Deep eutectic solvent and method for repairing positive electrode material of retired lithium ion battery

Abstract

The application provides a deep eutectic solvent and a method for repairing a positive electrode material of a retired lithium ion battery, and the deep eutectic solvent is prepared by a method comprising the following process: raw materials comprising an alcohol compound, a cobalt source and a lithium source in a molar ratio of (1-5):(0.5-1):(0.5-1) are reacted at 80-110 DEG C until the reaction system is transparent and the viscosity is not less than 95 MPa.s, and the deep eutectic solvent is obtained. The deep eutectic solvent can repair the positive electrode material of the retired lithium ion battery, and the repaired positive electrode material can be used in a lithium ion battery, so that the capacity, rate performance and cycle performance of the battery can be improved, and the regeneration of the positive electrode material of the retired lithium ion battery is realized.

Description

Technical Field

[0001] This invention belongs to the field of battery repair technology, and relates to a deep eutectic solvent, and more particularly to a deep eutectic solvent and a method for repairing the cathode material of retired lithium-ion batteries. Background Technology

[0002] With the increasing popularity of electric vehicles, wearable devices, and consumer electronics, global demand for lithium-ion batteries is constantly rising. However, at the same time, a large number of lithium-ion batteries are gradually entering their retirement phase. It is estimated that from 2023 to 2025, the number of retired new energy vehicles in China will reach 1.273 million, with the amount of retired power batteries reaching 63.8 GWh (530,000 tons). Therefore, the repair and utilization of retired batteries is urgent. Currently, the main methods for extracting metals (Co, Li, Ni) are pyrometallurgy and hydrometallurgy. The former has disadvantages such as high energy consumption and complex operation; the latter has high energy consumption, harsh conditions, and generates toxic substances during production, seriously polluting the environment. In the context of a sustainable circular economy, it is necessary to explore greener routes for repairing end-of-life lithium-ion batteries.

[0003] Taking lithium cobalt oxide batteries as an example, during the charging process, as the Li... + When lithium cobalt oxide is extracted, a portion of the material's crystal structure undergoes irreversible destruction. + It is difficult to perform fully reversible insertion / extraction, resulting in some capacity loss; and with the development of Li + As the oxygen continuously escapes, the lattice oxygen activity on the lithium cobalt oxide surface is further enhanced. When the lattice oxygen activity increases to a certain level, it will escape in the form of O2. After the gas escapes, the stability of Co atoms deteriorates, and they dissolve and dissolve into the electrolyte. The presence of lithium and cobalt has a crucial impact on the rate performance and cycle performance of the battery. Replenishing lithium and cobalt on the lithium cobalt oxide cathode material after capacity decay can replenish the lithium and cobalt elements in the lithium cobalt oxide and repair its crystal structure, thereby restoring the charge and discharge capacity. Summary of the Invention

[0004] To address the aforementioned deficiencies, this invention provides a deep eutectic solvent that can repair retired lithium-ion battery cathode materials. Using the repaired cathode materials in lithium-ion batteries can improve the battery's capacity, rate performance, and cycle performance, thereby achieving the regeneration of retired lithium-ion battery cathode materials.

[0005] This invention provides a method for repairing cathode materials of retired lithium-ion batteries. Since the method uses the aforementioned deep eutectic solvent, it can achieve a better repair effect. The repaired cathode material can be used to make lithium-ion batteries, which can improve their capacity, rate performance and cycle performance, thereby achieving effective repair of cathode materials of retired lithium-ion batteries.

[0006] This invention provides a deep eutectic solvent, which is prepared by a method comprising the following steps:

[0007] The raw materials, including an alcohol compound, a cobalt source, and a lithium source in a molar ratio of (1–5):(0.5–1):(0.5–1), are reacted at 80–110 °C until the reaction system is transparent and the viscosity is not less than 95 MPa·s, to obtain the deep eutectic solvent.

[0008] Furthermore, the viscosity of the reaction system is 100–800 MPa·s.

[0009] Furthermore, the molar ratio of the alcohol compound, cobalt source, and lithium source is (2.5–4):(0.7–0.9):(0.7–0.9).

[0010] Furthermore, the alcohol compounds include at least one of glycerol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, and sorbitol;

[0011] And / or, the cobalt source includes at least one of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt nitrate;

[0012] And / or, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium borohydride.

[0013] Furthermore, the alcohol compound is at least one of glycerol, ethylene glycol, and 1,2-propanediol; the cobalt source is at least one of cobalt oxide and cobalt nitrate; and the lithium source is at least one of lithium carbonate and lithium hydroxide.

[0014] The molar ratio of the alcohol compound, cobalt source, and lithium source is (2.5–3.5):(0.7–0.8):(0.7–0.8).

[0015] This invention provides a method for repairing the cathode material of retired lithium-ion batteries, using the deep eutectic solvent described in any of the above-mentioned methods to repair the cathode material of retired lithium-ion batteries.

[0016] Furthermore, this includes the following steps:

[0017] The deep eutectic solvent is mixed with the cathode material to be repaired and reacted at 80-150°C for 1-3 hours. After solid-liquid separation, a liquid phase and a solid phase are obtained. The solid phase is then annealed to obtain the repaired lithium-ion battery cathode material.

[0018] Furthermore, the cathode material to be repaired is a decommissioned lithium cobalt oxide cathode material, and the chemical composition of the decommissioned lithium cobalt oxide cathode material is as shown in Formula 1.

[0019] Li x Co y O2 type 1

[0020] In Equation 1, 0 < x ≤ 0.6 and 0 < y ≤ 0.6.

[0021] Furthermore, the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(10-50).

[0022] Furthermore, the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(30-40).

[0023] The deep eutectic solvent of this invention is obtained by reacting hydrogen bond donors, including alcohol compounds, and hydrogen bond acceptors, including cobalt and lithium sources, at 80–110°C until the reaction system is transparent and the viscosity is not less than 95 MPa·s. The molar ratio of alcohol compounds, cobalt sources, and lithium sources is (1–5):(0.5–1):(0.5–1). This results in a deep eutectic solvent that can effectively repair retired lithium-ion battery cathode materials, significantly increasing the lithium and cobalt ion content in the cathode material. When the repaired cathode material is used to make lithium-ion batteries, it can improve the battery's capacity, rate performance, and cycle performance, thereby realizing the regeneration of retired lithium-ion battery cathode materials. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] The first aspect of this invention provides a deep eutectic solvent, which is prepared by a method comprising the following steps:

[0026] The raw materials, including alcohols, cobalt sources, and lithium sources in a molar ratio of (1–5):(0.5–1):(0.5–1), are reacted at 80–110 °C until the reaction system is transparent and the viscosity is not less than 95 MPa·s, thus obtaining a deep eutectic solvent.

[0027] In this invention, the cobalt source refers to the raw material that provides cobalt, and the lithium source refers to the raw material that provides lithium. As long as the target element (cobalt or lithium) is present, it is within the scope of this invention.

[0028] The viscosity in this invention can be tested using a rotational viscometer: A sample of the reaction system is extracted, and a conical rotor with a diameter of 25–50 mm is immersed in the sample, ensuring the rotor is completely submerged and free of air bubbles. Measurement is performed at an angular velocity of 10 rad / s under constant temperature and standard atmospheric pressure. The test temperature is the reaction temperature of the reaction system. Equilibrium is required for 10–30 minutes during the measurement process, during which the viscosity change is observed. Once the viscosity stabilizes, the viscosity value is read to obtain the viscosity of the reaction system.

[0029] This invention does not specifically limit the types of alcohol compounds, cobalt sources, and lithium sources.

[0030] This invention does not specifically limit the sources of alcohol compounds, cobalt sources, and lithium sources; products prepared using commercially available products or conventional preparation methods known to those skilled in the art can be used.

[0031] The deep eutectic solvent of this invention is obtained by reacting raw materials, including hydrogen bond donor alcohol compounds and hydrogen bond acceptors cobalt and lithium sources, at 80–110°C until the reaction system is transparent and the viscosity is not less than 95 MPa·s. The molar ratio of alcohol compounds, cobalt sources, and lithium sources is controlled to be (1–5):(0.5–1):(0.5–1). This results in a deep eutectic solvent that can effectively increase the content of lithium ions and cobalt ions in the cathode material when repairing retired lithium-ion battery cathode materials. When the repaired cathode material is used in lithium-ion batteries, it can significantly improve the battery's capacity, rate performance, and cycle performance, thereby achieving efficient regeneration of retired cathode materials. Based on this phenomenon, the inventors analyzed the deep eutectic solvent and concluded that it might be due to the following: Hydrogen bond donor alcohol compounds and hydrogen bond acceptors cobalt and lithium sources react at specific temperatures and molar ratios. When the reaction system is transparent and the viscosity is not less than 95 MPa·s, a complex is generated. This complex can form hydrogen bonds with oxygen atoms on the surface of the cathode material to be repaired, tightly adsorbing the deep eutectic solvent onto the surface of the cathode material. This promotes the migration of lithium and cobalt ions from the complex to the surface and interior of the cathode material. Due to the lack of lithium and cobalt ions in the cathode material, a large number of vacancies or defects are formed inside and on the surface of the cathode material. Oxygen anions around these vacancies or defects combine with the migrating cobalt and lithium ions to form ionic bonds, stabilizing them in the cathode material and thus achieving a good repair effect. This increases the lithium and cobalt ion content in the retired cathode material. Using the repaired cathode material in lithium-ion batteries can give the batteries higher capacity, rate performance, and cycle performance, realizing the regeneration of retired lithium-ion battery cathode materials.

[0032] Furthermore, the alcohol compounds used in the deep eutectic solvent of this invention have lower toxicity and corrosivity compared to amines and organic acids. This not only effectively avoids the damage of organic acids to the structure of lithium-ion battery cathode materials (such as lithium cobalt oxide), but also provides higher safety and avoids secondary pollution. At the same time, the deep eutectic solvent of this invention can also reduce the reaction temperature and reaction time in the repair process of retired lithium-ion battery cathode active materials, improve production efficiency, and reduce energy consumption.

[0033] In one specific embodiment, the viscosity of the reaction system is 100–800 MPa·s. When the viscosity of the reaction system is within the aforementioned range, the hydrogen bond donor and hydrogen bond acceptor react more fully, and the resulting complex can interact better with the cathode material to be repaired. This allows lithium and cobalt ions in the complex to migrate more easily into the cathode material to be repaired, further increasing the content of lithium and cobalt ions in the cathode material and improving the repair effect.

[0034] In one specific embodiment, the molar ratio of the alcohol compound, cobalt source, and lithium source is (2.5–4):(0.7–0.9):(0.7–0.9). Within this range, the alcohol compound, lithium source, and cobalt source can better synergize and cooperate, allowing the resulting complex to interact better with the cathode material to be repaired, further promoting the migration of lithium and cobalt ions. This results in a higher lithium and cobalt ion content in the cathode material, improving the repair effect.

[0035] In one specific embodiment, the alcohol compound includes at least one of glycerol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, and sorbitol;

[0036] And / or, the cobalt source includes at least one of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt nitrate;

[0037] And / or, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium borohydride.

[0038] When the organic alcohol and / or cobalt source and / or lithium source include at least one of the aforementioned compounds, the reaction time can be further shortened and the reaction temperature lowered, thereby improving the remediation efficiency and reducing energy consumption. When the aforementioned three types of compounds each include two or more compounds, the present invention does not specifically limit the ratio between the various compounds, as long as the molar ratio between the alcohol compound, cobalt source and lithium source satisfies (1-5):(0.5-1):(0.5-1).

[0039] In one specific embodiment, the alcohol compound is at least one selected from glycerol, ethylene glycol, and 1,2-propanediol; the cobalt source is at least one selected from cobalt oxide and cobalt nitrate; and the lithium source is at least one selected from lithium carbonate and lithium hydroxide. The molar ratio of the alcohol compound, cobalt source, and lithium source is (2.5–3.5):(0.7–0.8):(0.7–0.8). This further enhances the repair effect of the deep eutectic solvent on the cathode material to be repaired, resulting in a cathode material with more cobalt and lithium ions. When the repaired cathode material is used in a lithium-ion battery, the battery exhibits higher capacity, rate performance, and cycle performance.

[0040] A second aspect of this invention provides a method for preparing a deep eutectic solvent, comprising the following steps:

[0041] Under conditions of 80–110 °C, raw materials including alcohol compounds, cobalt source and lithium source are mixed and reacted until the reaction system is transparent and the viscosity is not less than 95 MPa·s, to obtain a deep eutectic solvent; wherein, the molar ratio of alcohol compound, cobalt source and lithium source is (1–5):(0.5–1):(0.5–1).

[0042] Furthermore, stirring is performed during the reaction, preferably at a speed of 200–500 r / min. Within this range, the reaction can be made more complete.

[0043] Furthermore, the reaction time is preferably 0.2 to 2 hours.

[0044] The deep eutectic solvent prepared by the above method can increase the content of lithium ions and cobalt ions in the repaired cathode material of retired lithium-ion batteries. Using this cathode material in lithium-ion batteries can improve the battery's capacity, rate performance, and cycle performance. At the same time, no toxic and corrosive solvents are used in the repair process, which has high safety.

[0045] The third aspect of this invention provides a method for repairing the cathode material of a retired lithium-ion battery, using a deep eutectic solvent as described in the first aspect to repair the cathode material. This deep eutectic solvent is obtained by reacting hydrogen bond donors, including alcohol compounds, and hydrogen bond acceptors, including cobalt and lithium sources, at 80–110°C. The reaction system is transparent and has a viscosity not less than 95 MPa·s, and the molar ratio of alcohol compounds, cobalt source, and lithium source is (1–5):(0.5–1):(0.5–1). Therefore, using this deep eutectic solvent to repair the cathode material of a retired lithium-ion battery can effectively increase the content of lithium ions and cobalt ions in the repaired cathode material, achieving a better repair effect. Using the repaired cathode material to manufacture a lithium-ion battery can effectively improve the battery's capacity, rate performance, and cycle performance, thereby achieving efficient regeneration of the retired cathode material.

[0046] In one specific implementation, the following steps are included:

[0047] The deep eutectic solvent is mixed with the cathode material to be repaired and reacted at 80-150℃ for 1-3 hours. After solid-liquid separation, liquid and solid phases are obtained. The solid phase is then annealed to obtain the repaired lithium-ion battery cathode material.

[0048] Furthermore, stirring is performed during the reaction, preferably at a speed of 200–500 r / min. Within this range, the reaction can be made more complete, further improving the repair effect.

[0049] This invention does not specify the method of solid-liquid separation, as long as the solid and liquid phases in the reaction system can be separated. For example, separation can be achieved by vacuum filtration.

[0050] It is understandable that the solid phase obtained after solid-liquid separation still needs to be washed and dried.

[0051] The present invention does not specify the washing method; it is sufficient to wash away the residual solvent in the solid phase. For example, the solid phase can be washed with deionized water, and the washing number should not be less than 3 times.

[0052] This invention does not specify the drying temperature and time; it is sufficient to evaporate the moisture from the washed solid phase. For example, the drying temperature is 80–120°C and the drying time is 2–8 hours.

[0053] Furthermore, the annealing temperature is preferably 600–900°C, and the annealing time is preferably 2–4 hours.

[0054] The present invention does not specifically limit the preparation method of the cathode material to be repaired. For example, it can be prepared by including the following steps:

[0055] The cathode material is obtained by disassembling and peeling off retired lithium-ion batteries. The cathode material is then calcined at 300-600℃ for 2-10 hours to fully remove the binder, thus obtaining the cathode material to be repaired.

[0056] The above-mentioned method for repairing the cathode material of retired lithium-ion batteries can effectively increase the content of lithium ions and cobalt ions in the cathode material to be repaired, achieving a better repair effect. The repaired cathode material can be used to make lithium-ion batteries, which can effectively improve the battery's capacity, rate performance and cycle performance, thereby realizing the regeneration of the cathode material of retired lithium-ion batteries.

[0057] In one specific embodiment, the cathode material to be repaired is a decommissioned lithium cobalt oxide cathode material, and the chemical composition of the decommissioned lithium cobalt oxide cathode material is as shown in Formula 1.

[0058] Li x Co y O2 type 1

[0059] In Equation 1, 0 < x ≤ 0.6 and 0 < y ≤ 0.6. When the cathode material to be repaired is a decommissioned lithium cobalt oxide cathode material with the chemical composition of Equation 1, it is more conducive to the migration of lithium ions and cobalt ions in the composite to the surface and interior of the cathode material to be repaired, thereby further improving the repair effect and enabling the battery to have higher capacity, rate performance and cycle performance.

[0060] In one specific embodiment, the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(10-50). The solid-liquid ratio in this invention refers to the volume ratio of the cathode material to be repaired to the deep eutectic solvent, where the mass unit is g and the volume unit is mL. Within this range, the deep eutectic solvent can interact better with the cathode material to be repaired, allowing the reaction to proceed more fully, thereby further increasing the lithium-ion and cobalt-ion content in the repaired lithium-ion battery cathode material.

[0061] In one specific embodiment, the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(30-40). Within this range, the degree of reaction between the deep eutectic solvent and the cathode material to be repaired can be further increased, resulting in the repaired cathode material containing more lithium ions and cobalt ions, thereby achieving a higher repair effect.

[0062] In one specific embodiment, adding a solvent to the system after the reaction is complete to dilute the intermediate system can improve the solid-liquid separation effect and reduce the loss of positive electrode material during solid-liquid separation.

[0063] The present invention does not specifically limit the type of solvent, as long as the solvent is miscible with the system after the reaction. For example, the solvent includes at least one of acetone, methanol, acetonitrile, and deionized water.

[0064] The present invention does not specifically limit the source of the solvent, and can use commercially available products known to those skilled in the art or products prepared by conventional preparation methods.

[0065] Furthermore, the liquid phase obtained after solid-liquid separation is recovered through distillation to obtain the recovered deep eutectic solvent. This enables the recycling of the deep eutectic solvent, which not only reduces costs but also avoids secondary pollution.

[0066] It is understandable that when distillation is used to recover the liquid phase, the boiling point of the added solvent should not exceed 100℃. This is beneficial for the evaporation of the solvent during the distillation process, and also prevents the organic alcohols in the liquid phase from being evaporated during the distillation process, thus avoiding damage to the composition of the recovered deep eutectic solvent and affecting the remediation effect.

[0067] The deep eutectic solvent of the present invention will be described in detail below through specific embodiments.

[0068] Example 1

[0069] (1) Preparation of deep eutectic solvent: Glycerol, lithium hydroxide and cobalt oxide were mixed in a molar ratio of 3:0.8:0.7, placed in an oil bath and stirred at a speed of 350 r / min. The temperature was raised to 100℃ and reacted at this temperature for 30 min to form a clear and transparent viscous liquid with a viscosity of 750 MPa·s, thus obtaining the deep eutectic solvent.

[0070] (2) Preparation of cathode material to be repaired: The retired lithium cobalt oxide battery was disassembled and stripped to obtain cathode material, which was then placed in a tube furnace and calcined at 350°C for 5 hours to obtain a material with the chemical composition Li. 0.5 Co 0.5 O2 cathode material to be repaired;

[0071] (3) Repair of retired lithium-ion battery cathode material: The cathode material to be repaired is mixed with a deep eutectic solvent at a solid-liquid ratio of 1:35, and stirring is started at a stirring speed of 350 r / min. The mixture is reacted at 100℃ for 2 h. 30 mL of acetone is added to the reaction system, and after uniform mixing, the mixture is centrifuged to obtain a solid phase and a liquid phase. The solid phase is washed three times with deionized water and dried at 100℃ for 2 h. Then it is annealed at 850℃ for 2 h to obtain the repaired cathode material.

[0072] (4) The above liquid phase is recovered by distillation to obtain the recovered deep eutectic solvent.

[0073] Example 2

[0074] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), 1,2-propanediol, lithium carbonate, and cobalt nitrate are mixed in a molar ratio of 3:0.7:0.8, placed in an oil bath and stirred at a stirring speed of 400 r / min. The temperature is raised to 100°C and reacted at this temperature for 2 hours to form a clear and transparent viscous liquid with a viscosity of 650 MPa·s, thus obtaining a deep eutectic solvent.

[0075] In step (2), the retired ternary lithium-ion battery is disassembled and stripped to obtain the positive electrode material, which is then placed in a tube furnace and calcined at 350°C for 5 hours to obtain a material with the chemical composition LiNi. 0.3 Co 0.1 Mn 0.2 O2 cathode material to be repaired;

[0076] In step (3), the reaction time is 1.5 h.

[0077] Example 3

[0078] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), glycerol is replaced with ethylene glycol, lithium hydroxide is replaced with lithium carbonate, and the molar ratio between ethylene glycol, lithium carbonate and cobalt oxide is adjusted to 3:0.8:0.8. Accordingly, the viscosity of the reaction system is 550 MPa·s.

[0079] Example 4

[0080] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 2. The difference is that in step (1), the molar ratio of 1,2-propanediol, lithium carbonate and cobalt nitrate is adjusted to 2.5:0.7:0.8, and the viscosity of the reaction system is 500 MPa·s.

[0081] Example 5

[0082] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), 1,4-butanediol, lithium hydroxide, and cobalt nitrate are mixed in a molar ratio of 3:0.8:1, placed in an oil bath and stirred at a stirring speed of 350 r / min. The temperature is raised to 110°C and reacted at this temperature for 1.5 h to form a clear and transparent viscous liquid with a viscosity of 800 MPa·s, thus obtaining a deep eutectic solvent.

[0083] In step (3), the reaction time is 1 hour.

[0084] Example 6

[0085] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), 1,2-propanediol, lithium carbonate, and cobalt carbonate are mixed in a molar ratio of 4:1:0.8, placed in an oil bath and stirred at a stirring speed of 500 r / min. The temperature is raised to 90°C and reacted at this temperature for 2 hours to form a clear and transparent viscous liquid with a viscosity of 750 MPa·s, thus obtaining a deep eutectic solvent.

[0086] In step (3), the reaction time is 2 hours.

[0087] Example 7

[0088] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), glycerol is replaced with ethylene glycol, lithium hydroxide is replaced with lithium carbonate, cobalt oxide is replaced with cobalt hydroxide, and the molar ratio of ethylene glycol, lithium carbonate, and cobalt hydroxide is adjusted to 3.5:0.8:0.8. Accordingly, the viscosity of the reaction system is 700 MPa·s.

[0089] Example 8

[0090] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), sorbitol, lithium hydroxide, and cobalt carbonate are mixed in a molar ratio of 3:0.8:0.6, placed in an oil bath, and stirred at a stirring speed of 500 r / min. The temperature is raised to 110°C and reacted at this temperature for 1.5 h to form a clear and transparent viscous liquid with a viscosity of 700 MPa·s, thus obtaining a deep eutectic solvent.

[0091] In step (3), the reaction time is 3 hours.

[0092] Example 9

[0093] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Embodiment 1, except that in step (2), the chemical composition of the cathode material to be repaired is changed to Li. 0.4 Co 0.5 O2;

[0094] In step (3), the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is changed to 1:10, the reaction temperature is adjusted to 80℃, and the time is 3h.

[0095] Example 10

[0096] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Embodiment 1, except that in step (2), the chemical composition of the cathode material to be repaired is changed to Li. 0.4 Co 0.4 O2;

[0097] In step (3), the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is changed to 1:50, the reaction temperature is adjusted to 150℃, and the time is 1h.

[0098] Example 11

[0099] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (1), the preparation conditions of the deep eutectic solvent are changed. Specifically, the reaction temperature is adjusted to 80°C, and the molar ratio of glycerol, lithium hydroxide and cobalt oxide is adjusted to 4.5:0.9:0.8 to obtain a reaction system with a viscosity of 900 MPa·s, thus obtaining the deep eutectic solvent.

[0100] Example 12

[0101] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 7. The difference is that in step (1), the molar ratio between ethylene glycol, lithium carbonate and cobalt hydroxide is adjusted to 1:0.7:0.7; correspondingly, the viscosity of the reaction system is 450 MPa·s.

[0102] Example 13

[0103] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Example 1. The difference is that in step (3), the reaction temperature is adjusted to 70°C and the reaction time is adjusted to 3.5h.

[0104] Example 14

[0105] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in Embodiment 1, except that in step (2), the chemical composition of the cathode material to be repaired is Li 0.7 Co 0.8 O2.

[0106] Example 15

[0107] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in embodiment 1. The difference is that in step (3), the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is changed to 1:60.

[0108] Example 16

[0109] The method for repairing the cathode material of retired lithium-ion batteries in this embodiment is basically the same as that in embodiment 1. The difference is that in step (3), the solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is changed to 1:15.

[0110] Comparative Example 1

[0111] In this comparative example, the cathode material is an unrepaired lithium cobalt oxide cathode material (Li) to be repaired. 0.5 Co 0.5 O2.

[0112] Comparative Example 2

[0113] The cathode material in this comparative example is an unrepaired ternary cathode material to be repaired.

[0114] Comparative Example 3

[0115] In this comparative example, the cathode material is an unrepaired lithium cobalt oxide cathode material (Li) to be repaired. 0.4 Co 0.5 O2.

[0116] Comparative Example 4

[0117] In this comparative example, the cathode material is an unrepaired lithium cobalt oxide cathode material (Li) to be repaired. 0.4 Co 0.4 O2.

[0118] Comparative Example 5

[0119] In this comparative example, the cathode material is an unrepaired lithium cobalt oxide cathode material (Li) to be repaired. 0.7 Co 0.8 O2.

[0120] Comparative Example 6

[0121] The method for repairing the cathode material of retired lithium-ion batteries in this comparative example is basically the same as that in Example 1. The difference is that in step (1), the molar ratio between ethylene glycol, lithium carbonate and cobalt hydroxide is adjusted to 1:2:2, and the viscosity of the reaction system is 90 MPa·s.

[0122] Comparative Example 7

[0123] The method for repairing the cathode material of retired lithium-ion batteries in this comparative example is basically the same as that in Example 1. The difference is that in step (1), the reaction temperature is adjusted to 70°C, and the viscosity of the reaction system is 860 MPa·s.

[0124] Comparative Example 8

[0125] The method for repairing the cathode material of retired lithium-ion batteries in this comparative example is basically the same as that in Example 1, except that in step (1), glycerol is replaced with citric acid, a reducing organic acid.

[0126] Comparative Example 9

[0127] The method for repairing the cathode material of retired lithium-ion batteries in this comparative example is basically the same as that in Example 1, except that the lithium source is removed in step (1).

[0128] Comparative Example 10

[0129] The method for repairing the cathode material of retired lithium-ion batteries in this comparative example is basically the same as that in Example 1, except that the cobalt source is removed in step (1).

[0130] Test case

[0131] 1. The cathode materials prepared in the above examples and comparative examples were dissolved in 30 mL of 10% hydrochloric acid solution to obtain lithium cobalt solution and lithium nickel manganese cobalt solution. The concentrations were determined by ICP-MS, and the results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As shown in Table 1:

[0136] The content of cobalt and lithium in the repaired cathode materials in Examples 1-16 is higher than that in Comparative Examples 1-10. Therefore, it can be seen that the deep eutectic solvent of the present invention can effectively regenerate the cathode materials in retired lithium-ion batteries.

[0137] 2. The cathode materials prepared in the above examples and comparative examples are used to fabricate CR2032 coin-type lithium-ion half-cells. The specific steps are as follows:

[0138] The positive electrode materials prepared in the above examples and comparative examples were mixed with conductive agent carbon black, binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10 and solvent N-methyl-2-pyrrolidone (NMP) to form a positive electrode slurry with a solid content of 90%. The positive electrode slurry was uniformly coated on both sides of the functional surfaces of an aluminum foil with a coating density of 120 g / m². 2 After drying, rolling, and cutting, a positive electrode sheet is obtained, with a compaction density of 2.9 g / cm³. 3 A lithium metal sheet with a purity of 99.99%, a thickness of 150 μm, and a smooth, pore-free, and crack-free surface is used as the negative electrode of the half-cell. The positive electrode sheet, lithium metal sheet, porous polyethylene separator, and electrolyte are assembled into a new battery cell and sealed in a casing. The electrolyte includes lithium hexafluorophosphate (LiPF6) and anhydrous organic solvents (ethylene carbonate (EC), propylene carbonate (DMC), and dimethyl carbonate (DEC)). The concentration of LiPF6 is 1 M, and the volume ratio of EC, DMC, and DEC is 1:1:1.

[0139] The capacity, rate performance, and cycle performance of the lithium-ion batteries prepared above were tested:

[0140] (1) Capacity test

[0141] At room temperature, the half-cell was charged to 4.3V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 4.3V. After standing for 5 minutes, it was discharged to 2.5V at a constant current of 0.5C. The discharge capacity of the battery was recorded, where 1C = 160mA / g.

[0142] (2) Ratio Performance Test

[0143] Within a voltage range of 2.5–4.3 V, the sample was first subjected to 5 charge-discharge cycles at 0.05 C to activate it and stabilize its performance. Subsequently, 5 charge-discharge cycles were performed at 0.5 C, and the initial discharge specific capacity C0 was recorded. Then, 5 charge-discharge cycles were performed at current densities of 1 C, 2 C, and 3 C, respectively. Finally, a charge-discharge test was performed at 0.5 C to obtain the discharge specific capacity C1 after the cycles. The ratio of C1 to C0 was used to characterize the rate performance.

[0144] (3) Cyclic performance test

[0145] The half-cell was placed in a 45℃ constant temperature chamber. First, it was charged at a constant current of 0.5C to 4.3V, then charged at a constant voltage of 4.3V until the cutoff current was 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.5C to 2.5V. The initial capacity C3 was recorded. Then, a charge-discharge cycle of 0.5C charging / discharging was performed. After 200 cycles, the capacity C4 was recorded. The cycle capacity retention rate is the ratio of C4 to C3. Where 1C = 160mA / g.

[0146] The test results are shown in Table 2.

[0147] Table 2

[0148]

[0149]

[0150] As shown in Table 2:

[0151] Using the repaired cathode materials from Examples 1-16 in lithium-ion batteries can effectively improve the battery's capacity, rate performance, and cycle capacity retention. In these examples, the highest capacity reached 152.6 mAh / g, the highest C1 to C0 ratio was 95.65%, and the highest cycle capacity retention was 93.64%, significantly higher than the performance of the batteries in Comparative Examples 1-10. Therefore, the deep eutectic solvent of this invention can efficiently repair retired lithium-ion battery cathode materials, enabling the repaired cathode materials to effectively improve the battery's capacity, rate performance, and cycle performance.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still 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; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A deep eutectic solvent, characterized in that, The deep eutectic solvent is prepared by a method comprising the following steps: The raw materials, including an alcohol compound, a cobalt source, and a lithium source in a molar ratio of (2.5–4):(0.7–0.9):(0.7–0.9), are reacted at 80–110 °C until the reaction system is transparent and the viscosity is 100–800 MPa·s, to obtain the deep eutectic solvent. The deep eutectic solvent is used to repair Li chemical composition. x Co y O2 is a retired lithium cobalt oxide cathode material, wherein 0 < x ≤ 0.6 and 0 < y ≤ 0.6; The alcohol compounds include at least one of glycerol, ethylene glycol, and 1,2-propanediol.

2. The deep eutectic solvent according to claim 1, characterized in that, The cobalt source includes at least one of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt nitrate. And / or, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium borohydride.

3. The deep eutectic solvent according to claim 2, characterized in that, The cobalt source is at least one of cobalt oxide and cobalt nitrate, and the lithium source is at least one of lithium carbonate and lithium hydroxide; The molar ratio of the alcohol compound, cobalt source, and lithium source is (2.5–3.5):(0.7–0.8):(0.7–0.8).

4. A method for repairing cathode materials of retired lithium-ion batteries, characterized in that, Repairing retired lithium-ion battery cathode materials using the deep eutectic solvent described in any one of claims 1-3.

5. The method for repairing the positive electrode material of a retired lithium-ion battery according to claim 4, characterized in that, Includes the following steps: The deep eutectic solvent is mixed with the cathode material to be repaired and reacted at 80-150°C for 1-3 hours. After solid-liquid separation, a liquid phase and a solid phase are obtained. The solid phase is then annealed to obtain the repaired lithium-ion battery cathode material.

6. The method for repairing the positive electrode material of a retired lithium-ion battery according to claim 5, characterized in that, The cathode material to be repaired is a decommissioned lithium cobalt oxide cathode material, and the chemical composition of the decommissioned lithium cobalt oxide cathode material is as shown in Formula 1. Li x Co y O2 Formula 1 In Equation 1, 0 < x ≤ 0.6 and 0 < y ≤ 0.

6.

7. The method for repairing the cathode material of a decommissioned lithium-ion battery according to claim 5 or 6, characterized in that, The solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(10-50); the solid-liquid ratio is the volume ratio of the cathode material to be repaired to the deep eutectic solvent; wherein, the mass unit is g and the volume unit is mL.

8. The method for repairing the cathode material of a decommissioned lithium-ion battery according to claim 5 or 6, characterized in that, The solid-liquid ratio of the cathode material to be repaired to the deep eutectic solvent is 1:(30-40); the solid-liquid ratio is the volume ratio of the cathode material to be repaired to the deep eutectic solvent; wherein, the mass unit is g and the volume unit is mL.

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