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

Abstract

We provide a positive electrode active material for achieving high capacity and excellent stability, a positive electrode containing the same, and a lithium secondary battery. [Solution] A positive electrode active material is provided comprising a first positive electrode active material containing a lithium iron phosphate compound and a second positive electrode active material containing a lithium nickel composite oxide, wherein the second positive electrode active material is present in an amount of 1% to 15% by weight relative to 100% by weight of the total of the first and second positive electrode active materials. A positive electrode active material according to one embodiment, a positive electrode containing the same, and a lithium secondary battery can achieve high capacity and excellent stability.

Description

Technical Field

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

Background Art

[0002] Lithium secondary batteries having a high energy density and being easy to carry are mainly used as driving power sources for mobile information terminals such as mobile phones, notebook computers, and smart phones. Recently, research has been actively conducted on using lithium secondary batteries having a high energy density as driving power sources or power storage power sources for hybrid automobiles and electric automobiles.

[0003] In order to realize a lithium secondary battery suitable for such applications, various positive electrode active materials have been studied. Among them, lithium nickel-based oxides, lithium nickel-cobalt-based composite oxides, lithium cobalt oxide, lithium nickel-manganese-based composite oxides, etc. are mainly used as positive electrode active materials. However, such positive electrode active materials have a problem that heat is generated and thermal runaway occurs when a short circuit occurs in a lithium secondary battery, and research for solving this problem is still necessary at present.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Provided are a positive electrode active material for realizing a high capacity and excellent stability, a positive electrode containing the same, and a lithium secondary battery.

Means for Solving the Problems

[0005] In one embodiment, provided is a positive electrode active material including a first positive electrode active material containing a lithium iron phosphate-based compound and a second positive electrode active material containing a lithium nickel-based composite oxide, and containing 1% to 15% by weight of the second positive electrode active material with respect to a total of 100% by weight of the first positive electrode active material and the second positive electrode active material.

[0006] In other embodiments, a current collector and a positive electrode active material layer located on the current collector are included, and the positive electrode active material layer provides a positive electrode including the positive electrode active material and few-walled carbon nanotubes.

[0007] In other embodiments, a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte is provided.

Advantages of the Invention

[0008] The positive electrode active material, the positive electrode containing the same, and the lithium secondary battery according to one embodiment can achieve high capacity and excellent stability.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 2] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 3] It is a diagram schematically showing a lithium secondary battery according to one embodiment. [Figure 4] It is a diagram schematically showing a lithium secondary battery according to one embodiment.

Modes for Carrying Out the Invention

[0010] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0011] The terms used herein are merely used to explain exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0012] "These combinations" mean a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0013] Terms such as “include,” “equip,” or “possess” are intended to specify the existence of a feature, figure, stage, component, or combination thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0014] In the drawings, thicknesses are shown enlarged to clearly represent various layers and regions, and similar parts are denoted by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is described as being "on top" of another part, this includes not only when it is "directly above" another part, but also when there is another part in between. Conversely, when a part is described as being "directly above" another part, it means that there is no other part in between.

[0015] The term "layer" includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on only a portion of the surface.

[0016] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering, and the average particle size value can be calculated after performing data analysis to count the number of particles for each particle size range. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) can mean. Also, unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume, obtained by measuring the size (diameter or length of the major axis) of more than 20 random particles from a scanning electron microscope image. 50 This is taken as the average particle size.

[0017] "Or" is not interpreted in an exclusive sense; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0018] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids.

[0019] positive electrode active material In one embodiment, a positive electrode active material is provided comprising a first positive electrode active material containing a lithium iron phosphate compound and a second positive electrode active material containing a lithium nickel composite oxide, wherein the second positive electrode active material is present in an amount of 1% to 15% by weight relative to 100% by weight of the total amount of the first and second positive electrode active materials.

[0020] The positive electrode active material is obtained by mixing a lithium iron phosphate compound and a lithium nickel composite oxide in an appropriate ratio, thereby increasing capacity while ensuring safety and enabling operation at high voltages.

[0021] First positive electrode active material In one embodiment, the first positive electrode active material includes a lithium iron phosphate compound. The lithium iron phosphate compound can increase capacity and output while improving heat resistance and thermal stability. Specifically, the lithium iron phosphate compound may be represented by the following chemical formula 1 or chemical formula 2. [Chemical formula 1] Li a1 Fe (1-x1) M1 x1 PO4 In chemical formula 1, 0.90 ≤ a1 ≤ 1.5 and 0 ≤ x1 ≤ 0.4, where M1 may be Al, B, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90 ≤ a1 ≤ 1.5 is also possible; for example, 0.90 ≤ a1 ≤ 1.2 or 0.95 ≤ a1 ≤ 1.1. Furthermore, 0 ≤ x1 ≤ 0.4, 0 ≤ x1 ≤ 0.3, 0 ≤ x1 ≤ 0.2, 0 ≤ x1 ≤ 0.1 or 0 ≤ x1 ≤ 0.05. [Chemical Formula 2] Li a2 Mn x2 Fe (1-x2-y2) M2 y2 PO4 In Chemical Formula 2, 0.90 ≦ a2 ≦ 1.5, 0.1 ≦ x2 ≦ 0.9, 0 ≦ y2 ≦ 0.9, and M2 may be Al, B, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90 ≦ a2 ≦ 1.5 may also be satisfied, for example, 0.90 ≦ a2 ≦ 1.2, or 0.95 ≦ a2 ≦ 1.1. Also, 0.1 ≦ x2 ≦ 0.9, 0.3 ≦ x2 ≦ 0.9, or 0.4 ≦ x2 ≦ 0.8 may be satisfied, and 0 ≦ y2 ≦ 0.4, 0 ≦ y2 ≦ 0.3, 0 ≦ y2 ≦ 0.2, 0 ≦ y2 ≦ 0.1, or 0 ≦ y2 ≦ 0.05 may be satisfied.

[0022] More specifically, the lithium iron phosphate-based compound is LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, or may include a combination thereof.

[0023] The first positive electrode active material containing the lithium iron phosphate-based compound is in a particle form, and the average particle diameter (D50) of the particles may be 0.01 μm to 2 μm, for example, 0.1 μm to 1.8 μm, or 0.7 μm to 1.7 μm. Here, the average particle diameter (D50) may be obtained by measuring the sizes (diameter or major axis length) of randomly more than 20 particles from a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and taking the diameter of the particles with a cumulative volume of 50% volume in the particle size distribution as the average particle diameter.

[0024] The specific surface area of ​​the first positive electrode active material containing the lithium iron phosphate compound is 1 m². 2 / g~20m 2 It can also be expressed as / g, for example, 3m 2 / g~18m 2 / g, 5m 2 / g~15m 2 / g, or 8m 2 / g~12m 2 It may also be / g. The specific surface area of ​​the first positive electrode active material was measured using physical and chemical adsorption phenomena and the Brunauer-Emmett-Teller (BET) method. That is, after measuring the weight of the manufactured first positive electrode active material, nitrogen was adsorbed onto the surface of the first positive electrode active material, the amount of adsorbed nitrogen gas was measured, and then the specific surface area was calculated using the BET formula. When the specific surface area of ​​the first positive electrode active material falls within the above range, it can play a role in increasing capacity and output while improving heat resistance and thermal stability.

[0025] In one embodiment, the lithium iron phosphate compound may be in the form of first particles, second particles, or a mixture of first and second particles.

[0026] The first particle may be an assembly of multiple nano-sized primary particles or a secondary particle. The first particle may have a spherical or ellipsoidal shape due to the close aggregation of primary particles. The average particle size of the first particle may be, for example, 2 μm to 15 μm, 3 μm to 12 μm, or 3 μm to 10 μm. The average particle size of the first particle may be larger than the average particle size of the second particle, which will be described later. The average particle size of the primary particles of the first particle may be, for example, 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm. As an example, the average particle size of the first particle may be obtained by arbitrarily selecting more than 30 first particles from electron microscope images of lithium transition metal phosphorus oxide, measuring their particle sizes, and taking the diameter (D50) of the particle with a cumulative volume of 50 volume% in the particle size distribution as the average particle size. The average particle size of the first particle may be determined by measuring the size of more than 30 primary particles from electron microscope images of the surface or cross-section of the first particle, and taking the diameter (D50) of the particle with a cumulative volume of 50% in the particle size distribution as the average particle size.

[0027] The porosity of the first particle may be approximately 20% to approximately 50%. For example, the porosity may be determined by measuring the area ratio of the portion occupied by voids within the particle using an image analysis program such as Image J in a scanning electron microscope image of the cross-section of the first particle.

[0028] The second particle may have a single particle form. The average particle size of the second particle may be, for example, 10 nm to 900 nm, 50 nm to 500 nm, or 100 nm to 300 nm. The average particle size of the second particle may be smaller than the average particle size of the first particle, or it may be the same as or larger than the average particle size of the primary particles of the first particle. As an example, the average particle size of the second particle may be determined by arbitrarily selecting more than 30 second particles from electron microscope images of lithium iron phosphate compounds, measuring their particle sizes, and taking the diameter (D50) of the particle with a cumulative volume of 50% in the particle size distribution as the average particle size.

[0029] The lithium iron phosphate compound may further include a carbon coating layer located on the surface of the particles. The carbon coating layer can improve the electrical conductivity of the lithium iron phosphate compound and reduce the resistance of the positive electrode. The carbon coating layer may be formed using at least one raw material selected from the group consisting of, for example, polymers of glucose, sucrose, lactose, starch, oligosaccharides, polyoligosaccharides, fructose, cellulose, furfuryl alcohol, block copolymers of ethylene and ethylene oxide, vinyl resins, cellulosic resins, phenolic resins, pitch resins, and tar resins. Specifically, the carbon coating layer may be formed by a firing process after placing the raw material on the surface of the lithium iron phosphate compound particles.

[0030] Second positive electrode active material The second positive electrode active material according to one embodiment includes a lithium nickel-based composite oxide. By including the lithium nickel-based composite oxide, the heat resistance and thermal stability, which are characteristics of lithium iron phosphate compounds, are maintained, while the capacity is increased and high-voltage operation is possible. Specifically, the lithium nickel-based composite oxide may be represented by the following chemical formula 3. [Chemical formula 3] Li a3 Ni x3 M3 y3 M4 z3 O 2-b3 X b3 In chemical formula 3, 0.9 ≤ a3 ≤ 1.8, 0.3 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.7, 0 ≤ z3 ≤ 0.7, 0.9 ≤ x3 + y3 + z3 ≤ 1.1, and 0 ≤ b3 ≤ 0.1, where M3 and M4 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, 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.

[0031] In chemical formula 3, 0.6 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.4, and 0 ≤ z³ ≤ 0.4, or 0.8 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.2, and 0 ≤ z³ ≤ 0.2, or 0.9 ≤ x³ < 1, 0 <y3≦0.1、および0≦z3≦0.1であってもよい。

[0032] As an example, the lithium nickel-based composite oxide may be a high-nickel cathode active material in which the nickel content relative to 100 mol% of the total metal excluding lithium is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. High-nickel cathode active materials can achieve high capacity and are applicable to high-capacity, high-density lithium secondary batteries.

[0033] The second positive electrode active material containing the lithium nickel-based composite oxide may be in the form of particles, and these particles may be in the form of secondary particles formed by the aggregation of multiple primary particles, single particles, or a combination thereof. The secondary particles and single particles may be spherical, ellipsoidal, polyhedronal, or irregular in shape, and the primary particles forming the secondary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0034] The average particle size (D50) of the second positive electrode active material may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. Here, the average particle size (D50) may be obtained by measuring the size (diameter or length of the long axis) of more than 20 particles randomly from scanning electron microscope images of the positive electrode active material to obtain a particle size distribution, and then taking the diameter of the particle with a cumulative volume of 50 volume% in the particle size distribution as the average particle size.

[0035] The specific surface area of ​​the second positive electrode active material containing the aforementioned lithium nickel-based composite oxide is 0.1 m². 2 / g~1.0m 2 It can also be expressed as / g, for example, 0.15m 2 / g~0.8m 2 / g, 0.2m 2 / g~0.6m 2 / g, or 0.25m 2 / g~0.5m 2 It may also be / g. The specific surface area of ​​the second positive electrode active material was measured using physical and chemical adsorption phenomena and the Brunauer-Emmett-Teller (BET) method. That is, after measuring the weight of the manufactured second positive electrode active material, nitrogen was adsorbed onto the surface of the second positive electrode active material, the amount of adsorbed nitrogen gas was measured, and then the specific surface area was calculated using the BET formula. When the specific surface area of ​​the second positive electrode active material falls within the above range, it can play a role in increasing capacity and output while improving heat resistance and thermal stability.

[0036] In one embodiment, the second positive electrode active material may be present in an amount of 1% to 15% by weight relative to 100% by weight of the total amount of the first and second positive electrode active materials. For example, it may be present in amounts of 3% to 15% by weight, 1% to 12% by weight, or 5% to 10% by weight. Alternatively, the first positive electrode active material may be present in an amount of 85% to 99% by weight relative to 100% by weight of the total amount of the first and second positive electrode active materials. For example, it may be present in amounts of 85% to 97% by weight, 88% to 99% by weight, or 90% to 95% by weight. When the content of the first and second positive electrode active materials falls within these ranges, it is possible to increase capacity and output while improving heat resistance and thermal stability.

[0037] positive electrode In one embodiment, the device includes a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer provides a positive electrode comprising the positive electrode active material and minority-wall carbon nanotubes. The positive electrode active material layer may further contain other types of positive electrode active materials and, selectively, may further contain a binder and / or conductive material.

[0038] The aforementioned positive electrode uses a mixture of lithium iron phosphate compound and lithium nickel composite oxide as the positive electrode active material, thereby increasing capacity while ensuring safety and enabling high-voltage operation. Furthermore, by including small-wall carbon nanotubes as a conductive material and appropriately adjusting their content, it is possible to achieve excellent conductivity, low resistance, and smooth ion flow.

[0039] Cathode active material layer In one embodiment, the positive electrode active material layer is located on a current collector and includes the positive electrode active material and small-wall carbon nanotubes. A detailed explanation of the positive electrode active material has been given above and will be omitted here.

[0040] conductive material A conductive material according to one embodiment is used to impart conductivity to an electrode and comprises a few wall carbon nanotubes, and may further comprise carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0041] Thin-walled carbon nanotubes (TWCNTs) refer to carbon nanotubes with an average diameter of 10 nm or less and 2 to 7 carbon walls. In this case, the average diameter of the thin-walled carbon nanotube may be 1 nm to 10 nm, for example, 1 nm to 9 nm or 1 to 8 nm, and the number of carbon walls may be 3 to 6, for example, 4 to 5. When the average diameter and number of carbon walls of the thin-walled carbon nanotube fall within the above range, resistance can be reduced, thereby enabling the realization of a long-life lithium secondary battery.

[0042] The average length of the minority-walled carbon nanotubes may be 30 to 100 μm, for example, 30 to 90 μm or 30 to 80 μm. When the average length of the minority-walled carbon nanotubes falls within this range, resistance can be reduced, thereby enabling the realization of a long-life lithium secondary battery.

[0043] The major-axis ratio (average length / average diameter) of the minor-wall carbon nanotubes may be between 3000 and 10000, for example, between 3000 and 9000, or between 3000 and 8000. The major-axis ratio is defined as the ratio of the length of the major axis passing through the center of the carbon nanotube unit to the diameter perpendicular to the major axis. When the major-axis ratio of the minor-wall carbon nanotubes falls within the above range, the specific surface area of ​​the minor-wall carbon nanotubes can be increased, thereby increasing the contact area with the positive electrode active material, and thus improving the output characteristics by improving conductivity. At this time, the average diameter and average length of the minor-wall carbon nanotubes can be measured using a field emission scanning electron microscope.

[0044] The positive electrode active material layer can contain 0.1% to 1.0% by weight of the minor wall carbon nanotubes relative to 100% by weight of the total, for example, 0.2% to 1.0% by weight, 0.2% to 0.8% by weight, 0.4% to 1.0% by weight, 0.4% to 0.8% by weight, or 0.4% to 0.6% by weight. When the positive electrode active material layer contains minor wall carbon nanotubes within the above content range, it is advantageous in terms of resistance even with a smaller amount than conventionally used mixtures of carbon nanotubes and nanocarbons, and excellent results can be obtained in terms of interfacial resistance and ionic resistance.

[0045] The specific surface area of ​​the aforementioned small-wall carbon nanotube is 200 m². 2 / g~300m 2 It can also be / g, for example, 210m 2 / g~290m 2 / g, 220m 2 / g~280m 2 / g, or 235m 2 / g~275m 2It may also be / g. The specific surface area of ​​the minority wall carbon nanotubes was measured using physical and chemical adsorption phenomena and the Brunauer-Emmett-Teller (BET) method. That is, after measuring the weight of the minority wall carbon nanotubes, nitrogen was adsorbed onto the surface of the minority wall carbon nanotubes, and the amount of adsorbed nitrogen gas was measured, and then the specific surface area was calculated using the BET formula. When the specific surface area of ​​the minority wall carbon nanotubes falls within the above range, they have excellent conductivity and low resistance, and at the same time, ion flow is smooth, the amount of conductive material used can be reduced, and a decrease in capacity due to a decrease in the fraction of positive electrode active material can be prevented.

[0046] In the positive electrode active material layer, the ratio of the specific surface area of ​​the minority-wall carbon nanotubes to the specific surface area of ​​the positive electrode active material may be 10% to 40%, for example, 10% to 30%, or 15% to 30%.

[0047] The ratio of the specific surface area of ​​the conductive material to the specific surface area of ​​the positive electrode active material within the positive electrode is a parameter that allows us to understand the extent to which the conductive material surrounds or connects with the active material. Therefore, when the ratio of the specific surface area of ​​the small-wall carbon nanotubes to the specific surface area of ​​the positive electrode active material falls within the aforementioned range, the conductivity is excellent, the resistance is low, and at the same time, the ion flow is smooth, preventing the conductive material from clumping or being in excess and hindering the ion flow. In addition, the amount of conductive material used can be reduced, preventing a decrease in capacity due to a decrease in the fraction of the positive electrode active material.

[0048] On the other hand, the overall thickness of the positive electrode active material layer may be approximately 40 μm to 300 μm, for example, 40 μm to 250 μm, 50 μm to 200 μm, or 60 μm to 100 μm.

[0049] binder A binder according to one embodiment plays a role in ensuring that positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0050] With respect to 100% by weight of the positive electrode active material layer, the content of the positive electrode active material may be 90% to 99.8% by weight, or 95% to 99% by weight, and the content of the binder may be 0.1% to 5% by weight, or 0.5% to 2.5% by weight.

[0051] Current collector The current collector according to one embodiment is not particularly limited as long as it is conductive without inducing a chemical change in the lithium secondary battery. Specific examples 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 combinations thereof. For example, aluminum (Al) can be used. In this case, the current collector may be in the form of a plate or a thin body.

[0052] Lithium-ion rechargeable battery In one embodiment, a lithium secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. Here, the electrolyte may be a liquid electrolyte or a solid electrolyte.

[0053] For example, in one embodiment, a lithium secondary battery can be provided that includes the positive electrode described above, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte. In another example, an all-solid-state secondary battery can be provided that includes the positive electrode described above, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0054] The following describes a lithium secondary battery using an electrolyte as an example.

[0055] Lithium-ion batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, with Figure 1 being cylindrical, Figure 2 being prismatic, and Figures 3 and 4 being pouch-type batteries. Referring to Figures 1 to 4, the lithium-ion battery 100 can include an electrode assembly 40 with 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, negative electrode 20, and separator 30 may be immersed in an electrolyte (not shown). The lithium-ion battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium-ion battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0056] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer comprising a negative electrode active material and further comprising a binder, a conductive material, or a combination thereof.

[0057] negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0058] Examples of the material capable of reversibly intercalating / deintercalating lithium ions can include, as a carbon-based negative electrode active material, for example, 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, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0059] For the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0060] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. Examples of the Si-based negative electrode active material include silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. Examples of the Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof.

[0061] The silicon-carbon composite may also be a composite of silicon and amorphous carbon. The average particle size (D 50 The particle size may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coating on the surface of the silicon particles. For example, it may include secondary particles (core) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0062] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may be soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0063] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, and the amorphous carbon content may be 50% to 90% by weight. Furthermore, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight.

[0064] Furthermore, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D) of the silicon particles (primary particles) 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (0 < x ≤ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particles with a cumulative volume of 50% by volume in the particle size distribution.

[0065] The Si-based negative electrode active material or Sn-based negative electrode active material can be used in mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in mixture, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0066] binder The binder plays a role of well adhering the negative electrode active material particles to each other and well adhering the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0067] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0068] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylicated 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.

[0069] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound capable of imparting viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0070] The dry binder is a fiberizable polymeric substance, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0071] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0072] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0073] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0074] electrolyte The electrolyte for lithium secondary batteries may, for example, be an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0075] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0076] Suitable carbonate solvents 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). Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Suitable ether solvents include dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Suitable ketone solvents include cyclohexanone. Suitable alcohol solvents include ethyl alcohol and isopropyl alcohol. Suitable aprotic solvents include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0077] Non-aqueous organic solvents can be used individually or in combination of two or more. When using a mixture of two or more, the mixing ratio can be appropriately adjusted according to the desired performance of the battery, and this is generally understood by those working in this field.

[0078] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed and used together, and the cyclic carbonates and linear carbonates may be mixed in a volume ratio of 1:1 to 1:9.

[0079] The non-aqueous organic solvent may further contain aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0080] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0081] Representative examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0082] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are integers from 1 to 20) may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0083] The lithium salt concentration should ideally be within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0084] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Suitable separators include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. 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.

[0085] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0086] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0087] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0088] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, a second structural unit comprising a structural unit derived from (meth)acrylic acid or (meth)acrylate, and at least one structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0089] 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) of the inorganic particles is 50 The wavelength range may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0090] The organic and inorganic materials may be present mixed in a single coating layer, or in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are laminated together.

[0091] The thickness of the coating layer may be 0.5 μm to 20 μm, or for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0092] The following describes examples and comparative examples of the present invention. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0093] Manufacturing Example 1 The first cathode active material was prepared using LiFePO4 as the lithium iron phosphate compound.

[0094] Manufacturing Example 2 Ni 0.88 Co 0.11 Al 0.01(OH)2 and LiOH are mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours under an oxygen atmosphere, resulting in a composition of Li 1.05 Ni 0.88 Co 0.11 Al 0.01 A second cathode active material was fabricated containing a lithium nickel-based composite oxide in the form of secondary particles, which is O2 and has an average particle size (D50) of approximately 14 μm.

[0095] The final cathode active material was produced by mixing 99% by weight of the first cathode active material and 1% by weight of the second cathode active material produced according to Production Example 1.

[0096] Manufacturing Example 3 The cathode active material was produced in substantially the same manner as in Production Example 2, except that the final cathode active material was produced by mixing 95% by weight of the first cathode active material produced by Production Example 1 with 5% by weight of the second cathode active material.

[0097] Manufacturing Example 4 The cathode active material was produced in substantially the same manner as in Production Example 2, except that the final cathode active material was produced by mixing 90% by weight of the first cathode active material produced by Production Example 1 with 10% by weight of the second cathode active material.

[0098] Manufacturing Example 5 The cathode active material was produced in substantially the same manner as in Production Example 2, except that the final cathode active material was produced by mixing 85% by weight of the first cathode active material produced by Production Example 1 with 15% by weight of the second cathode active material.

[0099] Manufacturing Example 6 The cathode active material was produced in substantially the same manner as in Production Example 2, except that the final cathode active material was produced by mixing 80% by weight of the first cathode active material produced by Production Example 1 with 20% by weight of the second cathode active material.

[0100] Manufacturing example 7 The cathode active material was produced in substantially the same manner as in Production Example 2, except that the final cathode active material was produced by mixing 70% by weight of the first cathode active material produced by Production Example 1 with 30% by weight of the second cathode active material.

[0101] Example 1 (1) Manufacturing of the positive electrode A cathode active material slurry was prepared by mixing 97.4% by weight of the cathode active material produced in Production Example 3, 2.4% by weight of PVDF binder, and 0.2% by weight of minority-walled carbon nanotube conductive material with NMP solvent. The diameter of the minority-walled carbon nanotubes was measured to be 5 nm, and the specific surface area of ​​the minority-walled carbon nanotubes was 250 m². 2 The value was measured at / g. The manufactured positive electrode active material slurry was applied to an aluminum foil current collector, dried, and then rolled to produce the positive electrode.

[0102] (2) Manufacturing of the negative electrode A negative electrode active material slurry was prepared by mixing 97.3% by weight of graphite, 0.5% by weight of Denka Black, 0.9% by weight of carboxymethylcellulose, and 1.3% by weight of styrene-butadiene rubber in an aqueous solvent. The prepared negative electrode active material slurry was applied to a copper foil current collector, dried, and then rolled to produce a negative electrode.

[0103] (3) Manufacturing of lithium secondary batteries A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0104] Example 2 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode slurry was prepared by mixing 97.2% by weight of the positive electrode active material produced in Production Example 3, 2.4% by weight of PVDF binder, and 0.4% by weight of minority-wall carbon nanotube conductive material.

[0105] Example 3 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode slurry was prepared by mixing 97.0% by weight of the positive electrode active material produced in Production Example 3, 2.4% by weight of PVDF binder, and 0.6% by weight of minority-wall carbon nanotube conductive material.

[0106] Example 4 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode slurry was prepared by mixing 96.8% by weight of the positive electrode active material produced in Production Example 3, 2.4% by weight of PVDF binder, and 0.8% by weight of minority-wall carbon nanotube conductive material.

[0107] Example 5 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode slurry was prepared by mixing 96.6% by weight of the positive electrode active material produced in Production Example 3, 2.4% by weight of PVDF binder, and 1.0% by weight of minority-wall carbon nanotube conductive material.

[0108] Comparative Example 1 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that 95.8% by weight of the positive electrode active material, 2.4% by weight of the PVDF binder, and 1.8% by weight of the TDS-L conductive material, which is a mixture of L-carbon nanotubes (Long length carbon nanotubes) and LiTX66, were used. The diameter of the L-carbon nanotubes was measured to be 5 nm, and the specific surface area of ​​the L-carbon nanotubes was 250 m². 2 The value was measured at / g. The diameter of LiTX66 was measured at 5nm, and the specific surface area of ​​LiTX66 was 250m². 2 Measured at / g

[0109] Comparative Example 2 In the production of the positive electrode, the positive electrode and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that 97.0% by weight of the positive electrode active material, 2.4% by weight of the PVDF binder, and 0.6% by weight of the TDS-L conductive material manufactured in Production Example 3 were used.

[0110] Evaluation Example 1: Capacity and Heat Value Evaluation A cathode active material slurry was prepared by mixing 96.8% by weight of the cathode active material produced in Production Examples 1 to 7, 2.4% by weight of polyvinylidene fluoride binder, and 0.8% by weight of a conductive material consisting of carbon nanotubes and particulate nanocarbon mixed in a 7:3 weight ratio with an NMP solvent. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce a cathode.

[0111] A negative electrode active material slurry was prepared by mixing 97.3% by weight of graphite, 0.5% by weight of Denka Black, 0.9% by weight of carboxymethylcellulose, and 1.3% by weight of styrene-butadiene rubber in an aqueous solvent. The prepared negative electrode active material slurry was applied to a copper foil current collector, dried, and then rolled to produce a negative electrode.

[0112] A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0113] The manufactured lithium secondary battery was charged at 25°C with a constant current of 0.5C to an upper voltage limit of 4.2V, then at a constant voltage of 0.02C, and finally discharged at 0.0C to a cutoff voltage of 2.5V to perform initial charge and discharge. After the initial charge and discharge, the capacity was calculated by applying the product of the initial discharge capacity and the weight of the positive electrode, and the results are shown in Table 1 below.

[0114] Next, the heat flow of the manufactured positive electrode was measured using differential scanning calorimetry (DSC). A differential scanning calorimetry instrument (SETARAM SENSYS Evo) was used for the measurement. Specifically, 15 mg of positive electrode charged at 4.25 V (vs. Li / Li+) was taken, 20 μl of electrolyte was added, and the temperature was measured up to 400°C at a heating rate of 10°C per minute. The results are shown in Table 1 below.

[0115] [Table 1]

[0116] Referring to Table 1, it can be confirmed that the capacity increases as the content of lithium nickel-based composite oxide increases, compared to Production Example 1 which does not contain lithium nickel-based composite oxide. However, the amount of heat generated increases as the content of lithium nickel-based composite oxide increases, and in particular, it can be confirmed that the amount of heat generated increases sharply when the content of lithium nickel-based composite oxide is 20% by weight or more, as shown in Production Examples 6 and 7.

[0117] Evaluation Example 2 After measuring the weight of the positive electrode active material contained in the lithium secondary batteries manufactured according to the examples and comparative examples, nitrogen was adsorbed onto the surface of the positive electrode active material, and the amount of adsorbed nitrogen gas was measured. The specific surface area was then calculated using the BET formula. Similarly, after measuring the weight of the conductive material contained in the lithium secondary batteries according to the examples and comparative examples, nitrogen was adsorbed onto the surface of the conductive material, and the amount of adsorbed nitrogen gas was measured. The specific surface area was then calculated using the BET formula, and the ratio of the specific surface area of ​​the conductive material to the specific surface area of ​​the positive electrode active material was calculated and is shown in Table 2 below.

[0118] Evaluation Example 3: Evaluation of Total Resistivity and Interfacial Resistivity Four probe tips were aligned in a straight line at 1 mm intervals and brought into contact with the surface of the positive electrode manufactured according to the examples and comparative examples. A constant current was passed through the outer probes, and the potential difference across the inner probes was measured to determine the resistance. The total resistivity and interfacial resistance were then measured by multiplying these values ​​by the plate thickness and a correction factor, and are shown in Table 2 below.

[0119] Evaluation Example 4: Ionic Resistance A symmetric cell consisting of two positive electrodes was fabricated using the positive electrodes manufactured according to the examples and comparative examples. The amplitude Va value was set to 5 mV, and square current electrochemical impedance spectroscopy (SC-EIS) was measured. The measured values ​​were then used to isolate and measure only the ionic resistance from the internal resistance of the positive electrode using the transmission line model theory, and the results are shown in Table 2 below.

[0120] [Table 2]

[0121] Referring to Table 2, it can be confirmed that in the examples using the minority-wall carbon nanotube conductive material, the total resistivity, interfacial resistance, and ionic resistance are all lower compared to the comparative example without the minority-wall carbon nanotube conductive material. In particular, in Examples 2 to 4, which contain 0.4% to 0.8% by weight of minority-wall carbon nanotubes, it can be confirmed that the resistivity, interfacial resistance, and ionic resistance are even lower.

[0122] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0123] 100: Lithium secondary battery, 10: Positive electrode 11: Positive 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 member, 70: Electrode tab 71: Positive tab, 72: Negative tab

Claims

1. A first positive electrode active material containing a lithium iron phosphate compound, A second positive electrode active material containing a lithium nickel-based composite oxide, Includes, A positive electrode active material containing 1% to 15% by weight of the second positive electrode active material relative to 100% by weight of the total of the first positive electrode active material and the second positive electrode active material.

2. The lithium iron phosphate compound is represented by the following chemical formula 1 or chemical formula 2, and is the positive electrode active material according to claim 1: [Chemical formula 1] Li a1 Fe (1-x1) M1 x1 2O 4 In chemical formula 1, 0.90 ≤ a1 ≤ 1.5 and 0 ≤ x1 ≤ 0.4, where M1 is Al, B, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. [Chemical formula 2] Li a2 Mn x2 Fe (1-x2-y2) M2 y2 PO 4 In chemical formula 2, 0.90 ≤ a² ≤ 1.5, 0.1 ≤ x² ≤ 0.9, 0 ≤ y² ≤ 0.9, and M² is Al, B, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof.

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

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

5. The lithium nickel-based composite oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 3: [Chemical formula 3] Li a3 ii x3 73 y3 74 z3 9 2-b3 8 b3 In chemical formula 3, 0.9 ≤ a³ ≤ 1.8, 0.3 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.7, 0 ≤ z³ ≤ 0.7, 0.9 ≤ x³ + y³ + z³ ≤ 1.1, and 0 ≤ b³ ≤ 0.1, where M³ and M₄ are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, 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.

6. Current collector and, The current collector includes a positive electrode active material layer located on the current collector, The positive electrode active material layer comprises the positive electrode active material described in any one of claims 1 to 5 and a small-wall carbon nanotube.

7. The positive electrode according to claim 6, wherein the average diameter of the minority-walled carbon nanotubes is 1 nm to 10 nm.

8. The positive electrode according to claim 6, wherein the positive electrode active material layer contains 0.1% to 1.0% by weight of the minority-walled carbon nanotubes with respect to 100% by weight of the positive electrode active material layer.

9. The positive electrode according to claim 6, comprising 0.4% to 0.8% by weight of the minority-walled carbon nanotubes with respect to 100% by weight of the positive electrode active material layer.

10. The BET specific surface area of ​​the aforementioned small-wall carbon nanotube is 200 m². 2 / g to 300m 2 The positive electrode according to claim 6, wherein the value is / g.

11. The positive electrode according to claim 6, wherein in the positive electrode active material layer, the ratio of the specific surface area of ​​the minority-wall carbon nanotubes to the specific surface area of ​​the positive electrode active material is 10% to 40%.

12. The positive electrode according to claim 6, wherein in the positive electrode active material layer, the ratio of the specific surface area of ​​the minority-wall carbon nanotubes to the specific surface area of ​​the positive electrode active material is 15% to 30%.

13. The positive electrode described in claim 6, The negative electrode and, Electrolytes, Lithium-ion secondary batteries, including lithium-ion batteries.

14. The lithium secondary battery according to claim 13, wherein the negative electrode includes a carbon-based negative electrode active material, lithium metal, an alloy of lithium metal, a silicon-based negative electrode active material, or a combination thereof.

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