Method for regenerating positive electrode active material and regenerated positive electrode active material produced by the method

Abstract

The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material produced from the method. More specifically, the present invention relates to a method for regenerating a positive electrode active material, including the steps of: (i) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and thermally decomposing the binder and conductive material in the positive electrode active material layer to separate the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; and (ii) step (ii-1) of adding calcium or a calcium compound to the recovered positive electrode active material and reheating it at 600 to 750°C, or step (ii-2) of pre-washing the recovered positive electrode active material with a washing solution, then adding a lithium precursor and calcium or a calcium compound and annealing it, and the regenerated positive electrode active material produced from the method. According to the present invention, there is provided a method for regenerating a cathode active material having excellent efficiency, life characteristics, and resistance characteristics by adding calcium or a calcium compound to the cathode active material recovered after heat treatment and then re-heating the material, and a regenerated cathode active material manufactured from the method.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority from Korean Patent Application Nos. 10-2023-0137425 and 10-2023-0137423, both filed on October 16, 2023, and Korean Patent Application No. 10-2024-0138681, which was refiled on October 11, 2024 based on these applications, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a cathode active material and a regenerated cathode active material manufactured therefrom. More specifically, the present invention relates to a method for regenerating a cathode active material, which involves heat-treating a waste cathode including a current collector and a cathode active material layer coated on the current collector to recover the cathode active material, and then adding calcium or a calcium compound to the recovered cathode active material and re-heat-treating it, or pre-washing the recovered cathode active material and then adding a lithium precursor and calcium or a calcium compound to the recovered cathode active material and annealing it. The method provides excellent secondary battery efficiency, lifespan characteristics, and resistance characteristics. The recovery and regeneration processes are environmentally friendly because no acid is used, and the associated neutralization and wastewater treatment are unnecessary, reducing process costs. The cathode active material is regenerated directly without decomposition, so no metal elements are discarded. Furthermore, no organic solvents are used, so there is no risk of toxic gas generation or explosion. This significantly improves 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 disadvantages of causing environmental pollution, requiring a neutralization process and a wastewater treatment process, which significantly increases the process cost, and not being able to recover lithium, the main metal in the positive electrode active material.

[0007] To overcome these drawbacks, direct recycling methods have recently been studied to directly 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 safely and environmentally friendly regeneration of cathode active materials from waste cathodes, with fewer steps and fewer costs, that does not contain any discarded metal elements and has improved output performance. Summary of the Invention [Problem to be solved by the invention]

[0013] In order to solve the above-mentioned problems of the prior art, the present invention provides a method for recovering a cathode active material by heat-treating a used cathode including a current collector and a cathode active material layer coated on the current collector, and then adding calcium or a calcium compound to the recovered cathode active material and heat-treating it again, or pre-cleaning the recovered cathode active material and then adding a lithium precursor and calcium or a calcium compound to the recovered cathode active material and annealing it. The present invention also provides a method for recovering and regenerating a cathode active material that is environmentally friendly because it does not use an acid, 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 the risk of generating toxic gases or explosions, thereby significantly improving economy and productivity.

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

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

[0016] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, comprising: (i) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and thermally decomposing the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; and (ii) (ii-1) adding calcium or a calcium compound to the recovered positive electrode active material and re-heat-treating it at 600 to 750°C; or (ii-2) pre-washing the recovered positive electrode active material with a washing solution, and then adding a lithium precursor and calcium or a calcium compound and annealing it.

[0017] II) In I), the calcium compound may preferably be one or more of Ca(OH)2, CaO, and Ca(NO3)2, more preferably one or more of Ca(OH)2 and Ca(NO3)2, and even more preferably Ca(OH)2.

[0018] III) In the step (ii-1) of the step I) or II), calcium or a calcium compound may be added in an amount corresponding to 0.03 to 0.4 moles (calcium metal basis) per mole of the F component present in the positive electrode active material recovered after the heat treatment in the step (i).

[0019] IV) In the above I) to III), in step (i), the heat treatment may be preferably carried out at 300 to 650° C. for 10 minutes to 10 hours.

[0020] V) In the above I) to IV), the reheat treatment in the step (ii) may be preferably carried out for 5 to 15 hours.

[0021] VI) In the above I) to V), in the step (ii-2), calcium or a calcium compound may be added preferably in an amount corresponding to 50 to 1200 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

[0022] VII) In the above I) to VI), in the step (ii-2), the annealing may preferably include a first annealing step of adding a lithium precursor to the pre-washed positive electrode active material and annealing the material, and a second annealing step of adding calcium or a calcium compound after the first annealing and annealing the material.

[0023] VIII) In the above I) to VII), in the step (ii-2), annealing may be preferably carried out at a temperature of 270 to 1000°C.

[0024] IX) In the above I) to VIII), in the step (ii-2), the washing liquid may preferably be water or a basic aqueous solution of a lithium compound.

[0025] X) In the above I) to IX), in the step (ii-2), the pre-washing may preferably include a step of stirring the recovered positive electrode active material together with a washing liquid, followed by filtering.

[0026] XI) In the above I) to X), the positive electrode active material subjected to the step (ii-2) may preferably contain 50 to 1200 ppm of calcium.

[0027] XII) In the above I) to XI), the heat treatment in the step (i) and the reheat treatment and / or annealing in the step (ii) may be preferably carried out in an air or oxygen atmosphere.

[0028] XIII) In I) to XII), the positive electrode active material may preferably include at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co).

[0029] XIV) In the above I) to XIII), the method for regenerating a positive electrode active material may preferably include (iii) a step of washing the positive electrode active material reheat-treated in the step (ii-1) with a washing liquid.

[0030] XV) In the above I) to XIV), the method for regenerating the positive electrode active material may preferably include (iv) a step of adding a lithium precursor to the positive electrode active material reheat-treated in the above step (ii-1), and annealing the material.

[0031] XVI) In the above I) to XV), the lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0032] XVII) In the above I) to XVI), the lithium precursor in the annealing step (iv) may be added in an amount that is reduced from at least the molar ratio of lithium in the positive electrode active material in step (ii-1), based on the amount of lithium in the positive electrode active material in the raw materials.

[0033] XVIII) In the above I) to XVII), in the step (iv), annealing may be carried out preferably at 400 to 1000°C.

[0034] XIX) In the above I) to XVIII), the lithium precursor in the step (ii-2) may be added preferably in an amount that is at least reduced from the molar ratio of lithium in the positive electrode active material in the step (i), based on the amount of lithium in the positive electrode active material that has been pre-washed.

[0035] XX) In the above I) to XIX), the method for regenerating a positive electrode active material may preferably include a step of post-cleaning the positive electrode active material annealed in the step (ii-2) with a cleaning solution.

[0036] XXI) In the above I) to XX), the method for regenerating a positive electrode active material may preferably include a step of surface-coating the annealed positive electrode active material.

[0037] Further, XXII) the present invention provides a positive electrode active material, which 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, and which contains CaF2 or 50 to 1200 ppm of calcium, and has a residual F content of 2000 ppm or less.

[0038] XXIII) In the above XXII), the surface of the positive electrode active material may preferably be coated with a coating agent containing metal or carbon.

[0039] XXIV) In the above XXII) or XXIII), the metal may preferably be boron (B), tungsten (W), or a mixture thereof.

[0040] XXV) In the above XXII) to XXIV), the positive electrode active material may preferably be a recycled positive electrode active material. [Effects of the Invention]

[0041] According to the present invention, a used cathode including a current collector and a cathode active material layer coated on the current collector is heat-treated to recover the cathode active material, and the recovered cathode active material is then added with calcium or a calcium compound and heat-treated again, or the recovered cathode active material is pre-washed and then added with a lithium precursor and calcium or a calcium compound and annealed to provide a cathode active material with excellent efficiency, lifespan characteristics, and resistance characteristics. Furthermore, the cathode active material recovery and regeneration process is environmentally friendly because no acid is used, and the associated neutralization and wastewater treatment are not required, reducing process costs. The cathode active material is regenerated directly without decomposition, so no metal elements are discarded. Furthermore, no organic solvent is used, so there is no risk of toxic gas generation or explosion. This provides a method for regenerating a cathode active material with significantly improved economy and productivity.

[0042] 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. [Brief explanation of the drawings]

[0043] [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 flowchart illustrating a process for regenerating a positive electrode active material according to one embodiment of the present invention. [Figure 3] 1 is a graph showing the evaluation results of the initial capacity for each of the regenerated positive electrode active materials produced in Examples 1 to 4 and Comparative Examples 1 and 2. [Figure 4] 1 is a graph showing the results of coin cell evaluation of each of the recycled positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 and 2, showing the change in capacity retention and DCIR depending on the number of cycles. [Figure 5] 10 is a flowchart illustrating a process for regenerating a positive electrode active material according to another embodiment of the present invention. [Figure 6] 1 is a graph showing the results of coin half-cell evaluation of each of the regenerated or virgin positive electrode active materials manufactured or prepared in Additional Examples 1 and 2, Additional Comparative Example 1, and Additional Reference Example, illustrating the change in capacity retention rate depending on the number of cycles. [Figure 7] 1 is a graph showing the results of coin half-cell evaluation of each of the regenerated or newly produced positive electrode active materials manufactured or prepared in Additional Examples 2 to 4 and Additional Reference Examples, showing the change in capacity retention rate depending on the number of cycles. [Figure 8]1 is a graph showing the results of coin half-cell evaluation of regenerated or virgin positive electrode active materials manufactured or prepared in Additional Examples 1 and 5 and Additional Reference Examples, illustrating the change in capacity retention rate depending on the number of cycles. [Figure 9] 1 is a graph showing the results of coin half-cell evaluation of each of the regenerated or newly produced positive electrode active materials manufactured or prepared in Additional Examples 1, 6 to 9 and Additional Reference Examples, showing the change in capacity retention rate depending on the number of cycles. [Figure 10] 10 is a graph showing the results of coin half-cell evaluation of each of the regenerated or virgin positive electrode active materials manufactured or prepared in Additional Example 10, Additional Comparative Example 1, and Additional Reference Example, illustrating the change in capacity retention rate depending on the number of cycles. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present inventors have been researching a direct recycling method for recycling used cathodes into cathode active materials with excellent battery performance without decomposing the cathode active material. They discovered that the efficiency, lifespan, and resistance characteristics of secondary batteries can be improved by either heat-treating used cathodes including a current collector and a cathode active material layer coated on the current collector to recover the cathode active material, adding calcium or a calcium compound to the recovered cathode active material, and then heat-treating it again, or by pre-washing the recovered cathode active material and then adding a lithium precursor and calcium or a calcium compound to the recovered cathode active material and annealing it. Based on this, the inventors continued their research and completed the present invention.

[0045] The regeneration method for the positive electrode active material according to the present invention will be described in detail below, step by step.

[0046] However, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely examples of the present invention and do not represent the entire technical idea of ​​the present invention, and that various equivalents and modifications that can be substituted for them may exist, and that they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0047] 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.

[0048] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention includes the steps of: (i) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and thermally decomposing the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer, and recovering the positive electrode active material in the positive electrode active material layer; (ii) (ii-1) adding calcium or a calcium compound to the recovered positive electrode active material and re-heat-treating it at 600 to 750°C; or (ii-2) pre-washing the recovered positive electrode active material with a washing solution, and then adding a lithium precursor and calcium or a calcium compound and annealing it; In this case, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics. It is environmentally friendly because no additional acid is used, and process costs are reduced because neutralization and wastewater treatment are not required. The cathode active material is regenerated as it is without decomposition, so there are no metal elements to be discarded. The current collector is not dissolved, so it can be recovered. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. The process uses easy-to-manage processes such as heat treatment and sedimentation, so it is suitable for mass production. The cathode active material regenerated from this process has the advantages of excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0049] Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0050] (i) Recovering a positive electrode active material from a waste positive electrode The method for regenerating a positive electrode active material according to the present invention may include (a) recovering a positive electrode active material from a used positive electrode, and preferably includes heat-treating a used positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer. In this case, the process is simple and has the effect of neatly removing the binder, conductive material, and current collector.

[0051] 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.

[0052] The positive electrode active material layer in step (i) may preferably include a positive electrode active material, a binder, and a conductive material.

[0053] The positive electrode active material is preferably a lithium cobalt oxide such as LiCoO2 (hereinafter referred to as "LCO"); a lithium manganese oxide such as LiMnO2 or LiMn2O4; a lithium iron phosphate compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); a lithium nickel oxide such as LiNiO2; a nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and an NCM-based lithium composite transition metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co). It may be at least one selected from the group consisting of, more preferably, a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0054] 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 contains at least one 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.

[0055] As an example, based on 100 mol% of the total of the metals excluding lithium (Li), the positive electrode active material contains nickel (Ni) at 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, still more preferably 81 to 95 mol%, and even more preferably 85 to 95 mol%. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0056] In the present description, the nickel content may be 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, without any particular limitation. For example, the nickel content may be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectroscopy) analyzer, or an IC-ICP-AES (Atomic Emission Spectroscopy) analyzer.

[0057] 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.

[0058] 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.

[0059] For example, the heat treatment may be performed in an air or 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. The separated positive electrode active material has an advantage that it can be easily sorted in a powder form.

[0060] For example, the purity of the oxygen atmosphere may be 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%. Within this range, there is an advantage that the binder and conductive material are removed without remaining.

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

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

[0063] The heat treatment temperature may be, for example, 300 to 650°C, 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.

[0064] The heat treatment time may be, for example, 10 minutes to 10 hours, preferably 30 minutes to 7 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 3 hours, still more preferably 1 hour to 3 hours, and particularly preferably 2 hours to 3 hours. Within this range, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0065] 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.

[0066] 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.

[0067] Figure 1 below shows the cathode scrap that is discarded after cutting the cathode plates from the cathode sheet.

[0068] 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.

[0069] In addition, the positive electrode active material layer 20 is formed by coating a slurry containing a positive electrode active material, a conductive material, a binder, a solvent, etc., on the aluminum foil 10. Since the slurry is very sensitive to environmental factors such as temperature, it is very difficult to determine the coating conditions. Therefore, a considerable amount of waste positive electrode sheets is generated until the conditions for manufacturing a positive electrode sheet 30 of desired quality are found through predetermined tests.

[0070] For reference, in the following examples, scrap positive electrodes were used as waste positive electrodes.

[0071] (ii) Step (ii-1) of adding calcium or a calcium compound to the recovered positive electrode active material and reheating it at 600 to 750 ° C., or Step (ii-2) of pre-cleaning the recovered positive electrode active material with a cleaning solution, then adding a lithium precursor and calcium or a calcium compound and annealing it. The method for regenerating a positive electrode active material according to the present invention may include (ii) a step (ii-1) of adding calcium or a calcium compound to the recovered positive electrode active material and reheating it at 600 to 750°C, or a step (ii-2) of pre-washing the recovered positive electrode active material with a washing solution, then adding a lithium precursor and calcium or a calcium compound, and annealing the material. In this case, a positive electrode active material having excellent efficiency, life characteristics, and resistance characteristics can be provided.

[0072] In this description, a pre-clean refers to a wash performed before annealing, and a post-clean refers to a wash performed after annealing.

[0073] (ii-1) adding calcium or a calcium compound to the recovered positive electrode active material and reheating it at 600 to 750°C The step (ii-1) of re-heat-treating the recovered positive electrode active material may preferably be a step of adding calcium or a calcium compound to the recovered positive electrode active material and re-heat-treating it at 600 to 750°C. In this case, it is possible to provide a positive electrode active material having excellent efficiency, life characteristics, and resistance characteristics.

[0074] The calcium compound is a compound capable of providing calcium metal, and may be, for example, one or more of Ca(OH)2, CaO, and Ca(NO3)2, preferably Ca(OH)2, Ca(NO3)2, or a mixture thereof, and more preferably Ca(OH)2. In this case, there is an effect of providing a positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics, and in the case of Ca(OH)2, there is an advantage that residual fluorine (F) is further reduced.

[0075] During the heat treatment in step (i), the binder and conductive material in the positive electrode active material layer are vaporized and removed as CO2 and HO. During this process, CO2 and HO may react with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH. Fluorine (F) present in binders such as PVdF may react with metal elements that make up the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, battery performance will deteriorate when the positive electrode active material is reused.

[0076] In the re-heat treatment step (ii-1), preferably, calcium or a calcium compound is added and re-heat treatment is performed. This allows LiF or metal fluoride present in the positive electrode active material to react with calcium and be converted into a lithium compound and CaF2. The lithium compound serves as a lithium precursor in subsequent processes, and the CaF2 is contained in the positive electrode active material, which has the advantage of improving efficiency, life characteristics, and resistance characteristics.

[0077] In the reheat treatment step, when Ca(OH)2 is used as the calcium compound, the reaction process is as shown in the following chemical formula 2.

[0078] (Chemical formula 2) 2LiF+Ca(OH)2 → 2LiOH+CaF2

[0079] In Formula 2, LiOH produced after the re-heat treatment serves as a lithium precursor in the subsequent step of adding a lithium precursor and annealing, thereby advantageously reducing the amount of lithium precursor added in the annealing step.

[0080] In addition, in Chemical Formula 2, CaF2 produced after the reheat treatment has the advantage of being contained in the positive electrode active material, which improves efficiency, life characteristics, and resistance characteristics.

[0081] The calcium or calcium compound can be added in an amount corresponding to, for example, 0.03 to 0.4 moles (calcium metal basis) per mole of F component present in the positive electrode active material recovered after the heat treatment in step (i). The amount may be preferably 0.04 to 0.3 moles, more preferably 0.05 to 0.25 moles, even more preferably 0.07 to 0.23 moles, even more preferably 0.07 to 0.20 moles, and particularly preferably 0.10 to 0.15 moles. Within this range, LiF or metal fluoride is sufficiently converted to CaF and a lithium compound, which has the advantage of providing the positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0082] The reheat treatment in the step (ii-1) can be carried out, for example, at 600 to 750°C, preferably 630 to 730°C, and more preferably 670 to 730°C. This temperature range has the advantage that the reaction with LiF or metal fluoride proceeds smoothly.

[0083] The reheat treatment temperature in the step (ii-1) may preferably be higher than the heat treatment temperature in the step (i). In this case, there is an advantage that calcium or a calcium compound can easily react with LiF or a metal fluoride produced in the positive electrode active material.

[0084] The reheat treatment in step (ii-1) may be carried out for, for example, 5 to 15 hours, preferably 6 to 13 hours, more preferably 7 to 12 hours, and even more preferably 8 to 12 hours. Within this range, LiF or metal fluoride is sufficiently converted into CaF and a lithium compound, which has the advantage of providing the positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0085] The reheat treatment in step (ii-1) can be carried out, for example, in an air or oxygen atmosphere, preferably in air, which has the advantage that LiF or metal fluorides are sufficiently converted into CaF and lithium compounds.

[0086] The positive electrode active material after the re-heat treatment in step (ii-1) may contain, for example, 0.03 to 0.4 mol of CaF, preferably 0.04 to 0.3 mol, more preferably 0.05 to 0.25 mol, even more preferably 0.07 to 0.23 mol, still more preferably 0.07 to 0.20 mol, and particularly preferably 0.10 to 0.15 mol, per 1 mol of the F component (based on elemental F) measured in the positive electrode active material recovered after the heat treatment in step (i). Within this range, the secondary battery has the advantage of being excellent in efficiency, life characteristics, and resistance characteristics.

[0087] In the present description, the contents of F component and CaF2 are not particularly limited as long as they are measured by a measurement method using IC (Ion Chromatography) or the like commonly used in the technical field to which the present invention pertains. For example, they can be measured using XRD analysis or ICP analysis. Specifically, they can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectroscopy) analyzer, or an IC-ICP-AES (Atomic Emission Spectroscopy) analyzer.

[0088] (ii-2) A step of pre-washing the recovered positive electrode active material with a washing solution, then adding a lithium precursor and calcium or a calcium compound, and annealing the material. The method for regenerating a cathode active material of the present invention may include (ii-2) pre-washing the recovered cathode active material with a washing solution, followed by adding a lithium precursor and calcium or a calcium compound, and annealing the recovered cathode active material. In this case, metal fluorides such as LiF that may be present on the surface of the regenerated cathode active material are removed through washing, and the surface is modified to improve the rate performance of the battery. Annealing improves the crystallinity by increasing the crystallinity or restoring the crystal structure, and the calcium component provides a cathode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0089] During the heat treatment in step (i), the binder and conductive material in the positive electrode active material layer are vaporized and removed as CO2 and HO. During this process, CO2 and HO may react with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH, and fluorine (F) present in binders such as PVdF may react with metal elements that make up the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, the battery performance will deteriorate when the positive electrode active material is reused.

[0090] The cleaning solution for the pre-cleaning step may be, for example, water or a basic lithium compound aqueous solution, preferably water. In this case, the F component remaining on the surface of the regenerated positive electrode active material can be completely removed with a small amount of cleaning solution, which has the effect of significantly reducing wastewater generation and significantly improving the output performance of the battery.

[0091] The water may be preferably distilled water or deionized water, and more preferably distilled water. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby providing an excellent effect of modifying the surface.

[0092] The basic lithium compound aqueous solution preferably contains more than 0% by weight and not more than 15% by weight of lithium compound, and more preferably more than 0% by weight and not more than 10% by weight of lithium compound. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby modifying the surface. This solution also has the advantage of not dissolving transition metals present in the positive electrode active material, but also replenishing lithium that may be dissolved during the cleaning process. If the amount of lithium compound exceeds this range, excessive LiOH may remain on the surface of the positive electrode active material even after cleaning, which may adversely affect the subsequent annealing process.

[0093] The lithium compound may be, for example, LiOH, LiNO3, or a mixture thereof, and preferably LiOH. In this case, there is an effect of removing fluorine (F) from the surface of the positive electrode active material and lithium precursors that have not been involved in the reaction.

[0094] The pre-cleaning may preferably include a step of stirring the recovered positive electrode active material with a cleaning solution, followed by filtering, and more preferably a step of stirring the recovered positive electrode active material with a cleaning solution, followed by filtering, and a step of adding a rinse solution to the filtered positive electrode active material to rinse. In this case, the residual F component can be easily removed, while improving the output performance of the battery. Furthermore, the total amount of the cleaning solution, which is the combination of the cleaning solution and the rinse solution, can be reduced, which has the advantages of reducing the amount of wastewater, wastewater treatment costs, and environmental pollution.

[0095] In this description, the rinsing liquid may follow the definition used in the technical field to which the present invention belongs, and is the same as the cleaning liquid unless otherwise defined.

[0096] The mass ratio of the recovered positive electrode active material to the cleaning solution may be, for example, 1:1 to 1:30, preferably 1:1 to 1:20, more preferably 1:3 to 1:15, and even more preferably 1:5 to 1:12. Within this range, metal fluorides such as LiF are effectively removed, which is advantageous in improving battery performance.

[0097] The agitator may be, for example, an impeller type, a magnetic type, and / or an ultrasonic agitator, but is not particularly limited thereto.

[0098] The stirring can be carried out at, for example, 200 to 1000 rpm, preferably 300 to 800 rpm, and more preferably 400 to 700 rpm, and within this range, there is an advantage that metal fluorides are effectively removed.

[0099] The stirring can be carried out for, for example, 3 to 20 minutes, preferably 5 to 15 minutes, and more preferably 7 to 12 minutes, and within this range, there is an advantage that metal fluorides are effectively removed.

[0100] The filtration can be carried out, for example, by vacuum filtration using a filter or by using a filter press.

[0101] The mass ratio of the recovered positive electrode active material to the rinse solution may be, for example, 1:1 to 1:30, preferably 1:1 to 1:20, more preferably 1:3 to 1:15, and even more preferably 1:5 to 1:12. Within this range, metal fluorides such as LiF are effectively removed, which is advantageous in improving battery performance.

[0102] The pre-cleaning step may preferably include a step of recovering the solid cathode active material after the filtering or rinsing step and drying the recovered solid cathode active material. In this case, there is an advantage in that the subsequent annealing step is optimized and facilitated.

[0103] The drying can be carried out at preferably 50 to 200°C, more preferably 50 to 150°C, even more preferably 70 to 150°C, and even more preferably 100 to 150°C until there is no further change in mass, for example, for 1 to 24 hours. This range has the advantage of efficiently removing moisture contained in the washed positive electrode active material.

[0104] The calcium compound may be, for example, one or more of Ca(OH)2, CaO, and Ca(NO3)2, preferably Ca(OH)2, Ca(NO3)2, or a mixture thereof, and more preferably Ca(OH)2. In this case, there is an effect of providing a positive electrode active material excellent in efficiency, life characteristics, and resistance characteristics.

[0105] The calcium compound can be added in an amount corresponding to 50 to 1200 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material, for example, preferably 100 to 1000 ppm (calcium metal basis), more preferably 200 to 800 ppm (calcium metal basis), even more preferably 300 to 700 ppm (calcium metal basis), and even more preferably 330 to 650 ppm (calcium metal basis). Within this range, there is an advantage that a positive electrode active material excellent in efficiency, life characteristics, and resistance characteristics can be provided.

[0106] In this description, % and ppm are by weight unless otherwise specified.

[0107] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0108] The lithium precursor is preferably added based on the amount of lithium in the recovered positive electrode active material, at least the amount of lithium in the positive electrode active material pre-washed in step (ii-2) can be reduced by the amount of lithium. For example, when the positive electrode active material recovered in step (ii-2) 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 1 of 0.0001 to 0.2, preferably 0.001 to 0.2, more preferably 0.005 to 0.19, even more preferably 0.01 to 0.18, even more preferably 0.05 to 0.17, and most preferably 0.09 to 0.16. Within this range, the battery characteristics of the recycled positive electrode active material can be improved by improving crystallinity, such as increasing crystallinity or restoring the crystal structure.

[0109] As another example, when the total amount of lithium contained in the raw material positive electrode active material is taken as 100 mol%, the lithium precursor may be added in an amount corresponding to, for example, 1 to 40 mol%, preferably 1 to 30 mol%, more preferably 1 to 25 mol%, even more preferably 5 to 20 mol%, and even more preferably 7 to 11 mol%. Within this range, no residual precursor that could 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.

[0110] The annealing in step (ii-2) may preferably involve adding a lithium precursor and calcium or a calcium compound to the pre-cleaned cathode active material and annealing the resulting material, or may involve a first annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealing the resulting material, followed by a second annealing step in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealing the resulting material, or a first annealing step in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealing the resulting material, followed by a second annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealing the resulting material, followed by a second annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealing the resulting material, which may improve crystallinity by increasing crystallinity or restoring the crystal structure, and may also provide a cathode active material with excellent efficiency, life, and resistance characteristics due to the calcium component.

[0111] The annealing step (ii-2) may preferably be a step of adding a lithium precursor and calcium or a calcium compound to the washed cathode active material, and annealing the material in oxygen (O2) or air at 270 to 1000°C, more preferably 400 to 1000°C, even more preferably 600 to 900°C, even more preferably 650 to 800°C, and particularly preferably 670 to 750°C. In this case, the crystallinity of the cathode active material is improved, for example, by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated cathode active material.

[0112] The annealing temperature can be adjusted within a limited range depending on the melting points of the lithium precursor and calcium or calcium compound. For example, in the case of LiCO3, the melting point is 723°C, so annealing is preferably performed at 700 to 900°C, more preferably 710 to 780°C. In the case of LiOH, the melting point is 462°C, so annealing is preferably performed at 400 to 800°C, more preferably 500 to 700°C. In the case of Ca(OH)2, the melting point is 580°C, so annealing is preferably performed at 400 to 800°C, more preferably 450 to 750°C, even more preferably 470 to 720°C, and even more preferably 500 to 700°C. Within these temperature ranges, the crystal structure is restored, resulting in excellent battery output performance.

[0113] The annealing temperature may preferably be a temperature exceeding the melting points of the lithium precursor and calcium or calcium compound. 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.

[0114] In the step (ii-2), when the annealing is performed in a first annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealed, and a second annealing step in which calcium or a calcium compound is added after the first annealing, the annealing temperatures in the first annealing step and the second annealing step may be set to be the same or different. Preferably, the annealing temperature in the first annealing step may be set to be equal to or higher than the melting point of the lithium precursor, and the annealing temperature in the second annealing step may be set to be equal to or higher than the melting point of the lithium precursor. The annealing temperature may be equal to or higher than the melting point of calcium or the calcium compound. More preferably, the primary annealing is performed at 450 to 900°C, even more preferably 550 to 800°C, and even more preferably 650 to 750°C. The secondary annealing is performed at 270 to 850°C, even more preferably 400 to 800°C, even more preferably 450 to 750°C, particularly preferably 470 to 720°C, and especially preferably 500 to 700°C. Within these temperature ranges, the crystal structure of the regenerated positive electrode active material is restored, and the calcium component has the effect of improving efficiency, life characteristics, and resistance characteristics.

[0115] In the (ii-2) step, when the annealing is performed in a first annealing step in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealed, and a second annealing step in which a lithium precursor is added after the first annealing step and annealed, the annealing temperatures in the first annealing step and the second annealing step may be set to be the same or different. Preferably, the first annealing step may be performed at a temperature equal to or higher than the melting point of calcium or a calcium compound, and the second annealing step may be performed at a temperature equal to or higher than the melting point of calcium or a calcium compound. The annealing can be carried out at a temperature above the melting point of the lithium precursor, with the first annealing being preferably carried out at 270 to 850°C, even more preferably 400 to 800°C, even more preferably 450 to 750°C, particularly preferably 470 to 720°C, and even more preferably 500 to 700°C, and the second annealing being preferably carried out at 450 to 900°C, even more preferably 550 to 800°C, and even more preferably 650 to 750°C. Within these temperature ranges, the crystal structure of the regenerated positive electrode active material is restored, and the calcium component has the effect of improving efficiency, life characteristics, and resistance characteristics.

[0116] When the lithium precursor, calcium, or calcium compound is added and annealed, the annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 3 to 13 hours, even more preferably 5 to 13 hours, and even more preferably 7 to 11 hours. Within this range, the crystal structure is sufficiently restored, and the calcium component has the advantage of improving efficiency, life characteristics, and resistance characteristics.

[0117] When the lithium precursor is introduced and annealed for the first annealing, followed by introduction of calcium or a calcium compound for the second annealing, the first annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 3 to 13 hours, even more preferably 5 to 13 hours, and even more preferably 7 to 12 hours. The second annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 3 to 13 hours, even more preferably 5 to 13 hours, and even more preferably 7 to 12 hours. Within these ranges, the crystal structure is sufficiently restored, and the calcium component has the advantage of improving efficiency, life characteristics, and resistance characteristics.

[0118] When the calcium or calcium compound is added and a first annealing is performed, and then a lithium precursor is added and a second annealing is performed, the first annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 3 to 13 hours, even more preferably 5 to 13 hours, and even more preferably 7 to 12 hours. The second annealing time may be, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 3 to 13 hours, even more preferably 5 to 13 hours, and even more preferably 7 to 12 hours. Within these ranges, the crystal structure is sufficiently restored, and the calcium component has the advantage of improving efficiency, life characteristics, and resistance characteristics.

[0119] The annealing temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, more preferably at a temperature rise rate of 1 to 5°C / min, and even more preferably at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0120] The annealing step may, for example, include a cooling process, which may be natural cooling in a furnace, for example. In this case, the crystallinity of the recycled positive electrode active material may be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0121] The cooling step can be performed, for example, by cooling to 130°C or less, preferably 110°C or less, and more preferably 20 to 110°C. Within this range, the crystallinity of the recycled positive electrode active material can be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0122] For example, the annealing step may include a first annealing step, a cooling process, and then a second annealing step. In this case, the crystalline structure of the regenerated positive electrode active material is restored, resulting in excellent efficiency, life characteristics, and resistance characteristics.

[0123] In this description, annealing may follow the definition used in the technical field to which the present invention belongs. Specifically, annealing may be defined as a heat treatment operation in which a positive electrode active material having a deformed structure or lattice defects is heated for an appropriate time at a temperature at or above the recrystallization temperature at which atoms of the main component in the positive electrode active material can sufficiently diffuse and move, thereby healing the deformation or lattice defects and increasing crystallinity.

[0124] The annealed positive electrode active material may contain, for example, calcium in an amount of 50 to 1200 ppm, preferably 100 to 1000 ppm, more preferably 150 to 800 ppm, even more preferably 200 to 800 ppm, still more preferably 300 to 700 ppm, particularly preferably 330 to 700 ppm, and particularly preferably 330 to 650 ppm. Within these ranges, there are advantages such as excellent efficiency, life characteristics, and resistance characteristics.

[0125] In the present description, the calcium content can be measured by a method using IC (Ion Chromatography), which is commonly used in the technical field to which the present invention pertains, without particular limitation. Specific examples include an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectroscopy) analyzer, or an IC-ICP-AES (Atomic Emission Spectroscopy) analyzer. In the present description, IC-ICP (Inductively Coupled Plasma) can be used preferentially.

[0126] (iii) A step of pre-cleaning the reheat-treated positive electrode active material (surface modification step) The method for regenerating a positive electrode active material of the present invention includes (iii) a step of pre-cleaning the reheat-treated positive electrode active material. In this step, residual F components and residual Li compounds that have not reacted with calcium or calcium compounds and that may be present on the surface of the regenerated positive electrode active material are removed, and the surface is modified, thereby improving the rate performance of the battery.

[0127] The washing solution used in the washing step may be, for example, water or a basic aqueous solution of a lithium compound, preferably water. In this case, the F component and Li compound remaining on the surface of the reheat-treated cathode active material are completely removed, thereby significantly reducing the generation of wastewater and significantly improving the output performance of the battery.

[0128] The water may be preferably distilled water or deionized water, and more preferably distilled water. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby providing an excellent effect of modifying the surface.

[0129] The basic lithium compound aqueous solution preferably contains more than 0% by weight and not more than 15% by weight of lithium compound, and more preferably more than 0% by weight and not more than 10% by weight of lithium compound. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby modifying the surface. This solution also has the advantage of not dissolving transition metals present in the positive electrode active material, but also replenishing lithium that may dissolve during the cleaning process. If the amount of lithium compound exceeds this range, excessive LiOH may remain on the surface of the active material even after cleaning, which may affect the subsequent annealing process.

[0130] The lithium compound may be, for example, LiOH, LiNO3, or a mixture thereof, and preferably LiOH. In this case, there is an effect of removing fluorine (F) from the surface of the positive electrode active material and lithium precursors that have not been involved in the reaction.

[0131] The pre-cleaning step may preferably include a step of stirring the reheat-treated cathode active material with a cleaning solution, followed by filtering, and more preferably a step of stirring the reheat-treated cathode active material with a cleaning solution, followed by filtering, and a step of adding a rinse solution to the filtered cathode active material to rinse. In this case, residual F components and residual Li compounds that have not reacted with calcium or calcium compounds can be easily removed, while improving the output performance of the battery. Furthermore, the total amount of cleaning solution, which is the combination of the cleaning solution and the rinse solution, can be reduced, which has the advantages of reducing the amount of wastewater, wastewater treatment costs, and environmental pollution.

[0132] The mass ratio of the reheat-treated positive electrode active material to the cleaning solution may be, for example, 1:1 to 1:30, preferably 1:1 to 1:20, more preferably 1:3 to 1:15, and even more preferably 1:5 to 1:12. Within this range, there is an advantage that the F component and Li compound remaining on the surface of the positive electrode active material are effectively removed.

[0133] The agitator may be, for example, an impeller type, a magnetic type, and / or an ultrasonic agitator, but is not particularly limited thereto.

[0134] The stirring can be carried out at, for example, 200 to 1000 rpm, preferably 300 to 800 rpm, and more preferably 400 to 700 rpm, and within this range, there is an advantage that metal fluorides are effectively removed.

[0135] The stirring can be carried out for, for example, 3 to 20 minutes, preferably 5 to 15 minutes, and more preferably 7 to 12 minutes. Within this range, there is an advantage that the F component and Li compound remaining on the surface of the positive electrode active material are effectively removed.

[0136] The filtration can be carried out, for example, by vacuum filtration using a filter or by using a filter press.

[0137] The rinse solution may be, for example, water or a basic lithium compound aqueous solution, preferably water. In this case, the fluorine component and the Li compound remaining on the surface of the reheat-treated cathode active material are completely removed, thereby significantly reducing the generation of wastewater and significantly improving the output performance of the battery.

[0138] The mass ratio of the reheat-treated positive electrode active material to the rinse solution may be, for example, 1:1 to 1:30, preferably 1:1 to 1:20, more preferably 1:3 to 1:15, and even more preferably 1:5 to 1:12. Within this range, the F component and Li compound remaining on the surface of the reheat-treated positive electrode active material are effectively removed, thereby providing the advantage of improving battery performance.

[0139] The pre-cleaning step may preferably include recovering the solid cathode active material after the filtering or rinsing and drying the recovered solid cathode active material. In this case, there is an advantage in that the subsequent annealing step or surface coating step can be optimized and facilitated.

[0140] The drying can be carried out at preferably 50 to 200°C, more preferably 50 to 150°C, even more preferably 70 to 150°C, and even more preferably 100 to 150°C until there is no further change in mass, for example, for 1 to 24 hours. This range has the advantage of efficiently removing moisture contained in the washed positive electrode active material.

[0141] (iv) adding a lithium precursor to the washed positive electrode active material and annealing it; The method for regenerating a positive electrode active material of the present invention, for example, includes the step of (iv) adding a lithium precursor to a pre-washed positive electrode active material or a re-heat-treated positive electrode active material, followed by annealing. In this case, there is an advantage in providing a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0142] The annealing step (iv) may preferably be a step of adding a lithium precursor to the pre-cleaned cathode active material and annealing in oxygen (O2) or air at 400 to 1000°C, more preferably 600 to 900°C. In this case, the crystallinity of the cathode active material is improved, for example, by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated cathode active material.

[0143] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0144] The lithium precursor may be added preferably in an amount corresponding to at least the amount of lithium reduced from the amount of lithium in the cathode active material in step (ii-1) based on the amount of lithium contained in the raw cathode active material. Specifically, when the cathode active material reheat-treated in step (ii-1) is the cathode active material represented by Chemical Formula 1, the lithium precursor may be added in an amount that results in a molar ratio of lithium of, for example, 0.0001 to 0.2, preferably 0.001 to 0.2, relative to a molar ratio of lithium of 1 in the cathode active material. The amount of the lithium-containing compound to be added is preferably 0.005 to 0.19, more preferably 0.01 to 0.18, even more preferably 0.05 to 0.17, and most preferably 0.09 to 0.16. Within this range, the lithium that is insufficient in the regenerated positive electrode active material is replenished, and the crystallinity is improved by increasing the crystallinity and restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0145] As another example, the lithium precursor may be added in an amount corresponding to 1 to 40 mol %, preferably 1 to 30 mol %, and more preferably 7 to 20 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 could 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.

[0146] 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.

[0147] 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.

[0148] The annealing time is, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 2 to 10 hours, even more preferably 3 to 8 hours, and even more preferably 4 to 6 hours. As a specific example, it is preferably around 5 hours. Within this range, the crystal structure is sufficiently restored and there is an economic advantage.

[0149] The annealing temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, more preferably at a temperature rise rate of 1 to 5°C / min, and even more preferably at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0150] The annealing step may, for example, include a cooling process, which may be natural cooling in a furnace, for example. In this case, the crystallinity of the recycled positive electrode active material may be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0151] (v) post-cleaning the annealed positive electrode active material with a cleaning solution. The method for regenerating a positive electrode active material of the present invention may include (v) a step of post-cleaning the annealed positive electrode active material with a cleaning solution. In this case, the F component and / or lithium compound remaining on the surface of the positive electrode active material without being involved in the reaction after the addition of the lithium precursor is removed, thereby improving the battery characteristics.

[0152] The cleaning solution may be, for example, water, preferably distilled water or deionized water. In this case, by removing the F component and lithium compound that tend to remain on the surface of the positive electrode active material, wastewater treatment is not required and the output performance of the battery is significantly improved.

[0153] The post-washing step may be preferably carried out by mixing the annealed cathode active material with a washing solution and then filtering the mixture under reduced pressure or using a filter press. In this case, the F component and lithium compounds that tend to remain on the surface of the cathode active material are removed, thereby eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0154] In the latter-stage washing, the mass ratio of the positive electrode active material to the washing solution may be, for example, 1:1 to 1:5, preferably 1:1 to 1:3, and more preferably 1:1 to 1:2. By removing residual lithium compounds and calcium or calcium compounds that tend to remain on the surface of the positive electrode active material within this range, wastewater treatment is not required and the output performance of the battery is significantly improved.

[0155] The recycled cathode active material after the post-cleaning step may have a residual F content of, for example, 2000 ppm or less, preferably 1800 ppm or less, more preferably 1700 ppm or less, even more preferably 1600 ppm or less, even more preferably 1300 ppm or less, particularly preferably 1000 ppm or less, especially more preferably 700 ppm or less, most preferably 500 ppm or less, and even more preferably 300 ppm or less. In such cases, the battery output performance is improved, and the electrochemical performance, resistance characteristics, and capacity characteristics are excellent.

[0156] In this description, the content of residual F means the content of all F components present in not only LiF but also other residual components.

[0157] (vi) surface-coating the annealed or post-cleaned cathode active material to obtain a reusable cathode active material; The method for regenerating a positive electrode active material of the present invention optionally includes a step (vi) of surface-coating the annealed or post-cleaned 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.

[0158] 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.

[0159] 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.

[0160] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0161] 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.

[0162] The coating agent containing a carbon component is not particularly limited as long as it is a coating agent containing a carbon component that is commonly used in the technical field to which the present invention pertains, and a specific example thereof may be a sugar such as sucrose.

[0163] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol %, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and still more preferably 0.01 to 0.05 mol %, based on the components actually coated on the surface of the positive electrode active material excluding the solvent, relative to 100 mol % of the metal in the positive electrode active material before the coating treatment. Within this range, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] Regenerated cathode active material The regenerated cathode active material of the present invention is characterized by being produced by the above-described method for regenerating a cathode active material. In this case, it has the effect of improving the output performance of the battery and providing excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0171] In addition, the positive electrode active material of the present invention is at least one selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active materials, nickel cobalt manganese (NCM)-based positive electrode active materials, nickel cobalt aluminum (NCA)-based positive electrode active materials, and nickel cobalt manganese aluminum (NCMA)-based positive electrode active materials, and may contain CaF2. In this case, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics.

[0172] The positive electrode active material preferably contains 0.03 to 0.4 mol of CaF2 relative to 1 mol of the F component (based on elemental F) present in the positive electrode active material recovered after heat treatment, more preferably 0.04 to 0.3 mol, even more preferably 0.05 to 0.25 mol, still more preferably 0.07 to 0.20 mol, and particularly preferably 0.10 to 0.15 mol. Within these ranges, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics.

[0173] In addition, the recycled cathode active material is preferably 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 may contain 50 to 1200 ppm of calcium and 2000 ppm or less of residual F components. In this case, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics.

[0174] The regenerated positive electrode active material preferably contains calcium in an amount of 100 to 1000 ppm, more preferably 150 to 800 ppm, even more preferably 200 to 800 ppm, even more preferably 300 to 700 ppm, and particularly preferably 330 to 650 ppm. Within these ranges, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics.

[0175] The recycled positive electrode active material preferably has a residual F content of 2000 ppm or less, more preferably 1800 ppm or less, even more preferably 1700 ppm or less, still more preferably 1600 ppm or less, particularly preferably 1300 ppm or less, even particularly preferably 1000 ppm or less, and most preferably 700 ppm or less as an example, and may be 300 ppm or less as a more preferable example. In such cases, the output performance of the battery is improved, and there is an effect of being excellent in electrochemical performance, resistance characteristics, and capacity characteristics. In this description, the residual F content means the content of all F components in other residual components as well as LiF.

[0176] As an example, the positive electrode active material contains 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, even more preferably 81 to 95 mol%, and still more preferably 85 to 95 mol% of nickel (Ni) based on a total of 100 mol% of the remaining metals excluding lithium (Li). Within this range, there is an effect of being excellent in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0177] As still another specific example, the recycled 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 above Chemical Formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented thereby, and in this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] FIG. 2 below is a flowchart of a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0183] Referring to Figure 2, first, cathode scrap is 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 NMP (N-methyl pyrrolidone). The slurry is then coated on aluminum foil and dried in a vacuum oven at approximately 120°C to prepare a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] Next, the crushed 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 and conductive material in the positive electrode active material layer.

[0188] Through the heat treatment in air, the binder and conductive material in the positive electrode 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.

[0189] It is important that the heat treatment be performed in air or in the presence of oxygen. However, if the heat treatment is performed 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 cathode active material, which reduces 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, resulting in the complete removal of the binder and conductive material.

[0190] 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.

[0191] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and no thermal shock is caused to the cathode scrap.

[0192] 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 15 hours, and specifically for about 2 hours. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0193] 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.

[0194] After the heat treatment, the cathode active material may be cooled slowly or rapidly in the air. For example, the cathode active material may be recovered after being cooled to room temperature.

[0195] In this description, normal temperature may be a point within the range of 20±5°C.

[0196] For example, the recovered positive electrode active material may be pulverized through a sieve, preferably through a 270 to 400 mesh sieve, more preferably through a 300 to 350 mesh sieve. In this case, there is an advantage that the subsequent re-heat treatment step can be smoothly performed.

[0197] Next, calcium or a calcium compound is added to the recovered positive electrode active material, and the material is reheat-treated (step S40).

[0198] By performing the re-heat treatment, LiF or metal fluoride formed on the surface of the cathode active material in the heat treatment step (step S30) is converted into a lithium compound and CaF2 by adding calcium or a calcium compound, and the lithium compound serves as a lithium precursor in subsequent processes, and the CaF2 is contained in the cathode active material, which has the advantage of improving efficiency, life characteristics, and resistance characteristics.

[0199] The calcium compound may be, for example, one or more of Ca(OH)2, Ca(NO3)2, and CaO, and preferably one or more of Ca(OH)2 and Ca(NO3)2, for example, Ca(OH)2. In this case, there is an effect of providing a positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0200] The reheat treatment in step S40 can be performed at a temperature of 600 to 750°C, for example, at 700°C, which has the advantage that the reaction of calcium or a calcium compound with LiF or a metal fluoride can be carried out smoothly within this range.

[0201] The reheat treatment in step S40 can be carried out for, for example, 5 to 15 hours, and for example, for about 10 hours. Within this range, there is an advantage that the reaction of calcium or a calcium compound with LiF or a metal fluoride can be carried out smoothly.

[0202] The reheat treatment in step S40 can be carried out in an air or oxygen atmosphere, for example, which has the advantage that LiF or metal fluorides are sufficiently converted into CaF2 and lithium compounds.

[0203] Next, in a washing step (hereinafter also referred to as "pre-washing"), that is, a surface modification step, the re-heat-treated positive electrode active material is washed with a washing solution (step S50).

[0204] By performing the pre-cleaning step, foreign matter generated on the surface of the positive electrode active material in the re-heat treatment step (step S40) can be effectively removed.

[0205] The pre-washing step may preferably include stirring the reheat-treated cathode active material with a washing solution followed by filtering, and, for example, may include stirring the reheat-treated cathode active material with a washing solution followed by filtering, and rinsing the filtered cathode active material with a rinse solution. Here, the stirring may be performed using, but is not limited to, an impeller-type, magnetic-type, or ultrasonic stirrer. However, when the viscosity of the slurry is high or the amount of slurry is large, an impeller-type stirrer capable of transmitting a large force is preferred.

[0206] The cleaning solution is, for example, water or a basic lithium compound aqueous solution. If it is necessary to replenish the amount of lithium that may be eluted from the positive electrode active material during the cleaning process, the basic lithium compound aqueous solution is preferred.

[0207] The water may preferably be distilled or deionized water.

[0208] For example, the basic lithium compound aqueous solution contains more than 0 mass % and not more than 15 mass % of the basic lithium compound. If the basic lithium compound is not contained, it is difficult to replenish lithium. If the basic lithium compound aqueous solution contains more than 15 mass %, an excessive amount of lithium compound may remain on the surface of the positive electrode active material, which may adversely affect the subsequent annealing process.

[0209] The lithium compound may specifically be LiOH.

[0210] The cleaning liquid may be, for example, water, and may be used in an amount of 1 to 30 times the mass of the reheat-treated positive electrode active material, for example, 5 to 12 times, or about 10 times.

[0211] The stirring is carried out, for example, at 200 to 1000 rpm, preferably 400 to 600 rpm, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0212] The stirring is carried out for, for example, 3 to 20 minutes, preferably 5 to 15 minutes, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0213] The filtration can be carried out, for example, by vacuum filtration using a filter or by using a filter press.

[0214] The rinse liquid is, for example, water or a basic lithium compound aqueous solution, and may be, for example, water.

[0215] The amount of the rinse liquid may be preferably 1 to 30 times, for example, about 10 times the mass of the reheat-treated positive electrode active material.

[0216] After the rinsing, the solid content of the positive active material may be dried. For example, the solid content may be dried in an oven (convection type) at 50 to 150° C. in air or under vacuum.

[0217] The pre-cleaning step (step S50) removes residual F components and Li compounds that have not reacted with calcium or calcium compounds present on the surface of the regenerated cathode active material in the re-heat treatment step (step S40), and modifies the surface, thereby improving the efficiency, life characteristics, and resistance characteristics of the cathode active material.

[0218] Next, a lithium precursor is added to the pre-washed positive electrode active material or the re-heat-treated positive electrode active material, followed by annealing (step S60).

[0219] Because lithium loss occurs within the positive electrode active material during steps S30, S40, and S50, step S60 replenishes this lost lithium, allowing the positive electrode active material to contain calcium or a calcium compound. Furthermore, because a deformed structure (e.g., Co3O4 in the case of an LCO active material) may develop on the surface of the positive electrode active material during these steps, step S60 restores the crystalline structure of the positive electrode active material through annealing, thereby improving the battery performance 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 prepared for the first time, and is the same term as "raw material" used in the examples. Furthermore, the inclusion of calcium or a calcium compound in the positive electrode active material improves the life and resistance characteristics of the regenerated positive electrode active material.

[0220] The lithium precursor includes at least one of LiOH, Li2CO3, LiNO3, and Li2O, and LiOH is used as an example.

[0221] 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 positive electrode active material used in the positive electrode 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 positive electrode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0222] For example, based on a case where the molar ratio of lithium in the new positive electrode active material is 1 relative to the other metal (M), 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. As a specific example, 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. Here, the results of ICP analysis have an error of about ±0.02.

[0223] For example, the lithium precursor may be added in an amount corresponding to preferably 1 to 40 mol%, more preferably 1 to 30 mol%, even more preferably 1 to 25 mol%, even more preferably 5 to 20 mol%, and particularly preferably 7 to 11 mol%, when the total amount of lithium contained in the washed 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.

[0224] The annealing is carried out in air at a temperature of, for example, 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.

[0225] 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.

[0226] The annealing time is, for example, 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. A longer annealing time may allow for sufficient recovery of the crystal structure, but 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.

[0227] The annealing temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, specifically at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0228] Next, as a post-cleaning step, the annealed positive electrode active material is mixed with a cleaning solution, stirred, and then filtered (step S70).

[0229] The post-cleaning step S70 is a process for removing lithium compounds remaining in the positive electrode active material after annealing.

[0230] The latter cleaning step of step S70 is preferably performed in the same manner as the cleaning step (step S50) described above, except that a minimum amount of cleaning solution (for example, 1 to 2 times the mass of the positive electrode active material) is used and rinsing is not performed. Therefore, a description of the overlapping parts will be omitted.

[0231] Next, as an optional step, the post-cleaned positive electrode active material can be surface coated (step S80).

[0232] 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 a 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.

[0233] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a post-cleaned 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.

[0234] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0235] FIG. 5 below is a flowchart showing a process for regenerating a positive electrode active material according to another embodiment of the present invention.

[0236] Referring to Figure 5, 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.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] Next, the crushed 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 and conductive material in the positive electrode active material layer.

[0241] Through the heat treatment in air, the binder and conductive material in the positive electrode 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.

[0242] It is important that the heat treatment be performed in air or in the presence of oxygen. However, if the heat treatment is performed 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 cathode active material, which reduces 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, resulting in the complete removal of the binder and conductive material.

[0243] 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.

[0244] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and no thermal shock is caused to the cathode scrap.

[0245] 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.

[0246] 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.

[0247] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0248] Next, in a washing step (hereinafter also referred to as "pre-washing"), that is, a surface modification step, the recovered positive electrode active material is washed with a washing liquid (step S40).

[0249] The pre-cleaning step has the advantage of effectively removing foreign matter generated on the surface of the positive electrode active material during the heat treatment step (step S30).

[0250] The pre-washing step may preferably include a step of stirring the recovered cathode active material with a washing solution, followed by filtering, and, for example, a step of stirring the recovered cathode active material with a washing solution, followed by filtering, and a step of rinsing the filtered cathode active material by adding a rinse solution. Here, the stirring may be performed using, but is not limited to, an impeller-type, magnetic-type, or ultrasonic stirrer. However, when the viscosity of the slurry is high or the amount of the slurry is large, an impeller-type stirrer that can transmit a large force is preferred.

[0251] The cleaning solution is, for example, water or a basic lithium compound aqueous solution. If it is necessary to replenish the amount of lithium that may be eluted from the positive electrode active material during the cleaning process, the basic lithium compound aqueous solution is preferred.

[0252] The water may preferably be distilled or deionized water.

[0253] For example, the basic lithium compound aqueous solution contains more than 0 mass % and not more than 15 mass % of the basic lithium compound. If the basic lithium compound is not contained, it is difficult to replenish lithium. If the basic lithium compound aqueous solution contains more than 15 mass %, an excessive amount of lithium compound may remain on the surface of the positive electrode active material, which may adversely affect the subsequent annealing process.

[0254] The lithium compound may specifically be LiOH.

[0255] The washing liquid is used in an amount of 1 to 30 times the mass of the recovered positive electrode active material, for example, 5 to 12 times, or about 10 times.

[0256] The stirring is carried out, for example, at 200 to 1000 rpm, preferably 400 to 600 rpm, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0257] The stirring is carried out for, for example, 3 to 20 minutes, preferably 5 to 15 minutes, and within this range, a decrease in battery capacity due to excessive elution of lithium is prevented.

[0258] The filtration can be carried out, for example, by vacuum filtration using a filter or by using a filter press.

[0259] The amount of the rinse liquid may be preferably 5 to 20 times the mass of the recovered positive electrode active material, and may be, for example, about 10 times the mass.

[0260] After the rinsing, the solid content of the positive active material may be dried. For example, the solid content may be dried in an oven (convection type) at 50 to 150° C. in air or under vacuum.

[0261] The pre-cleaning step (step S40) removes LiCO, LiOH, etc., which are generated by reaction with lithium during the heat treatment step (step S30) when the binder and conductive material in the positive electrode active material layer are vaporized into CO and HO and removed, and LiF or metal fluorides, which are generated when F, which was present in a binder such as PVdF, reacts with lithium and other metal elements constituting the positive electrode active material, thereby preventing deterioration of battery characteristics when the positive electrode active material is reused.

[0262] Next, a lithium precursor and calcium or a calcium compound are added to the pre-washed positive electrode active material, and annealing is performed (step S50).

[0263] Because lithium loss occurs within the positive electrode active material during steps S30 and S40, step S50 replenishes this lost lithium, allowing the positive electrode active material to contain calcium or a calcium compound. Furthermore, because a deformed structure (e.g., Co3O4 in the case of an LCO active material) may develop on the surface of the positive electrode active material during these steps, step S50 restores the crystalline structure of the positive electrode active material through annealing, thereby improving the battery performance 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 prepared for the first time, and is the same term as "raw material" used in the examples. Furthermore, the inclusion of calcium or a calcium compound in the positive electrode active material improves the life and resistance characteristics of the regenerated positive electrode active material.

[0264] The lithium precursor includes at least one of LiOH, Li2CO3, LiNO3, and Li2O, and LiOH is used as an example.

[0265] 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 positive electrode active material used in the positive electrode 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 positive electrode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0266] For example, based on a case where the molar ratio of lithium in the new positive electrode active material is 1 relative to the other metal (M), 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. As a specific example, 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. Here, the results of ICP analysis have an error of about ±0.02.

[0267] For example, the lithium precursor may be added in an amount corresponding to preferably 1 to 40 mol%, more preferably 1 to 30 mol%, even more preferably 1 to 25 mol%, even more preferably 5 to 20 mol%, and particularly preferably 7 to 11 mol%, when the total amount of lithium contained in the washed 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.

[0268] The calcium compound may be, for example, one or more of Ca(OH)2, CaO, and Ca(NO3)2, and preferably Ca(OH)2. In this case, there is an advantage in that a positive electrode active material having excellent efficiency, life characteristics, and resistance characteristics is provided.

[0269] For example, the calcium compound can be added in an amount corresponding to 50 to 1200 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material, preferably an amount corresponding to 100 to 1000 ppm (calcium metal basis), more preferably an amount corresponding to 200 to 800 ppm (calcium metal basis), even more preferably an amount corresponding to 300 to 700 ppm (calcium metal basis), and even more preferably an amount corresponding to 330 to 650 ppm (calcium metal basis). Within this range, there is an advantage in providing a positive electrode active material excellent in efficiency, life characteristics, and resistance characteristics.

[0270] For example, the annealing in step S50 can be performed by adding a lithium precursor and calcium or a calcium compound to the pre-cleaned cathode active material and then annealing the material. In this case, the crystalline structure of the regenerated cathode active material is improved, and the contained calcium or calcium compound improves the life and resistance characteristics, which is a process advantage.

[0271] As another example, the annealing in step S50 may include a first annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealed, and a second annealing step in which calcium or a calcium compound is added after the first annealing and annealed. In this case, the crystalline structure of the regenerated cathode active material is improved, and the inclusion of calcium or a calcium compound in the cathode active material has the advantage of providing a cathode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0272] As another example, the annealing in step S50 may include a first annealing step in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealed, and a second annealing step in which a lithium precursor is added after the first annealing and annealed. In this case, the crystalline structure of the regenerated cathode active material is improved, and the inclusion of calcium or a calcium compound in the cathode active material provides a cathode active material with excellent efficiency, life characteristics, and resistance characteristics.

[0273] The annealing in step S50 may preferably be a step of adding a lithium precursor and calcium or a calcium compound to the washed cathode active material and annealing the material in oxygen (O2) or air at 270 to 1000°C, for example, around 700°C. In this case, the crystallinity of the cathode active material is improved, such as by increasing the crystallinity or restoring the crystal structure, and the cathode active material contains calcium or a calcium compound, which has the effect of improving the battery characteristics of the regenerated cathode active material.

[0274] The annealing temperature is preferably a temperature exceeding the melting points of the lithium precursor and calcium or calcium compound. 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 LiCO3 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. 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. When Ca(OH)2 is used as the calcium or calcium compound, the annealing temperature is preferably 550 to 800°C, more preferably 650 to 750°C, and even more preferably 670 to 720°C.

[0275] For example, the annealing in step S50 may be performed in two steps: a first annealing step in which a lithium precursor is added to the pre-cleaned cathode active material and annealed; and a second annealing step in which calcium or a calcium compound is added after the first annealing step and annealed. For example, the temperatures of the first annealing step and the second annealing step may be the same or different. Preferably, the first annealing step may be performed at a temperature equal to or higher than the melting point of the lithium precursor, and the second annealing step may be performed at a temperature equal to or higher than the melting point of the calcium or calcium compound. More preferably, the first annealing may be performed at a temperature between 450 and 900°C, for example, around 700°C. More preferably, the second annealing may be performed at a temperature between 270 and 850°C, for example, 500 and 700°C. Within these temperature ranges, the crystalline structure of the cathode active material is restored, and the cathode active material contains calcium or a calcium compound, resulting in excellent efficiency, life, and resistance characteristics.

[0276] In another example, when the annealing in step S50 is performed in a first annealing step in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealed, and a second annealing step in which a lithium precursor is added after the first annealing step and annealed, the temperatures of the first annealing step and the second annealing step may be set to be the same or different. Preferably, the first annealing step is performed in which calcium or a calcium compound is added to the pre-cleaned cathode active material and annealed. The first annealing step may be performed at a temperature equal to or higher than the melting point of the lithium precursor, and the second annealing step may be performed at a temperature equal to or higher than the melting point of the lithium precursor. More preferably, the first annealing may be performed at 270 to 850°C, for example, around 500 to 700°C. More preferably, the second annealing may be performed at 450 to 900°C, for example, around 700°C. Within these temperature ranges, the crystalline structure of the positive electrode active material is restored, and calcium or a calcium compound is contained in the positive electrode active material, resulting in excellent efficiency, life characteristics, and resistance characteristics.

[0277] The annealing time is, for example, 1 hour or more, preferably 15 hours or less, specifically 7 to 11 hours. A longer annealing time allows for sufficient recovery of the crystal structure and allows for a uniform coating, but even if annealed for a longer period of time, there is no significant change in performance. The annealing equipment can be the same as or similar to that used in the heat treatment step S30.

[0278] The annealing temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, specifically at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0279] The annealing in step S50 includes, for example, a cooling process, which may be, for example, natural cooling in a furnace. In this case, the crystallinity of the recycled positive electrode active material is further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0280] The annealing step (step S50) may preferably include a first annealing, a cooling process, and then a second annealing. In this case, the crystalline structure is restored and calcium or a calcium compound is contained in the positive electrode active material, resulting in excellent efficiency, life characteristics, and resistance characteristics.

[0281] The cooling step can be performed, for example, to a temperature of 130°C or less, for example, around 100°C. Within this range, the crystallinity of the recycled positive electrode active material can be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0282] Next, as a post-cleaning step, the annealed positive electrode active material is mixed with a cleaning solution, stirred, and then filtered (step S60).

[0283] The post-cleaning step S60 is a process for removing lithium compounds remaining in the positive electrode active material after annealing.

[0284] The latter cleaning step of step S60 is preferably performed in the same manner as the cleaning step (step S40) described above, except that a minimum amount of cleaning solution (for example, 1 to 2 times the mass of the positive electrode active material) is used and rinsing is not performed. Therefore, a description of the overlapping parts will be omitted.

[0285] Next, as an optional step, the post-cleaned positive electrode active material can be surface coated (step S70).

[0286] 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 a 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.

[0287] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a post-cleaned 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.

[0288] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0289] secondary battery The secondary battery of the present invention includes a recycled cathode active material prepared by the method for recycling a cathode active material. In this case, the battery has a significantly improved rate performance and excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0290] 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.

[0291] 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.

[0292] [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 (Ni:Co:Mn:Al molar ratio: 88:7:4:1)) was crushed and heat-treated in air at 590°C for 2 hours to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 3 L / min.

[0293] The content of LiF produced in the recovered positive electrode active material was measured, and Ca(OH)2 was added in an amount equivalent to 0.13 moles of Ca per mole of F component, and the material was reheated in air at 700°C for 10 hours. The temperature was increased at a rate of 2°C / min to reach the reheating temperature, and air was supplied at a rate of 3 L / min.

[0294] In this description, the LiF content, CaF content, etc. of the positive electrode active material were measured using an ICP analyzer. This can be measured using a general ICP analyzer commonly used in laboratories, and there is no difference depending on the measurement device or method.

[0295] Example 2 The same procedure as in Example 1 was carried out except that in the reheat treatment step of Example 1, Ca(OH)2 was added in an amount corresponding to 0.05 moles of Ca per mole of the F component.

[0296] Example 3 The same procedure as in Example 1 was carried out except that in the reheat treatment step of Example 1, Ca(OH)2 was added in an amount corresponding to 0.2 moles of Ca per mole of the F component.

[0297] Example 4 The same procedure as in Example 1 was carried out, except that in the reheat treatment step of Example 1, Ca(NO3)2 was added instead of Ca(OH)2.

[0298] Comparative Example 1 The same procedure as in Example 1 was carried out, except that the reheat treatment step was not carried out.

[0299] Comparative Example 2 The same procedure as in Example 1 was carried out except that a reheat treatment step was carried out without adding Ca(OH)2.

[0300] [Test Example I: Residual Lithium Content] The residual lithium content of the recycled positive electrode active materials obtained in Example 1 and Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 1 below.

[0301] *Residual lithium content: 5 g of the positive active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and filtered to obtain the positive 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 residual amounts of LiOH and Li2CO3 in the positive active material were calculated using the obtained pH titration curve.

[0302] [Table 1]

[0303] As shown in Table 1, the regenerated cathode active material (Example 1) that was reheat-treated with Ca(OH)2 had an increased LiOH content compared to the regenerated cathode active material (Comparative Example 1) that was not reheat-treated. This is because the Ca(OH)2 added in the reheat-treatment step combined with the LiF generated in the heat-treatment step to generate LiOH.

[0304] In addition, the regenerated cathode active material (Comparative Example 2) that was reheat-treated without adding Ca(OH)2 had an increased Li2CO3 content compared to Example 1 and Comparative Example 1. This is because the LiOH produced during the heat treatment step was converted to Li2CO3.

[0305] [Test Example II: Evaluation of CHC Cell] The electrochemical performance of the recycled positive electrode active materials obtained from Examples 1 to 4 and Comparative Examples 1 and 2 was measured through the CHC cell evaluation as follows, and the results are shown in Table 2 and FIG.

[0306] *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 CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under conditions where the electrolyte contained ethylene carbonate (EC):dimethyl methyl carbonate (DMC) = 3:7 (mass ratio) and other additives.

[0307] *Evaluation of the initial capacity (CH and DCH) of the cells: Each cell was charged and discharged once at 25°C under the following conditions.

[0308] Charge (CH): 0.2C, CC / CV, 4.25V, 0.05C cutoff Discharge (DCH): 0.2C, CC, 2.5V cutoff * Cell charge / discharge efficiency (Eff): The charge / discharge efficiency was calculated using Equation 1 based on the charge capacity and discharge capacity obtained from the evaluation of the initial capacity of the cell, and is shown in Figure 3 below.

[0309] [Formula 1] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] x 100

[0310] [Table 2]

[0311] As shown in Table 2 and FIG. 3 below, the regenerated cathode active materials (Examples 1 to 4) that were reheat-treated by adding a calcium compound according to the present invention were superior in initial charge capacity, initial discharge capacity, and / or charge / discharge efficiency compared to the regenerated cathode active material that was not subjected to the reheat-treatment step (Comparative Example 1) and the cathode active material that was reheat-treated without adding a calcium compound (Comparative Example 2). Examples 1 to 3, in which Ca(OH)2 was added as the calcium compound, were even superior to Example 4, in which Ca(NO3)2 was added.

[0312] [Test Example III: Evaluation of high-temperature life characteristics] The capacity retention rate and resistance increase rate of the CHC cells prepared using the recycled cathode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were measured as described above, and the results are shown in FIG. 4 below.

[0313] *Evaluation of high-temperature life characteristics: Each cell was charged and discharged 15 times at 45°C under the following conditions, and the capacity retention rate and the resistance increase rate (ΔDCIR) were calculated every 5 cycles using the following Equation 2 and Equation 3, respectively, and the results are shown in Figure 4 below.

[0314] Charge: 0.33C, CC / CV, 4.5V, 0.05C cutoff Discharge: 0.33C, CC, 3.0V, 0.05C cutoff [Formula 2] Capacity retention rate (%) = (discharge capacity after N cycles / discharge capacity after 1 cycle) x 100 [Formula 3] ΔDCIR = {(resistance after N cycles / resistance after 1 cycle) × 100}-100 FIG. 4 below shows the results of evaluating the life characteristics of a regenerated cathode active material (Examples 1 to 4) that was reheat-treated by adding the calcium compound according to the present invention, a regenerated cathode active material that was not subjected to the reheat-treatment step (Comparative Example 1), and a cathode active material that was reheat-treated without adding the calcium compound (Comparative Example 2), and is a graph showing the capacity retention rate and resistance increase rate as a function of the number of cycles (Cycle No.).

[0315] Referring to this, the positive electrode active materials (Examples 1 to 3) that were reheat-treated after adding Ca(OH)2 had a better capacity retention rate than those of Comparative Examples 1 and 2, and the positive electrode active material (Example 4) that was reheat-treated after adding Ca(NO3)2 had a better capacity retention rate than that of Comparative Example 1. Furthermore, the positive electrode active materials of Examples 1 to 4 had a lower resistance increase rate than that of Comparative Example 1 but a higher rate than that of Comparative Example 2. This is because the calcium component present in the positive electrode active material acted as a resistance layer, resulting in a slight increase in the resistance increase rate.

[0316] [Additional Examples] Additional Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCM-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was crushed and heat-treated in air at 550°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 3 L / min.

[0317] The recovered positive electrode active material and distilled water (hereinafter referred to as "cleaning solution") were mixed in a mass ratio of 1:10, stirred at 500 rpm for 10 minutes, and then filtered under reduced pressure using a filter to extract only the positive electrode active material. The obtained positive electrode active material was rinsed with a rinse solution (the same as the cleaning solution) with a mass 10 times that of the positive electrode active material, and then vacuum dried at 100 to 150°C to obtain a cleaned positive electrode active material.

[0318] To the pre-cleaned cathode active material, LiOH (lithium precursor) and Ca(OH)2 were added in an amount equivalent to 350 ppm (calcium metal basis) of lithium, based on the molar ratio of lithium to other metals in the raw cathode active material (ICP analysis) (lithium molar ratio of 1), to the recovered cathode active material. The amount was then annealed in air (addition rate: 3 L / min) at 700°C for 10 hours. Theoretically, the Li molar ratio of the nascent cathode active material is 1. However, since the average error of the ICP instrument used to determine this is ±0.05, preferably ±0.02, the Li molar ratio of the raw active material measured by ICP measurement can be 1±0.05:1. In this experiment, the lithium precursor was added based on the molar ratio measured by ICP analysis.

[0319] The annealed positive electrode active material and distilled water were mixed in a mass ratio of 1:1 and stirred at 500 rpm for 10 minutes. After that, the mixture was filtered (dehydrated) by vacuum filtration using a filter in the same manner as the previous pre-cleaning, to obtain a positive electrode active material. The obtained positive electrode active material was then vacuum dried at 100 to 150°C to obtain a positive electrode active material that had been subjected to post-cleaning.

[0320] The cathode active material after post-cleaning was coated with boric acid and then heated at 300°C for 5 hours to produce the final regenerated cathode active material. Here, the amount of boric acid added was equivalent to the amount 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.

[0321] In this description, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer, which can be used with a common ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0322] Additional Example 2 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, a lithium precursor was added and a first annealing was performed at 700°C for 10 hours, and then the material was naturally cooled to 100°C in a furnace. Then, Ca(OH)2 was added and a second annealing was performed at 700°C for 10 hours.

[0323] Additional Example 3 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, a lithium precursor was added and a first annealing was performed at 700°C for 10 hours, and then the material was naturally cooled to 100°C in a furnace. Then, Ca(OH)2 was added and a second annealing was performed at 500°C for 10 hours.

[0324] Additional Example 4 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, a lithium precursor was added and a first annealing was performed at 700°C for 10 hours, and then the material was naturally cooled to 100°C in a furnace. Then, Ca(OH)2 was added and a second annealing was performed at 300°C for 10 hours.

[0325] Additional Example 5 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, Ca(OH)2 was replaced with Ca(NO3)2.

[0326] Additional Example 6 A recycled positive electrode active material was produced in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, the amount of Ca(OH)2 was changed to 100 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

[0327] Additional Example 7 A recycled positive electrode active material was produced in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, the amount of Ca(OH)2 was changed to an amount equivalent to 200 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

[0328] Additional Example 8 A recycled positive electrode active material was produced in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, the amount of Ca(OH)2 was changed to an amount equivalent to 600 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

[0329] Additional Example 9 A recycled positive electrode active material was produced in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, the amount of Ca(OH)2 was changed to an amount equivalent to 1000 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

[0330] Additional Example 10 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, Ca(OH)2 was replaced with CaO.

[0331] Additional Comparative Example 1 A regenerated positive electrode active material was prepared in the same manner as in Additional Example 1, except that in the annealing step of Additional Example 1, only the lithium precursor was added, and annealing was performed without adding Ca(OH)2.

[0332] Additional Reference Examples Instead of a recycled active material, a fresh NCM-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1) was used.

[0333] [Additional Test Case I] The properties of the regenerated positive electrode active materials obtained from the additional Examples 1 to 5 and 10, the additional comparative example 1 and the additional reference example were measured by the following methods, and the results are shown in Table 3 below.

[0334] *ICP analysis: Using an ICP analyzer, the calcium content (mg / kg), residual F content (mg / kg), and the ratio of lithium (Li) and other metals (M) in the positive electrode active material were measured. 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.

[0335] [Table 3]

[0336] As can be seen from Table 3, the positive electrode active materials (Additional Examples 1 to 5 and 10) prepared by adding a lithium precursor and calcium or a calcium compound in the annealing step according to the present invention contained calcium in an amount of 50 to 1200 ppm and had residual F components of 2000 ppm or less.

[0337] [Additional Test Example II: Evaluation of Electrochemical Performance] The electrochemical performance of the regenerated or virgin positive electrode active materials manufactured or prepared in Additional Examples 1 to 10, Additional Comparative Example 1, and Additional Reference Example was measured through a coin half cell (hereinafter referred to as "CHC") evaluation as described below, and the results are shown in Table 4 below.

[0338] *CHC production: 96% by weight of recycled cathode active material, 2% by weight of carbon black (conductive material), and 2% by weight of PVdF (binder) were weighed and mixed with NMP to produce a slurry. This was coated onto aluminum foil to produce a cathode, and then a coin half cell (CHC) was produced. The electrochemical performance (charge capacity CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under conditions where the electrolyte contained ethylene carbonate (EC):dimethyl methyl carbonate (DMC) = 3:7 (mass ratio) and other additives.

[0339] *Evaluation of the initial capacity (CH and DCH) of the cells: Each cell was charged and discharged once at 25°C under the following conditions.

[0340] Charge (CH): 0.2C, CC / CV, 4.25V, 0.05C cutoff Discharge (DCH): 0.2C, CC, 2.5V cutoff *Cell charge / discharge efficiency (Eff): 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 Equation 1.

[0341] [Table 4]

[0342] As shown in Table 4 above, the positive electrode active materials (Additional Examples 1 to 10) prepared by adding a lithium precursor and calcium or a calcium compound in the annealing step and annealing according to the present invention were found to have similar initial capacities to the regenerated positive electrode active material (Additional Comparative Example 1) prepared by adding only a lithium precursor in the annealing step and annealing.

[0343] [Additional Test Example III: Evaluation of Life Characteristics] The life characteristics of CHCs prepared from the regenerated or virgin cathode active materials prepared or manufactured in Additional Examples 1 to 10, Additional Comparative Example 1, and Additional Reference Example were measured as described below, and the results are shown in Figures 6 to 10.

[0344] *Evaluation of high-temperature life characteristics of CHC: Each cell was charged and discharged 30 times at 45°C under the following conditions, and the capacity retention rate was calculated using Equation 2. The results are shown in Figures 6 to 10.

[0345] Charge: 0.33C, CC / CV, 4.5V, 0.05C cutoff Discharge: 0.33C, CC, 3.0V FIG. 6 below is a graph showing the change in capacity as a function of cycle number (Cycle No.) as a result of CHC evaluation of each of the regenerated or virgin cathode active materials manufactured or prepared in Additional Examples 1 and 2, Additional Comparative Example 1, and Additional Reference Example. Referring to this graph, it was confirmed that the regenerated cathode active materials according to the present invention (Additional Examples 1 and 2) have a superior capacity retention rate compared to the regenerated cathode active material (Additional Comparative Example 1) prepared by adding only a lithium precursor in the annealing step, and that the capacity retention rate is at a similar level to the virgin cathode active material (Additional Reference Example).

[0346] In addition, Figure 7 below shows the results of CHC evaluation of each of the regenerated or virgin cathode active materials manufactured or prepared in Additional Examples 2 to 4 and Additional Reference Example. It was confirmed that the regenerated cathode active materials (Additional Examples 2 and 3) in which the second annealing step was performed at 700°C and 500°C, respectively, had superior capacity retention rates compared to the virgin cathode active material (Additional Reference Example), while the regenerated cathode active material (Additional Example 4) in which the second annealing step was performed at 300°C showed a slight decrease in capacity retention rate as the number of cycles increased.

[0347] In addition, Figure 8 below shows the results of CHC evaluation of each of the regenerated or virgin cathode active materials manufactured or prepared in Additional Examples 1 and 5, and Additional Reference Example. The regenerated cathode active material (Additional Example 1) manufactured by adding Ca(OH)2 as a calcium compound in the annealing step had a superior capacity retention rate compared to the virgin cathode active material (Additional Reference Example), while the regenerated cathode active material (Additional Example 5) manufactured by adding Ca(NO3)2 as a calcium compound had a slightly lower capacity retention rate compared to the virgin cathode active material (Additional Reference Example).

[0348] 9 shows the results of CHC evaluation of the regenerated or virgin cathode active materials manufactured or prepared in Additional Examples 1, 6-9, and Additional Reference Example, confirming that the regenerated cathode active materials according to the present invention (Additional Examples 1 and 6-9) have similar or better capacity retention rates than the virgin cathode active material (Additional Reference Example).Here, the regenerated cathode active materials (Additional Examples 1, 7, and 8) containing 200 ppm, 350 ppm, and 600 ppm of calcium exhibited even better capacity retention rates.

[0349] FIG. 10 below shows the results of CHC evaluation of the regenerated or virgin cathode active materials manufactured or prepared in Additional Example 10, Additional Comparative Example 1, and Additional Reference Example. The regenerated cathode active material according to the present invention (Additional Example 10) had a superior capacity retention rate compared to the regenerated cathode active material manufactured by adding only a lithium precursor in the annealing step and annealing (Additional Comparative Example 1). [Explanation of symbols]

[0350] 10 Current collector 20 Active material layer 30 Positive electrode sheet 40 positive electrode plate 50 cathode scrap

Claims

1. (i) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and thermally decomposing the binder and conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; (ii) A method for regenerating a positive electrode active material, comprising: a step (ii-1) of adding calcium or a calcium compound to the recovered positive electrode active material and reheating it at 600 to 750°C; or a step (ii-2) of pre-washing the recovered positive electrode active material with a washing solution, and then adding a lithium precursor and calcium or a calcium compound thereto and annealing the material.

2. The calcium compound is Ca(OH). ２ and Ca(NO ３ ) ２ The method for regenerating a positive electrode active material according to claim 1 , wherein the positive electrode active material is one or more of the following:

3. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in the step (ii-1), calcium or a calcium compound is added in an amount corresponding to 0.03 to 0.4 moles (calcium metal basis) per mole of F component present in the positive electrode active material recovered after the heat treatment in the step (i).

4. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in step (i), the heat treatment is carried out at 300 to 650° C. for 10 minutes to 10 hours.

5. The method for regenerating a positive electrode active material according to claim 1, wherein in step (ii), the reheat treatment is carried out for 5 to 15 hours.

6. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in the step (ii-2), calcium or a calcium compound is added in an amount equivalent to 50 to 1200 ppm (calcium metal basis) relative to the mass of the recovered positive electrode active material.

7. 2. The method of claim 1, wherein in step (ii-2), the annealing includes a first annealing step of adding a lithium precursor to the pre-cleaned cathode active material and annealing the resultant, and a second annealing step of adding calcium or a calcium compound after the first annealing and annealing the resultant.

8. The method for regenerating a positive electrode active material according to claim 1, wherein in step (ii-2), the annealing is carried out at a temperature of 270 to 1000°C.

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

10. 2. The method for regenerating a positive electrode active material according to claim 1, wherein in the step (ii-2), the pre-cleaning includes a step of stirring the recovered positive electrode active material together with a cleaning solution, followed by filtering.

11. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material subjected to step (ii-2) contains 50 to 1200 ppm of calcium.

12. The method for regenerating a positive electrode active material according to claim 1 , wherein the heat treatment in step (i) and the reheat treatment and / or annealing in step (ii) are carried out in an air or oxygen atmosphere.

13. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material comprises at least one selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, lithium nickel cobalt aluminum oxide, lithium nickel oxide, a nickel manganese-based lithium composite metal oxide in which part of the nickel (Ni) in lithium nickel oxide is substituted with manganese (Mn), and an NCM-based lithium composite transition metal oxide in which part of the nickel (Ni) in lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co).

14. The method for regenerating a positive electrode active material according to claim 1, further comprising: (iii) washing the positive electrode active material reheat-treated in step (ii-1) with a cleaning solution.

15. The method for regenerating the positive electrode active material includes (iv) adding a lithium precursor to the positive electrode active material reheat-treated in step (ii-1) and annealing the material. The method for regenerating the positive electrode active material according to claim 1.

16. The lithium precursor is LiOH, Li ２ CO ３ , LiNO ３ and Li ２ 16. The method for regenerating a positive electrode active material according to claim 1 or 15, wherein the active material is one or more selected from the group consisting of O.

17. The lithium precursor in step (iv) is added in an amount that is reduced from the molar ratio of lithium in the positive electrode active material in at least step (ii-1), based on the amount of lithium in the positive electrode active material in the raw materials. The method for regenerating a positive electrode active material according to claim 15.

18. The method for regenerating a positive electrode active material according to claim 15, wherein in step (iv), the annealing is performed at 400 to 1000°C.

19. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the lithium precursor in step (ii-2) is added in an amount that is at least a fraction of the molar ratio of lithium in the positive electrode active material in step (i), based on the amount of lithium in the positive electrode active material that has been previously washed.

20. The method for regenerating a positive electrode active material according to claim 1, further comprising a step of post-cleaning the positive electrode active material annealed in step (ii-2) with a cleaning solution.

21. The method for regenerating a positive electrode active material according to claim 1 or 15, comprising the step of surface-coating the annealed positive electrode active material.

22. 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; CaF ２ or containing 50 to 1200 ppm of calcium, A positive electrode active material having a residual F component content of 2000 ppm or less.

23. The positive electrode active material according to claim 22 , wherein the surface of the positive electrode active material is coated with a coating agent containing metal or carbon.

24. 24. The cathode active material of claim 23, wherein the metal is boron (B), tungsten (W), or a mixture thereof.

25. 23. The cathode active material of claim 22, wherein the cathode active material is a regenerated cathode active material.

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