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

Abstract

The present invention relates to a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery. According to the present invention, after desorption and recovery of the positive electrode active material from a waste positive electrode, a coating agent is applied, and the firing conditions of the coated positive electrode active material are controlled. This results in a positive electrode active material exhibiting a structure similar to that of fresh positive electrode active material, while also reducing the area in which olivine-structured compounds are mixed within the carbon coating layer on the surface of the positive electrode active material. This provides a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery that offer good battery characteristics.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application is an application claiming priority based on Korean Patent Application No. 10-2024-0025873 dated February 22, 2024, and Korean Patent Application No. 10-2025-0001944, refiled thereunder on January 7, 2025, and all contents disclosed in said Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery. More specifically, the invention relates to a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery, which provide good battery characteristics by desorbing and recovering the positive electrode active material from a waste positive electrode, applying a coating agent, and controlling the firing conditions of the coated positive electrode active material, thereby exhibiting a structure similar to the crystalline structure of fresh positive electrode active material, and reducing the area in which olivine-structured compounds are mixed within the carbon coating layer on the surface of the positive electrode active material. [Background technology]

[0003] Demand for lithium-ion batteries has steadily increased since the 1990s, alongside the portable electronics market, and has surged globally recently with the rapid growth of the electric vehicle market. This could lead to instability in the supply and demand of lithium resources in the near future, and the sustained accumulation of end-of-life batteries could also cause significant environmental problems. To address these issues, the reuse of end-of-life lithium-ion batteries is a crucial technological challenge.

[0004] A lithium secondary battery generally consists of a positive electrode with a positive electrode active material layer coated on a metal foil such as aluminum, a negative electrode with a negative electrode active material layer coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing, and an electrolyte that allows lithium ions to move between the positive and negative electrodes. The positive electrode is manufactured by applying a positive electrode composition containing a positive electrode active material, a binder, a conductive material, a solvent, etc. to a current collector made of a metal foil such as aluminum, drying it, and then performing pressure molding.

[0005] The positive electrode accounts for 60% or more of the cost of a lithium secondary battery. As such positive electrode active materials, there are lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), lithium iron phosphate (LiFePO4), etc. Among these, lithium iron phosphate is increasingly being applied to large-capacity lithium secondary batteries used in electric vehicles, etc., due to its low cost per unit and supply stability. Therefore, there is much research being conducted on recycling technologies for selectively recovering valuable metals from the positive electrodes of lithium secondary batteries discarded after use, or positive electrode scraps generated during the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes"), or directly recovering the positive electrode active material.

[0006] However, due to the characteristics of the recycled positive electrode active material, the particle size distribution is not uniform and the crystal structure is not stable. Therefore, fine powder is easily generated due to particle cracking during the electrode manufacturing process, the thermal stability, etc. decreases, and there is a problem that the battery performance, such as the life characteristics, decreases in a high-voltage environment.

[0007] Therefore, there is a need to develop a recycling technology for positive electrode active materials that can provide good battery characteristics when applied to secondary batteries.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] In order to solve the problems of the prior art as described above, the present invention controls the firing conditions of the positive electrode active material coated with a coating agent after desorbing and recovering the positive electrode active material from the used positive electrode, so as to show a structure similar to that of a fresh positive electrode active material, and reduce the region where the olivine structure compound is mixed in the carbon coating layer on the surface of the positive electrode active material, thereby providing a positive electrode active material capable of providing good battery characteristics and a secondary battery including the same.

[0010] In addition, the present invention aims to provide a positive electrode active material having excellent life characteristics in a high voltage environment, high thermal stability, and a small amount of gas generation during charge and discharge, and a secondary battery including the same.

[0011] The above objects and other objects of the present invention can all be achieved by the present invention described below.

Means for Solving the Problems

[0012] In order to achieve the above object, the present invention provides a positive electrode active material having a carbon coating layer and a compound of an olivine structure, wherein the positive electrode active material satisfies the following mathematical formulas 1, 2, and 3.

[0013] [Mathematical formula 1] 0 < Carbon content × Area Ratio LFP ≦5

[0014] [Mathematical formula 2] 0.45 ≦ 1 / Area Ratio LFP ≦1

[0015] [Mathematical formula 3] 1.3 ≦ Carbon content ≦ 1.5 (Here, the carbon content is the total amount (weight %) of carbon measured by a carbon content analysis device, and Area Ratio LFP corresponds to the intensity of the Raman peak corresponding to the compound of the olivine structure among the intensities of all Raman peaks appearing in the Raman spectrum.)

[0016] II) In the above I), the positive electrode active material may be a recycled positive electrode active material.)

[0017] III) In the above I) to II), the positive electrode active material may be single particles.)

[0018] IV) In the above I) to III), the compound of the olivine structure may be represented by the following Chemical Formula 1.)

[0019] (Chemical Formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c (In the above Chemical Formula 1, M contains 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 contains 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.)

[0020] V) In the above I) to IV), the positive electrode active material having the compound of the olivine structure may contain lithium iron phosphate.)

[0021] Further, the present invention provides a positive electrode active material having a carbon coating layer and a compound of an olivine structure, wherein the positive electrode active material satisfies the following Mathematical Formulas 1, 2 and / or 3.)

[0022] [Mathematical Formula 1] 0 < Carbon content × Area Ratio LFP ≦ 5

[0023] [Formula 2] 0.45 ≤ 1 / Area Ratio LFP ≤1

[0024] [Formula 3] 1.3 ≤ Carbon content ≤ 1.5 (Here, the carbon content is the total amount of carbon (weight %) measured with carbon content analysis equipment, and the Area Ratio LFP This corresponds to the intensity of the Raman peak corresponding to the olivine structure compound, out of all the Raman peaks that appear in the Raman spectrum.

[0025] Furthermore, the present invention includes the steps of: VII) 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 onto a current collector to detach the positive electrode active material from the current collector; coating the surface of the detached positive electrode active material; and milling the coated positive electrode active material. The present invention provides a method for regenerating a positive electrode active material, characterized in that the coating step comprises applying a coating agent to the detached positive electrode active material, pre-milling it, and then spray-drying it; and firing the spray-dried positive electrode active material at 750 to 1200°C in a reducing atmosphere.

[0026] VIII) In VII) above, the heat treatment can be carried out by heating at a temperature of 300 to 650°C in an oxidizing atmosphere.

[0027] IX) In the above VII) to VIII), the heat treatment may be carried out by raising the temperature at a heating rate of 1 to 10°C / min and for 10 minutes to 5 hours after reaching the heat treatment temperature.

[0028] X) In VII) to IX) above, the coating agent may be a coating agent containing one or more of the following: metal, organometallic, and carbon components.

[0029] XI) In the above VII) to X), the firing can be carried out for 1 to 24 hours.

[0030] XII) In the preceding VII) to XI), the preliminary milling can be carried out using a ball mill, a high-energy ball mill, a vibrating mill, or a roll mill.

[0031] XIII) In VII) to XII) above, the milling step can be carried out using a jet mill.

[0032] XIV) In VII) to XIII) above, the olivine structure compound can be represented by the following chemical formula 1.

[0033] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

[0034] XV) A secondary battery is provided that includes the positive electrode active material described in any one of the above items I) to VI). [Effects of the Invention]

[0035] According to the present invention, the regenerated positive electrode active material, which is recycled from a waste positive electrode, exhibits a structure similar to that of a fresh positive electrode active material. Furthermore, the region in which olivine-structured compounds are mixed within the carbon coating layer on the surface of the positive electrode active material is reduced, which has the effect of providing good battery characteristics when applied to a secondary battery.

[0036] In particular, this has the effect of providing a regenerated positive electrode active material that exhibits excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging, as well as a secondary battery containing the same. [Brief explanation of the drawing]

[0037] The following drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited to the matters depicted in these drawings. [Figure 1] This graph shows the measurement results of variables used to measure the quality of the carbon coating of the recycled cathode active material obtained in Example 1 and Comparative Examples 1-3. [Figure 2] This graph shows the Raman spectral analysis results of the regenerated cathode active materials obtained in Example 1 and Comparative Examples 1-3. [Figure 3] This graph shows the evaluation results of the CHC capacity retention rate based on the number of cycles at 45°C for secondary batteries to which the regenerated positive electrode active materials obtained in Example 1 and Comparative Examples 1-3 were applied. [Best Mode for Carrying Out the Invention]

[0038] The inventors of this invention were researching a technology to directly regenerate positive electrode active material from waste positive electrodes containing positive electrode active material with an olivine structure, without going through a decomposition process. They found that when a coating agent is applied to the positive electrode active material recovered through a desorption process and the firing conditions of the positive electrode active material are controlled, the crystal structure is restored to that of fresh positive electrode active material, the area on the carbon coating surface where olivine structure compounds are mixed is reduced, and when this is applied to a secondary battery, the battery characteristics are improved. Based on this, they continued their research and completed the present invention.

[0039] In this description, the positive electrode active material layer of the discarded positive electrode may include a positive electrode active material, a binder, and a conductive material.

[0040] In this description, "oxidizing atmosphere" specifically refers to an atmosphere containing air or oxygen with a purity of 10% or more.

[0041] In this description, "fresh" cathode active material refers to newly synthesized cathode active material that is not obtained by recovering and recycling waste batteries.

[0042] The positive electrode active material and secondary batteries containing it described herein will be explained in detail below.

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

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

[0045] positive electrode active material The present invention includes, as an example, a cathode active material having a compound with an olivine structure.

[0046] The olivine structure compound may, for example, be a lithium iron phosphate (LFP) compound, preferably a compound represented by chemical formula 1, and more preferably, it may contain LiFePO4 with an olivine structure. In this case, there is an effect of excellent electrochemical performance, resistance characteristics, and capacitance characteristics.

[0047] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

[0048] The positive electrode active material may, for example, have a surface coated with carbon, and preferably has a structure in which a carbon coating layer is formed on the surface. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, by substituting a different element on the surface of the positive electrode active material, physicochemical properties are also improved through the effect of adjusting the amount of residual lithium and reducing pH.

[0049] The positive electrode active material of the present invention is a positive electrode active material having a carbon coating layer and an olivine structure compound, and is characterized by satisfying the following formulas 1, 2, and 3, in which case it has the effect of excellent battery performance.

[0050] [Formula 1] 0 < Carbon content × Area Ratio LFP ≤5

[0051] [Formula 2] 0.45 ≤ 1 / Area Ratio LFP ≤1

[0052] [Formula 3] 1.3 ≤ Carbon content ≤ 1.5 (Here, the carbon content is the total amount of carbon (weight %) measured with carbon content analysis equipment, and the Area Ratio LFPThis corresponds to the intensity of the Raman peak corresponding to the olivine structure compound, out of all the Raman peaks that appear in the Raman spectrum.

[0053] The above formula 1 is derived from the variable Area Ratio, which will be discussed later. LFP This is a correlation equation between the total amount of the variable carbon, where a smaller calculated value indicates a reduction in the region where olivine-structured compounds are present in the carbon coating.

[0054] For example, the above formula 1 may be greater than 0 and less than or equal to 5, preferably between 0.5 and 4, and more preferably between 1 and 3. In this case, there is the advantage of improving the coating quality of the carbon surface and having excellent electrochemical properties.

[0055] Equation 2 above represents the variable Area Ratio, which corresponds to the intensity of the Raman peak corresponding to the olivine structure compound, out of the total intensity of all Raman peaks appearing in the Raman spectrum. LFP This is the reciprocal of the calculated intensity of the Raman peak corresponding to the olivine structure compound among all the Raman peaks appearing in the Raman spectrum. A larger calculated value indicates a smaller region occupied by the olivine structure compound.

[0056] As an example, Figure 2 below shows the Raman spectral analysis graphs of the positive electrode active materials regenerated in Example 1 and Comparative Examples 1-3. In this graph, the peak labeled LFP corresponds to the Raman peak of lithium iron phosphate, which is the olivine structure compound mentioned above.

[0057] For example, formula 2 may be in the range of 0.45 to 1, preferably 0.5 to 1, and more preferably 0.6 to 1. In this case, there is the advantage of improving the coating quality of the carbon surface and having excellent battery life characteristics.

[0058] The aforementioned formula 3 represents the total amount of carbon (weight %) measured by carbon content analysis equipment, and may include not only the content of the carbon coating but also the content of the remaining uncoated carbon. Therefore, it may be difficult to use it alone to measure the quality of the carbon coating.

[0059] Therefore, in this invention, the total amount of carbon is used as a variable to create a correlation equation like the one shown in Equation 1 above, and it is predicted that the larger this value, the larger the area of ​​the carbon coating will be.

[0060] For example, formula 3 may be in the range of 1.3 to 1.5, preferably 1.33 to 1.5, and more preferably 1.35 to 1.5. In this case, there is the advantage of improving the coating quality of the carbon surface and having excellent electrochemical properties.

[0061] Furthermore, the positive electrode active material can satisfy, for example, equations 1 and 2, or equations 1 and 3, and preferably, equations 1 to 3 can be satisfied simultaneously. In this case, there is an advantage in that the coating quality of the carbon surface is significantly improved and the electrochemical properties are excellent.

[0062] In other words, the present invention can provide a positive electrode active material having a carbon coating layer and a compound with an olivine structure, wherein the positive electrode active material satisfies the following formulas 1, 2 and / or 3.

[0063] [Formula 1] 0 < Carbon content × Area Ratio LFP ≤5

[0064] [Formula 2] 0.45 ≤ 1 / Area Ratio LFP ≤1

[0065] [Formula 3] 1.3 ≤ Carbon content ≤ 1.5 (Here, the carbon content is the total amount of carbon (weight %) measured with carbon content analysis equipment, and the Area Ratio LFP This corresponds to the intensity of the Raman peak corresponding to the olivine structure compound, out of all the Raman peaks that appear in the Raman spectrum.

[0066] The positive electrode active material may preferably be a regenerated positive electrode active material, which has the advantage of being economical and productive.

[0067] The positive electrode active material may preferably be a single particle, and more preferably does not contain secondary particles. In this case, the particles do not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and the positive electrode active material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0068] The aforementioned single particle may, for example, be a particle consisting of 30 or fewer nodules, preferably a particle consisting of 1 to 20 nodules, more preferably a particle consisting of 1 to 10 nodules, even more preferably a particle consisting of 1 to 5 nodules, and most preferably a particle consisting of 1 nodule. In this case, since the particles do not break during the electrode manufacturing process, there is no degradation of battery performance due to fine powder, and the positive electrode active material has the effect of having excellent life characteristics in high voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0069] In this description, a nodule refers to a particle unit body that constitutes a single particle, and can mean either a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not visible when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM) or electron backscatter diffraction pattern analyzer (EBSD).

[0070] In this description, the number of nodules refers to the average number of nodules in the positive electrode active material particles. This can be determined by cutting the positive electrode containing the positive electrode active material using ion milling, obtaining a cross-sectional image of the thickness direction of the cut positive electrode using a scanning electron microscope (SEM), selecting at least 30 particles each for the largest and smallest positive electrode active material particles in the cross-sectional image, and then measuring the number of nodules in the cross-section of each positive electrode active material particle through SEM image analysis, and then taking the arithmetic mean of these values.

[0071] In this description, secondary particles refer to aggregates formed by the aggregation of multiple single particles, and which contain more than 30 nodules.

[0072] The positive electrode active material may, for example, have a fluorine (F) content of 1,000 mg / kg or less, preferably 900 mg / kg or less, and more preferably 10 to 800 mg / kg. Within this range, there is an advantage in that the coating quality of the carbon surface is improved, as well as excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0073] In this description, the fluorine (F) content can be measured using an ICP analyzer, and while this can be done with a general ICP analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0074] The positive electrode active material may, for example, have an average crystal size of 50 to 500 nm, preferably 50 to 300 nm, and more preferably 50 to 200 nm. Within this range, reducing the crystal size has the advantage of increasing conductivity and improving capacity.

[0075] In this description, the average crystal size can be measured by XRD crystallography, and there is no deviation due to the measurement device or method. Specifically, it can be determined by placing 5g of positive electrode active material particles in a holder and analyzing the diffraction grating produced when the particles are irradiated with X-rays. The method of determination can be based on the main peak or the full width at half maximum of three or more peaks, which can be considered to correspond to the average crystal size of the primary particles of the positive electrode active material.

[0076] The positive electrode active material, as an example, has a low LiOH content remaining on its surface, or preferably no detectable LiOH content. In this case, it has the advantage of improving the coating quality of the carbon surface and providing excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0077] The positive electrode active material may, for example, have a Li2CO3 content remaining on the surface of 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, there is an advantage in improving the coating quality of the carbon surface and providing excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0078] In this description, the residual amounts of LiOH and Li2CO3 on the surface of the positive electrode active material can be measured using a pH titrator (T5, manufactured by Mettler Toledo). Specifically, 5 g of positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The resulting solution (filtrate) is titrated with a 0.1 M HCl solution, and the change in pH value is measured to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material are calculated.

[0079] Method for regenerating positive electrode active material The present invention provides a method for regenerating positive electrode active material, comprising the steps of: heat-treating a waste positive electrode coated with a positive electrode active material layer containing a compound having an olivine structure on a current collector to detach the positive electrode active material from the current collector; applying a coating agent to the detached positive electrode active material, pre-milling it, and then spray-drying it; and firing the spray-dried positive electrode active material at 750-1200°C in a reducing atmosphere. In this case, the crystalline structure is restored to that of fresh positive electrode active material, and when applied as positive electrode active material in a battery, it can provide good battery characteristics. Furthermore, since the positive electrode active material can be regenerated without decomposition using a simple and environmentally friendly method, it has the advantage of greatly improving economy and productivity.

[0080] The method for regenerating positive electrode active material of the present invention allows for the recovery of regenerated positive electrode active material by performing preliminary milling, calcination, and milling in sequence as described above. Hereinafter, milling performed before calcination may be referred to as "pre-calcination milling or preliminary milling," and milling performed after calcination may be referred to as "post-calcination milling or milling."

[0081] The following describes in detail, step by step, the method for regenerating the positive electrode active material.

[0082] Detachment step In the present invention, the method for regenerating positive electrode active material includes the 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 onto a current collector, which has the advantage of improving the purity of the recovered positive electrode active material.

[0083] The aforementioned waste positive electrode may preferably be a positive electrode separated from a secondary battery that has been discarded after use, or a positive electrode sheet or positive electrode scrap that is discarded after defects or cutting during the manufacturing process of the secondary battery. For example, in the case of positive electrode scrap generated during the manufacturing process, there is no loss of lithium ions in the positive electrode active material, which has the advantage of enabling better battery characteristics.

[0084] The secondary battery may preferably be a lithium secondary battery.

[0085] If necessary, the waste positive electrode can be used after undergoing a crushing process.

[0086] The aforementioned crushing method is not limited to any commonly used physical crushing method, and the size of the crushed material is not limited to this, but as an example, it can be crushed into pieces of approximately 2 cm x 2 cm (width x height).

[0087] In this description, the olivine structure is a type of crystal structure with a 3D hexahedron lattice structure in which PO (phosphorus-oxygen) is strongly bonded. Therefore, it can maintain its structure even if all lithium ions are removed, resulting in less performance degradation due to charging and discharging, and excellent thermal stability. Consequently, it has the disadvantage of having a lower energy density, electrical conductivity, and lithium ion diffusivity compared to other cathode active materials, but it offers significant economic advantages because it uses inexpensive iron instead of expensive cobalt.

[0088] The olivine structure can be confirmed by methods commonly used in the art to which the present invention pertains, and as a specific example, it can be confirmed by X-ray diffraction analysis (XRD).

[0089] The olivine structure compound may, for example, be a compound represented by the following chemical formula 1, which has the advantages of excellent high-temperature stability and lifespan characteristics, as well as economic efficiency.

[0090] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

[0091] The olivine-structured compound may preferably include an olivine-structured LiFePO4, which has the advantages of excellent high-temperature stability and longevity characteristics, as well as being economically viable.

[0092] The conductive material may, for example, be a carbon-based conductive material, and preferably, carbon black, CNTs, or a mixture thereof.

[0093] The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0094] The positive electrode active material layer of the waste positive electrode may, for example, be manufactured with a solvent, the solvent being used to mix the positive electrode active material, binder and / or conductive material, and may be a solvent commonly used in the art to which the present invention belongs. For example, the solvent may be one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0095] The positive electrode active material layer of the aforementioned discarded positive electrode may, as an example, further contain a dispersant.

[0096] The dispersant may, as an example, be one or more selected from the group consisting of cellulosic compounds, polyalkylene oxides, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosans, starch, amylose, polyacrylamide, poly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly(2-methoxyethoxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile-butadiene-styrene (ABS) copolymer, acrylate-styrene-acrylonitrile (ASA) copolymer, a mixture of acrylate-styrene-acrylonitrile (ASA) copolymer and propylene carbonate, styrene-acrylonitrile (SAN) copolymer, and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymer.

[0097] The heat treatment step can, for example, be carried out by heating at a temperature of 300 to 650°C under an oxidizing atmosphere, preferably at 400 to 650°C, and more preferably at 500 to 600°C. In this case, foreign substances such as binders and conductive materials contained in the positive electrode active material of the waste positive electrode can be removed, and the positive electrode active material precursor can be recovered. This can simply be referred to as the "desorption step".

[0098] In this description, the term "positive electrode active material precursor" is a term proposed to distinguish it from the positive electrode active material that is ultimately regenerated through a surface coating step of the positive electrode active material described later, and means a substance that can provide regenerated positive electrode active material through a predetermined positive electrode active material coating process.

[0099] The desorption step can be carried out without particular limitation, as long as it is a method commonly used in the art to which the present invention belongs, and the heating rate and heating time can be adjusted as needed. This significantly reduces the amount of residual metal flowing in from the current collector, improving the purity of the positive electrode active material and simplifying the process, without requiring a separate pretreatment step to separate or remove the current collector.

[0100] The positive electrode active material in the waste positive electrode may, for example, be coated with a coating agent containing metal and / or carbon. In the field of secondary batteries, positive electrode active material is sometimes coated with various metal and / or carbon-containing coating agents to improve battery performance. However, if the structure of such a coating layer is destroyed during the process of recovering the positive electrode active material from the waste positive electrode, and it is reused in the battery without removing it, it can cause a decrease in battery performance. Therefore, if the positive electrode active material in 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, which has the advantage of improving the purity of the recovered positive electrode active material and preventing a decrease in battery performance.

[0101] The aforementioned desorption step can, for example, be carried out under an oxidizing atmosphere such as air or oxygen. In this case, foreign matter such as metal that has flowed in from the binder, conductive material, and current collector can be smoothly removed, and the target positive electrode active material can be recovered with high purity and high efficiency.

[0102] The oxidizing atmosphere may, for example, have an oxygen purity of 10% or more, preferably 20% or more, more preferably 30% or more or 50% or more, even more preferably 70% or more, even more preferably 80% or more, and even more preferably 90-99%. Within this range, there is the advantage that the target positive electrode active material can be recovered with high purity and high efficiency.

[0103] The purity percentage of the oxygen may be in volume percentage or mol%.

[0104] The purity of oxygen described herein is not particularly limited when measured by a measurement method commonly used in the art to which this invention pertains.

[0105] The heating rate to reach the aforementioned heat treatment temperature may be, for example, 1 to 10°C / min, preferably 2 to 9°C / min, and more preferably 3 to 7°C / min. Within this range, there is the advantage that the target positive electrode active material can be recovered with high purity and high efficiency.

[0106] The heat treatment time at the aforementioned heat treatment temperature may be, for example, 10 minutes to 5 hours, preferably 30 minutes to 5 hours, more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, there is the advantage that the target positive electrode active material can be recovered with high purity and high efficiency.

[0107] In this description, the heat treatment time refers to the time spent processing at the heat treatment temperature, and the time it takes to reach the heat treatment temperature is not included in the calculation.

[0108] In the heat treatment step, as an example, the positive electrode active material layer of the waste positive electrode can be separated from the current collector.

[0109] In the heat treatment step, as an example, after the heat treatment is completed, foreign matter is removed from the waste positive electrode, and a high-purity positive electrode active material precursor powder is obtained. Therefore, "positive electrode active material recovered in the heat treatment step" can refer to such a positive electrode active material precursor.

[0110] After the desorption step is completed, the recovered positive electrode active material precursor may preferably consist of components capable of providing LFP positive electrode active material, and as a specific example, it may include Fe2O3 and Li3Fe2(PO4)3. In this case, through subsequent regeneration processing, a high-purity regenerated LFP positive electrode active material can be provided in which the residual amounts of metallic foreign matter such as aluminum and carbon-based foreign matter are greatly reduced. Because the regenerated LFP positive electrode active material has high purity, when applied as a positive electrode active material for a secondary battery, it can provide good battery characteristics.

[0111] After the desorption step is completed, the recovered positive electrode active material precursor may, for example, have a metal content of 390 ppm or less remaining, preferably 250 ppm or less, more preferably 240 ppm or less, even more preferably 230 ppm or less, and even more preferably 225 ppm or less. The lower limit is not particularly limited, but from the viewpoint of balancing the purity of the positive electrode active material with the recovery rate and process efficiency, it may be 10 ppm or more, or 50 ppm or more. In this case, there is the advantage that a high-purity positive electrode active material can be recovered.

[0112] The metal flowing in from the current collector is not particularly limited as long as it is a metal commonly used in current collectors in the art to which the present invention belongs, and a specific example of this may be aluminum.

[0113] In this description, the measurement of the content of metal elements can be carried out without particular limitation, as long as it is a method commonly used in the art to which the present invention pertains. As a specific example, it can be measured by ICP (Inductively Coupled Plasma) analysis.

[0114] After the desorption step is completed, the recovered positive electrode active material precursor may, for example, have a carbon (C) content of 1.0% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, even more preferably 0.08% by weight or less, and even more preferably 0.06% by weight or less. The lower limit is not particularly limited, but from the viewpoint of balancing the purity of the positive electrode active material with the recovery rate and process efficiency, it may be 0.001% by weight or more, or 0.01% by weight or more. In this case, there is the advantage that a high-purity positive electrode active material can be recovered.

[0115] In this description, the measurement of the carbon element content can be carried out without particular limitations, as long as it is a method commonly used in the art to which the present invention pertains. As a specific example, it can be measured by quantitative analysis using a CS analyzer (Carbon / Sulfur Determinator).

[0116] Surface coating step for positive electrode active material In the present invention, the method for regenerating 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 is formed on the surface of the particles of the regenerated positive electrode active material. When this is applied to a secondary battery, it has the advantage of providing good battery characteristics at a level equivalent to that of a fresh positive electrode active material, such as improved output characteristics, charge / discharge performance, and lifespan. Furthermore, by exhibiting a structure similar to that of a fresh positive electrode active material before forming the coating layer, the coating layer can be formed uniformly on the surface of the particles, and the area in which olivine-structured compounds are mixed within the carbon coating layer on the surface of the positive electrode active material can be reduced. This has the advantage of further improving the battery characteristics.

[0117] The aforementioned coating can be performed, for example, using a coating agent containing one or more of metals, organometallics, and carbon components. Preferably, it may be a carbon coating using a coating agent containing carbon components, in which case there is the advantage of even better battery characteristics.

[0118] The carbon-containing coating agent is not particularly limited, as long as it contains a carbon component commonly used as a coating agent in the art to which the present invention belongs. For example, the carbon component may be one or more selected from the group consisting of sugars such as sucrose, glucose, and fructose, graphite, and polyvinylidene fluoride. Preferably, it may be a sugar, and more preferably, sucrose. In this case, coating is easy, there are economic advantages, and when applied to a battery, there is an advantage in improving battery characteristics.

[0119] The aforementioned metal-containing coating agent is preferably 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; even more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof; and even more preferably a coating agent containing tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0120] The coating agent containing the metal may, for example, include an oxide or acid that contains the metal as an element in its molecule.

[0121] The aforementioned organometallic coating agent is not particularly limited as long as it is a coating agent commonly used in the art to which the present invention belongs and contains an organometallic compound containing the aforementioned metal. Specific examples of organometallic compounds include metal alkoxides.

[0122] The aforementioned coating agent, as an example, has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m² for metal, organometallic, and carbon components. 2It may also be / g, preferably with an average diameter of 10 to 100 nm and a specific surface area of ​​5 to 100 m². 2 The value may be as low as / g, and within this range, it can uniformly adhere to the surface of the positive electrode active material, thereby improving the structural stability of the positive electrode active material and addressing the problem of low electrical conductivity of the positive electrode active material.

[0123] In this description, the average diameter can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured using the laser diffraction method. Specifically, particles of the positive electrode active material are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer such as Microtrac MT 3000, and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W. The average particle size (D) at the 50% reference of the particle size distribution in the measuring device is then measured. 50 It is possible to calculate ).

[0124] In this description, the specific surface area can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured by the BET (Brunauer-Emmett-Teller) method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

[0125] The coating agent may be present in an amount of 1 to 10% by weight, preferably 2 to 8% by weight, and more preferably 3 to 7% by weight, based on the component that is actually coated on the surface of the positive electrode active material excluding the solvent. Within this range, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0126] The coating method is not particularly limited as long as it is a coating method commonly used in the art to which the present invention belongs. For example, the coating agent can be introduced onto the surface of the positive electrode active material. More specifically, the coating method can be appropriately selected from the group consisting of a liquid phase method in which a liquid coating agent is manufactured and mixed with the positive electrode active material, a mechanochemical method using the high mechanical energy of ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which the coating agent is precipitated on the surface of the positive electrode active material in an aqueous solution, a method that utilizes the reaction between a gaseous coating agent and the positive electrode active material, and a sputtering method. The coating method may preferably be a spray drying method, in which case the coating is formed uniformly, aggregation of positive electrode active material particles is prevented, and the coating process is carried out smoothly, which has the advantage of excellent productivity.

[0127] The surface coating step of the positive electrode active material may, as a specific example, include the steps of applying a coating agent to the positive electrode active material obtained in the heat treatment step, pre-milling it, and then spray-drying it; and firing the spray-dried positive electrode active material at 750 to 1200°C in a reducing atmosphere. In this case, the coating efficiency is excellent, aggregation of positive electrode active material particles is prevented, and the coating is uniformly formed on the surface of the positive electrode active material particles. Furthermore, the area in which olivine-structured compounds are mixed within the carbon coating layer is reduced, which is advantageous for improving battery performance.

[0128] As an example, the coating can be a coating agent solution obtained by mixing the coating agent containing the carbon component with a suitable solvent. In this case, the solvent is not particularly limited as long as it is a commonly used solvent, and as a specific example, an aqueous solvent, or more specifically deionized water, can be used. The ratio of solids in the coating agent solution may be 20% by weight or less, preferably 1 to 15% by weight, and more preferably 2 to 10% by weight, relative to the total weight of the coating agent solution. In this case, there is an advantage that the coating efficiency is excellent and the subsequent milling process is carried out smoothly, resulting in the uniform formation of the coating layer that is ultimately formed on the surface of the positive electrode active material particles.

[0129] The aforementioned coating can be applied in various ways, such as a liquid-phase method in which a liquid coating agent is manufactured and mixed with the positive electrode active material, or a precipitation method in which the coating agent is precipitated on the surface of the positive electrode active material in an aqueous solution. However, methods that utilize the reaction between a gas-phase coating agent and the positive electrode active material, methods that simply mix a solid-phase coating agent and the positive electrode active material, or sputtering methods are not suitable for realizing the quality of the carbon coating layer, as can be seen from Comparative Example 3 described later.

[0130] The aforementioned spray drying can be carried out without particular limitations, as long as it is spray drying equipment commonly used in the art to which the present invention belongs. For example, an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, or an electrostatic spray dryer may be used. Specifically, it can be carried out using PSD-05 equipment (manufacturer: Eugene Tech Co., Ltd.), but is not limited thereto.

[0131] Other parameters, such as spray pressure and the supply rate of the coating solution, can be appropriately selected considering the amount of coating agent to be applied to the surface of the final regenerated cathode active material.

[0132] The firing process involves heat-treating the coated positive electrode active material at 750 to 1200°C in a reducing atmosphere after drying, preferably at 750 to 1100°C, more preferably at 750 to 1000°C, and even more preferably at 750 to 900°C. In this case, there is an advantage that the coating agent is stably coated onto the surface of the positive electrode active material while maintaining the properties inherent to the positive electrode active material. From Examples 1 and Comparative Examples 1 and 3 described later, it can be confirmed that the conditions of the firing process and the firing temperature are variables that embody the above equations 1 to 3.

[0133] For example, the firing process may involve a heating rate of 1 to 20°C / min, preferably 1 to 10°C / min, and more preferably 2 to 7°C / min, which has the advantage of being able to fully achieve the desired firing effect within this range.

[0134] The firing process can, for example, be carried out at the firing temperature for 1 to 24 hours, preferably 1 to 16 hours, and more preferably 3 to 16 hours. Within this range, the desired firing effect can be fully achieved.

[0135] The reducing atmosphere may, for example, be an argon (Ar) or nitrogen (N2) atmosphere. In a preferred example, the reducing atmosphere may have a nitrogen purity of 80% or more, preferably 90% or more, more preferably 90-99.8%, and even more preferably 95-99.8%. In this case, there is the advantage that oxidation of the coating agent is prevented during the firing process, and a coating layer is stably formed on the surface of the positive electrode active material.

[0136] The purity percentage of the nitrogen may be expressed as volume percentage or mol%.

[0137] The purity of nitrogen described herein is not particularly limited when measured by a measurement method commonly used in the art to which this invention pertains.

[0138] The coating layer may, for example, be 0.1 to 15% by weight, preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, even more preferably 0.7 to 3% by weight, and even 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, there is the advantage that the desired coating effect can be fully achieved.

[0139] The amount of the coating layer can be measured by methods commonly used in the art to which the present invention pertains. Specifically, it can be measured by quantitative analysis using thermogravimetric analysis (TGA) or a carbon / sulfur detector (CS analyzer).

[0140] The thickness of the coating layer can be appropriately controlled according to the desired coating amount. In this description, the thickness of the coating layer can be measured by methods commonly used in the art to which the present invention belongs. For example, it can be determined by measuring the major axes of 5 to 100 positive electrode active material particles observed using a transmission electron microscope (TEM) or scanning electron microscope (SEM), and then taking the arithmetic mean of these measurements.

[0141] The coating step may, for example, include a step of pre-milling (pre-firing milling step) after mixing the desorbed positive electrode active material with the coating agent and before spray drying. In this case, by adjusting the particle size within a predetermined range before introducing the coated positive electrode active material into the subsequent regeneration process, the particle size and particle size distribution of the ultimately obtained regenerated positive electrode active material are uniformly controlled, which has the advantage of controlling the particles to a state favorable for restoring the crystal structure of the positive electrode active material in subsequent steps, and significantly improving the battery characteristics.

[0142] The aforementioned pre-firing milling (preliminary milling) can be performed using, for example, a ball mill, a high-energy ball mill, a vibrating mill, or a roll mill. Preferably, a ball mill can be used, which has the advantage of easily controlling the particle size distribution of the positive electrode active material and the average particle size of the regenerated positive electrode active material obtained, and is advantageous for restoring the crystal structure of the positive electrode active material in subsequent steps.

[0143] The aforementioned pre-firing milling (preliminary milling) can, for example, be performed using a ball mill for 5 to 24 hours, preferably 5 to 20 hours, more preferably 5 to 16 hours, even more preferably 5 to 13 hours, even more preferably 6 to 12 hours, and particularly preferably 8 to 10 hours. Within this range, there is the advantage of suppressing the generation of fine powder and smoothly controlling the particle size distribution of the positive electrode active material within a narrow range.

[0144] The aforementioned pre-firing milling (preliminary milling) can be performed, for example, under conditions of 100-500 rpm, preferably 150-450 rpm, more preferably 180-420 rpm, even more preferably 190-410 rpm, even more preferably 200-400 rpm, and especially more preferably 250-320 rpm. In this case, there is the advantage that the generation of fine powder is suppressed, the crystalline structure of the positive electrode active material is maintained, and the desired effect can be fully expressed.

[0145] The average particle size (D) of the positive electrode active material powder obtained after the pre-sintering milling. 50 The particle size may be 0.3 to 0.7 μm, preferably 0.3 to 0.65 μm, more preferably 0.35 to 0.65 μm, even more preferably 0.4 to 0.6 μm, and even more preferably 0.45 to 0.55 μm. In this case, there is an advantage in suppressing the generation of fine particles and maintaining the crystalline structure of the positive electrode active material while controlling the particle size of the regenerated positive electrode active material obtained to within the desired range.

[0146] Milling step In the present invention, the method for regenerating positive electrode active material may include a step of milling the calcined positive electrode active material (post-calcination milling step). In this case, aggregation, particle cracking, and the generation of fine powder are prevented in the ultimately obtained regenerated positive electrode active material, and the particle size distribution is controlled to a narrow range, which has the advantage of enabling the production of the positive electrode active material as a single particle. Therefore, the deterioration of battery performance due to fine powder is prevented, and the thermal stability and life characteristics of the battery are further improved. Furthermore, when the regenerated positive electrode active material is ultimately applied to the positive electrode of a secondary battery, it has the advantage of providing battery characteristics that are at or above the level of fresh positive electrode active material.

[0147] The milling (post-sintering milling) may preferably be performed by a jet mill. In this case, damage to the crystal structure of the positive electrode active material can be prevented, while precisely controlling the particle size and particle distribution of the regenerated positive electrode active material obtained within a narrow range. Furthermore, the inflow of foreign matter that may occur during the milling process is prevented, which has the advantage of improving the purity of the regenerated positive electrode active material.

[0148] The jet mill can, for example, be performed using an inert gas that does not react with the regenerated positive electrode active material, at a temperature of -30°C to 30°C, preferably -20°C to 20°C, and a pressure of 0.8 to 10 bar. More specifically, it can be performed under conditions where the pressure of the feeding line is 2 to 8 bar, preferably 2.5 to 6 bar, more preferably 3 to 5 bar, and the pressure of the grinding line is 0.8 to 2 bar, preferably 0.9 to 1.5 bar, more preferably 1 to 1.3 bar. Within this range, there is an advantage in preventing damage to the crystal structure of the positive electrode active material and precisely controlling the particle size and particle distribution of the ultimately obtained regenerated positive electrode active material within a narrow range. The inert gas may, for example, be argon (Ar) or nitrogen (N2).

[0149] The average particle size (D) of the regenerated cathode active material finally recovered in the milling step. 50 The particle size may be, for example, 0.6 to 3.0 μm, preferably 0.7 to 2.0 μm, more preferably 0.8 to 1.5 μm, even more preferably 0.9 to 1.2 μm, and even more preferably 0.955 to 1.255 μm, in which case there is the advantage that excellent battery characteristics are exhibited.

[0150] In this description, the average particle size (D) of the positive electrode active material 50 The measurement method is not particularly limited as long as it is a measurement method commonly used in the art to which the present invention belongs, and as an example, it may be the average particle size on a 50% cumulative basis of the particle size distribution measured using laser diffraction.

[0151] The olivine-structured compound of the regenerated positive electrode active material recovered in the milling step may, for example, be a compound represented by the following chemical formula 1, and more preferably, it may contain olivine-structured LiFePO4, in which case it has the effect of having excellent electrochemical performance, resistance characteristics and capacitance characteristics.

[0152] (chemical formula 1) Li 1+a Fe 1-b M b (PO 4-c )X c (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

[0153] The regenerated positive electrode active material recovered in the milling step may, for example, have a crystal size of 120 to 180 nm as measured by XRD (X-Ray Diffraction), preferably 125 to 170 nm, more preferably 130 to 167 nm, even more preferably 140 to 166 nm, and even more preferably 150 to 165 nm. In this case, the structure of the positive electrode active material is restored to that of fresh positive electrode active material, which has the advantage of providing good battery characteristics.

[0154] The present invention provides a regeneration method for positive electrode active material that, as described above, involves desorbing and recovering the positive electrode active material from a waste positive electrode with high purity through a heat treatment step, then pre-milling and coating the recovered positive electrode active material with a coating agent, and finally milling the coated positive electrode active material. This regeneration process provides battery characteristics equivalent to those of a secondary battery manufactured with fresh positive electrode active material. Therefore, it has the advantage that regenerated positive electrode active material can replace secondary batteries manufactured with fresh positive electrode active material.

[0155] Furthermore, since the positive electrode active material can be regenerated from the waste positive electrode without decomposing it into its individual elements, and all of the metallic elements of the positive electrode active material can be regenerated without wasting any, and since there is no need to replenish lithium, iron, or phosphorus during the regeneration process of the positive electrode active material, economic efficiency and productivity can be greatly improved.

[0156] On the other hand, in the present invention, when evaluating the quality (surface quality) of the carbon coating layer of the positive electrode active material, a positive electrode active material having an olivine structure compound coated with a coating agent is manufactured, the total amount of carbon in the positive electrode active material is measured using carbon content analysis equipment, and the area ratio is obtained from the Raman peak obtained by analyzing the positive electrode active material using a Raman spectrum. LFP The Area Ratio is calculated. LFP This is obtained by dividing the intensity of the Raman peak corresponding to the olivine structure compound by the intensity of all Raman peaks appearing in the Raman spectrum. The total amount of carbon and the area ratio are measured in advance.LFP Calculate the product of the two factors and check if it satisfies all of the following equations 1 to 3. In such cases, there is the advantage that the quality of the carbon coating of the positive electrode active material can be easily measured.

[0157] [Formula 1] 0 < Carbon content × Area Ratio LFP ≤5

[0158] [Formula 2] 0.45 ≤ 1 / Area Ratio LFP ≤1

[0159] [Formula 3] 1.3 ≤ Carbon content ≤ 1.5 (Here, the carbon content is the total amount of carbon (weight %) measured with carbon content analysis equipment, and the Area Ratio LFP This corresponds to the intensity of the Raman peak corresponding to the olivine structure compound, out of all the Raman peaks that appear in the Raman spectrum.

[0160] The carbon content refers to the total weight of carbon material that contributes to the conductivity of the positive electrode active material. For example, the carbon content (weight %) contained within the positive electrode active material layer can be analyzed using a CS analyzer (Bruker, G-4 ICARUS series II). Specifically, it can be calculated from the total amount of CO2 generated by burning the positive electrode active material layer using a CS Analyzer.

[0161] The method for measuring the carbon coating quality of a positive electrode active material according to the present invention may encompass all of the above-described contents of the positive electrode active material and the secondary battery containing it. Therefore, redundant descriptions thereof are omitted here.

[0162] Furthermore, in order to easily communicate the method for measuring the carbon coating quality of the positive electrode active material of the present invention to ordinary technicians, only the absolutely necessary conditions and equipment are described, and other obvious auxiliary conditions and equipment are omitted.

[0163] secondary battery The secondary battery of the present invention has the advantages of having an increased carbon coating area due to the inclusion of the positive electrode active material, preventing degradation of battery performance, exhibiting excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging, resulting in superior electrochemical performance, resistance characteristics, and capacitance characteristics.

[0164] The secondary battery of the present invention may include all of the above-described positive electrode active material and its regeneration method. Therefore, redundant descriptions thereof are omitted here.

[0165] The method for manufacturing a secondary battery according to the present invention is not particularly limited if it is a method for manufacturing a lithium secondary battery commonly used in the art to which the present invention belongs.

[0166] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such changes and modifications fall within the scope of the appended claims.

[0167] [Examples] Example 1 As waste positive electrode material, which consists of an aluminum current collector coated with a positive electrode active material layer containing an olivine-structured LFP, binder, and conductive material, positive electrode scrap remaining after punching out positive electrode plates was prepared and crushed into 2cm x 2cm pieces.

[0168] Subsequently, the material was heated in a furnace under an air atmosphere at a heating rate of 5°C / min, and a heat treatment process was carried out at 580°C for 30 minutes. During 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.

[0169] After the heat treatment, the heat supply was stopped and the material was cooled to room temperature. Then, a coating agent composition, prepared by mixing sucrose with deionized water so that the carbon content was 4.4 parts by weight per 100 parts by weight of the positive electrode active material, was applied to the surface of the positive electrode active material powder. After that, the powder was pre-milled (pre-sintering milling) using a ball mill at 300 rpm for 10 hours, and then spray-dried. The average particle size (D) of the dried positive electrode active material powder was determined. 50 The thickness was 0.5 μm.

[0170] The dried positive electrode active material was heated in a furnace at a rate of 3°C / min while supplying nitrogen at 3 L / min, and fired at 800°C for 10 hours to form a carbon (C) coating layer on the surface of the positive electrode active material. After the firing was completed, CS analysis revealed that the coating amount was 1.43% by weight.

[0171] The coated positive electrode active material is milled (post-sintering milling) using a jet mill under an air atmosphere with a feeding line pressure of 4 bar and a grinding line pressure of 1 bar, until the particle size is D 40 0.885 μm, D 50 1.055 μm, D 60 A regenerated cathode active material with a thickness of 1.417 μm was obtained.

[0173] Comparative Example 1 The waste cathode scrap used in Example 1 was subjected to the following wet recycling process to produce a recycled cathode active material.

[0174] The aforementioned waste cathode scrap was treated with sulfuric acid to produce a lithium sulfate solution, after which the pH was adjusted to remove impurities, and then lithium carbonate was produced by carbonation.

[0175] Furthermore, the residue (iron and phosphorus residue) that remained undissolved during the sulfuric acid treatment was dissolved in an acidic solution to produce iron phosphate.

[0176] The manufactured lithium carbonate and iron phosphate were synthesized to obtain the positive electrode active material.

[0177] Comparative Example 2 Instead of using recycled cathode active material, we prepared a fresh LFP cathode active material. Analysis of the fresh LFP cathode active material by ICP confirmed that it was a LiFePO4 cathode active material with elemental ratios of Li / Fe:1.06, Li / P:1.00, and P / Fe:1.06.

[0178] Comparative Example 3 Regenerated cathode active material was produced in the same manner as in Example 1, except that instead of using the coating agent composition used in the coating step of Example 1, sucrose was mixed alone as a solid phase mixture so that the carbon content was 4.4 parts by weight per 100 parts by weight of cathode active material, and then the milled cathode active material was heated in a furnace under a nitrogen atmosphere at a heating rate of 3°C / min and fired at 700°C for 10 hours.

[0179] [Example Test I: Raman Spectroscopic Analysis] Raman spectral analysis was performed on the regenerated or newly generated cathode active materials obtained in Example 1 and Comparative Examples 1-3.

[0180] From the intensity of all Raman peaks appearing in the Raman spectral analysis, and the intensity of the Raman peaks corresponding to compounds with an olivine structure, the Area Ratio is calculated. LFP However, it was calculated based on the intensity of the Raman peak corresponding to the olivine structure of the compound, out of the intensities of all Raman peaks appearing in the Raman spectrum. The item in Table 1 below is its reciprocal value, 1 / Area Ratio. LFP This is shown (corresponding to equation 2), and is also shown in Figure 2 below.

[0181] [Test Example II: Analysis of Total Carbon Content] The carbon content of the recycled or newly generated cathode active materials obtained in Example 1 and Comparative Examples 1-3 was measured using carbon content analysis equipment.

[0182] Specifically, the carbon content (by weight) within the positive electrode active material layer was calculated using a CS-analyzer (Bruker, G-4 ICARUS series II) from the total amount of CO2 generated by burning the positive electrode active material layer.

[0183] Specifically, after measuring the calibration curve blank, the standard (Standard, JSS 514-8, carbon 0.2016 wt%) was measured at least three times, and then the sample was placed in a crucible and weighed out 30 mg.

[0184] Next, a combustion aid was added to the crucible containing the sample, positioned on the lower electrode, and the sample was poured in from the top to burn, and the carbon content (by weight) was measured.

[0185] The measurement results are shown in Table 1 and Figure 1 below (corresponding to Equation 3).

[0186] [Table 1]

[0187] As shown in Table 1 and Figure 1 below, in Example 1, it was confirmed that the Raman spectral analysis variables showed a different trend compared to Comparative Examples 1-3. Specifically, the total amount of carbon analyzed in Example 1 was 1.45% by weight, which was almost the same as the total amount of carbon analyzed in Comparative Example 3 (1.46% by weight), but the 1 / Area Ratio obtained from the Raman spectral analysis results... LFP The result of Formula 2, which reflects the items, was 0.72 in the case of Example 1, satisfying the requirement of 0.45 or higher. However, in the case of Comparative Example 3, the value was 0.08, which was found to be far below 0.45.

[0188] On the other hand, when compared to Comparative Example 1, which underwent a wet recycling process commonly performed in the art to which the present invention belongs, or Comparative Example 2, which was a fresh cathode active material, the value for Example 1 according to the present invention was 0.72, satisfying the requirement of 0.45 or higher, whereas the value for Comparative Example 1 was 0.13, and for Comparative Example 2 it was 0.16, both still far below 0.45.

[0189] [Test Example III: Selection of Measurement Indicators for Carbon Coating Quality] 1 / Area Ratio from Table 1 above LFP From the items (Formula 2) and the total amount of carbon (Formula 3), calculate Formula 1 below, and multiply the carbon content in Table 2 below by the Area Ratio. LFP This was shown in the section.

[0190] [Formula 1] Carbon content × Area Ratio LFP

[0191] [Table 2]

[0192] As shown in Table 2 above, the results calculated using Equation 1 tended not to match the total amount of carbon calculated using Equation 3, and it was confirmed that by adding the results of Raman spectral analysis, it can be used as an indicator to more accurately evaluate the quality of carbon coatings. Specifically, the total amount of carbon analyzed in Example 1 was 1.45 wt%, which was almost the same as the total amount of carbon analyzed in Comparative Example 3, which was 1.46 wt%, but the 1 / Area Ratio obtained from the Raman spectral analysis results LFP The result of Formula 1, which reflects the items, was 2.01 in the case of Example 1, satisfying the condition of being 5 or less. However, in the case of Comparative Example 3, the value was 18.25, which was confirmed to be far greater than 5.

[0193] In fact, when compared to Comparative Example 1, which underwent a wet recycling process commonly performed in the art to which the present invention belongs, or Comparative Example 2, which was a fresh cathode active material, the value for Example 1 according to the present invention was 2.01, satisfying the condition of 5 or less. However, in the case of Comparative Example 1, the value was 10.38, and in the case of Comparative Example 2, it was 8.81, both still far exceeding 5.

[0194] In particular, in Comparative Example 3, where the firing temperature conditions were different, the value was 18.25, which is still far above 5. This suggests that the firing temperature conditions significantly affect the parameter in Equation 1.

[0195] In addition, the above embodiment 1、 The electrochemical performance of the regenerated or newly generated cathode active materials obtained in Comparative Examples 1 to 3 was measured through evaluation of the CHC cell as described below.

[0196] [Test Example IV: Evaluation of CHC Cells] The electrochemical performance of the regenerated or newly generated cathode active materials obtained in Example 1 and Comparative Examples 1-3 was measured through evaluation using a CHC cell as described below. *Evaluation of CHC cells: 97.5% by weight of recycled positive electrode active material, 1% by weight of carbon black as a conductive material, and 1.5% by weight of PVdF as a binder were weighed and mixed with LFP to produce a slurry. After coating aluminum foil with this slurry to produce a positive electrode, a cell (Coin Half Cell, CHC) was manufactured. Under conditions of a voltage of 2.5~3.7V, with charging and discharging proceeding at 0.1C / 0.1C, and with an electrolyte of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (by weight ratio) and other additives, the electrochemical performance (charging capacity, discharging capacity, and efficiency) was evaluated, and the results are shown in Table 3 and Figure 3 below.

[0197] [Table 3]

[0198] Table 3 and Figure 3 below show the results of coin cell evaluation performed on each of the regenerated or newly generated cathode active materials obtained in Example 1 and Comparative Examples 1 to 3. As shown in Table 3 and Figure 3 below, it was confirmed that the regenerated cathode active material according to the present invention (Example 1) has superior charging capacity compared to Comparative Examples 1 to 3.

[0199] *Measurement of capacity retention rate at high temperature (45°C): Each monocell manufactured from the regenerated or newly generated positive electrode active material obtained in Example 1 and Comparative Examples 1-3 was formed at a rate of 0.1C, and then the gas inside the battery was removed (degassing process). Subsequently, CC / CV charging at 4.2V, 1C, and 0.05C cut-offs, and CC discharge at 2.5V, 0.5C were performed 200 times each at high temperature (45°C). The discharge capacity after one cycle and the discharge capacity after 200 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A), and the discharge capacity after one cycle was set as the initial capacity. Then, the discharge capacity after 200 cycles was compared with the initial capacity (100%), and the capacity retention rate was calculated using the following formula 4.

[0200] [Equation 4] Capacity retention rate (%) = (Discharge capacity after high-temperature cycle / Initial discharge capacity) × 100

[0201] The measurement results showed that as the number of cycles increased, the example 1 The recycled cathode active material was found to have a higher capacity retention rate compared to Comparative Examples 1-3.

[0202] *Measurement of resistance increase rate at high temperature (45°C): Each monocell manufactured from the regenerated or newly generated positive electrode active material obtained in Example 1 and Comparative Examples 1-3 was formed at a rate of 0.1C, and then the gas inside the battery was removed (degassing process). After the gas removed lithium secondary battery was transferred to a charger / discharger at room temperature (25°C), it was charged to 4.2V at a rate of 0.33C under constant current / constant voltage conditions and 0.05C cutoff charging, and then discharged at 0.33C 2.5V. Based on the discharge capacity after three charge / discharge cycles, the State of Charge (SOC) was adjusted to 50%. At this time, the DC internal resistance was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop that appeared when a discharge pulse was applied at 2.5C for 10 seconds, and this resistance was set as the initial resistance.

[0203] Subsequently, CC / CV charging was performed 200 times each at high temperature (45°C) with cutoffs of 4.2V, 1C, and 0.05C, and CC discharge was performed at 2.5V, 0.5C. After that, the lithium secondary battery was transferred to a room temperature (25°C) charge / discharge unit. Then, after adjusting the SOC (State of Charge) to 50%, the DC internal resistance was measured using a PNE-0506 charge / discharge unit (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop observed when a discharge pulse (2.5C) was applied for 10 seconds. This was compared to the initial resistance (0%), and the resistance increase rate (%) was calculated using formula 5 below.

[0204] [Formula 5] Resistance increase rate (%) = {(Resistance after high-temperature cycle - Initial resistance) / Initial resistance} × 100

[0205] The measurement results showed that as the number of cycles increased, the example 1 The recycled cathode active material was found to have a higher resistance increase rate compared to Comparative Examples 1-3.

Claims

1. A positive electrode active material having a carbon coating layer and a compound with an olivine structure, The positive electrode active material is a single particle and is characterized by satisfying the following formulas 1, 2, and 3. [Formula 1] 0 < Carbon content × Area Ratio ＬＦＰ ≤ 5 [Formula 2] 0.45≦1 / Area Ratio ＬＦＰ ≦1 [Equation 3] 1.3 ≤ carbon content ≤ 1.5 (Here, the carbon content is the total amount of carbon (weight %) measured with carbon content analysis equipment, and Area Ratio ＬＦＰ This corresponds to the intensity of the Raman peak (a.u.) that corresponds to the Raman peak corresponding to the olivine structure compound, out of all the Raman peaks (a.u.) that appear in the Raman spectrum.

2. The positive electrode active material according to claim 1, characterized in that the positive electrode active material is a regenerated positive electrode active material.

3. The positive electrode active material according to claim 1, characterized in that the compound with the olivine structure is represented by the following chemical formula 1. (Chemical formula 1) Li １＋ａ Fe １－ｂ M ｂ (PO ４－ｃ )X ｃ (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N; and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

4. The positive electrode active material according to claim 3, characterized in that the positive electrode active material having the olivine structure compound contains lithium iron phosphate.

5. A method for regenerating a positive electrode active material according to Claim 1, 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 onto a current collector, to detach the positive electrode active material from the current collector, The steps include: carbon coating the surface of the desorbed positive electrode active material, The process includes the step of milling the coated positive electrode active material to regenerate the positive electrode active material, The desorption step is performed by raising the temperature at a rate of 1 to 10°C / min, and then continuing for 10 minutes to 5 hours after reaching the heat treatment temperature. The carbon coating step includes applying a carbon coating agent to the detached positive electrode active material, pre-milling it, spray-drying it, and firing the spray-dried positive electrode active material at 750 to 1200°C in a reducing atmosphere. A method for regenerating a positive electrode active material, characterized in that the preliminary milling is performed using a ball mill, a high-energy ball mill, a vibratory mill, or a roll mill.

6. The method for regenerating a positive electrode active material according to claim 5, characterized in that the desorption step is performed by heating at a temperature of 300 to 650°C under an oxidizing atmosphere.

7. The method for regenerating a positive electrode active material according to claim 5, characterized in that the carbon coating agent comprises one or more of sucrose, glucose, fructose, graphite, and polyvinylidene fluoride.

8. The method for regenerating a positive electrode active material according to claim 5, characterized in that the carbon coating step is performed for 1 to 24 hours.

9. The method for regenerating a positive electrode active material according to claim 5, characterized in that the milling step is performed using a jet mill.

10. The method for regenerating a positive electrode active material according to claim 5, characterized in that the olivine structure 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 (In the above chemical formula 1, M comprises 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 comprises one or more elements selected from the group consisting of F, S, and N; and a, b, and c are -0.5 ≤ a ≤ 0.5, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.1, respectively.)

11. A secondary battery characterized by containing the positive electrode active material described in any one of claims 1 to 4.

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