Olivine cathode material for lithium secondary battery and manufacturing method thereof

Abstract

An olivine-type cathode active material, according to an embodiment of the present invention, comprises a lithium metal phosphate containing a halogen element, wherein the halogen element is chlorine (Cl), the lithium metal phosphate may be LiFePO4, and the content of the halogen element is 10 to 450 ppm, and a method of manufacturing the olivine cathode active material involves removing impurities during the manufacturing process, thereby improving the electrochemical performance of the resulting olivine cathode active material.

Description

Olive-based cathode active material for lithium secondary batteries and method for manufacturing the same

[0001] The present invention relates to an olivine-based cathode active material for a lithium secondary battery and a method for manufacturing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0187701, filed on December 16, 2024, the entire contents of which are incorporated herein by reference.

[0003] As the electric vehicle market becomes fully active, the market for cathode active materials, which account for more than 40% of the cost of lithium-ion batteries, is also growing rapidly every year. Automobiles are classified into six segments based on their overall length: Segment A for vehicles under 3,500mm and Segment F for vehicles over 5,000mm. Accordingly, electric vehicles using batteries utilize cathode active materials differently depending on their class and driving range. For electric vehicles with a driving range of over 600km on a single charge, high-energy-density lithium-ion batteries are required, necessitating the use of High-Ni NCM cathode active materials, while Mid-Ni NCM materials are used for vehicles with a range of around 400km. However, for electric vehicles that do not require a high driving range and are relatively inexpensive, using materials that offer high safety and excellent lifespan, even if they do not have high energy density, is advantageous in terms of cost. Lithium iron phosphate (IFP) cathode active material is an olivine-based structure composed of FeO6 octahedral sites and PO4 tetrahedral sites, allowing lithium ions to be deinserted and inserted via a one-dimensional pathway. As its main composition consists of Li, Fe, and P, this material offers a cost advantage due to lower metal mineral costs compared to NCA or NCM materials that primarily use Ni and Co. Furthermore, its structural stability, resulting from strong PO bonding, prevents oxygen dissociation at high temperatures during charging, thus providing excellent thermal stability. Additionally, due to its superior lifespan characteristics, there is a history of many electric vehicles utilizing this material being produced in China. However, since lithium ion deinsertion and insertion occur via one-dimensional diffusion, primary particles must be manufactured in nano-size. Additionally, due to the material's inherent lack of electrical conductivity, a uniform carbon coating on the surface is mandatory, which is a disadvantage.Nevertheless, as Cell-to-Pack and even Cell-to-Chassis technologies are being developed in earnest to emphasize high safety in electric vehicles, the gap in energy density compared to existing NCM systems is gradually narrowing.

[0004] Lithium iron phosphate (LFP) is generally known to be produced by hydrothermal synthesis using LiOH, FeSO4, and (NH4)3PO4, spray drying using Li2CO3 and FePO4 precursors, and milling methods using Li2CO3 and FePO4. However, these manufacturing methods generate toxic byproducts such as ammonia, which complicates downstream processing, and also present problems such as the high unit cost of iron raw materials.

[0005] Although methods using industrial iron oxide byproducts have been proposed to address the problem of high unit costs for iron raw materials, there is a problem with the electrochemical performance of the final product, lithium iron phosphate (LFP), being low due to the high amount of impurities.

[0006] Therefore, there is a need to develop lithium iron phosphate (LFP) cathode active materials with excellent electrochemical performance and methods to manufacture them economically and efficiently without process issues.

[0007] One objective of the present invention is to provide a method for manufacturing lithium iron phosphate (LFP) with low impurity content and a lithium iron phosphate (LFP) cathode active material with excellent electrochemical properties.

[0008] An olivine-type cathode active material according to one embodiment of the present invention comprises a lithium metal phosphate containing a halogen element, and the halogen element content is 10 to 450 ppm.

[0009] The lithium metal phosphate containing the above halogen element can be represented by the following chemical formula 1.

[0010] [Chemical Formula 1]

[0011] Li 1+a Fe 1-b M b (PO 4-c )X c

[0012] (In the above Chemical Formula 1, M is one or more metallic elements selected from Mn, Na, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga, X is one or more non-metallic elements selected from Cl, Br, and F, and a, b, and c are -0.5≤a≤+0.5, 0≤b<0.04, and 0.001≤c<0.05, respectively.)

[0013] The above halogen element is a chlorine (Cl) element, and the above lithium metal phosphate may be LiFePO4.

[0014] The average crystal grain size of the above positive active material may be 75.0 to 200.0 nm, and the average particle size (D50) may be 7.0 to 11.0.

[0015] The specific surface area (BET) of the above positive active material is 10.0 to 16.0 m² 2 It can be / g.

[0016] The rolled density of the above positive active material is 2.55 to 2.75 g / cm³ 3 It could be.

[0017] The above positive active material may further include a coating layer.

[0018] The coating layer contains carbon, and the carbon content may be 1.0 to 2.0 wt% based on the total weight of the positive electrode active material.

[0019] The above positive active material may be composed of a lithium metal phosphate containing a halogen element located while surrounding a void space and part or all of the void space.

[0020] A method for manufacturing an olivine-based cathode active material according to another embodiment of the present invention may include the steps of: obtaining a mixture by dry mixing lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and a chloride additive, followed by milling; obtaining lithium iron phosphate by first calcining the mixture in a reducing atmosphere; preparing a slurry by introducing a mixture of the lithium iron phosphate, a carbon additive, and a dispersant into a solvent and wet milling; obtaining a cathode active material precursor by spray drying the slurry; and obtaining an olivine-based cathode active material with a carbon coating layer formed by secondarily calcining the cathode active material precursor in a reducing atmosphere.

[0021] In the step of obtaining a mixture by dry mixing and milling the lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additive, the chloride additive may be mixed in an amount greater than 0.1 wt% and less than 10.0 wt% based on the total weight of the lithium dihydrogen phosphate (LiH2PO4) and ferric oxide (Fe2O3).

[0022] The chloride additive may include one or more selected from calcium chloride (CaCl2), ammonium chloride (NH4Cl), and sodium chloride (NaCl).

[0023] The method may further include the step of obtaining lithium iron phosphate by first calcining the above mixture in a reducing atmosphere, and then washing the obtained lithium iron phosphate.

[0024] An olivine-based cathode active material according to one embodiment of the present invention has the advantage of improved electrochemical performance by including an appropriate amount of chlorine.

[0025] A method for manufacturing an olivine-based cathode active material according to another embodiment of the present invention can improve the electrochemical performance of the finally manufactured olivine-based cathode active material by removing impurities during the manufacturing process.

[0026] Figures 1 to 3 show SEM analysis images of olivine-based cathode active materials according to Examples 1 to 3.

[0027] Figure 4 shows an SEM analysis image of the final cathode active material prepared in Example 1.

[0028] Figure 5 shows an SEM analysis image of the primary lithium iron phosphate obtained after primary calcination in Example 1.

[0029] In this specification, terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the invention.

[0030] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0031] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0032] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0033] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0034] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0035] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0036]

[0037] 1. Olivine-based cathode active material

[0038] One embodiment of the present invention provides an olivine-based positive electrode active material for a lithium secondary battery.

[0039] The olivine-type cathode active material according to the present invention comprises lithium manganese iron phosphate, and the olivine-type cathode active material comprises lithium metal phosphate containing a halogen element, and the halogen element content may be 10 to 450 ppm, specifically 40 to 150 ppm.

[0040] In the present invention, the halogen element content is based on mol%.

[0041] In the present invention, by including a halogen element in the above-mentioned concentration range in the oligonucleotide active material, lattice defects can be reduced and conduction paths optimized to improve electron conductivity and lithium ion conductivity, thereby having the advantage of improving the electrochemical performance of the battery.

[0042]

[0043] The average grain size of the lithium manganese iron phosphate according to the present invention may be 75.0 to 200.0 nm, and specifically 75.0 to 120.0 nm, or 80.0 to 100.0 nm.

[0044] In the present invention, by having a crystal grain size within the above range, lithium ion conductivity and battery conductivity are improved, and the crystal structure can be stably maintained during the charging and discharging process, thereby providing the advantage of enabling excellent electrochemical performance of the battery to which it is applied.

[0045] The above grain size can be specifically calculated by the Scherrer equation Equation 1.

[0046] τ=(K*λ) / (β*cosθ) (1)

[0047] In Equation 1 above, K is the shape factor, λ is the x-ray wavelength, β is the full width at half maximum, and θ is the Bragg angle. In the present invention, the shape factor is generally 1.0, but it may vary depending on the crystallite.

[0048]

[0049] The olivine-based cathode active material according to the present invention may be in the form of secondary particles formed by aggregating a plurality of primary particles.

[0050] The average particle size (D50_1) of the primary particles of the above olivine-based cathode active material may be 100 nm to 1 µm. The average particle size (D50_2) of the secondary particles of the above olivine-based cathode active material may be 7.0 to 11.0 µm.

[0051] In the present invention, when the crystal grain size, primary particle size, and secondary particle size of the olivine-based cathode active material satisfy the above range, there is an advantage in that the output characteristics and lifespan characteristics of the lithium secondary battery are improved.

[0052] In this specification, “secondary particle” means an aggregate, i.e., a secondary structure, formed by the aggregation of tens to hundreds of primary particles by physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles.

[0053] The above “primary particle” refers to a minimum particle unit that is distinguished as a single mass when the cross-section of the positive active material is observed through a scanning electron microscope (SEM), and may consist of a single crystal grain or multiple crystal grains.

[0054] In this specification, “grain” refers to a distinct region in which atoms within a primary particle form a lattice structure in a certain direction.

[0055] The average particle size of the above secondary particles can be measured using PSA (Particle size analysis).

[0056] The above primary particle size can be measured using an SEM image obtained through FIB cross-sectional analysis. The average particle size of the primary particles can be calculated as the average value of the particle sizes of 20 to 30 primary particles located consecutively adjacent to each other among the primary particles included in an image of size 1㎛ X 1㎛ from the results of the FIB cross-sectional analysis at 10,000x magnification SEM analysis.

[0057] The coating layer of the olivine-based cathode active material according to the present invention may be a carbon coating layer containing carbon. The carbon coating layer may be located on the surface of secondary particles and may be located between primary particles.

[0058] Meanwhile, it may be located on all or part of the surface of the secondary particle, and may be located between all primary particles or between some primary particles forming the secondary particle.

[0059] In the present invention, the average thickness of the carbon coating layer may be 10 to 50 nm.

[0060] In the present invention, the carbon content included in the olivine-based cathode active material may be 1.0 to 2.0 wt%.

[0061] In the present invention, when the carbon coating layer thickness and carbon content satisfy the above range, there is an advantage that the output characteristics and lifespan characteristics of the lithium secondary battery are improved.

[0062] In the present invention, the average thickness of the carbon coating layer can be measured using a TEM (Transmission Electron Microscopy) analysis image.

[0063] Specifically, the average value of the coating layer thickness at three or more points located at intervals of 5 to 10 nm on the TEM image can be calculated.

[0064] In the present invention, the carbon content was confirmed by measuring it using a high-precision carbon / sulfur analyzer. Specifically, the content of the total 100 parts by weight of the olivine-based cathode active material for a lithium secondary battery was measured by detecting the content of oxide carbon and sulfur generated by burning the sample together with a combustion promoter in an oxygen stream.

[0065]

[0066] The rolled density of the olivine-based cathode active material according to the present invention is 2.55 to 2.75 g / cm³ 3 It could be.

[0067] In the present invention, the rolling density was measured by applying pressure with a weight of 3 tons for 1 minute and checking the volume of the pellets.

[0068] In the present invention, when the tap density of the olivine-based cathode active material satisfies the above range, there is an advantage in that the energy density, output characteristics, and lifespan characteristics of the lithium secondary battery can all be excellently realized.

[0069] The specific surface area (BET) of the olivine-based cathode active material according to the present invention is 10.0 to 16.0.0 m 2 It can be / g, specifically 11.0 to 15.0.0m 2 / g can be.

[0070] In the present invention, when the specific surface area (BET) of the olivine-based positive electrode active material satisfies the above range, the positive electrode active material and the electrolyte can be in sufficient contact while reducing the occurrence of side reactions, and as a result, there is an advantage in that the output characteristics and lifespan characteristics of the lithium secondary battery are improved.

[0071] The olivine-based positive electrode active material according to the present invention may be a compound represented by the following chemical formula 1.

[0072] [Chemical Formula 1]

[0073] Li 1+a Fe 1-b M b (PO 4-c )X c

[0074] In the above chemical formula 1, M is one or more metal elements selected from Mn, Na, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga, X is one or more non-metal elements selected from Cl, Br, and F, and a, b, and c are each -0.5≤a≤+0.5, 0≤b<0.04, 0.001≤c<0.05).

[0075] In the present invention, the performance of the battery can be improved by further including the doping metal element (M) in the olivine-based cathode active material. For example, Co and Ni promote electron transfer in electrochemical reactions to increase conductivity, while elements such as Mg and Ca can strengthen structural stability to extend cycle life. Additionally, metals such as Ti, Zr, and Nb can increase high-temperature stability to improve thermal stability. In the present invention, by applying the doping elements independently or in combination, the charge / discharge efficiency of the battery can be increased, and stable performance can be achieved even at high temperatures and high current densities.

[0076] In the present invention, the doping metal element (M) may be included in an amount greater than 50 ppm and less than 400 ppm.

[0077] In the present invention, the olivine-based cathode active material may specifically be LiFePO4, which is a lithium metal phosphate, and the halogen element may specifically be a chlorine (Cl) element.

[0078] Chlorine elements possess strong polarity, which can reduce intermolecular forces between molecules constituting olivine-based cathode active materials and promote the uniform dispersion of each component. Additionally, since it allows for the maintenance of grain size and shape at an appropriate level, there is an advantage in that it enables the realization of excellent electrochemical performance in the batteries to which it is applied.

[0079] In the present invention, the olivine-based positive electrode active material may be composed of a void space and a positive electrode active material positioned to surround part or all of the void space.

[0080]

[0081] 2. Method for manufacturing olivine-based cathode active material

[0082] One embodiment of the present invention provides a method for manufacturing an olivine-based positive electrode active material.

[0083] A method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery according to the present invention may comprise the steps of: obtaining a mixture by dry mixing lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and a chloride additive, followed by milling; obtaining lithium iron phosphate by first calcining the mixture in a reducing atmosphere; preparing a slurry by introducing a mixture of the lithium iron phosphate, a carbon additive, and a dispersant into a solvent and wet milling; obtaining a positive electrode active material precursor by spray drying the slurry; and obtaining an olivine-based positive electrode active material with a carbon coating layer formed by secondarily calcining the positive electrode active material precursor in a reducing atmosphere.

[0084] First, a step is performed to obtain a mixture by dry-mixing and milling lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additives.

[0085] The above lithium dihydrogen phosphate (LiH2PO4) can be obtained by reacting lithium carbonate or lithium hydroxide, which are used in the manufacture of cathode materials for lithium-ion batteries from salt lakes and ore lithium, or lithium phosphate (Li3PO4) generated during the intermediate stages of their production, with a phosphoric acid (H3PO4) solution. The above ferric oxide (Fe2O3) can be recovered and used from steel pickling waste liquid, thereby reducing or suppressing the generation of wastewater, which enables the manufacture of an olivine-based cathode active material in an environmentally friendly manner. Furthermore, the above lithium dihydrogen phosphate (LiH2PO4) and ferric oxide (Fe2O3) may be powders having micro-sized particles, and are not particularly limited as long as an olivine-based cathode active material with excellent battery output characteristics can be manufactured according to the manufacturing method of the present invention.

[0086] In the present invention, the chloride additive may include one or more selected from calcium chloride (CaCl2), ammonium chloride (NH4Cl), and sodium chloride (NaCl).

[0087]

[0088] In the present invention, a chloride additive can be mixed in an amount greater than 0.1 wt% and less than 10.0 wt% based on the total weight of the lithium dihydrogen phosphate (LiH2PO4) and ferric oxide (Fe2O3).

[0089] In the present invention, by mixing the chloride additive within the above range, impurities can be removed during the subsequent calcination process, and there is an advantage in being able to manufacture a high-quality olivine-based cathode active material using low-cost raw materials.

[0090] For example, when ammonium chloride (NH4Cl) is used as a chloride additive, the following chemical reaction may occur during the first calcination step described below.

[0091] MnO + 2NH4Cl → MnCl2+ 2NH3+ H2O

[0092] Na2O + 2NH4Cl → 2NaCl + 2NH3+ H2O

[0093] K2O+ 2NH4Cl → 2KCl + 2NH3+ H2O

[0094] The metal chloride formed through the above chemical reaction can be removed by washing.

[0095] In the present invention, the lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additive can be introduced into a grinding device and mixed and milled. Specifically, the lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additive can be introduced into a grinding device and milled while mixing.

[0096] In the present invention, the grinding device may be a grinding device such as an air jet mill, a hammer, a screen mill, a fine impact mill, a ball mill, or a vibrator mill, and specifically, it may be a fine impact mill.

[0097] Meanwhile, an inert gas or a reducing gas can be continuously supplied into the above-mentioned grinding device to form a reducing atmosphere.

[0098] The above inert gas atmosphere or reducing gas atmosphere can continuously supply one or more gases selected from pure nitrogen gas, pure argon gas, hydrogen and nitrogen mixed gas, hydrogen and argon mixed gas, or coke oven gas.

[0099] By mixing and grinding as described above, raw materials of a more uniform size are uniformly mixed, resulting in a uniformly distributed composition during the subsequent firing stage and the advantage of obtaining a fired product with an excellent impurity removal rate.

[0100]

[0101] Next, a step is performed to obtain lithium iron phosphate by first calcining a mixture containing lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additives in a reducing atmosphere.

[0102] Specifically, the above mixture can be charged into a kiln and then continuously supplied with an inert gas atmosphere or a reducing gas. The process can be carried out while supplying the inert gas or reducing gas in a range of 3.8% to 40% of the kiln volume per minute.

[0103] Meanwhile, the above-mentioned kiln can be heated at a heating rate in the range of 2.5℃ / min to 10℃ / min to raise the internal temperature of the kiln to a temperature in the range of 400℃ to 700℃, and specifically to a temperature in the range of over 600℃ to 700℃. In addition, the process can be carried out specifically for 4 to 7 hours at the above temperature.

[0104] If calcination is performed under temperature conditions below the above temperature range or for a shorter time than the above calcination time range, a problem may occur in which the olivine-based structure is not properly formed. In addition, if calcination is performed under temperature conditions higher than the above temperature range or for a longer time than the above calcination time range, a problem may occur in which the activity of the anode active material is reduced due to over-calcination.

[0105] Meanwhile, metal elements included as impurities in the first calcination stage may react with chloride additives to be converted into water-soluble chlorides. As a detailed explanation of this has been provided above, it will be omitted here.

[0106]

[0107] Next, the step of washing the lithium iron phosphate obtained in the first calcination step may be further included.

[0108]

[0109] The above washing can be performed using distilled water, and residual chloride additives and metal chlorides formed in the first calcination step can be removed, thereby producing a high-purity olivine-based cathode active material.

[0110]

[0111] In addition, a step of grinding the obtained lithium iron phosphate can be additionally performed.

[0112] In the step of grinding the lithium iron phosphate in the present invention, the lithium iron phosphate powder finally obtained can be ground to have an average particle size of 1 to 10 μm.

[0113] By grinding as described above in the present invention, a uniformly dispersed slurry is prepared in the wet mixing milling step described later, which is advantageous for improving the quality of the final obtained olivine-based cathode active material.

[0114] The above mixture of lithium iron phosphate, carbon additive, and dispersant is introduced into a solvent and wet-milled to perform the slurry step.

[0115] In the present invention, the lithium iron phosphate, carbon additive, and dispersant can be introduced into a mixer and then stirred. Specifically, the mixture can be stirred at a stirring speed of 200 to 1,500 rpm for 30 to 90 minutes.

[0116] The above dispersant can be mixed in an amount of 1.0 to 5.0 wt%, specifically 2.0 to 4.0 wt%, based on the weight of the lithium iron phosphate.

[0117] At this time, the carbon additive can be mixed in an amount of 1.0 to 5.0 wt%, specifically 2.0 to 4.0 wt%, based on the total weight of the dried precipitate and the carbon additive.

[0118] The above-mentioned dispersant may be a carbon-containing dispersant, and specifically, may be one or more selected from citric acid, fumaric acid, adipic acid, succinic acid, tartaric acid, glutaric acid, maleic acid, oxalic acid, malonic acid, or ascorbic acid.

[0119] More specifically, the above dispersant may be citric acid.

[0120] The above dispersant can prevent the clumping of particulate materials and can also form a carbon coating layer on the surface of the particles.

[0121] The above carbon additive is a raw material that primarily forms a carbon coating layer. The above carbon additive may be one or more selected from glucose, sucrose, fructose, lactose, or maltose.

[0122] Specifically, the above carbon additive can be glucose.

[0123] In the present invention, by mixing the carbon additive within the above range, the electrical conductivity and ionic conductivity of the olivine-based cathode active material finally manufactured can be improved, thereby providing the advantage of improving the electrochemical performance of the battery to which it is applied.

[0124] The above solvent may be ethanol, water, distilled water, or deionized water. Specifically, it may be deionized water (DIW).

[0125] The above lithium iron phosphate, dispersant, and carbon additive can be mixed by introducing them into a bead mill-type milling device loaded with a solvent, and then milling for 30 minutes to 1 hour using a wet milling method to produce a slurry.

[0126] In the present invention, a slurry can be prepared by milling for 30 minutes to 1 hour using a wet milling method. Wet milling can be performed by introducing ZrO2 beads with an average diameter in the range of 0.1 mm to 0.5 mm into a reactor in a mass amount similar to that of the solids, and by performing wet bead milling in which the internal slurry continuously moves into and out of the reactor at a rotation speed of 10 m / s and a circulation speed of 200 mL / min.

[0127] In the present invention, the rotational speed of the wet milling device may be 100 to 1,000 rpm, and specifically 200 to 500 rpm.

[0128] The above-mentioned lithium iron phosphate, dispersant, and carbon additive solvent can be supplied continuously, and can be supplied continuously at a volume of 20% to 50% of the volume of the milling device per minute. By performing wet milling under such conditions, it is advantageous for the entire process to proceed stably and continuously.

[0129] By controlling the average particle size of the solid material included in the slurry to the above range, there is an advantage in being able to form a more uniform olivine-based cathode active material precursor in the subsequent spray drying step.

[0130]

[0131] Next, the step of spray-drying the above slurry to form a positive electrode active material precursor can be performed.

[0132] The spray device used for the above spray drying may use one or more selected from the group consisting of an ultrasonic spray device, a single-fluid air nozzle spray device, a two-fluid air nozzle spray device, an ultrasonic nozzle spray device, a filter expansion liquid crystal generator (FEAG), and a disc-type droplet generator, but is not limited thereto.

[0133] The above slurry spray drying can be performed using an atomizer, and can be performed under conditions where the hot air inlet temperature is 150 to 250°C and the outlet temperature is 100 to 150°C. The atomizer can spray the slurry at a disc rotation speed in the range of 15,000 RPM to 25,000 RPM, and specifically, can spray the slurry at a speed in the range of 18,000 RPM to 22,000 RPM.

[0134] Next, the step of obtaining an olivine-based positive active material with a carbon coating layer formed by secondarily calcining the positive active material precursor in a reducing atmosphere is performed.

[0135] The olivine-based cathode active material precursor obtained through the above spray drying process is loaded into a kiln, and then, while continuously supplying a reducing gas, it is calcined at a temperature of 700°C or higher for 4 to 6 hours or more to produce a carbon-coated olivine-based cathode active material.

[0136] If calcination is performed under temperature conditions below the above temperature range or for a shorter time than the above calcination time range, a problem may occur in which the olivine-based structure is not properly formed. In addition, if calcination is performed under temperature conditions higher than the above temperature range or for a longer time than the above calcination time range, a problem may occur in which the activity of the anode active material is reduced due to over-calcination.

[0137] In the present invention, the calcination was performed while flowing a reducing gas.

[0138]

[0139] After the calcination is complete, the carbon-coated olivine-based cathode active material, which is the final product, is manufactured by cooling using a self-cooling method.

[0140] A step of further grinding the carbon-coated olivine-based cathode active material may be performed. The grinding step may be performed using general methods used in processes for manufacturing olivine-based cathode active materials, and the present invention is not limited thereto.

[0141] As explained above, introducing lithium into the cathode active material in the same equivalent ratio as the transition metal has the advantage of enabling more precise control of the composition of the cathode active material, which is ultimately composed of lithium manganese iron phosphate, and improving the electrochemical performance of the manufactured cathode active material.

[0142]

[0143] 3. Cathode for lithium secondary batteries and lithium secondary batteries

[0144] A positive electrode for a lithium secondary battery according to another embodiment of the present invention comprises a current collector and a positive electrode active material layer located on at least one surface of the current collector, the positive electrode active material layer comprising a carbon-coated olivine-based positive electrode active material for a lithium secondary battery. Here, the positive electrode comprising the current collector and the positive electrode active material layer located on at least one surface of the current collector has a value of 2 g / cm³ 3 It is manufactured by applying pressure with the above electrode plate density.

[0145] The above-described pressurized anode comprises olivine-based anode active material particles having one or more concave portions formed therein. The longest diameter of the cross-sectional area of ​​the concave portion of the olivine-based anode active material particles having concave portions formed therein, which are included in the active material layer, may be in the range of 8㎛ to 15㎛.

[0146] The above current collector may be selected from the group consisting of, for example, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, aluminum foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0147] The above positive active material layer may further include a binder and a conductive material.

[0148] The above binder can perform the role of effectively attaching the positive active material particles for the lithium secondary battery to each other, and also effectively attaching the positive active material for the lithium secondary battery to the current collector.

[0149] In the battery being constructed, any electronically conductive material that does not cause chemical changes can be used as the above-mentioned conductive material.

[0150] Meanwhile, in another embodiment of the present invention, a lithium secondary battery comprising a positive electrode for the lithium secondary battery is provided.

[0151] The above lithium secondary battery may include a negative electrode and a non-aqueous electrolyte.

[0152] The above-mentioned cathode includes a current collector and a cathode active material layer formed on the current collector, and the cathode active material layer may include a cathode active material.

[0153] The above negative electrode active material may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0154] The material capable of reversibly intercalating / deintercalating the above lithium ions may be, for example, a carbon material, and any carbon-based negative electrode active material generally used in the above lithium secondary battery may be used. For example, crystalline carbon, amorphous carbon, or a combination thereof may be used.

[0155] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0156] Materials capable of doping and dedoping the above lithium include, for example, Si, SiO x Examples include (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn).

[0157] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, etc. The above negative electrode active material layer also includes a binder and may optionally further include a conductive material.

[0158] The above binder can serve to effectively attach the negative electrode active material particles to each other and also effectively attach the negative electrode active material to the current collector.

[0159] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electronically conductive material that does not cause chemical changes can be used.

[0160] For example, the above current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0161] The above-mentioned cathode and anode may be manufactured by preparing an active material composition by mixing an active material, a conductive material, and a binder in a solvent, and applying the composition to a current collector, and the present invention does not limit the method of manufacturing the electrodes.

[0162] The above solvent may include N-methylpyrrolidone, but is not limited thereto.

[0163] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and may be used in which a lithium salt is dissolved.

[0164] The above-mentioned non-aqueous electrolyte may include an organic solvent, and the above-mentioned non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0165] The above organic solvent may be, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran; nitriles such as acetonitrile; amides such as dimethylformamide. These may be used individually or in combination. In particular, a mixed solvent of cyclic carbonates and chain carbonates may be preferably used.

[0166] In addition, as an electrolyte, a gel-type polymer electrolyte in which an electrolyte solution is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N, is possible.

[0167] The above lithium salt is a material that is dissolved in an organic solvent and acts as a source of lithium ions within the battery, enabling the operation of a basic lithium secondary battery and facilitating the movement of lithium ions between the positive and negative electrodes.

[0168] The above lithium salt may be any commonly used in the art without limitation, provided that it does not impede the purpose of the present invention. For example, the above lithium salt may be one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiSbF6, LiAlO4, LiAlCl4, LiCl, and LiI.

[0169] Depending on the type of the above-mentioned lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0170] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used; they can be classified into cylindrical, prismatic, coin, and pouch types depending on their shape; and they can be divided into bulk and thin-film types depending on their size.

[0171] The present invention does not limit the structure and manufacturing method of the lithium secondary battery.

[0172]

[0173]

[0174] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0175]

[0176] (Example 1)

[0177] (1) Manufacturing of positive electrode active material

[0178] (Formation of raw material mixture)

[0179] Lithium dihydrogen phosphate (LiH2PO4) powder with an average particle size of 48.24 μm, ferric oxide (Fe2O3) powder with an average particle size of 2.07 μm, and ammonium chloride (NH4Cl) were mixed in the weight ratios shown in Table 1, and the mixture was uniformly mixed and milled using a ball mill or a powder mixer to obtain the mixed powder.

[0180] (1st firing)

[0181] After the above-mentioned mixed powder is loaded into a high-temperature kiln, it is heated to 650°C at a heating rate of 5°C / min while supplying nitrogen gas in the range of about 3.0 L / min, maintained at 650°C for 5 hours, and then naturally cooled to room temperature to produce primary lithium iron phosphate through a dry step.

[0182] (purifying)

[0183] The lithium iron phosphate prepared above can be washed using distilled water.

[0184] In the present invention, washing can be performed by mixing about 5 mL of distilled water per unit gram weight. Specifically, washing can be performed by stirring using a stirrer.

[0185] After washing was completed, the washed lithium iron phosphate was separated using a filter.

[0186] (Wet milling)

[0187] Next, in the wet milling step, 0.94g of citric acid, 5.43g of glucose, and deionized water are fed into a bead mill device based on the mass of the washed lithium iron phosphate (93.6g).

[0188] Wet milling was performed for 30 minutes at a stirring speed of 500 RPM.

[0189] The average particle size of the solid material in the final slurry produced through wet milling was made to be 1 μm or less.

[0190] In addition, the moisture content in the slurry was made to 70%.

[0191] The above amount of the mixture of citric acid and glucose is

[0192] (Spray drying)

[0193] The above slurry was spray-dried using a spray drying device.

[0194] Specifically, the above slurry was sprayed at a disk rotation speed of about 20,000 rpm, the hot air temperature around the disk part was about 230°C, and the outlet temperature of the outlet of the spray drying device for discharging the manufactured cathode active material was about 120°C to produce spherical olivine-based cathode active material precursor particles.

[0195] (Sintering)

[0196] The above-described olivine-based cathode active material precursor was loaded into a calcination furnace and calcined at 700°C for 5 hours under a reducing atmosphere to produce a carbon-coated LiFePO4 cathode active material.

[0197] Specifically, N2 gas was introduced into a box-shaped kiln at a rate of 60 L / min. Afterward, cooling was performed using a self-cooling method.

[0198] An SEM image of the final manufactured cathode active material is shown in Figure 1.

[0199] (2) Manufacturing of coin-type half-cells

[0200] After manufacturing a CR2032 coin cell using the above-mentioned olivine-based cathode active material, an electrochemical evaluation was performed.

[0201] Specifically, a slurry was prepared by adding 90 wt% of an olivine-based cathode active material, 5 wt% of a Super-P conductive agent, and 5 wt% of a PVDF binder to NMP.

[0202] The above-described slurry was coated onto an Al foil using a doctor blade and dry-rolled. The electrode thickness is 40 μm, and the electrode density is 2.2 g / cc.

[0203]

[0204] (Examples 2 to 4 and Comparative Examples 1 to 14)

[0205] Olive-based cathode active materials according to Examples 2 to 4 and Comparative Examples 1 to 14 were prepared in the same manner as Example 1, except that the raw material mixing ratios and process conditions shown in Tables 1 and 2 were used.

[0206]

[0207] Raw Material Mixture 1st Calcination Fe2O3 (g) LDP (g) Citric Acid (g) NH4Cl (mol%) 1st Calcination Temperature (°C) 1st Firing time (h) Example 1 199.6258.342.4916505 Example 2 199.6258.342.4936505 Example 3 199.6258.342.4916505 Example 4 199.6258.342.4936705 Comparative Example 1 199.6258.342.49106508 Comparative Example 2 199.6258.342.49106508 Comparative Example 3 199.6258.342.490.16508 Comparative Example 4 199.6258.342.490.16708

[0208] Slurry Preparation Secondary Calcination Solids (Based on 100wt%) Slurry Reference Moisture Content (%) Stirring Speed ​​(RPM) Stirring Time (h) Secondary Calcination Temperature (°C) Secondary Calcination Time (h) Lithium Iron Phosphate (wt%) Citric Acid (wt%) Glucose Weight (wt%) Example 1 93.60.945.43705000.57005 Example 2 93.60.945.43705000.57005 Example 3 93.60.945.437020017005 Example 4 93.60.945.437020017005 Comparative Example 1 93.60.945.43705000.57005 Comparative Example 2 93.60.945.437020017005 Comparative Example 3 93.60.945.43705000.57005 Comparative Example 4 93.60.945.437020017005

[0209] (Evaluation Example 1: XRD Analysis)

[0210] XRD analysis was performed on the olivine-based cathode active materials prepared according to the above examples and comparative examples, and the grain size was calculated and shown in Table 3.

[0211]

[0212] (Evaluation Example 2: Olivine-based positive electrode active material particle size)

[0213] The average particle size (D50) of the olivine-based cathode active materials prepared according to the examples and comparative examples was measured using PSA (Particle size analysis) and is shown in Table 3. The particle size corresponding to 50% of the volume accumulation was measured using the laser diffraction method.

[0214]

[0215] (Evaluation Example 3: Impurity Content Analysis)

[0216] The metal impurity content contained in the olivine-based cathode active material prepared according to the above examples and comparative examples was measured using the ICP trace element measurement method, and the measurement results are shown in Table 3 below.

[0217]

[0218] (Evaluation Example 4: Specific Surface Area BET)

[0219] The specific surface area of ​​the olivine-based cathode active material prepared according to the above examples and comparative examples was analyzed and is shown in Table 2.

[0220] The specific surface area was measured by the BET (Brunauer-Emmett-Teller) method, using Macsorb's HM Model-1201 instrument. It can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K).

[0221]

[0222] (Evaluation Example 5: Rolled Density)

[0223] The rolling density of the olivine-based cathode active material prepared according to the above examples and comparative examples was calculated by applying pressure of 3 tons for 1 minute and measuring the weight and volume, and the results are shown in Table 3 below.

[0224]

[0225] (Evaluation Example 6: SEM Analysis)

[0226] SEM images of the manufactured olivine-based cathode active material were analyzed and are shown in Figures 1 to 3.

[0227] Referring to FIGS. 1 to 3, it can be seen that the olivine-based cathode active material prepared according to Examples 1 to 3 consists of an internal empty space and an active material positioned to surround part or all of the empty space.

[0228] Figure 4 shows an SEM analysis image of the final cathode active material prepared in Example 1, and Figure 5 shows an SEM analysis image of the primary lithium iron phosphate obtained after primary calcination in Example 1.

[0229] Referring to Figures 4 and 5, it can be seen that the final cathode active material prepared in Example 1 has reduced particle aggregation compared to lithium iron phosphate obtained through primary calcination.

[0230]

[0231] Cl content (mol%) Molar content of impurities (Na+Mn+K+Zn) ppm Grain size (nm) Average particle diameter (D50) (㎛) BET (m 2 / g) Rolled density (g / cm²) 3 )C Content (wt%) C Coating Layer Thickness (nm) Example 1 1708 1.39.6 1 1.23 2.7 1 1.310 Example 2 3708 0.17.1 14.34 2.6 3 1.310 Example 3 1708 0.28.31 2.69 2.6 2 1.310 Example 4 3708 2.17.7 14.8 3 2.5 7 1.310 Comparative Example 1 10507 3.46.31 7.12 2.7 3 1.310 Comparative Example 2 10507 3.86.2 16.8 2 2.7 7 1.310 Comparative Example 3 0.14001 20.415.32 1.58 2.5 1 1.310 Comparative Example 40.1400131.211.119.862.441.310

[0232] Experimental Example 1: Evaluation of Initial Discharge Capacity and Initial Efficiency

[0233] The coin-type half-cell manufactured above was aged at room temperature (25℃) for 12 hours, and then a charge-discharge test was performed. To evaluate the initial capacity, 150 mAh / g was set as the reference capacity and charged to 3.65V with a constant current of 0.1C, then switched to a constant voltage and charged until the current reached 0.05C. After charging, a rest time of 10 minutes was taken, and then discharged until it reached 2.5V with a constant current of 0.1C and a reference capacity of 150 mAh / g.

[0234]

[0235] Experimental Example 2: Evaluation of Rate Characteristics (1C / 0.1C)

[0236] The rate characteristics were evaluated by dividing the capacity at 25℃ during 0.1C charging - 0.1C discharging by the capacity during 0.1C charging - 2C discharging.

[0237]

[0238] Experimental Example 3: Evaluation of Life Characteristics

[0239] The coin-type half-cell manufactured above was charged to 3.65V at 25℃ with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After charging, a rest time of 10 minutes was taken, and then discharge was performed with a constant current of 1.0C until it reached 2.5V. 100 charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 100th cycle was calculated relative to the first cycle.

[0240] The results of the evaluation of the measured horizontal characteristics are shown in Table 4 below.

[0241]

[0242] Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Initial Efficiency (%) Rate (1C / 0.1C) Life Cycle Characteristics @ 100 cycles (%) Example 1 164.7 161.4 98.7 90.9 94% Example 2 164.5 159.4 96.6 88.4 89% Example 3 166.0 163.7 98.6 91.1 95% Example 4 159.9 155.4 97.1 89.8 90% Comparative Example 1 147.1 142.6 97.0 85.1 85 Comparative Example 2 145.7 140.5 96.5 81.3 88 Comparative Example 3 159.0 154.5 97.1 87.1 84 Comparative Example 4158.0153.597.286.887

[0243] Referring to Tables 1 to 4 above, in Examples 1 to 4, the molar content of Cl in the olivine-based cathode active material prepared by mixing ammonium chloride (NH4Cl) at 1% and 3 wt% was found to be 50 ppm and 100 ppm, the initial discharge capacity was 155 mAh / g or higher, the 1C / 0.1C rate characteristic was 88% or higher, and the 100-cycle capacity retention rate was 89% or higher.

[0244] In Comparative Examples 1 to 4, the molar content of Cl in the olivine-based cathode active material prepared by mixing ammonium chloride (NH4Cl) at 10% and 0.1 wt% was found to be 500 ppm and 5 ppm, the initial discharge capacity was less than 155 mAh / g, the 1C / 0.1C rate characteristic was less than 88%, and the 100-cycle capacity retention rate was less than 89%.

[0245]

[0246] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0247] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. Contains lithium metal phosphate containing a halogen element, and The content of the above halogen element is 10 to 450 ppm, Olivine-based positive electrode active material.

2. In Paragraph 1, The lithium metal phosphate containing the above halogen element is represented by the following chemical formula 1, Olivine-based positive electrode active material. [Chemical Formula 1] Li 1+a Fe 1-b M b (PO 4-c )X c (In the above Chemical Formula 1, M is one or more metallic elements selected from Mn, Na, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga, X is one or more non-metallic elements selected from Cl, Br, and F, and a, b, and c are -0.5≤a≤+0.5, 0≤b<0.04, and 0.001≤c<0.05, respectively.) 3. In Paragraph 1, The above halogen element is a chlorine (Cl) element, Olivine-based positive electrode active material.

4. In Paragraph 1, The above lithium metal phosphate is LiFePO4, Olivine-based positive electrode active material.

5. In Paragraph 1, The average grain size of the above positive active material is 75.0 to 200.0 nm, Olivine-based positive electrode active material.

6. In Paragraph 1, The average particle size (D50) of the above positive active material is 7.0 to 11.0, Olivine-based positive electrode active material.

7. In Paragraph 1, The specific surface area (BET) of the above positive active material is 10.0 to 16.0 m² 2 / g thing, Olivine-based positive electrode active material.

8. In Paragraph 1, The rolled density of the above positive active material is 2.55 to 2.75 g / cm³ 3 thing that is, Olivine-based positive electrode active material.

9. In Paragraph 1, The above positive active material further comprises a coating layer, Olivine-based positive electrode active material.

10. In Paragraph 9, The above coating layer contains carbon, and Based on the total weight of the positive electrode active material, the carbon content is 1.0 to 2.0 wt%, Olivine-based positive electrode active material.

11. In Paragraph 1, The above positive active material is composed of a lithium metal phosphate containing a halogen element located while surrounding a void space and part or all of the void space. Olivine-based positive electrode active material.

12. A step of obtaining a mixture by dry mixing lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additives, followed by milling; A step of obtaining lithium iron phosphate by first calcining the above mixture in a reducing atmosphere; A step of preparing a slurry by introducing a mixture of the above-mentioned lithium iron phosphate, carbon additive, and dispersant into a solvent and wet milling; A step of obtaining a positive electrode active material precursor by spray-drying the above slurry; and A step comprising: a second calcination of the above-mentioned positive active material precursor in a reducing atmosphere to obtain an olivine-based positive active material having a carbon coating layer formed thereon; Method for manufacturing an olivine-based positive electrode active material.

13. In Paragraph 12, In the step of obtaining a mixture by dry mixing and then milling the above lithium dihydrogen phosphate (LiH2PO4), ferric oxide (Fe2O3), and chloride additive, Mixing a chloride additive in an amount greater than 0.1 wt% and less than 10.0 wt% based on the total weight of the above lithium dihydrogen phosphate (LiH2PO4) and ferric oxide (Fe2O3), Method for manufacturing an olivine-based positive electrode active material.

14. In Paragraph 12, The chloride additive comprises one or more selected from calcium chloride (CaCl2), ammonium chloride (NH4Cl), and sodium chloride (NaCl). Method for manufacturing an olivine-based positive electrode active material.

15. In Paragraph 12, After performing the step of obtaining lithium iron phosphate by first calcining the above mixture in a reducing atmosphere, The method further includes a step of washing the obtained lithium iron phosphate. Method for manufacturing an olivine-based cathode active material.

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