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

Abstract

The present invention relates to a cathode active material that includes a lithium-nickel-based transition metal oxide in the form of secondary particles, which are aggregates of primary particles, and that satisfies the following conditions: a) the number ratio of primary particles having an aspect ratio of 1.6 or more within a cross section of the secondary particles at a point 40% to 60% of the diameter of the secondary particles is 0.81 or more; and b) the K value calculated by the following Equation 1 is 12 to 40. The cathode active material having the above characteristics can reduce particle cracking during cycling, suppress battery degradation, and improve stability. [Formula 1] K=R AP ×N P / A S where R AP is the average aspect ratio of the primary particles, and N P is the number of primary particles, and A S is the cross-sectional area of ​​the secondary particle.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0184868, filed December 26, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery, and more particularly to a positive electrode active material including a lithium nickel-based transition metal oxide in the form of secondary particles that are aggregates of primary particles, and a positive electrode and a lithium secondary battery including the same. [Background technology]

[0003] A lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high cost and unstable supply of cobalt, the raw material, make its commercial application in large-capacity batteries difficult. Lithium nickel oxide has poor structural stability and is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but poor capacity characteristics. Therefore, to address the issues of lithium transition metal oxides containing only Ni, Co, or Mn, lithium nickel-based transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0005] Recently, there has been an increasing need for high-power, high-capacity batteries, such as those for electric vehicles, and as a result, the nickel content in the positive electrode active material is gradually increasing. When the nickel content in the positive electrode active material increases, the initial capacity characteristics improve, but the highly reactive nickel is easily absorbed during electrode rolling or during charge and discharge. 4+ A large amount of ions are generated, causing the structure of the positive electrode active material to collapse, which increases surface side reactions, increases the rate of deterioration of the positive electrode active material, reduces the life characteristics, and reduces the safety of the battery. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a positive electrode active material with improved durability by optimizing the shape of primary particles inside secondary particles to suppress the occurrence of particle breakage and cracks during electrode manufacturing and charge / discharge processes.

[0007] Another object of the present invention is to provide a positive electrode and a lithium secondary battery that contain the positive electrode active material and thereby have improved high-temperature life characteristics and high-temperature output characteristics. [Means for solving the problem]

[0008] In order to solve the above problems, in one aspect of the present invention, there is provided a positive electrode active material that includes a lithium nickel-based transition metal oxide in the form of secondary particles that are aggregates of primary particles, and that satisfies the following conditions a) and b) with respect to a cross section of the secondary particles at a point that is 40% to 60% of the diameter:

[0009] a) the number ratio of primary particles having an aspect ratio of 1.6 or more in the cross section is 0.81 or more, b) The K value calculated by the following formula 1 is 12 to 40. [Formula 1] K=R AP ×N P / A S where R APis the average aspect ratio of the primary particles, and N P is the number of primary particles, and A S is the cross-sectional area of ​​the secondary particle.

[0010] In order to solve the above problems, in another aspect of the present invention, there is provided a positive electrode including the positive electrode active material according to the present invention.

[0011] In order to solve the above problems, in yet another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode according to the present invention. [Effects of the Invention]

[0012] The positive electrode active material for a lithium secondary battery according to the present invention includes a lithium-nickel-based transition metal oxide in which the shape of primary particles within secondary particles is optimized, thereby reducing particle cracking due to rolling during electrode production, reducing the rate of cracking in active material particles during charge / discharge processes, reducing the amount of fine powder generated, and providing excellent durability.

[0013] In addition, the positive electrode active material for a lithium secondary battery according to the present invention minimizes particle cracking and crack generation, thereby reducing side reactions on the electrode surface and suppressing deterioration, and can provide excellent high-temperature life characteristics and high-temperature output characteristics. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a scanning electron microscope image of a cross section of a positive electrode active material particle prepared in Example 1 according to the present invention. [Figure 2] 1 is a scanning electron microscope image of a cross section of a positive electrode active material particle prepared in Comparative Example 1. [Figure 3] 1 is a scanning electron microscope image of a cross section of a positive electrode active material particle prepared according to Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0016] In this specification, the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0017] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of several tens to several hundreds of primary particles. More specifically, secondary particles are agglomerations of 50 or more primary particles.

[0018] In the present invention, "D 50 " means the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder. 50 can be measured using a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000). Ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and a volume cumulative particle size distribution graph is obtained. The particle size can be measured by determining the particle size corresponding to 50% of the volume cumulative amount.

[0019] The present invention will now be described in more detail.

[0020] positive electrode active material The positive electrode active material according to the present invention includes a lithium nickel-based transition metal oxide in the form of secondary particles, which are aggregates of primary particles, and is characterized in that, with respect to a cross section of the secondary particles at a point 40% to 60% of the diameter thereof, a) the number ratio of primary particles having an aspect ratio of 1.6 or more within the cross section is 0.81 or more, and b) the K value calculated by the following Equation 1 satisfies 12 to 40:

[0021] [Formula 1] K=R AP ×N P / A S where R AP is the average aspect ratio of the primary particles, and N P is the number of primary particles, and A S is the cross-sectional area of ​​the secondary particle.

[0022] According to one embodiment of the present invention, the lithium nickel-based transition metal oxide contained in the positive electrode active material satisfies the above conditions a) and b) on a cross section based on a point at 40% to 60% of the diameter of the secondary particle.

[0023] In this specification, the characteristics obtained from the cross section of the lithium nickel-based transition metal oxide are values ​​obtained by photographing the cross section of an oxide particle cut by ion milling with a field emission scanning electron microscope and analyzing it with an image diffraction program.

[0024] Condition a) means that the ratio of the number of primary particles having an aspect ratio of 1.6 or more to the total number of primary particles on the cross section of the secondary particle is 0.81 or more. That is, 81% or more of the primary particles have an aspect ratio of 1.6 or more, which may mean that a high ratio of thin and elongated primary particles is preferred. Preferably, the ratio is 0.82 or more, 0.83 or more, 0.84 or more, or 0.85 or more.

[0025] Furthermore, the condition b) means that the K value represented by the formula 1 is in the range of 12 to 40, and preferably, the K value may be 15 or more, 17 or more, or 20 or more, and 35 or less, 32 or less, or 28 or less. The K value is the ratio of the product of the aspect ratio and number of primary particles to the cross-sectional area of ​​the secondary particles, and the lower limit of the K value may mean that, when the aspect ratio of the primary particles relative to the area is the same, it is more preferable to have a larger number of primary particles, and when the number is the same, it is preferable to have a larger aspect ratio. The upper limit may mean that the aspect ratio and number relative to the area must be at an appropriate level, and if the appropriate level is exceeded, particle splitting and cracking may occur.

[0026] On the other hand, a positive electrode active material in the form of secondary particles is formed by agglomeration of primary particles, and its performance can be determined by the arrangement of the primary particles and the crystal orientation of the primary particles. The arrangement of the primary particles can have a greater effect than the crystal orientation of the primary particles. The grain boundaries between primary particles are areas where lithium ions and electrons move at high speeds. The greater the number of primary particles and the greater the number of grain boundaries, the better the performance. However, these areas are also prone to cracking and are most likely to undergo side reactions with the electrolyte. Therefore, the performance of the positive electrode active material, i.e., the performance of a lithium secondary battery, can be determined by the arrangement of the primary particles.

[0027] Specifically, the primary particles preferably have a large aspect ratio, and as mentioned above, if the number of primary particles within the cross-sectional area of ​​the secondary particles is large, the number of grain boundaries increases, which can improve the mobility of lithium ions and electrons, but conversely, it has the disadvantage of increasing the possibility of crack generation and side reactions. Therefore, taking these characteristics into consideration, the inventors have solved the above-mentioned problem by defining the ratio of the number of primary particles with a certain aspect ratio or more present on the cross-section of the secondary particle and the ratio of the product of the aspect ratio and the number of primary particles to the cross-sectional area of ​​the secondary particle.

[0028] According to one embodiment of the present invention, the lithium nickel-based transition metal oxide has a diameter of 40% to 60% of the secondary particle on a cross section based on the diameter of the secondary particle. 50 The minor axis of the primary particle (D S ) is 0.025 or less.

[0029] D of the secondary particles 50 The minor axis of the primary particle (D S ) ratio (D S / D 50 When the D of the secondary particles is 0.025 or less, the primary particles can have a thin shape, the size can be at an appropriate level, and the number of primary particles in the cross section of the secondary particles can be at an appropriate level. 50 The ratio of the minor axis of the primary particles to the minor axis of the primary particles is preferably 0.023 or less, and can be 0.020 or less. The lower limit can be controlled by the K value, but is preferably 0.010 or more, 0.012 or more, or 0.013 or more.

[0030] In addition, the lithium nickel transition metal oxide has a D 50 The major diameter of the primary particle (D L ) ratio (D L / D 50 ) can further satisfy the condition that the ratio is 0.035 to 0.075. This may mean that the primary particles preferably have an elongated shape, and within this range, primary particles having such a shape and present in an appropriate number can be present. Therefore, preferably, the ratio can be 0.035 or more, 0.038 or more, 0.040 or more, 0.045 or more, 0.050 or more, or 0.055 or more, and can be 0.070 or less, 0.065 or less, or 0.063 or less.

[0031] According to one embodiment of the present invention, the average aspect ratio of the primary particles within the secondary particles may be 2.0 to 3.5. While the ratio of the number of primary particles having an aspect ratio of 1.6 or greater to the total number of primary particles must be 0.81 or greater, if the overall average value is in the range of 2.0 to 3.5, this can help optimize the shape of the primary particles, thereby effectively achieving the technical goal of improving durability. The average aspect ratio may be 2.1 or greater, 2.2 or greater, 2.3 or greater, or 2.4 or greater, and 3.3 or less, 3.2 or less, or 3.0 or less.

[0032] Meanwhile, according to one embodiment of the present invention, the lithium nickel-based transition metal oxide has a crystal strain of 670×10 -6 The degree of crystal deformation of the secondary particles indicates the degree of deformation of the crystal lattice, and a large degree of deformation of the crystal lattice indicates low structural stability. If the above range is not satisfied, the structure may easily collapse during electrode rolling or cycling, causing electrode deterioration, resulting in poor high-temperature life and output characteristics. In addition, a positive electrode containing such a positive electrode active material has problems such as initial efficiency falling below a certain range, rate performance differences with the negative electrode, and lithium plating, in which lithium is deposited on the surface of the negative electrode, resulting in reduced energy density. Therefore, the degree of crystal deformation is 660×10 -6 Below, 655 x 10 -6 Below, 650 x 10 -6 or less, or 645 x 10 -6 It is preferable that:

[0033] According to one embodiment of the present invention, the lithium nickel-based transition metal oxide is D 50 The D of the secondary particles may be 7.0 μm to 20.0 μm. Preferably, the D may be 8.0 μm or more, 9.0 μm or more, 9.5 μm or more, or 10.0 μm or more, and may be 19.0 μm or less, 18.0 μm or less, 16.0 μm or less, 15.0 μm or less, or 14.0 μm or less. 50When the above range is satisfied, the life characteristics can be improved, the lithium mobility is excellent, and the resistance characteristics are improved, so that the output can be improved.

[0034] On the other hand, the positive electrode active material according to the present invention can contain a lithium nickel-based transition metal oxide, and specifically, can contain a lithium nickel-based transition metal oxide having a composition as shown in the following Chemical Formula 1.

[0035] [Chemical Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e In the above Chemical Formula 1, M 1 contains one or more selected from Mn and Al, and M 2 contains one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X contains one or more selected from the group consisting of N, P, S, F, and Cl, and 0 ≦ x ≦ 0.5, 0.6 ≦ a < 1.0, 0 < b ≦ 0.4, 0 < c ≦ 0.4, 0 ≦ d ≦ 0.05, and 0 ≦ e ≦ 0.05.

[0036] In the above Chemical Formula 1, M 1 contains Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, and M 2 contains one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably can contain Zr, Y, or a combination thereof. The M 2 element is not necessarily contained, but when contained in an appropriate amount, it can play a role in promoting the growth of particles during firing or improving the stability of the crystal structure. Further, the above X is an anion substituted at the oxygen site and can contain N, P, S, F, or Cl.

[0037] The 1+x represents the molar ratio of lithium in the lithium nickel-based transition metal oxide, and may be 0≦x≦0.50, 0≦x≦0.20, 0≦x≦0.15, or 0≦x≦0.10.

[0038] The a represents the molar ratio of nickel to all metals other than lithium in the lithium nickel-based transition metal oxide, and may be 0.60≦a<1.00, 0.65≦a<1.00, 0.70≦a≦0.99, 0.75≦a≦0.99, 0.80≦a≦0.99, 0.82≦a≦0.99, 0.84≦a≦0.99, or 0.86≦a≦0.99.

[0039] The b represents the molar ratio of cobalt to all metals other than lithium in the lithium nickel-based transition metal oxide, and is 0 <b≦0.40、0<b≦0.30、0.01≦b≦0.25、0.01≦b≦0.20、または0.01≦b≦0.15であることができる。

[0040] The c is M among all metals other than lithium in the lithium nickel-based transition metal oxide. 1 indicates the molar ratio of 0 <c≦0.40、0<c≦0.30、0.01≦c≦0.25、0.01≦c≦0.20、または0.01≦c≦0.15であることができる。

[0041] The d is M among all metals other than lithium in the lithium nickel-based transition metal oxide. 2 It represents the molar ratio of the elements and can be 0≦d≦0.05, 0≦d≦0.02, or 0≦d≦0.01.

[0042] The e represents the molar ratio of the X element to all nonmetals other than oxygen in the lithium nickel-based transition metal oxide, and may be 0≦e≦0.05, 0≦e≦0.02, or 0≦e≦0.01.

[0043] Method for producing positive electrode active material Next, a method for producing the positive electrode active material powder of the present invention will be described.

[0044] The method for producing a positive electrode active material powder according to the present invention comprises the steps of: (S1) preparing a positive electrode active material powder containing nickel (Ni), cobalt (Co), and M; 1 (S2) mixing the positive electrode active material precursor and the lithium source material, and heat-treating the mixture to produce a positive electrode active material powder.

[0045] The produced positive electrode active material contains a lithium nickel-based transition metal oxide in the form of secondary particles formed by agglomerations of tens to hundreds of primary particles.

[0046] Each step of the method for producing the positive electrode active material powder will be specifically described below.

[0047] First, nickel (Ni), cobalt (Co) and M 1 For example, the transition metal-containing solution may contain a nickel-containing source material, a cobalt-containing source material, a M 1 The raw material may be contained, and the M 1 The containing source material can be a manganese-containing source material and / or an aluminum-containing source material.

[0048] Next, an ammonium cation-containing complex-forming agent and a basic aqueous solution are added to the transition metal solution, and a coprecipitation reaction is carried out to produce a positive electrode active material precursor.

[0049] The nickel-containing source material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a fatty acid nickel salt, a nickel halide, or a combination thereof.

[0050] The cobalt-containing source material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0051] The manganese-containing source material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, the manganese-containing source material may be, but is not limited to, manganese oxides such as MnO, MnO, MnO, etc.; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0052] The aluminum-containing source material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halide, or combinations thereof.

[0053] The transition metal-containing solution contains a nickel-containing source material, a cobalt-containing source material, and M 1 The nickel-containing raw material is added to a solvent, specifically, a mixed solvent of water or an organic solvent (e.g., alcohol) that can be uniformly mixed with water, or the nickel-containing raw material is added to an aqueous solution of the cobalt-containing raw material and the cobalt-containing raw material. 1 It can be produced by mixing the raw materials involved.

[0054] The ammonium cation-containing complexing agent may be, for example, but not limited to, NHOH, (NH)SO, NHNO, NHCl, CHCOONH, (NH)CO, or a combination thereof. Meanwhile, the ammonium cation-containing complexing agent may be used in the form of an aqueous solution, in which the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0055] The basic compound may be a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH), a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0056] The basic compound is added to adjust the pH of the reaction solution, and can be added in an amount that makes the pH of the metal solution 8 to 12.

[0057] The co-precipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon at a temperature range of 35°C to 80°C.

[0058] This allows nickel, cobalt and M 1 A positive electrode active material precursor containing the cations can be produced.

[0059] By the above process, nickel-cobalt-M 1 The hydroxide positive electrode active material precursor particles are generated and precipitated in the reaction solution. 1By adjusting the concentrations of the raw materials contained, a positive electrode active material precursor can be produced in which the nickel (Ni) content is 60 mol% or more, 65 mol% or more, 70 mol% or more, 75 mol% or more, preferably 80 mol% or more, and more preferably 82 mol% or more, based on the total metal content. The precipitated positive electrode active material precursor particles can be separated and dried by a conventional method to produce the positive electrode active material precursor.

[0060] The temperature, time, amounts and order of raw materials added, additives used, and pH of the co-precipitation reaction can be appropriately controlled to prepare a cathode active material according to an embodiment of the present invention, and the morphology and arrangement of primary particles within secondary particles can be formed as desired.

[0061] Next, the positive electrode active material precursor and the lithium raw material are mixed and heat-treated.

[0062] The lithium source material may be, but is not limited to, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, as long as it is soluble in water. Specifically, the lithium source material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, or a mixture of two or more of these.

[0063] The positive electrode active material precursor and the lithium source material may be mixed in a molar ratio of 1:1 to 1:1.1, for example, about 1:1, about 1:1.02, about 1:1.05, about 1:1.07, or about 1:1.10, but are not limited thereto.

[0064] In the case of a high-nickel (High-Ni) NCM-based lithium transition metal composite oxide having a nickel (Ni) content of 60 mol % or more, the heat treatment can be carried out in a temperature range of 750°C to 1000°C. For example, the heat treatment can be carried out preferably in a temperature range of 800°C to 925°C, and more preferably in a temperature range of 850°C to 910°C.

[0065] As a result, the prepared positive electrode active material can reduce particle cracking and strain in the crystalline structure during the rolling process and during charging and discharging of a lithium secondary battery including the same, thereby improving initial resistance characteristics.

[0066] The heat treatment can be carried out in air or an oxygen atmosphere for, for example, 4 to 12 hours. Specifically, the heat treatment can be carried out for, for example, 4 hours or more, 6 hours or more, 8 hours or more, or 10 hours or more, or 12 hours or less, 10 hours or less, 8 hours or less, or 6 hours or less.

[0067] The calcination process can be divided into a primary calcination and a secondary calcination, and the temperature can be appropriately controlled within the above-mentioned range depending on the nickel content, and the calcination time can also be appropriately adjusted depending on the shape and structure of the cathode active material to be produced. By controlling the calcination process conditions in this way, it is possible to produce a cathode active material according to one embodiment of the present invention.

[0068] On the other hand, M 2 When preparing a lithium nickel-based transition metal oxide containing a metal, M 2 A metal-containing raw material can be further mixed. 2 Metal-containing raw materials are 2 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0069] Meanwhile, when a coating layer is to be formed on the surface of the lithium-nickel-based transition metal oxide, the heat treatment may be followed by a further step of mixing the lithium-nickel-based transition metal oxide produced by the heat treatment with a coating raw material, followed by further heat treatment. Here, the mixing may be performed as a solid-phase or liquid-phase mixture, and the heat treatment may be performed at an appropriate temperature depending on the coating raw material. For example, the heat treatment in the coating process may be performed at a temperature ranging from 200°C to 700°C or from 300°C to 600°C, but is not limited thereto.

[0070] positive electrode The positive electrode according to the present invention includes the positive electrode active material powder according to the present invention. Specifically, the positive electrode includes 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 includes the positive electrode active material powder according to the present invention. Since the positive electrode active material powder has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0071] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0072] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material powder, as required.

[0073] Here, the positive electrode active material powder may be contained in a content of 80 to 99 wt %, more specifically, 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and when contained in this content range, excellent capacity characteristics can be exhibited.

[0074] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the battery and has electronic conductivity. 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 tubes, such as carbon nanotubes; 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 can be used alone or in combination. The conductive material can be included in an amount of 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0075] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, 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), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0076] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material powder. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material powder and, optionally, a binder, a conductive material, and a dispersant in a solvent to form a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0077] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for the production of a positive electrode, taking into consideration the coating thickness of the slurry and production yield.

[0078] Alternatively, the positive electrode can be produced by casting the positive electrode slurry composition on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0079] Electrochemical elements (lithium secondary batteries) Next, an electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the above-described positive electrode of the present invention, and the electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0080] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0081] The lithium secondary battery may 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.

[0082] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0083] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the current collector may have fine irregularities on its surface to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0084] The negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

[0085] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof 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. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0086] The negative electrode active material may be contained in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0087] The binder is a component that helps bind the conductive material, active material, and current collector together, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, 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.

[0088] The conductive material 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 does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and 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 and metal fiber; carbon fluoride; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0089] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition, which is 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 and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0090] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitation. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure 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, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0091] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0092] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0093] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and more preferred are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate).

[0094] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0095] 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 phosphite, triethyl alcohol amine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Here, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0096] [Example] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0097] Example 1 A 20L coprecipitation reactor was charged with 4 L of distilled water and maintained at 50°C. A 3.2 mol / L transition metal solution (NiSO4, CoSO4, and MnSO4 mixed at a nickel:cobalt:manganese molar ratio of 0.83:0.11:0.06) was added at 300 mL / hr, followed by 28 wt% aqueous ammonia at 42 mL / hr. The impeller stirring speed was set to 400 rpm, and a 40 wt% sodium hydroxide solution was added to maintain the pH at 9.3. The coprecipitation reaction was then carried out for 10 hours to form precursor particles. The precursor particles were separated, washed, and then dried in an oven at 130°C to produce the precursor (tap density: 1.8 g / cc).

[0098] Ni synthesized by coprecipitation reaction 0.83 Co 0.11 Mn 0.06The (OH)2 precursor was mixed with LiOH so that the Li / Me(Ni+Co+Mn) molar ratio was 1.05, and then heat-treated at 870°C for 10 hours in an oxygen atmosphere to obtain LiNi 0.83 Co 0.11 Mn 0.06 A positive electrode active material having an O2 composition was produced.

[0099] Examples 2 to 4 and Comparative Examples 1 to 4 A positive electrode active material having particle size characteristics as shown in Table 1 below was prepared.

[0100] Experimental Example 1: Measurement of the characteristics of the positive electrode active material 1) Cross-sectional particle characteristics of the positive electrode active material For each of the positive electrode active materials prepared in the examples and comparative examples, a particle cross section at approximately 50% of the diameter was measured by Ar ion milling using a Dual Beam-FIB (Helios 450F1 / FEI) analyzer in SIM (Scanning ion microscope) / ETD (Everhart-Thornley SE detector) mode under the conditions of an acceleration voltage of 30 kV, a current of 24 pA, a working distance of 13 mm, and a magnification of 12,000 to 15,000 times. Then, the cross-sectional area (A) of the secondary particles was calculated using an image diffraction program. S ) Major diameter of primary particles (D 1 max ) and minor axis (D 1 min ) and calculate the average number (N p ) to determine the aspect ratio (R AP ) and their average were analyzed, and the K value was calculated by the following formula 1 and shown in Table 1 below. For data reliability, the above characteristics were analyzed for 50 particles, and the average value was used. Representative cross-sectional photographs of Example 1 and Comparative Examples 1 and 2 are shown in Figures 1 to 3.

[0101] [Formula 1] K=R AP ×N P / A S where R AP is the average aspect ratio of the primary particles, and N Pis the number of primary particles, and A S is the cross-sectional area of ​​the secondary particle.

[0102] 2) Particle size characteristics of positive electrode active material 0.005 g of each of the positive electrode active materials prepared in the examples and comparative examples was dispersed in a dispersion medium HO, and then introduced into a commercially available laser diffraction particle size analyzer (PSD, manufactured by Malvern, Mastersizer 3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph for each positive electrode active material. The D of the secondary particles was calculated using the graph. 50 The results are shown in Table 1 below.

[0103] 3) Crystal deformation degreeThe XRD data obtained by X-ray diffraction analysis of the positive electrode active material powder was analyzed by Rietveld refinement. The X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T position sensitive detector. The sample was placed in the groove of a general powder holder, and a glass slide was used to even out the sample surface and ensure the sample height matched the edge of the holder. The X-ray diffraction analysis was performed under conditions of FDS 0.5°, 2θ = 15° to 90°, step size = 0.02°, and total scan time = approximately 20 minutes. Rietveld refinement was performed on the measured data, taking into account the charge at each site (metal at the transition metal site is +3, Ni at the Li site is +2) and cation mixing. Specifically, for the analysis of crystal deformation, instrumental broadening was performed using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and all peaks in the measurement range were used for fitting. Peak shape was fitted using only the Lorenzian contribution in First Principle (FP) of the peak types available in TOPAS.

[0104] 4) Fine powder generation rate (volume %) For the examples and comparative examples, the fine powder increase rate was calculated by applying a pressure of 6 tons to the positive electrode active material using a Carver Pellet Press, and then calculating the area of ​​1 μm or less using the value obtained from the particle size distribution (PSD).

[0105] [Table 1]

[0106] Referring to Table 1, it can be seen that, compared to Examples 1 to 4, Comparative Examples 1 to 4 have K values ​​that do not satisfy the range of 12 to 40, and also have a lower ratio of the number of primary particles having an aspect ratio of 1.6 or more.

[0107] <Lithium secondary battery manufacturing> The positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4, respectively, carbon black conductive material, and PVDF binder were mixed in a weight ratio of 95:2:3 in N-methylpyrrolidone to prepare positive electrode slurries. The positive electrode slurries were applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare positive electrodes.

[0108] Graphite as an anode active material, super C as a conductive material, and SBR / CMC as a binder were mixed in a weight ratio of 95.6:1.0:3.4 to prepare an anode slurry, which was then applied to one side of a copper current collector, dried at 130°C, and rolled to prepare an anode.

[0109] An electrode assembly was fabricated by interposing a separator between the positive and negative electrodes, and then placed inside a battery case. An electrolyte solution was then injected into the case to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1M in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 1:2:1, and adding 2 wt% vinylene carbonate (VC).

[0110] Experimental Example 2: Measurement of the performance of the positive electrode active material 1) High temperature performance: The lithium secondary battery fabricated as described above was charged and discharged for 200 cycles at a temperature of 45°C under the condition of 0.33C / 0.33C, and then the capacity retention rate (%) of the mono-cell was measured based on the charge-discharge efficiency. When evaluating the lifespan using the above method and conditions, the resistance was calculated using the voltage and current during discharge ((V0-V1) / I, where V0 is the discharge start voltage, V1 is the voltage after 10 seconds of discharge, and I is the applied current). The resistance increase rate after cycling relative to the initial resistance was calculated, and the results are shown in Table 3 below.

[0111] 2) Difference in crack area before and after deterioration (%) The cross sections of the positive electrode were analyzed before and after cycling. A reference region was set at 20 μm in the depth direction and 200 μm in the plane direction from the surface of the active material layer. This region was divided into crack and particle regions, and their areas were calculated. The crack regions were areas where the particles were cracked, and the particle regions were areas where the particles were not cracked. The cross sections of the electrode were cut by ion milling and photographed with a field emission scanning electron microscope (FESEM, JEOL JSM-IT800SHL) under conditions of an accelerating voltage of 5 kV, an emission current of 10 μA, a working distance of 10 mm, and a detector BED.

[0112] The crack and particle areas of the FESEM cross-sectional image were quantified using an image diffraction program based on digital transformation. To improve accuracy, more than 50 reference areas were specified for the positive electrode cross-section, and the crack area of ​​each area was determined and the average value was calculated.

[0113] [Table 2]

[0114] Referring to Table 3, it can be seen that when the primary particle shape is optimized, as in Examples 1 to 4 according to one embodiment of the present invention, the electrode exhibits less deterioration, a high capacity retention rate at high temperatures, and excellent lifespan characteristics, as well as a low resistance increase rate and excellent output characteristics. However, as in Comparative Example 1, the primary particle aspect ratio is small and the number of secondary particles relative to the area of ​​the primary particles is low compared to the primary examples, which indicates a high rate of cracking and easy electrode deterioration, resulting in poor performance. Furthermore, in Comparative Example 2, although the aspect ratio is similar to that of the examples, both the major and minor axes of the primary particles are larger than those of the examples, and the number of secondary particles relative to the area of ​​the secondary particles is too small to satisfy the K value range. This indicates that the primary particle size itself is large, and such a shape results in a large increase in resistance and poor output characteristics. In addition, Comparative Example 3 has a shape that is the exact opposite of Comparative Example 2. Although the aspect ratio is large, the primary particles are very small and the K value cannot be satisfied. This causes a problem of cracks occurring in the active material particles when the electrode is rolled. As a result, although the degree of deterioration before and after cycling was small, the lifespan and output characteristics were very poor, indicating that the degree of particle cracking was significant.

Claims

1. The lithium nickel-based transition metal oxide includes a secondary particle form that is an aggregate of primary particles, A positive electrode active material that satisfies the following conditions a) and b) with respect to a cross section of the secondary particle at a point of 40% to 60% of the diameter: a) the number ratio of primary particles having an aspect ratio of 1.6 or more in the cross section is 0.81 or more; b) The K value calculated by the following formula 1 is 12 or more and 40 or less. [Formula 1] K=R ＡＰ ×N Ｐ / A Ｓ Here, R ＡＰ is the average aspect ratio of the primary particles, and N Ｐ is the number of primary particles, and A Ｓ is the cross-sectional area of ​​the secondary particle (μm ２ ) is a unitless number.

2. D of the secondary particles relative to the minor axis of the primary particles ５０ The positive electrode active material according to claim 1 , wherein the ratio of

3. D of the secondary particles relative to the major axis of the primary particles ５０ The positive electrode active material according to claim 1 , wherein the ratio of

4. 2. The positive electrode active material according to claim 1, wherein the average aspect ratio of the primary particles within the secondary particles is 2.0 to 3.

5.

5. The secondary particles are D ５０ The positive electrode active material according to claim 1 , wherein the average particle diameter is 7 μm or more and 20 μm or less.

6. The degree of crystal deformation of the secondary particles is 670 × 10 －６ The positive electrode active material according to claim 1 , wherein:

7. The degree of crystal deformation of the secondary particles is 645 × 10 －６ The positive electrode active material according to claim 6, wherein:

8. The positive electrode active material of claim 1 , wherein the lithium nickel-based transition metal oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２－ｅ X ｅ In the above Chemical Formula 1, M １ contains one or more selected from Mn and Al, ２ includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X includes one or more elements selected from the group consisting of N, P, S, F, and Cl, and 0≦x≦0.5, 0.6≦a<1, 0<b≦0.4, 0<c≦0.4, 0≦d≦0.05, and 0≦e≦0.

05.

9. The positive electrode active material according to claim 8 , wherein in Chemical Formula 1, 0.75≦a≦0.

99.

10. M １ The positive electrode active material according to claim 8 , wherein is Mn.

11. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 10.

12. A lithium secondary battery comprising the positive electrode according to claim 11.

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