Master batch containing positive electrode active material and irreversible additive, and positive electrode slurry for lithium secondary battery comprising the same

Abstract

The present invention relates to a master batch for a positive electrode additive and a positive electrode slurry for a lithium secondary battery including the same, in which the master batch contains a high content of an irreversible additive and a positive electrode active material, so that when a positive electrode is manufactured, a small amount of the irreversible additive is dispersed in the positive electrode slurry with high dispersibility without loss. Accordingly, the positive electrode for a lithium secondary battery manufactured thereby has higher electrical properties and reliability, and has the advantage of improving the degree of freedom in design when the positive electrode is manufactured.

Description

Technical Field

[0001] This invention relates to a masterbatch for positive electrode additives and a positive electrode slurry for lithium secondary batteries containing the same, wherein the masterbatch for positive electrode additives contains positive electrode active materials and a high content of irreversible additives.

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0069635, filed on May 31, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] With the development and increasing demand for technologies used in mobile devices, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium-ion batteries, which have high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, as lithium secondary batteries are used as a power source for large and medium-sized devices (such as electric vehicles), there is a further need for lithium secondary batteries to have high capacity, high energy density and low cost, and also for irreversible additives used in the electrodes to have higher irreversible capacity.

[0005] In response to the aforementioned needs, conventional irreversible additives, such as Li6CoO4, have been developed. However, conventional irreversible additives are structurally unstable and can generate large amounts of oxygen (O2) gas during secondary battery charging. Therefore, the use of high concentrations of irreversible additives in the cathode limits the charging and discharging efficiency and safety of lithium secondary batteries. Therefore, efforts have been made to reduce the irreversibility of lithium secondary batteries by using low concentrations of irreversible additives.

[0006]

[0007] However, when irreversible additives are used in low amounts, especially in small quantities of less than 2% by weight relative to the total weight of the cathode slurry, the following problems arise: it is difficult to ensure the dispersion of irreversible additives in the cathode slurry, thus reducing the reliability of lithium secondary batteries; and the loss of irreversible additives increases due to the dispersion of low-particle-size irreversible additives during the cathode manufacturing process, thus reducing the degree of freedom in process design.

[0008] Therefore, there is a need to develop a technology in which, when using very small amounts of irreversible additives, fairness and freedom in process design are improved by preventing the loss of irreversible additives during cathode manufacturing, and the reliability of lithium secondary batteries is ensured by ensuring the dispersibility of irreversible additives in the cathode slurry. Summary of the Invention

[0009] Technical issues

[0010] The purpose of this invention is to provide a positive electrode slurry and a positive electrode for lithium secondary batteries manufactured using the same, wherein the positive electrode slurry contains a very small amount of irreversible additives that are highly dispersible during positive electrode manufacturing without loss.

[0011] Technical solution

[0012] The present invention aims to solve the above-mentioned problems and provides a masterbatch for cathode additives, wherein, relative to 100 parts by weight of a first cathode active material, the masterbatch for cathode additives comprises 0.5 to 50 parts by weight of lithium cobalt oxide represented by the following chemical formula 1:

[0013] [Chemical Formula 1]

[0014] Li p Co 1-q M 1 q O4

[0015] In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0016] The masterbatch for cathode additives may also contain 1 to 10 parts by weight of a first binder, relative to 100 parts by weight of the first cathode active material.

[0017] The average particle size (D) of the masterbatch for cathode additives 50 The average particle size (D) of the first positive electrode active material contained in the masterbatch can be from 0.05 mm to 10 mm. 50 The particle size can range from 0.5 μm to 100 μm, and the average particle size (D) of lithium cobalt oxide is... 50 The particle size can be from 1 μm to 200 μm, wherein the average particle size of the lithium cobalt oxide can be greater than the average particle size of the first positive electrode active material.

[0018] The present invention also aims to provide a positive electrode slurry for lithium secondary batteries, comprising the positive electrode additive masterbatch described in the present invention, wherein, relative to 100 parts by weight of a first positive electrode active material, the positive electrode additive masterbatch comprises 0.5 to 50 parts by weight of lithium cobalt oxide represented by the following chemical formula 1; a second positive electrode active material; a conductive material; and a second binder.

[0019] [Chemical Formula 1]

[0020] Li p Co 1-q M 1 q O4

[0021] In the above chemical formula 1, M 1 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.4, respectively.

[0022] Relative to the total amount of 100 parts by weight of the positive electrode paste, the content of the lithium cobalt oxide represented by Chemical Formula 1 contained in the master batch may be 0.05 to 2.0 parts by weight.

[0023] Relative to 100 parts by weight of the second positive electrode active material, the content of the master batch for the positive electrode additive may be 1 to 150 parts by weight.

[0024] Each of the first positive electrode active material and the second positive electrode active material may contain a lithium metal composite oxide represented by the following Chemical Formula 2.

[0025] [Chemical Formula 2]

[0026] Li x [Ni y Co z Mn w M 2 v O u

[0027] In the above chemical formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 1, 0.1 < z ≤ 0.6, 0.1 < w ≤ 0.6, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 5, respectively.

[0028] Relative to the total amount of 100 parts by weight of the positive electrode paste, the content of the conductive material may be 1 to 5 parts by weight.

[0029] Relative to the total amount of 100 parts by weight of the positive electrode paste, the content of the second binder may be 1 to 5 parts by weight.

[0030] The present invention also aims to provide a positive electrode for lithium secondary batteries, having a structure in which a positive electrode current collector, a first positive electrode mixture layer and a second positive electrode mixture layer are sequentially laminated, wherein the first positive electrode mixture layer and the second positive electrode mixture layer are each formed using the positive electrode slurry for lithium secondary batteries described in the present invention.

[0031] The amount of lithium cobalt oxide represented by the following chemical formula 1 contained in the first cathode mixture layer may be 0.5 to 2.0 parts by weight relative to 100 parts by weight of the first cathode mixture layer, and the amount of lithium cobalt oxide represented by the following chemical formula 1 contained in the second cathode mixture layer may be 0.01 to 0.5 parts by weight relative to 100 parts by weight of the second cathode mixture layer.

[0032] [Chemical Formula 1]

[0033] Li p Co 1-q M 1 q O4

[0034] In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0035] The total amount of lithium cobalt oxide contained in the first and second cathode mixture layers may be less than or equal to 0.5 parts by weight, relative to the total amount of cathode active material contained in 100 parts by weight of the first cathode mixture layer and the second cathode mixture layer.

[0036] The ratio of the average thickness of the first cathode mixture layer to the average thickness of the second cathode mixture layer can be from 0.1 to 0.9.

[0037] The present invention also aims to provide a lithium secondary battery comprising the positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode as described in the present invention.

[0038] Beneficial effects

[0039] The masterbatch for cathode additives according to the present invention can contain a high content of irreversible additives and cathode active materials, so that when manufacturing the cathode, a small amount of irreversible additives are dispersed in the cathode slurry with high dispersibility without loss. Therefore, the cathode for lithium secondary batteries manufactured using irreversible additives can have high electrical performance and reliability, and can improve the degree of freedom in design when manufacturing the cathode. Detailed Implementation

[0040] This invention can have various modifications and alternative forms, and its specific implementation will be described in detail.

[0041] However, it should be understood that the invention is not intended to be limited to the specific forms disclosed; rather, the invention is intended to cover all modifications, equivalents and alternatives that fall within the spirit and scope of the invention.

[0042] It should be further understood that the terms “comprising” and / or “including” as used herein mean the presence of the said feature, integer, step, operation, component, part or combination thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, components, parts or combinations thereof.

[0043] Furthermore, when a layer, film, region, or plate is referred to as "formed on" another layer, film, region, or plate, this includes the case where the layer, film, region, or plate is directly formed on the other layer, film, region, or plate, and the case where another layer, film, region, or plate is disposed between the layer, film, region, or plate and the other layer, film, region, or plate. Conversely, when a layer, film, region, or plate is referred to as "formed under" another layer, film, region, or plate, this includes the case where the layer, film, region, or plate is directly formed under the other layer, film, region, or plate, and the case where another layer, film, region, or plate is disposed between the layer, film, region, or plate and the other layer, film, region, or plate. Additionally, in this specification, when an component is referred to as being "on" another component, this includes the case where the component is located above the other component and the case where the component is located below the other component.

[0044] Furthermore, in this invention, the term "masterbatch for cathode additives" can refer to a solid composition in which the components for manufacturing the cathode of a lithium secondary battery are formed in the form of pellets having a millimeter size, and contain non-reversible additives in fine particulate form as components at a higher content than the content of non-reversible additives actually contained in the cathode mixture layer. In this case, the term "high content" can be a content of more than twice the content of the components contained in the cathode mixture layer.

[0045] Additionally, in this invention, the term "main component" can refer to a component having a content of 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, 95% or more by weight, or 97.5% or more by weight relative to the total weight of the composition or a specific component. In some cases, it can refer to a component constituting the entire composition or a specific component, i.e., a component having an amount of 100 by weight.

[0046] Furthermore, in this invention, "Ah" is a unit of capacity for lithium secondary batteries, called "ampere-hour," which is the amount of current per hour. For example, when the battery capacity is "3000mAh," it means that the battery can discharge at a current of 3000mA for one hour.

[0047] The invention will be described in more detail below.

[0048] Masterbatch for cathode additives

[0049] In one embodiment, the present invention provides a masterbatch for cathode additives, wherein, relative to 100 parts by weight of a first cathode active material, the masterbatch for cathode additives comprises 0.5 to 50 parts by weight of lithium cobalt oxide represented by the following chemical formula 1:

[0050] [Chemical Formula 1]

[0051] Li p Co 1-q M 1 q O4

[0052] In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0053] The cathode additive masterbatch of the present invention is used to form a cathode mixture layer for a cathode used in a lithium secondary battery. Typically, when an irreversible additive of less than 2% by weight is included relative to the total weight of the cathode mixture layer during the formation of the cathode, the amount of irreversible additive is significantly small, resulting in substantial losses during the process and difficulty in uniformly dispersing the irreversible additive. This leads to limitations in the reliability of the manufactured cathode and the lithium secondary battery containing it. However, in the cathode additive masterbatch of the present invention, lithium cobalt oxide (represented by Chemical Formula 1), used as an irreversible additive, can be included in a high content along with the first cathode active material, and can be uniformly dispersed in the cathode slurry during the formation of the cathode mixture layer without loss of irreversible additive.

[0054] In this case, lithium cobalt oxide is included in the masterbatch as an irreversible additive that imparts irreversible capacity, together with the positive electrode active material exhibiting electroactivity, and includes lithium cobalt oxide represented by the following chemical formula 1:

[0055] [Chemical Formula 1]

[0056] Li p Co1-q M 1 q O4

[0057] In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0058] Specifically, lithium cobalt oxides can be used without particular restrictions, as long as they are lithium cobalt oxides represented by chemical formula 1, and preferably include Li6CoO4, Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 O4, etc.

[0059] The lithium cobalt oxides represented by the above chemical formula 1 include lithium cobalt oxides (Li₂O₃) that release large amounts of lithium ions. p The lithium cobalt oxide can have a structure where a transition metal is doped at the cobalt site of the lithium cobalt oxide (CoO4, 5 ≤ p ≤ 7). In this case, the amount of the doped transition metal can be less than or equal to 40 mole fractions (q ≤ 0.4), specifically 20 to 40 mole fractions (0.2 ≤ q ≤ 0.4), 10 to 30 mole fractions (0.1 ≤ q ≤ 0.3), 15 to 30 mole fractions (0.15 ≤ q ≤ 0.3), 30 to 40 mole fractions (0.3 ≤ q ≤ 0.4), or 5 to 20 mole fractions (0.05 ≤ q ≤ 0.2). In this invention, by adjusting the amount of metal doping within the above mole fraction range, a large amount of lithium ions can be released and the amount of oxygen generated due to the release of lithium ions can be reduced.

[0060] Furthermore, the lithium cobalt oxide represented by the above chemical formula 1 can have a tetragonal crystal structure, and the tetragonal crystal structure can have the space group P42 / nmc.

[0061] Furthermore, relative to 100 parts by weight of the first positive electrode active material, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the masterbatch can be 0.5 to 50 parts by weight. Specifically, relative to 100 parts by weight of the first positive electrode active material, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the masterbatch can be 0.5 to 40 parts by weight, 0.5 to 30 parts by weight, 0.5 to 25 parts by weight, 0.5 to 20 parts by weight, 0.5 to 10 parts by weight, 2 to 30 parts by weight, 2 to 15 parts by weight, 8 to 15 parts by weight, 8 to 28 parts by weight, 15 to 30 parts by weight, 9 to 22 parts by weight, or 4 to 11 parts by weight. In this invention, by controlling the amount of lithium cobalt oxide contained in the masterbatch as described above, the amount of masterbatch used in the positive electrode slurry is significantly reduced due to the excessive irreversible additive contained in the masterbatch, which can prevent the uneven dispersion of the irreversible additive and prevent the masterbatch preparation efficiency from decreasing due to a small amount of irreversible additive.

[0062] In addition, the average particle size D of the masterbatch used for cathode additives 50 The particle size can be from 0.05 mm to 10 mm, specifically from 0.1 mm to 10 mm, 0.5 mm to 10 mm, 1 mm to 10 mm, 0.1 mm to 2 mm, 5 mm to 10 mm, 1 mm to 5 mm, or 3 mm to 7 mm. In this invention, the average particle size D of the cathode additive masterbatch is... 50 By controlling the process within the above range, the loss of irreversible additives and changes in the composition of the cathode slurry caused by the dispersion of the masterbatch can be prevented during the preparation of the cathode slurry, and the efficiency of the working process can be improved.

[0063] In addition, the average particle size D of the first positive electrode active material 50 The average particle size D of lithium cobalt oxide can range from 0.5 to 100 μm. 50 The particle size can range from 1 to 200 μm, wherein the average particle size of the lithium cobalt oxide can be larger than the average particle size of the first positive electrode active material. Specifically, the average particle size D of the first positive electrode active material... 50 The average particle size D of lithium cobalt oxide can be 1 to 100 μm, 5 to 100 μm, 10 to 100 μm, 25 to 100 μm, 50 to 100 μm, 10 to 50 μm, 5 to 10 μm, or 0.5 to 5 μm. 50 The particle size can be 5 to 200 μm, 10 to 200 μm, 50 to 200 μm, 100 to 200 μm, 150 to 200 μm, 110 to 150 μm, 80 to 120 μm, 50 to 100 μm, 10 to 50 μm, 5 to 20 μm, 40 to 60 μm, 50 to 80 μm, or 1 to 5 μm. In this invention, the average particle size D of the first positive electrode active material and lithium cobalt oxide is... 50By controlling the process within the aforementioned range, the charge / discharge capacity and efficiency of the manufactured lithium secondary battery can be improved, and the amount of oxygen generated by lithium cobalt oxide, which releases large amounts of lithium ions, can be reduced. Furthermore, by containing more irreversible additives than the first positive electrode active material, side reactions of the irreversible additives can be reduced.

[0064] Furthermore, in order to form the first positive electrode active material and the lithium cobalt oxide represented by Chemical Formula 1 into pellets having a millimeter-scale size, the masterbatch for positive electrode additives of the present invention may further contain 1 to 10 parts by weight of the first positive electrode active material contained in the masterbatch. Specifically, the masterbatch for positive electrode additives of the present invention may further contain 1 to 5 parts by weight, 5 to 10 parts by weight, 3 to 8 parts by weight, or 4 to 6 parts by weight of the first binder relative to 100 parts by weight of the first positive electrode active material.

[0065] Here, the first adhesive may be used without particular limitation, as long as it is generally applicable in the positive electrode mixture layer. For example, the first adhesive may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the first adhesive may include polyvinylidene fluoride.

[0066] As described above, in this invention, by controlling the composition of the cathode additive masterbatch, a small amount of irreversible additive can be highly dispersed in the cathode slurry without loss during cathode manufacturing, thereby improving the performance and reliability of the manufactured lithium secondary battery.

[0067] Positive electrode slurry for lithium secondary batteries

[0068] In addition, in one embodiment, the present invention provides a positive electrode slurry for lithium secondary batteries, comprising the positive electrode additive masterbatch described in the present invention, a second positive electrode active material, a conductive material, and a second binder, wherein the positive electrode additive masterbatch comprises 0.5 to 50 parts by weight of lithium cobalt oxide represented by the following chemical formula 1, relative to 100 parts by weight of the first positive electrode active material.

[0069] [Chemical Formula 1]

[0070] Li p Co 1-q M 1 q O4

[0071] In the above chemical formula 1, M 1It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0072] The positive electrode slurry for lithium secondary batteries of the present invention is used to form a positive electrode mixture layer provided in the positive electrode for lithium secondary batteries, and includes the above-mentioned masterbatch for positive electrode additives, a second positive electrode active material, a conductive material and a second binder.

[0073] Here, relative to 100 parts by weight of the second positive electrode active material, the amount of the masterbatch for positive electrode additives of the present invention contained in the positive electrode slurry is 1 to 150 parts by weight. More specifically, relative to 100 parts by weight of the second positive electrode active material, the amount of the masterbatch for positive electrode additives contained in the positive electrode slurry can be 120 to 150 parts by weight, 1 to 100 parts by weight, 1 to 50 parts by weight, 1 to 30 parts by weight, 1 to 20 parts by weight, 1 to 9 parts by weight, 2 to 19 parts by weight, 4 to 17 parts by weight, 20 to 30 parts by weight, 10 to 20 parts by weight, or 1 to 7 parts by weight.

[0074] Furthermore, the cathode slurry may contain lithium cobalt oxide represented by the above-described chemical formula 1, which is included in the masterbatch and is an irreversible additive. The amount of said lithium cobalt oxide is 0.05 to 2.0 parts by weight relative to the total amount of 100 parts by weight of the cathode slurry. More specifically, the amount of lithium cobalt oxide represented by the above-described chemical formula 1 contained in the cathode slurry relative to the total amount of 100 parts by weight may be 0.05 to 1.5 parts by weight, 0.05 to 1.0 parts by weight, 0.05 to 0.5 parts by weight, 0.1 to 1.5 parts by weight, 0.1 to 1.0 parts by weight, or 0.1 to 0.9 parts by weight.

[0075] In this invention, by controlling the amount of the positive electrode additive masterbatch and the lithium cobalt oxide represented by the above chemical formula 1 contained in the positive electrode slurry within the above range, the dispersibility of the lithium cobalt oxide in the positive electrode slurry can be improved, and the charging / discharging capacity of the manufactured lithium secondary battery can be maximized.

[0076] Meanwhile, the positive electrode slurry of the present invention may include a first positive electrode active material (included in the masterbatch for positive electrode additives) and a second positive electrode active material as materials capable of reversible insertion and deintercalation, and in this case, the first positive electrode active material and the second positive electrode active material may each include a lithium metal composite oxide represented by the following chemical formula 2, wherein the composition of the lithium metal composite oxide may be the same or different.

[0077] [Chemical Formula 2]

[0078] Lix [Ni y Co z Mn w M 2 v O u

[0079] In the above Chemical Formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 1, 0.1 < z ≤ 0.6, 0.1 < w ≤ 0.6, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 5, respectively.

[0080] The lithium metal composite oxide represented by the above Chemical Formula 2 is a composite metal oxide containing lithium, nickel, cobalt, and manganese, and in some cases, may have the form doped with another transition metal M 2 . For example, the first positive electrode active material and the second positive electrode active material may each independently include one or more compounds selected from the group consisting of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2. As an example, the first positive electrode active material and the second positive electrode active material may be used alone or in combination with LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 O2 as the lithium metal composite oxide represented by the above Chemical Formula 2.

[0081] Furthermore, relative to 100 parts by weight of the positive electrode slurry, the total amount of the first positive electrode active material and the second positive electrode active material can be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight.

[0082] In addition, the positive electrode slurry may also contain conductive materials and a second binder, as well as a first positive electrode active material and a second positive electrode active material, and in some cases, may also contain another additive that can improve the physical properties of the positive electrode.

[0083] In this case, the conductive material can be used to improve the performance of the positive electrode, such as its conductivity, and can include one or more carbon-based materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers. For example, the conductive material may include acetylene black.

[0084] In addition, the content of conductive material may be 1 to 5 parts by weight relative to the total amount of 100 parts by weight of positive electrode paste, specifically, the content may be 1 to 4 parts by weight or 2 to 4 parts by weight.

[0085] Furthermore, the components of the second binder may be the same as or different from those of the first binder contained in the masterbatch for the positive electrode additive. Specifically, examples of the second binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the second binder may include polyvinylidene fluoride.

[0086] Furthermore, relative to the total amount of 100 parts by weight of the cathode slurry, the content of the second binder can be 1 to 5 parts by weight, specifically, the content can be 1 to 4 parts by weight or 2 to 4 parts by weight. Additionally, relative to the total amount of 100 parts by weight of the cathode slurry, the total amount of the first binder and the second binder contained in the cathode additive masterbatch can not exceed 6 parts by weight.

[0087] In this invention, by controlling the composition of the positive electrode slurry for lithium secondary batteries as described above, a positive electrode slurry in which a small amount of irreversible additives are quantitatively and uniformly dispersed without loss can be prepared. Therefore, the following advantages exist: the positive electrode of the lithium secondary battery made using the positive electrode slurry can have higher electrical characteristics and reliability, and the degree of freedom in the design can be improved when manufacturing the positive electrode.

[0088] Positive electrode for lithium secondary batteries

[0089] In another embodiment, the present invention provides a positive electrode for a lithium secondary battery, having a structure in which a positive electrode current collector, a first positive electrode mixture layer and a second positive electrode mixture layer are sequentially laminated, wherein the first positive electrode mixture layer and the second positive electrode mixture layer are each formed using the above-described positive electrode slurry for a lithium secondary battery of the present invention.

[0090] The positive electrode for lithium secondary batteries of the present invention comprises a first positive electrode mixture layer and a second positive electrode mixture layer, which are prepared by applying, drying and pressing the above-mentioned positive electrode slurry of the present invention onto a positive electrode current collector.

[0091] Here, in order to improve the irreversible efficiency of the lithium cobalt oxide represented by the following chemical formula 1 as an irreversible additive during the initial charging and discharging, the amount of lithium cobalt oxide represented by the following chemical formula 1 contained in the first cathode mixture layer and the second cathode mixture layer may be different:

[0092] [Chemical Formula 1]

[0093] Li p Co 1-q M 1 q O4

[0094] In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively.

[0095] Specifically, relative to 100 parts by weight of the first cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the first cathode mixture layer may be 0.5 to 2.0 parts by weight, and relative to 100 parts by weight of the second cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the second cathode mixture layer may be 0.01 to 0.5 parts by weight.

[0096] More specifically, relative to the total amount of 100 parts by weight of the first cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the first cathode mixture layer may be 0.5 to 1.5 parts by weight, 0.5 to 1.0 parts by weight, 0.5 to 0.9 parts by weight, 0.8 to 1.3 parts by weight, or 0.5 to 0.7 parts by weight. Furthermore, relative to the total amount of 100 parts by weight of the second cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the second cathode mixture layer may be 0.05 to 0.5 parts by weight, 0.05 to 0.35 parts by weight, 0.01 to 0.4 parts by weight, 0.01 to 0.3 parts by weight, 0.1 to 0.4 parts by weight, or 0.01 to 0.09 parts by weight.

[0097] As an example, relative to the total amount of 100 parts by weight of the first cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the first cathode mixture layer may be 0.6 ± 0.05 parts by weight, and relative to the total amount of 100 parts by weight of the second cathode mixture layer, the amount of lithium cobalt oxide represented by the above chemical formula 1 contained in the second cathode mixture layer may be 0.2 ± 0.05 parts by weight.

[0098] Furthermore, in the positive electrode for lithium secondary batteries of the present invention, the total amount of lithium cobalt oxide represented by Chemical Formula 1 contained in the entire positive electrode mixture layer, including the first positive electrode mixture layer and the second positive electrode mixture layer, relative to the total amount of positive electrode active material contained in the two positive electrode mixture layers (i.e., the first positive electrode active material and the second positive electrode active material) of 100 parts by weight, may be less than or equal to 0.5 parts by weight. More specifically, the total amount of lithium cobalt oxide contained in the entire positive electrode mixture layer of the positive electrode, relative to a total of 100 parts by weight of the first positive electrode active material and the second positive electrode active material, may be 0.01 to 0.5 parts by weight, 0.1 to 0.5 parts by weight, 0.05 to 0.4 parts by weight, 0.05 to 0.25 parts by weight, 0.1 to 0.4 parts by weight, 0.2 to 0.5 parts by weight, 0.1 to 0.3 parts by weight, or 0.4 to 0.5 parts by weight.

[0099] In this invention, by controlling the total amount of lithium cobalt oxide represented by chemical formula 1 contained in the entire positive electrode mixed layer within the above-mentioned range, the lithium ions consumed by irreversible reactions during the initial charging and discharging of the lithium secondary battery can be effectively replenished, and the generation of large amounts of oxygen due to additional side reactions or subsequent reactions due to residual materials can be prevented.

[0100] Here, by controlling the amount of lithium cobalt oxide contained in the cathode slurry of the present invention and the average thickness of each layer, the amount of lithium cobalt oxide contained in the cathode mixture layer can be adjusted. Therefore, the average thickness of the second cathode mixture layer can be greater than the average thickness of the first cathode mixture layer. Specifically, the ratio of the average thickness of the first cathode mixture layer to the average thickness of the second cathode mixture layer can be adjusted to 0.1 to 0.9, more specifically, it can be adjusted to 0.1 to 0.8, 0.1 to 0.6, 0.1 to 0.5, 0.1 to 0.3, 0.3 to 0.6, 0.4 to 0.8, 0.2 to 0.5, or 0.6 to 0.9.

[0101] Meanwhile, the total thickness of the first cathode mixture layer and the second cathode mixture layer is not particularly limited, but can be specifically 50 μm to 300 μm, or more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm or 150 μm to 190 μm.

[0102] Furthermore, the positive electrode current collector, used as the positive electrode, can be made of a material with high conductivity that does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used. When using aluminum or stainless steel, materials with surface treatments such as carbon, nickel, titanium, silver, etc., can be used. Additionally, the positive electrode current collector can have fine irregularities formed on its surface to increase the adhesion of the positive electrode active material, and can be formed in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc. Moreover, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the positive electrode current collector can be appropriately applied in the range of 3 to 500 μm.

[0103] Lithium secondary batteries

[0104] In addition, in one embodiment, the present invention provides a lithium secondary battery comprising the above-described positive electrode, negative electrode, and separator disposed between the positive electrode and the negative electrode.

[0105] The lithium secondary battery of the present invention may include the positive electrode of the present invention described above, so as to cause delithiation of the positive electrode additive at a high rate under low voltage conditions less than or equal to the available voltage during the initial charging period, so that the amount of oxygen generated during subsequent charging and discharging is significantly small, thus having the advantages of excellent electrical performance and safety of the lithium secondary battery.

[0106] The lithium secondary battery of the present invention has a structure including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode.

[0107] Here, the negative electrode can be manufactured by applying, drying, and pressing the negative electrode active material onto the negative electrode current collector, and optionally further includes the same conductive material, organic binder polymer, additives, etc. as in the positive electrode if necessary.

[0108] In addition, examples of the negative electrode active material can include carbon and graphite materials, such as hard carbon, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc. Among them, graphite has a completely layered crystal structure, such as natural graphite, soft carbon with a low-crystallinity layered crystal structure (graphene structure; a structure in which the hexagonal honeycomb planes of carbon are arranged in layers), and mixtures of these structures with amorphous parts, metal composite oxides (such as Li x Fe2O3(0 ≤ x ≤ 1), Li x WO2(0 ≤ x ≤ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc.), lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, metal oxides (such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, etc.), conductive polymers (such as polyacetylene, etc.), Li-Co-Ni-based materials, titanium oxide, lithium titanium oxide, etc.

[0109] As an example, the negative electrode active material can include graphite and silicon (Si)-containing particles. The graphite can include any one or more of natural graphite with a layered crystal structure and artificial graphite with an isotropic structure, and the silicon (Si)-containing particles can include silicon (Si) particles, silicon dioxide (SiO2) particles, or a mixture of silicon (Si) particles and silicon dioxide (SiO2) particles as particles containing silicon (Si) acting as a metal component as the main component.

[0110] In this case, relative to the total amount of 100 parts by weight of the negative electrode active material, the negative electrode active material can contain 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si)-containing particles. In the present invention, by adjusting the amounts of graphite and silicon (Si)-containing particles contained in the negative electrode active material within the above ranges, the charge capacity per unit mass can be increased while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery. <​Furthermore, the average thickness of the negative electrode mixture layer can be from 100 μm to 200 μm, and in particular, the average thickness can be from 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0112] Furthermore, the negative electrode current collector is not particularly limited to any type of current collector, as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc., can be used. When using copper or stainless steel, materials with surface treatments such as carbon, nickel, titanium, silver, etc., can be used. In addition, like the positive electrode current collector, the negative electrode current collector can have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and can be formed in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc. Furthermore, considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 500 μm.

[0113] Furthermore, a separator is placed between the positive and negative electrodes and uses an insulating film with high ion permeability and mechanical strength. There are no particular limitations on the separator, as long as it is commonly used in the art. Specifically, sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene, glass fiber, polyethylene, etc., can be used. In some cases, composite separators can be used, wherein a porous polymer substrate (e.g., sheet or nonwoven fabric) is coated with inorganic / organic particles by an organic binder polymer. When a solid electrolyte (e.g., a polymer) is used as the electrolyte, the solid electrolyte can also serve as the separator. Furthermore, the separator can have an average pore size of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0114] Meanwhile, the positive and negative electrodes can be wound in the form of gel rolls and can be housed in cylindrical batteries, square batteries, or pouch batteries, or housed in pouch batteries in a folded or stacked-folded form, but the invention is not limited thereto.

[0115] Furthermore, the lithium-containing electrolyte of the present invention can be composed of an electrolyte and a lithium salt, and the lithium-containing electrolyte can include non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc.

[0116] Examples of non-aqueous organic solvents may include aprotic organic solvents, such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc.

[0117] Examples of organic solid electrolytes may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylyzed lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymer materials containing ion-dissociating groups.

[0118] Examples of inorganic solid electrolytes can include lithium nitrides, halides, and sulfates, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0119] Lithium salts are materials that are readily soluble in non-aqueous electrolytes. Examples of lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate, and imides.

[0120] In addition, to improve charge / discharge characteristics and flame retardancy, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride can be added to the electrolyte. In some cases, to impart non-flammability, halogenated solvents such as carbon tetrachloride and trifluoroethylene can be further included. Furthermore, to improve high-temperature storage characteristics, carbon dioxide gas, fluoroethylene carbonate (FEC), and propylene sulfonate lactone (PRS) can be further added.

[0121] Example

[0122] The present invention will be described in more detail below with reference to embodiments and comparative examples.

[0123] However, the embodiments and comparative examples described below are only for illustrating the present invention, and the content of the present invention is not limited to the embodiments and comparative examples described below.

[0124] Preparation of masterbatch for positive electrode additives in Examples 1 to 4 and Comparative Examples 1 and 2.

[0125] Preparation of LiNi as the first positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size D) 50 Li6Co (1±0.05μm) as an irreversible additive 0.7 Zn 0.3 O4 (average particle size D) 50 The following components (3 ± 0.05 μm) and PVdF as the first binder were weighed and introduced into the reactor as shown in Table 1 below. Then, the above components were uniformly dried for approximately 90 minutes and mixed to prepare an average particle size D. 50 It is a masterbatch for cathode additives in pellet form with a diameter of 0.3 ± 0.005 mm.

[0126] Table 1

[0127]

[0128] Examples 5 to 10 and Comparative Examples 3 to 6: Preparation of Second Positive Electrode Slurry and Positive Electrode for Lithium Secondary Batteries

[0129] Prepare the masterbatch for positive electrode additives prepared in Examples 1 to 4 and Comparative Examples 1 to 2, and the LiNi as the second positive electrode active material. 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, acetylene black as a conductive material, and PVdF as a second binder were weighed as shown in Tables 2 and 3 below and introduced into the reactor together with N-methylpyrrolidone (NMP). The above components were then mixed at 3,000 rpm for about 60 minutes to prepare a first positive electrode slurry and a second positive electrode slurry for forming the first positive electrode mixture layer and the second positive electrode mixture layer, respectively.

[0130] Then, the first and second positive electrode slurries are sequentially applied to a surface of an aluminum current collector with dimensions of 10cm × 20cm, dried at 100°C, and rolled and pressed to manufacture the positive electrode. In this case, the total thickness of the positive electrode mixture layer is 130μm, and the total thickness of the manufactured positive electrode is approximately 200μm. Furthermore, the average thickness T of the first positive electrode mixture layer...1st The average thickness T of the mixture layer with the second cathode 2nd The ratio (i.e., the ratio of the average thickness of the first cathode mixture layer to the average thickness of the second cathode mixture layer (T)) 1st / T 2nd The components shown in Tables 2 and 3 below are described, and the content ratios of the components shown in Tables 2 and 3 below can be the same in the cathode slurry and cathode mixture layer.

[0131] Table 2

[0132]

[0133] Table 3

[0134]

[0135] Experimental Example

[0136] To evaluate the performance of the masterbatch of the present invention, the positive electrode slurry for lithium secondary batteries containing the masterbatch, and the positive electrode, the following experiments were conducted.

[0137] A) Evaluate oxygen production during the initial charging and discharging periods.

[0138] A negative electrode active material was prepared by mixing natural graphite and silicon particles (Si purity: ≥99.8%) at a weight ratio of 85:15, and adding 3 parts by weight of styrene-butadiene rubber (SBR) as a binder per 100 parts by weight of the prepared negative electrode active material to prepare a negative electrode slurry. The prepared negative electrode slurry was applied to the surface of a copper current collector with dimensions of 10 cm × 20 cm and dried to form a negative electrode mixture layer (average thickness: 120 μm). Under these conditions, the circulating air temperature was 80 °C. The prepared negative electrode slurry was then rolled and pressed, and dried in a vacuum oven at 130 °C for 12 hours to manufacture the negative electrode.

[0139] A separator made of porous polyethylene (PE) membrane (thickness: about 16 μm) was placed between the positive electrode and the negative electrode manufactured in the examples and comparative examples, and E2DVC was added as an electrolyte to manufacture a full-cell battery.

[0140] Here, “E2DVC” is a carbonate electrolyte and is a solution obtained by mixing lithium hexafluorophosphate (LiPF6, 1.0M) and ethylene carbonate (VC, 2% by weight) in a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0141] The manufactured full cell was charged at a charging current of 0.1C at 25°C to a charging termination voltage of 4.2V to 4.25V, and activated by charging until the current density reached 0.01C at a voltage of 0.02V. Under these conditions, the amount of oxygen produced was measured, and the results are shown in Table 4 below.

[0142] B) Evaluate initial charge / discharge capacity and capacity retention.

[0143] The full cells were manufactured in the same manner as those manufactured when measuring the amount of oxygen produced, using the positive electrode produced in the examples and comparative examples. Each manufactured full cell was charged at a charging current of 0.1C at 25°C to a charging termination voltage of 4.2V to 4.25V, and activated by charging until a current density of 0.01C was reached at a voltage of 0.02V. Subsequently, each manufactured full cell was discharged at a discharge current of 0.05C to a final voltage of 2V, and the electrode resistance and initial charge / discharge capacity per unit mass were measured.

[0144] Then, for the activated full cells, the capacity retention rate [%) was measured while the full cells were charged and discharged 100 times (n=100) at 25°C under the conditions of a charge termination voltage of 4.25V, a discharge termination voltage of 2.5V, and 0.5C / 0.5C. In this case, the capacity retention rate was calculated using the following expression 1, and the results are shown in Table 4 below.

[0145] [Expression 1]

[0146] Capacity retention rate (%) = (Discharge capacity during n charge / discharge cycles / Discharge capacity during one charge / discharge cycle) × 100

[0147] C) Battery resistance evaluation

[0148] The full cell was manufactured in the same manner as the full cell manufactured when measuring the amount of oxygen produced, using the positive electrode manufactured in the examples and comparative examples. The manufactured full cell was fast-charged for 10 seconds to achieve 50% SOC, and the sheet resistance of the charged secondary cell was measured using electrochemical impedance spectroscopy (EIS). The measurement results are shown in Table 4 below.

[0149] Table 4

[0150]

[0151]

[0152] As shown in Table 4, it can be seen that the positive electrode slurry of the present invention contains a masterbatch with a high content of irreversible additives, which makes the irreversible additives highly dispersible. Therefore, most of the irreversible additives react in the activation operation to achieve high charging capacity and high charge / discharge capacity retention rate, and exhibit low sheet resistance.

[0153] More specifically, the lithium secondary battery of the embodiments (which uses the masterbatch of Examples 1 to 4 containing a high content of lithium cobalt oxide represented by Chemical Formula 1 as an irreversible additive in the positive electrode mixture layer) was found to have the following configuration: a significantly smaller content of irreversible additive, ranging from 0.55 to 1.8 parts by weight relative to the total amount of the positive electrode mixture layer, was uniformly dispersed in the positive electrode mixture layer without loss, and the amount of oxygen generated increased as the irreversible additive reacted at a high rate during the activation operation; thus, a high initial charge capacity was confirmed. Furthermore, it was found that the increase in sheet resistance due to the use of the irreversible additive was improved.

[0154] The above results confirm that the masterbatch for cathode additives of the present invention contains a high content of irreversible additives and cathode active materials, so that when the cathode is manufactured, a small amount of irreversible additives are dispersed in the cathode slurry with high dispersibility without loss. Therefore, the cathode for lithium secondary batteries manufactured using irreversible additives has high electrical performance and reliability, and improves the degree of freedom in design when manufacturing the cathode.

[0155] While exemplary embodiments of the present invention and their advantages have been described in detail above, those skilled in the art will understand that various changes, substitutions and modifications may be made herein without departing from the scope of the invention as defined by the appended claims.

[0156] Therefore, the technical scope of the present invention should not be limited to the content described in the specific embodiments of the specification, but should be defined by the appended claims.

Claims

1. A positive electrode slurry for lithium secondary batteries, comprising: A masterbatch for cathode additives, the masterbatch for cathode additives comprising a first cathode active material, a first binder, and 0.5 to 50 parts by weight of lithium cobalt oxide represented by the following chemical formula 1 relative to 100 parts by weight of the first cathode active material: [Chemical Formula 1] Li p Co 1-q M 1 q O4 In the above chemical formula 1, M 1 It means that one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and p and q are 5≤p≤7 and 0≤q≤0.4, respectively. Second positive electrode active material; Conductive materials; as well as Second adhesive, Wherein, relative to the total amount of the positive electrode mixture layer formed from the positive electrode slurry, the content of lithium cobalt oxide represented by chemical formula 1 in the masterbatch is 0.05 to 2.0 parts by weight, and The content of the masterbatch for the positive electrode additive is 1 to 150 parts by weight relative to 100 parts by weight of the second positive electrode active material.

2. The positive electrode slurry as described in claim 1, wherein, The masterbatch for the positive electrode additive contains 1 to 10 parts by weight of the first binder relative to 100 parts by weight of the first positive electrode active material.

3. The positive electrode slurry as described in claim 1, wherein, The average particle size D of the masterbatch for the positive electrode additive 50 It ranges from 0.05 mm to 10 mm.

4. The positive electrode slurry as described in claim 1, wherein: The average particle size D of the first positive electrode active material 50 The range is from 0.5 μm to 100 μm; and The average particle size D of the lithium cobalt oxide 50 The range is from 1μm to 200μm. The average particle size of the lithium cobalt oxide is greater than the average particle size of the first positive electrode active material.

5. The positive electrode slurry as described in claim 1, wherein, The content of lithium cobalt oxide represented by chemical formula 1 in the masterbatch is 0.05 to 1.5 parts by weight relative to the total amount of 100 parts by weight of the positive electrode mixture layer formed from the positive electrode slurry.

6. The positive electrode slurry as described in claim 1, wherein, The content of the masterbatch for the positive electrode additive is 1 to 100 parts by weight relative to 100 parts by weight of the second positive electrode active material.

7. The positive electrode slurry as described in claim 1, wherein, The first positive electrode active material and the second positive electrode active material each contain a lithium metal composite oxide represented by chemical formula 2: [Chemical Formula 2] Li x [Ni y Co z Mr w M 2 v ]O u In the above Chemical Formula 2, M 2 represents one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 1, 0.1 < z ≤ 0.6, 0.1 < w ≤ 0.6, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 5, respectively.

8. The positive electrode slurry as described in claim 1, wherein, The content of the conductive material is 1 to 5 parts by weight relative to the total amount of 100 parts by weight of the positive electrode mixture layer formed from the positive electrode slurry.

9. The positive electrode slurry as described in claim 1, wherein, The content of the second binder is 1 to 5 parts by weight relative to the total amount of 100 parts by weight of the positive electrode mixture layer formed from the positive electrode slurry.

10. A positive electrode for a lithium secondary battery, comprising a structure formed by sequentially laminating a positive electrode current collector, a first positive electrode mixture layer, and a second positive electrode mixture layer. in, The first positive electrode mixture layer and the second positive electrode mixture layer are each formed using the positive electrode slurry for lithium secondary batteries as described in claim 1. Relative to 100 parts by weight of the first positive electrode mixture layer, the amount of the lithium cobalt oxide represented by Formula 1 contained in the first positive electrode mixture layer is 0.5 to 2.0 parts by weight; and The amount of the lithium cobalt oxide represented by chemical formula 1 contained in the second positive electrode mixture layer is 0.05 to 0.5 parts by weight relative to 100 parts by weight of the second positive electrode mixture layer.

11. The positive electrode as claimed in claim 10, wherein: Relative to 100 parts by weight of the first positive electrode mixture layer, the amount of the lithium cobalt oxide represented by Formula 1 contained in the first positive electrode mixture layer is 0.5 to 1.5 parts by weight; and The amount of the lithium cobalt oxide represented by chemical formula 1 contained in the second positive electrode mixture layer is 0.1 to 0.5 parts by weight relative to 100 parts by weight of the second positive electrode mixture layer.

12. The positive electrode as claimed in claim 10, wherein, The total amount of lithium cobalt oxide contained in the first positive electrode mixture layer and the second positive electrode mixture layer is less than or equal to 0.5 parts by weight relative to the total amount of positive electrode active material contained in 100 parts by weight of the first positive electrode mixture layer and the second positive electrode mixture layer.

13. The positive electrode as claimed in claim 10, wherein, The ratio of the average thickness of the first positive electrode mixture layer to the average thickness of the second positive electrode mixture layer is 0.1 to 0.

9.

14. A lithium secondary battery, comprising: The positive electrode according to any one of claims 10 to 13; Negative electrode; and A diaphragm is placed between the positive electrode and the negative electrode.

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