Polybasic eutectic solvent, preparation method thereof and method for selectively recovering positive electrode material of waste lithium cobalt oxide battery

Abstract

The application provides a kind of multi-component deep eutectic solvent and its preparation method, the method for selectively recovering waste cobalt lithium battery positive electrode material, the multi-component deep eutectic solvent includes at least two kinds of amide substances selected from chain amide, lactam and N-substituted amide and reducing organic carboxylic acid.The application can realize the selective leaching of lithium and the direct recovery of cobalt by one-step method, and has high leaching efficiency, mild leaching conditions, simple process, easy operation, green environmental protection, and high practical application value.

Description

Technical Field

[0001] This invention relates to the field of waste lithium-ion battery recycling technology, and in particular to a multi-element eutectic solvent and its preparation method, and a method for selectively recycling cathode materials from waste lithium cobalt oxide batteries. Background Technology

[0002] Rechargeable lithium-ion batteries (LIBs) meet the growing energy demand, but due to the short lifespan of lithium-ion batteries (only 3-10 years), a large amount of waste LIBs is expected to be generated in the future. The nickel, cobalt, and lithium resources in the cathode materials of these waste LIBs cause serious environmental pollution and harm human health; moreover, these resources are relatively scarce, expensive, and heavily reliant on imports. Therefore, to alleviate the current scarcity of mineral resources and prevent the severe environmental pollution caused by discarded LIBs, recycling waste LIBs has become a global hot topic.

[0003] Commercial technologies for recycling waste lithium-ion batteries (LIBs) primarily employ pyrometallurgy, hydrometallurgy, biometallurgy, and mechanical methods. Pyrometallurgy, the most commonly used industrial method, converts most lithium and aluminum into slag, generating large amounts of harmful gases, polluting the environment, and requiring high energy consumption (1400℃ or higher). Hydrometallurgical processes, using corrosive leaching agents such as hydrochloric acid, nitric acid, and sulfuric acid, indiscriminately leach metal ions, resulting in complex processes, high energy consumption, and the generation of large amounts of waste acid that pose a danger to the environment. While alkaline leaching offers high selectivity, it causes severe corrosion to equipment, and neutralizing the waste liquid is costly. "Green solvents," such as organic acids reported in the literature, are easily degradable and show some feasibility in addressing environmental safety issues; however, their leaching efficiency is limited, and they face their own set of challenges.

[0004] Deep eutectic solvents (DESs), as a green ionic liquid, can extract precious metals from LIB waste. They can act as both effective leaching agents and reducing agents, achieving metal extraction without the need for additional extractants. Using DESs to leach spent battery cathode materials offers significant environmental advantages; however, compared to inorganic acid-base leaching agents, DESs are relatively expensive, making it difficult to achieve high economic benefits in practical industrial applications. Therefore, to expand the large-scale application of DESs in industry, replace inorganic acid-base leaching agents, increase the number of leaching cycles, and shorten the process flow are crucial.

[0005] For eutectic solvent leaching of cathode materials, a common technique is choline chloride (ChCl)-based DESs. Patent application CN114644366A utilizes choline chloride-oxalate DESs, which, during the leaching process of the cathode material, removes Co from lithium cobalt oxide (LCO). 3+ The Cl in ChCl -Restored to Co 2+ Meanwhile, Co 2+ It will continue to react with Cl in ChCl - [CoCl4] is formed. 2- Complex ions, which will continuously consume Cl in ChCl - Furthermore, a precipitant needs to be introduced to precipitate the cobalt, making one-step recovery impossible, and the method for recovering Li is not specified. + The recycling and reuse of this material is very limited. Patent applications with publication numbers CN111074075A, CN111690813A, and CN113830842A also use choline chloride-organic acid DESs to leach LCO, achieving the separation and recovery of the cathode material, but they still face the challenge of introducing a third phase to precipitate Co. 2+ It requires cumbersome steps such as evaporation and concentration before it can be recycled.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] To address the poor cycle performance of ChCl-based DESs, this invention proposes an amide-based DES leaching cathode material. In the amide molecule, the nitrogen atom adopts an sp225° orientation. 2 Hybridization occurs when the p orbitals containing the lone pair electrons form p-π conjugation with the carbonyl group. This conjugation not only averages out the electron cloud density and bond length in the amide molecule but also hinders the rotation of the CN single bond. The C, N, and the four atoms bonded to C and N are all in the same plane. This structure promotes the stability of amide-based DES structures, preventing their consumption during LCO leaching. Furthermore, it provides a continuous reactive site for the leaching cathode active material of organic reducing carboxylic acids and is easily regenerated and recycled, enabling industrial applications.

[0008] One of the objectives of this invention is to provide a multi-element eutectic solvent that can achieve selective leaching and recovery of lithium and cobalt from lithium cobalt oxide, a cathode material in waste batteries, in a one-step process.

[0009] The second objective of this invention is to provide a method for preparing the aforementioned multi-element eutectic solvent.

[0010] The third objective of this invention is to provide a method for selectively recycling waste lithium cobalt oxide battery cathode materials, which uses the aforementioned multi-element eutectic solvent for leaching, and the multi-element eutectic solvent can be recycled during the leaching process.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] In a first aspect, the present invention provides a multi-element eutectic solvent, the multi-element eutectic solvent comprising:

[0013] At least two amides selected from chain amides, lactams, and N-substituted amides; and reducing organic carboxylic acids;

[0014] The amide is selected from at least one of formamide, acetamide, propionamide, n-butyramide, isobutyramide, n-valeramide, isovaleramide, neopentylamide, n-heptamide, n-octamide, dodecyl lactam, carbamide, and asparagine; preferably at least one of acetamide, propionamide, n-butyramide, isobutyramide, n-valeramide, and carbamide; more preferably at least one of acetamide and carbamide.

[0015] The lactam is selected from at least one of cyclopropionamide, butyrolactam, valproic acid, caprolactam, heptanolactam, octylolactam, dodecylolactam, and DL-aminocaprolactam; preferably at least one of butyrolactam, valproic acid, caprolactam, and dodecylolactam; more preferably at least one of butyrolactam and caprolactam.

[0016] The N-substituted amide is selected from at least one of N-methylformamide, N-methylacetamide, N-methylpropionamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N,N-diethylmethacrylamide, N-hydroxymethylmethacrylamide, and N-(methoxymethyl)methacrylamide; preferably at least one of N-methylacetamide, N,N-dimethylformamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, and N-isopropylmethacrylamide; more preferably at least one of N-methylacetamide and N,N-dimethylformamide.

[0017] The reducing organic carboxylic acid is selected from at least one of aliphatic carboxylic acids (such as formic acid, lactic acid, methanesulfonic acid, acetic acid, oxalic acid, propionic acid, malonic acid, maleic acid, tartaric acid, fumaric acid, adipic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, ricinoleic acid, citric acid, malic acid, etc.), alicyclic carboxylic acids (such as cyclopropionic acid, cyclobutaneacetic acid, cyclopentaneacetic acid, cyclohexaneacetic acid, etc.), and aromatic carboxylic acids (such as benzoic acid, p-toluenesulfonic acid, phthalic acid, terephthalic acid, cinnamic acid, etc.); aliphatic carboxylic acids are preferably at least one of formic acid, lactic acid, oxalic acid, maleic acid, and malic acid; alicyclic carboxylic acids are preferably at least one of cyclopropionic acid and cyclobutaneacetic acid; and aromatic carboxylic acids are preferably at least one of p-toluenesulfonic acid and cinnamic acid.

[0018] In one embodiment, in at least two amide substances, the molar ratio of chain amide: lactam: N-substituted amide is 1:(0-6):(0-10); and / or

[0019] The molar concentration of reducing organic carboxylic acids in multi-component eutectic solvents is 0.2-15 mol / L.

[0020] Preferably, the multi-component eutectic solvent comprises: a chain amide, a lactam, an N-substituted amide, and a reducing organic carboxylic acid; wherein the molar ratio of chain amide: lactam: N-substituted amide is 1:(1-6):(1-10), for example 1:1:5, 1:2:8, 1:2:6, 1:2:4, 1:3:5, 1:4:3, 1:5:2, etc., and the molar concentration of the reducing organic carboxylic acid in the multi-component eutectic solvent is 0.2-15 mol / L, for example 1, 2, 3, 5, 6, 8, 10, 12 mol / L. Particularly preferably, the chain amide is selected from one or two of acetamide and carbamate, the lactam is selected from one or two of butyrolactam and caprolactam, the N-substituted amide is selected from one or two of N-methylacetamide and N,N-dimethylformamide, and the reducing organic carboxylic acid is selected from one or more of lactic acid, malic acid, cyclopropionic acid, cyclobutaneacetic acid, cinnamic acid, malic acid, and maleic acid.

[0021] In one embodiment, the multi-component eutectic solvent according to the present invention is prepared by a method comprising the following steps: mixing at least two amide substances selected from chain amides, lactams and N-substituted amides, and heating at 50 to 100°C until clear and transparent to obtain an amide eutectic solvent; then mixing the amide eutectic solvent with a reducing organic carboxylic acid to form a transparent and homogeneous liquid at room temperature to obtain the multi-component eutectic solvent.

[0022] This invention provides a green, recyclable, eutectic solvent formed by amides and reducing organic carboxylic acids. This solvent is used in leaching experiments of lithium cobalt oxide (LCO) powder, the positive electrode active material for lithium-ion batteries, enabling selective leaching and recovery of lithium and cobalt in a one-step process. The leaching process consumes only the reducing organic carboxylic acid. The amide-based eutectic solvent, a stable DES, provides a reaction site for the efficient reduction leaching of the reducing organic carboxylic acid and is essentially not consumed, allowing for multiple leaching cycles. The reducing organic carboxylic acid provides active protons, disrupting oxygen acceptors in metal oxides, and lowers the valence state of high-valence metals, achieving the reduction leaching of Co. Being a liquid, it reduces the system viscosity, promoting continuous and efficient recycling.

[0023] Furthermore, compared to a single amide, a eutectic solvent using a mixture of two or more amides can reduce the melting point, freezing point, and viscosity of a single amide because the hydrogen bonding between different amide molecules is stronger than the hydrogen bonding within a single amide molecule. This makes it a novel and stable solvent for leaching cathode materials.

[0024] Secondly, the present invention provides a method for preparing the multi-component eutectic solvent, comprising the following steps: mixing at least two amide substances selected from chain amides, lactams and N-substituted amides, and heating at 50-100°C until clear and transparent to obtain an amide eutectic solvent; then mixing the amide eutectic solvent with a reducing organic carboxylic acid to form a transparent and homogeneous liquid at room temperature to obtain the multi-component eutectic solvent.

[0025] According to the present invention, the obtained amide-based eutectic solvent can be stored in an oven at 70°C for later use.

[0026] Thirdly, the present invention provides a method for selectively recycling waste lithium cobalt oxide battery cathode materials, including a leaching step: mixing the multi-element eutectic solvent and the waste lithium cobalt oxide battery cathode materials and heating for leaching, separating insoluble Co(HCOO)2·2H2O precipitate and Li-containing leachate.

[0027] In some embodiments, the leaching temperature is 50°C-150°C; and / or

[0028] The leaching time is 10 min to 300 min.

[0029] In some embodiments, the solid-liquid ratio of the waste lithium cobalt oxide battery cathode material and the multi-element eutectic solvent is 10 g / L to 100 g / L, preferably 10 g / L to 50 g / L.

[0030] In some embodiments, the method further includes a cyclic leaching step: adding new waste lithium cobalt oxide battery cathode material to the Li-containing leachate, repeating the leaching step three or more times (e.g., three, four, five, six, seven, eight, etc.), and each time adding an additional amount of reducing organic carboxylic acid to maintain a constant solid-liquid ratio.

[0031] In some embodiments, after leaching, ethanol and oxalic acid are added to the Li-containing leachate, wherein the volume ratio of ethanol to the multi-element eutectic solvent is 1:1-5, and the molar ratio of oxalic acid to lithium is 1-1.5:2, and lithium oxalate precipitate and leachate containing ethanol and oxalic acid are separated; the leachate containing ethanol and oxalic acid is heated to evaporate and remove ethanol and oxalic acid, and the leachate is recycled for the leaching step.

[0032] In one embodiment, such as Figure 1As shown, the process of leaching and recycling lithium cobalt oxide powder, the cathode material of waste batteries, using a multi-element eutectic solvent is as follows:

[0033] (1) The waste lithium cobalt oxide battery cathode material and the multi-element eutectic solvent are mixed at a solid-liquid ratio of 10 g / L to 50 g / L (e.g., 20, 30, 40 g / L) and heated and leached at 50℃-150℃ for 10 min-300 min to separate insoluble Co(HCOO)2·2H2O precipitate and Li-containing leachate;

[0034] (2) Add new waste lithium cobalt oxide battery cathode material to the Li-containing leachate, repeat step (1) three or more times, and each time add a certain amount of reducing organic carboxylic acid to maintain the original solid-liquid ratio of 10g / L to 50g / L (e.g., 20, 30, 40g / L).

[0035] (3) After leaching, ethanol and oxalic acid are added to the Li-containing leachate, wherein the volume ratio of ethanol to the multi-element eutectic solvent is 1:1-5, and the molar ratio of oxalic acid to lithium is 1-1.5:2. Lithium oxalate precipitate and leachate containing ethanol and oxalic acid are separated. The leachate containing ethanol and oxalic acid is heated to evaporate and remove ethanol and oxalic acid. The leachate is recycled for the leaching step.

[0036] The technical solution of the present invention has the following beneficial effects:

[0037] (1) The novel DESs of this invention is composed of amides and reducing organic carboxylic acids. It is a green and recyclable eutectic solvent. When used in the leaching experiment of lithium cobalt oxide (LCO) powder, the positive electrode active material of lithium-ion batteries, it can achieve selective leaching of lithium and direct recovery of cobalt in one step. Compared with a single amide, the eutectic solvent using a mixture of two or more amides has a greater hydrogen bonding force between different amide molecules than the hydrogen bonding force within a single amide molecule. Therefore, it can reduce the melting point, freezing point, and viscosity of the single amide, and thus can be used as a new type of stable solvent for leaching positive electrode materials.

[0038] (2) The advantages of the process route of the present invention are: (a) high leaching efficiency, one-step efficient separation of Li and Co, and reduced material and energy loss compared with ChCl-based DESs; (b) amide DES can be reused multiple times, that is, only reducing organic carboxylic acids are consumed in this leaching process. The performance of amide DES is stable, providing a reaction site for the efficient reduction leaching of reducing organic carboxylic acids. It is basically not consumed and can be continuously recycled with only simple filtration; (c) the strong reducing organic acid provides active protons on the one hand to destroy the oxygen acceptor in the metal oxide, and reduces the valence state of high-valence metals to achieve the reduction leaching of Co. Its addition also reduces the viscosity of the system, promoting the continuous high efficiency of the cycle.

[0039] (3) The raw materials of this invention are green, biodegradable, and low-polluting, with high leaching efficiency, mild leaching conditions, high purity of recovered products, simple process, and convenient operation. It replaces the inorganic acid and alkali leaching agents currently used in hydrometallurgical industry, reduces environmental pollution, and after multiple cycles, the raw material cost is lower than the leaching cost of inorganic acids and alkalis. The overall economic benefits are considerable, and it has high practical application value.

[0040] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments.

[0041] Unless otherwise expressly stated, numerical ranges throughout the application include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value. Unless otherwise expressly stated, numerical values ​​throughout the application represent an approximate measure or limitation of the range of embodiments including minor deviations from a given value and having approximately the mentioned value as well as having the mentioned precise value. Except in the detailed description of the working embodiments provided at the end, all numerical values ​​of parameters (e.g., quantities or conditions) in this application (including the appended claims) should in all cases be understood to be modified by the term “approximately,” regardless of whether “approximately” actually precedes the numerical value. “Approximately” indicates that the stated numerical value allows for slight inaccuracies (some close to precision at that value; approximately or reasonably close to the value; approximate). If the inaccuracy provided by “approximately” is not understood in this common sense in the art, then “approximately” as used herein at least indicates a variation that can be produced by common methods of measuring and using these parameters. For example, “approximately” can include variations less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a flowchart illustrating the process of leaching and recycling lithium cobalt oxide powder, a cathode material from waste batteries, using a multi-element eutectic solvent, according to one embodiment of the present invention.

[0044] Figure 2The XRD pattern of the precipitate Co(HCOO)2·2H2O obtained after one leaching in Example 1 of the present invention is shown. Detailed Implementation

[0045] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0046] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0047] raw material:

[0048] Acetamide (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Butyrolactam (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); N-Methylacetamide (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); N,N-Dimethylformamide (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Caprolactam (CPL, purity >99.9%, Cangzhou Xuyang Chemical Co., Ltd.); Carboamide (Urea, AR, Tianjin Chemical Reagent Wholesale Company); Anhydrous Formic Acid (FA, AR, Tianjin Kemeio Reagent); Maleic Acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.) Company); Malic acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Cyclopropionic acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Cyclobutaneacetic acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); p-Toluenesulfonic acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Cinnamic acid (AR, Shanghai Maclean Biochemical Technology Co., Ltd.); Anhydrous oxalic acid (OA, Tianjin Beichen Fangzheng Reagent Factory); Ethanol (EtOH, GR, Tianjin Kemao Chemical Reagent Co., Ltd.); Lithium cobalt oxide (LCO, 99.8%, Shanghai Maclean Biochemical Technology Co., Ltd.).

[0049] Device:

[0050] The XRD instrument used was a Rigaku D / max2500 from Japan, employing Cu Kα radiation at 40 kV and 300 mA. Peak positions were calibrated using the instrument's standard samples before use. The acquisition software was Diffrac PlusXRD Commander, and the analysis software was MDI Jade 6.0. Samples were tested at room temperature, placed on organic glass slides. Detailed detection conditions were as follows: 2θ angle range: 10–90°; scan rate: 10° / min. Unless otherwise specified, samples were not ground before detection.

[0051] Example

[0052] Example 1

[0053] Preparation of DESs: Take a certain amount of acetamide and caprolactam, mix them in a molar ratio of 1:2.5, place them in a single-necked flask, and heat them in an oil bath at 80℃ for 120 min until the liquid becomes clear and transparent. Remove the mixture and place it in a 70℃ oven for later use. This is designated as the acetamide-caprolactam eutectic solvent. Take a certain amount of acetamide-caprolactam, and add formic acid to make the acid (formic acid) concentration reach 5 mol / L. Stir at room temperature until a transparent and homogeneous liquid is formed. This is designated as the acetamide-caprolactam-formic acid multi-component eutectic solvent.

[0054] Leaching experiment: 0.6 g of positive electrode active material lithium cobalt oxide and 20 mL of acetamide-caprolactam-formic acid polyeuclide solvent were mixed in a three-necked flask at a solid-liquid ratio of 30 g / L. The mixture was reacted at 90 °C for 120 min. After cooling to room temperature, the flask was removed and the supernatant and precipitate were separated by centrifugation. The leaching rate of lithium in the supernatant was measured to be 98.6%. XRD showed that the precipitate obtained was pure Co(HCOO)2·2H2O.

[0055] The Li concentration was determined and the Li leaching rate was calculated using inductively coupled plasma optical emission spectrometry (ICP, Varian Limited, Australia): η = (CV / m Li )×100%;

[0056] Where η is the Li leaching rate (%), and C is the final Li concentration (mg·L⁻¹). -1 V is the initial volume of the leachate solution (L), m Li The value represents the mass (mg) of Li in the LiCoO2 powder.

[0057] Cyclic experiment: After centrifugation, 0.6 g of lithium cobalt oxide was added back to the supernatant, and formic acid was added to bring the volume to 20 mL, maintaining a solid-liquid ratio of 30 g / L. The leaching experiment was continued at 90℃ for 120 min. After leaching was completed, the supernatant was separated by centrifugation. This process was repeated 6 times. The lithium leaching rate in the supernatant was measured to be 98.9%. Then, 10 mL of ethanol and 2.3 g of oxalic acid (excess) were added to obtain lithium oxalate precipitate. The ethanol and oxalic acid were evaporated by heating to obtain an acetamide-caprolactam-formic acid multi-euclidean eutectic solvent, which was then used for cyclic leaching.

[0058] Example 2

[0059] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are carbamide, butyrolactam, and N,N-dimethylformamide, with a molar ratio of carbamide:butyrolactam:N,N-dimethylformamide = 1:3:5. A certain amount of lactic acid is added to achieve an acid concentration of 7 mol / L, denoted as carbamide-butyrolactam-N,N-dimethylformamide-lactic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 40 g / L. The leaching temperature is 100℃, the leaching time is 150 min, and after five cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. All other conditions remain the same. The leaching rate of lithium in the supernatant was determined to be 95.2% using inductively coupled plasma optical emission spectrometry.

[0060] Example 3

[0061] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are acetamide and N-methylacetamide, with a molar ratio of acetamide:N-methylacetamide = 1:4. Maleic acid is then added to achieve an acid concentration of 4 mol / L, resulting in an acetamide-N-methylacetamide-maleic acid multi-component eutectic solvent. The leaching temperature was 120°C, the leaching time was 80 min, and all other conditions were kept constant. After six cycles, the lithium leaching rate in the supernatant was determined to be 90.5% using inductively coupled plasma optical emission spectrometry.

[0062] Example 4

[0063] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are carbamide and caprolactam, with a molar ratio of carbamide:caprolactam = 1:2. P-toluenesulfonic acid is then added to achieve an acid concentration of 0.2 mol / L, denoted as the carbamide-caprolactam-p-toluenesulfonic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 50 g / L. The leaching temperature is 150℃, the leaching time is 20 min, and all other conditions are kept consistent. After three cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The lithium leaching rate in the supernatant was determined to be 98.3% using inductively coupled plasma optical emission spectrometry.

[0064] Example 5

[0065] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are acetamide, butyrolactam, and N-methylacetamide, with a molar ratio of acetamide:butyrolactam:N-methylacetamide = 1:2:3.5. Malic acid is then added to achieve an acid concentration of 4 mol / L, resulting in an acetamide-butyrolactam-N-methylacetamide-malic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 20 g / L. The leaching temperature is 70°C, and the leaching time is 300 min, with all other conditions kept consistent. After three cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to precipitate lithium oxalate. The leaching rate of lithium in the supernatant is determined to be 99.4% using inductively coupled plasma optical emission spectrometry.

[0066] Example 6

[0067] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are acetamide, butyrolactam, and N-methylacetamide, with a molar ratio of acetamide:butyrolactam:N-methylacetamide = 1:2:3.5. Cyclopropionic acid is then added to achieve an acid concentration of 5.5 mol / L, denoted as the acetamide-butyrolactam-N-methylacetamide-cyclopropionic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 30 g / L, the leaching temperature is 130℃, the leaching time is 10 min, and other conditions are kept consistent. After 5 cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The leaching rate of lithium in the supernatant was determined to be 96.8% using inductively coupled plasma optical emission spectrometry.

[0068] Example 7

[0069] The difference between this embodiment and Example 1 is that the raw materials used in the multi-component eutectic solvent are acetamide, caprolactam, and N-methylacetamide, with a molar ratio of acetamide:caprolactam:N-methylacetamide = 1:1:5. Cyclobutaneacetic acid is then added to achieve an acid concentration of 15 mol / L, denoted as the acetamide-caprolactam-N-methylacetamide-cyclobutaneacetic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 40 g / L, the leaching temperature is 140℃, the leaching time is 30 min, and other conditions are kept consistent. After 6 cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The leaching rate of lithium in the supernatant was determined to be 99.7% using inductively coupled plasma optical emission spectrometry.

[0070] Example 8

[0071] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are carbamide, butyrolactam, and N-methylacetamide, with a molar ratio of carbamide:butyrolactam:N-methylacetamide = 1:6:10. Cinnamic acid is then added to achieve an acid concentration of 3.5 mol / L, resulting in a carbamide-butyrolactam-N-methylacetamide-cinnamic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 10 g / L. The leaching temperature is 50°C, the leaching time is 300 min, and all other conditions are kept consistent. After 6 cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The lithium leaching rate in the supernatant was determined to be 90.3% using inductively coupled plasma optical emission spectrometry.

[0072] Example 9

[0073] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are acetamide, butyrolactam, caprolactam, N-methylacetamide, and N,N-dimethylformamide, with a molar ratio of acetamide:butyrolactam:caprolactam:N-methylacetamide:N,N-dimethylformamide = 1:1:4:3:6. Malic acid is then added to achieve an acid concentration of 6.5 mol / L, resulting in an acetamide-butyrolactam-caprolactam-N-methylacetamide-N,N-dimethylformamide-malic acid multi-element eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-element eutectic solvent is 20 g / L. The leaching temperature is 90℃, the leaching time is 240 min, and all other conditions are kept consistent. After four cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The lithium leaching rate in the supernatant was determined to be 94.5% using inductively coupled plasma optical emission spectrometry.

[0074] Example 10

[0075] The difference between this embodiment and Example 1 is that the raw materials used in the amide-based eutectic solvent are acetamide, carbamide, butyrolactam, and caprolactam, with a molar ratio of acetamide:carbamide:butyrolactam:caprolactam = 1:1:4:4. Maleic acid is then added to achieve an acid concentration of 7 mol / L, resulting in an acetamide-carbamide-butyrolactam-caprolactam-maleic acid multi-component eutectic solvent. The solid-liquid ratio of the positive electrode active material lithium cobalt oxide and the multi-component eutectic solvent is 25 g / L. The leaching temperature is 110℃, the leaching time is 180 min, and all other conditions are kept consistent. After 5 cycles, 10 mL of ethanol and oxalic acid (the molar ratio of oxalic acid to lithium is 1.2:2) are added to obtain lithium oxalate precipitate. The lithium leaching rate in the supernatant was determined to be 96.8% using inductively coupled plasma optical emission spectrometry.

[0076] Comparative Experiment 1

[0077] To demonstrate the high efficiency of leaching lithium cobalt oxide, the positive electrode active material, with a multi-component eutectic solvent, three binary eutectic solvents—acetamide-caprolactam, acetamide-formic acid, and caprolactam-formic acid—were prepared using the method described in Example 1. 0.6 g of lithium cobalt oxide and 20 mL of each eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 30 g / L. The mixture was reacted at 90 °C for 120 min. After cooling to room temperature, the flask was removed, and the lithium leaching rate in the supernatant was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The leaching rates were only 20.4%, 70.3%, and 81.5%, respectively, indicating that reducing organic carboxylic acids play a crucial role in the efficient leaching process, demonstrating the significant advantages of multi-component eutectic solvents.

[0078] Comparative Experiment 2

[0079] To compare the advantages of amide-based eutectic solvents in cyclic leaching, an acetamide-ethylene glycol-formic acid multi-component eutectic solvent was prepared using a similar method to that in Example 1. The molar ratio of this multi-component eutectic solvent was acetamide:ethylene glycol = 1:2.5. Formic acid was then added to achieve a concentration of 5 mol / L. Lithium cobalt oxide, the positive electrode active material, and 20 mL of this eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 30 g / L. The mixture was reacted at 90°C for 120 min. After cooling to room temperature, the flask was removed. The experimental results showed that after one leaching, part of the eutectic solvent structure was destroyed, making a second cyclic experiment impossible. The lithium leaching rate in the supernatant was determined to be 71.6% using inductively coupled plasma optical emission spectrometry. This indicates that because amide-based eutectic solvents are not consumed during the leaching process and only provide a reaction site for reducing organic carboxylic acids, they have an absolute advantage in cyclic leaching.

[0080] Comparative Experiment 3

[0081] To verify the feasibility of replacing choline chloride DESs with amide DESs, a eutectic solvent of choline chloride and formic acid was prepared using the method described in Example 1. The molar ratio of the eutectic solvent was choline chloride:formic acid = 1:1. Lithium cobalt oxide, the positive electrode active material, and 20 mL of the eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 30 g / L. The mixture was reacted at 90°C for 240 min. After cooling to room temperature, the flask was removed. Experimental results showed that after the first leaching, chlorine in choline chloride participated in the coordination of Co in lithium cobalt oxide. While consuming formic acid, choline chloride was also lost. Therefore, a second cycle experiment could not be directly performed. Inductively coupled plasma optical emission spectrometry (ICP-OES) determined the lithium leaching rate in the supernatant to be 90.1%, indicating that replacing choline chloride DESs with amide DESs is practically feasible and has a greater advantage in cyclic leaching than the choline chloride system.

[0082] Table 1 Summary of Li Leaching Rate

[0083]

[0084] Results analysis:

[0085] The above examples and comparative analyses demonstrate that amide-based eutectic solvents are key to the efficient leaching of spent lithium-ion battery cathode materials. Reducing organic carboxylic acids, on the one hand, provide active protons to disrupt oxygen acceptors in metal oxides, and on the other hand, lower the valence state of high-valence metals, achieving the reduction leaching of these metals. This is the core of efficient leaching of spent lithium-ion battery cathode materials. Amide-based DESs can replace the commonly used choline chloride.

[0086] The above embodiments are only used within the spirit and substance defined by the claims. Modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions are still within the scope defined by the claims of this invention.

Claims

1. A multi-element eutectic solvent, characterized in that, The multi-element eutectic solvent comprises: At least two amide compounds selected from chain amides, lactams, and N-substituted amides; and Reduced organic carboxylic acids; The amide is selected from at least one of formamide, acetamide, propionamide, n-butyramide, isobutyramide, n-pentanamide, isovaleramide, neopentanamide, n-heptamide, n-octamide, carbamide, and asparagine; The lactam is selected from at least one of cyclopropionamide, butyrolactam, valproic acid lactam, caprolactam, heptanolactam, octylolactam, dodecylolactam, and DL-aminocaprolactam; The N-substituted amide is selected from at least one of N-methylformamide, N-methylacetamide, N-methylpropionamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N,N-diethylmethacrylamide, N-hydroxymethylmethacrylamide, and N-(methoxymethyl)methacrylamide. The reducing organic carboxylic acid is selected from at least one of aliphatic carboxylic acids, alicyclic carboxylic acids, and aromatic carboxylic acids.

2. The multi-element eutectic solvent according to claim 1, characterized in that, The amide is selected from at least one of acetamide, propionamide, n-butyramide, isobutyramide, n-pentanamide, and carbamide; The lactam is selected from at least one of butyrolactam, valproic acid lactam, caprolactam, and dodecalactam; The N-substituted amide is selected from at least one of N-methylacetamide, N,N-dimethylformamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, and N-isopropylmethacrylamide; The aliphatic carboxylic acid is selected from at least one of formic acid, lactic acid, oxalic acid, maleic acid, and malic acid; the alicyclic carboxylic acid is selected from at least one of cyclopropionic acid and cyclobutaneacetic acid; and the aromatic carboxylic acid is selected from at least one of p-toluenesulfonic acid and cinnamic acid.

3. The multi-element eutectic solvent according to claim 1, characterized in that, The amide is selected from at least one of acetamide and carbamide; The lactam is selected from at least one of butyrolactam and caprolactam; The N-substituted amide is selected from at least one of N-methylacetamide and N,N-dimethylformamide.

4. The multi-element eutectic solvent according to claim 1, characterized in that, In at least two amide compounds, the molar ratio of chain amide: lactam: N-substituted amide is 1:(0-6):(0-10); and / or The molar concentration of reducing organic carboxylic acids in multi-component eutectic solvents is 0.2-15 mol / L.

5. The multi-element eutectic solvent according to claim 1, characterized in that, The multi-element eutectic solvent comprises: aliphatic amide, lactam, N-substituted amide, and reducing organic carboxylic acid; wherein the molar ratio of aliphatic amide: lactam: N-substituted amide is 1:(1-6):(1-10).

6. The multi-element eutectic solvent according to any one of claims 1-5, characterized in that, It is prepared by a method comprising the following steps: mixing at least two amide substances selected from chain amides, lactams and N-substituted amides, and heating at 50 to 100°C until clear and transparent to obtain an amide eutectic solvent; then mixing the amide eutectic solvent with a reducing organic carboxylic acid, and heating at 30 to 100°C to form a transparent and homogeneous liquid to obtain the multi-component eutectic solvent.

7. A method for preparing the multi-element eutectic solvent according to any one of claims 1-5, comprising the following steps: At least two amides selected from chain amides, lactams, and N-substituted amides are mixed and heated to a clear and transparent state at 50–100°C to obtain an amide eutectic solvent; the amide eutectic solvent is then mixed with a reducing organic carboxylic acid and heated to a clear and uniform liquid at 30–100°C to obtain the multi-component eutectic solvent.

8. A method for selectively recycling cathode materials from waste lithium cobalt oxide batteries, characterized in that, The process includes a leaching step: mixing the multi-element eutectic solvent described in any one of claims 1-6 with the waste lithium cobalt oxide battery cathode material and heating it for leaching, thereby separating insoluble Co(HCOO)2·2H2O precipitate and Li-containing leachate.

9. The method according to claim 8, characterized in that, The leaching temperature is 50 ℃-150 ℃; and / or the leaching time is 10 min-300 min.

10. The method according to claim 8, characterized in that, The solid-liquid ratio of the spent lithium cobalt oxide battery cathode material and the multi-element eutectic solvent is 10 g / L to 100 g / L.

11. The method according to claim 8, characterized in that, The solid-liquid ratio of the spent lithium cobalt oxide battery cathode material and the multi-element eutectic solvent is 10 g / L to 50 g / L.

12. The method according to claim 8, characterized in that, The method also includes a cyclic leaching step: adding new waste lithium cobalt oxide battery cathode material to the Li-containing leaching solution, repeating the leaching step three or more times, and adding a certain amount of reducing organic carboxylic acid each time to maintain a constant solid-liquid ratio.

13. The method according to any one of claims 8-11, characterized in that, After leaching, ethanol and oxalic acid are added to the Li-containing leachate, wherein the volume ratio of ethanol to the multi-element eutectic solvent is 1:1-5, and the molar ratio of oxalic acid to lithium is 1-1.5:

2. Lithium oxalate precipitate and leachate containing ethanol and oxalic acid are separated. The leachate containing ethanol and oxalic acid is heated to evaporate and remove ethanol and oxalic acid. The leachate is then recycled for the leaching step.

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