Composite positive electrode active material, positive electrode using the same, lithium battery and manufacturing method thereof

Abstract

Provided are a composite positive electrode active material, a positive electrode and a lithium battery comprising the same, and a method for preparing the composite positive electrode active material. The composite positive electrode active material comprises a core containing a lithium transition metal oxide, and a first shell and a second shell disposed on an outer side of a surface of the core, wherein the first shell comprises a compound represented by formula X a O b (0<a≤3, 0<b≤4, and b is an integer when a is 1, 2 or 3) or formula X a (OH) b (0<a≤3, 0<b≤4, and b is an integer when a is 1, 2 or 3) at least one first metal compound represented by, and the second shell comprises a compound represented by formula Y c O d (0

Description

Technical Field

[0001] The present disclosure relates to a composite cathode active material, a cathode and a lithium battery including the composite cathode active material, and a method of preparing the composite cathode active material. Background Art

[0002] For miniaturization and high performance of various devices, high energy density of lithium batteries has become increasingly important in addition to miniaturization and lighter weight. In other words, high-capacity lithium batteries have become increasingly important.

[0003] To achieve a lithium battery suitable for the above uses, cathode active materials having high capacity are being considered.

[0004] Nickel-based cathode active materials in the related art have degraded lifespan characteristics and poor thermal stability due to side reactions.

[0005] Therefore, there is a need for a method capable of preventing deterioration of battery performance while including a nickel-based cathode active material. Summary of Invention

[0006] Technical Problem

[0007] In one aspect, there is provided a novel composite cathode active material capable of suppressing side reactions of the composite cathode active material to prevent battery performance deterioration.

[0008] In another aspect, there is provided a cathode including the composite cathode active material.

[0009] In another aspect, there is provided a lithium battery including the cathode.

[0010] In another aspect, there is provided a method of preparing the composite cathode active material.

[0011] Technical Solution

[0012] According to one or more embodiments, there is provided a composite cathode active material, the composite cathode active material includes:

[0013] a core including a lithium transition metal oxide; and

[0014] a first shell and a second shell disposed on an outer side of a surface of the core,

[0015] wherein the first shell includes at least one first metal compound represented by formula X a O b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b is an integer when a is 1, 2, or 3) or formula X a (OH) b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b is an integer when a is 1, 2, or 3),

[0016] The second shell comprises: the formula Y c O d (wherein 0<c≤3, 0<d<4, and d is not an integer when c is 1, 2 or 3) at least one second metal compound represented by; and graphene,

[0017] said at least one second metal compound is disposed in a graphene matrix, and both X and Y are each independently at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the Periodic Table of Elements.

[0018] According to another aspect, a positive electrode is provided,

[0019] said positive electrode comprises the positive electrode active material.

[0020] According to another aspect, a lithium battery is provided,

[0021] said lithium battery comprises the positive electrode.

[0022] According to another aspect, a method for preparing the composite positive electrode active material is provided, the method comprising:

[0023] providing a lithium transition metal oxide;

[0024] providing the formula X a O b (wherein 0<a≤3, 0<b≤4, and b is an integer when a is 1, 2 or 3) or the formula X a (OH) b (wherein 0<a≤3, 0<b≤4, and b is an integer when a is 1, 2 or 3) at least one first metal compound represented by;

[0025] providing a composite, the composite comprising: at least one second metal compound represented by formula Y c O d (wherein 0<c≤3, 0<d<4, and d is not an integer when c is 1, 2 or 3) and graphene, wherein said at least one second metal compound is disposed in a graphene matrix; and

[0026] mechanically grinding the lithium transition metal oxide, the first metal compound and the composite,

[0027] wherein both X and Y are each independently at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the Periodic Table of Elements.

[0028] Beneficial Effects

[0029] According to one aspect, the composite positive electrode active material includes a first shell containing a first metal compound and a second shell containing a second metal compound and graphene. Therefore, lithium batteries containing composite positive electrode active materials can improve cycle characteristics at low and high temperatures, improve fast charging characteristics, and suppress side reactions between the composite positive electrode active material and the electrolyte solution. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a lithium battery according to an embodiment. Detailed Implementation

[0031] The inventive concept described below can have various modifications and embodiments, exemplary embodiments of which will be shown in the accompanying drawings and described more fully in the detailed description. However, the inventive concept should not be construed as limited to the exemplary embodiments set forth herein, but should be understood to cover all modifications, equivalents, or substitutions falling within the scope of the inventive concept.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. Unless it has a distinctly different meaning in the context, singular expressions include plural expressions. It will also be understood that when the terms “comprising” and / or variations thereof or “including” and / or variations thereof are used in this specification, it indicates the presence of the stated features, regions, integrals, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, regions, integrals, steps, operations, elements, components, and / or groups thereof. As used herein, “ / ” may be interpreted as “and” or “or” depending on the context.

[0033] In the accompanying drawings, thicknesses may be enlarged or exaggerated to clearly show the various layers and regions. Throughout the drawings and the following description, the same reference numerals may refer to the same elements. It will be understood that when an element, layer, film, segment, sheet, etc., is referred to as being "on" another element, it may be directly on said other element, or there may be intermediate elements therein.

[0034] As used herein, the term "particle diameter" of a particle refers to the average diameter of the particle when the particle is spherical, and refers to the average major axis length of the particle when the particle is non-spherical. A particle size analyzer (PSA) can be used to measure the particle diameter of particles. The "particle diameter" of particles may refer to, for example, the average particle diameter. The average particle diameter may be, for example, the median particle diameter (D50). The median particle diameter (D50) is the particle diameter corresponding to 50% cumulative volume calculated from particles having a small particle size in a particle size distribution measured by, for example, laser diffraction. For example, D10 is the particle diameter corresponding to 10% cumulative volume calculated from particles having a small particle size in a particle size distribution measured by, for example, laser diffraction. For example, D90 is the particle diameter corresponding to 90% cumulative volume calculated from particles having a small particle size in a particle size distribution measured by, for example, laser diffraction.

[0035] Hereinafter, 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 will be described in further detail according to exemplary embodiments.

[0036] The composite positive electrode active material includes: a core; and a first shell and a second shell disposed on an outer side of a surface of the core. The first shell may include at least one first metal compound represented by formula X a O b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2, or 3) or formula X a (OH) b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2, or 3), and the second shell may include: at least one second metal compound represented by formula Y c O d (wherein 0 < c ≤ 3, 0 < d < 4, and d may not be an integer when c is 1, 2, or 3); and graphene, wherein the at least one second metal oxide may be disposed in a graphene matrix, and both X and Y may each independently be at least one metal selected from Groups 2 to 13, Group 15, and Group 16 of the Periodic Table of Elements.

[0037] Hereinafter, a theoretical basis for providing the excellent effects of the composite positive electrode active material according to the embodiments will be described, but this theoretical basis is provided to facilitate understanding of the inventive concept, and is not intended to limit the inventive concept in any way.

[0038] Composite positive electrode active materials may include a first shell and a second shell disposed on the outer side of the surface of a core comprising a lithium transition metal oxide, wherein the first shell may include a first metal compound and the second shell may include a second metal compound and graphene. In composite positive electrode active materials of the art, a positive electrode electrolyte interface (CEI) is rapidly formed on the surface of the composite positive electrode active material due to side reactions between the composite positive electrode active material and the electrolyte solution during charging and discharging at high voltages, thereby rapidly increasing the interfacial resistance between the composite positive electrode active material and the electrolyte solution. Therefore, the internal resistance of lithium batteries including composite positive electrode active materials of the prior art increases, thereby rapidly deteriorating the electrochemical charging and discharging performance of the lithium battery. In contrast, the composite positive electrode active material disclosed herein, comprising a first shell comprising a first metal compound and a second shell comprising a second metal compound and graphene disposed on the outer side of the surface of the core, can effectively block contact between the core and the electrolyte solution, thus preventing side reactions caused by contact between the core and the electrolyte. In addition, since cation mixing caused by side reactions between the transition metal cations of the composite positive electrode active material and the electrolyte solution is suppressed, the formation of a resistance layer on the surface of the composite positive electrode active material can be suppressed. Furthermore, it can suppress the elution of transition metal ions from the surface of the composite positive electrode active material into the electrolyte solution. Therefore, it can suppress the performance degradation of lithium batteries that include composite positive electrode active materials.

[0039] In detail, since the first metal included in the first shell stabilizes the transition metal included in the core, the elution of the transition metal can be suppressed. Additionally, the graphene included in the second shell prevents the release of oxygen included in the core. Therefore, due to the double-shell structure including the first and second shells, the elution of transition metal and oxygen from the core can be suppressed. Furthermore, since the graphene included in the second shell has high electronic conductivity, the interfacial resistance between the composite positive electrode active material and the electrolyte solution can be reduced. Therefore, the fast-charging characteristics of the lithium battery including the composite positive electrode active material can be improved. Furthermore, since the first and second metal compounds have voltage resistance, the degradation of lithium transition metal oxides included in the core during charging and discharging at high voltages can be prevented. Therefore, the high-temperature and / or high-voltage cycling characteristics of the lithium battery including the composite positive electrode active material can be improved.

[0040] Regarding the first and second shells disposed on the outer side of the core surface, for example, the first and second shells can be sequentially disposed on the outer side of the core surface. Since the first metal compound is closer to the core, the first metal compound included in the first shell can further stabilize the transition metal included in the core, and since the graphene is closer to the electrolyte solution, the graphene can effectively reduce the interfacial resistance between the composite positive electrode active material and the electrolyte solution. Therefore, since the first and second shells are sequentially disposed on the outer side of the core surface, the cycle characteristics and fast charging characteristics of the lithium battery including the composite positive electrode active material can be further improved.

[0041] Regarding the first and second shells disposed on the outer side of the core surface, for example, the first shell can be directly disposed on the outer side of the core surface, and the second shell can be directly disposed on the outer side of the first shell surface. Since the first shell is closer to the core, the stabilizing effect of the first metal compound included in the first shell on the transition metal can be further improved. Furthermore, since the second shell is directly disposed on the outer side of the first shell surface, a bilayer structure of the first and second shells can be formed. Due to the bilayer structure, the effect of preventing the elution of transition metals and oxygen from the core can be further improved. Additionally, since the second shell is disposed on the outer side of the first shell surface, the interfacial resistance between the composite positive electrode active material and the electrolyte solution can be further reduced. Therefore, since both the first and second shells are directly disposed on the outer side of the core surface, the cycle characteristics of the lithium battery including the composite positive electrode active material can be further improved.

[0042] The thickness of the first shell included in the composite positive electrode active material can, for example, be in the range of about 1 nm to about 2 μm, about 10 nm to about 20 μm, about 50 nm to about 20 μm, about 100 nm to about 20 μm, about 200 nm to about 20 μm, about 500 nm to about 20 μm, about 1 μm to about 20 μm, about 2 μm to about 20 μm, about 5 μm to about 20 μm, about 1 nm to about 10 μm, 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, or about 1 nm to about 50 nm. When the thickness of the first shell is within the above range, the effect of preventing transition metal from eluting from the core can be further improved. Therefore, the cycle characteristics of the lithium battery including the composite positive electrode active material can be further improved.

[0043] The thickness of the second shell included in the composite positive electrode active material can, for example, be in the range of about 1 nm to about 2 μm, about 10 nm to about 20 μm, about 50 nm to about 20 μm, about 100 nm to about 20 μm, about 200 nm to about 20 μm, about 500 nm to about 20 μm, about 1 μm to about 20 μm, about 2 μm to about 20 μm, about 5 μm to about 20 μm, about 1 nm to about 10 μm, 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, or about 1 nm to about 50 nm. When the thickness of the second shell is within the above range, the effect of preventing transition metal from eluting from the core can be further improved, and therefore, the cycle characteristics of the lithium battery including the composite positive electrode active material can be further improved. In addition, since the side reactions between the composite positive electrode active material and the electrolyte solution are suppressed, the rate of increase in internal resistance of the lithium battery including the composite positive electrode active material can be further reduced.

[0044] The metal included in the first metal compound can be at least one selected from, for example, Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se. Because the metal is included in the first metal compound, the first shell can be uniformly disposed on the outer surface of the core. Furthermore, the stability of the transition metal included in the core can be further improved. Therefore, the elution of the transition metal from the composite positive electrode active material can be further effectively prevented. The first metal compound can include oxides or hydroxides of the aforementioned metals.

[0045] The metal included in the first metal compound can be, for example, Al. The first metal compound can include, for example, at least one selected from the group consisting of Al₂O₃ and Al(OH)₃. The first metal compound can include, for example, both Al₂O₃ and Al(OH)₃. Since the first shell includes such a first metal compound, the stability of the transition metal (e.g., cobalt (Co)) included in the core can be further improved. Therefore, the elution of the transition metal from the composite positive electrode active material can be further effectively prevented.

[0046] In composite positive electrode active materials, for example, a first metal compound included in the first shell and a transition metal included in a lithium transition metal oxide in the core can be chemically bonded. Because the first metal compound included in the first shell and the lithium transition metal oxide included in the core are chemically bonded, the core and the first shell can form a complex. In this respect, such a complex can be distinguished from a simple physical mixture of the first metal compound and the lithium transition metal oxide. Furthermore, since the stability of the transition metal included in the core is improved, the elution of the transition metal can be effectively suppressed.

[0047] The average particle size of the first metal compound included in the first shell can be, for example, in the range of about 10 nm to about 20 μm, about 50 nm to about 20 μm, about 100 nm to about 20 μm, about 150 nm to about 20 μm, about 1 nm to about 10 μm, about 1 nm to about 1 μm, about 1 nm to about 500 nm, about 1 nm to about 400 nm, about 1 nm to about 300 nm, or about 1 nm to about 200 nm. Since the average particle size of the first metal compound is within the above range, the first metal compound can be uniformly disposed on the outer surface of the core to form the first shell. Therefore, since the first shell is uniformly disposed on the outer surface of the core, the elution of transition metals can be further effectively suppressed. Therefore, the cycle characteristics of the lithium battery including the composite positive electrode active material can be further improved.

[0048] The average particle size of the first metal compound can be measured using, for example, a measuring device employing laser diffraction or dynamic light scattering. The average particle size can be measured using, for example, a laser scattering particle size analyzer (e.g., Horiba Manufacturing Co., Ltd.'s LA-920), and is the value of the median particle size (D50) when the metal oxide particles accumulate from small particles to 50% in volume conversion.

[0049] The metal included in the second metal compound may be, for example, at least one selected from Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se. The second metal compound may be, for example, selected from Al₂O₃. 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(wherein 0<z<3) and SeO y (wherein 0<y<2). Since the second metal compound is arranged in the graphene matrix, the uniformity of the second shell arranged on the core and the first shell can be improved, and the voltage resistance of the composite positive electrode active material can be further improved. For example, the second shell may include Al2O as the second metal compound x (wherein 0<x<3).

[0050] The second shell may further comprise a compound represented by formula Y c O e (wherein 0<c≤3, 0<e≤4, and e may be an integer when c is 1, 2 or 3) represented by at least one third metal compound. Here, Y may be at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the Periodic Table of the Elements. For example, the third metal compound may comprise the same metal as the second metal compound, and the ratio e / c of the third metal compound (i.e., the ratio of e to c) may be greater than the ratio d / c of the second metal oxide (i.e., the ratio of d to c). For example, e / c>d / c. The third metal compound may be, for example, selected from the group consisting of Al2O3, NbO, NbO2, Nb2O5, MgO, Sc2O3, TiO2, ZrO2, V2O3, WO2, MnO2, Fe2O3, Co3O4, PdO, CuO, AgO, ZnO, Sb2O3 and SeO2. The second metal compound may be a reduction product of the third metal compound. The second metal compound can be obtained by partially or completely reducing the third metal compound. Therefore, compared with the third metal compound, the second metal compound can have a lower oxygen content and a larger oxidation number. For example, the second shell may include Al2O as the second metal oxide x (wherein 0<x<3) and Al2O3 as the third metal compound.

[0051] In composite positive electrode active materials, for example, graphene included in the second shell and the metal of the first metal compound included in the first shell can be chemically bonded. The carbon atoms (C) of the graphene included in the second shell and the transition metal (Me) of the first metal compound included in the first shell can be chemically bonded, for example, via CO-Me bonds (e.g., CO-Co bonds) mediated by oxygen atoms. Since the graphene included in the second shell and the first metal compound included in the first shell are chemically bonded, the first and second shells can form a composite. Additionally, as described above, when the first metal compound included in the first shell and the lithium transition metal oxide included in the core are chemically bonded, the core and the first shell can form a composite. Therefore, the core, the first shell, and the second shell form a composite. In this respect, such a composite can be distinguished from a simple physical mixture of the first metal compound, the second metal compound, graphene, and the lithium transition metal oxide.

[0052] Furthermore, the second metal compound and graphene included in the second shell can also be chemically bonded. Here, the chemical bond can be, for example, a covalent bond or an ionic bond. The covalent bond can be, for example, a bond including at least one of ester, ether, carbonyl, amide, carbonate anhydride, and anhydride groups. The ionic bond can be, for example, a bond including carboxylic acid ions, ammonium ions, acyl cationic groups, etc.

[0053] The composite positive electrode active material may, for example, further include a fourth metal doped onto the core. For instance, after doping the surface of a lithium transition metal oxide included in the core with a fourth metal, a first shell and a second shell may be disposed on the outer side of the core surface. The fourth metal may include, for example, at least one of Al, Zr, W, and Co.

[0054] The second shell included in the composite positive electrode active material may include, for example, at least one selected from a composite comprising a second metal compound and graphene, and a milled product of the composite, wherein the second metal compound may be disposed within a graphene matrix. The second shell may be prepared, for example, from a composite of the second metal compound and graphene. In addition to the second metal compound, the composite may also include a third metal compound. The composite may include, for example, at least two types of second metal compounds. The composite may include, for example, at least two types of second metal compounds and at least two types of third metal compounds.

[0055] The average particle size of at least one selected from the second and third metal compounds included in the composite can be in the range of 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 70 nm, about 1 nm to about 50 nm, about 1 nm to about 30 nm, about 3 nm to about 1 μm, about 5 nm to about 1 μm, about 10 nm to about 1 μm, about 15 nm to about 1 μm, about 20 nm to about 1 μm, about 25 nm to about 1 μm, or about 30 nm to about 1 μm. Since the second and / or third metal compounds have particle sizes in the above nanometer range, the second and / or third metal compounds can be further uniformly distributed in the graphene matrix of the composite. Therefore, the composite can then be uniformly coated on the outer surface of the core and the first shell to form a second shell. Because the second and / or third metal compounds have particle sizes within the above range, they can be further uniformly disposed on the outer surfaces of the core and the first shell. Therefore, by uniformly disposing the second and / or third metal compounds on the outer surfaces of the core and the first shell, the voltage withstand characteristics of the lithium battery including the composite can be further effectively exhibited.

[0056] The average particle size of each of the second and third metal compounds can be measured in the same manner as the average particle size of the first metal compound.

[0057] The uniformity deviation of at least one of the second and third metal compounds included in the composite can be less than or equal to 3%, less than or equal to 2%, or less than or equal to 1%. Uniformity can be obtained, for example, by XPS. Therefore, at least one of the second and third metal compounds can be uniformly distributed in the composite with a deviation of less than or equal to 3%, less than or equal to 2%, or less than or equal to 1%.

[0058] The graphene included in the composite may, for example, have a branched structure, and a second metal compound 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 of this branched structure, graphene can provide various conduction pathways.

[0059] The graphene included in the composite can, for example, have a spherical structure, and a second metal compound can be distributed within the spherical structure of the graphene. The spherical structure of the graphene can have a size in the range of 50 nm to 300 nm. Multiple graphenes with spherical structures can be provided. When the graphene has such a spherical structure, the composite can have a rigid structure.

[0060] The graphene included in the composite may, for example, have a helical structure in which multiple spherical structures are interconnected, and a second metal compound may be distributed within the spherical structures of the helical structure. The helical structure of graphene may have a size in the range of 500 nm to 100 μm. Due to this helical structure of graphene, the composite may have a rigid structure.

[0061] The graphene included in the composite can, for example, have a cluster structure in which multiple spherical structures are interconnected, and a second metal compound can be distributed within the spherical structures of the cluster structure. The graphene cluster structure can have a size ranging from 0.5 mm to 10 cm. Due to this cluster structure of graphene, the composite can have a rigid structure.

[0062] The composite can have, for example, a wrinkled faceted-ball structure, and the second metal oxide can be distributed inside or on the surface of this structure. Because the composite has this faceted-ball structure, it can be easily coated onto irregular areas of the irregular surface of the core.

[0063] The complex may have, for example, a planar structure, and the second metal compound may be distributed within or on the surface of the structure. The complex may have, for example, a planar structure, and at least one selected from the second and third metal compounds may be distributed within or on the surface of the structure. Because the complex has such a two-dimensional planar structure, it can be easily coated onto irregular areas of the core surface.

[0064] The graphene included in the composite can extend from the second metal compound by a distance of less than or equal to about 10 nm, and can include at least 1 to 20 graphene layers. For example, when multiple graphene layers are stacked, graphene with a total thickness of less than or equal to about 12 nm can be disposed on the second metal compound. For example, the total thickness of the graphene can be in the range of about 0.6 nm to about 12 nm.

[0065] Based on the weight of the core, the total weight of the first metal compound, the second metal compound, and graphene can be in the range of about 0.001 wt% to about 1 wt%, about 0.005 wt% to about 1 wt%, about 0.001 wt% to about 1 wt%, about 0.01 wt% to about 1 wt%, about 0.02 wt% to about 1 wt%, about 0.05 wt% to about 1 wt%, about 0.1 wt% to about 1 wt%, about 0.001 wt% to about 0.5 wt%, about 0.001 wt% to about 0.2 wt%, about 0.001 wt% to about 0.15 wt%, or about 0.001 wt% to about 0.1 wt%. When the composite positive electrode active material includes a composite within the above range, the cycle characteristics of the lithium battery including the composite positive electrode active material can be further improved.

[0066] The core included in the composite positive electrode active material may include, for example, a lithium transition metal oxide represented by Formula 1:

[0067] Formula 1

[0068] Li a1 Co x1 M y1 O 2-b1 A b1

[0069] In Equation 1,

[0070] 1.0≤a1≤1.2, 0≤b1≤0.2, 0.9≤x1≤1, 0≤y1≤0.1, and x1+y1=1, and

[0071] M can be one or more of 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), and boron (B), and A can be F, S, Cl, Br, or a combination thereof.

[0072] The core included in the composite positive electrode active material may include, for example, a lithium transition metal oxide represented by Formula 2:

[0073] Formula 2

[0074] LiCoO2.

[0075] On the other hand, a positive electrode comprising a composite positive electrode active material is provided. By including a composite positive electrode active material, the positive electrode can provide improved cycle characteristics and increased thermal stability.

[0076] The positive electrode can be prepared, for example, according to the following methods, but the preparation method is not limited to the methods illustrated, and can be adjusted according to the required conditions.

[0077] First, a positive electrode active material composition is prepared by mixing the aforementioned composite positive electrode active material, conductive material, binder, and solvent. The prepared positive electrode active material composition can be directly coated and dried onto an aluminum current collector to form a positive electrode plate with a positive electrode active material layer. Alternatively, a film layer obtained by casting the positive electrode active material composition onto a separate carrier and separating it from the carrier can be laminated onto the aluminum current collector to prepare a positive electrode plate with a positive electrode active material layer formed thereon.

[0078] Examples of conductive materials may include: carbon black, graphite particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fibers; carbon nanotubes; metal powders, metal fibers, or metal tubes of copper, nickel, aluminum, silver, etc.; and conductive polymers such as polyphenylene derivatives. However, the embodiments are not limited thereto, and any suitable conductive material available in the art may be used.

[0079] Examples of adhesives include vinylidene fluoride / hexafluoropropylene copolymers, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE), mixtures of the above polymers, styrene-butadiene rubber polymers, etc., and examples of solvents include N-methylpyrrolidone (NMP), acetone, water, etc. However, the embodiments are not limited thereto, and any suitable adhesives and solvents available in the art can be used.

[0080] Pores can be formed inside the electrode plate by further adding plasticizers or pore-forming agents to the positive electrode active material composition.

[0081] The content of composite positive electrode active material, conductive material, binder, and solvent used in the positive electrode can be at the levels commonly used in lithium batteries. Depending on the application and construction of the lithium battery, one or more of the conductive material, binder, and solvent can be omitted.

[0082] In addition, the positive electrode may include general positive electrode active materials other than the composite positive electrode active materials mentioned above.

[0083] As a general positive electrode active material, any suitable lithium-containing metal oxide available in the art can be used without limitation. For example, a composite oxide consisting of lithium and at least one metal selected from Co, Mg, Ni, and combinations thereof can be used, a specific example being a compound represented by one of the following formula: Li a1 A 1-b1 B b1 D2 (where 0.90≤a1≤1 and 0≤b1≤0.5); Li a1 E 1-b1 B b1 O 2-c1 D cl (Where, 0.90≤a1≤1, 0≤b1≤0.5 and 0≤c1≤0.05); LiE 2-b1 B b1 O 4-c1 D cl (Where, 0 ≤ b1 ≤ 0.5 and 0 ≤ c1 ≤ 0.05); Li a1 Ni 1-b1-c1 Co b1 B c1 D α (Where, 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05 and 0<α≤2); Li a1 Ni 1-b1-c1 Co b1 B c1 O 2-α F α (Where, 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05 and 0<α<2); Li a1 Ni 1-b1-c1 Co b1 B cl O 2-α F2 (where 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05, and 0<α<2); Li a1 Ni 1-b1-c1 Mn b1 B c1 D α (Where, 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05 and 0<α≤2); Li a1 Ni 1-b1-c1 Mn b1 B cl O 2-α F α (Where, 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05 and 0<α<2); Li a1 Ni 1-b1-c1 Mnb1 B cl O 2-α F2 (where 0.90≤a1≤1, 0≤b1≤0.5, 0≤c1≤0.05 and 0<α<2); Li a1 Ni b1 E c1 G d1 O2 (where 0.90≤a1≤1, 0≤b1≤0.9, 0≤c1≤0.5 and 0.001≤d1≤0.1); Li a1 Ni b1 Co cl Mn d1 G e1 O2 (where 0.90≤a1≤1, 0≤b1≤0.9, 0≤c1≤0.5, 0≤d1≤0.5, and 0.001≤e1≤0.1); Li a1 NiG b1 O2 (where 0.90≤a1≤1 and 0.001≤b1≤0.1); Li a1 CoG b1 O2 (where 0.90≤a1≤1 and 0.001≤b1≤0.1); Li a1 MnG b1 O2 (where 0.90≤a1≤1 and 0.001≤b1≤0.1); Li a1 Mn2G b1 O4 (where 0.90≤a1≤1 and 0.001≤b1≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f1) J2(PO4)3 (where 0≤f1≤2); Li (3-f1) Fe2(PO4)3 (where 0≤f1≤2); and LiFePO4.

[0084] In the above formulas representing compounds, A can be Ni, Co, Mn or a combination thereof; B can be Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D can be O, F, S, P or a combination thereof; E can be Co, Mn or a combination thereof; F can be F, S, P or a combination thereof; G can be Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q can be Ti, Mo, Mn or a combination thereof; I can be Cr, V, Fe, Sc, Y or a combination thereof; and J can be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0085] Compounds in which a coating is further formed on the surface of the aforementioned compounds can be used, and mixtures of the aforementioned compounds and compounds with a further coating can also be used. The coating formed on the surface of the aforementioned compounds may include, for example, coating element compounds, such as oxides of coating elements, hydroxides of coating elements, hydroxy oxides of coating elements, oxycarbonates of coating elements, or hydroxycarbonates of coating elements. The compounds constituting the coating may be amorphous or crystalline. The coating elements included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The method of forming the coating can be selected within a range that will not adversely affect the physical properties of the positive electrode active material. The coating method may be, for example, spraying, dipping, etc. A detailed description of the coating method will be omitted, as those skilled in the art will readily understand the coating method.

[0086] On the other hand, a lithium battery is provided, which includes a positive electrode containing a composite positive electrode active material.

[0087] When lithium-ion batteries include a positive electrode containing composite positive electrode active materials, they can provide improved cycle characteristics, improved fast charging, and improved thermal stability. Furthermore, the formation of a CEI between the positive electrode and the electrolyte solution during charging and discharging can suppress the increase in internal resistance within the lithium-ion battery.

[0088] Lithium batteries can be prepared, for example, by the methods described below, but the preparation method is not limited to the methods illustrated, and can be adjusted according to the required conditions.

[0089] First, the positive electrode is prepared according to the above-mentioned method for preparing the positive electrode.

[0090] Next, the negative electrode can be manufactured as follows. Except for using a negative electrode active material instead of the composite positive electrode active material, the negative electrode can be prepared, for example, in the same manner as the positive electrode. Furthermore, in the negative electrode active material composition, the conductive materials, binders, and solvents used are substantially the same as those used in the preparation of the positive electrode.

[0091] For example, a negative electrode active material, a conductive material, a binder, and a solvent can be mixed to prepare a negative electrode active material composition. This composition can then be directly coated onto a copper current collector to prepare a negative electrode plate. Alternatively, a negative electrode active material film obtained by casting the negative electrode active material composition onto a separate carrier and separating it from the carrier can be laminated onto the copper current collector to prepare a negative electrode plate.

[0092] As the negative electrode active material, any suitable negative electrode active material that can be used in lithium batteries in the art can be used. For example, the negative electrode active material may include at least one selected from the group consisting of lithium metal, metals alloyable with lithium, transition metal oxides, non-transition metal oxides and carbon-based materials.

[0093] Examples of metals alloyable with lithium are silicon (Si), tin (Sn), aluminum (Al), germanium (Ge), lead (Pb), bismuth (Bi), antimony (Sb), Si-Y alloys (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and Y is not Si) and Sn-Y alloys (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and Y is not Sn). Element Y may be, for example, 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, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0094] Transition metal oxides may include, for example, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, and the like.

[0095] Non-transition metal oxides may be, for example, SnO₂, SiO x (wherein 0<x<2) and the like.

[0096] Carbon-based materials may be, for example, crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon may be, for example, graphite in amorphous, platy, flaky, spherical or fibrous form (such as natural graphite or artificial graphite). Amorphous carbon may be, for example, soft carbon (carbon sintered at low temperature) or hard carbon, mesophase pitch carbide, sintered coke, and the like.

[0097] The contents of the negative electrode active material, conductive material, binder and solvent can be at levels commonly used in lithium batteries. One or more of the conductive material, binder and solvent may be omitted depending on the use and construction of the lithium battery.

[0098] Next, a separator to be disposed between the positive electrode and the negative electrode is prepared.

[0099] The separator can be any suitable separator commonly used in lithium-ion batteries. For example, the separator can have low resistance to ion migration in the electrolyte and electrolyte solution moisturizing ability. The separator can be, for example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), and combinations thereof, each of which can be in non-woven or woven fabric form. For lithium-ion batteries, rollable separators including, for example, polyethylene or polypropylene can be used. Separators with good organic electrolyte solution moisturizing ability can be used in lithium-ion polymer batteries.

[0100] The diaphragm can be prepared, for example, according to the following example method, but the embodiments are not limited thereto, and the method can be controlled according to the desired conditions.

[0101] First, a membrane composition is prepared by mixing a polymer resin, filler, and solvent. Then, the membrane composition is directly coated onto the electrode and dried to form a membrane. Alternatively, a membrane can be formed by laminating a membrane obtained by casting the membrane composition onto a carrier, drying it, and separating it from the carrier onto the electrode.

[0102] There are no particular restrictions on the polymers used in the preparation of the diaphragm, and any suitable polymer that can be used as a binder 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.

[0103] Next, the electrolyte can be prepared.

[0104] The electrolyte can be, for example, an organic electrolyte solution. An organic electrolyte solution can be prepared, for example, by dissolving a lithium salt in an organic solvent.

[0105] For use as an organic solvent, any suitable organic solvent available in the art may be used. Examples of organic solvents are propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzyl nitrile, 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, or mixtures thereof.

[0106] For use as a lithium salt, any material available in the art as a lithium salt can be used. Lithium salts can be, for example, 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 x and y can be natural numbers), LiCl, LiI, or mixtures thereof.

[0107] Alternatively, the electrolyte may be a solid electrolyte. Solid electrolytes may be, for example, boron oxide, lithium oxynitride, etc., but the embodiments are not limited thereto. Any suitable solid electrolyte available in the art can be used. The solid electrolyte can be formed on the negative electrode by methods such as sputtering, or separate solid electrolyte sheets can be stacked on the negative electrode.

[0108] like Figure 1 As shown, the lithium battery 1 includes 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 be housed in a battery casing 5. The battery casing 5 can then be filled with an organic electrolyte solution and sealed with a cover assembly 6, thereby completing the manufacture of the lithium battery 1. The battery casing 5 can be cylindrical, but its shape is not limited to this. For example, the battery casing 5 can be square, thin-film, etc.

[0109] A pouch-type lithium battery may include at least one battery assembly. A separator 4 may be disposed between a positive electrode 3 and a negative electrode 2 to form the battery assembly. The battery assemblies may be stacked into a dual-cell structure, impregnated with an organic electrolyte solution, and housed and sealed in a pouch to complete the manufacture of the pouch-type lithium battery. Multiple battery assemblies may be stacked to form a battery pack, and the battery pack can be used in all types of devices requiring high capacity and high output. For example, the battery pack can be used in laptops, smartphones, electric vehicles, etc.

[0110] Because of their excellent lifespan and high-rate characteristics, lithium batteries can be used in applications such as electric vehicles (EVs). For example, they can be used in hybrid vehicles, such as plug-in hybrid electric vehicles (PHEVs). Additionally, lithium batteries are suitable for applications requiring high energy storage, such as electric bicycles and power tools.

[0111] On the other hand, a method for preparing a composite positive electrode active material is provided, the method comprising: providing a lithium transition metal oxide; providing a material of formula X a O b(wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2 or 3) or Formula X a (OH) b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2 or 3) at least one first metal compound represented by; providing a composite, wherein the composite comprises the compound represented by Formula Y c O d (wherein 0 < c ≤ 3, 0 < d < 4, and d may be a non-integer when c is 1, 2 or 3) at least one second metal compound represented by and graphene, wherein the second metal compound is disposed in a graphene matrix; and mechanically grinding a lithium transition metal oxide, the first metal compound and the composite, wherein both X and Y may each independently be at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the Periodic Table of Elements.

[0112] A lithium transition metal oxide can be provided. The lithium transition metal oxide can be, for example, a compound represented by Formula 1 or Formula 2.

[0113] In providing the compound represented by Formula X a O b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2 or 3) or Formula X a (OH) b (wherein 0 < a ≤ 3, 0 < b ≤ 4, and b may be an integer when a is 1, 2 or 3) when providing at least one first metal compound represented by, the at least one first metal compound may be mixed with the lithium transition metal oxide.

[0114] The first metal compound may include, for example, at least one metal selected from the group consisting of Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb and Se as described above. The first metal compound may include, for example, Al. The first metal compound may include, for example, at least one selected from the group consisting of Al2O3 and Al(OH)3. The first metal compound may include, for example, both Al2O3 and Al(OH)3.

[0115] The step of providing a composite may include, for example, supplying a reaction gas composed of a carbon source gas to a structure including a third metal compound and performing heat treatment thereon, the composite comprises the compound represented by Formula Y c O d (wherein 0 < c ≤ 3, 0 < d < 4, and d may be a non-integer when c is 1, 2 or 3) at least one second metal compound represented by, which is disposed in the graphene matrix, and graphene.

[0116] The step of providing a composite may include, for example, adding to Yc O e (wherein 0 < c ≤ 3, 0 < e ≤ 4, and e may be an integer when c is 1, 2 or 3) supplying at least one third metal oxide represented by with a reaction gas composed of a carbon supply source gas and performing heat treatment thereon, wherein Y may be at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the Periodic Table of Elements.

[0117] The carbon supply source gas may be a mixed gas of at least one selected from the group consisting of a compound represented by Chemical Formula 3, a compound represented by Chemical Formula 4, and an oxygen-containing gas represented by Chemical Formula 5:

[0118] Formula 3

[0119] C n H (2n+2-a2) [OH] a2

[0120] wherein in Formula 3, n may be an integer of 1 to 20, and a2 may be 0 or 1;

[0121] Formula 4

[0122] C n H 2n

[0123] wherein in Formula 4, n may be an integer of 2 to 6; and

[0124] Formula 5

[0125] C x2 H y2 O z2

[0126] wherein in Formula 5, x2 may be 0 or an integer of 1 to 20, y2 may be 0 or an integer of 1 to 20, and z2 may be 1 or 2.

[0127] The compound represented by Formula 3 and the compound represented by Formula 4 may be at least one selected from the group consisting of methane, ethylene, propylene, methanol, ethanol, and propanol. The oxygen-containing gas represented by Formula 5 may include, for example, carbon dioxide (CO2), carbon monoxide (CO), water vapor (H2O), or a mixture thereof.

[0128] In supplying to Y c O eAfter providing a reaction gas composed of a carbon supply source gas to the third metal compound represented by (wherein 0 < c ≤ 3, 0 < e ≤ 4, and e may be an integer when c is 1, 2 or 3) and performing heat treatment thereon, a cooling process may be further performed by using at least one inert gas selected from the group consisting of nitrogen, helium and argon. The cooling process refers to adjusting the reaction temperature to room temperature (20°C to 25°C). The carbon supply source gas may comprise at least one inert gas selected from the group consisting of nitrogen, helium and argon.

[0129] In the method for preparing the composite, the process of growing graphene can be performed under various conditions according to gas reaction.

[0130] According to the first condition, for example, Y disposed therein may be firstly supplied to c O e methane is supplied to a reactor provided with the third metal oxide represented by (wherein 0 < c ≤ 3, 0 < e ≤ 4, and e may be an integer when c is 1, 2 or 3), and the reaction temperature can be increased to a heat treatment temperature T. The time required for increasing the reaction temperature to the heat treatment temperature T can be in a range of 10 minutes to 4 hours, and the heat treatment temperature T can be in a range of 700°C to 1100°C. The heat treatment can be performed at the heat treatment temperature T for a reaction time. The reaction time can, for example, be in a range of 4 hours to 8 hours. The heat-treated product can be cooled to room temperature to prepare the composite. The time required for reducing the reaction temperature from the heat treatment temperature T to room temperature can, for example, be in a range of 1 hour to 5 hours.

[0131] According to the second condition, for example, Y disposed therein may be firstly supplied to c O e hydrogen is supplied to a reactor provided with the third metal oxide represented by (wherein 0 < c ≤ 3, 0 < e ≤ 4, and e may be an integer when c is 1, 2 or 3), and the reaction temperature can be increased to a heat treatment temperature T. The time required for increasing the reaction temperature to the heat treatment temperature T can be in a range of 10 minutes to 4 hours, and the heat treatment temperature T can be in a range of 700°C to 1100°C. After performing heat treatment at the heat treatment temperature T for a predetermined reaction time, methane gas can be supplied, and heat treatment for the remaining reaction time can be performed. The reaction time can, for example, be in a range of 4 hours to 8 hours. The heat-treated product can be cooled to room temperature to prepare the composite. In the cooling process, nitrogen gas can be supplied thereto. The time required for reducing the reaction temperature from the heat treatment temperature T to room temperature can, for example, be in a range of 1 hour to 5 hours.

[0132] In the preparation of the composite, a composite with excellent conductivity can be obtained when the carbon supply gas includes water vapor. The water vapor content in the gas mixture is not limited and can range from, for example, 0.01 vol% to 10 vol% based on 100 vol% of the total carbon supply gas. The carbon supply gas can be, for example, methane; a mixture of methane and an inert gas; or a mixture of methane and an oxygen-containing gas.

[0133] The carbon supply source gas can be, for example, methane; a mixture of methane and carbon dioxide; or a mixture of methane, carbon dioxide, and water vapor. The molar ratio of methane to carbon dioxide in the methane and carbon dioxide mixture can be in the range of about 1:0.20 to about 1:0.50, about 1:0.25 to about 1:0.45, or about 1:0.30 to about 1:0.40. The molar ratio of methane to carbon dioxide to water vapor in the methane, carbon dioxide, and water vapor mixture can be in the range of about 1:0.20 to about 0.50:0.01 to 1.45, about 1:0.25 to about 0.45:0.10 to 1.35, or about 1:0.30 to about 0.40:0.50 to 1.0.

[0134] The carbon supply gas can be, for example, carbon monoxide or carbon dioxide. The carbon supply gas can also be, for example, a mixture of methane and nitrogen. The molar ratio of methane to nitrogen in the methane and nitrogen mixture can be in the range of about 1:0.20 to about 1:0.50, about 1:0.25 to about 1:0.45, or about 1:0.30 to about 1:0.40. The carbon supply gas may not include inert gases such as nitrogen.

[0135] The heat treatment pressure can be selected by considering the heat treatment temperature, the composition of the gas mixture, and the required amount of carbon coating. The heat treatment pressure can be controlled by adjusting the amount of gas mixture flowing in and out. The heat treatment pressure can be, for example, greater than or equal to 0.5 atm, greater than or equal to 1 atm, greater than or equal to 2 atm, greater than or equal to 3 atm, greater than or equal to 4 atm, or greater than or equal to 5 atm.

[0136] There is no particular limitation on the duration of heat treatment, and it can be selected by considering the heat treatment temperature, heat treatment pressure, composition of the gas mixture, and the desired amount of carbon coating. For example, the reaction time at the heat treatment temperature can range from 10 minutes to 100 hours, 30 minutes to 90 hours, or 50 minutes to 40 hours. For example, as the heat treatment time increases, the amount of deposited graphene (e.g., carbon) increases, thus improving the electrical properties of the composite. However, this trend may not be directly proportional to time. For example, after a predetermined time period, graphene deposition may cease, or the graphene deposition rate may decrease.

[0137] Through the gas-phase reaction of the above-mentioned carbon supply source gas, even at a relatively low temperature, it can be prepared on at least one of a third metal compound represented by Y c O e cOe (wherein 0 < c ≤ 3, 0 < e ≤ 4, and when c is 1, 2 or 3, e may be an integer), and a reduction product of the third metal compound represented by Y c O d cOd (wherein 0 < c ≤ 3, 0 < d < 4, and when c is 1, 2 or 3, d may be an integer) which is the second metal compound, a composite can be obtained by providing a uniform graphene coating on said at least one metal compound.

[0138] The composite may include, for example: a graphene matrix having at least one structure selected from the group consisting of a spherical structure, a spiral structure in which a plurality of spherical structures are connected, a cluster structure in which a plurality of spherical structures are agglomerated, and a sponge structure; and at least one selected from the group consisting of a second metal compound represented by Y c O d cOd (wherein 0 < c ≤ 3, 0 < d < 4, and when c is 1, 2 or 3, d does not have to be an integer) disposed in the graphene matrix and a third metal compound represented by Y c O e cOe (wherein 0 < c ≤ 3, 0 < e ≤ 4, and when c is 1, 2 or 3, e may be an integer).

[0139] Next, the lithium transition metal oxide, the first metal compound and the composite can be mixed and subjected to mechanical grinding. For grinding, a Nobilta mixer or the like can be used. The rotation speed of the mixer during grinding can be, for example, in the range of 1,000 rpm to 2,500 rpm. When the grinding speed is less than 1,000 rpm, the shear force applied to the lithium transition metal oxide, the first metal compound and the composite is weak, so it may be difficult to form chemical bonds among the lithium transition metal oxide, the first metal compound and the composite. When the grinding speed is too high, the formation of the composite proceeds in an excessively short time, so it may be difficult to uniformly coat the lithium transition metal oxide with the first metal compound to form a uniform and continuous first shell, and it may be difficult to uniformly coat the lithium transition metal oxide with the composite to form a uniform and continuous second shell. The grinding time can be, for example, in the range of 5 minutes to 100 minutes, 5 minutes to 60 minutes, or 5 minutes to 30 minutes. When the grinding time is too short, it may be difficult to uniformly coat the lithium transition metal oxide with the first metal compound to form a uniform and continuous first shell, and it may be difficult to uniformly coat the lithium transition metal oxide with the composite to form a uniform and continuous second shell. When the grinding time is significantly long, the production efficiency will decrease.

[0140] As described above, based on the weight of the core, the sum of the weight of the first metal compound, the weight of the second metal compound and the weight of graphene may range from about 0.001 wt% to about 1 wt%.

[0141] As described above, the average particle diameter of the first metal compound may range from about 1 nm to about 200 μm. The average particle diameter (D50) of the composite obtained by mechanical milling of lithium transition metal oxides and composites may, for example, range from 1 μm to 20 μm, 3 μm to 15 μm, or 5 μm to 10 μm.

[0142] Exemplary embodiments will be described in more detail by the following examples and comparative examples. However, these examples are provided to illustrate the technical concept, and the scope of the present technical concept is not limited thereto.

[0143] (Preparation of Composite)

[0144] Al₂O₃@Gr Composite

[0145] Al₂O₃ particles (average particle diameter: about 20 nanometers (nm)) are placed in a reactor, then the temperature inside the reactor is increased to 1000°C under the condition that CH₄ is supplied to the reactor at about 300 standard cubic centimeters per minute (sccm) and about 1 atmosphere (atm) for about 30 minutes.

[0146] Subsequently, heat treatment is performed thereon while maintaining the temperature for 7 hours. Then, the temperature inside the reactor is adjusted to room temperature (20°C to 25°C) to obtain Al₂O z (wherein 0<z<3) particles embedded in graphene.

[0147] Here, the amount of graphene included in the composite is 30.9 wt%.

[0148] Gr (Graphene)

[0149] Graphene is obtained in the same manner as in Preparation Example 1, except that no Al₂O₃ particles are placed in the reactor.

[0150] (Preparation of Composite Cathode Active Material)

[0151] Preparation Example 1: LCO 100g (core) / Al(OH)₃ 0.05g (first shell) / Al₂O₃@Gr composite 0.05g (second shell)

[0152] By using a manual mixer, the specific surface area is 0.21 m 2 / g of LiCoO2 (hereinafter referred to as LCO), Al(OH)3 with an average particle size of 200nm and Al2O3@Gr composite were mixed for 5 minutes to obtain a composite positive electrode active material in which a composite coating of the first shell and the second shell is formed on the surface of LCO.

[0153] Here, the weight ratio of the LCO:Al(OH)3:Al2O3@Gr complex is 100:0.05:0.05.

[0154] Preparation Example 2: LCO 100g (core) / Al(OH)3 0.05g, Al2O3 0.03g (first shell) / Al2O3@Gr complex 0.02g (second shell)

[0155] In addition to LCO (specific surface area: 0.21m²), 2 The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the weight ratio of Al(OH)3 (average particle size: 200 nm), Al2O3 (average particle size: 20 nm) and Al2O3@Gr composite was changed to 100:0.05:0.03:0.02.

[0156] Preparation Example 3: LCO 100g (core) / Al(OH)3 0.05g, Al2O3 0.07g (first shell) / Al2O3@Gr complex 0.03g (second shell)

[0157] In addition to LCO (specific surface area: 2.21m²), 2 The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the weight ratio of Al(OH)3 (average particle size: 200 nm), Al2O3 (average particle size: 20 nm) and Al2O3@Gr composite was changed to 100:0.05:0.07:0.03.

[0158] Preparation Example 4: LCO 100g (core) / Al(OH)3 0.07g, Al2O3 0.07g (first shell) / Al2O3@Gr complex 0.06g (second shell)

[0159] In addition to LCO (specific surface area: 2.21m²), 2 The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the weight ratio of Al(OH)3 (average particle size: 200 nm), Al2O3 (average particle size: 20 nm) and Al2O3@Gr composite was changed to 100:0.07:0.07:0.06.

[0160] Comparative preparation example 1: naked LCO

[0161] LCO was used as the positive electrode active material in its original form.

[0162] Comparative preparation example 2: LCO 100g (core) / Al(OH)3 0.05g (first shell) / Gr 0.05g (second shell)

[0163] The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that Gr (graphene) was used instead of Al2O3@Gr composite.

[0164] Comparative preparation example 3: LCO 100g (core) / Al(OH)3 0.05g, Al2O3 0.03g (first shell) / Gr 0.02g (second shell)

[0165] The composite positive electrode active material was prepared in the same manner as in Preparation Example 2, except that Gr (graphene) was used instead of Al2O3@Gr composite.

[0166] Comparative preparation example 4: LCO 100g (core) / Al(OH)3 0.1g (shell)

[0167] The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that LCO and Al(OH)3 were used in a weight ratio of 100:0.1 and the Al2O3@Gr complex was not used.

[0168] Comparative preparation example 5: LCO 100g (core) / Al(OH)3 0.05g (shell)

[0169] The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that LCO and Al(OH)3 were used in a weight ratio of 100:0.05 and the Al2O3@Gr complex was not used.

[0170] Comparative preparation example 6: 100g LCO (core) / 0.1g Al2O3@Gr complex (shell)

[0171] The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the LCO and Al2O3@Gr composite were used in a weight ratio of 100:0.1 and Al(OH)3 was not used.

[0172] Comparative preparation example 7: 100g LCO (core) / 0.05g Al2O3@Gr complex (shell)

[0173] The composite positive electrode active material was prepared in the same manner as in Preparation Example 1, except that the LCO and Al2O3@Gr composite were used in a weight ratio of 100:0.05 and Al(OH)3 was not used.

[0174] (Manufacturing of lithium batteries (half-cells))

[0175] Example 1

[0176] (The manufacture of the positive electrode)

[0177] A mixture of the composite positive electrode active material of Preparation Example 1, carbon conductive material (e.g., superconducting acetylene black, Denka Black), and polyvinylidene fluoride (PVdF) in a weight ratio of 96:2:2 was mixed with N-methylpyrrolidone (NMP) in an agate mortar to prepare a slurry.

[0178] The slurry was prepared at 8.5 mg / cm³. 2 The coating is applied to an aluminum current collector with a thickness of 15 μm, rod-coated, dried at room temperature, and then vacuum-dried again at 120 °C. Finally, it is rolled and stamped to prepare a positive electrode plate with a thickness of 21 μm and an electrode density of 4.1 g / cc.

[0179] (The manufacture of button batteries)

[0180] Each coin cell was manufactured using the prepared positive electrode plate. Here, lithium metal was used as the counter electrode, a PTFE separator was used, and a solution in which 1.3 M LiPF6 was dissolved in ethylene carbonate (EC) + ethyl propionate (EP) + propyl propionate (PP) (volume ratio of 25:30:45) was used as the electrolyte.

[0181] Examples 2 through 4 and Comparative Examples 1 through 7

[0182] Except that the composite positive electrode active material prepared in each of Preparation Examples 2 to 4 and Comparative Preparation Examples 1 to 7 is used instead of the composite positive electrode active material in Preparation Example 1 of Example 1, the button cells are each manufactured in the same manner as in Example 1.

[0183] Evaluation Example 1: Evaluation of Charge / Discharge Characteristics at Room Temperature

[0184] Each of the lithium-ion batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 7 was charged at 25°C with a constant current at a rate of 0.1C until the voltage reached 4.55 V (relative to Li), and then cut off with a current at a rate of 0.05C while maintaining the voltage at 4.55 V in constant voltage mode. Subsequently, each lithium-ion battery was discharged at a constant current at a rate of 0.1C until the voltage reached 3.0 V (relative to Li) (formation cycling).

[0185] Each lithium-ion battery that has undergone formation cycling was charged at a constant current at a rate of 0.2C at 25°C until the voltage reached 4.55V (relative to Li), and then the current was cut off at a rate of 0.05C while maintaining the voltage at 4.55V in constant voltage mode. Subsequently, each lithium-ion battery was discharged at a constant current at a rate of 0.2C until the voltage reached 3.0V (relative to Li) (first cycle). Here, the DC internal resistance (DC-IR) was calculated by measuring the voltage drop (V) that occurred while carrying a current of 1C for 1 second at SOC 10 (i.e., the state of charging to 10% when the total charge capacity is set to 100%, which means discharging to 90%).

[0186] Each lithium-ion battery that had undergone its first cycle was charged at 25°C with a constant current at a rate of 1C until the voltage reached 4.55V (relative to Li), and then the current was cut off at a rate of 0.05C while maintaining the voltage at 4.55V in constant voltage mode. Subsequently, each lithium-ion battery was discharged at a constant current at a rate of 1C until the voltage reached 3.0V (relative to Li) (second cycle), and this cycle was repeated under the same conditions (60 times) until the 60th cycle.

[0187] Here, for a lithium battery that has undergone 60 cycles, DC-IR is calculated by measuring the voltage drop (V) that occurs while the battery is charged to 10% at SOC 10 (i.e., when the total charge capacity is set to 100%, it means that the battery is discharged to 90%) with a current of 1C for 1 second.

[0188] A 10-minute stop time is provided after each charge / discharge cycle in all charge / discharge cycles.

[0189] The results of charge / discharge tests at room temperature, including discharge capacity (0.2C, mAh / g), initial efficiency (0.2C, %), DC-IR (Ω, SOC 10), and the rate of increase in DC-IR (%, after 60 cycles), are shown in Table 1. The rate of increase in DC-IR at 60 cycles is defined by Equation 1.

[0190] Equation 1

[0191] The increase rate of DR-IR [%] = [((DC-IR at the 60th cycle) - (DC-IR at the 1st cycle)) / DC-IR at the 1st cycle] × 100%

[0192] Evaluation Example 2: Evaluation of charging and discharging characteristics at high temperature and high voltage

[0193] Each lithium battery prepared in Examples 1 to 4 and Comparative Examples 1 to 7 was charged at 45°C with a constant current at a rate of 0.1C until the voltage reached 4.58 V (relative to Li), and then cut off with a current at a rate of 0.05C while maintaining the voltage at 4.58 V in constant voltage mode. Subsequently, each lithium battery was discharged with a constant current at a rate of 0.1C until the voltage reached 3.0 V (relative to Li) (formation cycling).

[0194] Each lithium-ion battery that has undergone formation cycling is charged at 45°C with a constant current at a rate of 0.2C until the voltage reaches 4.58V (relative to Li), and then cut off with a current at a rate of 0.05C while maintaining the voltage at 4.58V in constant voltage mode. Subsequently, each lithium-ion battery is discharged at a constant current at a rate of 0.2C until the voltage reaches 3.0V (relative to Li) (Cycle 1).

[0195] Each lithium-ion battery that had undergone its first cycle was charged at 45°C with a constant current at a 1C rate until the voltage reached 4.58V (relative to Li), then cut off with a current at a 0.05C rate while maintaining the voltage at 4.58V in constant voltage mode. Subsequently, each lithium-ion battery was discharged at a constant current at a 1C rate until the voltage reached 3.0V (relative to Li) (second cycle), and this cycle was repeated under the same conditions (60 times) until the 60th cycle.

[0196] A 10-minute stop time is provided after each charge / discharge cycle in all charge / discharge cycles.

[0197] Some results of the charge / discharge tests at high temperatures are shown in Table 1. The capacity retention at the 60th cycle is defined by Equation 2.

[0198] Equation 2

[0199] Capacity retention (%) = (Discharge capacity at 60th cycle / Discharge capacity at 1st cycle) × 100%

[0200] Table 1

[0201]

[0202] As shown in Table 1, compared with the lithium batteries of Comparative Examples 1 to 7, the lithium batteries of Examples 1 to 4 have low DC-IR, improved high-temperature life characteristics and reduced DC-IR increase rate.

Claims

1. A composite positive electrode active material, said composite positive electrode active material comprising: Cores, including lithium transition metal oxides; and The first and second shells are disposed on the outer side of the surface of the core. wherein the first shell comprises at least one first metal compound represented by formula X a O b or formula X a (OH) b wherein 0 < a < 3, 0 < b < 4, and when a is 1, 2 or 3, b is an integer, The second shell comprises: at least one second metal compound represented by formula Y c O d , wherein 0 < c ≤ 3, 0 < d < 4, and d is not an integer when c is 1, 2 or 3; and graphene. The at least one second metal compound is disposed in a graphene matrix, and X and Y are each independently at least one metal selected from Groups 2 to 13, Group 15 and Group 16 of the periodic table. The first shell is disposed directly on the outer side of the surface of the core, and the second shell is disposed directly on the outer side of the surface of the first shell.

2. The composite positive electrode active material according to claim 1, wherein, The first shell has a thickness in the range of 1 nm to 2 μm.

3. The composite positive electrode active material according to claim 1, wherein, The second shell has a thickness in the range of 1 nm to 2 μm.

4. The composite positive electrode active material according to claim 1, wherein, The metal included in the at least one first metal compound includes at least one metal selected from Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se.

5. The composite positive electrode active material according to claim 1, wherein, The metal included in the at least one first metal is Al.

6. The composite positive electrode active material according to claim 1, wherein, The at least one first metal compound includes at least one selected from the group consisting of Al2O3 and Al(OH)3.

7. The composite positive electrode active material according to claim 1, wherein, The at least one first metal compound has an average particle size in the range of 10 nm to 2 μm.

8. The composite positive electrode active material according to claim 1, wherein, The metal included in the at least one second metal compound includes at least one metal selected from Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se.

9. The composite positive electrode active material according to claim 1, wherein, The at least one second metal compound is at least one selected from the group consisting of Al₂O z _z, wherein 0<z<3; NbO x _x, wherein 0<x<2.5; MgO x _x, wherein 0<x<1; Sc₂O z _z, wherein 0<z<3; TiO y _y, wherein 0<y<2; ZrO y _y, wherein 0<y<2; V₂O z _z, wherein 0<z<3; WO y _y, wherein 0<y<2; MnO y _y, wherein 0<y<2; Fe₂O z _z, wherein 0<z<3; Co₃O w _w, wherein 0<w<4; PdO x _x, wherein 0<x<1; CuO x _x, wherein 0<x<1; AgO x _x, wherein 0<x<1; ZnO x _x, wherein 0<x<1; Sb₂O z _z, wherein 0<z<3; and SeO y _y, wherein 0<y<2.

10. The composite positive electrode active material according to claim 1, wherein, The second shell comprises at least one selected from the following: a composite comprising the at least one second metal compound and the graphene; and a milled product of the composite.

11. The composite positive electrode active material according to claim 10, wherein, The graphene has a branched structure, and the at least one second metal compound is distributed within the branched structure. The branched structure comprises multiple graphene particles in contact with each other.

12. The composite positive electrode active material according to claim 10, wherein, The graphene has at least one structure selected from spherical structures, helical structures of interconnected spherical structures, and cluster structures of aggregated spherical structures. The at least one second metal compound is distributed in the spherical structure, and the size of the spherical structure is in the range of 50 nm to 300 nm, the size of the helical structure is in the range of 500 nm to 100 μm, and the size of the cluster structure is in the range of 0.5 mm to 10 cm. The composite has a wrinkled polyhedral spherical structure or a planar structure, and the at least one second metal compound is distributed inside or on the surface of the polyhedral spherical structure or the planar structure. The graphene extends from the at least one second metal compound by a distance of less than or equal to 10 nm and comprises at least 1 to 20 graphene layers, and the total thickness of the graphene is in the range of 0.6 nm to 12 nm.

13. The composite positive electrode active material according to claim 1, wherein, Based on the weight of the core, the total weight of the at least one first metal compound, the at least one second metal compound, and the graphene is in the range of 0.001 wt% to 1 wt%.

14. The composite positive electrode active material according to claim 1, wherein, The lithium transition metal oxide is represented by formula 1 or formula 2: Formula 1 Li a1 Co x1 M y1 O 2-b1 A b1 In Equation 1, 1.0≤a1≤1.2, 0≤b1≤0.2, 0.9≤x1≤1, 0≤y1≤0.1, and x1+y1=1. M is one or more selected from manganese, niobium, vanadium, magnesium, gallium, silicon, tungsten, molybdenum, iron, chromium, copper, zinc, titanium, aluminum and boron, and A is F, S, Cl, Br or a combination thereof; Formula 2 LiCoO2.

15. A positive electrode comprising the composite positive electrode active material according to any one of claims 1 to 14.

16. A lithium battery comprising a positive electrode according to claim 15.

17. A method for preparing a composite positive electrode active material, the method comprising: Provide lithium transition metal oxides; Provided is at least one first metal compound represented by formula X a O b or formula X a (OH) b , wherein 0 < a ≤ 3, 0 < b ≤ 4, and b is an integer when a is 1, 2 or 3; There is provided a composite, the composite comprising: at least one second metal compound represented by formula Y c O d , wherein 0 < c ≤ 3, 0 < d < 4, and d is not an integer when c is 1, 2 or 3; and graphene, wherein the at least one second metal compound is disposed in a graphene matrix; and Mechanically grinding the lithium transition metal oxide, the at least one first metal compound, and the composite yields a composite positive electrode active material comprising a core containing the lithium transition metal oxide, a first shell containing the at least one first metal compound disposed directly on the outer surface of the core, and a composite positive electrode active material containing the composite disposed directly on the outer surface of the first shell. Wherein, X and Y are each independently at least one metal selected from Groups 2 to 13, 15 and 16 of the periodic table.

18. The method according to claim 17, wherein, The at least one first metal compound has an average particle size in the range of 1 nm to 2 μm, and The at least one first metal compound includes at least one selected from the group consisting of Al2O3 and Al(OH)3.

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