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

Abstract

The present invention includes a lithium composite transition metal oxide represented by Chemical Formula 1 described in the present specification, which satisfies the formula (1) described in the present specification and has an average particle size D 50 The present invention relates to a positive electrode active material having a particle size of 1 μm to 8 μm, a method for producing the same, and a positive electrode material containing the same.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0181726, filed on December 23, 2020, and all the contents disclosed in the literature of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a positive electrode active material and a method for manufacturing the same, and more particularly, to a positive electrode active material and a method for manufacturing the same, which are developed to control the grain size to minimize a decrease in capacity and to reduce the amount of gas generation.

Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, light, and relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. Along with this, research and development efforts for improving the performance of lithium secondary batteries have been actively made.

[0004] A lithium secondary battery is filled with an organic electrolyte or a polymer electrolyte between a positive electrode and a negative electrode made of an active material capable of inserting and desorbing lithium ions, and electric energy is generated by an oxidation and reduction reaction when lithium ions are inserted / desorbed at the positive electrode and the negative electrode.

[0005] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate compound (LiFePO4), etc. have been used. Among them, lithium cobalt oxide (LiCoO2) has the advantages of a high operating voltage and excellent capacity characteristics, and is widely used and applied as a positive electrode active material for high voltages. However, due to the price increase and supply instability of cobalt (Co), there are limitations in its large-scale use as a power source in fields such as electric vehicles, and the need for the development of alternative positive electrode active materials is increasing.

[0006] Therefore, nickel cobalt manganese-based lithium composite transition metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") in which a part of cobalt (Co) is replaced with nickel (Ni) and manganese (Mn) have been developed. However, the conventionally developed NCM-based lithium composite transition metal oxides are generally in the form of secondary particles in which primary particles are aggregated, have a large specific surface area, low particle strength, and a high content of lithium by-products. Therefore, there is a problem of a large amount of gas generation and poor stability during cell operation.

[0007] In particular, in the case of high-content nickel (High-Ni) NCM-based lithium composite transition metal oxides in which the content of nickel (Ni) is increased to ensure high capacity, the structural and chemical stability is further reduced, and it is more difficult to ensure thermal stability. Therefore, various studies have been attempted to reduce the content of lithium by-products in high-content nickel-based lithium composite transition metal oxides and improve the stability.

[0008] Patent Document 1 discloses a technique in which, during the production of a positive electrode active material, two or more dopants are added and the firing temperature is increased to increase the crystal size, thereby reducing the specific surface area of the positive electrode active material, improving the particle strength, and reducing the content of lithium by-products. When forming a large crystal size as in Patent Document 1, the specific surface area of the positive electrode active material decreases, and accordingly, the contact area with the electrolyte decreases, and the effect of reducing the gas generation amount can be obtained, but there is a problem that the capacity characteristics are inferior.

[0009] Therefore, there is a demand for the development of a positive electrode active material that has excellent capacity characteristics and a small gas generation amount.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention is for solving the above problems, and an object thereof is to provide a positive electrode active material and a method for producing the same that can minimize a decrease in capacity characteristics and reduce the gas generation amount.

Means for Solving the Problems

[0012] According to one embodiment, the present invention provides a positive electrode active material containing a lithium composite transition metal oxide represented by the following Chemical Formula 1, satisfying the following formula (1), and having an average particle diameter D of secondary particles 50 being 1 μm to 8 μm. [Chemical Formula 1] Li a Ni x Co y M 1 z M 2 w O2 In the above Chemical Formula 1, M 1is one or more selected from Mn and Al, and M 2 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, where 0.9 ≦ a ≦ 1.1, 0.7 ≦ x < 1, 0 < y ≦ 0.2, 0 < z ≦ 0.2, and 0 ≦ w ≦ 0.1. Formula (1): 4 ≦ number of primary particles / average particle size D of secondary particles 50 ≦ 21 In the formula (1), the number of primary particles is the number of primary particles measured in the SEM image of the cross-section of the positive electrode active material, and the average particle size D 50 of the secondary particles is the particle size indicated by the maximum peak of the area cumulative particle size distribution of the positive electrode active material measured by a laser diffraction particle size analyzer.

[0013] According to another embodiment, the present invention provides a method for manufacturing a positive electrode active material, including the steps of mixing a positive electrode active material precursor represented by the following Chemical Formula 2 and a lithium raw material, and then performing a first firing to form a calcined product, and performing a second firing on the calcined product at a temperature of 800 °C to 880 °C to form a lithium composite transition metal oxide represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Ni x Co y M 1 z M 2 w O2 In the Chemical Formula 1, M 1 is one or more selected from Mn and Al, and M 2 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, where 0.9 ≦ a ≦ 1.1, 0.7 ≦ x < 1, 0 < y ≦ 0.2, 0 < z ≦ 0.2, and 0 ≦ w ≦ 0.1. [Chemical Formula 2] [Ni x Co y M 1 z M 2 w (OH)2 In the Chemical Formula 2, M 1is at least one selected from Mn and Al, and M 2 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, where 0.7 ≦ x < 1, 0 < y ≦ 0.2, 0 ≦ z ≦ 0.2, and 0 ≦ w ≦ 0.1.

[0014] According to still another embodiment, the present invention provides a bimodal cathode material including a first cathode active material and a second cathode active material having an average particle diameter D 50 different from that of the first cathode active material. At this time, the first cathode active material is the cathode active material of the present invention described above, and the second cathode active material can include a lithium composite transition metal oxide represented by the following Chemical Formula 3. [Chemical Formula 3] Li a’ Ni x’ Co y’ M 3 z’ M 4 w’ O2 In Chemical Formula 3, M 3 is at least one selected from Mn and Al, and M 4 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, where 0.9 ≦ a' ≦ 1.1, 0.8 ≦ x' < 1, 0 < y' < 0.2, 0 < z' < 0.2, and 0 ≦ w' ≦ 0.1.

[0015] According to still another embodiment, the present invention provides a cathode including the cathode material of the present invention and a lithium secondary battery including the cathode.

Advantages of the Invention

[0016] The cathode active material according to the present invention includes a high-nickel lithium composite transition metal oxide having a Ni content of 70 atm% or more among transition metals, and the number of aggregated primary particles per 1 μm in the cross-section of the cathode active material is 4 to 21. The cathode active material of the present invention as described above exhibits excellent capacity characteristics and can significantly reduce the amount of gas generation.

[0017] Further, the positive electrode active material according to the present invention can be usefully used in a bimodal positive electrode material containing two types of positive electrode active materials having different average particle diameters. When the positive electrode active material according to the present invention is applied to a bimodal positive electrode material, compared with the positive electrode active material in the form of secondary particles that has been generally used in the past while maintaining high capacity characteristics, the cracking of particles during rolling can be significantly reduced. As a result, the elution of transition metals and the generation of gas due to side reactions with the electrolytic solution can be effectively suppressed.

Brief Description of Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0019] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept that conform to the technical idea of the present invention, following the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0020] In the present invention, the "primary particle" means the smallest particle unit that can be distinguished as a single mass when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM). It can consist of one crystal grain or multiple crystal grains. In the present invention, the average particle size of the primary particle can be measured by measuring the respective particle sizes distinguished in the SEM image of the cross-section of the positive electrode active material particles and obtaining the arithmetic mean value thereof.

[0021] In the present invention, the "secondary particle" means a secondary structure formed by the aggregation of a plurality of primary particles. The average particle size of the secondary particle can be measured using a particle size analyzer. In the present invention, S3500 manufactured by Microtrac is used as the particle size analyzer.

[0022] In the present invention, the "particle size Dn" of the positive electrode active material means the particle size at the n% point of the area cumulative distribution according to the particle size. That is, D 50 is the particle size at the 50% point of the area cumulative distribution according to the particle size, and D 90 is the particle size at the 90% point of the area cumulative distribution according to the particle size, and D 10 is the particle size at the 10% point of the area cumulative distribution according to the particle size. The Dn can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and when the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle sizes at the 10%, 50%, and 90% points of the area cumulative distribution according to the particle size in the measuring device, D 10 、D 50 and D 90 can be measured.

[0023] Hereinafter, the present invention will be specifically described.

[0024] Positive electrode active material The positive electrode active material according to the present invention contains a high-nickel lithium composite transition metal oxide in which the Ni content among transition metals is 70 atm% or more, and the number of aggregated primary particles per 1 μm in the cross section of the positive electrode active material is 4 to 21.

[0025] The positive electrode active materials developed so far are in the form of secondary particles in which several hundred primary particles are aggregated, and the number of aggregated primary particles per 1 μm is at the level of 30 to 40. Such a conventional positive electrode active material in the form of secondary particles operates relatively stably when the nickel content is low. However, when the nickel content increases to 70 atm% or more, the structural stability rapidly decreases, the gas generation amount rapidly increases, the life characteristics rapidly deteriorate, and stability problems such as ignition and explosion may be caused.

[0026] In order to improve this, a positive electrode active material in the form of single particles with the number of aggregated primary particles less than 10 has been developed. In the case of such a positive electrode active material in the form of single particles, it is effective in reducing the gas generation amount, but the capacity characteristics are inferior and it has been difficult to apply to high-capacity batteries.

[0027] As a result of repeated studies to solve such problems, the inventors of the present invention have found that by controlling the number of aggregated primary particles per 1 μm in the cross section of the positive electrode active material particles to be 4 to 21, it is possible to excellently realize both the capacity characteristics and the gas generation characteristics of a high-nickel positive electrode active material with a nickel content of 70 atm% or more, and thus have completed the present invention.

[0028] Specifically, the positive electrode active material of the present invention contains a lithium composite transition metal oxide represented by the following Chemical Formula 1 and satisfies the following formula (1).

[0029] [Chemical Formula 1] Li a Ni x Co y M 1 z M 2 w O2

[0030] In the Chemical Formula 1 above, M 1is one or more selected from Mn and Al, and preferably can be Mn and Al.

[0031] M 2 can be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and it is particularly preferable to contain Zr in terms of improving the structural stability of the lithium composite transition metal oxide.

[0032] Said a represents the molar ratio of lithium in the lithium composite transition metal oxide, and can be 0.9 ≦ a ≦ 1.1, preferably 0.95 ≦ a ≦ 1.08, and more preferably 1 ≦ a ≦ 1.08.

[0033] Said x represents the molar ratio of nickel among the transition metals in the lithium composite transition metal oxide, and can be 0.7 ≦ x < 1, 0.80 ≦ x ≦ 0.99, 0.80 ≦ x ≦ 0.95, 0.85 ≦ x < 1, or 0.80 ≦ x ≦ 0.85. When the nickel content satisfies the above range, excellent capacity characteristics can be realized.

[0034] Said y represents the molar ratio of cobalt among the transition metals in the lithium composite transition metal oxide, and can be 0 < y ≦ 0.2, 0 < y ≦ 0.15, or 0.01 ≦ y ≦ 0.10.

[0035] Said z represents the molar ratio of M 1 among the transition metals in the lithium composite transition metal oxide, and can be 0 < z < 0.2, 0 < z ≦ 0.15, or 0.01 ≦ z ≦ 0.10.

[0036] Said w represents the molar ratio of M 2 among the transition metals in the lithium composite transition metal oxide, and can be 0 ≦ w ≦ 0.1, or 0 ≦ w ≦ 0.05.

[0037] Preferably, the lithium composite transition metal oxide can be represented by the following Chemical Formula 1-1.

[0038] [Chemical Formula 1-1] Li a Ni x Co y Mn z1 Al Z2 M 2 w O2

[0039] In the above Chemical Formula 1-1, M 2 , the definitions of a, x, y, and w are the same as those in Chemical Formula 1.

[0040] On the other hand, z1 represents the molar ratio of Mn among the transition metals in the lithium composite transition metal oxide, and can be 0 < z1 ≤ 0.15, or 0.01 ≤ z1 ≤ 0.10.

[0041] z2 represents the molar ratio of Al among the transition metals in the lithium composite transition metal oxide, and can be 0 < z2 ≤ 0.05.

[0042] When using a lithium composite transition metal oxide containing both Mn and Al as in Chemical Formula 1-1, a cathode active material with high capacity and relatively excellent structural stability can be obtained.

[0043] On the other hand, the cathode active material according to the present invention can further include a coating layer containing one or more 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 on the surface of the lithium composite transition metal oxide. In terms of improving the life characteristics and suppressing the increase in resistance, it is particularly preferable that the coating layer contains the B element.

[0044] When a coating layer is formed on the surface of the lithium composite transition metal oxide as described above, the contact between the lithium composite transition metal oxide and the electrolyte is blocked, and the generation of gas and the elution of transition metal due to the side reaction with the electrolyte can be effectively suppressed. The surface structure of the lithium composite transition metal oxide can be stabilized, and the deterioration of the structure of the positive electrode active material during charge and discharge can be suppressed.

[0045] On the other hand, the positive electrode active material according to the present invention satisfies the following formula (1).

[0046] Formula (1): 4 ≤ Number of primary particles / Average particle size D of secondary particles 50 ≤ 21

[0047] In the formula (1), the number of the primary particles is the number of primary particles measured by the SEM image of the cross section of the positive electrode active material, and the average particle size D of the secondary particles 50 means the particle size value at the point indicated by the maximum peak of the area cumulative particle size distribution of the positive electrode active material measured by a laser diffraction particle size analyzer.

[0048] The number of primary particles / average particle size of the secondary particles can preferably be 4 to 21, preferably 5 to 20, and more preferably 6 to 15.

[0049] When the value of the number of primary particles / average particle size of the secondary particles satisfies the scope of the present invention, a positive electrode active material excellent in both capacity characteristics and gas generation characteristics can be obtained. When the value of the number of primary particles / average particle size of the secondary particles is less than 4, the migration distance of lithium ions in the positive electrode active material becomes long and the lithium ion mobility decreases, resulting in a decrease in capacity. When it exceeds 21, the effect of reducing the gas generation amount cannot be obtained.

[0050] On the other hand, the positive electrode active material according to the present invention can have 20 to 100, preferably 30 to 100, and more preferably 40 to 95 primary particles measured by the SEM image of the cross section. When the number of primary particles in the cross section of the positive electrode active material particles is less than 20, the capacity characteristics deteriorate. When it exceeds 100, the effect of reducing the gas generation amount cannot be obtained.

[0051] On the one hand, the cathode active material according to the present invention has an average particle diameter D of the secondary particles 50 that can be 1 μm to 8 μm, preferably 2 μm to 7 μm. When the average particle diameter D of the secondary particles 50 is less than 1 μm, the degree of cracking of the secondary particles is low, but there is a problem that the life performance deteriorates due to an increase in the number of secondary particles and an increase in the exposed primary particles. When it exceeds 8 μm, the cracking of the secondary particles increases and the long-term life performance deteriorates, and when rolled at the same pressure, there is a problem that the density of the electrode becomes low. When the average particle diameter D of the cathode active material 50 satisfies the above range, when applying the bimodal cathode material, a cathode with a high rolling density and a low degree of cracking in the electrode rolling process can be manufactured.

[0052] In addition, the cathode active material according to the present invention can have a particle size change rate represented by the following formula (2) of -5 to 4.5, preferably 0 to 4, more preferably 0 to 3.5.

[0053] Formula (2): Particle size change rate = (P0 - P1) / P1

[0054] In the formula (2), P0 is the intensity of the maximum peak shown in the area cumulative particle size distribution graph of the cathode active material, and P1 is the intensity of the peak shown in the region corresponding to the particle diameter at which the P0 peak is shown in the area cumulative particle size distribution graph measured after pressing the cathode active material at 9 tons.

[0055] In addition, the cathode active material according to the present invention can have a particle size change amount represented by the following formula (3) of 0 to 12, preferably 0 to 10, more preferably 2 to 10.

[0056] Formula (3): Particle size change amount = P0 - P1

[0057] In the formula (3), P0 is the intensity of the maximum peak shown in the area cumulative particle size distribution graph of the positive electrode active material, and P1 is the intensity of the peak shown in the region corresponding to the particle diameter at which the P0 peak is shown in the area cumulative particle size distribution graph measured after pressing the positive electrode active material at 9 tons.

[0058] When the particle size change rate represented by the formula (2) and the particle size change amount represented by the formula (3) satisfy the above range, during the production of the positive electrode, cracking of particles due to rolling can be suppressed, and the effect of reducing the gas generation amount can be further improved.

[0059] Manufacturing method of positive electrode active material Next, the manufacturing method of the positive electrode active material according to the present invention will be described.

[0060] The manufacturing method of the positive electrode active material according to the present invention includes: (1) a step of mixing a positive electrode active material precursor and a lithium raw material substance, and then performing a primary firing to form a calcined product; and (2) a step of performing a secondary firing on the calcined product at a temperature of 800°C to 880°C to form a lithium composite transition metal oxide.

[0061] First, a positive electrode active material and a lithium raw material substance are mixed, and then a primary firing is performed to form a calcined product.

[0062] At this time, the positive electrode active material precursor can be a hydroxide compound represented by the following chemical formula 2.

[0063] [Chemical formula 2] [Ni x Co y M 1 z M 2 w (OH)2

[0064] In the chemical formula 2, M 1 can be one or more selected from Mn and Al, and preferably can be Mn.

[0065] M2 It can be at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0066] Said x represents the molar ratio of nickel in the positive electrode active material precursor, and can be 0.7 ≦ x < 1, 0.80 ≦ x ≦ 0.99, 0.80 ≦ x ≦ 0.95, 0.85 ≦ x < 1, or 0.80 ≦ x ≦ 0.85. When the nickel content satisfies the above range, excellent capacity characteristics can be realized.

[0067] Said y represents the molar ratio of cobalt in the positive electrode active material precursor, and can be 0 < y ≦ 0.2, 0 < y < 0.15, or 0.01 ≦ y ≦ 0.10.

[0068] Said z represents the molar ratio of M 1 in the positive electrode active material precursor, and can be 0 ≦ z < 0.2, 0 ≦ z < 0.15, or 0.01 ≦ z < 0.10.

[0069] Said w represents the molar ratio of M 2 in the positive electrode active material precursor, and can be 0 ≦ w ≦ 0.1, or 0 ≦ w ≦ 0.05.

[0070] Preferably, the positive electrode active material precursor can be a nickel-cobalt-manganese hydroxide represented by the following Chemical Formula 2-1.

[0071] [Chemical Formula 2-1] [Ni x Co y Mn z1 (OH)2

[0072] In said Chemical Formula 2-1, said x represents the molar ratio of nickel in the positive electrode active material precursor, and can be 0.7 ≦ x < 1, 0.80 ≦ x ≦ 0.99, 0.80 ≦ x ≦ 0.95, 0.85 ≦ x < 1, or 0.80 ≦ x ≦ 0.85. When the nickel content satisfies the above range, excellent capacity characteristics can be realized.

[0073] Wherein y represents the molar ratio of cobalt in the cathode active material precursor, and can be 0 < y ≦ 0.2, 0 < y < 0.15, or 0.01 ≦ y ≦ 0.10.

[0074] Wherein z1 represents the molar ratio of manganese in the cathode active material precursor, and can be 0 < z1 < 0.15, or 0.01 ≦ z1 < 0.10.

[0075] On the other hand, as the lithium raw material substance, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a mixture thereof can be used.

[0076] On the other hand, the lithium raw material substance and the cathode active material precursor can be mixed so that the molar ratio of Li: total transition metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium raw material substance and the transition metal in the cathode active material precursor satisfies the above range, a cathode active material with a well-developed crystal structure, excellent capacity characteristics, and structural stability can be produced.

[0077] On the other hand, when mixing the cathode active material precursor and the lithium raw material substance, if necessary, at least one of the M 1 containing raw material and the M 2 containing raw material can be further mixed.

[0078] The M 1 containing raw material is the M 1It can be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing an element, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese chloride, manganese hydroxide, Al2O3, Al(OH)3, Al(NO3)3·9H2O, Al2(SO4)3, etc., but is not limited thereto.

[0079] Said M 2 The raw material contained is 2 It can be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing an element.

[0080] In the present invention, said M 1 element and M 2 element may be introduced in the coprecipitation reaction step for producing the cathode active material precursor or may be introduced when mixing with the lithium raw material substance. Also, when using two or more elements as the M 1 element and M 2 element, the introduction time points of each M 1 element and M 2 element may be the same or different. For example, when including Mn and A 1 as the M 1 element, Mn can be introduced in the precursor coprecipitation step and Al can be introduced in the mixing step with the lithium raw material substance.

[0081] M 1 element and M 2 The introduction time points of the element can be appropriately adjusted in consideration of the final composition of the cathode active material to be produced. For example, when producing a cathode active material with a Ni content exceeding 80 atm%, it is more preferable to introduce the Al element in the mixing step with the lithium raw material substance rather than during the coprecipitation reaction. This is because when Al is introduced in the coprecipitation step, it can have an adverse effect on the growth of the crystal structure.

[0082] Mix the cathode active material precursor and the lithium raw material substance, and selectively, M 1Containing raw materials and M 2 After further mixing at least one of the raw materials, primary firing is performed to produce a calcined product.

[0083] The primary firing is to calcine the cathode active material precursor and the lithium raw material substance in advance to remove by-products such as CO2 and moisture generated during firing, so as to prevent the by-products from adversely affecting the formation of the crystal structure of the cathode active material and enable the production of a cathode active material of excellent quality.

[0084] The primary firing is performed at a temperature lower than the secondary firing described later. Specifically, it is preferably performed at a temperature 20°C to 250°C lower than the temperature of the secondary firing, more preferably at a temperature 40°C to 250°C lower than the temperature of the secondary firing. Specifically, the primary firing can be performed at a temperature of 600°C or higher and lower than 800°C, preferably 600°C to 780°C, more preferably 600°C or higher and 760°C. If the primary firing temperature is excessively high, crystal structure conversion occurs in the primary firing step where by-products are present and the crystal structure does not develop well. If the primary firing temperature is excessively low, the removal efficiency of by-products may decrease.

[0085] When the calcined product is formed by the primary firing, the calcined product is secondarily fired to form the lithium composite transition metal oxide represented by Chemical Formula 1.

[0086] At this time, the secondary firing is performed at a temperature of 800°C to 880°C, preferably 800°C to 860°C. When the secondary firing temperature satisfies the above range, a cathode active material that satisfies the range of Formula (1) and has a nickel content of 70 atm% or more can be produced. When producing a cathode active material with a nickel content of 70 atm% or more, if the secondary firing temperature is less than 800°C, a cathode active material with a ratio of the number of primary particles to the average particle size of secondary particles (number of primary particles / average particle size of secondary particles) exceeding 21 is produced. If the secondary firing temperature exceeds 800°C, a cathode active material with a ratio of the number of primary particles to the average particle size of secondary particles (number of primary particles / average particle size of secondary particles) less than 4 is produced.

[0087] On the other hand, after the secondary firing, if necessary, the step of washing the lithium composite transition metal oxide represented by Chemical Formula 1 with water can be further included.

[0088] The water washing step is for removing lithium by-products remaining on the surface of the lithium composite transition metal oxide, and can be carried out by a water washing method of a cathode active material well-known in the art. For example, the water washing step can be carried out by mixing the lithium composite transition metal oxide and a water washing solution, stirring, filtering to remove the water washing solution, and then drying. At this time, the drying can be carried out, for example, at a temperature of 50°C to 150°C.

[0089] Also, after the secondary firing, if necessary, the step of forming a coating layer on the surface of the lithium composite transition metal oxide can be further carried out.

[0090] The step of forming the coating layer can be carried out by mixing the lithium composite transition metal oxide and a coating raw material substance and then performing heat treatment.

[0091] At this time, the coating raw material substance can contain one or more 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. Specifically, it can be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing the above elements.

[0092] On the other hand, the heat treatment during the formation of the coating layer can be carried out at a temperature of 200°C to 500°C, preferably 240°C to 400°C.

[0093] Cathode material Next, the cathode material according to the present invention will be described.

[0094] The positive electrode material according to the present invention contains, as the first positive electrode active material, the positive electrode active material of the present invention described above (that is, a positive electrode active material containing a lithium composite transition metal oxide represented by Chemical Formula 1 and satisfying Formula (1)), and as the second positive electrode active material, a positive electrode active material having an average particle diameter D 50 different from that of the first positive electrode active material. Since the first positive electrode active material is as described above, the second positive electrode active material will be described below.

[0095] The second positive electrode active material contains a lithium composite transition metal oxide in which the nickel content among the transition metals is 80 atm% or more, and specifically contains a lithium composite transition metal oxide represented by the following Chemical Formula 3.

[0096] [Chemical Formula 3] Li a’ Ni x’ Co y’ M 3 z’ M 4 w’ O2

[0097] In Chemical Formula 3, the M 3 is one or more selected from Mn and Al, and preferably can be Mn and Al.

[0098] The M 4 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and it is particularly preferable to contain Zr in terms of improving the structural stability of the lithium composite transition metal oxide.

[0099] The a' represents the molar ratio of lithium in the lithium composite transition metal oxide, and can be 0.9 ≤ a ≤ 1.1, preferably 0.95 ≤ a ≤ 1.08, and more preferably 1 ≤ a ≤ 1.08.

[0100] Said x' represents the molar ratio of nickel among the transition metals in the lithium composite transition metal oxide, and can be 0.8 ≦ x' < 1, 0.83 ≦ x' < 1, 0.85 ≦ x' < 1 or 0.85 ≦ x' ≦ 0.95.

[0101] Said y' represents the molar ratio of cobalt among the transition metals in the lithium composite transition metal oxide, and can be 0 < y' ≦ 0.2, 0 < y' < 0.15, 0 < y' ≦ 0.1 or 0.01 ≦ y' ≦ 0.10.

[0102] Said z' represents the molar ratio of M among the transition metals in the lithium composite transition metal oxide 3 and can be 0 < z' < 0.2, 0 < z' < 0.15, 0 < z' ≦ 0.1 or 0.01 ≦ z' ≦ 0.10.

[0103] Said w' represents the molar ratio of M among the transition metals in the lithium composite transition metal oxide 4 and can be 0 ≦ w' ≦ 0.1, 0 ≦ w' < 0.1 or 0 ≦ w' ≦ 0.05.

[0104] On the other hand, in the present invention, the average particle diameter D of the secondary particles of the first positive electrode active material 50 can be 1 μm to 8 μm, preferably 2 μm to 8 μm, more preferably 3 μm to 8 μm, and the average particle diameter D of the secondary particles of the second positive electrode active material 50 can be more than 8 μm and 30 μm or less, preferably 8.5 μm to 25 μm, more preferably 9 μm to 20 μm.

[0105] When the average particle diameter D of the secondary particles of the first positive electrode active material and the second positive electrode active material 50 satisfies the above range, a positive electrode with a high packing density can be manufactured by filling the spaces between the second positive electrode active material particles with the first positive electrode active material particles, and by using a second positive electrode active material with a nickel content of 80 atm% or more in a large particle size, the capacity characteristics can be further improved.

[0106] On the one hand, the first positive electrode active material and the second positive electrode active material can be included in a weight ratio of 1:99 to 50:50, preferably 10:90 to 40:60, and more preferably 20:80 to 30:70. When the mixing ratio is satisfied, better capacity characteristics and life characteristics are exhibited.

[0107] Average particle size D 50 When manufacturing a positive electrode active material layer using a bimodal positive electrode material containing two types of positive electrode active materials with different average particle sizes, the small particle size positive electrode active material having a small average particle size is filled between the large particle size positive electrode active material particles having a large average particle size, and an electrode with a high energy density can be manufactured. However, in the case of conventional bimodal positive electrode materials, cracks occur in the small particle size positive electrode active material particles during the rolling process of the positive electrode, increasing the contact area with the electrolytic solution. Therefore, there is a problem that the gas generation amount increases and the life characteristics deteriorate.

[0108] To improve this, a method of increasing the firing temperature and using the manufactured single-particle form positive electrode active material as the small particle size positive electrode active material can be considered. However, in the case of the single-particle form positive electrode active material, not only is there a limit to realizing high capacity due to poor capacity characteristics, but there is also a problem that the particle strength of the small particle size positive electrode active material becomes excessively high and cracks can be generated in the large particle size positive electrode active material during the rolling process.

[0109] In comparison, when the positive electrode active material according to the present invention is used as the small particle size positive electrode active material of the bimodal positive electrode material, not only can the gas generation amount be reduced without a decrease in capacity, but side effects such as crack generation in the large particle size positive electrode active material during the rolling process can also be minimized.

[0110] Positive electrode The present invention provides a positive electrode for a lithium secondary battery including the positive electrode material of the present invention described above.

[0111] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and including the positive electrode material according to the present invention. Since the positive electrode material is as described above, other components other than the positive electrode material will be described below.

[0112] The positive current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Further, the positive current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can also be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0113] The positive electrode active material layer can include a conductive material and a binder together with the positive electrode material according to the present invention described above.

[0114] The positive electrode material can be contained in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, based on the total weight of the positive electrode active material layer. When contained within the above content range, excellent capacity characteristics can be exhibited.

[0115] The conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it does not cause a chemical change and has electron conductivity in the battery being formed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0116] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds can be used. The binder can be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0117] Except for using the positive electrode material according to the present invention, the positive electrode can be manufactured by a normal method for manufacturing a positive electrode. Specifically, after applying a composition for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the above positive electrode material, and optionally a binder and a conductive material in a solvent, onto a positive electrode current collector, it can be manufactured by drying and rolling. At this time, the types and contents of the positive electrode material, binder, and conductive material are as described above.

[0118] The solvent can be a solvent generally used in the technical field, and examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. Among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent used is such that, considering the coating thickness of the slurry and the production yield, it can dissolve or disperse the positive electrode material, conductive material, and binder, and then have a viscosity that can exhibit excellent thickness uniformity during coating for the production of the positive electrode.

[0119] As another method, the positive electrode can also be manufactured by laminating, on a positive electrode current collector, a film obtained by casting the composition for forming the positive electrode active material layer on another support and then peeling the film from the support.

[0120] Lithium secondary battery Further, the present invention can manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element can be a battery, a capacitor, or the like, and more specifically, it can be a lithium secondary battery.

[0121] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, a specific description thereof is omitted, and hereinafter, only the remaining configuration will be specifically described.

[0122] Further, the lithium secondary battery can optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0123] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0124] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Further, 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 binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0125] The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material.

[0126] As the negative electrode active material, a compound 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; metal oxides such as SiO β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides, which can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material, such as Si-C composites or Sn-C composites. Any one or a mixture of two or more of these can be used. Further, a thin film of metallic lithium can also be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0127] The negative electrode active material can be contained in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0128] The binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and can usually be added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, and various copolymers thereof.

[0129] 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, specifically 5% by weight or less, based on 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 has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, 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.

[0130] For example, the negative electrode active material layer is manufactured by applying and drying a negative electrode active material layer forming composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode active material layer forming composition on another support and then laminating the film obtained by peeling the support on the negative electrode current collector.

[0131] On the one hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a lithium secondary battery can be used without particular limitation. In particular, those with low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. can also be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and optionally, it can be used in a single-layer or multilayer structure.

[0132] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0133] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0134] As long as the organic solvent can serve as a medium through which ions involved in the electrochemical reaction of the battery can move, it can be used without particular limitation. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among them, 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, which can enhance the charge and discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred.

[0135] 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, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used within a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can move effectively.

[0136] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and thus is useful in portable devices such as mobile phones, notebook computers, digital cameras, and the like, and the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0137] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0138] The battery module or the battery pack can be used as a power source for one or more medium and large-sized devices such as power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0139] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and can be, for example, a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can.

[0140] The lithium secondary battery according to the present invention can be preferably used not only as a battery cell for powering small devices but also as a unit cell in medium and large-sized battery modules including a large number of battery cells.

[0141] Hereinafter, in order to specifically describe the present invention, examples will be given and described in detail. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0142] Example 1 The lithium raw material substance LiOH·H2O and the cathode active material precursor Ni 0.83 Co 0.05 Mn 0.12 (OH)2 (D 50 = 4.6 μm) were mixed so that the molar ratio of Li: transition metal (Ni + Co + Mn) in the precursor was 1.06:1, and ZrO2 and Al(OH)3 were further mixed. Then, the mixture was calcined at 640 °C for 5 hours to produce a calcined product. At this time, ZrO2 was mixed so that Zr was 3500 ppm with respect to the total weight of the calcined product, and Al(OH)3 was mixed in an amount such that Al was 2 mol% with respect to the total number of moles of Ni, Co, Mn, and Al. Thereafter, the calcined product was secondarily calcined at 830 °C to produce a lithium composite transition metal oxide LiNi 0.81 Co 0.05 Mn 0.12 Al 0.02 O2.

[0143] 200 g of the lithium composite transition metal oxide produced as described above and 240 g of water were mixed, stirred for 5 minutes, washed with water, and then separated and filtered through a filter press so that the water content in the washed product was 5 to 10%, and then dried at 130 °C. Thereafter, the washed and dried lithium composite transition metal oxide and H3BO3 were mixed at a weight ratio of 100:0.57 and heat-treated at 300 °C for 4 hours to produce a positive electrode active material coated with a B solid solution.

[0144] Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that the secondary firing was performed at 800 °C.

[0145] Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that the secondary firing was performed at 850 °C.

[0146] Comparative Example 1 A positive electrode active material was produced in the same manner as in Example 1, except that the secondary firing was performed at 780 °C.

[0147] Comparative Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that the secondary firing was performed at 900 °C.

[0148] Comparative Example 3 The average particle size (D 50 ) of the secondary particles was 8.5 μm, and a positive electrode active material was produced in the same manner as in Example 1, except that a positive electrode active material precursor was used.

[0149] Experimental Example 1 After dispersing 0.5 g of the positive electrode active material powder produced in Examples 1 to 3 and Comparative Examples 1 to 3 in water with a small amount of sodium hexametaphosphate ((NaPO3)6) added, the average particle size D of the secondary particles of the positive electrode active material was measured using a laser diffraction particle size analyzer (Microtrac, S-3500). 50 The measurement results are shown in Table 1.

[0150] Also, 10 g of the positive electrode active material particles were collected from the positive electrode active material powders produced in Examples 1 to 3 and Comparative Examples 1 to 3. After cutting the cross-section using an ion milling system (IM4000, manufactured by Hitachi), an SEM image of the cross-section was obtained with a scanning electron microscope. The obtained SEM image of the cross-section was analyzed, the number of primary particles in the cross-section of each positive electrode active material was measured, and the average value was calculated. The measurement results are shown in Table 1.

[0151] In addition, FIG. 1 shows an SEM image of the cross-section of the sample collected from the positive electrode active material powder of Example 1, FIG. 2 shows an SEM image of the cross-section of the sample collected from the positive electrode active material powder of Comparative Example 1, and FIG. 3 shows an SEM image of the cross-section of the sample collected from the positive electrode active material powder of Comparative Example 2.

[0152]

Table 1

[0153] Experimental Example 2 - Measurement of particle size change rate and particle size change amount After dispersing 0.5 g of the positive electrode active material powders produced in Examples 1 to 3 and Comparative Examples 1 to 3 in water with a small amount of sodium hexametaphosphate ((NaPO3)6) added, the area cumulative particle size distribution of the positive electrode active material secondary particles was measured using a laser diffraction particle size analyzer (S-3500, manufactured by Microtrac).

[0154] Thereafter, 2 g of the positive electrode active material powder was collected, pressed at a pressure of 9 tons, and then the pressed positive electrode active material powder was dispersed in water with a small amount of sodium hexametaphosphate ((NaPO3)6) added. The area cumulative particle size distribution of the positive electrode active material secondary particles after pressing at 9 tons was measured using a laser diffraction particle size analyzer (S-3500 of Microtrac).

[0155] Using the particle size distribution measurement results before and after the pressing, the particle size change rate represented by the following formula (2) and the particle size change amount represented by formula (3) were calculated.

[0156] Formula (2): Particle size change rate = (P0 - P1) / P1

[0157] Formula (3): Particle size change amount = P0 - P1

[0158] In the above formulas (2) and (3), P0 is the intensity of the maximum peak shown in the area particle size distribution graph of the positive electrode active material, and P1 is the intensity of the peak shown in the region corresponding to the particle size of the P0 peak in the measured area particle size distribution graph after pressing the positive electrode active material at 9 tons.

[0159] The measurement results are shown in Table 2 and Figures 4 to 6 below.

[0160] Figure 4 shows a graph showing the area cumulative particle size distribution before and after pressing the positive electrode active material powder of Example 1. Figure 5 shows a graph showing the area cumulative particle size distribution before and after pressing the positive electrode active material powder of Comparative Example 1. Figure 6 shows a graph showing the area cumulative particle size distribution before and after pressing the positive electrode active material powder of Comparative Example 2.

[0161]

Table 2

[0162] Experimental Example 3 - Evaluation of Capacity Characteristics The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 and an average particle size D 50 containing 10 μm of Zr 3500 ppm of LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 were mixed at a weight ratio of 2:8 to produce a positive electrode material.

[0163] The positive electrode material, conductive material (Denka black), and binder (PVDF) were mixed in a weight ratio of 97.5:1.15:1.35 in an N-methyl-2-pyrrolidone (NMP) solvent to produce a positive electrode slurry. The positive electrode slurry was coated on an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0164] As the negative electrode, a lithium metal electrode was used.

[0165] After manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, it was placed inside a battery case and then an electrolytic solution was injected to manufacture a lithium secondary battery. At this time, as the electrolytic solution, an electrolytic solution in which 1 M of LiPF6 was dissolved in an organic solvent obtained by mixing ethylene carbonate:ethyl methyl carbonate:diethyl carbonate in a volume ratio of 3:3:4 was used.

[0166] For each of the lithium secondary batteries manufactured as described above, after performing CC / CV mode charging at a constant current of 0.1C to 4.25V at 25°C (CV 0.05C), CC mode discharging was performed until it reached 3V, and the initial discharge capacity (unit: mAh / g) and capacity efficiency (unit: %) were measured. The measurement results are shown in Table 3.

[0167]

Table 3

[0168] Experimental Example 4 - Evaluation of Gas Generation Amount The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 and an average particle size D 50 containing 3500 ppm of Zr with a size of 10 μm, LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 positive electrode active materials were mixed in a weight ratio of 2:8 to produce a positive electrode material.

[0169] The above-mentioned positive electrode material, conductive material (Denka black), and binder (PVDF) were mixed in a weight ratio of 97.5:1.15:1.35 in an N-methyl-2-pyrrolidone (NMP) solvent to produce a positive electrode slurry. The positive electrode slurry was applied onto an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0170] Next, the negative electrode active material (natural graphite), conductive material (carbon black), and binder (SBR+CMC) were mixed in a weight ratio of 95:1.5:3.5 in water to produce a negative electrode slurry. The negative electrode slurry was applied onto a copper current collector, dried, and then rolled to produce a negative electrode.

[0171] After manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, it was placed inside a battery case and then an electrolytic solution was injected to manufacture three single cells with an electrode size of 3 cm×4 cm. At this time, as the electrolytic solution, an electrolytic solution in which 1 M of LiPF6 was dissolved in an organic solvent obtained by mixing ethylene carbonate:ethyl methyl carbonate:diethyl carbonate in a volume ratio of 3:3:4 was used.

[0172] The three single cells were charged at a constant current of 0.33 C to 4.25 V at 45 °C with a 0.05 C cut-off, and then the positive electrode was separated. The separated positive electrode was put into a cell pouch, more electrolytic solution was injected, and then it was sealed to prepare a sample. While storing the sample at 60 °C for 4 weeks, the cell volume change rate (unit: %) and the gas generation amount (unit: μl) were measured. The measurement results are shown in Table 4 and Table 5.

[0173]

Table 4

[0174]

Table 5

[0175] As shown in Tables 3 to 5 above, in the case of Examples 1 to 3 to which the positive electrode active material of the present invention was applied, both the capacity characteristics and the effect of reducing gas generation were excellently shown. On the other hand, Comparative Example 1 is excellent in capacity characteristics but has a high gas generation amount, Comparative Example 2 has extremely low capacity characteristics, and Comparative Example 3 has low capacity characteristics and a high gas generation amount problem.

Claims

1. comprising a lithium composite transition metal oxide represented by the following Chemical Formula 1, satisfying the following formula (1), Average particle size D of the secondary particles ５０ is 1 μm to 8 μm, and the positive electrode active material: [Chemical Formula 1] Li ａ Ni ｘ Co ｙ M １ ｚ M ２ ｗ O ２ In the above Chemical Formula 1, M １ is one or more selected from Mn and Al, and M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.9 ≤ a ≤ 1.1, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, and 0 ≤ w ≤ 0.

1. Formula (1): 4 μm －１ ≤ Number of primary particles / Average particle size D of secondary particles ５０ ≤ 21 μm －１ In the formula (1), the number of the primary particles is the number of the primary particles measured by the SEM image of the cross-section of the positive electrode active material, and the average particle diameter D of the secondary particles ５０ is the particle diameter indicated by the maximum peak of the area frequency particle size distribution of the positive electrode active material measured by a laser diffraction particle size analyzer.

2. The positive electrode active material according to Claim 1, wherein the lithium composite transition metal oxide is represented by the following Chemical Formula 1-1: [Chemical Formula 1-1] Li ａ Ni ｘ Co ｙ Mn ｚ１ Al Ｚ２ M ２ ｗ O ２ In the chemical formula 1-1, M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.9 ≤ a ≤ 1.1, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z1 ≤ 0.15, 0 < z2 ≤ 0.05, 0 ≤ w ≤ 0.

1.

3. The positive electrode active material according to Claim 1, wherein the number of primary particles measured by an SEM image of a cross section of the positive electrode active material is 20 to 100.

4. The positive electrode active material according to Claim 1, further comprising a coating layer formed on the surface of the lithium composite transition metal oxide and containing one or more 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.

5. A method for manufacturing the positive electrode active material according to Claim 1, comprising a step of mixing a positive electrode active material precursor represented by the following Chemical Formula 2 and a lithium raw material, and then performing a primary firing to form a calcined product, and a step of performing a secondary firing on the calcined product at a temperature of 800°C to 880°C to form a lithium composite transition metal oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Li ａ Ni ｘ Co ｙ M １ ｚ M ２ ｗ O ２ In the above Chemical Formula 1, M １ is one or more selected from Mn and Al, and M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S. 0.9 ≤ a ≤ 1.1, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ w ≤ 0.

1. [Chemical Formula 2] [Ni ｘ Co ｙ M １ ｚ M ２ ｗ (OH) ２ In the chemical formula (2), M １ is one or more selected from Mn and Al, and M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.7 ≦ x < 1, 0 < y ≦ 0.2, 0 ≦ z ≦ 0.2, 0 ≦ w ≦ 0.

1.

6. The method according to Claim 5, wherein the positive electrode active material precursor is represented by the following Chemical Formula 2-1: [Chemical Formula 2-1] [Ni ｘ Co ｙ Mn ｚ１ (OH) ２ In Chemical Formula 2-1, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z1 ≤ 0.

15.

7. During the first firing, M １ containing raw materials (where M １ is at least one or more of Mn and Al) and M ２ containing raw materials (where M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S), the method according to claim 5, further mixing at least one or more of them.

8. The method according to Claim 5, wherein the primary firing is performed at a temperature 20°C to 250°C lower than the temperature of the secondary firing.

9. The method according to Claim 8, wherein the primary firing is performed at a temperature of 600°C or higher and lower than 800°C.

10. After the secondary firing, the step of washing the lithium composite transition metal oxide represented by Chemical Formula 1 and the lithium composite transition metal oxide represented by Chemical Formula 1 and a coating raw material substance containing one or more 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 are mixed, and then heat-treated to form a coating layer. The method according to claim 5, further comprising at least one of the steps.

11. In the step of forming the coating layer, the heat treatment is performed at 200°C to 500°C. The method according to claim 10.

12. A bimodal positive electrode material containing a first positive electrode active material and a second positive electrode active material having an average particle diameter D different from that of the first positive electrode active material ５０ which contains a second positive electrode active material having an average particle diameter D different from that of the first positive electrode active material The first positive electrode active material is the positive electrode active material according to claim 1. The second positive electrode active material is a positive electrode material containing a lithium composite transition metal oxide represented by the following Chemical Formula 3: [Chemical Formula 3] Li ａ’ Ni ｘ’ Co ｙ’ M ３ ｚ’ M ４ ｗ’ O ２ In the chemical formula (3), M ３ is one or more selected from Mn and Al, and M ４ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, where 0.9 ≤ a' ≤ 1.1, 0.8 ≤ x' < 1, 0 < y' < 0.2, 0 < z' < 0.2, and 0 ≤ w' < 0.

1.

13. The average particle size D of the secondary particles of the first positive electrode active material ５０ is 1 μm to 8 μm, The average particle diameter D of the secondary particles of the second positive electrode active material ５０ is more than 8 μm and 20 μm or less, and the positive electrode material according to claim 12.

14. In Chemical Formula 3, 0.85 ≦ x' < 1, 0 < y' ≦ 0.1, 0 < z' ≦ 0.1, 0 ≦ w' ≦ 0.

1. The positive electrode material according to claim 12.

15. A positive electrode comprising the positive electrode material according to claim 12.

16. A lithium secondary battery comprising the positive electrode according to claim 15, a negative electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

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