Method for preparing organic carboxylic acid-based MOFs precursor and positive electrode material by recycling waste lithium ion batteries

Abstract

The invention discloses a method for preparing an organic carboxylic acid-based MOFs precursor and a positive electrode material by recycling a waste lithium ion battery. The invention relates to a method for preparing an organic carboxylic acid-based MOFs precursor by recycling a waste lithium ion battery. The method comprises the following steps: mixing a deep eutectic solvent prepared from an alcohol substance and reducing organic carboxylic acid with a positive electrode material of the waste lithium ion battery, heating and leaching, and carrying out solid-liquid separation to obtain an organic carboxylic acid-based MOFs solid precipitate and a Li-containing leachate; and hydrolyzing the organic carboxylic MOFs solid precipitate, filtering, and drying the filtrate to obtain the organic carboxylic MOFs precursor. 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.

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 preparing organic carboxylic acid-based MOFs precursors and positive electrode materials by recycling waste lithium-ion batteries using a low eutectic solvent, as well as the low eutectic solvent used, and the prepared organic carboxylic acid-based MOFs precursors and positive electrode materials. Background Art

[0002] Lithium-ion batteries (LIBs) have excellent electrochemical properties, including high stability, compact size, lightweight structure and high output power. The growing global demand for sustainable energy has led to a substantial increase in the production of LIBs. Waste LIBs contain valuable metal components, including manganese (Mn), cobalt (Co), lithium (Li) and nickel (Ni). Recycling these precious metals in the cathode of batteries is crucial to address the shortage of metal resources and reduce the manufacturing cost of lithium-ion batteries.

[0003] The preparation of NCM cathode material precursors is divided into solid phase method and liquid phase method. Among them, the solid phase method generally uses metal oxides in a certain proportion to synthesize NCM precursors through roasting and then prepares them into cathode materials. However, this method requires roasting, and the crystallinity and component ratio are difficult to control, and the energy consumption is high. It also causes environmental pollution. The coprecipitation method in the commonly used liquid phase method is to prepare the required precursor by adding hydroxide or carbonate to the metal salt solution in one step of coprecipitation, but the use of this method will cause uneven composition, affect the quality of the precursor, and the steps are more complicated and the cost is higher.

[0004] At present, there have been reports on the use of waste lithium-ion batteries to prepare precursor MOF and positive electrode materials. For example, CN110862110A discloses a method for preparing ternary positive electrode material precursors by recycling waste ternary lithium batteries. Its technical solution is to use inorganic acid leaching, and then add sodium hydroxide for coprecipitation to prepare NCM523 or NCM811 precursors. Although this method can prepare NCM precursors, a large amount of pretreatment of waste lithium-ion batteries and the use of extractants in the early stage increase the process cost and the process is complicated. For another example, CN 112812315A discloses a method for preparing manganese-based MOF materials based on waste lithium-ion battery leachate. Its technical solution is to leach waste lithium-ion batteries with organic acid and reducing agent, and then add organic ligands to the leachate, and then perform hydrothermal reaction to obtain manganese-based MOF materials. Although this method can prepare manganese-based MOF materials, its process is complicated and cannot directly prepare MOF in one step. The amount of waste liquid is large, which is not conducive to the environment and industrial production. Summary of the invention

[0005] In view of the complex process of using waste lithium-ion batteries to recycle and prepare precursor MOF and positive electrode materials in the prior art, a large amount of organic solvents are used in the process of preparing MOF, and a large amount of waste liquid is generated, which is not recyclable, has high production costs, and is difficult to industrialize, the present invention uses alcohol substances and reducing organic carboxylic acids to prepare a new low eutectic solvent for the first time to recover Ni, Co, and Mn in waste lithium-ion batteries, and prepares a new tetrahedral organic acid-based MOFs precursor from waste lithium-ion batteries by a one-step method, which can further prepare positive electrode materials. The organic acid-based MOFs precursor prepared by the present invention has a high recovery rate and high purity, and compared with the previous low eutectic solvent, it enhances the leaching effect on Mn, and achieves a high complexation degree and high leaching rate of Mn; the preparation method has a simple operation process, low raw material cost, is environmentally friendly, and has good economic and environmental benefits.

[0006] One of the objects of the present invention is to provide a deep eutectic solvent.

[0007] A second object of the present invention is to provide a method for preparing the above-mentioned deep eutectic solvent.

[0008] A third object of the present invention is to provide a method for preparing an organic carboxylic acid-based MOFs precursor.

[0009] A fourth object of the present invention is to provide an organic carboxylic acid-based MOFs precursor prepared by the above method.

[0010] A fifth object of the present invention is to provide a method for preparing a lithium-ion battery positive electrode material from the above-mentioned organic carboxylic acid-based MOFs precursor.

[0011] A sixth object of the present invention is to provide a lithium ion battery positive electrode material prepared by the above method.

[0012] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0013] In a first aspect, the present invention provides a deep eutectic solvent, wherein the deep eutectic solvent comprises:

[0014] Alcohols; and reducing organic carboxylic acids;

[0015] Wherein, the molar ratio of the alcohol substance to the reducing organic carboxylic acid is 1:(1-10).

[0016] In a specific embodiment, the alcohol substance is selected from monohydric fatty alcohols and polyhydric fatty alcohols, including but not limited to: at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, and glycerol;

[0017] The reducing organic carboxylic acid refers to an organic carboxylic acid that can reduce high-valent metal ions (such as Ni(III), Co(III), Mn(III / IV)) in lithium-ion batteries to low-valent metal ions (such as (Ni, Co, Mn)(II)), and is selected from at least one of a monovalent aliphatic carboxylic acid, a polyvalent aliphatic carboxylic acid, an alicyclic carboxylic acid, and an aromatic carboxylic acid, wherein the aliphatic carboxylic acid, alicyclic carboxylic acid, and aromatic carboxylic acid are optionally substituted by one or more hydroxyl groups and amino groups;

[0018] Preferably, the aliphatic carboxylic acid or substituted aliphatic carboxylic acid includes but is not limited to: formic acid, acetic acid, lactic 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.;

[0019] The above-mentioned alicyclic carboxylic acids or substituted alicyclic carboxylic acids include, but are not limited to: cyclopropylacetic acid, cyclobutaneacetic acid, cyclopentaneacetic acid, cyclohexaneacetic acid, 1,3,5-cyclohexanetric acid, etc.;

[0020] The above aromatic carboxylic acids or substituted aromatic carboxylic acids include, but are not limited to, benzoic acid, phthalic acid, terephthalic acid, trimesic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 2,6-naphthalene dicarboxylic acid, and the like.

[0021] Preferably, the reducing organic carboxylic acid is selected from at least one of formic acid, acetic acid, oxalic acid, trimesic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, and 1,3,5-cyclohexanetricarboxylic acid;

[0022] In a specific embodiment, the molar ratio of the alcohol substance to the reducing organic carboxylic acid is, for example, 1:1, 1:1.3, 1:1.4, 1:2, 1:2.25, 1:2.5, 1:2.6, 1:3, 1:3.5, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, but is not limited thereto.

[0023] In a second aspect, a method for preparing the above-mentioned deep eutectic solvent is provided, which comprises the following steps:

[0024] At 15-30° C., preferably 20-25° C., the alcohol substance and the reducing organic carboxylic acid are mixed in proportion until the mixture becomes clear and transparent, thereby obtaining the deep eutectic solvent.

[0025] In some embodiments, mixing can be performed by a common mixing method in the art, such as stirring, shaking, and the like.

[0026] In the present invention, the prepared deep eutectic solvent can be stored at room temperature for later use.

[0027] In a third aspect, the present invention provides a method for preparing an organic carboxylic acid-based MOFs precursor, which uses waste lithium-ion battery positive electrode materials as raw materials, comprising the following steps:

[0028] The low eutectic solvent and the waste lithium-ion battery positive electrode material are mixed and heated for leaching, and the solid-liquid separation is performed to obtain an organic carboxylic acid-based MOFs solid precipitate and a Li-containing leachate. The organic carboxylic acid-based MOFs solid precipitate is hydrolyzed, filtered, and the filtrate is dried to obtain an organic carboxylic acid-based MOFs precursor.

[0029] 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 have been pre-treated by discharging, disassembling, crushing, etc.

[0030] In some embodiments, the cathode materials of waste lithium-ion batteries include, but are not limited to, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide.

[0031] In some embodiments, the leaching temperature is 60°C to 140°C, preferably 70°C to 100°C; the leaching time is 30 min to 300 min, preferably 60 min to 200 min.

[0032] In some embodiments, the solid-to-liquid ratio of the waste lithium-ion battery positive electrode material and the low eutectic solvent is 15 g / L to 65 g / L, such as 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 g / L.

[0033] In some embodiments, the method further comprises a cyclic leaching step: adding new waste lithium-ion battery positive electrode material to the Li-containing leachate, and each time adding a certain amount of low eutectic solvent to maintain a constant solid-liquid ratio.

[0034] In some embodiments, the organic carboxylic acid-based MOFs solid precipitation hydrolysis comprises: hydrolyzing the organic carboxylic acid-based MOFs solid precipitation in water at 60-100° C. for 15-45 min.

[0035] In some embodiments, the solid-to-liquid ratio of the organic carboxylic acid-based MOFs solid precipitate to water is 1 to 10 g / L, such as 1, 2, 3, 5, 6, 8, or 10 g / L.

[0036] In some embodiments, the conditions for drying the filtrate are: temperature of 30 to 60° C. and time of 2 to 12 hours.

[0037] According to the above method for preparing an organic carboxylic acid-based MOFs precursor, the obtained organic carboxylic acid-based MOFs precursor is a tetrahedral organic carboxylic acid-based MOFs precursor.

[0038] In a fourth aspect, the present invention provides an organic carboxylic acid-based MOFs precursor prepared by the above method.

[0039] In a fifth aspect, the present invention provides a method for preparing a positive electrode material for a lithium ion battery, comprising the following steps:

[0040] The organic carboxylic acid-based MOFs precursor is mixed with a lithium compound, ground, and calcined in an air atmosphere to obtain a lithium-ion battery positive electrode material.

[0041] In some embodiments, the lithium compound is at least one selected from lithium carbonate and lithium oxalate.

[0042] In some embodiments, the molar ratio of the organic carboxylic acid-based MOFs precursor to the lithium compound is 1:(1.0-1.5), such as 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5.

[0043] In some embodiments, the calcination process is divided into two stages, the calcination temperature in the first stage is 400-600°C, and the calcination time is 3-5 hours; the calcination temperature in the second stage is 750-1000°C (e.g., 750-950°C), and the calcination time is 12-24 hours. In some embodiments, the rate of heating to the calcination temperature in the first stage is 3-5°C / min; the rate of heating to the calcination temperature in the second stage is 3-5°C / min.

[0044] In a sixth aspect, the present invention provides a lithium-ion battery positive electrode material prepared by the above method.

[0045] The present invention utilizes deep eutectic solvents (DESs) to leach waste LIBs. The high-valent Ni (III), Co (III), and Mn (III / IV) in lithium-ion batteries will be reduced to divalent (Ni, Co, Mn) (II) by the reducing organic carboxylic acid components in the DESs. These metal ions will form tetrahedral organic metal framework MOFs materials with carboxylic acids and alcohols in the DESs. Since the MOFs materials are insoluble in DESs, they can be separated from the Li-containing leachate. The metal ratio in the recovered organic carboxylic acid-based MOFs precursor material is basically the same as the ratio of Ni, Co, and Mn in the original waste LIBs positive electrode material. After adding a certain amount of lithium compounds, the positive electrode material can be obtained by high-temperature sintering.

[0046] The technical solution of the present invention has the following beneficial effects:

[0047] (1) The DESs of the present invention contain a high proportion of reducing organic carboxylic acids and a relatively low proportion of alcohols, which can selectively leach Li, separate Li from the supernatant, and reduce high-valent Ni, Co, and Mn in waste lithium-ion batteries. At the same time, the oxygen atoms provided by the alcohols in the DESs and the oxygen atoms provided by the carboxyls in the DESs cooperate with cobalt, nickel, and manganese ions, and the three combine to form a new tetrahedral MOFs, that is, the present invention prepares an organic carboxylic acid-based MOFs precursor by a one-step method; and the ratio of Ni, Co, and Mn in the organic carboxylic acid-based MOFs precursor obtained by this method is almost the same as that of the original LIBs positive electrode material, which can be used to further prepare positive electrode materials. In particular, compared with other existing low eutectic solvents, the DESs of the present invention enhance the leaching effect and complexing effect on Mn.

[0048] (2) The deep eutectic solvents (DESs) used in the present invention have good environmental compatibility, low toxicity, can be recycled, have low recovery costs, simple steps, and are conducive to industrial production.

[0049] 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.

[0050] 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

[0051] Figure 1This is an XRD comparison diagram of the organic carboxylic acid-based MOFs precursor prepared in one step from the NCM523 positive electrode active material of waste lithium-ion batteries using a methanol-formic acid low eutectic solvent in Example 1 and the standard methanol formate nickel cobalt manganese MOFs precursor.

[0052] Figure 2 This is an XRD comparison diagram of the positive electrode material prepared with the organic carboxylic acid-based MOFs precursor in Example 1 and the standard NCM523 sample. DETAILED DESCRIPTION

[0053] 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.

[0054] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0055] raw material:

[0056] Methanol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); ethanol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); n-propanol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); isopropanol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); n-butanol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); ethylene glycol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); propylene glycol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); benzyl alcohol (AR, Shanghai McLean Biochemical Technology Co., Ltd.); anhydrous formic acid (FA, AR, Tianjin Komiou Reagent); oxalic acid (Shanghai McLean Biochemical Technology Co., Ltd.); terephthalate Acid (AR, Shanghai McLean 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.); trimesic 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.); lithium cobalt oxide (LCO), lithium manganate (LMO), lithium nickel oxide (LNO), NCM333, NCM523, NCM622, NCM811, NCA are all from Hebei Sinochem Lithium Battery Technology Co., Ltd.

[0057] Device:

[0058] The instrument used for XRD was Rigaku D / max2500, Japan, using Cu Kα radiation, voltage of 40 kV, and current of 300 mA. The instrument was calibrated with the standard sample that came with the instrument before use. The acquisition software was DiffracPlusXRD Commander, and the analysis software was MDI Jade 9.0. 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: 10-80°; scanning rate of 4° / min. Unless otherwise specified, the samples were not ground before testing.

[0059] The instrument used for XRF is ZSX Primus III+ X-ray fluorescence spectrometer, Rigaku, Japan. The samples were ground and crushed to less than 250 mesh and pressed into tablets for testing. The test standard was based on JY / T 0569-2020.

[0060] Detection method:

[0061] Positive electrode powder leaching rate:

[0062]

[0063] Among them, η 1 is the positive electrode powder leaching rate (%), m 0 is the mass of the positive electrode powder initially added (g), m 1 is the mass of the unleached positive electrode powder (g).

[0064] Precursor recovery rate:

[0065]

[0066] Among them, η 2 is the precursor recovery rate (%), m 2 is the actual amount of precursor recovered (g), m 3 is the theoretical recovery amount of the precursor (g).

[0067] Cathode material synthesis rate:

[0068]

[0069] Among them, η 3 is the synthesis rate of positive electrode material (%), m 2 is the actual recovered amount of precursor (g), M 1 is the relative molecular mass of the precursor; m 4 is the actual synthesis amount of positive electrode material (g), M 2 is the relative molecular mass of the positive electrode material.

[0070] Example 1

[0071] Preparation of deep eutectic solvents (DESs): Take a certain amount of methanol and formic acid, mix them in a molar ratio of 1:4, oscillate evenly at room temperature, wait until the liquid becomes uniform, clear and transparent, and keep it for use at room temperature, which is recorded as methanol-formic acid deep eutectic solvent.

[0072] Mixed leaching and precursor preparation: Take 2g of waste lithium-ion battery NCM523 positive electrode active material and 100mL of the above-mentioned methanol-formic acid low eutectic solvent at a solid-liquid ratio of 20g / L in a three-necked flask, and react at 100°C for 150min. After cooling to room temperature, take out the flask, and separate the supernatant and precipitate by centrifugation. The lithium leaching rate in the supernatant is measured to be 99.5%. Deionized water is added to the solid precipitate at a solid-liquid ratio of 5g / L, and it is hydrolyzed at 90°C for 25min. After the hydrolysis is completed, it is filtered and the filtrate is placed in a 30°C oven and dried for 8h to obtain an organic carboxylic acid-based MOFs precursor, that is, a tetrahedral organic carboxylic acid-based MOFs precursor formed by alcohol, acid and Ni, Co, and Mn ions. Its XRD pattern is shown as follows Figure 1 As shown, comparing it with the standard formic acid methanol nickel cobalt manganese MOFs precursor diffraction pattern shows that the two are highly similar and the peak shapes are basically consistent.

[0073] At the end of the experiment, according to the above calculation method, the positive electrode material leaching rate was 99.8%, and the precursor recovery rate was 99.7%.

[0074] The supernatant after centrifugation was re-added with 2 g of NCM523 positive electrode active material and the above-mentioned methanol-formic acid low eutectic solvent was added to 100 mL, the solid-liquid ratio was maintained at 20 g / L, and the leaching experiment was continued at 100 ° C and 150 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 DESs, the leaching cycle could be continued, and the above-mentioned mixed leaching and precursor preparation steps were repeated.

[0075] Preparation of positive electrode material: The dried organic carboxylic acid-based MOFs precursor and lithium oxalate were mixed evenly at a molar ratio of 1:1.1, ground in a mortar, and placed in a muffle furnace. The temperature was programmed to rise to 550°C at 5°C / min and kept at this temperature for 5h, then raised to 950°C at 5°C / min and kept at this temperature for 12h. After cooling to room temperature in the furnace, a positive electrode material for a ternary lithium-ion battery was obtained (the synthesis rate of the positive electrode material was 99.4%). Its XRD pattern is shown in the figure below. Figure 2 As shown, compared with the diffraction pattern of the standard NCM523 sample (PDF#97-029-1342), it shows that the precursor directly prepared by DESs 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.

[0076] The XRF test data are shown in Table 1.

[0077] Table 1 Element ratios in ternary MOFs precursors made from waste lithium-ion battery NCM523 and DES leaching

[0078]

[0079] Example 2-11

[0080] Each step of Examples 2-11 is carried out according to the method of Example 1, and the differences are shown in Table 2. The element ratios in the cathode material of waste lithium batteries and the ternary MOFs precursor are shown in Table 3 (XRF test data).

[0081] Table 2 Composition and leaching effect of DESs in Examples 2-11

[0082]

[0083] Table 3 Element ratios in the waste lithium battery positive electrode materials and ternary MOFs precursors of Examples 2-11

[0084]

[0085]

[0086] Comparative Example 1

[0087] Preparation of deep eutectic solvents (DESs): Take a certain amount of choline chloride and ethylene glycol, mix them in a molar ratio of 1:2, put them into a single-necked flask and heat them in a 90°C water bath for 120 minutes. When the liquid becomes clear and transparent, take it out and put it into a 90°C oven for use, which is recorded as choline chloride-ethylene glycol deep eutectic solvent.

[0088] Mixed leaching: 2 g of NCM523 positive electrode active material of waste lithium-ion battery and 100 mL of the above-mentioned choline chloride-ethylene glycol low eutectic solvent are mixed in three flasks at a solid-liquid ratio of 20 g / L, reacted at 120°C for 240 min, cooled to about 50°C, centrifuged at 8000 r / min, separated the supernatant and the precipitate, and the metal ions in the waste lithium battery are leached into the supernatant.

[0089] Precursor preparation: Take the supernatant and add sodium carbonate with a molar ratio of 1.05-1.5 times the leached metal ions to co-precipitate Ni, Co, and Mn ternary precursors to achieve separation from Li. Ni, Co, and Mn co-precipitated with sodium carbonate are rinsed with ethanol and placed in a 70°C oven to dry for later use.

[0090] Preparation of positive electrode material: The Ni, Co, and Mn ternary precursors co-precipitated with sodium carbonate are uniformly mixed with lithium carbonate in a molar ratio of 1:1.1. In a muffle furnace, the temperature is programmed to rise to 450°C at 3°C / min and kept constant for 3 hours, then raised to 750°C at 3°C / min and kept constant for 6 hours. Cool to room temperature with the furnace to obtain a ternary lithium-ion battery positive electrode material. Analysis of results: Although Comparative Example 1 is a common method for DESs leaching, it is fundamentally different from the embodiment in principle. Comparative Example 1 treats waste positive electrode powder and leaches metal ions into the DESs solution. After the reaction is completed, the precursor cannot be generated in one step. Additional substances need to be added to precipitate the metal ions to prepare MOFs precursors by coprecipitation.

[0091] Comparative Example 2

[0092] Preparation of deep eutectic solvents (DESs): Take a certain amount of methanol and formic acid, mix them in a molar ratio of 4:1, oscillate evenly at room temperature, wait until the liquid becomes uniform, clear and transparent, and keep it for use at room temperature, which is recorded as methanol-formic acid deep eutectic solvent.

[0093] Mixed leaching and precursor preparation: 2g of waste lithium-ion battery NCM523 positive electrode active material and 100mL of the above-mentioned methanol-formic acid low eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 20g / L, and reacted at 100°C for 150min. After cooling to room temperature, the flask was taken out, and the supernatant and the precipitate were separated by centrifugation. The lithium leaching rate in the supernatant was measured to be 57.8%. Deionized water was added to the solid precipitate with a solid-liquid ratio of 5g / L, and hydrolyzed at 90°C for 25min. After the hydrolysis was completed, the filtrate was placed in a 30°C oven and dried for 8h to obtain an organic carboxylic acid-based MOFs precursor. According to the above calculation method, the positive electrode material leaching rate was 52.3% and the precursor recovery rate was 51.89%.

[0094] Preparation of positive electrode material: The dried organic carboxylic acid-based MOFs precursor and lithium oxalate were mixed evenly at a molar ratio of 1:1.1, ground in a mortar, and placed in a muffle furnace. The temperature was programmed to rise to 550°C at 5°C / min and kept for 5h, then raised to 950°C at 5°C / min and kept for 12h. The mixture was cooled to room temperature in the furnace to obtain a positive electrode material for a ternary lithium-ion battery (the synthesis rate of the positive electrode material was 50.2%).

[0095] The XRF test data are shown in Table 4.

[0096] Table 4 Element ratios in ternary MOFs precursors made from waste lithium-ion battery NCM523 and DES leaching

[0097]

[0098] Results analysis: Comparative Example 2 is a DESs leaching NCM523 with a higher alcohol molar amount than a carboxylic acid molar amount. From the results analysis, it can be seen that the positive electrode material leaching rate, precursor recovery rate and positive electrode material synthesis rate are far lower than those of the DESs with a higher carboxylic acid molar amount than the alcohol molar amount in Example 1. On the one hand, it may be because the high molar amount of alcohol reduces the leaching effect of carboxylic acid on the positive electrode material of waste lithium-ion batteries; on the other hand, it may be because the ligand consumption of the generated MOFs precursor is higher than that of alcohol, resulting in less and less carboxylic acid during the reaction process, reducing the leaching effect. At the same time, the XRF data of the precursor generated by the one-step method of DESs in this comparative example shows that the proportion of the precursor NCM generated in this comparative example is poor, and the leaching effect and complexation effect on Mn are poor.

[0099] Comparative Example 3

[0100] Preparation of deep eutectic solvents (DESs): Take a certain amount of methanol and formic acid, mix them in a molar ratio of 2:1, oscillate evenly at room temperature, wait until the liquid becomes uniform, clear and transparent, and keep it for use at room temperature. This is recorded as a methanol-formic acid deep eutectic solvent.

[0101] Mixed leaching and precursor preparation: 2g of waste lithium-ion battery NCM523 positive electrode active material and 100mL of the above-mentioned methanol-formic acid low eutectic solvent were mixed in a three-necked flask at a solid-liquid ratio of 20g / L, and reacted at 100°C for 150min. After cooling to room temperature, the flask was taken out, and the supernatant and the precipitate were separated by centrifugation. The lithium leaching rate in the supernatant was measured to be 62.5%. Deionized water was added to the solid precipitate with a solid-liquid ratio of 5g / L, and hydrolyzed at 90°C for 25min. After the hydrolysis was completed, the filtrate was placed in a 30°C oven and dried for 8h to obtain an organic carboxylic acid-based MOFs precursor. According to the above calculation method, the positive electrode material leaching rate was 62.45% and the precursor recovery rate was 60.97%.

[0102] Preparation of positive electrode material: The dried organic carboxylic acid-based MOFs precursor and lithium oxalate were mixed evenly at a molar ratio of 1:1.1, ground in a mortar, and placed in a muffle furnace. The temperature was programmed to rise to 550°C at 5°C / min and kept for 5h, then raised to 950°C at 5°C / min and kept for 12h. The mixture was cooled to room temperature in the furnace to obtain a positive electrode material for a ternary lithium-ion battery (the synthesis rate of the positive electrode material was 58.7%).

[0103] The XRF test data are shown in Table 5.

[0104] Table 5 Element ratios in ternary MOFs precursors made from waste lithium-ion battery NCM523 and DES leaching

[0105]

[0106] Result analysis: Comparative Example 3 is a DESs leaching NCM523 with a molar amount of alcohol slightly higher than the molar amount of carboxylic acid, but the molar amount of alcohol in DESs is lower than the molar amount of alcohol in DESs in Comparative Example 2. From the result analysis, it can be seen that the positive electrode material leaching rate, precursor recovery rate and positive electrode material synthesis rate are all lower than the DESs in Example 1 with a molar amount of carboxylic acid higher than the molar amount of alcohol, but slightly higher than the experimental data in Comparative Example 2, which shows that the higher the molar amount of alcohol, the more unfavorable it is for the leaching reaction. At the same time, the XRF data results of the precursor generated by the one-step method of the DESs in this comparative example show that compared with the precursor generated by the one-step method of the DESs in Example 1, the complexing effect and leaching effect of this comparative example on Mn are poor.

[0107] The above embodiments are only used to illustrate that within the scope of the spirit and substance defined by the claims, the technical solutions recorded in the above embodiments may be modified, or part or all of the technical features therein may be replaced by equivalents; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A deep eutectic solvent, comprising: Alcohols; and reducing organic carboxylic acids; The molar ratio of the alcohol substance to the reducing organic carboxylic acid is 1:(1-10).

2. The deep eutectic solvent according to claim 1, It is characterized in that The alcohol substance is selected from at least one of monohydric fatty alcohols and polyhydric fatty alcohols, preferably at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, and glycerol; The reducing organic carboxylic acid is selected from at least one of a monovalent aliphatic carboxylic acid, a polyvalent aliphatic carboxylic acid, an alicyclic carboxylic acid, and an aromatic carboxylic acid, wherein the aliphatic carboxylic acid, the alicyclic carboxylic acid, and the aromatic carboxylic acid are optionally substituted by one or more hydroxyl groups and amino groups; Preferably, the aliphatic carboxylic acid or substituted aliphatic carboxylic acid includes: formic acid, acetic acid, lactic 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; The alicyclic carboxylic acid or substituted alicyclic carboxylic acid includes: cyclopropylacetic acid, cyclobutaneacetic acid, cyclopentaneacetic acid, cyclohexaneacetic acid, 1,3,5-cyclohexanetric acid; The aromatic carboxylic acid or substituted aromatic carboxylic acid includes: benzoic acid, phthalic acid, terephthalic acid, trimesic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 2,6-naphthalene dicarboxylic acid; More preferably, the reducing organic carboxylic acid is at least one selected from formic acid, acetic acid, oxalic acid, trimesic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, and 1,3,5-cyclohexanetricarboxylic acid.

3. The method for preparing the deep eutectic solvent according to claim 1 or 2, wherein The following steps are involved: At 15 to 30° C., preferably 20 to 25° C., the alcohol substance and the reducing organic carboxylic acid are mixed in proportion until the mixture becomes clear and transparent, thereby obtaining the deep eutectic solvent; Preferably, mixing can be performed by stirring or shaking.

4. A method for preparing an organic carboxylic acid-based MOFs precursor, using waste lithium-ion battery positive electrode materials as raw materials, The following steps are involved: The low eutectic solvent according to claim 1 or 2 or the low eutectic solvent prepared by the preparation method according to claim 3 and the waste lithium-ion battery positive electrode material are mixed and heated for leaching, and the solid-liquid separation is performed to obtain an organic carboxylic acid-based MOFs solid precipitate and a Li-containing leachate. The organic carboxylic acid-based MOFs solid precipitate is hydrolyzed, filtered, and the filtrate is dried to obtain an organic carboxylic acid-based MOFs precursor.

5. The method for preparing an organic carboxylic acid-based MOFs precursor according to claim 4, It is characterized in that The waste lithium-ion battery positive electrode material is a positive electrode powder obtained by pre-processing waste lithium-ion battery positive electrode sheets including discharging, disassembling and crushing; Preferably, the cathode material of waste lithium-ion batteries includes lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide.

6. The method for preparing an organic carboxylic acid-based MOFs precursor according to claim 4, It is characterized in that The leaching temperature is 60°C to 140°C, preferably 70°C to 100°C; the leaching time is 30min to 300min, preferably 60min to 200min; Preferably, the solid-to-liquid ratio of the waste lithium-ion battery positive electrode material and the low eutectic solvent is 15 g / L to 65 g / L; Preferably, the method further comprises a cyclic leaching step: adding new waste lithium-ion battery positive electrode material to the Li-containing leachate, and each time additionally adding a low eutectic solvent to maintain a constant solid-liquid ratio.

7. The method for preparing an organic carboxylic acid-based MOFs precursor according to claim 4, It is characterized in that The organic carboxylic acid-based MOFs solid precipitation hydrolysis comprises: hydrolyzing the organic carboxylic acid-based MOFs solid precipitation in water at 60-100° C. for 15-45 minutes; preferably, the solid-liquid ratio of the organic carboxylic acid-based MOFs solid precipitation to water is 1-10 g / L; Preferably, the conditions for drying the filtrate are: temperature of 30-60°C and time of 2-12h; Preferably, the organic carboxylic acid-based MOFs precursor obtained by the method for preparing an organic carboxylic acid-based MOFs precursor is a tetrahedral organic carboxylic acid-based MOFs precursor.

8. An organic carboxylic acid-based MOFs precursor prepared by the method according to any one of claims 4 to 7.

9. A method for preparing a positive electrode material for a lithium ion battery, The following steps are involved: The organic carboxylic acid-based MOFs precursor of claim 8 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 oxalate; Preferably, the molar ratio of the organic carboxylic acid-based MOFs precursor to the lithium compound is 1:(1.0-1.5); Preferably, the calcination process is divided into two stages, the calcination temperature in the first stage is 400-600°C, and the calcination time is 3-5h; the calcination temperature in the second stage is 750-1000°C (preferably 750-950°C), and the calcination time is 12-24h; preferably, the rate of heating to the calcination temperature of the first stage is 3-5°C / min; the rate of heating to the calcination temperature of the second stage is 3-5°C / min.

10. The lithium ion battery positive electrode material prepared by the method of claim 9.

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