Method for manufacturing an electrode assembly

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, particularly, a method for manufacturing an electrode assembly using a negative electrode structure having a lithium metal layer interposed between two separators, the method including cutting a portion of the lithium metal layer protruding in a width direction to form a negative electrode tab, and bonding the negative electrode tab.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0136203 filed on October 21, 2022 and Korean Patent Application No. 10-2023-0129310 filed on September 26, 2023, and incorporates all contents disclosed in the documents of said Korean patent applications as part of this specification. [Background technology]

[0003] Recently, interest in energy storage technology has been increasing. As the application fields have expanded to include mobile phones, video cameras, and laptop computers, as well as the energy sources for electric vehicles, efforts in the research and development of batteries have become more and more concrete. Electrochemical devices are the field that has attracted the most attention in this regard, and in particular, with the recent trend toward miniaturization and weight reduction of electronic devices, the development of secondary batteries that are compact, lightweight, high capacity, and rechargeable has become a focus of attention.

[0004] Secondary batteries can also be classified according to the structure of the electrode assembly, which has a positive electrode / separator / negative electrode structure.Typical examples include a jelly-roll (wound-type) electrode assembly, in which long sheet-like positive and negative electrodes are wound with a separator between them, and a stack-type electrode assembly, in which multiple positive and negative electrodes cut into predetermined sizes are stacked in sequence with a separator between them.

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

[0006] First, the jelly-roll electrode assembly is fabricated by winding long sheet-like positive and negative electrodes in a dense state to form 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 when the accumulation of such stress exceeds a certain limit, deformation of the electrode assembly occurs. Furthermore, the deformation of the electrode assembly may cause problems such as uneven spacing between the electrodes, rapid deterioration of the battery performance, and internal short circuit threatening the safety of the battery. In addition, since the jelly-roll electrode assembly requires winding long sheet-like positive and negative electrodes, it is difficult to wind the electrode assembly quickly while maintaining a constant spacing between the positive and negative electrodes, resulting in reduced productivity.

[0007] Secondly, the stacked electrode assembly requires sequential stacking of a number of positive and negative electrode units, which requires a separate electrode plate transfer process for manufacturing the units and requires a lot of time and effort for the sequential stacking process, resulting in low productivity.

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

[0009] In the stack-folded electrode assembly, the electrodes of each layer are connected by extending a separator that is generally easier to fold than an electrode. In this case, the electrodes of each layer are supplied in a cut state to form the electrode assembly, similar to the stack-type electrode assembly. When a secondary battery is to be formed using only a material that is easy to cut or not easy to fold among various electrode materials constituting secondary batteries in the art, such a general stack-folded electrode assembly is more suitable. Meanwhile, lithium metal, which is well known in the art as a negative electrode material for secondary batteries, is not easily processed, such as cut, due to its physical properties of high ductility and viscosity, and is relatively easy to fold, so that it may not be suitable for the conventional stack-folded electrode assembly.

[0010] The present inventors have continuously studied the structure of an electrode assembly, and have designed a structure suitable for an electrode assembly, particularly an electrode assembly containing lithium metal in a negative electrode, and have completed the present invention. In the method for manufacturing an electrode assembly according to the present invention, processing of lithium metal can be minimized, and thus the productivity of the electrode assembly is expected to be improved. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 2021-0006231 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a method for manufacturing a stack-folded type electrode assembly having a new structure utilizing a negative electrode structure having a lithium metal layer between two separators, the method including the steps of cutting a portion of the lithium metal layer protruding in the width direction to form a negative electrode tab, and bonding the negative electrode tab. [Means for solving the problem]

[0013] According to a 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 the steps of: (1) positioning a lithium metal layer between two separators so that the lithium metal layer protrudes in the width direction; (2) laminating the lithium metal layer and the separator to manufacture a negative electrode structure; (3) stacking one positive electrode on the negative electrode structure and folding the negative electrode structure in the width direction to wrap the positive electrode; (4) repeating step (3) to manufacture an electrode stack including a plurality of positive electrodes; and (5) 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.

[0015] In one embodiment of the present invention, the lithium metal layer and the separator have the same length.

[0016] In one embodiment of the present invention, the lamination of the lithium metal layer and the separator in step (2) is performed by sequentially pressing the lithium metal layer and the separator using rolls placed on both sides.

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

[0018] In one embodiment of the present invention, the positive electrode included in the electrode laminate prepared 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 stack manufactured in step (4) includes a positive electrode tab of a notched current collector, and the positive electrode tab is located opposite to the negative electrode tab in step (5).

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

[0021] In one embodiment of the present invention, the formation of the negative electrode tab in step (5) is performed by ultrasonic cutting, and the joining of the negative electrode tab 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 protruding lithium metal layers in each layer of the electrode assembly are cut off by ultrasonic cutting in step (5), and the centers 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 a lead to the joined negative electrode tab. Effect of the Invention

[0024] Lithium metal, which is used as the negative electrode of a lithium secondary battery, has physical properties that make it difficult to process, and excessive processing of lithium metal may increase the defective rate of the finished product. For example, when notching lithium metal, not only is it difficult to produce lithium metal of a consistent shape because lithium metal is burned onto the blade, but if a blade contaminated by the burned lithium metal is repeatedly used, contamination may accumulate and affect the product. Therefore, in the method for manufacturing an electrode assembly according to the present invention, after manufacturing an electrode stack, the lithium metal layer is cut at once to form a negative electrode tab, and the negative electrode tab is joined, thereby minimizing the processing of the lithium metal. In this way, when the processing of the lithium metal is minimized, not only the defective rate of the finished product can be reduced, but also the processability can be improved, thereby improving the productivity of the electrode assembly. [Brief description of the drawings]

[0025] [Figure 1] 1A to 1C are schematic diagrams illustrating a process for producing a negative electrode structure by roll pressing according to one embodiment of the present invention. [Diagram 2] 1 is a front view showing a schematic diagram of an electrode stack according to an embodiment of the present invention. [Diagram 3] 1 is a plan view illustrating a schematic configuration of an electrode stack according to an embodiment of the present invention. [Figure 4] 4 is an enlarged view of the two-dot chain line in FIG. 3, and is a diagram illustrating roughly the cutting positions and welding positions in the lithium metal layer protruding in the width direction. [Diagram 5] 5 is a left side view showing a shape in which a tab is joined in an electrode assembly according to an embodiment of the present invention. In FIG. 5, in order to clearly show each layer portion, the folded portion of the negative electrode structure that can be seen in the side view is omitted. [Figure 6] 6 is a left side view showing a shape in which a lead is joined to a tab in an electrode assembly according to an embodiment of the present invention. In FIG. 6, in order to clearly show each layer portion, the folded portion of the negative electrode structure that can be seen in the side view is omitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the embodiments will be described in detail with reference to the drawings. When referring to the components in each drawing, it should be noted that the same components are given the same reference numerals as much as possible even if they are shown in different drawings. In addition, when describing the embodiments, if a detailed description of related known configurations or functions is deemed to hinder understanding of the embodiments, the detailed description will be omitted.

[0027] In addition, terms such as first, second, A, B, (a), (b), etc. may be used to describe components of the embodiment. These terms are used to distinguish the components from other components, and do not limit the nature, order, or sequence of the components. When a component is described as being "coupled," "connected," or "connected" to another component, it should be understood that the component may be directly connected or connected to the other component, but other components may also be "coupled," "connected," or "connected" between each component.

[0028] Components having a common function to those included in one embodiment will be described using the same names in other embodiments. Unless otherwise specified, the description of one embodiment may be applied to other embodiments, and detailed description 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 having a lithium metal layer interposed between two separators. In the past, when manufacturing an electrode assembly including lithium metal in a negative electrode, excessive lithium processing may reduce processability and reliability of the manufactured product. However, in the method for manufacturing an electrode assembly according to the present invention, after manufacturing an electrode stack, the lithium metal layer is cut at once to form a negative electrode tab, and the negative electrode tab is joined, thereby minimizing processing of the lithium metal. In this way, when the processing of the lithium metal is minimized, not only can the defective rate of the finished product be reduced, but also the processability can be improved, thereby improving the productivity of the electrode assembly.

[0030] In the present specification, the terms "electrode assembly" and "electrode laminate" are used. The term "electrode assembly" is interpreted in a more comprehensive sense than the term "electrode laminate," and the structure after the positive electrode, the negative electrode, and the separator are laminated may all be referred to as an electrode assembly. Thus, a structure in which the positive electrode, the negative electrode, and the separator are laminated and then a tab is formed, a laminated structure, a structure in which the positive electrode, the negative electrode, and the separator are laminated and then a tab is formed and joined, and a structure in which the positive electrode, the negative electrode, and the separator are laminated and then a lead is joined to the tab formed, may all be an electrode assembly. In contrast, the term "electrode laminate" refers only to a structure in which the positive electrode, the negative electrode, and the separator are laminated. In the positive electrode, the current collector, etc. may be notched to form a tab, and the electrode laminate 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" means the left-right direction in front views such as Figs. 1 and 2 and plan views such as Figs. 3 and 4, and means the undivided front-rear direction in left side views such as Figs. 5 and 6. In this specification, the "width direction" means the undivided front-rear direction in front views such as Figs. 1 and 2, the up-down direction in plan views such as Figs. 3 and 4, and means the left-right direction in left side views such as Figs. 5 and 6. In this specification, the "height direction" means the up-down direction in front views such as Figs. 1 and 2, the undivided front-rear direction in plan views such as Figs. 3 and 4, and means the up-down direction in left side views such as Figs. 5 and 6.

[0032] A method for manufacturing an electrode assembly according to an embodiment of the present invention includes a step of positioning a lithium metal layer between two separators so as to protrude in the width direction. In this specification, the two separators constituting the negative electrode structure may be simply called separators when there is no need to distinguish them, and may be called first and second separators when there is a need to distinguish them. Here, the protruding lithium metal layer is used to form a tab later, and the positive electrode does not protrude from the separator in the same direction, so the lithium metal layer and the positive electrode do not contact each other. In the case of the positive electrode tab, it is positioned to protrude in the width direction from the separator like the negative electrode tab, but when the lithium metal layer protruding in the width direction is cut later as in the present invention, it can only contact 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 includes lithium metal, and the lithium metal does not differ significantly in physical properties from lithium metal even if some components are added to lithium or the lithium metal is in the form of an alloy with some metal, and the same problems can occur when applying it to a conventional electrode assembly like lithium metal, so it can be broadly interpreted.

[0033] A method for manufacturing an electrode assembly according to an embodiment of the present invention includes a step of manufacturing a negative electrode structure by laminating a lithium metal layer and a separator. Here, lamination means that the lithium metal layer and the separator are integral and are used as one component in the manufacturing process of the electrode assembly, and does not necessarily require that the lithium metal layer and the separator are bonded with an adhesive or the like. Lithium metal is soft and has adhesiveness in relation to other materials, and the lithium metal and the separator can be relatively easily bonded together by applying a certain level of pressure or more.

[0034] In a method for manufacturing an electrode assembly according to an embodiment of the present invention, the lithium metal layer and the separator can be laminated by sequentially applying pressure to both sides of rolls. To facilitate understanding of this, FIG. 1 is a schematic diagram showing a process of forming a negative electrode structure by roll pressure according to an 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 FIG. 1. In the nip roll, the strength of pressure can be adjusted by adjusting the distance between the rolls. In an embodiment of the present invention, the lithium metal layer and the separator are laminated using rolls because the negative electrode structure can be continuously manufactured. In manufacturing the negative electrode structure, the lithium metal layer and the separator used in one electrode assembly can be cut and then fed to the nip roll to manufacture the negative electrode structure, but it is possible to continuously supply the lithium metal layer (11) and the separator (12) to continuously manufacture the negative electrode structure (10) and cut them to the required length for use, which can help improve processability.

[0035] As described above, the lithium metal layer is positioned between the separators so as to protrude in the width direction, and then the lithium metal layer and the separator are bonded together, so the width of the lithium metal layer may be longer than the width of the separator. However, in a continuous process of manufacturing the negative electrode structure, the lithium metal layer and the separator are cut at the same time, so the lengths of the lithium metal layer and the separator may be the same. However, depending on the method of cutting the negative electrode structure, a slight difference may occur in the lengths of the negative electrode and the separator, and in some cases, the end of the separator may be curved toward the center of the negative electrode structure. Even if the lengths of the negative electrode and the separator are the same during the supply process, the length of the lithium metal layer may be extended due to the ductility of lithium metal during the folding process when applied to an electrode assembly. Therefore, in one embodiment of the present invention, the negative electrode and the separator being the same length means that the negative electrode and the separator are cut at the same time and the lengths may be substantially the same, and in an actual product, the end of the negative electrode and the end of the separator may not be located on the same line depending on the situation.

[0036] A method for manufacturing an electrode assembly according to an embodiment of the present invention includes stacking one positive electrode on a negative electrode structure and folding the negative electrode structure in a width direction to encase the positive electrode. An electrode assembly according to an embodiment of the present invention includes one negative electrode structure and a plurality of positive electrodes. Although there is only one negative electrode structure, the negative electrode structure can also be formed into a plurality of layers by folding in the width direction. In this specification, folding in the width direction means that the length of the negative electrode structure is divided into two or more by folding. Since the negative electrode structure is much longer in the length direction than in the width direction, it is easy to form a plurality of layers by folding, and this expansion is free when the negative electrode structures are continuously manufactured.

[0037] A method for manufacturing an electrode assembly according to an embodiment of the present invention includes repeating a process of stacking positive electrodes and folding the negative electrode structure in the width direction to wrap the positive electrodes, thereby manufacturing an electrode stack including a plurality of positive electrodes. To facilitate understanding of the electrode stack, FIG. 2 provides a front view of an electrode stack according to an embodiment of the present invention. As can be seen in FIG. 2, when the negative electrode structure (10) is folded to wrap the positive electrode (20), the negative electrode structure has a direction opposite to the initial direction. In this way, when the positive electrodes (20) are stacked sequentially, the negative electrode structure (10) has a zigzag shape. Therefore, the folded parts of the negative electrode structure are also positioned alternately left and right. If no positive electrode is inserted in the space between the folded negative electrode structures or multiple positive electrodes are inserted, no potential difference is generated between the layers of the negative electrode structures or positive electrodes stacked consecutively, which may reduce the efficiency of the battery.

[0038] In an electrode stack according to an embodiment of the present invention, the total number of positive electrodes enclosed between the negative electrode structures may be 2n (where n is a natural number). As described above, when the negative electrode structure is folded to encase the positive electrode, the negative electrode structure has an orientation opposite to the initial direction. Here, in the electrode stack, if the total number of positive electrodes enclosed between the negative electrode structures is an even number, the negative electrode structure has the same orientation as the initial direction, and as shown in FIG. 2, one end of the negative electrode structure is located opposite to the other end in the electrode stack. In this case, when finishing the electrode stack, such as wrapping the electrode stack with the negative electrode structure, each end is close to one side, which may make it easier. According to an embodiment of the present invention, in addition to the positive electrode enclosed between the negative electrode structures, a positive electrode may be located at the upper or lower stage of the electrode stack, and a positive electrode may be located at the upper and lower stages 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 supporting the positive electrode active material layer. The positive electrode has a structure in which a positive electrode active material layer is formed on at least one surface, specifically, both surfaces, of a current collector. The positive electrode active material layer includes a positive electrode active material and may further include 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 commonly used in the technical field.

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

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

[0042] The positive electrode active material may be 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(O <y<1)、LiCo 1-y Mn y O2(O <y<1)、LiNi 1-y Mn y O2(O <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 thereof 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), 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, the electrode assembly according to one embodiment of the present invention 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] Considering the above content, the positive electrode is relatively not easy to fold and is 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 positive electrode tab of a notched current collector, and the positive electrode tab is located protruding from the separator in the opposite direction to the protruding direction of the lithium metal layer. To facilitate understanding of the position of the lithium metal layer and the positive electrode tab protruding from the separator, FIG. 3 provides a plan view that shows a schematic view of an electrode stack according to one embodiment of the present invention. In a typical electrode assembly of a lithium secondary battery, even if the positive electrode tab and the negative electrode tab are located in the same direction, if they are spaced apart so as not to contact 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 FIG. 3, the protruding lithium metal layer (11) that is not cut covers the entire length direction of the electrode assembly, so that the positive electrode tab (20T) cannot be located apart from the protruding lithium metal layer in the same direction. In addition, even if the lithium metal layer (11) and the positive electrode tab (20T) are located in different layers and separated from each other, when the lithium metal layer is cut to form the negative electrode tab, the positive electrode tab may be cut along with the lithium metal layer, which may be undesirable.

[0047] A method for manufacturing an electrode assembly according to an embodiment of the present invention includes cutting a portion of the lithium metal layer protruding in the width direction to form a negative electrode tab, and bonding the negative electrode tab. The method for manufacturing an electrode assembly according to an embodiment of the present invention can form the negative electrode tab at once in a state where an electrode stack is manufactured, thereby minimizing the number of times that a cutting device cuts the lithium metal. In addition, the tabs of each layer can be cut quickly at once, and the tabs of each layer are naturally lined up when cutting, thereby improving processability. The electrode assembly according to an embodiment of the present invention can have a stable structure when cut in that the lithium metal protruding in the width direction is continuously continued for each layer.

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

[0049] According to an embodiment of the present invention, the negative electrode tab is formed by ultrasonic cutting, and the negative electrode tab is joined by ultrasonic welding. The ultrasonic cutting may be performed using an ultrasonic cutter commonly used in the art for metal processing. The ultrasonic cutter generates high-frequency energy from a connected generator, and the generated energy is transferred to a cutting blade. When the cutting blade is brought into contact with the lithium metal to be cut, vibration friction heat is generated, and the lithium metal layer is cut. The ultrasonic welding may be performed using an ultrasonic welding machine commonly used in the art for metal processing. The ultrasonic welding machine generates high-frequency energy from a connected generator, and the generated energy is transferred to a horn or sonotrode. When the horn or sonotrode is brought into contact with the lithium metal to be joined, ultrasonic vibration is applied to the lithium metal layer to form a solid-state weld at the joining surface.

[0050] According to an embodiment of the present invention, ultrasonic cutting and ultrasonic welding are performed simultaneously. The ultrasonic cutting and ultrasonic welding positions are not in contact with each other, so ultrasonic cutting and ultrasonic welding can proceed simultaneously. To facilitate understanding of the ultrasonic cutting and ultrasonic welding positions, FIG. 4 provides a diagram that shows a schematic diagram of cutting positions and welding positions in a lithium metal layer protruding in the width direction. FIG. 4 is an enlarged view of the two-dot chain line in FIG. 3. In FIG. 4, the ultrasonic cutting position is the same as the dashed line and is indicated by C. Also, in FIG. 4, the ultrasonic welding position is the same as the square area and is indicated by W. As shown in FIG. 4, the corners of the lithium metal layer protruding from each layer of the electrode assembly can be cut by ultrasonic cutting, and the center 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 FIG. 4, and in the length direction, which is the horizontal direction in FIG. 4, respectively, but it may be more advantageous to perform the ultrasonic cutting in the width direction first in order to proceed simultaneously with ultrasonic welding. Also, it may be preferable to perform the cutting in the left-right direction so as to almost contact the separator as shown in FIG. 4.

[0051] In an electrode assembly according to an embodiment of the present invention, the length of the negative electrode tab may be appropriately adjusted in consideration of the length of each layer. Since the negative electrode is not cut but continues continuously, the length of each layer may be indicated by the length of the positive electrode. The length is based on the length direction of the negative electrode structure, and means the left-right direction in FIG. 4. The length of the negative electrode tab may mean the left-right length of the protruding lithium metal layer remaining after cutting the lithium metal layer along the dashed line in FIG. 4. According to an 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 formed too long, the processability when joining the negative electrode tab may be reduced.

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

[0053] The manufacturing method of the electrode assembly according to an embodiment of the present invention further includes a step of bonding a lead to the bonded negative electrode tab. To facilitate understanding of the shape of the lead bonded to the negative electrode tab, FIG. 6 provides a left side view showing the shape of the electrode assembly according to an embodiment of the present invention, in which the lead is bonded to the tab. FIG. 6 is shown in the same manner as FIG. 5. The negative electrode lead (11L) is located on the bonded negative electrode tab as in FIG. 6 and is bonded to the negative electrode tab. 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 may be made of a conductive material commonly used in the art.

[0054] In an electrode assembly according to an embodiment of the present invention, the negative electrode does not include a separate current collector supporting the lithium metal layer in addition to the lithium metal layer. Since the negative electrode does not include a current collector, the loading amount of the negative electrode active material in the electrode assembly can be improved, which can contribute to improving the performance of the battery. When the negative electrode is mainly composed of lithium metal, the lithium metal has high ductility and viscosity, which may make it difficult to process, such as cutting, but in an electrode assembly according to an embodiment of the present invention, the negative electrode is applied in the form of a negative electrode structure, which can minimize cutting and improve processability.

[0055] In the negative electrode structure, the type of the separator covering both sides of the negative electrode is not particularly limited as long as it does not contain a binder on the surface. Specifically, the separator can be, for example, a nonwoven fabric or a polyolefin-based porous substrate made of high-melting glass fiber, polyethylene terephthalate fiber, etc., but is not limited thereto.

[0056] The material of the porous substrate is not particularly limited in the present invention, and any porous substrate generally used in electrochemical devices may be used. According to one embodiment of the present invention, the porous substrate may be a polyolefin such as polyethylene or polypropylene, a polyester such as polyethyleneterephthalate or polybutyleneterephthalate, a polyamide, a polyacetal, a polycarbonate, a polyimide, a polyetheretherketone, a polyethersulfone, a polyphenyleneoxide, a polyphenylenesulfide, a polyethylenenaphthalate, a polytetrafluoroethylene, a polyvinylidene fluoride, a polyvinyl chloride, or a combination thereof. The insulating layer may include one or more materials selected from the group consisting of polyparaphenylene chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylene benzobisoxazole), and polyarylate.

[0057] In the electrode assembly according to an embodiment of the present invention, one negative electrode structure is folded to form a basic structure of the electrode assembly. The negative electrode structure should not be excessively thick so that it can be folded flexibly, and a certain level of lithium metal, which is a negative electrode active material, should be secured in the negative electrode structure in consideration of the performance of the battery. According to an embodiment of the present invention, the thickness of the lithium metal layer in the negative electrode structure occupies 50% to 90% based on the total thickness of the negative electrode structure. Specifically, the thickness of the lithium metal layer may be in the range of 50% to 90%, specifically 55% to 85%, more specifically 60% to 80%. When the lithium metal layer satisfies the above-mentioned thickness range, it can be useful for improving the processability and functionality of the electrode assembly. According to an embodiment of the present invention, since the negative electrode structure does not include a separate current collector, the thickness of the remaining part excluding the thickness of the lithium metal layer may mean the thickness of two separators.

[0058] According to an 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 may be appropriately adjusted according to the actual size of the battery.

[0059] In an electrode assembly according to an embodiment of the present invention, the positive electrode is cut in consideration of the characteristics of the material and is applied between the negative electrode structure that is folded. The positive electrode is independent from the negative electrode, for example, including a current collector in addition to a positive electrode active material, but the thickness can be adjusted in relation to the negative electrode or the negative electrode structure in consideration of the performance of the electrode. According to an embodiment of the present invention, the thickness of the positive electrode is greater than the thickness of the negative electrode structure. According to an embodiment of the present invention, the thickness of the positive electrode is greater than 100% and less than 400% based on the thickness of the negative electrode structure. Specifically, the thickness of the positive electrode may be in the range of greater than 100% and less than 400%, specifically 150% to 350%, more specifically 200% to 300%. When the positive electrode satisfies the above-mentioned thickness range, it can be appropriately matched with the negative electrode structure.

[0060] The electrode assembly according to an embodiment of the present invention is applied to an electrochemical device. The electrochemical device may include any device that performs an electrochemical reaction. For example, the electrochemical device may be any type of primary battery, secondary battery, fuel cell, solar cell, or capacitor. When the electrochemical device is a secondary battery, the electrochemical device may be a lithium secondary battery, and the lithium secondary battery may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0061] Any simple modifications or variations of the present invention are within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims. [Explanation of symbols]

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

Claims

1. (1) positioning a lithium metal layer between two separators so that the lithium metal layer protrudes in the width direction; (2) bonding the lithium metal layer and the separator to produce a negative electrode structure; (3) stacking one positive electrode on the negative electrode structure and folding the negative electrode structure in a width direction to enclose the positive electrode; (4) repeating the step (3) to manufacture an electrode stack including a plurality of positive electrodes; and (5) cutting a portion of the lithium metal layer protruding in a width direction to form a negative electrode tab, and joining the negative electrode tab; A method for manufacturing an electrode assembly, comprising:

2. The method for manufacturing an electrode assembly according to claim 1 , wherein the lithium metal layer and the separator have the same length.

3. 2 . The method of claim 1 , wherein in step (2), the lithium metal layer and the separator are bonded to each other by sequentially pressing the lithium metal layer and the separator together using rolls disposed on both sides of the lithium metal layer. 3 .

4. 2. The method of claim 1, wherein in the electrode stack manufactured in step (4), the total number of positive electrodes enclosed between the negative electrode structures is 2n (where n is a natural number).

5. 2 . The method of claim 1 , wherein the positive electrode included in the electrode stack manufactured in step (4) includes a positive electrode active material layer and a current collector supporting the positive electrode active material layer.

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

7. 2 . The method of claim 1 , wherein in step (5), the protruding portion of the lithium metal layer is cut off, and the negative electrode tab in the electrode assembly is separated into each layer. 3 . The method of claim 1 , wherein the protruding portion of the lithium metal layer is cut off and the negative electrode tab in the electrode assembly is separated into each layer.

8. 2. The method of claim 1, wherein in step (5), the negative electrode tab is formed by ultrasonic cutting, and the negative electrode tab is joined by ultrasonic welding, and the ultrasonic cutting and ultrasonic welding are performed simultaneously.

9. 9. The method of claim 8, wherein in step (5), corners of the protruding lithium metal layers in each layer of the electrode assembly are cut by ultrasonic cutting, and central portions of the protruding lithium metal layers are joined by ultrasonic welding.

10. The method for manufacturing an electrode assembly according to claim 1 , further comprising: (6) joining a lead to the joined negative electrode tab.

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