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

Abstract

To provide a lithium-manganese-rich positive electrode active material with high cost competitiveness, which ensures high capacity characteristics due to O-redox and minimizes side effects due to O-redox, thereby minimizing voltage drop and energy density reduction, and improving life characteristics.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, which contains a compound represented by Chemical Formula 1, and a positive electrode and a lithium secondary battery each containing the same. a[Li1+x(NiyMn1-y)1-xO2]+(1-a)[b(LiNizMn1-zO2)+c(Li2MnO3)] satisfies 0<a<1, 0.03≤x≤0.2, 0.35≤y≤0.7, 0<b<1, 0<c<1, and 0.5≤z≤1.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0002] Lithium-ion batteries, which have high energy density and are easily portable, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, there has been active research into using high-energy-density lithium-ion batteries as power sources or energy storage sources for hybrid and electric vehicles.

[0003] To realize lithium secondary batteries that meet these applications, a variety of cathode active materials are being considered. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are mainly used as cathode active materials. However, recently, while the demand for large, high-capacity, or high-energy-density lithium secondary batteries has surged, the supply of transition metals such as nickel and cobalt has become extremely scarce, leading to a serious problem of rising prices. Therefore, the development of low-cost, high-energy cathode active materials is necessary.

[0004] Lithium-manganese-rich (LMR) materials are layered cathode active materials with an excess of lithium and a relatively high manganese content. In addition to capacity generation through the oxidation-reduction of existing transition metals, they also utilize a new principle of oxygen oxidation-reduction (O-redox) to achieve high capacity. Furthermore, due to their high proportion of low-cost manganese, they are attracting attention as ultra-low-cost next-generation cathode active materials.

[0005] However, LMR materials have low reversibility in O-redox itself, which is the driving force behind their high capacity. This can lead to the release of oxygen gas during charging and discharging, which can degrade the crystal structure and cause voltage decay during the charging and discharging process. Furthermore, the higher the O-redox capacity in the total capacity, the lower the average discharge voltage of the positive electrode may become. Therefore, although O-redox is the driving force behind high capacity, if its specific gravity is excessive, it can lead to a decrease in lifespan characteristics or a reduction in energy density calculated as (capacity × voltage). [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention provides a lithium-manganese-rich cathode active material that is highly price-competitive, ensures high capacity characteristics through O-redox, minimizes the side effects of O-redox, thereby minimizing voltage drop and energy density reduction, and provides a cathode active material with improved lifetime characteristics. [Means for solving the problem]

[0007] One embodiment provides a positive electrode active material for a lithium secondary battery containing a compound represented by chemical formula 1. [Chemical formula 1] a[Li 1+x (Ni y Mn 1-y ) 1-x O2]+(1-a)[b(LiNi z Mn 1-z O2) + c(Li2MnO3)]

[0008] In the aforementioned chemical formula 1, 0 <a<1、0.03≦x≦0.2、0.35≦y≦0.7、0<b<1、0<c<1および0.5≦z≦1である。

[0009] In another embodiment, a positive electrode for a lithium secondary battery is provided, which includes a positive electrode active material.

[0010] In another embodiment, a lithium secondary battery is provided, comprising the positive electrode, the negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte.

[0011] In another embodiment, an all-solid-state secondary battery is provided, comprising the positive electrode, the negative electrode, and a solid electrolyte layer located between the positive and negative electrodes. [Effects of the Invention]

[0012] The positive electrode active material according to one embodiment is a lithium-manganese-rich positive electrode active material that is highly price-competitive, can achieve high capacity by utilizing O-redox, and can effectively improve voltage drop and energy density reduction problems by controlling the ratio of O-redox capacity to total capacity. As a result, it exhibits high discharge capacity and average discharge voltage, and can achieve excellent high-temperature life characteristics and high energy density. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment. [Figure 5] The graph shows the X-ray diffraction (XRD) analysis results for the positive electrode active materials of Example 2 (950°C), Example 5 (700°C), and Comparative Example 5 (500°C), with peaks in the (003) plane and the (020) plane. [Figure 6] This is a scanning electron microscope (SEM) image of the particle surface of the positive electrode active material manufactured in Example 2. [Figure 7] This is an SEM image of the particle surface of the positive electrode active material manufactured in Example 5. [Figure 8]This is an SEM image of the particle surface of the positive electrode active material produced in Comparative Example 5. [Modes for carrying out the invention]

[0014] The following describes specific embodiments in detail so that they can be easily implemented by a person with ordinary skill in the art. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein.

[0015] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0016] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0017] Here, terms such as “include,” “equip,” or “possess” are intended to specify the existence of the implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, figures, stages, components, or combinations thereof.

[0018] In the drawings, thicknesses are shown enlarged to clearly represent multiple layers and regions, and similar parts are denoted by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top" of another part, this includes not only when it is "directly above" another part, but also when there is another part in between. Conversely, when one part is said to be "directly above" another part, it means that there is no other part in between.

[0019] Furthermore, the term "layer" here includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on some of the surfaces.

[0020] The average particle diameter can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured with a transmission electron microscope image or a scanning electron microscope image. As another method, it can be measured using the dynamic light scattering method, data analysis is performed to count the number of particles for each particle size range, and then based on this, the average particle diameter value can be obtained by calculation. Unless otherwise defined, the average particle diameter may mean the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the particle size distribution. Also, unless otherwise defined, the average particle diameter is obtained by measuring the sizes (diameter or major axis length) of more than 20 randomly selected particles in a scanning electron microscope image to obtain a particle size distribution, and taking the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the said particle size distribution as the average particle diameter.

[0021] Here, "or" is not interpreted in an exclusive sense. For example, "A or B" is interpreted to include A, B, A + B, etc.

[0022] "Metal" is interpreted as a concept including general metals, transition metals, and metalloids (semimetals).

[0023] positive electrode active material In one embodiment, a positive electrode active material for a lithium secondary battery containing a compound represented by Chemical Formula 1 is provided. [Chemical Formula 1] a[Li 1+x (Ni y Mn 1-y ) 1-x O2]+(1 - a)[b(LiNi z Mn 1-z O2)+ c(Li2MnO3)]

[0024] In the said Chemical Formula 1, 0 < a < 1, 0.03 ≤ x ≤ 0.2, 0.35 ≤ y ≤ 0.7, 0 < b < 1, 0 < c < 1, and 0.5 ≤ z ≤ 1.0.

[0025] In the said Chemical Formula 1, [Li1+x (Ni y Mn 1-y ) 1-x O2] represents the solid-solution phase, and [b(LiNi z Mn 1-z The compound O2)+c(Li2MnO3)] can be said to represent a composite phase. In other words, the compound represented by chemical formula 1 can be said to contain both a solid solution phase and a composite phase. Existing lithium-manganese-rich materials can generally be said to have either a solid solution or a composite structure. On the other hand, the positive electrode active material according to one embodiment can be said to be a material in which not only a composite phase but also a solid solution phase is added, for example, a material in which the composite and solid solution are mixed, or a material in which the composite and solid solution compete to coexist.

[0026] Here, a solid solution is a solid mixture in which different elements are completely and uniformly mixed, meaning that other elements are mixed and uniformly distributed within a solid crystal, much like a solution in which a solute is uniformly distributed in a solvent. A solid solution may be a continuum quasi-isostructural compound with new properties formed by the strong interrelationship of two or more individual components. The solid solution is homogeneous, has almost the same composition, and can have a single phase or a single crystal structure. In contrast, a composite is formed by the bonding of two or more materials, consisting of materials with different physical properties, and it can be said that the materials maintain a state of physical distinction. A composite is heterogeneous, can have two or more compositions, and can have two or more phases or crystal structures.

[0027] The presence or absence of solid solutions and complexes can be confirmed through Energy above Hull analysis, or by XRD diffraction peaks, as described later.

[0028] In Chemical Formula 1, it can be said that a is the ratio of the solid solution phase and (1 - a) is the ratio of the composite phase. In Chemical Formula 1, the range of a is 0 < a < 1, and for example, it can be 0.1 ≦ a ≦ 0.9, 0.2 ≦ a ≦ 0.8, or 0.3 ≦ a ≦ 0.7, but the range is not particularly limited.

[0029] In Chemical Formula 1, y is the nickel content of the solid solution phase, and z indicates the nickel content of the layered material in the composite phase. The range of y is 0.35 ≦ y ≦ 0.7, and for example, it can be 0.35 ≦ y ≦ 0.66, 0.4 ≦ y ≦ 0.60, 0.45 ≦ y ≦ 0.55, or 0.5 ≦ y ≦ 0.66, etc. The range of z is 0.5 ≦ z ≦ 1.0, and for example, it can be 0.5 ≦ z ≦ 0.99, 0.5 ≦ z ≦ 0.95, 0.50 ≦ z ≦ 0.85, or 0.6 ≦ z ≦ 0.75, etc.

[0030] The positive electrode active material according to one embodiment can be said to be a lithium - manganese - rich material having a nickel content of 50 mol% to 70 mol%, or for example 50 mol% to 66 mol% with respect to 100 mol% of the total metal excluding lithium. The positive electrode active material with such a composition excludes or contains a very small amount of expensive cobalt, and contains inexpensive manganese, thereby ensuring price competitiveness. While ensuring the capacity due to the nickel content, it can also ensure the capacity due to O - redox to achieve a high capacity, and can effectively improve the problems of voltage drop and energy density reduction by restricting the O - redox ratio.

[0031] In Chemical Formula 1, x is related to the lithium content, and (1 + x) corresponds to the molar ratio of lithium. The range of x is 0.03 ≦ x ≦ 0.2, and for example, it can be 0.03 ≦ x ≦ 0.15, 0.03 ≦ x ≦ 0.13, 0.03 ≦ x ≦ 0.11, or 0.03 ≦ x ≦ 0.09. For example, the ratio of the lithium content (1 + x) to the content of the total metal excluding lithium (1 - x), that is, (1 + x) / (1 - x) can be 1.06 to 1.5, 1.06 to 1.3, or 1.1 to 1.2.

[0032] In Chemical Formula 1, b and c are each related to the ratios of (LiNi z Mn 1-z O2) and (Li2MnO3) in the composite phase, where 0 < b < 1 and 0 < c < 1. For example, 0.1 ≤ b ≤ 0.9, 0.2 ≤ b ≤ 0.8, or 0.3 ≤ b ≤ 0.7 may be satisfied, and 0.1 ≤ c ≤ 0.9, 0.2 ≤ c ≤ 0.8, or 0.3 ≤ c ≤ 0.7 may be satisfied, but the range is not particularly limited.

[0033] The cathode active material according to one embodiment may have an "Energy above Hull" of less than 25 meV / atom. Energy above Hull means the difference between the Formation energy of the composite phase in the most stable state and the Formation energy of the solid solution phase in the metastable state. 25 meV / atom is the energy that an atom can overcome at room temperature (300K), indicating the thermodynamic stability of the material at room temperature. It can be said that the larger the Energy above Hull, the lower the possibility of existing in the solid solution phase and the higher the possibility or ratio of existing in the stable composite phase. The cathode active material according to one embodiment can satisfy an Energy above Hull of less than 25 meV / atom, and thus the composite phase and the solid solution phase can coexist at room temperature.

[0034] Thus, the cathode active material according to one embodiment containing a solid solution phase can have relatively stable oxygen existing in the structure compared to the existing composite phase lithium-manganese-rich material. This is because in the existing composite material (a = 0), during the charge-discharge process, LiNi z Mn 1-zIt is known that the lattice constants and lithium concentrations of the O2 phase and the Li2MnO3 phase differ, leading to stress at the interface and the generation of oxygen vacancies. However, in one embodiment of the positive electrode active material containing a solid solution phase, the amount of interface is reduced, lowering the probability of problems occurring at the interface. As a result, structural changes due to oxygen vacancies during the charge-discharge process are minimized, and problems of voltage drop due to oxygen generation and structural degradation can be effectively improved. In short, in one embodiment, while utilizing a lithium-manganese-rich material with high capacity and price competitiveness, it is possible to provide a positive electrode active material that eliminates the problem of voltage drop during charge-discharge, improves lifespan characteristics, and enhances energy density.

[0035] In one embodiment, the positive electrode active material exhibits capacity due to O-redox, which is due to the solid solution phase Li 1+x (Ni y Mn 1-y ) 1-x It can be said that it is Li2MnO3 in the O2 and / or complex phase. 1+x (Ni y Mn 1-y ) 1-x Either O2 or Li2MnO3, or both, can contribute to O-redox.

[0036] In one embodiment, the positive electrode active material utilizes O-redox, but its composition minimizes the side effects of O-redox. For example, the ratio of the capacity expressed by O-redox to 100% of the total capacity of the positive electrode active material may be less than 15%, for example, 1% to 9.9% or 3% to 9.5%. When the O-redox specific gravity is controlled to less than 15% in a lithium-manganese-rich material with a Ni content of 50 to 70 mol%, as in one embodiment, the problem of voltage drop due to charging and discharging can be effectively improved, thereby improving lifespan characteristics and energy density.

[0037] One example of a method for measuring the ratio of the capacity expressed by O-redox to the total capacity of the positive electrode active material is as follows: A half-cell is manufactured using a positive electrode and lithium counter electrode to which the positive electrode active material is applied, and a carbonate-based electrolyte is applied. Charge and discharge are then performed under the following conditions. After the first set is performed, the second set is then performed.

[0038] [Set 1] (1) First cycle: Charge to 4.65V with a constant current of 0.1C at 25℃, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.1C.

[0039] (2) Second cycle: Charge to 4.45V with a constant current of 0.2C at 25℃, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C.

[0040] [Set 2] (1) First cycle: Charge to 4.45V with a constant current of 0.2C at 25℃, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C.

[0041] (2) Second cycle: Charge to 4.45V with a constant current of 0.2C at 25℃, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C.

[0042] When the discharge capacity in the second cycle of the first set is X and the discharge capacity in the second cycle of the second set is Y, the XY value can be said to be the O-redox capacity. When O-redox is activated by charging at 4.65V in the first cycle, the capacity increases in the second cycle, and this increase can be considered as the O-redox capacity. The ratio (%) of the capacity expressed by O-redox to the total capacity of the positive electrode active material can be calculated using the following formula 1. [Formula 1] {(XY) / X}×100

[0043] Generally, the O-redox reaction is known to occur in the first cycle of the cathode at a high voltage of approximately 4.45V or higher. However, the voltage at which the reaction is most pronounced can be influenced by various factors such as the surface condition and composition of the cathode and the electrolyte composition. In this high voltage range, the O-redox reaction is accompanied by electrolyte side reactions. The degree of these side reactions becomes more intense as the voltage increases, and if the voltage is increased excessively, the proportion of reactions other than O-redox increases, thus reducing the accuracy of O-redox capacity measurement. Conversely, if the voltage is excessively decreased to reduce electrolyte side reactions, the amount of O-redox reaction itself decreases, which also reduces the accuracy of O-redox capacity measurement. Therefore, through various experiments, the inventors set the upper limit voltage of the first cycle of the first set to 4.65V, which allows for the most effective measurement of O-redox capacitance. However, this value can vary depending on various factors such as the surface condition and composition of the positive electrode and the electrolyte composition, and can be set in a range of, for example, 4.55V to 4.8V, such as 4.55V, 4.6V, 4.7V, 4.75V, 4.8V, etc.

[0044] Generally, there is a problem that the more O-redox is expressed, the lower the average discharge voltage becomes after O-redox activation. However, in one embodiment of the positive electrode active material, the average discharge voltage can be improved by controlling the specific gravity of O-redox. For example, the average discharge voltage in the second cycle in the first set (vs. Li / Li + The average discharge voltage can be 3.83V or higher, and for example, 3.84V or higher. Here, the average discharge voltage may mean the average discharge voltage in the second cycle of the first set, in which a half cell was manufactured using the positive electrode to which the positive electrode active material was applied, and charging and discharging was performed in the first set described above. The average discharge voltage can be calculated, for example, by dividing the integral of the area under the curve (voltage-capacitance graph) by the discharge capacity.

[0045] The positive electrode active material according to one embodiment was analyzed by X-ray diffraction.

[0046]

number

[0047] LiNi corresponds to a space group. z Mn 1-z The ratio of the peak intensity of the (020) plane of the Li2MnO3 phase corresponding to the C2 / m space group to the peak intensity of the (003) plane of the O2 phase (I (020) / I (003) The intensity of the (020) plane may be 2% or less. Here, the (003) plane refers to the lattice plane corresponding to Miller index (003), and the (020) plane refers to the lattice plane corresponding to Miller index (020). In XRD, the peak of the (003) plane appears around 2θ = 18~19°, and the peak of the (020) plane appears around 2θ = 20.3~22°. The peak of the (020) plane can be said to be the peak that appears due to the Li2MnO3 phase in chemical formula 1. In one embodiment, the positive electrode active material has a (020) peak of Li2MnO3 in the composite phase, but its intensity is low, and the ratio of the peak intensity of the (020) plane to the peak intensity of the (003) plane is controlled to 2% or less. (020) / I (003) For example, it could be 1.9% or less, 1.8% or less, or 1.0% or less, and could be 0.5-2%, 0.8-1.9%, 0.3-1.8%, or 0.3-1.0%. (020) / I (003) If the ratio satisfies the aforementioned range, the O-redox specific gravity will be lower, which may improve the problem of voltage drop due to charging and discharging.

[0048] In one embodiment, the positive electrode active material may have an a-lattice constant of 2.865 Å or higher in XRD, for example, 2.870 Å or higher, and 2.875 Å to 2.885 Å. As an example, it is preferable that the a-lattice constant of the positive electrode active material is 2.875 Å or higher. Furthermore, the ratio of the c-lattice constant to the a-lattice constant may be 4.968 or lower, for example, 4.965 or lower, 4.960 or lower, and 4.955 to 4.965. When the a-lattice constant of the positive electrode active material and the ratio of the c-lattice constant to the a-lattice constant satisfy the above range, the problem of voltage drop during charging and discharging of the lithium secondary battery containing it can be effectively improved, and the life characteristics and energy density can be improved.

[0049] A positive electrode active material according to one embodiment can achieve a higher reversible discharge capacity ratio compared to existing lithium-manganese-rich materials. Here, the reversible discharge capacity ratio is a method of measuring the ratio of capacities exhibited by O-redox, and may be a value calculated as the ratio (X / A) of the discharge capacity (X) of the second cycle to the charge capacity (A) of the first cycle of the first set. The reversible discharge capacity ratio can affect the N / P ratio, which is the loading level ratio between the negative and positive electrodes in the design of a full cell. For example, the lower the reversible discharge capacity ratio, the more a negative electrode with a higher loading level must be in the cell to achieve the same positive electrode capacity, thus reducing the total energy density. In other words, a higher reversible discharge capacity ratio can be more advantageous in increasing the energy density of a lithium secondary battery.

[0050] In one embodiment, the positive electrode active material may have a reversible discharge capacity ratio of 63% or more, or 72% or more. The reversible discharge capacity ratio can be further improved by lowering the molar ratio of lithium to the total metal excluding lithium. In this case, the reversible discharge capacity ratio may be 77% or more, or 79% or more, thereby further improving the energy density of the lithium secondary battery.

[0051] The positive electrode active material according to one embodiment can achieve a higher pellet density compared to existing lithium-manganese-rich materials. The pellet density of the positive electrode active material may exceed 2.70 g / cc, and may be, for example, 2.71 g / cc or more, 2.74 g / cc or more, or 2.71 to 2.85 g / cc. Here, pellet density refers to the density measured after pelletizing the positive electrode active material under pressure of 3.3 tons. Generally, the higher the lithium and manganese content, the higher the specific gravity of LiMnO2, Li2MnO3, etc., which have low theoretical densities within the positive electrode active material, and therefore the lower the pellet density of the positive electrode active material. On the other hand, the positive electrode active material according to one embodiment has a slightly lower lithium and manganese content compared to existing lithium-manganese-rich materials, and the specific gravity of the phases with low theoretical densities is lower, so it is expected that a relatively high pellet density can be achieved, thereby enabling a high electrode density.

[0052] In one embodiment, the positive electrode active material may have a residual lithium content of 0.4% by weight or less on its surface, for example, 0.3% by weight or less, 0.2% by weight or less, 0.1% by weight or less, or 0.001% to 0.1% by weight. This can be said to be a characteristic that distinguishes it from high-nickel materials with a nickel content exceeding 70 mol%.

[0053] The positive electrode active material may be in the form of secondary particles formed by the aggregation of a plurality of primary particles. The average particle size (D) of the positive electrode active material. 50 The particle size can be 1 μm to 20 μm, for example, 5 μm to 15 μm, or 8 μm to 12 μm. For example, the positive electrode active material has an average particle size (D 50 Small particles with a diameter of 0.5 μm to 8 μm, and average particle size (D 50 ) may be a mixture of large particles with dimensions of 9 μm to 20 μm. Here, the average particle size is obtained by measuring the size (e.g., particle size, major axis, or major axis length) of any 20 or more particles in an SEM image of the positive electrode active material, and then obtaining the particle size distribution, where the size of the particle with a cumulative volume of 50 volume% is defined as the average particle size (D 50 It could be something obtained using ).

[0054] Method for manufacturing positive electrode active material One embodiment provides a method for producing a positive electrode active material, which includes mixing a precursor represented by chemical formula 2 with a lithium raw material and heat-treating the mixture. Here, the molar ratio of lithium in the lithium raw material to the total metal of the precursor is designed to be 1.06 to 1.5.

[0055] [Chemical formula 2] Ni y2 Mn 1-y2 (OH)2 In chemical formula 2, 0.5 ≤ y² ≤ 0.7.

[0056] In the aforementioned chemical formula 2, the following conditions may apply: 0.5 ≤ y² ≤ 0.66, 0.5 ≤ y² ≤ 0.60, or 0.5 ≤ y² ≤ 0.55. In other words, the molar content of nickel relative to the total metal in the precursor satisfies 50 mol% to 70 mol%, and can be, for example, 50 mol% to 66 mol%, 50 mol% to 60 mol%, or 50 mol% to 55 mol%.

[0057] By designing the nickel content of the positive electrode active material precursor in this way, it is possible to synthesize a positive electrode active material according to chemical formula 1 in which the desired solid solution and complex exist simultaneously. For example, if the nickel content of the precursor relative to the total metal is less than 50 mol% or more than 70 mol%, the Energy above Hull exceeds 25 meV / atom, making it difficult for the solid solution and complex to coexist at room temperature, and thus it may exist only as a complex phase. Also in this case,

[0058]

number

[0059] LiNi corresponds to the space group z Mn 1-z The O2 phase may not be formed or its formation ratio may be low, while the formation ratio of the Li2MnO3 phase, which corresponds to the C2 / m space group, may be high, and therefore the peak intensity of the (003) plane (I b Peak intensity of the (020) plane relative to (I a The ratio of ) that is, Ia / I b This can sometimes exceed 2%. In such cases, the O-redox capacity ratio increases, leading to a larger voltage drop during charging and discharging, which can degrade the lifespan characteristics.

[0060] The molar ratio of lithium in the lithium raw material to the total metal of the precursor (Li / (Ni+Mn)) is 1.06 to 1.5, and can be, for example, 1.06 to 1.4, 1.1 to 1.3, or 1.1 to 1.2. When the molar ratio of lithium satisfies the above range, it is possible to synthesize a positive electrode active material according to chemical formula 1 in which both a solid solution and a composite exist simultaneously.

[0061] The heat treatment can be carried out, for example, in a temperature range of 700°C to 1100°C, or in a temperature range of 700°C to 1000°C, or 750°C to 950°C, for a duration of 10 to 40 hours, 12 to 36 hours, or 20 to 30 hours.

[0062] The heat treatment may include a heating step, a temperature maintenance step, and a cooling step. The heating rate in the heating step and the cooling rate in the cooling step may be, for example, 1°C / min to 10°C / min or 2°C / min to 5°C / min, respectively, and satisfying this range is advantageous for effectively synthesizing the desired positive electrode active material according to chemical formula 1.

[0063] positive electrode In one embodiment, a positive electrode for a lithium secondary battery is provided, comprising the positive electrode active material described above. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode active material layer may contain the positive electrode active material described above. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the positive electrode active material described above, and may further selectively contain a binder, a conductive agent, or a combination thereof.

[0064] binder The binder plays a role in ensuring good adhesion between positive electrode active material particles and good adhesion of the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0065] Conductive agent Conductive agents are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Examples of conductive agents include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0066] The binder and conductive agent content may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0067] Al can be used as the positive electrode current collector, but it is not limited to this.

[0068] Lithium-ion rechargeable battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. The positive electrode active material described above is applicable not only to lithium-ion batteries but also to all-solid-state secondary batteries. Therefore, in one embodiment, a lithium secondary battery is provided that includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, and in another embodiment, an all-solid-state secondary battery is provided that includes the positive electrode, the negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. For convenience, the configuration of a lithium-ion battery using an electrolyte will be described in detail below.

[0069] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment; Figure 1 is a circular type, Figure 2 is a prismatic type, and Figures 3 and 4 are pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0070] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer comprising a negative electrode active material and further comprising a binder, a conductive agent, or a combination thereof.

[0071] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0072] Examples of the material capable of reversibly inserting / desorbing the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0073] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0074] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof.

[0075] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles. 50 The particle size can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0076] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may be soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0077] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, and the amorphous carbon content may be 50% to 90% by weight. Furthermore, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight.

[0078] Furthermore, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D) of the silicon particles (primary particles) 50) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 < x < 2) can be represented. At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0079] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0080] binder The binder plays a role in making the negative electrode active material particles adhere well to each other and making the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0081] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0082] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile-ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0083] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0084] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0085] Conductive agent Conductive agents are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0086] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive agent.

[0087] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0088] electrolyte The electrolyte for lithium secondary batteries can be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0089] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcoholic solvents, aprotic solvents, or combinations thereof.

[0090] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0091] Non-aqueous organic solvents can be used alone or in combination of two or more. When using a mixture of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, and this is generally understood by those working in this field.

[0092] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0093] Non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, carbonate-based solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0094] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0095] Typical examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0096] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0097] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0098] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, or polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0099] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0100] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from a copolymer or mixture of two or more of these polymers.

[0101] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0102] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0103] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 The wavelength can range from 1 nm to 2000 nm, for example, from 100 nm to 1000 nm or from 100 nm to 700 nm.

[0104] The organic and inorganic materials can exist mixed together in a single coating layer, or in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0105] The thickness of the coating layer can be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0106] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0107] Example 1 1. Manufacturing of positive electrode active material (1) Production of the precursor A mixed solution of metal raw materials was prepared by dissolving nickel sulfate (NiSO4·6H2O) and manganese sulfate (MnSO4·H2O) in distilled water as a solvent to a molar ratio of Ni:Mn = 50:50. Ammonia water (NH4OH) and sodium hydroxide (NaOH) as a precipitant were prepared for the formation of the complex compound.

[0108] Ammonia solution with a concentration of 0.25 M is placed in the reactor, and a stirring power of 3.0 kW / m is applied. 3 The reaction was started at a reaction temperature of 50°C by adding the mixed metal raw material solution and complexing agent at rates of 142 ml / min and 34 ml / min, respectively. The reaction was carried out for 30 hours while adding NaOH to maintain the pH. The reaction was terminated when the average size of the resulting particles reached approximately 10.5 μm. After washing the resulting product, it was dried with hot air at approximately 150°C for 24 hours to obtain nickel-manganese composite hydroxide (Ni 0.5 Mn 0.5 (OH)2) was manufactured.

[0109] (2) Manufacturing of positive electrode active material Manufactured Ni 0.5 Mn 0.5 (OH)2 and LiOH were mixed to achieve a molar ratio of Li / (Ni+Mn) of 1.3. The mixture was then heated in an oxygen atmosphere at a rate of 5°C / min, maintaining a heat treatment temperature of 950°C, and then cooled to room temperature at a rate of 5°C / min for a total of 24 hours. The positive electrode active material was 0.3[Li 1.13 Ni 0.44 Mn 0.44 O2]+0.7[0.61(LiNi 0.72 Mn 0.28 We manufactured O2)+0.26(Li2MnO3).

[0110] 2. Manufacturing of lithium-ion secondary batteries (Half-cell) A slurry of 97.7% by weight of the manufactured positive electrode active material, 1.2% by weight of polyvinylidene fluoride binder, and 1.1% by weight of carbon nanotube conductive agent was mixed to produce a positive electrode active material layer slurry. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the positive electrode. At this time, the loading level of the positive electrode active material layer was 10 mg / cm².2 Therefore, the density of the rolled final positive electrode is approximately 3.5 g / cc.

[0111] A lithium secondary battery was manufactured using a conventional method with a lithium counter electrode as the negative electrode, a polytetrafluoroethylene separator, and an electrolyte prepared by dissolving 1M LiPF6 in a solvent mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 2:4:4 volume ratio, and adding 1.5% by weight of vinylene carbonate.

[0112] Example 2 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the molar ratio of Ni to Mn was changed to 66:34 in the production of the positive electrode active material precursor. The positive electrode active material according to Example 2 was 0.15[Li 1.13 Ni 0.57 Mn 0.30 O2]+0.85[0.61(LiNi 0.94 Mn 0.06 It can be expressed as O2)+0.26(Li2MnO3).

[0113] Example 3 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the molar ratio of Li / (Ni+Mn) was changed to 1.2. The positive electrode active material according to Example 3 was 0.41[Li 1.09 Ni 0.46 Mn 0.46 O2]+0.59[0.85(LiNi 0.56 Mn 0.44 It can be represented as O2)+0.10(Li2MnO3).

[0114] Example 4 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the molar ratio of Li / (Ni+Mn) was changed to 1.1. The positive electrode active material according to Example 4 was 0.43[Li 1.05 Ni 0.48 Mn 0.48O2] + 0.57[0.85(LiNi 0.56 Mn 0.44 O2) + 0.10(Li2MnO3)] can be expressed as

[0115] Comparative Example 1 In the production of the cathode active material precursor, except that the molar ratio of Ni and Mn was changed to 34:66, the cathode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1. The cathode active material according to Comparative Example 1 can be expressed as 0.66(LiNi 0.50 Mn 0.50 O2) + 0.34(Li2MnO3).

[0116] Comparative Example 2 In the production of the cathode active material precursor, except that the molar ratio of Ni and Mn was changed to 40:60, the cathode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1. The cathode active material according to Comparative Example 2 can be expressed as 0.70(LiNi 0.57 Mn 0.43 O2) + 0.30(Li2MnO3).

[0117] Comparative Example 3 In the production of the cathode active material precursor, except that the molar ratio of Ni and Mn was changed to 75:25, the cathode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1. The cathode active material according to Comparative Example 3 can be expressed as 0.75·LiNiO2 + 0.25(Li2MnO3).

[0118] Comparative Example 4 In the production of the cathode active material precursor, except that the molar ratio of Ni and Mn was changed to 80:20, the cathode active material and the lithium secondary battery were produced in substantially the same manner as in Example 1. The cathode active material according to Comparative Example 4 can be expressed as 0.80·LiNiO2 + 0.20(Li2MnO3) + 0.05Li2O.

[0119] Example 5 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 2, except that the heat treatment temperature was changed to 700°C.

[0120] Comparative Example 5 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 2, except that the heat treatment temperature was changed to 500°C.

[0121] To aid understanding, the design details of the positive electrode active materials for Examples 1 and 2 and Comparative Examples 1 to 4 are briefly shown in Table 1 below, the details of Examples 1, 3, and 4 are shown in Table 2 below, and the details of Examples 2, 5, and Comparative Example 5 are shown in Table 3 below.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] Evaluation Example 1: Evaluation of XRD and SEM X-ray diffraction analysis was performed using Bruker's Powder XRD (D8 Advance) equipment under the following conditions.

[0126] -X-ray wavelength: 1.5406Å (CuKα1) - Slit conditions: Divergence Slit 0.5°, Scattering Slit 0.5°, Receiving Slit 0.20mm - Scan conditions: Continuous Scan, 10°≦2θ≦80°, 0.01° / step, 1.27° / min, total measurement time 55 min XRD analysis was performed on the positive electrode active materials of the examples and comparative examples.

[0127] [Number]

[0128] LiNi corresponding to the space group z Mn 1-z The peak intensity (I b ) of the (003) plane of the O2 phase of Li2MnO3 corresponding to the C2 / m space group with respect to the peak intensity (I a ) of the (020) plane was calculated and shown as I a / I b in Tables 1 to 3. Also, the a lattice constant (Å) and the ratio of the c lattice constant to the a lattice constant were calculated and shown as c / a in Tables 1 to 2.

[0129] Referring to Tables 1 to 3, it can be confirmed that the cathode active material of the example satisfies the ratio of I a / I b being 2% or less. In the case of Comparative Examples 1 and 2 where the nickel content is less than 50 mol%, it is confirmed that the ratio of I a / I b exceeds 2%. Referring to Table 2, as the molar ratio of lithium to the total metal excluding lithium decreases from 1.3 to 1.1, the ratio of I a / I b decreases, the ratio of the capacity by O-redox to the total capacity also decreases, the average discharge voltage increases, and it can be confirmed that the voltage drop tendency also decreases.

[0130] On the other hand, XRD analysis graphs of the cathode active materials of Example 2, 5 and Comparative Example 5 are shown in Fig. 5. In Fig. 5, the horizontal axis means 2θ (°). The large graph shows the peak at the (003) plane, and the small graph shows the graph at the (020) plane. Referring to Fig. 5 and the above Table 3, it can be seen that even for materials of the same composition, as the heat treatment temperature during the synthesis process increases, the peak intensity of the (003) plane becomes stronger and the peak intensity of the (020) plane becomes weaker. Therefore, I a / I bIt can be seen that the ratio of becomes smaller and smaller. Figures 6 to 8 are SEM images of the particle surface of the positive electrode active material produced in Examples 2, 5 and Comparative Example 5, respectively. Referring to Figures 6 to 8, it can be confirmed that the particle shape differs depending on the firing temperature.

[0131] Furthermore, in the example, it can be seen that the a-axis lattice constant is 2.865 Å or greater or 2.875 Å or greater, and at the same time, the ratio of the c-lattice constant to the a-lattice constant (c / a) is 4.968 or less. On the other hand, in Comparative Examples 1 and 2, the c / a ratio exceeds 4.968, and in Comparative Examples 3 and 4, the a-lattice constant is less than 2.865 Å. When the a-axis lattice constant is 2.865 Å or greater and the c / a ratio is 4.968 or less, as in the example, it can be confirmed that the ratio of the capacity due to O-redox to the total capacity decreases, the average discharge voltage increases, and the voltage drop trend also decreases.

[0132] Evaluation Example 2: Pellet Density The positive electrode active materials of Examples 1-4 and Comparative Examples 1-4 were pelletized under pressure of 3.3 tons, and their densities were measured. The results are shown in Tables 1 and 2 as P / D (pellet density). Referring to Tables 1 and 2, it can be seen that the pellet density of the positive electrode active materials in the Examples exceeds 2.70 g / cc, which is higher than that of Comparative Examples 1 and 2, which have a high manganese content and a high O-redox ratio. Referring to Table 2, it can be seen that the pellet density increases as the molar ratio of lithium to the total metal excluding lithium decreases from 1.3 to 1.1. In the case of Comparative Examples 3 and 4, which have a low manganese content, the pellet density is higher than that of the Examples, but it can be seen that it is difficult to achieve high capacity because the additional volume ratio due to O-redox is 0 or less. Therefore, it is understood that the positive electrode active materials in the Examples can achieve higher electrode density by achieving additional volume through O-redox and having a pellet density exceeding 2.70 g / cc.

[0133] The theoretical densities of LiNiO2, LiMnO2, and Li2MnO3, which are the basic materials for cathode active materials, are 4.62 g / cc, 4.04 g / cc, and 3.73 g / cc, respectively. Therefore, the theoretical density of lithium-manganese-rich materials, such as the cathode active material of one embodiment, tends to decrease as the Mn specific gravity increases and increase as the Ni specific gravity increases. However, as mentioned above, O-redox is expressed in Li2MnO3, and it can be seen that exhibiting high capacity through O-redox actually lowers the theoretical density, thus offsetting the benefit of increased capacity. From this perspective, the materials of Examples 1 and 2 have a lower Mn specific gravity and a higher Ni specific gravity and a higher theoretical density compared to Comparative Examples 1 and 2, which have a high O-redox specific gravity, and a higher Mn specific gravity and a lower theoretical density compared to Comparative Examples 3 and 4. However, since high capacity can be achieved through O-redox expression, it can be seen that a strategy to balance appropriate O-redox expression and theoretical density was applied. As will be discussed later, as the Li / Me ratio decreases while maintaining the same Ni and Mn ratio, the amount of Li2MnO3, which is an O-redox expressing substance, decreases. This increases the theoretical density while simultaneously limiting O-redox expression. The results of Examples 3 and 4 are consistent with this, indicating that this strategy is another effective way to balance O-redox volume regulation and theoretical density improvement.

[0134] Evaluation Example 3: Residual Lithium The residual lithium content on the surface of the positive electrode active material in Examples 1-4 and Comparative Examples 1-4 was measured by HCl titration, and the results are shown in Tables 1 and 2. In the tables, the unit of residual lithium content is ppm, and it is the content per 100% by weight of the positive electrode active material. -4 This refers to weight percent. Specifically, 10g of positive electrode active material was placed in 100ml of distilled water and stirred at a speed of 300rpm for 30 minutes, then HCl was added and the pH change was measured. Unreacted residual lithium on the surface of the positive electrode active material exists in the form of Li2CO3, LiOH, etc., therefore CO3 2- , OH - Ions and other elements of HCl +The reaction is followed by titration. The amount of HCl solution added was calculated to determine the amount of unreacted residual lithium. Referring to Tables 1 and 2, it can be seen that the positive electrode active material in the examples has a residual lithium content of approximately 0.4% by weight or less, 0.3% by weight or less, and 0.1% by weight or less. On the other hand, in Comparative Examples 3 and 4, where the nickel content exceeds 70 mol%, the residual lithium content exceeds 0.4% by weight.

[0135] Evaluation Example 4: Evaluation of O-redox capacity The half-cells of Examples 1-4 and Comparative Examples 1-4 underwent two charge-discharge cycles using the first set described above, and the discharge capacity (X) of the second cycle was entered in Tables 1 and 2 as "Discharge Capacity". Separately, two charge-discharge cycles were performed using the second set, and the discharge capacity (Y) of the second cycle was measured. The value obtained by subtracting Y from X is shown as "ΔC" in Tables 1 and 2, and this represents the capacity according to O-redox. {(XY) / X}×100 was calculated and entered as "ΔC / C" in Tables 1 and 2. tot This is indicated by '', which represents the ratio of O-redox volume to total volume. Referring to Tables 1 and 2, it can be confirmed that the O-redox specific gravity in the examples is less than 10%. In Table 1, Comparative Examples 1 and 2 show high O-redox specific gravity values ​​of 19.6% or higher, while Comparative Examples 3 and 4 show no O-redox expression volume. Referring to Table 2, it can be seen that the O-redox specific gravity decreases further as the molar ratio of lithium to the total metal excluding lithium decreases from 1.3 to 1.1.

[0136] Evaluation Example 5: Evaluation of Reversible Discharge Capacity Ratio In the O-redox capacity evaluation method of Evaluation Example 4, the value obtained by dividing the charge capacity of the first cycle of the first set by the discharge capacity of the second cycle was calculated and shown in Tables 1 and 2 as the reversible discharge capacity ratio. Referring to Table 2, it can be confirmed that in Examples 3 and 4, where the molar ratio of lithium to the total metal excluding lithium was reduced to 1.2 or less in the composition of the examples, the reversible discharge capacity ratio improved to 77% or more, indicating that it is possible to manufacture with materials optimized for high energy density.

[0137] Evaluation Example 6: Evaluation of Average Discharge Voltage The half-cells of Examples 1-4 and Comparative Examples 1-4 were charged and discharged in the first set, and the average discharge voltage was measured in the second cycle. The results are shown in Tables 1 and 2 as "Average Voltage". The average discharge voltage can be obtained by integrating the area under the discharge voltage curve (voltage-capacity graph) obtained after charging and discharging the half-cell, and then dividing that value by the discharge capacity.

[0138] Referring to Tables 1 and 2, it can be seen that the average discharge voltage of Comparative Examples 1 and 2 was shown to be below 3.80V, while the average discharge voltage of the Example improved to above 3.83V. Referring to Table 2, it can be seen that the average discharge voltage increases as the molar ratio of lithium to the total metal excluding lithium decreases from 1.3 to 1.1.

[0139] Evaluation Example 7: Evaluation of Lifetime Characteristics and Voltage Drop Characteristics After performing two charge-discharge cycles on the half-cells of Examples 1-4 and Comparative Examples 1-4 as the first set, the charging and discharging cycles at 1.0C in a voltage range of 3.0V to 4.45V at 45°C were repeated 50 or more times. The ratio of the discharge capacity after 50 cycles to the initial discharge capacity was calculated and is shown in Tables 1 and 2 as "High-Temperature Life". In addition, the value obtained by subtracting the average discharge voltage over 50 cycles from the average discharge voltage in the first 1.0C cycle is shown in Tables 1 and 2 as "Voltage Drop".

[0140] Referring to Tables 1 and 2, it can be seen that in Comparative Examples 3 and 4, the life characteristics, i.e., the capacity retention rate after 50 cycles, fall to a level of 71% or less, while the life characteristics of the Example achieve a level of 77% or more, or 94% or more. Furthermore, in Comparative Examples 1 and 2, the voltage drop is at a level of 90mV or more, while in the Example, the voltage drop falls to 70mV or less.

[0141] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0142] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Negative electrode 21: Negative lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tab 71: Positive Tab 72: Negative electrode tab

Claims

1. A positive electrode active material for a lithium secondary battery containing a compound represented by chemical formula 1, [Chemical formula 1] [L) 1+x (N y Mn 1-y ) 1-x O 2 ]+(1-a)[b(L-& z Mn 1-z O 2 )+c(L- 2 MnO 3 )] (In the above chemical formula 1, 0.1 ≤ a ≤ 0.7, 0.03 ≤ x ≤ 0.2, 0.35 ≤ y ≤ 0.7, 0.3 ≤ b ≤ 0.9, 0.1 ≤ c ≤ 0.7, and 0.5 ≤ z ≤ 1.0.) The positive electrode active material is a solid solution phase represented by [Li 1+x (Ni y Mn 1-y) 1-x O 2], and A positive electrode active material for lithium secondary batteries that contains all of the composite phases represented by [b(LiNi zMn 1-z O 2) + c(Li 2 MnO 3)].

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in the chemical formula 1, 0.5 ≤ y ≤ 0.66 and 0.5 ≤ z ≤ 0.

95.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in the chemical formula 1, 0.03 ≤ x ≤ 0.

15.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in the chemical formula 1, 0.3 ≤ a ≤ 0.7, 0.3 ≤ b ≤ 0.7, and 0.3 ≤ c ≤ 0.

7.

5. The capacity of oxygen due to oxidation-reduction is Li 1+x (Ni y Mn 1-y ) 1-x O 2 and / or Li 2 MnO 3 The positive electrode active material for a lithium secondary battery according to claim 1, which exhibits the effect of [the specified method].

6. The ratio of the volume expressed by the oxidation-reduction of oxygen to the total volume of the positive electrode active material is less than 15%. The ratio of the capacity expressed by the oxidation-reduction of oxygen to 100% of the total capacity of the positive electrode active material is calculated by formula 1, according to the positive electrode active material for lithium secondary battery according to claim 1: [Formula 1] {(X-Y) / X}×100 In Equation 1, X is the discharge capacity in the second cycle of the first set, and Y is the discharge capacity in the second cycle of the second set. The first and second sets mean that half cells are manufactured using a positive electrode to which the positive electrode active material is applied, and charging and discharging are performed under the following conditions, with the second set being performed immediately after the first set. [Set 1] (1) First cycle: Charge to 4.65V with a constant current of 0.1C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.1C. (2) Second cycle: Charge to 4.45V with a constant current of 0.2C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C. [Set 2] (1) First cycle: Charge to 4.45V with a constant current of 0.2C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C. (2) Second cycle: Charge to 4.45V with a constant current of 0.2C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C.

7. The positive electrode active material for a lithium secondary battery according to claim 6, wherein the upper limit voltage of the first cycle of the first set is 4.55V or more and 4.8V or less.

8. The average discharge voltage of the positive electrode active material is 3.83V (vs. Li / Li + The positive electrode active material for a lithium secondary battery according to claim 1, wherein the above is true.

9. X-ray diffraction analysis [Math 1] The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio of the peak intensity of the (020) plane of the C2 / m space group to the peak intensity of the (003) plane of the space group is 2% or less.

10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the reversible discharge capacity ratio calculated by the following formula 2 is 72% or more: [Formula 2] (X / A) × 100 In Equation 2, A is the charge capacity of the first cycle of the first set, and X is the discharge capacity of the second cycle of the first set. The first set means that a half-cell is manufactured using a positive electrode to which the positive electrode active material is applied, and charging and discharging are performed under the following conditions. [Set 1] (1) First cycle: Charge to 4.65V with a constant current of 0.1C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.1C. (2) Second cycle: Charge to 4.45V with a constant current of 0.2C at 25°C, then maintain the voltage until the current value is 0.05C, and then discharge to 2.5V with a constant current of 0.2C.

11. The positive electrode active material for a lithium secondary battery according to claim 10, wherein the upper limit voltage of the first cycle of the first set is 4.55V or more and 4.8V or less.

12. The positive electrode active material for a lithium secondary battery according to claim 10, wherein the reversible discharge capacity ratio is 77% or more.

13. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the pellet density of the positive electrode active material exceeds 2.70 g / cc.

14. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the pellet density of the positive electrode active material is 2.71 g / cc to 2.85 g / cc.

15. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the residual lithium content on the surface of the positive electrode active material is 0.4% by weight or less.

16. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the residual lithium content on the surface of the positive electrode active material is 0.1% by weight or less.

17. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the a-lattice constant is 2.865 Å or greater as determined by X-ray diffraction analysis.

18. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the a-lattice constant is 2.875 Å or greater as determined by X-ray diffraction analysis.

19. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio of the c lattice constant to the a lattice constant by X-ray diffraction analysis is 4.968 or less.

20. A method for producing a positive electrode active material according to Claim 1, This includes mixing a precursor represented by chemical formula 2 with a lithium raw material and then heat-treating it. A method for producing a positive electrode active material, wherein the molar ratio of lithium in the lithium raw material to the total metal of the precursor satisfies 1.06 to 1.5: [Chemical formula 2] Ni y2 Mn 1-y2 (OH) 2 In chemical formula 2, 0.5 ≤ y² ≤ 0.

7.

21. The method for producing a positive electrode active material according to claim 20, wherein the heat treatment is performed at a temperature range of 700°C to 1100°C for 10 to 40 hours.

22. The heat treatment includes a heating step, a temperature maintenance step, and a cooling step. The method for producing a positive electrode active material according to claim 20, wherein the heating rate in the heating stage and the cooling rate in the cooling stage are, respectively, 1°C / min to 10°C / min.

23. A positive electrode for a lithium secondary battery comprising the positive electrode active material described in any one of claims 1 to 19.

24. The positive electrode according to claim 23, negative electrode, A separator located between the positive electrode and the negative electrode, and A lithium secondary battery containing an electrolyte.

25. The positive electrode according to claim 23, Negative electrode, and An all-solid-state secondary battery comprising a solid electrolyte layer located between the positive electrode and the negative electrode.

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