Electrode assembly and secondary battery including the same

Abstract

An electrode assembly according to an embodiment of the present invention includes a plurality of unit cells stacked on each other, the unit cells including a cell stack part in which electrodes and a separator are alternately stacked and integrally combined, and a sub-unit cell stacked on the cell stack part, the sub-unit cell having a polymer film on the outermost side, and the alternately stacked electrodes and the separator are integrally combined with the polymer film. The polymer film may be flat or may be concavely curved toward the cell stack part such that the distance between a reference plane connecting both edges in a width direction and a center portion is less than 1 mm. The thickness of the polymer film may be equal to or greater than the thickness of the separator.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0109087 dated August 18, 2021 and Korean Patent Application No. 10-2022-0102965 dated August 17, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a secondary battery including the same, and more particularly to a lamination-and-stack type electrode assembly and a secondary battery including the same. [Background technology]

[0003] In general, a secondary battery refers to a battery that can be charged and discharged, unlike a primary battery that cannot be recharged, and is widely used in electronic devices such as mobile phones, laptops, and camcorders, as well as electric vehicles, etc. In particular, lithium secondary batteries have a larger capacity than nickel-cadmium batteries or nickel-metal hydride batteries and a higher energy density per unit weight, and therefore their use is rapidly increasing.

[0004] Meanwhile, lithium secondary batteries are classified according to the structure of the electrode assembly, which has a positive electrode / separator / negative electrode structure. Representative examples include a jelly roll electrode assembly in which long sheet-like positive and negative electrodes are wound with a separator interposed therebetween; a simple stack type electrode assembly in which a number of positive and negative electrodes cut into predetermined size units are stacked one after the other with a separator interposed therebetween; a lamination and stack type electrode assembly in which a number of unit cells manufactured by a lamination process are stacked; and a stack / fold type electrode assembly in which unit cells in which predetermined units of positive and negative electrodes are stacked with a separator interposed therebetween are wound.

[0005] In particular, lamination and stack type electrode assemblies are widely used because they have the advantages of shortening manufacturing time and increasing productivity because electrodes and separators are not laminated one by one, and of high efficiency because multiple electrodes are accurately aligned.

[0006] However, in conventional lamination-and-stack type electrode assemblies, a separator is typically positioned on the outermost layer, which can cause bending of the electrode assembly and lead to internal short circuits. Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode assembly that minimizes bending and a secondary battery including the same. [Means for solving the problem]

[0008] An electrode assembly according to an embodiment of the present invention includes a plurality of unit cells stacked on one another, each unit cell including a cell stack portion in which alternately stacked electrodes and separators are integrally combined; and a sub-unit cell stacked on the cell stack portion, the sub-unit cell having a polymer film on its outermost side, and the alternately stacked electrodes and separators integrally combined with the polymer film. The polymer film may be flat or may be curved toward the cell stack portion so that the distance between a reference plane connecting both edges in the width direction and the center is less than 1 mm. The thickness of the polymer film may be equal to or greater than the thickness of the separator.

[0009] The adhesive strength of the polymer film within the sub-unit cell may be stronger than the adhesive strength between the sub-unit cell and the cell stack portion.

[0010] The thickness of the polymer film may be three times or less the thickness of the separator.

[0011] The polymer film may be laminated on the electrode.

[0012] The polymer film may include at least one material selected from the group consisting of polyethylene terephthalate, polyvinyl chloride, polyamide, polyimide, polyaramid, and polypropylene.

[0013] The number of the electrodes included in the sub-unit cell may be less than the number of the electrodes included in the unit cell.

[0014] The polymer film may be positioned on one outermost side of the electrode assembly, and the separator at the outermost side of the cell stack portion may be positioned on the other outermost side of the electrode assembly.

[0015] An electrode assembly according to an embodiment of the present invention may include a plurality of unit cells stacked on one another, the unit cells including: a cell stack portion in which alternately stacked electrodes and separators are integrally bonded; a first sub-unit cell stacked on one side of the cell stack portion and having a first polymer film on its outermost side, in which the alternately stacked electrodes and separators are integrally bonded together with the first polymer film; and a second sub-unit cell stacked on the other side of the cell stack portion and having a second polymer film on its outermost side, in which the alternately stacked electrodes and separators are integrally bonded together with the second polymer film. The first polymer film may be flat or may be concave and curved toward the cell stack portion so that the distance between a reference plane connecting both edges in the width direction and the center is less than 1 mm. The thicknesses of the first and second polymer films may be equal to or greater than the thickness of the separator.

[0016] The second polymer film may be flat or may have a central portion in a width direction that is curved convexly toward the opposite side of the cell stack portion from both edges.

[0017] A secondary battery according to an embodiment of the present invention may include a pouch-type battery case and an electrode assembly housed in the battery case. The electrode assembly may include a plurality of unit cells stacked on one another, each unit cell including a cell stack portion in which alternately stacked electrodes and separators are integrally combined; and a sub-unit cell stacked on the cell stack portion, the sub-unit cell having a polymer film on its outermost side, and the alternately stacked electrodes and separators integrally combined with the polymer film. The polymer film may be flat or may be curved toward the cell stack portion so that the distance between a reference plane connecting both edges in the width direction and the center is less than 1 mm. The thickness of the polymer film may be equal to or greater than the thickness of the separator.

[0018] The polymer film may face one side of the inner surface of the battery case, and the outermost separator of the cell stack part may face the opposite side of the inner surface of the battery case.

[0019] A secondary battery according to an embodiment of the present invention may include a pouch-type battery case and an electrode assembly housed in the battery case. The electrode assembly may include a plurality of unit cells stacked on one another, the unit cells including a cell stack portion in which alternately stacked electrodes and separators are integrally bonded; a first sub-unit cell stacked on one side of the cell stack portion and having a first polymer film on its outermost side, in which the alternately stacked electrodes and separators are integrally bonded together with the first polymer film; and a second sub-unit cell stacked on the other side of the cell stack portion and having a second polymer film on its outermost side, in which the alternately stacked electrodes and separators are integrally bonded together with the second polymer film. The first polymer film may be flat or may be curved toward the cell stack portion so that the distance between a reference plane connecting both edges and the center in the width direction is less than 1 mm. The thicknesses of the first and second polymer films may be equal to or greater than the thickness of the separator.

[0020] The first polymer film may face one inner surface of the battery case, and the second polymer film may face the opposite inner surface of the battery case. [Effects of the Invention]

[0021] According to a preferred embodiment of the present invention, the polymer film has a sufficiently high rigidity so that bending of the electrode assembly can be effectively prevented or minimized.

[0022] In addition, in an embodiment in which the polymer film is located only on one outermost side of the electrode assembly, the polymer film may be located on one of the outermost sides of the electrode assembly that is concave and bent, thereby stably maintaining adhesion between the polymer film and the electrode and minimizing bending of the electrode assembly.

[0023] In addition, in an embodiment in which the polymer film is positioned only on one outermost side of the electrode assembly, it is possible to minimize a decrease in the energy density of the electrode assembly, and it is possible to manufacture the electrode assembly using only a single type of sub-unit cell.

[0024] Furthermore, in an embodiment in which the polymer film is positioned on both outermost sides of the electrode assembly, bending of the electrode assembly can be more effectively prevented or minimized.

[0025] In addition, the present invention can include other effects that can be easily predicted by a person skilled in the art from the configuration of the preferred embodiment of the present invention. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a plan view of a secondary battery according to an embodiment of the present invention; [Figure 2] 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view showing a stacked structure of an electrode assembly according to an embodiment of the present invention; [Figure 4]4 is a cross-sectional view showing a modified embodiment of the electrode assembly shown in FIG. 3. FIG. [Figure 5] 3 is an enlarged side view of a polymer film of an electrode assembly according to an embodiment of the present invention; FIG. [Figure 6] 10 is a cross-sectional view showing a stacked structure of an electrode assembly according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0027]

[0030] The present invention will now be described in detail with reference to the accompanying drawings, in order to enable those skilled in the art to easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the following embodiments.

[0028] In order to clearly explain the present invention, detailed descriptions of parts that are not relevant to the explanation or related known technologies that may unnecessarily obscure the gist of the present invention will be omitted, and in adding reference symbols to components in each figure in this specification, the same or similar reference symbols will be used for the same or similar components throughout the specification.

[0029] Furthermore, the terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that an inventor can define the concept of a term as appropriate in order to best explain his or her invention.

[0030] FIG. 1 is a plan view of a secondary battery according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of the secondary battery according to an embodiment of the present invention.

[0031] The secondary battery 1 according to the present invention may include an electrode assembly 100 and a pouch-type battery case 200 that houses the electrode assembly 100 .

[0032] The electrode assembly 100 may include a plurality of electrodes 130 and a plurality of separators 140 stacked alternately, and an outermost polymer film 150. The plurality of electrodes 130 may include a first electrode 131 and a second electrode 132 having opposite polarities and stacked alternately with the separator 140 sandwiched therebetween. For example, the first electrode 131 may be a positive electrode, and the second electrode 132 may be a negative electrode.

[0033] The polymer film 150 may be located on at least one of the outermost sides of the electrode assembly 100 and may be laminated on the electrode 130 .

[0034] The detailed structure of the electrode assembly 100 will be described later.

[0035] Meanwhile, the electrode assembly 100 may be provided with a plurality of electrode tabs 160 welded to each other. The plurality of electrode tabs 160 may be connected to the plurality of electrodes 130, protrude from the electrode assembly 100 to the outside, and act as a path through which electrons can move between the inside and outside of the electrode assembly 100.

[0036] The electrode tab 160 connected to the first electrode 131 and the electrode tab 160 connected to the second electrode 132 may protrude in different directions from each other with respect to the electrode assembly 100. For example, the electrode tab 160 connected to the first electrode 131 and the electrode tab 160 connected to the second electrode 132 may protrude in opposite directions from each other with respect to the overall length of the electrode assembly 100. However, the present invention is not limited thereto, and the electrode tab 160 connected to the first electrode 131 and the electrode tab 160 connected to the second electrode 132 may protrude in parallel with each other.

[0037] A lead 170 for supplying electricity to the outside of the secondary battery 1 may be connected to the plurality of electrode tabs 160 by spot welding or the like. One end of the lead 170 may be connected to the plurality of electrode tabs 160, and the other end may protrude outside the battery case 200.

[0038] A portion of the electrode lead 170 may be surrounded by an insulating portion 180. For example, the insulating portion 180 may include insulating tape. The insulating portion 180 may be located between a pair of terraces 240 (described later) of the battery case 200, and in this state, the pair of terraces 240 may be heat-sealed to each other. In this case, a portion of the pair of terraces 240 may be heat-sealed to the insulating portion 180. Therefore, the insulating portion 180 prevents electricity generated from the electrode assembly 100 from flowing to the battery case 200 via the lead 170, and maintains the sealing of the battery case 200.

[0039] Meanwhile, the battery case 200 may be formed by sealing a pair of cases 210 connected to each other by the folding portion 220. However, the present invention is not limited thereto, and the battery case 200 may also be formed by sealing the pair of cases 210 in a separated state.

[0040] In addition, a storage section 230 having a recessed shape may be formed in at least one of the pair of cases 210. The storage section 230 may be recessed a predetermined depth from the terrace 240 to form a recessed space S1. Hereinafter, a case where the storage section 230 is formed in each of the pair of cases 210 will be described as an example.

[0041] The receiving portions 230 of the pair of cases 210 may be connected to each other by the folding portion 220. That is, the folding portion 220 may be located between the pair of receiving portions 230, and the folding portion 220 may form a bridge when the pouch 20 is unfolded. The folding portion 220 may be formed long in the overall length direction of the battery case 200.

[0042] With the electrode assembly 100 accommodated in the recessed space S1 of one of the accommodation units 230, the folding unit 220 may be folded so that the pair of accommodation units 230 face each other. In this manner, the other accommodation unit 230 may cover the electrode assembly 100 from above. That is, the recessed spaces S1 of the accommodation units 230 may be connected to each other, and the electrode assembly 100 may be accommodated in the recessed space S1.

[0043] Each case 210 may include a terrace 240 located around the perimeter of the storage section 230. Even more specifically, the terrace 240 may be connected to the upper end of the peripheral surface of the storage section 230. The terrace 240 of each case 210 may have a generally "bow" shape.

[0044] With the electrode assembly 100 disposed between a pair of storage portions 230 of the battery case 200, the folding portion 220 is folded and the pair of terraces 240 are fused together to form a sealing portion, thereby forming a secondary battery 1 in which the pair of cases 210 are sealed together.

[0045] FIG. 3 is a cross-sectional view showing a stacked structure of an electrode assembly according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view showing a modified embodiment of the electrode assembly shown in FIG.

[0046] The electrode assembly 100 according to an embodiment of the present invention may include a cell stack unit 101 including a plurality of unit cells 110 stacked on one another, and sub-unit cells 120 stacked on the cell stack unit 101.

[0047] The cell stack part 101 may have a structure in which a plurality of electrodes 130 and a plurality of separators 140 are alternately stacked by stacking a plurality of unit cells 110 .

[0048] The cell stack part 101 may have a structure in which one type of unit cell 110 is repeatedly stacked as shown in FIG. 3, or may have a structure in which two or more types of unit cells 110 are stacked in a predetermined order as shown in FIG. 4.

[0049] Each unit cell 110 may be formed by integrally combining alternately stacked electrodes 130 and separators 140. That is, the electrodes 130 and separators 140 of each unit cell 110 may be bonded to each other by a lamination process, a rolling process, or the like.

[0050] The unit cells 110 included in the cell stack 101 may not be bonded to each other, or may be bonded to each other with an adhesive force weaker than the adhesive force between the electrode 130 and the separator 140 in each unit cell 110. Here, the adhesive force may refer to a peeling force. Therefore, the cell stack 101 may be easily separated into unit cells 110.

[0051] The number of electrodes 130 and the number of separators 140 included in each unit cell 110 may be the same. For example, as shown in Fig. 3, the unit cell 110 may be formed by stacking two electrodes 130 and two separators 140. For another example, as shown in Fig. 4, the unit cell 110 may be formed by stacking three electrodes 130 and three separators 140.

[0052] An electrode 130 may be located at one end of each unit cell 110, and a separator 140 may be located at the other end of each unit cell 110. Thus, the electrode 130 may be located at one outermost side of the cell stack part 101 formed by stacking a plurality of unit cells 110, and the separator 140 may be located at the other outermost side.

[0053] As shown in FIG. 3, when the cell stack portion 101 is formed by repeatedly stacking one type of unit cell 110, each unit cell 110 may have a four-layer structure in which a first electrode 131, a separator 140, a second electrode 132, and a separator 140 are sequentially stacked, or may have a structure in which the four-layer structure is repeatedly arranged (e.g., an eight-layer structure or a twelve-layer structure).

[0054] Meanwhile, as shown in FIG. 4, when the cell stack part 101 is formed by stacking two or more types of unit cells 110 in a predetermined order, the combination of two or more types of unit cells 110 may form the four-layer structure or a structure in which the four-layer structure is repeatedly arranged.

[0055] Hereinafter, a case where the plurality of unit cells 110 includes first unit cells 110a and second unit cells 110b that are alternately stacked will be described as an example.

[0056] The first unit cell 110a may have a first electrode 131 at one end thereof and a separator 140 at the other end thereof. The second unit cell 110b may have a second electrode 132 at one end thereof and a separator 140 at the other end thereof. Therefore, the four-layer structure or a structure in which the four-layer structure is repeatedly arranged may be formed by combining the adjacent first unit cell 110a and second unit cell 110b.

[0057] For example, the first unit cell 110a may have a six-layer structure in which the first electrode 131, the separator 140, the second electrode 132, the separator 140, the first electrode 131, and the separator 140 are stacked in this order, and the second unit cell 110b may have a six-layer structure in which the second electrode 132, the separator 140, the first electrode 131, the separator 140, the second electrode 132, and the separator 140 are stacked in this order. In this case, the six-layer structure of the first unit cell 110a and the six-layer structure of the second unit cell 110b may be stacked to form a twelve-layer structure in which the four-layer structure is repeatedly arranged.

[0058] Meanwhile, the sub-unit cell 120 may be formed by including a polymer film 150 on the outermost side, and the alternately stacked electrodes 130 and separators 140 may be integrally bonded to the polymer film 150. That is, the electrodes 130, separators 140, and polymer films 150 of the sub-unit cell 120 may be bonded to each other by a lamination process, a rolling process, or the like.

[0059] The polymer film 150 will be described in detail later.

[0060] The sub-unit cells 120 may not be adhered to the cell stack unit 101 or may be adhered to the cell stack unit 101 with an adhesive strength weaker than the adhesive strength between the electrodes 130, the separator 140, and the polymer film 150 in the sub-unit cells 120. Here, the adhesive strength may refer to a peel strength. Therefore, the sub-unit cells 120 may be easily separated from the cell stack unit 101.

[0061] The number of electrodes 130 included in the sub-unit cell 120 may be less than the number of electrodes 130 included in each unit cell 110 of the cell stack part 101. For example, as shown in FIG. 3, each unit cell 110 may include two electrodes 130, and each sub-unit cell 120 may include one electrode 130. For another example, as shown in FIG. 4, each unit cell 110 may include three electrodes, and each sub-unit cell 120 may include one electrode 130.

[0062] A polymer film 150 may be located on one outermost side of the sub-unit cell 120, and a separator 140 may be located on the other outermost side. Thus, the polymer film 150 located on one outermost side of the sub-unit cell 120 may be located at the outermost part of the electrode assembly 100, and the separator 140 located on the other outermost side of the sub-unit cell 120 may be stacked on the electrode 130 located on one outermost side of the cell stack part 101. The separator 140 located on the other outermost side of the cell stack part 101 may be located at the outermost part of the electrode assembly 100.

[0063] That is, the polymer film 150 may be located on one outermost side of the electrode assembly 100, and the outermost separator 140 of the cell stack unit 101 may be located on the other outermost side of the electrode assembly 100. Therefore, when the electrode assembly 100 is housed in the battery case 200 (see FIG. 2), the polymer film 150 may face one inner surface of the battery case 200, and the outermost separator 140 of the cell stack unit 101 may face the opposite inner surface of the battery case 200.

[0064] As described above, since the polymer film 150 is positioned on only one of the outermost sides of the electrode assembly 100, it is possible to manufacture the electrode assembly 100 using only a single type of sub-unit cell 120. Furthermore, as will be described later, the thickness t2 of the polymer film 150 is equal to or greater than the thickness t1 of the separator 140, thereby minimizing a decrease in the energy density of the electrode assembly 100.

[0065] The polymer film 150 may be laminated on the electrode 130. In the sub-unit cell 120, the polarity of the electrode 130 adjacent to the polymer film 150 may be the same as the polarity of the electrode 130 adjacent to the outermost separator 140 of the cell stack unit 101. For example, in the sub-unit cell 120, the polymer film 150 may be adjacent to the second electrode 132, and the outermost separator 140 of the cell stack unit 101 may also be adjacent to the second electrode 132.

[0066] Meanwhile, the polymer film 150 may have insulating properties, i.e., no electrical conductivity. More specifically, the polymer film 150 may include at least one material selected from the group consisting of polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamide (PA), polyimide (PI), polyaramid, and polypropylene (PP).

[0067] The polymer film 150 has higher stiffness than the separator 140 and can withstand a greater bending stress than the separator 140 .

[0068] More specifically, the separator 140 has many fine pores and is sufficiently impregnated with the electrolyte, which may result in a slight decrease in rigidity. On the other hand, the polymer film 150 does not have pores and is significantly less impregnated with the electrolyte, which may result in a significantly higher rigidity than the separator 140. Therefore, because the polymer film 150 is positioned at the outermost side of the electrode assembly 100, bending of the electrode assembly 100 may be minimized.

[0069] In addition, to ensure that the polymer film 150 has sufficiently high rigidity, the thickness t2 of the polymer film 150 may be equal to or greater than the thickness t1 of the separator 140, and may preferably be greater than the thickness t1 of the separator 140. However, if the thickness t2 of the polymer film 150 is too thick, the energy density of the electrode assembly 100 decreases, so the thickness t2 of the polymer film 150 may be three times or less the thickness t1 of the separator 140.

[0070] However, the present invention is not limited to this, and if the rigidity of the polymer film 150 is sufficiently high, the thickness t2 of the polymer film 150 may be formed to be thinner than the thickness t1 of the separator 140. For example, the thickness t2 of the polymer film 150 may be approximately 10 μm.

[0071] FIG. 5 is an enlarged side view of a polymer film of an electrode assembly according to an embodiment of the present invention.

[0072] The polymer film 150 located at the outermost side of the electrode assembly 100 may be flat or may be finely bent.

[0073] When minute bending occurs in the electrode assembly 100, the polymer film 150 may be bent such that the central portion 151 in the width direction is recessed toward the cell stack portion 101 side from both edges 152.

[0074] That is, the polymer film 150 may be located on one of the outermost concave and bent sides of the electrode assembly 100. Therefore, both edges of the electrode 130 adjacent to the polymer film 150 may be more strongly adhered to the polymer film 150 than the central portion in the width direction of the electrode 130. That is, it is possible to prevent the edges of the polymer film 150 from gradually peeling off from the electrode 130.

[0075] As a result, the adhesion between the polymer film 150 and the electrode 130 can be stably maintained, and the high rigidity of the polymer film 150 can more effectively reduce bending of the electrode assembly 100 .

[0076] More specifically, the distance between a reference plane P passing through both edges 152 of the polymer film 150 in the width direction and an outer surface (e.g., an upper surface) of the polymer film 150 may increase toward the center 151. The reference plane P may be an imaginary plane, and the outer surface of the polymer film 150 may be the surface opposite to the surface bonded to the electrode 130.

[0077] The maximum distance d between the reference plane P and the outer surface of the polymer film 150 may be less than 1 mm. That is, the distance d between the reference plane P and the central portion 151 may be less than 1 mm.

[0078] That is, the polymer film 150 may be flat or may be bent concavely toward the cell stack unit 101 so that the distance d between the reference plane P connecting both edges 152 in the width direction and the center portion 151 is less than 1 mm.

[0079] An experimental example showing the bending prevention effect of the polymer film 150 will now be described.

[0080] In Experimental Example 1, a seven-layer stack consisting of four separators, each 2 cm wide, 9 cm long, and 15 μm thick, and three anodes, each 2 cm wide and 9 cm long, was placed between a pair of protective sheets and pressed using a press. Separators were positioned at the top and bottom of the stack, and each protective sheet included a 7 cm wide, 10 cm long polyethylene terephthalate (PET) film in contact with the stack and a 7 cm wide, 10 cm long paper sheet covering the PET film. The press was heated to 60°C and a pressure of 5.2 MPa was applied. Then, flat objects were placed on both widthwise edges of the top separator of the bonded stack, and the distance between the bottom of the object and the center of the top surface of the top separator was measured. This distance indicates the degree of bending of the stack.

[0081] In Experimental Example 2, the same separator was additionally stacked on the top of the stack of Experimental Example 1, while maintaining the other conditions the same. That is, two separators were located on the top of the stack of Experimental Example 2.

[0082] In Experimental Example 3, the separator located at the top of the laminate in Experimental Example 1 was replaced with a polymer film made of PET (Polyethylene terephthalate) with a width of 2 cm, a length of 9 cm, and a thickness of 35 μm, while the other conditions were maintained the same. That is, a polymer film was located at the top of the laminate in Experimental Example 3. Then, flat objects were placed on both edges of the polymer film in the width direction, and the distance between the bottom of the object and the center of the top surface of the polymer film was measured.

[0083] As a result, the degree of bending of the laminate in each experimental example was measured to be 2.5 mm in experimental example 1, 2.0 mm in experimental example 2, and 0.3 mm in experimental example 3.

[0084] That is, when a polymer film is placed on the outermost side of the laminate instead of a separator, the degree of bending of the laminate is significantly reduced compared to when multiple separators are stacked on the outermost side.

[0085] FIG. 6 is a cross-sectional view showing a stacked structure of an electrode assembly according to another embodiment of the present invention.

[0086] The following description will be centered on the differences from the above description, with the same content as previously described being cited.

[0087] The electrode assembly 100′ according to this embodiment may have polymer films 150a and 150b positioned on both outermost sides, which may further minimize bending in the electrode assembly 100′ according to this embodiment compared to the electrode assembly 100 according to the embodiment described above.

[0088] In more detail, the electrode assembly 100' may include a cell stack part 101, a first sub-unit cell 121 stacked on one side of the cell stack part 101 and having a first polymer film 150a on its outermost side, and a second sub-unit cell 122 stacked on the other side of the cell stack part 101 and having a second polymer film 150b on its outermost side.

[0089] The first sub-unit cell 121 and the second sub-unit cell 122 may include a different number of electrodes 130. More specifically, the number of electrodes 130 included in the first sub-unit cell 121 may be less than the number of electrodes 130 included in the second sub-unit cell 122. Also, the number of electrodes 130 included in the second sub-unit cell 122 may be the same as the number of electrodes 130 included in each unit cell 110 of the cell stack part 101. For example, each unit cell 110 and the second sub-unit cell 122 may include two electrodes 130, and the first sub-unit cell 121 may include one electrode 130.

[0090] A first polymer film 150a may be located on one outermost side of the first sub-unit cell 121, and a separator 140 may be located on the other outermost side. An electrode 130 may be located on one outermost side of the second sub-unit cell 122, and a second polymer film 150b may be located on the other outermost side.

[0091] Therefore, the first polymer film 150 located on one outermost side of the first sub-unit cell 121 may be located at the outermost side of the electrode assembly 100′, and the separator 140 located on the other outermost side of the first sub-unit cell 121 may be stacked on the electrode 130 located on one outermost side of the cell stack unit 101. The electrode 130 located on one outermost side of the second sub-unit cell 122 may be stacked on the separator 140 located on the other outermost side of the cell stack unit 101, and the second polymer film 150b located on the other outermost side of the second sub-unit cell 122 may be located at the outermost side of the electrode assembly 100′.

[0092] That is, the first polymer film 150a may be located on one outermost side of the electrode assembly 100', and the second polymer film 150b may be located on the other outermost side of the electrode assembly 100'. Therefore, when the electrode assembly 100' is housed in a battery case 200 (see FIG. 2), the first polymer film 150a may face one inner surface of the battery case 200, and the second polymer film 150b may face the opposite inner surface of the battery case 200.

[0093] The first polymer film 150a and the second polymer film 150b may be laminated to the electrode 130.

[0094] In the first sub-unit cell 121, the polarity of the electrode 130 adjacent to the first polymer film 150a may be the same as the polarity of the electrode 130 adjacent to the second polymer film 150b in the second sub-unit cell 122. For example, in the first sub-unit cell 121, the first polymer film 150a may be adjacent to the second electrode 132, and in the second sub-unit cell 122, the second polymer film 150b may also be adjacent to the second electrode 132.

[0095] The thickness of each of the first polymer film 150a and the second polymer film 150b may be greater than the thickness of the separator 140. The first polymer film 150a and the second polymer film 150b may have the same thickness, but are not limited to this. Furthermore, the first polymer film 150a and the second polymer film 150b may be made of the same material, but are not limited to this.

[0096] The first polymer film 150a and the second polymer film 150b may be flat or may be finely bent.

[0097] When micro-bending occurs in the electrode assembly 100', the first polymer film 150a and the second polymer film 150a may bend in the same direction.

[0098] For example, the first polymer film 150a may have a central portion in the width direction that is bent in a concave shape toward the cell stack section 101 side relative to both edges, and the second polymer film 150b may have a central portion in the width direction that is bent in a convex shape toward the opposite side of the cell stack section 101 relative to both edges.

[0099] In this case, similar to the embodiment described above, the first polymer film 150a may be flat or may be curved toward the cell stack unit 101 so that the distance d between the reference plane P connecting both edges 152 (see FIG. 5) in the width direction and the center 151 is less than 1 mm. The second polymer film 150b may also be flat or may be slightly curved with the same or similar curvature as the first polymer film 150a.

[0100] In this embodiment, the energy density of the electrode assembly 100' may be somewhat higher, but the pair of polymer films 150a and 150b, which have high rigidity, has the advantage of more effectively preventing bending of the electrode assembly 100.

[0101] The above description is merely an illustrative example of the technical concept of the present invention, and various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention pertains without departing from the essential characteristics of the present invention.

[0102] Therefore, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by such embodiments.

[0103] The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent range thereof should be interpreted as being included in the scope of the present invention. [Explanation of symbols]

[0104] 1 Secondary battery 100 electrode assembly 101 Cell stack section 110 unit cells 120 sub-unit cells 130 electrodes 131 1st electrode 132 2nd electrode 140 Separation membrane 150 Polymer Film 200 Battery Case

Claims

1. a cell stack portion including a plurality of unit cells stacked on one another, the unit cells being formed by alternately stacking electrodes and separators integrally joined together; and a sub-unit cell stacked on the cell stack unit, the sub-unit cell having a polymer film on its outermost surface, the electrodes and the separators alternately stacked, and the polymer film integrally bonded to the sub-unit cell; the polymer film is flat or is bent concavely toward the cell stack portion so that the distance between the reference plane connecting both edges in the width direction and the center is less than 1 mm; The thickness of the polymer film is equal to or greater than the thickness of the separator; an adhesive strength of the polymer film within the sub-unit cell is stronger than an adhesive strength between the sub-unit cell and the cell stack portion; Electrode assembly.

2. The electrode assembly of claim 1 , wherein an adhesive force of the polymer film within the sub-unit cell is stronger than an adhesive force between the sub-unit cell and the cell stack portion.

3. The electrode assembly of claim 2 , wherein the thickness of the polymer film is three times or less the thickness of the separator.

4. The electrode assembly according to claim 1 , wherein the polymer film is laminated on the electrode.

5. 2. The electrode assembly of claim 1, wherein the polymer film includes at least one material selected from the group consisting of polyethylene terephthalate, polyvinyl chloride, polyamide, polyimide, polyaramid, and polypropylene.

6. The electrode assembly of claim 1 , wherein the number of the electrodes included in the sub-unit cell is less than the number of the electrodes included in the unit cell.

7. The polymer film is located on one outermost side of the electrode assembly, The electrode assembly of claim 1 , wherein the outermost separator of the cell stack portion is located on the other outermost side of the electrode assembly.

8. a cell stack portion including a plurality of unit cells stacked on one another, each unit cell having alternately stacked electrodes and separators integrally bonded to one another; a first sub-unit cell stacked on one side of the cell stack unit, the first sub-unit cell having a first polymer film on its outermost side, the electrodes and the separators alternately stacked, and the first polymer film integrally bonded to the first sub-unit cell; and a second sub-unit cell stacked on the other side of the cell stack unit, the second sub-unit cell having a second polymer film on its outermost side, the electrodes and the separators alternately stacked, and the second polymer film integrally bonded to each other; the first polymer film is flat or is bent toward the cell stack portion so that the distance between a reference plane connecting both edges in the width direction and the center is less than 1 mm; The thickness of each of the first polymer film and the second polymer film is equal to or greater than the thickness of the separator; an adhesive strength of the first polymer film in the first sub-unit cell is stronger than an adhesive strength between the first sub-unit cell and the cell stack part, or an adhesive strength of the second polymer film in the second sub-unit cell is stronger than an adhesive strength between the second sub-unit cell and the cell stack part; Electrode assembly.

9. The electrode assembly of claim 8 , wherein the second polymer film is flat or has a widthwise central portion that is curved convexly toward the opposite side of the cell stack portion from both edges.

10. a pouch-type battery case; and an electrode assembly housed in the battery case; The electrode assembly is a cell stack portion including a plurality of unit cells stacked on one another, the unit cells being formed by alternately stacking electrodes and separators integrally joined together; and a sub-unit cell stacked on the cell stack unit, the sub-unit cell having a polymer film on its outermost surface, the electrodes and the separators alternately stacked, and the polymer film integrally bonded to the sub-unit cell; the polymer film is flat or is bent concavely toward the cell stack portion so that the distance between the reference plane connecting both edges in the width direction and the center is less than 1 mm; The thickness of the polymer film is equal to or greater than the thickness of the separator; an adhesive strength of the polymer film within the sub-unit cell is stronger than an adhesive strength between the sub-unit cell and the cell stack portion; Secondary battery.

11. The polymer film faces one inner surface of the battery case, The secondary battery according to claim 10 , wherein the outermost separator of the cell stack portion faces the inner surface of the battery case on the opposite side.

12. a pouch-type battery case; and an electrode assembly housed in the battery case; The electrode assembly is a cell stack portion including a plurality of unit cells stacked on one another, each unit cell having alternately stacked electrodes and separators integrally bonded to one another; a first sub-unit cell stacked on one side of the cell stack unit, the first sub-unit cell having a first polymer film on its outermost side, the electrodes and the separators alternately stacked, and the first polymer film integrally bonded to the first sub-unit cell; and a second sub-unit cell stacked on the other side of the cell stack unit, the second sub-unit cell having a second polymer film on its outermost side, the electrodes and the separators alternately stacked, and the second polymer film integrally bonded to each other; the first polymer film is flat or is bent toward the cell stack portion so that the distance between a reference plane connecting both edges in the width direction and the center is less than 1 mm; The thickness of each of the first polymer film and the second polymer film is equal to or greater than the thickness of the separator; an adhesive strength of the first polymer film in the first sub-unit cell is stronger than an adhesive strength between the first sub-unit cell and the cell stack part, or an adhesive strength of the second polymer film in the second sub-unit cell is stronger than an adhesive strength between the second sub-unit cell and the cell stack part; Secondary battery.

13. the first polymer film faces one inner surface of the battery case; The secondary battery according to claim 12 , wherein the second polymer film faces an opposite inner surface of the battery case.

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