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

Abstract

The present invention relates to a positive electrode active material, and a positive electrode and a lithium secondary battery each comprising same and, specifically, to a positive electrode active material, and a positive electrode and a lithium secondary battery each comprising same, wherein the positive electrode active material contains a lithium composite transition metal oxide in the form of single particles, and the lithium composite transition metal oxide satisfies equation 1 described in the present specification.

Description

Cathode active material, cathode and lithium secondary battery containing same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0076837, filed June 15, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a cathode active material, a cathode comprising the same, and a lithium secondary battery. Specifically, the present invention relates to a cathode active material comprising a lithium composite transition metal oxide in the form of a single particle, a cathode comprising the same, and a lithium secondary battery.

[0005]

[0006] With the recent technological development and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0007] 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 as positive electrode active materials for lithium secondary batteries, and recently, Li[Ni a Co b Mn c ]O2, Li[Ni a Co b Al c ]O2, Li[Ni a Co b Mn c Al d ] Lithium composite transition metal oxides containing two or more transition metals, such as O2, have been developed and are widely used.

[0008] Lithium composite transition metal oxides containing two or more transition metals developed to date are usually manufactured in the form of spherical secondary particles in which tens to hundreds of primary particles are aggregated. Recently, in order to solve the structural and thermal stability problems of the secondary particle-type positive electrode active material itself, the development of single-particle positive electrode active materials is accelerating. Specifically, when the secondary particle-type positive electrode active material is applied to a lithium secondary battery, there is a problem that a large amount of gas is generated, causing the volume of the battery to expand. In addition, when the nickel content in the positive electrode material is increased for high capacity, the risk of fire also increases. Accordingly, the demand for the development of single-particle positive electrode active materials with excellent stability is increasing.

[0009] Therefore, there is a need to develop a single particle type cathode active material that has excellent stability and can improve various performances of batteries when applied to batteries.

[0010]

[0011] The present invention is an invention for solving the above problems, and aims to provide a cathode active material including a lithium composite transition metal oxide in the form of a single particle, which has excellent structural stability and can improve the capacity and lifespan of a battery when applied to a battery.

[0012] In addition, the present invention aims to provide a positive electrode and a lithium secondary battery with improved performance, including the positive electrode active material.

[0013]

[0014] The present invention provides a cathode active material, a cathode including the same, and a lithium secondary battery.

[0015] (1) The present invention provides a cathode active material comprising a lithium composite transition metal oxide in the form of a single particle, wherein the lithium composite transition metal oxide satisfies the following formula 1.

[0016] [Formula 1]

[0017]

[0018] In the above equation 1,

[0019] D EBSD is the average grain size (unit: ㎛) of the crystal grains recognized when the above lithium composite transition metal oxide is observed using EBSD,

[0020] D SEM is the average particle diameter (unit: ㎛) of the smallest unit particle recognized when the above lithium composite transition metal oxide is observed using SEM.

[0021] (2) The present invention provides a positive electrode active material in the above (1), wherein the lithium composite transition metal oxide further satisfies the following formula 2.

[0022] [Formula 2]

[0023]

[0024] In the above equation 2,

[0025] D EBSD is the average grain size (unit: ㎛) of the crystal grains recognized when the above lithium composite transition metal oxide is observed using EBSD,

[0026] D SEM is the average particle diameter (unit: ㎛) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using SEM.

[0027] [Ni] is the ratio of the number of moles of nickel to the total number of moles of transition metals excluding lithium.

[0028] (3) The present invention, in the above (1) or (2), the D EBSD / D SEM The value provides a positive electrode active material having a value greater than 0.4 and less than or equal to 0.9.

[0029] (4) The present invention is one of the above (1) to (3), wherein the D EBSD Provides a positive electrode active material having a diameter of 1 μm to 5 μm.

[0030] (5) The present invention is one of the above (1) to (4), wherein the D SEM Provides a positive electrode active material having a diameter of 1㎛ to 8㎛.

[0031] (6) The present invention provides a positive electrode active material in any one of the above (1) to (5), wherein the lithium composite transition metal oxide contains nickel at 60 mol% or more based on the total molar number of transition metals excluding lithium.

[0032] (7) The present invention provides a positive electrode active material in any one of the above (1) to (6), wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1.

[0033] [Chemical Formula 1]

[0034] Li x [Ni a Co b M1 c M2 d ]O2

[0035] In the above chemical formula 1,

[0036] M1 is at least one selected from Mn and Al,

[0037] M2 is at least one 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,

[0038] 0.9≤x≤1.2, 0.6≤a<1, 0≤b≤0.4, 0≤c≤0.4, 0≤d≤0.4.

[0039] (8) In any one of the above (1) to (7), the lithium composite transition metal oxide has an average particle diameter (D 50 ) provides a positive electrode active material having a diameter of 1 μm to 10 μm.

[0040] (9) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (8).

[0041] (10) The present invention provides a lithium secondary battery including a positive electrode according to (9).

[0042]

[0043] The positive electrode active material of the present invention includes a lithium composite transition metal oxide in the form of a single particle, and satisfies Equation 1 described herein, thereby improving the capacity, lifespan, etc. of a lithium secondary battery.

[0044]

[0045] Figure 1 is a segmentation image obtained by image processing of (A) the SEM image of the positive electrode active material of Example 1 and (B) an EBSD IPF map image.

[0046] Figure 2 is a segmentation image obtained by image processing of (A) the SEM image of the positive electrode active material of Example 2 and (B) an EBSD IPF map image.

[0047] Figure 3 shows a segmentation image obtained by image processing of (A) the SEM image of the positive electrode active material of Comparative Example 1 and (B) an EBSD IPF map image.

[0048]

[0049] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0050] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0051] In this specification, the term "single particle form" refers to a form composed of 10 or fewer primary particles, as opposed to a spherical secondary particle form formed by the agglomeration of tens to hundreds of primary particles. Specifically, the "single particle form" may be a single particle form composed of one primary particle, or a secondary particle form in which 2 to 10, specifically 2 to 5, primary particles are agglomerated.

[0052] In this specification, 'primary particle' means the smallest particle unit recognized when observing a positive electrode active material using a scanning electron microscope (SEM), and 'secondary particle' means a secondary structure formed by the aggregation of multiple primary particles.

[0053] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method, and more specifically, after dispersing a lithium composite transition metal oxide in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac Mt 3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle diameter (D) corresponding to 50% of the particle size distribution in the measuring device is measured. 50 ) can be produced.

[0054]

[0055] positive electrode active material

[0056] The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in the form of a single particle, wherein the lithium composite transition metal oxide satisfies the following formula 1.

[0057] [Formula 1]

[0058]

[0059] In the above equation 1,

[0060] D EBSD is the average grain size (unit: ㎛) of the crystal grains recognized when the above lithium composite transition metal oxide is observed using EBSD,

[0061] D SEM is the average particle diameter (unit: ㎛) of the smallest unit particle recognized when the above lithium composite transition metal oxide is observed using SEM.

[0062] Above D EBSD The cross-sectional sample of the positive electrode containing the positive electrode active material is prepared, an EBSD image of the cross-sectional sample is obtained, and then the average value is obtained from the crystal grain sizes measured by the EBSD analysis program.

[0063] In the present invention, the above D SEM is the average value of the equivalent circular diameter (ECD) of the circles having the same area as the particles separated based on the particle boundaries in the SEM image. The above D SEM The segmentation image can be measured from a segmentation image obtained by processing a SEM image using an artificial intelligence model into primary particle units. Specifically, the segmentation image can be obtained by obtaining an SEM image of a cathode material powder to be measured, inputting the obtained SEM image into a U-NET structure to generate a binary image, converting the binary image into a distance-converted image based on a distance-converted algorithm, filtering the binary image using a threshold value set based on the distance-converted image, identifying a plurality of objects included in the filtered binary image, and segmenting the SEM image into primary particle units based on the plurality of objects.

[0064]

[0065] The present inventors have found that when a cathode active material includes a lithium composite transition metal oxide in the form of a single particle and the lithium composite transition metal oxide satisfies the above formula 1, the interface between crystal grains of the cathode active material in the form of a single particle of Ni of 60% or more is secured at an appropriate level, and the cathode active material is structurally stable and has improved crystallinity compared to a polycrystalline cathode active material, and thus, when the cathode active material is applied to a secondary battery, the capacity, initial efficiency, lifespan, etc. of the battery can be improved, and thus the present invention has been completed.

[0066] When the lithium composite transition metal oxide does not satisfy the above formula 1, specifically, when the value according to formula 1 is 0.4 or less, there is a problem that the primary particles are not sufficiently aggregated, the interface between crystal grains is excessive, and degradation is accelerated during the cycle. When the value according to formula 1 is 1.0, there is a problem that the oxide is structurally unstable and rather the crystallinity is lowered.

[0067]

[0068] According to the present invention, the lithium composite transition metal oxide may further satisfy the following equation 2.

[0069] [Formula 2]

[0070]

[0071] In the above equation 2,

[0072] D EBSD is the average grain size (unit: ㎛) of the crystal grains recognized when the above lithium composite transition metal oxide is observed using EBSD,

[0073] D SEM is the average particle diameter (unit: ㎛) of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using SEM.

[0074] [Ni] is the ratio of the number of moles of nickel to the total number of moles of transition metals excluding lithium.

[0075] When the above lithium composite transition metal oxide satisfies the above formula 2, the positive electrode active material can have high capacity characteristics, while the structural stability and long-life characteristics of the single particle form can be improved.

[0076] When the lithium composite transition metal oxide does not satisfy the above formula 2, specifically, when the value according to formula 2 is less than 0.5, there is a problem of low capacity development due to insufficient inter-grain interfaces at the same nickel content, and when the value according to formula 2 is more than 1.3, there is a problem of low capacity development due to low nickel content even if sufficient inter-grain interfaces are maintained, and when the nickel content is the same, there is a problem of accelerated degradation as the battery cycle is repeated due to excessive inter-grain interfaces.

[0077] When the lithium composite transition metal oxide contains nickel in an amount of 60 to 80 mol% based on the total number of moles of transition metals excluding lithium, the value according to the above formula 2 may be 0.6 to 1.2. In addition, when the lithium composite transition metal oxide contains nickel in an amount of 80 mol% or more based on the total number of moles of transition metals excluding lithium, the value according to the above formula 2 may be 0.5 to 0.8.

[0078]

[0079] 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 can be greater than 0.4, less than or equal to 0.7, less than or equal to 0.8, or less than or equal to 0.9. D EBSD / D SEM When the value is within the above range, there is an advantage of structural stability and improved crystallinity compared to polycrystalline positive electrode active materials while securing an appropriate level of inter-crystal interface of the positive electrode active material in the form of a single particle.

[0080] According to the present invention, the D EBSDmay be 1㎛ to 5㎛. Specifically, the above D EBSD It may be 1㎛ or more, 4㎛ or less, or 5㎛ or less.

[0081] According to the present invention, the D SEM can be 1㎛ to 8㎛. Specifically, the above D SEM It may be 1㎛ or more, 6㎛ or less, 7㎛ or less, or 8㎛ or less.

[0082]

[0083] According to the present invention, the lithium composite transition metal oxide may contain nickel in an amount of 60 mol% or more based on the total number of moles of transition metals excluding lithium. Specifically, the lithium composite transition metal oxide may contain nickel in an amount of 60 mol%, 70 mol%, 80 mol%, 97 mol%, 98 mol%, or 99 mol% or less based on the total number of moles of transition metals excluding lithium. That is, the [Ni] value may be 0.60, 0.70, 0.80 or more, and 0.97, 0.98, or 0.99 or less.

[0084]

[0085] According to the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1.

[0086] [Chemical Formula 1]

[0087] Li x [Ni a Co b M1 c M2 d ]O2

[0088] In the above chemical formula 1,

[0089] M1 is at least one selected from Mn and Al,

[0090] M2 is at least one 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,

[0091] 0.9≤x≤1.2, 0.6≤a<1, 0≤b≤0.4, 0≤c≤0.4, 0≤d≤0.4.

[0092] The above M2 is a doping element or coating element.

[0093] The above x represents the ratio of the number of moles of Li to the total number of moles of transition metal, and may be 0.9 or more, 0.98 or more, 0.99 or more, 1.0 or more, 1.1 or less, or 1.2 or less.

[0094] The above a represents the molar ratio of Ni to the total molar ratio 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.

[0095] 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 more, greater than 0, 0.2 or less, or 0.4 or less.

[0096] The above c represents the ratio of the number of moles of M1 to the total number of moles of transition metal, and may be 0 or more, greater than 0, 0.2 or less, or 0.4 or less.

[0097] The above d represents the mole ratio of M2 to the total mole number of transition metals, and can be 0 or more, greater than 0, 0.2 or less, or 0.4 or less.

[0098]

[0099] According to the present invention, the lithium composite transition metal oxide has an average particle diameter (D 50 ) may be 1㎛ to 10㎛, specifically 1㎛ or more, 6㎛, 8㎛, or 10㎛ or less. The average particle diameter (D 50 ) is within the above range, when an electrode is formed of a lithium composite transition metal oxide in the form of a single particle or a blend electrode is formed of a single particle having a large average particle diameter and a polycrystalline positive electrode active material, an appropriate packing density and rolling rate can be secured.

[0100]

[0101] anode

[0102] The present invention provides a positive electrode comprising the positive electrode active material.

[0103] 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.

[0104] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0105] The above-mentioned positive electrode active material layer may optionally include a conductive material and a binder, together with the positive electrode active material, as needed. In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics may be exhibited within this range.

[0106] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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 or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0107] The above binder serves to improve 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), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0108] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode can be manufactured by applying a composition (slurry) for forming a positive electrode active material layer, prepared by dissolving or dispersing the positive electrode active material and optionally a binder, a conductive agent, and a dispersant in a solvent as needed, onto a positive electrode current collector, followed by drying and rolling, or by casting the composition for forming a positive electrode active material layer onto a separate support, peeling the film from the support, and laminating the resulting film onto a positive electrode current collector.

[0109] The solvent may be a solvent generally used in the relevant technical field, 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 thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0110]

[0111] lithium secondary battery

[0112] The present invention provides a lithium secondary battery including the positive electrode.

[0113]

[0114] The lithium secondary battery may include the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0115] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0116] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0117] The above negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0118] As the 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 alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical or fibrous shapes, 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 negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0119] The binder of the above-described negative electrode active material layer is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0120] The conductive material of the above-described 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 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include 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 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; and conductive materials such as polyphenylene derivatives.

[0121] The above negative electrode can be manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the film obtained by peeling it off from the support on a negative electrode current collector.

[0122] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0123] 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. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0124] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylene carbonate (PC); alcohol 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 an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, 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 linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0125] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. 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 - At least one selected from the group consisting of may be used, and the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0126] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0127]

[0128] A lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0129] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0130] 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 be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0131] Accordingly, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0132] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0133]

[0134] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0135]

[0136] Example

[0137] Example 1

[0138] Complex transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in LiOH ((Ni+Co+Mn):Li) was 1:1.05, and the first firing was performed at a temperature of 890℃ for 6 hours in an oxygen atmosphere to manufacture a plastic product. The average particle diameter (D) of the above plastic product was 50 ) was pulverized to 4㎛, and then calcined for a second time at a temperature of 820℃ in an oxygen atmosphere for 9 hours to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.86 Co 0.05 Mn 0.09 O2) (positive electrode active material) was manufactured.

[0139]

[0140] Example 2

[0141] Complex transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the total mole number of transition metals included in the complex transition metal hydroxide (Ni+Co+Mn) and the mole number of lithium included in LiOH (Li) had a ratio of 1:1.05 ((Ni+Co+Mn):Li), and the first firing was performed at a temperature of 850°C for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product had an average particle diameter (D 50 ) was pulverized to 4㎛, and then secondary calcined at 750℃ for 9 hours in an oxygen atmosphere to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.932 Co 0.05 Mn 0.02 O2) (positive electrode active material) was manufactured.

[0142]

[0143] Example 3

[0144] Complex transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in LiOH ((Ni+Co+Mn):Li) was 1:1.05, and the first firing was performed at a temperature of 860℃ for 6 hours in an oxygen atmosphere to manufacture a plastic product. The average particle diameter (D) of the above plastic product was 50 ) was pulverized to 4㎛, and then calcined for a second time at a temperature of 820℃ in an oxygen atmosphere for 9 hours to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.86 Co 0.05 Mn 0.09 O2) (positive electrode active material) was manufactured.

[0145]

[0146] Example 4

[0147] Complex transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in LiOH ((Ni+Co+Mn):Li) was 1:1.05, and the first firing was performed at a temperature of 830℃ for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was manufactured by having an average particle diameter (D 50 ) was pulverized to 4㎛, and then secondary calcined at 750℃ for 9 hours in an oxygen atmosphere to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.932 Co 0.05 Mn 0.02 O2) (positive electrode active material) was manufactured.

[0148]

[0149]

[0150] Example 5

[0151] Complex transition metal hydroxide (composition: Ni 0.62 Co 0.08 Mn 0.30 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material Li2CO3 were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.07, and the first firing was performed at a temperature of 970℃ for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was manufactured by having an average particle diameter (D 50 ) was pulverized to 4㎛, and then calcined for a second time at a temperature of 870℃ in an oxygen atmosphere for 9 hours to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi0.62 Co 0.08 Mn 0.30 O2) (positive electrode active material) was manufactured.

[0152]

[0153] Example 6

[0154] Complex transition metal hydroxide (composition: Ni 0.68 Co 0.10 Mn 0.22 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, Li2CO3, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.05, and the first firing was performed at a temperature of 920℃ for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was prepared by having an average particle diameter (D 50 ) was pulverized to 4㎛, and then secondary calcined at a temperature of 850℃ for 9 hours in an oxygen atmosphere to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.68 Co 0.10 Mn 0.22 O2) (positive electrode active material) was manufactured.

[0155]

[0156] Comparative Example 1

[0157] Complex transition metal hydroxide (composition: Ni 0.86 Co 0.05 Mn 0.09 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in LiOH ((Ni+Co+Mn):Li) was 1:1.03, and the first firing was performed at a temperature of 800℃ for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was manufactured by having an average particle diameter (D 50) was pulverized to 4㎛, and then calcined for a second time at a temperature of 780℃ in an oxygen atmosphere for 9 hours to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.86 Co 0.05 Mn 0.09 O2) (positive electrode active material) was manufactured.

[0158]

[0159] Comparative Example 2

[0160] Complex transition metal hydroxide (composition: Ni 0.93 Co 0.05 Mn 0.02 (OH)2, average particle size (D) 50 ): 4㎛) precursor and lithium raw material, LiOH, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in LiOH ((Ni+Co+Mn):Li) was 1:1.03, and the first firing was performed at a temperature of 850℃ for 9 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was manufactured by having an average particle diameter (D 50 ) was pulverized to 4㎛, and then secondary calcined at 750℃ for 9 hours in an oxygen atmosphere to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.932 Co 0.05 Mn 0.02 O2) (positive electrode active material) was manufactured.

[0161]

[0162] Comparative Example 3

[0163] Complex transition metal hydroxide (composition: Ni 0.62 Co 0.08 Mn 0.30 (OH)2, average particle size (D) 50): 4㎛) precursor and lithium raw material, Li2CO3, were mixed so that the ratio of the total mole number of transition metals (Ni+Co+Mn) included in the complex transition metal hydroxide and the mole number of lithium (Li) included in Li2CO3 ((Ni+Co+Mn):Li) was 1:1.03, and the first firing was performed at a temperature of 900℃ for 6 hours in an oxygen atmosphere to manufacture a sintered product. The sintered product was manufactured by having an average particle diameter (D 50 ) was pulverized to 4㎛, and then secondary calcined at a temperature of 850℃ for 9 hours in an oxygen atmosphere to obtain a lithium composite transition metal oxide in the form of a single particle (composition: LiNi 0.62 Co 0.08 Mn 0.30 O2) (positive electrode active material) was manufactured.

[0164]

[0165] Experimental example

[0166] Experimental Example 1

[0167] Using a field emission scanning electron microscope (FE-SEM, FEI Quanta 250 FEG), SEM images of each of the positive electrode active materials manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were obtained. Then, each image was image-processed using the particle shape analysis method described above to obtain a segmentation image divided into primary particle units, from which D SEM was measured.

[0168] In addition, the positive electrode active materials, carbon black (Denka, DenkaBlack) conductive agent, and PVdF (Kureha, KF1100) binder manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were mixed in a weight ratio of 7:2:1 in an NMP (Daejung Chemicals & Metals) solvent to manufacture 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 manufacture 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: 6 kV) 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, D EBSD was saved.

[0169] 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.

[0170] Figures 1 to 3 sequentially show (A) a segmentation image obtained by image processing of the SEM images of the positive electrode active materials of Examples 1 and 2 and Comparative Example 1, respectively, and (B) an EBSD IPF map image.

[0171] At this time, D EBSD is the average grain size recognized when the above lithium composite transition metal oxide is observed using EBSD, and D SEM is the average particle diameter of the smallest unit particle recognized when the lithium composite transition metal oxide is observed using SEM, and [Ni] is the mole ratio of nickel to the total mole number of transition metals excluding lithium.

[0172] DEBSD / D SEM (D EBSD / D SEM ) / [Ni] Example 10.54 0.628 Example 20.63 0.677 Example 30.50 0.581 Example 40.56 0.602 Example 50.70 1.13 Example 60.42 0.617 Comparative Example 10.40 0.465 Comparative Example 21.0 0.419 Comparative Example 30.37 0.597

[0173]

[0174] Experimental Example 2: Battery Performance Evaluation

[0175] Each of the positive electrode active materials, carbon black conductive agent, and polyvinylidene fluoride (PVDF) binder prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was mixed in an N-methylpyrrolidone (NMP) solvent at a ratio of 95:3:2 to prepare 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 prepare a positive electrode.

[0176] A lithium metal electrode was used as the cathode, and an electrode assembly was manufactured by interposing a porous polyethylene separator between the anode and cathode. After positioning the electrode assembly inside a battery case, an electrolyte was injected into the case to manufacture a half-cell.

[0177] For each half cell manufactured in this way, it was charged at 0.1 C in CC-CV mode at 25°C until 4.25 V (Cut-off current: 0.05 C), and discharged to 2.5 V at a constant current of 0.1 C. The initial charge capacity and initial discharge capacity were measured, and the initial efficiency was calculated, which is shown in Table 2 below.

[0178] Then, the cell that completed one cycle was moved to a chamber at 45°C, and the charge / discharge cycle was repeated 30 times at 0.33C to measure the capacity of the lithium secondary battery. The percentage of the 30th cycle discharge capacity to the 1st cycle discharge capacity was used as the capacity retention rate, and this is shown in Table 2 below.

[0179] ClassificationInitial charge capacity (mAh / g)Initial discharge capacity (mAh / g)Initial efficiency (%)Capacity retention rate (%)Example 1232.7205.588.397.5Example 2240.0212.888.793.8Example 3232.2204.888.297.2Example 4240.5213.188.692.6Example 5220.2200.390.997.3Example 6226.3206.691.395.2Comparative example 1230.8202.887.996.1Comparative example 2236.5210.489.090.8Comparative example 3218.2196.790.191.8

[0180]

[0181] Referring to Tables 1 and 2, it can be confirmed that the batteries including the positive electrode active materials of Examples 1 to 6 are excellent in capacity, initial efficiency, and life performance, satisfying Equation 1 described herein. On the other hand, it can be confirmed that the battery including the positive electrode active material of Comparative Example 1 has lower capacity, initial efficiency, and life performance compared to the batteries including the positive electrode active materials of Examples 1 and 3 having similar compositions. In addition, it can be confirmed that the battery including the positive electrode active material of Comparative Example 2 has lower capacity and life performance compared to the batteries including the positive electrode active materials of Examples 2 and 4 having similar compositions. In addition, it can be confirmed that the battery including the positive electrode active material of Comparative Example 3 has lower capacity, initial efficiency, and life performance compared to the batteries including the positive electrode active materials of Examples 5 and 6 having similar compositions.

Claims

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

2. In claim 1, The above lithium composite transition metal oxide is a positive electrode active material that further satisfies the following formula 2: [Formula 2] In the above equation 2, D EBSD is the average grain size (unit: ㎛) of the crystal grains recognized when the above lithium composite transition metal oxide is observed using EBSD, D SEM is the average particle diameter (unit: ㎛) of the smallest unit particle recognized 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.

3. In claim 1, Above D EBSD / D SEM A positive electrode active material having a value greater than 0.4 and less than or equal to 0.

9.

4. In claim 1, Above D EBSD A positive electrode active material having a diameter of 1㎛ to 5㎛.

5. In claim 1, Above D SEM A positive electrode active material having a diameter of 1㎛ to 8㎛.

6. In claim 1, The above lithium composite transition metal oxide is a cathode active material containing nickel at 60 mol% or more based on the total molar number of transition metals excluding lithium.

7. In claim 1, The above lithium composite transition metal oxide is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] The x [Nor a Co b M1 c M2 d ]O2 In the above chemical formula 1, M1 is at least one selected from Mn and Al, M2 is at least one 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. In claim 1, The above lithium composite transition metal oxide has an average particle diameter (D 50 ) A positive electrode active material having a diameter of 1㎛ to 10㎛.

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

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

Images