Precursor of positive electrode active material for secondary battery, positive electrode active material, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material precursor capable of significantly improving life characteristics and resistance increase when used in a lithium secondary battery, and a method of preparing the same.SOLUTION: The invention relates to a positive electrode active material precursor, a method of preparing the same, and a positive electrode active material prepared by using the positive electrode active material precursor. The positive electrode active material precursor comprises a hydroxide represented by chemical formula 1. The positive electrode active material precursor is of secondary particles in each of which multiple primary particles are aggregated, and includes grains in which major axes of the primary particles are arranged in a direction from a center of the secondary particle toward a surface thereof and the (001) plane of the primary particle is arranged parallel to the major axis of the primary particle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0010699, filed on January 29, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material precursor for a secondary battery, a positive electrode active material, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as a power source for portable devices. Therefore, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries generate electrical energy through oxidation and reduction reactions when lithium ions are inserted into and extracted from the positive and negative electrodes while an organic or polymer electrolyte solution is charged between the positive and negative electrodes, which are made of active materials that allow for the intercalation and deintercalation of lithium ions.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as positive electrode active materials in lithium secondary batteries. Among them, lithium cobalt oxide (LiCoO2) is widely used due to its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage applications. However, due to the rising price of cobalt (Co) and unstable supply, there are limitations on its mass use as a power source in fields such as electric vehicles, and there is an increasing need to develop alternative positive electrode active materials.

[0006] Therefore, nickel-cobalt-manganese-based lithium composite transition metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") have been developed, in which some of the cobalt (Co) is replaced with nickel (Ni) and manganese (Mn). Recently, with the increasing demand for high-capacity batteries, research has been conducted into technologies to increase capacity by increasing the nickel content in NCM-based positive electrode active materials. High-nickel NCM-based positive electrode active materials containing high concentrations of nickel have excellent capacity characteristics, but suffer from poor structural stability and reduced lifespan. Therefore, a method of doping high-nickel NCM-based positive electrode active materials with Al to improve structural stability has been proposed. Conventional methods for doping NCM-based positive electrode active materials with Al have been the dry doping method, in which an aluminum-containing raw material is mixed with the cathode active material precursor and lithium raw material, followed by calcination, or the wet doping method, in which Al is doped into the precursor by coprecipitation using a metal solution containing nickel, manganese, cobalt, and aluminum during the preparation of the cathode active material precursor.

[0007] However, dry doping has the problem that aluminum (Al) is difficult to distribute uniformly within the NCM-based cathode active material, making it difficult to control doping into the lithium layer. Furthermore, in the case of aluminum (Al) wet doping, in which aluminum (Al) is doped during co-precipitation of the NCM-based cathode active material precursor, if aluminum cations are dissolved in a transition metal solution containing nickel, cobalt, and manganese cations, as in the conventional method, undesired side reactions with the anions occur, hindering the growth of the precursor or making it difficult to control the crystal orientation.

[0008] Therefore, there is a need to develop a positive electrode active material precursor and a positive electrode active material that can exhibit excellent life and resistance characteristics when applied to a lithium secondary battery. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 2017-0063418 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a positive electrode active material precursor that can significantly improve the life characteristics and resistance increase when applied to a lithium secondary battery, and a method for producing the same.

[0011] Another object of the present invention is to provide a cathode active material prepared using the cathode active material precursor, a cathode for a secondary battery including the same, and a lithium secondary battery. [Means for solving the problem]

[0012] The present invention provides a cathode active material precursor for a secondary battery, which comprises a hydroxide represented by the following chemical formula 1, wherein the cathode active material precursor is a secondary particle formed by agglomeration of a plurality of primary particles, the major axes of the primary particles are aligned in a direction from the center toward the surface of the secondary particle, and the primary particles include crystal grains whose (001) planes are aligned parallel to the major axes of the primary particles: [Chemical formula 1] Ni x1 Co y1 Mn z1 Al s1 (OH)2 In the above chemical formula 1, 0.7≦x1≦0.99, 0 <y1<0.3、0<z1<0.3、0.01≦s1≦0.1である。

[0013] The present invention also provides a method for manufacturing a cathode active material precursor for a secondary battery, the method comprising the steps of: preparing a transition metal-containing solution containing nickel (Ni), cobalt (Co), and manganese (Mn) cations; and preparing an aluminum-containing solution containing aluminum (Al) cations. The method also includes the steps of: introducing the transition metal-containing solution and the aluminum-containing solution into a reactor; and introducing a basic aqueous solution and an ammonium solution into the reactor to cause a co-precipitation reaction to form a cathode active material precursor.

[0014] The present invention also provides a method for preparing a cathode active material for a secondary battery, comprising mixing the cathode active material precursor prepared as above with a lithium source and calcining the mixture to form a lithium transition metal oxide.

[0015] The present invention also provides a positive electrode active material for a secondary battery, comprising a lithium transition metal oxide represented by the following chemical formula 2, wherein the lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the major axes of the primary particles are aligned in a direction from the center toward the surface of the secondary particle, and the primary particles include crystal grains whose (003) planes are aligned parallel to the major axes of the primary particles: [Chemical formula 2] Li a [Ni b Co c Mn d Al e ]1-f M 1 f O2 In the above chemical formula 2, M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 0.8≦a≦1.2, 0.7≦b≦0.99, 0 <c<0.3、0<d<0.3、0.01≦e≦0.1、0≦f≦0.1である。

[0016] The present invention also provides a positive electrode and a lithium secondary battery containing the positive electrode active material. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a positive electrode active material precursor that can significantly improve life characteristics and resistance increase, and a positive electrode active material prepared using the same.

[0018] Furthermore, the life and resistance characteristics of a lithium secondary battery using the positive electrode active material can be significantly improved. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a TEM image of a cross section of a positive electrode active material precursor prepared in Example 1. [Figure 2] 1 is a TEM image of a cross section of the positive electrode active material produced in Example 2. [Figure 3] 1 is an SEM image of a positive electrode active material precursor prepared in Comparative Example 1. [Figure 4] 1 is a TEM image of a cross section of the positive electrode active material prepared in Comparative Example 2. [Figure 5] 1 is a graph showing the cycle characteristics of lithium secondary batteries using the positive electrode active materials produced in Example 2 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in more detail below to facilitate understanding of the present invention. The terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms to best describe their inventions.

[0021] In the present invention, the term "crystalline" refers to a single-crystal particle unit having a regular atomic arrangement. In the present invention, the arrangement of crystal planes of crystal grains can be confirmed by analyzing a cross section of a cathode active material precursor or cathode active material particle to be measured using a transmission electron microscope (TEM). In this case, the TEM analysis can be performed using a selected area diffraction pattern (SADP) and / or a fast Fourier transform (FFT).

[0022] In the present invention, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material particle or a positive electrode active material precursor particle is observed through a transmission electron microscopy (TEM), and may consist of one crystal grain or multiple crystal grains.

[0023] In the present invention, the aspect ratio of the primary particles may be calculated by measuring the length of the minor axis and the length of the major axis of each primary particle in a TEM image of a cross section of a cathode active material precursor or a cathode active material particle, and then calculating the ratio of the measured length of the major axis to the measured length of the minor axis. The average aspect ratio may be measured by calculating an arithmetic average value of the aspect ratios of each measured primary particle.

[0024] 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. In the present invention, a Microtrac S3500 particle size analyzer was used.

[0025] In the present invention, the "particle size Dn" of the positive electrode active material means the particle size at the n% point of the volume cumulative distribution of particle size. 50 is the particle size at the 50% point of the volume cumulative distribution by particle size, and D 90 is the particle size at 90% of the volume cumulative distribution by particle size, D 10 is the particle size at the 10% point of the cumulative volume distribution by particle size. The Dn can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium (distilled water), and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500). When the particles pass through a laser beam, the difference in the diffraction pattern due to particle size is measured to calculate the particle size distribution. By calculating the particle sizes at the 10%, 50%, and 90% points of the cumulative volume distribution by particle size in the measuring device, D 10 , D 50 and D 90 can be measured.

[0026] <Positive electrode active material precursor> First, a method for producing a positive electrode active material precursor according to the present invention will be described.

[0027] The method for producing a cathode active material precursor of the present invention includes the steps of preparing a transition metal-containing solution containing nickel (Ni), cobalt (Co), and manganese (Mn) cations and an aluminum-containing solution containing aluminum (Al) cations, and adding the transition metal-containing solution and the aluminum-containing solution to a reactor, and then adding a basic aqueous solution and an ammonium solution to cause a co-precipitation reaction to form a cathode active material precursor.

[0028] The method for producing the positive electrode active material precursor will be specifically described step by step.

[0029] First, a transition metal-containing solution containing cations of nickel (Ni), cobalt (Co) and manganese (Mn) and an aluminum-containing solution containing cations of aluminum (Al) are prepared.

[0030] The transition metal-containing solution can include, for example, a nickel (Ni)-containing source material, a cobalt (Co)-containing source material, and a manganese (Mn)-containing source material.

[0031] The nickel (Ni)-containing raw material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a fatty acid nickel salt, a nickel halide, or a combination thereof.

[0032] The cobalt (Co)-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0033] The manganese (Mn)-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, the manganese (Mn)-containing raw material may be, but is not limited to, 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, manganese chloride, or a combination thereof.

[0034] The transition metal-containing solution may be prepared by adding a nickel (Ni)-containing source material, a cobalt (Co)-containing source material, and a manganese (Mn)-containing source material to a solvent, specifically, water or a mixed solvent of an organic solvent (e.g., alcohol) that is uniformly miscible with water, or by mixing an aqueous solution of the nickel (Ni)-containing source material, an aqueous solution of the cobalt (Co)-containing source material, and a manganese (Mn)-containing source material. Meanwhile, the transition metal-containing solution may contain 70 atm% to 99 atm%, 80 atm% to 98 atm%, 85 atm% to 98 atm%, or 88 atm% to 95 atm% of nickel among all transition metals.

[0035] The transition metal-containing solution may contain cobalt at more than 0 atm% and less than 0.3 atm%, 0.01 atm% or more and less than 0.2 atm%, 0.01 atm% or more and less than 0.15 atm%, or 0.01 atm% or more and less than 0.12 atm% of the total transition metals.

[0036] The transition metal-containing solution may contain manganese at more than 0 atm% and less than 0.3 atm%, 0.01 atm% or more and less than 0.2 atm%, 0.01 atm% or more and less than 0.15 atm%, or 0.01 atm% or more and less than 0.12 atm% of the total transition metals.

[0037] The aluminum (Al)-containing solution includes an aluminum (Al)-containing source material, and the aluminum (Al)-containing source material may be, for example, but is not limited to, aluminum chloride, aluminum acetate, aluminum nitrate, aluminum hydroxide, or a combination thereof.

[0038] The aluminum (Al)-containing solution may be prepared by adding an aluminum (Al)-containing raw material to a solvent, specifically, water or a mixed solvent of an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0039] Next, the transition metal-containing solution and aluminum-containing solution are respectively charged into a reactor, and then a basic aqueous solution and an ammonium solution are charged to cause a coprecipitation reaction to form a positive electrode active material precursor.

[0040] In one embodiment of the present invention, the transition metal-containing solution and the aluminum-containing solution are separately introduced into a reactor. Conventionally, when preparing an aluminum-doped cathode active material precursor, a nickel-containing raw material, a cobalt-containing raw material, a manganese-containing raw material, and an aluminum-containing raw material are all mixed together to prepare a metal aqueous solution, which is then co-precipitated to form precursor particles. However, this conventional method can result in aluminum cations reacting with anions present in the metal aqueous solution to form aluminum sulfate, which can hinder particle growth. This problem is particularly pronounced when the nickel content of the metal aqueous solution is 70 atm% or more and the aluminum content is 1 atm% or more, making it difficult to prepare a precursor of the desired size.

[0041] However, according to one embodiment of the present invention, when a transition metal-containing solution containing nickel, cobalt, and manganese and an aluminum-containing solution are separately prepared and then introduced into a reactor, the growth of precursor particles is not inhibited and the precursor particles can be grown to a desired size even when the nickel content is 70 atm% or more and the aluminum content is 1 mol% or more.

[0042] Furthermore, when a coprecipitation reaction is performed using a transition metal-containing solution and an aluminum-containing solution that are separately prepared, as in the present invention, the orientation of the primary particles and the arrangement of the crystal planes can be specified and controlled. Specifically, when a cathode active material precursor is produced by the method of the present invention, it is possible to produce a cathode active material precursor that includes crystal grains in which the major axes of the primary particles are aligned from the center toward the surface of the secondary particles and the (001) plane is aligned parallel to the major axes of the primary particles.

[0043] Meanwhile, the arrangement of primary particles and the crystalline grain structure of the positive electrode active material are affected by the arrangement of primary particles and the crystalline grain structure of the positive electrode active material precursor. When a positive electrode active material is produced using a positive electrode active material precursor having a structure in which the long axes of the primary particles are arranged in a direction from the center toward the surface of the secondary particles, i.e., a radial arrangement structure, the primary particles of the positive electrode active material are also arranged in a direction from the center toward the surface of the secondary particles. Meanwhile, because lithium ions within the positive electrode active material particles migrate along the interfaces between the primary particles, when the primary particles are arranged radially, the migration path of lithium ions within the particles is shortened, resulting in improved lithium mobility.

[0044] Meanwhile, the (001) plane of the cathode active material precursor is converted to the (003) plane after calcination. Therefore, a cathode active material manufactured using a cathode active material precursor containing crystal grains whose (001) plane is aligned parallel to the long axis of the primary particles contains crystal grains whose (003) plane is aligned parallel to the long axis of the primary particles. In lithium transition metal oxides, the (003) plane is a stable crystal plane that does not allow lithium ion insertion / extraction. When the (003) plane is aligned parallel to the long axis of the primary particles, the stable (003) plane is widely formed on the surface of the primary particles, minimizing structural degradation due to lithium ion insertion / extraction and improving life characteristics.

[0045] Meanwhile, the transition metal-containing solution and the aluminum-containing solution may be added in amounts such that the molar ratio of the total transition metals (i.e., Ni, Co, and Mn) contained in the transition metal-containing solution to the aluminum contained in the aluminum-containing solution is 0.99:0.01 to 0.90:0.10, preferably 0.99:0.01 to 0.92:0.08, and more preferably 0.99:0.01 to 0.95:0.05. When the amounts of the transition metal-containing solution and the aluminum-containing solution added satisfy the above ranges, a cathode active material precursor having a desired composition can be prepared.

[0046] Meanwhile, the ammonium solution may contain a complexing agent such as, but not limited to, NHOH, (NH)SO, NHNO, NHCl, CHCOONH, (NH)CO, or a combination thereof. Meanwhile, the ammonium solution may be used in the form of an aqueous solution, and in this case, the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0047] The basic solution may contain, as a precipitant, an alkali compound such as a hydroxide of an alkali metal or alkaline earth metal, a hydrate thereof, or a combination thereof, such as NaOH, KOH, or Ca(OH). The basic solution may also be used in the form of an aqueous solution, and in this case, the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0048] The basic compound is added to adjust the pH of the reaction solution, and the amount of the basic compound can be adjusted so that the pH of the reaction solution is maintained at 10.5 to 12.2 during the coprecipitation reaction, more preferably at 11.0 to 11.5, and even more preferably at 11.3 to 11.45.

[0049] On the other hand, the coprecipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon, and the temperature inside the reactor during the coprecipitation reaction can be 45 to 65°C, more preferably 50 to 60°C, and even more preferably 53 to 58°C.

[0050] When the pH of the reaction solution, the temperature and the atmosphere of the reactor satisfy the above conditions, the crystallinity of the precursor particles increases, the ratio of the (001) plane increases, and the effect of improving the life characteristics can be obtained.

[0051] Next, the positive electrode active material precursor according to the present invention will be described.

[0052] The cathode active material precursor according to the present invention is produced by the method of the present invention, and comprises a hydroxide represented by the following chemical formula 1, and is a secondary particle formed by agglomeration of a plurality of primary particles, the major axes of the primary particles being aligned in a direction from the center toward the surface of the secondary particle, and the primary particles including crystal grains with their (001) planes aligned parallel to the major axes of the primary particles:

[0053] [Chemical formula 1] Ni x1 Co y1 Mn z1 Al s1 (OH)2

[0054] The x1 represents the molar ratio of nickel to all metal elements in the transition metal hydroxide, and may be 0.7≦x1≦0.99, 0.8≦x1≦0.98, 0.85≦x1≦0.98, or 0.88≦x1≦0.95. When the nickel content in the transition metal hydroxide satisfies this range, a positive electrode active material having high capacity characteristics can be prepared.

[0055] The y1 represents the molar ratio of cobalt to the total metal elements in the transition metal hydroxide, and 0 <y1<0.3、0.01≦y1<0.2、0.01≦y1<0.14、または0.01≦y1<0.12であることができる。

[0056] The z1 represents the molar ratio of manganese to all metal elements in the transition metal hydroxide, and 0 <z1<0.3、0.01≦z1<0.2、0.01≦z1<0.14、または0.01≦z1<0.12であることができる。

[0057] The s1 represents the molar ratio of aluminum to all metal elements in the transition metal hydroxide, and may be 0.01≦s1≦0.1, 0.01≦s1≦0.08, or 0.01≦s1≦0.05. When the aluminum (Al) content in the transition metal hydroxide satisfies this range, cation disordering and the formation of oxygen vacancies can be suppressed during the preparation of a positive electrode active material, thereby improving the life characteristics and resistance increase rate characteristics.

[0058] Meanwhile, the positive electrode active material precursor preferably has aluminum (Al) uniformly distributed throughout the particle. That is, aluminum can be contained without a concentration gradient within the secondary particles of the positive electrode active material precursor. The uniform distribution of aluminum (Al) within the secondary particles without a concentration gradient suppresses the entanglement of aluminum (Al), minimizing capacity loss and enhancing the effects of improving life characteristics and resistance increase rate characteristics with a small amount of aluminum (Al).

[0059] Preferably, the positive electrode active material precursor of the present invention can be one in which nickel, manganese, cobalt, and aluminum are distributed at uniform concentrations throughout the secondary particles without any concentration gradient.

[0060] Meanwhile, the cathode active material precursor according to the present invention may be a secondary particle formed by agglomerating a plurality of primary particles, the major axes of the primary particles being aligned in a direction from the center toward the surface of the secondary particles. As described above, the primary particle orientation of the cathode active material exhibits the same tendency as the primary particle orientation of the cathode active material precursor. Since lithium ions within the cathode active material particles migrate along the interfaces between the primary particles, a structure in which the major axes of the primary particles are aligned in a direction from the center toward the surface of the secondary particles, i.e., a radial structure, shortens the migration path of lithium ions within the cathode active material particles, thereby improving lithium mobility.

[0061] In addition, the primary particles of the cathode active material precursor according to the present invention include crystal grains whose (001) planes are aligned parallel to the long axes of the primary particles. The (001) planes of the cathode active material precursor are converted to (003) planes after calcination, and the primary particles of the cathode active material prepared using the cathode active material precursor containing such crystal grains include crystal grains whose (003) planes are aligned parallel to the long axes of the primary particles. When the (003) planes are aligned parallel to the long axes of the primary particles, the area of ​​the (003) planes exposed at the interfaces between the primary particles increases. Because the (003) plane is a stable crystal plane that does not allow lithium ions to intercalate or deintercalate, a large external exposure of the (003) planes suppresses structural degradation of the active material due to lithium ion intercalation or deintercalation, thereby improving the lifespan characteristics.

[0062] Meanwhile, the primary particles of the positive electrode active material precursor may be columnar, and in this case, the aspect ratio of the primary particles may be 3 or more. More preferably, the aspect ratio of the primary particles of the positive electrode active material precursor may be 3 to 15, and even more preferably 5 to 8. When the aspect ratio of the primary particles of the positive electrode active material precursor satisfies the above range, it is possible to effectively shorten the lithium migration path between the inside and outside of the primary particles.

[0063] The average particle size D of the secondary particles of the positive electrode active material precursor of the present invention 50When the average particle size of the secondary particles of the positive electrode active material precursor is within this range, advantageous effects can be obtained in terms of energy density, life, and gas generation.

[0064] <Cathode active material> Next, the positive electrode active material and the method for producing the same according to the present invention will be described.

[0065] The positive electrode active material according to the present invention can be prepared by mixing the positive electrode active material precursor of the present invention and a lithium source, followed by calcining the mixture to form a lithium transition metal oxide.

[0066] The positive electrode active material precursor is as described above.

[0067] The lithium source may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium source may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CHClO1, Li2O, Li2SO4, CHClO1, or Li3C6H5O7, or a mixture of two or more of these.

[0068] After mixing the positive electrode active material precursor and the lithium source, the mixture can be fired at 730 to 830° C., more preferably at 750 to 810° C., and even more preferably at 780 to 800° C., for 5 to 20 hours, and more preferably for 8 to 15 hours, to form a lithium transition metal oxide.

[0069] On the other hand, if necessary, a doping element M 1 The raw material containing M may be further mixed. 1can be, for example, one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and the doping element M 1 The raw material containing M 1 The compound may contain acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. 1 When further mixed, M 1 The element diffuses into the lithium transition metal oxide to be doped, thereby improving the structural stability of the positive electrode active material.

[0070] The cathode active material of the present invention thus prepared comprises a lithium transition metal oxide represented by the following chemical formula 2, wherein the lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the major axes of the primary particles being aligned in a direction from the center toward the surface of the secondary particle, and the primary particles comprising crystal grains with the (003) planes aligned parallel to the major axes of the primary particles.

[0071] [Chemical formula 2] Li a [Ni b Co c Mn d Al e ] 1-f M 1 f O2

[0072] In the above chemical formula 2, M 1 is a doping element doped into the lithium transition metal oxide, and can be, for example, one or more elements selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0073] The a represents the molar ratio of lithium in the lithium transition metal oxide, and may be 0.8≦a≦1.2, 0.85≦a≦1.15, or 0.9≦a≦1.1.

[0074] The b represents the molar ratio of nickel to the total number of moles of transition metals in the lithium transition metal oxide, and may be 0.7≦b≦0.99, 0.8≦b≦0.98, 0.85≦b≦0.98, or 0.85≦b≦0.95.

[0075] The c represents the molar ratio of cobalt to the total number of moles of transition metals in the lithium transition metal oxide, and is 0 <c<0.3、0.01≦c<0.2、0.01≦c<0.14または0.01≦c<0.12であることができる。

[0076] The d represents the molar ratio of manganese to the total number of moles of transition metals in the lithium transition metal oxide, and is 0 <d<0.3、0.01≦d<0.2、0.01≦d<0.14または0.01≦d<0.12であることができる。

[0077] The e represents the molar ratio of aluminum to the total number of moles of transition metals in the lithium transition metal oxide, and may be 0.01≦e≦0.1, 0.01≦e≦0.08, or 0.01≦e≦0.05.

[0078] The f is a doping element M doped into the transition metal layer in the lithium transition metal oxide. 1 and can be 0≦f≦0.1, 0≦f≦0.05, or 0≦f≦0.03.

[0079] Meanwhile, the positive electrode active material preferably has aluminum (Al) uniformly distributed throughout the secondary particles. That is, aluminum can be contained within the secondary particles of the positive electrode active material without a concentration gradient. The uniform distribution of aluminum (Al) within the secondary particles without a concentration gradient suppresses the entanglement of aluminum (Al), minimizing capacity loss and enhancing the effects of improving life characteristics and resistance increase rate characteristics with a small amount of aluminum (Al).

[0080] Preferably, the positive electrode active material of the present invention can be one in which nickel, manganese, cobalt, and aluminum are distributed in uniform concentrations throughout the secondary particles without any concentration gradient.

[0081] Meanwhile, the cathode active material according to the present invention may be a secondary particle formed by agglomeration of a plurality of primary particles, the major axes of the primary particles being aligned in a direction from the center to the surface of the secondary particle. Since lithium ions within the cathode active material particles migrate along the interfaces between the primary particles, when the cathode active material has a structure in which the major axes of the primary particles are aligned in a direction from the center to the surface of the secondary particle, i.e., a radial structure, the migration path of lithium ions within the cathode active material particles is shortened, thereby improving lithium mobility.

[0082] In addition, the primary particles of the positive electrode active material according to the present invention include crystal grains in which the (003) plane is aligned parallel to the long axis of the primary particle. When the (003) plane is aligned parallel to the long axis of the primary particle, the area of ​​the (003) plane exposed at the interface between the primary particles is increased. Because the (003) plane is a stable crystal plane that does not allow lithium ions to be inserted or extracted, a large externally exposed area of ​​the (003) plane suppresses structural deterioration of the active material due to the insertion or extraction of lithium ions, thereby improving the life characteristics.

[0083] Meanwhile, the primary particles of the positive electrode active material may be columnar, and in this case, the aspect ratio of the primary particles may be 1.5 or more, preferably 1.5 to 10, more preferably 2.5 to 8, and even more preferably 2.5 to 5. When the aspect ratio of the primary particles of the positive electrode active material satisfies the above range, it is possible to effectively shorten the lithium migration path between the inside and outside of the primary particles.

[0084] The average particle size D of the secondary particles of the positive electrode active material of the present invention 50 When the average particle size of the secondary particles of the positive electrode active material is within this range, more advantageous effects can be obtained in terms of energy density, life, and gas generation.

[0085] <Positive electrodes and lithium secondary batteries> According to another embodiment of the present invention, there is provided a positive electrode for a secondary battery and a lithium secondary battery, each including the positive electrode active material prepared as described above.

[0086] 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.

[0087] 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. It can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0088] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material.

[0089] 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 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 contained in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0090] The binder also serves to improve 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 included in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0091] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition containing the positive electrode active material described above and, optionally, a binder and a conductive material, onto the entire positive electrode assembly, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0092] 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 the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application to fabricate a positive electrode, taking into consideration the coating thickness of the slurry and manufacturing yield.

[0093] Alternatively, the positive electrode can be produced by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0094] According to another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0095] The lithium secondary battery specifically 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, and may optionally 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.

[0096] 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.

[0097] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0098] The negative electrode active material layer includes a negative electrode active material and, optionally, a binder and a conductive material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode-forming composition including the negative electrode active material and, optionally, the binder and the conductive material to a negative electrode current collector and drying the composition, or by casting the negative electrode-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0099] 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 Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are 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.

[0100] The binder and conductive material may be the same as those described above for the positive electrode.

[0101] 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 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.

[0102] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel 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.

[0103] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0104] 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), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents 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 low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries. In this case, the electrolyte exhibits excellent performance when the cyclic carbonate and linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9.

[0105] 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(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt is preferably used in a concentration range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0106] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0107] 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 the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0108] 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.

[0109] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0110] 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.

[0111] Example 1 After adding 4 L of distilled water to a 20 L reactor, the temperature was maintained at 58°C. A 2.29 mol / L transition metal solution (NiSO4, CoSO4, and MnSO4 mixed in a nickel:cobalt:manganese molar ratio of 88:5:7) was added at 500 mL / hr, and a 1.145 mol / L Al(NO3)3 solution was added at 20 mL / hr. A 9 wt% ammonia solution was also added at 510 mL / hr. A 15 wt% sodium hydroxide solution was then added at 306 mL / hr, adjusting the rate of the sodium hydroxide solution to maintain a pH of 11.4.

[0112] Nucleation was performed by stirring at 600 rpm for the first 30 minutes, and then the particles were grown by stirring at 250-600 rpm. After the coprecipitation reaction for 20 hours, when the batch reactor was filled, the stirring was stopped and the precursor particles were precipitated. The supernatant was removed, leaving 4 L of the reaction product, and the reaction was resumed. The reaction was continued for a total of 40 hours to form precursor particles. The precursor particles were separated and washed with water, then dried in a hot air dryer at 130°C for 12 hours or more, crushed, and sieved to obtain Ni. 0.86 Co 0.05 Mn 0.07 Al 0.02 A positive electrode active material precursor having the composition (OH)2 was prepared.

[0113] Example 2 The positive electrode active material precursor prepared in Example 1, LiOH, and ZrO were mixed so that the molar ratio of (Ni + Co + Mn + Al):Li:Zr was 1:1.07:0.0015, and the mixture was calcined at 790°C for 10 hours in an oxygen atmosphere to prepare a positive electrode active material doped with 1,500 ppm of Zr and having a molar ratio of Ni:Co:Mn:Al of 86:5:7:2.

[0114] Comparative Example 1 After adding 4 L of distilled water to a 20 L reactor, the temperature was maintained at 58°C. A 2.29 mol / L transition metal aqueous solution containing NiSO4, CoSO4, MnSO4, and AlSO4 mixed to a nickel:cobalt:manganese:aluminum molar ratio of 86:5:7:2 was added to the reactor at 500 mL / hr, and a 9 wt% ammonia aqueous solution was continuously added to the reactor at 510 mL / hr. Then, a 15 wt% sodium hydroxide aqueous solution was added at 306 mL / hr, and the sodium hydroxide aqueous solution addition was adjusted to maintain a pH of 11.4.

[0115] Nucleation was performed by stirring at 600 rpm for the first 30 minutes, and then the particles were grown by stirring at 250-600 rpm. After the coprecipitation reaction for 20 hours, when the batch reactor was filled, the stirring was stopped and the precursor particles were precipitated. The supernatant was removed, leaving 4 L of the reaction product, and the reaction was resumed. The reaction was continued for a total of 40 hours to form precursor particles. The precursor particles were separated and washed with water, then dried in a hot air dryer at 130°C for 12 hours or more, crushed, and sieved to obtain Ni. 0.86 Co 0.05 Mn 0.07 Al 0.02 A positive electrode active material precursor having the composition (OH)2 was prepared.

[0116] Comparative Example 2 After adding 4 L of distilled water to a 20 L reactor, the temperature was maintained at 58°C. A 2.29 mol / L transition metal aqueous solution, which was a mixture of NiSO4, CoSO4, and MnSO4 in a nickel:cobalt:manganese molar ratio of 88:5:7, was added to the reactor at 510 mL / hr. A 9 wt% ammonia aqueous solution was also continuously added to the reactor at 510 mL / hr. A 15 wt% sodium hydroxide aqueous solution was then added at 306 mL / hr, and the sodium hydroxide aqueous solution addition was adjusted to maintain a pH of 11.4.

[0117] Nucleation was performed by stirring at 600 rpm for the first 30 minutes, and then the particles were grown by stirring at 250-600 rpm. After the coprecipitation reaction for 20 hours, the batch reactor was filled with the precursor particles, and the stirring was stopped. After removing the supernatant liquid, leaving 4 L of the reaction product, the reaction was restarted. After a total of 40 hours of reaction, Ni 0.88 Co 0.05 Mn 0.07 Precursor particles were formed with a composition of (OH)2.

[0118] The prepared cathode active material precursor, LiOH, Al2O3, and ZrO2 were mixed so that the molar ratio of (Ni+Co+Mn):Li:Al:Zr was 1:1.07:0.02:0.0015, and calcined at 770°C for 10 hours in an oxygen atmosphere to prepare a cathode active material doped with 1,500 ppm of Zr and having a molar ratio of Ni:Co:Mn:Al of 86:5:7:2.

[0119] [Experimental Example 1: Confirmation of Positive Electrode Active Material Precursor and Positive Electrode Active Material] Transmission electron microscope (TEM) analysis was performed to measure the crystal structure and primary particle aspect ratio of the positive electrode active material precursors and positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 and 2. The TEM analysis was performed using selected area diffraction patterns (SADP) and fast Fourier transform (FFT).

[0120] The results are shown in Figures 1 to 4.

[0121] Figure 1 is a TEM image of a cross section of the cathode active material precursor prepared in Example 1. As shown in Figure 1, the cathode active material precursor of Example 1 had Al uniformly distributed throughout the particles, and the long axes of the primary particles were aligned from the center toward the surface of the secondary particles.

[0122] In addition, the length of the short axis and the length of the long axis of the primary particles were measured by TEM image analysis to calculate the aspect ratio of the primary particles, and the average aspect ratio of the measured primary particles was 6.7.

[0123] Furthermore, the crystal grain structure was confirmed by SADP, and it was confirmed that the (001) plane was aligned parallel to the long axis of the primary particles. The direction of the (001) plane is indicated by the arrow.

[0124] Figure 2 is a TEM image of a cross section of the cathode active material prepared in Example 2. As shown in Figure 2, in the cathode active material of Example 2, Al was uniformly distributed throughout the secondary particles, and the long axes of the primary particles were aligned from the center toward the surface of the secondary particles.

[0125] In addition, the length of the short axis and the length of the long axis of the primary particles were measured by TEM image analysis to calculate the aspect ratio of the primary particles, and the aspect ratio of the measured primary particles was found to be 3.2 on average.

[0126] Furthermore, the crystal grain structure was confirmed by SADP, and the (003) plane was found to be aligned parallel to the long axis of the primary particles. The direction of the (003) plane is indicated by the arrow.

[0127] FIG. 3 is an SEM image of the cathode active material precursor prepared in Comparative Example 1. As shown in FIG. 3, the cathode active material precursor of Comparative Example 1 shows the presence of small NCM seed-shaped particles and Al and sulfur compounds. In addition, even after 40 hours of reaction, the secondary particles D 50 It is clear that the grain size was 5 μm or less, and that almost no grain growth occurred.

[0128] Figure 4 is a TEM image of a cross section of the cathode active material prepared in Comparative Example 2. As shown in Figure 4, in the cathode active material of Comparative Example 2, Al was uniformly distributed throughout the secondary particles, and the long axes of the primary particles were aligned from the center toward the surface of the secondary particles.

[0129] In addition, the length of the short axis and the length of the long axis of the primary particles were measured by TEM image analysis to calculate the aspect ratio of the primary particles, and the average aspect ratio of the measured primary particles was 2.4.

[0130] Furthermore, the crystal grain structure was confirmed by SADP, and it was confirmed that the (003) plane was distributed in various directions. The direction of the (003) plane is indicated by the arrow.

[0131] [Experimental Example 2: Lifetime characteristics, resistance increase rate characteristics] The positive electrode active materials prepared in Example 2 and Comparative Example 2, the carbon black conductive material, and the PVdF binder were mixed in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2 to prepare a positive electrode mixture. The mixture was applied to one side of an aluminum current collector, dried at 100°C, and rolled to prepare a positive electrode.

[0132] The negative electrode used was lithium metal.

[0133] An electrode assembly was fabricated by interposing a porous polyethylene separator between the cathode and anode fabricated as described above, and the electrode assembly was placed inside a case. An electrolyte solution was then injected into the case to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (EC / EMC / DEC mixed in a volume ratio of 3 / 4 / 3).

[0134] Each lithium secondary battery cell thus fabricated was charged at 45°C at a constant current of 1 C to 4.25 V with a 3 C cutoff. It was then discharged at a constant current of 0.33 C to 3.0 V. This charge and discharge behavior constitutes one cycle. This cycle was repeated 100 times, and the capacity retention and resistance increase rates with each cycle were measured. The capacity retention rate was calculated by dividing the capacity at the 100th cycle by the initial capacity and multiplying by 100. The resistance increase rate was calculated by dividing the resistance at the 100th cycle by the initial resistance and multiplying by 100. The results are shown in Table 1 and Figure 5.

[0135] [Table 1]

[0136] Referring to Table 1 and FIG. 5, the positive electrode active material of Example 2 was significantly superior in the capacity retention rate and resistance increase rate, while the positive electrode active material of Comparative Example 2 prepared by Al dry doping was inferior in the capacity retention rate and resistance increase rate.

Claims

1. A positive electrode active material precursor comprising a hydroxide represented by the following chemical formula 1: the positive electrode active material precursor is a secondary particle formed by agglomeration of a plurality of primary particles, the primary particles are cylindrical, the major axes of the primary particles are aligned in a direction from the center to the surface of the secondary particles, the primary particles include crystal grains whose (001) planes are arranged parallel to the long axes of the primary particles, The positive electrode active material precursor is a positive electrode active material precursor for a secondary battery, in which aluminum (Al) is uniformly distributed in the secondary particles without a concentration gradient: [Chemical formula 1] Ni ｘ１ Co ｙ１ Mn ｚ１ Al ｓ１ (OH) ２ In the above Chemical Formula 1, 0.7≦x1≦0.99, 0<y1<0.3, 0<z1<0.3, and 0.01≦s1≦0.

1.

2. The positive electrode active material precursor for a secondary battery according to claim 1 , wherein the primary particles have an aspect ratio of 3 or more.

3. 3. The positive electrode active material precursor for a secondary battery according to claim 1, wherein the primary particles have an aspect ratio of 3 to 15.

4. 4. The positive electrode active material precursor for a secondary battery according to claim 1, wherein, in Chemical Formula 1, 0.85≦x1≦0.98, 0.01≦y1<0.14, and 0.01≦z1<0.

14.

5. 5. The positive electrode active material precursor for a secondary battery according to claim 1, wherein nickel, manganese, cobalt, and aluminum are distributed at uniform concentrations throughout the secondary particles without any concentration gradient.

6. 6. The positive electrode active material precursor for a secondary battery according to claim 1, wherein the positive electrode active material precursor has an average secondary particle size D50 of 3 μm to 20 μm.

7. It contains a lithium transition metal oxide represented by the following chemical formula 2: The lithium transition metal oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the primary particles are cylindrical, the major axes of the primary particles are aligned in a direction from the center to the surface of the secondary particles, the primary particles include crystal grains whose (003) planes are arranged parallel to the long axes of the primary particles, a positive electrode active material for a secondary battery, wherein aluminum is distributed at a uniform concentration throughout the secondary particles without a concentration gradient within the secondary particles; [Chemical formula 2] Li ａ [Ni ｂ Co ｃ Mn ｄ Al ｅ ] １－ｆ M １ ｆ O ２ In Chemical Formula 2, M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8≦a≦1.2, 0.7≦b≦0.99, 0<c<0.3, 0<d<0.3, 0.01≦e≦0.1, and 0≦f≦0.

1.

8. The positive electrode active material for a secondary battery according to claim 7 , wherein the primary particles have an aspect ratio of 1.5 or more.

9. 9. The positive electrode active material for a secondary battery according to claim 7, wherein, in Chemical Formula 2, 0.85≦b≦0.98, 0.01≦c<0.14, and 0.01≦d<0.

14.

10. 10. The positive electrode active material for a secondary battery according to claim 7, wherein nickel, manganese, and cobalt are distributed at uniform concentrations throughout the secondary particles without any concentration gradient.

11. The positive electrode active material according to any one of claims 7 to 10, wherein the positive electrode active material has an average particle size D50 of secondary particles of 3 µm to 20 µm.

12. A positive electrode for a secondary battery, comprising the positive electrode active material according to claim 7 .

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

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