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

Abstract

To provide a positive electrode active material capable of securing high capacity, long life, and high output, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery.SOLUTION: A positive electrode active material according to an embodiment includes a lithium nickel-based composite oxide and is in the form of a secondary particle in which a plurality of primary particles are agglomerated, wherein an average particle size of the primary particles measured by electron backscatter diffraction (EBSD) analysis on a cross-section of the secondary particle is in a range of 1.05 μm to 1.5 μ m, a standard deviation of the particle size of the primary particles is 0.3 μm or less, and an aspect ratio of the primary particles is 1.7 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lithium secondary batteries are widely used as power sources for mobile information terminals such as smartphones and laptops, as they offer high energy density and are easy to carry. Recently, there has been active research into lithium secondary batteries that offer high capacity, long life, and high output for use as power sources for hybrid and electric vehicles, or as power storage sources.

[0003] Lithium nickel-based composite oxides can ensure high capacity as a positive electrode active material. Lithium nickel-based composite oxides can have a polycrystalline form, where multiple primary particles gather to form secondary particles. The smaller the primary particles, the better the charge / discharge efficiency and output characteristics. However, as the reaction area with the electrolyte increases, the stability and lifespan deteriorate.

[0004] To solve the above problems, the industry has made efforts to apply coatings or to increase the grain size and apply single crystals, but there are limitations to improving the output.

[0005] This has led to a demand for a positive electrode active material containing a lithium nickel-based composite oxide that ensures high capacity, long life, and high output. Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment is intended to provide a positive electrode active material that can ensure high capacity, long life, and high output. [Means for solving the problem]

[0007] One embodiment provides a cathode active material in the form of secondary particles formed by aggregating a plurality of primary particles, the cathode active material including a lithium nickel-based composite oxide, wherein the average size of the primary particles measured through electron backscatter diffraction (EBSD) analysis of a cross section of the secondary particles is in the range of 1.05 μm to 1.5 μm, the standard deviation of the size of the primary particles is 0.3 μm or less, and the average aspect ratio of the primary particles is 1.7 or less.

[0008] Another embodiment provides a method for producing a positive electrode active material, which includes mixing a nickel-based composite oxide and a lithium raw material, followed by heat treatment to obtain the positive electrode active material.

[0009] Another embodiment provides a positive electrode including 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.

[0010] Another embodiment provides a lithium secondary battery including the above-described positive electrode, negative electrode, and electrolyte. [Effects of the Invention]

[0011] The positive electrode active material according to one embodiment may be advantageous in ensuring high capacity, long life, and high output. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a scanning electron microscope (SEM) photograph of a cross section of a positive electrode active material prepared in an example. [Figure 6] 1 is a scanning electron microscope (SEM) photograph of a cross section of a positive electrode active material prepared in a comparative example. [Figure 7] 1 is an electron backscatter diffraction (EBSD) photograph of a cross section of a positive electrode active material prepared in an example. [Figure 8] 1 is an electron backscatter diffraction (EBSD) image of a cross section of a positive electrode active material prepared in a comparative example. [Figure 9] 1 is a curve showing the aspect ratio distribution of primary particles in a cross section of a positive electrode active material prepared in an example. [Figure 10] 10 is a curve showing the aspect ratio distribution of primary particles in a cross section of a positive electrode active material prepared in a comparative example. [Figure 11] This is a graph combining FIG. 9 and FIG. 10. [Figure 12] 11 is a graph showing an analysis of the aspect ratio distribution curves of the primary particles of FIGS. 9 and 10. FIG. [Figure 13] 1 is a graph showing the high-rate characteristics of lithium secondary batteries manufactured in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0014] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0015] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] It should be understood that the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0017] In the drawings, the thickness of various layers and regions is exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another 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.

[0018] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0019] 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 image or a scanning electron microscope image. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles for each particle size range, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) unless otherwise defined, the average particle size is the diameter (D) of the particle that makes up 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected in a scanning electron microscope image. 50 ) can be taken as the average particle size.

[0020] 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.

[0021] The term "metal" is understood to include general metals, transition metals and metalloids.

[0022] positive electrode active material In one embodiment, a cathode active material is provided, the cathode active material comprising a lithium nickel-based composite oxide and in the form of secondary particles formed by agglomerating a plurality of primary particles, wherein the average size of the primary particles measured through electron backscatter diffraction (EBSD) analysis of a cross section of the secondary particles is in the range of 1.05 μm to 1.5 μm, the standard deviation of the size of the primary particles is 0.3 μm or less, and the aspect ratio of the primary particles is 1.7 or less.

[0023] The lithium nickel-based composite oxide can be represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0024] In the above chemical formula 1, 0.9≦a1≦1.2, 0.8≦x1<1, 0 <y1≦0.2、0≦z1≦0.2、0.9≦x1+y1+z1≦1.1、および0≦b1≦0.1であり、M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0025] In chemical formula 1, 0.85≦x1<1, 0 <y1≦0.15、および0≦z1≦0.15であってもよい。

[0026] The lithium nickel-based composite oxide can be represented by the following formula 2 or 3, for example. [Chemical formula 2] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0027] In the above chemical formula 2, 0.9≦a2≦1.2, 0.8≦x2<1, 0 <y2≦0.2、0≦z2≦0.2、0.9≦x2+y2+z2≦1.1、および0≦b2≦0.1であり、M 3 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is F, P, S, or a combination thereof.

[0028] In the above Chemical Formula 2, 0.8≦x2≦0.99, 0.01≦y2≦0.1, and 0≦z2≦0.1 may be satisfied. [Chemical formula 3] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0029] In the above chemical formula 3, 0.9≦a3≦1.2, 0.8≦x3≦0.98, 0.01≦y3≦0.19, 0.01≦z3≦0.19, 0≦w3≦0.19, 0.9≦x3+y3+z3+w3≦1.1, and 0≦b3≦0.1; M 4 is Al, Mn, or a combination thereof, and M 5 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is F, P, S, or a combination thereof.

[0030] In Chemical Formula 3, 0.8≦x3≦0.95, 0.01≦y3≦0.15, 0.01≦z3≦0.05, and 0≦w3≦0.05 may be satisfied.

[0031] The lithium-nickel-based composite oxide may contain nickel at a high concentration. For example, the nickel content in the lithium-nickel-based composite oxide relative to 100 mol% of all metals excluding lithium may be 80 mol% or more, and other examples include 81 mol% or more, 82 mol% or more, 83 mol% or more, 84 mol% or more, or 85 mol% or more, or 100 mol% or less, 99 mol% or less, 95 mol% or less, 90 mol% or less, 89 mol% or less, or 88 mol% or less.

[0032] In one embodiment, a high-capacity lithium nickel-based composite oxide is a polycrystalline form having a secondary particle form formed by agglomerating a plurality of primary particles. The smaller the primary particles, the better the efficiency and output characteristics. However, as the reaction area with the electrolyte increases, the stability and lifespan deteriorate. To solve this problem, the present invention provides a cathode active material that ensures the uniformity and sphericity of the primary particles.

[0033] The uniformity of the primary particles can be ensured by adjusting the average size of the primary particles and the standard deviation of the size of the primary particles within appropriate ranges.

[0034] According to one embodiment, the average size of the primary particles is 1.05 μm to 1.5 μm. Specifically, the average size of the primary particles may be 1.05 μm or more, 1.1 μm or more, 1.15 μm or more, or 1.2 μm or more, and may be 1.5 μm or less, 1.45 μm or less, 1.4 μm or less, 1.35 μm or less, 1.3 μm or less, or 1.25 μm or less. The primary particle size refers to the size of the primary particles observed in the cross section of a secondary particle, and may be measured through electron backscatter diffraction (EBSD) analysis of the cross section of the secondary particle. The primary particle size is determined by calculating the area of ​​each primary particle in an EBSD photograph of the cross section of the secondary particle, deriving a circle having the same area, and calculating the particle diameter of this circle as the primary particle size. In this case, the average size of the primary particles refers to the arithmetic average of the sizes of more than 10 primary particles. A cathode active material having an average primary particle size of 1.05 μm to 1.5 μm can be produced by appropriately adjusting raw materials and production conditions, such as using a nickel-based composite oxide as a raw material during production of the cathode active material, and can be provided, for example, by a production method according to one embodiment described below. When the average primary particle size satisfies this range, charge / discharge capacity, efficiency, and life characteristics can be improved, while output characteristics can be improved.

[0035] According to one embodiment, the standard deviation of the primary particle size is 0.3 μm or less. Specifically, the standard deviation of the primary particle size may be 0.25 μm or less or 0.2 μm or less. The standard deviation of the primary particle size is calculated by calculating the standard deviation of the average size of the primary particles measured through an EBSD photograph of the cross section of the secondary particles. A cathode active material having a standard deviation of the primary particle size of 0.3 μm or less can be produced by appropriately adjusting the raw materials, such as using a nickel-based composite oxide as a raw material, during the production of the cathode active material. A standard deviation of the primary particle size within this range means that the primary particles are highly uniform, which can improve the charge / discharge capacity, efficiency, and life characteristics of the battery while also improving output characteristics.

[0036] The sphericity of the primary particles can be ensured by adjusting the average aspect ratio of the primary particles within an appropriate range.

[0037] According to one embodiment, the average aspect ratio of the primary particles is 1.7 or less. The average aspect ratio of the primary particles refers to the average value of aspect ratios in the cross section of the primary particles observed in the cross section of the secondary particles, and may be measured using an image analysis program in electron backscatter diffraction (EBSD) analysis of the cross section of the secondary particles. For example, the secondary particles are cut using a focused ion beam (FIB), the cross section is photographed using electron backscatter diffraction (EBSD) analysis, and the primary particles are contoured in the EBSD photograph of the cross section using Image J, an image analysis program, and the aspect ratio of the contoured primary particles can be measured using the Image J program. The aspect ratio of the cross section of the primary particles can be measured using various image programs, and the Image J program can be used as an example. Image J is software developed by the National Institutes of Health, etc. https: / / ImageJ.net / ImageJ It can be downloaded from the website and detailed instructions are available at https: / / en.Wikipedia.org / wiki / ImageJ You can refer to sites such as:

[0038] The aspect ratio of a primary particle can be determined by drawing two parallel lines on an arbitrarily selected primary particle in an EBSD photograph so that it forms a sandwich. The longest distance between the parallel lines (long axis; horizontal; width; long side) is called "x," and the length perpendicular to this (short axis; vertical; height; shorter side) is called "y." Here, the aspect ratio of a primary particle is the ratio of x to y, i.e., x / y. Here, the average aspect ratio of a primary particle is the average aspect ratio of the primary particles within one secondary particle.

[0039] Specifically, the average aspect ratio of the primary particles may be 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, or 1.3 or less, or 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, or 1.5 or more. A cathode active material having an average aspect ratio of the primary particles of 1.7 or less can be prepared by appropriately controlling the preparation conditions, such as by using a nickel-based composite oxide as a raw material during the preparation of the cathode active material, thereby eliminating interference caused by hydrate evaporation during the reaction with lithium and improving the reaction between the lithium raw material and water. When the average aspect ratio of the primary particles satisfies the above ranges, the sphericity and uniformity of the primary particles can be improved, thereby improving the charge / discharge capacity, efficiency, and life characteristics of the battery, as well as output characteristics.

[0040] According to one embodiment, the ratio of the number of primary particles having an aspect ratio of 1.2 to 1.7 to the total number of primary particles in a cross section of one secondary particle may be 50% or more, and specifically, the ratio of primary particles having an aspect ratio of 1.2 to 1.7 may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0041] Specifically, the method for determining the proportion of primary particles with an aspect ratio of 1.2 to 1.7 can be as follows: The primary particles are contoured using the Image J program in an EBSD image of a cross section of a secondary particle cut with an FIB. The aspect ratios of all contoured primary particles are measured and the aspect ratio distribution is analyzed. The number ratio of primary particles with an aspect ratio of 1.2 to 1.7 can then be derived.

[0042] According to one embodiment, the ratio of the number of primary particles having an aspect ratio of 4 or more to the total number of primary particles in the cross section of one secondary particle may be 10% or less. Specifically, the ratio of the number of primary particles having an aspect ratio of 4 or more may be 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, 2% or less, or 1% or less, or may be 0.2% or more, 0.4% or more, 0.6% or more, or 0.8% or more.

[0043] When the primary particles have the above aspect ratio distribution, the primary particles tend to have a circular shape, ensuring high sphericity of the primary particles, thereby ensuring high capacity, long life, and high output of the positive electrode active material.

[0044] The average particle size of the secondary particles (D 50 ) may be 8 μm to 20 μm, 8 μm to 18 μm, or 10 μm to 15 μm. Here, the average particle size of the secondary particles is determined by measuring the size (particle size or major axis length) of about 20 secondary particles in an SEM image of the positive electrode active material to obtain a particle size distribution, and determining the particle size (D) where the cumulative volume is 50% by volume. 50 ) can be taken as the average particle size.

[0045] Method for producing positive electrode active material In one embodiment, there is provided a method for producing a positive electrode active material, comprising mixing a nickel-based composite oxide and a lithium raw material, followed by heat treatment to obtain the positive electrode active material.

[0046] The nickel-based composite oxide can be represented by the following chemical formula 4. Ni x4 M 6 y4 M 7 z4 O 2-b4 X b4

[0047] In the above chemical formula 4, 0.8≦x4<1, 0 <y4≦0.2、0≦z4≦0.2、0.9≦x4+y4+z4≦1.1、および0≦b4≦0.1であり、M 6 and M 7 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0048] In chemical formula 4, 0.85≦x4<1, 0 <y4≦0.15、および0≦z4≦0.15であってもよい。

[0049] The nickel-based composite oxide can be represented by the following formula 5 or 6, for example.

[0050] [Chemical formula 5] Ni x5 Co y5 M 8 z5 O 2-b5 X b5 In the above chemical formula 5, 0.8≦x5<1, 0 <y5≦0.2、0≦z5≦0.2、0.9≦x5+y5+z5≦1.1、および0≦b5≦0.1であり、M 8 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is F, P, S, or a combination thereof.

[0051] In Chemical Formula 5, 0.8≦x5≦0.99, 0.01≦y5≦0.1, and 0≦z5≦0.1 may be satisfied.

[0052] [Chemical formula 6] Ni x6 Co y6 M 9 z6 M 10 w6 O 2-b6 X b6 In the above chemical formula 6, 0.8≦x6≦0.98, 0.01≦y6≦0.19, 0.01≦z6≦0.19, 0≦w6≦0.19, 0.9≦x6+y6+z6+w6≦1.1, and 0≦b6≦0.1; M 9 is Al, Mn, or a combination thereof, and M 10 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is F, P, S, or a combination thereof.

[0053] In Chemical Formula 6, 0.8≦x6≦0.95, 0.01≦y6≦0.15, 0.01≦z6≦0.05, and 0≦w6≦0.05 may be satisfied.

[0054] The nickel-based composite oxide may be a high-concentration nickel-containing oxide. For example, the nickel content in the nickel-based composite oxide relative to 100 mol% of all metals may be 80 mol% or more, for example, 81 mol% or more, 82 mol% or more, 83 mol% or more, 84 mol% or more, or 85 mol% or more, or 100 mol% or less, 99 mol% or less, 95 mol% or less, 90 mol% or less, 89 mol% or less, or 88 mol% or less.

[0055] The nickel-based composite oxide may be a commercially available product, or may be produced using a nickel-based composite hydroxide. For example, the nickel-based composite oxide may be produced by heat-treating a nickel-based composite hydroxide produced by a coprecipitation method in an oxidizing atmosphere at a temperature of 500°C or less for 6 hours or less.

[0056] In one embodiment, a method for manufacturing a cathode active material involves mixing a nickel-based composite oxide with a lithium raw material and heat-treating the mixture. This allows the size, standard deviation, aspect ratio, and other properties of the primary particles of the cathode active material to be controlled within the above-described ranges while using a lower heat-treatment temperature than in a conventional method for mixing a nickel-based composite hydroxide with a lithium raw material and heat-treating the mixture. As a result, a cathode active material that can ensure high capacity, long life, and high output can be provided.

[0057] The lithium source may be, for example, Li2CO3, LiOH, hydrates thereof, or a combination thereof.

[0058] The lithium raw material can be mixed so that the ratio of lithium in the lithium raw material is 0.9 mol to 1.2 mol per 1 mol of all the metals in the nickel-based composite oxide. Specifically, the lithium in the lithium raw material can be mixed at a ratio of 0.9 mol or more, 0.95 mol or more, 1 mol or more, or 1.04 mol or more per 1 mol of all the metals in the nickel-based composite oxide, or at a ratio of 1.2 mol or less, 1.15 mol or less, 1.1 mol or less, or 1.06 mol or less.

[0059] Generally, to produce polycrystalline nickel using a nickel-based composite hydroxide containing a high concentration of nickel, the heat treatment temperature must be increased, but there is a limit to increasing the heat treatment temperature because the structure becomes unstable as the heat treatment temperature increases. However, a method for producing a positive electrode active material according to an embodiment uses a nickel-based composite oxide as a raw material, so that the heat treatment temperature can be appropriately adjusted to produce a positive electrode active material containing a high concentration of nickel, thereby ensuring high capacity, long life, and high output.

[0060] The heat treatment can be carried out within a range of 600° C. to 800° C. Specifically, the heat treatment can be carried out at 650° C. or higher, 700° C. or higher, or 750° C. or higher, and at 790° C. or lower, 780° C. or lower, or 770° C. or lower.

[0061] In one embodiment, the heat treatment includes a temperature rise step and a temperature maintenance step, and the temperature rise time may be, for example, 1 hour to 3 hours, and the temperature maintenance time may be, for example, 6 hours to 8 hours. In some cases, the temperature rise time and the temperature maintenance time may be adjusted appropriately, and the temperature rise time may be longer than the temperature maintenance time.

[0062] positive electrode The positive electrode for a lithium secondary battery may include 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 includes the positive electrode active material, and may further include a binder, a conductive material, or a combination thereof.

[0063] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders 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, and nylon.

[0064] The content of the binder in the positive electrode active material layer may be about 1 wt % to 5 wt % based on 100 wt % of the positive electrode active material layer.

[0065] The conductive material is used to impart conductivity to the electrode and can be any material that is electron-conductive and does not cause chemical changes in the battery. Examples of conductive materials 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 containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0066] The content of the conductive material in the positive electrode active material layer may be 1 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer.

[0067] The positive electrode current collector may be, but is not limited to, aluminum foil.

[0068] Lithium secondary battery Another embodiment provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte.

[0069] The lithium secondary battery includes a positive electrode and a negative electrode containing the positive electrode active material, so that a lithium secondary battery capable of ensuring high capacity, long life, and high output can be provided.

[0070] For 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. The electrolyte may be liquid or in the form of a gel polymer. Alternatively, the lithium secondary battery may be an all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte, or a semi-solid battery including a positive electrode, a negative electrode, and a semi-solid electrolyte. The term "semi-solid" may refer to a battery that contains both solid and liquid components, or a battery that is mostly solid but contains some liquid components. The all-solid-state battery and the semi-solid battery may not require a separator. The positive electrode active material according to an embodiment of the present invention can achieve high capacity, very high charge / discharge efficiency, and high-temperature life depending on its shape, making it suitable for use in the above-mentioned types of batteries and exhibiting excellent performance in each battery.

[0071] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. Referring to FIGS. 1 to 4, a 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 housing the electrode assembly 40. 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. Also, as shown in FIG. 2, the lithium secondary battery 100 may 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.

[0072] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer includes a negative electrode active material, and may further include a binder, a conductive material, or a combination thereof.

[0073] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0074] The material capable of reversibly intercalating / deintercalating lithium ions includes a carbon-based negative electrode active material.

[0075] The carbon-based negative electrode active material can include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like. Soft carbon refers to a carbon material that can be graphitized and is a material that can be easily graphitized by heat treatment at a high temperature, for example, about 2800°C. Hard carbon is a carbon material that cannot be graphitized or is finely graphitized by heat treatment.

[0076] The negative electrode active material layer can further include other types of negative electrode active materials in addition to the carbon-based negative electrode active material. For example, it can further include lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, and the like.

[0077] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0078] As the material capable of doping and dedoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0079] The silicon-carbon composite may be a composite of silicon and amorphous carbon. 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, the composite 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 may also be located between the primary silicon particles, e.g., the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0080] 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 core surface.

[0081] The Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio by weight may be 1:99 to 90:10.

[0082] The content of the negative electrode active material in the negative electrode active material layer may be 95 wt % to 99 wt % relative to 100 wt % of the negative electrode active material layer.

[0083] In one embodiment, the negative electrode active material layer may optionally further include a binder, a conductive material, or a combination thereof.

[0084] The binder serves to firmly adhere the negative active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0085] Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0086] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0087] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0088] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause a chemical change in the constructed battery can be used. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and carbon nanotubes; 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 conductive materials including mixtures thereof.

[0089] The content of the binder in the negative electrode active material layer may be 1 wt % to 5 wt % based on 100 wt % of the negative electrode active material layer, and the content of the conductive material in the negative electrode active material layer may be 1 wt % to 5 wt % based on 100 wt % of the negative electrode active material layer.

[0090] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0091] electrolyte The electrolyte for a lithium secondary battery may be, for example, an electrolytic solution, which includes a non-aqueous organic solvent and a lithium salt.

[0092] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0093] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0094] 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), and butylene carbonate (BC).

[0095] 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, and caprolactone.

[0096] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic 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; and sulfolanes.

[0097] The non-aqueous organic solvents can be used alone or in combination of two or more.

[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 lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. 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 F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0100] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0101] 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.

[0102] The porous substrate may be a polymer membrane formed from 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, and polytetrafluoroethylene (e.g., Teflon (registered trademark)), or a copolymer or mixture of two or more of these.

[0103] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0104] 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.

[0105] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

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

[0107] Example (1) Manufacturing of positive electrode active material Nickel-based composite oxides 0.88 Co 0.105 Al 0.015100 moles of O2 was mixed with 100 moles of LiOH, and the temperature was raised to 750°C at a uniform rate over 2 hours in an oxygen atmosphere. Then, the mixture was heat-treated at 750°C for 8 hours to obtain the final positive electrode active material, a lithium-nickel composite oxide (LiNi 0.88 Co 0.105 Al 0.015 O2) was obtained.

[0108] The lithium nickel composite oxide is in the form of secondary particles formed by agglomeration of a plurality of primary particles. The average size of the primary particles measured through EBSD analysis of the cross section of the secondary particles is about 1.24 μm, the standard deviation of the size of the primary particles is about 0.17 μm, and the average particle size (D 50 ) was about 13 μm.

[0109] (2) Manufacturing of the positive electrode The resulting cathode active material, polyvinylidene fluoride as a binder, and carbon nanotubes as a conductive material were mixed in a weight ratio of 97.7:1.0:1.3 to prepare a cathode active material composition. The resulting mixture was dispersed in N-methylpyrrolidone solvent to prepare a cathode active material layer slurry. The cathode active material layer slurry was coated onto aluminum foil to form an electrode plate, which was then dried at 135°C for at least 3 hours, followed by rolling and vacuum drying to fabricate a cathode.

[0110] (3) Manufacture of lithium secondary batteries A coin half-cell was fabricated using the positive electrode and a lithium metal counter electrode as the negative electrode. An electrolyte was injected between the positive electrode and the lithium metal counter electrode via a separator (thickness: approximately 16 μm) made of a porous polyethylene film. The electrolyte was a solution of 1.1 M LiPF6 dissolved in a solvent made of a 3:5 volume ratio mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0111] Comparative Example (1) Manufacturing of positive electrode active material Nickel-based composite hydroxides0.88 Co 0.105 Al 0.015 100 moles of (OH)2 was mixed with 100 moles of LiOH, and the mixture was heated to 750°C at a uniform rate over 2 hours in an oxygen atmosphere. The mixture was then heat-treated at 750°C for 8 hours to obtain the final positive electrode active material, a lithium nickel composite oxide (LiNi 0.88 Co 0.105 Al 0.015 O2) was obtained.

[0112] The nickel-based composite oxide is in the form of secondary particles formed by agglomeration of multiple primary particles. The average size of the primary particles measured by EBSD analysis of the cross section of the secondary particles is about 1.01 μm, the standard deviation of the size of the primary particles is about 0.14 μm, and the average particle size (D 50 ) was about 13 μm.

[0113] (2) Manufacturing of cathodes and lithium secondary batteries A positive electrode and a lithium secondary battery were produced in substantially the same manner as in Example.

[0114] Evaluation example 1: Analysis of cross section of positive electrode active material FIG. 5 is a scanning electron microscope (SEM) image of a cross section of the cathode active material prepared in the example, cut by FIB, and FIG. 7 is an electron backscatter diffraction (EBSD) image of the primary particles in FIG. 5, with outline processing.

[0115] FIG. 6 is a scanning electron microscope (SEM) image of a cross section of the cathode active material prepared in the comparative example, cut with an FIB, and FIG. 8 is an electron backscatter diffraction (EBSD) image of the primary particles in FIG. 6, with outline processing.

[0116] 7 and 8, it can be seen that the primary particles of the cathode active material prepared in the Examples are larger in size and more uniform in size than the primary particles of the cathode active material prepared in the Comparative Examples, and that the primary particles have an aspect ratio close to 1 and exhibit a spherical shape.

[0117] The average particle size of the secondary particles of the positive electrode active materials produced in the examples and the comparative examples was all about 13 μm.

[0118] Evaluation example 2. Evaluation of the average and standard deviation of primary particle size Ten randomly selected points were measured on the electron backscatter diffraction (EBSD) photographs of the cross sections of the positive electrode active materials prepared in the Examples and Comparative Examples, and the primary particle sizes at the ten points were measured using an image analysis program (Image J). The average and standard deviation of the primary particle sizes were calculated from the primary particle sizes measured at the ten points. The results are shown in Table 1 below. In Table 1, the numbers 1 to 10 in a row refer to ten randomly selected points on the electron backscatter diffraction (EBSD) photographs of the cross sections of the positive electrode active materials prepared in the Examples and Comparative Examples.

[0119] [Table 1]

[0120] Evaluation example 3. Primary particle aspect ratio analysis Using an image analysis program (Image J), ​​the aspect ratio distribution of the primary particles was analyzed in the photographs of Figures 7 and 8. When the average aspect ratio of the primary particles was calculated, the average aspect ratio of the primary particles of the Example was 1.58, and the average aspect ratio of the primary particles of the Comparative Example was 1.82. Referring to Figures 7 and 8, it can be seen that the primary particles of the Example are closer to spherical and more uniform than the primary particles of the Comparative Example, and that the primary particles of the Comparative Example are arranged in a relatively radial pattern.

[0121] 9 and 10 show the aspect ratio distribution of primary particles in the cross sections of the cathode active materials prepared in the examples and comparative examples, respectively. In Figures 9 and 10, the horizontal axis represents the aspect ratio of the primary particles, and the vertical axis represents the cumulative proportion of primary particles having the aspect ratio of the primary particles corresponding to the horizontal axis.

[0122] 9 and 10, it can be seen that the majority of the aspect ratios of the primary particles in the cross section of the positive electrode active material prepared in the examples are less than 4, while the positive electrode active material prepared in the comparative examples has a large number of primary particles with an aspect ratio of 4 or more in the cross section. Also, it can be seen in FIG. 11 that the graph of the aspect ratios of the primary particles in the cross section of the positive electrode active material prepared in the examples is biased to the left compared to the graph of the aspect ratios of the primary particles in the cross section of the positive electrode active material prepared in the comparative examples, indicating that the cumulative proportion of primary particles with an aspect ratio in the range of 1 to 2 is high.

[0123] Figure 12 is a graph analyzing the aspect ratio distribution curve of primary particles in Figure 9, and is a bar graph showing the proportion of primary particles within the aspect ratio range on the x-axis by analyzing the aspect ratio of primary particles within secondary particles in the cross sections of the cathode active materials prepared in Examples and Comparative Examples. The data in Figure 12 is shown in Table 2 below.

[0124] [Table 2]

[0125] 12 and Table 2, it can be seen that the proportion of primary particles having an aspect ratio of 4 or more in the cross section of the positive electrode active material prepared in the example was 0.8%. In contrast, the proportion of primary particles having an aspect ratio of 4 or more in the cross section of the positive electrode active material prepared in the comparative example was 1.51%. Considering this, it can be seen that the primary particles of the positive electrode active material prepared in the example were more uniform than the primary particles of the positive electrode active material prepared in the comparative example.

[0126] Evaluation example 4. High rate characteristic evaluation The lithium secondary batteries prepared in the examples and comparative examples were initially charged at 25°C at a constant current / constant voltage of 1C, 4.25V, and 0.05C cut-off, followed by a 10-minute rest, and then discharged at a constant current / constant voltage of 1C with a 3V cut-off, followed by a 10-minute rest. Subsequently, the C-rate of the charge / discharge conditions was changed to 2C, 3C, 4C, 5C, and 1C, and the charge / discharge cycle was repeated.

[0127] The discharge capacity graph for each cycle is shown in FIG. 13, and the ratio of the discharge capacity for each C rate cycle to the discharge capacity for the initial 1C cycle was calculated and the results are shown in Table 3 below.

[0128] [Table 3]

[0129] Referring to FIG. 13, the lithium secondary batteries prepared in the examples have a better discharge capacity retention rate at all C rates, especially at high rates (4C, 5C), than the lithium secondary batteries prepared in the comparative examples. Furthermore, the discharge capacity retention rate at the final 1C rate is also superior, indicating a superior capacity recovery rate.

[0130] summary The Example in which a cathode active material was prepared by mixing a nickel-based composite oxide and a lithium raw material and heat-treating the mixture had the same average particle size of secondary particles as the Comparative Example in which a cathode active material was prepared by mixing a nickel-based composite hydroxide and a lithium raw material and heat-treating the mixture. However, the Example had a relatively larger average primary particle size than the Comparative Example, a small standard deviation of the primary particle size of 0.3 μm or less, and an average aspect ratio of the primary particles of 1.7 or less, which showed a relatively uniform spherical shape.

[0131] On the contrary, in the comparative example, it can be seen that the primary particles are radially shaped with a relatively large aspect ratio.

[0132] In addition, it was confirmed that the Examples, in which the primary particles were relatively large, relatively uniform, and spherical, had superior discharge capacity retention and capacity recovery rates compared to the Comparative Examples, in which the primary particles were relatively small, had non-uniform aspect ratio distribution, and exhibited a spun form.

[0133] This indicates that positive electrode active materials with relatively large, uniform, and spherical primary particles have superior battery performance compared to positive electrode active materials without such particles. [Explanation of symbols]

[0134] 100: Lithium secondary battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tap 71: Positive tap 72: Negative tap

Claims

1. A positive electrode active material including a lithium nickel-based composite oxide and having a secondary particle form in which a plurality of primary particles are aggregated, The average size of the primary particles measured through electron backscatter diffraction (EBSD) analysis of the cross section of the secondary particles is in the range of 1.05 μm to 1.5 μm; The standard deviation of the size of the primary particles is 0.3 μm or less, The average aspect ratio of the primary particles is 1.7 or less. Cathode active material.

2. The positive electrode active material according to claim 1 , wherein the lithium nickel-based composite oxide is represented by the following chemical formula 1: [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 1, 0.9≦a1≦1.2, 0.8≦x1<1, 0<y1≦0.2, 0≦z1≦0.2, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is one or more elements selected from F, P, and S.

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

4. 2. The positive electrode active material according to claim 1, wherein the ratio of the number of primary particles having an aspect ratio of 1.2 to 1.7 to the total number of primary particles in a cross section of one secondary particle is 50% or more.

5. 2 . The positive electrode active material according to claim 1 , wherein the ratio of the number of primary particles having an aspect ratio of 4 or more to the total number of primary particles in a cross section of one secondary particle is 10% or less.

6. The average particle size of the secondary particles (D 50 2. The positive electrode active material according to claim 1, wherein the particle size is 8 μm to 20 μm.

7. A method for producing a positive electrode active material, comprising mixing a nickel-based composite oxide and a lithium raw material, followed by heat treatment to obtain the positive electrode active material according to claim 1.

8. The method for producing a positive electrode active material according to claim 7, wherein the nickel-based composite oxide is represented by the following chemical formula 4: [Chemical formula 4] Yes x4 M 6 y4 M 7 z4 Oh 2-b4 X b4 In the above chemical formula 4, 0.8≦x4<1, 0<y4≦0.2, 0≦z4≦0.2, 0.9≦x4+y4+z4≦1.1, and 0≦b4≦0.1; M 6 and M 7 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, and Zr, and X is one or more elements selected from F, P, and S.

9. The method for producing a positive electrode active material according to claim 7 , wherein the nickel content in the nickel-based composite oxide is 80 mol % or more relative to 100 mol % of the total metals.

10. 8. The method for producing a positive electrode active material according to claim 7, wherein the lithium raw material is mixed so that the ratio of lithium of the lithium raw material to 1 mole of all metals of the nickel-based composite oxide is 0.9 moles to 1.2 moles.

11. The method for producing a positive electrode active material according to claim 7, wherein the heat treatment is carried out in a range of 600°C to 800°C.

12. 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 claim 1 .

13. A lithium secondary battery comprising the positive electrode, negative electrode, and electrolyte according to claim 12.

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