Manufacturing method for electrode assemblies

Abstract

A method for manufacturing a stack-folded electrode assembly using a negative electrode structure having a lithium metal layer between two separators is provided. The method includes the steps of: positioning the lithium metal layer between two separators so that it protrudes in the width direction; laminating the lithium metal layer and the separator to manufacture a negative electrode structure; stacking one positive electrode on the negative electrode structure and folding the negative electrode structure in the width direction to encase the positive electrode; repeating the previous steps to manufacture an electrode stack including a plurality of positive electrodes; and cutting a portion of the lithium metal layer protruding in the width direction to form a negative electrode tab and joining the negative electrode tab. The method for manufacturing the electrode assembly can minimize processing of the lithium metal, thereby improving the productivity of the electrode assembly.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode assembly. Specifically, the present invention utilizes a negative electrode structure in which a lithium metal layer is interposed between two separation membranes, and relates to a method for manufacturing an electrode assembly that includes the steps of cutting a portion of the lithium metal layer protruding in the width direction to form a negative electrode tab, and joining the negative electrode tab.

[0002] This application claims priority rights under Korean Patent Application No. 10-2022-0136203 dated October 21, 2022, and Korean Patent Application No. 10-2023-0129310 dated September 26, 2023, and incorporates all the contents disclosed in the documents of said Korean Patent Applications as part of this Specification. [Background technology]

[0003] Recently, interest in energy storage technologies has been growing. With applications expanding to mobile phones, video cameras and laptops, and even electric vehicles, efforts in battery research and development are becoming increasingly concrete. Electrochemical devices are one of the most noteworthy fields in this regard, and especially with the recent trend towards miniaturization and weight reduction of electronic devices, the development of rechargeable batteries—small, lightweight, and high-capacity batteries that can be charged and discharged—has become a focal point of interest.

[0004] Furthermore, secondary batteries can sometimes be classified according to the structure of their electrode assembly, which consists of a positive electrode, a separator membrane, and a negative electrode. Typical examples of electrode assemblies include jelly-roll (wind-up type) electrode assemblies, which are constructed by winding long, sheet-like positive and negative electrodes with a separator membrane in between, and stack-type (stacked type) electrode assemblies, which are constructed by sequentially stacking numerous positive and negative electrodes cut into predetermined size units with a separator membrane in between.

[0005] However, such conventional electrode assemblies have several problems.

[0006] Firstly, the jelly-roll electrode assembly is manufactured by winding long, sheet-like positive and negative electrodes in a densely packed state, creating a cylindrical or elliptical structure in cross-section. In such a structure, stress induced by the expansion and contraction of the electrodes during charging and discharging accumulates inside the electrode assembly, and if such stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. Furthermore, this deformation of the electrode assembly can cause uneven spacing between electrodes, leading to a rapid decrease in battery performance and potentially jeopardizing battery safety due to internal short circuits. In addition, because the jelly-roll electrode assembly requires winding long, sheet-like positive and negative electrodes, it is difficult to wind them quickly while maintaining a constant spacing between the positive and negative electrodes, resulting in reduced productivity.

[0007] Secondly, the stacked electrode assembly requires sequentially stacking numerous positive and negative electrode units. This process necessitates a separate plate transfer process for manufacturing the units, and the sequential stacking process requires considerable time and effort. As a result, the stacked electrode assembly suffers from low productivity.

[0008] To solve these problems, an advanced stack-fold type electrode assembly, which is a hybrid form of the jelly-roll type and the stack type, has been developed. The stack-fold type electrode assembly has a structure in which bi-cells or full cells, which are stacked with a separation membrane interposed between predetermined units of positive and negative electrodes, are wound using a long, continuous separation membrane sheet (folded separation membrane).

[0009] The aforementioned stack-foldable electrode assembly connects the electrodes of each layer by extending a separator membrane, which is generally easier to fold than the electrodes themselves. In this case, the electrodes of each layer are supplied for electrode assembly formation in a cut state, similar to that of a stack-type electrode assembly. Among the various electrode materials that make up secondary batteries in the art, if a secondary battery is to be constructed using only materials that are either easy to cut or not easy to fold, such a general stack-foldable electrode assembly is more suitable. On the other hand, lithium metal, which is well known as a negative electrode material for secondary batteries in the art, has high ductility and viscosity, making it difficult to process such as cutting, and is relatively easy to fold, so it may not be suitable for conventional stack-foldable electrode assemblies.

[0010] After continuous research into the structure of electrode assemblies, the inventors have designed a structure particularly suitable for electrode assemblies containing lithium metal in the negative electrode, thereby completing the present invention. The method for manufacturing electrode assemblies according to the present invention minimizes processing of the lithium metal, which is expected to improve the productivity of electrode assemblies. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Korean Published Patent No. 2021-0006231 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention provides a method for manufacturing an electrode assembly in a stack-fold type electrode assembly with a novel structure that utilizes a negative electrode structure interposed between two separation membranes, the negative electrode comprising a lithium metal layer, and the method for manufacturing the electrode assembly, which includes the step of cutting a portion of the lithium metal layer protruding in the width direction to form a negative electrode tab and joining the negative electrode tab. [Means for solving the problem]

[0013] According to the first aspect of the present invention, the present invention provides a method for manufacturing an electrode assembly.

[0014] In one embodiment of the present invention, the manufacturing method includes: (1) positioning a lithium metal layer between two separator films so as to protrude in the width direction; (2) bonding the lithium metal layer and the separator film to manufacture a negative electrode structure; (3) laminating one positive electrode on the negative electrode structure and folding the negative electrode structure in the width direction so as to wrap the positive electrode; (4) repeating step (3) to manufacture an electrode laminate including a plurality of positive electrodes; and (5) cutting a part of the lithium metal layer protruding in the width direction to form a negative electrode tab and bonding the negative electrode tab.

[0015] In one embodiment of the present invention, the lengths of the lithium metal layer and the separator film are the same.

[0016] In one embodiment of the present invention, the bonding of the lithium metal layer and the separator film in step (2) is performed by positioning rolls on both sides and sequentially applying pressure.

[0017] In one embodiment of the present invention, the total number of positive electrodes wrapped between the negative electrode structures in the electrode laminate manufactured in step (4) is 2n (where n is a natural number).

[0018] In one embodiment of the present invention, the positive electrode included in the electrode laminate manufactured in step (4) includes a positive electrode active material layer and a current collector supporting the positive electrode active material layer.

[0019] In one embodiment of the present invention, the positive electrode included in the electrode laminate manufactured in step (4) includes a positive electrode tab of a notched current collector, and the positive electrode tab is positioned in the opposite direction to the negative electrode tab in step (5).

[0020] In one embodiment of the present invention, a part of the protruding lithium metal layer in step (5) is cut, and the negative electrode tab is separated into each layer in the electrode assembly.

[0021] In one embodiment of the present invention, the formation of the negative electrode tab in step (5) is performed by ultrasonic cutting, the joining of the negative electrode tabs is performed by ultrasonic welding, and the ultrasonic cutting and ultrasonic welding are performed simultaneously.

[0022] In one embodiment of the present invention, the corners of the lithium metal layers protruding from each layer of the electrode assembly are cut by ultrasonic cutting in step (5), and the central parts of the protruding lithium metal layers are joined by ultrasonic welding.

[0023] In one embodiment of the present invention, the method for manufacturing the electrode assembly further includes the step of (6) joining leads to the bonded negative electrode tabs. [Effects of the Invention]

[0024] Lithium metal, used as the negative electrode in lithium secondary batteries, has properties that make it difficult to process, and excessive processing of lithium metal can increase the defect rate of the finished product. For example, when notching lithium metal, it is difficult to produce lithium metal with a consistent shape because the lithium metal adheres to the blade. Furthermore, if a blade contaminated by lithium metal adhesion is used repeatedly, the contamination can accumulate and affect the product. Therefore, in the electrode assembly manufacturing method according to the present invention, after manufacturing the electrode stack, the lithium metal layer is cut in one step to form a negative electrode tab, and the negative electrode tab is joined, thereby minimizing the processing of lithium metal. Minimizing the processing of lithium metal in this way not only reduces the defect rate of the finished product but also improves process efficiency and increases the productivity of electrode assemblies. [Brief explanation of the drawing]

[0025] [Figure 1] This figure schematically illustrates the process by which a negative electrode structure is manufactured by roll pressurization according to one embodiment of the present invention. [Figure 2] This is a schematic front view showing an electrode stack according to one embodiment of the present invention. [Figure 3] This is a schematic plan view showing an electrode stack according to one embodiment of the present invention. [Figure 4] This is an enlarged view of the dashed line in Figure 3, illustrating the schematic cutting and welding positions in the lithium metal layer protruding in the width direction. [Figure 5] This is a left side view showing the shape of an electrode assembly according to one embodiment of the present invention, in which tabs are joined. In Figure 5, the folded portion of the negative electrode structure, which can be seen in the side view, is omitted in order to clearly show each layer. [Figure 6] This is a left side view showing an electrode assembly according to one embodiment of the present invention, in which leads are joined to a tab. In Figure 6, the folded portion of the negative electrode structure, which can be seen in the side view, is omitted in order to clearly show each layer. [Modes for carrying out the invention]

[0026] The embodiments will be described in detail below with reference to illustrative drawings. It should be noted that, when assigning reference numerals to the components in each drawing, the same component will, to the greatest extent possible, have the same reference numeral even if shown in different drawings. Furthermore, when describing the embodiments, if a specific description of a related known configuration or function is deemed to hinder understanding of the embodiments, such detailed description will be omitted.

[0027] Furthermore, when describing the components of an embodiment, terms such as First, Second, A, B, (a), (b), etc., may be used. These terms are used to distinguish a component from other components, and do not limit the nature, order, or sequence of the component. When it is stated that a component is “linked,” “joined,” or “connected” to another component, it should be understood that the component may be directly linked or connected to other components, but that other components may also be “linked,” “joined,” or “connected” between each component.

[0028] Components included in any one embodiment and components with common functions will be described using the same names in the other embodiments. Unless otherwise stated, descriptions in any one embodiment can be applied to the other embodiments, and specific descriptions will be omitted to the extent that they overlap.

[0029] The present invention relates to a method for manufacturing an electrode assembly including a negative electrode structure in which a lithium metal layer is interposed between two separation membranes. Conventionally, when manufacturing an electrode assembly containing lithium metal in the negative electrode, excessive processing of lithium can not only reduce process efficiency but also potentially decrease the reliability of the manufactured product. However, in the method for manufacturing an electrode assembly according to the present invention, after manufacturing the electrode stack, the lithium metal layer is cut in one step to form a negative electrode tab, and the negative electrode tab is joined, thereby minimizing processing of the lithium metal. Minimizing processing of the lithium metal in this way not only reduces the defect rate of the finished product but also improves process efficiency and increases the productivity of electrode assemblies.

[0030] In this specification, the terms "electrode assembly" and "electrode stack" are used. The term "electrode assembly" is interpreted in a more comprehensive sense than "electrode stack," and any structure after the positive electrode, negative electrode, and separator membrane have been stacked can be referred to as an electrode assembly. Therefore, a structure in which the positive electrode, negative electrode, and separator membrane are stacked, a structure in which tabs are formed after the positive electrode, negative electrode, and separator membrane are stacked, a stacked structure, a structure in which tabs are formed and joined after the positive electrode, negative electrode, and separator membrane are stacked, and a structure in which leads are joined to tabs formed after the positive electrode, negative electrode, and separator membrane are stacked can all be electrode assemblies. In contrast, "electrode stack" refers only to a structure in which the positive electrode, negative electrode, and separator membrane are stacked. In the case of the positive electrode, since a tab can be formed by notching the current collector, etc., the electrode stack may include a positive electrode tab.

[0031] In this specification, the terms “length direction,” “width direction,” and “height direction” (or “thickness direction”) are used. The “length direction” refers to the left-right direction in the front views such as Figures 1 and 2 and the top views such as Figures 3 and 4, and to the front-to-back direction that is not divided in the left side views such as Figures 5 and 6. In this specification, the “width direction” refers to the front-to-back direction that is not divided in the front views such as Figures 1 and 2, to the up-and-down direction in the top views such as Figures 3 and 4, and to the left-to-right direction in the left side views such as Figures 5 and 6. In this specification, the “height direction” refers to the up-and-down direction in the front views such as Figures 1 and 2, to the front-to-back direction that is not divided in the top views such as Figures 3 and 4, and to the up-and-down direction in the left side views such as Figures 5 and 6.

[0032] A method for manufacturing an electrode assembly according to one embodiment of the present invention includes the step of positioning a lithium metal layer so as to protrude in the width direction between two separation membranes. In this specification, the two separation membranes constituting the negative electrode structure may be simply named the separation membrane if there is no particular need to distinguish between them, and may be named the first and second separation membranes if there is a need to distinguish between them. Here, the protruding lithium metal layer is subsequently used to form a tab, and since the positive electrode does not protrude beyond the separation membrane in the same direction, the lithium metal layer and the positive electrode do not come into contact with each other. In the case of the positive electrode tab, similar to the negative electrode tab, it is positioned so as to protrude in the width direction beyond the separation membrane, but as in the present invention, if the lithium metal layer protruding in the width direction is later cut, it can only come into contact with the positive electrode tab before that, so the positive electrode tab protrudes in the opposite direction to the direction in which the lithium metal layer protrudes. The lithium metal layer contains lithium metal, and the lithium metal can be broadly interpreted as long as there is no significant difference in physical properties from lithium metal, even if it is lithium with some components added or in the form of an alloy with some metals, and the same problems can occur when applied to conventional electrode assemblies as with lithium metal.

[0033] A method for manufacturing an electrode assembly according to one embodiment of the present invention includes the step of manufacturing a negative electrode structure by bonding a lithium metal layer and a separation membrane. Here, bonding means that the lithium metal layer and the separation membrane are integrated and utilized as a single component in the manufacturing process of the electrode assembly, and it is not necessarily required that the lithium metal layer and the separation membrane be bonded with an adhesive or the like. Lithium metal is soft and has adhesive properties in relation to other materials, and by applying pressure above a certain level, the lithium metal and the separation membrane can be bonded relatively easily.

[0034] In a method for manufacturing an electrode assembly according to one embodiment of the present invention, the bonding of the lithium metal layer and the separation membrane can be performed by sequentially applying pressure with rolls positioned on both sides. To aid in understanding this, Figure 1 provides a schematic diagram illustrating the process of bonding the negative electrode structure by roll pressure according to one embodiment of the present invention. The roll (R) for manufacturing the negative electrode structure (10) may preferably be a nip roll capable of applying pressure from both sides, as shown in Figure 1. In the nip roll, the strength of the pressure can be adjusted by adjusting the distance between the rolls. In one embodiment of the present invention, the reason for bonding the lithium metal layer and the separation membrane using rolls is that the negative electrode structure can be manufactured continuously. When manufacturing the negative electrode structure, it is also possible to cut the lithium metal layer and separation membrane to be used in one electrode assembly and then supply them to the nip roll to manufacture the negative electrode structure. However, continuously supplying the lithium metal layer (11) and separation membrane (12) to continuously manufacture the negative electrode structure (10) and cutting only the required length can help improve process efficiency.

[0035] As described above, since the lithium metal layer is positioned to protrude in the width direction between the separation membranes and then bonded together, the width of the lithium metal layer may be longer than the width of the separation membrane. However, in the manufacturing process of a continuous negative electrode structure, the lithium metal layer and the separation membrane are cut simultaneously, so the lengths of the lithium metal layer and the separation membrane may be the same. However, depending on the method of cutting the negative electrode structure, slight differences may occur in the lengths of the negative electrode and the separation membrane, and in some cases, the end of the separation membrane may curve toward the center of the negative electrode structure. Even if the lengths of the negative electrode and the separation membrane are the same during the supply process, when applied to the electrode assembly, the length of the lithium metal layer may be extended due to the ductility of the lithium metal during the folding process. Therefore, in one embodiment of the present invention, the fact that the lengths of the negative electrode and the separation membrane are the same means that the negative electrode and the separation membrane are cut at the same time and their lengths may be substantially the same, and in actual products, depending on the circumstances, the end of the negative electrode and the end of the separation membrane may not be located on the same line.

[0036] A method for manufacturing an electrode assembly according to one embodiment of the present invention includes the step of stacking one positive electrode on a negative electrode structure and folding the negative electrode structure in the width direction so as to enclose the positive electrode. An electrode assembly according to one embodiment of the present invention includes one negative electrode structure and a plurality of positive electrodes. There is one negative electrode structure, but it can be folded in the width direction to form multiple layers. In this specification, folding in the width direction means dividing the length of the negative electrode structure into two or more parts through folding. Since the length direction of the negative electrode structure is much longer than the width direction, it is easy to form a large number of layers through folding, and this expansion is free when manufacturing negative electrode structures continuously.

[0037] A method for manufacturing an electrode assembly according to one embodiment of the present invention includes the step of manufacturing an electrode stack containing multiple positive electrodes by repeatedly stacking positive electrodes and folding negative electrode structures in the width direction so as to enclose the positive electrodes. To aid in understanding the electrode stack, Figure 2 provides a schematic front view of an electrode stack according to one embodiment of the present invention. As can be seen in Figure 2, when the negative electrode structure (10) is folded so as to enclose the positive electrode (20), the negative electrode structure has a directionality opposite to the initial direction. In this way, when positive electrodes (20) are stacked sequentially, the negative electrode structure (10) has a zigzag shape. Therefore, the folded portions of the negative electrode structure are also located alternately on the left and right. If a positive electrode is not placed in the space between the folded negative electrode structures, or if multiple positive electrodes are placed, a potential difference will not be generated between the negative electrode structures or the layers in which the positive electrodes are continuously stacked, which may reduce the efficiency of the battery.

[0038] In an electrode stack according to one embodiment of the present invention, the total number of positive electrodes enclosed between negative electrode structures may be 2n (where n is a natural number). As described above, when the negative electrode structure is folded to enclose the positive electrode, the negative electrode structure has a directionality opposite to the initial direction. In this case, if the total number of positive electrodes enclosed between the negative electrode structures in the electrode stack is even, the negative electrode structure has the same directionality as the initial direction, and as shown in Figure 2, in the electrode stack, one end of the negative electrode structure is located on opposite sides from the other end. In this case, when finishing the electrode stack, such as wrapping the electrode stack with negative electrode structures, it may be easier because each end is close to one side. According to one embodiment of the present invention, in addition to the positive electrodes enclosed between the negative electrode structures, positive electrodes can be located in the upper or lower layers of the electrode stack. In this case, the total number of positive electrodes included in the electrode stack may be 2n+1 or 2n+2.

[0039] According to one embodiment of the present invention, the positive electrode includes a positive electrode active material layer and a current collector that supports the positive electrode active material layer. The positive electrode has a structure in which the positive electrode active material layer is formed on at least one surface, specifically both surfaces, of the current collector. The positive electrode active material layer contains a positive electrode active material and may further contain a conductive material, a binder, an additive, and the like. The current collector, the positive electrode active material, the conductive material, the binder, the additive, and the like are not particularly limited as long as they are generally used in the art.

[0040] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not cause a chemical change in the battery, and has high conductivity. According to one embodiment of the present invention, the positive electrode current collector can be copper, stainless steel, aluminum, nickel, titanium, palladium, fired carbon, a material obtained by surface treatment of the surface of copper or stainless steel with carbon, nickel, silver, etc., an aluminum-cadmium alloy, or the like.

[0041] The positive electrode current collector can form fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, a non-woven fabric body, etc. can be used.

[0042] The positive electrode active material can use a lithium-containing transition metal oxide. According to one embodiment of the present invention, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O2(0 < y < 1), LiCo 1-y Mn y O2(0 < y < 1), LiNi 1-y Mn y O2(0 < y < 1), Li(Ni a Co b Mn c )O4(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni zO4(0 < z < 2), LiMn 2-z Co z Any one selected from the group consisting of O4(0 < z < 2), LiCoPO4, and LiFePO4 or a mixture of two or more of these may be used. In addition to these oxides, sulfides, selenides, halides, etc. can also be used.

[0043] The positive electrode active material may contain a sulfur compound. According to one embodiment of the present invention, the sulfur compound is elemental sulfur (S8), an organic sulfur compound Li2S n (n ≧ 1) and carbon-sulfur polymer ((C2S x ) n : x = 2.5 to 50, n ≧ 1), and may be one or more selected from the group consisting of. Preferably, inorganic sulfur (S8) may be used.

[0044] When the positive electrode active material contains a sulfur compound, according to one embodiment of the present invention, the electrode assembly can be applied to a lithium-sulfur battery. In the case of sulfur contained in the positive electrode active material, since it has no electrical conductivity alone, it can be used in combination with a conductive material such as a carbon material. Thereby, the sulfur is contained in the form of a sulfur-carbon composite, and preferably, the positive electrode active material can be a sulfur-carbon composite.

[0045] When considering the above content, the positive electrode is relatively not easy to fold but easy to cut compared to the negative electrode. Therefore, the positive electrode is cut to an appropriate size and a plurality of positive electrodes are applied inside the electrode assembly.

[0046] According to one embodiment of the present invention, the positive electrode included in the electrode stack includes a notched positive electrode tab of a current collector, the positive electrode tab protruding from the separator membrane in the direction opposite to the direction in which the lithium metal layer protrudes. To aid in understanding the positioning of the lithium metal layer protruding from the separator membrane and the positive electrode tab, Figure 3 provides a schematic plan view of the electrode stack according to one embodiment of the present invention. In a typical lithium secondary battery electrode assembly, even if the positive electrode tab and the negative electrode tab are located in the same direction, if they are positioned far enough apart that they do not come into contact with each other, a short circuit due to contact between the positive electrode tab and the negative electrode tab can be prevented. However, in the electrode stack according to one embodiment of the present invention, as shown in Figure 3, the uncut protruding lithium metal layer (11) covers the entire length of the electrode assembly, so the positive electrode tab (20T) cannot be positioned far enough apart from the protruding lithium metal layer in the same direction. Furthermore, even if the lithium metal layer (11) and the positive electrode tab (20T) are located in other layers and separated, when the lithium metal layer is cut to form the negative electrode tab, the positive electrode tab may also be cut, which is undesirable.

[0047] A method for manufacturing an electrode assembly according to one embodiment of the present invention includes the steps of cutting a portion of a lithium metal layer protruding in the width direction to form a negative electrode tab, and joining the negative electrode tab. In this method for manufacturing an electrode assembly according to one embodiment of the present invention, the negative electrode tab can be formed in one go while the electrode stack is manufactured, minimizing the number of times the cutting device cuts the lithium metal. Furthermore, the tabs of each layer can be cut quickly in one go, and the tabs of each layer are naturally lined up after cutting, thus improving process efficiency. In this embodiment of the present invention, the electrode assembly has a stable structure when cut, as the lithium metal protruding in the width direction continues continuously in each layer.

[0048] According to one embodiment of the present invention, a portion of the lithium metal layer protruding in the width direction from the separation membrane is cut, and the negative electrode tab is separated into each layer in the electrode assembly. Because the negative electrode tab has a typical shape, the corners of the lithium metal layer are cut, which allows the negative electrode tab to be separated into each layer. The negative electrode tabs of each layer are subsequently joined together, but joining may not be easy if the negative electrode tabs are not separated into each layer.

[0049] According to one embodiment of the present invention, the negative electrode tab is formed by ultrasonic cutting, and the negative electrode tab is joined by ultrasonic welding. For ultrasonic cutting, an ultrasonic cutter commonly used in the art for metalworking can be used. The ultrasonic cutter generates high-frequency energy with a connected generator, and this generated energy is transmitted to a cutting blade. When the cutting blade is brought into contact with the lithium metal to be cut, vibrational frictional heat is generated, and the lithium metal layer is cut. For ultrasonic welding, an ultrasonic welding machine commonly used in the art for metalworking can be used. The ultrasonic welding machine generates high-frequency energy with a connected generator, and this generated energy is transmitted to a horn or sonotrode. When the horn or sonotrode is brought into contact with the lithium metal to be joined, ultrasonic vibrations are applied to the lithium metal layer to form a solid-state weld at the joining surface.

[0050] According to one embodiment of the present invention, ultrasonic cutting and ultrasonic welding are performed simultaneously. Since the positions of ultrasonic cutting and ultrasonic welding do not touch each other, ultrasonic cutting and ultrasonic welding can proceed simultaneously. To aid in understanding the positions of ultrasonic cutting and ultrasonic welding, Figure 4 provides a schematic diagram showing the cutting and welding positions in a lithium metal layer protruding in the width direction. Figure 4 is an enlarged view of the dashed line in Figure 3. In Figure 4, the position of ultrasonic cutting is the same as the dashed line and is indicated by C. Also in Figure 4, the position of ultrasonic welding is the same as the square area and is indicated by W. As shown in Figure 4, the corners of the lithium metal layer protruding from each layer of the electrode assembly can be cut by ultrasonic cutting, and the central part of the protruding lithium metal layer can be joined by ultrasonic welding. The ultrasonic cutting is performed in the width direction, which is the vertical direction in Figure 4, and in the length direction, which is the left-right direction in Figure 4, but performing it in the width direction first may be more advantageous for simultaneous proceeding with ultrasonic welding. Also, for cutting in the left-right direction, it may be preferable to cut so as to be in substantially contact with the separation membrane, as shown in Figure 4.

[0051] In an electrode assembly according to one embodiment of the present invention, the length of the negative electrode tab can be appropriately adjusted considering the length of each layer. Since the negative electrode is continuous without being cut, the length of each layer can be expressed by the length of the positive electrode. The length is based on the length direction of the negative electrode structure, which in Figure 4 means the left-right direction. The length of the negative electrode tab can mean the length in the left-right direction of the protruding lithium metal layer remaining after cutting the lithium metal layer along the dashed line in Figure 4. According to one embodiment of the present invention, in the electrode assembly, the length of the negative electrode tab is 50% or less of the length of the positive electrode. Specifically, the length of the negative electrode tab may be 50% or less, 45% or less, 40% or less, 35% or less, or 30% or less of the length of the positive electrode. If the length of the negative electrode tab is made too long, the processability when joining the negative electrode tab may decrease.

[0052] The negative electrode tabs, formed by cutting, are located in each layer but can be brought together in one place through welding. To help understand the shape of the negative electrode tabs after welding, Figure 5 provides a left side view showing the shape of the joined tabs in an electrode assembly according to one embodiment of the present invention. The shape of the joined tabs is clearly visible when viewed from the left or right side, rather than the front. In the electrode assembly according to one embodiment of the present invention, there is a folded portion, and when the folded portion is facing forward in the left side view, the internal positive electrode may not be clearly visible. However, in Figure 5, the folded portion of the negative electrode structure, which can be seen in the side view, is omitted in order to clearly show each layer. As shown in Figure 5, the negative electrode tabs (11T) are brought together in one place by welding (W).

[0053] A method for manufacturing an electrode assembly according to one embodiment of the present invention further includes the step of joining leads to a bonded negative electrode tab. To aid in understanding the shape of the leads joined to the negative electrode tab, Figure 6 provides a left side view showing the shape of the leads joined to the tab in an electrode assembly according to one embodiment of the present invention. Figure 6 is shown in the same manner as Figure 5. The negative electrode lead (11L) is located on and bonded to the bonded negative electrode tab, as shown in Figure 6. The negative electrode lead (11L) serves to electrically connect the negative electrode located inside the battery to the outside of the battery, and the negative electrode lead can be made of a conductive material commonly used in the art.

[0054] An electrode assembly according to one embodiment of the present invention does not include a separate current collector supporting the lithium metal layer in addition to the lithium metal layer in the negative electrode. Since the negative electrode does not include a current collector, the amount of negative electrode active material loaded into the electrode assembly can be improved, contributing to improved battery performance. When the negative electrode is mainly composed of lithium metal, lithium metal has high ductility and viscosity, making processing such as cutting difficult. However, in an electrode assembly according to one embodiment of the present invention, the negative electrode can be applied in the form of a negative electrode structure while minimizing cutting and improving processability.

[0055] In the negative electrode structure, the type of separation membrane covering both sides of the negative electrode is not particularly limited, as long as it does not contain a binder on its surface. Specifically, the separation membrane may, but is not limited to, a nonwoven fabric or a polyolefin-based porous substrate made of, for example, high-melting-point glass fibers or polyethylene terephthalate fibers.

[0056] The material of the porous substrate is not particularly limited in this invention, and any porous substrate commonly used in electrochemical elements can be used. According to one embodiment of the present invention, the porous substrate is a polyolefin such as polyethylene and polypropylene, a polyester such as polyethylene terephthalate and polybutylene terephthalate, a polyamide, a polyacetal, a polycarbonate, a polyimide, a polyetheretherketone, a polyethersulfone, a polyphenylene oxide, a polyphenylene sulfide, a polyethylene naphthalate, a polytetrafluoroethylene, a polyvinylidene fluoride, or a polyvinyl chloride. It may also contain one or more materials selected from the group consisting of chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylene benzobisoxazole), and polyarylate.

[0057] In one embodiment of the present invention, the electrode assembly folds a single negative electrode structure to form the basic structure of the electrode assembly. In this respect, the negative electrode structure must not be excessively thick so that it can be flexibly folded, and a certain level or more of lithium metal, which is the negative electrode active material, must be ensured within the negative electrode structure, taking into consideration the performance of the battery. According to one embodiment of the present invention, in the negative electrode structure, the thickness of the lithium metal layer accounts for 50% to 90% of the total thickness of the negative electrode structure. Specifically, the thickness range of the lithium metal layer may be 50% to 90%, more specifically 55% to 85%, or more specifically 60% to 80%. When the lithium metal layer satisfies the aforementioned thickness range, it can help improve the processability and functionality of the electrode assembly. According to one embodiment of the present invention, since the negative electrode structure does not include a separate current collector, the thickness of the remaining portion excluding the thickness of the lithium metal layer can represent the thickness of two separator membranes.

[0058] According to one embodiment of the present invention, the thickness of the lithium metal layer may be 10 μm to 90 μm. Specifically, the thickness of the lithium metal layer may be 10 μm or more, 20 μm or more, or 30 μm or more, and may be 70 μm or less, 80 μm or less, or 90 μm or less. The thickness of the lithium metal layer is not necessarily limited thereto and can be appropriately adjusted according to the actual size of the battery.

[0059] In one embodiment of the present invention, unlike a negative electrode structure, the positive electrode is cut and folded considering the properties of the material and applied between the negative electrode structures. The positive electrode is distinct from the negative electrode and has independence, for example, by including a current collector in addition to the positive electrode active material, but its thickness can be adjusted in relation to the negative electrode or negative electrode structure, considering the performance of the electrode. According to one embodiment of the present invention, the thickness of the positive electrode is greater than the thickness of the negative electrode structure. According to one embodiment of the present invention, the thickness of the positive electrode is greater than 100% but less than or equal to 400% of the thickness of the negative electrode structure. Specifically, the range of the thickness of the positive electrode may be greater than 100% but less than or equal to 400%, specifically 150% to 350%, and more specifically 200% to 300%. When the positive electrode satisfies the aforementioned thickness range, it can be properly harmonized with the negative electrode structure.

[0060] An electrode assembly according to one embodiment of the present invention is applied to an electrochemical element. The electrochemical element can include any element that performs an electrochemical reaction. For example, the electrochemical element can be any kind of primary battery, secondary battery, fuel cell, solar cell, or capacitor. If the electrochemical element is a secondary battery, it can be a lithium secondary battery, and the lithium secondary battery can include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0061] Any simple modifications or changes to the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will become clear from the appended claims. [Explanation of symbols]

[0062] 10:Negative electrode structure 11: Negative electrode (lithium metal layer) 11T: Negative tab 11L: Negative lead 12: Separation membrane 20: Positive electrode 20T: Positive Tab R: Roll C: Cutting position W: Welding position

Claims

1. A method for manufacturing an electrode assembly, wherein the manufacturing method is: (1) The step of positioning the lithium metal layer so as to protrude in the width direction between the two separation membranes; (2) The step of manufacturing a negative electrode structure by bonding the lithium metal layer and the separation membrane together; (3) A step of stacking one positive electrode on the negative electrode structure and folding the negative electrode structure in the width direction so as to enclose the positive electrode; (4) A step of manufacturing an electrode stack including multiple positive electrodes by repeating step (3); and (5) Cutting a portion of the lithium metal layer that protrudes in the width direction to form a negative electrode tab, and joining the negative electrode tab, Includes, The electrode assembly does not include a current collector that supports the lithium metal layer. A method for manufacturing an electrode assembly, wherein in step (5) above, the negative electrode tab is formed by ultrasonic cutting, the negative electrode tab is joined by ultrasonic welding, and the ultrasonic cutting and ultrasonic welding are performed simultaneously.

2. A method for manufacturing an electrode assembly according to claim 1, characterized in that the length of the lithium metal layer and the separation membrane are the same.

3. The method for manufacturing an electrode assembly according to claim 1, characterized in that, in step (2) above, the bonding of the lithium metal layer and the separation membrane is performed by positioning rolls on both sides and sequentially applying pressure.

4. The method for manufacturing an electrode assembly according to claim 1, characterized in that, in the electrode laminate manufactured in step (4) above, the total number of positive electrodes enclosed between the negative electrode structures is 2n (where n is a natural number).

5. The method for manufacturing an electrode assembly according to claim 1, characterized in that the positive electrode included in the electrode laminate manufactured in step (4) includes a positive electrode active material layer and a current collector supporting the positive electrode active material layer.

6. The method for manufacturing an electrode assembly according to claim 1, wherein the positive electrode included in the electrode stack manufactured in step (4) includes a notched positive electrode tab of a current collector, and the positive electrode tab is positioned in the opposite direction to the negative electrode tab in step (5).

7. A method for manufacturing an electrode assembly according to claim 1, characterized in that a portion of the protruding lithium metal layer is cut in step (5) above, and the negative electrode tab is separated into each layer in the electrode assembly.

8. The method for manufacturing an electrode assembly according to claim 1, characterized in that, in step (5) above, the corners of the lithium metal layer protruding in each layer of the electrode assembly are cut by ultrasonic cutting, and the central parts of the protruding lithium metal layer are joined by ultrasonic welding.

9. The method for manufacturing an electrode assembly according to claim 1, wherein the thickness of the lithium metal layer is 60% to 80% of the total thickness of the negative electrode structure.

10. The method for manufacturing the electrode assembly according to any one of claims 1 to 9, further comprising the step of (6) joining leads to a bonded negative electrode tab.

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