Method for regenerating positive electrode active material and regenerated positive electrode active material manufactured thereby

Abstract

The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material manufactured thereby and, more specifically, to a method for regenerating a positive electrode active material and a regenerated positive electrode active material manufactured thereby, the method comprising: (a) a step for recovering a positive electrode material by heat-treating, in air or oxygen, a waste positive electrode including a current collector and a positive electrode active material layer coated thereon; (b) a step for adding a lithium precursor to the recovered positive electrode active material and heat-treating in air to restore the crystal structure of the positive electrode active material; (c) a step for adding a dopant precursor to the positive electrode active material with the restored crystal structure and heat-treating same to dope the positive electrode active material; and (d) a step for washing the doped positive electrode active material with a washing solution.　According to the present invention, the regenerated positive electrode active material is doped with a predetermined dopant using a predetermined method, thereby improving capacity characteristics and lifespan characteristics. Thus, the present invention has the effect of providing a method for regenerating a positive electrode active material having excellent crack resistance and a regenerated positive electrode active material manufactured thereby.

Description

Method for regenerating a cathode active material and regenerated cathode active material manufactured thereby

[0001] 〔Cross-citation with the applicant(s)〕

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0152017, dated November 6, 2023, and Korean Patent Application No. 10-2024-0144952, filed October 22, 2024, which is hereby incorporated by reference in its entirety.

[0003] The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material manufactured therefrom, and more particularly, to a method for regenerating a positive electrode active material having improved capacity characteristics and lifespan characteristics and excellent crack resistance by doping a predetermined dopant into the regenerated positive electrode active material by a predetermined method, and to a regenerated positive electrode active material manufactured therefrom.

[0004] In addition, the present invention relates to a method for regenerating a cathode active material suitable for mass production using an easy-to-manage process such as heat treatment or sedimentation, and a regenerated cathode active material manufactured therefrom, which is environmentally friendly and reduces process costs since neutralization and wastewater treatment are not required, does not decompose the cathode active material and is thus regenerated without discarding any metal elements, does not dissolve the current collector and thus enables its recovery, does not use an organic solvent and thus does not generate toxic gases or pose a risk of explosion, and has excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0005] A lithium secondary battery is largely composed of a cathode in which a positive active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative active material layer is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing, and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0006] The positive electrode active material layer mainly uses lithium oxide as an active material, and the negative electrode active material layer mainly uses carbon material as an active material. The lithium oxide generally contains rare metals such as cobalt, nickel, or manganese, and thus, much research is being conducted to recover and recycle rare metals from the positive electrode of a lithium secondary battery that is discarded after use or the positive electrode scrap generated in the lithium secondary battery manufacturing process (hereinafter referred to as “spent positive electrode”).

[0007] Conventional techniques for recovering rare metals from spent anodes mostly involve dissolving the spent anodes in hydrochloric acid, sulfuric acid, or nitric acid, and then extracting cobalt, manganese, nickel, etc. with an organic solvent to use them again as raw materials for synthesizing anode active materials.

[0008] However, the method of extracting rare metals using acids has the problem of environmental pollution, requires a neutralization process and a wastewater treatment process, which significantly increases the process cost, and has the disadvantage of not being able to recover lithium, the main metal of the positive electrode active material.

[0009] To overcome these shortcomings, a method of directly regenerating the positive electrode active material from the waste positive electrode without decomposing it (direct recycled method) has been recently studied, and four types of this method have been introduced, including calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0010] However, the above-mentioned sintering method, although simple in process, has the disadvantages of generating foreign substances on the surface of the regenerated positive electrode active material that reduce the output performance of the battery, generating waste gas, and consuming a lot of energy. In particular, in order to remove foreign substances such as LiF, an excessive amount of initial washing water must be used, which makes it difficult to apply the regeneration process. In addition, not only does the same amount of waste water be generated, but the washing causes the loss of Li in the functional coating layer and lattice of the regenerated positive electrode active material, and increases the occurrence of cracks that reduce the output performance of the secondary battery, which are major problems. Among these, byproducts generated during the degradation process can be removed by washing, and the loss of Li can be overcome to some extent by replenishing the Li source, but physically generated cracks cannot be restored to the same particle size distribution as the virgin positive electrode active material using the conventional direct recycled method. The occurrence of the above cracks causes an increase in the fine particles and specific surface area of ​​the regenerated positive electrode active material, which promotes side reactions between the electrolyte and the surface of the regenerated positive electrode active material, thereby reducing active lithium and increasing the overall cell resistance, which ultimately becomes a factor in lowering the life characteristics of the battery.

[0011] In addition, the above solvent dissolution method can obtain a regenerated positive electrode active material with a relatively clean surface, but has the disadvantage of poor stability due to the solvent such as N-methyl-2-pyrrolidone (NMP) used to dissolve the binder being a toxic gas and having a risk of explosion, and requiring an expensive solvent recovery process.

[0012] In addition, the above aluminum foil melting method has good process stability, low process cost, and easy binder removal, but has the disadvantages of generating foreign substances that are difficult to remove on the surface of the regenerated positive electrode active material, and generating hydrogen gas during the process of removing the aluminum foil, which poses a risk of explosion.

[0013] Lastly, although the above 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 changes during the crushing process, and the binder remains, which deteriorates the battery characteristics of the regenerated positive electrode active material.

[0014] Therefore, there is an urgent need to develop a method for regenerating anode active materials that can be safely and cost-effectively regenerated without discarding metal elements from waste cathodes, with improved output performance and lifespan characteristics, and that can improve crack resistance and significantly reduce wastewater.

[0015] In order to solve the problems of the prior art as described above, the present invention aims to provide a method for regenerating a positive electrode active material having improved capacity characteristics and lifespan characteristics and excellent crack resistance by doping a predetermined dopant into the positive electrode active material by a predetermined method, and a regenerated positive electrode active material manufactured thereby.

[0016] In addition, the present invention is environmentally friendly because it does not use acid, and thus the process cost is reduced because neutralization and wastewater treatment are not required, and since the cathode active material is regenerated as it is without decomposition, there are no discarded metal elements, and since the current collector is not dissolved, it can be recovered, and since no organic solvent is used, there is no risk of toxic gas generation or explosion, and it is suitable for mass production by using an easy-to-manage process such as heat treatment or sedimentation, and an object of the present invention is to provide a method for regenerating a cathode active material and a regenerated cathode active material manufactured therefrom having excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0017] The above and other objects of the present invention can all be achieved by the present invention described below.

[0018] In order to achieve the above object, I) the present invention provides a regenerable cathode active material comprising at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and 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), characterized in that the material is doped with a dopant and has no coating layer.

[0019] II) In the above I), the dopant may be included in an amount of 100 to 2000 ppm based on the total weight of the regenerative positive electrode active material.

[0020] III) In the above I) or II), the dopant may be at least one selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C, and N.

[0021] IV) In the above I) to III), the regenerative positive electrode active material may have a dopant element coated on the surface that is not doped and is 10 ppm or less based on EDS (Energy Dispersive Spectroscopy) surface mapping.

[0022] V) In the above I) to IV), the regenerative positive electrode active material may include 40 to 45 wt% of carbon element, 25 to 30 wt% of oxygen element, and 25 to 30 wt% of nickel element based on EDS (Energy Dispersive Spectroscopy) surface mapping.

[0023]

[0024] In addition, VI) the present invention provides a method for regenerating a positive electrode active material, comprising the steps of: (a) recovering a positive electrode active material by heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon under air or oxygen; (b) adding a lithium precursor to the recovered positive electrode active material and heat-treating it in air to restore a crystal structure; (c) adding a dopant precursor to the positive electrode active material of which the crystal structure has been restored and heat-treating it to dope it; and (d) washing the doped positive electrode active material with a washing solution.

[0025] VII) In the above VI), the heat treatment in step (a) can be performed under conditions of 300 to 650°C.

[0026] VIII) In the above VI) or VII), the heat treatment in step (b) can be performed at a temperature of 400 to 1000°C.

[0027] IX) In the above VI) to VIII), in the step (b), the lithium precursor may be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0028] X) In the above VI) to IX), the heat treatment in step (c) can be performed under conditions of 300 to 1000°C.

[0029] XI) In the above VI) to X), in the step (c), the dopant precursor may be 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, C and N as a dopant.

[0030] XII) In the above VI) to XI), the washing liquid in the step (d) may be water.

[0031] XIII) In the above VI) to XII), the method for regenerating the positive electrode active material may include (a-2) a step of washing the recovered positive electrode active material with a washing solution; and / or (b-2) a step of washing the positive electrode active material whose crystal structure has been restored.

[0032] XIV) In the above VI) to XIII), in the step (a-2), the washing liquid may be water or a basic lithium compound aqueous solution of more than 0 wt% to 15 wt% or less, and in the step (b-2), the washing liquid may be water.

[0033] XV) In the above VI) to XIV), in the step (c), the dopant precursor can be added in an amount of 100 to 2000 ppm (based on dopant element) based on the total weight of the regenerated positive electrode active material.

[0034] XVI) In the above VI) to XV), the positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co).

[0035]

[0036] In addition, XVII) The present invention provides a regenerated positive electrode active material characterized by being manufactured by the regeneration method of the positive electrode active material of VI) to XVI).

[0037]

[0038] In addition, XVIII) The present invention provides a secondary battery including a regenerative positive electrode active material according to I) to XVII).

[0039] According to the present invention, there is provided a method for regenerating a positive electrode active material having improved capacity characteristics and lifespan characteristics and excellent crack resistance by doping a predetermined dopant into a regenerated positive electrode active material using a predetermined method, and a regenerated positive electrode active material manufactured thereby.

[0040] In addition, according to the present invention, since it does not use acid, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced, since the cathode active material is regenerated as it is without decomposition, there are no discarded metal elements, since the current collector is not dissolved, it can be recovered, since no organic solvent is used, there is no risk of toxic gas generation or explosion, and since it uses an easy-to-manage process such as heat treatment or sedimentation, there is an effect of providing a method for regenerating a cathode active material suitable for mass production, and a regenerated cathode active material manufactured thereby and having excellent electrochemical performance and resistance characteristics.

[0041] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description given below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be construed as being limited to the matters described in these drawings.

[0042] Figure 1 is a drawing showing anode scrap that is discarded after cutting an electrode plate from a cathode sheet.

[0043] Figure 2 is a flowchart of a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0044] Figure 3 is a conceptual diagram schematically showing the structure of the regenerated positive electrode active materials manufactured in Example 1 and Comparative Examples 1 to 3, respectively.

[0045] Figures 4 and 5 are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images of the regenerated positive electrode active materials manufactured in Example 1 and Comparative Example 1, respectively. Here, the B2O3 coating layer is not found.

[0046] Figures 6 and 7 are EDS (Energy Dispersive Spectrometer) mapping images for the regenerated positive electrode active materials manufactured in Comparative Examples 2 and 3, respectively. Here, a boron coating layer was confirmed, and elemental analysis was performed at points #11, #13, #15, and #16 where a boron coating layer was formed, and points #12 and #14 where a boron coating layer was not formed.

[0047] Figure 8 is an XPS graph showing the change in the content of detected elements according to the etching time of the regenerated positive electrode active materials manufactured in Example 1 and Comparative Examples 1 to 3, respectively.

[0048] Figure 9 is a graph showing the results of the initial charge / discharge capacity of a coin half cell to which the positive electrode active material regenerated in Example 1 and Comparative Examples 1 to 3 was applied.

[0049] Figure 10 is a graph showing the change in capacity retention according to the number of cycles (Cycle No.) as a result of coin half cell evaluation for each of the regenerated positive electrode active materials manufactured in Example 1 and Comparative Examples 1 to 3.

[0050]

[0051] Hereinafter, a method for regenerating the positive electrode active material of the present invention and a regenerated positive electrode active material manufactured therefrom are described in detail.

[0052] The present inventors, while studying a method for further improving the capacity characteristics and life characteristics of a recycled positive electrode active material in a method for directly regenerating the positive electrode active material without decomposing the positive electrode active material from a waste positive electrode (direct recycled method), confirmed that when a predetermined dopant is doped on the recycled positive electrode active material by a predetermined method instead of coating it as in the conventional method, the crack resistance of the recycled positive electrode active material is improved, and the capacity characteristics and life characteristics of a battery using the same are greatly improved, and based on this, they devoted themselves to further research and completed the present invention.

[0053] The method for regenerating a positive electrode active material of the present invention comprises the steps of: (a) recovering a positive electrode active material by heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon under air or oxygen; (b) adding a lithium precursor to the recovered positive electrode active material and heat-treating it in air to restore the crystal structure; (c) adding a dopant precursor to the positive electrode active material whose crystal structure has been restored and heat-treating it to dope it; And (d) a step of washing the doped positive electrode active material with a washing solution, in which case, the capacity characteristics and life characteristics of the regenerated positive electrode active material are improved, crack resistance is excellent, and it is environmentally friendly because it does not use acid, and therefore, the process cost is reduced because neutralization and wastewater treatment are not required, the positive electrode active material is regenerated as it is without decomposition, so there are no discarded metal elements, the current collector is not dissolved, so it can be recovered, there is no generation of toxic gases or risk of explosion because an organic solvent is not used, and there is an advantage of providing a method for regenerating a positive electrode active material suitable for mass production using an easy-to-manage process such as heat treatment or sedimentation, and a regenerated positive electrode active material manufactured thereby and having excellent electrochemical performance and resistance characteristics.

[0054]

[0055] Below, the method for regenerating the positive electrode active material of this invention is examined in detail step by step.

[0056] However, the terms or words used in this specification and claims cannot be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own application in the best way. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are only one embodiment of the present invention and do not represent all of the technical idea of ​​the present invention, and it should be understood that there may be various equivalents and modified examples that can replace them, and that they can be arranged, replaced, combined, separated, or designed in various other configurations.

[0057] All technical and scientific terms used in this document, unless otherwise defined, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains.

[0058]

[0059] (a) A step of recovering positive electrode active material from a waste positive electrode.

[0060] According to the present invention, the step of recovering a positive electrode active material from a waste positive electrode (a) may be a step of recovering a positive electrode active material by heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon, and preferably, a step of recovering a positive electrode active material by heat-treating a waste positive electrode having a positive electrode active material layer including 60 mol% or more of Ni among transition metals formed on a current collector in air at 300 to 650° C. to thermally decompose a binder and a conductive material in the positive electrode active material layer, and in this case, the process is simple and has the effect of cleanly removing the binder, conductive material, and current collector.

[0061] The above-mentioned waste positive electrode may preferably be a positive electrode separated from a lithium secondary battery discarded after use, a defective positive electrode sheet or positive electrode scrap generated in a lithium secondary battery manufacturing process, and more preferably, a positive electrode scrap remaining after punching out a positive electrode plate from a positive electrode sheet.

[0062] The positive electrode active material layer of the above step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0063] The above-described positive electrode active material may be at least one selected from the group consisting of lithium cobalt oxide such as LiCoO2 (hereinafter referred to as 'LCO'); lithium manganese oxide such as LiMnO2 or LiMn2O4; lithium iron phosphate compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide such as LiNiO2; nickel manganese-based lithium composite metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co), and more preferably, nickel manganese-based lithium composite metal oxide, NCM-based lithium composite transition metal oxide, or a mixture thereof, in which case, excellent reversible capacity and thermal stability are achieved.

[0064] As another specific example, the positive electrode active material is represented by the following chemical formula 1

[0065] [Chemical Formula 1]

[0066] Li a Ni x Mn y Co z M w O 2+δ

[0067] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1이다.)로 표시되는 화합물일 수 있다.

[0068]

[0069] The above-mentioned positive electrode active material contains, for example, 60 mol% or more of Ni, preferably 80 mol% or more, more preferably 81 mol% or more, still more preferably 81 to 95 mol%, and still more preferably 85 to 95 wt%, based on 100 mol% of the total metals excluding Li, and within this range, it has excellent effects in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0070] In this description, the Ni content is not particularly limited when measured using a measurement method such as IC (Ion Chromatography) commonly used in the technical field to which the present invention belongs, and specific examples thereof include an IC-ICP (Inductively Coupled Plasma) analysis device, an IC-ICP-MS analysis device, or an IC-ICP-AEC analysis device.

[0071]

[0072] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, CNT, or a mixture thereof.

[0073] 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.

[0074]

[0075] The above heat treatment can be performed, for example, in an air or oxygen atmosphere, in which case the binder and the conductive material are thermally decomposed into CO2 and H2O and removed, thereby separating the positive electrode active material from the current collector, and the separated positive electrode active material has the advantage of being easily sorted in powder form.

[0076]

[0077] The above heat treatment temperature may be preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C, and within this range, the current collector does not melt, and only the binder, etc. is removed, so that the positive electrode active material is easily separated from the current collector.

[0078] The heat treatment time is preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour, and within this range, there is an advantage in that the current collector is not melted and only the binder, etc. are removed, so that the positive electrode active material is easily separated from the current collector.

[0079] In this description, the heat treatment time refers to the time spent at the corresponding heat treatment temperature, and the time spent reaching the corresponding heat treatment temperature is not counted.

[0080]

[0081] The above heat treatment can be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min, and can be performed within this range without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0082]

[0083] The following drawing 1 shows the anode scrap that is discarded after cutting the anode plate from the anode sheet.

[0084] Referring to Fig. 1, a positive electrode sheet (30) is manufactured by coating a positive electrode active material layer (20) including a positive electrode active material, a conductive material, a binder, etc. on a long sheet-shaped positive electrode current collector, aluminum foil (10), and then the positive electrode sheet (30) is punched to a certain size to produce a positive electrode plate (40), and the remaining portion is then used to produce positive electrode scrap (50). The punching is one means of cutting the positive electrode sheet.

[0085] In addition, the positive electrode active material layer (20) is formed by coating a slurry containing a mixture of a positive electrode active material, a conductive agent, a binder, and a solvent onto aluminum foil (10). The slurry is very sensitive to the environment, such as temperature, and it is not easy to determine the coating conditions. Therefore, a considerable amount of waste positive electrode sheets are generated until conditions for manufacturing a positive electrode sheet (30) of the desired quality are found through a predetermined test.

[0086] For reference, in the examples below, anode scrap was used as the anode.

[0087]

[0088] Step of washing the recovered positive electrode active material

[0089] The method for reusing a 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 “pre-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, thereby having the effect of improving the rate performance of the battery.

[0090] During the above heat treatment, the binder and conductive material inside the positive electrode active material are thermally decomposed, resulting in CO2 and H2O reacting with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH, and fluorine (F) present in the binder, such as PVdF, reacting with the metal elements constituting the positive electrode active material to form LiF or metal fluoride. If LiF or metal fluoride remains, the battery characteristics deteriorate when the positive electrode active material is reused.

[0091]

[0092] The step of washing the recovered positive electrode active material (a-2) may be, for example, a step of mixing the recovered positive electrode active material with a washing solution and then filtering it using a filter press to wash it. In this case, since the residual F content is determined by the amount of the rinsing solution, even if the amount of the positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, the total amount of the washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. In addition, by minimizing the amount of the initial washing solution injected into the stirring tank and controlling the amount of the rinsing solution, there is an effect of easily removing the residual F component and improving the rate performance of the battery.

[0093]

[0094] The filter press of the above (a-2) washing step can preferably be operated under an air pressure of 2 to 10 bar, more preferably an air pressure of 3 to 9 bar, even more preferably an air pressure of 3 to 8 bar, still more preferably an air pressure of 3 to 7 bar, and most preferably an air pressure of 3 to 6 bar, and within this range, the content of the residual F component is determined by the amount of the rinsing solution, so that even when the amount of the positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, the total amount of the washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. In addition, by minimizing the amount of the initial washing solution injected into the stirring tank and controlling the amount of the rinsing solution, there is an effect of easily removing the residual F component and improving the output performance of the battery.

[0095] The filter press of the above (a-2) washing step preferably has a ventilation rate of 0.1 to 15 cc / cm. 2 (sec) may include a filter cloth, more preferably having a breathability of 0.2 to 10 cc / cm. 2 (sec) filter cloth, more preferably with a permeability of 0.3 to 5 cc / cm 2 (sec) filter cloth, more preferably with a permeability of 0.5 to 2 cc / cm 2 (sec) filter cloth, most preferably with a permeability of 0.6 to 1 cc / cm 2(sec) filter cloth, and within this range, the residual F content is determined by the amount of rinsing solution, so that even when the amount of positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, the total amount of washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. In addition, by minimizing the amount of initial washing solution injected into the stirring tank and controlling the amount of rinsing solution, it is possible to easily remove the residual F component and at the same time improve the output performance of the battery.

[0096] The above filter cloth is not particularly limited as long as it is a material commonly used for filter presses according to the definition of the present invention, but as a specific example, it may be a polypropylene material.

[0097] The filter press of the present invention is not particularly limited in its type or material, etc., as long as it conforms to the definition of the present invention and is physically and chemically stable to the positive electrode active material slurry, and may include, for example, a frame, a filter plate, a filter cloth, a filter cloth pressurizing device, a filter plate separating device, a filter cloth washing device, and a transfer pump.

[0098]

[0099] The washing solution of the above (a-2) washing step may preferably be water or an aqueous alkaline lithium compound solution, and in this case, the F component remaining on the surface of the regenerated positive electrode active material is cleanly removed with a small amount of washing solution, thereby significantly reducing the generation of wastewater and at the same time, significantly improving the output performance of the battery.

[0100] In this description, water is not particularly limited as long as it is neutral water, and may be, for example, distilled water, ion-exchanged water, etc.

[0101] The washing solution of the washing step (a-2) may be, for example, an alkaline lithium compound aqueous solution, in which case, not only can the binder that may remain in trace amounts on the surface of the positive electrode active material recovered after the thermal decomposition in step (a) be removed, but also has the advantage of not dissolving transition metals, etc. present in the recovered positive electrode active material, and replenishing the amount of lithium that may be dissolved during washing. If an acidic aqueous solution, such as a sulfuric acid or hydrochloric acid aqueous solution, is used as the washing solution, the F component on the surface of the positive electrode active material may be washed, but the transition metals, etc. present in the positive electrode active material may be dissolved, thereby lowering the performance of the reused positive electrode active material.

[0102] The above basic lithium compound aqueous solution may preferably contain from more than 0 wt% to less than 15 wt% of the basic lithium compound, more preferably from more than 0 wt% to 10 wt% of the basic lithium compound, and even more preferably from 0.5 to 5 wt% of the basic lithium compound, and within this range, the surface modification effect such as the removal of LiF and metal fluoride as F components formed on the surface of the positive electrode active material in the preceding heat treatment process is excellent.

[0103]

[0104] The above (a-2) washing step may preferably include a step (a1) of mixing the recovered positive electrode active material with a washing solution to form a slurry; and a step (a2) of feeding the slurry into a filter press and filtering it, and more preferably, may include a step (a1) of mixing the recovered positive electrode active material with a washing solution to form a slurry; a step (a2) of feeding the slurry into a filter press and filtering it; and a step (a3) ​​of feeding a rinsing solution into the filter press and rinsing the filter cake. In this case, since the content of the residual F component is determined by the amount of the rinsing solution, even if the amount of the positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, the total amount of the washing solution, which is the sum of the initial washing solution and the rinsing solution, can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. In addition, by minimizing the amount of the initial washing solution fed into the stirring tank and controlling the amount of the rinsing solution, there is an effect of easily removing the residual F component and improving the output performance of the battery.

[0105] The step of forming a slurry by mixing the recovered positive electrode active material with a washing solution (a1) may preferably be a step of forming a slurry by stirring the recovered positive electrode active material and water or a basic lithium compound aqueous solution using a stirrer. In this case, it is a step of modifying the surface of the positive electrode active material, and has a great effect of removing foreign substances such as LiF or metal fluoride generated on the surface of the positive electrode active material during the preceding heat treatment process.

[0106] The above-mentioned stirrer may be, for example, an impeller-type, magnetic-type and / or ultrasonic stirrer, but is not particularly limited thereto.

[0107] The above stirring may be performed for, for example, within a week, preferably within a day, more preferably for 1 hour or less, 40 minutes or less, 30 minutes or less, or 20 minutes or less, or for example, 5 minutes or more, preferably 10 minutes or more, 20 minutes or more, or 30 minutes or more, and within this range, all F component foreign substances such as LiF or metal fluoride generated on the surface of the positive electrode active material are removed, and even then, excessive lithium elution does not occur, so that the capacity characteristics of the battery are excellent, which is an advantage.

[0108]

[0109] The washing solution of the above step (a1) may be 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, and within this range, residual F components such as LiF can be easily removed, and at the same time, the total amount of washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution, and improving the rate performance of the battery.

[0110]

[0111] The rinsing solution of the above step (a3) ​​may be preferably 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, and within this range, the total amount of the washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution, and since the amount of the initial washing solution injected into the stirring tank is minimized and the amount of the rinsing solution is controlled, there is an advantage of easily removing the residual F component and improving the output performance of the battery.

[0112]

[0113] The weight ratio of the washing solution of step (a1) and the rinsing solution of step (a3) ​​may be, for example, 1:2 to 15, preferably 1:7 to 15, more preferably 1:7 to 13, even more preferably 1:8 to 13, still more preferably 1:8 to 12, and particularly more preferably 1:9 to 11, and within this range, the residual F content is determined by the amount of the rinsing solution, so that even if the amount of the positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, the total amount of the washing solution including the initial washing solution and the rinsing solution can be greatly reduced, thereby reducing the amount of wastewater, wastewater treatment costs, and environmental pollution. In addition, by minimizing the amount of the initial washing solution injected into the stirring tank and controlling the amount of the rinsing solution, there is an effect of easily removing the residual F component and improving the output performance of the battery.

[0114]

[0115] The above (a-2) washing step may preferably include a process of collecting the solid content after the filtration or rinsing and drying it, in which case there is an advantage of optimizing and facilitating the subsequent crystal structure recovery process.

[0116] The drying can be carried out 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 there is no more weight change, for example, for 1 to 24 hours, and has the advantage of efficiently removing moisture contained in the washed positive electrode active material within this range.

[0117]

[0118] (b) Step of restoring the crystal structure of the washed positive electrode active material

[0119] The step of restoring the crystal structure (b) 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 the air to restore the crystal structure. In this case, there is an advantage of providing a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0120]

[0121] The step of restoring the crystal structure (b) above may preferably be a step of adding a lithium precursor to the positive electrode active material whose crystal structure has been restored and heat-treating the positive electrode active material 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, there is an effect of improving the crystallinity of the positive electrode active material, such as increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0122]

[0123] The lithium precursor may preferably be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0124]

[0125] The lithium precursor may preferably be added in an amount equal to at least the amount of lithium reduced from the amount of lithium in the positive electrode active material of step (a) based on the amount of lithium in the recovered positive electrode active material, and as a specific example, when the recovered positive electrode active material of step (a) is a positive electrode active material represented by the chemical formula 1, the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.0001 to 0.2 with respect to the molar ratio of lithium of 1 in the positive electrode active material, preferably in an amount such that the molar ratio of lithium is 0.001 to 0.02, more preferably in an amount such that the molar ratio of lithium is 0.005 to 0.017, even more preferably in an amount such that the molar ratio of lithium is 0.007 to 0.015, and even more preferably in an amount such that the molar ratio of lithium is 0.009 to 0.013, and within this range, the lithium insufficient in the regenerated positive electrode active material is supplemented, thereby improving the crystallinity, such as increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0126] As another example, the lithium precursor may be added in an amount corresponding to 1 to 40 mol% when the total lithium contained in the raw material positive electrode active material is 100 mol%, preferably may be added in an amount corresponding to 1 to 15 mol%, and more preferably may be added in an amount corresponding to 1 to 10 mol%, and within this range, no residual precursor that may increase the resistance of the regenerated positive electrode active material remains, which is very useful for improving battery characteristics, and has an economic advantage because the crystal structure can be restored with a smaller amount of lithium precursor than before.

[0127]

[0128] The above heat treatment temperature can be controlled within a limited range depending on the melting point of the lithium precursor, for example, in the case of LiCO3, which has a melting point of 723°C, heat treatment can be performed preferably at 700 to 900°C, more preferably at 710 to 780°C, and within this range, the crystal structure is recovered, resulting in excellent output performance of the battery.

[0129] The above heat treatment temperature may preferably be a temperature exceeding the melting point of the lithium precursor, but if it exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance, so it may preferably be 1000°C or lower.

[0130] 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, even more preferably 4 to 6 hours, and as a specific example, around 5 hours is preferable, and within this range, sufficient crystal structure recovery is achieved, and there is an economic advantage.

[0131] The above heat treatment temperature can be reached at a heating rate of preferably 1 to 10°C / min, more preferably 1 to 5°C / min, and even more preferably 2 to 4°C / min, and in this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby having the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0132] The above crystal structure recovery step includes, for example, a cooling process, and the cooling process may be, for example, natural cooling in a furnace, in which case the crystallinity of the regenerated positive electrode active material is further increased, thereby having the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0133]

[0134] In this description, crystal structure recovery can follow the definition used in the technical field to which the present invention belongs, and as a specific example, it can be defined as a heat treatment operation to cure deformation or lattice defects and appropriately control crystallinity by heating a positive electrode active material with a deformed structure or lattice defects at a temperature higher than the recrystallization temperature, at which atoms of the main component can sufficiently diffuse and move, for an appropriate period of time.

[0135]

[0136] Step of washing the positive electrode active material with restored crystal structure

[0137] The step of washing the positive electrode active material with the recovered crystal structure (hereinafter referred to as “post-washing”) according to the present invention (b-2) may be a step of mixing the positive electrode active material with the recovered crystal structure with a washing solution and then filtering it. In this case, there is an advantage in that the battery characteristics are improved by removing lithium compounds remaining on the surface of the positive electrode active material with the recovered crystal structure.

[0138] The above post-washing can preferably be performed by mixing the positive electrode active material whose crystal structure has been restored with a washing solution and then filtering it with a filter press. In this case, compared to the conventional vacuum filtration, the lithium remaining in the crystal structure restoration step can be washed with a small amount of washing solution, and thus the amount of wastewater, wastewater treatment costs, and environmental pollution can be reduced. In addition, even if the amount of positive electrode active material to be washed increases, there is no need to replace equipment such as a stirring tank, and further, by removing residual lithium compounds from the regenerated positive electrode active material, there is an effect of significantly improving the initial discharge capacity, rate performance, and capacity characteristics of the battery.

[0139]

[0140] The above-mentioned washing solution may be 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, even more preferably 0.9 to 2 times, and still more preferably 0.9 to 1.5 times, and within this range, there is an advantage in that the battery characteristics are improved by effectively removing lithium compounds remaining on the surface of the positive electrode active material whose crystal structure is restored without leaching of effective metals.

[0141]

[0142] The positive electrode active material obtained after the above-described post-washing may preferably have a residual lithium precursor (e.g., LiOH, etc.) content of 1000 ppm or less, more preferably 800 ppm or less, and within this range, the residual lithium precursor is suppressed from reacting 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, thereby having the advantage of improving doping efficiency and battery characteristics.

[0143]

[0144] The above post-washing may preferably include all contents except the rinsing step in the above-described (a-2) washing step, in addition to the contents separately defined herein, and therefore, the description of the overlapping portion will be omitted. However, in the (b-2) step herein, it may be preferable to use the rinsing solution in a minimal amount (e.g., 1 time or less, 0.5 times or less, or 0.1 times or less) or not use it at all, and in this case, there is an advantage that the effective metal is not leached from the positive electrode active material whose crystal structure has been restored.

[0145]

[0146] (c) Step of doping the positive electrode active material with restored crystal structure

[0147] The method for regenerating a positive electrode active material of the present invention includes (c) a step of adding a dopant precursor to a positive electrode active material whose crystal structure has been restored and heat-treating it to dope it. In this case, the regenerated positive electrode active material is doped with a dopant, so that the capacity characteristics and life characteristics are improved and there is an effect of excellent crack resistance.

[0148]

[0149] In the above step (c), the heat treatment can be performed at, for example, a temperature of 300 to 1000°C, preferably 300 to 600°C, and as a specific example, at a temperature of 400 to 900°C, preferably 450 to 800°C, more preferably 500 to 700°C, and even more preferably 550 to 650°C. Within this range, the regenerated positive electrode active material is stably doped with the dopant without causing loss due to deterioration, thereby improving capacity characteristics and life characteristics and enhancing crack resistance.

[0150] In the step (c), the dopant precursor is a compound that provides as a dopant at least one element 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 preferably a compound that provides as a dopant at least one element selected from the group consisting of B, Na, Mg and F, in which case the dopant is stably doped into the regenerative positive electrode active material, the surface coating layer is easily removed by washing or rinsing, and there is an effect of greatly improving the capacity characteristics, life characteristics and crack resistance.

[0151] In the step (c) above, the dopant precursor may be added preferably in an amount of 100 to 2000 ppm (based on the dopant element) based on the total weight of the regenerated positive electrode active material, more preferably in an amount of 300 to 1500 ppm, still more preferably in an amount of 400 to 1200 ppm, still more preferably in an amount of 500 to 1000 ppm, and still more preferably in an amount of 600 to 900 ppm, and within this range, the dopant is stably doped into the regenerated positive electrode active material, the capacity characteristics and life characteristics are greatly improved, and there is an effect of excellent crack resistance.

[0152]

[0153] The above step (c) may be, as a specific example, a step of adding or applying a dopant precursor alone or dissolved in a solvent to a positive electrode active material whose crystal structure has been restored and then heat-treating to dope, and as a preferred example, it may be a step of adding a dopant precursor alone to a positive electrode active material whose crystal structure has been restored and then doping through a solid-state reaction, i.e. heat-treating, and in this case, the dopant is doped into the regenerated positive electrode active material, thereby improving capacity characteristics and life characteristics and enhancing crack resistance. Here, a liquid-state reaction using a solvent is highly efficient, and a solid-state reaction using only a dopant precursor is advantageous for mass production, and thus can be selectively applied as needed.

[0154]

[0155] The above dopant precursor may be, for example, an oxide, an acid, an organometallic compound, etc. containing the above dopant element.

[0156]

[0157] The above heat treatment time can be preferably performed for 1 to 10 hours, more preferably for 3 to 5 hours, and within this range, the dopant is stably doped into the regenerated positive electrode active material, the capacity characteristics and life characteristics are greatly improved, and there is an effect of excellent crack resistance.

[0158]

[0159] The above heat treatment temperature can be reached at a heating rate of preferably 1 to 10°C / min, more preferably 1 to 7°C / min, and even more preferably 1 to 5°C / min, and within this range, the dopant is stably doped into the regenerated positive electrode active material, the capacity characteristics and life characteristics are greatly improved, and there is an effect of excellent crack resistance.

[0160] The above heat treatment can be performed under air or oxygen, and is preferably performed under oxygen. In this case, the dopant is stably doped into the regenerated positive electrode active material, the capacity characteristics and life characteristics are greatly improved, and the crack resistance is excellent.

[0161]

[0162] The solvent is not particularly limited as long as it is a solvent that does not affect the positive electrode active material, and may be, for example, an organic solvent such as water or alcohol, and the alcohol may preferably be methanol or ethanol.

[0163]

[0164] Regenerated cathode active material

[0165] The regenerated positive electrode active material of the present invention is characterized by being manufactured by the regenerated positive electrode active material regeneration method according to the above, and in this case, a predetermined dopant is doped into the regenerated positive electrode active material, thereby improving capacity characteristics and life characteristics and enhancing crack resistance.

[0166]

[0167] In addition, the regenerative cathode active material of the present invention includes at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and 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), characterized in that it is doped with a dopant and has no coating layer, and in this case, the capacity characteristics and life characteristics are improved, and there is an effect of excellent crack resistance.

[0168]

[0169] The above doping greatly reduces the increase in resistance on the surface of the positive electrode active material compared to the coating because the dopant element itself enters the crystal structure of the positive electrode active material with a thickness of several nm on the surface of the post-washed positive electrode active material particles, thereby playing a role in increasing the battery life. On the other hand, the coating layer is a layer formed when the oxide produced by the dopant precursor reacting with the lithium compound or thermal decomposition adheres to the surface of the post-washed positive electrode active material, and acts as a resistor, which causes the life characteristics to deteriorate. 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 recovered, heat-treat it at a predetermined heat treatment temperature, and then wash it by a predetermined method to remove the coating layer, leaving only the doped dopant.

[0170] The above coating layer may mean, for example, a collection of undoped dopant precursors that have changed into oxides or the like and are attached to the surface of the positive electrode active material in the form of nodules. During the washing, the coating layer is removed and only the doped dopant remains in the regenerated positive electrode active material.

[0171]

[0172] The following Figure 3 includes a schematic structure of a regenerated positive electrode active material finished with doping and without a coating layer manufactured in Example 1 and a regenerated positive electrode active material finished with a coating layer manufactured in Comparative Example 2. The regenerated positive electrode active material manufactured in Example 1 is not a surface coating like the conventional one, but is doped with a dopant. As a result, not only is the side reaction between the coating layer and the positive electrode active material eliminated, but also the nickel (Ni) element on the surface of the positive electrode active material is reduced due to the influence of the dopant, thereby stabilizing the surface, thereby achieving an improvement in long-term life characteristics and an increase in initial charge-discharge capacity. On the other hand, Comparative Example 2 formed a surface coating layer together with a doping layer on the regenerated positive electrode active material, but did not remove the surface coating layer. As the charge-discharge cycle progresses, cracks occur between the interface of the positive electrode active material surface and the coating layer, which causes resistance to occur between the different interfaces, thereby deteriorating the long-term life. Here, the surface coating layer may be a boron coating layer containing B2O3 and a trace amount of LBO (a reaction product between boric acid and LiOH remaining on the surface of the positive electrode active material).

[0173]

[0174] The following Figures 4 and 6 include EDS (Energy Dispersive Spectrometer) mapping images for the regenerated positive electrode active materials manufactured in Example 1 and Comparative Example 2. The regenerated positive electrode active material manufactured in Example 1 has only the doped dopant left and the coating layer is removed by washing, so that the entire surface is uniform, has the same composition ratio regardless of the location measured on the regenerated positive electrode active material, and no boron (B) element is found in the surface analysis. On the other hand, the regenerated positive electrode active material of Comparative Example 2, which only went through the coating step of forming the doping and coating layer and did not go through the coating layer removal (washing) step, has a large amount of boron (B) element found in the coating layer.

[0175]

[0176] The following Figures 9 and 10 include changes in the initial charge / discharge capacity and the capacity retention rate according to the number of cycles for the regenerated positive electrode active materials manufactured in Example 1 and Comparative Example 2. The regenerated positive electrode active material of Example 1, which is doped with a dopant without a coating layer, has low surface resistance and suppressed surface side reactions due to the doping effect, resulting in excellent initial charge / discharge capacity and charge / discharge efficiency, and also has low surface resistance and suppressed surface side reactions, resulting in excellent capacity retention rate, i.e., life cycle characteristics. On the other hand, the regenerated positive electrode active material of Comparative Example 2, which includes a coating layer, has some doping, but the B2O3 coating layer and the LiB3O5 coating layer act as surface resistance, resulting in lower initial charge / discharge capacity and lower charge / discharge efficiency, and also lower life cycle characteristics.

[0177]

[0178] The above dopant may be preferably included in an amount of 100 to 2000 ppm based on 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, and within this range, the capacity characteristics and life characteristics are greatly improved, and there is an effect of excellent crack resistance.

[0179] The above dopant is preferably at least one 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 at least one selected from the group consisting of B, Na, Mg and F. In this case, the capacity characteristics and life characteristics are greatly improved, and there is an excellent effect of crack resistance.

[0180]

[0181] The above-mentioned regenerative positive electrode active material is preferably undoped and has a dopant element coated (residual) on the surface of 10 ppm or less, preferably 5 ppm or less, based on EDS (Energy Dispersive Spectroscopy) surface mapping, and within this range, the resistance is low, the capacity characteristics and life characteristics are greatly improved, and the crack resistance is excellent.

[0182]

[0183] The above-mentioned regenerative positive electrode active material may preferably contain 40 to 45 wt% of carbon element, 25 to 30 wt% of oxygen element, and 25 to 30 wt% of nickel element based on EDS (Energy Dispersive Spectroscopy) surface mapping, and more preferably contain 42 to 45 wt% of carbon element, 26 to 29 wt% of oxygen element, and 27 to 30 wt% of nickel element, and within this range, the resistance is low, the capacity characteristics and life characteristics are greatly improved, and the crack resistance is excellent.

[0184]

[0185] The above-mentioned regenerated positive electrode active material has, for example, 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, and as a specific example, 1 to 8000 ppm, in which case the output performance of the battery is improved, and the electrochemical performance, resistance characteristics, and capacity characteristics are excellent. In the present disclosure, the residual F content means the content of all residual F components present in not only LiF but also other residual components.

[0186] In this description, the residual F content is not particularly limited when measured using a measurement method such as IC (Ion Chromatography) commonly used in the technical field to which the present invention belongs, and specific examples thereof include an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer. In this description, IC-ICP (Inductively Coupled Plasma) can be preferentially used.

[0187]

[0188] As another specific example, the above regenerative positive electrode active material is represented by the following chemical formula 1

[0189] [Chemical Formula 1]

[0190] Li a Ni x Mn y Co z M w O 2+δ

[0191] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1이다.)로 표시되는 화합물일 수 있고, 이 경우 전기화학적 성능, 저항 특성 및 용량 특성 등이 우수한 효과가 있다.

[0192]

[0193] The above-mentioned regenerative positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and even more preferably 81 to 95 mol% based on 100 mol% of the total of the remaining metals or transition metals excluding Li, and within this range, there is an excellent effect in charge capacity, resistance characteristics, and capacity characteristics.

[0194]

[0195] The following Figure 2 is a flowchart for a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0196] Referring to Figure 2, first, anode scrap is prepared using a waste cathode (Step S10). For example, a slurry prepared by mixing NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. After stamping out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0197] The above positive electrode scrap has a positive electrode active material layer on aluminum foil, and the positive electrode active material layer has a structure in which a binder binds the positive electrode active material and the conductive material after the solvent evaporates.

[0198]

[0199] Next, the prepared positive electrode scrap is shredded into an appropriate size (step S20). Here, shredding includes cutting or shredding the positive electrode scrap into a size that is easy to handle. As a specific example, the shredded positive electrode scrap may have a size of 1 cm x 1 cm. The shredding may be performed using various dry crushing equipment, such as a hand mill, a disc mill, a cutting mill, a hammer mill, or a high-speed cutter to increase productivity.

[0200] The above crushing can be preferably performed or not, and the size of the pieces, etc. can be determined by considering the characteristics required by the equipment used in the handling of the positive electrode scrap and the subsequent process. For example, if equipment capable of continuous processing is used, the positive electrode scrap must be crushed into smaller pieces because the fluidity must be good.

[0201]

[0202] Next, the shredded positive electrode scrap is heat-treated in air at 500 to 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 within the positive electrode active material layer.

[0203] Through the above-described heat treatment in air, the binder and conductive agent within 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.

[0204] It is important to perform the above heat treatment in air or in the presence of oxygen. If heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive agent will carbonize rather than undergo thermal decomposition. Carbonization will leave carbon components on the surface of the positive electrode active material, degrading the performance of the reusable positive electrode active material. However, if heat treatment is performed in air, the carbon components in the binder and conductive agent react with oxygen and disappear into gases such as CO and CO2, thus removing both the binder and conductive agent.

[0205]

[0206] The heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably 1 to 10°C / min, even more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min, and a specific example is 5°C / min. Within this range, the heat treatment can be performed without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock, etc., to the positive electrode active material layer powder.

[0207]

[0208] The above heat treatment can be performed for a period of time sufficient to allow the binder to be sufficiently thermally decomposed, for example, preferably 1.5 to 6 hours, preferably 2 to 5.5 hours, more preferably 3 to 5 hours, and even more preferably 4 to 5 hours, and within this range, the binder is sufficiently thermally decomposed and also has an excellent thermal decomposition efficiency.

[0209] The above heat treatment is performed using various types of furnaces, for example, a box-type furnace, and considering productivity, a rotary kiln capable of continuous treatment.

[0210] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0211]

[0212] Next, in the washing step (hereinafter also referred to as ‘pre-washing’), i.e., the surface modification step, the recovered positive electrode active material is mixed with a washing solution and then filtered using a filter press (step S40).

[0213] The above washing step has the advantage of effectively removing foreign substances generated on the surface of the positive electrode active material in the heat treatment step (step S30) even with a small amount of washing solution by including a filter press.

[0214] One embodiment of the above washing step may include a step of stirring the recovered positive electrode active material together with a washing solution in a stirring tank to form a slurry, then filtering the slurry with a filter press to form a filter cake inside the filter press, and then injecting a rinsing solution into the filter press to rinse the filter cake formed inside the filter press at high pressure. Here, the filtration and rinsing steps are performed in the same pressure range, and the stirring device is not particularly limited, but may be an impeller-type, magnetic, or ultrasonic stirrer. However, when the viscosity of the slurry is high or the amount of the slurry is large, an impeller-type stirrer capable of transmitting a large force may be preferable.

[0215] The above-mentioned washing solution is, for example, water or an aqueous alkaline lithium compound solution, and if it is necessary to supplement the amount of lithium that may be eluted from the positive electrode active material during the washing process, an aqueous alkaline lithium compound solution is preferable.

[0216] The above-mentioned basic lithium compound aqueous solution contains, for example, more than 0 wt% and less than 15 wt% of the basic lithium compound. If the lithium compound is not included, lithium supplementation is difficult, and if it exceeds 15 wt%, an excessive amount of lithium compound remains on the surface of the positive electrode active material, which may adversely affect a future annealing process.

[0217] The above lithium compound is LiOH in one embodiment.

[0218] The above-mentioned cleaning solution is used in an amount of 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 of 1 to 2 times or approximately 1 time.

[0219] The above stirring is performed for 1 to 20 minutes, preferably 5 to 10 minutes, in one embodiment, and within this range, a decrease in the capacity of the battery due to excessive lithium dissolution is prevented.

[0220] The above stirring is performed under conditions of 100 to 1000 RPM, preferably 250 to 750 RPM, in one embodiment, and within this range, a decrease in battery capacity due to excessive lithium dissolution is prevented.

[0221] The above filter press is operated under air pressure conditions of 2 to 10 bar, and in one embodiment, under air pressure conditions of 3 to 6 bar.

[0222] The above filter press is, in one embodiment, physically and chemically stable to the slurry, and includes a frame, a filter plate, a filter cloth, a filter cloth pressurizing device, a filter plate separating device, a filter cloth washing device, and a transfer pump.

[0223] The above filter cloth preferably has a permeability of 0.1 to 15 cc / cm. 2 (sec) and in one embodiment 0.8 cc / cm 2 It can be within (sec) or less.

[0224] The above rinsing solution may preferably be 5 to 20 times the weight of the recovered positive electrode active material, and in one embodiment, may be about 10 times.

[0225] The weight ratio of the above-mentioned washing liquid and rinsing liquid may preferably be 1:7 to 15, and in one embodiment, may be about 1:10.

[0226] The filter cake after the above rinsing can be dried as needed. In one embodiment, the drying can be done in air or under vacuum at 50 to 150°C using an oven (convection type). However, in this embodiment, the drying process was omitted in consideration of the heat treatment in the next step, the crystal structure recovery step.

[0227] The above washing step (step S40) removes Li2CO3, LiOH, etc., which are generated by reaction with lithium during the process in which the binder and conductive material inside the positive electrode active material layer are vaporized into CO2 and H2O and removed in the heat treatment step (step S30), and LiF or metal fluoride, which are generated by reaction of F present in the binder such as PVdF with lithium or other metal elements constituting the positive electrode active material, thereby preventing deterioration of battery characteristics when the positive electrode active material is reused.

[0228] In this document, % and ppm are based on weight unless otherwise specified.

[0229]

[0230] Next, a lithium precursor is added to the washed positive electrode active material and heat-treated to restore the crystal structure (step S50).

[0231] Since lithium loss occurs in the positive electrode active material during the preceding steps S30 and S40, step S50 compensates for such lithium loss. In addition, since a deformation structure (e.g., Co3O4 in the case of LCO active material) may appear 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 restore it to the level of a virgin or fresh positive electrode active material. Here, ‘virgin’ is a concept opposite to ‘regeneration’, meaning something that has been created for the first time, and is the same as the ‘raw material’ used in the examples.

[0232] The lithium precursor includes at least one of LiOH, Li2CO3, LiNO3, and Li2O, and in one embodiment, LiOH is used.

[0233] It is preferable that the lithium precursor be added in an amount at least equal to the molar ratio of lithium lost compared to the molar ratio of lithium and other metals in the newly formed positive electrode active material used in the positive electrode active material layer. Adding an excessive amount of lithium precursor compared to the amount of lithium lost will leave unreacted lithium precursor in the regenerated positive electrode active material, which will increase resistance, and therefore, an appropriate amount of lithium precursor must be added.

[0234] In one embodiment, when the molar ratio of lithium in the new positive electrode active material is 1 with respect to the other metal (M), the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.001 to 0.4, preferably in an amount such that the molar ratio of lithium is 0.01 to 0.4, and more preferably in an amount such that the molar ratio of lithium is 0.09 to 0.2. As a specific example, when the lithium precursor is added in an amount equivalent to the loss ratio of lithium content in the new positive electrode active material based on the ICP analysis results, the capacity improvement effect is shown to be equivalent to that of the new positive electrode active material. Here, the ICP analysis results have an error value of approximately ±0.02.

[0235]

[0236] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 40 mol%, more preferably 1 to 15 mol%, and even more preferably 7 to 11 mol%, when the total lithium contained in the washed positive electrode active material is 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.

[0237] The above heat treatment is performed in air at, for example, a temperature of 400 to 1000°C, preferably at a temperature of 600 to 900°C, and this temperature should be adjusted within a limited range depending on the type of lithium precursor.

[0238] The above heat treatment temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, at a temperature exceeding 1000°C, thermal decomposition of the positive electrode active material occurs, resulting in a decrease in performance, so the temperature should not exceed 1000°C. Accordingly, when LiOH or Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more preferably 750 to 780°C.

[0239] The heat treatment time is preferably 1 hour or longer, preferably 15 hours or shorter, and more preferably 5 to 13 hours. A longer heat treatment time allows sufficient crystal structure recovery, but even a longer heat treatment time does not significantly affect performance. The heat treatment equipment used in this case may be identical or similar to that used in heat treatment step S30.

[0240]

[0241] Next, as a post-washing step, the positive electrode active material with recovered crystal structure is mixed with a washing solution, stirred, and then filtered (step S60).

[0242] The above post-washing 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.

[0243] The above post-washing step preferably includes a filter press, so that foreign substances generated on the surface of the positive electrode active material in the crystal structure recovery step (step S50) can be effectively removed even with a small amount of washing liquid, and residual lithium and fine particles can be easily removed.

[0244] The above post-washing step is preferably performed in the same manner as the aforementioned washing step (step S40), except that the washing solution is used in a minimal amount (e.g., 1x the weight of the positive electrode active material) and no rinsing is performed. Therefore, the description of the overlapping portion will be omitted.

[0245]

[0246] Next, a step of doping the post-washed positive electrode active material can be performed (step S70).

[0247] The above doping step is, for example, adding a dopant precursor to a post-washed positive electrode active material and performing a heat treatment (solid-state reaction). However, if the heat treatment temperature is too low, the amount of dopant doped into the positive electrode active material is small, and a large coating layer is formed. If the heat treatment temperature is too high, the performance of the battery deteriorates due to thermal decomposition of the positive electrode active material and the dopant precursor itself.

[0248] The above doping greatly reduces the increase in resistance on the surface of the positive electrode active material compared to the coating because the dopant element itself enters the crystal structure of the positive electrode active material with a thickness of several nm on the surface of the post-washed positive electrode active material particles, thereby playing a role in increasing the battery life. On the other hand, the coating layer is a layer formed when the oxide generated by the dopant precursor reacting with or thermally decomposing a lithium compound adheres to the surface of the post-washed positive electrode active material, which acts as a resistance and causes the life characteristics to deteriorate.

[0249]

[0250] The method of adding the above dopant precursor to the post-washed positive electrode active material may be, for example, mixing, milling, spraying, or grinding.

[0251]

[0252] Finally, in the step of removing the coating layer, leaving only the doped dopant, the doped positive electrode active material is mixed with a washing solution, stirred, and then filtered (step S80).

[0253] The above-mentioned coating layer removal step is, for example, a step of mixing a doped positive electrode active material with a cleaning solution, stirring it, and then filtering it. Here, the coating layer may refer to, for example, a collection of undoped dopant precursors that have been converted into oxides or the like and are attached to the surface of the positive electrode active material in the form of nodules. During the cleaning, this coating layer is removed, and only the doped dopant remains in the regenerated positive electrode active material.

[0254] The above coating layer removal washing step can have the advantage of effectively removing the coating layer even with a small amount of washing liquid, preferably by using a filter press.

[0255] The above cleaning solution may preferably be water.

[0256] The above cleaning solution may preferably be used in an amount of 1 to 10 times the weight of the doped positive electrode active material.

[0257] The filter cake of the regenerated positive electrode active material after the washing process described above can be dried. In one example, the drying can be done using an oven (convection type) at 50 to 150°C in air, under vacuum, or under reduced pressure.

[0258] The above coating layer removal step can be performed in the same manner as the washing step (step S40) described above, except for the details defined in this step. Therefore, the description of the overlapping portion will be omitted.

[0259]

[0260] secondary battery

[0261] The secondary battery of the present invention includes a regenerated positive electrode active material manufactured by the method for regenerating the positive electrode active material, and in this case, the capacity characteristics and life characteristics are improved, and by including the regenerated positive electrode active material having excellent crack resistance, the rate performance of the battery is greatly improved, and the electrochemical performance and resistance characteristics are excellent.

[0262] The secondary battery of the present invention may include all of the contents of the positive electrode active material and the regeneration method thereof described above. Therefore, redundant description thereof is omitted herein.

[0263]

[0264] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0265]

[0266] [Example]

[0267] Example 1

[0268] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM type lithium composite transition metal oxide (mol% ratio of Ni:Co:Mn:Al: 88:6:4:2) was crushed and heat-treated in air at 570°C for 30 minutes to remove the binder and conductive agent, and the current collector and positive electrode active material were separated, and then the positive electrode active material was recovered. Here, the temperature increase rate until the heat treatment temperature was reached was 5°C / min, and air was supplied at 3 L / min.

[0269] The recovered positive electrode active material and 1 wt% LiOH aqueous solution (hereinafter referred to as “washing solution”) were mixed in a 1:1 weight ratio, stirred for 5 minutes under 700 RPM conditions to form a slurry, and then filtered through a filter press (manufactured by Daesung Filter Co., Ltd., air permeability 0.8 cc / cm). 2 (including a filter cloth made of PP material of (sec)) was used for filtration (dehydration) and a filter cake was formed in a filter press. The filter cake formed in the filter press was rinsed with a rinsing solution (same as the washing solution) having a weight 10 times that of the recovered positive electrode active material, and then a filter cake of the positive electrode active material was obtained.

[0270] Based on the molar ratio of lithium to other metals (ICP analysis) in the raw material positive electrode active material (lithium molar ratio 1), a lithium precursor LiOH was added in an amount corresponding to a lithium molar ratio of 0.10 to 0.15 to the filter cake of the washed positive electrode active material, and heat-treated in the air (supply rate: 3 L / min) at 750℃ for 3 hours to restore the crystal structure of the positive electrode active material. In theory, the Li molar ratio of the new positive electrode active material is 1, but since the average error of the ICP equipment used to confirm this is ±0.05, preferably ±0.02, the Li molar ratio of the raw material active material measured through ICP measurement can be 1±0.05:1. In this experiment, the lithium precursor was added based on the molar ratio measured through ICP analysis.

[0271] The positive electrode active material with recovered crystal structure and neutral water as a washing solution were mixed in a 1:1 weight ratio, stirred for 5 minutes under 700 RPM conditions to form a slurry, and then filtered (dehydrated) using a filter press in the same manner as the previous front-washing to remove residual Li compounds and obtain a filter cake of the positive electrode active material. The filter cake of the obtained positive electrode active material was dried under reduced pressure at 110°C to obtain a positive electrode active material that had undergone the post-washing process.

[0272] After the post-washing, boric acid was added as a dopant precursor to the cathode active material in an amount corresponding to 700 ppm of boron (B) based on the total weight (dry mass basis) of the post-washed cathode active material, and then heated at 600°C for 5 hours to produce the final regenerated cathode active material. At this time, the temperature increase rate until reaching the heating temperature was 2°C / min, and air was supplied at 3 L / min.

[0273] The doped positive electrode active material and neutral water as a washing solution were mixed in a 1:1 weight ratio, stirred for 2 minutes under 700 RPM conditions to form a slurry, and then filtered (dehydrated) using a filter press in the same manner as the previous post-washing to remove the coating layer and obtain a filter cake of the positive electrode active material. The filter cake thus obtained was dried under reduced pressure at 110°C to produce the final doped regenerated positive electrode active material.

[0274] In this paper, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. While this can be measured using a standard ICP analyzer commonly used in laboratories, there is no variation depending on the measuring device or method.

[0275]

[0276] Example 2

[0277] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that boric acid was added as a dopant precursor to the positive electrode active material after post-washing in an amount corresponding to 1400 ppm of boron (B) based on the total weight (dry mass basis) of the positive electrode active material after post-washing.

[0278]

[0279] Comparative Example 1

[0280] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the doping step of adding a dopant precursor and performing heat treatment and the step of washing the doped positive electrode active material with a washing solution were omitted.

[0281]

[0282] Comparative Example 2

[0283] A 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 washing solution in Example 1 was omitted.

[0284]

[0285] Comparative Example 3

[0286] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that boric acid (H3BO3), which is a dopant precursor, was added in an amount of 2:1 molar ratio with LiOH, which is a lithium precursor, and the step of washing the doped positive electrode active material with a washing solution was omitted.

[0287]

[0288] The following Figure 3 is a conceptual diagram schematically showing the structure of the regenerated positive electrode active material manufactured in Example 1 and Comparative Examples 1 to 3, respectively.

[0289] Referring to FIG. 3, the regenerated positive electrode active material manufactured in Example 1 is not surface coated as in the prior art, but is doped with a dopant, thereby eliminating side reactions between the coating layer and the positive electrode active material, and also achieving surface stabilization due to effects such as a decrease in nickel (Ni) elements on the surface of the positive electrode active material due to the influence of the dopant, thereby achieving improved long-term life characteristics and increased initial charge-discharge capacity.

[0290] On the other hand, the regenerated positive electrode active material manufactured in Comparative Example 1 is a positive electrode active material that has cracks due to deterioration caused by rolling or charge / discharge cycles during the positive electrode manufacturing process, and is regenerated without any special surface modification. Unlike the new positive electrode active material, the specific surface area due to the cracks is greatly increased, and this causes an increase in side reactions on the surface of the regenerated positive electrode active material, resulting in a decrease in the overall performance of the regenerated positive electrode active material.

[0291] In addition, Comparative Example 2 formed a surface coating layer together with a doping layer on the regenerated positive electrode active material, but did not remove the surface coating layer, so that cracks occurred between the interface of the positive electrode active material surface and the coating layer as the charge / discharge cycle progressed, and this caused resistance to occur between the different interfaces, thereby deteriorating the long-term service life. Here, the surface coating layer may be a boron coating layer containing B2O3 and a trace amount of LBO (a reaction product between boric acid and LiOH remaining on the surface of the positive electrode active material).

[0292] In addition, Comparative Example 3 attempted 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 this case, as the charge / discharge cycle progresses, cracks occur between the interface of the positive electrode active material surface and the coating layer, which causes resistance between the different interfaces and deteriorates the long-term lifespan. In this case, the surface coating layer may be a boron coating layer containing LBO as a main component due to LiOH injected simultaneously with the dopant precursor.

[0293]

[0294] [Example Exam I]

[0295] The surface composition and overall composition of the regenerated positive electrode active materials obtained in Examples 1 to 2 and Comparative Examples 1 to 3 were measured by the following methods, and the results are shown in Table 1 below.

[0296] * Atomic percent (at%): The composition ratio was measured using energy dispersive X-ray spectroscopy (EDS). Here, an EDS device equipped with an extreme detector from AZtec was used under conditions of 5 kV and 7 mm working distance.

[0297] * ICP Analysis: Using an ICP analyzer, the content of residual F components, 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 were measured. At this time, measurement can be performed using a general ICP analyzer widely used in laboratories, but there is no deviation depending on the measuring device or method.

[0298]

[0299] wt%Measuring pointAtomic percent(at%)BCONiTotalExample 1-043.8427.4828.68100.0Comparative example 1-041.4731.4727.05100.0Comparative example 2#1118.1615.2864.720100.0#1208.0064.0326.26100.0Comparative example 3#1314.3519.4061.084.97100.0#14012.7260.9424.57100.0#158.7613.8475.301.45100.0#1614.9112.6464.048.10100.0

[0300] As can be seen in Table 1 above, the regenerated positive electrode active material (Example 1) obtained through the doping step and coating layer removal (washing) step according to the present invention did not have boron (B) atoms found on the surface of the regenerated positive electrode active material, like the regenerated positive electrode active material (Comparative Example 1) that did not undergo the doping step according to the present invention. Figures 4 and 5 below are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images for the regenerated positive electrode active materials manufactured in Example 1 and Comparative Example 1, respectively, and the three images on the right in each figure are color-coded images for distinguishing carbon (C), oxygen (O), and nickel (Ni) elements, respectively.

[0301] Referring to FIGS. 4 and 5, the regenerated positive electrode active material manufactured in Example 1 had only the doped dopant left and the coating layer was removed by washing, so that all surfaces were uniform, and the regenerated positive electrode active material manufactured in Comparative Example 1 did not undergo a doping step, so that no boron coating layer itself was formed, so that all surfaces were uniform. Therefore, it was confirmed that the regenerated positive electrode active material had the same composition ratio regardless of where it was measured.

[0302] For reference, a regenerated cathode active material that only went through a doping step and not a coating layer removal (washing) step (Comparative Example 2) or a regenerated cathode active material (Comparative Example 4) manufactured by introducing LiOH together with boric acid in the doping step to induce a reaction with LiOH to form a coating layer before boron (B) atoms are inserted as a dopant, have a large amount of boron (B) element found on the surface.

[0303] The following Figures 6 and 7 are EDS (Energy Dispersive Spectrometer) cross-sectional mapping images for the regenerated positive electrode active materials manufactured in Comparative Examples 2 and 3, respectively. In each figure, the four images on the right are color-coded images to distinguish the elements boron (B), carbon (C), oxygen (O), and nickel (Ni) in that order.

[0304] Referring to Fig. 6, the regenerated positive electrode active material manufactured in Comparative Example 2 did not add additional LiOH together with the dopant precursor, so a B2O3 coating layer was formed. Accordingly, elemental analysis was performed at point #11 where a B2O3 coating layer was formed and point #12 where a B2O3 coating layer was not formed.

[0305] Referring to Fig. 7, the regenerated positive electrode active material manufactured in Comparative Example 3 was formed with an LBO coating layer by adding additional LiOH together with a dopant precursor, and therefore, elemental analysis was performed at points #13, #15, and #16 where an LBO coating layer was formed and point #14 where an LBO coating layer was not formed.

[0306]

[0307] Table 2 below shows the boron (B) content using IPC analysis.

[0308] Category B Content (weight ppm) Example 1213 Example 2217 Comparative Example 10 Comparative Example 2640 Comparative Example 3680

[0309] As can be confirmed in Table 2 above, in the regenerated positive electrode active material (Example 1) obtained through the doping step and coating layer removal (washing) step according to the present invention, boron (B) element was not found in the surface analysis using EDS, but boron (B) element was found in the overall component analysis using IPC analysis, confirming that it was doped with a dopant. In addition, in the case of Example 2, a similar level of boron (B) was detected despite the amount of boron compound added being doubled, indicating that even though a larger amount of boron compound was added compared to Example 1, only a similar amount was doped with a dopant and the remainder was removed in the final washing step. On the other hand, in the regenerated cathode active material (Comparative Example 1) that did not undergo the doping step, no boron (B) element was found even in the IPC analysis, and in the regenerated cathode active material (Comparative Examples 2 and 3) that only went through the doping step and did not undergo the coating layer removal (washing) step, an excess of boron (B) was found compared to Example 1, indicating that the boron (B) element doped with a dopant and the boron (B) element present in the coating layer were combined.

[0310]

[0311] [Exam Example II]

[0312] The change in the content of detected elements according to the X-ray etching time of the regenerated positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured through X-ray diffraction analysis (Thermo Ficher Scientific Inc., k-alpha system), and the results are shown in Figure 8 below.

[0313] As shown in the following Figure 8, the regenerated positive electrode active material of Example 1 obtained through the doping step and the coating layer removal (washing) step according to the present invention was able to detect only the doped boron (B) element dopant because the B2O3 generated on the surface as a coating layer was removed due to the coating layer removal (washing) step, and thus it was confirmed that a lower content of boron (B) element was detected compared to the regenerated positive electrode active materials of Comparative Examples 2 and 3.

[0314] On the other hand, boron (B) element was not detected in the regenerated positive electrode active material of Comparative Example 1 because boric acid was not added, and boron (B) element was detected at a similar level in the regenerated positive electrode active materials of Comparative Examples 2 and 3. However, unlike Comparative Example 3, Comparative Example 2 did not use an additional Li precursor (LiOH, Li2CO3, etc.) capable of forming a LiB3O5 coating layer, so it can be seen that the Li content is relatively low and the B2O3 coating layer was formed at 600°C, which is the thermal decomposition temperature of boric acid.

[0315]

[0316] [Test Example III: CHC Cell Evaluation]

[0317] The electrochemical performance of the regenerated positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured through the CHC cell evaluation as follows, and the results are shown in Figures 9 and 10 below.

[0318] * CHC cell manufacturing: 96 wt% of the regenerated cathode active material, 2 wt% of the conductive material carbon black, and 2 wt% of the binder PVdF were weighed and mixed in NMP to make a slurry. This was coated on aluminum foil to manufacture the cathode, and then a cell (Coin Half Cell, CHC) was manufactured. The electrochemical performance (charge capacity CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under the conditions of ethylene carbonate (EC): dimethyl methyl carbonate (DMC) = 3:7 (weight ratio) as the electrolyte and other additives included.

[0319] * Evaluation of initial capacity (CH and DCH) of the cell: At 25 ℃, one charge / discharge cycle was performed on each cell under the following conditions, and the results are shown in Figure 9 below.

[0320] Charge(CH): 0.2C, CC / CV, 4.25V, 0.05C cut-off

[0321] Discharge(DCH): 0.2C, CC, 2.5V, cut-off

[0322]

[0323] * Charge / discharge efficiency of cell (Eff): The charge / discharge efficiency was calculated using the following mathematical formula 1 using the charge capacity and discharge capacity obtained from the initial capacity evaluation of the cell.

[0324] [Mathematical Formula 1]

[0325] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] * 100

[0326]

[0327] The following Figure 9 is a graph showing the results of charging capacity of a coin half cell to which the positive electrode active material regenerated in Examples 1 to 2 and Comparative Examples 1 to 3 was applied.

[0328] Referring to FIG. 9, it was confirmed that the regenerated positive electrode active material of Example 1, which was doped with boron (B) element without a coating layer through the doping step and coating layer removal (washing) step according to the present invention, had low surface resistance and suppressed surface side reactions due to the doping effect, and thus had the best initial charge / discharge capacity and charge / discharge efficiency. In addition, it was confirmed that Example 2 showed similar results to the results of Example 1 because the amount of dopant doped into the regenerated positive electrode active material was similar to that of Example 1.

[0329] On the other hand, since the regenerated positive electrode active material of Comparative Example 1 did not undergo a doping step, no doping or coating was formed, resulting in the lowest initial charge / discharge capacity and charge / discharge efficiency, and the regenerated positive electrode active materials of Comparative Examples 2 and 3, which only underwent a doping step and did not undergo a coating layer removal (washing) step, showed that the initial charge / discharge capacity and charge / discharge efficiency were low even though some doping was performed because the B2O3 coating layer and LiB3O5 coating layer, respectively, acted as surface resistance.

[0330]

[0331] * Capacity retention rate (%) evaluation: After each cell was formed at a 0.1C rate, 0.33 / 0.33C charge / discharge, 0.05C cut-off CC / CV charge, and CC discharge were performed at 45℃. Measurements were made using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.), and the discharge capacity after one cycle was set as the initial capacity. Afterwards, the discharge capacity in each cycle was compared with the initial capacity (100%), and the capacity retention rate was calculated using the following mathematical equation 2, and the results are shown in Fig. 10.

[0332]

[0333] [Equation 2]

[0334] Capacity retention rate (%) = (discharge capacity after cycle / initial discharge capacity)*100

[0335]

[0336] The following Figure 10 is a graph showing the change in capacity retention according to the number of cycles (Cycle No.) as a result of coin half cell evaluation for each of the regenerated positive electrode active materials manufactured in Example 1 and Comparative Examples 1 to 3.

[0337] Referring to FIG. 10, it was confirmed that the regenerated positive electrode active material of Example 1, which was doped with boron (B) element without a coating layer through the doping step and coating layer removal (washing) step according to the present invention, had the best capacity retention rate, i.e., lifespan characteristics, due to the low surface resistance and suppressed surface side reactions caused by the doping effect.

[0338] On the other hand, since the regenerated cathode active material of Comparative Example 1 did not go through the doping step, no doping or coating was formed, and thus the life characteristics were the worst. In the case of the regenerated cathode active material of Comparative Example 2, which only went through the doping step and did not go through the coating layer removal (washing) step, even if some doping was performed, the B2O3 coating layer acted as surface resistance, resulting in a deterioration in the life characteristics. In the case of the regenerated cathode active material of Comparative Example 3, to which LiOH was added in the doping step of Comparative Example 2, even if some doping was performed, the LiB3O5 coating layer acted as surface resistance, although less than the B2O3 coating layer, resulting in a deterioration in the life characteristics.

[0339]

[0340] [Explanation of symbols]

[0341] 10: Whole house

[0342] 20: Active material layer

[0343] 30: Bipolar sheet

[0344] 40: Bipolar plate

[0345] 50: Bipolar scrap

Claims

1. Including at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). It is doped with a dopant and characterized by the absence of a coating layer. Regenerated cathode active material.

2. In paragraph 1, The above dopant is characterized in that it is included in an amount of 100 to 2000 ppm based on the total weight of the regenerative positive electrode active material. Regenerated cathode active material.

3. In paragraph 1, The above dopant is characterized in that it is at least one selected from the group consisting of B, Ti, S, Na, Nb, P, Al, F, Mg, Mn, K, Y, Si, Sn, W, C and N. Regenerated cathode active material.

4. In paragraph 1, The above-mentioned regenerative positive electrode active material is characterized by having a dopant element coated on the surface that is not doped and is less than 10 ppm based on EDS (Energy Dispersive Spectroscopy) surface mapping. Regenerated cathode active material.

5. In paragraph 1, The above-mentioned regenerative positive electrode active material is characterized in that it contains 40 to 45 wt% of carbon element, 25 to 30 wt% of oxygen element, and 25 to 30 wt% of nickel element based on EDS (Energy Dispersive Spectroscopy) surface mapping. Regenerated cathode active material. 6.(a) A step of recovering a positive electrode active material by heat-treating a waste positive electrode including a current collector and a positive electrode active material layer coated thereon under air or oxygen; (b) 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; (c) a step of adding a dopant precursor to the positive electrode active material whose crystal structure has been restored and heat-treating it to dope it; and (d) characterized by comprising a step of washing the doped positive electrode active material with a washing solution. Method for regenerating positive electrode active material.

7. In paragraph 6, In the above step (a), the heat treatment is characterized in that it is performed under conditions of 300 to 650 ℃. Method for regenerating positive electrode active material.

8. In paragraph 6, In the above step (b), the heat treatment is characterized in that it is performed under conditions of 400 to 1000 ℃. Method for regenerating positive electrode active material.

9. In paragraph 6, In the above step (b), the lithium precursor is characterized in that it is at least one selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O. Method for regenerating positive electrode active material.

10. In paragraph 6, In the above step (c), the heat treatment is characterized in that it is performed under conditions of 300 to 1000 ℃. Method for regenerating positive electrode active material.

11. In paragraph 6, In the above step (c), the dopant precursor is a compound that provides at least one element 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. Method for regenerating positive electrode active material.

12. In paragraph 6, In the above step (d), the washing liquid is characterized in that it is water. Method for regenerating positive electrode active material.

13. In paragraph 6, The method for regenerating the positive electrode active material is characterized by including a step (a-2) of washing the recovered positive electrode active material with a washing solution; a step (b-2) of washing the positive electrode active material with a recovered crystal structure with a washing solution; or all of these. Method for regenerating positive electrode active material.

14. In paragraph 6, In the step (a-2), the washing solution is water or a basic lithium compound aqueous solution of more than 0 wt% and less than 15 wt%, and in the step (b-2), the washing solution is water. Method for regenerating positive electrode active material.

15. In paragraph 6, In the above step (c), the dopant precursor is added in an amount of 100 to 2000 ppm (based on dopant element) based on the total weight of the regenerated positive electrode active material. Method for regenerating positive electrode active material.

16. In paragraph 6, The above cathode active material is characterized in that it includes at least one selected from the group consisting of lithium cobalt oxide; lithium manganese oxide; lithium iron phosphate compound; lithium nickel cobalt aluminum oxide; lithium nickel oxide; nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). Method for regenerating positive electrode active material.

17. Characterized in that it is manufactured by a method for regenerating a positive electrode active material according to any one of claims 6 to 16. Regenerated cathode active material.

18. Characterized in that it comprises a regenerative positive electrode active material of any one of claims 1 to 5. Secondary battery.

Images