Cathode for lithium secondary battery and manufacturing method therefor

Abstract

The present invention relates to a cathode and a manufacturing method therefor. The cathode comprises, as a first cathode active material and a second cathode active material, two or more types of metal oxides having different crystal structures from each other, and comprises, as a conductive material, a carbon-based conductive material and a metal-based conductive material. Accordingly, since the cathode can minimize different kinetic characteristic deviations exhibited by each cathode active material, a lithium secondary battery including the cathode has advantages of excellent rate characteristics and capacity characteristics during charging and discharging.

Description

Cathode for lithium secondary battery and method for manufacturing same

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

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0069710, dated May 29, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are now widely used not only in small devices like portable electronic devices, but also in medium- to large-sized devices like battery packs for hybrid and electric vehicles and power storage systems. In particular, with growing concern over environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles as alternatives to fossil fuel-powered vehicles like gasoline and diesel, which are major contributors to air pollution.

[0005] Typically, lithium secondary batteries have an electrode assembly structure comprising a positive electrode, a negative electrode, and a separator, each of which is impregnated with a lithium electrolyte. 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 imparting electrical conductivity, and a binder for adhering the electrode active material to the current collector and providing bonding strength between the electrode active material and the current collector, in a solvent such as NMP (N-methyl pyrrolidone).

[0006] The cathode can be a lithium-ion battery such as LCO (LiCoO2), LMO (LiMn2O4), LFP (LiFePO4), or NCM (LiNi) that can reversibly insert or de-insert lithium. 1 / 3 Co 1 / 3 Mn 1 / 3 It includes metal oxides such as O2 as positive electrode active materials.

[0007] Among these, NCM, LCO, and NCA compounds with layered crystal structures facilitate lithium ion storage and exhibit high lithium ion diffusion rates, making them suitable as cathode active materials for high-capacity / high-power secondary batteries. However, compounds with layered crystal structures exhibit poor chemical and structural stability, making them prone to decomposition under high-temperature conditions. This reduces the safety of secondary batteries.

[0008] On the other hand, LFP compounds with an olivine crystal structure have a hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded, and exhibit 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 the crystal structure does not easily decompose even under high-temperature conditions. However, compounds with an olivine crystal structure have a low energy density, which indicates the amount of energy that a battery can store per unit weight / volume. Therefore, in order for compounds with an olivine crystal structure to realize high energy density, the weight / volume of the cathode active material must be increased, which has the limitation that the size or weight of the secondary battery must increase excessively.

[0009] Accordingly, in order to maintain the high safety of conventional secondary batteries while increasing the capacity of the secondary batteries, attempts have been made to use a mixture of a compound having a layered crystal structure and a compound having an olivine crystal structure as a cathode active material. However, cathode active materials with a layered crystal structure and cathode active materials with an olivine crystal structure have different electromotive forces. In general, the electromotive force of the cathode active material affects the operating voltage during charge and discharge of the cathode. When manufacturing a cathode by mixing cathode active materials with different electromotive forces, the electromotive force deviation of the cathode active materials causes different kinetic patterns during charge and discharge of the secondary battery. In other words, a reaction bias phenomenon occurs in which a compound with a lower electromotive force among the mixed cathode active materials reacts more preferentially depending on the state of charge (SOC) of the secondary battery during charge and discharge. This reaction bias phenomenon prevents the rate characteristics and charge and discharge capacity characteristics of the cathode from being fully expressed, which limits the low charge and discharge performance of the secondary battery.

[0010] Therefore, in order to realize high safety and energy density of secondary batteries, there is a need for technology development for a lithium secondary battery cathode that includes two types of cathode active materials with different crystal structures while also having excellent rate characteristics and charge / discharge capacity characteristics.

[0011]

[0012] [Prior Art Literature]

[0013] Republic of Korea Patent Publication No. 10-2013-0136796

[0014]

[0015] The purpose of the present invention is to provide a positive electrode for a lithium secondary battery having excellent rate characteristics and charge / discharge capacity characteristics while including two types of positive electrode active materials having different crystal structures, and a method for manufacturing the same.

[0016]

[0017] To solve the above-mentioned problem,

[0018] The present invention,

[0019] anode current collector, and

[0020] Comprising a positive electrode active layer provided on at least one surface of the positive electrode current collector;

[0021] The above positive electrode active layer includes a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metal-based conductive material;

[0022] The first cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides having different structures;

[0023] The above metal-based conductive material provides an anode characterized by having a nanowire structure:

[0024] [Chemical Formula 1]

[0025] Li a [Ni b Co 1-b-c M 1 c ]O2

[0026] [Chemical Formula 2]

[0027] Li p [Mn 2-q M 2 q ]O4

[0028] [Chemical Formula 3]

[0029] LiFe 1-x M 3 x XO4

[0030] In the above chemical formulas 1 to 3,

[0031] M 1is at least one element among 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,

[0032] M 2 is at least one element among 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,

[0033] M 3 is at least one element among 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,

[0034] X is one or more of the elements P, Si, S, As, and Sb, and

[0035] 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.

[0036]

[0037] At this time, the first cathode active material may include at least one of a metal oxide having a layered structure and a metal oxide having a spinel structure, and the second cathode active material may include a metal oxide having an olivine structure.

[0038] Additionally, the first cathode active material and the second cathode active material may be included in a weight ratio ranging from 5:95 to 95:5.

[0039] Additionally, the metal-based 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.

[0040] In addition, the metal-based conductive material may include one or more metal elements selected from silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), iron (Fe), and stainless steel (SUS).

[0041] In addition, the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1 to 10 wt% based on the total weight of the positive electrode active layer, but the total content thereof may be 10 wt% or less based on the total weight of the positive electrode active layer.

[0042] Additionally, the carbon-based conductive material may be included in an amount of 0.1 wt% to 10 wt% based on the total weight of the first cathode active material, and the metal-based conductive material may be included in an amount of 0.1 wt% to 10 wt% based on the total weight of the second cathode active material.

[0043] Meanwhile, the carbon-based conductive material may include at least one of acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, carbon nanotubes, and carbon fibers.

[0044] In addition, the carbon-based conductive material has an average particle diameter (D) in the range of 0.5 μm to 5 μm. 50 ) can have.

[0045]

[0046] In addition, the present invention,

[0047] An electrode assembly for a secondary battery is provided, including a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode according to the present invention described above.

[0048]

[0049] Furthermore, the present invention,

[0050] A step of applying a cathode slurry to at least one surface of a cathode current collector, and

[0051] A step of drying the applied positive electrode slurry to form a positive electrode active layer;

[0052] The above positive electrode slurry includes a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metal-based conductive material;

[0053] The first cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides having different structures;

[0054] The above-described method for manufacturing the anode is provided, characterized in that the metal-based conductive material has a nanowire structure.

[0055] [Chemical Formula 1]

[0056] Li a [Ni b Co 1-b-c M 1 c ]O2

[0057] [Chemical Formula 2]

[0058] Li p [Mn 2-q M 2 q ]O4

[0059] [Chemical Formula 3]

[0060] LiFe 1-x M 3 x XO4

[0061] In the above chemical formulas 1 to 3,

[0062] M 1 is at least one element among 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,

[0063] M 2is at least one element among 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,

[0064] M 3 is at least one element among 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,

[0065] X is one or more of the elements P, Si, S, As, and Sb, and

[0066] 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.

[0067]

[0068] Here, the positive electrode slurry may further include a binder.

[0069] Additionally, the above positive electrode slurry can be manufactured by the following process:

[0070] A step of preparing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed; and

[0071] A step of preparing a cathode slurry by mixing a first cathode active material and a second cathode active material into the prepared mixed dispersion.

[0072]

[0073] The positive electrode according to the present invention includes a carbon-based conductive material and a gold-based conductive material as conductive materials in the positive electrode active layer, and even if it includes two or more types of metal oxides having different crystal structures as the first positive electrode active material and the second positive electrode active material, it can minimize the difference in kinetic characteristics between the positive electrode active materials, so that a secondary battery including the same has the advantage of excellent rate characteristics and capacity characteristics during charge and discharge.

[0074]

[0075] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0076] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0077] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0078] Also, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called the median diameter. The above average particle diameter can be measured by a method commonly applied in the art. For example, the above average particle diameter can be measured using a particle size analyzer or an analysis device using a laser diffraction scattering particle size distribution measurement method, but is not limited thereto.

[0079]

[0080] Hereinafter, the present invention will be described in more detail.

[0081]

[0082] anode

[0083] The present invention,

[0084] anode current collector, and

[0085] Comprising a positive electrode active layer provided on at least one surface of the positive electrode current collector;

[0086] The above positive electrode active layer includes a first positive electrode active material, a second positive electrode active material, a carbon-based conductive material, and a metal-based conductive material;

[0087] The first cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides that are different from each other;

[0088] The above metal-based conductive material provides an anode characterized by having a nanowire structure:

[0089] [Chemical Formula 1]

[0090] Li a [Ni b Co 1-b-c M 1 c ]O2

[0091] [Chemical Formula 2]

[0092] Li p [Mn 1-q M 2 q ]O2

[0093] [Chemical Formula 3]

[0094] LiFe 1-x M 3 x XO4

[0095] In the above chemical formulas 1 to 3,

[0096] M 1 is at least one element among 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,

[0097] M 2is at least one element among 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,

[0098] M 3 is at least one element among 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,

[0099] X is one or more of the elements P, Si, S, As, and Sb, and

[0100] 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≤0.5, and 0≤x≤0.8, respectively.

[0101]

[0102] The positive electrode according to the present invention may refer to a positive electrode for a secondary battery, and particularly, to 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 implements electrical activity of the positive electrode, and includes a positive electrode active material that implements an electrochemical redox reaction during charge and discharge of the battery as a main component. Specifically, the positive electrode active material may be included in an amount of 80 parts by weight to 99.8 parts by weight based on 100 parts by weight of the total positive electrode active layer, and specifically, may be included in an amount of 95 parts by weight or more, 98 parts by weight or more, 84 parts by weight to 99.8 parts by weight, 90 parts by weight to 99.8 parts by weight, 94 parts by weight to 99.8 parts by weight, 88 parts by weight to 96 parts by weight, or 92 parts by weight to 97.5 parts by weight.

[0103] In addition, the cathode active material includes a first cathode active material and a second cathode active material, which may include metal oxides having different crystal structures. Specifically, the first cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides having different crystal structures:

[0104] [Chemical Formula 1]

[0105] Li a [Ni b Co 1-b-c M 1 c ]O2

[0106] [Chemical Formula 2]

[0107] Li p [Mn 2-q M 2 q ]O4

[0108] [Chemical Formula 3]

[0109] LiFe 1-x M 3 x XO4

[0110] In the above chemical formulas 1 to 3,

[0111] M 1 is at least one element among 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,

[0112] M 2 is at least one element among 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,

[0113] M 3is at least one element among 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,

[0114] X is one or more of the elements P, Si, S, As, and Sb, and

[0115] 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.

[0116]

[0117] Generally, the cathode active materials used in the cathode for lithium secondary batteries are metal oxides represented by the chemical formulas 1 to 3.

[0118] Among these, the metal oxide represented by the above chemical formula 1 is a compound with a layered crystal structure. It facilitates lithium ion storage and has a high lithium ion diffusion rate, making it suitable for use as a cathode active material in high-capacity / high-power secondary batteries. However, compounds with a layered crystal structure have low chemical and structural stability, making them prone to decomposition under high-temperature conditions. This reduces the safety of secondary batteries.

[0119] In addition, the metal oxide represented by the above chemical formula 2 has a spinel crystal structure that is easily observed in general metal oxides. The spinel crystal structure has excellent characteristics of output because it contains various three-dimensional passages within it, making it easy for lithium ions to be inserted. However, compared to the metal oxide with the layered crystal structure, it has the characteristic of relatively high structural stability, but has the limitation of causing side reactions such as dissolution in the electrolyte at high temperatures of 60°C or higher.

[0120] In contrast, the LFP compound having the olivine crystal structure represented by the above chemical formula 3 has a hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded, and thus exhibits high structural stability. Therefore, the compound having the olivine crystal structure can easily maintain its crystal structure even when all lithium ions are desorbed during charging, and the crystal structure does not easily decompose even under high-temperature conditions. However, the compound having the olivine crystal structure has a low energy density, which indicates the amount of energy that a battery can store per unit weight / volume. Therefore, in order for the compound having the olivine crystal structure to realize high energy density, the weight / volume of the positive electrode active material must be increased, which has the limitation that the size or weight of the secondary battery must increase excessively.

[0121] Accordingly, the present invention comprises a first cathode active material and a second cathode active material in the cathode active layer, wherein the first cathode active material and the second cathode active material include metal oxides having different crystal structures. Accordingly, the safety and electrical performance of the cathode can be further improved by complementing or alleviating the limitations of the metal oxides having different crystal structures.

[0122] Specifically, the first cathode active material may include at least one of a metal oxide having a layered structure and a metal oxide having a spinel structure, and the second cathode active material may include a metal oxide having an olivine structure.

[0123] For example, the first cathode active material may include a metal oxide having a layered structure, and the second cathode active material may include a metal oxide having an olivine structure.

[0124] Additionally, the first cathode active material may include a metal oxide having a spinel structure, and the second cathode active material may include a metal oxide having an olivine structure.

[0125] Here, the metal oxide having a layered structure represented by the chemical formula 1 is a metal oxide containing nickel (Ni) and / or cobalt (Co) together with lithium, and in some cases, another transition metal (M 1 ) may have a doped form. For example, the metal oxide may 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 0.2 Al 0.15 Zr 0.05 )O2 and Li(Ni 0.7 Co 0.1 Al 0.1 Zr 0.1) may contain one or more types of O2.

[0126] In addition, the metal oxide of the spinel structure represented by the above chemical formula 2 is a metal oxide containing manganese (Mn), and in some cases, another transition metal (M 2 ) may have a doped form. For example, the 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 O4.

[0127] In addition, the metal oxide of the olivine structure represented by the above chemical formula 3 is a phosphate containing iron (Fe) among transition metals, and in some cases, another transition metal (M 3 ) may 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 May include PO4, etc.

[0128] In addition, the first cathode active material and the second cathode active material may be included in the cathode active layer at a predetermined content ratio. The performance of the cathode may vary depending on the content of the cathode active material included in the cathode active layer. Accordingly, the present invention may include the first cathode active material and the second cathode active material included in the cathode active layer at a predetermined content ratio. Specifically, the first cathode active material and the second cathode active material may be included at a weight ratio in the range of 5:95 to 95:5 (i.e., 5 to 95 parts by weight: 95 to 5 parts by weight). Specifically, the first cathode active material and the second cathode active material have a weight ratio of 10:90 to 90:10 (i.e., 10 to 90 parts by weight: 90 to 10 parts by weight), a weight ratio of 20:80 to 80:20 (i.e., 20 to 80 parts by weight: 80 to 20 parts by weight), a weight ratio of 25:75 to 75:25 (i.e., 25 to 75 parts by weight: 75 to 25 parts by weight), a weight ratio of 30:70 to 70:30 (i.e., 30 to 70 parts by weight: 70 to 30 parts by weight), a weight ratio of 35:65 to 65:35 (i.e., 35 to 65 parts by weight: 65 to 35 parts by weight), a weight ratio of 40:60 to 70:30 (i.e., 40 to 70 parts by weight: 60 to 30 parts by weight), and a weight ratio of 50:50 to 95:5. It can be included in a weight ratio of 50 to 95 parts by weight:50 to 5 parts by weight, a weight ratio of 50:50 to 85:15 (i.e., 50 to 85 parts by weight:15 to 50 parts by weight), a weight ratio of 50:50 to 75:25 (i.e., 50 to 75 parts by weight:25 to 50 parts by weight).

[0129] The present invention can improve the safety of a battery while achieving high electrical performance by controlling the content ratio of the first cathode active material and the second cathode active material included in the cathode active layer within the above-described range. Specifically, the present invention can minimize the decomposition of the cathode active material or the occurrence of a side reaction with the electrolyte when the cathode active layer is exposed to a high temperature environment by maintaining the content ratio of the second cathode active material equal to or higher than the lower limit of the above-described range. In addition, the present invention can improve the output during discharge while achieving high charge / discharge capacity and energy density of the cathode by maintaining the content ratio of the second cathode active material equal to or lower than the upper limit of the above-described range.

[0130] Furthermore, when two or more types of metal oxides having different crystal structures are included as cathode active materials in the cathode active layer as in the present invention, problems of the metal oxides can be supplemented or alleviated, and thus the cathode including the same can further improve safety and electrical performance. However, metal oxides having different crystal structures have different electromotive forces. In general, the electromotive force of the cathode active material affects the operating voltage during charge and discharge of the cathode. When the cathode is manufactured by mixing cathode active materials having different electromotive forces, different kinetic patterns are exhibited during charge and discharge of the secondary battery due to the deviation in the electromotive forces of the cathode active materials. That is, when charging and discharging, a reaction bias phenomenon occurs in which a compound having a lower electromotive force among the mixed cathode active materials reacts more preferentially depending on the state of charge (SOC) of the secondary battery. The reaction bias phenomenon prevents the rate characteristics and charge and discharge capacity characteristics of the cathode from being sufficiently expressed, and thus there is a limitation in that the charge and discharge performance of the secondary battery is low.

[0131] Accordingly, the present invention is characterized by using a carbon-based conductive material and a metal-based conductive material having a nanowire structure in combination in a positive electrode active layer. The metal-based conductive material has a nanowire structure, thereby forming a three-dimensional network within the positive electrode active layer, thereby further improving the electrical conductivity of the positive electrode active layer. In addition, the metal-based conductive material can have a relatively high electromotive force compared to carbon-based conductive materials such as carbon black, graphene, and carbon nanotubes (CNTs). Therefore, the metal-based conductive material can perform a function of alleviating or improving a reaction bias phenomenon caused by an electromotive force difference between a first positive electrode active material and a second positive electrode active material.

[0132] Here, the nanowire structure of the metal-based conductive material may refer to a wire structure composed of a metal having a size on the nanometer scale. The size at this time is not particularly limited as long as it is a wire structure having a diameter of several hundred nanometers (nm). Specifically, the metal-based 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.

[0133] More specifically, the metal-based conductive material has an average length of 0.5 µm to 900 µm; 0.5 µm to 750 µm; 0.5 µm to 500 µm; 0.5 µm to 300 µm; 0.5 µm to 250 µm; 0.5 µm to 100 µm; 0.5 µm to 50 µm; 0.5 µm to 30 µm; 0.5 µm to 20 µm; 0.5 µm to 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 it may be in the range of 0.8㎛ to 1.1㎛.

[0134] In addition, the metal conductive material may have an average diameter in a range of 1 nm to 400 nm; 1 nm to 300 nm; 1 nm to 200 nm; 50 nm to 200 nm; 100 nm to 300 nm; 250 nm to 500 nm; 300 nm to 400 nm; 1 nm to 100 nm; 1 nm to 50 nm; 1 nm to 20 nm; 1 nm to 15 nm; 1 nm to 10 nm; 5 nm to 10 nm; 10 nm to 30 nm; 11 nm to 50 nm; or 8 nm to 12 nm. The average length and average diameter of the metal conductive material may be measured by an analysis device capable of analyzing a two-dimensional projection image of particles, such as a scanning electron microscope (SEM), but is not limited thereto.

[0135] The present invention can easily form a conductive network even when included in a positive electrode active layer with a significantly small content by controlling the size of the metal-based conductive material to satisfy the above-described average length range and average diameter range, thereby realizing high charge / discharge capacity and energy density of the positive electrode.

[0136] In addition, the metal-based conductive material may be composed of a metal having excellent electrical conductivity. For example, the metal-based conductive material may include a pure metal such as silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), iron (Fe), or stainless steel (SUS), alone or in combination of two or more thereof. The materials having high electrical conductivity are excellent in increasing the conductivity of the positive electrode active layer during charging and discharging of the secondary battery. In addition, the materials are excellent in reducing the electromotive force deviation between the first positive electrode active material and the second positive electrode active material. Accordingly, when the materials are applied to the positive electrode active layer as a metal-based conductive material together with a carbon-based conductive material, they can improve the reaction bias phenomenon within the positive electrode, and thus have excellent effects in improving the rate characteristics and charge and discharge capacity characteristics.

[0137] In addition, the conductive material included in the positive electrode active layer may have a predetermined content range.

[0138] Specifically, the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1 to 10 wt% based on the total weight of the positive electrode active layer, and the total content thereof may be 10 wt% or less based on the total weight of the positive electrode active layer.

[0139] For example, the carbon-based conductive agent and the metal-based conductive agent may each be 0.1 to 10 wt% based on the total weight of the positive electrode active layer, specifically, 0.1 to 8 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 2 to 6 wt%, or 0.5 to 2 wt%. In addition, the total content of the carbon-based conductive agent and the metal-based conductive agent may be 10 wt% or less based on the total weight of the positive electrode active layer, specifically, 0.1 to 8 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 2 to 6 wt%, or 0.5 to 2 wt%.

[0140] The present invention can prevent a decrease in charge capacity due to an increase in resistance of the positive electrode caused by a low content of the conductive material by controlling the content of the conductive material within the above range, and can prevent a problem in which a decrease in charge capacity due to a decrease in the content of the positive electrode active material caused by an excessive amount of the conductive material or a decrease in rapid charge characteristics due to an increase in the loading amount of the positive electrode active layer.

[0141] In addition, the carbon-based conductive material and the metal-based conductive material may be affected by the content of the positive electrode active material included 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 metal-based conductive material may depend on the content of the second positive electrode active material. For example, the carbon-based conductive material may be included in an amount of 0.1 wt% to 10 wt% based on the total weight of the first positive electrode active material, and the metal-based conductive material may be included in an amount of 0.1 wt% to 10 wt% based on the total weight of the second positive electrode active material. In this case, the content ratio of the carbon-based conductive material and the metal-based conductive material may be proportional to the content ratio of the first positive electrode active material and the second positive electrode active material.

[0142] More specifically, the carbon-based conductive material may be present in an amount of 0.1 to 8 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 2 to 6 wt%, or 0.5 to 2 wt% relative to the total weight of the first cathode active material.

[0143] Additionally, the metal-based conductive material may be present in an amount of 0.1 to 8 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 2 to 6 wt%, or 0.5 to 2 wt% relative to the total weight of the second cathode active material.

[0144] The present invention effectively reduces the electromotive force deviation between the first and second cathode active materials by controlling the content of the carbon-based conductive agent and the metal-based conductive agent as described above. Accordingly, the phenomenon of reaction concentration within the cathode during charging and discharging of a secondary battery can be improved, thereby enhancing rate characteristics and charge / discharge capacity characteristics.

[0145] In addition, the carbon-based conductive material is a conductive material with carbon as its main component, and can be applied without particular limitation as long as it is a conductive material commonly used in the art as a conductive material for lithium secondary battery electrodes. Specifically, the carbon-based conductive material may include at least one of carbon black such as acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, and summer black; graphene; carbon nanotubes (CNT); and carbon fibers. For example, the carbon-based conductive material may include carbon nanotubes.

[0146] In addition, the shape of the carbon-based conductive material is not particularly limited, but the size can satisfy a certain range. Specifically, the carbon-based conductive material has an average particle diameter (D) in the range of 0.5 μm to 5 μm. 50 ) may have. More specifically, the carbon-based conductive material may have an average particle diameter (D) in the range of 0.5 µm to 4 µm; 0.5 µm to 3 µm; 0.5 µm to 2.5 µm; 0.5 µm to 2 µm; 0.5 µm to 1.5 µm; 0.5 µm to 1 µm; 0.5 µm to 0.9 µm; 0.8 µm to 1.1 µm; 1.1 µm to 1.5 µm; 0.7 µm to 0.3 µm; or 0.5 µm to 0.8 µm. 50 ) can have.

[0147] The present invention can implement an anode active layer in which a carbon-based conductive material is uniformly dispersed inside by controlling the average particle diameter of the carbon-based conductive material within the above-described range, thereby partially preventing an increase in the electrical resistance of the anode active layer.

[0148] Meanwhile, the positive electrode active layer may optionally further include a binder, other additives, etc., in addition to the positive electrode active material and conductive material as main components.

[0149] The above binder is a component that assists in the bonding of the positive electrode active material and the conductive material and the bonding to the current collector, and can be appropriately applied within a range that does not deteriorate the electrical properties of the positive electrode. Specifically, the binder may include at least one of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0150] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire positive electrode active layer, and specifically, may be 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 content of the binder contained in the positive electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the positive electrode from being lowered due to an excessive amount of binder.

[0151] In addition, the average thickness of the positive electrode active layer may be 50 ㎛ to 500 ㎛, and specifically, 100 ㎛ to 400 ㎛; 200 ㎛ to 350 ㎛; 50 ㎛ to 180 ㎛; 80 ㎛ to 150 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛. The present invention can not only implement high adhesion between the positive electrode active layer and the positive electrode current collector by controlling the average thickness of the positive electrode active layer within the above range, but also implement high energy density of the positive electrode.

[0152] Furthermore, the positive electrode current collector may be one having high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, a surface-treated material such as carbon, nickel, titanium, or silver may also be used. In addition, the average thickness of the positive electrode current collector may be appropriately applied within the range of 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode being manufactured.

[0153]

[0154] The positive electrode according to the present invention has the above-described configuration, and thus, even if it includes two or more types of metal oxides having different crystal structures as the first positive electrode active material and the second positive electrode active material, the deviation in kinetic characteristics between the positive electrode active materials can be minimized, and therefore, a secondary battery including the same has the advantage of excellent rate characteristics and capacity characteristics during charge and discharge.

[0155]

[0156] Electrode assembly for secondary batteries

[0157] In addition, the present invention,

[0158] The present invention provides an electrode assembly for a secondary battery including a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode.

[0159]

[0160] An electrode assembly for a secondary battery according to the present invention includes a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode, wherein the positive electrode has a configuration as the positive electrode of the present invention described above.

[0161] The above electrode assembly, as an anode, includes the anode of the present invention described above and has excellent safety, high energy density, and excellent rate characteristics and charge / discharge capacity.

[0162] Since the anode included in the above electrode assembly has the same configuration as that described above, a detailed description thereof is omitted.

[0163] Meanwhile, 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 implements electrical activity of the negative electrode, and includes as a main component a negative electrode active material that implements an electrochemical redox reaction during charging and discharging of the battery.

[0164] Here, the negative electrode active material may include a carbon-based negative electrode active material as a main component. Specifically, the carbon-based negative electrode active material may be included in an amount of 80 parts by weight to 99.8 parts by weight based on 100 parts by weight of the total negative electrode active layer, and specifically, may be included in an amount of 95 parts by weight or more, 98 parts by weight or more, 84 parts by weight to 99.8 parts by weight, 90 parts by weight to 99.8 parts by weight, 94 parts by weight to 99.8 parts by weight, 88 parts by weight to 96 parts by weight, or 92 parts by weight to 97.5 parts by weight.

[0165] In addition, the carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and such carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite. For example, the carbon-based negative electrode active material may include natural graphite or artificial graphite alone, and in some cases, may include a mixture of natural graphite and artificial graphite.

[0166] As an example, the carbon-based negative electrode active material may contain natural graphite and artificial graphite in a weight ratio ranging from 5 to 50:50 to 95, 20 to 45:55 to 80, or 30 to 50:50 to 70. In this case, the carbon-based negative electrode active material may strengthen the adhesion between the negative electrode current collector and the negative electrode active layer by containing natural graphite and artificial graphite in the above-mentioned mixing ratio.

[0167] As another example, the carbon-based anode active material may solely comprise artificial graphite. The present invention, by including artificial graphite solely in the anode active layer, significantly improves the lifespan of the anode, which can be advantageous in conditions such as automobile batteries that must withstand frequent charging for extended periods of time. Furthermore, artificial graphite offers the advantages of rapid charging and superior output performance compared to natural graphite.

[0168] In addition, it is preferable that the carbon-based negative electrode active material is a spherical graphite secondary particle formed by aggregating a plurality of graphite primary particles having a flake shape. Examples of the flake graphite include, in addition to natural graphite and artificial graphite, mesophase calcined carbon (bulk mesophase) using tar and pitch as raw materials, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), and in particular, one assembled using a plurality of highly crystalline artificial graphites is preferable. In addition, one graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, flake-shaped graphite particles.

[0169] At this time, the average particle diameter (D) of the secondary particles 50 ) may range from 1 μm to 50 μm. Specifically, the average particle diameter (D) of the secondary particles 50) has an average particle diameter (D) in the range of 1 µm to 40 µm; 1 µm to 30 µm; 10 µm to 40 µm; 15 µm to 30 µm; 25 µm to 50 µm; 11 µm to 19 µm; 15 µm to 25 µm; 20 µm to 30 µm; 1 µm to 20 µm; 1 µm to 10 µm; 5 µm to 15 µm; 10 µm to 20 µm; 15 µm to 30 µm; 15 µm to 20 µm; 21 µm to 26 µm; 25 µm to 30 µm; 11 µm to 17 µm; 16 µm to 23 µm; 2 µm to 7 µm; 0.5 µm to 5 µm; or 1 µm to 3 µm 50 ) can be expressed. In order to maximize the disorder in the direction of expansion of each particle so as to prevent expansion of the particles due to charging of lithium ions, it may be advantageous to make the particle size smaller for the spherical carbon-based negative electrode active material. However, when the particle size of the carbon-based negative electrode active material is less than 1.0 ㎛, 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 ㎛, the expansion rate of the negative electrode active material increases significantly during charge and discharge of the secondary battery, so that as charge and discharge are repeated, the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material particles and the current collector deteriorate, which may significantly reduce the cycle characteristics.

[0170] In addition, the above-mentioned negative electrode active layer may optionally further include a conductive agent, a binder, other additives, etc., as needed, along with the carbon-based negative electrode active material as the main component.

[0171] The above-mentioned challenge material may include one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0172] As an example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0173] At this time, the content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 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 the resistance of the negative electrode from increasing due to a low content of the conductive material, thereby reducing the charging capacity, and can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material, thereby reducing the charging capacity, or the problem of the rapid charging characteristics from decreasing due to an increase in the loading amount of the negative electrode active layer.

[0174] In addition, the binder may be appropriately applied as a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and may be applied within a range that does not deteriorate the electrical properties of the negative electrode. Specifically, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0175] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 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. The present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the negative electrode from being lowered due to an excessive amount of binder by controlling the content of the binder contained in the negative electrode active layer within the above range.

[0176] In addition, the average thickness of the negative electrode active layer may be in the range of 50 ㎛ to 500 ㎛, and specifically, may be in the range of 100 ㎛ to 400 ㎛; 200 ㎛ to 350 ㎛; 50 ㎛ to 180 ㎛; 80 ㎛ to 150 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛. The present invention can not only implement high adhesiveness between the negative electrode active layer and the negative electrode current collector by controlling the average thickness of the negative electrode active layer within the above range, but also implement high energy density of the negative electrode.

[0177] 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, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the negative electrode current collector can be appropriately applied in the range of 1 to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0178] Furthermore, the separator interposed between the anode and the cathode is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is one commonly used in the art, but specifically, one containing at least one polymer selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity can be used. The separator may have a porous polymer substrate form such as a sheet or non-woven fabric containing the above-described polymer, and in some cases, may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, the separator may have an average pore diameter of 0.01 to 10 μm, and an average thickness of 5 to 300 μm.

[0179] Meanwhile, the electrode assembly according to the present invention is not particularly limited, but may have a stacked shape, a zigzag shape, or a zigzag-stacked shape. By having the above-described shape, the electrode assembly can be packed at a high density within a limited space, thus having the advantage of high utilization in terms of energy density.

[0180]

[0181] The electrode assembly for a lithium secondary battery according to the present invention has the above-described configuration, and thus has excellent safety, high energy density, and excellent rate characteristics and charge / discharge capacity.

[0182]

[0183] Method for manufacturing anode

[0184] Furthermore, the present invention provides a method for manufacturing the anode according to the present invention described above.

[0185] Specifically, the method for manufacturing the positive electrode includes a step of applying positive electrode slurry to at least one surface of a positive electrode current collector, and a step of drying the applied positive electrode slurry to form a positive electrode active layer.

[0186] Here, the application of the positive electrode slurry refers to a process of coating the surface of a moving positive electrode current collector by discharging the 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 applied in the art, but a die coating method can be preferably used. The die coating method can be performed through 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, coating thickness, etc. of the positive electrode slurry applied on the positive electrode current collector can be easily controlled.

[0187] In addition, the positive electrode slurry is for forming the positive electrode active layer of the positive electrode. Therefore, the positive electrode slurry includes a positive electrode active material as a main component, and may further include a conductive material, a binder, etc., as needed. Here, since the composition of the first positive electrode active material, the second positive electrode active material, the conductive material, the binder, etc., included in the positive electrode slurry is the same as that of the positive electrode active layer of the positive electrode for a lithium secondary battery, a detailed description thereof is omitted.

[0188] Furthermore, the positive electrode slurry may be manufactured by a predetermined process. Specifically, the positive electrode slurry may include a binder, and in this case, the positive electrode slurry may be manufactured by a step of manufacturing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed; and a step of mixing a first positive electrode active material and a second positive electrode active material into the manufactured mixed dispersion to manufacture a positive electrode slurry.

[0189] Carbon-based and metal-based conductive materials are powders and are fine in size. Therefore, when mixed with an excessive amount of cathode active material for the preparation of a cathode slurry, these conductive materials may not be uniformly dispersed within the cathode slurry and may aggregate. In this case, a cathode manufactured using the cathode slurry may exhibit uniform conductivity throughout the cathode active layer, resulting in deteriorated electrical properties.

[0190] Accordingly, the present invention can overcome the problem of agglomeration of conductive materials in positive electrode slurry by preparing a dispersion in which a carbon-based conductive material and a metal-based conductive material are dispersed together with a binder when preparing positive electrode slurry, and mixing the prepared dispersion with the first positive electrode active material and the second positive electrode active material at the time of introducing them into a non-aqueous organic solvent.

[0191] Meanwhile, the method for manufacturing the positive electrode may include a process of forming a positive electrode active layer from the applied positive electrode slurry. The process of forming the positive electrode active layer may refer to a process of drying the positive electrode slurry. In this case, the drying of the positive electrode slurry may be applied without particular limitation as long as it is a method commonly applicable in the art. For example, the drying may be performed by applying heat energy to the positive electrode slurry using a hot air dryer, a vacuum oven, or the like, thereby drying the positive electrode slurry.

[0192] In addition, 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 density of the entire positive electrode active layer by applying pressure to the surface of the positive electrode active layer formed using a roll press or the like. To this end, the rolling may be performed under predetermined pressure and speed conditions at a temperature higher than room temperature.

[0193] Specifically, the rolling may be performed at a temperature in the range of 50°C to 100°C, more specifically, at a temperature in the range 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.

[0194] In addition, the rolling can be performed at a rolling speed in the range of 2 m / s to 7 m / s, and more specifically, it can be performed at a rolling speed 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.

[0195] In addition, the rolling can be performed under pressure conditions in the range of 50 MPa to 200 MPa, and specifically, can be performed under pressure conditions in the range of 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.

[0196] The present invention can maximize the energy density of the positive electrode active layer while minimizing damage to the positive electrode active layer formed by performing rolling under the above temperature, speed and / or pressure conditions.

[0197]

[0198] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0199] However, the following examples and comparative examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0200]

[0201] Examples 1 to 4 and Comparative Examples 1 to 2. Manufacturing of a positive electrode for a lithium secondary battery.

[0202] Inject N-methylpyrrolidone solvent into the homo mixer, and the first cathode active material (PEM 1st ) as LiNi 0.8 Co 0.1 Mn 0.1O2 (hereinafter, 'NCM', average particle size: about 3㎛), second cathode active material (PEM 2nd ) as LiFePO4 (hereinafter, 'LFP', average particle size: about 1.3㎛), carbon-based conductive material (CCM) and metal-based conductive material (MCM), and polyvinylidene fluoride (PVdF) as a binder were each introduced. Then, a cathode slurry was prepared by mixing at 3,000 rpm for 60 minutes. At this time, the carbon-based conductive material (CCM) used the materials shown in Table 1 below, and silver (Ag) nanowires were used as the metal-based conductive material (MCM). In addition, the cathode slurry was mixed to include 96 parts by weight of cathode active material, 1.5 parts by weight of conductive material, and 2.5 parts by weight of binder based on the solid content. The first cathode active material and the second cathode active material included in the above cathode active material were included in amounts of 64 parts by weight and 32 parts by weight, respectively, and the content ratio (CCM:MCM) of the carbon-based conductive material and the metal-based conductive material included in the conductive material was adjusted as shown in Table 1.

[0203] An aluminum foil (average thickness: 12 μm) was prepared as a cathode current collector, and the previously prepared cathode slurry was cast onto the prepared aluminum foil. The aluminum foil on which the cathode slurry was cast was dried in a 130°C vacuum oven and then rolled to produce a cathode. At this time, the total thickness of the rolled cathode composite layer was 150 μm.

[0204] Unit: Weight Conductive material type CCM: MCMCCMMCMExample 1 Carbon black nanowire 1.0:0.5Example 2 Carbon nanotube silver nanowire 0.5:1.0Example 3 Carbon nanotube silver nanowire 0.75:0.75Example 4 Carbon nanotube silver nanowire 1.0:0.5Comparative Example 1 Carbon nanotube-1.5:0Comparative Example 2-silver nanowire 0:1.5

[0205]

[0206] Examples 5 to 8 and Comparative Examples 3 to 4. Manufacturing of electrode assemblies and secondary batteries.

[0207] A negative electrode active material was prepared by mixing natural graphite and artificial graphite in a weight ratio of 1:1, and 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 foil as a negative electrode current collector. The copper foil on which the negative electrode slurry was cast was dried in a vacuum oven at 130°C and rolled to manufacture a negative electrode. At this time, the thickness of the negative electrode composite layer was 130 μm.

[0208] The manufactured negative electrode and the positive electrode prepared in Examples 1 to 4 and Comparative Examples 1 to 2, respectively, were placed face to face as shown in Table 2 below, and an 18 μm polypropylene separator was interposed therebetween to manufacture an electrode assembly. Each manufactured electrode assembly was inserted into a battery case, an electrolyte composition was injected into the battery case, and the case was sealed to manufacture a lithium secondary battery. At this time, as the electrolyte composition, a solution was used in which lithium hexafluorophosphate (LiPF6, 1.0 M) and vinyl carbonate (VC, 2 wt%) were mixed in a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0209] Type of anode used Example 5 Anode manufactured in Example 1 Example 6 Anode manufactured in Example 2 Example 7 Anode manufactured in Example 3 Example 8 Anode manufactured in Example 4 Comparative Example 3 Anode manufactured in Comparative Example 1 Comparative Example 4 Anode manufactured in Comparative Example 2

[0210]

[0211] Experimental example.

[0212] In order to evaluate the performance of the anode according to the present invention, the following experiments were conducted.

[0213] First, the lithium secondary batteries manufactured in Examples 5 to 8 and Comparative Examples 3 to 4 were activated by charging them under CC-CV conditions at a rate of 0.3 C to 4.2 V at 25°C, and then discharging them under CC conditions at a rate of 0.3 C to 2.5 V.

[0214] Each activated lithium secondary battery was subjected to constant current / constant voltage (CC / CV) charging at a temperature of 25°C, and the initial charge capacity was measured. The charging was performed with a constant current of 0.1C rate until the voltage reached 4.2 V, and then cut-off at a current of 0.005C rate in constant voltage mode to maintain 4.2 V. In addition, each charged secondary battery was subjected to constant current discharge (CC discharge), and the initial discharge capacity was measured. At this time, the constant current discharge was performed with a 1.0C rate until the voltage reached 1.5 V.

[0215] After that, each lithium secondary battery was fully charged at 25℃ with a charge current of 2.0C rate to a charge terminal voltage of 4.2~4.25V, and the charge capacity was measured. From the measured charge capacity, the relative charge capacity ratio based on the initial charge capacity was calculated to evaluate the high-rate charge characteristics of each lithium secondary battery. After that, the discharge capacity was measured while discharging the lithium secondary batteries in the range of 1.0~2.0C at 0.2C intervals. From the measured discharge capacity, the relative discharge capacity ratio based on 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.

[0216] Initial capacity [mAh / g] High-rate charge characteristics [%] High-rate discharge characteristics [%] Charge Discharge 1.0C 1.2C 1.4C 1.6C 1.8C 2.0C Example 5 46 6 40 5 9 0.89 5.29 4.09 2.99 1.69 0.08 8.4 Example 6 46 3 40 0 ​​87 29 4.29 2.89 0.58 9.38 6.98 5.5 Example 7 46 4 40 1 8 8.39 4.39 3.09 1.18 9.78 7.58 6.1 Example 8 46 4 40 4 9 0.69 5.19 3.99 2.79 1.48 9.88 8.4 Comparative example 345839784.491.890.488.785.583.379.2 Comparative example 446039986.292.291.889.587.384.981.5

[0217]

[0218] As shown in Table 3 above, it can be seen that the positive electrode for a lithium secondary battery according to the present invention has a high charge / discharge capacity and excellent rate characteristics.

[0219] Specifically, the lithium secondary batteries of the examples had a high charge capacity of 463 mAh / g or more, and exhibited excellent high-rate charge / discharge characteristics of 87% or more and 85% or more, respectively, during high-rate charge and discharge under 2C rate conditions.

[0220] This means that even if two types of metal oxides with different crystal structures are included as positive electrode active materials, the deviation in the different kinetic characteristics exhibited by each positive electrode active material can be minimized when a carbon-based negative electrode active material and a metal-based negative electrode active material are included.

[0221] From these results, it can be seen that the positive electrode for a lithium secondary battery according to the present invention has excellent rate characteristics and capacity characteristics during charge and discharge.

[0222]

[0223] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within a scope that does not depart from the technical scope of the present invention as set forth in the claims to be described below.

[0224] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. Anode current collector, and Comprising a positive electrode active layer provided on at least one surface of the positive electrode current collector; The above positive electrode active layer includes 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 cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides having different structures; The above metal-based conductive material is characterized by having a nanowire structure: [Chemical Formula 1] Li a [Ni b Co 1-b-c M 1 c ]O2 [Chemical Formula 2] Li p [Mn 2-q M 2 q ]O4 [Chemical Formula 3] LiFe 1-x M 3 x XO4 In the above chemical formulas 1 to 3, M 1 is at least one element among 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 at least one element among 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 at least one element among 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 of the elements P, Si, S, As, and Sb, and 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.

2. In paragraph 1, The above first cathode active material includes at least one of a metal oxide having a layered structure and a metal oxide having a spinel structure, The above second cathode active material is a cathode including a metal oxide having an olivine structure.

3. In paragraph 1, A cathode in which the first cathode active material and the second cathode active material are included in a weight ratio ranging from 5:95 to 95:

5.

4. In paragraph 1, The above metal-based conductive material is an anode which 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. In paragraph 1, The above metal-based conductive material is an anode containing at least one metal element selected from the group consisting of silver (Ag), gold (Au), copper (Cu), aluminum (Al), tungsten (W), iron (Fe), and stainless steel (SUS).

6. In paragraph 1, An anode in which the carbon-based conductive material and the metal-based conductive material are each included in an amount of 0.1 to 10 wt% based on the total weight of the anode active layer, and the total content thereof is 10 wt% or less based on the total weight of the anode active layer.

7. In paragraph 1, The above carbon-based conductive material is included in an amount of 0.1 wt% to 10 wt% based on the total weight of the first cathode active material, A cathode in which the above metal-based conductive material is included in an amount of 0.1 wt% to 10 wt% based on the total weight of the second cathode active material.

8. In paragraph 1, The above carbon-based conductive material is an anode comprising at least one of acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, carbon nanotubes, and carbon fibers.

9. In paragraph 1, The above carbon-based conductive material has an average particle diameter (D) in the range of 0.5 μm to 5 μm. 50 ) with a positive pole.

10. An electrode assembly for a secondary battery comprising a positive electrode, a negative electrode, and a separator provided between the positive electrode and the negative electrode according to paragraph 1.

11. A step of applying a cathode slurry to at least one surface of the cathode current collector, and A step of drying the applied positive electrode slurry to form a positive electrode active layer; The above positive electrode slurry includes 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 cathode active material and the second cathode active material each include at least one of a metal oxide having a layered structure represented by the following chemical formula 1, a metal oxide having a spinel structure represented by the following chemical formula 2, and a metal oxide having an olivine structure represented by the following chemical formula 3, but include metal oxides having different structures; A method for manufacturing an anode according to claim 1, wherein the metal-based conductive material has a nanowire structure: [Chemical Formula 1] Li a [Ni b Co 1-b-c M 1 c ]O2 [Chemical Formula 2] Li p [Mn 2-q M 2 q ]O4 [Chemical Formula 3] LiFe 1-x M 3 x XO4 In the above chemical formulas 1 to 3, M 1 is at least one element among 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 at least one element among 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 at least one element among 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 of the elements P, Si, S, As, and Sb, and 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. In paragraph 11, A method for manufacturing a positive electrode, wherein the positive electrode slurry further includes a binder.

13. In paragraph 12, The above positive electrode slurry is, A step of preparing a mixed dispersion in which a carbon-based conductive material, a metal-based conductive material, and a binder are dispersed; and A step of preparing a cathode slurry by mixing a first cathode active material and a second cathode active material into the prepared mixed dispersion; A method for manufacturing a cathode manufactured by .