Recycling method of lithium battery positive electrode active material

Abstract

The invention provides a lithium battery positive electrode active material recovery method which is characterized by comprising the following steps: S1, providing a eutectic solution which comprises choline chloride, urea and a lithium salt; s2, putting a positive pole piece in a lithium battery into the eutectoid solution to obtain a lithium-supplemented positive pole piece; s3, carrying out separation treatment on the lithium-supplemented positive pole piece obtained in S2 to obtain a lithium-supplemented positive active material; and S4, carrying out roasting treatment on the lithium-supplemented positive electrode active material obtained in S3 to obtain the repaired positive electrode active material.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a method for recovering positive electrode active materials of lithium batteries. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, high coulombic efficiency and long cycle life, making them the main power source for portable electronic products and electric vehicles. It is expected that the global manufacturing capacity of lithium-ion batteries will increase significantly at a rate of hundreds of GWh per year in the next five years. Among them, the positive electrode materials for power batteries will generate greater demand for raw materials as the electric vehicle market grows. Lithium-ion batteries usually reach the end of their life after 3-6 years, and scrapped lithium-ion batteries contain a large amount of Li and resources such as Co, Ni, and Mn. Reasonable treatment and recycling of lithium battery materials can serve as a supplement to the supply chain. Otherwise, it may cause greater environmental pollution and waste of resources. Under the strategic conditions of the national circular economy, recycling and reusing scrapped lithium-ion batteries to recover lithium and transition metal resources, as well as eliminating the pollution caused by the disposal of waste batteries, has become an imperative and thorny task.

[0003] Currently, the widely used recycling methods mainly include pyrometallurgy, hydrometallurgy and direct recycling to recycle lithium battery positive electrode materials. Pyrometallurgy requires high-temperature smelting and multi-stage purification and separation processes, which consumes a lot of energy; while hydrometallurgy requires acid leaching and subsequent complicated extraction and precipitation steps to recover valuable metal elements, and there are a lot of wastewater treatment problems. The direct recovery method combines the physical separation process to separate and collect positive electrode materials, as well as the subsequent lithium supplementation process to repair the composition and structural defects of the electrode materials, greatly shortening the recycling process and reducing energy consumption and emissions.

[0004] The current mainstream lithium replenishment technologies include solid-state sintering method, hydrothermal method, etc. The solid-state sintering method has high requirements for ICP measurement of lithium deficiency and the process is time-consuming. As for the hydrothermal lithium replenishment method, due to the sensitivity of the positive electrode material to water, the hydrothermal method has certain limitations and produces a large amount of wastewater. At the same time, the hydrothermal method is based on a high-pressure reactor container, which is difficult to scale up industrially and has certain risks. Summary of the invention

[0005] In response to the problems existing in the prior art, the present application aims to provide an environmentally friendly and simple process flow scheme for recycling positive active materials of lithium batteries. The present application aims to complete the repair and lithium replenishment at the positive electrode plate level of waste lithium batteries. Compared with the solid-state sintering lithium replenishment method, there is no need to perform ICP measurement to determine the amount of lithium deficiency. The adaptive lithium replenishment in a low eutectic solution is used to simplify the recycling process and shorten the production cycle. In addition, since the method of the present application adopts a low eutectic solvent, an organic degradable material, it can be reused and avoid the generation of secondary pollutants. At the same time, since the positive active material is easily affected by water, the low eutectic solvent system can replace the aqueous solution to dissolve the lithium salt and realize lithium replenishment and repair under low temperature conditions, thereby improving the effectiveness of energy saving, cost reduction and emission reduction.

[0006] The first aspect of the present application provides a method for recovering a positive electrode active material of a lithium battery, the method comprising the following steps:

[0007] S1, providing a eutectic solution, wherein the eutectic solution comprises choline chloride, urea and a lithium salt;

[0008] S2, placing the positive electrode sheet in the lithium battery into the eutectic solution to obtain a lithium-supplemented positive electrode sheet;

[0009] S3, separating the lithium-supplemented positive electrode sheet obtained in S2 to obtain a lithium-supplemented positive electrode active material;

[0010] S4, calcining the lithium-supplemented positive electrode active material obtained in S3 to obtain a repaired positive electrode active material.

[0011] In some embodiments of the present application, in S1, choline chloride and urea are mixed to obtain a mixed solution, and then a lithium salt is added to the mixed solution to obtain the eutectic solution.

[0012] In some embodiments of the present application, in S1, the choline chloride and urea are mixed at 50 to 90°C.

[0013] In some embodiments of the present application, in S1, the molar ratio of choline chloride, urea and lithium salt is 1:(0.5-5):(0.1-2).

[0014] In some embodiments of the present application, in S2, the positive electrode sheet is placed in the low eutectic solution, subjected to ultrasonic radiation treatment, and then cleaned and dried to obtain the lithium-supplemented positive electrode sheet.

[0015] In some embodiments of the present application, in S3, the separation treatment includes immersing the lithium-replenished positive electrode sheet in an N-methylpyrrolidone solvent and ultrasonically cleaning it, and obtaining the lithium-replenished positive electrode active material after mechanical separation.

[0016] In some embodiments of the present application, in S4, the calcination temperature is 700 to 900°C, the calcination time is 3 to 12 hours, the calcination atmosphere is air or nitrogen or oxygen, and the calcination heating rate is 1 to 10°C / minute.

[0017] In some preferred embodiments of the present application, the positive electrode active material includes one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate and their respective modified compounds; the lithium transition metal oxide is selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide and lithium manganese cobalt oxide, and at least one of the modified compounds of the above oxides.

[0018] In some preferred embodiments of the present application, in S3, before the electrode is separated after lithium replenishment, the electrode is immersed in N-methylpyrrolidone (NMP) solvent and ultrasonically cleaned; preferably, the temperature range of NMP cleaning the electrode is 20 to 80°C, the ultrasonic cleaning time range is 2 to 10 minutes, and the solid-liquid ratio of the suspension obtained after cleaning is in the range of 10 to 100 g / L.

[0019] In some preferred embodiments of the present application, in S4, the calcination temperature range is 700-900°C, the duration range is 3-12 hours, the atmosphere is air / nitrogen / oxygen, etc., the heating rate is 1-10°C / minute, and the cooling method after heating is natural cooling. Preferably, the calcination is performed in a muffle furnace.

[0020] In some preferred embodiments of the present application, the lithium-containing phosphate with an olivine structure is selected from one or more of lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof.

[0021] The second aspect of the present application also provides a secondary battery, which includes the positive electrode active material recovered according to the method.

[0022] The technical solution of this application has the following technical features:

[0023] 1. The prior art requires the pole piece to be de-powdered and then lithium replenishment and repair at the positive electrode active material powder level. Since lithium replenishment is performed using a solid-phase sintering method after de-powdering, it is necessary to quantitatively analyze the element content through ICP. The process is lengthy and complicated, and there will be measurement errors. In contrast, the scheme of the present invention utilizes the adaptability of the material structure to lithium ion embedding to directly achieve lithium replenishment and repair of waste positive electrode materials at the pole piece level. This is more direct and has a short process, which can greatly reduce process energy consumption and emissions, and achieve low-cost rapid repair and regeneration.

[0024] 2. The technical solution of the present application utilizes the adaptability of liquid-phase osmotic lithium replenishment, which can kinetically replenish the missing lithium ions in the structure of the positive electrode active material, while avoiding the error and time-consuming ICP measurement, and ensuring the rationality of the amount of lithium replenishment (neither too little nor too much), that is, the stoichiometric ratio of the recovered product. In addition, this solution can also provide an anhydrous lithium replenishment environment for ternary positive electrode active materials (such as NCM111, NCM532, NCM622, NCM811 or higher-content ternary high-nickel materials), avoiding the side reactions during the recovery process that have a negative impact on their structural morphology. And the present application realizes liquid-phase lithium replenishment at the pole piece level, and the separation of the pole piece and the liquid phase after lithium replenishment is easier, and the process is simple.

[0025] 3. The technical solution of the present application adopts organic degradable materials of low eutectic solvents, which can be reused and avoid the generation of secondary pollutants. At the same time, since the positive electrode active materials are easily affected by water, the low eutectic agent system can replace the aqueous solution to dissolve the lithium salt and realize lithium replenishment and repair under low temperature conditions, thereby improving the effectiveness of energy saving, cost reduction and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 A flow chart of a method for recycling positive electrode active materials of a lithium battery according to the present application is shown.

[0028] Figure 2 XRD patterns of fresh positive electrode active material, waste positive electrode active material and positive electrode active material on a positive electrode sheet recycled by the method of the present application are shown.

[0029] Figure 3 The material morphology photos at each process stage are shown, including scrapped positive electrode sheets (ac), positive electrode active material powder after lithium supplementation (d-e), positive electrode active material powder after calcination treatment and repair (g-i) and commercial new material powder (j-1). DETAILED DESCRIPTION

[0030] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0031] The term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation of less than or equal to ±10% of the numerical value, such as 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%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such a range format is for convenience and simplicity, and should be flexibly understood to include not only numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0032] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0033] 1. Lithium battery positive electrode active material recovery method

[0034] like Figure 1 As shown, taking the waste ternary lithium-ion battery as an example, the waste ternary lithium-ion battery is first discharged and disassembled into three parts, namely ① shell and diaphragm, etc.; ② waste positive electrode sheet and ③ waste negative electrode sheet. Among them, ① shell and diaphragm, etc. and ③ waste negative electrode sheet are recycled and processed by other means. Then ② waste positive electrode sheet is processed according to the following steps.

[0035] S1, providing a eutectic solution, wherein the eutectic solution comprises choline chloride, urea and a lithium salt;

[0036] S2, placing the positive electrode sheet in the lithium battery into the eutectic solution to obtain a lithium-supplemented positive electrode sheet;

[0037] S3, separating the lithium-supplemented positive electrode sheet obtained in S2 to obtain a lithium-supplemented positive electrode active material;

[0038] S4, calcining the lithium-supplemented positive electrode active material obtained in S3 to obtain a repaired positive electrode active material.

[0039] Preferably, in S1, choline chloride and urea are mixed to obtain a mixed solution, and then a lithium salt (such as lithium chloride) is added to the mixed solution to obtain a low eutectic solution of the lithium chloride. Urea and choline chloride are combined as hydrogen bond donors and acceptors to form a low eutectic solvent system, which can be used as a solvent to dissolve lithium salts. Lithium chloride is dissolved in the low eutectic agent system as a lithium source, has good solubility and stability, and provides a lithium replenishment environment for waste electrode sheets. The choline chloride and urea are stirred and mixed at 50 to 90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C. Too low a temperature may cause the lithium replenishment reaction to occur too slowly from a kinetic point of view; too high a temperature may cause the positive electrode active material to dissolve in the low eutectic agent system.

[0040] Preferably, in S1, the molar ratio of choline chloride, urea and lithium salt (such as lithium chloride) is 1: (0.5-5): (0.1-2). Within this range, the best eutectic effect can be achieved.

[0041] In some preferred embodiments, in S2, the positive electrode plate is placed in the low eutectic solution, subjected to ultrasonic radiation treatment, and then cleaned and dried to obtain the lithium-supplemented positive electrode plate.

[0042] In some preferred embodiments, in S3, the separation treatment includes immersing the lithium-replenished positive electrode sheet in an N-methylpyrrolidone solvent and ultrasonically cleaning it, and obtaining the lithium-replenished positive electrode active material after mechanical separation.

[0043] In some preferred embodiments, in S4, the calcination temperature is 700 to 900°C, the calcination time is 3 to 12 hours, the calcination atmosphere is air or nitrogen or oxygen, and the calcination heating rate is 1 to 10°C / min.

[0044] In some preferred embodiments, the positive electrode active material in the positive electrode plate includes one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds; the lithium transition metal oxide is selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, and lithium manganese cobalt oxide, and at least one of the modified compounds of the above oxides. The lithium-containing phosphate with an olivine structure is selected from one or more of lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their modified compounds.

[0045] 2. Secondary battery

[0046] The positive electrode material recovered from the waste battery is used to prepare a positive electrode slurry, which is coated on a current collector and dried to obtain a positive electrode sheet, which is then assembled with a separator, a negative electrode sheet, and an electrolyte into a new secondary battery.

[0047] Some embodiments of the present application provide a negative electrode sheet comprising the current collector and a negative electrode active material layer coated on the surface of the current collector. The negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, and of course may also include other additives that are beneficial to the electrochemical performance of the negative electrode.

[0048] In some embodiments, the negative electrode active material may be a commonly used negative electrode active material, including but not limited to: graphite, carbon material, silicon-based material, metal oxide, tin-based material. For example, silicon-based composite materials include but are not limited to silicon-carbon composite materials, silicon-metal oxide composite materials, silicon alloy composite materials, wherein the mass content of silicon in the composite material is 1-85wt.%. For example, metal oxides include but are not limited to iron oxide, lithium titanate, copper oxide, etc., which are regarded as all metal oxides that can be used for lithium extraction and storage.

[0049] In some embodiments, the conductive agent can be a commonly used conductive agent, including but not limited to: metal-based materials, carbon-based materials, conductive polymers and mixtures thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, nickel, copper, aluminum or silver. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, acetylene black, Ketjen black, carbon black, carbon fiber or any combination thereof. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0050] In some embodiments, the binder can be a commonly used binder, including but not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, ethylene oxide-containing polymers, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyurethane, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0051] In some embodiments, the electrolyte includes a lithium salt and a solvent.

[0052] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), or lithium difluorooxalatoborate.

[0053] In some embodiments, the solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0054] The secondary battery can be prepared using common methods in the prior art, such as assembling the battery pole pieces into the battery core, and then pouring the electrolyte into the battery core.

[0055] The electrolyte and the separator used in the present application are not particularly limited and can be prepared using materials, structures and manufacturing methods known in the art.

[0056] In some embodiments, the electrolyte includes a lithium salt and a solvent.

[0057] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), bistrifluoromethanesulfonyl imide lithium LiN(CF3SO2)2 (LiTFSI), bis(fluorosulfonyl)imide lithium Li(N(SO2F)2)(LiFSI), lithium bis(oxalate borate) LiB(C2O4)2 (LiBOB) or lithium difluorooxalate borate LiBF2(C2O4) (LiDFOB). In some embodiments, the concentration of the lithium salt in the electrolyte is: about 0.5mol / L to 3mol / L, about 0.5mol / L to 2mol / L, or about 0.8mol / L to 1.5mol / L.

[0058] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0059] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.

[0060] According to some embodiments of the present application, the secondary battery is a lithium metal secondary battery or a sodium metal secondary battery. In some embodiments, the lithium metal secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0061] According to some embodiments of the present application, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0062] According to some embodiments of the present application, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0063] In some embodiments, the present application further provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0064] In some embodiments, the present application further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0065] 4. Electrochemical Device

[0066] The present application also provides an electrochemical device, which includes the secondary battery.

[0067] In some embodiments, the electrochemical device includes but is not limited to electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the electrochemical device's requirements for high power and high energy density of lithium-ion batteries, a battery pack or battery module may be used.

[0068] In some embodiments, the electrochemical device may be a tablet computer, a mobile phone, a laptop computer, etc. The electrochemical device is usually required to be light and thin, and a lithium-ion battery may be used as a power source.

[0069] 3. Performance test of battery cells

[0070] The positive electrode active material recovered in the examples of the present application was used to prepare a positive electrode slurry, which was coated on a current collector, dried and cut into positive electrode sheets with a diameter of 12 mm. The positive electrode sheet, the graphite negative electrode sheet and the Cellgard 2400 polypropylene film were assembled into a 2032 button cell in an argon-filled glove box, and then the electrochemical performance of the cell was tested at a constant temperature of 25°C.

[0071] Embodiment 1:

[0072] Configuration of deep eutectic solvent:

[0073] 400 g of choline chloride and 340 g of urea were mixed and stirred at 80° C. for about 30 minutes. After the liquid became clear, 35 g of lithium chloride was added and stirred for 10 hours until the lithium chloride was completely dissolved. Thus, the eutectic solution of lithium chloride was prepared. In this embodiment, the molar ratio of choline chloride, urea and lithium chloride was 1:1.98:0.29.

[0074] Take about 100g of the positive electrode sheet (NCM523) of the waste ternary lithium-ion battery, put it into the LiCl low eutectic system solution, stir and react at 80°C for about 5 hours, take out the electrode sheet, wash it with ethanol, and vacuum dry it for 1 hour to obtain the positive electrode sheet after lithium supplementation.

[0075] The positive electrode pieces after lithium supplementation were immersed in NMP solvent, ultrasonically cleaned and powdered, and the black powder after lithium supplementation after centrifugal drying was placed in a muffle furnace and heated at 900°C for 6 hours in an air atmosphere to obtain the repaired ternary positive electrode active material powder. Then, the positive electrode active material was used to prepare positive positive pieces and batteries according to the method of the present application, and the positive positive pieces and batteries were characterized and tested.

[0076] Embodiment 2:

[0077] The difference from Example 1 is that the stirring reaction is changed to ultrasonic radiation treatment, the power of the ultrasonic transmitter is 600 W, the reaction temperature is 25° C., and the other parameters are the same as those in Example 1.

[0078] Embodiment 3:

[0079] The difference from Example 1 is that the lithium replenishment reaction time of the electrode in the DES solvent is changed to 1 hour, and the other content parameters are the same as those in Example 1.

[0080] Embodiment 4:

[0081] The difference from Example 1 is that the reaction temperature of the electrode lithium replenishment is changed to room temperature (20°C), and the other parameters are the same as those of Example 1.

[0082] Comparative Example 1:

[0083] Select 400g of choline chloride and 340g of urea, mix them and stir them at 80℃ for about 30 minutes. After the liquid becomes clear, take about 100g of the positive electrode sheet of the waste ternary lithium-ion battery, put it into the low eutectic system solution, stir and react at 80℃ for about 5 hours, take out the electrode sheet, wash it with ethanol, and then vacuum dry it for 1 hour to obtain the lithium-supplemented positive electrode sheet.

[0084] Test methods:

[0085] 1. ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer) element content test:

[0086] Place a certain amount of the sample to be tested in a digestion container, add an acid solution (such as hydrochloric acid, nitric acid or sulfuric acid), seal it, and heat and digest it in a microwave digester or oven. After the digestion is completed, transfer the digestion solution to a volumetric flask and perform the volume adjustment and shake steps. Use ICP-OES equipment to test the trace element content of the digestion solution. For liquid phase samples such as leaching solutions, use ICP-OES equipment to test the trace element content of the digestion solution after dilution.

[0087] 2. Electrochemical test

[0088] The waste positive electrode and the commercial new electrode were cut into circular electrodes, assembled with standard graphite negative electrode, Cellgard 2400 polypropylene film and commercial new electrolyte into 2032 button batteries, and then the electrochemical performance of the batteries was tested at a constant temperature of 25°C. The results are shown in Tables 1 and 2.

[0089] Table 1 shows the element content of the electrode materials by ICP-MS before and after the reaction. Table 1 shows that the lithium content and transition metal content ratio of the waste positive electrode plate are attenuated and missing to a certain extent compared with the commercial new plate. After the repair, the lithium metal and transition metal content ratio of the plate is increased and restored. The recovery of the lithium content and transition metal ratio is different according to the different conditions of different embodiments.

[0090] From the data in Table 2, it can be seen that the electrochemical performance of the materials repaired under different embodiments has been restored to varying degrees, and its charge-discharge capacity and cycle stability have increased with the increase of lithium supplementation. Among them, the electrochemical charge-discharge performance of Example 1 has reached the same level as the commercial new material, and its cycle stability has shown certain advantages over the commercial new material.

[0091] Figure 2The XRD diagram of the positive electrode sheet prepared in Example 1 before and after the reaction. Figure 2 It can be seen that the XRD peak shape of the waste electrode shows that the overall α-NaFeO2 crystal structure is still maintained, and no impurity peaks appear. Its 003 peak shifts to the left compared with the commercial standard material, and it is believed that there are missing lithium vacancies in its layered structure, while in the positive electrode active material recovered by the method of the present application (such as Example 1), the peak shifts to the right and returns to the position, and it is believed that its lithium replenishment reaction effectively re-embeds the missing lithium ions into the layered structure, realizing the repair and regeneration of the positive electrode active material.

[0092] At the same time, the morphology of the positive electrode active materials at each stage prepared in Example 1 was observed using SEM. The results are as follows: Figure 3 As shown, Figure 3 The material morphology photos of each process stage are shown, including scrapped positive electrode sheets (ac), positive electrode active material powder after lithium supplementation obtained in step S3 (de), positive electrode active material powder after heat treatment repair obtained in step S4 (g-i) and commercial new material powder (j-1). Figure 3 It can be seen that the material particles before being repaired by the method of the embodiments of the present application have crack defects of varying degrees. The morphology of the positive electrode active material powder after being repaired by the method of the embodiments of the present application presents a relatively smooth particle surface, and morphological defects such as microcracks basically disappear, which is consistent with the morphology of commercial new material powder.

[0093] Table 1 ICP-OES element measurement results

[0094]

[0095] Table 2 Electrochemical test data

[0096]

[0097] It is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recovering positive electrode active materials of lithium batteries, characterized in that: The method comprises the following steps: S1, providing a eutectic solution, wherein the eutectic solution comprises choline chloride, urea and a lithium salt; S2, placing the positive electrode sheet in the lithium battery into the eutectic solution to obtain a lithium-supplemented positive electrode sheet; S3, separating the lithium-supplemented positive electrode sheet obtained in S2 to obtain a lithium-supplemented positive electrode active material; S4, calcining the lithium-supplemented positive electrode active material obtained in S3 to obtain a repaired positive electrode active material.

2. The method according to claim 1, wherein: In S1, choline chloride and urea are mixed to obtain a mixed solution, and then a lithium salt is added to the mixed solution to obtain the eutectic solution.

3. The method according to claim 2, wherein: In S1, the choline chloride and urea are mixed at 50 to 90°C.

4. The method according to claim 1, wherein: In S1, the molar ratio of choline chloride, urea and lithium salt is 1:(0.5-5):(0.1-2).

5. The method according to claim 1, wherein: In S2, the positive electrode plate is placed in the low eutectic solution, subjected to ultrasonic radiation treatment, and then cleaned and dried to obtain the lithium-supplemented positive electrode plate.

6. The method according to claim 1, wherein: In S3, the separation treatment includes immersing the lithium-replenished positive electrode sheet in an N-methylpyrrolidone solvent and ultrasonically cleaning it, and obtaining the lithium-replenished positive electrode active material after mechanical separation.

7. The method according to claim 1, wherein: In S4, the calcination temperature is 700 to 900°C, the calcination time is 3 to 12 hours, the calcination atmosphere is air, nitrogen or oxygen, and the calcination temperature rise rate is 1 to 10°C / min.

8. The method according to any one of claims 1 to 7, wherein: The positive electrode active material includes one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate and their respective modified compounds. The lithium transition metal oxide is selected from at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide and lithium manganese cobalt oxide, and at least one of the modified compounds of the above oxides.

9. A secondary battery comprising a positive electrode active material recovered by the method according to claims 1 to 8.

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