Method for regenerating positive electrode active material and regenerated positive electrode active material produced thereby

Abstract

The present invention relates to a method for regenerating a cathode active material and a regenerated cathode active material produced therefrom. More specifically, the method includes the steps of: (a) recovering a cathode active material by heat-treating a used cathode, including a current collector and a cathode active material layer coated on the current collector, in air or oxygen; (b) adding a lithium precursor to the recovered cathode active material and heat-treating it in air to restore its crystalline structure; (c) doping the restored cathode active material with a dopant precursor and heat-treating it; and (d) washing the doped cathode active material with a cleaning solution. The present invention provides a method for regenerating a cathode active material and a regenerated cathode active material produced therefrom. The doping of a regenerated cathode active material with a predetermined dopant by a predetermined method improves capacity and life characteristics, and provides a method for regenerating a cathode active material with excellent crack resistance.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0152017 filed on November 6, 2023, and Korean Patent Application No. 10-2024-0144952, which was refiled on October 22, 2024 based on the Korean Patent Application No. 10-2023-0152017, and all contents disclosed in the documents of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material manufactured from the method. More specifically, the present invention relates to a method for regenerating a positive electrode active material, which has improved capacity characteristics and life characteristics and excellent crack resistance, by doping a regenerated positive electrode active material with a predetermined dopant in a predetermined manner, and a regenerated positive electrode active material manufactured from the method.

[0003] The present invention also relates to a method for regenerating a positive electrode active material that is environmentally friendly because it does not use an acid, reduces processing costs because it does not require neutralization or wastewater treatment, regenerates the positive electrode active material without decomposition, so no metal elements are discarded, and does not dissolve the current collector, making it possible to recover it. The present invention also relates to a method for regenerating a positive electrode active material that is suitable for mass production because it does not use an organic solvent, so there is no risk of toxic gas generation or explosion. The present invention also relates to a regenerated positive electrode active material produced from the method, which has excellent electrochemical performance, resistance characteristics, and capacity characteristics. [Background technology]

[0004] Lithium secondary batteries are broadly composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive electrode and negative electrode from mixing, and an electrolyte that allows lithium ions to move between the positive electrode and negative electrode.

[0005] The positive electrode active material layer mainly uses a lithium-based oxide as an active material, and the negative electrode active material layer mainly uses a carbon material as an active material. However, the lithium-based oxide generally contains rare metals such as cobalt, nickel, or manganese. Therefore, much research has been conducted into recovering and reusing rare metals from the positive electrodes of lithium secondary batteries that are discarded after use or from positive electrode scraps generated in the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0006] Conventional techniques for recovering rare metals from used positive electrodes mostly involve dissolving the used positive electrodes in hydrochloric acid, sulfuric acid, or nitric acid, then extracting cobalt, manganese, nickel, etc. with an organic solvent and using them again as raw materials for synthesizing positive electrode active materials.

[0007] However, the method of extracting rare metals using acid has the disadvantage of causing environmental pollution, requiring a neutralization process and a wastewater treatment process, which significantly increases the process cost, and making it impossible to recover lithium, the main metal in the positive electrode active material.

[0008] To overcome these drawbacks, direct recycling methods have recently been studied to directly recycle cathode active materials from waste cathodes without decomposing them. These methods can be broadly divided into four types: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0009] However, while the calcination method is simple, it has drawbacks such as the formation of foreign matter on the surface of the recycled cathode active material, which reduces the battery's output performance, the generation of waste gas, and high energy consumption. In particular, the use of excessive amounts of initial washing water is necessary to remove foreign matter such as LiF, making it difficult to apply to the regeneration process. In addition to generating a large amount of wastewater, significant problems arise, including the loss of Li in the functional coating layer and lattice of the recycled cathode active material due to washing, and the increased occurrence of cracks that reduce the output performance of secondary batteries. Among these, by-products generated during the degradation process can be removed by washing with water, and the loss of Li can be overcome to some extent by replenishing a Li source. However, the physically generated cracks cannot be restored to the same particle size distribution as virgin cathode active material using conventional direct recycling methods. The occurrence of cracks leads to an increase in the amount of fine powder and the specific surface area of ​​the recycled cathode active material, which promotes side reactions between the electrolyte and the surface of the recycled cathode active material, reducing active lithium and increasing the total cell resistance, ultimately resulting in a decrease in the battery life characteristics.

[0010] In addition, although the solvent dissolution method can produce recycled cathode active materials with a relatively clean surface, it has the disadvantage of being unstable because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and has the risk of explosion, and requires an expensive solvent recovery process.

[0011] In addition, the aluminum foil dissolution method has good process stability, low process costs, and easy binder removal, but has drawbacks in that it generates foreign matter that is difficult to remove on the surface of the recycled cathode active material, and hydrogen gas is generated during the aluminum foil removal process, which may pose an explosion risk.

[0012] Finally, the crushing and screening method has the advantage of being the simplest process, but has the disadvantages that it is difficult to completely separate the current collector from the cathode active material, the particle size distribution of the cathode active material changes during the crushing process, and the binder remains, which deteriorates the battery characteristics of the recycled cathode active material.

[0013] Therefore, there is an urgent need to develop a method for regenerating cathode active materials from waste cathodes that is environmentally friendly and safe, at low cost, and that has no discarded metal elements, has improved output performance and lifespan characteristics, and is particularly capable of improving crack resistance and significantly reducing wastewater. Summary of the Invention [Problem to be solved by the invention]

[0014] In order to solve the above-mentioned problems of the prior art, the present invention aims to provide a method for regenerating a cathode active material, which has improved capacity characteristics and life characteristics and excellent crack resistance, by doping a regenerated cathode active material with a predetermined dopant in a predetermined manner, and a regenerated cathode active material manufactured using the method.

[0015] The present invention also aims to provide a method for regenerating a positive electrode active material that is environmentally friendly because it does not use an acid, reduces processing costs because it does not require neutralization or wastewater treatment, regenerates the positive electrode active material without decomposition, so there are no metal elements to be discarded, and does not dissolve the current collector, making it possible to recover it, does not use an organic solvent, so there is no risk of toxic gas generation or explosion, and uses processes that are easy to manage, such as heat treatment and sedimentation, making it suitable for mass production, and to provide a regenerated positive electrode active material produced from the method that has excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0016] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0017] To achieve the above object, I) the present invention provides a regenerative cathode active material comprising at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and characterized in that the regenerative cathode active material is doped with a dopant and has no coating layer.

[0018] II) In the above I), the dopant may be contained in an amount of 100 to 2000 ppm based on the total weight of the regenerated positive electrode active material.

[0019] III) In I) or II), the dopant may be one or more selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N.

[0020] IV) In I) to III), the recycled positive electrode active material may have a dopant element coated on the surface without being doped at 10 ppm or less based on EDS (Energy Dispersive Spectroscopy) surface mapping.

[0021] V) In the above I) to IV), the regenerated positive electrode active material may contain 40 to 45 wt % carbon element, 25 to 30 wt % oxygen element, and 25 to 30 wt % nickel element based on EDS (Energy Dispersive Spectroscopy) surface mapping.

[0022] VI) The present invention also provides a method for regenerating a positive electrode active material, including: (a) a step of heat-treating, in air or oxygen, a used positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector, to recover the positive electrode active material; (b) a step of adding a lithium precursor to the recovered positive electrode active material, and heat-treating the material in air to recover its crystal structure; (c) a step of adding a dopant precursor to the positive electrode active material whose crystal structure has been recovered, and heat-treating the material to dope it; and (d) a step of washing the doped positive electrode active material with a washing solution.

[0023] VII) In the above VI), in the step (a), the heat treatment may be carried out under conditions of 300 to 650°C.

[0024] VIII) In the above VI) or VII), the heat treatment in the step (b) may be carried out under conditions of 400 to 1000°C.

[0025] IX) In the above VI) to VIII), in the step (b), the lithium precursor may be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0026] X) In the above VI) to IX), in the step (c), the heat treatment may be carried out under conditions of 300 to 1000°C.

[0027] XI) In VI) to X), in step (c), the dopant precursor may be a compound that provides one or more elements selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N as a dopant.

[0028] XII) In the above VI) to XI), in the step (d), the cleaning liquid may be water.

[0029] XIII) In the above VI) to XII), the method for regenerating the positive electrode active material may include: (a-2) a step of washing the recovered positive electrode active material with a washing solution; and / or (b-2) a step of washing the positive electrode active material whose crystal structure has been restored.

[0030] XIV) In the above VI) to XIII), the cleaning liquid in the step (a-2) may be water or a basic aqueous solution of a lithium compound having a concentration of more than 0 wt % and not more than 15 wt %, and the cleaning liquid in the step (b-2) may be water.

[0031] XV) In the above VI) to XIV), in the step (c), the dopant precursor may be added in an amount of 100 to 2000 ppm (dopant element basis) based on the total weight of the regenerated positive electrode active material.

[0032] XVI) In the above VI) to XV), the positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co).

[0033] Furthermore, XVII) the present invention provides a regenerated positive electrode active material, which is produced by the method for regenerating a positive electrode active material according to any one of VI) to XVI).

[0034] Furthermore, XVIII) the present invention provides a secondary battery containing the regenerated positive electrode active material according to any one of I) to XVII). [Effects of the Invention]

[0035] According to the present invention, by doping a predetermined dopant into a recycled positive electrode active material in a predetermined manner, the capacity characteristics and life characteristics are improved, and there is an effect of providing a method for recycling a positive electrode active material with excellent crack resistance, and a recycled positive electrode active material manufactured from the method.

[0036] Furthermore, the present invention provides a method for regenerating a positive electrode active material that is environmentally friendly because it does not use an acid, and reduces process costs because it does not require neutralization or wastewater treatment. The method regenerates the positive electrode active material without decomposition, so there are no metal elements to be discarded. The current collector is not dissolved, so it can be recovered. The method does not use an organic solvent, so there is no risk of toxic gas generation or explosion. The method uses processes that are easy to manage, such as heat treatment and sedimentation, making it suitable for mass production. It also provides a regenerated positive electrode active material manufactured from the method, which has excellent electrochemical performance and resistance characteristics.

[0037] The drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the details shown in these drawings. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 10 is a diagram showing positive electrode scraps that are discarded after cutting electrode plates from a positive electrode sheet. [Figure 2] 1 is a flowchart illustrating a process for regenerating a positive electrode active material according to one embodiment of the present invention. [Figure 3] FIG. 1 is a diagram conceptually illustrating the general structure of the regenerated positive electrode active materials produced in Example 1 and Comparative Examples 1 to 3. [Figure 4] 1 is an EDS (Energy Dispersive Spectrometer) cross-sectional mapping image of the recycled positive electrode active material prepared in Example 1. No B2O3 coating layer was found here. [Figure 5]1 is an EDS (Energy Dispersive Spectrometer) cross-sectional mapping image of the recycled positive electrode active material prepared in Comparative Example 1. No B2O3 coating layer was found here. [Figure 6] 1 is an EDS (Energy Dispersive Spectrometer) mapping image of the recycled positive electrode active material prepared in Comparative Example 2. A boron coating layer was confirmed here, and elemental analysis was performed at point #11 where the boron coating layer was formed and point #12 where the boron coating layer was not formed. [Figure 7] 1 is an EDS (Energy Dispersive Spectrometer) mapping image of the recycled cathode active material prepared in Comparative Example 3. A boron coating layer was confirmed here, and elemental analysis was performed at points #13, #15, and #16 where the boron coating layer was formed, and at point #14 where no boron coating layer was formed. [Figure 8] 1 is an XPS graph showing the change in the content of elements detected depending on the etching time of the recycled positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 3, respectively. [Figure 9] 1 is a graph showing the results of measuring the initial charge / discharge capacity of coin half cells using the positive electrode active materials regenerated in Example 1 and Comparative Examples 1 to 3. [Figure 10] 1 is a graph showing the results of coin half-cell evaluation of the recycled positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 3, illustrating the change in capacity retention depending on the number of cycles. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, the method for regenerating a positive electrode active material according to the present invention and the regenerated positive electrode active material produced therefrom will be described in detail.

[0040] The inventors have been researching ways to further improve the capacity and lifespan characteristics of recycled cathode active materials in a direct recycled method for recycling used cathodes into cathode active materials without decomposing them. They have found that when recycled cathode active materials are doped with a specific dopant in a specific manner, rather than coated as in the past, the crack resistance of the recycled cathode active materials is improved, and the capacity and lifespan characteristics of batteries using this are significantly improved. Based on this, the inventors have continued their research and have completed the present invention.

[0041] The method for regenerating a positive electrode active material of the present invention is characterized by comprising the steps of: (a) heat-treating a used positive electrode, including a current collector and a positive electrode active material layer coated on the current collector, in air or oxygen to recover the positive electrode active material; (b) adding a lithium precursor to the recovered positive electrode active material and heat-treating it in air to recover the crystal structure; (c) adding a dopant precursor to the positive electrode active material whose crystal structure has been recovered and heat-treating it to dope it; and (d) washing the doped positive electrode active material with a washing solution. In this case, the capacity characteristics and life characteristics of the regenerated positive electrode active material are improved. The method has the following advantages: improved corrosion resistance, excellent crack resistance, and is environmentally friendly because it does not use acid, and process costs are reduced because neutralization and wastewater treatment are not required; the positive electrode active material is regenerated as is without being decomposed, so there are no metal elements to be discarded; the current collector is not dissolved, so it can be recovered; no organic solvent is used, so there is no risk of toxic gas generation or explosion; and the method uses processes that are easy to manage, such as heat treatment and sedimentation, making it suitable for mass production. It also provides a regenerated positive electrode active material manufactured from the method, which has excellent electrochemical performance and resistance characteristics.

[0042] The method for regenerating a positive electrode active material according to the present invention will be described in detail below, step by step.

[0043] However, the terms and words used in this specification and claims should not be interpreted limitedly to their ordinary or dictionary meanings, but should be interpreted in terms and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the terms in order to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely examples of the present invention and do not represent the entire technical idea of ​​the present invention, and therefore there are various equivalents and modifications that can be substituted for them, and they can be arranged, substituted, combined, separated, or designed in various other configurations.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0045] (a) A step of recovering a positive electrode active material from a waste positive electrode The step (a) of recovering a positive electrode active material from a used positive electrode according to the present invention may be a step of recovering the positive electrode active material by heat-treating a used positive electrode including a current collector and a positive electrode active material layer coated on the current collector, and preferably a step of heat-treating a used positive electrode having a positive electrode active material layer containing 60 mol % or more of Ni among transition metals formed on a current collector at 300 to 650°C in air to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer. In this case, the process is simple and has the effect of completely removing the binder, conductive material, and current collector.

[0046] The discarded positive electrodes may preferably be positive electrodes separated from used and discarded lithium secondary batteries, defective positive electrode sheets or positive electrode scraps generated during the manufacturing process of lithium secondary batteries, or more preferably positive electrode scraps remaining after punching out positive electrode plates from positive electrode sheets.

[0047] The positive electrode active material layer in step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0048] The positive electrode active material is preferably a lithium cobalt oxide such as LiCoO2 (hereinafter referred to as "LCO"); a lithium manganese oxide such as LiMnO2 or LiMn2O4; a lithium iron phosphate compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); a lithium nickel oxide such as LiNiO2; a nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) of the lithium nickel oxide is replaced with manganese (Mn); and an NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) of the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). It may be at least one selected from the group consisting of, more preferably, a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0049] As still another specific example, the positive electrode active material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented by.

[0050] As an example, the positive electrode active material contains Ni at 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, still more preferably 81 to 95 mol%, and even more preferably 85 to 95 mol% based on 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0051] In the present application, the Ni content may be measured by a method using IC (Ion Chromatography) or the like, which is commonly used in the technical field to which the present invention pertains, without any particular limitation. For example, the Ni content may be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectrometer), or an IC-ICP-AES (Atomic Emission Spectrometer).

[0052] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT (carbon nanotube), or a mixture thereof.

[0053] The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0054] For example, the heat treatment may be performed in an air or oxygen atmosphere. In this case, the binder and the conductive material are thermally decomposed into CO and HO and removed, thereby separating the positive electrode active material from the current collector. The separated positive electrode active material has an advantage that it can be easily sorted in a powder form.

[0055] The heat treatment temperature may be preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0056] The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0057] In the present application, the heat treatment time refers to the time required for treatment at the heat treatment temperature, and does not include the time required to reach the heat treatment temperature.

[0058] The heat treatment may be performed with a temperature increase rate of, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min. Within this range, the heat treatment can be performed without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock or the like is caused to the cathode scrap.

[0059] FIG. 1 shows the cathode scrap that is discarded after cutting the cathode plates from the cathode sheet.

[0060] 1, a long sheet-shaped positive electrode current collector, aluminum foil 10, is coated with a positive electrode active material layer 20 containing a positive electrode active material, a conductive material, a binder, etc. to produce a positive electrode sheet 30, which is then punched to a predetermined size to produce a positive electrode plate 40, with the remaining portion being generated as positive electrode scrap 50. Punching is one method of cutting the positive electrode sheet.

[0061] In addition, the positive electrode active material layer 20 is formed by coating a slurry containing a positive electrode active material, a conductive material, a binder, a solvent, etc., on the aluminum foil 10. Since the slurry is very sensitive to environmental factors such as temperature, it is very difficult to determine the coating conditions. Therefore, a considerable amount of waste positive electrode sheets is generated until the conditions for manufacturing a positive electrode sheet 30 of desired quality are found through predetermined tests.

[0062] For reference, in the following examples, scrap positive electrodes were used as waste positive electrodes.

[0063] Step of washing the recovered positive electrode active material The method for reusing a positive electrode active material according to the present invention may include (a-2) a step of washing the recovered positive electrode active material (hereinafter referred to as "pre-washing"). In this case, metal fluorides such as LiF that may be present on the surface of the recycled positive electrode active material are removed, and the surface is modified, thereby improving the rate performance of the battery.

[0064] During the heat treatment, the binder and conductive material in the positive electrode active material are thermally decomposed, generating CO2 and HO, which can react with lithium on the surface of the active material to form Li2CO3 and LiOH. Fluorine (F) present in binders such as PVdF can also react with metal elements that make up the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, the battery performance will deteriorate when the positive electrode active material is reused.

[0065] The (a-2) step of washing the recovered cathode active material may, for example, be a step of mixing the recovered cathode active material with a washing solution, followed by filtering and washing using a filter press. In this case, the amount of rinsing solution determines the content of residual F, so even if the amount of cathode active material to be washed increases, replacement of equipment such as a stirring tank is not necessary. Furthermore, the total amount of cleaning solution, which is the combination of the initial cleaning solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. By minimizing the amount of initial cleaning solution added to the stirring tank and adjusting the amount of rinsing solution, residual F components can be easily removed, while also improving the rate performance of the battery.

[0066] The filter press in the (a-2) washing step may be operated at an air pressure of preferably 2 to 10 bar, more preferably 3 to 9 bar, even more preferably 3 to 8 bar, even more preferably 3 to 7 bar, and most preferably 3 to 6 bar. Within this range, the amount of rinsing solution determines the content of residual fluorine components. Therefore, even when the amount of cathode active material to be washed increases, replacement of equipment such as a stirring tank is not necessary. Furthermore, the total amount of cleaning solution, including the initial cleaning solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. By minimizing the amount of initial cleaning solution added to the stirring tank and adjusting the amount of rinsing solution, residual fluorine components can be easily removed, while improving the output performance of the battery.

[0067] The filter press in the (a-2) washing step preferably has an air permeability of 0.1 to 15 cc / cm 2 ( / sec), and more preferably, the filter cloth has an air permeability of 0.2 to 10 cc / cm 2 (sec), more preferably a filter cloth with an air permeability of 0.3 to 5 cc / cm 2 ( / sec), and more preferably, a filter cloth with an air permeability of 0.5 to 2 cc / cm 2 ( / sec), most preferably a filter cloth with an air permeability of 0.6 to 1 cc / cm 2 ( / sec) of filter cloth, and within this range, the residual F content is determined by the amount of rinse solution. Therefore, even if the amount of cathode active material to be washed increases, there is no need to replace equipment such as a stirring tank. Furthermore, the total amount of cleaning solution, which is the initial cleaning solution and the rinse solution combined, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. By minimizing the amount of initial cleaning solution added to the stirring tank and adjusting the amount of rinse solution, the residual F component can be easily removed, and at the same time, the output performance of the battery can be improved.

[0068] The filter cloth is not particularly limited as long as it is made of a material commonly used for filter presses as long as it complies with the definition of the present invention, and a specific example thereof may be made of polypropylene.

[0069] The filter press of the present application is not particularly limited in type or material as long as it meets the definition of the present invention and is physically and chemically stable with respect to the cathode active material slurry. For example, the filter press may include a frame, a filter plate, a filter cloth, a filter cloth pressurizing device, a filter plate separating device, a filter cloth washing device, and a transfer pump.

[0070] The cleaning solution in the (a-2) cleaning step may preferably be water or a basic lithium compound aqueous solution. In this case, the F component remaining on the surface of the regenerated positive electrode active material can be completely removed with a small amount of cleaning solution, which significantly reduces the generation of wastewater and at the same time significantly improves the output performance of the battery.

[0071] In the present application, the water is not particularly limited as long as it is neutral water, and examples thereof include distilled water and ion-exchanged water.

[0072] The washing solution in the (a-2) washing step may be, for example, a basic lithium compound aqueous solution, which not only removes trace amounts of binder that may remain on the surface of the cathode active material recovered after the thermal decomposition in step (a), but also replenishes the amount of lithium that may be leached during washing without leaching transition metals present in the recovered cathode active material. If an acidic aqueous solution such as a sulfuric acid or hydrochloric acid aqueous solution is used as the washing solution, it can wash away F components from the surface of the cathode active material, but it will leach transition metals present in the cathode active material, thereby reducing the performance of the reused cathode active material.

[0073] The basic lithium compound aqueous solution may preferably contain more than 0 wt % and not more than 15 wt % of the basic lithium compound, more preferably more than 0 wt % and not more than 10 wt %, and even more preferably 0.5 to 5 wt % of the basic lithium compound. Within this range, an excellent surface modification effect can be achieved, such as removal of F components formed on the surface of the positive electrode active material during the heat treatment, such as LiF and metal fluorides.

[0074] The (a-2) washing step preferably includes step (a1) of mixing the recovered cathode active material with a washing solution to form a slurry, and step (a2) of introducing the slurry into a filter press and filtering the slurry. More preferably, the method includes step (a1) of mixing the recovered cathode active material with a washing solution to form a slurry, step (a2) of introducing the slurry into a filter press and filtering the slurry, and step (a3) ​​of introducing a rinse solution into the filter press to rinse the filter cake. In this case, the amount of the rinse solution determines the content of residual fluorine components. Therefore, even if the amount of cathode active material to be washed increases, replacement of equipment such as a stirring tank is not necessary. Furthermore, the total amount of cleaning solution, which is the combination of the initial cleaning solution and the rinse solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. By minimizing the amount of initial cleaning solution introduced into the stirring tank and adjusting the amount of rinse solution, residual fluorine components can be easily removed, while improving the output performance of the battery.

[0075] The step (a1) of mixing the recovered positive electrode active material with a cleaning solution to form a slurry may preferably be a step of using a stirrer to stir the recovered positive electrode active material with water or a basic lithium compound aqueous solution to form a slurry. In this case, as a step of modifying the surface of the positive electrode active material, it is highly effective in removing foreign matter such as LiF or metal fluorides generated on the surface of the positive electrode active material during the previous heat treatment process.

[0076] The agitator may be, for example, an impeller type, a magnetic type, and / or an ultrasonic agitator, but is not particularly limited thereto.

[0077] The stirring may be carried out for, for example, within one week, preferably within one day, more preferably for one hour or less, 40 minutes or less, 30 minutes or less, or 20 minutes or less, or for, for example, 5 minutes or more, preferably 10 minutes or more, 20 minutes or more, or 30 minutes or more. Within this range, all of the foreign matter of F components, such as LiF or metal fluorides, generated on the surface of the positive electrode active material is removed, and yet excessive lithium elution does not occur, resulting in excellent battery capacity characteristics.

[0078] The amount of the cleaning solution used in step (a1) may be preferably 0.5 to 5 times, more preferably 0.5 to 4 times, even more preferably 0.8 to 3 times, and even more preferably 0.9 to 2 times the weight of the recovered positive electrode active material. Within this range, residual F components such as LiF can be easily removed, and the total amount of cleaning solution, including the initial cleaning solution and the rinse solution, can be significantly reduced. This reduces the amount of wastewater, wastewater treatment costs, and environmental pollution, and has the effect of improving the rate performance of the battery.

[0079] The amount of the rinse solution used in step (a3) ​​may be preferably 5 to 20 times the weight of the recovered positive electrode active material, more preferably 5 to 15 times, even more preferably 8 to 15 times, even more preferably 8 to 13 times, and even more preferably 8 to 12 times. Within this range, the total amount of the cleaning solution, including the initial cleaning solution and the rinse solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. Furthermore, the amount of the initial cleaning solution added to the stirring tank is minimized, and the amount of the rinse solution can be adjusted to easily remove residual F components, thereby improving the output performance of the battery.

[0080] For example, the weight ratio of the cleaning solution in step (a1) and the rinse solution in step (a3) ​​may be 1:2 to 15, preferably 1:7 to 15, more preferably 1:7 to 13, even more preferably 1:8 to 13, even more preferably 1:8 to 12, and particularly preferably 1:9 to 11. Within this range, the amount of rinse solution determines the content of residual F. Therefore, even when the amount of cathode active material to be washed increases, replacement of equipment such as a stirring tank is not necessary. Furthermore, the total amount of cleaning solution, including the initial cleaning solution and the rinse solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. The amount of initial cleaning solution added to the stirring tank can be minimized, and adjusting the amount of rinse solution can easily remove residual F components, while improving the output performance of the battery.

[0081] The (a-2) washing step may preferably include a step of recovering the solid content after the filtration or rinsing and drying it, which has the advantage of optimizing and facilitating the subsequent crystal structure recovery step.

[0082] The drying may be carried out at preferably 50 to 200°C, more preferably 50 to 150°C, even more preferably 70 to 150°C, and even more preferably 100 to 150°C until there is no further change in weight, for example, for 1 to 24 hours. Within this range, there is an advantage that moisture contained in the washed positive electrode active material can be efficiently removed.

[0083] (b) A step of restoring the crystalline structure of the washed positive electrode active material The step (b) of recovering the crystal structure according to the present invention may be a step of adding a lithium precursor to the recovered positive electrode active material and performing heat treatment in air to recover the crystal structure. In this case, there is an advantage in that a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0084] The step (b) of restoring the crystal structure may preferably be a step of adding a lithium precursor to the positive electrode active material whose crystal structure has been restored, and heat-treating the material in oxygen (O2) or air at 400 to 1000°C, more preferably 700 to 900°C, and even more preferably 710 to 780°C. In this case, improving the crystallinity of the positive electrode active material, such as increasing the crystallinity or restoring the crystal structure, has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0085] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0086] The lithium precursor is preferably added in an amount that is at least the amount of lithium subtracted from the amount of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. For example, when the recovered positive electrode active material in step (a) is a positive electrode active material represented by Chemical Formula 1, the lithium precursor is added in an amount that results in a lithium molar ratio of 0.0001 to 0.2 relative to the lithium molar ratio of 1 in the positive electrode active material, preferably an amount that results in a lithium molar ratio of 0.001 to 0.02, more preferably an amount that results in a lithium molar ratio of 0.005 to 0.017, even more preferably an amount that results in a lithium molar ratio of 0.007 to 0.015, and even more preferably an amount that results in a lithium molar ratio of 0.009 to 0.013. Within this range, the lithium that is insufficient in the regenerated positive electrode active material is replenished, and the crystallinity is improved, such as by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0087] As another example, the lithium precursor may be added in an amount corresponding to 1 to 40 mol %, preferably 1 to 15 mol %, and more preferably 1 to 10 mol %, when the total amount of lithium contained in the raw material positive electrode active material is 100 mol %. Within this range, no residual precursor that could increase resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics, and is economically advantageous because the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods.

[0088] As another example, the heat treatment temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, since the melting point of LiCO is 723°C, the heat treatment can be preferably performed at 700 to 900°C, more preferably 710 to 780°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance.

[0089] The heat treatment temperature may preferably be a temperature exceeding the melting point of the lithium precursor. However, if the temperature exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance. Therefore, it is preferable that the heat treatment temperature be 1000°C or less.

[0090] The heat treatment time is, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 2 to 10 hours, even more preferably 3 to 8 hours, and even more preferably 4 to 6 hours. As a specific example, it is preferably about 5 hours. Within this range, the crystal structure is sufficiently restored and there is an economic advantage.

[0091] The heat treatment temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, more preferably at a temperature rise rate of 1 to 5°C / min, and even more preferably at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0092] The crystalline structure recovery step includes, for example, a cooling process, which may be, for example, natural cooling in a furnace. In this case, the crystallinity of the recycled positive electrode active material is further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0093] In the present application, recovery of the crystal structure may follow the definition used in the technical field to which the present invention belongs. Specifically, it may be defined as a heat treatment operation in which a positive electrode active material having a deformed structure or lattice defects is heated for an appropriate time at a temperature at or above the recrystallization temperature at which atoms of the main component therein can sufficiently diffuse and move, thereby healing the deformation or lattice defects and appropriately adjusting the crystallinity.

[0094] A step of washing the positive electrode active material whose crystalline structure has been restored The step (b-2) of washing the positive electrode active material whose crystal structure has been recovered (hereinafter referred to as "post-washing") according to the present invention may be a step of mixing the positive electrode active material whose crystal structure has been recovered with a washing solution and then filtering the mixture. In this case, there is an advantage that the lithium compound remaining on the surface of the positive electrode active material whose crystal structure has been recovered is removed, thereby improving the battery characteristics.

[0095] The post-cleaning step can be preferably carried out by mixing the crystalline structure-recovered cathode active material with a cleaning solution and then filtering it using a filter press. In this case, compared to conventional vacuum filtration, a smaller amount of cleaning solution can be used to clean the lithium remaining in the crystalline structure recovery step, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. Furthermore, even if the amount of cathode active material to be cleaned increases, there is no need to replace equipment such as a stirring tank. Furthermore, by removing residual lithium compounds from the regenerated cathode active material, the initial discharge capacity, rate performance, and capacity characteristics of the battery can be significantly improved.

[0096] The amount of the cleaning solution may be preferably 0.5 to 5 times the weight of the recovered positive electrode active material, more preferably 0.5 to 4 times, even more preferably 0.8 to 3 times, even more preferably 0.9 to 2 times, and even more preferably 0.9 to 1.5 times. Within this range, there is an advantage that the lithium compound remaining on the surface of the positive electrode active material whose crystal structure has been restored is effectively removed without leaching out the effective metal, thereby improving the battery characteristics.

[0097] The cathode active material obtained after the post-cleaning step may preferably have a residual lithium precursor (e.g., LiOH) content of 1000 ppm or less, more preferably 800 ppm or less. Within this range, the residual lithium precursor is prevented from reacting with the dopant precursor in the subsequent doping step to form a LiB3O5 (LBO) coating layer on the surface of the regenerated cathode active material, thereby improving doping efficiency and battery characteristics.

[0098] The post-cleaning step may include all of the above-described steps except for the rinsing step in (a-2) cleaning, except for the steps separately defined herein. Therefore, the overlapping parts will not be described again. However, in step (b-2), it is preferable to use a minimal amount of rinsing solution (e.g., 1x or less, 0.5x or less, or 0.1x or less) or to not use it at all. In this case, there is an advantage that effective metals are not leached from the positive electrode active material whose crystalline structure has been restored.

[0099] (c) Doping the positive electrode active material whose crystal structure has been restored The method for regenerating a positive electrode active material of the present invention includes (c) a step of adding a dopant precursor to the positive electrode active material whose crystal structure has been restored, and heat-treating it to dope it. In this case, doping the regenerated positive electrode active material with a dopant improves the capacity characteristics and life characteristics, and has the effect of providing excellent crack resistance.

[0100] In step (c), the heat treatment can be carried out, for example, at 300 to 1000°C, preferably 300 to 600°C, specifically 400 to 900°C, preferably 450 to 800°C, more preferably 500 to 700°C, and even more preferably 550 to 650°C. Within this range, no loss due to deterioration occurs in the regenerated positive electrode active material, and the dopant is stably doped, resulting in improved capacity characteristics and life characteristics and improved crack resistance.

[0101] In step (c), the dopant precursor is, for example, a compound that provides one or more elements selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N as a dopant, and is preferably a compound that provides one or more elements selected from the group consisting of B, Na, Mg, and F as a dopant. In this case, the dopant is stably doped into the recycled positive electrode active material, the surface coating layer is easily removed by cleaning or rinsing with water, and the capacity characteristics, life characteristics, and crack resistance are greatly improved.

[0102] In step (c), the dopant precursor may be added preferably in an amount of 100 to 2000 ppm (dopant element basis) relative to the total weight of the recycled positive electrode active material, more preferably 300 to 1500 ppm, even more preferably 400 to 1200 ppm, even more preferably 500 to 1000 ppm, and even more preferably 600 to 900 ppm. Within this range, the dopant is stably doped into the recycled positive electrode active material, significantly improving capacity characteristics and life characteristics and providing excellent crack resistance.

[0103] For example, step (c) may involve adding or applying a dopant precursor, either alone or dissolved in a solvent, to the positive electrode active material whose crystal structure has been restored, followed by heat treatment to dope the material. A preferred example of step (c) involves adding a dopant precursor alone to the positive electrode active material whose crystal structure has been restored, followed by a solid-state reaction, i.e., heat treatment to dope the material. In this case, doping the regenerated positive electrode active material with the dopant improves capacity and life characteristics and crack resistance. Here, a liquid-phase reaction using a solvent is highly efficient, while a solid-phase reaction using only the dopant precursor is advantageous for mass production, and so these methods can be selectively applied as needed.

[0104] The dopant precursor may be, for example, an oxide, an acid, or an organometallic compound containing the dopant element.

[0105] The heat treatment time is preferably 1 to 10 hours, more preferably 3 to 5 hours. Within this range, the dopant is stably doped into the recycled positive electrode active material, which has the effect of significantly improving the capacity characteristics and life characteristics and providing excellent crack resistance.

[0106] The heat treatment temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, more preferably at a temperature rise rate of 1 to 7°C / min, and even more preferably at a temperature rise rate of 1 to 5°C / min. Within this range, the dopant is stably doped into the recycled positive electrode active material, which has the effect of significantly improving the capacity characteristics and life characteristics and providing excellent crack resistance.

[0107] The heat treatment can be carried out in air or oxygen, preferably in oxygen. In this case, the dopant is stably doped into the recycled positive electrode active material, which has the effect of significantly improving capacity characteristics and life characteristics and providing excellent crack resistance.

[0108] The solvent is not particularly limited as long as it does not affect the positive electrode active material, and may be, for example, water or an organic solvent such as alcohol, and the alcohol may preferably be methanol or ethanol.

[0109] Regenerated cathode active material The recycled positive electrode active material of the present invention is characterized by being produced by the above-described method for recycling a positive electrode active material. In this case, the recycled positive electrode active material is doped with a predetermined dopant, which has the effect of improving capacity characteristics and life characteristics and improving crack resistance.

[0110] In addition, the regenerated positive electrode active material of the present invention includes at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and is characterized by being doped with a dopant and having no coating layer. In such cases, there are effects such as improved capacity characteristics and life characteristics and excellent crack resistance.

[0111] In the doping process, the dopant element itself penetrates into the crystalline structure of the cathode active material to a thickness of several nanometers on the surface of the post-cleaned cathode active material particles, significantly reducing the increase in resistance at the surface of the cathode active material compared to coating, thereby improving battery life. However, the coating layer is formed when oxides produced by the reaction or thermal decomposition of the dopant precursor with a lithium compound adhere to the surface of the post-cleaned cathode active material, acting as resistance and causing deterioration of battery life. Therefore, to dope a regenerated cathode active material without a coating layer, it is important to add a predetermined dopant precursor to the cathode active material whose crystalline structure has been restored, heat-treat it at a predetermined heat-treatment temperature, and then wash it using a predetermined method to remove the coating layer, leaving only the doped dopant.

[0112] For example, the coating layer may refer to an aggregate of undoped dopant precursors that have converted into oxides or the like and are attached to the surface of the positive electrode active material in the form of nodules. During the cleaning, this coating layer is removed, and only the doped dopant remains on the regenerated positive electrode active material.

[0113] FIG. 3 shows the schematic structures of the regenerated cathode active material prepared in Example 1 by doping without a coating layer and the regenerated cathode active material prepared in Comparative Example 2 by coating with a coating layer. The regenerated cathode active material prepared in Example 1 is doped with a dopant rather than a conventional surface coating, eliminating side reactions between the coating layer and the cathode active material. The dopant also stabilizes the surface, resulting in improved long-term life and an increased initial charge / discharge capacity. In contrast, Comparative Example 2 formed a doping layer and a surface coating layer on the regenerated cathode active material, but the surface coating layer was not removed. As charge / discharge cycles progressed, cracks developed at the interface between the cathode active material surface and the coating layer, creating resistance between the dissimilar interfaces and deteriorating long-term life. The surface coating layer may be a boron coating layer containing B2O3 and a trace amount of LBO (a reaction product of boric acid and LiOH remaining on the surface of the cathode active material).

[0114] 4 and 6 show EDS (Energy Dispersive Spectrometer) mapping images of the recycled cathode active materials prepared in Example 1 and Comparative Example 2. The recycled cathode active material prepared in Example 1 had the coating layer removed by washing, leaving only the doped dopant, so the entire surface was uniform and had the same composition ratio regardless of the position on the recycled cathode active material. No boron (B) was detected in the surface analysis. In contrast, the recycled cathode active material of Comparative Example 2, which only underwent the doping and coating step of forming the coating layer without the coating layer removal (washing) step, had a large amount of boron (B) present in the coating layer.

[0115] 9 and 10 show the initial charge / discharge capacity and the change in capacity retention rate with the number of cycles for the recycled cathode active materials prepared in Example 1 and Comparative Example 2. The recycled cathode active material of Example 1, which is doped with a dopant without a coating layer, exhibits low surface resistance and suppressed surface side reactions due to the doping effect, resulting in excellent initial charge / discharge capacity and charge / discharge efficiency. Furthermore, the low surface resistance and suppressed surface side reactions result in excellent capacity retention rate, i.e., excellent life characteristics. In contrast, the recycled cathode active material of Comparative Example 2, which includes a coating layer, exhibits partial doping, but the B2O3 coating layer and LiB3O5 coating layer, respectively, act as surface resistance, resulting in reduced initial charge / discharge capacity and charge / discharge efficiency, as well as poor life characteristics.

[0116] The dopant may be preferably contained in an amount of 100 to 2000 ppm, more preferably 300 to 1500 ppm, even more preferably 400 to 1200 ppm, even more preferably 500 to 1000 ppm, and even more preferably 600 to 900 ppm, relative to the total weight of the recycled positive electrode active material. Within this range, the capacity characteristics and life characteristics are greatly improved, and excellent crack resistance is achieved.

[0117] The dopant is preferably one or more selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N, and more preferably one or more selected from the group consisting of B, Na, Mg, and F. In this case, the capacity characteristics and life characteristics are greatly improved, and excellent crack resistance is achieved.

[0118] The recycled positive electrode active material may preferably have a dopant element that is not doped but remains on the surface (coated) at 10 ppm or less, preferably 5 ppm or less, based on EDS (Energy Dispersive Spectroscopy) surface mapping. Within this range, the regenerated positive electrode active material has the effects of low resistance, significantly improved capacity characteristics and life characteristics, and excellent crack resistance.

[0119] The recycled positive electrode active material may preferably contain 40 to 45 wt % carbon, 25 to 30 wt % oxygen, and 25 to 30 wt % nickel, based on EDS (Energy Dispersive Spectroscopy) surface mapping, and more preferably contain 42 to 45 wt % carbon, 26 to 29 wt % oxygen, and 27 to 30 wt % nickel. Within these ranges, the resistance is low, capacity characteristics and life characteristics are greatly improved, and crack resistance is excellent.

[0120] The regenerated cathode active material has a residual F content of, for example, 8000 ppm or less, preferably 2000 ppm or less, more preferably 1800 ppm or less, even more preferably 1700 ppm or less, and even more preferably 1600 ppm or less, specifically 1 to 8000 ppm. In this case, the battery output performance is improved and the electrochemical performance, resistance characteristics, and capacity characteristics are excellent. In this application, the residual F content refers to the content of all residual F components in not only LiF but also other residual components.

[0121] In the present application, the residual F content may be measured by a method using IC (Ion Chromatography), which is commonly used in the technical field to which the present invention pertains, without particular limitation, and may be measured using, for example, an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectrometer), or an IC-ICP-AES (Atomic Emission Spectrometer), etc. In the present application, IC-ICP (Inductively Coupled Plasma) can be used preferentially.

[0122] In yet another specific example, the regenerated positive electrode active material is represented by the following chemical formula 1: (chemical formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the chemical formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. ) It may be a compound represented by this formula, and in this case, there is an effect that it is excellent in electrochemical performance, resistance characteristics, capacitance characteristics, and the like.

[0123] The recycled positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and still more preferably 81 to 95 mol% based on a total of 100 mol% of the remaining metals or transition metals excluding Li. Within this range, there is an effect that it is excellent in charge capacity, resistance characteristics, and capacitance characteristics.

[0124] FIG. 2 is a flowchart for the regeneration process of the positive electrode active material according to one embodiment of the present invention.

[0125] Referring to FIG. 2, first, positive electrode scrap is prepared as waste positive electrode (step S10). For example, NMP (N-methyl pyrrolidone) is added to NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride and mixed to produce a slurry, which is coated on an aluminum foil and dried in a vacuum oven at about 120 °C to produce a positive electrode sheet. After punching out a positive electrode plate of a certain size from this, the remaining positive electrode scrap can be prepared.

[0126] The positive electrode scrap has a positive electrode active material layer on an aluminum foil, and the positive electrode active material layer has a structure in which the positive electrode active material and the conductive material are bound by a binder after the solvent volatilizes.

[0127] Next, the prepared cathode scrap is crushed to an appropriate size (step S20). Here, crushing includes cutting or shredding the cathode scrap to a size that is easy to handle. As a specific example, the crushed cathode scrap may be 1 cm x 1 cm in size. For example, the crushing may be performed using various dry crushing devices such as a hand mill, a disc mill, a cutting mill, or a hammer mill, or a high-speed cutter may be used to increase productivity.

[0128] The decision as to whether or not to crush the cathode scrap and the size of the pieces can be made taking into consideration the handling of the cathode scrap and the properties required for the equipment used in the subsequent steps. For example, when using equipment capable of continuous processing, the cathode scrap must have good fluidity, so it is necessary to crush it into even smaller pieces.

[0129] Next, the crushed positive electrode scrap is heat-treated in air at 500 to 600°C to recover the positive electrode active material (step S30). Here, the heat treatment is carried out to thermally decompose the binder and conductive material in the positive electrode active material layer.

[0130] Through the heat treatment in air, the binder and conductive material in the positive electrode active material layer are thermally decomposed into CO2 and H2O and removed. As the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0131] It is important that the heat treatment be performed in air or in the presence of oxygen. However, if the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and conductive material will carbonize without being thermally decomposed. Carbonization results in carbon components remaining on the surface of the cathode active material, which reduces the performance of the reused cathode active material. However, if the heat treatment is performed in air, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, thereby removing both the binder and conductive material.

[0132] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 1 to 10°C / min, even more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and no thermal shock or the like is caused to the positive electrode active material layer powder.

[0133] The heat treatment can be carried out for a period of time sufficient to thermally decompose the binder, for example, preferably 1.5 to 6 hours, more preferably 2 to 5.5 hours, even more preferably 3 to 5 hours, and even more preferably 4 to 5 hours. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0134] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, or, in consideration of productivity, a rotary kiln capable of continuous treatment.

[0135] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0136] Next, in a washing step (hereinafter referred to as "pre-washing"), that is, a surface modification step, the recovered positive electrode active material is mixed with a washing liquid and then filtered with a filter press (step S40).

[0137] The washing step has an advantage that, by including a filter press, foreign matters formed on the surface of the positive electrode active material in the heat treatment step (step S30) can be effectively removed with a small amount of washing liquid.

[0138] In one embodiment, the washing step may include stirring the recovered cathode active material with a washing solution in a stirring tank to form a slurry, filtering the slurry through a filter press to form a filter cake in the filter press, and then introducing a rinse solution into the filter press to rinse the filter cake formed in the filter press under high pressure. Here, the filtering and rinsing steps are performed at the same pressure range. The stirring device is not particularly limited, and may be an impeller-type, magnetic-type, or ultrasonic stirrer. However, when the viscosity of the slurry is high or the amount of slurry is large, an impeller-type stirrer capable of transmitting a large force is preferred.

[0139] The cleaning solution is, for example, water or a basic lithium compound aqueous solution. If it is necessary to replenish the amount of lithium that may be eluted from the positive electrode active material during the cleaning process, the basic lithium compound aqueous solution is preferred.

[0140] For example, the basic lithium compound aqueous solution contains more than 0 wt % and not more than 15 wt % of the basic lithium compound. If the basic lithium compound is not contained, it is difficult to replenish lithium. If the basic lithium compound aqueous solution contains more than 15 wt %, an excessive amount of lithium compound may remain on the surface of the positive electrode active material, which may adversely affect the subsequent annealing process.

[0141] In one embodiment, the lithium compound is LiOH.

[0142] The washing liquid is used in an amount of 0.5 to 5 times the weight of the recovered positive electrode active material, and in one embodiment, it may be used in an amount of 1 to 2 times, or about 1 time.

[0143] In one embodiment, the stirring is carried out for 1 to 20 minutes, preferably 5 to 10 minutes, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0144] In one embodiment, the stirring is carried out at a speed of 100 to 1000 rpm, preferably 250 to 750 rpm, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0145] The filter press operates under an air pressure of 2 to 10 bar, and in one embodiment, under an air pressure of 3 to 6 bar.

[0146] In one embodiment, the filter press is physically and chemically stable to the slurry, and includes a frame, filter plates, filter cloth, a filter cloth pressurizing device, a filter plate separating device, a filter cloth washing device, and a transfer pump.

[0147] The filter cloth preferably has an air permeability of 0.1 to 15 cc / cm 2 ( / sec), and in one embodiment, 0.8 cc / cm 2 ( / sec) or so.

[0148] The amount of the rinse liquid may be preferably 5 to 20 times the weight of the recovered positive electrode active material, and in one embodiment, may be about 10 times the weight.

[0149] The weight ratio of the cleaning liquid to the rinsing liquid may be preferably 1:7 to 15, and in one embodiment, may be about 1:10.

[0150] The filter cake after rinsing can be dried as needed, and in one embodiment, it can be dried in an oven (convection type) in air or under vacuum at 50 to 150°C. However, in this example, the drying step was not performed in consideration of the heat treatment in the next step, the crystal structure recovery step.

[0151] The cleaning step (step S40) removes LiCO, LiOH, etc., which are generated by reaction with lithium during the heat treatment step (step S30) when the binder and conductive material in the positive electrode active material layer are vaporized into CO and HO and removed, and LiF or metal fluorides, which are generated when F, which was present in a binder such as PVdF, reacts with lithium and other metal elements constituting the positive electrode active material, thereby preventing deterioration of battery characteristics when the positive electrode active material is reused.

[0152] In this application, % and ppm are by weight unless otherwise specified.

[0153] Next, a lithium precursor is added to the washed positive electrode active material, and the material is heat-treated to recover the crystal structure (step S50).

[0154] Because lithium loss occurs within the positive electrode active material during steps S30 and S40, step S50 replenishes this lost lithium. Furthermore, because a deformed structure (e.g., Co3O4 in the case of an LCO active material) may develop on the surface of the positive electrode active material during these steps, step S50 restores the crystalline structure of the positive electrode active material to improve the battery performance of the regenerated positive electrode active material or restore it to the level of a virgin (or fresh) positive electrode active material. Here, "virgin" is the opposite concept of "regenerated," meaning that the material has been produced for the first time, and is the same term as "raw material" used in the examples.

[0155] The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3, and Li2O, and in one embodiment, LiOH is used.

[0156] The lithium precursor is preferably added in an amount at least equal to the molar ratio of the lost lithium relative to the molar ratio of lithium to other metals in the newly generated positive electrode active material used in the positive electrode active material layer. If an amount of lithium precursor that is excessively greater than the amount of lost lithium is added, unreacted lithium precursor will remain in the regenerated positive electrode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0157] In one embodiment, the lithium precursor can be added in an amount that results in a lithium molar ratio of 0.001 to 0.4, preferably 0.01 to 0.4, and more preferably 0.09 to 0.2, based on the case where the molar ratio of lithium in the new positive electrode active material is 1 relative to the other metal (M). Specifically, adding the lithium precursor in an amount that corresponds to the ratio of lithium lost in the new positive electrode active material based on the results of ICP analysis can improve capacity to a level equivalent to that of the new positive electrode active material. The ICP analysis results have an error of approximately ±0.02.

[0158] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 40 mol %, more preferably 1 to 15 mol %, and even more preferably 7 to 11 mol %, when the total amount of lithium contained in the washed positive electrode active material is 100 mol %. Within this range, no residual precursor that may increase resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics.

[0159] The heat treatment is carried out in air at a temperature of, for example, 400 to 1000°C, preferably 600 to 900°C, and this temperature needs to be adjusted within a limited range depending on the type of lithium precursor.

[0160] The heat treatment temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, temperatures exceeding 1000°C may cause thermal decomposition of the positive electrode active material, resulting in a decrease in performance, so the temperature should not exceed 1000°C. For example, when LiOH or Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more preferably 750 to 780°C.

[0161] The heat treatment time is, for example, 1 hour or more, preferably 15 hours or less, and more preferably 5 to 13 hours. If the heat treatment time is long, the crystal structure may be sufficiently restored, but even if the heat treatment is performed for a long time, there is no significant change in performance. Note that the heat treatment equipment can be the same as or similar to that used in the heat treatment step S30.

[0162] Next, as a post-cleaning step, the positive electrode active material whose crystal structure has been restored is mixed with a cleaning solution, stirred, and then filtered (step S60).

[0163] The post-cleaning step is a process for removing lithium compounds remaining in the positive electrode active material after the heat treatment in the crystal structure recovery step.

[0164] The latter washing step preferably includes a filter press, which has the advantage of effectively removing foreign matter generated on the surface of the positive electrode active material in the crystal structure recovery step (step S50) with a small amount of washing solution, and easily removing residual lithium and fine particles.

[0165] The latter cleaning step is preferably performed in the same manner as the cleaning step (step S40) described above, except that a minimum amount of cleaning solution (e.g., 1x the weight of the positive electrode active material) is used and rinsing is not performed. Therefore, a description of the overlapping parts will be omitted.

[0166] Next, a step of doping the post-cleaned positive electrode active material can be performed (step S70).

[0167] The doping step, for example, involves adding a dopant precursor alone to a post-cleaned cathode active material and then heat-treating (solid-state reaction). If the heat-treatment temperature is too low, the amount of dopant doped into the cathode active material is small, resulting in a large coating layer. If the heat-treatment temperature is too high, the cathode active material and the dopant precursor themselves are thermally decomposed, resulting in a decrease in battery performance.

[0168] In the doping process, the dopant element itself penetrates into the crystalline structure of the positive electrode active material to a thickness of several nanometers on the surface of the positive electrode active material particles after post-cleaning, thereby significantly reducing the increase in resistance on the surface of the positive electrode active material compared to coating, thereby improving battery life. However, the coating layer is formed when oxides produced by the reaction or thermal decomposition of the dopant precursor with the lithium compound adhere to the surface of the positive electrode active material after post-cleaning, and acts as a resistor, causing a deterioration in battery life.

[0169] The dopant precursor may be added to the subsequently washed cathode active material by, for example, mixing, milling, spraying, or grinding.

[0170] Finally, in a step of removing the coating layer and leaving only the doped dopant, the doped positive electrode active material is mixed with a cleaning liquid, stirred, and then filtered (step S80).

[0171] The coating layer removal step, for example, involves mixing the doped cathode active material with a cleaning solution, stirring, and then filtering. Here, the coating layer may refer to, for example, an aggregate of undoped dopant precursor that has converted into an oxide or the like and is attached to the surface of the cathode active material in the form of nodules. During the cleaning step, the coating layer is removed, leaving only the doped dopant remaining in the regenerated cathode active material.

[0172] The coating layer removal washing step preferably uses a filter press, which has the advantage of effectively removing the coating layer even with a small amount of washing liquid.

[0173] The cleaning liquid may preferably be water.

[0174] The washing liquid may be preferably used in an amount of 1 to 10 times the weight of the doped positive electrode active material.

[0175] The filter cake of the regenerated positive electrode active material after the washing can be dried. In one embodiment, the filter cake can be dried in an oven (convection type) in air, under vacuum, or under reduced pressure at 50 to 150°C.

[0176] The coating layer removing step can be performed in the same manner as the cleaning step (step S40) described above, except for the details defined in this step, and therefore, the overlapping parts will not be described again.

[0177] secondary battery The secondary battery of the present invention includes a recycled cathode active material prepared by the method for recycling a cathode active material. In this case, the battery includes a recycled cathode active material having improved capacity characteristics and life characteristics and excellent crack resistance, which significantly improves the rate performance of the battery and provides excellent electrochemical performance and resistance characteristics.

[0178] The secondary battery of the present invention may include all of the above-described positive electrode active materials and regeneration methods thereof, and therefore, redundant description thereof will be omitted here.

[0179] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0180] [Example] Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCM-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio: 88:6:4:2)) was crushed and heat-treated in air at 570°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 3 L / min.

[0181] The recovered positive electrode active material was mixed with a 1 wt% LiOH aqueous solution (hereinafter referred to as "cleaning solution") in a weight ratio of 1:1, and the mixture was stirred at 700 rpm for 5 minutes to form a slurry. The slurry was then filtered through a filter press (manufacturer: DAESUNG FILTER Co., Ltd., air permeability 0.8 cc / cm 2 The cathode active material was filtered (dehydrated) using a filter press (including a filter cloth made of PP material at a flow rate of 100 s / sec) to form a filter cake in the filter press. The filter cake formed in the filter press was rinsed with a rinse solution (the same as the cleaning solution) in an amount 10 times the weight of the recovered cathode active material, and a filter cake of the cathode active material was obtained.

[0182] To the washed filter cake of cathode active material, a lithium precursor, LiOH, was added in an amount equivalent to a 0.10-0.15 molar ratio of lithium, based on the molar ratio of lithium to other metals in the raw cathode active material (ICP analysis) (lithium molar ratio of 1). The crystalline structure of the cathode active material was restored by heat treatment in air (feed rate: 3 L / min) at 750°C for 3 hours. Theoretically, the Li molar ratio of a nascent cathode active material is 1. However, since the ICP instrument used to determine this has an average error of ±0.05, preferably ±0.02, the Li molar ratio of the raw active material measured by ICP measurement can be 1±0.05:1. In this experiment, the lithium precursor was added based on the molar ratio measured by ICP analysis.

[0183] The positive electrode active material with the restored crystal structure was mixed with neutral water as a washing solution in a 1:1 weight ratio and stirred at 700 rpm for 5 minutes to form a slurry, which was then filtered (dehydrated) using a filter press in the same manner as the previous pre-washing to remove residual Li compounds and obtain a filter cake of the positive electrode active material. The filter cake of the obtained positive electrode active material was dried under reduced pressure at 110°C to obtain the positive electrode active material that had been subjected to the post-washing.

[0184] After the second washing, boric acid (a dopant precursor) was added to the cathode active material in an amount equivalent to 700 ppm of boron (B) based on the total weight (dry mass) of the cathode active material, and then heated at 600°C for 5 hours to produce the final regenerated cathode active material. The temperature was increased at a rate of 2°C / min until the heating temperature was reached, and air was supplied at a rate of 3 L / min.

[0185] The doped cathode active material and neutral water as a cleaning solution were mixed in a weight ratio of 1:1 and stirred for 2 minutes at 700 rpm to form a slurry. The slurry was then filtered (dehydrated) using a filter press in the same manner as in the previous post-cleaning to remove the coating layer and obtain a filter cake of the cathode active material. The filter cake thus obtained was then dried under reduced pressure at 110°C to finally produce a doped regenerated cathode active material.

[0186] In this application, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. This can be measured using a common ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0187] Example 2 A regenerated positive electrode active material was produced in the same manner as in Example 1, except that boric acid was added as a dopant precursor to the positive electrode active material after the second-stage water washing in an amount equivalent to 1400 ppm of boron (B) based on the total weight (dry mass) of the positive electrode active material after the second-stage water washing.

[0188] Comparative Example 1 A recycled cathode active material was prepared in the same manner as in Example 1, except that the doping step of adding a dopant precursor and heat-treating the cathode active material and the step of washing the doped cathode active material with a washing solution were omitted.

[0189] Comparative Example 2 A regenerated positive electrode active material was produced in the same manner as in Example 1, except that the step of washing the doped positive electrode active material with a washing solution was omitted.

[0190] Comparative Example 3 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that the dopant precursor, boric acid (HBO), was added in an amount that gave a molar ratio of 2:1 to the lithium precursor, LiOH, and that the step of washing the doped positive electrode active material with a washing solution was omitted.

[0191] FIG. 3 is a diagram conceptually illustrating the general structure of the regenerated positive electrode active materials produced in Example 1 and Comparative Examples 1 to 3, respectively.

[0192] Referring to FIG. 3, the recycled cathode active material prepared in Example 1 is doped with a dopant instead of a conventional surface coating, which not only eliminates side reactions between the coating layer and the cathode active material, but also stabilizes the surface due to the effect of the dopant, such as reducing nickel (Ni) on the surface of the cathode active material, thereby achieving improved long-term life characteristics and an increase in initial charge / discharge capacity.

[0193] On the other hand, the recycled cathode active material prepared in Comparative Example 1 is a cathode active material that has cracks due to deterioration caused by rolling during the cathode electrode manufacturing process and the progression of charge-discharge cycles, and was recycled without any surface modification. Unlike a new cathode active material, the specific surface area is significantly increased due to the cracks, which increases side reactions on the surface of the recycled cathode active material, resulting in a decrease in the overall performance of the recycled cathode active material.

[0194] In Comparative Example 2, a surface coating layer was formed on the regenerated cathode active material along with the doping layer. However, by not removing the surface coating layer, cracks occurred at the interface between the cathode active material surface and the coating layer as the charge-discharge cycle progressed, which resulted in resistance at the heterogeneous interface and reduced long-term service life. Here, the surface coating layer may be a boron coating layer containing BO and a trace amount of LBO (a reaction product of boric acid and LiOH remaining on the surface of the cathode active material).

[0195] In Comparative Example 3, a coating layer was formed on the surface of the recycled cathode active material to address the side effects of cracking. However, as the charge-discharge cycles progressed, cracks developed at the interface between the cathode active material surface and the coating layer, resulting in resistance at the interface and reduced long-term service life. In this case, the surface coating layer was a boron coating layer containing LBO as its main component, formed by adding LiOH simultaneously with the dopant precursor.

[0196] [Test Example I] The surface composition and overall composition of the regenerated positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the following methods, and the results are shown in Table 1 below.

[0197] *Atomic percent (at%): The composition ratio was measured using energy dispersive x-ray spectroscopy (EDS) with an AZtec extreme detector at 5 kV and a working distance of 7 mm.

[0198] *ICP analysis: Using an ICP analyzer, the content of residual F components, the ratio of lithium (Li) to other metals (M) in the positive electrode active material, and the content (mg / kg) of specific elements such as B and W were measured. This can be measured using a general ICP analyzer commonly used in laboratories, and there is no difference depending on the measurement device or method.

[0199] [Table 1]

[0200] As can be seen from Table 1, the recycled cathode active material (Example 1) obtained through the doping step and coating layer removal (cleaning) step according to the present invention did not have boron (B) atoms on its surface, as did the recycled cathode active material (Comparative Example 1) that did not undergo the doping step according to the present invention. Figures 4 and 5 are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images of the recycled cathode active materials prepared in Example 1 and Comparative Example 1, respectively. In each figure, the three images on the right are color-coded to distinguish carbon (C), oxygen (O), and nickel (Ni) elements, respectively.

[0201] 4 and 5, the recycled cathode active material prepared in Example 1 has a uniform surface because only the doped dopant remains and the coating layer is removed by washing, while the recycled cathode active material prepared in Comparative Example 1 does not undergo a doping step and therefore does not form a boron coating layer, so the entire surface is uniform. Therefore, the recycled cathode active material has the same composition ratio regardless of the position where it is measured.

[0202] For reference, a regenerated positive electrode active material (Comparative Example 2) that underwent only the doping step and did not undergo the coating layer removal (cleaning) step, and a regenerated positive electrode active material (Comparative Example 3) that was produced by adding LiOH together with boric acid in the doping step to induce the boron (B) atoms to react with LiOH to form a coating layer before being inserted as a dopant, had large amounts of boron (B) elements found on the surface.

[0203] 6 and 7 are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images of the recycled cathode active materials prepared in Comparative Examples 2 and 3, respectively. In each figure, the four images on the right are color-coded images to distinguish the elements boron (B), carbon (C), oxygen (O), and nickel (Ni).

[0204] Referring to FIG. 6, the recycled cathode active material prepared in Comparative Example 2 had a B2O3 coating layer formed because no additional LiOH was added along with the dopant precursor. Therefore, elemental analysis was performed at point #11 where a B2O3 coating layer was formed and point #12 where a B2O3 coating layer was not formed.

[0205] Referring to FIG. 7, the regenerated cathode active material prepared in Comparative Example 3 was subjected to an LBO coating layer formation by adding additional LiOH along with the dopant precursor. Therefore, elemental analysis was performed at points #13, #15, and #16 where the LBO coating layer was formed, and at point #14 where the LBO coating layer was not formed.

[0206] Table 2 below shows the boron (B) content using IPC analysis.

[0207] [Table 2]

[0208] As can be seen from Table 2, the regenerated cathode active material (Example 1) obtained through the doping step and coating layer removal (washing) step according to the present invention did not detect boron (B) element in surface analysis using EDS, but boron (B) element was detected in overall component analysis using IPC analysis, confirming that it was doped with a dopant. Furthermore, in Example 2, even though the amount of boron compound added was doubled, a similar level of boron (B) was detected, confirming that even if a larger amount of boron compound was added compared to Example 1, only a similar amount was doped as a dopant, with the remainder being removed in the final water washing step. On the other hand, the recycled positive electrode active material (Comparative Example 1) that did not undergo the doping step did not contain any boron (B) element even in the IPC analysis, and the recycled positive electrode active materials (Comparative Examples 2 and 3) that only underwent the doping step but did not undergo the coating layer removal (cleaning) step contained an excessive amount of boron (B) compared to Example 1, which indicates that the boron (B) element doped as a dopant and the boron (B) element present in the coating layer combined.

[0209] [Test Example II] The changes in the content of elements detected in the recycled cathode active materials obtained in Example 1 and Comparative Examples 1 to 3 depending on the X-ray etching time were measured using an X-ray diffraction analysis (Thermo Ficher Scientific Inc., k-alpha system), and the results are shown in FIG. 8.

[0210] As shown in FIG. 8, the recycled positive electrode active material of Example 1 obtained through the doping step and coating layer removal (cleaning) step according to the present invention has undergone the coating layer removal (cleaning) step, so that the B2O3 formed on the surface as a coating layer is removed and only the doped boron (B) element dopant is detected. Therefore, it was confirmed that a lower content of boron (B) element was detected compared to the recycled positive electrode active materials of Comparative Examples 2 and 3.

[0211] In contrast, the recycled positive electrode active material of Comparative Example 1 did not contain boric acid, so boron (B) element was not detected. Similar levels of boron (B) element were detected in the recycled positive electrode active materials of Comparative Examples 2 and 3. However, unlike Comparative Example 3, Comparative Example 2 did not contain additional Li precursors (LiOH, Li2CO3, etc.) that can form a LiB3O5 coating layer, so the Li content was relatively low, and it can be seen that the B2O3 coating layer was formed at 600°C, the thermal decomposition temperature of boric acid.

[0212] [Test Example III: Evaluation of CHC Cell] The electrochemical performance of the recycled positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured through the CHC cell evaluation as follows, and the results are shown in FIGS. 9 and 10.

[0213] * CHC cell fabrication: 96% by weight of recycled positive electrode active material, 2% by weight of carbon black (conductive material), and 2% by weight of PVdF (binder) were weighed and mixed with NMP to create a slurry. This was coated onto aluminum foil to create a positive electrode, and a coin half cell (CHC) was fabricated. The electrochemical performance (charge capacity CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under conditions where the electrolyte contained ethylene carbonate (EC):dimethyl methyl carbonate (DMC) = 3:7 (weight ratio) and other additives.

[0214] *Evaluation of the initial capacity (CH and DCH) of the cells: Each cell was charged and discharged once at 25° C. under the following conditions, and the results are shown in FIG.

[0215] Charge (CH): 0.2C, CC / CV, 4.25V, 0.05C cutoff Discharge (DCH): 0.2C, CC, 2.5V, Cutoff *Cell charge / discharge efficiency (Eff): The charge / discharge efficiency was calculated using Equation 1 from the charge capacity and discharge capacity obtained from the evaluation of the initial capacity of the cell.

[0216] [Formula 1] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] x 100 FIG. 9 is a graph showing the results of measuring the charge capacity of coin half cells using the positive electrode active materials regenerated in Examples 1 and 2 and Comparative Examples 1 to 3.

[0217] 9, the recycled cathode active material of Example 1, which was doped with boron (B) without a coating layer after undergoing the doping step and coating layer removal (cleaning) step according to the present invention, exhibited low surface resistance and suppressed surface side reactions due to the doping effect, resulting in excellent initial charge / discharge capacity and charge / discharge efficiency. Furthermore, in the case of Example 2, the amount of dopant doped into the recycled cathode active material was similar to that of Example 1, and thus similar results were observed.

[0218] On the other hand, the recycled positive electrode active material of Comparative Example 1 did not undergo the doping step, so no doping or coating was formed, and the initial charge / discharge capacity and charge / discharge efficiency were the poorest. In the recycled positive electrode active materials of Comparative Examples 2 and 3, which underwent only the doping step and did not undergo the coating layer removal (cleaning) step, although some doping was performed, the B2O3 coating layer and LiB3O5 coating layer, respectively, acted as surface resistance, resulting in a decrease in the initial charge / discharge capacity and charge / discharge efficiency.

[0219] *Evaluation of capacity retention (%): After each cell was formed at a 0.1C rate, it was charged / discharged at 0.33 / 0.33C, charged / discharged at 0.05C cutoff CC / CV, and discharged at 45°C. Measurements were performed using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.), and the discharge capacity after one cycle was set as the initial capacity. The discharge capacity after each cycle was then compared with the initial capacity (100%) to calculate the capacity retention using Equation 2 below. The results are shown in Figure 10.

[0220] [Formula 2] Capacity retention rate (%) = (discharge capacity after cycling / initial discharge capacity) x 100 FIG. 10 is a graph showing the results of coin half-cell evaluation of the regenerated positive electrode active materials produced in Example 1 and Comparative Examples 1 to 3, illustrating the change in capacity retention rate depending on the number of cycles.

[0221] Referring to Figure 10, it was confirmed that the recycled positive electrode active material of Example 1, which was doped with boron (B) element without a coating layer after undergoing the doping step and coating layer removal (cleaning) step according to the present invention, had low surface resistance and suppressed surface side reactions due to the doping effect, resulting in the best capacity retention rate, i.e., life characteristics.

[0222] On the other hand, the recycled positive electrode active material of Comparative Example 1 did not undergo the doping step, so no doping or coating was formed, and therefore had the poorest life characteristics. The recycled positive electrode active material of Comparative Example 2, which underwent only the doping step and not the coating layer removal (cleaning) step, was partially doped, but the B2O3 coating layer acted as surface resistance, resulting in reduced life characteristics. The recycled positive electrode active material of Comparative Example 3, in which LiOH was added in the doping step of Comparative Example 2, was partially doped, but the LiB3O5 coating layer acted as surface resistance, although not as much as the B2O3 coating layer, resulting in reduced life characteristics. [Explanation of symbols]

[0223] 10 Current collector 20 Active material layer 30 Positive electrode sheet 40 positive electrode plate 50 cathode scrap

Claims

1. The material comprises at least one selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, lithium nickel cobalt aluminum oxide, lithium nickel oxide, nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn), and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), A recycled cathode active material that is doped with a dopant and has no coating layer.

2. The regenerated positive electrode active material according to claim 1, wherein the dopant is contained in an amount of 100 to 2000 ppm based on the total weight of the regenerated positive electrode active material.

3. 2. The regenerated positive electrode active material according to claim 1, wherein the dopant is at least one selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N.

4. The regenerated cathode active material according to claim 1 , wherein the amount of dopant element coated on the surface without being doped is 10 ppm or less based on EDS surface mapping.

5. 2. The regenerated cathode active material of claim 1, wherein the regenerated cathode active material contains 40 to 45 wt % carbon, 25 to 30 wt % oxygen, and 25 to 30 wt % nickel based on EDS surface mapping.

6. (a) heat-treating a waste positive electrode, including a current collector and a positive electrode active material layer coated on the current collector, in air or oxygen to recover the positive electrode active material; (b) adding a lithium precursor to the recovered positive electrode active material and heat treating it in air to restore the crystalline structure; (c) adding a dopant precursor to the positive electrode active material whose crystal structure has been restored, and performing a heat treatment to dope the positive electrode active material; (d) washing the doped positive electrode active material with a washing solution.

7. 7. The method for regenerating a positive electrode active material according to claim 6, wherein in step (a), the heat treatment is carried out under conditions of 300 to 650°C.

8. 7. The method for regenerating a positive electrode active material according to claim 6, wherein in step (b), the heat treatment is carried out under conditions of 400 to 1000°C.

9. In the step (b), the lithium precursor is LiOH, Li ２ CO ３ , LiNO ３ and Li ２ 7. The method for regenerating a positive electrode active material according to claim 6, wherein the active material is one or more selected from the group consisting of O.

10. 7. The method for regenerating a positive electrode active material according to claim 6, wherein in step (c), the heat treatment is carried out under conditions of 300 to 1000°C.

11. 7. The method for regenerating a positive electrode active material according to claim 6, wherein in step (c), the dopant precursor is a compound that provides one or more elements selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N as a dopant.

12. The method for regenerating a positive electrode active material according to claim 6 , wherein in step (d), the cleaning liquid is water.

13. The method for regenerating a positive electrode active material according to claim 6, further comprising: (a-2) washing the recovered positive electrode active material with a washing solution; (b-2) washing the positive electrode active material whose crystal structure has been restored with a washing solution; or both of these.

14. 7. The method for regenerating a positive electrode active material according to claim 6, wherein the cleaning liquid in step (a-2) is water or a basic aqueous lithium compound solution having a concentration of more than 0 wt % and not more than 15 wt %, and the cleaning liquid in step (b-2) is water.

15. 7. The method for regenerating a positive electrode active material according to claim 6, wherein in step (c), the dopant precursor is added in an amount of 100 to 2000 ppm (dopant element basis) based on the total weight of the regenerated positive electrode active material.

16. 7. The method for regenerating a positive electrode active material according to claim 6, wherein the positive electrode active material comprises at least one selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, lithium nickel cobalt aluminum oxide, lithium nickel oxide, a nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in lithium nickel oxide is substituted with manganese (Mn), and an NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co).

17. A regenerated positive electrode active material produced by the method for regenerating a positive electrode active material according to any one of claims 6 to 16.

18. A secondary battery comprising the recycled positive electrode active material according to claim 1 .

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