Positive electrode active material, positive electrode, and lithium secondary battery

Abstract

To provide a positive electrode active material, a positive electrode, and a lithium secondary battery that can operate at high voltage while maintaining price competitiveness, and that have improved initial charge / discharge capacity, initial charge / discharge efficiency, lifespan characteristics, capacity recovery rate, and energy density characteristics. [Solution] The positive electrode active material according to one embodiment is a positive electrode active material comprising a first positive electrode active material containing a lithium iron phosphate compound, a second positive electrode active material containing a lithium nickel composite oxide, and an irreversible positive electrode additive, wherein the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) is 1.5 to 8.5, and the irreversible positive electrode additive is contained in an amount of 0.1% to 1.9% by weight per 100% by weight of the positive electrode active material.

Description

[Technical Field]

[0001] This relates to positive electrode active materials, positive electrodes, and lithium secondary batteries. [Background technology]

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

[0003] Furthermore, in order to increase the size and mass production of lithium secondary batteries, there is a growing demand for new cathode active materials that are high-performance while also possessing safety and reliability. As one example, lithium iron phosphate-based cathode active materials are attracting attention because they are structurally stable, have high heat resistance, are made from abundant raw materials, and are cost-effective.

[0004] However, lithium iron phosphate-based cathode active materials have the disadvantage of low capacity and energy density. For the commercialization of such lithium iron phosphate-based cathode active materials, it is necessary to enable operation at high voltages and to improve initial charge / discharge capacity, initial charge / discharge efficiency, life characteristics, and energy density characteristics. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present invention provides a cathode active material, cathode, and lithium secondary battery that can operate at high voltage while maintaining price competitiveness, and that exhibit improved initial charge / discharge capacity, initial charge / discharge efficiency, lifespan characteristics, and energy density characteristics. [Means for solving the problem]

[0006] One embodiment provides a positive electrode active material comprising a first positive electrode active material containing a lithium iron phosphate compound, a second positive electrode active material containing a lithium nickel composite oxide, and an irreversible positive electrode additive, wherein the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) is 1.5 to 8.5, and the irreversible positive electrode additive is contained in an amount of 0.1% to 1.9% by weight per 100% by weight of the positive electrode active material.

[0007] Other embodiments provide a positive electrode comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector and containing the aforementioned positive electrode active material.

[0008] Another embodiment provides a lithium secondary battery comprising the aforementioned positive electrode, negative electrode, and electrolyte. [Effects of the Invention]

[0009] The positive electrode active material according to one embodiment can operate at high voltage while maintaining price competitiveness, and can improve initial charge / discharge capacity, initial charge / discharge efficiency, life characteristics, and energy density characteristics. [Brief explanation of the drawing]

[0010] [Figure 1] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 2] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 3] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 4] This figure schematically shows a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0011] The following describes specific embodiments in detail so that they can be easily implemented by those with ordinary skill in the art. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0012] In this specification, terms used are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0013] In this specification, “these combinations” means mixtures, laminates, composites, copolymers, alloys, blends, reaction products, etc. of the constituents.

[0014] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of implemented features, figures, stages, components, or combinations thereof, and should be understood not to presuppose the existence or possibility of adding one or more other features, figures, stages, components, or combinations thereof.

[0015] To clearly represent various layers and regions in the drawings, thicknesses are shown enlarged, and similar parts are given the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly on top of" another part, but also when there is another part in between. Conversely, when a part is said to be "directly on top of" another part, it means that there is no other part in between.

[0016] Furthermore, in this specification, "layer" includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a part of the surface.

[0017] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering, and the average particle size value can be calculated after counting the number of particles for each particle size range through data analysis. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) can mean. Also, unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume, obtained by measuring the size (diameter or length of the long axis) of more than 20 randomly selected particles in a scanning electron microscope image. 50 This could be the average particle size taken from ).

[0018] Here, "or" is not interpreted as having an exclusive meaning; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0019] The term "metal" is interpreted as encompassing the concepts of typical metals, transition metals, and metalloids.

[0020] positive electrode active material In one embodiment, a positive electrode active material is provided that includes a first positive electrode active material containing a lithium iron phosphate compound, a second positive electrode active material containing a lithium nickel composite oxide, and an irreversible positive electrode additive, wherein the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) is 1.5 to 8.5, and the irreversible positive electrode additive is contained in an amount of 0.1% to 1.9% by weight per 100% by weight of the positive electrode active material.

[0021] Lithium iron phosphate compounds, which offer excellent structural stability, high heat resistance, and competitive pricing, are attracting attention. However, when used alone, lithium iron phosphate compounds have the disadvantage of relatively low operating voltage, poor efficiency characteristics, and low energy density.

[0022] In one embodiment, the positive electrode active material is mixed with a lithium iron phosphate compound, a lithium nickel-based composite oxide capable of achieving high capacity and high energy density, and an irreversible positive electrode additive that can effectively compensate for lithium ion loss due to the negative electrode material, thereby increasing the operating voltage and improving efficiency characteristics, life characteristics, and energy density.

[0023] In particular, the positive electrode active material according to one embodiment can provide a lithium secondary battery that is excellent in initial charge / discharge capacity, efficiency, life characteristics, and energy density, while increasing the operating voltage, by controlling the weight ratio of the first positive electrode active material to the second positive electrode active material and the added content of the irreversible positive electrode additive to an optimal range.

[0024] The weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) may be 1.8-8, 2-7.5, 2.4-7, 3-6.5, 3.5-6, 3.7-5, or 3.9-4.5. When the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) satisfies the aforementioned range, the initial charge / discharge capacity, its efficiency, life characteristics, and energy density can be improved overall while maintaining price competitiveness. For example, when the weight ratio is less than 1.5, the first positive electrode active material is present in an excessively small amount compared to the second positive electrode active material, resulting in equivalent or superior initial charge / discharge capacity and energy density. However, this may increase the content of the more expensive second positive electrode active material, making it difficult to maintain price competitiveness and potentially resulting in lower efficiency. On the other hand, if the weight ratio exceeds 8.5, the first positive electrode active material may be present in an excessively large amount compared to the second positive electrode active material, resulting in inferior initial charge / discharge capacity and potentially excessively low energy density without satisfying the desired powder characteristics.

[0025] The irreversible cathode additive may be present in amounts of 0.15% to 1.8% by weight, 0.2% to 1.7% by weight, 0.3% to 1.6% by weight, or 0.5% to 1.5% by weight relative to 100% by weight of the cathode active material. When the content of the irreversible cathode additive satisfies the above range relative to 100% by weight of the cathode active material, the charge / discharge capacity is improved while simultaneously ensuring energy density without impairing powder properties, resulting in superior efficiency. When the amount of the irreversible cathode additive is less than 0.1% by weight relative to 100% by weight of the cathode active material, the capacity retention rate may be significantly inferior. When the amount of the irreversible cathode additive exceeds 1.9% by weight relative to 100% by weight of the cathode active material, the increased amount of the irreversible cathode additive results in superior capacity retention. However, this may lead to a relative decrease in the weight of the first and second cathode active materials, resulting in inferior charge / discharge efficiency and failure to satisfy the desired powder properties.

[0026] The following describes the specific details of the first positive electrode active material, the second positive electrode active material, and the irreversible positive electrode additive contained in the positive electrode active material.

[0027] First positive electrode active material The first positive electrode active material contains a lithium iron phosphate compound.

[0028] Lithium iron phosphate compounds can be represented, for example, by chemical formula 1 or chemical formula 2 below. [Chemical formula 1] Li a1 Fe (1-x1) M 1 x1 PO4 In chemical formula 1, 0.9 ≤ a1 ≤ 1.5 and 0 ≤ x1 ≤ 0.4, and M 1 is Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90 ≤ a1 ≤ 1.5 may also be, for example, 0.90 ≤ a1 ≤ 1.2 or 0.95 ≤ a1 ≤ 1.1. Also, 0 ≤ x1 ≤ 0.4, 0 ≤ x1 ≤ 0.3, 0 ≤ x1 ≤ 0.2, 0 ≤ x1 ≤ 0.1, or 0 ≤ x1 ≤ 0.05.

[0029] [Chemical formula 2] Li a2 Mn x2 Fe (1-x2-y2) M​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The first particle may be a secondary particle formed by the aggregation of multiple primary particles. The secondary particle of the first particle may have a spherical or ellipsoidal shape due to the close aggregation of primary particles with each other. The secondary particle can be described as an assembly. The average particle size (D) of the secondary particle of the first particle. 50 The particle size may be, for example, 5 μm to 20 μm, 6 μm to 20 μm, or 6 μm to 15 μm. The average particle size (D) of the secondary particles of the first particle. 50 ) is the average particle size of the second particle, as described later (D 50 It may be larger than ). The average particle size (D) of the primary particles that make up the secondary particles of the first particle. 50 The wavelength may be 0.1 μm to 2 μm, 0.1 μm to 1.2 μm, or 0.5 μm to 0.9 μm, and may be 500 nm or less, for example, 10 nm to 400 nm, 100 nm to 300 nm, or 100 nm to 200 nm.

[0034] The average particle size of the secondary particles of the first particle (D 50 As an example, the particle size of a particle whose cumulative volume in the particle size distribution is 50% by selecting more than 30 first particles arbitrarily from electron microscope images of the first positive electrode active material and measuring the particle size, is (D 50 ) may be taken as the average particle size. The average particle size of the primary particles that make up the secondary particles of the first particle is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by electron microscope images of the surface or cross-section of the first particle. 50 This could be the average particle size taken from ).

[0035] The secondary particles of the first particle may contain voids inside, and the porosity may be approximately 20% to 50%. As an example, the porosity can be measured by using an image analysis program such as ImageJ on a scanning electron microscope image of the cross-section of the first particle to determine the ratio of the area occupied by the voids inside the secondary particle to the cross-sectional area of ​​the secondary particle.

[0036] The second particle may have a single-particle form. The average particle size (D) of the second single particle is... 50The average particle size of the second particle (D 50 ) is the average particle size (D) of the secondary particles of the first particle. 50 It may be smaller than ), and the average particle size (D) of the primary particles that make up the secondary particles of the first particle. 50 ) may be the same as or even larger. The average particle size of the second particle can be measured by arbitrarily selecting more than 30 second particles from an electron microscope image of the first positive electrode active material and determining the particle size of the particle whose cumulative volume in the particle size distribution is 50% by volume (D 50 This could be the average particle size taken from ).

[0037] When the first positive electrode active material is in the form of a mixture of first and second particles, the weight ratio of the first and second particles is not specifically limited, but for example, the content of the first particles may be 10% to 80% by weight and the content of the second particles may be 20% to 90% by weight per 100% by weight of the first positive electrode active material. Alternatively, the content of the first particles may be 30% to 80% by weight and the content of the second particles may be 20% to 70% by weight. Or, the content of the first particles may be 40% to 60% by weight and the content of the second particles may be 40% to 60% by weight. When the content of the first and second particles per 100% by weight of the first positive electrode active material satisfies the above ranges, the density of the powder itself can be increased by improving the packing density through an appropriate ratio of the first and second particles, and based on this, the energy density can be improved.

[0038] For example, the first positive electrode active material may consist only of the second particle.

[0039] The first positive electrode active material may further include a carbon coating layer located on the surface of secondary particles, the surface of the primary particles forming the secondary particles, and / or on the surface of single particles. The carbon coating layer can improve the electrical conductivity of the first positive electrode active material and lower the resistance of the positive electrode. The carbon coating layer can be formed using at least one carbon raw material selected from, for example, polymers of glucose, sucrose, lactose, starch, oligosaccharides, polysaccharides, fructose, cellulose, furfuryl alcohol, block copolymers of ethylene and ethylene oxide, vinyl resins, cellulosic resins, phenolic resins, pitch resins, and tar resins. Specifically, the carbon coating layer can be formed by placing the carbon raw material on the surface of the first positive electrode active material particles and then performing a heat treatment process. For example, the carbon raw material and primary particles can be mixed and heat-treated to provide a carbon coating layer on the surface of the primary particles, and then secondary particles formed by agglomerating the primary particles can be produced through a subsequent process, or the carbon raw material and secondary particles can be mixed and heat-treated to form a carbon coating layer on the surface of the secondary particles.

[0040] The carbon coating layer may be present in an amount of 0.5% to 3% by weight per 100% by weight of the first particle, and in an amount of 1% to 2% by weight per 100% by weight of the second particle. For example, the carbon coating layer may be present in a higher amount in the first particle than in the second particle.

[0041] Second positive electrode active material The second positive electrode active material contains a lithium nickel-based composite oxide.

[0042] Lithium nickel-based composite oxides can be represented, for example, by the following chemical formula 3. [Chemical formula 3] Li a3 Ni x3 M 3 y3 M 4 z3 O 2-b3 X b3 In chemical formula 3, 0.9 ≤ a³ ≤ 1.2, 0.8 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.2, 0 ≤ z³ ≤ 0.2, 0.9 ≤ x³ + y³ + z³ ≤ 1.1, and 0 ≤ b³ ≤ 0.1, M 3 and M 4 Each of these is independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and M 3 and M 4 X is a distinct element from one another, and X is one or more elements selected from F, P, and S.

[0043] In chemical formula 3, the following may also be true: 0.8≦x3≦0.98, 0.01≦y3≦0.19, and 0.01≦z3≦0.19, 0.85≦x3≦0.98, 0.01≦y3≦0.14, and 0.01≦z3≦0.14, or 0.85≦x3≦0.95, 0.04≦y3≦0.14, and 0.01≦z3≦0.11.

[0044] Lithium nickel-based composite oxides can be represented by chemical formula 4 or chemical formula 5 below as specific examples. [Chemical formula 4] Li a4 Ni x4 Co y4 M 5 z4 O 2-b4 X b4 In chemical formula 4, 0.9≦a₄≦1.2, 0.8≦x₄≦0.99, 0.01≦y₄≦0.2, 0≦z₄≦0.19, 0.9≦x₄+y₄+z₄≦1.1, and 0≦b₄≦0.1, M 4 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0045] In chemical formula 4, 0.8≦x4≦0.98, 0.01≦y4≦0.19, and 0.01≦z4≦0.19, 0.85≦x4≦0.98, 0.01≦y4≦0.14, and 0.01≦z4≦0.14, or 0.85≦x3≦0.95, 0.04≦y3≦0.14, and 0.01≦z3≦0.11.

[0046] [Chemical formula 5] Li a5 Ni x5 Co y5 M 6 z5 M 7 w5 O 2-b5 X b5 In chemical formula 5, 0.9≦a5≦1.2, 0.8≦x5≦0.98, 0.01≦y5≦0.19, 0.01≦z5≦0.19, 0≦w5≦0.18, 0.9≦x5+y5+z5+w5≦1.1, and 0≦b5≦0.1, M 6 is Al, Mn, or a combination thereof, M 7 X is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0047] In chemical formula 5, 0.85≦x5≦0.98, 0.01≦y5≦0.14, 0.01≦z5≦0.14, and 0≦w5≦0.13, or 0.85≦x5≦0.95, 0.04≦y5≦0.14, 0.01≦z5≦0.11, and 0≦w5≦0.1.

[0048] The lithium nickel composite oxide may also be a high-nickel cathode active material. For example, in the lithium nickel composite oxide, the nickel content relative to 100 mol% of the total metal excluding lithium may be 80 mol% or more, for example, 85 mol% or more or 90 mol% or more, and may also be 100 mol% or less, 99 mol% or less, or 98 mol% or less. For example, in the lithium nickel composite oxide, the nickel content relative to 100 mol% of the total metal excluding lithium may be 80 mol% to 100 mol%, 80 mol% to 99 mol%, 80 mol% to 98 mol%, 85 mol% to 98 mol%, or 85 mol% to 95 mol%. Such a high-nickel cathode active material can achieve high capacity and high performance.

[0049] The second positive electrode active material may be in the form of secondary particles formed by the aggregation of multiple primary particles, or in the form of single particles, or in the form of a mixture thereof.

[0050] Average particle size of the second positive electrode active material (D 50 The particle size may be 1 μm to 20 μm, or 3 μm to 18 μm. The average particle size of secondary particles (D 50 The particle size may be 1 μm to 20 μm, or 3 μm to 18 μm. The average particle size (D) of the primary particles that make up the secondary particles. 50 The average particle size (D) of a single particle may be less than 1 μm, for example, 0.1 μm to 1 μm, 0.2 μm to 0.9 μm, 0.2 μm to 0.8 μm, or 0.3 μm to 0.6 μm. 50 The particle size may be 0.5 μm to 8 μm, or 1 μm to 5 μm. The average particle size is determined, for example, by measuring the size (particle size, major axis, or major axis length) of any 20 or more particles in a scanning electron microscope image, and determining the size of the particle whose cumulative volume in the particle size distribution is 50% by volume (D 50 This could be the result of calculating ( ).

[0051] The second positive electrode active material has an average particle size (D 50 Large particles with an average particle size of 9 μm to 20 μm (D 50The material may include small particles with a size of 1 μm to 9 μm, or combinations thereof. The large particles may be in the form of secondary particles formed by the aggregation of multiple primary particles, single particles, or mixtures thereof, and the small particles may also be in the form of secondary particles, single particles, or mixtures thereof. As an example, the second positive electrode active material may contain both large and small particles. In this case, the large and small particles may be mixed in a weight ratio of 20:80 to 95:5, for example, 30:70 to 90:10, 40:60 to 85:15, or 50:50 to 80:20. When the second positive electrode active material contains both large and small particles, the capacity, energy density, and lifetime characteristics can be improved.

[0052] Irreversible positive electrode additive During charging and discharging, some of the lithium (Li) contained in the positive electrode active material participates in the formation of an SEI (Solid Electrolyte Interface) film on the negative electrode surface, meaning it is converted into irreversible Li that no longer participates in the charge-discharge reaction. This can lead to a decrease in capacity. Irreversible positive electrode additives are compounds that act as sacrificial positive electrodes to compensate for the irreversible Li. They can decompose during initial charging to provide Li and do not participate in subsequent charge-discharge processes. By adding such irreversible positive electrode additives, the consumed lithium can be replenished, compensating for lithium loss and improving the battery's energy density, lifespan, stability, and capacity retention rate.

[0053] Irreversible cathode additives are compounds that act as sacrificial cathodes, such as Fe-containing oxides, Mn-containing oxides, and Co-containing oxides.

[0054] Fe-containing oxides can include Li5FeO4, LiFeO2, LiFe5O8, or combinations thereof. Mn-containing oxides include lithium-rich manganese oxides, such as Li6MnO4. Co-containing oxides include lithium-rich cobalt oxides, such as Li6CoO4.

[0055] An irreversible positive electrode additive according to one embodiment may include an Fe-containing oxide. Fe-containing oxides have higher electrochemical properties than Mn-containing oxides and can adequately compensate for irreversible Li, thereby increasing the utilization rate of the positive electrode active material. Furthermore, when a Co-containing oxide is used, during charging and discharging, Li6CoO4 decomposes to form Li2O and CoO, and the formed CoO in the electrolyte contains Co 2+ This can cause Co to dissolve and leach from the negative electrode, potentially degrading battery performance.

[0056] Fe-containing oxides may be in the form of secondary particles formed by the aggregation of multiple primary particles, single particles, or a mixture thereof. For example, Fe-containing oxides may be in the form of single particles.

[0057] Average particle size of Fe-containing oxides (D 50 The particle size (D) of the Fe-containing oxide may be 0.5 μm to 15 μm, for example, 1 μm to 14 μm, 2 μm to 13 μm, 3 μm to 12 μm, or 4 μm to 10 μm. 50 If the above range is satisfied, the compound density can be increased during subsequent cathode manufacturing. Average particle size (D) of Fe-containing oxides 50 ) For example, by arbitrarily selecting more than 30 Fe-containing oxides from electron microscope images of the positive electrode active material and measuring their particle size, the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% is determined. 50 This could be the average particle size taken from ).

[0058] The pellet density of the positive electrode active material is 2.2 g / cm³. 3 ~2.4g / cm 3 It may be 2.2 g / cm³, for example. 3 ~2.38 g / cm³ 3 , 2.2 g / cm³ 3 ~2.35 g / cm³ 3 , or 2.2 g / cm³ 3 ~2.33g / cm 3This may also be the case. The pellet density of the positive electrode active material can be calculated by dividing the mass of the positive electrode active material in pellet form obtained by placing 1.0 g of positive electrode active material in a mold and applying a pressure of 4 tons at a temperature of 25°C for 30 seconds by the volume. If the pellet density of the positive electrode active material satisfies the aforementioned range, the powder properties can be improved and the energy density can be increased. The pellet density of the positive electrode active material can be satisfied with the aforementioned range by controlling the weight ratio of the first positive electrode active material to the second positive electrode active material and the content of the irreversible positive electrode additive.

[0059] positive electrode A positive electrode according to one embodiment includes a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector and containing the aforementioned positive electrode active material. The positive electrode according to one embodiment, containing the aforementioned positive electrode active material, has improved overall battery performance, specifically by increasing the operating voltage while exhibiting high capacity, high efficiency, high energy density, and excellent life characteristics.

[0060] positive electrode current collector The positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the lithium secondary battery, and may be aluminum foil or stainless steel foil with a thickness of 10 μm to 15 μm.

[0061] Cathode active material layer The positive electrode active material layer contains the aforementioned positive electrode active material.

[0062] The specific details regarding the positive electrode active material are as described above.

[0063] The content of the positive electrode active material may be 60% to 99.9% by weight, 70% to 99.8% by weight, 80% to 99% by weight, or 90% to 98% by weight, based on 100% by weight of the positive electrode active material layer.

[0064] The positive electrode active material layer may further selectively include a binder, a conductive material, or a combination thereof.

[0065] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0066] The conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0067] The content of the binder in the positive electrode active material layer may be approximately 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer, and the content of the conductive material may be 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

[0068] The density of the positive electrode active material layer may be 2.2 g / cm 3 ~2.4 g / cm 3 For example, 2.2 g / cm 3 ~2.38 g / cm 3 、2.2 g / cm 3 ~2.35 g / cm 3 、or 2.2 g / cm 3 ~2.33 g / cm 3This may also be the case. If the density of the positive electrode active material layer satisfies the aforementioned range, high charge-discharge efficiency can be achieved while realizing high capacity per unit volume. The density of the positive electrode active material layer refers to the ratio of weight to volume of the positive electrode active material layer in a rolled positive electrode. The density of the positive electrode active material layer can be measured by measuring the cross-sectional area, thickness, and weight of the positive electrode active material layer excluding the positive electrode current collector, calculating the volume by multiplying the cross-sectional area and thickness, and then dividing the weight by the volume.

[0069] Lithium-ion rechargeable battery A lithium secondary battery according to one embodiment includes the positive electrode, negative electrode, and electrolyte described above. The lithium secondary battery may also include a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte.

[0070] A lithium secondary battery according to one embodiment includes the aforementioned positive electrode active material, resulting in overall improved battery performance. Specifically, it can exhibit high capacity, high efficiency, high energy density, and excellent lifespan characteristics while increasing the operating voltage.

[0071] For example, if the initial charge capacity measured by charging and discharging at a 0.2C rate on the positive electrode is 165mAh / g or more, the initial discharge capacity is 153mAh / g or more, the charge / discharge efficiency is 90% or more, and after 50 charge / discharge cycles, the ratio of the discharge capacity after 50 cycles to the initial discharge capacity, i.e., the lifespan, is 97% or more, the energy density is 1200Wh / L or more, and price competitiveness can be ensured at the same time.

[0072] Lithium secondary batteries are 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, where Figure 1 is cylindrical, Figure 2 is prismatic, 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 in which a separator 30 is interposed 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 tap 11 and a positive electrode terminal 12, a negative electrode lead tap 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode taps 70, namely a positive electrode tap 71 and a negative electrode tap 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0073] negative electrode The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material and may further optionally include a binder, a conductive material, or a combination thereof.

[0074] The negative electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the lithium secondary battery, and may be copper foil with a thickness of 10 μm to 15 μm.

[0075] The negative electrode active material includes a substance capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a substance that can be doped and dedoped with lithium, or a transition metal oxide.

[0076] As a substance capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0077] As an alloy of 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.

[0078] As a substance capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. Examples of the Si-based negative electrode active material include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), an Si-Q alloy (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 may also be used. Examples of the Sn-based negative electrode active material include Sn, SnO2, an Sn alloy, or a combination thereof.

[0079] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50The particle size may 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. 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.

[0080] 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. Examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0081] 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.

[0082] 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 The size may be 10 nm to 1 μm, or 10 nm to 200 nm. Silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO xIt can be expressed as (0 < x ≤ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may 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.

[0083] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in mixture with the 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 mixture, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0084] <000042L>The negative electrode active material may be contained at 90% to 99.8% by weight or 94% to 99% by weight based on 100% by weight of the negative electrode active material layer.

[0085] The binder serves to well adhere the negative electrode active material particles to each other and also well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0086] 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. <00004Z9> Note: There seems to be a typo in ID=9 where it should probably be "ID=9 " instead of "ID=9 <000042L> " and in ID=20 where it should be "ID=20

[0087] " instead of "ID=20 <00004Z9> ". Also, the tags are preserved as per the instructions but some of the tags might be specific to a particular document format and might need further context to fully understand their significance.The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated 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.

[0088] When using an aqueous binder 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. As the alkali metal, Na, K, or Li can be used.

[0089] 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.

[0090] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause 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 in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0091] The binder content may be 0.1% to 5% by weight relative to 100% by weight of the negative electrode active material layer, and the conductive material content may be 0.1% to 5% by weight relative to 100% by weight of the negative electrode active material layer.

[0092] electrolyte The electrolyte for lithium secondary batteries may be, for example, an electrolyte solution, which contains a non-aqueous organic solvent and a lithium salt.

[0093] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0094] As carbonate solvents, 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) can be used. As ester solvents, methyl acetate, ethyl acetate, n-propyl acetate, methyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone can be used. As ether solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. In addition, as a ketone solvent, cyclohexanone can be used. As alcoholic 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.

[0095] Non-aqueous organic solvents can be used alone or in combination of two or more, and the mixing ratio when using two or more can be appropriately adjusted according to the desired battery performance, which should be widely understood by those working in this field.

[0096] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0097] The non-aqueous organic solvent may further contain aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0098] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0099] Typical examples of ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0100] 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(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0101] The lithium salt concentration should ideally be within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte will have appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0102] 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, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0103] 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.

[0104] 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, and polytetrafluoroethylene (e.g., Teflon®), or from a copolymer or mixture of two or more of these polymers.

[0105] 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.

[0106] 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.

[0107] Inorganic materials may include, but are 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) of the inorganic particles. 50 The wavelength can be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0108] Organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are laminated together.

[0109] The thickness of the coating layer may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0110] Examples and comparative examples of the present invention are described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to these examples. [Examples]

[0111] Example 1-1 (1) Manufacturing of positive electrode active material As the first positive electrode active material, the average particle size (D 50 LiMn in single-particle form with a diameter of approximately 600 nm 0.5 Fe 0.5 PO4, as the second positive electrode active material, average particle size (D 50Large particles and average particle size (D) are approximately 14.7 μm. 50 A lithium nickel-based composite oxide (LiNi) is a mixture of small particles, approximately 3 μm in size, in a weight ratio of 64:36. 0.9 Co 0.08 Al 0.02 O2), and as an irreversible positive electrode additive, average particle size (D 50 The positive electrode active material was prepared by mixing Li5FeO4 in single-particle form, with a diameter of approximately 10 μm. In this case, all large and small particles of the second positive electrode active material were in single-particle form.

[0112] (2) Manufacturing of the positive electrode A positive electrode active material composition was prepared by mixing a positive electrode active material, polyvinylidene fluoride as a binder, and carbon nanotubes as a conductive material in a weight ratio of 97:1:2 (positive electrode active material:binder:conductive material). This was dispersed in N-methylpyrrolidone solvent to produce a positive electrode active material slurry, which was then coated onto a 13.5 μm thick Al foil, dried, and rolled to produce a positive electrode.

[0113] (3) Manufacturing of lithium secondary batteries A negative electrode active material slurry was prepared by dispersing 97.5% by weight of graphite as the negative electrode active material, 1.5% by weight of carboxymethylcellulose and 1% by weight of styrene-butadiene rubber as binders in distilled water. This slurry was coated onto a 10 μm thick Cu foil, dried, and rolled to produce the negative electrode.

[0114] An electrode assembly was manufactured by interposing a 10 μm thick polyethylene separator between the positive and negative electrodes, inserting it into a case, and then injecting an electrolyte to produce a lithium secondary battery (100 mAh level pouch cell). As the electrolyte, a solvent containing EC (ethylene carbonate):EMC (ethyl methyl carbonate):DMC (dimethyl carbonate) mixed in a volume ratio of 2:4:4 with 1.15 M LiPF6 dissolved in it was used.

[0115] Examples 1-2 to 2-4 and Comparative Examples 1-1 to 2-2 In Example 1-1, the positive electrode active material, positive electrode, and lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the first positive electrode active material, the second positive electrode active material, and the irreversible positive electrode additive were mixed according to Table 1 below. In Table 1 below, the content of the irreversible positive electrode additive was calculated based on 100% by weight of the positive electrode active material, and the weight ratio of the first positive electrode active material (a) to the second positive electrode active material (b) (a / b) was calculated by dividing the content of the first positive electrode active material contained in the positive electrode active material by the content of the second positive electrode active material, and rounding the result to two decimal places.

[0116] [Table 1]

[0117] Evaluation example (1) Measurement of initial charge / discharge capacity and efficiency The lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 were charged to a voltage of 3.8V at a rate of 0.2C at 25°C and discharged to a voltage of 2.5V at a rate of 0.2C to measure their initial charge / discharge capacity. Using this data, the initial charge / discharge efficiency was calculated using Equation 1 below. The results are shown in Table 2 below. In addition, the lithium secondary batteries manufactured in Examples 2-1 to 2-4 and Comparative Example 2-1 were measured for initial charge / discharge capacity under the same conditions as the lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3, and the results are shown in Table 3 below. On the other hand, Comparative Example 2-2's life characteristics did not meet the required level for commercial lithium secondary batteries (e.g., ≥95%), making actual application impossible. Therefore, the initial charge / discharge capacity data was omitted as it has no practical significance for technical judgment. [Formula 1] Initial charge / discharge efficiency (%) = (Discharge capacity in the first cycle / Charge capacity in the first cycle) × 100

[0118] (2) Average voltage measurement The average voltage at a state of charge (SOC) of 50% during initial discharge of the lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 is shown in Table 2 below. Specifically, the average voltage was obtained by integrating the area under the discharge voltage curve (voltage-capacity graph) after the initial charge and discharge of the lithium secondary battery, and dividing the integral value by the discharge capacity. In addition, the average voltage of the lithium secondary batteries manufactured in Examples 2-1 to 2-4 and Comparative Example 2-1 was measured under the same conditions as the lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3, and the results are shown in Table 3 below. On the other hand, Comparative Example 2-2's life characteristics do not meet the required level for commercial lithium secondary batteries (e.g., ≥95%), making actual application impossible, and the average voltage data is omitted as it has no practical significance for technical judgment.

[0119] (3) Life characteristics After the initial charge and discharge of the lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3, the batteries were then charged at 45°C with a constant current at a 1C rate until the voltage reached 3.8V, and then discharged with a constant current at a 1C rate until the voltage reached 2.5V. This cycle was repeated 50 or more times, and the ratio of the 50-cycle discharge capacity to the initial discharge capacity was calculated using Equation 2 below and is shown in Table 2. In addition, the 50-cycle discharge capacity of the lithium secondary batteries manufactured in Examples 2-1 to 2-4 and Comparative Example 2-1 was measured under the same conditions as the lithium secondary batteries manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3. The lithium secondary batteries manufactured in Examples 2-1 to 2-4 and Comparative Example 2-1 meet the required lifespan characteristics of commercial lithium secondary batteries (e.g., ≥95%). However, Comparative Example 2-2 does not meet the required lifespan characteristics of commercial lithium secondary batteries (e.g., ≥95%), making it impractical for actual use, and is therefore omitted from Table 3 below. [Formula 2] Lifespan [%] = [Discharge capacity at cycle 50 / Discharge capacity at cycle 1] × 100

[0120] (4) Pellet density measurement 1.0 g of the positive electrode active material produced in Examples 1-1 to 2-4 and Comparative Examples 1-1 to 2-1 was placed in a mold, and a pressure of 4 tons was applied for 30 seconds at a temperature of 25°C. The pellet density was calculated by dividing the mass of the positive electrode active material in pellet form by its volume, and the results are shown in Tables 2 and 3 below. On the other hand, Comparative Example 2-2's life characteristics did not meet the required level for commercial lithium secondary batteries (e.g., ≥95%), making it impractical for actual application, and the pellet density data was omitted as it had no substantial meaning for technical judgment.

[0121] (5) Energy density measurement The energy density per unit volume (capacity × average voltage / volume = AhV / L = Wh / L) of the lithium secondary batteries manufactured in Examples 1-1 to 2-4 and Comparative Examples 1-1 to 2-2 was relatively evaluated based on the volume difference, and the results are shown in Tables 2 and 3 below. On the other hand, Comparative Example 2-2's life characteristics did not meet the required level for commercial lithium secondary batteries (e.g., ≥95%), making it impossible to apply in practice, and the energy density data was omitted as it had no practical significance for technical evaluation.

[0122] [Table 2]

[0123] [Table 3]

[0124] conclusion Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 were manufactured by fixing the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) at a level of 3.85 to 3.98, with an error range of ±0.2, to approximately 4, and varying the weight percentage of the irreversible positive electrode additive. Furthermore, Table 3 below shows that Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-2 were manufactured by fixing the content of the irreversible positive electrode additive to 1% by weight and varying the weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b).

[0125] Referring to Tables 1 and 2, when the weight ratio of the first positive electrode active material (a) to the second positive electrode active material (b) (a / b) is fixed at approximately 4, considering the error range (±0.2), the lithium secondary batteries of Examples 1-1 to 1-3, in which the content of the irreversible positive electrode additive is 0.5% to 1.5% by weight relative to 100% by weight of the positive electrode active material, can be seen to be more efficient and have equivalent or improved energy density compared to the lithium secondary batteries of Comparative Examples 1-1 to 1-3, which contain an excessive amount of the irreversible positive electrode additive.

[0126] As a result, the weight of the first and second positive electrode active materials decreases as the weight of the irreversible positive electrode additive increases, leading to a decrease in efficiency and energy density. Therefore, by adjusting the weight of the irreversible positive electrode additive within an appropriate range, it is possible to provide a lithium secondary battery with superior initial charge / discharge capacity, efficiency, life characteristics, and energy density.

[0127] Referring to Tables 1 and 3, when the content of the irreversible positive electrode additive is fixed at 1% by weight relative to 100% by weight of the positive electrode active material, it was confirmed that lithium secondary batteries of Examples 2-1 to 2-4, where the weight ratio of the first positive electrode active material (a) to the second positive electrode active material (b) (a / b) satisfies 1.5 to 8.5, exhibit superior initial charge / discharge capacity, average voltage, pellet density, and energy density.

[0128] On the other hand, when the content of the irreversible positive electrode additive was fixed at 1% by weight relative to 100% by weight of the positive electrode active material, in Comparative Example 2-1, where the weight ratio of the first positive electrode active material (a) to the second positive electrode active material (b) (a / b) exceeded 8.5, it was confirmed that the initial charge / discharge capacity, average voltage, pellet density, and energy density were generally lower compared to Examples 2-1 to 2-4.

[0129] Furthermore, when the content of the irreversible positive electrode additive is fixed at 1% by weight relative to 100% by weight of the positive electrode active material, in the case of Comparative Example 2-2, where the weight ratio of the first positive electrode active material (a) to the second positive electrode active material (b) (a / b) is less than 1.5, the life characteristics do not reach the required level for commercial lithium secondary batteries (e.g., ≥95%) as described above, making actual application impossible. In addition, Comparative Example 2-2, which contains an excessive amount of the more expensive second positive electrode active material compared to Examples 2-1 to 2-4, may hinder the securing of price competitiveness.

[0130] As a result, if the weight of the irreversible positive electrode additive is fixed and only the weight ratio of the first positive electrode active material to the second positive electrode active material is adjusted, there is a problem that if the second positive electrode active material is included in an excessively large amount, the life characteristics will not reach the required level for commercial lithium secondary batteries (e.g., ≥95%). If the first positive electrode active material is included in an excessively large amount, the life characteristics required for commercial lithium secondary batteries will be satisfied, but there is a problem that the initial charge / discharge capacity, average voltage, pellet density, and energy density will generally decrease. In other words, by adjusting the weight ratio (a / b) of the first positive electrode active material to the second positive electrode active material (b) to an appropriate range, it is possible to provide a lithium secondary battery that satisfies the life characteristics required for commercial lithium secondary batteries while simultaneously providing excellent performance in all aspects of initial charge / discharge capacity, average voltage, pellet density, and energy density.

[0131] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. It can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention. [Explanation of Symbols]

[0132] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tap 71: Positive Tap 72: Negative electrode tap

Claims

1. First positive electrode active material containing a lithium iron phosphate compound, Second cathode active material containing lithium nickel-based composite oxide, and Irreversible positive electrode additive A positive electrode active material containing, The weight ratio (a / b) of the first positive electrode active material (a) to the second positive electrode active material (b) is 1.5 to 8.

5. The irreversible positive electrode additive is present in an amount of 0.1% to 1.9% by weight relative to 100% by weight of the positive electrode active material. Cathode active material.

2. The lithium iron phosphate compound is defined by the following chemical formula 1 or chemical formula 2: [Chemical formula 1] Li a1 Fe (1-x1) M 1 x1 PO 4 (In chemical formula 1, 0.9 ≤ a1 ≤ 1.5 and 0 ≤ x1 ≤ 0.4, M 1 (These are Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or combinations thereof.) [Chemical formula 2] Li a2 Mn x2 Fe (1-x2-y2) M 2 y2 PO 4 (In chemical formula 2, 0.9 ≤ a² ≤ 1.5, 0.1 ≤ x² ≤ 0.9, 0 ≤ y² < 0.9, M 2 (These are Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or combinations thereof.) The positive electrode active material according to claim 1, as represented by [the specified formula].

3. The lithium iron phosphate compound is LiFePO 4 LiMn 0.7 Fe 0.3 PO 4 LiMn 0.6 Fe 0.4 PO 4 LiMn 0.5 Fe 0.5 PO 4 LiMn 0.4 Fe 0.6 PO 4 LiMn 0.3 Fe 0.7 PO 4 The positive electrode active material according to claim 1, or a combination thereof.

4. The first positive electrode active material is in the form of first particles, second particles, or a mixture thereof. The first particle has an average particle size (D 50 Multiple primary particles with a size of 0.1 μm to 2 μm are aggregated, resulting in an average particle size (D 50 ) is a secondary particle form with a size of 5 μm to 20 μm, The second particle has an average particle size (D 50 ) is a single-particle form with a size of 100 nm to 7 μm. The positive electrode active material according to claim 1.

5. The positive electrode active material according to claim 4, wherein the first positive electrode active material consists of second particles.

6. The aforementioned lithium nickel-based composite oxide has the following chemical formula 3: [Chemical formula 3] Li a3 Ni x3 M 3 y3 M 4 z3 O 2-b3 X b3 (In chemical formula 3, 0.9 ≤ a³ ≤ 1.2, 0.8 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.2, 0 ≤ z³ ≤ 0.2, 0.9 ≤ x³ + y³ + z³ ≤ 1.1, and 0 ≤ b³ ≤ 0.1, M 3 and M 4 Each is independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, M 3 and M 4 (The elements are all different from each other, and X is one or more elements selected from F, P, and S.) The positive electrode active material according to claim 1, as represented by [the specified formula].

7. The positive electrode active material according to claim 1, wherein the lithium nickel-based composite oxide has a nickel content of 80 mol% or more relative to 100 mol% of the total metal excluding lithium.

8. The second positive electrode active material has an average particle size (D 50 Large particles with an average particle size of 9 μm to 20 μm (D 50 The positive electrode active material according to claim 1, comprising small particles having a size of 1 μm to 9 μm, or a combination thereof.

9. The positive electrode active material according to claim 8, wherein the weight ratio of the large particles to the small particles is 20:80 to 95:

5.

10. The aforementioned irreversible positive electrode additive is Li 5 FeO 4 LiFeO 2 LiFe 5 O 8 The positive electrode active material according to claim 1, or a combination thereof.

11. The non-reversible positive electrode additive has an average particle size (D 50 The positive electrode active material according to claim 1, wherein the particle size is 0.5 μm to 15 μm and is in single-particle form.

12. The pellet density of the positive electrode active material is 2.2 g / cm³. 3 ~2.4 g / cm 3 The positive electrode active material according to claim 1.

13. A positive electrode comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector and containing a positive electrode active material according to any one of claims 1 to 12.

14. The positive electrode according to claim 13, wherein the positive electrode active material layer further comprises a binder, a conductive material, or a combination thereof.

15. A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte according to claim 13.

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