Positive electrode active material and rechargeable lithium batteries

Abstract

To provide a lithium-manganese-rich-based positive electrode active material which is capable oof realizing a high capacity per volume by improving volume density while realizing a high capacity and realizes a long lifetime characteristic, and a rechargeable lithium battery including the same.SOLUTION: There are disclosed, a positive electrode active material, and a rechargeable lithium battery. The positive electrode active material includes a first positive electrode active material including a first lithium-manganese-rich composite oxide in which a molar ratio of lithium to a total metal excluding lithium is about 1.06 to about 1.2 and a manganese content based on 100 mol% of a total metal excluding lithium is greater than or equal to about 30 mol%, and a second positive electrode active material including a second lithium-manganese-rich composite oxide in which a molar ratio of lithium to a total metal excluding lithium is greater than about 1.2 and less than or equal to about 2 and a manganese content based on 100 mol% of a total metal excluding lithium is greater than or equal to about 30 mol%, and having the average particle diameter (D50) smaller than the average particle diameter (D50) of the first positive electrode active material.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Lithium secondary batteries, which have high energy density yet 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 suitable for such 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, while the demand for large-sized, high-capacity, or high-energy density lithium secondary batteries has recently increased sharply, 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 exclude cobalt or have a reduced cobalt content. Summary of the Invention [Problem to be solved by the invention]

[0004] Provided is a lithium-manganese-rich positive electrode active material that can realize high capacity while improving volume density to realize high capacity per volume and long life characteristics, and a lithium secondary battery including the same. [Means for solving the problem]

[0005] In one embodiment, a first positive electrode active material includes a first lithium-manganese-rich composite oxide having a molar ratio of lithium to all metals excluding lithium of 1.06 or more and 1.2 or less, and a manganese content of 30 mol% or more to 100 mol% of all metals excluding lithium; and a second lithium-manganese-rich composite oxide having a molar ratio of lithium to all metals excluding lithium of more than 1.2 to 2 or less, and a manganese content of 30 mol% or more to 100 mol% of all metals excluding lithium, and an average particle size (D 50 ) smaller than the average particle size (D 50 and a second positive electrode active material having a first conductivity type and a second positive electrode active material having a second conductivity type.

[0006] In another embodiment, a lithium secondary battery is provided that includes the positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. Effect of the Invention

[0007] The positive electrode active material according to an embodiment maximizes capacity while minimizing production costs, and minimizes the disadvantages caused by the low density of lithium-manganese-rich positive electrode active materials while maintaining the advantage of high capacity, thereby achieving high capacity, high density, and high capacity per volume, and achieving excellent high-temperature life characteristics. [Brief description of the drawings]

[0008] [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]1 is a graph showing the results of evaluating the life characteristics of a battery using the mixed positive electrode active material of Example 1, a battery using only the first positive electrode active material of Example 1 alone, and a battery using only the second positive electrode active material of Example 1 alone, the graph showing the capacity retention rate according to the number of cycles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings, in which: FIG.

[0010] 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.

[0011] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0012] It is to be understood herein that terms such as "comprise", "comprise", or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] 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" another part, this includes not only when it is "directly on" the other part, but also when 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.

[0014] In addition, 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.

[0015] The average particle size can be measured by any method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. Alternatively, it can be measured using dynamic light scattering, and data analysis can be performed to count the number of particles for each particle size range, and then the average particle size value can be calculated from this. Unless otherwise defined, the average particle size is the diameter (D) of the particles with a cumulative volume of 50% in the particle size distribution. 50 In addition, unless otherwise defined, the average particle size is the diameter (D) of the particle with a cumulative volume of 50% by volume in the particle size distribution obtained by measuring the size (diameter or major axis length) of 20 or more particles randomly in a scanning electron microscope image. 50 ) is taken as the average particle size.

[0016] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0017] The term "metal" is understood to include general metals, transition metals, and metalloids.

[0018] positive electrode active material In one embodiment, a first positive electrode active material includes a first lithium-manganese-rich composite oxide having a molar ratio of lithium to all metals excluding lithium of 1.06 or more and 1.2 or less, and a manganese content of 30 mol% or more to 100 mol% of all metals excluding lithium; and a second lithium-manganese-rich composite oxide having a molar ratio of lithium to all metals excluding lithium of more than 1.2 to 2 or less, and a manganese content of 30 mol% or more to 100 mol% of all metals excluding lithium, and an average particle size (D 50 ) smaller than the average particle size (D 50and a second positive electrode active material having a first conductivity type and a second positive electrode active material having a second conductivity type.

[0019] The positive electrode active material according to an embodiment may be a lithium-manganese-rich (LMR)-based positive electrode active material, or may be expressed as including a lithium-manganese-rich composite oxide. The LMR material is a layered-structure positive electrode active material containing an excess of lithium and a relatively high content of manganese, and exhibits high capacity by applying a new principle of oxygen oxidation-reduction (O-redox) in addition to the capacity by the oxidation-reduction of existing transition metals, and at the same time, it has a high ratio of low-cost manganese and is attracting attention as an ultra-low-cost next-generation positive electrode active material. Specifically, the LMR material can be said to be a layered-structure composite oxide in which the molar ratio of lithium to the total metals excluding lithium is more than 1 and is not more than 2, and the content of manganese to 100 mol % of the total metals excluding lithium is 30 mol % or more. The LMR material has completely different characteristics from existing layered positive electrode active materials due to the excess lithium, and can be said to have a composition to which a new mechanism called O-redox is applied.

[0020] However, the LMR material has a higher density of lithium and manganese than existing positive electrode active materials, and is LiCoO 2 (4.9g / cc), LiNiO 2 The ratio of LiMnO (4.6 g / cc) is decreased, and instead, the theoretical volume density is lowered to LiMnO 2 (4.04g / cc) and Li 2 MnO 3 The specific gravity (3.7g / cc) has increased, and the volume density is lower than that of existing layered materials, so even though high capacity (mAh / g) is achieved, the advantage in terms of total energy density (Wh / L) is diminished.

[0021] In one embodiment, a new cathode active material is proposed that minimizes the disadvantages caused by the low volume density of the LMR material while maintaining the advantage of high capacity. The cathode active material according to one embodiment is very low-cost and economical, highly mass-producible, and realizes high capacity by oxygen oxidation-reduction while increasing the volume density and improving the capacity per volume. When a lithium secondary battery using the cathode active material is installed in an electric vehicle or a hybrid vehicle, it enables long-distance driving. In one embodiment, the cathode active material in which the first cathode active material and the second cathode active material are mixed has improved volume density compared to a cathode active material made of a single type, while maintaining high capacity, thereby maximizing the advantages of the LMR material.

[0022] With respect to 100% by weight of the total of the first and second positive electrode active materials, the first positive electrode active material is included at more than 50% by weight and less than 100% by weight, for example, 60% to 95% by weight, 70% to 95% by weight, or 80% to 90% by weight, and the second positive electrode active material is included at more than 0% by weight and less than 50% by weight, for example, 5% to 40% by weight, 5% to 30% by weight, or 10% to 20% by weight. When mixed in the above ratios, high capacity is realized, energy density is maximized, and life characteristics are improved.

[0023] The first positive electrode active material is in the form of particles, and the average particle diameter (D 50 ) is the average particle size (D 50 ) and is expressed as a large grain or large particle. 50 ) may be 5 μm or more, for example, 5 μm or more and 20 μm or less, 6 μm to 15 μm, or 7 μm to 12 μm. The first positive electrode active material may be in the form of secondary particles formed by agglomeration of a plurality of primary particles.

[0024] The second positive electrode active material is in the form of particles, and the average particle diameter (D 50 ) is the average particle size (D 50 ) and is expressed as small grains or small particles. 50) may be 7 μm or less, for example, 1 μm or more and 7 μm or less, 1 μm or more and less than 7 μm, or 1 μm or more and 6.5 μm or less, or may be 2 μm to 6.5 μm, or 3 μm to 6 μm. The second positive electrode active material may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, or may be a single particle, or may be in a form in which these are mixed. When a single-particle second positive electrode active material is used, the life characteristics and cycle stability can be improved.

[0025] Here, the single particle means a particle that exists alone without a grain boundary and consists of one particle, and may mean a single particle that exists in an independent phase in which particles do not aggregate with each other in terms of morphology, a monolith structure, a single body structure, or a non-aggregated particle, for example, a single crystal. The single particle may exist alone or may be aggregated with each other. For example, 2 to 10 single particles may be aggregated and in contact with each other.

[0026] The first positive electrode active material is an LMR material and corresponds to large particles. In one embodiment, the amount of Mn and Li that reduce the volume density in the first positive electrode active material is minimized to improve the volume density of the entire positive electrode active material, and a small amount of O-Redox is used to improve the life characteristics and stability of the positive electrode active material.

[0027] The second positive electrode active material is an LMR material and corresponds to small particles, which can increase the overall capacity and improve the life characteristics, and although it has a low volume density by itself, it can minimize the voids and the decrease in density by being located in the empty space between the large particles. In one embodiment, the price of the material can be reduced by increasing the ratio of Mn in the second positive electrode active material.

[0028] Specifically, the first lithium-manganese-rich composite oxide of the first positive electrode active material is characterized in that the molar ratio of lithium to all metals excluding lithium is 1.06 or more and 1.2 or less, and may be, for example, more than 1.06 and 1.2 or less, 1.1 or more and 1.2 or less, more than 1.1 and 1.2 or less, or 1.1 or more and 1.15 or less. The second lithium-manganese-rich composite oxide of the second positive electrode active material is characterized in that the molar ratio of lithium to all metals excluding lithium is more than 1.2 and 2 or less, and may be, for example, more than 1.2 and 1.8 or less, more than 1.2 and 1.5 or less, 1.25 or more and 1.5 or less, or 1.3 or more and 1.45 or less. In the large particle first positive active material, lithium is applied in excess and its content is minimized to minimize the decrease in the volume density of the active material, while the ratio of O-redox is reduced to suppress gas generation and metal elution and improve the voltage decay problem, and in the small particle second positive active material, the lithium content is further increased to maintain high capacity by applying O-redox. In other words, when the lithium molar ratio in each of the first and second positive active materials is designed as above, the initial discharge capacity (mAh / g) and volume density (g / cc) are increased at the same time, improving the capacity per volume (mAh / cc), which in turn increases the energy density (Wh / L) and further improves the life characteristics.

[0029] Also, as an example, the first lithium-manganese-rich composite oxide of the first positive electrode active material may have a nickel content of 45 mol% or more relative to 100 mol% of all metals excluding lithium, and the second lithium-manganese-rich composite oxide of the second positive electrode active material may have a nickel content of less than 45 mol% relative to 100 mol% of all metals excluding lithium. That is, the first positive electrode active material may be a mid-nickel LMR material with a medium level of nickel content, and the second positive electrode active material may be a low-nickel LMR material with a relatively low nickel content. In the large particle first positive electrode active material, the Ni content is increased and the Mn content is decreased to minimize the decrease in volume density, and the amount of gas generation and metal elution are suppressed by using less O-redox, thereby improving the average voltage drop problem. In the small particle second positive electrode active material, the Ni content is reduced and the Mn content is increased, thereby reducing the cost of the material and maintaining the advantages of LMR, such as high capacity.

[0030] For example, the first lithium-manganese-rich composite oxide of the first positive electrode active material may have a nickel content of 45 mol% or more and a manganese content of 55 mol% or less, relative to a total of 100 mol% of nickel and manganese.Specific examples include a nickel content of 45 mol% to 65 mol% and a manganese content of 35 mol% to 55 mol%, or a nickel content of 50 mol% to 60 mol% and a manganese content of 40 mol% to 50 mol%.

[0031] Furthermore, the second lithium-manganese-rich composite oxide of the second positive electrode active material may have a nickel content of 10 mol% to less than 45 mol% and a manganese content of more than 55 mol% to 90 mol%, relative to 100 mol% of nickel and manganese; or, specifically, the nickel content may be 20 mol% to less than 45 mol% and the manganese content may be more than 55 mol% to 80%, or the nickel content may be 25 mol% to 40 mol% and the manganese content may be 60 mol% to 75%.

[0032] When the ratios of Ni and Mn in the first and second positive electrode active materials are designed as described above, the initial discharge capacity (mAh / g) and volume density (g / cc) can be increased simultaneously to improve the capacity per volume (mAh / cc), thereby improving the life characteristics.

[0033] Meanwhile, in the entire mixture of the first positive electrode active material and the second positive electrode active material, the molar ratio of lithium to all metals excluding lithium may be 1.1 to 1.3, for example, 1.1 to 1.2. Furthermore, the nickel content relative to 100 mol% in total of nickel and manganese may be 35 mol% to 65 mol%, or 40 mol% to 55 mol%, and the manganese content may be 35 mol% to 65 mol%, or 45 mol% to 60 mol%.

[0034] The first lithium-manganese-rich composite oxide of the first positive electrode active material is represented, for example, by a metal oxide including at least one of Chemical Formula 1 and Chemical Formula 2 below. [Chemical formula 1] Li 1+x1 (Ni y1 Mn z1 M 1 1-y1-z1 ) 1-x1 O 2-b1 X 1 b1

[0035] In the above formula 1, 0.03≦x1≦0.09, 0.45≦y1≦0.7, 0.3≦z1≦0.55, and 0≦b1≦0.1; M 1 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 1 is one or more elements selected from F, P and S.

[0036] [Chemical formula 2] (1-x2)(LiNi y2 Mn z2 M 2 1-y2-z2O 2-b2 X 2 b2 )+x2(Li 2 (M t1 M 2 1-t1 )O 3-b3 X 2 b3 )]

[0037] In the above formula 2, 0.06≦x2≦0.2, 0.5≦y2≦1.0, 0≦z2≦0.5, 0≦b2≦0.1, 0.9≦t1≦1, and 0≦b3≦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 2 is one or more elements selected from F, P and S.

[0038] It can be said that the formula 1 represents a solid-solution phase, and the formula 2 represents a composite phase. The first lithium-manganese-rich composite oxide may be expressed, for example, as a combination of the formulas 1 and 2 at room temperature. In this case, it is sufficient to include both the solid-solution phase and the composite phase, for example, a material in which the composite and the solid solution are mixed, or a material in which the composite and the solid solution competitively coexist. In this case, the first lithium-manganese-rich composite oxide can have oxygen in its structure relatively stable, so that the structural change due to oxygen vacancies during the charge and discharge process is small, and the voltage drop problem due to oxygen generation and structural deterioration can be effectively improved.

[0039] The second lithium-manganese-rich composite oxide of the second positive electrode active material may be represented by at least one of Chemical Formula 3 and Chemical Formula 4, for example, by either one of Chemical Formula 3 and Chemical Formula 4. It can be said that Chemical Formula 3 represents a solid solution phase, and Chemical Formula 4 represents a composite phase. As an example, the second lithium-manganese-rich composite oxide may be represented by Chemical Formula 4. [Chemical formula 3] Li1+x3 (Ni y3 Mn z3 M 3 1-y3-z3 ) 1-x3 O 2-b4 X 3 b4

[0040] In the above formula 3, 0.09 <x3≦0.33、0.1≦y3<0.45、0.55<z3≦0.9、および0≦b4≦0.1であり、M 3 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 3 is one or more elements selected from F, P and S.

[0041] [Chemical formula 4] (1-x4)(LiNi y4 Mn z4 M 4 1-y4-z4 O 2-b5 X 4 b5 )+x4(Li 2 (M t2 M 4 1-t2 )O 3-b6 X 4 b6 )]

[0042] In the above formula 4, 0.2 <x4≦1、0.5≦y4≦1.0、0≦z4≦0.5、0≦b5≦0.1、0.9≦t2≦1および0≦b6≦0.1であり、M 4 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 4 is one or more elements selected from F, P and S.

[0043] In each of the first lithium-manganese-rich composite oxide and the second lithium-manganese-rich composite oxide, the cobalt content relative to 100 mol % of all metals excluding lithium may be 0 mol % to 1 mol %, or 0 mol % to 0.1 mol %, or 0 mol % to 0.01 mol %.

[0044] On the other hand, the average particle size (D 50 ) and the average particle size of the second positive electrode active material (D 50 ), that is, the difference between the former and the latter may be 6 μm or less. In the case of existing layered cathode materials such as lithium nickel composite oxides and lithium cobalt oxides, many attempts have been proposed to increase energy density by mixing large and small particles, and in this case, resistance and other performance are not significantly affected regardless of whether the difference in particle size is large or small. In contrast, in the LMR material according to one embodiment, if the difference in particle size between the large and small particles is excessively large (for example, if it exceeds 6 μm), the capacity decreases or at least the effect of increasing capacity by mixing large and small particles does not appear. This is understood to be because the resistance difference between the large and small particles becomes large and ions flow mainly in the one with low resistance. Therefore, in one embodiment, the difference in particle size between the large and small particles is designed to be 6 μm or less, so that the volume density can be improved while maximizing the capacity.

[0045] The average particle size of the first positive electrode active material (D 50 ) to the average particle size (D 50 ) may be, for example, 1 μm to 6 μm, 2 μm to 5 μm, or 2.5 μm to 4.5 μm. By appropriately adjusting the particle size difference between the large particles and the small particles to within the above range, it is possible to realize a high capacity and at the same time increase the volume density and improve the energy density.

[0046] As described above, the positive electrode active material according to one embodiment can achieve a high pellet density. For example, the pellet density of the positive electrode active material may be 2.9 g / cc or more, for example, 2.9 g / cc to 3.7 g / cc, 2.9 g / cc to 3.6 g / cc, or 2.9 g / cc to 3.5 g / cc. A lithium secondary battery using such a positive electrode active material can achieve a high energy density. The pellet density can be measured by the following method. After weighing 3 g of the positive electrode active material, a mold (area: 1.298 cm2) is placed in a mold. 2 ) and slowly insert the Mold Bar into the Mold body. The Mold SET is placed in a hydraulic press and pressurized with 3.3 ton (metric ton) pressure for 30 seconds, after which the height is measured to measure the pellet density.

[0047] Meanwhile, the large particle first positive electrode active material may have an a lattice constant of 2.865 Å or more in X-ray diffraction analysis (XRD), for example, 2.865 Å or more, 2.870 Å or more, or 2.875 Å to 2.885 Å. As an example, the a lattice constant of the positive electrode active material may be 2.875 Å 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, or 4.955 to 4.965. When the first positive electrode active material in which the a lattice constant and the ratio of the c lattice constant to the a lattice constant satisfy the above range are used, the problem of the volume density of the LMR material decreasing can be minimized, and the energy density can be effectively improved.

[0048] The first and second positive electrode active materials may each have a surface residual lithium content of 0.3% by weight or less, for example, 0.2% by weight or less, 0.1% by weight or less, or 0.001% to 0.1% by weight. This is a feature that distinguishes them from high-nickel materials with a nickel content of more than 70 mol%.

[0049] 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.

[0050] 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 2 In addition, the density of the positive electrode active material layer in the final rolled positive electrode may be 2.6 g / cc to 3.7 g / cc, for example, 2.6 g / cc to 3.6 g / cc, or 2.8 g / cc to 3.58 g / cc. When the positive electrode active material according to an embodiment is applied, it is advantageous to realize such a loading level and positive electrode density, and a positive electrode satisfying the loading level and positive electrode density in the above ranges is suitable for realizing a lithium secondary battery with a high capacity and high energy density.

[0051] The positive electrode according to one embodiment is characterized in that it can achieve high capacity (mAh / g) while simultaneously achieving high volume density (g / cc), and thus the capacity per volume of the positive electrode may be 550 mAh / cc or more, for example, 560 mAh / cc or more, 570 mAh / cc or more, 580 mAh / cc or more, or may be 550 to 650 mAh / cc, or 580 to 630 mAh / cc.

[0052] 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.

[0053] Conductive material The conductive material is used to impart electrical conductivity to the electrode, and any material that is electronically conductive and does not cause a chemical change in the battery that is constructed 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 fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0054] The content of the binder and the conductive material may each be 0.5% by weight to 5% by weight relative to 100% by weight of the positive electrode active material layer.

[0055] The positive electrode current collector can be made of Al, but is not limited to this.

[0056] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the above-mentioned positive electrode, negative electrode, and electrolyte. The above-mentioned positive electrode active material is applicable not only to lithium ion batteries but also to all-solid-state secondary batteries. As an example, the lithium secondary battery includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte. In another embodiment, an all-solid-state secondary battery includes the positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. Hereinafter, for convenience, the configuration of a lithium ion battery using an electrolyte will be described in detail.

[0057] Lithium secondary batteries are 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 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is built. 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 may 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 may include a positive electrode lead tab 11, a positive electrode terminal 12, and 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.

[0058] The lithium secondary battery according to an embodiment may be suitable for being rechargeable at a high voltage or for being driven at a high voltage, and may be a battery with improved characteristics under high voltage conditions.

[0059] In order to use the reversible positive electrode capacity of the lithium-manganese-rich positive electrode active material, the first charge needs to be performed at 4.60V or more, and for example, the first charge can be performed at 4.65V. Subsequent charges are performed in a range lower than the first charge voltage, but since the lithium secondary battery according to an embodiment is designed to be driven in a high voltage region, charging can be performed in a voltage range of 4.3V or more. For example, the charge voltage after the second cycle may be 4.3V or more, and may be, for example, 4.3V to 4.6V, 4.3V to 4.55V, or 4.4V to 4.50V. The lithium secondary battery can achieve high capacity and long life characteristics even when charged at a high voltage by applying the positive electrode active material according to an embodiment.

[0060] Meanwhile, in general, the more O-redox is expressed, the lower the average discharge voltage after O-redox activation is. However, in the positive electrode active material according to an embodiment, the specific gravity of O-redox is appropriately controlled, so that the average discharge voltage can be improved. For example, in the lithium secondary battery according to an embodiment, the average discharge voltage (vs. Li / Li + ) may be 3.8 V or more, for example, 3.83 V or more, or 3.84 V or more. Here, the average discharge voltage may refer to an average discharge voltage measured in a second cycle in which a half cell is manufactured using a positive electrode to which the positive electrode active material according to an embodiment is applied, a first charge / discharge is performed to a voltage of 4.60 V or more, and then a second charge / discharge is performed in a voltage range lower than the first charge / discharge. The average discharge voltage may be calculated, for example, by dividing the integral value of the area under the curve in a voltage-capacity graph by the discharge capacity.

[0061] 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.

[0062] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0063] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0064] 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.

[0065] As the material capable of doping and dedoping 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, SiO x (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 a combination 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 a combination thereof), or a combination thereof may be used. As the Sn-based negative electrode active material, Sn, SnO 2 , an Sn alloy, or a combination thereof may be used.

[0066] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50 ) 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 the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon is also located between the primary silicon particles, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles may be present dispersed in an amorphous carbon matrix.

[0067] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including 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. The amorphous carbon may include soft or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0068] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight and the amorphous carbon content may be 50% to 90% by weight, relative to 100% by weight of the silicon-carbon composite. When the composite contains silicon, amorphous carbon and crystalline carbon, the silicon content may be 10% to 50% by weight, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight, relative to 100% by weight of the silicon-carbon composite.

[0069] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is 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 size (D 50 ) means the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution.

[0070] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in mixture, the mixing ratio may be 1:99 to 90:10 by weight.

[0071] binder The binder serves to make the negative electrode active material particles adhere well to each other and make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The dry binder may be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0076] Conductive material The conductive material is used to impart electrical conductivity to the electrodes, and any electronically conductive material that does not cause a chemical change 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, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0077] The content of the negative electrode active material may be 95% by weight 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% by weight 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% by weight to 99% by weight of the negative electrode active material, 0.5% by weight to 5% by weight of the binder, and 0.5% by weight to 5% by weight of the conductive material.

[0078] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in foil, sheet, or foam form. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0079] electrolyte The electrolyte for a lithium secondary battery may be, by way of example, an electrolytic solution, which may include a non-aqueous organic solvent and a lithium salt.

[0080] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and may be a carbonate-, ester-, ether-, ketone-, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0081] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. As the ketone solvent, cyclohexanone, etc. can be used. As the alcohol solvent, ethyl alcohol, isopropyl alcohol, etc. can be used. As the aprotic solvent, nitriles such as R-CN (R is a straight-chain, branched, or ring-structured hydrocarbon group having 2 to 20 carbon atoms, which 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; sulfolanes, etc. can be used.

[0082] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which is widely understood by those working in the field.

[0083] 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.

[0084] 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.

[0085] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0086] 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.

[0087] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries to enable basic lithium secondary battery operation and to facilitate the movement of lithium ions between the positive and negative electrodes. A representative example of a lithium salt is LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiPO 2 F 2 , LiCl, LiI, LiN(SO 3 C 2 F 5 ) 2 , Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC 4 F 9 SO 3 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0088] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt 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.

[0089] 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 can be used, and it goes without saying that a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] The organic material can include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0094] The inorganic material is Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CEO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 The inorganic particles may include, but are not limited to, inorganic particles selected from the group consisting of carbide, boehmite, and combinations thereof. 50) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0095] The organic material and the inorganic material may be mixed in one coating layer, or may be in the form of a laminate of a coating layer containing an organic material and a coating layer containing an inorganic material.

[0096] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0097] Examples of the present invention and comparative examples are described below. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0098] Example 1 1. Manufacturing of positive electrode active material (1) Preparation of large particles of first positive electrode active material Ni 0.5 Mn 0.5 (OH) 2 and LiOH were mixed so that the molar ratio of Li / (Ni+Mn) was about 1.12, and the resulting mixture was heat-treated at 1000°C for 24 hours in an oxygen atmosphere to obtain a lithium-manganese-rich composite oxide (Li 1.06 (Ni 0.5 Mn 0.5 ) 0.94 O 2 ), which is in the form of secondary particles, and the average particle diameter of the secondary particles (D 50 ) was about 7 μm.

[0099] (2) Preparation of small particles of second positive electrode active material Ni 0.35 Mn 0.65 CO 3 and LiOH were mixed so that the molar ratio of Li / (Ni+Mn) was about 1.35, and the mixture was heat-treated at 900°C for 24 hours to obtain a lithium-manganese-rich composite oxide (Li 1.15 (Ni 0.35 Mn 0.65) 0.85 O 2 ), which is in the form of secondary particles, and the average particle diameter of the secondary particles (D 50 ) was about 3.3 μm.

[0100] (3) Manufacturing of mixed positive electrode active material A mixed positive electrode active material having a final composition of Li / (Ni+Mn)=1.17, Ni:Mn=47:53 was prepared by mixing 80% by weight of the first positive electrode active material large particles and 20% by weight of the second positive electrode active material small particles.

[0101] 2. Manufacturing of lithium secondary batteries (half-cell) 92 wt% of the prepared positive electrode active material, 4 wt% of polyvinylidene fluoride binder, and 4 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. At this time, the loading level of the positive electrode active material layer was 10 mg / cm. 2 and the density of the final rolled cathode is about 3.5 g / cc.

[0102] A lithium counter electrode was used as the negative electrode, and a polytetrafluoroethylene separator was used. 1M LiPF was placed in a solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 2:4:4. 6 A lithium secondary battery was manufactured by a conventional method using an electrolyte solution to which 1.5% by weight of vinylene carbonate had been added.

[0103] Example 2 The composition is Li 1.06 (Ni 0.5 Mn 0.5 ) 0.94 O 2 and the average particle size (D 50 ) is about 10 μm, and the first positive electrode active material has a composition of Li 1.15 (Ni 0.35 Mn 0.65 ) 0.85 O 2 and the average particle size (D 50A lithium secondary battery was manufactured in a manner substantially similar to that of Example 1, except that a mixture of the first positive electrode active material having a particle size of about 6.5 μm and the second positive electrode active material having a particle size of about 6.5 μm in a weight ratio of 8:2 was used as the positive electrode active material.

[0104] Comparative Example 1 The composition is Li / (Ni+Mn)=1.17, Ni:Mn=47:53, and the average particle size (D 50 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that a positive electrode active material having a particle size of about 6.11 μm was used alone.

[0105] Comparative Example 2 The composition is Li 1.15 (Ni 0.35 Mn 0.65 ) 0.85 O 2 and the average particle size (D 50 ) is about 6.5 μm, and the first positive electrode active material has a composition of Li 1.15 (Ni 0.35 Mn 0.65 ) 0.85 O 2 and the average particle size (D 50 A lithium secondary battery was manufactured in substantially the same manner as in Example 1, except that a mixture of the first positive electrode active material having a particle size of about 3.3 μm and the second positive electrode active material having a particle size of about 3.3 μm in a weight ratio of 8:2 was used as the positive electrode active material.

[0106] Comparative Example 3 The composition is Li 1.06 (Ni 0.66 Mn 0.34 ) 0.94 O 2 and the average particle size (D 50 ) is about 10 μm, and the first positive electrode active material has a composition of Li 1.06 Ni 0.75 Mn 0.25 O 2 and the average particle size (D 50A lithium secondary battery was manufactured in a manner substantially similar to that of Example 1, except that the first positive electrode active material having a particle size of about 3.5 μm and the second positive electrode active material having a particle size of about 3.5 μm were mixed in a weight ratio of 7:3 to be used as a positive electrode active material having a final composition of Li / (Ni+Mn)=1.1, Ni:Mn=69:31.

[0107] Comparative Example 4 The composition is Li 1.03 Ni 0.75 Mn 0.25 O 2 and the average particle size (D 50 ) is about 9 μm, and the first positive electrode active material has a composition of Li 1.06 Ni 0.75 Mn 0.25 O 2 and the average particle size (D 50 A lithium secondary battery was manufactured in a manner substantially similar to that of Example 1, except that a mixture of the first positive electrode active material having a particle size of about 3.5 μm and the second positive electrode active material having a particle size of about 3.5 μm in a weight ratio of 8:2 was used as the positive electrode active material.

[0108] Evaluation example 1: Evaluation of initial charge / discharge capacity, initial charge / discharge efficiency, average voltage, pellet density, and capacity per volume In the case of batteries using lithium-manganese-rich materials, the initial charging was performed to 4.65V, and then the voltage was lowered to 4.45V for charging.

[0109] The lithium secondary batteries manufactured in Examples 1-2 and Comparative Examples 1-5 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. The initial charge capacity, initial discharge capacity, and efficiency, which is the ratio of the latter to the former, in the second charge-discharge cycle are shown in Tables 1 and 2 below.

[0110] In all the evaluation examples, not only the batteries using the mixed positive electrode active material in each of the examples and comparative examples, but also the batteries using only the first positive electrode active material and the batteries using only the second positive electrode active material were evaluated in the same manner, and the results are shown in Tables 1 and 2 below.

[0111] In addition, the average voltage (V vs. Li) during the initial discharge (discharge of the second cycle) was measured for each of the examples and comparative examples, and is shown in the following Tables 1 and 2. The average voltage was calculated by integrating the area under the discharge voltage curve (voltage-capacity graph) obtained after the initial charge and discharge of the battery, and then dividing the value by the discharge capacity.

[0112] The pellet density shown below is a value measured after applying a pressure of 3.3 tons to the positive electrode active materials of the examples and comparative examples for 30 seconds. The capacity per volume is the product of the initial discharge capacity and the pellet density.

[0113] [Table 1]

[0114] [Table 2]

[0115] Referring to Table 1, the initial discharge capacity when large and small particles were mixed in Example 1 was almost the same as the arithmetically predicted value obtained by adding 80% of the initial discharge capacity of the large particles alone and 20% of the initial discharge capacity of the small particles alone, and the density was higher than that of each of the large and small particles individually, resulting in a large increase in capacity per volume.

[0116] Similarly, in Example 2, when large and small particles were mixed, the initial discharge capacity was high and almost similar to the arithmetically predicted value, and the density also increased compared to each of the large and small particles, resulting in a significant improvement in capacity per volume.

[0117] Comparative Example 1 has the same final composition as Examples 1 and 2, but when a single positive electrode active material having a size of 6.11 μm is used, it has a smaller or similar initial discharge capacity compared to Examples 1 and 2, and the density is much lower, which is clearly disadvantageous in terms of capacity per volume.

[0118] In Table 2, it is clear that in Comparative Example 2, which is a lithium-manganese-rich system and in which the large and small particles have the same composition, the density does not increase by mixing.

[0119] In Comparative Example 3, a lithium nickel manganese based composite oxide that is not lithium-manganese rich was used as the small particles, but it was found that the initial discharge capacity did not increase by mixing, and the density did not increase either.

[0120] In Comparative Example 4, a lithium nickel manganese-based composite oxide that is not lithium-manganese-rich in both large and small particles was used, and a problem occurred in which the initial discharge capacity was rather reduced by the mixture.

[0121] Evaluation example 2: High temperature life characteristic evaluation For a battery using the mixed positive electrode active material of Example 1, a battery using only the first positive electrode active material of Example 1, and a battery using only the second positive electrode active material of Example 1, as in Evaluation Example 1, a cycle of charging at 1.0 C and discharging at 1.0 C in a voltage range of 2.5 V to 4.45 V at 45° C. was repeated 70 times or more, and the capacity retention (%) according to the cycle number, that is, the ratio of the discharge capacity in each cycle to the initial discharge capacity (discharge capacity in the second cycle), is shown in FIG. 5.

[0122] Referring to FIG. 5, the battery of Example 1 has significantly improved life characteristics compared to the battery using only the first positive electrode active material alone, and even though Example 1 contains 20 wt% small particles, the life characteristics are almost the same as the battery using only the small-particle second positive electrode active material alone.

[0123] 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 following claims also fall within the scope of the present invention. [Explanation of symbols]

[0124] 100: Lithium secondary battery, 10: Positive electrode 11: Positive electrode lead tab, 12: Positive electrode terminal 20: negative electrode, 21: negative electrode lead tab 22: negative electrode terminal, 30: separator 40: electrode assembly, 50: case 60: sealing member, 70: electrode tab 71: Positive electrode tab, 72: Negative electrode tab

Claims

1. a first positive electrode active material including a first lithium-manganese-rich composite oxide in which the molar ratio of lithium to all metals excluding lithium is 1.06 or more and 1.2 or less, and the manganese content relative to 100 mol % of all metals excluding lithium is 30 mol % or more; The first positive electrode active material includes a second lithium-manganese-rich composite oxide having a lithium molar ratio of more than 1.2 and not more than 2 with respect to the total metals excluding lithium, and a manganese content of 30 mol % or more with respect to 100 mol % of the total metals excluding lithium, and the first positive electrode active material has an average particle size (D 50 ) smaller than the average particle size (D 50 and a second positive electrode active material having a first positive electrode active material.

2. 2. The positive electrode active material according to claim 1, wherein the first positive electrode active material is contained in an amount of more than 50 wt% and less than 100 wt%, and the second positive electrode active material is contained in an amount of more than 0 wt% and less than 50 wt%, relative to 100 wt% in total of the first positive electrode active material and the second positive electrode active material.

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

4. The average particle size (D 50 ) is 5 μm or more and 20 μm or less, The average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the average particle diameter is 1 μm or more and 7 μm or less.

5. The first lithium-manganese-rich composite oxide of the first positive electrode active material has a molar ratio of lithium to all metals excluding lithium of more than 1.1 and not more than 1.2; 2. The positive electrode active material according to claim 1, wherein the second lithium-manganese-rich composite oxide of the second positive electrode active material has a molar ratio of lithium to all metals excluding lithium of more than 1.2 and not more than 1.

5.

6. The first lithium-manganese-rich composite oxide of the first positive electrode active material has a nickel content of 45 mol % or more relative to 100 mol % of all metals excluding lithium; 2. The positive electrode active material according to claim 1, wherein the second lithium-manganese-rich composite oxide of the second positive electrode active material has a nickel content of less than 45 mol % relative to 100 mol % of all metals excluding lithium.

7. The first lithium-manganese-rich composite oxide of the first positive electrode active material has a nickel content of 45 mol% to 70 mol% and a manganese content of 30 mol% to 55 mol% relative to 100 mol% of the total of nickel and manganese, The second lithium-manganese-rich composite oxide of the second positive electrode active material has a nickel content of 10 mol% to less than 45 mol% and a manganese content of more than 55 mol% to 90 mol% relative to 100 mol% of nickel and manganese. The positive electrode active material according to claim 1.

8. 2. The positive electrode active material according to claim 1, wherein in the entire mixture of the first positive electrode active material and the second positive electrode active material, the molar ratio of lithium to all metals excluding lithium is 1.1 to 1.3, the content of nickel is 35 mol% to 65 mol% and the content of manganese is 35 mol% to 65 mol% relative to 100 mol% in total of nickel and manganese.

9. The first lithium-manganese-rich composite oxide of the first positive electrode active material is represented by a metal oxide containing at least one of Chemical Formula 1 and Chemical Formula 2, [Chemical formula 1] Li 1+x1 (N y1 Mn z1 M 1 1-y1-z1 ) 1-x1 O 2-b1 X 1 b1 In the above formula 1, 0.03≦x1≦0.09, 0.45≦y1≦0.7, 0.3≦z1≦0.55, and 0≦b1≦0.1; M 1 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; X 1 is one or more elements selected from F, P and S. [Chemical formula 2] (1-12)(i) y2 7N z2 7. 2 1-y2-z2 9 2-b2 8 2 b2 )kx2(ii 2 (7n t1 7. 2 1-t1 )9 3-b3 8 2 b3 )) In the above formula 2, 0.06≦x2≦0.2, 0.5≦y2≦1.0, 0≦z2≦0.5, 0≦b2≦0.1, 0.9≦t1≦1, and 0≦b3≦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; X 2 is one or more elements selected from F, P and S.

10. The second lithium-manganese-rich composite oxide of the second positive electrode active material is represented by at least one of Chemical Formula 3 or Chemical Formula 4, [Chemical formula 3] Li 1+x3 (N y3 Mn z3 M 3 1-y3-z3 ) 1-x3 O 2-b4 X 3 b4 In the above formula 3, 0.09<x3≦0.33, 0.1≦y3<0.45, 0.55<z3≦0.9, and 0≦b4≦0.1; M 3 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; X 3 is one or more elements selected from F, P and S. [Chemical formula 4] (-x4)(iii) y4 7N z4 7. 4 1-y4-z4 9 2-b5 8 4 b5 )kx5Li 2 (7n t2 7. 4 1-t2 )9 3-b6 8 4 b6 )) In the above formula 4, 0.2<x4≦1, 0.5≦y4≦1.0, 0≦z4≦0.5, 0≦b5≦0.1, 0.9≦t2≦1, and 0≦b6≦0.1; M 4 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; X 4 is one or more elements selected from F, P and S.

11. 2. The positive electrode active material according to claim 1, wherein the first lithium-manganese-rich composite oxide and the second lithium-manganese-rich composite oxide each have a cobalt content of 0 mol % to 1 mol % relative to 100 mol % of all metals excluding lithium.

12. the first positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles, The cathode active material of claim 1 , wherein the second cathode active material is in a secondary particle form, a single particle form, or a combination thereof.

13. The average particle size (D 50 ) to the average particle size (D 50 2. The positive electrode active material according to claim 1, wherein the value obtained by subtracting

14. The average particle size (D 50 ) to the average particle size (D 50 12. The positive electrode active material according to claim 11, wherein the value obtained by subtracting

15. 2. The positive electrode active material according to claim 1, wherein the pellet density of the positive electrode active material is 2.9 g / cc or more.

16. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 15; A negative electrode; and an electrolyte.

17. 17. The lithium secondary battery according to claim 16, wherein the positive electrode has a capacity per volume of 550 mAh / cc or more.

18. The average discharge voltage of the lithium secondary battery is 3.8 V (vs. Li / Li + 17. The lithium secondary battery according to claim 16, wherein

19. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 15; A negative electrode; and a solid electrolyte layer located between the positive electrode and the negative electrode.

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