Positive electrode active material, method for preparing same, and positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material capable of improving the performance of a lithium secondary battery, in which the positive electrode active material comprises: a lithium composite transition metal oxide simultaneously comprising a Li2MnO3 phase and a LiMO2 (where M is an element comprising Ni, Mn or a combination thereof) phase; and a coating layer comprising a compound composed of vanadium (V) and oxygen (O) on the lithium composite transition metal oxide, in which the lithium composite transition metal oxide has a composition represented by chemical formula 1 described in the present application, and the content of vanadium (V) contained in the coating layer is 90 ppm to 2500 ppm based on the total weight of the lithium composite transition metal oxide, and the content of oxygen (O) contained in the coating layer is 100 ppm to 200 ppm based on the total weight of the lithium composite transition metal oxide. The present invention also relates to a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the same.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0116360, filed on September 1, 2023, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to positive electrode active materials, their preparation methods, and positive electrodes and lithium secondary batteries containing the same. Background Technology

[0004] A lithium-ion secondary battery consists of four components: the positive electrode, the negative electrode, the separator, and the electrolyte. Among these components, the positive electrode contains the positive electrode active material, which plays a crucial role in determining the battery's capacity, output, and lifespan. To achieve high energy density, output, and lifespan in lithium-ion secondary batteries, the performance of the positive electrode active material must be improved. Therefore, extensive research has been conducted in recent years to develop high-performance positive electrode active materials.

[0005] Lithium-rich (Li) layered oxides, as a type of positive electrode active material, are a mixed phase of Li₂MnO₃ and LiMO₂ (where M is an element containing Ni, Mn, Co, or a combination thereof), and exhibit high operating voltage (>3.5 V vs. Li / Li). + This provides an ultra-high capacity of 250 mAh / g. Therefore, lithium-rich layered oxides have attracted much attention as high-capacity cathode active materials.

[0006] However, lithium-rich layered oxides have problems due to their mixed-phase structure. Specifically, if a battery containing lithium-rich layered oxides is driven at high voltage, it suffers from irreversible capacity loss during the initial formation process, leading to reduced efficiency. Furthermore, during charge-discharge cycles, the structure transforms from a layered structure to a spinel structure and then to a rock salt structure, resulting in voltage decay, increased resistance, and O2 gas generation.

[0007] Furthermore, the rising price of cobalt raw materials contained in lithium-rich layered oxides has become a significant issue. Cobalt raw material prices are expected to continue rising, thus creating a demand for developing cathode active materials with reduced cobalt content.

[0008] Therefore, it is necessary to ensure the technology can improve the capacity, resistance, lifetime and cost-effectiveness of lithium-rich layered oxides.

[0009] [Existing technical documents]

[0010] [Patent Literature]

[0011] (Patent Document 1) Korean Patent Application Publication No. 10-2014-0025102 Summary of the Invention

[0012] Technical issues

[0013] To address the aforementioned problems, this invention aims to provide a positive electrode active material and its preparation method that can improve the capacity, resistance, and lifespan characteristics of batteries while reducing costs.

[0014] Furthermore, the present invention aims to provide a positive electrode and a secondary battery comprising the above-mentioned positive electrode active material, thereby exhibiting excellent capacity and resistance characteristics, a relatively low resistance growth rate, and being economical.

[0015] Technical solution

[0016] (1) The present invention provides a positive electrode active material comprising: a lithium composite transition metal oxide containing both a Li2MnO3 phase and a LiMO2 phase (where M is an element containing Ni, Mn or a combination thereof), and a coating on the lithium composite transition metal oxide containing a compound composed of vanadium (V) and oxygen (O), wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1, and the vanadium (V) content contained in the coating is from 90 ppm to 2500 ppm based on the total weight of the lithium composite transition metal oxide.

[0017] [Chemical Formula 1]

[0018] Li 1+x Ni a Mn b M 1 c O2

[0019] In the above chemical formula 1, M 1 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 <x≤0.5,0<a≤0.5,0.5≤b<1,0≤c≤0.01。

[0020] (2) In (1) above, the present invention provides a positive electrode active material, wherein the lithium composite transition metal oxide has the composition represented by the following chemical formula 2.

[0021] [Chemical Formula 2]

[0022] αLi2Mn (1-p) M 2 p O3·βLiNi q Mn r M 2s O2

[0023] In the above chemical formula 2, M 2 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 < α ≤ 0.5, 0 < β ≤ 1, 0 ≤ p ≤ 0.01, 0 <q≤0.8,0<r≤0.8,0≤s≤0.01,q+r+s=1。

[0024] (3) In (1) or (2) above, the present invention provides a positive electrode active material, wherein b is 0.5 to 0.75.

[0025] (4) In any of (1) to (3) above, the present invention provides a positive electrode active material, wherein the coating comprises V2O5.

[0026] (5) In any of (1) to (4) above, the present invention provides a positive electrode active material, wherein the coating content is 0.01 parts by weight to 0.1 parts by weight based on 100 parts by weight of the lithium composite transition metal oxide.

[0027] (6) In any one of (1) to (5) above, the present invention provides a positive electrode active material, wherein the average particle size (D) of the positive electrode active material is... 50 The range is from 1.0 μm to 15.0 μm.

[0028] (7) The present invention provides a method for preparing a positive electrode active material, the method comprising: (A) mixing a composite transition metal hydroxide and a lithium (Li) raw material and then calcining it to prepare a lithium composite transition metal oxide, and (B) mixing the lithium composite transition metal oxide and a vanadium (V) raw material and then heat-treating it to form a coating comprising a compound composed of vanadium (V) and oxygen (O) on the lithium composite transition metal oxide, wherein the heat treatment is performed at a temperature of 400°C to 600°C.

[0029] (8) In (7) above, the present invention provides a method for preparing a positive electrode active material, wherein the vanadium (V) raw material is V2O5.

[0030] (9) In (7) or (8) above, the present invention provides a method for preparing a positive electrode active material, wherein the vanadium (V)-containing raw material is mixed such that the vanadium (V) content is 100 ppm to 2500 ppm based on the total weight of the lithium composite transition metal oxide.

[0031] (10) In any of (7) to (9) above, the present invention provides a method for preparing a positive electrode active material, wherein, in step (B), the heat treatment is carried out in an oxygen atmosphere.

[0032] (11) In any of (7) to (10) above, the present invention provides a method for preparing a positive electrode active material, wherein the coating comprises V2O5.

[0033] (12) The present invention provides a positive electrode comprising any one of the positive electrode active materials described in (1) to (6) above.

[0034] (13) The present invention provides a lithium secondary battery comprising the positive electrode described in (12) above.

[0035] Beneficial effects

[0036] The positive electrode active material of the present invention comprises: a lithium composite transition metal oxide containing both a Li2MnO3 phase and a LiMO2 phase (where M is an element containing Ni, Mn, or a combination thereof), and a coating on the lithium composite transition metal oxide containing a compound composed of vanadium (V) and oxygen (O), wherein the vanadium (V) content in the coating meets a specific numerical range, thereby achieving the effect of improving lithium-ion absorption and release performance, conductivity, and structural stability. Therefore, the performance of the positive electrode active material and the positive electrode and lithium secondary battery containing it can be improved, such as capacity characteristics, resistance characteristics, and cycle life, and it also has the effect of cost savings.

[0037] Furthermore, the above-mentioned positive electrode active material can be effectively prepared using the method for preparing the positive electrode active material according to the present invention. Attached Figure Description

[0038] Figure 1 The XRD data are for the positive electrode active materials prepared in Examples 1 and 2, respectively. Detailed Implementation

[0039] The invention will be described in more detail below to facilitate understanding of it.

[0040] It will be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical ideas of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best interpret the invention.

[0041] In this specification, it should be understood that the terms “comprising,” “including,” or “having” are intended to specify the presence of the stated features, figures, steps, elements, or combinations thereof, but do not exclude the presence or inclusion of one or more other features, figures, steps, elements, or combinations thereof.

[0042] In this specification, the term "on" includes not only the case where a component is directly formed on another component, but also the case where a third component is inserted between them.

[0043] In this specification, "average particle size (D)" 50 The average particle size can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (particle size distribution graph). The average particle size can be measured by dispersing the powder to be tested in a dispersion medium, then introducing the mixture into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns as the particles pass through the laser beam. Subsequently, the particle size at the 50% point of the cumulative volume distribution based on particle size is calculated in the analyzer, thus measuring the average particle size (D). 50 .

[0044] Positive electrode active material

[0045] The positive electrode active material of the present invention will be described below.

[0046] The positive electrode active material of the present invention comprises: a lithium composite transition metal oxide containing both a Li2MnO3 phase and a LiMO2 phase (where M is an element containing Ni, Mn, or a combination thereof), and a coating on the lithium composite transition metal oxide containing a compound composed of vanadium (V) and oxygen (O), wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1, and the vanadium (V) content contained in the coating is from 90 ppm to 2500 ppm based on the total weight of the lithium composite transition metal oxide.

[0047] [Chemical Formula 1]

[0048] Li 1+x Ni a Mn b M 1 c O2

[0049] In the above chemical formula 1, M 1 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 <x≤0.5,0<a≤0.5,0.5≤b<1,0≤c≤0.01。

[0050] Lithium-rich (Li) layered oxides, as a type of positive electrode active material, are a mixture of Li2MnO3 phase and LiMO2 phase (where M is an element containing Ni, Mn, Co or a combination thereof). If the lithium-rich (Li) layered oxide contains Co, Co will act as an impurity, resulting in a decrease in the capacity characteristics of secondary batteries containing this Li-rich layered oxide and high manufacturing costs.

[0051] To address the aforementioned problems, the inventors conducted repeated research and confirmed that if a Li-rich layered oxide does not contain Co but includes a coating containing a compound composed of vanadium (V) and oxygen (O), it can improve lithium-ion absorption and release performance, thereby improving capacity characteristics; it can improve conductivity, thereby improving resistance characteristics; and it can improve structural stability, thereby improving lifetime characteristics. Therefore, the inventors discovered a method to improve the capacity characteristics, resistance characteristics, lifetime characteristics, and economic efficiency of conventional lithium-rich layered oxides, and thus completed this invention.

[0052] M 1 As a doping element, specifically, M 1 It can be one or more selected from the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. Although M 1 It is not necessary to contain it, but if it is included in an appropriate amount, it can improve the particle shape of the positive electrode active material and improve the stability of the crystal structure.

[0053] x can be greater than 0, greater than 0.1, greater than 0.2, or greater than 0.3, and can be less than 0.4 or less than 0.5. If x meets the above range, the Li2MnO3 phase and the LiMO2 phase can be formed in a suitable ratio, thereby achieving high capacity characteristics.

[0054] a can be greater than 0, above 0.2, or above 0.3, and can be less than 0.4 or less than 0.5. If a meets the above ranges, it can exhibit high energy density, thus achieving high capacity characteristics.

[0055] b can be greater than or equal to 0.5 or greater than 0.55, and can be less than 0.6, 0.7, 0.8, 0.9, or less than 1. If b meets the above ranges, high energy density can be exhibited, thereby achieving high capacity characteristics. In particular, if b is between 0.5 and 0.75, the Li2MnO3 phase and the LiMO2 phase can be formed in a suitable ratio, thereby achieving high capacity characteristics.

[0056] c can be greater than or equal to 0 or greater than 0.003, and can be less than or equal to 0.005, 0.007, or 0.01. If c meets the above range, the particle shape of the positive electrode active material can be improved, and the stability of the crystal structure can be improved.

[0057] The lithium composite transition metal oxide can be cobalt-free. In this case, it has the effect of reducing costs and improving the performance of lithium secondary batteries without cobalt.

[0058] According to the present invention, based on the total weight of the lithium composite transition metal oxide, the vanadium (V) content in the coating can be from 90 ppm to 2500 ppm. Specifically, based on the total weight of the lithium composite transition metal oxide, the vanadium (V) content in the coating can be 90 ppm or more, and can be 950 ppm or less, 1950 ppm or less, 2000 ppm or less, or 2500 ppm or less. If the vanadium (V) content is within the above range, the coating formed on the lithium composite transition metal oxide can improve conductivity and reduce side reactions between the positive electrode active material and the electrolyte, thereby improving the capacity characteristics, resistance characteristics, and lifespan characteristics of the battery containing the positive electrode active material. If the vanadium (V) content is less than 90 ppm, there are problems such as insufficient coating formation on the lithium composite transition metal oxide, resulting in deteriorated conductivity, and failure to reduce side reactions between the positive electrode active material and the electrolyte, resulting in deteriorated lifespan characteristics. If the vanadium (V) content exceeds 2500 ppm, there are problems such as excessive and uneven coating formation, which instead acts as a resistor, and deteriorated lifespan characteristics.

[0059] The coating comprising a compound consisting of vanadium (V) and oxygen (O) can be in the form of partially covering at least a portion of a lithium complex transition metal oxide, or covering the entire area. The shape of the coating can be island-shaped, film-shaped, or a combination thereof, but the shape of the coating is not limited thereto.

[0060] The structure of a coating containing a compound composed of vanadium (V) and oxygen (O) can be a layered structure, olivine structure, orthorhombic structure, or monoclinic structure, but not a spinel structure.

[0061] According to one embodiment of the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 2.

[0062] [Chemical Formula 2]

[0063] αLi2Mn (1-p) M 2 p O3·βLiNi q Mn r M 2s O2

[0064] In the above chemical formula 2, M 2 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 < α ≤ 0.5, 0 < β ≤ 1, 0 ≤ p ≤ 0.01, 0 <q≤0.8,0<r≤0.8,0≤s≤0.01,q+r+s=1。

[0065] M 2 As a doping element, specifically, M 2 It can be one or more selected from the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. Although M 2 It is not necessary to contain it, but if it is included in an appropriate amount, it can improve the particle shape of the positive electrode active material and improve the stability of the crystal structure.

[0066] α represents the molar ratio of the Li₂MnO₃ phase in the lithium-ion composite transition metal oxide, which can be greater than 0, greater than 0.4, or greater than 0.43, and less than 0.47, less than 0.48, or less than 0.5. If α meets the above ranges, a high energy density per unit volume can be exhibited, thereby achieving high capacity characteristics. Furthermore, the capacity characteristics, resistance characteristics, and lifetime characteristics of batteries containing this positive electrode active material can be further improved.

[0067] 1-p is the molar ratio of Mn in all metals except lithium in Li2MnO3.

[0068] p is the M content among all metals except lithium in Li₂MnO₃. 2 The molar ratio can be greater than 0, greater than 0.002, greater than 0.004, or greater than 0.006, and can be less than 0.008 or less than 0.01. Although M 2 It is not essential to contain it, but if included in an appropriate amount, it can improve the particle shape of the positive electrode active material and enhance the stability of the crystal structure. Furthermore, it can exhibit high energy density, thereby achieving high capacity characteristics.

[0069] β represents the molar ratio of the LiMO2 phase in the lithium-ion composite transition metal oxide, which can be greater than 0, greater than 0.2, or greater than 0.4, and less than 0.6, less than 0.8, or less than 1. If β meets the above ranges, high energy density per unit volume can be exhibited, thereby achieving high capacity characteristics. In addition, the capacity characteristics, resistance characteristics, and lifetime characteristics of batteries containing this positive electrode active material can be further improved.

[0070] q is the molar ratio of nickel (Ni) in all metals except lithium in LiMO2, which can be greater than 0, greater than 0.4, or greater than 0.5, and less than 0.6, less than 0.7, or less than 0.8. If q meets the above ranges, it can exhibit high energy density, thereby achieving high capacity characteristics.

[0071] r is the molar ratio of manganese (Mn) in all metals except lithium in LiMO2, which can be greater than 0, greater than 0.3, or greater than 0.4, and less than 0.5, less than 0.6, or less than 0.8. If r meets the above ranges, it can exhibit high energy density, thus achieving high capacity characteristics.

[0072] s is the M among all metals in LiMO2 except lithium. 2 The molar ratio can be greater than 0, greater than 0.002, greater than 0.004, or greater than 0.006, and can be less than 0.008 or less than 0.01. Although M 2 It is not necessary to contain it, but if it is included in an appropriate amount, it can improve the particle shape of the positive electrode active material and improve the stability of the crystal structure.

[0073] In the above chemical formula 2, q, r, and s are q + r + s = 1.

[0074] According to one embodiment of the invention, the coating may contain V₂O₅. In this case, structural stability can be improved, thereby minimizing structural changes in the particles and improving lifetime characteristics. Specifically, the coating may consist of only V₂O₅, or it may be a mixture of V₂O₅ and LiMn₂O₄.

[0075] According to one embodiment of the present invention, based on 100 parts by weight of lithium composite transition metal oxide, the content of the coating can be 0.01 parts by weight or more, 0.015 parts by weight or more, or 0.017 parts by weight or more, and can be 0.018 parts by weight or less, 0.02 parts by weight or less, 0.05 parts by weight or less, or 0.1 parts by weight or less. If the coating content is within the above range, the lithium-ion absorption and release performance, conductivity, and structural stability can be improved while maintaining the unit volume energy density of the positive electrode active material, thereby improving the capacity characteristics, resistance characteristics, and lifetime characteristics of the battery containing the positive electrode active material.

[0076] According to one embodiment of the present invention, the average particle size (D) of the positive electrode active material 50The particle size can be 1.0 μm or larger, 2.0 μm or larger, 3.0 μm or larger, or 4.0 μm or larger, and 10.0 μm or smaller, 11.0 μm or smaller, 12.0 μm or smaller, 13.0 μm or smaller, 14.0 μm or smaller, or 15.0 μm or smaller. If the average particle size (D...) 50 Within the above range, excellent electrode density can be achieved, and structural stability can be improved.

[0077] Preparation method of positive electrode active material

[0078] Next, the preparation method of the positive electrode active material of the present invention will be described. The preparation method of the positive electrode active material of the present invention is a method for preparing the positive electrode active material of the present invention.

[0079] The method for preparing the positive electrode active material includes: (A) mixing a composite transition metal hydroxide and a lithium (Li) raw material and then calcining it to prepare a lithium composite transition metal oxide, and (B) mixing the lithium composite transition metal oxide and a vanadium (V) raw material and then heat-treating it to form a coating on the lithium composite transition metal oxide containing a compound composed of vanadium (V) and oxygen (O).

[0080] According to the present invention, the positive electrode active material can be prepared by appropriately adjusting the type of raw materials, the mixing ratio of raw materials, the firing temperature, the heating rate of firing and heat treatment, the firing and heat treatment time, etc.

[0081] The steps of the present invention will be described in detail below.

[0082] Step (A)

[0083] The above-mentioned step (A) includes mixing a composite transition metal hydroxide with a lithium (Li)-containing raw material and then calcining it to prepare a lithium composite transition metal oxide.

[0084] This complex transition metal hydroxide can be prepared by introducing an aqueous solution of a complex transition metal, an ammonium cation complexing agent, and an alkaline compound into a reactor for a co-precipitation reaction.

[0085] Aqueous solutions of complex transition metals can be prepared by dissolving a raw material containing a transition metal in a solvent such as water. For example, they can be prepared by dissolving a nickel-containing (Ni) raw material and a manganese-containing (Mn) raw material in water. Furthermore, if necessary, the aqueous solution of complex transition metals may also contain a metal-containing raw material.

[0086] The nickel-containing raw material can be at least one selected from the group consisting of NiSO4, NiO, Ni(OH)2, NiO·OH, NiCO3·2Ni(OH)2·4H2O, NiC2O4·2H2O, Ni(NO3)2·6H2O, nickel fatty acids, and nickel halides, or any one or a mixture of two or more of these. Considering the strong base used to adjust the pH in the co-precipitation reaction, NiSO4 can be specifically used.

[0087] The manganese (Mn)-containing raw material can be at least one selected from the group consisting of MnSO4, MnCO3, Mn2O3, MnO2, Mn3O4, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, manganese salts of fatty acids, hydroxy oxides, and halides such as manganese chloride. One or a mixture of two or more of these halides can be used. Considering the strong base used to adjust the pH in the coprecipitation reaction, MnSO4 can be specifically used.

[0088] For nickel (Ni) and manganese (Mn) raw materials, the content of each metal element in the composite transition metal hydroxide can be considered to determine the appropriate content for use.

[0089] Meanwhile, the ammonium cation complexing agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and the compound may be introduced into the reactor in the form of a solution in a solvent. In this case, water or a mixture of water and an organic solvent (e.g., an alcohol) that can be uniformly mixed with water may be used as the solvent.

[0090] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and can be introduced into the reactor in the form of a solution in a solvent. In this case, water or a mixture of water and an organic solvent (e.g., an alcohol) that can be uniformly mixed with water can be used as the solvent.

[0091] When the composite transition metal aqueous solution, ammonium cation complexing agent and alkaline compound are introduced into the reactor as described above, precursor particles in the form of composite transition metal hydroxide are generated due to the co-precipitation reaction between the transition metal ions in the composite transition metal aqueous solution and the hydroxide ions in the alkaline compound.

[0092] The coprecipitation reaction can be carried out for 50 to 90 hours. If the time is within this range, the crystallinity of the precursor particles can be adjusted to a sufficient degree.

[0093] In this case, an alkaline compound can be introduced in an amount that keeps the pH of the reaction solution within the desired range.

[0094] After forming the precursor particles by the above method, the particles are separated from the reaction solution to obtain a composite transition metal hydroxide. Specifically, the reaction solution can be filtered to separate the particles from the reaction solution, and then the separated particles can be washed with water and dried to obtain a composite transition metal hydroxide. In this case, if necessary, processes such as pulverization and / or classification can be carried out.

[0095] The composite transition metal hydroxide containing nickel and manganese may have the composition represented by Ni x1 Mn y1 M 3 z1 (OH)2 (where M 3 is one or more selected from the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 < x1 ≤ 0.5, 0.5 ≤ y1 < 1, 0 ≤ z1 ≤ 0.01).

[0096] The lithium (Li)-containing raw material can be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, LiNO2, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, lithium acetate, lithium dicarboxylate, lithium citrate, lithium fatty acid, alkyl lithium, and lithium halide, and any one or a mixture of two or more thereof can be used. Considering the heat treatment at a high temperature of about 910°C, LiOH can be specifically used.

[0097] The mixing can be carried out by dry mixing or wet mixing. If the components are mixed by dry mixing, the firing process can be carried out without an additional drying process. If the components are mixed by wet mixing, it can be prepared by adding the components to a solvent, specifically water or a mixture of water and an organic solvent (specifically alcohol, etc.) that can be uniformly mixed with water, or a solution (specifically an aqueous solution) containing each raw material can be prepared and mixed, and then the mixed components are spray-dried and then the firing process is carried out. Each raw material and the composite transition metal hydroxide can be appropriately used in consideration of the content of each metal element in the finally prepared lithium composite metal oxide.

[0098] [[ID=该金属复合氧化物可以为选自由LiNi According to the present invention, in step (A), a composite transition metal hydroxide containing no cobalt but containing nickel and manganese and a lithium (Li)-containing raw material can be mixed in an amount having the composition represented by the above chemical formula 1.

[0099] The firing can be carried out in an air atmosphere. In this case, it is easy to maintain the firing atmosphere and it is economically advantageous.

[0100] Firing can be carried out at temperatures above 700°C, 750°C, 800°C, 850°C, or 900°C, and can also be carried out at temperatures below 950°C or 1000°C. Within the above temperature range, Li2MnO3 phase and LiMO2 phase can be formed in an appropriate ratio (where M is an element containing Ni, Mn, or a combination thereof).

[0101] Firing can take 7 to 10 hours. Within this timeframe, the crystallinity of the lithium composite transition metal oxide particles can be sufficiently controlled, which is beneficial for lithium-ion transport.

[0102] Step (B)

[0103] Subsequently, the above-described step (B) includes mixing the lithium composite transition metal oxide with a vanadium (V)-containing raw material and then heat-treating it to form a coating comprising a compound composed of vanadium (V) and oxygen (O) on the lithium composite transition metal oxide.

[0104] The vanadium (V)-containing raw material can be at least one selected from the group consisting of V₂O₅, vanadium sulfide, vanadium acetylacetonate, and vanadium oxides, and a mixture of one or more of these can be used. Specifically, V₂O₅ can be used, taking into account economic efficiency and processability.

[0105] Vanadium (V) raw materials can be mixed such that, based on the total weight of lithium complex transition metal oxides, the vanadium (V) content is above 100 ppm and below 950 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or 2500 ppm.

[0106] Heat treatment can be performed at temperatures above 400°C, above 450°C, above 500°C and below 550°C, or below 600°C. Such heat treatment provides sufficient thermal energy for coating. If the heat treatment temperature is below 400°C, insufficient thermal energy may not be provided, resulting in failure to form a coating. If the heat treatment temperature is above 600°C, not only vanadium (V) raw materials but also lithium complex transition metal oxides may be over-sintered, potentially leading to the formation of secondary phases.

[0107] If a lithium complex transition metal oxide and a vanadium (V)-containing raw material are mixed and heat-treated within the aforementioned temperature range, a coating comprising a compound of vanadium (V) and oxygen (O) can be formed on the lithium complex transition metal oxide. The coating comprising the compound of vanadium (V) and oxygen (O) can partially cover at least a portion of the lithium complex transition metal oxide or cover the entire area. The shape of the coating can be island-like, film-like, or a combination thereof, but the shape is not limited to these. The structure of the coating comprising the compound of vanadium (V) and oxygen (O) can be a layered structure, an olivine structure, an orthorhombic structure, or a monoclinic structure, etc., but not a spinel structure.

[0108] Heat treatment can be performed in an oxygen atmosphere. In this case, an oxidizing atmosphere is formed, which is suitable for forming coatings containing compounds composed of vanadium (V) and oxygen (O).

[0109] The coating may contain V₂O₅. In this case, lithium-ion absorption and release performance, conductivity, and structural stability are improved, thereby improving the capacity, resistance, and lifetime characteristics of the battery containing this positive electrode active material. Specifically, the coating may consist of only V₂O₅, or it may be a mixture of V₂O₅ and LiMn₂O₄.

[0110] positive electrode

[0111] Next, the positive electrode of the present invention will be described.

[0112] The positive electrode of the present invention comprises a positive electrode active material layer having the positive electrode active material of the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material. Since the positive electrode active material has been described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0113] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0114] The positive electrode active material layer may include conductive materials and binders along with the positive electrode active material. In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight, within which excellent capacity characteristics can be exhibited.

[0115] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause chemical changes in the battery in which it is formed. Specific examples may include: graphite, such as natural or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these may be used. Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.1% by weight to 15% by weight.

[0116] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. The adhesive content may be from 0.1% by weight to 15% by weight relative to the total weight of the positive electrode active material layer.

[0117] Besides using the aforementioned positive electrode active material, a positive electrode can be prepared according to conventional methods for preparing a positive electrode. Specifically, a positive electrode can be manufactured by coating a positive electrode active material layer forming composition, prepared by dissolving or dispersing the aforementioned positive electrode active material and optional binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and calendering. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above. Alternatively, in another method, a positive electrode can be prepared by casting the positive electrode active material layer forming composition onto a separate support, and then pressing the film layer obtained by peeling it off from the support onto the positive electrode current collector.

[0118] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more of these can be used. The amount of solvent is sufficient if it can dissolve or disperse the positive electrode active material, conductive material, and binder while considering the coating thickness and preparation yield of the slurry, and if it provides a viscosity that exhibits excellent thickness uniformity when subsequently coated to manufacture the positive electrode.

[0119] Lithium secondary batteries

[0120] Next, the lithium secondary battery of the present invention will be described.

[0121] This invention can manufacture an electrochemical device comprising the aforementioned positive electrode. Specifically, the electrochemical device can be a battery or capacitor, and more specifically, a lithium secondary battery.

[0122] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode located opposite the positive electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted. In the following text, only the other components will be described in detail.

[0123] Additionally, the lithium secondary battery may optionally include a battery housing that houses the electrode assembly of the positive electrode, negative electrode and separator, and a sealing component that seals the battery housing.

[0124] In the aforementioned lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0125] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0126] The negative electrode active material layer may optionally include an adhesive and a conductive material together with the negative electrode active material.

[0127] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide, or lithium vanadium oxide; or composites containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, or any one or a mixture of two or more of these. Additionally, lithium metal films can be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include irregular, planar, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0128] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight.

[0129] Adhesives are components used to facilitate the bonding between conductive materials, active materials, and current collectors, and are typically added in amounts ranging from 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0130] Conductive materials are components used to further improve the conductivity of the negative electrode active material, and their addition amount relative to the total weight of the negative electrode active material layer can be less than 10% by weight, specifically less than 5% by weight. There are no particular restrictions on the conductive materials, as long as they are conductive without causing chemical changes in the battery. Examples include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum powder 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.

[0131] For example, the negative electrode active material layer can be prepared by coating a negative electrode active material layer forming composition prepared by dissolving the negative electrode active material and optional binder and conductive material in a solvent onto a negative electrode current collector and then drying it, or by casting the negative electrode active material layer forming composition onto a separate support and then laminating a film peeled off from the support onto the negative electrode current collector.

[0132] Meanwhile, in the aforementioned lithium secondary battery, the separator separates the negative electrode from the positive electrode and provides a path for lithium ion movement. Any separator commonly used in lithium secondary batteries can be used without particular limitation; in particular, a separator with low impedance to electrolyte ion movement and excellent electrolyte retention is preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers), or stacked structures of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, for example, nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0133] In addition, the electrolyte used in this invention can be any organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte, or molten inorganic electrolyte that can be used in the manufacture of lithium secondary batteries, but is not limited to these.

[0134] Specifically, electrolytes may include organic solvents and lithium salts.

[0135] As an organic solvent, any organic solvent can be used without particular restriction, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following solvents can be used as organic solvents: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (wherein R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among the solvents described above, carbonate solvents are preferred, and more preferably, mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) that can improve the charge-discharge performance of the battery are preferred. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0136] Any compound can be used as a lithium salt without particular limitations, as long as it can provide lithium ions for lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 are suitable lithium salts. Lithium salts are well-suited for use in concentration ranges from 0.1 M to 5.0 M, specifically from 0.1 M to 3.0 M. If the concentration of the lithium salt falls within this range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent electrolyte performance, and lithium ions can move efficiently.

[0137] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, the electrolyte may also contain one or more additives, such as alkylene carbonate halogenated compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additives can be from 0.1% by weight to 10% by weight, specifically from 0.1% by weight to 5% by weight.

[0138] The lithium secondary battery containing the positive electrode active material of the present invention exhibits excellent resistance and capacity characteristics and has a relatively low resistance increase rate, thus making it suitable for portable devices (such as mobile phones, laptops and digital cameras) and electric vehicles (such as hybrid electric vehicles (HEVs)).

[0139] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0140] Battery modules or battery packs can be used as a power source for one or more medium to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0141] The lithium secondary battery of the present invention is not particularly limited in shape, and can be cylindrical, square, bag-shaped or coin-shaped, etc.

[0142] The lithium secondary battery of the present invention can be used as a battery cell for powering small devices, and can also preferably be used as a unit cell in medium and large battery modules comprising multiple battery cells.

[0143] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0144] Example

[0145] Preparation Example

[0146] Preparation Example 1

[0147] NiSO4 and MnSO4 were dissolved in deionized water to prepare a 2.4 M composite transition metal aqueous solution with a nickel:manganese molar ratio of 0.35:0.65. The composite transition metal aqueous solution and a 25 wt% sodium hydroxide aqueous solution were each connected to a 10 L continuous stirred tank reactor via inlet tubes. 2.6 L of deionized water and 3.5 mL of the 25 wt% sodium hydroxide aqueous solution were added to the reactor, which was maintained at 50 °C and stirred at 150 rpm, to prepare an initial solution with a pH of 12.0 to 13.0 (based on 25 °C). Furthermore, to remove dissolved oxygen and establish a non-oxidizing atmosphere inside the reactor, N2 gas was introduced at a rate of 2 L / min. Subsequently, while maintaining a stirring speed of 1000 rpm, the composition ratio of the gas introduced into the reactor was changed from 100% N2 to an N2:atmosphere ratio of 99.5:0.5 to 85.0:15.0 to establish a weakly oxygenated atmosphere, and the composite transition metal aqueous solution was continuously injected into the reactor at a flow rate of 0.85 L / h. By controlling the amount of NaOH introduced and the RPM, the pH was adjusted to 10.0 to 11.0 within 1 to 2 hours from the start of the reaction, thereby generating composite transition metal hydroxide seed crystals with a size of 0.1 μm to 1 μm. Subsequently, while maintaining the pH at 10.0 to 11.0 for 80 hours, composite transition metal hydroxide particles were grown via a co-precipitation reaction. The feed was stopped when the target particle size (4 μm) was reached. The particles were then separated from the reaction solution, washed, and dried to obtain a Ni-containing composite. 0.35 Mn 0.65 (OH)2 complex transition metal hydroxides.

[0148] Preparation Example 2

[0149] By controlling the amount of NaOH introduced and the RPM, the pH was adjusted to reach 10.0 to 11.0 within 1 to 2 hours from the start of the reaction, thereby generating composite transition metal hydroxide seed crystals with a size of 3 μm to 5 μm. Subsequently, composite transition metal hydroxide particles were grown via co-precipitation while maintaining the pH at 10.0 to 11.0 for 60 hours. The feedstock was stopped when the target particle size (10 μm) was reached. Ni-containing composite particles were then prepared in the same manner as in Preparation Example 1. 0.35 Mn 0.65 (OH)2 complex transition metal hydroxides.

[0150] Examples and Comparative Examples

[0151] Example 1

[0152] LiOH and Ni prepared in Example 1 were used. 0.35 Mn 0.65(OH)₂ is mixed to achieve a Li:(Ni+Mn) molar ratio of 1.32:1. The mixture is then calcined at 910°C under atmospheric conditions to obtain a product containing Li… 1.14 Ni 0.3 Mn 0.56 The lithium complex transition metal oxide with composition represented by O2. In this case, the lithium complex transition metal oxide has a composition of 0.47(Li2MnO3)·1.0(LiNi). 0.51 Mn 0.49 The composition represented by O2).

[0153] A positive electrode active material with a V2O5 coating formed on the lithium composite transition metal oxide is prepared by mixing lithium composite transition metal oxide and heat-treating the mixture at 500°C under an oxygen atmosphere. In this case, the V2O5 is mixed such that the vanadium (V) content is 100 ppm based on the total weight of the lithium composite transition metal oxide.

[0154] Example 2

[0155] Except that the V2O5 was mixed to such that the vanadium (V) content was 1000 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 1.

[0156] Example 3

[0157] Except that the V2O5 was mixed to such that the vanadium (V) content was 2000 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 1.

[0158] Example 4

[0159] LiOH and Ni prepared in Example 2 0.35 Mn 0.65 (OH)₂ is mixed to achieve a Li:(Ni+Mn) molar ratio of 1.31:1. The mixture is then calcined at 910°C under atmospheric conditions to obtain a product containing Li… 1.13 Ni 0.3 Mn 0.57 The lithium complex transition metal oxide with composition represented by O2. In this case, the lithium complex transition metal oxide has a composition of 0.43 (Li2MnO3)·1.0 (LiNi). 0.51 Mn 0.49 The composition represented by O2).

[0160] A positive electrode active material with a V2O5 coating formed on the lithium composite transition metal oxide is prepared by mixing lithium composite transition metal oxide and heat-treating the mixture at 500°C under an oxygen atmosphere. In this case, the V2O5 is mixed such that the vanadium (V) content is 100 ppm based on the total weight of the lithium composite transition metal oxide.

[0161] Example 5

[0162] Except that the V2O5 was mixed to such that the vanadium (V) content was 1000 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 4.

[0163] Example 6

[0164] Except that the V2O5 was mixed to such that the vanadium (V) content was 2000 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 4.

[0165] Comparative Example 1

[0166] LiOH and Ni prepared in Example 1 were used. 0.35 Mn 0.65 (OH)₂ is mixed to achieve a Li:(Ni+Mn) molar ratio of 1.32:1. The mixture is then calcined at 910°C under atmospheric conditions to obtain a product containing Li… 1.14 Ni 0.3 Mn 0.56 O2 represents a lithium complex transition metal oxide.

[0167] Comparative Example 2

[0168] Except that the V2O5 was mixed to such that the vanadium (V) content was 50 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 1.

[0169] Comparative Example 3

[0170] Except that the V2O5 was mixed to such that the vanadium (V) content was 3000 ppm based on the total weight of the lithium composite transition metal oxide, the positive electrode active material was prepared in the same manner as in Example 1.

[0171] Experimental Example

[0172] Experimental Example 1: XRD Analysis

[0173] XRD measurements were performed on the positive electrode active materials prepared in the examples and comparative examples. Subsequently, the XRD data of the positive electrode active materials prepared in Examples 1 and 2 are shown below. Figure 1 .

[0174] Figure 1 The XRD data are for the positive electrode active materials prepared in Examples 1 and 2, respectively.

[0175] In this case, 2 g to 3 g of positive electrode active material particles were collected from each positive electrode active material powder, and XRD was measured by X-ray diffraction analysis using Cu-Kα rays (wavelength 1.54 Å) at an accelerating voltage of 40 kV / 40 mA and a scan rate of 0.2° / sec in the 2θ range of 15° to 80°.

[0176] See Figure 1 It was confirmed that the positive electrode active materials prepared in Examples 1 and 2 simultaneously contain both the Li2MnO3 phase and the LiMO2 phase (where M is an element containing Ni, Mn, or a combination thereof). Specifically, the presence of the Li2MnO3 phase was confirmed by a small peak at 20° to 23°, and the presence of the LiMO2 phase (where M is an element containing Ni, Mn, or a combination thereof) was confirmed by a large peak at 18°.

[0177] Experimental Example 2: ICP Analysis

[0178] 0.1 g each of the lithium composite transition metal oxide and the positive electrode active material prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were taken, and 1 mL of hydrochloric acid was added to dissolve the positive electrode active material by heating. Subsequently, to promote the reaction, a small amount of hydrogen peroxide water was added to completely dissolve the positive electrode active material, thereby obtaining a solution. Then, the solution was diluted with deionized water to a total volume of 10 mL to prepare the analytical sample. The weight ratio of the constituent elements present in the analytical sample was determined using an ICP apparatus (Perkin Elmer Co., Ltd., OPTIMA 7300DV). The composition of the lithium composite transition metal oxide and the vanadium (V) content (ppm) contained in the coating are shown in Table 1 below.

[0179] [Table 1]

[0180] Referring to Table 1, the compositions of Examples 1 to 6 are represented by the above-described chemical formula 1, and the vanadium (V) content contained in the coating was confirmed to be between 90 ppm and 2500 ppm based on the total weight of the lithium composite transition metal oxide.

[0181] Experimental Example 3: Measurement of Coating Content

[0182] The vanadium (V) content in the coating of Example 1 was measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0183] Based on the vanadium (V) content obtained from the measurement results, the content of vanadium oxide and lithium vanadium oxide contained in the coating was calculated by reverse calculation. As a result, it was confirmed that the content of the coating in Example 1 was 0.0178 parts by weight based on 100 parts by weight of lithium composite transition metal oxide.

[0184] Experiment Example 4: Measurement of the average particle size of the positive electrode active material

[0185] To measure the average particle size of the positive electrode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3, the particle size of the positive electrode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was measured using a PSA (Microtrac Co., Ltd., S3500), and the results are shown in Table 2 below.

[0186] [Table 2]

[0187] Based on Table 2, the average particle size (D) of the positive electrode active material was confirmed. 50 The range is from 1.0 μm to 15.0 μm.

[0188] Experimental Example 5: Evaluation of Battery Characteristics

[0189] Manufacturing of coin-type half-cells

[0190] A positive electrode slurry was prepared by mixing 97.5% by weight of the positive electrode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3, 1.0% by weight of Super P as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then calendered to manufacture the positive electrode.

[0191] An electrode assembly is manufactured by using a lithium metal electrode as the negative electrode and inserting a porous polyethylene membrane between the positive and negative electrodes. The electrode assembly is placed inside a battery casing, and an electrolyte prepared by dissolving 1M LiPF6 in an organic solvent in a volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) is injected into the battery casing to manufacture a coin-shaped half-cell.

[0192] Evaluation of battery characteristics

[0193] The initial charge-discharge process was performed using coin-shaped half-cells containing the positive electrode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3, respectively. The cells were then charged to 4.4 V in CC-CV mode at 25°C and discharged to 2.5 V in CC mode, and the charge-discharge capacity and resistance were measured. The measured charge-discharge capacity (mAh / g) and resistance (Ω) are shown in Table 3 below.

[0194] The resistance of the first cycle and the resistance of the 30th cycle were measured by charging (0.33 C) to 4.4 V in CC-CV mode at 25°C and then discharging (0.33 C) to 2.5 V in CC mode as one cycle. The percentage of resistance of the 30th cycle relative to the resistance of the first cycle (resistance increase rate (%)) is then shown in Table 3 below.

[0195] [Table 3]

[0196] Referring to Table 3, it was confirmed that batteries containing the positive electrode active materials of Examples 1 to 6 (the coating comprises a compound consisting of vanadium (V) and oxygen (O), and the vanadium (V) content in the coating is 90 ppm to 2500 ppm based on the total weight of the lithium complex transition metal oxide) exhibited superior charge-discharge capacity and resistance in the first cycle compared to batteries containing the uncoated positive electrode active material of Comparative Example 1 and batteries containing the positive electrode active materials of Comparative Examples 2 and 3 (the vanadium (V) content in the coating is less than 90 ppm or greater than 2500 ppm). Conversely, in the case of batteries containing the positive electrode active materials of Comparative Examples 1 to 3, a significantly higher rate of increase in resistance at the 30th cycle was confirmed, which became a problem. In summary, it can be seen that the positive electrode active material of the present invention can improve the charge-discharge capacity and conductivity of the battery, and there are no significant structural changes even during charge-discharge cycling.

Claims

1. A positive electrode active material, comprising: A lithium composite transition metal oxide comprising both Li₂MnO₃ and LiMO₂ phases, wherein M is an element containing Ni, Mn, or a combination thereof; and A coating comprising a compound consisting of vanadium (V) and oxygen (O) on the lithium composite transition metal oxide. in: The lithium composite transition metal oxide has a composition represented by the following chemical formula 1; and Based on the total weight of the lithium composite transition metal oxide, the coating contains vanadium (V) at a content of 90 ppm to 2500 ppm. [Chemical Formula 1] Li 1+x Ni a Mr b M 1 c O2 In the aforementioned chemical formula 1, M 1 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 <x≤0.5,0<a≤0.5,0.5≤b<1,0≤c≤0.01。 2. The positive electrode active material as described in claim 1, wherein, The lithium composite transition metal oxide has the following composition represented by chemical formula 2: [Chemical Formula 2] αLi2Mn (1-p) M 2 p O3·βLiNi q Mn r M 2 s O2 In the aforementioned chemical formula 2, M 2 It is selected from one or more of the group consisting of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0 < α ≤ 0.5, 0 < β ≤ 1, 0 ≤ p ≤ 0.01, 0 <q≤0.8,0<r≤0.8,0≤s≤0.01,q+r+s=1。 3. The positive electrode active material as described in claim 1, wherein, b ranges from 0.5 to 0.

75.

4. The positive electrode active material as described in claim 1, wherein, The coating contains V2O5.

5. The positive electrode active material as described in claim 1, wherein, The coating content is from 0.01 parts by weight to 0.1 parts by weight, based on 100 parts by weight of the lithium composite transition metal oxide.

6. The positive electrode active material as described in claim 1, wherein, The average particle size D of the positive electrode active material 50 The range is from 1.0 μm to 15.0 μm.

7. A method for preparing the positive electrode active material according to claim 1, the method comprising the following steps: (A) A lithium composite transition metal oxide is prepared by mixing a composite transition metal hydroxide with a lithium (Li)-containing raw material and then calcining it; and (B) The lithium composite transition metal oxide and vanadium (V) raw material are mixed and then heat-treated to form a coating comprising a compound consisting of vanadium (V) and oxygen (O) on the lithium composite transition metal oxide, wherein the heat treatment is performed at a temperature of 400°C to 600°C.

8. The method of claim 7, wherein, The vanadium (V)-containing raw material is V2O5.

9. The method of claim 7, wherein, The vanadium (V)-containing raw materials are mixed such that the vanadium (V) content is between 100 ppm and 2500 ppm based on the total weight of the lithium complex transition metal oxide.

10. The method of claim 7, wherein, In step (B), the heat treatment is carried out in an oxygen atmosphere.

11. The method of claim 7, wherein, The coating contains V2O5.

12. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.

13. A lithium secondary battery comprising the positive electrode as described in claim 12.

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