Positive electrode active material for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a positive electrode active material for a lithium secondary battery that has excellent capacity characteristics and lifespan at high temperatures, reduces resistance during electrochemical reactions, allows homogenized electrochemical reaction, and suppresses gas generation.SOLUTION: A positive electrode active material for a lithium secondary battery includes i) first secondary particles having a size of 13 μm to 20 μm and containing aggregates of primary particles having a size of 1 μm or less, ii) second secondary particles having a size of 7 μm to 13 μm and containing aggregates of primary particles having a size of 1 μm or less, and iii) single particles having a size of 1 μm to 7 μm and containing primary particles; and a nickel content of each of the particles satisfies the following formula 1: [Formula 1] The nickel content of single particles>nickel content of first secondary particles>nickel content of second secondary particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development for improving the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolytic solution, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted and desorbed at the positive electrode and the negative electrode.

[0004] As the positive electrode active material, a nickel-based active material having a high nickel content and excellent capacity characteristics may be used.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one embodiment, there is provided a positive electrode active material for a lithium secondary battery, which is excellent in capacity characteristics and life at high temperature, has a reduced resistance in an electrochemical reaction, has a uniform electrochemical reaction, and suppresses gas generation.

[0006] Another aspect provides a lithium secondary battery including the positive electrode active material for a lithium secondary battery.

Means for Solving the Problems

[0007] According to one embodiment, the positive electrode active material for a lithium secondary battery includes: i) a first secondary particle having a size of 13 μm to 20 μm and containing an aggregate of primary particles having a size of 1 μm or less; ii) a second secondary particle having a size of 7 μm to 13 μm and containing an aggregate of primary particles having a size of 1 μm or less; and iii) a single particle having a size of 1 μm to 7 μm and containing primary particles. The nickel content in each of the respective particles satisfies the following formula 1: [Formula 1] Nickel content in single particle > Nickel content in first secondary particle > Nickel content in second secondary particle

[0008] According to another embodiment, a lithium secondary battery includes a positive electrode containing the positive electrode active material for a lithium secondary battery described above, a negative electrode, and an electrolyte interposed therebetween. [Advantages of the Invention]

[0009] According to one embodiment, the positive electrode active material for a lithium secondary battery is excellent in capacity characteristics and life characteristics at high temperatures, the electrochemical reaction is made uniform, and gas generation can be suppressed. [Brief Description of the Drawings]

[0010]

Figure 1

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Figure 4

Figure 5

Figure 6

[0011] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example and does not limit the present invention, which is defined by the scope of the claims described below.

[0012] Unless otherwise specifically mentioned in this specification, when a part such as a layer, film, region, or plate is "on" another part, this includes not only the case where it is "directly on" the other part but also the case where there are other parts in between.

[0013] Unless otherwise specifically mentioned in this specification, the singular form can also include the plural. Also, unless otherwise specifically mentioned, "A or B" can mean "including A, including B, or including both A and B".

[0014] In this specification, "these combinations" can mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0015] Unless otherwise defined herein, the particle size may be the average particle size. Also, the particle size means the average particle size (D50) which means the diameter of the particle with a cumulative volume of 50% in the particle size distribution. The measurement of the average particle size (D50) can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope photograph or a scanning electron microscope photograph. As another method, it can be measured with a measuring device using the dynamic light-scattering method, data analysis is performed, the number of particles is counted for each particle size range, and then the average particle size (D50) value can be obtained by calculation. Alternatively, the average particle size (D50) can be measured using the laser diffraction method. When measuring by the laser diffraction method, more specifically, after dispersing the particles to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, MT 3000 of Microtrac), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle size (D50) at the 50% standard of the particle size distribution in the measuring device can be calculated.

[0016] As used herein, the "nickel content" may mean the molar ratio of nickel among the total transition metal content excluding lithium in the positive electrode active material.

[0017] As used herein, "X to Y" may mean "X or more and Y or less (X ≤ and ≤ Y)".

[0018] Positive electrode active material for lithium secondary battery The positive electrode active material for a lithium secondary battery according to one embodiment includes: i) a first secondary particle having a size of 13 μm to 20 μm and containing an aggregate of primary particles having a size of 1 μm or less; ii) a second secondary particle having a size of 7 μm to 13 μm and containing an aggregate of primary particles having a size of 1 μm or less; and iii) a single particle (one body particle) having a size of 1 μm to 7 μm and containing primary particles.

[0019] As used herein, the term "size" refers to the average diameter when the positive electrode active material particles for a lithium secondary battery are spherical. When the positive electrode active material particles for a lithium secondary battery are not spherical, "size" refers to the maximum value among the lengths of the major axes obtained from the cross-section of the particles.

[0020] The average diameter can be measured using a PSD (Particle size distribution) measuring instrument or through SEM or the like. Unless otherwise defined, the average diameter means the diameter (D50) of the particles with a cumulative volume of 50% in the particle size distribution. The length of the major axis can be measured through SEM or the like.

[0021] As used herein, "single particle" means a structure in which each particle exists as an independent phase that is not mutually aggregated morphologically. Examples of particle structures contrasted with single particles include structures in which small particles (primary particles) are physically and / or chemically aggregated to form a relatively large particle form (secondary particles). "Single particle" is not a form in which a large number of crystal particles are aggregated, but a form in which the particles are separated and / or dispersed from each other so as to form independent and / or distinct phases for each particle, and may include forms in which 10 or fewer particles are attached to each other. That is, single particles may exist alone or may be aggregated with each other. For example, single particles may be aggregated and in contact with each other with 2 to 10 single particles.

[0022] In the cathode active material for a lithium secondary battery according to an embodiment, the nickel content among the first secondary particles, the second secondary particles, and the single particles satisfies the relationship of the following formula (1). [Formula (1)] Nickel content in single particles > Nickel content in first secondary particles > Nickel content in second secondary particles

[0023] The second secondary particles can solve the problem that although the first secondary particles have a relatively high lithium diffusion rate, the life of the lithium secondary battery is reduced due to a high degradation rate. Since the second secondary particles have a lower nickel content than the first secondary particles, the problem of life reduction can be solved. The single particles have the highest nickel content compared to each of the first secondary particles and the second secondary particles. This can increase the lithium diffusion rate that may be insufficient by including the second secondary particles.

[0024] According to an embodiment, in the cathode active material for a lithium secondary battery, the nickel content among the transition metals excluding lithium is 94 mol% or more.

[0025] When the cathode active material for a lithium secondary battery contains the first secondary particles, the second secondary particles, and the single particles and satisfies the relationship of the nickel content in the formula (1), and the nickel content is 94 mol% or more, the improvement in capacity characteristics, the improvement in life characteristics at high temperature, and the effect of suppressing gas generation can be remarkable.

[0026] For example, in the cathode active material for a lithium secondary battery, the nickel content may be 94 mol% to 99 mol%, or 95 mol% to 98 mol%.

[0027] According to an embodiment, in the cathode active material for a lithium secondary battery, when the single particles are contained in an amount of 5 parts by weight to 25 parts by weight with respect to 100 parts by weight of the first secondary particles, the second secondary particles can significantly enhance the improvement effects of capacity characteristics and life characteristics. For example, the single particles may be contained in an amount of 10 parts by weight to 25 parts by weight, 10 parts by weight to 20 parts by weight, or 15 parts by weight to 20 parts by weight with respect to 100 parts by weight of the first secondary particles.

[0028] The first secondary particles are secondary particles formed by physical and / or chemical aggregation of primary particles having a size of 1 μm or less, and having a size of 13 μm to 20 μm. If the size of the first secondary particles is less than 13 μm, there may be a problem that the energy density decreases. On the other hand, if the size of the first secondary particles exceeds 20 μm, there may be a problem that the life of the battery deteriorates due to collisions between secondary particles and crack formation during rolling of the electrode plate. For example, the size of the first secondary particles may be 14 μm to 20 μm, 15 μm to 20 μm, or 16 μm to 20 μm.

[0029] In the first secondary particles, the average particle size of the primary particles may be 0.01 μm to 1 μm, 0.02 μm to 0.8 μm, 0.03 μm to 0.5 μm, 0.04 μm to 0.1 μm, or 0.05 μm to 0.07 μm (50 nm to 70 nm). According to one embodiment, the first secondary particles may be secondary particles having a polycrystalline structure. As used herein, "polycrystalline" means a form in which a large number of crystal particles are aggregated.

[0030] The single particles have a size of 1 μm to 7 μm and can contain primary particles. The average particle size of the primary particles may be 0.01 μm to 1 μm, 0.02 μm to 0.8 μm, 0.03 μm to 0.5 μm, 0.04 μm to 0.1 μm, or 0.05 μm to 0.07 μm (50 nm to 70 nm).

[0031] The second secondary particles are secondary particles having a size of 7 μm to 13 μm formed by physical and / or chemical aggregation of primary particles having a size of 1 μm or less. The size of the second secondary particles is smaller than that of the first secondary particles. If the size of the second secondary particles is less than 7 μm, there may be a problem that the mixture density of the positive electrode is not good. On the other hand, if the size of the second secondary particles exceeds 13 μm, there may be a problem that the mixture density of the positive electrode is not good. For example, the size of the second secondary particles may be 7 μm to 12 μm, or 8 μm to 12 μm.

[0032] In the second secondary particles, the average particle size of the primary particles is 0.01 μm to 1 μm, 0.02 μm to 0.8 μm, 0.03 μm to 0.5 μm, 0.04 μm to 0.1 μm, or 0.05 μm to 0.07 μm (50 nm to 70 nm). According to one embodiment, the second secondary particles may be secondary particles having a polycrystalline structure.

[0033] According to one embodiment, the cathode active material for a lithium secondary battery can satisfy the following Mathematical Formula 2. [Mathematical Formula 2] Size of the first secondary particles > Size of the second secondary particles > Size of single particles

[0034] According to one embodiment, the nickel content of the first secondary particles may be 85 mol% to 97 mol%. Within the above range, it may be easy to satisfy the Mathematical Formula 1. For example, the nickel content of the first secondary particles may be 90 mol% to 97 mol%, or 94 mol% to 97 mol%.

[0035] According to one embodiment, the nickel content of the second secondary particles may be 80 mol% to 90 mol%. Within the above range, it may be easy to satisfy the Mathematical Formula 1. For example, the nickel content of the second secondary particles may be 85 mol% to 90 mol%, or 85 mol% to 89 mol%.

[0036] According to one embodiment, the nickel content of single particles may be 90 mol% to 99 mol%. Within the above range, it may be easy to satisfy the Mathematical Formula 1. For example, the nickel content of single particles may be 95 mol% to 99 mol%, or 95 mol% to 97 mol%.

[0037] According to one embodiment, the molar ratio of the nickel content of the first secondary particles to the nickel content of the second secondary particles may be 1.01 to 1.06. Within the above range, there may be an effect of improving the optimal capacity and life of the battery.

[0038] According to one embodiment, the molar ratio of the nickel content of the first secondary particles to the nickel content of a single particle may be from 0.94 to 0.99. Within this range, there may be an effect of improving the optimal capacity and lifespan of the battery.

[0039] The average particle size of each of the first secondary particles, the second secondary particles, and the primary particles constituting the single particle can be confirmed using SEM. For example, the average particle size of the primary particles can be determined from the average value of the diameters of 10 to 30 primary particles.

[0040] The positive electrode containing a positive electrode active material for a lithium secondary battery containing the first secondary particles, the second secondary particles, and the single particle has stabilized electrochemical reactivity, reduced gas generation at high voltages, improved reliability and safety, and can produce a lithium secondary battery exhibiting high output and long lifespan characteristics.

[0041] The size of the positive electrode active material for a lithium secondary battery according to one embodiment, for example, the average particle size, may be from 10 μm to 20 μm.

[0042] According to one embodiment, the content of the first secondary particles among a total of 100 parts by weight of the positive electrode active material for a lithium secondary battery may be even higher compared to each of the second secondary particles and the single particle. The positive electrode active material for a lithium secondary battery may have a further capacity improvement effect by containing more first secondary particles compared to each of the second secondary particles and the single particle.

[0043] According to one embodiment, among a total of 100 parts by weight of the positive electrode active material for a lithium secondary battery, for example, the total of the first secondary particles, the second secondary particles, and the single particle, the first secondary particles may be contained in an amount of 60 to 80 parts by weight. Within this range, the improvement effect on the capacity characteristics and lifespan characteristics can be excellent. For example, the first secondary particles may be contained in an amount of 70 to 80 parts by weight, or 75 to 80 parts by weight.

[0044] According to one embodiment, among a total of 100 parts by weight of a positive electrode active material for a lithium secondary battery, for example, a total of a first secondary particle, a second secondary particle, and a single particle, the second secondary particle may be contained in an amount of 5 to 35 parts by weight. Within the above range, the improvement effects on capacity characteristics and life characteristics can be excellent. For example, the second secondary particle may be contained in an amount of 5 to 30 parts by weight, 5 to 20 parts by weight, or 5 to 15 parts by weight.

[0045] According to one embodiment, among a total of 100 parts by weight of a positive electrode active material for a lithium secondary battery, for example, a total of a first secondary particle, a second secondary particle, and a single particle, the single particle may be contained in an amount of 5 to 25 parts by weight. Within the above range, there can be an improvement effect on capacity characteristics and life characteristics. For example, the single particle may be contained in an amount of 10 to 25 parts by weight or 10 to 20 parts by weight.

[0046] According to one embodiment, the total of the first secondary particle, the second secondary particle, and the single particle in the positive electrode active material for a lithium secondary battery may be contained in an amount of 95% by weight or more, for example, 98% to 100% by weight or 100% by weight. Within the above range, it can be easier to realize the effect by adding the positive electrode active material for the lithium secondary battery.

[0047] According to one embodiment, the positive electrode active material for a lithium secondary battery can have various detailed shapes while basically having a plate-like structure, such as spherical, elliptical, polygonal nanoplate shapes such as hexagonal, nanodisk shapes, and rectangular parallelepiped shapes. When the positive electrode active material for a lithium secondary battery is not spherical, the size means the length of the major axis.

[0048] According to one embodiment, the first secondary particle, the second secondary particle, and the single particle in the positive electrode active material for a lithium secondary battery may each be a lithium nickel-based composite oxide.

[0049] For example, examples of the lithium nickel-based composite oxide include a compound represented by the following Chemical Formula 1 or a compound represented by the following Chemical Formula 2. [Chemical Formula 1] Lix Ni 1-y Co y O 2-z X z

[0050] In Chemical Formula 1, 0.9 ≦ x ≦ 1.2, 0 < y ≦ 0.2, 0 ≦ z ≦ 0.5, 0.8 ≦ 1 - y < 1, X is F, S, P, or a combination thereof.

[0051] [Chemical Formula 2] Li x Ni 1-y-z Co y M z O 2-a X a

[0052] In Chemical Formula 2, 0.9 ≦ x ≦ 1.2, 0 < y < 0.5, 0.8 ≦ 1 - y - z < 1, 0 ≦ z ≦ 0.5, 0 < y + z ≦ 0.2, 0 ≦ a < 2, M is Ni, Co, Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element, or a combination thereof, and X is F, S, P, or a combination thereof.

[0053] In Chemical Formulas 1 and 2, the nickel content is 80 mol% or more, 80 mol% to 95 mol%, for example, 85 mol% to 92 mol%, x is 1 to 1.05, and y is, for example, 0.01 to 0.2. And in the said Chemical Formula 2, M is Al, and z is, for example, 0.01 to 0.05.

[0054] According to one embodiment, the lithium nickel-based composite oxide may be a compound represented by the following Chemical Formula 3 or a compound represented by the following Chemical Formula 4. [Chemical Formula 3] Li x Co a Ni b Mn c O 2

[0055] In Chemical Formula 3, 0.9 < x ≤ 1.2, 0 < a < 0.5, 0.8 ≤ b < 1, 0 < c < 0.5, and a + b + c = 1.

[0056] [Chemical Formula 4] Li x Co a Ni b Al c O 2

[0057] In Chemical Formula 4, 0.9 < x ≤ 1.2, 0 < a < 0.5, 0.8 ≤ b < 1, 0 < c < 0.5, and a + b + c = 1.

[0058] In the above Chemical Formulas 3 and 4, x may be 1.0 to 1.2, 1.0 to 1.1, or 1.0 to 1.05; a may be, for example, 0.001 to 0.45, 0.01 to 0.4, 0.01 to 0.3, 0.01 to 0.2, 0.01 to 0.1, 0.02 to 0.08, or 0.04 to 0.09; b may be 0.8 to 0.99, for example, 0.8 to 0.98, for example, 0.85 to 0.95. c may be, for example, 0.001 to 0.3, 0.001 to 0.2, 0.001 to 0.1, 0.005 to 0.02, or 0.005 to 0.01.

[0059] According to one embodiment, when adjusting the size of the positive electrode active material for a lithium secondary battery and realizing a lithium secondary battery using the same, the high-temperature characteristics and rate-determining performance are improved, the gas generation amount at high voltage is reduced, and the reliability and safety can be ensured.

[0060] According to one embodiment, for the positive electrode active material for a lithium secondary battery, by adjusting the mixing weight ratio of lithium to transition metal in the manufacturing process of the positive electrode active material, controlling the heat treatment conditions (heat treatment temperature, atmosphere, and time), adjusting the sizes of the primary particles and secondary particles of the positive electrode active material, reducing the specific surface area, and removing residual lithium to the maximum extent, the surface side reaction between the residual lithium and the electrolyte is suppressed. And by controlling the manufacturing process as described above, a positive electrode active material with improved crystallinity and ensured stability at high voltage can be obtained.

[0061] According to one embodiment, the positive electrode active material for a lithium secondary battery may further include a cobalt coating layer. The cobalt coating layer can further improve the life characteristics while realizing a high capacity.

[0062] According to one embodiment, the surface of one or more of the first secondary particles, the second secondary particles, and the single particles may include a cobalt coating layer.

[0063] For example, the first secondary particles may include a cobalt coating layer on the surface of the secondary particles. The first secondary particles may include the secondary particles and / or the cobalt coating layer on the surface of the secondary particles.

[0064] For example, the second secondary particles may include a cobalt coating layer on the surface of the secondary particles. The second secondary particles may include the secondary particles and / or the cobalt coating layer on the surface of the secondary particles.

[0065] For example, the single particles may include the primary particles and the cobalt coating layer on the surface of the primary particles.

[0066] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery will be described in detail.

[0067] According to one embodiment, the positive electrode active material for a lithium secondary battery may be manufactured by producing the first secondary particles, the second secondary particles, and the single particles and mixing them.

[0068] For example, the first secondary particles, the second secondary particles, and the single particles may be manufactured by a method including producing a mixture by mixing a nickel-based active material precursor and a lithium precursor in a certain molar ratio and subjecting the mixture to a first heat treatment.

[0069] The nickel-based active material precursor is a nickel-based hydroxide and can be produced by coprecipitating a nickel precursor and a precursor of other transition metals. For example, the nickel-based active material precursor may be a hydroxide or an oxide containing nickel, cobalt, and other metals.

[0070] According to one embodiment, the nickel-based active material precursor can be produced by mixing a nickel precursor, a cobalt precursor, and an aluminum precursor in a first solvent and coprecipitating them. The nickel precursor, cobalt precursor, and aluminum precursor can be any substances that can be used in the art, and the contents of the nickel precursor, cobalt precursor, and aluminum precursor may be stoichiometrically controlled so that the compound of Chemical Formula 4 is obtained.

[0071] As the first solvent, water, ethanol, propanol, butanol, etc. can be used. The content of the first solvent may be 100 parts by weight to 2000 parts by weight based on 100 parts by weight of the total weight of the nickel precursor, cobalt precursor, and aluminum precursor.

[0072] The nickel-based active material precursor may be represented by, for example, the following Chemical Formula 5. [Chemical Formula 5] Ni 1-y-z Co y M z (OH) 2 (In Chemical Formula 5, 0 < y < 0.5, 0.8 ≤ 1 - y - z < 1, 0 ≤ z < 0.5, M is Ni, Co, Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element, or a combination thereof.)

[0073] The lithium precursor may be, for example, lithium hydroxide, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, or a mixture thereof. The mixing ratio of the lithium precursor and the nickel-based active material precursor may be stoichiometrically adjusted, for example, so as to be able to produce the positive electrode active material for a lithium secondary battery of Chemical Formula 2.

[0074] According to one embodiment, the mixing of the lithium precursor and the nickel-based active material precursor may be dry mixing, and can be carried out using a mixer or the like. Dry mixing can be carried out using milling. The milling conditions are not particularly limited, but can be carried out so that almost no deformation such as the refinement of the precursor used as the starting material occurs. The size of the lithium precursor to be mixed with the nickel-based active material precursor can be controlled in advance. The size (average particle diameter) of the lithium precursor is in the range of 5 μm to 15 μm, for example, about 10 μm. By milling a lithium precursor having such a size with a nickel-based active material precursor at 300 rpm to 3,000 rpm, the required mixture can be obtained. When the internal temperature of the mixer rises above 30°C during the milling process, a cooling process can be passed through so that the internal temperature of the mixer can be maintained in the normal temperature (25°C) range.

[0075] According to another embodiment, a second solvent may be used when mixing the nickel-based active material precursor and the lithium precursor. As the second solvent, the same as the first solvent described above, water, ethanol, butanol, propanol, etc. are used, and the content of the second solvent is 100 parts by weight to 2,000 parts by weight with respect to 100 parts by weight of the lithium precursor. An ignition agent and a pH adjuster can be added and mixed to the mixture containing the nickel-based active material precursor and the lithium precursor.

[0076] The first heat treatment may be carried out in air or an oxygen atmosphere. The first heat treatment is carried out, for example, at 600°C to 900°C, specifically 650°C to 900°C.

[0077] The manufacturing method of the nickel-based active material can add a secondary heat treatment step that is performed in an air or oxygen atmosphere after the primary heat treatment. The secondary heat treatment may be carried out, for example, at 700°C to 900°C.

[0078] According to one embodiment, in the production of the first secondary particles, the primary heat treatment may be carried out in an air or oxygen atmosphere. The primary heat treatment is carried out, for example, at 600°C to 800°C, specifically 650°C to 800°C.

[0079] According to one embodiment, in the production of the second secondary particles, the primary heat treatment may be carried out in an air or oxygen atmosphere. The primary heat treatment is carried out, for example, at 600°C to 800°C, specifically 650°C to 800°C.

[0080] According to one embodiment, in the production of single particles, the primary heat treatment may be carried out in an air or oxygen atmosphere. The primary heat treatment is carried out, for example, at 800°C to 900°C.

[0081] According to other embodiments, the positive electrode active material for a lithium secondary battery may be produced by mixing the first secondary particles, the second secondary particles, and single particles to produce a mixture, and then performing cobalt coating on the mixture.

[0082] The mixing of the first secondary particles, the second secondary particles, and single particles can be carried out by the method described above, so a detailed description thereof is omitted. Hereinafter, only the cobalt coating process will be described.

[0083] The cobalt coating may be carried out by dry coating or wet coating.

[0084] For example, a cobalt raw material can be introduced into a mixture of the first secondary particles, the second secondary particles, and single particles and heat-treated to perform dry cobalt coating.

[0085] For example, a solvent such as distilled water is added to a mixture of the first secondary particles, the second secondary particles, and single particles, and the mixture is washed while being mixed, and a wet coating of cobalt can be performed by adding a cobalt raw material.

[0086] The cobalt raw material may be, for example, cobalt hydroxide, cobalt carbonate, cobalt sulfate, cobalt oxide, cobalt nitrate, or the like.

[0087] The cobalt raw material can be added so that the content of cobalt with respect to the total elements excluding lithium and oxygen in each of the first secondary particles, the second secondary particles, and single particles is 0.01 mol part to 5 mol parts, and for example, it can be added so as to be 0.01 mol part to 3 mol parts, or 0.1 mol part to 2.5 mol parts. In this case, a cobalt coating layer with an appropriate content can be formed.

[0088] After adding the cobalt raw material, the process may further include removing the solvent by filtering this and then drying. At this time, the drying can be performed, for example, in a temperature range of 100°C to 300°C for 5 hours to 15 hours, and preferably, it may be performed at 200°C for 10 hours.

[0089] Thereafter, the product and the lithium raw material are mixed and then charged into a firing furnace, and firing may be performed in an oxygen atmosphere at 650°C to 900°C, or 650°C to 800°C, for 5 hours to 30 hours or 10 hours to 24 hours.

[0090] Lithium secondary battery A lithium secondary battery according to an embodiment includes a positive electrode including a positive electrode active material for a lithium secondary battery according to an embodiment; a negative electrode; and an electrolytic solution.

[0091] The positive electrode may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material.

[0092] As an example, the positive electrode may further contain an additive that can serve as a sacrificial positive electrode.

[0093] The content of the positive electrode active material may be 90% by weight to 99.5% by weight based on 100% by weight of the positive electrode active material layer, and the contents of the binder and the conductive material may each be 0.5% by weight to 5% by weight based on 100% by weight of the positive electrode active material layer.

[0094] The positive electrode active material layer contains a positive electrode active material for a lithium secondary battery according to an embodiment.

[0095] The positive electrode active material layer may further contain a positive electrode active material different from the positive electrode active material for a lithium secondary battery according to an embodiment.

[0096] As different positive electrode active materials according to an embodiment, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium can be used.

[0097] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0098] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b Xc O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G e O 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1); Li a NiG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO 4 (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); Li (3-f) Fe 2 (PO 4 ) 3 (0 ≤ f ≤ 2); Li a FePO 4 (0.90 ≤ a ≤ 1.8).

[0099] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al, or a combination thereof.

[0100] As an example, the positive electrode active material may be a high-nickel-based positive electrode active material in which the content of nickel with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. Since the high-nickel-based positive electrode active material can achieve a high capacity, it can be applied to high-capacity and high-density lithium secondary batteries.

[0101] The binder serves to well adhere the positive electrode active materials to each other and also to well adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, and the like.

[0102] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the battery being constructed and has electron conductivity. Examples of conductive materials include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0103] Al can be used as the current collector, but is not limited thereto.

[0104] The negative electrode includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0105] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0106] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping with lithium, or a transition metal oxide.

[0107] The material capable of reversibly intercalating / deintercalating lithium ions can include, as a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon can include graphite such as amorphous, plate-like, flake, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0108] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0109] As the substance capable of doping and undoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO 2 , a Sn-based alloy, or a combination thereof.

[0110] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0111] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0112] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by being mixed with a carbon-based negative electrode active material.

[0113] The binder serves to well adhere each negative electrode active material particle to each other and also to well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0114] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0115] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and a combination thereof.

[0116] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0117] The dry binder is a polymer substance capable of being fibrillated, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0118] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material that does not cause a chemical change and is an electron - conductive material can be used. Specific examples include carbon - based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal - based substances including copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0119] As the negative electrode current collector, those selected from copper foil, nickel foil, stainless - steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0120] The electrolytic solution contains a non - aqueous organic solvent and a lithium salt.

[0121] The non - aqueous organic solvent serves as a medium through which each ion involved in the electrochemical reaction of the battery can move.

[0122] The non - aqueous organic solvent may be a carbonate - based solvent, an ester - based solvent, an ether - based solvent, a ketone - based solvent, an alcohol - based solvent, an aprotic solvent, or a combination thereof.

[0123] As the carbonate solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used.

[0124] As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. may be used.

[0125] As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Also, as the ketone solvent, cyclohexanone, etc. may be used. As the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0126] The non-aqueous organic solvent can be used alone or in combination of two or more.

[0127] Also, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed at a volume ratio of 1:1 to 1:9.

[0128] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery, enables the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts are LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl, LiI, LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC 4 F 9 SO 3 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB), and can include one or more selected therefrom.

[0129] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator can be used.

[0130] The separator can include a porous substrate and a coating layer located on one or both surfaces of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0131] The porous substrate may be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more of these.

[0132] The organic substance can include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer. The inorganic substance is Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 MgO, NiO, CaO, GaO, ZnO, ZrO 2 Y 2 O 3 SrTiO 3 BaTiO 3 Mg(OH) 2 boehmite, and inorganic particles selected from combinations thereof, but are not limited thereto.

[0133] The organic substance and the inorganic substance can be present mixed in one coating layer, or can be present in a form in which a coating layer containing the organic substance and a coating layer containing the inorganic substance are laminated.

[0134] Lithium secondary batteries may be classified into cylindrical, rectangular, pouch, coin, etc. according to their form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. It can be said that FIG. 1 shows a cylindrical battery, FIG. 2 shows a rectangular battery, and FIGS. 3 and 4 show pouch-type battery forms. Referring to FIGS. 1 to 4, the lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolytic solution (not shown). The lithium secondary battery 100 may include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0135] The lithium secondary battery according to an embodiment of the present invention is applicable to automobiles, mobile phones, and / or various forms of electrical devices, etc., but the present invention is not limited thereto.

Examples

[0136] The present invention will be described in more detail through the following examples and comparative examples, but the present invention is not limited to the following examples.

[0137] Production Example 1-1: Production of the first secondary particles LiNi with an average particle size of 18 μm 0.94 Co 0.04 Al 0.02 O 2 Production Al which is an aluminum precursor 2 (SO 4 ) 3 (H 2 O) 18 with NaOH, NH 4It was mixed with OH and water to produce an aluminum precursor aqueous solution.

[0138] Separately from this, NiSO which is a nickel precursor 4 (H 2 O) 6 , and CoSO which is a cobalt precursor 4 (H 2 O) 7 were each mixed with water to obtain a nickel precursor aqueous solution and a cobalt precursor aqueous solution.

[0139] The aluminum precursor aqueous solution was put into a reactor, and the nickel precursor aqueous solution and the cobalt precursor aqueous solution were dropped into the reactor to obtain a reaction mixture, and stirring of the reaction mixture was carried out for 10 to 20 hours. In the reaction mixture, the contents of the nickel precursor, the cobalt precursor, and the aluminum precursor were stoichiometrically controlled so that the mixing ratio of nickel, cobalt, and aluminum was 94:4:2 in molar ratio.

[0140] An aqueous sodium hydroxide solution was dropped into the reaction mixture to adjust the pH of the reaction mixture to 10 - 12. The obtained precipitate was filtered, washed with water, and the resulting product was vacuum dried at 100 °C to produce Ni 0.94 Co 0.04 Al 0.02 (OH) 2 powder which is nickel cobalt aluminum hydroxide by the coprecipitation method.

[0141] After mixing the nickel cobalt aluminum hydroxide and lithium hydroxide (LiOH) which is a lithium precursor in a mortar, it was put into a furnace, and a nickel-based active material was produced by heat-treating at 730 °C for 20 hours while flowing O 2 . The contents of the nickel cobalt aluminum hydroxide and the lithium precursor were controlled so that the mixing ratio of the transition metal and lithium was 1:1.03.

[0142] The nickel-based active material produced by the manufacturing method is a secondary particle composed of two or more primary particles with an average particle size of 1 μm or less, and the average particle size is 18 μm, and it is NCA (LiNi 0.94 Co 0.04 Al 0.02 O 2 ).

[0143] Production Example 1-2: Production of the first secondary particles The content of the nickel precursor, cobalt precursor, and aluminum precursor in Production Example 1-1 was changed, and the heat treatment temperature and heat treatment time were changed to produce the first secondary particles.

[0144] Production Example 1-3: Production of the first secondary particles The content of the nickel precursor, cobalt precursor, and aluminum precursor in Production Example 1-1 was changed, and the heat treatment temperature and heat treatment time were changed to produce the first secondary particles.

[0145] Production Example 2: Production of the second secondary particles LiNi with an average particle size of 10.4 μm 0.89 Co 0.09 Al 0.02 O 2 Production The aluminum precursor Al 2 (SO 4 ) 3 (H 2 O) 18 was mixed with NaOH, NH 4 OH and water to produce an aluminum precursor aqueous solution.

[0146] The nickel precursor NiSO 4 (H 2 O) 6 , and the cobalt precursor CoSO 4 (H 2 O) 7 were each mixed with water to obtain a nickel precursor aqueous solution and a cobalt precursor aqueous solution.

[0147] The aluminum precursor aqueous solution was placed in a reactor, and the nickel precursor aqueous solution and the cobalt precursor aqueous solution were dropped into the reactor to obtain a reaction mixture, and stirring of the reaction mixture was carried out for 10 to 20 hours. In the reaction mixture, the contents of the nickel precursor, the cobalt precursor, and the aluminum precursor were stoichiometrically controlled so that the mixing ratio of nickel, cobalt, and aluminum was 89:9:2 in molar ratio.

[0148] An aqueous sodium hydroxide solution was dropped into the reaction mixture to adjust the pH of the reaction mixture to 10 - 12. The obtained precipitate was filtered, washed with water, and the resultant was vacuum dried at 100 °C to produce Ni 0.89 Co 0.09 Al 0.02 (OH) 2 powder.

[0149] The nickel cobalt aluminum hydroxide and lithium hydroxide (LiOH) which is a lithium precursor were mixed in a mortar, then put into a furnace, and heat treated at 730 °C for 20 hours while flowing O 2 to produce a nickel-based active material. The contents of the nickel cobalt aluminum hydroxide and the lithium precursor were controlled so that the mixing ratio of the transition metal and lithium was 1:1.03.

[0150] The nickel-based active material produced by the manufacturing method is secondary particles composed of two or more primary particles with an average particle size of 1 μm or less, the average particle size is 10.4 μm, and it is NCA (LiNi 0.89 Co 0.09 Al 0.02 O 2 ).

[0151] Production Example 3-1: Production of single particles LiNi with an average particle size of 4.1 μm 0.97 Co 0.02 Al 0.01 O 2 (NCA)Production Al which is an aluminum precursor 2(SO 4 ) 3 (H 2 O) 18 was mixed with NaOH, NH 4 OH and water to produce an aluminum precursor aqueous solution.

[0152] Separately from this, NiSO 4 (H 2 O) 6 , which is a nickel precursor, and CoSO 4 (H 2 O) 7 , which is a cobalt precursor, were each mixed with water to obtain a nickel precursor aqueous solution and a cobalt precursor aqueous solution.

[0153] The aluminum precursor aqueous solution was put into a reactor, and the nickel precursor aqueous solution and the cobalt precursor aqueous solution were dropped into the reactor to obtain a reaction mixture, and stirring of the reaction mixture was carried out for 10 to 20 hours. In the reaction mixture, the contents of the nickel precursor, the cobalt precursor, and the aluminum precursor were stoichiometrically controlled so that the mixing ratio of nickel, cobalt, and aluminum was 97:2:1 in molar ratio.

[0154] An aqueous sodium hydroxide solution was dropped into the reaction mixture to adjust the pH of the reaction mixture to 10 - 12. The obtained precipitate was filtered, washed with water, and the resulting product was vacuum dried at 100 °C to produce Ni 0.97 Co 0.02 Al 0.01 O 2 (OH) 2 powder, which is nickel cobalt aluminum hydroxide.

[0155] The nickel cobalt aluminum hydroxide and lithium hydroxide (LiOH), which is a lithium precursor, were mixed in a mortar, then put into a furnace, and heat treated at 900 °C for 20 hours while flowing O 2 to produce a nickel-based active material. The contents of the nickel cobalt aluminum hydroxide and the lithium precursor were controlled so that the mixing ratio of the transition metal and lithium was 1:1.05.

[0156] The nickel-based active material produced by the manufacturing method is single particles with an average particle size of 4.1 μm and is NCA (LiNi 0.97 Co 0.01 Al 0.02 O 2 ).

[0157] Production Examples 3-2 to 3-4: Production of single particles Single particles were produced by changing the contents of the nickel precursor, cobalt precursor, and aluminum precursor in Production Example 3-1 and changing the heat treatment temperature and heat treatment time.

[0158] The specific specifications of the particles obtained in the production examples are as follows.

[0159]

Table 1

[0160] (Production of Cathode Active Material for Lithium Secondary Battery and Lithium Secondary Battery)

[0161] Example 1 The first secondary particles obtained by Production Example 1-1, the second secondary particles obtained by Production Example 2, and the single particles obtained by Production Example 3-1 were mixed in the contents (unit: parts by weight) shown in Table 2 below to produce a lithium nickel-based composite oxide.

[0162] Thereafter, a first step is performed in which a distilled water solvent and cobalt sulfate are charged into a mixer, and the produced lithium nickel-based composite oxide is charged and mixed. The cobalt sulfate is charged so that the content of cobalt with respect to the total elements excluding lithium and oxygen in the lithium nickel-based composite oxide is 2.5 mol parts. In the first step, after charging the lithium nickel-based composite oxide, sodium hydroxide serving as a precipitating agent and a pH adjuster is charged together and washed for 70 minutes.

[0163] The cobalt raw material may be, for example, cobalt hydroxide, cobalt carbonate, cobalt sulfate, cobalt oxide, cobalt nitrate, or the like.

[0164] Thereafter, the product and the lithium raw material are mixed and then charged into a firing furnace, and heat treatment is performed at about 710 °C for 15 hours in an oxygen atmosphere. At this time, the lithium raw material is charged so that the lithium content becomes 5 mole parts with respect to the total elements excluding lithium and oxygen in the product. Thereafter, the firing furnace is cooled to room temperature to obtain a final positive electrode active material in which a cobalt coating portion is formed on the surface of the lithium nickel-based composite oxide.

[0165] The obtained nickel-based active material was used and prepared as a positive electrode active material. In Table 2 below, "-" means that the content of the component is 0 parts by weight.

[0166] The positive electrode active material, a carbon conductive material (Super P), and a PVDF (polyvinylidene fluoride) binder solution were added and mixed to produce a positive electrode active material slurry. The mixing weight ratio of the active material: conductive material: binder in the active material slurry is 98:1:1. The slurry was coated on an aluminum current collector having a thickness of 12 μm using a thick film coater so that the loading level was 36 mg / cm 2 and dried at 120 °C for 1 hour or more, and then rolled to produce a positive electrode.

[0167] Graphite powder (japan carbon) as a negative electrode active material and a mixture of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) mixed at a weight ratio of 1:1 were mixed at a weight ratio of 98:2 to prepare a negative electrode active material slurry.

[0168] The prepared negative electrode active material slurry was applied to a copper foil current collector having a thickness of 8 μm at 19.5 mg / cm 2Coated at the level of. After drying the coated electrode plate at 100 °C for 1 hour or more, it was rolled, and the mixture density was 1.66 g / cm 3 A negative electrode with the following was manufactured.

[0169] Using the above positive and negative electrodes, a polyethylene separator (separator, STAR 20, Asahi) was used as the separator, and as the electrolyte, EC (ethylene carbonate): EMC (ethyl methyl carbonate): DMC (dimethyl carbonate) (volume ratio of 3:4:4) mixed solvent with 1.15 M of LiPF 6 dissolved therein was used to manufacture a lithium secondary battery having a capacity of 2000 mAh.

[0170] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the type and content of the particles were changed as shown in Table 2 below during the production of the nickel-based active material.

[0171] Comparative Examples 1 to 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the type and content of the particles were changed as shown in Table 2 below during the production of the nickel-based active material.

[0172]

Table 2

[0173] Evaluation Example 1: Size analysis of primary particles, secondary particles and single particles through scanning electron microscope (SEM) analysis The SEM image of the positive electrode active material for the lithium secondary battery obtained in Example 1 was measured. As the SEM measuring instrument, the model (Sirion) of (FEI, USA) was used.

[0174] The SEM analysis results are shown in Figure 5.

[0175] Referring to FIG. 5, it was found that the positive electrode active material for the lithium secondary battery of Example 1 contains all of the first secondary particles A, the second secondary particles B, and the single particles C.

[0176] Evaluation Example 2: Charge capacity, discharge capacity and efficiency For the lithium secondary batteries manufactured by the examples and comparative examples, charging was performed at a constant current of 25 ° C and 0.2C from 2.8V to the upper limit voltage of 4.3V, and after charging was performed until it dropped to 0.05C, the end condition, under constant voltage conditions, discharging was performed at 0.2C until the discharge cut-off voltage of 3.0V, and the initial discharge capacity was measured.

[0177] The efficiency was calculated as the ratio of (one discharge capacity) to (one charge capacity).

[0178] Evaluation Example 3: High temperature life characteristics For the lithium secondary batteries manufactured in the above examples and comparative examples, charging was performed at a constant current of 45 ° C and 0.2C until the voltage reached 4.3V, and charging was performed at a constant voltage until the current reached 0.05C while maintaining 4.3V. Subsequently, during discharging, discharging was performed at a constant current of 0.2C until the voltage reached 3.0V (formation stage).

[0179] Subsequently, charging was performed at a constant current of 0.7C until the voltage reached 4.35V, and charging was performed at a constant voltage until the current reached 0.05C while maintaining 4.35V. Subsequently, during discharging, discharging was performed at a constant current of 0.5C until the voltage reached 3.0V (standard stage).

[0180] In the lithium secondary battery that has undergone the above formation and standard stages, charging was performed at a constant current of 25 ° C and 45 ° C and 0.5C until the voltage reached 4.35V, and charging was performed at a constant voltage until the current reached 0.05C while maintaining 4.35V. Subsequently, during discharging, a cycle of discharging at a constant current of 0.5C until the voltage reached 3.0V was repeated 50 times. The high-temperature life was evaluated by the discharge capacity retention, and the discharge capacity retention was calculated as the ratio of (one-cycle discharge capacity) to (50-cycle discharge capacity). The high-temperature life characteristics obtained from the above charge-discharge experiment results are shown in FIG. 6 and Table 3 below.

[0181]

Table 3

[0182] In Table 3 above, *: the ratio of the nickel content among the total transition metal content excluding lithium in the nickel-based active material

[0183] As shown in Table 3 above, it can be confirmed that the lithium secondary battery of the example not only has high efficiency but also has improved high-temperature life characteristics. This can also be confirmed in FIG. 5. Referring to FIG. 6, it can be seen that in the 50th cycle, the lithium secondary battery of the example has improved high-temperature life characteristics compared to the lithium secondary battery of the comparative example.

[0184] Although the above has been described with reference to preferred manufacturing examples, those skilled in the art will understand that various modifications and changes can be made without departing from the spirit and scope described in the following claims.

Description of Reference Numerals

[0185] 100 Lithium secondary battery 10 Positive electrode 11 Positive electrode lead tab 12 Positive electrode terminal 20 Negative electrode 21 Negative electrode lead tab 22 Negative electrode terminal 30 Separator 40 Electrode assembly 50 Case 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. i) first secondary particles having a size between 13 μm and 20 μm containing agglomerates of primary particles having a size of 1 μm or less; ii) second secondary particles of size between 7 μm and 13 μm containing agglomerates of primary particles having a size of 1 μm or less; and iii) single particles having a size between 1 μm and 7 μm and including primary particles; The nickel content of each particle satisfies the following formula 1: [Formula 1] The nickel content of the single particle>the nickel content of the first secondary particle>the nickel content of the second secondary particle.

2. The positive electrode active material for a lithium secondary battery according to claim 1, which satisfies the following formula 2: [Formula 2] Size of first secondary particle>size of second secondary particle>size of single particle.

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material for a lithium secondary battery has a nickel content of 94 mol % or more among transition metals excluding lithium.

4. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the single particles are contained in an amount of 5 to 25 parts by weight based on 100 parts by weight of the first secondary particles.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein a total of the first secondary particles, the second secondary particles, and the single particles is contained in the positive electrode active material for a lithium secondary battery in an amount of 95% by weight or more.

6. The nickel content of the first secondary particles is 85 mol% to 97 mol%, The nickel content of the second secondary particles is 80 mol% to 90 mol%, 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel content of each of the single particles is 90 mol% to 99 mol%.

7. Of the total of 100 parts by weight of the positive electrode active material for lithium secondary batteries, The first secondary particles are 60 parts by weight to 80 parts by weight, The second secondary particles are 5 parts by weight to 35 parts by weight, The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the single particle is contained in an amount of 5 to 25 parts by weight.

8. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein a molar ratio of a nickel content of the first secondary particles to a nickel content of the second secondary particles is from 1.01 to 1.

06.

9. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein a molar ratio of the nickel content of the first secondary particles to the nickel content of the single particles is 0.94 to 0.

99.

10. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the positive electrode active material for a lithium secondary battery is a compound represented by the following Chemical Formula 1 or a compound represented by the following Chemical Formula 2: [Chemical formula 1] Li x Ni 1-y Co y O 2-z X z (In Chemical Formula 1, 0.9≦x≦1.2, 0<y≦0.2, 0≦z≦0.5, 0.8≦1−y<1, X is F, S, P or a combination thereof. [Chemical formula 2] Li x Ni 1-y-z Co y M z O 2-a X a (In Chemical Formula 2, 0.9≦x≦1.2, 0<y<0.5, 0.8≦1−y−z<1, 0≦z≦0.5, 0<y+z≦0.2, 0≦a<2, M is Ni, Co, Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element, or a combination thereof, and X is F, S, P, or a combination thereof.

11. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the positive electrode active material for a lithium secondary battery is a compound represented by the following Chemical Formula 3 or a compound represented by the following Chemical Formula 4: [Chemical formula 3] Li x Co a Ni b Mn c O 2 (In chemical formula 3, 0.9<x≦1.2, 0<a<0.5, 0.8≦b<1, 0<c<0.5, and a+b+c=1.) [Chemical formula 4] Li x Co a Ni b Al c O 2 (In chemical formula 4, 0.9<x≦1.2, 0<a<0.5, 0.8≦b<1, 0<c<0.5, and a+b+c=1.)

12. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein a surface of at least one of the first secondary particles, the second secondary particles, and the single particle includes a cobalt coating layer.

13. A lithium secondary battery comprising a positive electrode containing the positive electrode active material for lithium secondary batteries according to claim 1, a negative electrode, and an electrolyte.

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