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

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same, which includes a negative electrode active layer containing both a carbon-based negative electrode active material and a silicon-based negative electrode active material, thereby exhibiting high charge / discharge capacity. The negative electrode active layer of the negative electrode has a two-layer structure, and the second negative electrode active layer located on the outermost side has i) the degree of alignment (OI) of the carbon-based negative electrode active material and ii) the ratio of the degree of alignment (OI) to a specific X-ray diffraction peak area of ​​the silicon-based negative electrode active material adjusted to satisfy predetermined ranges, thereby advantageously improving the high-rate charge / discharge characteristics of a lithium secondary battery containing the negative electrode.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0076642 dated June 15, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

[0002] This invention relates to a negative electrode for lithium secondary batteries and a method for manufacturing the same. [Background technology]

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

[0004] Existing lithium-ion batteries are limited in their energy density, making them suitable only for short-distance electric vehicles and similar applications. Therefore, technological development has focused on increasing the energy density of lithium-ion batteries.

[0005] However, the lithium-ion batteries developed for automobiles have a problem: they require a long time to recharge after being discharged during vehicle operation. Therefore, as the adoption rate of electric vehicles increases, there is a growing demand to shorten charging times to a level that users can accept. In addition, electric vehicles must be able to operate without problems even in situations requiring high power, such as rapid acceleration. This requires high discharge rate performance for lithium-ion batteries, but the reality is that there is no technology that can meet this requirement.

[0006] On the other hand, lithium secondary batteries are power generation elements capable of charging and discharging, consisting of a stacked structure of a positive electrode / separator membrane / negative electrode. During charging, a lithium desorption reaction is induced at the positive electrode where lithium contained in the positive electrode active material is oxidized and released, and a lithium insertion reaction occurs at the negative electrode where lithium is reduced and enters the negative electrode active material. Generally, the desorption reaction at the positive electrode active material is faster than the insertion reaction at the negative electrode active material, so the rapid charge and discharge performance of a lithium secondary battery is mainly determined by the negative electrode.

[0007] In practice, graphite-containing materials are widely used as the negative electrode active material for the above-mentioned negative electrode. The average potential when a graphite-containing material releases lithium is approximately 0.2V (Li / Li + (Reference) The discharge potential is relatively flat. Therefore, when graphite is used as the negative electrode active material, there is the advantage that the voltage of the secondary battery is high and constant. However, the electrical capacity per unit mass of graphite material is small at 372 mAh / g. On the other hand, the capacity of current graphite materials has already been improved to approach the theoretical capacity mentioned above, so it is difficult to further increase the capacity. In addition, when graphite is used as the negative electrode active material, the lithium ion insertion reaction proceeds at a slow rate, which limits the rapid charging performance compared to when other negative electrode active materials are applied.

[0008] Therefore, various negative electrode active materials are being studied to increase the capacity and improve the rapid charging performance of lithium secondary batteries. As an example, silicon is known to be able to reversibly adsorb and release large amounts of lithium through compound formation reactions with lithium, and much research has recently been conducted on this. Silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much larger than that of graphite-based materials, and therefore has the advantage of being useful as a high energy density and / or high capacity negative electrode material. However, silicon induces a large volume change (~300%) during charging and discharging, and does not have high-rate discharge characteristics, so lithium secondary batteries containing silicon have limitations in terms of lifespan and rapid discharge efficiency.

[0009] Therefore, in order to fundamentally solve these problems, there is a strong need for negative electrode technology that can simultaneously achieve high capacity characteristics and high charge-discharge characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide a negative electrode for a lithium secondary battery that can simultaneously achieve high capacity characteristics and high charge-discharge characteristics, a method for manufacturing the same, and a lithium secondary battery containing the negative electrode. [Means for solving the problem]

[0011] To solve the above-mentioned problems, in one embodiment, the present invention provides negative electrode current collector, A first negative electrode active layer comprising a first carbon-based negative electrode active material is provided on at least one surface of the negative electrode current collector, and The first negative electrode active layer is provided above and includes a second negative electrode active layer comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material. The second negative electrode active layer has an alignment degree (OI) of 2.5 or less of the carbon-based negative electrode active material according to the following formula 1. The second negative electrode active layer provides a negative electrode for a lithium secondary battery that satisfies the following equation 2 with a value of 8 or less:

[0012] [Formula 1] OI=I 004 / I 110

[0013] [Formula 2] I Si ×OI

[0014] In Equations 1 and 2, I 004 This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I 110This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I si This represents the area ratio of peaks indicating the (111) crystal plane of the silicon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0015] In this case, the second negative electrode active layer may have an alignment degree (OI) of carbon-based negative electrode active material of 0.1 to 1.5, and equation 2 may be 0.7 to 6.

[0016] Furthermore, the first carbon-based anode active material and the second carbon-based anode active material may each contain one or more of natural graphite and artificial graphite.

[0017] Furthermore, the silicon-based negative electrode active material mentioned above includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO₂). q However, this may include one or more of the following (0.8 ≤ q ≤ 2.5).

[0018] The silicon-based anode active material may be included in an amount of 1% to 40% by weight, based on the total weight of the anode active layers contained in the first and second anode active layers.

[0019] Furthermore, the average particle size (Dc) of the second carbon-based anode active material is 1 μm to 50 μm, the average particle size (Ds) of the silicon-based anode active material is 0.1 μm to 10 μm, and the ratio of the average particle sizes of the second carbon-based anode active material to the silicon-based anode active material (Dc / Ds) can be 2 to 10.

[0020] Furthermore, the second negative electrode active layer may contain 1% to 40% by weight of silicon-based negative electrode active material based on the total weight of the negative electrode active layer.

[0021] Furthermore, in one embodiment of the present invention, A step of applying a first negative electrode slurry and a second negative electrode slurry such that the first negative electrode slurry is located on at least one surface of the negative electrode current collector, and the second negative electrode slurry is located on the first negative electrode slurry. applying a magnetic field to the coated first negative electrode slurry and second negative electrode slurry, and drying the first negative electrode slurry and the second negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer, the first negative electrode slurry contains a first carbon-based negative electrode active material, the second negative electrode slurry contains a second carbon-based negative electrode active material and a silicon-based negative electrode active material, there is provided a method for producing a negative electrode for a lithium secondary battery according to the present invention, wherein the magnetic field is applied at an intensity of 10,000 G or less.

[0022] At this time, the step of applying the magnetic field may be performed for 1 second to 20 seconds.

[0023] Furthermore, in one embodiment, the present invention provides: a lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode according to the present invention, and a separation membrane disposed between the positive electrode and the negative electrode.

[0024] At this time, the positive electrode is provided on at least one surface of a positive electrode current collector, and may contain one or more positive electrode active materials selected from lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2:

[0025] [Chemical Formula 1] Li x [Ni y Co z Mn w M 1 v O2

[0026] [Chemical Formula 2] LiM 2 p Mn 1-p O4

[0027] In the above Chemical Formula 1 and Chemical Formula 2, M 1is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, and 0 respectively. <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつ、y+z+w+v=1であり、 M 2 is Ni, Co, or Fe, p is 0.05 ≤ p ≤ 1.0.

[0028] As one example, the positive electrode active material mentioned above is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, LiLiLi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiLiLi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, LiLiLi 0.7 Mn 1.3 O4, LiSa 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 It may contain one or more species selected from the group consisting of O4.

[0029] On the other hand, the electrode assembly may be a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly. [Effects of the Invention]

[0030] The negative electrode for lithium secondary batteries according to the present invention contains a silicon-based negative electrode active material along with a carbon-based negative electrode active material in the negative electrode active layer, exhibiting a high charge-discharge capacity. Furthermore, the negative electrode active layer of the above negative electrode has a two-layer structure, and by adjusting i) the alignment (OI) of the carbon-based negative electrode active material and ii) the ratio of the above alignment (OI) and the specific X-ray diffraction peak area of ​​the silicon-based negative electrode active material in the second negative electrode active layer located in the outermost shell to satisfy a predetermined range, it has the advantage of being excellent in improving the high-rate charge-discharge characteristics of lithium secondary batteries containing it. [Modes for carrying out the invention]

[0031] Since the present invention can be modified in various ways and may have a variety of embodiments, specific embodiments will be described in detail in the detailed description.

[0032] However, this is not intended to limit the present invention to any particular embodiment, but rather should be understood to include all modifications, equivalents, or substitutions that fall within the technical scope of the present invention.

[0033] In the present invention, terms such as "includes" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof as described in the specification, and do not preemptively exclude the presence or possibility of adding one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0034] Furthermore, in this invention, when a part such as a layer, film, region, or plate is described as being "on top" of another part, this includes not only the case where it is "directly on top" of the other part, but also the case where another part is located in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "directly below" the other part, but also the case where another part is located in between. Also, in this application, being "on top" may include being located not only at the top but also at the bottom.

[0035] Furthermore, in the present invention, "contains as a main component" may mean that the defined component is contained in an amount of 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more) of the total weight (or total volume) of the defined component. For example, "contains graphite as a main component as the negative electrode active material" may mean that graphite is contained in an amount of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more of the total weight of the negative electrode active material, and in some cases, it may also mean that the entire negative electrode active material consists of graphite and contains 100% by weight of graphite.

[0036] Furthermore, in this specification, "orientation of carbon-based anode active material" or "alignment of carbon-based anode active material" means that specific crystal planes (for example, the ab-axis crystal plane of graphite) that represent the two-dimensional planar structure of the carbon-based anode active material constituting the anode active material particles are arranged to have a predetermined inclination with respect to the surface of the anode current collector. This may differ from the arrangement of the carbon-based anode active material particles themselves to have a specific orientation within the anode active layer.

[0037] Furthermore, "high orientation of carbon-based anode active material" may mean that a specific crystal plane (for example, the ab-axis crystal plane of graphite) exhibiting the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer has a high frequency of having a predetermined inclination with respect to the surface of the anode current collector. In some cases, it may also mean that the above crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (for example, an angle close to perpendicular, greater than 45°, specifically 60° or more) with respect to the surface of the anode current collector.

[0038] Furthermore, "high degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" referred to herein is large, and that specific crystal planes (e.g., the ab-axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer are aligned at a low angle (e.g., less than 45°) with respect to the surface of the anode current collector. Conversely, "low degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" is small, and that the above-mentioned crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (e.g., an angle close to perpendicular, 45° or more, specifically 60° or more) with respect to the surface of the anode current collector.

[0039] Furthermore, in this specification, "crystal plane of carbon-based anode active material" refers to a plane on which the atoms of the carbon-based anode active material form the outer shape of the crystal, and in the present invention, it may mean a crystal plane including the plane of the carbon-based anode active material, or a crystal plane including the a-axis / b-axis / ab-axis of the carbon-based anode active material crystal.

[0040] Furthermore, in this specification, "average particle size (D 50 "50%" refers to the particle size at which the cumulative value in the particle size distribution becomes 50%, and this is also called the median diameter.

[0041] The present invention will be described in more detail below.

[0042] <Negative electrode for lithium secondary batteries>

[0043] In one embodiment, the present invention is described as follows: negative electrode current collector, A first negative electrode active layer comprising a first carbon-based negative electrode active material is provided on at least one surface of the negative electrode current collector, and The first negative electrode active layer is provided above and includes a second negative electrode active layer comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material. The second negative electrode active layer has an alignment degree (OI) of 2.5 or less of the carbon-based negative electrode active material according to the following formula 1. The second negative electrode active layer provides a negative electrode for a lithium secondary battery that satisfies the following equation 2 with a value of 8 or less:

[0044] Formula 1] OI=I 004 / I 110

[0045] [Formula 2] I Si ×OI

[0046] In Equations 1 and 2, I 004 This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I 110 This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I si This represents the area ratio of peaks indicating the (111) crystal plane of the silicon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0047] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer on at least one surface of the negative electrode current collector. The negative electrode active layer is a layer that embodies the electrical activity of the negative electrode and mainly contains a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during charging and discharging of the battery.

[0048] In this case, the negative electrode active layer may have a two-layer structure in which a first negative electrode active layer and a second negative electrode active layer are sequentially stacked on the negative electrode current collector. Since the composition of each layer of the two-layer negative electrode active layer can be easily controlled, the performance of the negative electrode can be improved by controlling the type and amount of components contained in each layer according to specific purposes such as increasing the energy efficiency of the battery or improving the adhesion between the active layer and the current collector. For example, the negative electrode active layer may selectively contain a silicon-based negative electrode active material with high battery charge / discharge capacity only in the second negative electrode active layer that is in contact with the positive electrode. Alternatively, the negative electrode active layer may selectively contain natural graphite or other materials with good adhesion as a negative electrode active material only in the first negative electrode active layer that is in contact with the negative electrode current collector, or may contain a high amount of a binder that imparts binding properties to the components constituting the active layer.

[0049] In the present invention, the first negative electrode active layer contains a first carbon-based negative electrode active material, and the second negative electrode active layer contains a second carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0050] In this case, the first carbon-based anode active material and the second carbon-based anode active material contained in each anode active layer may be the same in type and / or in content, or they may be different. Specifically, the first carbon-based anode active material and the second carbon-based anode active material refer to materials mainly composed of carbon atoms, and such carbon-based anode active materials may include graphite. The graphite may include one or more of either natural graphite or artificial graphite. For example, the first carbon-based anode active material and the second carbon-based anode active material may contain natural graphite or artificial graphite individually, or in some cases, a mixture of natural graphite and artificial graphite. In this case, the mixing ratio of natural graphite and artificial graphite may be 5-50:50-95 or 20-45:55-80 by weight. By including natural graphite and artificial graphite in the above-mentioned mixing ratio, the carbon-based anode active material can achieve strong adhesion between the anode current collector and the anode active layer while also exhibiting high orientation of the carbon-based anode active material to the surface of the anode current collector.

[0051] As one example, the first carbon-based anode active material may contain natural graphite and artificial graphite in a weight ratio of 30-50:50-70, while the second carbon-based anode active material may contain artificial graphite alone.

[0052] Furthermore, the first carbon-based anode active material and the second carbon-based anode active material are preferably spherical graphite granules formed by the aggregation of multiple flake-shaped graphite particles. Examples of flake-shaped graphite include natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar and pitch, and graphitized cokes (green coke, green coke, pitch coke, needle coke, petroleum coke, etc.). In particular, those assembled using multiple highly crystalline natural graphite particles are preferred. Also, one graphite granule can be formed by the aggregation of 2 to 100, preferably 3 to 20, flake-shaped graphite particles.

[0053] Such carbon-based anode active materials may have a spherical particle morphology. In this case, the sphericity of the graphite particles can be 0.75 or greater, and may be, for example, 0.75 to 1.0, 0.75 to 0.95, 0.8 to 0.95, or 0.90 to 0.99. Here, "sphericity" can mean the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameter passing through the center of the particle. A sphericity of 1 means that the particle morphology is spherical. The above sphericity can be determined by measuring it through a particle shape analyzer, or by measuring the particle morphology using a scanning electron microscope (SEM) or energy-dispersive spectrometer and then analyzing the measured results.

[0054] The present invention makes it possible to achieve high electrical conductivity in the negative electrode active layer by making the shapes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material nearly spherical. Therefore, a negative electrode containing spherical carbon-based negative electrode active material has the advantage of improving the capacity of a secondary battery and increasing the specific surface area per unit weight of the negative electrode active material, thereby improving the adhesion between the negative electrode active layer and the current collector.

[0055] Furthermore, the silicon-based anode active material is a substance mainly composed of silicon (Si) and is contained only in the second anode active layer. The present invention makes it possible to increase the charge-discharge capacity of the anode by containing the silicon-based anode active material in the second anode active layer adjacent to the positive electrode active layer. However, the silicon-based anode active material has the problem that the durability of the anode is reduced when it is contained in the first anode active layer because the volume change of the silicon-based anode active material is large during charge-discharge. However, the present invention makes it possible to maintain high durability of the anode by applying the silicon-based anode active material to the second anode active layer.

[0056] Examples of such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO2), which may be included individually or in combination in the second negative electrode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or combined and included in the negative electrode active layer as the above silicon-based negative electrode active materials, these may be silicon oxide (SiO2). q However, this can be expressed as 0.8 ≤ q ≤ 2.5.

[0057] Furthermore, the silicon-based negative electrode active material may be doped with or alloyed with Li, Mg, Al, Ca, or Ti. Additionally, if the silicon-based negative electrode active material contains oxygen (O), its surface may be surface-treated with a carbon coating layer or the like to suppress volume expansion during charging and simultaneously improve the electrical conductivity of the negative electrode active material.

[0058] Furthermore, the carbon-based and silicon-based anode active materials contained in each layer of the anode active layer may be present in amounts of 85 parts by weight or more, based on 100 parts by weight of the entire anode active layer. Specifically, the carbon-based and silicon-based anode active materials contained in each layer of the anode active layer may be present in amounts of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more, based on 100 parts by weight of the entire anode active layer.

[0059] Furthermore, of these, the silicon-based anode active material may be present in an amount of 0.1 to 40% by weight relative to the total weight of the anode active material contained in the first anode active layer and the second anode active layer, specifically in amounts of 0.5 to 20% by weight, 1 to 9% by weight, 5 to 15% by weight, 3 to 7% by weight, 11 to 19% by weight, 13 to 17% by weight, 15 to 20% by weight, 10 to 30% by weight, 20 to 40% by weight, 25 to 35% by weight, 15 to 25% by weight, or 9 to 22% by weight. The present invention can improve the charging capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charging and discharging of a secondary battery by adjusting the ratio of the total content of the anode active material contained in the anode active layer and the ratio of the content of silicon-based anode active material contained in the total anode active material to the above ranges. Furthermore, by minimizing the volume change of the negative electrode active layer during charging and discharging of the secondary battery, the structural stability of the negative electrode active layer can be improved, thereby extending the lifespan of the secondary battery.

[0060] Furthermore, the negative electrode according to the present invention can further improve high-rate charge-discharge characteristics by controlling the crystal structure characteristics of the negative electrode active material contained in the second negative electrode active layer adjacent to the positive electrode.

[0061] As one example, the second carbon-based anode active material contained in the second anode active layer may have an alignment degree (OI) of 2.5 or less according to the following formula 1:

[0062] [Formula 1] OI=I 004 / I 110

[0063] In Equation 1, I 004 This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I 110 This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0064] The alignment (OI) of the second carbon-based anode active material can serve as an indicator of the degree to which the ab-axis crystal planes of the carbon-based anode active material are oriented in a specific direction, specifically relative to the surface of the anode current collector, during X-ray diffraction (XRD) measurements. Specifically, the second anode active layer exhibits peaks of 2θ = 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2° for graphite, which is the second carbon-based anode active material, during X-ray diffraction measurements. These represent the (002), (100), (101)R, (101)H, (004), and (110) planes of graphite. Here, the peak that appears at 2θ = 43.4 ± 0.2° can be considered to be an overlapping peak between the (1,0,1)R plane of the second carbon-based negative electrode active material and the (111) plane of the current collector, such as copper (Cu).

[0065] Of these, the degree of alignment (OI) of the second carbon-based anode active material can be measured by the ratio of the area obtained by integrating the intensities of the peak at 2θ = 54.7 ± 0.2°, which represents the (004) plane, and the peak at 2θ = 77.5 ± 0.2°, which represents the (110) plane.

[0066] The peak at 2θ = 54.7 ± 0.2° represents a crystal plane of the second carbon-based anode active material that has an inclination with respect to the anode current collector. Therefore, the closer the alignment degree (OI) is to 0, the closer the inclination with respect to the anode current collector surface is to 90°, and the larger the value, the closer the inclination with respect to the anode current collector surface is to 0° or 180°. In other words, the second anode active layer according to the present invention can be aligned such that the second carbon-based anode active material has an angle of 60° or more, 70° or more, 70-90°, 80-90°, 65-85°, or 70-85° with respect to the anode current collector. As a result, the alignment degree (OI) of the second carbon-based anode active material in the second anode active layer may be lower compared to the case where the second carbon-based anode active material is aligned at a lower angle of less than 60°. As an example, the second negative electrode active layer described above may have an alignment degree (OI) of the carbon-based negative electrode active material according to Equation 1 of 2.5 or less, 2.0 or less, 1.3 or less, 1.0 or less, 0.5 or less, 0.1 to 2.5, 0.1 to 2.0, 0.1 to 1.5, 0.2 to 1.3, 0.4 to 1.3, 0.4 to 1.3, 0.4 to 1.0, 0.5 to 1.3, 1.1 to 1.3, 0.5 to 0.9, or 0.4 to 0.6. Here, the above alignment degree (OI) indicates the degree of alignment of the ab-axis crystal plane of the carbon-based negative electrode active material, and does not indicate the degree to which the carbon-based negative electrode active material particles rotate and align themselves within the active layer.

[0067] The present invention makes it possible to secure ion mgration channels that allow lithium ions to move more quickly within the negative electrode active layer by adjusting the degree of alignment (OI) of the second carbon-based negative electrode active material contained in the second negative electrode active layer as described above. As a result, the negative electrode of the present invention can prevent an increase in resistance due to the long migration distance of lithium ions, thereby preventing a decrease in high-rate charging performance due to electrical resistance, and simultaneously improving high-rate discharge efficiency.

[0068] As another example, the second positive electrode active layer described above may satisfy equation 2 below with a value of 8 or less:

[0069] [Formula 2] I Si ×OI

[0070] In Equation 2, OI represents the degree of alignment of the second carbon-based anode active material according to Equation 1. I si This represents the area ratio of peaks indicating the (111) crystal plane of the silicon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0071] In pure silicon with a crystalline phase, the inter-elemental distances and density of silicon atoms differ depending on the type of crystal plane. Therefore, pure silicon (Si) with a crystalline phase can exhibit different electrical properties, such as electron mobility, depending on the direction of each crystal plane exposed on the surface (i.e., the crystal direction). For example, in a silicon crystal, the electron mobility can be highest in the crystal directions (100), (111), and (110) in the order of (100) > (111) > (110), and the insertion of metal ions, etc., can be highest in the order of (110) > (111) > (100).

[0072] Therefore, the present invention is characterized by controlling the properties exhibited by the (111) plane among the crystal planes of pure silicon having a crystalline phase. Specifically, the second anode active layer according to the present invention exhibits diffraction peaks indicating the silicon-based anode active material along with diffraction peaks indicating the crystal plane of the second carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis. For example, if the silicon-based anode active material is silicon oxide (SiO₂) q However, when 0.8 ≤ q ≤ 2.5), X-ray diffraction measurements of the second negative electrode active layer show a gentle, broad curve spectrum indicating amorphous silicon oxide, along with peaks indicating pure silicon (pure Si) at 2 = 28.4 ± 0.2°, 47.3 ± 0.5°, and 56.1 ± 0.2°. These peaks represent the (111) plane, (220) plane, and (311) plane of the crystal plane of pure silicon (pure Si), respectively.

[0073] In this case, the diffraction peak indicating the (111) crystal plane of pure silicon (pure Si) becomes stronger as the ab-axis crystal plane of the second carbon-based anode active material is aligned at a high angle with respect to the surface of the anode current collector, and the area value obtained by integrating the intensity of the above peak also tends to increase. This means that the exposure of the silicon (111) crystal plane on the surface of the second anode active layer becomes higher. However, as mentioned above, the degree of exposure of the (111) crystal plane can affect the mobility of electrons and metal ions, and there may be a trade-off relationship between electron mobility and metal ion mobility, so it is preferable to adjust the degree of exposure of the (111) crystal plane to satisfy a predetermined range.

[0074] Thus, the present invention achieves this by adjusting Equation 2 to 8 or less. Specifically, the second anode active layer can satisfy Equation 2 with values ​​of 7 or less, 6 or less, 4 or less, 3.5 or less, 3 or less, 0.7~8, 0.7~6, 1~6, 1.75~6, 1.75~4, 1.75~3.5, 1.75~3, 1.75~2.5, 1.75~2.1, 2~6, 2~4, 2.1~3.5, 2.1~3.1, 3~5, or 2.5~3. Here, Equation 2 refers to the degree of alignment (OI) calculated from the diffraction peaks for the second carbon-based anode active material during X-ray diffraction spectroscopy analysis of the second anode active layer, and reflecting the area integral value of the diffraction peak intensity showing the (111) plane of the silicon-based anode active material in the calculated degree of alignment (OI). By satisfying Equation 2 within the above-described range, the present invention can significantly improve the lithium ion mobility and insertion performance of the second anode active layer composed of a second carbon-based anode active material and a silicon-based anode active material, thereby significantly improving the high-rate charge-discharge efficiency of secondary batteries containing it.

[0075] Furthermore, the second carbon-based anode active material and the silicon-based anode active material contained in the second anode active layer may have predetermined particle sizes. Specifically, the average particle size (Dc) of the second carbon-based anode active material is 1 μm to 50 μm, the average particle size (Ds) of the silicon-based anode active material is 0.1 μm to 10 μm, and the ratio of the average particle sizes of the second carbon-based anode active material to the silicon-based anode active material (Dc / Ds) may be 2 to 10.

[0076] Specifically, the above-mentioned second carbon-based anode active material has an average particle size (D) of 1 μm to 50 μm. 50 The second carbon-based anode active material can exhibit a particle size (Dc) of 1 μm to 40 μm, 1 μm to 30 μm, 10 μm to 40 μm, 15 μm to 30 μm, 25 μm to 50 μm, 11 μm to 19 μm, 15 μm to 25 μm, 20 μm to 30 μm, 1 μm to 20 μm, 1 μm to 10 μm, 5 μm to 15 μm, 10 μm to 20 μm, 15 μm to 30 μm, 15 μm to 20 μm, 21 μm to 26 μm, 25 μm to 30 μm, 11 μm to 17 μm, 16 μm to 23 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm. 50 ) can be shown. For spherical second-carbon anode active materials, it may be advantageous to reduce the particle size to maximize the degree of disorder in the expansion direction for each particle so that the particles can be prevented from expanding due to lithium ion charging. However, when the particle size of the second-carbon anode active material is less than 1.0 μm, a large amount of binder is required due to the increase in the number of particles per unit volume, which may result in a low degree of spheroidization and spheroidization yield. On the other hand, when the maximum particle size exceeds 50 μm, the expansion rate of the anode active material during charging and discharging of the secondary battery increases significantly, and as charging and discharging are repeated, the interparticle bonding of the anode active material and the bonding between the anode active material particles and the current collector may decrease, which may significantly reduce the cycle characteristics.

[0077] Furthermore, the silicon-based negative electrode active material has an average particle size (D) of 0.1 μm to 10 μm. 50 It can show the average particle size (D) of 0.1μm~5μm, 0.1μm~3μm, 0.1μm~1μm, 0.5μm~2μm, 0.5μm~5μm, 1μm~5μm, 3μm~7μm, 5μm~10μm, 1μm~3μm, 4μm~9μm, 0.1μm~0.9μm, 0.8μm~1.2μm, or 0.3μm~0.8μm. 50 ) can be shown.

[0078] When the minimum particle size of the silicon-based anode active material is less than 0.1 μm, uniform dispersion of the second anode active layer is difficult. As the secondary battery is charged and discharged, oxidation-reduction reactions are unevenly induced between the aggregated and non-aggregated regions of the silicon-based anode active material, which can accelerate the degradation of the second anode active layer. Furthermore, when the maximum particle size of the silicon-based anode active material exceeds 10 μm, it becomes difficult to control the crystal plane of the silicon-based anode active material. This significantly increases the expansion rate of the second anode active layer per unit area during the charging and discharging of the secondary battery, resulting in a significant decrease in cycle characteristics with repeated charging and discharging.

[0079] Furthermore, the ratio of the average particle sizes (Dc / Ds) of the second carbon-based anode active material to the silicon-based anode active material can be between 2 and 10, specifically between 2 and 7, 2 and 5, 3 and 7, 4 and 8, 5 and 10, or 6 and 9.

[0080] The present invention makes it possible to induce a structure in which silicon-based anode active material is filled into voids formed by multiple second-carbon anode active materials by satisfying the above range for the ratio of the average particle sizes (Dc / Ds) of the second-carbon anode active material and the silicon-based anode active material. In this case, the voids act as a buffer to absorb the volume expansion of the silicon-based anode active material during charging and discharging of the secondary battery, thereby minimizing the volume expansion of the second anode active layer.

[0081] Furthermore, when the average particle size ratio (Dc / Ds) is below the lower limit of the range described above, the influence of the second-carbon anode active material on the silicon-based anode active material is reduced, and there is a limitation in that it is difficult to control the crystal plane of pure silicon having a crystalline phase. Also, when the average particle size ratio (Dc / Ds) exceeds the upper limit of the range described above, there is a problem that the degradation of the second anode active layer is accelerated during charging and discharging of the secondary battery, resulting in a shorter lifespan.

[0082] On the other hand, the average thickness of the negative electrode active layer may be 100 μm to 300 μm. Specifically, the average thickness of the negative electrode active layer may be 100 μm to 250 μm, 100 μm to 250 μm, or 130 μm to 190 μm. By adjusting the average thickness of the negative electrode active layer to the above range, the present invention makes it possible to easily control the crystalline properties of the negative electrode active material contained in the second negative electrode active layer, thereby improving the high-rate charge-discharge characteristics of the secondary battery containing the negative electrode of the present invention.

[0083] Furthermore, the average thicknesses of the first anode active layer and the second anode active layer may be the same or different. Specifically, the average thickness of the first anode active layer (D1) and the average thickness of the second anode active layer (D2) may be in a ratio of 1:0.5 to 3, and more specifically, in a ratio of 1:0.8 to 2.5, 1:1 to 2.5, 1:1.1 to 2, 1:0.9 to 1.1, or 1:1.5 to 3. By adjusting the ratio of the average thicknesses of the first anode active layer and the second anode active layer within the above range, the present invention can maximize the charge / discharge capacity while maintaining high durability of the anode.

[0084] Furthermore, the first and second anode active layers according to the present invention may, along with the main component anode active material, selectively further contain conductive materials, binders, other additives, etc., as needed.

[0085] The above conductive material may contain, but is not limited to, one or more of the following: carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc.

[0086] As one example, the above-mentioned negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., individually or in combination as conductive materials.

[0087] In this case, the content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer. Specifically, the content of the conductive material may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight per 100 parts by weight of the entire negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent an increase in the resistance of the negative electrode and a decrease in charging capacity due to a low content of conductive material. Furthermore, it can prevent problems such as a decrease in charging capacity due to a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, or a decrease in rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0088] Furthermore, the above-mentioned binder is a component that assists in the bonding of the negative electrode active material to conductive materials and to the current collector, and can be suitably applied within a range that does not degrade the electrical properties of the electrode. Specifically, it may contain one or more selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0089] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer. Specifically, the binder content may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight per 100 parts by weight of the entire negative electrode active layer. By controlling the binder content contained in the negative electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content, or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0090] Furthermore, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, and calcined carbon can be used, and in the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc., can also be used. The average thickness of the negative electrode current collector can be suitably applied in the range of 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0091] <Lithium-ion secondary battery>

[0092] Furthermore, in one embodiment of the present invention, The present invention provides a lithium secondary battery comprising an electrode assembly including a positive electrode, the negative electrode of the present invention as described above, and a separator membrane disposed between the positive electrode and the negative electrode.

[0093] The lithium secondary battery according to the present invention includes an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are arranged alternately, with a separator membrane positioned between them. The lithium secondary battery, equipped with the negative electrode of the present invention described above, not only has a high charge / discharge capacity but also excellent high-rate charge / discharge characteristics, and can therefore be usefully used as a power source for medium- and large-scale devices such as electric vehicles.

[0094] In this case, the negative electrode has the same configuration as described above, so a detailed explanation will be omitted.

[0095] Furthermore, the positive electrode includes a positive electrode active layer containing a positive electrode active material on a positive electrode current collector, and the positive electrode active layer may selectively further contain conductive materials, binders, and other additives as needed.

[0096] The above positive electrode active material is a substance capable of undergoing electrochemical reactions on the positive electrode current collector and may include one or more lithium metal oxides represented by the following chemical formulas 1 and 2, which are capable of reversible intercalation and deintercalation of lithium ions:

[0097] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0098] [Chemical formula 2] LiM 2 p Mn q P r O4

[0099] In the above chemical formulas 1 and 2, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, and 0 respectively. <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつ、y+z+w+v=1であり、 M 2 It is Ni, Co, or Fe, p is such that 0.05 ≤ p ≤ 1.0, q is 2-p, r is either 0 or 1.

[0100] The lithium metal oxides represented by the above Chemical Formula 1 and Chemical Formula 2 are substances each containing nickel (Ni) and manganese (Mn) at a high content, and when used as a positive electrode active material, they have the advantage of being capable of stably supplying electricity of high capacity and / or high voltage compared to conventionally and commonly used positive electrode active materials such as lithium iron phosphate (LiFePO₄).

[0101] At this time, examples of the lithium metal oxide represented by the above Chemical Formula 1 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, and the like, and the lithium metal oxide represented by the above Chemical Formula 2 includes LiNi 0.7 Mn 1.3 O₄, LiNi 0.5 Mn 1.5 O₄, and LiNi 0.3 Mn 1.7 O₄, and the like, and these may be used alone or in combination.

[0102] Further, the positive electrode active material may be contained in an amount of 85 parts by weight or more based on 100 parts by weight of the positive electrode active layer. Specifically, the positive electrode active material may be contained in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the positive electrode active layer.

[0103] Further, the positive electrode active layer may further contain a conductive material, a binder, other additives and the like together with the positive electrode active material.

[0104] In this case, the conductive material is used to improve the electrical performance of the positive electrode and may be one of those commonly used in the industry, but specifically may include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0105] Furthermore, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of each positive electrode active layer. Specifically, the conductive material may be included in an amount of 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight based on 100 parts by weight of each positive electrode active layer.

[0106] Furthermore, the binder plays a role in binding the positive electrode active material, positive electrode additive, and conductive material to each other, and any binder having such a function can be used without particular limitations. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0107] Furthermore, the above-mentioned binder may be included in an amount of 1 to 10 parts by weight based on the weight of each positive electrode active layer, specifically in an amount of 2 to 8 parts by weight or 1 to 5 parts by weight.

[0108] The total thickness of the positive electrode active layer is not particularly limited, but specifically it may be between 50 μm and 300 μm. More specifically, the total thickness of the positive electrode active layer may be between 100 μm and 200 μm, 80 μm and 150 μm, 120 μm and 170 μm, 150 μm and 300 μm, 200 μm and 300 μm, or 150 μm and 190 μm.

[0109] Furthermore, the positive electrode can be made of a material that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used. The average thickness of the current collector can be suitably set to 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0110] Furthermore, the separation membrane interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry, but specifically, it may contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer. The above separation membrane may have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the polymer described above. In some cases, the separation membrane may take the form of a composite membrane in which organic or inorganic particles are coated with an organic binder on the porous polymer substrate. The separation membrane may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0111] On the other hand, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery that includes a stacked type, a zigzag type, or a zigzag-stack type electrode assembly. As one example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a prismatic secondary battery.

[0112] Pouch-type and / or prismatic rechargeable batteries have the advantage of being highly practical in terms of energy density because they can pack unit cells of the rechargeable battery at a high density within a limited space.

[0113] <Method for manufacturing a negative electrode>

[0114] Furthermore, in one embodiment of the present invention, A step of applying a first negative electrode slurry and a second negative electrode slurry such that the first negative electrode slurry is located on at least one surface of the negative electrode current collector, and the second negative electrode slurry is located on the first negative electrode slurry. The steps include applying a magnetic field to the coated first negative electrode slurry and the second negative electrode slurry, and The process includes the step of drying a first negative electrode slurry and a second negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer. The above-mentioned first negative electrode slurry contains a first carbon-based negative electrode active material. The above-mentioned second negative electrode slurry contains a second carbon-based negative electrode active material and a silicon-based negative electrode active material. The above-mentioned magnetic field provides a method for manufacturing a negative electrode for a lithium secondary battery, applied with an intensity of 10,000 G or less.

[0115] The method for manufacturing a negative electrode according to the present invention refers to the method for manufacturing the negative electrode of the present invention as described above. The above method for manufacturing a negative electrode involves applying a negative electrode slurry onto a negative electrode current collector, applying a magnetic field to the surface of the applied negative electrode slurry, and then drying each negative electrode slurry, thereby producing a negative electrode having a negative electrode active layer in which the crystalline properties of the negative electrode active material are controlled.

[0116] Here, the step of applying the negative electrode slurry is a step of discharging and coating the surface of the moving negative electrode current collector with a negative electrode slurry containing a carbon-based negative electrode active material. The above step can be applied without particular limitations as long as it is a method commonly used in the industry, but preferably a die coating method can be used. The die coating method can be performed via a slot die equipped with a shim for controlling the discharging conditions of the negative electrode slurry. In this case, by controlling the shape of the shim, the loading amount of the negative electrode slurry applied to the negative electrode current collector, the coating thickness, etc., can be easily controlled.

[0117] In this invention, a dual die can be used to simultaneously apply a first negative electrode slurry and a second negative electrode slurry onto a negative electrode current collector. This has the advantage of significantly improving process efficiency compared to applying each slurry sequentially.

[0118] On the other hand, the step of applying a magnetic field to the negative electrode slurry may be a step of controlling the crystal properties of the negative electrode active material contained in the negative electrode slurry. Specifically, this step involves applying a magnetic field to the surfaces of the first negative electrode slurry and the second negative electrode slurry coated on the negative electrode current collector, thereby aligning the ab-axis crystal planes of the carbon-based negative electrode active material contained in each negative electrode slurry so that they are at a high angle with respect to the negative electrode current collector, and thereby controlling the properties of the (111) crystal plane of the silicon-based negative electrode active material contained in the second negative electrode slurry.

[0119] In this case, the magnetic field can be applied by magnets positioned above and below the negative electrode current collector, which is moved with a negative electrode slurry applied to its surface. Furthermore, the polarities of the magnets positioned above and below may be different.

[0120] Furthermore, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be adjusted by the strength of the applied magnetic field, thereby allowing the step of applying the magnetic field to be performed under conditions of a predetermined magnetic field strength.

[0121] Specifically, the step of applying the above-mentioned magnetic field may involve applying a magnetic field of 10,000G (Gauss) or less, and more specifically, a magnetic field may be applied with an intensity of 2,500G to 9,000G, 3,000G to 8,500G, 3,500G to 8,500G, 4,000G to 8,200G, 3,600G to 4,500G, 4,500G to 6,500G, 5,000G to 7,000G, 6,000G to 8,500G, 7,000G to 8,500G, or 6,000G to 6,500G.

[0122] Furthermore, the step of applying the magnetic field described above may be performed for 1 to 20 seconds, specifically for 1 to 15 seconds, 1 to 10 seconds, 5 to 20 seconds, 10 to 20 seconds, 11 to 18 seconds, 1 to 5 seconds, 4 to 9 seconds, or 6 to 11 seconds.

[0123] As one example, in the step of applying the magnetic field described above, a magnetic field of 6,250 ± 50 G may be applied to the negative electrode slurry for 1 to 5 seconds.

[0124] Furthermore, the step of applying the magnetic field is performed by magnets introduced to the upper and lower parts of the coated negative electrode slurry, as described above, and the size of the magnets can be adjusted to be larger than the size of the negative electrode slurry so that the magnetic field applied to the negative electrode slurry can be applied uniformly to the entire surface of the negative electrode slurry. For example, the magnets may have a length ratio of 105% to 200% of the width of the negative electrode slurry, and specifically, they may have a length ratio of 110% to 180%, 110% to 160%, 110% to 140%, 110% to 130%, 130% to 150%, or 105% to 120% of the width of the negative electrode slurry.

[0125] As described above in the step of applying a magnetic field, the present invention can satisfy equation 2 to 8 or less while satisfying the degree of alignment (OI) of the carbon-based anode active material contained in the second anode slurry to 2.5 or less by controlling the strength of the magnetic field, the application time, and / or the size of the magnet part.

[0126] Furthermore, the step of forming the negative electrode active layer may include the step of drying the negative electrode slurry and the step of rolling the dried negative electrode slurry.

[0127] In this case, the step of drying the negative electrode slurry can be applied without particular limitation as long as it is a method that can maintain the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0128] For example, the drying step described above can be performed by applying thermal energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like to dry the negative electrode slurry.

[0129] Furthermore, the step of rolling the dried anode slurry involves increasing the density of the anode active layer by applying pressure to the dried anode slurry using a roll press or the like. In this case, the rolling may be carried out at a temperature higher than room temperature.

[0130] Specifically, the rolling described above may be carried out at temperatures of 50°C to 100°C, more specifically at temperatures of 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C. Specifically, the above rolling can be carried out at rolling speeds of 2 m / s to 7 m / s, and more specifically at rolling speeds of 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s. Furthermore, the rolling described above may be carried out under pressure conditions of 50 MPa to 200 MPa, specifically under pressure conditions of 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0131] The present invention makes it possible to increase the energy density of the anode while minimizing changes in the alignment of the carbon-based anode active material contained in the anode active layer formed by rolling a dried anode slurry under the above temperature, speed, and / or pressure conditions.

[0132] The present invention will be described in more detail below with reference to examples and experimental examples.

[0133] However, the following examples and experimental examples are illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0134] <Examples 1-5 and Comparative Examples 1-3: Manufacturing of negative electrodes for lithium secondary batteries>

[0135] Natural graphite (average particle size (D)) is used as a carbon-based anode active material. 50 ): 18±1μm) and artificial graphite (average particle size (D 50 Carbon-based anode active material (16±1μm) and silicon oxide (SiO2) were prepared as silicon-based anode active materials, and a first anode slurry and a second anode slurry were manufactured using the prepared carbon-based anode active material and silicon-based anode active material.

[0136] Specifically, a mixed graphite, prepared by mixing natural graphite and artificial graphite in a weight ratio of 3.5-4.5:5.5-6.5, was used as the first carbon-based anode active material. Carbon black was used as the conductive material, and carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) were used as binders. Subsequently, 95 parts by weight of the mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethylcellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to produce a first anode slurry with a solid content of 50%.

[0137] Furthermore, a negative electrode active material was prepared by mixing artificial graphite and silicon dioxide (SiO2) in a weight ratio of 85-90:10-15, and carbon black was prepared as a conductive material, and carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) were prepared as binders. Subsequently, 95 parts by weight of the mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethylcellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to produce a solid content of 45% to produce a second negative electrode slurry.

[0138] Once each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a copper sheet (thickness: 10 μm) being transported roll-to-roll (transport speed: 5 m / min) using a dual die coater.

[0139] Permanent magnets having a length ratio of 110-120% of the width of the negative electrode slurry were placed on the upper part of the coated negative electrode slurry and on the lower part of the negative electrode current collector, and the magnetic field was applied for 2-3 seconds by adjusting the magnetic field strength as shown in Table 1 below. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a negative electrode active layer in which the first negative electrode active layer and the second negative electrode active layer were sequentially laminated on the negative electrode current collector. The formed negative electrode active layer was rolled at 50±1℃ at a pressure of 100-150 MPa and a transfer speed of 3 m / s to manufacture a negative electrode for lithium secondary batteries (average thickness of the first negative electrode active layer and the second negative electrode active layer: 110±5 μm each).

[0140] Furthermore, X-ray diffraction (XRD) spectroscopy was performed on the second anode active layer of each manufactured anode, and the spectrum was measured. In this XRD spectroscopy analysis, the second carbon-based anode active material and the silicon-based anode active material contained in the second anode active layer were targeted and measured once each. The XRD measurement conditions were as follows:

[0141] - Target: Cu (Kα-ray) graphite monochromator - Slit: Divergent slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree - Measurement area: (110) plane: 76.5°<2θ<78.5° / (004) plane: 53.5°<2θ<56.0°

[0142] Next, (1) from the spectrum measured with the second carbon-based anode active material as the target, the area integral values ​​of the peaks representing the (0,0,4) crystal plane and the peaks representing the (110) crystal plane are determined, and the ratio of these areas (I 004 / I 110 (111) The area integral value (I) of the peaks indicating crystal planes was calculated by (2) the area integral value (I) of the mixed graphite in each region. Si The value was calculated. The calculated value is shown in Table 1 below.

[0143] [Table 1]

[0144] <Examples 6-10 and Comparative Examples 4-6. Manufacturing of Lithium Secondary Batteries>

[0145] LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared and mixed with polyvinylidene fluoride and N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 as a carbon-based conductive material and binder to form a slurry. This slurry was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to produce a cathode.

[0146] A separation membrane made of 18 μm polypropylene was interposed between the positive electrode obtained above and the negative electrodes manufactured in Examples 1-5 and Comparative Examples 1-3, respectively. After inserting the membrane into a case, the electrolyte composition was injected to assemble the lithium secondary battery.

[0147] The types of negative electrodes applied to each lithium secondary battery are shown in Table 2 below.

[0148] [Table 2]

[0149] <Example of experiment>

[0150] To evaluate the performance of the negative electrode according to the present invention, the following experiments were conducted on lithium secondary batteries manufactured in Examples 6 to 10 and Comparative Examples 4 to 6.

[0151] 1) Evaluation of the expansion rate of secondary batteries during charging Each lithium secondary battery in the examples and comparative examples was charged to 4.2V at a rate of 0.3C under CC-CV conditions at 25°C, and then discharged to 2.5V under CC conditions at a rate of 0.3C to activate them. Subsequently, the volume of the activated lithium secondary batteries in the discharged state was measured using Archimedes' principle.

[0152] Each activated lithium secondary battery was charged to 4.5V at a rate of 2.0C at 25°C under CC-CV conditions, and the volume of the charged lithium secondary battery was measured in the same way as the volume measurement method used earlier. The volume change rate during charging of each lithium secondary battery was calculated using Equation 3 below, and the calculated volume change rate was judged based on the expansion rate of the negative electrode in each lithium secondary battery. The results are shown in Table 3 below.

[0153] [Formula 3] Volume change rate during charging = [(Volume during charging - Volume during discharging) / Volume during discharging] × 100

[0154] 2) Evaluation of initial charge capacity and high-rate charge / discharge characteristics Each lithium secondary battery produced in Examples 6-10 and Comparative Examples 4-6 was charged to 4.2V at a rate of 0.3C under CC-CV conditions at 25°C, and then discharged to 2.5V under CC conditions at a rate of 0.3C to activate them.

[0155] Each activated lithium secondary battery was subjected to constant current / constant voltage (CC / CV charge) charging at a temperature of 25°C, and its initial charge capacity was measured. The charging was performed with a constant current at a rate of 0.1C until the voltage reached 4.2V, and then cut off with a constant voltage at a rate of 0.005C to maintain 4.2V. Each charged secondary battery was then subjected to constant current discharge (CC discharge), and its initial discharge capacity was measured. In this case, the constant current discharge was performed at a rate of 1.0C until the voltage reached 1.5V.

[0156] Subsequently, each lithium secondary battery was fully charged at 25°C with a charging current of 2.0C to a charging termination voltage of 4.2 to 4.25V, and the charging capacity was measured. From the measured charging capacity, the ratio of the relative charging capacity relative to the initial charging capacity was calculated to evaluate the high-rate charging characteristics of each lithium secondary battery. Then, the lithium secondary battery was discharged at intervals of 0.2C in the range of 1.0 to 2.0C, and the discharge capacity was measured. From the measured discharge capacity, the ratio of the relative discharge capacity relative to the initial discharge capacity was calculated for each discharge rate, and the high-rate discharge characteristics of each lithium secondary battery were evaluated. The measured results are shown in Table 3.

[0157] [Table 3]

[0158] As shown in Table 3 above, the lithium secondary battery according to the present invention exhibits reduced expansion during charging, high charge / discharge capacity, and excellent high-rate charge / discharge efficiency.

[0159] Specifically, the lithium secondary battery in the example had a high charging capacity of 462 mAh / g or more, and exhibited excellent high-rate charge and discharge characteristics of 90% or more and 88% or more, respectively, during high-rate charging and discharging under 2C rate conditions. Furthermore, the lithium secondary battery in the example showed reduced volume increase, with an expansion rate of less than 40% during charging.

[0160] This demonstrates that by having a two-layer negative electrode active layer in the embodiment, and by controlling the crystal properties of the carbon-based negative electrode active material and silicon-based negative electrode active material contained in the second negative electrode active layer located in the outermost shell to satisfy the conditions of Equations 1 and 2, not only is the charge and discharge capacity of the lithium secondary battery increased, but the high-rate charge and discharge characteristics are also improved.

[0161] These results show that the negative electrode for lithium secondary batteries according to the present invention has a high charge / discharge capacity and excellent high-rate charge / discharge characteristics.

[0162] While preferred embodiments of the present invention have been described above with reference to those skilled in the art or those with ordinary knowledge in the art, it will be understood that the present invention can be modified and altered in various ways without departing from the technical scope of the invention as described in the claims below.

[0163] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in the specification, but is defined by the claims.

Claims

1. negative electrode current collector, A first negative electrode active layer provided on at least one surface of the negative electrode current collector, which includes a first carbon-based negative electrode active material but does not include a silicon-based negative electrode active material, and The first negative electrode active layer is provided on the first negative electrode active layer and includes a second negative electrode active layer comprising a second carbon-based negative electrode active material and a silicon-based negative electrode active material, The silicon-based negative electrode active material comprises one or more of silicon (Si), silicon carbide (SiC), and silicon oxide (SiO₂ q, where 0.8 ≤ q ≤ 2.5). The second negative electrode active layer has an alignment degree (O.I) of carbon-based negative electrode active material according to the following formula 1 of 2.5 or less. The second negative electrode active layer satisfies the following equation 2 with a value of 8 or less. [Formula 1] O.I=I ００４ / I １１０ [Formula 2] I Ｓｉ ×O.I In equations 1 and 2, I ００４ This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I １１０ This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I ｓｉ This represents the area ratio of peaks indicating the (111) crystal plane of the silicon-based negative electrode active material when X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, for a lithium secondary battery negative electrode.

2. The anode for a lithium secondary battery according to claim 1, wherein the second anode active layer has an alignment degree (O.I) of carbon-based anode active material of 0.1 to 1.

5.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein the second negative electrode active layer has formula 2 equal to 0.7 to 6.

4. The anode for a lithium secondary battery according to claim 1, wherein the first carbon-based anode active material and the second carbon-based anode active material each contain one or more of natural graphite and artificial graphite.

5. The silicon-based negative electrode active material is included in an amount of 1% to 40% by weight based on the total weight of the negative electrode active layers contained in the first negative electrode active layer and the second negative electrode active layer, as described in claim 1.

6. The average particle size (Dc) of the second carbon-based negative electrode active material is 1 μm to 50 μm. The average particle size (Ds) of the silicon-based negative electrode active material is 0.1 μm to 10 μm, and The anode for a lithium secondary battery according to claim 1, wherein the ratio of the average particle sizes (Dc / Ds) of the second carbon-based anode active material to the silicon-based anode active material is 2 to 10.

7. A step of applying a first negative electrode slurry and a second negative electrode slurry such that the first negative electrode slurry is located on at least one surface of the negative electrode current collector, and the second negative electrode slurry is located on the first negative electrode slurry. The steps include applying a magnetic field to the coated first negative electrode slurry and the second negative electrode slurry, and The process includes the step of drying a first negative electrode slurry and a second negative electrode slurry to which a magnetic field has been applied to form a negative electrode active layer. The first negative electrode slurry contains a first carbon-based negative electrode active material, The second negative electrode slurry comprises a second carbon-based negative electrode active material and a silicon-based negative electrode active material. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the magnetic field is applied with an intensity of 10,000 G or less.

8. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 7, wherein the step of applying the magnetic field is performed for 1 to 20 seconds.

9. A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode for a lithium secondary battery as described in claim 1, and a separator membrane disposed between the positive electrode and the negative electrode for a lithium secondary battery.

10. The positive electrode is provided on at least one surface of the positive electrode current collector and includes a positive electrode active layer containing one or more positive electrode active materials from among lithium metal oxides represented by the following chemical formulas 1 and 2. [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 2] LiM ２ ｐ Mn １－ｐ O ４ In the aforementioned chemical formulas 1 and 2, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. x, y, z, w, and v are such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, 0 < z ≤ 0.3, 0 < w ≤ 0.3, and 0 ≤ v ≤ 0.1, and y + z + w + v = 1. M ２ is Ni, Co, or Fe, The lithium secondary battery according to claim 9, wherein p is 0.05 ≤ p ≤ 1.

0.

11. The positive electrode active material is LiNi ０．８ Co ０．１ Mn ０．１ O ２ LiNi ０．６ Co ０．２ Mn ０．２ O ２ LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ LiNi ０．６ Co ０．２ Mn ０．１ Al ０．１ O ２ LiNi ０．６ Co ０．２ Mn ０．１５ Al ０．０５ O ２ LiNi ０．７ Co ０．１ Mn ０．１ Al ０．１ O ２ LiNi ０．７ Mn １．３ O ４ LiNi ０．５ Mn １．５ O ４ , and LiNi ０．３ Mn １．７ O ４ A lithium secondary battery according to claim 10, comprising one or more selected from the group consisting of the following.

12. The lithium secondary battery according to claim 9, wherein the electrode assembly is a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly.

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