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 manufactured using the method, and a secondary battery including the same. More specifically, the present invention relates to a method for regenerating a positive electrode active material, the method comprising the steps of: heat-treating a used positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material, and annealing the recovered positive electrode active material at 400 to 1000°C in an oxygen atmosphere; and washing the annealed positive electrode active material. According to the present invention, a positive electrode active material with excellent resistance and life characteristics is provided, with a significant reduction in wastewater and reduced residual lithium on the surface of the positive electrode active material. The positive electrode active material recovery and regeneration process is environmentally friendly because no acid is used, and therefore no neutralization or wastewater treatment is required, reducing process costs. The positive electrode active material is regenerated as is without decomposition, so no metal elements are discarded. No organic solvents are used, so there is no risk of toxic gas generation or explosion. In particular, the water-washing process is omitted, resulting in significant improvements in economy and productivity.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0094928 filed on July 20, 2023, and Korean Patent Application No. 10-2024-0087611, refiled on July 3, 2024, based thereon, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. The present invention relates to a method for regenerating a cathode active material, a regenerated cathode active material produced from the same, and a secondary battery including the same. More specifically, the present invention relates to a cathode active material that has excellent resistance and life characteristics, achieved by calcining a used cathode at a predetermined temperature, immediately adding a lithium precursor without a water-washing process, annealing the cathode in an oxygen atmosphere, and then removing the residual Li from the cathode active material with a small amount of cleaning solution, thereby significantly reducing wastewater and reducing the residual lithium on the surface of the cathode active material. The present invention also relates to a method for regenerating a cathode active material that 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 cathode active material is regenerated directly without decomposition, so there are no metal elements to be discarded. Since no organic solvents are used, there is no risk of toxic gas generation or explosion. In particular, the water-washing process is omitted, resulting in significant improvements in economy and productivity. [Background technology]

[0002] 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.

[0003] The positive electrode active material layer mainly uses a lithium-based oxide as the active material, and the negative electrode active material layer mainly uses a carbon material as the active material. However, the lithium-based oxide generally contains rare metals such as cobalt, nickel, or manganese. 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").

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] Finally, the crushing and screening method has the advantage of using the simplest process, but has the disadvantages that it is difficult to completely separate the current collector and the positive electrode active material, the particle size distribution of the positive electrode active material changes during the crushing process, and the binder remains, which deteriorates the battery characteristics of the recycled positive electrode active material.

[0011] Therefore, there is an urgent need to develop a method for safely and environmentally friendly regeneration of cathode active materials from waste cathodes, with fewer steps and less cost, that does not contain any discarded metal elements and has improved output performance. Summary of the Invention [Problem to be solved by the invention]

[0012] In order to solve the above-mentioned problems of the prior art, the present invention provides a method for regenerating a cathode active material by calcining a used cathode at a predetermined temperature, immediately adding a lithium precursor without a water-washing process, annealing the cathode in an oxygen atmosphere, and then removing the residual lithium from the cathode active material with a small amount of washing solution, thereby significantly reducing wastewater and reducing the residual lithium on the surface of the cathode active material, thereby providing a cathode active material with excellent resistance and life characteristics. Furthermore, the present invention provides a method for regenerating a cathode active material that 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 present invention also provides a method for regenerating a cathode active material without decomposition, thereby eliminating metal elements to be discarded, and eliminating the risk of toxic gas generation or explosion because it does not use an organic solvent. In particular, the present invention provides a method for regenerating a cathode active material by omitting the water-washing process, thereby significantly improving economy and productivity.

[0013] Another object of the present invention is to provide a secondary battery that is excellent in initial discharge capacity, rate performance, and capacity characteristics.

[0014] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0015] To achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material, and annealing the recovered positive electrode active material at 400 to 1000°C in an oxygen atmosphere; and washing the annealed positive electrode active material.

[0016] II) In the above I), the positive electrode active material layer may preferably contain Ni in an amount of 60 mol % or more, based on 100 mol % in total of the remaining metals excluding Li.

[0017] III) In the above I) or II), the positive electrode active material recovered after the thermal decomposition may be provided to the annealing step, preferably without washing.

[0018] IV) In the above I) to III), the positive electrode active material recovered in the annealing step may preferably contain crystalline LiF.

[0019] V) In the above I) to IV), the annealing step may preferably supply oxygen at a rate of 1 to 20 L / min.

[0020] VI) In the above I) to V), the oxygen may preferably have a purity of 59% or more.

[0021] VII) In the above I) to VI), the oxygen atmosphere may preferably not contain carbon dioxide (CO2).

[0022] VIII) In the above I) to VII), the lithium precursor may preferably include any one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0023] IX) In the above I) to VIII), the lithium precursor may be added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium contained in the recovered positive electrode active material is taken as 100 mol %.

[0024] X) In the above I) to IX), in the washing step, the weight ratio of the annealed positive electrode active material to the washing solution may preferably be 1:0.5 to 1:4.

[0025] XI) In the above I) to X), the washed positive electrode active material may preferably have a residual amount of Li2CO3 of 0.17% by weight or less.

[0026] XII) In the above I) to XI), the method for regenerating a positive electrode active material may further preferably include a step of surface-coating the washed positive electrode active material to obtain a reusable positive electrode active material.

[0027] XIII) In the above I) to XII), the surface coating may be preferably performed by coating the surface with one or more of a metal, an organic metal, and a carbon component by a solid phase or liquid phase method, followed by heat treatment at 100 to 1200°C.

[0028] 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.

[0029] XV) The present invention also provides a regenerated cathode active material, which is at least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel cobalt manganese (NCM)-based cathode active materials, nickel cobalt aluminum (NCA)-based cathode active materials, and nickel cobalt manganese aluminum (NCMA)-based cathode active materials, and which contains crystalline LiF and has a residual amount of Li2CO3 of 0.17 wt% or less.

[0030] XVI) In the above XV), the regenerated positive electrode active material may preferably contain 60 mol % or more of Ni, based on 100 mol % of the total of the remaining metals excluding Li.

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

[0032] Furthermore, XVIII) the present invention provides a secondary battery characterized by including the recycled positive electrode active material of any one of XV) to XVII). [Effects of the Invention]

[0033] According to the present invention, after calcining used positive electrodes at a predetermined temperature, a lithium precursor is immediately added without a water-washing step, and the cathode is annealed in an oxygen atmosphere. Residual Li on the cathode active material is then cleanly removed with a small amount of cleaning solution. This significantly reduces wastewater and reduces the residual lithium on the surface of the cathode active material, providing a cathode active material with excellent resistance and life characteristics. Furthermore, since no acid is used in the recovery and regeneration process of the cathode active material, this is environmentally friendly and eliminates the need for neutralization and wastewater treatment, thereby reducing process costs. Since the cathode active material is regenerated directly without decomposition, no metal elements are discarded. Furthermore, since no organic solvents are used, there is no risk of toxic gas generation or explosion. In particular, the omission of the water-washing step after calcining used positive electrodes provides a method for regenerating cathode active material with significantly improved economy and productivity. [Brief explanation of the drawings]

[0034] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the 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] 1 is a SEM photograph of the recycled positive electrode active materials produced in Example 1 and Comparative Example 1. [Figure 3] 1 is a graph showing the results of charge-discharge cycling of coin half cells (CHCs) using recycled cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3, illustrating the change in capacity retention rate (%) and resistance increase rate (%) depending on the number of cycles. [Figure 4] 2 is a flowchart of a process for regenerating a positive electrode active material according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The inventors have been researching a method for directly recycling used positive electrodes into a cathode active material without decomposing it, thereby improving the electrochemical performance, resistance characteristics, and capacity characteristics of the recycled cathode active material. They discovered that, when used positive electrodes are calcined at a predetermined temperature, a lithium precursor is immediately added without a water washing step, and the cathode is annealed in an oxygen atmosphere, and the residual lithium is then washed and removed from the surface of the cathode active material. This reduces the residual lithium on the surface of the cathode active material, and the residual lithium is completely removed with a small amount of washing solution, significantly reducing wastewater and improving the battery characteristics of the recycled cathode active material. Based on this, the inventors continued their research and completed the present invention.

[0036] 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.

[0037] 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.

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

[0039] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention includes the steps of: heat-treating a used positive electrode, which has a positive electrode active material layer formed on a current collector, at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C in an oxygen atmosphere; and washing the annealed positive electrode active material. In this case, wastewater is significantly reduced and residual lithium on the surface of the positive electrode active material is reduced, providing a positive electrode active material with excellent resistance and life characteristics. The positive electrode active material recovery and regeneration process is environmentally friendly because no acid is used, and the elimination of the need for neutralization and wastewater treatment reduces process costs. The positive electrode active material is regenerated directly without decomposition, so there are no discarded metal elements. The elimination of the use of organic solvents eliminates the risk of toxic gas generation or explosion. In particular, the elimination of the water-washing process significantly improves economic efficiency and productivity.

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

[0041] (a) A step of recovering a positive electrode active material from a waste positive electrode The step (a) of recovering a positive electrode active material from a used positive electrode according to the present invention may preferably be a step of heat-treating a used positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer. In this case, the process is simple, and further, the binder, conductive material, and current collector can be effectively removed cleanly.

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

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

[0044] The positive electrode active material is preferably at least one selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). More preferably, it is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0045] As still another specific example, the positive electrode active material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented thereby.

[0046] For example, the positive electrode active material contains 60 mol % or more, preferably 80 mol % or more, and more preferably 81 mol % or more of Ni, based on 100 mol % of the total of the remaining metals excluding Li. Within this range, the positive electrode active material has the effect of providing excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0047] 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.

[0048] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, carbon nanotubes (CNT), or a mixture thereof.

[0049] 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.

[0050] For example, the heat treatment may be performed in an air or oxygen atmosphere, preferably in an oxygen atmosphere. In this case, the binder and the conductive material are thermally decomposed into CO and HO and removed, thereby separating the positive electrode active material from the current collector, and the separated positive electrode active material has an advantage that it can be easily sorted in powder form.

[0051] The purity of the oxygen may be, for example, 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%. Within this range, there are advantages in that the binder and conductive material are removed without remaining and the stability of Ni in the active material is increased.

[0052] The oxygen purity % may be volume % or mol %.

[0053] The purity of oxygen described herein is not particularly limited, as long as it is measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0054] For example, the oxygen atmosphere may not contain carbon dioxide (CO2). In this case, there is an advantage that the positive electrode active material can be easily separated from the current collector and the separated positive electrode active material can be easily sorted in powder form.

[0055] For example, the oxygen atmosphere may contain argon as a component other than oxygen. In this case, there are advantages in that the positive electrode active material can be easily separated from the current collector and the separated positive electrode active material can be easily sorted in powder form.

[0056] The oxygen can be supplied at, for example, 1 to 20 L / min, preferably 3 to 17 L / min, more preferably 5 to 15 L / min, and even more preferably 7 to 13 L / min. Within this range, there are advantages in that the positive electrode active material is easily separated from the current collector, and the separated positive electrode active material can be easily sorted in powder form.

[0057] The heat treatment temperature may be preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 600°C. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0058] The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0059] 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.

[0060] The heat treatment may be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min. Within this range, the heat treatment can be performed without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock is caused to the cathode scrap.

[0061] Figure 1 below shows the cathode scrap that is discarded after cutting the cathode plates from the cathode sheet.

[0062] 1, a long sheet-shaped positive electrode current collector, aluminum foil 10, is coated with a positive electrode active material layer 20 containing a positive electrode active material, a conductive material, a binder, etc. to produce a positive electrode sheet 30, which is then punched to a predetermined size to produce a positive electrode plate 40, with the remaining portion being generated as positive electrode scrap 50. Punching is one method of cutting the positive electrode sheet.

[0063] In addition, the positive electrode active material layer 20 is formed by coating a slurry containing a positive electrode active material, a conductive material, a binder, a solvent, etc., on the aluminum foil 10. However, since the slurry is very sensitive to environmental factors such as temperature, it is very difficult to determine the coating conditions. Therefore, waste positive electrode sheets are generated until the conditions for manufacturing a positive electrode sheet 30 of desired quality are found through predetermined tests.

[0064] For reference, in the following examples, scrap positive electrodes were used as waste positive electrodes.

[0065] The positive electrode active material recovered after the pyrolysis can be preferably subjected to annealing without washing. In this case, the omission of the washing step can be advantageously achieved, resulting in significant improvements in economy and productivity, and the inclusion of crystalline LiF can improve battery performance.

[0066] (b) 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 (b) a step of adding a lithium precursor to the recovered positive electrode active material and annealing the material in an oxygen atmosphere. In this case, annealing in an oxygen atmosphere reduces the residual lithium on the surface of the positive electrode active material, and improves the crystallinity by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material. The elimination of the water washing step of the recovered positive electrode active material offers the advantages of significantly improving economy and productivity.

[0067] The recovered positive electrode active material may preferably contain crystalline LiF. In this case, there is an advantage in providing a positive electrode active material excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics. Therefore, it is preferable to immediately add a lithium precursor to the recovered positive electrode active material without washing it, and then anneal it, in order to improve battery characteristics.

[0068] In the annealing step, oxygen can be supplied at, for example, 1 to 20 L / min, preferably 3 to 15 L / min, more preferably 3 to 10 L / min, and even more preferably 3 to 7 L / min. Within this range, there are advantages in that residual lithium on the surface of the positive electrode active material is reduced and crystallinity is improved, such as increased crystallinity or recovery of the crystal structure.

[0069] The purity of the oxygen may be, for example, 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%. Within this range, there are significant advantages in that residual lithium on the surface of the positive electrode active material is reduced, and the crystallinity is increased or the crystal structure is restored, thereby improving the crystallinity.

[0070] For example, the oxygen atmosphere may not contain carbon dioxide (CO2). In this case, contact with carbon dioxide is suppressed, and the effect of reducing residual lithium on the surface of the positive electrode active material is maximized.

[0071] For example, the oxygen atmosphere may contain argon as a component other than oxygen. In this case, there is an advantage that the crystallinity of the positive electrode active material is improved, such as increasing the crystallinity or restoring the crystal structure.

[0072] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0073] The lithium precursor can be added preferably in an amount that is at least the amount of lithium that is reduced from the molar ratio of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. More preferably, the lithium precursor can be added in an amount that results in a molar ratio of lithium of 0.0001 to 0.2 relative to the molar ratio of lithium in the positive electrode active material in step (a). Within this range, the battery characteristics of the recycled positive electrode active material are improved by replenishing the deficient lithium in the recycled positive electrode active material and improving the crystallinity, such as by increasing the crystallinity or restoring the crystal structure.

[0074] The lithium precursor may be added in an amount corresponding to 1 to 40 mol %, more preferably 1 to 25 mol %, even more preferably 1 to 17 mol %, even more preferably 3 to 17 mol %, and particularly preferably 7 to 15 mol %, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol %. Within this range, no residual precursor that could increase resistance remains in the recycled positive electrode active material, which is very useful for improving battery characteristics.

[0075] 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 Li2CO3 is 723°C, annealing can be preferably performed at 700 to 900°C, more preferably 700 to 800°C, and even more preferably 710 to 780°C. Since the melting point of LiOH is 462°C, annealing can be preferably performed at 400 to 720°C, more preferably 420 to 700°C, even more preferably 450 to 700°C, even more preferably 450 to 600°C, and particularly preferably 450 to 480°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance.

[0076] 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.

[0077] The annealing time may be, for example, 1 hour or more, preferably 1 to 15 hours, more preferably 4 to 13 hours, and even more preferably 6 to 12 hours. Within this range, the crystal structure is restored, which has the effect of improving the battery's output performance.

[0078] For example, the annealed positive electrode active material may have a residual amount of Li2CO3 of 1.34 wt% or less, preferably 1.10 wt% or less, more preferably 0.95 wt% or less, and even more preferably 0.1 to 0.95 wt%, within this range, which is advantageous in that the positive electrode active material has excellent resistance characteristics and life characteristics.

[0079] For example, the annealed positive electrode active material may have a residual amount of LiOH of 1.0 wt % or less, preferably 0.1 to 1.0 wt %, and within this range, the positive electrode active material has the advantage of having excellent resistance and life characteristics.

[0080] For example, the annealed positive electrode active material may have a total residual amount of Li2CO3 and LiOH of 2.22 wt% or less, preferably 2.0 wt% or less, more preferably 1.90 wt% or less, and even more preferably 0.1 to 1.90 wt%. Within this range, the positive electrode active material has the advantage of having excellent resistance characteristics and life characteristics.

[0081] In this description, the amounts of LiOH and Li2CO3 remaining on the surface of the positive electrode active material can be measured using a pH titrator (MATi 06, Metrohm). Specifically, 5 g of the positive electrode active material is dispersed in 100 ml of distilled water, mixed at 500 rpm for 5 minutes, and then filtered to remove the active material. The filtrate is titrated with 0.1 M HCl solution, and the change in pH is measured to obtain a pH titration curve. The resulting pH titration curve is used to calculate the amounts of LiOH and Li2CO3 remaining in the positive electrode active material.

[0082] (c) Washing the annealed positive electrode active material The method for regenerating a positive electrode active material of the present invention includes (c) a step of washing the annealed positive electrode active material. 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 liquid, 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 significantly reducing wastewater.

[0083] The washing 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 is likely to remain in the cathode active material may be effectively removed.

[0084] The drying temperature may be 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, and within this range, there is an advantage that residual Li is effectively removed.

[0085] The drying may preferably be carried out under vacuum.

[0086] In this description, the vacuum drying is not particularly limited as long as it is vacuum drying that is commonly performed in the technical field to which the present invention pertains.

[0087] For example, the washing may be performed at a weight ratio of annealed cathode active material to washing solution of 1:0.5 to 1:4, preferably 1:0.5 to 1:3, more preferably 1:0.5 to 1:2, and even more preferably 1:0.5 to 1:1.5. Within this range, the amount of washing solution is significantly reduced, eliminating the need for wastewater treatment, and effectively removing lithium precursors such as LiOH and Li2CO3 that tend to remain in the cathode active material. Conventionally, the cathode active material recovered from a waste cathode is heat-treated and then washed with water. In this case, the amount of washing solution required to remove the residual lithium in the water washing step is 30 times the weight of the cathode active material. However, in the present invention, the recovered cathode active material is immediately annealed and washed without water washing, allowing the residual lithium to be easily removed with a small amount of washing solution, significantly reducing wastewater and achieving superior residual lithium removal efficiency compared to conventional methods.

[0088] The cleaning solution may be preferably water or a basic lithium compound aqueous solution, more 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 cleanly removed with a small amount of cleaning solution, thereby significantly reducing wastewater and significantly improving the output performance of the battery.

[0089] The water is preferably distilled water or deionized water. In this case, lithium precursors such as LiOH, LiCO, etc., which tend to remain on the surface of the positive electrode active material, can be cleanly removed with a small amount of cleaning solution, thereby significantly reducing wastewater and significantly improving the output performance of the battery.

[0090] The basic lithium compound aqueous solution may preferably contain more than 0 wt % to 15 wt % or less of the lithium compound, and more preferably more than 0 wt % to 10 wt % or less 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 can be cleanly removed with a small amount of cleaning solution, thereby significantly reducing wastewater and significantly improving the output performance of the battery.

[0091] The annealed positive electrode active material and the cleaning solution are preferably mixed by stirring. The stirring is not particularly limited, but may be, for example, impeller stirring, magnetic stirring, or ultrasonic stirring.

[0092] 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.

[0093] For example, the washed positive electrode active material may have a residual amount of Li2CO3 of 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and even more preferably 0.05 to 0.13 wt%, and within this range, the positive electrode active material has the advantage of having excellent resistance characteristics and life characteristics.

[0094] For example, the washed positive electrode active material may have a residual LiOH content of 0.42 wt % or less, preferably 0.39 wt % or less, and more preferably 0.05 to 0.39 wt %. Within this range, the positive electrode active material has the advantage of having excellent resistance and life characteristics.

[0095] The washed positive electrode active material may have a total residual amount of Li2CO3 and LiOH of, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0096] (d) 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 (d) 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.

[0097] The surface coating is preferably carried out 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.

[0098] 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 of this is a coating agent containing tungsten boride (WB), which has the effect of improving resistance characteristics and life characteristics.

[0099] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0100] 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.

[0101] 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.

[0102] 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, there is an effect of improving the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0103] The heat treatment temperature may be preferably 100 to 1000°C, more preferably 200 to 1000°C, and even more preferably 200 to 500°C. Within this range, there is an effect that performance degradation due to thermal decomposition of the positive electrode active material does not occur, and structural stability and electrochemical performance are improved.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] The coating agent may preferably have an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m / g, more preferably an average diameter of 10 to 100 nm and a specific surface area of ​​20 to 100 m / g. Within these ranges, the coating agent adheres uniformly to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material and improving the problems of deterioration in life characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0108] 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.

[0109] 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.

[0110] The cathode active material obtained by the method for regenerating a cathode active material of the present invention may have a residual amount of Li2CO3 of, for example, 0.17% by weight or less, preferably 0.15% by weight or less, more preferably 0.13% by weight or less, and even more preferably 0.05 to 0.13% by weight. Within this range, the cathode active material has the advantage of having excellent resistance characteristics and life characteristics.

[0111] For example, the positive electrode active material obtained by the method for regenerating a positive electrode active material may have a residual amount of LiOH of preferably 0.42 wt % or less, preferably 0.39 wt % or less, more preferably 0.05 to 0.39 wt %, and within this range, the positive electrode active material has the advantage of being excellent in resistance characteristics and life characteristics.

[0112] The positive electrode active material obtained by the method for regenerating a positive electrode active material may have a total residual amount of Li2CO3 and LiOH of, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of being excellent in resistance characteristics and life characteristics.

[0113] Regenerated cathode active material The regenerated cathode active material of the present invention is characterized by being produced by the regenerating method of the cathode active material. In this case, wastewater is significantly reduced, and residual lithium on the surface of the cathode active material is reduced, resulting in excellent resistance characteristics and life characteristics.

[0114] In addition, the recycled cathode active material of the present invention is at least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel cobalt manganese (NCM)-based cathode active materials, nickel cobalt aluminum (NCA)-based cathode active materials, and nickel cobalt manganese aluminum (NCMA)-based cathode active materials, and is characterized by containing crystalline LiF and having a residual amount of Li2CO3 of 0.17 wt% or less.In this case, the residual lithium on the surface of the cathode active material is reduced, which has the advantage of excellent resistance characteristics and life characteristics.

[0115] The recycled positive electrode active material, as an example, contains Ni at 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, based on a total of 100 mol% of the remaining metals excluding Li. Within this range, there is an effect that it is excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0116] The recycled positive electrode active material preferably contains one or more selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co). In this case, there is an effect that it is excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0117] The recycled positive electrode active material, as a specific example, has the following Chemical Formula 1 (Chemical Formula 1) Li [[ID= #13]] a Ni [[ID= #15]] x Mn [[ID= #17]] y Co [[ID= #19]] z M [[ID= #21]] w O [[ID= #23]] 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 can contain a compound represented by this, and in this case, there is an effect that it is excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0118] 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 %. Within this range, the regenerated positive electrode active material has the effect of providing excellent charge capacity, resistance characteristics, and capacity characteristics.

[0119] The crystalline phase LiF can be defined as a material having a 2theta peak in the XRD spectrum at 38 to 40°, preferably 38.5 to 39°. In this case, the material has the effect of exhibiting excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0120] The crystalline phase LiF may be contained in an amount of, for example, 0.1 to 1 wt % relative to the total weight of the positive electrode active material, preferably 0.3 to 1 wt %, and more preferably 0.3 wt % or more and less than 1 wt %. Within this range, the positive electrode active material has the effect of exhibiting excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0121] In the present description, the content of LiF in the crystalline phase is not particularly limited as long as it is measured by a method using IC (Ion Chromatography) or the like commonly used in the technical field to which the present invention pertains, and can be measured, for example, by using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, an IC-ICP-AEC analyzer, etc. Here, whether or not LiF is in a crystalline phase can be confirmed by an XRD spectrum, and the content of LiF can be measured by a method using IC or the like.

[0122] The crystalline phase LiF may be contained on the surface of the regenerated positive electrode active material in an amount of, for example, 0.1 to 10% by weight, preferably 0.1 to 8% by weight, and more preferably 0.1 to 7% by weight, based on an XPS surface analysis spectrum. Within this range, the initial discharge capacity, output performance, capacity characteristics, and resistance characteristics are excellent.

[0123] In the present invention, the LiF content of the crystalline phase on the surface of the recycled positive electrode active material can be measured using an X-ray photoelectron spectroscopy (XPS) surface analysis spectrum (K-alpha, Nexsa (Thermo Fisher Scientific)). The XPS surface analysis spectrum can quantify the composition ratio and elements of the constituent elements using the area and height of photoelectrons emitted from the surface of the sample.

[0124] The regenerated positive electrode active material may have a residual amount of Li2CO3 of, for example, 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and even more preferably 0.05 to 0.13 wt%, and within this range, the positive electrode active material has the advantage of having excellent resistance characteristics and life characteristics.

[0125] The regenerated positive electrode active material may have a residual amount of LiOH of, for example, 0.42 wt % or less, preferably 0.39 wt % or less, and more preferably 0.05 to 0.39 wt %. Within this range, the positive electrode active material has the advantage of having excellent resistance characteristics and life characteristics.

[0126] The regenerated positive electrode active material may have a total residual amount of Li2CO3 and LiOH of, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0127] For example, the surface of the positive electrode active material may be coated with a metal or carbon, preferably with a metal. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the surface of the positive electrode active material is substituted with a different element, thereby reducing the amount of residual lithium and the pH, thereby improving physicochemical properties.

[0128] 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.

[0129] 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 structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0130] The surface coating is preferably provided by applying a coating agent containing at least one of a metal, an organic metal, and a carbon component 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.

[0131] The positive electrode active material may preferably be a recycled positive electrode active material, which has the advantages of being economical and productive.

[0132] FIG. 4 below is a flowchart showing a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0133] Referring to Figure 4, first, cathode scraps are prepared as waste cathodes (step S10). For example, a slurry is prepared by mixing NCM-based lithium transition metal composite oxide, carbon black, and polyvinylidene fluoride with N-methyl pyrrolidone (NMP), and the slurry is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to prepare a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scraps can be prepared.

[0134] The cathode scrap has a cathode active material layer on an aluminum foil, and after the solvent evaporates, the cathode active material layer has a structure in which the cathode active material and the conductive material are bound by the binder. Therefore, when the binder is removed, the cathode active material is separated from the aluminum foil.

[0135] Next, the prepared cathode scrap is crushed to an appropriate size (step S20). Here, crushing includes cutting or shredding the cathode scrap to a size that is easy to handle. As a specific example, the crushed cathode scrap may be 1 cm x 1 cm in size. For example, the crushing may be performed using various dry crushing equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter may be used to increase productivity.

[0136] 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.

[0137] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is carried out to thermally decompose the binder in the active material layer.

[0138] Through the heat treatment, the binder and conductive material in the active material layer are thermally decomposed into CO2 and HO and removed. Because the binder is removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily sorted in powder form. Therefore, even by performing step S30 alone, the active material layer can be separated from the current collector, and the positive electrode active material in the active material layer can be recovered in powder form.

[0139] It is important to conduct the heat treatment in an air or oxygen atmosphere, preferably an oxygen atmosphere. If the heat treatment is conducted in a reducing gas or inert gas atmosphere, the binder and conductive material will carbonize without being thermally decomposed. Carbonization results in carbon components remaining on the surface of the positive electrode active material, reducing the performance of the reused positive electrode active material. However, if the heat treatment is conducted in an air or oxygen atmosphere, specifically an oxygen atmosphere, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, thereby removing both the binder and conductive material. More specifically, the heat treatment can be conducted in 95% pure oxygen and 5% argon, removing carbon dioxide.

[0140] The heat treatment is preferably carried out at 300 to 650°C, specifically at 590°C. If the temperature is lower than 300°C, it is difficult to remove the binder, making it impossible to separate the current collectors. If the temperature exceeds 650°C, the current collectors melt, making it impossible to separate them.

[0141] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 17°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 cathode scrap.

[0142] The heat treatment can be carried out for a period of time sufficient to thermally decompose the binder, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specifically for about 30 minutes. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0143] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, but considering productivity, it may be carried out using a rotary kiln capable of continuous treatment.

[0144] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0145] Next, a lithium precursor is added to the recovered positive electrode active material, and the material is annealed in an oxygen atmosphere (step S40).

[0146] It is important that the annealing step in step S40 involves adding a lithium precursor immediately to the recovered cathode active material and annealing it without a water washing step. In this case, the crystalline LiF formed on the surface of the cathode active material in the previous heat treatment step S30 is retained in the recycled cathode active material, which has the advantage of improving battery characteristics when used in a secondary battery.

[0147] The annealing step is preferably carried out in oxygen, preferably in oxygen with a purity of 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%. Specifically, the annealing step is carried out in 95% oxygen and 5% argon from which carbon dioxide has been removed. In this case, there is an advantage that residual lithium on the surface of the positive electrode active material is reduced, thereby improving battery characteristics.

[0148] In step S40, oxygen can be supplied at a rate of, for example, 1 to 20 L / min, and specifically, 3 to 8 L / min. Within this range, there are advantages in that residual lithium on the surface of the positive electrode active material is reduced and crystallinity is improved, such as by increasing the crystallinity or restoring the crystal structure.

[0149] Furthermore, because lithium loss occurs in the positive electrode active material during step S30, this loss is replenished in step S40. 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 S40 involves annealing in oxygen to restore the crystalline structure of the positive electrode active material, thereby improving the battery characteristics of the regenerated positive electrode active material or restoring it to the level of a virgin positive electrode active material. Here, "virgin" is the opposite concept of "regenerated," meaning something that has been produced for the first time, and is the same term as "raw material" used in the examples.

[0150] As the lithium precursor, LiOH is specifically used.

[0151] The lithium precursor is preferably added in an amount at least equal to the molar ratio of the lost lithium relative to the molar ratio of lithium to other metals in the newly generated cathode active material used in the cathode active material layer. If an amount of lithium precursor that is excessively greater than the amount of lost lithium is added, unreacted lithium precursor will remain in the regenerated cathode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0152] As an example, a lithium precursor can be added in an amount that results in a lithium molar ratio of 0.001 to 0.4, preferably 0.01 to 0.4, and more preferably 0.09 to 0.2, based on the case where the molar ratio of lithium to other metals (M) in the new positive electrode active material is 1. Specifically, adding a lithium precursor in an amount that corresponds to the ratio of lithium lost in the new positive electrode active material based on the results of ICP analysis can improve capacity to the same level as the new positive electrode active material. The ICP analysis results have an error of approximately ±0.02.

[0153] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 40 mol%, more preferably 1 to 25 mol%, even more preferably 1 to 17 mol%, even more preferably 3 to 17 mol%, and particularly preferably 7 to 15 mol%, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol%. Within this range, no residual precursor that may increase resistance remains in the recycled positive electrode active material, which is very useful for improving battery characteristics.

[0154] The annealing is performed, for example, in an oxygen (O) atmosphere at a temperature of 400 to 1000°C, preferably 600 to 900°C, and this temperature needs to be adjusted within a limited range depending on the type of lithium precursor.

[0155] 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 700 to 800°C, even more preferably 710 to 780°C, and most preferably 750 to 780°C. Furthermore, when LiOH is used as the lithium precursor, the annealing temperature is preferably 400 to 720°C, more preferably 420 to 700°C, and most preferably 450 to 700°C.

[0156] The annealing time may be, for example, 1 hour or more, preferably 1 to 15 hours, more preferably 4 to 13 hours, and even more preferably 6 to 12 hours, specifically 10 hours. A longer annealing time may allow for sufficient recovery of the crystal structure, but annealing for a longer period of time does not significantly affect performance. The annealing equipment may be the same as or similar to that used in the heat treatment step S30.

[0157] Next, the annealed positive electrode active material is washed (step S50).

[0158] The lithium precursor that did not participate in the reaction in the annealing step S40 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 it. The impurities in the form of LiOH and Li2CO3 must be thoroughly removed because they may later react with the electrolyte, degrading battery performance and generating gas.

[0159] The washing may be performed at a weight ratio of the annealed cathode active material to the washing solution of 1:0.5 to 1:4, specifically 1:1. In this case, residual lithium is removed with a small amount of washing solution, which is advantageous in that wastewater is significantly reduced and a cathode active material with excellent resistance and life characteristics can be obtained.

[0160] The washing can be preferably carried out using distilled water or a basic lithium compound aqueous solution containing more than 0 wt % and 10 wt % or less of a basic lithium compound, and more preferably distilled water, which is safe and inexpensive and has the advantage of not eluting transition metals present in the positive electrode active material.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The filtration is preferably reduced pressure filtration using a filter, and the drying is vacuum drying at 50 to 140°C.

[0165] Next, as an optional step, the washed positive electrode active material can be surface coated (step S60).

[0166] 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.

[0167] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a washed cathode active material and then heat-treated, a surface protection layer such as a lithium boron oxide layer is formed on the surface of the cathode active material.

[0168] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0169] If the annealing step (S40) 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 (S60), resulting in a lithium:other metals in the cathode active material molar ratio of less than 1:1, and this regenerated cathode active material will not be able to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step (S40) so that it is present in an amount of 0.0001 to 0.1 molar ratio greater than the other metals in the cathode active material, a surface protective layer will form in the surface coating step (S60), naturally achieving a 1:1 molar ratio of lithium to other metals in the cathode active material, and no capacity loss will occur.

[0170] secondary battery The secondary battery of the present invention includes the recycled cathode active material. In this case, residual lithium in the cathode active material is significantly reduced, resulting in excellent resistance characteristics and life characteristics. Furthermore, residual lithium can be completely removed with a small amount of cleaning solution, resulting in a significant reduction in wastewater. Furthermore, since no acid or organic solvent is used in the recovery and regeneration process of the cathode active material, the secondary battery is environmentally friendly. In particular, the initial water-washing process can be omitted, resulting in excellent economic efficiency and productivity.

[0171] The secondary battery of the present invention may include all of the above-described positive electrode active materials and regeneration methods thereof, and therefore, redundant description thereof will be omitted here.

[0172] 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.

[0173] [Example] Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCM-based lithium composite transition metal oxide (nickel content 88 mol%)) was crushed and heat-treated in an oxygen atmosphere at 590°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and the oxygen atmosphere contained 95% oxygen and 5% argon (hereinafter referred to as "reactive gas"), without carbon dioxide. The reactive gas was supplied at a rate of 10 L / min.

[0174] The recovered cathode active material was not washed with water, but was immediately charged with LiOH as a lithium precursor and annealed at 700°C for 10 hours under reactive gas. The reactive gas was supplied at 3 L / min. The lithium precursor was charged in an amount equivalent to 15 mol% when the total lithium contained in the recovered cathode active material was 100 mol%.

[0175] The annealed cathode active material and distilled water were mixed in a 1:1 weight ratio, stirred at 500 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid content, which was then vacuum-dried at 100 to 130°C for 12 hours to obtain a washed cathode active material.

[0176] The washed cathode active material was mixed with boric acid (H3BO3) in a solid state and heated at 300°C for 5 hours to produce a final recycled cathode active material coated with boron. Here, boric acid was added in an amount equivalent to 700 ppm of boron lost in the previous process, and the temperature was increased at a rate of 2°C / min to reach the heat treatment temperature, with air supplied at 3 L / min.

[0177] In this description, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. This can be measured using a general ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0178] Also, in this description, ppm is by weight unless otherwise specified.

[0179] Example 2 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that in the annealing step of Example 1, the reactive gas was supplied at 8 L / min.

[0180] Comparative Example 1 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that the annealing step was carried out in air.

[0181] Comparative Example 2 A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that the annealing step in Example 1 was carried out in air, and air was supplied at a rate of 8 L / min.

[0182] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the cathode active material recovered after heat treatment of the cathode scrap was washed with a basic lithium compound aqueous solution, and then annealed by adding LiOH, a lithium precursor. Here, the basic lithium compound aqueous solution contained 15 wt % LiOH, and the weight ratio of the recovered cathode active material to the basic lithium compound aqueous solution was 1:1.

[0183] [Test Example I: Residual Lithium Content After Annealing] The residual lithium content of the positive electrode active materials obtained after annealing in Examples 1 and 2 and Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 1 below.

[0184] *Residual lithium content: Measured using a pH titrator MATi 06 (Metrohm). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 500 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 amount of residual LiOH and Li2CO3 in the positive electrode active material.

[0185] [Table 1] As can be seen from Table 1, in Examples 1 and 2 according to the present invention, the residual amount of Li2CO3, the residual amount of LiOH, and the sum of these were reduced compared to Comparative Examples 1 and 2, and it was confirmed that the residual amount of LiOH was particularly significantly reduced.

[0186] [Test Example II: Residual Lithium Content of Regenerated Positive Electrode Active Material] The residual lithium content of the regenerated positive electrode active materials obtained after washing in Examples 1 and 2 and Comparative Examples 1 and 2 was measured as described above, and the results are shown in Table 2 below.

[0187] [Table 2] As can be seen from Table 2, in Examples 1 and 2 according to the present invention, the residual amount of Li2CO3, the residual amount of LiOH, and the sum of these were reduced compared to Comparative Examples 1 and 2. In particular, the residual amount of Li2CO3 was significantly reduced, which was expected to further improve the battery characteristics.

[0188] [Test Example III: SEM Analysis] The regenerated cathode active materials obtained in Example 1 and Comparative Example 1 were photographed using an SEM device, and the photographs are shown in Figure 2 below. The SEM photographs were taken using a common SEM device commonly used in laboratories. Specifically, they were taken using a Hitachi S-4200. However, there is no deviation due to the measurement device or method.

[0189] As can be seen from Figure 2 below, the recycled cathode active material prepared in Example 1 has no impurities on the surface and the small particles remain relatively spherical compared to the recycled cathode active material prepared in Comparative Example 1, while the recycled cathode active material prepared in Comparative Example 1 has impurities remaining on the surface, and the small particles are broken and clumped together.

[0190] [Test Example IV: Evaluation of CHC Cell] The capacity retention rate and resistance increase rate of the CHCs (Coin Half Cells) prepared using the recycled cathode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were measured through the following CHC evaluation, and the results are shown in FIG. 3 and Table 3 below.

[0191] *Preparation of CHC: 96.5 wt% recycled cathode active material, 1.5 wt% carbon black (conductive material), and 2 wt% PVdF (binder) were weighed and mixed with NMP to prepare cathode active material slurry. The prepared cathode active material slurry was applied to a 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then rolled to prepare a cathode. Lithium metal was used for the anode.

[0192] The fabricated positive and negative electrodes were bonded to a separator, and an electrolyte containing ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a weight ratio of 3:7 and other additives was injected to fabricate a CHC. The fabricated CHC was aged at 25°C for 10 hours, then charged in CC-CV mode at a constant current of 0.1C up to 4.25V with a 0.05C cutoff, and then discharged at a constant current of 0.1C down to 2.5V for activation, followed by a cycle evaluation.

[0193] Measurement of capacity retention at high temperature (45°C): Each of the CHCs prepared using the regenerated cathode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was subjected to formation at a 0.1C rate and then charged at 45°C with a constant current of 0.33C to 4.25V with a 0.05C cutoff. Subsequently, the cells were discharged at a constant current of 0.33C to 2.5V. This charge and discharge behavior constitutes one cycle. This cycle was repeated 25 times, and the discharge capacities after the first cycle to the 25th cycle were measured using a PNE-05-0.1 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 0.1A). The discharge capacity after the first cycle was set as the initial capacity. The discharge capacity at the 25th cycle was then compared with the initial capacity (100%), and the capacity retention was calculated using the following equation 1. The results are shown in Figure 3 and Table 3 below.

[0194] [Formula 1] Capacity retention rate (%) = (discharge capacity after high-temperature cycle / initial discharge capacity) x 100

[0195] *Measurement of resistance increase rate at high temperature (45°C): Each of the CHCs prepared using the recycled cathode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was subjected to formation at a 0.1C rate, and then charged at 45°C with a constant current of 0.33C up to 4.25V with a 0.05C cutoff. Then, the CHCs were discharged at a constant current of 0.33C down to 2.5V. This charge and discharge behavior constituted one cycle, and this cycle was repeated 25 times to measure the degree of resistance increase. The resistance increase rate was calculated using Equation 2 below, and the results are shown in Figure 3 and Table 3 below.

[0196] [Formula 2] Resistance increase rate (%) = {(DCIR2-DCIR1) / DCIR1} x 100 (In the above formula 2, DCIR1 is the measured resistance (Ohm) at 1 cycle, and DCIR2 is the measured resistance (Ohm) at 25 cycles.)

[0197] [Table 3]

[0198] As shown in Table 3, the regenerated positive electrode active materials of the present invention (Examples 1 and 2) have a higher capacity retention rate and a significantly lower resistance increase rate in the range of 53 to 60% compared to Comparative Examples 1 to 3, which confirms that the battery characteristics have been greatly improved.

[0199] Furthermore, as shown in Figure 3 below, the regenerated positive electrode active materials of the present invention (Examples 1 and 2) have a higher capacity retention rate and a significantly lower resistance increase rate even when the number of cycles increases, compared to Comparative Examples 1 to 3, confirming that the battery characteristics have been improved.

Claims

1. A method for regenerating a positive electrode active material, comprising: a step of recovering the positive electrode active material from the positive electrode active material layer by thermally treating the waste positive electrode having the positive electrode active material layer formed on the current collector at 300 to 650°C to thermally decompose the binder and the conductive material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing the resulting mixture at 400 to 1000°C in an oxygen atmosphere; washing the annealed positive electrode active material; A method for regenerating a positive electrode active material, comprising:

2. The method of claim 1 , wherein the positive electrode active material layer contains Ni in an amount of 60 mol % or more based on a total of 100 mol % of the remaining metals excluding Li.

3. The method of claim 1 , wherein the recovered positive electrode active material after the pyrolysis is provided to the annealing step without being washed.

4. The method of claim 1 , wherein the recovered positive electrode active material in the annealing step contains crystalline LiF.

5. 2. The method of claim 1, wherein the annealing step comprises supplying oxygen at a rate of 1 to 20 L / min.

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

7. The oxygen atmosphere is carbon dioxide (CO ２ 2. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material does not contain any of the above-mentioned compounds.

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 for regenerating a positive electrode active material according to claim 1, wherein the lithium precursor is added in an amount corresponding to 1 mol % to 40 mol % when the total amount of lithium contained in the recovered positive electrode active material is 100 mol %.

10. 2. The method of claim 1, wherein in the washing step, a weight ratio of the annealed positive active material to the washing solution is 1:0.5 to 1:

4.

11. The washed positive electrode active material is ２ CO ３ 2. The method for regenerating a positive electrode active material according to claim 1, wherein the residual amount of is 0.17% by weight or less.

12. 2. The method for regenerating a positive electrode active material according to claim 1, further comprising the step of surface-coating the washed positive electrode active material to obtain a reusable positive electrode active material.

13. 13. The method of claim 12, wherein the surface coating is performed by coating the surface with at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C.

14. 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 13.

15. A regenerated positive electrode active material, the positive electrode active material is at least one selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel cobalt manganese (NCM)-based positive electrode active material, a nickel cobalt aluminum (NCA)-based positive electrode active material, and a nickel cobalt manganese aluminum (NCMA)-based positive electrode active material; Contains LiF in a crystalline phase, Li ２ CO ３ A regenerated positive electrode active material characterized in that the residual amount of is 0.17 wt % or less.

16. The recycled cathode active material according to claim 15, wherein the recycled cathode active material contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li.

17. The recycled positive electrode active material according to claim 15, wherein the surface of the recycled positive electrode active material is coated with a coating agent containing metal or carbon.

18. A secondary battery comprising the recycled positive electrode active material according to any one of claims 15 to 17.

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