Regenerated positive electrode active material, method for regenerating the same, and secondary battery including the same

Abstract

The present invention relates to a recycled positive electrode active material, a regenerating method thereof, and a secondary battery including the same. More specifically, the present invention relates to a recycled positive electrode active material, a regenerating method thereof, and a secondary battery including the same, which are characterized by comprising the steps of: (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, thereby thermally decomposing a binder and a conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; and (b) adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material, and annealing the resulting material. According to the present invention, a lithium precursor and a Co-containing coating agent are added to a cathode active material obtained by heat-treating a waste cathode, and the cathode active material is annealed. This allows the recovery of the crystal structure and the recovery of the surface coating layer, as well as the advantages of the process, resulting in excellent initial capacity and resistance characteristics of a secondary battery. In addition, since no acid is used in the recovery and regeneration process, it is environmentally friendly and does not require neutralization or wastewater treatment, thereby reducing process costs. Since the cathode active material is regenerated as it is without being decomposed, there are no metal elements to be discarded. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. In particular, since the water washing process is omitted, there is an effect of providing a method for regenerating a cathode active material with greatly improved economy and productivity.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0153126 filed on November 15, 2022, and Korean Patent Application No. 10-2023-0059549, refiled on May 9, 2023 based thereon, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a recycled cathode active material, a recycling method thereof, and a secondary battery including the same. More specifically, the present invention relates to a method for recycling a cathode active material, which involves heat-treating a used cathode including a current collector and a cathode active material layer coated thereon to recover the cathode active material, followed by simultaneously adding a lithium precursor and a Co-containing coating agent and annealing the recovered cathode active material. This method restores the crystal structure and the surface coating layer, resulting in excellent initial capacity and resistance characteristics for the secondary battery. The recovery and recycling processes are environmentally friendly because no acid is used, and the associated neutralization and wastewater treatment are unnecessary, reducing process costs. The cathode active material is recycled directly without decomposition, so no metal elements are discarded. The use of organic solvents eliminates the risk of toxic gas generation or explosion. In particular, the water-washing process is omitted, resulting in significant improvements in economy and productivity. [Background technology]

[0003] A lithium secondary battery mainly comprises 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 the negative electrode from mixing, and an electrolyte that allows lithium ions to move between the positive electrode and the negative electrode.

[0004] The positive electrode active material layer mainly uses a lithium-based oxide as the active material, and the negative electrode active material layer mainly uses a carbon material as the active material. However, the lithium-based oxide generally contains rare metals such as cobalt, nickel, or manganese, and 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").

[0005] 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.

[0006] However, the method of extracting rare metals using acid has the disadvantages of causing environmental pollution, requiring a neutralization process and a wastewater treatment process, which significantly increases the process cost, and not being able to recover lithium, the main metal in the positive electrode active material.

[0007] To overcome these drawbacks, direct recycling methods have recently been studied to directly regenerate 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.

[0008] However, although the calcination method is simple, it has drawbacks in that foreign matter that reduces the output performance of the battery is generated on the surface of the regenerated positive electrode active material, waste gas is generated, and energy consumption is high.

[0009] In addition, although the solvent dissolution method can produce recycled cathode active materials with a relatively clean surface, it has the disadvantages of poor stability and the need for an expensive solvent recovery process since the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and has the risk of explosion.

[0010] In addition, the aluminum foil dissolving 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.

[0011] 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 can deteriorate the battery characteristics of the recycled cathode active material.

[0012] Therefore, there is an urgent need to develop a method for regenerating a positive electrode active material with improved output performance, with fewer steps and less cost, in an environmentally friendly and safe manner, without the metal elements discarded from used positive electrodes. Summary of the Invention [Problem to be solved by the invention]

[0013] In order to solve the above-mentioned problems of the prior art, the present invention provides a method for regenerating a cathode active material by heat-treating a used cathode including a current collector and a cathode active material layer coated thereon to recover the cathode active material, followed by simultaneously adding a lithium precursor and a Co-containing coating agent and annealing the resulting cathode active material. This method has process advantages and restores the crystalline structure and the surface coating layer, resulting in excellent initial capacity and resistance characteristics for secondary batteries. Furthermore, since the recovery and regeneration process of the cathode active material does not use an acid, it is environmentally friendly and does not require neutralization or wastewater treatment, thereby reducing process costs. Since the cathode active material is regenerated directly without decomposition, there are no metal elements to be discarded. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. In particular, the water-washing process is omitted, resulting in significant improvements in economy and productivity.

[0014] Another object of the present invention is to provide a secondary battery that is excellent in initial capacity and resistance characteristics.

[0015] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0016] In order to achieve the above object, the present invention provides a method for regenerating a positive electrode active material, comprising the steps of: (i) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, thereby thermally decomposing the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; and (b) adding a lithium precursor and a coating agent to the recovered positive electrode active material, and annealing the resulting mixture.

[0017] II) In I), the positive electrode active material layer may include at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and may include at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li.

[0018] III) In the above I) or II), in the step (a), the heat treatment may be carried out at 300 to 650° C. in an oxygen atmosphere.

[0019] IV) In the above I) to III), the oxygen may be oxygen (O2) with a purity of 59% or more.

[0020] V) In the above I) to IV), the positive electrode active material recovered in the step (a) may contain single particles.

[0021] VI) In the above I) to V), in the step (b), the lithium precursor may be added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium contained in the recovered positive electrode active material is 100 mol %.

[0022] VII) In the above I) to VI), in the step (b), the coating agent may be a Co-containing coating agent.

[0023] VIII) In I) to VII), in step (b), the coating agent may be added in an amount corresponding to 1 to 25,000 ppm based on the total amount of the recovered positive electrode active material and the additionally added lithium precursor.

[0024] IX) In I) to VIII), the lithium precursor may include one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0025] X) In the above I) to IX), the coating agent may be a Co-containing coating agent and may be one or more selected from the group consisting of Co(OH)2, Co2O3, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4.

[0026] XI) In the above I) to X), the annealing can be carried out at 400 to 800°C.

[0027] Furthermore, the present invention provides a positive electrode active material that is at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, the positive electrode active material comprising at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li, and a coating agent.

[0028] XIII) In the above XII), the coating agent may be a Co-containing coating agent.

[0029] XIV) In the above XII) or XIII), the coating agent may be a Co-containing coating agent and may be one or more selected from the group consisting of Co(OH)2, Co2O3, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4.

[0030] XV) In the above XII) to XIV), the positive electrode active material may include single particles.

[0031] XVI) In the above XII) to XV), the positive electrode active material may be a recycled positive electrode active material.

[0032] The present invention also provides XVII) a secondary battery containing the positive electrode active material according to any one of the above XII) to XVI). [Effects of the Invention]

[0033] According to the present invention, a used cathode including a current collector and a cathode active material layer coated thereon is heat-treated to recover the cathode active material, and then a lithium precursor and a Co-containing coating agent are simultaneously added and annealed. This not only provides process advantages, but also restores the crystalline structure and the surface coating layer, resulting in excellent initial capacity and resistance characteristics for secondary batteries. Furthermore, the recovery and regeneration process of the cathode active material is environmentally friendly because no acid is used, and the associated neutralization and wastewater treatment are not required, reducing process costs. The cathode active material is regenerated directly without decomposition, so there are no metal elements to be discarded. Furthermore, no organic solvent is used, so there is no risk of toxic gas generation or explosion. In particular, the water-washing process is omitted, resulting in significant improvements in economy and productivity. [Brief explanation of the drawings]

[0034] The following 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 matters depicted in these drawings. [Figure 1] 1 is a SEM photograph of a fresh positive electrode active material of Comparative Example 1. [Figure 2] This is an SEM photograph of the positive electrode active material from which the binder and conductive material have been removed by heat-treating waste positive electrodes. [Figure 3] 1 is a SEM photograph of a positive electrode active material obtained by heat-treating waste positive electrodes according to Examples 1 to 4 to remove binders and conductive materials, to which a lithium precursor and a Co-containing coating agent are added, followed by annealing. [Figure 4]10 is a SEM photograph of a positive electrode active material obtained by heat-treating a waste positive electrode according to Comparative Example 2 to remove the binder and conductive material, to which only a lithium precursor was added, followed by annealing. [Figure 5] 1 is an SEM photograph of the positive electrode active material regenerated in Example 4. [Figure 6] 1 is an SEM photograph of the positive electrode active material regenerated in Example 5. [Figure 7] 1 is a graph showing the results of charge capacity of coin cells using recycled or newly produced positive electrode active materials manufactured or prepared in Comparative Examples 1 to 3 and Examples 1 to 5. [Figure 8] 1 is a graph showing the results of mono-cell evaluation of each of the regenerated or newly produced positive electrode active materials manufactured or prepared in Examples 1 and 2 and Comparative Examples 1 and 2, showing the change in resistance depending on the change in SOC (State of charge; %) at 0.1 seconds. [Figure 9] 1 is a graph showing the results of monocell evaluation of each of the regenerated or newly produced positive electrode active materials manufactured or prepared in Examples 1 and 2 and Comparative Examples 1 and 2, showing the change in resistance as a function of the change in SOC (%) over 30 seconds. [Figure 10] 1 is a graph showing the results of mono-cell evaluation of each of the recycled or newly produced positive electrode active materials manufactured or prepared in Examples 1 and 2 and Comparative Examples 1 and 2, where the 0.1 second resistance is subtracted from the 30 second resistance. [Figure 11] 2 is a flowchart of a process for regenerating a positive electrode active material according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0035] The inventors have been researching a direct recycling method for recycling used cathodes into cathode active materials with excellent battery performance without decomposing the cathode active material. They discovered that when a used cathode including a current collector and a cathode active material layer coated thereon is heat-treated to recover the cathode active material, and then a lithium precursor and a Co-containing coating agent are simultaneously added to the recovered cathode active material and annealed, the crystalline structure and the surface coating layer are both restored, improving the initial capacity and resistance characteristics of the secondary battery. They also discovered advantages of this process, and further research led to the completion of the present invention.

[0036] The regenerated positive electrode active material, the regenerating method thereof, and the secondary battery including the same will be described in detail below.

[0037] However, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of 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 one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that various equivalents and modifications may be available to replace them, and that they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0038] 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.

[0039] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention is characterized by comprising the steps of: (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; and (b) adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material, followed by annealing. This method has the advantages of providing a secondary battery with excellent initial capacity and resistance characteristics, and reducing production costs as a process advantage.

[0040] Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0041] (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 waste positive electrode according to the present invention may preferably be a step of heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and 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 cleanly removing the binder, conductive material, and current collector.

[0042] The discarded positive electrodes may preferably be positive electrodes separated from used and discarded lithium secondary batteries, defective positive electrode sheets generated in the manufacturing process of lithium secondary batteries, or positive electrode scraps, and more preferably positive electrode scraps remaining after punching out positive electrode plates from positive electrode sheets.

[0043] The positive electrode active material layer in step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0044] The positive electrode active material may include, for example, at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material.

[0045] 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 a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and an NCM-based lithium composite transition metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). It may be one or more 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.

[0046] As still another specific example, the positive electrode active material has the following Chemical Formula 1 Li a Ni x Mn y Co z M w O 2+δ (Chemical Formula 1) (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.

[0047] As an example, the positive electrode active material can contain 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, and still more preferably 81 to 95 mol% of Ni based on 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of excellent initial capacity and resistance characteristics.

[0048] In the present description, the Ni content is not particularly limited as long as it is 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. For example, the Ni content can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer.

[0049] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT, or a mixture thereof.

[0050] 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.

[0051] In the step (a), the heat treatment may be performed, for example, in an oxygen atmosphere at 300 to 650°C, preferably 400 to 620°C, and more preferably 500 to 600°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.

[0052] The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, and even more preferably 30 minutes to 2 hours. 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.

[0053] In this description, 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.

[0054] The positive electrode active material recovered in step (a) may include, for example, single particles. In this case, the strength of the particles may be improved, and the occurrence of cracks and particle breakage in the positive electrode active material due to rolling may be reduced.

[0055] In this description, the term "single particle" is defined as a single particle, i.e., a single structure, not in the form of an aggregated secondary particle, but in an enlarged or large particle size, as commonly used in the technical field to which the present invention pertains. Here, the term "secondary particle" refers to an aggregate of particles.

[0056] In the present description, the enlargement is not particularly limited as long as it is an enlargement method commonly used for producing single particles in the technical field to which the present invention pertains.

[0057] The single particles have an average particle size (D 50 ) may be preferably 2 to 10 μm, more preferably 2 to 8 μm, and even more preferably 3 to 6 μm.

[0058] In this description, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured by, for example, a laser diffraction method. 50 The measurement method for the average particle size (D) is as follows: particles of the positive electrode active material are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. Then, the average particle size (D) corresponding to 50% of the cumulative volume in the measuring device is measured. 50 ) can be calculated.

[0059] For example, the positive electrode active material may contain 10 to 100 wt %, preferably 10 to 80 wt %, and more preferably 20 to 60 wt % of single particles. Within this range, the strength of the particles is improved, and the occurrence of cracks in the positive electrode active material and the breakage of the particles due to rolling are reduced.

[0060] For example, the purity of oxygen used in the heat treatment may be 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%. Within this range, the binder and conductive material are removed without remaining, and there are advantages in that the stability of Ni in the positive electrode active material is increased and the crystal size is reduced.

[0061] The oxygen purity % may be volume % or mol %.

[0062] The purity of oxygen described herein is not particularly limited, as long as it is measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0063] (b) adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material and annealing the material; The method for regenerating a positive electrode active material of the present invention includes (b) adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material and annealing the material. In this case, the crystal structure and the surface coating layer are both restored, resulting in excellent initial capacity and resistance characteristics of the secondary battery, and a process advantage of reduced production costs.

[0064] The lithium precursor may be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O, and preferably LiOH. In this case, the lithium precursor replenishes the lithium that is insufficient in the recycled positive electrode active material, and improves the crystallinity by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the recycled positive electrode active material.

[0065] The lithium precursor can be added preferably in an amount that is at least the amount of lithium that is reduced from the molar ratio of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. More preferably, the lithium precursor can be added in an amount that is 0.0001 to 0.2 molar ratio relative to the molar ratio of lithium in the positive electrode active material in step (a). Within this range, the deficient lithium in the regenerated positive electrode active material is replenished, and the crystallinity is improved, for example, by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0066] 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 1 to 10 mol%, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol%. Within this range, no residual precursor that may increase resistance remains in the recycled positive electrode active material, which is very useful for improving battery characteristics.

[0067] The Co-containing coating agent may be at least one selected from the group consisting of Co(OH)2, Co2O3, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4, and more preferably Co(OH)2. In this case, the surface of the positive electrode active material is uniformly coated, and the increased conductivity improves battery performance, such as output characteristics and life characteristics, and corrosion of the surface of the positive electrode active material and side reactions caused by hydrogen fluoride are suppressed.

[0068] In step (b), the Co-containing coating agent may be added to a Co content of 1 to 25,000 ppm, preferably 1 to 15,000 ppm, more preferably 100 to 10,000 ppm, even more preferably 500 to 7,000 ppm, and even more preferably 700 to 3,000 ppm, based on the total amount of the recovered positive electrode active material and the additionally added lithium precursor. In this case, the surface of the positive electrode active material is uniformly coated, thereby improving battery performance.

[0069] In this description, % and ppm are by weight unless otherwise specified.

[0070] The annealing step (b) may be, for example, a step of adding a lithium precursor and a Co-containing coating agent to the positive electrode active material and annealing the material in air or oxygen (O2) at 400 to 800°C, preferably 500 to 750°C, and more preferably 550 to 750°C. Within this range, the crystalline structure of the positive electrode active material is restored, and the crystallinity is improved by increasing or restoring the crystalline structure, thereby improving the structural stability of the positive electrode active material and the electrochemical performance of the regenerated positive electrode active material.

[0071] The annealing temperature can be adjusted within a limited range depending on the melting points of the lithium precursor and the Co-containing coating agent.

[0072] In the case of the lithium precursor, for example, LiCO3 has a melting point of 723°C, so it can be annealed preferably at 700 to 900°C, more preferably at 710 to 780°C, and LiOH has a melting point of 462°C, so it can be annealed preferably at 400 to 600°C, more preferably at 450 to 480°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance and improved structural stability and electrochemical performance of the positive electrode active material.

[0073] In the case of the Co-containing coating agent, for example, Co(OH)2 has a melting point of 168°C, and therefore can be annealed preferably at 400 to 800°C, more preferably 500 to 750°C, and even more preferably 550 to 750°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance and improved structural stability and electrochemical performance of the positive electrode active material.

[0074] The annealing temperature may preferably be a temperature exceeding the melting points of the lithium precursor and the Co-containing coating agent. However, if the annealing temperature exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance. Therefore, the annealing temperature is preferably 1000°C or less.

[0075] In the annealing step (b), the method of adding the lithium precursor and the Co-containing coating agent to the recovered positive electrode active material may be a method of adding the lithium precursor and the Co-containing coating agent to the recovered positive electrode active material in a solid phase or a liquid phase. As another example, a method of adding a lithium precursor solution and a Co-containing coating agent solution to the recovered positive electrode active material and spray drying may be used. This method has the advantages of reducing particle aggregation due to conventional drying, omitting the process of mixing a solid-phase lithium precursor, and allowing the material to be obtained in the form of a powder rather than a lump.

[0076] The lithium precursor solution and the Co-containing coating agent solution may be, for example, a lithium compound that is soluble in an aqueous solution or an organic solvent.

[0077] FIG. 11 below is a flowchart of a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0078] Referring to Figure 11, first, cathode scrap is prepared as waste cathodes (step S10). For example, a NCM-based lithium transition metal oxide containing 60 mol% or more of Ni (based on a total of 100 mol% of the remaining metals excluding Li), carbon black, and polyvinylidene fluoride are mixed with N-methyl pyrrolidone (NMP) to prepare a slurry. The slurry is then coated on aluminum foil and dried in a vacuum oven at approximately 120°C to prepare a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0079] The cathode scrap has a cathode active material layer on an aluminum foil, and after the solvent evaporates, the cathode active material layer has a structure in which the cathode active material and the conductive material are bound by the binder. Therefore, when the binder is removed, the cathode active material is separated from the aluminum foil.

[0080] 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 equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter may be used to increase productivity.

[0081] The decision as to whether or not to crush the cathode scrap and the size of the pieces may be determined taking into consideration the handling of the cathode scrap and the properties required for equipment used in subsequent processes. For example, when equipment capable of continuous processing is used, the cathode scrap should be crushed into smaller pieces because good fluidity is required.

[0082] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is carried out to thermally decompose the binder in the positive electrode active material layer.

[0083] The heat treatment is preferably performed in oxygen with a purity of 80% or higher, and more preferably in oxygen with a purity of 90% or higher. This ensures the stability of Ni in waste cathodes containing high-nickel (High-Ni) cathode materials and ensures the clean removal of binders and conductive materials. When heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive materials are carbonized without being thermally decomposed. Carbonization results in carbon components remaining on the surface of the cathode active material, reducing the performance of the recycled cathode active material. However, when heat treatment is performed in the presence of oxygen, the carbon components in the binder and conductive materials react with the oxygen and disappear as gases such as CO and CO2, thereby removing both the binder and conductive materials.

[0084] The heat treatment is preferably carried out at 300 to 650°C, specifically at 590°C. If the temperature is lower than 300°C, it is difficult to remove the binder, making it impossible to separate the current collector. If the temperature exceeds 650°C, the current collector melts, making it impossible to separate the current collector.

[0085] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, the heat treatment can be carried out without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock is caused to the cathode scrap.

[0086] The heat treatment can be carried out for a period of time sufficient to thermally decompose the binder, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specifically for about 30 minutes. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0087] 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.

[0088] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0089] Next, a lithium precursor and a Co-containing coating agent are added to the recovered positive electrode active material, and the resulting mixture is annealed (step S40).

[0090] The annealing step involves adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material and then annealing it. In this case, lithium loss and loss of the coating layer in the positive electrode active material may occur during step S30. In step S40, the lost lithium and coating layer are replenished. Furthermore, in step S40, the crystalline structure of the positive electrode active material is restored through annealing, thereby restoring or even improving the properties of the recycled positive electrode active material to the level of a new positive electrode active material that has never been used.

[0091] During step S30, a deformed structure may develop on the surface of the cathode active material. For example, in step S40, Ni in an NCM-based lithium composite transition metal oxide cathode active material may be converted into a rock salt (e.g., [NiCO3·2Ni(OH)2)H2O] by water, forming a spinel structure. Manufacturing a battery in this state could result in reduced capacity and other battery performance degradation. In the present invention, the crystalline structure is restored and the surface is uniformly coated through step S40. For example, the NCM-based lithium composite transition metal oxide cathode active material is restored to a hexagonal crystalline structure and the surface is uniformly coated with a Co-containing coating agent. This restores or improves the initial characteristics to a level similar to that of a virgin cathode active material, improving the structural stability and electrochemical performance of the cathode active material. Here, "virgin" or "fresh" is the opposite of "regenerated" and means something that has been newly produced. It is the same term as "raw material" used in the examples.

[0092] The lithium precursor in step S40 may be one or more of LiOH, Li2CO3, LiNO3, and Li2O, with LiOH being used as a specific example.

[0093] 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 cathode active material used in the cathode active material layer. Addition of an amount of lithium precursor that is excessively greater than the amount of lost lithium leaves unreacted lithium precursor in the regenerated cathode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0094] For example, when the total amount of lithium contained in the positive electrode active material recovered after the heat treatment in S30 is 100 mol %, the lithium precursor can be added in an amount corresponding to 1 to 40 mol %, preferably 1 to 15 mol %, and more preferably 1 to 10 mol %.

[0095] As yet another example, when the molar ratio of lithium to other metals in the newly produced positive electrode active material is 1, the lithium precursor can be added in an amount such that the lithium has a molar ratio of 0.001 to 0.4, and preferably, the lithium precursor can be added in an amount such that the lithium has a molar ratio of 0.01 to 0.2.

[0096] Specifically, when a lithium precursor is added in a molar ratio of 0.09 to 0.1 (based on lithium metal), which is the ratio of the lithium content lost to the newly produced positive electrode active material based on the results of ICP analysis, the capacity improvement effect is equivalent to that of the newly produced positive electrode active material. Here, the results of ICP analysis have an error value of about ±0.02.

[0097] The Co-containing coating agent in step S40 may be one or more selected from the group consisting of Co(OH)2, Co2O3, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4, and Co(OH)2 is used as a specific example.

[0098] For example, the Co coating agent may be added so that the Co content is 1 to 25,000 ppm, preferably 1 to 15,000 ppm, more preferably 100 to 10,000 ppm, even more preferably 500 to 7,000 ppm, and still more preferably 700 to 3,000 ppm, based on the total content of the recovered positive electrode active material and the additionally added lithium precursor.

[0099] As a specific example of a method for adding the lithium precursor and the Co-containing coating agent to the recovered positive electrode active material, the lithium precursor and the Co-containing coating agent in powder form can be mixed so that the powders are well mixed together, and then mixed with the recovered positive electrode active material so that they are uniformly mixed, followed by annealing.

[0100] The annealing is carried out in oxygen at a temperature of, for example, 400 to 800°C, preferably 500 to 750°C, more preferably 550 to 750°C, and this temperature must be adjusted within a limited range depending on the type of lithium precursor and Co-containing coating agent.

[0101] The annealing temperature is preferably a temperature exceeding the melting points of the lithium precursor and the Co-containing coating agent. 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. Therefore, when Li2CO3 is used as the lithium precursor and Co(OH)2 is used as the Co-containing coating agent, the annealing temperature is preferably 500 to 900°C, and more preferably 550 to 750°C. Furthermore, when LiOH is used as the lithium precursor and Co(OH)2 is used as the Co-containing coating agent, the annealing temperature is preferably 400 to 800°C, more preferably 500 to 750°C, and even more preferably 550 to 750°C.

[0102] The annealing time may be, for example, 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. A longer annealing time may allow for sufficient recovery of the crystal structure and surface coating, but even if annealing is performed for a long period of time, performance is not significantly affected. The annealing equipment may be the same as or similar to that used in the heat treatment step S30.

[0103] If the annealing step S40 is performed to achieve a 1:1 molar ratio of lithium to other metals in the positive electrode active material, the lithium in the positive electrode active material will react with the Co-containing coating agent, causing the lithium to be less than 1:1, resulting in a regenerated positive electrode active material that is unable to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step S40, so that it is present in an amount 0.0001 to 0.1 molar ratio greater than the other metals in the positive electrode active material, a surface protective layer will be formed by the Co-containing coating agent, naturally resulting in a 1:1 molar ratio of lithium to other metals in the positive electrode active material, and no capacity loss will occur.

[0104] As described above, the method for regenerating a positive electrode active material according to this embodiment has the advantage that the process is continuous and the crystal recovery process and the surface coating process are simultaneously performed in one step.

[0105] positive electrode active material The cathode active material of the present invention is at least one selected from the group consisting of nickel-cobalt-manganese (NCM)-based cathode active materials, nickel-cobalt-aluminum (NCA)-based cathode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and is characterized by containing at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li, and containing a Co-containing coating agent. In this case, increased conductivity improves battery performance such as output characteristics and life characteristics, and corrosion and side reactions of the surface of the cathode active material caused by hydrogen fluoride are suppressed.

[0106] The positive electrode active material may preferably include at least one selected from the group consisting of lithium cobalt oxides such as LiCoO (hereinafter referred to as "LCO"), lithium manganese oxides such as LiMnO or LiMnO, lithium iron phosphate compounds such as LiFePO, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt aluminum oxide (NCA), lithium nickel oxides such as LiNiO, nickel manganese-based lithium composite metal oxides in which nickel (Ni) in the lithium nickel oxide is partially substituted with manganese (Mn), and NCM-based lithium composite transition metal oxides in which nickel (Ni) in the lithium nickel oxide is partially substituted with manganese (Mn) and cobalt (Co). In this case, excellent electrochemical performance, resistance characteristics, and capacity characteristics can be obtained.

[0107] The positive electrode active material may be, for example, a compound represented by the following chemical formula 1: Li a Ni x Mn y Co z M w O 2+δ(Chemical Formula 1) (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. ) A compound represented by can be included, and in this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacitance characteristics, etc.

[0108] The 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 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of being excellent in initial capacity and resistance characteristics.

[0109] The Co-containing coating agent may preferably be one or more selected from the group consisting of Co(OH)2, Co2O3, Co3(PO4)2, CoF3, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co3O4, Co(SO4)2·7H2O, and CoC2O4, and more preferably Co(OH)2. In this case, the surface of the positive electrode active material is uniformly coated, and there is an effect that the battery performance such as the output characteristics and life characteristics of the battery is improved due to the increase in conductivity, and the corrosion and side reactions of the surface of the positive electrode active material by hydrogen fluoride are suppressed.

[0110] The positive electrode active material can include single particles as an example. In this case, there is an effect of improving the strength of the particles and reducing the generation of cracks and the cracking of the particles due to rolling.

[0111] In this description, a single particle, according to the definition commonly used in the technical field to which the present invention belongs, specifically means a single particle that is not in the form of aggregated secondary particles, that is, a hypertrophied or large-particle-size single particle, that is, a single structure. Here, a secondary particle means an aggregate in which particles are aggregated.

[0112] The single particles have an average particle size (D 50 ) may be preferably 2 to 10 μm, more preferably 2 to 8 μm, and even more preferably 3 to 6 μm. Within this range, the strength of the particles is improved, and there is an effect of being able to reduce the occurrence of cracks in the positive electrode active material and the breakage of the particles due to rolling.

[0113] The positive electrode active material may contain, for example, 10 to 100 wt %, preferably 10 to 80 wt %, and more preferably 20 to 60 wt % of single particles. Within this range, the strength of the particles is improved, and the occurrence of cracks in the positive electrode active material and the breakage of the particles due to rolling can be reduced.

[0114] The positive electrode active material may preferably be a recycled positive electrode active material, which has the advantages of being economical and productive.

[0115] secondary battery The secondary battery of the present invention includes the above-described positive electrode active material. In this case, the secondary battery has excellent initial capacity and resistance characteristics, and has advantages in process. In addition, since no acid or organic solvent is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly. In particular, since the initial water-washing process is omitted, it has advantages in terms of economy and productivity.

[0116] 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.

[0117] 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.

[0118] [Example] Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: single particles of NCMA with a nickel content of 80 mol%) was crushed and subjected to an oxidative heat treatment at 590°C for 30 minutes in oxygen with a purity of 90% or higher 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.

[0119] It was confirmed that the molar ratio of lithium to other metals in the recovered positive electrode active material was reduced by 0.02 molar ratio level compared to the molar ratio of lithium to other metals in the raw positive electrode active material.

[0120] To replenish the lost lithium, a lithium precursor, LiOH, was added in an amount that would result in 5 mol% lithium, assuming that the total lithium contained in the recovered positive electrode active material was 100 mol%. At the same time, a Co-containing coating agent, Co(OH)2, was added so that the Co content would be 1,000 ppm relative to the total content of the recovered positive electrode active material and the additionally added lithium precursor, LiOH, and the resulting mixture was annealed in oxygen at 700°C for 5 hours.

[0121] A regenerated positive electrode active material was obtained from the annealed positive electrode active material.

[0122] In this description, 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 general ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0123] Example 2 A recycled cathode active material was prepared in the same manner as in Example 1, except that in the annealing step, a Co-containing coating agent, Co(OH)2, was added so that the Co content was 2,000 ppm based on the sum of the content of the recovered cathode active material and the content of the additional lithium precursor, LiOH.

[0124] Example 3 A recycled cathode active material was prepared in the same manner as in Example 1, except that in the annealing step, a Co-containing coating agent, Co(OH)2, was added so that the Co content was 5,000 ppm based on the sum of the content of the recovered cathode active material and the content of the additional lithium precursor, LiOH.

[0125] Example 4 A recycled cathode active material was prepared in the same manner as in Example 1, except that in the annealing step, a Co-containing coating agent, Co(OH)2, was added so that the Co content was 10,000 ppm based on the sum of the content of the recovered cathode active material and the content of the additional lithium precursor, LiOH.

[0126] Example 5 A recycled cathode active material was prepared in the same manner as in Example 1, except that in the annealing step, a Co-containing coating agent, Co(OH)2, was added so that the Co content was 20,000 ppm based on the sum of the content of the recovered cathode active material and the content of the additional lithium precursor, LiOH.

[0127] Comparative Example 1 Fresh single particles of NCMA were used as the positive electrode active material.

[0128] Comparative Example 2 A recycled positive electrode active material was prepared in the same manner as in Example 1, except that only the lithium precursor was added and annealed in the annealing step.

[0129] Comparative Example 3 In Example 1, only the lithium precursor was added to the cathode active material in the annealing step, followed by annealing. Then, a Co-containing coating agent, Co(OH)2, was added to the cathode active material so that the Co content was 1,000 ppm based on the sum of the recovered cathode active material content and the additionally added lithium precursor, LiOH, and the surface was coated by heat treatment at 700°C for 5 hours to prepare a recycled cathode active material.

[0130] [Test Example I: SEM analysis] The regenerated or virgin positive electrode active materials manufactured or prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were photographed using an SEM device, and the photographs are shown in FIGS. 1 to 6. The SEM photographs were taken using a common SEM device commonly used in laboratories. Specifically, they were taken using a Hitachi S-4200. However, there is no deviation due to the measurement device or method.

[0131] As can be seen from Figure 1 below, it was confirmed that a protective layer was formed on the surface of the fresh positive electrode active material of Comparative Example 1. In Figure 1, the arrow indicates the surface protective layer.

[0132] FIG. 2 shows the positive electrode active material recovered from the positive electrode scrap after heat treatment, and it was confirmed that the binder and conductive material had been removed and the surface protective layer had been lost from the positive electrode active material.

[0133] FIG. 3 shows the positive electrode active material after simultaneously adding a lithium precursor and a Co-containing coating agent to the positive electrode active material recovered in Examples 1 to 4 and annealing it, and it was confirmed that the crystalline structure and the surface protective layer were restored.

[0134] FIG. 4 shows Comparative Example 2, in which only a lithium precursor was added to the recovered positive electrode active material and annealed. It was confirmed that the crystal structure was restored, but the surface protective layer was reduced.

[0135] Figure 5 is an SEM photograph of the cathode active material regenerated in Example 4, which confirms that the crystalline structure was restored and a surface protective layer was formed. The arrows in Figure 5 indicate the surface protective layer formed on the surface of the cathode active material, and it was confirmed that some aggregation occurred in the surface protective layer. The left side of Figure 5 was taken at a magnification of 10.0K, and the right side was taken at a magnification of 20.0K.

[0136] Figure 6 is an SEM photograph of the cathode active material recycled in Example 5. It can be seen that a protective layer was formed on the surface of the cathode active material, but that aggregation of the Co-containing coating agent occurred on the surface of the cathode active material, resulting in a slight decrease in uniformity. The arrows in Figure 6 indicate the surface protective layer formed on the surface of the cathode active material. The left side of Figure 6 was taken at a magnification of 10.0K, and the right side was taken at a magnification of 20.0K.

[0137] [Test Example II: Evaluation of CHC Cell] The electrochemical performance of the regenerated or newly generated positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was measured through the CHC cell evaluation as follows, and the results are shown in FIG. 7 and Table 1 below. *CHC cell evaluation: 97.5% by weight of recycled positive electrode active material, 1% by weight of carbon black (conductive material), and 1.5% 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 then fabricated. The voltage was set to 3-4.3V, and charging and discharging was performed at 0.1C / 0.1C. The electrochemical performance (charge capacity, discharge capacity, and efficiency) was evaluated under conditions where the electrolyte was ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 (weight ratio) and other additives.

[0138] As shown in Figure 7 below, the initial capacity performance of the recycled cathode active materials prepared in Examples 1 to 4 was improved compared to Comparative Example 2, confirming the benefits of the process. In addition, although the initial capacity performance of the recycled cathode active material prepared in Example 5 was somewhat lower, the process benefit of saving time, energy, and equipment was confirmed by simultaneously adding the lithium precursor and the Co-containing coating agent in the annealing step.

[0139] [Table 1]

[0140] As shown in Table 1, the initial capacity performance of the recycled cathode active materials prepared in Examples 1 to 4 was improved. In particular, the initial capacity performance of Example 1 was significantly improved compared to Comparative Examples 2 and 3. Furthermore, although the initial capacity performance of the recycled cathode active material prepared in Example 5 was somewhat lower, it was confirmed that the simultaneous addition of the lithium precursor and the Co-containing coating agent in the annealing step provided process benefits such as saving time, energy, and equipment.

[0141] [Test Example III: Evaluation of Monocell] The HPPC resistance characteristics and capacity retention rates of the recycled or virgin positive electrode active materials prepared or manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were measured through the following mono-cell evaluation, and the results are shown in Figures 8 to 10 and Table 2. The mono-cells prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured three times and the results are shown in the graphs in Figures 8 to 10.

[0142] * Manufacturing of monocell: The same positive electrode active material slurry as that used for the coin cell was applied to an aluminum foil with a thickness of 20 μm, dried at 130°C for 1 hour, and then punched into a size of 30 mm x 42 mm to manufacture a positive electrode.

[0143] Meanwhile, a negative electrode active material slurry was prepared by mixing 95.6 wt% of a 5:5 mixture of natural graphite and artificial graphite with 3.3 wt% of a conductive material and 1.1 wt% of a binder. The slurry was then applied to a copper foil with a thickness of 10 μm, rolled and dried, and then punched into a size of 31 mm × 43 mm to prepare a negative electrode.

[0144] The prepared positive and negative electrodes were joined with a separator, and then an electrolyte solution of ethylene carbonate (EC):ethyl methyl carbonate (EMC)=3:7 by weight ratio was injected to prepare a polymer cell type mono cell for testing.

[0145] *Measurement of resistance change according to SOC: The resistance change according to SOC was measured for the manufactured mono cells. Resistance according to SOC was measured using the HPPC (Hybrid Pulse Power Characterization) method, and both discharge resistance and charge resistance were measured by applying a current of 2C for 10 seconds. SOC was measured at six points: 95%, 80%, 50%, 20%, 10% and 5%.

[0146] Pulse discharge (DC-IR measurement) was performed for each SOC section, and the resistance was recorded. The resistance was calculated by dividing the change in voltage that occurred during discharge by the discharge current, as shown in Equation 1 below.

[0147] [Formula 1] R=V / I (Here, R is the resistance, V is the change in voltage that occurs during discharge, and I is the discharge current.)

[0148] The diffusion resistance is the 30-second resistance minus the 0.1-second resistance, and is calculated using the following formulas 2 to 4.

[0149] [Formula 2] 0.1sec resistance=R(ohm)+R(ct)

[0150] [Formula 3] 30sec resistance=R(ohm)+R(ct)+R(diff)

[0151] [Formula 4] R(diff)=30sec resistance-0.1sec resistance (In Equations 2 to 4, R(ohm) is ohmic resistance, which indicates the resistance within the cell; R(ct) is charge transfer resistance, which indicates the resistance when lithium moves from the electrolyte to the positive electrode active material; and R(diff) is diffusion resistance, which indicates the resistance when lithium that has penetrated into the positive electrode active material settles deep inside the positive electrode active material.)

[0152] *Measurement of capacity retention and resistance increase: The manufactured mono-cell was subjected to 100 charge-discharge cycles at 45°C in the range of 2.5 to 4.25 V at a constant current of 0.3 C, and the capacity and resistance of the mono-cell battery were measured, and the results are shown in Table 2 below. Here, the capacity retention (Capacity Retention, %) is the ratio of the capacity at the 100th cycle to the capacity at the 1st cycle, the capacity retention (Capacity Retention vs. Comparative Example 1, %) is the ratio of the capacity at the 100th cycle of Comparative Example 2 and Examples 1 and 2 to the capacity at the 100th cycle of Comparative Example 1, and the resistance increase (Resistance Increase, %) is the ratio of the resistance at the 100th cycle to the resistance at the 1st cycle.

[0153] As shown in Figures 8 to 10 below, Examples 1 and 2 showed some higher R(ct) and R(ohm) resistances than Comparative Example 2, which used only a lithium precursor without adding a Co-containing coating agent during annealing, but the effect of improving diffusion resistance was confirmed. A reduction in diffusion resistance reduces the resistance required for Li that has penetrated into the positive electrode active material to settle deep inside the positive electrode active material, resulting in improved battery performance.

[0154] [Table 2]

[0155] As shown in Table 2, in Examples 1 and 2 in which a lithium precursor and a Co-containing coating agent were simultaneously added to the recovered positive electrode active material and then annealed, the capacity retention rate and the resistance increase rate after 100 cycles were similar or equivalent to those of Comparative Example 1 and superior to those of Comparative Example 2, confirming that the battery performance was improved.

Claims

1. (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose the binder and the conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; (b) adding a lithium precursor and a Co-containing coating agent to the recovered positive electrode active material, and annealing the resulting material.

2. 2. The method of claim 1, wherein the positive electrode active material layer comprises at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li.

3. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (a), the heat treatment is performed at 300 to 650° C. in an oxygen atmosphere.

4. The oxygen is oxygen with a purity of 59% or more (O ２ 4. The method for regenerating a positive electrode active material according to claim 3, wherein the positive electrode active material is a soluble polymer.

5. The method for regenerating a positive electrode active material according to claim 1 , wherein the positive electrode active material recovered in step (a) includes single particles.

6. 2. The method of claim 1, wherein in step (b), the lithium precursor is added in an amount corresponding to 1 mol% to 40 mol% when the total amount of lithium contained in the recovered positive electrode active material is 100 mol%.

7. 2. The method of claim 1, wherein in step (b), the Co-containing coating agent is added so that the Co content is 1 to 25,000 ppm based on the sum of the content of the recovered positive electrode active material and the content of the additional lithium precursor.

8. The lithium precursor is LiOH, Li ２ CO ３ , LiNO ３ , and Li ２ 2. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material contains one or more of:

9. The Co-containing coating agent is Co(OH) ２ , Co ２ O ３ , Co ３ (P.O. ４ ) ２ , CoF ３ , CoOOH, Co(OCOCH ３ ) ２ ・4H ２ O, Co(NO ３ ) 6H ２ O, Co ３ O ４ , Co(SO ４ ) ２ ・7H ２ O, and CoC ２ O ４ The method for regenerating a positive electrode active material according to claim 1, wherein the active material is one or more selected from the group consisting of:

10. 2. The method of claim 1, wherein the annealing is performed at a temperature of 400 to 800°C.

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