Negative electrode for lithium secondary battery and method for manufacturing same

Abstract

The present invention relates to a negative electrode and a method for manufacturing same. The negative electrode includes a silicon-based negative electrode active material together with a carbon-based negative electrode active material, and thus has excellent charge / discharge capacity and energy density. The carbon-based negative electrode active material included in each negative electrode active layer is oriented to have a predetermined inclination with respect to a negative electrode current collector, thereby resulting in excellent rapid charging performance and lifespan characteristics.

Description

Anode for lithium secondary battery and method for manufacturing the same

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

[0002] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2024-0097947, dated July 24, 2024; Republic of Korea Patent Application No. 10-2024-0146303, dated October 24, 2024; and Republic of Korea Patent Application No. 10-2025-0019146, dated February 14, 2025, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are widely used not only in small devices like portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage systems. Recently, with growing concern for environmental issues, the demand base for high-capacity batteries is expanding, driven by the growth of the market for devices employing high-capacity batteries, such as electric vehicles and hybrid electric vehicles, which can replace fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution.

[0005] Typically, lithium secondary batteries are rechargeable power generation devices comprised of a stacked structure of a cathode / separator / cathode. When charging a lithium secondary battery, a lithium desorption reaction occurs at the cathode, where lithium contained in the cathode active material is oxidized and released. Furthermore, a lithium insertion reaction occurs at the anode, where lithium is reduced and inserted into the cathode active material. Generally, the desorption reaction in the cathode active material is faster than the insertion reaction in the anode active material, so the performance of a lithium secondary battery, such as the charging and discharging speed, is primarily determined by the anode.

[0006] As the negative electrode active material of the above-mentioned negative electrode, a material containing graphite is widely used. The average potential when a material containing graphite releases lithium is about 0.2 V (Li / Li + ) and the discharge potential shows a relatively flat pattern. Therefore, when graphite is used as an anode active material, the voltage of the secondary battery has the advantage of being high and constant. However, the electrical capacity per unit mass of the graphite material is small at 372 mAh / g. On the other hand, since the capacity of the current graphite material has been improved to be close to the theoretical capacity, further capacity increase is difficult. In addition, when graphite is used as an anode active material, the lithium ion insertion reaction proceeds at a slow rate, so there is a limitation that the rapid charging performance is low compared to cases where other anode active materials are applied.

[0007] Meanwhile, various anode materials are being studied to improve the high capacity and rapid charging performance of lithium secondary batteries. For example, silicon (Si) has recently been widely studied as it has become known that it can reversibly adsorb and release large amounts of lithium through a compound formation reaction with lithium. Silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much higher than that of graphite-based materials, making it a useful anode material for high energy density and / or high capacity. However, silicon not only induces a large volume change (~300%) in the anode during charging of a secondary battery, but also has poor high-rate discharge characteristics. Furthermore, when silicon oxides such as silicon carbide (SiC), SiO, or SiO2 are used as anode materials, their electrical resistance can increase under the temperature conditions encountered during charge and discharge of secondary batteries, resulting in their resistance to act as resistors. This has the limitation that the lifespan characteristics of the negative electrode are significantly reduced as the cycle of the secondary battery progresses, as it accelerates the deterioration of the negative electrode active layer.

[0008] Accordingly, there is a need for technological development for a lithium secondary battery cathode with excellent rapid charging performance and improved energy density and lifespan characteristics.

[0009]

[0010] [Prior Art Literature]

[0011] Republic of Korea Patent Publication No. 10-2024-0084840

[0012]

[0013] The purpose of the present invention is to provide a cathode having excellent rapid charging performance, as well as excellent energy density and lifespan characteristics, and a method for manufacturing the same.

[0014]

[0015] The present invention,

[0016] negative current collector,

[0017] A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and

[0018] A second negative electrode active layer is provided on the first negative electrode active layer and includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material;

[0019] When analyzing a cross-section in the thickness direction of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer by scanning electron microscopy, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material provide a negative electrode satisfying the following equation 1:

[0020] [Formula 1]

[0021] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0

[0022] In the above equation 1,

[0023] FL 60-120 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0024] SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0025] The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

[0026]

[0027] Here, the cathode may satisfy at least one of the following equations 2 and 3 when analyzed by scanning electron microscopy for a cross-section in the thickness direction:

[0028] [Formula 2]

[0029] 40 ≤ FL 30-150 ≤ 70

[0030] [Formula 3]

[0031] 5 ≤ SL 60-120 ≤ 20

[0032] In the above equations 2 and 3,

[0033] FL 30-150 represents the ratio (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, wherein the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 30° and less than 150°.

[0034] SL 60-120 It represents the ratio (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0035] The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

[0036] The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but may include one or more of (0.5≤q≤2.5).

[0037] The content of the above silicon-based negative electrode active material may be 0.1 wt% to 30 wt% based on the weight of the entire negative electrode active layer.

[0038] The average particle diameter (D) of the above silicon-based negative electrode active material 50 ) can range from 1㎛ to 20㎛.

[0039] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0040] At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It may contain graphite in the range of ㎤ / g.

[0041] The total pore volume above is 1 × 10 -5 ㎤ / g to 1 × 10 -1 The content of graphite in the range of ㎤ / g may be in the range of 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material.

[0042] In addition, the total thickness of the first cathode active layer and the second cathode active layer may be in the range of 50 ㎛ to 400 ㎛ on average, and the average thickness of the second cathode active layer may have a ratio in the range of 80% to 150% based on the average thickness of the first cathode active layer.

[0043]

[0044] Furthermore, the present invention,

[0045] A step (S1) of applying a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector;

[0046] A step (S2) of applying a second negative electrode slurry containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material on the applied first negative electrode slurry, and

[0047] A step (S3) of applying a magnetic field to the applied first cathode slurry and the second cathode slurry;

[0048] When analyzing a cross-section in the thickness direction of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer by a scanning electron microscope, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material provide a method for manufacturing a negative electrode satisfying the following equation 1:

[0049] [Formula 1]

[0050] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0

[0051] In the above equation 1,

[0052] FL 60-120 represents the percentage of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, wherein the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0053] SL 60-120represents the percentage of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, wherein the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0054] The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

[0055] Here, the silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but may include one or more of (0.5≤q≤2.5).

[0056] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0057] At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It may contain graphite in the range of ㎤ / g.

[0058] The above magnetic field can be performed with a magnetic field strength of 1,000 G to 12,000 G.

[0059]

[0060] The negative electrode according to the present invention comprises a silicon-based negative electrode active material along with a carbon-based negative electrode active material, thereby exhibiting excellent charge / discharge capacity and high energy density. Furthermore, the negative electrode exhibits excellent rapid charging performance and lifespan characteristics due to the application of a magnetic field during its manufacture, thereby reducing the curvature of the entire negative electrode active layer.

[0061]

[0062] Figure 1 is a conceptual diagram showing the inclination between the long axis of a carbon-based negative electrode active material and the negative electrode current collector.

[0063] Figures 2 to 4 are images of cross-sections in the thickness direction of the cathodes manufactured in examples and comparative examples according to the present invention, taken using a scanning electron microscope (SEM).

[0064]

[0065] 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.

[0066] 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.

[0067] Also, in this specification, "average particle diameter (D 50)" means a particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called a median diameter. The average particle diameter can be measured by a method commonly applied in the art. For example, the 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. In the present invention, it may be a value measured by an analysis device using a laser diffraction scattering particle size distribution measurement method.

[0068] In addition, in this specification, “the carbon-based negative electrode active material is oriented” means that the longest line segment (i.e., the major axis) passing through the center of the particle when the carbon-based negative electrode active material is two-dimensionally projected is distributed with a predetermined directionality based on the negative electrode current collector surface.

[0069] Additionally, “high alignment of the carbon-based negative electrode active material” may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high frequency with respect to the negative electrode current collector surface, and in some cases, may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle with respect to the negative electrode current collector surface.

[0070] Furthermore, in the present specification, "comprising as a main component" may mean including 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of the defined component with respect to the total weight (or total volume). For example, "comprising as a main component a carbon-based negative electrode active material" may mean including 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more with respect to the total 100 parts by weight of the negative electrode active layer, the negative electrode active material, and / or the negative electrode slurry. In some cases, it may mean that the entire negative electrode active layer, negative electrode active material and / or negative electrode slurry is comprised of 100 wt% carbon-based negative electrode active material.

[0071]

[0072] Hereinafter, the present invention will be described in more detail.

[0073]

[0074] cathode

[0075] The present invention,

[0076] negative current collector,

[0077] A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and

[0078] A negative electrode is provided, which includes a second negative electrode active layer provided on the first negative electrode active layer and including a second carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0079] The negative electrode according to the present invention refers to a negative electrode for a lithium secondary battery. The negative electrode includes a negative electrode active layer on at least one surface of a negative electrode current collector. The negative electrode active layer is a layer that implements electrical activity of the negative electrode, and is manufactured by applying a negative electrode slurry containing a negative electrode active material that implements an electrochemical redox reaction during charge / discharge of the battery to at least one surface of the negative electrode current collector, and then drying and rolling the same.

[0080] The above-described negative electrode active layer may have a two-layer structure in which a first negative electrode active layer and a second negative electrode active layer are sequentially laminated on a negative electrode current collector. The negative electrode active layer having a two-layer structure can easily control the composition of each layer. Therefore, the negative electrode active layer can improve the performance of the negative electrode by controlling the type or content of components contained in each layer according to a specific purpose, such as increasing the energy efficiency of the secondary battery or improving the adhesion between the active layer and the current collector. For example, the negative electrode active layer may selectively include a silicon-based negative electrode active material having a high charge / discharge capacity of the battery only in the second negative electrode active layer in contact with the positive electrode. In addition, the negative electrode active layer may selectively include natural graphite having good adhesive properties as a negative electrode active material only in the first negative electrode active layer in contact with the negative electrode current collector, or may include a binder that provides binding properties to the components constituting the active layer at a higher content ratio than that of the second negative electrode active layer.

[0081] In the present invention, the first negative electrode active layer includes a first carbon-based negative electrode active material, and the second negative electrode active layer includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0082] The negative electrode according to the present invention can realize high energy density by including a silicon-based negative electrode active material in the second negative electrode active layer, and at the same time, by controlling the directionality of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in the first negative electrode active layer and the second negative electrode active layer, respectively, with respect to the negative electrode current collector surface, the rapid charging performance and life characteristics of the negative electrode can be improved.

[0083] Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may have a cross-sectional shape in which any two line segments passing through the center of the particle have different lengths when projected as two-dimensional particles, as shown in Fig. 1. The cross-sectional shape may have the shape of an ellipsoid stretched in any one direction based on the center of the particle. In some cases, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may be amorphous particles having a shape that is difficult to define due to agglomeration of plate-like, sheet-like, flake-like, needle-like, etc. In this case, the amorphous particles do not include spherical particles.

[0084] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material can be oriented so that the long axis passing through the center of the particle (hereinafter referred to as the “long axis of the carbon-based negative electrode active material”) when the particle is two-dimensionally projected has a predetermined inclination with respect to the negative electrode current collector. The present invention can shorten the tortuosity of the negative electrode active layer including the negative electrode current collector and the carbon-based negative electrode active material by controlling the inclination formed by the long axis of the negative electrode current collector and the carbon-based negative electrode active material within a predetermined range. Since the tortuosity provides a movement path for lithium ions when charging a secondary battery, the shorter the tortuosity, the faster the charging speed of the secondary battery can be promoted.

[0085] For example, in the case of a scanning electron microscope (SEM) analysis of a thickness-wise cross-section of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer according to the present invention, the long axes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may be inclined at a predetermined incline with respect to the negative electrode current collector. In other words, when the incline of the long axis of the carbon-based negative electrode active material included in each negative electrode active layer with respect to the negative electrode current collector is measured, the following equation 1 may be satisfied:

[0086] [Formula 1]

[0087] 0.1 ≤ SL 60-120 / FL 60-120< 1.0

[0088] In the above equation 1,

[0089] FL 60-120 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0090] SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0091] The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

[0092]

[0093] The above formula 1 is the content ratio (FL) of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each negative electrode active layer, the long axis of which has an inclination of more than 60° and less than 120° with respect to the negative electrode current collector. 60-120 ) and the content of the second carbon-based negative electrode active material (SL 60-120 ) represents the liver ratio.

[0094] Specifically, the inclination of the long axis of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector may be 0° to 180°. In this case, when the inclination of the long axis with respect to the surface of the negative electrode current collector is 0° to 90° and when it is 90° to 180°, only the directionality of the long axis is different, and the angle formed with respect to the surface of the negative electrode current collector may actually be the same. For example, when it has an inclination of 60° and when it has an inclination of 120° with respect to the surface of the negative electrode current collector, only the directionality of the long axis of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector is different, and the angle formed by the long axis of the carbon-based negative electrode active material and the surface of the negative electrode current collector may be understood to be the same. Therefore, the ratio of the long axis of the carbon-based negative electrode active material exceeding 60° and less than 120° with respect to the surface of the negative electrode current collector refers to the content ratio of the carbon-based negative electrode active material whose long axis has an inclination exceeding 60° with respect to the surface of the negative electrode current collector, regardless of the directionality. This can be understood as the same as the content ratio of the carbon-based negative electrode active material in which the angle formed by the long axis of the carbon-based negative electrode active material with the surface of the negative electrode collector is greater than 60° and less than 90°. The above equation 1 means that the ratio of the carbon-based negative electrode active material in which the inclination formed by the long axis of the carbon-based negative electrode active material and the surface of the negative electrode collector is greater than 60° is higher in the first negative electrode active layer than in the second negative electrode active layer. The present invention can reduce the tortuosity inside the first negative electrode active layer adjacent to the negative electrode collector by implementing a high ratio of the first carbon-based negative electrode active material in which the long axis of the negative electrode collector is inclined greater than 60° and less than 120° in the first negative electrode active layer. Accordingly, the first negative electrode active layer improves electrolyte impregnation and / or lithium ion movement, so that the redox reaction inside the negative electrode active layer adjacent to the negative electrode collector can be facilitated during charge / discharge of the secondary battery. Therefore, uniform degradation can be induced in the entire negative electrode active layer. In addition, since the thickness-wise volume expansion of the first negative electrode active layer due to the insertion of lithium ions during charging of the secondary battery is suppressed, there is an advantage of improving the adhesive strength between the negative electrode active layer and the negative electrode current collector.Therefore, the cathode has the advantage of improved life characteristics.

[0095] Accordingly, the cathode of the present invention has the formula 1 as 0.1 or more and less than 1.0 (i.e., 0.1 ≤ SL 60-120 / FL 60-120 < 1.0), specifically, the cathode is 0.5 or more and less than 1.0 (i.e., 0.5 ≤ SL 60-120 / FL 60-120 < 1.0); 0.5 to 0.99 (i.e., 0.5 ≤ SL 60-120 / FL 60-120 ≤ 0.99); 0.5 to 0.85 (i.e., 0.5 ≤ SL 60-120 / FL 60-120 ≤ 0.85); 0.5 to 0.7 (i.e., 0.5 ≤ SL 60-120 / FL 60-120 ≤ 0.7); 0.6 to 0.99 (i.e., 0.6 ≤ SL 60-120 / FL 60-120 ≤ 0.99); 0.7 to 0.99 (i.e., 0.7 ≤ SL 60-120 / FL 60-120 ≤ 0.99); 0.4 to 0.7 (i.e., 0.4 ≤ SL 60-120 / FL 60-120 ≤ 0.7); 0.65 to 0.87 (i.e., 0.65 ≤ SL 60-120 / FL 60-120 ≤ 0.87); 0.88 to 0.99 (i.e., 0.88 ≤ SL 60-120 / FL 60-120 ≤ 0.99); or 0.55 to 0.85 (i.e., 0.55 ≤ SL 60-120 / FL 60-120 ≤ 0.85) can be satisfied.

[0096]

[0097] In addition, the cathode according to the present invention can further satisfy at least one of the following equations 2 and 3 in addition to the above equation 1:

[0098] [Formula 2]

[0099] 40 ≤ FL 30-150≤ 70

[0100] [Formula 3]

[0101] 5 ≤ SL 60-120 ≤ 20

[0102] In the above equations 2 and 3,

[0103] FL 30-150 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 30° and less than 150°.

[0104] SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0105] The above formula 2 is a parameter that means that the ratio of the slope of the major axis of the negative electrode current collector among the first carbon-based negative electrode active materials exceeds 30°, and can be satisfied at a ratio in the range of 40% to 70% of the entire first carbon-based negative electrode active materials. For example, the present invention satisfies the above formula 2 at 45% to 70% (i.e., 45% ≤ FL 30-150 ≤ 70%); 50% to 70% (i.e., 50% ≤ FL 30-150 ≤ 70%); 45% to 60% (i.e., 45% ≤ FL 30-150 ≤ 60%); 50% to 60% (i.e. 50% FL 30-150 ≤ 60%); or 51% to 57% (i.e., 51% ≤ FL 30-150 ≤ 57%) can be satisfied with the range of ratios.

[0106] The present invention can significantly reduce the curvature of the first negative electrode active layer by satisfying the ratio of the inclination of the long axis of the first carbon-based negative electrode active material with respect to the negative electrode current collector exceeding 30° within the above-described range. This has the advantage of enabling high rapid charging performance during secondary battery charging. In addition, when the long axis of the first carbon-based negative electrode active material has a high inclination exceeding 30° with respect to the negative electrode current collector, there is the effect of suppressing volume expansion in the thickness direction of the first negative electrode active layer during charging of the secondary battery. This has the advantage of further extending the life of the negative electrode because it can further strengthen the adhesion between the negative electrode current collector and the first negative electrode active layer.

[0107] The above formula 3 is a parameter that means that the ratio of the inclination of the major axis of the negative electrode collector among the second carbon-based negative electrode active materials is low, and can be satisfied with a ratio in the range of 5% to 20% of the entire second carbon-based negative electrode active materials. For example, the present invention satisfies the above formula 3 in the range of 10% to 20% (i.e., 10% ≤ SL 60-120 ≤ 20%); 5% to 15% (i.e., 5% ≤ SL 60-120 ≤ 15%); 6% to 11% (i.e., 6% ≤ SL 60-120 ≤ 11%); 8% to 18% (i.e., 8% ≤SL 60-120 ≤ 18%); 6% to 13% (i.e., 6% ≤ SL 60-120 ≤ 13%); 11% to 14% (i.e., 11% ≤ SL 60-120 ≤ 14%); 14% to 19% (i.e., 14% ≤ SL 60-120 ≤ 19%); or 15% to 19% (i.e., 15% ≤ SL 60-120 ≤ 19%) can be satisfied with the range of ratios.

[0108] The present invention can prevent rapid charging performance from deteriorating while implementing high energy density and charge / discharge capacity of the negative electrode by satisfying the ratio of the inclination exceeding 60° of the long axis of the second carbon-based negative electrode active material with respect to the negative electrode current collector within the above-described range. Specifically, if the ratio of the inclination exceeding 60° of the long axis of the second carbon-based negative electrode active material included in the negative electrode is lower than the above-described lower limit, not only is the electrolyte wettability of the negative electrode reduced, but there is also a problem of deterioration of the rapid charging performance of the negative electrode. In addition, if the ratio is higher than the above-described upper limit, there is a limitation that the energy density is reduced and the charge / discharge capacity of the negative electrode is reduced.

[0109] The major axis of the above carbon-based negative electrode active material is oriented with respect to the surface of the negative electrode current collector by a magnetic field applied to the negative electrode slurry containing the carbon-based negative electrode active material during the manufacture of the negative electrode. The carbon-based negative electrode active material is a diamagnetic material, and when a magnetic field is applied, it exhibits magnetization anisotropy in which diamagnetism varies depending on the axial direction of the crystals constituting the carbon-based negative electrode active material. On the other hand, the silicon-based negative electrode active material included in the second negative electrode active layer does not exhibit such magnetization anisotropy, and thus, even when a magnetic field is applied, the orientation behavior with respect to the negative electrode current collector is minimal. Due to this silicon-based negative electrode active material, even when a magnetic field is applied to the second carbon-based negative electrode active material, the magnetic anisotropy is not sufficiently implemented, and thus, the orientation with respect to the negative electrode current collector may be induced to be relatively lower than that of the first carbon-based negative electrode active material.

[0110] The major axis orientation of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may be affected by the type or content of the carbon-based negative electrode active material, average particle diameter, porosity, content ratio with respect to the silicon-based negative electrode active material, etc. Accordingly, in order to satisfy the above-described Equations 1 to 3, the negative electrode according to the present invention may be adjusted so that the type, content, and / or physical properties of the negative electrode active material included in the first negative electrode active layer and the second negative electrode active layer satisfy predetermined conditions.

[0111] For example, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each negative electrode active layer are materials containing carbon atoms as their main component, and their type and / or content may be the same or different.

[0112] Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0113] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each have the form of an assembly in which a plurality of particles are assembled. In this case, one graphite assembly may be formed by assembling 2 to 100 graphite particles, preferably 3 to 20 graphite particles. For example, the first carbon-based negative electrode active material may include artificial graphite. The artificial graphite may have the form of a graphite assembly in which 10 to 30 particles are aggregated. The artificial graphite has the advantage of superior high-rate charge-discharge performance and excellent life characteristics compared to natural graphite.

[0114] In addition, the second carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may have a form of a graphite assembly in which 10 to 30 particles are aggregated. In addition, the mixing ratio of the natural graphite and the artificial graphite may be 5 to 50:50 to 95, or 5 to 30:70 to 95, based on weight. By including natural graphite and artificial graphite in the mixing ratio as described above, the carbon-based negative electrode active material can strengthen the adhesion between the negative electrode current collector and the negative electrode active layer, and can highly implement the degree to which the long axis of the carbon-based negative electrode active material is oriented with respect to the surface of the negative electrode current collector by a magnetic field applied during the manufacture of the negative electrode.

[0115] The above first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material comprises low-expansion graphite. In the present invention, "low-expansion graphite" means graphite having low expansion characteristics when a secondary battery is charged. For example, when a secondary battery including graphite as an negative electrode active material is manufactured, if the expansion characteristics of the negative electrode active layer are low even when the secondary battery undergoes repeated charge and discharge cycles, the graphite may be referred to as low-expansion graphite. Here, the expansion characteristics of the low-expansion graphite can be determined through the change in thickness of the negative electrode active layer according to the charge and discharge cycle. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite.

[0116] In the present invention, the low-expansion graphite may be manufactured by a cold isotropic pressing (CIP) method that uniformly applies pressure to each particle in all directions at a low temperature. The low-expansion graphite manufactured by the cold isotropic pressing method is isotropic graphite, and isotropic graphite has low electrical resistance, resistance to thermal shock, and excellent mechanical properties, so it can improve the life characteristics of the negative electrode itself.

[0117] In addition, the low-expansion graphite may refer to natural graphite particles coated with carbon. In this case, the low-expansion graphite has a carbon layer, which not only suppresses the expansion of the graphite when charging a secondary battery, but also has the advantage of significantly reducing the amount of impurities generated due to physical damage during the manufacturing of carbon-based negative electrode active materials and / or the manufacturing of negative electrodes using the same or the assembly of batteries.

[0118] The above low-expansion graphite has a high porosity inside the graphite particles. The high porosity of the graphite particles can improve the volume expansion control ability of the negative electrode active material itself, so that the volume expansion characteristic is small when the secondary battery is charged, and the insertion of lithium ions into the particles is advantageous, so that the charging speed can be further improved. For example, the low-expansion graphite can have a total pore volume that satisfies a predetermined range. Specifically, the low-expansion graphite has a porosity of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It can have a total pore volume in the range of ㎤ / g. For example, the low expansion graphite has a pore volume of 5 × 10 -4 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 5 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -2 ㎤ / g; 5 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; or 5 × 10 -3 ㎤ / g to 2 × 10 -2It can have a total pore volume in the range of ㎤ / g. The total pore volume of the low-expansion graphite can be measured through a BET measurement method using the adsorption of nitrogen (N2) gas. The low-expansion graphite can reduce volume expansion during charging of a secondary battery by satisfying the above-described range. In addition, the low-expansion graphite having a total pore volume satisfying the above-described range can provide a path for the movement of lithium ions and / or electrons inside the particle, and thus can not only improve the charging speed of the secondary battery, but also effectively suppress the increase in electrical resistance of the negative electrode active layer according to the progress of the charge / discharge cycle of the secondary battery.

[0119] In addition, the low-expansion graphite may be included in the first negative electrode active layer and / or the second negative electrode active layer in a predetermined amount. Specifically, the low-expansion graphite may be included in a range of 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material. For example, the low-expansion graphite may be included in a range of 10 wt% to 30 wt%; 20 wt% to 40 wt%; 15 wt% to 45 wt%; 10 wt% to 50 wt%; 30 wt% to 60 wt%; 50 wt% to 70 wt%; 40 wt% to 60 wt%; 15 wt% to 25 wt%; or 45 wt% to 69 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material.

[0120] The present invention can minimize the volume change of the first negative electrode active layer during charge and discharge of a secondary battery by controlling the content of low-expansion graphite within the above-described range when the first carbon-based negative electrode active material includes low-expansion graphite, thereby improving the adhesive strength between the negative electrode current collector and the first negative electrode active layer. In addition, the low-expansion graphite controlled within the above-described content range can minimize the volume change of the first negative electrode active layer during charge and discharge of the secondary battery, thereby firmly fixing the negative electrode active material of the second negative electrode active layer. This reduces the movement of the carbon-based negative electrode active material that occurs as the cycle of the secondary battery progresses, thereby preventing an increase in the curvature of the entire negative electrode active layer, particularly the second negative electrode active layer, and / or a decrease in the slope formed by the oriented carbon-based negative electrode active material and the negative electrode current collector.

[0121] The present invention can realize high charge / discharge capacity of the second negative electrode active layer adjacent to the positive electrode active layer by controlling the content of the low-expansion graphite within the above-described range when the second carbon-based negative electrode active material includes low-expansion graphite. In addition, volume expansion caused by the silicon-based negative electrode active material included in the second negative electrode active layer during charging of a lithium secondary battery can be significantly reduced. Through this, the negative electrode can suppress an increase in the curvature of the second negative electrode active layer until the end of the life of the secondary battery. The curvature of the negative electrode active layer is a parameter that indirectly indicates the length of the path provided within the negative electrode active layer so that the electrolyte, etc. can move from the surface of the negative electrode active layer to the negative electrode current collector. The lower the curvature ratio, the shorter the path length, and the shorter the curvature ratio may correspond to a shorter migration gradient of lithium ions and / or electrons during charge / discharge of the secondary battery. However, in an actual lithium secondary battery, the volume expansion of the negative electrode active material inevitably occurs due to the insertion of lithium ions during charging, and the repeated volume change of the negative electrode active material due to charge and discharge may cause an increase in the curvature within the negative electrode active layer. However, the present invention can minimize the volume expansion of the second negative electrode active layer by including a low-expansion graphite as a second carbon-based negative electrode active material in a predetermined amount in a second negative electrode active layer including a silicon-based negative electrode active material having a large volume expansion during charging.

[0122] Meanwhile, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each negative electrode active layer may have an average particle diameter satisfying a predetermined range. Specifically, each of the carbon-based negative electrode active materials may have an average particle diameter (D) in the range of 0.5 μm to 20 μm. 50 ) can be represented. For example, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each have an average particle diameter (D) in the range of 0.5 µm to 15 µm; 0.5 µm to 10 µm; 5 µm to 20 µm; 10 µm to 20 µm; 12 µm to 18 µm; 2 µm to 7 µm; 0.5 µm to 5 µm; or 11 µm to 15 µm.50 ) can be expressed.

[0123] The average particle size of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may be advantageously made smaller to maximize the degree of disorder in the direction of expansion of each particle so as to prevent expansion of the particles due to charging of lithium ions. However, when the particle size of each carbon-based negative electrode active material is less than 0.5 ㎛, a large amount of binder may be required due to an increase in the number of particles per unit volume. On the other hand, when the maximum particle size exceeds 20 ㎛, expansion becomes severe, and as charge and discharge are repeated, the adhesion between particles and the adhesion between the particles and the current collector deteriorates, which may significantly reduce the cycle characteristics.

[0124] In addition, the silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and can increase the charge / discharge capacity and energy density per unit volume of the negative electrode. Such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), silicon monoxide (SiO), silicon dioxide (SiO2), and other silicon oxides (SiO). q ) can be included, and these can be included alone or in combination in the cathode active layer.

[0125] When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as the above silicon-based negative electrode active material and included in the negative electrode active layer, they are silicon oxide (SiO q , but can be expressed as 0.5≤q≤2.5).

[0126] In addition, among the above silicon-based negative electrode active materials, the composite is a material containing silicon (Si) and carbon (C) as main components, such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q ) may mean a complex with carbon (C). For example, the complex may be silicon (Si), silicon carbide (SiC), silicon oxide (SiO q) may have a core-shell structure in which carbon (C) is coated on the particle surface including the like. At this time, the carbon (C) may be formed by using CVD, PVD, ALD, etc. to form silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) or may have a form in which the particle surface is modified using plasma or UV, etc. In addition, the complex may include silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) and particles made of carbon (C) can be uniformly mixed / pulverized by applying mechanical and / or physical force to the mixture. In this case, the composite can mean that, unlike an alloy in which silicon (Si) atoms and carbon (C) atoms are physically and chemically bonded, particles including silicon (Si) components and particles made of carbon (C) are uniformly bonded while maintaining their original components.

[0127] In addition, the silicon-based negative electrode active material may be doped or alloyed with Li, Mg, Al, Ca, and / or Ti, etc. At this time, at least one of the metals may be doped or alloyed into the silicon-based negative electrode active material. In this case, the silicon-based negative electrode active material may be doped or alloyed with a metal in a range of 1 mol% to 10 mol%, specifically, 1 mol% to 5 mol%, with respect to silicon atoms. When a metal is added to the silicon-based negative electrode active material in the form of doping or an alloy, the electrical conductivity may increase and the mechanical strength may be improved. However, since the metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, the metals may be doped or alloyed into the silicon-based negative electrode active material in the above-described content in order to lower the electrical resistance without reducing the energy density per unit weight of the silicon-based negative electrode active material.

[0128] The silicon-based negative electrode active material may be included in an amount of 0.1 wt% to 30 wt% based on the weight of the entire negative electrode active layer. Specifically, the silicon-based negative electrode active material may be included in an amount of 0.1 wt% to 25 wt%, 20 wt% to 30 wt%, 10 wt% to 30 wt%, 0.5 wt% to 20 wt%, 1 wt% to 9 wt%, 5 wt% to 15 wt%, 3 wt% to 7 wt%, 11 wt% to 19 wt%, 13 wt% to 17 wt%, 15 wt% to 20 wt%, 3 wt% to 13 wt%, or 1 wt% to 15 wt% based on the weight of the entire negative electrode active layer. The present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge / discharge of a secondary battery by controlling the content ratio of the silicon-based negative electrode active material within the aforementioned range. In addition, by minimizing the volume change of the negative electrode active layer during charge / discharge of the secondary battery, the structural stability of the negative electrode active layer can be improved, thereby extending the lifespan of the secondary battery.

[0129] The above silicon-based negative electrode active material has a predetermined average particle diameter (D 50 ) can have. Specifically, the silicon-based negative electrode active material has an average particle diameter (D) in the range of 1 ㎛ to 20 ㎛. 50 ) may have. For example, the silicon-based negative electrode active material may have an average particle diameter (D) in the range of 1 µm to 15 µm; 1 µm to 10 µm; 1 µm to 9 µm; 1 µm to 7.5 µm; 1 µm to 5 µm; 2 µm to 8 µm; 3 µm to 7 µm; 5 µm to 10 µm; 5 µm to 15 µm; 10 µm to 20 µm; 11 µm to 18 µm; 6 µm to 14 µm; or 2 µm to 6 µm. 50 ) can have.

[0130] If the minimum particle size of the silicon-based negative electrode active material is less than the lower limit of the above-described range, it may be difficult to uniformly disperse the second negative electrode active layer. If the silicon-based negative electrode active material is unevenly dispersed, as the secondary battery is charged and discharged, the oxidation-reduction reaction of the agglomerated and non-agglomerated regions of the silicon-based negative electrode active material is unevenly induced, which may accelerate deterioration of the second negative electrode active layer. In addition, if the maximum particle size of the silicon-based negative electrode active material exceeds the upper limit of the above-described range, it is difficult to control the crystal plane of the silicon-based negative electrode active material, and the expansion rate per unit area of ​​the second negative electrode active layer significantly increases during charge and discharge of the secondary battery, which causes a problem in that the cycle characteristics significantly decrease as charge and discharge are repeated.

[0131] Furthermore, the first cathode active layer and the second cathode active layer may optionally further include a conductive material, a binder, other additives, etc., as needed, along with the cathode active material as the main component.

[0132] The above-mentioned challenge material may include, but is not limited to, one or more types of carbon black such as acetylene black, furnace black, lamp black, summer black, etc.; graphene; carbon nanotubes and carbon fibers.

[0133] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0134] The content of the conductive material may be in the range of 0.1 wt% to 10 wt% based on the weight of each negative electrode active layer. Specifically, the conductive material may be in the range of 0.1 wt% to 8 wt%, 0.1 wt% to 5 wt%, 0.1 wt% to 3 wt%, 2 wt% to 6 wt%, or 0.5 wt% to 2 wt% based on the weight of each negative electrode active layer. 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 charge capacity. In addition, the present invention can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material exceeding the above range, thereby reducing the charge capacity, or the problem of the electrical resistance from increasing due to an increase in the loading amount of the negative electrode active layer.

[0135] The above binder is 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 can be appropriately applied within a range that does not deteriorate the electrical properties of the negative electrode. For example, 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 fluoroelastomer.

[0136] The content of the binder may be in the range of 0.1 wt% to 10 wt% based on the weight of each negative electrode active layer. Specifically, the binder may be in the range of 0.1 wt% to 8 wt%, 0.1 wt% to 5 wt%, 0.1 wt% to 3 wt%, or 2 wt% to 6 wt% based on the weight of each negative electrode active layer. 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 each negative electrode active layer within the above range.

[0137] The negative electrode active layer may have a predetermined average thickness in order to realize a high charge / discharge capacity while achieving a fast charging speed. The negative electrode active layer exhibits a greater charge / discharge capacity as the loading amount of the negative electrode active material exhibiting electrochemical activity increases. However, in this case, since it is difficult to orient the long axis of the carbon-based negative electrode active material to have a predetermined incline with respect to the negative electrode current collector during the manufacturing process of the negative electrode active layer, there is a limitation in that the rapid charging performance of the manufactured negative electrode is low. Therefore, the present invention can adjust the average thickness of the negative electrode active layer within a predetermined range. Specifically, the negative electrode active layer may have an average thickness in the range of 50 ㎛ to 400 ㎛. For example, the negative electrode active layer may have a thickness of 100 ㎛ to 350 ㎛; 100 ㎛ to 300 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 200 ㎛; 150 ㎛ to 400 ㎛; It may have an average thickness in the range of 200 μm to 400 μm; 150 μm to 300 μm; 150 μm to 250 μm; 50 μm to 150 μm; 80 μm to 190 μm; 80 μm to 210 μm; or 150 μm to 220 μm.

[0138] In addition, the first negative electrode active layer and the second negative electrode active layer may have a predetermined thickness ratio. Specifically, the second negative electrode active layer may have a thickness ratio in the range of 80% to 150% based on the average thickness of the first negative electrode active layer. For example, the second negative electrode active layer may have a thickness ratio in the range of 80% to 120%; 80% to 100%; 80% to 99%; 100% to 150%; 125% to 150%; 90% to 120%; 110% to 140%; or 95% to 105% based on the average thickness of the first negative electrode active layer.

[0139] The present invention can prevent the charge / discharge capacity and cycle characteristics of the negative electrode from being reduced due to the average thickness ratio of the second negative electrode active layer being lower than the lower limit of the above-described range by controlling the thickness ratio of the first negative electrode active layer and the second negative electrode active layer within the above-described range. In addition, the present invention can prevent the charge / discharge capacity and rapid charging performance of the negative electrode from being reduced due to the average thickness ratio of the second negative electrode active layer being higher than the upper limit of the above-described range.

[0140] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be a thin plate or film containing copper, stainless steel, nickel, titanium, calcined carbon, etc., and when containing copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the average thickness of the negative electrode current collector may be appropriately applied from 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0141]

[0142] The anode according to the present invention, having the above-described configuration, exhibits excellent charge / discharge capacity and high energy density. Furthermore, the anode exhibits a shortened path for lithium ions within the anode active layer, significantly reducing lithium ion diffusion resistance, thereby exhibiting excellent rapid charging performance.

[0143]

[0144] lithium secondary battery

[0145] In addition, the present invention provides a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode of the present invention described above, and a separator disposed between the positive electrode and the negative electrode.

[0146]

[0147] A lithium secondary battery according to the present invention comprises an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged and a separator is positioned between them. The lithium secondary battery comprises the negative electrode of the present invention described above, thereby improving lithium ion diffusion capacity, and thus exhibiting excellent rapid charging performance as well as the advantage of high energy density.

[0148] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0149] In addition, the positive electrode includes a positive electrode active layer including a positive electrode active material on a positive electrode current collector, and the positive electrode active layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0150] The above cathode active material is a material capable of causing an electrochemical reaction on the cathode current collector, and may include at least one lithium metal oxide represented by the following chemical formulas 1 and 2, which is capable of reversibly intercalating and deintercalating lithium ions:

[0151] [Chemical Formula 1]

[0152] Li l [Ni m Co nMn w M 1 v ]O2

[0153] [Chemical Formula 2]

[0154] LiM 2 p Mn q P r O4

[0155] In the above chemical formulas 1 and 2,

[0156] M 1 is at least one element among W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0157] l, m, n, w and v are 1.0≤l≤1.30, 0.5≤m<1, 0, respectively. <n≤0.3, 0<w≤0.3, 0≤v≤0.1이되, m+n+w+v=1이고,

[0158] M 2 is Ni, Co or Fe,

[0159] p is 0.05≤p≤1.0,

[0160] q is 2-p,

[0161] r is either 0 or 1.

[0162]

[0163] The lithium metal oxides represented by the above chemical formulas 1 and 2 are substances containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as a cathode active material, they have the advantage of being able to stably supply electricity at a high capacity and / or high voltage compared to conventional cathode active materials such as lithium iron phosphate oxide (LiFeO4).

[0164] At this time, the lithium metal oxide represented by the chemical formula 1 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may include O2, etc. The lithium metal oxide represented by the above chemical formula 2 is LiNi 0.7 Mn 1.3 O4; LiNi 0.5 Mn 1.5 O4; LiNi 0.3 Mn 1.7 It may include O4, etc., and these may be used alone or in combination.

[0165] In addition, the positive electrode active material may be included in an amount of 85 wt% or more based on the total weight of the positive electrode active layer. Specifically, the positive electrode active material may be included in an amount of 90 wt% or more, 93 wt% or more, or 95 wt% or more based on the total weight of the positive electrode active layer.

[0166] The above positive electrode active layer may further include a conductive material, a binder, other additives, etc., along with the positive electrode active material.

[0167] At this time, the conductive material is used to improve the electrical performance of the anode, and can be applied as a material commonly used in the art, but specifically, it can include at least one of natural graphite; artificial graphite; carbon black such as acetylene black, furnace black, lamp black, and summer black; graphene; and carbon nanotubes.

[0168] The conductive material may be included in an amount of 0.1 to 5 wt% based on the total weight of the positive electrode active layer. Specifically, the conductive material may be included in an amount of 0.1 to 4 wt%; 2 to 4 wt%; 1.5 to 5 wt%; 1 to 3 wt%; 0.1 to 2 wt%; or 0.1 to 1 wt% based on the total weight of the positive electrode active layer.

[0169] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0170] The binder may be included in an amount of 1 to 10 wt% based on the total weight of the positive electrode active layer. Specifically, the binder may be included in an amount of 2 to 8 wt%; or 1 to 5 wt% based on the total weight of the positive electrode active layer.

[0171] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically in the range of 50 µm to 300 µm, and more specifically in the range of 100 µm to 200 µm; 80 µm to 150 µm; 120 µm to 170 µm; 150 µm to 300 µm; 200 µm to 300 µm; or 150 µm to 190 µm.

[0172] In addition, the positive electrode can be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, the positive electrode current collector can be a thin plate or film containing stainless steel, aluminum, nickel, titanium, calcined carbon, etc., and when containing aluminum or stainless steel, a surface-treated one with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 µm to 500 µm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0173] The separator interposed between the positive and negative electrodes of the lithium secondary battery 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 art. Specifically, the separator may include at least one polymer selected from the group consisting of chemically resistant and hydrophobic polypropylene; polyethylene; and polyethylene-propylene copolymers. The separator may have a porous polymer substrate form, such as a sheet or non-woven fabric, including 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 μm to 10 μm, and an average thickness of 5 μm to 300 μm.

[0174] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery in a form that may include a stacked, zigzag, or zigzag-stacked electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0175] Pouch-type secondary batteries and / or square secondary batteries have the advantage of high utilization in terms of energy density because the unit cells of the secondary batteries can be packed at a high density in a limited space.

[0176]

[0177] Method for manufacturing cathode

[0178] Furthermore, the present invention provides a method for manufacturing a cathode according to the present invention described above.

[0179] Specifically, the method for manufacturing a negative electrode according to the present invention includes a step (S1) of applying a first negative electrode slurry including a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector, a step (S2) of applying a second negative electrode slurry including a second carbon-based negative electrode active material and a silicon-based negative electrode active material onto the applied first negative electrode slurry, and a step (S3) of applying a magnetic field to the applied first negative electrode slurry and the second negative electrode slurry.

[0180] The above steps (S1) and (S2) refer to a process of coating a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material by simultaneously or continuously discharging them onto the surface of a moving negative electrode current collector. The first negative electrode slurry is applied to at least one surface of the negative electrode current collector, and the second negative electrode slurry is applied on the applied first negative electrode slurry.

[0181] The above steps (S1) and (S2) can be applied without particular limitation as long as they are methods commonly applied in the art, but preferably, a die coating method can be used. The die coating method is performed using a slot die coater, and the slot die coater can be equipped with a shim for controlling the discharge conditions of the negative electrode slurry. The slot die coater can easily control the loading amount, coating thickness, etc. of the negative electrode slurry applied on the negative electrode current collector by controlling the shape and position of the shim.

[0182] For example, the present invention can simultaneously apply a first negative electrode slurry and a second negative electrode slurry onto a negative electrode current collector using a dual die coater. In this case, there is an advantage in that process efficiency can be significantly increased compared to applying each slurry sequentially.

[0183] In addition, the first negative electrode slurry and the second negative electrode slurry each contain a first carbon-based negative electrode active material and a second carbon-based negative electrode active material as main components. Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may contain at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0184] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each have the form of an assembly in which a plurality of particles are assembled. In this case, one graphite assembly may be formed by assembling 2 to 100 graphite particles, preferably 3 to 20 graphite particles. For example, the first carbon-based negative electrode active material may include artificial graphite, and the artificial graphite may have the form of a graphite assembly in which 10 to 30 particles are aggregated. The artificial graphite has the advantage of superior high-rate charge-discharge performance and excellent life characteristics compared to natural graphite.

[0185] In addition, the second carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may have a form of a graphite assembly in which 10 to 30 particles are aggregated. In addition, the mixing ratio of the natural graphite and the artificial graphite may be 5 to 50:50 to 95, or 5 to 30:70 to 95, based on weight. By including natural graphite and artificial graphite in the mixing ratio as described above, the second carbon-based negative electrode active material can strengthen the adhesion between the negative electrode current collector and the negative electrode active layer, and can highly implement the degree to which the long axis of the carbon-based negative electrode active material is oriented with respect to the surface of the negative electrode current collector by a magnetic field applied during the manufacture of the negative electrode.

[0186] The first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material comprises low-expansion graphite. The carbon-based negative electrode active material comprises low-expansion graphite. In the present invention, "low-expansion graphite" refers to graphite having low expansion characteristics when a secondary battery is charged. Here, the expansion characteristics of the low-expansion graphite can be determined through the change in thickness of the negative electrode active layer according to the charge and discharge cycle. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite.

[0187] In the present invention, the low-expansion graphite may refer to natural graphite particles coated with carbon. The low-expansion graphite may be manufactured by a cold isotropic pressing (CIP) method in which plate-shaped natural graphite is spheroidized and then pressure is uniformly applied to each particle in all directions at a low temperature. The low-expansion natural graphite manufactured by the cold isotropic pressing method may be isotropic graphite. The isotropic graphite has low electrical resistance, resistance to thermal shock, and excellent mechanical properties, and thus can improve the life characteristics of the negative electrode itself.

[0188] The above low-expansion graphite has a carbon layer, which not only suppresses the expansion of the graphite when charging a secondary battery, but also has the advantage of significantly reducing the amount of impurities generated due to physical damage during the manufacturing of carbon-based negative electrode active materials and / or the manufacturing of negative electrodes using the same or the assembly of batteries.

[0189] In addition, the low-expansion graphite has a high porosity within the graphite particles. Graphite particles with high porosity have excellent volume expansion control capability of the negative electrode active material itself, and are advantageous in the insertion of lithium ions, so they have the advantage of excellent rapid charging performance. The low-expansion graphite can satisfy the total pore volume within a predetermined range. Specifically, the low-expansion graphite has a porosity of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It can have a total pore volume in the range of ㎤ / g. For example, the low expansion graphite has a pore volume of 5 × 10 -4 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 5 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -2 ㎤ / g; 5 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; or 5 × 10 -3 ㎤ / g to 2 × 10 -2It can have a total pore volume in the range of ㎤ / g. The total pore volume of the low-expansion graphite can be measured through a BET measurement method using the adsorption of nitrogen (N2) gas. The low-expansion graphite can reduce volume expansion during charging of a secondary battery by satisfying the above-described range. In addition, the low-expansion graphite having a total pore volume satisfying the above-described range can provide a path for the movement of lithium ions and / or electrons inside the particle, and thus can not only improve the charging speed of the secondary battery, but also effectively suppress the increase in electrical resistance of the negative electrode active layer according to the progress of the charge / discharge cycle of the secondary battery.

[0190] Furthermore, the second negative electrode slurry includes a silicon-based negative electrode active material. The silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and can increase the charge / discharge capacity and energy density per unit volume of the negative electrode. Such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), silicon monoxide (SiO), silicon dioxide (SiO2), and the like, silicon oxide (SiO). q ) can be included, and these can be included alone or in combination in the cathode active layer.

[0191] When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as the above silicon-based negative electrode active material and included in the negative electrode active layer, they are silicon oxide (SiO q , but can be expressed as 0.5≤q≤2.5).

[0192] Among the above silicon-based negative electrode materials, the composite is a material containing silicon (Si) and carbon (C) as main components, and includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q ) may mean a complex with carbon (C). For example, the complex may be silicon (Si), silicon carbide (SiC), silicon oxide (SiO q) may have a core-shell structure in which carbon (C) is coated on the particle surface including the like. At this time, the carbon (C) may be formed by using CVD, PVD, ALD, etc. to form silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) or may have a form in which the particle surface is modified using plasma or UV, etc. In addition, the complex may include silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) and particles made of carbon (C) can be uniformly mixed / pulverized by applying mechanical and / or physical force to the mixture. In this case, the composite can mean that, unlike an alloy in which silicon (Si) atoms and carbon (C) atoms are physically and chemically bonded, particles including silicon (Si) components and particles made of carbon (C) are uniformly bonded while maintaining their original components.

[0193] In addition, the silicon-based negative electrode active material may be doped or alloyed with Li, Mg, Al, Ca, and / or Ti, etc. At this time, at least one of the metals may be doped or alloyed into the silicon-based negative electrode active material. In this case, the silicon-based negative electrode active material may be doped or alloyed with a metal in an amount of 1 mol% to 10 mol%, specifically 1 mol% to 5 mol%, with respect to silicon atoms. When a metal is added to the silicon-based negative electrode active material in the form of doping or an alloy, the electrical conductivity may increase and the mechanical strength may be improved. However, since the metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, the metals may be doped or alloyed into the silicon-based negative electrode active material in the above-described amount in order to lower the electrical resistance without reducing the energy density per unit weight of the silicon-based negative electrode active material.

[0194] The silicon-based negative electrode active material may be included in an amount of 0.1 wt% to 30 wt% based on the solid weight of the entire negative electrode slurry. Specifically, the silicon-based negative electrode active material may be included in an amount of 0.1 wt% to 25 wt%, 20 wt% to 30 wt%, 10 wt% to 30 wt%, 0.5 wt% to 20 wt%, 1 wt% to 9 wt%, 5 wt% to 15 wt%, 3 wt% to 7 wt%, 11 wt% to 19 wt%, 13 wt% to 17 wt%, 15 wt% to 20 wt%, 3 wt% to 13 wt%, or 1 wt% to 15 wt% based on the solid weight of the entire negative electrode slurry. The present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge / discharge of a secondary battery by controlling the content ratio of the silicon-based negative electrode active material within the aforementioned range. In addition, by minimizing the volume change of the negative electrode active layer during charge / discharge of the secondary battery, the structural stability of the negative electrode active layer can be improved, thereby extending the lifespan of the secondary battery.

[0195] The above first negative electrode slurry and the second negative electrode slurry may further include a conductive material, a binder, and additives in addition to the negative electrode active material. Since each component included in the above negative electrode slurry is the same as the negative electrode active layer of the negative electrode for a lithium secondary battery, a detailed description thereof will be omitted.

[0196] Meanwhile, the orientation of the carbon-based negative electrode active material can be induced by applying a magnetic field after this step (S1 and S2).

[0197] Specifically, the above step (S3) means a process of applying a magnetic field to the first negative electrode slurry and the second negative electrode slurry applied on the negative electrode collector to align and / or orient the long axis of the carbon-based negative electrode active material particles included in each negative electrode slurry with respect to the negative electrode collector.

[0198] The degree to which the long axis of the carbon-based negative electrode active material is aligned and / or oriented may vary depending on the strength of the applied magnetic field. Therefore, in this step (S3), the magnetic field may have a strength in the range of 1,000 G to 12,000 G (Gauss) to enhance the effect of aligning and / or orienting the long axis of the carbon-based negative electrode active material particles with respect to the surface of the negative electrode current collector. Specifically, the magnetic field may be in the range of 1,500 G to 10,000 G; 2,000 G to 10,000 G; 3,000 G to 10,000 G; 1,000 G to 9,000 G; 3,000 G to 9,000 G; 7,000 G to 9,000 G; 2,000 G to 8,000 G; 3,000 G to 8,000 G; It can be applied at a strength in the range of 4,000G to 8,000G; 5,000G to 7,000G; 5,000G to 10,000G; 5,000G to 12,000G; 5,000G to 9,000G; 5,000G to 7,5000G; 6,000G to 6,5000G; 6,000G to 9,000G; 6,000G to 11,000G; 9,000G to 12,000G; 10,000G to 12,000G; or 10,000G to 11,000G.

[0199] The carbon-based negative electrode active material in the negative electrode slurry to which a magnetic field is applied can be oriented so that its long axis has a predetermined inclination with respect to the surface of the negative electrode current collector. This can be directly or indirectly confirmed through scanning electron microscopy (SEM) analysis of a cross-section in the thickness direction of the negative electrode active layer formed after drying the negative electrode slurry containing the carbon-based negative electrode active material.

[0200] For example, in the case of a scanning electron microscope (SEM) analysis of a thickness-wise cross-section of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer of the negative electrode manufactured according to the present invention, the long axes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each of the first negative electrode active layer and the second negative electrode active layer may be inclined at a predetermined incline with respect to the negative electrode current collector. In other words, when the incline of the long axis of the carbon-based negative electrode active material included in each negative electrode active layer with respect to the negative electrode current collector is measured, the following equation 1 may be satisfied:

[0201] [Formula 1]

[0202] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0

[0203] In the above equation 1,

[0204] FL 60-120 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0205] SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0206] The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

[0207]

[0208] Meanwhile, the method for manufacturing a cathode according to the present invention may further include a step (S4) of drying the cathode slurry to which a magnetic field is applied after the step (S3) to form a cathode active layer.

[0209] The above drying can be applied without particular limitations as long as it is a method that can be commonly applied in the art. For example, the above drying can be performed by applying heat energy to the cathode slurry using a hot air dryer, a vacuum oven, or the like, thereby drying the cathode slurry.

[0210] For example, the drying may be performed at 100°C to 250°C (specifically, 160°C to 200°C) for 1 to 15 hours.

[0211] In addition, a step (S5) of rolling the negative electrode active layer formed by drying after the above step (S4) may be further included. The rolling refers to a process of increasing the density of the entire negative electrode active layer by applying pressure to the surface of the formed negative electrode active layer using a roll press or the like.

[0212] The above rolling can be performed using rolling equipment such as a roll press, etc., under a pre-pressure condition that reaches the target thickness and target porosity, and then vacuum drying to manufacture a negative electrode having a final negative electrode active material layer formed on a current collector.

[0213] For example, the above rolling can be performed under conditions where the target thickness (i.e., the average thickness of the cathode active layer) is 100 μm to 400 μm and the target porosity (i.e., the porosity after rolling) is 21% to 30%.

[0214] Specifically, the rolling may be performed at a temperature in the range of 20°C to 100°C, more specifically, at a temperature in the range of 20°C to 80°C; 20°C to 60°C; 20°C to 40°C; 20°C to 30°C; 30°C to 100°C; 40°C to 100°C; 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.

[0215] The above rolling can be performed at a rolling speed in the range of 2 m / s to 7 m / s, and more specifically, 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.

[0216] The above rolling can be performed under pressure conditions ranging from 50 MPa to 200 MPa, and specifically, can be performed 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.

[0217] The present invention can maximize the energy density of the negative electrode active layer while minimizing the decrease in the inclination of the long axis of each carbon-based negative electrode active material with respect to the negative electrode current collector by performing rolling under the above-described temperature, speed, and / or pressure conditions.

[0218]

[0219] The method for manufacturing a negative electrode according to the present invention can manufacture a negative electrode having the above-described configuration, thereby not only having a high energy density but also having excellent rapid charging performance.

[0220]

[0221] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0222] 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.

[0223]

[0224] Examples 1 to 7 and Comparative Examples 1 to 2. Preparation of cathode

[0225] Natural graphite (average particle diameter (D 50 ): about 11~13㎛), artificial graphite (average particle diameter (D 50 ): about 15~16㎛) and low-expansion natural graphite (average particle diameter (D 50 ): about 16~20㎛, total pore volume: about 0.006~0.012㎤ / g) was prepared as a carbon-based negative electrode active material.

[0226] In addition, silicon monoxide (SiO, average particle size (D)) as a silicon-based negative electrode active material 50 ): approximately 18±0.5㎛); Styrene butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener were prepared, and carbon nanotubes (CNT) and carbon black (Super-P) were prepared as conductive materials.

[0227] Then, 95 wt% of the first carbon-based negative electrode active material, 1 wt% of carbon black, 3.0 wt% of styrene butadiene rubber (SBR), and 1 wt% of carboxymethyl cellulose (CMC) were mixed with water to obtain a solid content of 50% to prepare a first negative electrode slurry.

[0228] Separately, 95.55 wt% of the prepared second carbon-based negative electrode active material and silicon-based negative electrode active material, 1.13 wt% of carboxymethyl cellulose (CMC), 2.3 wt% of styrene butadiene rubber (SBR), 0.02 wt% of carbon nanotubes, and 1 wt% of carbon black were mixed with water to obtain a solid content of 50% to prepare a second negative electrode slurry.

[0229] At this time, ① the composition of the first carbon-based negative electrode active material, ② the composition of the second carbon-based negative electrode active material, and ③ the content ratio of the silicon-based negative electrode active material included in the second negative electrode slurry were adjusted as shown in Table 1 below.

[0230] The first cathode slurry and the second cathode slurry were simultaneously applied (S1 and S2) onto a copper foil (thickness: 6 μm) being transported roll-to-roll (transport speed: 6 m / min) using a dual die coater. Thereafter, a magnetic field was applied (S3) for 2 to 11 seconds from the upper and lower portions of the transported copper foil using a magnet. ④ Whether or not a magnetic field was applied and ⑤ the strength of the applied magnetic field were controlled as shown in Table 2 below.

[0231] The negative electrode slurry to which a magnetic field was applied was dried with hot air at a temperature ranging from about 180±10℃ to form a first negative electrode active layer and a second negative electrode active layer on the negative electrode current collector (S4). The negative electrode (average thickness: about 135±5㎛) was manufactured by rolling it using a roll press so that the porosity of the entire negative electrode active layer became 25±2% (S5).

[0232] For the thickness direction cross-section of each manufactured cathode, argon ion milling (Ar) was performed under an acceleration voltage condition of 6 kV. + Ion milling was performed, and scanning electron microscopy (SEM) analysis on the ion-milled cross-section was performed under conditions of an acceleration voltage of 5 kV and a working distance of 7 mm. The ion milling was performed using Hitachi's IM5000, and the scanning electron microscopy analysis was performed using JEOL's IT800SHL.

[0233] In the analyzed scanning electron microscope images, the total number of particles of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material contained in each negative electrode active layer was counted. Then, the longest line segment passing through the center of each particle was set as the major axis, and the inclination between the major axis and the negative electrode current collector was measured. After the inclination between the major axis of the negative electrode current collector and each carbon-based negative electrode active material was divided into six groups as follows, the carbon-based negative electrode active materials were classified into one of the following six groups based on the measured inclination:

[0234] - Group 1: The inclination of the long axis of the negative electrode current collector and the carbon-based negative electrode active material is greater than 0° and less than 30°.

[0235] - Group 2: The inclination of the long axis of the negative electrode current collector and the carbon-based negative electrode active material is more than 30° and less than 60°,

[0236] - Group 3: The inclination of the long axis of the negative electrode current collector and carbon-based negative electrode active material is greater than 60° and less than 90°.

[0237] - Group 4: The inclination of the long axis of the negative electrode current collector and carbon-based negative electrode active material is greater than 90° and less than 120°.

[0238] - Group 5: The inclination of the long axis of the negative electrode current collector and carbon-based negative electrode active material is greater than 120° and less than 150°.

[0239] - Group 6: The inclination of the long axis of the negative electrode current collector and the carbon-based negative electrode active material is greater than 150° and less than 180°.

[0240]

[0241] The number of carbon-based negative electrode materials classified into each group was counted, and the proportion of the corresponding group's carbon-based negative electrode materials among all carbon-based negative electrode materials was calculated. Using the calculated values, the values ​​of Equations 1 through 3 below were calculated, and the results are shown in Tables 3 and 4 below:

[0242] [Formula 1]

[0243] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0

[0244] [Formula 2]

[0245] 40 ≤ FL 30-150 ≤ 70

[0246] [Formula 3]

[0247] 5 ≤ SL 60-120 ≤ 20

[0248] In the above equations 1 to 3,

[0249] FL 60-120represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0250] SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°.

[0251] FL 30-150 It represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 30° and less than 150°.

[0252] Composition of the first carbon-based negative electrode active materialComposition of the second carbon-based negative electrode active materialContent of the silicon-based negative electrode active materialExample 1 Artificial graphite: low-expansion natural graphite = 1:2 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 2 Artificial graphite: low-expansion natural graphite = 1:1 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 3 Artificial graphite: low-expansion natural graphite = 2:1 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 4 Artificial graphite: natural graphite = 2:1 (wt% / wt%) Artificial graphite: low-expansion natural graphite = 1:1 (wt% / wt%) 12 wt%Example 5 Artificial graphite: natural graphite = 2:1 (wt% / wt%) Artificial graphite = 100 Weight % 12 Weight % Example 6 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 30 Weight % Example 7 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight % Comparative Example 1 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight % Comparative Example 2 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 0 Weight %

[0253] Magnetic field application statusMagnetic field strengthExample 106,000±500 GExample 206,000±500 GExample 306,000±500 GExample 406,000±500 GExample 506,000±500 GExample 606,000±500 GExample 7010,000±500 GComparative example 1X-Comparative example 206,000±500 G

[0254] SL 60-120 / FL 60-120 SL 60-120 Example 10.759.44 Example 20.789.57 Example 30.839.68 Example 40.989.27 Example 50.9310.21 Example 60.5113.98 Example 70.6317.95 Comparative Example 11.7424.14 Comparative Example 21.9229.20

[0255] FL 30-150 Example 154.33 Example 254.15 Example 354.26 Example 454.19 Example 554.27 Example 653.97 Example 754.00 Comparative Example 138.50 Comparative Example 251.32

[0256]

[0257] Examples 8 to 14 and Comparative Examples 3 to 4. Manufacturing of lithium secondary batteries

[0258] LiNi with a particle size of 5㎛ as a cathode active material 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder and N-methyl pyrrolidone (NMP) were mixed in a weight ratio of 94:3:3 to form a slurry, which was cast on an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to manufacture a cathode.

[0259] A separator made of 14 μm polypropylene was interposed between the positive electrode obtained above and the negative electrode manufactured in Examples 1 to 7 and Comparative Examples 1 to 2, respectively, and inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah-class lithium secondary battery.

[0260] At this time, the type of negative electrode applied to each lithium secondary battery is shown in Table 5 below.

[0261] Type of applied cathode Example 8 The cathode manufactured in Example 1 Example 9 The cathode manufactured in Example 2 Example 10 The cathode manufactured in Example 3 Example 11 The cathode manufactured in Example 4 Example 12 The cathode manufactured in Example 5 Example 13 The cathode manufactured in Example 6 Example 14 The cathode manufactured in Example 7 Comparative Example 3 The cathode manufactured in Comparative Example 1 Comparative Example 4 The cathode manufactured in Comparative Example 2

[0262]

[0263] Experimental example.

[0264] In order to evaluate the properties and performance of the cathode manufactured according to the present invention, the following experiments were conducted.

[0265]

[0266] 1) Rapid charging performance evaluation

[0267] The positive electrode was manufactured in the same manner as in Examples 8 to 14 and Comparative Examples 3 to 4, and separately, Li4Ti5O 12 (LTO) electrodes were prepared.

[0268] A three-electrode cell was manufactured by stacking the prepared positive and LTO electrodes and the negative electrodes prepared in Examples 1 to 7 and Comparative Examples 1 to 2 so that a separator was interposed between them, and then assembling the stacked LTO electrodes by coating a copper wire.

[0269] Charging and discharging were performed between the positive electrode and the LTO electrode so that the state of charge (SOC) of the LTO electrode reached 50%, and the three-electrode cell was charged to adjust the potential to 1.53 V.

[0270] Charging and discharging of a three-electrode cell were performed using an EC-Lab charger / discharger, while measuring the voltage between the positive and LTO electrodes, and between the positive and negative electrodes. At this time, the charging was performed under constant current conditions of 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, or 3.0C, respectively, and the charging time was calculated after confirming the depth of charge at each C-rate condition. In addition, the depth of charge was determined by checking the negative voltage profile, and when a plateau was confirmed in the negative profile during charging, that point was determined as the charge capacity (charge depth). The calculated charging times are shown in Table 6 below.

[0271]

[0272] 2) Energy density measurement

[0273] The loading per unit area and porosity of the negative electrodes for lithium secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 2 were measured. The loading was calculated by measuring the area and weight of each negative electrode, respectively. In addition, the porosity was determined by impregnating each negative electrode in polydimethylsiloxane (PDMS) for 7 days to fill the pores of the negative electrode active layer with PDMS. Then, argon ion milling (Ar+ ion milling) was performed on the thickness direction cross-section of each negative electrode under an acceleration voltage condition of 6 kV, and scanning electron microscope (SEM) analysis of the cross-section of the ion-milled negative electrode active layer was performed under the conditions of an acceleration voltage of 5 kV and a working distance of 7 mm. The ion milling was performed using an IM5000 from Hitachi, and the SEM analysis was performed using an IT800SHL from JEOL. The analyzed scanning electron microscope (SEM) images were cropped and equally divided. In each divided image, the ratio of each component and pore contained in the negative electrode active layer was calculated, and the volume fraction occupied by the porosity of the negative electrode active layer was calculated from the average value, and the calculated volume fraction was used as the porosity (%) of the negative electrode active layer.

[0274] Thereafter, the energy density of the large-sized secondary battery cell was calculated using the measured loading per unit area and porosity. At this time, the large-sized secondary battery cell was designed as a cell with dimensions of 99.7 mm × 301.5 mm × 8.2 mm that satisfies a discharge capacity of 40 Ah under 1 / 3C conditions. The results are shown in Table 6 below.

[0275]

[0276] 3) Life characteristics

[0277] The charge-discharge capacity retention rate at room temperature was measured for the lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 3 to 4. Specifically, one cycle was set as charging at a constant current of 1C at 22±3°C until the voltage reached 4.25 V, and discharging at a constant current of 1C until the voltage reached 2.5 V. Then, 300 cycles of charge-discharge were performed on each lithium secondary battery.

[0278] At this time, when charging and discharging each lithium secondary battery, 1 st Charging capacity of the cycle and 300 th The charging capacity of the cycle was measured. The measured 1 st 300 based on the charging capacity of the cycle th The capacity retention rate of each lithium secondary battery was evaluated by calculating the charge capacity retention rate of each cycle. The results are shown in Table 6 below.

[0279] Fast charging time [minutes] Energy density [Wh / L] 300 th Cycle capacity retention rate [%] Example 8 27.15 9 ​​8.18 6.4 Example 9 27.45 9 6.18 6.0 Example 10 27.65 9 7.08 4.7 Example 11 28.05 9 8.08 3.8 Example 12 28.65 9 8.08 3.1 Example 13 30.76 2 0.28 5.2 Example 14 29.56 0 1.88 3.3 Comparative example 3 42.15 9 ​​4.57 1.2 Comparative example 4 27.05 7 3.07 8.6

[0280]

[0281] As shown in Table 6 above, it can be seen that the negative electrode according to the present invention has excellent rapid charging performance while also having excellent energy density and lifespan characteristics.

[0282] Specifically, it was confirmed that the lithium secondary batteries manufactured in the examples took less than 30 minutes to charge to a depth of charge. In addition, the lithium secondary batteries manufactured in the examples exhibited a high energy density of approximately 595 Wh / L or more, and a capacity retention rate of approximately 80% or more after 300 charge / discharge cycles.

[0283] This means that when the particle orientation of the carbon-based negative electrode active material is controlled according to the position of the negative electrode active layer while including the silicon-based negative electrode active material, not only is the energy density of the negative electrode improved, but also the rapid charging performance and life characteristics are improved.

[0284] From these results, it can be seen that the negative electrode according to the present invention has excellent rapid charging performance, energy density, and lifespan characteristics.

[0285]

[0286] 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 features of the present invention described in the claims to be described later.

[0287] 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. Negative current collector, A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and A second negative electrode active layer is provided on the first negative electrode active layer and includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material; When analyzing the cross-section in the thickness direction of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer by scanning electron microscopy, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material satisfy the following equation 1: [Formula 1] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0 In the above equation 1, FL 60-120 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°. SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°. The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

2. In paragraph 1, The above cathode is a cathode that satisfies at least one of the following equations 2 and 3 when analyzed by scanning electron microscopy for a cross-section in the thickness direction: [Formula 2] 40 ≤ FL 30-150 ≤ 70 [Formula 3] 5 ≤ SL 60-120 ≤ 20 In the above equations 2 and 3, FL 30-150 represents the percentage (unit: %) of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, in which the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 30° and less than 150°. SL 60-120 It represents the percentage (unit: %) of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, in which the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°. The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

3. In paragraph 1, The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but a cathode containing at least one of 0.5≤q≤2.5).

4. In paragraph 1, A negative electrode in which the content of the above silicon-based negative electrode active material is in the range of 0.1 wt% to 30 wt% based on the weight of the entire negative electrode active layer.

5. In paragraph 1, The average particle diameter (D) of the above silicon-based negative electrode active material 50 ) is a cathode with a range of 1㎛ to 20㎛.

6. In paragraph 1, The first carbon-based negative electrode active material and the second carbon-based negative electrode active material are each a negative electrode including at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

7. In paragraph 1, At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 A cathode containing graphite in the range of ㎤ / g.

8. In paragraph 7, The total pore volume above is 1 × 10 -5 ㎤ / g to 1 × 10 -1 The graphite content in the range of ㎤ / g is A negative electrode having a range of 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material.

9. In paragraph 1, The total thickness of the first cathode active layer and the second cathode active layer is in the range of 50 ㎛ to 400 ㎛ on average, A cathode having an average thickness of the second cathode active layer in a ratio ranging from 80% to 150% based on the average thickness of the first cathode active layer.

10. A step (S1) of applying a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector; A step (S2) of applying a second negative electrode slurry containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material on the applied first negative electrode slurry, and A step (S3) of applying a magnetic field to the applied first cathode slurry and the second cathode slurry; When analyzing the cross-section in the thickness direction of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer using a scanning electron microscope, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material are a method for manufacturing a negative electrode that satisfies the following equation 1: [Formula 1] 0.1 ≤ SL 60-120 / FL 60-120 < 1.0 In the above equation 1, FL 60-120 represents the percentage of the first carbon-based negative electrode active material among the first carbon-based negative electrode active materials, wherein the angle formed by the long axis of the first carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°. SL 60-120 represents the percentage of the second carbon-based negative electrode active material among the second carbon-based negative electrode active materials, wherein the angle formed by the long axis of the second carbon-based negative electrode active material and the surface of the negative electrode current collector is greater than 60° and less than 120°. The major axis of the above carbon-based negative electrode material refers to the longest line segment among the line segments passing through the center of the carbon-based negative electrode material in an image taken with a scanning electron microscope.

11. In paragraph 10, The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but, a method for manufacturing a cathode including at least one of 0.5≤q≤2.5).

12. In paragraph 10, A method for manufacturing a negative electrode, wherein the first carbon-based negative electrode active material and the second carbon-based negative electrode active material each include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

13. In paragraph 10, At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 A method for manufacturing a cathode comprising graphite in the range of ㎤ / g.

14. In paragraph 10, A method for manufacturing a cathode, wherein the magnetic field is performed with a magnetic field strength of 1,000 G to 12,000 G.

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