Reuse method of active material of positive electrode

Abstract

The method for reusing a positive electrode active material according to the present invention comprises the steps of: immersing a stack cell comprising a stacked and combined positive electrode plate, a separator, and a negative electrode plate in a polar solvent to separate the positive electrode plate; heat-treating the separated positive electrode plate to thermally decompose a binder and a conductive material within the positive electrode active material layer of the positive electrode plate, thereby separating the current collector of the positive electrode plate from the active material layer and recovering the active material within the active material layer; washing the recovered active material with an aqueous solution of a lithium compound that exhibits basicity in an aqueous state; and adding a lithium precursor to the washed active material and annealing to obtain a reusable active material.

Description

Technology Field

[0001] The present invention relates to a method for recycling resources during the manufacture of lithium secondary batteries. In particular, the present invention relates to a method for recovering and reusing positive electrode active materials from defective stack cells generated during the lithium secondary battery manufacturing process or from lithium secondary batteries discarded after use. Background Technology

[0002] Lithium-ion batteries, capable of repeated charging and discharging, are gaining attention as an alternative to fossil energy. Lithium-ion batteries have traditionally been used primarily in handheld devices such as mobile phones, video cameras, and power tools. However, recently, their applications are gradually expanding to include electric vehicles (EVs, HEVs, PHEVs), large-capacity energy storage systems (ESS), and uninterruptible power supply systems (UPS).

[0003] A lithium-ion battery comprises an electrode assembly formed by assembling unit cells, each having a structure in which a positive electrode plate coated with an active material on a current collector and a negative electrode plate are arranged with a separator in between, and an outer casing, or battery case, that seals and houses this electrode assembly along with the electrolyte. The positive electrode active material of a lithium-ion battery primarily uses lithium-based oxides, while the negative electrode active material uses carbon materials. Lithium-based oxides contain metals such as cobalt, nickel, or manganese. In particular, cobalt, nickel, and manganese are very expensive precious metals; among them, cobalt is classified as a strategic metal, and countries around the world pay special attention to its supply and demand. Furthermore, as the number of cobalt-producing countries is limited, it is known as a metal with unstable global supply. If an imbalance in the supply and demand of raw materials for strategic metals occurs, there is a high possibility of a rise in raw material prices.

[0004] Previously, research has primarily focused on recovering and recycling these valuable metals from lithium-ion batteries (spent batteries) that have reached the end of their lifespan and are subsequently discarded. Conventional methods for recovering cathode active materials mostly involve dissolving the cathode in hydrochloric acid, sulfuric acid, or nitric acid to extract active material elements such as cobalt, nickel, and manganese, which are then reused as raw materials for the synthesis of cathode active materials. However, acid-based methods for extracting active material elements have disadvantages; not only is the process for recovering pure raw materials unenvironmentally friendly, but the requirement for neutralization and wastewater treatment also leads to increased processing costs. Furthermore, this method has the drawback of being unable to recover lithium, one of the key elements in cathode active materials. To overcome these limitations, a method is needed that allows for direct reuse by avoiding the dissolution of the cathode active material or the extraction of the active material in elemental form.

[0005] Meanwhile, among the types of lithium secondary batteries, pouch-type batteries utilize stack cells formed by laminating a positive electrode, a separator, and a negative electrode, and then heat-pressing them (so-called lamination). When a separator coated with ceramic particles, such as inorganic compounds or inorganic oxides, is used, these ceramic particles can be transferred to the positive active material side of the positive electrode during the heat-pressing process. To recover and reuse the positive active material from defective stack cells generated during the lithium secondary battery manufacturing process or from degraded electrodes discarded after use, it is essential to remove the ceramic particles transferred to the positive active material. However, existing methods for recovering positive active material do not provide a clear process for separating the positive electrode from the stack cell or the degraded electrode, and furthermore, there is a complete lack of methods that address the disposal of ceramic particles transferred to the positive active material. The problem to be solved

[0006] The problem that the present invention aims to solve is to provide a method for recovering and reusing positive active material from defective stack cells or degraded electrodes. means of solving the problem

[0007] To solve the above problem, the method for reusing a positive electrode active material according to the present invention comprises the steps of: immersing a stack cell comprising a stacked and combined positive electrode plate, a separator, and a negative electrode plate in a polar solvent to separate the positive electrode plate; heat-treating the separated positive electrode plate to thermally decompose the binder and conductive material within the positive electrode active material layer of the positive electrode plate, thereby separating the current collector of the positive electrode plate from the active material layer and recovering the active material within the active material layer; washing the recovered active material with an aqueous solution of a lithium compound that exhibits basicity in an aqueous state; and adding a lithium precursor to the washed active material and annealing to obtain a reusable active material.

[0008] In the present invention, it is preferable to use acetone as the polar solvent.

[0009] In the present invention, a step of surface coating on an annealed active material may be further included.

[0010] In the present invention, the step of washing the annealed active material and then surface coating may be further included.

[0011] The above heat treatment can be performed in air or an oxygen atmosphere at 300 to 650°C.

[0012] The above heat treatment can be performed at 550℃ for 30 minutes at a temperature rise rate of 5℃ / min.

[0013] The above lithium compound aqueous solution is prepared to contain more than 0% and less than or equal to 15% of the lithium compound, and preferably uses LiOH. The washing may be performed by stirring the recovered active material simultaneously with impregnation of the lithium compound aqueous solution.

[0014] The above lithium precursor may be one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0015] The above lithium precursor may be added in an amount that can compensate for the proportion of lithium lost relative to the ratio of lithium to other metals in the raw material active material used in the above active material layer.

[0016] For example, the above lithium precursor may be an amount of lithium added in a molar ratio of 0.001 to 0.4.

[0017] Furthermore, it is preferable to add the above lithium precursor in an amount such that 0.0001 to 0.1 molar ratio of lithium can be added based on a lithium:other metal molar ratio of 1:1.

[0018] The above annealing can be performed in air or an oxygen atmosphere at 400 to 1000°C.

[0019] The temperature of the annealing step may be a temperature exceeding the melting point of the lithium precursor.

[0020] The active material within the above active material layer is recovered in powder form, and carbon components resulting from the carbonization of the binder or conductive material may not remain on the surface.

[0021] The above surface coating step may involve coating one or more of metals, organometallics, and carbon components onto the surface in a solid or liquid manner, followed by heat treatment at 100 to 1200°C.

[0022] In the present invention, the positive electrode active material is a lithium composite transition metal oxide comprising nickel, cobalt and manganese or aluminum, and the nickel content may be 60 mol% or more based on the total moles of the transition metals.

[0023] The above-mentioned reusable active material may have a fluorine (F) content of 100 ppm or less.

[0024] After the washing step described above, the washing active material may further include a step of mixing it with a lithium precursor solution and spray-drying it. Effects of the invention

[0025] According to the present invention, the cathode active material can be reused without using acid, making it environmentally friendly. The method according to the present invention does not require a neutralization process or a wastewater treatment process, thereby mitigating environmental issues and reducing process costs.

[0026] According to the present invention, the positive electrode active material can be recovered without any metal elements that cannot be recovered. Since the current collector is not melted, the current collector can also be recovered. It is an economical method because the active material recovered in powder form can be directly reused, rather than extracting active material elements to use as raw materials for synthesizing the positive electrode active material.

[0027] According to the present invention, it is safe because it does not use toxic and explosive solvents such as NMP, DMC, and methanol, and it is suitable for mass production and easy process control because it utilizes simple processes such as heat treatment, washing, and annealing.

[0028] According to the present invention, the electrochemical performance of the recovered active material is not degraded, and excellent resistance and capacitance characteristics can be realized.

[0029] In particular, according to the present invention, there is an advantage in that a reusable active material can be obtained without the incorporation of foreign substances, such as ceramic particles from the separator in defective stack cells or degraded electrodes generated during the lithium secondary battery manufacturing process. Brief explanation of the drawing

[0030] The following drawings attached to this specification illustrate embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is a flowchart of a method for reusing an active material according to one embodiment of the present invention. FIG. 2 is a flowchart of a method for reusing active material according to another embodiment of the present invention. FIG. 3 is a flowchart of a method for reusing active material according to another embodiment of the present invention. Figure 4a is a photograph of a stack cell, Figure 4b is a photograph of the positive plate before the stack cell is formed, and Figures 4c and 4d are photographs of the positive plate after the stack cell is formed and the negative plate and separator are physically separated. Figure 5 is a photograph of the active material recovered after heat treatment of the positive plate of Figure 4c. Figure 6 is a photograph taken after a predetermined amount of time has passed after the anode plate of Figure 4c was immersed in acetone. FIG. 7a is a photograph of a stack cell immersed in acetone, FIG. 7b is a photograph of the anode plate being lifted from the stack cell after a predetermined amount of time, and FIG. 7c is a photograph of the anode plate completely separated from the stack cell. Figure 8 shows the results of cell evaluation using the active materials of the examples and comparative examples for the NCM-based active material. Figure 9 shows the results of cell evaluation using the active materials of the examples and comparative examples for the LCO active material. Figure 10 shows the results of cell evaluation using the active materials of the examples and comparative examples for other LCO active materials. Figure 11 shows the XRD (X-Ray Diffraction) patterns of the active materials of the examples and comparative examples. Figure 12 is a Scanning Electron Microscope (SEM) image of the active materials of the example and comparative example. Figure 13 is a graph of the particle size distribution of the active materials in the examples and comparative examples. Figures 14 and 15 show the results of cell evaluations performed using the active materials of the examples and comparative examples for other NCM-based active materials. Figures 16 and 17 show the results of cell evaluations conducted using the active materials of the examples and comparative examples for high-content Ni NCM-based active materials. Specific details for implementing the invention

[0031] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his application. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely one embodiment of the present invention and do not represent all of the technical spirit of the present invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of the present invention.

[0032] In the following description, reference is made to the accompanying drawings, which form part of the present invention. The embodiments, drawings, and claims described in the detailed description are not intended to be limiting. Other embodiments may be utilized and other modifications may be made without departing from the spirit and scope of the subject matter disclosed herein. Aspects of the invention as generally described herein and illustrated in the drawings may be arranged, substituted, combined, separated, and designed into various other configurations, all of which will be immediately apparent.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains (hereinafter referred to as "skilled in the art").

[0034] The present invention is not limited to the specific embodiments described herein. As will be apparent to those skilled in the art, many changes and modifications may be made without departing from the spirit and scope of the invention. In addition to those listed herein, functionally equivalent methods within the scope of this invention will be apparent to those skilled in the art from the preceding descriptions. Such changes and modifications fall within the scope of the appended claims. Together with the full range of equivalents qualified by such claims, the present invention will be limited only by the claims. It should be understood that the present invention is not limited to specific methods, which, of course, may be varied. It should also be understood that the technical terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting.

[0035] While conventional active material recycling processes primarily involve resynthesizing active materials by extracting valuable metals (nickel, cobalt, manganese, etc.) as elements from lithium secondary battery active materials whose performance has degraded after use, the present invention is differentiated in that it recovers active materials from defective stack cells or degraded electrodes containing stack cells generated during the lithium secondary battery manufacturing process.

[0036] Furthermore, in the case of previously known active material recycling processes, chemical methods are added, such as extracting valuable metals through acid / base dissolution or melting using reducing agents or additives, and manufacturing them into metals (direct reduction method) or re-synthesized active materials, which results in additional process complexity and economic costs. However, the present invention relates to a method for directly reusing cathode active materials without dissolving them.

[0037] To directly reuse the positive electrode active material, a method is required to remove the current collector from the positive electrode. Methods for removing the current collector from the positive electrode include removing the binder through high-temperature heat treatment, dissolving the binder using a solvent, completely dissolving the current collector, and separating the active material through dry grinding and sieving.

[0038] Solvent stability is crucial when dissolving binders using solvents. While NMP is the most efficient solvent, it has disadvantages such as toxicity and high cost. Additionally, it requires solvent recovery processes, such as reprocessing waste solvents. Dissolving the current collector would be less expensive than using solvents. However, it is difficult to remove impurities from the surface of the reused active material, and there is a risk of explosion due to the generation of hydrogen gas during the current collector removal process. It is difficult to completely separate the current collector from the active material using dry grinding and sieving. Since the particle size distribution of the active material changes during the grinding process and binder removal is difficult, there is a disadvantage in that the characteristics of the reused battery degrade.

[0039] In the present invention, the active material and the current collector are separated using high-temperature heat treatment. High-temperature heat treatment is advantageous for mass production and commercialization. However, foreign substances must not remain on the surface of the reusable active material. The present invention also proposes a step for removing foreign substances from the surface of the reusable active material.

[0040] In particular, when recycling positive active material from a stack cell, it is important to ensure that foreign matter from the separator is not mixed into the positive active material. The present invention proposes a method to recycle the positive active material by completely separating the positive plate so that the ceramic particles are not mixed into the positive active material, even if the ceramic particles are transferred to the positive active material side, by using a separator coated with ceramic particles such as inorganic compounds / inorganic oxides as the separator.

[0041] Hereinafter, a method for reusing an active material according to embodiments of the present invention will be described with reference to FIGS. 1 to 3.

[0042] First, Figure 1 is a method suitable for cases where the positive electrode active material is a lithium cobalt oxide such as LiCoO2 (LCO).

[0043] Referring to FIG. 1, a stack cell comprising a stacked and combined positive plate, a separator, and a negative plate is immersed in a polar solvent to separate the positive plate (step S10).

[0044] The positive plate may be formed from a positive sheet containing a positive active material layer on a positive current collector such as aluminum foil. The negative plate may also be formed from a negative sheet containing a negative active material layer on a negative current collector such as copper foil. The separator may be a polymer substrate coated with ceramic particles such as inorganic compounds or inorganic oxides. When coating ceramic particles onto the separator, a coating solution prepared by adding a binder, ceramic particles, and a dispersant to a highly volatile solvent is used to ensure thin and rapid drying.

[0045] Since the stack cell is assembled by heat pressing (so-called lamination), when a separator coated with ceramic particles such as inorganic compounds or inorganic oxides is used as the separator, the ceramic particles can be transferred to the positive active material side of the positive plate during heat pressing. Step S10 proposed in the present invention is highly suitable for separating the positive plate while removing the ceramic particles transferred to the positive active material.

[0046] In step S10, it is preferable to use the same polar solvent as the solvent used for manufacturing the separator. When the stack cell is immersed in this solvent, the ceramic particles detach into the solvent. Preferably, the polar solvent is acetone. Immersing the stack cell in acetone facilitates the separation of the stack cell components, namely the anode plate, cathode plate, and separator, and allows the ceramic particles transferred to the anode active material to be separated from the anode plate during heat pressing of the separator.

[0047] Experiments confirmed that performing subsequent steps by physically separating the anode plate from the stack cell without polar solvent loading, such as in step S10, results in a higher proportion of ceramic particles. It was also confirmed that obtaining a recycled active material containing ceramic particles leads to a decrease in capacity development rate. Therefore, a step such as step S10 of the method proposed in this invention is essential for increasing the capacity development rate.

[0048] Next, the separated anode plate is crushed into a suitable size (step S20). Crushing refers to cutting or shredding the anode plate into pieces of a size that is easy to handle. After crushing, the anode plate is cut into pieces, for example, 1 cm x 1 cm in size. Various dry grinding equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill may be used for crushing, or a high-speed cutter may be used.

[0049] Crushing can be performed by considering the characteristics required in the equipment used for handling the anode plate and in subsequent processes. For example, if equipment requiring continuous processing is used for loading and unloading the anode plate, the fluidity of the anode plate must be good, so anode plates that are too large must be crushed. If the anode plate is of an appropriate size, the crushing step S20 can be omitted.

[0050] Now, the anode plate is heat-treated (step S30).

[0051] The active material layer is formed by coating a slurry mixed with an active material, a conductive material, a binder, and a solvent, so the structure is such that the binder connects the active material and the conductive material after the solvent evaporates. Therefore, the present invention was arrived at based on the idea that if the binder is removed, the active material can be separated from the current collector.

[0052] In the present invention, heat treatment is performed to thermally decompose the binder within the active material layer. The heat treatment of step S30 can be performed at 300 to 650°C and can also be called high-temperature heat treatment. At temperatures below 300°C, it is difficult to remove the binder, which causes a problem in that the current collector cannot be separated, and at temperatures above 650°C, the current collector melts (Al melting point: 660°C), resulting in a phenomenon where the current collector cannot be separated.

[0053] The heat treatment time is maintained for a sufficient period for the binder to undergo sufficient thermal decomposition. For example, it is set to around 30 minutes. Preferably, it is set to 30 minutes or more. As the heat treatment time increases, the time required for the thermal decomposition of the binder will be extended, but beyond a certain time, there is no difference in the thermal decomposition effect. Preferably, the heat treatment time is set to 30 minutes or more and within 5 hours.

[0054] Heat treatment equipment can be of various types of furnaces. For example, it could be a box-type furnace, or, considering productivity, a rotary kiln capable of continuous processing.

[0055] After heat treatment, it can be slowly cooled or rapidly cooled in the atmosphere.

[0056] For example, heat treatment can be performed at 550°C for 30 minutes with a temperature rise rate of 5°C / min. The above temperature rise rate is such that it can be achieved without strain, for example in a box-type furnace, and is sufficient to heat the anode plate without causing thermal shock. 550°C is chosen to account for the melting point of the Al current collector while also allowing for efficient thermal decomposition of the binder. Since thermal decomposition is insufficient if heat treatment is performed for less than 10 minutes at this temperature, heat treatment must be carried out for at least 10 minutes, and preferably for at least 30 minutes.

[0057] Through heat treatment in air, the binder and conductive material within the active material layer undergo thermal decomposition, becoming CO2 and H2O, which are then removed. Since the binder is removed, the active material is separated from the current collector, and the active material to be recovered can be sorted into a powder form. Therefore, the current collector can be separated from the active material layer and the active material within the active material layer can be recovered solely through step S30.

[0058] It is important to perform the heat treatment in step S30 in air. If the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and conductive material will not undergo thermal decomposition but will only be carbonized. If only carbonization occurs, carbon components will remain on the surface of the active material, degrading the performance of the reusable active material. When the heat treatment is performed in air, the carbon materials in the binder and conductive material react with oxygen and are combusted and removed as CO and CO2 gases, so almost all of the binder and conductive material are removed without any residue.

[0059] Therefore, according to the present invention, the active material is recovered in powder form, and carbon components resulting from the carbonization of the binder or conductive material may not remain on the surface.

[0060] Next, the recovered active material is washed (step S40). During washing, it is important to wash with an aqueous solution of a lithium compound that is basic in an aqueous state. This aqueous solution of the lithium compound is prepared to contain more than 0% and less than or equal to 15% of the lithium compound, and preferably LiOH is used. It is desirable to limit the amount of LiOH to 15% or less. Using an excessive amount of LiOH may result in excess LiOH remaining on the surface of the active material even after washing, which could affect the subsequent annealing process. To ensure the surface of the active material is as clean as possible before the annealing step, the addition of an excessive amount of LiOH is not process-wise favorable, so it is limited to 15% or less.

[0061] Washing can be performed by immersing the recovered active material in an aqueous solution of the lithium compound. Washing can be performed for one week after immersion, preferably within one day, and even more preferably within one hour. If washing is performed for more than one week, there is a risk of capacity degradation due to excessive lithium leaching. Therefore, it is desirable to perform it within one hour. Washing includes immersing the active material in an aqueous solution of the lithium compound that is basic in the aqueous state, and stirring while immersed. It is preferable to perform stirring in conjunction. If only immersion is performed without stirring in the aqueous solution of the lithium compound, the washing process proceeds slowly and may cause lithium leaching. Since stirring in conjunction minimizes process time, it is desirable to perform stirring simultaneously with the impregnation in the aqueous solution of the lithium compound.

[0062] After washing, further steps including filtration and air drying in a convection oven can be performed.

[0063] The reason for washing with an aqueous solution of a lithium compound that is basic in an aqueous state is to remove LiF and metal fluoride that may be present on the surface of the recovered active material and to modify the surface. During the heat treatment of step S30, the binder and conductive material within the active material layer vaporize and are removed as they become CO2 and H2O. In this process, CO2 and H2O may 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, may react with metal elements constituting the positive active material to form LiF or metal fluoride. If LiF or metal fluoride remains, the battery characteristics deteriorate when the active material is reused. In the present invention, a washing step as in step S40 is added to remove reactants that may be generated on the surface of the reused active material during the heat treatment step (S30), thereby ensuring that no foreign substances remain on the surface of the recycled active material.

[0064] In step S40, it is important to wash with an aqueous solution of a lithium compound that is basic in an aqueous state. If an aqueous solution of sulfuric acid or hydrochloric acid is used instead of an aqueous solution of a lithium compound that is basic in an aqueous state, although it may be possible to wash F from the surface of the active material, it will leach out transition metals (Co, Mg), etc. present in the active material, thereby degrading the performance of the reusable cathode active material. The aqueous solution of a lithium compound that is basic in an aqueous state used in the present invention is highly desirable because it can not only remove any trace amounts of binder that may remain after the thermal decomposition in step S30, but also prevent the leaching of transition metals, etc. present in the active material, and simultaneously serve the role of replenishing the amount of lithium that may be leached out during the washing process.

[0065] Through step S40, the present invention can adjust the LiF content on the surface of the recovered active material to less than 500 ppm, thereby enabling an improvement in capacity. Preferably, the F content can be 150 ppm or less. More preferably, the F content can be 100 ppm or less. Even more preferably, the F content can be 30 ppm or less. According to the present invention, since an active material with reduced F content can be recovered, excellent resistance and capacity characteristics can be achieved by reusing it as an active material.

[0066] Next, a lithium precursor is added to the washed active material and annealed (step S50). Through step S50, a reusable active material can be obtained.

[0067] Lithium loss may occur within the active material during the preceding steps S30 and S40. In step S50, such lithium loss is replenished.

[0068] In addition, in step S50, the crystal structure of the active material is restored through annealing to restore or improve the characteristics of the reused active material to the level of a fresh active material that has never been used.

[0069] A deformation structure may appear on the surface of the active material during the preceding steps S30 and S40.

[0070] Furthermore, in the case of LCO active materials, Co3O4 may be generated on the surface through thermal decomposition. If a battery is manufactured while Co3O4 remains in the environment, the battery characteristics may deteriorate. In the present invention, through step S50, the crystal structure is restored and Co3O4 is removed, thereby restoring or improving the initial characteristics to a level similar to that of a fresh active material.

[0071] The lithium precursor of step S50 may be one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0072] The lithium precursor is added in an amount sufficient to compensate for the proportion of lithium lost relative to the ratio of lithium to other metals in the raw active material (i.e., fresh active material) used in the active material layer. For example, if the ratio of lithium to other metals in the fresh active material is 1, an amount of lithium precursor can be added to compensate for a molar ratio of 0.001 to 0.4. Ideally, it is preferable to add lithium in a molar ratio of 0.01 to 0.2. Adding an excess amount of lithium precursor beyond the amount of lithium lost through washing, etc., leaves unreacted lithium precursors in the reused active material, which increases resistance during the active material reuse process; therefore, it is necessary to administer an appropriate amount of lithium precursor.

[0073] Annealing can be performed in air at 400 to 1000°C. The annealing temperature may also be 600 to 900°C. This temperature must vary within a limited range depending on the type of lithium precursor. It is preferable to have an annealing time of at least one hour. Preferably, it is around five hours. Although a longer annealing time may allow for sufficient recovery of the crystal structure, a longer duration does not significantly affect performance. For example, the annealing time should be within 15 hours. The annealing equipment may be the same or similar equipment used in the heat treatment step S30.

[0074] For example, when using Li2CO3 as a lithium precursor, an annealing temperature of 700 to 900°C is suitable, and more preferably between 710 and 780°C. This is because the melting point of Li2CO3 is 723°C. Most preferably, it is performed at 750°C. When using LiOH as a lithium precursor, annealing temperature of 400 to 600°C is suitable, and more preferably between 450 and 480°C. This is because the melting point of LiOH is 462°C.

[0075] It is preferable that the annealing temperature be a temperature exceeding the melting point of the lithium precursor. However, since thermal decomposition of the cathode active material occurs at temperatures exceeding 1000℃, leading to a decrease in the performance of the active material, the temperature should not exceed 1000℃.

[0076] As such, according to the present invention, LiF or metal fluoride is removed in the washing step S40, and Co3O4 is removed in the annealing step S50. The washing step using an aqueous solution of a lithium compound that exhibits basicity in an aqueous state has the advantage of being safe and inexpensive, capable of removing LiF or metal fluoride without the loss of other elements, preventing the leaching of transition metals, and replenishing lithium loss occurring during the process. The annealing step also has the advantage of being safe and inexpensive, capable of effectively removing Co3O4, and restoring the crystal structure, that is, improving crystallinity, thereby restoring the battery characteristics of the reused active material.

[0077] The reusable active material obtained according to the present invention may have a particle size distribution similar to that of the active material present in the active material layer within the anode plate, so that no separate treatment may be required. Since carbon components generated by the binder or conductive material do not remain on the surface, steps such as removing such carbon components are not required. Therefore, the active material obtained through the method of FIG. 1 above can be reused as is without separate treatment and used for manufacturing the anode.

[0078] The reusable active material can be used as is without adjusting the composition, or it can be mixed with fresh LCO and mixed with a conductive material, binder, and solvent to form a slurry for use.

[0079] Next, a method according to another embodiment of the present invention will be described with reference to FIG. 2. FIG. 2 is a method suitable for cases where the positive electrode active material is a lithium composite transition metal oxide comprising nickel (Ni), cobalt (Co) and manganese (Mn) or aluminum (Al) (hereinafter simply referred to as 'NCM-based, NCA-based, NCMA-based lithium composite transition metal oxide').

[0080] Lithium composite transition metal oxides are utilized as cathode active materials for lithium secondary batteries; among these, lithium cobalt oxides such as LiCoO2, lithium manganese oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), or lithium nickel oxides (LiNiO2, etc.) are primarily used. Furthermore, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, nickel-manganese lithium composite metal oxides in which a portion of the nickel is substituted with manganese, which has excellent thermal stability, NCM-based lithium composite transition metal oxides substituted with manganese and cobalt, NCA-based lithium composite transition metal oxides substituted with cobalt and aluminum, and NCMA-based lithium composite transition metal oxides substituted with cobalt, manganese, and aluminum are used. The present embodiment is highly suitable for the reuse of such NCM-based, NCA-based, and NCMA-based lithium composite transition metal oxide active materials.

[0081] Referring to FIG. 2, a stack cell comprising a stacked and combined positive plate, a separator, and a negative plate is immersed in a polar solvent to separate the positive plate (step S110). Step S110 can be performed in the same manner as step S10 of FIG. 1 described above.

[0082] Next, the separated positive plate is crushed into a suitable size (step S120). The positive plate is heat-treated (step S130). Then, the recovered active material is washed (step S140). A lithium precursor is added to the washed active material and annealed (step S150). Here, steps S120, S130, S140, and S150 can be performed in the same way as steps S20, S30, S40, and S50 of FIG. 1 described above, respectively.

[0083] In particular, a deformed structure may appear on the surface of the active material during steps S130 and S140. For example, in the case of an active material that is an NCM-based lithium composite transition metal oxide, Ni may be rock-salted [NiCO3·2Ni(OH)2)H2O] by moisture in step S140, forming a spinel structure. If the battery is manufactured in this state, battery characteristics such as capacity reduction may deteriorate. In the present invention, the crystal structure is restored through step S150. For example, the active material that is an NCM-based lithium composite transition metal oxide is restored to a hexagonal structure. Accordingly, initial characteristics can be restored or improved to a level similar to that of a fresh active material.

[0084] Meanwhile, in the present embodiment, the method of adding a lithium precursor to the washed active material may involve drying the washed active material and then adding the lithium precursor in a solid or liquid state. As another example, the drying and the addition of the lithium precursor may be performed in a single step by adding a lithium precursor solution to the washed active material and spray-drying it. The lithium precursor solution may be a lithium compound soluble in an aqueous solution or an organic solvent.

[0085] If drying is performed immediately in an oven or similar device after a surface modification process by washing, the active material particles may clump together to form lumps. To mix a lithium precursor with these clumped particles, grinding of the lumps may be required; furthermore, if a solid lithium precursor is to be mixed, powder mixing or milling processes must be performed during material mixing, which can make the process complex and difficult to maintain as a continuous process. In addition, particularly in the case of NCM-based cathode active materials, if powder mixing or milling is performed with the lithium precursor in the presence of moisture, the cathode active material absorbs moisture, causing severe clumping. Therefore, this embodiment proposes mixing and dispersing the active material in a lithium precursor solution and spray drying it after washing in step S140. This eliminates the clumping of particles caused by drying and the inconvenience of mixing a solid lithium precursor. In other words, spray drying offers the advantage of producing the material in a powder form rather than as lumps.

[0086] During spray drying, the lithium precursor solution dries immediately after spraying, and the lithium precursor component is coated or comes into contact with the surface of the active material. At this time, there is also the advantage that the particles are aggregated by capillary force during the drying of the lithium precursor solution, which acts as the solvent, thereby controlling the particle size. In the case of positive plates made into electrodes, the particles on the surface may be compressed, cracked, or broken due to the rolling process. In particular, compared to LCO, NCM-based active materials experience greater particle splitting due to rolling during electrode formation; consequently, the recovered active material contains a large number of small particles compared to the fresh active material, leading to a problem of non-uniform particle size.

[0087] In particular, NCM-based active materials are used that contain secondary particles formed by the aggregation of primary particles ranging in size from tens to hundreds of nanometers. When a cathode manufactured with such active materials is rolled to control the porosity within the electrode, the secondary particles are broken down into primary particles or into microparticles that are larger than primary particles but smaller than the secondary particles. Since the specific surface area of ​​the active material increases as the number of particles broken by rolling increases, problems may arise in the case of recycled active materials obtained from rolled electrodes, which can affect slurry properties, electrode adhesion, and electrode performance upon reuse.

[0088] For an active material to be reusable, it is desirable that its particle size distribution does not differ from that of a fresh active material. The spray drying proposed in this embodiment can regroup small particles that are broken during rolling into larger particles, thereby resolving particle non-uniformity and making the particle size close to the initial characteristics of a fresh active material. This effect is particularly excellent in NCM-based active materials that suffer from severe particle breakage during the rolling process of the previous step. Therefore, it can be expected that the battery characteristics of a reused active material recovered by the method according to the present invention will be similar to those of a battery using a fresh active material.

[0089] As explained above, through the spray drying step, a lithium precursor is coated on the surface of the active material, and the active material is obtained with particle size control. Since the addition of the lithium precursor, particle formation, and drying are carried out in a single step, there is an effect of process simplification. Furthermore, the spray drying is special in that it is not merely a means to obtain the active material, but a means to re-particle the particles that have already been broken by rolling or other processes.

[0090] In addition, since the active material particles washed in the previous step only need to be mixed and dispersed in a lithium precursor solution of a certain concentration, there is an advantage that washing and spray drying can be performed as a continuous process. As such, the method for reusing active material according to the present embodiment has process continuity and also has the advantage that lithium precursor coating, drying, and particle formation (particle readjustment) are carried out simultaneously in a single step.

[0091] Meanwhile, in step S150, it is preferable to add the lithium precursor in an amount such that 0.0001 to 0.1 molar ratio of lithium can be added based on a lithium:other metal molar ratio of 1:1. The reason for adding an excess amount of lithium in this way is to form a surface protective layer on the active material through surface coating, which will be explained further below. When a secondary battery is manufactured using such an active material, it is possible to maintain lifespan characteristics while suppressing side reactions caused by the electrolyte.

[0092] Referring to FIG. 2, a surface coating is applied to the annealed active material (step S160).

[0093] Depending on the type of active material initially used, certain elements may be lost during the process. In particular, since they may be completely removed or remain in small quantities during step S140, which is a surface modification process through washing, it may be difficult to fully recover the characteristics by performing the process only up to the annealing step S150. In such cases, it is preferable to perform step S160, an additional surface coating step, as proposed in the present invention. The surface coating can serve as a surface protective layer for the cathode active material. The surface coating can serve as a process that replenishes the depleted specific elements while simultaneously rebuilding the surface protective layer present in the fresh active material.

[0094] The surface coating step may involve coating one or more of metals, organometallics, and carbon components onto the surface in a solid or liquid manner, followed by heat treatment at 100 to 1200°C. If heat treatment is performed at a temperature exceeding 1200°C, there is a risk of performance degradation due to thermal decomposition of the cathode active material. For surface coating, methods such as mixing, milling, spray drying, and grinding may be used to coat the surface in a solid or liquid manner.

[0095] A surface protective layer is formed by a heterogeneous metal through surface coating. When the molar ratio of lithium to other metals in the positive electrode active material is set to 1:1, 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 decreases to less than 1:1, 100% capacity cannot be achieved. Therefore, in the preceding step S150, the deficient lithium is added to ensure that the molar ratio of lithium to other metals in the positive electrode active material is 1:1, and an excess amount is added so that lithium is contained in an amount 0.0001 to 0.1 molar ratio greater than that of other metals in the positive electrode active material. Then, during surface coating, it becomes possible to form a surface protective layer while maintaining the molar ratio of lithium to other metals in the positive electrode active material at 1:1.

[0096] Specifically, when metal oxides such as B, W, and BW are coated onto an active material and then heat-treated, a lithium borooxide layer can be formed on the surface of the active material, which acts as a surface protective layer. In step S50, lithium added in greater amounts at a molar ratio of 0.0001 to 0.1 reacts with metal oxides such as B, W, and BW in step S160, and the molar ratio of lithium to other metals in the positive electrode active material does not decrease to less than 1:1, so there is no capacity degradation.

[0097] Next, a method according to another embodiment of the present invention will be described with reference to FIG. 3. FIG. 3 is a method suitable when the positive electrode active material is a high-content Ni-based (Ni-rich) positive electrode active material, particularly an NCM-based, NCA-based, or NCMA-based lithium composite transition metal oxide containing a high content of Ni. For example, the nickel content may be 60 mol% or more based on the total moles of the transition metal. Furthermore, the nickel content may be 80 mol% or more based on the total moles of the transition metal.

[0098] Referring to FIG. 3, a stack cell comprising a stacked and combined positive plate, a separator, and a negative plate is immersed in a polar solvent to separate the positive plate (step S210). Step S210 can be performed in the same manner as step S10 of FIG. 1 described above.

[0099] Next, the separated anode plate is crushed into a suitable size (step S220). Step S220 can be performed in the same way as step S20 of FIG. 1 described earlier.

[0100] Next, the anode plate is heat-treated (step S230). Step S230 can be performed in the same manner as Step S30 of FIG. 1 described above. In particular, when reusing a high-content Ni-based anode active material, it is preferable to perform the heat treatment in an oxygen atmosphere to ensure Ni stability. O2 with a purity of 80% or higher, preferably 90% or higher, can be used.

[0101] Then, the recovered active material is washed (step S240). A lithium precursor is added to the washed active material and annealed (step S250). Here, steps S240 and S250 can be performed in the same manner as steps S40 and S50 of FIG. 1 described above, respectively. When annealing in step S250, if a high-content Ni-based cathode active material is to be reused, it may be preferable to perform the annealing in an oxygen atmosphere for Ni stability. O2 with a purity of 80% or higher, preferably 90% or higher, may be used.

[0102] Next, the annealed active material is washed a second time (step S260). Since lithium precursors that did not participate in the reaction after the addition of the lithium precursor in step S250 exist on the surface of the active material in the form of LiOH and Li2CO3, a residual lithium removal process is required to remove them. Preferably, water (distilled water) can be used for the second washing. In particular, high-content Ni-based cathode active materials are prone to retaining lithium impurities, especially lithium carbonate (Li2CO3) impurities, on the surface as the Ni content increases. Since these impurities react with the electrolyte to degrade battery performance and generate gas, they must be strictly managed. This embodiment includes a first washing step S240 and a second washing step S260. In particular, step S260 is effective in removing residual lithium compounds, making it particularly suitable as a method for reusing high-content Ni-based cathode active materials.

[0103] Next, a surface coating is applied to the active material that has been washed twice (step S270). Step S270 can be performed in the same way as step S160 of FIG. 2 described above. Through this step S270, a reusable active material can be obtained.

[0104] The experimental examples of the present invention will be described in detail below.

[0105] <Experimental Example 1: Stack Cell>

[0106] Figure 4a is a photograph of a stack cell. Twenty-five stacks were formed by stacking a positive plate, a separator, a negative plate, etc. The separator is a polymer material that may shrink due to heat. To prevent this, ceramic particles ranging from tens to hundreds of nanometers are coated onto the separator material. During lamination, the ceramic particles of the separator are transferred to the positive plate, and rolling is applied to the positive plate. In this experimental example, the ceramic particles were Al2O3.

[0107] Figure 4b is a photograph of the positive plate before forming the stack cell. The positive plate appears black.

[0108] Figure 4c is a front view of the anode plate after the cathode plate and separator have been physically separated after forming a stack cell, and Figure 4d is a rear view of the anode plate. Compared to Figure 4b, a large amount of white area is visible on the anode plate. The white area is where ceramic particles from the separator have been transferred. When the anode plate and separator are combined, the ceramic particles are subjected to pressure during the lamination process and are transferred to the anode plate. It is confirmed that if the anode plate and separator are physically separated, the ceramic particles transferred to the surface of the anode plate remain on the anode plate. If a recycling process is carried out using such an anode plate, ceramic particles remain in the recovered recycled active material, which poses a problem.

[0109] <Experimental Example 2: Heat treatment without polar solvent support>

[0110] The heat treatment of step S30 of Fig. 1 was performed using an anode plate as shown in Figs. 4c and 4d. The heat treatment was performed at 550℃ / 0.5hr, with a temperature rise of 5℃ / min and 3L / min of air. Through this, the binder and conductive material components within the anode active material layer were removed, and the active material was detached from the current collector.

[0111] Figure 5 is a photograph of the active material recovered after such heat treatment. The positive active material detached from the positive current collector of the positive plate appears black, and the white part is a layer of ceramic particles transferred from the separator and remaining. Even if the active material of Figure 5, including the layer of ceramic particles, is sieved through a 325 mesh, ceramic particles of several hundred nanometers are filtered out along with it, making separation from the active material impossible. Therefore, as proposed in the present invention, a polar solvent loading step, which is a step for removing ceramic particles, must be performed before carrying out the heat treatment step.

[0112] <Experimental Example 3: Effect of Polar Solvent Immobilization 1>

[0113] The step corresponding to step S10 of Fig. 1 was performed using an anode plate as shown in Figs. 4c and 4d.

[0114] When coating ceramic particles onto a separator, a coating solution prepared by adding a binder, ceramic particles, and a dispersant to a highly volatile solvent is used to ensure thin and rapid drying. If a stack cell is immersed in a polar solvent identical to the one used for manufacturing the separator, the ceramic particles will detach into the polar solvent. The polar solvent used in this embodiment was acetone.

[0115] Figure 6 is a photograph taken after a certain amount of time has passed since the anode plate, in which the cathode plate and separator have been physically separated after forming a stack cell, was immersed in acetone. It can be seen that as the ceramic particles are separated from the anode plate, the black part of the anode plate is exposed.

[0116] <Experimental Example 4: Effect of Polar Solvent Support 2>

[0117] Step S10 of Fig. 1 was performed by immersing a stack cell as shown in Fig. 4a in acetone.

[0118] Figure 7a is a photograph of a stack cell immersed in acetone. Figure 7b is a photograph of the anode plate being lifted from the stack cell after a predetermined period of time. Unlike Figures 4c or 4d, it can be seen that the ceramic particles are transferred, and the black anode plate is cleanly separated from the separator without any white parts.

[0119] Figure 7c is a photograph of the anode plate completely separated from these stack cells. Compared to Figures 4c or 4d, it can be seen that the ceramic particle debris on the surface of the anode plate is significantly reduced after final separation.

[0120] <Experimental Example 5: Stack Cell Separation Charge / Discharge Experiment with NCM-based Cathode Active Material>

[0121] Comparative Example 1: It is an NCM-based lithium composite transition metal oxide fresh active material.

[0122] Example 1: A reusable active material was obtained by performing all the steps of the method of the present invention. Specifically, steps S110, S120, S130, S140, S150, and S160 of the method described with reference to FIG. 2 were performed. First, the stack cell was immersed in acetone to separate the positive plate, and the positive plate was heat-treated at 550°C / 0.5hr, with a temperature rise of 5°C / min and 3L / min of air to separate the active material. The active material was washed with LiOH for 10 minutes. Based on the molar ratio of lithium to other metals in the raw active material (ICP analysis), an amount of lithium precursor (LiOH) sufficient to allow for the additional addition of lithium at a molar ratio of 0.09 during the process was added to the active material, and the material was annealed at 750°C for 15 hours. Afterwards, to add boron, 1000 ppm H3BO3 was added and a coating step was performed at 300℃ / 5hr, a rise rate of 2℃ / min, and 3L / min of air.

[0123] Example 2: The cathode active material was recovered for recycling using the same process as in Example 1. However, the amount of lithium precursor added in step S150 was increased to 0.10 mol.

[0124] Example 3: The positive electrode active material was recovered using the same process as in Example 1. However, the amount of lithium precursor added in step S150 was increased to 0.11 mol.

[0125] Comparative Example 2: Without step S110 of the method described with reference to FIG. 2, that is, after physically separating the positive plate from the stack cell, the method was performed in the same manner as Example 2 starting from step S120.

[0126] In the above examples and comparative examples, the recovered or prepared positive active material was weighed at 96.25 wt%, the conductive material carbon black at 1.5 wt%, and the binder PVdF at 2.25 wt%, mixed with NMP to make a slurry, and then a positive electrode was manufactured, a cell (Coin Half Cell, CHC) was manufactured, and the electrochemical performance was evaluated.

[0127] Figure 8 shows the results of cell evaluations conducted using the active materials of the examples and comparative examples. Rate performance was examined by evaluating the capacity according to the number of cycle repetitions at different currents. The equipment used for the evaluation is a standard charge-discharge test apparatus commonly used in laboratories. There is no deviation depending on the measurement device or method. In the graph of Figure 8, the horizontal axis represents the number of cycles and the vertical axis represents capacity.

[0128] The voltage was set to 3–4.3V, and the charge / discharge cycles were performed as follows: 0.1C / 0.1C - 0.33C / 0.33C - 0.5C / 0.1C - 0.5C / 1C - 0.5C / 2C. The electrolyte constituting the cell was a carbonate-based solution with a composition of Ethylene Carbonate (EC) : Ethyl Methyl Carbonate (EMC) = 3 : 7 and containing some additives (LiPF6).

[0129] Table 1 summarizes the charging capacity, discharging capacity, efficiency, and efficiency relative to Comparative Example 1 of the examples and comparative examples.

[0130] [Table 1]

[0131]

[0132] Referring to Figure 8 and Table 1, Comparative Example 2 shows a result in which the charge / discharge capacity is inferior by more than 7 mAh / g compared to Examples 1 to 3. That is, when the positive plate with the transferred ceramic particles is physically separated from the stack cell as in Comparative Example 2 and the steps of the active material reuse method proposed in the present invention are carried out while retaining the transferred ceramic particles, this result occurs because the mixing ratio of the ceramic particles is higher compared to the case where the process, such as acetone loading, is carried out. A decrease in charge / discharge capacity occurs because the resistance increases due to the ceramic particle components.

[0133] In this way, according to Examples 1 to 3, the capacity expression rate can be increased compared to Comparative Example 2 through ceramic particle separation such as acetone loading.

[0134] <Experimental Example 6: Stack Cell Separation Charge / Discharge Experiment with LCO Cathode Active Material>

[0135] Comparative Example 3: It is an LCO fresh active material.

[0136] Example 4: A reusable active material was obtained by performing all the steps of the method of the present invention. Specifically, steps S10, S20, S30, S40, and S50 of the method described with reference to FIG. 1 were performed. The stack cell was immersed in acetone to separate the positive plate, and the positive plate was heat-treated at 550°C / 0.5hr, with a temperature rise of 5°C / min and 3L / min of air. The active material obtained thereby was washed with LiOH for 10 minutes. A lithium precursor (Li2CO3) with an excess amount of 2 mol% lithium relative to the lithium amount of the reusable LCO was added, and the mixture was annealed at 750°C for 15 hours.

[0137] Comparative Example 4: Without step S10 of the method described with reference to FIG. 1, i.e., physically separating the positive plate from the stack cell, the procedure was carried out in the same manner as Example 4 from step S20.

[0138] In the above examples and comparative examples, the recovered or prepared positive active material was weighed at 96 wt%, the conductive material carbon black at 2 wt%, and the binder PVdF at 2 wt%, mixed with NMP to make a slurry, and then a positive electrode was manufactured, a cell (CHC) was manufactured, and the electrochemical performance was evaluated.

[0139] Figure 9 shows the results of cell evaluation using the active materials of the examples and comparative examples. Rate performance was examined by evaluating the capacity according to the number of cycle repetitions at different currents. In the graph of Figure 9, the horizontal axis represents the number of cycles and the vertical axis represents the capacity.

[0140] The voltage was set to 3–4.55V, and the charge / discharge cycles were performed as follows: 0.2C / 0.2C - 0.1C / 0.1C - 0.5C / 0.2C - 0.5C / 1C - 0.5C / 2C - 0.5C / 1C. The electrolyte constituting the cell was a carbonate-based electrolyte with an EC:Dimethyl carbonate (DMC):EMC ratio of 3:4:3 and containing some additives (LiPF6).

[0141] Table 2 summarizes the charging capacity, discharging capacity, efficiency of the examples and comparative examples, and efficiency compared to Comparative Example 3.

[0142] [Table 2]

[0143]

[0144] Referring to Figure 9 and Table 2, Comparative Example 4 shows inferior charge / discharge capacity compared to Example 5. That is, when the positive plate with transferred ceramic particles is physically separated from the stack cell as in Comparative Example 4 and the steps of the active material reuse method proposed in the present invention are carried out while retaining the transferred ceramic particles, this result occurs because the mixing ratio of ceramic particles is higher compared to the case where the process, such as acetone loading, is carried out. A decrease in charge / discharge capacity occurs because the resistance increases due to the ceramic particle components.

[0145] In this way, according to Example 5, the capacity expression rate can be increased compared to Comparative Example 4 through ceramic particle separation such as acetone loading.

[0146] <Experimental Example 7: Verification of the Effect of the Reuse Method for LCO Cathode Active Material>

[0147] Each positive electrode active material was prepared in the same manner as the examples and comparative examples below, and the residual amount of LiF, electrochemical performance, etc., were evaluated.

[0148] Comparative Example 5: Fresh LCO was used instead of a recycled active material. It is a different active material from Comparative Example 3.

[0149] Example 6: Specifically, steps S10, S20, S30, S40, and S50 of the method described with reference to FIG. 1 were performed. After making a stack cell containing a positive plate made of the same positive active material as Comparative Example 5, the positive plate was separated by immersing it in acetone, and the positive plate was heat-treated in air at 550°C / 0.5hr. Washing was performed using LiOH for 10 minutes. A lithium precursor (Li2CO3) with an excess amount of 2 mol% lithium relative to the lithium amount of the reused LCO was added, and the cell was annealed at 750°C for 15 hours.

[0150] Comparative Example 6: Only the heat treatment of step S30 of the active material reuse method of the present invention as described above was performed to remove the binder and conductive material and separate the Al current collector, and to collect the LCO active material. Step S30 was performed under the same conditions as in Example 6. The surface modification of step S40 and the crystal structure recovery of step S50 of the active material reuse method of the present invention were not performed.

[0151] Comparative Example 7: Going further than Comparative Example 6, the LCO active material was collected by performing the surface modification of step S40 of the active material reuse method of the present invention as described above. That is, the surface modification was performed, but the crystal structure recovery of step S50 of the active material reuse method of the present invention was not performed. Step S40 was carried out under the same conditions as in Example 6.

[0152] To determine the residual amount of LiF in the active materials recovered in Comparative Example 6 and Comparative Example 7, F was detected and analyzed using ICP. In Comparative Example 6, the F content was measured at 1450 mg / kg, while in Comparative Example 7, it was measured at 30 ppm or less. It can be confirmed that the F content in the recovered cathode active material was significantly lower in Comparative Example 7 compared to Comparative Example 6. In other words, LiF was completely dissolved in the lithium compound aqueous solution by washing and removed to the extent that it could not be detected by ICP. Therefore, it can be seen that the removal of LiF by step S40 is excellent.

[0153] In the above examples and comparative examples, the recovered or prepared positive active material was weighed at 96 wt%, the conductive material carbon black at 2 wt%, and the binder PVdF at 2 wt%, mixed with NMP to make a slurry, and then a positive electrode was manufactured, a cell was manufactured, and the electrochemical performance was evaluated.

[0154] Figure 10 shows the results of cell evaluations conducted using the active materials of the examples and comparative examples. Rate performance was examined by evaluating the capacity according to the number of cycle repetitions at different currents. The equipment used for the evaluation is a standard charge-discharge test apparatus commonly used in laboratories. There is no deviation depending on the measurement device or method. In the graph of Figure 10, the horizontal axis represents the number of cycles and the vertical axis represents the capacity.

[0155] The voltage was set to 3~4.5V, and the initial formation charge / discharge was performed at 0.2C / 0.2C. The electrolyte used to form the cell had an EC : EMC = 3 : 7 ratio and contained some additives.

[0156] Referring to FIG. 10, the lowest rate performance can be observed in Comparative Example 6, which is a reusable active material but does not undergo surface modification and crystal structure recovery according to the present invention. This is because, during the high-temperature heat treatment process such as step S30, the binder and conductive material are removed as CO2 and H2O, reacting with lithium on the surface of the positive electrode active material to form Li2CO3 and LiOH, and reacting with F present in the binder to form LiF or metal fluoride. In addition, it is determined that the low battery characteristics are due to CO3O4 generated by thermal decomposition on the LCO surface.

[0157] Comparative Example 7 is a case in which surface modification was performed compared to Comparative Example 6. It is evaluated that Comparative Example 7 was able to obtain better results than Comparative Example 6 because the reactants generated on the surface were removed through washing.

[0158] Example 6 is a modified version of Comparative Example 7 that includes annealing. Li2CO3 was added to anneale the lithium lost during the process of recovering the active material and to restore crystallinity. It is confirmed that this not only replenishes the shortage of lithium occurring during the process but also reduces the deformed structure and Co3O4 that may appear on the surface of the active material during regeneration back to the LCO crystal structure, resulting in improved results compared to the fresh initial characteristics of the active material in Comparative Example 5.

[0159] As such, according to the present invention, active material can be recovered from anode scrap to a level suitable for direct reuse. It is safe as it does not use toxic or explosive solvents such as NMP, DMC, and methanol, and is suitable for mass production as it utilizes simple and safe methods such as heat treatment, washing and drying, and annealing.

[0160] Figure 11 shows the XRD patterns of the active materials of the examples and comparative examples. In the XRD patterns, the horizontal axis represents 2θ (Theta) (degrees), and the vertical axis represents intensity. The XRD patterns were obtained using a standard X-ray diffraction apparatus commonly used in laboratories. For example, the analysis can be performed using the Rigaku XG-2100 X-ray diffraction analyzer. However, there is no variation depending on the apparatus or method.

[0161] Figure 11 (a) is the XRD pattern of Comparative Example 5, i.e., fresh LCO. (b) is the XRD pattern of the active material of Comparative Example 6, and (c) is the XRD pattern of the active material of Comparative Example 7. When comparing (b) and (c) with (a), the Co3O4 phase is confirmed. That is, it can be confirmed that Co3O4 is formed on the surface of the LCO during the heat treatment process of step S30.

[0162] Figure 11 (d) is the XRD pattern of the active material of Example 6. Comparing (c) and (d), it can be seen that the Co3O4 phase is eliminated and the crystal structure is restored to LCO through the annealing of step S50. Looking at the positions of the diffraction peaks in the XRD pattern, the crystal structure of (d) is similar to the crystal structure of (a). Therefore, it can be confirmed that Example 6 according to the present invention has been restored to the level of the fresh active material of Comparative Example 5. As such, according to the present invention, the positive active material can be recovered from the stack cell to a level where it can be directly reused.

[0163] Figure 12 shows SEM images of the active materials of the examples and comparative examples. The SEM images were taken using a standard SEM device commonly used in laboratories. For example, images can be taken using the HITACHI s-4200. However, there is no variation depending on the measurement device or method.

[0164] Figure 12 (a) is an SEM image of the fresh LCO of Comparative Example 5, and (b) is an SEM image of the reused active material of Example 6. It can be confirmed that the recovered LCO of the example exhibits the same morphology as the fresh LCO. Furthermore, since only the LCO is observed, it is confirmed that the binder and conductive material were removed during the high-temperature heat treatment process. Therefore, it can be seen that the active material is separated from the current collector by heat treatment in air alone, and that almost no binder or conductive material remains on the surface of the active material. As such, according to the present invention, it is possible to separate the current collector and the active material without using complex methods or harmful substances, thereby enabling the environmentally friendly recovery of the active material. Since it can be reused without using acid, neutralization or wastewater treatment processes are not required, which can mitigate environmental issues and reduce process costs.

[0165] Figure 13 is a graph of the particle size distribution of the active materials of the examples and comparative examples. The particle size distribution can be obtained using a common particle size analyzer commonly used in laboratories. For example, it can be determined using a Horiba LA 950V2 particle size analyzer. However, there is no variation depending on the measuring device or method. In Figure 13, the horizontal axis represents particle size (um) and the vertical axis represents volume %.

[0166] The active materials recovered in Example 6 and Comparative Examples 6 and 7 all have a particle size distribution similar to that of the fresh LCO in Comparative Example 5. A similar particle size distribution is defined as having a difference in the volume percentage of particles with the same particle size within a range of + / - 2%. As such, according to the present invention, the particle size distribution of the active material does not change, so the initial characteristics are maintained almost as they are, and it can be expected that the characteristics of the reused battery will be similar to those of the battery using the fresh active material.

[0167] In addition to LCO cathode active materials, the method according to the present invention was applied to NCM-based cathode active materials to obtain and verify reusable active materials. As a result, it was found that reusable active materials similar in quality to fresh active materials can be obtained by the method according to the present invention. This is explained in Experimental Example 8.

[0168] <Experimental Example 8: Verification of the Effect of the Reuse Method for NCM-based Cathode Active Material>

[0169] Example 7: Steps S110, S120, S130, S140, and S150 of the method described with reference to FIG. 2 were performed. First, the stack cell was immersed in acetone to separate the positive plate, and the positive plate was heat-treated at 550°C / 0.5hr, with a temperature rise of 5°C / min and 3L / min of air to separate the active material. The active material was washed with LiOH for 10 minutes. Based on the molar ratio of lithium to other metals in the raw active material (ICP analysis), an amount of lithium precursor (Li2CO3) was added to the active material such that lithium could be further added at a molar ratio of 0.09 during the process, and the mixture was annealed at 750°C for 15 hours. Theoretically, for fresh active materials, the lithium:other metal molar ratio is 1:1, but since the average error of the ICP equipment used to verify this is ±0.05, preferably ±0.02, the lithium:other metal molar ratio of the raw active material measured via ICP may be 1 ± 0.05:1. In this experiment, a lithium precursor was added based on the analysis ratio obtained through ICP analysis.

[0170] Example 8: In addition to Example 7, the process of recovering the active material surface protective layer of step S160 of FIG. 2 was also carried out. To add boron, 1000 ppm H3BO3 was added, and a coating step was performed at 300℃ / 5hr, a rise rate of 2℃ / min, and 3L / min of air.

[0171] Comparative Example 8: A fresh NCM-based lithium composite transition metal oxide was used instead of a recycled active material.

[0172] Comparative Example 9: In the method for reusing the active material of the present invention as described above, only the heat treatment of step S130 was performed to remove the binder and conductive material and separate the Al current collector, and the NCM-based lithium composite transition metal oxide active material was collected. Step S130 was performed under the same conditions as in Example 7. The washing of step S140, the annealing of step S150, and the surface coating process of step S160 in the method for reusing the active material of the present invention were not performed.

[0173] Comparative Example 10: Going further than Comparative Example 9, the active material was collected by carrying out the washing step S140 of the active material reuse method of the present invention as described above. That is, surface modification was performed, but the crystal structure recovery step S150 and the surface coating process step S160 of the active material reuse method of the present invention were not carried out. Step S140 was carried out under the same conditions as in Example 7.

[0174] Comparative Example 11: Further than Comparative Example 9, the surface modification of step S140 of the method for reusing the active material of the present invention as described above was not performed, and only the crystal structure recovery of step S150 was carried out to collect an NCM-based lithium composite transition metal oxide active material. Unlike in Example 7, the annealing for crystal structure recovery was carried out without adding a lithium precursor.

[0175] Comparative Example 12: The process was carried out only up to steps S130, S140, and S150, just like in Example 7. However, unlike in Example 7, the annealing for crystal structure recovery was performed without adding a lithium precursor.

[0176] ICP analysis was performed on the cathode active materials recovered or prepared in each of the above examples and comparative examples to analyze the ratio of lithium to other metals in the active material, as well as the amount of specific elements such as B or W.

[0177] Then, the positive active material recovered or prepared in each of the above examples and comparative examples was weighed at 96.25 wt%, the conductive material carbon black at 1.5 wt%, and the binder PVdF at 2.25 wt%, mixed with NMP to make a slurry, and then a positive electrode was manufactured, a cell (CHC) was manufactured, and the electrochemical performance was evaluated.

[0178] In order to check whether there is a change in the lithium component in the positive electrode active material during steps S130 and S140 of the present invention, the ratio of lithium to other metals in the active material was analyzed by ICP. The results are shown in Table 3 below.

[0179] [Table 3]

[0180]

[0181] Referring to Table 3, it can be seen that the lithium / other metal ratio in Comparative Example 9 decreases by approximately 0.2 to 0.5 compared to Comparative Example 8 after heat treatment with S130, and in Comparative Example 10 decreases by approximately 0.2 to 0.5 compared to Comparative Example 9 after washing and drying with S140. It appears that the NCM-based lithium composite transition metal oxide exhibits a large decrease in the lithium ratio relative to other metals due to its relatively large particle specific surface area and the change to a spinel structure. Therefore, it is evident that the insufficient lithium must be replenished.

[0182] Table 3 shows the values ​​measured by ICP analysis, and as previously mentioned, ICP analysis has an error value of approximately ±0.02. Therefore, even in Comparative Example 8, which is a fresh active material, the ratio between lithium and other metals may be less than 1. Accordingly, the amount of lithium precursor added to replenish the lost lithium is such that the lithium content is added in an amount equal to the decrease in the ratio of lithium to other metals (molar ratio analyzed by ICP) in the raw material active material (i.e., fresh active material) used in the active material layer.

[0183] Figures 14 and 15 show the results of cell evaluations conducted using the active materials of the examples and comparative examples. Rate performance was examined by evaluating the capacity according to the number of cycle repetitions at different currents. The equipment used for the evaluation is a standard charge-discharge test apparatus commonly used in laboratories. There is no deviation depending on the measurement device or method. In the graphs of Figures 14 and 15, the horizontal axis represents the number of cycles and the vertical axis represents the capacity.

[0184] The voltage was set to 3~4.3V, and the initial formation charge / discharge was performed at 0.1C / 0.1C. The electrolyte constituting the cell was a carbonate-based electrolyte with an EC:EMC ratio of 3:7 and containing some additives.

[0185] First, referring to FIG. 14, when comparing Comparative Example 9 before surface modification and Comparative Example 10 after surface modification following a first heat treatment (550°C / 30 min) for delamination, the electrode capacity in Comparative Example 10, which underwent surface modification, shows a rapid decrease. This is because, as previously mentioned, the capacity was reduced as Ni in the NCM-based lithium composite transition metal oxide was chlorinated by moisture.

[0186] However, when annealing (750°C / 15 hours) is performed without surface modification, this corresponds to Comparative Example 11, and there is almost no improvement in capacity compared to Comparative Example 9. This is due to the LiF remaining on the surface of the active material when surface modification is not performed. This was shown in the previous Experimental Example 7, where washing was performed to remove LiF to a satisfactory level.

[0187] When surface modification and annealing are performed after the first heat treatment, the capacity increases as shown in Comparative Example 12. This is because, although the capacity decreases after the surface modification step as in Comparative Example 10, the Ni rock salt is reduced through annealing after LiF is removed by surface modification, and the structure is restored to a hexagonal state.

[0188] Next, referring to FIG. 15, the capacity improvement of Example 7 compared to Comparative Example 12 is confirmed. Example 7 is a sample in which a lithium precursor was added during annealing compared to Comparative Example 12. It can be seen that the capacity is improved by replenishing the lithium lost in the preceding steps through the addition of the lithium precursor. The loss of lithium during heat treatment and washing has been explained with reference to Table 3.

[0189] Based on the results of ICP analysis (Table 3), the lithium compound was added in an amount equal to the ratio lost relative to the lithium content in the existing cathode active material, and additional experiments confirmed that adding a molar ratio of 0.09 to 0.1 resulted in a capacity improvement effect equivalent to that of Comparative Example 8.

[0190] As such, according to the present invention, active material can be recovered from anode scrap to a level suitable for direct reuse. It is safe as it does not use toxic or explosive solvents such as NMP, DMC, and methanol, and is suitable for mass production as it utilizes simple and safe methods such as heat treatment, washing and drying, and annealing.

[0191] ICP analysis was performed on the cathode active materials recovered or prepared in each of the above examples and comparative examples to analyze the amount of specific elements. The results are shown in Table 4 below.

[0192] [Table 4]

[0193]

[0194] The fresh active material used in this experiment contained additional B and W, as seen in Comparative Example 8. Comparative Example 9 shows that the content of B and W decreases during heat treatment, and the remaining results indicate that almost all of B is removed in subsequent processes. ND means that it was measured at 30 ppm or less. In the case of W, as shown in Comparative Example 10, it can be seen that a large amount is removed during the surface modification process through washing.

[0195] Therefore, depending on the type of active material initially used, certain elements may be lost during the process, and in particular, since they may be completely removed or remain in small quantities during the surface modification process through washing, there may be cases where it is difficult to fully recover the characteristics by performing only up to the annealing step as in Example 7. In such cases, it is desirable to perform an additional surface coating step S160 as proposed in the present invention. In the case of this experimental example, the surface coating step involves coating B and W. The surface coating can act as a surface protective layer for the cathode active material. The surface coating can serve as a process that replenishes the specific elements that have been depleted while simultaneously rebuilding the surface protective layer present in the fresh active material. In the case of the fresh active material used in this experiment, the surface protective layer is BW, and the amount of lithium lost during the process is interpreted not as a 1:1 ratio of the active material's own lithium to other metals, but as a ratio of (lithium of the active material itself + lithium forming the surface protective layer) : other metals. Therefore, the 0.09 molar ratio lost in the above experiment, as in Comparative Example 10, can be interpreted as the combined amount of lithium in the positive electrode active material and lithium for forming the surface protective layer, and in the examples, a lithium precursor was added to replenish that amount of lithium.

[0196] <Experimental Example 9: Verification of the Effect of the Reuse Method for High-Content Ni NCM-Based Cathode Active Material>

[0197] Comparative Example 13: This is a high-content Ni NCM-based lithium composite transition metal oxide fresh active material.

[0198] Example 9: A reusable active material was obtained by performing all the steps of the method of the present invention. Specifically, steps S210, S220, S230, S240, S250, S260, and S270 of the method described with reference to FIG. 3 were performed. The stack cell was immersed in acetone to separate the positive plate, and the positive plate was heat-treated at 550°C / 0.5hr, a temperature rise of 5°C / min, and O2 3L / min. The washing of the active material obtained thereby was performed twice in step S240. In the first wash, the active material was stirred at a ratio of active material to washing solution = 1:30 for 300 rpm / 10 min, and then only the active material was extracted using a vacuum filter. It was washed again at a ratio of active material to washing solution = 1:10. Next, 0.11 mol of LiOH, a lithium precursor, was added, and annealing in step S250 of the method for reusing the positive active material of the present invention was performed by supplying O2 at 750°C / 5hr and O2 at 3L / min. Then, step S260, a washing process step to remove residual lithium from the surface, was performed. The washing was carried out by stirring the active material : washing solution = 1 : 1 at 300 rpm / 1 min, followed by vacuum drying overnight (drying at 130°C) after vacuum filtration. Subsequently, step S270 was performed by adding 1000 ppm H3BO3 to add boron and coating at 300°C / 5 hr, rising speed 2°C / min, and air 3 L / min.

[0199] Example 10: The positive electrode active material was recovered using the same process as in Example 9. However, the amount of lithium precursor added in step S250 was increased to 0.13 mol.

[0200] Example 11: The positive electrode active material was recovered using the same process as in Example 9. However, the amount of lithium precursor added in step S250 was increased to 0.15 mol.

[0201] Example 12: The positive electrode active material was recovered using the same process as in Example 9. However, the amount of lithium precursor added in step S250 was increased to 0.17 mol.

[0202] Comparative Example 14: Same as Example 9, but without the second washing step, i.e., step S260 was not performed.

[0203] Comparative Example 15: Same as Example 10, but without the second washing step, i.e., step S260 was not performed.

[0204] Comparative Example 16: Same as Example 11, but without the second washing step, i.e., step S260 was not performed.

[0205] 96.25 wt% of the positive active material, 1.5 wt% of the conductive material carbon black, and 2.25 wt% of the binder PVdF were weighed and mixed with NMP to make a slurry, and then a positive electrode was manufactured, a cell (CHC) was manufactured, and the electrochemical performance was evaluated.

[0206] Figures 16 and 17 show the results of cell evaluations conducted using the active materials of the examples and comparative examples. Rate performance was examined by evaluating the capacity according to the number of cycle repetitions at different currents. The equipment used for the evaluation is a standard charge-discharge test apparatus commonly used in laboratories. There is no deviation depending on the measurement device or method. In the graphs of Figures 16 and 17, the horizontal axis represents the number of cycles and the vertical axis represents the capacity.

[0207] The voltage was set to 3~4.3V, and the charge / discharge cycles were performed as follows: 0.1C / 0.1C - 0.33C / 0.33C - 0.5C / 0.1C - 0.5C / 1C - 0.5C / 2C. The electrolyte constituting the cell was a carbonate-based electrolyte with an EC:EMC ratio of 3:7 and containing some additives.

[0208] First, referring to FIG. 16, Comparative Example 13, which is a fresh active material, and Examples 9 to 12 are compared. And Table 5 summarizes their charging capacity, discharging capacity, and efficiency.

[0209] [Table 5]

[0210]

[0211] Referring to FIG. 16 and Table 5, when the surface residual lithium precursor is removed by a second wash after annealing following the addition of the lithium precursor according to an embodiment of the present invention, the charge / discharge capacity is equivalent to that of the fresh active material. When an excess amount of lithium (0.11 mol) is added, that is, when the capacity development rate increases from Example 9 to Examples 10 to 12, the capacity is higher. It was confirmed that not only the initial capacity but also the C-rate capacity is at a level similar to that of the fresh active material.

[0212] Next, FIG. 17 shows a comparison between Sample 1 and Comparative Examples 14 to 16. Comparative Examples 14 to 16 did not undergo a secondary washing step after annealing. Table 6 summarizes the charge capacity, discharge capacity, and efficiency.

[0213] [Table 6]

[0214]

[0215] Referring to Figure 17 and Table 6, it can be confirmed that even if annealing is performed after the addition of the lithium precursor, if the surface residual lithium precursor is not removed thereafter, a lower capacity development rate is observed compared to the fresh active material. There is no difference in initial capacity when the amount of lithium lost during the process (0.11 mol) and the amount of excess lithium added are added, but at the high C-rate, the capacity increases slightly when the excess amount of lithium is added.

[0216] The amount of residual lithium remaining on the surface residual lithium precursor was analyzed before and after washing. For Comparative Example 13, Example 11, Example 12, and Comparative Example 16, 5g of each active material was taken, dispersed in 100ml of distilled water, mixed at 300 rpm for 5 minutes, and then the active material was filtered. The pH and the concentrations of LiOH and Li2CO3 dissolved from the active material were calculated while titrating the resulting solution with a 0.1M HCl solution to obtain the values. If an excess amount of LiOH dissolves in the solvent (NMP) during the electrode fabrication process, it causes the solvent to become alkaline. The alkaline solvent mixes with the binder and causes the slurry to gel, making it impossible to fabricate the electrode. Additionally, an excess amount of Li2CO3 is easily attacked and decomposed by HF generated by minute amounts of water molecules present in the electrolyte, causing gas generation. Therefore, lithium compounds that provide residual lithium, such as LiOH or Li2CO3, must be removed.

[0217] [Table 7]

[0218]

[0219] When surface residual lithium is not removed as in Comparative Example 16, the total content of residual lithium is 0.823 wt.% Li, whereas when surface residual lithium is removed as in Examples 11 and 12 according to the present invention, it can be confirmed that residual lithium is managed at a level similar to Comparative Example 13.

[0220] As such, according to the present invention, the positive electrode active material can be recovered and reused from a stack cell using a simple, eco-friendly, and economical method, and even if a lithium secondary battery is manufactured using the reused positive electrode active material obtained in this way, there is no problem with the performance of the battery.

[0221] Although the present invention has been described above by limited embodiments and drawings, the present invention is not limited thereto and it is obvious that various modifications and variations are possible by those skilled in the art within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below.

Claims

Claim 1 A method for reusing an anode active material, comprising: a step of separating the anode plate by immersing a stack cell including a stacked and combined anode plate, a separator, and a cathode plate in a polar solvent; a step of heat-treating the separated anode plate in an air or oxygen atmosphere at 300 to 650°C to thermally decompose the binder and conductive material within the anode active material layer of the anode plate, thereby separating the current collector of the anode plate from the active material layer and recovering the active material within the active material layer; a step of washing the recovered active material with an aqueous solution of a lithium compound that exhibits basicity in an aqueous state; and a step of adding a lithium precursor to the washed active material and annealing to obtain a reusable active material, wherein the separator is a polymer substrate coated with ceramic particles. Claim 2 A method for reusing an anode active material according to claim 1, characterized by using acetone as the polar solvent. Claim 3 A method for reusing an anode active material according to claim 1, further comprising the step of surface coating the annealed active material. Claim 4 A method for reusing an anode active material according to claim 1, further comprising the step of washing the annealed active material and then surface coating it. Claim 5 delete Claim 6 A method for reusing a positive electrode active material according to claim 1, characterized in that the aqueous solution of the lithium compound is prepared to contain more than 0% and less than or equal to 15% of the lithium compound. Claim 7 A method for reusing a positive electrode active material according to claim 1, characterized in that the washing is performed by stirring the recovered active material simultaneously with impregnation with the lithium compound aqueous solution. Claim 8 A method for reusing a positive electrode active material according to claim 1, wherein the lithium precursor used in the annealing is one or more of LiOH, Li2CO3, LiNO3, and Li2O. Claim 9 A method for reusing a positive electrode active material according to claim 1, characterized in that the lithium precursor is added in an amount such that the ratio of lost lithium is added relative to the ratio of lithium to other metals in the raw material active material used in the active material layer. Claim 10 A method for reusing a positive electrode active material according to claim 9, characterized in that the lithium precursor is added in an amount of lithium in a molar ratio of 0.001 to 0.

4. Claim 11 A method for reusing an anode active material according to claim 9, characterized in that the lithium precursor is added in an amount such that lithium can be added in a molar ratio of 0.0001 to 0.1 based on a lithium:other metal molar ratio of 1:

1. Claim 12 A method for reusing an anode active material according to claim 1, characterized in that the annealing is performed in air or an oxygen atmosphere at 400 to 1000°C. Claim 13 A method for reusing a positive electrode active material according to claim 1, characterized in that the temperature of the annealing step is a temperature exceeding the melting point of the lithium precursor. Claim 14 A method for reusing an anode active material according to claim 1, characterized in that the active material within the active material layer is recovered in powder form and carbon components resulting from the carbonization of the binder or conductive material do not remain on the surface. Claim 15 A method for reusing an anode active material according to claim 3 or 4, characterized in that the surface coating step comprises coating one or more of a metal, an organometallic component, and a carbon component onto the surface in a solid or liquid manner, followed by heat treatment at 100 to 1200°C. Claim 16 A method for reusing an anode active material according to claim 4, wherein the anode active material is a lithium composite transition metal oxide comprising nickel, cobalt, manganese, or aluminum, and the nickel content is 60 mol% or more based on the total moles of the transition metals. Claim 17 A method for reusing an anode active material according to claim 1, characterized in that the reusable active material has a fluorine (F) content of 100 ppm or less. Claim 18 A method for reusing a positive electrode active material according to claim 1, further comprising the step of mixing the washed active material with a lithium precursor solution and spray-drying it after the washing step.

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