate Crystallization: Transfer the filtrate to a 250 mL three-necked flask and place it in a 25°C water bath, stirring at 300 rpm. A mixed gas of air and carbon dioxide in a 4:1 volume ratio is introduced into the liquid at a total flow rate of 100 mL / min. During the aeration process, the solution color gradually changes from dark red to light yellow. Aeration is stopped after 2 hours, and the solution is allowed to stand for 30 minutes.

[0060] S2. Product Separation: The precipitate was filtered, washed three times with deionized water, and dried under vacuum at 80°C for 12 hours to obtain 0.86 g of white lithium carbonate powder. Its purity was determined to be 99.5% by chemical titration.

[0061] S3. Solvent Regeneration: The filtrate provided in Example 3 was used as the electrolyte and injected into an H-type electrolytic cell. A platinum sheet (1 cm²) was used as the working and counter electrodes, and Ag / AgCl (3M KCl) was used as the reference electrode. Electrolysis reduction was performed for 2 hours under argon protection at a constant potential of -0.8 V (vs. Ag / AgCl). After electrolysis, the solution returned to a deep red color. Characterization by cyclic voltammetry confirmed successful ligand regeneration.

[0062] S4. Solvent cycling experiment: Use the regenerated solvent as a new round of leaching experiment (under the same conditions as S2-S3).

[0063] 3. Test Results: The test was repeated 5 times, and the key performance data are shown in Table 2 below. Table 2: Stability data of solvent recycling in Example 1

[0064] The results show that the solvent provided by this invention has good cycle stability.

[0065] The solvent effect in Example 2 is the same as in Example 1.

[0066] Experiment Example 3: Treatment of NCM materials with different proportions 1. The solvent of Example 1 and the process of Example 3 are used, the difference being the treatment of waste LiNi with a different metal ion ratio. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) positive electrode powder.

[0067] 2. Leaching rate detection method: Same as in Experiment 1.

[0068] 3. Leaching results: The lithium leaching rate was 93.5%, while the leaching rates for nickel, cobalt, and manganese were 7.2%, 5.5%, and 6.9%, respectively, and the βLi / Ni ratio was approximately 73.

[0069] The results show that this method is applicable to ternary materials with different nickel contents.

[0070] Industrial applicability The method described in this invention has a clear process route (e.g.) Figure 1 As shown in the diagram, the main equipment consists of a conventional heated and stirred reactor, a filtration device, a gas bubbling device, and an electrolytic cell, making it easy to scale up. Choline chloride is inexpensive and readily available, and 2,6-dihydroxyanthraquinone is a commercially available product. This method, through intelligent solvent design and process coupling, significantly simplifies the lithium recovery process and improves efficiency, while the recyclable solvent reduces operating costs. It is particularly suitable for the efficient and green recycling of spent ternary lithium batteries and has promising prospects for industrial application.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A eutectic solvent based on reversible redox ligands, characterized in that, Its raw materials include hydrogen bond acceptors, hydrogen bond donors and water, wherein the hydrogen bond acceptor is choline chloride and the hydrogen bond donor is an organic compound containing a reversible redox couple of "quinone-hydroquinone".

2. The functionalized eutectic solvent according to claim 1, characterized in that, The organic compound containing the "quinone-hydroquinone" reversible redox couple is selected from at least one of anthraquinone derivatives and naphthoquinone derivatives; preferably, the organic compound is 2,6-dihydroxyanthraquinone, 1,4-dihydroxyanthraquinone, or 5-hydroxy-1,4-naphthoquinone.

3. The eutectic solvent according to claim 1, characterized in that, The molar ratio of choline chloride to the hydrogen bond donor is 1:1 to 1:

3.

4. The eutectic solvent according to claim 1, characterized in that, The eutectic solvent contains 5% to 30% water by mass.

5. A method for preparing the eutectic solvent according to any one of claims 1-4, the method comprising the following steps: In an inert atmosphere, choline chloride, hydrogen bond donor and water are weighed in proportion and stirred at 60-90℃ until a homogeneous, transparent, dark red liquid is formed, which is the reduced active solvent.

6. The preparation method according to claim 5, characterized in that, The inert gas is nitrogen, argon, or a nitrogen-hydrogen mixture.

7. A method for recovering lithium from spent ternary lithium-ion battery cathode materials using the functionalized eutectic solvent according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Selective leaching of lithium: waste NCM cathode material powder is mixed with the eutectic solvent described in any one of claims 1-6, and stirred and reacted at 70-120°C under an inert atmosphere for 1-6 hours; S2. Solid-liquid separation: After the reaction is completed, filter or centrifuge while hot to achieve liquid-solid separation and obtain a lithium-ion-rich leachate A and a valence metal-rich leachate B. S3. Oxidation triggering and lithium carbonate crystallization: The leachate A is transferred to the crystallization reactor, and a mixture of oxidizing gas and carbon dioxide gas is introduced into it under stirring; S4. Product separation: The solid and liquid in step S3 are separated to obtain lithium carbonate solid. After washing and drying, it becomes the product. The mother liquor after separation is mainly a eutectic solvent containing oxidized ligands. The mother liquor is subjected to electrochemical reduction treatment to reduce and regenerate the oxidized organic ligands in the mother liquor into the reduced state. The regenerated solvent is returned to step S1 or S2 for recycling.

8. The method according to claim 7, characterized in that, In step S1, the ratio of waste NCM cathode material powder to eutectic solvent is 10-30 mL / g.

9. The method according to claim 7, characterized in that, The waste NCM positive electrode is either a waste NCM811 positive electrode or a waste NCM523 positive electrode.

10. The method according to claim 7, characterized in that, In step S4: The oxidizing gas is air, oxygen, or ozone; In a mixture of oxidizing gas and carbon dioxide gas, the volume ratio of air (or oxygen) to carbon dioxide is (1:1) to (10:1).

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