Positive electrode active material for lithium secondary batteries, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a nickel-containing layered lithium transition metal oxide positive electrode active material for lithium secondary batteries, having an average particle size (D50) of 5 to 8 μm, and containing single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles, satisfying the following formula 1. [Formula 1] 1.2μm ≤ D50 - D50 p ≤1.8μm In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 p This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same, and more specifically, to a single-particle positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] With the increasing adoption of electric vehicles in pursuit of carbon neutrality, and the surge in demand for energy storage devices such as ESS (Energy Storage Systems) for renewable energy use, lithium-ion batteries have become an irreplaceable, core energy storage element. In particular, since the characteristics of lithium-ion batteries are greatly influenced by the cathode material, research on cathode materials accounts for the largest proportion of lithium-ion battery research.

[0003] While research on NCM cathode materials, which are layered nickel-based cathode active materials with added cobalt and manganese, is active among cathode materials, conventional research has focused more on secondary particle active materials formed by the aggregation of primary particles. However, such secondary particle active materials have a large specific surface area and low particle strength, leading to problems such as cracking and life degradation due to gas generation. In response to this, the development of single-particle cathode materials composed of a single primary particle is progressing, and these are mainly produced for use as fine-particle cathode materials with an average particle size of approximately 3-5 μm in bimodal cathode materials.

[0004] The aforementioned small-particle single particles possess excellent mechanical particle strength characteristics, resulting in superior lifespan and stability. However, due to their small size, the rolling density is low, which limits the ability to increase the electrode energy density.

[0005] To address this, attempts were made to increase the electrode energy density by increasing the particle size of individual particles. However, arbitrarily increasing the particle size of individual particles leads to a problem where the lithium ion migration path becomes longer, resulting in a decrease in the electrochemical properties related to lithium diffusion (capacity, charge / discharge efficiency, and power characteristics). [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] One objective of the present invention is to provide a single-particle positive electrode active material for lithium secondary batteries that has excellent rolling density, can improve electrode energy density, has good capacity and charge / discharge efficiency characteristics, has excellent strength, and can improve battery life characteristics, as well as a method for producing the same and a lithium secondary battery containing the same. [Means for solving the problem]

[0007] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a nickel-containing layered lithium transition metal oxide having an average particle size (D50) of 5 to 8 μm, and includes single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles, satisfying the following formula 1.

[0008] [Formula 1] 1.2μm ≤ D50 - D50 p ≤1.8μm

[0009] In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 p This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

[0010] The average number of primary particles within the aforementioned quasi-single particle can be 8 or less.

[0011] The average aspect ratio of the primary particles within the aforementioned quasi-single particle can be 1.1 or greater.

[0012] The positive electrode active material for the lithium secondary battery can have a compressible density of 3.61 g / cc or more after applying a pressure of 9 tons.

[0013] The positive electrode active material for the lithium secondary battery has a BET specific surface area of ​​0.55 m². 2 It can be less than or equal to / g.

[0014] The lithium transition metal oxide can further contain a grain growth promoting element which is Zr, Al, B or a combination thereof.

[0015] The content of the grain growth promoting element can be 0.1 to 1 mol% based on the total number of moles of transition metals.

[0016] The positive electrode active material can further include a coating layer containing Co, Al or a combination thereof on the lithium transition metal oxide.

[0017] The lithium transition metal oxide can be represented by the following Chemical Formula 1.

[0018] [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2

[0019] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.60 ≦ x < 1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ w1 ≦ 0.01, 0 ≦ w2 ≦ 0.2, x + y + z + w1 + w2 = 1, M1 is Zr, Al, B or a combination thereof, and M2 is Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

[0020] Another embodiment of the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a nickel-containing transition metal precursor; forming a mixture containing the transition metal precursor and a lithium raw material, and then performing a main calcination to form a lithium transition metal oxide with an increased number of primary particles; post-calcining the lithium transition metal oxide; and crushing the post-calcined lithium transition metal oxide to form a lithium transition metal oxide containing single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles, wherein the main calcination temperature is higher than the post-calcination temperature and the main calcination time is shorter than the post-calcination time.

[0021] The transition metal precursor prepared in the step of preparing the transition metal precursor, or the lithium transition metal oxide formed in the step of calcining to form a lithium transition metal oxide with an increased number of primary particles, may further contain grain growth promoting elements, which are Zr, Al, B, or combinations thereof.

[0022] The content of the grain growth promoting element can be 0.1 to 1 mol% based on the total number of moles of transition metal in the transition metal precursor or the lithium transition metal oxide.

[0023] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material described above.

[0024] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode. [Effects of the Invention]

[0025] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has an average particle size range larger than that of conventional small-particle single particles, can improve electrode energy density, and includes quasi-single particles consisting of multiple primary particles in addition to single particles consisting of one primary particle, and satisfies Equation 1 described later, thereby uniformly improving the battery's capacity, charge / discharge efficiency, and life characteristics. [Brief explanation of the drawing]

[0026] [Figure 1] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Example 1. [Figure 2] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Example 2. [Figure 3] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Example 3. [Figure 4] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Example 4. [Figure 5] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 1. [Figure 6] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 2. [Figure 7] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 3. [Figure 8] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 4. [Figure 9] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 5. [Figure 10] This is an SEM image of the positive electrode active material for lithium secondary batteries manufactured according to Comparative Example 6. [Modes for carrying out the invention]

[0027] The terms "first," "second," and "third," etc., are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. 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 invention.

[0028] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes the plural form unless the context clearly indicates the opposite. The meaning of “includes” as used in this specification is to embody a particular characteristic, area, element, stage, operation, element and / or component, and does not preclude the presence or addition of other characteristics, areas, elements, stages, operations, elements and / or components.

[0029] When a part is described as being "on top of" or "above" another part, it may be directly above or directly above the other part, or the other part may be interposed between them. In contrast, when a part is described as being "directly above" another part, the other part is not interposed between them.

[0030] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are to be interpreted as having the meaning consistent with the relevant technical literature and the present disclosures, and not as ideal or highly formal unless otherwise defined.

[0031] Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0032] In this specification, the term “their combinations (groups)” as expressed in Markush notation means one or more mixtures or combinations selected from the group of components expressed in Markush notation, and means including one or more selected from the group of components.

[0033] The embodiments of the present invention will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0034] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, which is a nickel-containing layered lithium transition metal oxide with an average particle size (D50) of 5 to 8 μm, and includes single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles, satisfying the following formula 1.

[0035] [Formula 1] 1.2μm ≤ D50 - D50 p ≤1.8μm

[0036] In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 p This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

[0037] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single-particle systems.

[0038] In this specification, "single particle" is a term used to distinguish it from positive electrode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which have been commonly used in the past. The term includes both a single particle consisting of one primary particle and aggregate particles of 30 or fewer primary particles. The "secondary particle" refers to an aggregate, i.e., a secondary structure, in which primary particles are aggregated by physical or chemical bonding between primary particles without any intentional aggregation or assembly process for the primary particles.

[0039] The aforementioned "primary particle" refers to the smallest particle unit that can be distinguished as a single unit when observing a cross-section of the positive electrode active material using a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0040] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery is composed of single-particle systems, which increases particle strength and suppresses particle breakage during rolling. It also prevents cracks from forming between primary particles when charging and discharging is repeated, and reduces the specific surface area, thereby decreasing the amount of gas generated by side reactions with the electrolyte.

[0041] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has an average particle size (D50) of 5 to 8 μm, more specifically, 5.2 to 8 μm, 5.5 to 8 μm, or 6 to 8 μm.

[0042] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve. The average particle size (D50) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

[0043] By having a sufficiently large average particle size of the positive electrode active material, as described above, the tap density can be further improved compared to conventional small-particle single-particle designs, and consequently, the electrode energy density can be significantly improved. However, if the average particle size of the positive electrode active material is too large, the lithium ion migration path becomes longer, degrading electrochemical properties such as capacity and output; therefore, an upper limit is set as described above.

[0044] However, if the average particle size (D50) is increased as described above using only a single primary particle, the migration path of lithium ions within the particle becomes longer, leading to a problem of decreased electrochemical properties such as capacity and charge / discharge efficiency.

[0045] In contrast, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes both single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles. In this specification, "single particle" means a single particle consisting of one primary particle, and "quasi-single particle" means a single particle consisting of multiple primary particles. By including quasi-single particles in addition to single particles in the positive electrode active material, the degradation of the electrochemical properties described above can be minimized and the rolling density can be further maximized. In this specification, the spherical shape does not necessarily have to be a perfect sphere, but is a concept that includes similar spherical shapes.

[0046] Furthermore, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention satisfies the following formula 1.

[0047] [Formula 1] 1.2μm ≤ D50 - D50 p ≤1.8μm

[0048] In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 p This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

[0049] If the value of Equation 1 for the positive electrode active material is too small, particle strength may be excellent, but capacity and charge / discharge efficiency characteristics may decrease. If the value of Equation 1 for the positive electrode active material is too large, particle strength may deteriorate and life characteristics may decrease.

[0050] In this case, the average number of primary particles in the quasi-single particle consisting of the plurality of primary particles can be 8 or less, and more specifically, it can be 2 to 8 or 3 to 8.

[0051] In this specification, the "average number of primary particles in a quasi-single particle" can be determined by taking 25 μm × 20 μm 2D images at 5 points per sample, observed on a 5,000x magnification SEM (scanning electron microscope) image, and then deriving the arithmetic mean of the number of primary particles observed with the naked eye for each of at least 5 arbitrary single particles at each point. It should be noted that in this specification, the "average number of primary particles in a quasi-single particle" refers to the average number of primary particles observed on the 2D SEM image, not the average number of primary particles contained in a single particle in actual three-dimensional reality.

[0052] If the average number of primary particles within a quasi-single particle is too high, the voids formed between primary particles will increase proportionally, potentially leading to particle breakage due to repeated contraction and expansion of primary particles with different orientations during the rolling and charging / discharging processes. In other words, particle strength may deteriorate, and consequently, lifetime characteristics may be degraded. However, if the average number of primary particles within a quasi-single particle is too low, it will be similar to a single particle, and the lithium ion diffusion distance within the particle will be long, potentially reducing capacity and charge / discharge efficiency characteristics.

[0053] Furthermore, the average aspect ratio of the primary particles within the quasi-single particle can be 1.1 or greater, and more specifically, it can be between 1.1 and 2.5.

[0054] In this specification, "aspect ratio" can be defined as the ratio of the length of the longest side of a particle to the length of the shortest side, and "average aspect ratio" can be defined as the arithmetic mean of the aspect ratios derived by measuring the lengths of the shortest and longest sides, respectively, using software during the SEM image measurement process for particle shape analysis for at least 10 or more particles. Thus, the reason why the average aspect ratio of primary particles is 1.1 or greater, and the shape of primary particles is closer to a rod than a perfect sphere, is due to the characteristic that crystals tend to grow in the thermodynamically stable 003 plane direction, where surface energy differs depending on the crystal plane. While a larger aspect ratio has the advantage of increasing particle strength, if the average aspect ratio of primary particles is too large, problems may arise such as a decrease in capacity and efficiency due to an increase in lithium diffusion distance.

[0055] The value of Equation 1 can be more easily achieved within the target range according to the present invention when the positive electrode active material of the single-particle system includes single particles and quasi-single particles, and the average number of primary particles within the quasi-single particles and the average aspect ratio of primary particles within the quasi-single particles are appropriately adjusted.

[0056] The positive electrode active material for the lithium secondary battery can have a compressive density of 3.61 g / cc or more after applying a pressure of 9 tons. This property corresponds to the rolling density of the active material during electrode manufacturing, and having such a high compressive density can improve the electrode energy density.

[0057] In this specification, the compressive density of the active material after applying a pressure of 9 tons can be measured by loading 3g of the active material sample into a 13mm diameter pellet, applying a pressure of 9 tons using a Caver hydraulic press, and observing the change in the pellet's height before and after pressure application. The specific calculation formula is as follows.

[0058] [Formula 1] Density after applying a pressure of 9 tons = Weight of active material sample (3g) / (Φ × (1.3cm / 2)) 2 × (Change in height before and after pressure application)

[0059] In the above calculation formula 1, Φ represents pi.

[0060] The positive electrode active material for the lithium secondary battery has a BET specific surface area of ​​0.55 m². 2 It can be less than / g. When the specific surface area of ​​the active material is this small, side reactions between the active material and the electrolyte are reduced, and the battery life characteristics can be improved.

[0061] In this specification, the specific surface area of ​​the active material can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020) on the active material powder.

[0062] On the other hand, the lithium transition metal oxide may contain 60 mol% or more of nickel based on the total moles of the transition metal, and more specifically, 70, 80, or 90 mol% or more. Such a high nickel content enables the realization of high capacity characteristics.

[0063] The lithium transition metal oxide may further contain grain growth promoting elements, which are Zr, Al, B, or combinations thereof. By further containing grain growth promoting elements in the lithium transition metal oxide, the firing temperature for lithium transition metal oxide formation can be lowered, crystal defects such as an increase in the positive ion mixing ratio due to high-temperature firing can be prevented, and the average particle size of single particles can be efficiently increased during the firing process.

[0064] The content of the grain growth promoting element may be 0.1 to 1 mol% based on the total number of moles of the transition metal, and more specifically, it may be 0.3 to 1 mol%. More specifically, the content of Zr may be 0.1 to 0.3 mol% based on the total number of moles of the transition metal. The content of Al may be 0.3 to 1.0 mol% based on the total number of moles of the transition metal. The content of B may be 0.1 to 0.8 mol%.

[0065] When the content of grain growth promoting elements satisfies the aforementioned range, the effects of adding grain growth promoting elements and the effect of preventing deterioration of electrochemical properties due to excessive addition can be achieved uniformly.

[0066] The positive electrode active material may further include a coating layer on the lithium transition metal oxide containing Co, Al, or a combination thereof. By further including a coating layer of the above composition in the positive electrode active material, side reactions with the electrolyte can be suppressed, the structural stability of the active material can be improved, and the battery life characteristics can be further improved.

[0067] The aforementioned lithium transition metal oxide can be represented by the following chemical formula 1.

[0068] [Chemical formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2

[0069] In the above chemical formula 1, 0.8≦a≦1.2, 0.60≦x<1, 0≦y≦0.4, 0≦z≦0.4, 0≦w1≦0.01, 0≦w2≦0.2, x+y+z+w1+w2=1, M1 is Zr, Al, B or a combination thereof, and M2 is Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

[0070] In the lithium transition metal oxide of chemical formula 1, lithium can be present 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 positive electrode active material may increase, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of controlling the lithium content on improving the capacity characteristics of the positive electrode active material and the balance of sinterability during the production of the active material, the lithium can more preferably be present in an amount of 0.9 ≤ a ≤ 1.1.

[0071] In the lithium transition metal oxide of chemical formula 1, nickel can be present in a content corresponding to x, i.e., 0.6 ≤ x < 1, 0.6 ≤ x ≤ 0.97, 0.80 ≤ x ≤ 0.97, or 0.90 ≤ x ≤ 0.97. If the nickel content is too low, it becomes difficult to increase the battery capacity, and if the nickel content is too high, the stability of the active material structure may decrease, potentially reducing battery life and safety.

[0072] In the lithium transition metal oxide of chemical formula 1, cobalt can be present in a content corresponding to y, i.e., 0 ≤ y ≤ 0.4, 0 ≤ y ≤ 0.2, or 0 ≤ y ≤ 0.1. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and a high powder density of the active material. If the cobalt content is too high, the overall cost of the raw materials may increase and the reversible capacity may decrease.

[0073] In the lithium transition metal oxide of chemical formula 1, manganese can be present in an amount corresponding to z, i.e., 0 ≤ z ≤ 0.4. If the manganese content is too low, the production cost will 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.

[0074] In the lithium transition metal oxide of chemical formula 1, M1 can be present in an amount corresponding to w1, i.e., 0 ≤ w1 ≤ 0.01. In this case, M1 is a grain growth promoting element and is Zr, Al, B, or a combination thereof.

[0075] In the lithium transition metal oxide of chemical formula 1, M2 can be present in an amount equivalent to w2, i.e., 0 ≤ w2 ≤ 0.2. In this case, M2 is a doping element of Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0076] 2.Cathode active material manufacturing method Another embodiment of the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a nickel-containing transition metal precursor; forming a mixture containing the transition metal precursor and a lithium raw material, and then performing a main calcination to form a lithium transition metal oxide with an increased number of primary particles; post-calcining the lithium transition metal oxide; and crushing the post-calcined lithium transition metal oxide to form a lithium transition metal oxide containing single particles consisting of one primary particle and spherical quasi-single particles consisting of multiple primary particles, wherein the main calcination temperature is higher than the post-calcination temperature and the main calcination time is shorter than the post-calcination time.

[0077] The following describes, step by step, a method for producing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention.

[0078] First, prepare a nickel-containing transition metal precursor.

[0079] The transition metal precursor may be a transition metal hydroxide or a transition metal oxide.

[0080] The transition metal hydroxide can be produced as a positive electrode active material precursor by, for example, adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution containing a nickel raw material and selectively a cobalt raw material or a manganese raw material, and then causing a coprecipitation reaction.

[0081] The transition metal oxide can be produced by calcining a transition metal hydroxide in an oxygen or air atmosphere at a temperature of 250 to 650°C.

[0082] In this case, the average particle size (D50) of the transition metal precursor can be 5 μm or more. When the average particle size of the transition metal precursor satisfies the above range, single-particle lithium transition metal oxides of medium particle size, which are the target of the present invention, can be easily obtained.

[0083] The nickel raw material is not particularly limited as long as it is used in the production of cathode active material precursors in the industry. For example, the nickel raw material is a nickel-containing sulfate, acetate, nitrate, halogen compound, sulfide, hydroxide, oxide or oxyhydroxide, and may specifically be, but not limited to, NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO32)·6H2O, fatty acid nickel salt, nickel halide, or a combination thereof.

[0084] The aforementioned cobalt raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the cobalt raw material is a cobalt-containing sulfate, acetate, nitrate, halogen compound, sulfide, hydroxide, oxide or oxyhydroxide, and may specifically be, but not limited to, CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof.

[0085] The manganese raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the manganese raw material may be manganese-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof, and may, but is not limited to, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salts, manganese citrate and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride, or combinations thereof.

[0086] The transition metal-containing solution may be prepared by adding a nickel raw material and, selectively, a cobalt raw material or a manganese raw material to a solvent, specifically, water, or an organic solvent (e.g., alcohol) that can be homogeneously mixed with water, and a mixture of water.

[0087] The complexing agent-containing solution plays a role in complex formation, and the complexing agent may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof. On the other hand, the complexing agent-containing solution can be used in aqueous solution form, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (e.g., alcohol) can be used as the solvent.

[0088] The pH adjusting agent-containing solution may serve as a precipitating agent or pH adjuster and may contain alkali metal or alkaline earth metal hydroxides such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Alternatively, the pH adjusting agent-containing solution may be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent (e.g., alcohol) that is homogeneously miscible with water may be used as the solvent. In this case, the pH adjusting agent-containing solution may be added in an amount that brings the pH of the reaction solution to 11-13.

[0089] The aforementioned coprecipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon, at a temperature of 30-70°C, and at a pH of 11-13.

[0090] Through this process, nickel-cobalt-manganese (-doped element) hydroxide particles are generated and precipitate in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed with water, and dried to obtain the precursor. The precursor may be secondary particles formed by the aggregation of primary particles.

[0091] At this time, the concentrations of nickel, cobalt, and manganese raw materials can be adjusted to control the molar ratio of nickel, cobalt, and manganese in the precursor.

[0092] Alternatively, the doping element can be added during the preparation step of the positive electrode active material precursor. In this case, the doping element can be added to the precursor by adding the doping raw material to the transition metal-containing solution and allowing a coprecipitation reaction to occur.

[0093] Next, a mixture containing the transition metal precursor and lithium raw material is formed, and then calcined to form a lithium transition metal oxide with an increased number of primary particles.

[0094] More specifically, through the aforementioned calcination process, single-particle lithium transition metal oxides consisting of multiple primary particles can be formed.

[0095] Next, the grown lithium transition metal oxide is subjected to post-calcination.

[0096] In the method for producing an active material according to one embodiment of the present invention, the firing is carried out in two stages as described above, and in this case, the main firing temperature is higher than the post-firing temperature, and the main firing time is shorter than the post-firing time.

[0097] High-temperature, short-duration main firing allows for the growth of primary particles within a single particle to an appropriate level. Low-temperature, long-duration post-firing induces crystal rearrangement, relieving internal stresses increased during high-temperature main firing and reducing nickel ion mixing.

[0098] More specifically, conventional single particle manufacturing methods, such as a one-stage firing method involving high temperature and long firing time, have the problem of generating nickel positive ion mixing (cation mixing) and Rocksalt impurities. On the other hand, the manufacturing method according to one embodiment of the present invention can prevent the above problem through high temperature and short firing time and low temperature and long firing time, and can appropriately grow the number of primary particles within the single particle, thereby inducing the final produced active material to contain a single particle and single particles consisting of multiple primary particles.

[0099] At this time, the main firing temperature may be 850 to 900°C, and the main firing time may be 5 to 9 hours. Also, the post-firing temperature may be 760 to 820°C, and the post-firing time may be 9 to 12 hours. When the main firing temperature and time, and the post-firing temperature and time, satisfy the above ranges, it becomes easier to achieve the active material composition and physical properties targeted by the present invention.

[0100] The lithium raw material can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halogen compounds, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material can be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0101] The aforementioned firing can be carried out in an oxygen or air atmosphere. When firing is performed in the aforementioned atmosphere, the local oxygen partial pressure increases, which can improve the crystallinity of the positive electrode active material.

[0102] On the other hand, other doping elements can be added during the lithium transition metal oxide formation step. In this case, other doping raw materials are added during the mixture formation process and then calcined, thereby doping the lithium transition metal oxide with other doping elements.

[0103] On the other hand, the transition metal precursor prepared in the step of preparing the transition metal precursor, or the lithium transition metal oxide formed in the step of calcination to form a lithium transition metal oxide with an increased number of primary particles, may further contain grain growth promoting elements, which are Zr, Al, B, or combinations thereof. That is, the grain growth promoting elements can be doped in the transition metal precursor formation step, or they can be doped in the lithium transition metal oxide formation step, which is the active material.

[0104] In this case, the content of the grain growth promoting element may be 0.1 to 1 mol% based on the total number of moles of transition metal in the transition metal precursor or the lithium transition metal oxide, and more specifically, it may be 0.3 to 1 mol%. More specifically, the content of Zr may be 0.1 to 0.3 mol% based on the total number of moles of transition metal in the transition metal precursor or the lithium transition metal oxide. The content of Al may be 0.3 to 1.0 mol% based on the total number of moles of transition metal in the transition metal precursor or the lithium transition metal oxide. The content of B may be 0.1 to 0.8 mol%.

[0105] As mentioned above, the technical significance of introducing grain growth promoting elements and adjusting their content is as described previously and will therefore be omitted.

[0106] Next, the post-calcined lithium transition metal oxide is crushed to form lithium transition metal oxides containing single particles made of one primary particle and spherical quasi-single particles made of multiple primary particles.

[0107] This makes it possible to obtain the positive electrode active material according to the present invention.

[0108] The process may further include, if necessary, the step of forming a lithium transition metal oxide comprising a single particle consisting of one primary particle and a spherical single particle consisting of multiple primary particles, followed by the step of forming a coating layer comprising Co, Al, or a combination thereof.

[0109] More specifically, the single-particle lithium transition metal oxide can be mixed with a Co raw material, an Al raw material, or a combination thereof, and then heat-treated to form a coating layer. The technical significance of forming the coating layer is as described above and will therefore be omitted.

[0110] 3. Positive electrode and lithium secondary battery Another embodiment of the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material described above.

[0111] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode. More specifically, the lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0112] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0113] Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, which contains the positive electrode active material described above.

[0114] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector usually 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 adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric, etc.

[0115] The positive electrode active material layer may include a binder and / or conductive material together with the positive electrode active material described above.

[0116] At this time, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, recycled cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One or more of these can be used, but are not limited to these. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0117] The conductive material is used to impart conductivity to the electrodes and can be used in the battery without any special restrictions as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal 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 can be used alone or in mixtures of two or more, but this is not limited to these examples. The conductive material can usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0118] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0119] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the positive electrode active material described above and optionally a binder, conductive material, or solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0120] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or in mixtures of two or more. The amount of solvent used should be such that, considering the coating thickness of the slurry and the production yield, it is sufficient to have a viscosity that dissolves or disperses the positive electrode active material, conductive material, and binder, and subsequently exhibits excellent thickness uniformity when coated for positive electrode production.

[0121] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0122] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0123] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector usually has a thickness of 3 to 500 μm, and like the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0124] The negative electrode active material layer may selectively contain a binder and a conductive material along with the negative electrode active material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode active material layer forming composition, which includes the negative electrode active material and selectively a binder and a conductive material, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto another support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0125] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can 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; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more mixtures of these can be used. Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0126] The binder and conductive material may be the same as those described earlier for the positive electrode.

[0127] The separator, which separates the negative and positive electrodes and provides a pathway for lithium ions to move, can be used without special restrictions as long as it is the type normally used as a separator in lithium secondary batteries. In particular, it is desirable that it has low resistance to ion movement of the electrolyte while having excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics composed of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0128] The aforementioned electrolytes can be, 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 the manufacture of lithium secondary batteries. Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0129] The aforementioned organic solvent can be used without special limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; and dimethyl carbonate (DMC) and diethyl carbonate (DE). C) Carbonate solvents such as methylethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is even more preferable. In this case, using a mixture of cyclic carbonate and linear carbonate in a volume ratio of approximately 1:1 to approximately 1:9 can bring out the best performance of the electrolyte.

[0130] The lithium salt can be used without any special restrictions, as long as it is a compound that can provide lithium ions for use 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, etc. 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 this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0131] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0132] Another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0133] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Examples]

[0134] The following examples illustrate the realization of the present invention in more detail. However, the following examples represent only one preferred embodiment of the present invention, and the present invention is not limited to these examples.

[0135] Example 1 (1) Manufacture of positive electrode active material (Preparation of transition metal hydroxide) Following a general coprecipitation method, an average particle size (D50) of 7 μm (Ni 0.96 Co 0.03 Mn 0.01 Transition metal hydroxides with a )(OH)2 composition were prepared.

[0136] (Preparation of transition metal oxide) 500 g of the transition metal hydroxide was mixed with 0.993 g of ZrO2, which corresponds to 0.15 mol% of Zr based on a total transition metal content of 100 mol% of the transition metal hydroxide, and 2.096 g of Al(OH)3, which corresponds to 0.5 mol% of Al, as grain growth promoters. The mixture was then calcined at 500°C for 4 hours under an air atmosphere, and a dehydration reaction was carried out to produce a transition metal oxide precursor containing Zr and Al.

[0137] (Castration) Afterwards, 150 g of the transition metal oxide precursor was mixed with 83.963 g of LiOH·H2O as a lithium raw material so that the Li / Me molar ratio was 1.02. Then, the mixture was calcined at 850°C for 6.7 hours, followed by calcination at 790°C for 9.8 hours to produce lithium transition metal oxide.

[0138] (Disintegration) Subsequently, the post-calcined lithium transition metal oxide was disintegrated.

[0139] (Coating) Subsequently, 130 g of the crushed lithium transition metal oxide was mixed with 0.560 g of LiOH·H2O, 2.504 g of Co(OH), and 30.189 g of Al(OH), and then heat-treated at 650-700°C for 15 hours to produce a positive electrode active material in which a coating layer containing 2 mol% of Co and 0.2 mol% of Al was formed on the surface.

[0140] (2) Manufacturing of lithium secondary batteries The slurry for manufacturing the electrode plate was prepared by mixing the manufactured positive electrode active material, conductive material (carbon black, denkablack), and binder (PVDF, KF1100) in a ratio of 96.5:1.5:2 wt%, and adjusting the viscosity by adding NMP (N-Methyl-2-pyrrolidone) so that the solid content was approximately 30%. The manufactured slurry was coated onto 15 μm thick aluminum foil using a Doctor blade, and then dry-rolled. The electrode loading amount was 15.0 mg / cm². 2 The rolling density (25°C, 20kN) is 3.6 g / cm³. 3 That was the case.

[0141] The electrolyte used was 1M LiPF6in EC:DMC:EMC=3:4:3 (vol%) with 3.0 vol% VC added relative to the total electrolyte volume. Coin cells were manufactured using a PP separation membrane and a lithium anode (200 μm, Honzo metal).

[0142] Examples 2-4 and Comparative Example 1 As shown in Table 1 below, the positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the firing temperature and time for the main firing and post-firing steps were different.

[0143] Comparative Examples 2, 4-6 In the transition metal hydroxide preparation step, a transition metal hydroxide with an average particle size (D50) of 4 μm was prepared. The process was carried out in the same manner as in Example 1, except that the firing temperature and time for the main firing and post-firing steps were different, as shown in Table 1 below, to produce a positive electrode active material and a lithium secondary battery.

[0144] Comparative Example 3 Following a general coprecipitation method, the average particle size (D50) is 13 μm (Ni 0.96 Co 0.03 Mn 0.01 Transition metal hydroxides with a )(OH)2 composition were prepared.

[0145] Next, 150 g of the transition metal hydroxide was mixed with 71.992 g of LiOH·H2O so that the Li / Me molar ratio was 1.06. After firing at 750°C for 12 hours, the mixture was crushed, washed with water, and dried to produce lithium transition metal oxide.

[0146] Next, 130 g of the lithium transition metal oxide was mixed with 30.371 g of H3BO, and then heat-treated at 250-300°C for 6 hours to produce a positive electrode active material in which a coating layer containing 0.45 mol% of B was formed on the surface.

[0147] Next, a lithium secondary battery was manufactured in the same manner as in Example 1.

[0148] Table 1 below summarizes the manufacturing methods for the examples and comparative examples.

[0149] [Table 1]

[0150] Experimental Example 1: SEM Image Observation of Active Material SEM (scanning electron microscope) images of the positive electrode active materials produced by the examples and comparative examples were observed and are shown in Figures 1 to 10 in the order of Examples 1 to 4 and Comparative Examples 1 to 6, respectively.

[0151] Referring to Figures 1 to 10, it was confirmed that the active materials of Examples 1 to 4 and Comparative Examples 1 to 2 and 4 to 6 were not formed by the aggregation of tens to hundreds of primary particles, which is conventionally classified as a typical secondary particle shape, but rather had a single-particle structure. On the other hand, in the case of Comparative Example 3, it was confirmed that it had a conventional, typical secondary particle shape.

[0152] Furthermore, in Examples 1 to 4, it was confirmed that the particles had a medium particle size level and contained both single particles consisting of one primary particle and quasi-single particles consisting of multiple primary particles.

[0153] On the other hand, in the case of Comparative Example 1, it was confirmed that the number of primary particles within the quasi-single particle was clearly larger. Also, in the case of Comparative Example 2, it was confirmed that the particle size was smaller compared to the example.

[0154] Experimental Example 2: Evaluation of the physical properties of the positive electrode active material The physical properties of the positive electrode active materials produced according to the examples and comparative examples were evaluated, and the results are shown in Table 2 below. The experimental method is as follows.

[0155] (1) Average particle diameter (D50) measurement For the active material powder, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0156] (2) Equation 1 evaluation [Formula 1]=D50-D50 p We evaluated the values ​​shown.

[0157] In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 p This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

[0158] (3) Average number of primary particles in a single particle After capturing (25 μm) × (20 μm) 2D images at 5 points per sample using a 5,000x magnification SEM (scanning electron microscope), the arithmetic mean of the number of primary particles observed with the naked eye was calculated for each of at least 5 arbitrary single particles at each point.

[0159] (4) Compression density evaluation (9 tons) The density after applying a pressure of 9 tons was evaluated. Specifically, 3g of the active material sample was loaded into a 13mm diameter pellet, and then a pressure of 9 tons was applied using a Caver hydraulic press. The density was then measured by observing the change in pellet height before and after pressure application, and the specific calculation formula is as follows.

[0160] [Formula 1] Density after applying a pressure of 9 tons = Weight of active material sample (3g) / (Φ × (1.3cm / 2)) 2 × (Change in height before and after pressure application)

[0161] In the above calculation formula 1, Φ represents pi.

[0162] (5) BET specific surface area evaluation The specific surface area was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0163] [Table 2]

[0164] Referring to Table 2, in Examples 1-4, where the precursor particle size, main firing and post-firing temperatures and times were appropriately adjusted during active material production, it was confirmed that the average particle size, the value of Equation 1, the average number of primary particles within a quasi-single particle, the compressive density, and the specific surface area of ​​the active material were all appropriately obtained within the target range of the present invention. On the other hand, in Comparative Example 1, it was confirmed that the average number of primary particles within a single particle was too high as a result of the main firing temperature being too low. Consequently, it was confirmed that the value of Equation 1 was too large, resulting in low strength and an excessively large specific surface area.

[0165] In Comparative Example 2, it was confirmed that the average particle size of the obtained active material was too small as a result of the precursor particle size being too small. It was also confirmed that the value of Equation 1 was too large, resulting in weak strength and an excessively large specific surface area. Furthermore, it was confirmed that the compressive density also deteriorated as a result of the small average particle size of the active material.

[0166] In the case of Comparative Example 3, it was confirmed that the value of Equation 1 was too large for the conventionally used secondary particle active material, resulting in low strength and a large specific surface area.

[0167] In Comparative Example 4, it was confirmed that the value of Equation 1 became too small because the post-firing temperature was higher than the main firing temperature.

[0168] In Comparative Example 5, it was confirmed that the value of Equation 1 became too small as the post-firing time was shorter than the main firing time.

[0169] In Comparative Example 6, it was confirmed that the value of Equation 1 became too small when only a single-stage high-temperature, long-duration firing was performed instead of a two-stage firing.

[0170] Experimental Example 3: Evaluation of Battery Electrochemical Properties

[0171] (1) Initial charge and discharge capacity, initial efficiency evaluation After fabricating lithium secondary battery half-cells, charge-discharge tests were conducted after aging at 25°C for 12 hours. For initial capacity evaluation, a reference capacity of 200mAh / g was used, and the cells were charged to 4.25V with a constant current of 0.1C. Then, charging was switched to a constant voltage until the termination current reached 0.05C. After charging, a 10-minute rest time was allowed, and then the cells were discharged to 2.5V with a constant current of 0.1C, using a reference capacity of 200mAh / g.

[0172] (2) Evaluation of high-temperature life retention rate (45°C, 50 cycles) The high-temperature life retention rate was determined at 45°C. The battery was charged to 4.25V with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After charging, a 10-minute rest time was observed, followed by discharge at a constant current of 1.0C until the voltage reached 2.5V. Under these charge / discharge conditions, 50 charge / discharge cycles were performed, and the capacity retention rate at the 50th cycle compared to the first cycle was calculated.

[0173] (3) Evaluation of the rate of increase in high temperature resistance (45°C, 50 cycles) The high-temperature resistance increase rate was calculated at 45°C. The battery was charged to 4.25V with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After charging, a 10-minute rest time was observed, followed by discharge at a constant current of 1.0C until the voltage reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the resistance increase rate at the 50th cycle compared to the initial cycle was calculated.

[0174] [Table 3]

[0175] Referring to Table 3, it was confirmed that in Examples 1 to 4, where the average particle size of the active material, the value of Equation 1, the average number of primary particles within a quasi-single particle, and the specific surface area were appropriately adjusted, the battery capacity, initial efficiency, high-temperature life retention rate, and high-temperature resistance increase rate were uniformly excellent. On the other hand, in Comparative Example 1, where the average number of primary particles within a quasi-single particle was too large, it was confirmed that the particle strength deteriorated, resulting in a decrease in high-temperature life characteristics.

[0176] In Comparative Example 2, which has an average particle size in the small particle size range, the capacity and initial efficiency were good, but it was confirmed that the high-temperature lifetime retention rate was worse compared to the example. Furthermore, a deterioration in electrode energy density was expected.

[0177] In the case of Comparative Example 3, which uses conventional secondary particles, the capacity and initial efficiency are good, but it was confirmed that the high-temperature lifetime characteristics are significantly reduced as a result of the deterioration of particle strength as a secondary particle.

[0178] In comparative examples 4-6, the value of Equation 1 was too small, resulting in excellent particle strength, but it was confirmed that the battery capacity and initial efficiency decreased.

[0179] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. Various modifications can be made within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention.

[0180] Therefore, the substantial scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. Nickel-containing layered lithium transition metal oxide, The average particle size (D50) is 5 to 8 μm. It includes a single particle consisting of one primary particle and a spherical quasi-single particle consisting of multiple primary particles, Positive electrode active material for lithium secondary batteries that satisfies the following formula 1: [Formula 1] 1.2μm≦D50-D50 ｐ ≦1.8μm In the above formula 1, D50 is the average particle size (D50) of the positive electrode active material before the application of a pressure of 9 tons, and D50 ｐ This is the average particle size (D50) of the positive electrode active material after applying a pressure of 9 tons.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average number of primary particles in the quasi-single particle is 8 or less.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average aspect ratio of the primary particles within the quasi-single particle is 1.1 or greater.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the compressed density after applying a pressure of 9 tons is 3.61 g / cc or more.

5. BET specific surface area is 0.55 m² ２ The positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount is less than or equal to / g.

6. The lithium transition metal oxide contains 60 mol% or more nickel based on the total number of moles of the transition metal, as described in claim 1.

7. The positive electrode active material for a lithium secondary battery according to claim 1, further comprising a grain growth promoting element, which is Zr, Al, B, or a combination thereof, as the lithium transition metal oxide.

8. The positive electrode active material for lithium secondary batteries according to claim 7, wherein the content of the grain growth promoting element is 0.1 to 1 mol% based on the total number of moles of transition metals.

9. The positive electrode active material for a lithium secondary battery according to claim 1, further comprising a coating layer containing Co, Al, or a combination thereof on the lithium transition metal oxide.

10. The lithium transition metal oxide is the positive electrode active material for a lithium secondary battery according to claim 1, represented by the following chemical formula 1: [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ M1 ｗ１ M2 ｗ２ ]O ２ In the above chemical formula 1, 0.8 ≤ a ≤ 1.2, 0.60 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 ≤ w1 ≤ 0.01, 0 ≤ w2 ≤ 0.2, x + y + z + w1 + w2 = 1, M1 is Zr, Al, B or a combination thereof, and M2 is Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr or a combination thereof.

11. Steps to prepare nickel-containing transition metal precursors; The step of forming a mixture containing the transition metal precursor and lithium raw material, and then calcining it to form a lithium transition metal oxide with an increased number of primary particles; The step of post-calcining the lithium transition metal oxide; and The step includes crushing the post-calcined lithium transition metal oxide to form a lithium transition metal oxide containing a single particle made of one primary particle and a spherical single particle made of multiple primary particles, A method for producing a positive electrode active material for a lithium secondary battery, wherein the main firing temperature is higher than the post-firing temperature, and the main firing time is shorter than the post-firing time.

12. In the step of preparing the transition metal precursor, The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the average particle size (D50) of the transition metal precursor is 5 μm or more.

13. A method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the transition metal precursor prepared in the step of preparing the transition metal precursor, or the lithium transition metal oxide formed in the step of forming a lithium transition metal oxide in which the number of primary particles has grown by calcination, further comprises a grain growth promoting element which is Zr, Al, B, or a combination thereof.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 13, wherein the content of the grain growth promoting element is 0.1 to 1 mol% based on the total number of moles of transition metal in the transition metal precursor or the lithium transition metal oxide.

15. A positive electrode for a lithium secondary battery comprising the positive electrode active material described in any one of claims 1 to 10.

16. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 15.

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