Regenerated positive electrode active material

Abstract

The present invention relates to a method for regenerating a cathode active material and a regenerated cathode active material produced therefrom. More specifically, the method includes the steps of: (a) 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, in air or oxygen; (b) adding a lithium precursor to the recovered cathode active material and heat-treating it in air to restore its crystalline structure; (c) doping the restored cathode active material with a dopant precursor and heat-treating it; and (d) washing the doped cathode active material with a cleaning solution. The present invention provides a method for regenerating a cathode active material and a regenerated cathode active material produced therefrom. The doping of a regenerated cathode active material with a predetermined dopant by a predetermined method improves capacity and life characteristics, and provides a method for regenerating a cathode active material with excellent crack resistance.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application is an application claiming priority rights based on Korean Patent Application No. 10-2023-0152017 dated November 6, 2023, and Korean Patent Application No. 10-2024-0144952, refiled thereunder on October 22, 2024, and all contents disclosed in the documents of said Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material produced thereby, and more specifically, to a method for regenerating a positive electrode active material in which the capacity characteristics and life characteristics are improved and the regenerated positive electrode active material has excellent crack resistance by doping the regenerated positive electrode active material with a predetermined dopant in a predetermined manner, and to a regenerated positive electrode active material produced thereby.

[0003] Furthermore, the present invention relates to a method for regenerating positive electrode active material that is environmentally friendly because it does not use acid, reduces process costs because neutralization and wastewater treatment are not required, regenerates the positive electrode active material without decomposing it, so there are no discarded metal elements, does not dissolve the current collector so it can be recovered, does not use organic solvents so there is no risk of generating toxic gases or explosions, and is suitable for mass production by using a process that is easy to manage such as heat treatment and sedimentation, as well as a regenerated positive electrode active material produced therefrom that has excellent electrochemical performance, resistance characteristics and capacitance characteristics. [Background technology]

[0004] Lithium-ion batteries are broadly classified into a positive electrode, which has a positive electrode active material layer coated with metal foil such as aluminum; a negative electrode, which has a negative electrode active material layer coated with metal foil such as copper; a separation membrane to prevent the positive and negative electrodes from mixing; and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0005] The positive electrode active material layer mainly uses lithium-based oxides as the active material, and the negative electrode active material layer mainly uses carbon material as the active material. However, since lithium-based oxides generally contain rare metals such as cobalt, nickel, or manganese, much research is being conducted on recovering and reusing rare metals from the positive electrodes of lithium secondary batteries that are discarded after use, or from positive electrode scrap generated in the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0006] Conventional techniques for recovering rare metals from waste cathodes mostly involve dissolving the waste cathode in hydrochloric acid, sulfuric acid, or nitric acid, then extracting cobalt, manganese, nickel, etc., with an organic solvent, and using these as raw materials again for the synthesis of cathode active materials.

[0007] However, acid-based extraction methods for rare metals have environmental pollution problems, as they always require neutralization and wastewater treatment processes, significantly increasing process costs, and they have the drawback of not being able to recover lithium, the main metal in the cathode active material.

[0008] To overcome these drawbacks, recent research has focused on methods for directly recycling positive electrode active materials from waste positive electrodes without decomposing them (direct recycling methods). Four main types of such methods have been introduced: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0009] However, although the aforementioned firing method is simple in its process, it has drawbacks such as the generation of foreign matter on the surface of the recycled positive electrode active material that reduces the output performance of the battery, the generation of waste gas, and high energy consumption. In particular, removing foreign matter such as LiF requires the use of excessive initial washing water, making it difficult to apply to the recycling process. Furthermore, in addition to generating the same amount of waste water, major problems arise such as the loss of Li in the functional coating layer and lattice of the recycled positive electrode active material due to washing, and an increase in the occurrence of cracks that reduce the output performance of the secondary battery. Of these, by-products generated during the degradation process can be removed by washing with water, and the loss of Li can be overcome to some extent by replenishing the Li source, but the physically generated cracks cannot be restored to the same particle size distribution as the unused (virgin) positive electrode active material with the conventional direct recycled method. The occurrence of the aforementioned cracks leads to an increase in the fine powder and specific surface area of ​​the recycled positive electrode active material. This promotes side reactions between the electrolyte and the surface of the recycled positive electrode active material, resulting in a decrease in active lithium and an increase in overall cell resistance, ultimately reducing the battery's lifespan.

[0010] Furthermore, while the aforementioned solvent dissolution method can produce a regenerated cathode active material with a relatively clean surface, it has the disadvantage of poor stability and the need for an expensive solvent recovery process because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and poses an explosion risk.

[0011] Furthermore, while the aluminum foil melting method has good process stability, low process costs, and easy binder removal, it has the disadvantages of generating foreign matter that is difficult to remove on the surface of the recycled cathode active material, and of generating hydrogen gas during the aluminum foil removal process, which poses a risk of explosion.

[0012] Finally, while the aforementioned crushing and screening method has the advantage of being the simplest process, it has the disadvantages of being difficult to completely separate the current collector and the positive electrode active material, the particle size distribution of the positive electrode active material changing during the crushing process, and the binder remaining, which degrades the battery characteristics of the regenerated positive electrode active material.

[0013] Therefore, there is an urgent need to develop a method for recycling cathode active materials that is inexpensive, environmentally friendly, and safe, that eliminates discarded metal elements from waste cathodes, further improves output performance and lifespan characteristics, and, in particular, improves crack resistance and significantly reduces wastewater. [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] To solve the problems of the conventional technology described above, the present invention aims to provide a method for regenerating a cathode active material that has improved capacity characteristics and lifespan characteristics and excellent crack resistance by doping the regenerated cathode active material with a predetermined dopant in a predetermined manner, and to provide a regenerated cathode active material manufactured therefrom.

[0015] Furthermore, the present invention aims to provide a method for regenerating positive electrode active materials that is suitable for mass production by using a process that is easy to manage, such as heat treatment and sedimentation, and a regenerated positive electrode active material manufactured therefrom that has excellent electrochemical performance, resistance characteristics, and capacitance characteristics. This method is environmentally friendly because it does not use acid, and process costs are reduced because neutralization and wastewater treatment are not required. It also regenerates the positive electrode active material without decomposing it, so there are no discarded metal elements. It does not dissolve the current collector, so it can be recovered. It does not use organic solvents, so there is no risk of generating toxic gases or explosions.

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

[0017] To achieve the above object, I) The present invention provides a recycled cathode active material comprising one or more 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 nickel (Ni) of the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxide in which part of nickel (Ni) of the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), doped with a dopant and having no coating layer.

[0018] II) In the above I), the dopant may be contained at 100 to 2000 ppm based on the total weight of the recycled cathode active material.

[0019] III) In the above I) or II), the dopant may be one or more selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C and N.

[0020] IV) In the above I) to III), based on EDS (Energy Dispersive Spectroscopy) surface mapping, the recycled cathode active material may have 10 ppm or less of a dopant element coated on the surface without doping.

[0021] V) In the above I) to IV), based on EDS (Energy Dispersive Spectroscopy) surface mapping, the recycled cathode active material may contain 40 to 45% by weight of carbon element, 25 to 30% by weight of oxygen element and 25 to 30% by weight of nickel element.

[0022] Further, VI) The present invention provides a method for regenerating a cathode active material, comprising: (a) heat-treating a spent cathode including a current collector and a cathode active material layer coated on the current collector under air or oxygen to recover the cathode active material; (b) adding a lithium precursor to the recovered cathode active material and heat-treating it in air to restore the crystal structure; (c) adding a dopant precursor to the cathode active material with the restored crystal structure and heat-treating it for doping; and (d) washing the doped cathode active material with a washing liquid.

[0023] VII) In the above VI), in the step (a), the heat treatment may be carried out under the condition of 300 to 650 °C.

[0024] VIII) In the above VI) or VII), in the step (b), the heat treatment may be carried out under the condition of 400 to 1000 °C.

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

[0026] X) In the above VI) to IX), in the step (c), the heat treatment may be carried out under the condition of 300 to 1000 °C.

[0027] XI) In the above VI) to X), in the step (c), the dopant precursor may be a compound providing one or more elements selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C and N as dopants.

[0028] XII) In the above VI) to XI), in the step (d), the washing liquid may be water.

[0029] XIII) In VI) to XII) above, the method for regenerating the positive electrode active material may include (a-2) washing the recovered positive electrode active material with a washing solution; and / or (b-2) washing the positive electrode active material whose crystal structure has been restored.

[0030] XIV) In steps VI) to XIII) above, the cleaning solution in step (a-2) is water or an aqueous solution of a basic lithium compound in an amount of more than 0% by weight and less than or equal to 15% by weight, and the cleaning solution in step (b-2) may be water.

[0031] XV) In steps VI) to XIV) above, in step (c), the dopant precursor may be added at a concentration of 100 to 2000 ppm (based on the dopant element) relative to the total weight of the regenerated cathode active material.

[0032] XVI) In VI) to XV) above, the positive electrode active material may include one or more 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 lithium composite metal oxide in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co).

[0033] Furthermore, XVII) The present invention provides a regenerated positive electrode active material characterized by being manufactured by the positive electrode active material regeneration method described in VI) to XVI).

[0034] Furthermore, XVIII) the present invention provides a secondary battery containing a regenerated positive electrode active material according to I) to XVII). [Effects of the Invention]

[0035] According to the present invention, by doping a regenerated cathode active material with a predetermined dopant in a predetermined manner, the capacity characteristics and life characteristics are improved, and a method for regenerating a cathode active material with excellent crack resistance is provided, as well as a regenerated cathode active material manufactured therefrom.

[0036] Furthermore, according to the present invention, since no acid is used, it is environmentally friendly, neutralization and wastewater treatment are not required, thus reducing process costs, the positive electrode active material is regenerated without decomposition, so no metal elements are discarded, the current collector is not dissolved, so it can be recovered, and since no organic solvent is used, there is no risk of generating toxic gases or explosions, and by using a process that is easy to manage such as heat treatment and sedimentation, it provides a method for regenerating positive electrode active material suitable for mass production, and a regenerated positive electrode active material manufactured therefrom that has excellent electrochemical performance and resistance characteristics.

[0037] The drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further illustrate the technical concept of the present invention. Accordingly, the present invention is not construed to be limited to the matters described in these drawings. [Brief explanation of the drawing]

[0038] [Figure 1] This figure shows positive electrode scrap that is discarded after the electrode plates are cut from the positive electrode sheet. [Figure 2] This is a flowchart illustrating one embodiment of the present invention, for the regeneration process of the positive electrode active material. [Figure 3] This figure conceptually shows the approximate structure of the regenerated cathode active material produced in Example 1 and Comparative Examples 1-3, respectively. [Figure 4] This is an EDS (Energy Dispersive Spectrometer) cross-sectional mapping image of the regenerated cathode active material produced in Example 1. No B2O3 coating layer was found here. [Figure 5]This is an EDS (Energy Dispersive Spectrometer) cross-sectional mapping image of the regenerated cathode active material produced in Comparative Example 1. No B2O3 coating layer was found here. [Figure 6] This is an EDS (Energy Dispersive Spectrometer) mapping image of the regenerated cathode active material produced in Comparative Example 2. A boron coating layer was confirmed here, and elemental analysis was performed at location #11 where the boron coating layer was formed and at location #12 where the boron coating layer was not formed. [Figure 7] This is an EDS (Energy Dispersive Spectrometer) mapping image of the regenerated cathode active material produced in Comparative Example 3. A boron coating layer was confirmed here, and elemental analysis was performed at locations #13, #15, and #16 where the boron coating layer was formed, and at location #14 where the boron coating layer was not formed. [Figure 8] This XPS graph shows the change in the content of detected elements as the etching time of the regenerated cathode active materials produced in Example 1 and Comparative Examples 1-3, respectively. [Figure 9] This graph shows the results of the progression of the initial charge and discharge capacities of coin half cells to which the regenerated positive electrode active materials from Example 1 and Comparative Examples 1-3 were applied. [Figure 10] This graph shows the change in capacity retention rate with respect to the number of cycles (Cycle No.) for each of the regenerated cathode active materials produced in Example 1 and Comparative Examples 1-3, based on coin half-cell evaluation. [Modes for carrying out the invention]

[0039] The method for regenerating the positive electrode active material of this application and the regenerated positive electrode active material produced therefrom will be described in detail below.

[0040] The inventors of the present invention were researching a method to further improve the capacity characteristics and lifespan characteristics of a regenerated positive electrode active material in a direct recycled method, which involves directly regenerating the positive electrode active material from a waste positive electrode without decomposing it. They discovered that when a predetermined dopant is applied to the regenerated positive electrode active material using a predetermined method, rather than coating it as in the conventional method, the crack resistance of the regenerated positive electrode active material is improved, and the capacity characteristics and lifespan characteristics of a battery to which this method is applied are greatly enhanced. Based on this, they continued their research and completed the present invention.

[0041] The present invention provides a method for regenerating positive electrode active material, comprising the steps of: (a) heat-treating a waste positive electrode, including a current collector and a positive electrode active material layer coated on the current collector, under air or oxygen to recover the positive electrode active material; (b) adding a lithium precursor to the recovered positive electrode active material and heat-treating it in air to restore its crystalline structure; (c) adding a dopant precursor to the positive electrode active material whose crystalline structure has been restored and heat-treating it to dope it; and (d) washing the doped positive electrode active material with a cleaning solution. In this case, the capacity characteristics and life characteristics of the regenerated positive electrode active material are determined. This method offers several advantages: improved crack resistance, environmental friendliness due to the absence of acid, reduced process costs as neutralization and wastewater treatment are unnecessary, no discarded metal elements as the positive electrode active material is regenerated without decomposition, recovery of the current collector is possible as it is not dissolved, no toxic gas generation or explosion risk as organic solvents are not used, and the use of easily manageable processes such as heat treatment and sedimentation makes it suitable for mass production. It also provides a regenerated positive electrode active material with excellent electrochemical performance and resistance characteristics.

[0042] The method for regenerating the positive electrode active material of this invention will be described in detail below, in stages.

[0043] However, the terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Therefore, it should be understood that the embodiments and configurations shown in the drawings described herein are merely examples of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can substitute for them, and that they may be arranged, substituted, combined, separated or designed in various other configurations.

[0044] All technical and scientific terms used herein have the same meaning as those commonly understood by those ordinary skill in the art to which the present invention pertains, unless otherwise defined.

[0045] (a) Step of recovering the positive electrode active material from the waste positive electrode. (a) The step of recovering positive electrode active material from a waste positive electrode according to the present invention may be a step of recovering positive electrode active material by heat-treating the waste positive electrode, which includes a current collector and a positive electrode active material layer coated on the current collector. Preferably, the step of recovering positive electrode active material from the positive electrode active material layer is a step of heat-treating a waste positive electrode, on which a positive electrode active material layer containing 60 mol% or more of Ni among transition metals is formed on the current collector, in air at 300 to 650°C, by thermal decomposition of the binder and conductive material in the positive electrode active material layer. In this case, the process is simple and has the effect of cleanly removing the binder, conductive material and current collector.

[0046] The waste positive electrode may preferably be a positive electrode separated from a lithium secondary battery that has been discarded after use, a defective positive electrode sheet or positive electrode scrap generated in the manufacturing process of a lithium secondary battery, and more preferably positive electrode scrap remaining after punching out a positive electrode plate from a positive electrode sheet.

[0047] The positive electrode active material layer in step (a) above may preferably include a positive electrode active material, a binder, and a conductive material.

[0048] 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 one or more 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.

[0049] 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 one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≦ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≦ w ≦ 0.1, -0.02 ≦ δ ≦ 0.02, and x + y + z + w = 1.) It may be a compound represented by.

[0050] As an example, the positive electrode active material contains 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% based on 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0051] In this application, the Ni content is not particularly limited when measured using methods commonly used in the art to which the present invention pertains, such as IC (Ion Chromatography). Specific examples include IC-ICP (Inductively Coupled Plasma) analyzers, IC-ICP-MS (Mass Spectroscopy) analyzers, or IC-ICP-AES (Atomic Emission Spectroscopy) analyzers.

[0052] The conductive material may, for example, be a carbon-based conductive material, and preferably, carbon black, CNT (carbon nanotube), or a mixture thereof.

[0053] 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.

[0054] The heat treatment may, for example, be carried out in an air or oxygen atmosphere. In this case, the binder and conductive material are thermally decomposed into CO2 and H2O and removed, thereby separating the positive electrode active material from the current collector. The separated positive electrode active material has the advantage of being easily sorted into powder form.

[0055] The heat treatment temperature may preferably be 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0056] The heat treatment time may preferably be 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0057] In this application, the heat treatment time is the time spent processing at the heat treatment temperature, and the time it takes to reach that heat treatment temperature is not included in the calculation.

[0058] The aforementioned heat treatment has a temperature rise 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, it can be implemented without putting undue strain on the heat treatment equipment and has the advantage of not causing thermal shock to the positive electrode scrap.

[0059] Figure 1 shows the positive electrode scrap that is discarded after the positive electrode plate is cut from the positive electrode sheet.

[0060] Referring to Figure 1, a positive electrode sheet 30 is manufactured by coating a long sheet-shaped aluminum foil 10, which is a positive electrode current collector, with a positive electrode active material layer 20 containing positive electrode active material, conductive material, binder, etc. Then, this is punched out to a certain size to produce a positive electrode plate 40, and positive electrode scrap 50 is generated from the remaining portion. The punching is one means of cutting the positive electrode sheet.

[0061] Furthermore, the positive electrode active material layer 20 is formed by coating the aluminum foil 10 with a slurry containing a mixture of positive electrode active material, conductive material, binder, and solvent. Because the slurry is highly sensitive to environmental factors such as temperature, determining the coating conditions is extremely difficult. As a result, a considerable amount of waste positive electrode sheets are generated before the conditions for producing a positive electrode sheet 30 of the desired quality are found through predetermined tests.

[0062] For reference, in the embodiment described below, positive electrode scrap was used as the waste positive electrode.

[0063] Step to wash the recovered positive electrode active material. The method for reusing positive electrode active material according to the present invention may include (a-2) a step of washing the recovered positive electrode active material (hereinafter referred to as "preliminary washing"), in which case metal fluorides such as LiF that may be present on the surface of the regenerated positive electrode active material are removed and the surface is modified, which has the effect of improving the battery's output performance (rate performance).

[0064] During the heat treatment, CO2 and H2O generated by the thermal decomposition of the binder and conductive material within the positive electrode active material may react with lithium on the surface of the active material to form Li2CO3 and LiOH. Additionally, fluorine (F) present in binders such as PVdF may react with the metal elements constituting the positive electrode active material to form LiF or metallic fluorides. If LiF or metallic fluorides remain, the battery characteristics will deteriorate when the positive electrode active material is reused.

[0065] The step of washing the recovered positive electrode active material (a-2) may, for example, be a step of mixing the recovered positive electrode active material with a washing solution and then filtering it with a filter press. In this case, the amount of residual F is determined by the amount of rinsing solution, so even if the amount of positive electrode active material to be washed increases, there is no need to change equipment such as a stirring tank. Furthermore, the total amount of washing solution, including the initial washing solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. The amount of initial washing solution put into the stirring tank is minimized, and by adjusting the amount of rinsing solution, residual F components can be easily removed, while at the same time improving the battery's output performance (rate performance).

[0066] The filter press in the (a-2) washing step can preferably operate under an air pressure of 2 to 10 bar, more preferably under an air pressure of 3 to 9 bar, still more preferably under an air pressure of 3 to 8 bar, even more preferably under an air pressure of 3 to 7 bar, and most preferably under an air pressure of 3 to 6 bar. Within this range, since the content of the residual F component is determined by the amount of the rinse liquid, even when the amount of the positive electrode active material to be washed increases, it is not necessary to replace equipment such as the stirring tank. Furthermore, since the total amount of the washing liquid combining the initial washing liquid and the rinse liquid can be significantly reduced, the amount of waste water, the waste water treatment cost, and environmental pollution can be reduced. The amount of the initial washing liquid input into the stirring tank is minimized, and by adjusting the amount of the rinse liquid, the residual F component can be easily removed, and at the same time, the output performance of the battery can be improved.

[0067] The filter press in the (a-2) washing step can preferably include a filter cloth with an air permeability of 0.1 to 15 cc / cm 2 ( / sec), more preferably a filter cloth with an air permeability of 0.2 to 10 cc / cm 2 (sec), still more preferably a filter cloth with an air permeability of 0.3 to 5 cc / cm 2 ( / sec), even more preferably a filter cloth with an air permeability of 0.5 to 2 cc / cm 2 ( / sec), and most preferably a filter cloth with an air permeability of 0.6 to 1 cc / cm 2 ( / sec). Within this range, since the content of the residual F is determined by the amount of the rinse liquid, even when the amount of the positive electrode active material to be washed increases, it is not necessary to replace equipment such as the stirring tank. Furthermore, since the total amount of the washing liquid combining the initial washing liquid and the rinse liquid can be significantly reduced, the amount of waste water, the waste water treatment cost, and environmental pollution can be reduced. The amount of the initial washing liquid input into the stirring tank is minimized, and by adjusting the amount of the rinse liquid, the residual F component can be easily removed, and at the same time, the output performance of the battery can be improved.

[0068] The filter cloth is not particularly limited as long as it is a commonly used filter press material according to the definition of the present invention. As a specific example, it can be made of polypropylene.

[0069] The filter press of this application is not particularly limited in terms of type or material, as long as it conforms to the definition of the present invention and is physically and chemically stable in the positive electrode active material slurry. For example, it may include a frame, filter plates, filter cloth, filter cloth pressurizer, filter plate separator, filter cloth washing device, and transfer pump.

[0070] The cleaning solution in step (a-2) above may preferably be water or an aqueous solution of a basic lithium compound. In this case, the F component remaining on the surface of the regenerated positive electrode active material can be thoroughly removed with a small amount of cleaning solution, which significantly reduces the generation of wastewater and at the same time significantly improves the output performance of the battery.

[0071] In this application, water is not particularly limited as long as it is neutral water, and may include, for example, distilled water or deionized water.

[0072] The cleaning solution in step (a-2) above may, for example, be an aqueous solution of a basic lithium compound. In this case, not only can trace amounts of binder remain on the surface of the positive electrode active material recovered after the thermal decomposition in step (a), but it also has the advantage of not leaching out transition metals and other substances present in the recovered positive electrode active material, and replenishing the amount of lithium that could be leached out during cleaning. If an acidic aqueous solution such as sulfuric acid or hydrochloric acid solution is used as the cleaning solution, the F component on the surface of the positive electrode active material can be cleaned, but it will leach out transition metals and other substances present in the positive electrode active material, degrading the performance of the reused positive electrode active material.

[0073] The aqueous solution of the basic lithium compound preferably contains more than 0% by weight and 15% by weight or less of the basic lithium compound, more preferably more than 0% by weight and 10% by weight or less of the basic lithium compound, and even more preferably 0.5 to 5% by weight of the basic lithium compound. Within this range, the surface modification effect is excellent, such as the removal of LiF and metal fluorides as F components formed on the surface of the positive electrode active material during the heat treatment process.

[0074] The cleaning step (a-2) may preferably include a step of mixing the recovered positive electrode active material with a cleaning solution to form a slurry (a1) and a step of putting the slurry into a filter press and filtering it (a2). More preferably, it may include a step of mixing the recovered positive electrode active material with a cleaning solution to form a slurry (a1), a step of putting the slurry into a filter press and filtering it (a2), and a step of putting a rinsing solution into the filter press and rinsing the filter cake (a3). In this case, the amount of residual F component is determined by the amount of rinsing solution, so even if the amount of positive electrode active material to be cleaned increases, there is no need to replace equipment such as a stirring tank. Furthermore, the total amount of cleaning solution, including the initial cleaning solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. The amount of initial cleaning solution put into the stirring tank is minimized, and residual F component can be easily removed by adjusting the amount of rinsing solution, while at the same time improving the output performance of the battery.

[0075] The step of (a1) above, which involves mixing the recovered positive electrode active material with a cleaning solution to form a slurry, may preferably be a step of using a stirrer to stir the recovered positive electrode active material with water or an aqueous solution of a basic lithium compound to form a slurry. In this case, the step of modifying the surface of the positive electrode active material has a significant effect in removing foreign matter such as LiF or metal fluorides that have been generated on the surface of the positive electrode active material during the preceding heat treatment process.

[0076] The aforementioned agitator may, for example, be an impeller type, a magnetic type, and / or an ultrasonic agitator, but is not particularly limited.

[0077] The stirring may, for example, be carried out within one week, preferably within one day, more preferably within one hour, 40 minutes, 30 minutes, or 20 minutes, or for example, for 5 minutes or more, preferably 10 minutes or more, 20 minutes or more, or 30 minutes or more. Within this range, all foreign matter of F component such as LiF or metal fluoride generated on the surface of the positive electrode active material is removed, and yet excessive dissolution of lithium does not occur, which has the advantage of excellent battery capacity characteristics.

[0078] The cleaning solution in step (a1) above is preferably 0.5 to 5 times the weight of the recovered positive electrode active material, more preferably 0.5 to 4 times, even more preferably 0.8 to 3 times, and even more preferably 0.9 to 2 times. Within this range, residual F components such as LiF can be easily removed, and at the same time, the total amount of cleaning solution, including the initial cleaning solution and the rinsing solution, can be significantly reduced. This reduces the amount of wastewater, wastewater treatment costs, and environmental pollution, and has the effect of improving the battery's output performance (rate performance).

[0079] The rinsing solution in step (a3) ​​above may preferably be 5 to 20 times the weight of the recovered positive electrode active material, more preferably 5 to 15 times, even more preferably 8 to 15 times, even more preferably 8 to 13 times, and even more preferably 8 to 12 times. Within this range, the total amount of cleaning solution, including the initial cleaning solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. The amount of initial cleaning solution introduced into the stirring tank is minimized, and the amount of rinsing solution is adjusted to easily remove residual F components while simultaneously improving the output performance of the battery.

[0080] The cleaning solution in step (a1) and the rinsing solution in step (a3) ​​may, for example, have a weight ratio of 1:2 to 15 for cleaning solution to rinsing solution, preferably 1:7 to 15, more preferably 1:7 to 13, even more preferably 1:8 to 13, even more preferably 1:8 to 12, and particularly more preferably 1:9 to 11. Within this range, the amount of residual F is determined by the amount of rinsing solution, eliminating the need to replace equipment such as stirring tanks even when the amount of positive electrode active material to be cleaned increases. Furthermore, the total amount of cleaning solution, including the initial cleaning solution and the rinsing solution, can be significantly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. The amount of initial cleaning solution introduced into the stirring tank is minimized, and residual F components can be easily removed by adjusting the amount of rinsing solution, while simultaneously improving the output performance of the battery.

[0081] The washing step (a-2) may preferably include a step of recovering the solids after the filtration or rinsing and drying them, which has the advantage of optimizing and facilitating the subsequent crystal structure recovery step.

[0082] The drying process can be carried out, for example, for 1 to 24 hours at a temperature of 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 no further weight change occurs. Within this range, there is an advantage in efficiently removing moisture contained in the washed positive electrode active material.

[0083] (b) A step to restore the crystal structure of the cleaned positive electrode active material. The step of (b) restoring the crystal structure according to the present invention may be a step of adding a lithium precursor to the recovered positive electrode active material and heat-treating it in air to restore the crystal structure, in which case there is an advantage in providing a positive electrode active material with excellent initial discharge capacity, output performance, capacitance characteristics and resistance characteristics.

[0084] The step of (b) restoring the crystal structure may preferably involve adding a lithium precursor to the positive electrode active material whose crystal structure has been restored, and heat-treating it in oxygen (O2) or air at 400 to 1000°C, more preferably 700 to 900°C, and even more preferably 710 to 780°C. In this case, improving the crystallinity, such as increasing the crystallinity of the positive electrode active material or restoring the crystal structure, has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0085] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0086] Preferably, the lithium precursor can be added in an amount equal to the amount of lithium that has decreased from the amount of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. Specifically, when the recovered positive electrode active material in step (a) is the positive electrode active material represented by chemical formula 1, the amount of lithium that is added is such that the molar ratio of lithium in this positive electrode active material is 0.0001 to 0.2, preferably 0.001 to 0.02, more preferably 0.005 to 0.017, even more preferably 0.007 to 0.015, and even more preferably 0.009 to 0.013. Within this range, the deficient lithium in the regenerated positive electrode active material is replenished, and the battery characteristics of the regenerated positive electrode active material are improved by improving crystallinity, such as by increasing crystallinity or restoring the crystal structure.

[0087] As an example, the lithium precursor may be added in an amount equivalent to 1 to 40 mol%, preferably 1 to 15 mol%, and more preferably 1 to 10 mol%, when the total amount of lithium contained in the raw material positive electrode active material is considered to be 100 mol%, and within this range, no residual precursor that can increase the resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics, and it has an economic advantage because the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods.

[0088] The heat treatment temperature can be adjusted within a limited range, depending on the melting point of the lithium precursor, for example, in the case of LiCO3, since the melting point is 723°C, the heat treatment can be preferably performed at 700-900°C, more preferably at 710-780°C. Within this range, the crystal structure is restored, which has the effect of improving the output performance of the battery.

[0089] The heat treatment temperature may preferably exceed the melting point of the lithium precursor; however, if it exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, potentially leading to a decrease in battery performance; therefore, a temperature of 1000°C or lower is preferable.

[0090] The heat treatment 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. Specifically, around 5 hours is preferred, and within this range, the crystal structure is sufficiently restored, which is economically advantageous.

[0091] The heat treatment temperature can preferably be reached at a heating rate of 1 to 10°C / min, more preferably at 1 to 5°C / min, and even more preferably at 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, which has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0092] The crystal structure recovery step includes, for example, a cooling step, which may, specifically, be natural cooling in a furnace. In this case, the crystallinity of the regenerated cathode active material is further increased, thereby improving the battery characteristics of the regenerated cathode active material.

[0093] In this application, the restoration of the crystal structure can be defined according to the definition used in the art to which the present invention belongs. Specifically, it can be defined as a heat treatment operation that heals deformation or lattice defects and appropriately adjusts the crystallinity of a positive electrode active material that has a deformed structure or lattice defects by heating it for an appropriate time at a temperature above the recrystallization temperature, i.e., a temperature at which the atoms of the main component can sufficiently diffuse and move.

[0094] Step to clean the positive electrode active material whose crystal structure has been restored. The step (b-2) of the present invention, which involves cleaning the positive electrode active material whose crystal structure has been restored (hereinafter referred to as "subsequent cleaning"), may also be a step of mixing the positive electrode active material whose crystal structure has been restored with a cleaning solution and then filtering it. In this case, there is an advantage that the battery characteristics are improved by removing lithium compounds remaining on the surface of the positive electrode active material whose crystal structure has been restored.

[0095] Preferably, the subsequent cleaning can be performed by mixing the restored positive electrode active material with a cleaning solution and then filtering it using a filter press. In this case, compared to conventional vacuum filtration, a small amount of cleaning solution can be used to clean the lithium remaining in the crystal structure recovery step. Therefore, the amount of wastewater, wastewater treatment costs, and environmental pollution can be reduced. Furthermore, even when the amount of positive electrode active material to be cleaned increases, there is no need to replace equipment such as stirring tanks. Moreover, removing residual lithium compounds from the regenerated positive electrode active material has the effect of significantly improving the initial discharge capacity, output performance (rate performance), and capacity characteristics of the battery.

[0096] The cleaning solution may preferably be 0.5 to 5 times the weight of the recovered positive electrode active material, more preferably 0.5 to 4 times, even more preferably 0.8 to 3 times, even more preferably 0.9 to 2 times, and even more preferably 0.9 to 1.5 times. Within this range, there is an advantage in that the lithium compounds remaining on the surface of the positive electrode active material whose crystal structure has been restored are effectively removed without the leaching of the effective metal, thereby improving the battery characteristics.

[0097] The positive electrode active material obtained after the subsequent cleaning preferably has a residual lithium precursor (e.g., LiOH) content of 1000 ppm or less, more preferably 800 ppm or less. Within this range, the reaction of the residual lithium precursor with the dopant precursor in the subsequent doping step to form a LiB3O5 (LBO) coating layer on the surface of the regenerated positive electrode active material is suppressed, which has the advantage of improving doping efficiency and battery characteristics.

[0098] The aforementioned subsequent cleaning may preferably include all of the above-mentioned cleaning step (a-2) except for the rinsing step, in addition to the contents separately defined herein, and therefore, the explanation of the overlapping parts will be omitted. However, in step (b-2), it is preferable to use the rinsing solution in the minimum amount (for example, 1x or less, 0.5x or less, or 0.1x or less) or not to use it at all, in which case there is the advantage that the effective metal does not leach out from the positive electrode active material whose crystal structure has been restored.

[0099] (c) A step of doping the cathode active material whose crystal structure has been restored. The method for regenerating a positive electrode active material of the present invention includes the step of (c) adding a dopant precursor to the positive electrode active material whose crystal structure has been restored and doping it by heat treatment. In this case, doping the regenerated positive electrode active material with dopant improves its capacity characteristics and lifetime characteristics, and provides excellent crack resistance.

[0100] In step (c) above, the heat treatment can be carried out under conditions of 300 to 1000°C, preferably 300 to 600°C, specifically 400 to 900°C, preferably 450 to 800°C, more preferably 500 to 700°C, and still preferably 550 to 650°C. Within this range, no degradation loss occurs in the regenerated cathode active material, and the dopant is stably doped, resulting in improved capacity characteristics and life characteristics, and enhanced crack resistance.

[0101] In step (c) above, the dopant precursor is, for example, a compound that provides one or more elements selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N as a dopant, and preferably a compound that provides one or more elements selected from the group consisting of B, Na, Mg, and F as a dopant. In this case, the dopant is stably doped into the regenerated cathode active material, the surface coating layer can be easily removed by washing or rinsing with water, and the capacity characteristics, life characteristics, and crack resistance are greatly improved.

[0102] In step (c) above, the dopant precursor may preferably be added at a concentration of 100 to 2000 ppm (based on dopant element) relative to the total weight of the regenerated cathode active material, more preferably at 300 to 1500 ppm, even more preferably at 400 to 1200 ppm, even more preferably at 500 to 1000 ppm, and even more preferably at 600 to 900 ppm. Within this range, the dopant is stably doped into the regenerated cathode active material, resulting in a significant improvement in capacity characteristics and lifetime characteristics, as well as excellent crack resistance.

[0103] Step (c) above may, as a specific example, be a step of adding or coating a dopant precursor alone or dissolved in a solvent to the cathode active material whose crystal structure has been restored, and then doping by heat treatment. A preferred example is a step of adding a dopant precursor alone to the cathode active material whose crystal structure has been restored and doping by a solid-phase reaction, i.e., heat treatment. In this case, doping the regenerated cathode active material with dopant improves the capacity characteristics and lifetime characteristics, and enhances crack resistance. Here, liquid-phase reactions using a solvent are highly efficient, and solid-phase reactions using only a dopant precursor are advantageous for mass production, so they can be selectively applied as needed.

[0104] The dopant precursor may, for example, be an oxide containing the dopant element, an acid, an organometallic compound, or the like.

[0105] The heat treatment time can preferably be 1 to 10 hours, more preferably 3 to 5 hours. Within this range, the dopant is stably doped into the regenerated cathode active material, resulting in a significant improvement in capacity characteristics and lifespan characteristics, as well as excellent crack resistance.

[0106] The aforementioned heat treatment temperature can preferably be reached at a heating rate of 1 to 10°C / min, more preferably at 1 to 7°C / min, and even more preferably at 1 to 5°C / min. Within this range, the dopant is stably doped into the regenerated positive electrode active material, resulting in a significant improvement in capacitance characteristics and lifetime characteristics, as well as excellent crack resistance.

[0107] The heat treatment can be carried out under air or oxygen, preferably under oxygen. In this case, the dopant is stably doped into the regenerated positive electrode active material, resulting in a significant improvement in capacity characteristics and lifespan characteristics, as well as excellent crack resistance.

[0108] The solvent is not particularly limited, as long as it does not affect the positive electrode active material. For example, it may be water or an organic solvent such as alcohol, and the alcohol may preferably be methanol or ethanol.

[0109] Regenerated cathode active material The regenerated positive electrode active material of the present invention is characterized by being manufactured by the method for regenerating positive electrode active material described above. In this case, doping the regenerated positive electrode active material with a predetermined dopant improves its capacitance characteristics and lifespan characteristics, and enhances its crack resistance.

[0110] Furthermore, the regenerated positive electrode active material of the present invention comprises one or more 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 lithium composite metal oxide in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co), and is doped with a dopant and has no coating layer. In this case, capacity characteristics and life characteristics are improved, and crack resistance is excellent.

[0111] In the aforementioned doping process, the dopant element itself penetrates into the crystal structure of the positive electrode active material to a thickness of several nanometers on the surface of the subsequently cleaned positive electrode active material particles. As a result, the increase in resistance on the surface of the positive electrode active material is significantly reduced compared to coating, thereby contributing to an increase in battery life. On the other hand, the coating layer is formed when oxides generated by the reaction or thermal decomposition of the dopant precursor with lithium compounds adhere to the surface of the subsequently cleaned positive electrode active material, acting as a resistor and causing deterioration of the lifespan characteristics. Therefore, in order to finish the regenerated positive electrode active material with doping without a coating layer, it is important to add a predetermined dopant precursor to the positive electrode active material whose crystal structure has been restored, heat treat it at a predetermined heat treatment temperature, and then clean it using a predetermined method to remove the coating layer while leaving only the doped dopant.

[0112] The aforementioned coating layer can, for example, represent an aggregate of undoped dopant precursors that have been replaced by oxides or the like and are adhering to the surface of the positive electrode active material in the form of nodules. During the cleaning process, such a coating layer is removed, and only the doped dopants remain in the regenerated positive electrode active material.

[0113] Figure 3 shows the schematic structures of the regenerated cathode active material finished with doping without a coating layer, manufactured in Example 1, and the regenerated cathode active material finished with a coating layer, manufactured in Comparative Example 2. In the regenerated cathode active material manufactured in Example 1, doping with a dopant, rather than a conventional surface coating, not only eliminates side reactions between the coating layer and the cathode active material, but also stabilizes the surface due to effects such as a reduction in nickel (Ni) elements on the cathode active material surface due to the influence of the dopant, thereby achieving improved long-term life characteristics and increased initial charge / discharge capacity. On the other hand, in Comparative Example 2, a surface coating layer was formed on the regenerated cathode active material along with the doping layer, but by not removing the surface coating layer, cracks began to occur at the interface between the cathode active material surface and the coating layer as the charge / discharge cycle progressed, causing resistance between dissimilar interfaces and degrading the long-term life. Here, the surface coating layer may be a boron coating layer containing B2O3 and a small amount of LBO (a reaction product of boric acid and LiOH remaining on the surface of the cathode active material).

[0114] Figures 4 and 6 include EDS (Energy Dispersive Spectrometer) mapping images of the regenerated cathode active materials produced in Example 1 and Comparative Example 2. In Example 1, the regenerated cathode active material had a uniform surface throughout, with only the doped dopant remaining and the coating layer removed by washing. The composition ratio was the same regardless of the location measured on the regenerated cathode active material, and no boron (B) element was detected in the surface analysis. On the other hand, in Comparative Example 2, the regenerated cathode active material only underwent the coating step of doping and the formation of the coating layer, and did not undergo the coating layer removal (washing) step. A large amount of boron (B) element was detected in the coating layer.

[0115] Figures 9 and 10 show the initial charge / discharge capacity and the change in capacity retention rate with the number of cycles for the regenerated cathode active materials produced in Example 1 and Comparative Example 2. The regenerated cathode active material of Example 1, which was doped with a dopant without a coating layer, exhibits excellent initial charge / discharge capacity and charge / discharge efficiency due to the doping effect, resulting in low surface resistance and suppressed surface side reactions. Furthermore, the low surface resistance and suppressed surface side reactions result in excellent capacity retention rate, i.e., excellent lifetime characteristics. On the other hand, the regenerated cathode active material of Comparative Example 2, which included a coating layer, although partially doped, showed a decrease in initial charge / discharge capacity and charge / discharge efficiency, as well as a decrease in lifetime characteristics, due to the B2O3 coating layer and LiB3O5 coating layer acting as surface resistance, respectively.

[0116] The dopant may preferably be present in an amount of 100 to 2000 ppm relative to the total weight of the regenerated positive electrode active material, more preferably 300 to 1500 ppm, even more preferably 400 to 1200 ppm, even more preferably 500 to 1000 ppm, and even more preferably 600 to 900 ppm. Within this range, the capacity characteristics and life characteristics are greatly improved, and the crack resistance is excellent.

[0117] The dopant is preferably one or more selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N, and more preferably one or more selected from the group consisting of B, Na, Mg, and F. In this case, the capacity characteristics and life characteristics are greatly improved, and the crack resistance is excellent.

[0118] The regenerated positive electrode active material may preferably have a dopant element content of 10 ppm or less, more preferably 5 ppm or less, on its surface, based on EDS (Energy Dispersive Spectroscopy) surface mapping. Within this range, it exhibits low resistance, significantly improved capacitance and lifetime characteristics, and excellent crack resistance.

[0119] The regenerated positive electrode active material preferably contains 40-45% by weight of carbon, 25-30% by weight of oxygen, and 25-30% by weight of nickel, based on EDS (Energy Dispersive Spectroscopy) surface mapping, and more preferably contains 42-45% by weight of carbon, 26-29% by weight of oxygen, and 27-30% by weight of nickel. Within this range, it has the effect of low resistance, greatly improved capacitance characteristics and life characteristics, and excellent crack resistance.

[0120] The aforementioned regenerated positive electrode active material, as an example, has a residual F content of 8000 ppm or less, preferably 2000 ppm or less, more preferably 1800 ppm or less, even more preferably 1700 ppm or less, and even more preferably 1600 ppm or less, with a specific example being 1 to 8000 ppm. In such cases, the output performance of the battery is improved, and it has the effect of being excellent in electrochemical performance, resistance characteristics, and capacitance characteristics. In this application, the residual F content refers not only to LiF but also to the content of all residual F components in other residual components.

[0121] In this application, the residual F content is not particularly limited when measured using a measurement method that is commonly used in the art to which the present invention belongs, such as IC (Ion Chromatography). For example, it 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. In this application, IC-ICP (Inductively Coupled Plasma) can be used preferentially.

[0122] As yet another specific example, the regenerated positive electrode active material is given by 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 one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. It) may be a compound represented by this, and in this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacitance characteristics, and the like.

[0123] The recycled positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and still more preferably 81 to 95 mol% based on a total of 100 mol% of the remaining metals or transition metals excluding Li. Within this range, there is an effect of being excellent in charge capacity, resistance characteristics, and capacitance characteristics.

[0124] Figure 2 is a flowchart for the regeneration process of a positive electrode active material, which is one embodiment according to the present invention.

[0125] Referring to Figure 2, first, positive electrode scrap is prepared as waste positive electrodes (step S10). For example, a slurry prepared by adding NMP (N-methyl pyrrolidone) to an NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride and mixing them is coated on an aluminum foil and dried in a vacuum oven at about 120 °C to produce a positive electrode sheet. After punching out a positive electrode plate of a certain size from this, the remaining positive electrode scrap can be prepared.

[0126] The positive electrode scrap has a positive electrode active material layer on an aluminum foil, and the positive electrode active material layer has a structure in which a binder binds a positive electrode active material and a conductive material after the solvent volatilizes.

[0127] Next, the prepared positive electrode scrap is crushed to an appropriate size (step S20). Here, crushing includes cutting or shredding the positive electrode scrap to a size that is easy to handle. Specifically, the crushed positive electrode scrap may be 1 cm x 1 cm in size. For the crushing, various dry crushing equipment such as a hand mill, disc mill, cutting mill, or hammer mill may be used as an example, and a high-speed cutting machine may be used to increase productivity.

[0128] Preferably, the crushing process can be decided by considering the handling of the positive electrode scrap and the characteristics required by the equipment used in subsequent processes, such as whether or not to crush the scrap and the size of the small pieces. However, for example, if equipment capable of continuous processing is used, good fluidity is necessary, so the positive electrode scrap must be crushed into even smaller pieces.

[0129] Next, the crushed positive electrode scrap is heat-treated in air at 500-600°C to recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder and conductive material in the positive electrode active material layer.

[0130] Through the aforementioned 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.

[0131] It is important that the aforementioned heat treatment be carried out in air or in the presence of oxygen. However, if the heat treatment is performed in a reducing gas or inactive gas atmosphere, the binder and conductive material will carbonize instead of being thermally decomposed. When carbonization occurs, carbon components remain on the surface of the positive electrode active material, reducing the performance of the reused positive electrode active material. However, if the heat treatment is performed in air, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, thus removing both the binder and the conductive material.

[0132] The heat treatment preferably has a temperature rise rate of 1 to 20°C / min, more preferably 1 to 10°C / min, even more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min, with a specific example being 5°C / min. Within this range, the burden on the heat treatment equipment is suppressed, and there is an advantage in not causing thermal shock to the positive electrode active material layer powder.

[0133] The aforementioned heat treatment can be carried out for a period of time sufficient to adequately thermally decompose the binder, preferably 1.5 to 6 hours, more preferably 2 to 5.5 hours, even more preferably 3 to 5 hours, and even more preferably 4 to 5 hours. Within this range, the binder is adequately thermally decomposed, and the thermal decomposition efficiency is excellent.

[0134] The aforementioned heat treatment can be carried out using various types of furnaces, for example, a box-type furnace, or, considering productivity, a rotary kiln capable of continuous processing.

[0135] After the heat treatment, the device can be slowly or rapidly cooled in the atmosphere.

[0136] Next, in the cleaning step (hereinafter referred to as "pre-cleaning"), that is, the surface modification step, the recovered positive electrode active material is mixed with the cleaning solution and then filtered using a filter press (step S40).

[0137] The aforementioned cleaning step, by including a filter press, has the advantage of effectively removing foreign matter generated on the surface of the positive electrode active material in the heat treatment step (step S30) with a small amount of cleaning solution.

[0138] One embodiment of the cleaning step described above may include the following steps: first, the recovered positive electrode active material is stirred with a cleaning solution in a stirring tank to form a slurry; second, this slurry is filtered using a filter press to form a filter cake in the filter press; and third, a rinsing solution is introduced into the filter press to rinse the filter cake formed in the filter press with high pressure. Here, the filtration and rinsing steps are performed within the same pressure range, and the stirring device is not particularly limited, but may be an impeller type, a magnetic type, or an ultrasonic stirrer. However, if the viscosity of the slurry is high or the amount of slurry is large, an impeller type stirrer that can transmit a large force is preferred.

[0139] The cleaning solution is, for example, water or an aqueous solution of a basic lithium compound. If it is necessary to replenish the amount of lithium that can be leached from the positive electrode active material during the cleaning process, an aqueous solution of a basic lithium compound is preferred.

[0140] For example, the aqueous solution of the basic lithium compound contains more than 0% by weight and 15% by weight or less of the basic lithium compound. If it does not contain the lithium compound, it is difficult to replenish the lithium, and if it exceeds 15% by weight, an excess amount of lithium compound may remain on the surface of the positive electrode active material, which may adversely affect the subsequent annealing process.

[0141] In one embodiment, the lithium compound is LiOH.

[0142] The cleaning solution is used in an amount equal to 0.5 to 5 times the weight of the recovered positive electrode active material, and in one embodiment, it may be used in an amount equal to 1 to 2 times, or around 1 time.

[0143] The stirring is performed for 1 to 20 minutes, preferably 5 to 10 minutes, in one embodiment, within this range to prevent a decrease in battery capacity due to excessive lithium leaching.

[0144] The stirring is performed at a temperature of 100 to 1000 rpm, preferably 250 to 750 rpm, in one embodiment, within this range to prevent a decrease in battery capacity due to excessive lithium leaching.

[0145] The filter press operates under air pressure conditions of 2 to 10 bar, and in one embodiment, it operates under air pressure conditions of 3 to 6 bar.

[0146] In one embodiment, the filter press is physically and chemically stable in the slurry and includes a frame, a filter plate, a filter cloth, a filter cloth pressurizer, a filter plate separator, a filter cloth washing device, and a transfer pump.

[0147] The filter cloth preferably has an air permeability of 0.1 to 15 cc / cm². 2 ( / sec), and in one embodiment, 0.8 cc / cm³ 2 ( / sec) is also acceptable.

[0148] The rinsing solution may preferably be 5 to 20 times the weight of the recovered positive electrode active material, and in one embodiment, it may be around 10 times.

[0149] The weight ratio of the cleaning solution to the rinsing solution may preferably be 1:7 to 15, and in one embodiment, it may be around 1:10.

[0150] The filter cake after rinsing can be dried as needed. In one embodiment, it can be dried in an oven (convection type) at a temperature of 50-150°C in air or under vacuum. However, in this embodiment, the drying process was omitted considering that heat treatment would be performed in the next step, the crystal structure recovery step.

[0151] The cleaning step (step S40) removes Li2CO3, LiOH, etc., which are produced by the reaction of lithium during the process in which the binder and conductive material in the positive electrode active material layer are vaporized into CO2 and H2O and removed in the heat treatment step (step S30), as well as LiF or metal fluorides, which are produced when F present in the binder such as PVdF reacts with lithium and other metal elements constituting the positive electrode active material. This prevents deterioration of battery characteristics when the positive electrode active material is reused.

[0152] In this application, % and ppm are based on weight unless otherwise defined.

[0153] Next, a lithium precursor is added to the cleaned positive electrode active material and heat-treated to restore its crystalline structure (step S50).

[0154] Since lithium is lost from the positive electrode active material during the preceding steps S30 and S40, step S50 replenishes the amount of lithium lost. In addition, since deformation structures (for example, Co3O4 in the case of LCO active material) may form on the surface of the positive electrode active material during the preceding steps, step S50 restores the crystal structure of the positive electrode active material to improve the battery characteristics of the regenerated positive electrode active material or restores it to the level of a newly produced (virgin or fresh) positive electrode active material. Here, "newly produced" is the opposite concept of "regenerated," meaning it is manufactured for the first time, and is the same word as "raw material" used in the examples.

[0155] The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3, and Li2O, and in one embodiment, LiOH is used.

[0156] The lithium precursor is preferably added in an amount equal to at least the molar ratio of the lost lithium, compared 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. Adding an excessive amount of lithium precursor compared to the amount of lost lithium will leave unreacted lithium precursor in the regenerated positive electrode active material, which increases resistance; therefore, it is necessary to add an appropriate amount of lithium precursor.

[0157] In one embodiment, based on the case where the molar ratio of lithium in the newly generated positive electrode active material is 1 in relation to other metals (M), an amount of lithium precursor can be added such that the lithium molar ratio is 0.001 to 0.4. Preferably, an amount of lithium precursor can be added such that the lithium molar ratio is 0.01 to 0.4, and more preferably, an amount of lithium precursor can be added such that the lithium molar ratio is 0.09 to 0.2. As a specific example, by adding lithium precursor in proportion to the ratio lost relative to the lithium content in the newly generated positive electrode active material, based on the results of ICP analysis, a capacity improvement effect equivalent to that of the newly generated positive electrode active material can be obtained. Here, the results of ICP analysis have an error value of approximately ±0.02.

[0158] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 40 mol%, more preferably in an amount corresponding to 1 to 15 mol%, and even more preferably in an amount corresponding to 7 to 11 mol%, when the total amount of lithium contained in the washed positive electrode active material is considered to be 100 mol%, and within this range, no residual precursor that can increase the resistance of the regenerated positive electrode active material remains, which is very useful for improving battery characteristics.

[0159] The heat treatment is carried out, for example, in air under conditions of 400 to 1000°C, preferably under conditions of 600 to 900°C, and this temperature needs to be modified within a limited range depending on the type of lithium precursor.

[0160] The heat treatment temperature is preferably above the melting point of the lithium precursor. However, temperatures exceeding 1000°C will cause thermal decomposition of the positive electrode active material, leading to a decrease in performance, so the temperature should not exceed 1000°C. For example, when using LiOH or Li2CO3 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.

[0161] The heat treatment time is, for example, often 1 hour or more, preferably 15 hours or less, and more preferably 5 to 13 hours. A longer heat treatment time can sufficiently restore the crystal structure, but there is no significant change in performance even with prolonged heat treatment. The same or similar equipment used in heat treatment step S30 can be used for the heat treatment.

[0162] Next, as a subsequent cleaning step, the positive electrode active material whose crystalline structure has been restored is mixed with a cleaning solution, stirred, and then filtered (step S60).

[0163] The aforementioned subsequent cleaning step is a process for removing lithium compounds remaining in the positive electrode active material after the heat treatment in the crystal structure recovery step.

[0164] The aforementioned subsequent cleaning step preferably includes a filter press, which has the advantage of effectively removing foreign matter generated on the surface of the positive electrode active material in the crystal structure recovery step (step S50) with a small amount of cleaning solution, and easily removing residual lithium and fine particles.

[0165] The subsequent cleaning step is preferably carried out in the same manner as the cleaning step described above (step S40), except that a minimal amount of cleaning solution is used (for example, 1x the weight of the positive electrode active material) and rinsing is not performed. Therefore, the explanation of the overlapping parts will be omitted.

[0166] Next, a step of doping the subsequently cleaned positive electrode active material can be performed (step S70).

[0167] The doping step involves, for example, adding a dopant precursor to the positive electrode active material that has been washed in a subsequent step, and then heat-treating it (solid-phase reaction). However, if the heat treatment temperature is too low, the amount of dopant doped into the positive electrode active material will be small, and instead a large coating layer will be formed. If the heat treatment temperature is too high, the thermal decomposition of the positive electrode active material and the dopant precursor itself will reduce the performance of the battery.

[0168] In the aforementioned doping, the dopant element itself penetrates into the crystal structure of the positive electrode active material to a thickness of several nanometers on the surface of the subsequently cleaned positive electrode active material particles. As a result, the increase in resistance on the surface of the positive electrode active material is significantly reduced compared to coating, thereby contributing to an increase in battery life. On the other hand, the coating layer is formed when oxides generated by the reaction or thermal decomposition of the dopant precursor with the lithium compound adhere to the surface of the subsequently cleaned positive electrode active material, acting as a resistor and causing deterioration of the battery life characteristics.

[0169] The method for adding the dopant precursor to the subsequently washed cathode active material may, for example, be by mixing, milling, spraying, or grinding.

[0170] Finally, as a step to remove the coating layer and leave only the doped dopant, the doped cathode active material is mixed with a cleaning solution, stirred, and then filtered (step S80).

[0171] The coating layer removal step, for example, involves mixing the doped positive electrode active material with a cleaning solution, stirring, and then filtering. Here, the coating layer can refer to an aggregate of undoped dopant precursors that have been converted into oxides or the like and adhere to the surface of the positive electrode active material in the form of nodules. During the cleaning process, such a coating layer is removed, leaving only the doped dopant in the regenerated positive electrode active material.

[0172] The aforementioned coating layer removal cleaning step preferably has the advantage of effectively removing the coating layer even with a small amount of cleaning solution by using a filter press.

[0173] The cleaning solution may preferably be water.

[0174] The cleaning solution may preferably be used in an amount of 1 to 10 times the weight of the doped positive electrode active material.

[0175] The filter cake of the regenerated positive electrode active material after the cleaning can be dried, and in one embodiment, it can be dried in air under vacuum or reduced pressure at a temperature of 50 to 150°C using an oven (convection type).

[0176] The coating layer removal step can be carried out in the same manner as the cleaning step (step S40) described above, except for the contents defined in this step. Therefore, the explanation of the overlapping parts will be omitted.

[0177] secondary battery The secondary battery of the present invention includes a regenerated positive electrode active material produced by the method for regenerating the positive electrode active material. In this case, the capacity characteristics and life characteristics are improved, and the inclusion of a regenerated positive electrode active material with excellent crack resistance significantly improves the battery's output performance (rate performance) and provides excellent electrochemical performance and resistance characteristics.

[0178] The secondary battery of the present invention may include all of the above-described positive electrode active material and regeneration method. Therefore, redundant descriptions thereof are omitted here.

[0179] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such changes and modifications fall within the scope of the appended claims.

[0180] [Examples] Example 1 The positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide (molar ratio of Ni:Co:Mn:Al is 88:6:4:2)) discarded after punching out the positive electrode plates was crushed, and then heat-treated in air at 570°C for 30 minutes to remove the binder and conductive material, separate the current collector and positive electrode active material, and then recover the positive electrode active material. Here, the rate of temperature rise to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0181] The recovered positive electrode active material and a 1% by weight LiOH aqueous solution (hereinafter referred to as "washing solution") were mixed in a 1:1 weight ratio and stirred for 5 minutes under conditions of 700 rpm to form a slurry. After that, a filter press (manufacturer: DAESUNG FILTER Co., Ltd., air permeability 0.8 cc / cm²) was used. 2 The material was filtered (dewatered) using a filter cloth made of PP material ( / sec) to form a filter cake in a filter press. The filter cake formed in the filter press was rinsed with a rinsing solution (same as the washing solution) weighing 10 times the weight of the recovered positive electrode active material, and then a filter cake of the positive electrode active material was obtained.

[0182] To the washed positive electrode active material filter cake, an amount of lithium precursor LiOH corresponding to a lithium molar ratio of 0.10 to 0.15 was added, using the molar ratio of lithium to other metals in the raw positive electrode active material (ICP analysis) as a reference (lithium molar ratio of 1). The mixture was then heat-treated in air (supply rate: 3 L / min) at 750°C for 3 hours to restore the crystal structure of the positive electrode active material. Theoretically, in the case of newly formed positive electrode active material, the Li molar ratio is 1. However, since the average error of the ICP instrument used to confirm this is ±0.05, preferably ±0.02, the Li molar ratio of the raw active material measured by ICP may be 1 ± 0.05:1. In this experiment, the lithium precursor was added based on the molar ratio measured by ICP analysis.

[0183] The cathode active material, whose crystalline structure had been restored, was mixed with neutral water as a washing solution in a 1:1 weight ratio. The mixture was stirred at 700 rpm for 5 minutes to form a slurry. The slurry was then filtered (dehydrated) using a filter press in the same manner as the preceding washing to remove residual Li compounds and obtain a filter cake of the cathode active material. The obtained filter cake of the cathode active material was dried under reduced pressure at 110°C to obtain the cathode active material after the subsequent water washing.

[0184] After the subsequent water washing, boric acid was added as a dopant precursor to the cathode active material in an amount equivalent to 700 ppm of boron (B) based on the total weight (dry mass basis) of the cathode active material after the subsequent water washing. The material was then heated at 600°C for 5 hours to produce the final regenerated cathode active material. During this process, the temperature rise rate to reach the heating temperature was 2°C / min, and air was supplied at 3 L / min.

[0185] The doped cathode active material and neutral water as a washing solution were mixed in a 1:1 weight ratio and stirred at 700 rpm for 2 minutes to form a slurry. The slurry was then filtered (dewatered) using a filter press in the same manner as the subsequent washing step to remove the coating layer and obtain a filter cake of the cathode active material. This filter cake was then dried under reduced pressure at 110°C to produce the final doped regenerated cathode active material.

[0186] In this application, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. While this can be done using a general ICP analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0187] Example 2 In the same manner as in Example 1, a regenerated cathode active material was produced, except that boric acid was added as a dopant precursor to the cathode active material after the subsequent water washing, in an amount equivalent to 1400 ppm of boron (B) based on the total weight (on a dry mass basis) of the cathode active material after the subsequent water washing.

[0188] Comparative Example 1 In the above-mentioned Example 1, a regenerated cathode active material was produced in the same manner as in Example 1, except that the doping step of adding a dopant precursor and heat treatment, and the step of washing the doped cathode active material with a washing solution were omitted.

[0189] Comparative Example 2 In the above-described Example 1, the regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the step of washing the doped positive electrode active material with a cleaning solution was omitted.

[0190] Comparative Example 3 In the above-mentioned Example 1, a regenerated cathode active material was produced in the same manner as in Example 1, except that boric acid (H3BO3), which is a dopant precursor, was added in an amount that was in a molar ratio of 2:1 with LiOH, which is a lithium precursor, and the step of washing the doped cathode active material with a washing solution was omitted.

[0191] Figure 3 is a conceptual diagram showing the schematic structure of the regenerated cathode active material produced in Example 1 and Comparative Examples 1 to 3, respectively.

[0192] Referring to Figure 3, the regenerated cathode active material produced in Example 1 is doped with a dopant instead of a conventional surface coating. This not only eliminates side reactions between the coating layer and the cathode active material, but also stabilizes the surface due to effects such as a reduction in nickel (Ni) elements on the cathode active material surface caused by the dopant, thereby achieving improved long-term lifespan characteristics and increased initial charge / discharge capacity.

[0193] On the other hand, the regenerated positive electrode active material produced in Comparative Example 1 is a positive electrode active material that has been regenerated without any surface modification, as it has developed cracks due to deterioration caused by rolling and the progression of charge-discharge cycles during the manufacturing process of the positive electrode. Unlike the newly produced positive electrode active material, the specific surface area increases significantly due to the cracks, and this leads to an increase in side reactions on the surface of the regenerated positive electrode active material, resulting in an overall decrease in the performance of the regenerated positive electrode active material.

[0194] In Comparative Example 2, a surface coating layer was formed on the regenerated positive electrode active material along with a doping layer. However, by not removing the surface coating layer, cracks began to form at the interface between the positive electrode active material surface and the coating layer as the charge-discharge cycle progressed. This resulted in resistance between dissimilar interfaces, degrading the long-term lifespan. Here, the surface coating layer may be a boron coating layer containing B2O3 and a small amount of LBO (a reaction product of boric acid and LiOH remaining on the surface of the positive electrode active material).

[0195] Furthermore, in Comparative Example 3, an attempt was made to improve the side effects caused by cracks by forming a coating layer on the surface of the regenerated positive electrode active material. However, in such cases, as the charge-discharge cycle progresses, cracks begin to occur at the interface between the positive electrode active material surface and the coating layer, which causes resistance between dissimilar interfaces and degrades the long-term lifespan. In this case, the surface coating layer may be a boron coating layer containing LBO as the main component, due to the addition of LiOH simultaneously with the dopant precursor.

[0196] [Test Example I] The surface composition and overall composition of the regenerated cathode active materials obtained from Examples 1-2 and Comparative Examples 1-3 were measured by the following methods, and the results are shown in Table 1 below.

[0197] *Atomic percent (at%): The composition ratio was measured using energy dispersive X-ray spectroscopy (EDS). Here, an EDS instrument equipped with an AZtec extreme detector was used under conditions of 5kV and a working distance of 7mm.

[0198] *ICP analysis: An ICP analyzer was used to measure the content of residual F component, the ratio of lithium (Li) to other metals (M) in the positive electrode active material, and the content (mg / kg) of specific elements such as B and W. While this can be done using a standard ICP analyzer commonly used in laboratories, there is no difference depending on the measuring device or method.

[0199] [Table 1]

[0200] As can be seen from Table 1 above, the regenerated cathode active material obtained through the doping step and coating layer removal (cleaning) step according to the present invention (Example 1) did not contain boron (B) atoms on its surface, unlike the regenerated cathode active material that did not undergo the doping step according to the present invention (Comparative Example 1). Figures 4 and 5 are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images of the regenerated cathode active materials produced in Example 1 and Comparative Example 1, respectively. In each figure, the three images on the right are color-coded images to distinguish between the elements carbon (C), oxygen (O), and nickel (Ni), respectively.

[0201] Referring to Figures 4 and 5, it was confirmed that the regenerated cathode active material produced in Example 1 had a uniform surface because only the doped dopant remained and the coating layer was removed by washing. Similarly, the regenerated cathode active material produced in Comparative Example 1 did not undergo a doping step, so the boron coating layer itself was not formed, and thus all surfaces were uniform. Therefore, the composition ratio is the same regardless of where it is measured on the regenerated cathode active material.

[0202] For reference, a regenerated cathode active material (Comparative Example 2) that underwent only a doping step and did not undergo a coating layer removal (cleaning) step, and a regenerated cathode active material (Comparative Example 3) that was manufactured by adding LiOH together with boric acid in the doping step to induce a reaction with LiOH to form a coating layer before boron (B) atoms could be inserted as a dopant, showed a large amount of boron (B) element on its surface.

[0203] Figures 6 and 7 show EDS (Energy Dispersive Spectrometer) cross-sectional mapping images of the regenerated cathode active materials produced in Comparative Example 2 and Comparative Example 3, respectively. In each figure, the four images on the right are color-coded to distinguish between the elements boron (B), carbon (C), oxygen (O), and nickel (Ni), respectively.

[0204] Referring to Figure 6, in Comparative Example 2, since no additional LiOH was added along with the dopant precursor, a B2O3 coating layer was formed in the regenerated cathode active material. Therefore, elemental analysis was performed at location #11 where the B2O3 coating layer was formed, and at location #12 where the B2O3 coating layer was not formed.

[0205] Referring to Figure 7, the regenerated cathode active material produced in Comparative Example 3 was subjected to additional LiOH along with the dopant precursor to form an LBO coating layer. Therefore, elemental analysis was performed at locations #13, #15, and #16 where the LBO coating layer was formed, and at location #14 where the LBO coating layer was not formed.

[0206] Table 2 below shows the boron (B) content using IPC analysis.

[0207] [Table 2]

[0208] As can be seen from Table 2 above, in the regenerated cathode active material (Example 1) obtained through the doping step and coating layer removal (washing) step according to the present invention, no boron (B) element was detected in surface analysis using EDS, but boron (B) element was detected in the analysis of the entire component using IPC analysis, confirming that it was doped with a dopant. Furthermore, in the case of Example 2, even though the amount of boron compound added was doubled, a similar level of boron (B) was detected. This confirms that even if a larger amount of boron compound is added compared to Example 1, only a similar level of dopant is applied, and the remainder is removed in the final water washing step. On the other hand, in the regenerated cathode active material that did not undergo the doping step (Comparative Example 1), no boron (B) element was detected in IPC analysis. In contrast, in the regenerated cathode active materials that underwent only the doping step and did not undergo the coating layer removal (washing) step (Comparative Examples 2 and 3), an excess amount of boron (B) appeared compared to Example 1. This indicates that the boron (B) element doped as a dopant and the boron (B) element present in the coating layer were combined.

[0209] [Test Example II] The changes in the content of detected elements in the regenerated positive electrode active materials obtained from Example 1 and Comparative Examples 1-3 were measured by X-ray diffraction analysis (Thermo Ficher Scientific Inc., k-alpha system), and the results are shown in Figure 8.

[0210] As shown in Figure 8, the regenerated cathode active material of Example 1 obtained through the doping step and coating layer removal (washing) step according to the present invention had the B2O3 formed on the surface as a coating layer removed (washing) step, so only the doped boron (B) element dopant was detected. Therefore, it was confirmed that a lower content of boron (B) element was detected compared to the regenerated cathode active materials of Comparative Examples 2 and 3.

[0211] On the other hand, in Comparative Example 1, no boron (B) element was detected in the regenerated cathode active material because boric acid was not added. In Comparative Examples 2 and 3, similar levels of boron (B) element were detected in the regenerated cathode active materials, but in Comparative Example 2, unlike Comparative Example 3, no additional Li precursor (LiOH, Li2CO3, etc.) capable of forming a LiB3O5 coating layer was used, resulting in a relatively lower Li content. This indicates that the B2O3 coating layer was formed at 600°C, the thermal decomposition temperature of boric acid.

[0212] [Test Example III: Evaluation of CHC Cells] The electrochemical performance of the regenerated cathode active materials obtained from Example 1 and Comparative Examples 1-3 was measured by CHC cell evaluation as described below, and the results are shown in Figures 9 and 10.

[0213] *CHC cell manufacturing: 96% by weight of recycled cathode active material, 2% by weight of carbon black as a conductive material, and 2% by weight of PVdF as a binder were weighed and mixed with NMP to produce a slurry. After manufacturing the cathode by coating aluminum foil with this slurry, a cell (Coin Half Cell, CHC) was manufactured, and its electrochemical performance (charging capacity CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under conditions containing ethylene carbonate (EC):dimethylmethyl carbonate (DMC) = 3:7 (by weight ratio) as the electrolyte, and other additives.

[0214] *Evaluation of initial cell capacity (CH and DCH): Each cell was charged and discharged once at 25°C under the following conditions, and the results are shown in Figure 9.

[0215] Charging (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 with the charge capacity and discharge capacity obtained from the evaluation of the initial capacity of the cell.

[0216] [Formula 1] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] × 100 Figure 9 is a graph showing the results of the charging capacity of coin half cells to which the regenerated positive electrode active materials from Examples 1-2 and Comparative Examples 1-3 were applied.

[0217] Referring to Figure 9, it was confirmed that the regenerated cathode active material of Example 1, which was doped with boron (B) without a coating layer after the doping step and coating layer removal (cleaning) step according to the present invention, exhibited the best initial charge / discharge capacity and charge / discharge efficiency due to the doping effect, resulting in low surface resistance and suppressed surface side reactions. Furthermore, in the case of Example 2, since the amount of dopant doped into the regenerated cathode active material was similar to that of the regenerated cathode active material of Example 1, it was confirmed that it showed similar result values ​​to those of Example 1.

[0218] On the other hand, the regenerated cathode active material of Comparative Example 1 did not undergo a doping step, so no doping or coating was formed, resulting in the lowest initial charge / discharge capacity and charge / discharge efficiency. In Comparative Examples 2 and 3, the regenerated cathode active materials that underwent only a doping step and not a coating layer removal (cleaning) step, were partially doped, but the B2O3 coating layer and LiB3O5 coating layer, respectively, acted as surface resistance, resulting in a decrease in initial charge / discharge capacity and charge / discharge efficiency.

[0219] *Evaluation of Capacity Retention Rate (%): After forming each cell at a rate of 0.1C, charging / discharging at 0.33 / 0.33C, 0.05C cutoff CC / CV charging, and CC discharging were performed at 45°C. Measurements were taken using a PNE-0506 charge / discharger (manufacturer: PNE Solutions Co., Ltd.), and the discharge capacity after one cycle was set as the initial capacity. Subsequently, the discharge capacity in each cycle was compared with the initial capacity (100%), and the capacity retention rate was calculated using the following formula 2, and the results are shown in Figure 10.

[0220] [Formula 2] Capacity retention rate (%) = (Discharge capacity after cycle / Initial discharge capacity) × 100 Figure 10 shows the results of coin half-cell evaluation for each of the regenerated cathode active materials produced in Example 1 and Comparative Examples 1-3, and is a graph showing the change in capacity retention rate with respect to the number of cycles (Cycle No.).

[0221] Referring to Figure 10, it was confirmed that the regenerated cathode active material of Example 1, which was doped with boron (B) element without a coating layer after undergoing the doping step and coating layer removal (cleaning) step according to the present invention, exhibited the best capacity retention rate, i.e., lifetime characteristics, due to the doping effect, resulting in low surface resistance and suppression of surface side reactions.

[0222] On the other hand, the regenerated cathode active material of Comparative Example 1 did not undergo a doping step, so no doping or coating was formed, resulting in the worst lifetime characteristics. The regenerated cathode active material of Comparative Example 2, which underwent only a doping step and no coating layer removal (cleaning) step, was partially doped, but the B2O3 coating layer acted as a surface resistance, resulting in reduced lifetime characteristics. The regenerated cathode active material of Comparative Example 3, in which LiOH was added during the doping step of Comparative Example 2, was partially doped, but the LiB3O5 coating layer acted as a surface resistance, though not to the same extent as the B2O3 coating layer, resulting in reduced lifetime characteristics. [Explanation of symbols]

[0223] 10 Current collector 20 Active material layer 30 Positive electrode sheets 40 Positive plate 50 Positive electrode scrap

Claims

1. A regenerated cathode active material comprising one or more 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 lithium composite metal oxide in which a portion of the nickel (Ni) in lithium nickel oxide is replaced with manganese (Mn), and NCM-based lithium composite transition metal oxide in which a portion of the nickel (Ni) in lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co), The aforementioned regenerated cathode active material is finished by surface doping with a dopant without a coating layer. The regenerated cathode active material is a regenerated cathode active material in which the amount of dopant elements coated on the surface without doping is 10 ppm or less, based on EDS surface mapping.

2. The regenerated cathode active material according to claim 1, wherein the dopant is present in an amount of 100 to 2000 ppm relative to the total weight of the regenerated cathode active material.

3. The regenerated positive electrode active material according to claim 1, wherein the dopant is one or more selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N.

4. The regenerated cathode active material according to claim 1, wherein the regenerated cathode active material contains 40 to 45% by weight of carbon, 25 to 30% by weight of oxygen, and 25 to 30% by weight of nickel, based on EDS surface mapping.

5. A secondary battery comprising the regenerated positive electrode active material according to any one of claims 1 to 4.

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