Positive electrode additive and positive electrode for lithium secondary battery comprising the same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same. The positive electrode has a structure in which a positive electrode current collector, a first mixture layer, and a second mixture layer are sequentially stacked, and by using an adhesive having a higher hydrophobicity in the first mixture layer adjacent to the positive electrode current collector than an adhesive contained in the second mixture layer, the adhesion strength between the positive electrode current collector and the mixture layers can be further improved, and thus the durability of the positive electrode can be improved. In addition, when the first mixture layer contains a positive electrode additive, the first adhesive having a low affinity for water can minimize damage to the positive electrode additive at the time of manufacturing the positive electrode, and thus the electrical performance and the life of the lithium secondary battery can be further improved.

Description

Technical Field

[0001] This invention relates to a positive electrode additive for lithium secondary batteries and a positive electrode for lithium secondary batteries containing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2021-0071880, filed on June 3, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] In particular, with the development and increasing demand for mobile device technology, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density, high operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, with the increasing use of lithium-ion batteries as power sources for medium to large-sized devices such as electric vehicles, there are higher demands for high capacity, high energy density, and low cost in lithium-ion batteries, and the irreversible additives used in the electrodes need to have higher irreversible capacity. However, there are limitations in developing cathode additives with the aforementioned high irreversible capacity.

[0005] Existing irreversible additives, such as Li6CoO4, are generally prepared by reacting cobalt oxides with an excess of lithium oxides. Because irreversible additives prepared in this way are structurally unstable, they decompose and lose their irreversible activity when the cathode is manufactured under high temperature and / or high humidity conditions. Furthermore, as charging progresses, the irreversible additives generate large amounts of gases, such as oxygen (O2) and carbon dioxide (CO2). Since these gases not only reduce battery stability by causing volume expansion of the electrode assembly, but also cause side reactions such as CO2 decomposing the electrolyte, the generated gases may become a major factor leading to reduced battery performance.

[0006] Meanwhile, to ensure the adhesion strength between the positive electrode active material and the irreversible additive, as well as the adhesion strength between the positive electrode active material and the current collector, a binder is used in the positive electrode mixture layer. However, the adhesion strength of the binder can decrease depending on the type of positive electrode active material and the surface condition of the current collector. To prevent this decrease in adhesion strength, increasing the binder content presents a limitation: the electrode capacity and conductivity may decrease due to excessive binder.

[0007] Therefore, there is a need to develop a lithium secondary battery that exhibits excellent electrical performance and lifespan by minimizing damage to the positive electrode additives contained in the positive electrode and improving the adhesion strength between the positive electrode current collector provided in the positive electrode and the mixture layer.

[0008] [Relevant Existing Literature]

[0009] [Patent Literature]

[0010] Korean Patent Application Publication No. 10-2019-0078392 Summary of the Invention

[0011] Technical issues

[0012] The purpose of this invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery containing the same, wherein the positive electrode contains an irreversible additive in a positive electrode mixture layer disposed in the positive electrode, and the damage to the irreversible additive can be minimized, while the adhesion between the positive electrode mixture layer and the positive electrode current collector can be improved, thereby improving the electrical performance and lifespan of the battery.

[0013] Technical solution

[0014] In one embodiment of the present invention, a positive electrode for a lithium secondary battery is provided, having a structure in which a current collector, a first mixture layer, and a second mixture layer are stacked sequentially, wherein the first mixture layer includes a first adhesive composed of a rubber-based resin, and the second mixture layer includes a second adhesive composed of a fluorine-based resin derived from a fluorine (F) monomer.

[0015] The deviation between the static water contact angle of the first mixture layer and the static water contact angle of the second mixture layer can be greater than 5°, specifically 10° to 30°.

[0016] The rubber-based resin may include one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers.

[0017] Fluoropolymers may include resins derived from one or more monomers selected from the group consisting of vinylidene fluoride (VDF or VF2), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), trifluorochloroethylene (CTFE), hexafluoropropylene (HFP), fluorinated vinylide (VF), hexafluoroisobutylene (HFIB), perfluorobutylene (PFBE), pentafluoropropylene, 3,3,3-trifluoro-1-propene, and 2-trifluoromethyl-3,3,3-trifluoropropylene.

[0018] Based on 100 parts by weight of the first mixture layer, the content of the first adhesive may be 0.5 to 5 parts by weight; based on 100 parts by weight of the second mixture layer, the content of the second adhesive may be 0.5 to 10 parts by weight; and based on 100 parts by weight of the entire mixture layer, the total content of the first adhesive and the second adhesive may be 0.1 to 5 parts by weight.

[0019] Any one or more mixture layers among the first mixture layer and the second mixture layer may contain a cathode additive represented by the following Chemical Formula 1.

[0020] [Chemical Formula 1]

[0021] Li

[0027] , z ,

[0026] , x ,

[0025] , u ,

[0030] , 2 ,

[0029] ,

[0028] , w , y , , , , 2 , , v , Co (1-q) M 1 q O4

[0022] 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.

[0023] Based on 100 parts by weight of each cathode mixture layer, the content of the cathode additive may be 0.1 to 5 parts by weight.

[0024] The cathode additive may have a tetragonal structure with a space group of P42 / nmc.

[0025] The first mixture layer may contain a first cathode active material, a first conductive material, a cathode additive, and a first binder, and the second mixture layer may contain a second cathode active material, a second conductive material, and a second binder.

[0026] Each of the first cathode active material and the second cathode active material may include a lithium metal composite oxide represented by the following Chemical Formula 2.

[0027] [Chemical Formula 2]

[0028] Li x [Ni y Co z Mn w M<000001? v O u

[0029] 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.

[0030] The first conductive material and the second conductive material may each include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber.

[0031] Based on 100 parts by weight of each positive electrode mixture layer, the content of the first conductive material and the second conductive material can be from 0.5 to 5 parts by weight.

[0032] In one embodiment of the present invention, a method for manufacturing a positive electrode for a lithium secondary battery is provided, comprising forming a first mixture layer containing a first adhesive composed of a rubber-based resin on a positive electrode current collector, and forming a second mixture layer containing a second adhesive composed of a fluorine-based resin derived from a fluorine (F) monomer on the first mixture layer.

[0033] Either or more of the first and second mixture layers may contain a positive electrode additive represented by the following chemical formula 1.

[0034] [Chemical Formula 1]

[0035] Li p Co (1-q) M 1 q O4

[0036] In chemical formula 1, M 1 It means that at least one element is 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, where p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0037] The formation of the first mixture layer may include preparing a mixture composition by dry mixing a first positive electrode active material, a positive electrode additive represented by chemical formula 1, a first conductive material and a first binder composed of a rubber-based resin, and coating the prepared mixture composition onto a positive electrode current collector.

[0038] Beneficial effects

[0039] The positive electrode for a lithium secondary battery of the present invention has a structure in which a current collector, a first mixture layer, and a second mixture layer are stacked sequentially. By using an adhesive that is more hydrophobic than the adhesive contained in the second mixture layer in the first mixture layer adjacent to the positive electrode current collector, the adhesion strength between the positive electrode current collector and the mixture layer can be further improved, thereby improving the durability of the positive electrode. In addition, when the first mixture layer contains a positive electrode additive, the loss of the positive electrode additive can be minimized during the manufacture of the positive electrode due to the low affinity of the first adhesive for water, thus having the advantage of further improving the electrical performance and lifespan of the lithium secondary battery. Detailed Implementation

[0040] This invention can be modified in various forms and can have various implementation methods; therefore, specific implementation methods will be described in detail.

[0041] However, the embodiments should not be construed as limiting the invention to a particular embodiment, and should be interpreted as including all modifications, equivalents or substitutions that fall within the spirit and technical scope of the invention.

[0042] In this invention, the terms "comprising" and "having," etc., are used to specify the presence of the 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.

[0043] Furthermore, in this invention, when a portion of a layer, film, region, or plate is described as being "on" another portion, this includes not only the case where the portion is "directly" "on" the other portion, but also the case where another portion exists between the two portions. Conversely, when a portion of a layer, film, region, or plate is described as being "below" another portion, this includes not only the case where the portion is "directly" "below" the other portion, but also the case where another portion exists between the two portions. Additionally, in this application, "deposited on" can include not only being disposed on the upper part but also on the lower part.

[0044] In addition, in this invention, "main component" may refer to a total weight of 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 97.5% or more based on the total weight of the composition or specific component. In some cases, when constituting the entire composition or specific component, it may refer to 100% by weight.

[0045] Furthermore, in this invention, "Ah" is a unit of capacity for lithium secondary batteries, referred to as "ampere-hour," and refers to the current flow rate per hour. For example, a battery capacity of "3000mAh" means that the battery can discharge at a current of 3000mA for 1 hour.

[0046] In addition, in this invention, "contact angle" is the angle between the liquid surface and the solid surface when the liquid comes into contact with the solid surface.

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

[0048] Positive electrode for lithium secondary batteries

[0049] In one embodiment of the present invention, a positive electrode for a lithium secondary battery is provided, having a structure in which a current collector, a first mixture layer, and a second mixture layer are stacked sequentially, the first mixture layer comprising a first adhesive composed of a rubber-based resin, the second mixture layer comprising a second adhesive composed of a fluorine-based resin derived from a fluorine (F) monomer, and either or more of the first and second mixture layers containing a positive electrode additive represented by the following chemical formula 1.

[0050] [Chemical Formula 1]

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

[0052] In chemical formula 1, M 1 It means that at least one element is 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, where p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0053] The positive electrode for a lithium secondary battery of the present invention has a structure in which a mixture layer with a double-layer structure is disposed on the positive electrode current collector. In this case, the mixture layer forming the double-layer structure, specifically the first mixture layer and the second mixture layer, may include different types of adhesives with different affinities for water.

[0054] For example, the first mixture layer contains an adhesive composed of a rubber-based resin with low affinity for water as a first adhesive. The first adhesive may include one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers.

[0055] Additionally, the second mixture layer contains an adhesive as a second adhesive, composed of a fluorinated resin derived from fluorinated monomers with high affinity for water. The second adhesive may include a resin derived from one or more monomers selected from the group consisting of vinylidene fluoride (VDF or VF2), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), trifluorochloroethylene (CTFE), hexafluoropropylene (HFP), ethylene fluoride (VF), hexafluoroisobutylene (HFIB), perfluorobutylene (PFBE), pentafluoropropylene, 3,3,3-trifluoro-1-propene, and 2-trifluoromethyl-3,3,3-trifluoropropylene.

[0056] The second binder may have a crystalline phase and / or an amorphous phase in the positive electrode mixture layer. Specifically, it may simultaneously have a crystalline phase and an amorphous phase, and the amorphous phase may account for more than 51% or 55% of the total crystalline phase. As an example, the second binder may include an amorphous phase accounting for 51 to 95%, 51 to 90%, 51 to 85%, 51 to 80%, 51 to 75%, 51 to 70%, 51 to 65%, or 51 to 55% of the total crystalline phase. Depending on the crystalline phase in the mixture layer, the second binder may have different affinities for water. When the crystalline form is an amorphous phase, the affinity for water may be higher. In this invention, the content of the amorphous phase in the total crystalline phase of the second binder exceeds 50%, thus improving the wettability of the second mixture layer to the electrolyte.

[0057] In this invention, a rubber-based resin is contained as a first binder in a first mixture layer adjacent to the positive electrode current collector, and a fluorinated resin derived from a fluorinated monomer is contained as a second binder in a second mixture layer. In this case, the rubber-based resin as the first binder may have a lower affinity for water compared to the fluorinated resin as the second binder.

[0058] As an example, when measuring the static water contact angles of a first mixture layer containing a first adhesive and a second mixture layer containing a second adhesive, the deviation between the static water contact angles of the first mixture layer and the second mixture layer can be 5° or more, specifically 10° or more, 15° or more, or 20° or more, depending on the difference in water affinity between the first and second adhesives. Specifically, it can be 5° to 30°, 10° to 30°, 15° to 30°, 20° to 30°, 5° to 20°, 5° to 15°, 8° to 15°, 10° to 16°, 14° to 19°, or 5° to 10°. In this invention, by controlling the deviation of the static water contact angle between the first mixture layer and the second mixture layer within the above ranges, the adhesion strength between the positive electrode current collector and the first mixture layer, as well as the adhesion strength between the first mixture layer and the second mixture layer, can be improved. Simultaneously, the wettability of the second mixture layer to the electrolyte can be improved.

[0059] As an example, the first mixture layer has a relatively low affinity for water compared to the second mixture layer, and therefore can exhibit excellent adhesion strength to the metal current collector. Specifically, the positive electrode manufactured according to the present invention exhibits at least 1.5 times stronger adhesion strength between the current collector and the mixture layer compared to cases where an adhesive composed of a fluorinated resin such as PVdF (i.e., the second adhesive) is used in both the first and second mixture layers. More specifically, it can be at least 1.8 times stronger, at least 2 times stronger, at least 2.2 times stronger, or at least 2.5 times stronger.

[0060] Here, based on 100 parts by weight of the first mixture layer, the content of the first adhesive can be 0.5 to 5 parts by weight; based on 100 parts by weight of the second mixture layer, the content of the second adhesive can be 0.5 to 10 parts by weight; and based on 100 parts by weight of the entire mixture layer, the total content of the first adhesive and the second adhesive can be 0.1 to 5 parts by weight.

[0061] Specifically, based on 100 parts by weight of the first mixture layer, the content of the first adhesive can be 0.5 to 4 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2 parts by weight, 1 to 3 parts by weight, 2 to 5 parts by weight, or 1.5 to 2.5 parts by weight; and based on 100 parts by weight of the second mixture layer, the content of the second adhesive can be 0.5 to 8 parts by weight, 0.5 to 6 parts by weight, 0.5 to 5 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2 parts by weight, 1 to 3 parts by weight, or 2 to 4 parts by weight.

[0062] In addition, based on 100 parts by weight of the entire mixture layer, the total content of the first adhesive and the second adhesive may be 0.5 to 4 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2 parts by weight, 1 to 3 parts by weight, 2 to 5 parts by weight, or 1.5 to 2.5 parts by weight.

[0063] In this invention, as described above, by controlling the content of the first adhesive and the second adhesive respectively contained in the first mixture layer and the second mixture layer, the adhesion strength between the positive current collector and the first mixture layer and the adhesion strength between the first mixture layer and the second mixture layer can be easily improved.

[0064] Meanwhile, in the positive electrode of the present invention, any one or more of the first mixture layer and the second mixture layer may contain a positive electrode additive represented by the following chemical formula 1.

[0065] [Chemical Formula 1]

[0066] Li p Co (1-q) M 1 q O4

[0067] In chemical formula 1, M 1 It means that at least one element is 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, where p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0068] The positive electrode additive can contain excess lithium and can provide lithium for the lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during the initial charging, thus increasing the battery's charging capacity and reducing irreversible capacity, thereby improving lifespan characteristics.

[0069] Compared to nickel-containing oxides commonly used in the art, the cathode additive represented by Formula 1 has a higher lithium-ion content, thus replenishing the lithium-ions lost during the initial activation of the battery due to irreversible reactions, thereby significantly improving the battery's charge / discharge capacity. Furthermore, compared to iron- and / or manganese-containing oxides commonly used in the art, it does not exhibit side reactions due to the dissolution of transition metals during battery charging and discharging, thus offering the advantage of excellent battery stability. The lithium cobalt oxide represented by Formula 1 may include Li6CoO4, Li6Co... 0.5 Zn 0.5 O4 and Li6Co 0.7 Zn 0.3 O4, etc.

[0070] Furthermore, the average particle size of the lithium cobalt oxide represented by Chemical Formula 1 can be from 0.1 to 10 μm, specifically 0.1 to 8 μm, 0.1 to 5 μm, 0.1 to 3 μm, 0.5 to 2 μm, 0.1 to 0.9 μm, 0.1 to 0.5 μm, 0.6 to 0.9 μm, 1 to 4 μm, 4 to 6 μm, or 6 to 9 μm. In this invention, by controlling the average particle size of the lithium cobalt oxide within the above range, the irreversible activity of the lithium cobalt oxide can be improved, and the decrease in the powder conductivity of the lithium cobalt oxide can be prevented.

[0071] Furthermore, the lithium cobalt oxide represented by Chemical Formula 1 can have a tetragonal crystal structure, in which the lithium cobalt oxide can be contained in the space group P42 / nmc, which has a twisted tetrahedral structure formed by cobalt and oxygen elements. Since the cathode additive with the twisted tetrahedral structure is structurally unstable, it may be damaged during cathode manufacturing due to side reactions with moisture (H2O) in the air, potentially leading to a decrease in battery performance. However, in this invention, since a binder with low affinity for water is used as the binder for the mixture layer, damage to the cathode additive can be minimized, thereby further improving the electrical performance and lifespan of the lithium secondary battery.

[0072] In addition, based on 100 parts by weight of each cathode mixture layer, the content of cathode additive can be 0.1 to 5 parts by weight, specifically 0.1 to 4 parts by weight, 0.1 to 3 parts by weight, 0.1 to 2 parts by weight, 0.1 to 1 part by weight, 0.5 to 2 parts by weight, 1 to 3 parts by weight, 2 to 4 parts by weight, 1.5 to 3.5 parts by weight, 0.5 to 1.5 parts by weight, or 1 to 2 parts by weight.

[0073] As an example, the content of the positive electrode additive may be 0.1 to 0.5 parts by weight based on 100 parts by weight of the first mixture layer, and 0.2 to 0.6 parts by weight based on 100 parts by weight of the second mixture layer.

[0074] As another example, the positive electrode additive may be contained only in the first mixture layer, and in this case, based on 100 parts by weight of the entire mixture layer, the amount contained in the first mixture layer may be 0.5 to 2 parts by weight.

[0075] In addition, the first mixture layer may include a first positive electrode active material, a first conductive material and a first binder, the second mixture layer may include a second positive electrode active material, a second conductive material and a second binder, and the positive electrode additive may be included in either the first mixture layer and the second mixture layer.

[0076] As an example, the first mixture layer may comprise a first positive electrode active material, a first conductive material, a positive electrode additive, and a first binder, and the second mixture layer may comprise a second positive electrode active material, a second conductive material, and a second binder. In this invention, the positive electrode additive is included in the first mixture layer, thus minimizing damage to the positive electrode additive caused by high temperature and / or high humidity during the manufacture of the positive electrode, thereby having the advantage of further improving the electrical performance and lifespan of the lithium secondary battery.

[0077] In this case, the first positive electrode active material and the second positive electrode active material may each be a lithium composite transition metal oxide, which includes two or more elements selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), zinc (Zn), titanium (Ti), magnesium (Mg), chromium (Cr), and zirconium (Zr). For example, 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 that can be reversibly inserted and extracted.

[0078] [Chemical Formula 2]

[0079] Li x [Ni y Co z Mn w M 2 v O u

[0080] 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.

[0081] The lithium metal composite oxide represented by Chemical Formula 2 is a composite metal oxide including Li, nickel, cobalt, and manganese, and in some cases, may have a form doped with other transition metals (M 2 ). For example, the first positive electrode active material and the second positive electrode active material may each include one selected from the group consisting of LiNi 1 / 3 Co<​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​One or more compounds from the group consisting of O2. As an example, the first and second positive electrode active materials can each be lithium metal composite oxides represented by chemical formula 2, and LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 O2, alone or in combination, can be used as a positive electrode active material.

[0082] In addition, the first conductive material and the second conductive material can be used to improve the performance of the positive electrode, such as conductivity, and the first conductive material and the second conductive material can each include one or more of the following selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene and carbon fiber.

[0083] Here, based on each 100 parts by weight of the mixture layer, the content of the first conductive material and the second conductive material can be 0.5 to 5 parts by weight, specifically 0.5 to 4 parts by weight, 0.5 to 3 parts by weight, 0.5 to 1 part by weight, 0.5 to 2 parts by weight, 1 to 3 parts by weight, 2 to 4 parts by weight, 1.5 to 3.5 parts by weight, 0.5 to 1.5 parts by weight, or 1 to 2 parts by weight.

[0084] Furthermore, there is no particular limitation on the average thickness of the first mixture layer and the second mixture layer, specifically, it can be 50 μm to 200 μm, 50 μm to 150 μm, 50 μm to 100 μm, 50 μm to 80 μm, 70 μm to 120 μm, or 60 μm to 110 μm. Additionally, the total thickness of the first mixture layer and the second mixture layer can be 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.

[0085] Furthermore, the positive current collector in the positive electrode can be a material with high conductivity that will not cause chemical changes in the battery. For example, stainless steel, aluminum, Ni, titanium, or calcined carbon can be used, and when using aluminum or stainless steel, aluminum or stainless steel with a surface treated with carbon, Ni, titanium, or silver can be used. Additionally, fine irregularities can be formed on the surface of the positive current collector to enhance the bonding force of the positive electrode active material, and any form of positive current collector can be used, such as a film, sheet, foil, mesh, porous body, foam, or nonwoven fabric. Furthermore, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the positive current collector can be appropriately applied in the range of 3 μm to 500 μm.

[0086] Manufacturing method of positive electrode for lithium secondary batteries

[0087] In addition, according to one embodiment of the present invention, a method for manufacturing a positive electrode for a lithium secondary battery is provided, comprising forming a first mixture layer containing a first adhesive composed of a rubber-based resin on a positive electrode current collector, and forming a second mixture layer containing a second adhesive composed of a fluorine-based resin derived from a fluorine-containing monomer on the first mixture layer, wherein either or more of the first mixture layer and the second mixture layer contains a positive electrode additive represented by the following chemical formula 1.

[0088] [Chemical Formula 1]

[0089] Li p Co (1-q) M 1 q O4

[0090] In chemical formula 1, M 1 It means that at least one element is 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, where p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0091] The method for manufacturing the positive electrode for a lithium secondary battery of the present invention can be performed by forming a mixture layer having a double-layer structure on a positive electrode current collector. Specifically, the manufacturing method is performed by sequentially forming a first mixture layer and a second mixture layer on the positive electrode current collector. The first mixture layer and the second mixture layer may each include a first binder and a second binder with different affinities for water, and a positive electrode additive may be included in either or more of the first mixture layer and the second mixture layer.

[0092] Here, the first mixture layer can be formed by the following process: dry mixing the first positive electrode active material constituting the mixture layer, the positive electrode additive represented by chemical formula 1, the first conductive material and the first binder composed of rubber-based resin at room temperature (e.g., 22±3°C) at a speed of 1000 rpm to 4000 rpm to prepare a mixture composition, and coating the prepared mixture composition onto the positive electrode current collector.

[0093] In this invention, since the first mixture layer is formed by a dry process as described above, the drying step of the solvent used in the wet process can be omitted, thereby improving productivity and preventing the phenomenon of binder and conductive material moving to the surface of the mixture layer during the solvent drying process. Furthermore, the dry mixing method performed at a high speed of 1000 to 4000 rpm achieves the effect of uniformly coating the surface of each particle with the first binder, thereby not only improving the adhesion strength between particles and / or between the current collector and the mixture layer, but also effectively preventing the positive electrode additive from being damaged by moisture during the manufacture of the positive electrode when it is included in the first mixture layer.

[0094] Furthermore, the manufacturing method of the positive electrode for lithium secondary batteries includes a step of forming a second mixture layer on the formed first mixture layer. In this case, there are no particular limitations on the method of forming the second mixture layer, and any method in the art can be applied. Specifically, the second mixture layer can be formed by a wet process of forming a positive electrode slurry in which a second positive electrode active material, a second conductive material, and a second binder are mixed in a solvent. In some cases, the second mixture layer can be formed using a dry process, just like the first mixture layer.

[0095] In this case, when forming the second mixture layer using a wet process, the available solvents may include one or more polar aprotic solvents selected from: N-methyl-2-pyrrolidone (NMP), dimethylacetamide (N,N-dimethylacetamide (DMAc)), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (ACN), dimethylformamide (DMF), acetone, and ethyl acetate. In this invention, using the aforementioned solvents in a wet process when forming the second mixture layer allows for uniform mixing of the second positive electrode active material, the second conductive material, and the second binder when the positive electrode additive is included in the second mixture layer, while minimizing damage to the positive electrode additive.

[0096] In addition, when the process of forming the second mixture layer is carried out using a wet method, the drying of the positive electrode slurry coated on the positive electrode current collector can be carried out under vacuum at a temperature below 140°C, specifically at temperatures below 130°C, below 120°C, below 110°C, below 100°C, below 80°C, below 70°C, below 60°C, below 50°C, below 40°C, 20°C to 140°C, 20°C to 120°C, 20°C to 100°C, 20°C to 90°C, 20°C to 70°C, 20°C to 50°C, 40°C to 90°C, 60°C to 140°C, 90°C to 140°C, or 100°C to 130°C.

[0097] In this invention, the drying of the positive electrode slurry is carried out under the above conditions, making it easy to control the proportion of the amorphous phase in the crystalline phase of the fluoropolymer resin, which serves as the second binder, to be 51% or more.

[0098] The method for manufacturing a positive electrode for a lithium secondary battery according to the present invention includes the above-described operations, thereby having the following advantages: minimizing damage to the positive electrode additive to be manufactured, improving wettability to the electrolyte to improve the electrical performance of the battery, and improving the adhesion strength of the positive electrode for a lithium secondary battery to improve the battery life.

[0099] Lithium secondary batteries

[0100] In one embodiment of the present invention, a lithium secondary battery is provided, which includes the positive electrode, the negative electrode and the separator inserted between the positive electrode and the negative electrode as described above.

[0101] Since the lithium secondary battery of the present invention has the positive electrode of the present invention described above, the adhesion strength between the positive electrode current collector and the mixture layer can be further improved, thus improving the durability of the positive electrode and minimizing the damage to the positive electrode additives during the manufacturing of the positive electrode, thus having the advantage of further improving the electrical performance and lifespan of the lithium secondary battery.

[0102] The lithium secondary battery of the present invention has a structure including a positive electrode, a negative electrode and a separator inserted between the positive electrode and the negative electrode.

[0103] Here, the negative electrode is manufactured by coating, drying and pressing the negative electrode active material onto the negative electrode current collector, and may optionally include the same conductive materials, organic binder polymers and additives as in the positive electrode.

[0104] Additionally, the negative electrode active material may include, for example, carbon materials and silicon materials. Carbon materials refer to carbon materials containing carbon atoms as their main component. Carbon materials may include one or more selected from the group consisting of: graphite with a fully layered crystal structure, such as natural graphite; soft carbon with a low-crystallinity layered crystal structure (graphene structure is a structure in which hexagonal honeycomb planes of carbon are arranged in layers); hard carbon with these structures mixed with amorphous portions; artificial graphite; expanded graphite; carbon fibers; non-graphitized carbon; carbon black; acetylene black; Ketjen black; carbon nanotubes; fullerenes; activated carbon; graphene; and carbon nanotubes. More preferably, the carbon material may include natural graphite and / or artificial graphite, and may include any one or more of graphene and carbon nanotubes together with natural graphite and / or artificial graphite. In this case, based on a total of 100 parts by weight of carbon material, the carbon material may include 50 to 95 parts by weight of graphene and / or carbon nanotubes. More specifically, based on a total of 100 parts by weight of carbon material, the carbon material may include 60 to 90 parts by weight or 70 to 80 parts by weight of graphene and / or carbon nanotubes.

[0105] In addition, silicon materials, as a metallic component, are particles containing silicon (Si) as the main component, and may include both Si particles and silicon oxide (SiO). X And 1 ≤ X ≤ 2) is one or more of the following particles. As an example, silicon materials may include Si particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or mixtures thereof.

[0106] Furthermore, the silicon material can be in a mixed form of crystalline and amorphous particles, and based on 100 parts by weight of total silicon material, the proportion of amorphous particles is 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight. In this invention, since the proportion of amorphous particles contained in the silicon material is controlled within the above range, thermal stability and flexibility can be improved without reducing the electrical performance of the electrode.

[0107] In addition, the negative electrode active material includes carbon materials and silicon materials, and may be contained in 1 to 20 parts by weight of the negative electrode mixture layer based on 100 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 of the negative electrode mixture layer based on 100 parts by weight.

[0108] In this invention, the content of carbon and silicon materials in the negative electrode active material is adjusted to the above-mentioned range, thereby increasing the charging capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charging and discharging of the battery.

[0109] As an example, based on 100 parts by weight of the negative electrode mixture layer, the negative electrode active material may contain 95±2 parts by weight of graphite and 5±2 parts by weight of a mixture in which SiO particles and SiO2 particles are uniformly mixed. In this invention, by adjusting the content of carbon and silicon materials in the negative electrode active material to the above range, the charging capacity per unit mass can be increased, while reducing lithium consumption and irreversible capacity loss during the initial charging and discharging of the battery.

[0110] In addition, the average thickness of the negative electrode mixture layer can be from 100 μm to 200 μm, specifically 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.

[0111] Furthermore, there are no particular limitations on the negative electrode current collector, as long as the material has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, Ni, titanium, or calcined carbon can be used for the negative electrode current collector. When using copper or stainless steel, copper or stainless steel with a surface treated with carbon, nickel, titanium, or silver can be used. Additionally, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the negative electrode current collector to enhance the bonding force with the negative electrode active material. Various forms of negative electrode current collectors can be used, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Moreover, 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 μm to 500 μm.

[0112] Alternatively, an insulating film with high ion permeability and high mechanical strength can be used as the separator, inserted between the positive and negative electrodes. There are no particular limitations on the separator, as long as it is commonly used in the art; specifically, chemically resistant and hydrophobic polypropylene, glass fiber, or sheets or nonwoven fabrics made of polyethylene can be used as separators. In some cases, composite separators in which a porous polymer substrate, such as a sheet or nonwoven fabric, is coated with inorganic / organic particles by an organic adhesive polymer can be used as separators. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also be used as the separator. Furthermore, the separator can have an average pore size of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0113] Meanwhile, the positive and negative electrodes can be wound and housed in cylindrical, prismatic, or pouch-shaped batteries in the form of gel rolls, or housed in pouch-shaped batteries in a folded or stacked-folded form, but the present invention is not limited thereto.

[0114] In addition, the lithium salt-containing electrolyte of the present invention can be composed of an electrolyte and a lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte or an inorganic solid electrolyte can be used.

[0115] For example, as non-aqueous organic solvents, 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, or ethyl propionate can be used.

[0116] For example, as organic solid electrolytes, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylyzed lysine, polyester sulfides, polyvinyl alcohol (PVA), polyvinylidene fluoride, or polymers containing ion-dissociating groups can be used.

[0117] As an inorganic solid electrolyte, lithium nitrides, halides, or sulfates can be used, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, or Li3PO4-Li2S-SiS2.

[0118] Lithium salts are materials that are readily soluble in non-aqueous electrolytes. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB can be used as lithium salts. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate or imide.

[0119] In addition, to improve charge / discharge characteristics and flame retardancy, the electrolyte may contain, for example, 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 imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. In some cases, to impart non-flammability, halogenated solvents such as carbon tetrachloride and trifluoroethylene may be further included, and to improve high-temperature storage characteristics, carbon dioxide gas may be further included, and fluoroethylene carbonate (FEC) and propylene sulpholone (PRS) may be further included.

[0120] Example

[0121] The invention will be described in more detail below with reference to embodiments and experimental examples.

[0122] However, the following embodiments and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following embodiments and experimental examples.

[0123] Manufacturing of positive electrodes for lithium secondary batteries (Examples 1 to 3 and Comparative Examples 1 to 2)

[0124] Weigh 47.7 parts by weight of LiNi as the first positive electrode active material. 0.6 Co 0.2 Mn0.2 O2 (average particle size: 1±0.5μm), 0.8 parts by weight of Li6CoO4 as a positive electrode additive, 0.5 parts by weight of carbon black (average particle size: 2±0.5μm) as a first conductive material, and 1 part by weight of styrene-butadiene rubber (SBR) as a first binder are added to a homogeneous mixer and mixed at room temperature at a speed of 3,000±500 rpm for 50 to 70 minutes to prepare a mixture composition.

[0125] Specifically, N-methylpyrrolidone was injected into a homogeneous mixer, and based on the solid content of 100 parts by weight of the positive electrode slurry, 48.5 parts by weight of LiNi, as the second positive electrode active material, were weighed. 0.6 Co 0.2 Mn 0.2 O2 (average particle size: 1±0.5μm), 0.5 parts by weight of carbon black (average particle size: 2±0.5μm) as a second conductive material, and 1 part by weight of PVdF as a second binder were added and mixed at room temperature at a speed of 2,000±500 rpm for 50 to 70 minutes to prepare a positive electrode slurry.

[0126] Subsequently, the pre-prepared mixture composition is coated onto one surface of an aluminum current collector and passed between hot press rollers to form a first mixture layer. Then, a positive electrode slurry is continuously coated onto the first mixture layer, vacuum dried under the temperature conditions shown in Table 1, and rolled to manufacture a positive electrode for lithium secondary batteries. In this case, the thicknesses of the first and second mixture layers are 55 μm and 80 μm, respectively, and the total thickness of the prepared positive electrode is approximately 200 μm.

[0127] [Table 1]

[0128]

[0129] Comparative Example 3. Manufacturing of the positive electrode for lithium secondary batteries

[0130] The positive electrode for lithium secondary batteries was manufactured in the same manner as in Example 1, except that PVdF was used as the first binder and a first mixture layer was formed by preparing a positive electrode slurry containing a first positive electrode active material, a positive electrode additive, a first conductive material and a first binder in N-methylpyrrolidone.

[0131] Experimental Example

[0132] To evaluate the performance of the cathode additive of the present invention, the following experiments were conducted.

[0133] A) Evaluate the static water contact angle of the cathode mixture layer.

[0134] The positive electrode was manufactured in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3, and the static water contact angle relative to the surface of each mixture layer was measured when the first mixture layer and the second mixture layer were each formed. Here, the static water contact angle was measured by the net drop method. Specifically, the measurement was performed by dropping a drop of pure water onto the surface of each mixture layer, capturing an image of the dropped pure water drop, and then analyzing the captured image.

[0135] B) Evaluate the interfacial adhesion strength of the cathode mixture layer

[0136] The positive electrodes manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were cut into horizontal and vertical lengths of 25 mm and 70 mm, respectively, and laminated using a press at a temperature of 70°C and a pressure of 4 MPa to prepare test samples. The prepared test samples were attached and fixed to a glass plate using double-sided adhesive tape. In this case, the positive electrode current collector was positioned facing the glass plate. The separator portion of the test sample was peeled using a tensile testing machine at a 90° angle, a temperature of 25°C, and a speed of 100 mm / min. The peel force was measured in real time, and the average value of the measured peel force was defined as the interfacial adhesion strength between the first and second mixture layers. Then, the interfacial adhesion strength between the positive electrode current collector and the first mixture layer was also measured by continuously performing the same method. The results are shown in Table 2 below.

[0137] C) Evaluate battery charge / discharge capacity

[0138] First, based on the solid content of 100 parts by weight of the negative electrode slurry, 84 parts by weight of natural graphite and 14 parts by weight of silicon (SiO2) were prepared as the negative electrode active material. x The negative electrode slurry is prepared by combining 1 ≤ x ≤ 2 particles (here, 1 ≤ x ≤ 2) and 2 parts by weight of SBR as a binder, and in the same manner as the positive electrode slurry. In this case, the graphite used to form the negative electrode mixture layer is natural graphite (average particle size: 0.01 μm to 0.5 μm), and SiO₂ with an average particle size of 0.9 μm to 1.1 μm is used. x Particles. The prepared negative electrode slurry is coated onto one surface of a copper current collector, dried at 100°C, and rolled to manufacture the negative electrode. In this case, the total thickness of the negative electrode mixture layer is 150 μm, and the total thickness of the manufactured negative electrode is approximately 250 μm.

[0139] A separator made of porous polyethylene (PE) membrane (thickness: about 16 μm) was inserted between the positive and negative electrodes manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, and E2DVC was injected as an electrolyte to manufacture a lithium secondary battery in the form of a full cell.

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

[0141] The manufactured lithium secondary battery was charged at 25°C with a charging current of 0.1C to a charging termination voltage of 4.2V to 4.25V, and activated by charging at the charging termination voltage until the current density reaches 0.01C. Then, the lithium secondary battery was discharged at a discharging current of 0.1C to a termination voltage of 2V, and the initial charge / discharge capacity per unit mass was measured. The results are shown in Table 2 below.

[0142] [Table 2]

[0143]

[0144] Referring to Table 2, it can be seen that the positive electrode current collector and the positive electrode mixture layer of the positive electrode of the lithium secondary battery of the present invention have excellent adhesion strength, and the battery has high charging capacity.

[0145] Specifically, since the positive electrode for the lithium secondary battery according to the embodiments of the present invention contains rubber-based resin and fluorine-based resin as binders in the first and second mixture layers, respectively, the affinity of each mixture layer for water is controlled. Therefore, it is shown that the difference in static water contact angle deviation (AB) between the first mixture layer (A) and the second mixture layer (B), which have low affinity for water, is 5° or more. It can be seen that this difference improves the interfacial adhesion strength between the positive electrode current collector and the first mixture layer, as well as the interfacial adhesion strength between the first and second mixture layers. Furthermore, when a positive electrode additive is used in the first mixture layer with low affinity for water, it is seen that damage to the positive electrode additive is prevented, resulting in a higher initial charging capacity.

[0146] Based on the above results, the positive electrode for lithium secondary batteries of the present invention has a structure in which a positive electrode current collector, a first mixture layer, and a second mixture layer are stacked sequentially. Furthermore, by using an adhesive that is more hydrophobic than the adhesive contained in the second mixture layer in the first mixture layer adjacent to the positive electrode current collector, the adhesion strength between the positive electrode current collector and the mixture layer can be further improved. Therefore, it can be seen that the durability of the positive electrode can be improved. Moreover, when the first mixture layer contains positive electrode additives, the damage to the positive electrode additives can be minimized during the manufacture of the positive electrode due to the first adhesive having low affinity for water, thereby further improving the electrical performance and lifespan of the lithium secondary battery.

[0147] Although the invention has been described above with reference to exemplary embodiments thereof, it should be understood that various changes and modifications to the invention can be devised by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

[0148] Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of this specification, but should be determined by the scope of the appended claims.

Claims

1. A positive electrode for a lithium secondary battery, having a structure in which a current collector, a first mixture layer, and a second mixture layer are sequentially stacked, wherein: the first mixture layer includes a first binder composed of a rubber-based resin; and the second mixture layer includes a second binder composed of a fluorine-based resin derived from a fluorine-containing (F) monomer, wherein a static water contact angle of the first mixture layer is greater than a static water contact angle of the second mixture layer by 5° or more, and a positive electrode additive represented by the following Chemical Formula 1 is included only in the first mixture layer: [Chemical Formula 1] the static water contact angle of the first mixture layer is greater than the static water contact angle of the second mixture layer by 10° to 30°. the rubber-based resin includes one or more selected from the group consisting of styrene-butadiene rubber, nitrile butadiene rubber, methyl methacrylate-butadiene rubber, chlorobutadiene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymer. the fluorine-based resin includes a resin derived from one or more monomers selected from the group consisting of vinylidene fluoride (VDF or VF2), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), fluorinated ethylene (VF), hexafluoroisobutylene (HFIB), perfluorobutyl ethylene (PFBE), pentafluoropropylene, 3,3,3-trifluoro-1-propene, and 2-trifluoromethyl-3,3,3-trifluoropropene.

5. The positive electrode according to claim 1, wherein: a content of the first binder is 0.5 to 5 parts by weight based on 100 parts by weight of the first mixture layer; and a content of the second binder is 0.5 to 10 parts by weight based on 100 parts by weight of the second mixture layer, 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.

2. The positive electrode according to claim 1, wherein wherein a total content of the first and second binders is 0.1 to 5 parts by weight based on 100 parts by weight of a total weight of the first and second mixture layers.

3. The positive electrode according to claim 1, wherein an amount of the positive electrode additive is 0.1 to 5 parts by weight based on 100 parts by weight of the first mixture layer.

4. The positive electrode according to claim 1, wherein the positive electrode additive has a tetragonal structure with a space group of P42 / nmc.

8. The positive electrode according to claim 1, wherein: the first mixture layer contains a first positive electrode active material, a first conductive material, a positive electrode additive, and the first binder; and the second mixture layer contains a second positive electrode active material, a second conductive material, and the second binder. the first and second positive electrode active materials each include a lithium metal complex oxide represented by the following Chemical Formula 2: [Chemical Formula 2] the first and second conductive materials each include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, carbon nanotube, graphene, and carbon fiber.

6. The positive electrode according to claim 1, wherein the carbon black is selected from acetylene black or ketjen black.

7. The positive electrode according to claim 1, wherein a content of the first conductive material is 0.5 to 5 parts by weight based on 100 parts by weight of the first mixture layer, and wherein a content of the second conductive material is 0.5 to 5 parts by weight based on 100 parts by weight of the second mixture layer.

13. A method of manufacturing a positive electrode for a lithium secondary battery, the method comprising: forming a first mixture layer containing a first binder composed of a rubber-based resin on a positive electrode current collector; ​ 9. The positive electrode according to claim 8, wherein ​ ​ 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, 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.

10. The positive electrode according to claim 8, wherein ​ 11. The positive electrode according to claim 10, wherein ​ 12. The positive electrode according to claim 8, wherein ​ ​ ​ ​ Also forming a second mixture layer containing a second binder composed of a fluorine group resin derived from a fluorine (F) containing monomer on the first mixture layer, wherein the static water contact angle of the first mixture layer is greater than the static water contact angle of the second mixture layer by 5° or more, and a cathode additive represented by the following Chemical Formula 1 is included only in the first mixture layer: [Chemical Formula 1] 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.

14. The method of claim 13, wherein, The forming of the first mixture layer includes: dry-mixing a first cathode active material, the cathode additive represented by Chemical Formula 1, a first conductive material, and a first binder composed of a rubber-based resin, thereby forming a mixture composition; and applying the mixture composition on the current collector.

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