Negative electrode for lithium secondary battery and method for producing same

Abstract

The present invention relates to a negative electrode and a method for manufacturing the same. The negative electrode includes a two-layered negative electrode active layer on a negative electrode current collector, and the upper second negative electrode active layer contains a carbon-based negative electrode active material and a silicon-based negative electrode active material at a predetermined content ratio. The degree of alignment (OI) of the lower first negative electrode active layer and the ratio of the degrees of alignment (OI) between the first negative electrode active layer and the second negative electrode active layer are 1st / OI 2nd By adjusting the temperature within a predetermined range, it has a high charge / discharge capacity. In addition, lithium secondary batteries containing it have excellent output characteristics and can be charged in a short time even at a 1C rate.

Description

[Technical Field]

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0105352 dated August 11, 2023, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference. [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 have limited applications, such as short-distance electric vehicles, due to their limited energy density. Therefore, technology development has been 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 take a long time to charge after discharging during vehicle operation. Therefore, as the popularity of electric vehicles increases, there is an increasing demand to shorten the charging time to a level acceptable to users.

[0006] Meanwhile, lithium secondary batteries are chargeable and dischargeable power generating devices with a laminated structure of a positive electrode, separator, and negative electrode. When charging a lithium secondary battery, a lithium desorption reaction occurs in the positive electrode, where lithium contained in the positive electrode active material is oxidized and released, and a lithium insertion reaction occurs in the negative electrode, where lithium is reduced and inserted into the negative electrode active material. Generally, the desorption reaction in the positive electrode active material is faster than the insertion reaction in the negative electrode active material, so the rapid charge and discharge performance of a lithium secondary battery is primarily determined by the negative electrode.

[0007] Materials containing graphite are widely used as the negative electrode active material. The average potential at which graphite releases lithium is approximately 0.2 V (Li / Li + (reference), and the discharge potential is relatively flat. Therefore, when graphite is used as an anode active material, 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. Meanwhile, the capacity of current graphite materials has improved to near the theoretical capacity mentioned above, making it difficult to further increase the capacity. In addition, when graphite is used as an anode active material, the lithium ion insertion reaction proceeds at a slow rate, which limits fast charging performance compared to other anode 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 larger 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 realize high rapid charge / discharge performance and life characteristics while improving charge / discharge capacity. 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 has improved rapid charge / discharge performance, allowing the secondary battery to be charged in a short time, has a high charge / discharge capacity, and exhibits excellent life characteristics, and a method for producing the same. [Means for solving the problem]

[0011] To solve the above problem, The present invention provides a negative electrode current collector; a first negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a first carbon-based negative electrode active material; a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The first negative electrode active layer is The degree of alignment (OI) is expressed by the following formula 1. 1st ) is in the range of 5 to 15, The negative electrode is provided with the following formula 2, which is in the range of 0.2 to 0.6:

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

[0013] [Formula 2] OI 1st / OI 2nd

[0014] Here, in Equation 1 and Equation 2, I 004represents 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) spectroscopic analysis of the negative electrode active layer, OI 1st represents the degree of alignment of the first carbon-based negative electrode active material contained in the first negative electrode active layer, OI 2nd represents the degree of alignment of the second carbon-based negative electrode active material contained in the second negative electrode active layer.

[0015] In this case, the silicon-based negative electrode active material may be included in an amount of 1 wt % to 25 wt % based on the weight of the second negative electrode active layer.

[0016] The first negative electrode active layer may have an alignment index (OI) in the range of 7-12.

[0017] The carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite.

[0018] The silicon-based negative electrode active material includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

[0019] The total thickness of the first negative electrode active layer and the second negative electrode active layer may be in the range of 50 μm to 500 μm.

[0020] The present invention also provides applying a negative electrode slurry to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; and drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer.

[0021] At this time, the step of applying the magnetic field may be performed for 1 to 20 seconds.

[0022] The step of applying the magnetic field can be performed at a magnetic field strength in the range of 1,000G to 7,000G.

[0023] Furthermore, the present invention provides an electrode assembly including a positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition impregnated in the electrode assembly.

[0024] The positive electrode may include 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:

[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] Here, in the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 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] Specifically, 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 It may contain one or more of O4.

[0029] 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 is characterized by not only a high charge / discharge capacity but also excellent life characteristics. Furthermore, a lithium secondary battery containing the negative electrode has the advantage of being excellent in output characteristics and capable of being charged in a short time even at a 1C rate. DETAILED DESCRIPTION OF THE INVENTION

[0031] Because the present invention is susceptible to various modifications and variations, specific embodiments will be described in detail.

[0032] However, this is not intended to limit the invention to any particular embodiment, but rather it can be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

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

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

[0035] Additionally, in the present invention, "comprising as a main component" may mean containing 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of a defined component relative to the total weight (or volume). For example, "comprising graphite as a main component of the negative electrode active material" may mean containing 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more of graphite relative to the total weight of the negative electrode active material. In some cases, it may mean that the entire negative electrode active material is composed of graphite, with the graphite content being 100 wt%.

[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 aligned at a specific inclination with respect to the surface of the negative electrode current collector, which may differ from the carbon-based negative electrode active material particles themselves being aligned in a specific direction within the negative electrode active layer.

[0037] Furthermore, "high orientation of the carbon-based negative electrode active material" can 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 can 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, "high degree of alignment of the carbon-based negative electrode active material" 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, "low degree of alignment of the carbon-based negative electrode active material" 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 more; specifically, 60° or more) 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 in which 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 plane 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 50The term "average particle size" refers to the particle size at which the cumulative value is 50% in the particle size distribution of particles, and is also called the median diameter. The average particle size can be measured by a method commonly used in the art. For example, the average particle size can be measured using a particle size analyzer or an analytical instrument using a laser diffraction scattering particle size distribution measurement method.

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

[0042] <Anode for lithium secondary batteries>

[0043] The present invention provides a negative electrode current collector; a first negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a first carbon-based negative electrode active material; a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The first negative electrode active layer is The degree of alignment (OI) is expressed by the following formula 1. 1st ) is in the range of 5 to 15, Provided is a negative electrode for a lithium secondary battery that satisfies the following formula 2 in the range of 0.2 to 0.6:

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

[0045] [Formula 2] OI 1st / OI 2nd

[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, OI1st represents the degree of alignment of the first carbon-based negative electrode active material contained in the first negative electrode active layer, OI 2nd represents the degree of alignment of the second carbon-based negative electrode active material contained in the second 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 includes, as a main component, a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charge and discharge of the battery. The negative electrode active material includes a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0048] Here, the carbon-based negative electrode active material refers to a material mainly composed of carbon atoms, and may include graphite.

[0049] The graphite may include at least one of natural graphite and artificial graphite. In addition to natural graphite and artificial graphite, graphite may also include mesophase calcined carbon (bulk mesophase) made from tar and pitch, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.).

[0050] For example, the negative electrode active layer according to the present invention may contain artificial graphite alone. Since the negative electrode active layer according to the present invention contains artificial graphite alone, the life of the negative electrode is significantly improved, which is advantageous in situations where the negative electrode must withstand frequent charging for a long period of time, such as in automobile batteries. Furthermore, compared to natural graphite, artificial graphite has advantages in terms of fast charging and superior output performance.

[0051] The negative electrode active layer according to the present invention may also contain both natural graphite and artificial graphite. In this case, the mixing ratio of the natural graphite to the artificial graphite may be 5 wt% to 50 wt%:50 wt% to 95 wt%, 20 wt% to 45 wt%:55 wt% to 80 wt%, or 5 wt% to 15 wt%:85 wt% to 95 wt%. By including both natural graphite and artificial graphite in the negative electrode active layer in the above content ratios, the present invention can maintain a high rapid charging rate and output performance.

[0052] The carbon-based negative electrode active material may have a round particle shape, rather than a plate-like, sheet-like, scale-like, or needle-like shape. Here, a round particle shape may refer to particles that are not angular. When such particles are subjected to cross-sectional structure analysis or projected as two-dimensional particles, their shape may be spherical or ellipsoidal, or in some cases, may be shapeless, making it difficult to define the shape.

[0053] For example, the carbon-based negative electrode active material may be graphite having a spherical particle shape. In this case, the spherical particles may be processed to have a spherical shape / form during production, or may be spherical graphite granules formed by aggregating a plurality of flake graphite particles. When the spherical particles are granules, one graphite assembly may be formed by aggregating 2 to 100, preferably 3 to 20, flake graphite particles. By controlling the shape of the carbon-based negative electrode active material as described above, the present invention can further increase the electrical conductivity of the negative electrode active layer and maximize the contact area with the negative electrode current collector, thereby improving the adhesive strength between the negative electrode active layer and the negative electrode current collector.

[0054] The carbon-based negative electrode active material may also be ellipsoidal. In this case, the carbon-based negative electrode active material may be more easily secured as a lithium ion migration path within the negative electrode active layer, thereby enabling charging to be completed in a shorter time under the same conditions.

[0055] In addition, the carbon-based negative electrode active material may have a size adjusted to a certain range. Specifically, the average particle size (D 50 ) may be in the range of 1 μm to 30 μm, specifically 1 μm to 20 μm, 1 μm to 15 μm, 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 5 μm, 1 μm to 3 μm, 10 μm to 20 μm, 11 μm to 19 μm, 8 μm to 15 μm, 15 μm to 20 μm, 13 μm to 19 μm, 14 μm to 17 μm, 5 μm to 8 μm, 7 μm to 14 μm, 9 μm to 13 μm, 2 μm to 6 μm, 5 μm to 9 μm, 1 μm to 4.5 μm, or 1 μm to 3 μm.

[0056] In the present invention, by controlling the average particle size of the carbon-based negative electrode active material within the above range, an increase in the electrical resistance of the negative electrode active layer can be easily suppressed. Furthermore, within the above average particle size range, the carbon-based negative electrode active material can maximize the degree of disorder in the expansion direction of each particle, preventing particle expansion due to lithium ion charging while increasing the specific surface area per unit weight. This further enhances the adhesive strength between the negative electrode active layer and the negative electrode current collector. Furthermore, within the above average particle size range, the carbon-based negative electrode active material has the advantage of ensuring a lithium ion migration path, thereby further improving fast charging performance. Meanwhile, the carbon-based negative electrode active material, when the above average particle size (D 50 If the particle size is smaller than the lower limit of the average particle size (D), a large amount of binder is required due to the increase in the number of particles per unit volume, which may result in a deterioration in the electrical properties of the negative electrode active layer containing them. 50 ), the expansion rate of the negative electrode active material during charge and discharge of the secondary battery increases significantly, and as a result, the adhesion between particles of the negative electrode active material and the adhesion between the negative electrode active material particles and the current collector decreases with repeated charge and discharge, which can result in a significant decrease in cycle characteristics.

[0057] The silicon-based negative electrode active material refers to a material whose main component is silicon atoms. 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 negative electrode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or combined and contained in the negative electrode active layer as the silicon-based negative electrode active material, they are referred to as silicon oxide (SiO q , where 0.8≦q≦2.5).

[0058] 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.

[0059] In addition, the silicon-based negative electrode active material may have a size adjusted to a certain range. Specifically, the average particle size (D 50 ) may be in the range of 0.5 μm to 20 μm, specifically 0.5 μm to 15 μm, 0.5 μm to 13 μm, 0.5 μm to 9 μm, 0.5 μm to 6 μm, 0.5 μm to 4 μm, 0.5 μm to 2 μm, 9 μm to 18 μm, 10 μm to 17 μm, 7 μm to 14 μm, 14 μm to 18 μm, 12 μm to 18 μm, 11 μm to 15 μm, 4 μm to 8 μm, 4 μm to 13 μm, 5 μm to 12 μm, 7 μm to 11 μm, 1 μm to 5 μm, 3 μm to 8 μm, 1 μm to 3 μm, or 1 μm to 2 μm.

[0060] Meanwhile, 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 of 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 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 that provides high battery charge / discharge capacity only in the first negative electrode active layer that contacts the negative electrode current collector. Furthermore, the negative electrode active layer may selectively contain a highly adhesive negative electrode active material such as natural graphite or a high content of a binder that provides binding between the components that make up the active layer only in the first negative electrode active layer that contacts the negative electrode current collector.

[0061] In the present invention, the first negative electrode active layer includes a first carbon-based negative electrode active material, and the second negative electrode active layer includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material, and 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.

[0062] The present invention includes a silicon-based negative electrode active material in a second negative electrode active layer adjacent to a positive electrode active layer, thereby increasing the charge / discharge capacity of the negative electrode. Furthermore, the present invention includes a silicon-based negative electrode active material in a second negative electrode active layer not adjacent to the negative electrode current collector, thereby preventing a problem in advance where the adhesive strength between the negative electrode active layer and the negative electrode current collector is reduced due to volumetric changes in the silicon-based negative electrode active material during charge / discharge of the secondary battery. Furthermore, the silicon-based negative electrode active material reduces the degree of alignment (OI) of the first negative electrode active layer. 1st ) is the degree of alignment (OI) of the second negative electrode active layer 2nd ) This tendency of alignment within the entire negative electrode active layer can significantly increase the lithium mobility within the negative electrode active layer, resulting in an excellent initial lithium mobility rate during charge and discharge, which is advantageous in that it can shorten the charge and discharge time of the secondary battery at a low C rate.

[0063] The silicon-based negative electrode active material may be included in an amount of 1 wt% to 25 wt% based on the total weight of the negative electrode active material included in the second negative electrode active layer. Specifically, the amount of the silicon-based negative electrode active material may be 5 wt% to 25 wt%, 9 wt% to 23 wt%, 10 wt% to 20 wt%, 8 wt% to 18 wt%, 5 wt% to 15 wt%, 8 wt% to 13 wt%, 11 wt% to 23 wt%, 15 wt% to 20 wt%, 11 wt% to 19 wt%, 19 wt% to 25 wt%, or 18 wt% to 23 wt% based on the total weight of the negative electrode active material. By adjusting the content ratio of the silicon-based negative electrode active material within the above range, the present invention can minimize the volume change rate due to the silicon-based negative electrode active material during charge and discharge, thereby maintaining the lithium migration path of the carbon-based negative electrode active material implemented in the negative electrode active layer when a magnetic field is applied. Therefore, the negative electrode according to the present invention can significantly improve the lifespan characteristics while realizing a high charging capacity, and can also significantly reduce the charging speed of the secondary battery.

[0064] Furthermore, the negative electrode according to the present invention may control the crystalline structure characteristics of the carbon-based negative electrode active material contained in the negative electrode active layer to realize a fast charging rate. Specifically, the first negative electrode active layer may have an alignment degree (OI) of the carbon-based negative electrode active material according to the following Equation 1: 1st ) can range from 5 to 15:

[0065] [Formula 1] OI=I 004 / I 110

[0066] 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.

[0067] The degree of alignment (OI) of the 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, as measured by X-ray diffraction (XRD). Specifically, the 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 correspond to the graphite carbon-based negative electrode active material, as measured by X-ray diffraction. 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° is thought to be an overlap of the peaks corresponding to the (101)R plane of the carbon-based negative electrode active material and the (111) plane of the current collector, for example, copper (Cu).

[0068] The degree of alignment (OI) of the 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 calculating the area ratio.

[0069] The peak at 2θ=54.7±0.2° indicates a crystal plane of the 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 first negative electrode active layer according to the present invention, the first carbon-based negative electrode active material contained in the layer may be aligned to the negative electrode current collector at an angle of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, or 70° to 85°. Therefore, the first negative electrode active layer may have a lower OI of the carbon-based negative electrode active material than a carbon-based negative electrode active material aligned at a low angle of less than 60°. Here, the degree of alignment (OI) may represent the degree to which carbonaceous negative active material particles are aligned on the surface of the negative electrode current collector. In some cases, the degree of alignment (OI) may also represent the degree of alignment of the ab-axis crystal plane of the carbonaceous negative active material in the negative electrode active layer. When the ab-axis crystal plane of the carbonaceous negative active material is aligned, rotation of the carbonaceous negative active material particles contained in the negative electrode active layer may also be induced. However, because this particle rotation is affected by the particle morphology and is not equivalent to the degree to which the ab-axis crystal plane is aligned, it may be difficult to indicate that the carbonaceous negative active material particles are aligned using the degree of alignment (OI).

[0070] Here, the carbon-based negative electrode active material contained in the first negative electrode active layer has the degree of alignment (OI 1st ) may be in the range of 5 to 15, specifically 5 to 13, 5 to 11, 5 to 9, 7 to 15, 10 to 15, 7 to 12, 7.5 to 10, 6 to 9.5, or 7.5 to 9.5.

[0071] The degree of alignment (OI) of the carbon-based negative electrode active material contained in the first negative electrode active layer 1st If the degree of alignment (OI) of the carbon-based negative electrode active material contained in the first negative electrode active layer is less than the above-mentioned lower limit, the adhesive strength with the negative electrode current collector may be reduced. 1stBy adjusting the degree of alignment (OI) of the carbon-based first negative electrode active material contained in the negative electrode active layer to be equal to or greater than the above-mentioned lower limit, the proportion of the crystal faces of the carbon-based negative electrode active material molecules constituting the negative electrode active material particles that face the negative electrode current collector increases, thereby improving the fast charging performance of the negative electrode within a range in which the adhesive strength between the first negative electrode active layer and the negative electrode current collector is not reduced. 1st ) to the above upper limit or less, a shorter ion migration channel through which lithium ions can migrate can be secured within the negative electrode active layer. 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 further increasing the lithium ion migration rate during charge and discharge, and simultaneously improving fast charge performance and output performance with high safety.

[0072] Furthermore, the first negative electrode active layer can satisfy formula 2 in the range of 0.2 to 0.6:

[0073] [Formula 2] OI 1st / OI 2nd

[0074] In Equation 2, OI 1st represents the degree of alignment of the first carbon-based negative electrode active material contained in the first negative electrode active layer, OI 2nd represents the degree of alignment of the second carbon-based negative electrode active material contained in the second negative electrode active layer.

[0075] The above formula 2 represents the degree of alignment (OI) of the first carbon-based negative electrode active material contained in the first negative electrode active layer. 1st ) and the degree of alignment (OI) of the second carbon-based negative electrode active material contained in the second negative electrode active layer. 2nd ) and represents the ratio.

[0076] The second negative electrode active layer includes a first carbon-based negative electrode active material and a silicon-based negative electrode active material, and can influence the alignment and / or orientation of the first carbon-based negative electrode active material when oriented and / or aligned by applying a magnetic field. This allows the first negative electrode active layer and the second negative electrode active layer to have a predetermined range of alignment ratio and satisfy Equation 2. Specifically, the first negative electrode active layer can satisfy Equation 2 in the range of 0.2 to 0.6. For example, the first negative electrode active layer can satisfy Equation 2 in the range of 0.2 to 0.5, 0.25 to 0.5, 0.3 to 0.5, 0.2 to 0.4, 0.4 to 0.6, 0.25 to 0.45, or 0.3 to 0.45. The first negative electrode active layer of the present invention satisfies Formula 2 above within the above range, thereby enabling the establishment of a shortened lithium transport path within the first negative electrode active layer. This allows the charging rate of the secondary battery to be improved even at a low C rate of 1C, and provides excellent effects in improving the lifespan of the negative electrode.

[0077] Specifically, conventional fast charging of lithium secondary batteries employs a constant current-constant voltage (CC-CV) charging method, which increases the charging rate by charging at a high C rate (above 1C rate). Generally, in CC-CV charging, lithium ion diffusion within the electrode occurs during the CC charging step. However, prolonged diffusion inevitably leads to concentration polarization. This lithium ion concentration polarization easily leads to lithium deposition at the anode, particularly at high rates where the charging current (A) exceeds the standard value (i.e., 1A at 1C rate) relative to the rated capacity (Ah) of the secondary battery, significantly reducing the safety of the secondary battery. Furthermore, high-rate CC-CV charging reaches the upper voltage limit very quickly during the CC charging step, which can cause the current to drop to a preset limit before the active material is completely consumed. That is, the charging time increases significantly in the constant voltage (CV) charging step, and there is a problem in that the effect of reducing the total time required to charge the secondary battery is minimal.

[0078] However, the present invention can significantly reduce the resistance induced in the negative electrode active layer during charging by ensuring a short lithium ion migration path within the negative electrode active layer. This resistance reduction can be induced by the constant current (CC) charging step being longer than the constant voltage (CV) charging step during charging using a constant current-constant voltage (CC-CV) method. Here, the constant current (CC) charging step flows the same amount of current, so the charge capacity per unit time is the same, but the constant voltage (CV) charging step tends to reduce the current to maintain the same voltage. In other words, since the charge capacity per unit time decreases rapidly during the constant voltage (CV) charging step, the overall charge time can be significantly reduced as the constant current (CC) charging step time increases. Therefore, the present invention can reduce the degree of alignment (OI) of the carbon-based negative electrode active material. 2nd ) can increase the execution time of the constant current (CC) charging step, thereby completing the charging of the secondary battery within a significantly shorter time.

[0079] Furthermore, the rapid charging of such secondary batteries can be realized under standard conditions (e.g., 1C rate) rather than high-rate C rate conditions, which has the advantage of overcoming safety issues of lithium secondary batteries due to the concentration polarization of lithium ions induced in the negative electrode active layer during charging.

[0080] Meanwhile, the first negative electrode active layer and the second negative electrode active layer may each have a porosity in the range of 20% to 30%, specifically, 23% to 30%, 25% to 30%, 26% to 29%, or 24% to 28%.

[0081] The first and second negative electrode active layers are 0.62 m 2 / g or less, specifically 0.615 m 2 / g or less, 0.6m 2 / g or less, 0.5m 2 / g or less, 0.20m 2 / g~0.62m2 / g, 0.30m 2 / g~0.62m 2 / g, 0.40m 2 / g~0.62m 2 / g, 0.40m 2 / g~0.60m 2 / g, 0.40m 2 / g~0.55m 2 / g, 0.40m 2 / g~0.50m 2 / g, or 0.58m 2 / g~0.62m 2 It can exhibit a BET specific surface area in the range of / g.

[0082] The porosity and specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method, for example, using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) and a nitrogen gas adsorption / flow method in a BET 6-point method.

[0083] In the present invention, by adjusting the porosity and BET specific surface area of ​​each negative electrode active layer within the above ranges, the energy density of the negative electrode can be further increased without reducing the electrolyte wettability of each negative electrode active layer.

[0084] The total thickness of the first negative electrode active layer and the second negative electrode active layer may be in the range of 50 μm to 500 μm, specifically 100 μm to 400 μm, 200 μm to 350 μm, 50 μm to 180 μm, 80 μm to 150 μm, 100 μm to 250 μm, 200 μm to 290 μm, or 130 μm to 190 μm.

[0085] By adjusting the total thickness of the negative electrode active layer within the above range, the present invention can realize a high charge / discharge capacity of the negative electrode and can minimize volume change of the negative electrode during charge / discharge of the secondary battery, thereby advantageously improving the lifespan of the negative electrode.

[0086] In addition, the negative electrode active layer according to the present invention may further include, in addition to the negative electrode active material as the main component, a conductive material, a binder, other additives, and the like, as needed.

[0087] The conductive material may include one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0088] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0089] 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 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent a decrease in charge capacity due to an increase in negative electrode resistance caused by a low content of conductive material, and can prevent problems such as a decrease in charge capacity due to a decrease in the content of 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.

[0090] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, and between the negative electrode active material and the current collector. It may be appropriately 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.

[0091] The content of the binder may be 0.1 to 10 parts by weight, specifically 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.

[0092] 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 be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector may be appropriately selected from 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0093] <Lithium secondary battery>

[0094] In one embodiment, the present invention provides 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; and an electrolyte composition impregnated with the electrode assembly.

[0095] 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 a large charge / discharge capacity and excellent life characteristics. Since the lithium secondary battery can be charged in a short time even at a 1C rate, it can be effectively used as a power source for medium- to large-sized devices such as electric vehicles.

[0096] In this case, the negative electrode has the same configuration as that described above, and therefore a detailed description thereof will be omitted.

[0097] The positive electrode includes a positive electrode active layer including a positive electrode active material on a positive electrode current collector, and the positive electrode active layer may optionally further include a conductive material, a binder, other additives, and the like, as needed.

[0098] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include at least one lithium metal oxide represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating lithium ions:

[0099] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0100] [Chemical formula 2] LiM 2 p Mn q Pr O4

[0101] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 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.

[0102] The lithium metal oxides represented by the above chemical formulas 1 and 2 are substances containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as a positive electrode active material, they have the advantage of being able to stably supply electricity at a high capacity and / or high voltage compared to conventionally used positive electrode active materials such as iron phosphate oxide (LiFeO4).

[0103] 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 Al0.1 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, LiNi 0.3 Mn 1.7 O4, etc., which can be used alone or in combination.

[0104] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more, specifically 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.

[0105] In addition, the positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0106] 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.

[0107] 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 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.

[0108] 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.

[0109] The binder may be included 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 100 parts by weight of each positive electrode active layer.

[0110] The total thickness of the positive electrode active layer is not particularly limited, but may specifically be in the range of 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.

[0111] In addition, the positive electrode can use a positive electrode current collector that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, those that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately selected from 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0112] 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 may be any material commonly used in the art. Specifically, it may contain one or more polymers selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers, which are chemically resistant and hydrophobic. The separator may have a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymers. In some cases, the separator may have a composite separator formed by coating organic or inorganic particles on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0113] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a form that can include 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.

[0114] 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 densely in a limited space.

[0115] Furthermore, in the lithium secondary battery, the electrolyte composition can be any composition that is normally used in lithium secondary batteries, without any particular limitation.

[0116] Specifically, the electrolyte composition may include a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0117] Here, the non-aqueous organic solvent may be used without any particular limitation as long as it is used in the art for non-aqueous electrolytes. For example, examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), γ-butyrolactone, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0118] The non-aqueous organic solvent used in the present invention may be a single type, or two or more types may be mixed in any combination or ratio depending on the application. Among them, from the viewpoints of electrochemical stability against oxidation-reduction and chemical stability with respect to heat and reactions with solutes, it is particularly preferable to mix propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0119] In addition, the lithium salt may be any lithium salt used in non-aqueous electrolytes in the art without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0120] The lower limit of the appropriate concentration range for the lithium salt to be used appropriately is 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more, and the upper limit of the appropriate concentration range is 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the lithium salt concentration is below 0.5 mol / L, the ionic conductivity may decrease, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. Furthermore, if the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery may increase, which may also result in a decrease in ionic conductivity, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery.

[0121] Furthermore, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the temperature of the electrolyte may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt, the decomposition of a fluorine-containing lithium salt may be accelerated, resulting in the production of hydrogen fluoride (HF). Hydrogen fluoride (HF) is undesirable because it can cause deterioration of battery performance. Therefore, the temperature at which the lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to between −20° C. and 80° C., specifically between 0° C. and 60° C.

[0122] Furthermore, the electrolyte additives may be included as additional auxiliary components to improve the physical properties of the electrolyte composition. Commonly used electrolyte additives may be added to the nonaqueous electrolyte of the present invention in any proportion. Specific examples include compounds that have overcharge prevention effects, anode film formation effects, and cathode protection effects, such as cyclohexylbenzene, biphenyl, t-butylbenzene, carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate. Furthermore, similar to the use in nonaqueous electrolyte batteries known as lithium polymer batteries, the electrolyte for nonaqueous electrolyte batteries may be quasi-solidified using a gelling agent or crosslinked polymer.

[0123] The lithium secondary battery according to the present invention has the above-mentioned configuration, and therefore has the advantages of not only a large charge / discharge capacity and excellent life characteristics, but also the ability to be charged in a short time even at a 1C rate.

[0124] <Method of manufacturing the negative electrode>

[0125] In one embodiment, the present invention provides applying a negative electrode slurry to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; and drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer.

[0126] 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 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.

[0127] 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 for controlling 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 and position of the shim.

[0128] 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 align the ab-axis crystal planes of the carbon-based negative electrode active materials contained in the negative electrode slurry at a high angle relative to the negative electrode current collector by applying a magnetic field to the surface of the negative electrode slurry coated on the negative electrode current collector.

[0129] 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.

[0130] In addition, the degree of alignment (OI) of the carbon-based negative electrode active material contained in each negative electrode slurry may be adjusted by adjusting the strength and application time of the applied magnetic field, and thus, the step of applying the magnetic field may be performed under a predetermined magnetic field strength condition.

[0131] Specifically, the step of applying a magnetic field may apply a magnetic field in the range of 10,000 G (Gauss) or less, and more specifically, the magnetic field may be applied with a strength in the range of 1,000 G to 7,000 G, 2,000 G to 6,000 G, 1,500 G to 5,000 G, 1,500 G to 4,500 G, 4,000 G to 7,000 G, 2,000 G to 4,000 G, 2,500 G to 3,500 G, 3,000 G to 6,500 G, or 2,700 G to 3,300 G.

[0132] 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, 7 to 13 seconds, or 6 to 11 seconds.

[0133] For example, in the step of applying a magnetic field, a magnetic field of 3,000±50 G may be applied to the negative electrode slurry for 9 to 11 seconds.

[0134] 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 in the range of 105% to 200% based on the width of the negative electrode slurry, and more specifically, may have a length ratio in the range 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.

[0135] In the present invention, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be uniformly achieved within a predetermined range by controlling the strength of the magnetic field, the application time, and / or the size of the magnet unit in the step of applying the magnetic field as described above.

[0136] The step of forming the negative electrode active layer may include the steps of drying the negative electrode slurry and rolling the dried negative electrode slurry.

[0137] 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.

[0138] For example, the drying step can dry the negative electrode slurry by applying heat energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0139] 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.

[0140] Specifically, the rolling can be carried out at a temperature in the range of 50°C to 100°C, more specifically at a temperature in the range of 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, or 65°C to 90°C.

[0141] The rolling may be performed at a rolling speed in the range of 2 m / s to 7 m / s, specifically 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.

[0142] The rolling can be carried out under a pressure condition in the range 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.

[0143] The present invention can increase the energy density of the negative electrode while minimizing changes in the 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.

[0144] The present invention will be described in more detail below with reference to examples and experimental examples.

[0145] 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.

[0146] <Examples 1 to 4 and Comparative Examples 1 to 3. Production of negative electrodes for lithium secondary batteries>

[0147] The carbon-based negative electrode active material is made of scaly primary particles granulated, and the secondary particles of artificial graphite (average particle size (D 50 ):16±0.1μm) and silicon dioxide (SiO2, average particle size (D 50 ):8.0±0.1μm) was prepared. Along with this, styrene butadiene rubber (SBR) was prepared as a binder, and carboxymethyl cellulose (CMC) was prepared as a thickener.

[0148] Next, 96 parts by weight of first artificial graphite, 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 solid content of 50% to prepare a first negative electrode slurry.

[0149] A second negative electrode slurry was prepared by mixing 96 parts by weight of second artificial graphite and silicon dioxide (SiO2), 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene butadiene rubber (SBR) with water to a solid content of 50%. The content ratio of the second artificial graphite and silicon dioxide (SiO2) in the second negative electrode slurry constituting the second negative electrode active layer was adjusted as shown in Table 1 below, based on the total negative electrode active material contained in the second negative electrode slurry.

[0150] After each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a copper sheet (thickness: 10 μm) that was being transferred roll-to-roll (transfer speed: 5 m / min) using a dual die coater. At this time, the loading amounts of the cast first and second negative electrode slurries were adjusted to be the same.

[0151] Permanent magnets with a length ratio of 110% to 120% of the width of the negative electrode slurry were placed above the coated negative electrode slurry and below the negative electrode current collector, and a magnetic field with a magnetic field strength of 3,000±20 G was applied. The magnetic field application time is shown in Table 1. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a negative electrode 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 MPa to 150 MPa and a transfer speed of 3 m / s to form a negative electrode for a lithium secondary battery (average thickness of each negative electrode active layer: 120±5 μm, total loading: 21 mg / cm). 2 ~30mg / cm 2 ) was manufactured.

[0152] For each manufactured negative electrode, X-ray diffraction spectroscopy (XRD) was performed on the first negative electrode active layer and the second negative electrode active layer to measure the spectrum. In the case of the first negative electrode active layer, after measuring the X-ray diffraction spectroscopy (XRD) of the second negative electrode active layer, the second negative electrode active layer was peeled off and removed, and then X-ray diffraction was measured on the exposed surface of the first negative electrode active layer. The measurement conditions for X-ray diffraction (XRD) were as follows:

[0153] - 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°

[0154] From the spectra measured under the above conditions, the average degree of alignment (OI) of the carbon-based active material contained in each negative electrode active layer was calculated using Equation 1. The results are shown in Table 1:

[0155] [Formula 1] OI=I 004 / I 110

[0156] 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.

[0157] [Table 1]

[0158] <Comparative Example 4. Production of negative electrode for lithium secondary battery>

[0159] First and second negative electrode slurries were prepared in the same manner as in Example 1, and the prepared first and second negative electrode slurries were simultaneously cast onto a copper sheet (thickness: 10 μm) using a dual die coater. The cast first and second negative electrode slurries had the same loading amount, and the total loading amount of the first and second negative electrode slurries was 21 mg / cm. 2 ~30mg / cm 2 It was.

[0160] 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, and a magnetic field of 10,000±100 G was applied to the surface of the negative electrode slurry for 15 seconds. The negative electrode slurry to which the magnetic field had been applied was then dried with hot air to form a negative electrode 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 then rolled at 50±1°C under a pressure of 100MPa to 150MPa and a transfer speed of 3m / s to produce a negative electrode for a lithium secondary battery.

[0161] X-ray diffraction spectroscopy (XRD) was performed on the first and second negative electrode active layers of the negative electrodes fabricated in the same manner as in Example 1 to measure the spectra. From the measured spectra, the average degree of alignment (OI) of each negative electrode active layer was calculated using Equation 1. The first and second negative electrode active layers had an alignment degree (OI) of 4 and 24, respectively, and the ratio (OI) 1st / OI 2nd ) was 0.17.

[0162] <Examples 5 to 8 and Comparative Examples 5 to 8: Production of Lithium Secondary Batteries>

[0163] 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 a carbon-based conductive material and polyvinylidene fluoride as a binder were mixed in a weight ratio of 94:3:3, and the mixture was mixed with N-methylpyrrolidone (NMP) to a solid content of 50% to produce a positive electrode slurry.

[0164] The prepared positive electrode slurry was cast on an aluminum sheet, dried in a vacuum oven at 120° C., and then rolled to prepare a positive electrode.

[0165] A separator made of polypropylene having a thickness of 18 μm was interposed between the obtained positive electrode and the negative electrode prepared in each of Examples 1 to 4 and Comparative Examples 1 to 4, and the positive electrode was inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah class lithium secondary battery.

[0166] The type of negative electrode used in each lithium secondary battery is shown in Table 2 below.

[0167] [Table 2]

[0168] <Experimental Example>

[0169] In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were carried out on the negative electrodes and lithium secondary batteries prepared in the examples and comparative examples.

[0170] 1) Life characteristics evaluation Each of the lithium secondary batteries prepared in Examples 5 to 8 and Comparative Examples 5 to 8 was activated by charging at 25°C at a rate of 0.3C to 4.35V under CC-CV conditions and discharging at a rate of 0.3C to 3.0V under CC conditions.

[0171] Each activated lithium secondary battery was charged at 25°C at a rate of 1.0 C under CC-CV conditions to 4.35 V and then discharged at a rate of 1.0 C under CC conditions to 3.0 V. One cycle was defined as one charge-discharge cycle for each lithium secondary battery manufactured in the Examples and Comparative Examples. The capacity during charge-discharge was measured to confirm the charge-discharge capacity at the first cycle. Each lithium secondary battery was then subjected to 499 charge-discharge cycles, for a total of 500 charge-discharge cycles. The charge-discharge capacity at the 500th cycle, the final cycle, was confirmed. The charge-discharge capacity retention rate at the 500th cycle was calculated based on the measured charge-discharge capacity at the first cycle. The results are shown in Table 3 below.

[0172] 2) 1C rate fast charging evaluation Each of the lithium secondary batteries prepared in Examples 5 to 8 and Comparative Examples 5 to 8 was activated by charging at 25°C at a rate of 0.3C to 4.35V under CC-CV conditions and discharging at a rate of 0.3C to 3.0V under CC conditions.

[0173] The activated lithium secondary batteries were charged at 25°C using a constant current-constant voltage (CC-CV) method, and the time required for the state of charge (SOC) to reach 80% was measured. The charging was performed at a constant current (CC) rate of 1.0C until the voltage reached 4.35V, and then at a constant voltage (CV) rate of 0.005C after maintaining 4.35V, the battery was cut off. The measured charging times are shown in Table 3 below.

[0174] [Table 3]

[0175] As shown in Table 3 above, the negative electrode for a lithium secondary battery according to the present invention not only has excellent life characteristics but also completes charging at a fast rate under 1C rate conditions.

[0176] Specifically, it was confirmed that the negative electrode of the example had a charge / discharge capacity retention rate of 80% or more after 500 charge / discharge cycles.Furthermore, the secondary battery of the example including such a negative electrode reached a state of charge (SOC) of 80% in a short time of less than 25 seconds under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0177] On the other hand, the negative electrode of Comparative Example 3, which did not contain silicon dioxide (SiO2), a silicon-based negative electrode active material, as the negative electrode active material, showed a relatively high charge / discharge capacity retention rate of approximately 95% after 500 charge / discharge cycles, but it was confirmed that the charge / discharge capacity per cycle was significantly lower than that of the negative electrode of the Example, which contained silicon dioxide (SiO2).

[0178] The remaining comparative anodes containing silicon dioxide (SiO2) were also found to have high charge / discharge capacities, but they took longer than 39 seconds to reach 80% state of charge (SOC) under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0179] This means that by controlling the degree of alignment (OI) of the carbon-based anode active material and the position and content of the silicon-based anode active material contained in each anode active layer, i) the anode life characteristics and ii) the charging speed under standard C-rate conditions can be improved simultaneously.

[0180] These results show that the negative electrode for a lithium secondary battery according to the present invention has a large charge / discharge capacity and excellent life characteristics, and that a lithium secondary battery containing it can be charged in a short time even at a 1C rate.

[0181] Although the present invention has been described above with reference to preferred embodiments, it will be understood by those skilled in the art or those with ordinary knowledge in the art that the present invention can be modified and changed in various ways without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0182] 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 can be defined by the claims.

Claims

1. a negative electrode current collector; a first negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a first carbon-based negative electrode active material; a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The first negative electrode active layer is The degree of alignment (O.I.) is expressed by the following formula 1. １ｓｔ ) is in the range of 5 to 15, The following formula 2 is in the range of 0.2 to 0.6, negative electrode: [Formula 1] O.I=I ００４ / I １１０ [Formula 2] O.I. １ｓｔ / O.I ２ｎｄ Here, 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) spectroscopic analysis of the negative electrode active layer, O.I. １ｓｔ represents the degree of alignment of the first carbon-based negative electrode active material contained in the first negative electrode active layer, O.I. ２ｎｄ represents the degree of alignment of the second carbon-based negative electrode active material contained in the second negative electrode active layer.

2. The negative electrode of claim 1 , wherein the silicon-based negative electrode active material is contained in an amount of 1 wt % to 25 wt % based on the weight of the second negative electrode active layer.

3. The negative electrode of claim 1 , wherein the first negative electrode active layer has an alignment degree (O.I) in the range of 7 to 12.

4. The negative electrode of 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 according to claim 1, wherein q is selected from the group consisting of 0.8≦q≦2.5, 1.0≦q≦0.8, 2.5≦q≦0.8, 3.0≦q≦0.8, 4.0≦q≦0.8, 5.0≦q≦0.8, 6.0≦q≦0.8, 7.0≦q≦0.8, 8.0≦q≦0.8, 9.0≦q

6. 2. The negative electrode of claim 1, wherein the total thickness of the first negative electrode active layer and the second negative electrode active layer is in the range of 50 μm to 500 μm.

7. applying a negative electrode slurry to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying the negative electrode slurry to which the magnetic field is applied to form a negative electrode active layer; The method for producing a negative electrode according to claim 1 , comprising:

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

9. The method for manufacturing a negative electrode according to claim 7 , wherein the step of applying a magnetic field is performed at a magnetic field strength in the range of 1,000 G to 7,000 G.

10. an electrode assembly including a positive electrode, the negative electrode according to claim 1, and a separator disposed between the positive electrode and the negative electrode; an electrolyte composition impregnated in the electrode assembly; A lithium secondary battery comprising:

11. 11. The lithium secondary battery of claim 10, wherein the positive electrode comprises 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 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, 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 of:

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

Images