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

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing nickel (Ni) and manganese (Mn), and which is composed of single particles and has a crystal defect rate of less than 3%.

Description

[Technical Field]

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

[0002] In developing layered cathode materials for secondary batteries, attempts have been made to increase the nickel content. The reason for this is that using nickel with a higher specific gravity increases usable capacity within a certain charge / discharge voltage range. It also has advantages in terms of raw material supply and demand compared to cobalt, a typical alternative element. For example, two-thirds of the world's cobalt is mined in the Democratic Republic of the Congo. The ethical issues surrounding human rights and environmental protection during this mining process have become a driving force behind the movement to replace cobalt and expand nickel use.

[0003] For these reasons, layered composite oxides having a high nickel content are increasingly being used as cathode materials for lithium secondary batteries, and efforts are ongoing to realize secondary batteries with better life characteristics.

[0004] For example, nickel-based lithium composite oxide cathode materials, which have been widely used until now, have a secondary particle structure consisting of primary particles several hundred nanometers in size. However, such secondary particle cathode materials have a problem in that fine cracks develop between the primary particles as they are repeatedly charged and discharged, resulting in a deterioration in their lifespan. To solve this problem, there has been extensive development into materials with a single particle structure, in which the primary particles are primarily independent, rather than the secondary particle structure, which is an agglomeration of primary particles.

[0005] The most common method for synthesizing single-particle active materials involves sintering at temperatures above 850°C to enhance the growth of primary particles. However, such high-temperature sintering can pose serious problems when synthesizing high-nickel layered-structure composite oxides. Specifically, layered-structure cathode materials have well-defined "layers" composed of charge-carrying elements such as lithium and "layers" composed primarily of transition metal elements such as nickel and cobalt. A well-formed "layered structure" ensures smooth charge and discharge. However, when a high-temperature synthesis environment is created with a high nickel content, nickel tends to occupy the sheets within the "layers" composed of charge-carrying elements. If these crystallographic defects become severe, this can lead to reduced usable capacity and other performance degradation as a positive electrode material. This problem becomes more severe as the sintering temperature increases, making it difficult to realize single-particle active materials with individual primary particles larger than 2 μm in average size using high-nickel systems. Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above-mentioned problems, one object of the present invention is to provide a single-particle positive electrode active material that not only has a large particle size but also has excellent crystallinity.

[0007] Another object of the present invention is to provide a method for producing a single-particle positive electrode active material having the above-mentioned advantages.

[0008] It is still another object of the present invention to provide a lithium secondary battery including the positive electrode active material. [Means for solving the problem]

[0009] To achieve the above-mentioned object, one embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing nickel (Ni) and manganese (Mn), wherein the lithium transition metal oxide is composed of single particles and has a crystal defect rate of less than 3%.

[0010] The average particle size (Davg) of the single particles may be 2.5 μm or more.

[0011] The ratio of the average particle size (Davg) of the single particles to the crystal defect rate of the positive electrode active material may be 1 μm / % or more.

[0012] The positive electrode active material can satisfy the following formula 1. <Expression 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / ℃) In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.

[0013] The positive electrode active material for a lithium secondary battery may be detected by ICP component analysis to contain K, Li, Na, Rb, Cs, Fr, or a combination thereof, and the detected amount may be 50 ppm or more.

[0014] The positive electrode active material for a lithium secondary battery may have a Cl content of less than 50 ppm when analyzed by ICP.

[0015] The lithium transition metal oxide may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a (Ni b Me 1-b )O2 In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦b≦0.99, and Me is Co, Mn, Al, Zr, Nb, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, Fe, or a combination thereof.

[0016] In this case, B may be in the range of 0.9≦b≦0.99.

[0017] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, the method comprising: forming a mixture containing a positive electrode active material precursor including nickel and manganese and a particle growth agent; calcining the mixture to form a lithium transition metal oxide; and crushing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles.

[0018] The particle growth agent may be a hydroxide.

[0019] The grain growth agent can be lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH), francium hydroxide (FrOH), or a combination thereof.

[0020] In the step of forming the mixture, the particle growth agent may be mixed in an amount of 0.1 to 99 wt % based on the total weight of the mixture.

[0021] The firing may be carried out at a temperature of 740 to 850°C.

[0022] The baking may be carried out for 2 to 36 hours.

[0023] At this time, the positive electrode active material for a lithium secondary battery prepared by the above preparation method may satisfy the following formula 1. <Expression 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / ℃) In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.

[0024] In the step of forming the mixture, a doping source material may be further mixed, and the doping source material may be a compound containing one or more of Zr, Nb, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

[0025] The method may further include a heat treatment step after the step of crushing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles.

[0026] The heat treatment can be carried out at a temperature of 250 to 750°C.

[0027] The heat treatment can be carried out for 2 to 24 hours.

[0028] Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material.

[0029] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode. [Effects of the Invention]

[0030] The single particle positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has a low crystal defect rate and a sufficiently large average particle size, and therefore, when used to manufacture a lithium secondary battery, a high energy density can be achieved.

[0031] In another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery may include applying a particle growth agent to lower a firing temperature for synthesizing a lithium transition metal oxide, thereby increasing the average particle size of the single-particle positive electrode active material and simultaneously reducing the crystal defect rate. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graph showing the results of thermal analysis during the synthesis of lithium transition metal oxide, showing the weight loss curve of the reactants due to an increase in temperature when KOH is not used and the weight loss curve of the reactants due to an increase in temperature when KOH is used. [Figure 2] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 1. [Figure 3] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 2. [Figure 4] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 3. [Figure 5] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared according to Comparative Example 1. [Figure 6] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared according to Comparative Example 2. [Figure 7] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared according to Comparative Example 3. [Figure 8] 1 shows a scanning electron microscope (SEM) image of the positive electrode active material prepared in Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0033] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0034] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0035] When a part is referred to as being "on" another part, it means that it is directly on top of the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0036] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0037] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0038] In this specification, the term "combination thereof" used in a Markush expression means a mixture or combination of one or more elements selected from the group of elements described in the Markush expression, and means including any one or more elements selected from the group of elements.

[0039] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily practice the present invention. However, as the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0040] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a lithium transition metal oxide containing nickel (Ni) and manganese (Mn), wherein the lithium transition metal oxide is composed of single particles and has a crystal defect rate of less than 3%.

[0041] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single particles.

[0042] More specifically, the positive electrode active material may be classified into ungranulated primary particles or secondary particles formed by agglomeration of a plurality of primary particles, depending on whether or not the primary particles, which are unit particles, are granulated. In this regard, the positive electrode active material according to the present invention is composed of ungranulated primary particles, i.e., single particles.

[0043] As the positive electrode active material is composed of single particles, it can solve the problems of secondary particles, namely, the high risk of side reactions with the electrolyte due to a large specific surface area, and the problems of poor structural stability and deterioration of life characteristics due to the occurrence of fine cracks between primary particles as charging and discharging are repeated.

[0044] In addition, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has a crystal defect rate of less than 3%.

[0045] In this specification, the crystal defect rate refers to the ratio of nickel to a sheet of a charge-carrying element such as lithium in a layered cathode material. This crystal defect rate can be calculated from XRD diffraction analysis data using the Rietveld refinement method.

[0046] More specifically, layered cathode materials made of nickel-based transition metal oxides are divided into layers consisting of charge-carrying elements such as lithium and layers primarily composed of transition metal elements such as nickel and cobalt. When this layered structure is properly formed, battery charging and discharging is smooth. The most common method for synthesizing single-particle cathode materials is by firing at temperatures above 850°C to increase the growth of primary particles. However, firing a precursor with a high nickel content at high temperatures can result in crystallographic defects (i.e., reduced crystallinity) as nickel occupies the sheets within the layers composed of the charge-carrying element, i.e., lithium, which can reduce battery capacity and other performance.

[0047] The single particle cathode active material according to the present invention has a sufficiently large average particle size and a crystal defect rate of less than 3% (i.e., excellent crystallinity) due to the application of a particle growth agent that enables low-temperature sintering while increasing the particle size of the single particles during the manufacturing process, as described below. Therefore, when a lithium secondary battery is manufactured using the same, the battery has excellent capacity and initial efficiency.

[0048] The average particle size (Davg) of the positive electrode active material may be 2.5 μm or more, more specifically, 3 μm, 4 μm, 5 μm, 6 μm, or 6.5 μm or more.

[0049] In this specification, the average particle size (Davg) refers to the average value of a total of 50 values ​​obtained by measuring the horizontal and vertical particle sizes of 25 primary particles on a scanning electron microscope (SEM) analysis image. In the examples herein, the measurements were performed manually by an analyst using image analysis software, but by using a similar principle to automate particle size measurement and statistics within an image, more accurate and reliable particle size values ​​can be calculated.

[0050] Since the average particle diameter (Davg) of the single-particle positive electrode active material is sufficiently large, the particle strength is increased, which can suppress particle breakage during rolling, thereby improving the rolling density. Furthermore, since the specific surface area is reduced and lithium by-products are reduced, the amount of gas generated by side reactions with the electrolyte is reduced, thereby improving the lifespan. Furthermore, the lithium secondary battery can have excellent capacity and initial efficiency.

[0051] In particular, the ratio of the average particle diameter (Davg) of the positive electrode active material to the crystal defect rate may be 1 μm / % or more, more specifically, 1.5 μm / %, 2.0 μm / %, or 2.5 μm / % or more. The ratio of the average particle diameter (Davg) of the positive electrode active material to the crystal defect rate is a variable that can comprehensively evaluate the degree to which the crystal defect rate is low and the degree to which the average particle diameter is large. If this variable is too small, it means that the average particle diameter is too small or the crystal defect rate is too high, which can result in reduced capacity and initial efficiency of the lithium secondary battery, reduced rolling density, increased gas generation due to side reactions with the electrolyte, and reduced lifespan.

[0052] Moreover, the positive electrode active material can satisfy the following formula 1. <Expression 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / ℃) In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.

[0053] More specifically, the value of the formula 1 may be 5, 6, 7, or greater than 8. If the value of the formula 1 is too small, it means that the average particle size is too small or the sintering temperature is too high, which may result in a decrease in the capacity and initial efficiency of the lithium secondary battery, a decrease in rolling density, an increase in the amount of gas generated due to side reactions with the electrolyte, and a shortened lifespan.

[0054] Meanwhile, the cathode active material according to the present invention may contain K, Li, Na, Rb, Cs, Fr, or a combination thereof, which may be detected by ICP element analysis, by using a particle growth agent during the manufacturing process, as described below.

[0055] In this case, the detectable amount may be 50, 100, 200, 400, 600, or 800 ppm or more, and may be 3000, 2500, or 2000 ppm or less.

[0056] In addition, the positive electrode active material according to the present invention can be detected with a low Cl content of less than 50 ppm by ICP analysis, which is a result of using hydroxide instead of chloride as a particle growth agent during the manufacturing process of the active material, as will be described later.

[0057] The lithium transition metal oxide can be represented by the following Formula 1: [Chemical formula 1] Li a (Ni b Me 1-b )O2 In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦b≦0.99, and Me is Co, Mn, Al, Zr, Nb, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, Fe, or a combination thereof.

[0058] 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.

[0059] The b represents the molar ratio of nickel to the total moles of transition metals in the lithium transition metal oxide, and may be 0.60≦b≦0.99, 0.70≦b≦0.99, 0.80≦b≦0.99, 0.85≦b≦0.99, 0.90≦b≦0.99, or 0.90≦b≦0.95. When the nickel content in the lithium transition metal oxide satisfies this range, a positive electrode active material and a lithium secondary battery having high capacity characteristics can be manufactured.

[0060] In particular, b may be in the range of 0.9≦b≦0.99. In other words, the nickel content may be 90 mol% or more based on the total moles of transition metals. Generally, high-nickel single particle cathode materials with a high nickel content are synthesized by high-temperature sintering to increase the particle size, resulting in reduced crystallinity. However, the cathode active material according to the present invention can have all of a high nickel content, a large average particle size, and excellent crystallinity by applying a particle growth agent during production, as described below.

[0061] Meanwhile, the positive electrode active material may further include a coating layer located on a surface of the lithium transition metal oxide, and the coating layer may include Co, Al, Ti, W, B, F, P, Mg, Ni, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, S, or a combination thereof.

[0062] The coating layer may have a thickness of 1 nm to 100 nm.

[0063] 2. Manufacturing method of positive electrode active material Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, the method comprising: forming a mixture containing a positive electrode active material precursor including nickel and manganese and a particle growth agent; calcining the mixture to form a lithium transition metal oxide; and crushing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles.

[0064] Hereinafter, a method for preparing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described in detail step by step.

[0065] First, a mixture containing a positive electrode active material precursor containing nickel and manganese and a particle growth agent is formed.

[0066] By mixing a particle growth agent with a cathode active material precursor, the average particle size of the single-particle cathode active material can be increased. Because particle growth promotion by a particle growth agent occurs in a synthesis environment above a certain temperature, the intended effect can be achieved regardless of the stage of the process in which the agent is added to the raw materials, as long as it is added before the synthesis condition application process. Furthermore, it enables low-temperature sintering, reducing the crystal defect rate of the single-particle cathode active material (i.e., achieving excellent crystallinity of the single-particle cathode active material).

[0067] The particle growth agent may be a hydroxide. Generally, the cathode active material precursor and lithium source material that are frequently used in the manufacture of active materials are hydroxides. When a hydroxide is used as a particle growth agent, (OH) - It is advantageous to form a eutectic mixture containing the active material precursor and the lithium source material. In addition, the active material precursor and the lithium source material, which are reactants, and the lithium transition metal oxide, which is the product, are not heterogeneous with SO4 2- , Cl - Since it does not contain anions such as HCl, it dissolves reactants more easily and promotes the transfer of substances.

[0068] For example, the grain growth agent can be, but is not limited to, lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH), francium hydroxide (FrOH), or a combination thereof.

[0069] In particular, the particle growth agent may be potassium hydroxide (KOH). Figure 1 is a graph showing the results of thermal analysis during the synthesis of lithium transition metal oxides, showing the reactant weight loss curves with increasing temperature when KOH is not used and when KOH is used. Referring to Figure 1, potassium hydroxide has a low melting point of 360°C, which accelerates the temperature change of raw materials during the synthesis of lithium transition metal oxides, thereby enabling low-temperature firing. Furthermore, KOH tends to decompose into K2O and H2O when heated, and the melting point of K2O is known to be 740°C. This is the synthesis temperature level for typical Ni-based layered cathode materials, and the melting point may be further lowered by the addition of other components that can form a eutectic, such as Li2O. This is presumably to lower the synthesis temperature and facilitate smooth particle growth at low temperatures.

[0070] The particle growth agent may be added in an amount of 0.1 to 99 wt %, more specifically, 1 to 20 wt % or 5 to 15 wt %, based on the total weight of the mixture. By adding the particle growth agent in this range, the average particle size of the single-particle cathode active material can be effectively increased, and the synthesis temperature for achieving the desired cathode material shape can be lowered, thereby contributing to a reduction in the crystal defect rate. While the effect of particle growth agent increase can be greater with increasing amounts, excessively increasing the amount can adversely affect the production efficiency of the cathode material. Therefore, it is necessary to determine the optimal flux ratio taking into account the overall circumstances of cathode material production.

[0071] In particular, the positive electrode active material according to the present invention may contain K, Li, Na, Rb, Cs, Fr, or a combination thereof, which may be detected by ICP analysis due to the use of the particle growth agent in the manufacturing process. Further details regarding this will be omitted as they have been described above.

[0072] The positive electrode active material precursor may be a non-lithium precursor that does not contain lithium, or may be a precursor that contains lithium.

[0073] When the positive electrode active material precursor is a non-lithium precursor, it may be, for example, a hydroxide containing nickel and manganese. Such a positive electrode active material precursor may be represented by the following Chemical Formula 2:

[0074] [Chemical formula 2] Ni x2 Co y2 Mn z2 (OH)2 In the above Chemical Formula 2, 0.6≦x2≦0.99, 0≦y2≦0.3, 0 <z2≦0.3であり、x2+y2+z2=1である。

[0075] Said x2 represents the molar ratio of nickel in the total metal elements in the transition metal hydroxide, and can be 0.6 ≦ x2 ≦ 0.99, 0.7 ≦ x2 ≦ 0.99, 0.80 ≦ x2 ≦ 0.99, 0.85 ≦ x2 ≦ 0.99, 0.90 ≦ x2 ≦ 0.99 or 0.90 ≦ x2 ≦ 0.95. When the nickel content in the transition metal hydroxide satisfies the above range, a positive electrode active material having high capacity characteristics and a lithium secondary battery can be manufactured.

[0076] Said y2 represents the molar ratio of cobalt in the total metal elements in the transition metal hydroxide, and can be 0 ≦ y2 ≦ 0.3, 0.01 ≦ y2 ≦ 0.2, 0.01 ≦ y2 ≦ 0.1, 0.02 ≦ y2 ≦ 0.08 or 0.02 ≦ y2 ≦ 0.06.

[0077] Said z2 represents the molar ratio of manganese in the total metal elements in the transition metal hydroxide, and can be 0 < z2 ≦ 0.3, 0.01 ≦ z2 ≦ 0.2, 0.01 ≦ z2 ≦ 0.1, 0.02 ≦ z2 ≦ 0.08 or 0.02 ≦ z2 ≦ 0.06.

[0078] Also, when the positive electrode active material precursor is a non-lithium precursor, a lithium raw material substance can be mixed together at the stage of forming the mixture.

[0079] The lithium raw material substance can be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halogen compound, hydroxide or oxyhydroxide, etc., and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material substance can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, C2H3LiO2, Li2O, Li2O2, Li2SO4, Li2SO3, Li3C6H5O7 or a combination thereof, but is not limited thereto.

[0080] At the stage of forming the mixture, a doping raw material substance can be further mixed.

[0081] The doping source material may be a compound containing one or more of Nb, Zr, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

[0082] The mixture is then calcined to form the lithium transition metal oxide.

[0083] In particular, the sintering may be performed at a temperature of 740 to 850°C. In other words, by using the particle growth agent as described above, sintering can be performed at a temperature lower than the general sintering temperature when producing a single particle positive electrode active material. If the sintering temperature is too high, the crystal defect rate of the positive electrode active material may increase, while if the sintering temperature is too low, the positive electrode active material may not have a sufficient particle size.

[0084] The firing may be divided into a first firing and a second firing, if necessary.

[0085] More specifically, the primary firing is performed at a temperature of 800 to 850°C in the early stage of firing to highly promote particle growth, and the secondary firing is performed at a temperature of 250 to 800°C in the later stage of firing to induce crystal recovery, in other words, a reduction in the crystal defect rate.

[0086] The calcination may be carried out for 2 to 36 hours, more specifically, for 5 to 15 hours. If the calcination time is too short, the synthesis reaction may not be completed or the crystal structure may not be sufficiently developed, whereas if the calcination time is too long, productivity may be reduced.

[0087] The firing may be performed in an oxygen atmosphere. When a high-Ni-content (Ni-rich) positive electrode active material is fired at a high temperature for a long time, Ni is deposited in the lithium layer in a layered crystalline structure during the firing process. 2+In order to prevent this, it is preferable to synthesize the positive electrode active material in an oxygen atmosphere.

[0088] Next, the lithium transition metal oxide is crushed to form a lithium transition metal oxide composed of single particles.

[0089] The crushing step can break down the agglomerations of the synthesized lithium transition metal oxide to form a lithium transition metal oxide composed of single particles.

[0090] The crushing method is not particularly limited and may be performed by a common crushing method in the art, for example, a jet mill process.

[0091] At this time, the positive electrode active material for a lithium secondary battery prepared by the above preparation method may satisfy the following formula 1.

[0092] <Expression 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / ℃) In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.

[0093] More specifically, the value of the formula 1 may be equal to or greater than 5, 6, 7, or 8. The advantages of satisfying this condition have been described above and will not be repeated here.

[0094] After the step of forming the lithium transition metal oxide composed of single particles, the method may further include the steps of washing and filtering the lithium transition metal oxide.

[0095] The water washing is performed to remove particle growth agent residues and residual lithium present on the surface of the positive electrode active material. More specifically, lithium transition metal oxides containing a high concentration of nickel are structurally unstable compared to lithium transition metal oxides with a low nickel content, resulting in the generation of more lithium by-products, such as unreacted lithium hydroxide and lithium carbonate, during the manufacturing process. If a large amount of lithium by-products is present in the positive electrode active material, the lithium by-products may react with the electrolyte, resulting in gas generation and expansion, which significantly reduces high-temperature stability. Therefore, a water washing process may be performed to remove the lithium by-products from the lithium transition metal oxide containing a high concentration of nickel.

[0096] The washing method is not particularly limited, and can be carried out by a method generally known in the art as long as the performance is not deteriorated.

[0097] Specifically, the water washing can be carried out by adding the lithium composite transition metal oxide to a washing solution such as distilled water or tap water and stirring the mixture. The temperature of the washing solution used in the water washing can be 1°C to 80°C, more preferably 5°C to 50°C, and the water washing time can be 3 minutes to 60 minutes, more preferably 5 minutes to 40 minutes. When the temperature of the washing solution and the water washing time are within the above ranges, residual lithium on the surface of the lithium transition metal oxide can be effectively removed.

[0098] The filtration is performed to separate the lithium transition metal oxide from the solid phase lithium transition metal oxide in the mixture of the washing solution during the washing process.

[0099] After the washing and filtering steps, a drying step may be further included.

[0100] The drying is performed to remove the residual lithium and remove the remaining moisture from the solid-phase separated lithium transition metal oxide.

[0101] The drying method is not particularly limited, and can be performed by a method commonly known in the art as long as the drying does not deteriorate the performance. For example, the drying can be performed by a vacuum drying method.

[0102] At this time, the drying may be performed at a temperature of 110 to 170°C, more specifically, at a temperature of 120 to 160°C.

[0103] The drying may be carried out for 2 to 24 hours, more specifically for 8 to 16 hours.

[0104] Next, a step of heat treatment may be further included.

[0105] The heat treatment has the advantage of restoring the chemical structure of the surface of the cathode material that is damaged during the water washing process.

[0106] The heat treatment may be performed at a temperature of 250 to 800° C. If the heat treatment temperature is too low, the chemical structure of the surface of the cathode material may not be properly restored, whereas if the heat treatment temperature is too high, the crystallinity may be damaged.

[0107] The heat treatment may be performed for 2 to 24 hours, more specifically, for 4 to 18 hours or 5 to 12 hours. If the heat treatment time is too short, the desired effect may not be fully achieved, whereas if the heat treatment time is too long, productivity of the cathode material may be adversely affected.

[0108] The heat treatment may be carried out in an oxygen atmosphere.

[0109] 3.Positive electrode Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material. The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material described above.

[0110] The positive electrode current collector is not particularly limited as long as it does not induce 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. In addition, the positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0111] The positive electrode active material layer may optionally contain a binder and / or a conductive agent in addition to the positive electrode active material.

[0112] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0113] The conductive agent is used to impart conductivity to the electrode and can be any material that has electronic conductivity that does not undergo chemical changes in the resulting battery. 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 agent is typically present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0114] The positive electrode can be produced by a conventional method for producing a positive electrode. Specifically, the positive electrode may be fabricated by coating a positive electrode active material layer-forming composition containing a positive electrode active material and, optionally, a binder, a conductive agent, or a solvent on a positive electrode current collector, followed by drying and rolling. The types and amounts of the positive electrode active material, binder, and conductive agent are as described above.

[0115] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is determined in consideration of the coating thickness of the slurry and the production yield, and is sufficient to dissolve or disperse the cathode active material, conductive agent, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a cathode.

[0116] Alternatively, the positive electrode may be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0117] 4. Lithium secondary batteries Another embodiment of the present invention provides a lithium secondary battery including the above-described positive electrode. In particular, the lithium secondary battery according to the present invention may have an initial charge capacity of 240 mAh / g or 245 mAh / g or more, an initial discharge capacity of 195 mAh / g or 199 mAh / g or more, and an initial efficiency of 80% or more.

[0118] More specifically, the lithium secondary battery may include the above-described positive electrode; a negative electrode facing the positive electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0119] The lithium secondary battery may further include a battery container that houses an electrode assembly including a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0121] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the current collector surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0122] The negative electrode active material layer may optionally contain a binder and a conductive agent together with the negative electrode active material. For example, the negative electrode active material layer may be fabricated by coating a negative electrode active material layer-forming composition containing the negative electrode active material and, optionally, the binder and the conductive agent on a negative electrode current collector and drying the coating, 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.

[0123] 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 that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, 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.

[0124] The binder and conductive agent are the same as those described above for the positive electrode.

[0125] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric materials can also be used, and they can be selectively used in single-layer or multi-layer structures.

[0126] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0127] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0128] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of 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 high ionic conductivity and high dielectric constants, which can enhance 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. In this case, mixing the cyclic carbonate and the linear carbonate at a volume ratio of about 1:1 to about 1:9 can result in superior electrolyte performance.

[0129] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt can be 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 lithium salt concentration is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0130] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, and improving 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. [Example]

[0131] Hereinafter, the present invention will be described in more detail with reference to the following examples, but the following examples are merely preferred examples of the present invention and are not intended to limit the scope of the present invention.

[0132] Example 1 (1) Manufacturing of positive electrode active material Ni0.94 Co 0.05 Mn 0.01 1691 g of (OH)2, 808.6 g of LiOH-H2O, 4.483 g of ZrO2, and 186.0 g of KOH were mixed in an appropriate size mixer to form a mixture. The mixture was calcined in an oxygen atmosphere at 820°C for 8 hours to form a lithium transition metal oxide sample. The calcined lithium transition metal oxide sample was then crushed and 30 g of the sample was stirred in 30 g of distilled water for 10 minutes. After stirring, the solution was subjected to solid-liquid separation using vacuum filtration. The separated solid sample was dried in vacuum at 140°C for 12 hours. The dried sample was then heat treated in an oxygen atmosphere at 750°C for 5 hours.

[0133] (2) Manufacture of lithium secondary batteries A coin half-cell lithium secondary battery was fabricated using the cathode active material prepared by the above method. The slurry for electrode plate fabrication consisted of cathode active material, conductive agent (acetylene black), and binder (PVDF, KF1120) at a ratio of 96.5:1.5:2 wt%, with additional NMP (N-Methyl-2-pyrrolidone) added to adjust the solid content and slurry viscosity. The prepared slurry was coated onto Al foil using a doctor blade, dried, and rolled to fabricate an electrode plate. The electrode loading was 15-16 mg / cm. 2 The electrode composite density is 3.5 g / cm 3 That was all. The electrolyte used in the coin cell was 1M LiPF6in EC:DMC:EMC = 3:4:3 (vol%) + VC 3.0 wt%, and a coin half cell was fabricated using a PP separator and a lithium anode (300 μm).

[0134] Example 2 A positive electrode active material and a lithium secondary battery were produced in the same manner as in Example 1, except that the temperature during firing was 800°C.

[0135] Example 3 A positive electrode active material and a lithium secondary battery were produced in the same manner as in Example 1, except that the temperature during firing was 770°C.

[0136] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that KOH was not added during mixing and the firing temperature was 890°C.

[0137] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 186.0 g of Na2SO4 was added to the mixer instead of KOH during mixing, and the firing temperature was 890°C.

[0138] Comparative Example 3 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 186.0 g of NaCl was added to the mixer instead of KOH during mixing, and the firing temperature was 890°C.

[0139] Comparative Example 4 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 186.0 g of KCl was added to the mixer instead of KOH during mixing, and the firing temperature was 890°C.

[0140] Tables 1 and 2 below summarize the results of Experimental Examples 1 to 3, which will be described later.

[0141] [Table 1]

[0142] [Table 2]

[0143] Experimental Example 1: Evaluation of SEM image, average particle size (Davg) and crystal defect rate of positive electrode active material The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to SEM image analysis, average particle size (Davg) and crystal defect rate evaluation experiments, and the results are shown in Figure 2 and Table 1. The specific experimental method is as follows.

[0144] (1) Measurement of average particle size (Davg) The average particle size (Davg) was calculated by averaging the horizontal and vertical particle sizes of 25 primary particles on a scanning electron microscope (SEM) analysis image of the positive electrode active material, for a total of 50 values.

[0145] (2) Measurement of crystal defect rate The crystal defect rate was calculated using the Rietveld refinement method on the XRD diffraction analysis data. More specifically, the XRD diffraction analysis data was subjected to the Rietveld refinement method using Malvern Panalytical's Highscore software. This generally involves calculating virtual XRD data and approximating it to the actual XRD data using the least squares method, etc., and then calculating the composition of elements located at the crystallographic sites. The ratio of nickel located at the lithium sites, which can be calculated using this calculation, was defined as the crystal defect rate.

[0146] Referring to FIG. 2, it was confirmed that all of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were composed of single particles in which the primary particles were not aggregated.

[0147] In addition, in Examples 1 and 2, which used a KOH particle growth agent, the firing temperature was relatively low compared to Comparative Examples 1 to 4, but the average particle size (Davg) of the single particles was 6.7 μm and 5.0 μm, respectively, which was significantly larger than that of Comparative Examples 1 to 4, and the crystal defect rate was 2.4% and 1.9%, respectively, which was significantly smaller than that of Comparative Examples 1 to 4. Meanwhile, in Example 3, KOH was used, but the firing temperature was significantly lowered to 770°C, which resulted in an average particle size similar to that of the comparative example, but a crystal defect rate of 1.2%, which was significantly smaller.

[0148] Furthermore, in Examples 1 and 2, the average particle size / crystal defect rate (μm / %) was 2.79 and 2.63, and the Davg / firing temperature (nm / °C) was 8.17 and 6.25, which were significantly higher than those of Comparative Examples 1 to 4. In Example 3, the average particle size / crystal defect rate (μm / %) was 2.5, which was also significantly higher than those of Examples 1 to 4. However, the effect of reducing the firing temperature on the reduction in average particle size was so great that the Davg / firing temperature (nm / °C) was similar to that of the Comparative Examples.

[0149] Experimental Example 2: Evaluation of ICP component analysis of positive electrode active material The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to ICP component analysis, and the results are shown in Table 1 above.

[0150] More specifically, elemental analysis was performed using SPECTRO's ARCOS ICP-OES equipment in accordance with the KS M 0032 standard. For example, the sample was first dissolved in aqua regia to create a solution, and the stock solution containing the dissolved sample was then diluted to the appropriate concentration to prepare an analytical solution. This analytical solution was then injected into the analyzer, and plasma was applied to collect spectral information emitted by the components in the solution. The collected spectral information was compared with a calibration curve obtained using certified reference materials to evaluate the content of each element in the sample.

[0151] Referring to Table 1, it was confirmed that the positive electrode active materials according to Examples 1 to 3 had a high measured amount of detected K due to the use of a KOH particle growth agent in the manufacturing process. Also, it was confirmed that the positive electrode active material according to Comparative Example 4 had a high measured amount of detected K due to the use of a KCl particle growth agent. On the other hand, it was confirmed that the positive electrode active materials according to Comparative Examples 1 to 3 had a low measured amount of detected K due to the particle growth agent not containing K.

[0152] Regarding the detected amount of Cl, it was confirmed that the detected amount of Cl was low in the positive electrode active materials according to Examples 1 to 3 and Comparative Examples 1 and 2 because the particle growth agents did not contain Cl. On the other hand, it was confirmed that the detected amount of Cl was high, at 800 ppm or more, in the positive electrode active materials according to Comparative Examples 3 and 4 because NaCl and KCl particle growth agents were used, respectively.

[0153] Experimental Example 3: Evaluation of initial capacity and initial efficiency of lithium secondary batteries The initial capacity and initial efficiency of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated, and the results are shown in Table 2 above.

[0154] Specifically, after fabrication, the lithium secondary batteries were aged at room temperature for 10 hours and then subjected to a charge-discharge test. To evaluate the initial capacity, the batteries were charged to 4.25 V at a constant current of 0.2 C with a reference capacity of 200 mAh / g, then switched to a constant voltage and charged until the final current reached 0.05 C. After a 20-minute rest period, the batteries were discharged to 3.0 V at a constant current of 0.2 C with a reference capacity of 200 mAh / g.

[0155] Referring to Table 2, it was confirmed that in Examples 1 to 3, in which the average particle size, crystalline defect rate, average particle size (Davg) / crystalline defect rate, or average particle size (Davg) / firing temperature of the single particle positive electrode active material were appropriately adjusted, the initial charge capacity, discharge capacity, and initial efficiency were significantly superior to those in Comparative Examples 1 to 4, in which the average particle size, crystalline defect rate, average particle size (Davg) / firing temperature of the single particle positive electrode active material were appropriately adjusted.

[0156] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention.

[0157] Therefore, the true scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising a lithium transition metal oxide containing nickel (Ni) and manganese (Mn), the lithium transition metal oxide being composed of single particles and having a crystal defect rate of less than 3%.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle diameter (Davg) of the single particles is 2.5 μm or more.

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio of the average particle diameter (Davg) of the single particles to the crystal defect rate of the positive electrode active material is 1 μm / % or more.

4. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the positive electrode active material satisfies the following formula 1: <Formula 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / °C) (In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.)

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein K, Li, Na, Rb, Cs, Fr, or a combination thereof is detected in an amount of 50 ppm or more by ICP component analysis.

6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein the amount of Cl detected by the ICP analysis is less than 50 ppm.

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

8. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein 0.9≦b≦0.

99.

9. forming a mixture comprising a positive electrode active material precursor comprising nickel and manganese and a grain growth agent; calcining the mixture to form a lithium transition metal oxide; The method for producing a positive electrode active material for a lithium secondary battery includes crushing the lithium transition metal oxide to form a lithium transition metal oxide composed of single particles.

10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 , wherein the particle growth agent is a hydroxide.

11. 10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the particle growth agent is lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH), francium hydroxide (FrOH), or a combination thereof.

12. forming the mixture, 10. The method of claim 9, wherein the particle growth agent is mixed in an amount of 0.1 to 99 wt % based on the total weight of the mixture.

13. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the firing is carried out at a temperature of 740 to 850°C.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the calcination is carried out for 2 to 36 hours.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9 , wherein the positive electrode active material satisfies the following formula 1: <Formula 1> Average particle size of single particles (Davg) / firing temperature ≥ 5 (nm / °C) (In the above formula 1, the calcination temperature means the temperature during calcination to form the lithium transition metal oxide.)

16. forming the mixture, 10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, further comprising mixing a doping source material, wherein the doping source material is a compound containing one or more of Zr, Nb, Al, B, P, La, Mg, Ta, Ti, W, Mo, Si, Ga, Zn, Ag, Sn, Bi, Au, Y, Ge, V, Cr, and Fe, or a combination thereof.

17. 10. The method of claim 9, further comprising the step of heat-treating the lithium transition metal oxide after the step of crushing the lithium transition metal oxide to form single particles.

18. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the heat treatment is carried out at a temperature of 250 to 750°C.

19. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the heat treatment is carried out for 2 to 24 hours.

20. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 8.

21. A lithium secondary battery comprising the positive electrode according to claim 20.

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