Negative electrode manufacturing apparatus for secondary battery

Abstract

The present invention relates to an apparatus for manufacturing a negative electrode for a secondary battery and a method for manufacturing a negative electrode using the same. The apparatus for manufacturing a negative electrode includes an upper block, a lower block, and a slot die including a slot for discharging a negative electrode slurry through a gap between the upper block and the lower block, and has a configuration in which, when applying the negative electrode slurry, a magnetic field having the same polarity is applied to an upper lip and a lower lip forming a discharge port at each tip of the upper block and the lower block. As a result, the carbon-based negative electrode active material in the discharged negative electrode slurry can be applied in a state in which the crystal plane is oriented at a predetermined angle with respect to the surface of the negative electrode current collector. Therefore, the manufactured negative electrode has an advantage that not only the carbon-based negative electrode active material has an excellent degree of orientation, but also that it is easy to apply to a mass production process.

Description

[Technical field]

[0001] The present invention relates to an apparatus for producing a negative electrode for use in a secondary battery, and a method for producing a negative electrode for a secondary battery using the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0173302 dated December 13, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0003] 2. Description of the Related Art In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage devices.

[0004] Such a secondary battery is a power generating element capable of being charged and discharged, which has a laminated structure of a positive electrode / a separator / a negative electrode. In general, 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. When the secondary battery is charged, lithium ions released from the positive electrode are absorbed into the carbon-based negative electrode active material of the negative electrode, and when the secondary battery is discharged, the lithium ions contained in the carbon-based negative electrode active material are absorbed into the lithium metal oxide of the positive electrode, thereby repeating charging and discharging.

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

[0006] In this regard, a technique has been proposed for magnetically orienting the graphite contained in the negative electrode in order to improve the charging performance of the negative electrode in lithium secondary batteries that use graphite. Specifically, the (0,0,2) crystal plane of the graphite is oriented in a magnetic field during the formation of the negative electrode so that it is almost horizontal to the negative electrode current collector, and then fixed. In this case, the edge face of the graphite faces the positive electrode active layer, so that the insertion and desorption of lithium ions is smooth, and at the same time, the conduction path of electrons is shortened, improving the electronic conductivity of the negative electrode, thereby improving the charging performance of the battery.

[0007] Such graphite orientation can be induced by applying a magnetic field to the negative electrode slurry that is not dried after coating a negative electrode current collector with a graphite-containing negative electrode slurry. However, when considering the production speed during mass production of actual negative electrodes, it is difficult to ensure a sufficient magnetic field application time to induce graphite alignment in the negative electrode slurry. In addition, when the strength of the magnetic field applied to the negative electrode slurry coated on the electrode sheet is increased to solve this problem, a phenomenon occurs in which the graphite is attracted by the magnetic field at the end of the magnetic field, and the orientation of the graphite aligned perpendicular to the metal sheet is destroyed, resulting in a limited degree of graphite orientation in the final negative electrode active layer.

[0008] Therefore, there is a need for a negative electrode manufacturing technique that can realize a high degree of graphite orientation and is applicable to mass production of negative electrodes for secondary batteries. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2018-0048131 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for manufacturing a negative electrode, which can realize a high degree of crystal orientation of a carbon-based negative electrode active material such as graphite contained in a negative electrode active layer and can be applied to mass production of negative electrodes for secondary batteries. [Means for solving the problem]

[0011] To solve the above problems, In one embodiment, the present invention comprises: An apparatus for producing an electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material, a slot die including an upper block, a lower block, and a slot for discharging anode slurry through a gap between the upper block and the lower block; a coating roll that transports the electrode sheet on which the negative electrode slurry discharged from the slot die is applied, The upper block and the lower block each have an upper lip and a lower lip forming a discharge port at their respective tips, and the upper lip and the lower lip exhibit magnetic properties of the same polarity.

[0012] In this case, the upper lip and the lower lip may have a structure including at least one of a permanent magnet and an electromagnet.

[0013] Furthermore, the upper and lower lips can apply a magnetic field having a strength of 500 G to 3,000 G when discharging the negative electrode slurry.

[0014] In addition, the slot die may satisfy the following formula 1:

[0015] [Formula 1] 0.3≦G / D≦5

[0016] (In formula 1, G represents the strength of the magnetic field applied at the upper and lower lips (unit: G); D represents the distance between the upper and lower blocks (unit: μm)

[0017] In addition, the negative electrode manufacturing apparatus may further include a drying unit that dries the negative electrode slurry applied to the electrode sheet, and the drying unit may be disposed at a position where the drying unit can reach within 20 seconds from the time when the negative electrode slurry discharged from the slot die is applied to the electrode sheet.

[0018] In one embodiment, the present invention further comprises: The method includes applying the negative electrode slurry to which a magnetic field is applied onto an electrode sheet using the above-described negative electrode manufacturing apparatus according to the present invention, The negative electrode slurry contains a carbon-based negative electrode active material.

[0019] In this case, the average thickness of the negative electrode slurry applied to the electrode sheet may be greater than a distance between a slot of a slot die provided in a negative electrode manufacturing apparatus and a coating roll, and the average thickness of the negative electrode slurry applied to the electrode sheet may be 100 μm or more.

[0020] The step of applying the negative electrode slurry to the electrode sheet may be performed at a speed of 5 m / min to 100 m / min.

[0021] Also, after the step of applying the negative electrode slurry to the electrode sheet, the method may further include a step of drying the applied negative electrode slurry to form a negative electrode active layer.

[0022] Here, the negative electrode active layer may have an alignment degree of 0.9 or less of the carbon-based negative electrode active material with respect to the surface of the electrode sheet represented by the following Formula 2:

[0023] [Formula 2] OI=I 004 / I 110

[0024] In formula 2, I 004 represents the area of ​​the peak showing the (0,0,4) crystal plane in X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD). Effect of the Invention

[0025] The apparatus for manufacturing a negative electrode for a secondary battery according to the present invention can apply the carbon-based negative electrode active material in the discharged negative electrode slurry in a state where the carbon-based negative electrode active material is oriented nearly perpendicular to the surface of the negative electrode current collector, and therefore the manufactured negative electrode has an excellent degree of orientation of the carbon-based negative electrode active material, and is easily applicable to a mass production process. [Brief description of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an apparatus for manufacturing a negative electrode for a secondary battery according to the present invention. [Diagram 2] FIG. 2 is a perspective view showing the structure of a single die coater provided in the secondary battery negative electrode manufacturing apparatus according to the present invention. [Diagram 3] 4 is a conceptual diagram showing the principle in which a carbon-based negative electrode active material of a negative electrode slurry is applied to an electrode sheet in a magnetically aligned state by a single die coater according to the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0028] However, this is not intended to limit the invention to any particular embodiment, but it should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0029] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and may be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] In addition, in the present invention, when a layer, film, region, plate, or other part 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 layer, film, region, plate, or other part is described as being "under" the other 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. In addition, in the present application, being "on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0031] In the present invention, "containing as a main component" may mean containing 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more) of a defined component based on the total weight (or total volume). For example, "containing graphite as a main component as a negative electrode active material" may mean containing 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 of graphite based on the total weight of the negative electrode active material, and in some cases, it may mean that the entire negative electrode active material is made of graphite and contains 100% by weight of graphite.

[0032] In the present invention, the term "lip portion" refers to a region including an upper lip of an upper block and a lower lip of a lower block. The lip portion may include a region in which each lip is disposed in a space, i.e., a slot, formed between a plurality of lips.

[0033] Similarly, in the present invention, the term "main body" refers to a region including an upper body of an upper block and a lower body of a lower block. The main body may include a region in which each body is disposed with a space formed between the bodies, i.e., a slot.

[0034] The present invention will now be described in more detail.

[0035] <Negative electrode manufacturing equipment for secondary batteries>

[0036] In one embodiment, the present invention comprises: An apparatus for producing an electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material, a slot die including an upper block, a lower block, and a slot for discharging anode slurry through a gap between the upper block and the lower block; a coating roll that transports the electrode sheet on which the negative electrode slurry discharged from the slot die is applied, The upper block and the lower block each have an upper lip and a lower lip forming a discharge port at their respective tips, and the upper lip and the lower lip exhibit magnetic properties of the same polarity.

[0037] The secondary battery negative electrode manufacturing apparatus according to the present invention is an apparatus applied when manufacturing a negative electrode for use in a secondary battery, and has a configuration in which a negative electrode slurry containing a carbon-based negative electrode active material is applied onto a negative electrode current collector to manufacture an electrode sheet.

[0038] Specifically, Fig. 1 is a cross-sectional view showing a schematic structure of an apparatus for manufacturing a negative electrode for a secondary battery according to the present invention. Referring to Fig. 1, the apparatus for manufacturing a negative electrode 10 includes a slot die 100 and a coating roll 200, and has a structure in which an electrode sheet 300 is moved by the rotation of the coating roll 200 and a negative electrode slurry is applied to the surface of the electrode sheet 300.

[0039] In this case, as shown in FIG. 2, the slot die 100 may have a slot 140 through which the negative electrode slurry is discharged formed between the upper die 110 and the lower die 120 facing each other. For example, the slot die 100 may have a spacer 130 interposed between the upper die 110 and the lower die 120 to provide a gap therebetween, thereby forming a passage through which the negative electrode slurry can move. In this case, the vertical height of the slot 140 may be determined by the thickness (Y-axis direction) of the spacer 130. The thickness of the spacer 130 may be controlled depending on the application and capacity of the secondary battery. Specifically, the thickness of the spacer 130 may be 50 μm to 2,000 μm, specifically 50 μm to 1,500 μm, 500 μm to 1,200 μm, 800 μm to 1,200 μm, 80 μm to 200 μm, 200 μm to 500 μm, or 400 μm to 700 μm.

[0040] In addition, the spacer 130 may be cut open in one region to have an opening 130a, and may be interposed in the remaining edge regions of the opposing surfaces of the upper die 110 and the lower die 120 except for one side. As a result, an outlet, i.e., a slot 140 through which the negative electrode slurry can be discharged to the outside, is formed only between the front ends of the upper die 110 and the lower die 120. Here, the front end of the upper die 110 and the front end of the lower die 120 refer to the upper lip 111 and the lower lip 121, respectively, and the slot 140 through which the negative electrode slurry is discharged can be said to be a portion formed by the separation between the upper lip 111 and the lower lip 121.

[0041] In addition, the spacer 130 also functions as a gasket to prevent the negative electrode slurry from leaking from the gap between the upper die 110 and the lower die 120, except for the area where the slot 140 is formed, so it is preferable that the spacer 130 is made of a material having sealing properties.

[0042] Meanwhile, the slot die 100 is a single die including an upper die 110 and a lower die 120, and may coat one type of negative electrode slurry in a single layer on a negative electrode current collector. In this case, the upper die 110 and the lower die 120 may include an upper lip 111 and a lower lip 121 located at each end, as well as an upper body 112 and a lower body 122 extending from each lip and closely contacting a spacer 130 to form a passage through which the negative electrode slurry can move.

[0043] In addition, the upper lip 111 and the lower lip 121 may exhibit magnetism having the same polarity, so that a magnetic field may be formed in the slot 140 formed by the upper lip 111 and the lower lip 121 in the same direction as the direction in which the negative electrode slurry is discharged.

[0044] As shown in FIG. 3, the path along which the negative electrode slurry is discharged and applied is divided into a section A where the carbon-based negative electrode active material CM (e.g., graphite) is not oriented and a section B where it is oriented. The carbon-based negative electrode active material CM of the negative electrode slurry is not affected by magnetism in the non-oriented section A including the space between the upper body 112 and the lower body 122 (i.e., I: body section), and therefore moves with a high degree of freedom. However, the oriented section B includes the space between the upper lip 111 and the lower lip 121, which exhibit magnetism of the same polarity (i.e., II: lip section). In the lip section, a repulsive force acts, and a magnetic field direction MD may be formed in the same direction as the direction in which the negative electrode slurry is discharged. As a result, the carbon-based negative electrode active material CM, i.e., graphite, contained in the negative electrode slurry before the negative electrode slurry is discharged onto the negative electrode current collector may be oriented so that the (0,0,2) crystal plane is approximately horizontal to the negative electrode current collector. The oriented graphite is applied to the negative electrode current collector while maintaining the oriented state (i.e., corresponds to III: coating region), so that the graphite can have a high degree of orientation without the application of a separate magnetic field after application of the negative electrode slurry.

[0045] At this time, the upper lip 111 and the lower lip 121 may include an electromagnet and / or a permanent magnet to exhibit magnetism. The electromagnet may include both a DC electromagnet and an AC electromagnet. In addition, the permanent magnet may include both a ferromagnetic magnet and a soft magnetic magnet, including a NdFeB magnet, a SmCo magnet, a ferrite magnet, an Alnico magnet, a FeCrCo magnet, a bond magnet (Nd-Fe-B, Sm-Fe-N, Sm-Co, Ferrite), etc.

[0046] In addition, since the negative electrode manufacturing apparatus applies a magnetic field before the negative electrode slurry is discharged onto the electrode sheet, a magnetic field with a weaker strength may be applied compared to a case where a magnetic field is applied after the negative electrode slurry is applied onto the electrode sheet. At this time, the magnetic field strength may satisfy a predetermined range. In other words, a magnetic field that satisfies a predetermined strength range may be applied to the upper lip 111 and the lower lip 121 when the negative electrode slurry is discharged. Specifically, a magnetic field having the same polarity may be applied to the upper lip 111 and the lower lip 121. In this case, the strength of the applied magnetic field may be 500G to 3,000G (Gauss), more specifically, 500G to 2,500G, 500G to 2,000G, 500G to 1,500G, 1,000G to 2,000G, 2,000G to 2,500G, 2,000G to 3,000G, 500G to 1,500G, or 500G to 900G.

[0047] By adjusting the strength of the magnetic field applied to the upper lip 111 and the lower lip 121 within the above range, the present invention may uniformly realize the crystal orientation of the carbon-based negative active material before the negative electrode slurry is discharged through the slot 140. In addition, the present invention may maintain the orientation so that the uniformly crystal-oriented carbon-based negative active material is applied onto the negative electrode current collector without changing the degree of orientation after being discharged. In addition, the present invention may prevent a situation in which the strength of the magnetic field applied to the upper lip 111 and the lower lip 121 exceeds the above range, causing the distance between the upper lip 111 and the lower lip 121 to become narrow, making it difficult to discharge the negative electrode slurry.

[0048] In addition, the slot die 100 may control the ratio of the strength (G) of the magnetic field applied to the upper lip 111 and the lower lip 121 to the width of the slot 140, i.e., the distance (D) between the upper block 110 and the lower block 120, to a predetermined range so that the carbon-based negative electrode active material contained in the negative electrode slurry can be crystal-oriented perpendicular to the surface of the electrode sheet 300 (or the negative electrode current collector) and then applied to the electrode sheet 300 (or the negative electrode current collector) while maintaining the orientation. Specifically, the slot die 100 may satisfy the following formula 1:

[0049] [Formula 1] 0.3≦G / D≦5

[0050] In formula 1, G represents the strength of the magnetic field applied at the upper and lower lips (unit: G); D represents the distance (unit: μm) between the upper block and the lower block.

[0051] The orientation of the carbon-based negative electrode active material contained in the negative electrode slurry may be affected by the strength of the applied magnetic field, the distance between the magnet to which the magnetic field is applied, etc. Therefore, in the present invention, the ratio (G / D) of the strength of the magnetic field (G) applied by the upper lip 111 and the lower lip 121 to the distance (D) between the upper block 110 and the lower block 120 may be 0.3 to 5, satisfying formula 1, so that the carbon-based negative electrode active material contained in the negative electrode slurry may be applied with its crystal plane oriented relative to the surface of the electrode sheet 300. More specifically, the slot die 100 satisfies the following conditions for formula 1: 0.3 to 3.0 (i.e., 0.3≦G / D≦3.0), 0.4 to 2.6 (i.e., 0.4≦G / D≦2.6), 0.5 to 1.5 (i.e., 0.5≦G / D≦1.5), 1.0 to 3.0 (i.e., 1.0≦G / D≦3.0), 1.1 to 1.9 (i.e., 1.1≦G / D≦1.9), 1.5 to 3. 0.0 (i.e., 1.5≦G / D≦3.0), 2.0-4.0 (i.e., 2.0≦G / D≦4.0), 0.8-1.2 (i.e., 0.8≦G / D≦1.2), 1.2-1.6 (i.e., 1.2≦G / D≦1.6), 0.4-0.9 (i.e., 0.4≦G / D≦0.9), or 1.1-1.5 (i.e., 1.1≦G / D≦1.5).

[0052] Meanwhile, the slot 140 formed by the upper lip 111 and the lower lip 121 may be positioned such that the negative electrode slurry is discharged perpendicular to the surface of the negative electrode current collector. To this end, the slot die 100 may be disposed perpendicular to the surface of the electrode sheet 300. Preferably, the slot die 100 has a rotatably mounted coating roll 200 disposed to face the slot 140 of the slot die 100 as shown in FIG 1, and the negative electrode slurry may be applied to the surface of the electrode sheet 300 (or the negative electrode current collector) as the coating roll 200 rotates and moves.

[0053] The coating roll 200 may exhibit magnetism on its surface so that the carbon-based negative electrode active material of the negative electrode slurry applied to the electrode sheet 300 may maintain an oriented state inside the slot die 100. In this case, the magnetism may have a polarity different from that of the lip parts 111 and 121 of the slot die 100. The present invention may prevent the crystal orientation of the carbon-based negative electrode active material applied to the surface of the electrode sheet 300 from being reduced by imparting magnetism having a polarity different from that of the lip parts 111 and 121 of the slot die 100 to the surface of the coating roll 200. Such magnetism may be realized by introducing at least one of a permanent magnet and an electromagnet to the surface of the coating roll 200.

[0054] Furthermore, the negative electrode manufacturing apparatus 10 according to the present invention may further include a drying unit (not shown) that dries the negative electrode slurry applied to the electrode sheet. The drying unit may be disposed at a position where the drying unit can reach a drying time of within 20 seconds, specifically, 0.01 to 20 seconds, 0.01 to 15 seconds, 0.01 to 10 seconds, or 0.01 to 5 seconds, from the time when the negative electrode slurry discharged from the slot die 100 is applied to the electrode sheet.

[0055] The drying unit functions to remove the solvent contained in the negative electrode slurry to form a negative electrode active layer and also to fix the oriented carbon-based negative electrode active material in the negative electrode slurry. To this end, the drying unit may be disposed at a position where the negative electrode slurry can be dried before the crystal orientation of the carbon-based negative electrode active material applied to the surface of the electrode sheet 300 is reduced.

[0056] In addition, the drying section includes a wall (not shown) that blocks the periphery except for an entrance / exit through which the electrode sheet 300 coated with the negative electrode slurry is introduced and removed, and a dryer (not shown) for drying the electrode sheet on the wall on the side from which the electrode sheet 300 coated with the negative electrode slurry is removed.

[0057] When the electrode sheet 300 coated with the negative electrode slurry enters through an inlet of the drying unit, energy such as light, heat, and the like supplied from the opposite wall is transferred thereto. Therefore, the wall is preferably made of a heat insulating material to prevent internal energy from being transferred to the outside and causing heat loss.

[0058] The dryer can apply energy such as light, wavelength, heat, etc., and may be any dryer commonly used in the art without any particular limitations. For example, the dryer may be an ultraviolet dryer, a near-infrared dryer, a far-infrared dryer, a hot air dryer, a vacuum oven, etc., which may be used alone or in combination.

[0059] The negative electrode manufacturing apparatus according to the present invention has the above-mentioned configuration, and thus induces crystal orientation of the carbon-based negative electrode active material before the negative electrode slurry is discharged onto the negative electrode sheet, and the carbon-based negative electrode active material can be applied in a state where it is oriented nearly perpendicular to the surface of the negative electrode current collector. As a result, the negative electrode manufactured has an excellent degree of orientation of the carbon-based negative electrode active material. In addition, since a separate orientation process of the carbon-based negative electrode active material is not required after the application of the negative electrode slurry, there are advantages in that additional equipment for manufacturing the negative electrode is not required and that it is easily applicable to a mass production process.

[0060] <Method of manufacturing negative electrode for secondary battery>

[0061] In one embodiment, the present invention further comprises: The method includes applying a negative electrode slurry to which a magnetic field is applied, to an electrode sheet using the negative electrode manufacturing apparatus according to the present invention; The negative electrode slurry provides a method for producing a negative electrode for a secondary battery, which contains a carbon-based negative electrode active material.

[0062] The method for manufacturing a negative electrode for a secondary battery according to the present invention means a method for manufacturing a negative electrode using the above-described negative electrode manufacturing apparatus of the present invention. The method for manufacturing a negative electrode includes a step of applying a negative electrode slurry to which a magnetic field is applied onto an electrode sheet. That is, the method is characterized in that the application of a magnetic field to the negative electrode slurry containing a carbon-based negative electrode active material and the application of the negative electrode slurry onto an electrode sheet (i.e., a negative electrode current collector) are performed simultaneously. As a result, the method has the advantage that it is economical since the process is simple and easy to apply to mass production since it does not require separate crystal orientation of the carbon-based negative electrode active material after application of the negative electrode slurry.

[0063] Here, the negative electrode slurry may contain a carbon-based negative electrode active material that is magnetically oriented by the negative electrode manufacturing apparatus according to the present invention as described above, and the magnetic orientation may be performed by forming a magnetic field nearly perpendicular to the surface of the electrode sheet.

[0064] In addition, the manufacturing method may control the distance between the slot of a slot die provided in the negative electrode manufacturing apparatus, i.e., a lip portion including an upper lip and a lower lip, and the coating roll, depending on the average thickness of the negative electrode slurry to be applied to the electrode sheet while maintaining the crystal orientation of the carbon-based negative electrode active material.

[0065] Even if the carbon-based negative electrode active material is oriented before discharging such that a specific crystal plane has a predetermined angle with respect to the surface of the electrode sheet, the angle or degree of orientation may change due to fluid motion corresponding to the angle at which the negative electrode slurry is applied to the surface of the electrode sheet when discharging. Therefore, in the present invention, in order to minimize the fluid motion corresponding to the angle at which the negative electrode slurry is applied when discharging the negative electrode slurry, the average thickness of the negative electrode slurry applied to the electrode sheet may be adjusted to be greater than the distance between the slot of the slot die and the coating roll of the negative electrode manufacturing apparatus. For example, the average thickness of the negative electrode slurry applied to the electrode sheet may be adjusted to 1.01 to 2.00 times, 1.01 to 1.80 times, 1.01 to 1.50 times, 1.1 to 1.5 times, or 1.2 to 1.9 times the distance between the lip of the slot die and the coating roll of the negative electrode manufacturing apparatus. In addition, the average thickness of the negative electrode slurry applied to the electrode sheet may be 100 μm or more, specifically, 100 μm or more and 300 μm or less, 110 μm or more and 190 μm or less, 200 μm or more and 300 μm or less, 150 μm or more and 230 μm or less, 100 μm or more and 250 μm or less, or 100 μm or more and 200 μm or less.

[0066] In addition, the step of applying the negative electrode slurry to the electrode sheet to which the magnetic field has been applied may be performed on the electrode sheet transported at a predetermined speed. The transport speed may be the same as the speed at which the negative electrode slurry is applied to the electrode sheet. For example, the step of applying the negative electrode slurry to the electrode sheet may be performed at a speed of 5 m / min to 100 m / min, specifically, at a speed of 5 m / min to 35 m / min, 10 m / min to 35 m / min, 20 m / min to 35 m / min, 10 m / min to 30 m / min, 5 m / min to 20 m / min, 5 m / min to 25 m / min, or 15 m / min to 25 m / min.

[0067] By performing the step of applying the negative electrode slurry within the above speed range, the present invention can prevent the negative electrode slurry from being unevenly applied on the surface of the electrode sheet due to an extremely slow application speed, while preventing a decrease in process efficiency and productivity. In addition, the present invention can prevent a decrease in the degree of orientation due to a loss of crystal alignment of the carbon-based negative electrode active material present in the negative electrode slurry caused by an excessively fast application speed.

[0068] In addition, the method for manufacturing a negative electrode for a secondary battery according to the present invention may further include, after the step of applying the negative electrode slurry to the electrode sheet, a step of drying the applied negative electrode slurry to form a negative electrode active layer.

[0069] The step of forming the negative electrode active layer refers to a process of fixing the carbon-based negative electrode active material contained in the negative electrode slurry onto the electrode sheet by drying the negative electrode slurry. This step may be applied without any particular limitation as long as it can fix the carbon-based negative electrode active material of the negative electrode slurry applied to the electrode sheet while minimizing a change in the degree of orientation of the carbon-based negative electrode active material with respect to the surface of the electrode sheet.

[0070] Specifically, the drying may be performed by applying energy such as light, wavelength, heat, etc., and may be performed by using an ultraviolet dryer, a near-infrared dryer, a far-infrared dryer, a hot air dryer, a vacuum oven, etc., alone or in combination.

[0071] Meanwhile, the carbon-based negative electrode active material contained in the negative electrode slurry may include a carbon-based negative electrode active material that is generally used in lithium secondary batteries. Specifically, the carbon-based negative electrode active material may mean a material mainly composed of carbon atoms. Such a carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite, and preferably includes natural graphite or a mixture of natural graphite and artificial graphite.

[0072] The carbon-based negative electrode active material is preferably a spherical graphite granule formed by the aggregation of a plurality of flake graphite. Examples of flake graphite include natural graphite and artificial graphite, as well as mesophase calcined carbon (bulk mesophase) made from tar pitch as a raw material, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), and in particular, those assembled using a plurality of highly crystalline natural graphite are preferred. In addition, one graphite granule may be formed by the aggregation of 2 to 100 flake graphite particles, preferably 3 to 20 flake graphite particles.

[0073] Such a carbon-based negative electrode active material, specifically graphite, may have a spherical particle shape, and the sphericity of the graphite particles may be 0.75 or more, for example, 0.75 to 1.0, 0.75 to 0.95, 0.8 to 0.95, or 0.90 to 0.99. Here, the "sphericity" may 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, and when the sphericity is 1, it means that the particle shape is spherical. The sphericity may be measured using a particle shape analyzer. The present invention may realize a shape of the carbon-based negative electrode active material close to a sphere, thereby realizing a high electrical conductivity of the negative electrode active layer. Therefore, the present invention has the advantage of improving the capacity of a secondary battery and increasing the specific surface area of ​​the negative electrode active material, thereby improving the adhesive force between the negative electrode active layer and the current collector.

[0074] In addition, the carbon-based negative electrode active material has an average particle size (D 50 ), specifically, the average particle size (D 50 ) can be shown.

[0075] The average particle size of the spherical natural graphite is preferably as small as possible to maximize the degree of disorder in the direction of expansion of each particle so as to prevent the expansion of the particles due to charging with lithium ions. However, if the particle size of the natural graphite is less than 5.0 μm, a large amount of binder is required due to the increase in the number of particles per unit volume, and the sphericity and sphericity yield may be reduced. On the other hand, if the maximum particle size exceeds 10 μm, the expansion becomes so intense that repeated charging and discharging reduces the adhesion between particles and between the particles and the current collector, and the cycle characteristics may be significantly reduced.

[0076] In addition, the negative electrode slurry may further include a conductive material, a binder, a thickener, and the like, in addition to the carbon-based negative electrode active material, and these may be materials commonly used in the art.

[0077] The conductive material may include, but is not limited to, one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like.

[0078] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0079] At this time, the content of the conductive material may be 0.1 parts by weight to 10 parts by weight, specifically 0.1 parts by weight to 8 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 3 parts by weight, 2 parts by weight to 6 parts by weight, or 0.5 parts by weight to 2 parts by weight. 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 due to a low content of the conductive material, resulting in a decrease in the charging capacity. In addition, the present invention can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of the conductive material, resulting in a decrease in the charging capacity, or a decrease in the rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0080] In addition, the binder is a component that aids in bonding between the negative electrode active material and the conductive material and the like and bonding to the negative electrode current collector, and may be suitably applied within a range that does not deteriorate the electrical properties of the electrode. Specifically, the binder may include any one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber.

[0081] The content of the binder may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight, based on 100 parts by weight of the total negative electrode slurry. By controlling the content of the binder contained in the negative electrode slurry within the above range, the present invention can prevent a decrease in adhesive strength of the negative electrode active layer due to a low content of the binder, or a decrease in electrical properties of the electrode due to an excessive amount of the binder.

[0082] The method for producing a secondary battery negative electrode sheet according to the present invention has the above-mentioned configuration, and thus has the advantage that the carbon-based negative electrode active material of the negative electrode slurry applied onto the negative electrode current collector can be uniformly aligned with a high degree of orientation.

[0083] <Secondary battery negative electrode>

[0084] Further, in one embodiment, the present invention provides The negative electrode of a secondary battery is prepared by the above-mentioned method.

[0085] 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 as a main component on at least one surface of a negative electrode current collector. The negative electrode active layer is a layer that realizes the electrical activity of the negative electrode, and is manufactured by coating both surfaces of the electrode current collector with an electrode slurry containing a carbon-based negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charging and discharging of the battery, and then drying and rolling the same. Here, the negative electrode active layer is formed by coating and drying the negative electrode slurry to which a magnetic field is applied using the above-mentioned negative electrode manufacturing device on an electrode sheet, and is characterized by high crystal orientation of the carbon-based negative electrode active material, which is the main component, with respect to the surface of the electrode sheet. As a result, the negative electrode having the negative electrode active layer has the advantage of exhibiting high energy density and charge / discharge performance.

[0086] Specifically, in the negative electrode according to the present invention, the carbon-based negative active material contained in the negative active layer may be aligned at a predetermined angle with respect to the electrode sheet (or negative current collector). Such alignment of the carbon-based negative active material may reduce the degree of disorder in the negative active layer, thereby reducing the electrode resistance and providing a path for lithium ions to move. In this case, the crystal orientation of the carbon-based negative active material (e.g., graphite) may be determined by crystal plane analysis of the carbon-based negative active material contained in the negative active layer.

[0087] As one example, in the negative electrode active layer, the carbon-based negative electrode active material may be aligned in a certain direction with respect to the negative electrode current collector, and when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD), the average alignment degree of the carbon-based negative electrode active material represented by the following Formula 2 may be 0.9 or less:

[0088] [Formula 2] OI=I 004 / I 110

[0089] In formula 2, I 004 represents the area of ​​the peak showing the (0,0,4) crystal plane in X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0090] The formula 2 above can be an index showing the degree to which the crystal structure of the spherical carbon-based negative electrode active material is aligned in a certain direction, specifically, with respect to the surface of the negative electrode current collector, when measured by X-ray diffraction. More specifically, the negative electrode active layer shows 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 negative electrode active material graphite when measured by X-ray diffraction, which indicate the (0,0,2) plane, (1,0,0) plane, (1,0,1)R plane, (1,0,1)H plane, (0,0,4) plane, and (1,1,0) plane. In addition, the peak appearing at 2θ=43.4±0.2° may be due to an overlap of the (1,0,1)R plane of the carbon-based negative electrode active material and the peak corresponding to the (1,1,1) plane of the current collector, for example, copper (Cu).

[0091] Among these, the degree of alignment (OI) of the carbon-based negative electrode active material can be measured by the area ratio of the peak at 2θ=77.5±0.2° indicating the (1,1,0) plane and the peak at 2θ=54.7±0.2° indicating the (0,0,4) plane, specifically, the area ratio obtained by integrating the intensities of the above peaks. Here, the peak at 2θ=54.7±0.2° is a peak indicating the (0,0,4) plane, which is one of the crystal planes of graphite and has an inclination with respect to the negative electrode current collector, so that the degree of alignment (OI) closer to 0 means that the inclination with respect to the surface of the negative electrode current collector is closer 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 view of this, in the negative electrode active layer according to the present invention, the carbon-based negative electrode active material is aligned nearly perpendicular to the negative electrode current collector, for example, at an angle of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, or 70° to 85° to the negative electrode current collector, so that the degree of alignment (OI) of the carbon-based negative electrode active material may be lower than when the carbon-based negative electrode active material is not magnetically aligned.

[0092] In the negative electrode according to the present invention, the degree of alignment (OI) according to formula 2 when measured by X-ray diffraction on the surface of the negative electrode active layer may be 0.9 or less, specifically 0.8 or less, 0.7 or less, 0.6 or less, 0.1 to 0.9, 0.2 to 0.8, 0.3 to 0.7, 0.2 to 0.6, or 0.4 to 0.6.

[0093] Meanwhile, the average thickness of the negative electrode active layer may be 50 μm to 300 μm, specifically 50 μm to 250 μm, 100 μm to 250 μm, or 100 μm to 200 μm. By adjusting the average thickness of the negative electrode active layer within the above range, the present invention can not only increase the energy density of the electrode, but also uniformly control the degree of disorder of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0094] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, the negative electrode current collector may include copper, stainless steel, nickel, titanium, calcined carbon, etc., and in the case of copper or stainless steel, it may also include those that are surface-treated with carbon, nickel, titanium, silver, etc. In addition, the average thickness of the negative electrode current collector may be suitably applied to be 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0095] The present invention will now be described in more detail with reference to examples and experimental examples.

[0096] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0097] Examples 1 to 5 and Comparative Examples 1 to 2. Production of sheets for secondary battery negative electrodes

[0098] A graphite mixture of natural graphite and artificial graphite in a weight ratio of 2:8 was prepared as the negative electrode active material, carbon black was prepared as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were prepared as the binder. 95 parts by weight of the graphite mixture, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to a solid content of 50% to produce a negative electrode slurry.

[0099] Separately, a negative electrode manufacturing apparatus was prepared, which included a slot die in which an upper block, a spacer, and a lower block were sequentially stacked and which had a slot at its tip through which negative electrode slurry could be discharged, and a coating roll arranged to face the slot of the slot die. In this case, in the negative electrode manufacturing apparatus, i) the type of magnetic polarity imparted to the upper lip of the upper block and the lower lip of the lower block, ii) the type of magnetic polarity imparted to the coating roll, and iii) the ratio (G / D) of the strength of the magnetic field applied to the upper lip and the lower lip and the distance (D) between the upper block and the lower block were adjusted as shown in Table 1 below.

[0100] The negative electrode slurry prepared earlier was put into the prepared negative electrode manufacturing equipment, and the negative electrode slurry was applied to the surface of a copper sheet (thickness: 8 μm) that was being transported at a speed of 10 m / min. Next, hot air was continuously blown onto the applied negative electrode slurry to dry it, forming a negative electrode active layer.

[0101] [Table 1]

[0102] Experimental Example

[0103] The orientation exhibited by the carbon-based negative electrode active material of the secondary battery negative electrode produced using the negative electrode production apparatus according to the present invention was evaluated.

[0104] Specifically, X-ray diffraction spectroscopy (XRD) was performed on three arbitrary points of the negative electrode active layer to measure the spectrum for each of the negative electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 and 2. The measurement conditions for X-ray diffraction (XRD) were as follows:

[0105] - Target: Cu (Kα-ray) Graphite monochromator - Slit: Divergence slit = 1 degree, Receiving slit = 0.1mm, Scattering slit = 1 degree - Measurement area: (1,1,0) plane: 76.5 degrees < 2θ < 78.5 degrees / (0,0,4) plane: 53.5 degrees < 2θ < 56.0 degrees

[0106] From the spectrum measured under the above conditions, the degree of alignment (OI) of each carbon-based negative electrode active material according to formula 2 was calculated, and the average degree of alignment (OI) of the carbon-based negative electrode active material at the three calculated points was obtained. The results are shown in Table 2.

[0107] [Formula 2] OI=I 004 / I 110

[0108] In formula 2, I 004 represents the area of ​​the peak showing the (0,0,4) crystal plane in X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

[0109] [Table 2]

[0110] As shown in Table 2, the negative electrode manufactured using the negative electrode manufacturing apparatus according to the present invention has a high degree of orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0111] This means that when the tips of the upper and lower blocks constituting the slot die, i.e., the lip portions, are given magnetism of the same polarity when the negative electrode slurry is discharged, the crystal plane of the carbon-based negative electrode active material is oriented nearly perpendicular to the electrode sheet before the negative electrode slurry is applied to the electrode sheet (or negative electrode current collector), and the carbon-based negative electrode active material is applied to the electrode sheet and maintained in this induced orientation to form a negative electrode active layer.

[0112] From these results, the negative electrode manufacturing apparatus according to the present invention can apply the carbon-based negative electrode active material in the discharged negative electrode slurry in a state in which the carbon-based negative electrode active material is oriented at a predetermined angle relative to the surface of the negative electrode current collector, and therefore has the advantage that not only is the orientation of the carbon-based negative electrode active material of the manufactured negative electrode excellent, but it is also easily applicable to mass production processes.

[0113] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art may make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as described in the claims below.

[0114] Therefore, the technical scope of the present invention is not limited to the contents described in the Summary of the Invention of the specification, but can be defined by the claims. [Explanation of symbols]

[0115] 10: Apparatus for manufacturing anodes for secondary batteries according to the present invention 100: Single die coater 110: Upper die 111: Upper lip 112: Upper body 120: Lower die 121: Lower lip 122: Lower body 130: Spacer 130a: Open part 140: Slot 200: Coating roll 300: Electrode sheet A: Unoriented section B: Orientation section I: Main body II: Lip section III: Coating area MD: Magnetic field direction CM: Carbon-based negative electrode active material

Claims

1. An apparatus for producing an electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material, a slot die including an upper block, a lower block, and a slot for discharging anode slurry through a gap between the upper block and the lower block; a coating roll that transports the electrode sheet on which the negative electrode slurry discharged from the slot die is applied, the upper block and the lower block each have an upper lip and a lower lip that form an outlet at their respective tips, and the upper lip and the lower lip exhibit magnetic properties having the same polarity.

2. 2. The apparatus for manufacturing a negative electrode for a secondary battery according to claim 1, wherein the upper lip and the lower lip apply a magnetic field having a strength of 500 G to 3,000 G when the negative electrode slurry is discharged.

3. The apparatus for manufacturing a negative electrode for a secondary battery according to claim 1, wherein the slot die satisfies the following formula 1: [Formula 1] 0.3≦G / D≦5 In Formula 1, G represents the strength of the magnetic field applied at the upper and lower lips (units: G); D represents the distance (unit: μm) between the upper block and the lower block.

4. The apparatus for manufacturing a negative electrode for a secondary battery according to claim 1 , wherein the upper lip and the lower lip have a structure including at least one of a permanent magnet and an electromagnet.

5. The negative electrode manufacturing apparatus further includes a drying unit that dries the negative electrode slurry applied to the electrode sheet, 2 . The apparatus for manufacturing a negative electrode for a secondary battery according to claim 1 , wherein the drying unit is disposed at a position where the negative electrode slurry discharged from the slot die reaches within 20 seconds from the time when the negative electrode slurry is applied to the electrode sheet.

6. The method includes applying the negative electrode slurry to which a magnetic field is applied, to the electrode sheet by using the negative electrode manufacturing apparatus according to any one of claims 1 to 5, The negative electrode slurry contains a carbon-based negative electrode active material.

7. 7. The method of claim 6, wherein an average thickness of the negative electrode slurry applied to the electrode sheet is greater than a distance between the slot of the slot die and the coating roll of the negative electrode manufacturing apparatus.

8. The method for producing a negative electrode for a secondary battery according to claim 6 , wherein the average thickness of the negative electrode slurry applied to the electrode sheet is 100 μm or more.

9. 7. The method for producing a negative electrode for a secondary battery according to claim 6, wherein the step of applying the negative electrode slurry to the electrode sheet is performed at a speed of 5 m / min to 100 m / min.

10. 7. The method of claim 6, further comprising the step of drying the applied negative electrode slurry to form a negative electrode active layer after the step of applying the negative electrode slurry to the electrode sheet.

11. 11. The method of claim 10, wherein the negative electrode active layer has an alignment degree of the carbon-based negative electrode active material with respect to the surface of the electrode sheet, which is represented by the following formula 2, of 0.9 or less: [Formula 2] O.I=I ００４ / I １１０ In formula 2, I ００４ represents the area of ​​the peak indicating the (0,0,4) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD), I １１０ represents the area of ​​the peak indicating the (1,1,0) crystal plane when the negative electrode active layer is measured by X-ray diffraction spectroscopy (XRD).

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