Positive electrode active material for rechargeable lithium battery and rechargeable lithium battery including the same

Abstract

To provide a positive electrode active material for a rechargeable lithium battery exhibiting high stability at high voltage, and a rechargeable lithium battery of which the resistance is reduced and the lifetime characteristics at high voltage and high temperature are improved while a high capacity is realized.SOLUTION: Disclosed are: a positive electrode active material for a rechargeable lithium battery; a positive electrode including the positive electrode active material; a method of manufacturing the positive electrode; and a rechargeable lithium battery. The positive electrode active material for the rechargeable lithium battery includes: a first positive electrode active material including a first lithium cobalt-based oxide doped with aluminum; and a second positive electrode active material including a second lithium cobalt-based oxide doped with aluminum. An average particle diameter (D50) of the first positive electrode active material is greater than an average particle diameter (D50) of the second positive electrode active material. An amount of aluminum based on 100 wt% of a total metal amount in the second positive electrode active material excluding lithium is greater than an amount of aluminum based on 100 wt% of a total metal amount in the first positive electrode active material excluding lithium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In modern society, the convenience of portable electronic devices is changing even lifestyles. Portable electronic devices are gradually replacing many parts of the home, and the lithium secondary batteries used as driving power sources are being required to meet increasingly high specifications.

[0003] The cathode active material used in lithium secondary batteries for portable electronic devices is primarily lithium cobalt oxide, and in recent years, research has been progressing to achieve higher capacities. Lithium cobalt oxide has a high theoretical capacity of 274 mAh / g, but in practice, only half of this capacity can be used due to capacity reduction caused by phase transition. In particular, high-voltage charging and discharging is required to achieve high energy density. However, due to the irreversible phase transition of lithium cobalt oxide that occurs at high voltages and side reactions with the electrolyte, research is needed to improve structural safety. Summary of the Invention [Problem to be solved by the invention]

[0004] Provided is a positive electrode active material for a lithium secondary battery that exhibits high stability at high voltages, and a lithium secondary battery that has low resistance and improved life characteristics at high voltages and high temperatures while realizing high capacity. [Means for solving the problem]

[0005] In one embodiment, a cathode active material includes a first cathode active material including a first lithium-cobalt-based oxide doped with aluminum; and a second cathode active material including a second lithium-cobalt-based oxide doped with aluminum; and the first cathode active material has an average particle size (D 50 ) is the average particle size (D 50) and the aluminum content in the second positive electrode active material relative to 100% by weight of all metals excluding lithium is higher than the aluminum content in the first positive electrode active material relative to 100% by weight of all metals excluding lithium.

[0006] In one embodiment, a positive electrode for a lithium secondary battery is provided, the positive electrode comprising: 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 comprising the positive electrode active material for a lithium secondary battery.

[0007] In one embodiment, a method for manufacturing a positive electrode for a lithium secondary battery includes the steps of: preparing a composition including a first positive electrode active material including an aluminum-doped lithium cobalt-based oxide; and a second positive electrode active material including an aluminum-doped lithium cobalt-based oxide; coating the composition on a current collector; and drying and rolling the composition; wherein the average particle size (D 50 ) is the average particle size (D 50 ) and the aluminum content in the second positive electrode active material relative to 100% by weight of all metals excluding lithium is higher than the aluminum content in the first positive electrode active material relative to 100% by weight of all metals excluding lithium.

[0008] In one embodiment, a lithium secondary battery is provided, comprising: a positive electrode for a lithium secondary battery; a negative electrode; and an electrolyte solution. [Effects of the Invention]

[0009] The positive electrode active material for a lithium secondary battery prepared according to an embodiment has high stability at high voltage, and a lithium secondary battery including the positive electrode active material can exhibit low resistance and excellent high-temperature life while achieving high capacity and high energy density. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 shows TEM and RAMAN images of a cross section of the positive electrode of Example 1. [Figure 6] 1 shows TEM and RAMAN images of a cross section of the positive electrode of Example 2. [Figure 7] 1 shows TEM and RAMAN images of a cross section of the positive electrode of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention is not limited to the embodiments set forth herein.

[0012] 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.

[0013] "Combinations thereof" means mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "comprise," or "have" 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.

[0015] To clearly illustrate the various layers and regions in the drawings, thicknesses have been exaggerated, and similar parts have been given 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 when it is "directly on" that other part, but also when there are other parts between them. Conversely, when a part is said to be "directly on" another part, it means that there are no other parts between them.

[0016] The term "layer" includes not only shapes formed on the entire surface but also shapes formed on a portion of the surface when observed in a plan view.

[0017] The average particle size can be measured by methods 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 is performed to count the number of particles in each particle size range, and then the average particle size can be calculated from this. Unless otherwise defined, the average particle size is the diameter (D) of particles with a cumulative volume of 50% in the particle size distribution. 50 ) Furthermore, unless otherwise defined, the average particle size is determined by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, and then determining the diameter (D) of the particles with a cumulative volume of 50% from the particle size distribution. 50 ) may be taken as the average particle size.

[0018] "Or" is not to be construed as exclusive; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0019] The term "metal" is understood to include general metals, transition metals, and metalloids.

[0020] positive electrode The positive electrode for a lithium secondary battery 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 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0021] positive electrode active material In order to prevent contraction and expansion due to charge and discharge within the positive electrode active material and to support the structure that collapses due to rearrangement of the layered structure, a different element is doped to produce a positive electrode active material with excellent stability at high voltage. In particular, Al is used to strengthen the structural stability of the lithium cobalt oxide used in the positive electrode active material. 3+ Doping is possible. 3+ Co 3+ The size of the ions is similar to that of Al 3+ :0.535Å, Co 3+ Since it has the same oxidation number as Co—O (0.545Å), it can be easily used as a dopant. In addition, it has a stronger Al-O bond energy (511±3kJ / mol) than the Co-O bond energy (384.5±13.4kJ / mol). Although Al does not participate in electrochemical reactions, it can support the structure of the active material when it contracts and expands during charge and discharge, making it advantageous for use as a dopant.

[0022] High-capacity lithium secondary batteries require greater capacity at higher voltages, so Al doping is essential to improve structural safety at high voltages. However, while improving structural safety, the specific capacity of the positive electrode active material must be maintained above a certain level, and an appropriate amount of doping is required to avoid a trade-off with other properties such as resistance.

[0023] In one embodiment, two types of lithium-cobalt-based positive electrode active materials having different particle sizes are mixed, and the aluminum content and content ratio doped into the large and small particles are finely adjusted. In particular, the aluminum doping amount of the small particles, which deteriorate relatively rapidly, is increased, thereby ensuring structural stability at high voltages and simultaneously improving capacity, resistance, and life characteristics at high voltages. This provides a positive electrode active material for lithium secondary batteries.

[0024] In one embodiment, a cathode active material includes a first cathode active material including an aluminum-doped lithium cobalt-based oxide; and a second cathode active material including an aluminum-doped lithium cobalt-based oxide; and the first cathode active material has an average particle size (D 50 ) is the average particle size (D 50 ) and the aluminum content in the second positive electrode active material relative to 100% by weight of all metals excluding lithium is higher than the aluminum content in the first positive electrode active material relative to 100% by weight of all metals excluding lithium.

[0025] First positive electrode active material The first positive electrode active material includes a first lithium cobalt-based oxide doped with aluminum, and the first lithium cobalt-based oxide doped with aluminum may be represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Co x1 Al y1 M 1 z1 O 2-b1 X b1

[0026] In the above Chemical Formula 1, 0.9≦a1≦1.8, 0.881≦x1≦0.987, 0.013≦y1≦0.019, 0≦z1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 is at least one element selected from B, Ba, Ca, Ce, 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 the group consisting of F, P and S.

[0027] In Chemical Formula 1, for example, 0.883≦x1≦0.987, 0.013≦y1≦0.017, 0≦z1≦0.1, or 0.883≦x1≦0.985, 0.015≦y1≦0.017, 0≦z1≦0.1, or 0.9≦a1≦1.5, 0.9≦a1≦1.2, or 0.98≦a1≦1.0.

[0028] The aluminum-doped first lithium-cobalt-based oxide may have an Al content of 0.9 wt % or less (9000 ppm or less) relative to 100 wt % of all metals excluding lithium, such as 0.88 wt % or less, 0.86 wt % or less, 0.84 wt % or less, 0.82 wt % or less, or 0.8 wt % or more, 0.6 wt % or more, 0.62 wt % or more, 0.64 wt % or more, 0.66 wt % or more, 0.68 wt % or more, or 0.7 wt % or more. When the aluminum-doped first lithium-cobalt-based oxide contained in the first positive electrode active material has an Al content within this range, the positive electrode active material containing the aluminum-doped first lithium-cobalt-based oxide is structurally stable at high voltages and may exhibit improved capacity, resistance, and life characteristics.

[0029] The first positive electrode active material including the first lithium cobalt-based oxide doped with aluminum may be expressed as large grains or large particles. 50 ) is 7 μm to 30 μm, and may be, for example, 9 μm to 25 μm, 10 μm to 25 μm, or 12 μm to 20 μm. Here, the average particle size of the first positive electrode active material is larger than the average particle size of the second positive electrode active material described below. The positive electrode active material according to one embodiment is in a form in which the first positive electrode active material, which is a large particle, is mixed with the second positive electrode active material, which is a small particle, described below, and this can improve the mixture density, thereby realizing high capacity and high energy density.

[0030] In one embodiment, the first positive electrode active material is included in an amount of 50 wt% to 90 wt%, for example, 60 wt% to 90 wt%, or 70 wt% to 90 wt%, based on the total amount of the first positive electrode active material and the second positive electrode active material. In this case, a positive electrode active material including this first positive electrode active material can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0031] Second positive electrode active material The second positive electrode active material includes a second lithium cobalt-based oxide doped with aluminum, and the second lithium cobalt-based oxide doped with aluminum can be represented by the following Chemical Formula 2: [Chemical formula 2] Li a2 Co x2 Al y2 M 2 z2 O 2-b2

[0032] In the above Chemical Formula 2, 0.9≦a2≦1.8, 0.878≦x2≦0.985, 0.015≦y2≦0.022, 0≦z2≦0.1, 0.9≦x2+y2+z2≦1.1, and 0≦b2≦0.1; M 2 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr.

[0033] In Chemical Formula 2, for example, 0.881≦x2≦0.984, 0.016≦y2≦0.019, 0≦z2≦0.1, and may be 0.9≦a2≦1.5, 0.9≦a2≦1.2, or 0.98≦a2≦1.0.

[0034] The aluminum-doped second lithium-cobalt-based oxide contained in the second positive electrode active material may have an Al content of 1.0 wt % or less, for example, 0.98 wt % or less, 0.96 wt % or less, 0.94 wt % or less, 0.92 wt % or less, or 0.90 wt % or less, or 0.70 wt % or more, 0.71 wt % or more, 0.72 wt % or more, 0.73 wt % or more, 0.74 wt % or more, or 0.75 wt % or more. When the aluminum-doped second lithium-cobalt-based oxide contained in the second positive electrode active material has an Al content within this range, the positive electrode active material containing the aluminum-doped second lithium-cobalt-based oxide may be structurally stable at high voltages and exhibit excellent capacity, resistance, and life characteristics.

[0035] The second positive electrode active material including the second lithium cobalt-based oxide doped with aluminum can be expressed as small grains or small particles. 50 ) is 1 μm to 9 μm, and may be, for example, 1 μm to 8 μm, or 2 μm to 6 μm. Here, the average particle size of the second positive electrode active material is smaller than the average particle size of the first positive electrode active material described above. The positive electrode active material according to one embodiment is in a form in which the first positive electrode active material, which is a large particle, and the second positive electrode active material, which is a small particle, are mixed, thereby improving the mixture density and realizing high capacity and high energy density.

[0036] In one embodiment, the second positive electrode active material is included in an amount of 10 wt% to 50 wt%, for example, 10 wt% to 40 wt%, or 10 wt% to 30 wt%, based on the total amount of the first positive electrode active material and the second positive electrode active material. When the content ratio of the first positive electrode active material to the second positive electrode active material is within this range, the positive electrode active material including these materials can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0037] In one embodiment, the second positive electrode active material may have a higher aluminum content relative to 100 wt % of all metals excluding lithium than the first positive electrode active material. The aluminum content relative to 100 wt % of all metals excluding lithium in the second positive electrode active material may be higher by 0.01 wt % or more, for example, 0.01 wt % to 0.20 wt %, 0.01 wt % to 0.15 wt %, 0.01 wt % to 0.10 wt %, 0.02 wt % to 0.10 wt %, 0.03 wt % to 0.10 wt %, 0.04 wt % to 0.10 wt %, or 0.05 wt % to 0.10 wt %, than the aluminum content relative to 100 wt % of all metals excluding lithium in the first positive electrode active material. In this case, the positive electrode active material containing these can maintain a very stable structure even after repeated charging and discharging at high voltage, and can improve all of the characteristics of capacity, resistance, and normal temperature / high temperature life.

[0038] In one embodiment, the aluminum content of the first and second positive electrode active materials relative to 100% by weight of all metals excluding lithium is 0.7% by weight or more, for example, 0.7% to 1.0% by weight, 0.65% to 0.9% by weight, 0.7% to 0.9% by weight, or 0.7% to 0.8% by weight. In this case, a positive electrode active material containing these materials can maintain a very stable structure even after repeated charge and discharge at high voltages, and can improve all of the characteristics of capacity, resistance, and room temperature / high temperature life.

[0039] The first and second positive electrode active materials may each include a coating layer located on the surface thereof. The coating layer may include at least one coating element selected from the group consisting of Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof, and may include an oxide, hydroxide, or combinations thereof containing such a coating element.

[0040] In one embodiment, a positive electrode for a lithium secondary battery is provided, the positive electrode including the positive electrode active material described above. The positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector. The positive electrode active material layer includes the positive electrode active material described above and may optionally further include a binder and / or a conductive material.

[0041] The density of the positive electrode active material layer containing the first and second positive electrode active materials is 4.0 g / cc to 4.5 g / cc, and may be, for example, 4.0 g / cc to 4.4 g / cc, 4.0 g / cc to 4.3 g / cc, 4.1 g / cc to 4.3 g / cc, or 4.1 g / cc to 4.2 g / cc. The density of the positive electrode active material layer refers to the density measured on a rolled positive electrode. When the density of the positive electrode active material layer satisfies the above range, very high energy density and high capacity can be achieved. However, such high-density positive electrodes can sometimes suffer from damage to the positive electrode active material due to repeated charge and discharge. However, according to a positive electrode design of one embodiment, damage to the positive electrode active material can be effectively suppressed while achieving very high density.

[0042] The total thickness of the positive electrode active material layer is about 10 μm to 200 μm, and may be, for example, 10 μm to 180 μm, 10 μm to 160 μm, 20 μm to 160 μm, 20 μm to 140 μm, 20 μm to 120 μm, 30 μm to 120 μm, or 30 μm to 100 μm. When the total thickness of the positive electrode active material layer satisfies this range, a high capacity can be achieved, the problem of deterioration of the positive electrode active material due to repeated charge and discharge can be effectively prevented, and the battery life characteristics can be improved.

[0043] binder 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 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, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0044] The content of the binder in the positive electrode active material layer may be about 1% by weight to 5% by weight based on the total weight of the positive electrode active material layer.

[0045] Conductive material The conductive material according to one embodiment is used to impart conductivity to the electrode, and any material that is electron-conductive and does not undergo 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 containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0046] The content of the positive electrode active material may be 90% by weight to 99.8% by weight, or 95% by weight to 99% by weight, and the contents of the binder and conductive material may be 0.1% by weight to 5% by weight, or 0.5% by weight to 2.5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0047] current collector The positive electrode current collector according to an embodiment is not limited as long as it does not cause chemical changes in the lithium secondary battery and has conductivity, and specific examples thereof include aluminum (Al), stainless steel (SUS), indium (In), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), germanium (Ge), lithium (Li), or a combination thereof, and one example is aluminum (Al). In this case, the current collector may be in the form of a plate or a thin film.

[0048] Positive electrode manufacturing method According to one embodiment, a method for producing a positive electrode active material includes the steps of: preparing a composition including a first positive electrode active material including a first lithium-cobalt-based oxide doped with aluminum; and a second positive electrode active material including a second lithium-cobalt-based oxide doped with aluminum; coating the composition on a current collector; and drying and rolling the composition. The method further includes the steps of: preparing a composition including a first positive electrode active material including a first lithium-cobalt-based oxide doped with aluminum; and coating the composition on a current collector; and drying and rolling the composition. 50 ) is the average particle size (D 50 ) and the aluminum content relative to 100% by weight of all metals excluding lithium in the first positive electrode active material is higher than the aluminum content relative to 100% by weight of all metals excluding lithium in the second positive electrode active material.

[0049] The first and second positive electrode active materials are produced by mixing a lithium raw material with a precursor, which is cobalt hydroxide, cobalt oxide, cobalt-based metal composite oxide, or cobalt-based metal composite hydroxide, and then heat-treating the mixture. The heat treatment is carried out at a temperature of, for example, 800°C to 1100°C, 850°C to 1050°C, or 890°C to 1010°C for 5 to 25 hours, for example, 8 to 15 hours. The precursors can be produced by a common coprecipitation method or the like.

[0050] A method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment can include the steps of: mixing a first cobalt-based metal composite hydroxide with a lithium raw material and heat-treating the mixture to obtain a first positive electrode active material; mixing a second cobalt-based metal composite hydroxide with a lithium raw material and heat-treating the mixture to obtain a second positive electrode active material; and mixing the first positive electrode active material with the second positive electrode active material.

[0051] The first cobalt-based metal composite hydroxide is represented by the following chemical formula 11, and the second cobalt-based metal composite hydroxide is represented by the following chemical formula 12.

[0052] [Chemical formula 11] Co x11 Al y11 M 11 z1(OH)2

[0053] In chemical formula 11, 0.881≦x11≦0.987, 0.013≦y11≦0.019, 0≦z11≦0.1, and 0.9≦x11+y11+z11≦1.1; M 11 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y and Zr.

[0054] [Chemical formula 12] Co x12 Al y12 M 12 z 12 (OH)2

[0055] In the formula 12, 0.878≦x12≦0.985, 0.015≦y12≦0.022, 0≦z12≦0.1, and 0.9≦x12+y12+z12≦1.1; M 12 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, Y, Zr, and combinations thereof.

[0056] The first cobalt-based metal composite hydroxide may be in particulate form with an average particle size of 7 μm to 30 μm, and the second cobalt-based metal composite hydroxide may be in particulate form with an average particle size of 1 μm to 9 μm.

[0057] In the composition containing the first and second positive electrode active materials, the first positive electrode active material is contained in an amount of 50% to 90% by weight, for example, 60% to 90% by weight, or 70% to 90% by weight, based on the total amount of the first and second positive electrode active materials. The second positive electrode active material is contained in an amount of 10% to 50% by weight, for example, 10% to 40% by weight, or 10% to 30% by weight, based on the total amount of the first and second positive electrode active materials. When the content ratio of the first and second positive electrode active materials is within this range, a positive electrode active material containing these materials can achieve high capacity, improve the mixture density, and exhibit high energy density.

[0058] In the coating step, the loading level is 5 mg / cm based on the cross section of the positive electrode active material layer. 2 ~50mg / cm 2 Loading at, for example, 5 mg / cm 2 ~40mg / cm 2 , 10 mg / cm 2 ~40mg / cm 2 , or 10 mg / cm 2 ~30mg / cm 2 Loading the positive electrode active material in this range has the advantage that an appropriate amount of the positive electrode active material can be uniformly coated on the current collector.

[0059] The density of the final rolled positive electrode may be 4.0 g / cc to 4.5 g / cc, for example, 4.0 g / cc to 4.4 g / cc, 4.0 g / cc to 4.3 g / cc, 4.1 g / cc to 4.3 g / cc, or 4.1 g / cc to 4.2 g / cc. When the density of the positive electrode active material layer satisfies the above range, very high energy density and high capacity can be achieved. However, such high-density positive electrodes can sometimes suffer from damage to the positive electrode active material due to repeated charge and discharge. However, the positive electrode design of one embodiment can effectively suppress damage to the positive electrode active material while achieving very high density.

[0060] Lithium secondary battery In one embodiment, there is provided a lithium secondary battery comprising the positive electrode; a negative electrode; and an electrolyte, wherein the electrolyte may be a liquid electrolyte or a solid electrolyte.

[0061] For example, in one embodiment, a lithium secondary battery can be provided that includes the above-described positive electrode, negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte solution. As another example, an all-solid-state secondary battery can be provided that includes the above-described positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0062] As an example, a lithium secondary battery using an electrolyte solution will be described below.

[0063] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other shapes depending on their shape. FIGS. 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, with FIG. 1 showing a circular battery, FIG. 2 showing a prismatic battery, and FIGS. 3 and 4 showing pouch-type batteries. 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 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 are 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, 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.

[0064] negative electrode The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0065] The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0066] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of the amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0067] 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.

[0068] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material 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 of these. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0069] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface 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 dispersed in an amorphous carbon matrix.

[0070] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0071] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0072] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0073] The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0074] 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, and combinations thereof.

[0075] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate 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.

[0076] When an aqueous 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.

[0077] The dry binder is a polymeric material that can be fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0078] The conductive material is used to impart conductivity to the electrode and may be any material that is electronically conductive and does not cause chemical changes in the battery. 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.

[0079] 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.

[0080] electrolyte The electrolyte for the lithium secondary battery includes a non-aqueous organic solvent and a lithium salt.

[0081] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0082] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0083] Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, cyclohexanone can be used as a ketone solvent. Ethyl alcohol, isopropyl alcohol, etc. can be used as an alcohol solvent. Aprotic solvents include nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, 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.

[0084] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0085] 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.

[0086] The lithium salt is a substance that dissolves in an organic solvent, acts as a lithium ion source in the battery, enables basic lithium secondary battery operation, and promotes 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(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0087] Separator Depending on the type of lithium secondary battery, a separator is placed 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 materials. Of course, mixed multilayer films 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.

[0088] 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.

[0089] 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, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0090] 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.

[0091] The organic material may 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 (meth)acrylate, and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0092] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) is 1 nm to 2000 nm, and may be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0093] 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.

[0094] Examples and comparative examples of the present invention will be described below. The following examples are illustrative of the present invention, and the present invention is not limited to the following examples.

[0095] Example 1 Manufacturing of positive electrode active materials The first cobalt transition metal composite oxide (Co) with an Al content of 7000 ppm (0.7 wt%) 0.985 Al 0.015 O2), and Li2CO3 were mixed with the entire metal of the first cobalt transition metal composite oxide and the lithium of Li2CO3 in a molar ratio of 1:1.04, and then heat-treated in an air atmosphere at approximately 1000°C for 10 hours to obtain an average particle size (D 50 ) is about 15 μm of the first positive electrode active material (Li 1.04 Co 0.985 Al 0.015 O2) was produced.

[0096] The Al content of the second cobalt transition metal composite oxide (Co 0.984 Al 0.016 O2), and Li2CO 3、 The whole metal of the cobalt-transition metal composite oxide and the lithium of Li2CO3 were mixed in a molar ratio of 1:1.02, and the mixture was heat-treated in an air atmosphere at approximately 900°C for 10 hours to obtain an average particle size (D 50 ) is about 4 μm thick, and the second positive electrode active material (Li 1.02 Co 0.985 Al 0.015 O2) was produced.

[0097] The prepared first and second positive electrode active materials were mixed in a weight ratio of 8:2 to prepare a positive electrode active material.

[0098] Cathode manufacturing 98.5 wt% of the prepared positive electrode active material, 1.0 wt% of polyvinylidene fluoride binder, and 0.5 wt% of carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, which was then coated on an aluminum foil current collector, dried, and rolled to prepare a positive electrode. At this time, the loading level of the positive electrode active material layer was 20 mg / cm. 2 and the density of the final rolled cathode is about 4.1 g / cc.

[0099] Lithium secondary battery manufacturing Anode active material layer slurry was prepared by mixing 97.5 wt% graphite anode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene-butadiene rubber in an aqueous solvent. The anode active material layer slurry was coated onto a copper foil current collector, dried, and rolled to prepare anodes.

[0100] A lithium secondary battery was fabricated in a conventional manner using a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0101] Examples 2 and 3 and Comparative Examples 1 to 8 In preparing the positive electrode active material of Example 1, the Al content of the first positive electrode active material and the Al content of the second positive electrode active material were changed as shown in Table 1 below, and the positive electrode active material, positive electrode, and battery were prepared in substantially the same manner as in Example 1. The ratio of the Al weight of the second positive electrode active material to the Al weight of the first positive electrode active material is also shown in Table 1 below.

[0102] [Table 1]

[0103] Referring to Table 1, it can be seen from the rightmost column that the ratio of the Al weight in the second positive electrode active material to the Al weight in the first positive electrode active material exceeds 1 in Examples 1 to 3, whereas it is 1 or less in Comparative Examples 1 to 8.

[0104] Evaluation example 1: Initial capacity evaluation The batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were charged at a constant current of 0.2 C at 25°C up to an upper limit voltage of 4.56 V, and then discharged at 0.2 C down to an end-of-discharge voltage of 3.0 V, and the initial discharge capacity was measured. The ratio of the discharge capacity to the charge capacity was calculated as efficiency, and the results are shown in Table 2 below.

[0105] Evaluation example 2: Resistance evaluation Resistance was measured for the batteries of Examples 1 to 3 and Comparative Examples 1 to 8 in a state of SOC10 (residual capacity 10%) after initial charge and discharge in Evaluation Example 1. The results are shown in Table 2 below.

[0106] Evaluation example 3: High temperature life evaluation The battery that had been initially charged and discharged in Evaluation Example 1 was repeatedly charged and discharged 30 times at 45°C and 0.35C, and the discharge capacity after 30 cycles was measured. The ratio of the 30th discharge capacity to the initial discharge capacity is shown in Table 2 below as the capacity retention rate, i.e., the high-temperature life characteristics.

[0107] [Table 2]

[0108] Referring to Table 2, Comparative Examples 1 to 3 were analyzed to have a very low 4.56V high temperature life of less than 90%, and Comparative Examples 4 and 5 had an initial discharge capacity of less than 190 mAh / g.

[0109] On the other hand, Examples 1 to 3 show excellent results in all aspects of evaluation, with high initial discharge capacity of 190 mAh / g or more, high initial charge / discharge efficiency of 92% or more, and 4.56 V high temperature life of 92% or more.

[0110] For example, comparing Example 2 and Comparative Example 3, the Al content of the first positive electrode active material is the same at 7000 ppm, but the Al content of the second positive electrode active material differs, at 8000 ppm and 7000 ppm, respectively. As a result, the ratio of the Al content of the second positive electrode active material to the Al content of the first positive electrode active material is 1.14 and 1, respectively. While Example 2 has a higher Al content in the second positive electrode active material than in the first positive electrode active material, Comparative Example 3 does not meet this requirement. Referring to Table 2, it can be seen that Comparative Example 3 has a shorter 4.56 V high-temperature life than Example 2.

[0111] Meanwhile, comparing Comparative Example 3 with Comparative Example 1, the Al content of the first and second positive electrode active materials in Comparative Example 3 was 7000 ppm, while the Al content of the first and second positive electrode active materials in Comparative Example 1 was 6000 ppm. Referring to Table 2, it can be seen that Comparative Example 1 had a shorter 4.56 V high-temperature life compared to Comparative Example 3. Comparing Comparative Example 3 with Comparative Example 5, the Al content of the first and second positive electrode active materials in Comparative Example 3 was 7000 ppm, while the Al content of the first and second positive electrode active materials in Comparative Example 5 was 9000 ppm. Referring to Table 2, it can be seen that Comparative Example 1 had a significantly lower initial discharge capacity than Comparative Example 3.

[0112] Furthermore, it can be seen that Comparative Examples 6 and 7, in which the ratio of the Al weight in the second positive electrode active material to the Al weight in the first positive electrode active material is lower than 1, have significantly low high-temperature lifetimes of less than 90%, and Comparative Example 8 has low initial charge-discharge efficiency of less than 92%.

[0113] Evaluation example 4: Deterioration analysis After evaluating the high-temperature life characteristics of the batteries fabricated in Example 1, Example 2, and Comparative Example 1 in the same manner as in Evaluation Example 3, the positive electrodes were separated, and cross sections of each positive electrode were photographed using a TEM and subjected to RAMAN analysis. The results for the regions corresponding to LCO (lithium cobalt oxide) and Co3O4 are shown in Figures 5 to 7. In Figure 7, the TEM image (top) and RAMAN analysis image (bottom) of Comparative Example 1 show that there are more green regions than red regions, indicating that the positive electrode active material had deteriorated severely and was converted to Co3O4. Meanwhile, Figure 5 shows the TEM and RAMAN images of Example 1, and Figure 6 shows the TEM and RAMAN images of Example 2. The red regions are more numerous and the green regions are fewer, confirming a reduction in the deterioration of the positive electrode active material.

[0114] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0115] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. a first positive electrode active material comprising a first lithium cobalt-based oxide doped with aluminum; and a second positive electrode active material comprising a second lithium cobalt-based oxide doped with aluminum; Including, The average particle size (D 50 ) is the average particle size (D 50 ) is larger than a content of aluminum relative to 100% by weight of all metals excluding lithium in the second positive electrode active material is higher than a content of aluminum relative to 100% by weight of all metals excluding lithium in the first positive electrode active material.

2. In the first positive electrode active material, the content of aluminum relative to 100% by weight of all metals excluding lithium is 0.6% by weight to 0.9% by weight, In the second positive electrode active material, the content of aluminum relative to 100% by weight of all metals excluding lithium is 0.7% by weight to 1.0% by weight. The positive electrode active material for a lithium secondary battery according to claim 1 .

3. The average particle size (D 50 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle diameter is 7 μm to 30 μm.

4. The average particle size (D 50 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the particle size is 1 μm to 9 μm.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the first positive electrode active material is included in an amount of 50 wt % to 90 wt % and the second positive electrode active material is included in an amount of 10 wt % to 50 wt % based on the total amount of the first positive electrode active material and the second positive electrode active material.

6. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of aluminum relative to 100% by weight of all metals excluding lithium in the second positive electrode active material is 0.01% by weight to 0.10% by weight higher than the content of aluminum relative to 100% by weight of all metals excluding lithium in the first positive electrode active material.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of aluminum relative to 100% by weight of all metals excluding lithium in the first positive electrode active material and the second positive electrode active material is 0.7% by weight to 1.0% by weight.

8. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the first lithium cobalt-based oxide doped with aluminum is represented by Chemical Formula 1: [Chemical formula 1] Li a1 Co x1 Al y1 M 1 z1 O 2-b1 X b1 In the formula 1, 0.9≦a1≦1.8, 0.881≦x1≦0.987, 0.013≦y1≦0.019, 0≦z1≦0.1, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

9. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the aluminum-doped second lithium cobalt-based oxide is represented by Chemical Formula 2: [Chemical formula 2] Li a2 Co x2 Al y2 M 2 z2 O 2-b2 In the formula 2, 0.9≦a2≦1.8, 0.878≦x2≦0.985, 0.015≦y2≦0.022, 0≦z2≦0.1, 0.9≦x2+y2+z2≦1.1, and 0≦b2≦0.1; M 2 is at least one element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr.

10. A positive electrode for a lithium secondary battery comprising 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 for lithium secondary batteries according to any one of claims 1 to 9.

11. 11. The positive electrode for a lithium secondary battery according to claim 10, wherein the density of the positive electrode active material layer is 4.0 g / cc to 4.5 g / cc.

12. A method for producing a positive electrode for a lithium secondary battery, comprising: providing a composition including: a first active cathode material including a first lithium-cobalt-based oxide doped with aluminum; and a second active cathode material including a second lithium-cobalt-based oxide doped with aluminum; coating the composition onto a current collector; and drying and then rolling; Including, The average particle size (D 50 ) is the average particle size (D 50 ) is larger than a content of aluminum relative to 100% by weight of all metals excluding lithium in the second positive electrode active material is higher than a content of aluminum relative to 100% by weight of all metals excluding lithium in the first positive electrode active material.

13. In the step of coating the composition, the loading level is 10 mg / cm based on the cross section of the positive electrode active material layer. 2 ~30 mg / cm 2 The method for producing a positive electrode for a lithium secondary battery according to claim 12,

14. The positive electrode for a lithium secondary battery according to claim 10; a negative electrode; and electrolyte A lithium secondary battery comprising:

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