Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, and more specifically to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, comprising a lithium composite transition metal oxide in single-particle form, wherein the lithium composite transition metal oxide satisfies Formula 1 as described herein.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0076837 filed on June 15, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference as part of this specification.

[0002] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. Specifically, the present invention relates to a positive electrode active material including a lithium composite transition metal oxide in a single particle form, a positive electrode including the same, and a lithium secondary battery.

Background Art

[0003] In recent years, with the development of technologies and the increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

[0004] As positive electrode active materials for lithium secondary batteries, lithium transition metal oxides such as lithium cobalt oxide such as LiCoO2, lithium nickel oxide such as LiNiO2, lithium manganese oxide such as LiMnO2 or LiMn2O4, and lithium iron phosphate oxide such as LiFePO4 have been developed. In recent years, lithium composite transition metal oxides containing two or more transition metals, such as a Co b Mn c O2, a Co b Al c O2, a Co b Mn c Al d O2, have been developed and widely used.

[0005] Lithium composite transition metal oxides containing two or more transition metals developed to date are typically manufactured in the form of spherical secondary particles, where tens to hundreds of primary particles are aggregated. However, in recent years, the development of single-particle cathode active materials has been accelerated to solve problems related to the structure and thermal stability of secondary-particle cathode active materials. Specifically, secondary-particle cathode active materials have the problem of generating a large amount of gas when applied to lithium secondary batteries, causing the battery volume to expand. Furthermore, increasing the nickel content in the cathode material to achieve high capacity also increases the risk of fire. Therefore, there is a growing demand for the development of single-particle cathode active materials with superior stability.

[0006] Therefore, there is a need to develop single-particle positive electrode active materials that offer excellent stability and can improve various aspects of battery performance when applied to batteries. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems and to provide a positive electrode active material containing a single-particle lithium composite transition metal oxide that has excellent structural stability and can improve the capacity, lifespan, and other aspects of a battery when applied to it.

[0008] Furthermore, the present invention aims to provide a positive electrode and a lithium secondary battery that include the positive electrode active material and have improved performance. [Means for solving the problem]

[0009] The present invention provides a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery.

[0010] (1) The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in single-particle form, wherein the lithium composite transition metal oxide satisfies the following formula 1.

[0011]

number

[0012] In the above formula 1, D EBSD This is the average grain size (unit: μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D SEM This is the average particle size (in μm) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using a scanning electron microscope (SEM).

[0013] (2) The present invention provides the positive electrode active material described in (1) above, wherein the lithium composite transition metal oxide further satisfies the following formula 2.

[0014]

number

[0015] In the above formula 2, D EBSD This is the average grain size (unit: μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D SEM This is the average particle size (in μm) of the smallest recognizable unit particle when the lithium composite transition metal oxide is observed using SEM. [Ni] is the ratio of the number of moles of nickel to the total number of moles of transition metals excluding lithium.

[0016] (3) The present invention relates to the D EBSD / D SEM The present invention provides a positive electrode active material according to (1) or (2) above, wherein the value is greater than 0.4 and less than or equal to 0.9.

[0017] (4) The present invention relates to the D EBSD The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the particle size is 1 μm to 5 μm.

[0018] (5) The present invention relates to the D SEMThe present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the particle size is 1 μm to 8 μm.

[0019] (6) The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the lithium composite transition metal oxide contains 60 mol% or more of nickel with respect to the total number of moles of transition metals excluding lithium.

[0020] (7) The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1.

[0021] [Chemical formula 1] Li x [Ni a Co b M1 c M2 d ]O2

[0022] In the aforementioned chemical formula 1, M1 is one or more selected from Mn and Al. M2 is one or more elements selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, V, Ca, Zn, F, P, and S. 0.9≦x≦1.2, 0.6≦a<1, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.4.

[0023] (8) The present invention relates to the average particle size (D) of the lithium composite transition metal oxide. 50 The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein the diameter is 1 μm to 10 μm.

[0024] (9) The present invention provides a positive electrode comprising a positive electrode active material described in any one of (1) to (8) above.

[0025] (10) The present invention provides a lithium secondary battery including the positive electrode described in (9) above. [Effects of the Invention]

[0026] The positive electrode active material of the present invention comprises a lithium composite transition metal oxide in single-particle form and satisfies Formula 1 described herein, thereby improving the capacity, lifespan, and other aspects of lithium secondary batteries. [Brief explanation of the drawing]

[0027] [Figure 1] (A) A segmentation image and (B) an EBSD IPF map image obtained by image processing of the positive electrode active material of Example 1. [Figure 2] (A) A segmentation image and (B) an EBSD IPF map image obtained by image processing of the positive electrode active material of Example 2. [Figure 3] (A) A segmentation image and (B) an EBSD IPF map image obtained by image processing of the positive electrode active material of Comparative Example 1. [Modes for carrying out the invention]

[0028] The present invention will be described in more detail below to facilitate understanding of it.

[0029] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0030] In this specification, "single-particle form" is a concept contrasted with a spherical secondary-particle form formed by the aggregation of tens to hundreds of primary particles, and means a form consisting of 10 or fewer primary particles. Specifically, "single-particle form" may be a single-particle form consisting of one primary particle, or it may be a secondary-particle form formed by the aggregation of 2 to 10, specifically 2 to 5, primary particles.

[0031] In this specification, "primary particle" refers to the smallest particle unit recognized when observing a positive electrode active material using a scanning electron microscope (SEM), and "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0032] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 The particle size can be measured, for example, by laser diffraction. More specifically, after dispersing lithium composite transition metal oxide in a dispersion medium, the material is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac Mt 3000), and ultrasonic waves at approximately 28 kHz are irradiated at an output of 60 W. The average particle size (D) corresponding to 50% of the particle size distribution in the measuring device is then measured. 50 It is possible to calculate ).

[0033] positive electrode active material The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in single-particle form, wherein the lithium composite transition metal oxide satisfies the following formula 1.

[0034]

number

[0035] In the above formula 1, D EBSD This is the average grain size (unit: μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D SEM This is the average particle size (in μm) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using a scanning electron microscope (SEM).

[0036] The aforementioned D EBSDThis can be obtained by preparing a cross-sectional sample of the positive electrode containing the positive electrode active material, obtaining an EBSD image of the cross-sectional sample, and then calculating the average value from the grain size measured by an EBSD analysis program.

[0037] In the present invention, the D SEM This is the average value of the equivalent circular diameter (ECD) of a circle having the same area as a particle separated based on the particle boundary in the SEM image. SEM This can be measured from a segmentation image, which is obtained by processing an SEM image using an artificial intelligence model and is divided into primary particle units. Specifically, the segmentation image can be obtained by first acquiring an SEM image of the cathode material powder to be measured, inputting the acquired SEM image into a U-NET structure to generate a binary image, converting the binary image into a distance-transformed image based on a distance-transformed algorithm, filtering the binary image using a threshold set based on the distance-transformed image, identifying multiple objects contained in the filtered binary image, and then segmenting the SEM image into primary particle units based on the multiple objects.

[0038] The inventors have discovered that when the positive electrode active material contains a lithium composite transition metal oxide in single-particle form, and the lithium composite transition metal oxide satisfies Formula 1, the inter-grain interface of the single-particle positive electrode active material containing 60% or more Ni is secured at an appropriate level, and the structure is more stable and crystallinity is improved compared to polycrystalline positive electrode active materials. As a result, when the positive electrode active material is applied to a secondary battery, the battery capacity, initial efficiency, and lifespan can be improved, thus completing the present invention.

[0039] If the lithium composite transition metal oxide does not satisfy Equation 1, specifically if the value according to Equation 1 is 0.4 or less, there is a problem that the primary particles are not sufficiently aggregated, the inter-grain interfaces are excessive, and degeneration is accelerated as the cycle progresses. If the value according to Equation 1 is 1.0, there is a problem that the structure is unstable and the crystallinity is actually lower.

[0040] According to the present invention, the lithium composite transition metal oxide can further satisfy the following formula 2.

[0041]

number

[0042] In the above formula 2, D EBSD This is the average grain size (unit: μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D SEM This is the average particle size (in μm) of the smallest recognizable unit particle when the lithium composite transition metal oxide is observed using SEM. [Ni] is the ratio of the number of moles of nickel to the total number of moles of transition metals excluding lithium.

[0043] When the lithium composite transition metal oxide satisfies formula 2, the positive electrode active material can have high capacity characteristics, and the structural stability and lifetime characteristics of the single-particle form can be improved.

[0044] If the lithium composite transition metal oxide does not satisfy Equation 2, specifically, if the value according to Equation 2 is less than 0.5, there is a problem that the intergrain interface is insufficient for the same nickel content, resulting in low capacity development. If the value according to Equation 2 exceeds 1.3, even if sufficient intergrain interfaces are maintained, there is a problem that the nickel content is low, resulting in low capacity development. If the nickel content is the same, there is a problem that the intergrain interfaces are excessive, and degeneration accelerates as the battery cycle is repeated.

[0045] If the lithium composite transition metal oxide contains 60 mol% to 80 mol% nickel relative to the total number of moles of the transition metal excluding lithium, the value calculated by formula 2 may be 0.6 to 1.2. Furthermore, if the lithium composite transition metal oxide contains 80 mol% or more nickel relative to the total number of moles of the transition metal excluding lithium, the value calculated by formula 2 may be 0.5 to 0.8.

[0046] According to the present invention, the D EBSD / D SEM The value may be greater than 0.4 and less than or equal to 0.9. Specifically, the above D EBSD / D SEM The value may be greater than 0.4 and may be 0.7 or less, 0.8 or less, or 0.9 or less. D EBSD / D SEM When the value falls within the above range, it ensures an appropriate level of inter-grain interface in the single-particle positive electrode active material, and offers advantages such as structural stability and improved crystallinity compared to polycrystalline positive electrode active materials.

[0047] According to the present invention, the D EBSD The diameter may be 1 μm to 5 μm. Specifically, the above D EBSD It may be 1 μm or larger, 4 μm or smaller, or 5 μm or smaller.

[0048] According to the present invention, the D SEM The particle size may be 1 μm to 8 μm. Specifically, the particle D SEM It may be 1 μm or larger, and may be 6 μm or smaller, 7 μm or smaller, or 8 μm or smaller.

[0049] According to the present invention, the lithium composite transition metal oxide may contain 60 mol% or more of nickel relative to the total number of moles of the transition metal excluding lithium. Specifically, the lithium composite transition metal oxide may contain 60 mol% or more, 70 mol% or more, 80 mol% or more, 97 mol% or less, 98 mol% or less, or 99 mol% or less of nickel relative to the total number of moles of the transition metal excluding lithium. That is, the [Ni] value may be 0.60 or more, 0.70 or more, 0.80 or more, 0.97 or less, 0.98 or less, or 0.99 or less.

[0050] According to the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1.

[0051] [Chemical formula 1] Li x [Ni a Co b M1 c M2 d ]O2

[0052] In the aforementioned chemical formula 1, M1 is one or more selected from Mn and Al. M2 is one or more elements selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, V, Ca, Zn, F, P, and S. 0.9≦x≦1.2, 0.6≦a<1, 0≦b≦0.4, 0≦c≦0.4, 0≦d≦0.4.

[0053] The aforementioned M2 is a doped element or a coating element.

[0054] The aforementioned x represents the ratio of the number of moles of Li to the total number of moles of the transition metal, and may be 0.9 or greater, 0.98 or greater, 0.99 or greater, 1.0 or greater, 1.1 or less, or 1.2 or less.

[0055] The above-mentioned 'a' represents the ratio of the number of moles of Ni to the total number of moles of transition metals, and may be 0.6 or more, 0.7 or more, 0.8 or more, 0.97 or less, 0.98 or less, or 0.99 or less.

[0056] The above b represents the ratio of the number of moles of Co to the total number of moles of transition metals, and may be 0 or greater, greater than 0, 0.2 or less, or 0.4 or less.

[0057] The aforementioned c represents the ratio of the number of moles of M1 to the total number of moles of the transition metal, and may be 0 or greater, greater than 0, 0.2 or less, or 0.4 or less.

[0058] The above d represents the ratio of the number of moles of M2 to the total number of moles of the transition metal, and may be 0 or greater, greater than 0, 0.2 or less, or 0.4 or less.

[0059] According to the present invention, the lithium composite transition metal oxide has an average particle size (D 50 ) may be 1 μm to 10 μm, specifically 1 μm or more, 6 μm or less, 8 μm or less, or 10 μm or less. Average particle size (D 50 If the above range is met, an appropriate packing density and rolling ratio can be ensured when forming an electrode made of a single-particle lithium composite transition metal oxide, or when forming a blend electrode with a single-particle and polycrystalline positive electrode active material with a large average particle size.

[0060] positive electrode The present invention provides a positive electrode containing the positive electrode active material.

[0061] The 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.

[0062] The positive electrode current collector may contain a highly conductive metal and is not particularly limited as long as the positive electrode active material layer adheres to it easily and it is unreactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment using carbon, nickel, titanium, silver, etc. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and the adhesion strength of the positive electrode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0063] The positive electrode active material layer may, as necessary, selectively contain a conductive material and a binder along with the positive electrode active material. In this case, the positive electrode active material may be present in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer. When within this range, excellent capacitance characteristics can be observed.

[0064] The conductive material is used to impart conductivity to the electrodes and is not particularly limited as long as it does not cause chemical changes in the battery it is used in. 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 fiber; metal powders 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. One of these may be used alone, or a mixture of two or more. The 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.

[0065] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode 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 the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these can be used alone, or a mixture of two or more. The binder may be present in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0066] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material described above is used. Specifically, the positive electrode may be manufactured by applying a composition (slurry) for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the positive electrode active material and, if necessary, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling. Alternatively, the positive electrode may be manufactured by casting the composition for forming a positive electrode active material layer onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0067] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing, taking into account the coating thickness and production yield of the slurry.

[0068] Lithium-ion rechargeable battery The present invention provides a lithium secondary battery including the positive electrode.

[0069] The lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may also selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0070] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0071] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0072] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0073] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can 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 lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites; any one or more mixtures of these can be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, both low-crystallinity carbon and high-crystallinity carbon can be used. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, 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 carbons such as petroleum or coal tar pitch-derived cokes. The anode active material may be present in an amount of 80% to 99% by weight based on the total weight of the anode active material layer.

[0074] The binder in the negative electrode active material layer is a component that helps to bond the conductive material, the active material, and the current collector, and is usually added at a concentration 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.

[0075] The conductive material in the 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 does not cause a chemical change in the battery and is conductive, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0076] The negative electrode may be manufactured by coating a negative electrode active material layer-forming composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode active material layer-forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0077] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is one that is commonly used as a separator in lithium secondary batteries. In particular, one that has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability is preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be used selectively as a single-layer or multi-layer structure.

[0078] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0079] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, and is not particularly limited. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0080] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries, without any particular limitations. Specifically, the anion of the 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 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, etc. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. 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.

[0081] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0082] The lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity characteristics, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, including hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0083] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0084] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0085] This provides a battery module that includes the lithium secondary battery as a unit cell, and a battery pack that includes the same.

[0086] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Examples]

[0087] Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0088] Examples Example 1 Composite transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D 50 A precursor (D):4μm) and LiOH as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH ((Ni+Co+Mn):Li) was 1:1.05. The mixture was then subjected to primary calcination at a temperature of 890°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to a primary calcination process with an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 820°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.86 Co 0.05 Mn 0.09 We manufactured O2 (the positive electrode active material).

[0089] Example 2 Composite transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D 50): 4 μm) precursor, and LiOH as a lithium raw material substance, were mixed so that the ratio ((Ni + Co + Mn):Li) of the total number of moles of transition metals (Ni + Co + Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH was 1:1.05, and calcined once at a temperature of 850 °C for 6 hours in an oxygen atmosphere to produce a calcined product. The calcined product was ground so that the average particle size (D 50 ) became 4 μm, and then secondarily calcined at a temperature of 750 °C for 9 hours in an oxygen atmosphere to produce a single-particle form lithium composite transition metal oxide (composition: LiNi 0.932 Co 0.05 Mn 0.02 O2) (cathode active material).

[0090] Example 3 Composite transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D 50 ): 4 μm) precursor, and LiOH as a lithium raw material substance, were mixed so that the ratio ((Ni + Co + Mn):Li) of the total number of moles of transition metals (Ni + Co + Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH was 1:1.05, and calcined once at a temperature of 860 °C for 6 hours in an oxygen atmosphere to produce a calcined product. The calcined product was ground so that the average particle size (D 50 ) became 4 μm, and then secondarily calcined at a temperature of 820 °C for 9 hours in an oxygen atmosphere to produce a single-particle form lithium composite transition metal oxide (composition: LiNi 0.86 Co 0.05 Mn 0.09 O2) (cathode active material).

[0091] Example 4 Composite transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D 50A precursor (D):4μm) and LiOH as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH ((Ni+Co+Mn):Li) was 1:1.05. The mixture was then subjected to primary calcination at a temperature of 830°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to primary calcination at an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 750°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.932 Co 0.05 Mn 0.02 We manufactured O2 (the positive electrode active material).

[0092] Example 5 Composite transition metal hydroxide (composition: Ni 0.62 Co 0.08 Mn 0.30 (OH)2, average particle size (D 50 A precursor (4 μm) and Li2CO3 as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.07. The mixture was then subjected to primary calcination at 970°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to a primary calcination process with an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at a temperature of 870°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.62 Co 0.08 Mn 0.30 We manufactured O2 (the positive electrode active material).

[0093] Example 6 Composite transition metal hydroxide (composition: Ni 0.68 Co 0.10 Mn 0.22 (OH)2, average particle size (D 50A precursor (4 μm) and Li2CO3 as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.05. The mixture was then subjected to primary calcination at 920°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to a primary calcination process with an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 850°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.68 Co 0.10 Mn 0.22 We manufactured O2 (the positive electrode active material).

[0094] Comparative Example 1 Composite transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D 50 A precursor (D):4μm) and LiOH as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH ((Ni+Co+Mn):Li) was 1:1.03. The mixture was then subjected to primary calcination at a temperature of 800°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to primary calcination at an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 780°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.86 Co 0.05 Mn 0.09 We manufactured O2 (the positive electrode active material).

[0095] Comparative Example 2 Composite transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D 50A precursor (D):4μm) and LiOH as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the composite transition metal hydroxide to the number of moles of lithium (Li) contained in LiOH ((Ni+Co+Mn):Li) was 1:1.03. The mixture was then subjected to primary calcination at a temperature of 850°C for 9 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to primary calcination at an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 750°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.932 Co 0.05 Mn 0.02 We manufactured O2 (the positive electrode active material).

[0096] Comparative Example 3 Composite transition metal hydroxide (composition: Ni 0.62 Co 0.08 Mn 0.30 (OH)2, average particle size (D 50 A precursor (D):4μm) and Li2CO3 as a lithium raw material were mixed such that the ratio of the total number of moles of transition metals contained in the composite transition metal hydroxide (Ni+Co+Mn) to the number of moles of lithium contained in Li2CO3 (Li) ((Ni+Co+Mn):Li) was 1:1.03. The mixture was then subjected to primary calcination at a temperature of 900°C for 6 hours under an oxygen atmosphere to produce a calcined product. The calcined product was then subjected to primary calcination at an average particle size (D 50 After grinding the particles to a size of 4 μm, secondary calcination is performed at 850°C for 9 hours under an oxygen atmosphere to obtain single-particle lithium composite transition metal oxide (composition: LiNi 0.62 Co 0.08 Mn 0.30 We manufactured O2 (the positive electrode active material).

[0097] Experimental example Experimental Example 1 Using a field emission scanning electron microscope (FE-SEM, FEI, Quanta 250 FEG), SEM images of the cathode active materials produced in Examples 1-6 and Comparative Examples 1-3 were obtained. Then, each image was processed using the particle shape analysis method described above to obtain segmentation images partitioned into primary particle units, and then DSEM We measured it.

[0098] Furthermore, the positive electrode active materials, carbon black (Denka Co., Ltd., DenkaBlack) conductive material, and PVdF (Kureha Corporation, KF1100) binder produced in Examples 1-6 and Comparative Examples 1-3 were mixed in NMP (Daejon Chemicals & Metals) solvent in a weight ratio of 7:2:1 to produce a positive electrode slurry. After coating one surface of an aluminum current collector with the positive electrode slurry, it was dried at 120°C and rolled to produce a positive electrode. Each positive electrode was subjected to Ar ion milling for 2 hours using an ion milling system (JEOL, IB-19520CCP) (acceleration voltage: 6kV) to prepare cross-sectional samples. EBSD images were obtained for each of these cross-sectional samples using EBSD (JEOL, JSM-7900F with Symmetry EBSD detector (Oxford Instruments)). Using the EBSD program Aztec Crystal, the EBSD images were analyzed. EBSD They sought it.

[0099] D obtained from each image SEM and D EBSD The values ​​obtained using Equations 1 and 2 described in this specification are shown in Table 1 below.

[0100] Figures 1 to 3 show, in order, (A) segmentation images obtained by image processing of SEM images and (B) EBSD IPF map images of the positive electrode active materials of Examples 1 and 2 and Comparative Example 1, respectively.

[0101] In this case, D EBSD D is the average grain size of the crystal grains recognized when the lithium composite transition metal oxide is observed by EBSD. SEM [N] is the average particle size of the smallest unit particle recognized when the lithium composite transition metal oxide is observed by SEM, and [Ni] is the ratio of the number of moles of nickel to the total number of moles of the transition metal excluding lithium.

[0102] [Table 1]

[0103] Experiment Example 2: Battery Performance Evaluation The positive electrode active materials, carbon black conductive material, and polyvinylidene fluoride (PVDF) binder prepared in Examples 1-6 and Comparative Examples 1-3 were mixed in N-methylpyrrolidone (NMP) solvent in a ratio of 95:3:2 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 120°C, and rolled to produce a positive electrode.

[0104] A lithium metal electrode was used as the negative electrode, and an electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. After positioning the electrode assembly inside a battery case, an electrolyte solution was injected into the case to manufacture a half-cell.

[0105] Each half-cell manufactured in this manner was charged at 25°C in CC-CV mode at 0.1C until it reached 4.25V (Cut-off current: 0.05C), and then discharged to 2.5V at a constant current of 0.1C. The initial charge capacity and initial discharge capacity were measured, and the initial efficiency was calculated and is shown in Table 2 below.

[0106] Then, the cells that had completed one cycle were moved to a 45°C chamber, and the capacity of the lithium secondary battery was measured by repeating 30 charge-discharge cycles at 0.33C. The capacity retention rate was defined as the percentage of the discharge capacity after the 30th cycle relative to the discharge capacity after the 1st cycle, and is shown in Table 2 below.

[0107] [Table 2]

[0108] Referring to Tables 1 and 2, it can be confirmed that the batteries containing the positive electrode active materials of Examples 1 to 6 satisfy Formula 1 described herein and are excellent in capacity, initial efficiency, and lifespan. On the other hand, it can be confirmed that the battery containing the positive electrode active material of Comparative Example 1 is inferior in capacity, initial efficiency, and lifespan compared to the batteries containing the positive electrode active materials of Examples 1 and 3, which have similar compositions. Furthermore, it can be confirmed that the battery containing the positive electrode active material of Comparative Example 2 is inferior in capacity and lifespan compared to the batteries containing the positive electrode active materials of Examples 2 and 4, which have similar compositions. In addition, it can be confirmed that the battery containing the positive electrode active material of Comparative Example 3 is inferior in capacity, initial efficiency, and lifespan compared to the batteries containing the positive electrode active materials of Examples 5 and 6, which have similar compositions.

Claims

1. It contains a lithium composite transition metal oxide in single-particle form, The lithium composite transition metal oxide is a positive electrode active material that satisfies the following formula 1. [Math 1] (In formula 1 above, D ＥＢＳＤ This is the average grain size (in μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D ＳＥＭ This is the average particle size (in μm) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using a SEM.

2. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide further satisfies the following formula 2. [Math 2] (In the above equation 2, D ＥＢＳＤ This is the average grain size (in μm) of the crystal grains recognized when the lithium composite transition metal oxide is observed using EBSD. D ＳＥＭ This is the average particle size (in μm) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using SEM. [Ni] is the ratio of moles of nickel to the total number of moles of transition metals excluding lithium.

3. The aforementioned D ＥＢＳＤ / D ＳＥＭ The positive electrode active material according to claim 1, wherein the value is greater than 0.4 and less than or equal to 0.

9.

4. The aforementioned D ＥＢＳＤ The positive electrode active material according to claim 1, wherein the particle size is 1 μm to 5 μm.

5. The aforementioned D ＳＥＭ The positive electrode active material according to claim 1, wherein the diameter is 1 μm to 8 μm.

6. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide contains 60 mol% or more of nickel with respect to the total number of moles of transition metals excluding lithium.

7. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li ｘ [Ni ａ Co ｂ M1 ｃ M2 ｄ ]O ２ (In the above chemical formula 1, M1 is one or more selected from Mn and Al. M2 is one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, V, Ca, Zn, F, P, and S. (0.9 ≤ x ≤ 1.2, 0.6 ≤ a < 1, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4.)

8. The average particle size (D) of the lithium composite transition metal oxide. ５０ The positive electrode active material according to claim 1, wherein the diameter is 1 μm to 10 μm.

9. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 8.

10. A lithium secondary battery comprising the positive electrode described in claim 9.

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