Composite cathode active material, method for preparing the same, and cathode and lithium battery including the same

Abstract

Provided are a composite cathode active material, a cathode including the composite cathode active material, a lithium battery, and a method of preparing the composite cathode active material, the composite cathode active material including: a first core including a first lithium transition metal oxide; a second core including a second lithium transition metal oxide; and a shell disposed along a surface of at least one of the first core and the second core, wherein the shell includes at least one first metal oxide and a carbonaceous material, the first metal oxide being represented by the formula M a O b (0

Description

[0001] This application is based on and claims priority to Korean Patent Application No. 10-2021-0166114, filed on November 26, 2021, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] One or more embodiments relate to a composite positive electrode active material, a positive electrode and a lithium battery including the composite positive electrode active material, and a method for preparing the composite positive electrode active material. Background Technology

[0003] As devices become smaller and perform better, it is becoming increasingly important for lithium batteries to be not only smaller and lighter, but also to have higher energy density. In other words, high-capacity lithium batteries are becoming increasingly important.

[0004] To achieve lithium batteries suitable for this purpose, high-capacity positive electrode active materials are being researched.

[0005] Due to side reactions, conventional nickel-based cathode active materials exhibit reduced lifetime characteristics and unsatisfactory thermal stability.

[0006] Therefore, a method is needed to prevent battery performance degradation while incorporating nickel-based cathode active materials. Summary of the Invention

[0007] One aspect provides a novel composite positive electrode active material that can prevent the degradation of lithium battery performance by suppressing side reactions of the composite positive electrode active material and improving the reversibility of electrode reactions.

[0008] On the other hand, a positive electrode comprising the aforementioned composite positive electrode active material is provided.

[0009] On the other hand, a lithium secondary battery employing the aforementioned positive electrode is provided.

[0010] On the other hand, a method for preparing the composite positive electrode active material is provided.

[0011] Additional aspects will be set forth in part in the description which follows, and in part will be apparent from the description or from practice of the disclosed embodiments.

[0012] According to one or more embodiments, a composite cathode active material is provided. The composite cathode active material includes: a first core including a first lithium transition metal oxide; a second core including a second lithium transition metal oxide; and a shell disposed along the surface of at least one of the first core and the second core, wherein the shell includes at least one first metal oxide and a carbonaceous material, and the first metal oxide is represented by the formula M a O b (0 < a ≤ 3 and 0 < b < 4, where if a is 1, 2, or 3, b is not an integer), and wherein the first metal oxide is disposed in a carbonaceous material matrix, M is at least one metal selected from Groups 2 to 13, 15, and 16 of the periodic table, the first lithium transition metal oxide and the second lithium transition metal oxide have different particle sizes from each other, and the second lithium transition metal oxide includes primary particles having a particle size of 1 μm or greater.

[0013] According to one or more embodiments, a cathode including the composite cathode active material is provided.

[0014] According to one or more embodiments, a lithium battery including the cathode is provided.

[0015] According to one or more embodiments, a method for preparing a composite cathode active material is provided. The method includes the following steps: providing a first lithium transition metal oxide; providing a second lithium transition metal oxide; providing a composite; preparing at least one of a first core / shell structure and a second core / shell structure by mechanically grinding the first lithium transition metal oxide and the composite to obtain the first core / shell structure and by mechanically grinding the second lithium transition metal oxide and the composite to obtain the second core / shell structure; and mixing the first core / shell structure with the second lithium transition metal oxide, mixing the second core / shell structure with the first lithium transition metal oxide, or mixing the first core / shell structure with the second core / shell structure, wherein the composite includes at least one first metal oxide and a carbonaceous material, the first metal oxide is represented by the formula M a O b (0 < a ≤ 3 and 0 < b < 4, where if a is 1, 2, or 3, b is not an integer), and wherein the first metal oxide is disposed within a carbonaceous material matrix, M is at least one metal selected from Groups 2 to 13, 15, and 16 of the periodic table, the first lithium transition metal oxide and the second lithium transition metal oxide have different particle sizes from each other, and the second lithium transition metal oxide includes primary particles having a particle size of 1 μm or greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other aspects, features, and advantages of some embodiments disclosed will become more apparent through the following description in conjunction with the drawings.

[0017] Figure 1 This is a scanning electron microscope image of the second lithium transition metal oxide particle used in Example 1.

[0018] Figure 2 This is a scanning electron microscope image of the first lithium transition metal oxide particle used in Example 1.

[0019] Figure 3 This is a schematic diagram of a cross-section of the first lithium transition metal oxide particle used in Example 1.

[0020] Figure 4 This is a schematic diagram of a lithium battery according to an embodiment.

[0021] Figure 5 This is a schematic diagram of a lithium battery according to an embodiment.

[0022] Figure 6 This is a schematic diagram of a lithium battery according to an embodiment. Detailed Implementation

[0023] Reference will now be made in detail to embodiments, examples of which are shown in the accompanying drawings, wherein the same reference numerals always denote the same elements. In this regard, the embodiments may take different forms and should not be construed as limited to the description set forth herein. Therefore, the embodiments are described below only by reference to the accompanying drawings to explain aspects of this specification. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of…” modify the entire list of elements when following a list of elements, without modifying individual elements within the list.

[0024] The inventive concept, which will be described more fully below, can have various variations and embodiments, and specific embodiments will be shown and described in more detail with reference to the accompanying drawings. However, the inventive concept should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are to be understood to cover all variations, equivalents, or alternatives that fall within the scope of the inventive concept.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are also intended to include the plural forms. As used herein, when the terms “comprising” and / or “including” and variations thereof are used, it indicates the presence of the stated features, regions, integers, steps, operations, elements, components, ingredients, materials, or combinations thereof, but does not exclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, ingredients, materials, or combinations thereof. Depending on the context, as used herein, “and / or” can be interpreted as “and” or “or.”

[0026] In the figures, the thickness of layers and regions may be exaggerated for clarity and convenience. Throughout the specification, the same reference numerals denote the same elements. When describing a component (such as a layer, film, region, or plate) as "above" or "on" another component, that component may be directly above the other component, or a third component may be placed between them. It will be understood that although the terms "first," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another.

[0027] In this application, if the particles are spherical, the term "particle size" refers to the average particle size, while for non-spherical particles, the term refers to the average principal axis length of the particles. The particle size can be measured using a particle size analyzer (PSA). The "particle size" can be, for example, the average diameter of the particles. The average particle size can be, for example, the median particle size (D50). The median particle size (D50) refers to the particle size corresponding to 50 vol% of the cumulative volume in a particle size distribution, such as that measured by laser diffraction, when counting from the smallest particle size.

[0028] The composite positive electrode active material, the positive electrode containing the composite positive electrode active material, and the lithium battery, as well as the method for preparing the composite positive electrode active material, will be described in more detail below according to exemplary embodiments.

[0029] The composite positive electrode active material may include: a first core comprising a first lithium transition metal oxide; a second core comprising a second lithium transition metal oxide; and a shell disposed along the surface of at least one of the first core and the second core, wherein the shell comprises at least one first metal oxide and a carbonaceous material, the first metal oxide being of formula M a O b(0 < a ≤ 3, 0 < b < 4, where, if a is 1, 2, or 3, then b is not an integer) represents, wherein the first metal oxide is disposed within the carbonaceous material matrix, M is at least one metal selected from Groups 2 to 13, 15, and 16 of the Periodic Table of the Elements, the first lithium transition metal oxide and the second lithium transition metal oxide have different average particle sizes from each other, and the second lithium transition metal oxide includes primary particles having a particle size of about 1 μm or greater.

[0030] Hereinafter, the following description is for the purpose of providing a theoretical basis, and this is only for helping to understand the inventive concept disclosed herein and does not mean to limit the inventive concept in any way. This theoretical basis provides the excellent effects of the composite cathode active material according to the embodiments.

[0031] Referring to Figure 1 , the primary particles included in the second lithium transition metal oxide may have a monolithic particle shape. By including primary particles (i.e., monolithic particles) having a particle size of 1 μm or greater, the second lithium transition metal oxide has a reduced specific surface area and reduced crack formation during charge / discharge, and thus the side reaction with the electrolyte during charge / discharge can be reduced. Therefore, the cycle characteristics of a lithium battery employing the composite cathode active material containing the above-described second lithium transition metal oxide can be further improved. When the second lithium transition metal oxide is an aggregate of a plurality of primary particles having a particle size of less than 1 μm, the specific surface area of the aggregate increases, and as the formation of cracks during charge / discharge increases, the side reaction with the electrolyte during the charge / discharge process increases. The primary particles included in the second lithium transition metal oxide having a particle size of 1 μm or greater may be, for example, single crystal particles.

[0032] Furthermore, the composite positive electrode active material may include a first core corresponding to a first lithium transition metal oxide and a second core corresponding to a second lithium transition metal oxide. Since the first and second lithium transition metal oxides have different particle sizes, the second core can be disposed in the pores between the first cores, or vice versa. Therefore, when one core particle is additionally disposed in the pores between other core particles, the ionic conductivity of the positive electrode containing the aforementioned composite positive electrode active material can be improved. Furthermore, since the shell of the core particle contains a carbonaceous material, when one core particle is additionally disposed in the pores between other core particles, the electronic conductivity of the positive electrode containing the aforementioned composite positive electrode active material can be improved. Therefore, the high-temperature cycle characteristics of the lithium battery containing the composite positive electrode active material can be improved, and the increase in its internal resistance can be suppressed. Furthermore, since one core particle is additionally disposed in the pores between other core particles, the energy density of the lithium battery containing the composite positive electrode active material can be improved. Meanwhile, in conventional cathodes, the electronic conductivity of the cathode is improved because carbonaceous conductive materials are placed in the pores between the active material particles. However, since carbonaceous conductive materials lack ionic conductivity, the ionic conductivity of the cathode decreases. Furthermore, this decrease in ionic conductivity becomes more pronounced as the thickness of the active material layer increases. Therefore, the performance degradation of lithium batteries using this conventional cathode becomes more significant.

[0033] By utilizing a composite comprising multiple first metal oxides disposed within a carbonaceous material matrix, the composite positive electrode active material can prevent the aggregation of the carbonaceous material and allow for the formation of a uniform shell on the first and / or second cores. Therefore, by effectively preventing contact between the core and the electrolyte, side reactions resulting from such contact can be prevented. Furthermore, the formation of a resistive layer can be suppressed due to the inhibition of cation mixing caused by the electrolyte. Additionally, the elution of transition metal ions can be suppressed. The carbonaceous material can be, for example, a crystalline carbonaceous material. The carbonaceous material can be, for example, a carbonaceous nanostructure. The carbonaceous material can be, for example, a carbonaceous two-dimensional nanostructure. The carbonaceous material can be, for example, graphene. In this case, the shell comprising graphene and / or a graphene matrix is ​​elastic, thus flexibly adapting to volume changes in the composite positive electrode active material during charging / discharging, resulting in the suppression of crack formation within the composite positive electrode active material. Due to the high electronic conductivity of graphene, the interfacial resistance between the composite positive electrode active material and the electrolyte can be reduced. Therefore, even when a shell containing graphene is introduced, the internal resistance of the lithium battery can remain unchanged or decrease. Conversely, conventional carbonaceous materials tend to aggregate, making it difficult to form a uniform coating on lithium transition metal oxide cores.

[0034] Compared to conventional carbonaceous materials derived from graphite, the carbonaceous material included in the shell of the composite positive electrode active material is derived from a graphene matrix, thus exhibiting relatively low density and high porosity. The interplanar spacing d002 of the carbonaceous material included in the shell of the composite positive electrode active material can be, for example... or larger or larger or larger or larger or larger or larger or Or larger. The interplanar spacing d002 of the carbonaceous material included in the shell of the composite positive electrode active material can be, for example, approximately to approximately about to approximately about to approximately about to approximately Or about to approximately Meanwhile, the interplanar spacing d002 of conventional carbonaceous materials derived from graphite can be, for example... or smaller or about to approximately

[0035] When charged / discharged at high voltages, the first metal oxide, due to its voltage-resistant properties, can prevent the degradation of the lithium transition metal oxide contained in the core. For example, the casing can include a single type of first metal oxide or two or more different types of first metal oxides. Therefore, lithium batteries incorporating the aforementioned composite positive electrode active material can exhibit improved high-temperature and high-voltage cycle characteristics.

[0036] In the composite positive electrode active material, for example, the content of the shell relative to the total weight of the composite positive electrode active material can be from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2.5 wt%, from about 0.5 wt% to about 2 wt%, or from about 0.1 wt% to about 1.5 wt%. Furthermore, the content of the first metal oxide relative to the total weight of the composite positive electrode active material can be, for example, from about 0.06 wt% to about 1.8 wt%, from about 0.06 wt% to about 1.5 wt%, from about 0.06 wt% to about 1.2 wt%, or from about 0.06 wt% to about 0.9 wt%. Since the composite positive electrode active material includes a shell and a first metal oxide within such ranges, the cycle characteristics of the lithium battery can be further improved.

[0037] Reference Figure 2The composite positive electrode active material may include a first lithium transition metal oxide, and the first lithium transition metal oxide may include secondary particles comprising multiple primary particles. (See reference...) Figure 3 Secondary particles can have a structure in which multiple primary particles are arranged radially. For example, primary particles can be plate-like particles. The main axes of plate-like primary particles can be arranged radially. Therefore, secondary particles of the first lithium transition metal oxide can have a structure in which multiple plate-like primary particles are arranged radially. As used herein, the term "radial" means that the thickness direction of the primary particles is perpendicular to the direction toward the center of the secondary particle. As used herein, the term "plate-like particle" means a particle whose thickness is less than the length of its main axis (planar direction). The main axis length of a plate-like particle refers to the maximum length of the widest plane of the plate-like particle. That is, a plate-like particle is a primary particle structure in which the length of the primary particles in one axial direction (i.e., the thickness direction) is less than the length of the main axis in another direction (i.e., the planar direction). Plate-like primary particles can have shapes such as polygonal nanoplates (e.g., hexagonal plates), circular nanodisks, rectangular shapes, etc. The ratio of the average thickness to the average length of the plate-like primary particles can be from about 1:2 to about 1:19 or from about 1:2 to about 1:5. A structure in which multiple plate-shaped primary particles are arranged radially refers to a structure in which the plate-shaped primary particles are arranged such that the thickness direction of the plate-shaped primary particles is perpendicular to the direction from the surface of the secondary particles toward the center of the secondary particles.

[0038] Reference Figure 2For example, since the first lithium transition metal oxide secondary particles have a structure in which multiple plate-like primary particles are arranged radially, the lithium diffusion paths between relatively enlarged grain boundaries and the crystal planes (e.g., (001) planes) capable of transporting lithium outwards can be more exposed on and around the surface of the first lithium transition metal oxide secondary particles. Therefore, the lithium diffusion rate can be increased in the first lithium transition metal oxide secondary particles having this structure. As a result, the initial capacity of the lithium battery containing the first lithium transition metal oxide secondary particles can be improved and the discharge capacity increased. In addition, since the first lithium transition metal oxide secondary particles have a structure in which plate-like primary particles are arranged radially, the pores exposed on the surface between the plate-like primary particles are positioned toward the center of the secondary particles. As a result, the diffusion of lithium from the surface of the secondary particles into the secondary particles can be promoted. The inner and outer portions of the first lithium transition metal oxide secondary particles can have closed pores and / or open pores. Closed pores are difficult to contain electrolytes, while open pores can contain electrolytes, etc. Since the first lithium transition metal oxide secondary particles include radially arranged plate-like primary particles, uniform contraction and expansion during lithium insertion and extraction are possible. The pores present in the (001) direction, which is the direction of primary particle expansion during lithium insertion and extraction, can be used to buffer volume changes. Due to the small size of the primary plate particles, the likelihood of cracks appearing in the secondary particles during the contraction and expansion of the primary particles can be reduced. Since the pores inside the secondary particles can accommodate the volume changes of the plate-like primary particles, the likelihood of cracks appearing between the plate-like primary particles can be further reduced during charging and discharging. Therefore, lithium batteries containing first lithium transition metal oxide secondary particles can have improved lifespan characteristics and reduced internal resistance increases.

[0039] The first lithium transition metal oxide secondary particles may contain pores within the secondary particles. The first lithium transition metal oxide secondary particles may include an inner portion and an outer portion, and the porosity of the inner portion may be higher than that of the outer portion. As used herein, the term "outer portion of the secondary particle" refers, for example, a region within approximately 2 μm from the surface of the secondary particle toward its center. Alternatively, the term "outer portion of the secondary particle" refers to a region representing approximately 40% of the total distance from the center of the secondary particle to its surface from the surface of the secondary particle. As used herein, the term "inner portion of the secondary particle" refers to the remaining region excluding the region within approximately 2 μm from the surface of the secondary particle. Alternatively, the term "inner portion of the secondary particle" refers to a region representing approximately 60% of the total distance from the center of the secondary particle to its surface from the center of the secondary particle. As used herein, the term "porosity of the inner portion" refers to the ratio of the volume occupied by pores to the volume of the inner portion of the secondary particle. As used herein, the term "porosity of the outer portion" refers to the ratio of the volume occupied by pores to the volume of the outer portion of the secondary particle.

[0040] In the composite cathode active material, the first lithium transition metal oxide can be a large-diameter lithium transition metal oxide with a larger particle size than the second lithium transition metal oxide. For example, the second lithium transition metal oxide can be a small-diameter lithium transition metal oxide with a smaller particle size than the first lithium transition metal oxide. For example, the first core can be a large-diameter lithium transition metal oxide, and the second core can be a small-diameter lithium transition metal oxide. For example, the second core, with an average particle size smaller than the average particle size of the first core, can be disposed in the pores between the first cores. Since the second core particles, as small-diameter particles, are disposed in the pores between the first core particles, as large-diameter particles, both the ionic conductivity and electronic conductivity of the cathode including the composite cathode active material can be improved simultaneously. Furthermore, the energy density of the cathode including the composite cathode active material can be improved. As a result, the lithium battery including the composite cathode active material can have improved energy density and improved cycle characteristics.

[0041] The first lithium transition metal oxide and the second lithium transition metal oxide can exhibit, for example, a bimodal particle size distribution in the particle size distribution diagram. For instance, in a particle size distribution diagram obtained using a particle size analyzer (PSA), the composite positive electrode active material can display a bimodal particle size distribution with two peaks. This bimodal particle size distribution can have a first peak corresponding to the first lithium transition metal oxide and a second peak corresponding to the second lithium transition metal oxide.

[0042] The first lithium transition metal oxide and the second lithium transition metal oxide may have a particle size ratio, for example, from about 3:1 to about 40:1, from about 3:1 to about 30:1, from about 3:1 to about 20:1, from about 3:1 to about 10:1, or from about 3:1 to about 5:1. Because the first lithium transition metal oxide and the second lithium transition metal oxide have a particle size ratio within such a range, the energy density and / or cycle characteristics of the lithium battery including the composite cathode active material can be further improved.

[0043] The particle size of the first lithium transition metal oxide can be, for example, about 8 μm to about 30 μm, about 9 μm to about 25 μm, about 9 μm to about 20 μm, about 9 μm to about 15 μm, or about 9 μm to about 12 μm. The particle size of the first lithium transition metal oxide can be, for example, a median particle size (D50). The particle size of the second lithium transition metal oxide can be, for example, about 1 μm to about less than 8 μm, about 1 μm to about 7 μm, about 1 μm to about 6 μm, about 1 μm to about 5 μm, or about 1 μm to about 4 μm. The particle size of the second lithium transition metal oxide can be, for example, a median particle size (D50). Since the first lithium transition metal oxide and the second lithium transition metal oxide each have an average particle size within such ranges, the energy density and / or cycle characteristics of the lithium battery including the composite cathode active material can be further improved. The particle size of the first lithium transition metal oxide and the second lithium transition metal oxide can be measured, for example, using a measuring device for laser diffraction or dynamic light scattering. The average particle size can be measured, for example, by a laser scattering particle size distribution analyzer (e.g., the LA-920 manufactured by HORIBA) and is the volume-based median particle size (D50) at 50% cumulative percentage from the minimum particle size.

[0044] The weight ratio of the first lithium transition metal oxide to the second lithium transition metal oxide can be, for example, about 90:10 to about 60:40, about 85:15 to about 65:35, about 80:20 to about 65:35, or about 75:25 to about 65:35. Because the first lithium transition metal oxide and the second lithium transition metal oxide have a weight ratio within such a range, the energy density and / or cycle characteristics of the lithium battery including the composite cathode active material can be further improved.

[0045] In composite cathode active materials, for example, the shell may be disposed only on the first core. Specifically, the shell may be disposed on the first core but not on the second core. For example, the shell may be disposed on the first lithium transition metal oxide, which is a large-diameter lithium transition metal oxide, but not on the second lithium transition metal oxide, which is a small-diameter lithium transition metal oxide. The first core / shell structure can be obtained by disposing the shell on the first core. By disposing the shell on the surface of the large-diameter lithium transition metal oxide, the specific surface area of ​​the large-diameter composite cathode active material can be reduced, the side reactions between the large-diameter lithium transition metal oxide and the electrolyte can be reduced, and the electronic conductivity of the large-diameter lithium transition metal oxide can be improved. As a result, the energy density and / or cycle characteristics of the lithium battery can be further improved.

[0046] In composite positive electrode active materials, for example, the shell can be disposed only on the second core. Specifically, the shell can be disposed on the second core but not on the first core. For example, the shell can be disposed on the second lithium transition metal oxide, which is a small-diameter lithium transition metal oxide, but not on the first lithium transition metal oxide, which is a large-diameter lithium transition metal oxide. The second core / shell structure can be obtained by disposing the shell on the second core. By disposing the shell on the surface of the small-diameter lithium transition metal oxide, side reactions between the small-diameter lithium transition metal oxide and the electrolyte can be reduced, and the electronic conductivity of the small-diameter lithium transition metal oxide can be improved. As a result, the energy density and / or cycle characteristics of the lithium battery can be further improved.

[0047] In composite cathode active materials, for example, a shell can be disposed on both a first core and a second core. That is, the shell can be disposed on both the first core and the second core simultaneously. For example, the shell can be disposed on a first lithium transition metal oxide, which is a large-diameter lithium transition metal oxide, and also on a second lithium transition metal oxide, which is a small-diameter lithium transition metal oxide. A first core / shell structure can be obtained by disposing the shell on the first core, and a second core / shell structure can be obtained by disposing the shell on the second core. Since the composite cathode active material includes both the first core / shell structure and the second core / shell structure, the energy density and / or cycle characteristics of the lithium battery can be further improved.

[0048] The first metal oxide may include at least one metal selected from Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se. The first metal oxide may be, for example, selected from Al₂O₃. z (0 <z<3)、NbO x (0 <x<2.5)、MgO x (0 <x<1)、Sc2O z (0 <z<3)、TiOy (0 < y < 2), ZrO y (0 < y < 2), V2O z (0 < z < 3), WO y (0 < y < 2), MnO y (0 < y < 2), Fe2O z (0 < z < 3), Co3O w (0 < w < 4), PdO x (0 < x < 1), CuO x (0 < x < 1), AgO x (0 < x < 1), ZnO x (0 < x < 1), Sb2O z (0 < z < 3) and SeO y At least one of (0 < y < 2). Since such a first metal oxide is disposed within the carbonaceous material matrix, the uniformity of the shell disposed on the core can be improved, and the voltage resistance property of the composite positive electrode active material can be further improved. For example, the shell may include Al2O x (0 < x < 3) as the first metal oxide.

[0049] The shell may further include at least one second metal oxide represented by M a O c (0 < a ≤ 3 and 0 < c ≤ 4, where if a is 1, 2, or 3, then c is an integer). M may be at least one metal selected from Groups 2 to 13, 15, and 16 of the periodic table of elements. For example, the second metal oxide may include the same metal as the first metal oxide, and the ratio (c / a) of c to a in the second metal oxide may have a value greater than the ratio (b / a) of b to a in the first metal oxide. For example, c / a > b / a. The second metal oxide may be selected from, for example, Al2O3, NbO, NbO2, Nb2O5, MgO, Sc2O3, TiO2, ZrO2, V2O3, WO2, MnO2, Fe2O3, Co3O4, PdO, CuO, AgO, ZnO, Sb2O3, and SeO2. The first metal oxide may be, for example, a reduction product of the second metal oxide. The first metal oxide may be obtained by partial or complete reduction of the second metal oxide. Therefore, compared with the second metal oxide, the first metal oxide may have a lower oxygen content and a lower oxidation number. For example, the shell may include the first metal oxide (Al2O x (0 < x < 3)) and the second metal oxide (Al2O3).

[0050] Hereinafter, unless otherwise specified, the term "core" is interpreted to include at least one of "first core" and "second core".

[0051] In the following text, unless otherwise stated, the term "lithium transition metal oxide" is to be interpreted as including at least one of "first lithium transition metal oxide" and "second lithium transition metal oxide".

[0052] In composite cathode active materials, for example, the carbonaceous material included in the shell and the transition metal of the lithium transition metal oxide included in the core can be chemically bonded via chemical bonds. The carbon atoms (C) of the carbonaceous material included in the shell and the transition metal (Me) of the lithium transition metal oxide can be chemically bonded, for example, via CO-Me bonds (e.g., CO-Ni bonds or CO-Co bonds) through oxygen atoms. When the carbonaceous material included in the shell and the lithium transition metal oxide included in the core are chemically bonded, the core and shell form a complex. Therefore, the resulting complex can be distinguished from a simple physical mixture of carbonaceous material and lithium transition metal oxide.

[0053] Furthermore, the carbonaceous material and the first metal oxide included in the shell can also be chemically bonded via chemical bonds. Here, chemical bonds can be, for example, covalent bonds or ionic bonds. Covalent bonds can be bonds including at least one of, for example, ester groups, ether groups, carbonyl groups, amide groups, carbonate groups, and anhydride groups. Ionic bonds can be bonds including, for example, carboxylate ions, ammonium ions, acyl cation groups, etc.

[0054] The thickness of the shell can be, for example, about 1 nm to about 5 μm, about 1 nm to about 1 μm, about 1 nm to about 500 nm, about 1 nm to about 200 nm, about 1 nm to about 100 nm, about 1 nm to about 90 nm, about 1 nm to about 80 nm, about 1 nm to about 70 nm, about 1 nm to about 60 nm, about 1 nm to about 50 nm, about 1 nm to about 40 nm, about 1 nm to about 30 nm, or about 1 nm to about 20 nm. Because the shell has a thickness within such a range, the cathode including the composite positive electrode active material can have further improved electronic conductivity.

[0055] The composite positive electrode active material may also include, for example, a third metal doped on the core or a third metal oxide coated on the core. Furthermore, a shell may be disposed on the third metal doped in the core, or on the third metal oxide coated on the core. For example, after a third metal is doped on the surface of a lithium transition metal oxide included in the core, or a third metal oxide is coated on the surface of a lithium transition metal oxide included in the core, a shell may be disposed on the third metal and / or the third metal oxide. For example, the composite positive electrode active material may include: a core; an intermediate layer disposed on the core; and a shell disposed on the intermediate layer, wherein the intermediate layer may include a third metal or a third metal oxide. The third metal may be at least one metal selected from Al, Zr, W, and Co, and the third metal oxide may be Al2O3, Li2O-ZrO2, WO2, CoO, Co2O3, Co3O4, or combinations thereof.

[0056] A shell disposed along the surface of at least one of the first and second cores may include at least one selected from, for example, a composite and a milling product of the composite, the composite comprising a first metal oxide and a carbonaceous material (e.g., graphene). The first metal oxide may be disposed in a matrix of carbonaceous material (e.g., a graphene matrix). The shell may be prepared, for example, from a composite comprising a first metal oxide and a carbonaceous material (e.g., graphene). In addition to the first metal oxide, the composite may also include a second metal oxide. The composite may include, for example, two or more types of first metal oxides. The composite may include, for example, two or more types of first metal oxides and two or more types of second metal oxides.

[0057] Relative to the total weight of the composite positive electrode active material, the amount of at least one of the composite and its polished articles included in the composite positive electrode active material can be 3 wt% or less, 2 wt% or less, 1 wt% or less, or 0.5 wt% or less. Relative to the total weight of the composite positive electrode active material, the amount of at least one of the composite and its polished articles can be from about 0.01 wt% to about 3 wt%, from about 0.01 wt% to about 1 wt%, from about 0.01 wt% to about 0.7 wt%, or from about 0.01 wt% to about 0.5 wt%. Because the composite positive electrode active material includes at least one of the composite and its polished articles in amounts within such ranges, lithium batteries including the composite positive electrode active material can have further improved cycle characteristics.

[0058] The amount of at least one of the composite and its polished articles included in the first core / shell structure relative to the total weight of the first core / shell structure can be 3 wt% or less, 2 wt% or less, 1 wt% or less, or 0.5 wt% or less. The amount of at least one of the composite and its polished articles relative to the total weight of the first core / shell structure can be about 0.01 wt% to about 3 wt%, about 0.01 wt% to about 1 wt%, about 0.01 wt% to about 0.7 wt%, or about 0.01 wt% to about 0.5 wt%. Because the first core / shell structure contains at least one of the composite and its polished articles in amounts within such ranges, lithium batteries including composite positive electrode active materials can have further improved cycle characteristics.

[0059] The content of at least one of the composite and its milled articles included in the second core / shell structure relative to the total weight of the second core / shell structure can be 3 wt% or less, 2 wt% or less, 1 wt% or less, or 0.5 wt% or less. The amount of at least one of the composite and its milled articles relative to the total weight of the second core / shell structure can be from about 0.01 wt% to about 3 wt%, from about 0.01 wt% to about 1 wt%, from about 0.01 wt% to about 0.7 wt%, or from about 0.01 wt% to about 0.5 wt%. Because the second core / shell structure includes at least one of the composite and its milled articles in such ranges, the lithium battery including the composite positive electrode active material can have further improved cycle characteristics.

[0060] The particle size of at least one of the first and second metal oxides included in the composite can be from about 1 nm to about 1 μm, from about 1 nm to about 500 nm, from about 1 nm to about 100 nm, from about 1 nm to about 50 nm, from about 1 nm to about 30 nm, from about 3 nm to about 30 nm, from about 3 nm to about 25 nm, from about 5 nm to about 25 nm, from about 5 nm to about 20 nm, from about 7 nm to about 20 nm, or from about 7 nm to about 15 nm. Due to the particle size within such a nanoscale range, the first and / or second metal oxides can be more uniformly distributed within the carbonaceous matrix of the composite. Therefore, the composite can be uniformly coated on the core without aggregation, thereby forming a shell. Furthermore, due to the particle size within such a range, the first and / or second metal oxides can be more uniformly distributed on the core. Therefore, since the first and / or second metal oxides are uniformly disposed on the core, voltage withstand properties can be achieved more effectively. The particle size of the first and second metal oxides can be measured, for example, by using a measuring device utilizing laser diffraction or dynamic light scattering. Particle size can be measured, for example, by a laser scattering particle size distribution analyzer (e.g., the LA-920 manufactured by HORIBA), and is the volume-based median particle size (D50) at a cumulative percentage of 50% from the smallest particle size.

[0061] The uniformity deviation of at least one selected from the first metal oxide and the second metal oxide included in the composite can be 3% or less, 2% or less, or 1% or less. For example, uniformity can be obtained by XPS. Therefore, in the composite, at least one selected from the first metal oxide and the second metal oxide can be uniformly distributed with a deviation of 3% or less, 2% or less, or 1% or less.

[0062] The carbonaceous material included in the composite may have, for example, a branched structure, and at least one metal oxide selected from a first metal oxide and a second metal oxide may be distributed within the branched structure of the carbonaceous material. The branched structure of the carbonaceous material may include, for example, multiple carbonaceous material particles in contact with each other. Because the carbonaceous material has this branched structure, various conductive paths (or "conduction pathways") can be provided. The carbonaceous material included in the composite may be, for example, graphene. Graphene may have, for example, a branched structure, and at least one metal oxide selected from a first metal oxide and a second metal oxide may be distributed within the branched structure of the graphene. The branched structure of the graphene may include, for example, multiple graphene particles in contact with each other. Because the graphene has this branched structure, various conductive paths can be provided.

[0063] The carbonaceous material included in the composite can have, for example, a spherical structure, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structure. The spherical structure of the carbonaceous material can have a size of about 50 nm to about 300 nm. Multiple such carbonaceous materials with spherical structures can be present. Because the carbonaceous material has a spherical structure, the composite can have a robust structure. The carbonaceous material included in the composite can be, for example, graphene. Graphene can have, for example, a spherical structure, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structure. The spherical structure of graphene can have a size of about 50 nm to about 300 nm. Multiple such graphenes with spherical structures can be present. Because graphene has a spherical structure, the composite can have a robust structure.

[0064] The carbonaceous material included in the composite can have, for example, a helical structure in which multiple spherical structures are connected, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structures of the helical structure. The helical structure of the carbonaceous material can have a size of about 500 nm to about 100 μm. Because the carbonaceous material has a helical structure, the composite can have a robust structure. The carbonaceous material included in the composite can be, for example, graphene. Graphene can have, for example, a helical structure in which multiple spherical structures are connected, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structures of the helical structure. The helical structure of graphene can have a size of about 500 nm to about 100 μm. Because graphene has a helical structure, the composite can have a robust structure.

[0065] The carbonaceous material included in the composite can have a cluster structure, for example, comprising multiple spherical clusters, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structure of the cluster structure. The cluster structure of the carbonaceous material can have a size of about 0.5 mm to about 10 mm. Because the carbonaceous material has a cluster structure, the composite can have a robust structure. The carbonaceous material included in the composite can be, for example, graphene. Graphene can have a cluster structure, for example, comprising multiple spherical clusters, and at least one metal oxide selected from a first metal oxide and a second metal oxide can be distributed within the spherical structure of the cluster structure. The cluster structure of graphene can have a size of about 0.5 mm to about 10 mm. Because graphene has a cluster structure, the composite can have a robust structure.

[0066] The composite may have, for example, a faceted-ball structure, and at least one selected from the first metal oxide and the second metal oxide may be distributed within or on the surface of the structure. Since the composite has such a faceted-ball structure, the composite can easily coat the irregular surface bumps of the core.

[0067] The composite may have, for example, a planar structure, and at least one selected from the first metal oxide and the second metal oxide may be distributed within or on the surface of the structure. Since the composite has such a two-dimensional planar structure, the composite can easily coat the irregular surface bumps of the core.

[0068] The carbonaceous material included in the composite may extend a distance of 10 nm or less from the first metal oxide and may include at least 1 to 20 carbonaceous material layers. For example, when multiple carbonaceous material layers are deposited, the carbonaceous material having a total thickness of 12 nm or less may be disposed on the first metal oxide. For example, the total thickness of the carbonaceous material may be about 0.6 nm to about 12 nm. The carbonaceous material included in the composite may be, for example, graphene. The graphene may extend a distance of 10 nm or less from the first metal oxide and may include at least 1 to 20 graphene layers. For example, when multiple graphene layers are deposited, the graphene having a total thickness of 12 nm or less may be disposed on the first metal oxide. For example, the total thickness of the graphene may be about 0.6 nm to about 12 nm.

[0069] The first core and the second core included in the composite cathode active material may each independently include, for example, a lithium transition metal oxide represented by the following Formula 1 to Formula 5.

[0070] <Formula 1>

[0071] Li a Ni x Co y M z O 2-b A b

[0072] In Formula 1, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.8 ≤ x ≤ 1, 0 ≤ y ≤ 0.3, and 0 < z ≤ 0.3, where x + y + z = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof, and A is F, S, Cl, Br, or a combination thereof.

[0073] <Formula 2>

[0074] LiNi x Co y Mn z O2

[0075] <Formula 3>

[0076] LiNi x Co y Al z O2

[0077] In Formulas 2 and 3, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, and 0 < z ≤ 0.2, where x + y + z = 1.

[0078] <Formula 4>

[0079] LiNi x Co y Mn z Al w O2

[0080] In Formula 4, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, and 0 < w ≤ 0.2, where x + y + z + w = 1.

[0081] The lithium transition metal oxides in Formulas 1 to 4 can provide excellent initial capacity, room temperature life characteristics, and high temperature life characteristics while having a high nickel content of 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more relative to the total mole number of the transition metals. For example, relative to the total mole number of the transition metals, the lithium transition metal oxides in Formulas 1 to 4 can have a nickel content of about 80 mol% to about 99 mol%, about 85 mol% to about 99 mol%, or about 90 mol% to about 97 mol%.

[0082] <Formula 5>

[0083] Li a Co x M y O 2-b A b

[0084] In Formula 5, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.9 ≤ x ≤ 1, and 0 ≤ y ≤ 0.1, where x + y = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof, and A is F, S, Cl, Br, or a combination thereof.

[0085] According to another embodiment, the positive electrode includes the aforementioned composite positive electrode active material. By including the aforementioned composite positive electrode active material, the positive electrode can provide improved energy density, improved cycle characteristics, and increased conductivity.

[0086] The positive electrode can be prepared by the exemplary method described below, but the method is not limited thereto and can be adjusted according to the desired conditions.

[0087] First, a positive electrode active material composition can be prepared by mixing the aforementioned composite positive electrode active material, conductive agent, binder, and solvent. The prepared positive electrode active material composition can then be directly coated onto an aluminum current collector and dried on the aluminum current collector to produce a positive electrode plate with a positive electrode active material layer formed thereon. Alternatively, the positive electrode active material composition can be cast onto a separate support, and then a film layer peeled from the support can be stacked onto the aluminum current collector to form a positive electrode plate with a positive electrode active material layer formed thereon.

[0088] Examples of conductive agents may include: carbon black, graphite powder, natural graphite, artificial graphite, acetylene black, Ketjen black, and carbon fibers; carbon nanotubes; metal powders, metal fibers, or metal tubes such as copper, nickel, aluminum, silver, etc.; and conductive polymers such as polyphenylene derivatives, but are not limited to the foregoing components, and examples of conductive agents may be any material used as a conductive agent in the art. Optionally, for example, the positive electrode may contain any conductive agent.

[0089] Examples of adhesives may include vinylidene fluoride / hexafluoropropylene copolymers, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE), mixtures of the foregoing polymers, styrene-butadiene rubber polymers, and solvents such as N-methylpyrrolidone (NMP), acetone, water, etc., but are not limited thereto, and the solvent may be any solvent used in the art.

[0090] It is also possible to create pores inside the electrode plate by further adding plasticizer and pore forming agent to the positive electrode active material composition.

[0091] The amounts of positive electrode active material, conductive agent, binder, and solvent used in the positive electrode are at levels commonly used in lithium batteries. Depending on the intended use and composition of the lithium battery, one or more of the conductive agent, binder, and solvent may be omitted.

[0092] The amount of binder included in the positive electrode may be from about 0.1 wt% to about 10 wt% or from about 0.1 wt% to about 5 wt% relative to the total weight of the positive electrode active material layer. The amount of composite positive electrode active material included in the positive electrode may be from about 80 wt% to about 99 wt%, from about 90 wt% to about 99 wt% or from about 95 wt% to about 99 wt% relative to the total weight of the positive electrode active material layer.

[0093] In addition to the aforementioned composite positive electrode active materials, the positive electrode can also include other common positive electrode active materials.

[0094] Such common positive electrode active materials can be, but are not limited to, any lithium-containing metal oxide commonly used in the art. Examples of such common positive electrode active materials include one or more composite oxides selected from lithium and metals selected from cobalt, manganese, nickel, and combinations thereof, and as specific examples include compounds represented by any one of the following formulas: Li a A 1-b B b D2 (in this formula, 0.90≤a≤1 and 0≤b≤0.5); Li a E 1-b B b O 2-c D c (In this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B b O 4-c D c (In this formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b- c Co b B c O 2-α F α (In this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Co b B c O 2-α F2 (in this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mnb B c D α (In this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b B c O 2-α F α (In this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b B c O 2-α F2 (in this formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2 (in this formula, 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2 (in this formula, 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NiG b O2 (in this formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a CoG b O2 (in this formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a MnG b O2 (in this formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a Mn2G b O4 (in this formula, 0.90≤a≤1, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3 (0≤f≤2); Li (3-f) Fe2(PO4)3 (0≤f≤2); and LiFePO4.

[0095] In the formulas representing the above compounds, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. Compounds having a coating added to the surface of the above compounds can also be used, and mixtures of the above compounds and compounds having a coating added thereon can also be used. The coating added to the surface of the above compounds can include, for example, compounds of the coating element, such as oxides and hydroxides of the coating element, hydroxyoxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compounds forming the above coatings can be amorphous or crystalline. The coating elements included in the coating can be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The method by which the coating is formed can be selected from those that do not adversely affect the physical properties of the positive electrode active material. Examples of coating methods can include spraying, dipping, etc. Specific coating methods are well known to those skilled in the art and will therefore not be described in further detail.

[0096] According to another embodiment, the lithium battery uses a positive electrode containing the aforementioned composite positive electrode active material.

[0097] By using a cathode containing the aforementioned composite cathode active material, lithium batteries can provide improved energy density, cycle characteristics, and thermal stability.

[0098] Lithium batteries can be prepared by the exemplary methods described below, but the methods are not limited thereto and can be adjusted according to desired conditions.

[0099] First, the cathode can be prepared using the cathode preparation method described above.

[0100] Next, the negative electrode can be prepared as follows. Except, for example, by using a negative electrode active material instead of the composite positive electrode active material, the negative electrode can be prepared using essentially the same method as the positive electrode. Furthermore, in the negative electrode active material composition, the conductive agent, binder, and solvent can be used that are essentially the same as those used for the positive electrode.

[0101] For example, a negative electrode active material composition can be prepared by mixing a negative electrode active material, a conductive agent, a binder, and a solvent, and the prepared negative electrode active material composition can be directly coated on a copper current collector to form a negative electrode plate. Alternatively, the prepared negative electrode active material composition can be cast on a separate support, and then the negative electrode active material film peeled from the support can be laminated on the copper current collector to form a negative electrode plate.

[0102] The negative electrode active material can be any material used as a negative electrode active material for a lithium battery in the art. For example, the negative electrode active material can include one or more selected from the group consisting of lithium metal, metals that can be alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbonaceous materials. Examples of metals that can be alloyed with lithium can include Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth metal, or a combination thereof, but not Si), Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth metal, or a combination thereof, but not Sn), etc. For example, Y can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof. The transition metal oxide can be, for example, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc. The non-transition metal oxide can be, for example, SnO2, SiO x (0 < x < 2), etc. The carbonaceous material can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. Examples of crystalline carbon can include graphite containing artificial graphite or natural graphite in amorphous, plate-like, sheet-like, spherical, or fibrous forms. Examples of amorphous carbon can include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, etc.

[0103] The amounts of the negative electrode active material, the conductive agent, the binder, and the solvent can be at levels commonly used in lithium batteries. Depending on the intended use and composition of the lithium battery, one or more of the conductive agent, the binder, and the solvent can be omitted.

[0104] The amount of binder included in the negative electrode, relative to the total weight of the negative electrode active material layer, can be, for example, from about 0.1 wt% to about 10 wt% or from about 0.1 wt% to about 5 wt%. The amount of conductive agent included in the negative electrode, relative to the total weight of the negative electrode active material layer, can be, for example, from about 0.1 wt% to about 10 wt% or from about 0.1 wt% to about 5 wt%. The amount of negative electrode active material included in the negative electrode, relative to the total weight of the negative electrode active material layer, can be, for example, from about 80 wt% to about 99 wt%, from about 90 wt% to about 99 wt%, or from about 95 wt% to about 99 wt%. If the negative electrode active material is lithium metal, the negative electrode may not include binder and conductive agent.

[0105] Next, a separator can be prepared to be placed between the positive and negative electrodes.

[0106] The separator can be any separator commonly used in lithium-ion batteries. For example, any separator exhibiting low resistance to ion migration in the electrolyte while retaining a large amount of electrolyte solution can be used. For instance, the separator can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof. Furthermore, the separator can be in the form of non-woven or woven fabric. Lithium-ion batteries can include, for example, rollable separators formed from polyethylene, polypropylene, etc. Lithium-ion polymer batteries can include, for example, separators with excellent immersion capability in organic liquid electrolytes.

[0107] The diaphragm can be prepared by the exemplary method described below, but the method is not limited thereto and can be adjusted according to the desired conditions.

[0108] First, a membrane composition can be prepared by mixing a polymer resin, filler, and solvent. The membrane composition can be directly coated onto an electrode and dried on the electrode to form a membrane. Alternatively, the membrane composition can be cast onto a support and dried on the support, and a membrane peeled from the support can be laminated on top of the electrode to form a membrane.

[0109] There are no particular restrictions on the polymers used in the preparation of the diaphragm, and any polymer that can be used in the adhesives used for the electrode plates can be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof can be used.

[0110] Next, electrolytes can be prepared.

[0111] Electrolytes can be, for example, organic electrolyte solutions. Organic electrolyte solutions can be prepared by dissolving lithium salts in organic solvents.

[0112] The organic solvent can be any material used as an organic solvent in the art. Examples of the organic solvent can include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and mixtures thereof.

[0113] The lithium salt can be any material used as a lithium salt in the art. For example, the lithium salt can be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where both x and y are natural numbers from 1 to 20), LiCl, LiI, or mixtures thereof.

[0114] Optionally, the electrolyte can be a solid electrolyte. Examples of the solid electrolyte can include boron oxide, lithium oxynitride, etc., but are not limited thereto, and can be any material used as a solid electrolyte in the art. For example, the solid electrolyte can be formed on the negative electrode by a method such as sputtering, or a separate solid electrolyte sheet can be stacked on the negative electrode.

[0115] The solid electrolyte can be, for example, an oxide-based solid electrolyte or a sulfide-based solid electrolyte.

[0116] The solid electrolyte can be, for example, an oxide-based solid electrolyte. The oxide-based solid electrolyte can be selected from Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2 and 0 ≤ y < 3), BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT) (0 ≤ x < 1 and 0 ≤ y < 1), PB(Mg3Nb 2 / 3)O3-PbTiO3 (PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3 (0 < x < 2 and 0 < y < 3), Li x Al y Ti z (PO4)3 (0 < x < 2, 0 < y < 1 and 0 < z < 3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), Li x La y TiO3 (0 < x < 2 and 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2 and Li 3+x La3M2O 12 (M = Te, Nb or Zr and x is an integer from 1 to 10). The solid electrolyte can be prepared by a sintering method or the like. For example, the oxide-based solid electrolyte can be selected from Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M-doped LLZO, M = Ga, W, Nb, Ta or Al, and x is an integer from 1 to 10) among the garnet-type solid electrolytes.

[0117] The sulfide-based solid electrolyte can include, for example, lithium sulfide, silicon sulfide, phosphorus sulfide, boron sulfide or a combination thereof. The sulfide-based solid electrolyte particles can include Li2S, P2S5, SiS2, GeS2, B2S3 or a combination thereof. The sulfide-based solid electrolyte particles can be Li2S or P2S5. It is known that the sulfide-based solid electrolyte particles have a higher lithium ion conductivity than other inorganic compounds. For example, the sulfide-based solid electrolyte can include Li2S and P2S5. If the sulfide solid electrolyte material constituting the sulfide-based solid electrolyte includes Li2S - P2S5, the mixed molar ratio of Li2S to P2S5 can be, for example, in the range of about 50:50 to about 90:10. In addition, by using materials such as Li3PO4, halogens, halogen compounds, Li 2+2xZn 1- x GeO4 (“LISICON”, 0 ≤ x < 1), Li 3+y PO 4-x N x (“LIPON”, 0 < x < 4, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4 (“thio-LISICON”), Li2O - Al2O3 - TiO2 - P2O5 (“LATP”)) added to an inorganic solid electrolyte (such as Li2S - P2S5, SiS2, GeS2, B2S3 or a combination thereof) to prepare an inorganic solid electrolyte can be used as a sulfide solid electrolyte. Non - limiting examples of sulfide solid electrolyte materials can include Li2S - P2S5, Li2S - P2S5 - LiX (X = halogen element), Li2S - P2S5 - Li2O, Li2S - P2S5 - Li2O - LiI, Li2S - SiS2, Li2S - SiS2 - LiI, Li2S - SiS2 - LiBr, Li2S - SiS2 - LiCl, Li2S - SiS2 - B2S3 - LiI, Li2S - SiS2 - P2S5 - LiI, Li2S - B2S3, Li2S - P2S5 - Z m S n (0 < m < 10, 0 < n < 10, Z = Ge, Zn or Ga), Li2S - GeS2, Li2S - SiS2 - Li3PO4 and Li2S - SiS2 - Li p MO q (0 < p < 10, 0 < q < 10, M = P, Si, Ge, B, Al, Ga or In). In this regard, a sulfide - based solid electrolyte material can be prepared by processing raw materials (e.g., Li2S, P2S5, etc.) of the sulfide - based solid electrolyte material such as melt quenching, mechanical grinding, etc. In addition, a calcination process can be performed after the above - mentioned processing. The sulfide - based solid electrolyte can be amorphous, crystalline, or a mixture thereof.

[0118] Refer to Figure 4 , according to Example 1, the lithium secondary battery 1 can include a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 can be wound or folded to form a battery structure 7. The battery structure 7 can be accommodated in a battery case 5. Subsequently, the battery case 5 can be injected with an organic electrolyte solution and sealed with a lid assembly 6, thus completing the lithium secondary battery 1. The battery case 5 has a cylindrical shape, but is not limited thereto, and can have a polygonal shape, a thin - film shape, etc.

[0119] Refer to Figure 5 The lithium secondary battery 1 according to an embodiment may include a positive electrode 3, a negative electrode 2, and a separator 4. The separator 4 may be disposed between the positive electrode 3 and the negative electrode 2, and the positive electrode 3, the negative electrode 2, and the separator 4 may be wound or folded to form a battery structure 7. The battery structure 7 may be housed in a battery casing 5. Electrode terminals 8 may be included as electrical paths for guiding current formed in the battery structure 7 to the outside. The battery casing 5 may be filled with an organic electrolyte solution and sealed to complete the lithium secondary battery 1. The battery casing 5 may have a polygonal shape, but is not limited to this, and may have a cylindrical shape, a thin film shape, etc.

[0120] Reference Figure 6 The lithium secondary battery 1 according to an embodiment may include a positive electrode 3, a negative electrode 2, and a separator 4. The separator 4 may be disposed between the positive electrode 3 and the negative electrode 2 to form a battery structure. The battery structure may be stacked in a bi-cell structure and then housed in a battery casing 5. Electrode terminals 8 may be included as electrical paths for guiding current formed in the battery structure 7 to the outside. The battery casing 5 may be filled with an organic electrolyte solution and sealed to complete the lithium secondary battery 1. The battery casing 5 may have a polygonal shape, but is not limited to this, and may have a cylindrical shape, a thin film shape, etc.

[0121] Pouch-type lithium batteries that use a pouch as the battery casing and Figures 4 to 6 Each of the lithium batteries shown corresponds to a pouch-type lithium battery. A pouch-type lithium battery may include one or more battery structures. A separator may be disposed between the positive and negative electrodes to form the battery structure. The battery structures may be stacked in a dual-cell structure, immersed in an organic electrolyte solution, and housed and sealed in a pouch to form a pouch-type lithium battery. For example, although not shown in the figures, the aforementioned positive, negative, and separator components may simply be stacked and then housed in a pouch as an electrode assembly, or they may be rolled or folded into an electrode assembly in the form of a jelly roll and then housed in a pouch. Subsequently, the pouch may be filled with an organic electrolyte solution and then sealed to complete the lithium battery.

[0122] Lithium-ion batteries possess excellent lifespan and high-rate characteristics, making them suitable for use in electric vehicles (EVs), energy storage systems (ESS), and more. For example, lithium-ion batteries can be used in hybrid vehicles (such as plug-in hybrid electric vehicles (PHEVs)). Furthermore, lithium-ion batteries can be used in any field requiring large-scale energy storage. For instance, they can be used in electric bicycles and power tools.

[0123] Multiple lithium batteries are stacked to form a battery module, and multiple battery modules form a battery pack. Such a battery pack can be used in all types of devices that require high capacity and high output. For example, such a battery pack can be used in laptop computers, smartphones, electric vehicles, etc. The battery module can include, for example, multiple batteries and a frame for holding the batteries. The battery pack can include, for example, multiple battery modules and busbars connecting the battery modules. The battery module and / or the battery pack can also include a cooling device. Multiple battery packs can be managed by a battery management system. The battery management system can include a battery pack and a battery control device connected to the battery pack.

[0124] A method for preparing a composite cathode active material according to another embodiment may include the following steps: providing a first lithium transition metal oxide; providing a second lithium transition metal oxide; providing a composite; preparing at least one of a first core / shell structure and a second core / shell structure by mechanically grinding the first lithium transition metal oxide with the composite to obtain the first core / shell structure and mechanically grinding the second lithium transition metal oxide with the composite to obtain the second core / shell structure; and mixing the first core / shell structure with the second lithium transition metal oxide, mixing the second core / shell structure with the first lithium transition metal oxide, or mixing the first core / shell structure with the second core / shell structure, wherein the composite may include at least one first metal oxide and a carbonaceous material, and the first metal oxide is represented by the formula M a O b (0 < a ≤ 3 and 0 < b < 4, where if a is 1, 2, or 3, then b is not an integer), wherein the first metal oxide may be disposed within the carbonaceous material matrix, and M may be at least one metal selected from Groups 2 to 13, 15, and 16 of the periodic table. The first lithium transition metal oxide and the second lithium transition metal oxide have different particle sizes from each other, and the second lithium transition metal oxide includes primary particles having a particle size of 1 μm or greater.

[0125] The grinding method in the mechanical grinding is not particularly limited and can be any method available in the art that can bring the lithium transition metal oxide into contact with the composite by mechanical means.

[0126] The first lithium transition metal oxide can be provided. For example, the first lithium transition metal oxide can be a compound represented by Formulas 1 to 5 above.

[0127] The second lithium transition metal oxide can be provided. For example, the second lithium transition metal oxide can be a compound represented by Formulas 1 to 5 above.

[0128] A composite can be provided. Providing the composite can include, for example, providing the composite by supplying a reaction gas composed of a carbon source gas to a structure including a metal oxide and performing a heat treatment. Providing the composite can include: for example, by supplying a reaction gas composed of a carbon source gas to at least one second metal oxide represented by M a O c (0 < a ≤ 3 and 0 < c ≤ 4, where, if a is 1, 2, or 3, then b is an integer) and then performing a heat treatment to provide the composite, where M can be at least one metal selected from the elements of Groups 2 to 13, 15, and 16 of the periodic table.

[0129] The carbon source gas can be a gas composed of a compound represented by Formula 6, or can be at least one mixed gas selected from the group consisting of a compound represented by Formula 6, a compound represented by Formula 7, and an oxygen-containing gas represented by Formula 8.

[0130] <Formula 6>

[0131] C n H (2n+2-a) [OH] a

[0132] In Formula 6, n is from 1 to 20, and a is 0 or 1.

[0133] <Formula 7>

[0134] C n H 2n

[0135] In Formula 7, n is from 2 to 6.

[0136] <Formula 8>

[0137] C x H y O z

[0138] In Formula 8, x is 0 or an integer from 1 to 20, y is 0 or an integer from 1 to 20, and z is 1 or 2.

[0139] The compound represented by Formula 6 and the compound represented by Formula 7 can be at least one selected from the group consisting of methane, ethylene, propylene, methanol, ethanol, and propanol. The oxygen-containing gas represented by Formula 8 can include, for example, carbon dioxide (CO2), carbon monoxide (CO), water vapor (H2O), or a mixture thereof.

[0140] When supplying the reaction gas composed of the carbon source gas to M a O cAfter heat treatment of the second metal oxide represented by (0 < a ≤ 3 and 0 < c ≤ 4, where c is an integer if a is 1, 2, or 3), subsequent cooling can be further carried out using at least one inert gas selected from the group consisting of nitrogen, helium, and argon. Cooling can refer to adjusting to room temperature (20 - 25 °C). The carbon source gas can include at least one inert gas selected from the group consisting of nitrogen, helium, and argon.

[0141] In the method for preparing the composite, the process of growing a carbonaceous material (such as graphene) can be carried out under various conditions according to a gas-phase reaction.

[0142] According to the first condition, for example, methane can be first supplied to a reactor containing the second metal oxide represented by M a O c (0 < a ≤ 3 and 0 < c ≤ 4, where c is an integer if a is 1, 2, or 3), and then the temperature can be raised to the heat treatment temperature (T). The time taken to raise the temperature to the heat treatment temperature (T) can be about 10 minutes to about 4 hours, and the heat treatment temperature (T) can be in the range of about 700 °C to about 1100 °C. At the heat treatment temperature (T), heat treatment can be carried out for a reaction time. The reaction time can be, for example, about 4 hours to about 8 hours. The heat-treated product can be cooled to room temperature to produce the composite. The time taken for the process of cooling from the heat treatment temperature (T) to room temperature can be, for example, about 1 hour to about 5 hours.

[0143] According to the second condition, for example, hydrogen can be first supplied to a reactor containing the second metal oxide represented by M a O c (0 < a ≤ 3 and 0 < c ≤ 4, where c is an integer if a is 1, 2, or 3), and then the temperature can be raised to the heat treatment temperature (T). The time taken to raise the temperature to the heat treatment temperature (T) can be about 10 minutes to about 4 hours, and the heat treatment temperature (T) can be in the range of about 700 °C to about 1100 °C. At the heat treatment temperature (T), after heat treatment for a part of the reaction time, methane gas can be supplied, and then heat treatment can be carried out for the remaining reaction time. The reaction time can be, for example, about 4 hours to about 8 hours. The heat-treated product can be cooled to room temperature to produce the composite. Nitrogen can be supplied during the cooling process. The time taken for the process of cooling from the heat treatment temperature (T) to room temperature can be, for example, about 1 hour to about 5 hours.

[0144] According to the third condition, for example, hydrogen can be first supplied to a reactor containing the second metal oxide represented by M a O cIn a reactor of a second metal oxide represented by (0 < a ≤ 3 and 0 < c ≤ 4, where if a is 1, 2, or 3, c is an integer), the temperature can then be raised to the heat treatment temperature (T). The time taken to raise the temperature to the heat treatment temperature (T) can be from about 10 minutes to about 4 hours, and the heat treatment temperature (T) can be in the range of about 700 °C to about 1100 °C. At the heat treatment temperature (T), after heat treatment for a part of the reaction time, a mixed gas of methane and hydrogen can be supplied, and then heat treatment can be carried out for the remaining reaction time. The reaction time can be, for example, from about 4 hours to about 8 hours. The heat-treated product can be cooled to room temperature to produce a composite. Nitrogen can be supplied during the cooling process. The time taken for the process of cooling from the heat treatment temperature (T) to room temperature can be, for example, from about 1 hour to about 5 hours.

[0145] In the process for preparing the composite, if the carbon source gas contains water vapor, the obtained composite can have excellent electrical conductivity. The content of water vapor in the gas mixture is not limited and can be, for example, from about 0.01 vol% to about 10 vol% relative to the total volume of 100 vol% of the carbon source gas. The carbon source gas can be, for example, methane, a mixed gas including methane and an inert gas, or a mixed gas including methane and an oxygen-containing gas.

[0146] The carbon source gas can be, for example: methane; a mixed gas of methane and carbon dioxide; or a mixed gas of methane, carbon dioxide, and water vapor. In the mixed gas of methane and carbon dioxide, the molar ratio of methane to carbon dioxide can be from about 1:0.20 to about 1:0.50, from about 1:0.25 to about 1:0.45, or from about 1:0.30 to about 1:0.40. In the mixed gas of methane, carbon dioxide, and water vapor, the molar ratio of methane, carbon dioxide, and water vapor can be from about 1:0.20 to about 0.50:0.01 to about 1.45, can be from about 1:0.25 to about 0.45:0.10 to about 1.35, or can be from about 1:0.30 to about 0.40:0.50 to about 1.0.

[0147] The carbon source gas can be, for example, carbon monoxide or carbon dioxide. The carbon source gas can be, for example, a mixed gas of methane and nitrogen. In the mixed gas of methane and nitrogen, the molar ratio of methane to nitrogen can be from about 1:0.20 to about 1:0.50, from about 1:0.25 to about 1:0.45, or from about 1:0.30 to about 1:0.40. The carbon source gas may not include inert gases such as nitrogen.

[0148] The heat treatment pressure can be selected considering the heat treatment temperature, the composition of the gas mixture, the amount of the desired carbon coating, etc. The heat treatment pressure can be controlled by adjusting the amount of the inflowing gas mixture and the amount of the outflowing gas mixture. The heat treatment pressure can be, for example, 0.5 atm or greater, 1 atm or greater, 2 atm or greater, 3 atm or greater, 4 atm or greater, or 5 atm or greater. The heat treatment pressure can be, for example, about 0.5 atm to about 10 atm, about 1 atm to about 10 atm, about 2 atm to about 10 atm, about 3 atm to about 10 atm, about 4 atm to about 10 atm, or about 5 atm to about 10 atm. <​​​​​​​​​​​​​​​​​​​​O c (0 < a ≤ 3 and 0 < c ≤ 4, where c is an integer if a is 1, 2, or 3) indicates that the first metal oxide and the second metal oxide are disposed within the graphene matrix.

[0152] Next, the first core / shell structure can be prepared by mechanically grinding the first lithium transition metal oxide and the composite. For the grinding, a Nobilta mixer or the like can be used. For the grinding, the rotation rate of the mixer can be, for example, about 1000 rpm to about 2500 rpm. If the grinding speed is less than 1000 rpm, the shear force applied to the first lithium transition metal oxide and the composite will be weak, making it difficult to form a chemical bond between the first lithium transition metal oxide and the composite. If the grinding speed is too high, complexation will occur in too short a time, making it difficult for the composite to uniformly coat the first lithium transition metal oxide to form a uniform and continuous shell. The grinding time can be, for example, about 5 minutes to about 100 minutes, about 5 minutes to about 60 minutes, or about 5 minutes to about 30 minutes. If the grinding time is too short, it will be difficult for the composite to uniformly coat the first lithium transition metal oxide to form a uniform and continuous shell. If the grinding time is too long, the production efficiency will be reduced. The content of the composite can be 3 wt% or less, 2 wt% or less, or 1 wt% or less of the total weight of the first lithium transition metal oxide and the composite. Relative to the total weight of the first lithium transition metal oxide and the composite, the content of the composite can be, for example, about 0.01 wt% to about 3 wt%, about 0.1 wt% to about 2 wt%, or about 0.1 wt% to about 1 wt%. For example, relative to 100 parts by weight of the mixture of the first lithium transition metal oxide and the composite, the content of the composite can be about 0.01 part by weight to about 3 parts by weight, about 0.1 part by weight to about 3 parts by weight, about 0.1 part by weight to about 2 parts by weight, or about 0.1 part by weight to about 1 part by weight. The average particle size (D50) of the composite used for mechanically grinding the first lithium transition metal oxide and the composite can be, for example, about 1 μm to about 20 μm, about 3 μm to about 15 μm, or about 5 μm to about 10 μm.

[0153] Optionally, the second core / shell structure can be prepared by mechanically grinding the second lithium transition metal oxide and the composite. Except for using the second lithium transition metal oxide instead of the first lithium transition metal oxide, the second core / shell structure can be prepared according to the same process as the first core / shell structure.

[0154] Optionally, according to the above method, the first core / shell structure and the second core / shell structure can be prepared separately.

[0155] Next, a composite cathode active material is prepared by mixing a first core / shell structure with a second lithium metal oxide. The mixing of the first core / shell structure and the second lithium transition metal oxide can be carried out at a weight ratio of, for example, about 90:10 to about 60:40, about 85:15 to about 65:35, or about 80:20 to about 70:30. Since the first core / shell structure and the second lithium transition metal oxide have a weight ratio within such a range, the energy density and / or cycle characteristics of a lithium battery including the composite cathode active material can be further improved.

[0156] Alternatively, a composite cathode active material can be prepared by mixing a first lithium transition metal oxide with a second core / shell structure. The mixing of the first lithium transition metal oxide and the second core / shell structure can be carried out at a weight ratio of, for example, about 90:10 to about 60:40, about 85:15 to about 65:35, or about 80:20 to about 70:30. Since the first lithium transition metal oxide and the second core / shell structure have a weight ratio within such a range, the energy density and / or cycle characteristics of a lithium battery including the composite cathode active material can be further improved.

[0157] Alternatively, a composite cathode active material can be prepared by mixing a first core / shell structure with a second core / shell structure. The mixing of the first core / shell structure and the second core / shell structure can be carried out at a weight ratio of, for example, about 90:10 to about 60:40, about 85:15 to about 65:35, or about 80:20 to about 70:30. Since the first core / shell structure and the second core / shell structure have a weight ratio within such a range, the energy density and / or cycle characteristics of a lithium battery including the composite cathode active material can be further improved.

[0158] The following examples and comparative examples are provided to describe the embodiments in more detail. However, it will be understood that the examples provided are only for illustrating the embodiments and should not be construed as limiting the scope of the embodiments.

[0159] (Preparation of the composite)

[0160] Preparation Example 1: Al2O3@Gr composite

[0161] Once the Al2O3 particles (average particle size: about 20 nm) are placed in the reactor, the temperature in the reactor is raised to 1000 °C while CH4 is supplied to the reactor at about 300 sccm and 1 atm for about 30 minutes.

[0162] Subsequently, heat treatment is carried out while maintaining the above temperature for 7 hours. Subsequently, by adjusting the temperature in the reactor to room temperature (20 - 25 °C), a composite having Al2O3 particles embedded in graphene and its reduced product (Al2O z (0 < z < 3) particles) is obtained.

[0163] The content of alumina included in the composite is 60 wt%.

[0164] Comparative Preparation Example 1: SiO2@Gr composite

[0165] Once the SiO2 particles (average particle size: about 15 nm) are placed in the reactor, the temperature in the reactor is raised to 1000 °C, and CH4 is supplied to the reactor at about 300 sccm and 1 atm for about 30 minutes.

[0166] Subsequently, heat treatment is carried out while maintaining the above temperature for 7 hours. Subsequently, by adjusting the temperature in the reactor to room temperature (20 - 25 °C), a composite with SiO2 particles and its reduced products (SiO y (0 < y < 2) particles) embedded in graphene is obtained.

[0167] (Preparation of composite positive electrode active material)

[0168] Example 1: Large-diameter NCA91 coated with 0.4 wt% (0.24 wt% alumina) of Al2O3@Gr composite and small-diameter NCA91 coated with 0.4 wt% (0.24 wt% alumina) of Al2O3@Gr composite

[0169] Large-diameter LiNi with an average particle size of 10 μm 0.91 Co 0.05 Al 0.04 O2 (hereinafter referred to as large-diameter NCA91) and the composite prepared in Preparation Example 1 are used together with a Nobilta mixer (Hosokawa, Japan) and ground at a rotation rate of about 1000 rpm to 2000 rpm for about 5 - 30 minutes to produce a first core / shell structure. The mixing weight ratio of large-diameter NCA91 and the composite obtained according to Preparation Example 1 is 99.6:0.4. Large-diameter NCA91 is a secondary particle having a structure in which plate-like primary particles are radially arranged. Large-diameter NCA91 has a structure in which the long axes of the plate-like primary particles included in the large-diameter NCA91 are radially arranged. Large-diameter NCA91 can have, for example Figure 3 the structure shown in

[0170] Small-diameter LiNi with an average particle size of 3 μm 0.91 Co 0.05 Al 0.04O2 (hereinafter referred to as small-diameter NCA91) and the composite prepared in Preparation Example 1 were milled together using a Nobilta mixer (Hosokawa, Japan) at a rotational rate of approximately 1000 rpm to 2000 rpm for approximately 5–30 minutes to produce a second core / shell structure. The mixing weight ratio of small-diameter NCA91 to the composite obtained according to Preparation Example 1 was 99.6:0.4. The small-diameter NCA91 has a monolithic particle shape and is a particle with a single-crystal structure.

[0171] Composite positive electrode active materials are prepared by mixing the first core / shell structure and the second core / shell structure at a weight ratio of 7:3.

[0172] The bimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0173] Example 2: 0.4 wt% Al2O3@Gr composite (0.24 wt% alumina) coated with large-diameter NCA91 and bare small-diameter NCA91

[0174] Except for using a small-diameter NCA91 instead of the second core / shell structure, the composite positive electrode active material was prepared using the same process as in Example 1.

[0175] Composite positive electrode active material was prepared by mixing the first core / shell structure and small-diameter NCA91 in a weight ratio of 7:3.

[0176] The bimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0177] Example 3: Bare large-diameter NCA91 and 0.4 wt% Al2O3@Gr composite coated with small-diameter NCA91 (0.24 wt% alumina).

[0178] Except for using a large-diameter NCA91 to replace the first core / shell structure, the composite positive electrode active material was prepared using the same process as in Example 1.

[0179] Composite positive electrode active material was prepared by mixing large-diameter NCA91 and a second core / shell structure at a weight ratio of 7:3.

[0180] The bimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0181] Comparison Example 1: Bare large-diameter NCA91 and bare small-diameter NCA91

[0182] The composite positive electrode active material was prepared using the same process as in Example 1, except that a large-diameter NCA91 was used to replace the first core / shell structure and a small-diameter NCA91 was used to replace the second core / shell structure.

[0183] Composite positive electrode active material was prepared by mixing large-diameter NCA91 and small-diameter NCA91 in a weight ratio of 7:3.

[0184] The bimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0185] Comparative Example 2: Large-diameter NCA91 coated with 0.4wt% SiO2@Gr composite (0.24wt% silica) and small-diameter NCA91 coated with 0.4wt% SiO2@Gr composite (0.24wt% silica).

[0186] Except that the SiO2@Gr composite prepared in Comparative Preparation Example 1 was used instead of the Al2O3@Gr composite prepared in Preparation Example 1, the composite positive electrode active material was prepared according to the same process as in Example 1.

[0187] Comparison Example 3: Large-diameter NCA91 coated with 0.4wt% Al2O3 and small-diameter NCA91 coated with 0.4wt% Al2O3

[0188] The composite positive electrode active material was prepared according to the same process as in Example 1, except that Al2O3 particles (average particle size: about 20 nm) were used instead of the composite shell prepared in Preparation Example 1.

[0189] Composite positive electrode active material was prepared by mixing alumina-coated large-diameter NCA91 and alumina-coated small-diameter NCA91 in a weight ratio of 7:3.

[0190] The bimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0191] Comparison Example 4: Bare Large-Diameter NCA91

[0192] Except for using large-diameter NCA91 as the composite positive electrode active material and excluding small-diameter NCA91, the composite positive electrode active material was prepared according to the same process as in Example 1.

[0193] The unimodal particle size distribution of the composite positive electrode active material was confirmed by measuring the particle size distribution using a particle size analyzer (PSA).

[0194] (Manufacturing of lithium batteries (half-cells))

[0195] Example 4

[0196] (Preparation of the positive electrode)

[0197] A slurry was prepared by mixing the composite positive electrode active material, carbon conductive agent (Denka Black), and polyvinylidene fluoride (PVdF) contained in Example 1 with N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2 using an agate mortar and pestle.

[0198] The slurry rod was coated onto an aluminum current collector with a thickness of 15 μm, dried at room temperature, dried again under vacuum and at 120 °C, and rolled and stamped to produce a positive electrode with a thickness of 60 μm.

[0199] (Preparation of button batteries)

[0200] A button cell was prepared using the positive electrode prepared above, and lithium metal as the counter electrode, a PTFE membrane, and a solution containing 1.5 M LiPF6 dissolved in EC (ethylene carbonate) + EMC (ethyl methyl carbonate) + DMC (dimethyl carbonate) (volume ratio 2:1:7) as the electrolyte.

[0201] Example 5 and Example 6

[0202] Except that the composite positive electrode active material prepared in Example 2 and Example 3 is used instead of the composite positive electrode active material prepared in Example 1, the button cell is prepared according to the same process as in Example 4.

[0203] Comparison Examples 5 to 8

[0204] Except that the composite positive electrode active material prepared in Comparative Examples 1 to 4 was used instead of the composite positive electrode active material prepared in Example 1, the button cell was prepared according to the same process as in Example 4.

[0205] Evaluation Example 1: Evaluation of XPS Spectroscopy

[0206] In the preparation process of the complex prepared in Example 1, XPS spectra over time were obtained using a Qunatum 2000 (Physical Electronics). XPS spectra of the C1s and Al 2p orbitals of the sample were obtained before heating, 1 minute after heating, 5 minutes after heating, 30 minutes after heating, 1 hour after heating, and 4 hours after heating. At the beginning of temperature increase, the XPS spectra only showed the Al 2p peak, but the C1s peak was not shown. After 30 minutes, the C1s peak became prominent, while the size of the Al 2p peak decreased significantly.

[0207] After 30 minutes, near 284.5 eV, the C1s peak attributed to C-C bonds and C═C bonds due to graphene growth has become prominent.

[0208] Since the oxidation number of aluminum decreases as the reaction time extends, the position of the 2p peak of aluminum shifts to a lower binding energy (eV).

[0209] Therefore, it was confirmed that as the reaction proceeds, graphene grows on the Al2O3 particles, and Al2O, which is a reduction product of Al2O3, is produced x (0 < x < 3).

[0210] From the XPS analysis results, the average contents of carbon and aluminum were measured in 10 regions of the composite sample prepared in Preparation Example 1. For the measurement results, the deviation of the aluminum content in each part was calculated. The deviation of the aluminum content is expressed as a percentage relative to the average value and is then referred to as uniformity. The percentage of the deviation of the aluminum content relative to the average value (i.e., the uniformity of the aluminum content) was 1%. Therefore, the uniform distribution of alumina within the composite prepared in Preparation Example 1 was confirmed.

[0211] Evaluation Example 2: SEM, HR-TEM, and SEM-EDAX Analyses

[0212] Scanning electron microscopy, high-resolution transmission electron microscopy, and EDAX analysis were performed on the composite prepared in Preparation Example 1, the composite positive electrode active material prepared in Example 1, and the composite positive electrode active material prepared in Comparative Example 1.

[0213] For the SEM-EDAX analysis, the FEI Titan 80-300 from Philips was used.

[0214] The composite prepared in Preparation Example 1 showed a structure in which Al2O3 particles and their reduction products (Al2O z (0 < z < 3) particles) are embedded in graphene. It was confirmed that graphene layers are provided on the outside of one or more kinds of particles selected from Al2O3 particles and Al2O <www. z (0 < z < 3) particles. One or more kinds of particles selected from Al2O3 particles and Al2O z (0 < z < 3) particles can be uniformly distributed within the graphene matrix. One or more kinds of particles selected from Al2O3 particles and Al2O z (0 < z < 3) particles can have a particle size of about 20 nm. The particle size of the composite prepared in Preparation Example 1 is about 100 nm to about 200 nm. In the composite positive electrode active material prepared in Example 1, it was confirmed that a shell formed of a composite including graphene is provided on the NCA core.

[0215] SEM-EDAX analysis of the composite positive electrode active materials prepared in Comparative Example 1 and Example 1 confirmed that the concentration of aluminum (Al) on the surface of the composite positive electrode active material of Example 1 was increased compared with that of the composite positive electrode active material of Comparative Example 1.

[0216] Therefore, it was confirmed that in the composite positive electrode active material of Example 1, the composite prepared in Preparation Example 1 was uniformly coated on the NCA core to form a shell.

[0217] Evaluation Example 3: Measurement of Aggregate Density

[0218] The agglomerate density of the composite positive electrode active materials prepared in Examples 1 to 3 and Comparative Example 4 was measured, and the results are shown in Table 1 below.

[0219] Measurements were performed by placing 1 g of each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Example 4 into a circular mold with a diameter of 1 cm, and then applying 1000 kgf / cm². 2 The density (in mass / volume) of the positive electrode active material obtained under pressure in the form of granules.

[0220] [Table 1]

[0221] Particle density [g / cc] Example 1: Large-particle / small-particle coating 3.7 Example 2: Large particle coating 3.7 Example 3: Small particle coating 3.8 Comparison Example 4: Large particles without coating 3.3

[0222] As shown in Table 1, compared with the composite positive electrode active material of Comparative Example 4 which has a unimodal particle size distribution, the composite positive electrode active materials of Examples 1 to 3 which have a bimodal particle size distribution have increased agglomeration density.

[0223] It was confirmed that lithium batteries including composite positive electrode active materials of Examples 1 to 3 can provide improved energy density compared to lithium batteries including composite positive electrode active materials of Comparative Example 4.

[0224] Evaluation Example 4: Evaluation of High-Temperature (45℃) Charge / Discharge Characteristics

[0225] The lithium batteries prepared in Examples 4 to 6 and Comparative Examples 5 to 8 were charged at 25°C at a constant current rate of 0.1C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium batteries were discharged at a constant current rate of 0.1C until the lithium battery voltage reached 2.8V (relative to Li) during discharge (formation cycling).

[0226] The formed lithium-ion battery was charged at 45°C with a constant current rate of 0.2C until the lithium-ion battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium-ion battery was discharged at a constant current rate of 0.2C until the lithium-ion battery voltage reached 2.8V during discharge (cycle 1). The above cycle was repeated under the same conditions until the 100th cycle.

[0227] A 10-minute rest period was provided after each charge / discharge cycle. A portion of the high-temperature charge / discharge test results are shown in Table 2 below. Initial efficiency is defined by Equation 1, and capacity retention is defined by Equation 2.

[0228] Equation 1

[0229] Initial efficiency [%] = [Discharge capacity at the beginning of the first cycle / Charge capacity at the beginning of the first cycle] × 100%

[0230] Equation 2

[0231] Capacity retention rate [%] = [Discharge capacity at 100th cycle / Discharge capacity at 1st cycle] × 100%

[0232] Evaluation Example 5: Evaluation of DC Internal Resistance (DC-IR) before and after high-temperature charging / discharging

[0233] The DC internal resistance (DC-IR) of the lithium batteries prepared in Examples 4 to 6 and Comparative Examples 5 to 8 was measured before and after the high-temperature charge / discharge evaluation using the following method.

[0234] In the first cycle, the lithium battery was charged to 50% SOC (state of charge) at a constant current rate of 0.5C and then stopped at a constant current rate of 0.02C, and then left to stand for 10 minutes.

[0235] Then, discharge the lithium battery at a constant current rate of 0.5C for 30 seconds and let it stand for 30 seconds, then charge it at a constant current rate of 0.5C for 30 seconds and let it stand for 10 minutes.

[0236] Then, discharge the lithium battery at a constant current rate of 1.0C for 30 seconds, let it rest for 30 seconds, then charge it at a constant current rate of 0.5C for 1 minute, and let it rest for 10 minutes.

[0237] Then, discharge the lithium battery at a constant current rate of 2.0C for 30 seconds and let it rest for 30 seconds, then charge it at a constant current rate of 0.5C for 2 minutes and let it rest for 10 minutes.

[0238] Then, discharge the lithium battery at a constant current rate of 3.0C for 30 seconds and let it rest for 30 seconds, then charge it at a constant current rate of 0.5C for 3 minutes and let it rest for 10 minutes.

[0239] The DC internal resistance (DC-IR, R = ΔV / ΔI) is calculated by the ratio of the average voltage change (ΔV) and the average current change (ΔI) during constant current discharge at each C-rate, and their average value is used as the measurement.

[0240] A portion of the DC internal resistance measured before the high-temperature charge / discharge evaluation and the DC internal resistance measured after the high-temperature charge / discharge evaluation are shown in Table 2 below.

[0241] [Table 2]

[0242]

[0243] As shown in Table 2, compared with the lithium battery of Comparative Example 5, the lithium batteries of Examples 4 to 6 have improved high-temperature life characteristics and suppressed DC internal resistance increase.

[0244] Although not shown in Table 2, the lithium batteries of Examples 4 to 6 have improved high-temperature life characteristics compared to the lithium batteries of Comparative Examples 6 and 7.

[0245] Compared with the lithium battery in Comparative Example 5, the increase in DC internal resistance after high-temperature charging / discharging is significantly suppressed in the lithium batteries of Examples 4 to 6.

[0246] Evaluation Example 6: Evaluation of High-Rate Performance at Room Temperature

[0247] The lithium batteries prepared in Examples 4 to 6 and Comparative Examples 5 to 8 were charged at 25°C at a constant current rate of 0.1C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium batteries were discharged at a constant current rate of 0.1C until the lithium battery voltage reached 2.8V (relative to Li) during discharge (formation cycling).

[0248] The formed-cycled lithium battery was charged at 25°C with a constant current rate of 0.2C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium battery was discharged at a constant current rate of 0.2C until the lithium battery voltage reached 2.8V during discharge (first cycle).

[0249] After the first cycle, the lithium battery was charged at 25°C at a constant current rate of 0.2C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium battery was discharged at a constant current rate of 0.5C until the lithium battery voltage reached 2.8V during discharge (second cycle).

[0250] After the second cycle, the lithium battery was charged at 25°C at a constant current rate of 0.2C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium battery was discharged at a constant current rate of 4.0C until the lithium battery voltage reached 2.8V (relative to Li) during discharge (third cycle).

[0251] After the third cycle, the lithium battery was charged at 25°C at a constant current rate of 0.2C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium battery was discharged at a constant current rate of 2.0C until the lithium battery voltage reached 2.8V (relative to Li) during discharge (fourth cycle).

[0252] After the fourth cycle, the lithium battery was charged at 25°C at a constant current rate of 0.2C until the lithium battery voltage reached 4.3V (relative to Li), and then cut off at a rate of 0.05C at 4.3V in constant voltage mode. Subsequently, the lithium battery was discharged at a constant current rate of 4.0C until the lithium battery voltage reached 2.8V during discharge (fifth cycle).

[0253] A 10-minute rest period is provided after each charge / discharge cycle. A portion of the room temperature charge / discharge test results are shown in Table 3 below. High-rate characteristics are defined by Equation 3.

[0254] Equation 3

[0255] High-rate performance [%] = [4.0C rate discharge capacity (5th cycle discharge capacity) / 0.2C rate discharge capacity (1st cycle discharge capacity)] × 100%

[0256] [Table 3]

[0257]

[0258] As shown in Table 3, the lithium batteries of Examples 4 to 6 have improved high-rate characteristics compared to the lithium battery of Comparative Example 5.

[0259] Although not shown in Table 3, the lithium batteries of Examples 4 to 6 have improved high-rate characteristics compared to the lithium batteries of Comparative Examples 6 and 7.

[0260] According to one aspect, since the composite positive electrode active material includes a shell comprising a core containing a first metal oxide and a carbonaceous material and disposed on a core of at least one of a large-diameter lithium transition metal oxide and a small-diameter lithium transition metal oxide, and the small-diameter lithium transition metal oxide has an integral particle shape, the lithium battery can have improved high-temperature cycling characteristics, suppress the increase of internal resistance, and have improved high-rate characteristics.

[0261] It should be understood that the embodiments described herein are to be considered in a descriptive sense only and not for limiting purposes. The description of features or aspects within each embodiment should generally be considered applicable to other similar features or aspects in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. A composite positive electrode active material, said composite positive electrode active material comprising: The first core includes a first lithium transition metal oxide; The second core includes a second lithium transition metal oxide; as well as A shell is disposed along the surface of at least one of the first core and the second core. Wherein, the shell comprises at least one first metal oxide and a carbonaceous material having a branched structure, and the first metal oxide is represented by the formula M a O b where 0 < a ≤ 3 and 0 < b < 4, and if a is 1, 2 or 3, then b is not an integer, and Wherein, the first metal oxide is distributed within the branched structure, and M is at least one metal selected from groups 2 to 13, 15, and 16 of the periodic table. The first lithium transition metal oxide and the second lithium transition metal oxide have different particle sizes, and The second lithium transition metal oxide comprises primary particles with a particle size of 1 μm or larger.

2. The composite positive electrode active material according to claim 1, wherein, The first lithium transition metal oxide includes secondary particles comprising a plurality of primary particles, and The secondary particles comprise a structure in which the plurality of primary particles are arranged in a radial shape.

3. The composite positive electrode active material according to claim 2, wherein, The primary particles are plate-shaped particles, and the main axis of the plate-shaped particles is arranged radially.

4. The composite positive electrode active material according to claim 1, wherein, The first lithium transition metal oxide is a large-diameter lithium transition metal oxide with a larger particle size than the second lithium transition metal oxide, and The second lithium transition metal oxide has a smaller particle size than the first lithium transition metal oxide.

5. The composite positive electrode active material according to claim 1, wherein, The first lithium transition metal oxide and the second lithium transition metal oxide exhibit a bimodal particle size distribution in the particle size distribution diagram, and The particle size ratio of the first lithium transition metal oxide to the second lithium transition metal oxide is 3:1 to 40:

1.

6. The composite positive electrode active material according to claim 1, wherein, The first lithium transition metal oxide has a particle size of greater than 8 μm to 30 μm, and the second lithium transition metal oxide has a particle size of 1 μm to less than 8 μm.

7. The composite positive electrode active material according to claim 1, wherein, The weight ratio of the first lithium transition metal oxide to the second lithium transition metal oxide is 90:10 to 60:

40.

8. The composite positive electrode active material according to claim 1, wherein, The shell is only disposed on the first core. The shell is only disposed on the second core, or The shell is disposed on the first core and the second core.

9. The composite positive electrode active material according to claim 1, wherein, The first metal oxide comprises at least one metal selected from Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se, and The first metal oxide is selected from at least one of the following substances: Al2O z , where 0 < z < 3; NbO x , where 0 < x < 2.5; MgO x , where 0 < x < 1; Sc2O z , where 0 < z < 3; TiO y , where 0 < y < 2; ZrO y , where 0 < y < 2; V2O z , where 0 < z < 3; WO y , where 0 < y < 2; MnO y , where 0 < y < 2; Fe2O z , where 0 < z < 3; Co3O w , where 0 < w < 4; PdO x , where 0 < x < 1; CuO x , where 0 < x < 1; AgO x , where 0 < x < 1; ZnO x , where 0 < x < 1; Sb2O z , where 0 < z < 3; and SeO y , where 0 < y < 2.

10. The composite positive electrode active material according to claim 1, wherein, The shell further includes a second metal oxide, and the second metal oxide is represented by the formula M a O c where 0 < a ≤ 3, 0 < c ≤ 4, and if a is 1, 2, or 3, then c is an integer. The second metal oxide comprises the same metal as the first metal oxide, and The ratio c / a of a and c in the second metal oxide has a larger value than the ratio b / a of a and b in the first metal oxide.

11. The composite positive electrode active material according to claim 10, wherein, The second metal oxide is selected from Al2O3, NbO, NbO2, Nb2O5, MgO, Sc2O3, TiO2, ZrO2, V2O3, WO2, MnO2, Fe2O3, Co3O4, PdO, CuO, AgO, ZnO, Sb2O3, and SeO2, and The first metal oxide is a reduction product of the second metal oxide.

12. The composite positive electrode active material according to claim 1, wherein, The shell has a thickness of 1 nm to 5 μm.

13. The composite positive electrode active material according to claim 1, wherein, The shell comprises at least one selected from the composite and the polished article of the composite, the composite comprising the first metal oxide and the carbonaceous material, and The content of at least one selected from the complex and the milled product of the complex is 3 wt% or less relative to the total weight of the composite positive electrode active material.

14. The composite positive electrode active material according to claim 13, wherein, The complex further includes a second metal oxide having a composition different from that of the composition of the first metal oxide. At least one selected from the first metal oxide and the second metal oxide has a particle size of 1 nm to 1 μm, and At least one selected from the first metal oxide and the second metal oxide has a uniformity deviation of 3% or less.

15. The composite positive electrode active material according to claim 13, wherein, The branched structure includes a plurality of carbonaceous material particles in contact with each other.

16. The composite positive electrode active material according to claim 1, wherein, The first lithium transition metal oxide and the second lithium transition metal oxide are each independently represented by Formula 1 to Formula 5 <Formula 1> Li a Ni x Co y M z O 2-b A b In Formula 1, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.8 ≤ x < 1, 0 < y ≤ 0.3, and 0 < z ≤ 0.3, where x + y + z = 1, M is Mn, Nb, V, Mg, Ga, Si, W, Mo, Fe, Cr, Cu, Zn, Ti, Al, B, or a combination thereof, and A is F, S, Cl, Br, or a combination thereof. <Formula 2> LiNi x Co y Mr z O2 <Formula 3> LiNi x Co y Al z O2 In Formulas 2 and 3, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.2, and 0 < z ≤ 0.2, where x + y + z = 1. <Formula 4> LiNi x Co y Mr z Al w O2 In Formula 4, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.2, 0 < z ≤ 0.2, and 0 < w ≤ 0.2, where x + y + z + w = 1. <Formula 5> Li a Co x M y O 2-b A b In Formula 5, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.9 ≤ x ≤ 1, and 0 ≤ y ≤ 0.1, where x + y = 1, M is Mn, Nb, V, Mg, Ga, Si, W, Mo, Fe, Cr, Cu, Zn, Ti, Al, B, or a combination thereof, and A is F, S, Cl, Br, or a combination thereof.

17. A positive electrode comprising the composite positive electrode active material according to any one of claims 1 to 16.

18. A lithium battery, the lithium battery comprising: The positive electrode according to claim 17; a negative electrode; and an electrolyte between the positive electrode and the negative electrode.

19. A method for preparing a composite positive electrode active material, the method comprising the following steps: Providing a first lithium transition metal oxide; Providing a second lithium transition metal oxide; Providing a complex; Preparing at least one of a first core / shell structure and a second core / shell structure by mechanically milling the first lithium transition metal oxide with the complex to obtain the first core / shell structure and by mechanically milling the second lithium transition metal oxide with the complex to obtain the second core / shell structure; And Mixing the first core / shell structure with the second lithium transition metal oxide, mixing the second core / shell structure with the first lithium transition metal oxide, or mixing the first core / shell structure with the second core / shell structure, Among them, the composite includes: at least one first metal oxide and a carbonaceous material having a branched structure, and the first metal oxide is represented by the formula M a O b where 0 < a ≤ 3, 0 < b < 4, and if a is 1, 2, or 3, then b is not an integer, and Wherein, the first metal oxide is distributed within the branched structure, and M is at least one metal selected from Groups 2 to 13, 15, and 16 of the periodic table. The first lithium transition metal oxide and the second lithium transition metal oxide have different particle sizes, and The second lithium transition metal oxide comprises primary particles having a particle size of 1 μm or larger.

20. The method according to claim 19, wherein, The step of providing the complex includes: A reaction gas composed of a carbon source gas is supplied to at least one second metal oxide and heat treatment is performed, the at least one second metal oxide being represented by M a O c where 0 < a ≤ 3 and 0 < c ≤ 4, and where c is an integer if a is 1, 2, or 3 M is at least one metal selected from groups 2 to 13, 15 and 16 of the periodic table.

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