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 secondary particles formed by aggregation of a plurality of primary particles; a first coating layer which contains B and covers, in the form of a film, the entire surface of each secondary particle; and a second coating layer which contains Al and covers, in the form of a film, the entire surface of the first coating layer.

Description

A positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same

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

[0002]

[0003] As the application range of lithium-ion batteries expands from small electronic devices to electric vehicles and power storage devices, there is a growing demand for cathode materials with excellent high energy density and high power characteristics.

[0004] In this regard, lithium and manganese-excess layered lithium metal oxides are attracting attention as next-generation cathode active material candidates due to their very high capacity, such as a charge capacity of 300 mAh / g and a discharge capacity of 250 mAh / g or more, and research on this is currently being actively conducted worldwide.

[0005] However, since lithium and manganese-excess lithium metal oxides utilize oxygen oxidation-reduction reactions in addition to transition metals, oxygen on the surface or within the bulk is prone to evolving into oxygen gas. Consequently, dense, non-reactive, or low-reactivity spinel / rock salt structures can easily form within the particles, leading to increased structural instability. This structural instability poses a problem that causes overall degradation of lifespan characteristics as cycles progress, including reduced capacity retention, voltage decay, increased resistance growth, and gas evolution.

[0006] To address this, technology development involving coating lithium and manganese-excess lithium metal oxides is underway; however, while this improves lifespan characteristics, it has limitations in that capacity characteristics are degraded due to reduced lithium ion mobility.

[0007]

[0008] Accordingly, one objective of the present invention is to provide a positive electrode active material for a lithium secondary battery having a lithium metal oxide composition with an excess of lithium and manganese, which can improve overall lifespan characteristics such as improved capacity retention rate, reduced voltage drop, and reduced resistance increase rate as cycles progress, while simultaneously improving capacity characteristics, a method for manufacturing the same, and a lithium secondary battery including the same.

[0009]

[0010] This application claims priority to Korean Patent Application No. 10-2024-0155128 filed on November 5, 2024, the contents of said priority application may be included for reference to this application.

[0011]

[0012] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising: a lithium metal oxide in the form of secondary particles formed by aggregating a plurality of primary particles having an excess composition of lithium and manganese; a first coating layer containing B that covers the entire surface of the secondary particles in the form of a film; and a second coating layer containing Al that covers the entire surface of the first coating layer in the form of a film.

[0013] It may include a third coating layer containing Al or B that wraps the surface of at least some of the plurality of primary particles present inside the secondary particle in the form of a film.

[0014] The above third coating layer may also exist in an area within a distance of (3 / 4)R from the center of the secondary particle, where R is the distance from the center of the secondary particle to the surface.

[0015] The above third coating layer may also exist in an area within a distance of 1 μm from the center of the secondary particle.

[0016] The average thickness of the first coating layer may be 0.17 to 0.85 nm.

[0017] The average thickness of the second coating layer may be 0.3 to 1.15 nm.

[0018] The ratio of the average thickness of the second coating layer to the average thickness of the first coating layer (second coating layer / first coating layer) may be 0.8 to 3.5.

[0019] The first coating layer above includes a B-containing compound, and the B-containing compound may include B2O3 as a main component.

[0020] The second coating layer above includes an Al-containing compound, and the Al-containing compound may include Al2O3 as a main component.

[0021] The above B2O3 may be amorphous.

[0022] The above Al2O3 may be amorphous.

[0023] The content of B in the above positive active material may be 0.005 to 0.026 mol% based on the total molar amount of lithium metal oxide.

[0024] The content of Al in the above positive active material may be 0.006 to 0.023 mol% based on the total molar amount of lithium metal oxide.

[0025] The average porosity of the lithium metal oxide above may be 10 to 20%.

[0026] The above-mentioned positive active material has a BET specific surface area of ​​2.5 to 3.5 m² 2 It can be / g.

[0027] The above positive active material may have a tap density of 1.6 to 2.2 g / cc.

[0028] The above primary particles may have an average aspect ratio of 2.4 to 3.5.

[0029] The above lithium metal oxide can be represented by the following chemical formula 1.

[0030] [Chemical Formula 1]

[0031] Li 1+a (Nix Co y Mn z M w ) 1-a O2

[0032] 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.

[0033]

[0034] 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 an excess composition of lithium and manganese in the form of secondary particles formed by the aggregation of a plurality of primary particles; forming a first coating layer in the form of a film containing B on the lithium metal oxide by an atomic layer deposition (ALD) method; and forming a second coating layer in the form of a film containing Al on the first coating layer by an atomic layer deposition method.

[0035] In the step of forming the first coating layer or the step of forming the second coating layer, a third coating layer containing Al or B may be formed by wrapping the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film.

[0036] The average porosity of the prepared lithium metal oxide can be 10 to 20%.

[0037] One cycle of atomic layer deposition in the step of forming the first coating layer may include the step of supplying and reacting a B-containing gas and a first reactant on a lithium metal oxide.

[0038] One cycle of atomic layer deposition in the step of forming the second coating layer may include the step of supplying and reacting an Al-containing gas and a second reactant on the first coating layer.

[0039] In the step of forming the first coating layer, atomic layer deposition can be performed in 4 to 17 cycles.

[0040] In the step of forming the second coating layer, atomic layer deposition can be performed in 3 to 11 cycles.

[0041]

[0042] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0043] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for the lithium secondary battery.

[0044]

[0045] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is coated with a first coating layer containing B that covers the entire surface of a lithium metal oxide secondary particle having an excess composition of lithium and manganese, and a second coating layer containing Al that covers the entire surface of the first coating layer. Accordingly, lifespan characteristics such as improved capacity retention rate, reduced voltage drop, and reduced resistance increase rate during cycle progression are generally improved, and at the same time, capacity characteristics can be improved.

[0046]

[0047] Figure 1 is a Bright Field Scanning Transmission Electron Microscopy (BF-STEM) image of a secondary particle cross-section after Focused Ion Beam (FIB) milling of the positive electrode active material prepared according to Example 1.

[0048] Figure 2 is an Energy Dispersive Spectroscopy (EDS) element mapping image of the Al element in the upper marked area of ​​the image in Figure 1.

[0049] Figure 3 is an Energy Dispersive Spectroscopy (EDS) elemental mapping image of the Al element in the lower marked area of ​​the image in Figure 1.

[0050] Figure 4 is an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the upper display area of ​​the image in Figure 1.

[0051] Figure 5 is an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the lower marked area of ​​the image in Figure 1.

[0052] Figure 6 is a TEM (transmission electron microscope) image of primary particles inside the positive electrode active material according to Experimental Example 2.

[0053] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0054] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0055] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0056] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0057] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0058] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0059] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0060]

[0061] 1. Cathode active material

[0062] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium transition metal oxide having an excess composition of lithium and manganese. Although the lithium transition metal oxide with an excess composition of lithium and manganese has a low nickel content, it can undergo oxidation / reduction reactions of anions (oxygen) as well as transition metals during battery operation. Additionally, since excess lithium may exist in the transition metal layer in addition to the lithium layer, the insertion and extraction efficiency of lithium ions can be increased. As a result, the initial discharge capacity is 250 mAh / g or higher, and the capacity characteristics can be significantly improved compared to a conventional NCM composition positive electrode material. Furthermore, it offers excellent economic efficiency as it allows for a reduction in the content of relatively expensive nickel and cobalt and an increase in the content of inexpensive manganese.

[0063] More specifically, the lithium metal oxide may have a molar ratio of lithium to the lithium metal oxide of 1.1 to 1.3. As the lithium content increases, the amount of lithium involved in the insertion and extraction of lithium ions increases, thereby improving capacity characteristics. However, if the lithium content becomes too high, problems with phase stability may occur due to excessive oxygen oxidation / reduction reactions, which may lead to a decrease in lifespan characteristics.

[0064] In addition, the molar ratio of nickel to the total metal excluding lithium in the lithium metal oxide may be 0.2 to 0.4. When the nickel content satisfies the above range, the capacity, output, and lifespan characteristics of the battery can be more preferably realized. If the nickel content is too low, the amount of oxygen oxidation / reduction reaction increases too much, and the lifespan characteristics may deteriorate. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, and the capacity and output characteristics may deteriorate.

[0065] In addition, the above 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 the excess manganese content may be negligible. If the manganese content is too high, lifespan characteristics deteriorate due to the excessive use of oxygen in oxidation / reduction reactions, and there may be a problem of manganese leaching.

[0066] In addition, the lithium metal oxide may have a molar ratio of cobalt to the total metal excluding lithium of 0.2 or less, more specifically 0.1 or 0.05 or less, and may not contain cobalt. Cobalt is usually added in a predetermined amount to improve the lifespan or output characteristics of a battery, but there is a problem with its high cost. Since the lithium metal oxide according to the present invention includes a coating layer containing both Al and B, good lifespan or output characteristics can be achieved even if the cobalt content is reduced to the above range. Accordingly, the present invention can simultaneously achieve economic efficiency and product quality.

[0067] Meanwhile, the lithium metal oxide according to the present invention is in the form of secondary particles formed by the aggregation of a plurality of primary particles. In this specification, “primary particle” refers to a minimum particle unit distinguished as a single mass when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may consist of a single crystal grain or a plurality of crystal grains. In this specification, “crystal grain” refers to a distinct region in which atoms within the primary particle form a lattice structure in a certain direction.

[0068] At this time, the primary particle may have a rod shape. In this specification, “rod shape” is a term used to distinguish it from spherical shape, and refers to a particle having a shape that is closer to an elongated rod shape rather than a sphere, with an aspect ratio of 1.6 or higher. Meanwhile, in this specification, “aspect ratio” refers to the ratio of the length of the longest side to the shortest side within the primary particle. The rod-shaped primary particle can form a porous lithium metal oxide structure.

[0069] In addition, the primary particle may have an orientation in which the long axis of the primary particle faces from the center of the secondary particle toward the surface. By having such an orientation of the primary particle, lithium ion mobility is improved, and capacity or output characteristics can be realized more preferably.

[0070] However, since the lithium and manganese-excess lithium metal oxides of the above composition utilize oxygen oxidation-reduction reactions in addition to transition metals, oxygen on the surface or within the bulk is prone to evolving into oxygen gas. Consequently, dense, non-reactive, or low-reactivity spinel / rock salt structures can easily form within the particles, leading to increased structural instability. This structural instability causes problems such as overall degradation of lifespan characteristics as the cycle progresses, including reduced capacity retention, voltage decay, increased resistance growth rate, and gas evolution.

[0071] Accordingly, the positive electrode active material according to the present invention is coated with a first coating layer containing B using an atomic layer deposition (ALD) coating method with a B-containing gas on a porous lithium metal oxide having an excess composition of lithium and manganese. Additionally, a second coating layer containing Al is subsequently coated on the first coating layer using an atomic layer deposition (ALD) coating method with an Al-containing gas.

[0072] At this time, the first coating layer and the second coating layer have a sequential stacked structure, and since they are coated by an atomic layer deposition method, they may be a full conformal coating layer in the form of a film having a very thin thickness at the atomic level and good thickness homogeneity. Accordingly, the structural stability of the lithium metal oxide is improved, thereby enhancing lifespan characteristics and, at the same time, capacity characteristics can be improved. More detailed information regarding the atomic layer deposition coating method will be explained in the manufacturing method described later.

[0073] More specifically, the positive active material according to the present invention covers the entire surface of the secondary particle in the form of a film and includes a first coating layer containing B.

[0074] By including B in the first coating layer, the effect of increasing the interslab thickness of the layered structure of the lithium metal oxide can be realized, thereby improving lithium ion mobility and enhancing capacity characteristics, and the lifespan characteristics can be improved due to the structural stabilization effect of the coating itself.

[0075] At this time, the first coating layer is not an island-type coating layer that discontinuously and sparsely covers the surface of the secondary particles, but a conformal-type coating layer that uniformly covers the entire surface. In addition, the first coating layer has good thickness uniformity and can have a film-like appearance. Accordingly, the effect of improving capacity and lifespan characteristics due to the coating of the first coating layer can be more preferably realized.

[0076] In addition, the positive active material according to the present invention comprises a second coating layer containing Al that covers the entire surface of the first coating layer in the form of a film.

[0077] Since the second coating layer contains Al, the surface structure of the lithium metal oxide is stabilized, and the lifespan characteristics can be improved.

[0078] The second coating layer is also a conformal type coating layer, similar to the first coating layer, and may have a film-like appearance. Accordingly, the effect of improving lifespan characteristics due to the application of the second coating layer can be more preferably realized.

[0079] That is, the cathode active material according to the present invention comprises a coating layer having a structure in which a first coating layer containing B and a second coating layer containing Al are sequentially stacked, thereby maximizing the effect of each element coating and allowing capacity and lifespan characteristics to be desirablely improved simultaneously. If only B is coated or only Al is coated, the effect of improving capacity and lifespan characteristics may deteriorate.

[0080] In addition, the positive electrode active material according to the present invention may include, in addition to the first coating layer and the second coating layer, a third coating layer containing Al or B that wraps the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film.

[0081] That is, in the cathode active material according to the present invention, an Al or B-containing coating layer can be uniformly formed with a thin thickness not only on the surface of the secondary particles but also deep into the primary particles located inside the secondary particles. This structure can be obtained by applying an Atomic Layer Deposition (ALD) coating method using an Al-containing gas and a B-containing gas to a porous lithium transition metal oxide with an excess composition of lithium and manganese. In this way, by coating not only the surface of the secondary particles but also a significant number of primary particles located inside the secondary particles with a coating layer, the effect of improving capacity and lifespan characteristics due to the coating can be more preferably realized.

[0082] As the coating layer is formed deep within the primary particle inside the secondary particle in this manner, the third coating layer may exist within a (3 / 4)R distance from the center of the secondary particle, and more specifically, within a (1 / 2)R distance or a (1 / 4)R distance.

[0083] Specifically, the third coating layer may exist in an area within a distance of 1 μm from the center of the secondary particle, and more specifically, may exist in an area within a distance of 0.5 or 0.3 μm.

[0084] As the maximum depth position where the third coating layer exists is closer to the center of the secondary particle as described above, the effect of improving lithium ion mobility and structural stabilization for the internal primary particle is maximized, so that the effect of improving capacity and lifespan characteristics due to the coating can be more preferably realized.

[0085] In addition, the average thickness of the first coating layer may be 0.17 to 0.85 nm, and more specifically, 0.25 to 0.7 nm. When the average thickness of the first coating layer satisfies the above range, the coating is applied to an appropriate degree, preventing the acting as a resistance layer due to excessive coating, thereby allowing the effect of improving capacity and lifespan characteristics due to the coating to be more preferably realized.

[0086] 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 a single secondary positive material particle can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the secondary positive material particle, randomly selecting 20 locations on the surface of the secondary particle, and obtaining the average value of the B-containing coating layer thickness at the selected locations. Next, the average thickness of the first coating layer can be calculated by obtaining the average of the first coating layer thicknesses measured in the same way as above for 20 random secondary positive material particles among the positive material powder.

[0087] In addition, the average thickness of the second coating layer may be 0.3 to 1.15 nm, and more specifically, 0.45 to 1.0 nm. When the average thickness of the second coating layer satisfies the above range, the coating is applied to an appropriate degree, preventing it from acting as a resistance layer due to excessive coating, thereby allowing the effect of improving capacity and lifespan characteristics due to the coating to be implemented more preferably.

[0088] 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 a single secondary particle of the positive active material can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the secondary particle of the positive active material, randomly selecting 20 locations on the surface of the secondary particle, and obtaining the average value of the Al-containing coating layer thickness at the selected locations. Next, the average thickness of the second coating layer can be calculated by obtaining the average of the second coating layer thicknesses measured in the same way as above for 20 randomly selected secondary particles of the positive active material among the positive active material powder.

[0089] In addition, the ratio of the average thickness of the second coating layer to the average thickness of the first coating layer (second coating layer / first coating layer) may be 0.8 to 3.5, and more specifically, 1.0 to 2.5. When the ratio of the average thickness between the first coating layer and the second coating layer satisfies the above range, the relative coating content of Al and B is optimized, and the effect of improving capacity and lifespan characteristics according to the coating can be more preferably realized.

[0090] In addition, the content of B in the positive electrode active material may be 0.005 to 0.026 mol% based on the total molar amount of lithium metal oxide, and more specifically, 0.007 to 0.022 mol%. When the content of B in the positive electrode active material satisfies the above range, B coating is applied in an appropriate amount, preventing the action of a resistive layer due to excessive coating, thereby allowing the effect of improving capacity and lifespan characteristics due to coating to be more preferably realized.

[0091] In addition, the content of Al in the positive electrode active material may be 0.006 to 0.023 mol% based on the total molar amount of lithium metal oxide, and more specifically, 0.009 to 0.020 mol%. When the content of Al in the positive electrode active material satisfies the above range, Al coating is applied in an appropriate amount, preventing it from acting as a resistive layer due to excessive coating, thereby allowing the effect of improving capacity and lifespan characteristics due to coating to be more preferably realized.

[0092] Meanwhile, the content of Al or B in the above-mentioned positive electrode active material can be measured by obtaining the weight% of Al or B through ICP (Inductively Coupled Plasma Analysis) component analysis of the positive electrode active material and converting it into a mol% relative to the total molar amount of lithium metal oxide.

[0093] In addition, the first coating layer comprises a B-containing compound, and the B-containing compound may include B2O3 as a main component. In this case, the B2O3 may be amorphous. As the coating layer contains amorphous B2O3, the energy barrier for lithium ion movement is lower compared to a crystalline structure, thereby increasing lithium ion mobility and enabling more desirable capacity characteristics. Additionally, structural stability is provided, allowing for more desirable lifespan characteristics.

[0094] In addition, the second coating layer comprises an Al-containing compound, and the Al-containing compound may include Al2O3 as a main component. In this case, the Al2O3 may be amorphous. As the coating layer contains amorphous Al2O3, the energy barrier for lithium ion movement is lower compared to a crystalline structure, thereby increasing lithium ion mobility and enabling more desirable capacity characteristics. Additionally, structural stability is imparted, allowing for more desirable lifespan characteristics.

[0095]

[0096] That is, the effect of improving capacity and lifespan characteristics according to the coating of the present invention is attributed to the coating itself in a sequential stacking method of B and Al, and can be further maximized by the amorphousness of the Al-containing compound and the B-containing compound within the coating layer.

[0097] Meanwhile, in this specification, “main component” may mean that it accounts for about 70% by weight or more of the total weight of the Al-containing compound or B-containing compound in the coating layer.

[0098] In addition, the composition of Al-containing compounds or B-containing compounds can be confirmed through TEM-EDX analysis, and the amorphous structure can be confirmed through TEM image analysis.

[0099] Meanwhile, in order for the coating layer structure according to the present invention to be easily formed, the physical properties of the lithium metal oxide or the positive electrode active material are also important, and this will be explained.

[0100] 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 coating layer may not be easily formed to the deep internal regions of the secondary particles, so the effect of improving lifespan and capacity characteristics due to the coating may be negligible, and output characteristics may be degraded. If the average porosity of the lithium metal oxide is too large, the density of the positive active material becomes too low, making it difficult to achieve high-energy positive density, and particle cracks may occur during rolling.

[0101] Meanwhile, the “porosity” of a single lithium metal oxide secondary particle can be derived by cutting a single secondary particle using the FIB (Focused Ion Beam) milling method and then observing a TEM image of the cut cross-section, converting the ratio of the total area of ​​the hollow void portion to the total cross-sectional area of ​​the secondary particle into a percentage value. In addition, the “average porosity” of the lithium metal oxide can be obtained by calculating the average of 30 randomly selected secondary particles within the cathode active material powder using the above method.

[0102] In addition, the above-mentioned positive active material has a BET specific surface area of ​​2.5 to 3.5 m² 2 It can be / g, and more specifically, 2.6 to 3.1 m 2 / g. If the BET specific surface area of ​​the positive active material is too small, the density of the positive active material becomes too low, making it difficult to achieve high-energy positive density, and particle cracking may occur during rolling. If the BET specific surface area of ​​the positive active material is too large, the coating layer may not easily form deep within the secondary particles, so the effect of improving lifespan and capacity characteristics due to the coating may be negligible.

[0103] In this specification, the specific surface area can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0104] In addition, the above-mentioned positive active material may have a tap density of 1.6 to 2.2 g / cc, and more specifically, 1.7 to 2.0 g / cc. If the tap density of the positive active material is too low, it may be difficult to achieve high-energy positive density, and particle cracking may occur during rolling. If the tap density of the positive active material is too high, the coating layer may not be easily formed to the deep internal region of the secondary particle, so the effect of improving lifespan and capacity characteristics due to the coating may be negligible.

[0105] In this specification, tap density may be measured by a method commonly used in the art to measure the degree of sample filling per unit volume. For example, it may be the density (sample weight / volume) calculated from the change in volume after mechanically tapping a measuring container containing a sample from a certain height a predetermined number of times, in accordance with the measuring instruments and methods specified in ASTM B527.

[0106] In addition, the primary particles may have an average aspect ratio of 2.4 to 3.5, and more specifically, 2.6 to 3.2. If the average aspect ratio of the primary particles is too small, the porosity of the lithium metal oxide decreases, and the coating layer may not be easily formed in the deep internal regions of the secondary particles, so the effect of improving lifespan and capacity characteristics due to the coating may be negligible, and output characteristics may be degraded. If the average aspect ratio of the primary particles is too large, the density of the positive active material becomes too low, making it difficult to achieve high-energy positive density, and particle cracks may occur during rolling.

[0107] In this specification, the “aspect ratio” of a primary particle may refer to the ratio of the length of the longest side to the shortest side within the primary particle. Additionally, the average aspect ratio of a plurality of primary particles can be obtained by deriving the average aspect ratio of 30 randomly selected primary particles observed during TEM (Transmission Electron Microscope) image analysis of the cut cross-section after cutting the cathode active material using the FIB (Focused Ion Beam) milling method.

[0108]

[0109] The lithium metal oxide according to the present invention can be represented more specifically by the following chemical formula 1.

[0110] [Chemical Formula 1]

[0111] Li 1+a (Ni x Co y Mn z M w )1-a O2

[0112] 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.

[0113] In the lithium transition metal oxide of Chemical Formula 1 above, 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 the excess lithium content may be negligible. However, if a is too large, lifespan characteristics may deteriorate due to reduced phase stability.

[0114] In the lithium transition metal oxide of Chemical Formula 1 above, 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 increases too much, and the lifespan characteristics may deteriorate. If the nickel content is too high, the amount of oxygen oxidation / reduction reaction decreases, and the capacity and output characteristics may deteriorate.

[0115] In the lithium transition metal oxide of Chemical Formula 1 above, 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 cost of the raw material increases overall and the reversible capacity may decrease.

[0116] In the lithium transition metal oxide of Chemical Formula 1 above, manganese may be included in an amount corresponding to z, i.e., 0.5≤z≤0.75. If the manganese content is too low, the production cost may increase, the stability of the active material may decrease, and the capacity may deteriorate. If the manganese content is too high, there may be a decrease in lifespan characteristics due to excessive use of oxygen oxidation / reduction reactions and a problem with manganese leaching.

[0117] In the lithium transition metal oxide of Chemical Formula 1 above, the other doping element M may be included in an amount corresponding to w, i.e., 0≤w≤0.2. The content of the doping element may be appropriately selected and controlled to achieve a doping effect within a range that does not degrade electrochemical properties. 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.

[0118]

[0119] 2. Method for manufacturing positive electrode active material

[0120] 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 an excess composition of lithium and manganese in the form of secondary particles formed by the aggregation of a plurality of primary particles; forming a first coating layer in the form of a film containing B on the lithium metal oxide by an atomic layer deposition (ALD) method; and forming a second coating layer in the form of a film containing Al on the first coating layer by an atomic layer deposition method.

[0121] 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.

[0122]

[0123] First, a lithium metal oxide with an excess composition of lithium and manganese in the form of secondary particles formed by the aggregation of multiple primary particles (rod-shaped) is prepared.

[0124] More specifically, the lithium metal oxide may comprise the steps of: mixing a nickel raw material, a manganese raw material, and a solvent to form a metal-containing solution; introducing the metal-containing solution, a complexing agent-containing solution, and a pH regulator-containing solution into a reactor to form a reaction solution; co-precipitating the reaction solution to form a metal precursor; and mixing the metal precursor and the lithium raw material, and then calcining to form a lithium metal oxide.

[0125] First, nickel raw material, manganese raw material, and a solvent are mixed to form a metal-containing solution.

[0126] Of course, additional cobalt raw materials may be mixed in as needed during the above mixing process.

[0127] The above nickel raw material is not particularly limited as long as it is used in the industry for manufacturing a cathode active material precursor. For example, the above nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0128] The above manganese raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0129] The above-mentioned cobalt raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above-mentioned cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO₄ 4, It may be CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof, but is not limited thereto.

[0130] The above solvent is not particularly limited as long as it is capable of dissolving the metal raw materials, but, for example, it may be water.

[0131] Next, the metal-containing solution, the complexing agent-containing solution, and the pH adjuster-containing solution are introduced into a reactor to form a reaction solution.

[0132] The above-mentioned complexing agent-containing solution performs the role of forming a complex, and may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent, but is not limited thereto. Meanwhile, the above-mentioned complexing agent-containing solution may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol, etc.) may be used as the solvent.

[0133] The above-mentioned solution containing a pH adjuster performs the role of a precipitating agent or a pH adjuster and may include alkali compounds such as hydroxides of alkali metals or alkaline earth metals like NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Meanwhile, the above-mentioned solution containing a pH adjuster may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol) may be used as the solvent.

[0134] 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 total 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 relative to the molar rate of introduction of the total 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.

[0135] The total metal concentration of the metal-containing solution may be 2.0 to 3.0 M (mol / L), and 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, a lithium metal oxide, can be easily obtained within the range according to the present invention.

[0136] In addition, the concentration of the complexing agent in the complexing agent-containing solution may be 12 to 16 M (mol / L), and more specifically, 13 to 15 M (mol / L). When the concentration of the complexing agent in 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, the lithium metal oxide, can be easily obtained within the range according to the present invention.

[0137] Next, the above reaction solution is subjected to a co-precipitation reaction to form a metal precursor.

[0138] The above co-precipitation reaction can be carried out by stirring the reaction solution.

[0139] At this time, the above co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0140] In addition, the above co-precipitation reaction can be carried out at a temperature of 30 to 70°C, and more specifically, at a temperature of 40 to 60°C.

[0141] By the above process, particles of nickel-manganese (-cobalt-doping element) hydroxide are generated and precipitated in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed, and dried to obtain a precursor. The precursor may be a secondary particle formed by the aggregation of primary particles.

[0142] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by adjusting the concentrations of the nickel raw material, cobalt raw material, and manganese raw material.

[0143] Accordingly, the molar ratio (Mn / M) of manganese (Mn) to the metal (M) in the metal precursor may be 0.5 to 0.75. Additionally, the molar ratio (Ni / M) of nickel (Ni) to the metal (M) in the metal precursor may be 0.2 to 0.4. Furthermore, the molar ratio (Co / M) of cobalt (Co) to the metal (M) in the metal precursor 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 is therefore omitted.

[0144] Meanwhile, the doping element may also be doped during the preparation stage of the anode active material precursor. In this case, the doping element can be doped into the metal precursor by additionally adding a doping raw material to a transition metal-containing solution and causing a co-precipitation reaction.

[0145] Next, the above metal precursor and lithium raw material are mixed and then calcined to form a lithium metal oxide.

[0146] At this time, a lithium raw material is introduced such that the molar ratio (Li / M) of lithium to the total metal in the metal precursor is 1.1 to 1.5. As the amount of lithium raw material introduced is controlled to the above range, the lithium content in the lithium metal oxide can be appropriately controlled to the range according to the present invention.

[0147] The above lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the above lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof, but is not limited thereto.

[0148] The above calcination can be performed at 800 to 900°C, and more specifically at a temperature of 820 to 880°C. The above calcination can be performed for 5 to 20 hours, and more specifically at 7 to 15 hours. If the calcination temperature or time is too low or too short, the layered structure of the lithium transition metal oxide is not formed well, which may result in a decrease in 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 over-calcination, which may result in a decrease in electrochemical properties.

[0149] In the step of forming the lithium metal oxide, the calcination may be performed in an oxygen atmosphere. As calcination proceeds in an oxygen atmosphere, sufficient oxidation of the metal precursor occurs during the calcination process, allowing for better electrochemical properties to be realized.

[0150] The average porosity of the lithium metal oxide prepared through the above series of processes may be 10 to 20%, and more specifically, 12 to 18%. By coating this porous lithium metal oxide with Al and B using the atomic layer deposition method described later, an Al or B-containing coating layer can be uniformly formed with a thin thickness not only on the surface of the secondary particles but also deep into the primary particles existing inside the secondary particles.

[0151]

[0152]

[0153] Next, a first coating layer in the form of a film containing B is formed on the lithium metal oxide using an atomic layer deposition (ALD) method.

[0154] At this time, the first coating layer can be coated in a conformal form that covers the entire surface of the lithium metal oxide. This is due to a vapor-phase atomic layer deposition coating method using a B-containing gas.

[0155] More specifically, in the step of forming the first coating layer, one cycle of atomic layer deposition may include the step of supplying and reacting a B-containing gas and a first reactant on a lithium metal oxide.

[0156] The above B-containing gas may be, for example, boron tribromide (BBr3).

[0157] The first reactant above may be, for example, water (H2O).

[0158] The above reaction can be carried out by the following reaction scheme 1.

[0159] [Reaction Equation 1]

[0160] 2BBr3 + 3H2O = B2O3 + 6HBr

[0161] The supply amount of the B-containing gas per cycle can be adjusted so that the content of B is 0.3 to 1.2 mol% based on the total molar amount of lithium metal oxide. When the supply amount of the B-containing gas per cycle satisfies the above range, a very thin B coating layer with a thickness of about 0.05 nm per cycle can be formed, and the average thickness of the first coating layer can be appropriately controlled to the range according to the present invention by adjusting the number of additional cycles.

[0162] In particular, in the step of forming the first coating layer, atomic layer deposition can be performed in 4 to 17 cycles, and more specifically in 5 to 14 cycles. When the number of atomic layer deposition cycles of the first coating layer is controlled within the above range, the average thickness of the first coating layer is appropriately implemented within the range according to the present invention, so that the effect of improving capacity and lifespan characteristics can be preferably realized.

[0163] 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 material diffuses well and is uniformly coated even into the interior of the cathode material, so that the coating layer structure according to the present invention can be easily formed.

[0164] The above atomic layer deposition can be performed at a temperature of 100 to 200°C, and more specifically at a temperature of 130 to 170°C. When the atomic layer deposition temperature satisfies the above range, the coating reaction yield is increased, and the formation of crystalline coating layer compounds due to high temperature is prevented, thereby more preferably realizing the effect of improving lifespan and capacity characteristics due to the coating.

[0165]

[0166] Next, a second coating layer in the form of a film containing Al is formed on the first coating layer using an atomic layer deposition method.

[0167] At this time, the second coating layer can be coated in a conformal form that covers the entire surface of the first coating layer. This is due to a vapor-phase atomic layer deposition coating method using an Al-containing gas.

[0168] More specifically, in the step of forming the second coating layer, one cycle of atomic layer deposition may include the step of supplying and reacting an Al-containing gas and a second reactant on the first coating layer.

[0169] The above Al-containing gas may be, for example, trimethylaluminum (Tri-methyl Aluminium, TMA, Al(CH3)-3).

[0170] The second reactant mentioned above may be, for example, water (H2O).

[0171] The above reaction can be carried out by the following reaction scheme 2.

[0172] [Reaction Equation 2]

[0173] 2Al(CH3)3 + 3H2O = Al2O3 + 6CH4

[0174] The supply amount of the Al-containing gas per cycle can be adjusted so that the Al content is 0.2 to 1 mol% based on the total molar amount of lithium metal oxide. When the supply amount of the Al-containing gas per cycle satisfies the above range, a very thin Al coating layer with a thickness of about 0.1 nm per cycle can be formed, and the average thickness of the second coating layer can be appropriately controlled to the range according to the present invention by adjusting the number of additional cycles.

[0175] In particular, in the step of forming the second coating layer, atomic layer deposition can be performed in 3 to 11 cycles, and more specifically in 5 to 9 cycles. When the number of atomic layer deposition cycles of the second coating layer is controlled within the above range, the average thickness of the second coating layer is appropriately implemented within the range according to the present invention, so that the effect of improving capacity and lifespan characteristics can be preferably realized.

[0176] 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 material diffuses well and is uniformly coated even into the interior of the cathode material, so that the coating layer structure according to the present invention can be easily formed.

[0177] The above atomic layer deposition can be performed at a temperature of 100 to 200°C, and more specifically at a temperature of 130 to 170°C. When the atomic layer deposition temperature satisfies the above range, the coating reaction yield is increased, and the formation of crystalline coating layer compounds due to high temperature is prevented, thereby more preferably realizing the effect of improving lifespan and capacity characteristics due to the coating.

[0178] At this time, in the step of forming the first coating layer or the step of forming the second coating layer, a third coating layer containing Al or B may be formed by wrapping the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film. As previously mentioned, this may be achieved by applying an atomic layer deposition coating method while simultaneously controlling the average porosity to the range according to the present invention, as the prepared lithium metal oxide is porous.

[0179]

[0180] Meanwhile, prior to the step of forming a coating layer on a lithium metal oxide by an atomic layer deposition method, a step of treating the lithium metal oxide with inductively coupled plasma may be further included. By treating the lithium metal oxide with inductively coupled plasma, the adhesion between the lithium metal oxide substrate and the coating layer formed by the atomic layer deposition method can be further improved.

[0181]

[0182] 3. Anodes and Lithium Secondary Batteries

[0183] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0184] More specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector and comprising the aforementioned anode active material.

[0185] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes 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 above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0186] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0187] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0188] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes may be used without any particular limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight percent relative to the total weight of the positive electrode active material layer.

[0189] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0190] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0191] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0192] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0193]

[0194] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0195] More specifically, the above lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0196] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0197] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0198] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0199] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0200] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, 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.

[0201] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0202]

[0203] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0204]

[0205] The above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0206] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0207] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0208] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0209] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0210] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0211] Accordingly, another embodiment of the present invention provides a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same.

[0212] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0213]

[0214] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0215]

[0216] Preparation Example 1: Preparation of Precursor

[0217] (Precursor manufacturing)

[0218] Nickel-manganese hydroxide was prepared using a 20L co-precipitation reactor.

[0219] (Formation of metal-containing solution) NiSO4·6H2O and MnSO4·H2O were dissolved in DI water to form a 2.5M metal-containing solution. At this time, the molar ratio of Ni to Mn was set to 0.33:0.67.

[0220] After (co-precipitation), the metal-containing solution, a 14M aqueous NH4(OH) solution as a complexing agent solution, and an aqueous NaOH solution as a pH adjuster solution were introduced into a co-precipitation reactor to form a reaction solution, and the co-precipitation reaction was carried out while stirring. At this time, the ratio of the molar rate of NH4(OH) input (mol / hr) to the molar rate of total metal input into the co-precipitation reactor (mol / hr) 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℃.

[0221] The above co-precipitation reaction was carried out for a total of 22 hours to grow the metal precursor to an average particle size (D50) of 10 μm. After filtering the co-precipitated metal precursor and washing it with DI water, it was vacuum dried in a 100°C oven for 24 hours to obtain the metal precursor powder. The composition of the precursor 1 formed thereby is Ni 0.33 Mn 0.67 It was (OH)2.

[0222]

[0223] Preparation Example 2: Preparation of Lithium Metal Oxide

[0224] A mixture was formed by mixing the precursor prepared in Preparation Example 1 and Li2CO3, a lithium raw material, using a mixer. Subsequently, the mixture was placed in a refractory material (saggar) and then placed in a box furnace. A lithium metal oxide was formed by firing with a temperature profile in which air at 180 LPH was injected into the box furnace, the temperature was raised to 850°C over 5 hours, maintained at 850°C for 10 hours, and then cooled to room temperature over 5 hours.

[0225] Subsequently, the above lithium metal oxide was pulverized and then classified into 325 mesh to produce a lithium metal oxide with an excess composition of lithium and manganese.

[0226] The composition of the lithium metal oxide produced thereby is Li 1.14 Ni0.28 Mn 0.58 It was O2.

[0227]

[0228] Example 1

[0229] (1) Manufacturing of positive electrode active material

[0230] An atomic layer deposition (ALD) coating process was performed using the lithium metal oxide prepared in Preparation Example 2.

[0231] (ALD Process Conditions) A fluidized bed type reactor was used for coating, and low vacuum conditions were maintained to keep the reaction temperature at 150°C and the chamber pressure at 0.8 Torr. The syringe inlet for coating was configured to allow the precursors of two different coating materials to be injected alternately. Two precursors were used for the ALD coating: the first precursor was Boron tribromide (BBr3, Sigma-Aldrich), using H2O as the first reactant, and the second precursor was Trimethylaluminum (TMA, Al(CH3)3, Sigma-Aldrich), using H2O as the second reactant. N2 gas was used as the carrier gas and purge gas for the precursors and reactants, and was injected into the reactor at a rate of 80 sccm.

[0232] (Formation of the first coating layer) First, the lithium metal oxide prepared in Preparation Example 2 was introduced into a reactor, and BBr3 was injected along with N2 gas for 0.5 seconds to cause chemical adsorption and saturation on the substrate. Then, H2O was injected for 1 second to induce a chemical reaction, thereby forming a first coating layer containing B2O3. At this time, when N2 gas was supplied from the bottom of the reactor, an inductively coupled plasma was generated inside the reactor to plasma treat the surface of the lithium metal oxide, thereby improving the adhesion of the coating layer due to ALD. In addition, the amount of BBr3 introduced per cycle was set to 0.7 mol% based on the total molar amount of the lithium metal oxide.

[0233] When this series of processes is referred to as 1 cycle, a total of 4 cycles were performed to form the first coating layer.

[0234] At this time, the reaction equation of the ALD chemical reaction of the first coating layer is as follows.

[0235] [Reaction Equation 1]

[0236] 2BBr3 + 3H2O = B2O3 + 6HBr

[0237] After (formation of the second coating layer), TMA was injected for 0.5 seconds to cause chemical adsorption and saturation in the first coating layer, and then H2O was injected again for 1 second to induce a chemical reaction, thereby forming a second coating layer containing Al2O3. At this time, the amount of TMA added per cycle was set to 0.6 mol% based on the total molar amount of lithium metal oxide.

[0238] When this series of processes is referred to as 1 cycle, a total of 4 cycles were performed to form a second coating layer.

[0239] At this time, the reaction equation of the ALD chemical reaction of the second coating layer is as follows.

[0240] [Reaction Equation 2]

[0241] 2Al(CH3)3 + 3H2O = Al2O3 + 6CH4

[0242] Meanwhile, the CH4 and HBr byproduct gases generated after the reaction were treated through a scrubber to prevent them from being released into the atmosphere.

[0243] (2) Lithium secondary battery manufacturing

[0244] The slurry for manufacturing the electrode plate was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF1100) in a ratio of 92.5 : 3.5 : 4 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content concentration was approximately 30%. The prepared slurry was coated onto 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 / cm². 2 It was.

[0245] A CR2032 coin cell was manufactured using an electrolyte of 1M LiPF6 in EC:EMC=3:7 (vol%) with 3.0 vol% FEC added relative to the total amount of the electrolyte, a PP separator, and a lithium anode (200 μm, Honzo metal).

[0246]

[0247] Examples 2 to 5 and Reference Examples 1 to 4

[0248] A positive electrode active material and a lithium secondary battery were prepared in the same manner as Example 1, except that the number of ALD cycles was varied as shown in Table 1 below.

[0249]

[0250] Comparative Example 1

[0251] After preparing the lithium metal oxide prepared in Preparation Example 2, a positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that a separate coating process was not performed.

[0252]

[0253] Comparative Example 2

[0254] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as Example 1, except that only B was coated during the ALD coating process and the number of cycles during B coating was set as shown in Table 1 below.

[0255]

[0256] Comparative Example 3

[0257] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as Example 1, except that only Al was coated during the ALD coating process and the number of cycles during Al coating was set as shown in Table 1 below.

[0258]

[0259] Comparative Example 4

[0260] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that the lithium metal oxide prepared in Preparation Example 2 and B(OH)3 were dry-mixed and then coated at 500°C to dry-coat B in an island type. At this time, the amount of B(OH)3 added was 0.11 mol% based on the total molar amount of the lithium metal oxide.

[0261]

[0262] Comparative Example 5

[0263] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that the lithium metal oxide prepared in Preparation Example 2 and Al2O3 nanopowder of 500 nm size were dry-mixed and then coated at 500°C to dry-coat Al in an island type. At this time, the amount of Al2O3 nanopowder added was 0.17 mol% based on the total molar amount of the lithium metal oxide.

[0264]

[0265] Table 1 below is a table summarizing the process conditions of the examples, comparative examples, and reference examples.

[0266] Process Conditions Ammonia / Metal Salt Input Molar Rate Ratio Cathode Material Composition Coating Process Type 1st Coating (B Coating) Cycle 2nd Coating (Al Coating) Cycle Number Comparison Example 11Li 1.14 Ni 0.28 Mn 0.58 O2---Comparative Example 2 ALD20-Comparative Example 3 ALD-10 Example 1 ALD44 Example 2 ALD65 Example 3 ALD86 Example 4 ALD128 Example 5 ALD1611 Reference Example 1 ALD32 Reference Example 2 ALD1812 Reference Example 3 ALD48 Reference Example 4 ALD165 Comparative Example 4 Dry Form B(OH)3--Comparative Example 5 Dry Form Al2O3--

[0267] Tables 2 to 4 below summarize the results of the evaluation of the physical properties of the cathode active material and the electrochemical characteristics of the lithium secondary battery according to Experimental Examples 1 to 3 described below.

[0268] Active material properties Coating layer form Average thickness of 1st coating layer (nm) Average thickness of 2nd coating layer (nm) Ratio of 2nd coating layer thickness to 1st coating layer average thickness B Elemental content (based on total moles of lithium metal oxide, mol%) Al Elemental content (based on total moles of lithium metal oxide, mol%) Comparative Example 1------Comparative Example 2 Conformal film form 1--0.03- Comparative Example 3 Conformal film form-1--0.02 Example 1 Conformal film form 0.2 0.4 20.00 60.00 8 Example 2 Conformal film form 0.3 0.5 1.6 70.00 90.01 Example 3 Conformal film form 0.4 0.6 1.4 0.01 20.01 2 Example 4 Conformal film form 0.6 0.8 1.3 30.01 80.016 Example 5 Conformal film form 0.8 1.1 1.3 80.02 40.022 Reference Example 1 Conformal film form 0.1 50.2 1.3 30.00 4 50.004 Reference Example 2 Conformal film form 0.9 1.2 1.3 30.02 70.024 Reference Example 3 Conformal film form 0.2 0.8 40.00 60.016 Reference Example 4 Conformal film form 0.8 0.5 0.6 30.02 40.01 Comparative Example 4 Island---0.11- Comparative Example 5 Island ---- 0.17

[0269] Active Material Properties Lithium Metal Oxide Average Porosity (%) Specific Surface Area (m²) 2 / g) Tap density (g / cc) Primary particle average aspect ratio Comparative Example 1 14.7 2.9 31.8 12.8 Comparative Example 2 14.3 2.9 1.8 32.8 Comparative Example 3 14.3 2.9 1.8 32.8 Example 1 14.7 2.9 21.8 12.82 Example 2 14.6 2.9 11.8 22.81 Example 3 14.3 2.9 1.8 32.8 Example 4 14.2 2.8 91.8 42.8 Example 5 14.2 8 81.8 42.79 Reference Example 1 14.4 2.9 21.8 12.78 Reference Example 2 13.8 2.8 71.8 52.83 Reference Example 3 14.3 2.9 1.8 32.85 Reference Example 414.22.891.842.83 Comparative Example 413.72.81.882.88 Comparative Example 513.62.811.922.8

[0270] Battery Performance Formation Discharge Capacity (mAh / g) Initial Formation Efficiency (%) 2nd Cycle Discharge Capacity (mAh / g) Capacity Retention Rate (%, 50 cycles) Voltage Drop (mV, 50 cycles) Resistance Increase Rate (%, 50 cycles) Comparative Example 1 268.5 89.8 192.1 92.1 42.1 43.2 Comparative Example 2 270.1 90.1 197.2 95.3 30.2 18.3 Comparative Example 3 268.5 89.8 19198.7 33.2 19.3 Example 1 269.3 89.7 195.4 97.7 29.1 17.2 Example 2 269.5 89.8 196.3 98.1 28.4 16.8 Example 3269.690.4197.598.328.216.4 Example 4269.890.3197.798.128.816.9 Example 527089.7197.997.629.217.5 Reference Example 1268.289.7193.293.136.338.5 Reference Example 2270.489.6192.594.333.332.1 Reference Example 3268.789.6193.695.931.425.2 Reference Example 4270.189.7195.894.533.225.9 Comparative Example 4269.389.5190.397.240.225.3 Comparative Example 5268.589.1190.397.139.226.3

[0271] Experimental Example 1: Evaluation of Anode Active Material Base and Coating Layer Morphology

[0272] Bright Field Scanning Transmission Electron Microscopy (BF-STEM) images were observed on the cross-section of secondary particles milled by Focused Ion Beam (FIB) milling of the positive electrode active material prepared according to Example 1, and these images are shown in Fig. 1.

[0273] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image for the Al element in the upper marked area of ​​the image in Fig. 1 is shown in Fig. 2.

[0274] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image for the Al element in the lower marked area of ​​the image in Fig. 1 is shown in Fig. 3.

[0275] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the upper display area of ​​the image in Fig. 1 is shown in Fig. 4.

[0276] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the lower marked area of ​​the image in Fig. 1 is shown in Fig. 5.

[0277] Referring to Fig. 1, it was confirmed that the positive electrode active material of Example 1 has a secondary particle shape formed by the aggregation of rod-shaped primary particles with an aspect ratio of 1.6 or higher, and that the long axis of the primary particles has an orientation directed from the center of the secondary particles toward the surface. In addition, it was confirmed that the resistance issue caused by the low nickel content and high manganese content can be overcome by having a porous structure in which internal pores are uniformly present within the positive electrode active material particles, due to the structure that facilitates the penetration of the electrolyte. Furthermore, it was confirmed that a film-like coating layer is formed on the entire surface of the secondary particles (i.e., conformal type).

[0278] Referring to FIGS. 2 to 5, it was confirmed that in the cathode active material of Example 1, an Al and B-containing coating layer (i.e., a third coating layer) covering the surface of the primary particle was formed not only in the region near the surface within the particle interior but also in the region near the center. This coating layer was also found to exist in a region very close to the center of the secondary particle, extending to a region within a distance of about 0.5 μm from the center of the secondary particle (or, if the distance from the center of the secondary particle to the surface is R, it was found to exist within a distance of (1 / 4)R). This can be interpreted as a result of the vapor-phase coating source penetrating well into the interior of the secondary particle and undergoing a coating reaction by applying an atomic layer deposition (ALD) coating method to a porous lithium metal oxide with a large average porosity.

[0279]

[0280] Experimental Example 2: Evaluation of Crystallinity of Anode Active Material Coating Layer

[0281] To more clearly confirm the crystallinity of the coating layer, the first coating layer formation ALD cycle was performed 10 times and the second coating layer formation ALD cycle was performed 5 times to prepare an anode active material. One primary particle inside the anode active material prepared accordingly was selected, and a TEM (transmission electron microscope) image was observed, which is shown in Fig. 6.

[0282] Referring to Fig. 6, it was confirmed that the lithium metal oxide substrate of the positive electrode active material according to the present invention has a well-structured atomic arrangement in a layered crystal structure, and the coating layer has a random atomic arrangement and is amorphous.

[0283]

[0284] Experimental Example 3: Evaluation of Physical Properties of Anode Active Material

[0285] (1) Evaluation of the average thickness of the first coating layer

[0286] The average thickness of the first coating layer was measured by the following method. First, the thickness of the first coating layer for a single secondary positive material particle was calculated by analyzing cross-sectional TEM images after FIB (Focused Ion Bean) milling of the secondary positive material particle, randomly selecting 20 locations on the surface of the secondary particle, and obtaining the average value of the B-containing coating layer thickness at the selected locations. Next, the average thickness of the first coating layer was calculated by obtaining the average of the first coating layer thicknesses measured by the same method as above for 20 randomly selected secondary positive material particles among the positive material powder.

[0287] (2) Evaluation of the average thickness of the second coating layer

[0288]

[0289] The average thickness of the second coating layer was measured by the following method. First, the thickness of the second coating layer for a single secondary particle of the positive active material was calculated by analyzing cross-sectional TEM images after FIB (Focused Ion Bean) milling of the secondary particle of the positive active material, randomly selecting 20 locations on the surface of the secondary particle, and determining the average value of the Al-containing coating layer thickness at the selected locations. Next, the average thickness of the second coating layer was calculated by determining the average of the second coating layer thicknesses measured by the same method as above for 20 randomly selected secondary particles of the positive active material among the positive active material powder.

[0290] (3) Evaluation of average porosity of lithium metal oxide

[0291] The “porosity” of a single lithium metal oxide secondary particle was derived by cutting a single secondary particle using the FIB (Focused Ion Beam) milling method and then converting the ratio of the total area of ​​the hollow void portion to the total cross-sectional area of ​​the secondary particle into a percentage value when observing a TEM image of the cut cross-section. In addition, the “average porosity” of the lithium metal oxide was calculated by determining the average of 30 randomly selected secondary particles within the cathode active material powder using the above method.

[0292] (4) Evaluation of the specific surface area of ​​the positive electrode active material

[0293] The specific surface area of ​​the cathode active material was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0294] (5) Evaluation of positive electrode active material tap density

[0295] Based on ASTM B527, 15g of active material powder was placed in a 50mL container and tapped at 3000 cycles @ 284 cycles / min to measure the packing density.

[0296] (6) Evaluation of the average aspect ratio of primary particles

[0297] The average aspect ratio of primary particles was calculated by averaging the aspect ratios of 30 random primary particles observed during TEM (Transmission Electron Microscope) image analysis of the cross-section after cutting the cathode active material using the FIB (Focused Ion Beam) milling method. In this case, the “aspect ratio” of a primary particle refers to the ratio of the length of the longest side to the shortest side within the primary particle.

[0298] (7) Evaluation of Al and B content

[0299] The content of Al or B in the cathode active material was measured by obtaining the weight percent of Al or B through ICP (Inductively Coupled Plasma Analysis) component analysis of the prepared cathode active material, and then converting this to a mol percent relative to the total molar amount of lithium metal oxide.

[0300]

[0301] Experimental Example 4: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0302] (1) Evaluation of initial formation discharge capacity and efficiency

[0303] After fabricating the lithium secondary battery half cell, it was aged at 25°C for 10 hours, and then formation was performed 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 charged to 4.65V with a constant current of 0.1C, then switched to a constant voltage and continued charging until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged until it reached 2V with a constant current of 0.1C and a 1C reference capacity of 200 mAh / g.

[0304] (2) 2nd cycle discharge capacity evaluation

[0305] After the above formation, the second charge and discharge test was conducted under conditions of 4.4V charging and 2.5V discharging to evaluate the 2nd cycle discharge capacity.

[0306] (3) Evaluation of room temperature capacity retention rate (25℃, 50 cycles)

[0307] After fabricating a lithium secondary battery half cell, it was charged to 4.6V at 25°C with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a rest time of 10 minutes following charging, it was discharged with a constant current of 0.2C until it reached 2.5V. From the second cycle onwards, 50 charge-discharge cycles were performed under the same conditions as above, except that the charging termination voltage was set to 4.4V, and the capacity retention rate of the 50th cycle was calculated relative to the first cycle.

[0308] (4) Evaluation of average voltage drop

[0309] In the charge-discharge voltage range, when the voltage at the half point of the energy obtained by multiplying the discharge charge and the voltage is defined as the average voltage, the difference between the initial average voltage and the average voltage after 50 cycles is defined as the average voltage drop and measured.

[0310] (5) Evaluation of room temperature resistance increase rate (25℃, 50 cycles)

[0311] After fabricating a lithium secondary battery half cell, it was charged to 4.25V at 25℃ with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the resistance increase rate of the 50th cycle compared to the first cycle was calculated.

[0312]

[0313] Referring to Tables 1 to 4, in the case of Examples 1 to 5, where the various process conditions, such as the number of atomic layer deposition cycles during the formation of the first and second coating layers, were appropriately controlled within the range according to the present invention, it was confirmed that the various physical properties, including the average thickness of the first and second coating layers, were appropriately obtained within the range according to the present invention. Furthermore, in this case, it was confirmed that the capacitance retention rate, average voltage drop, and resistance increase rate were comprehensively significantly improved compared to Comparative Example 1, which is the base material, thereby greatly enhancing the lifespan characteristics. In addition, 2 nd It was confirmed that the cycle discharge capacity was improved to 195 mAh / g or more compared to Comparative Example 1, which is the basic base material.

[0314] On the other hand, in the case of Comparative Example 1, which is not coated, the capacitance retention rate, average voltage drop, and resistance increase rate are lower compared to the example, and the lifespan characteristics deteriorate, and 2 nd It was confirmed that the cycle discharge capacity also deteriorated compared to the example.

[0315] In the case of Comparative Example 2, as a result of coating only B using an atomic layer deposition method, it was confirmed that the capacitance retention rate, average voltage drop, and resistance increase rate characteristics were degraded compared to the example.

[0316] In the case of Comparative Example 3, as a result of coating only Al by the atomic layer deposition method, particularly 2 nd It was confirmed that the cycle discharge capacity was at the level of 191 mAh / g, which is significantly degraded compared to the example, and that the average voltage drop and resistance increase rate characteristics were somewhat degraded compared to the example.

[0317] In other words, it was confirmed that the positive electrode active material according to the present invention showed a more enhanced effect in capacity and lifespan characteristics through sequential stacking ALD coating of B and Al compared to ALD coating of B or Al alone.

[0318] Meanwhile, in the case of Comparative Example 4, to which a conventional dry B coating was applied, 2 ndIt was confirmed that the cycle discharge capacity was significantly degraded compared to the example, with a level of 190 mAh / g, and that the capacity retention rate, average voltage drop, and resistance increase rate characteristics were also somewhat degraded compared to the example.

[0319] In addition, in the case of Comparative Example 5, to which a conventional dry Al coating was applied, 2 nd It was confirmed that the cycle discharge capacity was significantly degraded compared to the example, with a level of 190 mAh / g, and that the capacity retention rate, average voltage drop, and resistance increase rate characteristics were also somewhat degraded compared to the example.

[0320] In the case of Reference Example 1, it was confirmed that the average thickness of the first coating layer and the second coating layer was obtained to be too thin because the number of atomic layer deposition cycles during the formation of the first coating layer and the second coating layer was each too small. And, as a result, 2 nd It was confirmed that the improvement effects on cycle discharge capacity, capacity retention rate, average voltage drop, and resistance increase rate characteristics were somewhat degraded compared to the examples.

[0321] In the case of Reference Example 2, it was confirmed that the average thickness of the first and second coating layers was obtained to be too thick as a result of the number of atomic layer deposition cycles being too high, respectively, during the formation of the first and second coating layers. And, as a result, 2 nd It was confirmed that the improvement effects on cycle discharge capacity, capacity retention rate, average voltage drop, and resistance increase rate characteristics were somewhat degraded compared to the examples.

[0322] In the case of Reference Example 3, as a result of the ratio of the average thickness of the second coating layer to the average thickness of the first coating layer being too large, 2 nd It was confirmed that the improvement effects on cycle discharge capacity, capacity retention rate, average voltage drop, and resistance increase rate characteristics were somewhat degraded compared to the examples.

[0323] In the case of Reference Example 4, as a result of the ratio of the average thickness of the second coating layer to the average thickness of the first coating layer being too small, it was confirmed that the improvement effect of the capacitance retention rate, average voltage drop, and resistance increase rate characteristics was somewhat degraded compared to the example.

[0324] Meanwhile, when comparing Examples 1 to 5, in the case of Examples 2 to 4, where the thicknesses of the first coating layer and the second coating layer are more appropriately controlled, compared to Example 1 or 5, 2 nd It was confirmed that the cycle discharge capacity (196 mAh / g or more), capacity retention rate (98% or more), average voltage drop (29mV or less), and resistance increase rate characteristics (17% or less) were implemented more desirablely overall.

[0325]

[0326] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0327] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A lithium metal oxide in the form of secondary particles formed by the aggregation of multiple primary particles, having an excess composition of lithium and manganese; A first coating layer containing B that wraps the entire surface of the above secondary particle in the form of a film; and A positive electrode active material for a lithium secondary battery comprising a second coating layer containing Al that wraps the entire surface of the first coating layer in the form of a film.

2. In Paragraph 1, A positive electrode active material for a lithium secondary battery comprising a third coating layer containing Al or B, which encases the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film.

3. In Paragraph 2, The above third coating layer is a positive electrode active material for a lithium secondary battery that exists in a region within a distance of (3 / 4)R from the center of the secondary particle, where R is the distance from the center of the secondary particle to the surface.

4. In Paragraph 2, The above third coating layer is a positive electrode active material for a lithium secondary battery that is also present in an area within a distance of 1 μm from the center of the secondary particle.

5. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the first coating layer is 0.17 to 0.85 nm.

6. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the second coating layer is 0.3 to 1.15 nm.

7. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the ratio of the average thickness of the second coating layer to the average thickness of the first coating layer (second coating layer / first coating layer) is 0.8 to 3.

5.

8. In Paragraph 1, The first coating layer comprises a B-containing compound, and the B-containing compound comprises B2O3 as a main component. A positive electrode active material for a lithium secondary battery.

9. In Paragraph 1, The above second coating layer comprises an Al-containing compound, and the Al-containing compound comprises Al2O3 as a main component, forming a positive electrode active material for a lithium secondary battery.

10. In Paragraph 8, The above B2O3 is an amorphous positive electrode active material for lithium secondary batteries.

11. In Paragraph 9, The above Al2O3 is an amorphous positive electrode active material for lithium secondary batteries.

12. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of B in the above positive electrode active material is 0.005 to 0.026 mol% based on the total molar amount of lithium metal oxide.

13. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of Al in the above positive electrode active material is 0.006 to 0.023 mol% based on the total molar amount of lithium metal oxide.

14. In Paragraph 1, A positive electrode active material for a lithium secondary battery having an average porosity of 10 to 20% of the lithium metal oxide.

15. In Paragraph 1, BET specific surface area is 2.5 to 3.5 m² 2 A positive electrode active material for lithium secondary batteries with a g content.

16. In Paragraph 1, A positive electrode active material for a lithium secondary battery having a tap density of 1.6 to 2.2 g / cc.

17. In Paragraph 1, The above primary particles are positive electrode active materials for lithium secondary batteries having an average aspect ratio of 2.4 to 3.

5.

18. In Paragraph 1, The above lithium metal oxide is a positive electrode 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 O2 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.

19. A step of preparing a lithium metal oxide having an excess composition of lithium and manganese in the form of secondary particles formed by the aggregation of multiple primary particles; A step of forming a first coating layer in the form of a film containing B on the lithium metal oxide using an atomic layer deposition (ALD) method; and A step comprising forming a second coating layer in the form of an Al-containing film on the first coating layer using an atomic layer deposition method, Method for manufacturing a positive electrode active material for a lithium secondary battery.

20. In Paragraph 19, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein, in the step of forming a first coating layer or a second coating layer, a third coating layer containing Al or B is formed by covering the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film.

21. In Paragraph 19, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the average porosity of the prepared lithium metal oxide is 10 to 20%.

22. In Paragraph 19, In the step of forming the first coating layer, one cycle of atomic layer deposition is, A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the step of supplying and reacting a B-containing gas and a first reactant on a lithium metal oxide.

23. In Paragraph 19, In the step of forming the second coating layer above, one cycle of atomic layer deposition is, A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the step of supplying and reacting an Al-containing gas and a second reactant on a first coating layer.

24. In Paragraph 19, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein atomic layer deposition is performed in 4 to 17 cycles in the step of forming the first coating layer.

25. In Paragraph 19, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein atomic layer deposition is performed in 3 to 11 cycles in the step of forming the second coating layer.

26. A positive electrode for a lithium secondary battery comprising the positive electrode active material of claim 1.

27. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 26.

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