Positive electrode for lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a positive electrode and a method for manufacturing the same. The positive electrode comprises two or more metal oxides having different crystal structures as a first positive electrode active material and a second positive electrode active material, and comprises a carbon-based conductive material and a metal-based conductive material as conductive materials. As a result, the positive electrode can minimize the different kinetic characteristic deviations exhibited by each positive electrode active material, and a lithium secondary battery containing it has the advantage of having excellent charge-discharge rate characteristics and capacity characteristics.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for lithium secondary batteries and a method for manufacturing the same.

[0002] This application claims priority under Korean Patent Application No. 10-2024-0069710 dated 29 May 2024, and all content disclosed in the documents of said patent application is incorporated herein by reference. [Background technology]

[0003] In recent years, lithium-ion batteries have been widely applied not only to small devices such as portable electronic devices, but also to medium and large-scale devices such as battery packs for hybrid and electric vehicles, and power storage devices. In particular, with the growing concern for environmental issues in recent years, there has been a great deal of research into electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Generally, lithium secondary batteries have a structure in which an electrode assembly consisting of a positive electrode, a negative electrode, and a separator membrane is impregnated with a lithium electrolyte. In this case, each electrode is manufactured by coating a current collector with an electrode slurry. The electrode slurry is manufactured by mixing an electrode active material for storing energy, a conductive material for providing electrical conductivity, and a binder for adhering it to the current collector and providing bonding force, in a solvent such as NMP (N-methyl pyrrolidone).

[0005] The positive electrode can be made of LCO (LiCoO2), LMO (LiMn2O4), LFP (LiFePO4), or NCM (LiNi), which can reversibly insert or remove lithium. 1 / 3 Co 1 / 3 Mn 1 / 3 It contains metal oxides such as O2 as the positive electrode active material.

[0006] Among these, NCM, LCO, and NCA compounds, which have a layered crystalline structure, are suitable as positive electrode active materials for high-capacity / high-power secondary batteries because they easily store lithium ions and have a high lithium ion diffusion rate. However, compounds with a layered crystalline structure have low chemical and structural stability and can easily decompose under high-temperature conditions. This acts as a factor that reduces the safety of secondary batteries.

[0007] On the other hand, LFP-based compounds with an olivine crystal structure have a hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded, exhibiting high structural stability. Therefore, compounds with an olivine crystal structure can easily maintain their crystal structure even when all lithium ions are desorbed during charging, and decomposition of the crystal structure is less likely to occur even under high-temperature conditions. However, compounds with an olivine crystal structure have a low energy density, which indicates the amount of energy that the battery can store per unit weight / volume. Therefore, in order for compounds with an olivine crystal structure to achieve high energy density, the weight / volume value of the positive electrode active material must be increased, which imposes a limitation in that the size and weight of the secondary battery must be excessively increased.

[0008] Therefore, in order to achieve high capacity while maintaining the high safety of conventional secondary batteries, attempts continue to use a mixture of compounds having a layered crystal structure and compounds having an olivine crystal structure as a positive electrode active material. However, positive electrode active materials with a layered crystal structure and positive electrode active materials with an olivine crystal structure have different electromotive forces. Generally, the electromotive force of a positive electrode active material affects the operating voltage during charging and discharging of the positive electrode. However, when a positive electrode is manufactured by mixing positive electrode active materials with different electromotive forces, the difference in electromotive force of the positive electrode active materials causes them to exhibit different kinetic patterns during charging and discharging of the secondary battery. In other words, during charging and discharging, a reaction bias phenomenon occurs in which the compound with the lower electromotive force among the mixed positive electrode active materials reacts more dominantly depending on the state of charge (SOC) of the secondary battery. This reaction bias phenomenon prevents the positive electrode's rate characteristics and charge / discharge capacity characteristics from being fully expressed, resulting in a limitation of low charge / discharge performance for the secondary battery.

[0009] Therefore, in order to achieve high safety and energy density in secondary batteries, there is a need for technological development of lithium secondary battery cathodes that contain two types of cathode active materials with different crystal structures while also exhibiting excellent rate characteristics and charge / discharge capacity characteristics. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Korean Published Patent Publication No. 10-2013-0136796 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a positive electrode for lithium secondary batteries and a method for manufacturing the same, which contains two positive electrode active materials with different crystal structures and exhibits excellent rate characteristics and charge / discharge capacity characteristics. [Means for solving the problem]

[0012] To solve the above problems, the present invention provides a positive electrode current collector, and a positive electrode active layer provided on at least one surface of the positive electrode current collector; the positive electrode active layer contains a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metal-based conductive material; the first positive electrode active material and the second positive electrode active material each contain one or more of a layered metal oxide represented by the following chemical formula 1, a spinel metal oxide represented by the following chemical formula 2, and an olivine metal oxide represented by the following chemical formula 3, and contain metal oxides having different structures from each other; the metal-based conductive material has a nanowire structure, and provides a positive electrode characterized by:

[0013] [Chemical formula 1] Li a [Ni b Co 1-b-c M 1 c O2

[0014] [Chemical formula 2] Li p [Mn 2-q M 2 q O4

[0015] [Chemical formula 3] LiFe 1-x M 3 x XO4

[0016] In the above chemical formulas 1 to 3, M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo, M 2is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 3 is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. a, b, c, p, q, and x are such that 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

[0017] In this case, the first positive electrode active material may include one or more metal oxides with a layered structure and metal oxides with a spinel structure, and the second positive electrode active material may include metal oxides with an olivine structure.

[0018] Furthermore, the first positive electrode active material and the second positive electrode active material may be included in a weight ratio in the range of 5:95 to 95:5.

[0019] Furthermore, the above-mentioned metallic conductive material may be a nanowire having an average length in the range of 0.5 μm to 900 μm and an average diameter in the range of 1 nm to 500 nm.

[0020] Furthermore, the above-mentioned metallic conductive material may contain one or more metallic elements from among silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), iron (Fe), and stainless steel (SUS).

[0021] Furthermore, the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode active layer, and their total content may be 10% or less by weight based on the total weight of the positive electrode active layer.

[0022] Furthermore, the carbon-based conductive material may be included in an amount of 0.1% to 10% by weight relative to the total weight of the first positive electrode active material, and the metallic conductive material may be included in an amount of 0.1% to 10% by weight relative to the total weight of the second positive electrode active material.

[0023] On the other hand, the carbon-based conductive material may include one or more of the following: acetylene black, Denka Black (registered trademark), Ketjen Black, Super P, Channel Black, Furnace Black, Lamp Black, Thermal Black, graphene, carbon nanotubes, and carbon fibers.

[0024] Furthermore, the above carbon-based conductive material has an average particle size (D) in the range of 0.5 μm to 5 μm. 50 ) can have.

[0025] Furthermore, the present invention is The present invention provides an electrode assembly for a secondary battery, comprising a positive electrode, a negative electrode, and a separation membrane provided between the positive electrode and the negative electrode.

[0026] Furthermore, the present invention is The steps include: applying a positive electrode slurry to at least one surface of the positive electrode current collector, and The process includes the step of drying the coated positive electrode slurry to form a positive electrode active layer; The above positive electrode slurry comprises a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metallic conductive material; The first positive electrode active material and the second positive electrode active material each contain one or more of the following: a layered metal oxide represented by chemical formula 1, a spinel metal oxide represented by chemical formula 2, and an olivine metal oxide represented by chemical formula 3, and each contains metal oxides with different structures from each other; The above-mentioned metallic conductive material provides a method for manufacturing the positive electrode described above, characterized by having a nanowire structure:

[0027] [Chemical formula 1] Li a [Ni b Co 1-b-c M1 c ]O2

[0028] [Chemical formula 2] Li p [Mn 2-q M 2 q ]O4

[0029] [Chemical formula 3] LiFe 1-x M 3 x XO4

[0030] In the above chemical formulas 1 to 3, M 1 is one or more elements from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 2 is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 3 is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. a, b, c, p, q, and x are such that 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

[0031] Here, the positive electrode slurry may further include a binder.

[0032] Furthermore, the above positive electrode slurry can be manufactured by the following process:

[0033] A step of producing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed, A step of producing a positive electrode slurry by mixing the first positive electrode active material and the second positive electrode active material into the manufactured mixed dispersion. [Effects of the Invention]

[0034] The positive electrode according to the present invention includes a carbon-based conductive material and a metal-based conductive material as conductive materials in the positive electrode active layer, and even if two or more metal oxides having different crystal structures are included as the first positive electrode active material and the second positive electrode active material, the kinetic characteristic deviation between the positive electrode active materials can be minimized. Therefore, secondary batteries containing this electrode have the advantage of having excellent charge-discharge rate characteristics and capacity characteristics. [Modes for carrying out the invention]

[0035] Since the present invention can be modified in various ways and has many different embodiments, specific embodiments will be described in detail.

[0036] However, this is not intended to limit the present invention to any particular embodiment, but rather to be understood to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0037] In the present invention, terms such as “includes” or “having” are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof as described in the specification, without prejudice to the presence or possibility of adding one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0038] Furthermore, in this specification, "average particle size (D 50"Average particle size" refers to the particle size at which the cumulative value in the particle size distribution reaches 50%, and is also called the median diameter. The above average particle size can be measured using methods commonly applied in this industry. For example, the above average particle size can be measured using a particle size analyzer or an analytical instrument using laser diffraction scattering particle size distribution measurement, but is not limited to these.

[0039] The present invention will be described in more detail below.

[0040] <Positive electrode> The present invention Positive electrode current collector, and The positive electrode current collector includes a positive electrode active layer provided on at least one surface of the positive electrode current collector; The above positive electrode active layer comprises a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metallic conductive material; The first positive electrode active material and the second positive electrode active material each contain one or more of the following metal oxides: a layered metal oxide represented by chemical formula 1, a spinel metal oxide represented by chemical formula 2, and an olivine metal oxide represented by chemical formula 3, and each contains different metal oxides from each other; The above-mentioned metallic conductive material provides a positive electrode characterized by having a nanowire structure:

[0041] [Chemical formula 1] Li a [Ni b Co 1-b-c M 1 c ]O2

[0042] [Chemical formula 2] Li p [Mn 1-q M 2 q ]O2

[0043] [Chemical formula 3] LiFe 1-x M 3 x XO4

[0044] In the above chemical formulas 1 to 3, M 1 is one or more elements from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 2 is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 3 is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. a, b, c, p, q, and x are such that 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

[0045] The positive electrode according to the present invention is a positive electrode for a secondary battery, and more particularly a positive electrode used in a lithium secondary battery. The positive electrode includes a positive electrode active layer provided on at least one surface of a positive electrode current collector. Here, the positive electrode active layer is a layer that embodies the electrical activity of the positive electrode and mainly contains a positive electrode active material that embodies an electrochemical oxidation-reduction reaction during charging and discharging of the battery. Specifically, the positive electrode active material can be included in an amount of 80 to 99.8 parts by weight per 100 parts by weight of the entire positive electrode active layer, and more specifically, in an amount of 95 parts by weight or more, 98 parts by weight or more, 84 to 99.8 parts by weight, 90 to 99.8 parts by weight, 94 to 99.8 parts by weight, 88 to 96 parts by weight, or 92 to 97.5 parts by weight.

[0046] Furthermore, the above positive electrode active material includes a first positive electrode active material and a second positive electrode active material, which may include metal oxides having different crystal structures. Specifically, the first positive electrode active material and the second positive electrode active material each contain one or more of the following: a layered metal oxide represented by chemical formula 1 below, a spinel metal oxide represented by chemical formula 2 below, and an olivine metal oxide represented by chemical formula 3 below, and may include metal oxides having different crystal structures:

[0047] [Chemical formula 1] Li a [Ni b Co 1-b-c M 1 c ]O2

[0048] [Chemical formula 2] Li p [Mn 2-q M 2 q ]O4

[0049] [Chemical formula 3] LiFe 1-x M 3 x XO4

[0050] In the above chemical formulas 1 to 3, M 1 is one or more elements from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 2 is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M 3 is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. a, b, c, p, q, and x are such that 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

[0051] Generally, metal oxides represented by chemical formulas 1 to 3 above are used as positive electrode active materials for lithium secondary batteries.

[0052] Of these, the metal oxide represented by chemical formula 1 is a compound having a layered crystalline structure, readily stores lithium ions, has a high lithium ion diffusion rate, and is suitable for use as a positive electrode active material in high-capacity / high-power secondary batteries. However, compounds having a layered crystalline structure have low chemical and structural stability and can easily decompose under high-temperature conditions. This acts as a factor that reduces the safety of secondary batteries.

[0053] Furthermore, the metal oxide represented by the above chemical formula 2 has a spinel crystal structure, which is readily observed in common metal oxides. This spinel crystal structure contains various three-dimensional passages internally, facilitating lithium ion insertion and thus exhibiting excellent power output. However, while it has relatively higher structural stability compared to the above layered crystal structure metal oxides, it has limitations, such as the occurrence of side reactions like dissolution in the electrolyte at temperatures above 60°C.

[0054] In contrast, LFP compounds having an olivine crystal structure represented by the above chemical formula 3 have a hexahedral crystal structure in which phosphorus (P) and oxygen (O) are strongly bonded, exhibiting high structural stability. Therefore, compounds having an olivine crystal structure can easily maintain their crystal structure even if all lithium ions are desorbed during charging, and decomposition of the crystal structure is less likely to occur even under high-temperature conditions. However, compounds having an olivine crystal structure have a low energy density, which indicates the amount of energy that the battery can store per unit weight / volume. Therefore, in order for compounds having an olivine crystal structure to achieve high energy density, the weight / volume of the positive electrode active material must be increased, which limits the size and weight of the secondary battery to an excessive increase.

[0055] Accordingly, the present invention comprises a first positive electrode active material and a second positive electrode active material in the positive electrode active layer, wherein the first positive electrode active material and the second positive electrode active material contain metal oxides having different crystal structures. This allows for further improvement of the safety and electrical performance of the positive electrode by complementing or mitigating the limitations of metal oxides having different crystal structures.

[0056] Specifically, the first positive electrode active material may include one or more metal oxides with a layered structure and metal oxides with a spinel structure, and the second positive electrode active material may include metal oxides with an olivine structure.

[0057] For example, the first positive electrode active material may include a layered metal oxide, and the second positive electrode active material may include a metal oxide with an olivine structure.

[0058] Furthermore, the first positive electrode active material may include a metal oxide with a spinel structure, and the second positive electrode active material may include a metal oxide with an olivine structure.

[0059] Here, the layered metal oxide represented by the above chemical formula 1 is a metal oxide containing nickel (Ni) and / or cobalt (Co) together with lithium, and in some cases other transition metals (M 1) can have a doped form. For example, the above metal oxide can be LiCoO2, LiNiO2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Mn 0.15 Zr 0.05 )O2, Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Al 0.2 )O2, Li(Ni 0.7 Co 0.15 Al 0.15 )O2, Li(Ni 0.8 Co 0.1 Al 0.1 )O2, Li(Ni 0.9 Co 0.05 Al 0.05 )O2, Li(Ni 0.6 Co 0.2 Al 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co[[ID=—83]] 0.2 Al 0.15 Zr 0.05 )O2, and can contain one or more of Li(Ni 0.7 Co 0.1 Al 0.1 Zr 0.1 )O2.

[0060] Further, the metal oxide having a spinel structure represented by the above Chemical Formula 2 is a metal oxide containing manganese (Mn), and in some cases, other transition metals (M2 ) can have a doped form. For example, the above metal oxide may be LiMn2O4, LiMn 1.7 Al 0.3 O4, LiMn 1.5 Al 0.5 It may contain one or more of the O4 species.

[0061] Furthermore, the metal oxide with the olivine structure represented by the above chemical formula 3 is a phosphorus oxide containing iron (Fe) among transition metals, and in some cases, other transition metals (M) may be present. 3 ) can have a doped form. For example, the metal oxide may be LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.7 Mn 0.3 PO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, LiFe 0.2 Mn 0.8 This can include PO4, etc.

[0062] Furthermore, the first positive electrode active material and the second positive electrode active material can be included in the positive electrode active layer in a predetermined content ratio. The performance of the positive electrode can change depending on the content of the positive electrode active material included in the positive electrode active layer. Therefore, the present invention allows the first positive electrode active material and the second positive electrode active material included in the positive electrode active layer to be included in a predetermined content ratio. Specifically, the first positive electrode active material and the second positive electrode active material can be included in a weight ratio in the range of 5:95 to 95:5 (i.e., 5 parts by weight to 95 parts by weight: 95 parts by weight to 5 parts by weight). Specifically, the first positive electrode active material and the second positive electrode active material are weight ratios in the range of 10:90 to 90:10 (i.e., 10 parts by weight to 90 parts by weight: 90 parts by weight to 10 parts by weight), 20:80 to 80:20 (i.e., 20 parts by weight to 80 parts by weight: 80 parts by weight to 20 parts by weight), 25:75 to 75:25 (i.e., 25 parts by weight to 75 parts by weight: 75 parts by weight to 25 parts by weight), 30:70 to 70:30 (i.e., 30 parts by weight to 70 parts by weight: 70 parts by weight to 30 parts by weight), and 35:65 to 65:35. It can be included in the following weight ratios (i.e., 35 to 65 parts by weight: 65 to 35 parts by weight), weight ratios in the range of 40:60 to 70:30 (i.e., 40 to 70 parts by weight: 60 to 30 parts by weight), weight ratios in the range of 50:50 to 95:5 (i.e., 50 to 95 parts by weight: 50 to 5 parts by weight), weight ratios in the range of 50:50 to 85:15 (i.e., 50 to 85 parts by weight: 15 to 50 parts by weight), and weight ratios in the range of 50:50 to 75:25 (i.e., 50 to 75 parts by weight: 25 to 50 parts by weight).

[0063] The present invention can achieve high electrical performance while improving battery safety by adjusting the content ratio of the first positive electrode active material and the second positive electrode active material contained in the positive electrode active layer to the above-mentioned range. Specifically, the present invention can minimize the decomposition of the positive electrode active material or the occurrence of side reactions with the electrolyte when the positive electrode active layer is exposed to a high-temperature environment by maintaining the content ratio of the second positive electrode active material at a level equal to or higher than the lower limit of the above-mentioned range. Furthermore, the present invention can improve the output during discharge while achieving high charge / discharge capacity and energy density of the positive electrode by maintaining the content ratio of the second positive electrode active material at a level equal to or lower than the upper limit of the above-mentioned range.

[0064] Furthermore, when the positive electrode active layer contains two or more metal oxides with different crystal structures as positive electrode active materials, as in the present invention, the problems associated with the metal oxides can be complemented or mitigated, thus improving the safety and electrical performance of the positive electrode containing these materials. However, metal oxides with different crystal structures have different electromotive forces. Generally, the electromotive force of the positive electrode active material affects the operating voltage during charging and discharging of the positive electrode. However, when a positive electrode is manufactured by mixing positive electrode active materials with different electromotive forces, the electromotive force deviation of the positive electrode active materials causes them to exhibit different kinetic patterns during charging and discharging of the secondary battery. In other words, during charging and discharging, a reaction bias phenomenon occurs in which the compound with the lower electromotive force among the mixed positive electrode active materials reacts more predominantly depending on the state of charge (SOC) of the secondary battery. This reaction bias phenomenon prevents the positive electrode's rate characteristics and charge / discharge capacity characteristics from being fully expressed, resulting in a limitation of low charge / discharge performance for the secondary battery.

[0065] Therefore, the present invention is technically characterized by using a combination of a carbon-based conductive material and a metal-based conductive material having a nanowire structure in the positive electrode active layer. The metal-based conductive material has a nanowire structure and can further improve the electrical conductivity of the positive electrode active layer by forming a three-dimensional network within the positive electrode active layer. Furthermore, the metal-based conductive material can have a relatively higher electromotive force compared to carbon-based conductive materials such as carbon black, graphene, and carbon nanotubes (CNTs). Accordingly, the metal-based conductive material can perform the function of mitigating or improving the reaction bias phenomenon caused by the electromotive force difference between the first positive electrode active material and the second positive electrode active material.

[0066] In this context, the nanowire structure of the metallic conductive material can refer to a wire structure composed of metal having a size at the nanometer level. The size is not particularly limited as long as it is a wire structure with a diameter of several hundred nanometers (nm). Specifically, the metallic conductive material may be a wire structure having an average length in the range of 0.5 μm to 900 μm and an average diameter in the range of 1 nm to 500 nm.

[0067] More specifically, the above metallic conductive materials have average lengths of 0.5μm~900μm, 0.5μm~750μm, 0.5μm~500μm, 0.5μm~300μm, 0.5μm~250μm, 0.5μm~100μm, 0.5μm~50μm, 0.5μm~30μm, 0.5μm~20μm, and 0.5μm~ The particle size can be in the range of 10 μm, 0.5 μm to 9 μm, 0.5 μm to 5 μm, 0.5 μm to 3 μm, 0.5 μm to 2 μm, 0.5 μm to 1 μm, 0.5 μm to 0.9 μm, 1 μm to 2 μm, 1.5 μm to 4.5 μm, 2 μm to 9 μm, 5 μm to 10 μm, 1 μm to 3 μm, or 0.8 μm to 1.1 μm.

[0068] Furthermore, the above-mentioned metallic conductive materials may have an average diameter in the range of 1nm to 400nm, 1nm to 300nm, 1nm to 200nm, 50nm to 200nm, 100nm to 300nm, 250nm to 500nm, 300nm to 400nm, 1nm to 100nm, 1nm to 50nm, 1nm to 20nm, 1nm to 15nm, 1nm to 10nm, 5nm to 10nm, 10nm to 30nm, 11nm to 50nm, or 8nm to 12nm. The average length and average diameter of the above-mentioned metallic conductive materials can be measured by analytical instruments capable of analyzing two-dimensional projection images of particles, such as scanning electron microscopes (SEM), but are not limited to these methods.

[0069] This invention controls the size of the metallic conductive material to satisfy the above-mentioned average length range and average diameter range, thereby enabling the formation of a conductive network even when included in the positive electrode active layer with a significantly small content. This allows for the realization of high charge / discharge capacity and energy density of the positive electrode.

[0070] Furthermore, the above-mentioned metallic conductive material can be composed of a metal with excellent electrical conductivity. For example, the above-mentioned metallic conductive material may contain pure metals such as silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), and iron (Fe), or stainless steel (SUS) individually, or may contain two or more of them together. The above-mentioned material is a substance with high electrical conductivity and is excellent in improving the conductivity of the positive electrode active layer during charging and discharging of secondary batteries. In addition, the above-mentioned material is excellent in reducing the electromotive force deviation between the first positive electrode active material and the second positive electrode active material. As a result, when the above-mentioned material is applied to the positive electrode active layer as a metallic conductive material together with a carbon-based conductive material, it can improve the reaction bias phenomenon inside the positive electrode, and is excellent in improving the rate characteristics and charge / discharge capacity characteristics.

[0071] Furthermore, the conductive material contained in the positive electrode active layer can have a predetermined content range.

[0072] Specifically, the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode active layer, and their total content may be 10% or less by weight relative to the total weight of the positive electrode active layer.

[0073] For example, the carbon-based conductive material and the metal-based conductive material may each be present in amounts of 0.1% to 10% by weight relative to the total weight of the positive electrode active layer, specifically 0.1% to 8% by weight, 0.1% to 5% by weight, 0.1% to 3% by weight, 2% to 6% by weight, or 0.5% to 2% by weight. Furthermore, the total content of the carbon-based conductive material and the metal-based conductive material may be 10% or less by weight based on the total weight of the positive electrode active layer, specifically 0.1% to 8% by weight, 0.1% to 5% by weight, 0.1% to 3% by weight, 2% to 6% by weight, or 0.5% to 2% by weight.

[0074] The present invention prevents a decrease in charging capacity due to increased positive electrode resistance caused by a low content of conductive material, by controlling the content of conductive material within the above-mentioned range. It also prevents problems such as a decrease in charging capacity due to a reduction in the content of positive electrode active material caused by an excessive amount of conductive material, or a decrease in rapid charging characteristics due to an increase in the loading amount of the positive electrode active layer.

[0075] Furthermore, the carbon-based conductive material and the metallic conductive material may be affected by the content of the positive electrode active material contained in the positive electrode active layer. Specifically, the content of the carbon-based conductive material may depend on the content of the first positive electrode active material, and the content of the metallic conductive material may depend on the content of the second positive electrode active material. For example, the carbon-based conductive material can be included in an amount of 0.1% to 10% by weight relative to the total weight of the first positive electrode active material, and the metallic conductive material can be included in an amount of 0.1% to 10% by weight relative to the total weight of the second positive electrode active material. In this case, the content ratio of the carbon-based conductive material and the metallic conductive material may be proportional to the content ratio of the first positive electrode active material and the second positive electrode active material.

[0076] More specifically, the carbon-based conductive material may be present in amounts of 0.1% to 8% by weight, 0.1% to 5% by weight, 0.1% to 3% by weight, 2% to 6% by weight, or 0.5% to 2% by weight relative to the total weight of the first positive electrode active material.

[0077] Furthermore, the above-mentioned metallic conductive material may be present in amounts of 0.1% to 8% by weight, 0.1% to 5% by weight, 0.1% to 3% by weight, 2% to 6% by weight, or 0.5% to 2% by weight, relative to the total weight of the second positive electrode active material.

[0078] The present invention effectively reduces the electromotive force deviation between the first positive electrode active material and the second positive electrode active material by adjusting the content of carbon-based conductive material and metal-based conductive material as described above. This improves the reaction bias phenomenon inside the positive electrode during charging and discharging of the secondary battery, thereby improving the rate characteristics and charge / discharge capacity characteristics.

[0079] Furthermore, the carbon-based conductive material described above is a conductive material whose main component is carbon, and can be applied without particular limitation as long as it is a conductive material that is commonly used in this industry as a conductive material for electrodes of lithium secondary batteries. Specifically, the carbon-based conductive material may include one or more of the following: carbon black such as acetylene black, Denka Black (registered trademark), Ketjen Black, Super P, Channel Black, Furnace Black, Lamp Black, and Thermal Black; graphene; carbon nanotubes (CNTs); and carbon fibers. For example, the carbon-based conductive material may include carbon nanotubes.

[0080] Furthermore, the carbon-based conductive material described above is not particularly limited in form, but its size can satisfy a predetermined range. Specifically, the carbon-based conductive material has an average particle size (D) in the range of 0.5 μm to 5 μm. 50) can have. More specifically, the carbon-based conductive material has an average particle size (D) in the range of 0.5μm~4μm, 0.5μm~3μm, 0.5μm~2.5μm, 0.5μm~2μm, 0.5μm~1.5μm, 0.5μm~1μm, 0.5μm~0.9μm, 0.8μm~1.1μm, 1.1μm~1.5μm, 0.7μm~0.3μm, or 0.5μm~0.8μm. 50 ) can have.

[0081] The present invention makes it possible to realize a positive electrode active layer in which carbon-based conductive material is uniformly dispersed by adjusting the average particle size of the carbon-based conductive material to the above range, thereby preventing a partial increase in the electrical resistance of the positive electrode active layer.

[0082] On the other hand, the positive electrode active layer may selectively further contain binders, other additives, etc., along with the main components, the positive electrode active material and the conductive material.

[0083] The above-mentioned binder is a component that helps to bond the positive electrode active material to conductive materials and to the current collector, and can be applied appropriately within a range that does not degrade the electrical properties of the positive electrode. Specifically, it may contain one or more of the following: vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0084] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire positive electrode active layer, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the binder content in the positive electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content, or a decrease in the electrical properties of the positive electrode due to an excessive amount of binder.

[0085] Furthermore, the average thickness of the positive electrode active layer can be 50 μm to 500 μm, specifically 100 μm to 400 μm, 200 μm to 350 μm, 50 μm to 180 μm, 80 μm to 150 μm, 100 μm to 250 μm, 100 μm to 250 μm, or 130 μm to 190 μm. By adjusting the average thickness of the positive electrode active layer to the above range, the present invention not only enables high adhesion between the positive electrode active layer and the positive electrode current collector, but also enables high energy density of the positive electrode.

[0086] Furthermore, the positive electrode current collector can be made of a material that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc., may be used. The average thickness of the current collector can be appropriately set between 3 μm and 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0087] The positive electrode according to the present invention, having the above-described configuration, includes a carbon-based conductive material and a metal-based conductive material as conductive materials in the positive electrode active layer, and even if it includes two or more metal oxides having different crystal structures as the first positive electrode active material and the second positive electrode active material, it can minimize the kinetic characteristic deviation between the positive electrode active materials. Therefore, secondary batteries containing this have the advantage of having excellent charge-discharge rate characteristics and capacity characteristics.

[0088] <Electrode Assembly for Secondary Battery> Furthermore, the present invention is The present invention provides an electrode assembly for a secondary battery, comprising the positive electrode, the negative electrode, and a separation membrane provided between the positive electrode and the negative electrode as described above.

[0089] The electrode assembly for a secondary battery according to the present invention includes a positive electrode, a negative electrode, and a separation membrane provided between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode of the present invention as described above.

[0090] The electrode assembly described above is a positive electrode and includes the positive electrode of the present invention as described above. It is highly safe, has a high energy density, and is characterized by excellent rate characteristics and charge / discharge capacity.

[0091] The positive electrode included in the above electrode assembly has the same configuration as described above, so a detailed explanation will be omitted.

[0092] On the other hand, the negative electrode includes a negative electrode active layer on at least one surface of the negative electrode current collector. The negative electrode active layer in the negative electrode is a layer that embodies the electrical activity of the negative electrode and mainly contains a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during charging and discharging of the battery.

[0093] Here, the above-mentioned anode active material may mainly consist of a carbon-based anode active material. Specifically, the above-mentioned carbon-based anode active material may be included in an amount of 80 to 99.8 parts by weight per 100g of the total weight of the anode active layer, and more specifically, in amounts of 95 parts by weight or more, 98 parts by weight or more, 84 to 99.8 parts by weight, 90 to 99.8 parts by weight, 94 to 99.8 parts by weight, 88 to 96 parts by weight, or 92 to 97.5 parts by weight.

[0094] Furthermore, the carbon-based anode active material mentioned above refers to a material whose main component is carbon atoms, and such a carbon-based anode active material may include graphite. The graphite may include one or more of either natural graphite or artificial graphite. For example, the carbon-based anode active material may contain natural graphite or artificial graphite alone, and in some cases, it may contain a mixture of natural graphite and artificial graphite.

[0095] As one example, the carbon-based anode active material described above can contain natural graphite and artificial graphite in weight ratios ranging from 5 to 50:50 to 95, 20 to 45:55 to 80, or 30 to 50:50 to 70. In this case, by including natural graphite and artificial graphite in the above-mentioned mixing ratios, the carbon-based anode active material can strengthen the adhesion between the anode current collector and the anode active layer.

[0096] As another example, the carbon-based anode active material described above can contain artificial graphite alone. The present invention incorporates artificial graphite alone in the anode active layer, significantly improving the lifespan of the anode, thus proving advantageous in conditions requiring prolonged, frequent charging, such as in automotive batteries. Furthermore, artificial graphite offers advantages over natural graphite, including superior output performance and suitability for rapid charging.

[0097] Furthermore, the carbon-based anode active material is preferably spherical graphite secondary particles formed by the aggregation of multiple flaky graphite primary particles. Examples of flaky graphite include natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar and pitch, and graphitized cokes (green coke, green coke, pitch coke, needle coke, petroleum coke, etc.). In particular, granulated graphite produced using multiple highly crystalline artificial graphite particles is preferred. Also, one graphite granule can be formed by the aggregation of 2 to 100, preferably 3 to 20, flaky graphite particles.

[0098] At this time, the average particle size (D) of the secondary particles 50 The average particle size (D) of the secondary particles can be in the range of 1 μm to 50 μm. Specifically, the average particle size (D) of the secondary particles is...50 ) are 1μm~40μm, 1μm~30μm, 10μm~40μm, 15μm~30μm, 25μm~50μm, 11μm~19μm, 15μm~25μm, 20μm~30μm, 1μm~20μm, 1μm~10μm, 5μm~15μm, The average particle size (D 50 ) can be represented. For spherical carbon-based anode active materials, it may be advantageous to reduce the particle size to maximize the degree of disorder in the expansion direction for each particle, so as to prevent particle expansion due to lithium ion charging. However, when the particle size of the carbon-based anode active material is less than 1.0 μm, there is a problem that a large amount of binder is required due to the increase in the number of particles per unit volume. On the other hand, when the maximum particle size exceeds 50 μm, the expansion rate of the anode active material during charging and discharging of the secondary battery increases significantly, so as charging and discharging are repeated, the inter-particle adhesion of the anode active material and the adhesion between the anode active material particles and the current collector decreases, which can greatly reduce the cycle characteristics.

[0099] Furthermore, the above-mentioned negative electrode active layer may selectively further contain conductive materials, binders, and other additives as needed, along with the carbon-based negative electrode active material, which is the main component.

[0100] The above conductive material may contain, but is not limited to, one or more of the following: carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc.

[0101] As one example, the above-mentioned negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., individually or in combination as conductive materials.

[0102] In this case, the content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent an increase in the resistance of the negative electrode due to a low content of conductive material, which reduces the charging capacity, and can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, which reduces the charging capacity, or a decrease in rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0103] Furthermore, the above-mentioned binder is a component that assists in the bonding of the negative electrode active material to conductive materials and to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the negative electrode. Specifically, it may include one or more selected from the group consisting of vinylidene fluoride hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0104] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the binder content in the negative electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content, or a decrease in the electrical properties of the negative electrode due to an excessive amount of binder.

[0105] Furthermore, the average thickness of the negative electrode active layer may be in the range of 50 μm to 500 μm, specifically in the range of 100 μm to 400 μm, 200 μm to 350 μm, 50 μm to 180 μm, 80 μm to 150 μm, 100 μm to 250 μm, 100 μm to 250 μm, or 130 μm to 190 μm. By adjusting the average thickness of the negative electrode active layer to the above range, the present invention not only enables high adhesion between the negative electrode active layer and the negative electrode current collector, but also enables high energy density of the negative electrode.

[0106] Furthermore, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, and calcined carbon can be used, and in the case of copper or stainless steel, those with surface treatment with carbon, nickel, titanium, silver, etc. can be used. The average thickness of the negative electrode current collector can be appropriately applied from 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0107] Furthermore, the separation membrane interposed between the positive and negative electrodes is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry, but specifically, it can contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, or polyethylene-propylene copolymer. The above separation membrane can have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above polymer, and in some cases, it may have the form of a composite separation membrane in which organic or inorganic particles are coated with an organic binder on the above porous polymer substrate. The above separation membrane may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0108] On the other hand, the electrode assembly according to the present invention is not particularly limited, but can have a stacked type; a zigzag type; or a zigzag-stacked type configuration. The above electrode assembly has the advantage of being highly usable in terms of energy density because it can be packed at high density within a limited space by having the above configuration.

[0109] The electrode assembly for lithium secondary batteries according to the present invention, having the above-described configuration, is not only highly safe and has high energy density, but also features excellent rate characteristics and charge / discharge capacity.

[0110] <Manufacturing method for positive electrode> Furthermore, the present invention provides a method for manufacturing a positive electrode according to the present invention as described above.

[0111] Specifically, the above method for manufacturing a positive electrode includes the steps of applying a positive electrode slurry to at least one surface of a positive electrode current collector and drying the applied positive electrode slurry to form a positive electrode active layer.

[0112] Here, the application of the positive electrode slurry refers to the process of coating the surface of a moving positive electrode current collector by discharging a positive electrode slurry containing a carbon-based negative electrode active material. This process can be applied without particular limitation as long as it is a method commonly used in the industry, but a die coating method is preferably used. The die coating method can be performed via a slot die equipped with a shim for controlling the discharge conditions of the positive electrode slurry. In this case, by controlling the shape, position, etc., of the shim, the loading amount and coating thickness of the positive electrode slurry applied to the positive electrode current collector can be easily controlled.

[0113] Furthermore, the above-mentioned positive electrode slurry is for forming the positive electrode active layer of the positive electrode. Therefore, the above-mentioned positive electrode slurry mainly contains positive electrode active material and may further contain conductive materials, binders, etc., as needed. Here, the composition of the first positive electrode active material, second positive electrode active material, conductive material, binder, etc. contained in the positive electrode slurry is the same as that of the positive electrode active layer of the lithium secondary battery positive electrode described above, so a detailed explanation is omitted.

[0114] Furthermore, the positive electrode slurry can be manufactured by a predetermined process. Specifically, the positive electrode slurry may contain a binder, in which case it can be manufactured by the steps of: manufacturing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed; and manufacturing a positive electrode slurry by mixing a first positive electrode active material and a second positive electrode active material into the manufactured mixed dispersion.

[0115] Carbon-based and metal-based conductive materials exist in powder form and are very fine in size. Therefore, when these conductive materials are mixed with an excess amount of positive electrode active material for the production of a positive electrode slurry, they may aggregate rather than be uniformly dispersed in the slurry. In this case, the positive electrode produced using the above-mentioned slurry may exhibit uniform conductivity in the positive electrode active layer, potentially leading to a decrease in its electrical properties.

[0116] Therefore, the present invention overcomes the problem of aggregation of conductive materials in the positive electrode slurry by producing a dispersion in which a carbon-based conductive material and a metal-based conductive material are dispersed together with a binder during the production of the positive electrode slurry, and by mixing the produced dispersion at the time when the first positive electrode active material and the second positive electrode active material are added to a non-aqueous organic solvent.

[0117] On the other hand, the above method for manufacturing a positive electrode may include a step of forming a positive electrode active layer from the coated positive electrode slurry. The step of forming the positive electrode active layer may mean a step of drying the positive electrode slurry. In this case, the drying of the positive electrode slurry can be applied without particular limitation as long as it is a method that can be commonly applied in the industry. For example, the drying can be performed by applying thermal energy to the positive electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0118] Furthermore, the manufacturing method according to the present invention may further include a step of rolling the positive electrode active layer formed by drying the positive electrode slurry. The rolling refers to a process of increasing the overall density of the positive electrode active layer by applying pressure to the surface of the formed positive electrode active layer using a roll press or the like. For this purpose, the rolling can be carried out under predetermined pressure and speed conditions under a temperature higher than room temperature.

[0119] Specifically, the rolling described above can be carried out at temperatures in the range of 50°C to 100°C, more specifically, in the ranges of 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C.

[0120] Furthermore, the rolling described above can be carried out at rolling speeds in the range of 2 m / s to 7 m / s, more specifically, at rolling speeds in the range of 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s.

[0121] Furthermore, the rolling described above can be carried out under pressure conditions ranging from 50 MPa to 200 MPa, specifically under pressure conditions ranging from 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0122] The present invention makes it possible to maximize the energy density of the positive electrode active layer while minimizing damage to the positive electrode active layer formed by rolling under the above temperature, speed, and / or pressure conditions.

[0123] The present invention will be described in more detail below with reference to examples and comparative examples.

[0124] However, the following examples and comparative examples are illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0125] <Examples 1-4 and Comparative Examples 1-2. Manufacturing of Cathodes for Lithium Secondary Batteries> N-methylpyrrolidone solvent is injected into a homo mixer, and the first positive electrode active material (PEM) is added. 1st ) as LiNi 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as "NCM", average particle size: approximately 3 μm), second positive electrode active material (PEM) 2ndLiFePO4 (hereinafter referred to as "LFP," average particle size: approximately 1.3 μm), carbon-based conductive material (CCM), metallic conductive material (MCM), and polyvinylidene fluoride (PVDF) as a binder were added. The mixture was then mixed at 3,000 rpm for 60 minutes to prepare the positive electrode slurry. At this time, the carbon-based conductive material (CCM) used was the material shown in Table 1 below, and silver (Ag) nanowires were used as the metallic conductive material (MCM). The positive electrode slurry was mixed to contain 96 parts by weight of positive electrode active material, 1.5 parts by weight of conductive material, and 2.5 parts by weight of binder, based on solid content. The first positive electrode active material and the second positive electrode active material contained in the positive electrode active material were contained in amounts of 64 parts by weight and 32 parts by weight, respectively, and the content ratio of carbon-based conductive material to metallic conductive material (CCM:MCM) contained in the conductive material was adjusted as shown in Table 1.

[0126] A thin aluminum sheet (average thickness: 12 μm) was prepared as the positive electrode current collector, and the previously manufactured positive electrode slurry was cast onto the prepared aluminum sheet. After drying the aluminum sheet with the cast positive electrode slurry in a vacuum oven at 130°C, the positive electrode was manufactured by rolling. At this time, the total thickness of the rolled positive electrode composite layer was 150 μm.

[0127] [Table 1]

[0128] <Examples 5-8 and Comparative Examples 3-4: Manufacturing of Electrode Assemblies and Secondary Batteries> A negative electrode active material was prepared by mixing natural graphite and artificial graphite in a 1:1 weight ratio. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a negative electrode slurry, which was then cast onto a copper sheet that would serve as the negative electrode current collector. The copper sheet with the cast negative electrode slurry was dried in a vacuum oven at 130°C and rolled to produce the negative electrode. At this time, the thickness of the negative electrode composite layer was 130 μm.

[0129] As shown in Table 2 below, the manufactured negative electrode was placed opposite the positive electrodes prepared in Examples 1-4 and Comparative Examples 1-2, respectively, with an 18 μm polypropylene separator interposed between them to create an electrode assembly. Each manufactured electrode assembly was inserted into a battery case, and after injecting the electrolyte composition into the battery case, the case was sealed to produce a lithium secondary battery. In this case, the electrolyte composition used was a solution prepared by mixing ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) = 1:1:1 (volume ratio) with lithium hexafluorophosphate (LiPF6, 1.0 M) and vinylene carbonate (VC, 2 wt%).

[0130] [Table 2]

[0131] <Example of experiment> The following experiment was conducted to evaluate the performance of the positive electrode according to the present invention.

[0132] First, the lithium secondary batteries produced in Examples 5-8 and Comparative Examples 3-4 were each charged at 25°C at a rate of 0.3C to 4.2V under CC-CV conditions, and then discharged at a rate of 0.3C to 2.5V under CC conditions to be activated.

[0133] Each activated lithium secondary battery was subjected to constant current / constant voltage (CC / CV charge) charging at a temperature of 25°C, and its initial charge capacity was measured. The charging was performed using a constant current at a rate of 0.1C until the voltage reached 4.2V, and then cut-off using a constant voltage mode at a rate of 0.005C to maintain 4.2V. Each charged secondary battery was then subjected to constant current discharge (CC discharge), and its initial discharge capacity was measured. This constant current discharge was performed at a rate of 1.0C until the voltage reached 1.5V.

[0134] Subsequently, each lithium secondary battery was fully charged at 25°C with a charging current of 2.0C rate to a charging termination voltage of 4.2 to 4.25V, and the charging capacity was measured. From the measured charging capacity, the ratio of the relative charging capacity relative to the initial charging capacity was calculated to evaluate the high-rate charging characteristics of each lithium secondary battery. Then, the lithium secondary battery was discharged at 0.2C intervals in the range of 1.0C rate to 2.0C rate, and the discharge capacity was measured. From the measured discharge capacity, the ratio of the relative discharge capacity relative to the initial discharge capacity for each discharge rate was calculated to evaluate the high-rate discharge characteristics of each lithium secondary battery. The measured results are shown in Table 3.

[0135] [Table 3]

[0136] As shown in Table 3 above, the positive electrode for lithium secondary batteries according to the present invention has a large charge / discharge capacity and excellent rate characteristics.

[0137] Specifically, the lithium secondary battery in the example had a large charging capacity of 463 mAh / g or more, and exhibited excellent high-rate charge and discharge characteristics of 87% or more and 85% or more, respectively, during high-rate charging and discharging under 2C rate conditions.

[0138] This means that even when the positive electrode active material contains two metal oxides with different crystal structures, or when it contains both a carbon-based negative electrode active material and a metal-based negative electrode active material, the difference in kinetic characteristics exhibited by each positive electrode active material can be minimized.

[0139] These results show that the positive electrode for lithium secondary batteries according to the present invention exhibits excellent charge-discharge rate characteristics and capacity characteristics.

[0140] While preferred embodiments of the present invention have been described above with reference to those skilled in the art or those with ordinary knowledge in the art, it will be understood that the present invention can be modified and altered in various ways without departing from the technical scope of the invention as described in the claims below.

[0141] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in the specification, but can be defined by the claims.

Claims

1. Positive electrode current collector, and The positive electrode current collector includes a positive electrode active layer provided on at least one surface of the positive electrode current collector, The positive electrode active layer comprises a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metallic conductive material. The first positive electrode active material and the second positive electrode active material each contain one or more of the following: a layered metal oxide represented by the following chemical formula 1, a spinel metal oxide represented by the following chemical formula 2, and an olivine metal oxide represented by the following chemical formula 3, and each contains metal oxides with different structures from each other. The aforementioned metallic conductive material has a nanowire structure, [Chemical formula 1] Li ａ [Ni ｂ Co １－ｂ－ｃ M １ ｃ ]O ２ [Chemical formula 2] Li ｐ [Mn] ２－ｑ M ２ ｑ ]O ４ [Chemical formula 3] LiFe １－ｘ M ３ ｘ XO ４ In the aforementioned chemical formulas 1 to 3, M １ is one or more elements from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M ２ is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M ３ is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. a, b, c, p, q, and x are the positive poles such that 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

2. The first positive electrode active material comprises one or more of the layered metal oxides and the spinel metal oxides, The positive electrode according to claim 1, wherein the second positive electrode active material comprises a metal oxide having the olivine structure.

3. The positive electrode according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are contained in a weight ratio in the range of 5:95 to 95:

5.

4. The positive electrode according to claim 1, wherein the metallic conductive material is a nanowire having an average length in the range of 0.5 μm to 900 μm and an average diameter in the range of 1 nm to 500 nm.

5. The positive electrode according to claim 1, wherein the metallic conductive material comprises one or more metallic elements selected from silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), iron (Fe), and stainless steel (SUS).

6. The positive electrode according to claim 1, wherein the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode active layer, and the total content thereof is 10% by weight or less based on the total weight of the positive electrode active layer.

7. The carbon-based conductive material is included in an amount of 0.1% to 10% by weight relative to the total weight of the first positive electrode active material. The positive electrode according to claim 1, wherein the metallic conductive material is included in an amount of 0.1% to 10% by weight relative to the total weight of the second positive electrode active material.

8. The positive electrode according to claim 1, wherein the carbon-based conductive material comprises one or more of acetylene black, denka black, ketjen black, super p, channel black, furnace black, lamp black, thermal black, graphene, carbon nanotubes, and carbon fibers.

9. The carbon-based conductive material has an average particle size (D) in the range of 0.5 μm to 5 μm. ５０ The positive electrode according to claim 1, having )

10. An electrode assembly for a secondary battery, comprising a positive electrode, a negative electrode, and a separation membrane provided between the positive electrode and the negative electrode, as described in claim 1.

11. The steps include: applying a positive electrode slurry to at least one surface of the positive electrode current collector, and The process includes the step of drying the coated positive electrode slurry to form a positive electrode active layer, The positive electrode slurry comprises a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metallic conductive material. The first positive electrode active material and the second positive electrode active material each contain one or more of the following: a layered metal oxide represented by the following chemical formula 1, a spinel metal oxide represented by the following chemical formula 2, and an olivine metal oxide represented by the following chemical formula 3, and each contains metal oxides with different structures from each other. The aforementioned metallic conductive material has a nanowire structure, [Chemical formula 1] Li ａ [Ni ｂ Co １－ｂ－ｃ M １ ｃ ]O ２ [Chemical formula 2] Li ｐ [Mn] ２－ｑ M ２ ｑ ]O ４ [Chemical formula 3] LiFe １－ｘ M ３ ｘ XO ４ In the aforementioned chemical formulas 1 to 3, M １ is one or more elements from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M ２ is one or more elements from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. M ３ is one or more elements from W, Cu, Fe, V, Cr, Ni, Co, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo. X is one or more elements from P, Si, S, As, and Sb. The method for manufacturing a positive electrode according to claim 1, wherein a, b, c, p, q, and x are 1.0 ≤ a ≤ 1.30, 0 ≤ b < 1, 0 ≤ c ≤ 0.4, 1.0 ≤ p ≤ 1.30, 0 ≤ q ≤ 1.0, and 0 ≤ x ≤ 0.8, respectively.

12. The method for manufacturing a positive electrode according to claim 11, wherein the positive electrode slurry further comprises a binder.

13. The positive electrode slurry is A step of producing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed, The steps include: mixing a first positive electrode active material and a second positive electrode active material into the manufactured mixed dispersion to produce a positive electrode slurry; A method for manufacturing a positive electrode according to claim 12, which is produced by the method described above.

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