Method for regenerating positive electrode active material and positive electrode active material regenerated therefrom

Abstract

The present invention relates to a method for regenerating a positive electrode active material and a positive electrode active material regenerated therefrom. More specifically, the present invention relates to a method for regenerating a positive electrode active material and a positive electrode active material regenerated therefrom, the method including the steps of (a) heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon at 300 to 650°C in an air or oxygen atmosphere to recover a positive electrode active material, (b) mixing the recovered positive electrode active material with a cleaning solution, (c) filtering the positive electrode active material mixed with the cleaning solution, and (d) adding a lithium precursor to the filtered positive electrode active material and annealing the resulting material in air at 400 to 1000°C, wherein the positive electrode active material filtered in the step (c) has a water content of 5 to 10.5% by weight. According to the present invention, the positive electrode active material immediately before the annealing step is adjusted to have a predetermined water content, thereby minimizing residual fluorine (F) and improving the capacity characteristics of a secondary battery. In addition, since the method is environmentally friendly and does not use an organic solvent, there is no risk of toxic gas generation or explosion, and the cost and productivity are greatly improved. The present invention also provides a positive electrode active material regenerated from the method, which has excellent electrochemical performance, resistance characteristics, and capacity characteristics.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0158164, filed on November 23, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a positive electrode active material and a positive electrode active material regenerated therefrom. More specifically, the present invention relates to a positive electrode active material in which residual fluorine (F) is minimized by adjusting the positive electrode active material immediately before an annealing step to have a predetermined water content, thereby improving the capacity characteristics of a secondary battery. The present invention also relates to a method for regenerating a positive electrode active material that is environmentally friendly, does not pose a risk of toxic gas generation or explosion, and is particularly economically and productively improved. The present invention also relates to a regenerated positive electrode active material regenerated therefrom that has excellent electrochemical performance, resistance characteristics, and capacity characteristics. [Background technology]

[0003] A lithium secondary battery mainly consists of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive electrode and 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 disadvantage of causing environmental pollution, requiring a neutralization process and a wastewater treatment process, which significantly increases the process cost, and making it impossible to recover lithium, the main metal in the positive electrode active material.

[0007] To overcome these drawbacks, direct recycling methods have recently been studied to directly regenerate cathode active materials from waste cathodes without decomposing them. These methods can be broadly divided into four types: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

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

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

[0010] In addition, the aluminum foil dissolving method has good process stability, low process costs, and easy binder removal, but has drawbacks in that it generates foreign matter that is difficult to remove on the surface of the recycled cathode active material, and hydrogen gas is generated during the aluminum foil removal process, which may pose an explosion risk.

[0011] Finally, the crushing and screening method has the advantage of being the simplest process, but has the disadvantages that it is difficult to completely separate the current collector from the cathode active material, the particle size distribution of the cathode active material changes during the crushing process, and the binder remains, which can deteriorate the battery characteristics of the recycled cathode active material.

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

[0013] In order to solve the above-mentioned problems of the prior art, the present invention aims to provide a method for regenerating a cathode active material, which minimizes residual fluorine (F) by adjusting the water content of the cathode active material immediately before the annealing step to a predetermined level, thereby improving the capacity characteristics of a secondary battery. The method is also environmentally friendly, safe, and does not pose a risk of toxic gas generation or explosion. Furthermore, the method uses processes such as heat treatment and sedimentation that are easy to manage, making it suitable for mass production.

[0014] Another object of the present invention is to provide a positive electrode active material that is excellent in electrochemical performance, resistance characteristics, and capacity characteristics.

[0015] Another object of the present invention is to provide a secondary battery that is excellent in electrochemical performance, resistance characteristics, and capacity characteristics.

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

[0017] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, comprising: (a) heat-treating a waste positive electrode, which includes a current collector and a positive electrode active material layer coated on the current collector, at 300 to 650°C in an air or oxygen atmosphere to recover the positive electrode active material; (b) mixing the recovered positive electrode active material with a cleaning solution; (c) filtering the positive electrode active material mixed with the cleaning solution; and (d) adding a lithium precursor to the filtered positive electrode active material, followed by annealing at 400 to 1000°C in air; wherein the positive electrode active material filtered in step (c) has a water content of 5 to 10.5% by weight, as calculated by the following Equation 1:

[0018] [Formula 1] Moisture content (weight%)=[(AB) / A]×100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.) II) In I), the positive electrode active material layer may include 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.

[0019] III) In the above I) or II), in the step (b), the cleaning liquid may be water or an aqueous solution of a lithium compound.

[0020] IV) In the above I) to III), the lithium compound aqueous solution can contain more than 0 wt % and 15 wt % or less of the lithium compound.

[0021] V) In the above I) to IV), in the step (c), filtration can be performed using a belt press, a filter press, a screw press, a screw decanter, or a centrifuge.

[0022] VI) In the above I) to V), in the step (c), filtration can be carried out for 3 to 14 minutes.

[0023] VII) In the above I) to VI), the positive electrode active material filtered in the step (c) may be in the form of a cake.

[0024] VIII) In the above I) to VII), the positive electrode active material filtered in step (c) may have an F content of 405 ppm or less.

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

[0026] X) In the above I) to IX), the lithium precursor may be added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium contained in the positive electrode active material in step (a) is 100 mol %.

[0027] XI) In the above I) to X), the method for regenerating the positive electrode active material may include a step of coating the annealed positive electrode active material with a coating agent to obtain a reusable positive electrode active material.

[0028] XII) In the above I) to XI), the 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.

[0029] Furthermore, XIII) the present invention provides a regenerated positive electrode active material, which is produced by the method for regenerating a positive electrode active material described in any one of I) to XII).

[0030] Furthermore, XIV) the present invention provides a regenerative cathode active material comprising at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and characterized in that the fluorine (F) content is 405 ppm or less.

[0031] XV) In the above XIV), the surface of the regenerated positive electrode active material may be coated with a coating agent containing metal or carbon.

[0032] Furthermore, XVI) the present invention provides a secondary battery characterized by including the recycled positive electrode active material of XIV) or XV). [Effects of the Invention]

[0033] According to the present invention, by adjusting the water content of the cathode active material immediately before the annealing step to a predetermined level, residual fluorine (F) is minimized, significantly improving the capacity characteristics of the battery, and the method is environmentally friendly and reduces process costs. The cathode active material is regenerated without being decomposed, so no metal elements are discarded. The current collector is not dissolved, so it can be recovered. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. The method uses processes that are easy to manage, such as heat treatment and sedimentation, making it suitable for mass production. The present invention also provides a method for regenerating a cathode active material, which has excellent electrochemical performance, resistance characteristics, and capacity characteristics. [Brief explanation of the drawings]

[0034] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in these drawings. [Figure 1] 1 is a graph showing the water content of a positive electrode active material mixed with a cleaning solution filtered through a filter press over a filtration time period (5 minutes, 10 minutes, and 20 minutes). [Figure 2] 1 is a graph showing the water content depending on the amount of a positive electrode active material mixed with a cleaning solution when the positive electrode active material is filtered for 5 minutes using a filter press. [Figure 3] 1 is a graph showing the water content and residual F content depending on the filtration time (1 minute, 2 minutes, 5 minutes, 8 minutes, 10 minutes, 20 minutes, and 30 minutes) when a positive electrode active material mixed with a cleaning solution is filtered through a filter press. [Figure 4] 1 is a photographic image of a cathode active material of Comparative Example 2 that has been filtered to a moisture content of 17.6 wt % and then dried. [Figure 5] 1 shows an SEM photograph (left) of the filtered and dried cathode active material, and an EDS mapping image (right) of the F component. The upper image is Comparative Example 1, and the lower image is Comparative Example 2. [Figure 6] 1 is a photographic image of the positive electrode active material obtained after filtration in Example 1 and Comparative Example 2. [Figure 7] 1 is a graph showing the capacity retention rates of mono-cells fabricated using the regenerated positive electrode active materials produced in Example 1 and Comparative Example 2. [Figure 8] 1 is a flowchart showing a process for regenerating a positive electrode active material according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0035] The inventors were researching a direct recycled method for directly recycling used positive electrodes into positive electrode active materials with excellent battery performance without decomposing the positive electrode active materials. They discovered that the battery characteristics of the recycled positive electrode active materials could be further improved by adjusting the positive electrode active material to a predetermined water content just before the annealing step, which involves heat-treating used positive electrodes and then mixing the recovered positive electrode active material with a cleaning solution, filtering, and annealing the mixture. Based on this finding, they further pursued their research and completed the present invention.

[0036] The method for regenerating the positive electrode active material described herein and the positive electrode active material regenerated therefrom will be described in detail below.

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

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0039] Method for regenerating positive electrode active material The method for regenerating a cathode active material of the present invention includes the steps of: (a) heat-treating a waste cathode, including a current collector and a cathode active material layer coated thereon, in an air or oxygen atmosphere at 300 to 650°C to recover the cathode active material; (b) mixing the recovered cathode active material with a cleaning solution; (c) filtering the cathode active material mixed with the cleaning solution; and (d) adding a lithium precursor to the filtered cathode active material and annealing the resulting material in air at 400 to 1000°C. The cathode active material filtered in step (c) has a water content of 5 to 10.5 wt. % as calculated by the following Equation 1. In this case, residual fluorine (F) on the surface of the regenerated cathode active material is minimized, providing a cathode active material with excellent capacity characteristics for secondary batteries. Furthermore, the method is environmentally friendly and does not use an organic solvent, so there is no risk of toxic gas generation or explosion, and it has the advantages of significantly improving economy and productivity.

[0040] [Formula 1] Moisture content (weight%)=[(AB) / A]×100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.) Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0041] (a) A step of recovering a positive electrode active material from a waste positive electrode The step of recovering a positive electrode active material from a waste positive electrode according to the present invention may preferably be a step of (a) recovering the positive electrode active material by heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon at 300 to 650°C in an air or oxygen atmosphere. In this case, the process is simple and has the effect of completely removing the binder, conductive material, and current collector.

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

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

[0044] The positive electrode active material may include, for example, at least one selected from the group consisting of a 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.

[0045] The positive electrode active material may be at least one selected from the group consisting of lithium cobalt oxides such as LiCoO (hereinafter referred to as "LCO"), lithium manganese oxides such as LiMnO or LiMnO, lithium iron phosphate compounds such as LiFePO, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt aluminum oxide (NCA), lithium nickel oxides such as LiNiO, nickel manganese-based lithium composite metal oxides in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn), and NCM-based lithium composite transition metal oxides in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co). More preferably, the positive electrode active material is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, excellent reversible capacity and thermal stability can be obtained.

[0046] As another specific example, the positive electrode active material is represented by the following chemical formula 1 [C1] Li a Ni x Mn y Co z M w O 2+δ (In the above Chemical Formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. It) may be a compound represented by.

[0047] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT, or a mixture thereof.

[0048] The binder may be, for example, a polymer binder, and preferably may be polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably may be polyvinylidene fluoride.

[0049] The heat treatment may be carried out, for example, in an air or oxygen atmosphere, and preferably can be carried out in an air atmosphere. In this case, the carbon substances in the binder and the conductive material react with oxygen and are burned and removed as CO and CO2 gases, so almost all are removed without residue of the binder and the conductive material.

[0050] The oxygen may be, for example, with a purity of 59% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 90 - 99%. Within this range, there are advantages that the binder and the conductive material are removed without residue, the stability of Ni in the active material increases, and the crystal size becomes smaller.

[0051] The purity % of the oxygen may be volume % or mol %.

[0052] The purity of the oxygen described herein is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0053] The heat treatment temperature may be preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0054] The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0055] In this description, the heat treatment time refers to the time required for treatment at the heat treatment temperature, and does not include the time required to reach the heat treatment temperature.

[0056] (b) Mixing the recovered positive electrode active material with a cleaning solution The method for regenerating a positive electrode active material of the present invention includes (b) a step of mixing the recovered positive electrode active material with a cleaning solution. In this case, there is an advantage that metal fluorides such as LiF that may be present on the surface of the regenerated positive electrode active material are removed and the surface is modified.

[0057] During the heat treatment, CO2 and H2O in the binder and the conductive material in the positive electrode active material may react with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH. Fluorine (F) present in the binder, such as PVdF, may react with the metal elements that make up the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, battery performance will deteriorate when the positive electrode active material is reused.

[0058] The cleaning solution may be, for example, water or a basic lithium compound aqueous solution, preferably a basic lithium compound aqueous solution. In this case, there is an advantage that metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby modifying the surface.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] In the mixing, 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, and more preferably 1:1 to 1:30. Within this range, there is an advantage that metal fluorides such as LiF can be effectively removed.

[0063] The mixing can be performed, for example, by immersing the recovered positive electrode active material in the cleaning solution. The immersion can be performed, for example, for one week, preferably within one day, more preferably within one hour, even more preferably for 5 to 50 minutes, and even more preferably for 10 to 40 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.

[0064] The mixing may preferably include stirring the positive electrode active material while immersed in the cleaning solution. In this case, the mixing process may be carried out quickly, thereby suppressing lithium elution and shortening the process time.

[0065] (c) filtering the positive electrode active material mixed with the cleaning solution; The method for regenerating a positive electrode active material of the present invention includes (c) filtering the positive electrode active material mixed with the cleaning solution, which has the advantage of more effectively removing metal fluorides such as LiF.

[0066] The filtration may be performed using, for example, a belt press, a filter press, a screw press, a screw decanter, or a centrifuge, and preferably a filter press, which has the advantage of more effectively removing metal fluorides such as LiF.

[0067] The filter press is not particularly limited as long as it is a filter press generally used for filtration in the technical field to which the present invention pertains.

[0068] The filtration can be performed for, for example, 3 to 14 minutes, preferably 3 to 11 minutes, and more preferably 4 to 8 minutes. Within this range, water is efficiently removed and the content of metal fluorides such as LiF is significantly reduced. If the filtration time is less than this range, the cleaning solution is not sufficiently removed, resulting in a high water content. If the filtration time is more than this range, the water content increases slightly, the content of metal fluorides such as LiF is not reduced, and energy consumption increases.

[0069] The amount of the filtration to be added at one time may be, for example, 2 to 3.1 kg, preferably 2.5 to 3.1 kg, and more preferably 2.7 to 3.0 kg. Within this range, the cleaning solution is efficiently removed and the content of metal fluorides such as LiF is reduced.

[0070] The cathode active material filtered in step (c) may have a water content of, for example, 5 to 10.5 wt%, preferably 5 to 8 wt%, and more preferably 5 to 7 wt%, calculated using the following equation: Within this range, metal fluorides such as LiF, which tend to remain in the regenerated cathode active material, are more effectively removed, resulting in reduced processing costs and superior battery capacity characteristics. Furthermore, increasing the filtration time to reduce the water content below this range does not lower the water content, does not change the amount of remaining metal fluorides such as LiF, and simply requires more energy and time.

[0071] [Formula 1] Moisture content (weight%)=[(AB) / A]×100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.) The cathode active material filtered in step (c) may be in the form of a cake, for example, which has the advantage of reducing the amount of residual metal fluorides such as LiF and shortening the drying time. If the moisture content exceeds the above range, the cathode active material is in a slurry state, the amount of residual metal fluorides such as LiF is high, and the drying time is increased, which may cause lithium leaching from the cathode active material.

[0072] The cathode active material filtered in step (c) may have an F content of, for example, 405 ppm or less, preferably 1 to 405 ppm, and within this range, the capacity characteristics of the secondary battery are improved.

[0073] In this description, the fluorine (F) content can be measured using an ICP analyzer. 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.

[0074] Also, in this description, ppm is by weight unless otherwise specified.

[0075] The positive electrode active material filtered in step (c) may preferably be subjected to a drying process, which has the advantage of facilitating recovery of the crystalline structure in the subsequent annealing step.

[0076] The drying may preferably be vacuum drying, and specifically, it can be performed in a vacuum at 70 to 200°C, more preferably 80 to 130°C, until the weight no longer changes, for example, for 1 to 24 hours. Within this range, there is an effect of efficiently removing moisture contained in the washed positive electrode active material.

[0077] In the present invention, the vacuum drying is not particularly limited as long as it is a common vacuum drying in the technical field to which the present invention pertains, and may include, for example, drying in a partial vacuum state or a low pressure state.

[0078] (d) adding a lithium precursor to the filtered cathode active material and annealing The method for regenerating a positive electrode active material of the present invention includes (d) adding a lithium precursor to the filtered 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 even improving the characteristics of the regenerated positive electrode active material to the level of a fresh positive electrode active material that has never been used.

[0079] The annealing step (d) may preferably be a step of adding a lithium precursor to the cathode active material that has been filtered to a water content of 5 to 10.5 wt %, and annealing the material in air or oxygen at 400 to 1000°C, more 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.

[0080] The annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 2 hours or more or 10 hours or less, more preferably 3 hours or more or 8 hours or less, and even more preferably 4 hours or more or 6 hours or less. Within this range, the crystallinity of the recycled positive electrode active material is further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0081] The annealing temperature may be reached at a temperature increase rate of preferably 1 to 10°C / min, more preferably 1 to 5°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0082] The annealing step includes, for example, a cooling process, and the cooling process may be, for example, natural cooling in a furnace. In this case, the crystallinity of the recycled positive electrode active material is further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0083] In this description, annealing may follow the definition used in the technical field to which the present invention belongs. Specifically, annealing may be defined as a heat treatment operation in which a positive electrode active material having a deformed structure or lattice defects is heated for an appropriate time at a temperature at or above the recrystallization temperature at which atoms of the main component in the positive electrode active material can sufficiently diffuse and move, thereby healing the deformation or lattice defects and increasing crystallinity.

[0084] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0085] The lithium precursor is preferably added based on the amount of lithium in the raw positive electrode active material or the recovered positive electrode active material, at least in step (c). The amount of lithium added is the amount of lithium that is reduced from the amount of lithium in the positive electrode active material. More preferably, the amount of lithium in the positive electrode active material in step (a) is 0.0001 to 0.2 molar ratio, even more preferably, 0.001 to 0.2 molar ratio of lithium. Even more preferably, the amount of lithium is 0.01 to 0.17 molar ratio. Particularly preferably, the amount of lithium is 0.1 to 0.17 molar ratio. Particularly preferably, the amount of lithium is 0.12 to 0.17 molar ratio. Within this range, the insufficient lithium in the regenerated positive electrode active material is replenished, and by improving crystallinity such as increasing crystallinity or restoring the crystal structure, the battery characteristics of the regenerated positive electrode active material are improved.

[0086] The lithium precursor may be added in an amount corresponding to 1 to 40 mol%, more preferably 1 to 25 mol%, even more preferably 1 to 15 mol%, and even more preferably 3 to 15 mol%, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol%. Within this range, no residual precursor that may increase resistance remains in the recycled positive electrode active material, which is very useful for improving battery characteristics.

[0087] 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.

[0088] 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, it is preferable that the annealing temperature be 1000°C or less.

[0089] In the annealing step (d), the lithium precursor may be added to the filtered cathode active material in a solid or liquid phase, for example, by drying the filtered cathode active material and then adding the lithium precursor. Preferably, the solid phase lithium precursor may be added, which has the advantage of reducing process costs. Adding a liquid phase lithium precursor has the advantage of allowing the cathode active material and the lithium precursor to be uniformly mixed. Alternatively, a lithium precursor solution may be added to the filtered cathode active material and then spray-dried, thereby performing the drying of the cathode active material and the addition of the lithium precursor in a single step. This reduces particle agglomeration due to drying, eliminates the need for the solid phase lithium precursor, and allows the cathode active material to be produced in powder form rather than in lumps through spray drying.

[0090] The lithium precursor solution may be, for example, a lithium compound that is soluble in an aqueous solution or an organic solvent.

[0091] The lithium precursor solution may have a concentration of, for example, 1 to 15% (grams of solute dissolved in 100 g of solution), preferably 3 to 10%, and within this range, the lithium precursor can be uniformly sprayed onto the positive electrode active material.

[0092] (e) surface-coating the annealed cathode active material to obtain a reusable cathode active material; The method for regenerating a positive electrode active material of the present invention optionally includes a step (e) of surface-coating the annealed positive electrode active material with a coating agent 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.

[0093] 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 are improved while maintaining the properties of the positive electrode active material itself.

[0094] The metal-containing coating agent is preferably a coating agent containing one or more 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 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.

[0095] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0096] 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.

[0097] The carbon-containing coating agent is not particularly limited as long as it is a carbon-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.

[0098] 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 %, relative to 1 mol % of the metal in the positive electrode active material before the coating treatment, based on the components actually coated on the surface of the positive electrode active material excluding the solvent. Within this range, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] The coating agent may preferably have an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m / g, more preferably an average diameter of 10 to 100 nm and a specific surface area of ​​20 to 100 m / g. Within these ranges, the coating agent adheres uniformly to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material and 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.

[0104] 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.

[0105] 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.

[0106] FIG. 8 below is a flowchart of a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0107] Referring to FIG. 8, 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 about 120°C to prepare a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scraps can be prepared.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is carried out to thermally decompose the binder in the active material layer.

[0112] The heat treatment is performed in an air or oxygen atmosphere, preferably an air atmosphere. Through the heat treatment in air, the binder and conductive material in the positive electrode active material layer are thermally decomposed into CO2 and HO and removed. Because the binder is removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily sorted in powder form. Therefore, even by performing only step S30, the active material layer can be separated from the current collector, and the positive electrode active material in the active material layer can be recovered in powder form.

[0113] It is important that the heat treatment be performed in air. However, if the heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive material will carbonize without being thermally decomposed. Carbonization leaves carbon components on the surface of the cathode active material, reducing the performance of the reused cathode active material. However, if the heat treatment is performed in air, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, removing both the binder and conductive material.

[0114] The heat treatment is preferably carried out at 300 to 650°C, specifically at 550°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.

[0115] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, the heat treatment can be carried out without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock is caused to the cathode scrap.

[0116] The heat treatment can be carried out for a period of time sufficient to thermally decompose the binder, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specifically for about 30 minutes. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0117] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, or, in consideration of productivity, a rotary kiln capable of continuous treatment.

[0118] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0119] Next, the recovered positive electrode active material is mixed with a cleaning liquid (step S40).

[0120] In the mixing step S40, fluorine (F) and lithium remain on the surface of the recovered positive electrode active material, so a step of removing them is necessary.

[0121] In the mixing step, the recovered positive electrode active material is washed with water or a basic lithium compound aqueous solution as a washing solution. The water may be preferably distilled water or deionized water, and in this case, metal fluorides such as LiF are removed, thereby improving the surface.

[0122] 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 lithium compound. In this case, the basic lithium compound aqueous solution has the advantage of modifying the surface by removing metal fluorides such as LiF that may be present on the surface of the regenerated cathode active material. 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.

[0123] The lithium compound may specifically be LiOH.

[0124] The reason for mixing the recovered positive electrode active material with a basic lithium compound aqueous solution is to remove LiF and metal fluorides that may be present on the surface of the recovered active material and perform surface modification. During the heat treatment in step S30, the binder and conductive material in the positive electrode active material layer are vaporized and removed as CO2 and HO. During this process, CO2 and HO may react with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH. 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, battery performance will deteriorate when the positive electrode active material is reused. In the present invention, the mixing step in step S40 removes reactants that may be generated on the surface of the reused positive electrode active material during the heat treatment step (S30), thereby preventing foreign matter from remaining on the surface of the reused positive electrode active material.

[0125] In step S40, it is important to mix with a basic lithium compound aqueous solution. Using a sulfuric acid or hydrochloric acid aqueous solution rather than a basic lithium compound aqueous solution can remove F from the surface of the positive electrode active material, but it also dissolves transition metals (Co, Mg) present in the positive electrode active material, reducing the performance of the reused positive electrode active material. The basic lithium compound aqueous solution used in the present invention is highly preferred because it not only removes traces of binder that may remain after the heat treatment in step S30, but also prevents the dissolution of transition metals present in the positive electrode active material and replenishes the amount of lithium that may dissolve during the washing process.

[0126] The mixing can be performed by immersing the recovered positive electrode active material in the cleaning solution. After immersion, the mixing can be performed within one week, preferably within one day, and more preferably within one hour. If the mixing is performed for more than one week, excessive lithium elution may cause a decrease in capacity. Therefore, it is preferable to perform the mixing within one hour.

[0127] The mixing may involve immersing the positive electrode active material in the cleaning solution or stirring the solution while immersed. It is preferable to perform stirring simultaneously. When using a basic lithium compound aqueous solution as the cleaning solution, immersion without stirring may slow down the cleaning process and cause lithium leaching. Since stirring simultaneously can minimize the process time, it is preferable to perform stirring simultaneously with the impregnation of the basic lithium compound aqueous solution.

[0128] In the mixing, 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, there is an advantage that metal fluorides such as LiF can be effectively removed.

[0129] Next, the mixed positive electrode active material is filtered (step S50).

[0130] The filtering can include filtering the preferably mixed positive electrode active material.

[0131] The filtration can be carried out using, for example, a belt press, a filter press, a screw press, a screw decanter, or a centrifuge, and preferably a filter press.

[0132] It is important to adjust the moisture content of the filtered cathode active material within a predetermined range, as this allows metal fluorides such as LiF, which tend to remain in the recycled cathode active material, to be more effectively removed, reducing the required time and energy, thereby reducing process costs, and improving the capacity characteristics of the secondary battery.

[0133] The water content of the filtered cathode active material can be calculated by the following Equation 1. For example, the water content should be within 5 to 10.5 wt %, preferably 5 to 8 wt %, and more preferably 5 to 7 wt %, in order to minimize the content of metal fluorides such as LiF and reduce processing costs.

[0134] [Formula 1] Moisture content (weight%)=[(AB) / A]×100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.) The water content of the positive electrode active material can be reached by filtering for, for example, 3 to 14 minutes, preferably 3 to 11 minutes, and more preferably 3 to 8 minutes. If the filtering time is less than 3 minutes, the cleaning solution is not sufficiently removed, resulting in a high water content and an increased content of metal fluorides such as LiF. If the filtering time exceeds 14 minutes, the water content increases, resulting in an increased content of metal fluorides such as LiF, and energy consumption increases.

[0135] During the filtration, the amount of the positive electrode active material mixed with the washing solution added at one time may be, for example, 2 to 3.1 kg, preferably 2.5 to 3.1 kg, and more preferably 2.7 to 3.1 kg. Within this range, filtration efficiency is excellent. If the amount is less than 2 kg, the process cost increases, and if the amount is more than 3.1 kg, the moisture content increases, and the content of metal fluorides such as LiF increases.

[0136] The positive electrode active material filtered to have a water content of 5 to 10.5% by weight may be preferably obtained in the form of a cake.

[0137] The filtered positive electrode active material may preferably have an F content of 405 ppm or less, more preferably 1 to 405 ppm, and within this range, there is an advantage in that the capacity characteristics of the secondary battery are improved.

[0138] The cake-like cathode active material obtained after the filtration may preferably be dried, which has the advantage of facilitating the annealing process.

[0139] The drying can be performed by vacuum drying at, for example, 70 to 140°C, preferably 100 to 140°C, and more preferably 120 to 140°C.

[0140] Next, a lithium precursor is added to the filtered positive electrode active material, and the material is annealed (step S60).

[0141] The annealing step S60 involves adding a lithium precursor to the filtered cathode active material to achieve a predetermined water content, followed by annealing. In this case, lithium loss may occur in the cathode active material during steps S30 and S40. Step S60 compensates for this loss.

[0142] Furthermore, in step S60, 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 fresh active material that has never been used.

[0143] During steps S30 and S40, a deformed structure may occur on the surface of the positive electrode active material. For example, in step S40, Ni in the NCM-based lithium transition metal composite oxide active material may be converted into a rock salt (e.g., [NiCO3·2Ni(OH)2)H2O] by water, forming a spinel structure. If a battery is manufactured in this state, the battery characteristics, such as a decrease in capacity, may be degraded. In the present invention, the crystalline structure is restored through step S60. For example, the NCM-based lithium transition metal composite oxide active material is restored to a hexagonal crystalline structure. This allows the initial characteristics to be restored or improved to a level similar to that of a fresh active material.

[0144] The lithium precursor in step S60 may be any one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0145] The method of adding a lithium precursor to the filtered positive electrode active material may involve drying the filtered 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 filtered positive electrode active material and then spray-dried, 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. Specifically, the filtered positive electrode active material may be dried and then the lithium precursor may be added in a solid phase, which has the advantage of reducing process costs.

[0146] If the cathode active material particles are dried immediately after the surface modification process by mixing with a cleaning solution, they may aggregate and form clumps. Mixing the lithium precursor with these aggregated particles requires grinding the clumps, 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 is mixed with the powder or milled in the presence of moisture, the cathode active material absorbs moisture and causes severe aggregation. Therefore, by adjusting the moisture content of the cathode active material by mixing with a cleaning solution and filtering, and then mixing and dispersing the cathode active material in a lithium precursor solution and spray-drying it, particle aggregation due to drying and the hassle of mixing a solid lithium precursor can be eliminated. In other words, spray-drying allows the cathode active material to be produced in powder form rather than clumps.

[0147] Specifically, the lithium precursor solution may have a concentration of 3 to 10%, and may be added in an amount that contains lithium corresponding to 1 to 40 mol%, preferably 1 to 15 mol%, and more preferably 1 to 10 mol%, relative to a total of 100 mol% of the lithium contained in the positive electrode active material.

[0148] During spray drying, the lithium precursor solution dries immediately after spraying, coating or contacting the lithium precursor components on the surface of the positive electrode active material. This process also has the advantage of controlling particle size by agglomerating particles due to capillary force as the solvent, the lithium precursor solution, dries. 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-based active materials, NCM-based active materials tend to crack more due to greater particle cracking during rolling during electrode formation, resulting in the recovered active material containing more small particles than fresh active material, resulting in uneven particle size.

[0149] 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.

[0150] 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.

[0151] As described above, the surface of the active material is coated with the lithium precursor through the spray drying step, and the active material is obtained with a controlled particle size. The addition of the lithium precursor, granulation, and drying are performed in a single step, which simplifies the process.

[0152] Another advantage is that the filtering and spray drying can be performed continuously because the active material particles filtered in the previous step are simply mixed and dispersed in a lithium precursor solution of a certain concentration. Thus, the method for reusing an active material according to this embodiment has a continuous process, and the coating, drying, and granulation of the lithium precursor (in other words, the readjustment of the particles) can be performed simultaneously in one step.

[0153] Additionally, because lithium loss occurs in the positive electrode active material during steps S30 and S40, this loss of lithium is replenished in step S60. 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 the previous steps, step S60 restores the crystalline structure of the positive electrode active material through annealing, thereby improving the battery characteristics of the regenerated positive electrode active material or 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.

[0154] As the lithium precursor, LiOH is specifically used.

[0155] 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 0.4, and more preferably 0.09 to 0.2.

[0156] Specifically, when a lithium precursor is added in a molar ratio of 0.09 to 0.1 (based on lithium metal), which is the ratio of the lithium content lost to the newly produced positive electrode active material based on the results of ICP analysis, the capacity improvement effect is equivalent to that of the newly produced positive electrode active material. Here, the results of ICP analysis have an error value of about ±0.02.

[0157] As another example, the lithium precursor may be added in an amount corresponding to 1 to 40 mol%, preferably 1 to 25 mol%, more preferably 1 to 15 mol%, and even more preferably 3 to 15 mol%, when the total amount of lithium contained in the raw positive electrode active material is 100 mol%.

[0158] 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.

[0159] 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. Therefore, 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. Furthermore, 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.

[0160] 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 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.

[0161] Next, as an optional step, the annealed positive electrode active material can be surface-coated with a coating agent (step S70).

[0162] For example, the coating is performed by applying a coating agent containing a metal, an organic metal, or a carbon component to the surface 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.

[0163] Specifically, when a metal oxide or acid such as B, W, or BW 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.

[0164] The solid or liquid phase coating method may be, for example, mixing, milling, spray drying, or grinding.

[0165] If the annealing step (S60) 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), causing the lithium to be less than 1:1, resulting in a regenerated cathode active material that is unable to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step (S60) 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), naturally achieving a 1:1 molar ratio of lithium to other metals in the cathode active material, preventing battery capacity loss.

[0166] Regenerated cathode active material The recycled cathode active material of the present invention is characterized by being produced by the above-mentioned method for recycling a cathode active material, and preferably has a fluorine (F) content of 405 ppm or less, preferably 1 to 405 ppm or less. In this case, the recycled cathode active material has the advantages of excellent capacity characteristics of the secondary battery, being environmentally friendly, and not using an organic solvent, so there is no risk of toxic gas generation or explosion, and greatly improving economic efficiency and productivity.

[0167] In addition, the recycled positive electrode active material of the present invention comprises at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and is characterized by having a fluorine (F) content of 405 ppm or less. In this case, the recycled positive electrode active material has excellent capacity characteristics of the secondary battery, is environmentally friendly, and does not use an organic solvent, so there is no risk of toxic gas generation or explosion, and has the advantages of greatly improving economy and productivity.

[0168] The regenerated positive electrode active material may preferably include at least one 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 (NCA), lithium nickel oxides such as LiNiO2, nickel manganese-based lithium composite metal oxides in which part of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn), and NCM-based lithium composite transition metal oxides in which part of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). In this case, excellent electrochemical performance, resistance characteristics, and capacity characteristics can be obtained.

[0169] The positive electrode active material may be, for example, a compound represented by the following chemical formula 1: [C1] Li a Ni x Mn y Co z M w O 2+δ (In the chemical formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, 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 contains a compound represented by, and the content of fluorine (F) is 405 ppm or less, and the surface is coated with a coating agent containing metal or carbon. In this case, there is an effect that it is excellent in electrochemical performance, resistance characteristics, capacitance characteristics, etc.).

[0170] The content of the fluorine (F) may preferably be 1 to 405 ppm. Within this range, there is an effect that excellent resistance characteristics and capacitance characteristics are realized.

[0171] The regenerated cathode active material may preferably be coated with a coating agent containing metal or carbon. Preferably, it is coated with a coating agent containing metal. In this case, the structural stability of the cathode active material is improved without chemical and material changes in the cathode active material itself, so that electrochemical characteristics such as output performance, life characteristics, and capacitance are improved. By being substituted with a different element on the surface of the cathode active material, the physicochemical characteristics are also improved due to the effects of reducing the residual lithium amount and decreasing the pH.

[0172] The metal is preferably one or more 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, it is one or more selected from the group consisting of B, W, Al, Ti, and Mg. Even more preferably, it is boron (B), tungsten (W), or a mixture thereof. Even more preferably, it is tungsten (W) and boron (B). A specific example is tungsten boride (WB). In this case, there is an effect that resistance characteristics and life characteristics, etc. are improved.

[0173] 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 even 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.

[0174] The coating is preferably performed by coating the surface with a coating agent containing metal or carbon in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0175] The regenerated cathode active material of the present invention may include all of the contents of the above-mentioned method for regenerating a cathode active material, and therefore, a redundant description thereof will be omitted here.

[0176] secondary battery The secondary battery of the present invention includes a positive electrode including a positive electrode current collector and a positive electrode active material layer coated thereon, a negative electrode including a negative electrode current collector and a negative electrode active material layer coated thereon, and a separator, wherein the positive electrode active material layer includes the recycled positive electrode active material according to the present invention. In this case, there is an advantage in providing a secondary battery with excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0177] The separation membrane is not particularly limited as long as it is a separation membrane commonly used in the technical field to which the present invention pertains. Preferably, the separation membrane has a pore size of 0.01 to 10 μm and a thickness of 5 to 300 μm. Specific examples include an olefin polymer such as polypropylene; a sheet or nonwoven fabric made of glass fiber or polyethylene; and the like. In this case, the separation membrane has advantages such as high ion permeability, mechanical strength, insulating properties, chemical resistance, and hydrophobicity.

[0178] In this description, the pore diameter can be measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0179] The secondary battery may include, for example, an electrolyte, specifically, an electrolytic solution, and the electrolytic solution may include, for example, an organic solvent and a lithium salt.

[0180] The organic solvent may be, for example, an aprotic solvent, and specific examples thereof may be one or more selected from the group consisting of N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0181] Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiAlCl4, CH3SO3Li, CF3SO3Li, and (CF3SO2)2NLi.

[0182] The secondary battery may be preferably used as a power source for electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0183] 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.

[0184] [Example] [Test Example I: Change in moisture content with filtration time] The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCM-based lithium composite transition metal oxide) was crushed and heat-treated in air at 570°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 3 L / min.

[0185] The recovered cathode active material was immersed in a LiOH aqueous solution as a cleaning solution and stirred for 5 minutes. 3.1 kg of the mixed cathode active material was filtered using a filter press for 5, 10, and 20 minutes, and the moisture content was calculated using the following Equation 1. The change in moisture content over time is shown in Figure 1.

[0186] [Formula 1] Moisture content (weight%)=[(AB) / A]×100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.) As shown in Figure 1 below, the moisture content was lowest when the filtration time was 5 minutes. Furthermore, there was no significant difference in moisture content between 5 and 10 minutes of filtration, but when the filtration time was increased to 20 minutes, the moisture content actually increased. Therefore, the following experiment was conducted with the filtration time fixed at 5 minutes.

[0187] [Test Example II: Change in water content depending on the amount of positive electrode active material added] The positive electrode active material recovered in Test Example I was immersed in a LiOH aqueous solution as a cleaning solution while simultaneously stirring and mixing for 5 minutes. The mixed positive electrode active material was filtered for 5 minutes at input amounts of 2.8 kg, 2.9 kg, 3.0 kg, 3.1 kg, 3.2 kg, and 3.4 kg into a filter press. The water content was calculated using Equation 1, and the change in water content depending on the input amount of positive electrode active material is shown in Figure 2 below.

[0188] As shown in Figure 2 below, the moisture content was lowest when the amount of cathode active material fed into the filter press was 3.0 kg. As the amount of cathode active material fed increased from 2.8 kg to 3.0 kg, the moisture content gradually decreased, but when the amount fed exceeded 3.2 kg, the moisture content actually increased.

[0189] [Test Example III: Changes in moisture content and residual F content with filtration time] The positive electrode active material recovered in Test Example I was immersed in a LiOH aqueous solution used as a cleaning solution and simultaneously stirred for 5 minutes. 3.0 kg of the mixed positive electrode active material was filtered using a filter press for 1 minute, 2 minutes, 5 minutes, 8 minutes, 10 minutes, 20 minutes, and 30 minutes, and the water content was calculated using Equation 1. The fluorine (F) content remaining in the positive electrode active material after filtration was measured using an ICP analyzer, and the results are shown in Figure 3 below. Measurements were performed using a commonly used ICP analyzer in laboratories, and there is no deviation due to the measurement device or method.

[0190] As shown in Figure 3 below, when the filtration time was less than 3 minutes, the moisture content was very high and the residual F content was high. Also, when the filtration time exceeded 14 minutes, the moisture content did not decrease any further, the residual F content did not change, and a lot of energy was consumed.

[0191] 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) was crushed and heat-treated in air at 570°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 3 L / min.

[0192] The recovered positive electrode active material was immersed in a LiOH aqueous solution as a cleaning solution and stirred for 5 minutes. The mixed positive electrode active material was filtered for 5 minutes using a filter press to obtain a cake-like positive electrode active material with a water content of 6.8% by weight.

[0193] The filtered positive electrode active material had a lithium content of 0.1 mole less than that of the raw material, based on 1 mole of lithium in the positive electrode active material.

[0194] The filtered cathode active material was dried overnight at 100°C, and then 0.15 mol of LiOH (based on 1 mol of lithium in the raw (fresh) cathode active material) was added and annealed in air at 750°C for 5 hours, with air supplied at 3 L / min.

[0195] The annealed 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.

[0196] 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.

[0197] Comparative Example 1 A recycled positive electrode active material was prepared in the same manner as in Example 1, except that in the filtering step of Example 1, filtering was performed so that the water content of the positive electrode active material became 12.5 wt %.

[0198] Comparative Example 2 A recycled positive electrode active material was prepared in the same manner as in Example 1, except that in the filtering step of Example 1, filtering was performed so that the water content of the positive electrode active material became 17.6 wt %.

[0199] [Test Example III: Photographic Image Analysis] 1 is a photographic image of the positive electrode active material obtained after filtration in Comparative Example 2 (water content: 17.6 wt %), which was dried at 100° C. for 12 hours.

[0200] Figure 4 below is a photograph of the cathode active material obtained after filtration and drying in Comparative Example 2, which shows that the F compound and various impurities that were not completely removed during the mixing step were mixed with the cathode active material, then filtered and dried, and recrystallized to precipitate in a mixed form with the recycled cathode active material. The red arrow in Figure 4 indicates the area where the F compound and various impurities were recrystallized and precipitated in a mixed form with the cathode active material.

[0201] [Test Example IV: EDS Analysis] The material precipitated from the filtered and dried cathode active material in Comparative Example 2 was analyzed by EDS (energy dispersive spectroscopy), and the components and contents are shown in Table 1 below.

[0202] [Table 1] As shown in Table 1, in Comparative Example 2, the F component had the largest specific gravity in the portion that was recrystallized and precipitated from the filtered and dried cathode active material.

[0203] [Test Example V: Analysis of SEM and EDS Mapping Images] The filtered and dried cathode active materials in Comparative Examples 1 and 2 were observed with an SEM, and EDS mapping images of the F component distribution were shown in Figure 5. In Figure 5, the upper and lower rows are Comparative Examples 1 and 2, respectively, with the left side being an SEM photograph and the right side being an EDS mapping image showing the F component distribution.

[0204] As shown in Figure 5 below, it was confirmed that the F (fluorine) element derived from LiF was detected throughout the surface of the cathode active material that had been dried after filtration. The green area in the image on the right side of Figure 5 is the F component.

[0205] [Test Example VI: Photographic images of positive electrode active material depending on water content] FIG. 6 shows photographic images of the positive electrode active materials obtained after filtration in Example 1 and Comparative Example 2.

[0206] As shown in Figure 6 below, it was confirmed that the cathode active material in Example 1, which was filtered to a moisture content of 6.8 wt%, was in a cake state, while the cathode active material in Comparative Example 2, which was filtered to a moisture content of 17.6 wt%, was in a slurry state. When the cathode active material was in a slurry state due to a high moisture content, as in Comparative Example 2, the capacity and lifespan of the secondary battery were reduced due to the large amount of residual F component in the cathode active material, and the subsequent drying process consumed a lot of time and energy.

[0207] [Test Example VII: Fluorine (F) Content] The fluorine (F) content remaining in the cathode active material recovered after heat treatment in Example 1 and the cathode active materials obtained after filtration in Example 1, Comparative Example 1, and Comparative Example 2 was measured using an ICP analyzer, and the results are shown in Table 2 below.

[0208] [Table 2] As shown in Table 2, the positive electrode active material recovered after the heat treatment had a high fluorine content, but Example 1, which was filtered to a water content of 6.8 wt%, had a significantly reduced fluorine content. It was also confirmed that Example 1 had a lower fluorine content than Comparative Examples 1 and 2, which had water contents of 12.5 wt% and 17.6 wt%, respectively. This indicates that adjusting the water content in the filtration step reduces the residual F component.

[0209] [Test Example VIII: Evaluation of Monocell] The electrochemical performance of the recycled cathode active materials prepared in Example 1 and Comparative Example 2 was measured through the following mono-cell evaluation, and the results are shown in FIG.

[0210] *Monocell evaluation: 96% by weight of recycled positive electrode active material, 2% by weight of carbon black (conductive material), and 2% by weight of PVdF (binder) were weighed and mixed with NMP to create a slurry. The positive electrode active material slurry was applied to a 20μm thick aluminum foil, dried at 130℃ for 1 hour, and then punched out to a size of 30mm x 42mm to produce a positive electrode.

[0211] 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.

[0212] The prepared positive and negative electrodes were joined with a separator, and then an electrolyte solution of ethylene carbonate (EC):ethyl methyl carbonate (EMC)=3:7 by weight ratio was injected to prepare a polymer cell type mono cell for testing.

[0213] The manufactured mono-cell was charged at 45°C in CC-CV mode at 0.7 C up to 4.25 V, and then discharged at a constant current of 0.5 C down to 2.5 V, and the capacity retention rate was measured after 100 charge-discharge cycles to evaluate the lifespan characteristics. The results are shown in Figure 7.

[0214] Figure 7 below shows the results of a monocell evaluation of the regenerated positive electrode active materials produced in Example 1 and Comparative Example 2. It was confirmed that the regenerated positive electrode active material (Example 1), in which the water content of the positive electrode active material immediately before the annealing step according to the present invention was controlled to 6.8 wt%, had a superior capacity retention rate even when the number of charge / discharge cycles increased, compared to the regenerated positive electrode active material (Comparative Example 2), in which the water content was controlled to 17.6 wt%.

Claims

1. (a) heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated on the current collector at 300 to 650°C in an air or oxygen atmosphere to recover the positive electrode active material; (b) mixing the recovered positive electrode active material with a cleaning solution; (c) filtering the positive electrode active material mixed with the cleaning solution; (d) adding a lithium ion-containing compound to the filtered positive electrode active material, and annealing the mixture in air at 400°C or higher and 1000°C or lower; Including, The cathode active material filtered in step (c) has a water content of 5 to 10.5 wt % calculated by the following Equation 1: [Formula 1] Moisture content (wt%) = [(AB) / A] x 100 (In the above formula 1, A is the weight (g) of the filtered positive electrode active material, and B is the weight (g) of the filtered positive electrode active material after drying it in a vacuum at 100°C for 12 hours.)

2. 2. The method of claim 1, wherein the positive electrode active material layer comprises at least one material selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a lithium nickel cobalt manganese (NCM)-based positive electrode active material, a lithium nickel cobalt aluminum (NCA)-based positive electrode active material, and a lithium nickel cobalt manganese aluminum (NCMA)-based positive electrode active material.

3. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (b), the cleaning liquid is water or an aqueous solution of a lithium compound.

4. 4. The method for regenerating a positive electrode active material according to claim 3, wherein the lithium compound aqueous solution contains more than 0% by weight and 15% by weight or less of a lithium compound.

5. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (c), the filtration is performed using a belt press, a filter press, or a screw press.

6. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (c), the filtration is performed for 3 to 14 minutes.

7. 2. The method of claim 1, wherein the positive active material filtered in step (c) is in a cake form.

8. 2. The method of claim 1, wherein the filtered cathode active material has a fluorine content of 405 ppm or less.

9. In the step (d), the lithium ion-containing compound 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 at least one selected from the group consisting of ammonium hydroxide, ammonium nitrate ...

10. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the lithium ion-containing compound is added in an amount corresponding to 1 mol% to 40 mol% when the total amount of lithium contained in the positive electrode active material in step (a) is 100 mol%.

11. 2. The method of claim 1, further comprising the step of coating the annealed positive electrode active material with a coating agent to obtain a reusable positive electrode active material.

12. 12. The method of claim 11, wherein the 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, followed by heat treatment at 100 to 1200°C.

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