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

Abstract

The present disclosure relates to a negative electrode and a method of manufacturing the same. The negative electrode includes a silicon-based negative electrode active material and a carbon-based negative electrode active material to have excellent charge / discharge capacity and energy density, and to have excellent fast charging performance and lifespan characteristics because 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.

Description

Technical Field

[0001] This disclosure 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 Korean Patent Application No. 10-2024-0097947, filed on July 24, 2024; Korean Patent Application No. 10-2024-0146303, filed on October 24, 2024; and Korean Patent Application No. 10-2025-0019146, filed on February 14, 2025, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Lithium-ion rechargeable batteries are widely used not only in small devices, such as portable electronic devices, but also in medium and large devices, such as battery packs for hybrid or electric vehicles, and in energy storage devices. With the recent increase in concern about environmental issues, the demand base for high-capacity batteries is expanding due to the growing market for devices using high-capacity batteries, such as electric vehicles and hybrid electric vehicles, which can replace vehicles using fossil fuels, such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Typically, lithium-ion batteries are rechargeable and dischargeable power generation devices with a stacked structure of positive / separator / negative electrodes. When a lithium-ion battery is charged, a lithium deintercalation reaction is induced (where lithium contained in the positive electrode active material is oxidized and released at the positive electrode inside the battery), and a lithium insertion reaction occurs (where lithium is reduced and enters the negative electrode active material at the negative electrode). Generally, because the deintercalation reaction in the positive electrode active material is faster than the insertion reaction in the negative electrode active material, the performance (such as speed) of a lithium-ion battery during charging and discharging is primarily determined by the negative electrode.

[0005] Graphite-containing materials are widely used as negative electrode active materials. Graphite-containing materials exhibit an average lithium discharge potential of approximately 0.2 V (based on Li / Li⁺) and a relatively flat discharge potential. Therefore, when graphite is used as the negative electrode active material, the secondary battery has the advantage of high and constant voltage. However, the capacity per unit mass of graphite materials is as low as 372 mAh / g. On the other hand, since the capacity of graphite materials has now been improved to near its theoretical capacity, further capacity increases are difficult. Furthermore, when graphite is used as the negative electrode active material, there is a limitation of low fast-charging performance compared to the application of other negative electrode active materials, because the lithium-ion insertion reaction occurs at a low rate.

[0006] Meanwhile, various anode active materials are being investigated to increase the capacity and improve the fast-charging performance of lithium-ion batteries. As an example, it is known that silicon (Si) can reversibly adsorb and release large amounts of lithium through a compound formation reaction with lithium, and much research has been conducted on this recently. Silicon possesses a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is significantly larger than that of graphite-based materials, making it a useful material for high energy density and / or high capacity anodes. However, silicon not only causes a large volume change (~300%) in the anode during charging of the secondary battery, but also exhibits poor high-rate discharge characteristics. Furthermore, when silicon oxides such as silicon carbide (SiC), SiO, or SiO2 are used as anode active materials, they exhibit high resistance under the temperature conditions performed during the charging and discharging of the secondary battery and can act as resistors. This promotes the degradation of the anode active layer as the secondary battery cycles, thus significantly reducing the lifetime characteristics of the anode.

[0007] Therefore, there is a need to develop technologies for the negative electrode of lithium secondary batteries that have excellent fast charging performance as well as improved energy density and lifespan characteristics.

[0008] [Related Technical Documents]

[0009] Korean Patent Publication No. 10-2024-0084840 Summary of the Invention

[0010] Technical issues

[0011] The purpose of this disclosure is to provide a negative electrode with excellent fast charging performance, excellent energy density, and excellent lifespan characteristics, and a method for manufacturing the same.

[0012] Technical solution

[0013] This disclosure provides a negative electrode, comprising:

[0014] Negative electrode current collector;

[0015] A first negative electrode active layer, wherein the first negative electrode active layer is disposed on at least one surface of the negative electrode current collector, and comprises a first carbon-based negative electrode active material; and

[0016] The second negative electrode active layer is disposed 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.

[0017] When the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed 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:

[0018] [Formula 1]

[0019]

[0020] In Equation 1 above,

[0021] FL 60-120 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°.

[0022] Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0023] The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

[0024] Here, when the cross-section in the thickness direction is analyzed by scanning electron microscopy, the negative electrode can satisfy any one or more of the following equations 2 and 3:

[0025] [Equation 2]

[0026] 40≤FL 30-150 ≤70

[0027] [Formula 3]

[0028] 5≤SL 60-120 ≤20

[0029] In equations 2 and 3 above,

[0030] FL 30-150 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle formed between 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°.

[0031] Among them SL 60-120This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0032] The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

[0033] The silicon-based anode active material may include materials selected from silicon (Si), silicon carbide (SiC), silicon-containing (Si) and carbon (C) composite materials, and silicon oxide (SiO) q , where 0.5≤q≤2.5) is one or more of the following.

[0034] Based on the total weight of the negative electrode active layer, the content of the silicon-based negative electrode active material can be from 0.1% by weight to 30% by weight.

[0035] The average particle size (D) of the silicon-based anode active material 50 It can be in the range of 1 μm to 20 μm.

[0036] The first carbon-based anode active material and the second carbon-based anode active material may each include one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

[0037] Any one or more of the first carbon-based anode active material and the second carbon-based anode active material may include having a 1×10 -5 cm 3 / g to 1×10 -1 cm 3 Graphite with a total pore volume within the range of / g.

[0038] Based on the total weight of the first carbon-based anode active material or the second carbon-based anode active material, the material having a weight of 1×10 -5 cm 3 / g to 1×10 -1 cm 3 The graphite content in the total pore volume ranges from 10% to 70% by weight within the range of / g.

[0039] Furthermore, the total thickness of the first negative electrode active layer and the second negative electrode active layer can be in an average range of 50 μm to 400 μm, and the average thickness of the second negative electrode active layer can be a ratio in the range of 80% to 150% based on the average thickness of the first negative electrode active layer.

[0040] Furthermore, this disclosure provides a method for manufacturing a negative electrode, comprising the following steps:

[0041] A first negative electrode slurry comprising a first carbon-based negative electrode active material is coated on at least one surface of the negative electrode current collector (S1);

[0042] A second negative electrode slurry, comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material, is coated onto a coated first negative electrode slurry (S2); and

[0043] A magnetic field is applied to the coated first negative electrode slurry and second negative electrode slurry (S3);

[0044] When the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed 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:

[0045] [Formula 1]

[0046]

[0047] In Equation 1 above,

[0048] Among them, FL 60-120 This represents the percentage of the first carbon-based negative electrode active material in which the angle between 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°.

[0049] Among them SL 60-120 This represents the percentage of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0050] The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

[0051] Here, the silicon-based anode active material may include materials selected from silicon (Si), silicon carbide (SiC), composite materials containing silicon (Si) and carbon (C), and silicon oxide (SiO2). q, where 0.5≤q≤2.5) is one or more of the following.

[0052] The first carbon-based anode active material and the second carbon-based anode active material may each include one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

[0053] Any one or more of the first carbon-based anode active material and the second carbon-based anode active material may include having a 1×10 -5 cm 3 / g to 1×10 -1 cm 3 Graphite with a total pore volume within the range of / g.

[0054] The magnetic field can be applied with a magnetic field strength of 1,000 G to 12,000 G.

[0055] Beneficial effects

[0056] The negative electrode according to this disclosure includes silicon-based and carbon-based negative electrode active materials, thereby exhibiting excellent charge and discharge capacity and high energy density. Furthermore, because a magnetic field is applied during manufacturing to reduce the tortuosity of the entire negative electrode active layer, the negative electrode possesses excellent fast charging performance and lifetime characteristics. Attached Figure Description

[0057] Figure 1 This is a conceptual diagram showing the inclination between the long axis of the carbon-based negative electrode active material and the negative electrode current collector.

[0058] Figures 2 to 4 These are images of the thickness-direction cross-section of the negative electrode manufactured according to the embodiments and comparative examples of this disclosure, taken by scanning electron microscopy (SEM). Detailed Implementation

[0059] This disclosure can have various modifications and implementations, and specific implementations will be described in detail below.

[0060] In this disclosure, the terms “comprising” or “having” indicate the presence of a feature, number, step, action, component, part or combination thereof described in the specification, and it should be understood that the possibility of the presence or addition of one or more other features, numbers, steps, actions, components, parts or combinations thereof is not excluded in advance.

[0061] Furthermore, in this specification, "average particle size (D)" 50 The average particle size refers to the particle size at which the cumulative value in the particle size distribution becomes 50%, also known as the median diameter. The average particle size can be measured using methods conventionally applied in the art. For example, it can be measured using a particle size analyzer or an analyzer employing a laser diffraction scattering particle size distribution measurement method. In this disclosure, it can be a value measured by an analyzer using a laser diffraction scattering particle size distribution measurement method.

[0062] Furthermore, in this specification, "the carbon-based negative electrode active material is oriented" means that when the carbon-based negative electrode active material is projected in two dimensions, the longest line segment (i.e., the long axis) passing through the center of the particle is distributed with a predetermined orientation relative to the surface of the negative electrode current collector.

[0063] In addition, "the carbon-based anode active material has high orientation" can mean that the carbon-based anode active material contained in the anode active layer is aligned with the surface of the anode current collector at a high frequency, and in some cases, it can mean that the carbon-based anode active material contained in the anode active layer is aligned with the surface of the anode current collector at a high angle.

[0064] Furthermore, in this specification, "comprising as a major component" can mean a defined component comprising 50% or more (or 50% or more (or 60% or more (or 60% or more (or 70% or more (or 70% or more (or 80% or more (or 80% or more (or 90% or more (or 90% or more (or 90% or more (or 95% or more ( (100 parts by weight) of total weight (or total volume)). For example, "comprising carbon-based anode active material as a major component" can mean comprising 50% or more (or 60% or more (or 70% or more (or 80% or more (or 90% or more (or 95% or more (100 parts by weight) of the anode active layer, anode active material, and / or anode slurry). In some cases, this may mean that the entire anode active layer, anode active material, and / or anode slurry is composed of carbon-based anode active material and comprises it in an amount of 100% by weight.

[0065] This disclosure will be described in more detail below.

[0066] negative electrode

[0067] This disclosure provides a negative electrode, comprising:

[0068] Negative electrode current collector;

[0069] A first negative electrode active layer, wherein the first negative electrode active layer is disposed on at least one surface of the negative electrode current collector, and comprises a first carbon-based negative electrode active material; and

[0070] The second negative electrode active layer is disposed 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.

[0071] According to this disclosure, the negative electrode refers to a negative electrode used in 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 realizes the electroactivity of the negative electrode and is manufactured by coating a negative electrode slurry comprising a negative electrode active material onto at least one surface of the negative electrode current collector, the negative electrode active material undergoing an electrochemical redox reaction during battery charging and discharging, followed by drying and rolling.

[0072] The negative electrode active layer can have a two-layer structure, wherein a first negative electrode active layer and a second negative electrode active layer are stacked sequentially on a negative electrode current collector. The composition of each layer in a two-layer structure can be easily controlled. Therefore, the performance of the negative electrode can be improved by controlling the type or content of components contained in each layer according to a specific purpose (e.g., improving 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 can selectively include only a silicon-based negative electrode active material with high charge and discharge capacity of the battery in the second negative electrode active layer in contact with the positive electrode. Furthermore, the negative electrode active layer can selectively include only natural graphite, which has good adhesion as a negative electrode active material, in the first negative electrode active layer in contact with the negative electrode current collector, or it can include a binder that imparts binding properties to the components constituting the active layer in a higher proportion than in the second negative electrode active layer.

[0073] In this disclosure, 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.

[0074] According to this disclosure, the negative electrode includes a silicon-based negative electrode active material in the second negative electrode active layer to achieve high energy density, and at the same time, the fast charging performance and lifespan characteristics of the negative electrode can be improved by controlling the orientation 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, relative to the surface of the negative electrode current collector.

[0075] Specifically, such as Figure 1As shown, the first and second carbon-based anode active materials can have cross-sectional shapes, wherein, when projected as two-dimensional particles, the lengths of any two line segments passing through the center of the particle are different. The cross-sectional shape can be an ellipsoid elongated in any direction based on the particle center. In some cases, the first and second carbon-based anode active materials can be amorphous particles, where plate-like, sheet-like, flake-like, needle-like particles are aggregated, making it difficult to define a specific shape. In this case, amorphous particles do not include spherical particles.

[0076] Such first and second carbon-based anode active materials can be oriented such that the long axis passing through the center of the particle (hereinafter referred to as the "long axis of the carbon-based anode active material") when the particle is projected in two dimensions has a predetermined inclination relative to the anode current collector. This disclosure can shorten the tortuosity of the anode active layer comprising it by controlling the inclination formed between the anode current collector and the long axis of the carbon-based anode active material within a predetermined range. Since tortuosity provides a migration path for lithium ions during the charging of the secondary battery, shortening this path accelerates the charging speed of the secondary battery.

[0077] For example, in the negative electrode according to this disclosure, when the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed by scanning electron microscopy (SEM), the long axes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material can be tilted relative to the negative electrode current collector at a predetermined angle. In other words, when the angle of inclination of the long axis of the carbon-based negative electrode active material included in each negative electrode active layer relative to the negative electrode current collector is measured, the following equation 1 can be satisfied:

[0078] [Formula 1]

[0079]

[0080] In Equation 1 above,

[0081] FL 60-120 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°.

[0082] Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0083] The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

[0084] Equation 1 above represents the content ratio of the first carbon-based anode active material (FL). 60-120 The ratio of the content of the second carbon-based anode active material to that of the first carbon-based anode active material (SL) 60-120 The ratio between the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each negative electrode active layer, wherein the long axis has an inclination of greater than 60° and less than 120° relative to the negative electrode current collector.

[0085] Specifically, the inclination between the long axis of the carbon-based negative electrode active material and the surface of the negative electrode current collector can be from 0° to 180°. In this case, the cases where the inclination of the long axis relative to the surface of the negative electrode current collector is 0° to 90° and 90° to 180° differ only in the directionality of the long axis, and the angle formed with the surface of the negative electrode current collector can actually be the same. For example, the cases with an inclination of 60° relative to the surface of the negative electrode current collector and the cases with an inclination of 120° differ only in the directionality of the long axis of the carbon-based negative electrode active material relative to the surface of the negative electrode current collector, and the angle formed between the surface of the negative electrode current collector and the long axis of the carbon-based negative electrode active material can be understood as the same. Therefore, a ratio where the angle formed by the long axis of the carbon-based negative electrode active material relative to the surface of the negative electrode current collector is greater than 60° and less than 120° indicates the content ratio of carbon-based negative electrode active material with an inclination of more than 60° relative to the surface of the negative electrode current collector, regardless of directionality. This can be understood as the same ratio of carbon-based negative electrode active material with an angle greater than 60° and less than 90° formed between the surface of the negative electrode current collector and the long axis of the carbon-based negative electrode active material. Formula 1 refers to the ratio of carbon-based negative electrode active material with an inclination greater than 60° between the long axis of the carbon-based negative electrode active material and the surface of the negative electrode current collector being higher in the first negative electrode active layer than in the second negative electrode active layer. By achieving a high ratio of the first carbon-based negative electrode active material with an inclination greater than 60° and less than 120° between the long axis of the negative electrode current collector and the first negative electrode active layer, this disclosure can reduce the tortuosity within the first negative electrode active layer adjacent to the negative electrode current collector. Therefore, due to improved electrolyte impregnation and / or lithium-ion migration in the first negative electrode active layer, redox reactions within the negative electrode active layer adjacent to the negative electrode current collector can be promoted during the charging and discharging of the secondary battery. Therefore, uniform degradation can be induced throughout the entire negative electrode active layer. Furthermore, since the volume expansion in the thickness direction of the first negative electrode active layer caused by lithium ion insertion during the charging of the secondary battery is suppressed, there is an advantage in improving the adhesion between the negative electrode active layer and the negative electrode current collector. Therefore, the negative electrode has the advantage of improved lifetime characteristics.

[0086] Therefore, the negative electrode of this disclosure can satisfy Equation 1 as 0.1 or greater and less than 1.0 (i.e., 0.1 ≤ SL). 60-120 / FL 60-120 <1.0). Specifically, the negative electrode can satisfy the following range: 0.5 or greater 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).

[0087] Furthermore, the negative electrode according to this disclosure can further satisfy any one or more of Equations 2 and 3 below, as well as Equation 1:

[0088] [Equation 2]

[0089] 40≤FL 30-150 ≤70

[0090] [Formula 3]

[0091] 5≤SL 60-120 ≤20

[0092] In equations 2 and 3 above,

[0093] FL 30-150 The percentage (in %) of the first carbon-based anode active material in which the angle between the long axis of the first carbon-based anode active material and the surface of the anode current collector is greater than 30° and less than 150°.

[0094] Among them SL 60-120 The percentage (in %) of the second carbon-based anode active material in which the angle between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0095] Equation 2 above refers to a parameter where the ratio of the inclination of the long axis relative to the negative electrode current collector in the first carbon-based negative electrode active material to be greater than 30° is high, and this ratio can be satisfied within the range of 40% to 70% in the entire first carbon-based negative electrode active material. For example, this disclosure can satisfy Equation 2 with a ratio within the following range: 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%).

[0096] This disclosure significantly reduces the tortuosity of the first negative electrode active layer by ensuring that the ratio of the tilt angle between the negative electrode current collector and the long axis of the first carbon-based negative electrode active material exceeds 30°, which is within the aforementioned range. This has the advantage of achieving high fast-charging performance during secondary battery charging. Furthermore, when the long axis of the first carbon-based negative electrode active material has a high tilt angle of more than 30° relative to the negative electrode current collector, it has the effect of suppressing volume expansion in the thickness direction of the first negative electrode active layer during secondary battery charging. This has the advantage of further extending the negative electrode lifetime because the adhesion between the negative electrode current collector and the first negative electrode active layer can be stronger.

[0097] Equation 3 above refers to a parameter where the ratio of the inclination of the long axis relative to the negative electrode current collector in the second carbon-based negative electrode active material to a value greater than 60° and to a value of 120° or greater is low, and this ratio can be satisfied within the range of 5% to 20% in the entire second carbon-based negative electrode active material. For example, this disclosure can satisfy Equation 3 with a ratio within 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%).

[0098] This disclosure achieves high energy density and charge / discharge capacity of the negative electrode by ensuring that the ratio of the inclination angle between the long axis of the second carbon-based negative electrode active material and the negative electrode current collector exceeds 60° within the aforementioned range, while simultaneously preventing degradation of fast-charging performance. Specifically, if the ratio of the inclination angle between the long axis of the second carbon-based negative electrode active material and the negative electrode current collector exceeding 60° is lower than the aforementioned lower limit, there is a problem of reduced electrolyte wettability of the negative electrode and degradation of fast-charging performance. Furthermore, if the ratio is higher than the aforementioned upper limit, there is a limitation of reduced energy density and reduced charge / discharge capacity of the negative electrode.

[0099] The orientation of the long axis of the carbon-based anode active material relative to the surface of the anode current collector is achieved by applying a magnetic field to the anode slurry comprising the carbon-based anode active material during the manufacture of the anode. The carbon-based anode active material is diamagnetic and exhibits magnetic anisotropy when a magnetic field is applied, wherein the magnetism varies depending on the axial orientation of the crystals constituting the carbon-based anode active material. On the other hand, since the silicon-based anode active material included in the second anode active layer does not exhibit this magnetic anisotropy, its orientation behavior relative to the anode current collector is not significant even when a magnetic field is applied. Due to this silicon-based anode active material, and since the second carbon-based anode active material is insufficient to achieve magnetic anisotropy even when a magnetic field is applied, a relatively lower orientation relative to the anode current collector can be induced compared to the first carbon-based anode active material.

[0100] The orientation of the long axis of the first and second carbon-based anode active materials can be affected by the type or content of the carbon-based anode active material, its average particle size, porosity, and the content ratio with the silicon-based anode active material. Therefore, in order to satisfy Equations 1 to 3 above, the anode according to this disclosure can be adjusted so that the type, content, and / or physical properties of the anode active materials included in the first and second anode active layers meet predetermined conditions.

[0101] 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 with carbon atoms as the main component, and their types and / or contents may be the same or different.

[0102] Specifically, the first carbon-based anode active material and the second carbon-based anode active material may include one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

[0103] The first carbon-based anode active material and the second carbon-based anode active material can each be in the form of an assembly of multiple particles. In this case, a graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, graphite particles. For example, the first carbon-based anode active material may include artificial graphite. Artificial graphite can be in the form of a graphite assembly in which 10 to 30 particles are aggregated. Compared with natural graphite, artificial graphite has the advantages of superior high-rate charge and discharge performance and superior lifetime characteristics.

[0104] Furthermore, the second carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may be in the form of graphite assemblies containing 10 to 30 particles. Additionally, the mixing ratio of natural graphite to artificial graphite may be 5 to 50:50 to 95, or 5 to 30:70 to 95, based on weight. The carbon-based negative electrode active material comprising natural graphite and artificial graphite in the mixing ratio described above results in strong adhesion between the negative electrode current collector and the negative electrode active layer, and achieves a high degree of orientation of the long axis of the carbon-based negative electrode active material relative to the surface of the negative electrode current collector through a magnetic field applied during the manufacture of the negative electrode.

[0105] The first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material include low-expansion graphite. In this disclosure, "low-expansion graphite" refers to graphite that exhibits low expansion characteristics during secondary battery charging. For example, when manufacturing a secondary battery comprising a negative electrode active material including graphite as the negative electrode, if the expansion characteristics of the negative electrode active layer remain low even after repeated charge and discharge cycles of the secondary battery, the corresponding graphite can be referred to as low-expansion graphite. Here, the expansion characteristics of low-expansion graphite can be known from the thickness variation of the negative electrode active layer during charge and discharge cycles. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion synthetic graphite.

[0106] In this disclosure, low-expansion graphite can be manufactured by cold isostatic pressing (CIP), a method in which pressure is uniformly applied to each direction of the particles at low temperature. Low-expansion graphite manufactured by cold isostatic pressing is isotropic graphite, and isotropic graphite possesses low electrical resistance, thermal shock resistance, and excellent mechanical properties, thereby improving the lifetime characteristics of the negative electrode itself.

[0107] Furthermore, low-expansion graphite can refer to natural graphite particles coated with carbon. In this case, low-expansion graphite has a carbon layer, which suppresses graphite expansion during the charging of the secondary battery, and advantageously, the amount of impurities generated due to physical damage during the manufacture of carbon-based anode active materials and / or the use of them in the manufacture of anodes or battery assembly processes is significantly less.

[0108] Low-expansion graphite possesses high porosity within graphite particles. This high porosity improves the volume expansion control of the negative electrode active material, resulting in minimal volume expansion during secondary battery charging. Furthermore, since lithium-ion insertion into the particle interior is advantageous, charging speed can be further improved. For example, low-expansion graphite can achieve a total pore volume within a predetermined range. Specifically, low-expansion graphite can have a total pore volume of 1 × 10⁻⁶. -5 cm 3 / g to 1×10 -1 cm 3 Total pore volume within the range of / g. For example, low-expansion graphite can have a total pore volume within the range of 5 × 10⁻⁶ g. -4 cm 3 / g to 1×10 -1 cm 3 / g; 1 × 10 -3 cm 3 / g to 1 × 10 -1 cm 3 / g; 5 × 10 -3 cm 3 / g to 1 × 10 -1 cm 3 / g; 1× 10 -3 cm 3 / g to 5 × 10 -2 cm 3 / g; 1 × 10 -3 cm 3 / g to 1 × 10 -2 cm 3 / g; 5 × 10 -3 cm 3 / g to 5× 10 -2 cm 3 / g; or 5 × 10 -3 cm 3 / g to 2 × 10 -2 cm 3 / g. The total pore volume of low-expansion graphite can be measured using the BET measurement method with adsorbed nitrogen (N2) gas. Low-expansion graphite can reduce volume expansion during secondary battery charging by meeting the above-mentioned range. Furthermore, since low-expansion graphite meeting the above-mentioned total pore volume range provides pathways through which lithium ions and / or electrons can move within the particles, it can not only improve the charging speed of the secondary battery, but also effectively suppress the increase in resistance of the negative electrode active layer according to the progress of the secondary battery's charge and discharge cycles.

[0109] Furthermore, low-expansion graphite can be included in the first and / or second negative electrode active layers at a predetermined content. Specifically, based on the total weight of the first or second carbon-based negative electrode active material, low-expansion graphite can be included in the range of 10% by weight or higher and 70% by weight or lower. For example, based on the total weight of the first or second carbon-based negative electrode active material, low-expansion graphite can be included in the range of 10% to 30% by weight, 20% to 40% by weight, 15% to 45% by weight, 10% to 50% by weight, 30% to 60% by weight, 50% to 70% by weight, 40% to 60% by weight, 15% to 25% by weight, or 45% to 69% by weight.

[0110] When the first carbon-based negative electrode active material includes low-expansion graphite, this disclosure can minimize the volume change of the first negative electrode active layer during the charging and discharging of the secondary battery by controlling the content of low-expansion graphite within the aforementioned range, thereby improving the adhesion between the negative electrode current collector and the first negative electrode active layer. Furthermore, since controlling the content of low-expansion graphite within the aforementioned range minimizes the volume change of the first negative electrode active layer during the charging and discharging of the secondary battery, the negative electrode active material of the second negative electrode active layer can be firmly fixed. This reduces the movement of the carbon-based negative electrode active material that occurs during the cycling of the secondary battery, thereby preventing an increase in the tortuosity of the entire negative electrode active layer (especially the second negative electrode active layer), and / or preventing a decrease in the tilt formed between the oriented carbon-based negative electrode active material and the negative electrode current collector.

[0111] When the second carbon-based negative electrode active material includes low-expansion graphite, this disclosure achieves high charge and discharge capacity of the second negative electrode active layer adjacent to the positive electrode active layer by controlling the content of low-expansion graphite within the aforementioned range. Furthermore, the volume expansion caused by the silicon-based negative electrode active material included in the second negative electrode active layer during lithium secondary battery charging can be significantly reduced. This suppresses the increase in the tortuosity of the second negative electrode active layer until the secondary battery's lifespan is exhausted. The tortuosity of the negative electrode active layer is a parameter indirectly indicating the length of the path disposed within the negative electrode active layer, allowing electrolytes and the like to move from the surface of the negative electrode active layer to the negative electrode current collector. A lower tortuosity ratio corresponds to a shorter path length, and a shorter tortuosity may be equivalent to a shorter migration path for lithium ions and / or electrons during the charging and discharging of the secondary battery. However, in practical lithium secondary batteries, volume expansion of the negative electrode active material due to lithium ion insertion during charging is unavoidable, and repeated volume changes of the negative electrode active material due to charging and discharging can lead to an increase in the tortuosity within the negative electrode active layer. However, this disclosure can minimize the volume expansion of the second negative electrode active layer by including low-expansion graphite as the second carbon-based negative electrode active material in the second negative electrode active layer at a predetermined content, the second negative electrode active layer comprising a silicon-based negative electrode active material having large volume expansion during charging.

[0112] Meanwhile, the first carbon-based anode active material and the second carbon-based anode active material included in each anode active layer can meet a predetermined range of average particle size. Specifically, each of the carbon-based anode active materials can exhibit an average particle size (D) in the range of 0.5 μm to 20 μm. 50 For example, the first carbon-based anode active material and the second carbon-based anode active material can each exhibit an average particle size (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 ).

[0113] The average particle size of the first and second carbon-based anode active materials can be advantageous for smaller particle sizes, maximizing the disorder of the expansion direction of each particle and thus preventing particle expansion due to lithium-ion charging. However, if the particle size of each carbon-based anode active material is less than 0.5 μm, a large amount of binder may be required due to the increased number of particles per unit volume. On the other hand, if the maximum particle size exceeds 20 μm, expansion becomes severe, causing a decrease in the bonding characteristics between particles and between particles and the current collector with repeated charging and discharging, and potentially a significant reduction in cycle performance.

[0114] Furthermore, silicon-based anode active materials are materials containing silicon (Si) as the main component, and can increase the charge and discharge capacity per unit volume of the anode as well as the energy density. Examples of such silicon-based anode active materials include silicon (Si), silicon carbide (SiC), silicon (Si) and carbon (C) composites, silicon monoxide (SiO), silicon dioxide (SiO2), and other silicon oxides (SiO2). q These can be included individually or in combination in the negative electrode active layer.

[0115] When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited into a silicon-based negative electrode active material and included in the negative electrode active layer, they can be represented as silicon oxide (SiO2). q (where 0.5≤q≤2.5).

[0116] Furthermore, in silicon-based anode active materials, composite materials are materials containing silicon (Si) and carbon (C) as main components, and can specifically refer to silicon (Si), silicon carbide (SiC), and silicon oxide (SiO) composites with carbon (C). q For example, composite materials can have a core-shell structure, wherein carbon (C) is coated on a core-shell substrate including silicon (Si), silicon carbide (SiC), and silicon oxide (SiO2). q Carbon (C) can be deposited on the surface of particles such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO) through CVD, PVD, ALD, etc. q The composite material can be applied to the surface of particles containing silicon (Si), silicon carbide (SiC), silicon oxide (SiO2), etc.; or it can have a form in which the particle surface is modified using plasma, UV, etc. Furthermore, the composite material can have a surface modified by applying materials containing silicon (Si), silicon carbide (SiC), silicon oxide (SiO2), etc. q Composite particles are formed by applying mechanical and / or physical forces to uniformly mix / crush a mixture of silicon (Si) and carbon (C) particles. In this case, unlike alloys in which silicon (Si) atoms and carbon (C) atoms form a physicochemical bond, composite particles may mean that particles containing silicon (Si) components and particles made of carbon (C) are uniformly combined while retaining their original composition.

[0117] Furthermore, silicon-based anode active materials can be doped with Li, Mg, Al, Ca, and / or Ti, or form alloys containing Li, Mg, Al, Ca, and / or Ti. In this case, one or more metals can be doped into the silicon-based anode active material or alloyed with it. Specifically, the silicon-based anode active material can be doped with or alloyed with a metal in the range of 1 mol% to 10 mol% relative to silicon atoms. When metals are added in the form of doping or alloying, the silicon-based anode active material can increase conductivity and improve mechanical strength. However, since metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, metals can be doped into or alloyed with the silicon-based anode active material at the aforementioned content to reduce resistance without reducing the energy density per unit weight of the silicon-based anode active material.

[0118] Based on the total weight of the negative electrode active layer, silicon-based negative electrode active material can be included in the range of 0.1 wt% to 30 wt%. Specifically, based on the total weight of the negative electrode active layer, silicon-based negative electrode active material can be included in the ranges 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%. This disclosure can increase the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss of the secondary battery during initial charging and discharging by adjusting the content ratio of silicon-based negative electrode active material within the above ranges. Furthermore, the lifespan of the secondary battery can be increased because the structural stability of the negative electrode active layer can be improved by minimizing the volume change of the negative electrode active layer during the charging and discharging of the secondary battery.

[0119] Silicon-based anode active materials can have a predetermined average particle size (D). 50 Specifically, silicon-based anode active materials can have an average particle size (D) in the range of 1 μm to 20 μm. 50 For example, silicon-based anode active materials can have an average particle size (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 ).

[0120] If the minimum particle size of the silicon-based anode active material is smaller than the lower limit of the aforementioned range, uniform dispersion in the second anode active layer may be difficult. If the silicon-based anode active material is not uniformly dispersed, redox reactions in the aggregated and non-aggregated regions are unevenly initiated during the charging and discharging of the secondary battery, which can contribute to the degradation of the second anode active layer. Furthermore, if the maximum particle size of the silicon-based anode active material exceeds the upper limit of the aforementioned range, it becomes difficult to control the crystal planes of the silicon-based anode active material, and the expansion rate per unit area of ​​the second anode active layer increases significantly during the charging and discharging of the secondary battery, resulting in a significant decrease in cycle characteristics with repeated charging and discharging.

[0121] In addition, as needed, the first negative electrode active layer and the second negative electrode active layer may optionally further include conductive materials, adhesives, other additives, and negative electrode active materials as main components.

[0122] Conductive materials may include one or more selected from the following: carbon black, such as acetylene black, furnace black, lamp black and pyrolytic black; graphene; carbon nanotubes and carbon fibers, but are not limited thereto.

[0123] For example, the negative electrode active layer can contain carbon black, carbon nanotubes, carbon fibers, etc. as conductive materials, either alone or in combination.

[0124] Based on the weight of each negative electrode active layer, the content of conductive material can range from 0.1 wt% to 10 wt%. Specifically, based on the weight of each negative electrode active layer, the content of conductive material can range from 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%. This disclosure prevents a decrease in charging capacity due to an increase in the resistance of the negative electrode caused by a low content of conductive material by controlling the content of conductive material within the above range. Furthermore, this disclosure can prevent the problem of reduced charging capacity due to a decrease in the content of negative electrode active material caused by an excess of conductive material exceeding the above range, or the problem of increased resistance due to an increase in the loading of the negative electrode active layer.

[0125] Adhesives are components that facilitate the bonding of the negative electrode active material and the conductive material to the current collector, and can be applied appropriately within a range that does not degrade the electrical performance of the negative electrode. For example, adhesives may include one or more of the following: vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0126] The binder content can range from 0.1 wt% to 10 wt% based on the weight of each negative electrode active layer. Specifically, the binder content can range from 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. This disclosure prevents reduced adhesion of the active layer due to low binder content, or reduced electrical performance of the negative electrode due to excessive binder content, by controlling the binder content in each negative electrode active layer within the above ranges.

[0127] The negative electrode active layer can have a predetermined average thickness to achieve high charge and discharge capacity while maintaining a fast charging speed. The charge and discharge capacity of the negative electrode active layer increases with increasing loading of the electrochemically active negative electrode material. However, in this case, the fast charging performance of the manufactured negative electrode is limited because it is difficult to orient the long axis of the carbon-based negative electrode active material to a predetermined tilt relative to the negative electrode current collector during the fabrication of the negative electrode active layer. Therefore, this disclosure allows the average thickness of the negative electrode active layer to be adjusted to a predetermined range. Specifically, the negative electrode active layer can have an average thickness in the range of 50 μm to 400 μm. For example, the average thickness of the negative electrode active layer can be in the range of 100 μm to 350 μm, 100 μm to 300 μm, 100 μm to 250 μm, 100 μm to 200 μm, 150 μm to 400 μm, 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.

[0128] Furthermore, the first negative electrode active layer and the second negative electrode active layer can have a predetermined thickness ratio. Specifically, the thickness ratio of the second negative electrode active layer based on the average thickness of the first negative electrode active layer can be in the range of 80% to 150%. For example, the thickness ratio of the second negative electrode active layer based on the average thickness of the first negative electrode active layer can be 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%.

[0129] This disclosure can prevent a decrease in the charging and discharging capacity and cycle characteristics of the negative electrode caused by the average thickness ratio of the second negative electrode active layer based on the first negative electrode active layer being lower than the lower limit of the aforementioned range by adjusting the thickness ratio of the first negative electrode active layer to the aforementioned range. Furthermore, it can prevent a decrease in the charging and discharging capacity and fast charging performance of the negative electrode caused by the average thickness ratio of the second negative electrode active layer based on the first negative electrode active layer being higher than the upper limit of the aforementioned range.

[0130] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and will not cause chemical changes in the battery. For example, thin plates or films including copper, stainless steel, nickel, titanium, calcined carbon, etc., can be used as negative electrode current collectors, and when copper or stainless steel is included, materials that have been surface-treated with carbon, nickel, titanium, silver, etc., can also be used. Furthermore, considering the conductivity and total thickness of the manufactured negative electrode, the average thickness of the negative electrode current collector can be appropriately applied in the range of 1 μm to 500 μm.

[0131] The negative electrode according to this disclosure exhibits excellent charge and discharge capacity and high energy density due to its above-described structure. Furthermore, the negative electrode also possesses excellent fast-charging performance because the migration path of lithium ions in the active layer of the negative electrode is shortened and the diffusion resistance of lithium ions is significantly low.

[0132] Lithium secondary batteries

[0133] In addition, this disclosure provides a lithium secondary battery including an electrode assembly, which includes a positive electrode, the negative electrode described above, and a separator disposed between the positive electrode and the negative electrode.

[0134] The lithium secondary battery according to this disclosure includes 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 located between them. The lithium secondary battery includes the negative electrode described above, thereby exhibiting not only excellent fast-charging performance due to improved lithium-ion diffusion capability, but also the advantage of high energy density.

[0135] Since the negative electrode has the same structure as described above, its detailed description will be omitted.

[0136] In addition, the positive electrode includes a positive electrode active layer, the positive electrode active layer includes 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 required.

[0137] The positive electrode active material is a material capable of causing an electrochemical reaction on the positive electrode current collector, and may include one or more lithium metal oxides represented by Chemical Formula 1 and Chemical Formula 2 below, which are capable of reversibly intercalating and deintercalating lithium ions:

[0138] [Chemical Formula 1]

[0139] Li l [Ni m Co n Mn w M 1 v O2]

[0140] [Chemical Formula 2]

[0141] LiM 2 p Mn q P r O4

[0142] In the above Chemical Formula 1 and Chemical Formula 2,

[0143] where M 1 is one or more elements selected from 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,

[0144] where l, m, n, w, and v are 1.0 ≤ l ≤ 1.30, 0.5 ≤ m < 1, 0 < n ≤ 0.3, 0 < w ≤ 0.3, and 0 ≤ v ≤ 0.1, and m + n + w + v = 1,

[0145] [[ID=Q49]]where M 2 is Ni, Co, or Fe,

[0146] where p is 0.05 ≤ p ≤ 1.0,

[0147] where q is 2 - p, and

[0148] where r is 0 or 1.

[0149] The lithium metal oxides represented by the above chemical formulas 1 and 2 are materials containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as positive electrode active materials, they have the advantage of stably supplying high capacity and / or high voltage power compared with conventional positive electrode active materials (such as lithium iron phosphate (LiFeO4)).

[0150] At this point, the lithium metal oxide represented by chemical formula 1 may include LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, etc. Lithium metal oxides represented by chemical formula 2 may include LiNi. 0.7 Mn 1.3 O4; LiNi 0.5 Mn 1.5 O4; LiNi 0.3 Mn 1.7 O4, etc., and these can be used alone or in combination.

[0151] Furthermore, based on the total weight of the positive electrode active layer, the positive electrode active material may be included in an amount of 85% by weight or greater. Specifically, based on the total weight of the positive electrode active layer, the positive electrode active material may be included in an amount of 90% by weight or more, 93% by weight or more, or 95% by weight or more.

[0152] The positive electrode active layer may also include conductive materials, adhesives, other additives, and the positive electrode active material itself.

[0153] At this point, conductive materials are used to improve the electrical properties of the positive electrode, and those conventionally used in the art can be applied. Specifically, conductive materials may include one or more selected from: natural graphite; artificial graphite; carbon black, such as acetylene black, furnace black, lampblack, and pyrolytic black; graphene; and carbon nanotubes.

[0154] Based on the total weight of the positive electrode active layer, conductive material may be included in an amount from 0.1 wt% to 5 wt%. Specifically, based on the total weight of the positive electrode active layer, conductive material may be included in an amount from 0.1 wt% to 4 wt%, 2 wt% to 4 wt%, 1.5 wt% to 5 wt%, 1 wt% to 3 wt%, 0.1 wt% to 2 wt%, or 0.1 wt% to 1 wt%.

[0155] In addition, the adhesive serves to bond the positive electrode active material, positive electrode additive, and conductive material together, and can be used without particular restrictions, as long as it has this function. Specifically, the adhesive may include one or more resins selected from: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. For example, the adhesive may include polyvinylidene fluoride.

[0156] The binder may be included in an amount of 1% to 10% by weight, based on the total weight of the positive electrode active layer. Specifically, the binder may be included in an amount of 2% to 8% by weight, or 1% to 5% by weight, based on the total weight of the positive electrode active layer.

[0157] There is no particular limitation on the total thickness of the positive electrode active layer, but it can specifically be 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.

[0158] Furthermore, those materials with high conductivity that do not cause changes in battery chemistry can be used as the positive electrode current collector. For example, thin plates or films containing stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used as the positive electrode current collector, and when aluminum or stainless steel is included, those surface-treated with carbon, nickel, titanium, silver, etc., can be used. Moreover, considering the conductivity and total thickness of the manufactured positive electrode, the average thickness of the current collector can be appropriately applied in the range of 3 μm to 500 μm.

[0159] The separator, inserted between the positive and negative electrodes of a lithium-ion secondary battery, is an insulating film with high ion permeability and mechanical strength, and is not particularly limited, provided it is conventionally used in the art. Specifically, the separator can use those comprising one or more polymers selected from: chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers. The separator can be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric comprising the aforementioned polymers, and in some cases, it can be in the form of a composite separator, wherein organic or inorganic particles are coated onto the porous polymer substrate by an organic adhesive. Furthermore, the separator can have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0160] Furthermore, the lithium secondary battery according to this disclosure is not particularly limited, but can be a secondary battery in the form of a stacked electrode assembly, a zigzag electrode assembly, or a zigzag stacked electrode assembly. For example, the lithium secondary battery according to this disclosure can be a pouch-type secondary battery or a prismatic secondary battery.

[0161] Pouch cells and / or prismatic cells have the advantage of high energy density because the individual cells of the secondary cell can be packed in a limited space at a high density.

[0162] Methods for manufacturing negative electrodes

[0163] Furthermore, this disclosure provides a method for manufacturing the negative electrode according to this disclosure.

[0164] Specifically, the method of manufacturing the negative electrode according to the present disclosure includes coating at least one surface of the negative electrode current collector with a first negative electrode slurry comprising a first carbon-based negative electrode active material (S1), coating the coated first negative electrode slurry with a second negative electrode slurry comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material (S2), and applying a magnetic field to the coated first negative electrode slurry and the coated second negative electrode slurry (S3).

[0165] Steps (S1) and (S2) above refer to a method of simultaneously or sequentially discharging and 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 onto the surface of a moving negative electrode current collector. The first negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and the second negative electrode slurry is coated onto the coated first negative electrode slurry.

[0166] Steps (S1) and (S2) described above can be applied without specific limitations, as long as they are methods conventionally used in the art; however, a mold coating method is preferred. The mold coating method is performed using a grooved mold coating machine, which may include a shim for controlling the discharge conditions of the negative electrode slurry. The grooved mold coating machine can easily control the loading amount, coating thickness, etc., of the negative electrode slurry coated on the negative electrode current collector by controlling the shape or position of the shim.

[0167] For example, this disclosure allows the simultaneous coating of a first negative electrode slurry and a second negative electrode slurry onto a negative electrode current collector using a dual-die coating machine. In this case, there is a significant advantage in improving process efficiency compared to sequentially coating each slurry.

[0168] Furthermore, the first and second negative electrode slurries each include a first carbon-based negative electrode active material and a second carbon-based negative electrode active material as main components. Specifically, the first and second carbon-based negative electrode active materials may include one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

[0169] The first carbon-based anode active material and the second carbon-based anode active material can each be in the form of an assembly of multiple particles. In this case, a graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, graphite particles. For example, the first carbon-based anode active material may include artificial graphite, and the artificial graphite may be in the form of a graphite assembly in which 10 to 30 particles are aggregated. Compared with natural graphite, artificial graphite has the advantages of superior high-rate charge and discharge performance and superior lifetime characteristics.

[0170] Furthermore, the second carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may be in the form of a graphite assembly in which 10 to 30 particles are aggregated. Furthermore, based on weight, the mixing ratio of natural graphite and artificial graphite may be (5 to 50):(50 to 95), or (5 to 30):(70 to 95). The second carbon-based negative electrode active material includes natural graphite and artificial graphite in the mixing ratio described above, thereby ensuring strong adhesion between the negative electrode current collector and the negative electrode active layer, and achieving a high degree of orientation of the long axis of the carbon-based negative electrode active material relative to the surface of the negative electrode current collector by applying a magnetic field during the manufacture of the negative electrode.

[0171] The first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material include low-expansion graphite. The carbon-based negative electrode active material includes low-expansion graphite. In this disclosure, "low-expansion graphite" refers to graphite that exhibits low expansion characteristics during secondary battery charging. Here, the expansion characteristics of low-expansion graphite can be known from the thickness variation of the negative electrode active layer during charge and discharge cycles. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion synthetic graphite.

[0172] In this disclosure, low-expansion graphite can refer to carbon-coated natural graphite particles. Low-expansion graphite can be manufactured by spheroidizing plate-shaped natural graphite and then using a cold isostatic pressing (CIP) method, in which pressure is uniformly applied to each direction of the particles at low temperature. Low-expansion natural graphite manufactured by the cold isostatic pressing method can be isotropic graphite. Isotropic graphite possesses low electrical resistance, thermal shock resistance, and excellent mechanical properties, thereby improving the lifetime characteristics of the negative electrode itself.

[0173] Low-expansion graphite has a carbon layer, which suppresses graphite expansion during secondary battery charging, and advantageously, the amount of impurities generated due to physical damage during the manufacture of carbon-based anode active materials and / or the manufacture of anodes or battery assembly processes using them is significantly less.

[0174] Furthermore, low-expansion graphite possesses high porosity within graphite particles. Graphite particles with high porosity exhibit excellent volume expansion control of the anode active material itself, and due to their facilitating lithium-ion insertion, they offer superior fast-charging performance. Low-expansion graphite can satisfy a predetermined range of total pore volume. Specifically, low-expansion graphite can have a total pore volume of 1 × 10⁻⁶. -5 cm 3 / g to 1×10 -1 cm 3 Total pore volume within the range of / g. For example, low-expansion graphite can have a total pore volume within the range of 5 × 10⁻⁶ g. -4 cm 3 / g to 1×10 -1 cm 3 / g; 1 × 10 -3 cm 3 / g to 1× 10 -1 cm 3 / g; 5 × 10 -3 cm 3 / g to 1 × 10 -1 cm 3 / g; 1 × 10 -3 cm 3 / g to 5 × 10 -2 cm 3 / g; 1× 10-3 cm 3 / g to 1 × 10 -2 cm 3 / g; 5 × 10 -3 cm 3 / g to 5 × 10 -2 cm 3 / g; or 5 × 10 -3 cm 3 / g to 2 × 10 -2 cm 3 / g. The total pore volume of low-expansion graphite can be measured using the BET measurement method with adsorbed nitrogen (N2) gas. Low-expansion graphite can reduce volume expansion during secondary battery charging by meeting the above-mentioned range. Furthermore, since low-expansion graphite meeting the above-mentioned total pore volume range provides pathways through which lithium ions and / or electrons can move within the particles, it can not only improve the charging speed of the secondary battery, but also effectively suppress the increase in resistance of the negative electrode active layer according to the progress of the secondary battery's charge and discharge cycles.

[0175] Furthermore, the second negative electrode slurry includes a silicon-based negative electrode active material. Silicon-based negative electrode active materials are materials containing silicon (Si) as a major component and can increase the charge and discharge capacity per unit volume of the negative electrode, as well as its energy density. Examples of such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), silicon (Si) and carbon (C) composites, silicon monoxide (SiO), silicon dioxide (SiO2), and other silicon oxides (SiO2). q These can be included individually or in combination in the negative electrode active layer.

[0176] When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited into a silicon-based negative electrode active material and included in the negative electrode active layer, they can be represented as silicon oxide (SiO2). q (where 0.5≤q≤2.5).

[0177] In silicon-based anode active materials, composite materials are materials containing silicon (Si) and carbon (C) as the main components, and can specifically refer to silicon (Si), silicon carbide (SiC), and silicon oxide (SiO) composites with carbon (C). q For example, composite materials can have a core-shell structure, wherein carbon (C) is coated on a core-shell substrate including silicon (Si), silicon carbide (SiC), and silicon oxide (SiO2). q Carbon (C) can be deposited on the surface of particles such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO) through CVD, PVD, ALD, etc. qThe composite material can be applied to the surface of particles containing silicon (Si), silicon carbide (SiC), silicon oxide (SiO2), etc.; or it can have a form in which the particle surface is modified using plasma, UV, etc. Furthermore, the composite material can have a surface modified by applying materials containing silicon (Si), silicon carbide (SiC), silicon oxide (SiO2), etc. q Composite particles are formed by applying mechanical and / or physical forces to uniformly mix / crush a mixture of silicon (Si) and carbon (C) particles. In this case, unlike alloys in which silicon (Si) atoms and carbon (C) atoms form a physicochemical bond, composite particles may mean that particles containing silicon (Si) components and particles made of carbon (C) are uniformly combined while retaining their original composition.

[0178] Furthermore, silicon-based anode active materials can be doped with Li, Mg, Al, Ca, and / or Ti, or form alloys containing Li, Mg, Al, Ca, and / or Ti. In this case, one or more metals can be doped into the silicon-based anode active material or alloyed with it. Specifically, the silicon-based anode active material can be doped with or alloyed with a metal in the range of 1 mol% to 10 mol% relative to silicon atoms. When metals are added in the form of doping or alloying, the silicon-based anode active material can increase conductivity and improve mechanical strength. However, since metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, metals can be doped into or alloyed with the silicon-based anode active material at the aforementioned content to reduce resistance without reducing the energy density per unit weight of the silicon-based anode active material.

[0179] Based on the total solids content of the negative electrode slurry, silicon-based negative electrode active material can be included in the range of 0.1 wt% to 30 wt%. Specifically, based on the total solids content of the negative electrode slurry, silicon-based negative electrode active material can be included in the ranges 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%. This disclosure can increase the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss of the secondary battery during initial charging and discharging by adjusting the content ratio of silicon-based negative electrode active material within the above ranges. Furthermore, the lifespan of the secondary battery can be increased because the structural stability of the negative electrode active layer can be improved by minimizing the volume change of the negative electrode active layer during the charging and discharging of the secondary battery.

[0180] In addition to the negative electrode active material, the first and second negative electrode slurries may also include conductive materials, binders, additives, etc. Since each component in the negative electrode slurry is the same as the negative electrode active layer of the aforementioned lithium secondary battery, its detailed description will be omitted.

[0181] Meanwhile, the orientation of the carbon-based anode active material can be induced by the magnetic field applied after steps (S1 and S2).

[0182] Specifically, step (S3) refers to the process of applying a magnetic field to the first and second negative electrode slurries coated on the negative electrode current collector so that the long axis of the carbon-based negative electrode active material particles included in each negative electrode slurry is aligned and / or oriented relative to the negative electrode current collector.

[0183] The degree to which the long axis of the carbon-based negative electrode active material is aligned and / or oriented relative to the negative electrode current collector can vary depending on the strength of the applied magnetic field. Therefore, in step (S3), the magnetic field can have a strength in the range of 1,000 G to 12,000 G (Gauss) to enhance the effect of aligning and / or oriented the long axis of the carbon-based negative electrode active material particles relative to the surface of the negative electrode current collector. Specifically, the magnetic field can be between 1,500 G and 10,000 G, 2,000 G and 10,000 G, 3,000 G and 10,000 G, 1,000 G and 9,000 G, 3,000 G and 9,000 G, 7,000 G and 9,000 G, 2,000 G and 8,000 G, 3,000 G and 8,000 G, 4,000 G and 8,000 G, 5,000 G and 7,000 G, 5,000 G and 10,000 G, 5,000 G and 12,000 G, 5,000 G and 9,000 G, 5,000 G and 7,500 G, and 6,000 G and 6,500 G. Apply at an intensity within the range of G, 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.

[0184] The carbon-based anode active material in the anode slurry under an applied magnetic field can be oriented such that its long axis has a predetermined tilt relative to the surface of the anode current collector. This can be confirmed directly or indirectly by means of scanning electron microscopy (SEM) analysis of the thickness-direction cross-section of the anode active layer formed after drying the anode slurry containing the carbon-based anode active material.

[0185] For example, in the negative electrode manufactured according to this disclosure, when the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed by scanning electron microscopy (SEM), the long axes 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, can be tilted relative to the negative electrode current collector at a predetermined tilt angle. In other words, when the tilt angle of the long axis of the carbon-based negative electrode active material included in each negative electrode active layer relative to the negative electrode current collector is measured, the following equation 1 can be satisfied:

[0186] [Formula 1]

[0187]

[0188] In Equation 1 above,

[0189] FL 60-120 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°.

[0190] Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0191] The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

[0192] Meanwhile, the method for manufacturing a negative electrode according to this disclosure may further include step (S4): after step (S3), drying the negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer.

[0193] Drying can be applied without particular restrictions, as long as it is a method conventionally applicable in the art. For example, drying can be achieved by applying heat to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0194] For example, drying can be carried out at a temperature of 100°C to 250°C (specifically 160°C to 200°C) for 1 to 15 hours.

[0195] Furthermore, the method may also include step (S5): after step (S4), the negative electrode active layer formed by drying is rolled. Rolling refers to the 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 rolling mill or the like.

[0196] Roll forming can be performed using rolling equipment such as a roll-press at linear pressure conditions required to achieve the target thickness and target porosity, followed by vacuum drying to produce a negative electrode with a final negative electrode active material layer formed on the current collector.

[0197] For example, rolling can be performed under the conditions that the target thickness (i.e., the average thickness of the negative electrode active layer) is 100 μm to 400 μm and the target porosity (i.e., the porosity after rolling) is 21% to 30%.

[0198] Specifically, the rolling can be carried out at temperatures ranging from 20°C to 100°C, more specifically from 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.

[0199] Rolling can be performed at rolling speeds ranging from 2 m / s to 7 m / s, and more specifically, at rolling speeds ranging from 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.

[0200] Roll forming can be carried out under pressure conditions ranging from 50 MPa to 200 MPa, and specifically, under pressure conditions ranging from 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0201] This disclosure can maximize the energy density of the negative electrode active layer by performing rolling under the above-described temperature, speed and / or pressure conditions, while minimizing the reduction in the tilt of the long axis of each carbon-based negative electrode active material relative to the negative electrode current collector.

[0202] The method for manufacturing a negative electrode according to this disclosure can produce a negative electrode with not only high energy density but also excellent fast charging performance by having the above-described configuration.

[0203] The present disclosure will be described in more detail below with reference to embodiments and comparative examples.

[0204] However, the following embodiments and comparative examples are merely illustrative of this disclosure, and the content of this disclosure is not limited to the following embodiments and comparative examples.

[0205] Examples 1 to 7 and Comparative Examples 1 to 2: Manufacturing of the negative electrode

[0206] Preparation of natural graphite (average particle size (D) 50 ): Approximately 11 μm to 13 μm), artificial graphite (average particle size (D 50 (Approximately 15 μm to 16 μm) and low-expansion natural graphite (average particle size (D) 50 ): Approximately 16 μm to 20 μm, total pore volume: approximately 0.006 cm³ 3 / g to 0.012 cm 3 / g) is used as a carbon-based anode active material.

[0207] In addition, silicon monoxide (SiO) was prepared with an average particle size (D). 50 (Approximately 18 ± 0.5 μm) was used as a silicon-based anode active material; styrene-butadiene rubber (SBR) was used as a binder; and carboxymethyl cellulose (CMC) was used as a thickener. Carbon nanotubes (CNTs) and carbon black (Super-P) were also prepared as conductive materials.

[0208] Then, 95% by weight of the first carbon-based negative electrode active material, 1% by weight of carbon black, 3.0% by weight of styrene-butadiene rubber (SBR) and 1% by weight of carboxymethyl cellulose (CMC) were mixed with water to obtain a solid content of 50% to prepare the first negative electrode slurry.

[0209] Individually, 95.55% by weight of the prepared second carbon-based anode active material and silicon-based anode active material, 1.13% by weight of carboxymethyl cellulose (CMC), 2.3% by weight of styrene-butadiene rubber (SBR), 0.02% by weight of carbon nanotubes, and 1% by weight of carbon black were mixed with water to obtain a 50% solids content to prepare a second anode slurry.

[0210] At this point, the composition of ① the first carbon-based anode active material, the composition of ② the second carbon-based anode active material, and the content ratio of silicon-based anode active material included in ③ the second anode slurry are adjusted as shown in Table 1 below.

[0211] The prepared first and second negative electrode slurries were simultaneously coated onto a copper sheet (thickness: 6 μm) transported in roll-to-roll fashion (transport speed: 6 m / min) using a dual-mode coating machine (S1 and S2). Subsequently, a magnetic field was applied from the top and bottom of the transported copper sheet for 2 to 11 seconds using a magnet (S3). Whether a magnetic field was applied (④) and whether the intensity of the applied magnetic field was adjusted (⑤) are shown in Table 2 below.

[0212] The negative electrode slurry, under a magnetic field, is dried with hot air at approximately 180±10°C to form a first and a second negative electrode active layer on the negative electrode current collector (S4). The negative electrode manufactured by rolling using a roller press (average thickness: approximately 135±5 μm) results in a porosity of 25±2% for the entire negative electrode active layer (S5).

[0213] Argon ion milling was performed on the thickness-direction cross-section of each manufactured negative electrode under an accelerating voltage of 6 kV, and scanning electron microscopy (SEM) analysis of the ion-milled cross-section was performed under an accelerating voltage of 5 kV and a working distance of 7 mm. Ion milling was performed using an IM5000 from Hitachi, and SEM analysis was performed using an IT800SHL from JEOL.

[0214] In the analyzed scanning electron microscope images, the total number of particles of the first and second carbon-based anode active materials included in each anode 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 formed between the major axis and the anode current collector was measured. After classifying the inclination formed between the anode current collector and the major axis of each carbon-based anode active material into six groups as follows, the carbon-based anode active materials were classified into one of the following six groups based on the measured inclination:

[0215] Group 1: The inclination of the long axis of the carbon-based negative electrode active material relative to the negative electrode current collector is greater than 0° and 30° or less.

[0216] Group 2: The inclination of the long axis of the carbon-based negative electrode active material relative to the negative electrode current collector is greater than 30° and is 60° or less.

[0217] Group 3: The inclination of the long axis of the carbon-based negative electrode active material relative to the negative electrode current collector is greater than 60° and is 90° or less.

[0218] Group 4: The long axis of the carbon-based negative electrode active material is tilted relative to the negative electrode current collector at an angle greater than 90° and less than 120°.

[0219] Group 5: The inclination of the long axis of the carbon-based negative electrode active material relative to the negative electrode current collector is greater than 120° and less than 150°.

[0220] Group 6: The long axis of the carbon-based negative electrode active material is tilted relative to the negative electrode current collector at an angle greater than 150° and less than 180°.

[0221] The number of carbon-based anode active materials classified into each group was counted to calculate the ratio of the corresponding group of carbon-based anode active materials in the entire carbon-based anode active material portfolio. 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:

[0222] [Formula 1]

[0223]

[0224] [Equation 2]

[0225] 40≤FL 30-150 ≤70

[0226] [Formula 3]

[0227] 5≤SL 60-120 ≤20

[0228] In equations 1 to 3 above,

[0229] FL 60-120 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°.

[0230] Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°.

[0231] Among them, FL 30-150 The percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°.

[0232] [Table 1]

[0233]

[0234] [Table 2]

[0235]

[0236] [Table 3]

[0237]

[0238] [Table 4]

[0239]

[0240] Examples 8 to 14 and Comparative Examples 3 to 4: Manufacturing of lithium secondary batteries

[0241] Preparation of LiNi with a particle size of 5 μm 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, as the positive electrode active material, is mixed with carbon-based conductive material and polyvinylidene fluoride as a binder in N-methylpyrrolidone (NMP) at a weight ratio of 94:3:3 to form a slurry, which is then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to manufacture the positive electrode.

[0242] A separator made of 14 μm thick polypropylene was inserted between the positive and negative electrodes produced in Examples 1 to 7 and Comparative Examples 1 to 2, respectively, and inserted into the casing. Then, an electrolyte composition was injected to assemble a 1Ah-class lithium secondary battery.

[0243] At this point, the type of negative electrode applied to each lithium secondary battery is shown in Table 5 below.

[0244] [Table 5]

[0245]

[0246] Experimental Example

[0247] The following experiments were conducted to evaluate the physical properties and performance of the negative electrode manufactured according to this disclosure.

[0248] 1) Fast charging performance evaluation

[0249] The positive electrode was manufactured in the same manner as in Examples 8 to 14 and Comparative Examples 3 to 4, and Li4Ti5O was prepared separately. 12 (LTO) electrode.

[0250] A separator was inserted between the prepared positive electrode and LTO electrode and the negative electrode prepared in Examples 1 to 7 and Comparative Examples 1 to 2, and a three-electrode battery cell was manufactured by coating copper wires on the stacked LTO electrodes for assembly.

[0251] The process involves charging and discharging between the positive electrode and the LTO electrode, resulting in a state of charge (SOC) of 50% for the LTO electrode, and charging and adjusting the three-electrode battery cells to achieve a potential of 1.53 V.

[0252] Using the EC-Lab charge / discharge apparatus, charging and discharging of a three-electrode battery cell were performed, while simultaneously measuring the voltage between the positive and LTO electrodes, and between the positive and negative electrodes. Charging was conducted at constant currents of 0.5 C, 1.0 C, 1.5 C, 2.0 C, 2.5 C, or 3.0 C, and the depth of charge was calculated after confirming the depth of charge at each C rate. Furthermore, for the depth of charge, the negative electrode voltage distribution was confirmed, and when a plateau was confirmed in the negative electrode distribution during charging, that point was determined as the charging capacity (depth of charge). The calculated charging times are shown in Table 6 below.

[0253] 2) Energy density measurement

[0254] The loading and porosity per unit area of ​​the negative electrodes of the 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 separately. Furthermore, for porosity, each negative electrode was immersed in polydimethylsiloxane (PDMS) for 7 days to fill the pores of the negative electrode active layer with PDMS. Then, argon ion milling was performed on the thickness-direction cross-section of each negative electrode at an accelerating voltage of 6 kV, and scanning electron microscopy (SEM) analysis was performed on the cross-section of the negative electrode active layer at an accelerating voltage of 5 kV and a working distance of 7 mm. Ion milling was performed using an IM5000 from Hitachi, and scanning electron microscopy analysis was performed using an IT800SHL from JEOL. The analyzed SEM images were cropped and divided equally. The ratio of each component and pore included in the negative electrode active layer is calculated from each segmented image, and the volume fraction occupied by the porosity of the negative electrode active layer is calculated from their average value. The calculated volume fraction is used as the porosity (%) of the negative electrode active layer.

[0255] Subsequently, the energy density of the large secondary battery cell was calculated using the measured load per unit area and porosity. The large secondary battery cell was then designed with dimensions of 99.7 mm × 301.5 mm × 8.2 mm, achieving a discharge capacity of 40 Ah at 1 / 3 C. The results are shown in Table 6 below.

[0256] 3) Lifetime characteristics

[0257] The charge and discharge capacity retention rates of the lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 3 to 4 were measured at room temperature. Specifically, charging was performed at a constant current of 1C at 22±3°C until the voltage reached 4.25 V, and discharging was performed at a constant current of 1C until the voltage reached 2.5 V. This was set as one cycle, and then 300 charge and discharge cycles were performed for each lithium secondary battery.

[0258] At this point, the charge capacity of each lithium secondary battery during the first and 300th cycles of charging and discharging were measured. The capacity retention rate of the 300th cycle was calculated based on the measured charge capacity of the first cycle to evaluate the capacity retention rate of each lithium secondary battery. The results are shown in Table 6 below.

[0259] [Table 6]

[0260]

[0261] As shown in Table 6 above, it can be seen that the negative electrode according to this disclosure has excellent fast charging performance, as well as excellent energy density and lifespan characteristics.

[0262] Specifically, the lithium secondary batteries manufactured in the examples were confirmed to have a charging time of 30 minutes or less to reach the depth of charge. Furthermore, the lithium secondary batteries manufactured in the examples exhibited a high energy density of approximately 595 Wh / L or higher, and it was confirmed that the capacity retention was approximately 80% or greater after 300 charge-discharge cycles.

[0263] This means that when the particle orientation of the carbon-based anode active material is controlled according to the position of the anode active layer, and silicon-based anode active material is also included, not only is the energy density of the anode improved, but also the fast charging performance and lifespan characteristics are enhanced.

[0264] These results demonstrate that the negative electrode according to this disclosure exhibits excellent fast charging performance, energy density, and lifespan characteristics.

[0265] Although this disclosure has been described with reference to preferred embodiments thereof, those skilled in the art will understand that various modifications and variations may be made therein without departing from the scope of this disclosure as defined by the appended claims.

[0266] Therefore, the scope of this disclosure should not be limited by the detailed description in the specification, but should be determined by the appended claims.

Claims

1. A negative electrode, comprising: Negative electrode current collector; A first negative electrode active layer is disposed on at least one surface of the negative electrode current collector and includes a first carbon-based negative electrode active material. and The second negative electrode active layer is disposed 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 the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed 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] In Equation 1 above, FL 60-120 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle between 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°. Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°. The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

2. The negative electrode according to claim 1, wherein when the cross-section in the thickness direction is analyzed by scanning electron microscopy, the negative electrode satisfies any one or more of the following formulas 2 and 3: [Equation 2] 40≤FL 30-150 ≤70 [Formula 3] 5≤SL 60-120 ≤20 In equations 2 and 3 above, FL 30-150 This represents the percentage (in %) of the first carbon-based negative electrode active material in which the angle formed between 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°. Among them SL 60-120 This represents the percentage (in %) of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°. The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

3. The negative electrode according to claim 1, wherein the silicon-based negative electrode active material comprises silicon (Si), silicon carbide (SiC), a composite material containing silicon (Si) and carbon (C), and silicon oxide (SiO2). q , where 0.5≤q≤2.5) is one or more of the following.

4. The negative electrode according to claim 1, wherein, Based on the weight of the entire negative electrode active layer, the content of the silicon-based negative electrode active material is in the range of 0.1% to 30% by weight.

5. The negative electrode according to claim 1, wherein the average particle size (D) of the silicon-based negative electrode active material is... 50 The range is from 1 μm to 20 μm.

6. The negative electrode according to claim 1, wherein the first carbon-based negative electrode active material and the second carbon-based negative electrode active material each comprise one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

7. The negative electrode according to claim 1, wherein any one or more of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material comprises having a content of 1×10 -5 cm 3 / g to 1×10 -1 cm 3 Graphite with a total pore volume within the range of / g.

8. The negative electrode according to claim 7, wherein, based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material, the material having a content of 1×10 -5 cm 3 / g to 1×10 -1 cm 3 The graphite content in the total pore volume ranges from 10% to 70% by weight within the range of / g.

9. The negative electrode according to claim 1, wherein the total thickness of the first negative electrode active layer and the second negative electrode active layer is in an average range of 50 μm to 400 μm, and the average thickness of the second negative electrode active layer has a ratio in the range of 80% to 150% based on the average thickness of the first negative electrode active layer.

10. A method for manufacturing a negative electrode, comprising the following steps: A first negative electrode slurry comprising a first carbon-based negative electrode active material is coated on at least one surface of the negative electrode current collector (S1); A second negative electrode slurry, comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material, is coated onto a coated first negative electrode slurry (S2); and A magnetic field (S3) is applied to the coated first and second negative electrode slurries. When the cross-section of the entire negative electrode active layer, including the first negative electrode active layer and the second negative electrode active layer, is analyzed 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] In Equation 1 above, Among them, FL 60-120 This represents the percentage of the first carbon-based negative electrode active material in which the angle between 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°. Among them SL 60-120 This represents the percentage of the second carbon-based anode active material in which the angle formed between the long axis of the second carbon-based anode active material and the surface of the anode current collector is greater than 60° and less than 120°. The long axis of a carbon-based anode active material refers to the longest line segment in an image taken by a scanning electron microscope that passes through the center of the corresponding carbon-based anode active material.

11. The method for manufacturing a negative electrode according to claim 10, wherein the silicon-based negative electrode active material comprises silicon (Si), silicon carbide (SiC), a composite material containing silicon (Si) and carbon (C), and silicon oxide (SiO2). q , where 0.5≤q≤2.5) is one or more of the following.

12. The method for manufacturing a negative electrode according to claim 10, wherein the first carbon-based negative electrode active material and the second carbon-based negative electrode active material each comprise one or more selected from natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon based on tar and pitch, and graphitized coke.

13. The method for manufacturing a negative electrode according to claim 10, wherein any one or more of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material comprises having a concentration of 1×10 -5 cm 3 / g to 1×10 -1 cm 3 Graphite with a total pore volume within the range of / g.

14. The method of manufacturing a negative electrode according to claim 10, wherein the magnetic field is applied with a magnetic field strength of 1,000 G to 12,000 G.

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