Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a lithium transition metal oxide containing nickel (Ni), which is a positive electrode active material for a lithium secondary battery, and which is composed of single particles, has an average particle size (D50) of 2 to 4 μm, and has a maximum pole density value corresponding to the (001) plane of 20 or less in a pole figure diagram obtained by electron backscatter diffraction analysis.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same, and more specifically to a positive electrode active material for a lithium secondary battery composed of single particles, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Carbon neutrality is becoming increasingly important to prevent the depletion of fossil fuels and global warming. To achieve this, the development of new renewable energy sources and electric vehicles to replace internal combustion engine vehicles are essential. To achieve this, lithium-ion secondary batteries are used as energy storage devices. Various positive electrode active materials are being developed to realize secondary batteries with higher energy density and stability.

[0003] Among these, the most active research has focused on materials that substitute cobalt, manganese, or aluminum ions into nickel-based layered cathode active materials (LiNiO2). These cathode active materials typically have a secondary agglomerate multiparticle structure, where primary particles are aggregated. However, these agglomerates have a large non-surface area, which increases the risk of gas generation due to side reactions with the electrolyte. Furthermore, when lithium transition metal oxides are rolled to high electrode densities to achieve high-density electrodes, particle cracking can occur due to volume changes during charge and discharge, resulting in poor structural stability. To address these issues, bimodal active materials combining large and small particle diameters have been studied. However, the small particle diameter active materials have a larger specific surface area than the large particle diameter active materials, significantly impacting cell degradation.

[0004] To solve this problem, research and development of single-particle anode active materials is being conducted. However, synthesizing a single-particle cathode active material requires firing at a higher temperature than that required for multi-particle cathode active materials, which can significantly degrade the electrochemical properties of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a small particle size single particle positive electrode active material that has excellent electrochemical properties while solving the cell deterioration problem caused by cracking or gas generation that occurs in conventional small particle size multi-particle active materials.

[0006] Another object of the present invention is to provide a method for producing a small particle size single particle positive electrode active material having the above-mentioned advantages.

[0007] It is still another object of the present invention to provide a lithium secondary battery including the positive electrode active material. [Means for solving the problem]

[0008] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing nickel (Ni), wherein the lithium transition metal oxide is composed of single particles, has an average particle size (D50) of 2 to 4 μm, and has a maximum pole density value corresponding to the (001) plane in a pole figure diagram obtained by electron backscatter diffraction (EBSD) analysis of 20 or less.

[0009] In the positive electrode active material, the (001) plane may not be preferentially aligned when analyzing an EBSD image.

[0010] The positive electrode active material can be derived from a positive electrode active material precursor having an average particle size (D50) of 5 to 15 μm.

[0011] The lithium transition metal oxide may be represented by the following Chemical Formula 1. [Chemical formula 1] Li a (Ni b Me 1-b )O2

[0012] In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦b≦0.99, and Me is Co, Mn, Al, Zr, Nb, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, Fe, or a combination thereof.

[0013] In this case, the b may be in the range of 0.8≦b≦0.99.

[0014] The positive electrode active material may further include a coating layer located on a surface of the lithium transition metal oxide, and the coating layer may include Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, Ga, or a combination thereof.

[0015] Another embodiment of the present invention provides a method for manufacturing a cathode active material for a lithium secondary battery, the method comprising the steps of: forming a mixture containing a cathode active material precursor containing nickel (Ni) and a lithium source material; calcining the mixture to form a lithium transition metal oxide; and pulverizing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles, wherein the average particle size (D50) of the cathode active material precursor is larger than the average particle size (D50) of the cathode active material.

[0016] The grinding can be carried out so that the (001) plane of the lithium transition metal oxide is ground.

[0017] The grinding can be carried out at a rotation speed of 3000 to 3600 rpm.

[0018] The grinding can be carried out at a grinding pressure of 1.4 bar or more.

[0019] The positive electrode active material precursor may have an average particle size (D50) of 5 to 15 μm.

[0020] The positive electrode active material may have an average particle size (D50) of 2 to 4 μm.

[0021] The firing can be carried out at 830 to 870° C. for 5 to 15 hours.

[0022] The step of forming the mixture further includes mixing a doped source material, which may be a compound containing one or more of Zr, Nb, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

[0023] After the step of forming the lithium transition metal oxide composed of single particles, the method may further include a step of mixing the lithium transition metal oxide composed of single particles with a coating raw material, and then heat-treating the mixture to form a coating layer, wherein the coating raw material may be a compound containing one or more of Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, and Ga, or a combination thereof.

[0024] Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material.

[0025] Another embodiment of the present invention provides a lithium secondary battery including the above-described positive electrode. [Effects of the Invention]

[0026] The cathode active material according to one embodiment of the present invention is composed of single particles, which provides excellent structural stability and enables high electrode density. It also has excellent lifespan and safety due to reduced side reactions with the electrolyte. Furthermore, the Ni-based layered structure reduces the electrochemically inactive (001) plane, resulting in excellent electrochemical properties such as capacity.

[0027] According to another embodiment of the present invention, a method for preparing a positive electrode active material can reduce the (001) plane of a single particle positive electrode active material by using a top-down method with a medium- or large-particle precursor. In addition, the use of a medium- or large-particle precursor can increase the loading amount of the mixture before calcination, thereby improving the productivity of the active material. [Brief explanation of the drawings]

[0028] [Figure 1] 1A and 1B are EBSD images and pole figures of the positive electrode active materials prepared in Example 1 and Comparative Example 1. [Figure 2] 1 is a diagram showing scanning electron microscope (SEM) images of the positive electrode active materials prepared in Example 1 and Comparative Example 1. FIG. [Figure 3] FIG. 2 is a diagram showing the results of evaluating the capacity characteristics of the lithium secondary batteries produced in Example 1 and Comparative Example 1. [Figure 4] FIG. 1 is a diagram showing the results of high-temperature life characteristics of lithium secondary batteries manufactured in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0029] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0030] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used herein, the term "comprises" refers to the inclusion of specific properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0031] When a part is described as being "on" or "above" another part, it may be exactly on or above the other part, or it may have other parts between them. In contrast, when a part is described as being "on" another part, there are no other parts between them.

[0032] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined.

[0033] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0034] As used herein, the term "combination thereof" in a maxi-expression means a mixture or combination of one or more selected from the group of components set forth in the maxi-expression, and means including one or more selected from the group of components.

[0035] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0036] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing nickel (Ni), wherein the lithium transition metal oxide is composed of single particles, has an average particle size (D50) of 2 to 4 μm, and has a maximum pole density value corresponding to the (001) plane in a pole figure obtained by electron backscatter diffraction (EBSD) analysis of 20 or less.

[0037] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single particles.

[0038] More specifically, the positive electrode active material may be classified into unassembled primary particles or secondary particles formed by the assembly of a plurality of primary particles, depending on whether the primary particles are assembled or not. In this regard, the positive electrode active material according to the present invention is composed of unassembled primary particles, i.e., single particles.

[0039] As the positive electrode active material is composed of single particles, it solves the problems of secondary particles, namely, the large specific surface area increases the risk of side reactions with the electrolyte, reducing the safety of the battery, and when lithium transition metal oxide is rolled to a high electrode density to realize a high-density electrode, fine cracks occur between the primary particles as charging and discharging are repeated, resulting in low structural stability and a deterioration in lifespan characteristics.

[0040] The single particle positive electrode active material according to the present invention has an average particle size (D50) of 2 to 4 μm.

[0041] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0042] The particle size within this range is suitable for a small particle size active material, and is particularly suitable for use as a small particle size active material to be mixed with a large particle size active material when manufacturing a bimodal positive electrode active material for realizing a high density electrode.

[0043] However, single-particle positive electrode active materials generally undergo sintering at higher temperatures than multi-particle positive electrode active materials, and the stable (001) plane grows predominantly, resulting in particles that are elongated from side to side. However, because the (001) plane is the plane that serves as the path for lithium ions to travel, if the (001) plane grows predominantly, the distance that lithium ions must travel increases, which can lead to problems with deterioration of the battery's electrochemical properties, such as capacity, initial efficiency, and high-temperature life.

[0044] To solve the above problem, the positive electrode active material according to the present invention has suppressed growth of the (001) plane, and the maximum pole density value corresponding to the (001) plane in a pole figure diagram obtained by electron backscatter diffraction (EBSD) analysis is 20 or less.

[0045] The maximum pole density value corresponding to the (001) plane in the pole figure diagram obtained by EBSD analysis is a measure of the degree of growth of the (001) plane. By satisfying this range, the diffusion distance of lithium ions can be reduced, minimizing the deterioration of the battery's electrochemical characteristics. Suppression of the growth of the (001) plane can be achieved through a top-down process using medium- or large-particle active material precursors, as described below. This will be described in more detail later.

[0046] In this specification, the maximum pole density value corresponding to the (001) plane in the pole figure diagram obtained by EBSD analysis means that it was measured using Hitachi's SU5000 as an FESEM image observation device and EDAX's Velocity Super as an EBSD data analysis device under the conditions of an area of ​​20 x 50 μm and a step size of 50 nm.

[0047] The maximum pole density value is more specifically 18 or 15 or less, and may be 10 or more.

[0048] Meanwhile, in the positive electrode active material according to an embodiment of the present invention, when an X-ray diffraction pattern is measured, I(003) / I(104), which is the peak intensity ratio of the (003) plane to the peak intensity of the (104) plane, may be 1.4 or less, more specifically, 1.3 or less.

[0049] Generally, the peak intensity value means the peak height value or the integrated area value obtained by integrating the area of ​​the peak, and in this specification, the peak intensity value means the area value of the peak.

[0050] This value is also a measure of the degree of growth of the (001) plane. In the cathode active material according to one embodiment of the present invention, the growth of the (001) plane is suppressed, so that I(003), which corresponds to the XRD peak value of the (001) plane, is relatively small compared to I(104), and the I(003) / I(104) ratio can be sufficiently small, at 1.4 or less.

[0051] Therefore, the positive electrode active material according to the present invention may not exhibit preferential orientation in the (001) plane during EBSD image analysis.

[0052] The positive electrode active material may be derived from a positive electrode active material precursor having an average particle size (D50) of 5 to 15 μm. That is, the positive electrode active material according to the present invention may be a small particle size active material prepared from a medium or large particle size active material precursor using a top-down method, as described below.

[0053] The lithium transition metal oxide is represented by the following Chemical Formula 1. [Chemical formula 1] Li a (Ni b Me 1-b )O2

[0054] In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦b≦0.99, and Me is Co, Mn, Al, Zr, Nb, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, Fe, or a combination thereof.

[0055] The a indicates the molar ratio of lithium in the lithium transition metal oxide, and may be 0.8≦a≦1.2, 0.85≦a≦1.15, or 0.9≦a≦1.1.

[0056] The b represents the molar ratio of nickel to the total moles of transition metals in the lithium transition metal oxide, and may be 0.60≦b≦0.99, 0.70≦b≦0.99, 0.80≦b≦0.99, 0.85≦b≦0.99, 0.90≦b≦0.99, or 0.90≦b≦0.95. When the nickel content in the lithium transition metal oxide satisfies this range, a positive electrode active material and a lithium secondary battery having high capacity characteristics can be manufactured.

[0057] In particular, the b may be in the range of 0.8≦b≦0.99. That is, the positive electrode active material according to the present invention has a high nickel content of 80 mol % or more based on the total mole number of transition metals, and can achieve high capacity.

[0058] The positive electrode active material further includes a coating layer located on the surface of the lithium transition metal oxide, and the coating layer can include Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, Ga, or a combination thereof. Such a coating layer can reduce residual lithium present on the active material surface and further improve the structural and chemical stability of the active material.

[0059] Preferably, the coating layer may contain Co and Al.

[0060] The coating layer may have a thickness of 1 nm to 100 nm.

[0061] 2.Cathode active material manufacturing method Another embodiment of the present invention provides a method for manufacturing a cathode active material for a lithium secondary battery, the method comprising the steps of: forming a mixture containing a cathode active material precursor containing nickel (Ni) and a lithium source material; calcining the mixture to form a lithium transition metal oxide; and pulverizing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles, wherein the average particle size (D50) of the cathode active material precursor is larger than the average particle size (D50) of the cathode active material.

[0062] Hereinafter, a method for manufacturing a positive electrode active material according to another embodiment of the present invention will be described in detail step by step.

[0063] First, a mixture containing a positive electrode active material precursor containing nickel (Ni) and a lithium source material is formed.

[0064] More specifically, the positive electrode active material precursor may be a hydroxide containing nickel and manganese, and such a positive electrode active material precursor is represented by the following chemical formula 2: [Chemical formula 2] Ni x2 Co y2 Mn z2 (OH)2

[0065] In the above chemical formula 1, 0.6≦x2≦0.99, 0≦y2≦0.3, 0 <z2≦0.3であり、x2+y2+z2=1である。

[0066] The x2 represents the molar ratio of nickel to all metal elements in the transition metal hydroxide, and may be 0.6≦x2≦0.99, 0.7≦x2≦0.99, 0.80≦x2≦0.99, 0.85≦x2≦0.99, 0.90≦x2≦0.99, or 0.90≦x2≦0.95. When the nickel content in the transition metal hydroxide satisfies this range, a positive electrode active material and a lithium secondary battery having high capacity characteristics can be manufactured.

[0067] The y2 represents the molar ratio of cobalt to all metal elements in the transition metal hydroxide, and may be 0≦y2≦0.3, 0.01≦y2≦0.2, 0.01≦y2≦0.1, 0.02≦y2≦0.08, or 0.02≦y2≦0.06.

[0068] The z2 represents the molar ratio of manganese to all metal elements in the transition metal hydroxide, and is 0 <z2≦0.3、0.01≦z2≦0.2、0.01≦z2≦0.1、0.02≦z2≦0.08または0.02≦z2≦0.06であってもよい。

[0069] In particular, the average particle size (D50) of the positive electrode active material precursor may be 5 to 15 μm.

[0070] More specifically, conventional methods for manufacturing single-particle cathode active materials use a bottom-up approach, in which small-particle active material precursors are used and then calcined to grow particles to a desired size. However, this approach suffers from the problem of the electrochemically stable (001) plane preferentially growing during the calcination process, which increases particle size, resulting in a degradation of the electrochemical properties of secondary batteries. In contrast, the present invention uses a medium- or large-particle precursor with an average particle size (D50) of 5 to 15 μm, calcines the precursor, and then randomly pulverizes the active material surface through a milling process, as described below. This enables the manufacture of cathode active materials with a reduced (001) plane preferential orientation compared to the conventional bottom-up approach. Furthermore, the use of medium- or large-particle precursors allows for an increased loading of the pre-calcination mixture, thereby improving active material productivity.

[0071] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium source material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, C2H3LiO2, Li2O, Li2O2, Li2SO4, Li2SO3, Li3C6H5O7, or a combination thereof.

[0072] The step of forming the mixture may further include mixing a doping source material, which may be a compound containing one or more of Zr, Nb, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

[0073] The mixture is then calcined to form the lithium transition metal oxide.

[0074] Through the calcination, a lithium transition metal oxide in the form of a mixture of single particles and multiparticles, in which primary particles and secondary particles formed by aggregation of the primary particles are all present, is formed.

[0075] The sintering can be carried out at a temperature of 830 to 870°C. If the sintering temperature is too low, the primary particles may be too small, resulting in problems of gas generation or shortened lifespan, while if the sintering temperature is too high, problems such as reduced capacity and efficiency due to overgrowth and cation mixing, in which Ni ions move to Li sites, may occur.

[0076] The calcination can be performed for 5 to 15 hours, more specifically, for 8 to 12 hours or 9 to 11 hours. If the calcination time is too short, the crystallinity may not decrease or grow sufficiently, as with the temperature, which may result in problems such as gas generation or reduced lifespan. If the calcination time is too long, problems such as reduced capacity and efficiency due to overgrowth and cation mixing may occur.

[0077] The firing can be carried out in an oxygen atmosphere. When a high-Ni-content nickel (Ni-rich) positive electrode active material is fired at a high temperature for a long time, Ni is deposited in the lithium layer in a layered crystalline structure during the firing process. 2+ In order to prevent this, it is preferable to synthesize the positive electrode active material in an oxygen atmosphere.

[0078] The calcination can be divided into a primary calcination and a secondary calcination as needed. The secondary calcination recrystallizes the primary calcined product to form a lithium transition metal oxide with better structural stability.

[0079] Next, the lithium transition metal oxide is pulverized to form a lithium transition metal oxide composed of single particles, and the pulverization can be performed so that the (001) plane of the lithium transition metal oxide is pulverized.

[0080] More specifically, the pulverization can disaggregate the lithium transition metal oxide in the form of multi-particles, which are secondary particles formed by agglomeration of primary particles, to form a lithium transition metal oxide composed only of single particles.

[0081] Furthermore, by performing pulverization at an appropriate rotation speed and pulverization pressure, it is possible to form a lithium transition metal oxide having a small particle size. In particular, by performing pulverization at an appropriate rotation speed and pulverization pressure, as described above, random pulverization of the active material surface occurs, making it possible to form a positive electrode active material with a reduced (001) plane.

[0082] More specifically, the pulverization can be carried out at a rotation speed of 3000 to 3600 rpm. By setting the rotation speed within this range, it is possible to form an active material with a small particle size having an appropriate size, and to efficiently reduce the (001) plane of the active material.

[0083] The pulverization can be performed at a pulverization pressure of 1.4 bar or more, more specifically, at a pulverization pressure of 1.4 bar or 1.5 bar or more and 2 bar or 1.8 bar or less. By using a pulverization pressure within this range, a small particle size active material having an appropriate size can be formed, and the (001) plane of the active material can be efficiently reduced.

[0084] The pulverization method is not particularly limited and can be performed by a pulverization method commonly used in the art, for example, a jet mill process.

[0085] Through this pulverization process, it is possible to obtain a small particle size positive electrode active material that is composed of single particles, has an average particle size (D50) of 2 to 4 μm, and in which the growth of the (001) plane is suppressed.

[0086] After the step of forming the lithium transition metal oxide composed of single particles, the method may further include the step of mixing the lithium transition metal oxide composed of single particles with a coating raw material, and then heat-treating the mixture to form a coating layer.

[0087] In this case, the coating raw material may be a compound containing one or more of Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, and Ga, or a combination thereof.

[0088] More specifically, the coating source material can include Co3O4 and Al(OH)3.

[0089] The content of the coating raw material may be 1 to 5 wt %, more specifically 1.5 to 3 wt %, based on the total weight of the lithium transition metal oxide. If the content of the coating raw material is too low, there is a problem of reduced electrochemical capacity and lifespan due to residual lithium present on the surface, and if the content of the coating raw material is too high, there is a problem of increased surface resistance, resulting in reduced capacity and efficiency.

[0090] The heat treatment can be carried out at a temperature of 550 to 800°C, more specifically, at a temperature of 600 to 750°C or 650 to 700°C.

[0091] The heat treatment can be carried out for 2 to 10 hours, more specifically, for 3 to 7 hours or 4 to 6 hours.

[0092] When the heat treatment temperature and heat treatment time are within the above ranges, residual lithium is suppressed and a uniform surface coating can be achieved.

[0093] 3.Positive electrode Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material.

[0094] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material described above.

[0095] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0096] The positive electrode active material layer may optionally contain a binder and / or a conductive material in addition to the positive electrode active material.

[0097] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0098] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the battery and has electronic conductivity can be used without any particular limitations. 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 powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material is typically present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0099] The positive electrode can be produced by a conventional method for producing a positive electrode.

[0100] Specifically, the positive electrode may be fabricated by coating a positive electrode active material layer-forming composition containing a positive electrode active material and, optionally, a binder, a conductive material, or a solvent on a positive electrode current collector, followed by drying and rolling. The types and amounts of the positive electrode active material, binder, and conductive material are as described above.

[0101] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0102] Alternatively, the positive electrode can be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0103] 4. Lithium secondary batteries Another embodiment of the present invention provides a lithium secondary battery including the above-described positive electrode.

[0104] In particular, the lithium secondary battery according to the present invention may have an initial charge capacity of 228 mAh / g or 229 mAh / g or more, an initial discharge capacity of 205 mAh / g or 206 mAh / g or more, and an initial efficiency of 90% or more.

[0105] Furthermore, the lithium secondary battery according to the present invention may have a high-temperature life retention rate of 91.3% or more and a high-temperature resistance increase rate of 169% or less.

[0106] More specifically, the lithium secondary battery may include the above-described positive electrode; a negative electrode facing the positive electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0107] The lithium secondary battery may further include a battery container that houses an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0108] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0109] The negative electrode current collector is not limited as long as it does not cause chemical changes in the battery and has high conductivity. Examples of materials that can be used include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the current collector surface can be provided with fine irregularities to strengthen the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0110] The negative electrode active material layer may include a negative electrode active material, and optionally a binder and a conductive material. For example, the negative electrode active material layer may be fabricated by coating a negative electrode active material, and optionally a binder and a conductive material, on a negative electrode current collector and drying the coating, or by casting the negative electrode active material on a separate support, peeling the coating from the support, and laminating the resulting film on the negative electrode current collector.

[0111] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these can be used. A thin film of metallic lithium can also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleumor coal tar pitch-derived cokes.

[0112] The binder and conductive material are the same as those described above for the positive electrode.

[0113] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without limitation. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte humidification are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric materials can also be used, and they can be selectively used in single-layer or multi-layer structures.

[0114] 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 manufacturing lithium secondary batteries.

[0115] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0116] The organic solvent can be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; dibutyl ether; ether-based solvents such as ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylenecarbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte can be improved by mixing the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9.

[0117] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, iCl, LiI, and LiB(C2O4)2. The lithium salt concentration is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0118] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity decline, and improving battery discharge capacity. In this case, the additives may be included in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte. [Example]

[0119] Hereinafter, the present invention will be described in more detail with reference to the following examples, but the following examples are only preferred examples of the present invention and are not intended to limit the scope of the present invention.

[0120] Example 1: Top-down method positive electrode active material production (1) Manufacture of positive electrode active material With an average particle size (D50) of 15 μm (Ni 0.88 Co 0.04 Mn 0.08 275 g of an active material precursor having the composition )(OH)2, 125 g of LiOH·H2O, and 0.729 g of ZrO2 were charged into a mixer and mechanically mixed to form a mixture.

[0121] The mixture was then calcined at 850°C for 10 hours under an O2 atmosphere to form lithium transition metal oxide.

[0122] Thereafter, the lithium transition metal oxide was pulverized through a jet mill process to break up agglomerations and control the particle size of the active material, thereby forming a lithium transition metal oxide composed of single particles, under conditions of a pulverization pressure of 1.5 bar and a rotation speed of 3300 rpm.

[0123] Then, 40 g of the obtained lithium transition metal oxide was mixed with 0.172 g of LiOH·H2O, 0.533 g of Co3O4, and 0.162 g of Al(OH)3, and the mixture was heat-treated at 650 to 700°C for 5 hours.

[0124] Finally, LiNi 0.88 Co 0.04 Mn 0.08 Zr 0.002 A single particle positive electrode active material was prepared by coating the surface of a lithium transition metal oxide with 1 mol% of Li, 5 mol% of Co, and 0.5 mol% of Al.

[0125] (2) Lithium secondary battery manufacturing A coin half-cell lithium secondary battery was fabricated using the cathode active material prepared by the above method.

[0126] The slurry for electrode plate production was made with a positive electrode active material: conductive material (acetylene black): binder (PVDF, KF1120) ratio of 96.5:1.5:2 wt%, and additional NMP (N-Methyl-2-pyrrolidone) was added to adjust the solid content and slurry viscosity. The produced slurry was coated on Al foil using a doctor blade, dried, and rolled to produce an electrode plate. The electrode loading was 15-16 mg / cm. 2 The electrode mixture density is 3.5 g / cm 3 That was all.

[0127] The electrolyte used in the coin cell was 1M LiPF6 in EC:DMC:EMC = 3:4:3 (vol%) + VC 3.0 wt%, and a coin half cell was fabricated using a PP separator and a lithium anode (300 μm).

[0128] Comparative example 1: Bottom-up method positive electrode active material production The average particle size (D50) of 3.5 μm (Ni 0.88 Co 0.04 Mn 0.08 A positive electrode active material and a lithium secondary battery were produced in the same manner as in Example 1, except that an active material precursor having a composition of )(OH)2 was used and crushing was carried out under conditions of a crushing pressure of 1.3 bar and a rotation speed of 3300 rpm.

[0129] Table 1 below summarizes the process conditions and physical properties of the positive electrode active materials according to Experimental Examples 1 and 2 described below.

[0130] [Table 1]

[0131] Experimental example 1: EBSD analysis of positive electrode active material The positive electrode active materials prepared in Example 1 and Comparative Example 1 were analyzed for the maximum pole density value of the (001) plane through the EBSD images (top of FIG. 1) and the pole figure diagrams (bottom of FIG. 1) in the (001) plane direction obtained by EBSD analysis, and the results are shown in FIG. 1 and Table 1. The specific measurement method is as follows.

[0132] Hitachi's SU5000 was used as the FESEM image observation device, and EDAX's Velocity Super was used as the EBSD data analysis device, and measurements were taken under the conditions of an area of ​​20 x 50 um and a step size of 50 nm.

[0133] Referring to the EBSD image in Figure 1, it was confirmed that the growth of the (001) plane was suppressed and no preferential arrangement of the (001) plane occurred in the positive electrode active material of Example 1. On the other hand, it was confirmed that the excessive growth of the (001) plane occurred and preferential arrangement of the (001) plane occurred in the positive electrode active material of Comparative Example 1.

[0134] Referring to the pole figure diagram of FIG. 1, it was confirmed that the maximum pole density value of the positive electrode active material according to Example 1 was 14.348, and the maximum pole density value of the positive electrode active material according to Comparative Example 1 was 29.022.

[0135] Experimental Example 2: Evaluation of the shape and average particle size (D50) of the positive electrode active material The shapes of the positive electrode active materials prepared in Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM), and the results are shown in FIG.

[0136] Referring to FIG. 2, it was confirmed that all of the positive electrode active materials according to Example 1 and Comparative Example 1 had a single particle morphology consisting of unassembled primary particles.

[0137] It was also confirmed that the average particle size (D50) of the positive electrode active material according to Example 1 was approximately 3.00 μm, and the average particle size (D50) of the positive electrode active material according to Comparative Example 1 was approximately 3.56 μm.

[0138] Experimental Example 3: Evaluation of electrochemical characteristics of lithium secondary batteries An experiment to evaluate the electrochemical characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 was carried out. The specific experimental method is as follows.

[0139] (1) Initial capacity and efficiency evaluation After fabrication, the lithium secondary battery was aged at room temperature for 10 hours and then subjected to a charge-discharge test. To evaluate the initial capacity, 200mAh / g was used as the reference capacity, and the battery was charged to 4.25V at a constant current of 0.1C, then switched to a constant voltage and charged until the final current reached 0.05C.

[0140] After charging, the battery was allowed to rest for 20 minutes, and then discharged at a constant current of 0.1 C until the voltage reached 3.0 V, with a reference capacity of 200 mAh / g.

[0141] The associated results are shown in Figure 3 and Table 1 below.

[0142] (2) High-temperature lifespan characteristics evaluation To evaluate the high temperature lifespan, the battery was charged at 0.5C and discharged at 1.0C for 100 cycles at 45°C. The capacity retention rate and resistance increase rate at the 100th cycle compared to the first cycle were measured, and the results are shown in Figure 4 and Table 2 below.

[0143] [Table 2]

[0144] 3 and Table 2, it was confirmed that the lithium secondary battery according to Example 1 was superior in all of the initial charge capacity, discharge capacity, and initial efficiency compared to the lithium secondary battery according to Comparative Example 1. Furthermore, it was confirmed that the lithium secondary battery according to Example 1 had a higher high-temperature life retention rate and a lower high-temperature resistance increase rate compared to the lithium secondary battery according to Comparative Example 1, and thus was superior in high-temperature life characteristics.

[0145] This can be interpreted as the result of the positive electrode active material of Example 1 being composed of single particles and reducing the (001) plane, thereby improving the battery capacity, initial efficiency, and high-temperature life characteristics.

[0146] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, which also fall within the scope of the present invention.

[0147] Therefore, the true scope of the invention will be defined by the appended claims and their equivalents.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising a lithium transition metal oxide containing nickel (Ni), the lithium transition metal oxide being composed of single particles, having an average particle size (D50) of 2 to 4 μm, and having a maximum pole density value corresponding to a (001) plane of 20 or less in a pole figure diagram obtained by electron backscatter diffraction (EBSD) analysis.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the (001) plane is not preferentially aligned in EBSD image analysis.

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is derived from a positive electrode active material precursor having an average particle size (D50) of 5 to 15 μm.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ａ (N ｂ Me １－ｂ )O ２ In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦b≦0.99, and Me is Co, Mn, Al, Zr, Nb, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, Fe, or a combination thereof.

5. 5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein 0.8≦b≦0.

99.

6. 2. The positive electrode active material for a lithium secondary battery according to claim 1, further comprising a coating layer located on a surface of the lithium transition metal oxide, the coating layer comprising Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, Ga, or a combination thereof.

7. forming a mixture including a positive electrode active material precursor including nickel (Ni) and a lithium source material; calcining the mixture to form a lithium transition metal oxide; A method for producing a positive electrode active material for a lithium secondary battery, comprising: pulverizing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles, The method for producing a positive electrode active material for a lithium secondary battery, wherein the average particle size (D50) of the positive electrode active material precursor is larger than the average particle size (D50) of the positive electrode active material.

8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7 , wherein the pulverization is carried out so that the (001) plane of the lithium transition metal oxide is pulverized.

9. 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, wherein the pulverization is carried out at a rotation speed of 3000 to 3600 rpm.

10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8 , wherein the pulverization is performed at a pulverization pressure of 1.4 bar or more.

11. 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, wherein the average particle size (D50) of the positive electrode active material precursor is 5 to 15 μm.

12. 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, wherein the average particle size (D50) of the positive electrode active material is 2 to 4 μm.

13. 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, wherein the calcination is carried out at a temperature of 830 to 870° C. for 5 to 15 hours.

14. In forming the mixture, 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, further comprising mixing a doping source material, the doping source material being a compound containing one or more of Zr, Nb, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

15. After the step of forming the lithium transition metal oxide composed of single particles, 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7, further comprising the step of mixing the lithium transition metal oxide composed of single particles with a coating raw material, and then heat-treating the mixture to form a coating layer, wherein the coating raw material is a compound containing one or more of Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, La, Ta, and Ga, or a combination thereof.

16. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.

17. A lithium secondary battery comprising the positive electrode according to claim 16.

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