Cathode active material for lithium secondary battery, manufacturing method of the same and lithium secondary battery comprising the same

Abstract

The present invention comprises a lithium transition metal oxide in the form of a single particle containing 50 to 70 mol% of nickel based on the total molar amount of the transition metal, and The volume-based average particle size (Dv50) of the above lithium transition metal oxide is 3.5 to 4.5 μm, and The number-based average particle size (Dn50) of the above lithium transition metal oxide is 1 μm or less, and The present invention relates to a positive electrode active material for a lithium secondary battery satisfying the following Equation 2. [Equation 2] Dv50 - Dn50 ≥ 2.5 μm In the above Equation 2, Dv50 is the average particle size based on the volume of the positive active material, and Dn50 is the average particle size based on the number of positive active materials.

Description

Technology Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. More specifically, the invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery in the form of a single particle, a positive electrode active material manufactured therefrom, and a lithium secondary battery including the same. Background Technology

[0003] In a lithium secondary battery, electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted into or removed from the positive and negative electrodes, which are composed of active materials capable of lithium ion intercalation and deintercalation, with an organic or polymer electrolyte charged between them.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as cathode active materials for lithium-ion batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used and applied as a cathode active material for high-voltage applications due to its advantages of high operating voltage and excellent capacity characteristics. However, due to the rising price and supply instability of cobalt (Co), there are limitations to its mass use as a power source in fields such as electric vehicles, leading to the emergence of a need for the development of cathode active materials that can replace it.

[0005] Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') was developed in which a portion of the cobalt (Co) was replaced with nickel (Ni) and manganese (Mn). However, the conventionally developed NCM-based lithium composite transition metal oxide generally has a secondary particle form in which primary particles are aggregated, and has a large specific surface area, low particle strength, and high lithium byproduct content, resulting in a large amount of gas generated during cell operation and consequently a decrease in lifespan and stability.

[0006] Accordingly, development of cathode active materials in the form of single particles, rather than the existing secondary particle form, is underway. The problem to be solved

[0008] Accordingly, one objective of the present invention is to provide a positive electrode active material for a lithium secondary battery with improved capacity and high-temperature life characteristics as a lithium transition metal oxide in the form of a single particle, a method for manufacturing the same, and a lithium secondary battery including the same. means of solving the problem

[0010] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising a lithium transition metal oxide in the form of a single particle containing 50 to 70 mol% of nickel based on the total molar amount of the transition metal, and satisfying Formula 1 below.

[0011] [Equation 1]

[0012] Dv50 / Dn50 ≥ 3.0

[0013] In the above Equation 1, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0015] The above positive electrode active material for a lithium secondary battery can satisfy the following Equation 2.

[0016] [Equation 2]

[0017] Dv50 - Dn50 ≥ 2.5 μm

[0018] In the above Equation 2, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0019] The volume-based average particle size (Dv50) of the above lithium transition metal oxide may be 3.5 to 4.5 μm.

[0020] The average particle size (Dn50) based on the number of the above lithium transition metal oxides may be 1 μm or less.

[0021] The crystallite size of the above lithium transition metal oxide may be 190 nm or less.

[0022] The ratio of the c-axis lattice constant to the a-axis lattice constant of the above lithium transition metal oxide (Lc / La) may be 4.955 or higher.

[0023] The c-axis lattice constant (Lc) of the above lithium transition metal oxide may be 14.2472 Å or greater.

[0024] The a-axis lattice constant (La) of the above lithium transition metal oxide may be 2.8752 Å or less.

[0025] The above lithium transition metal oxide can be represented by the following chemical formula 1.

[0026] [Chemical Formula 1]

[0028] *Li a [Ni x Co y Mn z M w ]O2

[0029] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0031] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total molar amount of the transition metal; mixing the transition metal precursor and a lithium raw material, and then performing a first calcination and a second calcination to form a lithium transition metal oxide; and performing a first disintegration and a second disintegration of the lithium transition metal oxide to form a lithium transition metal oxide in the form of a single particle, wherein the second calcination is performed in an oxygen (O2) atmosphere.

[0032] The above secondary disintegration can be performed so that the volume-based average particle size (Dv50) of the lithium transition metal oxide is 3.5 to 4.5 μm.

[0033] The above first disintegration can be performed at a stirring speed of 15,000 to 20,000 rpm.

[0034] The above secondary crushing can be performed at a crushing pressure of 3.5 to 4.5 bar.

[0035] The above first firing can be performed in an air atmosphere.

[0036] The above first firing and the above second firing can each be performed independently at a temperature of 900 to 960°C.

[0038] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0039] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for the lithium secondary battery. Effects of the invention

[0041] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is in the form of a single particle, and by appropriately controlling the ratio of the average particle size based on volume to the average particle size based on number, the capacity and electrode energy density can be improved, as well as the high-temperature life characteristics can be improved. Brief explanation of the drawing

[0043] Figure 1 is an SEM image of the positive electrode active material prepared according to Example 1. Figure 2 is an SEM image of the positive electrode active material prepared according to Comparative Example 1. Specific details for implementing the invention

[0044] 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 solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0045] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0046] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0047] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0048] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0049] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0050] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0052] 1. Cathode active material

[0053] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium transition metal oxide in the form of a single particle. The active material in the form of a single particle has a smaller specific surface area compared to conventional secondary particles, which reduces the amount of gas generated due to side reactions with the electrolyte. Additionally, it has a higher particle strength, which can suppress particle breakage during rolling and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has the advantage of superior lifespan and safety compared to secondary particles, and can achieve high energy density of the electrode.

[0054] In this specification, “single particle” is a term used to distinguish it from cathode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which were conventionally used; it is a concept that includes a single particle consisting of one primary particle and aggregate particles of 30 or fewer primary particles. Additionally, “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by the aggregation of tens to hundreds of primary particles through physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles.

[0055] Meanwhile, the lithium transition metal oxide according to one embodiment of the present invention contains 50 to 70 mol% of nickel based on the total molar amount of the transition metal. Conventional NCM-based (nickel-cobalt-manganese ternary) cathode active materials have sought to achieve high capacity of the battery by increasing the nickel content; however, if the nickel content is too high, there may be a thermal propagation issue, i.e., a problem with thermal safety, and the manufacturing cost may increase due to the high price of nickel. Therefore, the nickel content of the lithium transition metal oxide according to the present invention is controlled to the above range to secure appropriate capacity and thermal safety characteristics while simultaneously achieving economic feasibility.

[0056] However, in order to manufacture lithium transition metal oxides in the form of single particles, the calcination temperature is higher than that of secondary particles, so there is a problem that the capacity characteristics are essentially inferior to those of secondary particles.

[0057] As a result of repeated research to solve the problem of capacity degradation, the inventors have discovered that capacity characteristics can be improved by appropriately controlling the ratio of the volume average particle size (Dv50) and the number average particle size (Dn50) of the lithium transition metal oxide. Furthermore, they have discovered that high-temperature life characteristics are simultaneously improved. This will be explained in more detail below.

[0059] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention satisfies the following Formula 1.

[0060] [Equation 1]

[0061] Dv50 / Dn50 ≥ 3.0

[0062] In Equation 1 above, Dv50 is the volume-based average particle size of the lithium transition metal oxide, and Dn50 is the number-based average particle size of the lithium transition metal oxide. More specifically, the volume-based average particle size (Dv50) can be defined as the particle size corresponding to 50% of the volume-cumulative amount in the particle size distribution curve. The number-based average particle size (Dn50) can be defined as the particle size corresponding to 50% of the number-cumulative amount in the particle size distribution curve. The volume-based average particle size (Dv50) and the number-based average particle size (Dn50) can be measured, for example, using a laser diffraction method.

[0063] More specifically, the Dv50 / Dn50 value of the lithium transition metal oxide may be 3.5, 4.0, or 4.3 or higher, and 5.0 or 4.8 or lower.

[0064] In addition, the positive electrode active material for the above lithium secondary battery can further satisfy the following Equation 2.

[0065] [Equation 2]

[0067] *Dv50 - Dn50 ≥ 2.5 μm

[0068] In the above Equation 2, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0069] More specifically, the Dv50 - Dn50 value of the above lithium transition metal oxide may be 2.7 μm or 3.0 μm or greater, and 3.5 μm or 3.2 μm or less.

[0070] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery satisfies Equation 1 or Equation 2, thereby not only improving capacity and electrode energy density but also improving high-temperature life characteristics.

[0071] More specifically, satisfying Equation 1 or Equation 2 for the cathode active material may mean that the number of small-diameter particles in the overall particle size distribution is relatively greater than the number of medium-diameter or large-diameter particles. Accordingly, when implementing the cathode in practice, small-diameter particles may exist between medium-diameter or large-diameter particles, thereby improving the electrode rolling density. In addition, as the pores within the electrode are reduced, the diffusion path length of lithium ions is shortened, which can improve the lithium ion diffusion rate. Consequently, excellent electrode energy density, capacity, and initial efficiency can be achieved.

[0072] Furthermore, the inventors confirmed that when the positive electrode active material satisfies Equation 1 or Equation 2, high-temperature lifetime characteristics are improved in addition to the electrochemical characteristics. This appears to be because reducing pores within the electrode increases the lithium ion diffusion rate, thereby promoting the electrochemical reaction and reducing irreversible characteristics.

[0073] However, if the Dv50 / Dn50 value or the Dv50 - Dn50 value is too large, it means that the number of small-diameter particles becomes too high, which may lead to an excessive increase in the surface area of ​​the active material in contact with the electrolyte and cause a problem of increased gas generation due to side reactions.

[0075] More specifically, the volume-based average particle size (Dv50) of the lithium transition metal oxide may be 3.5 to 4.5 μm. If the volume-based average particle size (Dv50) is too small, the electrode rolling density decreases, which may degrade the electrode energy density. If the volume-based average particle size (Dv50) is too large, the crystal grain and particle size become too large, causing the lithium ion migration length to become too long, which may degrade the capacity and output characteristics. In addition, as described in the manufacturing method described below, the particle size distribution of the lithium transition metal oxide can be determined by controlling the process conditions of the final disintegration step. When the volume-based average particle size (Dv50) is controlled to the above range during the disintegration process, the physical properties of Equations 1 and 2 mentioned above can be more easily satisfied.

[0076] In addition, the average particle size (Dn50) based on the number of lithium transition metal oxides may be 1 μm or less. As the average particle size (Dn50) based on the number of lithium transition metal oxides satisfies the above range, not only can the electrode energy density and capacity be improved, but high-temperature life characteristics can also be improved.

[0078] Meanwhile, the crystallite size of the lithium transition metal oxide may be 190 nm or less, and more specifically, 185 nm or less.

[0079] In this specification, “grain” refers to a distinct region in which atoms within a primary particle form a lattice structure in a certain direction, and “grain size” can be estimated using peak broadening of XRD data and can be quantitatively calculated through the Scherrer equation.

[0080] Generally, as the grain size of lithium transition metal oxides increases, lifespan characteristics improve, but capacity characteristics deteriorate. On the other hand, the cathode active material according to the present invention can improve high-temperature lifespan characteristics even when the grain size is reduced in this way. Consequently, as the grain size of the lithium transition metal oxide satisfies the above range, not only the effect of improving capacity characteristics due to the reduction in grain size but also the effect of improving high-temperature lifespan characteristics can be realized simultaneously. This appears to be because, as described below, the c-axis lattice constant of the lithium transition metal oxide according to the present invention is sufficiently large, facilitating the intercalation of lithium ions and reducing irreversible reactions.

[0082] Meanwhile, the ratio of the c-axis lattice constant to the a-axis lattice constant of the lithium transition metal oxide (Lc / La) may be 4.955 or higher, and more specifically, 4.9553 or higher. The fact that the ratio of the c-axis lattice constant to the a-axis lattice constant of the lithium transition metal oxide (Lc / La) satisfies the above range may mean that the c-axis lattice constant is sufficiently large compared to the a-axis lattice constant. Accordingly, a layered structure is well formed within the lithium transition metal oxide, which can promote the intercalation of lithium ions. As a result, the capacity and initial efficiency of the battery may be improved.

[0083] More specifically, the c-axis lattice constant (Lc) of the lithium transition metal oxide may be 14.2472 Å or greater. Additionally, the a-axis lattice constant (La) of the lithium transition metal oxide may be 2.8752 Å or less.

[0085] The above lithium transition metal oxide can be represented more specifically by the following chemical formula 1.

[0086] [Chemical Formula 1]

[0087] Li a [Ni x Co y Mnz M w ]O2

[0088] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0089] In the lithium transition metal oxide of Chemical Formula 1 above, lithium may be included in an amount corresponding to a, i.e., 0.8 ≤ a ≤ 1.2. If a is too small, the capacity may decrease, and if a is too large, the strength of the calcined cathode active material may increase, making it difficult to grind, and the amount of gas generated may increase due to an increase in lithium by-products. Considering the effect of improving the capacity characteristics of the cathode active material by controlling the lithium content and the balance of sinterability during the manufacture of the active material, the lithium may more preferably be included in an amount of 0.9 ≤ a ≤ 1.1.

[0090] In the lithium transition metal oxide of Chemical Formula 1 above, nickel may be included in an amount corresponding to x, i.e., 0.5≤x≤0.7. If the nickel content is too low, it may be difficult to achieve high capacity of the battery, and if the nickel content is too high, the battery life and thermal safety may decrease due to reduced structural stability of the active material, and the manufacturing cost may increase.

[0091] In the lithium transition metal oxide of Chemical Formula 1 above, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.2 or 0.05≤y≤0.2. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt content is too high, the cost of raw materials increases overall and the reversible capacity may decrease.

[0092] In the lithium transition metal oxide of Chemical Formula 1 above, manganese may be included in an amount corresponding to z, i.e., 0≤z≤0.4 or 0.1≤z≤0.4. If the manganese content is too low, the production cost may increase and the stability of the active material may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0093] In the lithium transition metal oxide of Chemical Formula 1 above, M may be included in an amount corresponding to w, i.e., 0≤w≤0.2. At this time, M may be a doping element and may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0095] 2. Method for manufacturing positive electrode active material

[0096] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total molar amount of the transition metal; mixing the transition metal precursor and a lithium raw material, and then performing a first calcination and a second calcination to form a lithium transition metal oxide; and performing a first disintegration and a second disintegration of the lithium transition metal oxide to form a lithium transition metal oxide in the form of a single particle, wherein the second calcination is performed in an oxygen (O2) atmosphere.

[0097] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described step by step.

[0099] First, a transition metal precursor containing 50 to 70 mol% of nickel based on the total molar amount of the transition metal is prepared.

[0100] The above transition metal precursor may be a transition metal hydroxide.

[0101] The above transition metal hydroxide may be prepared by co-precipitating a transition metal-containing solution containing a nickel raw material and optionally a cobalt raw material or a manganese raw material by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to the transition metal-containing solution.

[0102] The above nickel raw material is not particularly limited as long as it is used in the industry for manufacturing a cathode active material precursor. For example, the above nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0103] The above-mentioned cobalt raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above-mentioned cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO₄ 4, It may be CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof, but is not limited thereto.

[0104] The above manganese raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0105] The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally a cobalt raw material or a manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent that can be uniformly mixed with water (e.g., alcohol).

[0106] The above-mentioned complexing agent-containing solution performs the role of forming a complex, and may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent, but is not limited thereto. Meanwhile, the above-mentioned complexing agent-containing solution may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol, etc.) may be used as the solvent.

[0107] The above pH-adjusting solution acts as a precipitating agent or a pH adjuster and may include alkali compounds such as hydroxides of alkali metals or alkaline earth metals like NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Meanwhile, the above pH-adjusting solution may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol) may be used as the solvent. In this case, the above pH-adjusting solution may be added in an amount such that the pH of the reaction solution becomes 11 to 13.

[0108] The above co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon, at a temperature of 30 to 70°C, and at a pH of 11 to 13.

[0109] By the above process, particles of nickel-cobalt-manganese (-doping element) hydroxide are generated and precipitated in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed, and dried to obtain a precursor. The precursor may be a secondary particle formed by the aggregation of primary particles.

[0110] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by adjusting the concentrations of the nickel raw material, cobalt raw material, and manganese raw material.

[0111] Accordingly, the nickel content in the transition metal precursor may be 50 to 70 mol% based on the total molar amount of the transition metal. The technical significance of controlling the nickel content in the transition metal precursor is as described above and is therefore omitted.

[0113] Next, the above transition metal precursor and lithium raw material are mixed, and then subjected to first calcination and second calcination to form a lithium transition metal oxide.

[0114] Conventionally, to form a lithium transition metal oxide in the form of a single particle, the process was carried out using only a primary calcination at a high temperature for a long time. However, in this case, there was a problem in which the electrochemical properties of the active material deteriorated due to nickel cation mixing caused by over-calcination and the formation of rocksalt impurities. On the other hand, the manufacturing method according to the present invention can prevent the above problems by performing the calcination in two stages, and the particle strength of the active material can be improved and the production volume can be increased.

[0115] At this time, the atmosphere during the first calcination is not particularly limited. For example, it may be performed in an air or oxygen (O2) atmosphere, but more specifically, it may be performed in an air atmosphere. When high-nickel cathode active materials are performed in an air atmosphere, the formation of a layered crystal structure is not well achieved, resulting in a significant degradation of electrochemical properties; therefore, it is generally common to perform the process in an oxygen atmosphere. On the other hand, when the nickel content is relatively low as in the present invention, the degradation of electrochemical properties does not occur significantly even when calcined in an air atmosphere, and process costs can be reduced.

[0116] In particular, the above secondary calcination is performed in an oxygen (O2) atmosphere. More specifically, the oxygen atmosphere may have an oxygen partial pressure of 90%, 95%, 97%, or 99% or higher. Through secondary calcination under an oxygen atmosphere, the ratio of fine particles, i.e., particles of small particle size, can be appropriately increased during the disintegration process described later, so that the obtained cathode active material can satisfy physical properties such as Equation 1 described above. This appears to be because the particle strength of the lithium transition metal oxide obtained when secondary calcination is performed under an oxygen atmosphere is weaker compared to when secondary calcination is performed under an atmospheric atmosphere. In particular, unlike conventional technology that indiscriminately increased the particle strength of the lithium transition metal oxide to improve lifespan characteristics, the present invention enables the simultaneous improvement of capacity and lifespan characteristics by forming a lithium transition metal oxide with somewhat weak particle strength and then appropriately forming the ratio of fine particles through disintegration.

[0117] The first and second calcination steps can each be performed independently at a temperature of 900 to 960°C. If the temperatures of the first and second calcination steps are too low, lithium transition metal oxides in the form of single particles may not be easily formed. If the temperatures of the first and second calcination steps are too high, over-calcination may occur, and electrochemical properties such as capacity may deteriorate.

[0118] The above first calcination can be performed for 2 to 6 hours. If the first calcination time is too short, there may be a problem in that lithium ions are not fully inserted into the precursor, and if the first calcination time is too long, there may be a problem in that the production speed is reduced due to difficulty in disintegration caused by over-calcination.

[0119] The above secondary firing can be performed for 7 to 14 hours. If the secondary firing time is too short, the shape of a single particle is not fully formed, and there may be a problem of electrochemically inferior performance due to insufficient annealing time to have a layered structure. If the secondary firing time is too long, there may be a problem of capacity reduction due to under-firing.

[0121] Next, the lithium transition metal oxide is first broken down and second broken down to form a lithium transition metal oxide in the form of a single particle.

[0122] By dividing the disintegration into primary and secondary disintegration, aggregated secondary particles can be efficiently broken down into single-particle forms, and the proportion of fine particles, i.e., particles with small particle sizes, can be increased, so that the obtained cathode active material can satisfy the physical properties of Equation 1 or Equation 2 described above.

[0123] The above primary disintegration can be performed using disintegration equipment commonly used in the industry. For example, the above primary disintegration can be performed using a rotor mill, but is not necessarily limited thereto.

[0124] At this time, the first disintegration can be performed at a stirring speed of 15,000 to 20,000 rpm. When the stirring speed during the first disintegration satisfies the above range, the first disintegration is performed with appropriate force, thereby allowing for appropriate control of the ratio of fine particles, i.e., particles of small diameter, so that the obtained anode active material can satisfy physical properties such as those of Equation 1 described above.

[0125] The above secondary disintegration can be performed using disintegration equipment commonly used in the industry. For example, the above secondary disintegration can be performed using a jet mill, but is not necessarily limited thereto.

[0126] At this time, the secondary disintegration can be performed such that the volume-based average particle size (Dv50) of the lithium transition metal oxide is 3.5 to 4.5 μm. As the secondary disintegration is controlled so that the volume-based average particle size (Dv50) of the lithium transition metal oxide is within the above range, the obtained cathode active material can more easily satisfy the physical properties of Formula 1 and others described above.

[0127] The above secondary disintegration can be performed with a grinding pressure of 3.5 to 4.5 bar, and more specifically, with a grinding pressure of 3.5 to 3.9 bar. When the grinding pressure during secondary disintegration satisfies the above range, the secondary disintegration is performed with appropriate force, thereby allowing for appropriate control of the ratio of fine particles, i.e., particles of small particle size, so that the obtained cathode active material can satisfy physical properties such as those of Equation 1 described above.

[0129] Through the above series of manufacturing methods, a lithium transition metal oxide in the form of a single particle according to the present invention can be formed, and the obtained lithium transition metal oxide can satisfy physical properties such as those of Formula 1. Accordingly, the electrode energy density can be improved, and the capacity and high-temperature life characteristics of the battery can be improved.

[0131] 3. Anodes and Lithium Secondary Batteries

[0132] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0133] More specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector and comprising the aforementioned anode active material.

[0134] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0135] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0136] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0137] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes may be used without any particular limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight percent relative to the total weight of the positive electrode active material layer.

[0138] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0139] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0140] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0141] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0143] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0144] More specifically, the above lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0145] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0146] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0147] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0148] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0149] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0150] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0152] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0154] The above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0155] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0156] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0157] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may 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 concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0158] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0159] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0160] Accordingly, another embodiment of the present invention provides a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same.

[0161] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0163] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0165] Example 1

[0166] (1) Manufacturing of positive electrode active material

[0167] (Mixed) Ni 0.6 Co 0.1 Mn 0.3 A mixture was formed by mechanically mixing a (OH)2 precursor and LiOH·H2O in a mixer such that the molar ratio of lithium to the transition metal of the precursor (Li / M) was 1.07.

[0168] After the (first firing), the mixture was heated to 940°C through heat treatment in an air atmosphere, then fired at a constant temperature of 940°C for 4 hours, and then cooled naturally. Afterward, the first fired product was crushed using a rotor mill.

[0169] After (second calcination), the above-mentioned crushed first calcined product was second calcined for 10 hours at a constant temperature of 940°C under an oxygen atmosphere with an oxygen partial pressure of 99%, and then naturally cooled to form a lithium transition metal oxide.

[0170] After (first disintegration), the lithium transition metal oxide was first disintegrated using a rotor mill at a stirring speed of 17,000 rpm.

[0171] After (second disintegration), a lithium transition metal oxide in the form of single particles was formed by second disintegration using a jet mill at a grinding pressure of 3.7 bar.

[0172] The composition of the finally obtained lithium transition metal oxide is Li 1.07 Ni 0.6 Co 0.1 Mn 0.3 It was O2.

[0173] (2) Lithium secondary battery manufacturing

[0174] The slurry for electrode manufacturing was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF9700) in a ratio of 95.0 : 2.0 : 3.0 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content was approximately 60%. The prepared slurry was coated onto a 20 µm thick Al foil using a doctor blade and then dry-rolled. The electrode loading amount was 16.0 mg / cm². 2 It was, and the rolled density (25 ℃, 20 kN) was 3.5 g / cm³ 3 It was.

[0175] A coin cell was manufactured using an electrolyte of 1M LiPF6 in EC:DMC:DEC=1:2:1 (vol%) with 2.0 vol% of VC added relative to the total amount of the electrolyte, a PP separator, and a lithium anode (400 μm, Niba metal).

[0177] Example 2

[0178] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second calcination step, the second calcination was performed for 11 hours.

[0180] Comparative Example 1

[0181] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second calcination step, the secondary calcination was performed under an air atmosphere with an oxygen partial pressure of 21%, and then the secondary disintegration was performed using a jet mill at a grinding pressure of 4.1 bar.

[0184] * Comparative Example 2

[0185] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second calcination step, the secondary calcination was performed for 9 hours under an air atmosphere with an oxygen partial pressure of 21%, and then the secondary disintegration was performed using a jet mill at a grinding pressure of 4.1 bar.

[0187] Comparative Example 3

[0188] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second calcination step, the secondary calcination was performed for 8 hours under an air atmosphere with an oxygen partial pressure of 21%, and then the secondary disintegration was performed using a jet mill at a grinding pressure of 4.0 bar.

[0190] Experimental Example 1: SEM image of cathode active material

[0191] SEM images of the cathode active materials prepared according to Example 1 and Comparative Example 1 were observed and are shown in Figures 1 and 2, respectively.

[0192] Referring to Figures 1 and 2, it was confirmed that the positive active materials of the examples and comparative examples have a single particle form.

[0194] Experimental Example 2: Evaluation of Physical Properties of Anode Active Material

[0195] The properties of the cathode active materials of the examples and comparative examples were evaluated using the method below, and are shown in Table 2.

[0196] (1) Dv50 and Dn50, Dv50 / Dn50, Dv50 - Dn50 evaluation

[0197] The average particle size based on volume (Dv50) was measured by using the laser diffraction method to determine the particle size corresponding to 50% of the volume accumulation, and the average particle size based on number (Dn50) was measured by determining the particle size corresponding to 50% of the number accumulation. Subsequently, Dv50 / Dn50 and Dv50 - Dn50 were calculated using these values.

[0198] (2) Grain size, a-axis lattice constant (La), c-axis lattice constant (Lc), Lc / La evaluation

[0199] XRD data of the active material was measured using Bruker’s D8 Discover with GADDS XRD instrument, and the crystal size, a-axis lattice constant (La), and c-axis lattice constant (Lc) were determined using the Reitveld refinement method embedded in Bruker’s DIFFRAC.TOPAS program, and Lc / La was calculated by dividing the c-axis lattice constant (Lc) by the a-axis lattice constant (La).

[0200] Process conditions 1st firing Secondary firing Second firing atmosphere 1st unpacking 2nd unpacking Comparative Example 1 940℃, 4h, air 940℃, 10h air (oxygen partial pressure 21%) Rotor mill 17,000 rpm Jet Mill 4.1 bar Comparative Example 2 940℃, 9h air (oxygen partial pressure 21%) Rotor mill 17,000 rpm Jet Mill 4.1 bar Comparative Example 3 940℃, 8h air (oxygen partial pressure 21%) Rotor mill 17,000 rpm Jet Mill 4.0 bar Example 1 940℃, 10h O2 (oxygen partial pressure 99%) Rotor mill 17,000 rpm Jet Mill 3.7 bar Example 2 940℃, 11h O2 (oxygen partial pressure 99%) Rotor mill 17,000 rpm Jet Mill 3.7 bar

[0201] Entry Dv50(μm) Dn50(μm) Dv50 / Dn50 Dv50 - Dn50(μm) Comparative Example 1 3.99 2.8 1.42 1.19 Comparative Example 2 3.98 2.79 1.42 1.19 Comparative Example 3 3.86 2.52 1.53 1.34 Example 1 4.03 0.89 4.54 3.14 Example 2 3.99 0.9 4.43 3.09

[0202] XRD Crystal Size(nm) lattice constant La(Å) of the a-axis lattice constant Lc(Å) of the c-axis Lc / La Comparative Example 1 210 2.8753 14.2456 4.9545 Comparative Example 2 208 2.8755 14.2463 4.9544 Comparative Example 3 200 2.8755 14.247 4.9546 Example 1 181 2.8751 14.2475 4.9555 Example 2 183 2.875 14.2473 4.9556

[0203] Referring to Tables 1 to 3, in the case of Examples 1 and 2, where the active material manufacturing process conditions were appropriately controlled, such as performing the second calcination under an oxygen atmosphere and performing the second disintegration, it was confirmed that Dv50 / Dn50, Dv50-Dn50, and other XRD properties were appropriately obtained within the range according to the present invention. On the other hand, in the case of Comparative Examples 1 to 3, where the second calcination was performed under an air atmosphere, it was confirmed that Dv50 / Dn50, Dv50-Dn50, and other XRD properties fell outside the range according to the present invention.

[0205] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0206] The electrochemical characteristics of the lithium secondary batteries of the examples and comparative examples were evaluated using the method below, and are shown in Table 4.

[0207] (1) Evaluation of initial capacity and initial efficiency

[0208] After fabricating a lithium secondary battery half cell, it was aged at 25°C for 12 hours, and then a charge-discharge test was performed at 25°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.4V with a constant current of 0.1C. Then, the voltage was switched to a constant voltage, and charging continued until the terminal current reached 0.05C. After a 10-minute rest time following charging, the battery was discharged with a reference capacity of 200 mAh / g and a constant current of 0.1C until it reached 2.5V.

[0209] (2) Evaluation of high-temperature life characteristics (high-temperature capacity retention rate) (45℃, 50 cycles)

[0210] After fabricating a lithium secondary battery half cell, it was charged to 4.4V at 45°C with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 50th cycle was calculated relative to the first cycle.

[0211] (3) Evaluation of high-temperature resistance increase rate (45℃, 50 cycles)

[0212] After fabricating a lithium secondary battery half cell, it was charged to 4.4V at 45℃ with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the resistance increase rate of the 50th cycle compared to the first cycle was calculated.

[0213] 0.1C / 0.1C Initial Cycle High temperature test Charge(mAh / g) Discharge(mAh / g) Efficiency (%) Retention @50th ΔDCIR @50th Comparative Example 1 213.6 191.8 89.80% 94.20% 154.30% Comparative Example 2 213.4 191.5 89.70% 94.10% 154.20% Comparative Example 3 213.6 191.7 89.70% 94.30% 155.70% Example 1 214 193.7 90.50% 94.90% 134.20% Example 2 213.7 193.7 90.70% 94.90% 135.10%

[0214] Referring to Table 4, it was confirmed that in the case of Examples 1 and 2, where the physical properties of the positive electrode active material, such as Equation 1, satisfy the range according to the present invention, the initial charge capacity, discharge capacity, initial efficiency, high-temperature life characteristics, and high-temperature resistance characteristics were all excellent. On the other hand, in the case of Comparative Examples 1 to 3, where the physical properties of the positive electrode active material, such as Equation 1, fall outside the range according to the present invention, it was confirmed that the initial charge capacity, discharge capacity, initial efficiency, high-temperature life characteristics, and high-temperature resistance characteristics were inferior to those of the examples.

[0216] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0217] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising a single-particle lithium transition metal oxide containing 50 to 70 mol% nickel based on the total molar amount of the transition metal, wherein the volume-based average particle size (Dv50) of the lithium transition metal oxide is 3.5 to 4.5 μm and the number-based average particle size (Dn50) of the lithium transition metal oxide is 1 μm or less, and satisfying the following Equation 2: [Equation 2] Dv50 - Dn50 ≥ 2.5 μm In the above Equation 2, Dv50 is the volume-based average particle size of the positive electrode active material, and Dn50 is the number-based average particle size of the positive electrode active material. Claim 2 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the crystallite size of the lithium transition metal oxide is 190 nm or less. Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the c-axis lattice constant (Lc) of the lithium transition metal oxide is 14.2472 Å or greater. Claim 4 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the a-axis lattice constant (La) of the lithium transition metal oxide is 2.8752 Å or less. Claim 5 In claim 1, the lithium transition metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1]Li a [Ni x Co y Mn z M w ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr or a combination thereof. Claim 6 A positive electrode for a lithium secondary battery comprising a positive electrode active material according to any one of claims 1 to 5. Claim 7 A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 6.

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