Positive electrode active material, method for preparing the same, and positive electrode and lithium

Abstract

The positive electrode active material according to the present invention comprises a single particle consisting of one single nodule, a quasi-single particle as a composite of at most 30 nodules, or a combination thereof, in which the positive electrode active material comprises a lithium nickel-based oxide having a molar ratio of Ni of at least 60 mol% in all transition metals, and a negative skew factor (NSF) represented by the following Equation 1 is 0.20 to 0.35: [Equation 1] NSF = (D50-D10) / Imax In Equation 1, D50 is a particle diameter at a cumulative volume of 50% in a volume cumulative particle diameter distribution diagram of the positive electrode active material, D10 is a particle diameter at a cumulative volume of 10% in a volume cumulative particle diameter distribution diagram of the positive electrode active material, and Imax is a particle diameter at a cumulative volume of 10% in a volume cumulative particle diameter distribution diagram of the positive electrode active material. Imax is the maximum volume fraction in the volume cumulative particle size profile of the positive electrode active material.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application Nos. 10-2022-0166990, filed on December 2, 2022, 10-2022-0166991, filed on December 2, 2022, and 10-2023-0172466, filed on December 1, 2023, the disclosures of which are incorporated herein by reference in their entireties.

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

[0003] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include active materials capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMnO4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used as positive electrode active materials for lithium secondary batteries. Among them, lithium cobalt oxide has the advantages of a high working voltage and excellent capacity characteristics. However, due to the high price and unstable supply of cobalt as a raw material, it is difficult to commercially apply lithium cobalt oxide to large-capacity batteries. The structural stability of lithium nickel oxide is poor, so it is difficult to achieve sufficient life characteristics. At the same time, lithium manganese oxide has excellent stability, but there is a limitation in that the capacity characteristics are poor. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to compensate for the limitations of lithium transition metal oxides containing only Ni, Co, or Mn. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in electric vehicle batteries.

[0005] Conventional lithium metal oxides are generally in the form of spherical secondary particles formed by agglomeration of dozens to hundreds of primary particles. However, when applying lithium nickel cobalt manganese oxide in the form of secondary particles formed by agglomeration of multiple primary particles as described above, there are the following limitations: particle breakage is likely to occur (primary particles fall off during the roll pressing process in the preparation of the positive electrode), and particles crack during charging and discharging. When particle breakage or cracking occurs in the positive electrode active material, since the contact area with the electrolyte solution increases, the gas generation and active material deterioration caused by side reactions with the electrolyte solution increase. As a result, there is a limitation in the deterioration of life characteristics.

[0006] To solve the above limitations, a technique has been proposed to prepare a cathode active material in the form of single particles rather than secondary particles by increasing the sintering temperature during the preparation of lithium nickel cobalt manganese oxide. Compared with the conventional cathode active material in the form of secondary particles, the cathode active material in the form of single particles has a smaller contact area with the electrolyte solution, so there are fewer side reactions with the electrolyte, and the particle strength is excellent, so there is less particle breakage during the manufacturing process of the electrode. Therefore, when the cathode active material in the form of single particles is applied, there are advantages of excellent gas generation and life characteristics. However, the conventional cathode active material in the form of single particles has the limitation of high resistance, so when applied, sufficient output performance cannot be obtained.

[0007] At the same time, only by increasing the average particle diameter of the cathode active material in the form of single particles can the tap density and bulk density be increased, but when the average particle diameter increases above a certain level, there are limitations of an increased diffusion distance of lithium ions in the particles and an increased initial resistance.

[0008] Therefore, a technique is needed that can increase the bulk density while minimizing the average particle diameter of the cathode active material in the form of single particles. SUMMARY OF THE INVENTION

[0009] [Technical Problem]

[0010] One aspect of the present invention provides a cathode active material having low initial resistance characteristics and high energy density due to a specific particle size distribution, and also provides a method for preparing the same, a cathode including the same, and a lithium secondary battery.

[0011] [Technical Solution]

[0012] According to one aspect of the present invention, there is provided a cathode active material including single particles composed of one single nodule, quasi-single particles that are composites of up to 30 nodules, or a combination thereof, wherein the cathode active material includes a lithium nickel-based oxide in which the molar ratio of Ni in all transition metals is at least 60 mol%, and the negative skewness factor (NSF) represented by the following Equation 1 is 0.20 to 0.35:

[0013] [Equation 1]

[0014] NSF = (D 50 - D 10 ) / I max

[0015] In the above Equation 1, D 50 is the particle diameter at a cumulative volume of 50% in the volume cumulative particle size distribution diagram of the cathode active material, D 10 is the particle diameter at a cumulative volume of 10% in the volume cumulative particle size distribution diagram of the cathode active material, and I maxis the maximum volume fraction in the volume cumulative particle size distribution diagram of the positive electrode active material.

[0016] The D of the positive electrode active material 50 can be 5.0 μm to 7.0 μm.

[0017] The lithium nickel-based oxide can be represented by the following formula 1:

[0018] [Formula 1]

[0019] Li a Ni b Co c M 1 d M 2 e O2

[0020] In the above formula 1, M 1 is Mn, Al or a combination thereof, M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, 1.0 ≤ a ≤ 1.5, 0.6 ≤ b < 1.0, 0 < c < 0.1, 0 < d < 0.2, 0 ≤ e ≤ 0.1, and 0 < c + d + e ≤ 0.4.

[0021] The average particle size of the nodules of the positive electrode active material can be 1.0 μm to 7.0 μm.

[0022] The tap density of the positive electrode active material can be 2.40 g / cc to 2.60 g / cc.

[0023] The pellet density (under 9 tons) of the positive electrode active material can be 3.60 g / cc to 3.80 g / cc.

[0024] The initial resistance of a single cell manufactured using the positive electrode active material at an SOC of 50 can be 1.45 Ω to 1.50 Ω.

[0025] According to another aspect of the present invention, there is provided a method for preparing a positive electrode active material, the method comprising: mixing a positive electrode active material precursor with a lithium raw material and performing a first sintering; and pulverizing the product after the first sintering and performing a second sintering.

[0026] The D of the positive electrode active material precursor 50 can be 4.0 μm to 10.0 μm.

[0027] The pulverizing can be performed by jet mill pulverization.

[0028] The jet mill pulverization can be performed under the conditions of 2.0 bar to 4.0 bar and 1000 rpm to 2500 rpm.

[0029] According to another aspect of the present invention, there is provided a positive electrode including the above positive electrode active material, and a lithium secondary battery including the positive electrode.

[0030] [Advantageous Effects]

[0031] The positive electrode active material of the present invention has an NSF satisfying a specific range, so that small particles fill the spaces between relatively large particles, increasing the tap density and the granule density, thereby enabling the lithium secondary battery including the positive electrode active material to achieve a high energy density.

[0032] In addition, the positive electrode active material of the present invention has an NSF satisfying a specific range, thereby reducing the diffusion distance of lithium ions in the particles, so that the lithium secondary battery including the positive electrode active material can achieve a low initial resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. shows graphs of the volume cumulative particle size distribution of the positive electrode active materials prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention.

[0034] Figure 2 is a graph showing the tap density of the positive electrode active materials prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention as a function of D 50 variation.

[0035] Figure 3 is a graph showing the granule density of the positive electrode active materials prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention as a function of D 50 variation.

[0036] Figure 4 is a graph showing the granule density of the positive electrode active materials prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention as a function of NSF.

[0037] Figure 5 is a graph showing the initial resistance of the lithium secondary batteries including the positive electrode active materials prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention as a function of D 50 variation. DETAILED DESCRIPTION

[0038] It will be understood that the terms or words used in this specification and the claims should not be construed as being limited to the meanings defined in a commonly used dictionary, but should be interpreted as having meanings and concepts consistent with the technical idea of the present invention based on the principle that the inventor can appropriately define the terms to best explain the present invention.

[0039] As used herein, the term "single particle" refers to a particle composed of a single nodule. As used herein, the term "quasi-single particle" refers to a particle that is a composite particle formed of at most 30 nodules.

[0040] As used herein, the term "nodule" refers to the main body of the particle unit that constitutes single particles and quasi-single particles, and the nodule can be a single crystal without a crystalline grain boundary, or can be a polycrystal that has no grain boundary in appearance when observed in a field of view with a magnification of 5000 to 20000 times using a scanning electron microscope (SEM). The average particle size of the nodules can be determined by the arithmetic mean of the particle sizes of each nodule measured using a scanning electron microscope (SEM).

[0041] As used herein, the term "secondary particle" refers to a particle formed by the aggregation of dozens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of at least 40 primary particles.

[0042] The expression "particle" used herein can include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0043] As used herein, the term "D 50 " refers to the particle size at 50% of the volume cumulative particle size distribution based on the positive electrode active material. D 50 can be measured using the laser diffraction method. For example, the powder of the positive electrode active material can be dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (such as Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. Then, a volume cumulative particle size distribution graph can be obtained, and then the particle size corresponding to 50% of the volume cumulative amount can be determined to measure the average particle size D 50 .

[0044] Hereinafter, the present invention will be described in more detail.

[0045] Positive electrode active material

[0046] The positive electrode active material of the present invention contains single particles composed of a single nodule, quasi-single particles that are composites of at most 30 nodules, or a combination thereof.

[0047] Since lithium nickel-based oxides in the form of single particles and / or quasi-single particles have higher particle strength compared to conventional lithium nickel-based oxides in the form of secondary particles formed by the aggregation of dozens to hundreds of primary particles, there is less particle breakage during the rolling process.

[0048] In addition, the number of sub-components (i.e., nodules) constituting the particles in the lithium nickel-based oxide in the form of single particles or quasi-single particles of the present invention is small, thereby reducing the changes caused by the volume expansion and contraction of the primary particles during charging and discharging, and thus significantly reducing the cracking within the particles.

[0049] In particular, the inventors of the present invention have found that when applying a positive electrode active material having a negative skewness factor (NSF) within a certain range, i.e., the NSF represented by the following Equation 1, the particle breakage can be minimized during the electrode manufacturing process to reduce gas generation, the change in the crystal structure can be minimized during charging and discharging, the diffusion distance of lithium ions in the particles can be reduced to achieve low initial resistance characteristics, and the energy density can be improved by maximizing the tap density and the pellet density.

[0050] [Equation 1]

[0051] NSF = (D 50 - D 10 ) / I max

[0052] In the above Equation 1, D 50 is the particle size at which the cumulative volume is 50% in the volume cumulative particle size distribution diagram of the positive electrode active material, D 10 is the particle size at which the cumulative volume is 10% in the volume cumulative particle size distribution diagram of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution diagram of the positive electrode active material.

[0053] The positive electrode active material of the present invention may include a lithium nickel-based oxide in which the molar ratio of Ni in all transition metals is at least 60 mol%, at least 70 mol%, or at least 80 mol%.

[0054] The NSF value of the positive electrode active material of the present invention may be 0.20 to 0.35, 0.21 to 0.35, or 0.21 to 0.34. According to the research of the present inventors, when the NSF value is less than 0.20 or greater than 0.35, it is found that the tap density and the pellet density decrease.

[0055] When the NSF value satisfies the above range, since the small particles fill the space between the relatively large particles, the tap density and the pellet density increase. When the NSF value is less than 0.20, the small particles are not sufficient to fill the space between the large particles. When the NSF value is greater than 0.35, after the small particles fill the space between the large particles, the small particles still remain, resulting in a decrease in the pellet density. Therefore, even when D 50 is at the same level, when the NSF value is optimized, the tap density and the pellet density can be maximized.

[0056] The D of the positive electrode active material of the present invention50 can be from 5.0 μm to 7.0 μm, from 5.5 μm to 6.5 μm, or from 5.6 μm to 6.2 μm. When the D of the positive electrode active material of the present invention 50 satisfies the above range, low initial resistance characteristics and high energy density can be achieved. When the NSF value is the same, as the D of the positive electrode active material 50 increases, the pellet density increases. When the D of the positive electrode active material 50 is less than 5.0 μm, it may be difficult to achieve a relatively high pellet density even when the NSF reaches the optimal level. When D 50 is greater than 7.0 μm, the lithium mobility of the positive electrode active material decreases, and thus the initial resistance of the lithium secondary battery containing the positive electrode active material may increase.

[0057] Meanwhile, the positive electrode active material of the present invention may include a lithium nickel-based oxide. Specifically, it may include a lithium nickel-based oxide having a composition represented by the following Formula 1.

[0058] [Formula 1]

[0059] Li a Ni b Co c M 1 d M 2 e O2

[0060] In the above Formula 1, M 1 is Mn, Al, or a combination thereof, and is preferably Mn or a combination of Mn and Al. And M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo. The M 2 element is not necessarily included, but when the M 2 element is included in an appropriate amount, the M 2 element can be used to promote particle growth during sintering or improve crystal structure stability.

[0061] The above a represents the molar ratio of lithium in the lithium nickel-based oxide, and can satisfy 1.0 ≤ a ≤ 1.5, 1.1 ≤ a ≤ 1.4, or 1.2 ≤ a ≤ 1.3. When the molar ratio of lithium satisfies the above range, a stable layered crystal structure can be formed.

[0062] The above b represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide, and can satisfy 0.6 ≤ b < 1.0, 0.8 ≤ b < 1.0, or 0.82 ≤ b < 1.0. When the molar ratio of nickel satisfies the above range, the capacity characteristics are excellent. In particular, when the molar ratio of nickel is 0.8 or more, better capacity characteristics can be achieved.

[0063] The above c represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 < c < 0.1, 0 < c < 0.08, or 0 < c < 0.06.

[0064] The above d represents the molar ratio of M among all metals other than lithium in the lithium nickel-based oxide 1 and can satisfy 0 < d < 0.2, 0 < d < 0.18, or 0 < d < 0.15.

[0065] The above e represents the molar ratio of the M element among all metals other than lithium in the lithium nickel-based oxide 2 and can satisfy 0 ≤ e ≤ 0.1, 0 ≤ e ≤ 0.08, or 0 ≤ e ≤ 0.06.

[0066] The average particle size of the agglomerates of the positive electrode active material of the present invention can be 1.0 μm to 7.0 μm, 2.0 μm to 6.0 μm, or 3.0 μm to 5.0 μm. When the average particle size of the agglomerates of the positive electrode active material of the present invention satisfies the above range, high energy density and low initial resistance characteristics can be achieved. When the average particle size of the agglomerates of the positive electrode active material of the present invention is less than 1.0 μm, the total specific surface area of the positive electrode active material increases, so the side reaction of the electrolyte solution may increase. When the average particle size of the agglomerates is greater than 7.0 μm, the lithium mobility of the positive electrode active material decreases, so the output characteristics of the battery may deteriorate.

[0067] The tap density of the positive electrode active material of the present invention can be 2.40 g / cc to 2.60 g / cc, 2.42 g / cc to 2.56 g / cc, or 2.43 g / cc to 2.54 g / cc. When the tap density of the positive electrode active material of the present invention satisfies the above range, high energy density can be achieved.

[0068] The pellet density (under 9 tons) of the positive electrode active material of the present invention can be 3.60 g / cc to 3.80 g / cc, 3.61 g / cc to 3.78 g / cc, or 3.62 g / cc to 3.75 g / cc. When the pellet density of the positive electrode active material of the present invention satisfies the above range, high energy density can be achieved.

[0069] Meanwhile, the initial resistance of a single cell manufactured using this positive electrode active material at an SOC of 50 can be 1.45 Ω to 1.50 Ω, preferably 1.47 Ω to 1.50 Ω, and more preferably 1.48 Ω to 1.49 Ω.

[0070] Preparation method of positive electrode active material

[0071] Next, the preparation method of the positive electrode active material of the present invention will be described.

[0072] The method for preparing the positive electrode active material of the present invention includes the following steps: (A) mixing a positive electrode active material precursor with a lithium raw material and performing a first sintering; and (B) pulverizing the product after the first sintering and performing a second sintering.

[0073] In addition, the prepared positive electrode active material includes single particles composed of a single nucleus, quasi-single particles that are composites of up to 30 nuclei, or a combination thereof, wherein the positive electrode active material contains a lithium nickel-based oxide in which the molar ratio of Ni in all transition metals is at least 60 mol%, and the negative skewness factor (NSF) represented by the following Equation 1 is 0.20 to 0.35:

[0074] [Equation 1]

[0075] NSF = (D 50 - D 10 ) / I max

[0076] In the above Equation 1, D 50 is the particle size at which the cumulative volume is 50% in the volume cumulative particle size distribution diagram of the positive electrode active material, D 10 is the particle size at which the cumulative volume is 10% in the volume cumulative particle size distribution diagram of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution diagram of the positive electrode active material.

[0077] The same description above applies to the above Equation 1, and the repeated description will be omitted.

[0078] Hereinafter, each step of the method for preparing the positive electrode active material will be described in detail.

[0079] First, a positive electrode active material precursor is mixed with a lithium raw material, and then a first sintering is performed (step (A)).

[0080] In this case, the positive electrode active material precursor can be prepared by purchasing a precursor such as a commercially available nickel cobalt manganese hydroxide or the like, or by a precursor preparation method known in the art such as the coprecipitation method.

[0081] For example, a transition metal-containing solution containing cations of nickel (Ni), cobalt (Co), and M 1 can be prepared, and then a complexing agent containing an ammonium cation and an alkaline aqueous solution can be added to the transition metal-containing solution for a coprecipitation reaction to prepare a positive electrode active material precursor.

[0082] The transition metal-containing solution can contain a nickel-containing raw material, a cobalt-containing raw material, and an M 1 -containing raw material, and the M 1 -containing raw material can be a manganese-containing raw material and / or an aluminum-containing raw material.

[0083] The nickel-containing raw materials may include, for example, nickel acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and may specifically include Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel salt of fatty acid, nickel halide, or a combination thereof, but the present invention is not limited thereto.

[0084] The cobalt-containing raw materials may include cobalt acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and may specifically include Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof, but the present invention is not limited thereto.

[0085] The manganese-containing raw materials may include, for example, manganese acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and may specifically include manganese oxides such as Mn2O3, MnO2 and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate and nickel salt of fatty acid; manganese oxyhydroxide, manganese chloride, or a combination thereof, but the present invention is not limited thereto.

[0086] The aluminum-containing raw materials may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide, or a combination thereof.

[0087] The solution containing transition metals can be prepared by adding the nickel-containing raw materials, cobalt-containing raw materials and the raw materials containing M 1 to a solvent (specifically water) or a mixed solvent of an organic solvent (such as alcohol, etc.) that can be uniformly mixed with water, or can be prepared by mixing an aqueous solution of the nickel-containing raw materials, an aqueous solution of the cobalt-containing raw materials and the raw materials containing M 1 of the raw materials.

[0088] The complexing agent containing ammonium cations may include, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof, but the present invention is not limited thereto. At the same time, the complexing agent containing ammonium cations can be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent (specifically alcohol, etc.) that can be uniformly mixed with water can be used as the solvent.

[0089] The basic compound may include hydroxides of alkali metals or alkaline earth metals, such as NaOH, KOH or Ca(OH)2, their hydrates, or combinations thereof. The basic compound may also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically alcohols, etc.) may be used as the solvent.

[0090] A basic compound is added to adjust the pH of the reaction solution, and the addition amount of the basic compound may be such that the pH of the metal solution is 8 to 12.

[0091] The coprecipitation reaction may be carried out in an inert atmosphere (such as nitrogen or argon) in the temperature range of 35°C to 80°C.

[0092] The precursor particles of the positive electrode active material nickel-cobalt-M 1 hydroxide is formed by the above process and precipitates in the reaction solution. The precursor of the positive electrode active material with a nickel (Ni) content of at least 60 mol% in the total metal content can be prepared by controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material, and the raw material containing M 1 . The precipitated precursor particles of the positive electrode active material can be separated and dried according to conventional methods to prepare the precursor of the positive electrode active material.

[0093] Meanwhile, the D 50 of the positive electrode active material precursor prepared as above can be 4.0 μm to 10.0 μm, preferably 5.0 μm to 9.0 μm, more preferably 6.0 μm to 8.0 μm. When the D 50 of the positive electrode active material precursor is less than 4.0 μm, the possibility that the D 50 of the positive electrode active material is less than the appropriate range increases. When the D 50 of the positive electrode active material precursor is greater than 10.0 μm, the specific surface area (BET) decreases, so the reactivity when mixed with the lithium raw material decreases, thereby reducing the integrity of the structure of the positive electrode active material.

[0094] Thereafter, the positive electrode active material precursor can be mixed with the lithium raw material.

[0095] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides or hydroxyoxides can be used, and these materials are not particularly limited as long as they can be dissolved in water. Specifically, the lithium raw material may include Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, etc., and any one of them or a mixture of two or more of them can be used.

[0096] For example, the precursor of the positive electrode active material and the lithium raw material can be mixed at a molar ratio of about 1:1, about 1:1.05, about 1:1.10, about 1:1.15, or about 1:1.20, but the present invention is not limited thereto.

[0097] Thereafter, the mixture can be sintered once.

[0098] The first sintering can be carried out in an air or oxygen atmosphere.

[0099] The first sintering can be carried out at a temperature of 700 °C to 1000 °C, 800 °C to 900 °C, or 825 °C to 875 °C.

[0100] The first sintering can be carried out for 6 hours to 18 hours, 8 hours to 16 hours, or 10 hours to 14 hours.

[0101] Next, the product after the first sintering is pulverized and secondarily sintered (step (B)).

[0102] In this case, for example, the pulverization can be carried out by jet mill pulverization. The jet mill pulverization can be carried out within a pressure range of 2.0 bar to 4.0 bar, 2.2 bar to 3.8 bar, or 2.4 bar to 3.5 bar.

[0103] In addition, the jet mill pulverization can be carried out within a speed range of 1000 rpm to 2500 rpm, 1200 rpm to 2400 rpm, or 1300 rpm to 2300 rpm. The NSF value of the positive electrode active material prepared by carrying out within this pulverization speed range can be 0.20 to 0.35, 0.21 to 0.35, or 0.21 to 0.34. Therefore, the prepared positive electrode active material can achieve low initial resistance characteristics and high energy density.

[0104] By jet mill pulverization, the integrity of the surface structure exposed due to particle breakage can be improved.

[0105] The second sintering can be carried out at a temperature of 500 °C to 1000 °C, 600 °C to 900 °C, or 700 °C to 800 °C.

[0106] The second sintering can be carried out for 6 hours to 18 hours, 8 hours to 16 hours, or 10 hours to 14 hours.

[0107] Through the recrystallization reaction generated by the second sintering, the integrity of the structure of the positive electrode active material can be improved compared with the positive electrode active material after the second sintering.

[0108] After the jet mill pulverization, the second sintering can be carried out to recrystallize the surface exposed due to particle breakage and remove the fine powder during the recrystallization process.

[0109] Meanwhile, in the case of preparing a lithium composite transition metal oxide containing M 2 metal, a raw material containing M 2 metal can be additionally mixed during the coprecipitation reaction process or in the sintering step. In this case, the raw material containing M 2 metal can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of M 2 metal.

[0110] Positive electrode

[0111] The positive electrode of the present invention contains the positive electrode active material of the present invention as described above. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material of the present invention. Since the positive electrode active material has been described above, its detailed description will be omitted, and only the remaining structure will be described in detail below.

[0112] The positive electrode current collector can include a metal having high electrical conductivity, and there is no particular limitation as long as the positive electrode active material layer can easily adhere thereto and there is no reactivity within the voltage range of the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the positive electrode current collector. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and fine unevenness can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies.

[0113] When necessary, in addition to the positive electrode active material, the positive electrode active material layer can optionally contain a conductive agent and a binder.

[0114] In this case, the content of the positive electrode active material can be 80% by weight to 99% by weight, more specifically 90% by weight to 98% by weight, based on the total weight of the positive electrode active material layer.

[0115] The conductive agent is used to provide conductivity to the electrode. Among them, any conductive agent can be used without particular limitation as long as it has appropriate electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive agent can be: 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 cracking carbon black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them or a mixture of two or more of them can be used. Relative to the total weight of the positive electrode active material layer, the content of the conductive agent can be 0.01% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, more preferably 0.1% by weight to 5% by weight.

[0116] The binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is replaced by Li, Na, or Ca, or various copolymers thereof, and any one of them or a mixture of two or more of them can be used. Relative to the total weight of the positive electrode active material layer, the content of the binder can be 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, more preferably 1% by weight to 10% by weight.

[0117] The positive electrode can be prepared according to a conventional positive electrode preparation method, except that the above-mentioned positive electrode active material is used. Specifically, by dissolving or dispersing the positive electrode active material and, optionally, a binder, a conductive agent, and a dispersant as needed in a solvent to prepare a positive electrode slurry composition, coating the positive electrode slurry composition on the positive electrode current collector, and then the positive electrode can be prepared by drying and rolling the coated positive electrode current collector.

[0118] The solvent can be a solvent commonly used in the art. The solvent can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and any one of them or a mixture of two or more of them can be used. If the coating thickness and productivity of the slurry are taken into account, the solvent can dissolve or disperse the positive electrode active material, the conductive agent, the binder, and the dispersant, and can have a viscosity that can provide excellent thickness uniformity in the subsequent coating process for preparing the positive electrode, then the amount of the solvent used may be sufficient.

[0119] Alternatively, as another method, the positive electrode can be prepared by casting the positive electrode slurry composition on a separate carrier and then laminating the film separated from the carrier on the positive electrode current collector.

[0120] Lithium secondary battery

[0121] Next, the lithium secondary battery of the present invention will be described.

[0122] The lithium secondary battery specifically includes a positive electrode, a negative electrode disposed to face the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Among them, since the positive electrode is the same as the above, its detailed description will be omitted, and only the remaining structures will be described in detail below.

[0123] In addition, the lithium secondary battery may optionally include a battery container for accommodating the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0124] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0125] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. In addition, the thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and the same as the case of the positive electrode current collector, fine concavities and convexities can be formed on the surface of the negative electrode current collector to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0126] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive agent.

[0127] A compound capable of reversibly embedding and de-embedding lithium can be used as the negative electrode active material. Specific examples of the negative electrode active material can be carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal materials capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and de-doping lithium such as SiOβ (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing metal materials and carbonaceous materials such as Si-C composite or Sn-C composite, and any one of them or a mixture of two or more of them can be used. In addition, a thin film of metallic lithium can be used as the negative electrode active material. Further, low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon can be soft carbon and hard carbon, and typical examples of high-crystalline carbon can be natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microspheres, mesophase pitch in an irregular shape, planar shape, flake shape, spherical shape, or fibrous shape, and carbon such as coke derived from high-temperature heat treatment of petroleum or coal tar pitch, etc.

[0128] Relative to the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80 wt% to 99 wt%, 82 wt% to 99 wt%, or 84 wt% to 99 wt%.

[0129] The binder is a component that aids in binding the conductive agent, active material, and current collector. Among them, based on the total weight of the negative electrode active material layer, the addition amount of the binder is generally 0.1 wt% to 10 wt%. Examples of the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, various copolymers thereof, etc.

[0130] The conductive agent is a component used to further improve the conductivity of the negative electrode active material, and relative to the total weight of the negative electrode active material layer, its content can be 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt%. There is no particular limitation on the conductive agent as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, the following can be used: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fiber or metal fiber; fluorocarbons; metal powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives, etc.

[0131] The negative electrode active material layer can be prepared by dissolving or dispersing a negative electrode active material and, optionally, a binder and a conductive agent in a solvent to prepare a negative electrode paste composition, coating the negative electrode paste composition on a negative electrode current collector, and drying the coated negative electrode current collector; or, it can be prepared by casting the negative electrode paste composition on a separate carrier and then laminating the film separated from the carrier on the negative electrode current collector.

[0132] Meanwhile, in a lithium secondary battery, a separator separates the negative electrode from the positive electrode and provides a migration path for lithium ions. Any separator can be used as this separator without particular limitation as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having a high water retention capacity for an electrolyte and a low resistance to the transfer of electrolyte ions can be prepared. Specifically, a porous polymer membrane can be used, such as a porous polymer membrane prepared from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure having two or more layers can be used. In addition, a conventional porous non-woven fabric can be used, such as a non-woven fabric formed from high melting point glass fibers or polyethylene terephthalate fibers. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be optionally used.

[0133] In addition, the electrolyte used in the present invention can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that can be used to prepare a lithium secondary battery, but the present invention is not limited thereto.

[0134] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0135] Any organic solvent can be used as the organic solvent without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, as the organic solvent, the following can be used: 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 solvents such as benzene and fluorobenzene; or carbonate 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 solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents can be used. For example, a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a linear carbonate compound with low viscosity (such as ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used.

[0136] A lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt can be selected from F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -At least one of the components in the group, and as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. Preferably, the lithium salt is used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, more preferably 1.0 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can have appropriate conductivity and viscosity, thus exhibiting excellent performance, and lithium ions can migrate effectively.

[0137] To improve the life characteristics of the battery, suppress the reduction of the battery capacity, and improve the discharge capacity of the battery, in addition to the above electrolyte components, at least one additive can be included in the electrolyte, for example, halogenated alkylene carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additive can be 0.1% by weight to 10.0% by weight.

[0138] As described above, since the lithium secondary battery including the positive electrode active material of the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, the lithium secondary battery is suitable for portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEV).

[0139] Therefore, according to another embodiment of the present invention, there are provided a battery module including the above lithium secondary battery as a unit cell, and a battery pack including the battery module.

[0140] The battery module or the battery pack can be used as a power source for at least one of the following medium and large-sized devices: power tools; electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); or power storage systems.

[0141] Hereinafter, embodiments of the present invention will be described in detail in a manner that can be easily implemented by those skilled in the art to which the present invention pertains. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0142] Examples and comparative examples

[0143] Example 1

[0144] Mix D 50 The precursor of the positive electrode active material Ni with a diameter of 7.0 μm 0.90 Co 0.05 Mn 0.05 (OH)2 with the lithium raw material LiOH, and then perform a first sintering at 850 °C for 12 hours.

[0145] Thereafter, pulverize the product after the first sintering with a jet mill at 2.5 bar and 1400 rpm for 1 hour, and then perform a second sintering at 750 °C for 12 hours to prepare the positive electrode active material LiNi 0.90 Co 0.05 Mn 0.05 (OH)2.

[0146] Example 2

[0147] Prepare the positive electrode active material in the same manner as in Example 1, except that D 50 The precursor of the positive electrode active material with a diameter of 8.0 μm is used, and jet mill pulverization is performed at 2.5 bar and 1800 rpm for 1 hour.

[0148] Example 3

[0149] Prepare the positive electrode active material in the same manner as in Example 1, except that D 50 The precursor of the positive electrode active material with a diameter of 9.0 μm is used, and jet mill pulverization is performed at 2.5 bar and 2400 rpm for 1 hour.

[0150] Example 4

[0151] Prepare the positive electrode active material in the same manner as in Example 1, except that D 50 The precursor of the positive electrode active material with a diameter of 9.0 μm is used, and jet mill pulverization is performed at 3.0 bar and 2400 rpm for 1 hour.

[0152] Comparative Example 1

[0153] Prepare the positive electrode active material in the same manner as in Example 1, except that D 50 The precursor of the positive electrode active material with a diameter of 3.5 μm is used, and jet mill pulverization is performed at 2.5 bar and 800 rpm for 1 hour.

[0154] Comparative Example 2

[0155] The positive electrode active material was prepared in the same manner as in Example 1, except that D 50 a positive electrode active material precursor with a size of 5.5 μm was used, and jet mill comminution was carried out for 1 hour under the conditions of 2.5 bar and 800 rpm.

[0156] Comparative Example 3

[0157] The positive electrode active material was prepared in the same manner as in Example 1, except that D 50 a positive electrode active material precursor with a size of 7.0 μm was used, and jet mill comminution was carried out for 1 hour under the conditions of 2.5 bar and 800 rpm.

[0158] Comparative Example 4

[0159] The positive electrode active material was prepared in the same manner as in Example 1, except that D 50 a positive electrode active material precursor with a size of 9.0 μm was used, and jet mill comminution was carried out for 1 hour under the conditions of 2.5 bar and 2800 rpm.

[0160] Experimental Example 1: Particle size distribution of positive electrode active material

[0161] The positive electrode active materials (0.005 g) prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were each dispersed in H2O as a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasonic waves at 28 kHz with an output of 60 W, to obtain the volume-based particle size distribution diagram of each positive electrode active material, and the D 50 D 10 I max and the NSF value of the following Equation 1 were calculated.

[0162] [Equation 1]

[0163] NSF=(D 50 -D 10 ) / I max

[0164] In the above Equation 1, D 50 is the particle size at a cumulative volume of 50% in the volume-based particle size distribution diagram of the positive electrode active material, D 10 is the particle size at a cumulative volume of 10% in the volume-based particle size distribution diagram of the positive electrode active material, and I max is the maximum volume fraction in the volume-based particle size distribution diagram of the positive electrode active material.

[0165] The volume-based particle size distribution diagrams of each positive electrode active material are shown in Figure 1 D 50, D 10 , I max The NSF values of Equation 1 and are shown in Table 1 below.

[0166] [Table 1]

[0167] <![CDATA[D 50 [μm]]]> <![CDATA[D 10 [μm]]]> <![CDATA[I max > NSF Example 1 5.62 3.10 12.00 0.21 Example 2 5.81 2.92 10.40 0.28 Example 3 6.01 2.95 9.65 0.32 Example 4 5.90 2.82 9.35 0.33 Comparative Example 1 3.96 2.17 11.90 0.15 Comparative Example 2 5.64 3.60 14.80 0.14 Comparative Example 3 7.41 4.79 14.50 0.18 Comparative Example 4 6.80 3.11 9.79 0.38

[0168] Experimental Example 2: Tap density and pellet density of positive electrode active material

[0169] The tapped density of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was measured using a tapped density tester (Micromeritics GeoPyc1365). Specifically, 10 g of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were loaded into a 45 cc container and then vibrated until a force of 108 N was applied horizontally to measure the tapped density. The measurement results are shown in Table 2 below, and the change in tapped density with D 50 is shown in Figure 2 .

[0170] The pellet density of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was measured using a densitometer (Carver Pellet Press). Specifically, 5 g of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were subdivided and loaded into a cylindrical holder with a diameter of 13 mm without any gaps, and then the pellet density was measured by applying a pressure of 9 tons. The measurement results are shown in Table 2 below, the change in pellet density with D 50 is shown in Figure 3 , and the change in pellet density with the NSF value is shown in Figure 4 .

[0171] [Table 2]

[0172] Tap density [g / cc] Pellet density [g / cc] Example 1 2.43 3.62 Example 2 2.45 3.64 Example 3 2.54 3.71 Example 4 2.52 3.70 Comparative Example 1 2.29 3.54 Comparative Example 2 2.34 3.58 Comparative Example 3 2.39 3.59 Comparative Example 4 2.40 3.61

[0173] Referring to Table 2 above, it was found that the positive electrode active materials of Examples 1 to 4 had higher tapped density and higher pellet density compared to the positive electrode active materials of Comparative Examples 1 to 4. Referring to Figure 2 and Figure 3 , even when the positive electrode active materials had the same D 50When the NSF value is within the numerical range of the embodiments of the present invention, it can be seen that the positive electrode active material has a high tap density and a high pellet density. In this case, it is considered that as small particles fill the space between relatively large particles, the tap density and the pellet density increase. On the other hand, in the case of Comparative Examples 1 to 3 where the NSF value is less than 0.20, there are insufficient small particles to fill the space between large particles, and in the case of Comparative Example 4 where the NSF value is greater than 0.35, even after small particles fill the space between large particles, small particles still remain, resulting in a decrease in the pellet density.

[0174] Experimental Example 3: Initial resistance of lithium secondary battery

[0175] <Manufacture of Lithium Secondary Battery>

[0176] The positive electrode active materials, conductive agents (carbon black, Denka), and PVDF binders prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were mixed in a weight ratio of 96:1:3 in N-methylpyrrolidone to prepare a positive electrode paste. The positive electrode paste was coated on one surface of an aluminum current collector, dried at 130 °C, and then roll-pressed to prepare a positive electrode.

[0177] The negative electrode active material, binder, and conductive agent were mixed in a weight ratio of 97:1.5:1.5 in N-methylpyrrolidone to prepare a negative electrode mixture. Specifically, artificial graphite was used as the negative electrode active material, carboxymethyl cellulose (CMC) was used as the binder, and carbon black was used as the conductive agent. The prepared negative electrode mixture was coated on one surface of a copper current collector, dried at 110 °C, and then roll-pressed to prepare a negative electrode.

[0178] An electrode assembly was prepared by disposing a separator between the positive electrode and the negative electrode, and then the electrode assembly was placed in a battery case, and then an electrolyte solution was injected into the case to manufacture a battery cell. The electrolyte solution was prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 and adding 5 wt% vinylene carbonate (VC) thereto to obtain a mixed organic solvent, and dissolving 1 M LiPF6 in the mixed organic solvent.

[0179] When a current of 2.5 C was applied for 10 seconds in a state where the SOC was 50 (the battery was half-charged), the initial resistance value of the manufactured battery cell was measured by voltage change. The measurement results are shown in Table 3 below and Figure 5 are shown in:

[0180] [Table 3]

[0181] Initial resistance (SOC 50%) Example 1 1.48 Example 2 1.48 Example 3 1.49 Example 4 1.49 Comparative Example 1 1.41 Comparative Example 2 1.47 Comparative Example 3 1.55 Comparative Example 4 1.50

[0182] Referring to Table 3 above and Figure 5, it was found that the initial resistance value of the positive electrode active material of Comparative Example 3 with an NSF value of 0.18 and D 50 greater than 7.0 μm was higher than that of the positive electrode active materials of Examples 1 to 4. It is considered that the diffusion distance of lithium ions in the positive electrode active material particles increases, resulting in a decrease in lithium mobility, and thus the initial resistance of the lithium secondary battery containing the positive electrode active material increases. As described above with reference to Experimental Examples 2 to 3, it can be seen that the positive electrode active material of the present invention has a low initial resistance characteristic while improving the energy density by maximizing the tap density and the pellet density.

Claims

1. A positive electrode active material comprising single particles composed of a single nucleus, quasi-single particles that are composites of up to 30 nuclei, or a combination thereof, Among them, The positive electrode active material contains a lithium nickel-based oxide in which the molar ratio of Ni in all transition metals is at least 60 mol%, and The negative skewness factor (NSF) represented by the following Equation 1 is 0.20 to 0.35: [Equation 1] NSF=(D 50 -D 10 ) / I max Among them, in the above Equation 1, D 50 is the particle size at which the cumulative volume is 50% in the volume cumulative particle size distribution diagram of the positive electrode active material, D 10 is the particle size at which the cumulative volume is 10% in the volume cumulative particle size distribution diagram of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution diagram of the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein, The D of the positive electrode active material 50 is from 5.0 μm to 7.0 μm.

3. The positive electrode active material according to claim 1, wherein, The lithium nickel-based oxide is represented by the following Formula 1: [Formula 1] Li a Ni b Co c M 1 d M 2 e O2 Among them, in Formula 1 above, M 1 is Mn, Al or a combination thereof, and M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo, 1.0 ≤ a ≤ 1.5, 0.6 ≤ b < 1.0, 0 < c < 0.1, 0 < d < 0.2, 0 ≤ e ≤ 0.1, and 0 < c + d + e ≤ 0.

4.

4. The positive electrode active material according to claim 1, wherein, The average particle size of the nuclei of the positive electrode active material is 1.0 μm to 7.0 μm.

5. The positive electrode active material according to claim 1, wherein The tap density of the positive electrode active material is 2.40 g / cc to 2.60 g / cc.

6. The positive electrode active material according to claim 1, wherein, The pellet density of the positive electrode active material at 9 tons is 3.60 g / cc to 3.80 g / cc.

7. The positive electrode active material according to claim 1, wherein, The initial resistance of a single cell manufactured using the positive electrode active material is 1.45 Ω to 1.50 Ω when the SOC is 50.

8. A method for preparing a positive electrode active material, the method comprising: (A) Mixing a positive electrode active material precursor with a lithium raw material and performing a first sintering; And (B) Crushing the product after the first sintering and performing a second sintering.

9. The method according to claim 8, wherein The D of the positive electrode active material precursor 50 is from 4.0 μm to 10.0 μm.

10. The method according to claim 8, wherein, The crushing is performed by jet milling.

11. The method according to claim 10, wherein, The jet milling is performed under conditions of 2.0 bar to 4.0 bar and 1000 rpm to 2500 rpm.

12. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 7.

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

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