Cathode active material for lithium secondary battery, manufacturing method of same, and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising: a lithium metal oxide which has a lithium and manganese-rich composition, and is in the form of a secondary particle formed by aggregating a plurality of rod-shaped primary particles; a first coating layer which surrounds the entire surface of the secondary particle in the form of a film and contains Al; a second coating layer which surrounds the surfaces of at least some of the plurality of primary particles present in a core part in the secondary particle in the form of a film and contains Al; and a third coating layer which surrounds the surfaces of at least some of the plurality of primary particles present in a shell part in the secondary particle in the form of a film and contains Al.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

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

[0002]

[0003] As the scope of application of lithium secondary batteries expands from small electronic devices to electric vehicles and power storage devices, the demand for cathode materials with excellent high energy density and high output characteristics is increasing.

[0004] In this regard, lithium and manganese-rich layered lithium transition metal oxides have a very high capacity of over 240 mAh / g and are attracting attention as candidates for next-generation cathode active materials, and research on them is actively being conducted recently.

[0005] However, lithium- and manganese-rich lithium transition metal oxides utilize oxygen redox reactions in addition to the transition metals, making it easy for oxygen on the surface or within the bulk to evolve into oxygen gas. This can easily lead to the formation of dense, non-reactive or less reactive spinel / rock salt structures within the particles, increasing structural instability. This structural instability causes an overall deterioration in life characteristics, such as reduced capacity retention, voltage decay, increased resistance increase, and gas evolution as cycling progresses.

[0006]

[0007] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery having improved life characteristics overall, such as improved capacity retention rate, reduced voltage drop, and reduced resistance increase rate as the cycle progresses, as a lithium metal oxide having an excess composition of lithium and manganese, by improving structural stability, a method for producing the same, and a lithium secondary battery including the same.

[0008]

[0009] One embodiment of the present invention provides a cathode active material for a lithium secondary battery, comprising: a lithium metal oxide in the form of secondary particles having a lithium and manganese excess composition and formed by agglomeration of a plurality of rod-shaped primary particles; a first coating layer covering the entire surface of the secondary particles in the form of a film and containing Al; a second coating layer covering the surface of at least a portion of the plurality of primary particles present in the core portion within the secondary particles in the form of a film and containing Al; and a third coating layer covering the surface of at least a portion of the plurality of primary particles present in the shell portion within the secondary particles in the form of a film and containing Al.

[0010] The second coating layer may also be present in an area within a distance of 1 μm from the center of the secondary particle.

[0011] The average thickness of the first coating layer may be thicker than the average thickness of the third coating layer.

[0012] The average thickness of the third coating layer may be thicker than the average thickness of the second coating layer.

[0013] The average thickness of the first coating layer may be 0.4 to 2.4 nm.

[0014] The average thickness of the second coating layer may be 0.34 to 2.2 nm.

[0015] The average thickness of the third coating layer may be 0.36 to 2.3 nm.

[0016] The ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) may be 1.03 to 1.2.

[0017] The ratio of the average thickness of the third coating layer to the average thickness of the second coating layer (third coating layer / second coating layer) may be 1.01 to 1.15.

[0018] The first coating layer, the second coating layer, and the third coating layer may include an Al-containing compound, and the Al-containing compound may include Al2O3 as a main component.

[0019] The above Al2O3 may be amorphous.

[0020] The content of Al in the positive electrode active material may be 0.04 to 0.23 mol% based on the total mole number of the lithium metal oxide.

[0021] The average porosity of the lithium metal oxide may be 10 to 20%.

[0022] The above positive electrode active material has a BET specific surface area of ​​3.4 to 4.3 m 2 / g may be.

[0023] The above positive electrode active material may have a tap density of 1.5 to 2.0 g / cc.

[0024] The average aspect ratio of the above primary particles may be 6.5 to 13.

[0025] The above lithium metal oxide can be represented by the following chemical formula 1.

[0026] [Chemical Formula 1]

[0027] Li 1+a (Ni x Co y Mn z M w ) 1-a O2

[0028] In the above chemical formula 1, 0.1≤a≤0.3, 0.2≤x≤0.4, 0≤y≤0.2, 0.5≤z≤0.75, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof.

[0029]

[0030] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium metal oxide having a lithium and manganese excess composition in the form of secondary particles formed by agglomeration of a plurality of rod-shaped primary particles; and forming a coating layer containing Al on the lithium metal oxide by an atomic layer deposition method, wherein in the step of forming the coating layer containing Al, a first coating layer containing Al is formed to cover the entire surface of the secondary particles in the form of a film, a second coating layer containing Al is formed to cover at least a portion of the surfaces of the plurality of primary particles present in the core portion within the secondary particles in the form of a film, and a third coating layer containing Al is formed to cover at least a portion of the surfaces of the plurality of primary particles present in the shell portion within the secondary particles in the form of a film.

[0031] The above atomic layer deposition can be performed for 4 to 23 cycles.

[0032] The above atomic layer deposition can be performed at a temperature of 120 to 180°C.

[0033]

[0034] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0035] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0036]

[0037] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery can have improved structural stability by coating a thin and uniform Al-containing coating layer on the entire surface of lithium metal oxide secondary particles with a lithium and manganese-rich composition and on the inner primary particles. Accordingly, the life characteristics can be improved overall, such as improved capacity retention rate as the cycle progresses, reduced voltage drop, reduced resistance increase rate, and suppressed gas generation.

[0038]

[0039] Figure 1 is a cross-sectional SEM image of a secondary particle after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1.

[0040] FIG. 2 is an Al element EDS (Energy Dispersive Spectroscopy) mapping image of a secondary particle cross-section after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1.

[0041] FIG. 3 is an EDS (Energy Dispersive Spectroscopy) mapping image of Ni elements on a secondary particle cross-section after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1.

[0042] FIG. 4 is an EDS (Energy Dispersive Spectroscopy) mapping image of Co element on a secondary particle cross-section after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1.

[0043] FIG. 5 is an EDS (Energy Dispersive Spectroscopy) mapping image of Mn element on a secondary particle cross-section after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1.

[0044] Figure 6 is a TEM image of one internal primary particle after FIB (Focused Ion Beam) milling of the positive electrode active material manufactured according to Example 1.

[0045] Figure 7 is a graph showing the results of cross-sectional EDS (Energy Dispersive Spectroscopy) line scan concentration analysis for one internal primary particle after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 8.

[0046] Figure 8 is a cross-sectional TEM image of the primary particles in the shell after FIB (Focused Ion Beam) milling of the positive electrode active material manufactured according to Example 3.

[0047] Figure 9 is a cross-sectional TEM image of the primary particles in the core after FIB (Focused Ion Beam) milling of the positive electrode active material manufactured according to Example 3.

[0048] Figure 10 is a cross-sectional TEM image of the primary particles in the shell after FIB (Focused Ion Beam) milling after 100 charge / discharge cycles of the positive electrode active material manufactured according to Example 3.

[0049]

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0055] 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.

[0056] 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.

[0057]

[0058] 1. Positive active material

[0059] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium transition metal oxide having a lithium and manganese excess composition. Although the lithium and manganese excess composition of the lithium transition metal oxide has a low nickel content, it can involve oxidation / reduction reactions of not only the transition metal but also anions (oxygen) during battery operation. In addition, since the excess lithium can exist in the transition metal layer in addition to the lithium layer, the insertion and de-insertion efficiency of lithium ions can be increased. As a result, the initial discharge capacity can be 240 mAh / g or more, which is significantly improved in capacity characteristics compared to a cathode material having a conventional NCM composition. In addition, the cost-effectiveness is excellent because the content of relatively expensive nickel and cobalt can be reduced and the content of inexpensive manganese can be increased.

[0060] More specifically, the lithium metal oxide may have a molar ratio of lithium to lithium metal oxide of 1.1 to 1.3. As the lithium content increases, the amount of lithium that can participate in the insertion and deintercalation of lithium ions increases, thereby improving capacity characteristics. However, if the lithium content increases too much, phase stability problems may occur due to excessive occurrence of oxygen oxidation / reduction reactions, which may result in deterioration of life characteristics.

[0061] In addition, the lithium metal oxide may have a molar ratio of nickel to the total metal excluding lithium of 0.2 to 0.4. When the nickel content satisfies the above range, the capacity, output, and life characteristics of the battery can be more preferably implemented. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction increases too much, which may deteriorate the life characteristics. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, which may deteriorate the capacity and output characteristics.

[0062] In addition, the lithium metal oxide may have a molar ratio of manganese to the total metal excluding lithium of 0.5 to 0.75. If the manganese content is too low, manufacturing costs increase, the safety of the active material decreases, and the capacity improvement effect due to excessive manganese content may be minimal. If the manganese content is too high, the life characteristics may be deteriorated due to excessive use of oxygen oxidation / reduction reactions, and there may be a problem of manganese dissolution.

[0063] In addition, the lithium transition metal oxide may have a molar ratio of cobalt to transition metal of 0.2 or less, more specifically 0.1, 0.05 or less, and may not contain cobalt. Cobalt is usually added in a certain amount to improve the lifespan and output characteristics of a battery, but it has the problem of being expensive. Since the lithium transition metal oxide according to the present invention includes a carbon-containing coating layer, even if the cobalt content is reduced to the above range, the lifespan and output characteristics can be well implemented. Accordingly, the present invention can simultaneously implement economic feasibility and product quality.

[0064] Meanwhile, the lithium transition metal oxide according to one embodiment of the present invention is in the form of a secondary particle formed by agglomeration of a plurality of primary particles. As used herein, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be formed of a single crystal grain or a plurality of crystal grains. As used herein, the term "crystal grain" refers to a distinct region in the form of a lattice structure in which atoms within a primary particle form a lattice structure with a certain direction.

[0065] At this time, the primary particle has a rod shape. In this specification, “rod shape” is a term used to distinguish it from a spherical shape, and means a particle having a shape closer to an elongated rod shape rather than a spherical shape, and having an aspect ratio of greater than 1.6. Meanwhile, “aspect ratio” in this specification means the ratio of the length of the longest side to the shortest side within a primary particle.

[0066] However, since the lithium and manganese-rich lithium transition metal oxides of the above composition utilize oxygen redox reactions in addition to the transition metals, oxygen on the surface or within the bulk can easily be generated as oxygen gas. This can easily lead to the formation of dense, non-reactive or low-reactivity spinel / rock salt structures within the particles, increasing structural instability. This structural instability causes an overall deterioration in life characteristics, such as reduced capacity retention, voltage decay, increased resistance increase, and gas evolution as cycling progresses.

[0067] Accordingly, the lithium transition metal oxide according to the present invention can be uniformly coated with an Al coating layer in an extremely thin thickness on the atomic level on secondary particles, and further on primary particles existing inside secondary particles, through a vapor phase atomic layer deposition (ALD) coating method using an Al-containing gas on a lithium transition metal oxide having a porous lithium and manganese-rich composition. Accordingly, the structural stability of the lithium metal oxide is improved, and the life characteristics of the battery can be improved. More details on the vapor phase atomic layer deposition coating method will be described in the manufacturing method described below.

[0068] More specifically, the positive electrode active material according to the present invention includes a first coating layer containing Al that wraps the entire surface of a secondary particle in the form of a film. That is, the first coating layer is not an island-type coating layer that partially and sparsely covers the surface of the secondary particle, but a conformal-type coating layer that uniformly wraps the entire surface. In addition, the first coating layer has good thickness uniformity and can thus have a film-like form.

[0069] In addition, the cathode active material according to the present invention includes a second coating layer containing Al that wraps the surface of at least some of the plurality of primary particles present in the core portion within the secondary particle in the form of a film, and a third coating layer containing Al that wraps the surface of at least some of the plurality of primary particles present in the shell portion within the secondary particle in the form of a film.

[0070] Here, in this specification, the term “core portion within a secondary particle” means a region within a distance of (1 / 3)r from the center of the secondary particle, when the distance from the center of the secondary particle to the surface is r. In addition, the term “shell portion within a secondary particle” means a region within a distance of (1 / 3)r to r from the center of the secondary particle, when the distance from the center of the secondary particle to the surface is r.

[0071] That is, the cathode active material according to the present invention can uniformly form an Al-containing coating layer with a thin thickness not only on the surface of the secondary particle but also deep into the primary particle inside the secondary particle. This structure can be obtained by applying a vapor phase atomic layer deposition (ALD) coating method using an Al-containing gas to a lithium transition metal oxide having a porous lithium and manganese-rich composition. In this way, since not only the surface of the secondary particle but also a significant number of the primary particles located inside the secondary particle are coated with the Al-containing coating layer, the structural stability is desirably improved, and the effect of improving the life characteristics of the battery can be desirably implemented.

[0072] As the Al-containing coating layer is formed deep within the primary particle inside the secondary particle in this way, the second coating layer may also be present in an area within a distance of 1 μm from the center of the secondary particle, and more specifically, may also be present in an area within a distance of 0.5 or 0.3 μm.

[0073] Meanwhile, the average thickness of the first coating layer may be thicker than the average thickness of the third coating layer. In addition, the average thickness of the third coating layer may be thicker than the average thickness of the second coating layer. That is, the average thickness of the Al-containing coating layer may exhibit a tendency to become thinner from the surface of the secondary particle to the interior of the secondary particle. Accordingly, the structural stability of the positive electrode active material may be desirably improved, and the effect of improving the life characteristics of the battery may be desirably implemented.

[0074] The average thickness of the first coating layer may be 0.4 to 2.4 nm, and more specifically, 0.44 to 2.2 nm. If the average thickness of the first coating layer is too thin, the effect of improving the life characteristics of the battery due to the improved structural stability of the positive electrode active material may be minimal. If the average thickness of the first coating layer is too thick, lithium ion mobility may be inhibited, which may deteriorate the capacity or output characteristics of the battery.

[0075] Meanwhile, the average thickness of the first coating layer can be measured by the following method. First, the thickness of the first coating layer for one positive electrode active material secondary particle can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 locations on the surface of the secondary particle, and then calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the first coating layer can be calculated by calculating the average of the first coating layer thicknesses measured for 20 random positive electrode active material secondary particles among the positive electrode active material powders by the same method as above.

[0076] The average thickness of the second coating layer may be 0.34 to 2.2 nm, and more specifically, 0.37 to 2.1 nm. If the average thickness of the second coating layer is too thin, the effect of improving the life characteristics of the battery due to the improved structural stability of the positive electrode active material may be minimal. If the average thickness of the second coating layer is too thick, lithium ion mobility may be inhibited, which may deteriorate the capacity or output characteristics of the battery.

[0077] Meanwhile, the average thickness of the second coating layer can be measured by the following method. First, the thickness of the second coating layer for one positive electrode active material secondary particle can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 locations among the core portions within the secondary particle, and then calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the second coating layer can be calculated by calculating the average of the second coating layer thicknesses measured for 20 random positive electrode active material secondary particles among the positive electrode active material powders by the same method as above.

[0078] The average thickness of the third coating layer may be 0.36 to 2.3 nm, and more specifically, 0.4 to 2.15 nm. If the average thickness of the third coating layer is too thin, the effect of improving the life characteristics of the battery due to the improved structural stability of the positive electrode active material may be minimal. If the average thickness of the third coating layer is too thick, lithium ion mobility may be inhibited, which may deteriorate the capacity or output characteristics of the battery.

[0079] Meanwhile, the average thickness of the third coating layer can be measured by the following method. First, the thickness of the third coating layer for one positive electrode active material secondary particle can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 positions among the shell portions in the secondary particle, and then calculating the average value of the coating layer thickness at the selected positions. Next, the average thickness of the third coating layer can be calculated by calculating the average of the third coating layer thicknesses measured for 20 random positive electrode active material secondary particles among the positive electrode active material powders by the same method as above.

[0080] Meanwhile, the ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) may be 1.03 to 1.2. In addition, the ratio of the average thickness of the third coating layer to the average thickness of the second coating layer (third coating layer / second coating layer) may be 1.01 to 1.15. When the ratio of the average thicknesses among the first, second, and third coating layers satisfies the above range, the structural stability of the positive electrode active material is preferably improved, and the effect of improving the life characteristics of the battery can be preferably implemented.

[0081] In addition, the content of Al in the positive electrode active material may be 0.04 to 0.23 mol% based on the total mole number of the lithium metal oxide, and more specifically, 0.045 to 0.22 mol%. If the content of Al is too low, the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal. If the content of Al is too high, lithium ion mobility may be inhibited, which may deteriorate the capacity or output characteristics of the battery.

[0082] Meanwhile, the first coating layer, the second coating layer, and the third coating layer may include an Al-containing compound, and the Al-containing compound may include Al2O3 as a main component. At this time, the Al2O3 may be amorphous. In the present specification, the main component may mean that it accounts for about 80 wt% or more based on the total weight of the Al-containing compound in the coating layer. Since the coating layer contains amorphous Al2O3 in this way, the energy barrier for lithium ions to move is lower than that in a crystalline structure, so that the lithium ions of the electrolyte can easily pass through, and when it is uniformly coated on the surface, it provides structural stability, so that the life characteristics can be preferably improved. Meanwhile, the composition of the Al-containing compound can be confirmed through TEM-EDX analysis, and the amorphous structure can be confirmed through TEM (transmission electron microscope) image analysis.

[0083] Meanwhile, in order for the coating layer structure according to the present invention to be easily formed, the properties of the lithium metal oxide or positive electrode active material are also important, and this will be described.

[0084] First, the average porosity of the lithium metal oxide may be 10 to 20%, and more specifically, 12 to 18%. If the average porosity of the lithium metal oxide is too small, the Al-containing coating layer may not be easily formed deep inside the secondary particle, so that the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal, and the output characteristics may deteriorate. If the average porosity of the lithium metal oxide is too large, the density of the positive electrode active material may be too low, making it difficult to implement a high-energy positive electrode density, and particle cracks may occur during rolling. Meanwhile, the “porosity” of one lithium metal oxide secondary particle can be derived by converting the ratio of the total area of ​​the hollow pore portion to the entire cross-sectional area of ​​the secondary particle into a percentage value when cutting one secondary particle by the FIB (Focused Ion Beam) milling method and observing the TEM image of the cut cross-section. Additionally, the “average porosity” of the lithium metal oxide can be obtained by deriving the average for 30 random secondary particles in the positive electrode active material powder in the above manner.

[0085] In addition, the above positive electrode active material has a BET specific surface area of ​​3.4 to 4.3 m 2 / g, more specifically 3.6 to 4.1 m 2 / g. If the BET specific surface area of ​​the positive electrode active material is too small, the density of the positive electrode active material may be too low, making it difficult to achieve high-energy positive electrode density, and particle cracks may occur during rolling. If the BET specific surface area of ​​the positive electrode active material is too large, the Al-containing coating layer may not be easily formed deep inside the secondary particle, so the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal, and the output characteristics may deteriorate. In this specification, the specific surface area can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0086] In addition, the positive electrode active material may have a tap density of 1.5 to 2.0 g / cc, and more specifically, 1.6 to 1.9 g / cc. If the tap density of the positive electrode active material is too small, it may be difficult to realize high-energy positive electrode density, and particle cracks may occur during rolling. If the tap density of the positive electrode active material is too large, the Al-containing coating layer may not be easily formed deep inside the secondary particle, so the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal, and the output characteristics may deteriorate. In the present specification, the tap density can be measured by a method generally used in the art for measuring the degree of filling of a sample per unit volume. For example, it can be the density (sample weight / volume) calculated through the change in volume after a measuring container containing a sample is mechanically dropped (tapped) from a fixed height a fixed number of times in accordance with the measuring device and method specified in ASTM B527.

[0087] In addition, the average aspect ratio of the primary particles may be 6.5 to 13, and more specifically, 6.8 to 12. If the average aspect ratio of the primary particles is too small, the porosity of the lithium metal oxide may become small, and the Al-containing coating layer may not be easily formed deep inside the secondary particles, so that the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal, and the output characteristics may deteriorate. If the average aspect ratio of the primary particles is too large, the density of the positive electrode active material may become too low, making it difficult to implement high-energy positive electrode density, and particle cracks may occur during rolling. In the present specification, the “aspect ratio” of the primary particles may mean the ratio of the length of the longest side to the shortest side in the primary particles. In addition, the average aspect ratio of a plurality of primary particles can be obtained by cutting the cathode active material using a FIB (Focused Ion Beam) milling method and then deriving the average aspect ratio for 30 random primary particles observed during TEM (Transmission Electron Microscope) image analysis of the cut cross-section.

[0088]

[0089] The lithium metal oxide according to the present invention can be more specifically represented by the following chemical formula 1.

[0090] [Chemical Formula 1]

[0091] Li 1+a (Ni x Co y Mn z M w ) 1-a O2

[0092] In the above chemical formula 1, 0.1≤a≤0.3, 0.2≤x≤0.4, 0≤y≤0.2, 0.5≤z≤0.75, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof.

[0093] In the lithium transition metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to 1+a, where a may be 0.1≤a≤0.3. If a is too small, the effect of improving capacity characteristics due to excessive lithium content may be minimal. However, if a is too large, the life characteristics may deteriorate due to decreased phase stability.

[0094] In the lithium transition metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 0.2≤x≤0.4. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction may increase too much, which may deteriorate the life characteristics. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction may decrease, which may deteriorate the capacity and output characteristics.

[0095] In the lithium transition metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0≤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.

[0096] In the lithium transition metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0.5≤z≤0.75. If the manganese content is too low, production costs may increase, the stability of the active material may decrease, and capacity may deteriorate. If the manganese content is too high, there may be a decrease in life characteristics due to excessive use of oxygen oxidation / reduction reactions and manganese dissolution problems.

[0097] In the lithium transition metal oxide of the above chemical formula 1, M, which is another doping element, may be included in a content corresponding to w, that is, 0≤w≤0.2. The content of the doping element may be appropriately selected and controlled to implement the doping effect within a range that does not deteriorate the electrochemical characteristics. At this time, M may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir, or a combination thereof.

[0098]

[0099] 2. Method for manufacturing positive electrode active material

[0100] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium metal oxide having a lithium and manganese excess composition in the form of secondary particles formed by agglomeration of a plurality of rod-shaped primary particles; and forming a coating layer containing Al on the lithium metal oxide by an atomic layer deposition method, wherein in the step of forming the coating layer containing Al, a first coating layer containing Al is formed to cover the entire surface of the secondary particles in the form of a film, a second coating layer containing Al is formed to cover at least a portion of the surfaces of the plurality of primary particles present in the core portion within the secondary particles in the form of a film, and a third coating layer containing Al is formed to cover at least a portion of the surfaces of the plurality of primary particles present in the shell portion within the secondary particles in the form of a film.

[0101] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described in detail step by step.

[0102]

[0103] First, a lithium metal oxide with a lithium and manganese excess composition in the form of secondary particles formed by the aggregation of multiple rod-shaped primary particles is prepared.

[0104] The lithium metal oxide may more specifically include a step of forming a metal-containing solution by mixing a nickel raw material, a manganese raw material, and a solvent; a step of forming a reaction solution by introducing the metal-containing solution, a complexing agent-containing solution, and a pH regulator-containing solution into a reactor; a step of forming a metal precursor by performing a co-precipitation reaction on the reaction solution; and a step of forming a lithium metal oxide by mixing the metal precursor and the lithium raw material and then calcining them.

[0105] First, a metal-containing solution is formed by mixing nickel raw material, manganese raw material, and solvent.

[0106] Of course, cobalt raw material may be further mixed in as needed during the above mixing.

[0107] 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.

[0108] 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.

[0109] The above cobalt 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 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.

[0110] The above solvent is not particularly limited as long as it can dissolve the above metal raw materials, but may be water, for example.

[0111] Next, the metal-containing solution, the complexing agent-containing solution, and the pH regulator-containing solution are introduced into the reactor to form a reaction solution.

[0112] The above complexing agent-containing solution performs the function 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.

[0113] The solution containing the pH adjusting agent acts as a precipitant or pH adjusting agent, and may include an alkaline compound such as a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. Meanwhile, the solution containing the pH adjusting agent may also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be evenly mixed with water may be used as the solvent.

[0114] At this time, the ratio of the molar rate of introduction of the complexing agent in the complexing agent-containing solution to the molar rate of introduction of the entire metal in the metal-containing solution (mol / hr) may be 0.5 to 1.5, and more specifically, 0.7 to 1.3. When the molar rate of introduction of the complexing agent to the molar rate of introduction of the entire metal satisfies the above range, the porosity of the metal precursor is appropriately controlled so that the average porosity of the final product, lithium metal oxide, can be easily obtained within the range according to the present invention.

[0115] The total metal concentration of the metal-containing solution may be 2.0 to 3.0 M (mol / L), more specifically, 2.2 to 2.8 M (mol / L). When the total metal concentration of the metal-containing solution satisfies the above range, the porosity of the metal precursor is appropriately controlled so that the average porosity of the final product, lithium metal oxide, can be easily obtained within the range according to the present invention.

[0116] In addition, the complexing agent concentration of the complexing agent-containing solution may be 12 to 16 M (mol / L), more specifically, 13 to 15 M (mol / L). When the complexing agent concentration of the complexing agent-containing solution satisfies the above range, the porosity of the metal precursor is appropriately controlled so that the average porosity of the final product, lithium metal oxide, can be easily obtained within the range according to the present invention.

[0117] Next, the above reaction solution is subjected to a co-precipitation reaction to form a metal precursor.

[0118] The above coprecipitation reaction can be carried out by stirring the reaction solution.

[0119] At this time, the coprecipitation reaction can be performed under an inert atmosphere such as nitrogen or argon.

[0120] Additionally, the co-precipitation reaction can be performed at a temperature of 30 to 70°C, and more specifically, at a temperature of 40 to 60°C.

[0121] Through the above process, nickel-manganese (cobalt-doped element) hydroxide particles are generated and precipitated within the reaction solution. The precipitated precursor particles can be separated, washed, and dried using conventional methods to obtain the precursor. The precursor may be a secondary particle formed by the agglomeration of primary particles.

[0122] 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.

[0123] Accordingly, the molar ratio of manganese (Mn) to metal (M) in the metal precursor (Mn / M) may be 0.5 to 0.75. In addition, the molar ratio of nickel (Ni) to metal (M) in the metal precursor (Ni / M) may be 0.2 to 0.4. In addition, the molar ratio of cobalt (Co) to metal (M) in the metal precursor (Co / M) may be 0.2 or less, more specifically, 0.1 or less, 0.05 or less, and the metal precursor may not contain cobalt. The technical significance of controlling the content of each metal is as described above, and thus is omitted.

[0124] Meanwhile, the doping element may also be doped during the preparation stage of the positive electrode active material precursor. In this case, the doping raw material may be additionally added to a transition metal-containing solution and a co-precipitation reaction may be performed to dope the metal precursor with the doping element.

[0125] Next, the metal precursor and lithium raw material are mixed and then calcined to form lithium metal oxide.

[0126] At this time, the lithium raw material is added so that the molar ratio of lithium to the total metal in the metal precursor (Li / M) is 1.1 to 1.5. As the amount of lithium raw material added is adjusted within the above range, the lithium content in the lithium metal oxide can be appropriately adjusted within the range according to the present invention.

[0127] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0128] The above calcination may be performed at a temperature of 800 to 900°C, and more specifically, at a temperature of 820 to 880°C. The calcination may be performed for 5 to 20 hours, and more specifically, for 7 to 15 hours. If the calcination temperature or time is too low or too short, the lithium transition metal oxide having a layered structure may not be properly formed, which may deteriorate the electrochemical properties of the active material. If the calcination temperature or time is too high or too long, crystal defects may occur due to overcalcination, which may deteriorate the electrochemical properties.

[0129] In the step of forming the lithium metal oxide, the firing may be performed in an oxygen atmosphere. As the firing proceeds in an oxygen atmosphere, sufficient oxidation of the metal precursor occurs during the firing process, thereby enabling better electrochemical properties to be realized.

[0130] The average porosity of the lithium metal oxide manufactured through the above series of processes may be 10 to 20%, and more specifically, 12 to 18%. By coating such porous lithium metal oxide with Al using the atomic layer deposition method described below, a positive electrode active material having a coating structure according to the present invention can be formed.

[0131]

[0132] Next, a step of forming a coating layer containing Al on the lithium metal oxide by an atomic layer deposition method is included, and the coating layer containing Al is formed.

[0133] At this time, the Al-containing coating layer may be formed by wrapping the entire surface of the secondary particle in a film form, a first coating layer containing Al, wrapping the surface of at least some of the plurality of primary particles present in the core portion within the secondary particle in a film form, a second coating layer containing Al, and wrapping the surface of at least some of the plurality of primary particles present in the shell portion within the secondary particle in a film form, and a third coating layer containing Al.

[0134] More specifically, the atomic layer deposition may be performed for 4 to 23 cycles, and more specifically, for 5 to 22 cycles. If the number of cycles for performing atomic layer deposition is too small, the average thickness of the formed coating layers (the first coating layer, the second coating layer, and the third coating layer) may become too thin overall, so that the effect of improving the life characteristics of the battery due to the improvement in the structural stability of the positive electrode active material may be minimal. If the number of cycles for performing atomic layer deposition is too large, the average thickness of the formed coating layers (the first coating layer, the second coating layer, and the third coating layer) may become too thick overall, so that lithium ion mobility may be inhibited, and thus the capacity or output characteristics of the battery may deteriorate.

[0135] At this time, one cycle of the atomic layer deposition may more specifically include a step of supplying an Al-containing gas onto the lithium metal oxide to adsorb the Al-containing gas onto the lithium metal oxide; and a step of supplying and reacting a reactant onto the lithium metal oxide on which the Al-containing gas is adsorbed.

[0136] The above Al-containing gas may be, for example, trimethoxy aluminum (Tri Methoxy Aluminum, TMA).

[0137] The above reactant may be, for example, water.

[0138] The formation of an Al-containing coating layer through the above atomic layer deposition method can proceed according to the following reaction scheme 1.

[0139] [Reaction Formula 1]

[0140] 2Al(CH3)3+ 3H2O = Al2O3+ 6CH4

[0141] The supply amount of the Al-containing gas may be 0.1 to 0.5 wt% based on the total weight of the lithium metal oxide, and more specifically, 0.15 to 0.4 wt%. When the supply amount of the Al-containing gas satisfies the above range, the amount of Al introduced per cycle is appropriately controlled, so that the Al content in the positive electrode active material can be appropriately obtained within the range according to the present invention.

[0142] The supply amount of the above reactant may be 0.05 to 0.16 wt% based on the total weight of the lithium metal oxide, and more specifically, 0.07 to 0.14 wt%. When the supply amount of the reactant satisfies the above range, the supply amount of the reactant per cycle is appropriately controlled, so that an Al-containing coating layer in the positive electrode active material can be appropriately obtained within the range according to the present invention.

[0143] The above atomic layer deposition can be performed at a pressure of 2.0 torr or less, and more specifically, at a pressure of 1.5 torr or 1.0 torr or less. Accordingly, the coating raw material can be well diffused and uniformly coated even within the cathode material, thereby providing an advantage in that the coating layer structure according to the present invention can be easily formed.

[0144]

[0145] 3. Cathode ray and lithium secondary battery

[0146] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0147] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and including the positive electrode active material described above.

[0148] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0149] The above-described positive electrode active material layer may include a binder and / or a conductive material together with the above-described positive electrode active material.

[0150] 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.

[0151] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, 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.

[0152] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

[0153] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on 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.

[0154] 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.

[0155] Alternatively, the positive electrode may be manufactured by casting the composition for forming the 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.

[0156]

[0157] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0158] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0159] The above lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0160] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The above binder and conductive material may be the same as those described above for the positive electrode.

[0165]

[0166] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0167]

[0168] The above electrolyte may include, but is 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.

[0169] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0170] 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.

[0171] 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.

[0172] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0173] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, 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).

[0174] Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0175] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0176]

[0177] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0178]

[0179] Manufacturing Example 1: Manufacturing of Precursor 1

[0180] (Precursor manufacturing)

[0181] Nickel-manganese hydroxide was prepared using a 20 L co-precipitation reactor.

[0182] (Formation of metal-containing solution) NiSO4·6H2O and MnSO4·H2O were dissolved in DI water to form a 2.5 M metal-containing solution. At this time, the molar ratio of Ni:Mn was set to 0.33:0.67.

[0183] (Co-precipitation) After, the metal-containing solution, 14M NH4(OH) aqueous solution as a complexing agent-containing solution, and NaOH aqueous solution as a pH adjusting agent-containing solution were added to the co-precipitation reactor to form a reaction solution, and the co-precipitation reaction was performed while stirring. At this time, the ratio of the NH4(OH) input mole rate (mol / hr) to the total metal input mole rate (mol / hr) into the co-precipitation reactor was 1. In addition, N2 was purged to prevent oxidation of metal ions during the co-precipitation reaction, and the temperature inside the co-precipitation reactor was maintained at 50°C.

[0184] The above coprecipitation reaction was carried out for a total of 22 hours to grow the average particle size (D50) of the metal precursor to 8 μm, and the coprecipitated metal precursor was filtered, washed with DI water, and vacuum dried in an oven at 100°C for 24 hours to obtain a metal precursor powder. The composition of the precursor 1 thus formed was Ni 0.33 Mn 0.67 It was (OH)2.

[0185]

[0186] Manufacturing Example 2: Manufacturing of Precursor 2

[0187] (Precursor manufacturing)

[0188] Nickel-manganese-cobalt hydroxide was prepared using a 20 L co-precipitation reactor.

[0189] (Formation of metal-containing solution) NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O were dissolved in DI water to form a 2.5 M metal-containing solution. At this time, the molar ratio of Ni:Co:Mn was set to 0.33:0.05:0.62.

[0190] (Co-precipitation) After, the metal-containing solution, 14M NH4(OH) aqueous solution as a complexing agent-containing solution, and NaOH aqueous solution as a pH adjusting agent-containing solution were added to the co-precipitation reactor to form a reaction solution, and the co-precipitation reaction was performed while stirring. At this time, the ratio of the NH4(OH) input mole rate (mol / hr) to the total metal input mole rate (mol / hr) into the co-precipitation reactor was 1. In addition, N2 was purged to prevent oxidation of metal ions during the co-precipitation reaction, and the temperature inside the co-precipitation reactor was maintained at 50°C.

[0191] The above coprecipitation reaction was carried out for a total of 22 hours to grow the average particle size (D50) of the metal precursor to 8 μm, and the coprecipitated metal precursor was filtered, washed with DI water, and vacuum dried in an oven at 100°C for 24 hours to obtain a metal precursor powder. The composition of the precursor 2 thus formed was Ni 0.33 Co 0.05 Mn 0.62 It was (OH)2.

[0192]

[0193] Manufacturing Example 3: Manufacturing of lithium metal oxide 1

[0194] Precursor 1 manufactured in Manufacturing Example 1 and lithium raw material LiOH·H2O were mixed using a mixer to form a mixture. Thereafter, the mixture was loaded into a refractory (Saggar) and placed in a box furnace. 180 LPH of air was injected into the box furnace, and the temperature was raised to 850°C for 5 hours, maintained at 850°C for 10 hours, and then cooled to room temperature for 5 hours, thereby forming lithium metal oxide.

[0195] Afterwards, the lithium metal oxide was induced to be crushed and then classified through 325 mesh to produce a lithium metal oxide positive electrode active material having an excess composition of lithium and manganese.

[0196] The composition of the lithium metal oxide 1 thus manufactured is Li 1.14 Ni 0.28 Mn 0.58 It was O2.

[0197]

[0198] Manufacturing Example 4: Manufacturing of lithium metal oxide 2

[0199] Precursor 2 manufactured in Manufacturing Example 2 and lithium raw material LiOH·H2O were mixed using a mixer to form a mixture. Thereafter, the mixture was loaded into a refractory (Saggar) and placed in a box furnace. 180 LPH of air was injected into the box furnace, and the temperature was raised to 850°C for 5 hours, maintained at 850°C for 10 hours, and then cooled to room temperature for 5 hours, thereby forming lithium metal oxide.

[0200] Afterwards, the lithium metal oxide was induced to be crushed and then classified through 325 mesh to produce a lithium metal oxide positive electrode active material having an excess composition of lithium and manganese.

[0201] The composition of the lithium metal oxide 2 thus manufactured is Li 1.14 Ni 0.28 Co 0.04 Mn 0.54 It was O2.

[0202]

[0203] Example 1

[0204] (1) Manufacturing of positive electrode active material

[0205] An atomic layer deposition (ALD) coating process was performed using the lithium metal oxide 1 manufactured in Manufacturing Example 3.

[0206] The coating reactor used a fluidized bed type, and low vacuum conditions were maintained to maintain the reaction temperature at 150℃ and the pressure inside the chamber at 0.8 Torr. Trimethylaluminum (TMA, Al(CH3)3) was used as an aluminum-containing gas as a precursor, and water (H2O) was used as a reactant.

[0207] N2 gas was used as a carrier gas and purge gas for precursors and reactants, and 80 sccm was injected into the reactor. The reaction sequence was as follows: after introducing the cathode material into the reactor, TMA was injected together with N2 gas for 0.02 seconds to cause chemisorption and saturation of the parent material, and then H2O was injected again for 0.02 seconds to induce a chemical reaction so that Al2O3 was ultimately present. The purging time was then set to 30 seconds.

[0208]

[0209] This series of processes is called 1 cycle, and a total of 10 cycles were performed.

[0210] At this time, the reaction formula of ALD that occurs is

[0211] 2Al(CH3)3+ 3H2O = Al2O3+ 6CH4

[0212] , and after the reaction, methane gas such as CH4 is released. The released methane gas is treated through a scrubber so that it is not released into the atmosphere.

[0213] (2) Lithium secondary battery manufacturing

[0214] The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (carbon black, denka black): binder (PVDF, KF1100) = 92.5:3.5:4 wt%, and the viscosity was adjusted so that the solid concentration was approximately 30% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 15 μm thick Al foil using a doctor blade, dried, and then rolled. At this time, the electrode loading amount was approximately 14 mg / cm 2 It was.

[0215] The electrolyte was 1M LiPF6in EC:EMC=3:7 (vol%), with 3.0 vol% FEC added to the total amount of the electrolyte, and a CR2032 coin cell was manufactured using a PP separator and a lithium negative electrode (200 μm, Honzo metal).

[0216]

[0217] Example 7

[0218] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that an atomic layer deposition (ALD) coating process was performed using lithium metal oxide 2 manufactured in Manufacturing Example 4.

[0219]

[0220] Comparative Example 1

[0221] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a separate coating process was not performed on the lithium metal oxide 1 manufactured in Manufacturing Example 3.

[0222]

[0223] Comparative Example 2

[0224] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a separate coating process was not performed on the lithium metal oxide 1 manufactured in Manufacturing Example 4.

[0225]

[0226] Comparative Example 3

[0227] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Al(OH)3 nanopowder having a size of 500 nm was dry-mixed into lithium metal oxide 1 manufactured in Manufacturing Example 3, and then Al was dry-coated by heat treatment at 500°C. At this time, the amount of Al(OH)3 nanopowder added was 0.5 mol% based on the total mole number of lithium metal oxide.

[0228]

[0229] Comparative Example 4

[0230] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Al(OH)3 nanopowder having a size of 500 nm was dry-mixed into lithium metal oxide 1 manufactured in Manufacturing Example 3, and then Al was dry-coated by heat treatment at 500°C. At this time, the amount of Al(OH)3 nanopowder added was 1 mol% based on the total mole number of lithium metal oxide.

[0231]

[0232] Comparative Example 5

[0233] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Al(OH)3 nanopowder having a size of 500 nm was dry-mixed into lithium metal oxide 2 manufactured in Manufacturing Example 4, and then Al was dry-coated by heat treatment at 500°C. At this time, the amount of Al(OH)3 nanopowder added was 0.5 mol% based on the total mole number of lithium metal oxide.

[0234]

[0235] Comparative Example 6

[0236] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Al(OH)3 nanopowder having a size of 500 nm was dry-mixed into lithium metal oxide 2 manufactured in Manufacturing Example 4, and then Al was dry-coated by heat treatment at 500°C. At this time, the amount of Al(OH)3 nanopowder added was 1 mol% based on the total mole number of lithium metal oxide.

[0237]

[0238] Other Examples and Reference Examples

[0239] As described in Table 1 below, positive electrode active materials and lithium secondary batteries were manufactured under different process conditions.

[0240]

[0241] Ammonia / metal salt input mol rate Non-anode material composition Coating process type 1 cycle TMA input amount (wt%, based on total weight of lithium metal oxide) 1 cycle reactant input amount (wt%, based on total weight of lithium metal oxide) ALD cycle number of cycles Comparison example 11 Li 1.14 Ni 0.28 Mn 0.58 O2----Comparative example 21Li 1.14 Ni 0.28 Co 0.04 Mn 0.54 O2----Example 11Li 1.14 Ni 0.28 Mn 0.58 O2ALD0.30.1110 Example 21 Same as above ... 1.14 Ni 0.28 Co 0.04 Mn 0.54 O2 homologous homologous 10 embodiment 71 homologous homologous 15 embodiment 81 homologous homologous 20 embodiment 91 homologous homologous 7 embodiment 101 homologous homologous 5 reference example 31 homologous homologous 25 reference example 41 homologous homologous 3 comparative example 31Li 1.14 Ni 0.28 Mn 0.58O2 dry Al(OH)3 / 0.5 mol%---Comparative Example 41 Dry Al(OH)3 / 1 mol%---Comparative Example 51 Li 1.14 Ni 0.28 Co 0.04 Mn 0.54 O2 dry Al(OH)3 / 0.5 mol%---Comparative example 61 dry Al(OH)3 / 1 mol%---

[0242]

[0243] Tables 2 and 3 below summarize the properties of positive electrode active materials and the electrochemical characteristics of lithium secondary batteries according to Experimental Examples 2 and 3 described below.

[0244] Active material properties Average thickness of the first coating layer (nm) Average thickness of the second coating layer (nm) Average thickness of the third coating layer (nm) Average thickness ratio of the first coating layer / second coating layer Average thickness ratio of the third coating layer / second coating layer Al element content (based on the total moles of lithium metal oxide, mol%) Average porosity (%) Specific surface area (m) 2 / g)Tap density (g / cc)Comparative example 1--- --143.871.68Comparative example 2--- --143.861.70Example 110.860.921.161.070.1143.821.72Example 21.51.341.431.121.070.15143.841.74Example 321.731.891.161.090.2143.811.67Example 40.70.630.671.111.060.07143.781.73Example 50.50.470.491.061.040.05143.771.71Reference example 12.52.232.431.121.090.25143.751.79 Reference Example 20.30.280.291.071.040.03143.851.68 Exemplary Example 610.880.941.141.070.1143.851.73 Exemplary Example 71.51.361.451.101.070.15143.841.69 Exemplary Example 821.771.921.131.080.2143.781.71 Exemplary Example 90.70.640.681.101.060.07143.811.77 Exemplary Example 100.50.470.491.061.040.05143.831.81Reference Example 32.52.242.41.121.090.25143.791.67Reference Example 40.30.280.291.071.040.03143.81.66Comparative Example 3-----0.5143.921.62Comparative Example 4-----1143.931.58Comparative Example 5-----0.5143.921.63Comparative Example 6-----1143.91.59

[0245] Battery PerformanceFormationDischarge Capacity (mAh / g)Initial Formation Efficiency (%)2nd CycleDischarge Capacity (mAh / g)Lifespan (50 times, %)Voltage Drop (mV @50 times)Resistance Increase Rate (50 times, %)Comparative Example 1268.589.8192.192.142.143.2Comparative Example 2269.389.9192.592.74242.1Example 1268.589.819198.733.219.3Example 2268.290.1190.799.233.319.2Example 326889.9189.399.533.119.1Example 4269.389.8191.598.633.419.3Example 5269.289.9191.898.333.319.8Reference Example 1263.788.2171.298.531.717.2Reference Example 2268.489.919293.137.237.2Example 6268.989.9191.598.932.518.6Example 7268.589.8191.49932.718.8Example 8268.289.7189.799.432.718.6Example 9269.590.1192.398.732.818.9Example 10269.490.1192.598.13319.1Reference Example 3263.988.3170.49932.317.4Reference Example 4268.889.9192.193.339.336.2Comparative Example 3267.489.4190.495.135.524,2Comparative Example 4264.588.5190.195.535.224.1Comparative Example 5267.789.5190.695.335.322.5Comparative Example 6264.888.6190.295.835.122.1

[0246]

[0247] Experimental Example 1: Evaluation of SEM, TEM, and EDS element mapping images of the positive electrode active material.

[0248] The SEM (Scanning Electron Microscope) image of the cross-section of the FIB (Focused Ion Beam) milled positive electrode active material manufactured according to Example 1 was observed, and is shown in Fig. 1. In addition, the EDS (Energy Dispersive Spectroscopy) mapping images for each element of Al, Ni, Co, and Mn were observed, and are shown in Figs. 2 to 5, for the cross-section of the FIB (Focused Ion Beam) milled positive electrode active material manufactured according to Example 1.

[0249] Referring to Figure 1, it was found that the positive electrode active material of Example 1 had a secondary particle shape formed by agglomeration of primary particles in the shape of rods.

[0250] Referring to FIGS. 2 to 5, it was confirmed that Al in the positive electrode active material of Example 1 was evenly coated on the entire surface of the secondary particle. In addition, it was confirmed that Al in the positive electrode active material of Example 1 penetrated not only into the shell region of the secondary particle but also into the core region, and was evenly coated on the surface of the primary particle existing in the shell region and core region of the secondary particle. In addition, it was confirmed that the Al coating element existed in a region very close to the center of the secondary particle, and existed in a region within a distance of about 0.5 μm from the center of the secondary particle.

[0251] Figure 6 is a TEM (transmission electron microscope) image of one internal primary particle after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 1. Referring to this, it can be confirmed that an Al coating layer is uniformly and thinly coated on the surface of the primary particle, and it can be confirmed that the Al compound is amorphous.

[0252] Fig. 7 is a graph showing the results of cross-sectional EDS (Energy Dispersive Spectroscopy) line scan concentration analysis of one internal primary particle after FIB (Focused Ion Beam) milling of a positive electrode active material manufactured according to Example 8. Referring to Fig. 7, it was confirmed that the Al element was concentrated and distributed on the surface of the primary particle, and through this, it was confirmed that the Al element was evenly coated on the surface of the primary particle.

[0253] Fig. 8 is a cross-sectional TEM image of the primary particles in the shell after FIB (Focused Ion Beam) milling of the positive electrode active material manufactured according to Example 3. Referring to Fig. 8, it can be confirmed that an Al coating layer with a thickness of about 2 nm was formed on the surface of the primary particles in the shell. Fig. 9 is a cross-sectional TEM image of the primary particles in the core after FIB (Focused Ion Beam) milling of the positive electrode active material manufactured according to Example 3. Referring to Fig. 9, it can be confirmed that an Al coating layer with a thickness of about 1.4 nm was formed on the surface of the primary particles in the core. In addition, it can be confirmed through these results that the thickness of the coating layer decreases from the surface of the secondary particle to the inside of the secondary particle.

[0254] Fig. 10 is a cross-sectional TEM image of a primary particle within a shell after FIB (Focused Ion Beam) milling after 100 charge / discharge cycles of a positive electrode active material manufactured according to Example 3. Referring to Fig. 10, it was confirmed that an Al coating layer with a thickness of about 1.8 nm was well maintained on the surface of the primary particle even after 100 charge / discharge cycles, thereby confirming that the coating layer according to the present invention can be well coated without structural deterioration even after the life cycle.

[0255]

[0256] Experimental Example 2: Evaluation of the properties of positive electrode active materials

[0257] (1) Evaluation of the average thickness of the first coating layer

[0258] The average thickness of the first coating layer was measured by the following method. First, the thickness of the first coating layer for one positive electrode active material secondary particle was calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 locations on the surface of the secondary particle, and calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the first coating layer was calculated by calculating the average of the first coating layer thicknesses measured by the same method as above for 20 random positive electrode active material secondary particles among the positive electrode active material powders.

[0259] (2) Evaluation of the average thickness of the second coating layer

[0260] The average thickness of the second coating layer was measured by the following method. First, the thickness of the second coating layer for one positive electrode active material secondary particle was calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 locations among the core portions within the secondary particle, and calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the second coating layer was calculated by calculating the average of the second coating layer thicknesses measured for 20 random positive electrode active material secondary particles among the positive electrode active material powders by the same method as above.

[0261] (3) Evaluation of the average thickness of the third coating layer

[0262] The average thickness of the third coating layer was measured using the following method. First, the thickness of the third coating layer for one positive electrode active material secondary particle was calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material secondary particle, randomly selecting 10 positions among the shell portions within the secondary particle, and calculating the average value of the coating layer thickness at the selected positions. Next, the average thickness of the third coating layer was calculated by calculating the average of the third coating layer thicknesses measured using the same method as above for 20 random positive electrode active material secondary particles among the positive electrode active material powders.

[0263] (4) Evaluation of average porosity of lithium metal oxide

[0264] The “porosity” for one lithium metal oxide secondary particle was obtained by cutting one secondary particle using the FIB (Focused Ion Beam) milling method, observing the TEM image of the cut cross-section, and converting the ratio of the total area of ​​the empty pore portion to the entire cross-sectional area of ​​the secondary particle into a percentage value. In addition, the “average porosity” of the lithium metal oxide was obtained by deriving the average for 30 random secondary particles in the positive electrode active material powder using the above method.

[0265] (5) Evaluation of the specific surface area of ​​positive electrode active material

[0266] The specific surface area of ​​lithium transition metal oxides was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0267] (6) Evaluation of the tap density of the positive electrode active material

[0268] Based on ASTM B527, 15 g of active material powder was placed in a 50 mL container and tapped at 3000 cycles @ 284 cycles / min to measure the packing density.

[0269] (7) Evaluation of the average aspect ratio of primary particles

[0270] The average aspect ratio of the primary particles was obtained by cutting the cathode active material using the FIB (Focused Ion Beam) milling method, and then analyzing the TEM (Transmission Electron Microscope) image of the cut cross-section to derive the average aspect ratio of 30 random primary particles observed. Here, the “aspect ratio” of the primary particle refers to the ratio of the length of the longest side to the shortest side within the primary particle.

[0271]

[0272] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0273] (1) Evaluation of initial formation discharge capacity and efficiency

[0274] After fabricating a lithium secondary battery half-cell, it was aged at 25°C for 10 hours, and then formed at 45°C to maximize the initial oxygen generation. At this time, to evaluate the initial capacity, 200 mAh / g was set as the 1C reference capacity, and the battery was charged to 4.65 V at a constant current of 0.1 C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a 10-minute rest time after charging, the battery was discharged to 2 V at a constant current of 0.1 C, with 200 mAh / g as the 1C reference capacity.

[0275] (2) 2nd cycle discharge capacity evaluation

[0276] After the above formation, the second charge and discharge test was conducted under 4.4 V charge and 2.5 V discharge conditions to evaluate the 2nd cycle discharge capacity.

[0277] (3) Evaluation of room temperature capacity retention rate (25℃, 50 cycles)

[0278] After fabricating a lithium secondary battery half-cell, it was charged to 4.6 V at a constant current of 0.5 C at 25°C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, it was discharged at a constant current of 0.2 C until it reached 2.5 V. From the second cycle onwards, 50 charge / discharge cycles were performed under the same charge / discharge cycle conditions as above, except that the end voltage was set to 4.4 V, and the capacity retention rate of the 50th cycle compared to the first cycle was calculated.

[0279] (4) Average voltage drop evaluation

[0280] When the voltage at the halfway point of the energy obtained by multiplying the discharge charge and voltage in the charge / discharge voltage range is called the average voltage, the difference between the initial average voltage and the average voltage after 50 cycles was defined as the average voltage drop and measured.

[0281] (5) Evaluation of room temperature resistance increase rate (25℃, 50 cycles)

[0282] After fabricating a lithium secondary battery half-cell, it was charged to 4.25 V at a constant current of 0.5 C at 25°C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, it was discharged at a constant current of 1.0 C until it reached 2.5 V. Under these charge-discharge cycle conditions, 50 charge-discharge cycles were performed, and the resistance increase rate of the 50th cycle compared to the first cycle was calculated.

[0283]

[0284] Referring to Tables 1 to 3, it was confirmed that, in the examples in which the process conditions according to the present invention were appropriately controlled, various physical properties, including the average thickness of the first coating layer, were appropriately obtained within the ranges specified in the present invention. Accordingly, it was confirmed that the battery's lifespan characteristics were very desirable in terms of capacity retention, average voltage drop, and resistance increase rate.

[0285] On the other hand, in the case of uncoated comparative examples 1 and 2, it was confirmed that the life characteristics of capacity retention rate, average voltage drop, and resistance increase rate were significantly deteriorated compared to the example.

[0286] In addition, in the case of Comparative Examples 3 to 7, where a conventional dry Al coating process was applied, the formation discharge capacity was somewhat lower than in the examples, resulting in deterioration of capacity characteristics, and it was confirmed that the life characteristic improvement effect of capacity retention rate, average voltage drop, and resistance increase rate was lower than in Comparative Examples 1 and 2.

[0287] In addition, in the case of Reference Examples 1 and 3 where the number of ALD cycles was too high, it was confirmed that the average thickness of the first coating layer was obtained too thick. As a result, the formation discharge capacity, initial formation efficiency, and 2 nd It was confirmed that the cycle discharge capacity was somewhat deteriorated compared to the examples.

[0288] In addition, in the case of Reference Examples 2 and 4, where the number of ALD cycles was too small, it was confirmed that the average thickness of the first coating layer, etc. was obtained too thin. As a result, it was confirmed that the life characteristic improvement effect of capacity retention rate, average voltage drop, and resistance increase rate was somewhat lower than that of the examples.

[0289] In addition, in the case of Reference Example 5, where the ALD performance temperature was too low, it was confirmed that the coating layer was not formed properly, resulting in the average thickness of the first coating layer being too thin. As a result, it was confirmed that the life characteristic improvement effect of capacity retention rate, average voltage drop, and resistance increase rate was somewhat lower than in the examples.

[0290] In addition, in the case of Reference Example 6, where the ALD performance temperature was too high, it was confirmed that the life characteristic improvement effect of capacity retention rate, average voltage drop, and resistance increase rate was somewhat lower than that of the example.

[0291]

[0292] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0293] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Lithium metal oxide in the form of secondary particles having a lithium and manganese excess composition and formed by the agglomeration of a plurality of rod-shaped primary particles; A first coating layer containing Al, which covers the entire surface of the secondary particle in the form of a film; A second coating layer containing Al, which covers the surface of at least some of the plurality of primary particles present in the core portion of the secondary particle in the form of a film; and A third coating layer containing Al, which covers the surface of at least some of the plurality of primary particles present in the shell portion of the secondary particle in the form of a film, Cathode active material for lithium secondary batteries.

2. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the second coating layer is also present in an area within a distance of 1 μm from the center of the secondary particle.

3. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the first coating layer is thicker than the average thickness of the third coating layer.

4. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the third coating layer is thicker than the average thickness of the second coating layer.

5. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average thickness of the first coating layer is 0.4 to 2.4 nm.

6. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average thickness of the second coating layer is 0.34 to 2.2 nm.

7. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average thickness of the third coating layer is 0.36 to 2.3 nm.

8. In paragraph 1, A cathode active material for a lithium secondary battery, wherein a ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) is 1.03 to 1.

2.

9. In paragraph 1, A cathode active material for a lithium secondary battery, wherein a ratio of the average thickness of the third coating layer to the average thickness of the second coating layer (third coating layer / second coating layer) is 1.01 to 1.

15.

10. In paragraph 1, The first coating layer, the second coating layer and the third coating layer contain an Al-containing compound, and the Al-containing compound contains Al as a main component. 2 O 3 A cathode active material for a lithium secondary battery comprising:

11. In paragraph 10, Above Al 2 O 3 is an amorphous cathode active material for lithium secondary batteries.

12. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the content of Al in the cathode active material is 0.04 to 0.23 mol% based on the total mole number of the lithium metal oxide.

13. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average porosity of the lithium metal oxide is 10 to 20%.

14. In paragraph 1, BET surface area is 3.4 to 4.3 m 2 / g cathode active material for lithium secondary batteries.

15. In paragraph 1, A cathode active material for a lithium secondary battery having a tap density of 1.5 to 2.0 g / cc.

16. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average aspect ratio of the primary particles is 6.5 to 13.

17. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a (Ni x Co y Mr z M w ) 1-a O 2 In the chemical formula 1, 0.1≤a≤0.3, 0.2≤x≤0.4, 0≤y≤0.2, 0.5≤z≤0.75, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Mo, Ru, Ir or a combination thereof.

18. A step for preparing a lithium metal oxide having a lithium and manganese excess composition in the form of secondary particles formed by agglomeration of a plurality of rod-shaped primary particles; and Comprising a step of forming a coating layer containing Al on the lithium metal oxide by an atomic layer deposition method, A method for manufacturing a cathode active material for a lithium secondary battery, wherein, in the step of forming the coating layer containing Al, a first coating layer containing Al is formed to wrap the entire surface of the secondary particle in the form of a film, at least some of the surfaces of a plurality of primary particles present in the core portion within the secondary particle are wrapped in the form of a film, a second coating layer containing Al and a third coating layer containing Al are formed to wrap at least some of the surfaces of a plurality of primary particles present in the shell portion within the secondary particle in the form of a film.

19. In Article 18, A method for producing a cathode active material for a lithium secondary battery, wherein the average porosity of the lithium metal oxide prepared above is 10 to 20%.

20. In paragraph 18, A method for manufacturing a cathode active material for a lithium secondary battery, wherein the above atomic layer deposition is performed for 4 to 23 cycles.

21. A cathode for a lithium secondary battery comprising a cathode active material according to Article 1.

22. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to Article 22.

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