Negative electrode for lithium secondary battery and method for producing 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 the benefit of priority based on Korean Patent Application No. 10-2023-0076642, filed June 15, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a method for producing the same. [Background technology]

[0003] In recent years, lithium secondary batteries have been widely used not only in small devices such as portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles, power storage devices, etc. In particular, with the recent growing interest in environmental issues, much research has been conducted on electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Existing lithium secondary batteries are limited in their energy density and can only be used in short-distance electric vehicles. As a result, technology development has focused on increasing the energy density of lithium secondary batteries.

[0005] However, the lithium secondary batteries developed for automobiles have a problem in that they require a long charging time after discharging during vehicle operation. Therefore, as the popularity of electric vehicles increases, there is an increasing demand to shorten charging times to a level acceptable to users. Furthermore, electric vehicles must be able to operate smoothly even in situations requiring high power output, such as sudden acceleration. To achieve this, lithium secondary batteries must have high-rate discharge performance, but the current situation is that no technology exists that can meet this requirement.

[0006] Meanwhile, lithium secondary batteries are power-generating elements that can be charged and discharged and are made up of a laminated structure of a positive electrode, separator, and negative electrode. When charging a lithium secondary battery, a lithium desorption reaction occurs in which 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 in which lithium is reduced at the negative electrode and inserted into 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 reality, materials containing graphite are widely used as the negative electrode active material for the above-mentioned negative electrode. When materials containing graphite release lithium, the average potential is about 0.2 V (Li / Li + (reference), and the discharge potential shows a relatively flat pattern. Therefore, when graphite is used as a negative electrode active material, the voltage of the secondary battery is high and constant, which is an advantage. However, the electrical capacity per unit mass of graphite material is small at 372 mAh / g. Meanwhile, the capacity of current graphite materials has already been improved to approach the theoretical capacity, making it difficult to further increase the capacity. In addition, when graphite is used as a negative electrode active material, the lithium ion insertion reaction proceeds at a slow rate, which limits fast charging performance compared to other negative electrode active materials.

[0008] Therefore, various anode active materials have been investigated to improve the capacity and fast charging performance of lithium secondary batteries. Silicon, for example, is known to be able to reversibly adsorb and release large amounts of lithium through a compound-forming reaction with lithium, and much research has been conducted on this topic recently. Silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is significantly higher than graphite-based materials, making it useful as a high-energy density and / or high-capacity anode material. However, silicon undergoes a large volume change (approximately 300%) during charging and discharging, and its high-rate discharge characteristics are poor, limiting the lifespan and fast discharge efficiency of lithium secondary batteries containing silicon.

[0009] Therefore, in order to fundamentally solve these problems, there is a strong need for a negative electrode technology that can simultaneously achieve high capacity characteristics and high rate charge / discharge characteristics. Summary of the Invention [Problem to be solved by the invention]

[0010] An 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 rate charge / discharge characteristics, a method for manufacturing the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, in one embodiment, the present invention comprises: negative electrode current collector, a first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material; and a second negative electrode active layer provided on the first negative electrode active layer and including a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The second negative electrode active layer has an alignment index (OI) of 2.5 or less of the carbon-based negative electrode active material represented by the following formula 1: The second negative electrode active layer provides a negative electrode for a lithium secondary battery that satisfies the following formula 2 by 8 or less:

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

[0013] [Formula 2] I Si ×OI

[0014] In Equation 1 and Equation 2, I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I si represents the area ratio of the peak representing the (111) crystal plane of the silicon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

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

[0016] In addition, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each include at least one of natural graphite and artificial graphite.

[0017] The silicon-based negative electrode active material includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

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

[0019] The second carbon-based negative electrode active material may have an average particle size (Dc) of 1 μm to 50 μm, the silicon-based negative electrode active material may have an average particle size (Ds) of 0.1 μm to 10 μm, and the ratio (Dc / Ds) of the average particle sizes of the second carbon-based negative electrode active material and the silicon-based negative electrode active material may be 2 to 10.

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

[0021] In one embodiment, the present invention further comprises: applying the first and second negative electrode slurries to at least one surface of the negative electrode current collector such that the first negative electrode slurry is positioned on at least one surface of the negative electrode current collector and the second negative electrode slurry is positioned on the first negative electrode slurry; applying a magnetic field to the applied first and second negative electrode slurries; 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, The magnetic field is applied at an intensity of 10,000 G or less in the method for producing a negative electrode for a lithium secondary battery according to the present invention.

[0022] In this case, the step of applying the magnetic field can be carried out for 1 to 20 seconds.

[0023] Furthermore, in one embodiment, the present invention provides A lithium secondary battery is provided, which includes an electrode assembly including a positive electrode, a negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0024] In this case, the positive electrode may be provided on at least one surface of a positive electrode current collector and may include 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 1.0≦x≦1.30, 0.5≦y<1, 0 <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 in the range of 0.05≦p≦1.0.

[0028] As an example, the positive electrode active material is 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, LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, and LiNi 0.3 Mn 1.7 O4.

[0029] Meanwhile, 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 a lithium secondary battery according to the present invention includes a carbon-based negative electrode active material and a silicon-based negative electrode active material in the negative electrode active layer, 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 including the negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0031] Because the present invention is susceptible to various modifications and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0032] However, this is not intended to limit the invention to any particular embodiment, but rather to be understood as including all modifications, equivalents, or alternatives falling within the scope of the present invention.

[0033] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and may be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0034] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0035] Furthermore, in the present invention, "comprising as a main component" can 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 defined component relative to the total weight (or total volume). For example, "comprising graphite as a main component as a negative electrode active material" can 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 relative to the total weight of the negative electrode active material. In some cases, it can mean that the entire negative electrode active material is composed of graphite, with graphite being contained in an amount of 100% by weight.

[0036] Furthermore, in this specification, "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" means that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based negative electrode active material constituting the negative electrode active material particles is arranged at a specific inclination with respect to the surface of the negative electrode current collector, which may be different from the carbon-based negative electrode active material particles themselves being arranged in a specific direction within the negative electrode active layer.

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

[0038] Furthermore, "a carbon-based negative electrode active material with a high degree of alignment" may mean that the "degree of alignment (OI)" referred to herein is large, and that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) exhibiting a two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a low angle (e.g., less than 45°) relative to the surface of the negative electrode current collector. Conversely, "a carbon-based negative electrode active material with a low degree of alignment" may mean that the "degree of alignment (OI)" is small, and that the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle (e.g., an angle close to perpendicular, 45° or greater, specifically 60° or greater) relative to the surface of the negative electrode current collector.

[0039] Furthermore, in this specification, the term "crystal plane of a carbon-based negative electrode active material" refers to a plane where atoms of the carbon-based negative electrode active material form the outer shape of a crystal, and in the present invention, may refer to a crystal plane including a flat surface of the carbon-based negative electrode active material, or a crystal plane including the a-axis / b-axis / ab-axis of the carbon-based negative electrode active material crystal.

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

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

[0042] <Anode for lithium secondary batteries>

[0043] In one embodiment, the present invention comprises: negative electrode current collector, a first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material; and a second negative electrode active layer provided on the first negative electrode active layer and including a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The second negative electrode active layer has an alignment index (OI) of 2.5 or less of the carbon-based negative electrode active material represented by the following formula 1: The second negative electrode active layer provides a negative electrode for a lithium secondary battery that satisfies the following formula 2 by 8 or less:

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

[0045] [Formula 2] I Si ×OI

[0046] In Equation 1 and Equation 2, I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I si represents the area ratio of the peak representing the (111) crystal plane of the silicon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode 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 a negative electrode current collector. The negative electrode active layer is a layer that realizes electrical activity of the negative electrode and contains, as a main component, a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charge and discharge of the battery.

[0048] 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 a negative electrode current collector. Because the composition of each layer in a two-layer negative electrode active layer can be easily controlled, the performance of the negative electrode can be improved by controlling the type and content of components contained in each layer for 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 that provides high battery charge / discharge capacity only in the second negative electrode active layer that contacts the positive electrode. Furthermore, the negative electrode active layer may selectively contain a negative electrode active material such as natural graphite, which has good adhesive properties, only in the first negative electrode active layer that contacts the negative electrode current collector, or may contain a high content of a binder that provides binding between the components that make up 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] The first carbon-based negative electrode active material and the second carbon-based negative electrode active material contained in each negative electrode active layer may be the same or different in type and / or content. Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material refer to materials primarily composed of carbon atoms, and such carbon-based negative electrode active materials may include graphite. The graphite may include at least one of natural graphite and artificial graphite. For example, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may include natural graphite or artificial graphite alone, or may include a mixture of natural graphite and artificial graphite in some cases. In this case, the mixture ratio of natural graphite to artificial graphite may be 5-50:50-95 or 20-45:55-80 by weight. The carbon-based negative electrode active material contains natural graphite and artificial graphite in the above-described mixing ratio, thereby strengthening the adhesion between the negative electrode current collector and the negative electrode active layer and achieving high orientation of the carbon-based negative electrode active material on the surface of the negative electrode current collector.

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

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

[0053] Such a carbon-based negative electrode active material may have a spherical particle shape. In this case, the sphericity of the graphite particles may be 0.75 or more, 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" refers to the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameters passing through the center of a particle. A sphericity of 1 indicates that the particle shape is spherical. The sphericity can be measured using a particle shape analyzer or by measuring the particle shape using a scanning electron microscope (SEM) or an energy dispersive spectrometer, and then analyzing the measurement results.

[0054] The present invention can achieve high electrical conductivity of the negative electrode active layer by implementing the first carbon-based negative electrode active material and the second carbon-based negative electrode active material in a nearly spherical shape. Therefore, a negative electrode including a spherical carbon-based negative electrode active material can improve the capacity of a secondary battery and can increase 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] The silicon-based negative electrode active material is a material containing silicon (Si) as a main component and is contained only in the second negative electrode active layer. The present invention can increase the charge / discharge capacity of the negative electrode by containing the silicon-based negative electrode active material in the second negative electrode active layer adjacent to the positive electrode active layer. Furthermore, the silicon-based negative electrode active material has a problem in that its volume change during charge / discharge is large, and therefore, when contained in the first negative electrode active layer, the durability of the negative electrode is reduced. However, the present invention can maintain high durability of the negative electrode by applying the silicon-based negative electrode active material to the second negative electrode active layer.

[0056] Examples of such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2), which may be contained alone or in combination in the second negative electrode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as the silicon-based negative electrode active material and contained in the negative electrode active layer, they are referred to as silicon oxide (SiO q , where 0.8≦q≦2.5).

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

[0058] The carbon-based negative electrode active material and silicon-based negative electrode active material contained in each layer of the negative electrode active layer may be present in an amount of 85 parts by weight or more, based on 100 parts by weight of the total negative electrode active layer. Specifically, the carbon-based negative electrode active material and silicon-based negative electrode active material contained in each layer of the negative electrode active layer may be present 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 total negative electrode active layer.

[0059] The silicon-based negative electrode active material may be included in an amount of 0.1 to 40 wt % of the total weight of the negative electrode active materials included in the first and second negative electrode active layers, specifically 0.5 to 20 wt %, 1 to 9 wt %, 5 to 15 wt %, 3 to 7 wt %, 11 to 19 wt %, 13 to 17 wt %, 15 to 20 wt %, 10 to 30 wt %, 20 to 40 wt %, 25 to 35 wt %, 15 to 25 wt %, or 9 to 22 wt %. By adjusting the ratio of the total content of the negative electrode active materials included in the negative electrode active layer to the content of the silicon-based negative electrode active material included in the total negative electrode active materials within the above ranges, the present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery, while improving charge capacity per unit mass. Furthermore, the volume change of the negative electrode active layer during charging and discharging of the secondary battery can be minimized, thereby improving the structural stability of the negative electrode active layer, thereby improving 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] For example, the second carbon-based negative electrode active material contained in the second negative electrode active layer may have an alignment index (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 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based negative electrode active material when the negative electrode active layer is subjected to X-ray diffraction (XRD) spectroscopy.

[0064] The degree of alignment (OI) of the second carbon-based negative electrode active material can be an index indicating the degree to which the ab-axis crystal plane of the carbon-based negative electrode active material is oriented in a certain direction, specifically relative to the surface of the negative electrode current collector, during X-ray diffraction (XRD) measurement. Specifically, the second negative electrode 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°, which are the peaks for the graphite second carbon-based negative electrode active material during X-ray diffraction measurement. These peaks represent the (002), (100), (101)R, (101)H, (004), and (110) planes of graphite. Here, the peak appearing at 2θ=43.4±0.2° may be due to the overlap of a peak corresponding to the (1,0,1)R plane of the second carbon-based negative electrode active material and a peak corresponding to the (111) plane of the current collector, for example, copper (Cu).

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

[0066] The peak at 2θ=54.7±0.2° indicates a crystal plane of the second carbon-based negative electrode active material that is tilted relative to the negative electrode current collector. Therefore, the closer the OI value is to 0, the closer the tilt relative to the negative electrode current collector surface is to 90°, and the larger the OI value is, the closer the tilt relative to the negative electrode current collector surface is to 0° or 180°. That is, in the second negative electrode active layer according to the present invention, the second carbon-based negative electrode active material may be aligned at an angle of 60° or more, 70° or more, 70-90°, 80-90°, 65-85°, or 70-85° relative to the negative electrode current collector. Therefore, the second negative electrode active layer may have a lower OI of the second carbon-based negative electrode active material than a layer in which the second carbon-based negative electrode active material is aligned at an angle less than 60°. For example, the second negative electrode active layer may have an alignment index (OI) of the carbon-based negative electrode active material represented by Formula 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 alignment index (OI) indicates the degree of alignment of the ab-axis crystal plane of the carbon-based negative electrode active material, but does not indicate the degree to which the carbon-based negative electrode active material particles are rotated and aligned within the active layer.

[0067] By controlling 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, the present invention can secure a shorter ion migration channel within the negative electrode active layer, thereby preventing an increase in resistance due to the long migration distance of lithium ions, thereby preventing a decrease in high-rate charge performance due to electrical resistance and simultaneously improving high-rate discharge efficiency.

[0068] As another example, the second positive electrode active layer may satisfy the following formula 2 at 8 or less:

[0069] [Formula 2] I Si ×OI

[0070] In Equation 2, OI represents the degree of alignment of the second carbon-based negative electrode active material according to Formula 1, I si represents the area ratio of the peak representing the (111) crystal plane of the silicon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0071] Pure silicon with a crystalline phase has different interatomic distances and densities 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 orientation of each crystal plane exposed on the surface (i.e., the crystal orientation). For example, in silicon crystals, the (100), (111), and (110) crystal orientations can exhibit the highest electron mobility in the order (100) > (111) > (110), while the insertion of metal ions and the like can exhibit the highest mobility in the order (110) > (111) > (100).

[0072] Therefore, the present invention is characterized by controlling the characteristics of the (111) plane among the crystal planes of pure silicon having a crystalline phase. Specifically, the second negative electrode active layer according to the present invention exhibits diffraction peaks indicating the crystal plane of the second carbon-based negative electrode active material and diffraction peaks indicating the silicon-based negative electrode active material when analyzed by X-ray diffraction (XRD) spectroscopy. For example, when the silicon-based negative electrode active material is silicon oxide (SiO q When q is 0.8≦q≦2.5, X-ray diffraction measurement of the second negative electrode active layer shows a gentle, broad curve indicative of amorphous silicon oxide, as well as peaks of pure silicon (pure Si) at angles 28.4±0.2°, 47.3±0.5°, and 56.1±0.2°. These peaks represent the (111), (220), and (311) crystal planes of pure silicon, respectively.

[0073] In this case, the diffraction peak representing the (111) crystal plane of pure silicon (Si) tends to be stronger and the area value obtained by integrating the peak intensity increases as the ab-axis crystal plane of the second carbon-based negative electrode active material is aligned at a higher angle relative to the surface of the negative electrode current collector. This indicates that the (111) crystal plane of silicon is more exposed to the surface of the second negative electrode active layer. However, as described above, the degree of exposure of the (111) crystal plane can affect the mobility of electrons and metal ions, and there can be a trade-off between electron mobility and metal ion mobility. Therefore, it is preferable to adjust the degree of exposure of the (111) crystal plane to satisfy a predetermined range.

[0074] This was achieved by adjusting the value of formula 2 to 8 or less. Specifically, the second negative electrode active layer may satisfy formula 2 as 7 or less, 6 or less, 4 or less, 3.5 or less, 3 or less, 0.7 to 8, 0.7 to 6, 1 to 6, 1.75 to 6, 1.75 to 4, 1.75 to 3.5, 1.75 to 3, 1.75 to 2.5, 1.75 to 2.1, 2 to 6, 2 to 4, 2.1 to 3.5, 2.1 to 3.1, 3 to 5, or 2.5 to 3. Here, formula 2 represents the degree of alignment (OI) calculated from the diffraction peak of the second carbon-based negative electrode active material during X-ray diffraction spectroscopy analysis of the second negative electrode active layer, and reflecting the area integral value of the diffraction peak intensity representing the (111) plane of the silicon-based negative electrode active material in the calculated degree of alignment (OI). By satisfying Formula 2 within the above-mentioned range, the present invention can significantly improve the lithium ion mobility and intercalation performance of the second negative electrode active layer composed of the second carbon-based negative electrode active material and the silicon-based negative electrode active material, thereby significantly improving the high-rate charge-discharge efficiency of a secondary battery including the same.

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

[0076] Specifically, the second carbon-based negative electrode active material has an average particle size (D 50 , Dc), and may be selectively applied within the above range according to the average thickness of the second negative electrode active layer. For example, the second carbon-based negative electrode active material may have an average 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 observed. The spherical second carbon-based negative electrode active material is advantageously small in particle size to maximize the degree of disorder in the expansion direction of each particle, preventing particle expansion during lithium ion charging. However, if the particle size of the second carbon-based negative electrode active material is less than 1.0 μm, the number of particles per unit volume increases, requiring a large amount of binder, which can result in low sphericity and sphericity yield. On the other hand, if the maximum particle size exceeds 50 μm, the expansion rate of the negative electrode active material during charge and discharge of the secondary battery increases significantly. This can reduce the adhesion between particles of the negative electrode active material and between the negative electrode active material particles and the current collector with repeated charge and discharge, resulting in a significant decrease in cycle performance.

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

[0078] If the silicon-based negative electrode active material has a minimum particle size of less than 0.1 μm, it is difficult to uniformly disperse the silicon-based negative electrode active material in the second negative electrode active layer, and as the secondary battery is charged and discharged, oxidation-reduction reactions are unevenly induced between regions where the silicon-based negative electrode active material aggregates and regions where it does not aggregate, which can accelerate deterioration of the second negative electrode active layer. Furthermore, if the silicon-based negative electrode active material has a maximum particle size of more than 10 μm, it is difficult to control the crystal plane of the silicon-based negative electrode active material, and the expansion rate per unit area of ​​the second negative electrode active layer during charge and discharge of the secondary battery increases significantly, resulting in a significant decrease in cycle performance due to repeated charge and discharge.

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

[0080] By setting the average particle size ratio (Dc / Ds) of the second carbon-based negative electrode active material to the silicon-based negative electrode active material within the above range, the present invention can induce a structure in which the silicon-based negative electrode active material fills voids formed by a plurality of second carbon-based negative electrode active materials. In this case, the voids act as a buffer to buffer the volumetric expansion of the silicon-based negative electrode active material during charge and discharge of the secondary battery, thereby minimizing the volumetric expansion of the second negative electrode active layer.

[0081] Furthermore, if the average particle size ratio (Dc / Ds) is less than the lower limit of the above range, the influence of the second carbon-based negative electrode active material on the silicon-based negative electrode 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. Furthermore, if the average particle size ratio (Dc / Ds) exceeds the upper limit of the above range, there is a problem in that deterioration of the second negative electrode active layer is accelerated during charge and discharge of the secondary battery, resulting in a shortened lifespan.

[0082] Meanwhile, 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 within the above range, the present invention can easily control the crystalline characteristics of the negative electrode active material contained in the second negative electrode active layer, thereby improving the high-rate charge / discharge characteristics of a secondary battery including the negative electrode of the present invention.

[0083] The first and second negative electrode active layers may have the same or different average thicknesses. Specifically, the ratio of the average thickness of the first negative electrode active layer (D1) to the average thickness of the second negative electrode active layer (D2) may be 1:0.5 to 3, more specifically, 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 and second negative electrode active layers within the above range, the present invention can maximize charge / discharge capacity while maintaining high durability of the negative electrode.

[0084] Furthermore, the first negative electrode active layer and the second negative electrode active layer according to the present invention may further selectively contain, in addition to the negative electrode active material as the main component, a conductive material, a binder, other additives, and the like, as necessary.

[0085] The conductive material may include, but is not limited to, one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like.

[0086] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0087] The content of the conductive material may be 0.1 to 10 parts by weight, based on 100 parts by weight of the total 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, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent a decrease in charge capacity due to an increase in the resistance of the negative electrode caused by a low content of conductive material. Furthermore, it can prevent problems such as a decrease in charge capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of conductive material, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0088] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, etc., and between the negative electrode active material and the current collector, and may be suitably used within a range that does not degrade the electrical properties of the electrode. Specifically, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

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

[0090] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery, and may be made of, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector is preferably 1 to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0091] <Lithium secondary battery>

[0092] In one embodiment, the present invention further comprises: A lithium secondary battery is provided, which includes an electrode assembly including a positive electrode, the above-described negative electrode of the present invention, and a separator 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 alternately arranged with a separator disposed therebetween. The lithium secondary battery includes the negative electrode according to the present invention and has high charge / discharge capacity and excellent high-rate charge / discharge characteristics, and therefore can be useful as a power source for medium- to large-sized devices such as electric vehicles.

[0094] In this case, the negative electrode has the same structure as that described above, and therefore a detailed description thereof will be omitted.

[0095] The positive electrode includes a positive electrode active layer including a positive electrode active material on a positive electrode current collector, and the positive electrode active layer may further include a conductive material, a binder, other additives, and the like, as needed.

[0096] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include one or more lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating 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 Formula 1 and Chemical Formula 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 1.0≦x≦1.30, 0.5≦y<1, 0 <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, q is 2-p, r is 0 or 1.

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

[0101] In this case, the lithium metal oxide represented by the above chemical formula 1 is 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., and the lithium metal oxide represented by the above chemical formula 2 is LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, and LiNi 0.3 Mn 1.7 O4, etc., which may be used alone or in combination.

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

[0103] The positive electrode active layer may further include a conductive material, a binder, and other additives in addition to 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 a conductive material commonly used in the art. Specifically, the conductive material may include at least one 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] The conductive material may be contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of each positive electrode active layer. Specifically, the conductive material may be contained 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 per 100 parts by weight of each positive electrode active layer.

[0106] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. 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, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

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

[0108] The total thickness of the positive electrode active layer is not particularly limited, but may be 50 μm to 300 μm, more specifically, 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.

[0109] The positive electrode may be made of a current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector may be preferably 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0110] The separator 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 a thin film commonly used in the art. Specifically, it may contain one or more polymers selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymer, which are chemically resistant and hydrophobic. The separator may have the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymer. In some cases, the separator may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0111] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a stack type, a zigzag type, or a zigzag-stack type electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch type secondary battery or a prismatic type secondary battery.

[0112] Pouch-type secondary batteries and / or prismatic secondary batteries have the advantage of being highly usable in terms of energy density since unit cells of the secondary battery can be packed at high density in a limited space.

[0113] <Method of manufacturing the negative electrode>

[0114] In one embodiment, the present invention further comprises: applying the first and second negative electrode slurries to at least one surface of the negative electrode current collector such that the first negative electrode slurry is positioned on at least one surface of the negative electrode current collector and the second negative electrode slurry is positioned on the first negative electrode slurry; applying a magnetic field to the applied first and second negative electrode slurries; 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, The magnetic field is applied at an intensity of 10,000 G or less in a method for producing a negative electrode for a lithium secondary battery.

[0115] The method for manufacturing a negative electrode according to the present invention refers to a method for manufacturing the above-described negative electrode according to the present invention. The method for manufacturing a negative electrode includes coating a negative electrode slurry on a negative electrode current collector, applying a magnetic field to the surface of the coated negative electrode slurry, and then drying the coated negative electrode slurry, thereby manufacturing a negative electrode having a negative electrode active layer in which the crystalline properties of the negative electrode active material are controlled.

[0116] The negative electrode slurry coating step involves discharging and coating the negative electrode slurry containing a carbon-based negative electrode active material onto the surface of a moving negative electrode current collector. This step can be performed using any method commonly used in the art, but preferably, a die coating method can be used. The die coating method can be performed using a slot die equipped with a shim to control the discharging conditions of the negative electrode slurry. In this case, the loading amount and coating thickness of the negative electrode slurry coated on the negative electrode current collector can be easily controlled by controlling the shape of the shim.

[0117] In the present invention, the first and second negative electrode slurries may be simultaneously coated onto the negative electrode current collector using a dual die, which has the advantage of significantly improving process efficiency compared to sequentially coating each slurry.

[0118] Meanwhile, the step of applying a magnetic field to the negative electrode slurry may be a step of controlling the crystalline properties of the negative electrode active material contained in the negative electrode slurry. Specifically, this step may control the crystalline properties of the (111) crystalline plane of the silicon-based negative electrode active material contained in the second negative electrode slurry by applying a magnetic field to the surfaces of the first and second negative electrode slurries 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 at a high angle relative to the negative electrode current collector.

[0119] In this case, the magnetic field may be applied by magnets disposed above and below the negative electrode current collector, which is moved with the negative electrode slurry coated on its surface, and the polarities of the magnets disposed above and below the negative electrode current collector may be opposite to each other.

[0120] In addition, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry may be adjusted depending on the strength of the applied magnetic field, and thus, the step of applying the magnetic field may be performed under a predetermined magnetic field strength condition.

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

[0122] Furthermore, the step of applying the magnetic field can be carried out for 1 to 20 seconds, specifically 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 a magnetic field, 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 above and below the applied negative electrode slurry, as described above, and the size of the magnets may 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 uniformly applied across the entire surface of the negative electrode slurry. For example, the magnets may have a length ratio of 105% to 200% based on the width of the negative electrode slurry, and specifically, 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% based on 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 at 8 or less while satisfying the degree of alignment (OI) of the carbon-based negative electrode active material contained in the second negative electrode slurry at 2.5 or less by controlling the strength of the magnetic field, the application time, and / or the size of the magnet unit.

[0126] The step of forming the negative electrode active layer may also include the steps of drying the negative electrode slurry and rolling the dried negative electrode slurry.

[0127] At this time, the step of drying the negative electrode slurry may be performed in any manner 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 may involve applying heat energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like to dry the negative electrode slurry.

[0129] The step of rolling the dried negative electrode slurry is a step of increasing the density of the negative electrode active layer by applying pressure to the dried negative electrode slurry using a roll press, etc. Here, the rolling may be performed at a temperature higher than room temperature.

[0130] Specifically, the rolling can be carried out at a temperature of 50°C to 100°C, more specifically at a temperature 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 rolling can be performed at a rolling speed of 2 m / s to 7 m / s, more specifically, at a rolling speed 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. The rolling can be carried out under a pressure of 50 MPa to 200 MPa, specifically 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 can increase the energy density of the negative electrode while minimizing changes in the degree of alignment of the carbon-based negative electrode active material contained in the negative electrode active layer formed by rolling the dried negative electrode slurry under the above-mentioned 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 merely 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 to 5 and Comparative Examples 1 to 3. Production of negative electrodes for lithium secondary batteries>

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

[0136] Specifically, a graphite mixture consisting of natural graphite and artificial graphite in a weight ratio of 3.5-4.5:5.5-6.5 was prepared as the first carbon-based negative electrode active material, carbon black was used as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were used as binders. 95 parts by weight of the graphite mixture, 1 part by weight of carbon black, 1.5 parts by weight of CMC, and 2.5 parts by weight of SBR were mixed with water to a solids content of 50% to prepare a first negative electrode slurry.

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

[0138] After each negative electrode slurry was prepared, the first negative electrode slurry and the second negative electrode slurry were simultaneously cast onto a copper thin plate (thickness: 10 μm) that was being transferred roll-to-roll (transfer speed: 5 m / min) using a dual die coater.

[0139] Permanent magnets with a length ratio of 110 to 120% of the width of the negative electrode slurry were placed on top of the coated negative electrode slurry and below the negative electrode current collector. A magnetic field was applied for 2 to 3 seconds with the magnetic field strength adjusted 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 a first negative electrode active layer and a second negative electrode active layer were sequentially stacked on the negative electrode current collector. The formed negative electrode active layer was rolled at 50±1°C under a pressure of 100 to 150 MPa and a transfer speed of 3 m / s to prepare a negative electrode for a lithium secondary battery (average thickness of the first negative electrode active layer and the second negative electrode active layer: 110±5 μm each).

[0140] In addition, X-ray diffraction spectroscopy (XRD) was performed on the second negative electrode active layer of each manufactured negative electrode to measure the spectrum. In this case, X-ray diffraction (XRD) spectroscopy was performed once for each of the second carbon-based negative electrode active material and silicon-based negative electrode active material contained in the second negative electrode active layer. The X-ray diffraction (XRD) measurement conditions were as follows:

[0141] - Target: Cu (Kα line) graphite monochromator - Slit: Divergence 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) the area integral values ​​of the peak representing the (0,0,4) crystal plane and the peak representing the (110) crystal plane were calculated from the spectrum measured using the second carbon-based negative electrode active material as a target, and the ratio of these areas (I 004 / I 110 ) was calculated to calculate the degree of alignment (OI) of the mixed graphite in each region. (2) The area integral value (I Si ) was calculated. The calculated values ​​are shown in Table 1 below.

[0143] [Table 1]

[0144] <Examples 6 to 10 and Comparative Examples 4 to 6. Production 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 as a carbon-based conductive material and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0146] A separator made of 18 μm polypropylene was interposed between the obtained positive electrode and the negative electrode prepared in each of Examples 1 to 5 and Comparative Examples 1 to 3, and the electrode was inserted into a case. Then, an electrolyte composition was injected to assemble a lithium secondary battery.

[0147] The type of negative electrode used in each lithium secondary battery is shown in Table 2 below.

[0148] [Table 2]

[0149] <Experimental Example>

[0150] In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were carried out on the lithium secondary batteries produced in Examples 6 to 10 and Comparative Examples 4 to 6.

[0151] 1) Evaluation of the expansion rate of secondary batteries during charging Each of the lithium secondary batteries of the Examples and Comparative Examples was activated by charging at 25° C. at a rate of 0.3 C under CC-CV conditions to 4.2 V and discharging at a rate of 0.3 C under CC conditions to 2.5 V. Then, the volume of the activated lithium secondary batteries in a discharged state was measured using Archimedes' principle.

[0152] Each activated lithium secondary battery was charged at 2.0 C up to 4.5 V under CC-CV conditions at 25°C, and the volume of the charged lithium secondary battery was measured in the same manner as the previous volume measurement. The volume change rate of each lithium secondary battery during charge was calculated using Equation 3 below, and the calculated volume change rate was determined from the expansion rate of the negative electrode provided 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] x 100

[0154] 2) Evaluation of initial charge capacity and high-rate charge / discharge characteristics Each of the lithium secondary batteries prepared in Examples 6 to 10 and Comparative Examples 4 to 6 was activated by charging at 25° C. at a rate of 0.3 C to 4.2 V under CC-CV conditions and discharging at a rate of 0.3 C to 2.5 V under CC conditions.

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

[0156] Each lithium secondary battery was then fully charged at 25°C with a charging current of 2.0C to a charge cut-off voltage of 4.2 to 4.25V, and the charge capacity was measured. The relative charge capacity ratio based on the initial charge capacity was calculated from the measured charge capacity, and the high-rate charge characteristics of each lithium secondary battery were evaluated. The lithium secondary battery was then discharged at a rate range of 1.0 to 2.0C at 0.2C intervals, and the discharge capacity was measured. The relative discharge capacity ratio based on the initial discharge capacity for each discharge rate was calculated from the measured discharge capacity, and the high-rate discharge characteristics of each lithium secondary battery were evaluated. The measurement 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 has a reduced expansion rate during charging, a high charge / discharge capacity, and excellent high-rate charge / discharge efficiency.

[0159] Specifically, the lithium secondary batteries of the examples had a high charge capacity of 462 mAh / g or more, and exhibited excellent high-rate charge / discharge characteristics of 90% or more and 88% or more during high-rate charge and discharge at a 2 C rate, respectively. Furthermore, the lithium secondary batteries of the examples showed a small expansion rate of less than 40% during charging, indicating a reduced increase in volume.

[0160] This indicates that the negative electrode of the embodiment has a two-layered negative electrode active layer, and by controlling the crystalline properties of the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the second negative electrode active layer located at the outermost layer to satisfy the conditions of Equation 1 and Equation 2, not only the charge / discharge capacity of the lithium secondary battery but also the high-rate charge / discharge characteristics are improved.

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

[0162] Although the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art or those with ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the technical scope of the present invention as set forth in the claims below.

[0163] Therefore, the technical scope of the present invention is not limited to the content described in the Summary of the Invention of 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 and including a first carbon-based negative electrode active material; and a second negative electrode active layer disposed on the first negative electrode active layer and including a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The second negative electrode active layer has a degree of alignment (O.I) of 2.5 or less of the carbon-based negative electrode active material represented by the following formula 1: The second negative electrode active layer satisfies the following formula 2 with a value of 8 or less: [Formula 1] O.I=I ００４ / I １１０ [Formula 2] I Ｓｉ ×O.I In Equation 1 and Equation 2, I ００４ represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopic analysis of the negative electrode active layer, I １１０ represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I ｓｉ represents the area ratio of the peak representing the (111) crystal plane of the silicon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, negative electrode for lithium secondary battery.

2. 2. The negative electrode of claim 1, wherein the second negative electrode active layer has an alignment degree (O.I) of the carbon-based negative electrode active material of 0.1 to 1.

5.

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

4. The negative electrode for a lithium secondary battery according to claim 1 , wherein the first carbon-based negative electrode active material and the second carbon-based negative electrode active material each include at least one of natural graphite and artificial graphite.

5. The silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO ｑ 2. The negative electrode for a lithium secondary battery according to claim 1, wherein q is at least one of q and ...

6. 2. The negative electrode of claim 1, wherein the silicon-based negative electrode active material is contained in an amount of 1 wt % to 40 wt % based on the total weight of the negative electrode active layers included in the first negative electrode active layer and the second negative electrode active layer.

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

8. applying the first and second negative electrode slurries to at least one surface of the negative electrode current collector such that the first negative electrode slurry is positioned on at least one surface of the negative electrode current collector and the second negative electrode slurry is positioned on the first negative electrode slurry; applying a magnetic field to the applied first and second negative electrode slurries; and drying the first and second negative electrode slurries to which a magnetic field has been applied to form a negative electrode active layer; the first negative electrode slurry includes a first carbon-based negative electrode active material; the second negative electrode slurry includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The method for producing a negative electrode for a lithium secondary battery according to claim 1 , wherein the magnetic field is applied at an intensity of 10,000 G or less.

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

10. A lithium secondary battery comprising an electrode assembly including a positive electrode, the negative electrode for a lithium secondary battery according to claim 1, and a separator disposed between the positive electrode and the negative electrode for a lithium secondary battery.

11. The positive electrode includes a positive electrode active layer provided on at least one surface of a positive electrode current collector and including one or more positive electrode active materials selected from lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 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 above Chemical Formula 1 and Chemical Formula 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 in the ranges 1.0≦x≦1.30, 0.5≦y<1, 0<z≦0.3, 0<w≦0.3, 0≦v≦0.1, respectively, and y+z+w+v=1; M ２ is Ni, Co or Fe, 11. The lithium secondary battery according to claim 10, wherein p is in the range of 0.05≦p≦1.

0.

12. 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 The lithium secondary battery according to claim 11, comprising one or more selected from the group consisting of:

13. The lithium secondary battery according to claim 10, wherein the electrode assembly is a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly.

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