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 that has a lithium- and manganese-rich composition and is provided in the form of secondary particles formed by aggregation of a plurality of rod-shaped primary particles; a first coating layer that contains Al and B and covers, in the form of a film, the entire surface of each secondary particle; and a second coating layer that contains Al and B and covers, in the form of a film, the surfaces of at least a portion of the plurality of primary particles present inside each secondary particle.

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] This application claims priority to Korean Patent Application No. 10-2024-0132986, filed on September 30, 2024, the entire contents of which are incorporated herein by reference.

[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 cycling progresses, 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] 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.

[0008] 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 rod-shaped primary particles having an excess composition of lithium and manganese; a first coating layer containing Al and B that covers the entire surface of the secondary particles in the form of a film; and a second coating layer containing Al and B that covers the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film.

[0009] The above second 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.

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

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

[0012] The average thickness of the first coating layer may be 0.4 to 2.5 nm.

[0013] The average thickness of the second coating layer may be 0.2 to 2.1 nm.

[0014] The ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) may be 1.1 to 2.

[0015] The first coating layer and the second coating layer above contain an Al-containing compound, and the Al-containing compound may include Al2O3 as a main component.

[0016] The first coating layer and the second coating layer above contain a B-containing compound, and the B-containing compound may include B2O3 as a main component.

[0017] The above Al2O3 may be amorphous.

[0018] The above B2O3 may be amorphous.

[0019] The content of Al in the above positive active material may be 0.003 to 0.03 mol% based on the total molar amount of lithium metal oxide.

[0020] The content of B in the above positive active material may be 0.003 to 0.023 mol% based on the total molar amount of lithium metal oxide.

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

[0022] The above-mentioned positive active material has a BET specific surface area of ​​2.5 to 3.5 m² 2 It can be / g.

[0023] The above positive active material may have a tap density of 1.6 to 2.2 g / cc.

[0024] The above primary particles may have an average aspect ratio of 2.4 to 3.5.

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

[0026] [Chemical Formula 1]

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

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

[0029]

[0030] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium metal oxide having an excess composition of lithium and manganese in the form of secondary particles formed by aggregating a plurality of rod-shaped primary particles; and forming a coating layer containing Al and B on the lithium metal oxide by an atomic layer deposition (ALD) method, wherein in the step of forming the coating layer containing Al and B, a first coating layer containing Al and B is formed by wrapping the entire surface of the secondary particles in the form of a film, and a second coating layer containing Al and B is 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.

[0031] The average porosity of the prepared lithium metal oxide can be 10 to 20%.

[0032] One cycle of the above atomic layer deposition may include the step of forming a B-containing coating layer by supplying a B-containing gas and a first reactant onto a lithium metal oxide; and the step of forming an Al-containing coating layer by supplying an Al-containing gas and a second reactant onto a lithium metal oxide.

[0033] The above atomic layer deposition can be performed in 3 to 16 cycles.

[0034]

[0035] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0036] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for the lithium secondary battery.

[0037]

[0038] According to one embodiment of the present invention, a positive electrode active material for a lithium secondary battery has a thin and uniform coating layer containing Al and B applied to the entire surface of a lithium metal oxide secondary particle and an internal primary particle having an excess composition of lithium and manganese, thereby improving overall lifespan characteristics such as improved capacity retention rate during cycle progression, reduced voltage drop, reduced resistance increase rate, and suppression of gas generation, while simultaneously improving capacity characteristics.

[0039]

[0040] 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.

[0041] Figure 2 is an enlarged image of the center of the positive active material in the image of Figure 1.

[0042] Figure 3 is an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the image of Figure 2.

[0043] Figure 4 is an Energy Dispersive Spectroscopy (EDS) elemental mapping image of the Al element in the image of Figure 2.

[0044] Figure 5 is a TEM (transmission electron microscope) image of primary particles inside the positive electrode active material according to Experimental Example 2.

[0045] 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.

[0046] 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.

[0047] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other part is interposed in between.

[0048] 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.

[0049] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0050] 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.

[0051] 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.

[0052]

[0053] 1. Cathode active material

[0054] 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 a composition with excess lithium and manganese. Although the lithium transition metal oxide with an excess lithium and manganese composition has a low nickel content, it can undergo oxidation / reduction reactions of anions (oxygen) as well as potential 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] At this time, the primary particle has a rod shape. In this specification, “rod shape” is a term used to distinguish it from a sphere, 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.

[0061] 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.

[0062] 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 cycling progresses, including reduced capacity retention, voltage decay, increased resistance growth, and gas evolution.

[0063] Accordingly, the positive electrode active material according to the present invention can have an Al and B-containing coating layer uniformly coated with an atomic-level very thin thickness on secondary particles, and furthermore on primary particles existing inside secondary particles, through a vapor-phase atomic layer deposition (ALD) coating method using an Al-containing gas and a B-containing gas on a porous lithium metal oxide having an excess composition of lithium and manganese. As a result, the structural stability of the lithium metal oxide is improved, thereby enhancing lifespan characteristics and simultaneously improving capacity characteristics. More detailed information regarding the above vapor-phase atomic layer deposition coating method will be explained in the manufacturing method described below.

[0064] 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 Al and B.

[0065] By the first coating layer containing Al, the surface structure of the lithium metal oxide is stabilized, thereby improving lifespan characteristics. By the first coating layer containing B, the effect of increasing the interslab thickness of the layered structure of the lithium metal oxide can be realized, which can improve capacity. That is, the cathode active material according to the present invention, by having the first coating layer simultaneously contain Al and B, can not only improve lifespan characteristics but also simultaneously improve capacity characteristics.

[0066] 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 lifespan and capacity characteristics due to the coating can be more preferably realized.

[0067] In particular, the positive electrode active material according to the present invention further comprises a second coating layer containing Al and B, which wraps the surface of at least some of the plurality of primary particles present inside the secondary particles in the form of a film in addition to the first coating layer.

[0068] That is, in the cathode active material according to the present invention, an Al and 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 lifespan and capacity characteristics due to the coating can be more preferably realized.

[0069] As the coating layer is formed deep within the primary particle inside the secondary particle in this manner, the second 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.

[0070] Specifically, the second 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.

[0071] Meanwhile, the average thickness of the first coating layer may be thicker than the average thickness of the second coating layer. That is, the average thickness of the Al and B-containing coating layer may have a tendency to become thinner inside than on the surface of the secondary particles. Accordingly, the structural stability of the cathode active material is more preferably realized, and the effect of improving lifespan characteristics due to the coating can be more preferably realized.

[0072] In addition, the average thickness of the first coating layer may be 0.4 to 2.5 nm, and more specifically, 0.43 to 2.3 nm. If the average thickness of the first coating layer is too thin, the effect of improving lifespan and capacity characteristics due to the coating may be negligible. If the average thickness of the first coating layer is too thick, lithium ion mobility may be reduced, and capacity or output characteristics may deteriorate.

[0073] 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 Focused Ion Bean (FIB) 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 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.

[0074] In addition, the average thickness of the second coating layer may be 0.2 to 2.1 nm, and more specifically, 0.23 to 2.0 nm. If the average thickness of the second coating layer is too thin, the effect of improving lifespan and capacity characteristics due to the coating may be negligible. If the average thickness of the second coating layer is too thick, lithium ion mobility may be reduced, and capacity or output characteristics may deteriorate.

[0075] 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 within the secondary particle, and obtaining the average value of the coating layer thickness at the selected locations. Next, the average thickness of the second coating layer can be calculated by obtaining the average of the second coating layer thicknesses measured in the same manner as above for 20 random secondary particles of the positive active material among the positive active material powder.

[0076] Meanwhile, the ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) may be 1.1 to 2, and more specifically, 1.11 to 1.8. When the ratio of the average thickness between the first coating layer and the second coating layer satisfies the above range, the structural stability of the positive electrode active material is more preferably realized, and the effect of improving the lifespan characteristics due to the coating can be more preferably realized.

[0077] In addition, the content of Al in the above-mentioned positive electrode active material may be 0.003 to 0.03 mol% based on the total molar amount of lithium metal oxide, and more specifically, 0.004 to 0.028 mol%. If the content of Al is too low, the lifespan improvement effect due to Al coating may be negligible. If the content of Al is too high, lithium ion mobility may be inhibited, and the capacity or output characteristics of the battery may deteriorate.

[0078] In addition, the content of B in the above-mentioned positive active material may be 0.003 to 0.023 mol% based on the total molar amount of lithium metal oxide, and more specifically, 0.0035 to 0.022 mol%. If the content of B is too low, the capacity improvement effect due to the B coating may be negligible. If the content of B is too high, lithium ion mobility may be inhibited, which may instead lead to a deterioration in capacity or output characteristics.

[0079] 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.

[0080] Meanwhile, the first coating layer and the second coating layer contain 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 provided, enabling more desirable lifespan characteristics.

[0081] In addition, the first and second coating layers contain 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, enabling more desirable lifespan characteristics.

[0082] That is, the effect of improving the lifespan and capacity characteristics of the coating of the positive electrode active material according to the present invention is attributed to the composition of the coating layer containing both Al and B itself, and can be further maximized by the amorphousness of the Al-containing compound and the B-containing compound within the coating layer.

[0083] Meanwhile, in this specification, “main component” may mean that it accounts for about 80% or more of the total weight of the Al-containing compound or B-containing compound in the coating layer.

[0084] 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 (transmission electron microscope) image analysis.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] In this specification, the specific surface area can be measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094]

[0095] The lithium metal oxide according to the present invention can be represented more specifically by the following chemical formula 1.

[0096] [Chemical Formula 1]

[0097] Li 1+a (Ni x Co y Mn z M w ) 1-a O2

[0098] 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.

[0099] 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, the lifespan characteristics may deteriorate due to a decrease in phase stability.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104]

[0105] 2. Method for manufacturing positive electrode active material

[0106] 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 aggregating a plurality of rod-shaped primary particles; and forming a coating layer containing Al and B on the lithium metal oxide by an atomic layer deposition (ALD) method, wherein in the step of forming the coating layer containing Al and B, a first coating layer containing Al and B is formed by wrapping the entire surface of the secondary particles in the form of a film, and a second coating layer containing Al and B is 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.

[0107] 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.

[0108]

[0109] 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 rod-shaped primary particles is prepared.

[0110] 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.

[0111] First, nickel raw material, manganese raw material, and a solvent are mixed to form a metal-containing solution.

[0112] Of course, additional cobalt raw materials may be mixed in as needed during the above mixing process.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] Next, the above reaction solution is subjected to a co-precipitation reaction to form a metal precursor.

[0124] The above co-precipitation reaction can be carried out by stirring the reaction solution.

[0125] At this time, the above co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] Next, the above metal precursor and lithium raw material are mixed and then calcined to form a lithium metal oxide.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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 using the atomic layer deposition method described later, an anode active material having a coating structure according to the present invention can be formed.

[0137]

[0138] Next, a coating layer containing Al and B is formed on the lithium metal oxide using an atomic layer deposition method.

[0139] At this time, the Al and B-containing coating layer may be formed by wrapping the entire surface of the secondary particle in the form of a film, and by wrapping the surface of at least some of the plurality of primary particles present inside the secondary particle in the form of a film, and by forming a second coating layer containing Al and B.

[0140] In addition, the atomic layer deposition can be performed in 3 to 16 cycles. If the number of atomic layer deposition cycles is too low, the average thickness of the formed coating layer (first coating layer, second coating layer) becomes too thin overall, and the effect of improving lifespan and capacity characteristics due to the coating may be negligible. If the number of atomic layer deposition cycles is too high, the average thickness of the formed coating layer (first coating layer, second coating layer) becomes too thick overall, which impedes lithium ion mobility and may degrade capacity or output characteristics.

[0141] More specifically, one cycle of the atomic layer deposition may include the step of forming a B-containing coating layer by supplying a B-containing gas and a first reactant onto a lithium metal oxide; and the step of forming an Al-containing coating layer by supplying an Al-containing gas and a second reactant onto a lithium metal oxide.

[0142] At this time, the temporal order of the step of forming the B-containing coating layer and the step of forming the Al-containing coating layer is not particularly limited. In one example, in one cycle of atomic layer deposition, the step of forming the B-containing coating layer may precede the step of forming the Al-containing coating layer. In another example, in one cycle of atomic layer deposition, the step of forming the Al-containing coating layer may precede the step of forming the B-containing coating layer.

[0143] The above Al-containing gas may be, for example, trimethylaluminum (Tri-methyl Aluminium, TMA, Al(CH3)-3).

[0144] The first reactant above may be, for example, water (H2O).

[0145] The above B-containing gas may be, for example, boron tribromide (BBr3).

[0146] The second reactant mentioned above may be, for example, water (H2O).

[0147] The formation of an Al-containing coating layer through the above atomic layer deposition method can proceed according to the following reaction scheme 1.

[0148] [Reaction Equation 1]

[0149] 2Al(CH3)3 + 3H2O = Al2O3 + 6CH4

[0150] The formation of a B-containing coating layer through the above atomic layer deposition method can proceed according to the following reaction scheme 2.

[0151] [Reaction Equation 2]

[0152] 2BBr3 + 3H2O = B2O3 + 6HBr

[0153] 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 coating layer (first coating layer and second coating layer) can be appropriately controlled to the range according to the present invention by adjusting the number of additional cycles.

[0154] 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 coating layer (first coating layer and second coating layer) can be appropriately controlled to the range according to the present invention by adjusting the number of additional cycles.

[0155] 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.

[0156] 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.

[0157]

[0158] Meanwhile, prior to the step of forming a coating layer containing Al and B 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.

[0159]

[0160] 3. Anodes and Lithium Secondary Batteries

[0161] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0162] 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.

[0163] 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.

[0164] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0165] 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.

[0166] 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.

[0167] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0168] 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.

[0169] 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.

[0170] 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.

[0171]

[0172] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0173] More specifically, the above lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0174] 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.

[0175] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0180]

[0181] 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.

[0182]

[0183] 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.

[0184] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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).

[0189] 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.

[0190] 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.

[0191]

[0192] 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.

[0193]

[0194] Preparation Example 1: Preparation of Precursor

[0195] (Precursor manufacturing)

[0196] Nickel-manganese hydroxide was prepared using a 20L co-precipitation reactor.

[0197] (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.

[0198] 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℃.

[0199] 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.

[0200]

[0201] Preparation Example 2: Preparation of Lithium Metal Oxide

[0202] 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.

[0203] 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.

[0204] The composition of the lithium metal oxide produced thereby is Li 1.14 Ni0.28 Mn 0.58 It was O2.

[0205]

[0206] Example 1

[0207] (1) Manufacturing of positive electrode active material

[0208] An atomic layer deposition (ALD) coating process was performed using the lithium metal oxide prepared in Preparation Example 2.

[0209] A fluidized bed type reactor was used for the 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 a carrier gas for the precursors and reactants, as well as a purge gas, and was injected into the reactor at a rate of 80 sccm.

[0210] The reaction sequence involved introducing the lithium metal oxide prepared in Preparation Example 2 into a reactor, injecting BBr3 with N2 gas for 0.5 seconds to achieve chemical adsorption and saturation on the substrate, and then injecting H2O for 1 second to induce a chemical reaction, thereby finally forming B2O3. At this time, when supplying N2 gas from the bottom of the reactor, 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.

[0211] Afterwards, TMA was injected again for 0.5 seconds to cause chemical adsorption and saturation on the base material, and then H2O was injected again for 1 second to induce a chemical reaction, finally forming Al2O3.

[0212] When this series of processes is referred to as 1 cycle, a total of 7 cycles were performed to form a coating layer.

[0213] At this time, the reaction equation of the ALD chemical reaction is as follows.

[0214] [Reaction Equation 1]

[0215] 2Al(CH3)3 + 3H2O = Al2O3 + 6CH4

[0216] [Reaction Equation 2]

[0217] 2BBr3 + 3H2O = B2O3 + 6HBr

[0218] In addition, the CH4 and HBr byproduct gases generated after the reaction were treated through a scrubber to prevent them from being released into the atmosphere.

[0219] (2) Lithium secondary battery manufacturing

[0220] 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.

[0221] 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).

[0222]

[0223] Examples 2 to 5 and Reference Examples 1 to 2

[0224] 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.

[0225]

[0226] Comparative Example 1

[0227] 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.

[0228]

[0229] Comparative Examples 2 to 3

[0230] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as Example 1, except that the Al coating process was not performed in one cycle of the ALD coating process and the number of ALD cycles was varied as shown in Table 1 below.

[0231]

[0232] Comparative Examples 4 to 5

[0233] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as Example 1, except that the B coating process was not performed in one cycle of the ALD coating process and the number of ALD cycles was varied as shown in Table 1 below.

[0234]

[0235] Comparative Example 6

[0236] 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.

[0237]

[0238] Comparative Example 7

[0239] 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.

[0240]

[0241] Table 1 below is a table summarizing the process conditions of the examples, comparative examples, and reference examples.

[0242] Coating Process Type Amount of BBr3 added per cycle (mol%, based on total moles of lithium metal oxide) BBr3 addition time per cycle (sec) Amount of TMA added per cycle (mol%, based on total moles of lithium metal oxide) TMA addition time per cycle (sec) Number of ALD cycles ALD execution temperature Comparative Example 1 ------- Example 1 ALD 0.7 0.5 0.6 0.5 7 150 Example 2 0.5 0.5 10 150 Example 3 0.5 0.5 14 150 Example 4 0.5 0.5 4 150 Example 5 0.5 0.5 3 150 Reference Example 1 0.5 0.5 2 150 Reference Example 20.5 0.5 17 150 Comparative Example 20.7 0.5 -- 20 150 Comparative Example 30.7 0.5 -- 14 150 Comparative Example 4--0.6 0.5 10 150 Comparative Example 5--0.6 0.5 7 150 Comparative Example 6 Dry Form H3BO3------Comparative Example 7 Dry Form Al2O3------

[0243] 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 Example 2 and Experimental Example 3 described below.

[0244] Average thickness of the first coating layer (nm) Average thickness of the second coating layer (nm) Ratio of the average thickness of the first coating layer to the second coating layer B element content (based on the total moles of lithium metal oxide, mol%) Al element content (based on the total moles of lithium metal oxide, mol%) Comparative Example 1 ----- Example 1 10.8 7 1.1 49 0.0 1 0.0 13 Example 2 1.5 1.3 2 1.1 36 0.0 1 40.0 21 Example 3 2.1 1.8 8 1.1 17 0.0 2 10.0 27 Example 4 0.6 0.4 3 1.3 95 0.0 6 0.0 8 Example 5 0.4 50.2 6 1.7 31 0.0 4 0.0 5 Reference Example 10.3 0.1 6 1.8 75 0.0 2 0.0 2 Reference Example 22.6 2.2 41.1 6 10.0 2 5 0.0 32 Comparative Example 2 10.8 81.1 3 6 0.0 30 Comparative Example 3 30.7 0.6 21.1 2 9 0.0 2 10 Comparative Example 4 10.8 71.1 4 9 0 0.0 2 Comparative Example 5 50.7 0.6 31.1 1 10 0.0 1 2 Comparative Example 6 0.1 1 Comparative Example 7 0.1 7

[0245] 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 Example 1 14.2 2.9 1.8 32.8 Example 2 13.8 2.8 81.8 52.8 5 Example 3 13.3 2.8 61.8 72.9 Example 4 14.4 2.9 11.8 22.8 Example 5 14.6 2.9 21.8 22.8 Reference Example 1 14.7 2.9 31.8 12.8 Reference Example 2 13.2 2.8 51.8 92.8 7 Comparative Example 2 14.3 2.9 1.8 32.8 Comparative Example 3 14.4 2.9 11.8 22.8 Comparative Example 4 14.3 2.9 1.8 32.8 Comparative Example 514.42.911.822.8 Comparative Example 613.72.81.882.88 Comparative Example 713.62.811.922.8

[0246] 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 Example 1 270.1 90.2 196.3 99.3 30.1 17.2 Example 2 270.4 90.3 196.5 99.4 30.2 17.2 Example 3 263.3 88.7 193.5 99.2 34.2 19.2 Example 4 271.3 90.4 196.5 99.4 29.8 17.1 Example 5271.890.6196.299.329.917.4 Reference Example 1 263.388.7193.493.437.232.3 Reference Example 2236.280.4166.595.239.233.2 Comparative Example 2270.190.1197.295.330.218.3 Comparative Example 327090196.895.130.518.8 Comparative Example 4268.589.819198.733.219.3 Comparative Example 5269.389.8191.598.633.419.3 Comparative Example 6269.389.5190.397.240.225.3 Comparative Example 7268.589.1190.397.139.226.3

[0247] Experimental Example 1: Evaluation of the morphology of the positive electrode active material coating layer

[0248] 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.

[0249] In addition, the center of the cross-section of the positive active material in the image of Fig. 1 was magnified and observed, and this is shown in Fig. 2.

[0250] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image for element B in the image of Fig. 2 is shown in Fig. 3.

[0251] In addition, an Energy Dispersive Spectroscopy (EDS) element mapping image of the Al element in the image of Fig. 2 is shown in Fig. 4.

[0252] Referring to Fig. 1, 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 it was confirmed that the major axis of the primary particles has an orientation directed from the center of the secondary particles toward the surface. In addition, by having a porous structure in which internal pores are uniformly present within the positive electrode active material particles, it was confirmed that resistance issues arising from low nickel content and high manganese content can be overcome due to a 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).

[0253] Referring to FIGS. 2 to 4, it was confirmed that the positive electrode active material of Example 1 had a uniformly formed Al and B-containing coating layer on the surface of the primary particle located in the center of the particle. This coating layer was also present in an area very close to the center of the secondary particle, and it was confirmed that it existed 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 confirmed that it existed 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 by applying a vapor-phase atomic layer deposition (ALD) coating method to the porous lithium metal oxide.

[0254]

[0255] Experimental Example 2: Evaluation of Crystallinity of Anode Active Material Coating Layer

[0256] To more clearly confirm the crystallinity of the coating layer, the ALD cycle was performed 20 times to prepare the cathode active material, and one primary particle inside the cathode active material prepared accordingly was selected and a TEM (transmission electron microscope) image was observed, which is shown in Fig. 5.

[0257] Referring to Fig. 5, 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.

[0258]

[0259] Experimental Example 3: Evaluation of Physical Properties of Anode Active Material

[0260] (1) Evaluation of the average thickness of the first coating layer

[0261] 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 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.

[0262] (2) Evaluation of the average thickness of the second coating layer

[0263] 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 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 within the secondary particle, and obtaining the average value of the coating layer thickness at the selected locations. Next, the average thickness of the second coating layer was calculated by obtaining the average of the second coating layer thicknesses measured by the same method as above for 20 randomly selected secondary positive material particles among the secondary positive material powder.

[0264] (3) Evaluation of average porosity of lithium metal oxide

[0265] 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.

[0266] (4) Evaluation of the specific surface area of ​​the positive electrode active material

[0267] The specific surface area of ​​lithium transition metal oxides was measured using the BET method (Surface Area and Porosity Analyzer) (Micromeritics, ASAP2020).

[0268] (5) Evaluation of positive electrode active material tap density

[0269] 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.

[0270] (6) Evaluation of the average aspect ratio of primary particles

[0271] 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.

[0272] (7) Evaluation of Al and B content

[0273] 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.

[0274]

[0275] Experimental Example 4: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0276] (1) Evaluation of initial formation discharge capacity and efficiency

[0277] 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.

[0278] (2) 2nd cycle discharge capacity evaluation

[0279] 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.

[0280] (3) Evaluation of room temperature capacity retention rate (25℃, 50 cycles)

[0281] 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.

[0282] (4) Evaluation of average voltage drop

[0283] 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.

[0284] (5) Evaluation of room temperature resistance increase rate (25℃, 50 cycles)

[0285] 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.

[0286]

[0287] Referring to Tables 1 through 4, in the case of Examples 1 through 5, where process conditions such as the number of atomic layer deposition cycles were appropriately controlled within the range according to the present invention, it was confirmed that various physical properties, including the average thickness of the first coating layer, 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 realized in a very desirable manner, resulting in excellent lifespan characteristics. In addition, 2 nd It was confirmed that the cycle discharge capacity was excellently achieved at 193 mAh / g or higher.

[0288] 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. That is, it was confirmed that the anode active material according to the present invention has an Al and B-containing coating layer uniformly coated on the entire surface of the secondary particle and the internal primary particle, thereby improving both the lifespan characteristics and the capacity characteristics.

[0289] In the case of Comparative Examples 2 and 3, when only B was coated using an atomic layer deposition method, it was confirmed that the capacity retention rate was at the 95% level, which was significantly degraded compared to the example.

[0290] In the case of Comparative Examples 4 and 5, as a result of coating only Al by atomic layer deposition, 2 nd It was confirmed that the cycle discharge capacity was significantly degraded compared to the example, at a level of 191 mAh / g, and the capacity retention rate was also somewhat degraded compared to the example, at a level of 98%.

[0291] In other words, it was confirmed that the positive electrode active material according to the present invention maximizes the improvement in lifespan and capacity characteristics through a dual ALD coating of Al and B compared to a single ALD coating of Al or B.

[0292] Meanwhile, in the case of Comparative Example 6, to which a conventional dry B coating was applied, 2 nd It was confirmed that the cycle discharge capacity was significantly degraded compared to the example, at a level of 190 mAh / g, and the capacity retention rate was also somewhat degraded compared to the example, at a level of 97%.

[0293] In addition, in the case of Comparative Example 7, 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, at a level of 190 mAh / g, and the capacity retention rate was also somewhat degraded compared to the example, at a level of 97%.

[0294] 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 too thin as a result of the number of atomic layer deposition cycles being too low. As a result, it was confirmed that the capacitance retention rate, voltage drop, and resistance increase rate characteristics were all degraded compared to the example, and the effect of improving lifespan characteristics was negligible.

[0295] In the case of Reference Example 2, it was confirmed that the average thickness of the first coating layer and the second coating layer was obtained to be too thick as a result of the excessive number of atomic layer deposition cycles. And, as a result, 2 nd It was confirmed that the cycle discharge capacity was significantly degraded compared to the example, with a level of 166 mAh / g, and that the capacity retention rate, voltage drop, and resistance increase rate characteristics were somewhat degraded compared to the example.

[0296]

[0297] 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.

[0298] 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 rod-shaped primary particles, having an excess composition of lithium and manganese; A first coating layer containing Al and B that wraps the entire surface of the above secondary particle in the form of a film; and A second coating layer comprising Al and B, which encases the surface of at least some of the plurality of primary particles present inside the secondary particle in the form of a film. Cathode active material for lithium secondary batteries.

2. In Paragraph 1, The above second 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.

3. In Paragraph 1, The above second 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.

4. In Paragraph 1, A positive electrode active material for a lithium secondary battery in which the average thickness of the first coating layer is thicker than the average thickness of the second coating layer.

5. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the average thickness of the first coating layer is 0.4 to 2.5 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 0.2 to 2.1 nm.

7. In Paragraph 1, A positive electrode active material for a lithium secondary battery in which the ratio of the average thickness of the first coating layer to the average thickness of the second coating layer (first coating layer / second coating layer) is 1.1 to 2.

8. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the first coating layer and the second coating layer comprise an Al-containing compound, the Al-containing compound comprises Al2O3 as a main component, the first coating layer and the second coating layer comprise a B-containing compound, and the B-containing compound comprises B2O3 as a main component.

9. In Paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of Al in the positive electrode active material is 0.003 to 0.03 mol% based on the total molar amount of lithium metal oxide, and the content of B in the positive electrode active material is 0.003 to 0.023 mol% based on the total molar amount of lithium metal oxide.

10. 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.

11. In Paragraph 1, BET specific surface area is 2.5 to 3.5 m² 2 A positive electrode active material for a lithium secondary battery having a g / g and a tap density of 1.6 to 2.2 g / cc.

12. 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.

13. 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.

14. 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 rod-shaped primary particles; and The method includes the step of forming a coating layer containing Al and B on the lithium metal oxide using an atomic layer deposition method. A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein, in the step of forming a coating layer containing Al and B, the entire surface of the secondary particle is covered in a film form, and a first coating layer containing Al and B and the surface of at least some of the plurality of primary particles existing inside the secondary particle are covered in a film form, and a second coating layer containing Al and B is formed.

15. In Paragraph 14, One cycle of the above atomic layer deposition is, A step of forming a B-containing coating layer by supplying a B-containing gas and a first reactant onto a lithium metal oxide; and A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the step of supplying an Al-containing gas and a second reactant onto a lithium metal oxide to form an Al-containing coating layer.

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