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 the positive electrode active material, and a secondary battery. According to the present invention, there is the effect of providing a positive electrode active material, a method for regenerating the positive electrode active material, a secondary battery, and the like, in which, by detaching and recovering a positive electrode active material from a waste positive electrode, applying a coating agent thereonto, and controlling firing conditions and the like of the positive electrode active material on which the coating agent is applied, a structure similar to the crystal structure of a fresh positive electrode active material can be exhibited while reducing a region where a compound having an olivine structure is mixed in a carbon coating layer on the surface of the positive electrode active material, thus providing satisfactory battery characteristics.

Description

Cathode active material, method for regenerating cathode active material, and secondary battery

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

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0025873, dated February 22, 2024, and Korean Patent Application No. 10-2025-0001944, filed January 7, 2025, which is hereby incorporated by reference in its entirety.

[0003] The present invention relates to a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery, and more particularly, to a positive electrode active material, a method for regenerating a positive electrode active material, and a secondary battery, which exhibit a structure similar to the crystal structure of a fresh positive electrode active material while reducing the area where an olivine structure compound is mixed in a carbon coating layer on the surface of the positive electrode active material by removing and recovering a positive electrode active material from a spent positive electrode, applying a coating agent, and controlling the sintering conditions of the positive electrode active material to which the coating agent has been applied, thereby providing good battery characteristics.

[0004] Demand for lithium secondary batteries has steadily increased since the 1990s alongside the portable electronic device market, and has recently surged further worldwide due to the rapid growth of the electric vehicle market. This could lead to instability in the lithium resource supply and demand in the near future, and the continuous accumulation of spent batteries at the end of their useful life could also pose significant environmental problems. To address these issues, recycling spent lithium secondary batteries is a critical technological challenge.

[0005] Lithium secondary batteries are largely composed of a cathode in which a cathode active material layer is coated on a metal foil such as aluminum, a cathode in which a cathode active material layer is coated on a metal foil such as copper, a separator that prevents the cathode and anode from mixing with each other, and an electrolyte that allows lithium ions to move between the cathode and anode. The cathode is manufactured by applying a cathode composition including a cathode active material, a binder, a conductive agent, and a solvent to a current collector made of a metal foil such as aluminum, drying the composition, and then pressurizing and molding the resulting composition.

[0006] The cathode accounts for more than 60% of the cost of a lithium secondary battery, and the active materials of these cathodes include lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), and lithium iron phosphate (LiFePO4). Among these, lithium iron phosphate is increasingly being used in large-capacity lithium secondary batteries for electric vehicles due to its low unit price and supply stability. Accordingly, much research is being conducted on recycling processing technologies that selectively recover valuable metals from the cathodes of lithium secondary batteries that are discarded after use or cathode scrap generated in the lithium secondary battery manufacturing process (hereinafter referred to as “waste cathodes”), or to directly recover cathode active materials.

[0007] However, due to the nature of the regenerative cathode active material, the particle size distribution is uneven and the crystal structure is not stable, so fine powder is easily generated due to particle breakage during the electrode manufacturing process, and thermal stability is poor, so there is a problem that battery performance, such as life characteristics, deteriorates in a high-voltage environment.

[0008] Therefore, there is a need to develop a technology to regenerate positive electrode active materials that can provide good battery characteristics when applied to secondary batteries.

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] Japanese Patent Publication No. 2024-503575

[0012] In order to solve the problems of the prior art as described above, the present invention provides a positive electrode active material capable of providing good battery characteristics and a secondary battery including the same by removing and recovering a positive electrode active material from a waste positive electrode, applying a coating agent, and controlling the firing conditions of the positive electrode active material to which the coating agent has been applied, thereby exhibiting a structure similar to the crystal structure of a fresh positive electrode active material and reducing the area where an olivine structure compound is mixed in a carbon coating layer on the surface of the positive electrode active material.

[0013] In addition, the present invention aims to provide a cathode active material having excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation during charge and discharge, and a secondary battery including the same.

[0014] The above and other objects of the present invention can all be achieved by the present invention described below.

[0015] In order to achieve the above purpose, the present invention provides a positive electrode active material having a carbon coating layer and an olivine structure compound, wherein the positive electrode active material satisfies the following mathematical expressions 1, 2, and 3.

[0016] [Mathematical Formula 1]

[0017] 0 < Carbon Content x Area RatioLFP ≤ 5

[0018] [Equation 2]

[0019] 0.45 ≤ 1 / Area RatioLFP ≤ 1

[0020] [Equation 3]

[0021] 1.3 ≤ Carbon content ≤ 1.5

[0022] (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, and Area Ratio LFPcorresponds to the intensity of the Raman peak corresponding to the compound of the olivine structure among the intensities of all Raman peaks visible in the Raman spectrum.)

[0023] II) In the above I), the positive electrode active material may be a regenerated positive electrode active material.

[0024] III) In the above I) to II), the positive electrode active material may be a single particle.

[0025] IV) In the above I) to III), the compound of the olivine structure can be represented by the following chemical formula 1.

[0026] [Chemical Formula 1]

[0027]

[0028] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0029] V) In the above I) to IV), the positive electrode active material having the compound of the olivine structure may include lithium iron phosphate.

[0030]

[0031] In addition, the present invention provides a positive electrode active material having a carbon coating layer and an olivine structure compound, VI), wherein the positive electrode active material is characterized by satisfying the following mathematical expressions 1, 2 and / or 3.

[0032] [Mathematical Formula 1]

[0033] 0 < Carbon Content x Area RatioLFP ≤ 5

[0034] [Equation 2]

[0035] 0.45 ≤ 1 / Area RatioLFP ≤ 1

[0036] [Equation 3]

[0037] 1.3 ≤ Carbon content ≤ 1.5

[0038] (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, 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 visible in the Raman spectrum.)

[0039]

[0040] In addition, the present invention includes the steps of VII) heat-treating a waste positive electrode having a positive electrode active material layer including a positive electrode active material having an olivine structure compound applied on 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.

[0041] The present invention provides a method for regenerating a positive electrode active material, characterized in that the coating step includes: a step of applying a coating agent to a detached positive electrode active material, pre-milling, and spray drying; and a step of calcining the spray-dried positive electrode active material at 750 to 1200°C under a reducing atmosphere.

[0042] VIII) In the above VII), the heat treatment can be performed by heating at a temperature of 300 to 650°C in an oxidizing atmosphere.

[0043] IX) In the above VII) to VIII), the heat treatment can be performed at a heating rate of 1 to 10°C / min, and the heat treatment temperature can be reached and performed for 10 minutes to 5 hours.

[0044] X) In the above VII) to IX), the coating agent may be a coating agent containing at least one of a metal, an organometallic, and a carbon component.

[0045] XI) In the above VII) to X), the firing can be performed for 1 to 24 hours.

[0046] XII) In the above VII) to XI), the preliminary milling can be performed using a ball mill, a high energy ball mill, a vibrating mill, or a roll mill.

[0047] XIII) In the above VII) to XII), the milling step can be performed using a jet mill.

[0048] XIV) In the above VII) to XIII), the compound of the olivine structure can be represented by the following chemical formula 1.

[0049] [Chemical Formula 1]

[0050]

[0051] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0052]

[0053] XV) A secondary battery is provided, characterized in that it includes a positive electrode active material according to any one of the above I) to VI).

[0054] According to the present invention, a regenerated positive electrode active material regenerated from a waste positive electrode exhibits a structure similar to the crystal structure of a fresh positive electrode active material, and an area where an olivine structure compound is mixed in a carbon coating layer on the surface of the positive electrode active material is reduced, thereby providing an effect of providing good battery characteristics when applied to a secondary battery.

[0055] In particular, there is an effect of providing a regenerative positive electrode active material having excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation during charge and discharge, and a secondary battery including the same.

[0056] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description given below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be construed as being limited to the matters described in these drawings.

[0057] Figure 1 is a graph showing the 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 the results of Raman spectrum analysis of the regenerated positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3.

[0059] Figure 3 is a graph showing the results of evaluating the CHC capacity retention rate according to the number of cycles at 45°C for secondary batteries using the regenerated positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3.

[0060] The present inventors, while studying a technology for directly regenerating a spent positive electrode containing a positive electrode active material having an olivine structure compound into a positive electrode active material without going through a decomposition process, confirmed that when a coating agent is applied to the positive electrode active material recovered through a desorption process and the sintering conditions of the positive electrode active material are controlled, the crystal structure is restored to the structure of the fresh positive electrode active material and the area where the olivine structure compound is mixed on the carbon coating surface is reduced, and when this is applied to a secondary battery, the battery characteristics, etc. are improved, and based on this, they devoted themselves to further research and completed the present invention.

[0061] In the present invention, the positive electrode active material layer of the positive electrode may include a positive electrode active material, a binder, and a conductive material.

[0062] In this description, “oxidizing atmosphere” may specifically be air, or an atmosphere having an oxygen purity of 10% or more.

[0063] In this description, fresh positive electrode active material means a new positive electrode active material manufactured through new synthesis, rather than being obtained by recovery and regeneration from a spent battery.

[0064]

[0065] Below, the cathode active material of this invention and the secondary battery including the same are described in detail.

[0066] However, the terms or words used in this specification and claims cannot be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own application in the best way. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are only one embodiment of the present invention and do not represent all of the technical idea of ​​the present invention, and it should be understood that there may be various equivalents and modified examples that can replace them, and that they can be arranged, replaced, combined, separated, or designed in various other configurations.

[0067] All technical and scientific terms used in this document, unless otherwise defined, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains.

[0068]

[0069] positive electrode active material

[0070] The present invention includes, for example, a positive electrode active material having an olivine structure compound.

[0071] The compound of the above olivine structure may be, for example, a lithium iron phosphate (LFP) compound, preferably a compound represented by chemical formula 1, and more preferably may include LiFePO4 of an olivine structure, in which case there are excellent effects in terms of electrochemical performance, resistance characteristics, and capacity characteristics.

[0072] [Chemical Formula 1]

[0073]

[0074] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0075]

[0076] The above-mentioned positive electrode active material may have, for example, a surface coated with carbon, and preferably may have 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 chemical and physical changes in the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. In addition, the physicochemical properties are also improved due to the effect of controlling the amount of residual lithium and reducing pH by substituting a different element on the surface of the positive electrode active material.

[0077]

[0078] 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 mathematical formulas 1, 2, and 3, and in this case, excellent battery performance is achieved.

[0079] [Mathematical Formula 1]

[0080] 0 < Carbon Content x Area Ratio LFP ≤ 5

[0081] [Equation 2]

[0082] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0083] [Equation 3]

[0084] 1.3 ≤ Carbon content ≤ 1.5

[0085] (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, 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 visible in the Raman spectrum.)

[0086]

[0087] The above mathematical expression 1 is the variable Area Ratio described later. LFP As a correlation equation between the total amount of carbon and the variable, a smaller calculated value indicates a reduction in the area where olivine structure compounds are mixed in the carbon coating.

[0088] The above mathematical expression 1 may be, for example, greater than 0 and less than or equal to 5, preferably 0.5 to 4, and more preferably 1 to 3. In this case, there is an advantage of improving the coating quality of the carbon surface and thus having excellent electrochemical characteristics.

[0089]

[0090] The above mathematical expression 2 is a variable Area Ratio corresponding to the intensity of the Raman peak corresponding to the compound of the olivine structure among the intensities of all Raman peaks visible in the Raman spectrum. LFP It refers to the reciprocal of the calculated intensity of the Raman peak corresponding to the compound of the olivine structure among the intensities of all Raman peaks visible in the Raman spectrum, and the larger the calculated value, the smaller the area occupied by the compound of the olivine structure.

[0091] For example, Figure 2 is a Raman spectrum analysis graph of the positive electrode active material regenerated in Example 1 and Comparative Examples 1 to 3, and among them, the peak indicated as LFP corresponds to the Raman peak of lithium iron phosphate corresponding to the compound of the above-mentioned olivine structure.

[0092] The above mathematical expression 2 may be, for example, in the range of 0.45 to 1, preferably 0.5 to 0.1, and more preferably 0.6 to 1, and in this case, there is an advantage of improving the coating quality of the carbon surface, thereby providing excellent life characteristics of the battery.

[0093]

[0094] The above mathematical expression 3 is the total carbon amount (weight %) measured by a carbon content analysis device, and may include not only the carbon coating content but also the remaining uncoated carbon content, so it may be difficult to use it alone to measure the carbon coating quality.

[0095] Accordingly, in the present invention, the total amount of carbon is used as a variable to create a correlation equation such as the aforementioned mathematical equation 1, and it is predicted that the larger the value, the greater the area of ​​the carbon coating will be.

[0096] The above mathematical expression 3 may be, for example, in the range of 1.3 to 1.5, preferably 1.33 to 1.5, and more preferably 1.35 to 1.5, and in this case, there is an advantage of improving the coating quality of the carbon surface and thus providing excellent electrochemical characteristics.

[0097]

[0098] In addition, the positive electrode active material may satisfy, for example, mathematical expressions 1 and 2, or mathematical expressions 1 and 3, and preferably, may satisfy mathematical expressions 1 to 3 simultaneously. In this case, there is an advantage of excellent electrochemical properties by significantly improving the coating quality of the carbon surface.

[0099] That is, the present invention can provide a positive electrode active material having a carbon coating layer and an olivine structure compound, wherein the positive electrode active material is characterized by satisfying the following mathematical expressions 1, 2 and / or 3.

[0100] [Mathematical Formula 1]

[0101] 0 < Carbon Content x Area RatioLFP ≤ 5

[0102] [Equation 2]

[0103] 0.45 ≤ 1 / Area RatioLFP ≤ 1

[0104] [Equation 3]

[0105] 1.3 ≤ Carbon content ≤ 1.5

[0106] (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, 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 visible in the Raman spectrum.)

[0107]

[0108] The above positive electrode active material may preferably be a regenerated positive electrode active material, in which case there is an advantage of excellent economic efficiency and productivity.

[0109] The above-described positive electrode active material may preferably be a single particle, and more preferably does not include secondary particles. In this case, there is no particle breakage during the electrode manufacturing process, so there is no deterioration in battery performance due to fine particles, and there is an effect of providing a positive electrode active material having excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation during charge and discharge.

[0110] The single particle may be, for example, a particle composed of 30 or fewer nodules, preferably a particle composed of 1 to 20 nodules, more preferably a particle composed of 1 to 10 nodules, even more preferably a particle composed of 1 to 5 nodules, and most preferably a particle composed of 1 nodule. In this case, there is no particle breakage during the electrode manufacturing process, so there is no deterioration in battery performance due to fine powder, and there is an effect of providing a cathode active material having excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation due to charge and discharge.

[0111] In this description, a nodule refers to a particle unit body that constitutes a single particle, and may refer to a single crystal lacking a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM) or an electron backscatter diffraction pattern analyzer (EBSD).

[0112] In this description, the number of nodules means the average number of nodules of positive electrode active material particles, and a positive electrode including positive electrode active material is cut by 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), and then at least 30 particles are selected for each of the largest positive electrode active material particle and the smallest positive electrode active material particle in the cross-sectional image, and then the number of nodules in the cross-section of each positive electrode active material particle is measured through SEM image analysis, and the arithmetic mean is obtained.

[0113] In this description, a secondary particle means a particle that is an aggregate formed by the agglomeration of multiple single particles and contains more than 30 nodules.

[0114]

[0115] The above-mentioned positive electrode active material may have a fluorine (F) content of, for example, 1,000 mg / kg or less, preferably 900 mg / kg or less, and more preferably 10 to 800 mg / kg, and within this range, it has the advantage of excellent charging capacity, resistance characteristics, and capacity characteristics along with improved coating quality of the carbon surface.

[0116] In this paper, the fluorine (F) content can be measured using an ICP analyzer, and at this time, it can be measured using a general ICP analyzer widely used in laboratories, but there is no deviation depending on the measuring device or method.

[0117]

[0118] The above positive electrode active material may have, for example, an average crystal size of 50 to 500 nm, preferably 50 to 300 nm, and more preferably 50 to 200 nm, and within this range, as the crystal size decreases, there is an advantage of increasing conductivity and improving capacity.

[0119] In this paper, the average crystal size can be measured by XRD crystal analysis, and there is no deviation depending on the measuring device or method. Specifically, it can be obtained by placing 5 g of positive electrode active material particles in a holder, irradiating the particles with X-rays, and analyzing the resulting diffraction grating. The method for obtaining the size is from the half-width of the main peak or three or more peaks, and this can be considered to correspond to the average crystal size of the primary particles of the positive electrode active material particles.

[0120]

[0121] The above-mentioned positive electrode active material has, for example, a small amount of LiOH remaining on the surface, or preferably, no LiOH content detected. In this case, the coating quality of the carbon surface is improved, and thus there is an advantage of excellent charging capacity, resistance characteristics, and capacity characteristics.

[0122] The above-mentioned positive electrode active material may have a Li2CO3 content remaining on the surface of, for example, 0.51 wt% or less, preferably 0.50 wt% or less, more preferably 0.01 to 0.50 wt%, and within this range, the coating quality of the carbon surface is improved, thereby providing the advantage of excellent charging capacity, resistance characteristics, and capacity characteristics.

[0123] In this paper, 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). Specifically, 5 g of the positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, filtered to remove the active material, and the resulting solution (filtrate) is titrated with a 0.1 M HCl solution while measuring the change in pH value to obtain a pH titration curve. The residual amount of LiOH and residual amount of Li2CO3 in the positive electrode active material are calculated using the pH titration curve obtained above.

[0124]

[0125] Method for regenerating positive electrode active material

[0126] The method for regenerating a positive electrode active material of the present invention comprises the steps of: heat-treating a waste positive electrode having a positive electrode active material layer including a positive electrode active material having an olivine structure compound applied to a current collector, thereby detaching the positive electrode active material from the current collector; applying a coating agent to the detached positive electrode active material, pre-milling the same, and spray-drying the same; and calcining the spray-dried positive electrode active material at 750 to 1200°C in a reducing atmosphere. In this case, the crystal structure is restored to the structure of a fresh positive electrode active material, so that when this is applied as a positive electrode active material of a battery, good battery characteristics can be provided, and the positive electrode active material can be regenerated as is without decomposing in a simple and environmentally friendly manner, thereby greatly improving economic efficiency and productivity.

[0127]

[0128] The method for regenerating the positive electrode active material of the present invention can recover the regenerated positive electrode active material by sequentially performing preliminary milling, calcination, and milling 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'.

[0129]

[0130] Below, the method for regenerating the positive electrode active material is described in detail step by step.

[0131]

[0132] Tali stage

[0133] In the present invention, a method for regenerating a positive electrode active material includes a step of heat-treating a waste positive electrode on which a positive electrode active material layer including a positive electrode active material having an olivine structure compound is applied on a current collector, and in this case, there is an advantage in that the purity of the recovered positive electrode active material is improved.

[0134]

[0135] The above-mentioned waste positive electrode may preferably be a positive electrode separated from a secondary battery discarded after use, or a positive electrode sheet or positive electrode scrap discarded after defects or cutting occurring in the secondary battery manufacturing process. For example, in the case of positive electrode scrap occurring in the manufacturing process, there is an advantage in that better battery characteristics can be realized because there is no loss of lithium ions in the positive electrode active material.

[0136] The above secondary battery may preferably be a lithium secondary battery.

[0137] If necessary, the above-mentioned positive electrode can be used after undergoing a crushing process.

[0138] The above shredding is not limited to a commonly used physical shredding method, and the shredding size is not limited thereto, but for example, it can be shredded to a size of about 2 cm x 2 cm (width x length).

[0139]

[0140] The olivine structure in this paper is a type of crystal structure with a 3D hexahedral lattice structure, and since PO (phosphorus-oxygen) is strongly bonded, the structure can be maintained even when all lithium ions are lost, so there is little performance degradation due to charge and discharge, and it is a structure with excellent thermal stability. Therefore, it has the disadvantage of having a lower energy density than other positive electrode active materials and low electrical conductivity and lithium ion diffusion, but it has great economic advantages because it uses inexpensive iron instead of expensive cobalt.

[0141] The above olivine structure can be confirmed by a method generally practiced in the technical field to which the present invention belongs, and as a specific example, can be confirmed through X-ray diffraction analysis (XRD).

[0142]

[0143] The compound of the above olivine structure may be, for example, a compound represented by the following chemical formula 1, and in this case, it has the advantages of excellent high-temperature stability and lifespan characteristics and excellent economic efficiency.

[0144] [Chemical Formula 1]

[0145]

[0146] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0147] The compound of the above olivine structure may preferably include LiFePO4 of the olivine structure, in which case it has the advantages of excellent high-temperature stability and lifespan characteristics and excellent economic efficiency.

[0148]

[0149] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, CNT, or a mixture thereof.

[0150] 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.

[0151] The positive electrode active material layer of the above-mentioned positive electrode can be manufactured by including, for example, a solvent, and the solvent can be a solvent generally used in the technical field to which the present invention pertains for mixing the positive electrode active material, binder, and / or conductive agent. The solvent can be, for example, at least one selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0152] The positive electrode active material layer of the above-mentioned positive electrode may further include, for example, a dispersant.

[0153] The above dispersant is, for example, a cellulose compound, polyalkylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosan, 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, an acrylate-styrene-acrylonitrile (ASA) copolymer, a mixture of an acrylate-styrene-acrylonitrile (ASA) copolymer and propylene carbonate, It may be at least one selected from the group consisting of styrene-acrylonitrile (SAN) copolymers and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymers.

[0154]

[0155] The above heat treatment step can be carried out, for example, by heating at a temperature of 300 to 650°C in an oxidizing atmosphere, preferably at 400 to 650°C, more preferably at 500 to 600°C. In this case, foreign substances such as binders and conductive agents included in the positive electrode active material of the waste positive electrode are removed, and the positive electrode active material precursor can be recovered, which can be simply referred to as a 'desorption process'.

[0156]

[0157] 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 finally regenerated through the positive electrode active material surface coating step described below, and refers to a material capable of providing a regenerated positive electrode active material through a predetermined positive electrode active material coating process.

[0158] The above-mentioned detachment step can be carried out without particular limitation if it is a method commonly practiced in the technical field to which the present invention belongs, and the heating rate and heating time can be appropriately adjusted as needed, and accordingly, the residual amount of metal introduced from the current collector is greatly reduced without a separate pretreatment process for separating or removing the current collector, thereby improving the purity of the positive electrode active material and simplifying the process.

[0159] The cathode active material in the waste positive electrode may be coated with a coating agent containing, for example, metal and / or carbon. In the secondary battery field, the cathode active material may often be coated with a coating agent containing various metals and / or carbon for the purpose of improving battery performance. However, in the process of recovering the cathode active material from the waste positive electrode, the structure of this coating layer is destroyed, and if it is reused in a battery without being removed, it may cause a decline in battery performance. Therefore, if the cathode active material in the waste positive electrode is coated, it is advantageous to remove it. In the heat treatment step, the carbon coating on the surface of the cathode active material can be removed. In this case, the purity of the recovered cathode active material is improved and there is an advantage of preventing a decline in battery performance.

[0160]

[0161] The above-mentioned detachment step can be carried out, for example, in an oxidizing atmosphere including air or oxygen, in which case, foreign substances such as metals introduced from the binder, conductive material, and current collector are smoothly removed, so that the desired positive electrode active material can be recovered with high purity and high efficiency.

[0162] The above oxidizing atmosphere may have an oxygen purity of, for example, 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, and still more preferably 90 to 99%, and within this range, there is an advantage in that the desired positive electrode active material can be recovered with high purity and high efficiency.

[0163] The purity % of the above oxygen may be volume % or mol %.

[0164] The purity of the oxygen of this invention is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0165] The heating rate until the above heat treatment temperature is reached may be, for example, 1 to 10°C / min, preferably 2 to 9°C / min, and more preferably 3 to 7°C / min, and within this range, there is an advantage in that the desired positive electrode active material can be recovered with high purity and high efficiency.

[0166] The heat treatment time within the above 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, and within this range, there is an advantage in that the desired positive electrode active material can be recovered with high purity and high efficiency.

[0167] In this description, the heat treatment time refers to the time spent at the corresponding heat treatment temperature, and the time spent reaching the corresponding heat treatment temperature is not counted.

[0168]

[0169] In the above heat treatment step, for example, the positive electrode active material layer of the positive electrode can be separated from the current collector.

[0170] In the above heat treatment step, for example, after the heat treatment is completed, foreign substances can be removed from the waste positive electrode, and a high-purity positive electrode active material precursor powder can be obtained. Accordingly, the "positive electrode active material recovered in the above heat treatment step" can refer to such positive electrode active material precursor.

[0171] The recovered cathode active material precursor after completion of the above-described desorption step may preferably be composed of components capable of providing an LFP cathode active material, and may include, for example, Fe2O3 and Li3Fe2(PO4)3. In this case, a high-purity regenerated LFP cathode active material with significantly reduced residual metal-based foreign substances such as aluminum and carbon-based foreign substances can be provided through subsequent regeneration treatment. The regenerated LFP cathode active material has high purity and can provide good battery characteristics when applied as a cathode active material of a secondary battery.

[0172] After the above-mentioned detachment step is completed, the recovered positive electrode active material precursor may have a content of metal introduced from the current collector remaining therein of, for example, 390 ppm or less, 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, and the lower limit thereof is not particularly limited, but may be 10 ppm or more, or 50 ppm or more, in terms of the balance between the purity and recovery rate of the positive electrode active material and the process efficiency. In this case, there is an advantage in that a high-purity positive electrode active material can be recovered.

[0173] The metal introduced from the above-mentioned collector is not particularly limited as long as it is a metal commonly applied to collectors in the technical field to which the present invention belongs, and a specific example thereof may be aluminum.

[0174] In this description, the measurement of the content of metal elements can be performed without particular limitation in the case of a method commonly performed in the technical field to which the present invention belongs, and as a specific example, the measurement can be performed by ICP (Inductively Coupled Plasma) analysis.

[0175] After the above-mentioned detachment step is completed, the recovered positive electrode active material precursor may have, for example, a carbon element (C) content of 1.0 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less, even more preferably 0.08 wt% or less, and even more preferably 0.06 wt% or less, and the lower limit thereof is not particularly limited, but may be 0.001 wt% or more, or 0.01 wt% or more, in terms of the balance between the purity and recovery rate of the positive electrode active material and the process efficiency. In this case, there is an advantage in that a high-purity positive electrode active material can be recovered.

[0176] In this description, the measurement of the carbon element content can be performed without particular limitation in the case of a method commonly performed in the technical field to which the present invention belongs, and as a specific example, it can be measured by quantitative analysis using a CS analyzer (Carbon / Sulfur Determinator).

[0177]

[0178] Positive electrode active material surface coating step

[0179] In the present invention, the method for regenerating a positive electrode active material includes a step of coating the surface of the positive electrode active material recovered in the heat treatment step, in which case a coating layer is formed on the surface of the particles of the regenerated positive electrode active material, and when applied to a secondary battery, the output characteristics, charge / discharge performance, and life performance of the battery are improved, and thus there is an advantageous advantage in providing good battery characteristics equivalent to those of the case where a fresh positive electrode active material is applied. In addition, since the method exhibits a structure similar to the crystal structure of a fresh positive electrode active material before forming the coating layer, the coating layer can be uniformly formed on the surface of the particles, and the area where an olivine structure compound is mixed in the carbon coating layer on the surface of the positive electrode active material can be reduced, and thus there is an advantage in that the effect of improving battery characteristics is even more excellent.

[0180]

[0181] The above coating can be performed using, for example, a coating agent including at least one of a metal, an organic metal, and a carbon component, and preferably, it can be a carbon coating using a coating agent including a carbon component, in which case there is an advantage of even better battery characteristics.

[0182] The coating agent containing the carbon is not particularly limited as long as it contains a carbon component commonly used as a coating agent in the technical field to which the present invention belongs, and as a specific example, the carbon component may be at least one selected from the group consisting of sugars such as sucrose, glucose, and fructose, graphite, and polyvinylidene fluoride, preferably sugars, and more preferably sucrose. In this case, there is an advantage that the coating is easy and economical, and when applied to a battery, there is an advantage that the effect of improving battery characteristics is excellent.

[0183] The coating agent including the above metal is preferably a coating agent including at least one 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 including at least one selected from the group consisting of B, W, Al, Ti and Mg, and even more preferably a coating agent including boron (B), tungsten (W) or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B), and 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.

[0184] The coating agent containing the metal may include, for example, an oxide or acid containing the metal as an element within the molecule.

[0185] The coating agent containing the above-mentioned organic metal is not particularly limited as long as it is a coating agent containing an organic metal compound commonly used in the technical field to which the present invention belongs and containing the above-mentioned metal, and a specific example of the organic metal may be a metal alkoxide, etc.

[0186]

[0187] The coating agent may have, for example, an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m2 / g for metal, organic metal, and carbon components, and preferably an average diameter of 10 to 100 nm and a specific surface area of ​​5 to 100 m2 / g, and within this range, may be uniformly attached to the surface of the positive electrode active material, and may provide structural stability to the positive electrode active material, thereby improving the problem of low electrical conductivity of the positive electrode active material.

[0188] In the present invention, the average diameter can be measured by a measuring method commonly used in the technical field to which the present invention belongs, and for example, can be measured using a laser diffraction method. Specifically, after dispersing the particles of the positive electrode active material in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and the average particle diameter (D50) based on 50% of the particle diameter distribution in the measuring device can be calculated.

[0189] In this description, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention belongs, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0190]

[0191] The above coating agent may be included in an amount of 1 to 10 wt%, preferably 2 to 8 wt%, and more preferably 3 to 7 wt%, based on the components coated on the surface of the actual positive electrode active material excluding the solvent, and within this range, it has the effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0192]

[0193] The above coating method is not particularly limited as long as it is a coating method commonly used in the technical field to which the present invention pertains, and for example, it can be carried out by injecting the coating agent 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 method in which a liquid coating agent is prepared 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 a coating agent is precipitated onto the surface of the positive electrode active material in an aqueous solution state, a method utilizing the reaction between a gaseous coating agent and the positive electrode active material, or a sputtering method. The coating method may preferably be a spray drying method, in which case the coating is uniformly formed, agglomeration of positive electrode active material particles is prevented, and the coating process is smoothly performed, thereby providing the advantage of excellent productivity.

[0194]

[0195] The above-described positive electrode active material surface coating step may include, as a specific example, a step of applying a coating agent to the positive electrode active material obtained in the above-described heat treatment step, pre-milling, and then 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 coating efficiency is excellent, agglomeration of positive electrode active material particles is prevented, and a coating is evenly formed on the surface of positive electrode active material particles. In addition, an area where an olivine structure compound is mixed in the carbon coating layer is reduced, which is advantageous in improving battery performance.

[0196] The above coating can be achieved, for example, by using a coating solution in which a coating agent including the carbon component is mixed with an appropriate solvent. The solvent is not particularly limited as long as it is a commonly used solvent, and a specific example thereof is an aqueous solvent, more specifically, deionized water. The proportion of solids in the coating solution may be 20 wt% or less, preferably 1 to 15 wt%, and more preferably 2 to 10 wt%, relative to the total weight of the coating solution. In this case, the coating efficiency is excellent, and the subsequent milling process proceeds smoothly, so that the coating layer ultimately formed on the surface of the positive electrode active material particles is advantageously formed uniformly.

[0197] The above coating can be applied in various ways, such as a liquid method in which a liquid coating agent is prepared and mixed with a positive electrode active material, a precipitation method in which a coating agent in an aqueous solution is precipitated onto the surface of a positive electrode active material, etc. However, as shown in Comparative Example 3 described below, it has been confirmed that methods such as a method utilizing 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, or a sputtering method are not suitable for implementing the quality of a carbon coating layer.

[0198] The above spray drying can be performed without particular limitation if it is a spray drying equipment commonly used in the technical field to which the present invention belongs, and for example, an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generating device, or an electrostatic spray drying device can be used, and as a specific example, it can be performed using a PSD-05 (manufactured by Eugene Tech Co., Ltd.) equipment, but is not limited thereto.

[0199] In addition, the spraying pressure, the supply speed of the coating solution, etc. can be appropriately selected considering the amount of coating agent to be coated on the surface of the final regenerated positive electrode active material.

[0200]

[0201] The above-described sintering may be a heat treatment at 750 to 1200°C in a reducing atmosphere on the positive electrode active material to which the coating agent has been applied after the drying, preferably a heat treatment at 750 to 1100°C, more preferably 750 to 1000°C, and even more preferably 750 to 900°C. In this case, there is an advantage in that the coating agent is stably coated on the surface of the positive electrode active material while maintaining the inherent properties of the positive electrode active material. It can be confirmed from Example 1 and Comparative Examples 1 and 3 described below that the conditions of the sintering process and the sintering temperature are variables that implement the mathematical expressions 1 to 3.

[0202] The above-mentioned firing has the advantage that the heating rate until reaching the above-mentioned firing temperature can be, for example, 1 to 20°C / min, preferably 1 to 10°C / min, and more preferably 2 to 7°C / min, and the desired firing effect can be sufficiently expressed within this range.

[0203] The above firing can be performed, for example, at the above firing temperature for 1 to 24 hours, preferably 1 to 16 hours, more preferably 3 to 16 hours, and has the advantage of sufficiently expressing the desired firing effect within this range.

[0204] The reducing atmosphere may be, for example, an argon (Ar) or nitrogen (N2) atmosphere. Preferably, the reducing atmosphere may have a nitrogen purity of 80% or more, preferably 90% or more, more preferably 90 to 99.8%, and even more preferably 95 to 99.8%. In this case, 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.

[0205] The purity % of the above nitrogen can be volume % or mol %.

[0206] The purity of the nitrogen of this invention is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0207]

[0208] The coating layer may be, for example, 0.1 to 15 wt%, preferably 0.2 to 10 wt%, more preferably 0.5 to 5 wt%, even more preferably 0.7 to 3 wt%, and even more preferably 0.8 to 2 wt%, based on the total weight of the regenerated positive electrode active material including the weight of the coating layer, and has the advantage of being able to sufficiently exhibit the desired coating effect within this range.

[0209] The amount of the above coating layer can be measured by a method commonly practiced in the technical field to which the present invention belongs, and as a specific example, can be measured by quantitative analysis using thermogravimetric analysis (TGA) or a CS analyzer (Carbon / Sulfur Determinator).

[0210] The thickness of the coating layer can be appropriately controlled depending on the desired coating amount. In the present disclosure, the thickness of the coating layer can be measured by a method commonly practiced in the technical field to which the present invention pertains, and for example, the major diameter of 5 to 100 positive electrode active material particles observed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM) can be measured and then the arithmetic average can be obtained.

[0211]

[0212] The above coating step may include, for example, a step of pre-milling (pre-sintering milling step) before mixing the separated positive electrode active material and the coating agent and spray drying them, and in this case, by controlling the particle size of the coated positive electrode active material within a predetermined range before inputting it into a subsequent regeneration process, the particle size and particle size distribution of the finally obtained regenerated positive electrode active material are evenly controlled, and the particles are controlled in a state that is advantageous for restoring the crystal structure of the positive electrode active material in the subsequent step, so that the battery characteristics are greatly improved.

[0213]

[0214] The above pre-milling (preliminary milling) can be performed using, for example, a ball mill, a high energy ball mill, a vibrating mill, or a roll mill, and is preferably performed using a ball mill. In this case, it is easy to control the particle size distribution of the positive electrode active material and the average particle size of the finally obtained regenerated positive electrode active material, and there is an advantage in that it is advantageous for restoring the crystal structure of the positive electrode active material in a subsequent step.

[0215]

[0216] The above pre-milling (preliminary milling) can be performed using a ball mill for, for example, 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, and within this range, there is an advantage in that the generation of fine particles can be suppressed and the particle size distribution of the positive electrode active material can be smoothly controlled within a narrow range.

[0217]

[0218] The above pre-milling (preliminary milling) can be performed under conditions of, for example, 100 to 500 rpm, preferably 150 to 450 rpm, more preferably 180 to 420 rpm, even more preferably 190 to 410 rpm, still more preferably 200 to 400 rpm, and particularly more preferably 250 to 320 rpm, and in this case, there is an advantage in that the generation of fine particles is suppressed, the crystal structure of the positive electrode active material is maintained, and the desired effect can be sufficiently expressed.

[0219]

[0220] The average particle size (D) of the positive electrode active material powder obtained after the above pre-milling 50 ) may be 0.3 to 0.7 ㎛, preferably 0.3 to 0.65 ㎛, more preferably 0.35 to 0.65 ㎛, even more preferably 0.4 to 0.6 ㎛, and even more preferably 0.45 to 0.55 ㎛, and in this case, there is an advantageous advantage in that the particle size of the finally obtained regenerated positive electrode active material can be controlled within the desired range while suppressing the generation of fine particles and maintaining the crystal structure of the positive electrode active material.

[0221]

[0222] Milling stage

[0223] In the present invention, the method for regenerating a positive electrode active material may include a step of milling the calcined positive electrode active material (post-calcination milling step), in which case, agglomeration, particle breakage, and generation of fine particles in the finally obtained regenerated positive electrode active material are prevented, and the particle size distribution is controlled to a narrow range, so that the positive electrode active material can be manufactured as a single particle, thereby preventing degradation of battery performance due to fine particles and further improving the thermal stability and life characteristics of the battery. In addition, when the regenerated positive electrode active material is ultimately applied to the positive electrode of a secondary battery, there is an advantage in that it can provide good battery characteristics equivalent to or superior to those of a fresh positive electrode active material.

[0224]

[0225] The above milling (milling after calcination) may preferably be a jet mill, in which case the crystal structure of the positive electrode active material is prevented from being damaged, while the particle size and particle distribution of the final obtained regenerated positive electrode active material can be precisely controlled within a narrow range, and further, the inflow of foreign substances that may occur during the milling process is prevented, thereby improving the purity of the regenerated positive electrode active material.

[0226] The jet mill can be operated, for example, under conditions of a temperature of -30°C to 30°C, preferably -20°C to 20°C, and a pressure of 0.8 to 10 bar using an inert gas that does not react with the regenerated positive electrode active material. More specifically, the jet mill can be operated under conditions of a feeding line pressure of 2 to 8 bar, preferably 2.5 to 6 bar, more preferably 3 to 5 bar, and a grinding line pressure of 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 that damage to the crystal structure of the positive electrode active material is prevented, and the particle size and particle distribution of the final obtained positive electrode active material can be precisely controlled within a narrow range. The inert gas can be, for example, argon (Ar) or nitrogen (N2).

[0227]

[0228] The average particle size (D) of the regenerated positive electrode active material finally recovered in the above milling step 50 ) may be, for example, 0.6 to 3.0 ㎛, preferably 0.7 to 2.0 ㎛, more preferably 0.8 to 1.5 ㎛, even more preferably 0.9 to 1.2 ㎛, and even more preferably 0.955 to 1.255 ㎛, and in this case, there is an advantage in that excellent battery characteristics are exhibited.

[0229] In this paper, the average particle diameter (D) of the positive electrode active material 50 ) is not particularly limited as long as it is a measurement method commonly performed in the technical field to which the present invention belongs, and for example, it may be the average particle diameter based on 50% of the cumulative particle diameter distribution measured using laser diffraction.

[0230]

[0231] The olivine structure compound of the regenerated positive electrode active material recovered in the above milling step may be, for example, a compound represented by the following chemical formula 1, and more preferably, may include LiFePO4 having an olivine structure, in which case the electrochemical performance, resistance characteristics, and capacity characteristics are excellent.

[0232] [Chemical Formula 1]

[0233]

[0234] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.)

[0235]

[0236] The regenerated positive electrode active material recovered in the above milling step may have a crystal size measured by XRD (X-Ray Diffraction) of, for example, 120 to 180 nm, 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 positive electrode active material structure is restored to a fresh positive electrode active material structure, which has the advantage of providing good battery characteristics.

[0237]

[0238] The method for regenerating a positive electrode active material of the present invention comprises a step of removing and recovering a positive electrode active material with high purity from a waste positive electrode through a heat treatment step as described above, a step of coating the recovered positive electrode active material by pre-milling it with a coating agent, and a step of milling the coated positive electrode active material, thereby providing battery characteristics equivalent to those of a secondary battery manufactured with a fresh positive electrode active material, and thereby has the advantage of being able to replace a secondary battery manufactured with a fresh positive electrode active material with a regenerated positive electrode active material.

[0239] In addition, since the cathode active material is regenerated without being decomposed into each element in the waste cathode, all metal elements of the cathode active material can be regenerated from the waste cathode without waste, and since supplementation of lithium, iron, or phosphorus is not required during the regeneration process of the cathode active material, economic feasibility and productivity can be greatly improved.

[0240]

[0241] Meanwhile, in the present invention, the quality (surface quality) of the carbon coating layer of the positive electrode active material is determined by manufacturing a positive electrode active material having an olivine structure compound coated with a coating agent, measuring the total amount of carbon in the positive electrode active material using a carbon content analysis device, and then analyzing the positive electrode active material with a Raman spectrum to obtain the Area Ratio from the obtained Raman peak. LFP Calculate the Area Ratio LFP The intensity of the Raman peak corresponding to the compound of the olivine structure is obtained by dividing it by the intensity of all Raman peaks visible in the Raman spectrum, and the total amount of carbon measured in advance and the Area Ratio LFP It is characterized by obtaining the product of and checking whether all of the following mathematical equations 1 to 3 are satisfied. In this case, there is an advantage in that the carbon coating quality of the positive electrode active material can be easily measured.

[0242] [Mathematical Formula 1]

[0243] 0 < Carbon Content x Area Ratio LFP ≤ 5

[0244] [Equation 2]

[0245] 0.45 ≤ 1 / Area Ratio LFP ≤ 1

[0246] [Equation 3]

[0247] 1.3 ≤ Carbon content ≤ 1.5

[0248] (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, 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 visible in the Raman spectrum.)

[0249]

[0250]

[0251] The above carbon content refers to the total weight of carbon material contributing to the conductive performance of the positive electrode active material, and for example, the carbon content (weight %) contained in the positive electrode active material layer can be analyzed using a CS-analyzer (Bruker, G-4 ICARUS series II), and specifically, can be calculated from the total amount of CO2 generated by burning the positive electrode active material layer using the CS Analyzer.

[0252] The method for measuring the carbon coating quality of the positive electrode active material of the present invention may include all of the contents of the positive electrode active material and the secondary battery containing the same described above. Therefore, redundant description thereof is omitted herein.

[0253] In addition, in order to easily convey the method for measuring the carbon coating quality of the positive electrode active material of the present invention to a person skilled in the art, only the conditions and devices absolutely necessary are described, and other obvious auxiliary conditions and devices are omitted.

[0254]

[0255] secondary battery

[0256] The secondary battery of the present invention has the advantages of including the positive electrode active material, thereby increasing the carbon coating area, preventing degradation of battery performance, excellent life characteristics in a high-voltage environment, high thermal stability, and low gas generation during charge and discharge, and thus has excellent electrochemical performance, resistance characteristics, and capacity characteristics.

[0257] The secondary battery of the present invention may include all of the contents of the positive electrode active material and the regeneration method thereof described above. Therefore, redundant description thereof is omitted herein.

[0258] 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 technical field to which the present invention belongs.

[0259]

[0260] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0261]

[0262] [Example]

[0263] Example 1

[0264] A waste cathode material, in which a cathode active material layer including an olivine-structured LFP, a binder, and a conductive agent is applied on an aluminum current collector, was prepared by crushing the remaining cathode scrap after the cathode plate was pressed into a size of 2 cm x 2 cm.

[0265] Then, a heat treatment process was performed in a furnace under an air atmosphere at a heating rate of 5°C / min and heating at 580°C for 30 minutes. At this time, the air supply rate was 3 L / min. During 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.

[0266] After the above heat treatment, the heat supply was stopped and the powder was cooled to room temperature, and then a coating composition was mixed with sucrose as a coating agent in deionized water so that the carbon content was 4.4 parts by weight per 100 parts by weight of the positive electrode active material, and applied to the surface of the positive electrode active material. Then, pre-milling (milling before firing) was performed using a ball mill at 300 rpm for 10 hours, and then spray drying was performed. The average particle diameter (D) of the dried positive electrode active material powder 50 ) was 0.5 μm.

[0267] The above dried positive electrode active material was heated at a heating rate of 3°C / min in a furnace while supplying nitrogen at a rate of 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 completion of the firing, the CS analysis result showed that the coating amount was 1.43 wt%.

[0268] The above coated positive electrode active material is milled (milled after firing) using a jet mill under an air atmosphere with a feeding line pressure of 4 bar and a grinding line pressure of 1 bar, so that the particle diameter is D 40 0.885 ㎛, D 50 1.055 ㎛, D 60 A regenerated positive electrode active material having a diameter of 1.417 μm was obtained.

[0269]

[0270] Example 2

[0271] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the milling time in the preliminary milling step in the coating step of Example 1 was changed to 6 hours.

[0272]

[0273] Comparative Example 1

[0274] The following wet recycling treatment was performed on the waste cathode scrap used in Example 1 to manufacture a regenerated cathode active material.

[0275] The above waste cathode scrap was treated with sulfuric acid to prepare a lithium sulfate solution, then the pH was adjusted to remove impurities, and lithium carbonate was prepared by carbonation.

[0276] In addition, the residue (iron and phosphorus residue) that did not dissolve during the sulfuric acid treatment was dissolved in an acidic solution to produce iron phosphate.

[0277] A cathode active material was obtained by synthesizing the manufactured lithium carbonate and iron phosphate.

[0278]

[0279] Comparative Example 2

[0280] Fresh LFP cathode active material, not a recycled cathode active material, was prepared. The fresh LFP cathode active material was analyzed by ICP analysis and confirmed to be a LiFePO4 cathode active material with an element ratio of Li / Fe: 1.06, Li / P: 1.00, and P / Fe: 1.06.

[0281]

[0282] Comparative Example 3

[0283] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that instead of the coating composition used in the coating step of Example 1, sucrose was mixed in a solid state so that the carbon content was 4.4 parts by weight per 100 parts by weight of the positive electrode active material, and then the milled positive electrode active material was heated at a heating rate of 3°C / min in a furnace under a nitrogen atmosphere and fired at 700°C for 10 hours.

[0284]

[0285] [Experimental Example I: Raman Spectrum Analysis]

[0286] Raman spectrum analysis was performed on the regenerated or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3.

[0287] From the intensity of all Raman peaks seen in the Raman spectrum analysis and the intensity of the Raman peak corresponding to the compound of the olivine structure among these, the intensity of the Raman peak corresponding to the compound of the olivine structure among the intensities of all Raman peaks seen in the Raman spectrum is calculated to obtain the Area Ratio. LFP was calculated, and the result is shown in Table 1 below as the reciprocal value 1 / Area RatioLFP (corresponding to mathematical formula 2), and is also shown in Figure 2 below.

[0288]

[0289] [Experimental Example II: Total Carbon Amount Analysis]

[0290] The carbon content of the regenerated or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured using a carbon content analysis device.

[0291] Specifically, the carbon content (weight %) contained in the positive electrode active material layer was calculated from the total amount of CO2 generated by burning the positive electrode active material layer using a CS-analyzer (Bruker, G-4 ICARUS series II):

[0292] Specifically, the blank for the calibration curve was measured, then 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 at 30 mg.

[0293] Next, a catalyst was added to the crucible containing the sample, placed on the lower electrode, and the sample was injected from the top to combust, and the carbon content (weight %) was measured.

[0294] The measured results are shown in Table 1 and Figure 1 below (corresponding to mathematical formula 3).

[0295] Active Material: LFP1 / Area Ratio LFP Mathematical Formula 2 Total Carbon Amount (wt%) Mathematical Formula 3 Example 10.72 1.45 Comparative Example 10.13 1.35 Comparative Example 20.16 1.41 Comparative Example 30.08 1.46

[0296] As shown in Table 1 above and Figure 1 below, in the case of Example 1, it was confirmed that the Raman spectrum analysis variables showed different tendencies compared to Comparative Examples 1 to 3. Specifically, the total amount of carbon analyzed in Example 1 was 1.45 wt%, which was almost similar to the total amount of carbon analyzed in Comparative Example 3, which was 1.46 wt%, but the 1 / Area Ratio obtained from the Raman spectrum analysis results LFP The result value of mathematical expression 2 reflecting the items was 0.72 in the case of Example 1, satisfying 0.45 or higher, but in the case of Comparative Example 3, the value was 0.08, showing a value far below 0.45.

[0297] Meanwhile, when compared with Comparative Example 1, which underwent a wet recycling process commonly performed in the technical field to which the present invention belongs, or Comparative Example 2, which is a fresh positive electrode active material, it was confirmed that in the case of Example 1 according to the present invention, the value was 0.72, satisfying 0.45 or higher, whereas 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 are still far below 0.45.

[0298]

[0299] [Test Example III: Selection of Carbon Coating Quality Measurement Indicators]

[0300] The following mathematical expression 1 was calculated from the 1 / Area RatioLFP item (Mathematical Expression 2) and the total carbon amount (Mathematical Expression 3) of Table 1 above, and is shown in the Carbon Content x Area RatioLFP item of Table 2 below.

[0301] [Mathematical Formula 1]

[0302] Carbon Content x Area Ratio LFP

[0303] Active material: LFP1 / (Area Ratio LFP ) Mathematical formula 2 Total carbon (wt%) Mathematical formula 3 Carbon content x (Area Ratio LFP ) Mathematical Formula 1 Example 10.72 1.45 2.01 Comparative Example 10.13 1.35 10.38 Comparative Example 20.16 1.41 8.81 Comparative Example 30.08 1.46 18.25

[0304] As shown in Table 2 above, the result calculated according to Equation 1 tends to not match the total carbon amount calculated in Equation 3, and it was confirmed that it can be used as an indicator for evaluating carbon coating quality more accurately by adding the Raman spectrum analysis results. Specifically, the total carbon amount analyzed in Example 1 was 1.45 wt%, which was almost similar to the total carbon amount of 1.46 wt% analyzed in Comparative Example 3, but the 1 / Area Ratio obtained from the Raman spectrum analysis results LFPThe result value of mathematical expression 1 reflecting the items was 2.01 in the case of Example 1, satisfying 5 or less, but in the case of Comparative Example 3, the value was 18.25, indicating a value far exceeding 5.

[0305] In fact, when compared with Comparative Example 1, which underwent a wet recycling process commonly practiced in the technical field to which the present invention belongs, or Comparative Example 2, which is a fresh positive electrode active material, it was confirmed that in the case of Example 1 according to the present invention, the value was 2.01, satisfying 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 far exceeded 5.

[0306] In particular, in the case of Comparative Example 3, which differs in firing temperature conditions, etc., it is inferred that the firing temperature conditions have a significant influence on mathematical expression 1, which is a parameter, as it is still 18.25, which is far greater than 5.

[0307]

[0308] Additionally, the electrochemical performance of the regenerated or newly produced positive electrode active materials obtained in Examples 1 to 2 and Comparative Examples 1 to 3 was measured through the following CHC cell evaluation.

[0309]

[0310] [Experimental Example IV: CHC Cell Evaluation]

[0311] The electrochemical performance of the regenerated or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was measured through the following CHC cell evaluation.

[0312] * CHC cell evaluation: 97.5 wt% of the regenerated cathode active material, 1 wt% of the conductive material carbon black, and 1.5 wt% of the binder PVdF were weighed and mixed with LFP to make a slurry. This was coated on aluminum foil to manufacture the cathode, and then the cell (Coin Half Cell, CHC) was manufactured. The voltage was set to 2.5 to 3.7 V, and charge / discharge was performed at 0.1 C / 0.1 C. The electrochemical performance (charge capacity, discharge capacity, and efficiency) was evaluated under the conditions of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 (weight ratio) as the electrolyte and other additives included, and the results are shown in Table 3 and Fig. 3 below.

[0313] Charging capacity Discharging capacity Efficiency (%) Example 1162.2158.797.6 Comparative example 1159.2156.398.2 Comparative example 2160.0157.098.1 Comparative example 3157.5154.798.2

[0314] Table 3 above and Figure 3 below are the results of coin cell evaluations conducted on each of the regenerated or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3. As shown in Table 3 above and Figure 3 below, it was confirmed that the regenerated positive electrode active material (Example 1) according to the present invention had a superior charging capacity compared to Comparative Examples 1 to 3.

[0315] * Measurement of capacity retention at high temperature (45 ℃): Each monocell manufactured with the recycled or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was formed at a 0.1C rate, and then the gas inside the cell was removed (degas process). Thereafter, 4.2 V, 1 C, 0.05 C cut-off CC / CV charge and 2.5 V, 0.5 C CC discharge were performed 200 times each at high temperature (45 ℃), and the discharge capacity after 1 cycle and after 200 cycles were measured using a PNE-0506 charger / discharger (Manufacturer: PNE Solution Co., Ltd., 5 V, 6 A), and the discharge capacity after 1 cycle was set as the initial capacity. Thereafter, the capacity retention rate was calculated by comparing the 200th discharge capacity with the initial capacity (100%) using the following mathematical equation 4.

[0316] [Equation 4]

[0317] Capacity retention rate (%) = (discharge capacity after high temperature cycling / initial discharge capacity) X 100

[0318]

[0319] As a result of the measurement, it was confirmed that the regenerated positive electrode active materials of Examples 1 to 2 had a higher capacity retention rate than those of Comparative Examples 1 to 3 as the number of cycles increased.

[0320]

[0321] * Measurement of high temperature (45 ℃) resistance increase rate: Each monocell manufactured with the regenerated or newly produced positive electrode active materials obtained in Example 1 and Comparative Examples 1 to 3 was formed at a 0.1C rate, and then the gas inside the battery was removed (degas process). The lithium secondary battery from which the gas was removed was transferred to a charger / discharger at room temperature (25 ℃), and then charged at a 0.33C rate under constant current / constant voltage conditions up to 4.2 V and a 0.05C cut-off charge was performed, and then discharged at 0.33C 2.5 V. The SOC (State Of Charge) was set to 50% based on the discharge capacity after each of the charge / discharge cycles. At this time, the DC internal resistance was measured through the voltage drop that appeared when a discharge pulse was given at 2.5C for 10 seconds using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the resistance at this time was set as the initial resistance.

[0322] Afterwards, 4.2 V, 1C, 0.05C cut-off CC / CV charging and 2.5 V, 0.5C CC discharging were performed 200 times each at high temperature (45 ℃), and then the lithium secondary battery was transferred to a charger / discharger at room temperature (25 ℃), and after adjusting the SOC (State Of Charge) to 50%, a discharge pulse was applied at 2.5C for 10 seconds. The DC internal resistance was measured through the voltage drop that appeared using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A). This was compared with the initial resistance (0%) and the resistance increase rate (%) was calculated according to the above mathematical equation 5.

[0323] [Equation 5]

[0324] Resistance increase rate (%) = {(Resistance after high temperature cycle - initial resistance) / initial resistance} X 100

[0325]

[0326] As a result of the measurement, it was confirmed that the regenerated positive electrode active materials of Examples 1 to 2 had a higher resistance increase rate compared to Comparative Examples 1 to 3 as the number of cycles increased.

Claims

1. A cathode active material having a carbon coating layer and an olivine structure compound, The above positive electrode active material is characterized by satisfying the following mathematical formulas 1, 2 and 3. Positive active material. [Mathematical Formula 1] 0 < Carbon Content x Area RatioLFP ≤ 5 [Equation 2] 0.45 ≤ 1 / Area RatioLFP ≤ 1 [Equation 3] 1.3 ≤ Carbon content ≤ 1.5 (Here, carbon content is the total amount of carbon (weight%) measured by carbon content analysis equipment, 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 visible in the Raman spectrum.) 2. In paragraph 1, The above positive electrode active material is characterized in that it is a regenerative positive electrode active material. Positive active material.

3. In paragraph 1, The above positive electrode active material is characterized by being a single particle. Positive active material.

4. In paragraph 1, The compound of the above olivine structure is characterized by being represented by the following chemical formula 1. Positive active material. [Chemical Formula 1] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.) 5. In paragraph 4, The positive electrode active material having the above olivine structure compound is characterized in that it includes lithium iron phosphate. Positive active material.

6. A step of heat-treating a waste positive electrode on which a positive electrode active material layer including a positive electrode active material having an olivine structure compound is applied on a current collector, thereby detaching the positive electrode active material from the current collector; A step of coating the surface of the separated positive electrode active material; and A step of milling a coated positive electrode active material; The coating step is characterized in that it is performed including a step of applying a coating agent to the detached positive electrode active material, pre-milling, and spray drying; and a step of calcining the spray-dried positive electrode active material at 750 to 1200° C. under a reducing atmosphere. Method for regenerating positive electrode active material.

7. In paragraph 6, The above-mentioned detachment step is characterized in that it is performed by heating at a temperature of 300 to 650°C under an oxidizing atmosphere. Method for regenerating positive electrode active material.

8. In paragraph 6, The above-mentioned detachment step is characterized in that the temperature is increased at a temperature increasing rate of 1 to 10 ℃ / min, the heat treatment temperature is reached, and the temperature is increased for 10 minutes to 5 hours. Method for regenerating positive electrode active material.

9. In paragraph 6, The coating agent is characterized in that it contains at least one of a metal, an organic metal, and a carbon component. Method for regenerating positive electrode active material.

10. In paragraph 6, In the above coating step, the firing is characterized in that it is performed for 1 to 24 hours. Method for regenerating positive electrode active material.

11. In paragraph 6, In the above coating step, the preliminary milling is characterized by being performed using a ball mill, a high energy ball mill, a vibrating mill or a roll mill. Method for regenerating positive electrode active material.

12. In paragraph 6, The above milling step is characterized in that it is performed using a jet mill. Method for regenerating positive electrode active material.

13. In paragraph 6, The compound of the above olivine structure is characterized by being represented by the following chemical formula 1. Method for regenerating positive electrode active material. [Chemical Formula 1] (In the above chemical formula 1, M includes at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X includes at least one element 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.) 14. Characterized in that it comprises a positive electrode active material according to any one of claims 1 to 5. Secondary battery.

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