Positive electrode active material, and positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a lithium iron phosphate-based positive electrode active material, and a positive electrode and a lithium secondary battery comprising same. The positive electrode active material includes: a lithium iron phosphate-based compound; and a coating layer formed on the lithium iron phosphate-based compound and containing carbon (C), wherein the value of X according to Equation 1 described in the present specification is 65-300.

Description

Cathode active material, a cathode including the same, and a lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0129887 filed September 25, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a lithium iron phosphate-based cathode active material, a cathode containing the same, and a lithium secondary battery.

[0005]

[0006] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0007] Lithium secondary batteries consist of four major components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the positive electrode active material, which is included in the positive electrode, plays a significant role in determining the battery's capacity, output, and lifespan. Currently used positive electrode active materials include NCM-based positive electrode active materials containing nickel, cobalt, manganese, and / or aluminum, and LFP (lithium iron phosphate)-based positive electrode active materials. Meanwhile, improving the performance of the positive electrode active material is essential for lithium secondary batteries to have high energy density, output, and lifespan; consequently, much research is currently being conducted to develop high-performance positive electrode active materials.

[0008] LFP-based cathode active materials, which are olivine-structured cathode active materials, possess high structural stability, excellent thermal stability and lifespan, and are price-competitive due to their low cost. However, LFP-based cathode active materials suffer from poor power output characteristics due to low electronic and ionic conductivity. Therefore, there is a need to develop improved LFP-based cathode active materials.

[0009]

[0010] The problem to be solved by the present invention is to provide a lithium iron phosphate-based cathode active material capable of improving the capacity and output characteristics of a lithium secondary battery.

[0011]

[0012] The present invention provides a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0013]

[0014] (1) The present invention provides a positive electrode active material comprising a lithium iron phosphate-based compound; and a coating layer formed on the lithium iron phosphate-based compound and containing carbon (C), wherein the X value according to Formula 1 below is 65 to 300.

[0015] [Equation 1]

[0016]

[0017] In the above Equation 1,

[0018] The unit of the BET specific surface area value is m 2 It is the value when / g, and

[0019] The carbon content value is the carbon content (weight%) relative to the total weight of the cathode active material, and

[0020] Average particle size (D 50 The value is the value when the unit is μm.

[0021] (2) In the above (1), the BET specific surface area is 10 m 2 / g to 30m 2 Provides a positive electrode active material with a g / g content.

[0022] (3) In the above (1) or (2), the carbon content is 1.0% to 3.0% by weight relative to the total weight of the positive active material.

[0023] (4) In any one of (1) to (3) above, the average particle size (D 50 ) provides a positive electrode active material having a thickness of 0.20㎛ to 0.60㎛.

[0024] (5) In any one of (1) to (4) above, the lithium iron phosphate compound is doped with one or more doping elements selected from the group consisting of V, Mg, Al, Co and W, thereby providing a positive electrode active material.

[0025] (6) In any one of (1) to (5) above, the lithium iron phosphate compound has a composition represented by the following chemical formula 1 and provides a positive electrode active material.

[0026] [Chemical Formula 1]

[0027] Li 1+x [Fe 1-a-b-c Mn a M 1 b M 2 c ]PO4

[0028] In the above chemical formula 1,

[0029] M 1 is one or more selected from the group consisting of V, Mg, Al, Co, and W, and

[0030] M 2 is one or more selected from the group consisting of Mg, Nd, and Ni, and

[0031] 0≤x≤0.05, 0≤a≤0.8, 0≤b≤0.02, 0≤c≤0.02.

[0032] (7) In any one of (1) to (6) above, the positive active material has a press density of 1.60 g / cm³ 3Up to 2.00g / cm² 3 Provides a positive electrode active material.

[0033] (8) Provides a positive electrode comprising a positive electrode active material according to any one of (1) to (7) above.

[0034] (9) Provides a lithium secondary battery including a positive electrode according to (8) above.

[0035]

[0036] The positive electrode active material according to the present invention satisfies specific conditions regarding the relationship between BET specific surface area, carbon content, and particle size, and accordingly, the mobility of ions and charges is improved, thereby improving the capacity characteristics and output characteristics of a battery containing the same.

[0037]

[0038] The present invention will be described in more detail below to aid in understanding. In this regard, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0039] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0040] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0041] In this specification, 'D n ' represents the particle size at the n% point of the cumulative volume distribution according to particle size. That is, D 50 is the particle size at the 50% point of the cumulative volume distribution according to particle size. The above D n It can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern Panalytical Mastersizer 3000), and the particle size distribution is calculated by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam. By calculating the particle diameter at the point where the cumulative volume distribution according to particle size in the measuring device reaches 50%, D 50 It can measure.

[0042]

[0043] positive electrode active material

[0044] The positive electrode active material according to the present invention comprises: a lithium iron phosphate-based compound; and a coating layer formed on the lithium iron phosphate-based compound and containing carbon (C), wherein the X value according to Formula 1 below is 65 to 300.

[0045] [Equation 1]

[0046]

[0047] In the above Equation 1,

[0048] The unit of the BET specific surface area value is m 2 It is the value when / g, and

[0049] The carbon content value is the carbon content (weight%) relative to the total weight of the cathode active material, and

[0050] Average particle size (D 50 The value is the value when the unit is μm.

[0051] The value of X according to Equation 1 above is a dimensionless number.

[0052]

[0053] The positive electrode active material according to the present invention comprises a carbon-containing coating layer formed on a lithium iron phosphate-based compound, and satisfies an X value according to Formula 1 of 65 to 300, thereby having the advantage of improved ion and charge mobility. Furthermore, satisfying the above conditions has the advantage of reducing the rolling density of the positive electrode active material, and consequently, the performance of the electrode and battery containing it can be improved. In particular, the capacity of the electrode and battery can be increased and the output characteristics can be improved.

[0054] Meanwhile, even if the positive active material includes a carbon coating layer on its surface, if the value according to Equation 1 is less than 65, the movement of ions and charges is restricted and performance may be degraded, and if it exceeds 300, the rolling density is lowered and there is a problem with electrode processability.

[0055] According to the present invention, the value according to Formula 1 may specifically be 65 or more, 70 or more, 75 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 105 or more, 110 or more, 115 or more, or 120 or more, and may be 195 or less, 200 or less, 210 or less, 220 or less, 230 or less, 240 or less, 250 or less, 260 or less, 270 or less, 280 or less, 290 or less, or 300 or less.

[0056]

[0057] For reference, a higher BET specific surface area of ​​the cathode active material increases the reaction surface area with the electrolyte, thereby improving electrochemical performance, while the large surface area reduces rolling density. Additionally, a higher carbon content in the cathode active material improves performance and reduces rolling density. Furthermore, a smaller average particle size of the cathode active material shortens the lithium ion pathway, improving performance and reducing rolling density.

[0058] That is, the BET specific surface area and carbon content are in a proportional relationship with the performance of the cathode active material, and the average particle size is inversely proportional to the performance of the cathode active material. The inventors of the present invention defined the X value according to Equation 1 as described above, and discovered that the higher the X value, the better the performance of the cathode active material, but if the X value becomes too high, the rolling density is significantly lower, resulting in a problem of low energy density, and thus completed the present invention.

[0059]

[0060] Hereinafter, the positive active material according to the present invention will be described in detail.

[0061]

[0062] According to the present invention, the BET specific surface area of ​​the positive electrode active material is 10 m² 2 / g to 30m 2 It may be / g. Specifically, the BET specific surface area of ​​the anode active material is 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, or 19m 2 It can be more than / g, and 24m 2 / g, 25m 2 / g, 26m 2 / g, 27m 2 / g, 28m 2 / g, 29m 2 / g, or 30m 2 It may be less than / g. When the BET specific surface area of ​​the positive electrode active material is within the above range, an appropriate surface area reacting with the electrolyte may exist.

[0063]

[0064] According to the present invention, the carbon content included in the positive electrode active material may be 1.0% to 3.0% by weight relative to the total weight of the positive electrode active material. Specifically, the carbon content included in the positive electrode active material may be 1.0% or more by weight, 1.1% or more by weight, 1.2% or more by weight, 1.3% or more by weight, 1.4% or more by weight, 1.5% or more by weight, 1.6% or more by weight, 1.7% or more by weight, or 1.8% or more by weight relative to the total weight of the positive electrode active material, and may be 2.3% or less by weight, 2.4% or less by weight, 2.5% or less by weight, 2.6% or less by weight, 2.7% or less by weight, 2.8% or less by weight, 2.9% or less by weight, or 3.0% or less by weight. When the carbon content included in the positive electrode active material is within the above range, electrical conductivity is improved, and at the same time, the entry and exit of lithium ions may not be hindered.

[0065]

[0066] According to the present invention, the average particle size (D) of the positive electrode active material 50 ) may be 0.20㎛ to 0.60㎛. Specifically, the average particle size (D) of the positive electrode active material 50 ) may be 0.20㎛ or more, 0.21㎛ or more, 0.22㎛ or more, 0.23㎛ or more, 0.24㎛ or more, 0.25㎛ or more, 0.26㎛ or more, or 0.27㎛ or more, and may be 0.29㎛ or less, 0.30㎛ or less, 0.35㎛ or less, 0.40㎛ or less, 0.45㎛ or less, 0.50㎛ or less, 0.55㎛ or less, or 0.60㎛ or less. The average particle size (D) of the cathode active material 50 When ) is within the above range, the distance of lithium ions entering and exiting the positive active material is shortened due to the small particle size, which is advantageous in terms of capacity and output.

[0067]

[0068] According to the present invention, the lithium iron phosphate-based compound may be doped with one or more doping elements selected from the group consisting of V, Mg, Al, Co, and W. In this case, performance may be improved and structural stability may be improved by the doping material.

[0069]

[0070] According to the present invention, the lithium iron phosphate-based compound may have a composition represented by Chemical Formula 1.

[0071] [Chemical Formula 1]

[0072] Li 1+x [Fe 1-a-b-c Mn a M 1 b M 2 c ]PO4

[0073] In the above chemical formula 1,

[0074] M 1 is one or more selected from the group consisting of V, Mg, Al, Co, and W, and

[0075] M 2 is one or more selected from the group consisting of Mg, Nd, and Ni, and

[0076] 0≤x≤0.05, 0≤a≤0.8, 0≤b≤0.02, 0≤c≤0.02.

[0077] The above 1-abc represents the atomic fraction of iron among the metal elements excluding lithium in the above lithium iron phosphate-based compound, and may be greater than 0, 0.1 or more, 0.2 or more, 0.3 or more, or 0.4 or more, and may be 0.4 or less, 0.5 or less, 0.6 or less, 0.7 or less, 0.8 or less, 0.9 or less, or 1.0.

[0078] The above 'a' refers to the atomic fraction of manganese among the metal elements excluding lithium in the above lithium iron phosphate-based compound, and may be 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more, and may be 0.6 or less, 0.7 or less, or 0.8 or less.

[0079] The above lithium iron phosphate-based compound is the above M 1 or M 2 It can be doped. In this case, the iron phosphate-based lattice structure and distance are changed, increasing the diffusivity of lithium ions, and consequently, the electrochemical properties of the battery containing the positive electrode active material can be improved.

[0080]

[0081] The lithium iron phosphate-based compound according to the present invention may be in the form of a single particle consisting of only one primary particle, or in the form of an irregular secondary particle consisting of 2 to 50 primary particles. Furthermore, the lithium iron phosphate-based compound may include an olivine structure, and specifically, may consist solely of an olivine structure. The coating layer according to the present invention may be formed not only on the secondary particles but also on the primary particles. That is, the coating layer according to the present invention may be uniformly present on the surface of the primary particles existing inside the secondary particles.

[0082] According to the present invention, the thickness of the coating layer may be 0.5 nm to 5 nm. When the thickness of the coating layer is within the above range, sufficient coverage and a graphite structure formation rate are secured, thereby improving electrical conductivity while ensuring that the entry and exit of lithium ions are not obstructed. Specifically, the thickness of the coating layer may be 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, or 3.0 nm or more, and may be 5.0 nm or less.

[0083] The coating layer according to the present invention may be uniformly coated on the surface of the lithium iron phosphate-based compound. That is, the coating layer may be in the form of a thin film. The coating layer can improve ion conductivity and electron conductivity during charging and discharging of a battery containing a positive electrode active material. The coating layer may contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen in addition to carbon.

[0084]

[0085] According to the present invention, the positive active material has a rolled density of 1.60 g / cm³ 3 Up to 2.00g / cm² 3 It may be. Specifically, the above-mentioned positive active material has a rolled density of 1.60 g / cm³ 3 Above, 1.61 g / cm³ 3 Above, 1.62 g / cm³ 3 Above, 1.63g / cm² 3 Above, 1.64g / cm² 3 Above, 1.65 g / cm² 3 Above, 1.66 g / cm³ 3 Above, 1.67 g / cm³ 3 Above, or 1.68 g / cm³ 3 It may be abnormal, 1.77 g / cm³ 3 Below, 1.78 g / cm³ 3 Below, 1.79 g / cm³ 3 Below, 1.80 g / cm³ 3 Below, 1.85 g / cm³ 3 Below, 1.90 g / cm³ 3 Below, 1.95 g / cm³ 3 Less than or equal to 2.00 g / cm³ 3 It may be less than or equal to this. In this case, the energy density of the battery containing the positive electrode active material is high, so the performance of the battery can be improved.

[0086] In this specification, the rolling density is determined by placing 2.5 g of lithium iron phosphate-based cathode active material powder into a cylindrical mold with an inner diameter of 2.25 cm and forming it into a cylinder with an outer diameter of 2.2 cm under a pressure of 2000 kgf / cm² 2The value obtained by measuring the thickness of the pellet formed by applying force until it becomes [value], and then using the following Equations 3 and 4.

[0087] [Equation 3]

[0088] Pellet volume (cm²) 3 ) = π((inner diameter of cylindrical mold [unit: cm]) / 2) 2 × (Pellet thickness [Unit: cm])

[0089] [Equation 4]

[0090] Rolled density (g / cm²) 3 ) = (Weight of positive active material [Unit: g]) / (Volume of pellet [Unit: cm²) 3 ])

[0091]

[0092] The positive electrode active material according to the present invention can be manufactured by the following manufacturing method, and more specifically, by the manufacturing method described in the examples, but is not limited thereto.

[0093] Specifically, the cathode active material according to the present invention may be manufactured by a manufacturing method comprising the steps of: mixing a lithium raw material (e.g., Li2CO3), an iron raw material (e.g., FePO4), a manganese raw material (e.g., MnCO3), a phosphorus raw material (e.g., NH4H2PO4), and other doping element raw materials in water such that the lithium iron phosphate-based compound included in the finally manufactured cathode active material has a composition according to Chemical Formula 1, and then additionally adding a carbon raw material, particularly a carbon raw material including polyvinylpyrrolidone (PVP); wet grinding the mixed solution with a bead mill to obtain a slurry; drying the slurry through spray drying; calcining the dried powder to produce a calcined product; and crushing the calcined product with a jet mill. At this time, the carbon raw material may further include sucrose in addition to polyvinylpyrrolidone, and may be introduced in an amount such that it is greater than 3% by weight and less than 6% by weight relative to the total weight of lithium raw material (e.g., Li2CO3), iron raw material (e.g., FePO4), manganese raw material (e.g., MnCO3), phosphorus raw material (e.g., NH4H2PO4), and other doping element raw materials, specifically 4% by weight or more and 5.5% by weight or less.

[0094]

[0095] anode

[0096] The present invention provides a positive electrode comprising the above-mentioned lithium iron phosphate-based positive electrode active material.

[0097] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0098] The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0099] The positive active material layer may include, together with the positive active material, a conductive material and a binder as needed. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

[0100] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0101] The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive active material layer.

[0102] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, the above-described anode may be manufactured by applying a composition for forming an anode active material layer (anode slurry), prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, onto an anode current collector, followed by drying and rolling, or by casting the composition for forming an anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0103] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for anode manufacturing thereafter.

[0104]

[0105] lithium secondary battery

[0106] The present invention provides a lithium secondary battery comprising the above positive electrode.

[0107]

[0108] The above lithium secondary battery may comprise the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. Additionally, the lithium secondary battery may optionally further comprise a battery container housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

[0109] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0110] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0111] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material.

[0112] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. The above-mentioned cathode active material may be included in an amount of 80% to 99% by weight based on the total weight of the cathode active material layer.

[0113] The binder of the above-mentioned negative electrode active material layer is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0114] The conductive material of the above-mentioned negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0115] The above cathode may be manufactured by applying a composition for forming a cathode active material layer (cathode slurry), prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto a cathode current collector.

[0116] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0117] Examples of the above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these. As a specific example, the above electrolyte may include an organic solvent and a lithium salt.

[0118] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0119] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0120] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

[0121]

[0122] Since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent resistance characteristics and energy density characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0123] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0124] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0125] Accordingly, a battery module including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0126] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0127]

[0128] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily perform the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0129]

[0130] Examples and Comparative Examples

[0131] Example 1

[0132] Li2CO3, FePO4, MnCO3, and NH4H2PO4 were mixed with water in amounts such that the molar ratio of lithium:iron:manganese:phosphorus (Li:Fe:Mn:P) was 1.02:0.4:0.6:1.0 (mixed so that the total content of solids was 20% by weight of the solution), and polyvinylpyrrolidone (PVP) was additionally added in an amount such that it was 4% by weight relative to the total weight of solids to prepare a mixed solution.

[0133] The above mixed solution was wet-ground using a bead mill (Nanointec, NPM-1L) to obtain a slurry. At this time, the wet-ground grinding process using the bead mill was repeated 25 times for 3 minutes each (total grinding time: 75 minutes).

[0134] The above slurry was dried by spray drying. At this time, spray drying was performed using Buchi’s Mini spray dryer B-290 at an inlet temperature of 170°C and an outlet temperature of 95°C.

[0135] Afterwards, the dried powder (hereinafter referred to as the mixture) was introduced into a kiln and fired under a nitrogen atmosphere to obtain a fired product. At this time, the firing profile was set to increase the temperature from room temperature to 700°C at a rate of 5°C / min and maintain the temperature at 700°C for 10 hours.

[0136] The above-mentioned calcined product is pulverized using a jet mill (ISAC E&C, 04-626C-WC Micron-Master) at 1.5 bar, and a lithium iron phosphate-based compound (Composition: Li 1.02 Mn 0.6 Fe 0.4 A positive electrode active material was prepared comprising a coating layer containing carbon (C) formed on PO4) and the above lithium iron phosphate-based compound.

[0137]

[0138] Example 2

[0139] A positive electrode active material was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone (PVP) was added in an amount such that it was 5.5% by weight rather than 4% by weight relative to the total weight of the solids.

[0140]

[0141] Example 3

[0142] A positive electrode active material was prepared in the same manner as in Example 1, except that Li2CO3, FePO4, MnCO3, and NH4H2PO4 were mixed with water in amounts such that the molar ratio of lithium:iron:manganese:phosphorus (Li:Fe:Mn:P) was 1.02:0.4:0.6:1.0 (mixed so that the total content of solids was 20% by weight of the solution), and a mixed solution was prepared by additionally adding sucrose in an amount such that it was 1.5% by weight relative to the total weight of solids, and polyvinylpyrrolidone (PVP) in an amount such that it was 3% by weight relative to the total weight of solids.

[0143]

[0144] Example 4

[0145] A positive electrode active material was prepared in the same manner as in Example 1, except that Li2CO3, FePO4, MnCO3, and NH4H2PO4 were mixed with water in amounts such that the molar ratio of lithium:iron:manganese:phosphorus (Li:Fe:Mn:P) was 1.02:0.4:0.6:1.0 (mixed so that the total content of solids was 20% by weight of the solution), and a mixed solution was prepared by additionally adding sucrose in an amount such that it was 1.5% by weight relative to the total weight of the solids, and polyvinylpyrrolidone (PVP) in an amount such that it was 4% by weight relative to the total weight of the solids.

[0146]

[0147] Comparative Example 1

[0148] Li2CO3, FePO4, MnCO3, and NH4H2PO4 were mixed with water in amounts such that the molar ratio of lithium:iron:manganese:phosphorus (Li:Fe:Mn:P) was 1.02:0.4:0.6:1.0 (mixed so that the total content of solids was 20% by weight of the solution), and sucrose was additionally added in an amount such that it was 3% by weight relative to the total weight of solids to prepare a mixed solution.

[0149] The above mixed solution was wet-ground using a bead mill (Nanointec, NPM-1L) to obtain a slurry. At this time, the wet-ground grinding process using the bead mill was repeated 25 times for 3 minutes each (total grinding time: 75 minutes).

[0150] The above slurry was dried by spray drying. At this time, spray drying was performed using Buchi’s Mini spray dryer B-290 at an inlet temperature of 170°C and an outlet temperature of 95°C.

[0151] Afterwards, the dried powder (hereinafter referred to as the mixture) was introduced into a kiln and fired under a nitrogen atmosphere to obtain a fired product. At this time, the firing profile was set to increase the temperature from room temperature to 700°C at a rate of 5°C / min and maintain the temperature at 700°C for 10 hours.

[0152] The above-mentioned calcined product is pulverized using a jet mill (ISAC E&C, 04-626C-WC Micron-Master) at 1.5 bar, and a lithium iron phosphate-based compound (Composition: Li 1.02 Mn 0.6 Fe 0.4 A positive electrode active material was prepared comprising a coating layer containing carbon (C) formed on PO4) and the above lithium iron phosphate-based compound.

[0153]

[0154] Comparative Example 2

[0155] A positive electrode active material was prepared in the same manner as Comparative Example 1, except that sucrose was added in an amount such that it was 3.5% by weight rather than 3% by weight relative to the total weight of the solids.

[0156]

[0157] Comparative Example 3

[0158] A positive electrode active material was prepared in the same manner as Comparative Example 1, except that sucrose was added in an amount such that it was 4% by weight rather than 3% by weight relative to the total weight of the solids.

[0159]

[0160] Comparative Example 4

[0161] A positive electrode active material was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone (PVP) was added in an amount such that it was 2% by weight rather than 4% by weight relative to the total weight of the solids.

[0162]

[0163] Comparative Example 5

[0164] A positive electrode active material was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone (PVP) was added in an amount such that it was 3% by weight rather than 4% by weight relative to the total weight of the solids.

[0165]

[0166] Comparative Example 6

[0167] A positive electrode active material was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone (PVP) was added in an amount such that it was 6% by weight rather than 4% by weight relative to the total weight of the solids.

[0168]

[0169] Experimental Example

[0170] Experimental Example 1: BET Specific Surface Area Evaluation

[0171] The BET specific surface area of ​​the cathode active material was measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BEL SORP-mini from BEL Japan.

[0172]

[0173] Experimental Example 2: Evaluation of Carbon Content

[0174] The carbon content relative to the total weight of the cathode active material was analyzed using a carbon analyzer (Skalar Analytica, Primacs).

[0175]

[0176] Experimental Example 3: Verification of Average Particle Size

[0177] 15 mg of each cathode active material powder prepared in the above examples and comparative examples was dispersed in 10 ml of a solution of Triton X-100 diluted to 1 wt% in distilled water, and then introduced into a laser diffraction particle size measuring device (Malvern Panalytical, Mastersizer 3000) to measure the average particle size (D) of the cathode active material. 50 ) was measured, and the results are shown in Table 1 below.

[0178]

[0179] Then, the value of X according to Equation 1 below was calculated and shown in Table 1 below.

[0180] [Equation 1]

[0181]

[0182] In the above Equation 1,

[0183] The unit of the BET specific surface area value is m 2 It is the value when / g, and

[0184] The carbon content value is the carbon content (weight%) relative to the total weight of the cathode active material, and

[0185] Average particle size (D 50 The value is the value when the unit is μm.

[0186]

[0187] Classification BET Specific Surface Area (m 2 / g) Carbon content (weight%) Average particle size (D 50 )X Example 1 19.4 231.8 20.28 3124.9 Example 2 23.24 52.26 0.27 6190.3 Example 3 17.05 21.5 00.28 490.1 Example 4 23.19 52.4 10.27 1206.3 Comparative Example 1 11.98 50.9 20.5 43 20.3 Comparative Example 2 13.11 21.1 20.4 08 36.0 Comparative Example 3 15.32 31.36 0.32 264.7 Comparative Example 4 11.88 10.9 00.38 927.5 Comparative Example 5 15.37 31.29 0.33 259.7 Comparative Example 626.3212.780.231316.8

[0188]

[0189] Referring to Table 1 above, it can be seen that the positive active materials of Examples 1 to 4 satisfy an X value according to Formula 1 of 65 to 300, whereas the positive active materials of Comparative Examples 1 to 5 have an X value according to Formula 1 of less than 65, and the positive active material of Comparative Example 6 has an X value according to Formula 1 of greater than 300.

[0190]

[0191] Experimental Example 4: Evaluation of Rolled Density

[0192] Using a rolled density meter (Hantech, HPRM-A2), the cathode active material powder was 2,000 kgf / cm³ 2 The rolling density was calculated after pressing with pressure.

[0193] Specifically, 2.5 g of each cathode active material powder prepared in the above examples and comparative examples was placed in a cylindrical mold with an inner diameter of 2.25 cm, and a pressure of 2000 kgf / cm² was applied to a cylinder with an outer diameter of 2.2 cm. 2 The thickness of the pellet formed by applying force until [it] was measured. Subsequently, the pellet volume was calculated using Equation 3 below, and the rolling density was calculated using Equation 4 below, and the results are shown in Table 1 below.

[0194] [Equation 3]

[0195] Pellet volume (cm²) 3 ) = π((inner diameter of cylindrical mold [unit: cm]) / 2) 2 × (Pellet thickness [Unit: cm])

[0196] [Equation 4]

[0197] Rolled density (g / cm²) 3 ) = (Weight of positive active material [Unit: g]) / (Volume of pellet [Unit: cm²) 3 ])

[0198]

[0199] Separately rolled density (g / cm³) 3 Example 11.77 Example 21.68 Example 31.80 Example 41.66 Comparative Example 11.81 Comparative Example 21.77 Comparative Example 31.77 Comparative Example 41.85 Comparative Example 51.90 Comparative Example 61.60

[0200]

[0201] Experimental Example 5: Evaluation of Battery Characteristics

[0202] An anode slurry was prepared by mixing the respective anode active materials prepared in the above examples and comparative examples, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 90:5:5. The prepared anode slurry was applied to one surface of an aluminum current collector (thickness: 20 μm) (loading amount: 300 mg / 25 cm²). 2 After ) and drying at 130℃, the anode was manufactured by rolling to achieve a porosity of 26 volume%.

[0203] An electrode assembly was manufactured by using a lithium metal electrode (thickness: 300 μm) as the negative electrode and interposing a porous polyethylene separator (thickness: 20 μm) between the positive electrode and the negative electrode. This was placed inside a battery case, and a coin half-cell was manufactured by injecting an electrolyte solution in which 1.0 M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) in a volume ratio of 1:2:1.

[0204] Using each coin half-cell manufactured as described above, a cycle was performed in which the cell was charged to 4.25V in CC (0.1C)-CV (Cut-off current: 0.05C) mode at 25℃ and then discharged to 2.5V at 0.1C. The charge and discharge capacities at this time were designated as the initial charge capacity and initial discharge capacity, and are shown in Table 3 below.

[0205] Subsequently, while keeping the charging speed fixed at 0.1C, the discharge speed was increased from 1.0C to 2.0C, 3.0C, and 4.0C, and the discharge capacity at each discharge speed was measured. Then, the percentage of the discharge capacity at 1.0C relative to the initial discharge capacity (1.0C output) and the percentage of the discharge capacity at 4.0C relative to the initial discharge capacity (4.0C output) were calculated and are shown in Table 3 below.

[0206]

[0207] Classification Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) 1.0C Output (= (1.0C Discharge Capacity) / (Initial Discharge Capacity) × 100) (%) 4.0C Output (= (4.0C Discharge Capacity) / (Initial Discharge Capacity) × 100) (%) Example 1 154.6 152.69 3.228 5.69 Example 2 153.8 152.69 4.158 8.58 Example 3 153.7 150.19 2.018 5.01 Example 4 153.7 152.49 4.308 8.92 Comparative Example 1 146.3 142.28 7.49 7.75 Comparative Example 2 148.7 145.68 9.378 0.25 Comparative Example 3152.9150.291.3384.06 Comparative Example 4148.3142.589.2080.79 Comparative Example 5153.4150.991.4584.57 Comparative Example 6153.2152.194.6789.02

[0208]

[0209] Referring to Table 2 above, it can be seen that the rolling density of the cathode active materials of Examples 1 to 4 is similar to or lower than that of the cathode active materials of Comparative Examples 1 to 5. This is because the rolling density of the cathode active materials of Examples 1 to 4 decreases as the BET specific surface area increases, the pores increase, and the relatively light carbon increases.

[0210] Also, referring to Table 3 above, it can be seen that the batteries containing the positive active materials of Examples 1 to 4 have excellent initial charge / discharge capacity and output characteristics.

[0211] For reference, the positive electrode active material of Comparative Example 6 has a significantly low rolling density and thus has a problem of poor energy density, and it can be confirmed that the battery containing it has a somewhat lower initial charge capacity and / or discharge capacity compared to the positive electrode active materials of Examples 1 to 4.

Claims

1. Lithium iron phosphate-based compounds; and A coating layer formed on the above lithium iron phosphate compound and containing carbon (C); comprising Anode active material having an X value of 65 to 300 according to Formula 1 below: [Equation 1] In the above Equation 1, The unit of the BET specific surface area value is m 2 It is the value when / g, and The carbon content value is the carbon content (weight%) relative to the total weight of the cathode active material, and Average particle size (D 50 The value is the value when the unit is μm.

2. In Claim 1, The above BET specific surface area is 10 m² 2 / g to 30m 2 positive active material in g.

3. In Claim 1, A positive electrode active material having a carbon content of 1.0% to 3.0% by weight relative to the total weight of the positive electrode active material.

4. In Claim 1, The above average particle size (D 50 ) is a positive electrode active material having a thickness of 0.20㎛ to 0.60㎛.

5. In Claim 1, The above lithium iron phosphate-based compound is a positive electrode active material doped with one or more doping elements selected from the group consisting of V, Mg, Al, Co, and W.

6. In Claim 1, The above lithium iron phosphate-based compound is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-a-b-c Mn a M 1 b M 2 c ]PO4 In the above chemical formula 1, M 1 is one or more selected from the group consisting of V, Mg, Al, Co, and W, and M 2 is one or more selected from the group consisting of Mg, Nd, and Ni, and 0≤x≤0.05, 0≤a≤0.8, 0≤b≤0.02, 0≤c≤0.

02.

7. In Claim 1, The above-mentioned positive active material has a press density of 1.60 g / cm³ 3 Up to 2.00g / cm² 3 Phosphorus positive electrode active material.

8. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 7.

9. A lithium secondary battery comprising a positive electrode according to claim 8.

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