Method for regenerating positive electrode active material, regenerated positive electrode active material produced therefrom, and secondary battery including the same

Abstract

The present invention relates to a method for regenerating a positive electrode active material, a regenerated positive electrode active material produced from the method, and a secondary battery including the same. More specifically, the present invention relates to the method for regenerating a positive electrode active material, the regenerated positive electrode active material produced from the method, and a secondary battery including the same, which include the steps of: (a) pulverizing a used positive electrode, including a current collector and a positive electrode active material layer coated thereon, using a pin mill under dry conditions to obtain a powder of the positive electrode active material layer; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. The present invention provides a cathode active material with excellent battery characteristics, including advantages such as easy removal of binders and conductive materials even at a lower heat treatment temperature than conventional methods, minimizing damage to the cathode active material due to washing, reducing lithium loss in the cathode active material, and enabling recovery of the crystalline structure with a small amount of lithium precursor. The present invention also provides a method for regenerating a cathode active material, which is environmentally friendly because it does not use an acid in the recovery and regeneration process of the cathode active material, eliminating the need for neutralization and wastewater treatment, thereby reducing process costs, and regenerating the cathode active material without decomposition, thereby eliminating the risk of discarding metal elements and generating toxic gases or explosions, because no organic solvents are used.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0078759 filed on June 20, 2023, and Korean Patent Application No. 10-2024-0005347, refiled on January 12, 2024 based thereon, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a cathode active material, a regenerated cathode active material manufactured from the same, and a secondary battery including the same. More specifically, the present invention relates to a method for regenerating a cathode active material, which involves grinding a used cathode using a pin mill under dry conditions before heat-treating it to obtain a powdered cathode active material layer, which is then heat-treated at a temperature lower than conventional methods to recover the cathode active material. A lithium precursor is then directly added to the recovered cathode active material without washing, and annealing the material. This allows the binder and conductive material to be easily removed even at a lower heat treatment temperature than conventional methods, minimizing damage to the cathode active material caused by washing. This reduces the loss of lithium in the cathode active material and allows the crystalline structure to be restored with a small amount of lithium precursor, resulting in a cathode active material with excellent capacity and life characteristics. The present invention also relates to a method for regenerating a cathode active material, which is environmentally friendly because it does not use an acid in the recovery and regeneration process, and reduces process costs because it does not require neutralization or wastewater treatment. The method also relates to a method for regenerating a cathode active material without decomposition, thereby eliminating the need for discarded metal elements and the risk of toxic gas generation or explosion because it does not use an organic solvent, resulting in significant improvements in economy and productivity. [Background technology]

[0003] Lithium secondary batteries are broadly composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive electrode and negative electrode from mixing, and an electrolyte that allows lithium ions to move between the positive electrode and negative electrode.

[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 recycle cathode active materials from waste cathodes without decomposing them. These methods can be broadly divided into four types: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[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 disadvantage of being unstable because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and has the risk of explosion, and requires an expensive solvent recovery process.

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

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

[0012] Therefore, there is an urgent need to develop a method for regenerating a cathode active material with improved output performance, which is easy to do, inexpensive, environmentally friendly, and safe, without discarding metal elements from used cathodes. Summary of the Invention [Problem to be solved by the invention]

[0013] To address the above-mentioned problems of the prior art, the present invention provides a method for regenerating a cathode active material by pulverizing a used cathode using a pin mill under dry conditions before calcining it to obtain a powder of a cathode active material layer, heat-treating the powder at a temperature lower than conventional methods, and then directly adding a lithium precursor to the recovered cathode active material without washing, followed by annealing. This method allows for easy removal of binders and conductive materials even at a lower heat treatment temperature than conventional methods, minimizes damage to the cathode active material caused by washing, reduces lithium loss in the cathode active material, and allows the crystalline structure to be restored with a small amount of lithium precursor. This method also provides a cathode active material with excellent capacity and life characteristics. Furthermore, the recovery and regeneration process of the cathode active material does not use an acid, which is environmentally friendly and does not require neutralization or wastewater treatment, thereby reducing process costs. The cathode active material is regenerated directly without decomposition, so there are no metal elements to be discarded. Furthermore, the method does not use an organic solvent, so there is no risk of toxic gas generation or explosion. This method significantly improves economy and productivity.

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

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

[0016] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, comprising: (a) grinding a waste positive electrode, including a current collector and a positive electrode active material layer coated thereon, using a pin mill under dry conditions to obtain a powder of the positive electrode active material layer; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution.

[0017] II) In the above I), in the step (a), the pulverization using a pin mill may be carried out under conditions of 5,000 to 10,000 rpm.

[0018] III) In I) or II), the step (a) may include a pretreatment step of shredding or cutting the waste positive electrodes.

[0019] IV) In the above I) to III), the positive electrode active material recovered after the heat treatment in step (b) may be subjected to the annealing in step (c) without being washed.

[0020] V) In the above I) to IV), in step (b), the total amount of LiOH and Li2CO3, which are surface residues of the positive electrode active material recovered after the heat treatment, may be adjusted to 1.35 wt % or less.

[0021] VI) In I) to V), the positive electrode active material may be at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and may contain 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li.

[0022] VII) In the above I) to VI), in the step (b), the heat treatment may be carried out for 1.5 hours to 6 hours.

[0023] VIII) In I) to VII), the lithium precursor may be added in an amount corresponding to 3 to 17 mol % when the total amount of lithium in the raw material positive electrode active materials used in the positive electrode active material layer is 100 mol %.

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

[0025] X) In the above I) to IX), the annealing may be carried out at 400 to 1000° C. in oxygen or air.

[0026] XI) In the above I) to X), the cleaning liquid may be water.

[0027] XII) In any of I) to XI), the method for regenerating a positive electrode active material may further include the step (e) of surface-coating the washed positive electrode active material.

[0028] XIII) In the above I) to XII), the surface coating step may include a step of coating one or more of a metal, an organic metal, and a carbon component on the surface of the positive electrode active material in a solid phase or liquid phase manner, and then heat-treating the coated surface at 100 to 1200°C.

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

[0030] The present invention also provides XV) a recycled positive electrode active material, which comprises at least one material selected from the group consisting of a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, in which Ni is contained in an amount of 60 mol% or more based on 100 mol% of the total of the remaining metals excluding Li, and the total amount of residual LiOH and Li2CO3 is 1.35 wt% or less, and the length of the a-axis of the crystal structure measured by XRD is 2.871 to 2.888 Å, the length of the c-axis is 14.200 to 14.210 Å, and the cell volume is 101.45 to 101.82 Å. 3 and a crystal size of 72 to 84 nm.

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

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

[0033] XVIII) The present invention also provides a method for regenerating a positive electrode active material, comprising the steps of: (a) applying an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) to a waste positive electrode comprising a current collector and a positive electrode active material layer coated thereon under dry conditions to obtain a powder of the positive electrode active material layer; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing the material at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. [Effects of the Invention]

[0034] According to the present invention, prior to heat treatment, waste cathodes are pulverized in a pin mill under dry conditions to obtain a cathode active material layer as a powder. This is then heat-treated at a temperature lower than conventional methods to recover the cathode active material. A lithium precursor is directly added to the recovered cathode active material without washing, and annealing is performed. This allows the binder and conductive material to be easily removed even at a lower heat treatment temperature than conventional methods, minimizes damage to the cathode active material caused by washing, maintains the small particle shape, reduces the crystal size, and reduces strain, thereby minimizing the occurrence of cracks in the active material. Furthermore, lithium loss in the cathode active material is reduced, and the crystal structure can be restored with a small amount of lithium precursor, providing a cathode active material with excellent capacity and life characteristics.

[0035] Furthermore, according to the present invention, the recovery and regeneration process of the positive electrode active material does not use an acid, which is environmentally friendly, and since there is no need for neutralization or wastewater treatment, process costs are reduced. The positive electrode active material is regenerated as it is without being decomposed, so there are no metal elements to be discarded. Furthermore, since no organic solvent is used, there is no risk of toxic gas generation or explosion. [Brief explanation of the drawings]

[0036] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the details shown in these drawings. [Figure 1] FIG. 10 is a diagram showing positive electrode scraps that are discarded after cutting electrode plates from a positive electrode sheet. [Figure 2] The positive electrode active material layer powder obtained after pin mill pulverization was analyzed by TGA (Thermogravimetric Analysis), and the results show the weight change rate depending on the heat treatment time. [Figure 3] The positive electrode active material layer powder obtained after pin mill pulverization was analyzed by TGA (Thermogravimetric Analysis), and the results show the weight change rate depending on the heat treatment temperature. [Figure 4] 1 is an SEM cross section of the regenerated positive electrode active material produced in Example 2-3. [Figure 5] 1 is an SEM cross section of a regenerated positive electrode active material produced in Comparative Example 2-1. [Figure 6] 1 is an SEM cross section of a regenerated positive electrode active material layer produced in Comparative Example 2-2. [Figure 7] 1 is a graph showing the results of coin cell evaluation of each of the recycled positive electrode active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-3, illustrating the initial capacity upon charging and discharging. [Figure 8] 1 is a graph showing the results of coin cell evaluation of the regenerated positive electrode active materials produced in Examples 2-1 to 2-7 and Comparative Example 2-1, illustrating high-temperature life characteristics. [Figure 9] 1 is a flowchart illustrating a process for regenerating a positive electrode active material according to one embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0037] The inventors discovered that prior to heat treatment, waste cathodes were pulverized in a pin mill under dry conditions to obtain a powdered cathode active material layer, which was then heat-treated to recover the cathode active material. When a lithium precursor was directly added to the recovered cathode active material without washing and annealed, the binder and conductive material were easily removed even at a lower heat treatment temperature than conventional methods, damage to the cathode active material due to washing was minimized, the small particle shape was maintained without collapse, the crystal size was reduced, strain was reduced, cracks in the cathode active material were minimized, and the crystal structure could be restored with a small amount of lithium precursor, resulting in economical advantages and improved battery characteristics of the recycled cathode active material. Based on this, the inventors conducted further research and completed the present invention.

[0038] The method for regenerating a cathode active material according to the present invention, the regenerated cathode active material produced therefrom, and a secondary battery including the same will now be described in detail.

[0039] However, the terms and words used in this specification and claims should not be interpreted limitedly to their ordinary or dictionary meanings, but should be interpreted in terms and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms 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.

[0040] 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.

[0041] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention is characterized by comprising the steps of: (a) pulverizing a waste positive electrode, including a current collector and a positive electrode active material layer coated thereon, using a pin mill under dry conditions to obtain a powder of the positive electrode active material layer; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a lower temperature than conventional methods, the amount of residual lithium generated during the thermal decomposition of the binder and conductive material is reduced, the small particle shape in the positive electrode active material is maintained, the crystal size is reduced, strain is reduced, and cracks can be minimized. In addition, the amount of lithium precursor required for the crystalline structure recovery process is reduced. By immediately annealing the recovered positive electrode active material without washing, damage to the positive electrode active material is minimized, and battery characteristics are improved.

[0042] Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0043] (a) Step of obtaining a positive electrode active material layer as powder from a waste positive electrode The method for regenerating a cathode active material of the present invention includes (a) grinding a used cathode, including a current collector and a cathode active material layer coated thereon, in a pin mill under dry conditions to obtain a powder of the cathode active material layer. This method has the advantage that the cathode active material layer and the current collector can be easily separated, allowing the cathode active material layer to be obtained as a powder, and that the binder and conductive material can be removed at a lower temperature than conventional methods in the subsequent heat treatment process. However, if other types of grinders such as a blender, mixer, or disc mill are used instead of a pin mill, the cathode active material layer and the current collector cannot be completely separated from the used cathode, resulting in partial contamination of the cathode active material layer and the current collector remaining in the recycled cathode active material, resulting in reduced battery performance.

[0044] The pin mill may be any pin mill commonly used in the technical field of the present invention. Specifically, the pin mill may comprise a rotor with pins attached radially and a stator attached to the rotor. The raw material is supplied to the center of the rotor and stator, dispersed by the airflow generated during rotation, and subjected to continuous strong impacts as the circumferential speed of the pins increases. The raw material is then pulverized and discharged through a screen. The pin mill can be configured to pulverize the scrap to a desired particle size by adjusting the shape and number of pins and the size of the screen. When cathode scrap is pulverized in a pin mill, the current collector pieces are finely chopped, and the cathode active material layer is peeled off from the current collector pieces. The current collector pieces remain inside the screen, while the cathode active material layer that passes through the screen is discharged as powder. The cathode active material layer powder is in the form of an aggregate of the cathode active material, binder, and conductive material. In this way, the positive electrode active material layer and the current collector can be separated by pulverization using a pin mill under dry conditions.

[0045] The pin milling can be carried out at a speed of, for example, 5,000 to 10,000 rpm, preferably 5,000 to 8,000 rpm, more preferably 5,000 to 7,000 rpm, and even more preferably 5,500 to 6,500 rpm. Within this range, the positive electrode active material layer and the current collector are smoothly separated, allowing the positive electrode active material layer powder to be separated. Specifically, if the speed is less than this range, the positive electrode active material layer and the current collector cannot be separated, reducing productivity. If the speed is greater than this range, there is a problem of the current collector being mixed into the positive electrode active material layer powder.

[0046] The pulverization using the pin mill may be preferably performed in a dry room under a nitrogen atmosphere. In this case, there is an advantage that the conversion of lithium carbonate present in the positive electrode active material layer to lithium hydroxide due to heat generated during the pulverization process is suppressed, and the positive electrode active material layer can be easily separated from the current collector.

[0047] In this description, a dry room means that the temperature is 20 to 22°C and the wet bulb temperature is maintained at -60 to -50°C.

[0048] The average particle size of the positive electrode active material layer obtained as the powder may preferably be the same as or similar to the average particle size of the positive electrode active material layer of the raw material. In this case, there is an advantage that the battery characteristics of the recycled positive electrode active material are excellent.

[0049] Before the waste positive electrodes are pulverized using a pin mill, a pretreatment step, for example, shredding or cutting, may be included. In this case, there is an advantage that the positive electrode active material layer and the current collector can be more easily separated.

[0050] The shredding or cutting may be performed using, for example, dry grinding equipment, specifically, one or more of a hand mill, a disc mill, a cutting mill, and a hammer mill, and a high-speed cutter may be used to increase productivity.

[0051] In this description, the dry conditions are not particularly limited as long as they are dry conditions commonly defined in the technical field to which the present invention pertains, and may be, for example, a state in which no solvent is added, and / or a dry state, and / or a condition using dry grinding equipment.

[0052] 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.

[0053] The positive electrode active material layer in step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0054] The positive electrode active material is preferably at least one selected from the group consisting of nickel-cobalt-manganese (NCM)-based positive electrode active materials, nickel-cobalt-aluminum (NCA)-based positive electrode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials, and may contain 60 mol % or more of Ni based on 100 mol % of the total of the remaining metals excluding Li. In this case, excellent reversible capacity and thermal stability can be achieved.

[0055] As another specific example, the positive electrode active material may be a compound represented by the following Chemical Formula 1, in which case, there is an effect of excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0056] (chemical formula 1) Li a Ni x Mn y Co z M w O2+ δ (In the above Chemical Formula 1, M includes 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、x+y+z+w=1である。)

[0057] The positive electrode active material may contain, for example, 60 mol % or more, preferably 80 mol % or more, more preferably 81 mol % or more, and even more preferably 81 to 95 mol % of Ni, based on 100 mol % of the total of the remaining metals excluding Li. Within this range, there is an effect of excellent charge capacity, resistance characteristics, and capacity characteristics.

[0058] In the present description, the Ni content is not particularly limited as long as it is measured by a method using IC (Ion Chromatography) or the like, which is commonly used in the technical field to which the present invention pertains. For example, the Ni content can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer.

[0059] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT, or a mixture thereof.

[0060] The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0061] (b) heat-treating the obtained positive electrode active material layer powder The method for regenerating a positive electrode active material of the present invention includes (b) heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C to recover the positive electrode active material. In this case, the binder and conductive material can be removed at a lower temperature than conventional methods, thereby minimizing damage to the positive electrode active material, reducing the amount of residual lithium generated by thermal decomposition of the binder and conductive material, maintaining the small particle shape in the positive electrode active material, reducing the crystal size, reducing strain, and minimizing cracks, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0062] The heat treatment temperature may be preferably 480 to 530°C, more preferably 480 to 500°C. Within this range, damage to the positive electrode active material is minimized, the amount of residual lithium generated during the thermal decomposition of the binder and conductive material is reduced, the small particle shape is maintained without being distorted, the crystal size is reduced, and strain is reduced, minimizing cracks in the positive electrode active material and improving battery characteristics.

[0063] The heat treatment time may be, for example, 1.5 hours to 6 hours, preferably 2 hours to 5.5 hours, more preferably 2 hours to 5 hours, even more preferably 2.5 hours to 5 hours, and even more preferably 3 hours to 5 hours. Within this range, thermal decomposition of the binder and conductive material is actively carried out, damage to the positive electrode active material is minimized, the amount of residual lithium generated during the decomposition process of the binder and conductive material is reduced, the small particle shape is maintained without collapse, the crystal size is reduced, strain is reduced, cracks in the positive electrode active material are minimized, and battery characteristics are improved.

[0064] 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.

[0065] The heat treatment may be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 1 to 10°C / min, more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min. Within this range, the heat treatment can be performed without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock or the like is caused to the positive electrode active material layer powder.

[0066] The heat treatment equipment is not particularly limited as long as it is heat treatment equipment commonly used in the technical field to which the present invention pertains. Specifically, the heat treatment equipment may be any of various types of furnaces, and examples thereof include a box-type furnace or a rotary kiln.

[0067] The rotary kiln is advantageous in that it allows continuous processing and therefore has excellent productivity.

[0068] In step (b), the total amount of surface residue LiOH and Li2CO3 of the positive electrode active material recovered after the heat treatment may be, for example, 1.35 wt % or less, preferably 1.28 wt % or less, more preferably 1.10 wt % or less, and even more preferably 0.1 to 1.10 wt %. Within this range, a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0069] In the step (b), the amount of Li2CO3 remaining on the surface of the recovered positive electrode active material after the heat treatment may be, for example, 0.40 wt % or less, preferably 0.32 wt % or less, more preferably 0.25 wt % or less, even more preferably 0.20 wt % or less, still more preferably 0.15 wt % or less, and particularly preferably 0.05 to 0.15 wt %. Within this range, a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided. In the step (b), the amount of LiOH remaining on the surface of the recovered positive electrode active material after the heat treatment may be, for example, 0.99 wt % or less, preferably 0.96 wt % or less, and more preferably 0.05 to 0.96 wt %. Within this range, a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0070] In this description, the surface residual LiOH and Li2CO3 contents of the positive electrode active material can be measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The filtrate was titrated with 0.1 M HCl solution, and the change in pH was measured to obtain a pH titration curve. The resulting pH titration curve was used to calculate the residual amounts of LiOH and Li2CO3 in the positive electrode active material.

[0071] The positive electrode active material recovered in step (b) may be preferably subjected to annealing in step (c) without washing. In this case, damage to the surface of the positive electrode active material is minimized, and the phenomenon in which large and small particles of the positive electrode active material consisting of secondary particles are dissolved and converted into primary particles is minimized.

[0072] In the present invention, the term "primary particle" refers to a primary structure of a single particle, and the term "secondary particle" refers to an aggregate or assembly formed by aggregation or assembly of primary particles through physical or chemical bonding between the primary particles, in other words, a secondary structure.

[0073] (c) adding a lithium precursor to the recovered positive electrode active material and annealing it; The method for regenerating a positive electrode active material of the present invention includes (c) adding a lithium precursor to the recovered positive electrode active material and annealing the material at 400 to 1000°C. In this case, a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided. The cleaning process of the recovered active material is omitted, which has the advantages of significantly improving economy and productivity and minimizing damage to the positive electrode active material.

[0074] The annealing step (c) may preferably be a step of adding a lithium precursor to the recovered cathode active material without washing it, and annealing it in oxygen (O2) or air at 400 to 1000°C. In this case, the crystallinity of the cathode active material can be improved, for example, by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the recycled cathode active material.

[0075] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0076] The lithium precursor is preferably added in an amount that is at least the amount of lithium that is reduced from the molar ratio of lithium in the positive electrode active material in step (b), based on the amount of lithium in the raw positive electrode active material. For example, when the recovered positive electrode active material in step (b) is a positive electrode active material represented by Chemical Formula 1, the lithium precursor is added in an amount that results in a lithium molar ratio of 0.0001 to 0.2, preferably an amount that results in a lithium molar ratio of 0.001 to 0.02, more preferably an amount that results in a lithium molar ratio of 0.005 to 0.17, even more preferably an amount that results in a lithium molar ratio of 0.007 to 0.015, and even more preferably an amount that results in a lithium molar ratio of 0.009 to 0.013. Within this range, the lithium that is insufficient in the regenerated positive electrode active material is replenished, and by improving crystallinity, such as increasing crystallinity or restoring the crystal structure, the battery characteristics of the regenerated positive electrode active material are improved. The lithium precursor may be added in an amount corresponding to 3 to 17 mol %, more preferably 5 to 15 mol %, and even more preferably 8 to 13 mol %, when the total amount of lithium contained in the raw material positive electrode active material is 100 mol %. Within this range, no residual precursor that may increase resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics, and is economically advantageous because the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods.

[0077] 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.

[0078] 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.

[0079] (d) washing the annealed positive electrode active material with a washing solution; The method for regenerating a positive electrode active material of the present invention includes (d) a step of washing the annealed positive electrode active material with a washing solution. In this case, the lithium precursor that tends to remain in the positive electrode active material can be removed with a small amount of washing solution, which has the advantage of preventing a decrease in battery performance and gas generation due to the subsequent reaction between the remaining lithium precursor and the electrolyte, and eliminating the need for wastewater treatment.

[0080] The washing step may preferably include the steps of mixing the annealed cathode active material with a washing solution, followed by filtering, and drying the solid cathode active material obtained after the filtration. In this case, excess lithium that tends to remain in the cathode active material may be effectively removed.

[0081] The drying may be carried out at a temperature of preferably 100 to 500°C, more preferably 120 to 400°C, even more preferably 120 to 300°C, and even more preferably 120 to 200°C, which has the advantage that residual Li can be effectively removed within this range.

[0082] The drying may preferably be vacuum drying.

[0083] In this description, the vacuum drying is not particularly limited as long as it is vacuum drying that is commonly performed in the technical field to which the present invention belongs.

[0084] The washing step preferably includes the steps of mixing the annealed cathode active material with a washing solution in a weight ratio of 1:1.5 to 1:5.5, filtering the mixture, and drying the solid cathode active material obtained after the filtration. This step effectively removes lithium precursors such as LiOH and Li2CO3 that tend to remain due to the excess lithium added, thereby preventing cation mixing, which is likely to occur in high-nickel cathode active materials. This cation mixing occurs due to the similar particle sizes of nickel and lithium.

[0085] In this description, a high-nickel (High-Ni) positive electrode active material refers to a positive electrode active material containing 60 mol % or more of Ni, based on 100 mol % of the total of the remaining metals excluding Li.

[0086] The annealed active material and the cleaning solution may be mixed in a weight ratio of preferably 1:1.5 to 1:4, more preferably 1:1.5 to 1:3, and even more preferably 1:1.5 to 1:2.5. In this case, in order to suppress the cation mixing phenomenon that is likely to occur in high-nickel positive electrode active materials, lithium precursors such as LiOH and Li2CO3 that tend to remain due to the excess lithium added can be effectively removed.

[0087] In particular, when the annealed active material and the washing solution are mixed in a weight ratio of 1:1.5 to 1:3, preferably 1:1.5 to 2.5, the initial discharge capacity (DCH) and efficiency of the regenerated positive electrode active material are further improved.

[0088] Furthermore, in the conventional technology in which the positive electrode active material recovered from waste positive electrodes after heat treatment is washed with water and then annealed, a volume of washing solution 30 times or more the volume of the positive electrode active material is required to remove residual lithium in the washing step. However, in the present invention, the recovered positive electrode active material is washed after annealing, so a small amount of washing solution is used, eliminating the need for wastewater treatment and achieving superior residual lithium removal efficiency compared to conventional methods.

[0089] The cleaning solution may be, for example, water or a basic lithium compound aqueous solution, preferably water. In this case, lithium precursors such as LiOH and Li2CO3 that tend to remain on the surface of the positive electrode active material can be sufficiently removed with a small amount of cleaning solution, thereby eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0090] The water is more preferably distilled water or deionized water. In this case, lithium precursors such as LiOH, Li2CO3, etc., which tend to remain on the surface of the positive electrode active material, can be sufficiently removed with a small amount of cleaning solution, thereby eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0091] The basic lithium compound aqueous solution may preferably contain more than 0 wt % and not more than 15 wt % of the lithium compound, and more preferably more than 0 wt % and not more than 10 wt % of the lithium compound. In this case, lithium precursors such as LiOH and Li2CO3 that tend to remain on the surface of the positive electrode active material are sufficiently removed with a small amount of cleaning solution, thereby eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0092] The annealed positive electrode active material and the cleaning solution are preferably mixed by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0093] The stirring may be carried out preferably for 30 minutes or less, more preferably for 20 minutes or less, even more preferably for 15 minutes or less, and even more preferably for 5 to 10 minutes, within which range residual lithium is effectively removed.

[0094] e) surface-coating the washed positive electrode active material to obtain a reusable positive electrode active material; The method for regenerating a positive electrode active material of the present invention includes a step (e) of surface-coating the washed positive electrode active material to obtain a reusable positive electrode active material, which has the effect of improving the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0095] In the surface coating, a coating agent containing at least one of a metal, an organic metal, and a carbon component is preferably applied to the surface 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.

[0096] 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.

[0097] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m 2 / g, and more preferably, the average diameter is 10 to 100 nm and the specific surface area is 20 to 100 m 2 / g, and within this range, the particles are uniformly attached to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material, thereby improving the problems of deterioration in life characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0105] 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.

[0106] 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.

[0107] As another example, the method for regenerating a positive electrode active material of the present invention includes the steps of: (a) applying an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) to a waste positive electrode comprising a current collector and a positive electrode active material layer coated thereon under dry conditions to obtain a powder of the positive electrode active material layer; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a lower temperature than conventional methods, the amount of residual lithium generated during the thermal decomposition of the binder and conductive material is reduced, the small particle shape in the positive electrode active material is maintained, the crystal size is reduced, strain is reduced, and cracks can be minimized. In addition, the amount of lithium precursor required for the crystal structure recovery process is reduced. By immediately annealing the recovered positive electrode active material without washing, damage to the positive electrode active material is minimized, and battery characteristics are improved.

[0108] In step (a), the impact force may be preferably 5.1 to 8.1 N (Newton), more preferably 5.1 to 7.1 N (Newton), and even more preferably 5.6 to 6.6 N (Newton). Within this range, the positive electrode active material layer and the current collector are smoothly separated, allowing the positive electrode active material layer powder to be separated alone. Specifically, if the impact force is less than this range, the positive electrode active material layer and the current collector are not separated, reducing productivity, and if the impact force exceeds this range, there is a problem of the current collector being mixed into the positive electrode active material layer powder.

[0109] In step (a), the centrifugal force may be preferably 2600 to 6900 N, more preferably 2600 to 5300 N, and even more preferably 3200 to 4500 N. Within this range, the positive electrode active material layer and the current collector are smoothly separated, thereby allowing the positive electrode active material layer powder to be separated alone. Specifically, if the centrifugal force is less than this range, the positive electrode active material layer and the current collector are not separated, resulting in reduced productivity, and if the centrifugal force exceeds this range, there is a problem that the current collector is mixed into the positive electrode active material layer powder.

[0110] Specifically, under the dry conditions, the waste positive electrodes can be pulverized in a pulverizer with an impact force of 5.1 to 10.2 N (Newton) and discharged with a centrifugal force of 2600 to 10700 N (Newton).

[0111] In this description, the method for measuring the impact force and centrifugal force is not particularly limited as long as it is a measurement method commonly used in the technical field to which the present invention pertains. As an example, the mass (kg) of the waste positive electrodes, the number of rotations per minute (rpm) of the pin mill, and the radius (m) of the pin mill can be calculated using the following Equation 1 and Equation 3, assuming that the milling time is 1 second and the speed after the waste positive electrodes collide with the pins is 0.

[0112] [Formula 1] Centrifugal force (N) = m × v 2 / r

[0113] In the above formula 1, m is the mass (kg) of the waste positive electrodes, v is the value obtained by converting the number of rotations per minute (rpm) of the pin mill into a speed (m / s) using the following formula 2, and r is the radius (m) of the pin mill.

[0114] [Formula 2] Speed ​​(m / s)=(2r×π×rpm) / 60

[0115] In the above formula 2, r is the radius (m) of the pin mill, π is the ratio of the circumference of a circle to its diameter, and rpm is the number of revolutions per minute (rpm) of the pin mill.

[0116] [Formula 3] Impact force (N) = m × (v1-v2) / △t

[0117] In Equation 3, m is the mass (kg) of the waste positive electrodes, v1 is the speed (m / s) of the waste positive electrodes just before they collide with the pins, v2 is the speed (m / s) of the waste positive electrodes after they collide with the pins, and Δt is the collision time (sec.), i.e., the pulverization time, which is the time it takes from v1 to v2.

[0118] In the present invention, v2 is 0 and the collision time is 1 second.

[0119] The steps (b), (c), and (d) share all of the technical features of the steps (b), (c), and (d) of the method for regenerating a positive electrode active material described above, and therefore, a description of the overlapping parts will be omitted.

[0120] Regenerated cathode active material The recycled cathode active material of the present invention is characterized by being produced by the above-described method for recycling a cathode active material. In this case, by performing heat treatment at a temperature lower than conventional methods, the amount of residual lithium generated during the thermal decomposition of the binder and conductive material is reduced, the small particle shape in the cathode active material is maintained, the crystal size is reduced, strain is reduced, and cracks are minimized. This reduces the amount of lithium precursor required for the crystal structure recovery process. By immediately annealing the recovered cathode active material without washing, damage to the cathode active material is reduced, and battery characteristics are improved.

[0121] In addition, the regenerated cathode active material of the present invention is one or more selected from the group consisting of nickel-cobalt-manganese (NCM)-based cathode active materials, nickel-cobalt-aluminum (NCA)-based cathode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, the total sum of residual LiOH and Li₂CO₃ is 1.35 wt% or less, the length of the a-axis of the crystal structure measured by XRD is 2.872 to 2.878 Å, the length of the c-axis is 14.200 to 14.210 Å, and the cell volume is 101.45 to 101.82 Å 3 and the crystal size is 72 to 80 nm. In such a case, by heat-treating at a temperature lower than before, the damage applied to the cathode active material is minimized, the residual lithium amount generated in the decomposition process of the binder and the conductive material is reduced, the small particle shape is maintained without collapsing, the crystal size becomes smaller, the strain is reduced, the cracks of the cathode active material are minimized, and by annealing the recovered cathode active material immediately without washing, there is an advantage of reducing the damage applied to the cathode active material, and the battery characteristics are improved.

[0122] As still another specific example, the regenerated cathode active material has the following Chemical Formula 1

[0123] (Chemical Formula 1) 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, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented by this, and in this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0124] The regenerated positive electrode active material preferably contains 80 mol % or more of Ni, more preferably 81 mol % or more, and even more preferably 81 to 95 mol %, based on 100 mol % of the total of the remaining metals excluding Li. Within this range, the regenerated positive electrode active material has the effect of providing excellent charge capacity, resistance characteristics, and capacity characteristics.

[0125] The regenerated positive electrode active material may have a residual amount of Li2CO3 of, for example, 0.40% by weight or less, preferably 0.32% by weight or less, more preferably 0.25% by weight or less, even more preferably 0.20% by weight or less, even more preferably 0.15% by weight or less, and particularly preferably 0.05 to 0.15% by weight. Within this range, a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0126] The regenerated positive electrode active material may have a residual LiOH content of, for example, 0.99 wt % or less, preferably 0.96 wt % or less, more preferably 0.05 to 0.96 wt %, and within this range, a positive electrode active material with excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0127] The regenerated positive electrode active material may have a total amount of residual Li2CO3 and residual LiOH of, for example, 1.35 wt% or less, preferably 1.28 wt% or less, more preferably 1.10 wt% or less, and even more preferably 0.1 to 1.10 wt%, and within this range, a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0128] The length of the a-axis of the crystal structure of the regenerated positive electrode active material as measured by XRD may be, for example, 2.871 to 2.888 Å, preferably 2.872 to 2.878 Å, and more preferably 2.874 to 2.876 Å. Within this range, the regenerated positive electrode active material has the effect of restoring to a lattice structure similar to that of the raw material positive electrode active material.

[0129] The length of the c-axis of the crystal structure of the regenerated positive electrode active material as measured by XRD may be, for example, 14.200 to 14.210 Å, preferably 14.203 to 14.206 Å, and within this range, there is an effect of restoring the lattice structure to a similar one to that of the raw material positive electrode active material.

[0130] The regenerated positive electrode active material has a cell volume measured by XRD of, for example, 101.45 to 101.82 Å. 3 , preferably 101.55 to 101.67 Å 3 Within this range, the lattice structure can be restored to a similar structure to that of the starting positive electrode active material.

[0131] The regenerated positive electrode active material may have a crystal size measured by XRD of, for example, 72 to 84 nm, preferably 72 to 82 nm, more preferably 72 to 80 nm, even more preferably 72 to 78 nm, and even more preferably 72 to 74 nm. Within this range, the regenerated positive electrode active material has the effect of restoring a lattice structure similar to that of the raw material positive electrode active material.

[0132] For example, the recycled cathode active material may have a surface coated with metal or carbon, preferably metal. In this case, the structural stability of the cathode active material is improved without any chemical or physical changes to the cathode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the surface of the cathode active material is substituted with a different element, thereby reducing the amount of residual lithium and the pH, thereby improving physicochemical properties.

[0133] The metal is preferably at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably at least one selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably boron (B), tungsten (W), or a mixture thereof, and even more preferably tungsten (W) and boron (B). A specific example is tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0134] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol % relative to 1 mol % of the metal in the positive electrode active material before the coating treatment, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and still more preferably 0.01 to 0.05 mol %. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0135] 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, 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.

[0136] FIG. 9 below is a flowchart of a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0137] Referring to Fig. 9, 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.

[0138] The positive electrode scrap has a positive electrode active material layer on an aluminum foil, and after the solvent volatilizes, the positive electrode active material layer has a structure in which the positive electrode active material and the conductive material are bound by the binder.

[0139] 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, a disc mill, a cutting mill, or a hammer mill, or a high-speed cutter may be used to increase productivity. 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.

[0140] Next, the crushed positive electrode scrap is pulverized in a pin mill under dry conditions to obtain the positive electrode active material layer as a powder (step S30).

[0141] The pin mill consists of a rotor with pins attached radially and a stator that engages with the rotor. The raw material is supplied to the center of the rotor and stator and dispersed by the airflow generated during rotation. As the circumferential speed of the pins increases, the raw material is subjected to continuous strong impacts, resulting in pulverization. The raw material then passes through a screen and is discharged. This pin mill can pulverize the raw material to a desired particle size by adjusting the shape and number of pins and the size of the screen. When cathode scrap is pulverized in a pin mill, the current collector pieces are finely chopped, and the cathode active material layer is peeled off from the current collector pieces. The current collector pieces remain inside the screen, while the cathode active material layer that passes through the screen is discharged as powder. The cathode active material layer powder is in the form of an aggregate of the cathode active material, binder, and conductive material. In this way, the cathode active material layer and the current collector can be separated by grinding using a pin mill under dry conditions.

[0142] The pin milling can be performed, for example, at a speed of 5,000 to 10,000 rpm, preferably 5,000 to 8,000 rpm, more preferably 5,000 to 7,000 rpm, and even more preferably 5,500 to 6,500 rpm. Specifically, the speed is 6,000 rpm. Within this range, the positive electrode active material layer and the current collector are smoothly separated, allowing the positive electrode active material layer powder to be isolated. If the milling speed is less than 5,000 rpm, the positive electrode active material layer and the current collector are not easily separated, requiring a long processing time. If the milling speed exceeds 10,000 rpm, the current collector may become mixed into the positive electrode active material layer powder.

[0143] Next, the obtained positive electrode active material layer powder is heat-treated in air at 460 to 530°C to recover the positive electrode active material (step S40). Here, the heat treatment is carried out to thermally decompose the binder and conductive material in the active material layer.

[0144] Through the heat treatment in air, the binder and conductive material in the active material layer are thermally decomposed into CO2 and H2O and removed. As the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0145] 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.

[0146] Since the current collector was separated in the previous process, the heat treatment is performed at a lower temperature than conventional methods, at 460 to 530°C, preferably 480 to 530°C, and more preferably 480 to 500°C. However, temperatures below 460°C prevent smooth thermal decomposition of the binder and conductive material, while temperatures above 530°C increase the amount of residual lithium generated during the thermal decomposition of the binder and conductive material, destroy the small particle shape, increase the crystal size, and increase distortion, resulting in increased cracking of the positive electrode active material. Furthermore, removing the binder and conductive material by performing heat treatment at a lower temperature than conventional methods offers the economic advantage of reduced costs.

[0147] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 1 to 10°C / min, even more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and no thermal shock occurs to the positive electrode active material layer powder.

[0148] The heat treatment can be carried out for a period of time sufficient to thermally decompose the binder, for example, preferably 1.5 to 6 hours, preferably 2 to 5.5 hours, more preferably 3 to 5 hours, and even more preferably 4 to 5 hours. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0149] 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.

[0150] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0151] Next, a lithium precursor is added to the recovered positive electrode active material, and the material is annealed (step S50).

[0152] It is important that the annealing step involves immediately adding a lithium precursor to the recovered cathode active material and annealing it without a washing step. In this case, the crystalline LiF formed on the surface of the cathode active material in the previous heat treatment step S40 is retained in the recycled cathode active material. This has the advantage that when this is applied to a secondary battery, battery characteristics are improved and damage to the cathode active material due to washing is minimized.

[0153] Furthermore, because lithium loss occurs in the positive electrode active material during step S40, this loss is replenished in step S50. Furthermore, because a deformed structure (e.g., Co3O4 in the case of an LCO active material) may develop on the surface of the positive electrode active material during the previous steps, step S50 restores the crystalline structure of the positive electrode active material through annealing, thereby improving the battery characteristics of the regenerated positive electrode active material or restoring it to the level of a virgin positive electrode active material. Here, "virgin" is the opposite concept of "regenerated," meaning that the material has been produced for the first time, and is the same term as "raw material" used in the examples.

[0154] The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3, and Li2O, and LiOH is used as a specific example.

[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 results in unreacted lithium precursor remaining in the regenerated cathode active material, which increases resistance. Therefore, it is necessary to add an appropriate amount of lithium precursor. For example, if the molar ratio of lithium to other metals in the new cathode active material is 1, the lithium precursor can be added in an amount that results in a lithium molar ratio of 0.001 to 0.4, preferably 0.01 to 0.2.

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

[0157] By performing the heat treatment at a temperature lower than conventionally used in the previous step S40, the amount of lithium lost is reduced. Therefore, when the total amount of lithium in the raw material positive electrode active materials used for the positive electrode active material layer is taken as 100 mol %, the lithium precursor is added in an amount corresponding to preferably 3 to 17 mol %, more preferably 5 to 15 mol %, and even more preferably 8 to 13 mol %.

[0158] The annealing is carried out in air at a temperature of 400 to 1000°C, preferably 600 to 900°C, for example. 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. For example, when Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more 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 even more preferably 470 to 480°C.

[0160] The annealing time may be, for example, 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. A longer annealing time may allow sufficient recovery of the crystal structure, but annealing for a longer period of time does not significantly affect performance. The annealing device used in the heat treatment step S40 may be the same as or similar to the device used in the heat treatment step S40.

[0161] Next, the annealed positive electrode active material is washed with a washing solution (step S60).

[0162] The lithium precursor that did not participate in the reaction in the annealing step S50 exists on the surface of the positive electrode active material in the form of LiOH and Li2CO3, so a residual lithium removal process is required to remove this. The impurities in the form of LiOH and Li2CO3 may later react with the electrolyte, reducing battery performance and generating gas, so the residual lithium must be removed thoroughly.

[0163] The washing solution may be prepared by mixing the annealed positive electrode active material and the washing solution in a weight ratio of preferably 1:1.5 to 1:5.5, more preferably 1:1.5 to 1:4, even more preferably 1:1.5 to 1:3, and even more preferably 1:1.5 to 1:2.5. In this case, residual lithium is removed with a small amount of washing solution, which is advantageous in that wastewater treatment is not required and a positive electrode active material having excellent initial discharge capacity, rate performance, and capacity characteristics can be obtained.

[0164] The cleaning liquid is preferably water, which is safe and inexpensive and has the advantage that the transition metals present in the positive electrode active material are not eluted.

[0165] The washing is preferably performed by mixing the annealed cathode active material with a washing solution, filtering the mixture, and then drying the solid cathode active material.

[0166] The annealed positive electrode active material and the cleaning solution are preferably mixed by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0167] The mechanical stirring is preferably carried out at 100 to 1000 rpm for 5 to 30 minutes, more preferably at 250 to 350 rpm for 5 to 10 minutes.

[0168] The filtration is preferably reduced pressure filtration using a filter, and the drying is preferably vacuum drying at 50 to 140°C.

[0169] Next, as an optional step, the washed positive electrode active material can be surface coated (step S70).

[0170] For example, the surface coating is performed by coating the surface with a coating agent containing a metal, an organic metal, or a carbon component in a solid or liquid phase manner, followed by heat treatment. If the heat treatment temperature is too low, the desired surface protection layer made of a different metal will not be formed, and if the heat treatment temperature is too high, the battery performance will be reduced due to thermal decomposition of the positive electrode active material.

[0171] Specifically, a metal oxide or acid such as B, W, or BW is coated on a washed cathode active material, followed by heat treatment, to form a surface protection layer such as a lithium boron oxide layer on the surface of the cathode active material.

[0172] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0173] If the annealing step S50 is performed to achieve a 1:1 molar ratio of lithium to other metals in the cathode active material, the lithium in the cathode active material will react with the coating agent in the surface coating step S70, resulting in a lithium:other metals molar ratio of less than 1:1. Such a regenerated cathode active material will not be able to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step S50, at a molar ratio of 0.0001 to 0.1 or more relative to the other metals in the cathode active material, a surface protection layer will form 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.

[0174] secondary battery The secondary battery of the present invention includes the recycled cathode active material. In this case, by performing heat treatment at a temperature lower than conventional temperatures, the amount of residual lithium generated during the thermal decomposition of the binder and conductive material is reduced, the small particle shape in the cathode active material is maintained, the crystal size is reduced, strain is reduced, and cracks are minimized, improving battery characteristics. Furthermore, residual lithium is sufficiently removed with a small amount of cleaning solution, eliminating the need for wastewater treatment. Furthermore, no acid or organic solvent is used in the recovery and regeneration process of the cathode active material, resulting in environmentally friendly, economical, and productive advantages.

[0175] The secondary battery of the present invention may include all of the above-described positive electrode active material and regeneration method thereof, and therefore, redundant description thereof will be omitted here.

[0176] 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.

[0177] [Example] Manufacturing Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCMA-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio 88:7:4:1)) was shredded and cut into 2 cm x 2 cm pieces, and then pulverized in a pin mill while still dry to obtain the cathode active material layer as powder. The pin mill pulverization was performed at 6000 rpm. The average particle size (D50) of the cathode active material layer powder obtained after pulverization was 8.9 μm, and the average particle size (D50) of the raw cathode active material was 8.4 μm.

[0178] The average particle size of the positive electrode active material layer powder was measured using a laser diffraction method. Specifically, particles of the positive electrode active material were dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device such as a Microtrac MT 3000. Ultrasonic waves of about 28 kHz were irradiated at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution measured by the measuring device was calculated.

[0179] Manufacturing Example 2 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCMA-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio 88:7:4:1)) was shredded and cut, and then pulverized in a dry state in a blender (WARING COMMERCIAL BLENDER 8010S, model HGBTWTS3) for 1 minute to obtain the cathode active material layer as powder. The obtained cathode active material layer powder had an average particle size (D50) of 8.9 μm, while the average particle size (D50) of the raw cathode active material was 8.4 μm.

[0180] [Test Example I: Analysis of Heat Treatment Temperature by TGA] The positive electrode active material layer powder obtained in Production Example 1 was analyzed using TGA to determine the weight change rate depending on the heat treatment time, and the results are shown in Figure 2. The temperature conditions during the TGA analysis were as follows: starting from 50°C, the temperature was increased to 480°C at a rate of 5°C / min, and then maintained for 5 hours, and then the temperature was increased again to 900°C at a rate of 5°C / min.

[0181] Referring to Figure 2 below, it can be seen that the binder and conductive material were thermally decomposed and the weight decreased until the heat treatment time was 210 minutes, there was no change in weight from 210 minutes to 510 minutes, and the weight increased slightly after 510 minutes, which indicates that the binder and conductive material were not thermally decomposed any further after the thermal decomposition time exceeded 510 minutes.

[0182] [Test Example II: Analysis of thermal decomposition temperatures of binders and conductive materials by TGA] The weight change rate of the positive electrode active material layer powder obtained in Preparation Example 1 as a function of heat treatment temperature was analyzed using TGA, and the results are shown in Figure 3. The temperature conditions were as follows: starting from 50°C and ending at 900°C, and the temperature rise rate was 5°C / min.

[0183] Referring to Figure 3 below, it was confirmed that the binder in the positive electrode active material layer powder begins to thermally decompose at around 360°C, and the conductive material begins to thermally decompose at around 450°C. This confirms that the positive electrode active material layer powder obtained by separating the current collector from the positive electrode scrap by pin milling can be heat-treated at a lower temperature than conventional methods to obtain a positive electrode active material from which the binder and conductive material have been sufficiently removed.

[0184] Furthermore, from Figure 3 below, it was confirmed that at temperatures below 460°C, at which the binder is thermally decomposed and its weight is reduced, the binder is not thermally decomposed sufficiently, making it difficult to remove the binder and conductive material from the positive electrode active material layer powder.

[0185] Example 1-1 The positive electrode active material layer powder obtained in Production Example 1 was heat-treated in air at 480°C for 3 hours to recover the positive electrode active material. The temperature was increased at a rate of 5°C / min until the heat treatment temperature was reached.

[0186] Example 1-2 The same operation as in Example 1-1 was carried out, except that the positive electrode active material layer powder obtained in Production Example 1 was heat-treated in air at 500° C. for 2 hours to recover the positive electrode active material.

[0187] Examples 1-3 The same operation as in Example 1-1 was carried out, except that the positive electrode active material layer powder obtained in Production Example 1 was heat-treated in air at 520° C. for 2 hours to recover the positive electrode active material.

[0188] Examples 1-4 The same operation as in Example 1-1 was carried out, except that the positive electrode active material layer powder obtained in Production Example 1 was heat-treated in air at 480° C. for 5 hours to recover the positive electrode active material.

[0189] Comparative Example 1-1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCMA-based lithium transition metal oxide (Ni:Co:Mn:Al molar ratio: 88:7:4:1)) was shredded and cut, and then heat-treated in air at 590°C for 2 hours to recover the cathode active material. The temperature was increased at a rate of 5°C / min until the heat treatment temperature was reached.

[0190] Comparative Example 1-2 The same operation as in Example 1-1 was carried out, except that the positive electrode active material layer powder obtained in Production Example 1 was heat-treated in air at 550° C. for 2 hours to recover the positive electrode active material.

[0191] Comparative Examples 1-3 The positive electrode active material layer powder obtained in Production Example 2 was heat-treated in air at 480°C for 3 hours to recover the positive electrode active material. The temperature was increased at a rate of 5°C / min until the heat treatment temperature was reached.

[0192] [Test Example III: Residual Lithium Content] The residual lithium content of the positive electrode active materials obtained from Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 was measured as follows, and the results are shown in Table 1 below.

[0193] *Residual lithium content: Measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The filtrate was titrated with 0.1 M HCl solution, and the change in pH was measured to obtain a pH titration curve. The resulting pH titration curve was used to calculate the residual amounts of LiOH and Li2CO3 in the positive electrode active material.

[0194] [Table 1] As shown in Table 1, in Examples 1-1 to 1-4 according to the present invention, the contents of LiOH and Li2CO3 remaining in the positive electrode active material were significantly reduced compared to Comparative Example 1-1 corresponding to the prior art. It was also confirmed that the contents of LiOH and Li2CO3 remaining in the positive electrode active material were reduced even compared to Comparative Example 1-2, which was outside the heat treatment temperature range of the present invention.

[0195] Example 2-1 The cathode active material recovered in Example 1-1 was immediately added with LiOH as a lithium precursor without a washing process, and annealed in air at 650°C for 5 hours. The lithium precursor was added in an amount corresponding to 5 mol% based on the total lithium in the cathode active materials used in the cathode active material layer, which was 100 mol%.

[0196] The annealed cathode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was vacuum-dried at 100-130°C for 12 hours to obtain a washed cathode active material. Air was supplied at 3 L / min.

[0197] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. The temperature was increased at a rate of 2°C / min until the heat treatment temperature was reached, and air was supplied at a rate of 3 L / min.

[0198] Example 2-2 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and LiOH was added as a lithium precursor in an amount corresponding to 7 mol % based on the total lithium in the raw material positive electrode active material used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0199] Example 2-3 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and LiOH was added as a lithium precursor in an amount corresponding to 10 mol % based on the total amount of lithium in the raw material positive electrode active materials used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0200] Examples 2-4 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and LiOH was added as a lithium precursor in an amount corresponding to 12 mol % based on the total lithium in the raw material positive electrode active materials used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0201] Examples 2-5 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and LiOH was added as a lithium precursor in an amount corresponding to 13 mol % based on the total lithium in the raw material positive electrode active materials used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0202] Examples 2-6 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and LiOH was added as a lithium precursor in an amount corresponding to 14 mol % based on the total lithium in the raw material positive electrode active materials used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0203] Examples 2-7 In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-1, and LiOH was added as a lithium precursor in an amount corresponding to 15 mol % based on the total amount of lithium in the raw material positive electrode active materials used for the positive electrode active material layer being 100 mol %, and then annealing was performed, except that the same operation as in Example 2-1 was performed.

[0204] Comparative Example 2-1 LiOH was added as a lithium precursor to the cathode active material recovered in Comparative Example 1-1, and the mixture was annealed in air at 650°C for 5 hours. The lithium precursor was added in an amount corresponding to 15 mol% of the total lithium in the cathode active materials used in the cathode active material layer, with the total lithium being 100 mol%.

[0205] The annealed cathode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was vacuum-dried at 100-130°C for 12 hours to obtain a washed cathode active material. Air was supplied at 3 L / min.

[0206] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 1000 ppm of boron lost in the previous process, the temperature was increased at a rate of 2°C / min until the heat treatment temperature was reached, and air was supplied at a rate of 3 L / min.

[0207] Comparative Example 2-2 LiOH was added as a lithium precursor to the cathode active material recovered in Comparative Example 1-3, and the mixture was annealed in air at 650°C for 5 hours. The lithium precursor was added in an amount corresponding to 15 mol% of the total lithium in the cathode active materials used in the cathode active material layer, with the total amount being 100 mol%.

[0208] The annealed cathode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was vacuum-dried at 100-130°C for 12 hours to obtain a washed cathode active material. Air was supplied at 3 L / min.

[0209] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. The temperature was increased at a rate of 2°C / min until the heat treatment temperature was reached, and air was supplied at a rate of 3 L / min.

[0210] Comparative Example 2-3 LiOH was added as a lithium precursor to the cathode active material recovered in Comparative Example 1-1, and the mixture was annealed in air at 650°C for 5 hours. The lithium precursor was added in an amount corresponding to 10 mol% of the total lithium in the cathode active materials used in the cathode active material layer, with the total amount being 100 mol%.

[0211] The annealed cathode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was vacuum-dried at 100-130°C for 12 hours to obtain a washed cathode active material. Air was supplied at 3 L / min.

[0212] The washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to prepare a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 1000 ppm of boron lost in the previous process, the temperature was increased at a rate of 2°C / min until the heat treatment temperature was reached, and air was supplied at a rate of 3 L / min.

[0213] Reference Example Instead of a recycled positive electrode active material, a fresh NCMA-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1) was used.

[0214] [Test Example IV: SEM Analysis] The results of SEM analysis of the regenerated positive electrode active materials produced in Example 2-3, Comparative Example 2-1, and Comparative Example 2-2 are shown in the following FIGS. 4 to 6. FIG.

[0215] Figure 4 below shows a cross-section of the recycled cathode active material produced in Example 2-3 by pin milling, Figure 5 below shows the recycled cathode active material produced in Comparative Example 2-1 according to the prior art, and Figure 6 below shows the recycled cathode active material produced in Comparative Example 2-2 by blender milling. Figure 4 below shows that pin mill milling allows for the separation of the current collector from the cathode scrap to produce a cathode active material layer, and the recycled cathode active material layer produced from this maintains its small particle shape without being distorted compared to Figure 5 below. In contrast, Figure 6 below shows the result of blender milling, where the current collector was not completely separated from the cathode scrap, resulting in the presence of the aluminum current collector in the cathode active material layer.

[0216] [Test Example V: XRD Analysis] The regenerated positive electrode active materials obtained in Examples 2-1 to 2-7 and Comparative Example 2-1 were each subjected to XRD analysis to measure the a-axis length, c-axis length, cell volume, and crystal size of the crystal structure, and the results are shown in Table 2 below.

[0217] [Table 2] As shown in Table 2 above, Examples 2-1 to 2-7 have a-axis lengths, c-axis lengths, and cell volumes of the crystal structure at levels similar to those of the Reference Example, and it was expected that the battery characteristics would be further improved by reducing the crystal size.

[0218] [Test Example VI: Evaluation of CHC Cell] The electrochemical performance of the recycled cathode active materials prepared in Examples 2-1 to 2-7, Comparative Example 2-1, and Comparative Example 2-3 was measured through the CHC cell evaluation as follows, and the results are shown in FIGS. 7, 8, and Table 3 below.

[0219] * CHC cell fabrication: 96% by weight of recycled positive electrode active material, 2% by weight of carbon black (conductive material), and 2% by weight of PVdF (binder) were weighed and mixed with NMP to create a slurry. This was coated onto aluminum foil to create a positive electrode, and a coin half cell (CHC) was fabricated. The electrochemical performance (charge capacity, discharge capacity, and efficiency) and lifespan characteristics were evaluated under conditions where the electrolyte contained ethylene carbonate (EC):dimethyl carbonate (DMC) = 3:7 (weight ratio) and other additives.

[0220] *Evaluation of the initial capacity of the cell: Each cell was charged and discharged once at 25°C under the following conditions.

[0221] Charge:0.2C, CC / CV, 4.5V, 0.05C cut-off Discharge:0.2C, CC, 3.0V, cut-off

[0222] *Charge-discharge efficiency of cell: The charge-discharge efficiency was calculated using the charge capacity and discharge capacity obtained from the evaluation of the initial capacity of the cell according to the following Equation 1, and is shown in Table 3 below.

[0223] [Formula 1] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] x 100

[0224] *Evaluation of high-temperature lifespan characteristics of cells: Each cell was charged and discharged 20 times at 45°C under the following conditions, and the capacity retention rate and resistance increase rate (ΔDCIR) for each cycle were calculated using the following Equation 2 and Equation 3, respectively, and are shown in Figure 8 below.

[0225] Charge:0.33C, CC / CV, 4.5V, 0.05C cut-off Discharge:0.33C, CC, 3.0V, 0.05C cut-off

[0226] [Formula 2] Capacity retention rate (%) = (discharge capacity after N cycles / discharge capacity after 1 cycle) x 100

[0227] [Formula 3] △DCIR={(resistance after N cycles / resistance after 1 cycle)×100}-100

[0228] FIG. 7 below is a graph showing the initial charge / discharge capacity as a result of coin cell evaluation of each of the regenerated positive electrode active materials produced in Examples 2-1 to 2-7 and Comparative Example 2-3.

[0229] As shown in Figure 7 below, the recycled cathode active material according to the present invention thermally decomposes the binder and conductive material at a lower temperature than the conventional technology, thereby reducing the loss of lithium in the cathode active material compared to the conventional technology, and thus the amount of lithium precursor required for the crystalline structure recovery process. Specifically, when comparing Example 2-3 and Comparative Example 2-3, which contain the same amount of lithium precursor at 10 mol%, Example 2-3 had a better initial capacity evaluation result than Comparative Example 2-3. Furthermore, Example 2-2, which contains 7 mol% lithium precursor, had an initial capacity evaluation result equivalent to Comparative Example 2-3, which contains 10 mol% lithium precursor.

[0230] [Table 3] As shown in Table 3 above, the regenerated positive electrode active materials according to the present invention (Examples 2-1 to 2-7) had charge / discharge efficiencies equal to or higher than those of Comparative Example 2-3 according to the prior art.

[0231] In addition, Figure 8 below is a graph showing the capacity retention and resistance increase rate over 20 cycles, which are the results of coin cell evaluation of the recycled cathode active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-1. Referring to this graph, it was confirmed that the recycled cathode active materials (Examples 2-1 to 2-7) according to the present invention have superior cell capacity retention rates even at high temperatures and lower resistance increase rates than Comparative Example 2-1 according to the prior art. Example 2-5 has a lower capacity retention rate than Comparative Example 2-1, but a lower resistance increase rate. Example 2-1 has a lower resistance increase rate than Comparative Example 2-1, but a superior capacity retention rate. [Explanation of symbols]

[0232] 10 Current collector 20 Active material layer 30 Positive electrode sheet 40 positive electrode plate 50 cathode scrap

Claims

1. (a) crushing a waste positive electrode including a current collector and a positive electrode active material layer coated thereon in a pin mill under dry conditions to obtain a positive electrode active material layer as a powder; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing the material at 400 to 1000°C; (d) washing the annealed positive electrode active material with a washing solution; Including, The positive electrode active material recovered after the heat treatment in step (b) is subjected to the annealing in step (c) without washing.

2. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (a), the pulverization using a pin mill is carried out under conditions of 5,000 to 10,000 rpm.

3. The method of claim 1 , wherein step (a) includes a pretreatment step of shredding or cutting the waste positive electrodes.

4. The step (b) is to remove LiOH and Li, which are surface residues of the positive electrode active material recovered after the heat treatment. ２ CO ３ 2. The method for regenerating a positive electrode active material according to claim 1, wherein the total amount of the positive electrode active material is adjusted to 1.35% by weight or less.

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

6. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (b), the heat treatment is carried out for 1.5 to 6 hours.

7. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the lithium precursor is added in an amount corresponding to 3 to 17 mol % when the total amount of lithium in the raw material positive electrode active materials used in the positive electrode active material layer is 100 mol %.

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

9. 2. The method of claim 1, wherein the annealing is performed in oxygen or air at 400 to 1000° C.

10. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the cleaning solution is water.

11. The method for regenerating a positive electrode active material according to claim 1 , further comprising the step of (e) surface-coating the washed positive electrode active material.

12. 12. The method of claim 11, wherein the surface-coating step comprises coating the surface of the positive active material with at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase, and then heat-treating the surface at 100 to 1200°C.

13. A regenerated positive electrode active material, characterized in that it is produced by the method for regenerating a positive electrode active material according to any one of claims 1 to 12.

14. (a) subjecting a waste positive electrode, including a current collector and a positive electrode active material layer coated thereon, to an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) under dry conditions to obtain a positive electrode active material layer as a powder; (b) heat-treating the obtained powder of the positive electrode active material layer in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing the material at 400 to 1000°C; (d) washing the annealed positive electrode active material with a washing solution; Including, The positive electrode active material recovered after the heat treatment in step (b) is subjected to the annealing in step (c) without washing.

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