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

Abstract

The present invention relates to a positive electrode active material, which contains a lithium composite transition metal oxide and is a secondary particle formed by agglomeration of primary particles, and the primary particles are 1 The present invention relates to a positive electrode active material including a coating portion containing a metal, the coating portion being locally present on the surface of a primary particle or between boundaries between primary particles, a method for producing the same, and a lithium secondary battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0108997, filed on August 18, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a cathode active material including a high-nickel (High Ni) lithium composite transition metal oxide, which can improve the life characteristics of a lithium secondary battery and minimize the rate of increase in resistance by introducing a coating portion on the surface of primary particles or between the boundaries of primary particles using a segregation phenomenon, a manufacturing method thereof, and a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the advancement of technologies such as electric vehicles, the need for high-capacity secondary batteries is increasing, and as a result, research into high-nickel (High Ni) positive electrode active materials with excellent capacity characteristics is being actively conducted.

[0004] High-nickel cathode active materials, which are formed by a secondary particle structure in which primary particles are aggregated, have anisotropy in the crystal structure between the primary particles at the boundaries between the primary particles. This occurs when lithium is desorbed and inserted during the charge and discharge process of a lithium secondary battery, causing volume changes and generating microcracks between the particles. This exposes the interior of the particles to the electrolyte, causing side reactions and reducing the lifespan of the lithium secondary battery.

[0005] To solve this problem, various methods have been proposed to prevent or minimize cracks during charge and discharge processes, but the problem caused by the inherent anisotropy of the crystal orientation between primary particles has not been resolved. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2020-0036424 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been devised to solve the problems of the prior art, and aims to provide a cathode active material that can improve the life characteristics of a lithium secondary battery and minimize the rate of increase in resistance by introducing a coating portion on the surface of the primary particles or between the boundaries of the primary particles using a segregation phenomenon in order to prevent cracks due to anisotropy of the crystal orientation between primary particles in a cathode active material containing a high-nickel (High Ni) lithium composite transition metal oxide.

[0008] Another object of the present invention is to provide a method for producing the cathode active material, which can introduce a coating portion onto the surface of a primary particle or between boundaries of the primary particles using a segregation phenomenon.

[0009] Another object of the present invention is to provide a lithium secondary battery including the positive electrode active material, which has improved life characteristics and minimized resistance increase rate. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a positive electrode active material, a method for producing a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0011] (1) The present invention relates to secondary particles comprising a lithium composite transition metal oxide and formed by agglomeration of primary particles, and the primary particles are represented by the following chemical formula 1: 1 The lithium composite transition metal oxide includes a coating portion containing a metal, and the coating portion is locally present on the surface of the primary particles or between the boundaries of the primary particles. The lithium composite transition metal oxide includes the coating portion and provides a positive electrode active material having an average composition represented by the following Chemical Formula 1: [Chemical formula 1] Li x Ni a Co b Mn c M 1 d M 2 e O2 In the above Chemical Formula 1, M 1 is one or more selected from the group consisting of lanthanides, and M 2 is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S and Y, and 0.9≦x≦1.1, 0.8≦a<1.0, 0 <b<0.2、0<c<0.2、0<d≦0.1、0≦e≦0.1、a+b+c+d+e=1である。

[0012] (2) The present invention provides the above-mentioned (1), 1 provides a positive electrode active material that is Ce.

[0013] (3) The present invention provides the positive electrode active material according to (1) or (2), wherein the coating portion is not a coating portion formed on the surface of a secondary particle.

[0014] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the primary particles have a crystal size of 90 nm to 140 nm.

[0015] (5) In any one of the above (1) to (4), the present invention is characterized in that the secondary particles have an average particle size (D 50 ) is 8 μm to 20 μm.

[0016] (6) The present invention provides a cathode active material according to any one of (1) to (5) above, wherein the cathode active material includes a coating layer containing boron formed on part or all of the surfaces of primary particles; and on part or all of the surfaces of secondary particles.

[0017] (7) The present invention provides a nickel source material, a cobalt source material, a manganese source material, and M represented by the following chemical formula 3: 1 The present invention provides a method for producing a cathode active material, comprising the steps of: (S10) mixing metal source materials in an aqueous solution and co-precipitating them to produce a cathode active material precursor having an average composition represented by the following chemical formula 3; (S20) mixing the cathode active material precursor and a lithium source material; and (S30) firing the mixture obtained in step (S20) under an oxygen atmosphere. [Chemical formula 3] [Ni a Co b Mn c M 1 d ](OH)2 In the above Chemical Formula 3, M 1 is one or more selected from the group consisting of lanthanides, 0.8≦a<1.0, 0 <b<0.2、0<c<0.2、0<d≦0.1、a+b+c+d=1である。

[0018] (8) The present invention provides the method according to (7), wherein the M 1 The metal source material is M 1 A method for producing a positive electrode active material that is a metal nitrate is provided.

[0019] (9) The present invention provides the method for producing a positive electrode active material according to (7) or (8), wherein the pH is maintained at 11.3 to 11.5 during the coprecipitation reaction in step (S10).

[0020] (10) The present invention provides the method for producing a positive electrode active material according to any one of (7) to (9), wherein the coprecipitation reaction in step (S10) is carried out for 10 to 30 hours.

[0021] (11) The present invention provides the method for producing a positive electrode active material according to any one of (7) to (10), wherein the positive electrode active material precursor produced in the step (S10) has an average particle size of 1 μm to 20 μm.

[0022] (12) The present invention provides the method for producing a positive electrode active material according to any one of (7) to (11), wherein step (S20) is carried out by further including one or more doping materials selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S, and Y.

[0023] (13) The present invention provides the method for producing a positive electrode active material according to any one of (7) to (12), wherein the firing in the step (S30) is carried out at a temperature of 700°C to 800°C for 4 hours to 6 hours.

[0024] (14) The present invention provides a method for producing a positive electrode active material according to any one of (7) to (13), further comprising the step (S40) of washing and drying the fired product fired in the step (S30).

[0025] (15) The present invention provides a method for producing a positive electrode active material according to (14), further comprising the step (S50) of mixing a boron raw material with the fired material washed and dried in the step (S40), followed by heat treatment.

[0026] (16) The present invention provides a positive electrode containing the positive electrode active material according to any one of (1) to (6) above.

[0027] (17) The present invention provides a lithium secondary battery comprising the positive electrode according to (17), a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0028] The cathode active material of the present invention is a cathode active material including a high-nickel (High Ni) lithium composite transition metal oxide, and a coating portion is introduced on the surface of the primary particles or between the boundaries of the primary particles due to a segregation phenomenon, thereby improving the life characteristics of a lithium secondary battery and minimizing the rate of increase in resistance.

[0029] Furthermore, according to the method for producing a positive electrode active material of the present invention, a segregation phenomenon can be induced to effectively introduce a coating portion onto the surface of a primary particle or between the boundaries of the primary particles, without the need for a separate coating step. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram showing that the layered crystal structure of transition metals in primary particles is maintained when a cathode active material is prepared by firing according to a conventional technique. [Figure 2] 1 is a schematic diagram illustrating that, when a cathode active material is prepared by calcination according to the present invention, cerium in a cathode active material precursor particle is segregated to the surface of a primary particle or between the boundaries of the primary particles to form a coating portion. [Figure 3] 1 is a cross-sectional SEM (Scanning Electron Microscope) image of the positive electrode active material of Example 1. [Figure 4] 1 shows the results of EDS mapping of a cross-sectional SEM image of the positive electrode active material of Example 1. [Figure 5] 1 shows the results of EDS line scan of a cross-sectional SEM image of the positive electrode active material of Example 1. [Figure 6] 1 is a cross-sectional SEM (Scanning Electron Microscope) image of the positive electrode active material of Comparative Example 1. [Figure 7] 1 shows the results of EDS mapping of a cross-sectional SEM image of the positive electrode active material of Comparative Example 1. [Figure 8] 1 shows an EDS line scan result of a cross-sectional SEM image of the positive electrode active material of Comparative Example 1. [Figure 9] 1 shows an SEM image of the positive electrode active material of Example 1 and EDS mapping results for Ce. [Figure 10] 1 shows an SEM image of the positive electrode active material of Comparative Example 2 and EDS mapping results for Ce. [Figure 11] 1 shows an SEM image of the positive electrode active material of Comparative Example 3 and EDS mapping results for Ce. [Figure 12] 1 shows an EDS line scan result of a cross-sectional SEM image of the positive electrode active material of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0032] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is 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 describe their inventions.

[0033] In the present invention, the term "primary particle" means the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of multiple crystal grains.

[0034] In the present invention, the term "secondary particles" refers to secondary structures formed by aggregation of a plurality of primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer.

[0035] In the present invention, the term "average particle size (D 50 )" means the particle diameter at the 50% point of the volume cumulative distribution of particle diameters. The average particle diameter is determined by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., S3500 manufactured by Microtrac), measuring the difference in the diffraction pattern depending on the particle diameter when the particles pass through a laser beam, and calculating the particle size distribution. The particle diameter at the 50% point of the volume cumulative distribution of particle diameters in the measuring device is then calculated. 50 can be measured.

[0036] positive electrode active material The present invention provides a positive electrode active material.

[0037] According to one embodiment of the present invention, the positive electrode active material includes a lithium composite transition metal oxide, and is a secondary particle formed by aggregation of primary particles, and the primary particles are represented by M 1 The lithium composite transition metal oxide may include a coating portion containing a metal, the coating portion being locally present on the surface of the primary particles or between the boundaries of the primary particles, and the lithium composite transition metal oxide may have an average composition including the coating portion and represented by the following Chemical Formula 1:

[0038] [Chemical formula 1] Li x Ni a Co b Mn c M 1 d M 2 e O2

[0039] In the above Chemical Formula 1, M 1 is one or more selected from the group consisting of lanthanides, and M 2 is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S and Y, and 0.9≦x≦1.1, 0.8≦a<1.0, 0 <b<0.2、0<c<0.2、0<d≦0.1、0≦e≦0.1、a+b+c+d+e=1である。

[0040] According to one embodiment of the present invention, the lithium composite transition metal oxide having an average composition represented by Chemical Formula 1 is a high-nickel (High Ni) lithium composite transition metal oxide containing nickel at a molar ratio of 80 mol % or more among transition metals, as represented by Chemical Formula 1.

[0041] According to one embodiment of the present invention, in Formula 1, M 1 can be Ce, in which case the capacity, life and output are all excellent.

[0042] According to one embodiment of the present invention, in Chemical Formula 1, b, c, and d can each be 0 < b < 0.1, 0 < c < 0.1, and 0 < d < 0.1. As a specific example, 0 < b ≤ 0.08, 0 < c ≤ 0.08, and 0 < d ≤ 0.01 can be satisfied.

[0043] According to one embodiment of the present invention, the lithium composite transition metal oxide represented by Chemical Formula 1 can be a lithium composite transition metal oxide represented by the following Chemical Formula 2.

[0044] [Chemical Formula 2] Li x Ni a Co b Mn c Ce d M 2 e O2

[0045] In Chemical Formula 2, M 2 can be one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S, and Y, and 0.9 ≤ x ≤ 1.1, 0.8 ≤ a < 1.0, 0 < b < 0.2, 0 < c < 0.2, 0 < d ≤ 0.1, 0 ≤ e ≤ 0.1, and a + b + c + d + e = 1 can be satisfied.

[0046] According to one embodiment of the present invention, in Chemical Formula 2, b, c, and d can each be 0 < b < 0.1, 0 < c < 0.1, and 0 < d < 0.1. As a specific example, 0 < b ≤ 0.08, 0 < c ≤ 0.08, and 0 < d ≤ 0.01 can be satisfied. <了

[0047] According to one embodiment of the present invention, the coating portion locally present between the surface of the primary particles or at the boundary between the primary particles contains the M 1 metal, and the M 1 metal in the coating portion is present inside the cathode active material precursor formed by coprecipitation with the transition metal. 1The metal may be concentrated and formed on the surface of the primary particles or between the boundaries of the primary particles due to a segregation phenomenon during sintering. That is, the coating portion is different from a coating portion or coating layer formed on the lithium composite transition metal oxide by dry coating or wet coating. When the coating portion is present on the surface of the primary particles or between the boundaries of the primary particles, the presence of the coating portion between primary particles that exhibits anisotropy in crystal direction can minimize the generation of microcracks between particles caused by volume changes due to lithium deintercalation and intercalation during charge and discharge. Even if cracks do occur, they can be protected by the coating portion, thereby improving the life characteristics of the lithium secondary battery. As a specific example, the coating portion may be locally present on the surface of the primary particles and between the boundaries of the primary particles. Specifically, the local presence of the coating portion refers to the presence of segregated M. 1 It can be said that the metal does not escape from the surface of the primary particles and the boundaries between the primary particles, but is uniformly distributed between the surface of the primary particles and the boundaries between the primary particles. 1 The coating is not a coating formed on the surface of a secondary particle due to excessive segregation of the metal, which protrudes from the surface of the primary particle and between the boundaries between the primary particles to the surface of the secondary particle, nor is it a coating or layer formed on the surface of a secondary particle by dry coating or wet coating. The coating or layer formed on the surface of a secondary particle has a shape in which a single coating or layer covers the surfaces of multiple primary particles, which differs in shape from the coating formed on the surface of the primary particle and between the boundaries between the primary particles of the present invention.

[0048] According to one embodiment of the present invention, the lithium composite transition metal oxide has an average composition represented by Formula 1 including the coating portion, and the M 1The metal is concentrated on the surface of the primary particles or between the boundaries of the primary particles due to a segregation phenomenon, so that the lithium transition metal composite oxide other than the coating portion has the M 1 That is, the lithium composite transition metal oxide having the average composition represented by Chemical Formula 1 can be simply formed by adding M 1 This is distinguished from lithium composite transition metal oxides that contain metals not as coatings but as doping elements within the particles or crystals of the lithium composite transition metal oxide.

[0049] According to one embodiment of the present invention, the primary particles may be polycrystalline primary particles. Therefore, the crystal size of the primary particles may refer to the crystal size of the crystal grains of the polycrystalline primary particles. As a specific example, the crystal size of the primary particles may be 90 nm to 140 nm, 100 nm to 130 nm, 110 nm to 130 nm, or 120 nm to 130 nm. In this way, when the crystal size is adjusted to the range of 90 nm to 140 nm, M 1 This induces metal segregation and prevents adverse effects due to excessive segregation, thereby improving the lifespan of lithium secondary batteries and reducing the rate of increase in resistance. Meanwhile, the crystal size of the primary particles was measured using an X-ray diffraction analysis method using a D4 ENDEAVOR from Bruker AXS GmbH under the conditions of a Cu target, an accelerating voltage of 40 kV, an accelerating current of 40 mA, and an angle range of 10° to 90° at a rate of 3° per minute, and calculated using the TOPAS program from Bruker AXS GmbH.

[0050] According to one embodiment of the present invention, the secondary particles have an average particle size (D 50) can be 8 μm to 20 μm, 10 μm to 20 μm, 10 μm to 18 μm, 10 μm to 15 μm, 10 μm to 13 μm, 10 μm to 12 μm, 10 μm to 11.5 μm, 10.5 μm to 11.5 μm, or 11 μm to 11.5 μm, and within this range, excellent capacity characteristics can be achieved, and in particular, there is an effect of being able to improve the capacity characteristics of a bimodal type positive electrode material that contains the secondary particles as large particles and also contains a small particle positive electrode active material.

[0051] According to one embodiment of the present invention, the positive electrode active material may include a coating layer containing boron formed on a part or all of the surface of the primary particles and a part or all of the surface of the secondary particles, which has the effect of improving the life of the lithium secondary battery. Here, the coating layer containing boron is formed on the M 1 It refers to a separate coating layer that is distinct from the metal-containing coating portion.

[0052] According to one embodiment of the present invention, the boron-containing coating layer may contain boron in the form of an amorphous boron compound, such as lithium boron oxide or boron oxide. Specific examples of the coating layer include LiBO2, Li2B4O7, LiB3O5, and BO3. Unlike crystalline compounds, which can only be applied as discontinuous coatings in the form of particles, the amorphous boron compound can be applied as a continuous coating in the form of a film, islands, or a mixture thereof.

[0053] According to one embodiment of the present invention, the coating layer may contain 500 ppm to 1,500 ppm, 500 ppm to 1,200 ppm, or 500 ppm to 1,000 ppm of the lithium composite transition metal oxide. Within this range, it is possible to prevent a decrease in capacity of the lithium secondary battery and further improve its lifespan.

[0054] Method for producing positive electrode active material The present invention provides a method for producing the above-mentioned positive electrode active material.

[0055] According to one embodiment of the present invention, the method for preparing the positive electrode active material includes mixing a nickel source material, a cobalt source material, a manganese source material, and M represented by the following Formula 3: 1 The method may include a step (S10) of mixing metal source materials in an aqueous solution and co-precipitating them to prepare a cathode active material precursor having an average composition represented by the following Chemical Formula 3, a step (S20) of mixing the cathode active material precursor and a lithium source material, and a step (S30) of firing the mixture mixed in the step (S20) under an oxygen atmosphere.

[0056] [Chemical formula 3] [Ni a Co b Mn c M 1 d ](OH)2

[0057] In the above Chemical Formula 3, M 1 is one or more selected from the group consisting of lanthanides, 0.8≦a<1.0, 0 <b<0.2、0<c<0.2、0<d≦0.1、a+b+c+d=1である。

[0058] According to one embodiment of the present invention, the step (S10) is a step of inducing a segregation phenomenon to form a coating portion on the surface of the primary particles or between the boundaries of the primary particles. 1 This is a step for producing a positive electrode active material precursor by co-precipitation of a metal with a transition metal.

[0059] According to one embodiment of the present invention, step (S10) can be initiated by charging distilled water, an ammonium ion-containing solution, and a basic aqueous solution into a reactor and purging the reactor with nitrogen gas. The reactor can be a batch reactor, in which case reaction conditions such as reactant concentration, temperature, and residence time within the reactor can be maintained constant, allowing for the production of a relatively uniform product. Here, an initial reaction solution containing distilled water, an ammonium ion-containing solution, and a basic aqueous solution can be charged into the reactor to a predetermined volume, and the pH within the reactor can be adjusted.

[0060] According to one embodiment of the present invention, the ammonium ion-containing solution may contain at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3. The solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0061] According to one embodiment of the present invention, the basic aqueous solution may include one or more selected from the group consisting of NaOH, KOH, and Ca(OH), and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0062] According to an embodiment of the present invention, in the step (S10), a nickel source material, a cobalt source material, a manganese source material, and M represented by Formula 3 are added to the reactor. 1 The metal source materials can be mixed in the form of an aqueous solution, and the mixed aqueous solution, the ammonium ion-containing solution, and the basic aqueous solution are then introduced to carry out the coprecipitation reaction.

[0063] According to an embodiment of the present invention, the nickel source material, the cobalt source material, and the manganese source material may include acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide of each transition metal.

[0064] According to one embodiment of the present invention, the nickel source material may be Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a fatty acid nickel salt, or a nickel halide, or a mixture of two or more of these may be used.

[0065] According to one embodiment of the present invention, the cobalt source material may be Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or Co(SO4)2·7H2O, or a mixture of two or more of these may be used.

[0066] According to one embodiment of the present invention, the manganese source material may be manganese oxides such as MnO, MnO, and MnO; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide or manganese chloride; or a mixture of any one or more of these.

[0067] According to one embodiment of the present invention, the M 1 The metal source material is M 1 It can be a metal nitrate, and a specific example is Ce(NO3)3.

[0068] According to one embodiment of the present invention, the pH may be maintained at 11.3 to 11.5 during the coprecipitation reaction in step (S10). As a specific example, at the beginning of the reaction, an ammonium ion-containing solution and an alkaline aqueous solution are first introduced to adjust the pH to a range of 11.3 to 11.5. Thereafter, a nickel source material, a cobalt source material, a manganese source material, and the M of Formula 3 are introduced into the reactor. 1Particle nuclei can be generated by adding an aqueous solution containing metal raw materials. Since the pH value in the reactor changes as particle nuclei are generated by adding the aqueous solution, the pH can be controlled to be 11.3 to 11.5 by continuously adding an ammonium ion-containing solution and an alkaline aqueous solution along with the addition of the aqueous solution.

[0069] According to one embodiment of the present invention, the co-precipitation reaction in step (S10) may be carried out for 10 to 30 hours, 11 to 25 hours, or 12 to 20 hours, and within this range, the particle growth reaction can be sufficiently induced.

[0070] According to one embodiment of the present invention, the coprecipitation reaction in step (S10) may be performed while stirring. Specifically, from the initial stage of the reaction until particle growth by the coprecipitation reaction, stirring may be performed at a stirring speed of 500 rpm to 1,000 rpm, 600 rpm to 800 rpm, or 650 rpm to 750 rpm. After the particle growth reaction, the stirring speed may be gradually reduced to 100 rpm to 500 rpm, 200 rpm to 500 rpm, or 300 rpm to 400 rpm, and then the reaction may be terminated.

[0071] According to one embodiment of the present invention, the positive electrode active material precursor prepared in step (S10) may have an average particle size of 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 13 μm.

[0072] According to one embodiment of the present invention, the cathode active material precursor prepared in step (S10) is a nickel-cobalt-manganese-Mn alloy for forming a high nickel (High Ni) lithium composite transition metal oxide containing nickel at a molar ratio of 80 mol % or more among the transition metals, as represented by Chemical Formula 3. 1 It can be a metal hydroxide, and when the nickel content satisfies the above range, the lithium secondary battery has excellent capacity.

[0073] According to one embodiment of the present invention, in the chemical formula 3, M 1 can be Ce.

[0074] According to one embodiment of the present invention, in the chemical formula 3, b, c, and d can be 0 < b < 0.1, 0 < c < 0.1, and 0 < d < 0.1, respectively. As specific examples, 0 < b ≤ 0.08, 0 < c ≤ 0.08, and 0 < d ≤ 0.01 can be possible.

[0075] According to one embodiment of the present invention, the positive electrode active material precursor represented by the chemical formula 3 can be a positive electrode active material precursor represented by the following chemical formula 4.

[0076] [Chemical formula 4] [Ni a Co b Mn c Ce d (OH)2

[0077] In the chemical formula 4, 0.8 ≤ a < 1.0, 0 < b < 0.2, 0 < c < 0.2, 0 < d ≤ 0.1, 0 ≤ e ≤ 0.1, and a + b + c + d + e = 1 can be possible.

[0078] According to one embodiment of the present invention, in the chemical formula 4, b, c, and d can be 0 < b < 0.1, 0 < c < 0.1, and 0 < d < 0.1, respectively. As specific examples, 0 < b ≤ 0.08, 0 < c ≤ 0.08, and 0 < d ≤ 0.01 can be possible.

[0079] According to one embodiment of the present invention, the step (S20) is a step of mixing a positive electrode active material precursor and a lithium raw material substance to form a lithium composite transition metal oxide.

[0080] According to an embodiment of the present invention, 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.

[0081] According to one embodiment of the present invention, the lithium source material and the cathode active material precursor may be mixed so that the molar ratio of Li:total transition metals in the precursor is 1:1 to 1.2:1, or 1:1 to 1.1:1. When the mixing ratio of the lithium source material and the transition metals in the cathode active material precursor satisfies this range, the crystalline structure of the cathode active material is well developed, and a cathode active material with excellent capacity characteristics and structural stability can be produced.

[0082] According to one embodiment of the present invention, step (S20) may be performed by further adding at least one doping material selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S, and Y. The doping material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing the element, and specific examples thereof may include Al2O3, Al(OH)3, Al(NO3)3·9H2O, and Al2(SO4)3.

[0083] According to an embodiment of the present invention, the step (S30) is a step for firing the mixture mixed in the step (S20), in which the lithium source material is melted and reacts with the cathode active material precursor to grow crystals of the cathode active material, and the M in the cathode active material precursor represented by Chemical Formula 3 is melted and fired. 1This may be a step of inducing a segregation phenomenon of metal. As a specific example, the firing in step (S30) may be performed at a temperature of 700 to 800°C, 750 to 800°C, or 770 to 790°C for 4 to 6 hours.

[0084] According to one embodiment of the present invention, the driving principle of the segregation phenomenon can be expressed by the following Equation 1.

[0085] [Formula 1]

number

[0086] In the above formula 1,

number

number

number

number

number

number

number

number

[0087] The method for producing a positive electrode active material according to the present invention is to calculate M 1 Steps (S10) to (S30) may be adjusted to induce metal segregation.

[0088] According to one embodiment of the present invention, the method for preparing a positive electrode active material may include a step (S40) of washing and drying the fired product obtained in step (S30). The washing in step (S40) is for removing lithium by-products remaining on the surface of the lithium composite transition metal oxide and may be performed by washing with water, and may be performed using a method for washing a positive electrode active material well known in the art. As a specific example, step (S40) may be performed by mixing the lithium composite transition metal oxide with a washing solution, stirring, filtering to remove the washing solution, and then drying. Here, the drying may be performed at a temperature of, for example, 50°C to 150°C.

[0089] According to one embodiment of the present invention, the method for preparing the positive electrode active material may include a step (S50) of mixing a boron source with the calcined product that has been washed and dried in the step (S40), followed by a heat treatment. Here, the boron source may be mixed in an amount of 500 ppm to 1,500 ppm. The heat treatment may be performed at a temperature of 250°C to 350°C.

[0090] positive electrode The present invention provides a positive electrode containing the positive electrode active material.

[0091] According to an embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0092] According to one embodiment of the present invention, 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 voltage range of the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined 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 μm to 500 μm, and the surface of the current collector may be micro-irregularized to enhance adhesion 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.

[0093] According to one embodiment of the present invention, the positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material. The positive electrode active material may be contained in an amount of 80 wt % to 99 wt %, more specifically, 85 wt % to 98.5 wt %, based on the total weight of the positive electrode active material layer. Within this range, excellent capacity characteristics can be exhibited.

[0094] According to one embodiment of the present invention, 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 resulting 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 may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0095] According to an embodiment of the present invention, the binder improves 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% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

[0096] According to one embodiment of the present invention, the positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition, which is prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, on a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode active material layer-forming composition on a separate support, peeling it from the support, and laminating the resulting film on a positive electrode current collector.

[0097] According to an embodiment of the present invention, 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 may be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0098] Lithium secondary battery The present invention provides a lithium secondary battery including the positive electrode.

[0099] According to an embodiment of the present invention, the lithium secondary battery may include the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may further include a battery container that houses the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0100] According to an embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0101] According to one embodiment of the present invention, the negative electrode current collector may be made of any material that does not cause chemical changes in the battery and has high conductivity. Examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, the current collector may have a surface with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be made in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0102] According to an embodiment of the present invention, the negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

[0103] According to one embodiment of the present invention, the negative electrode active material may be a compound capable of reversible lithium intercalation and deintercalation. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ(0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; 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. Alternatively, a metallic lithium thin film may be used as the negative electrode active material. The carbonaceous material may be either low-crystalline carbon or high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, while representative examples of high-crystalline carbon 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-calcined carbon such as petroleum or coal tar pitch-derived cokes. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% of the total weight of the negative electrode active material layer.

[0104] According to one embodiment of the present invention, the binder in the negative electrode active material layer is a component that helps bind the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0105] According to one embodiment of the present invention, the conductive material in the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material may be any conductive material that does not cause chemical changes in the battery and has conductivity. Examples of such conductive materials 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 powders 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.

[0106] According to one embodiment of the present invention, the negative electrode may be fabricated by coating a negative electrode active material layer-forming composition, 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 active material layer-forming composition may be fabricated by casting the negative electrode active material layer-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0107] According to one embodiment of the present invention, 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.

[0108] According to an embodiment of the present invention, the electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used in manufacturing a lithium secondary battery. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0109] According to an embodiment of the present invention, the organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can migrate. 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), 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 hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and 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.

[0110] According to one embodiment of the present invention, the lithium salt may be any compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt may 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 a range of 0.1M to 2.0M. 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.

[0111] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds (e.g., 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, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. Here, the additives may be included in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0112] A lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0113] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0114] The lithium secondary battery according to the present invention can be used as a battery cell used as a power source for a small device, and can also be preferably used as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0115] Therefore, according to one 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.

[0116] According to one embodiment of the present invention, the battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0117] 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.

[0118] Examples and Comparative Examples Example 1 4.5 L of distilled water, 450 g of aqueous ammonia (NH4OH), and 6.5 g of sodium hydroxide (NaOH) were charged into a reactor equipped with a stirrer, and the internal temperature of the reactor was maintained at 54°C while stirring at 700 rpm.

[0119] A 3.14 M transition metal-containing aqueous solution was prepared by mixing NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Ce(NO3)3 in deionized water in amounts such that the molar ratio of nickel:cobalt:manganese:cerium was 87.9:5.0:7.0:0.1.

[0120] The transition metal-containing aqueous solution was fed into the reactor at a flow rate of 8 mL / min, and ammonia water (NH4OH) was fed at a flow rate of 4 mL / min, and a 40 wt% aqueous sodium hydroxide (NaOH) solution was fed so that the pH of the solution inside the reactor was 11.4.

[0121] Then, particle growth was carried out in the reactor for 12 hours, and Ni with an average particle size of 11.5 μm was added for 8 hours while the stirring speed was reduced to 400 rpm. 0.879 Co 0.050 Mn 0.070 Ce 0.001A positive electrode active material precursor having an average composition of (OH)2 was prepared.

[0122] The lithium source material LiOH·H2O and the prepared cathode active material precursor were mixed so that the molar ratio of Li:metals in the precursor (Ni+Co+Mn+Ce) was 1.05:1. This mixture was calcined at 780°C for 5 hours in an oxygen (O2) atmosphere to produce a lithium composite transition metal oxide Li 1.05 Ni 0.879 Co 0.050 Mn 0.070 Ce 0.001 Produced O2.

[0123] 100 g of the prepared lithium composite transition metal oxide was mixed with 100 g of water, stirred for 5 minutes, and washed with water. The washed product was then separated and filtered using a filter press so that the water content of the washed product was 5 wt% to 10 wt%, and then dried at 130°C for 4 hours. Next, the washed and dried lithium composite transition metal oxide was mixed with 1,000 ppm of H3BO3 and heat-treated at 300°C for 4 hours to prepare a cathode active material coated with a B solid solution.

[0124] Example 2 A cathode active material coated with a B solid solution was prepared in the same manner as in Example 1, except that when preparing the transition metal-containing aqueous solution, NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Ce(NO3)3 were mixed in amounts such that the molar ratio of nickel:cobalt:manganese:cerium was 87.8:5.0:7.0:0.2 instead of 87.9:5.0:7.0:0.1. The average particle size of the cathode active material precursor prepared here was 11.4 μm, and the average composition was Ni 0.878 Co 0.050 Mn 0.070 Ce 0.002 (OH)2, and the lithium composite transition metal oxide produced is Li 1.05 Ni 0.878 Co 0.050 Mn 0.070 Ce 0.002 It is O2.

[0125] Comparative Example 1 A cathode active material coated with a B solid solution was prepared in the same manner as in Example 1, except that when preparing the transition metal-containing aqueous solution, NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and Ce(NO3)3 were replaced with NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in amounts such that the molar ratio of nickel:cobalt:manganese was 88:5:7. The average composition of the cathode active material precursor was Ni 0.88 Co 0.05 Mn 0.07 (OH)2, and the lithium composite transition metal oxide produced is Li 1.05 Ni 0.88 Co 0.05 Mn 0.07 It is O2.

[0126] Comparative Example 2 A cathode active material coated with a B solid solution was prepared in the same manner as in Example 1, except that the lithium source material LiOH·H2O and the prepared cathode active material precursor were mixed so that the molar ratio of Li:metals (Ni+Co+Mn+Ce) in the precursor was 1.05:1, and the mixture was calcined at 900°C for 5 hours in an oxygen (O2) atmosphere instead of at 780°C for 5 hours. 1.05 Ni 0.879 Co 0.050 Mn 0.070 Ce 0.001 It is O2.

[0127] Comparative Example 3 4.5 L of distilled water, 450 g of aqueous ammonia (NH4OH), and 6.5 g of sodium hydroxide (NaOH) were charged into a reactor equipped with a stirrer, and the temperature inside the reactor was maintained at 54°C while stirring at 700 rpm.

[0128] NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O were mixed in deionized water in amounts such that the molar ratio of nickel:cobalt:manganese was 88:5:7 to prepare a 3.14 M transition metal-containing aqueous solution.

[0129] The transition metal-containing aqueous solution was fed into the reactor at a flow rate of 8 mL / min, and ammonia water (NH4OH) was fed at a flow rate of 4 mL / min, and a 40 wt% aqueous sodium hydroxide (NaOH) solution was fed so that the pH of the solution inside the reactor was 11.4.

[0130] Then, particle growth was carried out in the reactor for 12 hours, and Ni with an average particle size of 11.5 μm was added for 8 hours while the stirring speed was reduced to 400 rpm. 0.88 Co 0.05 Mn 0.07 A positive electrode active material precursor having an average composition of (OH)2 was prepared.

[0131] The lithium source material LiOH·H2O and the prepared cathode active material precursor were mixed so that the molar ratio of Li:metals (Ni+Co+Mn) in the precursor was 1.05:1. This mixture was calcined at 780°C for 5 hours in an oxygen (O2) atmosphere to produce a lithium composite transition metal oxide Li 1.05 Ni 0.88 Co 0.05 Mn 0.07 Produced O2.

[0132] 100 g of the prepared lithium composite transition metal oxide was mixed with 100 g of water, stirred for 5 minutes, and washed with water. The mixture was then separated and filtered using a filter press so that the water content of the washed product was 5 wt% to 10 wt%, and then dried at 130°C for 4 hours. Next, CeO2 was added to the washed and dried lithium composite transition metal oxide in an amount such that the lithium composite transition metal oxide:CeO2 molar ratio was 1:0.1, and 1,000 ppm of H3BO3 was added. The mixture was then heat-treated at 300°C for 4 hours to prepare a cathode active material coated with a Ce and B solid solution.

[0133] Experimental Example Experimental Example 1: Average particle size, crystal size, and average particle size of secondary particles of the positive electrode active material precursor (D 50 ) The average particle diameters of the positive electrode active material precursors prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were measured as follows and are shown in Table 1 below.

[0134] Furthermore, the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were subjected to XRD measurement by the following method, and the crystal sizes were calculated and shown in Table 1 below.

[0135] In addition, the average particle size of secondary particles (D 50 ) was measured as follows and is shown in Table 1 below.

[0136] *Average particle size (μm) of the positive electrode active material precursor: 0.2 g of the positive electrode active material precursor particles was collected from the positive electrode active material precursor powders prepared in Examples 1 and 2 and Comparative Examples 1 to 3, and dispersed in water containing a small amount of sodium hexametaphosphate ((NaPO3)6). The average particle size (D) of the positive electrode active material precursor particles was then measured using a laser diffraction particle size analyzer (Microtrac S3500) based on the volume cumulative distribution of the positive electrode active material precursor particles. 50 ) was measured.

[0137] *Crystalline size (nm): 2 g of positive electrode active material particles were collected from the positive electrode active material powders prepared in Examples 1 and 2 and Comparative Examples 1 to 3. The crystalline size was measured by X-ray diffraction analysis using a D4 ENDEAVOR from Bruker AXS GmbH under the conditions of a Cu target, an accelerating voltage of 40 kV, an accelerating current of 40 mA, and an angle range of 10° to 90° at a rate of 3° per minute. The crystalline size of the primary particles was calculated using the TOPAS program from Bruker AXS GmbH.

[0138] *Average particle size (μm) of secondary particles: 0.2 g of positive electrode active material particles was collected from the positive electrode active material powders produced in Examples 1 and 2 and Comparative Examples 1 to 3, and dispersed in water containing a small amount of sodium hexametaphosphate ((NaPO3)6). The average particle size (D) of the positive electrode active material secondary particles was measured using a laser diffraction particle size analyzer (Microtrac S3500) based on the cumulative volume distribution. 50 ) was measured.

[0139] [Table 1]

[0140] As shown in Table 1, it was confirmed that positive electrode active materials of secondary particles having the same average particle size were prepared in Examples 1 and 2 and Comparative Examples 2 and 3.

[0141] On the other hand, in the case of Comparative Example 1, which did not contain cerium, it was confirmed that the average particle size of the positive electrode active material precursor and secondary particles was smaller than that of the Examples, and in the case of Comparative Example 2, which was fired at a higher temperature than that of the Examples, it was confirmed that the crystal size was larger.

[0142] Experimental Example 2: Confirmation of the molar ratio of the positive electrode active material precursor by ICP analysis The positive electrode active material precursors prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were subjected to ICP analysis by the following method to confirm the molar ratios of the positive electrode active material precursors, which are shown in Table 2 below.

[0143] *ICP analysis: 0.1 g of the cathode active material precursor particles prepared in Examples 1 and 2 and Comparative Examples 1 to 3 was collected and accurately weighed and placed in a vial, after which 1 mL of hydrochloric acid was added. The sample was then heated on a hot plate to dissolve. A small amount of hydrogen peroxide was added to promote the sample reaction. After the sample was completely dissolved, it was diluted to 10 mL with tertiary ultrapure water to prepare an analytical sample for ICP analysis.

[0144] Thereafter, ICP analysis was carried out on the prepared analytical sample using an ICP-OES Quant under the following conditions.

[0145] -RF Power: 1,300W -Torch Height: 15.0mm -Plasma Gas Flow: 15.00L / min -Sample Gas Flow: 0.80L / min -Aux.Gas Flow: 0.20L / min -Pump Speed: 1.5mL / min -Internal Standard: Y or Sc

[0146] [Table 2]

[0147] As shown in Table 2, in Examples 1 and 2 and Comparative Example 2, in which Ce was introduced during the preparation of the positive electrode active material precursor, it was confirmed that the Ce in the positive electrode active material precursor was contained in the intended amount.

[0148] Experimental Example 3: SEM observation and EDS analysis of positive electrode active materials of Example 1 and Comparative Examples 1 to 3 Cross sections of the positive electrode active materials prepared in Example 1 and Comparative Example 1 were photographed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). The cross-sectional SEM image of the positive electrode active material of Example 1 is shown in FIG. 3, the EDS mapping results for the cross-sectional SEM image of the positive electrode active material of Example 1 are shown in FIG. 4, the EDS line scan results for the cross-sectional SEM image of the positive electrode active material of Example 1 are shown in FIG. 5, the cross-sectional SEM image of the positive electrode active material of Comparative Example 1 is shown in FIG. 6, the EDS mapping results for the cross-sectional SEM image of the positive electrode active material of Comparative Example 1 are shown in FIG. 7, and the EDS line scan results for the cross-sectional SEM image of the positive electrode active material of Comparative Example 1 are shown in FIG. 8.

[0149] The EDS line scan results for the cross sections of the positive electrode active materials of Example 1 and Comparative Example 1 are shown in Table 3 below.

[0150] [Table 3]

[0151] As shown in Figures 3 to 8 and Table 3, the cathode active material of Example 1 of the present invention was found to have coatings locally formed on the surfaces of the primary particles and between the boundaries of the primary particles, even though no separate coating using cerium was applied. This indicates that the coatings are formed by concentrating cerium on the surfaces of the primary particles or between the boundaries of the primary particles due to the segregation phenomenon that occurs during the preparation of the cathode active material. On the other hand, in the case of Comparative Example 1, only noise related to Ce was observed, confirming the absence of coatings.

[0152] In addition, the positive electrode active materials prepared in Example 1 and Comparative Example 2 were photographed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). The SEM image of the positive electrode active material of Example 1 and the EDS mapping results for Ce are shown in FIG. 9, and the SEM image of the positive electrode active material of Comparative Example 2 and the EDS mapping results for Ce are shown in FIG. 10.

[0153] As shown in Figures 9 and 10, the cathode active material of Example 1 of the present invention exhibited localized coatings on the surfaces of the primary particles and between the boundaries of the primary particles. However, the cathode active material of Comparative Example 2, which was prepared using the same cathode active material precursor prepared by co-precipitation of Ce but at a higher sintering temperature, exhibited increased crystal size due to the high sintering temperature, resulting in excessive segregation. This resulted in protruding coatings on the surfaces of the secondary particles, rather than localized coatings on the surfaces of the primary particles and between the boundaries of the primary particles. This, as will be seen in Experimental Example 4 below, leads to a decrease in capacity characteristics.

[0154] The cathode active material prepared in Comparative Example 3 was photographed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). The SEM image of the cathode active material of Comparative Example 3 and the EDS mapping results for Ce are shown in FIG. 11, and the EDS line scan results for the cross-sectional SEM image of the cathode active material of Comparative Example 3 are shown in FIG. 12.

[0155] As shown in FIGS. 9 and 11, it was confirmed that the cathode active material of Example 1 of the present invention had coatings formed locally on the surfaces of the primary particles and between the boundaries of the primary particles, whereas the cathode active material of Comparative Example 3, which was simply coated with Ce, had a crystalline structure formed on the surface of the cathode active material.

[0156] In particular, as shown in FIGS. 5 and 12, it was confirmed that Ce was uniformly observed in the positive electrode active material of Example 1 of the present invention, but that Ce was concentrated on the surface portions of the secondary particles in the positive electrode active material of Comparative Example 3.

[0157] These results confirm that the coating was formed on the surface of the secondary particles, rather than on the surface of the primary particles or between the boundaries of the primary particles, in the cathode active material of Comparative Example 3. This is the reason why the improvement of capacity and life characteristics was not affected, as will be confirmed in Experimental Example 4 described below.

[0158] Experimental Example 4: Evaluation of capacity and life characteristics The positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3 96 % by weight, 2.0% by weight of carbon black as a conductive material, and 2.0% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode.

[0159] A lithium metal electrode was used as the negative electrode, and a porous polyethylene separator was interposed between the positive and negative electrodes to fabricate an electrode assembly. This was placed inside a battery case, and an electrolyte was poured into it to fabricate a coin-type half-cell. The electrolyte was prepared by dissolving 1M LiPF6 in an organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0160] The coin-type half cells containing the prepared cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 were charged at 25°C in CC and CV modes at 0.1 C to 4.3 V, and discharged at a constant current of 0.1 C to 3.0 V, and the charge capacity, discharge capacity, and direct current internal resistance (DCIR) were measured and are shown in Table 4 below.

[0161] In addition, the battery was charged at 45°C in CC / CV mode at 0.33 C until the voltage reached 4.3 V, and then discharged at a constant current of 0.33 C until the voltage reached 3.0 V, counting as one cycle. After 30 cycles of charge and discharge, the capacity retention rate and the resistance increase rate were measured, and the results are shown in Table 5 below.

[0162] [Table 4]

[0163] [Table 5]

[0164] As shown in Tables 4 and 5, the batteries including the cathode active materials of Examples 1 and 2 according to the present invention have excellent charge and discharge capacities, high capacity retention rates after 30 cycles, and low resistance increase rates, and thus have excellent capacity and life characteristics.

[0165] On the other hand, the battery containing the positive electrode active material of Comparative Example 1, which did not contain any cerium, had somewhat low charge and discharge capacities. In particular, after 30 cycles, the capacity retention rate decreased and the resistance increase rate increased sharply, indicating poor life characteristics.

[0166] In addition, it was confirmed that the battery including the cathode active material of Comparative Example 2, which contained cerium but formed protruding coatings on the surfaces of secondary particles through excessive segregation, rather than forming coatings locally present on the surfaces of primary particles or between the boundaries of primary particles through high temperature firing, exhibited a sharp decrease in charge capacity and discharge capacity, resulting in poor capacity characteristics.

[0167] In addition, it was confirmed that the battery including the cathode active material of Comparative Example 3, in which cerium was introduced by simple coating rather than segregation and a coating portion was formed on the surface of the secondary particles, showed only slight improvements in both capacity characteristics and life characteristics compared to Comparative Example 1.

[0168] These results confirm that the cathode active material of the present invention is a cathode active material containing a high-nickel (High Ni) lithium composite transition metal oxide, and that a coating portion is introduced on the surface of the primary particles or between the boundaries of the primary particles through segregation, thereby improving the life characteristics of the lithium secondary battery and minimizing the rate of increase in resistance. Furthermore, it was confirmed that the method for manufacturing the cathode active material of the present invention can effectively introduce a coating portion on the surface of the primary particles or between the boundaries of the primary particles by inducing segregation without the need for a separate coating step.

Claims

1. a lithium composite transition metal oxide; These are secondary particles formed by agglomeration of primary particles, The primary particles are M of the following formula 1: １ a coating portion containing a metal, the coating portion is locally present on the surface of the primary particle or between the boundaries of the primary particles, The lithium composite transition metal oxide, including the coating portion, is a positive electrode active material having an average composition represented by the following Chemical Formula 1: [Chemical formula 1] Li ｘ Ni ａ Co ｂ Mn ｃ M １ ｄ M ２ ｅ O ２ In the above Chemical Formula 1, M １ is Ce, M ２ is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S and Y, 0.9≦x≦1.1, 0.8≦a<1.0, 0<b<0.2, 0<c<0.2, 0<d≦0.1, 0≦e≦0.1, and a+b+c+d+e=1.

2. The positive electrode active material according to claim 1 , wherein the coating portion is not a coating portion formed on a surface of a secondary particle.

3. 2. The positive electrode active material according to claim 1, wherein the primary particles have a crystal size of 90 nm to 140 nm.

4. The secondary particles have an average particle size (D ５０ 2. The positive electrode active material according to claim 1, wherein the average particle diameter is 8 μm to 20 μm.

5. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material comprises: a coating layer containing boron formed on a part or all of the surfaces of primary particles; and a coating layer containing boron formed on a part or all of the surfaces of secondary particles.

6. A nickel source material, a cobalt source material, a manganese source material, and M represented by the following formula 3 １ S10: mixing metal source materials in an aqueous solution and co-precipitating them to prepare a cathode active material precursor having an average composition represented by the following Chemical Formula 3; A step (S20) of mixing a positive electrode active material precursor and a lithium source material; and (S30) firing the mixture mixed in the (S20) step under an oxygen atmosphere, The sintering step (S30) is carried out at a temperature of 700°C to 800°C. [Chemical formula 3] [Ni ａ Co ｂ Mn ｃ M １ ｄ ](OH) ２ In the above Chemical Formula 3, M １ is Ce, 0.8≦a<1.0, 0<b<0.2, 0<c<0.2, 0<d≦0.1, a+b+c+d=1.

7. Said M １ The metal source material is M １ The method for producing a positive electrode active material according to claim 6 , wherein the active material is a metal nitrate.

8. The method for producing a positive electrode active material according to claim 6, wherein the pH is maintained at 11.3 to 11.5 during the coprecipitation reaction in step (S10).

9. The method for producing a positive electrode active material according to claim 6, wherein the co-precipitation reaction in step (S10) is carried out for 10 to 30 hours.

10. The method for producing a positive electrode active material according to claim 6, wherein the positive electrode active material precursor produced in step (S10) has an average particle size of 1 μm to 20 μm.

11. 7. The method for producing a positive electrode active material according to claim 6, wherein step (S20) is performed by further adding at least one doping material selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, F, P, S, and Y.

12. 7. The method of claim 6, wherein the firing in step (S30) is performed at a temperature of 700° C. to 800° C. for 4 hours to 6 hours.

13. The method for producing a positive electrode active material according to claim 6, further comprising the step (S40) of washing and drying the fired product fired in the step (S30).

14. The method for producing a positive electrode active material according to claim 13, further comprising the step of: (S50) mixing a boron source with the fired product washed and dried in the step (S40), and then heat-treating the mixture.

15. A positive electrode comprising the positive electrode active material according to claim 1 .

16. A lithium secondary battery comprising: the positive electrode according to claim 15; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

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