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

Abstract

The present invention relates to a positive electrode active material comprising a lithium transition metal composite oxide in a quasi-single particle form that is a single particle consisting of one nodule and / or an aggregate of 30 or less nodules, the lithium transition metal composite oxide comprising Ni, Co, Mn, and Al, in which a molar ratio of Ni to the total number of moles of metal elements other than lithium is 0.83 or more and less than 1, a ratio of the number of moles of Co to the number of moles of Mn is 0.5 or more and less than 1, and a ratio of the number of moles of Co to the number of moles of Al is 5 to 15.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0187147, filed December 24, 2021, 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, a positive electrode including the same, and a lithium secondary battery, and more particularly to a positive electrode active material in the form of at least one of a single particle and a quasi-single particle, 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 composite 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] Conventional lithium nickel cobalt manganese oxides generally have a spherical secondary particle form, consisting of an agglomeration of tens to hundreds of primary particles. However, lithium nickel cobalt manganese oxides in this secondary particle form, consisting of an agglomeration of many primary particles, are prone to particle cracking, in which the primary particles break off during the rolling process during positive electrode production, and also suffer from internal cracks during charge and discharge. When particle cracking or cracking occurs in the positive electrode active material, the contact area with the electrolyte increases, which increases gas generation and degradation of the active material due to side reactions with the electrolyte, resulting in reduced lifespan.

[0006] Recently, there has been an increasing demand for high-power, high-capacity batteries, such as those for electric vehicles, and as a result, the content of nickel in the positive electrode active material is gradually increasing. When the content of nickel in the positive electrode active material increases, the initial capacity characteristics improve, but as charging and discharging are repeated, the reactivity of nickel decreases. +4 A large amount of ions are generated, causing the structure of the positive electrode active material to collapse, which increases the rate of deterioration of the positive electrode active material, shortening the lifespan characteristics and reducing the safety of the battery. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above problems, and aims to provide a positive electrode active material that can suppress the occurrence of particle breakage and cracks during electrode manufacturing and charge / discharge processes, has a high cobalt content with a low content, and can achieve excellent life characteristics, and a positive electrode and a lithium secondary battery including the same. [Means for solving the problem]

[0008] According to one embodiment, the present invention provides a cathode active material comprising a lithium composite transition metal oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is a composite of 30 or less nodules, wherein the lithium composite transition metal oxide comprises Ni, Co, Mn, and Al, and in the lithium composite transition metal oxide, a molar ratio of Ni to the total number of moles of metal elements other than lithium is 0.83 or more and less than 1, a ratio of the number of moles of Co to the number of moles of Mn (Co / Mn) is 0.5 or more and less than 1, and a ratio of the number of moles of Co to the number of moles of Al (Co / Al) is 5 to 15, preferably 5 to 10. Specifically, in the lithium composite transition metal oxide, the ratio of the number of moles of Co to all the metals other than lithium can be more than 0 and 0.1 or less, preferably 0.01 to 0.1, more preferably 0.03 to 0.1, and even more preferably 0.03 to 0.07; the ratio of the number of moles of Ni to the total number of moles of all the metals other than lithium can be 0.83 or more and less than 1, preferably 0.83 to 0.95 or less, and more preferably 0.83 to 0.90; the ratio of the number of moles of Mn to the total number of moles of all the metals other than lithium can be more than 0 and less than 0.17, preferably 0.01 or more and less than 0.17, and more preferably 0.05 to 0.15; and the ratio of the number of moles of Al to the total number of moles of all the metals other than lithium can be more than 0 and 0.02 or less, preferably 0.001 to 0.02, and more preferably 0.003 to 0.01.

[0009] In the lithium composite transition metal oxide, the sum of the molar ratio of Co and the molar ratio of Al to the total number of moles of all metals other than lithium can be less than 0.1, preferably 0.01 or more and less than 0.1, and more preferably 0.03 to 0.08.

[0010] Specifically, the lithium composite transition metal oxide may be represented by the following [Chemical Formula 1]. [Chemical formula 1] Li 1+x Ni a Co b Mn c Al d M 1 e O2

[0011] In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0≦x≦0.5, 0.83≦a<1, 0 <b≦0.1、0<c<0.17、0<d≦0.02、0≦e≦0.05、b<c、0.5≦b / c<1、5≦b / d≦15である。

[0012] Meanwhile, the lithium transition metal composite oxide according to the present invention may have an average particle size of nodules of 0.5 μm to 3 μm, and the average particle size D 50 The average crystallite diameter can be 2 μm to 6 μm, and the average crystallite diameter can be 150 nm to 300 nm.

[0013] In addition, the positive electrode active material according to the present invention may further include a coating layer formed on the surface of the lithium composite transition metal oxide particles, if necessary, and the coating layer may include one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0014] On the other hand, the positive electrode active material according to the present invention has a BET specific surface area of ​​0.1 to 1 m 2 / g, preferably 0.3 to 1 m 2 / g, more preferably 0.5 to 1 m 2 / g.

[0015] Furthermore, the powder of the positive electrode active material according to the present invention can have a press density of 2 to 4 g / cc, preferably 2.5 to 3.5 g / cc, measured after being pressed under a pressure of 2000 kgf.

[0016] In addition, the powder of the positive electrode active material according to the present invention may be pressed under a pressure of 9 tons, and then the ratio of particles having a particle size of 1 μm or less in the volume cumulative particle size distribution measured may be 1 vol% or less, preferably 0.8 vol% or less, and more preferably 0.5 vol% or less.

[0017] According to another embodiment, the present invention provides a positive electrode including a positive electrode active material layer comprising the positive electrode active material according to the present invention.

[0018] According to yet another embodiment, the present invention provides a lithium secondary battery comprising the positive electrode according to the present invention. [Effects of the Invention]

[0019] The cathode active material according to the present invention is formed in at least one form of single particle or quasi-single particle, which has excellent particle strength, and thus reduces particle breakage or cracking due to rolling during electrode manufacturing. As a result, gas generation due to side reactions with the electrolyte and deterioration of the cathode active material are reduced, thereby achieving excellent life characteristics and high-temperature characteristics.

[0020] Furthermore, the cathode active material according to the present invention contains Al as an essential element, and by adjusting the Co / Al molar ratio and the Co / Mn molar ratio to satisfy specific ranges, cracking in the cathode active material can be minimized despite the relatively small amount of Co contained. When the Co content in a cathode active material is low, the Li ion diffusion resistance increases, which causes uneven lithium insertion and extraction during charge and discharge, resulting in severe strain in the crystal structure and the formation of cracks within the particles. However, when Al is included as an essential element, as in the present invention, even when the Co content is low (e.g., less than 10 mol%), deformation of the crystal structure can be minimized, thereby preventing a decrease in lifespan characteristics due to cracking.

[0021] However, the inventors' extensive research has shown that if the Co / Al molar ratio and the Co / Mn molar ratio deviate from a specific range, the resistance increases and the capacity and life characteristics decrease. Therefore, in the present invention, by including Al as an essential component and controlling the Co / Al molar ratio and the Co / Mn molar ratio within a specific range, it is possible to achieve excellent life characteristics and capacity characteristics. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a graph showing the change in particle size distribution when the positive electrode active material powder of Example 1 is pressed at a pressure of 9 tons. [Figure 2] 10 is a graph showing the change in particle size distribution when the positive electrode active material powder of Comparative Example 4 is pressed at a pressure of 9 tons. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in more detail below.

[0024] 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.

[0025] In the present invention, the term "single particle" refers to a particle consisting of one nodule. The "nodule" may be a single crystal with no grain boundaries, or a polycrystal with no apparent grain boundaries when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope. In addition, in the present invention, the term "quasi-single particle" refers to a complex formed of 30 or fewer nodules.

[0026] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of several tens to several hundreds of primary particles. Specifically, secondary particles are agglomerations of 50 or more primary particles.

[0027] In the present invention, the term "particle" is a concept that includes any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0028] In the present invention, the "average particle size D 50" means the particle size at 50% of the volume cumulative particle size distribution of the lithium composite transition metal oxide powder or the positive electrode active material powder, and when the lithium composite transition metal oxide is a secondary particle, it means the average particle size of the secondary particle, and when the lithium composite transition metal oxide is a combination of a single particle and a quasi-single particle, the average particle size means the average particle size of the particles in the combination. The average particle size D 50 can be measured using a laser diffraction method. For example, after dispersing a lithium composite transition metal oxide powder or a positive electrode active material powder in a dispersion medium, the dispersion is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. A volume cumulative particle size distribution graph is obtained, and the particle diameter corresponding to 50% of the volume cumulative amount is determined.

[0029] In the present invention, the term "crystallite" refers to a particle unit having substantially the same crystal orientation, which can be identified by EBSD (Electron Backscatter Diffraction) analysis. Specifically, the term "crystallite" refers to the smallest particle unit that is represented by the same color in an IPF map obtained by EBSD analysis of a cross section of a cathode active material cut by ion milling.

[0030] Meanwhile, in the present invention, the "average crystallite size" can be quantitatively analyzed using X-ray diffraction analysis (XRD) using Cu-Kα X-rays. Specifically, the particles to be measured are placed in a holder, and the particles are irradiated with X-rays. The diffraction grating output is analyzed to quantitatively analyze the average crystal grain size. Sampling was performed by placing a powder sample of the particles to be measured in the central groove of a general powder holder, smoothing the surface using a glass slide, and aligning the sample height with the holder's periphery. X-ray diffraction analysis was then performed using a Bruker D8 Endeavor (light source: Cu Kα, λ = 1.54 Å) equipped with a LynxEye XE-T position-sensitive detector under the following conditions: FDS 0.5°, 2θ = 15° to 90°, step size 0.02°, and a total scan time of approximately 20 minutes. The measured data were subjected to Rieveld refinement, taking into account the charge at each site (metal ions at transition metal sites are +3, Ni ions at Li sites are +2) and cation mixing. When analyzing grain size, instrumental brodding was considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and peaks across the entire measurement range were used for fitting. Peak shapes were fitted using only the Lorenzian contribution as the First Principle (FP) of the peak types available in TOPAS, without considering strain.

[0031] In the present invention, the "press density" was measured using an HPRM-1000. Specifically, 5 g of the positive electrode active material powder was placed in a cylindrical mold, and then the mold containing the positive electrode active material was pressed with a force of 2000 kgf. Next, the height of the pressed mold was measured with Vernier calipers to determine the press density.

[0032] In the present invention, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0033] positive electrode active material The positive electrode active material according to the present invention will be described below.

[0034] The positive electrode active material according to the present invention includes a lithium composite transition metal oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is a composite of 30 or less nodules, the lithium composite transition metal oxide including Ni, Co, Mn, and Al. Here, in the lithium composite transition metal oxide, the ratio of the number of moles of Ni to the total number of moles of all metal elements other than lithium is 0.83 or more and less than 1, the ratio of the number of moles of Co to the number of moles of Mn is 0.5 or more and less than 1, and the ratio of the number of moles of Co to the number of moles of Al is 5 to 15.

[0035] The positive electrode active material according to the present invention includes a lithium composite transition metal oxide in the form of a single particle consisting of one nodule, a quasi-single particle which is a composite of 30 or less, preferably 2 to 20, and more preferably 2 to 10 nodules, or a mixture thereof.

[0036] Such a lithium composite transition metal oxide in the form of a single particle and / or a quasi-single particle has higher particle strength than existing lithium composite transition metal oxides in the form of a secondary particle in which tens to hundreds of primary particles are aggregated, and therefore suffers from fewer particle cracks during rolling.

[0037] Furthermore, in the case of the lithium transition metal composite oxide in the form of a single particle and / or a quasi-single particle according to the present invention, the number of nodules constituting the particle is small, and therefore, there is little change in the volume of the nodules due to expansion and contraction during charge and discharge, and therefore, the occurrence of cracks inside the particle is significantly reduced.

[0038] On the other hand, the lithium composite transition metal oxide may contain Ni, Co, Mn, and Al, and the ratio of the number of moles of Ni to the total number of moles of metal elements other than lithium may be 0.83 or more and less than 1, preferably 0.83 to 0.95, and more preferably 0.83 to 0.90, the ratio of the number of moles of Co to the number of moles of Mn (Co / Mn molar ratio) may be 0.5 or more and less than 1, preferably 0.5 to 0.8, and the ratio of the number of moles of Co to the number of moles of Al (Co / Al molar ratio) may be 5 to 15, and preferably 5 to 10. When the composition of the lithium composite transition metal oxide satisfies these conditions, even when the lithium composite transition metal oxide contains a small number of moles of Co, for example, less than 10 mol%, deformation of the crystal structure (strain) and the occurrence of cracks are effectively suppressed, thereby achieving excellent life characteristics and excellent capacity and resistance characteristics.

[0039] Lithium composite transition metal oxide particles in the form of single particles and / or quasi-single particles contain nodules that are relatively larger in size than the primary particles of conventional lithium composite transition metal oxide particles in the form of secondary particles, and have fewer interfaces between the nodules that serve as diffusion paths for lithium ions, resulting in reduced lithium mobility. Furthermore, because they are manufactured at relatively high sintering temperatures, a rocksalt phase forms on the particle surfaces, resulting in high surface resistance. Therefore, lithium composite transition metal oxide particles in the form of single particles and / or quasi-single particles have high lithium diffusion resistance, and lithium ions move unevenly during charge and discharge, easily causing deformation of the crystal structure and resulting particle cracks, which can lead to a rapid decrease in life characteristics.

[0040] In addition, manganese (Mn) is generally unfavorable for the formation of a layered structure and inhibits grain growth due to its high oxidation state, while cobalt (Co) is an element favorable for the formation of a layered structure and promotes grain growth. Therefore, when the manganese (Mn) content is high, crystal grain growth is difficult during sintering of the lithium composite transition metal oxide, making it difficult to form single particles and increasing lithium ion diffusion resistance. On the other hand, when the cobalt (Co) content is high, crystal grain growth is promoted, making it easier to form single particles, smoothly forming a layered structure, reducing lithium ion diffusion resistance, and suppressing crystal structure deformation and particle cracking, thereby improving life characteristics.

[0041] For this reason, conventionally, single particle or pseudo-single particle cathode active materials typically contain a higher amount of cobalt (Co) than manganese (Mn). However, because cobalt is expensive and its supply is unstable, positive electrode active materials with a high cobalt content have high manufacturing costs and are less price competitive, making them difficult to apply to large-capacity batteries such as those for electric vehicles.

[0042] Therefore, the present inventors have conducted extensive research to develop a positive electrode active material in a single particle and / or quasi-single particle form that contains a small amount of Co and has excellent life characteristics and resistance characteristics. As a result, they have found that such an object can be achieved when a material contains Ni, Co, and Mn as transition metal elements, as well as a small amount of Al as an essential element, and when the molar ratios of Co / Mn and Co / Al satisfy specific ranges, thereby completing the present invention.

[0043] Specifically, the ratio of the number of moles of Ni to the total number of moles of all metals other than lithium in the lithium composite transition metal oxide can be 0.83 or more and less than 1, preferably 0.83 to 0.95, and more preferably 0.83 to 0.90. When the molar ratio of Ni in the lithium composite transition metal oxide satisfies the above range, a high energy density can be achieved.

[0044] Furthermore, the lithium composite transition metal oxide may have a ratio of the number of moles of Co to the number of moles of Mn (Co / Mn molar ratio) of 0.5 or more and less than 1, preferably 0.5 to 0.8. If the Co / Mn molar ratio in the lithium composite transition metal oxide is less than 0.5, particle growth may occur non-uniformly, and if the Co / Mn molar ratio is 1 or more, the increased Co content will not be effective in reducing costs.

[0045] Furthermore, the lithium transition metal composite oxide may have a ratio of the number of moles of Co to the number of moles of Al (Co / Al molar ratio) of 5 to 15, preferably 5 to 10. If the Co / Al molar ratio is less than 5, the resistance increases, the capacity decreases, and the cycle characteristics also deteriorate. If the Co / Al molar ratio exceeds 15, the effect of suppressing crack generation is not sufficient, and the effect of improving life characteristics decreases.

[0046] Meanwhile, in the lithium composite transition metal oxide, the molar ratio of Co to the total number of moles of all metals other than lithium can be greater than 0 and less than 0.1, preferably 0.01 or more and less than 0.1, more preferably 0.03 to 0.09, and even more preferably 0.03 to 0.07, the molar ratio of Mn can be greater than 0 and less than 0.17, 0.01 or more and less than 0.17, and preferably 0.05 to 0.15, and the molar ratio of Al can be greater than 0 and 0.02 or less, preferably 0.001 to 0.02, and more preferably 0.003 to 0.01. When the molar ratios of Ni, Co, Mn, and Al in the lithium composite transition metal oxide satisfy the above ranges, the high-temperature life characteristics, rate characteristics, and resistance characteristics are particularly excellent.

[0047] Meanwhile, in the lithium composite transition metal oxide, the sum of the molar ratio of Co and the molar ratio of Al relative to all metals other than lithium can be less than 0.12, preferably 0.01 or more and less than 0.12, and more preferably 0.03 to 0.08. If the sum of the molar ratio of Co and the molar ratio of Al exceeds 0.12, the price competitiveness may be poor and the life characteristics and resistance characteristics may be degraded.

[0048] More specifically, the lithium composite transition metal oxide may be represented by the following [Chemical Formula 1].

[0049] [Chemical formula 1] Li 1+x Ni a Co b Mn c Al d M 1 e O2

[0050] In the above Chemical Formula 1, M 1 is at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, preferably at least one selected from the group consisting of Zr, Y, Mg and Ti, more preferably Zr, Y or a combination thereof. 1 Although the elements are not essential, when contained in an appropriate amount, they can promote grain growth during firing or improve the stability of the crystal structure.

[0051] The 1+x represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be 0≦x≦0.5, 0≦x≦0.3, or 0≦x≦0.2.

[0052] The a represents the ratio of the number of moles of nickel to the total number of moles of all metals other than lithium in the lithium composite transition metal oxide, and may be 0.83≦a<1, 0.83≦a≦0.95, or 0.83≦a≦0.90.

[0053] The b represents the ratio of the number of moles of cobalt to the total number of moles of all metals other than lithium in the lithium composite transition metal oxide, and is 0 <b≦0.1、0.01≦b<0.1、または0.03≦b≦0.09であることができる。

[0054] The c represents the ratio of the number of moles of manganese to the total number of moles of all metals other than lithium in the lithium composite transition metal oxide, and is 0 <c<0.17、0.01≦c<0.17、または0.05≦c≦0.15であることができる。

[0055] On the other hand, in the lithium composite transition metal oxide, the molar ratio c of manganese is greater than the molar ratio b of cobalt. <cである。

[0056] Furthermore, the ratio of the number of moles of cobalt to the number of moles of manganese, i.e., b / c, is 0.5≦b / c<1, or 0.5≦b / c≦0.8.

[0057] The d represents the molar ratio of Al to all metals other than lithium in the lithium composite transition metal oxide, and is 0 <d≦0.02、0.001≦d≦0.02、または0.003≦d≦0.01であることができる。

[0058] Also, the ratio of the number of moles of cobalt to the number of moles of aluminum, ie, b / d, can be 5≦b / d≦15 or 5≦b / d≦10.

[0059] The e is M among all metals other than lithium in the lithium composite transition metal oxide. 1 It denotes the molar ratio of the elements and can be 0≦e≦0.05, 0≦e≦0.02 or 0≦e≦0.01.

[0060] Meanwhile, the lithium composite transition metal oxide according to the present invention may have an average particle size of nodules of 0.5 μm to 3 μm, preferably 0.8 μm to 2.5 μm, and more preferably 0.8 μm to 1.5 μm. When the average particle size of the nodules satisfies this range, a positive electrode active material in the form of a single particle and / or a quasi-single particle with excellent electrochemical properties can be formed. If the average particle size of the nodules is too small, the number of agglomerates of the nodules forming the lithium composite transition metal oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the nodules is too large, the lithium diffusion path within the nodules becomes longer, increasing resistance and potentially reducing output characteristics.

[0061] The lithium composite transition metal oxide has an average particle size D 50 The D of the lithium composite transition metal oxide can be 2 μm to 6 μm, preferably 2 μm to 5 μm, and more preferably 3 μm to 5 μm. 50 If the value is too small, the specific surface area of ​​the active material increases, which requires an increase in the amount of conductive material, resulting in a decrease in electrode density, a decrease in the solid content of the electrode slurry, which can reduce productivity during electrode production, a decrease in electrolyte impregnation, which can reduce electrochemical properties, and D 50 If it is too large, the resistance increases and the output characteristics deteriorate.

[0062] Additionally, the lithium composite transition metal oxide may have an average crystallite diameter of 150 nm to 300 nm, 200 nm to 280 nm, or 230 nm to 280 nm. When the average crystallite diameter is within this range, the formation of a rock salt phase during the preparation of the lithium composite transition metal oxide is reduced, allowing the preparation of a single-particle and / or quasi-single-particle positive electrode active material with excellent resistance characteristics. Generally, single-particle and / or quasi-single-particle positive electrode active materials are prepared by increasing the sintering temperature to increase the nodule size. However, increasing the nodule size while the crystallite diameter is small can result in the formation of a rock salt phase on the surface of the nodules, resulting in an increase in resistance. However, increasing both the average crystallite diameter and the average particle diameter of the nodules can minimize the formation of the rock salt phase, thereby suppressing the increase in resistance.

[0063] Meanwhile, the positive electrode active material according to the present invention may further include, if necessary, a coating layer containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S on the surface of the lithium composite transition metal oxide particles.

[0064] When a coating layer is present on the surface of the lithium composite transition metal oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby achieving the effect of reducing elution of the transition metal and generation of gas due to side reactions with the electrolyte.

[0065] Preferably, the coating element includes Co. When a coating layer including Co is formed on the surface of the lithium composite transition metal oxide particles, it is possible to obtain the effects of suppressing side reactions with the electrolyte, improving output, and reducing resistance.

[0066] On the other hand, the positive electrode active material according to the present invention has a BET specific surface area of ​​0.1 to 1 m 2 / g, preferably 0.3 to 1 m2 / g, more preferably 0.5 to 1 m 2 If the BET specific surface area of ​​the positive electrode active material is too small, the lithium migration path becomes long, which increases resistance and may reduce discharge capacity, whereas if the BET specific surface area is too large, the amount of conductive material required during electrode production increases, which reduces electrode density, and the solid content of the electrode slurry decreases, which may reduce productivity during electrode production.

[0067] Furthermore, the powder of the positive electrode active material according to the present invention may have a pressed density of 2 to 4 g / cc, preferably 2.5 to 3.5 g / cc, measured after being pressed under a pressure of 2000 kgf. When the pressed density of the positive electrode active material powder satisfies the above range, an electrode with excellent energy density can be produced.

[0068] Furthermore, the cathode active material of the present invention includes a lithium composite transition metal oxide in the form of at least one of a single particle and a quasi-single particle. This results in higher particle strength and less generation of fine powder due to particle cracking after rolling, compared to conventional cathode active materials including lithium composite transition metal oxides in the form of secondary particles consisting of an aggregation of tens to hundreds of primary particles. Specifically, the cathode active material powder of the present invention is pressed under a pressure of 9 tons, and the volume cumulative particle size distribution measured thereafter shows a ratio of particles having a particle size of 1 μm or less of 1 vol% or less, preferably 0.8 vol% or less, and more preferably 0.5 vol% or less. Thus, the cathode active material of the present invention exhibits less particle cracking and fine powder generation even under high pressure, thereby increasing electrode density. Furthermore, when electrodes and batteries are manufactured using the cathode active material of the present invention, gas generation and deterioration of service life due to particle cracking can be minimized.

[0069] The cathode active material of the present invention may be prepared by mixing a cathode active material precursor and a lithium source material and then calcining the mixture.

[0070] Here, the positive electrode active material precursor may be a commercially available positive electrode active material precursor, or may be prepared by a precursor preparation method well known in the art.

[0071] For example, the precursor can be prepared by forming an ammonium cation complex with an aqueous solution of a transition metal and then co-precipitation with a basic compound in a reactor under stirring.

[0072] The transition metal aqueous solution may be prepared by dissolving a transition metal-containing source material in a solvent such as water, for example, by dissolving a nickel-containing source material, a cobalt-containing source material, or a manganese-containing source material in water. If necessary, the transition metal aqueous solution may further include an aluminum-containing source material.

[0073] Meanwhile, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halite, sulfide, or oxide of the transition metal.

[0074] Specifically, the nickel-containing source material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0075] The cobalt-containing source material can be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0076] The manganese-containing source material can be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0077] The aluminum-containing source material may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halide, or a combination thereof. However, in the case of Al, it may be added together with the lithium source material in the calcination step described below, without being added to the transition metal aqueous solution.

[0078] Here, the amount of each transition metal-containing raw material added may be determined taking into consideration the molar ratio of the transition metal in the cathode active material to be finally produced. For example, in the present invention, the transition metal-containing raw materials may be added in an amount such that the ratio of the number of moles of nickel to the total number of moles of all transition metals contained in the aqueous transition metal solution is 0.83 or more, the ratio of the number of moles of cobalt to manganese is 0.5 or more but less than 1, and the ratio of the number of moles of cobalt to aluminum is 5 to 15.

[0079] The ammonium cation complexing agent may include at least one compound selected from the group consisting of NHOH, (NH)SO, NHNO, NHCl, CHCOONH, and (NH)CO, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0080] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0081] As described above, when the aqueous transition metal solution, the ammonium cation complexing agent, and the basic compound are charged into a reactor and stirred, the transition metal in the aqueous transition metal solution is coprecipitated to produce precursor particles in the form of transition metal hydroxide.

[0082] Here, the aqueous transition metal solution, the ammonium cation complex-forming agent, and the basic compound are added in amounts such that the pH of the reaction solution falls within a desired range.

[0083] After the precursor particles are formed by the above method, the cathode active material precursor is separated from the reaction solution to obtain the cathode active material precursor. For example, the reaction solution is filtered to separate the cathode active material precursor from the reaction solution, and the separated cathode active material precursor is then washed with water and dried to obtain the cathode active material precursor. Here, steps such as pulverization and / or classification can be performed as necessary.

[0084] Next, the positive electrode active material precursor and a lithium raw material are mixed and then calcined to produce a lithium composite transition metal oxide. 1 The metal-containing raw materials can be mixed together and fired.

[0085] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, such as Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a mixture thereof.

[0086] Meanwhile, the lithium source material and the cathode active material precursor may be mixed so that the molar ratio of Li:total metals in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1, and more preferably 1:1 to 1.06:1. When the mixing ratio of the lithium source material and the metals in the cathode active material precursor satisfies this range, the layered crystal structure of the cathode active material is well developed, and a cathode active material with excellent capacity characteristics and structural stability can be produced.

[0087] Meanwhile, the calcination is performed at a temperature that allows the formation of monoparticles or quasi-monoparticles. To form monoparticles or quasi-monoparticles, calcination must be performed at a higher temperature than that used in the preparation of conventional lithium composite transition metal oxides in the form of secondary particles. For example, when the precursor composition is the same, calcination must be performed at a temperature that is 30°C to 100°C higher than that used in the preparation of conventional lithium composite transition metal oxides in the form of secondary particles. The calcination temperature for forming monoparticles or quasi-monoparticles may vary depending on the metal composition of the precursor. For example, when a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is to be formed in the form of monoparticles or quasi-monoparticles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies this range, a positive electrode active material having at least one of the monoparticle and quasi-monoparticle forms with excellent electrochemical properties can be produced. If the calcination temperature is less than 790°C, a positive electrode active material in the form of secondary particles is produced, and if the temperature exceeds 950°C, excessive calcination occurs, resulting in an insufficient formation of a layered crystal structure and reduced electrochemical properties.

[0088] The firing may be carried out for 5 to 35 hours in an oxygen atmosphere. In this specification, the term "oxygen atmosphere" refers to an atmosphere containing sufficient oxygen for firing, including the air atmosphere. In particular, firing is preferably carried out in an atmosphere having a higher oxygen partial pressure than the air atmosphere.

[0089] Meanwhile, when preparing a cathode active material having a coating layer, the calcination step may be followed by a step of mixing the lithium composite transition metal oxide prepared by calcination with a coating raw material, followed by a heat treatment. Here, the mixing may be performed as a solid-phase or liquid-phase mixture, and the heat treatment may be performed at a temperature appropriate for the coating raw material. For example, the heat treatment in the coating process may be performed at a temperature of 200°C to 700°C or 300°C to 600°C, but is not limited thereto.

[0090] In addition, it is preferable not to perform a water washing process after the calcination when preparing the cathode active material of the present invention. Conventionally, when preparing a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 83 mol% or more, a water washing process has been performed after calcination to reduce the content of lithium by-products. However, research by the present inventors has shown that performing a water washing process when preparing a lithium composite transition metal oxide in a single-particle or quasi-single-particle form can deteriorate the surface properties of the lithium composite transition metal oxide during the washing process, resulting in increased resistance. Therefore, it is preferable not to perform water washing when preparing the cathode active material of the present invention, and instead consume the remaining lithium on the surface of the lithium composite transition metal oxide during the coating layer formation process. In this way, when preparing a cathode active material without washing the lithium composite transition metal oxide with water, an increase in resistance due to surface defects can be suppressed.

[0091] positive electrode Next, the positive electrode according to the present invention will be described.

[0092] The positive electrode according to the present invention includes a positive electrode active material layer including the single particle or quasi-single particle positive electrode active material 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 including the positive electrode active material.

[0093] The positive electrode current collector in the positive electrode 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, calcined 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, mesh, porous material, foam, or nonwoven fabric.

[0094] The positive electrode active material layer may contain a conductive material and a binder in addition to the above-mentioned positive electrode material.

[0095] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the resulting battery and has electronic conductivity can be used without 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, carbon fiber, and carbon nanotubes; metal powders or fibers, 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 can be used alone or in combination. The conductive material is typically present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0096] 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 %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0097] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode. For example, the positive electrode may be manufactured by mixing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, applying the positive electrode slurry to a positive electrode current collector, and then drying and rolling the slurry. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0098] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used is determined in consideration of the coating thickness of the slurry and the manufacturing yield, and is sufficient as long as the solvent has a viscosity that can dissolve or disperse the positive electrode active material, conductive material, and binder and provide excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0099] Alternatively, the positive electrode can be produced by casting the positive electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film onto a positive electrode current collector.

[0100] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0101] The lithium secondary battery of the present invention includes the positive electrode according to the present invention. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the positive electrode being as described above. The lithium secondary battery may also optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0102] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0103] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance 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, mesh, porous material, foam, or nonwoven fabric.

[0104] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0105] 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. β (0<β<2), metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0106] The negative electrode active material may be a thin film of metallic lithium. The carbon material may be either low-crystalline or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon. 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-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0107] 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 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, carbon fiber, and carbon nanotubes; metal powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or 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 is typically present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0108] The binder improves adhesion between negative electrode active material particles and between the negative electrode active material and the negative 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 included in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0109] For example, the negative electrode active material layer may be manufactured by coating a negative electrode slurry containing 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 slurry on a separate support, peeling the negative electrode slurry from the support, and laminating the resulting film on the negative electrode current collector.

[0110] 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 limitations. In particular, a separator that exhibits low resistance to ion migration and excellent humidification ability for the electrolyte solution 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.

[0111] 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.

[0112] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0113] 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 (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, and sulfolanes. Among these, carbonate-based solvents are preferred, and 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) are more preferred.

[0114] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt concentration is preferably within a range of 0.1 to 5.0 M, and more preferably 0.1 to 3.0 M. When the lithium salt concentration is within this range, the electrolyte exhibits appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0115] In addition to the electrolyte components, the electrolyte may further contain additives for purposes such as improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Examples of additives include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcohol amine, 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-methoxyethyl alcohol, and aluminum trichloride, which may be used alone or in combination. The additives may be present in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %, based on the total weight of the electrolyte.

[0116] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0117] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0118] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0119] Although the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the 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.

[0120] Example 1 A coprecipitation reactor (20 L capacity) was charged with 4 L of distilled water, and then 100 mL of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. A transition metal solution, consisting of NiSO4, CoSO4, and MnSO4 mixed in a nickel:cobalt:manganese molar ratio of 87:5:8, an aqueous ammonia solution, and a sodium hydroxide solution were then added to the reactor, and a coprecipitation reaction was carried out to form a precursor. The precursor was separated, washed, and then dried in an oven at 130°C to produce the precursor.

[0121] The precursor synthesized as described above was mixed with LiOH and aluminum hydroxide so that the molar ratio of Ni+Co+Mn:Al:Li was 99:1:1.05, and the mixture was heat-treated in an oxygen atmosphere at 850°C for 12 hours to obtain a lithium transition metal composite oxide Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4.13 μm and the average crystallite diameter was 280 nm.

[0122] Example 2 The same procedure as in Example 1 was used to prepare a lithium composite transition metal oxide Li[Ni 0.86 Co 0.06 Mn 0.07 Al 0.01 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4.1 μm and the average crystallite diameter was 270 nm.

[0123] Example 3 The lithium composite transition metal oxide Li[Ni 0.83 Co 0.06 Mn 0.10 Al 0.01 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2.1 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4 μm and the average crystallite diameter was 280 nm.

[0124] Example 4 A lithium composite transition metal oxide Li[Ni 0.865 Co 0.05 Mn 0.08 Al 0.005The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4 μm and the average crystallite diameter was 270 nm.

[0125] Comparative Example 1 A coprecipitation reactor (20 L capacity) was charged with 4 L of distilled water, and then 100 mL of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. A transition metal solution, consisting of NiSO4, CoSO4, and MnSO4 mixed in a nickel:cobalt:manganese molar ratio of 87:5:8, an aqueous ammonia solution, and a sodium hydroxide solution were then added to the reactor, and a coprecipitation reaction was carried out to form a precursor. The precursor was separated, washed, and then dried in an oven at 130°C to produce the precursor.

[0126] The precursor synthesized as above and LiOH were mixed so that the molar ratio of Ni+Co+Mn:Li was 1:1.05, and the mixture was heat-treated in an oxygen atmosphere at 850°C for 12 hours to obtain a lithium composite transition metal oxide Li[Ni 0.87 Co 0.05 Mn 0.08 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4.1 μm and the average crystallite diameter was 280 nm.

[0127] Comparative Example 2 The same procedure as in Example 1 was used to prepare a lithium composite transition metal oxide Li[Ni 0.83 Co 0.10 Mn 0.6 Al 0.01 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50The average crystallite size was 4.2 μm and the average crystallite diameter was 270 nm.

[0128] Comparative Example 3 The same procedure as in Example 1 was used to prepare a lithium composite transition metal oxide Li[Ni 0.86 Co 0.03 Mn 0.10 Al 0.01 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 1.8 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 3.9 μm and the average crystallite diameter was 260 nm.

[0129] Comparative Example 4 The precursor synthesized by the coprecipitation reaction was mixed with LiOH and aluminum hydroxide so that the molar ratio of Ni+Co+Mn:Al:Li was 99:1:1.05, and the mixture was heat-treated in an oxygen atmosphere at 760°C for 12 hours to produce a lithium transition metal composite oxide Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 The produced lithium transition metal composite oxide was in the form of secondary particles, with an average primary particle size of 0.2 μm, an average secondary particle size of 4 μm, and an average crystallite size of 120 nm.

[0130] Comparative Example 5 The lithium composite transition metal oxide Li[Ni] was synthesized in the same manner as in Example 1, except that a transition metal solution in which NiSO4, CoSO4, and MnSO4 were mixed so that the molar ratio of nickel:cobalt:manganese was 83:8:9 was used, and the precursor synthesized by the coprecipitation reaction, LiOH, and aluminum hydroxide were mixed so that the molar ratio of Ni+Co+Mn:Al:Li was 98:2:1.05. 0.81 Co 0.08 Mn 0.09 Al 0.02The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4 μm and the average crystallite diameter was 270 nm.

[0131] Comparative Example 6 The lithium composite transition metal oxide Li[Ni] was synthesized in the same manner as in Example 1, except that a transition metal solution in which NiSO4, CoSO4, and MnSO4 were mixed so that the molar ratio of nickel:cobalt:manganese was 83:8:9 was used, and the precursor synthesized by the coprecipitation reaction, LiOH, and aluminum hydroxide were mixed so that the molar ratio of Ni+Co+Mn:Al:Li was 99.5:0.5:1.05. 0.825 Co 0.08 Mn 0.09 Al 0.005 The lithium composite transition metal oxide produced was in a single particle and / or pseudo-single particle form, with an average particle size of 2 μm and a D of the lithium composite transition metal oxide. 50 The average crystallite size was 4 μm and the average crystallite diameter was 270 nm.

[0132] [Table 1]

[0133] Experimental example 1: Particle crack evaluation The positive electrode active material powders produced in Examples 1 to 4 and Comparative Examples 1 to 6 were placed in a cylindrical metal mold with a diameter of 2 cm and pressed at a pressure of 9 tons. The volume cumulative particle size distribution (PSD) was then measured, and the rate of fine powder less than 1 μm was determined. The particle size distribution was measured using a Microtrac S-3500, and the rate of fine powder less than 1 μm in particle size was converted into weight percent based on the total weight of the positive electrode active material. The measurement results are shown in Table 2 below. Furthermore, Figures 1 and 2 show the particle size distributions of the positive electrode active material powders produced in Example 1 and Comparative Example 4 before and after pressing, respectively.

[0134] [Table 2]

[0135] As can be seen from Table 2, the rate of fine powder generation after rolling of the single particle positive active material is significantly lower than that of the secondary particle positive active material (Comparative Example 4). Therefore, the use of the single particle positive active material can significantly reduce gas generation and electrolyte side reactions compared to the use of fine powder.

[0136] <Secondary battery manufacturing> The positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 6, Super P, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 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.

[0137] Graphite as the negative electrode active material, Super C as the conductive material, and SBR / CMC as the binder were mixed in a weight ratio of 96:1:3 to prepare a negative electrode slurry, which was then applied to one side of a copper current collector, dried at 130°C, and rolled to prepare a negative electrode.

[0138] 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 1M LiPF6 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).

[0139] After the electrolyte was injected, the battery was charged at 25° C. in CC-CV mode at 0.1 C up to 4.25 V, and then discharged at a constant current of 0.1 C down to 2.5 V to carry out an activation step.

[0140] Experimental example 2: Evaluation of high temperature life Each of the lithium secondary batteries prepared above was charged at 45°C in CC-CV mode at 1 C up to 4.25 V and then discharged at a constant current of 0.5 C down to 2.5 V, and after 50 charge-discharge cycles, the capacity retention rate was measured to evaluate the lifespan characteristics. The measurement results are shown in Table 3 below.

[0141] Experimental Example 3: Evaluation of capacitance and resistance characteristics Each of the lithium secondary batteries prepared above was charged and discharged once at 2.5 to 4.25 V under the condition of 0.1 C / 0.1 C, and then the initial discharge capacity (unit: mAh) and resistance (unit: Ω) were measured. Here, the resistance was measured by the change in voltage when a current of 2.5 C was applied for 10 seconds. The measurement results are shown in Table 3 below.

[0142] [Table 3]

[0143] From Table 3, it can be seen that the lithium secondary batteries employing the positive electrode active materials of Examples 1 to 4 satisfying the composition of the present invention have superior high-temperature life characteristics, capacity characteristics, and resistance characteristics compared to the lithium secondary batteries employing the positive electrode active materials of Comparative Examples 1 to 6.

Claims

1. A positive electrode active material comprising a lithium composite transition metal oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is a composite of 30 or less nodules, The lithium transition metal oxide contains Ni, Co, Mn, and Al, and a molar ratio of Ni to the total number of moles of metal elements other than lithium is 0.83 or more and less than 1, a molar ratio of Co to the number of moles of Mn is 0.5 or more and less than 1, and a molar ratio of Co to the number of moles of Al is 5 to 15. The lithium transition metal composite oxide has an average crystallite diameter of 150 nm to 300 nm.

2. 2 . The positive electrode active material according to claim 1 , wherein a ratio of the number of moles of Co to the total number of moles of all metal elements other than lithium in the lithium composite transition metal oxide is greater than 0 and equal to or less than 0.

1.

3. The positive electrode active material according to claim 1 , wherein the lithium composite transition metal oxide has a ratio of the number of moles of Al to the total number of moles of all metals other than lithium of more than 0 and not more than 0.

02.

4. The positive electrode active material according to claim 1 , wherein the lithium composite transition metal oxide has a ratio of the number of moles of Mn to the total number of moles of all metals other than lithium of more than 0 and less than 0.

17.

5. 2. The positive electrode active material according to claim 1, wherein a ratio of the sum of the number of moles of Co and the number of moles of Al to the total number of moles of all metals other than lithium in the lithium composite transition metal oxide is less than 0.

12.

6. The positive electrode active material according to claim 1 , wherein the lithium composite transition metal oxide is represented by the following [Chemical Formula 1]: [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M １ ｅ O ２ In the above formula 1, M １ is one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0≦x≦0.5, 0.83≦a<1, 0<b≦0.1, 0<c<0.17, 0<d≦0.02, 0≦e≦0.05, b<c, 0.5≦b / c<1, 5≦b / d≦15.

7. 2. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has nodules with an average particle size of 0.5 μm to 3 μm.

8. The lithium composite transition metal oxide has an average particle size D ５０ The positive electrode active material according to claim 1, wherein the average particle size is 2 μm to 6 μm.

9. The lithium composite transition metal oxide further includes a coating layer formed on the surface of the lithium composite transition metal oxide particles, 2. The positive electrode active material according to claim 1, wherein the coating layer comprises one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

10. The positive electrode active material has a BET specific surface area of ​​0.1 m ２ / g to 1m ２ The positive electrode active material according to claim 1 , wherein the SiO 2 content is 1 / g.

11. 2. The positive electrode active material according to claim 1, wherein the powder of the positive electrode active material has a pressed density of 2 g / cc to 4 g / cc, measured after being pressed under a pressure of 2000 kgf.

12. 2. The positive electrode active material according to claim 1, wherein a cumulative volume particle size distribution measured after pressing the powder of the positive electrode active material under a pressure of 9 tons contains particles having a particle size of 1 μm or less at a ratio of 1 vol % or less.

13. 2. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has an average crystallite diameter of 230 nm to 300 nm.

14. A positive electrode comprising a positive electrode active material layer containing the positive electrode active material according to claim 1 .

15. A lithium secondary battery comprising the positive electrode according to claim 14.

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