Positive electrode active material, positive electrode containing the positive electrode active material, and secondary battery containing the positive electrode

Abstract

The present invention includes a core and a coating layer disposed on the core, the core comprising Li 1+x M y O 2+z wherein M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, and -0.2≦x≦0.2, 0

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0111333, filed on September 1, 2020, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention includes a core and a coating layer disposed on the core, the core contains Li 1+x M y O 2+z where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, -0.2 ≦ x ≦ 0.2, 0 < y ≦ 2, and 0 ≦ z ≦ 2. The coating layer contains carbon-based particles, the carbon-based particles have a structure in which a plurality of graphene sheets are connected to each other, and the D / G peak ratio is 0.9 to 1. .3 during Raman spectrum measurement. The present invention relates to a positive electrode active material, a positive electrode including the positive electrode active material, and a secondary battery including the positive electrode.

Background Art

[0003] Recently, with the increase in technology development and demand for mobile devices, the demand for batteries as an energy source has increased rapidly. Therefore, various researches on batteries that can meet various needs are being conducted. In particular, research on lithium secondary batteries having a high energy density and excellent life and cycle characteristics as a power source for such devices is actively underway.

[0004] A lithium secondary battery means a battery including a positive electrode containing a positive electrode active material capable of inserting / removing lithium ions, a negative electrode containing a negative electrode active material capable of inserting / removing lithium ions, and a non-aqueous electrolyte containing lithium ions in an electrode assembly in which a fine porous separator is interposed between the positive electrode and the negative electrode.

[0005] Lithium transition metal oxides can be used as positive electrode active materials, and examples of such transition metals include cobalt, nickel, and manganese. Among these, lithium transition metal oxides with high nickel or manganese content are increasingly being used as a substitute for expensive cobalt. In particular, lithium transition metal oxides with high nickel content have the advantage of high energy density and low cost.

[0006] However, lithium transition metal oxides with a high nickel content exhibit lower electrical conductivity compared to those with a high cobalt content. Furthermore, due to the layered structure of nickel, a high nickel content necessitates a high lithium content. This results in a large amount of lithium remaining on the surface of the positive electrode active material, leading to a problem where the positive electrode active material readily reacts with moisture, causing the surface structure to collapse in the atmosphere. Additionally, the lithium remaining on the surface readily reacts with carbon dioxide in the atmosphere to form lithium carbonate, significantly increasing the surface resistance of the positive electrode active material. Moreover, when lithium remains in the form of LiOH, the OH of the LiOH reacts with the binder. - Because a reaction occurs, causing gelation of the positive electrode slurry, the manufacturing process efficiency of the positive electrode can be significantly reduced.

[0007] To solve these problems, methods for forming a carbon coating layer on the surface of lithium transition metal oxides with high nickel content using polymers, pitch, etc., are being actively investigated. However, in the above-mentioned method, a high-temperature heat treatment process is required for carbonization, and at this time, oxygen atoms and carbon atoms on the surface of the lithium transition metal oxide with high nickel content react, causing a large change in the metal oxidation state within the lithium transition metal oxide with high nickel content. As a result, the transition metal may dissolve when the battery is in operation, accelerating the collapse of the surface structure of the lithium transition metal oxide, and significantly reducing the input / output characteristics and lifespan characteristics of the battery.

[0008] Therefore, it is possible to effectively block contact with moisture, suppress elution of transition metals, minimize collapse of the surface structure of the lithium transition metal oxide, minimize changes in the metal oxidation number within the lithium transition metal oxide, and a cathode active material with high electrical conductivity is required. Summary of the Invention Problems to be Solved by the Invention

[0009] One problem to be solved by the present invention is to improve the electrical conductivity of the cathode active material, effectively block contact between the lithium transition metal oxide and moisture within the cathode active material, minimize collapse of the surface structure of the lithium transition metal oxide, minimize changes in the metal oxidation number within the lithium transition metal oxide, and provide a cathode active material capable of minimizing elution of transition metals.

[0010] Another problem to be solved by the present invention is to provide a cathode including the cathode active material and a secondary battery including the cathode, with improved input / output characteristics and life characteristics. Means for Solving the Problems

[0011] According to one embodiment of the present invention, it includes a core and a coating layer disposed on the core, the core contains Li 1+x M y O 2+z where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, -0.2 ≦ x ≦ 0.2, 0 < y ≦ 2, 0 ≦ z ≦ 2, the coating layer contains carbon-based particles, the carbon-based particles include a structure in which a plurality of graphene sheets are connected to each other, and a cathode active material with a D / G peak ratio of 0.9 to 1.3 during Raman spectrum measurement is provided.

[0012] Also, according to another embodiment of the present invention, a cathode including the cathode active material is provided.

[0013] Furthermore, according to yet another embodiment of the present invention, a secondary battery including the positive electrode is provided. [Effects of the Invention]

[0014] According to the present invention, contact between the core and external moisture is effectively blocked, preventing structural collapse of the core, thereby improving the battery's input / output characteristics and lifespan. Furthermore, a coating layer containing carbon-based particles can be formed uniformly and thinly, significantly improving the electrical conductivity of the positive electrode active material, thereby improving the battery's input / output characteristics. Additionally, since there is no separate heat treatment process during the formation of the coating layer, excessive changes in the metal oxidation state of the transition metals within the core are prevented, suppressing the problem of transition metal leaching from the positive electrode active material, and improving the battery's input / output characteristics and lifespan. [Brief explanation of the drawing]

[0015] [Figure 1] These are schematic diagrams and TEM images illustrating the process of forming graphene sheets from preliminary carbon-based particles in Manufacturing Example 1. [Figure 2] These are TEM and STEM (scanning TEM) images of preliminary carbon-based particles from manufacturing example 1. [Figure 3] This is an SEM image of the preliminary carbon-based particles from manufacturing example 1. [Figure 4] TEM images (a) of preliminary carbon-based particles from manufacturing example 1 and (b) of preliminary carbon-based particles from manufacturing example 2. [Figure 5] This is an SEM image of carbon black sample 1. [Figure 6] This is an SEM image of Li[Ni0.6Co0.2Mn0.2]O2 used in Example 1. [Figure 7] This is an SEM image of the positive electrode active material of Example 1 of the present invention. [Figure 8] This is an SEM image of the positive electrode active material of Comparative Example 1 of the present invention. [Figure 9] This is an SEM image of the positive electrode active material of Comparative Example 2 of the present invention.

Best Mode for Carrying Out the Invention

[0016] Hereinafter, in order to facilitate the understanding of the present invention, the present invention will be described in more detail. Here, the terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meanings and concepts consistent with the technical idea of the present invention, following the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0017] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation amount in the particle size distribution curve of the particles. The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to about several millimeters, and can obtain results with high reproducibility and high resolution.

[0018] <Positive Electrode Active Material> The positive electrode active material according to an embodiment of the present invention includes a core and a coating layer disposed on the core. The core contains Li 1+x M y O 2+z , where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, -0.2 ≦ x ≦ 0.2, 0 < y ≦ 2, 0 ≦ z ≦ 2. The coating layer contains carbon-based particles, and the carbon-based particles include a structure in which a plurality of graphene sheets are connected to each other, and the D / G peak ratio can be 0.9 to 1.3 during Raman spectrum measurement.

[0019] The core contains Li 1+x M y O 2+zcomprising, M can be at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, and -0.2 ≦ x ≦ 0.2, 0 < y ≦ 2, 0 ≦ z ≦ 2 can be satisfied. Preferably, the x satisfies -0.1 ≦ x ≦ 0.1, and more preferably 0 ≦ x ≦ 0.1. Specifically, the Li 1+x M y O 2+z is Li 1+x [Ni a Co b M 1 c M 2 d O2, or the Li 1+x [Ni a Co b M 1 c M 2 d O2. In the Li 1+x [Ni a Co b M 1 c M 2 d O2, the M 1 can be at least one element of Al and Mn, and M 2 can be at least one element selected from the group consisting of Fe, P, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V. The a satisfies 0 < a < 1, preferably 0.3 ≦ a < 1, and more preferably 0.5 ≦ a < 1. The b satisfies 0 <0 < b < 1, preferably 0 < b < 0.7, and more preferably 0 < b < 0.5. The c satisfies 0 < c < 1, preferably 0 < c < 0.7, and more preferably 0 < c < 0.5. The d satisfies 0 ≦ d ≦ 0.2, preferably 0 ≦ d ≦ 0.1. The Li 1+x M<( y O<00(00044>is LiCoO2, LiNiO2, LiMnO2, Li[Ni 0.5 C o0.3 Mn0.2 ]O2, Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2, Li[Ni 0.7 Co 0.1 Mn 0.2 ]O2, Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2, LiMn2O4, LiFePO4, 0.5Li2MnO3·0.5Li[Mn 0.4 Ni 0.3 Co 0.3 It may include at least one selected from the group consisting of ]O2. Preferably, the Li 1+x M y O 2+z The Li[R] 0.6 Co 0.2 Mn 0.2 ]O2, Li[Ni 0.7 Co 0.1 Mn 0.2 ]O2, Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, Li[Ni 0.9 Co 0.05 Mn 0.05 The core may contain one of the following: 1+x M y O 2+z Because it contains, lithium can be sufficiently supplied to the negative electrode, Li 1+x M y O 2+z Since this does not cause a decrease in the overall performance of the battery and exhibits electrochemical activity after the first cycle, the loss of battery capacity due to the irreversible capacity of the negative electrode can be eliminated.

[0020] The Li 1+x M y O 2+z These can be in the form of secondary particles formed by the bonding or granulation of primary particles, or, conversely, in the form of single particles.

[0021] The Li1+x M y O 2+z When in the form of secondary particles, the energy density of the positive electrode can be improved, and the 1+x M y O 2+z has a large contact area with the electrolyte, and the migration distance of lithium ions in the 1+x M y O 2+z is short, and the capacity and output characteristics of the battery can be improved. Also, in the case of the form of secondary particles, the coating layer described later can be generally uniformly formed over the surface of the secondary particles including the surface of the primary particles of the 1+x M y O 2+z and the concave spaces between the primary particles. When the 1+x M y O 2+z is in the form of single particles, the coating layer described later can be formed on the surface of the 1+x M y O 2+z with a uniform thickness and shape.

[0022] The coating layer can be disposed on the core. Specifically, the coating layer can cover at least a part of the surface of the core.

[0023] The coating layer can contain carbon-based particles.

[0024] The carbon-based particles may include a structure in which multiple graphene sheets are linked together. In the present invention, a graphene sheet means a carbonaceous structure having a thickness of 20 nm or less, being flexible, and in the form of a thin film. Specifically, the carbon-based particles may consist of at least two or more graphene sheets directly or indirectly linked to each other. Because the carbon-based particles include a structure in which multiple graphene sheets are linked together, the surface of the core can be smoothly covered by the carbon-based particles. That is, since most of the surface of the core is covered by the carbon-based particles, contact between the core and external moisture is effectively blocked, and the collapse of the core structure can be prevented. The carbon-based particles may include graphene sheets having different planar orientations from each other.

[0025] The carbon-based particles may be in the form of secondary particles formed by linking together a plurality of graphene sheets. Specifically, the plurality of graphene sheets can be linked together to form long linear secondary particles, and more specifically, the linear secondary particles may include regions in which the plurality of graphene sheets are partially aggregated. Because the secondary particles have a unique linear linkage structure, the carbon-based particles exhibit excellent electrical and thermal conductivity.

[0026] The carbon-based particles may further include connecting portions linked to at least some of the graphene sheets among a plurality of graphene sheets. In the present invention, when the carbon-based particles are manufactured, carbonaceous materials such as carbon black may rupture through repeated oxidation to form the graphene sheets, and there may also be portions that maintain their initial form without rupturing. Here, the portions that maintain their form may correspond to the connecting portions. Therefore, the connecting portions may be in a non-graphene form, and the non-graphene form may mean a lumpy form having a greater thickness than the graphene sheets, unlike the graphene sheets described above.

[0027] A portion of each of the multiple graphene sheets may be directly connected to one another. Alternatively, at least some of the multiple graphene sheets may be connected to one another via the connecting portion, specifically, at least a portion of each of the multiple graphene sheets may be connected to the connecting portion. The carbon-based particles may include both of the above-mentioned methods of connection.

[0028] The carbon-based particles are formed by coating the core with preliminary carbon-based particles. The preliminary carbon-based particles may be formed by oxidizing carbon black, such as acetylene black, furnace black, thermal black, channel black, and lamp black, which have a nearly spherical particle form and whose form is altered. Referring to the schematic diagram in Figure 1, the microstructure of carbon black can be altered by oxidation to form preliminary carbon-based particles containing multiple graphene sheets, and these preliminary carbon-based particles can be coated onto the core to become carbon-based particles. If the carbon black is in the form of secondary particles, carbon-based particles in the form of secondary particles, where the particles containing the multiple graphene sheets are aggregated, can be formed.

[0029] The average thickness of the graphene sheet can be 10 nm or less, specifically 0.34 nm to 10 nm, and more specifically 0.34 nm to 5 nm. When this range is met, the flexibility characteristic of graphene sheets can be exhibited, surface contact by the graphene sheet can be improved, and the electrical conductivity of carbon-based particles can be excellent. The graphene sheet can be in a form in which 10 or fewer graphene layers are stacked. The average thickness of the graphene sheet can be confirmed by TEM analysis, specifically by measuring the thickness of 100 graphene sheets and then calculating the average value.

[0030] The maximum length (lateral size) of the graphene sheet can be 10 nm to 500 nm, specifically 10 nm to 300 nm or less, more specifically 10 nm to 100 nm, for example, 50 nm to 90 nm. The maximum length of the graphene sheet can be controlled by the degree of heat treatment; for example, after an oxidation treatment process, another heat treatment in an inert atmosphere can be performed to control the maximum length of the graphene sheet. When the above range is met, ions in the electrolyte can diffuse smoothly within the electrode. Therefore, the rapid charging characteristics of the battery can be improved, and the rate-limiting characteristics can also be improved. Furthermore, since the graphene sheet can effectively cover the surface of the core, contact between the core and external moisture is effectively blocked, preventing the collapse of the core structure. Also, side reactions by lithium on the core surface can be suppressed. As a result, the input / output characteristics and life characteristics of the battery can be improved. The longest length of the graphene sheet refers to the average size of 100 graphene sheets observed by SEM or TEM, where the size refers to the longest length when assuming a line connecting one point to another within a single graphene sheet.

[0031] The thickness of the coating layer can be 1 nm to 500 nm, more specifically 10 nm to 300 nm, and more specifically 10 nm to 100 nm. When this range is met, the diffusion for insertion and deinsertion of lithium ions is not inhibited, and the Li 1+x M y O 2+z By minimizing the change in the metal oxidation state of the transition metals within the battery, the leaching of transition metals can be suppressed. This improves the battery's input / output characteristics and lifespan.

[0032] The weight ratio of the core and the coating layer can be 99.9:0.1 to 90:10, more specifically 99.9:0.1 to 95:5, and more specifically 99.9:0.1 to 99:1. When this range is satisfied, the diffusion for lithium ion insertion and deinsertion is not inhibited, and the Li 1+x M y O 2+z This minimizes changes in the metal oxidation state of the transition metals within the battery, thereby suppressing the leaching of transition metals. This improves the battery's input / output characteristics and lifespan.

[0033] When measuring the Raman spectrum of the positive electrode active material, the D / G peak ratio can be 0.9 to 1.3, more specifically 0.9 to 1.1, and more specifically 0.9 to 1.0. In the Raman spectrum, at 1590 cm⁻¹ -1 The G peak in the vicinity is due to carbon sp. 2 Bond E 2g This is caused by the vibration mode, 1350cm -1 The nearby D peak is due to carbon sp. 2 This appears when there is a defect in the bonding. When the aforementioned D / G peak ratio is satisfied, it means that carbon-based particles with a high degree of graphitization are coated onto the core surface by a strong shear force. As a result, when using these carbon-based particles, the high electrical conductivity of the carbon-based particles can improve the capacity and electrical characteristics of the battery.

[0034] The specific surface area of ​​the positive electrode active material is 2m². 2 / g~8m 2 It can be / g, specifically 2m 2 / g~5m 2 The specific surface area of ​​the positive electrode active material is 2 m². 2 If the value is less than / g, the energy density of the positive electrode may decrease. The specific surface area of ​​the positive electrode active material is 8m². 2 If the amount exceeds / g, excessive electrolyte side reactions may occur. Therefore, if the specific surface area of ​​the positive electrode active material is 2m² 2 / g~8m 2When the value is / g, the energy density can be maintained and electrolyte side reactions can be suppressed.

[0035] When forming the coating layer, if a simple mixing method (e.g., using an acoustic mixer, paint shaker, blade mixer, etc.) is used, sufficient shear force cannot be provided to rearrange the carbon within the coating layer, and the coating layer cannot uniformly coat the core, making it impossible to determine the range of the D / G peak ratio and the range of the specific surface area. In the present invention, by applying a strong shear force using a mechanofusion method, it is possible to form a coating layer that is strong enough to rearrange the carbon structure, and a range of low-level D / G peak ratios (high degree of graphitization) and specific surface area can be determined, and the D / G peak ratio can change significantly before and after coating.

[0036] The electrical conductivity of the positive electrode active material powder is 1.0 × 10⁻⁶ -3 The s / cm can be approximately 1.0 × 10 s / cm, specifically 1.0 × 10 -3 s / cm~1.0×10 -1 It can be s / cm, more specifically 1.0 × 10 -2 s / cm~1.0×10 -1 It can be s / cm. In the production of the positive electrode active material of the present invention, the carbon-based particles are arranged on the core by a mechanofusion method that can apply a strong shear force. Here, a dense coating layer is formed to the extent that the carbon structure within the carbon-based particles is rearranged, so the electrical conductivity of the powder can be derived. When the above range is satisfied, the diffusion for insertion and deinsertion of lithium ions is not inhibited, and the Li 1+x M y O 2+z This minimizes changes in the metal oxidation state of the transition metals within the powder, thereby suppressing the elution of transition metals. This improves the input / output characteristics and lifespan characteristics of the battery. The electrical conductivity of the powder can be measured using the 4 Probe powder resistance measurement method.

[0037] <Positive electrode> A positive electrode according to another embodiment of the present invention may include the positive electrode active material of the embodiment described above. A description of the positive electrode active material is omitted as it has been described above.

[0038] The positive electrode may include a current collector and a positive electrode active material layer disposed on the current collector, which contains a positive electrode active material. Furthermore, each of the positive electrode active material layers may further include a binder.

[0039] The current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, can be used as current collectors. The positive electrode active material layer can be arranged on one or both sides of the current collector.

[0040] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0041] <Secondary battery> A secondary battery according to yet another embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode of the above-described embodiment. Therefore, a description of the positive electrode is omitted.

[0042] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on one or both sides of the negative electrode current collector.

[0043] The negative electrode current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, can be used as current collectors.

[0044] The negative electrode active material layer can include a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0045] The negative electrode active material can be graphite-based active material particles or silicon-based active material particles. The graphite-based active material particles can use one or more selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads. In particular, when using artificial graphite, the rate characteristics can be improved. The silicon-based active material particles are Si, SiO x (0 < x < 2), Si-C composite, and Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a transition metal, a Group 13 element, a Group 14 element, a rare earth element, and combinations thereof), and one or more selected from the group can be used. In particular, when using Si, SiO x (0 < x < 2), the high capacity of the battery can be derived.

[0046] The negative electrode binder includes at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid, and substances obtained by substituting hydrogen thereof with Li, Na, Ca, etc., and can also include various copolymers thereof.

[0047] The negative electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. Examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0048] As the separator, any material commonly used as a separator in secondary batteries to separate the negative and positive electrodes and provide a pathway for lithium ions can be used without particular limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0049] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0050] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0051] Examples of non-aqueous organic solvents that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0052] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used because they are high-viscosity organic solvents with high dielectric constants, thus effectively dissociating lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, electrolytes with high electrical conductivity can be produced, and these can be used even more preferably.

[0053] The metal salt can be a lithium salt, which is a substance that dissolves easily in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3- CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0054] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds including difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0055] According to yet another embodiment of the present invention, a battery module and a battery pack including the secondary battery as a unit cell are provided. Since the battery module and battery pack include the secondary battery having high capacity, high rate-limiting characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0056] <Method for manufacturing positive electrode active material> According to still another embodiment of the present invention, a method for manufacturing a positive electrode active material includes a step of preparing preliminary carbon-based particles and a step of coating the core with the preliminary carbon-based particles to form a coating layer. The step of coating the core with the preliminary carbon-based particles to form a coating layer containing carbon-based particles includes applying a mechanofusion method after mixing the preliminary carbon-based particles and the core. The core contains Li 1+x M y O 2+z where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, 0 ≦ x ≦ 5, 0 < y ≦ 2, 0 ≦ z ≦ 2, and the carbon-based particles can include a structure in which a plurality of graphene sheets are connected to each other. By the manufacturing method, the positive electrode active material of the above-described embodiment can be formed. The core, coating layer, carbon-based particles, etc. finally included in the positive electrode active material are the same as the core, coating layer, carbon-based particles, etc. of the above-described embodiment.

[0057] The step of preparing the preliminary carbon-based particles includes a step of preparing a carbonaceous material and a step of subjecting the carbonaceous material to an oxidation treatment to deform it. The step of subjecting the carbonaceous material to an oxidation treatment to deform it can include at least one of a) subjecting the carbonaceous material to a first heat treatment at a temperature of 200°C to 800°C in at least one of an oxygen atmosphere and an air atmosphere and b) reacting the carbonaceous material with an acidic vapor at 120°C to 300°C.

[0058] The step of preparing the preliminary carbon-based particles can include a step of preparing a carbonaceous material and a step of subjecting the carbonaceous material to an oxidation treatment to deform it.

[0059] In the step of preparing the carbonaceous material, the carbonaceous material may be carbon black. Specifically, the carbonaceous material may be at least one selected from the group consisting of acetylene black, furnace black, thermal black, channel black, and lamp black. More specifically, the carbonaceous material may be acetylene black, which is produced at the highest temperature and basically has excellent graphitization.

[0060] The step of preparing the carbonaceous material may include thermally decomposing acetylene gas, which can form carbon black, specifically acetylene black. The acetylene gas may be high-purity acetylene gas, specifically acetylene gas with a purity of 95% or higher, and more specifically acetylene gas with a purity of 98% or higher.

[0061] In the aforementioned thermal decomposition, the acetylene gas can be thermally decomposed at a temperature of 1500°C or higher, specifically 1500°C to 2200°C, and more specifically 1500°C to 2000°C. When this range is met, the degree of graphitization of the produced carbonaceous material can be increased, and the degree of graphitization of the resulting pre-carbon particles can also be increased. Therefore, the electrical conductivity of the pre-carbon particles can be improved.

[0062] The carbonaceous material can be carbon black, but acetylene black is preferred for the following reasons. The graphene sheet contained in the carbon-based particles included in the coating layer of the positive electrode active material of the present invention can be formed by deforming the surface of the carbonaceous material through oxidation treatment. The acetylene black formed by thermal decomposition has a high degree of graphitization on its surface. Therefore, compared to the case of oxidizing other carbon blacks that always contain some oxygen functional groups on their surface, the structure of the graphene sheet can be formed more smoothly when oxidizing the acetylene black.

[0063] The aforementioned pyrolysis can be carried out by adjusting the internal temperature of the reactor within the aforementioned temperature range, then introducing acetylene gas into the reactor and performing instantaneous pyrolysis. Furthermore, during this process, air, oxygen, H2O, etc., can be added to control the density of the preliminary carbon-based particles, the oxygen functional groups, etc., and thus control the linkage structure within the preliminary carbon-based particles.

[0064] The step of oxidizing and deforming the carbonaceous material may include at least one of the following: a) performing a first heat treatment on the carbonaceous material in at least one of an oxygen atmosphere and an air atmosphere at a heat treatment temperature of 200°C to 800°C (step a); and b) reacting the carbonaceous material with acidic vapor at 120°C to 300°C (step b).

[0065] In step a, at least one of the oxygen atmosphere and the air atmosphere can be formed by introducing oxygen and / or air into a reactor containing the carbonaceous material. Specifically, a graphene sheet structure can be formed in the reactor by an oxidation process depending on the appropriate amount and rate of oxygen or air inflow, reaction temperature, and reaction time during the first heat treatment. Furthermore, the conditions of the oxidation process may vary depending on differences in the density of the carbonaceous material, the content of oxygen functional groups, etc.

[0066] In step a, the first heat treatment can be carried out in a reactor containing the carbonaceous material by adjusting the temperature of the reactor. The first heat treatment can be carried out at a heat treatment temperature of 200°C to 800°C, specifically at a heat treatment temperature of 200°C to 450°C. When this temperature range is met, excessive and rapid oxidation of the carbonaceous material can be prevented, and a graphene sheet of a preferred size can be formed. The first heat treatment can be carried out for 1 to 50 hours.

[0067] In step b, the carbonaceous material can react with acidic vapor and be oxidized to form graphene. Specifically, the acidic vapor can be vapor derived from an acidic solution such as HCl or HNO3. The temperature of the acidic vapor reacting with the carbonaceous material can be between 120°C and 300°C.

[0068] After the step of oxidizing and deforming the carbonaceous material, an additional step of second heat treatment in an inert atmosphere may be performed to increase the size of the formed graphene sheet. Specifically, the method for producing the positive electrode active material may further include a step of second heat treatment of the oxidized and deformed carbonaceous material at a temperature of 500°C or higher in an inert atmosphere, before coating the core with pre-carbon-based particles to form a coating layer containing carbon-based particles, after the step of oxidizing and deforming the carbonaceous material. Here, the inert atmosphere can be formed with any one gas selected from the group consisting of vacuum, helium, argon, and nitrogen. The second heat treatment temperature can be 500°C or higher, specifically 600°C to 1600°C.

[0069] The mechanism by which the preliminary carbon-based particles described in the present invention are formed by the step of preparing the preliminary carbon-based particles is as follows. During the production of the preliminary carbon-based particles, spherical or linear carbon black, specifically acetylene black, is subjected to oxidation treatment under specific conditions, where the average particle size of the spherical primary particles is 50 nm or less and the primary particles share a common structure. In this case, the penetration of an oxidizing agent such as oxygen or acidic vapor and the oxidation reaction occur from defect portions such as grain boundaries and dislocations present in the fine unit structure of the carbon black. When the oxidation treatment is carried out for a predetermined time within the temperature range mentioned in the production method, the oxidizing agent penetrates to the microstructure inside the carbon black and oxidation occurs. Here, in order to relieve the structural stress of the microstructure inside the primary particles, which have a radius of curvature larger than the radius of curvature of the surface of the spherical primary particles, the oxidation reaction is carried out rapidly inside. As a result, the carbon inside is oxidized to gases such as CO, CO2, and CH4, and the primary particles are changed to a hollow type. Repeated oxidation treatment destroys the surface structure of the hollow primary particles, and almost eliminates the structural stress remaining in the spherical primary particles, during which the graphene sheet appears. Therefore, the smaller the average particle size of the carbon black primary particles, the lower the internal density of the particles, and the higher the content of oxygen functional groups inside the primary particles rather than on the surface, the more the deformation process can be accelerated. Furthermore, step a is more preferable to step b in that it can further accelerate the deformation process.

[0070] The aforementioned preliminary carbon-based particles, like the carbon-based particles of the above-described embodiment, have a structure in which multiple graphene sheets are linked together, and have the same physical properties as the graphene sheets in the carbon-based particles of the above-described embodiment, such as the longest length and thickness.

[0071] The aforementioned preliminary carbon particles have a specific surface area (m²) measured by the nitrogen adsorption BET method. 2 ( / g) is 200m 2 It can be 300m or more per gram, specifically 300m 2 / g~1100m2 It can be / g, and more specifically 500m 2 / g~900m 2 It can be / g. When the above specific surface area range is satisfied, it means that the area of ​​the graphene sheet in the reserve carbon-based particles is large, and as a result, conductivity of the electrode can be ensured even if the content of conductive material in the electrode is small. In addition, contact between the core and external moisture is effectively blocked, and the collapse of the core structure can be prevented. As a result, the initial charge capacity of the battery can be improved.

[0072] The oxygen content of the pre-carbon particles can be 1% by weight or more, specifically 1% to 10% by weight, and more specifically 1% to 5% by weight. When this range is met, the pre-carbon particles can be dispersed smoothly in the dispersion when forming the coating layer by a wet process, and the coating layer can be formed more uniformly. The oxygen content can be measured by elemental analysis of C, H, O, and N.

[0073] The oxygen content can be achieved during the oxidation treatment of carbon black. Specifically, the oxidation treatment can form oxygen-containing functional groups on the surface of the preliminary carbon-based particles. The oxygen-containing functional group can be at least one selected from the group consisting of carboxyl groups, hydroxyl groups, carbonyl groups, etc. After the oxidation treatment step, the oxygen content can be further controlled by heat-treating the preliminary carbon-based particles in an inert atmosphere.

[0074] From this perspective, the aforementioned pre-carbon particles differ from general graphene. In other words, general graphene is manufactured by crushing particles such as artificial graphite, so it is not possible to obtain a material with an oxygen content of 1% by weight or more, and the oxygen content is very low or even zero. Furthermore, in the general method of manufacturing graphene formed by crushing, graphene is formed one sheet at a time (graphene sheet), but according to the present invention, pre-carbon particles are formed that include a structure in which multiple graphene sheets are linked together.

[0075] The aforementioned pre-carbon particles can have a higher degree of graphitization compared to carbon black before oxidation treatment. Specifically, the high structural stress generated by the surface tension of the carbon black is partially relieved by the formation of a graphene sheet, thereby increasing the degree of graphitization of the manufactured pre-carbon particles.

[0076] The aforementioned preliminary carbon-based particles can have a value of 0.12 or less calculated by the following formula 1, specifically between 0 and 0.1, and more specifically between 0 and 0.07.

[0077]

number

[0078] In the above formula 1, a is the specific surface area (m²) of the preliminary carbon-based particles measured by the nitrogen adsorption BET method. 2The formula is given by ( / g), where b is the iodine adsorption value (mg / g) of the preliminary carbon-based particles. When the preliminary carbon-based particles contain pore structures inside or between particles, many small nitrogen (N2) molecules can be adsorbed into the pores. On the other hand, iodine (I2), which is a relatively large molecule, is less likely to enter the pores than nitrogen, and therefore does not show a large iodine adsorption value. In other words, the value given by formula 1 becomes large when a pore structure is present. To put it another way, for the preliminary carbon-based particles, a value given by formula 1 of 0.12 or less means that the preliminary carbon-based particles do not contain fine pores. That is, when pores are absent, the degree to which iodine is adsorbed and the degree to which nitrogen is adsorbed are similar, so the value given by formula 1 becomes small. This means that the surface of the preliminary carbon-based particles is in a smooth state (free surface). Specifically, most carbon black is transformed into a hollow structure by oxidation treatment, and repeated oxidation treatments destroy the structure to form a graphene sheet. Here, a shape can be formed in which no void structure is formed and the graphene sheet is open to the outside.

[0079] The step of coating the core with the pre-carbonized particles to form a coating layer containing carbonized particles includes mixing the pre-carbonized particles with the core and then applying a mechanofusion method.

[0080] Specifically, the mechanofusion method can be performed using a Nobilta apparatus manufactured by Hosokawa Micron. After the mixture of the preliminary carbon-based particles and the core is placed in a container, the container is rotated to move the mixture to the inner wall of the container by centrifugal force. Next, a strong shear force is applied by an arm head that is in close proximity to the inner wall of the container with a small gap between them, and the preliminary carbon-based particles are strongly coated onto the core by the interaction between the surfaces of the mixture, forming a coating layer containing carbon-based particles, and the preliminary carbon-based particles can be deformed into the carbon-based particles described above.

[0081] The shear force can be between 1 m / s and 500 m / s, and specifically between 10 m / s and 100 m / s.

[0082] Unlike the present invention, when using an acoustic mixer, since the acoustic mixer uses a simple vibration method, the preliminary carbon-based particles are arranged relatively unevenly on the core surface rather than forming a coating layer containing carbon-based particles, thus differing from the positive electrode active material of the present invention. On the other hand, the mechanofusion method is a method that can apply high mechanical shear force, so in the present invention, the mechanofusion method is used when manufacturing the positive electrode active material in order to significantly improve conductivity through a uniform coating.

[0083] On the other hand, the mechanofusion method has the problem that it is difficult to control the particle breakage phenomenon because it applies a strong shear force with arm heads that are spaced very close together. However, the researchers of the present invention have diligently researched and discovered that the particle breakage phenomenon can be suppressed by using pre-carbon-based particles having multiple graphene sheets. As a result, the particle breakage phenomenon is suppressed, and a uniform coating layer can be formed by the mechanofusion method.

[0084] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0085] Manufacturing Example 1: Production of Reserve Carbon-Based Particles (1) Formation of carbonaceous material (acetylene black) Acetylene black was formed by instantaneously injecting 98% pure acetylene gas into a reactor with an internal temperature of 2000°C to cause thermal decomposition.

[0086] (2) Production of preliminary carbon-based particles Next, the internal temperature of the reactor containing the acetylene black was raised to 250°C, and then the oxidation treatment was carried out for 30 hours while oxygen was introduced. As a result, preliminary carbon-based particles with a secondary particle structure, including a configuration in which numerous graphene sheets with a longest lateral size of 41 nm were linked together, were obtained. (See Figures 2 and 3)

[0087] The Raman spectral D / G ratio of the aforementioned preliminary carbon-based particles was 1.42. The Raman spectral D / G ratio was measured by analyzing the Raman spectrum using a 514.5 nm wavelength argon-ion laser with a Raman spectrometer (NRS-2000B, Jasco).

[0088] Manufacturing Example 2: Production of Reserve Carbon-Based Particles The preliminary carbon-based particles obtained in the preparation step of Production Example 1 were subjected to an additional heat treatment at 900°C for 1 hour in an inert atmosphere to obtain preliminary carbon-based particles with a secondary particle structure, including a form in which numerous graphene sheets with a longest length (lateral size) of 65 nm are linked together. Referring to Figure 4, it can be seen that the preliminary carbon-based particles of Production Example 1 (Figure 4(a)) were transformed into the preliminary carbon-based particles of Production Example 2 (Figure 4(b)) by the heat treatment.

[0089] The Raman spectrum D / G ratio of the aforementioned preliminary carbon-based particles was 1.27.

[0090] Sample 1: Preparation of carbon black Carbon black (acetylene black) in the form of secondary particles, where primary particles are aggregated, was prepared. The average particle size of the prepared carbon black primary particles was 12 nm. (Denka, SAB (Small Acetylene Black)) (See Figure 5)

[0091] The Raman spectrum D / G ratio of the carbon black was 1.68.

[0092] Sample 2: Preparing Graphene Graphene with an average thickness of 100 nm and an average size of 7 μm was prepared (KNANO Corporation, Graphene Powder). The Raman spectrum D / G ratio of the said graphene was 0.22.

[0093] [Table 1]

[0094] a is the specific surface area (m²) of the carbon-based particles measured by the nitrogen adsorption BET method. 2 b is the iodine adsorption value of the carbon-based particles (mg / g), where b is the iodine adsorption value of the carbon-based particles (mg / g).

[0095] 1) Nitrogen adsorption specific surface area (m²) 2 The measurement was performed using a BET measuring device (BEL-SORP-MAX, Nippon Bell) after degassing at 200°C for 8 hours and then N2 adsorption / desorption at 77K.

[0096] 2) Iodine adsorption value (mg / g): Measured according to the ASTM D1510 method.

[0097] 3) Oxygen content (weight %): The content of C, H, and N elements was measured using an elemental analyzer (CHN-coder MT-5, Yanako), and the oxygen content (differential) was calculated, reflecting the amount of residual ash.

[0098] Example 1: Production of positive electrode active material Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2(average particle size (D 50 After mixing the 9.0 μm (see Figure 6) and the preliminary carbon-based particles of Production Example 1 in a weight ratio of 99:1, the Li[Ni] secondary particles were formed using a mechanofusion apparatus (Nobilta NOB-130, Hosokawa Micron) at 3,000 rpm for 10 minutes. 0.6Co 0.2 Mn 0.2 A coating layer containing the carbon-based particles was formed on O2 to produce a positive electrode active material (see Figure 7).

[0099] Example 2: Production of positive electrode active material The cathode active material was manufactured by forming a coating layer in the same manner as in Example 1, except that the preliminary carbon-based particles from Manufacturing Example 2 were used instead of the preliminary carbon-based particles used in Example 1.

[0100] Comparative Example 1: Preparation of the positive electrode active material Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2(average particle size (D 50 After mixing the 9.0 μm (of the Li[Ni) particles with the preliminary carbon-based particles from Production Example 1 in a weight ratio of 99:1, the mixture was then mixed three times (totaling 6 minutes) using an acoustic mixer (Lab RAM-II, Resodyn) at 1,500 rpm for 2 minutes. This resulted in Li[Ni 0.6 Co 0.2 Mn 0.2 The positive electrode active material was formed by arranging preliminary carbon-based particles on the O2 surface (see Figure 8).

[0101] Comparative Example 2: Preparation of the positive electrode active material The cathode active material was manufactured by forming a coating layer in the same manner as in Example 1, except that the carbon black from Sample 1 was used instead of the reserve carbon-based particles used in Example 1 (see Figure 9).

[0102] Comparative Example 3: Preparation of the positive electrode active material The cathode active material was manufactured by forming a coating layer in the same manner as in Comparative Example 1, except that the carbon black from Sample 1 was used instead of the reserve carbon-based particles used in Comparative Example 1.

[0103] Comparative Example 4: Preparation of the positive electrode active material The cathode active material was manufactured by forming a coating layer in the same manner as in Comparative Example 1, except that the graphene from Sample 2 was used instead of the reserve carbon-based particles used in Comparative Example 1.

[0104] [Table 2]

[0105] The longest length (lateral size) (nm) of the graphene sheet was determined by measuring the size of 100 graphene sheets within the coating layer using TEM (JEOL, JEM-2010F) and then averaging these measurements. The specific surface area (m²) of the positive electrode active material was also determined. 2 The D / G peak ratio ( / g) was measured by the BET method, specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. The D / G peak ratio of the positive electrode active material was measured using a Raman spectrometer (NRS-2000B, Jasco) with a 514.5 nm wavelength argon ion laser.

[0106] The electrical conductivity (s / cm) of the positive electrode active material powder was measured by placing 5g of the manufactured positive electrode active material into a dedicated holder, rolling it with a force of 30kN, and then measuring it using a powder-specific 4-Probe powder resistance measuring electrode (powder resistance system (MCP-PD51), Mitsubishi Chemical).

[0107] Experimental Example 1: Evaluation of SEM Images Figures 7, 8, and 9 are SEM images of the positive electrode active materials for Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0108] Referring to Figure 7, Li[Ni 0.6 Co 0.2 Mn 0.2 Not only the interface between primary particles of ]O2, but also Li[Ni 0.6 Co 0.2 Mn 0.2It can be seen that carbon-based particles are uniformly arranged across the entire surface of the O2, forming a coating layer. Specifically, in Example 1, the graphene sheet shape of the carbon-based particles completely collapses, the graphene sheets are re-stacking and rearranged, and the surface is observed to be smoothly coated with carbon-based particles.

[0109] On the other hand, referring to Figure 8, in the positive electrode active material of Comparative Example 1, the preliminary carbon-based particles are Li[Ni 0.6 Co 0.2 Mn 0.2 It differs from the positive electrode active material of Example 1 in that it is locally present only on a portion of the surface of ]O2. Also, referring to Figure 9, in the positive electrode active material of Comparative Example 1, carbon black is Li[Ni 0.6 Co 0.2 Mn 0.2 It can be seen that the carbon microstructure aggregates and exists at the interface between primary O2 particles without any change in its structure.

[0110] Experimental Example 2: Evaluation of Battery Performance (Evaluation of Output / Discharge Characteristics) After manufacturing the batteries using the method described below, the manufactured secondary batteries were CC / CV charged to 4.3V at 0.1C, charged to the cut-off point at 0.005C, CC discharged to 3.0V at 0.1C, and the charge capacity was measured for one cycle. The results are shown in Table 2 below.

[0111] Battery manufacturing method: (1) Manufacturing of the positive electrode Positive electrodes containing the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 4 were manufactured. PVdF was used as the binder, and carbon black was used as the conductive material.

[0112] A positive electrode slurry was prepared by mixing the positive electrode active material, binder, and conductive material in NMP, a solvent, in a weight ratio of 97.5:1.5:1. The positive electrode slurry was applied to a positive electrode current collector (Al) with a thickness of 20 μm, and dried at 130°C to produce a positive electrode.

[0113] (2) Battery manufacturing A negative electrode slurry was prepared by mixing a negative electrode active material consisting of SiO and artificial graphite in a weight ratio of 1:9, a negative electrode conductive material (carbon black), and negative electrode binders (styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC)) in distilled water in a weight ratio of 96.5:2:1:0.5. The prepared slurry was applied to a negative electrode current collector (Cu) with a thickness of 10 μm and dried at 100°C to produce a negative electrode.

[0114] Next, a monocell was manufactured by combining the manufactured negative electrode and positive electrode with a 15 μm thick polyethylene separator interposed between them. Then, an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio), lithium hexafluorophosphate (LiPF 61 mol)) was injected into the monocell to manufacture a lithium secondary battery.

[0115] The manufactured batteries were charged at 25°C with a constant current of 0.2C to 4.25V using a 0.05C cutoff. Subsequently, they were discharged with a constant current of 0.2C to 2.5V, and the initial charge and discharge capacities were measured.

[0116] Next, the battery was charged to 4.25V with a constant current of 0.2C and a 0.05C cutoff, and then discharged to 2.5V with a constant current of 2.0C. This charging and discharging process constituted one cycle, and two cycles were performed. After that, the discharge capacity at 2.0C was measured for the battery compared to the discharge capacity at 0.2C, and these results are shown in Table 3 below.

[0117] Experimental Example 3: Evaluation of Battery Performance (Evaluation of Lifetime Characteristics) Each of the manufactured batteries was subjected to a 0.33C / 0.33C charge / discharge cycle at 45°C within a voltage range of 4.25V to 2.8V. After a total of 100 cycles, the discharge capacity after 100 cycles was evaluated, with the discharge capacity after one cycle set as the 100% baseline, and this is shown in Table 3 below.

[0118] [Table 3]

[0119] Referring to Table 3 above, it was confirmed that when using the positive electrode active materials of Examples 1 and 2, the output / discharge characteristics were better and the lifespan characteristics were improved compared to when using the positive electrode active materials of Comparative Examples 1 to 4.

Claims

1. It is a positive electrode active material, The core and a coating layer disposed on the core, The aforementioned core is Li １＋ｘ M ｙ O ２＋ｚ It includes, where M is at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, and -0.2 ≤ x ≤ 0.2, 0 < y ≤ 2, 0 ≤ z ≤ 2, The coating layer contains carbon-based particles, The carbon-based particles include a structure in which multiple graphene sheets are linked together. When measuring the Raman spectrum of the positive electrode active material, the D / G peak ratio is 0.9 to 1.

1. The graphene sheet has a maximum length of 10 nm to 500 nm, which is the positive electrode active material.

2. The Li １＋ｘ M ｙ O ２＋ｚ is Li １＋ｘ [Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ and includes Said M １ is at least one element of Al and Mn, Said M ２ is at least one element selected from the group consisting of Fe, P, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V. The positive electrode active material according to claim 1, wherein 0 < a < 1, 0 < b < 1, 0 < c < 1, and 0 ≤ d ≤ 0.

2.

3. The invention further includes a connecting portion connected to at least some of the graphene sheets among the plurality of graphene sheets, The positive electrode active material according to claim 1 or 2, wherein the connecting portion is in a non-graphene form.

4. The positive electrode active material according to claim 3, wherein at least a portion of each of the plurality of graphene sheets is connected to the connecting portion.

5. The positive electrode active material according to any one of claims 1 to 4, wherein the average thickness of the graphene sheet is 0.34 nm to 10 nm.

6. The positive electrode active material according to any one of claims 1 to 5, wherein the thickness of the coating layer is 1 nm to 500 nm.

7. The electrical conductivity of the positive electrode active material powder is 1.0 × 10⁻⁶. －３ A positive electrode active material according to any one of claims 1 to 6, wherein the current is s / cm to 1.0 × 10 s / cm.

8. The positive electrode active material according to any one of claims 1 to 7, wherein the weight ratio of the core and the coating layer is 99.9:0.1 to 90:

10.

9. The specific surface area is 2 m ２ / g to 8m ２ A positive electrode active material according to any one of claims 1 to 8, wherein the value is / g.

10. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 9.

11. A secondary battery comprising the positive electrode described in claim 10.

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