Method for preparation of olivine-based positive active material, and olivine-based positive active material prepared using same

Abstract

A method for preparation of an olivine-based positive active material according to an embodiment of the present invention comprises the steps of: mixing and milling a lithium raw material, a phosphorus raw material, and an iron raw material to obtain a mixture; reductively calcining the mixture to obtain lithium iron phosphate; adding a mixture of the lithium iron phosphate, a carbon additive, and a dispersant into a solvent and wet-milling to prepare a slurry; spray-drying the slurry to obtain a positive active material precursor; and secondarily calcining the positive active material precursor in a reducing atmosphere to obtain an olivine-based positive active material having a carbon coating layer, wherein the moisture content in the slurry may be greater than 25 wt% and at most 60 wt%.

Description

Method for manufacturing an olivine-based cathode active material and an olivine-based cathode active material manufactured thereby

[0001] The present invention relates to a method for manufacturing an olivine-based positive electrode active material and an olivine-based positive electrode active material manufactured thereby.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0189152, filed on December 17, 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 (LiIP) cathode active material is an olivine-based structure composed of FeO6 octahedral sites and PO4 octahedral 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, it has a history of being used in the production of many electric vehicles 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 typically known to be manufactured by hydrothermal synthesis using LiOH, FeSO4, and (NH4)3PO4 as raw materials, spray drying using Li2CO3 and FePO4 precursors, or milling using Li2CO3 and FePO4. Meanwhile, since LFP itself lacks electrical conductivity, it is necessary to uniformly coat the surface of the cathode active material with carbon during the manufacturing process in order to use it as a cathode active material. In the case of LFP cathode active materials composed of LFP primary particles with a size of several hundred nanometers, the slurry stability for electrode manufacturing is low due to the size of the secondary particles, and adhesion to the electrode plate is also not high. Furthermore, when the particle size is small, it is difficult to increase the electrode plate density, which leads to a problem where the energy density per unit volume is not high when manufactured into a cell. To improve this, LFP primary particles with a size of several hundred nanometers can be converted into spherical secondary particles. Increasing the secondary particle size in this way can be effective in increasing the electrode plate energy density, thereby significantly improving the cell energy density per unit volume when increasing the electrode plate thickness.

[0005] However, in the case of the above and conventional spray drying methods, due to the high water content in the slurry, the slurry becomes excessively liquid, making it difficult for raw materials to be uniformly dispersed, and an excessive water removal process is required in the subsequent heat treatment process, which may result in a problem where the electrochemical performance of the finally manufactured lithium iron phosphate deteriorates.

[0006] In addition, the non-uniform particle shape of the manufactured lithium iron phosphate may lead to a longer grinding time, which can result in a decrease in overall production efficiency.

[0007] Therefore, there is a need to develop technology for a simple and economical method to manufacture lithium iron phosphate with a uniform composition and excellent electrochemical performance.

[0008] One objective of the present invention is to provide a method for manufacturing an olivine-based cathode active material capable of achieving excellent electrochemical performance in an economical and simple manner, and an olivine-based cathode active material manufactured therefrom.

[0009] A method for manufacturing an olivine-based cathode active material according to one embodiment of the present invention comprises the steps of: mixing and milling a lithium raw material, a phosphorus raw material, and an iron raw material to obtain a mixture; reducing and calcining the mixture to obtain lithium iron phosphate; introducing a mixture of the lithium iron phosphate, a carbon additive, and a dispersant into a solvent and wet-milling to prepare a slurry; spray-drying the slurry to obtain a cathode active material precursor; and secondarily calcining the cathode active material precursor in a reducing atmosphere to obtain an olivine-based cathode active material with a carbon coating layer formed thereon; wherein the moisture content in the slurry may be greater than 25 wt% and less than or equal to 60 wt%.

[0010] The moisture content in the above slurry may be 50 wt% to 60 wt%.

[0011] The average particle size of the solid material in the above slurry may be 0.8 to 1.1 μm.

[0012] The specific surface area (BET) of the obtained cathode active material is 8.0 to 12.0 m² 2 It can be / g.

[0013] The rolled density of the obtained positive electrode active material is 2.5 g / cm³ 3 It could be more than that.

[0014] The above lithium raw material and phosphorus raw material include lithium dihydrogen phosphate (LiH2PO4), and the above iron raw material may include ferric oxide (Fe2O3).

[0015] An olivine-based cathode active material according to one embodiment of the present invention comprises a lithium manganese iron phosphate core portion; and a coating layer located on the surface of the core portion; and may have an average grain size of 200 nm to 300 nm.

[0016] The specific surface area (BET) of the above positive active material is 12.0 m² 2 It may be less than / g.

[0017] The rolled density of the above positive active material is 2.50 g / cm³ 3 It could be more than that.

[0018] The above positive active material can satisfy the following relationship 1.

[0019] [Relationship 1]

[0020] 1.20≤ D50 / BET*ρ ≤3.00

[0021] Here, D50 is the average particle size of the positive active material (unit: μm), and BET is the specific surface area (unit: m²). 2 / g), ρ is the rolling density (unit: g / cm³ 3 )am.

[0022] The above positive active material can satisfy the following relationship 2.

[0023] [Relationship 2]

[0024] 80.0≤ Cs / D50*ρ ≤150.0

[0025] Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the cathode active material (unit: μm), and ρ is the rolled density (unit: g / cm³). 3 )am.

[0026] The above positive active material can satisfy the following relationship 3.

[0027] [Relationship 3]

[0028] 40.0≤ Cs*D50 / BET ≤100.0

[0029] Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the positive active material (unit: μm), and BET is the specific surface area (unit: m²). 2 / g) is.

[0030] The coating layer comprises a carbon (C) element and may contain 1.0 wt% to 2.0 wt% of the carbon based on the total weight of the positive electrode active material.

[0031]

[0032] The method for manufacturing an olivine-based cathode active material according to an embodiment of the present invention can improve the rolling density of the final cathode active material and increase the energy density per unit volume by controlling the moisture content in the slurry to a predetermined range, and can extend battery life by increasing electrochemical stability.

[0033] The method for manufacturing an olivine-based cathode active material according to an embodiment of the present invention can improve the energy density per unit volume of the cathode active material by manufacturing an olivine-based cathode active material with a large crystal grain size.

[0034] Figure 1 shows an SEM analysis image of an olivine-based cathode active material according to Example 1.

[0035] Figure 2 shows an SEM analysis image of an olivine-based cathode active material according to Example 4.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0041] 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.

[0042] 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.

[0043]

[0044] 1. Method for manufacturing olivine-based cathode active material

[0045] One embodiment of the present invention provides a method for manufacturing an olivine-based positive electrode active material.

[0046] A method for manufacturing an olivine-based positive electrode active material for a lithium secondary battery according to the present invention may include the steps of: mixing and milling a lithium raw material, a phosphorus raw material, and an iron raw material to obtain a mixture; reducing and calcining the mixture to obtain lithium iron phosphate; introducing a mixture of the lithium iron phosphate, a carbon additive, and a dispersant into a solvent and wet-milling to produce a slurry; spray-drying the slurry to obtain a positive electrode active material precursor; and secondarily calcining the positive electrode active material precursor in a reducing atmosphere to obtain an olivine-based positive electrode active material having a carbon coating layer formed thereon.

[0047]

[0048] First, a step is performed to obtain a mixture by mixing and milling lithium raw material, phosphorus raw material, and iron raw material.

[0049] In the present invention, the lithium raw material and the phosphorus raw material include lithium dihydrogen phosphate (LiH2PO4), and the iron raw material may include ferric oxide (Fe2O3).

[0050] The above lithium dihydrogen phosphate (LiH2PO4) can be obtained by reacting lithium phosphate (Li3PO4), which is generated as an intermediate step in the production of lithium carbonate or lithium hydroxide used in the manufacture of cathode materials for lithium-ion batteries from salt lakes and ore lithium, with a phosphoric acid (H3PO4) solution. The above ferric oxide (Fe2O3) can be recovered and used from steel pickling wastewater, and by reducing or suppressing the generation of wastewater through this, carbon-coated olivine-based cathode active materials can be manufactured in an environmentally friendly manner.

[0051] In addition, the 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.

[0052]

[0053] In the present invention, mixing milling can be performed by introducing the lithium raw material, phosphorus raw material, and iron raw material into a grinding device. Specifically, the lithium dihydrogen phosphate (LiH2PO4) and ferric oxide (Fe2O3) can be introduced into a grinding device and milled while mixing.

[0054] In the present invention, the grinding device may be, for example, an air jet mill, a hammer, a screen mill, a fine impact mill, a ball mill, or a vibrator mill, and specifically, a fine impact mill.

[0055] Meanwhile, in this embodiment, an inert gas or a reducing gas can be continuously supplied into the grinding device during mixing milling to form a reducing atmosphere.

[0056] The above inert gas atmosphere or reducing gas atmosphere can be formed by continuously supplying one or more gases selected from pure nitrogen gas, pure argon gas, a mixture of hydrogen and nitrogen gas, a mixture of hydrogen and argon gas, or coke oven gas.

[0057] 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.

[0058]

[0059] Next, a step is performed to obtain lithium iron phosphate by first calcining the mixture obtained by mixing and milling the lithium raw material, phosphorus raw material, and iron raw material in a reducing atmosphere.

[0060] 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.

[0061] 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℃, 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.

[0062] 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.

[0063]

[0064] In addition, a step of grinding the obtained lithium iron phosphate can be additionally performed.

[0065] 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 10 to 50 μm.

[0066] 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 olivine-based cathode active material.

[0067] The above mixture of lithium iron phosphate, carbon additive, and dispersant is introduced into a solvent and wet-milled to perform the slurry step.

[0068] In the present invention, the lithium iron phosphate, carbon additive, and dispersant can be introduced into a mixer and then stirred and mixed.

[0069] The above dispersant can be mixed in an amount of 1 to 5 wt%, specifically 2 to 4 wt%, based on the weight of the lithium iron phosphate.

[0070] At this time, the carbon additive can be mixed in an amount of 1 to 5 wt%, specifically 2 to 4 wt%, based on the total weight of the dried precipitate and the carbon additive.

[0071] 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.

[0072] More specifically, the above dispersant may be citric acid.

[0073] The above dispersant can prevent the clumping of particulate materials and can also form a carbon coating layer on the surface of the particles.

[0074] In the present invention, a dispersant can be mixed in an amount of 4 wt% to 6 wt% based on the total weight of the iron raw material. By mixing the dispersant within the above range, the raw materials in the slurry being manufactured are uniformly dispersed, which is advantageous for manufacturing a carbon-coated olivine-based cathode active material of excellent quality.

[0075] 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. Specifically, glucose may be used as the carbon additive.

[0076] In the present invention, the carbon additive can be mixed in a range of 0.5 wt% to 3.0 wt% based on the total weight of the phosphorus raw material, lithium raw material, and iron raw material, and specifically, in a range of 1.0 wt% to 2.0 wt%.

[0077] 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.

[0078] The above solvents are, for example, alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, and diacetone alcohol; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; ethers such as diethyl ether, ethylene glucose monomethyl ether (methyl cellosolve), ethylene glucose monoethyl ether (ethyl cellosolve), ethylene glucose monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; and ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone, and cyclohexanone. Examples include amides such as dimethylformamide, N,N-dimethylacetoacetamide and N-methylpyrrolidone; and glycols such as ethylene glycol, diethylene glycol and propylene glycol, but are not limited thereto.

[0079] In the present invention, the solvent may be ethanol, water, distilled water, or deionized water. Specifically, it may be deionized water (DIW).

[0080] In the step of preparing the above slurry, a raw material containing one or more elements selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, or Ga may be additionally added. Through this, an olivine-based cathode active material containing the above elements can be prepared.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085]

[0086] In the step of preparing a slurry by introducing the mixture into a solvent and wet milling in the present invention, the average particle size of the solid material included in the slurry may be 2.0 μm or less, and specifically may be 0.8 to 1.1 μm.

[0087] 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.

[0088]

[0089] Next, the step of spray-drying the above slurry to form a positive electrode active material precursor can be performed.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] In the present invention, the calcination was performed while flowing a reducing gas.

[0096] 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.

[0097] 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.

[0098] 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.

[0099]

[0100] 2. Olivine-based cathode active material

[0101] An olivine-based cathode active material according to another embodiment of the present invention may include a lithium manganese iron phosphate core portion and a coating layer located on the surface of the core portion.

[0102] The average grain size of the lithium manganese iron phosphate according to the present invention may be 200.0 nm or larger, specifically 200 to 300 nm or 200 to 250 nm.

[0103] 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.

[0104] The above grain size can be specifically calculated by the Scherrer equation Equation 1.

[0105] τ=(K*λ) / (β*cosθ) (1)

[0106] 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.

[0107] In the present invention, the shape factor is generally 1.0, but it may vary depending on the crystallite.

[0108] 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.

[0109] The average particle size (D50) of the secondary particles of the above olivine-based cathode active material may be 5.0 μm or more, and specifically may be 5.0 to 10.0 μm.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] In this specification, “grain” refers to a distinct region in which atoms within a primary particle form a lattice structure in a certain direction.

[0114] The average particle size of the above secondary particles can be measured using PSA (Particle size analysis).

[0115]

[0116] 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.

[0117] 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.

[0118] In the present invention, the carbon content included in the olivine-based cathode active material may be 1.0 to 2.0 wt%.

[0119] In the present invention, when the carbon content satisfies the above range, there is an advantage that the output characteristics and lifespan characteristics of the lithium secondary battery are improved.

[0120] In the present invention, the carbon content was confirmed by measuring it using a high-precision carbon / sulfur analyzer. Specifically, the content of the olivine-based cathode active material for a lithium secondary battery was measured in 100 parts by weight of the total by detecting the content of oxide carbon and sulfur generated by burning the sample together with a combustion agent in an oxygen stream.

[0121]

[0122] The rolled density of the olivine-based cathode active material according to the present invention is 2.50 / cm³ 3 It may be more than, specifically 2.50 to 3.50 / cm 3 , or 2.70 to 3.10 / cm 3 It could be.

[0123] 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.

[0124] 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.

[0125] The specific surface area (BET) of the olivine-based cathode active material according to the present invention is 12.0 m² 2 It may be less than / g, and 8.0 to 12.0 m² 2 / g can be.

[0126] 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.

[0127] In the present invention, the positive active material can satisfy the following relationship 1.

[0128] [Relationship 1]

[0129] 1.20≤ D50 / BET*ρ ≤3.00

[0130] In the above Equation 1, D50 is the average particle size of the positive active material (unit: μm), and BET is the specific surface area (unit: m²). 2 / g), ρ is the rolling density (unit: g / cm³ 3 )am.

[0131] In the above relationship 1, the value of D50 / BET*ρ can be 1.20 to 3.00, and specifically 1.30 to 2.70.

[0132] In the present invention, the unit of D50 / BET*ρ in the above relationship 1 is made dimensionless.

[0133]

[0134] The above positive active material can satisfy the following relationship 2.

[0135] [Relationship 2]

[0136] 80.0≤ Cs / D50*ρ ≤150.0

[0137] Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the cathode active material (unit: μm), and ρ is the rolled density (unit: g / cm³). 3 )am.

[0138] In the present invention, the value of Cs / D50*ρ in the above relationship 2 may be 80.0 to 150.0, and specifically 90.0 to 130.0.

[0139] In the above relationship 2, the unit of Cs / D50*ρ was made dimensionless.

[0140]

[0141] The above positive active material can satisfy the following relationship 3.

[0142] [Relationship 3]

[0143] 40.0≤ Cs*D50 / BET ≤100.0

[0144] Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the positive active material (unit: μm), and BET is the specific surface area (unit: m²). 2 / g) is.

[0145] In the above relationship 3, the value of Cs*D50 / BET can be 40.0 to 100.0, and specifically 45.0 to 90.0.

[0146] In the present invention, the unit of Cs*D50 / BET in the above relationship 3 is made dimensionless.

[0147]

[0148] When one or more of the above equations 1, 2, or 3 are satisfied, the crystal grain size, average particle size, specific surface area, or rolling density of the positive electrode active material are controlled in combination, so that ion conductivity can be improved while maintaining structural stability, and the contact area of ​​the positive electrode active material with the electrolyte can be increased while suppressing the occurrence of side reactions, thereby improving the discharge capacity, rate characteristics, and life characteristics of the battery to which it is applied.

[0149] The olivine-based positive electrode active material according to the present invention may be a compound represented by the following chemical formula 1.

[0150] [Chemical Formula 1]

[0151] Li 1+a Fe 1-b M b (PO 4-c )X c

[0152] 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≤c<0.05).

[0153] 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.

[0154] In the present invention, the doping metal element (M) may be included in an amount greater than 50 ppm and less than 400 ppm.

[0155] 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.

[0156] 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.

[0157] 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.

[0158]

[0159] 3. Cathode for lithium secondary batteries and lithium secondary batteries

[0160] 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.

[0161] Here, the positive electrode active material may be an olivine-based positive electrode active material or an olivine-based positive electrode active material manufactured according to the method for manufacturing an olivine-based positive electrode active material described above.

[0162] 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.

[0163] The above positive active material layer may further include a binder and a conductive material.

[0164] 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.

[0165] In the battery being constructed, any electronically conductive material that does not cause chemical changes can be used as the above-mentioned conductive material.

[0166] Meanwhile, in another embodiment of the present invention, a lithium secondary battery comprising a positive electrode for the lithium secondary battery is provided.

[0167] The above lithium secondary battery may include a negative electrode and a non-aqueous electrolyte.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] Materials capable of doping and dedoping the above lithium include, for example, Si, SiO xExamples 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).

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] The above solvent may include N-methylpyrrolidone, but is not limited thereto.

[0179] The above electrolyte may be a non-aqueous electrolyte or a solid electrolyte, and may be used in which a lithium salt is dissolved.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] The present invention does not limit the structure and manufacturing method of the lithium secondary battery.

[0188]

[0189] 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.

[0190]

[0191] (Example 1)

[0192] (1) Manufacturing of positive electrode active material

[0193] (Formation of raw material mixture)

[0194] Lithium dihydrogen phosphate (LiH2PO4) powder with an average particle size of 48.24 μm and ferric oxide (Fe2O3) powder with an average particle size of 2.07 μm were mixed in the weight ratio shown in Table 1, and the mixture was uniformly milled using a ball mill or a powder mixer to obtain the mixed powder.

[0195] (1st firing)

[0196] 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.

[0197] (purifying)

[0198] The lithium iron phosphate prepared above can be washed using distilled water.

[0199] 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.

[0200] After washing was completed, the washed lithium iron phosphate was separated using a filter.

[0201] (Wet milling)

[0202] Next, in the wet milling step, the washed lithium iron phosphate (93.6g) is fed into a bead mill device along with 0.94g of citric acid, 5.43g of glucose, and deionized water by mass.

[0203] For wet milling, 300 ml of ZrO2 balls were fed into a wet milling machine in an amount similar to the solid content, and wet bead milling was performed at a wet milling machine rotation speed of 10 m / s and a circulation speed of 200 mL / min.

[0204] At this time, the wet milling machine was set to a rotational speed of 200 rpm and performed for 30 minutes.

[0205] The average particle size of the solid material in the final slurry produced through wet milling was made to be 3㎛ or less.

[0206] In addition, the moisture content in the slurry was made to 55 wt%.

[0207] In the present invention, the wet milling machine used was the ECM-AP 05 (Grinding container volume 0.5L).

[0208] (Spray drying)

[0209] The above slurry was spray-dried using a spray drying device.

[0210] 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.

[0211] (Sintering)

[0212] The above-described olivine-based cathode active material precursor was loaded into a kiln and calcined at 700°C for 5 hours under a reducing atmosphere with nitrogen (N2) gas flowing through it to produce a carbon-coated LiFePO4 cathode active material.

[0213] Specifically, nitrogen (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.

[0214] An SEM image of the final manufactured cathode active material is shown in Figure 1.

[0215] Tables 1 and 2 show the process conditions of Example 1.

[0216]

[0217] (2) Manufacturing of coin-type half-cells

[0218] After manufacturing a CR2032 coin cell using the above-mentioned olivine-based cathode active material, an electrochemical evaluation was performed.

[0219] 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.

[0220] 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.

[0221]

[0222] (Examples 2 to 5 and Comparative Examples 1 to 5)

[0223] Olivene-based cathode active materials of Examples 2 to 5 and Comparative Examples 1 to 5 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.

[0224]

[0225] Raw Material Mixture 1st Calcination Fe2O3 Weight (g) LDP Weight (g) Citric Acid (g) 1st Calcination Temperature (°C) 1st Firing Time (h) Example 1 199.6258.342.496505 Example 2 199.6258.342.496505 Example 3 199.6258.342.496505 Example 4 199.6258.342.496505 Example 5 199.6258.342.496505 Comparative Example 1 199.6258.342.496508 Comparative Example 2 199.6258.342.496508 Comparative Example 3 199.6258.342.496508 Comparative Example 4 199.6258.342.496708 Comparative Example 5 199.6258.342.496708

[0226]

[0227] Slurry Preparation Secondary Calcination Solids (Based on 100wt%) Slurry Moisture Content (wt%) Average Particle Size of Solids in Slurry (㎛) 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: 3.6 0.9 45.4 35 51.0 9 200 0.5 70 0 5 Example 2: 3.6 0.9 45.4 35 51.0 9 200 0.5 70 0 5 Example 3: 3.6 0.9 45.4 35 50.8 75 00 170 0 5 Example 4: 3.6 0.9 45.4 36 00 9 15 00 170 0 5 Example 5 93.60.945.43500.952000.57005 Comparative Example 1 93.60.945.43651.1120017005 Comparative Example 2 93.60.945.43751.2020017005 Comparative Example 3 93.60.945.43651.135000.57005 Comparative Example 4 93.60.945.43751.085000.57005 Comparative Example 5 93.60.945.43801.165000.57005

[0228] (Evaluation Example 1: XRD Analysis)

[0229] 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.

[0230]

[0231] (Evaluation Example 2: Olivine-based positive electrode active material particle size)

[0232] The average particle size (D50) of the olivine-based cathode active material prepared according to the above examples and comparative examples was measured using PSA (Particle size analysis) and is shown in Table 3. Specifically, the particle size corresponding to 50% of the volume accumulation was measured using the laser diffraction method.

[0233]

[0234] (Evaluation Example 3: Specific Surface Area BET)

[0235] The specific surface area of ​​the olivine-based cathode active materials prepared according to the above examples and comparative examples was analyzed and is shown in Table 3.

[0236] 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).

[0237]

[0238] (Evaluation Example 4: Rolled Density)

[0239] 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.

[0240]

[0241] (Evaluation Example 5: C content)

[0242] The carbon content of the olivine-based cathode active material prepared according to the examples and comparative examples was confirmed by measuring it using a high-precision carbon analyzer. Specifically, the content was measured for 100 parts by weight of the total cathode active material by detecting the content of oxide carbon generated by burning the sample together with a combustion promoter in an oxygen stream.

[0243] Table 3 below shows the results of the characteristic analysis of the cathode active materials prepared according to Examples 1 to 5 and Comparative Examples 1 to 5, and the values ​​of Equations 1 to 3 calculated therefrom.

[0244]

[0245] Grain size (nm) Average grain diameter (D50) (㎛) BET (m 2 / g) Rolled density (g / cm²) 3)C Content (wt%) [Equation 1] D50 / BET*ρ (Unit: Dimensionless) [Equation 2] Cs / D50*ρ (Unit: Dimensionless) [Equation 3] Cs*D50 / BET (Unit: Dimensionless) Example 1 2256.5 10.2 02.8 21.3 1.8 097.6 262.21 Example 2 2186.29.1 32.9 41.3 2.0 0103.3 770.20 Example 3 2307.18.2 73.0 31.3 2.6 098.1 584.27 Example 4 2055.6 11.2 32.7 11.3 1.3 599.2 149.47 Example 52425.78.363.011.32.05127.7987.13 Comparative Example 11865.812.522.121.30.9867.9931.50 Comparative Example 21536.313.352.341.31.1056.8326.82 Comparative Example 31886.113.752.351.31.0472.4332.13 Comparative Example 4986.215.341.931.30.7830.5112.33 Comparative Example 51036.415.282.081.30.8733.4814.02

[0246] Experimental Example 1: Evaluation of Initial Discharge Capacity and Initial Efficiency

[0247] 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.

[0248]

[0249] Experimental Example 2: Evaluation of Rate Characteristics (1C / 0.1C)

[0250] 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.

[0251]

[0252] Experimental Example 3: Evaluation of Life Characteristics

[0253] The coin-type half-cell manufactured above was charged to 4.2V at 25°C 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.

[0254] The results of the measured horizontal characteristic evaluation are shown in Table 4 below.

[0255]

[0256] Slurry Moisture Content (wt%) Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Rate (1C / 0.1C) Lifetime Characteristics @ 100 cycles (%) Example 1: 55 162.3 159.0 91.2 91.1 Example 2: 55 163.1 159.5 90.2 90.3 Example 3: 55 164.0 161.8 92.5 93.8 Example 4: 60 164.7 161.4 90.9 94.0 Example 5: 50 164.2 158.0 90.1 92.5 Comparative Example 1: 65 159.3 155.6 87.3 89.0 Comparative Example 2: 75 158.0 151.3 85.9 83.8 365160.3152.189.590.1 Comparative Example 475153.2148.785.789.1 Comparative Example 580153.2149.484.680.8

[0257] Referring to Tables 1 to 4 above, in Examples 1 to 5, when an olivine-based cathode active material prepared by controlling the water content in the slurry to a range of more than 25 wt% to 60 wt% according to the method for preparing an olivine-based cathode active material of the present invention is applied, the initial discharge capacity is 156 mAh / g or more, the 1C / 0.1C rate characteristic is 90% or more, and the 100-cycle capacity retention rate is 90.3% or more.

[0258] In Comparative Examples 1 to 5, when an olivine-based cathode active material prepared by controlling the moisture content in the slurry to be greater than 25 wt% and outside the range of 60 wt% was applied, the initial discharge capacity was less than 156 mAh / g, the 1C / 0.1C rate characteristic was less than 90%, and the 100-cycle capacity retention rate was less than 90.3%.

[0259]

[0260] 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.

[0261] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A step of obtaining a mixture by mixing and milling lithium raw material, phosphorus raw material, and iron raw material; A step of obtaining lithium iron phosphate by reducing and calcining the above mixture; 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 The method comprises the step of obtaining an olivine-based positive electrode active material with a carbon coating layer formed by secondarily calcining the above positive electrode active material precursor in a reducing atmosphere; The moisture content in the above slurry is greater than 25 wt% and less than or equal to 60 wt%, Method for manufacturing an olivine-based positive electrode active material.

2. In Paragraph 1, The moisture content in the above slurry is 50 wt% to 60 wt%, Method for manufacturing an olivine-based positive electrode active material.

3. In Paragraph 1, The average particle size of the solid material in the above slurry is 0.8 to 1.1 μm, Method for manufacturing an olivine-based positive electrode active material.

4. In Paragraph 1, The specific surface area (BET) of the obtained cathode active material is 8.0 to 12.0 m² 2 / g thing, Method for manufacturing an olivine-based positive electrode active material.

5. In Paragraph 1, The rolled density of the obtained positive electrode active material is 2.5 g / cm³ 3 The thing that is ideal Method for manufacturing an olivine-based positive electrode active material.

6. In Paragraph 1, The above lithium raw material and phosphorus raw material include lithium dihydrogen phosphate (LiH2PO4), and The above iron raw material includes ferric oxide (Fe2O3), Method for manufacturing an olivine-based positive electrode active material.

7. Lithium manganese iron phosphate core part; and A coating layer located on the surface of the core portion; comprising, One having an average grain size of 200 nm to 300 nm, Olivine-based positive electrode active material.

8. In Paragraph 7, The specific surface area (BET) of the above positive active material is 12.0 m² 2 that is less than or equal to / g, Olivine-based positive electrode active material.

9. In Paragraph 7, The rolled density of the above positive active material is 2.50 g / cm³ 3 The thing that is ideal Olivine-based positive electrode active material.

10. In Paragraph 7, The above positive active material satisfies the following relationship 1, Olivine-based positive electrode active material. [Relationship 1] 1.20≤ D50 / BET*ρ ≤3.00 (Here, D50 is the average particle size of the positive active material (unit: μm), BET is the specific surface area (unit: m²) 2 / g), ρ is the rolling density (unit: g / cm³ 3 )am.) 11. In Paragraph 7, The above positive active material satisfies the following relationship 2, Olivine-based positive electrode active material. [Relationship 2] 80.0≤ Cs / D50*ρ ≤150.0 (Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the positive active material (unit: μm), and ρ is the rolled density (unit: g / cm³) 3 )am.) 12. In Paragraph 7, The above positive active material satisfies the following relationship 3, Olivine-based positive electrode active material. [Relationship 3] 40.0≤ Cs*D50 / BET ≤100.0 (Here, Cs is the average grain size (unit: nm), D50 is the average particle size of the positive active material (unit: μm), and BET is the specific surface area (unit: m²) 2 / g)is.) 13. In Paragraph 7, The above coating layer contains carbon (C) elements, and The above-mentioned positive electrode active material comprises 1.0 wt% to 2.0 wt% of carbon based on the total weight of the above-mentioned positive electrode active material. Olivine-based positive electrode active material.

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