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

Abstract

To provide a positive electrode active material that can achieve high density, high capacity, and a long life characteristic, a positive electrode including the same, and a lithium secondary battery.SOLUTION: A positive electrode active material includes a first positive electrode active material containing layered lithium nickel manganese complex oxide, and a second positive electrode active material containing lithium manganese rich complex oxide in which the molar ratio of lithium to the entire metal excluding lithium is 1.1 to 3 and the manganese content per 100 mol% of the entire metal excluding lithium is 60 mol% or more. A positive electrode including this positive electrode active material and a lithium secondary battery are also provided.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as the driving power source for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted on using high-energy-density lithium secondary batteries as driving power sources or power storage sources for hybrid and electric vehicles.

[0003] In order to realize lithium secondary batteries that meet these applications, various positive electrode active materials have been studied. Among them, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, lithium cobalt oxide, etc. are mainly used as positive electrode active materials. However, in recent years, while the demand for large-sized, high-capacity, or high-energy density lithium secondary batteries has rapidly increased, the supply of positive electrode active materials containing the rare metal cobalt is expected to be extremely short. In other words, since cobalt is expensive and there are not many remaining reserves, it is necessary to develop positive electrode active materials that do not contain cobalt or have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode active material capable of realizing high density, high capacity, and long life characteristics, and a positive electrode and a lithium secondary battery using the same. [Means for solving the problem]

[0005] In one embodiment of the present invention, there is provided a positive electrode active material comprising a first positive electrode active material containing a layered lithium nickel-manganese based composite oxide, and a second positive electrode active material containing a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3 and the manganese content is 60 mol % or more relative to 100 mol % of all metals excluding lithium.

[0006] In another embodiment of the present invention, a positive electrode is provided that includes 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 including the positive electrode active material described above.

[0007] In yet another embodiment of the present invention, there is provided a lithium secondary battery comprising the positive electrode, the negative electrode, and an electrolyte. Effect of the Invention

[0008] The positive electrode active material according to an embodiment of the present invention minimizes production costs and maximizes capacity, while ensuring long life characteristics and improving high voltage characteristics and high temperature storage characteristics. A lithium secondary battery using the positive electrode active material can exhibit high initial charge / discharge capacity and efficiency even under high voltage driving conditions, realize long life characteristics, and effectively suppress gas generation problems caused by high voltage and high temperature driving. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view illustrating a lithium secondary battery according to an embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a lithium secondary battery according to an embodiment. [Diagram 3] 1 is a cross-sectional view illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view illustrating a lithium secondary battery according to an embodiment. [Diagram 5] 3 is a scanning electron microscope (SEM) image of large particles of a first positive electrode active material prepared in Example 1. [Figure 6]3 is a scanning electron microscope (SEM) image of large particles of a first positive electrode active material prepared in Example 1. [Figure 7] 1 is a SEM image of small particles of a first positive electrode active material prepared in Example 1. [Figure 8] 1 is a SEM image of small particles of a first positive electrode active material prepared in Example 1. [Figure 9] 1 is a SEM image of a second positive electrode active material prepared in Example 1. [Figure 10] 1 is a SEM image of a second positive electrode active material prepared in Example 1. [Figure 11] 1 is a graph comparing the positive electrode mixture densities produced in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is not limited to the embodiments described herein, but may be embodied in various different forms.

[0011] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless otherwise clearly indicated in the context.

[0012] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0013] It is to be understood that the terms "including," "comprising," or "having" are intended to specify the presence of embodied features, numerals, steps, components, or combinations thereof, but do not preclude the presence or additional possibility of one or more other features, numerals, steps, components, or combinations thereof.

[0014] In the drawings, the thickness of the various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0015] Further, the term "layer" as used herein includes not only a shape formed on the entire surface when observed in a plan view, but also a shape formed on a portion of the surface.

[0016] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope or a scanning electron microscope image. Alternatively, it can be measured using a dynamic light scattering method, and data analysis can be performed to count the number of particles for each particle size range, and the average particle size can be calculated from this. Unless otherwise defined, the average particle size is the diameter (D 50 In addition, unless otherwise defined, the average particle size is the diameter (D) of the particle that occupies 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or major axis length) of 20 or more particles randomly selected from a scanning electron microscope image. 50 ) may be taken as the average particle size.

[0017] As used herein, "or" is not to be construed in an exclusive sense, e.g., "A or B" is to be construed as including A, B, A+B, etc.

[0018] The term "metal" is interpreted as including general metals, transition metals, and metalloids (semimetals).

[0019] positive electrode active material In one embodiment, a positive electrode active material is provided, comprising: a first positive electrode active material containing a layered lithium nickel-manganese based composite oxide; and a second positive electrode active material containing a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3 and the manganese content is 50 mol % or more relative to 100 mol % of all metals excluding lithium.

[0020] The positive electrode active material does not contain expensive cobalt or contains only a small amount of cobalt, and contains low-value manganese, thereby reducing costs and increasing mass productivity, and achieving excellent characteristics at high voltage and high density while further increasing capacity. Since such a positive electrode active material is low-cost and satisfies high capacity, high voltage and high density characteristics, when a lithium secondary battery using the positive electrode active material is installed in an electric vehicle or a hybrid vehicle, it can enable long-distance driving.

[0021] With respect to the total weight of the first and second positive electrode active materials being 100%, the first positive electrode active material is included at 60% to 95% by weight, for example, 70% to 95% by weight, or 80% to 90% by weight, and the second positive electrode active material is included at 5% to 40% by weight, for example, 5% to 30% by weight, or 10% to 20% by weight. When mixed in the above ratios, it is possible to maximize the energy density and realize high capacity.

[0022] First positive electrode active material In recent years, as the price of cobalt, a rare metal, has soared, there is a demand for the development of positive electrode active materials that do not contain cobalt or that have a reduced cobalt content. Among them, positive electrode active materials with an olivine crystal structure such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP), or a spinel crystal structure such as lithium manganese oxide (LMO), have limitations in achieving high capacity due to the small amount of lithium that can be utilized within the structure. Layered lithium nickel-manganese positive electrode active materials have excellent capacity and efficiency characteristics because they can increase the amount of lithium within the structure, making them suitable as materials for high-capacity batteries. However, the removal of cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and makes it difficult to ensure long life characteristics. In addition, the removal of cobalt accelerates side reactions between the positive electrode active material and the electrolyte under high voltage and high temperature conditions, increasing the amount of gas generated and reducing life characteristics.

[0023] Therefore, in one embodiment, a method is proposed for improving the capacity and life characteristics at high voltage of the first positive electrode active material by appropriately adjusting the ratio of nickel and manganese in the lithium nickel-manganese composite oxide, introducing other elements such as aluminum in addition to nickel and manganese, or introducing a uniform coating layer by applying an appropriate coating method.

[0024] Lithium nickel-manganese composite oxide In the lithium nickel-manganese composite oxide, the nickel content is 60 mol% or more relative to 100 mol% of all metals excluding lithium, and can be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%, etc. When the nickel content satisfies the above range, a high capacity can be realized, and structural stability can be improved even if the cobalt content is reduced.

[0025] The manganese content is, for example, 15 mol% or more relative to 100 mol% of all metals excluding lithium in the lithium nickel-manganese composite oxide, and can be, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%, etc. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity and improve structural stability.

[0026] The lithium nickel-manganese composite oxide may be, for example, a lithium nickel-manganese-aluminum composite oxide further containing aluminum in addition to nickel and manganese. When the composite oxide contains aluminum, it is advantageous to maintain a stable layered structure even if the cobalt element is excluded from the structure. The content of aluminum relative to 100 mol% of the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. When the aluminum content satisfies the above range, a stable layered structure can be maintained even if cobalt is excluded, and the problem of the structure collapsing due to charging and discharging can be suppressed, and the long life characteristics of the positive electrode active material can be realized.

[0027] According to one embodiment, the aluminum concentration may be uniform in the particles containing the lithium nickel-manganese composite oxide. That is, the aluminum concentration gradient is not present in the particles from the center to the surface, or the aluminum concentration is not higher or lower in the particles than in the inside, and the aluminum is uniformly dispersed in the particles. This structure can be obtained by synthesizing the composite oxide using nickel-manganese-aluminum hydroxide as a precursor by not doping aluminum during the synthesis of the lithium nickel-manganese composite oxide and using an aluminum raw material in the preparation of the precursor. The particles may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the aluminum content in the primary particles is the same or similar regardless of the position of the primary particles. That is, when the primary particles are selected from any position in the cross section of the secondary particles and the aluminum content is measured in the inside of the primary particles, not at the interface of the primary particles, the aluminum content can be expressed as the same / similar / uniform regardless of the position of the primary particles, that is, whether the primary particles are close to the center or the surface of the secondary particles. In such a structure, even if cobalt is absent or present in only a very small amount, a stable layered structure can be maintained and no aluminum by-products or aluminum agglomerates are generated, thereby simultaneously improving the capacity, efficiency, and life characteristics of the positive electrode active material.

[0028] The lithium nickel-manganese composite oxide is specifically represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0029] In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0030] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.5, or 0.9 ≦ a1 ≦ 1.2 may hold. Further, Chemical Formula 1 contains aluminum, and in this case, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 ≦ z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied. For example, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 < z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied.

[0031] In Chemical Formula 1, for example, 0.6 ≦ x1 ≦ 0.79, 0.6 ≦ x1 ≦ 0.78, 0.6 ≦ x1 ≦ 0.75, 0.65 ≦ x1 ≦ 0.8, or 0.7 ≦ x1 ≦ 0.79, 0.1 ≦ y1 ≦ 0.35, 0.1 ≦ y1 ≦ 0.30, 0.1 ≦ y1 ≦ 0.29, 0.15 ≦ y1 ≦ 0.39, or 0.2 ≦ y1 ≦ 0.3, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019, 0 ≦ w1 ≦ 0.28, 0 ≦ w1 ≦ 0.27, 0 ≦ w1 ≦ 0.26, 0 ≦ w1 ≦ 0.25, 0 ≦ w1 ≦ 0.24, 0 ≦ w1 ≦ 0.23, 0 ≦ w1 ≦ 0.22, 0 ≦ w1 ≦ 0.21, 0 ≦ w1 ≦ 0.2, 0 ≦ w1 ≦ 0.15, 0 ≦ w1 ≦ 0.1, or 0 ≦ w1 ≦ 0.09, etc. may hold.

[0032] As an example, the lithium nickel - manganese - based composite oxide may not contain cobalt or may contain a small amount, and the content of cobalt with respect to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0033] The particles containing the lithium nickel-manganese composite oxide may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, or may be single particles, or a combination thereof. The secondary particles and single particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles constituting the secondary particles may be spherical, ellipsoidal, plate-like, or a combination thereof.

[0034] Coating Layer The first positive electrode active material may include a core particle containing a layered lithium nickel-manganese composite oxide, and a coating layer located on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

[0035] The lithium nickel-manganese composite oxide is susceptible to chemical attack by components in the electrolyte when the battery is operated under high voltage or high temperature conditions, and may undergo many side reactions with the electrolyte, which may result in a large amount of gas generation and reduced battery life and safety. However, by introducing a coating layer according to one embodiment, such problems can be solved.

[0036] The coating layer may be, for example, an Al coating layer containing Al, and may further include elements such as B, Mg, Ti, V, W, Y, and Zr. When an Al coating layer is introduced, the high voltage performance of the first positive electrode active material can be further improved.

[0037] The layered lithium nickel-manganese composite oxide has a significantly different content of residual lithium on the particle surface from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxide, lithium nickel-cobalt-aluminum composite oxide, and lithium cobalt-based oxide, and has many different surface properties, so that it is impossible to form a good coating layer with a uniform film shape by the existing coating method. Therefore, in one embodiment, (i) a coating solution in which salt is completely dissolved is first prepared by adding and mixing coating raw materials into an aqueous solvent, (ii) core particles are added to this coating solution and mixed to perform coating, and (iii) a uniform coating layer can be introduced to the first positive electrode active material by removing the solvent, drying, and then heat treating. It is a salt-dissolving wet coating method, and may be a pre-addition method in which the salt, which is the coating raw material, is first completely dissolved and then the active material particles are added. By this method, a uniform and thin film-shaped coating layer can be successfully formed on the surface of the layered lithium nickel-manganese composite oxide.

[0038] According to the coating method, the content of the coating element on the active material surface can be further increased compared to the general dry method or the post-addition wet method. For example, the coating content on the surface of the first positive electrode active material measured by EP-EDS analysis can be 5 at% to 35 at% relative to 100 at% of the total metals excluding lithium on the surface, for example, 5 at% to 30 at%, 5 at% to 25 at%, 5 at% to 25 at%, or 10 at% to 20 at%. Within this content range, the coating layer can effectively improve the high voltage characteristics without increasing the resistance of the first positive electrode active material.

[0039] The coating layer may be, for example, a film that continuously surrounds the surface of the core particle, for example, a shell that surrounds the entire surface of the core particle. This is different from a structure in which only a part of the surface of the core particle is partially coated. According to one embodiment, the coating layer may be formed in a form that entirely surrounds the surface of the core particle, but may be formed with a very thin and uniform thickness, so that the positive electrode active material does not increase in resistance or decrease in capacity, improves structural stability, effectively suppresses side reactions with the electrolyte, reduces gas generation under high voltage and high temperature conditions, and achieves long life characteristics.

[0040] According to the method, the thickness of the coating layer of the first positive electrode active material is 5 nm to 200 nm, for example, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 5 nm to 50 nm, or 10 nm to 50 nm. When the coating layer satisfies the above thickness range, the coating does not increase the resistance or decrease the capacity, but improves the structural stability of the positive electrode active material and effectively suppresses side reactions with the electrolyte. The thickness of the coating layer can be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and can be measured, for example, by EDS line profile analysis of a cross section of the positive electrode active material.

[0041] According to an embodiment, the coating layer has a thickness of tens to hundreds of nanometers and is uniform. For example, the deviation of the coating layer thickness within one positive electrode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the deviation of the coating layer thickness refers to the thickness of the coating layer within one positive electrode active material particle. The deviation of the coating layer thickness means, for example, that the thickness of 10 or more points is measured in an electron microscope image of a cross section of one positive electrode active material particle, the arithmetic average is calculated, and the absolute value of the difference between one data and the arithmetic average value is divided by the arithmetic average value and multiplied by 100. The deviation or standard deviation of the coating layer thickness satisfies the above range, which means that a coating layer of uniform thickness is well formed in the form of a film on the surface of the positive electrode active material particle, thereby improving the structural stability of the positive electrode active material, effectively suppressing side reactions with the electrolyte, and minimizing the increase in resistance and the decrease in capacity due to the coating.

[0042] The content of the coating element relative to 100 mol % of all metals excluding lithium in the entire first positive electrode active material varies depending on the type of coating element, but may be approximately 0.01 mol % to 5 mol %, for example, 0.05 mol % to 3 mol %, or 0.1 mol % to 2 mol %.

[0043] For example, when an Al coating layer is introduced, the Al content of the coating layer can be 0.1 mol % to 3.0 mol % relative to 100 mol % of all metals excluding lithium in the entire first positive electrode active material, and can be, for example, 0.1 mol % to 2.0 mol %, 0.5 mol % to 1.5 mol %, or 0.7 mol % to 1.3 mol %.

[0044] When an Al coating layer is introduced, the coating layer can include, for example, a layered type aluminum compound, such as aluminum oxide, lithium aluminum oxide, or a combination thereof, and can include LiAlO2 as an example.

[0045] Large and small particles In one embodiment, the first positive electrode active material contains a layered lithium nickel-manganese composite oxide having an average particle size (D 50 The average particle size (D 50 In this case, a positive electrode having a high energy density can be realized. 50 ) may be obtained by measuring the sizes (diameter or major axis length) of more than 20 random particles in a scanning electron microscope image of the positive active material to obtain a particle size distribution, and taking the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution as the average particle size.

[0046] The large particles may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the small particles may be in the form of secondary particles or single particles.

[0047] The large particles are contained in an amount of 60% by weight to 95% by weight, or 70% by weight to 90% by weight, and the small particles are contained in an amount of 5% by weight to 40% by weight, or 10% by weight to 30% by weight, based on a total of 100% by weight of the large particles and the small particles.

[0048] When the first positive electrode active material contains large particles and small particles, the large particles are contained in an amount of 40% by weight to 90% by weight, the small particles are contained in an amount of 5% by weight to 40% by weight, and the second positive electrode active material is contained in an amount of 5% by weight to 30% by weight, based on a total weight of the large particles, the small particles, and the second positive electrode active material being 100%. When such a mixing ratio is satisfied, the energy density and capacity can be maximized.

[0049] As an example, the average particle size (D 50 ) is the average particle size of the large particles (D 50 ) and the average particle size (D 50 In this case, the second positive electrode active material may be a type of medium particle, and the positive electrode may be in the form of a mixture of large particles, medium particles, and small particles, thereby effectively improving high voltage characteristics while maximizing energy density.

[0050] In one embodiment, the large particles may include a core particle in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and a coating layer located on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. The small particles may include a core particle in the form of a single particle, and a coating layer located on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof. This design can maximize performance at high voltages.

[0051] For example, the coating layer of the large particles may include Al, Zr, or a combination thereof, and the coating layer of the small particles may include Al, Y, or a combination thereof. This may be the optimal coating composition for each of the large particles and the small particles, and may further improve the capacity characteristics, life characteristics, etc. at high voltages.

[0052] For example, the coating layer of the large particles may contain Al, and the Al content of the coating layer may be 0.5 mol % to 2 mol % based on 100 mol % of all metals in the large particles excluding lithium. Also, the coating layer of the small particles may contain Al, and the Al content of the coating layer may be 0.1 mol % to 1 mol % based on 100 mol % of all metals in the small particles excluding lithium.

[0053] In this case, the coating layer of the small particles may further contain Y, and the Y content of the coating layer relative to 100 mol % of all metals excluding lithium in the small particles may be, for example, 0.01 mol % to 0.5 mol %.

[0054] Meanwhile, the first positive electrode active material may include a sulfur (S) component on the surface, which may be a characteristic derived by applying a sulfate-based coating material such as aluminum sulfate in the coating process.

[0055] Second positive electrode active material The second positive electrode active material includes a lithium-manganese-rich (LMR) composite oxide. LMR materials are positive electrode active materials with a layered structure that contain an excess of lithium and a relatively high manganese content, and in addition to the capacity expression based on the existing oxidation-reduction of transition metals, they apply a new principle of oxygen oxidation-reduction to express high capacity, while at the same time containing a high proportion of low-cost manganese, drawing attention as an ultra-low-cost next-generation positive electrode active material.

[0056] In the second positive electrode active material, the molar ratio of lithium to all metals excluding lithium is 1.1 to 3, and can be, for example, 1.2 to 2.5, 1.3 to 2.3, or 1.5 to 2.1. In addition, the content of manganese to all metals excluding lithium (100 mol%) in the second positive electrode active material is 60 mol% or more, and can be, for example, 60 mol% to 90 mol%, 60 mol% to 80 mol%, 60 mol% to 75 mol%, 60 mol% to 70 mol%, or 62 mol% to 68 mol%.

[0057] The lithium-manganese-rich composite oxide of the second positive electrode active material is represented by, for example, the following chemical formula 2. [Chemical formula 2] Li 1+x2 (Ni y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2

[0058] In Chemical Formula 2, 0.04≦x2≦0.5, 0.1≦y2≦0.5, 0.5≦z2≦0.9, and 0≦b2≦0.1; M 2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0059] In the above Chemical Formula 2, for example, 0.05≦x2≦0.4, or 0.06≦x2≦0.3, 0.2≦y2≦0.4 and 0.6≦z2≦0.8, or 0.3≦y2≦0.4 and 0.6≦z2≦0.7.

[0060] The second positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle size (D 50 ) is 3 μm to 13 μm, and can be, for example, 4 μm to 12 μm, 5 μm to 10 μm, or 6 μm to 9 μm.

[0061] In the lithium-manganese-rich composite oxide of the second positive electrode active material, the content of cobalt relative to 100 mol % of all metals excluding lithium may be 0 mol % to 0.01 mol %.

[0062] The second positive electrode active material has an a-lattice constant of 2.865A or more, for example, 2.870A or more, and may be 2.875A to 2.885A, as determined by X-ray diffraction analysis (XRD). As an example, the a-lattice constant of the positive electrode active material may be 2.875A or more. In addition, the ratio of the c-lattice constant to the a-lattice constant may be 4.968 or less, for example, 4.965 or less, 4.960 or less, and may be 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 caused by the second positive electrode active material can be effectively improved, the energy density can be improved, and the capacity characteristics and life characteristics in a high voltage region can be improved.

[0063] The residual lithium content on the surface of the second positive electrode active material is 0.3 wt% or less, for example, 0.2 wt% or less, 0.1 wt% or less, or 0.001 wt% to 0.1 wt%, which may be a feature that distinguishes it from high-nickel materials having a nickel content of more than 70 mol%.

[0064] Pellet Density The positive electrode active material according to one embodiment can achieve high pellet density. For example, the pellet density of the positive electrode active material can be 3.0 g / cc to 3.7 g / cc, for example, 3.1 g / cc to 3.6 g / cc, or 3.1 g / cc to 3.5 g / cc. A lithium secondary battery using such a positive electrode active material can achieve high energy density.

[0065] The pellet density can be measured by the following method. After weighing 3 g of the positive electrode active material, 2 The mold set was placed in a hydraulic press and pressed at a pressure of 4 ton (metric ton) for 30 seconds, after which the height was measured to measure the pellet density.

[0066] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material described above. The positive electrode active material layer may further include other types of positive electrode active materials in addition to the positive electrode active materials described above. The positive electrode active material layer may also optionally include a binder, a conductive material, or a combination thereof.

[0067] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm 2 ~40mg / cm 2 For example, 10 mg / cm 2 ~30mg / cm 2 or 10 mg / cm 2 ~20mg / cm 2In addition, the density of the positive electrode active material layer in the final rolled positive electrode may be 3.3 g / cc to 3.7 g / cc, for example, 3.3 g / cc to 3.6 g / cc, 3.4 g / cc to 3.58 g / cc, or 3.5 g / cc to 3.58 g / cc. When the positive electrode active material according to an embodiment is applied, it is advantageous to achieve such a loading level and positive electrode density, and a positive electrode satisfying the above-mentioned ranges of loading level and positive electrode density is suitable for realizing a lithium secondary battery with high capacity and high energy density.

[0068] binder The binder serves to make the positive electrode active material particles adhere well to each other and to 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0069] Conductive material The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause a chemical change in the battery that is constructed and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials containing copper, nickel, aluminum, silver, and the like in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0070] The content of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0071] The positive electrode current collector can be made of Al, but is not limited to this.

[0072] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte described above. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0073] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, and other types according to their shapes. FIGS. 1 to 4 are schematic diagrams showing a lithium secondary battery according to an embodiment, in which FIG. 1 shows a circular battery, FIG. 2 shows a square battery, and FIGS. 3 and 4 show a pouch battery. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 between a positive electrode 10 and a negative electrode 20, with a separator 30 interposed therebetween, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the 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 FIG. 1. In addition, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0074] The lithium secondary battery according to an embodiment is suitable for being charged at a high voltage or driven at a high voltage, and may be a battery with improved characteristics under high voltage conditions.

[0075] The lithium secondary battery includes a second positive electrode active material of a lithium-manganese-rich material, and in order to use the reversible positive electrode capacity of the second positive electrode active material, the first charge needs to be performed at 4.60V or more, for example, 4.65V. Subsequent charges are performed in a range lower than the first charge voltage, and since the lithium secondary battery according to an embodiment is designed to be driven in a high voltage region, the charge can be performed in a voltage range of 4.45V or more. For example, the charge voltage after the second cycle is 4.45V or more, for example, 4.45V to 4.6V, 4.45V to 4.55V, or 4.45V to 4.50V. By applying the positive electrode active material according to an embodiment, the lithium secondary battery can significantly reduce the amount of gas generation even when charged at a high voltage, and can achieve high capacity and long life characteristics.

[0076] negative electrode The negative electrode can include a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer including a negative electrode active material and can further include a binder, a conductive material, or a combination thereof.

[0077] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0078] The material capable of reversibly inserting / extracting lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0079] 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.

[0080] As the substance capable of doping and undoping the lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), an Si-Q alloy (wherein Q is an element selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, 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 can be used. As the Sn-based negative electrode active material, Sn, SnO2, an Sn alloy, or a combination thereof can be used.

[0081] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle diameter (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0082] 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 the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0083] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, based on 100% by weight of the silicon-carbon composite, the content of silicon may be 10% to 50% by weight, the content of crystalline carbon may be 10% to 70% by weight, and the content of amorphous carbon may be 20% to 40% by weight.

[0084] In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) may 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 may be represented by SiO x (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 diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0085] 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 is mixed with the carbon-based negative electrode active material, the mixing ratio may be 1:99 to 90:10 by weight.

[0086] binder The binder serves to adhere the negative active material particles to each other and to the current collector well. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0087] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymers, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0088] 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.

[0089] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0090] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0091] Conductive material The conductive material is used to impart electrical conductivity to the electrodes, and may be any material that does not cause chemical changes in the battery and is electronically conductive. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0092] 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 material.

[0093] Current collector The negative electrode current collector can 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 can be in foil, sheet, or foam form. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0094] electrolyte The electrolyte for a lithium secondary battery can be, by way of example, an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0095] The non-aqueous organic solvent serves as a medium through which the ions involved in the electrochemical reactions of the battery can migrate. The non-aqueous organic solvent may be a carbonate-, ester-, ether-, ketone-, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0096] Examples of the carbonate solvent 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), butylene carbonate (BC), etc. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of the ketone solvent include cyclohexanone. Examples of the alcohol solvent include ethyl alcohol and isopropyl alcohol. Examples of the aprotic solvent include nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0097] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When using in combination of two or more kinds, the mixing ratio may be appropriately adjusted according to the desired battery performance, which is widely understood by those working in the field.

[0098] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0099] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0100] The electrolyte may further contain a vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compound to improve the battery life.

[0101] Representative examples of the ethylene carbonate-based compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0102] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in the battery to enable basic lithium secondary battery operation and facilitate the movement of lithium ions between the positive and negative electrodes. Representative 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, LiN(C x F 2x+1 SO2)(C y F2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0103] The lithium salt is preferably used at a concentration within the range of 0.1 M to 2.0 M. If the lithium salt concentration is within the above range, the electrolyte has appropriate ion conductivity and viscosity, and therefore can exhibit excellent performance and allow lithium ions to migrate effectively.

[0104] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers of these may be used, and it is of course possible to use a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene.

[0105] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0106] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0107] The porous substrate can have a thickness of about 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.

[0108] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide, a structural unit derived from (meth)acrylic acid or a (meth)acrylate, and a second structural unit including at least one of a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0109] 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 ) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0110] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer including an organic material and a coating layer including an inorganic material.

[0111] The thickness of each of the coating layers may be from 0.5 μm to 20 μm, for example, from 1 μm to 10 μm, or from 1 μm to 5 μm.

[0112] Examples of the present invention and comparative examples are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0113] Example 1 1. Manufacturing of positive electrode active material (1) Preparation of large particles of the first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A first lithium nickel-manganese based composite oxide having a secondary particle shape with a particle size of about 14 μm was prepared.

[0114] Aluminum sulfate was added to the distilled water solvent and stirred at about 350 rpm for about 5 minutes to produce a coating solution. It was confirmed that the salt was completely dissolved in the coating solution and was colorless and transparent. 500 g of the first lithium nickel-manganese composite oxide was added to the continuously stirred coating solution for 1.5 minutes and stirred for about 45 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100 mol% of the total metal excluding lithium in the final large particles. The pH of the supernatant after stirring was completed was 5.5. The solvent was removed from the mixed solution using an aspirator and a filter press, and the solution was vacuum dried at 190°C to obtain a coating product.

[0115] The coated product was subjected to a second heat treatment at 750° C. for 8 hours in an oxygen atmosphere to produce large particles in the first positive electrode active material.

[0116] 5 and 6 are SEM images of the large particles.

[0117] (2) Preparation of small particles of the first positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2, LiOH and Al2O3 were mixed in a molar ratio of 1:1:0.02 and subjected to a first heat treatment at 850℃ for 8 hours in an oxygen atmosphere to obtain a composition of LiNi 0.75 Mn 0.23 Al 0.02 O2 and the average particle size (D 50 A second lithium nickel-manganese composite oxide having a single particle shape and a particle size of about 3 μm was prepared.

[0118] Aluminum sulfate and yttrium nitrate were added to a distilled water solvent and mixed, and then the second lithium nickel-manganese composite oxide was added and mixed for about 45 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 0.4 mol% based on 100 mol% of the total metals excluding lithium in the final small particles, and the yttrium content in the yttrium nitrate was designed to be 0.05 mol%. The solvent was removed from the mixed solution, which was then dried at 190°C and heat-treated at 825°C for 8 hours in an oxygen atmosphere to produce small particles of the first positive electrode active material.

[0119] 7 and 8 are SEM images of the small particles produced.

[0120] (3) Preparation of the second positive electrode active material Ni 0.35 Mn 0.65 (OH)2 and LiOH were mixed so that the molar ratio of Li / (Ni+Mn) was about 2.1, and then heat-treated in an oxygen atmosphere at 950°C for 24 hours to obtain a lithium-manganese-rich composite oxide (Li 1.35 (Ni 0.35 Mn0.65 ) 0.65 O2) in the form of secondary particles, and the average particle size of the secondary particles (D 50 ) was about 8 μm.

[0121] 9 and 10 are SEM images of the second positive electrode active material.

[0122] (4) Manufacturing the final positive electrode active material The final positive electrode active material was prepared by mixing 70% by weight of the large particles of the first positive electrode active material, 20% by weight of the small particles of the first positive electrode active material, and 10% by weight of the second positive electrode active material. The final positive electrode active material was pressurized at 4 tons for 30 seconds, and the pellet density was measured to be about 3.47 g / cc.

[0123] 2. Manufacturing of lithium secondary batteries 98.5 wt % of the prepared positive electrode active material, 1.0 wt % of polyvinylidene fluoride binder, and 0.5 wt % of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0124] A negative electrode active material layer slurry was prepared by mixing 97.5 wt% graphite negative electrode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene butadiene rubber in an aqueous solvent. The negative electrode active material layer slurry was coated on a copper foil current collector, and then dried and rolled to prepare a negative electrode.

[0125] A polytetrafluoroethylene separator was used, and a lithium secondary battery was fabricated in a conventional manner using an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0126] Example 2 A positive electrode active material and a lithium secondary battery were manufactured in a manner substantially similar to that of Example 1, except that the final positive electrode active material was manufactured by mixing 90 wt % of the large particles of the first positive electrode active material and 10 wt % of the second positive electrode active material.

[0127] The final positive electrode active material produced in Example 2 had a pellet density of about 3.10 g / cc.

[0128] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in a manner substantially similar to that of Example 1, except that the final positive electrode active material was manufactured by mixing 70% by weight of the large particles of the first positive electrode active material and 30% by weight of the small particles of the first positive electrode active material.

[0129] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in a manner substantially similar to that of Example 1, except that only the large particles of the first positive electrode active material were used alone as the final positive electrode active material.

[0130] Comparative Example 3 A positive electrode active material and a lithium secondary battery were manufactured in a manner substantially similar to that of Example 1, except that only the small particles of the first positive electrode active material were used alone as the final positive electrode active material.

[0131] Evaluation example 1: Positive electrode mixture density 11 shows the mixture density according to the rolling strength for the positive electrode plates manufactured in Example 1 and Comparative Example 1. Referring to FIG. 11, the rolled positive electrode density is 3.52 g / cc in Example 1 and 3.47 g / cc in Comparative Example 1, so that Example 1 can achieve a higher mixture density than Comparative Example 1.

[0132] Evaluation example 2: Battery performance evaluation In Examples 1 and 2, the lithium-manganese-rich second positive electrode active material was applied, and the method of initially charging to 4.65V and then lowering the voltage to 4.45V and charging was applied. That is, the lithium secondary batteries manufactured in Examples 1 and 2 were charged to 4.65V at a constant current of 0.1C at 25°C, and then the voltage was maintained until the current value reached 0.05C, and then discharged to 2.5V at a constant current of 0.1C to perform the first charge / discharge. Next, the batteries were charged to 4.45V at a constant current of 0.2C at 25°C, and then the voltage was maintained until the current value reached 0.05C, and then discharged to 2.5V at a constant current of 0.2C to perform the second charge / discharge. In Table 1 below, the second discharge capacity is represented as "1st 4.65V, 2nd 4.45V capacity".

[0133] Next, the cycle of charging at 1.0 C and discharging at 1.0 C in the voltage range of 3.0 V to 4.45 V at 45° C. was repeated 50 times or more, and the ratio of the 50th cycle discharge capacity to the second discharge capacity was calculated and shown as “4.45 V life” in Table 1 below.

[0134] Separately, the lithium-lithium secondary batteries manufactured in Comparative Examples 1 to 3 were initially charged and discharged at a constant current of 0.2 C at 25° C. up to an upper limit voltage of 4.45 V, and at a constant voltage of 0.05 C, and then discharged at 0.2 C down to an end voltage of 3.0 V. The initial discharge capacity is shown in Table 1 below as "4.45 V capacity".

[0135] Next, a cycle of charging at 1.0 C and discharging at 1.0 C in the voltage range of 3.0 V to 4.45 V at 45° C. was repeated 50 or more times, and the ratio of the 50 cycle discharge capacity to the initial discharge capacity was calculated and shown as "4.45 V life" in Table 1 below.

[0136] [Table 1]

[0137] Referring to Table 1 above, it can be seen that in Examples 1 and 2, the utilization rate of the positive electrode is improved and the life characteristics are improved as compared to the comparative example.

[0138] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0139] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing material 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. A first positive electrode active material including a layered lithium nickel-manganese composite oxide; and A positive electrode active material comprising a second positive electrode active material containing a lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.1 to 3, and the manganese content relative to 100 mol % of all metals excluding lithium is 50 mol % or more.

2. 2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is included in an amount of 60% by weight to 95% by weight, and the second positive electrode active material is included in an amount of 5% by weight to 40% by weight, based on a total weight of the first positive electrode active material and the second positive electrode active material being 100% by weight.

3. 2. The layered lithium nickel-manganese composite oxide of the first positive electrode active material has a nickel content of 60 mol% to 80 mol% and a manganese content of 10 mol% or more relative to 100 mol% of all metals excluding lithium.

4. The layered lithium nickel-manganese composite oxide of the first positive electrode active material further contains aluminum, and the aluminum content is 1 mol% to 3 mol% relative to 100 mol% of all metals excluding lithium. The positive electrode active material according to claim 1.

5. 5. The positive electrode active material according to claim 4, wherein the aluminum concentration is uniform within the layered lithium nickel-manganese composite oxide of the first positive electrode active material.

6. 2. The positive electrode active material according to claim 1, wherein in the layered lithium nickel-manganese composite oxide of the first positive electrode active material, the content of cobalt relative to 100 mol % of all metals excluding lithium is 0 mol % to 0.01 mol %.

7. The layered lithium nickel-manganese composite oxide of the first positive electrode active material is represented by chemical formula 1, the positive electrode active material according to claim 1: [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 In Chemical Formula 1, 0.9≦a1≦1.8, 0.6≦x1≦0.8, 0.1≦y1≦0.4, 0≦z1≦0.03, 0≦w1≦0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y and Zr, and X is one or more elements selected from F, P and S.

8. The first positive electrode active material comprises core particles containing a layered lithium nickel-manganese composite oxide; 10. The cathode active material of claim 1, comprising a coating layer located on a surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

9. The positive electrode active material according to claim 8 , wherein the coating layer contains Al and has a shell shape that continuously surrounds the surface of the core particle.

10. The positive electrode active material according to claim 8, wherein the coating layer has a thickness of 5 nm to 200 nm.

11. The positive electrode active material according to claim 8, wherein the content of the coating layer component is 0.01 mol % to 5 mol % based on 100 mol % of all metals excluding lithium in the first positive electrode active material.

12. The first positive electrode active material contains a layered lithium nickel-manganese composite oxide and has an average particle size (D 50 The present invention contains large particles having an average particle size (D) of 10 μm to 25 μm, and layered lithium nickel-manganese composite oxide. 50 2. The positive electrode active material of claim 1, comprising small particles having a diameter of 0.5 μm to 8 μm.

13. The large particles are in the form of secondary particles formed by agglomeration of a plurality of primary particles, 13. The cathode active material of claim 12, wherein the small particles are in single particle form.

14. 13. The positive electrode active material according to claim 12, wherein the large particles are contained in an amount of 60% by weight to 95% by weight, and the small particles are contained in an amount of 5% by weight to 40% by weight, based on a total of 100% by weight of the large particles and the small particles.

15. With respect to 100% by weight of the large particles, the small particles, and the second positive electrode active material combined, The large particles are included in an amount of 40% to 90% by weight, The small particles are present in an amount of 5% to 40% by weight. The positive electrode active material of claim 12, wherein the second positive electrode active material is included in an amount of 5% by weight to 30% by weight.

16. The average particle size (D 50 ) is the average particle size of the large particles (D 50 ) and the average particle size (D 50 13. The positive electrode active material of claim 12, wherein the positive electrode active material has a molecular weight of 1.0 or more.

17. The large particle includes a core particle in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and a coating layer located on the surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof, 13. The positive electrode active material of claim 12, wherein the small particles include a core particle in the form of a single particle and a coating layer located on a surface of the core particle and containing Al, B, Mg, Ti, V, W, Y, Zr, or a combination thereof.

18. the coating layer of the large particles comprises Al, Zr, or a combination thereof; 20. The cathode active material of claim 17, wherein the small particle coating layer comprises Al, Y, or a combination thereof.

19. the coating layer of the large particle contains Al, and the Al content of the coating layer is 0.5 mol % to 2 mol % based on 100 mol % of all metals in the large particle excluding lithium; The positive electrode active material according to claim 17, wherein the coating layer of the small particles contains Al, and the Al content of the coating layer is 0.1 mol% to 1 mol% relative to 100 mol% of all metals excluding lithium in the small particles.

20. The positive electrode active material according to claim 19, wherein the coating layer of the small particles further contains Y, and the Y content of the coating layer is 0.01 mol % to 0.5 mol % relative to 100 mol % of all metals excluding lithium in the small particles.

21. The lithium-manganese-rich composite oxide of the second positive electrode active material is represented by chemical formula 2, the positive electrode active material according to claim 1: [Chemical formula 2] Li 1+x2 (N y2 Mn z2 M 2 1-y2-z2 ) 1-x2 O 2-b2 X b2 In Chemical Formula 2, 0.04≦x2≦0.5, 0.1≦y2≦0.5, 0.5≦z2≦0.9, and 0≦b2≦0.1; M 2 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

22. The positive electrode active material according to claim 1 , wherein the second positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles.

23. The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 3 μm to 13 μm.

24. 2. The positive electrode active material according to claim 1, wherein in the lithium-manganese-rich composite oxide of the second positive electrode active material, the content of cobalt relative to 100 mol % of all metals excluding lithium is 0 mol % to 0.01 mol %.

25. 2. The positive electrode active material according to claim 1, wherein the pellet density of the positive electrode active material is 3.0 g / cc to 3.7 g / cc.

26. 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 comprises the positive electrode active material according to any one of claims 1 to 25.

27. 27. The positive electrode of claim 26, wherein the positive electrode active material layer has a density of 3.3 g / cc to 3.7 g / cc.

28. 27. The positive electrode according to claim 26 . a negative electrode, and A lithium secondary battery comprising an electrolyte.

29. The initial charging voltage is 4.60V or more.

29. The lithium secondary battery according to claim 28, wherein the subsequent charging voltage is lower than the initial charging voltage and is 4.45 V or higher.

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