Positive electrode for lithium secondary battery having improved structural stability, method for manufacturing same, and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery having improved structural stability, a method for manufacturing the same, and a lithium secondary battery including the same. Specifically, the positive electrode for a lithium secondary battery according to the present invention comprises a current collector and a mixture layer formed on one surface or both surfaces of the current collector, in which the mixture layer has a double-layer structure in which a first mixture layer containing a positive electrode active material, a positive electrode additive, a conductive material, and a binder and a second mixture layer containing a positive electrode active material, a positive electrode additive, and a conductive material are stacked, the first mixture layer and the second mixture layer are formed under specific temperature conditions, and the porosity of the first mixture layer is 15% to 40%, and the porosity of the second mixture layer is 40% to 70%. When manufacturing a positive electrode containing a positive electrode additive, there is an advantage that it is possible to improve the structural and electrical properties of the first mixture layer and the second mixture layer because the conditions of the first and second rolling steps are controlled.

Description

[0001] This application is a divisional application of PCT International Application No. PCT / KR2022 / 006464, filed on May 6, 2022, which is a nonprovisional application of an application for a patent for invention, entered into the National Phase in the People's Republic of China as Application No. 202280006346.5, titled "Cathode for lithium secondary battery with improved structural stability, method for manufacturing the same, and lithium secondary battery comprising the same." TECHNICAL FIELD

[0002] The present application relates to a cathode for lithium secondary battery with improved structural stability, a method for manufacturing the same, and a lithium secondary battery comprising the same.

[0003] This application claims priority based on Korean Patent Application No. 10-2021-0071223, filed on June 2, 2021, the entire contents of which are incorporated herein by reference. BACKGROUND

[0004] Recently, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

[0005] Graphite is mainly used as a negative electrode material for lithium secondary batteries. However, since the unit mass capacity of graphite is small, 372 mAh / g, it is difficult to achieve high capacity of lithium secondary batteries. Therefore, in order to achieve high capacity of lithium secondary batteries, as a non-carbon-based negative electrode material having higher energy density than graphite, negative electrode materials forming intermetallic compounds with lithium, such as silicon, tin, and oxides thereof, have been developed and used. However, such non-carbon-based negative electrode materials have a problem in that, although the capacity is large, the initial efficiency is low, and thus lithium is consumed a lot during initial charging and discharging, and the irreversible capacity loss is large.

[0006] In this regard, a method has been proposed that can provide a lithium ion source or reservoir for a cathode material and use a material having electrochemical activity after the first cycle to overcome the irreversible capacity loss of the anode without reducing the overall performance of the battery. Specifically, a method of applying an oxide containing excess lithium (e.g., Li6CoO4) as a sacrificial cathode material or an irreversible additive (or over-discharge inhibitor) to a cathode is known.

[0007] Meanwhile, the existing irreversible additive such as Li6CoO4 is generally prepared by reacting cobalt oxide or the like with excess lithium oxide. The irreversible additive prepared as described above is structurally unstable and generates a large amount of oxygen (O2) when charged as follows. When the secondary battery is initially charged, that is, when all of the irreversible additive is not reacted and remains at the time of activation of the battery, the reaction can occur in the subsequent charge / discharge process to cause a side reaction or a large amount of oxygen inside the battery. The generated oxygen causes the volume expansion of the electrode assembly and becomes one of the main factors causing the degradation of the performance of the battery.

[0008]

[0009] In addition, the irreversible additive conventionally used exhibits a very low powder conductivity of about 10 -11 S / cm, close to an insulator, due to a two-dimensional (2D) percolation network. The low powder conductivity increases the resistance of the positive electrode. In this case, a large capacity of 200 mAh / g or more is exhibited at a low C-rate, and when the C-rate is increased, the performance is rapidly reduced as the charging and discharging proceed due to the large resistance, so there is a limit to the reduction of the charge / discharge capacity of the battery, and it is difficult to charge and discharge at high speed.

[0010] Therefore, there is a need to develop a lithium secondary battery having excellent electrical performance and improved battery safety.

[0011] Prior Art Documents

[0012] Patent Documents

[0013] Japanese Patent Application Laid-Open No. 2019-061751 SUMMARY

[0014] TECHNICAL PROBLEM

[0015] An object of the present application is to provide a positive electrode for a lithium secondary battery having improved electrical performance and improved structural stability, a method for preparing the same, and a lithium secondary battery comprising the same.

[0016] TECHNICAL SOLUTION

[0017] The present application aims to provide a positive electrode for a lithium secondary battery, the positive electrode including a current collector and a binder layer formed on one surface or both surfaces of the current collector, wherein the binder layer is a double-layer structure in which a first binder layer and a second binder layer are stacked, the first binder layer including a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder, the porosity of the first binder layer being 15% to 40%, the porosity of the second binder layer being 40% to 70%.

[0018] [Chemical Formula 1]

[0019] Li p Co (1-q) M 1 q O4

[0020] In Chemical Formula 1, M 1 represents at least one element 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 ≤ 0.5, respectively.

[0021] The average thickness of the first binder layer can be from 0.1 μm to 20 μm, and the average thickness of the second binder layer can be from 50 μm to 300 μm.

[0022] The ratio (D1:D2) of the average thickness (D1) of the first binder layer to the average thickness (D2) of the second binder layer can be from 4:6 to 1:10.

[0023] Based on the total weight of the first binder layer, the content of the positive electrode additive can be from 0.1% by weight to 5% by weight.

[0024] The positive electrode active material can be a lithium nickel 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 Chemical Formula 2, M 2 represents at least one element 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, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

[0028] The present application also aims to provide a method of manufacturing the positive electrode for a lithium secondary battery of the present application, the method including: a first binder layer forming process of forming a first binder layer by applying a first slurry including a positive electrode active material and a positive electrode additive represented by Chemical Formula 1 on one side or both sides of a current collector; a first rolling process of rolling the formed first binder layer; a second binder layer forming process of forming a second binder layer by applying a second slurry including a positive electrode active material on the rolled first binder layer; and a second rolling process of rolling the formed second binder layer, wherein the porosity of the first binder layer is 15% to 40%, and the porosity of the second binder layer is 40% to 70%.

[0029] [Chemical Formula 1]

[0030] Li p Co (1-q) M 1 q O4

[0031] In Chemical Formula 1, M 1 represents at least one element 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≤0.5, respectively.

[0032] The first rolling process can be performed at a speed of 0.5 m / s to 6 m / s, the second rolling process can be performed at a speed of 2 m / s to 7 m / s, and the second rolling process can be performed at a speed faster than the first rolling process.

[0033] The first rolling process can be performed at a temperature in the range of 10℃ to 40℃, and the second rolling process can be performed at a temperature in the range of 40℃ to 100℃.

[0034] The first binder layer can satisfy the thickness variation rate condition of the following Mathematical Formula 1.

[0035] [Mathematical Formula 1]

[0036] D 2 min / D 1 max × 100 ≥ 70%

[0037] In Mathematical Formula 1, D 1 max may represent the maximum thickness of the first binder layer after the first rolling process, D 2 min may represent the minimum thickness of the first binder layer after the second rolling process.

[0038] The present application also aims to provide a lithium secondary battery including the above-described positive electrode, negative electrode, and separator interposed between the positive electrode and the negative electrode of the present application.

[0039] The negative electrode can include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector and including a negative electrode active material, and the negative electrode active material can include a carbon material and a silicon material.

[0040] Advantages

[0041] The positive electrode for a lithium secondary battery of the present application, the method of manufacturing the same, and the lithium secondary battery including the same are advantageous in that, when a positive electrode including a positive electrode additive is manufactured, the conditions of the first and second roll pressing processes are controlled, and thus the structure and electrical properties of the first and second active material layers can be improved. DETAILED DESCRIPTION

[0042] The present application can be modified in various forms and can have various embodiments, and thus a specific embodiment will be described in detail.

[0043] However, these embodiments should not be understood to limit the present application to the specific embodiments, but should be understood to include modifications, equivalents, or alternatives within the spirit and technical scope of the present application.

[0044] In the present application, the terms "comprising", "having", and the like are used to designate the presence of features, numbers, steps, operations, components, elements, or combinations thereof described herein, and they do not exclude the presence or addition of one or more other features, numbers, steps, operations, components, elements, or combinations thereof.

[0045] Further, in the present application, when a part of a layer, film, region, plate, or the like is described as being "on" another part, this includes not only the case where the part is "directly on" the other part, but also the case where a further part is present between the part and the other part. In contrast, when a part of a layer, film, region, plate, or the like is described as being "under" another part, this includes not only the case where the part is "directly under" the other part, but also the case where a further part is present between the part and the other part. Further, in the present application, being "on" can include not only the case of being disposed on the upper portion, but also the case of being disposed on the lower portion.

[0046] Hereinafter, the present application will be described in more detail.

[0047] Positive electrode for lithium secondary battery

[0048] In one embodiment of the present application, provided is a positive electrode for a lithium secondary battery, including a current collector and a binder layer formed on one surface or both surfaces of the current collector, wherein the binder layer is a double layer structure in which a first binder layer and a second binder layer are stacked, the first binder layer contains a positive electrode active material, a positive electrode additive represented by Chemical Formula 1 below, a conductive material, and a binder, the porosity of the first binder layer is 15% to 40%, and the porosity of the second binder layer is 40% to 70%.

[0049] [Chemical Formula 1]

[0050] Li p Co (1-q) M 1 q O4

[0051] In Chemical Formula 1, M 1 represents at least one element 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≤0.5, respectively.

[0052] Specifically, in Chemical Formula 1, M 1 may represent a Zn element, and q can be 0.2≤q≤0.4.

[0053] The positive electrode for a lithium secondary battery of the present application has a double layer structure in which a first binder layer and a second binder layer are sequentially stacked on a current collector, and has a structure in which the second binder layer is located in the outermost portion. In particular, the positive electrode for a lithium secondary battery of the present application can improve the structure and electrical properties of the first and second binder layers by controlling the conditions of the first and second roll-pressing processes when manufacturing the positive electrode.

[0054] The positive electrode additive can contain excess lithium (Li), and can provide Li consumed by irreversible chemical and physical reactions at the negative electrode during initial charging, so that the charging capacity of the battery is increased, the irreversible capacity is reduced, and the life characteristics can be improved.

[0055] According to the present application, a lithium cobalt oxide represented by Chemical Formula 1 can be used as a positive electrode additive. In this case, as the lithium cobalt oxide represented by Chemical Formula 1, Li6CoO4, Li6Co 0.5 Zn 0.5 O4and Li6Co 0.7 Zn 0.3O4, or a combination thereof. When compared with a nickel-containing oxide commonly used in the art, the lithium cobalt oxide represented by Chemical Formula 1 is advantageous in that, since the content of lithium ions is high and the voltage range required for delithiation is low, lithium ions can be desorbed when the battery is activated without affecting the reaction of the positive active material.

[0056] Further, the lithium cobalt metal oxide represented by Chemical Formula 1 can have a tetragonal crystal structure, and have a space group of P42 / nmc in the tetragonal crystal structure. The lithium cobalt metal oxide represented by Chemical Formula 1 exhibits excellent charge / discharge characteristics and life characteristics in a lithium secondary battery, but has a problem of low thermal stability. Specifically, when the lithium cobalt metal oxide represented by Chemical Formula 1 is used as a positive electrode additive, structural deformation can occur due to the influence of the temperature (e.g., the temperature of a slurry) during the preparation of a positive electrode mixture layer, so that the battery characteristics can be reduced.

[0057] Accordingly, when a positive electrode containing a positive electrode additive is manufactured, the positive electrode for a lithium secondary battery of the present application prevents the occurrence of structural deformation of the positive electrode additive by controlling the conditions of the first and second roll-pressing processes, and improves the structure and electrical properties of the first and second mixture layers.

[0058] As an example, in X-ray diffraction (XRD) analysis of the first mixture layer, the positive electrode for a lithium secondary battery of the present application can satisfy the following Equation 1.

[0059] [Equation 1]

[0060] A / B ≤ 1

[0061] A represents the intensity of the strongest peak among peaks shown in the range of 2θ = 38.5 ± 0.1°, and B represents the intensity of the strongest peak among peaks shown in the range of 2θ = 47.9 ± 0.1°.

[0062] In Equation 1, the peak B shown in the range of 2θ = 47.9 ± 0.1° is realized by the crystal of the lithium cobalt metal oxide represented by Chemical Formula 1, and the peak A shown in the range of 2θ = 38.5 ± 0.1° is realized by impurities. This means that the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1 increases as the intensity ratio of the peaks, i.e., “A / B”, decreases. In the positive electrode of the present application, the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1 in the positive electrode additive contained in the first mixture layer is increased to 98% or more, so that A / B can satisfy 1 or less, 0.35 or less, 0.25 or less, or 0.1 or less. In some cases, since the proportion of the lithium cobalt metal oxide represented by Formula 1 in the positive electrode additive is 100%, A / B can satisfy zero.

[0063] Further, the porosity of the first mixture layer can range from 15% to 40%, specifically, from 20% to 40%, from 20% to 35%, from 25% to 40%, from 25% to 35%, or from 25% to 30%.

[0064] When the porosity of the first mixture layer is too small, the electrolyte can have difficulty penetrating to the surface of the current collector, and when the porosity is too large, the density of the electrode decreases, and thus the amount of active material in contact with the current collector can decrease, which can result in a decrease in capacity and output. Accordingly, the porosity of the first mixture layer can be within the above range.

[0065] The measurement of the porosity is not particularly limited, and in one embodiment of the present application, the porosity can be measured by, for example, a Brunauer-Emmett-Teller (BET) measurement method or a mercury (Hg) porosimeter.

[0066] Further, the content of the positive electrode additive can range from 0.1 parts by weight to 5 parts by weight, specifically, from 0.1 parts by weight to 3 parts by weight, or from 1 parts by weight to 3 parts by weight, based on 100 parts by weight of the first mixture layer.

[0067] The first mixture layer is a positive electrode active material capable of reversible intercalation and deintercalation, and can include a lithium-nickel composite oxide represented by Chemical Formula 2 below.

[0068] [Chemical Formula 2]

[0069] Li x [Ni y Co z Mn w M 2 v ]O u

[0070] In Chemical Formula 2, M 2 represents at least one element 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, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

[0071] The lithium-nickel composite oxide represented by Chemical Formula 2 is a composite metal oxide including Li, nickel, cobalt, and manganese, and in some cases, can have a form doped with another transition metal (M 2 ). For example, the positive electrode active material can include at least one selected from the group consisting of LiNi 1 / 3 Co1 / 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 O2and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2of the group. As an example, in the positive active material, LiNi 0.6 Co 0.2 Mn 0.2 O2and LiNi 0.8 Co 0.1 Mn 0.1 O2may be used alone or in combination as a lithium nickel complex metal oxide represented by Chemical Formula 2.

[0072] Further, the content of the positive active material can range from 85 parts by weight to 95 parts by weight, specifically, from 88 parts by weight to 95 parts by weight, from 90 parts by weight to 95 parts by weight, from 86 parts by weight to 90 parts by weight, or from 92 parts by weight to 95 parts by weight, based on 100 parts by weight of the first mixture layer.

[0073] In this case, an electrically conductive material can be used to improve the performance such as electrical conductivity of the positive electrode, and one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber can be used as the electrically conductive material. For example, the electrically conductive material can include acetylene black.

[0074] Further, the content of the electrically conductive material can be 1 part by weight to 10 parts by weight, specifically, 2 parts by weight to 8 parts by weight, or 2 parts by weight to 6 parts by weight, based on 100 parts by weight of the first mixture layer.

[0075] Further, the binder can include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. For example, the binder can include polyvinylidene fluoride.

[0076] Further, the content of the binder can be 1 to 10 parts by weight, specifically, 2 to 8 parts by weight, or 2 to 6 parts by weight, based on 100 parts by weight of the first mixture layer.

[0077] In addition, the average thickness of the first mixture layer is not particularly limited, but specifically, it can range from 0.1 to 20 μm, more specifically, from 0.1 to 15 μm, from 0.1 to 10 μm, from 2 to 10 μm, from 4 to 10 μm, or from 5 to 9 μm.

[0078] Further, the second mixture layer is formed on the first mixture layer formed on the current collector, contains the positive electrode active material, and can further contain the conductive material and the binder as needed in addition to the positive electrode active material.

[0079] Further, the porosity of the second mixture layer can range from 40 to 70%, specifically, from 40 to 65%, from 40 to 60%, from 45 to 60%, from 45 to 55%, or from 45 to 50%. In particular, the second mixture layer located at the outermost side of the positive electrode can increase the impregnation performance of the electrolyte in the electrode by increasing the porosity. Thus, the energy density is increased, so that the capacity, output characteristics, and charging / discharging speed of the secondary battery including the above-described positive electrode can be improved.

[0080] On the other hand, the first mixture layer and the second mixture layer as described above can be respectively applied and roll-pressed so as to have a difference in porosity and form an interface without being mixed with each other.

[0081] The positive electrode active material contained in the second mixture layer can be applied without particular limitation as long as it is a lithium metal complex oxide represented by Chemical Formula 2, and the positive electrode active material can contain 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.

[0082] As an example, the positive electrode active material can be a lithium nickel composite metal oxide represented by Chemical Formula 2, and LiNi 0.6 Co 0.2 Mn 0.2 O2and LiNi 0.8 Co 0.1 Mn 0.1 O2may be used alone or in combination as the positive electrode active material.

[0083] Further, the content of the positive electrode active material can be 80 parts by weight to 98 parts by weight, specifically, 84 parts by weight to 96 parts by weight, or 88 parts by weight to 96 parts by weight, based on 100 parts by weight of the second binder layer.

[0084] In this case, the performance such as the electrical conductivity of the positive electrode can be improved using the conductive material contained in the second binder layer, and one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber can be used as the conductive material. For example, the conductive material can include acetylene black.

[0085] Further, the content of the conductive material can be 1 part by weight to 10 parts by weight, specifically, 2 parts by weight to 8 parts by weight, or 2 parts by weight to 6 parts by weight, based on 100 parts by weight of the second binder layer.

[0086] Further, the binder contained in the second binder layer can include one or more resins selected from the group consisting of PVDF-co-HFP, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. For example, the binder can include polyvinylidene fluoride.

[0087] Further, the content of the binder can be 1 part by weight to 10 parts by weight, specifically, 2 parts by weight to 8 parts by weight, or 2 parts by weight to 6 parts by weight, based on 100 parts by weight of the second binder layer.

[0088] In addition, the average thickness of the second binder layer can range from 50 μm to 300 μm, 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.

[0089] In a particular example, the thickness of the second binder layer can be greater than the thickness of the first binder layer.

[0090] Further, a ratio (D1:D2) of an average thickness (D1) of the first slurry layer to an average thickness (D2) of the second slurry layer can be 4:6 to 1:10. Specifically, the average thickness ratio (D1:D2) between the first and second positive electrode slurry layers can be 3:7 to 1:10, or 2:8 to 1:9. In the present application, the thickness of the second negative electrode slurry layer is formed to be relatively thick, such that the binding force with the current collector is increased, and the stability of the electrode is increased.

[0091] Meanwhile, in the positive electrode for a lithium secondary battery of the present application, a material having high electrical conductivity without causing chemical changes in the battery can be used as the current collector. For example, stainless steel, aluminum, nickel, titanium, and calcined carbon can be used, and aluminum or stainless steel treated with carbon, nickel, titanium, and silver on the surface can be used as the current collector. Further, fine irregularities can be formed on the surface of the current collector to enhance the binding force of the positive electrode active material, and various forms of positive electrode current collectors, such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric, can be used. Further, the average thickness of the current collector can be appropriately applied in the range of 3 μm to 500 μm in consideration of the electrical conductivity and the total thickness of the positive electrode to be manufactured.

[0092] Method for manufacturing positive electrode for lithium secondary battery

[0093] One embodiment of the present application manufactures a method of manufacturing a positive electrode for a lithium secondary battery, including: a first slurry layer forming process of forming a first slurry layer by applying a first slurry including a positive electrode active material and a positive electrode additive represented by Chemical Formula 1 on one side or both sides of a current collector; a first roll pressing process of roll pressing the formed first slurry layer; a second slurry layer forming process of forming a second slurry layer by applying a second slurry including a positive electrode active material on the first slurry layer after roll pressing; and a second roll pressing process of roll pressing the formed second slurry layer, wherein the porosity of the first slurry layer is 15% to 40%, and the porosity of the second slurry layer is 40% to 70%.

[0094] [Chemical Formula 1]

[0095] Li p Co (1-q) M 1 q O4

[0096] In Chemical Formula 1, M 1 represents at least one element 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≤0.5, respectively.

[0097] The method of manufacturing a cathode for a lithium secondary battery according to the present application can improve excellent charge / discharge characteristics and life characteristics of a lithium secondary battery by adding a cathode additive to a first mixture layer in contact with a current collector. In addition, by sequentially forming a second mixture layer on the first mixture layer such that the second mixture layer is located at the outermost portion, but controlling the conditions of the first and second roll pressing processes, there is an advantage that the structure and electrical properties of the first and second mixture layers can be improved.

[0098] In addition, in the method of manufacturing a cathode for a lithium secondary battery according to the present application, roll pressing of the first mixture layer is performed using a roll press before forming the second mixture layer, and two roll pressing processes are performed to perform secondary roll pressing after forming the second mixture layer, so that the thickness uniformity of the first mixture layer can also be improved.

[0099] As an example, when a cross section of a cathode for a lithium secondary battery manufactured by the method of manufacturing a cathode for a lithium secondary battery described above is analyzed in the thickness direction of the cathode using a scanning electron microscope (SEM), the following mathematical formula 1 can be satisfied.

[0100] [mathematical formula 1]

[0101] D 2 min / D 1 max × 100 ≥ 70%

[0102] In mathematical formula 1, D 1 max represents the maximum thickness of the first mixture layer after the first roll pressing process, D 2 min represents the minimum thickness of the first mixture layer after the second roll pressing process.

[0103] Mathematical formula 1 represents the thickness variation rate of the two roll pressing processes of the first mixture layer, and means that, when the first roll pressing process and the second roll pressing process are performed and the cross section of the cathode is analyzed, the minimum thickness D 2 min of the first mixture layer after the second roll pressing process is higher than the maximum thickness D 1 max of the first mixture layer after the first roll pressing process, the thickness deviation of the first mixture layer is lower. Specifically, since the uniformity of the first mixture layer is very high, the deviation between the minimum thickness D 2 min and the maximum thickness D 1 max is very small, and the condition of 1 when written can be satisfied to be 75% or more (for example, D 2 min / D 1 maxx 100 ≥ 75%), 80% or more (e.g., D 2 min x 100 ≥ 75%), 80% or more (e.g., D 1 max x 100 ≥ 75%), 80% or more (e.g., D 2 min x 100 ≥ 75%), 80% or more (e.g., D 1 max x 100 ≥ 75%), 80% or more (e.g., D 2 min x 100 ≥ 75%), 80% or more (e.g., D 1 max x 100 ≥ 75%), 80% or more (e.g., D 2 min x 100 ≥ 75%), 80% or more (e.g., D 1 max x 100 ≤ 95%).

[0104] First, in the present application, the first mixture layer forming process is performed in a temperature range of 10°C to 40°C. Specifically, the first mixture layer forming process means that, when the first slurry is applied to the current collector, the temperature of the first slurry or the temperature of the reactor in which the first slurry is stored is controlled in a temperature range of 10°C to 40°C. More specifically, in the first mixture layer forming process, the temperature of the reactor in which the first slurry is stored can be controlled in a range of 10°C to 30°C, 10°C to 20°C, 15°C to 25°C, 22°C to 28°C, 20°C to 30°C, or 18°C to 25°C. When the temperature of the slurry is controlled to a temperature lower than 10°C in the first mixture layer forming process, the slurry can not be uniformly applied to the current collector, and when the temperature is controlled to a temperature exceeding 40°C, the positive electrode additive included in the first slurry can be deteriorated. Therefore, in the first mixture layer forming process, the temperature of the first slurry can be controlled in the above range.

[0105] Further, in the first rolling process, the thickness of the first slurry layer is uniformly maintained, and the rolling density is increased, so that when the second slurry layer is rolled, the influence of the positive active material on the interface uniformity can be reduced. Further, the rolling temperature is controlled in the first rolling process, and thus the deterioration of the positive additive contained in the first slurry layer can be minimized. To this end, the first rolling process can be performed at a low temperature at a high speed. Specifically, similar to the control of the slurry temperature when the above-described slurry layer is formed, the first rolling process can be performed in a temperature range of 10°C to 40°C, 10°C to 30°C, 10°C to 20°C, 15°C to 25°C, 22°C to 28°C, 20°C to 30°C, or 18°C to 25°C. Further, the rolling speed at which the first rolling process is performed can be in a range of 0.5 m / s to 6 m / s, specifically, 0.5 m / s to 5.5 m / s, 0.5 m / s to 5 m / s, 0.5 m / s to 4.5 m / s, 0.5 m / s to 4 m / s, 0.5 m / s to 3.5 m / s, 0.7 m / s to 3 m / s, 0.7 m / s to 2.5 m / s, 0.7 m / s to 2 m / s, 0.9 m / s to 2 m / s, 1 m / s to 1.5 m / s, 1 m / s to 1.2 m / s, 2 m / s to 5 m / s, 2 m / s to 5.5 m / s, or 3 m / s to 5 m / s.

[0106] Next, similar to the first slurry layer forming process, the second slurry layer forming process can be performed in a temperature range of 10°C to 40°C. As described above for the first slurry layer forming process, the second slurry layer forming process means that, when the second slurry is applied to the current collector, the temperature of the second slurry or the temperature of the reactor in which the second slurry is stored is controlled in a range of 10°C to 40°C. Since the positive additive is not contained in the second slurry, the second slurry layer forming process can be performed at a temperature higher than the first slurry layer forming temperature. However, when the temperature of the second slurry is high, since the positive additive contained in the first slurry layer is directly affected, the temperature of the reactor in which the second slurry is stored can be controlled in a range of 10°C to 40°C.

[0107] Further, the second rolling process can be performed at a relatively high temperature and at a high speed when compared to the first rolling process. Specifically, the temperature range in which the second rolling process is performed can be 50°C to 100°C, more specifically, 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C. Specifically, the rolling speed range in which the second rolling process is performed can be 2 m / s to 7 m / s, more specifically, 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s.

[0108] Further, the pressure conditions in which the first and second rolling processes are performed can each be 50 MPa to 200 MPa, specifically, 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa. In this case, in order to optimize the rolling density of the first mixture layer, the first rolling process can be performed at the same pressure conditions as the second rolling process, or can be performed at pressure conditions that are less than twice the pressure conditions of the second rolling process, for example, less than 1.5 times, less than 1.2 times, or 1.1 to 1.4 times the pressure conditions of the second rolling process. In this way, the ratio (D1:D2) of the average thickness (D1) of the prepared first mixture layer to the average thickness (D2) of the prepared second mixture layer can be 4:6 to 1:10. Specifically, the average thickness ratio (D1:D2) between the first and second positive electrode mixture layers can be 3:7 to 1:10, or 2:8 to 1:9. In the present application, the thickness of the second positive electrode mixture layer is formed to be relatively thick, so that the binding force to the current collector is increased, and the stability of the electrode is increased.

[0109] According to the present application, the first mixture layer and the second mixture layer are sequentially formed on the current collector under the above temperature conditions and the above rolling conditions, so that a positive electrode containing a positive electrode additive and having minimized deterioration can be manufactured.

[0110] Lithium secondary battery

[0111] In one embodiment of the present application, a lithium secondary battery is provided, which includes the above-described positive electrode, negative electrode, and separator of the present application, interposed between the positive electrode and the negative electrode.

[0112] The lithium secondary battery of the present application can include the above-described positive electrode of the present application, thereby reducing the amount of oxygen generated during charging and discharging, and exhibiting excellent charging and discharging performance.

[0113] The lithium secondary battery of the present application has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0114] Here, the negative electrode is manufactured by applying, drying, and pressing a negative active material on a negative current collector, and as needed, can further selectively contain a conductive material, an organic binder polymer, an additive, as in the positive electrode.

[0115] Further, the negative active material can contain, for example, a carbon material and a silicon material. The carbon material refers to a carbon material containing carbon atoms as a main component. The carbon material can contain one or more selected from the group consisting of graphite having a complete layered crystal structure such as natural graphite, soft carbon having a low crystallinity layered crystal structure (graphene structure is a structure in which hexagonal honeycomb planes of carbon are arranged in layers), hard carbon in which these structures are mixed with amorphous portions, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotube, fullerene, activated carbon, graphene, and carbon nanotube. More preferably, the carbon material can contain natural graphite and / or artificial graphite, and can contain any one or more of graphene and carbon nanotube and natural graphite and / or artificial graphite. In this case, the carbon material can contain 0.1 parts by weight to 10 parts by weight of graphene and / or carbon nanotube, based on 100 parts by weight of the total carbon material, more specifically, the carbon material can contain 0.1 parts by weight to 5 parts by weight, or 0.1 parts by weight to 2 parts by weight of graphene and / or carbon nanotube, based on 100 parts by weight of the total carbon material.

[0116] Further, the silicon material is a particle containing a metal component of silicon (Si) as a main component, and can contain one or more of Si particles and silicon oxide (SiO X and 1≤X≤2) particles. For example, the silicon material can contain silicon particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture thereof.

[0117] Further, the silicon material can have a mixed form of crystalline particles and amorphous particles, and the proportion of the amorphous particles is 50 parts by weight to 100 parts by weight, specifically, 50 parts by weight to 90 parts by weight, 60 parts by weight to 80 parts by weight, or 85 parts by weight to 100 parts by weight, based on 100 parts by weight of the total silicon material. In the present application, the proportion of the amorphous particles contained in the silicon material is controlled within the above-described range, thereby improving thermal stability and flexibility within a range in which the electrical performance of the electrode is not reduced.

[0118] Further, the negative active material contains a carbon material and a silicon material, and the content thereof can be 1 to 20 parts by weight, specifically, 5 to 20 parts by weight, 3 to 10 parts by weight, 8 to 15 parts by weight, 13 to 18 parts by weight, or 2 to 7 parts by weight, based on 100 parts by weight of the negative electrode mixture layer.

[0119] In the present application, the content of the carbon material and the silicon material contained in the negative active material is adjusted to the above range, so that the charge capacity per unit mass can be increased while reducing Li consumption and irreversible capacity loss during initial charge and discharge of the battery.

[0120] As an example, the negative active material can contain 95 ± 2 parts by weight of graphite and 5 ± 2 parts by weight of a mixture obtained by uniformly mixing SiO particles and SiO2 particles, based on 100 parts by weight of the negative electrode mixture layer. In the present application, the content of the carbon material and the silicon material contained in the negative active material is adjusted to the above range, so that the charge capacity per unit mass can be increased while reducing Li consumption and irreversible capacity loss during initial charge and discharge of the battery.

[0121] Further, the average thickness of the negative electrode mixture layer can be 100 to 200 μm, specifically, 100 to 180 μm, 100 to 150 μm, 120 to 200 μm, 140 to 200 μm, or 140 to 160 μm.

[0122] Further, the negative current collector is not particularly limited as long as it has high electrical conductivity without causing chemical changes in the battery, for example, copper, stainless steel, nickel, titanium, and calcined carbon can be used as the negative current collector, and copper or stainless steel treated with carbon, nickel, titanium, or silver on the surface can be used. Further, as in the case of the positive current collector, a fine concavo-convex can be formed on the surface of the negative current collector to improve the adhesion to the negative active material, and various forms of the negative current collector such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric can be used. Further, the average thickness of the negative current collector can be appropriately applied in the range of 3 to 500 μm in consideration of the electrical conductivity and the total thickness of the negative electrode to be manufactured.

[0123] Further, a separator is interposed between the positive electrode and the negative electrode, and an insulating film having high ion permeability and high mechanical strength is used as the separator. The separator is not particularly limited as long as it is generally used in the art, and specifically, polypropylene, glass fiber, or a sheet or nonwoven fabric made of polyethylene having chemical resistance and hydrophobicity can be used as the separator. In some cases, a composite separator in which a porous polymer base material such as a sheet or nonwoven fabric is coated with inorganic particles / organic particles by an organic binder polymer can be used as the separator. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also be used as the separator. Further, the separator can have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0124] Meanwhile, the positive electrode and the negative electrode can be wound in the form of a jelly-roll and housed in a cylindrical battery, a prismatic battery, or a pouch-type battery, or can be housed in a pouch-type battery in a folded or stacked-folded form, but the present application is not limited thereto.

[0125] Further, the electrolyte containing a lithium salt of the present application can consist of an electrolyte and a lithium salt, and a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte can be used as the electrolyte.

[0126] For example, as the non-aqueous organic solvent, aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0127] For example, as the organic solid electrolyte, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly-stirred lysine, polyester sulfide, polyvinyl alcohol (PVA), polyvinylidene fluoride, or a polymer containing an ion-dissociating group can be used.

[0128] As the inorganic solid electrolyte, nitrides, halides, sulfates of lithium such as Li3N, Lil, Li5NI2, Li3N-Lil-LiOH, LiSiO4, LiSiO4-Lil-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-Lil-LiOH, Li3PO4-Li2S-SiS2, and the like can be used.

[0129] Lithium salts are materials that are easily soluble in nonaqueous electrolytes. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, or imide can be used as the lithium salt.

[0130] In addition, in order to improve charge / discharge characteristics and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphoric acid, a nitrobenzene derivative, sulfur, a quinone imine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride can be added to the electrolyte. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene can be further included, and in order to improve high-temperature storage characteristics, carbon dioxide gas can be further included, and fluorinated ethylene carbonate (FEC) or propylene sulfite (PRS) can be further included.

[0131] Meanwhile, according to one embodiment of the present application, a battery module including the above-described secondary battery as a unit cell, and a battery pack including the battery module are provided.

[0132] The battery pack can be used as a power source for large- and medium-sized devices requiring high-temperature stability, long cycle characteristics, and high-rate characteristics. Specific examples of the large- and medium-sized devices include power tools driven by electric motors, electric vehicles (EVs) including EVs, hybrid EVs (HEVs), and plug-in HEVs (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters), electric golf carts, electric trucks, and systems for electric power storage, and more specifically, examples include HEVs, but the present application is not limited thereto.

[0133] Embodiments

[0134] Hereinafter, the present application will be described in greater detail with reference to examples and experimental examples.

[0135] However, the following examples and experimental examples are merely illustrative of the present application, and the scope of the present application is not limited to the following examples and experimental examples.

[0136] Examples 1 to 4 and Comparative Examples 1 to 7: Manufacture of a cathode for a lithium secondary battery

[0137] 95 parts by weight of LiNi 0.8 Co0.1 Mn 0.1 O2, 0.9 parts by weight of Li6CoO4 as a positive electrode additive, 1.6 parts by weight of PVdF as a binder, and 2.5 parts by weight of carbon black as a conductive material, and mixed with an N-methyl pyrrolidone (NMP) solvent to prepare a first slurry for a first mixture layer.

[0138] In addition, 95 parts by weight of LiNi 0.8 Co 0.1 Mn 0.1 O2, 2 parts by weight of PVdF as a binder, and 3 parts by weight of carbon black as a conductive material, and mixed with an NMP solvent to prepare a second slurry for a second mixture layer.

[0139] The first slurry was applied to an aluminum foil and dried, and then a first roll-pressing process was performed to form a first mixture layer (average thickness: 8 μm). Subsequently, the second slurry was applied to the first mixture layer and dried, and then a second roll-pressing process was performed to form a second mixture layer (average thickness: 100 μm). In this case, by analyzing a cross-section of the first mixture layer immediately after the first roll-pressing process and the second roll-pressing process were respectively performed, the maximum thickness D 1 max and the minimum thickness D 2 min of the first mixture layer after the first roll-pressing process and the second roll-pressing process were measured, respectively. Also, the ratio (D 2 min / D 1 max ) of the measured values and the conditions in which the first roll-pressing process and the second roll-pressing process were performed are shown in Table 1 below. In addition, the conditions for performing the first and second mixture layer forming processes and the first and second roll-pressing processes are shown in Table 1 below.

[0140] [Table 1]

[0141]

[0142] Experimental Example 1:

[0143] 1) observation of xrd pattern of first mixture layer

[0144] To confirm the change in the positive electrode additive with temperature when manufacturing a positive electrode for a lithium secondary battery, X-ray diffraction measurement was performed on the first binder layer of the positive electrode for a lithium secondary battery manufactured in Examples 1 to 4 and Comparative Examples 1 to 4, and the proportion contained in each positive electrode additive was calculated from the measured X-ray diffraction. In this case, X-ray diffraction was measured using an X-ray diffractometer of Rigaku Corporation, and the wavelength of 1.5406 A (Cu Ka radiation, 40 kV and 100 mA) was scanned, and an X-ray diffraction pattern in the range of 15° to 64° was obtained at an angle of 2 theta and a scan speed of 5° / sec.

[0145] As a result, peaks appearing in Li6CoO4 in the first binder layer of Examples 1 to 4 were observed. Specifically, an A peak was observed in the range of 2 theta = 38.5 ± 0.1°, and a B peak was observed in the range of 2 theta = 47.9 ± 0.1°. For reference, the A / B of Examples 1 to 4 was less than or equal to 0.1.

[0146] On the other hand, in Comparative Examples 1 to 4, the peaks shown in Examples 1 to 4 were not observed. It is considered that the structure of the positive electrode additive is deformed due to high temperature in the binder layer forming process and the roll pressing process when manufacturing the positive electrode.

[0147] Experimental Example 2:

[0148] To evaluate the performance of the positive electrode for a lithium secondary battery and the lithium secondary battery of the present application, the following experiments were performed.

[0149] 1) evaluation of positive electrode porosity

[0150] The electrode porosity of the first and second binder layers of the positive electrode manufactured in the examples and comparative examples was measured. Further, the results are shown in Table 2 below.

[0151] 2) evaluation of initial resistance value

[0152] A lithium secondary battery was manufactured using each of the positive electrodes manufactured in the examples and comparative examples. Specifically, a slurry for forming a negative electrode was prepared by mixing natural graphite as a negative electrode active material, a carbon black conductive material, and a PVdF binder at a weight ratio of 85:10:5 with an NMP solvent, and the slurry was applied to a copper foil to manufacture a negative electrode. A separator made of a porous polyethylene (PE) film (thickness: about 16 μm) was laminated and interposed between each of the positive electrodes manufactured in the examples and comparative examples and the negative electrode manufactured to manufacture an electrode assembly. The manufactured electrode assembly was put into a battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. In this case, the electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC, mixed volume ratio of 3 / 4 / 3) at a concentration of 1.0 M.

[0153] Further, each of the manufactured lithium secondary batteries was charged with a constant current (CC) at a rate of 0.3 C using a CC-CV (constant voltage) method such that the voltage of the lithium secondary battery became 4.2 V at a current of 333 mA, and after the voltage of the battery reached 4.2 V, the lithium secondary battery was charged once by cutting off the current at a rate of 0.05 C while maintaining CV at 4.2 V. For the once-charged battery, one cycle of CC discharge was repeatedly performed three times at a CC of 333 mA and a rate of 0.3 C until the voltage of the battery reached 3 V. After recording the voltage drop occurring when discharging at a current of 2 A (2 C) for ten seconds, the direct current (DC) discharge resistance value measured at the time of initial evaluation and calculated using R = V / I (Ohm's law) was shown in Table 2 below. In this case, the DC resistance is closely related to the output characteristics of the secondary battery.

[0154] 3) evaluation of cycle life performance

[0155] In the same manner as the evaluation of the initial resistance value, a lithium secondary battery was manufactured using each of the positive electrodes manufactured in the examples and comparative examples. For each of the manufactured lithium secondary batteries, the capacity retention rate was measured when 100 charge / discharge cycles (n = 100) and 200 charge / discharge cycles (n = 200) were performed at a temperature of 25°C under the conditions of a final charge voltage of 4.25 V, a final discharge voltage of 2.5 V, and 0.5 C / 0.5 C. In this case, the capacity retention rate was calculated using Mathematical Formula 2 below, and the results were shown in Table 2 below.

[0156] [Mathematical Formula 2]

[0157] Capacity retention rate (%) = (discharge capacity at n times of charge / discharge / discharge capacity at 1 time of charge / discharge) x 100

[0158] [Table 2]

[0159]

[0160] As shown in Table 2, in the case of the lithium secondary batteries manufactured in the examples, it was confirmed that the resistance values were lower than those of the comparative examples. In particular, the lithium secondary batteries including the positive electrodes of Comparative Examples 1 to 4 had the highest resistance values. This is considered to be due to the fact that when the positive electrodes of the comparative examples were manufactured, the high temperature in the mixture layer forming process and the roll pressing process caused the structure of the positive electrode additive to be deformed. In addition, it was found that when 100 and 200 times of charging and discharging were performed, the batteries having the positive electrodes of the examples had improved electrical properties, and had high capacity retention rates of 97% or more and 95% or more, respectively.

[0161] On the other hand, in the case of Comparative Example 5, it was confirmed that the porosity of the first mixture layer was too small, so the electrolyte was difficult to penetrate to the surface of the current collector, so that the electrical properties of the battery were reduced. In addition, it was confirmed that in each of the batteries having the positive electrodes of Comparative Examples 6 and 7, the porosity of the first mixture layer was significantly reduced, so that the electrical properties of the batteries were reduced.

[0162] From the above results, it can be known that the method of manufacturing a positive electrode for a lithium secondary battery according to the present application can have excellent charging / discharging characteristics and improve the life characteristics of a lithium secondary battery by adding a positive electrode additive to the first mixture layer in contact with the current collector. In addition, by sequentially forming the second mixture layer on the first mixture layer so that the second mixture layer is located in the outermost portion, and controlling the conditions of the first and second roll pressing processes, the degradation of the positive electrode additive contained in the first mixture layer can be minimized, so that high battery performance can be achieved.

[0163] Although the present application has been described with reference to exemplary embodiments, it is to be understood that various changes and modifications can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application, which are defined by the appended claims.

[0164] Therefore, the technical scope of the present application should not be limited to the contents described in the detailed description of the specification, but should be determined by the scope of the appended claims.

Claims

1. A positive electrode for a lithium secondary battery, comprising: a current collector; and a mixture layer formed on one surface or both surfaces of the current collector, wherein the mixture layer is a double layer structure stacked with a first mixture layer and a second mixture layer, the first mixture layer contains a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a conductive material, and a binder, wherein the first mixture layer is formed by applying and drying a first slurry, and then performing a first roll-pressing process, wherein the second mixture layer is formed by applying and drying a second slurry, and then performing a second roll-pressing process, the temperature of the first slurry and the second slurry during the application is 10°C to 40°C, the temperature of the first roll-pressing process is 10°C to 40°C, and the porosity of the first mixture layer is 15% to 40%, and the porosity of the second mixture layer is 40% to 70%; [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In 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≤0.5, respectively. 2.The positive electrode according to claim 1, wherein the average thickness of the first mixture layer is 0.1 μm to 20 μm, and the average thickness of the second mixture layer is 50 μm to 300 μm.

3. The positive electrode according to claim 1, wherein the ratio D1:D2 of the average thickness D1 of the first mixture layer to the average thickness D2 of the second mixture layer is 4:6 to 1:

10.

4. The positive electrode according to claim 1, wherein the content of the positive electrode additive is 0.1% by weight to 5% by weight, based on the total weight of the first mixture layer.

5. The positive electrode according to claim 1, wherein the positive electrode active material is a lithium metal complex oxide represented by the following Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mn w M 2 v ]O u In 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, v, and u are respectively 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0.01<w≤0.5, 0≤v≤0.2, and 1.5≤u≤4.

5. 6.A lithium secondary battery, comprising: the positive electrode according to claim 1; a negative electrode; and a separator interposed between the positive electrode and the negative electrode. 7.The lithium secondary battery according to claim 6, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material on the negative electrode current collector, and the negative electrode active material contains a carbon material and a silicon material.

8. The lithium secondary battery according to claim 7, wherein the carbon material contains at least one of natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizing carbon, carbon black, carbon nanotube, fullerene, activated carbon, and graphene.

9. The lithium secondary battery according to claim 7, wherein the silicon material contains silicon particles, silicon monoxide particles, silicon dioxide particles, or a mixture thereof.

10. The lithium secondary battery according to claim 7, wherein the content of the silicon material is 1 parts by weight to 20 parts by weight, based on 100 parts by weight of the negative electrode mixture layer.

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