Positive electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode, wherein the positive electrode is manufactured by using a pre-dispersion containing a positive electrode additive represented by Chemical Formula 1 and a conductive material having a linear structure as an irreversible additive in a positive electrode mixture layer, and by adjusting the electrode sheet resistance to meet a specific range, the amount of oxygen generated during charging and discharging can be reduced, and the charging and discharging efficiency of the lithium secondary battery can be easily improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same. This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0072238 filed on June 3, 2021, and Korean Patent Application No. 10-2022-0041454 filed on April 4, 2022, and incorporates the entire contents of the Korean patent application documents as a part of this specification. Background Art

[0002] In recent years, the demand for secondary batteries as energy sources has been rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life and low self-discharge rate have been commercialized and widely used.

[0003] Although graphite is mainly used as a negative electrode material for lithium secondary batteries, it is difficult to increase the capacity of lithium secondary batteries because graphite has a small unit mass capacity of 372 mAh / g. Therefore, in order to increase the capacity of lithium secondary batteries, as non-carbon negative electrode materials with higher energy density than graphite, negative electrode materials that form intermetallic compounds with lithium, such as silicon, tin and their oxides, have been developed and used. However, in the case of such non-carbon negative electrode materials, although the capacity is large, the initial efficiency is low, there is a problem of large lithium consumption during the initial charge / discharge period, and large irreversible capacity loss.

[0004] In this regard, a method for overcoming irreversible capacity loss in the negative electrode has been proposed, which uses a material that can provide a lithium ion source or reservoir for the positive electrode material and is electrochemically active after the initial cycle, thereby not reducing the overall performance of the battery. Specifically, as a sacrificial positive electrode material or irreversible additive (or overdischarge inhibitor), for example, a method of applying an oxide containing excess lithium, such as Li6CoO4, to the positive electrode is known.

[0005] On the other hand, conventional irreversible additives such as Li6CoO4 are generally prepared by reacting cobalt oxide, etc. with excess lithium oxide. The irreversible additive structure prepared in this way is unstable, and as charging proceeds, a large amount of oxygen (O2) is generated as follows, and when the irreversible additive remains unreacted during the initial charging of the secondary battery, that is, during the activation of the battery, it may react during the subsequent charging and discharging process, thereby generating side reactions or a large amount of oxygen inside the battery. The oxygen thus generated may cause volume expansion of the electrode assembly, etc., and may be one of the main factors causing battery performance degradation.

[0006]

[0007] Furthermore, conventionally used irreversible additives exhibit very low 10 -11 S / cm powder conductivity, which is close to that of an insulator. This low powder conductivity increases the resistance of the positive electrode, and in this case, a large capacity of over 200 mAh / g is exhibited at a low C rate. However, as the C rate increases, the performance rapidly degrades due to the high resistance caused by the progress of charge / discharge, resulting in a decrease in the charge / discharge capacity of the battery and a limitation of difficulty in high-speed charging and discharging.

[0008] Therefore, there is a need to develop lithium secondary batteries having excellent electrical performance and improved safety.

[0009] [Related technical documents]

[0010] Korean Patent Publication No. 10-2019-0064423 Summary of the Invention

[0011] Technical issues

[0012] Therefore, an object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery including the same, the positive electrode having improved safety while effectively improving the electrical properties of the lithium secondary battery.

[0013] Technical Solution

[0014] In order to solve the above problems, in one embodiment, the present invention provides a positive electrode for a lithium secondary battery, the positive electrode comprising:

[0015] a positive electrode current collector; and

[0016] a positive electrode mixture layer provided on the positive electrode current collector,

[0017] wherein the positive electrode mixture layer comprises a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, and a binder;

[0018] wherein the first conductive material comprises one or more of the following: carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers;

[0019] The sheet resistance of the positive electrode is less than 3.0Ω / sq,

[0020] [Chemical Formula 1]

[0021] Li p Co (1-q) M 1 q O4

[0022] in,

[0023] M 1 is 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

[0024] p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0025] In this case, the positive electrode mixture layer may further include a second conductive material, wherein the second conductive material may contain one or more of the following: natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, and thermal black.

[0026] Furthermore, the electrode sheet resistance (R12) of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer may have the following ratio:

[0027] The ratio (R12 / R1) of the electrode sheet resistance (R1) of the positive electrode containing the first conductive material alone in the positive electrode mixture layer is 0.5 to 1.2, or

[0028] The ratio (R12 / R2) of the electrode sheet resistance (R2) relative to the positive electrode containing the second conductive material alone in the positive electrode mixture layer is 0.1 to 0.8.

[0029] Specifically, the electrode sheet resistance (R12) of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer may have the following ratio:

[0030] The ratio (R12 / R1) of the electrode sheet resistance (R1) of the positive electrode containing the first conductive material alone in the positive electrode mixture layer is 0.7 to 1.0, or

[0031] The ratio (R12 / R2) of the electrode sheet resistance (R2) relative to the positive electrode containing the second conductive material alone in the positive electrode mixture layer is 0.2 to 0.6.

[0032] In addition, the positive electrode additive may have a tetragonal structure with a space group of P42 / nmc.

[0033] In addition, the positive electrode additive may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer.

[0034] In addition, the first conductive material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer.

[0035] In addition, when the first conductive material and the second conductive material are included together, the total content of the first conductive material and the second conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer, and in this case, the second conductive material may be included in an amount of 20 to 60 parts by weight based on 100 parts by weight of the first conductive material.

[0036] On the other hand, the positive electrode active material may be a lithium metal composite oxide represented by the following Chemical Formula 2:

[0037] [Chemical Formula 2]

[0038] Li x [Ni y Co z Mn w M 2 v ]O u

[0039] in,

[0040] M 2 is 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

[0041] 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、1.5≤u≤4.5。

[0042] In addition, in one embodiment, the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, the method comprising the steps of:

[0043] A pre-dispersion is prepared by mixing a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, and a binder;

[0044] preparing a positive electrode slurry by mixing the prepared pre-dispersion, a positive electrode active material, and a binder; and

[0045] preparing a positive electrode mixture layer by coating a positive electrode slurry on a positive electrode current collector;

[0046] wherein the first conductive material comprises one or more of carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers; and

[0047] The sheet resistance of the manufactured positive electrode is less than 3.0Ω / sq.

[0048] [Chemical Formula 1]

[0049] Li p Co (1-q) M 1 q O4

[0050] in,

[0051] M 1 is 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

[0052] p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0053] In this case, the step of preparing the pre-dispersion may be performed under the condition of a relative humidity of 10% or less.

[0054] In addition, in the step of preparing the positive electrode slurry, a second conductive material may be further mixed.

[0055] Furthermore, in one embodiment, the present invention provides a lithium secondary battery comprising the positive electrode according to the present invention described above; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0056] Beneficial effects

[0057] The positive electrode for a lithium secondary battery according to the present invention is manufactured by using a pre-dispersion containing a positive electrode additive represented by Chemical Formula 1 and a conductive material having a linear structure as an irreversible additive in a positive electrode mixture layer, and by adjusting the electrode sheet resistance to meet a specific range, the amount of oxygen generated during charge and discharge can be reduced, and the charge and discharge efficiency of the lithium secondary battery can be easily improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Graph showing the sheet resistance of the positive electrodes manufactured in Examples 1 and 2 and Comparative Example 2. DETAILED DESCRIPTION

[0059] Since the present invention is capable of various changes and various embodiments, specific embodiments will be described in detail in the detailed description.

[0060] However, this is not intended to limit the present invention to specific embodiments, and should be construed as encompassing all variations, equivalents, and substitutes encompassed within the spirit and scope of the present invention.

[0061] In the present invention, it should be understood that the terms "comprising" or "having" etc. are intended to clearly indicate the existence of the described features, quantities, steps, operations, components, parts or their combinations, but do not exclude the existence or addition of one or more other features or numbers, steps, operations, components, parts and their combinations.

[0062] Furthermore, in the present invention, when a portion of a layer, film, region, plate, or the like is described as being "on" another portion, this includes not only the case where the other portion is "directly on" the other portion, but also the case where the other portion is present in between. Conversely, when a portion of a layer, film, region, plate, or the like is described as being "under" another portion, this includes both the case where the other portion is present in between and the case where the other portion is "directly under." Furthermore, the phrase "disposed on" herein includes not only being disposed on top but also being disposed on bottom.

[0063] In addition, in the present invention, "main component" refers to 50 weight% or more, 60 weight% or more, 70 weight% or more, 80 weight% or more, 90 weight% or more, 95 weight% or more, or 97.5 weight% or more based on the total weight of the composition or specific component. In some cases, when constituting the entire composition or specific component, that is, the "main component" may refer to 100 weight%.

[0064] In addition, in the present invention, "Ah" is a capacity unit of a lithium secondary battery, called "ampere-hour", and refers to the amount of current per hour. For example, when the battery capacity is "3000mAh", this means that it can discharge at a current of 3000mA for 1 hour.

[0065] Hereinafter, the present invention will be described in more detail.

[0066] Positive electrode for lithium secondary battery

[0067] In one embodiment, the present invention provides a positive electrode for a lithium secondary battery, the positive electrode comprising:

[0068] a positive electrode current collector; and

[0069] A positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, and a binder;

[0070] wherein the first conductive material comprises one or more of graphene, carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers;

[0071] The sheet resistance of the positive electrode is less than 3.0Ω / sq:

[0072] [Chemical Formula 1]

[0073] Li p Co (1-q) M 1 q O4

[0074] in,

[0075] M 1 is 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

[0076] p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0077] The positive electrode for a lithium secondary battery according to the present invention includes a positive electrode mixture layer manufactured by coating, drying and pressing a positive electrode slurry on a positive electrode collector, and the positive electrode mixture layer has a configuration containing a positive electrode active material, a positive electrode additive, a conductive material and a binder.

[0078] In this case, the positive electrode additive may be lithium cobalt oxide represented by the following Chemical Formula 1:

[0079] [Chemical Formula 1]

[0080] Li p Co (1-q) M 1 q O4

[0081] in,

[0082] M 1 is 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

[0083] p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0084] The positive electrode additive may contain lithium in excess, thereby providing lithium for lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during initial charge, thereby increasing the charge capacity of the battery and reducing the irreversible capacity to improve life characteristics.

[0085] Among them, compared with the nickel-containing oxides commonly used in the art, the positive electrode additive represented by Chemical Formula 1 has a higher lithium ion content, thereby being able to supplement the lithium ion loss caused by the irreversible reaction during the initial activation of the battery, thereby significantly improving the charge and discharge capacity of the battery. In addition, compared with the iron-containing oxides and / or manganese-containing oxides commonly used in the art, there is no side reaction due to the dissolution of transition metals during the charge and discharge of the battery, so there is an advantage of excellent battery stability. The lithium metal oxide represented by Chemical Formula 1 may include Li6CoO4, Li6Co 0.5 Zn 0.5 O4、Li6Co 0.7 Zn 0.3 O4, etc.

[0086] In addition, the positive electrode additive represented by Chemical Formula 1 may have a tetragonal crystal structure, wherein it may be contained in a space group of P42 / nmc having a distorted tetrahedral structure formed by cobalt elements and oxygen elements. Since the positive electrode additive has a distorted tetrahedral structure formed by cobalt atoms and oxygen atoms and is structurally unstable, when the positive electrode additive is used in an amount of 5 parts by weight or less based on 100 parts by weight of the positive electrode mixture layer in the manufacture of the positive electrode, a side reaction with moisture or oxygen in the air may be caused during the mixing of the positive electrode slurry. However, an advantage of the present invention is that when preparing the positive electrode slurry, a side reaction with moisture or oxygen in the air is prevented by using a composition in which the positive electrode additive is pre-dispersed.

[0087] In addition, the positive electrode additive may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer. Specifically, the positive electrode additive may be included in an amount of 0.1 to 8 parts by weight; 0.1 to 5 parts by weight; 1 to 10 parts by weight; 2 to 10 parts by weight; 5 to 10 parts by weight; 2 to 8 parts by weight; 3 to 7 parts by weight; or 4 to 5.5 parts by weight based on 100 parts by weight of the positive electrode mixture layer. According to the present invention, by adjusting the content of the positive electrode additive within the above range, it is possible to prevent deterioration of the charge and discharge capacity due to insufficient replenishment of lithium ions lost by irreversible reaction due to a low content of the positive electrode additive, and it is also possible to avoid the generation of a large amount of oxygen during charge and discharge of the battery due to an excess of the positive electrode additive.

[0088] In addition, the positive electrode for a lithium secondary battery may include a first conductive material in the positive electrode mixture layer, wherein the first conductive material may contain one or more of graphene having a linear structure, carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers.

[0089] In this case, the average size of the first conductive material may be 500 nm or less, specifically, 10 to 500 nm; 10 to 400 nm; 10 to 300 nm; 10 to 200 nm; 10 to 100 nm; 50 to 500 nm; 100 to 500 nm; 200 to 500 nm; 250 to 500 nm; 300 to 500 nm; 400 to 500 nm; 100 to 300 nm; 200 to 400 nm; or 50 to 250 nm. Here, the average size may refer to the average length of the first conductive material.

[0090] According to the present invention, by controlling the average size of the first conductive material having a linear structure within the above range, a conductive path can be formed on the surface of the positive electrode additive having low powder conductivity, thereby reducing the resistance of the positive electrode.

[0091] In addition, in addition to the first conductive material, the positive electrode mixture layer may further include a second conductive material, which contains one or more of the following: natural graphite, artificial graphite, carbon black, acetylene black, Danka black, Ketjen black, Super-P, channel black, furnace black, lamp black and thermal black.

[0092] In this case, the average size of the second conductive material can be 1 to 100 μm, specifically, 1 to 80 μm; 1 to 60 μm; 1 to 50 μm; 1 to 40 μm; 1 to 20 μm; 1 to 10 μm; 1 to 5 μm; 10 to 100 μm; 50 to 100 μm; 10 to 20 μm; 25 to 50 μm; 2 to 4 μm; it can be 1 to 3 μm.

[0093] In addition, when the positive electrode for a lithium secondary battery includes the first conductive material alone or the first conductive material and the second conductive material, and includes the positive electrode additive represented by Chemical Formula 1, it can exhibit a sheet resistance of 3.0 Ω / sq or less. Specifically, the positive electrode of the lithium secondary battery can exhibit a sheet resistance of 2.8 Ω / sq or less; 2.6 Ω / sq or less; 2.4 Ω / sq or less; 2.2 Ω / sq or less; 2.0 Ω / sq or less; 1.0 Ω / sq to 3.0 Ω / sq; 1.0 Ω / sq to 2.6 Ω / sq; 1.2 Ω / sq to 2.6 Ω / sq; 1.5 Ω / sq to 2.5 Ω / sq; or 1.4 Ω / sq to 2.3 Ω / sq.

[0094] In addition, when the positive electrode for a lithium secondary battery contains a first conductive material and a second conductive material, and the positive electrode additive represented by Chemical Formula 1, the sheet resistance of the electrode can be further reduced compared to the case where the first conductive material or the second conductive material is contained alone. Specifically, the ratio (R12 / R1) of the electrode sheet resistance (R12) of the positive electrode containing the first and second conductive materials in the positive electrode mixture layer to the resistance (R1) of the positive electrode containing the first conductive material alone in the positive electrode mixture layer can be 0.5 to 1.2, or the ratio (R12 / R2) of the electrode sheet resistance (R2) of the positive electrode containing the second conductive material alone in the positive electrode mixture layer can be 0.1 to 0.8.

[0095] More specifically, the ratio (R12 / R1) of the electrode sheet resistance (R12) of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer to the electrode sheet resistance (R1) of the positive electrode containing the first conductive material alone in the positive electrode mixture layer can be 0.5 to 1.1; 0.5 to 1.0; 0.5 to 0.9; 0.6 to 1.1; 0.65 to 1.0; or 0.7 to 0.98.

[0096] In addition, the ratio (R12 / R2) of the electrode sheet resistance (R12) of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer to the electrode sheet resistance (R2) of the positive electrode containing the second conductive material alone in the positive electrode mixture layer can be 0.1 to 0.7; 0.1 to 0.6; 0.1 to 0.5; 0.1 to 0.45; 0.1 to 0.4; 0.2 to 0.8; 0.2 to 0.55; or 0.2 to 0.5.

[0097] As an example, the ratio of the electrode sheet resistance (R12) of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer to the electrode sheet resistance (R1) of the positive electrode containing the first conductive material alone in the positive electrode mixture layer can be 0.7 to 1.0, or the ratio to the electrode sheet resistance (R2) of the positive electrode containing the second conductive material alone in the positive electrode mixture layer can be 0.2 to 0.6.

[0098] The present invention can further improve the electrical performance of the battery by preventing the reduction in the charging and discharging capacity and capacity retention rate of the lithium secondary battery, by controlling the sheet resistance of the positive electrode for the lithium secondary battery and the sheet resistance ratio (R12 / R1 and R12 / R2) depending on the type of conductive material contained in the positive electrode mixture layer within the above-mentioned range, the reduction being caused by: high sheet resistance exceeding 3.0Ω / sq; sheet resistance ratio (R12 / R1) exceeding 1.2; and sheet resistance ratio (R12 / R2) exceeding 0.8.

[0099] In addition, based on 100 parts by weight of the positive electrode mixture layer, the content of the first conductive material can be 0.1 to 10 parts by weight, specifically 0.1 to 7.5 parts by weight; 0.1 to 5 parts by weight; 0.1 to 3 parts by weight; 0.1 to 1.5 parts by weight; 2 to 5 parts by weight; 4 to 7 parts by weight; 5 to 10 parts by weight; 7 to 9 parts by weight; or 0.1 to 0.9 parts by weight.

[0100] In addition, when the first conductive material and the second conductive material are used together, based on 100 parts by weight of the positive electrode mixture layer, the total content of the first conductive material and the second conductive material can be 0.1 to 10 parts by weight, specifically 0.1 to 7.5 parts by weight; 0.1 to 5 parts by weight; 0.1 to 3 parts by weight; 0.1 to 1.5 parts by weight; 2 to 5 parts by weight; 4 to 7 parts by weight; 5 to 10 parts by weight; 7 to 9 parts by weight; or 0.1 to 0.9 parts by weight.

[0101] Here, based on 100 parts by weight of the first conductive material, the content of the second conductive material may be 20 to 60 parts by weight, specifically 20 to 50 parts by weight; 20 to 45 parts by weight; 30 to 60 parts by weight; 25 to 50 parts by weight; or 30 to 50 parts by weight.

[0102] The present invention can not only effectively improve the increase in sheet resistance of the electrode due to the positive electrode additive represented by Chemical Formula 1, but also prevent the activity of the positive electrode active material from being reduced due to excessive conductive material exceeding 10 parts by weight by controlling the content of the first conductive material and the total content of the combined first and second conductive materials within the above range.

[0103] On the other hand, the positive electrode active material is a positive electrode active material capable of reversible intercalation and deintercalation, and may contain a lithium metal composite oxide represented by the following Chemical Formula 2 as a main component:

[0104] [Chemical Formula 2]

[0105] Li x [Ni y Co z Mn w M 2 v ]O u

[0106] in,

[0107] M 2 is 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

[0108] 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、1.5≤u≤4.5。

[0109] The lithium metal composite oxide represented by Chemical Formula 2 is a composite metal oxide containing lithium and nickel, and may include one or more compounds selected from the following: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2.

[0110] In addition, the positive electrode active material may be contained in an amount of 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, based on 100 parts by weight of the positive electrode mixture layer.

[0111] In addition, the binder is used to bind the positive electrode active material, the positive electrode additive and the conductive material to each other, and as long as it has such a function, it can be used without particular limitation. Specifically, the binder may include one or more resins selected from the following: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0112] In addition, the binder may be included in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, based on a total of 100 parts by weight of the mixture layer; or the conductive material may be included in an amount of 1 to 5 parts by weight.

[0113] In addition, the average thickness of the mixture layer is not particularly limited, and may be specifically 50 to 300 μm, more specifically 100 to 200 μm; 80 to 150 μm; 120 to 170 μm; 150 to 300 μm; 200 to 300 μm; or 150 to 190 μm.

[0114] In addition, in the positive electrode, as the positive electrode current collector, a current collector with high conductivity without causing chemical changes in the battery can be used. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, etc. can be used, and in the case of aluminum or stainless steel, aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. can be used. In addition, fine concave and convex can be formed on the surface of the positive electrode current collector to increase the adhesion with the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics are feasible. In addition, taking into account the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied in the range of 3 to 500 μm.

[0115] Method for manufacturing positive electrode for lithium secondary battery

[0116] In addition, in one embodiment, the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, the method comprising the steps of:

[0117] A pre-dispersion is prepared by mixing a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, and a binder;

[0118] preparing a positive electrode slurry by mixing the prepared pre-dispersion, a positive electrode active material, and a binder; and

[0119] preparing a positive electrode mixture layer by coating a positive electrode slurry on a positive electrode current collector;

[0120] wherein the first conductive material comprises one or more of graphene, carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers;

[0121] The sheet resistance of the manufactured positive electrode is less than 3.0Ω / sq.

[0122] [Chemical Formula 1]

[0123] Li p Co (1-q) M 1 q O4

[0124] in,

[0125] M 1is 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

[0126] p and q are 5≤p≤7 and 0≤q≤0.5 respectively.

[0127] In the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, a positive electrode additive represented by Chemical Formula 1, a first conductive material, and a binder are first mixed to prepare a pre-dispersion, and the prepared pre-dispersion is further mixed with a positive electrode active material and a binder to prepare a slurry, and then the positive electrode slurry is coated on a positive electrode collector and dried to prepare a positive electrode mixture layer.

[0128] Here, the step of preparing the pre-dispersion is a step of mixing the positive electrode additive, the conductive material, and the binder, and can be performed in a conventional manner for preparing a slurry in the art. For example, the step of preparing the pre-dispersion can be performed by adding the various components to a homogenizer, stirring at 1,000 to 5,000 rpm for 30 to 600 minutes, and the viscosity can be controlled while adding the solvent during stirring. As an example, for the positive electrode pre-dispersion according to the present invention, the positive electrode additive, the conductive material, and the binder represented by Chemical Formula 1 are introduced into a homogenizer, and N-methylpyrrolidone solvent is injected while mixing at 3,000 rpm for 60 minutes to prepare a form in which the viscosity at 25±1°C is adjusted to 7,500±300cps.

[0129] Furthermore, the step of preparing the pre-dispersion may be performed under temperature and / or humidity conditions that satisfy a specific range, thereby preventing the structurally unstable positive electrode additive from being decomposed and / or damaged.

[0130] Specifically, the step of preparing the pre-dispersion can be carried out under the following temperature conditions: below 40°C, more specifically, 10°C to 40°C; 10°C to 35°C; 10°C to 30°C; 10°C to 25°C; 10°C to 20°C; 15°C to 40°C; 20°C to 40°C; 15°C to 35°C; or 18°C ​​to 30°C.

[0131] In addition, the step of preparing the pre-dispersion can be carried out under the following relative humidity (RH) conditions: 10% or less, more specifically, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less or 1% or less.

[0132] In the present invention, by controlling the temperature and / or humidity conditions as described above during the preparation of the pre-dispersion, the positive electrode additive in the form of particles undergoes a side reaction with moisture and / or oxygen in the air during mixing with a conductive material or the like, thereby preventing degradation of irreversible activity and achieving low sheet resistance of the positive electrode mixture layer.

[0133] In addition, the step of preparing the positive electrode slurry can be performed as follows: when the positive electrode active material and the binder are further mixed with the prepared pre-dispersion, the second conductive material is further mixed. When preparing the pre-dispersion, the second conductive material can be mixed with the first conductive material. However, the present invention further mixes the second conductive material with the prepared pre-dispersion, so that the positive electrode additive and the first conductive material contained in the pre-dispersion can be uniformly dispersed, and at the same time, the first conductive material can more effectively form an electrical network on the surface of the positive electrode additive.

[0134] lithium secondary batteries

[0135] Furthermore, in one embodiment, the present invention provides a lithium secondary battery comprising the positive electrode according to the present invention described above; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0136] By having the positive electrode of the present invention as described above, the lithium secondary battery according to the present invention can exhibit excellent charge and discharge performance, and a small amount of oxygen generated during charge and discharge.

[0137] The lithium secondary battery of the present invention has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0138] Here, the negative electrode is prepared by coating, drying and pressing a negative electrode active material on a negative electrode current collector, and may optionally further include a conductive material, an organic binder polymer, additives, etc. as described above in the positive electrode, if necessary.

[0139] In addition, the negative electrode active material may include, for example, a carbon material and a silicon material. A carbon material refers to a carbon material containing carbon atoms as a main component, and examples of carbon materials may include: graphite with a complete layered crystal structure such as natural graphite, soft carbon with a low crystalline layered crystal structure (graphene structure; hexagonal honeycomb carbon plane) and hard carbon in which these structures are mixed with an amorphous portion, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, fullerenes, activated carbon, graphene, etc., preferably selected from one or more of natural graphite, artificial graphite, 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 and natural graphite and / or artificial graphite. In this case, the carbon material may contain 0.1 to 10 parts by weight of graphene and / or carbon nanotubes based on 100 parts by weight of the total carbon material, more specifically, 0.1 to 5 parts by weight or 0.1 to 2 parts by weight of graphene and / or carbon nanotubes based on 100 parts by weight of the total carbon material.

[0140] In addition, the silicon material is a particle containing silicon (Si) as a metal component as a main component, and may contain silicon (Si) particles and silicon oxide (SiO X As an example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture thereof.

[0141] Furthermore, the silicon material may be a mixture of crystalline particles and amorphous particles, with the proportion of the amorphous particles being 50 to 100 parts by weight, particularly 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight, based on 100 parts by weight of the total silicon material. In the present invention, by controlling the proportion of amorphous particles contained in the silicon material within the above range, thermal stability and flexibility can be improved without degrading the electrical properties of the electrode.

[0142] In addition, the negative electrode active material contains a carbon material and a silicon material, and based on 100 parts by weight of the negative electrode mixture layer, it can contain 1 to 20 parts by weight, specifically, based on 100 parts by weight of the negative electrode mixture layer, it can contain 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.

[0143] According to the present invention, by controlling the contents of the carbon material and the silicon material contained in the negative electrode active material within the above range, the charge capacity per unit mass can be improved while reducing lithium consumption and irreversible capacity loss during initial charge and discharge of the battery.

[0144] As an example, the negative electrode active material may include: 95±2 parts by weight of graphite based on 100 parts by weight of the negative electrode mixture layer; and 5±2 parts by weight of a mixture in which silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles are uniformly mixed. According to the present invention, by controlling the content of the carbon material and silicon material included in the negative electrode active material within the above range, the charge capacity per unit mass can be improved while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery.

[0145] In addition, the average thickness of the negative electrode mixture layer may be 100 μm to 200 μm, specifically, 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.

[0146] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, sintered carbon, etc. can be used, and in the case of copper or stainless steel, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. can be used. In addition, like the positive electrode current collector, the negative electrode current collector may have fine concavoconvexities formed on its surface to enhance the bonding force with the negative electrode active material, and may take various forms such as films, sheets, foils, nets, porous materials, foams, non-woven materials, etc. In addition, considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector may be appropriately applied within the range of 3 to 500 μm.

[0147] In addition, the separator is inserted between the negative electrode and the positive electrode, and an insulating film with high ion permeability and mechanical strength is used. Although there is no particular limitation on the separator as long as it is commonly used in the art, specifically, a sheet or non-woven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; polyethylene, etc. can be used, and in some cases, a composite separator can be used in which a porous polymer substrate such as a sheet or non-woven fabric is coated with inorganic particles / organic particles through an organic binder polymer. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also be used as the separator. In addition, the average pore size of the separator can be 0.01 to 10 μm, and the average thickness can be 5 to 300 μm.

[0148] On the other hand, the positive electrode and the negative electrode may be wound in a roll form and housed in a cylindrical battery, a prismatic battery, or a pouch-type battery, or may be housed in a pouch-type battery in a folded or stacked and folded form, but is not limited thereto.

[0149] Furthermore, the lithium salt-containing electrolyte according to the present invention may be composed of an electrolyte and a lithium salt, and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used as the electrolyte.

[0150] As the nonaqueous organic solvent, for example, an aprotic organic solvent 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0151] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyalginate-lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymer materials containing ion dissociative groups, and the like can be used.

[0152] As an inorganic solid electrolyte, Li nitrides, halides, sulfates, etc. can be used, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2.

[0153] Lithium salts are materials that are easily soluble in non-aqueous 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, lithium imide, etc.

[0154] Furthermore, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the following may be added to the electrolyte: for example, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further contained, and carbon dioxide gas may be further contained to improve high-temperature storage characteristics, and fluoroethylene carbonate (FEC), propene sultone (PRS), etc. may be further contained.

[0155] Preferred Implementation

[0156] Hereinafter, the present invention will be described in detail by way of examples.

[0157] However, the following Examples and Experimental Examples are merely illustrations of the present invention, and the contents of the present invention are not limited to the following Examples and Experimental Examples.

[0158] Examples 1 to 6 and Comparative Examples 1 to 2: Production of positive electrodes for lithium secondary batteries

[0159] N-methylpyrrolidone was injected into the homogenizer, and 5 parts by weight of Li6Co as a positive electrode additive was weighed and added based on 100 parts by weight of the solid content of the positive electrode slurry. 0.7 Zn 0.3 O4; and 1 part by weight of PVdF as a binder, and carbon nanotubes (average size: 60±10 nm) as a first conductive material were added, followed by mixing at 2,000 rpm for 30 minutes to prepare a pre-dispersion for manufacturing a positive electrode. The content of the first conductive material, as well as the temperature and relative humidity (RH) conditions used in preparing the pre-dispersion are shown in Table 1 below.

[0160] Then, LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2; Danka black (average size: 2±0.5 μm) as a second conductive material; and PVdF as a binder were weighed and added to a homomixer containing the prepared pre-dispersion. A secondary mixing process was performed at 2,500 rpm for 30 minutes to prepare a positive electrode slurry for a lithium secondary battery. The PVdF content was 1 part by weight based on 100 parts by weight of the solid content of the positive electrode slurry. The contents of the positive electrode active material and the second conductive material were adjusted as shown in Table 1 below.

[0161] The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 100° C., and roll-pressed to produce a positive electrode. At this time, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the produced positive electrode was about 200 μm.

[0162] [Table 1]

[0163]

[0164] Comparative Example 3: Production of a positive electrode for a lithium secondary battery

[0165] N-methylpyrrolidone was injected into a homogenizer, and 92.3 parts by weight of LiNi as a positive electrode active material was weighed and added based on 100 parts by weight of the solid content of the positive electrode slurry. 0.6 Co 0.2 Mn 0.2 O2; 5 parts by weight of Li6Co as a positive electrode additive 0.7 Zn 0.3 O4; 0.7 parts by weight of carbon nanotubes (average size: 60±10 nm) as a first conductive material; 0.2 parts by weight of Danka Black (average size: 2±0.5 μm) as a second conductive material; and 2 parts by weight of PVdF as a binder were mixed at 2,000 rpm for 60 minutes to prepare a positive electrode slurry for a lithium secondary battery. The temperature and relative humidity (RH) were adjusted to 20°C to 25°C and 3%, respectively.

[0166] The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 100° C., and roll-pressed to produce a positive electrode. At this time, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the produced positive electrode was about 200 μm.

[0167] Comparative Example 4: Production of a positive electrode for a lithium secondary battery

[0168] The positive electrode was prepared in the same manner as in Example 1, except that, in the preparation of the predispersion, Danka black (average size: 2±0.5 μm) was used instead of carbon nanotubes (average size: 60±10 nm) as the first conductive material, and in the preparation of the positive electrode slurry, carbon nanotubes (average size: 60±10 nm) were used instead of Danka black (average size: 2±0.5 μm) as the second conductive material.

[0169] Examples 7 to 12 and Comparative Examples 5 to 8: Production of Lithium Secondary Batteries

[0170] Prepare natural graphite and silicon (SiOx, 1≤x≤2) particles as negative electrode active materials; and styrene-butadiene rubber (SBR) as a binder, and prepare the negative electrode slurry in the same way as the positive electrode slurry. At this time, the graphite used in the preparation of the negative electrode mixture layer is natural graphite (average particle size: 0.01 to 0.5 μm), and silicon (SiOx) particles with an average particle size of 0.9 to 1.1 μm are used. The prepared negative electrode slurry is applied to one side of a copper current collector, dried at 100°C, and rolled to manufacture the negative electrode. At this time, the total thickness of the negative electrode mixture layer is 150 μm, and the total thickness of the manufactured negative electrode is about 250 μm.

[0171] Separators made of porous polyethylene (PE) films (thickness: about 16 μm) were stacked to be inserted between the negative electrodes and positive electrodes manufactured in Examples 1 to 6 and Comparative Examples 1 to 4, and E2DVC was injected as an electrolyte to manufacture batteries in the form of full cells.

[0172] Here, “E2DVC” is a carbonate-based electrolyte, which refers to a solution obtained by mixing lithium hexafluorophosphate (LiPF6, 1.0 M) and ethylene carbonate (VC, 2 wt %) in a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0173] [Table 2]

[0174] Positive electrode for lithium secondary battery lithium secondary batteries Example 1 Example 7 Example 2 Example 8 Example 3 Example 9 Example 4 Example 10 Example 5 Example 11 Example 6 Example 12 Comparative Example 1 Comparative Example 5 Comparative Example 2 Comparative Example 6 Comparative Example 3 Comparative Example 7 Comparative Example 4 Comparative Example 8

[0175] Experimental example

[0176] In order to evaluate the performance of the positive electrode for a lithium secondary battery according to the present invention, the following experiment was performed.

[0177] A) Electrode sheet resistance evaluation

[0178] For the positive electrodes manufactured in Examples 1 to 6 and Comparative Examples 1 to 4, the sheet resistance of the electrodes was measured by a 4-point probe method, and the results are shown in Tables 3 and 4 below. Figure 1 middle.

[0179] B) Evaluation of the amount of outgassed oxygen during charge and discharge

[0180] For the lithium secondary batteries manufactured in Examples 7 to 12 and Comparative Examples 5 to 8, initial charging (forming) was performed at 55°C under the conditions of 3.5V and 1.0C, and the gas generated at the positive electrode was degassed while performing the initial charging to analyze the content of oxygen generated during the initial charging. Then, charging and discharging were repeated 50 times at 45°C under the conditions of 0.3C to further analyze the oxygen content during each charge / discharge period. The analysis results are shown in Table 3 below.

[0181] C) Evaluation of charge and discharge capacity and retention rate

[0182] The lithium secondary batteries manufactured in Examples 7 to 12 and Comparative Examples 5 to 8 were charged at a temperature of 25°C with a charge current of 0.1C to a charge cutoff voltage of 4.2 to 4.25V, and then charged until the current density at the cutoff voltage reached 0.01C for activation. They were then discharged at a discharge current of 0.1C to a cutoff voltage of 2V, and the initial charge / discharge capacity per unit mass was measured.

[0183] Then, the charge and discharge capacity was measured while repeating charge and discharge 50 times at 45° C. under the condition of 0.3 C, and the charge / discharge capacity retention ratio after charging and discharging 50 times was calculated. The results are shown in Table 3 below.

[0184] [Table 3]

[0185]

[0186] Refer to Table 3 and Figure 1 , it was found that the positive electrode for the lithium secondary battery of the embodiment manufactured according to the present invention, although containing the positive electrode additive represented by Chemical Formula 1 with low conductivity, has a low sheet resistance of 2.5Ω / sq or less by containing a first conductive material having a linear structure, and it was found that it exhibited a lower sheet resistance than the case where it contained the first conductive material alone or the second conductive material without a linear structure. In addition, the lithium secondary battery including the embodiment of the positive electrode not only had a high initial charge / discharge capacity of more than 102Ah, but also exhibited a high capacity retention rate of more than 91%. In addition, it was confirmed that the lithium secondary battery has high safety because the amount of oxygen generated after initial charge and discharge is significantly reduced.

[0187] According to these results, the positive electrode for a lithium secondary battery according to the present invention is manufactured by using a pre-dispersion containing a positive electrode additive represented by Chemical Formula 1 and a conductive material having a linear structure as an irreversible additive in a positive electrode mixture layer, and by adjusting the electrode sheet resistance to meet a specific range, it is possible to reduce the amount of oxygen generated during charge and discharge, and easily improve the charge and discharge efficiency of the lithium secondary battery.

[0188] While the foregoing has been described with reference to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art or ordinary skill in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as described in the appended claims.

[0189] Therefore, the technical scope of the present invention should not be limited to the contents described in the specific embodiments of the specification, but should be defined by the claims.

Claims

1. A positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material, a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, a second conductive material, and a binder; wherein the first conductive material comprises one or more of the following: carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers; The sheet resistance of the positive electrode is less than 2.6Ω / sq, wherein the second conductive material comprises one or more of the following: natural graphite, artificial graphite, acetylene black, Ketjen black, Super-P, channel black, furnace black, lamp black and thermal black, wherein the first conductive material forms an electrical network on the surface of the positive electrode additive, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 in, M 1 is 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 electrode sheet resistance R12 of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer has the following ratio: The ratio R12 / R1 of the electrode sheet resistance R1 of the positive electrode containing the first conductive material alone in the positive electrode mixture layer is 0.5 to 1.2, or The ratio R12 / R2 of the electrode sheet resistance R2 of the positive electrode containing the second conductive material alone in the positive electrode mixture layer is 0.1 to 0.

8.

3. The positive electrode according to claim 1, wherein The electrode sheet resistance R12 of the positive electrode containing the first conductive material and the second conductive material in the positive electrode mixture layer has the following ratio: The ratio R12 / R1 of the electrode sheet resistance R1 of the positive electrode containing the first conductive material alone in the positive electrode mixture layer is 0.7 to 1.0, or The ratio R12 / R2 of the electrode sheet resistance R2 of the positive electrode containing the second conductive material alone in the positive electrode mixture layer is 0.2 to 0.

6. The positive electrode according to claim 1 , wherein the positive electrode additive has a tetragonal structure with a space group of P42 / nmc. 5 . The positive electrode according to claim 1 , wherein a content of the positive electrode additive is 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer. 6 . The positive electrode according to claim 1 , wherein a content of the first conductive material is 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer. 7 . The positive electrode according to claim 1 , wherein a total content of the first conductive material and the second conductive material is 0.1 to 10 parts by weight based on 100 parts by weight of the positive electrode mixture layer. 8 . The positive electrode according to claim 1 , wherein the second conductive material is contained in an amount of 20 to 60 parts by weight based on 100 parts by weight of the first conductive material.

9. The positive electrode according to claim 1, wherein the positive electrode active material is a lithium metal composite oxide represented by the following Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mr w M 2 v ]O u in, M 2 is 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 1.0≤x≤1.30, 0.1≤y<0.95, 0.01 <z≤0.5、0.01<w≤0.5、0≤v≤0.2、1.5≤u≤4.5。 10. A method for manufacturing the positive electrode for a lithium secondary battery according to claim 1, the method comprising the following steps: A pre-dispersion is prepared by mixing a positive electrode additive represented by the following Chemical Formula 1, a first conductive material, and a binder; preparing a positive electrode slurry by mixing the prepared pre-dispersion, a positive electrode active material, a second conductive material, and a binder; and preparing a positive electrode mixture layer by coating the positive electrode slurry on a positive electrode current collector; wherein the first conductive material comprises one or more of the following: carbon nanotubes, graphite nanofibers, carbon nanofibers, vapor-grown carbon fibers, and activated carbon fibers; The sheet resistance of the manufactured positive electrode is less than 2.6Ω / sq. wherein the second conductive material comprises one or more of the following: natural graphite, artificial graphite, acetylene black, Ketjen black, Super-P, channel black, furnace black, lamp black and thermal black, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 in, M 1 is 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.

11. The method according to claim 10, wherein the step of preparing the pre-dispersion is carried out under the condition of a relative humidity of 10% or less.

12. A lithium secondary battery, comprising: The positive electrode according to claim 1; a negative electrode; and A separator is placed between the positive electrode and the negative electrode.

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