Negative electrode and method for manufacturing the same

Abstract

The present invention relates to a negative electrode and a method for manufacturing the same. The negative electrode includes a first negative electrode active layer and a second negative electrode active layer on a negative electrode current collector. In this case, the negative electrode has excellent life characteristics because the degree of alignment (OI) of each negative electrode active layer satisfies a predetermined range, resulting in high adhesion of the negative electrode active layer to the negative electrode current collector. Furthermore, a secondary battery containing the same has the advantage of excellent output characteristics and the ability to be charged in a short time even at a 1C rate.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode and a method for manufacturing the same.

[0002] This application is an application claiming priority rights based on Korean Patent Applications No. 10-2023-0142600, No. 10-2023-0142612, and No. 10-2023-0142616 dated October 24, 2023, and Korean Patent Application No. 10-2024-0144799 dated October 22, 2024, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference. [Background technology]

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

[0004] Existing lithium-ion batteries are limited to applications such as short-distance electric vehicles due to their energy density limitations. Therefore, to date, intensive development has focused on technologies to increase the energy density of lithium-ion batteries.

[0005] However, the lithium-ion batteries developed for automobiles have a problem: they take a long time to recharge after being discharged during vehicle operation. Therefore, as the adoption rate of electric vehicles increases, there is a growing demand to shorten charging times to a level that is acceptable to users.

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

[0007] In practice, graphite-containing materials are widely used as the negative electrode active material for the above-mentioned negative electrode. The average potential when a graphite-containing material releases lithium is approximately 0.2V (Li / Li + (Reference) and exhibits a relatively flat discharge potential. Therefore, when graphite is used as the negative electrode active material, there is the advantage that the voltage of the secondary battery is high and constant.

[0008] Amorphous or crystalline carbon is used as the negative electrode active material, with crystalline carbon being the most commonly used due to its higher capacity. Examples of such crystalline carbon include graphite-based carbons such as natural graphite and artificial graphite.

[0009] The graphite-based carbons mentioned above have different properties depending on their type. For example, natural graphite is inexpensive and exhibits excellent adhesion to current collectors, but it is relatively inferior to artificial graphite in terms of high-rate charge / discharge performance and lifespan characteristics. However, artificial graphite has weak adhesion to current collectors due to its low content of surface defects and functional groups, and when propylene carbonate (PC) is mixed into the electrolyte to improve low-temperature performance, the propylene carbonate causes the layers that make up the interlayer structure of the graphite to delaminate and break down.

[0010] Therefore, there have been attempts to combine natural and artificial graphite appropriately to utilize the advantages of each, and to apply this mixed graphite as the negative electrode active material for lithium secondary batteries. However, in the case of such mixed graphite, the adhesive strength to the current collector decreases, and it is difficult to reach a satisfactory level in terms of lifespan characteristics and impact resistance stability.

[0011] Therefore, in order to fundamentally solve these problems, there is a high demand for negative electrode technology that has high adhesion to the current collector, excellent lifespan characteristics, excellent output characteristics, and high rapid charging characteristics. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Korean Published Patent Publication No. 10-2022-0064389 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The object of the present invention is to provide a negative electrode and a method for manufacturing the same, which have high adhesion to the current collector, excellent lifespan characteristics, excellent output characteristics, and high rapid charging characteristics. [Means for solving the problem]

[0014] To solve the above problem, The present invention negative electrode current collector, A first negative electrode active layer is provided on the negative electrode current collector and includes a first carbon-based negative electrode active material, and A second negative electrode active layer is provided on the first negative electrode active layer and contains a second carbon-based negative electrode active material. Includes, The second negative electrode active layer has an alignment degree (OI) represented by the following formula 1. 2nd ) is 6 or less, The degree of alignment of the first negative electrode active layer (OI 1st ) is the degree of alignment of the second negative electrode active layer (OI2nd The negative electrode is provided with a ratio of 200% to 900% based on ).

[0015] [Equation 1] OI = I 004 / I 110

[0016] In Equation 1, I 004 This represents the area value of the peak indicating the (004) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer. I 110 This represents the area value of the peak indicating the (110) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0017] Here, the ratio (D2 / D1) of the average particle size (D2) of the second carbon-based anode active material to the average particle size (D1) of the first carbon-based anode active material can be in the range of 2.0 or more.

[0018] The first carbon-based anode active material and the second carbon-based anode active material may each contain one or more of natural graphite and artificial graphite.

[0019] The average particle size (D1) of the first carbon-based anode active material can be in the range of less than 5 μm, and the average particle size (D2) of the second carbon-based anode active material can be in the range of 10 μm to 25 μm.

[0020] The first negative electrode active layer may include a carbon structure having an average size in the range of 5 nm to 900 nm.

[0021] The carbon structure may include one or more of the following: a point-like carbon structure, a fibrous carbon structure, and a planar carbon structure.

[0022] The carbon structure content can range from 0.001% by weight to 10% by weight, based on the total weight of the first negative electrode active layer.

[0023] The first negative electrode active layer and the second negative electrode active layer can each contain a first thickening agent and a second thickening agent, and the content ratio of the first thickening agent can be 80% to 120% based on the content ratio of the second thickening agent.

[0024] The first thickening agent and the second thickening agent can each contain one or more of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), poly-N-vinyl acetamide (PNVA), styrene-butadiene rubber (SBR), acrylic resins, and fluorine-based resins.

[0025] The first thickening agent can be contained at 0.5% by weight to 3% by weight based on the weight of the entire first negative electrode active layer.

[0026] Furthermore, the present invention provides a step of applying a first negative electrode slurry containing a first carbon-based negative electrode active material onto at least one surface of a negative electrode current collector, a step of applying a second negative electrode slurry containing a second carbon-based negative electrode active material onto the applied first negative electrode slurry, a step of applying a magnetic field to the negative electrode current collector onto which the second negative electrode slurry has been applied, and a step of drying the first negative electrode slurry and the second negative electrode slurry to which the magnetic field has been applied to form a first negative electrode active layer and a second negative electrode active layer, and includes The second negative electrode active layer has an orientation degree (O.I 2nd ) of 6 or less, The orientation degree (O.I 1st ) of the first negative electrode active layer is 200% to 900% based on the orientation degree (O.I 2nd ) of the second negative electrode active layer, and provides a method for manufacturing a negative electrode.

[0027] [Formula 1] O.I = I 004 / I 110

[0028] In Formula 1, I004 This represents the area value of the peak indicating the (004) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer. I 110 This represents the area value of the peak indicating the (110) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0029] In this case, the steps of applying the first negative electrode slurry and applying the second negative electrode slurry can be performed simultaneously.

[0030] The magnetic field can be applied with an intensity of 3,000G to 10,000G.

[0031] The magnetic field can be applied for a period of 1 to 60 seconds.

[0032] The solid content of the first negative electrode slurry can be in the range of 35% to 85%.

[0033] The viscosity at room temperature of the first negative electrode slurry may be higher than the viscosity at room temperature of the second negative electrode slurry.

[0034] The ratio (D2 / D1) of the average particle size (D2) of the second carbon-based anode active material to the average particle size (D1) of the first carbon-based anode active material can be in the range of 2.0 or more.

[0035] The first negative electrode slurry may include a carbon structure having an average size in the range of 5 nm to 900 nm.

[0036] The content of the carbon structure can range from 0.001% by weight to 10% by weight, based on the total weight of the solids in the first negative electrode slurry.

[0037] The first negative electrode slurry and the second negative electrode slurry can be mixed with a first thickener and a second thickener, respectively, in solution form during manufacturing, and the concentrations of each solution containing the first and second thickeners may differ.

[0038] The concentration of the solution containing the second thickener may be in the range of 0.5% to 1.5% by weight based on the total weight of the solution, and the concentration of the solution containing the first thickener may have a concentration ratio of 150% to 250% based on the concentration of the solution containing the second thickener. [Effects of the Invention]

[0039] The negative electrode according to the present invention has excellent lifespan characteristics due to its high adhesion to the negative electrode current collector. Furthermore, secondary batteries containing it have the advantage of excellent output characteristics and can be charged in a short time even at a 1C rate. [Modes for carrying out the invention]

[0040] Since the present invention can be modified in various ways and has many different embodiments, specific embodiments will be described in detail.

[0041] However, this is not intended to limit the present invention to any particular embodiment, but rather can be understood to include all modifications, equivalents, or substitutions that fall within the technical scope of the present invention.

[0042] In the present invention, terms such as “includes” and “have” are intended to indicate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and do not presuppose the presence or possibility of adding one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0043] Furthermore, in the present invention, "contains as a main component" can mean that the component defined on a basis of total weight (or total volume) is contained in an amount of 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more). For example, "contains graphite as a main component as the negative electrode active material" can mean that graphite is contained in an amount of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more relative to the total weight of the negative electrode active material, and in some cases, it can also mean that the entire negative electrode active material consists of graphite and contains 100% by weight of graphite.

[0044] Furthermore, in this specification, "orientation of carbon-based anode active material" or "alignment of carbon-based anode active material" means that a specific crystal plane (for example, the ab-axis crystal plane of graphite) that shows the two-dimensional planar structure of the carbon-based anode active material constituting the anode active material particles is arranged to have a predetermined inclination with respect to the surface of the anode current collector. This may differ from arrangement in which the particles of carbon-based anode active material themselves have a specific orientation within the anode active layer.

[0045] Furthermore, "high orientation of carbon-based anode active material" can mean that a specific crystal plane (for example, the ab-axis crystal plane of graphite) exhibiting the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer has a high frequency of having a predetermined inclination with respect to the surface of the anode current collector. In some cases, it can also mean that the above crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (for example, an angle close to perpendicular, greater than 45°, specifically 60° or more) with respect to the surface of the anode current collector.

[0046] Furthermore, "high degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" referred to herein is large, and can be interpreted as meaning that specific crystal planes (e.g., the ab-axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based anode active material contained in the anode active layer are aligned at a low angle (e.g., less than 45°) with respect to the surface of the anode current collector. Conversely, "low degree of alignment of carbon-based anode active material" means that the "degree of alignment (OI)" is small, and can be interpreted as meaning that the above-mentioned crystal planes of the carbon-based anode active material contained in the anode active layer are aligned at a high angle (e.g., an angle close to perpendicular, 45° or more, specifically 60° or more) with respect to the surface of the anode current collector.

[0047] Furthermore, in this specification, "crystal plane of carbon-based anode active material" refers to a plane on which the atoms of the carbon-based anode active material form the outer shape of the crystal, and in the present invention, it can mean a crystal plane including the plane of the carbon-based anode active material, or a crystal plane including the a-axis / b-axis / ab-axis of the carbon-based anode active material crystal.

[0048] Furthermore, in this specification, "average particle size (D 50 "Average particle size" refers to the particle size at which the integrated value in the particle size distribution becomes 50%, and is also called the median diameter. The above average particle size can be measured using methods commonly applied in this industry. For example, the above average particle size can be measured using a laser diffraction scattering particle size analyzer or a centrifugal particle size analyzer. In this invention, it may be a value measured with an analytical instrument using the laser diffraction scattering particle size analysis method.

[0049] In this specification, "room temperature" can mean a temperature in the range of 10°C to 30°C. For example, room temperature can refer to temperatures in the range of 15°C to 30°C, 20°C to 30°C, 21°C to 29°C, 15°C to 26°C, 18°C ​​to 26°C, or 21°C to 26°C.

[0050] The present invention will be described in more detail below.

[0051] <Negative electrode>

[0052] The present invention negative electrode current collector, A first negative electrode active layer is provided on the negative electrode current collector and includes a first carbon-based negative electrode active material, and A second negative electrode active layer is provided on the first negative electrode active layer, and contains a second carbon-based negative electrode active material. A negative electrode containing is provided.

[0053] The negative electrode according to the present invention may refer to a negative electrode for a lithium secondary battery. The negative electrode includes a negative electrode active layer on at least one surface of the negative electrode current collector. The negative electrode active layer is a layer that embodies the electrical activity of the negative electrode and mainly contains a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during charging and discharging of the battery.

[0054] Here, 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. Since the composition of each layer of the two-layer negative electrode active layer can be easily controlled, the performance of the negative electrode can be improved by changing the type and amount of components contained in each layer, or by controlling their physical properties to differ, 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.

[0055] For example, the first and second negative electrode active layers can be aligned such that specific crystal planes of the carbon-based negative electrode active material have a predetermined inclination relative to the negative electrode current collector. In this case, the carbon-based negative electrode active material contained in the first negative electrode active layer, which is in direct contact with the negative electrode current collector, can be aligned such that the inclination of specific crystal planes with respect to the negative electrode current collector is small, and the carbon-based negative electrode active material contained in the second negative electrode active layer, which is in contact with the positive electrode, can be aligned such that specific crystal planes are nearly perpendicular to the negative electrode current collector.

[0056] Furthermore, the first anode active layer and the second anode active layer may each contain a first carbon-based anode active material and a second carbon-based anode active material. The first carbon-based anode active material and the second carbon-based anode active material contained in each anode active layer may be the same in type and / or in content, or they may be different. Specifically, the first carbon-based anode active material and the second carbon-based anode active material refer to materials mainly composed of carbon atoms, and such carbon-based anode active materials may include graphite. The graphite may include one or more of natural graphite and artificial graphite. For example, the first carbon-based anode active material and the second carbon-based anode active material may each contain natural graphite or artificial graphite individually, or may contain a mixture of natural graphite and artificial graphite.

[0057] For example, the first carbon-based anode active material can contain natural graphite and artificial graphite in weight ratios of 5-50:50-95, 20-45:55-80, or 30-50:50-70, and the second carbon-based anode active material can contain artificial graphite alone. In this case, by containing natural graphite and artificial graphite in the above-mentioned mixing ratios, the carbon-based anode active material can strengthen the adhesion between the anode current collector and the anode active layer while increasing the orientation of the carbon-based anode active material to the surface of the anode current collector.

[0058] Furthermore, the first carbon-based anode active material and the second carbon-based anode active material can each contain artificial graphite alone. The present invention incorporates artificial graphite alone in the anode active layer, significantly improving the lifespan of the anode, and thus can be advantageous in conditions where frequent charging must be endured for long periods, such as in automobile batteries. Moreover, artificial graphite has the advantage of being advantageous for rapid charging and having superior output performance compared to natural graphite.

[0059] On the other hand, in order to increase the charging speed during charging of a secondary battery, lithium ion movement can be facilitated by controlling the type of carbon-based negative electrode active material contained in the negative electrode active layer, or by oriented the carbon-based negative electrode active material so that a specific crystal plane (specifically, the (002) crystal plane of graphite) has an inclination that is nearly perpendicular to the negative electrode current collector. However, in this case, the contact area between the negative electrode current collector and the negative electrode active layer (for example, the first negative electrode active layer) is significantly reduced, which leads to a problem of decreased adhesion between them. Therefore, the present invention can improve the adhesion between the negative electrode current collector and the first negative electrode active layer by satisfying one or more of the following conditions.

[0060] (Condition 1) The ratio of the average particle size of the second carbon-based anode active material (D2) to the average particle size of the first carbon-based anode active material (D1) (D2 / D1): 2.0 or more. (Condition 2) The first negative electrode active layer contains a carbon structure, (Condition 3) The first negative electrode active layer and the second negative electrode active layer each contain the first thickener and the second thickener, respectively.

[0061] The present invention satisfies (Condition 1) and / or (Condition 2), and can increase the specific surface area of ​​the particles contained in the first negative electrode active layer, thereby directly increasing the interfacial adhesion between the negative electrode current collector and the first negative electrode active layer. Furthermore, by satisfying one or more of the above three conditions, the room-temperature viscosity of the first negative electrode slurry containing the first carbon-based negative electrode active material during negative electrode manufacturing can be increased. At high room-temperature viscosity, when the carbon-based negative electrode active material is oriented using a magnetic field, the (002) crystal plane of the carbon-based negative electrode active material is aligned with respect to the surface of the negative electrode current collector at an inclination of less than 90°, thus preventing a decrease in the adhesion between the negative electrode current collector and the first negative electrode active layer.

[0062] (Condition 1) Specifically, the anode according to the present invention has a first carbon-based anode active material contained in the first anode active layer and a second carbon-based anode active material contained in the second anode active layer, and the morphology and / or average particle size (D 50 ) may differ.

[0063] The above-mentioned first carbon-based anode active material and second carbon-based anode active material have an average particle size (D 50 Each of these can satisfy a predetermined range, and they can have a specific particle size ratio.

[0064] The ratio (D2 / D1) of the average particle size (D2) of the second carbon-based anode active material to the average particle size (D1) of the first carbon-based anode active material may be in the range of 2.0 or greater. For example, the above ratio (D2 / D1) may be in the range of 2.0~15, 2.0~13, 2.0~11, 2.0~9.0, 2.0~7.0, 2.0~6.0, 2.0~5.0, 3.0~8.0, 3.0~7.0, 3.0~4.5, 4.0~7.0, 5.0~7.0, 4.0~10, 4.0~9.0, 6.0~11, 8.0~14, 9.0~13, or 3.1~5.5.

[0065] In this invention, the average particle size ratio (D2 / D1) of the second carbon-based negative electrode active material and the first carbon-based negative electrode active material satisfies the above-mentioned range, thereby improving the adhesion between the negative electrode current collector and the first negative electrode active layer, and thus improving the lifespan of the negative electrode. Furthermore, within the above-mentioned range, the negative electrode of this invention can significantly improve the charging speed of the secondary battery not only under high-rate conditions but also at low rate-limiting conditions of 1C or less, thus having the advantage of enabling charging in a short time even at a 1C rate.

[0066] The average particle size (D1) of the first carbon-based anode active material may be in the range of less than 5 μm, and the average particle size (D2) of the second carbon-based anode active material may be in the range of 10 μm to 25 μm.

[0067] For example, the average particle size (D1) of the first carbon-based anode active material may be in the range of 0.1 μm to 4.9 μm, 0.5 μm to 4.9 μm, 0.5 μm to 4.5 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.5 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.5 μm, 1.0 μm to 4.6 μm, 1.5 μm to 4.9 μm, 2.0 μm to 4.9 μm, 2.5 μm to 4.9 μm, 0.8 μm to 1.5 μm, 2.5 μm to 3.5 μm, 2.7 μm to 4.6 μm, 3.5 μm to 4.9 μm, or 4.1 μm to 4.9 μm.

[0068] The first carbon-based anode active material described above consists of primary particles with an average particle size (D1) of less than 5 μm. Since the specific surface area can be significantly increased in proportion to the small particle size, the adhesion between the anode current collector and the first anode active layer can be made stronger. However, if the average particle size (D1) of the first carbon-based anode active material is lower than the lower limit of the range described above, a large amount of binder will be required due to the increase in the number of particles per unit volume, which may degrade the electrical properties of the anode active layer containing these binders. Also, if the average particle size (D1) of the first carbon-based anode active material is higher than the upper limit of the range described above, the specific surface area of ​​the first carbon-based anode active material will be significantly reduced, so the effect of improving the adhesion between the anode current collector and the first anode active layer may be slight.

[0069] Furthermore, the average particle size (D2) of the above-mentioned second carbon-based anode active material may be in the range of 10 μm to 22.5 μm, 11 μm to 20 μm, 11 μm to 17.5 μm, 11 μm to 15 μm, 11 μm to 19 μm, 13 μm to 17 μm, 17 μm to 22 μm, 14 μm to 18 μm, 14 μm to 22 μm, 16 μm to 21 μm, or 14.5 μm to 16.5 μm.

[0070] The above-mentioned second carbon-based anode active material is a granule formed by combining 2 to 100, preferably 3 to 20, active material particles. Compared to the first carbon-based anode active material, it has a larger particle size, which improves the electrical properties during charging and discharging of the secondary battery and mitigates safety issues. For example, if the average particle size (D2) of the above-mentioned second carbon-based anode active material is lower than the lower limit of the above-mentioned range, the migration path of lithium ions formed inside the second anode active layer becomes longer, which can reduce the charging and discharging efficiency of the secondary battery.

[0071] Generally, the degree of sphericity of carbon-based anode active material is one indicator of particle shape, and the electrical performance and adhesive strength of the anode active layer can differ depending on the shape of the carbon-based anode active material. The present invention makes it possible to improve the adhesive strength between the anode current collector and the anode active layer while simultaneously improving the output and rapid charging of the anode by differentiating the shape / morphology of the carbon-based anode active material contained in each anode active layer.

[0072] Specifically, the first carbon-based anode active material contained in the first anode active layer may have a spheroidization degree of 0.9 or higher, while the second carbon-based anode active material contained in the second anode active layer may have a spheroidization degree of less than 0.9.

[0073] For example, the above-mentioned first carbon-based anode active material may have a degree of spheroidization in the range of 0.90-1.00, 0.90-0.99, 0.92-0.98, 0.95-0.99, 0.92-0.97, 0.95-0.98, or greater than 0.90 but less than 1.0. Furthermore, the above-mentioned second carbon-based anode active material may have a degree of spheroidization in the range of 0.10-0.75, 0.25-0.75, 0.25-0.70, 0.25-0.60, 0.25-0.50, 0.25-0.40, 0.40-0.65, 0.50-0.70, 0.50-0.65, 0.60-0.75, 0.20-0.35, 0.10-0.40, 0.40-0.50, or 0.2 or more and less than 0.7.

[0074] In this invention, "degree of spheroidization" can mean 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 in two dimensions. When the degree of spheroidization is 1, the particle can have a spherical shape. The degree of spheroidization can be determined by measuring it using a particle shape analyzer, or by measuring the particle morphology using a scanning electron microscope (SEM) or energy-dispersive spectrometer, and then analyzing the measured results.

[0075] In other words, the first carbon-based anode active material in the present invention can have a spherical shape, and the second carbon-based anode active material can have an ellipsoidal shape that is stretched in any one direction with respect to the center of the particle. Since the spherical first carbon-based anode active material can minimize the volume of the particles, the density of the first anode active layer can be increased, and the area in contact with the first anode active layer at the interface with the anode current collector can be increased, thereby further increasing the energy density of the first anode active layer and the adhesion force with the anode current collector. Furthermore, the second carbon-based anode active material having an ellipsoidal shape stretched in one direction has the advantage of being able to increase the output performance of the anode because it can reduce the degree of bending on the surface of the second anode active layer and further increase the migration speed of lithium ions.

[0076] (Condition 2) Furthermore, the anode according to the present invention may include a carbon structure having a predetermined size in the first anode active layer. Here, the carbon structure refers to a compound having an average size on the nanometer (nm) level and whose main component is carbon atoms (C).

[0077] The above carbon structure serves to increase the viscosity of the first anode slurry without degrading the performance of the first carbon-based anode active material contained in the first anode slurry that forms the first anode active layer during anode manufacturing. Specifically, "room temperature viscosity" refers to the magnitude of physical and / or chemical interactions such as friction and resistance between each raw material substance (e.g., carbon-based anode active material, additives, conductive materials, binders, etc.) present in the anode slurry at room temperature. Such interactions increase as the number of raw material substances, i.e., the number of particles, increases, even for raw material substances with the same volume fraction. The present invention makes it possible to increase the viscosity of the first anode slurry that forms the first anode active layer during anode manufacturing by applying a carbon structure having an average size at the nanometer (nm) level. Furthermore, conventional thickeners such as carboxymethylcellulose (CMC) used to control the viscosity of anode slurries have a limitation: as the amount used increases, the electrical resistance of the manufactured anode active layer increases, reducing the content of the first carbon-based anode active material in the manufactured first anode slurry and lowering the charge-discharge capacity. However, the present invention allows for the application of a carbon structure instead of a thickening agent such as carboxymethylcellulose (CMC) to increase the viscosity of the first anode slurry without affecting the electrical properties of the first anode slurry, thereby improving the alignment (OI) of the first anode active layer produced. 1st ) can be realized to a high degree.

[0078] Such carbon structures may include one or more of the following, having an average size on the nanometer (nm) level: carbon nanotubes, carbon nanofilaments, nanofibers, fullerenes, graphene, and graphite.

[0079] For example, the carbon structure described above may include carbon nanotubes containing one or more types of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The carbon nanotubes have a size on the nanometer (nm) level, and the degree of alignment (OI) of the first negative electrode active layer, in which the carbon-based negative electrode active material is oriented by a magnetic field, is... 1stThis can increase the conductivity. Furthermore, the carbon nanotubes have a linear structure and can achieve high electrical conductivity by forming an intercarbon nanotube network within the first negative electrode active layer, thereby lowering the interfacial resistance generated at the interface between the negative electrode current collector and the first negative electrode active layer. Such low interfacial resistance, combined with the high degree of alignment (OI) of the first carbon-based negative electrode active material, can offset the reduction in charging speed during secondary battery charging.

[0080] The above carbon structure can have an average size in the range of 5nm to 900nm, specifically an average size in the range of 5nm to 750nm, 5nm to 500nm, 5nm to 250nm, 5nm to 100nm, 50nm to 200nm, 50nm to 400nm, 100nm to 500nm, 100nm to 250nm, 250nm to 500nm, 300nm to 700nm, 500nm to 900nm, 700nm to 900nm, 600nm to 800nm, 150nm to 300nm, 10nm to 90nm, 50nm to 90nm, 50nm to 150nm, 110nm to 390nm, or 310nm to 490nm.

[0081] Here, "average size" can be interpreted differently depending on the form of the carbon structure. For example, in the case of carbon structures having a two-dimensional linear structure such as carbon nanotubes, carbon nanofilaments, and nanofibers, it can mean either the average diameter and average length of the linear structure, or an intermediate value between them. In this invention, it can mean an intermediate value between the average diameter and average length of the carbon structure. In this case, the average diameter can be in the range of several to tens of nanometers (e.g., 1 to 99 nm), and the average length can be in the range of tens of nanometers to tens of micrometers (e.g., 11 nm to 99 μm), and the average length can be greater than the average diameter. Specifically, if a carbon structure having a two-dimensional linear structure has an average diameter of 10 nm and an average length of 350 nm, the average size may be 180 nm. Also, for carbon structures with a three-dimensional spherical structure such as fullerenes, it can mean their average diameter. Furthermore, for carbon structures with a two-dimensional planar structure such as graphene and graphite, it can mean the average value of the shortest diameter (minor axis) and the longest diameter (major axis) among any diameter passing through the center of the particle. Furthermore, the average size of the carbon structure can be confirmed by analyzing a two-dimensional projection image obtained by scanning electron microscopy (SEM) or transmission electron microscopy (TEM) of the cross-section of the first negative electrode active layer, which is observed when the negative electrode is cut in the thickness direction. In some cases, it can be confirmed using commercially obtained information on carbon structures. For example, the average size of the carbon structure can be calculated from a two-dimensional projection image obtained via scanning electron microscopy (SEM).

[0082] The above carbon structure can be applied to the first anode active layer within a predetermined content range. Specifically, the above carbon structure can be included in the first anode active layer in a range of 0.001% to 10% by weight, based on the total weight of the first anode active layer. More specifically, the carbon structure can be included in the first anode active layer in the range of 0.001% to 9% by weight, 0.001% to 7% by weight, 0.001% to 5% by weight, 0.001% to 3% by weight, 0.001% to 1% by weight, 0.001% to 0.5% by weight, 0.01% to 0.5% by weight, 0.1% to 2% by weight, 1% to 10% by weight, 1% to 8% by weight, 1% to 6% by weight, 1% to 5% by weight, 1% to 3% by weight, 3% to 8% by weight, 6% to 9% by weight, 5% to 8% by weight, 2% to 4% by weight, or 1.5% to 4.5% by weight, based on the total weight of the first anode active layer. The content of the carbon structure can be adjusted depending on the type and average size applied to the first anode active layer.

[0083] For example, the first negative electrode active layer may contain single-walled carbon nanotubes (SWCNTs) as carbon structures in an amount ranging from 0.01% to 0.9% by weight relative to the total weight of the first negative electrode active layer.

[0084] Furthermore, the first negative electrode active layer may contain multi-walled carbon nanotubes (MWCNTs) as a carbon structure in an amount ranging from 1% to 8% by weight relative to the total weight of the first negative electrode active layer.

[0085] (Condition 3) Furthermore, the anode according to the present invention contains a first thickener and a second thickener in the first anode active layer and the second anode active layer, respectively. The first thickener and the second thickener are included in the first anode slurry and the second anode slurry, respectively, when the first anode active layer and the second anode active layer are formed, and serve to give each slurry a viscosity higher than its original viscosity.

[0086] The present invention makes it possible to make the viscosity of a negative electrode slurry different by including the same proportion of thickener in each negative electrode slurry that forms the negative electrode active layer based on the total weight of the solids during the manufacturing of the negative electrode, and by changing the concentration of the thickener in each negative electrode slurry during the manufacturing of the negative electrode. Specifically, the first thickener and the second thickener in the present invention are included in the same weight ratio based on the total weight of the solids in the negative electrode slurry that constitutes each negative electrode active layer (i.e., the total weight of the negative electrode active layer), and by making the concentration of the first thickener solution applied to the first negative electrode slurry higher than the concentration of the second thickener solution applied to the second negative electrode slurry, the viscosity of the first negative electrode slurry can be made higher than the viscosity of the second negative electrode slurry.

[0087] The viscosity of the negative electrode slurry not only affects the loading amount and thickness of the negative electrode active layer, but also primarily affects the alignment of the carbon-based negative electrode active material contained within the slurry when a magnetic field is applied. In a negative electrode slurry with high viscosity, the orientation of the carbon-based negative electrode active material contained within decreases when a magnetic field is applied, making it difficult to increase the tilt relative to the negative electrode current collector. Therefore, the present invention controls the viscosity of the first negative electrode slurry to be relatively higher than the viscosity of the second negative electrode slurry, thereby improving the degree of alignment of the first negative electrode active layer (OI 1st ) the degree of alignment of the second negative electrode active layer (OI 2nd It can be made larger than ).

[0088] In this case, the first and second thickeners can be those commonly used in the industry to control the viscosity of electrode slurries. Specifically, the first and second thickeners may each contain one or more of the following: carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), poly-N-vinylacetamide (PNVA), styrene-butadiene rubber (SBR), acrylic resins, and fluororesins.

[0089] Furthermore, the first and second thickeners can each be included in amounts ranging from 0.5% to 3% by weight, based on the total weight of the first and second anode active layers. For example, the first and second thickeners can be included in amounts ranging from 0.5% to 2% by weight, 0.5% to 1% by weight, 1% to 3% by weight, 1% to 2% by weight, 1.5% to 3% by weight, 0.5% to 1.9% by weight, or 1.1% to 1.9% by weight, based on the total weight of the first and second anode active layers.

[0090] Furthermore, the content of the first thickening agent can be 80% to 120% of the content of the second thickening agent, specifically 90% to 110%, or 95% to 105%.

[0091] For example, the first and second thickeners are carboxymethylcellulose (CMC), and are included in an amount ranging from 1.2% to 1.7% by weight relative to the total weight of each negative electrode active layer, with the content of the first thickener being 100±2% based on the content of the second thickener.

[0092] On the other hand, if the negative electrode according to the present invention satisfies (condition 2) and / or (condition 3), the first carbon-based negative electrode active material and the second carbon-based negative electrode active material have an average particle size (D 50 ) and / or the shape may satisfy (condition 1), but may not. Specifically, if the above (condition 1) is not satisfied, the first carbon-based anode active material and the second carbon-based anode active material shall each have an average particle size (D) in the range of 0.1 μm to 20 μm. 50 ) and a degree of spheroidization in the range of 0.8 or less can be present.

[0093] For example, the average particle size (D) of the first carbon-based anode active material and the second carbon-based anode active material. 50) may be in the range of 5μm~20μm, 10μm~20μm, 11μm~19μm, 8μm~15μm, 15μm~20μm, 13μm~19μm, 14μm~17μm, 5μm~8μm, 0.1μm~15μm, 0.1μm~10μm, 0.1μm~8μm, 0.1μm~5μm, 0.1μm~3μm, 0.1μm~1μm, 0.5μm~10μm, 0.5μm~5μm, 0.5μm~4.5μm, 0.5μm~3μm, 1μm~4.5μm, 1μm~3μm, or 0.8μm~1.8μm.

[0094] The present invention can suppress the increase in electrical resistance of the first negative electrode active layer by controlling the average particle size of the first carbon-based negative electrode active material to the above range. Furthermore, the first carbon-based negative electrode active material can maximize the degree of disorder in the expansion direction for each particle so as to increase the specific surface area within the above average particle size range while preventing particle expansion due to lithium ion charging. Therefore, the adhesion force between the first negative electrode active layer containing it and the negative electrode current collector can be further increased. In addition, the present invention has the advantage that by adjusting the average particle size of the second carbon-based negative electrode active material to the above range, the electrical conductivity of the second negative electrode active layer can be increased and a lithium ion migration path can be secured at the same time.

[0095] On the other hand, the first carbon-based anode active material and the second carbon-based anode active material have the above average particle size (D 50 If the particle size is lower than the lower limit of ), a large amount of binder is required due to the increase in the number of particles per unit volume, which may degrade the electrical properties of the negative electrode active layer containing these particles. Furthermore, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material have the above average particle size (D 50 If the particle size exceeds the upper limit of ), the expansion rate of the negative electrode active material during charging and discharging of the secondary battery increases significantly. As charging and discharging are repeated, the interparticle bonding properties of the negative electrode active material and the bonding properties between the negative electrode active material particles and the current collector decrease, which can significantly reduce the cycle performance.

[0096] Furthermore, the first carbon-based anode active material and the second carbon-based anode active material can each have a degree of spheroidization in the range of 0.10-0.80, 0.25-0.80, 0.35-0.80, 0.25-0.70, 0.25-0.60, 0.25-0.50, 0.25-0.40, 0.40-0.65, 0.50-0.80, 0.50-0.65, 0.60-0.80, 0.60-0.75, 0.70-0.05, 0.10-0.40, or 0.2 or more and less than 0.8, respectively.

[0097] The above-mentioned degree of spheroidization being 0.80 or less, specifically 0.60 or less, can be interpreted as having an ellipsoidal shape that is stretched in any one direction with respect to the center of the particle. By satisfying the above-mentioned range for the degree of spheroidization of the first carbon-based anode active material and the second carbon-based anode active material, the present invention can further shorten the migration path of lithium ions formed inside the first anode active layer and the second anode active layer. As a result, the anode can improve its output characteristics and shorten the charging time. Specifically, if the degree of spheroidization of the first carbon-based anode active material and the second carbon-based anode active material exceeds the upper limit of the above-mentioned range, the degree of curvature at the anode surface can increase significantly. In this case, the anode active layer has the problem of reduced charging speed during secondary battery charging because the lithium ion migration speed is reduced. Furthermore, if the degree of spheroidization of the first carbon-based anode active material and the second carbon-based anode active material is below the lower limit of the above-mentioned range, the electrical conductivity of the carbon-based anode active material itself will be reduced, which may decrease the capacity of the anode. In particular, in the case of the first carbon-based anode active material, the contact area between the anode current collector and the anode active layer is significantly reduced, so even if the degree of alignment of the first anode active layer is controlled, there is a limit in that the adhesive force between the anode current collector and the first anode active layer is significantly reduced.

[0098] Furthermore, the anode according to the present invention allows for control over the crystalline structure characteristics of the carbon-based anode active material contained in the first anode active layer and the second anode active layer, in order to enhance the adhesion between the first anode active layer and the anode current collector while achieving a fast charging speed.

[0099] For example, the second negative electrode active layer has an alignment degree (OI) related to the following formula 1. 2nd ) may be 6 or less.

[0100] [Formula 1] OI=I 004 / I 110

[0101] In Equation 1, I 004 This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I 110 This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0102] The alignment (OI) of the carbon-based anode active material can serve as an indicator of the degree to which the ab-axis crystal planes of the carbon-based anode active material are oriented in a specific direction, specifically, relative to the surface of the anode current collector, as measured by X-ray diffraction (XRD). For example, the anode active layer exhibits peaks of 2θ = 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2° for the carbon-based anode active material, black smoke, as measured by X-ray diffraction. These correspond to the (002), (100), (101)R, (101)H, (004), and (110) planes of graphite, respectively. Here, the peak that appears at 2θ = 43.4 ± 0.2° can be considered to be an overlap of peaks corresponding to the (101)R surface of the carbon-based negative electrode active material and the (111) surface of the current collector, such as copper (Cu).

[0103] Of these, the degree of alignment (OI) of the carbon-based anode active material can be measured by the ratio of the area obtained by integrating the intensities of the peak at 2θ = 54.7 ± 0.2°, which represents the (004) plane, and the peak at 2θ = 77.5 ± 0.2°, which represents the (110) plane.

[0104] The peak at 2θ = 54.7 ± 0.2° represents a crystal plane of the carbon-based negative electrode active material that has an inclination with respect to the negative electrode current collector. Therefore, the closer the alignment degree (OI) is to 0, the closer the inclination with respect to the negative electrode current collector surface is to 90°, and the larger the value, the closer the inclination with respect to the negative electrode current collector surface is to 0° or 180°. In other words, if the alignment degree (OI) of the present invention is low and close to 0, the negative electrode active layer can contain carbon-based negative electrode active material aligned to have angles of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, or 70° to 85° with respect to the negative electrode current collector. That is, the alignment degree (OI) can indicate the degree to which the particles of the carbon-based negative electrode active material are aligned with respect to the negative electrode current collector surface. Furthermore, in some cases, the above-mentioned degree of alignment (OI) can indicate the degree of alignment of the ab-axis crystal planes of the carbon-based anode active material within the anode active layer. When the ab-axis crystal planes of the carbon-based anode active material are aligned, rotation of the particles of the carbon-based anode active material contained in the anode active layer can also be induced. However, since this particle rotation is influenced by the particle morphology, it is not equal to the degree of alignment of the ab-axis crystal planes, and therefore it may be difficult to indicate that the above-mentioned degree of alignment (OI) is aligned.

[0105] The negative electrode according to the present invention can have a first negative electrode active layer with a greater degree of alignment (OI) than the second negative electrode active layer. This means that the crystal plane of the first carbon-based negative electrode active material contained in the first negative electrode active layer has a lower angle of inclination with respect to the negative electrode current collector than the crystal plane of the second carbon-based negative electrode active material contained in the second negative electrode active layer.

[0106] For example, the second negative electrode active layer described above has a degree of alignment (OI 2nd) may be in the range of 0.5 to 6, specifically in the range of 1 to 5, 1 to 3, 1.5 to 6, 3 to 6, 4.5 to 6, 2.5 to 5, 4 to 6, 2.5 to 4.5, 2.1 to 5.0, 2.1 to 4.0, 2.3 to 4.5, 2.4 to 5.5, 1.5 to 2.9, 1.6 to 2.9, 2.1 to 3.3, 1.6 to 3.0, 3 to 4.5, 3 to 5.5, 4.5 to 5.5, 4.1 to 4.9, 4.9 to 5.6, 5 to 6, or 5.5 to 6.

[0107] The present invention relates to the degree of alignment (OI) of the second carbon-based anode active material contained in the second anode active layer. 2nd By adjusting the parameters as described above, it is possible to secure an ion migration channel that allows lithium ions to move over a shorter distance 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 increasing the lithium ion migration speed during charging and discharging, and simultaneously improving rapid charging performance and output performance with high safety.

[0108] Specifically, conventional rapid charging of lithium secondary batteries employs a constant current-constant voltage (CC-CV) method, increasing the charging speed by charging under high C-rate conditions exceeding 1C rate. Generally, in constant current-constant voltage (CC-CV) charging, lithium ion diffusion within the electrodes proceeds in the constant current (CC) charging step, but prolonged diffusion inevitably causes concentration polarization. Such lithium ion concentration polarization easily causes lithium deposition on the negative electrode, especially under high-rate conditions where the charging current (A) exceeds the standard value (i.e., the current at 1C rate: 1A) compared to the rated capacity (Ah) of the secondary battery, thus significantly reducing the safety of the secondary battery. Furthermore, in high-rate constant current-constant voltage (CC-CV) charging, the upper voltage limit is reached at a very rapid rate in the constant current (CC) charging step, so the current may drop to a preset limit before the active material is completely consumed. In other words, the constant voltage (CV) charging step significantly increases the charging time, resulting in a problem where the reduction in the total charging time of the secondary battery is minimal.

[0109] However, since the present invention can ensure a short lithium ion migration path within the negative electrode active layer, the resistance induced in the negative electrode active layer during charging can be significantly reduced. Such resistance reduction can be induced so that, in a constant current-constant voltage (CC-CV) system, the execution time of the constant current (CC) charging step is longer than the execution time of the constant voltage (CV) charging step within the total charging time. Here, since the same amount of current flows in the constant current (CC) charging step, the charging capacity per unit time is the same, but in the constant voltage (CV) charging step, the current tends to be reduced in order to maintain the same voltage. That is, since the charging capacity per unit time decreases sharply in the constant voltage (CV) charging step, the total charging time can be significantly reduced as the execution time of the constant current (CC) charging step increases. Therefore, the present invention relates to the degree of alignment (OI) of the second carbon-based negative electrode active material. 2nd By controlling the constant current (CC) charging step, the execution time can be increased, thereby enabling the secondary battery to be fully charged in a significantly shorter time.

[0110] Furthermore, since rapid charging of such secondary batteries can be achieved not only under high C-rate conditions but also under standard conditions (e.g., 1C rate), it has the advantage of overcoming the safety issues of lithium secondary batteries caused by the concentration polarization phenomenon of lithium ions induced in the negative electrode active layer during charging.

[0111] The first carbon-based anode active material contained in the first anode active layer described above has such alignment (OI 1st ) can be in the range of 5 or more, specifically in the range of 5-20, 5-15, 5-13, 5-10, 8-20, 8-17, 8-15, 8-13, 8-10, 10-17, 10-14.5, 10-13, 10.5-12, 11-15, 15-19, or 9-14.

[0112] The degree of alignment of the first negative electrode active layer (OI 1stIf the degree of alignment (OI) of the first carbon-based anode active material contained in the first anode active layer is less than the lower limit of the above range, the adhesion force with the anode current collector may be reduced. Therefore, the present invention relates to the degree of alignment (OI) of the first carbon-based anode active material contained in the first anode active layer. 1st By adjusting the degree of alignment (OI) of the first negative electrode active layer as described above, the proportion of the crystal planes of the carbon-based negative electrode active material constituting the negative electrode active material particles that face the negative electrode current collector increases, thereby improving the adhesion between the first negative electrode active layer and the negative electrode current collector without reducing the rapid charging performance of the negative electrode. 1st If the above range exceeds the upper limit, lithium ions have difficulty easily inserting and removing from the first negative electrode active layer, which leads to a decrease in the negative electrode's charge / discharge capacity and a delay in charging time.

[0113] Furthermore, the first negative electrode active layer has an alignment degree (OI) represented by formula 1. 1st ) is the degree of alignment of the second negative electrode active layer (OI 2nd Based on the standard, the ratio can be 200% to 900%. Specifically, the degree of alignment of the first negative electrode active layer (OI 1st ) is the degree of alignment of the second negative electrode active layer (OI 2nd Based on ), the percentages are 200%~900%, 200%~700%, 200%~500%, 200%~400%, 210%~290%, 250%~400%, 370%~590%, 300%~500%, 400%~830%, 400%~700%, 400%~600%, 400%~550%, and 450%~7 The percentages can range from 50%, 210% to 450%, 600% to 800%, 600% to 900%, 410% to 580%, 410% to 500%, 410% to 490%, 510% to 580%, 420% to 450%, 440% to 500%, 460% to 550%, or 510% to 560%.

[0114] The present invention relates to the degree of alignment of the first negative electrode active layer (OI 1st ) and the degree of alignment of the second negative electrode active layer (OI 2nd ) Percentage (OI 1st / OI 2nd*100) can be controlled within the above range to prevent a decrease in adhesion force with the negative electrode current collector due to a value lower than the lower limit of the above range. Furthermore, the present invention can prevent a reduction in lithium ion migration speed due to a value higher than the upper limit of the above range, thereby further improving the charging speed of the secondary battery.

[0115] On the other hand, the first anode active layer and the second anode active layer according to the present invention may, as needed, further selectively contain conductive materials, binders, and other additives in addition to the carbon-based anode active material which is the main component.

[0116] The conductive material described above may contain one or more of the following: carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, etc., but is not limited to these.

[0117] For example, the first negative electrode active layer and the second negative electrode active layer may each contain carbon black and carbon fibers as conductive materials individually or in combination.

[0118] In this case, the content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 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 an increase in the resistance of the negative electrode due to a low content of conductive material, which reduces the charging capacity, and can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, which reduces the charging capacity, or a decrease in rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0119] Furthermore, the above-mentioned binder is a component that assists in the bonding of the negative electrode active material to conductive materials and to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the electrode. Specifically, the above-mentioned binder may contain one or more of the following: vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0120] The binder content may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active layer, specifically 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. By controlling the binder content in the negative electrode active layer within the above range, the present invention can prevent a decrease in the adhesive strength of the active layer due to a low binder content, or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0121] Furthermore, the average thickness of the overall negative electrode active layer of the negative electrode may be in the range of 50 μm to 500 μm, specifically in the ranges of 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, 100 μm to 250 μm, or 130 μm to 190 μm. By adjusting the average thickness of the negative electrode active layer to the above range, the present invention makes it possible to easily control the crystal properties of each carbon-based negative electrode active material contained in the first negative electrode active layer and the second negative electrode active layer. As a result, the negative electrode of the present invention not only can achieve high adhesion between the first negative electrode active layer and the negative electrode current collector, but also has the advantage of enabling rapid charging, which can complete charging in a short time even under standard conditions (1C rate).

[0122] The first and second anode active layers described above may have the same or different average thicknesses. Specifically, the average thickness (L1) of the first anode active layer can be in the range of 1% to 100% (L1 / L2) of the average thickness (L2) of the second anode active layer, and can be in the range of 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, 1% to 10%, 1% to 5%, 5% to 10%, 10% to 20%, or 15% to 30%. By adjusting the ratio of the average thickness of the first anode active layer within the above range, the present invention makes it possible to increase the charge / discharge capacity while maintaining high durability of the anode, and to maximize the output characteristics.

[0123] The negative electrode current collector described above is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, thin sheets or films containing copper, stainless steel, nickel, titanium, or calcined carbon can be used as the negative electrode current collector, and in the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc., can also be used. Furthermore, the average thickness of the negative electrode current collector can be appropriately applied from 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0124] The negative electrode according to the present invention has the above-described configuration, which results in high adhesion to the negative electrode current collector, and therefore exhibits excellent lifespan characteristics. Furthermore, lithium secondary batteries containing it have excellent output characteristics and the advantage of being able to be charged in a short time even at a 1C rate.

[0125] <Method for manufacturing a negative electrode>

[0126] Furthermore, one embodiment of the present invention is, Step (S1): Apply a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of the negative electrode current collector. Step (S2): Apply a second negative electrode slurry containing a second carbon-based negative electrode active material onto the applied first negative electrode slurry. Step (S3) of applying a magnetic field to a negative electrode current collector coated with a second negative electrode slurry, and Step (S4): Dry the first negative electrode slurry and the second negative electrode slurry to which a magnetic field has been applied to form the first negative electrode active layer and the second negative electrode active layer. The present invention provides a method for manufacturing a negative electrode, including the following:

[0127] The method for manufacturing a negative electrode according to the present invention refers to the method for manufacturing the negative electrode of the present invention as described above. The above method for manufacturing a negative electrode involves applying a negative electrode slurry onto a negative electrode current collector, applying a magnetic field to the surface of the applied negative electrode slurry, and then drying each negative electrode slurry, thereby enabling the production of a negative electrode having a negative electrode active layer in which the crystalline properties of the negative electrode active material are controlled.

[0128] Here, steps S1 and S2, which involve applying the negative electrode slurry, are steps of discharging and coating the surface of the moving negative electrode current collector with a negative electrode slurry containing a carbon-based negative electrode active material. This step can be applied without particular limitations as long as it is a method commonly used in the industry, but preferably a die coating method can be used. The die coating method can be performed via a slot die equipped with a shim for controlling the discharging conditions of the negative electrode slurry. In this case, by controlling the shape, position, etc., of the shim, the loading amount and coating thickness of the negative electrode slurry applied to the negative electrode current collector can be easily controlled.

[0129] In particular, the present invention allows for the simultaneous application of a first negative electrode slurry and a second negative electrode slurry onto a negative electrode current collector using a dual die. This has the advantage of significantly improving process efficiency compared to the case where each slurry is applied sequentially.

[0130] Furthermore, the first negative electrode slurry and the second negative electrode slurry each mainly contain a first carbon-based negative electrode active material and a second carbon-based negative electrode active material, respectively.

[0131] Specifically, the first anode slurry and the second anode slurry may contain the first carbon-based anode active material and the second carbon-based anode active material in amounts of 80 to 99.8 parts by weight relative to the total weight of each anode slurry, more specifically, in amounts of 95 parts by weight or more, 98 parts by weight or more, 84 to 99.8 parts by weight, 90 to 99.8 parts by weight, 94 to 99.8 parts by weight, 88 to 96 parts by weight, or 92 to 97.5 parts by weight.

[0132] The above-mentioned first negative electrode slurry and second negative electrode slurry can satisfy one or more of the following conditions in order to improve the charging performance of the negative electrode while increasing the adhesion between the negative electrode current collector and the first negative electrode active layer formed on the negative electrode current collector.

[0133] (Condition A) The ratio of the average particle size of the second carbon-based anode active material (D2) to the average particle size of the first carbon-based anode active material (D1) (D2 / D1): 2.0 or more.

[0134] (Condition B) The first negative electrode slurry contains a carbon structure,

[0135] (Condition C) The first negative electrode slurry and the second negative electrode slurry each contain the first thickener and the second thickener, respectively.

[0136] If the first negative electrode slurry satisfies (condition A) and / or (condition B), the specific surface area of ​​the particles contained in the first negative electrode slurry can be increased, thereby directly increasing the interfacial adhesion between the first negative electrode active layer formed from the first negative electrode slurry and the negative electrode current collector.

[0137] Furthermore, by satisfying one or more of the above three conditions, the viscosity of the first negative electrode slurry at room temperature can be made higher than that of the second negative electrode slurry. The high viscosity at room temperature aligns the (002) crystal plane of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector at an angle lower than 90° when the carbon-based negative electrode active material is oriented using a magnetic field. This ensures a short lithium migration path in the formed negative electrode active layer while preventing a decrease in the adhesion between the negative electrode current collector and the first negative electrode active layer.

[0138] (Condition A) The above-mentioned first negative electrode slurry and second negative electrode slurry are defined by the form and / or average particle size (D) of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material contained in each negative electrode slurry. 50 ) may differ.

[0139] Specifically, the first negative electrode slurry has a relatively lower average particle size (D) compared to the second carbon-based negative electrode active material. 50 It can contain a first carbon-based anode active material with a small ) value, which allows for a higher viscosity at room temperature than the second anode slurry.

[0140] Specifically, the average particle size (D1) of the first carbon-based anode active material may be in the range of less than 5 μm. For example, the average particle size (D1) of the first carbon-based anode active material may be in the range of 0.1 μm to 4.9 μm, 0.5 μm to 4.9 μm, 0.5 μm to 4.5 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.5 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.5 μm, 1.0 μm to 4.6 μm, 1.5 μm to 4.9 μm, 2.0 μm to 4.9 μm, 2.5 μm to 4.9 μm, 0.8 μm to 1.5 μm, 2.5 μm to 3.5 μm, 2.7 μm to 4.6 μm, 3.5 μm to 4.9 μm, or 4.1 μm to 4.9 μm.

[0141] The first carbon-based anode active material described above consists of primary particles with an average particle size (D1) of less than 5 μm. Since the specific surface area can be significantly increased in proportion to the small particle size, the contact area between the carbon-based anode active material in the first anode slurry and the surface of the anode current collector can be increased, thereby strengthening the adhesion between the anode current collector and the first anode active layer. However, if the average particle size (D1) of the first carbon-based anode active material is lower than the lower limit of the above range, a large amount of binder will be required due to the increased number of particles per unit volume, which may degrade the electrical properties of the anode active layer containing these binders. Furthermore, if the average particle size (D1) of the first carbon-based anode active material is higher than the upper limit of the above range, the specific surface area of ​​the first carbon-based anode active material is significantly reduced, resulting in only a slight improvement in the adhesion between the anode current collector and the first anode active layer.

[0142] The ratio (D2 / D1) of the average particle size (D2) of the second carbon-based anode active material to the average particle size (D1) of the first carbon-based anode active material may be 2.0 or greater, and more specifically, the ratio (D2 / D1) may be in the range of 2.0-15, 2.0-13, 2.0-11, 2.0-9.0, 2.0-7.0, 2.0-6.0, 2.0-5.0, 3.0-8.0, 3.0-7.0, 3.0-4.5, 4.0-7.0, 5.0-7.0, 4.0-10, 4.0-9.0, 6.0-11, 8.0-14, 9.0-13, or 3.1-5.5.

[0143] Furthermore, the first carbon-based anode active material contained in the first anode slurry may have a spheroidization degree of 0.9 or higher, while the second carbon-based anode active material contained in the second anode slurry may have a spheroidization degree of less than 0.9.

[0144] For example, the above-mentioned first carbon-based anode active material may have a degree of spheroidization in the range of 0.90-1.00, 0.90-0.99, 0.92-0.98, 0.95-0.99, 0.92-0.97, 0.95-0.98, or greater than 0.90 but less than 1.0. Furthermore, the above-mentioned second carbon-based anode active material may have a degree of spheroidization in the range of 0.10-0.75, 0.25-0.75, 0.25-0.70, 0.25-0.60, 0.25-0.50, 0.25-0.40, 0.40-0.65, 0.50-0.70, 0.50-0.65, 0.60-0.75, 0.20-0.35, 0.10-0.40, 0.40-0.50, or 0.2 or more and less than 0.7.

[0145] In this invention, "degree of spheroidization" can mean 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 in two dimensions. When the degree of spheroidization is 1, the particle can have a spherical shape. The degree of spheroidization can be determined by measuring it using a particle shape analyzer, or by measuring the particle's morphology using a scanning electron microscope (SEM) or energy-dispersive spectrometer, and then analyzing the measured results.

[0146] If the above-mentioned first negative electrode slurry and second negative electrode slurry satisfy (condition A), they can have a room temperature viscosity in the range of 7,000 mPa·s or more at 25°C. Specifically, the above room temperature viscosity is in the ranges of 7,000 mPa·s to 20,000 mPa·s, 7,000 mPa·s to 18,000 mPa·s, 7,000 mPa·s to 16,000 mPa·s, 7,000 mPa·s to 13,000 mPa·s, 7,000 mPa·s to 10,000 mPa·s, 7,000 mPa·s to 9,000 mPa·s, 8,000 mPa·s to 10,000 mPa·s, and 9,000 mPa·s to 11,000 mPa·s. It can have a room-temperature viscosity in the range of mPa·s, 7,500mPa·s to 8,500mPa·s, 11,000mPa·s to 20,000mPa·s, 12,000mPa·s to 19,000mPa·s, 12,500mPa·s to 18,500mPa·s, 14,000mPa·s to 18,000mPa·s, 15,000mPa·s to 17,500mPa·s, or 7,000mPa·s to 7,500mPa·s.

[0147] The above-mentioned second negative electrode slurry can have a room temperature viscosity in the range of less than 7,000 mPa·s at 25°C, specifically in the ranges of 3,000 mPa·s to 6,900 mPa·s, 3,000 mPa·s to 5,000 mPa·s, 4,000 mPa·s to 6,000 mPa·s, 5,000 mPa·s to 6,500 mPa·s, 3,000 mPa·s to 3,500 mPa·s, 6,100 mPa·s to 6,900 mPa·s, or 4,500 mPa·s to 5,900 mPa·s.

[0148] (Condition B) Furthermore, the first negative electrode slurry may include a carbon structure having a predetermined size while satisfying condition B. In this case, the carbon structure refers to a compound having an average size on the nanometer (nm) level and whose main component is carbon atoms (C).

[0149] The carbon structure described above may include one or more of the following, having an average size on the nanometer (nm) level: carbon nanotubes, carbon nanofilaments, nanofibers, fullerenes, graphene, and graphite.

[0150] For example, the carbon structure described above may include carbon nanotubes containing one or more types of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Since carbon nanotubes have a size on the nanometer (nm) level and exhibit strong interparticle interactions, the viscosity of the first negative electrode slurry containing them can be significantly increased. Furthermore, the carbon nanotubes have a linear structure and can increase electrical conductivity by forming an inter-carbon nanotube network within the first negative electrode active layer.

[0151] The above carbon structure can have an average size in the range of 5nm to 900nm, specifically an average size in the range of 5nm to 750nm, 5nm to 500nm, 5nm to 250nm, 5nm to 100nm, 50nm to 200nm, 50nm to 400nm, 100nm to 500nm, 100nm to 250nm, 250nm to 500nm, 300nm to 700nm, 500nm to 900nm, 700nm to 900nm, 600nm to 800nm, 150nm to 300nm, 10nm to 90nm, 50nm to 90nm, 50nm to 150nm, 110nm to 390nm, or 310nm to 490nm.

[0152] The above carbon structure can be applied to the first negative electrode slurry within a predetermined content range. Specifically, the carbon structure can be included in the first negative electrode slurry in an amount ranging from 0.001% by weight to 10% by weight, based on the solid content. More specifically, the carbon structures may be present in amounts ranging from 0.001% to 9% by weight, 0.001% to 7% by weight, 0.001% to 5% by weight, 0.001% to 3% by weight, 0.001% to 1% by weight, 0.001% to 0.5% by weight, 0.01% to 0.5% by weight, 0.1% to 2% by weight, 1% to 10% by weight, 1% to 8% by weight, 1% to 6% by weight, 1% to 5% by weight, 1% to 3% by weight, 3% to 8% by weight, 6% to 9% by weight, 5% to 8% by weight, 2% to 4% by weight, or 1.5% to 4.5% by weight, based on the solid content of the first anode slurry. The content of the carbon structures may be adjusted depending on the type and average size applied to the first anode slurry.

[0153] For example, the first negative electrode slurry described above may contain single-walled carbon nanotubes (SWCNTs) as carbon structures in an amount ranging from 0.01% to 0.9% by weight relative to the solid content of the first negative electrode slurry.

[0154] Furthermore, the first negative electrode slurry may contain multi-walled carbon nanotubes (MWCNTs) as carbon structures in an amount ranging from 1% to 8% by weight relative to the solid content of the first negative electrode slurry.

[0155] If the above first negative electrode slurry satisfies (condition B), it can have a relatively higher viscosity than the second negative electrode slurry at room temperature. For example, the above first negative electrode slurry can have a viscosity in the range of 11,000 mPa·s or more at room temperature. For example, the above first negative electrode slurry can have a viscosity in the range of 11,000 mPa·s to 25,000 mPa·s, 11,000 mPa·s to 20,000 mPa·s, 17,000 mPa·s to 20,000 mPa·s, 11,000 mPa·s to 18,000 mPa·s, 11,000 mPa·s to 16,000 mPa·s, 11,000 mPa·s to 15,000 mPa·s, 13,000 mPa·s to 25,000 mPa·s at room temperature. It can have viscosities in the range of 15,000 mPa·s to 25,000 mPa·s, 17,000 mPa·s to 25,000 mPa·s, 20,000 mPa·s to 25,000 mPa·s, 13,000 mPa·s to 19,000 mPa·s, 14,000 mPa·s to 17,000 mPa·s, 16,000 mPa·s to 19,000 mPa·s, or 15,000 mPa·s to 18,000 mPa·s.

[0156] The above-mentioned second negative electrode slurry can have a viscosity in the range of less than 10,000 mPa·s at 25°C. For example, the above-mentioned second negative electrode slurry can have a viscosity in the range of 3,000 mPa·s to 9,000 mPa·s, 3,000 mPa·s to 8,000 mPa·s, 3,000 mPa·s to 7,000 mPa·s, 5,000 mPa·s to 7,000 mPa·s, 4,000 mPa·s to 6,500 mPa·s, 5,000 mPa·s to 6,500 mPa·s, 3,000 mPa·s to 5,500 mPa·s, 5,500 mPa·s to 6,500 mPa·s, or 5,500 mPa·s to 6,900 mPa·s at 25°C.

[0157] (Condition C) Furthermore, the first negative electrode slurry and the second negative electrode slurry satisfy (condition C) and contain a first thickener and a second thickener, respectively. In the present invention, the first thickener and the second thickener are included in the same proportion based on the solid content of the negative electrode slurry to constitute each negative electrode active layer (i.e., the total weight of the negative electrode active layer), and the viscosity of the first negative electrode slurry can be made higher than that of the second negative electrode slurry by making the concentration of the first thickener solution applied to the first negative electrode slurry higher than the concentration of the second thickener solution applied to the second negative electrode slurry.

[0158] The first and second thickeners described above can be those commonly used in the industry to control the viscosity of electrode slurries. Specifically, the first and second thickeners may each contain one or more of the following: carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), poly-N-vinylacetamide (PNVA), styrene-butadiene rubber (SBR), acrylic resins, and fluororesins.

[0159] The first and second thickeners described above may be included in amounts of 0.5% to 3% by weight, based on the solid content of the first and second negative electrode slurry, respectively. Specifically, they may be included in amounts of 0.5% to 2% by weight, 0.5% to 1% by weight, 1% to 3% by weight, 1% to 2% by weight, 1.5% to 3% by weight, 0.5% to 1.9% by weight, or 1.1% to 1.9% by weight.

[0160] For example, the first and second thickening agents are each carboxymethylcellulose (CMC), and may be included in an amount of 1.2% to 1.7% by weight based on the solid content of each negative electrode slurry.

[0161] The first and second thickeners described above can be applied to the anode slurry in solution form during the manufacturing of each anode slurry. In this case, each solution containing the first and second thickeners contains the thickeners in the same weight ratio relative to the total weight of the solids in the anode slurry to which they are applied, but the concentrations can be adjusted to be different.

[0162] For example, the concentration of the solution containing the second thickener can be adjusted to a range of 0.5% by weight to 1.5% by weight based on the total weight of the solution, specifically to a range of 0.5% to 1.1% by weight, 0.5% to 0.9% by weight, 1.0% to 1.5% by weight, or 0.8% to 1.2% by weight.

[0163] Furthermore, the concentration of the solution containing the first thickener can be in the range of 150% to 250% of the concentration of the solution containing the second thickener, specifically, it can be in the range of 150% to 230%, 150% to 210%, 150% to 190%, 180% to 250%, 210% to 250%, 170% to 230%, or 190% to 210% of the concentration of the solution containing the second thickener.

[0164] The present invention prevents the thickeners from being uniformly dispersed in the negative electrode slurry at concentrations exceeding the upper limit of the above range, by adjusting the concentrations of the solutions containing the first and second thickeners to satisfy the above range. Furthermore, it prevents a decrease in the solid content of the negative electrode slurry at concentrations lower than the lower limit of the above range.

[0165] The above-mentioned first negative electrode slurry and second negative electrode slurry can be applied in the same proportion while satisfying (condition C), and the room temperature viscosity of the first negative electrode slurry can be made relatively higher than the room temperature viscosity of the second negative electrode slurry.

[0166] Specifically, the first negative electrode slurry can have a room temperature viscosity in the range of 7,000 mPa·s or more at 25°C. For example, the first negative electrode slurry can have a viscosity of 7,000 mPa·s to 20,000 mPa·s, 7,000 mPa·s to 19,000 mPa·s, 7,000 mPa·s to 15,000 mPa·s, 7,000 mPa·s to 13,000 mPa·s, 7,000 mPa·s to 11,000 mPa·s, 11,000 mPa·s to 19,000 mPa·s, and 13,000 mPa·s at 25°C. It can have a room-temperature viscosity in the range of ~18,000 mPa·s, 15,000 mPa·s~18,000 mPa·s, 7,000 mPa·s~9,000 mPa·s, 8,000 mPa·s~10,000 mPa·s, 9,000 mPa·s~11,000 mPa·s, 7,000 mPa·s~8,500 mPa·s, or 7,100 mPa·s~7,900 mPa·s.

[0167] The above-mentioned second negative electrode slurry may have a room temperature viscosity in the range of less than 5,000 mPa·s at 25°C. For example, the above-mentioned second negative electrode slurry may have a room temperature viscosity in the range of 1,000 mPa·s to 4,900 mPa·s, 1,500 mPa·s to 4,500 mPa·s, 2,500 mPa·s to 4,000 mPa·s, 3,500 mPa·s to 4,500 mPa·s, 4,000 mPa·s to 4,500 mPa·s, 3,100 mPa·s to 3,900 mPa·s, or 3,100 mPa·s to 4,500 mPa·s at 25°C.

[0168] On the other hand, the first negative electrode slurry and the second negative electrode slurry can each have a solid content in the range of 35% to 80%, and more specifically, they can have a solid content in the range of 35% to 70%, 35% to 60%, 35% to 50%, 40% to 60%, 45% to 70%, 60% to 75%, 45% to 65%, 45% to 55%, or 50% to 60%.

[0169] Furthermore, step S3, which involves applying a magnetic field to the negative electrode slurry, can be interpreted as a process for controlling the crystal plane characteristics of the carbon-based negative electrode active material contained in the negative electrode slurry. Specifically, step S3 involves applying a magnetic field to the surface of the second negative electrode slurry coated on the negative electrode current collector, thereby aligning the ab-axis crystal planes of each carbon-based negative electrode active material contained in the second negative electrode slurry and the first negative electrode slurry located beneath it, so that they have a high angle with respect to the negative electrode current collector.

[0170] The above magnetic field application can be achieved by magnets positioned above and below a negative electrode current collector that is moved with a negative electrode slurry applied to its surface. In this case, the polarities of the magnets positioned above and below may be different.

[0171] The degree of alignment (OI) of the carbon-based anode active material contained in each anode slurry can be adjusted by the strength and duration of the applied magnetic field, thereby enabling the step of applying the magnetic field to be carried out under predetermined magnetic field strength conditions.

[0172] Specifically, in step S3, where the above magnetic field is applied, a magnetic field in the range of 10,000 G (Gauss) or less can be applied. For example, in step S3, where the above magnetic field is applied, a magnetic field can be applied with an intensity in the range of 3,000G~10,000G, 5,000G~10,000G, 7,000G~10,000G, 3,000G~8,000G, 5,000G~8,000G, 5,500G~6,500G, 1,000G~7,000G, 2,000G~6,000G, 1,500G~5,000G, 1,500G~4,500G, 4,000G~7,000G, 2,000G~4,000G, 2,500G~3,500G, 3,000G~6,500G, or 2,700G~3,300G.

[0173] Furthermore, step S3, in which the above magnetic field is applied, can be performed for 1 to 60 seconds, specifically 1 to 45 seconds, 1 to 30 seconds, 10 to 30 seconds, 30 to 50 seconds, 1 to 15 seconds, 1 to 10 seconds, 5 to 20 seconds, 10 to 20 seconds, 11 to 18 seconds, 1 to 9 seconds, 1 to 5 seconds, 7 to 13 seconds, or 6 to 11 seconds.

[0174] For example, in the step of applying the magnetic field described above, a magnetic field in the range of 6,000 ± 50 G can be applied to the negative electrode slurry for 3 to 7 seconds, or 8 to 12 seconds.

[0175] Furthermore, step S3, in which the magnetic field is applied, is performed by magnets introduced to the upper and lower parts of the coated negative electrode slurry, as described above, and the size of the magnets can be adjusted to be larger than the size of the negative electrode slurry so that the magnetic field applied to the negative electrode slurry can be applied uniformly to the entire surface of the negative electrode slurry. For example, the magnets can have a length ratio in the range of 105% to 200% with respect to the width of the negative electrode slurry, and specifically, they can 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% with respect to the width of the negative electrode slurry.

[0176] In the present invention, by controlling the magnetic field strength, application time, and / or the size of the magnet in step S3, as described above, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be made uniform to satisfy a predetermined range.

[0177] When a magnetic field is applied to the first and second negative electrode slurries through step S3, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material contained in each negative electrode slurry can be oriented such that their respective crystal planes have a predetermined inclination with respect to the negative electrode current collector.

[0178] In this case, the first negative electrode slurry and the second negative electrode slurry satisfy one or more of the above-mentioned conditions A to C, and the room-temperature viscosity of the first negative electrode slurry can be controlled to be relatively larger than the room-temperature viscosity of the second negative electrode slurry. Therefore, when a magnetic field is applied to each negative electrode slurry in step S3, the degree to which the crystal planes of each carbon-based negative electrode active material contained in each negative electrode slurry are oriented relative to the negative electrode current collector may differ. This can be confirmed by measuring X-ray diffraction after drying the negative electrode slurry.

[0179] Specifically, if the viscosity of the first negative electrode slurry is high at room temperature, the movement of the first carbon-based negative electrode active material is restricted when a magnetic field is applied, making it difficult for the crystal planes of the first carbon-based negative electrode active material to align. Therefore, in the present invention, by making the first negative electrode slurry have a higher viscosity at room temperature than the second negative electrode slurry, the degree of alignment of the first carbon-based negative electrode active material (OI) when measuring X-ray diffraction for each negative electrode active layer after magnetic field application and drying is improved in the negative electrode slurry. 1st ) is the degree of alignment of the second carbon-based anode active material (OI 2nd It can be significantly increased to over 200% based on the baseline.

[0180] For example, the second negative electrode active layer formed from the above second negative electrode slurry has a degree of alignment of the second carbon-based negative electrode active material (OI 2nd ) can be in the range of 0.5 to 6, specifically in the range of 1 to 5, 1 to 3, 1.5 to 6, 3 to 6, 4.5 to 6, 2.5 to 5, 4 to 6, 2.5 to 4.5, 2.1 to 5.0, 2.1 to 4.0, 2.3 to 4.5, 2.4 to 5.5, 1.5 to 2.9, 1.6 to 2.9, 2.1 to 3.3, 1.6 to 3.0, 3 to 4.5, 3 to 5.5, 4.5 to 5.5, 4.1 to 4.9, 4.9 to 5.6, 5 to 6, or 5.5 to 6.

[0181] Furthermore, the degree of alignment (OI) of the first negative electrode active layer formed from the first negative electrode slurry. 1st ) is the degree of alignment (OI) of the second negative electrode active layer formed from the second negative electrode slurry. 2ndThe ratio can be in the range of 200% to 900% based on the degree of alignment of the first negative electrode active layer (OI 1st ) is the degree of alignment of the second negative electrode active layer (OI 2nd Based on ), the percentages are 200%~900%, 200%~700%, 200%~500%, 200%~400%, 210%~290%, 250%~400%, 370%~590%, 300%~500%, 400%~830%, 400%~700%, 400%~600%, 400%~550%, and 450%~7 The percentages can range from 50%, 210% to 450%, 600% to 800%, 600% to 900%, 410% to 580%, 410% to 500%, 410% to 490%, 510% to 580%, 420% to 450%, 440% to 500%, 460% to 550%, or 510% to 560%.

[0182] Furthermore, step S4, which forms the negative electrode active layer, may include step S4-1, which dries the negative electrode slurry to which a magnetic field has been applied.

[0183] In this case, step S4-1, which dries the negative electrode slurry, can be applied without particular limitations, as long as it is a method that can maintain the orientation of the carbon-based negative electrode active material contained in the first negative electrode slurry and the second negative electrode slurry, respectively. For example, step S4-1, which dries the negative electrode slurry, can be performed by applying thermal energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0184] Step S4, which forms the negative electrode active layer, may further include step S4-2, which involves drying the negative electrode slurry to form the negative electrode active layer and then rolling it. Step S4-2, which involves rolling the negative electrode active layer, is a step in which pressure is applied to the surface of the formed negative electrode active layer (specifically, the surface of the second negative electrode active layer) using a roll press or the like to increase the overall density of the negative electrode active layer. At this time, the rolling can be carried out under temperature conditions higher than room temperature.

[0185] For example, the above rolling can be carried out at temperatures in the range of 50°C to 100°C, specifically 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.

[0186] Furthermore, the above rolling can be carried out at rolling speeds in the range of 2 m / s to 7 m / s, specifically at rolling speeds in the range 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.

[0187] The above rolling can be carried out under pressure conditions ranging from 50 MPa to 200 MPa, specifically under pressure conditions ranging from 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0188] The present invention makes it possible to increase the energy density of the anode while minimizing changes in the alignment of each carbon-based anode active material contained in the first anode active layer and the second anode active layer formed by performing rolling under the above temperature, speed, and / or pressure conditions.

[0189] The negative electrode manufacturing method according to the present invention, having the above-described configuration, allows for easy control of the alignment (OI) of each negative electrode active layer to satisfy a predetermined range. Therefore, the negative electrode manufactured by the above manufacturing method has excellent lifespan characteristics, and the lithium secondary battery containing it has the advantage of not only having excellent output characteristics but also being able to be charged in a short time even at a 1C rate.

[0190] <Lithium-ion secondary battery>

[0191] Furthermore, the present invention is An electrode assembly comprising a positive electrode, a negative electrode of the present invention as described above, and a separation membrane disposed between the positive electrode and the negative electrode, The electrolyte composition in which the electrode assembly is impregnated, We provide lithium secondary batteries, including [specific components / features].

[0192] The lithium secondary battery according to the present invention includes an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are arranged alternately, with a separator membrane placed between them. The above lithium secondary battery, equipped with the negative electrode of the present invention described above, not only has excellent lifespan characteristics and output characteristics, but can also be charged in a short time even at a 1C rate, making it significantly usable as power for medium- and large-scale devices such as electric vehicles.

[0193] Here, the negative electrode has the same configuration as described above, so a detailed explanation will be omitted.

[0194] Furthermore, the positive electrode includes a positive electrode active layer containing a positive electrode active material on at least one surface of the positive electrode current collector, and the positive electrode active layer may optionally further contain conductive materials, binders, other additives, etc.

[0195] The above-mentioned positive electrode active material is a substance capable of undergoing electrochemical reactions and may include one or more lithium metal oxides represented by the following chemical formulas 1 and 2, which are capable of reversible intercalation and deintercalation of lithium ions.

[0196] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0197] [Chemical formula 2] LiM 2 p Mn q P r O4

[0198] In the above chemical formulas 1 and 2, M 1It is one or more elements 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 such that 1.0 ≤ x ≤ 1.30, 0.5 ≤ y < 1, and 0 respectively. <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 It is Ni, Co, or Fe, p is 0.05 ≤ p ≤ 1.0, q is 2-p, r is either 0 or 1.

[0199] The lithium metal oxide represented by the above chemical formula 1 is a metal oxide containing lithium along with nickel (Ni), cobalt (Co), and manganese (Mn). It has the advantage of containing a high amount of nickel (Ni), which allows for the stable supply of high-capacity and / or high-voltage electricity.

[0200] The lithium metal oxide represented by the above chemical formula 1 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.9 Co 0.05 Mn 0.05 O2, LiLiLi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiLiLi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiLiLi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may contain O2 and other elements, and these can be used alone or in combination.

[0201] In addition, the lithium metal oxide represented by the above chemical formula 2 is an iron phosphate compound having an olivin structure, and has the advantages of being most excellent in structural stability, having excellent life characteristics, and being excellent in all safety aspects including overcharge and overdischarge.

[0202] Examples of the lithium metal oxide represented by the above chemical formula 2 include LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, etc., and these can be used alone or in combination.

[0203] In addition, the above positive electrode active material can be contained at 85% by weight or more based on the weight of the entire positive electrode active layer, and specifically can be contained at 90% by weight or more, 93% by weight or more, or 95% by weight or more.

[0204] In addition, the above positive electrode active layer can further contain a conductive material, a binder, other additives, etc. together with the positive electrode active material.

[0205] Here, the above conductive material is used to improve the electrical performance of the positive electrode, and those commonly used in the industry can be applied. Specifically, it can contain one or more of natural graphite, artificial graphite, carbon black, acetylene black, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0206] In addition, the above conductive material can be contained at 0.1% by weight to 5% by weight based on the weight of the entire positive electrode active layer, and specifically can be contained at 0.1% by weight to 4% by weight, 2% by weight to 4% by weight, 1.5% by weight to 5% by weight, 1% by weight to 3% by weight, 0.1% by weight to 2% by weight, or 0.1% by weight to 1% by weight.

[0207] Furthermore, the binder plays a role in binding the positive electrode active material, positive electrode additive, and conductive material to each other, and any binder having this function can be used without particular limitations. Specifically, the binder can include one or more resins from among polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As one example, the binder can include polyvinylidene fluoride.

[0208] Furthermore, the above binder can be included in an amount of 1% to 10% by weight based on the total weight of the positive electrode active layer, specifically in an amount of 2% to 8% by weight, or 1% to 5% by weight.

[0209] The average thickness of the positive electrode active layer described above is not particularly limited, but it may be in the range of 50 μm to 300 μm, and more specifically, it may be in the range of 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0210] Furthermore, the positive electrode can be made of a material that has high conductivity without inducing chemical changes in the battery. For example, thin sheets or films containing stainless steel, aluminum, nickel, titanium, or calcined carbon can be used as the positive electrode current collector. If aluminum or stainless steel is included, the thin sheets or films may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector can be appropriately set between 3 μm and 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0211] The above-mentioned separation membrane is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry. Specifically, the above-mentioned separation membrane may contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer. The above-mentioned separation membrane may have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above-mentioned polymer, and may also have the form of a composite separation membrane in which organic or inorganic particles are coated with an organic binder on the above-mentioned porous polymer substrate. Furthermore, the above-mentioned separation membrane may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0212] On the other hand, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery that includes a stacked type, a zigzag type, or a zigzag-stack type electrode assembly.

[0213] For example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a prismatic secondary battery. Pouch-type secondary batteries and / or prismatic secondary batteries have the advantage of being highly usable in terms of energy density because they can pack the unit cells of the secondary battery at high density within a limited space.

[0214] In the lithium secondary battery described above, the electrolyte composition can be used without particular limitations, as long as it is one that is normally applied to lithium secondary batteries.

[0215] Specifically, the above-mentioned electrolyte composition may include a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0216] The above non-aqueous organic solvent can be applied without particular limitation as long as it is used in non-aqueous electrolytes in the art. For example, as the above non-aqueous organic solvent, N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate (PC), propylene carbonate, 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, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP) and other aprotic organic solvents can be used.

[0217] In addition, the non-aqueous organic solvent used in the present invention may be used alone or in combination of two or more in any combination and ratio according to the application. Among them, from the viewpoints of electrochemical stability against oxidation-reduction and chemical stability regarding reaction with heat and solute, it is particularly preferable that propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed.

[0218] The above lithium salt can be applied without particular limitation as long as it is used in non-aqueous electrolytes in the art. Specifically, the above lithium salt can contain one or more of LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0219] The lower limit of the appropriate concentration range for the above lithium salt is 0.5 mol / L or higher, specifically 0.7 mol / L or higher, and more specifically 0.9 mol / L or higher. The upper limit of the appropriate concentration range is 2.5 mol / L or lower, specifically 2.0 mol / L or lower, and more specifically 1.5 mol / L or lower. If the lithium salt concentration falls below 0.5 mol / L, the ionic conductivity decreases, which may reduce the cycle characteristics and output characteristics of the non-aqueous electrolyte battery. Furthermore, if the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the non-aqueous electrolyte battery increases, which may also reduce the ionic conductivity and potentially reduce the cycle characteristics and output characteristics of the non-aqueous electrolyte battery.

[0220] Furthermore, dissolving a large amount of lithium salt in a non-aqueous organic solvent at once may cause the electrolyte temperature to 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 in this way, in the case of lithium salts containing fluorine, decomposition may be accelerated and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is undesirable because it causes deterioration of battery performance. Therefore, the temperature at which the above lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to -20°C to 80°C, and more specifically, to 0°C to 60°C.

[0221] Furthermore, the above-mentioned electrolyte additives may be included as additional auxiliary components to improve the physical properties of the electrolyte composition. Generally used electrolyte additives may be added to the non-aqueous electrolyte of the present invention in any proportion. Specifically, examples include compounds having overcharge prevention effects, negative electrode film formation effects, and positive electrode protection effects, such as cyclohexylbenzene, biphenyl, t-butylbenzene, carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propanesultone, succinonitrile, and dimethylvinylene carbonate. Also, similar to its use in non-aqueous electrolyte batteries called lithium polymer batteries, the electrolyte for non-aqueous electrolyte batteries can be pseudo-solidified using a gelling agent and a crosslinking polymer.

[0222] The lithium secondary battery according to the present invention has the advantage of not only having excellent battery life characteristics and output characteristics due to the above-described configuration, but also being able to be charged in a short time even at a 1C rate.

[0223] The present invention will be described in more detail below with reference to examples and comparative examples.

[0224] However, the following examples and comparative examples are illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0225] Measurement method

[0226] <Normal temperature viscosity> The measurement was performed using a B-type rotational viscometer at 25°C and a shear rate of 12 rpm.

[0227] <Orderliness (OI)> X-ray diffraction (XRD) spectroscopy was performed on the first and second anode active layers of each anode manufactured in the examples or comparative examples, and the spectra were measured. In the case of the first anode active layer, after the X-ray diffraction (XRD) measurement of the second anode active layer, the second anode active layer was peeled off and removed, and then X-ray diffraction was measured on the exposed surface of the first anode active layer. The X-ray diffraction (XRD) measurement conditions were as follows.

[0228] - Target: Cu (Kα-ray) graphite monochromator - Slit: Divergent slit = 1°, Receiving slit = 0.1 mm, Scattering slit = 1° - Measurement area: (110) plane: 76.0°<2θ<79.0° / (004) plane: 53.0°<2θ<57.0°.

[0229] From the spectra measured under the above conditions, the average alignment (OI) of the carbon-based active material contained in each negative electrode active layer was calculated using Equation 1.

[0230] [Formula 1] OI=I004 / I 110

[0231] In Equation 1, I 004 This represents the area of ​​the peak indicating the (004) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer. I 110 This represents the area of ​​the peak indicating the (110) crystal plane of the carbon-based anode active material during X-ray diffraction (XRD) spectroscopy analysis of the anode active layer.

[0232] <Adhesion strength between negative electrode current collector and negative electrode active layer> Each negative electrode manufactured in the examples or comparative examples was cut to a length of 20 mm horizontally and 70 mm vertically to prepare specimens. The prepared specimens were attached to a glass plate using double-sided tape, with the current collector facing the glass plate. After fixing the specimens to the glass plate, they were fixed to a tensile testing machine, and the negative electrode active layer of each negative electrode was pulled at a speed of 100 mm / min at 25°C so that it formed a 90° angle with the negative electrode current collector to detach it. The peeling force measured in real time at this time was defined as the interfacial adhesion force between the negative electrode current collector and the negative electrode active layer.

[0233] <1C rate charging time> LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared and mixed with polyvinylidene fluoride and N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 as a carbon-based conductive material and binder to form a slurry. This slurry was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to produce a cathode.

[0234] A 1Ah class lithium secondary battery was assembled by interposing an 18 μm polypropylene separation membrane between the positive electrode obtained above and each negative electrode manufactured in the example or comparative example, inserting them into a case, and then injecting the electrolyte composition.

[0235] Each lithium secondary battery was charged under CC-CV conditions to 4.2 V at a rate of 0.3 C at 25°C, and discharged under CC conditions to 2.5 V at a rate of 0.3 C for activation.

[0236] Each activated lithium secondary battery was charged by a constant current-constant voltage (CC-CV) method at a temperature of 25°C, and the time required for the state of charge (SOC) to reach 90% was measured. At this time, in the above charging, constant current (CC) charging was performed at a current of 1.0 C rate until the voltage reached 4.2 V, and then 4.2 V was maintained, and constant voltage (CV) charging was performed until the current reached 0.005 C rate and then cut-off. The measured charging time was defined as the time for rapid charging at 1 C rate.

[0237] Examples 1 to 9 and Comparative Examples 1 to 3. Production of negative electrode I

[0238] Natural graphite and artificial graphite were prepared as carbon-based negative electrode active materials, and styrene-butadiene rubber (SBR) was prepared as a binder.

[0239] Thereafter, 97.5 parts by weight of the first carbon-based negative electrode active material and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water so that the solid content became 50% to produce a first negative electrode slurry.

[0240] Also, 97.5 parts by weight of the second carbon-based negative electrode active material and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water so that the solid content became 50% to produce a second negative electrode slurry.

[0241] At this time, the (1) type, (2) average particle size (D 50 ) and (3) sphericity of each carbon-based negative electrode active material were adjusted as shown in Table 1.

[0242] After each negative electrode slurry was prepared, the first negative electrode slurry and the second negative electrode slurry were simultaneously cast on a copper thin plate (thickness: 10 μm) that was being transferred roll-to-roll (transfer speed: 5 m / min) using a die coater.

[0243] Permanent magnets having a length ratio of 110% to 120% of the width of the negative electrode slurry were placed on the upper part of the coated negative electrode slurry and on the lower part of the negative electrode current collector, and a magnetic field was applied at a magnetic field strength of 6,000 ± 20 G for 4 to 6 seconds. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a configuration in which the first negative electrode active layer and the second negative electrode active layer were sequentially laminated on the negative electrode current collector. The formed negative electrode active layers were rolled at a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s at 50 ± 1 °C to produce a negative electrode (average thickness of the first negative electrode active layer and the second negative electrode active layer: 60 ± 5 μm and 160 ± 5 μm, respectively).

[0244] [Table 1]

[0245] [Table 2]

[0246] [Table 3]

[0247] Comparative Examples 4-6. Manufacturing of the Negative Electrode II

[0248] As carbon-based negative electrode active materials, we prepared artificial graphite I with an average particle size of approximately 3.0 μm and a spheroidization degree of 0.95, artificial graphite II with an average particle size of approximately 15 μm and a spheroidization degree of 0.45, and natural graphite I with an average particle size of approximately 3.0 μm and a spheroidization degree of 0.95.

[0249] The anode was manufactured in the same manner as in Example 2, except that graphite, prepared as a carbon-based anode active material, was applied as shown in Table 4 below to form a single-layer anode active layer (average thickness: 220 ± 10 μm).

[0250] Also, the degree of alignment (O.I) of each negative electrode produced by performing the same method as in Example 2 with respect to the negative electrode active layer was calculated, and the results are shown in Table 4 below.

[0251]

Table 4

[0252] Experimental Example 1

[0253] To evaluate the performance of the negative electrode according to the present invention, the adhesive force between the negative electrode current collector and the negative electrode active layer and the charging time at a 1C rate were measured for each negative electrode produced in Examples 1 to 9 and Comparative Examples 1 to 6. The results are shown in Table 5 below.

[0254]

Table 5

[0255] As shown in Table 5 above, the negative electrodes of the examples were shown to have a high adhesive force of 30 gf / cm or more between the first negative electrode active layer and the negative electrode current collector. Further, a secondary battery including such a negative electrode reached a state of charge (SOC) of 90% in a short time of 35 minutes or less under the standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0256] On the other hand, the negative electrodes of the comparative examples were shown to have a low adhesive force of 25 gf / cm or less between the first negative electrode active layer and the negative electrode current collector. However, the negative electrodes of Comparative Example 3 and Comparative Example 4 were shown to have an adhesive force of 30 gf / cm or more between the first negative electrode active layer and the negative electrode current collector. However, it was confirmed that a secondary battery including the same took 43 minutes or more to reach a state of charge (SOC) of 90%.

[0257] This means that by controlling the average particle size conditions of 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, respectively, and the degree of alignment (O.I) of each negative electrode active layer within a predetermined range, the adhesive force between the negative electrode current collector and the negative electrode active layer and the charging rate under the standard C rate conditions can be improved.

[0258] Examples 10-19 and Comparative Examples 7-9. Manufacturing of the negative electrode III

[0259] Average particle size (D 50 Artificial graphite and natural graphite (sphericity: 0.45) with dimensions of 15 μm to 16 μm were prepared as carbon-based anode active materials, and styrene-butadiene rubber (SBR) was prepared as a binder. Separately, the following carbon structures were prepared: (1) single-walled carbon nanotubes (SWCNT, average size: 450 ± 10 nm), (2) multi-walled carbon nanotubes (MWCNT, average size: 550 ± 10 nm), (3) carbon nanofilaments (average size: 750 ± 10 nm), (4) graphene (average size: 200 ± 10 nm), and (5) carboxymethylcellulose (CMC) solution.

[0260] Subsequently, a first anode slurry was prepared by mixing 96% by weight of a first carbon-based anode active material, 1.5% by weight of a carbon structure, and 2.5% by weight of styrene-butadiene rubber (SBR) with water to a solid content of 50%.

[0261] Furthermore, a second anode slurry was prepared by mixing 97.5% by weight of a second carbon-based anode active material and 2.5% by weight of styrene-butadiene rubber (SBR) with water to a solid content of 50%.

[0262] At this time, the (1) type and (2) degree of spheroidization of the first carbon-based anode active material were adjusted as shown in Table 6, and artificial graphite with a degree of spheroidization of 0.45 was used as the second carbon-based anode active material.

[0263] After each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a thin copper plate (thickness: 10 μm) that was being transported roll-to-roll using a die coater (transport speed: 5 m / min).

[0264] Permanent magnets having a length ratio of 110% to 120% of the width of the negative electrode slurry were placed on the upper part of the coated negative electrode slurry and on the lower part of the negative electrode current collector, and a magnetic field was applied at a magnetic field strength of 6,000 ± 20 G for 4 to 6 seconds. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a configuration in which the first negative electrode active layer and the second negative electrode active layer were sequentially laminated on the negative electrode current collector. The formed negative electrode active layers were rolled at a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s at 50 ± 1 °C to produce a negative electrode (average thickness of the first negative electrode active layer and the second negative electrode active layer: 60 ± 5 μm and 130 ± 5 μm, respectively).

[0265] For each manufactured anode, the average alignment (OI) of the carbon-based active material contained in the first anode active layer and the second anode active layer was calculated. The results are shown in Table 8.

[0266] [Table 6]

[0267] [Table 7]

[0268] [Table 8]

[0269] Experimental Example 2

[0270] To evaluate the performance of the negative electrode according to the present invention, the adhesion strength between the negative electrode current collector and the negative electrode active layer and the charging time at a 1C rate were measured for each negative electrode manufactured in Examples 10 to 19 and Comparative Examples 7 to 9. The results are shown in Table 9 below.

[0271] [Table 9]

[0272] As shown in Table 9 above, the negative electrodes of Examples 10 to 19 showed high adhesion between the first negative electrode active layer and the negative electrode current collector, at 39 gf / cm or more. Furthermore, secondary batteries containing such negative electrodes reached a state of charge (SOC) of 90% in a short time of 29 minutes or less under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0273] On the other hand, in Comparative Examples 7-9, the adhesion between the first negative electrode active layer and the negative electrode current collector was low, at 35 gf / cm or less. It was confirmed that secondary batteries containing these negative electrodes took more than 30 minutes to reach a state of charge (SOC) of 90% under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0274] This means that by including a carbon structure that satisfies a predetermined average particle size in the first negative electrode active layer, and by controlling the degree of alignment (OI) of each negative electrode active layer within a predetermined range, the adhesion between the negative electrode current collector and the negative electrode active layer and the charging speed under standard C-rate conditions can be improved.

[0275] Examples 20-24 and Comparative Examples 10-14. Manufacturing of the negative electrode IV

[0276] Average particle size (D 50 Artificial graphite and natural graphite (spheroidization degree: 0.45) with dimensions of 15 μm to 16 μm were prepared as carbon-based negative electrode active materials. Along with these, styrene-butadiene rubber (SBR) was prepared as a binder, and carboxymethylcellulose (CMC) was prepared as the first and second thickeners.

[0277] Subsequently, 96% by weight of a first-carbon anode active material, 1.5 parts by weight of carboxymethylcellulose (CMC), and 2.5% by weight of styrene-butadiene rubber (SBR) were mixed with water to produce a first-carbon anode slurry with a solid content of 50%.

[0278] Furthermore, a second anode slurry was prepared by mixing 96% by weight of a second-carbon anode active material, 1.5 parts by weight of carboxymethylcellulose (CMC), and 2.5% by weight of styrene-butadiene rubber (SBR) with water to a solid content of 50%.

[0279] At this time, the (1) type and (2) degree of spheroidization of the first carbon-based anode active material are adjusted as shown in Table 10, and the second carbon-based anode active material is artificial graphite (average particle size (D)) with a degree of spheroidization of 0.45. 50 (Approximately 15 μm to 16 μm) was used.

[0280] Furthermore, the first and second thickening agents were added to each negative electrode slurry in a dispersed state in water. The concentrations of each solution and the room-temperature viscosity of each negative electrode slurry containing them are shown in Table 11.

[0281] After each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a thin copper plate (thickness: 10 μm) that was being transported roll-to-roll using a die coater (transport speed: 5 m / min).

[0282] Permanent magnets having a length ratio of 110% to 120% of the width of the negative electrode slurry were placed on the upper part of the coated negative electrode slurry and on the lower part of the negative electrode current collector, and a magnetic field was applied for 9 to 11 seconds at a magnetic field strength of 6,000 ± 20 G. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a configuration in which the first negative electrode active layer and the second negative electrode active layer were sequentially laminated on the negative electrode current collector. The formed negative electrode active layers were rolled at 50 ± 1 °C at a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s to produce a negative electrode (average thickness of the first negative electrode active layer and the second negative electrode active layer: 60 ± 5 μm and 130 ± 5 μm, respectively).

[0283] For each manufactured anode, the average alignment (OI) of the carbon-based active material contained in the first anode active layer and the second anode active layer was calculated. The results are shown in Table 12.

[0284] [Table 10]

[0285] [Table 11]

[0286] [Table 12]

[0287] Experimental Example 3

[0288] To evaluate the performance of the negative electrode according to the present invention, the adhesion strength between the negative electrode current collector and the negative electrode active layer and the charging time at a 1C rate were measured for each negative electrode manufactured in Examples 20-24 and Comparative Examples 10-14. The results are shown in Table 13 below.

[0289] [Table 13]

[0290] As shown in Table 13 above, the negative electrode of the example demonstrated a high adhesion strength of 38 gf / cm or more between the first negative electrode active layer and the negative electrode current collector. Furthermore, a secondary battery containing such a negative electrode reached a state of charge (SOC) of 90% in a short time of 37 minutes or less under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0291] On the other hand, the negative electrode of the comparative example had a low adhesion strength of 29 gf / cm or less between the first negative electrode active layer and the negative electrode current collector. In particular, it was confirmed that the secondary batteries of comparative examples 11 and 14, in which the concentration of the thickening agent solution during negative electrode manufacturing was significantly high, or in which no magnetic field was applied, took more than 45 minutes to reach a state of charge (SOC) of 90% under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0292] This means that the first negative electrode active layer, to which a first thickening agent solution with a high concentration is applied during negative electrode manufacturing, has a greater degree of alignment (OI) than the second negative electrode active layer, to which a second thickening agent solution with a relatively lower concentration is applied, thereby improving the adhesion between the negative electrode current collector and the negative electrode active layer, as well as the charging speed under standard C-rate conditions.

[0293] Examples 25-28. Manufacturing of the negative electrode V

[0294] Artificial graphite was prepared as the carbon-based anode active material, multi-walled carbon nanotubes (MWCNTs, average size: 550±10nm) as the carbon structure, and carboxymethylcellulose (CMC) as the thickener. Styrene-butadiene rubber (SBR) was also prepared as the binder.

[0295] Subsequently, 96 parts by weight of the first carbon-based anode active material, 1.5 parts by weight of the carbon structure and / or the first thickener, and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to produce a first anode slurry with a solid content of 50%.

[0296] Furthermore, a second anode slurry was prepared by mixing 96 parts by weight of a second carbon-based anode active material, 1.5 parts by weight of carboxymethylcellulose (CMC) and 2.5 parts by weight of styrene-butadiene rubber (SBR) as second thickeners with water to a solid content of 50%.

[0297] At this time, the average particle size (D) of each carbon-based negative electrode active material 50 The spheroidization degree and carbon structure content were adjusted as shown in Table 14. In addition, the content of the first thickener, the concentration of the solution in which the first and second thickeners were dissolved, and the room temperature viscosity of the first and second negative electrode slurries were adjusted as shown in Table 15.

[0298] After each negative electrode slurry was prepared, the first and second negative electrode slurries were simultaneously cast onto a thin copper plate (thickness: 10 μm) that was being transported roll-to-roll using a die coater (transport speed: 5 m / min).

[0299] Permanent magnets having a length ratio of 110% to 120% of the width of the negative electrode slurry were placed on the upper part of the coated negative electrode slurry and on the lower part of the negative electrode current collector, and a magnetic field was applied at a magnetic field strength of 6,000 ± 20 G for 4 to 6 seconds. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a configuration in which the first negative electrode active layer and the second negative electrode active layer were sequentially laminated on the negative electrode current collector. The formed negative electrode active layers were rolled at a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s at 50 ± 1 °C to produce a negative electrode (average thickness of the first negative electrode active layer and the second negative electrode active layer: 60 ± 5 μm and 160 ± 5 μm, respectively).

[0300] [Table 14]

[0301] [Table 15]

[0302] [Table 16]

[0303] Experimental Example 4

[0304] To evaluate the performance of the negative electrode according to the present invention, the adhesion strength between the negative electrode current collector and the negative electrode active layer and the charging time at a 1C rate were measured for each negative electrode manufactured in Examples 2, 11, 21, and 25-28. The results are shown in Table 17 below.

[0305] [Table 17]

[0306] As shown in Table 17 above, the negative electrode of the example demonstrated a high adhesion strength of 38 gf / cm or more between the first negative electrode active layer and the negative electrode current collector. Furthermore, a secondary battery containing such a negative electrode reached a state of charge (SOC) of 90% in a short time of 32 minutes or less under standard constant current-constant voltage (CC-CV) charging conditions at a 1C rate.

[0307] These results show that the negative electrode according to the present invention has excellent lifespan characteristics due to its high adhesion to the negative electrode current collector, and that the secondary battery containing it has excellent output characteristics and can be charged in a short time even at a 1C rate.

[0308] Although preferred embodiments of the present invention have been described above with reference to the present invention, a person skilled in the art or with ordinary knowledge in the art will understand that the present invention can be modified and altered in various ways without departing from the technical domain of the present invention as described in the claims below.

[0309] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in the specification, but can be defined by the claims.

Claims

1. negative electrode current collector, A first negative electrode active layer is provided on the negative electrode current collector and includes a first carbon-based negative electrode active material, and A second negative electrode active layer is provided on the first negative electrode active layer and contains a second carbon-based negative electrode active material. Includes, The second negative electrode active layer has an alignment degree (O.I) represented by the following formula 1. ２ｎｄ ) is 6 or less, The degree of alignment of the first negative electrode active layer (O.I.) １ｓｔ ) is the degree of alignment of the second negative electrode active layer (O.I. ２ｎｄ The negative electrode has a ratio of 200% to 900% based on ) [Equation 1] O. I = I ００４ / I １１０ In Equation 1, I ００４ This represents the area value of the peak indicating the crystal plane when X-ray diffraction (XRD) spectroscopy analysis (004) is performed on the negative electrode active layer. I １１０ This represents the area value of the peak indicating the (110) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

2. The average particle size (D １ ) of the first carbon-based negative electrode active material relative to the average particle size (D ２ ) of the second carbon-based negative electrode active material, the ratio (D ２ / D １ ) is in the range of 2.0 or more. The negative electrode according to claim 1.

3. The anode according to claim 1, wherein the first carbon-based anode active material and the second carbon-based anode active material each contain one or more of natural graphite and artificial graphite.

4. The average particle size (D) of the first carbon-based negative electrode active material １ The negative electrode according to claim 1, wherein the diameter is in the range of less than 5 μm.

5. The average particle size (D) of the second carbon-based negative electrode active material. ２ The negative electrode according to claim 1, wherein the diameter is in the range of 10 μm to 25 μm.

6. The anode according to claim 1, wherein the first anode active layer includes a carbon structure having an average size in the range of 5 nm to 900 nm.

7. The negative electrode according to claim 6, wherein the carbon structure includes one or more of a point-like carbon structure, a fibrous carbon structure, and a planar carbon structure.

8. The anode according to claim 6, wherein the content of the carbon structure is in the range of 0.001% by weight to 10% by weight based on the total weight of the first anode active layer.

9. The first negative electrode active layer and the second negative electrode active layer each contain a first thickener and a second thickener, The negative electrode according to claim 1, wherein the content of the first thickener is 80% to 120% based on the content of the second thickener.

10. The negative electrode according to claim 9, wherein the first thickening agent and the second thickening agent each contain one or more of the following: carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), poly-N-vinylacetamide (PNVA), styrene-butadiene rubber (SBR), acrylic resin, and fluororesin.

11. The anode according to claim 9, wherein the first thickening agent is included in an amount of 0.5% to 3% by weight based on the total weight of the first anode active layer.

12. A step of applying a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of the negative electrode current collector, The step of applying a second negative electrode slurry containing a second carbon-based negative electrode active material onto the applied first negative electrode slurry, The steps include applying a magnetic field to the negative electrode current collector coated with the second negative electrode slurry, and The steps include drying the first negative electrode slurry and the second negative electrode slurry to which a magnetic field has been applied to form a first negative electrode active layer and a second negative electrode active layer, Includes, The second negative electrode active layer has an alignment degree (O.I) represented by the following formula 1. ２ｎｄ ) is 6 or less, The degree of alignment of the first negative electrode active layer (O.I.) １ｓｔ ) is the degree of alignment of the second negative electrode active layer (O.I. ２ｎｄ A method for manufacturing a negative electrode having a ratio of 200% to 900% based on ): [Equation 1] O. I = I ００４ / I １１０ In Equation 1, I ００４ This represents the area value of the peak indicating the crystal plane when X-ray diffraction (XRD) spectroscopy analysis (004) is performed on the negative electrode active layer. I １１０ This represents the area value of the peak indicating the (110) crystal plane during X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

13. The method for manufacturing a negative electrode according to claim 12, wherein the steps of applying the first negative electrode slurry and applying the second negative electrode slurry are performed simultaneously.

14. The method for manufacturing a negative electrode according to claim 12, wherein the magnetic field is applied with an intensity of 3,000 G to 10,000 G.

15. The method for manufacturing a negative electrode according to claim 12, wherein the magnetic field is applied for 1 to 60 seconds.

16. The method for manufacturing a negative electrode according to claim 12, wherein the solid content of the first negative electrode slurry is in the range of 35% to 85%.

17. The method for manufacturing a negative electrode according to claim 12, wherein the viscosity at room temperature of the first negative electrode slurry is higher than the viscosity at room temperature of the second negative electrode slurry.

18. The average particle size (D) of the first carbon-based negative electrode active material １ ) The average particle size (D ２ ) ratio (D ２ / D １ The method for manufacturing a negative electrode according to claim 12, wherein the value is in the range of 2.0 or more.

19. The method for manufacturing a negative electrode according to claim 12, wherein the first negative electrode slurry includes a carbon structure having an average size in the range of 5 nm to 900 nm.

20. The method for producing a negative electrode according to claim 19, wherein the content of the carbon structure is in the range of 0.001% by weight to 10% by weight relative to the total weight of the solid content of the first negative electrode slurry.

21. The first negative electrode slurry and the second negative electrode slurry are mixed with a first thickener and a second thickener, respectively, in a solution state during manufacturing. The method for producing a negative electrode according to claim 12, wherein each solution containing the first thickener and the second thickener has a different concentration.

22. The concentration of the solution containing the second thickener is in the range of 0.5% by weight to 1.5% by weight, based on the total weight of the solution. The method for producing a negative electrode according to claim 21, wherein the concentration of the solution containing the first thickener is in the range of 150% to 250% of the concentration of the solution containing the second thickener.

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