Positive electrode active material, method for regenerating positive electrode active material, and secondary battery

Abstract

The invention relates to a positive electrode active material, a method for regenerating the positive electrode active material, and a secondary battery. According to the present invention, by desorbing and recovering a positive electrode active material from a waste positive electrode, applying a coating agent thereto, and controlling calcination conditions of the positive electrode active material coated with the coating agent, a structure similar to a crystal structure of a new positive electrode active material can be obtained. And a region in which an olivine structure compound is mixed in a carbon coating layer on the surface of the positive electrode active material can be reduced, so that the positive electrode active material, a method for regenerating the positive electrode active material, a secondary battery, and the like, which have excellent battery characteristics, can be provided.

Description

TECHNICAL FIELD

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2024-0025873, filed on February 22, 2024, in the Korean Intellectual Property Office, and to Korean Patent Application No. 10-2025-0001944, filed on January 7, 2025, based on the priority of the preceding patent, the disclosures of which are incorporated herein by reference.

[0003] The present invention relates to a positive electrode active material, a method of regenerating a positive electrode active material, and a secondary battery. According to the present invention, by detaching and recovering a positive electrode active material from a waste positive electrode, coating the same with a coating agent, and controlling the calcination conditions of the positive electrode active material coated with the coating agent, a structure similar to that of a newly manufactured positive electrode active material can be obtained, and the area in which an olivine structure compound is mixed in a carbon coating layer on the surface of the positive electrode active material can be reduced. Accordingly, excellent battery characteristics can be provided. BACKGROUND

[0004] Since the 1990s, the demand for lithium secondary batteries has increased with the continuous increase in the market for portable electronic devices. Recently, with the rapid growth of the market for electric vehicles, the demand for lithium secondary batteries has rapidly increased worldwide. This increase in the demand for lithium secondary batteries can lead to instability in the supply and demand of lithium resources in the near future. In addition, the continuous accumulation of waste batteries can lead to a major environmental problem. To address these problems, the regeneration of waste lithium secondary batteries is a very important technical challenge.

[0005] In general, a lithium secondary battery is composed of a positive electrode formed by coating a metal foil (e.g., aluminum) with a positive electrode active material layer; a negative electrode formed by coating a metal foil (e.g., copper) with a negative electrode active material layer; a separator for preventing the positive and negative electrodes from mixing; and an electrolyte solution that allows lithium ions to move between the positive and negative electrodes. A positive electrode composition including a positive electrode active material, a binder, a conductive material, and a solvent is coated onto a current collector made of a metal foil (e.g., aluminum), dried, and then press-formed, thereby manufacturing a positive electrode.

[0006] The positive electrode accounts for 60% or more of the cost of a lithium secondary battery. Active materials of these positive electrodes include lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), and lithium iron phosphate (LiFePO4). Among them, lithium iron phosphate is increasingly used as a raw material for large-capacity lithium secondary batteries used in electric vehicles because it is low in unit price and stable in supply. Therefore, various studies are being made on regeneration processing technology to selectively recover valuable metals or directly recover positive active materials from positive electrodes of lithium secondary batteries discarded after use or positive electrode waste (hereinafter referred to as "waste positive electrode") generated in the lithium secondary battery manufacturing process.

[0007] However, due to the characteristics of the regenerated positive active material, the particle size distribution is not uniform and the crystal structure is unstable. Therefore, in the electrode manufacturing process, the particles can easily be broken and fine particles can easily occur. In addition, the thermal stability can be reduced, which can deteriorate the battery performance such as the life characteristics in a high voltage environment.

[0008] Therefore, there is a need to develop a regeneration technology of a positive active material that can provide excellent battery characteristics when applied to a secondary battery.

[0009] [Related Art Documents]

[0010] [Patent Documents]

[0011] Japanese Patent Application Publication No. 2024-503575 SUMMARY

[0012] [Technical Problem]

[0013] Therefore, the present application has been made in view of the above problems, and it is an object of the present application to provide a positive active material and a secondary battery including the same. By desorbing and recovering a positive active material from a waste positive electrode, coating the same with a coating agent, and controlling the calcination conditions of the positive active material coated with the coating agent, a structure similar to that of a newly manufactured positive active material can be obtained, and the area in which an olivine structure compound is mixed within a carbon coating layer on the surface of the positive active material can be reduced. Therefore, excellent battery characteristics can be provided.

[0014] Another object of the present application is to provide a positive active material and a secondary battery including the same. According to the present application, the life characteristics can be excellent in a high voltage environment, the thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0015] The above and other objects can be achieved by the present application described below.

[0016] [Technical Solution]

[0017] I) According to one aspect of the present application, there is provided a positive electrode active material having a carbon coating layer and an olivine structure compound, and satisfying the following mathematical formulas 1, 2 and 3:

[0018] [mathematical formula 1]

[0019] 0 < carbon content × Area Ratio LFP ≤ 5

[0020] [mathematical formula 2]

[0021] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0022] [mathematical formula 3]

[0023] 1.3 ≤ carbon content ≤ 1.5

[0024] wherein the carbon content is the total amount of carbon (wt%) measured by a carbon content analysis device, and AreaRatio LFP corresponds to the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all Raman peaks observed in the Raman spectrum.

[0025] II) According to I), the positive electrode active material can be a regenerated positive electrode active material.

[0026] III) According to I) to II), the positive electrode active material can be a single particle.

[0027] IV) According to I) to III), the olivine structure compound can be represented by the following Chemical Formula 1:

[0028] [Chemical Formula 1]

[0029] Li 1+a Fe 1-b M b (PO 4-c )X c

[0030] wherein M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y; X includes one or more elements selected from the group consisting of F, S and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

[0031] V) According to I) to IV), the positive electrode active material having the olivine structure compound can include lithium iron phosphate.

[0032] VI) According to another aspect of the present application, there is provided a positive electrode active material having a carbon coating and an olivine structure compound, and satisfying the following mathematical formulae 1, 2 and / or 3:

[0033] [mathematical formula 1]

[0034] 0 < carbon content x Area Ratio LFP ≤ 5

[0035] [mathematical formula 2]

[0036] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0037] [mathematical formula 3]

[0038] 1.3 ≤ carbon content ≤ 1.5

[0039] wherein the carbon content is the total amount of carbon (wt%) measured by a carbon content analysis device, and AreaRatio LFP corresponds to the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all Raman peaks observed in the Raman spectrum.

[0040] VII) According to still another aspect of the present application, there is provided a method of regenerating a positive electrode active material, the method including: heat-treating a waste positive electrode having a positive electrode active material layer containing a positive electrode active material having an olivine structure compound coated on a current collector to cause the positive electrode active material to be detached from the current collector; coating a surface of the detached positive electrode active material; and grinding the coated positive electrode active material,

[0041] wherein the coating step includes: applying a coating agent to the detached positive electrode active material, performing pre-grinding and performing spray drying; and calcining the spray-dried positive electrode active material at 750 to 1200°C under a reducing atmosphere.

[0042] VIII) According to VII), the heat-treating can be performed by heating at a temperature of 300-650°C under an oxidizing atmosphere.

[0043] IX) According to VII) to VIII), the heat-treating can be performed by increasing the temperature at a heating rate of 1 to 10°C / min to reach the heat-treating temperature, and can be performed for 10 minutes to 5 hours.

[0044] X) According to VII) to IX), the coating agent can be a coating agent including one or more of a metal, an organometallic and a carbon component.

[0045] XI) According to VII) to X), the calcining can be performed for 1 to 24 hours.

[0046] XII) According to VII) to XI), the pre-grinding can be performed using a ball mill, a high-energy ball mill, a vibration mill, or a roll mill.

[0047] XIII) According to VII) to XII), the grinding step can be performed using a jet mill.

[0048] XIV) According to VII) to XIII), the olivine-structured compound can be represented by the following Chemical Formula 1:

[0049] [Chemical Formula 1]

[0050] Li 1+a Fe 1-b M b (PO 4-c )X c ,

[0051] wherein M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

[0052] XV) According to still another aspect of the present application, there is provided a secondary battery including the positive electrode active material according to any one of I) to VI).

[0053] [Advantageous Effects]

[0054] According to the present application, the positive electrode active material regenerated from the waste positive electrode can have a structure similar to the crystal structure of a newly manufactured positive electrode active material, and can reduce the area in which the olivine-structured compound is mixed within the carbon coating on the surface of the positive electrode active material. Accordingly, when the positive electrode active material is applied to a secondary battery, excellent battery characteristics can be provided.

[0055] In particular, the present application has the effect of providing a regenerated positive electrode active material and a secondary battery including the same. According to the present application, the life characteristics can be excellent in a high-voltage environment, the thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0056] The following accompanying drawings, attached to the specification, illustrate embodiments of the present application and are presented to further understand the technical idea of the present application in conjunction with the detailed description described below. Accordingly, the present application is not limited to these drawings.

[0057] Figure 1is a graph showing measurement results of variables for measuring the carbon-coating quality of the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1 to 3.

[0058] Figure 2 is a graph showing Raman spectroscopic analysis results of the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1 to 3.

[0059] Figure 3 is a graph showing evaluation results of the CHC capacity retention rate according to the number of cycles at 45°C for a secondary battery including the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0060] The present inventors have studied a method of obtaining a positive electrode active material by directly regenerating a waste positive electrode containing a positive electrode active material containing a compound having an olivine structure without decomposing the waste positive electrode. During the study, the present inventors confirmed that, when a coating agent is applied to the positive electrode active material recovered through a desorption process and the calcination conditions of the positive electrode active material are controlled, the crystal structure is restored to that of a newly manufactured positive electrode active material, and the area in which the olivine structure compound remains on the carbon coating surface is reduced. In addition, when this positive electrode active material is applied to a secondary battery, the battery characteristics are improved. Based on these results, the present inventors made further studies to complete the present application.

[0061] In the present application, the positive electrode active material layer of the waste positive electrode can include a positive electrode active material, a binder, and a conductive material.

[0062] In the present application, the "oxidizing atmosphere" can specifically be air or an atmosphere having an oxygen purity of 10% or more.

[0063] In the present application, the newly manufactured positive electrode active material refers to a newly manufactured positive electrode active material that is newly synthesized and manufactured, not obtained by recovery and regeneration from a waste battery.

[0064] Hereinafter, the positive electrode active material of the present application and a secondary battery including the same will be described in detail.

[0065] The terms and words used in the present specification and the appended claims should not be construed as limited to the commonly- or dictionary- defined meanings but interpreted as having meanings and concepts that are consistent with the technical spirit of the present application. In addition, since the configurations shown in the embodiments of the present specification and the drawings are merely the embodiments of the present application and do not represent all technical spirits of the present application, it should be understood that there are many equivalents and modifications to the above-described configurations and the present application can be arranged, replaced, combined, separated, or designed in various other configurations.

[0066] Unless otherwise defined, all technical and scientific terms used in the present specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0067] Positive electrode active material

[0068] For example, the present application includes a positive electrode active material having an olivine-structured compound.

[0069] For example, the olivine-structured compound can be a lithium iron phosphate (LFP)-based compound, preferably a compound represented by Chemical Formula 1, more preferably LiFePO4 having an olivine structure. In this case, the electrochemical properties, the resistance properties, and the capacity properties can be excellent.

[0070] [Chemical Formula 1]

[0071] Li 1+a Fe 1-b M b (PO 4-c )X c

[0072] In Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

[0073] For example, the surface of the positive electrode active material can be coated with carbon. Preferably, a carbon coating layer can be formed on the surface of the positive electrode active material. In this case, the structural stability of the positive electrode active material can be improved without chemical and physical changes in the positive electrode active material, thereby improving the electrochemical properties such as rate capability, life characteristics, and capacity. In addition, by substituting with a heterogeneous element on the surface of the positive electrode active material, thereby controlling the amount of residual lithium and reducing the pH, the physicochemical properties can be improved.

[0074] The positive electrode active material of the present application is a positive electrode active material having a carbon coating layer and an olivine-structured compound, and satisfies the following Mathematical Formulas 1, 2, and 3.

[0075] [Mathematical Formula 1]

[0076] 0 < Carbon content × Area Ratio LFP ≤ 5

[0077] [Mathematical Formula 2]

[0078] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0079] [Math. 3]

[0080] 1.3 ≤ carbon content ≤ 1.5

[0081] Here, the carbon content is the total amount of carbon (wt%) measured by a carbon content analyzer, and the Area Ratio LFP corresponds to the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all the Raman peaks observed in the Raman spectrum.

[0082] Math. 1 is a correlation mathematical formula between the Area Ratio LFP and the total amount of carbon. A smaller calculated value indicates that the area in which the olivine structure compound is mixed in the carbon coating layer decreases.

[0083] For example, Math. 1 is greater than 0 and 5 or less, preferably 0.5 to 4, and more preferably 1 to 3. In this case, the electrochemical properties can be improved by improving the coating quality of the carbon surface.

[0084] Math. 2 is the reciprocal of the Area Ratio LFP corresponding to the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all the Raman peaks shown in the Raman spectrum, and refers to the reciprocal of the calculated value of the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all the Raman peaks shown in the Raman spectrum. As the calculated value increases, the area occupied by the olivine structure compound decreases.

[0085] For example, the following Figure 2 is a Raman spectrum analysis chart of the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1 to 3. Among these peaks, the peak identified as LFP corresponds to the Raman peak of lithium iron phosphate corresponding to the above-described olivine structure compound.

[0086] For example, Math. 2 can be 0.45 to 1, preferably 0.5 to 0.1, and more preferably 0.6 to 1. In this case, the coating quality of the carbon surface can be improved, and thus the life characteristics of the battery can be excellent.

[0087] Math. 3 is the total amount of carbon (wt%) measured using a carbon content analyzer, and can include not only the carbon coating content but also the residual uncoated carbon content, and thus Math. 3 can be difficult to use alone to measure the carbon coating quality.

[0088] Therefore, in the present application, the total amount of carbon is used as a variable to write a correlation mathematical formula such as Math. 1 described above, and it is predicted that the area of carbon coating will increase as the corresponding value increases.

[0089] For example, the mathematical formula 3 is 1.3 to 1.5, preferably 1.33 to 1.5, and more preferably 1.35 to 1.5. In this case, the coating quality of the carbon surface can be improved, and thus the electrochemical characteristics can be excellent.

[0090] Further, for example, the positive electrode active material can satisfy the mathematical formulae 1 and 2 or the mathematical formulae 1 and 3, and preferably satisfy the mathematical formulae 1 to 3 at the same time. In this case, the coating quality of the carbon surface can be greatly improved, and thus the electrochemical characteristics can be excellent.

[0091] In other words, the present application can provide a positive electrode active material having a carbon coating layer and an olivine structure compound, and the positive electrode active material can satisfy the following mathematical formulae 1, 2, and / or 3.

[0092] [mathematical formula 1]

[0093] 0 < carbon content x Area Ratio LFP ≤ 5

[0094] [mathematical formula 2]

[0095] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0096] [mathematical formula 3]

[0097] 1.3 ≤ carbon content ≤ 1.5

[0098] Here, the carbon content is the total amount (wt%) of carbon measured by a carbon content analyzer, and the Area Ratio LFP corresponds to the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all Raman peaks observed in the Raman spectrum.

[0099] The positive electrode active material can preferably be a regenerated positive electrode active material. In this case, the economy and productivity can be excellent.

[0100] The positive electrode active material can preferably be a single particle. More preferably, the positive electrode active material does not include secondary particles. In this case, since particle breakage does not occur during the electrode manufacturing process, degradation of battery performance due to fine particles can be prevented, the life characteristics can be excellent in a high voltage environment, the thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0101] For example, the single particle can be a particle composed of 30 or less nuclei, preferably a particle composed of 1 to 20 nuclei, more preferably a particle composed of 1 to 10 nuclei, still more preferably a particle composed of 1 to 5 nuclei, and most preferably a particle composed of 1 nucleus. In this case, it is possible to provide a positive electrode material that can prevent a decrease in battery performance due to fine particles that do not cause particle breakage during electrode manufacturing, has excellent life characteristics in a high-voltage environment, has high thermal stability, and generates a small amount of gas during charging and discharging.

[0102] In the present application, the nucleus refers to a particle unit that constitutes a single particle, and can be a single crystal having no grain boundaries, or a polycrystal in which grain boundaries do not exist in appearance when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM) or electron backscatter diffraction (EBSD).

[0103] In the present application, the number of nuclei refers to the average number of nuclei of the positive electrode active material particles. The positive electrode containing the positive electrode active material is cut using an ion milling method, and a cross-sectional image in the thickness direction of the cut positive electrode is obtained using a scanning electron microscope (SEM). Then, within the cross-sectional image, at least 30 particles are selected for each of the large-diameter positive electrode active material particles and the small-diameter positive electrode active material particles. Then, the number of nuclei in the cross section of each positive electrode active material particle is measured by SEM image analysis, and the arithmetic mean is calculated.

[0104] In the present application, the secondary particle is an agglomerate formed by agglomeration of a plurality of single particles, and refers to a particle containing more than 30 nuclei.

[0105] For example, the fluorine (F) content of the positive electrode active material can be 1,000 mg / kg or less, preferably 900 mg / kg or less, and more preferably 10 to 800 mg / kg. Within this range, the coating quality of the carbon surface can be improved, and the charge capacity, resistance characteristics, and capacity characteristics can be excellent.

[0106] In the present application, the fluorine (F) content can be measured using an ICP analyzer. At this time, a general ICP analyzer widely used in laboratories can be used, but there is no deviation depending on the measurement device or method.

[0107] For example, the average crystal size of the positive electrode active material can be 50 to 500 nm, preferably 50 to 300 nm, and more preferably 50 to 200 nm. Within this range, the capacity can be improved by increasing the electrical conductivity as the crystal size decreases.

[0108] In the present application, the average crystal size can be measured by XRD crystal analysis, and is not biased according to the measuring device or method. Specifically, 5 g of the positive electrode active material particles are placed in a holder, the particles are irradiated with X-rays, and the resulting diffraction lattice is analyzed to obtain the average crystal size. At this time, according to the calculation method, the average crystal size of the primary particles of the positive electrode active material particles can be obtained from the half-peak width of the main peak or three or more peaks.

[0109] For example, the content of LiOH remaining on the surface of the positive electrode active material is small. Preferably, LiOH is not detected on the surface of the positive electrode active material. In this case, the coating quality of the carbon surface can be improved, and thus the charge capacity, the resistance characteristics, and the capacity characteristics can be excellent.

[0110] For example, the content of Li2CO3 remaining on the surface of the positive electrode active material can be 0.51% by weight or less, preferably 0.50% by weight or less, and more preferably 0.01 to 0.50% by weight. Within this range, the coating quality of the carbon surface can be improved, and thus the charge capacity, the resistance characteristics, and the capacity characteristics can be excellent.

[0111] In the present application, the residual amount of LiOH and Li2CO3 remaining on the surface of the positive electrode active material can be measured using a pH titrator T5 (Mettler Toledo Co.). Specifically, 5 g of the positive electrode active material is dispersed in 100 ml of distilled water and mixed at 300 rpm for 5 minutes, and then filtered to filter out the active material and obtain a solution (filtrate). While titrating the filtrate with a 0.1M HC1 solution, the change in the pH value is measured. Based on the measurement results, a pH titration curve is obtained. Using the pH titration curve, the residual amount of LiOH and Li2CO3 in the positive electrode active material is calculated.

[0112] Method for regenerating a positive electrode active material

[0113] The regeneration method of the positive electrode active material of the present application includes: a step of heat-treating a waste positive electrode in which a positive electrode active material layer containing a positive electrode active material having an olivine structure compound is coated on a current collector, to cause the positive electrode active material to be desorbed from the current collector; a step of coating a coating agent to the desorbed positive electrode active material, performing pre-milling, and performing spray drying; and a step of calcining the spray-dried positive electrode active material at 750 to 1200°C in a reducing atmosphere. In this case, the crystal structure can be restored to that of a newly manufactured positive electrode active material. Therefore, when this positive electrode active material is used as a positive electrode active material of a battery, excellent battery characteristics can be provided. Furthermore, the positive electrode active material can be regenerated in a simple and environmentally friendly manner without decomposing the positive electrode active material, and the economy and productivity can be greatly improved.

[0114] According to the regeneration method of the positive electrode active material according to the present application as described above, pre-milling, calcination, and milling can be sequentially performed to recover the regenerated positive electrode active material. Hereinafter, the milling performed before calcination is referred to as “pre-calcination milling or pre-milling”, and the milling performed after calcination is referred to as “post-calcination milling or milling”.

[0115] Hereinafter, each step of the regeneration method of the positive electrode active material is described in detail.

[0116] Desorption step

[0117] In the present application, the regeneration method of the positive electrode active material includes a step of heat-treating a waste positive electrode on which a positive electrode active material layer containing a positive electrode active material having an olivine structure compound is coated on a current collector. In this case, the purity of the recovered positive electrode active material can be improved.

[0118] The waste positive electrode can be preferably a positive electrode separated from a secondary battery discarded after use, a defective positive electrode tab or a positive electrode scrap generated in a secondary battery manufacturing process, or a positive electrode tab or a positive electrode scrap discarded after cutting. For example, in the case of the positive electrode scrap generated in the manufacturing process, excellent battery characteristics can be achieved because there is no loss of lithium ions in the positive electrode active material.

[0119] The secondary battery can be preferably a lithium secondary battery.

[0120] If necessary, the waste positive electrode can be used after a crushing process is performed.

[0121] The crushing can be performed using a generally used physical crushing method without any particular limitation, and is not limited to a crushing size. For example, the crushing can be performed in a size of about 2 cm x 2 cm (width x length).

[0122] In the present application, the olivine structure is a kind of crystal structure, which is a 3D hexahedral lattice structure. In this structure, P-O (phosphorus-oxygen) is strongly bonded so that the structure can be maintained even when all lithium ions are lost. Therefore, performance deterioration due to charging and discharging can be prevented, and thermal stability can be excellent. The positive electrode active material having the olivine structure has disadvantages such as low energy density, low electrical conductivity, and low lithium ion diffusion compared to other positive electrode active materials, but the positive electrode active material has a great economic advantage because inexpensive iron is used instead of expensive cobalt.

[0123] The olivine structure can be confirmed by a measurement method generally implemented in the technical field to which the present application pertains, by X-ray diffraction analysis (XRD) as a specific example.

[0124] For example, the olivine-structured compound can be a compound represented by Chemical Formula 1 below. In this case, high-temperature stability, life characteristics, and economy can be excellent.

[0125] [Chemical Formula 1]

[0126] Li 1+a Fe 1-b M b (PO 4-c )X c

[0127] In Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

[0128] The olivine-structured compound can preferably include LiFePO4 having an olivine structure. In this case, high-temperature stability, life characteristics, and economy can be excellent.

[0129] For example, the conductive material can be a carbon-based conductive material, preferably carbon black, CNT, or a mixture thereof.

[0130] For example, the binder can be a polymer binder, preferably polyvinylidene fluoride (PVDF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, more preferably polyvinylidene fluoride.

[0131] For example, the positive electrode active material layer of the waste positive electrode can include a solvent. The solvent can be used to mix the positive electrode active material, the binder, and / or the conductive material, and can be a solvent commonly used in the art to which the present application pertains. For example, the solvent can include one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0132] For example, the positive electrode active material layer of the waste positive electrode can further include a dispersant.

[0133] For example, the dispersant can include one or more selected from the group consisting of cellulose compounds, polyalkylene oxides, polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl aldehydes, polyvinyl ethers, polyvinyl sulfonic acids, polyvinyl chlorides (PVCs), polyvinylidene fluorides, chitosans, starches, amylose, polyacrylamides, poly-N-isopropyl acrylamides, poly-N,N-dimethyl acrylamides, polyethylene imines, polyoxyethylenes, poly(2-methoxyethoxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile-butadiene-styrene (ABS) copolymers, acrylate-styrene-acrylonitrile (ASA) copolymers, mixtures of acrylate-styrene-acrylonitrile (ASA) copolymers and propylene carbonate, styrene-acrylonitrile (SAN) copolymers, and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymers.

[0134] For example, the heat treatment step can be performed by heating to a temperature of 300-650°C, preferably 400-650°C, more preferably 500-600°C, in an oxidizing atmosphere. In this case, foreign substances included in the positive electrode active material of the spent positive electrode, such as a binder and a conductive material, can be removed, and a positive electrode active material precursor can be recovered, which is referred to as a "desorption process".

[0135] In the present application, the positive electrode active material precursor is a term raised to distinguish the positive electrode active material precursor from the positive electrode active material regenerated by the step of coating the surface of the positive electrode active material described below, and refers to a material that can provide the regenerated positive electrode active material through a predetermined positive electrode active material coating process.

[0136] The desorption step can be performed by a method generally performed in the art to which the present application pertains without any particular limitation, and the heating rate and the heating time can be appropriately adjusted as necessary. Accordingly, the residual amount of metal eluted from the current collector can be significantly reduced without a separate pretreatment process to separate or remove the current collector. Thus, the purity of the positive electrode active material can be increased, and process simplification can be achieved.

[0137] For example, the positive electrode active material within the waste positive electrode can be coated with a coating agent containing metal and / or carbon. Conventionally, in the field of secondary batteries, the positive electrode active material can be coated with various coating agents containing metal and / or carbon for the purpose of improving the performance of the battery. In the process of recovering the positive electrode active material from the waste positive electrode, the structure of the coating is destroyed, and when the positive electrode active material is reused in the battery without removing the coating, it can cause deterioration in the performance of the battery. Therefore, when the positive electrode active material within the waste positive electrode is coated, it is advantageous to remove the coating. In the heat treatment step, the carbon coating on the surface of the positive electrode active material can be removed. In this case, the purity of the recovered positive electrode active material can be increased, and a decrease in the performance of the battery can be prevented.

[0138] For example, the desorption step can be performed under an oxidative atmosphere including an air atmosphere or an oxygen atmosphere. In this case, metal foreign matter introduced from the binder, the conductive material, and the current collector can be smoothly removed, so that the desired positive electrode active material can be recovered with high purity and high yield.

[0139] For example, the oxygen purity of the oxidative atmosphere can be 10% or more, preferably 20% or more, more preferably 30% or more or 50% or more, still more preferably 70% or more, still more preferably 80% or more, still more preferably 90-99%. Within this range, the desired positive electrode active material can be recovered with high purity and high efficiency.

[0140] The purity of oxygen (%) can be expressed in vol% or mol%.

[0141] The purity of oxygen in the present application can be measured using a measurement method commonly used in the technical field to which the present application pertains without particular limitation.

[0142] For example, until the heat treatment temperature is reached, the heating rate can be 1 to 10°C / min, preferably 2 to 9°C / min, more preferably 3 to 7°C / min. Within this range, the desired positive electrode active material can be recovered with high purity and high efficiency.

[0143] For example, at the heat treatment temperature, the heat treatment time can be 10 minutes to 5 hours, preferably 30 minutes to 5 hours, more preferably 30 minutes to 2 hours, still more preferably 30 minutes to 1 hour. Within this range, the desired positive electrode active material can be recovered with high purity and high efficiency.

[0144] In the present application, the heat treatment time is the time for which heat treatment is performed at the corresponding heat treatment temperature, and does not include the time required to reach the corresponding heat treatment temperature.

[0145] For example, in the heat treatment step, the positive electrode active material layer of the waste positive electrode can be separated from the current collector.

[0146] For example, in the heat treatment step, after the heat treatment is completed, foreign matter can be removed from the waste positive electrode, and a high-purity positive electrode active material precursor powder can be obtained. Thus, the "positive electrode active material recovered in the heat treatment step" can refer to a positive electrode active material precursor.

[0147] After the desorption step is completed, the recovered positive electrode active material precursor can preferably be composed of components capable of providing an LFP positive electrode active material. As a specific example, Fe2O3 and Li3Fe2(PO4)3 can be included. In this case, the amount of residual metal foreign matter (e.g., aluminum) and carbon-based foreign matter can be significantly reduced by a subsequent regeneration treatment, thereby providing a high-purity regenerated LFP positive electrode active material. The regenerated LFP positive electrode active material has a high purity. Thus, when the regenerated LFP positive electrode active material is used as a positive electrode active material for a secondary battery, excellent battery characteristics can be achieved.

[0148] For example, after the desorption step is completed, the content of residual metal introduced from the current collector in the recovered positive electrode active material precursor can be 390 ppm or less, preferably 250 ppm or less, more preferably 240 ppm or less, still more preferably 230 ppm or less, still more preferably 225 ppm or less, and the lower limit of the content is not particularly limited. The content of residual metal can be 10 ppm or more, or 50 ppm or more, in terms of the balance between the purity and the recovery rate of the positive electrode active material and the process efficiency. In this case, a high-purity positive electrode active material can be recovered.

[0149] The metal introduced from the current collector is not particularly limited, as long as the metal is a metal that is typically applied to a current collector in the technical field to which the present application pertains, and as a specific example, it can be aluminum.

[0150] In the present application, as a method of measuring the content of a metal element, a method typically implemented in the technical field to which the present application pertains can be used without particular limitation, and as a specific example, the content of a metal element can be measured by ICP (inductively coupled plasma) analysis.

[0151] For example, after the desorption step is completed, the content of carbon element (C) in the recovered positive electrode active material precursor can be 1.0% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, still more preferably 0.08% by weight or less, still more preferably 0.06% by weight or less, and the lower limit thereof is not particularly limited. The content of carbon element (C) can be 0.001% by weight or more, or 0.01% by weight or more, in terms of the balance between the purity and the recovery rate of the positive electrode active material and the process efficiency. In this case, a high-purity positive electrode active material can be recovered.

[0152] In the present application, as a method of measuring the carbon element content, a method of measuring the carbon element content commonly practiced in the technical field to which the present application pertains can be used without particular limitation, and as a specific example, the carbon element content can be measured by quantitative analysis using a carbon / sulfur (CS) determinator.

[0153] Coating the surface of a positive electrode active material

[0154] In the present application, the method of regenerating the positive electrode active material includes a step of coating the surface of the positive electrode active material recovered in the heat treatment step. In this case, a coating layer can be formed on the surface of the particles of the regenerated positive electrode active material. Therefore, when the regenerated positive electrode active material is applied to a secondary battery, the output characteristics, charge / discharge performance, and life performance of the battery can be improved, and battery characteristics comparable to those when a newly manufactured positive electrode active material is applied can be provided. Furthermore, a structure similar to the crystal structure of the newly manufactured positive electrode active material can be obtained before the coating layer is formed. Therefore, the coating layer can be uniformly formed on the surface of the particles, the area in which the olivine structure compound is mixed within the carbon coating layer on the surface of the positive electrode active material can be reduced, and thus the battery performance can be improved.

[0155] For example, the coating can be performed using a coating agent including one or more of a metal, an organometallic, and a carbon component. Preferably, the coating can be carbon coating using a coating agent including a carbon component. In this case, the battery characteristics can be further improved.

[0156] As the coating agent containing a carbon component, a coating agent containing a carbon component commonly used in the technical field to which the present application pertains can be used without particular limitation. As a specific example, the carbon component can include one or more selected from the group consisting of a sugar (for example, sucrose, glucose, and fructose), graphite, and polyvinylidene fluoride, preferably a sugar, and more preferably sucrose. In this case, the coating can be easily performed, and economic efficiency can be improved. Furthermore, when applied to a battery, the battery characteristics can be significantly improved.

[0157] The coating agent containing a metal can preferably be a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, and Mg, and still more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof, and still more preferably a coating agent containing tungsten (W) and boron (B), as a specific example, a coating agent containing tungsten boride (WB). In this case, the resistance characteristics and life characteristics can be improved.

[0158] For example, the coating agent containing a metal can be an oxide or an acid including a metal as an element in its molecule.

[0159] As the coating agent containing an organic metal, a coating agent containing an organic metal compound containing a metal, which is commonly used in the field of the present application, can be used without particular limitation. As a specific example, a metal alkoxide can be used.

[0160] For the metal, organic metal, and carbon components, the coating agent can preferably have an average diameter of 1 to 1000 nm and a specific surface area of 10 to 100 m 2 / g, more preferably an average diameter of 10 to 100 nm and a specific surface area of 5 to 100 m 2 / g. Within this range, the coating agent can adhere uniformly to the surface of the positive electrode active material, can impart structural stability to the positive electrode active material, and thus can improve the problem of low electrical conductivity of the positive electrode active material.

[0161] In the present application, the average diameter can be measured by a measurement method commonly used in the field of the present application. For example, the average diameter can be measured by a laser diffraction method. Specifically, the positive electrode active material particles are dispersed in a dispersion medium, the dispersed particles are placed in a commercially available laser diffraction particle size measurement device such as Microtrac MT 3000, and the particles are irradiated with ultrasonic waves of about 28 kHz with an output of 60 W. Then, the average particle diameter (D50) is calculated based on the particle size distribution in the measurement device at 50%.

[0162] In the present application, the specific surface area can be measured by a measurement method commonly used in the field of the present application. For example, the specific surface area can be measured by a Brunauer-Emmett-Teller (BET) method. Specifically, the specific surface area can be calculated based on the amount of adsorbed nitrogen at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan Co.

[0163] For example, the content of the coating agent can be 1 to 10% by weight, preferably 2 to 8% by weight, and more preferably 3 to 7% by weight, based on the components coated on the surface of the positive electrode active material excluding the solvent. Within this range, the structural stability and the electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0164] The coating method commonly used in the field to which the present application pertains can be used as the coating method of the present application, and is not particularly limited. For example, coating can be performed by adding a coating agent to the surface of the positive electrode active material. As specific examples, a liquid method of mixing a positive electrode active material and a liquid coating agent, a mechanochemical method using high mechanical energy of a ball mill, a fluidized bed coating method, a spray drying method, a precipitation method of precipitating a coating agent onto the surface of a positive electrode active material in an aqueous solution, a method using a reaction between a gaseous coating agent and a positive electrode active material, or sputtering can be used. In this case, a coating layer can be uniformly formed, agglomeration of the positive electrode active material particles can be prevented, and the coating process can be smoothly performed, thereby resulting in excellent productivity.

[0165] As specific examples, the step of coating the surface of the positive electrode active material can include a step of applying a coating agent to the positive electrode active material obtained in the heat treatment step, performing pre-milling, and performing spray drying; and a step of calcining the spray-dried positive electrode active material at 750 to 1200°C under a reducing atmosphere. In this case, the coating efficiency can be excellent, agglomeration of the positive electrode active material particles can be prevented, and a coating layer can be uniformly formed on the surface of the positive electrode active material particles. Furthermore, the area in which the olivine structure compound is mixed in the carbon coating layer can be reduced, thereby the battery performance can be improved.

[0166] For example, coating can be performed using a coating agent solution obtained by mixing a coating agent containing a carbon component in a suitable solvent. At this time, any solvent commonly used can be used as the solvent, without any particular limitation. As specific examples, an aqueous solvent, more specifically, deionized water, can be used as the solvent. The solid content in the coating agent solution can be 20% by weight or less, preferably 1 to 15% by weight, more preferably 2 to 10% by weight, based on the total weight of the coating agent solution. In this case, the coating efficiency can be excellent, and the subsequent milling process can be smoothly performed. Therefore, the coating layer finally formed on the surface of the positive electrode active material particles can be uniform.

[0167] For example, coating can be performed using various methods, such as a liquid method of mixing a positive electrode active material and a liquid coating agent, and a precipitation method of precipitating a coating agent onto the surface of a positive electrode active material in an aqueous solution. In the case of a method using a reaction between a gaseous coating agent and a positive electrode active material, a method of simply mixing a solid coating agent and a positive electrode active material, and a sputtering method, as shown in Comparative Example 3 described later, it was found that the above-described methods are not suitable for achieving the quality of the carbon coating layer.

[0168] The spray drying can be performed using a spray drying device commonly used in the technical field to which the present application pertains, without any particular limitation. For example, an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expanded droplet generating device, or an electrostatic spray drying device can be used. As a specific example, a PSD-05 (manufactured by Eugene Tech Co., Ltd.) device can be used, but the present application is not limited thereto.

[0169] Further, the spray pressure and the supply speed of the coating agent solution, etc. can be appropriately selected in consideration of the amount of the coating agent coated on the surface of the regenerated positive electrode active material.

[0170] The calcination can be performed by heating the coated positive electrode active material coated with the coating agent at 750 to 1200°C, preferably 750 to 1100°C, more preferably 750 to 1000°C, still more preferably 750 to 900°C, under a reducing atmosphere after drying. In this case, the coating agent can be stably coated on the surface of the positive electrode active material while maintaining the inherent properties of the positive electrode active material. From Example 1 and Comparative Examples 1 and 3 described below, it can be confirmed that the calcination process conditions and the calcination temperature thereof are variables that can achieve Mathematical Formulas 1 to 3.

[0171] For example, in the calcination, the heating rate can be 1 to 20°C / min, preferably 1 to 10°C / min, more preferably 2 to 7°C / min, until the calcination temperature is reached. Within this range, the desired calcination effect can be sufficiently achieved.

[0172] For example, the calcination can be performed at the calcination temperature for 1 to 24 hours, preferably 1 to 16 hours, more preferably 3 to 16 hours. Within this range, the desired calcination effect can be sufficiently achieved.

[0173] For example, the reducing atmosphere can be an argon (Ar) or nitrogen (N2) atmosphere. As a preferred example, in the reducing atmosphere, the purity of the nitrogen gas can be 80% or more, preferably 90% or more, more preferably 90% to 99.8%, still more preferably 95% to 99.8%. In this case, during the calcination process, oxidation of the coating agent can be prevented, and a coating layer can be stably formed on the surface of the positive electrode active material.

[0174] The purity of the nitrogen gas (%) can be vol% or mol%.

[0175] In the present specification, the purity of the nitrogen gas can be measured by a measurement method commonly used in the technical field to which the present application pertains, without any particular limitation.

[0176] For example, the amount of the coating layer can be 0.1 to 15% by weight, preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, still more preferably 0.7 to 3% by weight, still more preferably 0.8 to 2% by weight, based on the total weight of the regenerated positive electrode active material including the weight of the coating layer. Within this range, the desired coating effect can be sufficiently achieved.

[0177] The amount of the coating layer can be measured using a measurement method commonly used in the art to which the present application pertains, and as a specific example, can be quantitatively measured by thermogravimetric analysis (TGA) or a carbon / sulfur (CS) determinator.

[0178] The thickness of the coating layer can be appropriately controlled according to the desired coating amount. In the present application, the thickness of the coating layer can be measured by a measurement method commonly practiced in the art to which the present application pertains. For example, the long side diameter of 5 to 100 positive electrode active material particles can be measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM), and then the arithmetic mean of the measured values is calculated, thereby obtaining the thickness of the coating layer.

[0179] For example, the coating step can include a step of performing pre-milling (pre-calcination milling step) before spray drying after mixing the desorbed positive electrode active material with the coating agent. In this case, by controlling the particle diameter within a predetermined range before performing a subsequent regeneration process on the coated positive electrode active material, the particle diameter and the particle diameter distribution of the finally obtained regenerated positive electrode active material can be uniformly controlled. In addition, by controlling the particles in a state that is advantageous for recovering the crystal structure of the positive electrode active material in the subsequent step, the battery characteristics can be significantly improved.

[0180] For example, before calcination, milling (pre-milling) can be performed using a ball mill, a high-energy ball mill, a vibration mill, or a roll mill, and preferably using a ball mill. In this case, the particle diameter distribution of the positive electrode active material can be easily controlled, and the average particle diameter of the finally obtained regenerated positive electrode active material can be easily controlled, which can be advantageous for recovering the crystal structure of the positive electrode active material in the subsequent step.

[0181] For example, before calcination, the milling (pre-milling) can be performed for 5 hours to 24 hours, preferably 5 hours to 20 hours, more preferably 5 hours to 16 hours, still more preferably 5 hours to 13 hours, still more preferably 6 hours to 12 hours, still more preferably 8 hours to 10 hours. Within this range, the occurrence of fine particles can be suppressed, and the particle diameter distribution of the positive electrode active material can be smoothly controlled within a narrow range.

[0182] For example, the grinding (pre-grinding) can be performed at 100 to 500 rpm, preferably 150 to 450 rpm, more preferably 180 to 420 rpm, still more preferably 190 to 410 rpm, still more preferably 200 to 400 rpm, still more preferably 250 to 320 rpm, before the calcination. In this case, the occurrence of fine particles can be inhibited, and the desired effect can be sufficiently achieved while maintaining the crystal structure of the positive active material.

[0183] The average particle diameter (D50) of the positive active material powder obtained after the grinding before the calcination can be 0.3 to 0.7 μm, preferably 0.3 to 0.65 μm, more preferably 0.35 to 0.65 μm, still more preferably 0.4 to 0.6 μm, still more preferably 0.45 to 0.55 μm. In this case, the occurrence of fine particles can be inhibited, and the particle diameter of the finally obtained regenerated positive active material can be controlled within the desired range while maintaining the crystal structure of the positive active material. 50 ) can be 0.3 to 0.7 μm, preferably 0.3 to 0.65 μm, more preferably 0.35 to 0.65 μm, still more preferably 0.4 to 0.6 μm, still more preferably 0.45 to 0.55 μm. In this case, the occurrence of fine particles can be inhibited, and the particle diameter of the finally obtained regenerated positive active material can be controlled within the desired range while maintaining the crystal structure of the positive active material.

[0184] Grinding

[0185] In the present application, the method for regenerating the positive active material can include a step of grinding the calcined positive active material (post-calcination grinding step). In this case, the agglomeration and particle breakage of the finally obtained regenerated positive active material can be prevented, and the generation of fine particles can be prevented. Further, since the particle diameter distribution is controlled within a narrow range, the positive active material can be prepared as a single crystal particle. Accordingly, the battery performance deterioration due to fine particles can be prevented, and the thermal stability and life characteristics of the battery can be further improved. Further, finally, when the regenerated positive active material is used as a positive electrode of a secondary battery, battery characteristics equivalent to or superior to those of a newly manufactured positive active material can be provided.

[0186] The grinding (post-calcination grinding) can be preferably performed using a jet mill. In this case, the particle diameter and the particle distribution of the finally obtained regenerated positive active material can be precisely controlled within a narrow range while preventing the damage to the crystal structure of the positive active material. Further, since the inflow of foreign matters which can occur during the grinding is prevented, the purity of the regenerated positive active material can be increased.

[0187] For example, the jet mill can be operated at a temperature of -30 to 30°C, preferably -20 to 20°C, and a pressure of 0.8 to 10 bar under an inert gas that does not react with the regenerated positive electrode active material. More specifically, the jet milling can be performed under conditions in which the pressure of the feed line is 2 to 8 bar, preferably 2.5 to 6 bar, more preferably 3 to 5 bar, and the pressure of the milling line is 0.8 to 2 bar, preferably 0.9 to 1.5 bar, more preferably 1 to 1.3 bar. Within this range, damage to the crystal structure of the positive electrode active material can be prevented, and the particle size and particle distribution of the finally obtained regenerated positive electrode active material can be accurately controlled within a narrow range. For example, the inert gas can be argon (Ar) or nitrogen (N2).

[0188] For example, in the milling step, the average particle size (D 50 ) of the finally recovered regenerated positive electrode active material can be 0.6 to 3.0 pm, preferably 0.7 to 2.0 pm, more preferably 0.8 to 1.5 pm, still more preferably 0.9 to 1.2 pm, still more preferably 0.955 to 1.255 pm. In this case, excellent battery characteristics can be achieved.

[0189] In the present application, as a method of measuring the average particle size (D 50 ) of the positive electrode active material, a measurement method commonly used in the technical field to which the present application pertains can be used without particular limitation. For example, the average particle size can be an average particle size based on a cumulative 50% standard in a particle size distribution measured using a laser diffraction method.

[0190] For example, in the milling step, the olivine-structured compound of the recovered regenerated positive electrode active material can be a compound represented by the following Chemical Formula 1, more preferably LiFeP04having an olivine structure. In this case, the electrochemical properties, the resistance characteristics, and the capacity characteristics can be excellent.

[0191] [Chemical Formula 1]

[0192] Li 1+a Fe 1-b M b (PO 4-c )X c

[0193] In Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 £ a £ 0.5, 0 £ b £ 0.5, 0 £ c £ 0.1, respectively.

[0194] For example, in the grinding step, the crystal size of the recovered regenerated cathode active material measured by X-ray diffraction (XRD) can be 120 to 180 nm, preferably 125 to 170 nm, more preferably 130 to 167 nm, still more preferably 140 to 166 nm, still more preferably 150 to 165 nm. In this case, the cathode active material structure is restored to that of a newly manufactured cathode active material, and thus excellent battery characteristics can be provided.

[0195] The regeneration method of the cathode active material according to the present application, the regeneration process is performed by desorbing and recovering a high-purity cathode active material from a waste cathode through a heat treatment step, coating by pre-grinding the recovered cathode active material and a coating agent, and grinding the coated cathode active material. Through the regeneration process, battery characteristics equivalent to those of a secondary battery manufactured using a newly manufactured cathode active material can be provided. Thus, a secondary battery manufactured using the regenerated cathode active material can replace a secondary battery manufactured using a newly manufactured cathode active material.

[0196] Further, by regenerating the cathode active material from the waste cathode without decomposing the cathode active material into each element, all of the cathode active material can be regenerated from the waste cathode without wasting the metal elements of the cathode active material. Further, since lithium, iron, and phosphorus do not need to be supplemented in the regeneration process of the cathode active material, the economic efficiency and productivity can be significantly improved.

[0197] Further, in the present application, when evaluating the quality (surface quality) of the carbon coating layer of the cathode active material, the cathode active material having an olivine structure compound coated with a coating agent is prepared, the total amount of carbon in the cathode active material is measured using a carbon content analysis device, AreaRatio LFP is obtained by dividing the intensity of the Raman peak corresponding to the olivine structure compound by the intensity of all Raman peaks shown in the Raman spectrum, LFP the pre-measured total amount of carbon is multiplied by AreaRatio LFP and it is determined whether all of the following mathematical formulas 1 to 3 are satisfied. In this case, the carbon coating quality of the cathode active material can be easily measured.

[0198] [mathematical formula 1]

[0199] 0 < carbon content × AreaRatio LFP ≤ 5

[0200] [mathematical formula 2]

[0201] 0.45 ≤ 1 / AreaRatio LFP ≤ 1

[0202] [Equation 3]

[0203] 1.3 ≤ carbon content ≤ 1.5

[0204] Here, the carbon content is the total amount (wt%) of carbon measured by a carbon content analyzer, and the Area Ratio LFP corresponds to the intensity of the Raman peak of the olivine structure compound among the intensities of all Raman peaks observed in the Raman spectrum.

[0205] The carbon content refers to the total weight of carbon material that contributes to the electrical conductivity of the positive electrode active material. For example, the carbon content (wt%) contained in the positive electrode active material layer can be analyzed using a CS analyzer (Bruker, G-4 ICARUS series II). Specifically, the carbon content can be calculated from the total amount of CO2 generated when the positive electrode active material layer is burned using the CS analyzer.

[0206] The method of measuring the carbon coating quality of the positive electrode active material of the present application can include all of the above-described positive electrode active material and secondary batteries including the same. Therefore, redundant explanations thereof are omitted here.

[0207] In addition, in order to easily convey the method of measuring the carbon coating quality of the positive electrode active material of the present application to those skilled in the art, only absolutely necessary conditions and devices are described, and other self-evident auxiliary conditions and devices are omitted.

[0208] Secondary battery

[0209] The secondary battery of the present application includes the positive electrode active material. As a result, the carbon coating area can be increased. Therefore, the degradation of battery performance can be prevented, the life characteristics can be excellent in a high voltage environment, the thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced. Therefore, the electrochemical performance, resistance characteristics, and capacity characteristics can be excellent.

[0210] The description of the secondary battery of the present application can include all of the above-described regenerated positive electrode active material and the method of regenerating the positive electrode active material, and therefore redundant descriptions are omitted in the present specification.

[0211] The method of manufacturing the secondary battery of the present application is not particularly limited, as long as the method is a method of manufacturing a lithium secondary battery commonly used in the technical field to which the present application pertains.

[0212] Hereinafter, the present application will be described in greater detail with reference to the following preferred embodiments. However, these embodiments are provided for illustrative purposes only, and should not be construed as limiting the scope and spirit of the present application. In addition, it will be obvious to those skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope of the present application, and such changes and modifications are also within the scope of the appended claims.

[0213] EMBODIMENT

[0214] Example 1

[0215] On an aluminum current collector coated with a positive electrode active material layer including LFP having an olivine structure, a binder, and a conductive material as a waste positive electrode material, a positive electrode waste material remaining after punching a positive electrode plate was prepared. Then, the positive electrode waste material was pulverized to a size of 2 cm x 2 cm.

[0216] Then, a heat treatment process was performed by heating in an air atmosphere at a heating rate of 5°C / min in a furnace and heating at 580°C for 30 minutes. At this time, the air supply rate was 3 L / min. In this process, the binder in the waste positive electrode was thermally decomposed, and the positive electrode active material powder separated from the current collector was recovered.

[0217] After the heat treatment, the heat supply was stopped, and cooling was performed at room temperature. Then, a coating agent composition obtained by mixing sucrose in deionized water such that the carbon content was 4.4 parts by weight (based on 100 parts by weight of the positive electrode active material) was coated as a coating agent onto the recovered positive electrode active material powder, pre-milling (pre-calcination milling) was performed using a ball mill at 300 rpm for 10 hours, and then spray drying was performed. The average particle diameter (D 50 ) of the dried positive electrode active material powder was 0.5 μm.

[0218] The dried positive electrode active material was heated in a furnace at a heating rate of 3°C / min while supplying nitrogen at a rate of 3 L / min, and then calcination was performed at 800°C for 10 hours to form a carbon (C) coating layer on the surface of the positive electrode active material. At this time, the coating amount according to the CS analysis result after calcination was completed was 1.43 wt%.

[0219] The coated positive electrode active material was milled (post-calcination milling) using a jet mill at a feed line pressure of 4 bar and a milling line pressure of 1 bar in an air atmosphere to obtain a regenerated positive electrode active material having particle diameters of D 40 0.885 μm, D 50 1.055 μm, and D 60 1.417 μm.

[0220] Example 2

[0221] A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that a pre-milling step was performed for 6 hours in addition to the coating step.

[0222] Comparative Example 1

[0223] The following wet-type regeneration process was performed on the waste positive electrode scrap used in Example 1 to prepare a regenerated positive electrode active material.

[0224] The waste positive electrode scrap was treated with sulfuric acid to produce a lithium sulfate solution, and then the pH was adjusted to remove impurities, and lithium carbonate was produced through carbonation.

[0225] In addition, a residue (iron and phosphorus residue) that was not dissolved during the sulfuric acid treatment was dissolved in an acid solution to produce iron phosphate.

[0226] The positive electrode active material was obtained by synthesizing the lithium carbonate and iron phosphate produced.

[0227] Comparative Example 2

[0228] Instead of the regenerated positive electrode active material, a freshly prepared LFP positive electrode active material was prepared. When the freshly prepared LFP positive electrode active material was analyzed by ICP analysis, it was confirmed that the freshly prepared LFP positive electrode active material was a LiFePO4positive electrode active material having an elemental ratio of Li / Fe: 1.06, Li / P: 1.00, and P / Fe: 1.06.

[0229] Comparative Example 3

[0230] A regenerated positive electrode active material was prepared in the same manner as in Example 1, except that instead of the coating agent composition used in the coating step of Example 1, sucrose was mixed in a solid phase such that the carbon content was 4.4 parts by weight based on 100 parts by weight of the positive electrode active material, and then calcination of the milled positive electrode active material was performed by heating at a heating rate of 3℃ / min under a nitrogen atmosphere and heating at 700℃ for 10 hours.

[0231] [TEST EXAMPLE I: RAMAN SPECTROSCOPY ANALYSIS]

[0232] Raman spectroscopy analysis was performed on the regenerated or freshly prepared positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3.

[0233] Based on the intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all the Raman peaks shown in the Raman spectrum, the Area Ratio LFPThe item in Table 1 below shows the reciprocal value of the above value 1 / AreaRatio LFP (corresponding to Mathematical Formula 2), and the result is also shown in Table 1 below Figure 2 .

[0234] [Test Example II: Total Carbon Analysis]

[0235] The carbon content of the regenerated or newly manufactured positive electrode active material obtained in Example 1 and Comparative Examples 1 to 3 was measured using a carbon content analyzer.

[0236] Specifically, the carbon content (wt%) contained in the positive electrode active material layer was calculated based on the total amount of CO2 generated when the positive electrode active material layer was combusted using a CS analyzer (Bruker, G-4 ICARUS series II).

[0237] Specifically, after measuring the blank of the calibration curve, the standard sample (JSS514-8, carbon: 0.2016 wt%) was measured at least three times, and the sample was placed in the crucible and weighed in an amount of 30 mg.

[0238] Next, the catalyst was added to the crucible with the sample, placed on the lower electrode, and the sample was injected from the top to combust and measure the carbon content (wt%).

[0239] The measurement results are shown in Table 1 below and Figure 1 (corresponding to Mathematical Formula 3).

[0240] Table 1

[0241]

[0242] As shown in Table 1 and Table 2 below, Figure 1 in the case of Example 1, it was confirmed that the Raman spectroscopy analysis variable showed a different tendency from Comparative Examples 1 to 3. Specifically, the total carbon content analyzed in Example 1 was 1.45 wt%, which was almost similar to the total carbon content analyzed in Comparative Example 3, which was 1.46 wt%. The result of Mathematical Formula 2 reflecting the 1 / AreaRatio LFP item obtained from the result of Raman spectroscopy analysis was 0.72 for Example 1, which satisfied 0.45 or more, but for Comparative Example 3, the value was 0.08, showing a value much lower than 0.45.

[0243] Further, when compared with Comparative Example 1, which has undergone a wet-type regeneration process generally implemented in the technical field to which the present application pertains, or Comparative Example 2, which is a newly manufactured positive electrode active material, in the case of Example 1 of the present application, it was confirmed that the value was 0.72, which satisfied greater than 0.45, while in the case of Comparative Example 1, the value was 0.13, and in the case of Comparative Example 2, the value was 0.16, which was still much lower than 0.45.

[0244] [Test Example III: Selection of Carbon Coating Quality Measurement Index]

[0245] According to 1 / Area Ratio in Table 1 LFP Item (Mathematical Formula 2) and total carbon content (Mathematical Formula 3) calculated the following Mathematical Formula 1, and the results in the following Table 2 in carbon content x Area Ratio LFP Item shows.

[0246] [Mathematical Formula 1]

[0247] Carbon content x Area Ratio LFP

[0248] Table 2

[0249]

[0250] As shown in Table 2, the results calculated according to Mathematical Formula 1 showed a tendency not to match the total carbon content calculated in Mathematical Formula 3, and by the results of additional Raman spectroscopy analysis, it was confirmed that it can be used as an index for more accurately evaluating carbon coating quality. Specifically, the total carbon content analyzed in Example 1 was 1.45 wt%, which was almost similar to the total carbon content analyzed in Comparative Example 3, which was 1.46 wt%. Reflecting the 1 / Area Ratio LFP The results of Mathematical Formula 1 of Item were 2.01 in Example 1, satisfying a value of 5 or less, but in Comparative Example 3, the value was 18.25, which was much greater than 5.

[0251] In fact, even compared to Comparative Example 1, which has undergone a wet-type regeneration process generally implemented in the technical field to which the present application pertains, or Comparative Example 2, which is a newly manufactured positive active material, Example 1 according to the present application exhibited 2.01, satisfying a value of 5 or less, but in the case of Comparative Example 1, the value was 10.38, and in the case of Comparative Example 2, the value was 8.81, which still showed a value much exceeding 5.

[0252] In particular, for Comparative Example 3, which has different calcination temperature conditions, the value was 18.25, exceeding 5. Based on this result, it can be inferred that the calcination temperature conditions have a significant influence on the parameter Mathematical Formula 1.

[0253] In addition, the electrochemical performance of the regenerated or newly manufactured positive active materials obtained from Examples 1 and 2 and Comparative Examples 1 to 3 was measured through the following CHC battery evaluation.

[0254] [Test Example IV: CHC Battery Evaluation]

[0255] The electrochemical performance of the regenerated or freshly prepared cathode active material obtained from Example 1 and Comparative Examples 1 to 3 was measured by the following CHC battery evaluation.

[0256] *CHC battery evaluation: 97.5 wt% of the regenerated cathode active material, 1 wt% of carbon black as an electrically conductive material, and 1.5 wt% of PVDF as a binder were prepared and mixed with LFP to obtain a slurry. Then, the slurry was coated on an aluminum foil to manufacture a cathode, and then a battery (coin half cell, CHC) was manufactured. Then, the voltage was set to 2.5 to 3.7 V, charging and discharging were performed at 0.1 C / 0.1 C, and the electrochemical performance (charge capacity, discharge capacity, and efficiency) was evaluated under the condition including ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3:7 and other additives as an electrolyte. The results are shown in Table 3 below and in the following Figure 3

[0257] Table 3

[0258] Charging capacity Discharging capacity Efficiency (%) Example 1 162.2 158.7 97.6 Comparative Example 1 159.2 156.3 98.2 Comparative Example 2 160.0 157.0 98.1 Comparative Example 3 157.5 154.7 98.2

[0259] Table 3 and in the following Figure 3 The results of the coin battery evaluation of each of the regenerated or freshly prepared cathode active materials obtained in Example 1 and Comparative Examples 1 to 3 are shown. As shown in Table 3 below and in the following Figure 3

[0260] *Capacity retention rate measurement at high temperature (45℃): formation of each single cell using the regenerated or freshly prepared cathode active material obtained from Example 1 and Comparative Examples 1 to 3 was performed at a rate of 0.1 C, and gas inside the cell was removed (degassing process). Thereafter, CC / CV charging of 4.2 V, 1 C, 0.05 C cut-off and CC discharging of 2.5 V, 0.5 C were each performed 200 times at high temperature (45℃). The discharge capacity at the time of one time and the discharge capacity after 200 times were measured using a PNE-0506 charge-discharge device (manufacturer: PNE Solution Co., Ltd., 5 V, 6 A). The discharge capacity at the time of one time was set as the initial capacity. Then, the capacity retention rate was calculated by comparing the discharge capacity at the 200th time with the initial capacity (100%) using the following mathematical formula 4.

[0261] [mathematical formula 4]

[0262] Capacity retention rate (%) = (discharge capacity after high-temperature cycling / initial discharge capacity) x 100

[0263] ​​The measurement results show that the regenerated positive electrode active materials of Examples 1 and 2 have higher capacity retention rates compared to Comparative Examples 1 to 3 as the number of cycles increases.

[0264] * Measurement of resistance increase at high temperature (45°C): Formation of each single core using the regenerated or freshly prepared positive electrode active materials obtained from Examples 1 and Comparative Examples 1 to 3 was performed at a rate of 0.1C, and gas inside the battery was removed (degassing process). After the degassed lithium secondary battery was transferred to a charge-discharge device at room temperature (25°C), the battery was charged to 4.2V at a rate of 0.33C under constant current / constant voltage conditions, and discharged to 2.5V at 0.05C cut-off, then discharged to 2.5V at 0.33C. Based on the discharge capacity after each charge-discharge cycle of 3 times, the SOC (state of charge) was set to 50%. At this time, the DC internal resistance was measured by using a PNE-0506 charge-discharge device (manufacturer: PNE Solution Co., Ltd., 5V, 6A) to provide the voltage drop occurring at the time of applying a discharge pulse for 10 seconds at 2.5C, and the resistance at this time was set as the initial resistance.

[0265] After that, 4.2V, 1C, 0.05C cut-off CC / CV charging and 2.5V, 0.5C CC discharging were each performed 200 times at high temperature (45°C). The lithium secondary battery was moved to a charge-discharge device at room temperature (25°C), and then the SOC (state of charge) was adjusted to 50%. The DC internal resistance was measured by using a PNE-0506 charge-discharge device (manufacturer: PNE Solution Co., Ltd., 5V, 6A) to provide the voltage drop occurring at the time of applying a discharge pulse for 10 seconds at 2.5C. The obtained results were compared with the initial resistance (0%), and the resistance increase rate (%) was calculated according to Mathematical Formula 5.

[0266] [Mathematical Formula 5]

[0267] Resistance increase rate (%) = {(resistance after high-temperature cycling - initial resistance) / initial resistance} x 100

[0268] The measurement results show that the regenerated positive electrode active materials of Examples 1 and 2 exhibit higher resistance increase rates compared to Comparative Examples 1 to 3 as the number of cycles increases.

Claims

1. A positive electrode active material having a carbon coating and an olivine-structured compound, and satisfying the following mathematical formulae 1, 2, and 3: [mathematical formula 1] 0 < carbon content x Area Ratio LFP ≤ 5 [mathematical formula 2] 0.45 < 1 / Area Ratio LFP < 1 [mathematical formula 3] 1.3 ≤ carbon content ≤ 1.5 wherein The carbon content is the total amount of carbon in wt% measured by a carbon content analyzing device, and AreaRatio LFP The intensity of the Raman peak corresponding to the olivine structure compound among the intensities of all Raman peaks observed in the Raman spectrum.

2. The positive electrode active material according to claim 1, wherein The positive electrode active material is a regenerated positive electrode active material.

3. The positive electrode active material according to claim 1, wherein The positive electrode active material is a single particle.

4. The positive electrode active material according to claim 1, wherein The olivine-structured compound is represented by the following Chemical Formula 1: [Chemical Formula 1] Li 1+a Fe 1-b M b (PO 4-c )X c wherein M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

5. The positive electrode active material according to claim 4, wherein The positive electrode active material having the olivine-structured compound includes lithium iron phosphate.

6. A method for regenerating a positive electrode active material, comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer containing a positive electrode active material having an olivine-structured compound coated on a current collector to desorb the positive electrode active material from the current collector; coating a surface of the desorbed positive electrode active material; and grinding the coated positive electrode active material, wherein the coating step includes: applying a coating agent to the desorbed positive electrode active material, performing pre-grinding, and performing spray drying; and calcining the spray-dried positive electrode active material at 750 to 1200°C under a reducing atmosphere.

7. The method of claim 6, wherein, The desorption step is performed by heating at a temperature of 300 to 650°C under an oxidizing atmosphere.

8. The method of claim 6, wherein, The desorption step is performed by increasing the temperature at a heating rate of 1 to 10°C / min to reach the heat-treatment temperature, and for 10 minutes to 5 hours.

9. The method of claim 6, wherein, The coating agent includes one or more of a metal, an organometallic, and a carbon component.

10. The method of claim 6, wherein, In the coating step, the calcination is performed for 1 to 24 hours.

11. The method of claim 6, wherein, In the coating step, the pre-grinding is performed using a ball mill, a high-energy ball mill, a vibration mill, or a roll mill.

12. The method of claim 6, wherein, The grinding step is performed using a jet mill.

13. The method of claim 6, wherein, The olivine-structured compound is represented by the following Chemical Formula 1: [Chemical Formula 1] Li 1+a Fe 1-b M b (PO 4-c )X c , wherein M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, respectively.

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

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