Cathode active material for lithium secondary battery, and lithium secondary battery comprising same

Abstract

A cathode active material for a lithium secondary battery according to the present invention is a cathode active material for a single-crystal active material for a lithium secondary battery, wherein the cathode active material comprises an aggregate of 1 to 20 single particles, and the single particles may satisfy equation 1 in the present specification.

Description

Cathode active material for lithium secondary batteries and lithium secondary batteries containing the same

[0001] These examples relate to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

[0002] Recently, demand for IT mobile devices, small electric powertrains (e-bikes, small EVs, etc.), and energy storage systems (ESS) has been explosively increasing. Accordingly, the development of high-capacity, high-energy-density secondary batteries to power these devices is actively underway worldwide. Manufacturing these high-capacity batteries requires the use of high-capacity cathode materials.

[0003] Among the existing layered cathode active materials, the material with the highest capacity is LiNiO2, but its structural collapse occurs easily during charge and discharge, and its thermal stability is low due to oxidation number issues, making commercialization difficult.

[0004] To solve these problems, the unstable Ni site must be replaced with another stable transition metal (Co, Mn, etc.), and for this purpose, a ternary NCM system with Co and Mn substituted was developed.

[0005] Conventional NCM-based cathode active materials are composed of secondary particles formed by agglomeration of primary particles. However, cathode materials composed of secondary particles formed by agglomeration of primary particles ranging in size from tens of nanometers to several micrometers have a large specific surface area, resulting in a high potential for gas generation. Furthermore, the secondary particles are weak in strength, which can lead to the secondary particles breaking back into their primary form during the electrode rolling process, resulting in deteriorated cycle life.

[0006] To address this issue, a method has been proposed: instead of forming secondary particles with agglomerates of primary particles, a method of manufacturing the cathode material by maximizing the size of the primary particles and then applying the resulting agglomerates. However, this method suffers from the problem of creating a rocksalt structure on the particle surface, which degrades the electrochemical performance of the cathode active material.

[0007] Therefore, there is a need to develop a cathode active material that can exhibit excellent electrochemical properties such as charge / discharge capacity while increasing the life stability of the battery by deriving an appropriate size of the primary particles.

[0008] In this embodiment, in a single crystal cathode active material, the first to third diameters of a single particle are derived through SEM (Scanning Electron Microscopy) image analysis, and the single particle satisfies a specific range of a relationship composed of the first to third diameters, thereby providing a cathode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same, in which electrochemical characteristics and stability can be improved.

[0009] This application claims priority to Republic of Korea Patent Application No. 10-2024-0043321, filed March 29, 2024, the entire contents of which are incorporated herein by reference.

[0010] According to one embodiment, a cathode active material for a lithium secondary battery may be a cathode active material for a single-crystal lithium secondary battery, wherein the cathode active material includes a form in which 1 to 20 single particles are aggregated, and the single particles satisfy the following formula 1.

[0011] [Formula 1]

[0012] 1.40 ㎛ ≤ (D2*D3) / D1 ≤ 1.80 ㎛

[0013] In the above equation 1,

[0014] D1 means the first diameter of a single particle (D1=2*R1) derived by assuming the circumference of a single particle measured from the SEM (Scanning Electron Microscopy) image of the positive electrode active material to be the circumference of an ideal circle (2πR1).

[0015] D2 is the area of ​​a single particle measured from the SEM image of the positive electrode active material, which is the area of ​​an ideal circle (πR2 2 ) refers to the second diameter of a single particle (D2=2*R2) derived after assuming that

[0016] D3 refers to the third diameter of a single particle (D3=2*R3) derived from the diameter of the circumscribed circle of a single particle measured from the SEM image of the positive electrode active material.

[0017] According to another embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery may be a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; mixing the transition metal precursor and a lithium raw material and then calcining them to form a lithium transition metal oxide; and crushing the lithium transition metal oxide to form a positive electrode active material for a single-crystal lithium secondary battery, wherein the crushing is performed at a crushing pressure of 3.4 to 4.5 bar, and the calcination is performed in an air atmosphere.

[0018] A lithium secondary battery according to another embodiment may be a lithium secondary battery including a positive electrode for a lithium secondary battery including the positive electrode active material according to one embodiment.

[0019] According to the present embodiment, the stability and electrochemical properties of a positive electrode active material for a lithium secondary battery can be improved by appropriately controlling the manufacturing process to satisfy a specific range of a relationship consisting of the first to third diameters of single particles.

[0020] Accordingly, the lithium secondary battery manufactured as in this example can have improved electrochemical performance, such as stability and capacity.

[0021] Figure 1 is an SEM image measured for the positive electrode active material manufactured in Example 1.

[0022] Figure 2 is an SEM image measured for the positive electrode active material manufactured in Example 2.

[0023] Figure 3 is an SEM image measured for the positive electrode active material manufactured in Example 3.

[0024] Figure 4 is an SEM image measured for the positive electrode active material manufactured in Example 4.

[0025] Figure 5 is an SEM image measured for the positive electrode active material manufactured in Comparative Example 3.

[0026] Figure 6 is an SEM image measured for the positive electrode active material manufactured in Comparative Example 4.

[0027] Figure 7 is an image obtained by performing AI program-based image analysis on a SEM image measured for a positive electrode active material manufactured in Example 1.

[0028] Figure 8 is an image obtained by performing AI program-based image analysis on a SEM image measured for a positive electrode active material manufactured in Example 2.

[0029] Figure 9 is an image obtained by performing AI program-based image analysis on an SEM image measured for a positive electrode active material manufactured in Example 3.

[0030] Figure 10 is an image obtained by performing AI program-based image analysis on an SEM image measured for a positive electrode active material manufactured in Example 4.

[0031] Figure 11 is an image obtained by performing AI program-based image analysis on a SEM image measured for a positive electrode active material manufactured in Comparative Example 3.

[0032] Figure 12 is an image obtained by performing AI program-based image analysis on a SEM image measured for a positive electrode active material manufactured in Comparative Example 4.

[0033] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0035] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0036] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0037] Also, unless otherwise stated, % means mol%.

[0038] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0039] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0040]

[0041] Cathode active material for lithium secondary batteries

[0042] As described above, the existing cathode active material for lithium secondary batteries has problems such as reduced energy density and energy and capacity, particle breakage during rolling, increased surface area leading to increased exposure of electrolyte, increased gas generation within the battery, and deterioration of electrochemical characteristics.

[0043] However, in the present embodiment, the first to third diameters of single particles were derived through SEM (Scanning Electron Microscopy) image analysis of the single crystal positive electrode active material, and the primary particles of the single crystal positive electrode active material were satisfied with a specific range of the relationship composed of the first to third diameters, thereby solving this problem.

[0044] Specifically, the cathode active material for a lithium secondary battery according to one embodiment is a cathode active material for a single-crystal lithium secondary battery, and the cathode active material may include a form in which 1 to 20 single particles are aggregated.

[0045] In this specification, a single particle may mean a single particle composed of one particle, and the single crystal positive electrode active material may be a single particle composed of one particle, or may be in the form of 1 to 20 or 2 to 20 single particles aggregated together, and more preferably, may include both the single particle and the form of aggregated single particles.

[0046] At this time, the single particle may be a positive electrode active material for a lithium secondary battery that satisfies the following equation 1.

[0047] [Formula 1]

[0048] 1.40 ㎛ ≤ (D2*D3) / D1 ≤ 1.80 ㎛

[0049] In the above equation 1,

[0050] D1 means the first diameter of a single particle (D1=2*R1) derived by assuming the circumference of a single particle measured from the SEM (Scanning Electron Microscopy) image of the positive electrode active material to be the circumference of an ideal circle (2πR1).

[0051] D2 is the area of ​​a single particle measured from the SEM image of the positive electrode active material, which is the area of ​​an ideal circle (πR2 2 ) refers to the second diameter of a single particle (D2=2*R2) derived after assuming that

[0052] D3 refers to the third diameter of a single particle (D3=2*R3) derived from the diameter of the circumscribed circle of a single particle measured from the SEM image of the positive electrode active material.

[0053]

[0054] The above first diameter (D1) to third diameter (D3) may be derived by measuring the circumference, area, and circumscribed circle of each single particle appearing in the SEM image using an AI (Artificial Intelligence) program-based image analysis of the SEM image.

[0055] Here, the circumscribed circle refers to an ideal circle that includes two or more points located at the outermost sides of a single particle. This means that the entire area of ​​the single particle is contained within the circumscribed circle.

[0056] Specifically, AI-based image analysis can detect particles in SEM images, and then calculate the area and perimeter of each particle using a simple Python function. Since the units are pixels, a scale bar can be used to convert these values ​​to International System of Units (SI) units, such as μm.

[0057] When deriving the first diameter (D1) to the third diameter (D3), in addition to the above derivation process, the accuracy in measuring the size of a single particle can be further increased through an additional task of taking and analyzing SEM images several times, specifically 3 to 100 times, or 10 to 30 times, and checking whether the SEM images correspond to images identified in the AI ​​program-based image analysis.

[0058] The degree of single particle growth can be accurately measured through the measured first diameter (D1) to third diameter (D3), and risk factors that may occur during battery evaluation can be accurately identified, enabling the use of a cathode active material exhibiting excellent electrochemical properties.

[0059] On the other hand, analysis using a particle size analyzer may not correspond to the analysis using SEM images in the present disclosure. Specifically, analysis using a particle size analyzer may not accurately measure the degree of single particle growth. Specifically, while the present invention was able to identify the size of individual particles even in active material particles that were confirmed to be overlapping or formed aggregates of single particles, existing analysis methods may struggle with this analysis. Consequently, existing analysis methods may not be able to adequately identify potential risk factors during battery evaluation.

[0060]

[0061] Meanwhile, in the above formula 1, (D2*D3 / D1) may be in the range of 1.45 to 1.75 μm, or 1.55 to 1.75 μm. By satisfying the range of the above formula 1, stability and high-capacity electrochemical characteristics can be satisfied at the same time.

[0062] Specifically, 67.8 kN / cm 2 After pressurization, the ratio of fine particle size distribution of 1.0 μm or less in the volume-based particle size distribution curve of the positive active material may be 5.0% or less, and more specifically, the ratio of fine particles may be 0.5% to 4.5%, 1.0% to 4.0%, 2.0% to 4.0%, or 2.1% to 3.6%. Accordingly, the generation of fine particles due to particle breakage can be reduced, and as a result, the generation of gas due to fine particles can be prevented, thereby maximizing the safety of the battery.

[0063] Additionally, for a battery including a positive electrode active material satisfying the range of the above formula 1, the discharge capacity may be 196.0 mAh / g or more. More specifically, the discharge capacity may be 196.0 to 200.0 mAh / g or 196.1 to 198.0 mAh / g.

[0064] If the range of the above equation 1 is exceeded, excessive single crystal growth of the positive electrode active material occurs, resulting in significant shrinkage of the structure, which inhibits the diffusion and desorption of lithium ions within the positive electrode active material. This may tend to result in a decrease in the capacity and rate characteristics of the electrode.

[0065] In addition, if the pressure is lower than the range of the above equation 1, a large amount of fine particles may be generated due to particle breakage when pressure is applied. Specifically, 67.8 kN / cm 2 When pressure is applied, the fine particle ratio with a particle size of 1 μm or less may be 5.0% or more.

[0066] While satisfying the range of the above equation 1, the following ranges can be satisfied independently or simultaneously.

[0067]

[0068] The above D1 may be in the range of 1.90 to 2.20 μm, specifically, in the range of 1.92 to 2.20 μm, or 1.94 to 2.19 μm. D1 may have a tendency to decrease as the shape of the single particle approaches a circle, and when the above appropriate range is satisfied, the positive electrode active material may exhibit the aforementioned stability and excellent electrochemical properties.

[0069] The above D2 may be in the range of 1.40 to 1.75 μm, specifically, in the range of 1.45 to 1.71 μm, or 1.50 to 1.67 μm. D2 may have a tendency to increase as the shape of the single particle approaches a circle, and when the above appropriate range is satisfied, the positive electrode active material may exhibit the aforementioned stability and excellent electrochemical properties.

[0070] The above D3 may be in the range of 1.90 to 2.35 μm, specifically, in the range of 1.93 to 2.31 μm, or 1.96 to 2.27 μm. D3 may have a tendency to decrease as the shape of the single particle approaches a circle, and when the above appropriate range is satisfied, the positive electrode active material may exhibit the aforementioned stability and excellent electrochemical properties.

[0071] In addition, the positive electrode active material for the lithium secondary battery may have an average particle diameter (D50) of 2.0 to 5.5 μm, 2.5 to 5.0 μm, or 3.0 to 4.5 μm when measuring the volume-based particle size distribution of the positive electrode active material. When the average particle diameter of the positive electrode active material satisfies the above range, the rolling density can be improved, thereby improving the electrode energy density and simultaneously exhibiting excellent stability characteristics. In the present specification, the average particle diameter (D50) can be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve of the particles. The average particle diameter (D50) can be measured using, for example, a general laser diffraction method.

[0072]

[0073] In addition, the cathode active material for the lithium secondary battery may contain 50 to 70 mol% nickel (Ni) based on the total mole number of transition metals. If the nickel content is too high, there may be thermal propagation issues and the cost may increase. However, if the nickel content is too low, the capacity may be too low. Therefore, the cathode active material according to the present invention can produce an appropriate capacity while having excellent thermal safety and reducing manufacturing costs by having a nickel content of 50 to 70 mol%.

[0074] More specifically, it can be represented by the following chemical formula 1.

[0075] [Chemical Formula 1]

[0076] Li a [Ni x Co y Mn z M w ]O2

[0077] In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0.05≤y≤0.2, 0≤z≤0.4, 0≤w<0.03, x+y+z+w=1, and M is Zr, Y, B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0078] In the positive electrode active material of the above chemical formula 1, lithium may be included in an amount corresponding to a, that is, 0.8≤a≤1.2. If a is too small, the capacity may be reduced, and if a is too large, the strength of the sintered positive electrode active material may be increased, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the control of the lithium content and the sinterability balance during the production of the active material, the lithium may be included in an amount of 0.9≤a≤1.1 more preferably.

[0079] In the positive electrode active material of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 0.5≤x≤0.7. As described above, if the nickel content is too low, it may be difficult to achieve high capacity of the battery, and if the nickel content is too high, the battery life and thermal safety may be reduced due to a decrease in the structural stability of the active material, and the manufacturing cost may increase.

[0080] In the positive electrode active material of the above chemical formula 1, cobalt may be included in a content corresponding to y of 0.05≤y≤0.2. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt content is too high, the overall cost of the raw material may increase and the reversible capacity may decrease.

[0081] In the positive electrode active material of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0≤z≤0.4 or 0.1≤z≤0.4. If the manganese content is too low, the production cost may increase and the stability of the positive electrode active material may deteriorate. If the manganese content is too high, the capacity and output characteristics of the battery may deteriorate.

[0082] In the positive electrode active material of the above chemical formula 1, the positive electrode active material may specifically include Zr and Y, and the total content of Zr and Y may be 3000 to 5800 ppm based on the weight of the positive electrode active material, and more specifically, 4000 to 5200 ppm or 4200 to 5000 ppm. Below the above range, particle size growth may be minimal, and above the above range, excessive elements may be distributed at the precursor interface during the sintering process, which may rather inhibit particle size growth. Therefore, when the total content of Zr and Y satisfies the above range, the size of single particles in the positive electrode active material may be formed within an appropriate range.

[0083]

[0084] In addition, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include a coating layer on the surface of the positive electrode active material. Specifically, the coating layer may include Al, W, Co, V, Ti, Nb, Ce, B, P, or a combination thereof.

[0085] More specifically, the coating layer may include Al and W, and the content ratio of W to the Al content (W / Al) may be in a range of more than 0 and less than 4.0, more specifically, more than 0.5 and less than 3.0.

[0086] When the above content ratio is satisfied, there is an advantage in that the effects of improved discharge capacity and improved high-temperature lifespan can be obtained. When the above content ratio is exceeded, there is a problem in that the effect of improving high-temperature lifespan is reduced due to the formation of unstable LiWOx on the surface of the positive electrode active material or at the interface between the positive electrode active materials in the form of single particles.

[0087]

[0088] Method for manufacturing positive electrode active material for lithium secondary batteries

[0089] In another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery is provided, comprising the steps of: preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; mixing the transition metal precursor and a lithium raw material and then calcining them to form a lithium transition metal oxide; and crushing the lithium transition metal oxide to form a positive electrode active material for a single-crystal lithium secondary battery, wherein the crushing is performed using compressed air at a crushing pressure of 3.4 to 4.5 bar, specifically 3.5 to 4.3 bar, and the calcination is performed in an air atmosphere.

[0090] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described step by step.

[0091] First, a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals is prepared.

[0092] The nickel-containing transition metal precursor is not particularly limited, but may be, for example, a transition metal hydroxide.

[0093] The above transition metal hydroxide may be manufactured by, for example, adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution including a nickel raw material and optionally a cobalt raw material or a manganese raw material, and performing a co-precipitation reaction.

[0094] The above nickel raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide, or a combination thereof, but is not limited thereto.

[0095] The above cobalt raw material is not particularly limited as long as it is used in the manufacture of a cathode active material precursor in the art. For example, the cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO 4, It may be, but is not limited to, CoSO4ㆍ7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O or a combination thereof.

[0096] The manganese raw material is not particularly limited as long as it is used in the art for manufacturing a precursor of a cathode active material. For example, the manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically, may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylic acid salt, manganese citrate, and manganese fatty acid salt, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0097] The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally a cobalt raw material or a manganese raw material to a solvent, specifically, water, or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water.

[0098] The above complexing agent-containing solution performs the role of forming a complex, and may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent. Meanwhile, the complexing agent-containing solution may be used in the form of an aqueous solution, and at this time, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water may be used as the solvent.

[0099] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by controlling the concentration of nickel raw material, cobalt raw material, and manganese raw material.

[0100] Accordingly, the content of nickel in the transition metal precursor may be 50 to 70 mol% based on the total mole number of transition metals.

[0101] Additionally, the content of cobalt in the transition metal precursor may be 5 to 20 mol% based on the total mole number of transition metals.

[0102] In addition, the content of manganese in the transition metal precursor may be 10 mol% or more based on the total mole number of transition metals, and more specifically, 15 mol%, 20 mol%, 25 mol%, 30 mol%, or 40 mol% or more.

[0103] The technical significance of controlling the nickel, cobalt, and manganese content in the transition metal precursor is omitted as described above.

[0104] Additionally, in the step of preparing the first mixture by mixing the transition metal precursor and the lithium raw material, a doping raw material may be further included. Specifically, the doping raw material may be a Zr raw material and a Y raw material.

[0105] The above Zr raw material may be Zr(SO4)2, ZrS2, ZrO2, Zr(NO3)4 or a combination thereof, but is not necessarily limited thereto.

[0106] The above Y raw material may be Y(SO4)2, Y2(SO4)3, Y2O3, Y(NO3)3 or a combination thereof, but is not necessarily limited thereto.

[0107]

[0108] Next, the transition metal precursor and lithium raw material are mixed and then calcined to obtain a lithium transition metal oxide. Specifically, lithium metal oxide can be obtained through the first calcination or the second calcination.

[0109] In the past, the formation of lithium metal oxide in the form of a single crystal was carried out through sintering at high temperatures for a long time. However, in this case, there was a problem that the electrochemical properties of the active material were deteriorated due to nickel cation mixing phenomenon and formation of rock salt impurity phase caused by oversintering. On the other hand, the manufacturing method according to the present invention can prevent the above problem by controlling the sintering temperature and time when performing the sintering as the first sintering or the first and second sintering, and has the advantage of increasing particle strength and production volume.

[0110] At this time, the atmosphere during the sintering is not particularly limited. For example, it can be performed in an air or oxygen (O2) atmosphere, but more specifically, it can be performed in an air atmosphere. Since the formation of a layered crystal structure is not well performed in an air atmosphere for a cathode active material with a high nickel composition, a significant deterioration in electrochemical properties occurs, so it is generally performed in an oxygen atmosphere. On the other hand, in the case of the present invention, when the nickel content is relatively low, even if the sintering is performed in an air atmosphere, a significant deterioration in electrochemical properties does not occur, and the process cost can be reduced.

[0111] The above firing can be performed at a temperature of 830 to 990°C, 840 to 980°C, or 845 to 960°C, and the above firing can be performed for a total of 8 to 20 hours, 9 to 18 hours, or 10 to 15 hours. More specific control ranges of the firing temperature and time are described in more detail below.

[0112] When the above-mentioned sintering includes only the first sintering, the first sintering may be performed at a temperature of 920 to 960°C or 930 to 950°C, and the first sintering may be performed for a total of 8 to 16 hours or 10 to 14 hours. If the first sintering temperature is lower than 930°C, specifically 920°C, the growth of each single particle in the lithium transition metal oxide may be slowed, so that a lithium transition metal oxide in the form of a single crystal may not be easily formed. If the first sintering temperature is too high, over-sintering may occur, and in particular, the rock-salt structure crystal phase within the surface portion of the positive electrode active material may increase, thereby deteriorating the electrochemical properties of the active material, such as the capacity.

[0113] When the above-mentioned calcination includes a first calcination and a second calcination, the first calcination may be performed at a temperature of 920 to 960°C or 930 to 950°C, the second calcination may be performed at a temperature of 840 to 920°C or 850 to 910°C, the first calcination and the second calcination may be performed for a total of 12 to 16 hours or 12 to 14 hours, and the first calcination time may be the same as or longer than the second calcination time. When the first calcination temperature is lower than 930°C, specifically 920°C, the growth of each single particle in the lithium transition metal oxide may be reduced, so that a lithium transition metal oxide in a single crystal form may not be easily formed. If the first sintering temperature is too high, undersintering may occur, which may deteriorate the electrochemical properties of the active material, such as the capacity, as the rock-salt structure crystal phase increases, especially within the surface of the positive electrode active material. More specifically, the second sintering time may be performed for 6 hours or more, and if the second sintering is performed at a lower temperature than the first sintering, the structural stability of the first sintered active material is increased, while the heat required for sintering the active material is reduced compared to when only the first sintering is performed at a temperature of 930°C, specifically, 940°C or higher, thereby reducing the process cost.

[0114] In particular, when the secondary firing is performed within the temperature and time ranges, it is preferable because the crystal structure of the positive electrode active material can be stabilized. In addition, the lithium byproduct remaining on the surface of the metal oxide is decomposed by heat and diffuses into the metal oxide, thereby reducing the amount of lithium remaining on the surface, and the lithium ions react with the surface of the metal oxide to form a stable layered structure, thereby stabilizing the surface structure of the metal oxide surface, thereby improving the resistance characteristics and life characteristics of the battery, which is preferable.

[0115] It may be characterized in that the first firing and the second firing are performed continuously at different temperatures without including a cooling or crushing step between the first firing and the second firing, thereby suppressing the reaction between external moisture and the fired product, suppressing the increase of residual lithium, suppressing deterioration of the active material due to over-firing, and structurally stabilizing the active material.

[0116] The method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention includes a step of disintegrating lithium metal oxide to obtain a positive electrode active material in the form of single particles or in the form of 1 to 20 aggregated single particles.

[0117] The above-mentioned disintegration can be performed after cooling the calcined lithium transition metal oxide to 50 to 200°C. Cooling to the above-mentioned cooling temperature can suppress the reaction between external moisture and the calcined material and suppress the increase of residual lithium.

[0118] The above-mentioned disintegration can be performed by a method commonly performed in the art, for example, it can be performed using a rotor mill, a jet mill, a ball mill, a pin mill, a jet mill, a bead mill, or a roll mill equipment, but in particular, it is performed using a jet mill, more specifically, an air jet mill using compressed air, and can be performed at a disintegration pressure of 3.4 to 4.5 bar, specifically 3.5 to 4.3 bar. The disintegration can be performed by adjusting different disintegration pressures according to the cohesion between single particles depending on the sintering temperature or time during the disintegration, but when performed within the above range, it is possible to suppress the generation of fine particles due to unnecessary particle breakage, thereby suppressing side reactions with the electrolyte during operation when the electrode including the positive electrode active material is included in a secondary battery, and separation between sufficiently grown single particles can be performed, thereby realizing the stability of the desired single crystal positive electrode active material.

[0119] Additionally, after the step of obtaining a single-crystal positive electrode active material through the above-mentioned disintegration, a step of mixing the single-crystal positive electrode active material and the coating raw material and then performing a heat treatment to obtain a positive electrode active material having a coating layer formed on the surface may be further included. At this time, the technical definition, significance, characteristics, etc. of the coating layer are as described above, and the heat treatment may be performed at 400 to 500°C, more specifically, at 410 to 450°C, and may be performed for 5 to 8 hours.

[0120]

[0121] anode

[0122] In another embodiment of the present invention, a positive electrode is provided, comprising a current collector and a positive electrode active material layer positioned on one surface of the current collector and including a positive electrode active material manufactured according to the above-described embodiment.

[0123] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as described above. Therefore, a detailed description of the positive electrode active material will be omitted.

[0124] The above-mentioned collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0125] Meanwhile, the positive electrode active material layer may include a binder and a conductive material.

[0126] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one kind alone or a mixture of two or more kinds thereof may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0127] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0128] The above anode can be manufactured according to a conventional anode manufacturing method, except that it is manufactured to fall within the above range.

[0129] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, optionally including a binder, a conductive agent, or a solvent, as needed, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0130] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0131] Alternatively, the positive electrode may be manufactured by casting a composition for forming a positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0132]

[0133] lithium secondary battery

[0134]

[0135] In another embodiment, a lithium secondary battery including the positive electrode is provided.

[0136] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0137] In the above lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0138] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength 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, etc.

[0139] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0140] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 ≤ β ≤ 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0141] The above binder and conductive material may be the same as those described above for the positive electrode.

[0142] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, and mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0143] In addition, in the lithium secondary battery, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0144] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0145] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0146] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0147] As described above, a lithium secondary battery including a positive electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0148]

[0149] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0150]

[0151] Manufacturing of positive electrode active materials

[0152] Example 1

[0153] (Mixed) Ni 0.6 Co 0.1 Mn 0.3Li2CO3 was added to a mixer so that the molar ratio (Li / M) of lithium to the precursor of (OH)2 composition and the transition metal of the precursor was 1.06, and doping raw materials ZrO2 and Y2O3 were added so that Zr and Y were 3000 ppm and 1500 ppm, respectively, and mechanically mixed to form a mixture.

[0154] (Calcination and Disintegration) After that, the mixture was heated to 945℃ through heat treatment under an air atmosphere, and then first calcined at a constant temperature of 945℃ for 14 hours, and then naturally cooled to form a lithium transition metal oxide. After that, the lithium metal oxide was disintegrated using an air jet mill to obtain a single-crystal positive electrode active material. The composition of the obtained single-crystal positive electrode active material was Li 1.06 Ni 0.6 Co 0.1 Mn 0.3 It was O2.

[0155] (Coating and heat treatment) When mixing the single crystal positive electrode active material and the coating raw materials Al2O3 and WO3, Al and W were added in amounts of 1700 ppm and 3200 ppm, respectively, of the total mixture weight, mixed in a mixer, and heat-treated at 420°C for 6 hours to obtain a single crystal positive electrode active material having a coating layer including Al and W formed on the surface.

[0156]

[0157] Examples 2 to 6 and Comparative Examples 1 to 7

[0158] A positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering and disintegration conditions were adjusted as shown in Table 1 below.

[0159]

[0160] 1st firing 2nd firing Disintegration Firing temperature (℃) Firing time (hour) Firing temperature (℃) Firing time (hour) Crushing pressure (bar) Example 194514-4.3 Example 2945890063.9 Example 3940890063.9 Example 494012-3.8 Example 5940790073.8 Example 6945885063.5 Comparative example 196016-4.5 Comparative example 296014-4.4 Comparative example 395514-4.2 Comparative example 495014-4.2 Comparative example 594514-4.1 Comparative example 6945785073.5 Comparative example 7945785073.3

[0161] Experimental Example 1: Analysis of particle circumference of positive electrode active material using SEM images.

[0162] The positive electrode active materials manufactured according to the above examples and comparative examples were analyzed using SEM (Scanning Electron Microscopy) equipment at a magnification of 5000 times and under 5 kV conditions to obtain positive electrode active material images. Among these, the SEM images of Examples 1 to 4 and Comparative Examples 3 and 4 are shown in FIGS. 1 to 6.

[0163] Figures 1 to 6 are SEM (Scanning Electron Microscopy) images at 5,000x magnification of positive electrode active materials manufactured according to Examples and Comparative Examples. Referring to Figures 1 to 6, it can be confirmed that the manufactured single-crystal positive electrode active materials include an average of 1 to 50 single particles, specifically 1 to 20 single particles.

[0164] Using AI-based image analysis, the perimeter, area, and circumscribed circle of each particle in the measured SEM images were measured. The circumscribed circle is an ideal circle encompassing at least two outermost points of a single particle. This implies that the entire surface area of ​​the particle is contained within the circumscribed circle.

[0165] Figures 7 to 12 are images obtained by performing image analysis based on an AI (Artificial Intelligence) program on SEM images of positive electrode active materials manufactured according to Examples and Comparative Examples. Using Figures 7 to 12, the perimeter, area, and circumscribed circle of each single particle in the manufactured positive electrode active materials can be derived.

[0166] Specifically, after particles are detected in SEM images, the area and perimeter of each particle are calculated using a simple Python function. Since the unit of measurement is pixels, a scale bar is used to convert these values ​​to SI (International System of Units) units, such as μm.

[0167] Afterwards, the circumference of the measured particle was assumed to be the circumference of an ideal circular particle (2πR1), and the first diameter of the particle (D1=2*R1) was derived, and the area of ​​the measured particle was assumed to be the area of ​​an ideal circular particle (πR2 2 ) was assumed, and the second diameter of the particle (D2=2*R2) was derived. In addition, the third diameter of the particle (D3=2*R3) was derived from the diameter of the circumcircle of the measured particle.

[0168] And by calculating the relationship between the first to third diameters, Equation 1 (D2*D3 / D1), the difference between the examples and the comparative examples could be confirmed.

[0169] The results are shown in Table 2 below.

[0170] Particle diameter measured by SEM image Unit: [㎛] Relationship between first to third diameters Formula 1: D2*D3 / D1 Unit: [㎛] First diameter (D1) Second diameter (D2) Third diameter (D3) Example 12.18 1.65 2.15 1.627 Example 22.09 1.63 2.20 1.716 Example 32.09 1.64 2.22 1.742 Example 42.04 1.64 2.12 1.704 Example 51.96 1.58 1.99 1.604 Example 61.95 1.57 2.01 1.618 Comparative example 12.89 2.34 3.11 2.518 Comparative example 22.89 2.26 3.04 2.377 Comparative example 32.712.132.942.311Comparative example 42.401.792.521.880Comparative example 52.221.792.41.935Comparative example 61.871.391.881.397Comparative example 71.841.351.831.343

[0171] Referring to Table 2 above, it can be confirmed that in the examples, formula 1 (D2*D3 / D1) satisfies a range of 1.40 to 1.80 μm, specifically 1.45 to 1.75 μm, or 1.55 to 1.75 μm, and in the comparative examples, it does not satisfy the range. In addition, it can be confirmed that in the examples, the first diameter (D1) satisfies a range of 1.90 to 2.20 μm, specifically 1.92 to 2.20 μm, or 1.94 to 2.19 μm, and in the comparative examples, it does not satisfy the range.

[0172] In addition, it can be confirmed that in the embodiment, the second diameter (D2) satisfies the range of 1.40 to 1.75 ㎛, specifically 1.45 to 1.71 ㎛, or 1.50 to 1.67 ㎛, and the comparative example does not satisfy the range.

[0173] In addition, it can be confirmed that in the embodiment, the third diameter (D3) satisfies the range of 1.90 to 2.35 ㎛, specifically 1.93 to 2.31 ㎛, or 1.96 to 2.27 ㎛, and the comparative example does not satisfy the range.

[0174]

[0175] Experimental Example 2: Analysis of the differential ratio during rolling of the positive electrode active material

[0176] In order to analyze the differential ratio due to particle breakage when a certain pressure is applied to the positive electrode active material particles according to the examples and comparative examples, the following experiment was conducted. For reference, applying pressure to the positive electrode active material can correspond to the rolling process during the positive electrode manufacturing process.

[0177] Specifically, 3.00 g of positive electrode active material powder was placed in a mold with a diameter of 1.3 cm, and then 67.8 kN / cm was applied using a press machine. 2 After applying the force, the pressurized pellet-shaped positive electrode active material was placed in a mortar and ground to break up the clumped particles. Then, 10 wt% (NaPO3) 61 mL was mixed with 500 mL of water as a dispersant, and the broken-up positive electrode active material was added to the mixture, followed by ultrasonic treatment for about 1 minute. Afterwards, the particle size was analyzed using Malvern (MS3000) equipment to measure the volume % of fine particles with a particle size of less than 1.0 μm, thereby obtaining the fine particle ratio.

[0178] The results are shown in Table 3 below.

[0179] 67.8kN / cm 2 After rolling, fine particle ratio less than 1.0㎛ [%] Example 12.97 Example 22.81 Example 32.95 Example 42.20 Example 53.59 Example 63.21 Comparative Example 11.53 Comparative Example 21.57 Comparative Example 31.40 Comparative Example 41.77 Comparative Example 52.49 Comparative Example 65.25 Comparative Example 75.39

[0180] The cathode active material according to the embodiment satisfying the above-mentioned formula 1 (D2*D3 / D1) is 1.7 tonf / cm 2It was confirmed that the fine particle ratio with a particle size of 1 μm or less when pressure was applied was 5.0% or less. More specifically, the fine particle ratio was 0.5% to 4.5%, 1.0% to 4.0%, 2.0% to 4.0%, or 2.1% to 3.6%. Accordingly, it is expected that the generation of fine particles due to particle breakage can be reduced, and as a result, the safety of the battery can be maximized by preventing gas generation due to fine particles. In addition, particle breakage caused by compression can lower the density between particles in the electrode and increase the contact resistance between particles, which can lower the performance of the electrode. That is, it can be confirmed that the positive electrode active material according to the present embodiment has the effect of suppressing particle breakage caused by compression and improving the performance of the electrode.

[0181] However, it was confirmed that the differential ratio was reduced in Comparative Examples 1 to 5, which exceeded the upper limit of the appropriate range of the aforementioned Equation 1 (D2*D3 / D1) in the positive electrode active material.

[0182] However, when the equation 1 (D2*D3 / D1) is exceeded, excessive single crystal growth of the positive electrode active material occurs, causing significant shrinkage of the structure, which inhibits the diffusion and desorption of lithium ions within the positive electrode active material. This may tend to result in a decrease in the capacity and rate characteristics of the electrode. Specifically, in the case of Comparative Examples 1 to 5, it was confirmed that the electrochemical characteristics were deteriorated through the capacity evaluation using the coin cell described below.

[0183]

[0184] Experimental Example 3: Evaluation of Electrochemical Characteristics Using Coin Cells

[0185] In order to evaluate the physical properties and electrochemical properties of the positive electrode active materials according to the examples and comparative examples, coin cells were manufactured as follows.

[0186] Specifically, a positive electrode active material, a polyvinylidene fluoride binder (trade name: KF9700), and a carbon black conductive material were mixed in a weight ratio of 96.5:1.5:2, and the mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 60 wt% to prepare a positive electrode active material slurry.

[0187] The above slurry was coated on an aluminum foil (Al foil, thickness: 20 ㎛) as a positive electrode current collector using a doctor blade, dried, and rolled to manufacture a positive electrode. The loading amount of the positive electrode was about 16 mg / cm2, and the rolling density was about 3.5 g / cm 3 It was.

[0188] A 2032 coin cell was manufactured using the above positive electrode, lithium metal negative electrode (200 μm thick, Welcos), electrolyte, and polyethylene separator by a conventional method. The electrolyte was a mixed solution prepared by dissolving 1 M LiPF6 in a mixed solvent of 2% VC (vinylene carbonate) ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) (mixing ratio EC:DMC:DEC = 1:2:1 volume %).

[0189] (1) Initial capacity and initial efficiency evaluation

[0190] After manufacturing the coin cell, it was aged at 25℃ for 12 hours and then a charge-discharge test was conducted at 25℃. To evaluate the discharge capacity, 200 mAh / g was used as the reference capacity, and the cell was charged to 4.4 V at a constant current of 0.1C, then switched to a constant voltage and charged until the end current reached 0.05C. After a 10-minute rest period after charging, the cell was discharged to 2.5 V at a constant current of 0.1C, using 200 mAh / g as the reference capacity.

[0191]

[0192] (2) High temperature life evaluation (45℃, 50 cycles)

[0193] After fabricating a lithium secondary battery half-cell, it was charged to 4.4 V at a constant current of 0.5 C at 45°C, then switched to constant voltage and charged until the end current reached 0.05 C. After a 10-minute rest period after charging, it was discharged at a constant current of 1.0 C until the voltage reached 2.5 V. Under these charge-discharge cycle conditions, 50 charge-discharge cycles were performed, and the capacity retention rate of the 50th cycle was calculated compared to the first cycle.

[0194]

[0195] The discharge capacity and high-temperature capacity retention characteristics derived as a result are shown in Table 4 below.

[0196] Discharge capacity [mAh / g] High temperature capacity retention [%] Example 1 196.2 96.3 Example 2 197.6 96.1 Example 3 196.5 96.2 Example 4 196.8 96.1 Example 5 196.5 96.1 Example 6 196.3 96.0 Comparative Example 1 192.8 96.4 Comparative Example 2 191.6 96.5 Comparative Example 3 193.2 96.3 Comparative Example 4 194.1 96.3 Comparative Example 5 195.9 96.4 Comparative Example 6 196.8 95.2 Comparative Example 7 197.3 95.0

[0197] It was confirmed that the cathode active material according to an embodiment satisfying the appropriate range of the aforementioned Equation 1 (D2*D3 / D1) had a discharge capacity of 196.0 mAh / g or more. More specifically, the discharge capacity was 196.0 to 200.0 mAh / g or 196.1 to 198.0 mAh / g. In addition, it was confirmed that the cathode active material according to an embodiment satisfying the appropriate range of the aforementioned Equation 1 (D2*D3 / D1) had a high-temperature capacity retention rate of 96.0% or more. More specifically, the high-temperature capacity retention rate was 95.3% to 96.3% or 96.0% to 96.3%. A high high-temperature capacity retention rate means that the capacity does not decrease significantly even when charge / discharge is performed at high temperatures, and thus means that the life characteristics at high temperatures are excellent.

[0198] As described above, in Comparative Examples 1 to 5, particle breakage was prevented, but it was confirmed that electrochemical characteristics were impaired. Specifically, although the high-temperature life characteristics correspond to 96.3 to 96.5%, the discharge capacity corresponds to 196.0 mAh / g or less, and it was confirmed that the electrochemical capacity characteristics were impaired compared to the examples.

[0199] Meanwhile, in the case of Comparative Examples 6 and 7, the discharge capacity is 196.0 mAh / g or more, but the high-temperature life characteristic is 96.0% or less, so that, as described above, particle breakage occurs seriously during rolling, significantly reducing stability.

[0200] Therefore, through comparison between the examples and comparative examples, it can be confirmed that the cathode active materials according to examples 1 to 6 and the batteries including the same are electrochemically superior and at the same time have excellent stability.

[0201]

[0202] In summary of the results of the experimental examples, the positive electrode active material that can reduce the occurrence of fine particles due to particle breakage and at the same time has excellent electrochemical properties such as discharge capacity and high-temperature resistance increase rate is the positive electrode active material according to Examples 1 to 6 that satisfies the appropriate range of Equation 1 (D2*D3 / D1).

[0203] In addition, in the case of a lithium secondary battery including the positive electrode active material, it is expected that the safety of the battery will be maximized by preventing gas generation due to fine particles, and at the same time, it will be possible to provide a lithium secondary battery that can be used for a long time at high capacity and high temperatures.

[0204]

[0205] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. As a positive electrode active material for a single-crystal lithium secondary battery, The above positive electrode active material comprises a form in which 1 to 20 single particles are aggregated, The above single particle satisfies the following equation 1: Cathode active material for lithium secondary batteries: [Formula 1] 1.40 ㎛ ≤ (D2*D3) / D1 ≤ 1.80 ㎛ In the above equation 1, D1 means the first diameter of a single particle (D1=2*R1) derived by assuming the circumference of a single particle measured from the SEM (Scanning Electron Microscopy) image of the positive electrode active material to be the circumference of an ideal circle (2πR1). D2 is the area of ​​a single particle measured from the SEM image of the positive electrode active material, which is the area of ​​an ideal circle (πR2 2 ) refers to the second diameter of a single particle (D2=2*R2) derived after assuming that D3 refers to the third diameter of a single particle (D3=2*R3) derived from the diameter of the circumscribed circle of a single particle measured from the SEM image of the positive electrode active material.

2. In paragraph 1, The above D1 is in the range of 1.90 to 2.20㎛, Cathode active material for lithium secondary batteries.

3. In paragraph 1, The above D2 is in the range of 1.40 to 1.75㎛, Cathode active material for lithium secondary batteries.

4. In paragraph 1, The above D3 is in the range of 1.90 to 2.35㎛, Cathode active material for lithium secondary batteries.

5. In paragraph 1, The above positive electrode active material is 67.8 kN / cm 2 After pressurization, the ratio of fine particle size distribution of 1.0 μm or less in the volume-based particle size distribution curve of the positive electrode active material is 5.0% or less. Cathode active material for lithium secondary batteries.

6. In paragraph 1, The above positive electrode active material has an average particle diameter (D50) in the range of 2.0 to 5.5 μm when measuring the particle size distribution based on the volume of the positive electrode active material. Cathode active material for lithium secondary batteries.

7. In paragraph 1, A cathode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Co y Mr z M w ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.5≤x≤0.7, 0.05≤y≤0.2, 0≤z≤0.4, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Y, B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

8. In paragraph 7, The above positive electrode active material contains Zr and Y, The total content of Zr and Y is in the range of 3000 to 5800 ppm based on the weight of the positive electrode active material. Cathode active material for lithium secondary batteries.

9. In paragraph 1, The above positive electrode active material includes a coating layer on the surface, The above coating layer comprises Al, W, Co, V, Ti, Nb, Ce, B, P or a combination thereof. Cathode active material for lithium secondary batteries.

10. In paragraph 9, The above coating layer contains Al and W, The W content ratio (W / Al) to the above Al content is in the range of more than 0 and less than or equal to 4.

0. Cathode active material for lithium secondary batteries.

11. A step of preparing a transition metal precursor containing 50 to 70 mol% of nickel based on the total mole number of transition metals; A step of mixing the above transition metal precursor and lithium raw material and then calcining them to form a lithium transition metal oxide; and It comprises a step of forming a positive electrode active material for a single-crystal lithium secondary battery by crushing the lithium transition metal oxide, The above crushing is performed at a crushing pressure of 3.4 to 4.5 bar, The above firing is performed in an air atmosphere. A method for manufacturing a cathode active material for a lithium secondary battery.

12. In paragraph 11, The above firing is performed at a temperature of 830 to 990°C, The above firing is performed for a total of 8 to 20 hours. A method for manufacturing a cathode active material for a lithium secondary battery.

13. In paragraph 11, The above firing includes only the first firing, The above first firing is performed at a temperature of 920 to 960°C, The above first firing is performed for a total of 8 to 16 hours. A method for manufacturing a cathode active material for a lithium secondary battery.

14. In paragraph 11, The above firing includes primary firing and secondary firing, The above first firing is performed at a temperature of 920 to 960°C, The above secondary firing is performed at a temperature of 840 to 920°C, The above first and second firings are performed for a total of 12 to 16 hours, The above first firing time is performed equal to or longer than the above second firing time. A method for manufacturing a cathode active material for a lithium secondary battery.

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

Images