Method for preparing MOF precursor and lithium ion battery positive electrode material

Abstract

The invention provides a method for preparing an MOF precursor and a lithium ion battery positive electrode material, which comprises the following steps: firstly, dissolving waste ternary battery positive electrode powder in a eutectic solvent prepared from amino-containing substances and reducing organic carboxylic acid, heating, stirring and centrifuging to obtain a precursor solution; the metal ammonium carboxylate solid and the eutectic solvent which contains the lithium salt and can be recycled are obtained. After the metal ammonium carboxylate solid is subjected to alcohol washing and water dissolving, water is removed, and a precursor of the corresponding positive electrode material can be obtained. The one-step separation of lithium and the MOF material and the preparation of the precursor are realized for the first time, and the method is high in separation efficiency, simple in process, green and environment-friendly, and has very high practical application value. The positive electrode material prepared by taking the MOF material as the precursor reaches the commercial level.

Description

Technical Field

[0001] The present invention relates to the technical field of waste lithium-ion battery recycling, and in particular to a method for directly preparing MOF precursors and lithium-ion battery positive electrode materials by using waste lithium-ion batteries and a low eutectic solvent in a one-step process. Background Art

[0002] Lithium-ion batteries (LIBs) are very popular because of their high energy density, many rechargeable times, and easy portability. Especially after the large-scale promotion and application of new energy vehicles, the number of lithium-ion batteries has ushered in an explosive growth. The number of waste lithium-ion batteries has also increased. If they are not treated, they will not only cause great pollution to the environment, but also waste resources. In this case, the recycling of waste lithium-ion batteries is very necessary. Traditional lithium-ion battery recycling mainly includes pyrometallurgy, hydrometallurgy, biometallurgy, mechanical methods, etc. These methods mainly use high temperature or solvents to destroy lithium-containing compounds, turning them into single substances, oxides or ions, and then separate them through a series of means to obtain each single metal or its compound. However, the high energy consumption caused by high temperature and the environmental problems caused by the use of acid and alkali reagents cannot be ignored.

[0003] Leaching lithium-ion batteries with deep eutectic solvents (DESs) is an emerging, greener and more environmentally friendly recycling method. Compared with the currently common pyrometallurgy and hydrometallurgy, the DESs leaching reaction conditions are milder, and the introduction of organic acids replaces the more difficult to handle inorganic acids, but the leaching rate has not shown a significant decrease.

[0004] At present, the preparation of positive electrode material precursors mainly includes co-precipitation method, hydrothermal method, sol-gel method, solid phase method, redox method and other methods. Among them, the hydroxide co-precipitation method is the most commonly used method for preparing precursors. The required precursor is generated by the action of nickel, cobalt and manganese metal salts, precipitants and complexing agents. However, the addition of precipitants may cause local concentrations to be too high, resulting in agglomeration or uneven composition, affecting the quality of the precursor.

[0005] Patent CN115893527A discloses a method for preparing a ternary cathode material precursor by recycling waste ternary lithium batteries. The technical scheme is to use a mixed acid solution of an organic acid and an inorganic acid, leaching by high temperature and pressure, and then adding an alkali solution to the leaching solution for co-precipitation to obtain a ternary cathode material precursor. Although this method can improve the leaching rate, it will introduce a large amount of impurities, and more purification steps are required in the later stage; Patent CN113802003A discloses a method for recycling waste lithium batteries and preparing a ternary precursor. The technical scheme is to use a mixed acid solution of an organic acid and an inorganic acid, leaching by high temperature and pressure, and then adding an alkali solution to the leaching solution for co-precipitation to obtain a ternary cathode material precursor. Although this method can improve the leaching rate, it will introduce a large amount of impurities, and more purification steps are required in the later stage. The technical scheme is to first roast the battery powder to make pulp, add metal chloride to leach it, and then obtain the ternary precursor by acid leaching extraction evaporation crystallization. This method has a complex process flow, high operating requirements, and high cost, which is not conducive to industrial production; Patent CN112940281A discloses a method for preparing a lithium battery precursor and a positive electrode material, wherein the preparation method includes mixing Mn salt, MOF ligand and conductive medium with an organic solvent to obtain a mixed solution; and the mixed solution is subjected to an electrodeposition reaction to obtain a Mn-based MOF lithium battery precursor. Although this method can stabilize the structure of the positive electrode material and improve the capacity and stability, the preparation of the Mn-based MOF precursor uses an electrodeposition device, which consumes high energy and is relatively expensive, with a large initial investment, and high requirements for industrial production. At present, the main problems in the recycling of waste lithium-ion batteries to prepare positive electrode materials are complex processes, high energy consumption, and acid-base reagents that pollute the environment. The sample purity needs to be further improved, which undoubtedly further increases the production cost. Summary of the invention

[0006] The present invention realizes a one-step method for recovering and preparing metal ammonium carboxylate MOF precursors from waste lithium-ion batteries. The operation process is simple, the operating cost is low, the raw materials are cheap and easily available, the prepared MOF precursor has high purity and good performance, and the positive electrode material synthesized from the prepared MOF precursor meets commercialization requirements, achieving a win-win situation in environmental and economic benefits.

[0007] One of the objects of the present invention is to provide a deep eutectic solvent.

[0008] A second object of the present invention is to provide a method for preparing a MOF precursor.

[0009] A third object of the present invention is to provide a method for preparing a positive electrode material for a lithium ion battery.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] In a first aspect, the present invention provides a deep eutectic solvent, wherein the deep eutectic solvent comprises:

[0012] Contains polyamino substances; and

[0013] Reducing organic carboxylic acids;

[0014] The polyamino-containing substance is selected from at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, benzidine, 4,4'-diamino-3,3'-dimethylbiphenyl, dianisidine, 2,6-diaminoanthracene and 4,4'-diaminoterphenyl;

[0015] 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 cyclopropylacetic acid, cyclobutaneacetic acid, cyclopentaneacetic acid, cyclohexaneacetic acid, 1,3,5-cyclohexanetricarboxylic acid, etc.), and aromatic carboxylic acids (such as benzoic acid, p-toluenesulfonic acid, phthalic acid, terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 2,6-naphthalene dicarboxylic acid, etc.); preferably at least one of formic acid, terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 2,6-naphthalene dicarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid.

[0016] In one embodiment, the molar ratio of the polyamino-containing substance to the reducing organic carboxylic acid is (1-5):(1-15), such as 1:2, 1:9, 2:5, 2:7, 2:10, 3:7, 4:12, 4:15, 5:8, but not limited thereto.

[0017] In one embodiment, the low eutectic solvent according to the present invention is prepared by a method comprising the following steps: mixing a polyamino-containing substance with a reducing organic carboxylic acid, and heating at 50 to 100° C. for 10 to 120 min until the mixture becomes clear and transparent, thereby obtaining the low eutectic solvent.

[0018] According to the present invention, the obtained deep eutectic solvent can be stored in an oven at 70° C. for later use.

[0019] In a second aspect, the present invention provides a method for preparing a MOF precursor, comprising a leaching step: mixing the low eutectic solvent and the waste lithium-ion battery positive electrode material and heating and leaching, separating to obtain a MOF solid precipitate and a lithium-containing leachate, and washing and purifying the MOF solid precipitate to obtain a MOF precursor.

[0020] The positive electrode material of waste lithium-ion batteries is the positive electrode powder obtained after the positive electrode sheets of waste lithium-ion batteries are pre-treated by discharging, disassembling, crushing, etc. The positive electrode materials of waste lithium-ion batteries include but are not limited to lithium cobalt oxide, lithium manganese oxide, nickel cobalt lithium manganese oxide, lithium nickel oxide and other materials.

[0021] In some embodiments, the leaching temperature is 50°C-150°C; and / or

[0022] The leaching time is 10min-300min.

[0023] In some embodiments, the solid-to-liquid ratio of the waste lithium-ion battery positive electrode material and the low eutectic solvent is 10 g / L to 50 g / L, such as 10, 20, 30, 40, or 50 g / L.

[0024] In some embodiments, the method further comprises a cyclic leaching step: adding new waste lithium-ion battery positive electrode material to the lithium-containing leachate, and each time adding a certain amount of low eutectic solvent to maintain a constant solid-liquid ratio.

[0025] In some embodiments, the MOF solid precipitate is washed with alcohol, dissolved with water, filtered, and the filtrate is dried to obtain a MOF precursor;

[0026] Preferably, the solid-liquid ratio of the alcohol wash is 50-100 g / L, such as 50, 60, 70, 80, 90, 100 g / L;

[0027] Preferably, the solid-to-liquid ratio of water dissolution is 1-10 g / L, such as 1, 2, 3, 5, 6, 8, 10 g / L;

[0028] Preferably, the drying temperature is 80-100° C. and the drying time is 5-15 h.

[0029] In a third aspect, the present invention provides a method for preparing a positive electrode material for a lithium ion battery, comprising the following steps:

[0030] Prepare a MOF precursor according to the method for preparing a MOF precursor as described above;

[0031] The MOF precursor is mixed with a lithium compound, ground, and calcined in an air atmosphere to obtain a lithium-ion battery positive electrode material.

[0032] In some embodiments, the lithium compound is at least one selected from lithium carbonate and lithium hydroxide.

[0033] In some embodiments, the molar ratio of the MOF precursor to the lithium compound is 1:1-1.5, such as 1:1, 1:2, 1:3, 1:4, 1:5.

[0034] In some embodiments, the calcination process is divided into two times, the first calcination temperature is 450-550° C., the calcination time is 3-5 hours, and the second calcination temperature is 800-1000° C., the calcination time is 10-15 hours.

[0035] The present invention utilizes deep eutectic solvents (DESs) to leach waste LIBs, and the elements Ni, Co, Mn, etc. in lithium batteries will be converted from high-valent state (Ni 2+ 、Co 3+ , Mn 3+ / Mn 4+ ) is reduced to a low-valent state (Ni 2+ 、Co 2+ , Mn 2+ ), the low-valent metal ions will form an octahedral inorganic-organic metal framework MOF material with the carboxylic acid and amine components in DES, and this MOF material is insoluble in DES, so it is precipitated and separated. The metal ratio in the recovered metal ammonium carboxylate MOF material is basically the same as the ratio of Ni, Co, and Mn in the positive electrode material. After adding lithium salt and calcining, the positive electrode material can be obtained.

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

[0037] (1) The present invention innovatively provides a method for recycling positive electrode materials from waste lithium batteries for direct preparation of metal ammonium carboxylate MOF materials as precursors. The MOF materials can be directly obtained by leaching waste LIBs with a specific low eutectic solvent. The method is simple to operate, low in cost, high in separation efficiency, reduces the use of additives such as precipitants, and can also recycle precious metals to reduce resource waste. The obtained MOF material has high purity and stable structure. After lithium supplementation and calcination, a ternary positive electrode material can be obtained, which is convenient for industrial production.

[0038] (2) The XRD spectrum of the ternary positive electrode material recycled and prepared by the present invention was analyzed and compared with the XRD spectrum of the standard positive electrode material. It was found that the two can correspond well and meet the requirements of commercialization.

[0039] (3) The deep eutectic solvent (DESs) used in the present invention is an environmentally friendly organic solvent, non-toxic, and can be recycled, which can achieve a win-win situation in economic and environmental benefits. The waste lithium battery powder is fully dissolved by DESs leaching, and valuable metals such as nickel, cobalt, and manganese are selectively leached with a high recovery rate.

[0040] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples.

[0041] Unless otherwise expressly stated, the numerical ranges throughout the application documents include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value therein. Unless otherwise expressly stated, the numerical values ​​throughout the application documents represent approximate measurements or limitations of the range of embodiments including slight deviations from the given values ​​and having approximately the values ​​mentioned and having the exact values ​​mentioned. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this application document (including the appended claims) should be understood in all cases as modified by the term "approximately", regardless of whether "approximately" actually appears before the numerical value. "Approximately" means that the numerical value described allows for slight imprecision (some close to precision in the value; approximately or reasonably close to the value; approximately). If the imprecision provided by "approximately" is not understood in this ordinary sense in the art, the "approximately" used herein at least represents the variation that can be produced by ordinary methods of measuring and using these parameters. For example, "approximately" can include a variation of 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%. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The XRD pattern of the ternary positive electrode material obtained in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0044] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0045] raw material:

[0046] Ethylenediamine (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); divinyltriamine (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); trivinyltetramine (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); benzidine (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); 4,4'-diamino-3,3'-dimethylbiphenyl (AR, Shanghai Aladdin Biochemical Technology Co., Ltd.); dianisidine (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); 2,6-diaminoanthracene (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); 4,4'-diaminoterphenyl (AR, Shanghai Aladdin Biochemical Technology Co., Ltd.); choline chloride (AR, Shanghai Aladdin Biochemical Technology Co., Ltd.); anhydrous formic acid (FA, AR, Tianjin Komiou Reagent); terephthalic acid (AR, Shanghai MacLean Biochemical Technology Co., Ltd.); 2,5-dihydroxyterephthalic acid (AR, Shanghai McLean Biochemical Technology Co., Ltd.); 2-aminoterephthalic acid (AR, Shanghai McLean Biochemical Technology Co., Ltd.); 2,6-naphthalene dicarboxylic acid (AR, Shanghai McLean Biochemical Technology Co., Ltd.); 2,5-dihydroxyterephthalic acid (AR, Shanghai McLean Biochemical Technology Co., Ltd.); 1,3,5-cyclohexanetricarboxylic acid (AR, Shanghai McLean Biochemical Technology Co., Ltd.); lactic acid (AR, Tianjin Komio Chemical Reagent Co., Ltd.); ethanol (EtOH, GR, Tianjin Komio Chemical Reagent Co., Ltd.); lithium cobalt oxide (LCO), lithium manganate (LMO), lithium nickel oxide (LNO), NCM333, NCM523, NCM622, NCM811, and NCA were all from Hebei Sinochem Lithium Battery Technology Co., Ltd.

[0047] Device:

[0048] The instrument used for XRD was Rigaku D / max2500, Japan, using Cu Kα radiation, voltage of 40 kV, and current of 300 mA. The peak position was calibrated with the standard sample provided by the instrument before use. The acquisition software was Diffrac PlusXRD Commander, and the analysis software was MDI Jade 6.0. The samples were tested at room temperature, and the samples to be tested were placed on organic glass slides. The detailed test conditions are as follows: 2θ angle range: 10-90°; scanning rate of 10° / min. Unless otherwise specified, the samples were not ground before testing.

[0049] The instrument used for XRF is ZSX Primus III+ X-ray fluorescence spectrometer, Rigaku, Japan. The samples were ground and crushed to less than 200 mesh and pressed into tablets for testing. The test standard was carried out in accordance with JY / T 0569-2020.

[0050] Positive electrode powder leaching rate:

[0051]

[0052] Where η1 is the positive electrode powder leaching rate (%), m0 is the mass of the positive electrode powder initially added (g), and m1 is the mass of the positive electrode powder not leached (g).

[0053] Precursor recovery rate:

[0054]

[0055] Where η2 is the precursor recovery rate (%), m2 is the actual recovery amount of the precursor (g), and m3 is the theoretical recovery amount of the precursor (g).

[0056] Cathode material synthesis rate:

[0057]

[0058] Wherein η3 is the synthesis rate of the positive electrode material (%), m2 is the actual recovery amount of the precursor (g), and M1 is the relative molecular mass of the precursor; m4 is the actual synthesis amount of the positive electrode material (g), and M2 is the relative molecular mass of the positive electrode material.

[0059] Example

[0060] Example 1

[0061] Preparation of DESs: Take a certain amount of ethylenediamine and formic acid, mix them in a molar ratio of 1:2, put them into a single-necked flask and heat them in an oil bath at 80°C for 120 minutes. When the liquid becomes clear and transparent, take it out and put it into a 70°C oven for use. This is recorded as ethylenediamine-formic acid low eutectic solvent.

[0062] Mixed leaching and precursor preparation: 2g NCM523 positive electrode active material and 100mL low eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 20g / L, reacted at 90°C for 120min, cooled to room temperature, removed the flask, and separated the supernatant and precipitate by centrifugation. The lithium leaching rate in the supernatant was determined to be 97%. The precipitate was first washed and filtered with ethanol at a solid-liquid ratio of 60g / L, and then dissolved with deionized water at a solid-liquid ratio of 2g / L. Dry in an oven at 80°C for 15h to obtain a ternary MOF precursor. The supernatant after centrifugation was re-added with 2 g of NCM523 positive electrode active material and DES was added to 100 mL, the solid-liquid ratio was maintained at 20 g / L, and the leaching experiment was continued at 90 ° C and 120 min. After the leaching was completed, the supernatant and the precipitate were separated by centrifugation. The precipitation treatment steps were the same as before. After the supernatant was supplemented with the consumed amount of DES, the leaching cycle could be continued, and the above mixed leaching and precursor preparation steps were repeated.

[0063] Preparation of positive electrode material: The dried ternary MOF precursor and lithium carbonate were mixed evenly at a molar ratio of 1:1.1. The temperature was raised in a muffle furnace under air atmosphere: the temperature was raised to 500°C at 5°C / min and kept at this temperature for 5 hours, and then the temperature was raised to 900°C at 5°C / min and kept at this temperature for 10 hours. After cooling to room temperature, the positive electrode material of the ternary lithium-ion battery was obtained. Its XRD pattern is shown in the figure below. Figure 1 As shown in the figure, PDF#97-029-1342 in the analysis software is the standard NCM523 sample. XRD characterization shows that the precursor directly prepared by DES one-step leaching of waste lithium-ion batteries has the same diffraction peaks as the standard sample after being made into positive electrode powder, indicating that the proportion of leached precursor elements is the same as before leaching. The sharper diffraction peaks indicate that the sample has good crystallinity.

[0064] The XRF test data are shown in Table 1.

[0065] Table 1 Element ratios in ternary MOF precursors made from waste lithium-ion battery NCM523 and DES leaching

[0066]

[0067] Embodiment 2-10

[0068] The differences between Example 2-10 and Example 1 are shown in Table 2.

[0069] Table 2 DES composition and leaching effect of Examples 2-10

[0070]

[0071]

[0072] Comparative Example 1

[0073] Preparation of DESs: Take a certain amount of choline chloride and lactic acid, mix them in a molar ratio of 1:2, put them into a single-necked flask and heat them in an oil bath at 80°C for 120 minutes. When the liquid becomes clear and transparent, take it out and put it into a 70°C oven for later use. This is recorded as lactic acid-choline chloride low eutectic solvent.

[0074] Mixed leaching: 2 g of NCM523 positive electrode active material and 100 mL of low eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 20 g / L, reacted at 90 ° C for 120 min, and after cooling to room temperature, the flask was taken out and the supernatant and graphite were separated by centrifugation. The metal ions in the waste lithium battery were leached into the supernatant.

[0075] Precursor preparation: Take the supernatant and add oxalic acid with a molar ratio of 1.05-1.5 times the leached metal ions to co-precipitate to obtain Ni, Co, and Mn ternary precursors to achieve separation from lithium. Ni, Co, and Mn co-precipitated with oxalic acid are rinsed with ethanol and placed in a 70°C oven to dry for later use.

[0076] Preparation of positive electrode material: The precipitated ternary precursor of oxalic acid and lithium carbonate were mixed evenly at a molar ratio of 1:1.1, and programmed to heat in a muffle furnace under air atmosphere: heating to 500°C at 5°C / min and keeping the temperature constant for 5h, then heating to 900°C at 5°C / min and keeping the temperature constant for 10h. The mixture was cooled to room temperature with the furnace to obtain the positive electrode material of ternary lithium-ion battery.

[0077] Comparative Example 2

[0078] Preparation of DESs: The difference from Example 1 is that ethylenediamine is replaced by n-butylamine.

[0079] Mixed leaching: 2 g of NCM523 positive electrode active material and 100 mL of low eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 20 g / L, reacted at 90 ° C for 120 min, and after cooling to room temperature, the flask was taken out and the supernatant and graphite were separated by centrifugation. The metal ions in the waste lithium battery were leached into the supernatant.

[0080] Precursor preparation: Take the supernatant and add oxalic acid with a molar ratio of 1.05-1.5 times the leached metal ions to co-precipitate to obtain Ni, Co, and Mn ternary precursors to achieve separation from lithium. Ni, Co, and Mn co-precipitated with oxalic acid are rinsed with ethanol and placed in a 70°C oven to dry for later use.

[0081] Preparation of positive electrode material: The precipitated ternary precursor of oxalic acid and lithium carbonate were mixed evenly at a molar ratio of 1:1.1, and programmed to heat in a muffle furnace under air atmosphere: heating to 500°C at 5°C / min and keeping the temperature constant for 5h, then heating to 900°C at 5°C / min and keeping the temperature constant for 10h. The mixture was cooled to room temperature with the furnace to obtain the positive electrode material of ternary lithium-ion battery.

[0082] Results analysis: Comparative Example 1 is a common DES leaching method. There is a fundamental difference between Comparative Example 1 and Example 1 in the reaction principle. Comparative Example 1 treats waste positive electrode powder and leaches metal ions into the DES solution. The separation of metal ions requires the addition of an additional separation agent. The difference between Comparative Example 2 and Example 1 is that the polyamino substance is replaced with a monoamino substance. After the reaction of Comparative Example 2 is completed, no MOF precursor can be generated.

[0083] The above embodiments can modify the technical solutions recorded in the above embodiments, or replace part or all of the technical features therein by equivalents only within the scope of the spirit and substance defined by the claims; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A deep eutectic solvent, characterized in that: The deep eutectic solvent comprises: Contains polyamino substances; and Reducing organic carboxylic acids; The polyamino-containing substance is selected from at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, benzidine, 4,4'-diamino-3,3'-dimethylbiphenyl, dianisidine, 2,6-diaminoanthracene and 4,4'-diaminoterphenyl; The reducing organic carboxylic acid is at least one selected from aliphatic carboxylic acids, alicyclic carboxylic acids, and aromatic carboxylic acids.

2. The deep eutectic solvent according to claim 1, characterized in that The reducing organic carboxylic acid is selected from at least one of 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, cyclopropylacetic acid, cyclobutaneacetic acid, cyclopentaneacetic acid, cyclohexaneacetic acid, 1,3,5-cyclohexanetricarboxylic acid, benzoic acid, p-toluenesulfonic acid, phthalic acid, terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, and 2,6-naphthalene dicarboxylic acid; preferably at least one of formic acid, terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 2,6-naphthalene dicarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid.

3. The deep eutectic solvent according to claim 1 or 2, characterized in that The molar ratio of the polyamino-containing substance to the reducing organic carboxylic acid is (1-5): (1-15).

4. The deep eutectic solvent according to claim 1 or 2, characterized in that It is prepared by a method comprising the following steps: The polyamino-containing substance is mixed with a reducing organic carboxylic acid, and heated at 50 to 100° C. for 10 to 120 minutes until the mixture becomes clear and transparent, thereby obtaining the low eutectic solvent.

5. A method for preparing a MOF precursor, characterized in that: The method comprises a leaching step of mixing the low eutectic solvent according to any one of claims 1 to 4 and the waste lithium-ion battery positive electrode material and heating and leaching, separating to obtain a MOF solid precipitate and a lithium-containing leaching solution, and washing and purifying the MOF solid precipitate to obtain a MOF precursor.

6. The method for preparing a MOF precursor according to claim 5, characterized in that: The leaching temperature is 50°C-150°C; and / or The leaching time is 10min-300min.

7. The method for preparing a MOF precursor according to claim 5, characterized in that: The solid-to-liquid ratio of the waste lithium-ion battery positive electrode material and the low eutectic solvent is 10g / L to 50g / L.

8. The method for preparing a MOF precursor according to claim 5, characterized in that: The method also includes a cyclic leaching step: adding new waste lithium-ion battery positive electrode materials to the lithium-containing leachate, and each time adding a certain amount of low eutectic solvent to maintain a constant solid-liquid ratio.

9. The method for preparing a MOF precursor according to claim 5, characterized in that: The MOF solid precipitate is washed with alcohol, dissolved in water, filtered, and the filtrate is dried to obtain a MOF precursor; Preferably, the solid-liquid ratio of alcohol washing is 50-100 g / L; Preferably, the solid-to-liquid ratio of water dissolution is 1-10 g / L; Preferably, the drying temperature is 80-100° C. and the drying time is 5-15 h.

10. A method for preparing a positive electrode material for a lithium ion battery, characterized in that: The following steps are involved: Prepare a MOF precursor according to the method for preparing a MOF precursor according to any one of claims 5 to 9; The MOF precursor is mixed with a lithium compound, ground, and calcined in an air atmosphere to obtain a positive electrode material for a lithium-ion battery; Preferably, the lithium compound is at least one selected from lithium carbonate and lithium hydroxide; Preferably, the molar ratio of MOF precursor to lithium compound is 1:1-1.5; Preferably, the calcination process is divided into two times, the first calcination temperature is 450-550°C, the calcination time is 3-5h, and the second calcination temperature is 800-1000°C, the calcination time is 10-15h.

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