Method and apparatus for manufacturing electrodes for secondary batteries

Abstract

The present invention provides a method for manufacturing an electrode for a secondary battery in which thickness unevenness such as sliding and side rings is improved, a method for manufacturing an electrode for a secondary battery in which sliding deviation between the top surface and the back surface of a current collector is minimized when a slurry is sequentially coated on the top surface and the back surface, and an apparatus suitable for carrying out such a method. The method for manufacturing an electrode for a secondary battery according to the present invention includes the steps of forming an artificial step on a current collector and coating an electrode active material layer on the step.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for manufacturing an electrode for a secondary battery, and more particularly to a method including a step of coating a current collector with a slurry containing an electrode active material, and an apparatus capable of carrying out such a method.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0185030, filed on December 26, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] Secondary batteries, which have high applicability across a range of products and electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are powered by electrical sources. These secondary batteries not only have the temporary advantage of dramatically reducing the use of fossil fuels, but also have the advantage of producing no by-products associated with energy use, and are therefore attracting attention as a new energy source that is environmentally friendly and improves energy efficiency.

[0004] Known examples of such secondary batteries include lithium-ion batteries, lithium polymer batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries. A battery module or battery pack can be constructed by connecting multiple battery cells in series or parallel. Depending on the required charge / discharge capacity of the battery pack, multiple battery cells can also be connected in parallel to construct a battery pack. Among these, lithium-ion batteries are widely used in IT devices, electric vehicles, and other applications due to their long life and easy charging. Lithium secondary batteries can be broadly classified into prismatic secondary batteries, in which an electrode assembly is housed in a metal can, and pouch-type secondary batteries, in which an electrode assembly is housed in a pouch case made of an aluminum laminate sheet, based on the shape of the battery case. Furthermore, they can be broadly classified into cylindrical cells and prismatic cells, based on the shape of the metal can.

[0005] In addition, the electrode assembly housed in the battery case is a chargeable and dischargeable power generating element having a laminated structure of a positive electrode / separator / negative electrode, and examples thereof include a jelly-roll type electrode assembly in which a separator is interposed between long sheet-like positive and negative electrodes coated with an active material and the electrodes is wound up; a stack type electrode assembly in which a plurality of positive and negative electrodes cut into units of a predetermined size are stacked in this order with a separator interposed; and a stack / folding type electrode assembly in which a bi-cell or full cell in which a predetermined unit of positive and negative electrodes and a separator are interposed is wound up.

[0006] The positive and negative electrodes of such an electrode assembly are manufactured by coating a current collector with a slurry containing an electrode active material in a predetermined pattern and to a predetermined thickness to form an electrode active material layer, followed by drying and rolling. A slot die coater including a shim can be used to coat the slurry. However, because the slurry is a fluid, it tends to flow down after coating, and this flowing of the slurry is called sliding.

[0007] FIG. 1 shows a part of a cross section of an electrode sheet 10 in which one side of the current collector is coated with a slurry, showing the state in which sliding has occurred.

[0008] Referring to FIG. 1, an electrode active material layer 12 is formed on a current collector 11. At the edge of the electrode active material layer, part of the slurry flows down, and the thickness of the electrode active material layer 12 gradually decreases toward the side, resulting in an electrode sliding (S) phenomenon.

[0009] Such sliding may occur frequently at both widthwise ends of the support portion, where the slurry is coated, resulting in variations in loading. Sliding also leads to variations during rolling, and further results in the NP ratio (the face-to-face ratio between the negative and positive electrode active material layers) failing to meet the design requirements. While the discharge capacity ratio between the positive and negative electrodes in the flat coating area is maintained at the designed value, sliding occurs at the location where the edge of the positive electrode faces the edge of the negative electrode, resulting in deviations in the discharge capacity ratio and potentially reduced stability. For these reasons, it is necessary to control sliding during the slurry coating process. In particular, when coating a stripe pattern using a slot die coater, it is necessary to control the shape of the interface (sliding area), particularly the sliding length.

[0010] As shown in Figure 1, the typical shape of the sliding region S in the electrode profile is one in which the thickness increases as the width distance from the coating start point Ps increases, and then the rate of thickness increase gradually decreases beyond a certain width distance, resulting in a flattened shape where the thickness barely increases and converges to a constant value. The sliding length SL can be defined as the width distance from the coating start point Ps to the sliding end point Pe. The sliding end point Pe can be considered the point where the electrode profile begins to flatten. For example, it can be considered the point where the target coating layer thickness is reached or is close to reaching a certain percentage range.

[0011] However, to form electrode active material layers on both sides of a current collector, a sequential coating method is sometimes used, in which the top surface is coated first and then the back surface. However, the sliding length of the top surface tends to be longer than that of the back surface. Therefore, even if coating is performed using a slot die coater with the same shim, this can cause a problem of reduced electrode quality on the top surface. Furthermore, even if the electrode active material layer on the top surface is formed with a good edge shape, the electrode active material layer on the back surface may suffer from side rings. Therefore, simultaneous management of the top and back surfaces is required during sequential slurry coating.

[0012] Meanwhile, in order to manufacture high-energy density secondary batteries, the thickness of electrode active material layers has gradually increased from approximately 130 μm to as much as 300 μm. When thick electrode active material layers are formed using a conventional slot die coater, migration of the binder and conductive material in the slurry becomes severe during drying, resulting in uneven final electrodes. To address this issue, a thick electrode active material layer is first applied thinly and then dried, and then another layer is applied on top of that and dried again. This double-layer coating process, however, has the drawback of taking a long time. To simultaneously improve electrode performance and productivity, double-layer coating is often performed using a dual slot die coater with two shims, allowing the slurry to be applied to the top and bottom layers simultaneously.

[0013] Even in double-layer coating, sliding occurs at the edge during top surface coating, and this sliding at the edge of the top surface acts as a sagging of the substrate during back surface coating, causing slurry bias at the edge during back surface coating, which can lead to a side ring phenomenon in which the edge of the back surface protrudes upward. Furthermore, in the case of double-layer coating, as shown in Figure 2, there is a risk of defects occurring, such as a width difference W between the upper layer 18a and the lower layer 19a on the top surface of the current collector 11. The loading reduction L due to this width difference W can cause the substrate to sag more severely than in single-layer coating.

[0014] Previously, slurry coating was performed by placing a flat coating roll along the width direction at the front end of a slot die coater. Attempts to improve sliding have been made by modifying the shim and manifold configuration of the slot die coater. However, designing and replacing shims each time to match the slurry properties and pattern shape requires considerable effort and cost, and process management is extremely strict due to the need to disassemble and reassemble the die. Furthermore, designing various shims and selecting one of them is costly, time-consuming, and cumbersome. This process must be repeated as electrode specifications change. Another drawback is that the electrode loading conditions must be re-stabilized every time the shim configuration is changed. Furthermore, because the manifold cannot be changed in a slot die coater that includes a manifold that has already been designed, a new slot die coater must be installed whenever a manifold change is required. Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made under the above-mentioned circumstances to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing an electrode for a secondary battery in which thickness unevenness phenomena such as sliding and side rings are improved.

[0016] Another object of the present invention is to provide a method for manufacturing an electrode for a secondary battery, which can minimize sliding deviation between the top surface and the back surface of a current collector when coating the top surface and the back surface of the current collector with a slurry sequentially.

[0017] A further object of the present invention is to provide an apparatus suitable for carrying out such a method for manufacturing electrodes for secondary batteries.

[0018] However, the technical problems that the present invention aims to solve are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention given below. [Means for solving the problem]

[0019] In order to solve the above-mentioned problems, a method for manufacturing an electrode for a secondary battery according to the present invention includes the steps of forming an artificial step on a current collector and coating an electrode active material layer on the step.

[0020] To create an artificial step in the current collector, tape can be applied locally to the coating roll on which the current collector rests.

[0021] In order to create an artificial step on the current collector, a metal or metal alloy coating layer may be locally formed on the coating roll on which the current collector is placed.

[0022] The step may be formed to a width narrower than the coating width of the electrode active material layer, and may be formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from the edge of the electrode active material layer.

[0023] The method for manufacturing an electrode for a secondary battery may further include coating an additional electrode active material layer at a position aligned with the electrode active material layer on the opposite surface of the current collector on which the electrode active material layer is coated.

[0024] The method for manufacturing an electrode for a secondary battery may further include a step of coating the current collector with the electrode active material layer while running the current collector over the coating roll, drying the current collector, and winding the current collector onto a take-up roll, and then unwinding the take-up roll in the opposite direction to coat an additional electrode active material layer at a position aligned with the electrode active material layer on the opposite surface of the current collector coated with the electrode active material layer.

[0025] The electrode active material layer is formed by coating a slurry containing 40% to 50% solid content to a thickness of 70 μm to 200 μm, and the step is formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from the edge of the electrode active material layer. Compared to an electrode active material layer formed under the same conditions without the step, the sliding length may be improved by 15% to 20% and the sliding thickness may be improved by 20% to 30%.

[0026] In order to solve the above-mentioned other problems, a method for manufacturing an electrode for a secondary battery according to the present invention includes the steps of: placing a current collector on a coating roll having a step formed thereon that is narrower than a coating width over which an electrode active material layer is to be coated; and discharging a slurry through a slot die coater to coat an electrode active material layer on the step, thereby coating a top surface of the current collector; and inverting the current collector whose top surface has been coated, placing it on a coating roll having no step, and discharging a slurry through a slot die coater to coat an additional electrode active material layer at a position aligned with the electrode active material layer, thereby coating a back surface of the current collector.

[0027] The stepped coating roll may include a tape locally attached thereto.

[0028] The stepped coating roll may also include a locally formed metal or metal alloy coating layer.

[0029] The step may be formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from the edge of the electrode active material layer.

[0030] The step may cause a difference in the coating gap between the edge / center die lip of the slot die coater and the current collector.

[0031] By allowing the slurry to flow onto the side of the step, sliding can be reduced in the coating profile of the electrode active material layer.

[0032] The electrode active material layer and the additional electrode active material layer may have substantially the same sliding length of 3 mm to 4 mm.

[0033] In order to solve the above-mentioned further problem, an apparatus for manufacturing an electrode for a secondary battery according to the present invention includes a coating roll for top surface coating, which has a step formed thereon that is narrower than the coating width of an electrode active material layer, a coating roll for back surface coating, which does not have a step formed thereon, and a slot die coater.

[0034] The coating roll for the top surface coating application may include locally applied tape.

[0035] The coating roll for the top surface coating application may include a locally formed metal or metal alloy coating layer.

[0036] The step may be formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from the edge of the electrode active material layer.

[0037] The step can result in a difference in coating gap between the edge / center die lip of the slot die coater and the current collector placed on the coating roll for the top surface coating application.

[0038] The coating roll for coating the top surface may have a step formed thereon, the center of the electrode active material layer being higher than both edge portions thereof. [Effects of the Invention]

[0039] According to the present invention, sliding can be improved by creating an artificial step on the current collector and coating the electrode active material layer on the step, which can prevent variations in loading due to sliding and solve the problem of variations during rolling.

[0040] According to the present invention, a stepped coating roll can be used as a means for creating an artificial step on a current collector. The stepped coating roll can be easily realized by applying tape, or can be achieved with precision and durability by forming a metal or metal alloy coating layer. In particular, tape can be easily applied and removed, which is advantageous in that it can be realized as a variable coating roll that can flexibly accommodate model numbers with changed coating widths.

[0041] According to the present invention, it is possible to manufacture an electrode for a secondary battery by improving the deviation of the sliding portion between the top surface and the back surface, so that the NP ratio, which is the face-to-face ratio between the negative electrode active material layer and the positive electrode active material layer, satisfies the design condition, and the discharge capacity of the positive electrode does not exceed the discharge capacity of the negative electrode, preventing lithium precipitation and ensuring the safety of the secondary battery.

[0042] According to the present invention, in a sequential coating method in which the back surface is coated after the top surface is coated, it is possible to prevent side rings from occurring on the back surface, and there is an advantage in that the top surface and the back surface can be easily and simultaneously controlled.

[0043] According to the present invention, not only for single layers but also for double layers, the shape of the boundary surface (sliding portion) can be controlled effectively when coating a stripe pattern using a slot die coater.

[0044] According to the present invention, the device only needs to be operated by selectively using a coating roll for top surface coating and a coating roll for back surface coating, which significantly reduces replacement costs, labor, and time compared to conventional methods that utilize shims or improvements to the manifold shape.

[0045] According to the present invention, there is no need to change the shim or improve the manifold to meet the electrode design requirements. The simple method of simply adjusting the step formed on the coating roll is highly effective in improving sliding. According to the present invention, there is no need to replace the slot die or reassemble the shim, so there is no problem with deviations caused by these.

[0046] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical concepts of the present invention as well as the content of the invention, and therefore the present invention should not be interpreted as being limited to only the matters depicted in the drawings. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 10 is a cross-sectional view of an electrode sheet showing electrode sliding. [Figure 2] FIG. 10 is a diagram showing a state in which a difference in width occurs between the upper layer and the lower layer in a double layer. [Figure 3] 1 is a schematic diagram of an electrode in stages according to a conventional sequential coating method, which is the background to the invention. [Figure 4] 1 is a schematic cross-sectional view in the X direction of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention. [Figure 5] 1 is a schematic diagram of a cross section in the Y direction of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention. [Figure 6] 1 is a schematic top view of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention; [Figure 7]FIG. 7 is a perspective view of a coating roll that can be included in the apparatus shown in FIGS. [Figure 8] 1 is a diagram showing a profile of an electrode active material layer according to a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention in comparison with a conventional method. [Figure 9] 5A to 5C are schematic views illustrating steps in a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention. [Figure 10] 1 is a schematic diagram of an electrode manufacturing apparatus for a secondary battery according to an embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing the position where tape is attached to the coating roll. DETAILED DESCRIPTION OF THE INVENTION

[0048] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventor can appropriately define the concepts of terms himself / herself in order to best describe the invention. Therefore, it should be understood that the embodiment described in this specification and the configuration shown in the drawings are merely a preferred embodiment of the present invention and do not represent the entire technical ideas of the present invention, and therefore, various equivalent and modified embodiments may be available as of the time of filing this application.

[0049] The inventors of the present invention analyzed the cause of the tendency for the sliding length on the top surface to be long and the sliding length on the back surface to be short during sequential coating. They found that this is due to whether or not the electrode active material layer is coated on the current collector during top and back surface coating. When coating the top surface, the sliding length is long due to limitations on the fluid interface characteristics caused by coating the current collector. However, they determined that the sliding length on the back surface is short because a stripe coating of the same width is applied to the opposite side of the top surface, and the electrode active material slurry flows into the area where sliding occurs on the top surface. Therefore, they found that thickness variations such as sliding in the electrode coating profile can be eliminated by first coating the top surface under the same conditions as the back surface, leading to the present invention.

[0050] 3 is a schematic diagram of an electrode in stages according to a conventional sequential coating method, which is the background to the invention as described above. The background of the invention will be described in detail with reference to FIG. 3.

[0051] FIG. 3(a) shows the state in which the top surface of the current collector 11 is coated with a double layer of an upper layer 18a and a lower layer 19a. When coating the top surface, a sliding phenomenon (S) occurs, causing loading depressions at the edge. The sliding length of the top surface is TS. Experiments have shown that TS is approximately 4 mm to 6 mm under typical negative electrode active material slurry conditions.

[0052] Figure 3(b) shows the current collector 11 flipped over so that the back surface faces up and placed on the coating roll 20. The uncoated portion of the current collector 11 contacts the coating roll 20, causing a substrate depression H. In this way, the sliding S that occurs at the edge during top surface coating acts as a substrate depression H during back surface coating. This is a problem that inevitably occurs with conventional sequential coating.

[0053] In this state, if the back surface of the current collector 11 is coated with a double layer of upper and lower layers 18b and 19b, as shown in Figure 3(c), the slurry bias (SS) at the edge of the back surface increases loading at the edge. Even if the thickness of both sides of the coated electrode is sufficient, if the current collector 11 is left flat after the back surface coating is completed, as shown in Figure 3(d), the slurry bias (SS) generated during the back surface coating will cause the edge of the back surface to protrude upward, resulting in a side ring (SR) phenomenon. Sliding also occurs on the back surface, with a length (BS). Experiments have shown that the sliding length (BS) under typical negative electrode active material slurry conditions is approximately 2 mm to 4 mm. Thus, the sliding length (TS) of the top surface is greater than the sliding length (BS) of the back surface (TS > BS).

[0054] Thus, in the sequential coating method, the sliding length TS of the top surface and the sliding length BS of the back surface are different. This phenomenon occurs in coaters with one or two drying ovens. In a one-stage coater, after the top surface is dried, the current collector is flipped over and the back surface is coated. In a two-stage coater, the top surface is dried before coating the back surface.

[0055] The inventors of the present invention focused on the difference in coating gap between the top and back surfaces in sequential coating methods in which the top surface is coated first and then the back surface. As shown in Figure 3(a), when coating the top surface, the current collector 11 is coated, which limits the interfacial characteristics of the fluid, resulting in a long sliding length TS. In contrast, when coating the back surface, as shown in Figure 3(c), the slurry flows into the area where sliding S has already occurred on the top surface, resulting in a short sliding length BS on the back surface. Since the top and back surfaces are not coated simultaneously, there is a difference in the coating gap. The inventors of the present invention therefore realized that the sliding lengths can be made approximately the same by making the conditions for coating the top and back surfaces as nearly identical as possible. In other words, when coating the top surface, the back surface is uncoated, while when coating the back surface, the top surface is coated, so a difference in the coating gap is inevitable. Therefore, if the top surface is first coated under the same or nearly the same conditions as the back surface coating after the top surface coating, the difference in coating gap can be eliminated or reduced. Therefore, the inventors of the present invention propose to create an artificial step on the current collector during the top surface coating and form the electrode active material layer on the step.

[0056] Fig. 4 is a schematic cross-sectional view in the X direction of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention. Fig. 5 is a schematic cross-sectional view in the Y direction of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention. Fig. 6 is a schematic top view of an apparatus for explaining a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention. Fig. 7 is a perspective view of a coating roll that can be included in the apparatus shown in Figs. 4 to 6. Fig. 8 is a view showing a profile of an electrode active material layer according to a method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention in comparison with a conventional method.

[0057] A method for manufacturing an electrode for a secondary battery according to one embodiment of the present invention includes the steps of forming an artificial step 115 on a current collector 110 and coating an electrode active material layer 130 on the step 115. To perform this method, an apparatus including a coating roll 120 and a slot die coater 140 as shown in FIGS. 4 to 6 can be used.

[0058] The slot die coater 140 may have a single slot or dual slots. The illustrated example shows a single slot. The slot die coater 140 includes a lower die 141, an upper die 142, and a shim 144 disposed between them to form a slot 143. In this embodiment, the slot die coater 140 includes two die blocks, the lower die 141 and the upper die 142, but the number of die blocks may be two or more. The end of the slot 143 is the discharge port 143a. In FIG. 4, the slot die coater 140 is disposed with the direction in which the slurry is discharged (X direction) approximately horizontal (mostly ±5°). However, the present invention is not limited to the shape given as an example here. For example, it is also possible to configure the slot die as a vertical die with the direction in which the slurry is discharged upward (Z direction).

[0059] The slot 143 is formed between the upper die 142 and the lower die 141 where they face each other. A shim 144 is interposed therebetween to provide a gap between them, thereby forming the slot 143 which corresponds to a passage through which the slurry can flow. The thickness of the shim 144 determines the vertical width of the slot 143 (Z direction, slot gap).

[0060] Either the upper die 142 or the lower die 141 may have a manifold 145 having a predetermined depth and communicating with the slot 143. In this embodiment, an example is given in which the manifold 145 is provided in the lower die 141. Although not shown, such a manifold 145 is connected to an externally disposed slurry supply chamber (not shown) by a supply pipe to receive the supply of slurry. When the manifold 145 is filled with slurry, the flow of the slurry is guided along the slot 143 and discharged to the outside through the discharge port 143a.

[0061] The shim 144 has a region intermittently cut out to provide multiple openings, and can be interposed in the remaining portion of the edge region of the opposing surfaces of the upper die 142 and the lower die 141 except for one side. Therefore, a discharge port 143a through which the slurry can be discharged to the outside is formed between the die lips 141a and 142a, which are the tips of the lower die 141 and the upper die 142. The discharge port 143a can also be said to be a location formed by separating the die lips 141a and 142a. Figures 5 and 6 show an example in which the shim 144 has two openings, allowing for lane-by-lane coating of two patterns side by side.

[0062] 4 to 6, the slot die coater 140 has a rotatable coating roll 120 disposed in front of the slot die coater 140, and by rotating the coating roll 120, the current collector 110 is moved in the MD direction while the slurry is discharged and continuously contacts the surface of the current collector 110, thereby coating the current collector 110. Alternatively, the supply of the slurry can be alternately started and stopped to intermittently coat the current collector 110 in a pattern.

[0063] In this manner, the slurry discharged from the slot die coater 140 may be coated onto the current collector 110 being conveyed by the coating roll 120. The slurry discharged from the slot die coater 140 is applied to one side of the current collector 110 to form the electrode active material layer 130. The coating width CW of the electrode active material layer 130 coated on the current collector 110 is determined by the width of the slot 143. If the coating width CW needs to be changed, various coating widths CW can be achieved by changing the shim 144. Here, a step 125 is formed on the coating roll 120, a step 115 is formed on the current collector 110, and the electrode active material layer 130 formed by coating the slurry may be formed on the step 115.

[0064] Fig. 7 is a perspective view of the coating roll 120 that can be included in the apparatus shown in Fig. 4 to Fig. 6. In order to create an artificial step 115 in the current collector 110, tape 150a can be attached locally to the coating roll 120 where the current collector 110 is placed.

[0065] Instead of adhering the tape 150a to the coating roll 120, a metal or metal alloy coating layer 150b can be formed. For example, the coating layer 150b can be made of an alloy such as tungsten carbide (WC). Such a tape 150a or coating layer 150b protrudes a predetermined height from the surface of the coating roll 120, forming a step 125. The current collector 110 is typically a conductive metal foil, such as aluminum or copper, and is selected appropriately depending on the polarity of the electrode. Generally, the thickness of a positive electrode current collector is 10 μm to 20 μm, while the thickness of a negative electrode current collector is as thin as 5 μm to 15 μm. Therefore, the step 125 of the coating roll 120 can be directly transferred to the thin current collector 110, forming a step 115 on the current collector 110.

[0066] The steps 115, 125 are formed with a width SDW narrower than the coating width CW of the electrode active material layer 130 (CW>SDW), and may be formed with a thickness d of 10 μm to 50 μm from a position i 5 mm to 10 mm inward from the edge 130s of the electrode active material layer 130. For example, if a 50 μm thick tape 150a with a width SDW of 90 mm is attached to the coating roll 120 in a process with a coating width CW of 100 mm, a step 125 with a thickness d of 45 μm can be formed from a position i 5 mm inward from the edge 130s of the electrode active material layer 130, which may become the step 115 of the current collector 110. Although this varies depending on the slurry properties, coating gap, and coating width (CW), we have confirmed that forming the steps 115, 125 at a position i 5 mm to 10 mm from the edge 130s of the electrode active material layer 130 with a thickness d of 10 μm to 50 μm can provide satisfactory sliding improvement under commonly used slurry conditions. If the distance p between the edge 130s of the electrode active material layer 130 and the edge of the step 125 is smaller than 5 mm, or if the step thickness d is smaller than 10 μm, the degree to which the slurry flows into the step 115 is minimal, potentially resulting in a weak improvement in sliding length. If the distance p between the edge 130s of the electrode active material layer 130 and the edge of the step 125 is larger than 10 mm, or if the step thickness d is larger than 50 μm, the edge shape of the electrode active material layer 130 may become undesirable.

[0067] As described above, the coating roll 120 with the step 125 can be easily realized by adhering the tape 150a, or can be realized with precision and durability by forming the metal or metal alloy coating layer 150b. In particular, the tape 150a can be easily attached and peeled off, which is advantageous in that it can be realized as a variable coating roll that can flexibly accommodate model numbers with changed coating widths CW.

[0068] 4 to 7, a method for manufacturing an electrode for a secondary battery according to an embodiment of the present invention will be described in more detail. For example, a tape 150a having a width SDW narrower than the actual coating width CW is attached to a coating roll 120 to form a step 125 on the coating roll 120, and the step 125 is then transferred to a current collector 110 to form a step 115. A slurry is then coated on the step 115. For example, a 45 μm-thick tape 150a is attached to a position 5 mm from an edge 130s of the electrode active material layer 130. The current collector 110 is placed on the coating roll 120 and is then run. As the current collector 110 is then run, slurry is dispensed onto the current collector 110 through a slot die coater 140 to coat the electrode active material layer 130 on the step 115 of the current collector 110.

[0069] Through this, an electrode profile as shown in FIG. 8 is obtained, but the electrode active material slurry flows into the artificially created step 115, so that the sliding length TS' of the electrode active material layer 130 becomes shorter than the conventional sliding length TS (TS' <TS)。

[0070] For example, if steps 115 and 125 of this level are formed on an electrode in which the solid content of the negative electrode active material slurry is around 40% to 50% and the coating layer thickness is 70 μm to 200 μm (excluding the current collector), there is an improvement effect in that the length is reduced by about 15% to 20% compared to existing sliding levels.

[0071] In terms of controlling the sliding shape, the sliding criteria or control factor can be sliding thickness in addition to sliding length, but this definition can be modified. For example, the sliding thickness has traditionally been controlled so that it is 65% or more of the target coating layer thickness at 50% of the sliding length. However, this can be modified as needed, for example, so that the sliding thickness can be controlled so that it is 69.5% or more of the target coating layer thickness at 40% of the sliding length. For example, in an electrode with a coating layer thickness of 70 μm to 200 μm (excluding the current collector) where the solid content of the negative electrode active material slurry is around 40% to 50%, forming steps 115, 125 of this level can result in an improvement of 20% to 30% increase in thickness compared to the existing sliding level.

[0072] In other words, according to the present invention, compared to an electrode active material layer formed under the same conditions without a step, the sliding length TS' can be reduced by 15% to 20%, and the sliding thickness can be increased by 20% to 30% at the 40% position of the sliding length.

[0073] In this way, by creating an artificial step 115 in the current collector 110 and coating the electrode active material layer 130 on the step 115, it is possible to form an electrode active material layer 130 having a sliding length TS' that is shorter than conventional ones, thereby improving sliding. This prevents variations in loading due to sliding and also solves the problem of variations during rolling.

[0074] On the other hand, in the method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention, it may further include a step of coating an additional electrode active material layer at a position aligned with the electrode active material layer 130 on the opposite surface of the current collector 110 coated with the electrode active material layer 130. For example, while running the current collector 110 on the coating roll 120, coating the electrode active material layer 130 and drying it while winding it around a winding roll (not shown), and then feeding out the winding roll in the opposite direction to coat an additional electrode active material layer at a position aligned with the electrode active material layer 130 on the opposite surface of the current collector 110 coated with the electrode active material layer 130.

[0075] FIG. 9 is a schematic diagram of an electrode step by step according to a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention, and can be described as follows in comparison with the schematic diagram of the conventional electrode step by step in FIG. 3.

[0076] FIG. 9(a) shows a state in which the upper layer 180a and the lower layer 190a are coated on the top surface of the current collector 110 in a double layer. For example, it is the case where the slot die coater 140 in FIG. 4 is a dual slot die coater. When coating the top surface, as described above, an artificial step 115 is formed on the current collector 110, and the slurry is discharged through the slot die coater 140 onto it for coating. Therefore, the sliding length TS' of the top surface is shorter than the sliding length of the conventional top surface (TS in FIG. 3) (TS' < TS). Since the slurry can flow into the side of the step 125, the sliding can be reduced.

[0077] In this way, the top surface is coated using a coating roll 120 with a step 125 formed to match the coating width CW of a specific model. As a result, sliding can be improved by artificially creating a coating gap at the sliding area. As such, according to the present invention, excellent shape control of the interface (sliding area) is achieved when coating a stripe pattern using a slot die coater 140 for not only single layers but also double layers.

[0078] In Fig. 9(b), the current collector 110 is turned over so that the back surface faces up. In this case, instead of the coating roll 120 with the step 125 formed as in Fig. 4, another coating roll 160 without the step is used, and Fig. 9(b) shows the state in which the current collector 110 is placed on the coating roll 160. The part of the current collector 110 on which the coating layer is not formed abuts against the coating roll 160, causing a phenomenon of base material depression H'. However, since sliding is reduced compared to the conventional case, the magnitude of the base material depression H' is smaller (H') than the magnitude of the base material depression (H in Fig. 3) in the conventional case. <H)。

[0079] In this state, as shown in Figure 9(c), an additional electrode active material layer 130' is formed by coating the back surface of the current collector 110 with an upper layer 180b and a lower layer 190b in a double layer. The current collector 110 with its top surface coated is then turned over and placed on a flat coating roll 160, and slurry is discharged through the same slot die coater 140 to coat the additional electrode active material layer 130' at a position aligned with the electrode active material layer 130. When coating the back surface of the current collector 110, slurry bias SS' may occur at the edge of the back surface, but this is not as severe as in the past because the sliding length TS' of the top surface has been shortened.

[0080] After completing the coating of the back surface, if the current collector 110 is kept flat as shown in Figure 9(d), side ring will not occur even if the slurry becomes unevenly distributed SS' during coating of the back surface. Then, the sliding length BS' on the back surface will be approximately the same as the sliding length TS' on the top surface (BS' ≒ TS').

[0081] In this way, if the current collector 110 is coated on which the step 115 is artificially formed so that the conditions for coating the top surface first can be the same or nearly the same as those for coating the back surface after the top surface coating, it becomes possible to form an electrode active material layer 130 with a reduced sliding length TS'. Furthermore, because the sliding of the top surface is improved, the amount of slurry flowing in when coating the opposite surface, the back surface, is reduced, and the sliding length BS' of the back surface becomes longer than before. As a result, the sliding deviation (TS' - BS') between the top surface and the back surface can be reduced, ensuring uniform sliding quality.

[0082] Under commonly used slurry conditions, it was confirmed that the sliding lengths TS' and BS' of the electrode active material layer 130 and the additional electrode active material layer 130' were 3 mm to 4 mm, and were also confirmed to be substantially the same.

[0083] In this way, the present invention can provide an artificial step on the top surface to uniformize the sliding shape between the top surface and the back surface. The deviation in the sliding areas between the top surface and the back surface can be improved to manufacture an electrode for a secondary battery. This allows the NP ratio to satisfy the design conditions, ensuring the stability of the secondary battery. By ensuring that the NP ratio satisfies the design conditions, the discharge capacity of the positive electrode does not exceed the discharge capacity of the negative electrode, preventing lithium precipitation. According to the present invention, in a sequential coating method in which the back surface is coated after the top surface is coated, the occurrence of side rings on the back surface can be prevented. The present invention has the advantage of excellent simultaneous control of the top and back surfaces.

[0084] FIG. 10 is a schematic diagram of an electrode manufacturing apparatus for a secondary battery according to one embodiment of the present invention.

[0085] As explained with reference to Fig. 5 and the like, as previously presented, the coating roll 120 with the step 125 can be used as a coating roll for coating the top surface as a means for creating the artificial step 115 on the current collector 110. Therefore, as shown in Fig. 10, an electrode manufacturing apparatus 200 for a secondary battery according to one embodiment of the present invention may include the coating roll 120 with the step 125, a coating roll 160 for coating the back surface without the step, and a slot die coater 140.

[0086] The step 125 may cause a difference in the coating gap between the edge / center die lips 141a, 142a of the slot die coater 140 and the current collector 110 placed on the coating roll 120. The coating roll 120 has a step 125 formed in which the center portion of the electrode active material layer is higher than both edge portions. The slurry flows into the side of the step 125, thereby reducing sliding in the coating profile of the electrode active material layer.

[0087] According to the present invention, the only difference between the coating roll 120 for top surface coating and the coating roll 160 for back surface coating is the amount of equipment required for operation, which significantly reduces replacement costs, labor, and time compared to conventional methods that utilize shims or manifold shape improvements. Furthermore, when the step 125 is achieved by applying tape 150a, the tape 150a is easy to apply and remove. Therefore, after applying top surface coating using the coating roll 120 with the tape 150a applied, the coating roll from which the tape 150a has been removed can be used as the coating roll 160 for back surface coating. Therefore, with the additional cost of the tape 150a, a conventional slot die coater and coating roll can be used as they are.

[0088] According to the present invention, there is no need to change shims or improve the manifold to meet electrode design requirements. The simple method of simply adjusting the step 125 formed on the coating roll 120 is highly effective in reducing sliding. According to the present invention, there is no need to replace the slot die or reassemble the shims, so there is no risk of deviation.

[0089] The above-described method and apparatus enable stable formation of an electrode active material layer. According to the present invention, it is possible to control the coating width, loading amount, and sliding, resulting in an electrode active material layer of very good quality. For example, the thickness of the coating layer along the width direction of the current collector is uniform regardless of position, allowing the profile of the sliding region to be formed according to a desired shape. As a result, according to the present invention, an electrode active material layer can be stably formed without causing pattern defects.

[0090] For example, the present invention can be applied to the production of a positive electrode for a secondary battery by coating a positive electrode active material slurry.

[0091] The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector. The current collector is made of an electrically conductive material such as Al or Cu, and can be selected from materials known in the field of secondary batteries according to the polarity of the current collector electrode. The positive electrode active material layer may further include one or more of a plurality of positive electrode active material particles, a conductive material, and a binder. The positive electrode may further include various additives to complement or improve electrochemical properties.

[0092] The active material is not limited to any particular component as long as it can be used as a positive electrode active material for lithium-ion secondary batteries. Non-limiting examples include layered compounds such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), and lithium nickel oxide (LiNiO2), as well as compounds substituted with one or more transition metals; 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); 2-x M x The positive electrode may contain one or a mixture of two or more of the following solid electrolyte materials: a lithium manganese composite oxide represented by LiMnO2 (where M=Co, Ni, Fe, Cr, Zn, or Ta, and x=0.01 to 0.1) or Li2Mn3MO8 (where M=Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; and Fe2(MoO4)3. In the present invention, the positive electrode may contain, as the solid electrolyte material, one or more of a polymer-based solid electrolyte, an oxide-based solid electrolyte, and a sulfide-based solid electrolyte.

[0093] The conductive material may typically be added in an amount of 1 wt % to 20 wt % based on the total weight of the mixture containing the active material. Such a conductive material is not particularly limited as long as it is conductive without causing any chemical change in the secondary battery, and may include, for example, one or a mixture of two or more conductive materials selected from the following: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fiber and metal fiber; metal powders, such as carbon fluoride, aluminum, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0094] The binder is not particularly limited as long as it is a component that aids in bonding the active material and conductive material, etc., and bonding to the current collector, and examples thereof include polyvinylidene fluoride polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc. The binder may typically be contained in a range of 1 wt% to 30 wt% or 1 wt% to 10 wt% relative to 100 wt% of the electrode layer.

[0095] For another example, the negative electrode of a secondary battery can be manufactured by coating the negative electrode active material slurry. The negative electrode includes a current collector and a negative electrode active material layer formed on the surface of the current collector. The negative electrode active material layer may further include one or more of a plurality of negative electrode active material particles, a conductive material, and a binder. The negative electrode may also include various additives to complement or improve electrochemical properties.

[0096] Examples of the negative electrode active material include carbon materials such as graphite, amorphous carbon, diamond-like carbon, fullerene, carbon nanotubes, and carbon nanohorns, lithium metal materials, alloy materials such as silicon and tin, Nb2O5, and Li5Ti4O 12 For the negative electrode, see the description of the conductive material, and for the binder and current collector, see the description of the positive electrode.

[0097] Slurries containing such positive and negative electrode active materials have very high viscosities. For example, the viscosity may be 1,000 cps or more. The viscosity of active material slurries used to form secondary battery electrodes may be 2,000 cps to 30,000 cps. For example, negative electrode active material slurries may have a viscosity of 2,000 cps to 4,000 cps. Positive electrode active material slurries may have a viscosity of 8,000 cps to 30,000 cps. Such slurries may contain active materials having an average particle size of, for example, about 10 μm.

[0098] Hereinafter, experimental examples related to the present invention will be further explained to deepen understanding of the present invention.

[0099] As a result of experiments under given conditions, the electrode active material layer formed using the conventional coating method was formed to have the electrode profile shown in Figure 1, with a sliding length TS of approximately 4.5 mm. Furthermore, the inventors of the present invention confirmed through experiments that the conventional sliding occurs mainly in the area 5 mm to 10 mm inward from the edge of the electrode. Therefore, in order to reduce the difference in the coating gap in this area, a 45 μm thick tape, which is 10 mm smaller than the electrode coating width, was masked onto a conventional flat coating roll and tests were conducted.

[0100] FIG. 11 is a diagram showing the position where the tape is attached to the coating roll.

[0101] For example, in a process with a coating width CW of 100 mm, a 50 μm-thick tape 150a with a width SDW of 90 mm is attached to the coating roll 120. A 45 μm-thick step 125 can be formed from a position i that is 5 mm inward from the edge 130s of the electrode active material layer 130. A step test was conducted by attaching a tape 150a that is 10 mm smaller than the electrode coating width CW so that the tape 150a could be positioned 5 mm inward from the edge of the electrode coating width CW.

[0102] Before the tape was applied, the coating roll (a conventional flat coating roll with no steps) had no steps, so the surface of the copper foil, which was the current collector placed on top of it, was also flat.

[0103] In the experimental example, a laser marking process was performed to mark the position on the coating roll where the tape should be applied. A line corresponding to the electrode coating width was marked on the coating roll. Tape was applied to the coating roll. The tape was applied inside the marked line. This resulted in a coating roll with a step.

[0104] When the copper foil was placed on the stepped coating roll, the steps were transferred to the copper foil. According to the experimental example, an electrode active material layer was coated on the steps of the stepped copper foil using a normal negative electrode active material slurry.

[0105] Measurements were taken of the electrodes after they had dried, and it was found that by taping them to form a step, as in the experimental example, the sliding length of the top surface was 3.6 mm, an improvement of 20% compared to the conventional sliding length of 4.5 mm.

[0106] The back surface was coated using a flat coating roll. When the back surface was coated, the sliding length was approximately the same as that of the top surface.

[0107] In the past, when coating the top surface, the back surface was left uncoated, but when coating the back surface, the top surface was coated, which inevitably resulted in a difference in coating gap. However, in the present invention, when coating the top surface first, the conditions are the same or nearly the same as when coating the back surface after coating the top surface, eliminating or reducing the difference in coating gap. This can improve sliding.

[0108] Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific preferred embodiments described above, and it goes without saying that anyone having ordinary knowledge in the technical field to which the present invention pertains can make various modifications without departing from the gist of the present invention as claimed in the claims, and such modifications are within the scope of the claims. [Explanation of symbols]

[0109] 110 Current collector 115, 125 steps 120, 160 coating roll 130, 130' electrode active material layer 140 Slot die coater 141 Lower die 142 Upper die 141a, 142a Dielip 143 Slots 144 Sim 145 manifold 150a tape 150b Covering layer 200 Electrode manufacturing equipment for secondary batteries

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising the steps of creating an artificial step on a current collector and coating an electrode active material layer on the step.

2. 2. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein tape is locally attached to a coating roll on which the current collector is placed in order to create an artificial step on the current collector.

3. 2. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein a metal or metal alloy coating layer is locally formed on a coating roll on which the current collector is placed, in order to create an artificial step on the current collector.

4. 4. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein the step is formed to have a width narrower than a coating width of the electrode active material layer, and is formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from an edge of the electrode active material layer.

5. 2. The method for manufacturing an electrode for a secondary battery according to claim 1, further comprising the step of coating an additional electrode active material layer on the opposite surface of the current collector on which the electrode active material layer is coated, at a position aligned with the electrode active material layer.

6. 4. The method for manufacturing an electrode for a secondary battery according to claim 2 or 3, further comprising the steps of coating the current collector with the electrode active material layer while running the current collector over the coating roll, drying the current collector, and winding the current collector onto a take-up roll, and then unwinding the take-up roll in the opposite direction to coat an additional electrode active material layer at a position aligned with the electrode active material layer on the opposite surface of the current collector coated with the electrode active material layer.

7. 2. The method of claim 1, wherein the electrode active material layer is formed by coating a slurry containing 40% to 50% solids to a thickness of 70 μm to 200 μm, and the step is formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from an edge of the electrode active material layer, and the sliding length is improved by 15% to 20% and the sliding thickness is improved by 20% to 30% compared to an electrode active material layer formed under the same conditions without the step.

8. placing a current collector on a coating roll having a step formed thereon, the step having a width narrower than the coating width of the electrode active material layer to be coated, and discharging a slurry through a slot die coater to coat the electrode active material layer on the step, thereby coating a top surface of the current collector; coating the back surface of the current collector by turning the top surface coated current collector over and placing it on a flat coating roll, and discharging a slurry through a slot die coater to coat an additional electrode active material layer at a position aligned with the electrode active material layer; A method for manufacturing an electrode for a secondary battery, comprising:

9. 9. The method for manufacturing an electrode for a secondary battery according to claim 8, wherein the coating roll having the step includes a tape locally attached thereto.

10. 9. The method for manufacturing an electrode for a secondary battery according to claim 8, wherein the stepped coating roll includes a locally formed metal or metal alloy coating layer.

11. 11. The method for manufacturing an electrode for a secondary battery according to claim 8, wherein the step is formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from an edge portion of the electrode active material layer.

12. The method for manufacturing an electrode for a secondary battery according to claim 8 , wherein the step causes a difference in coating gap between the edge / center die lip of the slot die coater and the current collector.

13. The method for manufacturing an electrode for a secondary battery according to claim 12 , wherein the slurry flows onto the side of the step, thereby reducing sliding in the coating profile of the electrode active material layer.

14. 14. The method of manufacturing an electrode for a secondary battery according to claim 13, wherein the sliding lengths of the electrode active material layer and the additional electrode active material layer are approximately the same, ranging from 3 mm to 4 mm.

15. a coating roll for top surface coating, in which a step is formed to a width narrower than the coating width of the electrode active material layer; a coating roll for back surface coating, which does not have a step; A slot die coater; An electrode manufacturing apparatus for a secondary battery, comprising:

16. 16. The apparatus for manufacturing an electrode for a secondary battery according to claim 15, wherein the coating roll for coating the top surface includes a tape locally attached thereto.

17. The apparatus for manufacturing an electrode for a secondary battery according to claim 15 , wherein the coating roll for coating the top surface includes a locally formed metal or metal alloy coating layer.

18. 18. The electrode manufacturing apparatus for a secondary battery according to claim 15, wherein the step is formed to a thickness of 10 μm to 50 μm from a position 5 mm to 10 mm inward from an edge portion of the electrode active material layer.

19. 16. The electrode manufacturing apparatus for a secondary battery according to claim 15, wherein the step causes a difference in coating gap between an edge / center die lip of the slot die coater and a current collector placed on a coating roll for the top surface coating.

20. 16. The apparatus for manufacturing an electrode for a secondary battery according to claim 15, wherein the coating roll for coating the top surface has a step formed thereon such that the height of a center portion is higher than that of both edge portions of the electrode active material layer.

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