Magnetic alignment device for negative electrode and method for manufacturing negative electrode using the same

Abstract

The present invention relates to a magnetic alignment device used in manufacturing a negative electrode and a method for manufacturing a negative electrode using the same. The magnetic alignment device measures the thickness of a negative electrode slurry applied to a negative electrode current collector in real time, and can easily control the strength of a magnetic field by adjusting the separation distance of a magnet part according to the thickness of the negative electrode slurry measured in this way, which is advantageous in that the degree of alignment of the crystal planes of a carbon-based negative electrode active material contained in a manufactured negative electrode active layer, i.e., the orientation, is uniformly high.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0116200 filed on September 15, 2022, and all contents disclosed in the document of the Korean Patent Application are included as part of this specification.

[0002] The present invention relates to a magnetic alignment device capable of uniformly aligning a negative electrode active material in a negative electrode active layer during the manufacture of a negative electrode, and a method for manufacturing a negative electrode using the same.

Background Art

[0003] In recent years, secondary batteries have been widely applied not only to small devices such as portable electronic devices but also to medium and large-sized devices such as battery packs or power storage devices for hybrid vehicles and electric vehicles.

[0004] Such a secondary battery is a power generation element capable of charge and discharge having a laminated structure of a positive electrode / separator / negative electrode. Generally, the positive electrode contains a lithium metal oxide as a positive electrode active material, and the negative electrode contains a carbon-based negative electrode active material such as graphite. During charging, lithium ions released from the positive electrode are occluded inside the carbon-based negative electrode active material of the negative electrode, and during discharging, lithium ions contained inside the carbon-based negative electrode active material are occluded in the lithium metal oxide of the positive electrode, and charge and discharge are repeated.

[0005] At this time, examples of the negative electrode active material used for the negative electrode include graphite materials such as natural graphite. Such graphite has a layered structure, in which carbon atoms form a network structure, and a large number of planar layers are stacked. During charging, lithium ions penetrate from the edge surface (the surface where the layers overlap) of such a graphite layer and diffuse between the layers. Also, during discharging, lithium ions can desorb and be released from the edge surface of the layer. In addition, since the electrical resistivity in the plane direction of the graphite layer is lower than that in the stacking direction of the layers, an electron conduction path that detours along the plane direction of the layer is formed.

[0006] Regarding this, in a conventional lithium secondary battery using graphite, a technique has been proposed to magnetically orient the graphite contained in the negative electrode in order to improve the charging performance of the negative electrode. Specifically, it has a configuration in which the (002) crystal plane of graphite is oriented to be substantially perpendicular to the negative electrode current collector during the formation of the negative electrode and fixed. In this case, since the edge plane of the graphite layer faces the positive electrode active layer, the insertion and desorption of lithium ions can be smoothly performed. At the same time, the conduction path of electrons is shortened, and the electron conductivity of the negative electrode can be improved, thereby improving the charging performance of the battery.

[0007] However, although a magnetic field can be applied to the undried negative electrode slurry to induce the orientation of graphite, the conditions of the applied magnetic field can vary depending on various variables such as the loading amount and thickness of the negative electrode slurry containing graphite. However, there is a limit in that it is difficult to reflect such variables in real time during actual negative electrode manufacturing, so there is a problem that it is difficult to achieve uniform orientation of graphite.

[0008] In addition, although various models of negative electrodes with different specifications will be manufactured in a single negative electrode manufacturing apparatus, it is not easy to control the magnetic field applying means provided in the manufacturing apparatus, that is, permanent magnets, etc., according to the specifications of the manufactured negative electrodes.

[0009] Therefore, a technique is required that can easily control the magnetic field applying means according to the specifications of the manufactured negative electrodes such as the thickness of the negative electrode active layer and / or the negative electrode manufacturing conditions such as the loading amount and thickness of the negative electrode slurry, and can manufacture a negative electrode active layer in which the crystal planes of carbon-based negative electrode active materials such as graphite are uniformly aligned.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to provide an alignment device capable of uniformly aligning crystal planes of a carbon-based negative electrode active material contained in a negative electrode active layer by adjusting the intensity of a magnetic field according to the thickness of a negative electrode slurry containing the carbon-based negative electrode active material, and a method for manufacturing a negative electrode using the same.

Means for Solving the Problems

[0012] In order to solve the above-described problems, in one embodiment, the present invention A magnetic alignment device for a negative electrode that applies a magnetic force to a negative electrode sheet on which a negative electrode slurry containing a carbon-based negative electrode active material is coated to align the carbon-based negative electrode active material, A first magnet part and a second magnet part respectively arranged above and below the electrode sheet during travel; A thickness measurement unit that is arranged upstream of the first magnet part and the second magnet part with respect to the traveling direction of the electrode sheet and measures the thickness of the negative electrode slurry arranged on the electrode sheet; A control unit that adjusts the separation distance between the first magnet part and the second magnet part according to the thickness of the negative electrode slurry measured by the thickness measurement unit, and provides a magnetic alignment device for a negative electrode including the control unit.

[0013] At this time, the control unit includes a database in which an interval reference value between the first magnet part and the second magnet part corresponding to the thickness of the negative electrode slurry is stored, and calculates an interval reference value corresponding to the thickness of the negative electrode slurry measured by the thickness measurement unit, and can adjust the separation distance between the first magnet part and the second magnet part.

[0014] Here, the separation distance between the first magnet part and the second magnet part can be 10 mm to 50 mm.

[0015] Further, the first magnet portion and the second magnet portion may each include a single permanent magnet disposed in the width direction of the negative electrode slurry during running, a support portion to which the magnet is fixed, and distance adjusting means connected to the support portion and guiding the lifting and lowering movement of the support portion in a direction perpendicular to the electrode sheet during running.

[0016] Further, the first magnet portion and the second magnet portion may include magnets having opposite poles to each other.

[0017] Further, the thickness measuring portion may include one or more of a confocal measuring device, a web gauge, and an IR (infrared) thickness measuring device.

[0018] Furthermore, the magnetic alignment device may further include a drying portion for drying the negative electrode slurry in which the carbon-based negative electrode active material is aligned by the first magnet portion and the second magnet portion.

[0019] Also, in one embodiment of the present invention, applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; aligning the carbon-based negative electrode active material contained in the negative electrode slurry using the magnetic alignment device according to the present invention; drying the negative electrode slurry in which the carbon-based negative electrode active material is aligned to form a negative electrode active layer, and includes: The step of aligning the carbon-based negative electrode active material is controlled by adjusting the distance between the negative electrode slurry and the magnet portion of the magnetic alignment device according to the thickness of the negative electrode slurry, and provides a method for manufacturing a negative electrode.

[0020] At this time, the negative electrode slurry may be applied with a thickness of 50 μm to 500 μm.

[0021] Also, the negative electrode active layer formed on the negative electrode current collector may have an alignment degree (O.I) of the carbon-based negative electrode active material represented by the following formula 1 of 0.1 to 5.0.

[0022] [Formula 1] O.I = I 004 / I 110

[0023] In Formula 1, I 004 represents the area of the peak indicating the (004) crystal plane during X-ray diffraction spectroscopy (XRD) measurement with respect to the negative electrode active layer, I 110 represents the area of the peak indicating the (110) crystal plane during X-ray diffraction spectroscopy (XRD) measurement with respect to the negative electrode active layer.

Advantages of the Invention

[0024] The magnetic alignment device according to the present invention can measure in real time the thickness of the negative electrode slurry coated on the negative electrode current collector, and can easily control the intensity of the magnetic field by adjusting the separation distance of the magnet part according to the thickness of the negative electrode slurry thus measured. Therefore, there is an advantage that the degree of alignment of the crystal planes of the carbon-based negative electrode active material contained in the manufactured negative electrode active layer is uniformly high.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0026] The present invention can be subjected to various modifications and can have various embodiments. Therefore, specific embodiments will be described in detail in the detailed description.

[0027] However, this is not intended to limit the present invention to specific embodiments, and is understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0028] In the present invention, terms such as "comprising" and "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and are understood not to preclude in advance the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0029] Also, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is directly "on" the other part but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only the case where it is directly "under" the other part but also the case where there is another part in between. Also, in this application, being "disposed on" can include not only the upper part but also the case of being disposed on the lower part.

[0030] Also, in the present invention, "comprising as a main component" may mean containing a component defined with respect to the total weight (or total volume) 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, "comprising graphite as a main component as the negative electrode active material" may mean containing graphite 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 with respect to the total weight of the negative electrode active material, and in some cases, it may also mean that the entire negative electrode active material consists of graphite and graphite is contained at 100% by weight.

[0031] In addition, in this specification, "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" may mean that, as shown in FIG. 2(b), a specific crystal plane (for example, the a-b axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based negative electrode active material constituting the negative electrode active material particles is arranged with a predetermined inclination with respect to the surface of the negative electrode current collector. This may be different from the case where, as shown in FIG. 2(a), the particles of the carbon-based negative electrode active material are aligned only in a predetermined direction inside the negative electrode active layer but have no directionality with respect to the negative electrode current collector.

[0032] In addition, "the carbon-based negative electrode active material has a high degree of orientation" may mean that the frequency of a specific crystal plane (for example, the a-b axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer having a predetermined inclination with respect to the surface of the negative electrode current collector is high. In some cases, it may also mean that the above crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is arranged at a high angle (for example, an angle close to perpendicular, more than 45°, specifically 60° or more) with respect to the surface of the negative electrode current collector.

[0033] In addition, "the carbon-based negative electrode active material has a high degree of alignment" means that the "degree of alignment (O.I)" mentioned in this specification has a large value, and a specific crystal plane (for example, the a-b axis crystal plane of graphite) showing the two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer is arranged at a low angle (for example, less than 45°) with respect to the surface of the negative electrode current collector. Conversely, "the carbon-based negative electrode active material has a low degree of alignment" means that the "degree of alignment (O.I)" has a small value, and the above crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is arranged at a high angle (for example, an angle close to perpendicular, 45° or more, specifically 60° or more) with respect to the surface of the negative electrode current collector.

[0034] Furthermore, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value in the particle size distribution becomes 50%, and this is also referred to as the median diameter.

[0035] Hereinafter, the present invention will be described in more detail.

[0036] <Magnetic alignment device for negative electrode> In one embodiment of the present invention, a magnetic alignment device for a negative electrode that applies a magnetic force to a negative electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material on a negative electrode current collector to align the carbon-based negative electrode active material, a first magnet part and a second magnet part respectively arranged above and below the electrode sheet during running, a thickness measurement part arranged upstream of the first magnet part and the second magnet part with respect to the running direction of the electrode sheet and measuring the thickness of the negative electrode slurry arranged on the electrode sheet, and a control part that adjusts the separation distance between the first magnet part and the second magnet part according to the thickness of the negative electrode slurry measured by the thickness measurement part, and provides a magnetic alignment device for a negative electrode including the same.

[0037] The magnetic alignment device for a negative electrode according to the present invention is a device applied during the manufacture of a negative electrode used in a secondary battery, and by applying a magnetic field to the surface of a negative electrode current collector coated with a negative electrode slurry containing a carbon-based negative electrode active material, that is, the negative electrode slurry surface, the carbon-based negative electrode active material contained in the negative electrode slurry can be aligned in a direction perpendicular to the negative electrode current collector. Here, the magnetic alignment device can measure the conditions of the negative electrode slurry coated on the negative electrode current collector during magnetic field application, specifically, the thickness of the negative electrode slurry in real time, and control the magnetic fields of the magnet parts arranged above and below the running negative electrode, that is, the electrode sheet. Thereby, the magnetic alignment device can realize uniform alignment of the carbon-based negative electrode active material contained in the negative electrode slurry, and the negative electrode manufactured in this way can show the effect of increasing the mobility of lithium ions during charge and discharge of the battery, reducing the resistance, and improving the charge and discharge performance.

[0038] Here, being aligned in the direction perpendicular to the negative electrode current collector means that the crystal planes of the carbon-based negative electrode active material are aligned. Specifically, "the carbon-based negative electrode active material is aligned perpendicular to the negative electrode current collector" may mean that the crystal planes of the carbon-based negative electrode active material constituting the spherical particles, specifically, the crystal planes indicating the planar direction of graphite having a two-dimensional structure among the crystal planes of graphite, are aligned and arranged perpendicular to the surface of the negative electrode current collector. At this time, the planar direction of graphite may have an average inclination of 60 to 120° with respect to the negative electrode current collector, preferably an average inclination of 70 to 110°, or 80 to 100°.

[0039] For this purpose, as shown in FIG. 1, the magnetic alignment device 10 according to the present invention includes a first magnet part 120a and a second magnet part 120b respectively arranged above and below the electrode sheet during traveling, that is, the negative electrode current collector C coated with the negative electrode slurry S, and is arranged upstream of the first magnet part 120a and / or the second magnet part 120b with reference to the traveling direction of the electrode sheet, and measures the thickness of the negative electrode slurry S of the electrode sheet. It has a configuration including a thickness measurement unit 110 and a control unit 130 that adjusts the separation distance between the first magnet part 120a and the second magnet part 120b according to the thickness of the negative electrode slurry measured by the thickness measurement unit.

[0040] In the magnetic alignment device 10, the thickness measurement unit 110 is located upstream of the first magnet part 120a and / or the second magnet part 120b with reference to the traveling direction of the electrode sheet, and before the magnetic field applied by the magnet part affects the negative electrode slurry, it plays a role of measuring the thickness of the negative electrode slurry S. At this time, the thickness measurement unit 110 is not particularly limited and can be applied as long as it is a means / method usually used in the industry to measure the thickness of the negative electrode slurry S, but may include a non-contact measuring instrument that can prevent loss and / or state change of the negative electrode slurry. As an example, the thickness measurement unit 110 may include one or more of a confocal measuring instrument, a web gauge, and an IR (infrared) thickness measuring instrument.

[0041] Further, in order to more precisely measure the thickness of the negative electrode slurry S, the thickness measurement unit 110 may arrange two or more non-contact measuring devices in the width direction of the negative electrode slurry S during running to measure the thickness of the negative electrode slurry in real time, and the thickness value measured in this way may be transmitted to the control unit, and the average value thereof may be reflected as the thickness of the negative electrode slurry. In this case, there is an advantage that the thickness of the negative electrode slurry applied using a die coater or the like can be measured more precisely.

[0042] Further, the thickness measurement unit 110 may include two or more non-contact measuring devices along the running direction of the electrode sheet. Specifically, in the thickness measurement unit 110, a first measuring device 111 and a second measuring device 112 may be continuously arranged along the running direction of the electrode sheet. In this case, the error rate with respect to the thickness of the negative electrode slurry measured in real time can be reduced.

[0043] In the magnetic alignment device 10, the control unit 130 may play a role of controlling the separation distance between the first magnet unit 120a and the second magnet unit 120b. For this purpose, in the magnetic alignment device 10, the thickness of the negative electrode slurry S measured by the thickness measurement unit 110 is transmitted, and the interval reference value corresponding to the measured thickness of the negative electrode slurry is recognized by comparing with the interval reference value, and the recognized interval reference value is transmitted to the first magnet unit 120a and the second magnet unit 120b respectively, and the separation distance between the first magnet unit 120a and the second magnet unit 120b can be adjusted.

[0044] At this time, the interval reference value is a value indicating the interval, that is, the separation distance, between the first magnet unit 120a and the second magnet unit 120b according to the thickness of the negative electrode slurry, and this value may be stored in a database (not shown) provided in the control unit 130. The interval reference value is obtained by using an existing prior art measuring device to obtain data on the separation distance between the first magnet unit 120a and the second magnet unit 120b according to the thickness of the negative electrode slurry S, and among the obtained data, only the data in which the alignment of the carbon-based negative electrode active material contained in the negative electrode slurry is most effectively realized is selected and combined and stored in the database.

[0045] Further, even if the negative electrode slurry S has the same thickness, the content of the carbon-based negative electrode active material contained in the negative electrode slurry may differ depending on the density (or concentration) of the carbon-based negative electrode active material. Also, since the content of the carbon-based negative electrode active material affects the alignment of the crystal planes with respect to the negative electrode current collector C, the magnetic field strength can be adjusted according to the content at the time of alignment. Therefore, the above database includes information on the separation distance between the first magnet portion 120a and the second magnet portion 120b according to the thickness of the negative electrode slurry S, and, for each thickness of the negative electrode slurry S for correcting the thickness of the negative electrode slurry S, may further include density (or concentration) information regarding the carbon-based negative electrode active material in the negative electrode slurry.

[0046] Also, as described above, since the density (or concentration) of the carbon-based negative electrode active material can affect the magnetic field strength for correcting the thickness of the negative electrode slurry S, the interval reference value stored in the above database can be a value reflecting the data regarding the density (or concentration) of the carbon-based negative electrode active material in the negative electrode slurry stored in the database.

[0047] Furthermore, in the magnetic alignment device 10, the first magnet portion 120a and the second magnet portion 120b are respectively disposed above and below the traveling electrode sheet and serve to apply a magnetic field to the surface of the negative electrode slurry S.

[0048] The first magnet portion 120a and the second magnet portion 120b each include magnets 122a and 122b for applying a magnetic field to the surface of the negative electrode slurry S, and may include means 121a and 121b for adjusting the interval therebetween, i.e., the separation distance, by performing lifting and lowering motions above and below the negative electrode slurry. Specifically, the first magnet portion 120a and the second magnet portion 120b each include a single permanent magnet 122a and 122b disposed in the width direction of the traveling negative electrode slurry, a support portion (not shown) to which the magnet is fixed, and distance adjusting means 121a and 121b connected to the support portion and guiding the lifting and lowering motion of the support portion (or the lifting and lowering motion of the single magnet) in a direction perpendicular to the traveling electrode sheet.

[0049] At this time, the distance adjusting means 121a and 121b can operate to adjust the separation distance between the first magnet part 120a and the second magnet part 120b in accordance with the interval reference value transmitted from the control unit 130.

[0050] By having such a configuration, the first magnet part 120a and the second magnet part 120b can easily control the intensity of the magnetic field applied to the negative electrode slurry S through the adjustment of their separation distance. That is, the closer the separation distance between the first magnet part 120a and the second magnet part 120b, the stronger the intensity of the magnetic field applied to the negative electrode slurry S, and the wider the separation distance, the weaker the intensity of the magnetic field applied to the negative electrode slurry S.

[0051] In addition, the first magnet part 120a and the second magnet part 120b can be positioned in the width direction of the negative electrode slurry S so as to face each other, and can be arranged to have opposite poles. For example, the N pole of the first magnet 122a of the first magnet part 120a faces the S pole of the second magnet 122b of the second magnet part 120b, or the S pole of the first magnet 122a of the first magnet part 120a faces the N pole of the second magnet 122b of the second magnet part 120b. When the electrode sheet passes between the spaces where the N pole and the S pole face each other in this way, the vertical alignment of the carbon-based negative electrode active material with respect to the negative electrode current collector C can be more effectively performed between the first magnet part 120a and the second magnet part 120b.

[0052] Further, the first magnet part 120a is arranged above the traveling electrode sheet, and in order to apply a high magnetic field to the carbon-based negative electrode active material of the negative electrode slurry S, a Halbach array can be applied to the first single permanent magnet 122a. Here, the Halbach array is a permanent magnet array, and can provide a magnet with a high magnetic field intensity by changing the magnetization direction of the magnet step by step. When a magnet having a Halbach array is applied as the magnet 122a of the first magnet part 120a, there is an advantage that the intensity of the magnetic field applied to the negative electrode slurry S can be adjusted without significantly changing the separation distance between the first magnet part 120a and the second magnet part 120b.

[0053] On the one hand, the separation distance between the first magnet part 120a and the second magnet part 120b can be 10 mm to 50 mm, specifically 10 mm to 40 mm, 20 mm to 50 mm, or 15 mm to 45 mm. The separation distance between the first magnet part 120a and the second magnet part 120b can be the same as the separation distance between the first single permanent magnet 122a and the second single permanent magnet 122b. By adjusting the separation distance between the first magnet part 120a and the second magnet part 120b within the above range, the present invention can more efficiently align the carbon-based negative electrode active material contained in the negative electrode slurry S.

[0054] Further, the magnetic alignment device 10 may further include a drying unit 140 for drying the negative electrode slurry S in which the carbon-based negative electrode active material is aligned by the first magnet part 120a and the second magnet part 120b.

[0055] The drying unit 140 includes a wall body (not shown) that blocks the periphery except for the inlet and outlet through which the electrode sheet coated with the slurry S is introduced and carried out, and a dryer (not shown) for drying the electrode sheet on the wall body on the side where the electrode sheet coated with the electrode slurry is drawn out.

[0056] When the electrode sheet coated with the electrode slurry enters through the inlet of the drying unit 140, energy such as light, wavelength, and heat supplied from the opposite wall body is transmitted. Therefore, it is preferable that the wall body is made of a heat insulating material so as to prevent internal energy from being transmitted to the outside and heat loss from occurring.

[0057] Further, although the method of the dryer is not limited, it may have a configuration for performing a two-stage drying process in order to maintain the alignment of the carbon-based negative electrode active material contained in the negative electrode active layer. Specifically, the dryer may include a first dryer for drying the negative electrode slurry using light and a second dryer for drying the negative electrode slurry using heat, and the first dryer and the second dryer can operate continuously to dry the negative electrode slurry.

[0058] The first dryer is a device for pre-drying the negative electrode slurry, and as described above, it can irradiate light or a wavelength on the surface of the negative electrode slurry. Generally, when drying the negative electrode slurry, it can be carried out by adding hot air at a high temperature. However, in this case, since the drying time of the negative electrode slurry becomes long, the alignment of the carbon-based negative electrode active material in the negative electrode slurry can be disturbed. Further, when increasing the temperature of the hot air to solve such a problem, the tendency to be dried on the slurry surface becomes large, so a phenomenon (migration) in which the binder is concentrated on the slurry surface by the volatile solvent occurs, and there is a problem that the adhesion strength between the active material layer and the negative electrode current collector decreases. The present invention can pre-dry the electrode slurry by irradiating energy in the form of light or a wavelength using the first dryer so as to dry the negative electrode slurry while maintaining a high degree of alignment of the carbon-based negative electrode active material without such problems. Such a first dryer may include, for example, an ultraviolet dryer, a near-infrared dryer, a far-infrared dryer, etc., and specifically, a far-infrared dryer that emits energy with a wavelength of 1 μm or more, more specifically 5 μm or more, 10 μm or more, or 20 μm or more may be included to achieve a uniform drying rate of the electrode slurry. The above far-infrared dryer is different from the near-infrared dryer and infrared rays usually applied in the industry, has a long light or wavelength, and high energy efficiency. Further, the above far-infrared dryer has an advantage that it can uniformly apply energy not only to the surface of the negative electrode slurry but also to the inside, so that the adhesive force between the negative electrode slurry and the negative electrode current collector can be increased in a short time.

[0059] At this time, the first dryer can emit energy at an output density of 50 kW / m 2 ~1,000 kW / m 2 Specifically, 50 kW / m 2 ~500 kW / m 2 50 kW / m 2 ~250 kW / m 2 Or 50 kW / m 2 And 200 kW / m 2It can release energy at the output density. By controlling the output density of the first dryer within the above range, the present invention can prevent the non-uniform drying of the active material layer from being induced by excessive output density.

[0060] In addition, the second dryer can apply heat to uniformly and completely dry the negative electrode slurry that has been pre-dried by light or wavelength. Such a second dryer is not particularly limited as long as it is commonly applied in the industry and can be included, and specifically, it can include a hot air dryer, a vacuum oven, etc. alone or in combination.

[0061] Due to having the above-described configuration, the magnetic alignment device according to the present invention can reflect the state of the negative electrode slurry in real time and uniformly induce the alignment of the internal carbon-based negative electrode active material. Therefore, the manufactured negative electrode can show the effect of increasing the mobility of lithium ions during charge and discharge of the battery, reducing the resistance, and improving the charge and discharge performance.

[0062] <Method for manufacturing negative electrode> Moreover, in one embodiment of the present invention, a step of applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector; a step of aligning the carbon-based negative electrode active material contained in the negative electrode slurry using the magnetic alignment device according to the present invention described above; a step of drying the negative electrode slurry in which the carbon-based negative electrode active material is aligned to form a negative electrode active layer, and includes The present invention provides a method for manufacturing a negative electrode, wherein the step of aligning the carbon-based negative electrode active material is controlled by adjusting the distance between the negative electrode slurry and the magnet part of the magnetic alignment device according to the thickness of the negative electrode slurry.

[0063] The method for manufacturing a negative electrode according to the present invention involves applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector, and applying a magnetic field to the surface of the applied negative electrode slurry using the magnetic alignment device of the present invention described above, so that the carbon-based negative electrode active material in the negative electrode slurry can be aligned perpendicular to the surface of the negative electrode current collector (or perpendicular to the running direction of the electrode sheet). Further, in the above manufacturing method, thereafter, by continuously drying the negative electrode slurry, a negative electrode active layer in which the vertical alignment of the carbon-based negative electrode active material is maintained can be formed.

[0064] By using the magnetic alignment device described above, the method for manufacturing the negative electrode can reflect the state of the negative electrode slurry, specifically the thickness, in real time and uniformly induce the alignment of the internal carbon-based negative electrode active material. Therefore, the manufactured negative electrode can exhibit the effect of increasing the mobility of lithium ions during charge and discharge of the battery, reducing the resistance, and improving the charge and discharge performance.

[0065] Here, the step of applying the negative electrode slurry to the negative electrode current collector and the step of drying the negative electrode slurry can be performed in a manner commonly applied in the art.

[0066] Also, the negative electrode slurry applied in the step of applying the negative electrode slurry can be applied to have a thickness within a certain range in consideration of the alignment efficiency of the carbon-based negative electrode active material contained in the negative electrode slurry and the drying efficiency of the negative electrode slurry.

[0067] As an example, the negative electrode slurry can be applied with a thickness of 50 μm to 500 μm, specifically with a thickness of 50 μm to 400 μm, 50 μm to 300 μm, 80 μm to 250 μm, 100 μm to 200 μm, 100 μm to 180 μm, or 110 μm to 180 μm.

[0068] Also, in the step of aligning the carbon-based negative electrode active material contained in the negative electrode slurry using the magnetic alignment device, the application conditions of the magnetic field can be adjusted to enhance the alignment efficiency of the carbon-based negative electrode active material. Specifically, the degree of alignment of the carbon-based negative electrode active material can be adjusted by the strength of the magnetic field, the application time, etc.

[0069] For example, the magnetic field can be applied at a magnetic field strength of 0.5 to 2.0 T, and more specifically, it can be applied at a magnetic field strength of 0.9 to 1.5 T, 1.0 to 1.4 T, or 1.0 to 1.2 T.

[0070] In addition, the magnetic field can be applied for 0.1 to 20 seconds, and more specifically, it can be applied for 0.5 to 15 seconds, 0.5 to 12 seconds, 1 to 10 seconds, or 2 to 8 seconds.

[0071] <Negative electrode for lithium secondary battery> In one embodiment, the present invention provides a negative electrode manufactured using the magnetic alignment device according to the present invention described above.

[0072] The negative electrode manufactured according to the present invention contains a carbon-based negative electrode active material, includes a negative electrode active layer on at least one surface of the negative electrode current collector, and the degree of alignment (O.I) of the carbon-based negative electrode active material represented by the following formula 1 in the negative electrode active layer can be 0.1 to 5.0.

[0073] [Formula 1] O.I = I 004 / I 110

[0074] In formula 1, I 004 represents the area of the peak indicating the (004) crystal plane during X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110 represents the area of the peak indicating the (110) crystal plane during X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer.

[0075] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer containing a carbon-based negative electrode active material on both sides of a negative electrode current collector. The above-mentioned negative electrode active layer is a layer that realizes the electrical activity of the negative electrode, and after applying an electrode slurry containing a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charging and discharging of the battery to both sides of the electrode current collector, it is dried and rolled to manufacture it. The above-mentioned negative electrode active layer contains a carbon-based negative electrode active material as a negative electrode active material in order to realize electrical activity through a reversible oxidation-reduction reaction during charging and discharging of the battery. Specifically, the above-mentioned carbon-based negative electrode active material means a material mainly composed of carbon atoms, and such a carbon-based negative electrode active material may include graphite. The above-mentioned graphite may include any one or more of natural graphite and artificial graphite, preferably includes natural graphite, or may include a mixture of natural graphite and artificial graphite. For example, the above-mentioned carbon-based negative electrode active material may contain natural graphite or artificial graphite alone, and in some cases, may contain a mixture of natural graphite and artificial graphite. In this case, the mixing ratio of natural graphite and artificial graphite may be 5 to 40:60 to 95, or 10 to 30:70 to 90 based on weight. By containing natural graphite and artificial graphite in the above mixing ratio, the carbon-based negative electrode active material can strongly adhere the negative electrode current collector and the negative electrode active layer while highly realizing the orientation of the carbon-based negative electrode active material on the surface of the negative electrode current collector.

[0076] The above-mentioned carbon-based negative electrode active material is preferably a spherical graphite granule formed by aggregating a plurality of flaky graphite. Examples of flaky graphite include those obtained by graphitizing mesophase carbon (bulk mesophase) made from tar pitch, cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), etc., in addition to natural graphite and artificial graphite. In particular, those assembled using a plurality of highly crystalline natural graphite are preferred. Also, one graphite granule can be formed by aggregating 2 to 100, preferably 3 to 20, flaky graphite.

[0077] Such a carbon-based negative electrode active material, specifically, graphite can have a spherical particle form. At this time, the sphericity of the graphite particles can be 0.75 or more, for example, 0.75 to 1.0, 0.75 to 0.95, 0.8 to 0.95, or 0.90 to 0.99. Here, the "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 the particle. When the degree of spheroidization is 1, it means that the particle form is spherical. The above degree of spheroidization can be measured through a particle shape analyzer. The present invention can highly embody the electrical conductivity of the negative electrode active layer by making the shape of the carbon-based negative electrode active material close to spherical, so that the capacity of the battery can be improved, the specific surface area of the negative electrode active material can be increased, and the adhesive force between the negative electrode active layer and the current collector can be improved.

[0078] In addition, the above carbon-based negative electrode active material can exhibit an average particle size (D 50 ) of 0.5 μm to 10 μm, specifically, an average particle size (D 50 ) of 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm.

[0079] The average particle size of spherical natural graphite can be more advantageous as the particle size is made smaller in order to maximize the degree of disorder in the expansion direction for each particle so as to prevent the expansion of the particles due to the charging of lithium ions. However, when the particle size of natural graphite is less than 0.5 μm, a large amount of binder may be required due to an increase in the number of particles per unit volume, and the degree of spheroidization and the spheroidization yield may be low. On the other hand, when the maximum particle size exceeds 10 μm, the expansion becomes intense, and when charge and discharge are repeated, the inter-particle binding property and the binding property between the particles and the current collector decrease, and the cycle characteristics may be greatly reduced.

[0080] The negative electrode active layer containing such a carbon-based negative electrode active material can have the alignment degree of the carbon-based negative electrode active material controlled constantly. The present invention can make the electrode resistance lower by aligning the crystal planes of the carbon-based negative electrode active material contained in the negative electrode active layer in a certain direction, and thereby can further improve the charging performance of the negative electrode active layer.

[0081] Here, the degree of alignment (i.e., orientation) of the carbon-based negative electrode active material (e.g., graphite) can be determined by crystal plane analysis of graphite.

[0082] As an example, in the negative electrode active layer, the carbon-based negative electrode active material is aligned perpendicular to the negative electrode current collector, and the degree of alignment (O.I) of the carbon-based negative electrode active material represented by the following formula 1 satisfies 0.1 to 5.0 during X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer.

[0083] [Formula 1] O.I = I 004 / I 110

[0084] In formula 1, I 004 represents the area of the peak indicating the (004) crystal plane during X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110 represents the area of the peak indicating the (110) crystal plane during X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer.

[0085] In the above formula (1), the crystal plane orientation of the spherical carbon-based negative electrode active material during X-ray diffraction measurement, which is an index indicating the degree of alignment in a certain direction, specifically, in a direction perpendicular to the surface of the negative electrode current collector, can be determined by crystal plane analysis of the carbon-based negative electrode active material such as X-ray diffraction spectroscopic analysis. The degree of alignment (O.I) of the carbon-based negative electrode active material represented by the above formula (1) can be an index indicating the degree of alignment of the crystal structure of the carbon-based negative electrode active material in the aligned direction during X-ray diffraction measurement, specifically, the degree of alignment of the a-b axis crystal plane showing the two-dimensional planar structure of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector. For example, when the negative electrode active layer contains graphite as the carbon-based negative electrode active material, peaks for graphite during X-ray diffraction spectroscopic analysis of the negative electrode active layer are shown at 2θ = 26.5 ± 0.2°, 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, 54.7 ± 0.2°, and 77.5 ± 0.2°. These represent the (002) plane, (100) plane, (101)R plane, (101)H plane, (004) plane, and (110) plane among the crystal planes of the graphite contained in the negative electrode active layer. Generally, in the case of graphite, graphene layers are placed on the a-axis and b-axis planes, and such graphene layers are stacked along the c-axis, resulting in a hexagonal or rhombohedral crystal structure. Here, the above crystal plane peaks are peaks indicating the plane characteristics of such a crystal structure. Also, it is considered that the peak appearing at 2θ = 43.4 ± 0.2° is due to the overlap of the peak corresponding to the (101)R plane of the carbon-based material and the (111) plane of the current collector, such as Cu.

[0086] The present invention can measure the alignment degree (O.I) of graphite by the area ratio of the peak at 2θ = 77.5 ± 0.2° showing the (110) plane and the peak at 2θ = 54.7 ± 0.2° showing the (004) plane, specifically, the ratio of the areas obtained by integrating the intensities of the above peaks. Also, X-ray diffraction was measured using CuKα line as the target line, and in order to improve the peak intensity resolution, the target line was extracted by a monochromator device for measurement. At this time, the measurement conditions were 2θ = 10° to 90°, the scan speed (° / s) was 0.044 to 0.089, and the step size was 0.026° / step. Further, the (004) plane appearing at 2θ = 54.7 ± 0.2° shows the thickness direction characteristics (c-axis direction characteristics) of the layered structure in which the two-dimensional planar structure of the graphite layer is laminated, and the (110) plane appearing at 2θ = 77.5 ± 0.2° shows the planar characteristics (a-b axis direction characteristics) of the laminated graphite layer. Therefore, the smaller the (004) plane peak showing the thickness direction characteristics of the graphite layer plane, and the larger the (110) plane peak showing the planar characteristics of the graphite layer, the higher the angle at which the graphite plane is aligned with respect to the surface of the negative electrode current collector. That is, the closer the value of the above alignment degree (O.I) is to 0, the closer the angle or inclination of the graphite layer surface with respect to the surface of the negative electrode current collector is to 90°, and the larger the value, the closer the inclination with respect to the surface of the negative electrode current collector is to 0° or 180°. In such an aspect, since the carbon-based negative electrode active material in the negative electrode active layer according to the present invention is aligned perpendicular to the negative electrode current collector, the alignment degree (O.I) of graphite may be lower compared to the case where no magnetic field is applied.Specifically, the alignment degree of the carbon-based negative electrode active material contained in the negative electrode active layer can be 0.1 to 5.0, more specifically 0.1 to 4.5, 0.1 to 4.0, 0.1 to 3.5, 0.1 to 3.0, 0.1 to 2.5, 0.1 to 2.0, 0.1 to 1.0, 0.5 to 2.9, 1.0 to 4.5, 1.1 to 4.1, 1.5 to 4.0, 1.1 to 3.5, 1.5 to 3.0, 0.9 to 2.9, 0.1 to 2.4, 0.1 to 2.1, 0.1 to 1.9, 2.0 to 5.0, 2.0 to 4.0, 2.1 to 3.9, 2.5 to 3.9, 3.1 to 4.5, 0.1 to 0.6, 0.15 to 0.6, 0.15 to 0.5, 0.2 to 0.5, 0.2 to 0.4, 0.25 to 0.45, or 0.3 to 0.5.

[0087] As another example, the negative electrode active layer may have a small alignment degree of 1.0 or less according to the following formula 2 during the measurement by a near-edge X-ray fluorescence spectrometer (NEXAFS).

[0088] [Formula 2] S 60 / 0 = I60 B / A / I0 B / A

[0089] In the above formula 2, S 60 / 0 represents the ratio of the peak intensity at an incident angle of 60° (I0 B / A ) to the peak intensity ratio (I60 B / A ) at an incident angle of 0° during the measurement by a near-edge X-ray fluorescence spectrometer (NEXAFS).

[0090] The near-edge X-ray absorption spectrum is also called the near-edge X-ray absorbance fine structure (NEXAFS) spectrum. The near-edge X-ray absorption spectrum is an absorption spectrum observed when electrons (K-shell inner-shell electrons) existing in the inner-shell level (1s orbital) of carbon atoms in the occupied state absorb the energy of irradiated X-rays and are excited to various unoccupied levels in the unoccupied state.

[0091] Here, as the unoccupied levels to which the electrons in the inner-shell level are excited, sp that reflects the crystallinity (such as the basal plane and orientation) in natural graphite2 π attributed to the antibonding orbitals of the bond * Levels, sp reflecting the crystal disorder (such as edge planes and non-orientation) 3 σ attributed to the antibonding orbitals of the bond * Levels, or vacant levels attributed to the antibonding orbitals such as C-H bonds and C-O bonds, etc. sp 2 In graphite having a crystal structure in which hexagonal net structures are stacked by bonds, the basal plane is the plane of the hexagonal net plane (AB plane described later), and the plane where the ends of the hexagonal net appear is the edge plane. On the edge plane, since carbon may have -C=O or the like at the terminal, sp 3 The bonding ratio may be high.

[0092] Also, unlike X-ray photoelectron spectroscopy (XPS) that measures the binding energy between atoms constituting a compound, the near-edge NEXAFS spectrum reflects the local structure near the carbon atom including the excited inner-shell electrons and can reflect only the surface structure of the measured graphite particles. Therefore, by using the near-edge NEXAFS spectrum, the present invention can measure the crystalline state (orientation) of the carbon-based negative electrode active material in the form of spherical particles, that is, graphite.

[0093] On the other hand, the measurement of the near-edge NEXAFS spectrum can irradiate the sample with synchrotron radiation having a fixed incident angle with respect to the sample, and while scanning the energy of the irradiated synchrotron radiation from 280 eV to 320 eV, the total electron yield method can be used to measure the sample current flowing into the sample to complement the photoelectrons emitted from the sample. Specifically, the present invention can measure the degree of alignment (S 60 / 0 ) represented by Equation 2 in order to more quantitatively measure the degree of alignment of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0094] Generally, since synchrotron radiation has a high degree of linear polarization, when the incident direction of the synchrotron radiation is parallel to the bond axis direction of the sp 2 bond (-C=C-), from the C1s level to π *The absorption peak intensity attributed to the transition to the level increases, and conversely, the absorption peak intensity decreases when orthogonal. Therefore, highly oriented graphite (e.g., HOPG, single crystal graphite) has sp 2 -bonded graphite crystals highly aligned near the surface, so when the incident angle of the synchrotron radiation on the sample is changed, the spectral shape changes significantly. In contrast, lowly oriented graphite (e.g., non-graphitic carbon deposited film) has a low orientation of the carbon material forming sp 2 -bonds near the surface, so the spectral shape hardly changes even when the incident angle of the synchrotron radiation on the sample is changed.

[0095] Further, when measuring the near-edge NEXAFS spectrum (i.e., near-edge X-ray fluorescence spectrometer (NEXAFS)) at different incident angles with respect to the surface of the negative electrode active layer, the ratio (I A ) of an arbitrary second absorption peak intensity (I B ) to an arbitrary first absorption peak intensity (I B / A ) can vary depending on the incident angle, which may mean that the carbon-based negative electrode active material contained in the measured negative electrode active layer is regularly arranged (i.e., highly oriented). On the other hand, when the ratio I does not change depending on the incident angle, it may mean that the carbon-based negative electrode active material contained in the measured negative electrode active layer is arranged irregularly (i.e., lowly oriented).

[0096] Therefore, in the present invention, in order to measure the degree of alignment of the carbon-based negative electrode active material contained in the negative electrode active layer, a near-edge NEXAFS spectrum (i.e., near-edge X-ray fluorescence spectrometer (NEXAFS)) is measured, and synchrotron radiation is incident at different incident angles (0° and 60°) with respect to the negative electrode active layer. After obtaining the ratio (I * ) of the intensity of the absorption peak (peak A = 287 ± 0.2 eV) attributed to the transition from the C1s level to the π * level to the intensity of the absorption peak (peak B = 293 ± 0.2 eV) attributed to the transition from the C1s level to the σ B / A level for each incident angle, the ratio (S 60 / 0 ) of the intensity ratios between the incident angles (60° and 0°) is calculated as S B / A = I60 B / A) the degree of alignment of the carbon-based negative electrode active material can be quantitatively measured.

[0097] That is, the degree of alignment of the carbon-based negative electrode active material contained in the negative electrode active layer is expressed by i) the C1s level measured at an incident angle of 60° to π * Absorption peak intensity (peak A = 287 ± 0.2 eV) attributed to the transition to the level (I60 A ) from the C1s level to σ * Absorption peak intensity (peak B = 293 ± 0.2 eV) attributed to the transition to the level (I60 B ) percentage (I60 B / A ) is calculated, and ii) π * The intensity of the absorption peak (peak A = 287 ± 0.2 eV) attributed to the transition to the level (I0 A ) from the C1s level to σ * Absorption peak intensity (peak B = 293 ± 0.2 eV) attributable to the transition to the level (I0 B ) percentage (I0 B / A ) and then iii) calculate the ratio of these (S 60 / 0 =I60 B / A / I0 B / A ) can be evaluated.

[0098] [Formula 3] I60 B / A =I60 B / I60 A

[0099] [Formula 4] I0 B / A =I0 B / I0 A

[0100] In Equation 3 and Equation 4, I60 A indicates the intensity of the strongest peak among the peaks present at 286±1.0 eV when the incident angle is 60°, I60 Brepresents the intensity of the peak with the strongest intensity among the peaks existing at 292.5 ± 1.0 eV when the incident angle is 60°, I0 A represents the intensity of the peak with the strongest intensity among the peaks existing at 286 ± 1.0 eV when the incident angle is 0°, I0 B represents the intensity of the peak with the strongest intensity among the peaks existing at 292.5 ± 1.0 eV when the incident angle is 0°.

[0101] Here, the above S 60 / 0 may mean that the closer it is to 1, the lower the alignment of the graphite crystals, and the closer it is to 0, the higher the alignment of the graphite crystals. The negative electrode active layer according to the present invention may satisfy that the value (S 60 / 0 ) is 1.0 or less, and more specifically, may satisfy 0.9 or less, 0.8 or less, 0.7 or less, 0.1 to 0.7, or 0.3 to 0.7.

[0102] Furthermore, in the above negative electrode active layer, the vertical alignment of the carbon-based negative electrode active material with respect to the negative electrode current collector may be uniformly induced, and the alignment degree deviation of a plurality of carbon-based negative electrode active materials arbitrarily measured per unit area may be low.

[0103] As an example, in the above negative electrode active layer, when performing X-ray diffraction spectroscopy (XRD) measurement on any three points existing in the unit area (10 cm × 10 cm) of the negative electrode active layer, the alignment degree deviation of the carbon-based negative electrode active material represented by Equation 1 may be less than 5% based on the average value, and specifically may be 4% or less, 3% or less, 2% or less, or 1% or less.

[0104] As another example, in the above negative electrode active layer, when performing near-edge X-ray absorption fine structure spectroscopy (NEXAFS) measurement on any three points existing in the unit area (10 cm × 10 cm) of the negative electrode active layer, the alignment degree deviation of the carbon-based negative electrode active material represented by Equation 2 may be less than 5% based on the average value, and specifically may be 4% or less, 3% or less, 2% or less, or 1% or less.

[0105] On the one hand, the negative electrode active layer according to the present invention may further selectively contain, together with the negative electrode active material, a conductive material, a binder, other additives, etc. as necessary.

[0106] The above conductive material may contain one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0107] As an example, the negative electrode active layer may contain carbon nanotubes or carbon fibers alone or in combination as the conductive material.

[0108] At this time, the content of the above conductive material may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight with respect to 100 parts by weight of the entire negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing and the charging capacity from decreasing due to a low content of the conductive material. Further, by controlling the content of the conductive material within the above range, the present invention can prevent the problem that the content of the negative electrode active material decreases due to an excessive amount of the conductive material and the charging capacity decreases, or the rapid charging characteristics decrease due to an increase in the loading amount of the negative electrode active layer.

[0109] In addition, the above binder is a component that assists in the binding of the active material and the conductive material, etc., and the binding to the current collector, and can be preferably applied within a range that does not reduce the electrical properties of the electrode. Specifically, it can include any one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber, and fluorine rubber.

[0110] The content of the above binder can be 0.1 to 10 parts by weight with respect to 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 content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive force of the active layer from decreasing due to a low content of the binder or the electrical properties of the electrode from decreasing due to an excessive amount of the binder.

[0111] In addition, the above negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, copper, stainless steel, nickel, titanium, fired carbon, etc. can be used. In the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Further, the average thickness of the above negative electrode current collector can be preferably applied within 1 to 500 μm in consideration of the conductivity and the total thickness of the manufactured negative electrode.

[0112] Hereinafter, the present invention will be described in more detail with reference to examples and experimental examples.

[0113] However, the following examples and experimental examples illustrate the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0114] <Examples 1 and 2. Production of negative electrode for lithium secondary battery> Using the magnetic alignment device of the present invention having the structure shown in FIG. 1, a negative electrode was produced, and the number of non-contact measuring instruments provided in the thickness measuring unit was adjusted as shown in Table 1 to produce a negative electrode for a lithium secondary battery.

[0115] Specifically, first, natural graphite was prepared as a negative electrode active material, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a negative electrode slurry. Then, the negative electrode slurry was cast on a copper thin plate being transferred by roll-to-roll (transfer speed: 3 m / min) using a die coater.

[0116] At this time, the negative electrode slurry was cast on the copper thin plate for 20 seconds so that the average thickness of the applied negative electrode slurry became 100 μm, and the negative electrode slurry was cast on the copper thin plate for 20 seconds so that the average thickness of the continuously applied negative electrode slurry became 200 μm.

[0117] Thereafter, a magnetic field was applied to the negative electrode slurry by moving the copper thin plate so that the applied negative electrode slurry passed between the first magnet part and the second magnet part through the thickness measuring unit.

[0118] At this time, the thickness measuring unit included a confocal measuring instrument as a non-contact measuring instrument, and the confocal measuring instrument was included in the number shown in Table 1 below along the traveling direction of the copper thin plate. Further, the thickness of the negative electrode slurry measured by the thickness measuring unit was transmitted to the control unit, and the control unit recognized the interval reference value corresponding to the measured thickness of the negative electrode slurry by comparing it with the interval reference value stored in the database, and transmitted the recognized interval reference value to the first magnet part and the second magnet part, respectively.

[0119] Further, the first magnet part and the second magnet part were adjusted by adjusting the distance adjusting means so that the separation distance between the first unit permanent magnet and the second unit permanent magnet fixed to the support part was in accordance with the interval reference value transmitted from the control part. Here, the separation distance between the first unit permanent magnet and the second unit permanent magnet was adjusted to 20 to 40 mm according to the interval reference value transmitted from the control part, and the intensity of the applied magnetic field was 1.0 T.

[0120]

Table 1

[0121] A negative electrode for a lithium secondary battery was manufactured by moving a copper thin plate to which a magnetic field was applied to the negative electrode slurry to the drying part to dry the negative electrode slurry.

[0122] <Comparative Example 1. Manufacture of Negative Electrode for Lithium Secondary Battery> A negative electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that a magnetic alignment device not including a thickness measurement part and a control part was used. At this time, the separation distance between the first unit permanent magnet of the first magnet part and the second unit permanent magnet of the second magnet part was adjusted to 30 mm.

[0123] <Experimental Example. Evaluation of Alignment Uniformity of Carbon-Based Negative Electrode Active Material> In order to evaluate the alignment uniformity of the carbon-based negative electrode active material as the performance of the magnetic alignment device according to the present invention, the following experiment was conducted.

[0124] Specifically, in each negative electrode manufactured in the example and the comparative example, i) a first unit area (10 cm × 10 cm) existing in the casting area with an average thickness of the negative electrode slurry of 100 μm and ii) a second unit area (10 cm × 10 cm) existing in the casting area with an average thickness of the negative electrode slurry of 100 μm were arbitrarily set.

[0125] Thereafter, X-ray diffraction spectroscopy (XRD) and near-edge X-ray fluorescence spectrometer (NEXAFS) were performed on three arbitrary points for the set first unit area and second unit area, respectively, to measure the spectra.

[0126] At this time, the measurement conditions of the above-mentioned near-edge X-ray fluorescence spectrometer (NEXAFS) and X-ray diffraction (XRD) are as follows.

[0127] (1) Near-edge X-ray fluorescence spectrometer (NEXAFS) - Accelerating voltage: 1.0 GeV to 1.5 GeV - Accumulated current: 80 to 350 mA - Incident angle: 60° or 0°

[0128] (2) X-ray diffraction (XRD) - Target: Cu (Kα-ray) graphite monochromator - Slit: Divergence slit = 1 degree, receiving slit = 0.1 mm, scattering slit = 1 degree

[0129] From the spectra measured under the above conditions, i) the average alignment degree (i.e., the average value of the alignment degrees at each point) and ii) the error rate between each point and the average alignment degree of each carbon-based negative electrode active material were calculated according to Formula 1 and Formula 2, respectively. The results are shown in Table 2.

[0130] [Formula 1] O.I = I 004 / I 110

[0131] In Formula 1, I 004 represents the area of the peak indicating the (004) crystal plane during the X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110 represents the area of the peak indicating the (110) crystal plane during the X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer.

[0132] [Formula 2] S 60 / 0 = I60 B / A / I0 B / A

[0133] In Formula 2, S 60 / 0is the peak intensity ratio (I60 B / A ) at an incident angle of 60° with respect to the peak intensity ratio (I0 B / A ) at an incident angle of 0° during near-edge X-ray fluorescence spectrometer (NEXAFS) measurement.

[0134]

Table 2

[0135] As shown in Table 2 above, it was found that the negative electrode manufactured using the magnetic alignment device according to the present invention has a high degree of alignment of the carbon-based negative electrode active material contained in the negative electrode active layer. In addition, it was confirmed that the negative electrode active layer of the manufactured negative electrode has a low error rate of 3% or less between the alignment degrees at any three points and their average value. This means that the magnetic alignment device according to the present invention aligns the carbon-based negative electrode active material uniformly on the negative electrode current collector with a high degree of alignment.

[0136] From these results, it can be seen that the magnetic alignment device according to the present invention can measure the thickness of the negative electrode slurry in real time and reflect it in the distance between the first magnet part and the second magnet part, thereby uniformly aligning the carbon-based negative electrode active material with a high degree of alignment with respect to the negative electrode current collector.

[0137] Although the preferred embodiments of the present invention have been described above, those skilled in the art or those with ordinary knowledge in the technical field can understand that the present invention can be variously modified and changed without departing from the spirit and technical scope of the present invention described in the claims to be described later.

[0138] Therefore, the technical scope of the present invention is not limited to the content described in the summary of the invention in the specification, but is defined by the claims.

Explanation of Reference Numerals

[0139] 10: Magnetic alignment device 20: Transfer part 30: Coating part (die coater) 110: Thickness measurement part 111: First common focus measuring device 112: Second common focus measuring device 120a: First magnet part 121a: First distance adjusting means 122a: First single permanent magnet 120b: Second magnet part 121b: Second distance adjusting means 122b: Second single permanent magnet 130: Control unit 140: Drying unit C: Negative electrode current collector S: Negative electrode slurry

Claims

1. A magnetic alignment device for a negative electrode that applies a magnetic force to a negative electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material on a negative electrode current collector to align the carbon-based negative electrode active material, comprising: a first magnet part and a second magnet part respectively arranged above and below the electrode sheet during running; a thickness measurement part arranged upstream of the first magnet part and the second magnet part with respect to the running direction of the electrode sheet, and measuring the thickness of the negative electrode slurry arranged on the electrode sheet; a control part that adjusts the separation distance between the first magnet part and the second magnet part according to the thickness of the negative electrode slurry measured by the thickness measurement part. The magnetic alignment device for the negative electrode includes the above components.

2. The control part is provided with a database in which an interval reference value between the first magnet part and the second magnet part corresponding to the thickness of the negative electrode slurry is stored, calculates an interval reference value corresponding to the thickness of the negative electrode slurry measured by the thickness measurement part, and adjusts the separation distance between the first magnet part and the second magnet part. The magnetic alignment device for the negative electrode according to Claim 1.

3. The first magnet part and the second magnet part each include a single permanent magnet arranged in the width direction of the negative electrode slurry during running, a support part to which the single permanent magnet is fixed, and a distance adjustment means connected to the support part and guiding the lifting movement of the support part in a direction perpendicular to the electrode sheet during running. The magnetic alignment device for the negative electrode according to Claim 1.

4. The separation distance between the first magnet part and the second magnet part is 10 mm to 50 mm. The magnetic alignment device for the negative electrode according to Claim 1.

5. The first magnet part and the second magnet part include magnets having opposite poles to each other. The magnetic alignment device for the negative electrode according to Claim 1.

6. The thickness measurement part includes one or more of a confocal measuring instrument, a web gauge, and an IR (infrared) thickness measuring instrument. The magnetic alignment device for the negative electrode according to Claim 1.

7. The magnetic alignment device further includes a drying part that dries the negative electrode slurry in which the carbon-based negative electrode active material is aligned by the first magnet part and the second magnet part. The magnetic alignment device for the negative electrode according to Claim 1.

8. A step of applying a negative electrode slurry containing a carbon-based negative electrode active material on a negative electrode current collector; a step of aligning the carbon-based negative electrode active material contained in the negative electrode slurry using the magnetic alignment device for the negative electrode according to Claim 1; a step of drying the negative electrode slurry in which the carbon-based negative electrode active material is aligned to form a negative electrode active layer, including the above steps. The step of aligning the carbon-based negative electrode active material is controlled by adjusting the distance between the negative electrode slurry and the magnet part of the magnetic alignment device according to the thickness of the negative electrode slurry, a method for manufacturing a negative electrode.

9. The negative electrode slurry is applied with a thickness of 50 μm to 500 μm, the method for manufacturing a negative electrode according to claim 8.

10. In the negative electrode active layer, the alignment degree (O.I) of the carbon-based negative electrode active material represented by the following formula 1 is 0.1 to 5.0, [Formula 1] O.I = I ００４ / I １１０ In formula 1, I ００４ represents the area of the peak indicating the (004) crystal plane during X-ray diffraction spectroscopic measurement on the negative electrode active layer, I １１０ is the method for manufacturing a negative electrode according to claim 8, which indicates the area of the peak showing the (110) crystal plane during X-ray diffraction spectroscopic measurement with respect to the negative electrode active layer.

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