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 manufacturing method thereof. The negative electrode has a structure in which a first negative electrode active layer and a second negative electrode active layer are sequentially laminated on a negative electrode current collector, the first negative electrode active layer contains artificial graphite and natural graphite as a carbon-based negative electrode active material, and the degree of alignment (OI) of the carbon-based negative electrode active material contained in the first negative electrode active layer is 0.01 to 0.01. 1st By adjusting the content of the carbon black and the artificial graphite within a specific range, the adhesive strength between the negative electrode active layer and the negative electrode current collector is excellent, and the secondary battery including the same has an excellent life.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183044, dated December 23, 2022, and all contents disclosed in the documents of this 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] BACKGROUND ART In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices but also in medium to large devices such as battery packs for hybrid cars and electric cars or power storage devices.

[0004] Such secondary batteries are chargeable and dischargeable power generating elements having a laminated structure of a positive electrode / separator / negative electrode. Generally, the positive electrode contains a lithium metal oxide as a positive electrode active material, and the negative electrode contains a carbon-based active material such as graphite. During charging, lithium ions released from the positive electrode are absorbed into the carbon-based active material of the negative electrode, and during discharging, the lithium ions contained in the carbon-based active material are absorbed into the lithium metal oxide of the positive electrode, thereby allowing for repeated charging and discharging.

[0005] On the other hand, amorphous carbon or crystalline carbon is used as the negative electrode active material for the negative electrode, and among them, crystalline carbon is mainly used due to its high capacity. Such crystalline carbon includes graphite-based carbon such as natural graphite and artificial graphite.

[0006] The characteristics of graphite-based carbon vary depending on the type. For example, natural graphite exhibits high output and excellent adhesion to the current collector, but is relatively inferior to artificial graphite in terms of resistance and lifespan. However, artificial graphite has few surface defects and functional groups, resulting in weak adhesion to the current collector. Furthermore, when propylene carbonate (PC) is mixed into the electrolyte to improve low-temperature performance, the propylene carbonate exfoliates and destroys the interlayer structure of the graphite.

[0007] Therefore, attempts have been made to use mixed graphite as the negative electrode active material for lithium secondary batteries, which combines the properties of each type to take advantage of their respective advantages. However, such mixed graphite has limitations in terms of reduced adhesion to the current collector, life characteristics, and impact stability, making it difficult to achieve satisfactory levels.

[0008] Therefore, it is necessary to develop a new technology that can utilize the advantages of graphite-based carbon as a negative electrode active material while overcoming its drawbacks. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a negative electrode for a lithium secondary battery which contains graphite-based carbon as a negative electrode active material, yet has high adhesive strength to a current collector and is excellent in battery performance such as life characteristics, and a method for producing the same. [Means for solving the problem]

[0010] To solve the above-mentioned problems, In one embodiment, the present invention comprises: 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; and a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material, The first carbon-based negative electrode active material includes natural graphite and artificial graphite, The first and second negative electrode active layers provide negative electrodes for lithium secondary batteries, each having an alignment degree (OI) of 0.1 to 0.9 of the carbon-based negative electrode active material represented by the following formula 1:

[0011] [Formula 1] OI=I 004 / I 110

[0012] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0013] In this case, the content of the artificial graphite contained in the first carbon-based negative electrode active material may exceed 50 wt % based on the total weight of the first carbon-based negative electrode active material.

[0014] The second carbon-based negative electrode active material may include artificial graphite.

[0015] In addition, the degree of alignment (OI) of the second carbon-based negative electrode active material 2nd ) is the degree of alignment (OI) of the first carbon-based negative electrode active material. 1st ) may have a ratio of 10% to 100%.

[0016] The artificial graphite may be in the form of flake particles, and the natural graphite may be in the form of spherical particles. The average particle size of the artificial graphite is 5 μm to 20 μm, and the average particle size of the natural graphite is 15 μm to 25 μm, and the average particle size of the artificial graphite may be smaller than the average particle size of the natural graphite.

[0017] Meanwhile, the total thickness of the first negative electrode active layer and the second negative electrode active layer may be 50 μm to 300 μm.

[0018] Here, the average thickness of the first negative electrode active layer may be 10% to 100% of the average thickness of the second negative electrode active layer.

[0019] In one embodiment, the present invention further comprises: Simultaneously applying a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material onto a negative electrode current collector; applying a magnetic field to the applied first and second negative electrode slurries; and drying the first and second negative electrode slurries to which the magnetic field is applied to form the first and second negative electrode active layers, The first carbon-based negative electrode active material includes natural graphite and artificial graphite, The first and second negative electrode active layers each have an alignment degree (OI) of 0.1 to 0.9 of the carbon-based negative electrode active material represented by the following formula 1:

[0020] [Formula 1] OI=I 004 / I 110

[0021] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0022] At this time, in the step of applying a magnetic field, a magnetic field of 2,000 G to 6,000 G can be applied.

[0023] The magnetic field application may be performed for 5 to 60 seconds.

[0024] In addition, forming the first and second negative electrode active layers may include drying the first and second negative electrode slurries and rolling the dried first and second negative electrode slurries. [Effects of the Invention]

[0025] The negative electrode for a lithium secondary battery according to the present invention has a 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, and the first negative electrode active layer contains artificial graphite and natural graphite as carbon-based negative electrode active materials, and the degree of alignment (OI) of the carbon-based negative electrode active materials contained in the first negative electrode active layer is 1st By adjusting the content of the carbon black and artificial graphite within a specific range, the adhesive strength between the negative electrode active layer and the negative electrode current collector is excellent, and the secondary battery including the same has an excellent lifespan. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a scanning electron microscope image showing the shape of artificial graphite in a carbon-based negative electrode active material according to the present invention; [Figure 2] 1 is a scanning electron microscope image showing the shape of natural graphite in a carbon-based negative electrode active material according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0027] Because the present invention can be modified in various ways and can have various embodiments, specific embodiments will be described in detail in the detailed description.

[0028] 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 spirit and scope of the invention.

[0029] 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 possibility of addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0030] 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.

[0031] Furthermore, 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 the defined component relative to the total weight (or volume). For example, "comprising graphite as a main component as a 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 graphite accounting for 100 wt%.

[0032] The present invention will now be described in more detail.

[0033] <Anode for lithium secondary batteries> In one embodiment, the present invention comprises: 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; and a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material, The first carbon-based negative electrode active material includes natural graphite and artificial graphite, The first and second negative electrode active layers provide negative electrodes for lithium secondary batteries, each having an alignment degree (OI) of 0.1 to 0.9 of the carbon-based negative electrode active material represented by the following formula 1:

[0034] [Formula 1] OI=I 004 / I 110

[0035] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0036] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer including a carbon-based active material on at least one surface of a negative electrode current collector. The negative electrode active layer is a layer that realizes the electrical activity of the negative electrode and is prepared by coating both surfaces of the electrode current collector with an electrode slurry including a negative electrode active material that realizes an electrochemical redox reaction during charge and discharge of the battery, followed by drying and rolling.

[0037] The negative electrode active layer includes a carbon-based active material as a negative electrode active material to realize electrical activity through a reversible oxidation-reduction reaction during charge and discharge of the battery. Specifically, the carbon-based active material refers to a material mainly composed of carbon atoms, and the carbon-based active material may include graphite-based carbon. The graphite-based carbon may include at least one of natural graphite and artificial graphite.

[0038] The graphite carbon is in the form of a powder, and the powder may be composed of particles having a shape such as a spherical shape, a scaly shape, an irregular shape, etc. Here, "scaly particles" refers to particles having a thin plate-like shape, and the particle surface may have an average aspect ratio of 1:2 to 1:20.

[0039] As one example, artificial graphite may include flake particles, while natural graphite may include spherical particles.

[0040] In this case, the artificial graphite preferably has a structure in which a plurality of scale-like particles aggregate to form spherical granules, as shown in FIG. 1. Furthermore, one graphite granule may be formed by aggregating 2 to 100, preferably 3 to 20, scale-like graphite particles. The present invention can improve energy density by controlling the particle shape of the artificial graphite as described above. Furthermore, since the specific surface area relative to the average size of the artificial graphite can be increased, the adhesive strength to the negative electrode current collector can be improved.

[0041] Furthermore, the natural graphite may include spherical particles as shown in FIG. 2 and have a sphericity of 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 when the carbon-based negative electrode active material is projected onto a two-dimensional particle. A sphericity of 1 indicates that the particle shape is spherical. The sphericity can be measured using a particle shape analyzer or by analyzing particle images taken with a scanning electron microscope (SEM). The present invention advantageously achieves a nearly spherical shape of natural graphite, thereby improving the electrical conductivity of the negative electrode active layer and thereby improving battery capacity, and by increasing the specific surface area of ​​the particles and thereby improving the adhesion between the negative electrode active layer and the current collector.

[0042] Furthermore, the size of graphite-based carbon can be controlled to satisfy a predetermined range. Specifically, the average particle size of artificial graphite can be 5 μm to 20 μm, and the average particle size of natural graphite can be 15 μm to 25 μm, and the average particle size of natural graphite can be larger than the average particle size of artificial graphite. Here, the average particle size of artificial graphite can refer to the average size of granules formed by aggregating multiple scale-like particles.

[0043] Specifically, the average particle size of the artificial graphite (D 50 ) may be 5 μm to 15 μm, 5 μm to 12 μm, 10 μm to 20 μm, 15 μm to 20 μm, 12 μm to 18 μm, or 8 μm to 14 μm, and the average particle size (D 50 ) can be 15 μm to 20 μm, 20 μm to 25 μm, 18 μm to 23 μm, or 21 μm to 25 μm.

[0044] As an example, the average particle size of artificial graphite may be 8 μm to 10 μm, and the average particle size of natural graphite may be 18 μm to 20 μm.

[0045] If the minimum particle size of artificial graphite and natural graphite is less than 5 μm and 15 μm, respectively, the number of particles per unit volume increases, requiring a large amount of binder, which can result in reduced electrical properties of the negative electrode, a high volume change rate due to contraction and expansion of the negative electrode active material during battery charge and discharge, and reduced durability of the negative electrode active layer.On the other hand, if the maximum particle size of artificial graphite and natural graphite is more than 20 μm and 25 μm, respectively, expansion becomes severe, and with repeated charge and discharge, the adhesion between particles and the current collector decreases, which can significantly reduce cycle performance.

[0046] In addition, the present invention may realize a structure in which the artificial graphite is densely packed among a plurality of natural graphite particles contained in the negative electrode active layer by controlling the average particle size of the artificial graphite to be smaller than that of the natural graphite. Due to this structure, the negative electrode of the present invention may have reduced resistance in the negative electrode active layer and increased energy density of the negative electrode, thereby further improving output performance.

[0047] Meanwhile, the negative electrode active layer may have a structure in which two individual layers are stacked. Specifically, the negative electrode according to the present invention may have a structure in which a first negative electrode active layer is provided on a negative electrode current collector, and a second negative electrode active layer is provided on the first negative electrode active layer. By implementing a two-layer structure for the negative electrode active layer according to the present invention, the physical properties required for each region of the negative electrode active layer can be more easily controlled. That is, the negative electrode active layer according to the present invention has advantages in that it can achieve higher adhesion between the active layer and the negative electrode current collector in the region adjacent to the negative electrode current collector, and can achieve higher density of energy generated by the electrochemical reaction in the region adjacent to the surface of the active layer where the electrochemical reaction density is high.

[0048] For this reason, the first and second negative electrode active layers constituting the negative electrode active layer may have different compositions.

[0049] Specifically, 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. The first and second carbon-based active materials may include at least one type of graphite-based carbon selected from natural graphite and artificial graphite, and the type, content, and content ratio of the graphite-based carbon included in each carbon-based active material may differ.

[0050] As one example, the first carbon-based negative electrode active material may include natural graphite and artificial graphite, and the second carbon-based negative electrode active material may include only artificial graphite.

[0051] Here, the first carbon-based negative electrode active material may contain more than 50 wt% of artificial graphite relative to the total weight of the first carbon-based negative electrode active material, and more specifically, may contain 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, 80 wt% or more, 60 wt% to 99 wt%, 60 wt% to 90 wt%, 65 wt% to 95 wt%, 70 wt% to 95 wt%, 75 wt% to 95 wt%, or 75 wt% to 90 wt% relative to the total weight of the first carbon-based negative electrode active material.

[0052] In the present invention, by controlling the content of artificial graphite in the first carbon-based negative electrode active material contained in the first negative electrode active layer within the above range, the electrical resistance in the region adjacent to the negative electrode current collector can be reduced, thereby improving the high-power performance of the negative electrode and suppressing deterioration of the negative electrode active layer when the secondary battery is charged and discharged for a long period of time.

[0053] Furthermore, in the negative electrode according to the present invention, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material contained in the first negative electrode active layer and the second negative electrode active layer may be oriented at a predetermined angle. Here, "the carbon-based negative electrode active material is oriented (or aligned)" may mean that a specific crystal plane exhibiting the planar molecular structure of the carbon-based negative electrode active material, specifically, graphite-based carbon, is arranged at a predetermined angle / inclination relative to the negative electrode current collector. This differs from the case where a specific plane of the graphite-based carbon particles themselves is arranged at a predetermined angle / inclination relative to the negative electrode current collector.

[0054] In the present invention, the carbon-based negative electrode active material, i.e., graphite-based carbon, contained in the negative electrode active layer may have a crystal plane aligned nearly perpendicular to the negative electrode current collector, specifically, aligned at an angle of 60° or more, 70° or more, 70-90°, 80-90°, 65-85°, or 70-85° with respect to the negative electrode current collector. The degree of alignment of such a carbon-based negative electrode active material (e.g., graphite-based carbon) may be determined by crystal plane analysis of the carbon-based active material contained in the negative electrode active layer.

[0055] For example, in the negative electrode active layer, the carbon-based active material is aligned in a certain direction relative to the negative electrode current collector, and when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD), the average degree of alignment of the carbon-based active material, represented by the following formula 1, may satisfy 0.1 to 0.9:

[0056] [Formula 1] OI=I 004 / I 110

[0057] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0058] Equation 1 above can be used as an index of the degree to which the crystalline structure of the carbon-based active material, i.e., graphite-based carbon, is aligned in a certain direction, specifically, relative to the surface of the negative electrode current collector, during X-ray diffraction measurement. More specifically, the negative electrode active layer exhibits peaks corresponding to graphite, the carbon-based active material, at 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° during X-ray diffraction measurement. These peaks represent the (0,0,2) plane, (1,0,0) plane, (1,0,1)R plane, (1,0,1)H plane, (0,0,4) plane, and (1,1,0) plane of graphite, respectively. In addition, the peak appearing at 2θ=43.4±0.2° may be due to the overlap of the peak corresponding to the (1,0,1)R plane of the carbon-based active material and the (1,1,1) plane of the current collector, for example, copper (Cu).

[0059] The degree of alignment (OI) of a carbon-based active material (i.e., graphite carbon) can be measured by the area ratio of the peak at 2θ = 54.7 ± 0.2°, which indicates the (0,0,4) plane, to the peak at 2θ = 77.5 ± 0.2°, which indicates the (1,1,0) plane, specifically, the area ratio obtained by integrating the intensities of these peaks. Here, the peak at 2θ = 54.7 ± 0.2° is a peak indicating the (0,0,4) plane, which is one of the crystal planes of graphite that is tilted with respect to the negative electrode current collector. Therefore, the closer the OI value is to 0, the closer the tilt to 90° with respect to the surface of the negative electrode current collector, and the larger the OI value is, the closer the tilt to 0° or 180° with respect to the surface of the negative electrode current collector is.

[0060] In addition, in the negative electrode of the present invention, the carbon-based active materials contained in the first and second negative electrode active layers may be aligned in a predetermined direction relative to the negative electrode current collector, and thus the carbon-based active materials contained in the first and second negative electrode active layers may have different degrees of alignment (OI). Specifically, the first carbon-based active material contained in the first negative electrode active layer may have a higher degree of alignment (OI) than the second carbon-based active material contained in the second negative electrode active layer.

[0061] As an example, the degree of alignment (OI) of the second carbon-based active material contained in the second negative electrode active layer 2nd ) is the degree of alignment (OI) of the carbon-based active material contained in the first negative electrode active layer. 1st ) may have a ratio of 10% to 100%, and more specifically may have a ratio of 50% to 99%, 60% to 99%, 70% to 99%, 80% to 99%, or 60% to 85%.

[0062] In this case, the degree of alignment (OI) of the carbon-based active material contained in the second negative electrode active layer 2nd ) can be 0.1 to 0.9, and more specifically, can be 0.1 to 0.7, 0.1 to 0.5, 0.2 to 0.6, 0.4 to 0.7, 0.3 to 0.5, or 0.1 to 0.4.

[0063] In the negative electrode according to the present invention, by controlling the degree of alignment (OI) of the carbon-based active material contained in each of the first and second negative electrode active layers as described above, the electrolyte and lithium mobility in the second negative electrode active layer can be improved, the electrode capacity can be increased, and the adhesion between the first negative electrode active layer and the negative electrode current collector can be further strengthened.

[0064] Furthermore, in the second negative electrode active layer, the second carbon-based negative electrode active material is aligned to the negative electrode current collector at a certain angle / inclination, and can exhibit a predetermined color difference value when any three points on the surface are analyzed with a CIE color difference meter.

[0065] For example, the second negative electrode active layer may have an L* value of 40 or less when analyzed with a CIE colorimeter at any three points on the surface, and a ΔL* value of less than 10. More specifically, the second negative electrode active layer may have an L* value of 30 to 40, 30 to 35, 32 to 35, or 31 to 34.5 when analyzed with a CIE colorimeter at any three points on the surface, and a ΔL* value of less than 8, less than 5, less than 3, or less than 2.

[0066] The L* value is a factor indicating color brightness, with L* = 0 indicating black and L* = 100 indicating white. The negative electrode active layer of the present invention contains graphite as a carbon-based negative electrode active material as a main component and exhibits black color, and therefore has an L* of 30 or more. The graphite contained in the negative electrode active layer has uniform crystal orientation relative to the negative electrode current collector, and the L* deviation (i.e., ΔL*) at multiple points can be low.

[0067] Meanwhile, the total thickness of the first and second negative electrode active layers may be 50 μm to 300 μm, specifically 50 μm to 250 μm, 100 μm to 250 μm, or 100 μm to 200 μm. By adjusting the total thickness of the negative electrode active layers within this range, the present invention not only increases the energy density of the electrode but also uniformly controls the degree of alignment of the carbon-based active material contained in the negative electrode active layers.

[0068] Furthermore, the average thickness of the first negative electrode active layer may be 10% to 100% of the average thickness of the second negative electrode active layer, and more specifically, may be 10% to 50%, 10% to 40%, 30% to 50%, 40% to 70%, 50% to 99%, 60% to 99%, 70% to 99%, 60% to 85%, or 80% to 100% of the average thickness of the second negative electrode active layer. By adjusting the average thickness of the first negative electrode active layer within the above range, the present invention can easily increase the charge / discharge capacity and output that the entire negative electrode active layer can achieve while improving the adhesion between the negative electrode current collector and the negative electrode active layer.

[0069] Meanwhile, the first and second negative electrode active layers according to the present invention may further include a silicon-based negative electrode active material in addition to the carbon-based negative electrode active material.

[0070] Such silicon-based negative electrode active materials may include silicon-based materials containing at least one of silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2). Here, when silicon monoxide (SiO2) and silicon dioxide (SiO2) are uniformly mixed or composited and contained in the negative electrode active layer, they are called silicon oxide (SiO q , where 0.8≦q≦2.5).

[0071] The silicon-based negative electrode active material may be contained in an amount of 1 to 20% by weight relative to the total weight of the negative electrode active material contained in each negative electrode active layer, and specifically, may be contained in an amount of 1 to 9 parts by weight, 3 to 7 parts by weight, 5 to 15 parts by weight, 11 to 19 parts by weight, or 13 to 17 parts by weight relative to the total weight of the negative electrode active material.

[0072] By adjusting the content of the silicon-based negative electrode active material within the above range, the present invention can minimize the volume change rate of the negative electrode active layer due to charge and discharge, and simultaneously reduce the amount of lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery, while improving the charge capacity per unit mass.

[0073] 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, a conductive material, a binder, other additives, and the like, as needed.

[0074] The conductive material may include one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like, but is not limited thereto.

[0075] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0076] The content of the conductive material 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, 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 low content of conductive material from increasing the resistance of the negative electrode and reducing the charge capacity. Furthermore, it can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, thereby reducing the charge capacity, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0077] The binder is a component that aids in bonding the active material and conductive material, etc., and in bonding to the current collector, and can be suitably used within a range that does not degrade the electrical properties of the electrode. Specifically, the binder can 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, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber.

[0078] 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 the adhesive strength of the active layer due to a low content of binder or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0079] 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 μm to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0080] <Lithium secondary battery> In one embodiment, the present invention further comprises: There is provided a lithium secondary battery including 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.

[0081] The lithium secondary battery according to the present invention includes an electrode assembly in which a plurality of positive electrodes, separators, and negative electrodes are sequentially arranged, and an electrolyte composition in which a lithium salt and an electrolyte additive are dissolved in a non-aqueous organic solvent. The lithium secondary battery has a 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, the first negative electrode active layer includes artificial graphite and natural graphite as carbon-based negative electrode active materials, and the degree of alignment (OI) of the carbon-based negative electrode active material contained in the first negative electrode active layer is 1st The negative electrode of the present invention includes a negative electrode having a specific content of the anode active layer and the anode current collector, and the content of the artificial graphite is adjusted to a specific range. As a result, the lithium secondary battery has excellent adhesion between the anode active layer and the anode current collector, and the secondary battery including the negative electrode has an excellent lifespan.

[0082] The negative electrode has the same configuration as described above, and therefore a detailed description thereof will be omitted.

[0083] The positive electrode includes a positive electrode active layer prepared by applying a slurry containing a positive electrode active material onto a positive electrode current collector, followed by drying and pressing, and may optionally further include a conductive material, a binder, other additives, and the like, as needed.

[0084] The positive electrode active material is a material that can undergo an electrochemical reaction on the positive electrode current collector and may include one or more lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2 that are capable of reversibly intercalating and deintercalating lithium ions:

[0085] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0086] [Chemical formula 2] LiM 2 p Mn q P r O4

[0087] 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 1-p or 2-p, r is 0 or 1.

[0088] The lithium metal oxides represented by Chemical Formula 1 and Chemical Formula 2 above are materials containing high amounts 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 high-capacity and / or high-voltage electricity.

[0089] 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 O 2、 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 O 4、 LiNi 0.3 Mn 1.7 O 4、 LiFePO4, LiFe q Mn 1-q PO4, etc., which may be used alone or in combination.

[0090] 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 the weight of the positive electrode active layer.

[0091] The positive electrode active layer may further include a conductive material, a binder, other additives, and the like in addition to the positive electrode active material.

[0092] 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, summer black, graphene, and carbon nanotubes.

[0093] The conductive material may be contained in an amount of 0.1 to 5 parts by weight based on the 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.

[0094] The binder functions to bind the positive electrode active material, positive electrode additive, and conductive material together, and any binder may be used without particular limitation as long as it has this function. 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. As one example, the binder may include polyvinylidene fluoride (PVDF).

[0095] 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.

[0096] The total thickness of the positive electrode active layer is not particularly limited, but may specifically 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.

[0097] 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 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0098] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film with high ion permeability and mechanical strength. It may be made of any material commonly used in the industry, including at least one polymer 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, it may have a composite separator formed by coating organic or inorganic particles on a 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.

[0099] 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.

[0100] <Method of manufacturing the negative electrode> In one embodiment, the present invention further comprises: Simultaneously applying a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material onto a negative electrode current collector; applying a magnetic field to the applied first and second negative electrode slurries; and drying the first and second negative electrode slurries to which the magnetic field is applied to form the first and second negative electrode active layers, The first carbon-based negative electrode active material includes natural graphite and artificial graphite, The first and second negative electrode active layers each have an alignment degree (OI) of 0.1 to 0.9 of the carbon-based negative electrode active material represented by the following formula 1:

[0101] [Formula 1] OI=I 004 / I 110

[0102] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0103] The method for manufacturing a negative electrode according to the present invention involves applying a negative electrode slurry containing a carbon-based active material onto a negative electrode current collector, applying a magnetic field to the surface of the applied negative electrode slurry to align the carbon-based active material in the negative electrode slurry at a predetermined angle relative to the surface of the negative electrode current collector, and then drying the negative electrode slurry in which the degree of disorder of the carbon-based active material has been reduced to form a negative electrode active layer, thereby manufacturing a negative electrode.

[0104] Here, the step of applying the negative electrode slurries may be performed at once by simultaneously discharging two types of negative electrode slurries onto the negative electrode current collector.

[0105] Specifically, the step of applying the negative electrode slurries may be performed by simultaneously applying a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material onto the negative electrode current collector.

[0106] The first and second negative electrode slurries may have different compositions. Specifically, the first negative electrode slurry includes a first carbon-based negative electrode active material, and the second negative electrode slurry includes a second carbon-based negative electrode active material. The first and second carbon-based active materials may include at least one graphite-based carbon selected from natural graphite and artificial graphite, and the type, content, and content ratio of the graphite-based carbon included in each carbon-based active material may differ.

[0107] As one example, the first carbon-based negative electrode active material may include natural graphite and artificial graphite, and the second carbon-based negative electrode active material may include only artificial graphite.

[0108] The particle shape, average particle size, etc. of natural graphite and artificial graphite are the same as those described above, so detailed description thereof will be omitted.

[0109] The steps of applying the first and second negative electrode slurries may be performed by any method commonly used in the art, without any particular limitations. For example, the application may be performed by dip coating, die coating, comma coating, gravure coating, or bar coating, and preferably by die coating using a dual slot die.

[0110] Furthermore, applying a magnetic field to the first and second negative electrode slurries may align the crystal planes of the carbon-based negative electrode active materials contained in each negative electrode slurry at a predetermined angle relative to the negative electrode current collector. To this end, the magnetic field may be applied to the surfaces of the negative electrode slurries coated in sequence on the negative electrode current collector, i.e., the exposed surface of the second negative electrode slurry, and the applied magnetic field may also align the crystal planes of the carbon-based negative electrode active materials in the first negative electrode slurry located below the second negative electrode slurry at a predetermined angle.

[0111] Here, the degree of alignment (OI) of the carbon-based active material contained in each of the negative electrode slurries can be adjusted by controlling the strength of the applied magnetic field and the time of exposure to the magnetic field.

[0112] For example, in the step of applying a magnetic field, a magnetic field of 2,000 G (Gauss) to 6,000 G (Gauss) may be applied, specifically a magnetic field of 2,500 G to 5,500 G, 3,000 G to 5,500 G, 3,500 G to 5,500 G, 4,000 G to 5,500 G, 3,500 G to 4,500 G, or 4,500 G to 5,000 G may be applied.

[0113] Furthermore, the step of applying the magnetic field may be carried out for 5 to 60 seconds, specifically 10 to 60 seconds, 10 to 30 seconds, 30 to 60 seconds, 40 to 50 seconds, 15 to 35 seconds, or 10 to 50 seconds.

[0114] For example, in the step of applying a magnetic field, a magnetic field of 4,700±100 G may be applied to the negative electrode slurry for 12 to 33 seconds.

[0115] In the present invention, by applying a magnetic field to the second negative electrode slurry with the above-described magnetic field strength and application time, not only the second carbon-based negative electrode active material contained in the second negative electrode slurry but also the first carbon-based active material of the first negative electrode slurry located below the second negative electrode slurry may be aligned at a predetermined angle with respect to the negative electrode current collector.

[0116] In addition, forming the first and second negative electrode active layers may include drying the first and second negative electrode slurries and rolling the dried first and second negative electrode slurries.

[0117] At this time, the step of drying the first and second negative electrode slurries may be performed in any manner that can maintain the alignment of the carbon-based active material contained in the negative electrode active layer.

[0118] 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.

[0119] In addition, 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.

[0120] Specifically, 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, rolling can be performed at a rolling speed of 2 m / s to 7 m / s, and more specifically, rolling speeds of 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s. 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.

[0121] The present invention can increase the energy density of the negative electrode while minimizing changes in the alignment of the carbon-based active material contained in the first and second negative electrode active layers formed by rolling the dried negative electrode slurry under the above-mentioned temperature, speed, and / or pressure conditions.

[0122] Meanwhile, the negative electrode slurry may further include a conductive material, a binder, a thickener, etc. in addition to the carbon-based active material, and these may be materials commonly used in the art.

[0123] The present invention will be described in more detail below with reference to examples and experimental examples.

[0124] 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.

[0125] <Examples 1 to 4 and Comparative Examples 1 and 2. Production of negative electrode for lithium secondary battery> A negative electrode for a lithium secondary battery was manufactured according to the conditions shown in Table 1 below.

[0126] First, natural graphite and artificial graphite were prepared as carbon-based active materials, carbon black as a conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders.

[0127] 95 parts by weight of the prepared carbon-based negative electrode active material, 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 solid content of 50% to prepare a first negative electrode slurry and a second negative electrode slurry.

[0128] The first carbon-based negative electrode active material contained in the first negative electrode slurry had (1) particle shape, (2) average particle size, and (3) content within each carbon-based negative electrode active material adjusted as shown in Table 1 below. However, when the particle shape of the carbon-based negative electrode active material was spherical, the sphericity satisfied a range of 0.70 to 0.95. The second carbon-based negative electrode active material contained in the second negative electrode slurry was the same as the artificial graphite contained in the first carbon-based negative electrode active material.

[0129] After each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a copper sheet (thickness: 8 μm) being transported roll-to-roll (transport speed: 5 m / min) using a dual die coater. The first and second negative electrode slurries were cast to average thicknesses of 90 μm and 100 μm, respectively, along the transport direction of the copper sheet.

[0130] A magnetic field of 4,750±50 G was then applied to the coated second negative electrode slurry surface for the time shown in Table 1 below, and the negative electrode slurry to which the magnetic field was applied was dried with hot air to form a negative electrode active layer. The formed negative electrode active layer was rolled at 50±1°C, 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.

[0131] [Table 1]

[0132] X-ray diffraction spectroscopy (XRD) was performed on the first and second negative electrode active layers of the fabricated negative electrodes to measure their spectra. For the spectrum 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 X-ray diffraction was measured on the exposed surface of the first negative electrode active layer. The X-ray diffraction (XRD) measurement conditions were as follows:

[0133] - Target: Cu (Kα line) graphite monochromator -Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area: (1,1,0) plane: 76.5 degrees < 2θ < 78.5 degrees / (0,0,4) plane: 53.5 degrees < 2θ < 56.0 degrees

[0134] The average degree of alignment (OI) of each carbon-based active material represented by Formula 1 was calculated from the spectrum measured under the above conditions. The results are shown in Table 2.

[0135] [Formula 1] OI=I 004 / I 110

[0136] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane when measuring the negative electrode active layer by X-ray diffraction spectroscopy (XRD), I 110represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0137] Separately, for each negative electrode fabricated, three randomly selected points were set within a unit area of ​​10 cm wide and 10 cm long on the surface of the second negative electrode active layer. Then, using a spectrophotometer, the three selected points were measured with a CIE colorimeter. The average L* value was calculated from the measured values ​​at the three points, and the average deviation between the three points was calculated based on the average L* value to obtain ΔL*. Next, the second negative electrode active layer that had been measured with the CIE colorimeter was peeled and removed, and the exposed surface of the first negative electrode active layer was measured with the CIE colorimeter in the same manner. The measurement results are shown in Table 2 below.

[0138] [Table 2]

[0139] <Comparative Example 3. Production of negative electrode for lithium secondary battery> A negative electrode for a lithium secondary battery was manufactured in the same manner as in Example 2, except that a magnetic field was not applied after casting the first and second negative electrode slurries.

[0140] The first and second negative electrode active layers of the fabricated negative electrodes had carbon-based active material alignment indexes (OI) of 5.41 and 16.87, respectively. The L* and ΔL of the first negative electrode active layer were 43 and 0.4, respectively, and the L* and ΔL of the second negative electrode active layer were 39 and 0.3, respectively.

[0141] <Examples 5 to 8 and Comparative Examples 4 to 6. Production of Lithium Secondary Batteries> 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 0.1O2 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.

[0142] A separator made of 18 μm polypropylene was interposed between the obtained positive electrode and the negative electrode produced in each of Examples 1 to 4 and Comparative Examples 1 to 3, and the resulting electrode was inserted into a case, after which an electrolyte composition was injected to assemble a lithium secondary battery.

[0143] The type of negative electrode used in each lithium secondary battery is shown in Table 3 below.

[0144] [Table 3]

[0145] <Experimental Example> The following experiments were carried out to evaluate i) the adhesive strength between the negative electrode current collector and the negative electrode active layer, and ii) the energy density of the negative electrode according to the present invention.

[0146] a) Evaluation of adhesion between the negative electrode current collector and the negative electrode active layer The negative electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were cut into specimens with horizontal and vertical lengths of 25 mm and 70 mm, respectively.

[0147] The prepared specimens were attached to a glass plate using double-sided tape, with the current collector facing the glass plate. The specimens attached to the glass plate were then mounted in a tensile tester, and the negative electrode active layer of each negative electrode was peeled off at a 90° angle at a rate of 100 mm / min at 25°C. The peel force measured in real time was defined as the interfacial adhesion strength between the negative electrode current collector and the negative electrode active layer, and the measurement results are shown in Table 4 below.

[0148] b) Energy density evaluation Each of the negative electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 was cut into 2 cm 2 A hole of the same size as the negative electrode was drilled, and constant-current charging and discharging was performed using a three-terminal method to measure the charge-discharge capacity. Specifically, the energy density of each negative electrode was evaluated by fabricating a sample battery containing each negative electrode as a sample electrode. The sample battery was designed to include a laminate consisting of each negative electrode, a separator, and a counter electrode, with a reference electrode installed separately on top. The sample battery was also used with an electrolyte solution of LiPF6 dissolved to a concentration of 1 M in a mixed solution of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC:MEC = 1:2, vol.:vol.). Metallic lithium was used as the counter electrode and reference electrode, and a polyethylene microporous membrane was used as the separator.

[0149] The resulting sample battery had a current of 0.2 mA / cm for each negative electrode area. 2 At a constant current of 0V (V vs. Li / Li + ) and charge to 0.2mA / cm 2 1V (V vs. Li / Li) at a constant current of + After discharging to 0.1 V, the initial charge-discharge efficiency per unit volume of each sample battery was calculated. The calculated results are shown in Table 4 below.

[0150] [Table 4]

[0151] As shown in Table 4, the negative electrode for a lithium secondary battery according to the present invention has a high adhesive strength between the negative electrode current collector and the negative electrode active layer, resulting in a high energy density. Specifically, the negative electrode prepared in the examples required a peel force of 35 gf / cm or more to peel the negative electrode current collector from the negative electrode active layer, and the initial charge / discharge efficiency was confirmed to be 93.6% or more.

[0152] This is because the negative electrode of the embodiment has a 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, the first negative electrode active layer contains artificial graphite and natural graphite as carbon-based negative electrode active materials, and the degree of alignment (OI) of the carbon-based negative electrode active materials contained in the first negative electrode active layer is 1st This means that the adhesive strength between the negative electrode current collector and the negative electrode active layer is increased by adjusting the content of the graphite and artificial graphite within a specific range, thereby improving the electrical performance of the negative electrode active layer.

[0153] These results show that the negative electrode for a lithium secondary battery according to the present invention has excellent adhesive strength between the negative electrode current collector and the negative electrode active layer, and has a high energy density.

[0154] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0155] 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; and a second negative electrode active layer provided on the first negative electrode active layer and containing a second carbon-based negative electrode active material, the first carbon-based negative electrode active material includes natural graphite and artificial graphite; the second carbon-based negative electrode active material includes artificial graphite; the first negative electrode active layer and the second negative electrode active layer have different compositions; The first negative electrode active layer and the second negative electrode active layer each have an alignment degree (O.I) of 0.1 to 0.9 of the carbon-based negative electrode active material represented by the following formula 1: [Formula 1] O.I=I ００４ / I １１０ In Formula 1, I ００４ represents the area of ​​the peak representing the (0,0,4) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD), I １１０ represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the artificial graphite is more than 50 wt % based on the total weight of the first carbon-based negative electrode active material.

3. Artificial graphite is a scaly particle, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the natural graphite is in the form of spherical particles.

4. The average particle size of the artificial graphite is 5 μm to 20 μm, The average particle size of the natural graphite is 15 μm to 25 μm, and 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the average particle size of the artificial graphite is smaller than the average particle size of the natural graphite.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the total thickness of the first negative electrode active layer and the second negative electrode active layer is 50 μm to 300 μm.

6. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the average thickness of the first negative electrode active layer is 10% to 100% of the average thickness of the second negative electrode active layer.

7. The degree of alignment (O.I.) of the second carbon-based negative electrode active material ２ｎｄ ) is the degree of alignment (O.I.) of the first carbon-based negative electrode active material １ｓｔ 7. The negative electrode for a lithium secondary battery according to claim 1, wherein the ratio of the total weight of the negative electrode to the total weight of the lithium secondary battery is 10% to 100%.

8. Simultaneously applying a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material onto a negative electrode current collector; applying a magnetic field to the applied first and second negative electrode slurries; and drying the first and second negative electrode slurries to which the magnetic field has been applied to form the first and second negative electrode active layers, the first carbon-based negative electrode active material includes natural graphite and artificial graphite; the second carbon-based negative electrode active material includes artificial graphite; the first negative electrode active layer and the second negative electrode active layer have different compositions; a first negative electrode active layer and a second negative electrode active layer, each of which has an alignment degree (O.I) of a carbon-based negative electrode active material represented by the following formula 1 of 0.1 to 0.9: [Formula 1] O.I=I ００４ / I １１０ In Formula 1, I ００４ represents the area of ​​the peak representing the (0,0,4) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD), I １１０ represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

9. 9. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, wherein a magnetic field of 2,000 G to 6,000 G is applied in the step of applying a magnetic field.

10. 9. The method of claim 8, wherein the applying of the magnetic field is performed for 5 to 60 seconds.

11. The step of forming the first negative electrode active layer and the second negative electrode active layer includes: drying the first negative electrode slurry and the second negative electrode slurry; and rolling the dried first and second negative electrode slurries.

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