Method for regenerating positive electrode active material

Abstract

To provide a method for regenerating a positive electrode active material with improved output performance, without using metal elements discarded from waste positive electrodes, with fewer steps and less cost, in an environmentally friendly and safe manner. The method for recycling cathode active materials, which provides cathode active materials with excellent charge capacity, resistance characteristics, and capacitance characteristics, involves adding oxygen to used cathodes containing high-nickel cathode materials, subjecting them to oxidative heat treatment, followed by a primary wash. The lithium precursor is then added, annealing is performed, and the secondary wash reduces the fluorine content on the surface of the recycled cathode active material. Furthermore, by dividing the oxidative heat treatment step into two steps, the binder is burned cleanly, reducing the amount of fluorine and residual lithium generated during the heat treatment step and resulting in a smaller crystal size.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority from Korean Patent Application No. 10-2022-0082984, filed July 6, 2022, and Korean Patent Application No. 10-2022-0082985, filed July 6, 2022, and Korean Patent Application No. 10-2023-0081265, refiled June 23, 2023, 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, in which a used cathode containing a high-nickel (High-Ni) cathode material is subjected to an oxidative heat treatment by introducing oxygen, followed by a primary wash. Subsequently, a lithium precursor is added, annealing is performed, and a secondary wash is performed to remove fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the recycled cathode active material. Furthermore, by performing the oxidation heat treatment step in two separate steps, the binder is cleanly burned, and the fluorine (F) generated during the heat treatment step and residual lithium are reduced, resulting in a smaller crystallite size, resulting in a cathode active material with excellent charge capacity, resistance characteristics, and capacitance characteristics. The recovery and recycling processes do not use acid, which is environmentally friendly. Since neutralization and wastewater treatment are not required, process costs are reduced. Since the cathode active material is recycled 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. [Background technology]

[0003] A lithium secondary battery generally 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 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").

[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 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.

[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] To address the above-mentioned problems of the prior art, the present invention provides a method for regenerating a cathode active material by subjecting a used cathode containing a high-nickel (High-Ni) cathode material to an oxidative heat treatment using oxygen, followed by a primary wash. Subsequently, a lithium precursor is added, annealing is performed, and a secondary wash is performed to remove fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the regenerated cathode active material. Furthermore, by performing the oxidative heat treatment step in two steps, the binder is cleanly burned, and the fluorine (F) generated during the heat treatment step and residual lithium are reduced, resulting in a smaller crystallite size, thereby providing a cathode active material with excellent charge capacity, resistance characteristics, and capacitance characteristics. 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, thereby reducing process costs. The cathode active material is regenerated directly without decomposition, so there are no discarded metal elements. Furthermore, the use of no 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.

[0014] Another object of the present invention is to provide a secondary battery that is excellent in initial discharge capacity, rate performance, and capacity 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] To achieve the above object, the present invention provides I) a cathode active material that is at least one selected from the group consisting of a lithium nickel oxide (LNO)-based cathode active material, a nickel cobalt manganese (NCM)-based cathode active material, a nickel cobalt aluminum (NCA)-based cathode active material, and a nickel cobalt manganese aluminum (NCMA)-based cathode active material, the cathode active material comprising at least 60 mol% of Ni, a fluorine (F) content of 250 mg / kg or less, and an average crystallite size of 122 nm or less.

[0017] II) In the above I), the surface of the positive electrode active material may be coated with a coating agent containing metal or carbon.

[0018] III) In I) or II), the metal may be boron (B), tungsten (W), or a mixture thereof.

[0019] IV) In the above I) to III), the positive electrode active material may be a recycled positive electrode active material.

[0020] The present invention also provides V) a method for regenerating a positive electrode active material, comprising the steps of: subjecting a waste positive electrode, having a positive electrode active material layer containing 60 mol % or more of Ni formed on a current collector, to an oxidative heat treatment by introducing oxygen 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; primarily washing the recovered positive electrode active material; adding a lithium precursor to the primarily washed positive electrode active material and annealing it; and secondarily washing the annealed positive electrode active material.

[0021] VI) In the above V), the oxidation heat treatment can be carried out at 300 to 650°C.

[0022] VII) In the above V) or VI), the oxidation heat treatment can be a primary heat treatment at 300 to 450°C, followed by a secondary heat treatment at 500 to 650°C.

[0023] VIII) In the above V) to VII), the first heat treatment can be carried out for 10 minutes to 3 hours, and the second heat treatment can be carried out for 10 minutes to 2 hours.

[0024] IX) In the above V) to VIII), the oxygen may have a purity of 59% or more.

[0025] X) In the above V) to IX), the primary washing can be carried out by immersing the recovered positive electrode active material in water or a basic lithium compound aqueous solution as a washing liquid, or by stirring the material while immersing it.

[0026] XI) In the above V) to X), the basic lithium compound aqueous solution may contain more than 0 wt % and 15 wt % or less of the lithium compound.

[0027] XII) In the above V) to XI), the method of adding a lithium precursor to the primarily washed positive electrode active material in the annealing step can be to mix the primarily washed positive electrode active material with a lithium precursor solution and spray-dry the mixture.

[0028] XIII) In steps V) to XII), the second washing may include mixing the annealed cathode active material with water as a washing solution, followed by filtering, and drying the solid cathode active material obtained after the filtration.

[0029] XIV) In the above V) to XIII), the lithium precursor can include one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0030] XV) In the above V) to XIV), the lithium precursor may be added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium in the raw material positive electrode active materials used in the positive electrode active material layer is 100 mol %.

[0031] XVI) In the above V) to XV), the annealing can be carried out at 400 to 1000°C.

[0032] XVII) In the above V) to XVI), the method for regenerating a positive electrode active material may further include a step of surface-coating the second-washed positive electrode active material to obtain a reusable positive electrode active material.

[0033] XVIII) In the above V) to XVII), the surface coating can be performed by coating the surface with one or more of metal, organic metal, and carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C.

[0034] The present invention also provides XIX) a regenerated positive electrode active material, which is produced by the method for regenerating a positive electrode active material according to any one of V) to XVIII).

[0035] The present invention also provides XX) a cathode active material that is at least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, 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, the cathode active material containing 60 mol% or more of Ni, a fluorine (F) content of 305 mg / kg or less, and an average crystallite size of 139 nm or less.

[0036] XXI) In the above XX), the positive electrode active material may have a residual Li2CO3 content of 0.16 wt% or less.

[0037] XXII) In the above XX) or XXI), the positive electrode active material may be a recycled positive electrode active material.

[0038] The present invention also provides XXIII) a secondary battery comprising the positive electrode active material according to any one of I) to IV), XIX), XX) and XXII). [Effects of the Invention]

[0039] According to the present invention, used positive electrodes containing high-nickel (High-Ni) positive electrode material are subjected to an oxidative heat treatment by introducing oxygen, followed by a primary wash. Subsequently, a lithium precursor is added, annealing is performed, and then a secondary wash is performed. This removes fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the recycled positive electrode active material, thereby reducing the crystallite size. Furthermore, by performing the oxidative heat treatment step in two steps, the binder is cleanly burned, and the fluorine (F) generated during the heat treatment step and residual lithium are reduced, thereby reducing the crystallite size, thereby providing a positive electrode active material with excellent charge capacity, resistance characteristics, and capacitance characteristics. Furthermore, since no acid is used in the recovery and regeneration process of the positive electrode active material, this is environmentally friendly. Since no neutralization or wastewater treatment is required, process costs are reduced. Since the positive electrode active material is regenerated directly without decomposition, there are no discarded metal elements. 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, this method of regenerating positive electrode active material significantly improves economy and productivity. [Brief explanation of the drawings]

[0040] 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] FIG. 10 is a diagram showing positive electrode scraps that are discarded after cutting electrode plates from a positive electrode sheet. [Figure 2] 1 shows SEM photographs of the positive electrode active materials regenerated in Example 1 and Comparative Examples 1 to 3. [Figure 3] 1 is a graph showing the results of charge capacity of coin cells to which the positive electrode active materials regenerated in Example 1 and Comparative Examples 1 to 3 are applied. [Figure 4] 1 is a graph showing the results of charge-discharge cycles of mono-cells using the positive electrode active materials regenerated in Example 1 and Comparative Examples 1 to 3, illustrating the changes in capacity retention rate (%) and resistance increase rate (%) depending on the number of cycles. [Figure 5] 10 is a graph showing the results of charge capacity of coin cells to which the positive electrode active materials regenerated in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2 are applied. [Figure 6] 1 is a graph showing the results of charge-discharge cycles of mono-cells employing the positive electrode active materials regenerated in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2, and showing the change in capacity retention rate (%) depending on the number of cycles. [Figure 7] 2 is a flowchart of a process for regenerating a positive electrode active material according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The inventors were researching a direct recycling method for recycling used cathodes into cathode active materials with excellent battery performance without decomposing the cathode active material. They found that when used cathodes containing high-nickel (High-Ni) cathode materials are subjected to an oxidative heat treatment with oxygen, followed by a primary wash, and then annealed with a lithium precursor and a secondary wash, fluorine (F) and lithium precursor that did not participate in the reaction are removed from the surface of the recycled cathode active material, reducing the crystallite size. Furthermore, when the oxidative heat treatment step is divided into two steps, the binder is burned cleanly, and the fluorine (F) generated during the heat treatment step and residual lithium are reduced, reducing the crystallite size, thereby improving the battery characteristics of the recycled cathode active material. Based on this, they continued their research and completed the present invention.

[0042] The regenerated positive electrode active material, the regenerating method thereof, and the secondary battery including the same will be described in detail below.

[0043] However, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted 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 to best describe his / 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.

[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] positive electrode active material The positive electrode active material of the present invention is at least one selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active materials, nickel cobalt manganese (NCM)-based positive electrode active materials, nickel cobalt aluminum (NCA)-based positive electrode active materials, and nickel cobalt manganese aluminum (NCMA)-based positive electrode active materials, and is characterized by containing 60 mol% or more of Ni, a fluorine (F) content of 250 mg / kg or less, and an average crystal size of 122 nm or less, which has the effect of providing excellent charge capacity, resistance characteristics, and capacity characteristics.

[0046] The positive electrode active material preferably includes one or more selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co). In this case, there is an effect of excellent electrochemical performance, resistance characteristics, capacity characteristics, and the like.

[0047] Specific examples of the positive electrode active material include the following Chemical Formula 1 [Chemical Formula 1] Li a Ni x Mn y Co z M w O 2+δ (In 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 can include a compound represented by this, and in this case, there is an effect of excellent electrochemical performance, resistance characteristics, capacity characteristics, and the like.

[0048] 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%. Within this range, there is an effect of excellent charge capacity, resistance characteristics, and capacity characteristics.

[0049] 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.

[0050] For example, the positive electrode active material may have a fluorine (F) content of 250 mg / kg or less, preferably 200 mg / kg or less, and more preferably 10 to 200 mg / kg. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0051] In this description, the fluorine (F) content can be measured using an ICP analyzer, and in this case, it can be measured using a general ICP analyzer commonly used in laboratories, and there is no deviation due to the measuring device or method.

[0052] For example, the positive electrode active material may have an average crystal size of 122 nm or less, preferably 115 to 122 nm, and more preferably 120 to 122 nm. Within this range, a smaller crystal size can reduce strain and minimize cycle cracking, thereby extending the battery life.

[0053] In this description, the average crystal size can be measured by XRD crystal analysis, and there is no deviation depending on the measurement device or method. Specifically, 5 g of positive electrode active material particles are placed in a holder, and the particles are irradiated with X-rays. The average crystal size can be determined by analyzing the diffraction grating produced by irradiating the particles with X-rays. The measurement method can be based on the half-width of the main peak or three or more peaks, which can be considered to correspond to the average crystal size of the primary particles of the positive electrode active material particles.

[0054] For example, the positive electrode active material may have 0.32 wt % or less, preferably 0.31 wt % or less, and more preferably 0.01 to 0.31 wt % of LiOH remaining on the surface. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0055] For example, the positive electrode active material may have 0.19 wt % or less, preferably 0.01 to 0.19 wt %, of Li2CO3 remaining on the surface. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0056] For example, the positive electrode active material may have a total of LiOH and Li2CO3 remaining on the surface of 0.51 wt % or less, preferably 0.50 wt % or less, and more preferably 0.01 to 0.50 wt %, and within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0057] In this description, the amounts of LiOH and Li2CO3 remaining on the surface of the positive electrode active material can be measured using a pH titrator (T5, manufactured by Mettler Toledo). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The filtrate was titrated with 0.1 M HCl solution, and the change in pH was measured to obtain a pH titration curve. The resulting pH titration curve was used to calculate the amounts of LiOH and Li2CO3 remaining in the positive electrode active material.

[0058] In addition, the cathode active material of the present invention is at least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, 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 60 mol% or more of Ni, a fluorine (F) content of 305 mg / kg or less, and a crystallite size of 139 nm or less, which has the effect of providing excellent capacity characteristics and life characteristics.

[0059] The positive electrode active material preferably contains 80 mol % or more of Ni, more preferably 81 mol % or more, and even more preferably 81 to 95 mol %. Within this range, excellent charge capacity, resistance characteristics, and capacity characteristics are obtained.

[0060] For example, the positive electrode active material may have a fluorine (F) content of 305 mg / kg or less, preferably 250 mg / kg or less, more preferably 200 mg / kg or less, and even more preferably 10 to 200 mg / kg. Within this range, there is an advantage in that the capacity characteristics are excellent.

[0061] For example, the positive electrode active material may have an average crystal size of 139 nm or less, preferably 120 to 139 nm, more preferably 130 to 139 nm, even more preferably 133 to 139 nm, and even more preferably 133 to 136 nm. Within this range, a smaller crystal size can reduce distortion and minimize cycle cracking, thereby advantageously extending the battery life.

[0062] For example, the positive electrode active material may have a surface-residual Li2CO3 content of 0.16 wt % or less, preferably 0.14 wt % or less, more preferably 0.1 wt % or less, and even more preferably 0.01 to 0.1 wt %. Within this range, there are advantages in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0063] For example, the positive electrode active material may have a surface-remaining LiOH content of 0.32 wt % or less, preferably 0.3 wt % or less, more preferably 0.01 to 0.3 wt %, and even more preferably 0.01 to 0.28 wt %. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0064] For example, the positive electrode active material may have a total of LiOH and Li2CO3 remaining on the surface of 0.45 wt % or less, preferably 0.42 wt % or less, more preferably 0.40 wt % or less, and even more preferably 0.01 to 0.4 wt %, and within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0065] For example, the surface of the positive electrode active material may be coated with a metal or carbon, preferably with a metal. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the surface of the positive electrode active material is substituted with a different element, which adjusts the amount of residual lithium and reduces the pH, thereby improving physicochemical properties.

[0066] The metal is preferably at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably at least one selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably boron (B), tungsten (W), or a mixture thereof, and even more preferably tungsten (W) and boron (B), a specific example of which is tungsten boride (WB). In this case, there is an effect of improving resistance characteristics and life characteristics.

[0067] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol % relative to 1 mol % of the metal in the positive electrode active material before the coating treatment, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and still more preferably 0.01 to 0.05 mol %. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0068] The surface coating is preferably performed by coating the surface with a coating agent containing at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance of the positive electrode active material can be improved while maintaining the properties of the positive electrode active material itself.

[0069] The positive electrode active material may preferably be a recycled positive electrode active material, which has the advantages of being economical and productive.

[0070] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention includes the steps of: subjecting a waste positive electrode, which has a positive electrode active material layer containing 60 mol % or more of Ni formed on a current collector, to an oxidative heat treatment by introducing oxygen 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; primarily washing the recovered positive electrode active material; adding a lithium precursor to the primarily washed positive electrode active material and annealing it; and secondarily washing the annealed positive electrode active material. In this case, fluorine (F) and the lithium precursor that did not participate in the reaction are removed from the surface of the regenerated positive electrode active material, and the crystallite size is reduced, thereby achieving excellent charge capacity, resistance characteristics, and capacity characteristics.

[0071] Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0072] (a) A step of recovering a positive electrode active material from a waste positive electrode The step (a) of recovering a cathode active material from a waste cathode according to the present invention may preferably be a step of recovering a cathode active material by subjecting a waste cathode including a current collector and a cathode active material layer coated thereon to an oxidative heat treatment by introducing oxygen, in which case the process is simple and has the effect of completely removing the binder, conductive material, and current collector.

[0073] 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.

[0074] The positive electrode active material layer in step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0075] The positive electrode active material may include, for example, at least one selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, 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.

[0076] The positive electrode active material is preferably one or more selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co), and can contain 60 mol% or more of Ni, more preferably, it is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof, and in this case, there is an effect of excellent reversible capacity and thermal stability.

[0077] As yet 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 Chemical Formula 1 above, M contains 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 this.

[0078] The positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and even more preferably 81 to 95 mol%, and within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0079] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT, or a mixture thereof.

[0080] 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.

[0081] The temperature for the oxidation heat treatment 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 does not melt, and carbon substances in the binder and conductive material react with oxygen to produce CO and CO gas and are removed by combustion, which has the advantage that almost all of the binder and conductive material can be easily removed without leaving any residue.

[0082] The oxidation 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.

[0083] In this description, the oxidation heat treatment time refers to the time required for treatment at the oxidation heat treatment temperature, and does not include the time required to reach the heat treatment temperature.

[0084] For example, the oxidation heat treatment may be performed in two steps. Preferably, the first heat treatment is performed at 300 to 450°C, followed by the second heat treatment at 500 to 650°C. In this case, the process is simple, and the binder, conductive material, and current collector are completely removed, and fluorine (F) generated during the thermal decomposition process and residual lithium are reduced, resulting in a smaller crystallite size.

[0085] The primary heat treatment temperature may be more preferably 300 to 430°C, and even more preferably 320 to 400°C, and within this range, there is an advantage that the thermal decomposition of the binder and organic substances occurs smoothly.

[0086] The primary heat treatment time may be preferably 10 minutes to 3 hours, more preferably 20 minutes to 160 minutes. 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.

[0087] The secondary heat treatment temperature may be more preferably 510 to 630°C, and even more preferably 520 to 630°C. Within this range, the binder and the conductive material are completely combusted, the amount of fluorine (F) generated during the thermal decomposition process and residual lithium are reduced, and the crystal size is reduced.

[0088] The secondary heat treatment time may be preferably 10 minutes to 2 hours, more preferably 20 minutes to 100 minutes. 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.

[0089] The total time of the first heat treatment and the second heat treatment may be, for example, 20 minutes to 5 hours, preferably 30 minutes to 4 hours. Within this range, the current collector is not dissolved and only the binder is removed, which has the advantages of easily separating the positive electrode active material from the current collector, reducing the amount of fluorine (F) and residual lithium generated during the thermal decomposition process, and reducing the crystal size.

[0090] For example, the purity of oxygen used in the oxidation 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 any residue, and the stability of Ni in the active material is increased, resulting in a smaller crystal size.

[0091] The oxygen purity % may be volume % or mol %.

[0092] The purity of oxygen described herein is not particularly limited, and can be measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0093] FIG. 1 shows the cathode scrap that is discarded after cutting the cathode plates from the cathode sheet.

[0094] 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.

[0095] 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, waste positive electrode sheets are generated until the conditions for manufacturing a positive electrode sheet 30 of desired quality are found through predetermined tests.

[0096] For reference, in the following examples, scrap positive electrodes were used as waste positive electrodes.

[0097] (b) A step of first washing the recovered positive electrode active material The method for regenerating a positive electrode active material of the present invention includes (b) a step of primarily washing the recovered positive electrode active material, which has the advantage of removing metal fluorides such as LiF that may be present on the surface of the regenerated positive electrode active material and modifying the surface.

[0098] During the oxidation heat treatment, CO2 and H2O from the binder and conductive material in the active material layer may react with lithium on the surface of the active material to form Li2CO3 and LiOH, or fluorine (F) present in binders such as PVdF may 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 characteristics will deteriorate when the active material is reused.

[0099] The primary cleaning may use, as a cleaning solution, for example, water or a basic lithium compound aqueous solution, and more preferably water.

[0100] The water may be preferably distilled water or deionized water, and more preferably distilled water. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby providing an excellent effect of modifying the surface.

[0101] The basic lithium compound aqueous solution preferably contains more than 0 wt. % to 15 wt. % of the lithium compound, and more preferably more than 0 wt. % to 10 wt. % of the lithium compound. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby modifying the surface. This solution also has the advantage of not dissolving transition metals present in the positive electrode active material, but also replenishing lithium that may dissolve during the cleaning process. If the amount of lithium compound exceeds this range, excessive LiOH may remain on the surface of the active material even after cleaning, which may affect the subsequent annealing process.

[0102] The lithium compound may be, for example, LiOH, LiNO3, or a mixture thereof, and preferably LiOH. In this case, fluorine (F) on the surface of the positive electrode active material and lithium precursors that could not participate in the reaction are removed.

[0103] In the primary cleaning, the weight ratio of the recovered positive electrode active material to the cleaning solution may be, for example, 1:1 to 1:40, preferably 1:1 to 1:35, more preferably 1:1 to 1:30, and even more preferably 1:1 to 1:20. Within this range, there is an advantage that metal fluorides such as LiF can be effectively removed.

[0104] The primary washing can be performed, for example, by immersing the recovered positive electrode active material in a washing solution. The immersion can be performed, for example, for one week, preferably within one day, more preferably within one hour, and even more preferably for 10 to 50 minutes. If the immersion time is longer than one week, there is a risk of a decrease in capacity due to excessive elution of lithium.

[0105] The primary cleaning may preferably include stirring the cathode active material while immersed in the cleaning solution. In this case, the cleaning process can be performed quickly, thereby suppressing lithium elution and shortening the process time.

[0106] The first washing may preferably include filtering the positive electrode active material and the washing solution after washing, and drying the solid positive electrode active material obtained after the filtration. In this case, metal fluorides such as LiF may be more effectively removed.

[0107] The filtration may preferably be vacuum filtration using a filter.

[0108] The drying may be carried out at a temperature of preferably 100 to 500°C, more preferably 120 to 400°C, even more preferably 120 to 300°C, and even more preferably 120 to 200°C.

[0109] The drying may preferably be carried out under vacuum.

[0110] In this description, the vacuum drying is not particularly limited as long as it is vacuum drying that is commonly performed in the technical field to which the present invention pertains.

[0111] (c) adding a lithium precursor to the first washed positive electrode active material and annealing it; The method for regenerating a positive electrode active material of the present invention includes (c) adding a lithium precursor to the primarily washed positive electrode active material and annealing the material. In this case, the crystalline structure of the positive electrode active material is restored, thereby restoring or further improving the properties of the reused active material to the level of a new active material that has never been used.

[0112] The annealing step (c) may be a step of adding a lithium precursor to the primarily washed cathode active material and annealing the material in air or oxygen (O2) at 400 to 1000°C, preferably in air at 400 to 1000°C. In this case, the battery characteristics of the regenerated cathode active material can be improved by improving the crystallinity, such as by increasing the crystallinity or restoring the crystal structure.

[0113] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0114] 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.

[0115] 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 in the raw cathode active material used in the cathode active material layer is 100 mol%. Within this range, no residual precursor that may increase resistance remains in the recycled cathode active material, which is very useful for improving battery characteristics.

[0116] The annealing 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, annealing can be preferably performed at 700 to 900°C, more preferably 710 to 780°C. Since the melting point of LiOH is 462°C, annealing can be preferably performed at 400 to 600°C, more preferably 450 to 480°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance.

[0117] The annealing temperature may preferably be a temperature exceeding the melting point of the lithium precursor. 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.

[0118] In the (c) annealing step, the lithium precursor may be added to the primarily washed cathode active material in a solid or liquid phase after drying the washed cathode active material. As another example, a lithium precursor solution may be added to the washed cathode active material and then spray-dried, thereby performing drying and adding the lithium precursor in a single step. This has the advantages of reducing particle agglomeration due to drying and omitting the process of mixing a solid-phase lithium precursor, and of producing a powder form rather than a lump through spray-drying.

[0119] The lithium precursor solution may be, for example, a lithium compound that is soluble in an aqueous solution or an organic solvent.

[0120] (d) Secondary washing of the annealed positive electrode active material The method for regenerating a positive electrode active material of the present invention includes (d) a step of secondly washing the annealed positive electrode active material. In this step, after the addition of the lithium precursor, the lithium precursor that does not participate in the reaction and remains on the surface of the positive electrode active material in the form of LiOH, Li2CO3, etc. is removed, which has the advantage of preventing a decrease in battery performance and gas generation due to a subsequent reaction between the remaining lithium precursor and the electrolyte.

[0121] The second cleaning may be performed using water as a cleaning solution, for example, and preferably distilled water or deionized water. In this case, lithium precursors such as LiOH, Li2CO3, etc., which tend to remain due to excessive lithium added in the (c) annealing step, can be effectively removed.

[0122] The second washing step may preferably include the steps of mixing the annealed cathode active material and a washing solution in a weight ratio of 1:1 to 1:20, followed by filtering, and drying the solid cathode active material obtained after the filtration. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to excessive lithium added in the (c) annealing step, may be effectively removed.

[0123] The annealed active material and the cleaning solution may be mixed in a weight ratio of preferably 1:1 to 1:20, more preferably 1:1 to 1:15, even more preferably 1:1 to 1:10, and even more preferably 1:1 to 1:5. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to the excessive addition of lithium in the (c) annealing step, can be effectively removed.

[0124] The second washing may include a step of mixing the annealed cathode active material with a washing solution, followed by filtering, and a step of drying the solid cathode active material obtained after the filtration. In this case, excellent charge capacity, resistance characteristics, and capacitance characteristics may be achieved.

[0125] (e) A step of surface-coating the second washed positive electrode active material to obtain a reusable positive electrode active material. The method for regenerating a positive electrode active material of the present invention includes (e) a step of surface-coating the second-washed positive electrode active material to obtain a reusable positive electrode active material, which has the effect of improving the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0126] The surface coating is preferably performed by coating the surface with a coating agent containing at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance of the positive electrode active material can be improved while maintaining the properties of the positive electrode active material itself.

[0127] The metal-containing coating agent is preferably a coating agent containing one or more elements selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably a coating agent containing one or more elements selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB), in which case resistance characteristics and life characteristics are improved.

[0128] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0129] The coating agent containing the organometallic is not particularly limited as long as it is a coating agent that is commonly used in the technical field to which the present invention pertains and contains an organometallic compound containing the metal, and a specific example thereof may be a metal alkoxide.

[0130] The carbon component-containing coating agent is not particularly limited as long as it is a carbon component-containing coating agent commonly used in the technical field to which the present invention pertains, and a specific example thereof may be a sugar such as sucrose.

[0131] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol %, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and still more preferably 0.01 to 0.05 mol %, based on the components actually coated on the surface of the positive electrode active material excluding the solvent, relative to 1 mol % of the metal in the positive electrode active material before the coating treatment. Within this range, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0132] The heat treatment temperature may be preferably 100 to 1000°C, more preferably 200 to 1000°C, and even more preferably 200 to 500°C. Within this range, there is an effect of preventing performance degradation due to thermal decomposition of the positive electrode active material and improving structural stability and electrochemical performance.

[0133] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0134] The coating method is not particularly limited as long as it is a coating method commonly used in the technical field to which the present invention pertains, and examples thereof include a liquid phase method in which a liquid coating agent is prepared and mixed with a positive electrode active material, a mechanochemical method using high mechanical energy such as ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which a coating agent in an aqueous solution state is precipitated on the surface of a positive electrode active material, a method utilizing a reaction between a gaseous coating agent and a positive electrode active material, and a sputtering method.

[0135] The metal, organometallic, and carbon components may be, for example, spherical, plate-like, angular, or needle-like, and such shapes can be adjusted by changing process conditions during the manufacturing process. The definition of each shape is not particularly limited as long as it follows the definition generally accepted in the technical field to which the present invention belongs.

[0136] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m 2 / g, and more preferably, the average diameter is 10 to 100 nm and the specific surface area is 20 to 100 m 2 / g, and within this range, the particles are uniformly attached to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material, thereby improving the problems of deterioration in life characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0137] In this description, the average diameter can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by using a laser diffraction method. Specifically, particles of a positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer such as a Microtrac MT 3000. Ultrasonic waves of about 28 kHz and an output of 60 W are irradiated, and the average particle size (D50) based on 50% of the particle size distribution measured by the analyzer can be calculated.

[0138] In this description, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II from BEL Japan.

[0139] The positive electrode active material produced by the method for regenerating a positive electrode active material of the present invention may have a fluorine (F) content of, for example, 250 mg / kg or less, preferably 200 mg / kg or less, and more preferably 10 to 200 mg / kg. Within this range, the positive electrode active material has the advantage of excellent charge capacity, resistance characteristics, and capacity characteristics.

[0140] For example, the positive electrode active material may have 0.32 wt % or less, preferably 0.31 wt % or less, and more preferably 0.01 to 0.31 wt % of LiOH remaining on the surface. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0141] For example, the positive electrode active material may have 0.19 wt % or less, preferably 0.01 to 0.19 wt %, of Li2CO3 remaining on the surface. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0142] For example, the positive electrode active material may have a total of LiOH and Li2CO3 remaining on the surface of 0.51 wt % or less, preferably 0.50 wt % or less, and more preferably 0.01 to 0.50 wt %, and within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0143] For example, the positive electrode active material may have an average crystal size of 122 nm or less, preferably 115 to 122 nm, and more preferably 120 to 122 nm. Within this range, a smaller crystal size can reduce distortion and minimize cycle cracking, thereby extending the battery life.

[0144] Furthermore, the positive electrode active material produced by the method for regenerating a positive electrode active material of the present invention may have a fluorine (F) content of, for example, 305 mg / kg or less, preferably 250 mg / kg or less, more preferably 200 mg / kg or less, and even more preferably 10 to 200 mg / kg.Within this range, there is an advantage in that the capacity characteristics are excellent.

[0145] For example, the positive electrode active material may have a surface-residual Li2CO3 content of 0.16 wt % or less, preferably 0.14 wt % or less, more preferably 0.10 wt % or less, and even more preferably 0.01 to 0.10 wt %, and within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0146] For example, the positive electrode active material may have a surface-remaining LiOH content of 0.32 wt % or less, preferably 0.30 wt % or less, more preferably 0.01 to 0.30 wt %, and even more preferably 0.01 to 0.28 wt %. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0147] For example, the positive electrode active material may have a total of LiOH and Li2CO3 remaining on the surface of 0.45 wt % or less, preferably 0.42 wt % or less, more preferably 0.40 wt % or less, and even more preferably 0.01 to 0.40 wt %. Within this range, there is an advantage in that the charge capacity, resistance characteristics, and capacity characteristics are excellent.

[0148] For example, the positive electrode active material may have an average crystal size of 139 nm or less, preferably 120 to 139 nm, more preferably 130 to 139 nm, even more preferably 133 to 139 nm, and even more preferably 133 to 136 nm. Within this range, a smaller crystal size can reduce distortion and minimize cycle cracking, thereby advantageously extending the battery life.

[0149] FIG. 7 is a flowchart showing a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0150] Referring to Figure 7, first, cathode scraps are prepared as waste cathodes (step S10). For example, a slurry is prepared by mixing NCM-based lithium transition metal composite oxide, carbon black, and polyvinylidene fluoride with N-methyl pyrrolidone (NMP), and the slurry is 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 scraps can be prepared.

[0151] In particular, the present invention can be effectively applied to waste positive electrodes that have used a positive electrode active material containing 60 mol % or more of Ni, preferably a positive electrode active material containing 80 mol % or more of Ni, more preferably a positive electrode active material containing 81 mol % or more of Ni, and even more preferably a positive electrode active material containing 81 to 95 mol % of Ni.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] Next, oxygen is introduced into the positive electrode scrap to perform an oxidation heat treatment, and the positive electrode active material is recovered (step S30). Here, the heat treatment is carried out to thermally decompose the binder in the active material layer.

[0156] The oxidative heat treatment is preferably performed using oxygen with a purity of 80% or higher, and more preferably with oxygen with a purity of 90% or higher. This ensures the stability of Ni in used 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 reused cathode active material. In contrast, when oxidative heat treatment is performed using 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.

[0157] The oxidation 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.

[0158] The oxidation 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 imposing a strain on the heat treatment equipment, and there are advantages in that no thermal shock is caused to the cathode scrap.

[0159] The oxidation 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.

[0160] In this description, a high-nickel positive electrode active material refers to a positive electrode active material containing 60 mol % or more of nickel.

[0161] The oxidation heat treatment step can be preferably performed in two steps, more preferably a first oxidation heat treatment at 300 to 430°C and a second heat treatment at 510 to 630°C. In this case, the two-step heat treatment has the advantage of reducing fluorine (F) generated during the thermal decomposition process and residual lithium, thereby reducing the crystal size.

[0162] The primary oxidation heat treatment may be carried out at a temperature of more preferably 320 to 400°C.

[0163] The primary heat treatment may be carried out for a time period of preferably 10 minutes to 3 hours, more preferably 20 minutes to 160 minutes.

[0164] The secondary oxidation heat treatment temperature may more preferably be 520 to 630°C. Within this range, the binder and the conductive material are sufficiently pyrolyzed, and the amount of fluorine (F) and residual lithium generated during the pyrolysis process is reduced, resulting in a smaller crystal size.

[0165] The secondary heat treatment time may be preferably 10 minutes to 2 hours, more preferably 20 minutes to 100 minutes. 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.

[0166] The oxidation 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 imposing a strain on the heat treatment equipment, and there are advantages in that no thermal shock is caused to the cathode scrap.

[0167] The oxidation 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.

[0168] After the oxidation heat treatment, the material can be cooled slowly or rapidly in the air.

[0169] Next, the recovered positive electrode active material is subjected to a primary washing (step S40).

[0170] Since fluorine (F) and lithium remain on the surface of the positive electrode active material recovered in the oxidation heat treatment step S30, a cleaning step is required to remove them.

[0171] In the first washing step, the recovered positive electrode active material is washed with water or a basic lithium compound aqueous solution, preferably water, as a washing liquid.

[0172] The water may preferably be distilled or deionized water, which has the advantage that metal fluorides such as LiF are removed, thereby modifying the surface.

[0173] The basic lithium compound aqueous solution contains more than 0 wt.% to 15 wt.% or less, preferably more than 0 wt.% to 10 wt.% or less, of the lithium compound. In this case, metal fluorides such as LiF that may be present on the surface of the recycled cathode active material are removed, thereby improving the surface. If the lithium compound exceeds 15 wt.%, excessive amounts of lithium compounds such as LiOH and LiNO3 may remain on the surface of the cathode active material even after washing, which may affect the subsequent annealing process.

[0174] The lithium compound may specifically be LiOH.

[0175] The primary cleaning can be performed by immersing the recovered active material in a cleaning solution. After immersion, cleaning can be performed within one week, preferably within one day, and more preferably within one hour. Washing for more than one week may result in a decrease in capacity due to excessive lithium elution. Therefore, it is preferable to perform the cleaning within one hour. The primary cleaning involves immersing the active material in the cleaning solution and stirring it while immersed. It is recommended to perform stirring in parallel whenever possible. When using an aqueous lithium compound solution as the cleaning solution, immersion without stirring may slow down the cleaning process and cause lithium elution. Since simultaneous stirring can minimize the process time, it is preferable to perform stirring simultaneously with the impregnation of the aqueous lithium compound solution.

[0176] After the first washing, filtering and drying in air in an oven (convection type) may be further carried out.

[0177] In the first cleaning, the weight ratio of the recovered positive electrode active material to the cleaning solution may be 1:1 to 1:40, preferably 1:1 to 1:35, and more preferably 1:1 to 1:30. Within this range, metal fluorides such as LiF can be effectively removed.

[0178] The first washing may preferably include filtering the positive electrode active material and the washing solution after washing, and drying the solid positive electrode active material obtained after the filtration.

[0179] The filtration is preferably reduced pressure filtration using a filter, and the drying is vacuum drying at 120 to 140°C.

[0180] Next, a lithium precursor is added to the primarily washed positive electrode active material, and annealing is performed (step S50).

[0181] The annealing step S50 is important in that a lithium precursor is added to the pre-washed cathode active material and then annealed. Lithium loss may occur in the cathode active material during steps S30 and S40, and step S50 replenishes this lost lithium.

[0182] Furthermore, in step S50, the crystalline structure of the active material is restored through annealing, thereby restoring or even improving the properties of the reused active material to the level of a new active material that has never been used.

[0183] During steps S30 and S40, a deformed structure may develop on the surface of the positive electrode active material. For example, in step S40, Ni in an NCM-based lithium transition metal composite oxide active material may be converted into rock salt (NiCO3·2Ni(OH)2)H2O) by water, forming a spinel structure. Manufacturing a battery in this state may result in a decrease in battery performance, such as a decrease in capacity. In the present invention, the crystal structure is restored through step S50. For example, the NCM-based lithium transition metal composite oxide positive electrode active material is restored to a hexagonal crystal structure. This allows the initial performance to be restored or improved to a level similar to that of an unused positive electrode active material.

[0184] The lithium precursor in step S50 may be any one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0185] The method of adding a lithium precursor to the first-washed active material may involve drying the washed positive electrode active material and then adding the lithium precursor in a solid or liquid phase. As another example, a lithium precursor solution may be added to the washed positive electrode active material, followed by spray drying, thereby performing drying and adding the lithium precursor in a single step. The lithium precursor solution may be a lithium compound that is soluble in an aqueous solution or an organic solvent.

[0186] If the cathode active material particles are dried immediately after the surface modification process using a primary cleaning method, such as in an oven, they may aggregate and form clumps. Mixing the agglomerated particles with the lithium precursor requires grinding the agglomerates, which can complicate the process and make continuous processing difficult. Furthermore, especially in the case of NCM-based cathode active materials, if the lithium precursor and powder are mixed and milled in the presence of moisture, the cathode active material absorbs moisture, resulting in severe agglomeration. Therefore, mixing the cathode active material with a lithium precursor solution after the primary cleaning method, dispersing the material, and then spray-drying the mixture can eliminate particle aggregation due to drying and the hassle of mixing a solid lithium precursor. In other words, spray-drying has the advantage of producing the product in powder form rather than clumps.

[0187] During spray drying, the lithium precursor solution dries immediately after spraying, coating or contacting the lithium precursor components on the surface of the cathode active material. This has the advantage of controlling particle size as the particles aggregate due to capillary force during the drying of the lithium precursor solution solvent. In the case of cathode scraps made from electrodes, the surface particles can be pressed during the rolling process, causing cracks or breakage. In particular, compared to LCO, NCM-based cathode active materials are prone to greater particle cracking during rolling during electrode formation, resulting in the problem of a greater number of small particles in the recovered cathode active material compared to unused cathode active material, resulting in uneven particle size.

[0188] In addition, NCM-based active materials contain large particles that are formed by the aggregation of primary particles having a size of tens to hundreds of nanometers into secondary particles. In a positive electrode manufactured from such an active material, the secondary particles may be cracked and formed into primary particles during the rolling process to adjust the porosity within the electrode, or may be formed into small particles that are larger in size but smaller than the large particles.

[0189] The more particles are broken by rolling, the greater the specific surface area of ​​the active material. Therefore, in the case of reused active materials obtained from rolled electrodes, there may be problems that the slurry properties, electrode adhesive strength, and electrode performance may be adversely affected during reuse.

[0190] As described above, the surface of the positive electrode active material is coated with a lithium precursor through the spray-drying process, and the positive electrode active material is obtained in a particle-controlled state. Addition of the lithium precursor, particle formation, and drying are all performed in a single step, which simplifies the process. Furthermore, spray-drying is unique in that it is not simply a method for obtaining an active material, but rather a method for re-particleizing particles that have been previously used and broken by rolling or other processes.

[0191] Another advantage is that the washing and spray drying can be performed continuously because the washed cathode active material particles are simply mixed and dispersed in a lithium precursor solution of a certain concentration. Thus, the cathode active material regeneration method according to this embodiment has the advantage of being continuous, with the lithium precursor coating, drying, and granulation (i.e., particle readjustment) being performed simultaneously in a single step.

[0192] Additionally, because lithium loss occurs within the positive electrode active material during steps S30 and S40, this loss is replenished in step S50. 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 through annealing, thereby improving the battery characteristics of the regenerated positive electrode active material and restoring it to the level of a virgin positive electrode active material. Here, "virgin" is the opposite concept of "regenerated," meaning something that has been created for the first time, and is the same term as "raw material" used in the examples.

[0193] As the lithium precursor, LiOH is specifically used.

[0194] The lithium precursor is preferably added in an amount at least equal to the molar ratio of lost lithium relative to the molar ratio of lithium to other metals in the new cathode active material used in the cathode active material layer. Adding 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. For example, if the molar ratio of lithium to other metals in the new cathode active material is 1, 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 0.2.

[0195] Specifically, when a lithium precursor is added in a molar ratio (based on lithium metal) of 0.09 to 0.1, 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.

[0196] Specifically, the lithium precursor may be added in an amount corresponding to 1 mol % to 40 mol %, preferably 1 to 15 mol %, and even more preferably 1 to 10 mol %, when the total amount of lithium in the raw material positive electrode active materials used in the positive electrode active material layer is 100 mol %.

[0197] The annealing is carried out in air at a temperature of 400 to 1000°C, preferably 600 to 900°C, and this temperature must be adjusted within a limited range depending on the type of lithium precursor.

[0198] The annealing 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 Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and most preferably 750 to 780°C. When LiOH is used as the lithium precursor, the annealing temperature is preferably 400 to 600°C, more preferably 450 to 480°C, and most preferably 470 to 480°C.

[0199] The annealing time is, 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, but even if annealing is performed for a long period of time, the performance is not significantly affected. The annealing equipment may be the same as or similar to that used in the heat treatment step S30.

[0200] Next, the annealed positive electrode active material is subjected to a second cleaning (step S60).

[0201] Lithium precursors that did not participate in the reaction in the annealing step (S50) remain on the surface of the positive electrode active material in the form of LiOH and Li2CO3, so a residual lithium removal process is required. In particular, high-nickel (High-Ni) positive electrode active materials require an excess amount of Li due to the phenomenon of cation mixing, which makes it easy for lithium impurities such as lithium carbonate (Li2CO3) to remain on the surface. These impurities must be thoroughly removed because they can later react with the electrolyte, reducing battery performance and generating gas.

[0202] In the second washing, distilled water can be preferably used as the washing liquid, which has the advantage that it is safe and inexpensive and does not leach out transition metals present in the positive electrode active material.

[0203] The washing step may include the steps of mixing the annealed cathode active material and the washing solution in a weight ratio of preferably 1:1 to 1:10, more preferably 1:1 to 1:5, followed by filtering, and drying the solid cathode active material obtained after the filtration. In this case, lithium precursors such as LiOH and LiCO, which are likely to remain due to the excessive lithium added in step S50, may be effectively removed.

[0204] The annealed positive electrode active material and distilled water are preferably mixed by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0205] The filtration is preferably reduced pressure filtration using a filter, and the drying is vacuum drying at 120 to 140°C.

[0206] Next, as an optional step, the washed positive electrode active material can be surface coated (step S70).

[0207] For example, the surface coating is performed by coating the surface with a coating agent containing a metal, an organic metal, or a carbon component in a solid or liquid phase manner, followed by heat treatment. If the heat treatment temperature is too low, the desired surface protection layer made of a different metal will not be formed, and if the heat treatment temperature is too high, the battery performance will be reduced due to thermal decomposition of the positive electrode active material.

[0208] Specifically, when a metal oxide or acid containing B, W, BW, etc. is coated on a washed cathode active material and then heat-treated, a surface protection layer such as a lithium boron oxide layer is formed on the surface of the cathode active material.

[0209] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0210] If the annealing step (S50) is performed to achieve a 1:1 molar ratio of lithium to other metals in the cathode active material, the lithium in the cathode active material will react with the coating agent in the surface coating step (S70), resulting in a lithium:other metals molar ratio of less than 1:1, and this regenerated cathode active material will not be able to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step (S50) so that it is present in an amount 0.0001 to 0.1 molar ratio greater than the other metals in the cathode active material, a surface protective layer will be formed in the surface coating step (S70), and the lithium:other metals molar ratio will be 1:1, preventing battery capacity loss.

[0211] secondary battery The secondary battery of the present invention includes the cathode active material. In this case, fluorine (F) and lithium precursor that did not participate in the reaction are removed from the surface of the cathode active material, thereby reducing the crystallite size, thereby providing excellent charge capacity, resistance characteristics, and capacity characteristics. Furthermore, since no acid or organic solvent is used in the recovery and regeneration process of the cathode active material, the secondary battery is environmentally friendly. In particular, since the initial water washing process is omitted, the secondary battery has excellent economic efficiency and productivity.

[0212] 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.

[0213] 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.

[0214] [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 with 85 mol% nickel content) was crushed and subjected to an oxidative heat treatment at 590°C for 30 minutes in 95% pure oxygen 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 oxygen (O2) was supplied at 10 L / min.

[0215] The recovered positive electrode active material was subjected to a primary wash by immersing and stirring in distilled water. The weight ratio of the recovered positive electrode active material to distilled water was 1:30, and the mixture was stirred at 500 rpm for 10 minutes. The active material was then filtered under reduced pressure using a filter. The positive electrode active material after the primary wash had a 0.11 mole reduction in lithium content relative to the raw material, based on 1 mole of lithium in the positive electrode active material.

[0216] The washed cathode active material was dried overnight at 100°C, and then LiOH was added as a lithium precursor. The mixture was annealed in air at 750°C for 5 hours. Air was supplied at a rate of 3 L / min. The lithium precursor was added in an amount corresponding to 18 mol% of the total lithium in the cathode active material, which was 100 mol%.

[0217] The annealed cathode active material was mixed with distilled water in a 1:1 weight ratio, stirred at 500 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was then vacuum-dried at 100°C for 12 hours to obtain a washed cathode active material.

[0218] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 1000 ppm of boron lost in the previous process, the temperature was increased at a rate of 2°C / min to reach the heat treatment temperature, and air was supplied at a rate of 3 L / min.

[0219] In this description, the molar ratio of lithium to other metals in the positive electrode active material, the amount of remaining LiF, etc. were 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.

[0220] Comparative Example 1 A regenerated positive electrode active material was produced in the same manner as in Example 1, except that in the oxidation heat treatment step of Example 1, air (containing 21% oxygen) was introduced instead of oxygen to perform the heat treatment.

[0221] Comparative Example 2 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that in the oxidation heat treatment step of Example 1, air (containing 21% oxygen) was introduced instead of oxygen and the primary washing step was not performed.

[0222] Comparative Example 3 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that the first washing step was not performed.

[0223] [Test Example I: SEM analysis] The regenerated cathode active materials obtained in Example 1 and Comparative Examples 1 to 3 were photographed using an SEM device and are shown in Figure 2. 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.

[0224] As can be seen from Figure 2, the recycled cathode active material produced in Example 1 was broken into small particles, and these broken particles were in contact with or dispersed among larger particles. In contrast, in Comparative Examples 1 to 3, the particles were not broken into small particles but were agglomerated.

[0225] [Test Example II: XRD Analysis] The crystal size of the recycled positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured by XRD crystal analysis.

[0226] Specifically, 5 g of each of the recycled positive electrode active material particles obtained in Example 1 and Comparative Examples 1 to 3 was placed in a holder, and the particles were irradiated with X-rays to generate diffraction gratings, which were then analyzed. The diffraction gratings were determined from the half-width of the main peak or three or more peaks, which corresponded to the average crystal size of the primary particles of the recycled positive electrode active material particles. The average crystal size of the primary particles of the recycled positive electrode active material obtained from this analysis is shown in Table 1 below.

[0227] [Table 1]

[0228] As shown in Table 1, the crystal size of the recycled cathode active material prepared in Example 1 was smaller than those of Comparative Examples 1 to 3. Such a smaller crystal size reduces distortion and minimizes cycle cracking, which has the advantage of extending the battery life.

[0229] [Test Example III: Residual Fluorine (F) Content] The content of fluorine (F) remaining in the recycled cathode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured using an ICP analyzer, and the results are shown in Table 2. The measurement can be performed using a general ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0230] [Table 2]

[0231] As can be seen from Table 2, Example 1 according to the present invention had a significantly reduced residual fluorine content compared to Comparative Examples 1 to 3.

[0232] [Test Example IV: Residual Lithium Content] The residual lithium content of the recycled positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured as follows, and the results are shown in Table 3 below. *Residual lithium content: 5 g of the positive active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and filtered to remove the active material. The filtrate was titrated with 0.1 M HCl solution, and the pH change was measured to obtain a pH titration curve. The resulting pH titration curve was used to calculate the amount of residual LiOH and Li2CO3 in the positive active material.

[0233] [Table 3]

[0234] As shown in Table 3, it was confirmed that Example 1 had a reduced amount of residual lithium in the recycled positive electrode active material compared to Comparative Examples 1 to 3.

[0235] [Test Example V: 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 described below, and the results are shown in FIG. *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.

[0236] FIG. 3 shows the results of evaluating coin cells for each of the recycled positive electrode active materials manufactured or prepared in Example 1 and Comparative Examples 1 to 3. It was confirmed that the recycled positive electrode active material of the present invention (Example 1) has superior charging capacity compared to Comparative Examples 1 to 3.

[0237] [Test Example VI: Evaluation of Mono Cell] The capacity retention rate and resistance increase rate of the mono-cells prepared using the recycled positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 were measured through the following mono-cell evaluation, and the results are shown in FIG. * 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.

[0238] 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.

[0239] The prepared positive and negative electrodes were bonded to a separator, and then an electrolyte solution of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 by weight was injected, followed by vacuum sealing to prepare a mono cell, which was then aged for 10 hours before undergoing electrochemical evaluation.

[0240] Measurement of capacity retention at high temperature (45°C): Each mono-cell prepared using the regenerated cathode active material obtained in Example 1 and Comparative Examples 1-3 was subjected to formation at a 0.1C rate, followed by degassing. Then, 200 cycles of CC / CV charging at 4.2V, 1C, and 0.05C cutoff, and CC discharging at 2.5V and 0.5C were performed at high temperature (45°C). The discharge capacities at the first cycle and after 200 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A). The discharge capacity at the first cycle was set as the initial capacity. The capacity retention was calculated by comparing the 200th discharge capacity with the initial capacity (100%) using Equation 1 below. The results are shown in Figure 4.

[0241] [Formula 1] Capacity retention rate (%) = (discharge capacity after high-temperature cycle / initial discharge capacity) x 100

[0242] Measurement of resistance increase rate at high temperature (45°C): Each mono-cell prepared using the regenerated cathode active material obtained in Example 1 and Comparative Examples 1 to 3 underwent formation at a 0.1C rate, followed by degassing. The degassed lithium secondary battery was transferred to a charger / discharger at room temperature (25°C) and charged at a 0.33C rate under constant current / constant voltage conditions up to 4.2V, followed by a 0.05C cutoff charge and discharge at 0.33C to 2.5V. The SOC (State of Charge) was adjusted to 50% based on the discharge capacity after three charge / discharge cycles. The DC internal resistance was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop observed when a 10-second discharge pulse was applied at 2.5C. This resistance was set as the initial resistance.

[0243] After that, 200 cycles of 4.2V, 1C, 0.05C cutoff CC / CV charging and 2.5V, 0.5C CC discharging were performed at high temperature (45°C), and the lithium secondary battery was then transferred to a charger / discharger at room temperature (25°C). After adjusting the SOC (State of Charge) to 50%, a 10-second discharge pulse was applied at 2.5C. The DC internal resistance was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop that occurred when the battery was charged. This was compared to the initial resistance (0%), and the resistance increase rate (%) was calculated using Equation 2 below. The results are shown in Figure 4.

[0244] [Formula 2] Resistance increase rate (%) = {(resistance after high-temperature cycle - initial resistance) / initial resistance} x 100

[0245] As shown in FIG. 4, it was confirmed that, as the number of cycles increased, Example 1 had a higher capacity retention rate and a lower resistance increase rate than Comparative Examples 1 to 3.

[0246] [Additional Example] Additional 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 with 86 mol% nickel) was crushed and subjected to a primary heat treatment at 350°C for two hours in 95% pure oxygen. The temperature was then increased to 590°C for a secondary heat treatment for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were then separated and recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and oxygen (O2) was supplied at 10 L / min.

[0247] The recovered positive electrode active material was subjected to a primary wash by immersing and stirring in distilled water as a washing solution. The weight ratio of the recovered positive electrode active material to the washing solution was 1:30, and the mixture was stirred at 500 rpm for 10 minutes. The active material was then filtered under reduced pressure using a filter to remove the active material. The positive electrode active material that had undergone the primary wash had a loss of 0.11 moles of lithium, based on 1 mole of lithium in the positive electrode active material, compared to the raw material.

[0248] The washed cathode active material was dried overnight at 100°C, and then LiOH was added as a lithium precursor. The cathode active material was annealed in air at 750°C for 5 hours. Air was supplied at 3 L / min. The lithium precursor was added in an amount corresponding to 18 mol% of the total lithium in the cathode active material used in the cathode active material layer, assuming a total of 100 mol%.

[0249] The annealed cathode active material was mixed with distilled water in a weight ratio of 1:10, stirred at 500 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was then vacuum-dried at 100°C for 12 hours to obtain a washed cathode active material.

[0250] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 1000 ppm of boron lost in the previous process, the temperature was increased at a rate of 2°C / min to reach the heat treatment temperature, and air was supplied at a rate of 3 L / min.

[0251] In this description, the molar ratio of lithium to other metals in the positive electrode active material, the amount of remaining LiF, etc. were 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.

[0252] In this description, ppm is by weight unless otherwise specified.

[0253] Additional Example 2 A recycled cathode active material was prepared in the same manner as in Additional Example 1, except that the primary heat treatment was performed at 350°C for 30 minutes and the secondary heat treatment was performed at 590°C for 30 minutes.

[0254] Additional Example 3 A recycled cathode active material was prepared in the same manner as in Additional Example 1, except that the primary heat treatment was performed at 350°C for 30 minutes and the secondary heat treatment was performed at 570°C for 30 minutes.

[0255] Additional Comparative Example 1 A recycled positive electrode active material was prepared in the same manner as in Additional Example 1, except that the first and second heat treatment steps were performed at 550° C. for 30 minutes.

[0256] Additional Comparative Example 2 A recycled positive electrode active material was prepared in the same manner as in Additional Example 1, except that the recovered positive electrode active material was directly subjected to the annealing step without undergoing the first washing.

[0257] [Test Example I: XRD Analysis] The crystal size of the recycled positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Example 1 was measured by XRD crystal analysis.

[0258] Specifically, 5 g of each of the recycled positive electrode active material particles obtained in Additional Examples 1 to 3 and Additional Comparative Example 1 was placed in a holder, and the particles were irradiated with X-rays. The diffraction grating was analyzed to determine the average crystal size of the primary particles of the recycled positive electrode active material particles. The average crystal size of the primary particles of the recycled positive electrode active material obtained from this analysis is shown in Table 4 below.

[0259] [Table 4]

[0260] As shown in Table 4, the crystal size of the recycled positive electrode active materials prepared in Additional Examples 1 to 3 was smaller than that of Additional Comparative Example 1. This smaller crystal size reduces distortion and minimizes cycle cracking, which has the advantage of extending the battery life.

[0261] [Test Example II: Residual Fluorine (F) Content] The content of fluorine (F) remaining in the recycled positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2 was measured using an ICP analyzer, and the results are shown in Table 5. The measurement can be performed using a general ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0262] [Table 5]

[0263] As can be seen from Table 5, Additional Examples 1 to 3 according to the present invention had reduced residual fluorine content compared to Additional Comparative Examples 1 and 2. In particular, Additional Comparative Example 2, which did not undergo primary cleaning, had a significantly higher residual fluorine content.

[0264] [Test Example III: Residual Lithium Content] The residual lithium content of the recycled positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 6 below. *Residual lithium content: 5 g of the positive active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and filtered to remove the active material. The filtrate was titrated with 0.1 M HCl solution, and the pH change was measured to obtain a pH titration curve. The resulting pH titration curve was used to calculate the amount of residual LiOH and Li2CO3 in the positive active material.

[0265] [Table 6]

[0266] As shown in Table 6, it was confirmed that the residual lithium content of the recycled positive electrode active material in Additional Examples 1 to 3 was reduced compared to Additional Comparative Examples 1 and 2.

[0267] [Test Example IV: Evaluation of CHC Cell] The electrochemical performance of the recycled positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2 was measured through the CHC cell evaluation as described below, and the results are shown in FIG. *CHC cell evaluation: 97.5 wt% recycled positive electrode active material, 1 wt% carbon black (conductive material), and 1.5 wt% PVdF (binder) were weighed and mixed with NMP to prepare a slurry. This was coated onto aluminum foil to prepare a positive electrode, and a coin half cell (CHC) was fabricated using an electrolyte of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (weight ratio) and other additives. The coin cell was charged at 25°C with a constant current of 0.1 C up to 4.3 V with a 0.05 C cutoff. It was then discharged at a constant current of 0.1 C down to 3.0 V. The charge capacity was measured and is shown in Figure 5.

[0268] Figure 5 shows the results of evaluating coin cells for each of the recycled positive electrode active materials produced in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2. It was confirmed that the recycled positive electrode active materials according to the present invention (Additional Examples 1 to 3) have superior charging capacities compared to Additional Comparative Examples 1 and 2.

[0269] [Test Example V: Evaluation of Mono Cell] The capacity retention rates of the mono-cells manufactured using the recycled positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Examples 1 and 2 were measured through the following mono-cell evaluation, and the results are shown in FIG. * 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.

[0270] 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.

[0271] The prepared positive and negative electrodes were bonded to a separator, and then an electrolyte solution of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 by weight was injected, followed by vacuum sealing to prepare a mono cell, which was then aged for 10 hours before undergoing electrochemical evaluation.

[0272] Measurement of capacity retention at high temperature (45°C): Each mono-cell prepared using the regenerated cathode active material obtained in Additional Examples 1-3 and Additional Comparative Examples 1 and 2 underwent formation at a 0.1C rate, followed by degassing. Subsequently, 100 cycles of CC / CV charging at 4.2V, 1C, and 0.05C cutoff, and CC discharging at 2.5V and 0.5C were performed at high temperature (45°C). The discharge capacities at the first cycle and after 100 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A). The discharge capacity at the first cycle was set as the initial capacity. The capacity retention was calculated by comparing the 100th discharge capacity with the initial capacity (100%) using Equation 1 below, and the results are shown in Figure 6.

[0273] [Formula 1] Capacity retention rate (%) = (discharge capacity after high-temperature cycle / initial discharge capacity) x 100

[0274] As shown in FIG. 6, it was confirmed that Additional Examples 1 to 3 had higher capacity retention rates than Additional Comparative Examples 1 and 2 as the number of cycles increased. [Explanation of symbols]

[0275] 10 Current collector 20 Active material layer 30 Positive electrode sheet 40 positive electrode plate 50 cathode scrap

Claims

1. a step of subjecting a waste positive electrode having a positive electrode active material layer containing 60 mol % or more of Ni formed on a current collector to an oxidative heat treatment by introducing oxygen 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; a step of primarily washing the recovered positive electrode active material; adding a lithium precursor to the primarily washed positive electrode active material and annealing the positive electrode active material; and secondly washing the annealed positive electrode active material.

2. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the oxidation heat treatment is carried out at a temperature of 300 to 650°C.

3. 3. The method of claim 2, wherein the oxidation heat treatment comprises a first heat treatment at 300 to 450°C and a second heat treatment at 500 to 650°C.

4. 4. The method of claim 3, wherein the first heat treatment is performed for 10 minutes to 3 hours, and the second heat treatment is performed for 10 minutes to 2 hours.

5. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the oxygen has a purity of 59% or more.

6. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the primary cleaning is performed by immersing the recovered positive electrode active material in water or a basic lithium compound aqueous solution as a cleaning solution, or by stirring the recovered positive electrode active material while immersing it in water or a basic lithium compound aqueous solution as a cleaning solution.

7. 7. The method of claim 6, wherein the basic lithium compound aqueous solution contains more than 0 wt % and not more than 15 wt % of the lithium compound.

8. 2. The method of claim 1, wherein the method of adding the lithium precursor to the primarily washed positive electrode active material in the annealing step comprises mixing the primarily washed positive electrode active material with a lithium precursor solution and spray-drying the mixture.

9. 2. The method of claim 1, wherein the second washing comprises: mixing the annealed cathode active material with water as a washing solution, filtering the mixture, and drying the solid cathode active material obtained after the filtration.

10. 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:

11. 2. The method of claim 1, wherein the lithium precursor is added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium in the raw material positive electrode active material used in the positive electrode active material layer is 100 mol %.

12. 2. The method of claim 1, wherein the annealing is performed at a temperature of 400 to 1000°C.

13. 2. The method of claim 1, further comprising the step of: surface-coating the second-washed positive electrode active material to obtain a reusable positive electrode active material.

14. 14. The method of claim 13, wherein the surface coating is performed by coating the surface with at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, and then heat-treating the surface at 100 to 1200°C.

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