Method for recycling positive electrode active material

Abstract

A method for recovering and reusing active materials from cathode waste is provided. The method for reusing cathode active materials according to the present invention includes the following steps: (a) heat-treating cathode waste comprising a cathode active material layer including a lithium composite transition metal oxide on a current collector in air to pyrolyze the binder and conductive material in the active material layer, thereby separating the current collector from the active material layer and recovering the active material in the active material layer; (b) rinsing the recovered active material with a cleaning solution; and (c) adding a lithium precursor to the rinsed active material and annealing the active material to obtain reusable active material, wherein the decrease in the molar ratio of lithium to other metals in the active material after heat treatment or after rinsing, compared to the molar ratio of lithium to other metals in the active material in the cathode waste before heat treatment, is within 20%.

Description

Technical Field

[0001] This disclosure relates to a method for recycling resources during the manufacture of lithium-ion secondary batteries. In particular, this disclosure relates to a method for recovering and reusing positive electrode active materials from positive electrode waste generated during the manufacture of lithium-ion secondary batteries or from lithium-ion secondary batteries that have been discarded after use. This application claims priority to Korean Patent Application 10-2020-0082622, filed on July 6, 2020, the disclosure of which is incorporated herein by reference. Background Technology

[0002] Rechargeable lithium-ion batteries are gaining attention as an alternative to fossil fuels. While primarily used in traditional handheld devices such as mobile phones, cameras, and power tools, their applications have recently expanded to electric vehicles (EVs, HEVs, and PHEVs), high-capacity energy storage systems (ESS), and uninterruptible power supply systems (UPS).

[0003] A lithium-ion secondary battery comprises: an electrode assembly, wherein each cell has a structure with a positive electrode plate and a negative electrode plate coated with an active material on a current collector, and a separator inserted between the positive and negative electrode plates; and an external material (i.e., a battery casing) that seals and houses the electrode assembly and the electrolyte together. The positive electrode active material of a lithium-ion secondary battery primarily utilizes lithium-based oxides, while the negative electrode active material utilizes carbon materials. Lithium-based oxides contain metals such as cobalt, nickel, or manganese. In particular, cobalt, nickel, and manganese are very expensive precious metals. Cobalt, in particular, is a strategic metal, and every country in the world pays special attention to its supply and demand. Due to the limited quantity produced by cobalt countries, it is considered a metal whose supply and demand are unstable globally. If the supply and demand of raw materials for strategic metals become unbalanced, the price of these raw materials is highly likely to rise.

[0004] Traditionally, research has primarily focused on recovering and recycling these precious metals from lithium-ion batteries discarded at the end of their lifespan (waste batteries). However, recovering resources from waste discarded after the positive electrode plates are cut, or from positive electrode plates that are defective in the process, is a more preferable approach, in addition to waste batteries.

[0005] Currently, in the manufacture of lithium secondary batteries, such as Figure 1As shown, a positive electrode plate 30 is manufactured by forming a positive electrode active material layer 20. In this layer 20, a long sheet-type positive electrode current collector 10, such as aluminum (Al) foil, is coated with a positive electrode slurry containing positive electrode active material, conductive material, binder, solvent, etc. The positive electrode plate 40 is then punched to a predetermined size. The remaining portion after punching is discarded as positive electrode waste 50. If the positive electrode active material can be recovered from the positive electrode waste 50 and reused, it would be highly desirable from both an industrial economic and environmental perspective.

[0006] Traditionally, the method for recovering positive electrode active materials in most cases involves dissolving the positive electrode in hydrochloric acid, sulfuric acid, nitric acid, etc., and then extracting active material elements such as cobalt, nickel, and manganese. These active material elements are then reused as raw materials for synthesizing positive electrode active materials. However, the method of extracting active material elements using acids has the disadvantage that the process of using pure raw materials or recovering pure raw materials is not environmentally friendly and requires neutralization and wastewater treatment processes, which increases process costs. In addition, this method also has the disadvantage that lithium, one of the main elements of positive electrode active materials, may not be able to be recovered. To overcome these disadvantages, a method is needed that does not dissolve the positive electrode active material and does not extract the active material in elemental form, but directly reuses the active material.

[0007] Furthermore, a method is needed to minimize the loss of constituent elements such as lithium during the process of obtaining reusable active materials. The loss of constituent elements such as lithium must be prevented as much as possible so as not to result in a significant difference in composition from fresh, unused active materials. By doing so, the process of adding insufficient components can be minimized. Summary of the Invention

[0008] Technical issues

[0009] This disclosure aims to address the problems of the prior art, and therefore aims to provide a method for recovering and reusing active materials from cathode waste.

[0010] Technical solution

[0011] In one aspect of this disclosure, a method for reusing positive electrode active material is provided, the method comprising: (a) heat-treating positive electrode waste including a lithium composite transition metal oxide positive electrode active material layer on a current collector in air, thermally decomposing the binder and conductive material in the active material layer, separating the current collector from the active material layer, and recovering the active material in the active material layer; (b) washing the recovered active material with a cleaning solution; and (c) obtaining reusable active material by adding a lithium precursor to the washed active material and annealing the active material, wherein the molar ratio of lithium to other metals in the heat-treated active material or the molar ratio of lithium to other metals in the washed active material decreases by less than 20% compared to the molar ratio of lithium to other metals in the positive electrode waste before heat treatment.

[0012] In this disclosure, the method for reusing the positive electrode active material may further include: (d) coating the surface of the annealed active material.

[0013] Heat treatment can be carried out at 300°C to 650°C, especially for 10 minutes to 24 hours.

[0014] The heat treatment can be carried out at 550°C for 30 minutes at a temperature rise rate of 5°C / min.

[0015] The cleaning solution may be water. Alternatively, the cleaning solution may be an aqueous solution of a lithium compound that is alkaline in its aqueous state. The aqueous solution of the lithium compound may be prepared to contain greater than 0% and equal to or less than 15% of lithium compound, and preferably uses LiOH. Washing can be performed within one week, preferably within one day, and more preferably within one hour. Preferably, a cleaning solution with a LiF solubility of 0.127 g / 100 ml (18°C) and 0.134 g / 100 ml (25°C) is used, and the ratio of the active material to the cleaning solution during washing is equal to or less than 1:200, preferably 1:30 or greater.

[0016] Washing can be performed by immersing the recovered active material in the aqueous solution of the lithium compound while stirring the recovered active material.

[0017] The lithium precursor used in annealing may include at least one of LiOH, Li2CO3, LiNO3, and Li2O.

[0018] The lithium precursor can be added in the same amount as the lithium loss rate compared to the ratio of lithium to other metals in the raw material active material used in the active material layer.

[0019] For example, the lithium precursor can be added at a lithium addition amount of 0.001 to 0.4 molar ratio.

[0020] In addition, the lithium precursor may be added in a molar ratio of 0.0001 to 0.1 with respect to the 1:1 molar ratio of lithium to other metals. The additionally added lithium is used as a material for the surface protective layer in the surface coating on the active material after annealing.

[0021] As another embodiment, without drying after the washing, the lithium precursor may be added in step (c) by mixing the washed active material in a lithium precursor solution and spray-drying the active material. In addition, the temperature of the spray drying is preferably 100°C to 300°C.

[0022] The annealing may be performed in air at 400°C to 1,000°C.

[0023] The temperature of the annealing may exceed the melting point of the lithium precursor.

[0024] The active material in the active material layer may be recovered in powder form, and the carbon component generated by the carbonization of the binder or the conductive material may not remain on the surface.

[0025] Performing the surface coating may include coating at least one of a metal, an organometal, and a carbon component on the surface in a solid or liquid manner, and then performing heat treatment at 100°C to 1,200°C.

[0026] The reusable active material may be represented by the following Chemical Formula 1,

[0027] Li , , 2+δ , z , , ,

[0030] , w ,

[0029] ,

[0028] ,

[0031] Ni x Mn y Co z M w O 2+δ

[0028] (In the above Chemical Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 ≤ x < 0.95, 0 ≤ y < 0.8, 0 ≤ z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.)

[0029] The available active material may include fluorine (F) having a content equal to or less than 100 ppm.

[0030] Advantageous Effects ​According to this disclosure, waste positive electrode active materials (such as positive electrode waste generated during the manufacturing process of lithium secondary batteries) can be reused without the use of acid, thus being eco-friendly. The method according to this disclosure eliminates the need for neutralization or wastewater treatment processes, thereby mitigating environmental problems and reducing processing costs.

[0032] According to this disclosure, the positive electrode active material can be recovered without any unrecoverable metal elements. Since the current collector is not dissolved, it can also be recovered. This method allows for the direct reuse of the active material recovered in powder form, rather than extracting the active material elements and using them as raw materials to resynthesize the positive electrode active material, thus making it economical.

[0033] According to this disclosure, it is safe because it does not use toxic and explosive solvents such as NMP, DMC, acetone, and methanol, and it employs simple processes such as heat treatment, washing, and annealing, making it an easy-to-manage process suitable for large-scale production.

[0034] According to this disclosure, the electrochemical performance of the recovered active material will not deteriorate, and excellent resistance and capacity characteristics can be achieved.

[0035] In particular, according to this disclosure, lithium loss in the active material can be minimized in the heat treatment process for separating the current collector and the washing process (e.g., residue removal) for surface modification. By optimizing the heat treatment process, lithium loss can be minimized, as can the amount of current collector reacting with the active material or precipitated through heat treatment. Furthermore, by adjusting the ratio between the active material and the cleaning solution in the washing process, lithium loss in the active material can be minimized while removing LiF, as residual LiF may act as a resistor. Since lithium loss is minimized in the process of obtaining reusable active material, the composition of fresh active material is not significantly different from that of reusable active material. Insufficient lithium is added through an additional lithium precursor addition process. In this respect, the amount of added lithium precursor is minimized, making it preferred in terms of process and cost.

[0036] According to another aspect of this disclosure, since the active material to be reused can be re-granulated by spray drying, even if the particles are broken due to rolling in the previous process, the particle size and specific surface area can be improved. Furthermore, if the washed active material is mixed with a lithium precursor solution and spray-dried, the lithium precursor can be replenished while the active material is being re-granulated, thus simplifying the process and providing the advantage of forming a continuous process with the preceding washing step. Attached Figure Description

[0037] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the foregoing disclosure, serve to provide a further understanding of the technical features of the present disclosure; therefore, the present disclosure is not to be construed as limited to the drawings.

[0038] Figure 1 This is a diagram showing the waste positive electrode material discarded after the positive electrode plate is punched out from the positive electrode sheet.

[0039] Figure 2 This is a flowchart of a method for reusing active materials according to this disclosure.

[0040] Figure 3 The results of battery evaluation using the active materials of the embodiments and comparative examples are shown.

[0041] Figure 4 and Figure 5 These are scanning electron microscope (SEM) images of the samples and active materials of the embodiments and comparative examples.

[0042] Figure 6 This is a graph showing the particle size distribution of the active material in the sample compared to the active materials in the embodiments and comparative examples. Detailed Implementation

[0043] The preferred embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general and dictionary meanings, but should be interpreted according to the meanings and concepts corresponding to the technical aspects of this disclosure, based on the principle that inventors are allowed to appropriately define the terms to obtain the best interpretation. Therefore, the descriptions presented herein are merely preferred embodiments for illustrative purposes and are not intended to limit the scope of this disclosure. It should be understood that other equivalent examples and variations can be made without departing from the scope of this disclosure.

[0044] In the following description, reference is made to the accompanying drawings, which form a part of this document. The illustrative embodiments described in the detailed description, figures, and claims are not intended to be limiting. Other embodiments and changes may be utilized without departing from the spirit and scope of the subject matter set forth herein. It will be readily understood that the various aspects of this disclosure, as generally described and illustrated herein, can be arranged, substituted, combined, separated, and designed into a variety of different configurations, all of which are expressly contemplated herein.

[0045] Unless otherwise defined, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0046] This disclosure should not be limited to the specific embodiments described herein, which are intended to illustrate various aspects. It will be apparent to those skilled in the art that many variations and modifications can be made without departing from the spirit and scope of this disclosure. In addition to the methods and apparatuses listed herein, functionally equivalent methods and apparatuses within the scope of this disclosure will be apparent to those skilled in the art based on the foregoing description. Such variations and modifications should fall within the scope of the appended claims. This disclosure is limited only by the terms of the appended claims and the scope of all their equivalents. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0047] In the case of traditional active material recycling processes, the main purpose is to extract precious metals (nickel, cobalt, manganese, etc.) that are used as elements in lithium secondary battery active materials. These precious metals deteriorate in performance after use and are then resynthesized into active materials. However, the difference in this disclosure is that active materials are recovered from positive electrode waste generated in the lithium secondary battery manufacturing process.

[0048] Furthermore, in known active material recycling processes, the addition of chemical methods—such as acid / alkali dissolution or melting with reduction / additives to extract precious metals and then manufacturing them into metals (direct reduction method) or resynthesizing active materials—further complicates the process and incurs economic costs. However, this disclosure relates to a method for directly reusing positive electrode active materials without dissolving them.

[0049] To directly reuse the positive electrode active material, a method for removing the current collector from the positive electrode is needed. This can be achieved through methods such as high-temperature heat treatment to remove the binder, melting the binder with a solvent, completely melting the current collector, and selecting the active material through dry grinding and sieving.

[0050] Solvent stability is crucial for dissolving binders using solvents. While NMP is the most effective solvent, it suffers from toxicity and high cost. Furthermore, it requires solvent recovery processes, such as reprocessing waste solvents. Melting the current collector is cheaper than using solvents. However, it is difficult to remove foreign matter from the surface of the reused active material, and the removal of the current collector generates hydrogen gas, posing an explosion hazard. Dry grinding and sieving are insufficient to completely separate the current collector from the active material. The particle size distribution of the active material changes during the grinding process, and the binder is difficult to remove, resulting in performance degradation in the reused battery.

[0051] In this disclosure, the active material and the current collector are separated by high-temperature heat treatment. In particular, since the heat treatment is carried out in air, no specialized equipment configuration is required, and because it is a relatively simple process requiring only heating, it is advantageous for large-scale production and commercialization. However, foreign matter should not remain on the surface of the reusable active material. This disclosure even proposes a step for removing foreign matter from the surface of the reusable active material.

[0052] In the following text, refer to Figure 2 A method for reusing active materials according to one embodiment of the present disclosure is described. Figure 2 This is a flowchart of a method for reusing active materials according to this disclosure.

[0053] refer to Figure 2 First, waste positive electrode material is prepared (step S10).

[0054] As referenced above Figure 1 The cathode waste can be the residue remaining after manufacturing a cathode sheet including a lithium composite transition metal oxide cathode active material layer on a current collector and punching the cathode sheet. Alternatively, cathode waste can be prepared by collecting cathodes that have defects during the process. Furthermore, cathode waste can be prepared by separating the cathode from discarded lithium-ion batteries after use.

[0055] For example, a slurry is prepared by adding N-methylpyrrolidone (NMP) to lithium cobalt oxide (LiCoO2(LCO)) or NCM-based active materials (including nickel (Ni), cobalt (Co) and manganese (Mn)), carbon-based carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder, and then coating the slurry onto a sheet current collector made of aluminum foil. The sheet is then dried in a vacuum furnace at about 120°C to produce a positive electrode sheet, and the positive electrode sheet is punched to a specific size. Residual positive electrode waste can also be prepared.

[0056] Lithium-based composite transition metal oxides are used as positive electrode active materials in lithium-ion secondary batteries, primarily utilizing lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), or nickel lithium oxide (LiNiO2, etc.). Furthermore, as a method to improve low thermal stability while maintaining the excellent reversible capacity of LiNiO2, nickel-manganese-based lithium composite metal oxides (in which a portion of nickel (Ni) is replaced by manganese (Mn) with excellent thermal stability) and NCM-based lithium composite transition metal oxides (in which a portion of nickel (Ni) is replaced by manganese (Mn) and cobalt (Co)) are used. This disclosure specifically proposes the reuse of NCM-based lithium composite transition metal oxide active materials.

[0057] As described above, the positive electrode waste has an active material layer on a current collector made of metal foil (such as aluminum foil). This active material layer is formed by coating a slurry containing active material, conductive material, binder, solvent, etc., and has a structure in which the binder connects the active material and the conductive material after the solvent evaporates. Therefore, if the binder is removed, the active material can be separated from the current collector.

[0058] Next, the cathode waste is pulverized to an appropriate size (step S20). Pulverization refers to cutting or shredding the cathode waste into suitable, easily manageable fragments. After pulverization, the cathode waste is cut into small fragments, for example, 1 cm × 1 cm. For pulverization, various dry grinding equipment (such as hand grinders, pin grinders, disc grinders, cutting grinders, and hammer grinders) can be used, or a high-speed cutter can be used.

[0059] When shredding, the characteristics of the equipment used in processing cathode waste and subsequent processes should be taken into account. For example, if cathode waste is loaded and unloaded using equipment that requires continuous processing, the waste must have good flowability, so it must be shredded to remove large amounts of cathode waste.

[0060] Now, the positive electrode waste is heat-treated in air (step S30).

[0061] In this disclosure, heat treatment is performed to thermally decompose the binder in the active material layer. Preferably, the molar ratio of lithium to other metals in the active material after heat treatment decreases by up to 20% compared to the molar ratio of lithium to other metals in the active material before heat treatment in the cathode waste. More preferably, a decrease of up to 10% is desirable. If the decrease in molar ratio is greater than 20%, the amount of additional material (such as lithium precursor) required will increase, which is undesirable. If the decrease is within 10%, the amount of lithium precursor added can be minimized. If the decrease in molar ratio is close to 0%, no lithium precursor needs to be added, but since lithium loss is inevitable during heat treatment, it is difficult to achieve a decrease close to 0%. In this disclosure, by optimizing the heat treatment conditions (see Experimental Example 1), the decrease can be within 20%, more preferably within 10%, and most preferably within 3%.

[0062] Therefore, heat treatment can be performed at temperatures between 300°C and 650°C, which can be called high-temperature heat treatment. Below 300°C, it is difficult to remove the binder, resulting in the current collector not being able to be separated. At temperatures equal to or greater than 650°C, the current collector melts (aluminum melting point: 660°C), leading to the phenomenon that the current collector cannot be separated.

[0063] A certain heat treatment time is maintained to allow for sufficient thermal decomposition of the binder. For example, the heat treatment time is maintained at the aforementioned heat treatment temperature for 10 minutes to 24 hours. Preferably, the heat treatment time is set to be equal to or greater than 30 minutes. The longer the heat treatment time, the longer the time for thermal decomposition of the binder, but when the heat treatment time exceeds a certain period, the effect of thermal decomposition becomes indistinguishable. Furthermore, a reduction in lithium is not desirable. If the heat treatment time is set to 10 minutes to 24 hours, the molar ratio of lithium to other metals in the active material of the cathode waste after heat treatment may decrease by up to 20% compared to the molar ratio of lithium to other metals in the active material before heat treatment. The heat treatment equipment can be various types of furnaces. For example, considering productivity, the heat treatment equipment can be a box furnace or a rotary kiln capable of continuous processing.

[0064] After heat treatment, the cathode waste can be slowly or rapidly cooled in the atmosphere.

[0065] For example, a heat treatment can be performed at 550°C for 30 minutes at a temperature rise rate of 5°C / min. This temperature rise rate can be implemented without difficulty (e.g., in a box furnace) and heating can be performed without causing thermal shock to the positive electrode waste. 550°C allows for good thermal decomposition of the binder while taking into account the melting point of the aluminum current collector. At this temperature, since thermal decomposition is insufficient to occur in less than 10 minutes of heat treatment, heat treatment should be performed for more than 10 minutes, and if possible, for more than 30 minutes.

[0066] Because the binder and conductive material in the active material layer are thermally decomposed in air through heat treatment, turning into CO2 and H2O and being removed. Since the binder is removed, the active material is separated from the current collector, and the active material to be recycled can be in powder form. Therefore, in step S30 alone, the current collector can be separated from the active material layer, and the active material in the active material layer can be recycled.

[0067] Performing the heat treatment in step S30 in air is important. If the heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive material will not be thermally decomposed, but only carbonized. When the binder and conductive material are only carbonized, the carbon component remains on the surface of the active material, which will reduce the performance of the reusable active material. When heat treatment is performed in air, both the binder and conductive material are almost completely removed, leaving no residue, because the carbon material in the binder or conductive material reacts with oxygen and is burned and removed as CO and CO2 gases.

[0068] Therefore, according to this disclosure, the active material is recovered in powder form, and the carbon components generated by the carbonization of the binder or conductive material do not remain on its surface.

[0069] Next, the recovered active material is washed (step S40). During washing, a cleaning solution is used. This cleaning solution can be simply water. Alternatively, the cleaning solution can be an aqueous solution of a lithium compound. In particular, an aqueous solution of a lithium compound that exhibits alkalinity in its aqueous state is preferred. This aqueous solution of the lithium compound is prepared to contain greater than 0% and equal to or less than 15% of a lithium compound, and preferably uses LiOH. The amount of LiOH is preferably equal to or less than 15%. Using excess LiOH may leave excess LiOH on the surface of the active material even after washing, which may affect the subsequent annealing process. In order to clean the surface of the active material as thoroughly as possible in the pre-annealing step, the amount added is limited to equal to or less than 15% because the addition of excess LiOH is detrimental to the process.

[0070] Washing can be performed by immersing the recovered active material in an aqueous solution of a lithium compound. After immersion, washing can be carried out within one week (preferably within one day, more preferably within one hour). If washing is performed after one week, there is a risk of capacity reduction due to excessive lithium leaching. The washing time can be determined taking into account lithium dissipation. For example, in the case of compositions with a relatively high nickel content in NCM active materials, since the amount of lithium dissipation increases with the washing time, it is best not to extend the washing time as much as possible. Therefore, it is preferable to set the washing time within one day or one hour. In the case of compositions with a relatively low nickel content, if the washing time does not exceed one week, the lithium dissipation is relatively small. Therefore, it is preferable to wash within one week (preferably within one day or one hour). Washing includes immersing the active material in a cleaning solution (such as an aqueous solution of a lithium compound that is alkaline in its aqueous state), stirring the active material while it is immersed, etc. It is preferable to combine stirring with immersion whenever possible. If the active material is only immersed in the cleaning solution without stirring, the washing process may proceed slowly and may result in lithium leaching. Since the process time can be minimized if agitation and soaking are performed together, it is preferable to agitate while soaking in the cleaning solution. After washing, drying can be performed simply, or the spray drying step described in another embodiment below can be performed without drying. First, when drying is performed immediately after washing, air drying can be carried out in a convection oven after filtration.

[0071] The purpose of washing is to remove LiF and metal fluorides that may be present on the surface of the recycled active material and to perform surface modification. During the heat treatment in step S30, the binder and conductive material in the active material layer are converted into CO2 and H2O, evaporated, and then removed. During this process, CO2 and H2O react with lithium on the surface of the active material to form Li2CO3 and LiOH, and fluorine (F) present in the binder (such as PVdF) reacts with the metal elements constituting the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, the battery performance will deteriorate when the active material is reused. In this disclosure, the reactants that may be generated on the surface of the recycled active material during the heat treatment in step S30 are removed by adding the washing in step S40, so that foreign matter will not remain on the surface of the recycled active material.

[0072] In particular, it is more preferable to wash the active material using an aqueous solution of lithium compounds that exhibits alkalinity in the aqueous state. While using an aqueous solution of sulfuric acid or hydrochloric acid instead of an aqueous solution of lithium compounds that exhibits alkalinity in the aqueous state can wash away F from the surface of the active material, the performance of the reused cathode active material will decrease because transition metals (Co and Mg) present in the active material will be eluted. The aqueous solution of lithium compounds that exhibits alkalinity in the aqueous state used in this disclosure is highly desirable because it can remove binders that may still exist in trace amounts even after the thermal decomposition in step S30, and can replenish the amount of lithium that may be eluted during the washing process without eluting transition metals, etc., present in the active material.

[0073] In step S40, particularly preferably, the molar ratio of lithium to other metals in the active material after washing decreases by up to 20% compared to the molar ratio of lithium to other metals in the active material before heat treatment of the cathode waste. More preferably, a decrease of up to 10% is desirable. If the decrease in molar ratio is greater than 20%, the amount of additional material (such as lithium precursor) required increases, which is undesirable. If the decrease is within 10%, the amount of lithium precursor added can be minimized. If the decrease in molar ratio is close to 0%, no lithium precursor needs to be added, but it is difficult to achieve a decrease close to 0% because lithium loss inevitably occurs during the washing process for LiF removal. In this disclosure, by optimizing the washing conditions (see Experimental Example 1), the decrease can be within 20%, more preferably within 10%, and most preferably within 9%.

[0074] Therefore, cleaning solutions with LiF solubility of 0.127 g / 100 ml (18°C) and 0.134 g / 100 ml (25°C) are used, and preferably, the ratio of active material to cleaning solution during washing is equal to or less than 1:200. Cleaning solutions with LiF solubility different from those proposed herein, or with an active material to cleaning solution ratio equal to or greater than 1:30, can be used. If the ratio of cleaning solution to active material differs from that proposed herein, severe lithium dissolution will occur.

[0075] Through step S40, in this disclosure, the LiF content on the surface of the recovered active material can be adjusted to less than 500 ppm, thereby achieving an increased capacity. Preferably, the F content can be set to be equal to or less than 100 ppm. More preferably, the F content can be set to be equal to or less than 30 ppm. As described above, through washing, LiF or lithium metal compounds formed by the decomposition of the binder are removed, thus improving the resistivity.

[0076] Next, the lithium precursor is added to the washed active material and annealed (step S50).

[0077] Although the preceding steps S30 and S40 aim to minimize lithium loss from the active material, unavoidable lithium loss may occur. This lithium loss is compensated for in step S50. A solid or liquid lithium precursor can be added. The lithium precursor used in the annealing process can be any one or more of LiOH, Li₂CO₃, LiNO₃, and Li₂O.

[0078] To mix the solid lithium precursor, drying is performed after step S40, followed by material mixing, in which case powder mixing or milling processes are used.

[0079] To mix the liquid lithium precursor, it is preferable to mix the washed active material with the lithium precursor solution after step S40 without drying, and then spray-dry the lithium precursor solution. The lithium precursor solution can be a lithium compound soluble in aqueous solution or organic solvent. The temperature of the spray-drying step can be from 100°C to 300°C. Preferably, the minimum temperature is equal to or greater than 80°C. This is because when the minimum temperature is equal to or lower than 80°C, the solution may not be completely dried. More preferably, when the minimum temperature is equal to or greater than 100°C, the solution can be completely dried.

[0080] During spray drying, the lithium precursor solution is dried immediately after spraying, coating or contacting the active material surface with the lithium precursor components. Another advantage in this regard is that, during the drying of the lithium precursor solution as a solvent, particles agglomerate under capillary forces, and the particle size is adjusted. In the case of positive electrode waste made from electrodes, particles on the surface may be pressed and cracked or broken due to the rolling process. In particular, compared to LCO, NCM-based active materials exhibit a high degree of particle splitting during electrode formation due to rolling. Compared to fresh active materials, recycled active materials contain many small particles, resulting in particle inhomogeneity. This is especially true for NCM-based active materials that utilize large particles formed by secondary granulation through the aggregation of primary particles with sizes ranging from tens to hundreds of nanometers. In the process of rolling positive electrodes made from such active materials to adjust the porosity in the electrode, secondary particles split into primary granulated particles or smaller particles, which are larger than the secondary particles but smaller than the large particles. Since the specific surface area of ​​the active material increases with the number of particles crushed by rolling, problems may arise that affect slurry properties, electrode adhesion, and electrode performance when the active material is reused from the rolled electrode.

[0081] To ensure the reusability of active materials, it is desirable that the particle size distribution not differ from that of fresh active materials. Spray drying addresses particle inhomogeneity by recovering larger particles from smaller particles that break down during the agglomeration rolling process, and also brings the particle size closer to the initial characteristics of fresh active materials. This is particularly effective for NCM-based active materials, which previously suffered from severe particle breakage during rolling processes.

[0082] Therefore, when using spray drying, the lithium precursor is coated onto the surface of the active material, and the active material is obtained by adjusting the particle size. Since the addition of the lithium precursor, granulation, and drying are performed in one step, the process is simplified. Because the active material particles washed in step S40 are simply mixed and dispersed in a lithium precursor solution of a certain concentration before spray drying, the advantage lies in the fact that washing in step S40 and adding the lithium precursor in step S50 can be a continuous process.

[0083] In step S50, the crystal structure of the active material is restored by annealing, thereby restoring or improving the performance of the reused active material to the level of a fresh, unused active material. Through the preceding steps S30 and S40, deformed structures may appear on the surface of the active material. For example, in an active material that is an NCM-based lithium composite transition metal oxide, a spinel structure may form in step S40, where nickel becomes hydrated and rock-salted [NiCO3·2Ni(OH)2)H2O]. If the battery is manufactured as is, the battery performance may deteriorate (e.g., capacity decrease). In this disclosure, the crystal structure is restored by step S50. For example, the active material that is an NCM-based lithium composite transition metal oxide is restored to a hexagonal structure again. Therefore, it is possible to restore or improve the initial performance of the active material to a level similar to that of a fresh active material.

[0084] Furthermore, in the case of LCO active materials, Co3O4 can be generated through thermal decomposition on the surface. If a battery containing Co3O4 is manufactured, the battery performance may deteriorate. In this disclosure, by restoring the crystal structure and removing Co3O4 in step S50, the initial performance of the active material can be restored or improved to a level similar to that of fresh active material.

[0085] Before annealing, a lithium precursor is added, and the amount added should be the same as the lithium loss rate compared to the lithium-to-other-metal ratio in the raw active material (i.e., fresh active material) used in the active material layer. For example, when the lithium-to-other-metal ratio in the fresh active material is 1, a lithium precursor can be added at a lithium addition amount of 0.001 to 0.4 molar ratio. A lithium addition amount of 0.01 to 0.2 molar ratio is appropriate. Besides the amount of lithium lost through washing, etc., adding excessive lithium precursor will result in unreacted lithium precursor residues in the recycled active material, which increases resistance in the active material recycling process; therefore, it is necessary to apply an appropriate amount of lithium precursor.

[0086] Furthermore, it is preferable that the molar ratio of lithium to other metals is 1:1, and the lithium precursor can be added in an amount of 0.0001 to 0.1 molar ratio. The reason for adding excess lithium as described above is to form a surface protective layer on the surface coating of the active material, which will be further described below. When using this active material to manufacture secondary batteries, it is possible to maintain lifespan characteristics while suppressing side reactions caused by the electrolyte.

[0087] Annealing can be performed in air at 400°C to 1000°C. The annealing temperature can be 600°C to 900°C. This temperature should be varied within a limited range depending on the type of lithium precursor. Preferably, the annealing time is set to be equal to or greater than one hour. Preferably, the annealing time is about 5 hours. If the annealing time is long, the crystal structure may be fully restored, but even with a long annealing time, the performance of the active material will not be significantly affected. For example, the annealing time is within 15 hours. The annealing equipment can be the same or similar to the heat treatment in step S30.

[0088] For example, when Li₂CO₃ is used as a lithium precursor, the annealing temperature is preferably 700°C to 900°C, more preferably 710°C to 780°C. This is because the melting point of Li₂CO₃ is 723°C. Most preferably, annealing is performed at 750°C. When LiOH is used as a lithium precursor, the annealing temperature is preferably 400°C to 600°C, more preferably 450°C to 480°C. This is because the melting point of LiOH is 462°C.

[0089] The annealing temperature is preferably above the melting point of the lithium precursor. However, at temperatures exceeding 1000°C, the positive electrode active material will undergo thermal decomposition, and the performance of the active material will deteriorate; therefore, the temperature should not exceed 1000°C.

[0090] Through this step S50, reusable active materials can be obtained.

[0091] Next, as an optional step, step S60 may be performed. In step S60, a surface coating is applied to the active material annealed in step S50.

[0092] The surface coating step may involve coating a surface with at least one of a metal, organometallic material, and carbon component in a solid or liquid manner, followed by heat treatment of the coated material at a temperature between 100°C and 1200°C. When heat treatment is performed at temperatures exceeding 1200°C, performance degradation may occur due to the thermal decomposition of the positive electrode active material. In the surface coating step, the coating process, whether solid or liquid, can utilize methods such as mixing, milling, spray drying, and grinding.

[0093] By surface coating, a surface protection layer is formed on the heterogeneous metal. When the molar ratio of lithium in the positive electrode active material to other metals is 1:1 by replenishing the lost lithium, if the lithium in the active material reacts with the surface coating material and the molar ratio of lithium to other metals in the positive electrode active material drops to less than 1:1, it may not be possible to achieve 100% capacity performance. Therefore, in the previous step S50, insufficient lithium is added to make the molar ratio of lithium to other metals in the positive electrode active material 1:1, and an excessive amount of lithium is added such that, compared with other metals in the positive electrode active material, it includes more lithium in a molar ratio of 0.0001 to 0.1. Then, during the surface coating process, the molar ratio of lithium to other metals in the positive electrode active material is 1:1, and a surface protection layer can be formed. Therefore, when even when performing the process of forming the surface protection layer, in addition to adding only the lost lithium in this process, it is preferable to additionally add lithium as a material for the surface protection layer.

[0094] Specifically, when a metal oxide such as B, W, B-W is coated on the active material and then heat treatment is performed, a lithium borate layer can be formed on the surface of the active material and serve as a surface protection layer. The additional lithium added in a molar ratio of 0.0001 to 0.1 in step S50 reacts with a metal oxide such as B, W, B-W in step S60, and the molar ratio of lithium to other metals in the positive electrode active material does not drop to less than 1:1, so there is no capacity drop.

[0095] The reusable active material obtained by the above method can be represented by the following Chemical Formula 1.

[0096] [Chemical Formula 1]

[0097] Li a Ni x Mn y Co z M w O 2+δ

[0098] (In the above Chemical Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 ≤ x < 0.95, 0 ≤ y < 0.8, 0 ≤ z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.)

[0099] The F content of the reusable active material is equal to or lower than 100 ppm. According to the present disclosure, since it is possible to recycle the active material with a reduced F content, if the active material with a reduced F content is reused as the active material, excellent resistance performance and capacity performance can be achieved.

[0100] As described above, according to this disclosure, the active material and the current collector are separated during the heat treatment process in step S30. By optimizing the temperature, time, etc., of the heat treatment process, the molar ratio of lithium to other metals in the active material after heat treatment can be reduced by up to 20% compared to the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment. For example, if the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment is 1:1, then the molar ratio of lithium to other metals in the active material after heat treatment is within 0.8:1. Therefore, the amount of lithium precursor to be added subsequently can be minimized.

[0101] During the washing process in step S40, LiF or metal fluorides are removed. Washing is safe and inexpensive, removing LiF or metal fluorides without loss of other elements and preventing the elution of transition metals. In particular, by optimizing the conditions of the cleaning solution, washing time, and the ratio of active material to cleaning solution, the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment can be reduced by up to 20% after washing. For example, if the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment is 1:1, the molar ratio of lithium to other metals in the active material of the active material after washing is within 0.8:1. Thus, the amount of lithium precursor to be added subsequently can be minimized. If an aqueous solution of lithium compounds that exhibits alkalinity in aqueous solution is used as the cleaning solution in the washing process, it also has the advantage of replenishing the lithium loss that occurs in this process.

[0102] As described above, according to this disclosure, lithium loss in the active material can be minimized in the heat treatment process for separating the current collector and the washing process (e.g., residue removal) for surface modification. By optimizing the heat treatment process, lithium loss can be minimized, as can the amount of current collector reacting with the active material or precipitated through heat treatment. Furthermore, by adjusting the ratio between the active material and the cleaning solution during washing, lithium loss in the active material can be minimized while removing LiF, as residual LiF may act as a resistor. Since lithium loss is minimized during the process of obtaining reusable active material, the composition of the fresh active material is not significantly different from that of the reusable active material. Insufficient lithium is added through an additional lithium precursor addition process. In this respect, the amount of added lithium precursor is minimized, making it preferred in terms of process and cost.

[0103] If spray drying is used to add lithium precursors, the active material to be reused can be re-granulated through spray drying, improving particle size and specific surface area even if the particles are broken due to rolling in the previous process. Furthermore, if the cleaned active material is mixed with the lithium precursor solution and then spray-dried, the lithium precursor can be added while the active material is being re-granulated, resulting in a simplified process and the advantage of forming a continuous process with the preceding washing step.

[0104] The annealing step following the addition of lithium precursors also has the advantages of being safe and inexpensive, effectively removing Co3O4, and restoring the battery performance of reusable active materials by restoring the crystal structure (i.e., increasing crystallinity).

[0105] The reusable active material obtained according to this disclosure can have a particle size distribution similar to that of fresh active material, thus potentially eliminating the need for separate processing to adjust the particle size distribution. Since the carbon components generated by the carbonization of binders or conductive materials do not remain on the surface, steps such as carbon removal are unnecessary. Therefore, through the above... Figure 2 The active material obtained by this method can be reused as is without additional processing and used to manufacture the positive electrode.

[0106] The reused active material can also be used 100% as is without adjusting the composition, or the reused active material can be mixed with new active material, or the reused active material can be mixed with conductive material, binder and solvent to form a slurry for use.

[0107] The experimental examples of this disclosure will be described in detail below.

[0108] <Experimental Example>

[0109] Experimental Example 1: Analyze the heat treatment time, molar ratio of lithium to other metals, and... residual amount of F

[0110] Each positive electrode active material was prepared using the following method, and the molar ratio of lithium to other metals and the contents of F and Al were measured according to the heat treatment time. The heat treatment step, which separates the active material from the current collector in air, was carried out at a temperature equal to or below 660°C, at which aluminum, serving as the current collector, was melted.

[0111] Sample 1: Utilizing fresh NCM-based lithium composite transition metal oxides instead of recycled active materials.

[0112] Sample 2: The positive electrode waste to be discarded after preparing the punched positive electrode plate with NCM-based lithium composite transition metal oxide active material was heat-treated in air at 500°C for 5 hours, and then the active material was collected. That is, in the above-disclosed method for reusing active materials, only the heat treatment in step S30 is performed to remove the binder and conductive material, separate the aluminum current collector, and collect the NCM-based lithium composite transition metal oxide active material. At this time, the positive electrode plate is made from a slurry, which is prepared as follows: 96.25 wt% of positive electrode active material, 1.5 wt% of carbon black as conductive material, and 2.25 wt% of PVdF as binder (resin content of 9.8 wt% relative to PVdF 1100) are weighed and mixed with NMP.

[0113] Sample 3: The positive electrode waste was prepared in the same manner as Sample 2, heat-treated in air at 600°C for 5 hours, and then the active material was collected. The heat treatment temperature was higher than that of Sample 2.

[0114] Sample 4: The positive electrode waste was prepared in the same manner as Sample 2, heat-treated in air at 550°C for 30 minutes, and then the active material was collected. Although the heat treatment temperature was higher than that of Sample 2, the heat treatment time was shorter.

[0115] Sample 5: In addition to Sample 4, the active material was washed for 10 minutes using the washing step S40 of the active material reuse method according to this disclosure. A cleaning solution was prepared, and this cleaning solution was used as an aqueous solution with or without LiOH. The cleaning solution was prepared using LiF with a solubility of 0.127 g / 100 ml (18°C) and 0.134 g / 100 ml (25°C). The active material was washed at a washing ratio of 1:30 relative to 5 g of positive electrode active material, wherein the ratio of active material to cleaning solution was 1:30.

[0116] Reducing the residual amount of phosphorus (F) is important because during heat treatment, residual F from the decomposition of the binder reacts with Li ions in the active material to form LiF, which can act as a resistor. The F content was measured by ICP, and the results, based on the characteristics of heat treatment temperature and time, are summarized in Table 1.

[0117] [Table 1]

[0118]

[0119] ND means that the content of F is equal to or less than 30 ppm. The unit of content is ppm, which means mg / kg.

[0120] Sample 3 was heat-treated at a higher temperature than Sample 2, and had less residual F, but the molar ratio of lithium to other metals decreased, and the Al current collector composition was 350 ppm, higher than that of Sample 2. This shows that a higher heat-treatment temperature is not always desirable. As can be seen from Samples 2 and 3, the molar ratio of lithium to other metals in the positive electrode active material is affected as the heat-treatment temperature increases. Therefore, it is preferable to utilize the appropriate heat-treatment temperature proposed in this disclosure.

[0121] The heat treatment temperature of Sample 4 was higher than that of Sample 2, but the heat treatment time was reduced. Even as shown, with the increase in heat treatment temperature, the molar ratio of lithium to other metals did not change when the heat treatment time was reduced. In Sample 4, it can be seen that the molar ratio of lithium to other metals and the residual amount of F maintained the same performance as Sample 2, and the aluminum current collector composition also remained at the same level.

[0122] Compared to Sample 4, Sample 5 underwent a washing step. Washing reduced the residual amounts of F and Al, particularly the residual amount of F. However, the molar ratio of lithium to other metals decreased compared to Sample 4. The molar ratio of lithium to other metals in Sample 5 was 0.94, a decrease of less than 10% compared to the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment (1.03 if considered similar to Comparative Example 1). This level of decrease is sufficient to easily replenish the insufficient lithium by subsequently adding lithium precursors. Therefore, it can be concluded that the heat treatment conditions of Samples 4 and 5 are preferred, even considering the lithium loss due to washing in Sample 5. The molar ratio of lithium to other metals in Sample 4 was 1, a decrease of less than 3% compared to the molar ratio of lithium to other metals in the active material of the cathode waste before heat treatment (1.03 if considered similar to Comparative Example 1). Therefore, it can be seen that a decrease of less than 3% in the heat treatment step (sample 4) leads to a decrease of less than 10% during washing. Considering that more lithium will be lost after washing, the lithium loss in the preceding heat treatment step should also be managed. Therefore, in this disclosure, the molar ratio of lithium to other metals needs to decrease by less than 20% before and after heat treatment. The reason is that when the washing step is performed as in sample 5, lithium ions are released by the cleaning solution, resulting in more lithium loss. Therefore, it is preferable, as in this disclosure, to manage and control the decrease in the molar ratio of lithium to other metals even in the heat treatment step before the washing step.

[0123] Experimental Example 2: Analysis based on washing time, molar ratio of lithium to other metals, and residual amount of F.

[0124] Although the sample preparation method is the same as the sample preparation method described above, a sample with a different washing time was further prepared, and the molar ratio of lithium to other metals and the content of F were measured according to the washing time.

[0125] Sample 6: The washing step was performed in the same manner as Sample 5, and the washing time was 1 hour, which is an increase compared to Sample 5.

[0126] Sample 7: The washing step was carried out in the same manner as Sample 5, and the washing time was 24 hours, which is a further increase compared to Sample 5.

[0127] The experimental results are summarized in Table 2.

[0128] [Table 2]

[0129]

[0130] It was confirmed that, depending on the washing time, the molar ratio of lithium to other metals did not show significant differences in samples 5, 6, and 7. Furthermore, the F component showed similar results, remaining within 100 ppm. In comparison, excessive lithium dissolution occurred in the active materials soaked in the cleaning solution for more than a week. Therefore, as with samples 5 to 7, washing within one day is preferable, and more preferably within one hour.

[0131] Experimental Example 3: Analysis based on the washing ratio, the molar ratio of lithium to other metals, and the residual amount of F.

[0132] Although the sample preparation method is the same as the sample preparation method described above, samples with a different washing ratio of active material to cleaning solution are further prepared, and the molar ratio of lithium to other metals and the content of F are measured according to the washing ratio. Samples 8 to 12 below are washed in the same way as sample 5, except for the washing ratio.

[0133] Sample 8: Cleaning was performed using an active material to cleaning solution ratio of 1:1.

[0134] Sample 9: Cleaning was performed with an active material to cleaning solution ratio of 1:3.

[0135] Sample 10: Cleaning was performed with an active material to cleaning solution ratio of 1:5.

[0136] Sample 11: Cleaning was performed with an active material to cleaning solution ratio of 1:10.

[0137] Sample 12: Cleaning was performed with an active material to cleaning solution ratio of 1:100.

[0138] Sample 13: Cleaning was performed using an active material to cleaning solution ratio of 1:200.

[0139] The experimental results are summarized in Table 3.

[0140] [Table 3]

[0141]

[0142] It can be confirmed that all experiments in Table 2 were conducted at the same washing ratio of 1:30. The effects on samples 5, 6, and 7 were not significantly different depending on the washing time. However, in Table 3, the molar ratio of lithium to other metals was affected by the ratio of active material to cleaning solution, and the residual amount of F was also affected. When washing was performed, lithium decreased compared to sample 4 which was not washed. As the washing ratio increased, i.e., as the amount of cleaning solution and active material increased, lithium decreased further. With increasing washing ratio, ideal results were obtained regarding the residual amount of F.

[0143] When the residual amount of F is below 100 ppm, the impact on electrode capacity is small. Therefore, from the perspective of residual F amount, a washing ratio greater than 1:10 in sample 11 is preferred, while a washing ratio equal to or greater than 1:30 in sample 5 is advantageous. When the washing ratio is equal to or greater than 1:100, as in samples 12 and 13, the molar ratio of lithium to other metals tends to converge to 0.92. Since there is no change even when the washing ratio is greater than 1:200, it can be seen that from the perspective of cleaning solution utilization and cost, a washing ratio equal to or less than 1:200 is preferred.

[0144] Experiment Example 4: Analysis based on the washing ratio, the molar ratio of lithium to other metals, and the residual amount of F.

[0145] Using a different positive electrode waste than that used in Experiments 1 to 3 above, the same experiment as in Experiment 3 was conducted.

[0146] The positive electrode waste was discarded from positive electrode plates made from a slurry, which was prepared as follows: 95 wt% of positive electrode active material, 1.2 wt% of carbon black as a conductive material, and 3.7 wt% of PVdF as a binder (resin content of 9.8 wt% relative to PVdF 1100) were weighed and mixed with NMP. Compared with Experimental Examples 1 to 3, the positive electrode waste used in Experimental Example 4 had a higher PVdF content as a binder.

[0147] Sample 14: Active materials were collected in the same manner as Sample 4, except for the positive electrode waste.

[0148] Sample 15: Active materials were collected in the same manner as in Sample 8, except for the positive electrode waste.

[0149] Sample 16: Active materials were collected in the same manner as in Sample 10, except for the cathode waste.

[0150] Sample 17: Active materials were collected in the same manner as in Sample 11, except for the cathode waste.

[0151] Sample 18: Active materials were collected in the same manner as in Sample 5, except for the positive electrode waste.

[0152] Sample 19: Active materials were collected in the same manner as Sample 12, except for the cathode waste.

[0153] Sample 20: Active materials were collected in the same manner as in Sample 13, except for the cathode waste.

[0154] The experimental results are summarized in Table 4.

[0155] [Table 4]

[0156]

[0157] As can be seen, in Table 2, the effect of time is not significantly different under the same washing ratio. However, in Table 4, the molar ratio of lithium to other metals is affected by the ratio of active material to cleaning solution, and the residual amount of F is also affected as in Table 3.

[0158] As can be seen, Table 4 shows the increase in binder content compared to Table 3. When comparing samples 8 and 15, 10 and 16 with the same washing ratio, the residual amount of F in Table 4 is higher. The molar ratio of lithium to other metals tends to be similar.

[0159] It can also be seen in Table 4, similar to Table 3, that when the residual amount of F is less than 100 ppm, the washing ratio greater than 1:30, as in sample 18, is advantageous from the perspective of residual F because it has little impact on electrode capacity. When the washing ratio is equal to or greater than 1:100, as in samples 19 and 20, the molar ratio of lithium to other metals tends to 0.92.

[0160] In the case of the positive electrode for secondary batteries, the binder content in the manufactured electrode is within approximately 3.7 wt% (compared to 9.8 wt% resin content for PVdF 1100). Table 4 shows that the binder content has increased compared to Table 3, but even in this case, with an active material to cleaning solution ratio of 1:200, the removal of F is within 100 ppm, and the molar ratio of lithium to other metals tends to 0.92. Since there is no change even when the washing ratio is greater than 1:200, it can be seen that from the perspective of cleaning solution utilization and cost, a washing ratio of 1:200 is preferably equal to or less than 1:200.

[0161] As can be confirmed from Tables 3 and 4 above, the washing ratio is preferably equal to or greater than 1:30 and equal to or less than 1:200.

[0162] Experimental Example 5: Comparison of capacity characteristics based on washing conditions and the amount of lithium precursor added.

[0163] Each positive electrode active material was prepared using the methods described in the following examples and comparative examples, a positive electrode was manufactured, and then a battery (Coin Half Cell, CHC) was manufactured, and its electrochemical performance was evaluated.

[0164] Implementation Method 1: Sample 5 is further processed to step S50. A lithium precursor (Li₂CO₃) is applied relative to the molar ratio of lithium to other metals in the raw active material (ICP analysis). The amount applied is such that an additional 0.05 molar ratio of lithium can be added in this process, and the sample is annealed at 750°C for 15 hours. Theoretically, in the case of fresh active material, the molar ratio of lithium to other metals is 1:1. However, since the average error of the ICP equipment used to check the molar ratio is ±0.05 (preferably about ±0.02), the molar ratio of lithium to other metals in the raw active material may be 1 ± 0.05:1 as measured by ICP. In this experiment, the lithium precursor is added relative to the analytical ratio obtained by ICP analysis.

[0165] Implementation Method 2: Same as Implementation Method 1, except that a lithium precursor is applied in this process. The amount of lithium applied is such that a molar ratio of 0.1 can be added to the process, and annealing is performed. The amount of lithium precursor is greater than that in Implementation Method 1.

[0166] Comparative Example 1: Fresh NCM-based lithium composite transition metal oxide was used instead of recycled active material. That is, Sample 1 was used.

[0167] Comparative Example 2: The active material of Sample 5 was used as is. The active material used was only used up to the washing step.

[0168] Comparative Example 3: The active material of Sample 5 was annealed at 750°C for 15 hours, but no lithium precursor was added. That is, washing and annealing were performed, but no lithium precursor was added.

[0169] Comparative Example 4: The active material of unwashed Sample 4 was annealed at 750°C for 15 hours by applying a lithium precursor. The amount of lithium precursor added was such that lithium could be added at a molar ratio of 0.1. Compared with Comparative Example 3, this is an experimental example that confirms the washing effect.

[0170] The positive electrode plate is made from a slurry prepared as follows: 96.25 wt% of the positive electrode active material recovered or prepared in the above embodiments and comparative examples, 1.5 wt% of carbon black as a conductive material, and 2.25 wt% of PVdF as a binder (resin content of 9.8 wt% relative to PVdF 1100) are weighed and mixed with NMP.

[0171] Figure 3The results of battery evaluation using the active materials of the embodiments and comparative examples are shown. Rate performance was evaluated by assessing capacity based on the number of cycle repetitions at different currents. The equipment used for evaluation was a general charge / discharge test apparatus commonly used in a laboratory. There was no bias based on the measurement equipment or method. Figure 3 In the chart, the horizontal axis represents the number of cycles, and the vertical axis represents the capacity. The voltage was set from 3 to 4.3V, and initial charging / discharging was performed at 0.1C / 0.1C. A carbonate-based electrolyte was used to construct the battery, with an ethylene carbonate (EC) to ethyl carbonate (EMC) ratio of 3:7, and additives were also included.

[0172] In Embodiments 1 and 2, a lithium precursor was added compared to Comparative Examples 2 and 3. It was confirmed that by replenishing the amount of lithium lost during the washing process, the capacity of the lithium precursor increased to a level similar to Comparative Example 1. Although the capacity decreased as in Comparative Example 2 after the surface modification step following washing, the capacity increased in Embodiments 1 and 2 because the Ni rock salt was reduced by annealing after removing LiF through surface modification, and the structure of the lithium precursor was restored to a hexagonal crystal.

[0173] In Comparative Example 4, a lithium precursor was added but no washing was performed. Without washing, the capacity improvement effect was not as good as in Embodiments 1 and 2, where washing was performed, because residual materials such as LiF remained and these materials acted as resistors.

[0174] As described above, according to this disclosure, active materials can be recovered from cathode waste through heat treatment, washing, addition of lithium precursors, and annealing for direct reuse. It is safe because no toxic or explosive solvents such as NMP, DMC, acetone, or methanol are used; and it is suitable for large-scale production because simple and safe methods such as heat treatment, washing, and annealing are employed.

[0175] Figure 4 and Figure 5 These are scanning electron microscope (SEM) images of the samples and active materials used in the embodiments and comparative examples. The SEM images were taken using common laboratory SEM equipment. For example, SEM images could be taken using a HITACHI S-4200. However, there is no bias based on the measuring equipment or method.

[0176] Figure 4 (a) is a SEM image of fresh active material from Sample 1 (or Comparative Example 1), and Figure 4 (b) is Figure 4 Enlarged photograph of (a). Figure 4 (c) is a photograph of the surface of cathode waste made from this fresh active material. Figure 4(d) is Figure 4 Enlarged photograph of (c). Fresh active material shows no particle breakage, but positive electrode waste made from electrodes shows that the particles on the surface were pressed and broken by a rolling process.

[0177] Figure 4 (e) is the SEM image of sample 2, and Figure 4 (f) is Figure 4 A magnified view of (e). (See reference) Figure 4 (e) and Figure 4 In (f), no binder or conductive material was observed in the recovered active material. That is, it can be confirmed that the binder or conductive material was removed during the high-temperature heat treatment. Therefore, it can be seen that the active material was separated from the current collector only by heat treatment in air, and almost no binder or conductive material remained on the surface of the active material.

[0178] Figure 5 (a) is a SEM image of sample 5 (comparative example 2), and Figure 5 (b) is Figure 5 Enlarged photograph of (a). In comparison with photographs of positive electrode waste. Figure 4 (c) and Figure 4 As shown in (d), the particles are released through this process.

[0179] Figure 5 (c) is the SEM image of Comparative Example 3, and Figure 5 (d) is Figure 5 Enlarged photograph of (c). Figure 5 (e) is a SEM image of embodiment 1, and Figure 5 (f) is Figure 5 A magnified view of (e). It can be seen that the particles released in the previous step agglomerate through annealing. In comparison... Figure 5 (f) and Figure 4 As can be seen from (a), the reusable active material of Embodiment 1 has the same shape as the fresh active material.

[0180] Figure 6 This is a graph showing the particle size distribution of the active material in the samples and the active materials in the embodiments and comparative examples. The particle size distribution can be obtained using a common laboratory particle size analyzer; for example, it can be measured using a Horiba LA950V2 particle size analyzer. However, there is no bias based on the measuring equipment or method. Figure 6 In the diagram, the horizontal axis represents particle size (μmm), and the vertical axis represents volume (%).

[0181] Figure 6 The particle size distribution results in the chart are consistent with Figure 4 and Figure 5 The SEM results were the same. The NCM-based active material exhibits high particle splitting due to rolling during electrode formation. Therefore, it can be seen that many small particles were formed in the particle size distribution of Sample 2 after a single heat treatment, and it can be confirmed that a relatively large number of small particles remained even after surface modification in Comparative Example 2. However, when annealing was performed, as seen in the previous SEM results, particle agglomeration increased, thus the particle size distribution of Comparative Example 3 or Embodiment 1 was similar to that of Comparative Example 1, which was a fresh active material. In particular, the particle size distribution of Embodiment 1 was more similar to that of Comparative Example 1. This is defined as a similar particle size distribution when the volume percentage of particles with the same particle size differs by only ±2%. As described above, according to this disclosure, since the particle size distribution of the reusable active material is not different from that of the fresh active material, the initial characteristics are almost maintained, and it is expected that the characteristics of the battery using the reusable active material will be similar to those of the battery using the fresh active material.

[0182] ICP analysis was performed on the positive electrode active materials recovered or prepared from the embodiments and comparative examples, and the content of specific elements was also analyzed. The results are shown in Table 5 below.

[0183] [Table 5]

[0184] B content (mg / kg) W content (mg / kg) Comparative Example 1 (Sample 1) 500 3100 Sample 2 200 2700 Comparative Example 2 (Sample 5) ND 200 Comparative Example 3 ND 200 Implementation Method 1 ND 200

[0185] As shown in Comparative Example 1, the fresh active materials used in this experiment also included B and W. Sample 2 shows that the content of B and W decreased through heat treatment, and the remaining results indicate that almost all of the B was removed in subsequent processes. In the case of W, a large amount of W can be seen to be removed by washing during the surface modification process (as in Comparative Example 2).

[0186] Therefore, due to the type of active material initially utilized, specific elements may be lost during the processing, especially in the surface modification process by washing, where specific elements may be completely removed or a small amount of the element may remain. There may be a situation where it is difficult to fully restore the characteristics by only performing the annealing step in Embodiment 1. In this case, it is preferable to perform the additional surface coating step proposed in the present disclosure. In the case of this experimental example, the surface coating step is to coat B and W. The surface coating can act as a surface protection layer for the positive electrode active material. The surface coating can also be a process to supplement specific deficient elements while reconstructing the surface protection layer in the fresh active material. In the case of the fresh active material utilized in this experiment, the surface protection layer is made of B-W. In this process, the meaning of the loss of lithium is interpreted as the ratio of (lithium in the active material itself + lithium forming the surface protection layer) to other metals, rather than the 1:1 ratio of lithium in the active material itself to other metals. Therefore, the molar ratio of 0.09 lost in the above experiment (as in Comparative Example 2) can be interpreted as the sum of the amount of lithium in the positive electrode active material and the amount of lithium forming the surface protection layer.

[0187] The surface coating step requires a heat treatment process after a solid-phase or liquid-phase reaction.

[0188] When the reusable 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 Chemical Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 ≤ x < 0.95, 0 ≤ y < 0.8, 0 ≤ z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1).

[0192] It can be considered that M in Chemical Formula 1 is supplemented by this surface coating.

[0193] When the surface coating layer includes B, B-W, B-Ti, and B-W-Ti, the surface coating heat treatment can be performed at a temperature of 200°C to 500°C, and other components can also be coated with metal components, carbon components, and organometallic components at a temperature within 100°C to 1200°C.

[0194] As described above, according to this disclosure, cathode waste can be reused using simple, environmentally friendly, and economical methods. Even when lithium secondary batteries are manufactured by reusing the NCM-based lithium composite transition metal oxide cathode active material prepared as described above, the battery performance remains unaffected.

[0195] This disclosure has been described in detail. However, it should be understood that while the detailed description and specific embodiments illustrate preferred embodiments of this disclosure, they are given by way of illustration only, as various changes and modifications within the scope of this disclosure will be apparent to those skilled in the art based on this detailed description.

Claims

1. A method for reusing a positive electrode active material, the method comprising the following steps: (a) By thermally treating the cathode waste, including the lithium composite transition metal oxide cathode active material layer on the current collector, in air, the binder and conductive material in the active material layer are thermally decomposed, the current collector is separated from the active material layer, and the active material in the active material layer is recovered. (b) Wash the recovered active material with a cleaning solution; as well as (c) A reusable active material is obtained by adding a lithium precursor to the washed active material and annealing the active material. Specifically, compared to the molar ratio of lithium to other metals in the cathode waste before heat treatment, the decrease in the molar ratio of lithium to other metals in the active material after heat treatment, or in the active material after washing, is within 20%. The cleaning solution is an aqueous solution of lithium compound that is alkaline in the aqueous solution state. The aqueous solution of lithium compound is prepared to contain more than 0% and equal to or less than 15% lithium compound. Washing is performed within one week, and the washing time is adjusted according to the nickel content in the active material to inhibit excessive leaching of lithium.

2. The method for reusing positive electrode active materials according to claim 1, further comprising the following steps: (d) Surface coating of the annealed active material.

3. The method for reusing positive electrode active materials according to claim 1, wherein, Perform heat treatment at 300℃ to 650℃ for 10 minutes to 24 hours.

4. The method for reusing positive electrode active materials according to claim 1, wherein, The cleaning solution used had a LiF solubility of 0.127 g / 100 ml at 18 °C and 0.134 g / 100 ml at 25 °C, and the ratio of the active material to the cleaning solution during the washing process was equal to or less than 1:

200.

5. The method for reusing positive electrode active materials according to claim 1, wherein, Washing is performed by immersing the recovered active material in the cleaning solution while stirring the recovered active material.

6. The method for reusing positive electrode active materials according to claim 1, wherein, The lithium precursors used in annealing include at least one of LiOH, Li2CO3, LiNO3, and Li2O.

7. The method for reusing positive electrode active materials according to claim 1, wherein, The lithium precursor is added in an amount that results in the same rate of lithium loss as the ratio of lithium to other metals in the raw material active material used in the active material layer.

8. The method for reusing the positive electrode active material according to claim 7, wherein, The lithium precursor is added at a lithium addition amount of 0.001 to 0.4 molar ratio.

9. The method for reusing the positive electrode active material according to claim 7, wherein, The lithium precursor is added in an amount of lithium at a molar ratio of 0.0001 to 0.1 relative to a 1:1 molar ratio of lithium to other metals.

10. The method for reusing the positive electrode active material according to claim 1, wherein, Without drying after washing, the lithium precursor is added in step (c) by mixing the washed active material in a lithium precursor solution and spray-drying the active material.

11. The method for reusing the positive electrode active material according to claim 10, wherein, The spray drying temperature is between 100°C and 300°C.

12. The method for reusing positive electrode active materials according to claim 1, wherein, The annealing is carried out in air at 400°C to 1000°C.

13. The method for reusing the positive electrode active material according to claim 1, wherein, The annealing temperature exceeds the melting point of the lithium precursor.

14. The method for reusing the positive electrode active material according to claim 13, wherein, The annealing temperature shall not exceed 1000℃.

15. The method for reusing the positive electrode active material according to claim 1, wherein, The active material in the active material layer is recycled in powder form, and the carbon components generated by the carbonization of the binder or the conductive material do not remain on the surface.

16. The method for reusing positive electrode active materials according to claim 2, wherein, Performing the surface coating involves coating the surface with at least one of a metal, organometallic, and carbon component in a solid or liquid manner, followed by heat treatment at 100°C to 1200°C.

17. The method for reusing positive electrode active materials according to claim 1, wherein, The reusable active material is represented by the following Chemical Formula 1, Li a Ni x Mr y Co z M w O 2+δ In Chemical Formula 1 above, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 ≤ x < 0.95, 0 ≤ y < 0.8, 0 ≤ z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.

18. The method for reusing positive electrode active materials according to claim 1, wherein, The reusable active material includes fluorine F with a content equal to or less than 100 ppm.

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