Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material comprising a large particle size lithium nickel-based transition metal oxide and a small particle size lithium nickel-based transition metal oxide, wherein the large particle size lithium nickel-based transition metal oxide is in the form of secondary particles that are aggregates of primary particles, and the small particle size lithium nickel-based transition metal oxide is in the form of at least one of a single particle consisting of one nodule and a quasi-single particle that is a complex of 30 or less nodules, and wherein the P value, which is defined as a factor related to the particle shape of the large particle size and a factor related to the specific surface area of ​​the small particle size, is 1.00 or more. By applying the positive electrode active material to a positive electrode, particle cracking of the positive electrode active material is suppressed, thereby improving life and output characteristics and providing a lithium secondary battery with reduced gas generation.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0184869 dated December 26, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode contain an active material that allows for the insertion and deintercalation of lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Of these, lithium cobalt oxide has the advantage of a high operating voltage and excellent capacity characteristics, but the high price of cobalt, the raw material, and its unstable supply make commercial application to high-capacity batteries difficult. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. On the other hand, lithium manganese oxide has excellent stability but suffers from poor capacity characteristics. Therefore, in order to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, lithium nickel-based transition metal oxides containing two or more transition metals have been developed, and among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0005] Conventional lithium nickel cobalt manganese oxide typically consists of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide with such a secondary particle form, during the manufacturing of the positive electrode, particle cracking is likely to occur as primary particles detach during the rolling process, and cracks can develop inside the particles during the charge-discharge process. When cracking or fractures occur in the particles of the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material, thus reducing its lifespan characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to solve the above-mentioned problems and provides a positive electrode active material that can suppress the occurrence of particle cracking and fissures during electrode manufacturing and charge / discharge processes, and has excellent rolling density.

[0007] Furthermore, the present invention provides a positive electrode and a lithium secondary battery that, by including the positive electrode active material, have a low crack rate (fine particle generation rate), improved high-temperature life and output characteristics due to reduced side reactions with the electrolyte, and improved high-temperature storage characteristics. [Means for solving the problem]

[0008] To solve the above problems, in one aspect of the present invention, a positive electrode active material is provided which comprises a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide, wherein the large-particle lithium nickel-based transition metal oxide is in the form of secondary particles which are aggregates of primary particles, and the small-particle lithium nickel-based transition metal oxide is in the form of at least one of single particles consisting of one nodule and pseudo-single particles which are composites of 30 or fewer nodules, and the P value defined by the following formula 1 is 1.00 or more. [Formula 1] P=(A L ×R L ×C L) / B S In Formula 1 above, A L , R L and C L are, respectively, the aspect ratio, circularity, and convexity of the large-particle-size lithium nickel-based transition metal oxide, and B S is the unitless number of the BET specific surface area (m 2 / g) of the small-particle-size lithium nickel-based transition metal oxide.

[0009] In order to solve the above problems, in another aspect of the present invention, a positive electrode including the positive electrode active material according to the present invention is provided.

[0010] In order to solve the above problems, in still another aspect of the present invention, a lithium secondary battery including the positive electrode according to the present invention is provided.

Effects of the Invention

[0011] The positive electrode active material for a lithium secondary battery according to the present invention includes a lithium nickel-based transition metal oxide in the form of single particles and / or pseudo-single particles having excellent particle strength, and a lithium nickel-based transition metal oxide in the form of secondary particles which are aggregates of primary particles. By mixing the particles of the two forms that satisfy specific conditions, during the manufacture of the electrode, the occurrence of particle cracking and cracks due to rolling can be reduced, and an excellent level of rolling density can be achieved.

[0012] In addition, the positive electrode active material for a lithium secondary battery according to the present invention minimizes particle cracking, reduces side reactions with the electrolyte, thereby reducing the amount of gas generated, suppresses deterioration of the positive electrode active material by minimizing changes in the crystal structure during the charge and discharge process, has excellent high-temperature life characteristics and high-temperature storage characteristics, has a low rate of increase in resistance, and can have excellent output characteristics.

Modes for Carrying Out the Invention

[0013] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0014] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0015] In this invention, "single particle" refers to a particle consisting of a single nodule. In this invention, "nodule" refers to a particle unit that may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which no grain boundaries are visible when observed with a scanning electron microscope (SEM) at a field of view of 5000x to 20000x. In this invention, "pseudo-single particle" refers to a particle that is a composite formed of 30 or fewer nodules.

[0016] In this invention, "secondary particle" refers to a particle formed by the aggregation of several tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0017] As used in this invention, the term "particle" may include one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0018] In the present invention, "D 50 " refers to the particle size at the 50% reference level of the volume cumulative particle size distribution of the positive electrode active material powder. The average particle size D 50This can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, the particle size can be measured by introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasound at approximately 28 kHz with an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume-cumulative amount.

[0019] In this invention, "aspect ratio," "circularity," and "convexity" are determined by two-dimensionalizing the particles using an image obtained by scanning electron microscopy (SEM) imaging of positive electrode active material particles, and then using an image analysis program to determine the minimum particle size (D) of the two-dimensionalized image. min , minor diameter), maximum particle diameter (D max This value is derived from the major axis, area, actual perimeter, and perimeter of the protrusion, and represents the average value of tens to hundreds of particles, preferably 300 particles in this invention.

[0020] Here, the aspect ratio, circularity, and convexity can be calculated using equations A to C below.

[0021] [Formula A] Aspect Ratio = D min / D max

[0022] [Formula B] Roundness = (4 × area) / (π × (D) max ) 2 )

[0023] [Formula C] Convexity = (Perimeter of the protrusion) / (Actual perimeter)

[0024] In the above formula C, the perimeter of the protruding portion is the perimeter of the particle obtained by connecting the protruding portions in a straight line relative to the two-dimensional particle, and represents the perimeter when the elastic band encloses the periphery of the particle being measured, while the actual perimeter is the perimeter of the particle obtained by connecting the actual outer edge lines of the particle.

[0025] The present invention will be described in more detail below.

[0026] positive electrode active material The positive electrode active material according to the present invention comprises a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide, wherein the large-particle lithium nickel-based transition metal oxide is in the form of secondary particles which are aggregates of primary particles, and the small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle consisting of one nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and is characterized in that the P value defined by the following formula 1 is 1.00 or more.

[0027] [Formula 1] P=(A L ×R L ×C L ) / B S

[0028] In the above formula 1, A L , R L and C L These are the aspect ratio, circularity, and convexity of the large-particle lithium nickel-based transition metal oxide, respectively, and B S This is the BET specific surface area (m²) of small-particle lithium nickel-based transition metal oxides. 2 It is a unitless number ( / g).

[0029] The inventors propose particle properties that allow for both advantages in terms of active material particle fracture phenomena and energy density by mixing large-particle lithium nickel-based transition metal oxides in secondary particle form, which have advantages in terms of energy density, with small-particle lithium nickel-based transition metal oxides in single-particle and / or pseudo-single-particle form, which exhibit reduced particle fracture phenomena.

[0030] According to one embodiment of the present invention, the P value derived by formula 1 is 1.00 or greater, preferably 1.01 or greater, 1.02 or greater, more preferably 2.50 or less, 2.30 or less, 2.10 or less, or 2.05 or less, and even more preferably 2.01 or less.

[0031] The aforementioned P-value represents the ratio of the aspect ratio, circularity, and convexity of large-particle lithium nickel-based transition metal oxides to the specific surface area of ​​small-particle lithium nickel-based transition metal oxides. In the case of secondary particle morphology, due to the characteristics of particles formed by the aggregation of hundreds of primary particles, particle shape acts as a more major factor than specific surface area in terms of crack rate and rolling density. However, in the case of single-particle and / or pseudo-single-particle morphology, since it is a form in which primary particles, i.e., nodules, exist in quantities of approximately 30 or less, the specific surface area can act as a more major factor than particle shape.

[0032] In other words, if the P value is 1.00 or higher, it may mean that both the energy density and the particle cracking and cracking rate can be compensated for. If the P value is less than 1.00, there may be many secondary particles with irregular shapes, leading to excessive gas generation due to side reactions caused by particle cracking, which can result in a decrease in lifetime characteristics. Alternatively, the energy density may be low, resulting in inferior capacity and output characteristics.

[0033] In other words, even if the secondary particles consist only of those with a shape close to spherical, the aforementioned problem may occur if the specific surface area of ​​the single-particle and / or pseudo-single-particle active material particles mixed in is large. Conversely, even if the shape of the secondary particles is not perfectly spherical, if the specific surface area of ​​the single-particle and / or pseudo-single-particle active material particles is small, the occurrence of the aforementioned problem can be prevented by compensating for this.

[0034] According to one embodiment of the present invention, the large-particle lithium nickel-based transition metal oxide can have an aspect ratio of 0.85 or more, a circularity of 0.85 or more, and a convexity of 0.935 or more. Here, the aspect ratio, circularity, and convexity can be values ​​obtained by driving an image analysis program on an image obtained by capturing lithium nickel-based transition metal oxide particles with a scanning electron microscope, and can be the average value of about 100 particles.

[0035] The large-particle-grain lithium nickel-based transition metal oxide can preferably have an aspect ratio of 0.87 or more, 0.88 or more, 0.90 or more, or 0.91 or more, a circularity of 0.87 or more, 0.88 or more, 0.90 or more, or 0.91 or more, and a convexity of 0.937 or more, 0.939 or more, 0.940 or more, or 0.941 or more.

[0036] Furthermore, according to one embodiment of the present invention, the small-particle lithium nickel-based transition metal oxide has a BET specific surface area of ​​0.60 m². 2 / g~1.10m 2 It can be / g. Preferably, the BET specific surface area is 0.63m². 2 / g or more, 0.65m 2 / g or more, or 0.66m 2 It can be 1.07m or more per gram. 2 / g or less, 1.05m 2 Less than / g, or 1.03m 2 It can be less than or equal to / g.

[0037] When the aspect ratio, circularity, and convexity of the large-particle lithium nickel-based transition metal oxide, and the BET specific surface area of ​​the small-particle lithium nickel-based transition metal oxide satisfy the aforementioned range, it is easy to control the particle characteristics of the mixed active material so that the P value is 1.00 or higher, and improvements in the performance of electrodes and even batteries can be expected.

[0038] According to one embodiment of the present invention, a small-particle-sized lithium nickel-based transition metal oxide can have an aspect ratio of 0.80 or more, a circularity of 0.80 or more, and a convexity of 0.900 or more. Preferably, the small-particle-sized lithium nickel-based transition metal oxide can have an aspect ratio of 0.81 or more, 0.82 or more, 0.83 or more, or 0.85 or more, a circularity of 0.81 or more, 0.82 or more, 0.83 or more, or 0.85 or more, and a convexity of 0.937 or more, 0.939 or more, 0.940 or more, or 0.941 or more.

[0039] Furthermore, according to one embodiment of the present invention, the large-particle lithium nickel-based transition metal oxide has a BET specific surface area of ​​0.40 m². 2 / g~0.60m 2 It can be / g, preferably 0.42m 2 / g or more, 0.45m 2 / g or more, or 0.47m 2 It can be 0.57m or more 2 / g or less, 0.55m 2 / g or less, 0.53m 2 It can be less than or equal to / g.

[0040] The aspect ratio, circularity, and convexity of the small-particle lithium nickel-based transition metal oxide, and the BET specific surface area of ​​the large-particle lithium nickel-based transition metal oxide, do not affect the P value and do not significantly affect particle cracking. However, if they satisfy the above range, the energy density can be improved, which can help improve performance.

[0041] According to one embodiment of the present invention, the mixed weight ratio of large-particle lithium nickel-based transition metal oxide to small-particle lithium nickel-based transition metal oxide can be 90:10 to 40:60, preferably 85:15 or less, 80:20 or less, 50:50 or more, or 60:40 or more. When considering together the problems of reduced lifespan and increased gas generation due to particle cracking, insufficient conductive paths, problems in the slurry process, and increased linear pressure during the rolling process, it is preferable that the mixed weight ratio of large-particle lithium nickel-based transition metal oxide and small-particle lithium nickel-based transition metal oxide satisfies the above range.

[0042] On the other hand, the positive electrode active material according to the present invention may include a lithium nickel-based transition metal oxide, and more specifically, it may include a lithium nickel-based transition metal oxide having a composition as shown in the following chemical formula 1.

[0043] [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0044] In the above chemical formula 1, M 1 It includes one or more selected from Mn and Al, and M 2 x contains one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X contains one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.5, 0.5 ≤ a < 1, 0 <b≦0.4、0<c≦0.4、0≦d≦0.05および0≦e≦0.05である。

[0045] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, M 2This is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 While elements are not essential, when present in appropriate amounts, they can promote grain growth during calcination or improve the stability of the crystal structure. Furthermore, X is an anion substituted at the oxygen site and can include N, P, S, F, or Cl.

[0046] The aforementioned 1+x represents the molar ratio of lithium in the lithium nickel-based transition metal oxide, and can be 0≦x≦0.30, 0≦x≦0.20, or 0≦x≦0.15.

[0047] The above value 'a' represents the molar ratio of nickel to the total metals other than lithium in the lithium-nickel transition metal oxide, and can be 0.60 ≤ a < 1.00, 0.70 ≤ a < 1.00, 0.75 ≤ a ≤ 0.99, 0.80 ≤ a ≤ 0.99, or 0.82 ≤ a ≤ 0.99, 0.84 ≤ a ≤ 0.99, or 0.86 ≤ a ≤ 0.99. Here, the above value 'a', i.e., the content of nickel in the transition metal, is 60 mol% or more, preferably 70 mol% or more or 75 mol% or more. The higher the nickel content and the lower the cobalt content, the more problematic gas generation and capacity retention may become. Here, if the P value is satisfied, particle cracking phenomena can be reduced, the rolling density can be increased, and the positive electrode active material properties of high-content nickel, which have high capacity and high power characteristics, can be obtained, and the disadvantages can be offset, thus creating further synergy.

[0048] The above b represents the molar ratio of cobalt among the total metals other than lithium in the lithium nickel-based transition metal oxide, and 0 <b<0.30、0.01≦b<0.25、0.01≦b<0.20、または0.01≦b≦0.15であることができる。

[0049] The aforementioned c is M, which is the total amount of metal other than lithium in the lithium nickel-based transition metal oxide. 1 The molar ratio is shown, 0 <c<0.30、0.01≦c<0.25、0.01≦c<0.20、または0.01≦c≦0.15であることができる。

[0050] The above d is M, which is the total amount of metal other than lithium in the lithium nickel-based transition metal oxide. 2 This indicates the molar ratio of elements and can be 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.03, or 0 ≤ d ≤ 0.02.

[0051] The aforementioned e represents the molar ratio of element X among all nonmetals other than oxygen in the lithium nickel-based transition metal oxide, and can be 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02, or 0 ≤ e ≤ 0.01.

[0052] On the other hand, the lithium nickel-based transition metal oxide may further include a coating layer on the surface of the particles containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0053] When a coating layer is present on the surface of lithium nickel-based transition metal oxide particles, the coating layer suppresses contact between the electrolyte and the lithium nickel-based transition metal oxide. This reduces the leaching of transition metals and the generation of gases due to side reactions with the electrolyte.

[0054] Preferably, the coating layer may contain Co as a coating element. When a coating layer containing Co is formed on the surface of small-particle lithium nickel-based transition metal oxide particles in single-particle and / or pseudo-single-particle form and / or large-particle lithium nickel-based transition metal oxide particles in secondary-particle form, an effect of suppressing side reactions with the electrolyte and an effect of improving output can be obtained.

[0055] Method for manufacturing positive electrode active material Next, the method for producing the positive electrode active material of the present invention will be described.

[0056] The method for producing a positive electrode active material according to the present invention comprises (S1) nickel (Ni), cobalt (Co), and M 1 (S2) The process includes the steps of (S2) adding a transition metal-containing solution containing cations, a basic aqueous solution, and an ammonium solution, and causing a coprecipitation reaction to produce a positive electrode active material precursor, and (S2) mixing the positive electrode active material precursor and a lithium raw material, and heat-treating the mixture to produce a positive electrode active material.

[0057] Furthermore, the manufactured positive electrode active material can be in the form of a single particle consisting of one nodule or a pseudo-single particle, which is a composite of 30 or fewer nodules, or in the form of a secondary particle, which is an aggregate of primary particles, depending on the conditions of the coprecipitation reaction and the firing conditions such as the firing temperature and time of the lithium raw material and precursor. The positive electrode active material according to the present invention can be obtained by first manufacturing large-particle lithium nickel-based transition metal oxide and small-particle lithium nickel-based transition metal oxide, and then mixing them.

[0058] The following describes in detail each step of the method for producing the positive electrode active material.

[0059] First, nickel (Ni), cobalt (Co), and M 1 A transition metal-containing solution containing the cation of is provided. For example, the transition metal-containing solution may be a nickel-containing raw material, a cobalt-containing raw material, and M 1 It may contain raw material substances, and the M 1 The raw materials contained may be manganese-containing raw materials and / or aluminum-containing raw materials.

[0060] Next, an ammonium cation-containing complex-forming agent and a basic aqueous solution can be added to the transition metal solution and a coprecipitation reaction can be carried out to produce a cathode active material precursor.

[0061] Nickel-containing raw materials can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically, they can be, but are not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0062] The cobalt-containing raw material can be cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically can be, but are not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, CoSO4·7H2O, or combinations thereof.

[0063] Manganese-containing raw materials can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof, and specifically, they can be, but are not limited to, manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salts, manganese citrate, manganese fatty acid salts; manganese oxyhydroxides, manganese chloride, or combinations thereof.

[0064] Aluminum-containing raw materials can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides, or combinations thereof.

[0065] Transition metal-containing solutions include nickel-containing raw materials, cobalt-containing raw materials, and M 1The contained raw materials are added to a solvent, specifically water, or a mixed solvent of an organic solvent that can be homogeneously mixed with water (e.g., alcohol), to produce the product, or an aqueous solution of nickel-containing raw materials, an aqueous solution of cobalt-containing raw materials and M 1 It can be manufactured by mixing the contained raw materials.

[0066] The ammonium cation-containing complex-forming agent may be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, (NH4)2CO3, or a combination thereof, but is not limited thereto. On the other hand, the ammonium cation-containing complex-forming agent may also be used in the form of an aqueous solution, where the solvent may be water or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0067] Basic compounds can be hydroxides of alkali metals or alkaline earth metals such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Basic compounds may also be used in aqueous solution form, where water or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol) can be used as the solvent.

[0068] Basic compounds are added to adjust the pH of the reaction solution, and can be added in amounts that bring the pH of the metal solution between 8 and 12.

[0069] The coprecipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon, at a temperature range of 35°C to 80°C.

[0070] This results in nickel, cobalt and M 1 A cathode active material precursor containing cations can be produced.

[0071] Through the process described above, nickel-cobalt-M 1Hydroxide cathode active material precursor particles are generated and precipitate in the reaction solution. Nickel-containing raw material, cobalt-containing raw material and M 1 By adjusting the concentration of the contained raw materials, a positive electrode active material precursor can be produced in which the nickel (Ni) content is 70 mol% or more, 75 mol% or more, preferably 80 mol% or more, and more preferably 82 mol% or more, relative to the total metal content. The precipitated positive electrode active material precursor particles can be separated by conventional methods and dried to produce the positive electrode active material precursor.

[0072] Next, the cathode active material precursor and lithium raw material are mixed and heat-treated.

[0073] Lithium raw materials can include lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and are not particularly limited as long as they are soluble in water. Specifically, the lithium raw materials can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and one or more of these can be used as a mixture.

[0074] The positive electrode active material precursor and lithium raw material can be mixed in a molar ratio of 1:1 to 1:1.30. The positive electrode active material precursor and lithium raw material can be mixed in molar ratios of approximately 1:1, 1:1.05, 1:1.07, 1:1.10, 1:1.5, 1:1.20, or 1:1.30, for example, but are not limited to these ratios.

[0075] For high-content nickel (High-Ni) NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 70 mol% or more, the heat treatment can be carried out in a temperature range of 650°C to 1000°C. The heat treatment can, for example, preferably be carried out in a temperature range of 700°C to 925°C, and more preferably in a temperature range of 750°C to 910°C. The formation of single-particle and / or pseudo-single-particle positive electrode active material powder is affected by the heat treatment temperature conditions.

[0076] As a result, the manufactured positive electrode active material can reduce particle cracking and strain within the crystal structure during the rolling process and charging / discharging of lithium secondary batteries containing it, thereby improving its initial resistance characteristics.

[0077] The heat treatment can be carried out in an air or oxygen atmosphere and for, for example, 4 to 12 hours. Specifically, the heat treatment can be carried out for, for example, 4 hours or more, 6 hours or more, 8 hours or more, 10 hours or more, 12 hours or less, 10 hours or less, 8 hours or less, or 6 hours or less.

[0078] On the other hand, M 2 When attempting to produce a lithium nickel-based transition metal oxide containing metal, or a lithium nickel-based transition metal oxide containing nonmetal for anion substitution at oxygen sites such as X, M is used during the coprecipitation reaction or calcination step. 2 Metal-containing raw materials and / or element X-containing raw materials can be further mixed. Here, the M 2 Metal-containing raw materials are M 2 The raw material can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, and the element X-containing raw material can be a lithium salt of X or an acid containing X.

[0079] On the other hand, when attempting to form a coating layer on the surface of a lithium nickel-based transition metal oxide, a further step can be performed after the heat treatment: mixing the lithium nickel-based transition metal oxide produced by the heat treatment with a coating raw material, followed by another heat treatment. Here, the mixing can be performed using either solid-phase or liquid-phase mixing, and the heat treatment can be performed at an appropriate temperature depending on the coating raw material. For example, the heat treatment in the coating step can be performed at a temperature in the range of 200°C to 700°C or 300°C to 600°C, but is not limited thereto.

[0080] Furthermore, it is preferable not to perform a water washing step after the heat treatment when manufacturing the positive electrode active material of the present invention. Conventionally, when manufacturing high-content nickel (High-Ni)NCM-based lithium composite transition metal oxides, it has been common to perform a water washing step after heat treatment in order to reduce the content of lithium by-products. However, according to the inventors' research, when a water washing step is performed when manufacturing lithium nickel-based transition metal oxides in single-particle and / or pseudo-single-particle form, the surface properties of the lithium nickel-based transition metal oxide deteriorate and the resistance increases during the water washing process. Therefore, when manufacturing the positive electrode active material of the present invention, it is preferable not to perform water washing and to consume the residual lithium on the surface of the lithium nickel-based transition metal oxide during the coating layer formation process. In this way, when manufacturing the positive electrode active material without water washing the lithium nickel-based transition metal oxide, the increase in resistance due to surface defects can be suppressed.

[0081] positive electrode The positive electrode according to the present invention includes 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 powder according to the present invention. Since the positive electrode active material powder has been described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0082] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. It can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0083] The positive electrode active material layer may, as needed, selectively contain a conductive material and a binder along with the positive electrode active material powder.

[0084] Here, the positive electrode active material powder can be included in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight, relative to the total weight of the positive electrode active material layer, and when included within this range of content, it can exhibit excellent capacity characteristics.

[0085] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, 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 tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The conductive material can be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0086] 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 current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more materials can be used. The binder can be present in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0087] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material powder is used. Specifically, the positive electrode slurry composition, which is prepared by dissolving or dispersing the positive electrode active material powder and, if necessary, a binder, a conductive material, and a dispersant in a solvent, is applied to a positive electrode current collector, followed by drying and rolling.

[0088] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more can be used. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0089] Alternatively, the positive electrode can also be manufactured by casting the positive electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0090] Electrochemical elements Next, the electrochemical element according to the present invention will be described. The electrochemical element according to the present invention includes the positive electrode of the present invention as described above, and the electrochemical element can be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0091] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. As the positive electrode is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0092] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0093] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0094] 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, heat-treated carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to 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, mesh, porous material, foam, and nonwoven fabric.

[0095] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0096] 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; and SiO2. βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch-derived cokes.

[0097] The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0098] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0099] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0100] The negative electrode active material layer can be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and, selectively, a binder and a conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0101] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made 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 as single-layer or multi-layer structures.

[0102] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0104] The aforementioned organic solvent can be used without particular 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can 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 solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that 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 more preferred.

[0105] The 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, as the anion of the lithium salt, 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 - can be at least one or more selected from the group consisting of. 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 is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0106] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0107] Examples Hereinafter, embodiments of the present invention will be described in detail 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 various different forms and is not limited to the embodiments described herein.

[0108] Example 1 As a large-particle lithium nickel-based transition metal oxide, the molar ratio of Ni:Co:Mn is 8:1:1. As a secondary particle powder, which is an aggregate of primary particles, the aspect ratio (ratio of minor axis to major axis) is 0.94, the circularity is 0.93, the convexity is 0.943, and the BET specific surface area is 0.48 m². 2 A lithium nickel-based transition metal oxide was produced at a concentration of / g. The small-particle lithium nickel-based transition metal oxide had a Ni:Co:Mn molar ratio of 8:1:1, and as single-particle and pseudo-single-particle powders, it had an aspect ratio of 0.86, a circularity of 0.85, a convexity of 0.925, and a BET specific surface area of ​​0.80 m². 2 A lithium nickel-based transition metal oxide with a particle size of / g was produced. The large-particle and small-particle lithium nickel-based transition metal oxides were mixed in a weight ratio of 7:3 to produce a positive electrode active material having the P values ​​shown in Table 1 below.

[0109] Examples 2 to 4 and Comparative Examples 1 to 4 Large-particle-size and small-particle-size lithium nickel-based transition metal oxides having particle size characteristics as described in Table 1 below were mixed to produce cathode active materials of Examples 2 to 4 and Comparative Examples 1 to 4 having a P value as described in Table 1 below.

[0110] Experimental Example 1: Confirmation of Particle Characteristics of Cathode Active Material For each of the cathode active materials produced in Examples 1 to 4 and Comparative Examples 1 to 4, scanning electron microscopy (SEM, Hitachi, S-4800) was used to photograph the particles at 800 times magnification to obtain an image in which about 300 particles were photographed. For the SEM image, the particles in the image were two-dimensionalized by an image analysis program (Image J), and for the two-dimensionalized image, the minimum particle size (D min , short diameter), maximum particle size (D max , long diameter), area (Area), actual perimeter, and perimeter of the protruding part were measured. The measured values were substituted into the following formulas A to C to derive the average values of the aspect ratio, roundness, and convexity, respectively, and were described in Table 1 below.

[0111] [Formula A] Aspect Ratio = D min / D max

[0112] [Formula B] Roundness = (4 × Area) / (π × (D max )) 2 ))

[0113] [Formula C] Convexity = (Perimeter of the protruding part) / (Actual perimeter)

[0114] The perimeter of the protruding part is the perimeter of the particles obtained by connecting the protruding parts of the two-dimensionalized particles in a straight line, which means the perimeter when the periphery of the measurement target particles is wrapped with an elastic band, and the actual perimeter is the perimeter of the particles obtained by connecting the actual outer edge lines of the particles.

[0115] Also, the BET specific surface area (m²) 2 The values ​​( / g) were measured using the BET method, calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan, and are shown in Table 1 below.

[0116] The p-values ​​expressed by Equation 1 are also listed in Table 1 below.

[0117] [Formula 1] P=(A L ×R L ×C L ) / B S

[0118] In the above formula 1, A L , R L and C L These are the aspect ratio, circularity, and convexity of the large-particle lithium nickel-based transition metal oxide, respectively, and B S This is the BET specific surface area (m²) of small-particle lithium nickel-based transition metal oxides. 2 It is a unitless number ( / g).

[0119] [Table 1]

[0120] Experimental Example 2: Rolling Density of Cathode Active Material Using a density measuring instrument (Caver Pellet Press), the rolling density (g / cm³) of the positive electrode active materials produced in Examples 1-4 and Comparative Examples 1-4 was determined. 3 The rolling density (g / cm³) was measured. Specifically, 3g of the positive electrode active material produced in the above examples and comparative examples was divided into smaller portions and packed tightly into a cylindrical holder with a diameter of 13mm, and then a pressure of 9 tons was applied to measure the rolling density (g / cm³). 3 The following measurements were taken, and the results are shown in Table 2 below.

[0121] Furthermore, the amount of fine powder generated (volume %) was calculated using a rolling density analyzer (Carver Pellet Press) after applying a pressure of 6 tons to the positive electrode active material and rolling it. The values ​​obtained from the aforementioned particle size distribution (PSD) were then used to calculate the region of 1 μm or less.

[0122] [Table 2]

[0123] Referring to Table 2 above, the rolling density of the example that satisfies the P value is, Comparative Example 1 and 3 Comparative Example 4, which is superior to the previous example and has a relatively high rolling density, can be seen to have a considerably higher amount of fine powder generated.

[0124] Experimental Example 3: Evaluation of High-Temperature Storage Characteristics After manufacturing pouch cells containing the positive electrode active material for each of Examples 1-4 and Comparative Examples 1-4, and the carbon negative electrode, they were charged at 4.2V. Subsequently, the electrodes charged at 4.2V were subjected to a loading amount of 400mg / 25cm². 2 Two ) and two separators were placed in a 6x6cm aluminum pouch, then placed on the bottom plate of the coin cell and secured with a gasket. After that, 400 μl of electrolyte (EC / EMC) was injected twice under vacuum, and each side was vacuum sealed to a thickness of 0.5 cm. Here, vacuum sealing means sealing under monocell vacuum sealing conditions of 95 kPa / 93 kPa. Next, the coin half cells manufactured as described above were stored in a 60°C convection oven for 10 weeks, and the change in cell volume was compared to evaluate the amount of gas generated (volume change rate, %), and the results are shown in Table 3 below.

[0125] Experimental Example 4: Evaluation of High-Temperature Life and Resistive Characteristics Monocells containing a positive electrode and a negative electrode were fabricated. For the positive electrode, the positive electrode active material powders produced in Examples 1-4 and Comparative Examples 1-4 were applied to a current collector and dried. For the negative electrode, natural graphite and artificial graphite were mixed in a 5:5 ratio and used as the negative electrode active material. The negative electrode was manufactured with a composition of 95.6 wt% negative electrode active material, 0.9 wt% conductive material, and 3.4 wt% binder. The loading of the negative electrode was 10.7 mg / cm³. 2 The N / P ratio of the negative and positive electrodes was fixed at 1.08.

[0126] At a temperature of 45°C, the capacity retention rate (%) of monocells containing the positive electrode active material powders of Examples 1-4 and Comparative Examples 1-4 was measured over 300 cycles. When evaluating the lifetime under the above method and conditions, the resistance was calculated using the discharge voltage and current ((V0-V1) / I, where V0 is the discharge start voltage, V1 is the voltage 60 seconds after discharge, and I is the applied current). The resistance increase rate was calculated using the resistance after the cycle relative to the initial resistance, and the results are shown in Table 3 below.

[0127] [Table 3]

[0128] Referring to Table 3, the volume change rate after 4 weeks of storage is relatively lower for cells using the positive electrode active materials of Examples 1-4 compared to cells using the positive electrode active materials of Comparative Examples 1-4. This indicates that the high-temperature storage characteristics of the battery have improved when the positive electrode active material according to the present invention is applied. In particular, in the case of Comparative Example 4, the high crack rate confirms that a significant amount of gas was generated due to a side reaction with the electrolyte. Furthermore, under conditions of 300 cycles, the capacity retention rate of monocells using the positive electrode active materials of Examples 1-4 is 92% or higher, while the capacity retention rate of monocells using the positive electrode active material powders of Comparative Examples 1-4 is at a lower level, indicating an increase in resistance. ,difference Furthermore, it can be confirmed that the output performance is also superior in the examples. In other words, it can be seen that when the positive electrode active material according to the present invention is applied, the high-temperature life and output characteristics are improved.

Claims

1. It contains large-particle lithium nickel-based transition metal oxides and small-particle lithium nickel-based transition metal oxides, The aforementioned large-particle lithium nickel-based transition metal oxide is in the form of secondary particles, which are aggregates of primary particles. The small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle consisting of one nodule and a pseudo-single particle which is a composite of 30 or fewer nodules. Positive electrode active material having a P value of 1.00 or higher, as defined by the following formula 1: [Formula 1] P=(A Ｌ ×R Ｌ ×C Ｌ ) / B Ｓ In the formula 1, A Ｌ , R Ｌ and C Ｌ are, respectively, the aspect ratio, circularity, and convexity of the large particle size lithium nickel-based transition metal oxide, and B Ｓ is the unitless number of the BET specific surface area (m ２ / g) of the small particle size lithium nickel-based transition metal oxide.

2. The positive electrode active material according to claim 1, wherein the P value derived by formula 1 is 1.00 to 2.

50.

3. The positive electrode active material according to claim 1, wherein the large-particle lithium nickel-based transition metal oxide has an aspect ratio of 0.85 or more, a circularity of 0.85 or more, and a convexity of 0.935 or more.

4. The positive electrode active material according to claim 1, wherein the small particle size lithium nickel-based transition metal oxide has an aspect ratio of 0.80 or more, a circularity of 0.80 or more, and a convexity of 0.900 or more.

5. The aforementioned large-particle lithium nickel-based transition metal oxide has a BET specific surface area of ​​0.40 m². ２ / g ~ 0.60m ２ The positive electrode active material according to claim 1, wherein the value is / g.

6. The aforementioned small-particle lithium nickel-based transition metal oxide has a BET specific surface area of ​​0.60 m². ２ / g to 1.10m ２ The positive electrode active material according to claim 1, wherein the value is / g.

7. The lithium nickel-based transition metal oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1: [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２－ｅ X ｅ In the above chemical formula 1, M １ M includes one or more selected from Mn and Al, ２ x includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and x includes one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.5, 0.5 ≤ a < 1, 0 < b ≤ 0.4, 0 < c ≤ 0.4, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.

05.

8. The positive electrode active material according to claim 1, wherein the large-particle lithium nickel-based transition metal oxide and the small-particle lithium nickel-based transition metal oxide each independently have a nickel content of 70 mol% or more among the transition metals.

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

10. A lithium secondary battery comprising the positive electrode described in claim 9.

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