Method for regenerating positive electrode material of waste lithium ion battery

Abstract

The invention belongs to the technical field of lithium battery material recovery, and discloses a method for regenerating a positive electrode material of a waste lithium ion battery. The regeneration method comprises the following steps: recovering a positive active material from a waste positive plate, uniformly mixing the positive active material with water, sequentially adding a lithium salt and reducing amino acid, carrying out a hydrothermal reaction, cooling to room temperature after the reaction, and carrying out centrifugation and purification treatment to obtain the regenerated positive material. According to the regeneration method, only a one-step hydrothermal method is needed, structure repairing and element supplementing are carried out on the recycled positive electrode active material under the condition that elements contained in the recycled positive electrode active material are not changed, and the regeneration method is easy to operate, nontoxic, harmless, energy-saving, environmentally friendly and excellent in economic advantage. The positive electrode material regenerated by the method is low in price, the capacity of a battery assembled by the positive electrode material can be improved to a commercial standard, and the positive electrode material has good cycle stability.

Description

Technical Field

[0001] The invention relates to the technical field of lithium battery material recovery, in particular to a method for regenerating positive electrode materials of a lithium ion battery. Background Art

[0002] With the large-scale application of lithium-ion batteries in many fields such as electric vehicles and portable electronic devices, the amount of scrapped lithium-ion batteries is also increasing sharply. Waste lithium-ion batteries contain a large amount of valuable metals (such as lithium, iron, phosphorus, etc.) and substances that are harmful to the environment (such as heavy metals, organic electrolytes, etc.). Recycling and regenerating positive electrode materials can, on the one hand, effectively recover the valuable metal resources in them, alleviate dependence on primary mineral resources, and ensure the resource supply of related industries; on the other hand, it can reduce the pollution caused by waste batteries to the environment, and achieve a win-win situation of sustainable resource utilization and environmental protection.

[0003] Lithium iron phosphate has an olivine-type crystal structure, which makes its chemical properties relatively stable. During the use and scrapping of the battery, the structure is not easily destroyed. Accordingly, it is difficult to break this stable structure and achieve effective extraction of valuable elements during recycling. In order to reuse the recycled materials in lithium-ion batteries, it is necessary to ensure that their performance is equivalent to that of the original materials, such as meeting the requirements in terms of crystal structure and electrochemical properties. However, due to many factors such as the recycling process and residual impurities, it is a major challenge to ensure that the quality of the recycled products is stable and meets the battery production standards. At present, the recycling methods for waste lithium-ion battery positive electrode materials mainly include pyrolysis and hydrolysis. The purpose of these two methods is to separate valuable metal elements from the waste positive electrode.

[0004] Hydrometallurgy mainly uses acid, alkali and other leachates to dissolve the electrode materials of lithium iron phosphate batteries, and separates the elements through precipitation, filtration, extraction and other methods to obtain high-purity recycled products. This method is suitable for treating waste lithium iron phosphate materials with high impurity content and high recovery rate. Wet recycling generally includes disassembly, pretreatment, dissolution, extraction, ion exchange and electrodeposition and other processing steps. Various parameters need to be precisely controlled during the processing, and the operation is difficult. Therefore, wet recycling not only has many steps and a long process flow, but also requires the use of corrosive solvents such as acid and alkali solutions during the recycling process, which has high requirements for equipment and certain hazards to the environment and operators. At the same time, wet recycling will produce a large amount of waste liquid, and the treatment of the waste liquid will consume a lot of energy. If it is not handled properly, it will cause serious pollution to the environment. The wet recycling process is seriously limited in its application due to its long process flow, corrosive solvents, waste liquid pollution, high energy consumption, complex operation, and high equipment requirements.

[0005] Pyrometallurgy mainly uses high-temperature melting to extract lithium, which requires high-temperature smelting and refining of waste batteries. This process consumes a lot of energy and produces a lot of waste gas, waste slag and wastewater. If not handled properly, it will also cause serious pollution to the environment. Therefore, due to the energy consumption and pollution problems of pyrometallurgy, this method is not suitable for large-scale recycling of waste lithium battery positive electrode materials.

[0006] Existing recycling technologies often involve multiple steps, and different methods need to be reasonably connected. The process is relatively complicated, which leads to high equipment investment, labor costs and energy consumption, making the cost of recycling relatively high. In terms of economic benefits, it sometimes lacks sufficient competitiveness compared with directly obtaining virgin materials. It is necessary to further optimize the process flow, reduce costs, and improve the economic efficiency of recycling. Whether it is acidic or alkaline wastewater produced by chemical methods, or waste gas and dust emissions that may be caused by thermal treatment methods, they all need to be treated in strict accordance with environmental protection standards, which increases the environmental protection operating costs of enterprises and also puts forward higher requirements for the greening and harmlessness of recycling processes. It is necessary to continuously develop and adopt more environmentally friendly recycling technologies and supporting environmental protection treatment measures. The recycled lithium iron phosphate positive electrode material must be used in lithium-ion battery production, and its quality stability and consistency must be guaranteed. For example, in terms of crystal structure and electrochemical properties (such as charge and discharge capacity, cycle life, etc.), it must reach the level of virgin materials. However, due to factors such as impurity residues and process control difficulties in the recycling process, there are still certain difficulties in ensuring that product quality meets high standards. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for regenerating the positive electrode material of waste lithium-ion batteries, which can directly regenerate the positive electrode material in waste lithium-ion batteries, requires only one hydrothermal step, does not require annealing treatment, and has the characteristics of simple steps, non-toxicity, harmlessness, energy saving and environmental protection. At the same time, the present invention also provides a regenerated positive electrode material obtained by the regeneration method and its application in lithium-ion batteries. After the regenerated positive electrode material is applied to lithium-ion batteries, its performance can reach commercial standards.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for regenerating positive electrode materials of waste lithium-ion batteries, the regeneration method comprising the following steps:

[0009] Step (1): recovering positive electrode active material from waste positive electrode sheets;

[0010] Step (2): the positive electrode active material and water are mixed evenly, and then lithium salt and reducing amino acid are added in sequence, and after heating for reaction, the mixture is cooled to room temperature, and solid powder is obtained by centrifugation. After purification, a regenerated positive electrode material is obtained.

[0011] In the regeneration method of the positive electrode material of the waste lithium ion battery described in the present invention, reducing amino acid is used as a reducing agent, and the recovered positive electrode active material is regenerated by a hydrothermal method. The method has a significant effect on improving the capacity of the positive electrode material of the waste lithium ion battery.

[0012] As a preferred embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, the lithium salt is at least one of lithium acetate, lithium carbonate and lithium hydroxide. The lithium salt is used to supplement and recover the lithium ions missing in the positive electrode active material, and the selection includes but is not limited to at least one of lithium acetate, lithium carbonate and lithium hydroxide. More preferably, the lithium salt is lithium acetate.

[0013] As a preferred embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, the mass ratio of the lithium salt to the volume ratio of water in step (2) is ≥9g / L. The amount of the lithium salt used is closely related to the amount of the positive electrode active material used. It is necessary to first determine the failure degree of the recovered positive electrode active material, that is, the degree of lithium ion deficiency therein, and then determine the content of the lithium salt to be added according to the degree of lithium ion deficiency. The amount of lithium salt added should be higher than the actual lithium ion content in the positive electrode active material. The positive electrode active material needs to be mixed evenly with water, and the mass concentration of the lithium salt in the water needs to be ≥9g / L to ensure that sufficient lithium ions are provided. More preferably, the mass ratio of the lithium salt to the volume ratio of water is ≥12g / L to provide a better lithium ion supplement effect. At the same time, combined with the influence of economic and environmental factors, the concentration of the lithium salt does not need to be too high, for example, the mass ratio of the lithium salt to the volume ratio of water is 12-18g / L.

[0014] As a preferred embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, the reducing amino acid is at least one of L-threonine, L-serine and L-cysteine. The reducing amino acid is used as a reducing agent in the regeneration method and participates in the reaction in the hydrothermal process. The selection of the reducing amino acid includes but is not limited to at least one of L-threonine, L-serine and L-cysteine, and more preferably, the reducing amino acid is L-threonine or L-serine.

[0015] As a preferred embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, the volume ratio of the molar amount of the reducing amino acid to water is 0.8-1.8 mmol / L. The amount of the reducing amino acid added is too small to reduce Fe 3+ The inventors of this application have found through repeated experiments that the molar concentration of the reducing amino acid in water is preferably 0.8-1.8 mmol / L, which can fully reduce Fe 3+The molar ratio of the reducing amino acid to water can be any point value among 0.8 mmol / L, 1.0 mmol / L, 1.2 mmol / L, 1.4 mmol / L, 1.6 mmol / L, and 1.8 mmol / L, and the range value formed.

[0016] As a preferred embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, the temperature of the heating reaction in the step (2) is 140-180°C, and the reaction time is ≥6h. The inventors of the present application have found in their research that the temperature of the heating reaction in the step (2) should be controlled at 140-180°C. If the temperature is too low, the hydrothermal effect cannot be achieved, and the performance of the regenerated positive electrode material is significantly reduced; if the temperature is too high, the hydrothermal system will be destroyed, and the performance of the regenerated positive electrode material will also be adversely affected. The temperature of the hydrothermal reaction can be, for example, any point value or range value among 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, and 180°C. The time of the heating reaction in the step (2) generally needs to be ≥6h. If the reaction time is too short, the regeneration of the positive electrode material is insufficient, and the regenerated positive electrode material cannot meet the commercial performance requirements. However, the time of the heating reaction should not be too long. If the time is too long, it will not only cause energy consumption, but also bring adverse effects. More preferably, the heating reaction time is 6 to 12 hours. For example, the heating reaction time can be any one of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours, or a range formed by the two.

[0017] As a preferred embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries of the present invention, the waste positive electrode sheet in step (1) is a waste lithium iron phosphate positive electrode sheet. The method for regenerating positive electrode materials of waste lithium-ion batteries of the present invention can be applied to the regeneration of waste lithium iron phosphate positive electrode materials, but is not limited to it.

[0018] As a preferred embodiment of the method for regenerating cathode materials of waste lithium-ion batteries of the present invention, the mass volume ratio of the cathode active material to water in step (2) is 1: (10-20) g / ml. The water in step (2) is mainly used as a solvent, and the mass volume ratio of the cathode active material to water includes but is not limited to 1: (10-20) g / ml, and more preferably, the mass volume ratio of the cathode active material to water is 1: 15 g / ml.

[0019] As a preferred embodiment of the method for regenerating the cathode material of waste lithium-ion batteries of the present invention, the purification method in step (2) is: washing the obtained solid powder with deionized water and ethanol, and then vacuum drying. In the regeneration method of the present invention, the solid powder obtained after the hydrothermal reaction needs to be further purified, and the purification method includes but is not limited to washing with deionized water and ethanol, and vacuum drying for 12 hours after washing to obtain the regenerated cathode material.

[0020] In the second aspect, the present invention provides a regenerated positive electrode material with low raw material price and capacity that can be increased to commercial standards. To achieve this purpose, the technical solution adopted by the present invention is: a regenerated positive electrode material prepared by the above-mentioned method for regenerating waste lithium-ion battery positive electrode materials. The regenerated positive electrode material in the present invention is obtained by regenerating positive electrode active materials recovered from waste lithium-ion batteries. The raw material price is low. The regeneration method repairs the structure and repairs the elements of the positive electrode active materials of lithium-ion batteries without changing the elements contained in the positive electrode active materials of lithium-ion batteries, thereby obtaining a relatively uniform regenerated positive electrode material. After the regenerated positive electrode material is assembled into a lithium-ion battery, the capacity can be increased to commercial standards, and at 0.5C, the capacity retention rate is still above 98.25% after 300 cycles, and the cycle stability is good.

[0021] Finally, the present invention provides the use of the above-mentioned regenerated positive electrode material in a lithium-ion battery. The regenerated positive electrode material of the present invention is prepared by regenerating the positive electrode active material recovered from waste lithium-ion batteries, and the capacity of the regenerated positive electrode material can be increased to commercial standards after being assembled into a lithium-ion battery, providing a low-cost option for lithium-ion battery positive electrode materials.

[0022] The method for regenerating waste lithium-ion battery positive electrode materials of the present invention uses a reducing amino acid as a reducing agent and a hydrothermal method to directly regenerate the recovered positive electrode active material, and repairs the structure and supplements the elements of the recovered positive electrode active material without changing the elements contained in the recovered positive electrode active material, so as to obtain a relatively uniform regenerated positive electrode material. The method only requires a one-step hydrothermal method, and the positive electrode material can be regenerated without annealing. The method is simple to operate, non-toxic and harmless, energy-saving and environmentally friendly, and has excellent economic advantages. The regenerated positive electrode material prepared by the regeneration method of the present invention is low-priced, and the capacity after being assembled into a battery can be increased to commercial standards, and it has good cycle stability. The application of the regenerated positive electrode material of the present invention in lithium-ion batteries provides a new choice for lithium-ion battery positive electrode materials with low price, excellent performance and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Cycling performance test results of batteries assembled from positive electrode materials of Examples 1 to 4 of the present invention, Comparative Example 1, and a blank group.

[0024] Figure 2 The test results of cycle performance of batteries assembled with positive electrode materials of Examples 1, 5-7, Comparative Example 2 and a blank group are shown.

[0025] Figure 3 The test results of cycle performance of batteries assembled with positive electrode materials of Examples 1, 8-9, Comparative Example 3 and a blank group are shown.

[0026] Figure 4 These are the cycle performance test results of batteries assembled from positive electrode materials of Examples 10-12 of the present invention, Comparative Examples 4-5 and a blank group.

[0027] Figure 5 This is a graph showing the X-ray diffraction test results of the positive electrode materials of Example 1 of the present invention and a blank group.

[0028] Figure 6 Graph showing the X-ray diffraction test results of the positive electrode materials of Example 10 of the present invention and the blank group.

[0029] Figure 7 This is the inductively coupled plasma (ICP) test result of the cathode material regenerated by adding different amounts of reducing amino acids.

[0030] Figure 8 This is the inductively coupled plasma (ICP) test result of the positive electrode material regenerated with different lithium salt addition amounts.

[0031] Fig. 9 This is the inductively coupled plasma (ICP) test results of the positive electrode material regenerated at different hydrothermal temperatures.

[0032] Fig.10 The transmission electron microscope (TEM) test results of the positive electrode materials of Example 1 and the blank group are shown. DETAILED DESCRIPTION

[0033] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0034] The substances used in the following examples are all common substances in the art and can be prepared by known methods or directly purchased from the market.

[0035] Example 1

[0036] An embodiment of the method for regenerating waste lithium-ion battery positive electrode materials of the present invention, which uses waste lithium iron phosphate positive electrode sheets, specifically comprises the following steps:

[0037] (1) Recovering positive electrode active materials from waste lithium iron phosphate positive electrode sheets;

[0038] (2) The positive electrode active material and water are mixed evenly and then added to a reactor, wherein the mass volume ratio of the positive electrode active material to water is 1:15 g / ml, and then lithium salt and reducing amino acid are added in sequence, wherein the lithium salt is lithium acetate, and the volume ratio of the added amount to water is 12 g / L; the reducing amino acid is L-serine, and the volume ratio of the molar amount to water is 1.8 mmol / L; after stirring and mixing evenly, the mixture is heated to 180° C. for reaction for 6 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid powder; the obtained solid powder is washed with deionized water and ethanol, and then vacuum dried for 12 h to obtain the regenerated positive electrode material described in this embodiment.

[0039] Example 2

[0040] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 1 except that the heating reaction time in step (2) is different from that in Example 1. The heating reaction time in step (2) in this embodiment is 8 hours.

[0041] Example 3

[0042] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 1 except that the heating reaction time in step (2) is different from that in Example 1. The heating reaction time in step (2) in this embodiment is 10 hours.

[0043] Example 4

[0044] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 1 except that the heating reaction time in step (2) is different from that in Example 1. The heating reaction time in step (2) in this embodiment is 12 hours.

[0045] Example 5

[0046] An embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries according to the present invention, except that the amount of L-serine added in step (2) is different from that in Example 1, the rest is the same as that in Example 1. The volume ratio of the molar amount of L-serine to water in step (2) of this embodiment is 0.8 mmol / L.

[0047] Example 6

[0048] An embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries according to the present invention, except that the amount of L-serine added in step (2) is different from that in Example 1, the rest is the same as that in Example 1. In step (2) of this embodiment, the volume ratio of the molar amount of L-serine to water is 1 mmol / L.

[0049] Example 7

[0050] An embodiment of the method for regenerating the positive electrode material of waste lithium-ion batteries according to the present invention, except that the amount of L-serine added in step (2) is different from that in Example 1, the rest is the same as that in Example 1. In step (2) of this embodiment, the volume ratio of the molar amount of L-serine to water is 1.5 mmol / L.

[0051] Example 8

[0052] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention, except that the amount of lithium acetate added in step (2) is different from that in embodiment 1, the rest is the same as embodiment 1. The volume ratio of the amount of lithium acetate added to water in step (2) of this embodiment is 15 g / L.

[0053] Example 9

[0054] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 1 except that the amount of lithium acetate added in step (2) is different from that in Example 1. The volume ratio of the amount of lithium acetate added to water in step (2) of this embodiment is 9 g / L.

[0055] Example 10

[0056] An embodiment of the method for regenerating waste lithium-ion battery positive electrode materials of the present invention, which uses waste lithium iron phosphate positive electrode sheets, specifically comprises the following steps:

[0057] (1) Recovering positive electrode active materials from waste lithium iron phosphate positive electrode sheets;

[0058] (2) The positive electrode active material and water are mixed evenly and then added to a reactor, wherein the mass volume ratio of the positive electrode active material to water is 1:15 g / ml, and then lithium salt and reducing amino acid are added in sequence, wherein the lithium salt is lithium acetate, and the volume ratio of the added amount to water is 15 g / L; the reducing amino acid is L-threonine, and the volume ratio of the molar amount to water is 1 mmol / L; after stirring and mixing evenly, the mixture is heated to 140° C. for reaction for 12 h, and then naturally cooled to room temperature, and centrifuged to obtain a solid powder; the obtained solid powder is washed with deionized water and ethanol, and then vacuum dried for 12 h to obtain the regenerated positive electrode material described in this embodiment.

[0059] Embodiment 11

[0060] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 10 except that the temperature of the heating reaction in step (2) is different from that in Example 10. The temperature of the heating reaction in step (2) in this embodiment is 160°C.

[0061] Example 12

[0062] An embodiment of the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention is the same as that of Example 10 except that the temperature of the heating reaction in step (2) is different from that in Example 10. The temperature of the heating reaction in step (2) in this embodiment is 180°C.

[0063] Comparative Example 1

[0064] A comparative example of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, except that the heating reaction time in step (2) is different from that in Example 1, the rest is the same as Example 1. The heating reaction time in step (2) in this comparative example is 5 hours.

[0065] Comparative Example 2

[0066] A comparative example of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, except that the amount of L-serine added in step (2) is different from that in Example 1, the rest is the same as Example 1. The volume ratio of the molar amount of L-serine to water in step (2) of this comparative example is 0.7 mmol / L.

[0067] Comparative Example 3

[0068] A comparative example of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, except that the amount of lithium acetate added in step (2) is different from that in Example 1, the rest is the same as Example 1. The volume ratio of the amount of lithium acetate added in step (2) of this comparative example to water is 8 g / L

[0069] Comparative Example 4

[0070] A comparative example of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, except that the temperature of the heating reaction in step (2) is different from that in Example 10, the rest is the same as that in Example 10. The temperature of the heating reaction in step (2) in this comparative example is 130°C.

[0071] Comparative Example 5

[0072] A comparative example of the method for regenerating the positive electrode material of waste lithium-ion batteries of the present invention, except that the temperature of the heating reaction in step (2) is different from that in Example 10, the rest is the same as that in Example 10. The temperature of the heating reaction in step (2) in this comparative example is 200°C.

[0073] Effect Example 1

[0074] Cyclic performance experiment of battery made of regenerated positive electrode material prepared by the method for regenerating positive electrode material of waste lithium-ion battery according to the present invention

[0075] In this effect example, the regenerated positive electrode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 5 were respectively used as experimental objects, and the positive electrode active materials recovered from waste lithium iron phosphate positive electrode sheets without regeneration treatment were used as blank groups to investigate the effects of changes in the amount of raw materials added and process conditions in the method for regenerating waste lithium-ion battery positive electrode materials described in this application on the cycle performance of batteries prepared from the regenerated positive electrode materials.

[0076] The method for preparing batteries from groups of regenerated positive electrode materials or directly recovered positive electrode active materials without regeneration treatment is as follows:

[0077] (1) Preparation of pole pieces: Regenerated positive electrode material or recycled positive electrode material, N-methylpyrrolidone (nmp) solution containing 2.5wt% polyvinylidene fluoride (PVDF), and superconducting carbon black (sp) are stirred for 4-6 hours at a mass ratio of 8:1:1 to fully mix and obtain a slurry. The slurry is then coated on aluminum foil with a coating thickness of 150μm. After drying in a forced air oven at 80°C for 2h, it is evenly dried in a vacuum oven at 120°C for 12 hours to obtain a pole piece.

[0078] (2) Battery assembly: The lithium sheet was used as the counter electrode, the separator was a polypropylene film (Celgard 2400), and the electrolyte was an ethylene carbonate / dimethyl carbonate solution (EC:DMC volume was 1:1) containing 1 mol / L LiPF6 to assemble the LFP battery.

[0079] The assembled LFP battery was then subjected to a battery cycle performance test. The test method was as follows: the prepared LFP battery was first allowed to stand at room temperature for 4 hours, then activated at 0.2C for two cycles, and then cycled at 0.5C.

[0080] The cycle performance test results of the batteries in Examples 1 to 4, Comparative Example 1 and Blank Group are shown in the attached Figure 1 As shown. Figure 1 It can be seen that the cycle performance of the regenerated positive electrode materials obtained in Examples 1-4 of the present invention is significantly higher than that of the blank group before regeneration, indicating that the regeneration method of the present invention can significantly improve the capacity of the waste positive electrode materials after being assembled into a battery, and improve it to the commercial standard. At the same time, it can be seen from Examples 1-4 and Comparative Example 1 that in the method for regenerating waste lithium-ion battery positive electrode materials of the present invention, when the amount of each raw material and the hydrothermal temperature are the same, the hydrothermal reaction time has a direct impact on the performance of the regenerated positive electrode material. If the reaction time is too short, the capacity of the regenerated positive electrode material after being assembled into a battery is not significantly improved and cannot reach the commercial standard. The hydrothermal reaction time needs to be ≥6h. In the range of 6 to 12h, the discharge specific capacity of the obtained regenerated material is basically stable.

[0081] The cycle performance test results of the batteries described in Example 1, Examples 5-7, Comparative Example 2 and the blank group are shown in the attached Figure 2 As shown. Figure 2 It can be seen that, under the condition that other conditions are the same, the regenerated materials obtained in Example 1 and Examples 5-7, in which the amount of the reducing amino acid L-serine added is 0.8-1.8 mmol / L, have a significant effect on improving the discharge specific capacity of the battery compared with the blank group, while in Comparative Example 2, in which the amount of the reducing amino acid L-serine added is 0.7 mmol / L, although the discharge specific capacity is improved to a certain extent compared with the blank group, it is significantly lower than that in Example 1 and Examples 5-7, indicating that the amount of reducing amino acid added is too small and cannot achieve the purpose of increasing the battery capacity to the commercial standard.

[0082] The cycle performance test results of the batteries described in Examples 1, 8-9, Comparative Example 3 and the blank group are shown in the attached Figure 3 As shown. Figure 3 It can be seen that compared with the blank group, the discharge specific capacity of the battery in Examples 1 and 8-9 is significantly improved and can reach the commercial standard. However, in Comparative Example 3, due to insufficient addition of lithium salt, the discharge specific capacity of the battery prepared from the regenerated positive electrode material is improved to a certain extent, but is far from meeting the requirements.

[0083] The cycle performance test results of the batteries described in Examples 10-12, Comparative Examples 4-5 and the blank group are shown in the attached Figure 4 As shown. Figure 4 It can be seen that, under the same conditions, the hydrothermal temperature has a significant effect on the battery capacity of the regenerated positive electrode material. Compared with the blank group, the battery capacity of Comparative Example 4 with a lower hydrothermal temperature and Comparative Example 5 with a too high hydrothermal temperature has a certain improvement, but it is significantly lower than that of Examples 10-12 and cannot meet commercial standards.

[0084] Effect Example 2

[0085] X-ray diffraction test (XRD) of the regenerated positive electrode material prepared by the method for regenerating the positive electrode material of waste lithium-ion batteries according to the present invention

[0086] The regenerated positive electrode materials obtained in Example 1 and Example 10 were used as test objects, and the positive electrode active materials recovered from waste lithium iron phosphate positive electrode sheets without regeneration were used as blank groups, and X-ray diffraction tests were performed on them. The test results are shown in the attached table. Figure 5 and 6 shown.

[0087] By the attached Figure 5 and 6 It can be seen that the structures of the regenerated positive electrode materials obtained in Example 1 and Example 10 were effectively repaired and the elements were significantly supplemented compared with the blank group, respectively. This shows that the regeneration method of the present invention has significant structural repair and element supplement effects on the recycling and regeneration of positive electrode materials.

[0088] Effect Example 3

[0089] Inductively coupled plasma (ICP) testing of the regenerated positive electrode material prepared by the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention

[0090] 1. Comparison of the regenerated positive electrode material obtained in Example 10 with the blank group

[0091] The regenerated positive electrode material obtained in Example 10 was used as the test object, and the positive electrode active material recovered from the waste lithium iron phosphate positive electrode sheet without regeneration treatment was used as the blank group. They were tested by inductively coupled plasma technology (ICP). The test results are shown in Table 1.

[0092] Table 1 ICP test results of Example 10 and blank group

[0093] Group Li(wt%) Fe(wt%) Li / Fe (wt%) Example 10 4.262 37.061 1.01 Blank group 3.351 36.015 0.75

[0094] It can be seen from the results in Table 1 that, compared with the blank group, the Li content and Li / Fe in the regenerated positive electrode material after regeneration using the method of the present invention are significantly improved.

[0095] 2. Effect of the amount of reducing amino acid added on the Li / Fe ratio of the regenerated positive electrode material

[0096] Taking the regeneration method of Example 10 as a benchmark, the amount of reducing amino acid added in Example 10 was changed to 0.1mmol / L, 0.5mmol / L, 1.5mmol / L, and 2.0mmol / L, respectively, to investigate the effect of the amount of reducing amino acid added on the Li / Fe molar ratio in the regenerated positive electrode material. The positive electrode active material recovered from the waste lithium iron phosphate positive electrode sheet without regeneration treatment was used as a blank group, and they were tested by inductively coupled plasma technology (ICP). The test results are shown in the attached Figure 7 shown.

[0097] By the attached Figure 7 It can be seen that as the amount of reducing amino acids added gradually increases, the Li / Fe molar ratio in the regenerated positive electrode material gradually increases, especially when the amount of reducing amino acids added is 1.5mmol / L, the Li / Fe molar ratio in the regenerated positive electrode material reaches the highest, and then as the amount of reducing amino acids added further increases, the Li / Fe molar ratio in the regenerated positive electrode material does not increase but decreases, indicating that the amount of reducing amino acids added is too high, which has an adverse effect on the regenerated positive electrode material. The inventor of the present application has found through experimental exploration that the amount of reducing amino acids added is preferably 0.8 to 1.8mmol / L, which can significantly increase the Li / Fe molar ratio in the regenerated positive electrode material and reach the commercial standard for the reuse of positive electrode materials to prepare batteries.

[0098] 3. Effect of lithium salt addition on Li / Fe in regenerated positive electrode materials

[0099] Taking the regeneration method of Example 10 as a benchmark, the addition amount of lithium salt in Example 10 was changed to 3 g / L, 6 g / L, 9 g / L, and 12 g / L, respectively, to investigate the effect of lithium salt concentration on the Li / Fe molar ratio in the regenerated positive electrode material. The positive electrode active material recovered from the waste lithium iron phosphate positive electrode sheet without regeneration treatment was used as a blank group, and they were tested by inductively coupled plasma technology (ICP). The test results are shown in the attached figure. Figure 8 shown.

[0100] By the attached Figure 8It can be seen that in the process of increasing the amount of lithium salt added from 3g / L to 15g / L, the Li / Fe molar ratio in the regenerated positive electrode material shows a trend of gradually increasing and then stabilizing, which shows that the amount of lithium salt added is too little, and the effect of improving the Li / Fe molar ratio in the regenerated positive electrode material does not meet the corresponding requirements. If the amount of lithium salt added is too much, the performance of the regenerated positive electrode material is not further improved, but it causes certain economic and environmental adverse effects. Therefore, after repeated experiments, the inventors of the present application finally determined that the amount of lithium salt added should be ≥9g / L in volume ratio with water to ensure complete replenishment of missing lithium ions, more preferably 12-18g / L, which is more sufficient to replenish the missing lithium ions.

[0101] 4. Effect of hydrothermal temperature on Li / Fe in regenerated cathode materials

[0102] Taking the regeneration method of Example 10 as a benchmark, the hydrothermal reaction temperature in Example 10 was changed to 160°C, 180°C and 200°C respectively, and the effect of the hydrothermal reaction temperature on the Li / Fe molar ratio in the regenerated positive electrode material was investigated. The positive electrode active material recovered from the waste lithium iron phosphate positive electrode sheet without regeneration treatment was used as a blank group, and they were subjected to inductively coupled plasma technology (ICP) testing. The test results are shown in the attached figure. Fig. 9 shown.

[0103] By the attached Fig. 9 It can be seen that during the hydrothermal reaction from 140°C to 200°C, the Li / Fe molar ratio in the regenerated positive electrode material shows a trend of first steadily increasing and then significantly decreasing, indicating that the temperature of the hydrothermal reaction is too high, which will destroy the hydrothermal system and also have an adverse effect on the performance of the regenerated positive electrode material. After repeated experiments and explorations, the inventors of the present application finally determined that the hydrothermal reaction temperature in the regeneration method of the present invention is preferably 140-180°C.

[0104] Effect Example 4

[0105] Transmission electron microscope (TEM) test of the regenerated positive electrode material prepared by the method for regenerating positive electrode materials of waste lithium-ion batteries according to the present invention

[0106] The regenerated positive electrode material obtained by the regeneration method of Example 1 was used as the test object, and the positive electrode active material recovered from the waste lithium iron phosphate positive electrode sheet without regeneration treatment was used as the blank group. Electron microscope (TEM) tests were performed on the positive electrode materials of Example 1 and the blank group, respectively. The test results are shown in the attached figure. Fig.10 shown.

[0107] Attached Fig.10 In the figure, a is the test result of the blank group, and b is the test result of Example 1. Fig.10It can be seen that the crystal structure of the regenerated positive electrode material obtained by the regeneration method of Example 1 has changed significantly compared with that before regeneration, which further proves that the regeneration method described in the present invention can repair the structure of the positive electrode material.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for regenerating positive electrode materials of waste lithium-ion batteries, characterized in that: The regeneration method comprises the following steps: Step (1): recovering positive electrode active material from waste positive electrode sheets; Step (2): the positive electrode active material and water are mixed evenly, and then lithium salt and reducing amino acid are added in sequence, and after heating for reaction, the mixture is cooled to room temperature, and solid powder is obtained by centrifugation. After purification, a regenerated positive electrode material is obtained.

2. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: The lithium salt is at least one of lithium acetate, lithium carbonate and lithium hydroxide.

3. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: In the step (2), the volume ratio of the lithium salt to water is ≥9 g / L.

4. The method for regenerating positive electrode materials of waste lithium-ion batteries as claimed in claim 3, characterized in that: In the step (2), the volume ratio of the lithium salt to water is 12-18 g / L.

5. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: The reducing amino acid is at least one of L-threonine, L-serine and L-cysteine.

6. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: The volume ratio of the molar amount of the reducing amino acid to water is 0.8-1.8 mmol / L.

7. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: The heating reaction temperature in step (2) is 140-180° C., and the reaction time is ≥6 h.

8. The method for regenerating positive electrode materials of waste lithium-ion batteries according to claim 1, characterized in that: The waste positive electrode sheet in step (1) is a waste lithium iron phosphate positive electrode sheet; And / or, in step (2), the mass volume ratio of the positive electrode active material to water is 1: (10-20) g / ml; And / or, the purification method in step (2) is: washing the obtained solid powder with deionized water and ethanol, and then vacuum drying.

9. A regenerated positive electrode material prepared by the method for regenerating positive electrode materials of waste lithium-ion batteries as claimed in any one of claims 1 to 8.

10. Use of the regenerated positive electrode material as claimed in claim 9 in a lithium ion battery.

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